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-text diff --git a/2023/Mining bias-target Alignment from Voronoi Cells/45d7f31f-5be7-4011-90ca-1ebee3489169_content_list.json b/2023/Mining bias-target Alignment from Voronoi Cells/45d7f31f-5be7-4011-90ca-1ebee3489169_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..0a6dc9e40cd874ef2d8d68081f6646e614ec32d6 --- /dev/null +++ b/2023/Mining bias-target Alignment from Voronoi Cells/45d7f31f-5be7-4011-90ca-1ebee3489169_content_list.json @@ -0,0 +1,1587 @@ +[ + { + "type": "text", + "text": "Mining bias-target Alignment from Voronoi Cells", + "text_level": 1, + "bbox": [ + 235, + 130, + 736, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Rémi Nahon Van-Tam Nguyen Enzo Tartaglione LTCI, Télecom Paris, Institut Polytechnique de Paris, France {remi.nahon, van-tam.nguyen, enzo tartaglione}@telecom-paris.fr", + "bbox": [ + 202, + 181, + 761, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Despite significant research efforts, deep neural networks remain vulnerable to biases: this raises concerns about their fairness and limits their generalization. In this paper, we propose a bias-agnostic approach to mitigate the impact of biases in deep neural networks. Unlike traditional debiasing approaches, we rely on a metric to quantify \"bias alignment/misalignment\" on target classes and use this information to discourage the propagation of bias-target alignment information through the network. We conduct experiments on several commonly used datasets for debiasing and compare our method with supervised and bias-specific approaches. Our results indicate that the proposed method achieves comparable performance to state-of-the-art supervised approaches, despite being bias-agnostic, even in the presence of multiple biases in the same sample.", + "bbox": [ + 75, + 301, + 473, + 527 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 556, + 209, + 571 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Today, deep Neural Networks (DNNs) are renowned for their high performance and resilience in many areas of computer vision, such as image classification, semantic segmentation, and object detection, used in fields ranging from self-driving vehicles to face recognition or surgical guidance. However, it is well known that their tendency to rely heavily on any type of correlation present in the training data exposes them to potential pitfalls [3, 16, 40]: some \"spurious correlations\" may be erroneously learned by the DNN. These can act as biases [35].", + "bbox": [ + 75, + 582, + 468, + 733 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Learned biases can reduce the generalization of the DNN [3, 5, 8, 16, 24, 30]. For example, if a DNN has learned to distinguish airplanes flying in the sky from boats sailing in the ocean, the model will probably use the background as a base for its classification: detecting it instead of learning the vehicle shape is a much simpler task. However, the model does not generalize to scenarios such as a landing seaplane. Differently from domain adaptation [9, 29, 36], where the objective is to learn general features that compensate for the domain shift or to adapt extracted features to different domains, the goal of debiasing is to discourage the learning", + "bbox": [ + 75, + 734, + 470, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e3af36cc3de9feb6dfa2ff54a85379eebb5e62f2a86fe3a3418350e1fb6435af.jpg", + "image_caption": [ + "Figure 1. Our proposed approach to agnostically remove the bias." + ], + "image_footnote": [], + "bbox": [ + 509, + 266, + 883, + 411 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "of spurious correlations.", + "bbox": [ + 498, + 460, + 663, + 474 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Many current debiasing approaches rely on prior information about the bias, such as the existence of an auxiliary label indicating some side information, the presence of bias(es) or their quality [5, 6, 8, 11, 34, 37]. However, obtaining these labels or information on the nature of the bias can be either very costly (due to annotation costs) or very noisy: this is what motivates the development of bias-agnostic approaches. Recent works have shown that bias features are learned \"early\" [26, 30]; there are bias-target aligned samples, for which the bias is learned, and the performance on the train set increases, and some misaligned ones, for which the prediction is wrong. Since bias-agnostic approaches delve into the biased information from the training set, it is common to amplify the first features learned using Generalized Cross-Entropy [41] and then discourage their learning in an \"unbiased\" model. However, there is no guarantee that the very first features learned are the biased ones: detecting them agnostically and effectively remains an open question.", + "bbox": [ + 496, + 476, + 892, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this work, we propose a method that identifies the best time to extract bias-target alignment information by observing the relative distance of misclassified samples to the Voronoi boundary of the correct target class. We use this information to train an unbiased model, where we give higher weight to bias-misaligned samples, and remove the bias-alignment information from the bottleneck layer (Fig. 1).", + "bbox": [ + 496, + 763, + 890, + 869 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "At a glance, our contributions are the following:", + "bbox": [ + 500, + 869, + 818, + 883 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "- we propose a bias-agnostic approach that indicates,", + "bbox": [ + 517, + 885, + 890, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "4946", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "during the training of a vanilla model, when to extract bias-target alignment information. More precisely, we extract it when the distance of misclassified samples to the Voronoi boundary of the target class is maximal (Sec. 3.3);", + "bbox": [ + 107, + 90, + 467, + 165 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- we use the bias alignment information to weight the loss contribution of every single sample: this will favor the learning of misaligned samples (Sec. 3.4.1);", + "- we propose an approach to eliminate bias information: specifically, we minimize the extractability of bias alignment information at the bottleneck of the DNN, conditioned to bias-target misalignment (Sec. 3.4.2);", + "- we study the behavior on several datasets typically used for debiasing and compare both supervised and bias-agnostic approaches: although our proposed technique is bias-agnostic, its performance is comparable to that of supervised approaches (Sec. 4.3)." + ], + "bbox": [ + 96, + 167, + 467, + 347 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related works", + "text_level": 1, + "bbox": [ + 76, + 364, + 220, + 378 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We will review debiasing approaches below, which can be divided into supervised methods (where we have access to a \"bias label\"), and unsupervised methods.", + "bbox": [ + 76, + 390, + 467, + 434 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Fairness methods", + "text_level": 1, + "bbox": [ + 76, + 446, + 246, + 462 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "While bias can have ethical implications and some debiasing methods can be useful for Fairness, the goals of the two areas of research remain distinct. Fairness aims at minimizing the treatment inequalities between certain groups (according to some ethical principles [12, 14, 22, 39]) generated by classifiers that base their predictions on specific predetermined sets of features or classes (labeled as \"sensitive\"). Some fairness metrics measure these types of inequalities: Demographic Parity, Equalized Odds, or Equal Opportunity are some representative examples [12, 15, 17] and trying to lead the classifier to optimize them in its learning process can help mitigate unfair discriminations. Debiasing does not necessarily target the protection of specific sample groups or set the \"sensitive\" features in advance: it aims at promoting the learning of features that will generalize to a real-life distribution. In this work, we tackle debiasing approaches and we will therefore focus on it in the remainder of the article.", + "bbox": [ + 76, + 470, + 467, + 742 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Supervised methods", + "text_level": 1, + "bbox": [ + 76, + 755, + 266, + 771 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Supervised debiasing methods are divided into three categories: pre-processing methods, which modify the dataset before classification; in-processing methods, which modify the learning process of the model; and post-processing methods, which directly modify the output of the DNN.", + "bbox": [ + 76, + 780, + 467, + 854 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Preprocessing methods. Among the most used preprocessing methods in the literature, driven data augmentation plays a prominent role. Generative Adversarial Networks", + "bbox": [ + 76, + 856, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "(GANs) are widely used to generate realistic images: StyleGANs [10] is indeed one of the mostly used GANs in this context. For example, Kang et al. [23] used it to generate handwritten text in specific styles. In image classification, Geirhos et al. [16] used style transfer to augment ImageNet with texture-bias-conflicting elements to create a more texture-balanced dataset.", + "bbox": [ + 496, + 90, + 890, + 195 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Postprocessing methods. These methods have the advantage of neither re-training models nor requiring additional data for the training. With their Reject Option Classification, for example, Kamiran et al. [21] proposed to take the samples classified with the most uncertainty (outside a predefined confidence margin) and to change their class to decrease the Disparate Impact metric. In this same context, Equalized Odds Postprocessing proposed by Hardt et al. [17] maximizes the Equalized Odds metric. Despite the potential advantages of these approaches, a major drawback lies in the low degrees of freedom for the corrections (since they can only access post-classification information), which limits their practical effectiveness.", + "bbox": [ + 496, + 196, + 890, + 392 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In-processing: debiasing within training. Most of the debiasing methods in the literature work directly on the model, learning from a biased dataset. In general, unbiased elements are weighted more than biased elements. This simple yet effective approach is nowadays very popular in supervised setups [20]. Other methods tackle supervised debiasing by adding regularization terms during the training of the deep model, which is the case of methods such as EnD [34] and FairKL [6]. Another intuitive approach relies upon simply removing the biased features from each sample in the dataset and performing the so-called fairness by blindness. However, the phenomenon known as encoding redundancy [17] states that information is very rarely encoded only once in the data [31], so removing a single value or label is probably not sufficient to remove the effect of the bias on classification.", + "bbox": [ + 496, + 393, + 890, + 633 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.3. Unsupervised methods", + "text_level": 1, + "bbox": [ + 500, + 648, + 709, + 665 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Some recent methods do not rely on bias labels because they can be difficult to obtain on real-life datasets and we will refer to them as \"unsupervised\" or \"bias-agnostic\". All of these approaches follow a general scheme, which is typically divided into two phases: bias inference, where a first model, often called \"bias capturing\", aims to capture biases in the data; and bias mitigation, where a second model is trained to avoid the biases captured by the first model. These approaches rely on prior knowledge, which may be more or less specific to the target task.", + "bbox": [ + 496, + 674, + 890, + 824 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Bias is in the texture. Some work focuses on the bias specifically present in texture, as it is prominent in image classification [16]. Rebias [5], for example, promoted learning with representations that are maximally different from using small receptive fields in convolutional layers. These", + "bbox": [ + 496, + 825, + 890, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "4947", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/ee9c3617f456cfb43b62b1e9b0784bbbb5064fd4e2b7ce27aa7596f1d23e6289.jpg", + "image_caption": [ + "Figure 2. Overview of the proposed debiasing approach: the bias is first extracted (left) and then the unbiased model is trained (right). Blue arrows represent forward propagation while red arrows represent backpropagation." + ], + "image_footnote": [], + "bbox": [ + 89, + 90, + 872, + 303 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "are biased-by-design, toward learning specific textures. For the same texture debiasing task, HEX [37] proposed to use the gray-level co-occurrence matrix and to promote representation independent of colors.", + "bbox": [ + 75, + 361, + 468, + 421 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Bias generates imbalances between groups. Some unsupervised approaches involve finding the bias groups that optimize some fairness metric and train the model to have representations orthogonal to those inferred by the biases. With DebiAN [27], Li et al. for example proposes a method that alternates between the training of bias-capturing and unbiased models, minimizing the Equal Opportunity fairness metric. In EIIL [13], Creager et al. identified biases by finding the groups that maximize violation of an invariance principle measured by the objective function IRMv1 [4]. Similarly, PGI [1] built upon EIIL by minimizing the KL-Divergence of the prediction over these groups.", + "bbox": [ + 75, + 422, + 468, + 602 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Bias is learned early. Some recent methods are based on the assumption that bias features are easy to learn. These features can be extracted at a given point, at the beginning of the training. With LfF [30], Nam et al. proposed a loss reweighing method based on this assumption: they train a biased neural network and amplify its early stages prediction. In parallel, they train a debiased model increasing the weights of \"difficult samples\". Based on this, with DFA [26], Lee et al. performed data augmentation attempting to disentangle bias features from intrinsic features through latent representations of the bias-capturing and unbiased models. Similarly, with LWBC [25], Kim et al. focus the training of their main classifier on the most \"difficult samples\" for their classifier committee. With PGD, Ahn et al. [2] use the magnitude of the sample gradient as a metric to increase their importance.", + "bbox": [ + 75, + 603, + 468, + 843 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The closest competing strategy to the one we propose is LfF [30]. Differently from theirs, our main assumption is not that the first features learned by the model are biased:", + "bbox": [ + 75, + 845, + 468, + 888 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "we assume that the model, at some point, will adapt to the bias and that it is possible to identify this moment by examining the latent representation of the dataset. This particular point can occur at any time during the training, and so emphasizing the earlier choices of the model can prevent it from efficiently adapting to the bias. Moreover, unlike [30], we do not seek to extract the information from the bias, but its alignment with target classes, which allows our approach to easily scale to multi-biased setups.", + "bbox": [ + 496, + 361, + 892, + 497 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed Method", + "text_level": 1, + "bbox": [ + 500, + 516, + 671, + 532 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overview of the proposed method", + "text_level": 1, + "bbox": [ + 500, + 542, + 794, + 559 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Let us consider a supervised learning setup, where we have a dataset $\\mathcal{D}$ containing $N$ input samples $(\\pmb{x}_1,\\dots,\\pmb{x}_N)\\in \\mathcal{X}$ , each associated to a ground truth target label $(\\hat{y}_1,\\dots,\\hat{y}_N)\\in \\mathcal{Y}$ and an index $n\\in \\mathcal{N}_{\\mathcal{D}}$ . A given deep neural network $\\mathcal{M}$ , trained for $e$ epochs, produces $\\forall n\\in N_{\\mathcal{D}}$ an output $\\pmb{y}_{e,n}$ given some $\\pmb{x}_n$ , and is typically trained to match $\\hat{y}_n$ through the minimization of a loss function $\\mathcal{L}(\\pmb{y}_{e,n},\\hat{y}_n)$ . Unfortunately, this learning process does not impose any prior on the specific subset of features that are extracted, which leads to a biased prediction over unseen data. We want to fight this effect.", + "bbox": [ + 496, + 568, + 890, + 733 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Fig. 2 provides an overview of the proposed debiasing approach. First, the bias is inferred by the learning of a vanilla model: at the end of each epoch (or after a few iterations), the target class centroids and the Voronoi boundaries between them are computed from the well-classified samples at the bottleneck layer (Sec. 3.2). The distance of the misclassified samples to the Voronoi boundary is computed to find the epoch $e^{*}$ when the bias-target alignment is maximally learned (Sec. 3.3). Then, a debiasing process follows (Sec. 3.4): from the distances gathered from the previous step, we assign each sample a weight, which will be used", + "bbox": [ + 496, + 734, + 892, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "4948", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "in the weighted loss (Sec. 3.4.1). In addition, at the bottleneck layer, we minimize the information about bias misalignment: this favors the unbiasedness of the classification head (Sec. 3.4.2). In the rest of this section, we will detail all the steps of our proposed technique.", + "bbox": [ + 75, + 90, + 468, + 167 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Bottleneck latent representation", + "text_level": 1, + "bbox": [ + 76, + 175, + 359, + 191 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The debiasing method we propose stems from the concept of latent representation: the output of each layer of a DNN consists of a representation of the input $\\mathbf{x}_n$ . Thus, the classification phase, which takes place just before the output of the model, consists in partitioning the feature space into each of the different classes. Therefore, the output of the bottleneck layer (the output of the backbone) is the compressed representation of the input sample, which is often referred to as latent representation. Therefore, each $\\mathbf{x}_n$ has a vector of latent attributes $\\mathbf{a}_{e,n} \\in \\mathbb{R}^K$ (where $K$ is the number of neurons in the bottleneck layer) associated to a specific epoch (or iteration) $e$ for the model $\\mathcal{M}$ : this forms its latent bottleneck representation.", + "bbox": [ + 75, + 199, + 468, + 393 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We define $\\mathcal{D}_e^{\\parallel}$ the set of samples well classified by the model $\\mathcal{M}$ at epoch $e$ , and $\\mathcal{D}_e^{\\perp}$ the misclassified samples. For each $t$ -th target class (of $T$ classes), it is possible to define a class centroid $C_{e,t}$ as the average of the bottleneck representations of each well-classified samples of the $t$ -th target class:", + "bbox": [ + 76, + 396, + 468, + 473 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nC _ {e, t} = \\frac {1}{\\left| \\mathcal {D} _ {e , t} ^ {\\parallel} \\right|} \\sum_ {n \\in \\mathcal {N} _ {\\mathcal {D} _ {e, t} ^ {\\parallel}}} \\boldsymbol {a} _ {e, n}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 176, + 482, + 468, + 527 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{D}_{e,t}^{\\parallel}$ is the subset of correctly classified samples for the $t$ -th class, and $|\\cdot|$ denotes the cardinality of a set. Such centroids are proxies for the representations of the correctly classified elements of the class by the model. Let us define Voronoi boundary $H_{e,i,j}$ as the hyperplane equidistant from $C_{e,i}$ and $C_{e,j}$ in the bottleneck representation space of $\\mathcal{M}$ : $H_{e,i,j}$ divides the latent space into two Voronoi cells of generators $C_{e,i}$ and $C_{e,j}$ .", + "bbox": [ + 75, + 536, + 468, + 657 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In Fig. 3, we have two target classes (the triangles and the squares) and the bias is pictured as the color (blue and red). The first image (\"Initialization\") shows the latent representation of the dataset by the model at its initialization: the samples are scattered randomly in the feature space, a first classification occurs, materialized by the Voronoi boundary $H_{0,\\Delta,\\circ}$ . Ideally, as shown in the picture the furthest to the right (\"Ideal classification\"), a deep learning model should minimize the intra-class distance and maximize the inter-class one. However, in the presence of bias, another kind of attractor can emerge: the bias-conflicting elements will be attracted by the wrong class. The more the model is biased, the more the sample clusters that form will represent the bias classes more than the target class. For instance, in the second picture, the samples are clustered by color and not by shape: the red triangles have been attracted by the", + "bbox": [ + 75, + 659, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "circle class that is correlated with the color red. The samples misclassified at that specific moment are bias-target misaligned. If the model is, then, over-parametrized, the biased elements will be attracted as well towards the target centroid (third figure \"Epoch $e > e^{*}$ \"): although a set of bias-misaligned features are learned, the model still holds biased ones, which leads to a subpar generalization performance: our first goal will be, hence, to detect the $e^{*}$ moment of the learning where it is possible to extract the bias-target misalignment information.", + "bbox": [ + 496, + 90, + 890, + 242 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Bias alignment capture", + "text_level": 1, + "bbox": [ + 500, + 250, + 714, + 266 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To distinguish between bias-misaligned samples and bias-aligned ones, we assume that, after a few learning steps, the farther a misclassified sample is distant from its target Voronoi cell, the more it has been strongly pulled by an attractor. Such an attractor, since it is not its target class centroid, can be considered as resulting from some bias. Hence, when the average distance between the misclassified samples and their target Voronoi cell reaches its maximum, the model has learned bias features. This scenario is visualized in Fig. 3 (second figure \"Epoch $e^{*}$ \"). To select the exact moment when to extract the bias-target alignment, we are looking for the epoch $e^{*}$ defined by:", + "bbox": [ + 496, + 273, + 890, + 455 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ne ^ {*} = \\underset {e} {\\operatorname {a r g m a x}} \\frac {\\sum_ {i} d ^ {*} \\left(\\boldsymbol {a} _ {e , n}\\right)}{\\left| \\mathcal {D} _ {e} ^ {\\perp} \\right|}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 606, + 460, + 890, + 491 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where", + "bbox": [ + 500, + 497, + 544, + 510 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} d ^ {*} \\left(\\boldsymbol {a} _ {e, n}\\right) = d \\left(\\boldsymbol {a} _ {e, n}, \\boldsymbol {H} _ {e, \\operatorname {a r g m a x} \\left(\\boldsymbol {y} _ {e, n}\\right), \\hat {\\boldsymbol {y}} _ {n}}\\right) \\tag {3} \\\\ \\cdot \\left(1 - \\delta_ {\\operatorname {a r g m a x} (\\boldsymbol {y} _ {e, n}), \\hat {y} _ {n}}\\right), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 562, + 518, + 890, + 559 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "and $d(\\pmb{a},\\pmb{H})$ indicates the $\\ell_2$ distance between $\\pmb{a}$ and the closest point of $\\pmb{H}$ and $\\delta_{\\cdot ,\\cdot}$ is the Kronecker delta. At this point, we can collect the bias-target alignment information $\\mathcal{B}^{*} = (b_{n}^{*})_{n\\in \\mathcal{N}_{\\mathcal{D}}}$ , where $\\forall b\\in \\mathcal{N}_{\\mathcal{D}}$ , $b_{n}^{*} = \\mathrm{argmax}(\\pmb{y}_{e*,n})$ . We can hereby identify the subset of bias-target misaligned samples $\\mathcal{D}^{\\perp} = \\mathcal{D}_{e^{*}}^{\\perp}$ , and the set of bias-target aligned ones $\\mathcal{D}^{\\parallel} = \\mathcal{D}_{e^{*}}^{\\parallel}$ . Given that vanilla learning strategies employ weight-decay, where the distances tend to diminish when reaching the loss minimum, we propose to modify (3) as", + "bbox": [ + 496, + 566, + 890, + 705 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} d ^ {*} \\left(\\boldsymbol {a} _ {e, n}\\right) = d \\left(\\boldsymbol {a} _ {e, n}, \\boldsymbol {H} _ {e, \\operatorname {a r g m a x} \\left(\\boldsymbol {y} _ {e, n}\\right), \\hat {\\boldsymbol {y}} _ {n}}\\right) \\\\ \\cdot \\frac {2 \\cdot \\left(1 - \\delta_ {\\operatorname* {a r g m a x} \\left(\\boldsymbol {y} _ {e , n}\\right) , \\hat {y} _ {n}}\\right)}{\\| \\boldsymbol {C} _ {e , \\operatorname* {a r g m a x} \\left(\\boldsymbol {y} _ {e , n}\\right)} \\| _ {2} + \\| \\boldsymbol {C} _ {e , \\hat {y} _ {n}} \\| _ {2}}, \\tag {4} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 539, + 713, + 890, + 771 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where we scale the distance by the averaged $\\ell_2$ norm (denoted by $\\| \\cdot \\| _2$ ) of the two considered centroids.", + "bbox": [ + 496, + 779, + 888, + 809 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We highlight that our hypothesis is similar but substantially different, from the one formulated in LfF [30]: here, we are free from the assumption bias features are learned earlier than all the more robust ones by the models, and even more from the assumption that they are the very first features learned by the models.", + "bbox": [ + 496, + 810, + 890, + 898 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "4949", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/5f8262c6d519db8a50b79d7f460ce2930f0d72b2b58107372f3dbb4b23a1f0a0.jpg", + "image_caption": [ + "Figure 3. Representation of latent representations of a dataset at different learning stages. The target classes are shapes and the bias is color. Arrows represent the distance between misclassified elements and the Voronoi boundary." + ], + "image_footnote": [], + "bbox": [ + 99, + 90, + 285, + 234 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/7624e1b67b0f3e4f5cd21f846788d0476b450fb232c4d44f5210ff2a7c0c7512.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 292, + 90, + 478, + 236 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/704b819a2078f34a43573164c6ed7bec39fd582b19911484ff3c7e7e9f6737ab.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 483, + 90, + 671, + 236 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/3c21f2c9ef4f99741977bb73c73675467ee09f5a3fe059b3d24568922337297f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 679, + 90, + 864, + 236 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Debiasing the model", + "text_level": 1, + "bbox": [ + 76, + 301, + 269, + 318 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Once having extracted the bias alignment labels for each sample, we can start training and debiasing our actual model. In this work, we propose unbiased models having the same architecture and learning parameters as the bias-extracting one, although no explicit constraint forbids us to use different models. Our approach here consists of modifying the objective function optimized during the training of the model with two goals: increasing the weight of the bias-misaligned samples (as they contain relevant information for generalization compared to other representatives of the same class) and moving these samples away from the bias centroid that tends to attract them.", + "bbox": [ + 75, + 325, + 473, + 508 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4.1 Loss function reweighting", + "text_level": 1, + "bbox": [ + 76, + 532, + 313, + 547 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As shown by LfF [30] and other works like [20], reweighting the loss function to up-weigh the bias-conflicting elements is an efficient method to orient the training in a less biased direction as the correlation bias-target will be less emphasized in the loss. In this work, we assign the weight $r_n$ to the $n$ -th sample according to", + "bbox": [ + 75, + 556, + 468, + 650 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nr _ {n} = \\frac {1}{\\rho_ {b _ {n} ^ {*}}} \\cdot \\delta_ {b _ {n} ^ {*}, \\hat {y} _ {n}} + \\frac {1}{1 - \\rho_ {b _ {n} ^ {*}}} \\cdot \\left(1 - \\delta_ {b _ {n} ^ {*}, \\hat {y} _ {n}}\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 124, + 659, + 468, + 696 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where we define", + "bbox": [ + 76, + 705, + 191, + 720 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\rho_ {t} = \\frac {\\left| \\mathcal {D} _ {e ^ {*} , t} ^ {\\parallel} \\right|}{\\left| \\mathcal {D} _ {e ^ {*} , t} ^ {\\parallel} \\cup \\mathcal {D} _ {e ^ {*} , t} ^ {\\perp} \\right|}. \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 197, + 729, + 468, + 782 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In a nutshell, misaligned samples receive a weight that is proportionally inverse to their cardinality in the $t$ -th class. This has the effect of strongly encouraging the learning of bias-misaligned samples, over bias-aligned ones. In the feature space, we can interpret the resulting reweighted loss $\\mathcal{L}(r_n,\\pmb{y}_{e,n},\\hat{y}_n)$ as an attractive force on the bias-misaligned samples, that are being pulled toward their class centroids.", + "bbox": [ + 76, + 794, + 470, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4.2 Bias alignment information removal", + "text_level": 1, + "bbox": [ + 500, + 303, + 805, + 318 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Besides having a loss reweighting to favor misaligned sample learning, we can also discourage the model from learning any information related to bias alignment to the target. To estimate how much of this information is learned by the model, at the bottleneck we plug an auxiliary classification head that we call information removal head (IRH). This head is trained to minimize a cross-entropy loss $\\mathcal{L}(b_{e,n}, b_n^*)$ . Its performance is an important indicator for us, as it reveals how much the latent space is similar (or different) from the vanilla bias-capturing model, when it was the most fitted to the bias (at epoch $e^*$ ), from the bias-target misalignment perspective. To estimate this similarity more precisely, we compute the mutual information between $\\mathcal{B} = (b_{e,n})_{n \\in \\mathcal{N}_{\\mathcal{D}}}^*$ and $\\mathcal{B}^*$ under the bias misalignment condition as", + "bbox": [ + 496, + 325, + 893, + 539 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {I} ^ {\\perp} = \\sum_ {j, k} p _ {\\mathcal {B}, \\mathcal {B} ^ {*}} ^ {\\perp} (j, k) \\log_ {T} \\left[ \\frac {p _ {\\mathcal {B} , \\mathcal {B} ^ {*}} ^ {\\perp} (j , k)}{p _ {\\mathcal {B}} ^ {\\perp} (j) p _ {\\mathcal {B} ^ {*}} ^ {\\perp} (k)} \\right], \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 544, + 549, + 890, + 592 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where", + "bbox": [ + 500, + 604, + 545, + 616 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\np _ {\\mathcal {B}, \\mathcal {B} ^ {*}} ^ {\\perp} (j, k) = \\frac {1}{| \\mathcal {D} ^ {\\perp} |} \\sum_ {n \\in \\mathcal {N} _ {\\mathcal {D}}} \\delta_ {j, b _ {n} ^ {*}} \\boldsymbol {\\sigma} \\left(\\boldsymbol {b} _ {e, n}\\right) _ {k} \\left(1 - \\delta_ {b _ {n} ^ {*}, \\hat {y} _ {n}}\\right) \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 508, + 626, + 890, + 664 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "is the joint probability between $\\mathcal{B}$ and $\\mathcal{B}^*$ calculated on the bias-target misaligned samples, $\\sigma$ is the softmax function and $p_{\\mathcal{B}}^{\\perp}, p_{\\mathcal{B}^*}^{\\perp}$ are the two marginals. (7) is differentiable, as we work with $\\sigma(\\boldsymbol{b}_{e,n})$ , the softmax-ed output of the IRH. Hence, we are allowed to minimize this term, eventually scaled by a hyper-parameter $\\lambda_{\\mathcal{I}^{\\perp}}$ .", + "bbox": [ + 496, + 672, + 890, + 763 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As displayed in Fig. 2, the mutual information does not contribute to the IRH's update but is propagated directly back to the backbone. Minimizing information over misaligned samples can be seen as a repulsive force, pushing them away from their attractor class. We focus on minimizing conditional mutual information to avoid pushing aligned samples away from their target class, preserving information needed for classification. In the next section, we will test and compare our approach with other state-of-the-art methods.", + "bbox": [ + 496, + 765, + 893, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "4950", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 89, + 209, + 107 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Every result here presented is averaged over three seeds as done in most of the literature, and every algorithm is implemented in Python, using PyTorch 1.13, and trained on GPUs Nvidia GeForce RTX3090 Ti equipped with 24GB RAM. As we compare our method to the other unsupervised state-of-the-art methods, the best-unsupervised accuracies are systematically in bold and the second best are underlined. Besides, we highlight in red the best-overall to see how our method compares even to the supervised ones.", + "bbox": [ + 75, + 114, + 470, + 252 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Datasets", + "text_level": 1, + "bbox": [ + 76, + 263, + 179, + 279 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Here below we describe at a glance the datasets employed for the quantitative evaluation. They were chosen to reflect different problematics bound to biases, from the very simple control case of Biased MNIST to multiple and different biases, synthetic and real-world images.", + "bbox": [ + 75, + 287, + 468, + 364 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Biased MNIST. The first dataset we are using is Biased MNIST, which was first introduced by Bahng et al. [5]. The 60k samples of this dataset consist of a colored version of the famous handwritten digits dataset MNIST with some correlation $\\rho$ between the color and the digits. To build it, first one specific color gets assigned to each of the ten digits; then each of the samples gets its background color. We will test on four levels of color-digit correlation $\\rho$ : 0.99, 0.995, 0.997, and 0.999. The effect of the bias (namely, the background color) is evaluated by testing the model on a completely unbiased dataset, with $\\rho = 0.1$ .", + "bbox": [ + 75, + 364, + 470, + 529 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Multi-Color MNIST. Building on top of Biased MNIST, Li et al. proposed in [27] a bi-colored version to better benchmark the performance of current models on multiple biases at once. Here, the left and the right side of the background have two different colors, with a correlation to the target $\\rho_{L}$ for the left background color of the image and $\\rho_{R}$ for the right one. We follow their proposed setup, with $\\rho_{L} = 0.99$ and $\\rho_{R} = 0.95$ .", + "bbox": [ + 75, + 529, + 470, + 650 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "CelebA. CelebA [28] is a real-world dataset commonly used to test debiasing performance. It is a face classification dataset provided with 40 attributes for each of the 203k image samples. The task we solve here is to classify \"blond\" or \"not blond\" hair, with the main bias lying on the gender, as in the dataset there is a natural bias for \"females\" to have the \"blond\" attribute.", + "bbox": [ + 75, + 651, + 468, + 755 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "9-class ImageNet. The 9-class ImageNet dataset was proposed by [5], consisting of the extraction of a subset of 9 super-classes from ImageNet-1k, balanced to have each class correlated to a specific texture bias.", + "bbox": [ + 75, + 756, + 470, + 816 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "ImageNet-A. ImageNet-A was proposed by Hendrycks et al. in [18] as a subset of cropped images from ImageNet, purposely selected to be very hard to", + "bbox": [ + 75, + 816, + 470, + 863 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/ef01dd70096ee2c12c5bb341c83e28b6b6b4f463de3cfc231e8673ebca2fadd5.jpg", + "table_caption": [ + "Table 1. Results on Balanced Biased MNIST when training with different correlations color-digit $\\rho$ ." + ], + "table_footnote": [], + "table_body": "
MethodBias agnosticTest accuracy [%] (↑)
ρ=0.999ρ=0.997ρ=0.995ρ=0.99
Vanilla✓11.240.572.488.4
Rubi [8]X13.790.443.093.6
EnD [34]X52.383.793.996.0
BCon+BBal [19]X94.097.397.798.1
HEX [37]BT10.816.619.724.7
ReBias [5]BT26.565.875.488.4
LearnedMixin [11]✓12.150.278.288.3
LfF [30]✓15.363.790.395.1
SoftCon [19]✓65.088.693.195.2
Ours✓58.7±21.892.7±1.295.5±0.897.7±0.3
", + "bbox": [ + 504, + 114, + 890, + 258 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "be classified by state-of-the-art CNNs. They were precisely selected among the subset misclassified by a cluster of ResNet-50 models. Following [5, 6, 19], we use it to test our performance when training on 9-class ImageNet.", + "bbox": [ + 498, + 284, + 893, + 345 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Model architecture and training details", + "text_level": 1, + "bbox": [ + 498, + 357, + 836, + 373 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In our experiments, we consistently employed the same architecture for both the vanilla model and the model used for measuring distances to Voronoi boundaries and debiasing. The architecture details for each dataset are provided below. For the Information Removal Head (IRH), we used SGD optimization with a learning rate of 0.1 for each model and dataset. The cross-entropy loss was used for all our losses, and $\\lambda_{\\mathcal{I}^{\\perp}}$ was set to 2 for all experiments.", + "bbox": [ + 496, + 380, + 890, + 501 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Regarding the experiments on Biased MNIST, we used the same fully convolutional network used for Rebias [5] and Irene [33], of four convolutional layers with $7 \\times 7$ kernels, with a batch normalization after each of these layers. For training, we followed the implementation used in [33] of 80 epochs, with an initial learning rate of 0.1 decayed by 0.1 at epochs 40 and 60, and a weight decay of $10^{-4}$ . For Multi-Color MNIST, we employ as architecture the same 3-layer MLP used in [27], trained for 500 epochs (until the model starts overfitting on the training set), using the same optimization strategy as in [27]. For the experiments on CelebA and 9-class ImageNet, we used a pre-trained ResNet-18 and the same optimization strategy as in [19, 30].", + "bbox": [ + 496, + 501, + 892, + 699 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Discussion", + "text_level": 1, + "bbox": [ + 500, + 710, + 617, + 724 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Here we compare our method to the current state-of-the-art, both supervised and unsupervised, on the multiple datasets presented in Sec. 4.1. In what follows, we divide the supervision level of the method into three categories: bias-agnostic, bias-aware (using an extra ground-truth bias label), and \"bias tailored\" (BT) where the method does not rely on bias labels, but by construction, it captures specific biases (like the texture [5, 37]).", + "bbox": [ + 496, + 734, + 890, + 854 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Results on Biased MNIST. Our results on Biased MNIST, presented in Table 1, show that our method achieves state-of-the-art performance, even when compared with super", + "bbox": [ + 498, + 854, + 890, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "1The source code for our method is available at https://github.com/renahon/mining.bias_target Alignment_from_voronoi.cells/.", + "bbox": [ + 75, + 875, + 488, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "4951", + "bbox": [ + 480, + 944, + 513, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/a71f012d1bb907ee80d773f60aaf67fe788c0300ece91e57532a2ab2c3331e45.jpg", + "table_caption": [ + "Table 2. Results on CelebA, targeting the attribute \"blond\", with a bias towards gender." + ], + "table_footnote": [], + "table_body": "
MethodBias agnosticTest accuracy [%] (↑)
UnbiasedBias-Conflicting
Vanilla✓79.059.0
EnD [34]✗86.976.4
LNL [24]✗80.161.2
DI [38]✗90.986.3
BiasCon + BiasBal [19]✗91.487.2
Group DRO [32]✓85.483.4
LfF [30]✓84.281.2
Ours✓90.2±1.184.5±2.0
", + "bbox": [ + 78, + 114, + 467, + 250 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "vised ones, for not extreme values of $\\rho$ : the only method that yields better results on the three lower correlations levels is the use of the associated BiasContrastive and BiasBalanced losses [19]. On the unsupervised field, we get better accuracies than our competitors except for the highest correlation level. We can observe in this case a very high standard deviation because of the high stochastic noise of the gradient: the very few bias-target misaligned (60 in total, constituting $0.1\\%$ of the train set) searches for the perfect moment to mark. We hypothesize these difficulties are caused by the large gradients, which make the bias-target alignment information extraction noisy: we tried to perform the bias extraction for this specific setup having a smaller learning rate (0.01), and the performance improved to $72.6\\% \\pm 11.6$ . Tuning properly the learning rate in extreme scenarios is a key element towards a successful bias-target alignment information extraction.", + "bbox": [ + 75, + 273, + 468, + 527 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results on Multi-Color MNIST. The Multi-Color MNIST dataset [27] helps us to test the performance of our method on multiple biases at the same time. To differentiate performance in different bias-alignment configurations, we will refer to two distinct partitions of the dataset $\\mathcal{D}$ :", + "bbox": [ + 75, + 529, + 468, + 604 + ], + "page_idx": 6 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {D} = R ^ {\\parallel} \\cup R ^ {\\perp} = L ^ {\\parallel} \\cup L ^ {\\perp}, \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 176, + 614, + 468, + 633 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "where $R^{\\parallel}(L^{\\parallel})$ is the subset of samples whose right (left) background is aligned with its digit, and $R^{\\perp}(L^{\\perp})$ when it's not. As previously done in the state-of-the-art [27], we compute separately the accuracies for the four subsets intersections. The average of these four metrics constitutes \"unbiased accuracy\". The most difficult subset is $R^{\\perp} \\cap L^{\\perp}$ : the performance of the vanilla model is below that of random guessing, and the same is true for three out of five tested debiasing methods. In contrast, every method reaches $100\\%$ accuracy or close for samples in $R^{\\parallel} \\cap L^{\\parallel}$ . Even in this case, our method achieves state-of-the-art results for this dataset. More specifically, we record the best-unbiased accuracy, and we improve the best score on the double-conflicting setup by $+8\\%$ . For instance, LfF [30], whose main assumption is close to ours, while emphasizing the early choices of its bias-extracting model seems to perform very unevenly regarding the two biases (around $5\\%$ accu", + "bbox": [ + 75, + 642, + 470, + 901 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/61f84dcd86bf79a79c81006289e9c427e83c4eb7ea53a1e64691651103d89cd1.jpg", + "image_caption": [ + "Figure 4. Evolution of the relative distance to the target Voronoi boundary for the misclassified elements (red curve) and the match between the misclassified samples $\\{n|\\arg \\max (\\pmb{y}_{e,n})\\neq \\hat{y}_n\\}$ and the misaligned samples $\\{n|\\hat{b}_n\\neq \\hat{y}_n\\}$ (blue dashed line)." + ], + "image_footnote": [], + "bbox": [ + 506, + 80, + 883, + 208 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "racy when for $R^{\\perp}$ ). This further strengthens our choice of not extracting a bias label, but the bias-target alignment information, and waiting for the best time to extract it.", + "bbox": [ + 496, + 295, + 890, + 339 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results on CelebA. On the CelebA dataset, two test setups are employed: the \"unbiased\", where the average of the scores obtained on each of the target-bias combinations (here blond-male, blond-female, not blond-male and not blond-female) is considered, and the \"bias-conflicting\" one, where the two bias-aligned combinations are not considered. On both metrics, our approach ranks the best unsupervised $(+4.8\\%)$ on the \"unbiased\" metric), and third overall.", + "bbox": [ + 496, + 340, + 892, + 460 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results on 9-class ImageNet. When working at debiasing 9-class ImageNet, all other state-of-the-art methods become bias-tailored (BT): indeed, they use BagNet-18 [7] as a bias-extracting model for its known tendency to fit texture (as these datasets are known to be very biased towards texture [16]). If we want to perform bias-agnostic debiasing, we shouldn't rely on that kind of bias-extracting model chosen to fit the bias type of the dataset. However, to compare our method to theirs on an equal footing we tested two configurations:", + "bbox": [ + 496, + 460, + 890, + 611 + ], + "page_idx": 6 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- ours (+BagNet), where we extract the bias-conflicting samples from training BagNet-18 and then proceed to debiasing ResNet-18;", + "- ours, where we extract the bias-conflicting samples directly from the ResNet-18, which makes us the only bias-agnostic method tested on this dataset." + ], + "bbox": [ + 517, + 613, + 890, + 702 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We obtain comparable results to the state-of-the-art on ImageNet-A (respectively $1.2\\%$ and $1.5\\%$ below the best-performing method in FairKL [6]) and the two best results overall on 9-class ImageNet. Interestingly, we get state-ofthe-art results with our method, when extracting information directly from ResNet-18.", + "bbox": [ + 496, + 704, + 890, + 794 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation study. We tested the effect of the different modules of our method on Biased MNIST, training with $\\rho = 0.99$ . The results in Table 5 show that the use of the reweighted loss function $\\mathcal{L}$ yields an average increase in accuracy of $+7.1\\%$ and that the use of the IRH further increases it by $+1.7\\%$ . Finally, employing a conditional mutual information term (on the bias-target misaligned ele", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "4952", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/9c0aa69e37a05a27f70b44674ef4b872033c8eecc9cd81e82c76f8b0b2955842.jpg", + "table_caption": [ + "Table 3. Test accuracy on four subsets of Multi-Color MNIST. The \"Unbiased\" accuracy is the average of the four subsets." + ], + "table_footnote": [], + "table_body": "
MethodBias agnosticTest accuracy [%] (↑)
L|| ∩ R||L|| ∩ R↓L↓ ∩ R||L↓ ∩ R↓Unbiased
Vanilla✓100.097.127.55.257.4
LfF [30]✓99.64.798.65.152.0
EIIL [13]✓100.097.270.810.969.7
PGI [1]✓98.682.626.69.554.3
DebiAN [27]✓100.095.676.516.072.0
Ours✓100 ±0.090.9 ±3.577.5 ±2.824.1 ±1.873.1 ±0.9
", + "bbox": [ + 202, + 102, + 771, + 227 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/6e51fe59e4f5ce0b45d4b7542cabcd5285ec3157dfa70e699691aafd45388f6d.jpg", + "table_caption": [ + "Table 4. Test accuracy on 9-class ImageNet and ImageNet-A." + ], + "table_footnote": [], + "table_body": "
MethodBias agnosticTest accuracy [%] (↑)
9-class ImageNetImageNet-A
Vanilla✓94.030.5
ReBias [5]X94.030.5
StyllmageNet [16]BT88.424.6
LearnedMixin [11]BT79.219.0
RUBi [8]BT93.931.0
LfF [30]BT91.229.4
SoftCon [19]BT95.334.1
FairKL [6]BT95.135.7
Ours (BagNet [7])BT96.4 ±0.034.5 ±3.4
Ours✓95.5 ±0.234.2 ±0.9
", + "bbox": [ + 78, + 261, + 468, + 436 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/20540aa79828bfc6f48fd5b659c75486dea5172f7008b76ecbb0d225e30db666.jpg", + "table_caption": [ + "Table 5. Ablation study on Biased MNIST with $\\rho = {0.99}$ ." + ], + "table_footnote": [], + "table_body": "
Weighted LIRHMisaligned onlyTest accuracy [%](↑)
88.4 ±0.5
✓95.5 ±0.5
✓✓97.2 ±0.4
✓✓✓97.7 ±0.4
", + "bbox": [ + 78, + 459, + 468, + 539 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "ments only) in place of total information removal provides an extra gain in performance.", + "bbox": [ + 75, + 561, + 468, + 590 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We also measured the average relative distances from the misclassified samples at each epoch, comparing it to the match of the extracted bias alignment information $\\mathcal{B}$ to the ideal ground truth $\\hat{\\mathcal{B}} = (\\hat{b}_n)_{n\\in \\mathcal{N}_{\\mathcal{D}}}($ (which is provided in Biased MNIST), expressed by", + "bbox": [ + 75, + 590, + 468, + 667 + ], + "page_idx": 7 + }, + { + "type": "equation", + "text": "\n$$\n\\zeta = \\frac {1}{| \\mathcal {D} ^ {\\perp} |} \\sum_ {n \\in \\mathcal {N} _ {\\mathcal {D} ^ {\\perp}}} \\delta_ {\\operatorname {a r g m a x} \\left(\\boldsymbol {y} _ {e, n}\\right), \\hat {\\boldsymbol {b}} _ {n}}. \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 153, + 672, + 468, + 712 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In Fig. 4, we can see a peak in the average distances (marked with $\\star$ ) after the first few iterations: the model fits the color bias in less than one epoch of training. As the training continues, the average relative distance decreases as expected: the misclassified samples stay closer to the Voronoi boundary. We observe that the relative average distance is a good proxy for knowing when to learn the optimal bias alignment $\\hat{\\mathcal{B}}$ , as the two curves show a similar trend.", + "bbox": [ + 75, + 719, + 468, + 839 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "General discussion and limitations. Through the conducted experiments, we have observed that our method establishes, in most of the considered setups, a new state-of-the-art for bias-agnostic approaches, and in some cases even", + "bbox": [ + 75, + 839, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "outperforms supervised methods, such as in 9-class ImageNet and the double-biased Multi-Color MNIST. A limitation of the proposed approach appears when the correlation between bias and target is extremely high ( $\\rho = 0.999$ in Biased MNIST). Since it heavily relies on the extraction of these bias-conflicting samples, when the stochastic noise overwhelms the extraction of the bias misalignment information, the proposed method will be sub-optimal. A possible solution to this problem relies upon using a \"sufficiently small\" learning rate. Finally, our method strongly depends on the existence of these bias-conflicting elements: in a fully-biased dataset, where the alignment bias-target $\\rho = 1$ , since we have no information to extract from the training set, our approach is expected to fail.", + "bbox": [ + 496, + 251, + 890, + 464 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 508, + 617, + 525 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we have presented an unsupervised, bias-agnostic debiasing approach, whose performance is generally of the same order as that of state-of-the-art supervised methods. We proposed a new bias-target alignment extraction method based on the distance between the misclassified samples and the Voronoi boundary separating them from their target class. Based on this distilled information, we proposed a debiasing method composed of two synergetic elements. The first is a reweighted loss, where sample weights reflect the bias-target (mis)alignment. The second is a bias-target alignment information removal term, acting as a regularizer for the latent space. We tested our method on several debiasing benchmarks, recording a new state-of-the-art for unsupervised debiasing in most of the considered scenarios, although no specific hyperparameters tuning was performed. In extreme cases, where the bias-target alignment is extremely high, we observed that the appropriate choice of the vanilla model's learning setup is crucial to the success of the proposed approach, and its exploration is left as future work.", + "bbox": [ + 496, + 546, + 890, + 847 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments. This work was granted access to the HPC resources of IDRIS under the allocation 2023-AD011014080 made by GENCI.", + "bbox": [ + 496, + 858, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "4953", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Faruk Ahmed, Yoshua Bengio, Harm van Seijen, and Aaron C. Courville. Systematic generalisation with group invariant predictions. 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Advances in neural information processing systems, 31, 2018. 1" + ], + "bbox": [ + 78, + 90, + 470, + 868 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "4955", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Mining bias-target Alignment from Voronoi Cells/45d7f31f-5be7-4011-90ca-1ebee3489169_model.json b/2023/Mining bias-target Alignment from Voronoi Cells/45d7f31f-5be7-4011-90ca-1ebee3489169_model.json new file mode 100644 index 0000000000000000000000000000000000000000..94533a18fb2be4b76bf28a1129d63d75bb9d283b --- /dev/null +++ b/2023/Mining bias-target Alignment from Voronoi Cells/45d7f31f-5be7-4011-90ca-1ebee3489169_model.json @@ -0,0 +1,2079 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.236, + 0.131, + 0.737, + 0.154 + ], + "angle": 0, + "content": "Mining bias-target Alignment from Voronoi Cells" + }, + { + "type": "text", + "bbox": [ + 0.204, + 0.182, + 0.763, + 0.234 + ], + "angle": 0, + "content": "Rémi Nahon Van-Tam Nguyen Enzo Tartaglione LTCI, Télecom Paris, Institut Polytechnique de Paris, France {remi.nahon, van-tam.nguyen, enzo tartaglione}@telecom-paris.fr" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.302, + 0.474, + 0.529 + ], + "angle": 0, + "content": "Despite significant research efforts, deep neural networks remain vulnerable to biases: this raises concerns about their fairness and limits their generalization. In this paper, we propose a bias-agnostic approach to mitigate the impact of biases in deep neural networks. Unlike traditional debiasing approaches, we rely on a metric to quantify \"bias alignment/misalignment\" on target classes and use this information to discourage the propagation of bias-target alignment information through the network. We conduct experiments on several commonly used datasets for debiasing and compare our method with supervised and bias-specific approaches. Our results indicate that the proposed method achieves comparable performance to state-of-the-art supervised approaches, despite being bias-agnostic, even in the presence of multiple biases in the same sample." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.558, + 0.21, + 0.573 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.583, + 0.47, + 0.734 + ], + "angle": 0, + "content": "Today, deep Neural Networks (DNNs) are renowned for their high performance and resilience in many areas of computer vision, such as image classification, semantic segmentation, and object detection, used in fields ranging from self-driving vehicles to face recognition or surgical guidance. However, it is well known that their tendency to rely heavily on any type of correlation present in the training data exposes them to potential pitfalls [3, 16, 40]: some \"spurious correlations\" may be erroneously learned by the DNN. These can act as biases [35]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Learned biases can reduce the generalization of the DNN [3, 5, 8, 16, 24, 30]. For example, if a DNN has learned to distinguish airplanes flying in the sky from boats sailing in the ocean, the model will probably use the background as a base for its classification: detecting it instead of learning the vehicle shape is a much simpler task. However, the model does not generalize to scenarios such as a landing seaplane. Differently from domain adaptation [9, 29, 36], where the objective is to learn general features that compensate for the domain shift or to adapt extracted features to different domains, the goal of debiasing is to discourage the learning" + }, + { + "type": "image", + "bbox": [ + 0.51, + 0.267, + 0.885, + 0.412 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.421, + 0.89, + 0.436 + ], + "angle": 0, + "content": "Figure 1. Our proposed approach to agnostically remove the bias." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.462, + 0.664, + 0.476 + ], + "angle": 0, + "content": "of spurious correlations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.477, + 0.893, + 0.764 + ], + "angle": 0, + "content": "Many current debiasing approaches rely on prior information about the bias, such as the existence of an auxiliary label indicating some side information, the presence of bias(es) or their quality [5, 6, 8, 11, 34, 37]. However, obtaining these labels or information on the nature of the bias can be either very costly (due to annotation costs) or very noisy: this is what motivates the development of bias-agnostic approaches. Recent works have shown that bias features are learned \"early\" [26, 30]; there are bias-target aligned samples, for which the bias is learned, and the performance on the train set increases, and some misaligned ones, for which the prediction is wrong. Since bias-agnostic approaches delve into the biased information from the training set, it is common to amplify the first features learned using Generalized Cross-Entropy [41] and then discourage their learning in an \"unbiased\" model. However, there is no guarantee that the very first features learned are the biased ones: detecting them agnostically and effectively remains an open question." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.87 + ], + "angle": 0, + "content": "In this work, we propose a method that identifies the best time to extract bias-target alignment information by observing the relative distance of misclassified samples to the Voronoi boundary of the correct target class. We use this information to train an unbiased model, where we give higher weight to bias-misaligned samples, and remove the bias-alignment information from the bottleneck layer (Fig. 1)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.819, + 0.885 + ], + "angle": 0, + "content": "At a glance, our contributions are the following:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "- we propose a bias-agnostic approach that indicates," + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4946" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.108, + 0.092, + 0.468, + 0.166 + ], + "angle": 0, + "content": "during the training of a vanilla model, when to extract bias-target alignment information. More precisely, we extract it when the distance of misclassified samples to the Voronoi boundary of the target class is maximal (Sec. 3.3);" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.168, + 0.468, + 0.211 + ], + "angle": 0, + "content": "- we use the bias alignment information to weight the loss contribution of every single sample: this will favor the learning of misaligned samples (Sec. 3.4.1);" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.213, + 0.468, + 0.272 + ], + "angle": 0, + "content": "- we propose an approach to eliminate bias information: specifically, we minimize the extractability of bias alignment information at the bottleneck of the DNN, conditioned to bias-target misalignment (Sec. 3.4.2);" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.274, + 0.468, + 0.348 + ], + "angle": 0, + "content": "- we study the behavior on several datasets typically used for debiasing and compare both supervised and bias-agnostic approaches: although our proposed technique is bias-agnostic, its performance is comparable to that of supervised approaches (Sec. 4.3)." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.168, + 0.468, + 0.348 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.365, + 0.222, + 0.38 + ], + "angle": 0, + "content": "2. Related works" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.391, + 0.468, + 0.435 + ], + "angle": 0, + "content": "We will review debiasing approaches below, which can be divided into supervised methods (where we have access to a \"bias label\"), and unsupervised methods." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.448, + 0.247, + 0.463 + ], + "angle": 0, + "content": "2.1. Fairness methods" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.472, + 0.468, + 0.743 + ], + "angle": 0, + "content": "While bias can have ethical implications and some debiasing methods can be useful for Fairness, the goals of the two areas of research remain distinct. Fairness aims at minimizing the treatment inequalities between certain groups (according to some ethical principles [12, 14, 22, 39]) generated by classifiers that base their predictions on specific predetermined sets of features or classes (labeled as \"sensitive\"). Some fairness metrics measure these types of inequalities: Demographic Parity, Equalized Odds, or Equal Opportunity are some representative examples [12, 15, 17] and trying to lead the classifier to optimize them in its learning process can help mitigate unfair discriminations. Debiasing does not necessarily target the protection of specific sample groups or set the \"sensitive\" features in advance: it aims at promoting the learning of features that will generalize to a real-life distribution. In this work, we tackle debiasing approaches and we will therefore focus on it in the remainder of the article." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.756, + 0.267, + 0.772 + ], + "angle": 0, + "content": "2.2. Supervised methods" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.781, + 0.468, + 0.855 + ], + "angle": 0, + "content": "Supervised debiasing methods are divided into three categories: pre-processing methods, which modify the dataset before classification; in-processing methods, which modify the learning process of the model; and post-processing methods, which directly modify the output of the DNN." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.857, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Preprocessing methods. Among the most used preprocessing methods in the literature, driven data augmentation plays a prominent role. Generative Adversarial Networks" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.196 + ], + "angle": 0, + "content": "(GANs) are widely used to generate realistic images: StyleGANs [10] is indeed one of the mostly used GANs in this context. For example, Kang et al. [23] used it to generate handwritten text in specific styles. In image classification, Geirhos et al. [16] used style transfer to augment ImageNet with texture-bias-conflicting elements to create a more texture-balanced dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.198, + 0.892, + 0.393 + ], + "angle": 0, + "content": "Postprocessing methods. These methods have the advantage of neither re-training models nor requiring additional data for the training. With their Reject Option Classification, for example, Kamiran et al. [21] proposed to take the samples classified with the most uncertainty (outside a predefined confidence margin) and to change their class to decrease the Disparate Impact metric. In this same context, Equalized Odds Postprocessing proposed by Hardt et al. [17] maximizes the Equalized Odds metric. Despite the potential advantages of these approaches, a major drawback lies in the low degrees of freedom for the corrections (since they can only access post-classification information), which limits their practical effectiveness." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.394, + 0.892, + 0.634 + ], + "angle": 0, + "content": "In-processing: debiasing within training. Most of the debiasing methods in the literature work directly on the model, learning from a biased dataset. In general, unbiased elements are weighted more than biased elements. This simple yet effective approach is nowadays very popular in supervised setups [20]. Other methods tackle supervised debiasing by adding regularization terms during the training of the deep model, which is the case of methods such as EnD [34] and FairKL [6]. Another intuitive approach relies upon simply removing the biased features from each sample in the dataset and performing the so-called fairness by blindness. However, the phenomenon known as encoding redundancy [17] states that information is very rarely encoded only once in the data [31], so removing a single value or label is probably not sufficient to remove the effect of the bias on classification." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.65, + 0.71, + 0.666 + ], + "angle": 0, + "content": "2.3. Unsupervised methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.892, + 0.825 + ], + "angle": 0, + "content": "Some recent methods do not rely on bias labels because they can be difficult to obtain on real-life datasets and we will refer to them as \"unsupervised\" or \"bias-agnostic\". All of these approaches follow a general scheme, which is typically divided into two phases: bias inference, where a first model, often called \"bias capturing\", aims to capture biases in the data; and bias mitigation, where a second model is trained to avoid the biases captured by the first model. These approaches rely on prior knowledge, which may be more or less specific to the target task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Bias is in the texture. Some work focuses on the bias specifically present in texture, as it is prominent in image classification [16]. Rebias [5], for example, promoted learning with representations that are maximally different from using small receptive fields in convolutional layers. These" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4947" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.09, + 0.092, + 0.873, + 0.304 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.309, + 0.893, + 0.339 + ], + "angle": 0, + "content": "Figure 2. Overview of the proposed debiasing approach: the bias is first extracted (left) and then the unbiased model is trained (right). Blue arrows represent forward propagation while red arrows represent backpropagation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.362, + 0.47, + 0.422 + ], + "angle": 0, + "content": "are biased-by-design, toward learning specific textures. For the same texture debiasing task, HEX [37] proposed to use the gray-level co-occurrence matrix and to promote representation independent of colors." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.423, + 0.47, + 0.603 + ], + "angle": 0, + "content": "Bias generates imbalances between groups. Some unsupervised approaches involve finding the bias groups that optimize some fairness metric and train the model to have representations orthogonal to those inferred by the biases. With DebiAN [27], Li et al. for example proposes a method that alternates between the training of bias-capturing and unbiased models, minimizing the Equal Opportunity fairness metric. In EIIL [13], Creager et al. identified biases by finding the groups that maximize violation of an invariance principle measured by the objective function IRMv1 [4]. Similarly, PGI [1] built upon EIIL by minimizing the KL-Divergence of the prediction over these groups." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.604, + 0.47, + 0.844 + ], + "angle": 0, + "content": "Bias is learned early. Some recent methods are based on the assumption that bias features are easy to learn. These features can be extracted at a given point, at the beginning of the training. With LfF [30], Nam et al. proposed a loss reweighing method based on this assumption: they train a biased neural network and amplify its early stages prediction. In parallel, they train a debiased model increasing the weights of \"difficult samples\". Based on this, with DFA [26], Lee et al. performed data augmentation attempting to disentangle bias features from intrinsic features through latent representations of the bias-capturing and unbiased models. Similarly, with LWBC [25], Kim et al. focus the training of their main classifier on the most \"difficult samples\" for their classifier committee. With PGD, Ahn et al. [2] use the magnitude of the sample gradient as a metric to increase their importance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.846, + 0.469, + 0.89 + ], + "angle": 0, + "content": "The closest competing strategy to the one we propose is LfF [30]. Differently from theirs, our main assumption is not that the first features learned by the model are biased:" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.362, + 0.893, + 0.498 + ], + "angle": 0, + "content": "we assume that the model, at some point, will adapt to the bias and that it is possible to identify this moment by examining the latent representation of the dataset. This particular point can occur at any time during the training, and so emphasizing the earlier choices of the model can prevent it from efficiently adapting to the bias. Moreover, unlike [30], we do not seek to extract the information from the bias, but its alignment with target classes, which allows our approach to easily scale to multi-biased setups." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.517, + 0.673, + 0.534 + ], + "angle": 0, + "content": "3. Proposed Method" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.544, + 0.795, + 0.56 + ], + "angle": 0, + "content": "3.1. Overview of the proposed method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.569, + 0.892, + 0.734 + ], + "angle": 0, + "content": "Let us consider a supervised learning setup, where we have a dataset \\(\\mathcal{D}\\) containing \\(N\\) input samples \\((\\pmb{x}_1,\\dots,\\pmb{x}_N)\\in \\mathcal{X}\\), each associated to a ground truth target label \\((\\hat{y}_1,\\dots,\\hat{y}_N)\\in \\mathcal{Y}\\) and an index \\(n\\in \\mathcal{N}_{\\mathcal{D}}\\). A given deep neural network \\(\\mathcal{M}\\), trained for \\(e\\) epochs, produces \\(\\forall n\\in N_{\\mathcal{D}}\\) an output \\(\\pmb{y}_{e,n}\\) given some \\(\\pmb{x}_n\\), and is typically trained to match \\(\\hat{y}_n\\) through the minimization of a loss function \\(\\mathcal{L}(\\pmb{y}_{e,n},\\hat{y}_n)\\). Unfortunately, this learning process does not impose any prior on the specific subset of features that are extracted, which leads to a biased prediction over unseen data. We want to fight this effect." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Fig. 2 provides an overview of the proposed debiasing approach. First, the bias is inferred by the learning of a vanilla model: at the end of each epoch (or after a few iterations), the target class centroids and the Voronoi boundaries between them are computed from the well-classified samples at the bottleneck layer (Sec. 3.2). The distance of the misclassified samples to the Voronoi boundary is computed to find the epoch \\( e^{*} \\) when the bias-target alignment is maximally learned (Sec. 3.3). Then, a debiasing process follows (Sec. 3.4): from the distances gathered from the previous step, we assign each sample a weight, which will be used" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "4948" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.168 + ], + "angle": 0, + "content": "in the weighted loss (Sec. 3.4.1). In addition, at the bottleneck layer, we minimize the information about bias misalignment: this favors the unbiasedness of the classification head (Sec. 3.4.2). In the rest of this section, we will detail all the steps of our proposed technique." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.176, + 0.36, + 0.192 + ], + "angle": 0, + "content": "3.2. Bottleneck latent representation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.2, + 0.47, + 0.395 + ], + "angle": 0, + "content": "The debiasing method we propose stems from the concept of latent representation: the output of each layer of a DNN consists of a representation of the input \\( \\mathbf{x}_n \\). Thus, the classification phase, which takes place just before the output of the model, consists in partitioning the feature space into each of the different classes. Therefore, the output of the bottleneck layer (the output of the backbone) is the compressed representation of the input sample, which is often referred to as latent representation. Therefore, each \\( \\mathbf{x}_n \\) has a vector of latent attributes \\( \\mathbf{a}_{e,n} \\in \\mathbb{R}^K \\) (where \\( K \\) is the number of neurons in the bottleneck layer) associated to a specific epoch (or iteration) \\( e \\) for the model \\( \\mathcal{M} \\): this forms its latent bottleneck representation." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.397, + 0.469, + 0.474 + ], + "angle": 0, + "content": "We define \\(\\mathcal{D}_e^{\\parallel}\\) the set of samples well classified by the model \\(\\mathcal{M}\\) at epoch \\(e\\), and \\(\\mathcal{D}_e^{\\perp}\\) the misclassified samples. For each \\(t\\)-th target class (of \\(T\\) classes), it is possible to define a class centroid \\(C_{e,t}\\) as the average of the bottleneck representations of each well-classified samples of the \\(t\\)-th target class:" + }, + { + "type": "equation", + "bbox": [ + 0.177, + 0.483, + 0.47, + 0.528 + ], + "angle": 0, + "content": "\\[\nC _ {e, t} = \\frac {1}{\\left| \\mathcal {D} _ {e , t} ^ {\\parallel} \\right|} \\sum_ {n \\in \\mathcal {N} _ {\\mathcal {D} _ {e, t} ^ {\\parallel}}} \\boldsymbol {a} _ {e, n}, \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.537, + 0.469, + 0.659 + ], + "angle": 0, + "content": "where \\(\\mathcal{D}_{e,t}^{\\parallel}\\) is the subset of correctly classified samples for the \\(t\\)-th class, and \\(|\\cdot|\\) denotes the cardinality of a set. Such centroids are proxies for the representations of the correctly classified elements of the class by the model. Let us define Voronoi boundary \\(H_{e,i,j}\\) as the hyperplane equidistant from \\(C_{e,i}\\) and \\(C_{e,j}\\) in the bottleneck representation space of \\(\\mathcal{M}\\): \\(H_{e,i,j}\\) divides the latent space into two Voronoi cells of generators \\(C_{e,i}\\) and \\(C_{e,j}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.66, + 0.47, + 0.901 + ], + "angle": 0, + "content": "In Fig. 3, we have two target classes (the triangles and the squares) and the bias is pictured as the color (blue and red). The first image (\"Initialization\") shows the latent representation of the dataset by the model at its initialization: the samples are scattered randomly in the feature space, a first classification occurs, materialized by the Voronoi boundary \\( H_{0,\\Delta,\\circ} \\). Ideally, as shown in the picture the furthest to the right (\"Ideal classification\"), a deep learning model should minimize the intra-class distance and maximize the inter-class one. However, in the presence of bias, another kind of attractor can emerge: the bias-conflicting elements will be attracted by the wrong class. The more the model is biased, the more the sample clusters that form will represent the bias classes more than the target class. For instance, in the second picture, the samples are clustered by color and not by shape: the red triangles have been attracted by the" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.243 + ], + "angle": 0, + "content": "circle class that is correlated with the color red. The samples misclassified at that specific moment are bias-target misaligned. If the model is, then, over-parametrized, the biased elements will be attracted as well towards the target centroid (third figure \"Epoch \\( e > e^{*} \\)\"): although a set of bias-misaligned features are learned, the model still holds biased ones, which leads to a subpar generalization performance: our first goal will be, hence, to detect the \\( e^{*} \\) moment of the learning where it is possible to extract the bias-target misalignment information." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.251, + 0.715, + 0.267 + ], + "angle": 0, + "content": "3.3. Bias alignment capture" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.274, + 0.892, + 0.456 + ], + "angle": 0, + "content": "To distinguish between bias-misaligned samples and bias-aligned ones, we assume that, after a few learning steps, the farther a misclassified sample is distant from its target Voronoi cell, the more it has been strongly pulled by an attractor. Such an attractor, since it is not its target class centroid, can be considered as resulting from some bias. Hence, when the average distance between the misclassified samples and their target Voronoi cell reaches its maximum, the model has learned bias features. This scenario is visualized in Fig. 3 (second figure \"Epoch \\( e^{*} \\)\"). To select the exact moment when to extract the bias-target alignment, we are looking for the epoch \\( e^{*} \\) defined by:" + }, + { + "type": "equation", + "bbox": [ + 0.607, + 0.461, + 0.891, + 0.492 + ], + "angle": 0, + "content": "\\[\ne ^ {*} = \\underset {e} {\\operatorname {a r g m a x}} \\frac {\\sum_ {i} d ^ {*} \\left(\\boldsymbol {a} _ {e , n}\\right)}{\\left| \\mathcal {D} _ {e} ^ {\\perp} \\right|}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.498, + 0.545, + 0.511 + ], + "angle": 0, + "content": "where" + }, + { + "type": "equation", + "bbox": [ + 0.563, + 0.519, + 0.891, + 0.56 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} d ^ {*} \\left(\\boldsymbol {a} _ {e, n}\\right) = d \\left(\\boldsymbol {a} _ {e, n}, \\boldsymbol {H} _ {e, \\operatorname {a r g m a x} \\left(\\boldsymbol {y} _ {e, n}\\right), \\hat {\\boldsymbol {y}} _ {n}}\\right) \\tag {3} \\\\ \\cdot \\left(1 - \\delta_ {\\operatorname {a r g m a x} (\\boldsymbol {y} _ {e, n}), \\hat {y} _ {n}}\\right), \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.567, + 0.892, + 0.706 + ], + "angle": 0, + "content": "and \\(d(\\pmb{a},\\pmb{H})\\) indicates the \\(\\ell_2\\) distance between \\(\\pmb{a}\\) and the closest point of \\(\\pmb{H}\\) and \\(\\delta_{\\cdot ,\\cdot}\\) is the Kronecker delta. At this point, we can collect the bias-target alignment information \\(\\mathcal{B}^{*} = (b_{n}^{*})_{n\\in \\mathcal{N}_{\\mathcal{D}}}\\), where \\(\\forall b\\in \\mathcal{N}_{\\mathcal{D}}\\), \\(b_{n}^{*} = \\mathrm{argmax}(\\pmb{y}_{e*,n})\\). We can hereby identify the subset of bias-target misaligned samples \\(\\mathcal{D}^{\\perp} = \\mathcal{D}_{e^{*}}^{\\perp}\\), and the set of bias-target aligned ones \\(\\mathcal{D}^{\\parallel} = \\mathcal{D}_{e^{*}}^{\\parallel}\\). Given that vanilla learning strategies employ weight-decay, where the distances tend to diminish when reaching the loss minimum, we propose to modify (3) as" + }, + { + "type": "equation", + "bbox": [ + 0.54, + 0.714, + 0.892, + 0.772 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} d ^ {*} \\left(\\boldsymbol {a} _ {e, n}\\right) = d \\left(\\boldsymbol {a} _ {e, n}, \\boldsymbol {H} _ {e, \\operatorname {a r g m a x} \\left(\\boldsymbol {y} _ {e, n}\\right), \\hat {\\boldsymbol {y}} _ {n}}\\right) \\\\ \\cdot \\frac {2 \\cdot \\left(1 - \\delta_ {\\operatorname* {a r g m a x} \\left(\\boldsymbol {y} _ {e , n}\\right) , \\hat {y} _ {n}}\\right)}{\\| \\boldsymbol {C} _ {e , \\operatorname* {a r g m a x} \\left(\\boldsymbol {y} _ {e , n}\\right)} \\| _ {2} + \\| \\boldsymbol {C} _ {e , \\hat {y} _ {n}} \\| _ {2}}, \\tag {4} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.89, + 0.81 + ], + "angle": 0, + "content": "where we scale the distance by the averaged \\(\\ell_2\\) norm (denoted by \\(\\| \\cdot \\| _2\\)) of the two considered centroids." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.9 + ], + "angle": 0, + "content": "We highlight that our hypothesis is similar but substantially different, from the one formulated in LfF [30]: here, we are free from the assumption bias features are learned earlier than all the more robust ones by the models, and even more from the assumption that they are the very first features learned by the models." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4949" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.1, + 0.092, + 0.287, + 0.236 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.293, + 0.091, + 0.48, + 0.237 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.485, + 0.091, + 0.673, + 0.237 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.68, + 0.092, + 0.866, + 0.237 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.25, + 0.895, + 0.281 + ], + "angle": 0, + "content": "Figure 3. Representation of latent representations of a dataset at different learning stages. The target classes are shapes and the bias is color. Arrows represent the distance between misclassified elements and the Voronoi boundary." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.303, + 0.271, + 0.319 + ], + "angle": 0, + "content": "3.4. Debiasing the model" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.327, + 0.474, + 0.509 + ], + "angle": 0, + "content": "Once having extracted the bias alignment labels for each sample, we can start training and debiasing our actual model. In this work, we propose unbiased models having the same architecture and learning parameters as the bias-extracting one, although no explicit constraint forbids us to use different models. Our approach here consists of modifying the objective function optimized during the training of the model with two goals: increasing the weight of the bias-misaligned samples (as they contain relevant information for generalization compared to other representatives of the same class) and moving these samples away from the bias centroid that tends to attract them." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.533, + 0.315, + 0.549 + ], + "angle": 0, + "content": "3.4.1 Loss function reweighting" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.558, + 0.47, + 0.651 + ], + "angle": 0, + "content": "As shown by LfF [30] and other works like [20], reweighting the loss function to up-weigh the bias-conflicting elements is an efficient method to orient the training in a less biased direction as the correlation bias-target will be less emphasized in the loss. In this work, we assign the weight \\( r_n \\) to the \\( n \\)-th sample according to" + }, + { + "type": "equation", + "bbox": [ + 0.125, + 0.66, + 0.47, + 0.697 + ], + "angle": 0, + "content": "\\[\nr _ {n} = \\frac {1}{\\rho_ {b _ {n} ^ {*}}} \\cdot \\delta_ {b _ {n} ^ {*}, \\hat {y} _ {n}} + \\frac {1}{1 - \\rho_ {b _ {n} ^ {*}}} \\cdot \\left(1 - \\delta_ {b _ {n} ^ {*}, \\hat {y} _ {n}}\\right), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.706, + 0.192, + 0.721 + ], + "angle": 0, + "content": "where we define" + }, + { + "type": "equation", + "bbox": [ + 0.199, + 0.731, + 0.47, + 0.784 + ], + "angle": 0, + "content": "\\[\n\\rho_ {t} = \\frac {\\left| \\mathcal {D} _ {e ^ {*} , t} ^ {\\parallel} \\right|}{\\left| \\mathcal {D} _ {e ^ {*} , t} ^ {\\parallel} \\cup \\mathcal {D} _ {e ^ {*} , t} ^ {\\perp} \\right|}. \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.795, + 0.471, + 0.903 + ], + "angle": 0, + "content": "In a nutshell, misaligned samples receive a weight that is proportionally inverse to their cardinality in the \\(t\\)-th class. This has the effect of strongly encouraging the learning of bias-misaligned samples, over bias-aligned ones. In the feature space, we can interpret the resulting reweighted loss \\(\\mathcal{L}(r_n,\\pmb{y}_{e,n},\\hat{y}_n)\\) as an attractive force on the bias-misaligned samples, that are being pulled toward their class centroids." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.304, + 0.807, + 0.319 + ], + "angle": 0, + "content": "3.4.2 Bias alignment information removal" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.327, + 0.895, + 0.54 + ], + "angle": 0, + "content": "Besides having a loss reweighting to favor misaligned sample learning, we can also discourage the model from learning any information related to bias alignment to the target. To estimate how much of this information is learned by the model, at the bottleneck we plug an auxiliary classification head that we call information removal head (IRH). This head is trained to minimize a cross-entropy loss \\(\\mathcal{L}(b_{e,n}, b_n^*)\\). Its performance is an important indicator for us, as it reveals how much the latent space is similar (or different) from the vanilla bias-capturing model, when it was the most fitted to the bias (at epoch \\(e^*\\)), from the bias-target misalignment perspective. To estimate this similarity more precisely, we compute the mutual information between \\(\\mathcal{B} = (b_{e,n})_{n \\in \\mathcal{N}_{\\mathcal{D}}}^*\\) and \\(\\mathcal{B}^*\\) under the bias misalignment condition as" + }, + { + "type": "equation", + "bbox": [ + 0.545, + 0.55, + 0.892, + 0.593 + ], + "angle": 0, + "content": "\\[\n\\mathcal {I} ^ {\\perp} = \\sum_ {j, k} p _ {\\mathcal {B}, \\mathcal {B} ^ {*}} ^ {\\perp} (j, k) \\log_ {T} \\left[ \\frac {p _ {\\mathcal {B} , \\mathcal {B} ^ {*}} ^ {\\perp} (j , k)}{p _ {\\mathcal {B}} ^ {\\perp} (j) p _ {\\mathcal {B} ^ {*}} ^ {\\perp} (k)} \\right], \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.605, + 0.547, + 0.617 + ], + "angle": 0, + "content": "where" + }, + { + "type": "equation", + "bbox": [ + 0.509, + 0.627, + 0.892, + 0.665 + ], + "angle": 0, + "content": "\\[\np _ {\\mathcal {B}, \\mathcal {B} ^ {*}} ^ {\\perp} (j, k) = \\frac {1}{| \\mathcal {D} ^ {\\perp} |} \\sum_ {n \\in \\mathcal {N} _ {\\mathcal {D}}} \\delta_ {j, b _ {n} ^ {*}} \\boldsymbol {\\sigma} \\left(\\boldsymbol {b} _ {e, n}\\right) _ {k} \\left(1 - \\delta_ {b _ {n} ^ {*}, \\hat {y} _ {n}}\\right) \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.674, + 0.892, + 0.765 + ], + "angle": 0, + "content": "is the joint probability between \\(\\mathcal{B}\\) and \\(\\mathcal{B}^*\\) calculated on the bias-target misaligned samples, \\(\\sigma\\) is the softmax function and \\(p_{\\mathcal{B}}^{\\perp}, p_{\\mathcal{B}^*}^{\\perp}\\) are the two marginals. (7) is differentiable, as we work with \\(\\sigma(\\boldsymbol{b}_{e,n})\\), the softmax-ed output of the IRH. Hence, we are allowed to minimize this term, eventually scaled by a hyper-parameter \\(\\lambda_{\\mathcal{I}^{\\perp}}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.766, + 0.895, + 0.903 + ], + "angle": 0, + "content": "As displayed in Fig. 2, the mutual information does not contribute to the IRH's update but is propagated directly back to the backbone. Minimizing information over misaligned samples can be seen as a repulsive force, pushing them away from their attractor class. We focus on minimizing conditional mutual information to avoid pushing aligned samples away from their target class, preserving information needed for classification. In the next section, we will test and compare our approach with other state-of-the-art methods." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4950" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.09, + 0.21, + 0.108 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.116, + 0.471, + 0.253 + ], + "angle": 0, + "content": "Every result here presented is averaged over three seeds as done in most of the literature, and every algorithm is implemented in Python, using PyTorch 1.13, and trained on GPUs Nvidia GeForce RTX3090 Ti equipped with 24GB RAM. As we compare our method to the other unsupervised state-of-the-art methods, the best-unsupervised accuracies are systematically in bold and the second best are underlined. Besides, we highlight in red the best-overall to see how our method compares even to the supervised ones." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.265, + 0.18, + 0.28 + ], + "angle": 0, + "content": "4.1. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.289, + 0.47, + 0.365 + ], + "angle": 0, + "content": "Here below we describe at a glance the datasets employed for the quantitative evaluation. They were chosen to reflect different problematics bound to biases, from the very simple control case of Biased MNIST to multiple and different biases, synthetic and real-world images." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.365, + 0.471, + 0.53 + ], + "angle": 0, + "content": "Biased MNIST. The first dataset we are using is Biased MNIST, which was first introduced by Bahng et al. [5]. The 60k samples of this dataset consist of a colored version of the famous handwritten digits dataset MNIST with some correlation \\(\\rho\\) between the color and the digits. To build it, first one specific color gets assigned to each of the ten digits; then each of the samples gets its background color. We will test on four levels of color-digit correlation \\(\\rho\\): 0.99, 0.995, 0.997, and 0.999. The effect of the bias (namely, the background color) is evaluated by testing the model on a completely unbiased dataset, with \\(\\rho = 0.1\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.53, + 0.471, + 0.651 + ], + "angle": 0, + "content": "Multi-Color MNIST. Building on top of Biased MNIST, Li et al. proposed in [27] a bi-colored version to better benchmark the performance of current models on multiple biases at once. Here, the left and the right side of the background have two different colors, with a correlation to the target \\(\\rho_{L}\\) for the left background color of the image and \\(\\rho_{R}\\) for the right one. We follow their proposed setup, with \\(\\rho_{L} = 0.99\\) and \\(\\rho_{R} = 0.95\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.652, + 0.47, + 0.756 + ], + "angle": 0, + "content": "CelebA. CelebA [28] is a real-world dataset commonly used to test debiasing performance. It is a face classification dataset provided with 40 attributes for each of the 203k image samples. The task we solve here is to classify \"blond\" or \"not blond\" hair, with the main bias lying on the gender, as in the dataset there is a natural bias for \"females\" to have the \"blond\" attribute." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.757, + 0.471, + 0.817 + ], + "angle": 0, + "content": "9-class ImageNet. The 9-class ImageNet dataset was proposed by [5], consisting of the extraction of a subset of 9 super-classes from ImageNet-1k, balanced to have each class correlated to a specific texture bias." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.818, + 0.471, + 0.864 + ], + "angle": 0, + "content": "ImageNet-A. ImageNet-A was proposed by Hendrycks et al. in [18] as a subset of cropped images from ImageNet, purposely selected to be very hard to" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.088, + 0.892, + 0.115 + ], + "angle": 0, + "content": "Table 1. Results on Balanced Biased MNIST when training with different correlations color-digit \\(\\rho\\)." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.115, + 0.892, + 0.259 + ], + "angle": 0, + "content": "
MethodBias agnosticTest accuracy [%] (↑)
ρ=0.999ρ=0.997ρ=0.995ρ=0.99
Vanilla✓11.240.572.488.4
Rubi [8]X13.790.443.093.6
EnD [34]X52.383.793.996.0
BCon+BBal [19]X94.097.397.798.1
HEX [37]BT10.816.619.724.7
ReBias [5]BT26.565.875.488.4
LearnedMixin [11]✓12.150.278.288.3
LfF [30]✓15.363.790.395.1
SoftCon [19]✓65.088.693.195.2
Ours✓58.7±21.892.7±1.295.5±0.897.7±0.3
" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.285, + 0.894, + 0.346 + ], + "angle": 0, + "content": "be classified by state-of-the-art CNNs. They were precisely selected among the subset misclassified by a cluster of ResNet-50 models. Following [5, 6, 19], we use it to test our performance when training on 9-class ImageNet." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.358, + 0.838, + 0.374 + ], + "angle": 0, + "content": "4.2. Model architecture and training details" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.381, + 0.892, + 0.502 + ], + "angle": 0, + "content": "In our experiments, we consistently employed the same architecture for both the vanilla model and the model used for measuring distances to Voronoi boundaries and debiasing. The architecture details for each dataset are provided below. For the Information Removal Head (IRH), we used SGD optimization with a learning rate of 0.1 for each model and dataset. The cross-entropy loss was used for all our losses, and \\(\\lambda_{\\mathcal{I}^{\\perp}}\\) was set to 2 for all experiments." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.502, + 0.893, + 0.7 + ], + "angle": 0, + "content": "Regarding the experiments on Biased MNIST, we used the same fully convolutional network used for Rebias [5] and Irene [33], of four convolutional layers with \\(7 \\times 7\\) kernels, with a batch normalization after each of these layers. For training, we followed the implementation used in [33] of 80 epochs, with an initial learning rate of 0.1 decayed by 0.1 at epochs 40 and 60, and a weight decay of \\(10^{-4}\\). For Multi-Color MNIST, we employ as architecture the same 3-layer MLP used in [27], trained for 500 epochs (until the model starts overfitting on the training set), using the same optimization strategy as in [27]. For the experiments on CelebA and 9-class ImageNet, we used a pre-trained ResNet-18 and the same optimization strategy as in [19, 30]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.711, + 0.618, + 0.725 + ], + "angle": 0, + "content": "4.3. Discussion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.855 + ], + "angle": 0, + "content": "Here we compare our method to the current state-of-the-art, both supervised and unsupervised, on the multiple datasets presented in Sec. 4.1. In what follows, we divide the supervision level of the method into three categories: bias-agnostic, bias-aware (using an extra ground-truth bias label), and \"bias tailored\" (BT) where the method does not rely on bias labels, but by construction, it captures specific biases (like the texture [5, 37])." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Results on Biased MNIST. Our results on Biased MNIST, presented in Table 1, show that our method achieves state-of-the-art performance, even when compared with super" + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.875, + 0.49, + 0.901 + ], + "angle": 0, + "content": "1The source code for our method is available at https://github.com/renahon/mining.bias_target Alignment_from_voronoi.cells/." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "4951" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.088, + 0.47, + 0.115 + ], + "angle": 0, + "content": "Table 2. Results on CelebA, targeting the attribute \"blond\", with a bias towards gender." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.115, + 0.468, + 0.25 + ], + "angle": 0, + "content": "
MethodBias agnosticTest accuracy [%] (↑)
UnbiasedBias-Conflicting
Vanilla✓79.059.0
EnD [34]✗86.976.4
LNL [24]✗80.161.2
DI [38]✗90.986.3
BiasCon + BiasBal [19]✗91.487.2
Group DRO [32]✓85.483.4
LfF [30]✓84.281.2
Ours✓90.2±1.184.5±2.0
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.274, + 0.47, + 0.529 + ], + "angle": 0, + "content": "vised ones, for not extreme values of \\(\\rho\\): the only method that yields better results on the three lower correlations levels is the use of the associated BiasContrastive and BiasBalanced losses [19]. On the unsupervised field, we get better accuracies than our competitors except for the highest correlation level. We can observe in this case a very high standard deviation because of the high stochastic noise of the gradient: the very few bias-target misaligned (60 in total, constituting \\(0.1\\%\\) of the train set) searches for the perfect moment to mark. We hypothesize these difficulties are caused by the large gradients, which make the bias-target alignment information extraction noisy: we tried to perform the bias extraction for this specific setup having a smaller learning rate (0.01), and the performance improved to \\(72.6\\% \\pm 11.6\\). Tuning properly the learning rate in extreme scenarios is a key element towards a successful bias-target alignment information extraction." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.53, + 0.47, + 0.606 + ], + "angle": 0, + "content": "Results on Multi-Color MNIST. The Multi-Color MNIST dataset [27] helps us to test the performance of our method on multiple biases at the same time. To differentiate performance in different bias-alignment configurations, we will refer to two distinct partitions of the dataset \\(\\mathcal{D}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.177, + 0.615, + 0.469, + 0.634 + ], + "angle": 0, + "content": "\\[\n\\mathcal {D} = R ^ {\\parallel} \\cup R ^ {\\perp} = L ^ {\\parallel} \\cup L ^ {\\perp}, \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.643, + 0.471, + 0.902 + ], + "angle": 0, + "content": "where \\( R^{\\parallel}(L^{\\parallel}) \\) is the subset of samples whose right (left) background is aligned with its digit, and \\( R^{\\perp}(L^{\\perp}) \\) when it's not. As previously done in the state-of-the-art [27], we compute separately the accuracies for the four subsets intersections. The average of these four metrics constitutes \"unbiased accuracy\". The most difficult subset is \\( R^{\\perp} \\cap L^{\\perp} \\): the performance of the vanilla model is below that of random guessing, and the same is true for three out of five tested debiasing methods. In contrast, every method reaches \\( 100\\% \\) accuracy or close for samples in \\( R^{\\parallel} \\cap L^{\\parallel} \\). Even in this case, our method achieves state-of-the-art results for this dataset. More specifically, we record the best-unbiased accuracy, and we improve the best score on the double-conflicting setup by \\( +8\\% \\). For instance, LfF [30], whose main assumption is close to ours, while emphasizing the early choices of its bias-extracting model seems to perform very unevenly regarding the two biases (around \\( 5\\% \\) accu" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.081, + 0.885, + 0.209 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.211, + 0.894, + 0.27 + ], + "angle": 0, + "content": "Figure 4. Evolution of the relative distance to the target Voronoi boundary for the misclassified elements (red curve) and the match between the misclassified samples \\(\\{n|\\arg \\max (\\pmb{y}_{e,n})\\neq \\hat{y}_n\\}\\) and the misaligned samples \\(\\{n|\\hat{b}_n\\neq \\hat{y}_n\\}\\) (blue dashed line)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.296, + 0.892, + 0.34 + ], + "angle": 0, + "content": "racy when for \\( R^{\\perp} \\)). This further strengthens our choice of not extracting a bias label, but the bias-target alignment information, and waiting for the best time to extract it." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.341, + 0.893, + 0.461 + ], + "angle": 0, + "content": "Results on CelebA. On the CelebA dataset, two test setups are employed: the \"unbiased\", where the average of the scores obtained on each of the target-bias combinations (here blond-male, blond-female, not blond-male and not blond-female) is considered, and the \"bias-conflicting\" one, where the two bias-aligned combinations are not considered. On both metrics, our approach ranks the best unsupervised \\((+4.8\\%)\\) on the \"unbiased\" metric), and third overall." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.462, + 0.892, + 0.612 + ], + "angle": 0, + "content": "Results on 9-class ImageNet. When working at debiasing 9-class ImageNet, all other state-of-the-art methods become bias-tailored (BT): indeed, they use BagNet-18 [7] as a bias-extracting model for its known tendency to fit texture (as these datasets are known to be very biased towards texture [16]). If we want to perform bias-agnostic debiasing, we shouldn't rely on that kind of bias-extracting model chosen to fit the bias type of the dataset. However, to compare our method to theirs on an equal footing we tested two configurations:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.614, + 0.892, + 0.658 + ], + "angle": 0, + "content": "- ours (+BagNet), where we extract the bias-conflicting samples from training BagNet-18 and then proceed to debiasing ResNet-18;" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.659, + 0.891, + 0.703 + ], + "angle": 0, + "content": "- ours, where we extract the bias-conflicting samples directly from the ResNet-18, which makes us the only bias-agnostic method tested on this dataset." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.614, + 0.892, + 0.703 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.892, + 0.795 + ], + "angle": 0, + "content": "We obtain comparable results to the state-of-the-art on ImageNet-A (respectively \\(1.2\\%\\) and \\(1.5\\%\\) below the best-performing method in FairKL [6]) and the two best results overall on 9-class ImageNet. Interestingly, we get state-ofthe-art results with our method, when extracting information directly from ResNet-18." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Ablation study. We tested the effect of the different modules of our method on Biased MNIST, training with \\(\\rho = 0.99\\). The results in Table 5 show that the use of the reweighted loss function \\(\\mathcal{L}\\) yields an average increase in accuracy of \\(+7.1\\%\\) and that the use of the IRH further increases it by \\(+1.7\\%\\). Finally, employing a conditional mutual information term (on the bias-target misaligned ele" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4952" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.124, + 0.088, + 0.846, + 0.102 + ], + "angle": 0, + "content": "Table 3. Test accuracy on four subsets of Multi-Color MNIST. The \"Unbiased\" accuracy is the average of the four subsets." + }, + { + "type": "table", + "bbox": [ + 0.204, + 0.103, + 0.772, + 0.228 + ], + "angle": 0, + "content": "
MethodBias agnosticTest accuracy [%] (↑)
L|| ∩ R||L|| ∩ R↓L↓ ∩ R||L↓ ∩ R↓Unbiased
Vanilla✓100.097.127.55.257.4
LfF [30]✓99.64.798.65.152.0
EIIL [13]✓100.097.270.810.969.7
PGI [1]✓98.682.626.69.554.3
DebiAN [27]✓100.095.676.516.072.0
Ours✓100 ±0.090.9 ±3.577.5 ±2.824.1 ±1.873.1 ±0.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.079, + 0.249, + 0.442, + 0.262 + ], + "angle": 0, + "content": "Table 4. Test accuracy on 9-class ImageNet and ImageNet-A." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.262, + 0.47, + 0.438 + ], + "angle": 0, + "content": "
MethodBias agnosticTest accuracy [%] (↑)
9-class ImageNetImageNet-A
Vanilla✓94.030.5
ReBias [5]X94.030.5
StyllmageNet [16]BT88.424.6
LearnedMixin [11]BT79.219.0
RUBi [8]BT93.931.0
LfF [30]BT91.229.4
SoftCon [19]BT95.334.1
FairKL [6]BT95.135.7
Ours (BagNet [7])BT96.4 ±0.034.5 ±3.4
Ours✓95.5 ±0.234.2 ±0.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.099, + 0.447, + 0.443, + 0.46 + ], + "angle": 0, + "content": "Table 5. Ablation study on Biased MNIST with \\( \\rho = {0.99} \\) ." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.46, + 0.47, + 0.54 + ], + "angle": 0, + "content": "
Weighted LIRHMisaligned onlyTest accuracy [%](↑)
88.4 ±0.5
✓95.5 ±0.5
✓✓97.2 ±0.4
✓✓✓97.7 ±0.4
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.562, + 0.469, + 0.592 + ], + "angle": 0, + "content": "ments only) in place of total information removal provides an extra gain in performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.592, + 0.469, + 0.668 + ], + "angle": 0, + "content": "We also measured the average relative distances from the misclassified samples at each epoch, comparing it to the match of the extracted bias alignment information \\(\\mathcal{B}\\) to the ideal ground truth \\(\\hat{\\mathcal{B}} = (\\hat{b}_n)_{n\\in \\mathcal{N}_{\\mathcal{D}}}(\\) (which is provided in Biased MNIST), expressed by" + }, + { + "type": "equation", + "bbox": [ + 0.155, + 0.674, + 0.469, + 0.713 + ], + "angle": 0, + "content": "\\[\n\\zeta = \\frac {1}{| \\mathcal {D} ^ {\\perp} |} \\sum_ {n \\in \\mathcal {N} _ {\\mathcal {D} ^ {\\perp}}} \\delta_ {\\operatorname {a r g m a x} \\left(\\boldsymbol {y} _ {e, n}\\right), \\hat {\\boldsymbol {b}} _ {n}}. \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.469, + 0.84 + ], + "angle": 0, + "content": "In Fig. 4, we can see a peak in the average distances (marked with \\(\\star\\)) after the first few iterations: the model fits the color bias in less than one epoch of training. As the training continues, the average relative distance decreases as expected: the misclassified samples stay closer to the Voronoi boundary. We observe that the relative average distance is a good proxy for knowing when to learn the optimal bias alignment \\(\\hat{\\mathcal{B}}\\), as the two curves show a similar trend." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.469, + 0.901 + ], + "angle": 0, + "content": "General discussion and limitations. Through the conducted experiments, we have observed that our method establishes, in most of the considered setups, a new state-of-the-art for bias-agnostic approaches, and in some cases even" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.252, + 0.892, + 0.465 + ], + "angle": 0, + "content": "outperforms supervised methods, such as in 9-class ImageNet and the double-biased Multi-Color MNIST. A limitation of the proposed approach appears when the correlation between bias and target is extremely high (\\(\\rho = 0.999\\) in Biased MNIST). Since it heavily relies on the extraction of these bias-conflicting samples, when the stochastic noise overwhelms the extraction of the bias misalignment information, the proposed method will be sub-optimal. A possible solution to this problem relies upon using a \"sufficiently small\" learning rate. Finally, our method strongly depends on the existence of these bias-conflicting elements: in a fully-biased dataset, where the alignment bias-target \\(\\rho = 1\\), since we have no information to extract from the training set, our approach is expected to fail." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.51, + 0.619, + 0.526 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.547, + 0.892, + 0.848 + ], + "angle": 0, + "content": "In this paper, we have presented an unsupervised, bias-agnostic debiasing approach, whose performance is generally of the same order as that of state-of-the-art supervised methods. We proposed a new bias-target alignment extraction method based on the distance between the misclassified samples and the Voronoi boundary separating them from their target class. Based on this distilled information, we proposed a debiasing method composed of two synergetic elements. The first is a reweighted loss, where sample weights reflect the bias-target (mis)alignment. The second is a bias-target alignment information removal term, acting as a regularizer for the latent space. We tested our method on several debiasing benchmarks, recording a new state-of-the-art for unsupervised debiasing in most of the considered scenarios, although no specific hyperparameters tuning was performed. In extreme cases, where the bias-target alignment is extremely high, we observed that the appropriate choice of the vanilla model's learning setup is crucial to the success of the proposed approach, and its exploration is left as future work." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.859, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgments. This work was granted access to the HPC resources of IDRIS under the allocation 2023-AD011014080 made by GENCI." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4953" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Faruk Ahmed, Yoshua Bengio, Harm van Seijen, and Aaron C. Courville. Systematic generalisation with group invariant predictions. 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Advances in neural information processing systems, 31, 2018. 1" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.472, + 0.869 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.515, + 0.956 + ], + "angle": 0, + "content": "4955" + } + ] +] \ No newline at end of file diff --git a/2023/Mining bias-target Alignment from Voronoi Cells/45d7f31f-5be7-4011-90ca-1ebee3489169_origin.pdf b/2023/Mining bias-target Alignment from Voronoi Cells/45d7f31f-5be7-4011-90ca-1ebee3489169_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..c3845d614c876ba2747718edb7350d5229f630c5 --- /dev/null +++ b/2023/Mining bias-target Alignment from Voronoi Cells/45d7f31f-5be7-4011-90ca-1ebee3489169_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:4132d8cbdf1fec1059ad16780568a0a639ca727cf4637ff723e9f3ddd8f57493 +size 845966 diff --git a/2023/Mining bias-target Alignment from Voronoi Cells/full.md b/2023/Mining bias-target Alignment from Voronoi Cells/full.md new file mode 100644 index 0000000000000000000000000000000000000000..ba6d64fb9b325d69d756dcbf2861e4d46df74b78 --- /dev/null +++ b/2023/Mining bias-target Alignment from Voronoi Cells/full.md @@ -0,0 +1,312 @@ +# Mining bias-target Alignment from Voronoi Cells + +Rémi Nahon Van-Tam Nguyen Enzo Tartaglione LTCI, Télecom Paris, Institut Polytechnique de Paris, France {remi.nahon, van-tam.nguyen, enzo tartaglione}@telecom-paris.fr + +# Abstract + +Despite significant research efforts, deep neural networks remain vulnerable to biases: this raises concerns about their fairness and limits their generalization. In this paper, we propose a bias-agnostic approach to mitigate the impact of biases in deep neural networks. Unlike traditional debiasing approaches, we rely on a metric to quantify "bias alignment/misalignment" on target classes and use this information to discourage the propagation of bias-target alignment information through the network. We conduct experiments on several commonly used datasets for debiasing and compare our method with supervised and bias-specific approaches. Our results indicate that the proposed method achieves comparable performance to state-of-the-art supervised approaches, despite being bias-agnostic, even in the presence of multiple biases in the same sample. + +# 1. Introduction + +Today, deep Neural Networks (DNNs) are renowned for their high performance and resilience in many areas of computer vision, such as image classification, semantic segmentation, and object detection, used in fields ranging from self-driving vehicles to face recognition or surgical guidance. However, it is well known that their tendency to rely heavily on any type of correlation present in the training data exposes them to potential pitfalls [3, 16, 40]: some "spurious correlations" may be erroneously learned by the DNN. These can act as biases [35]. + +Learned biases can reduce the generalization of the DNN [3, 5, 8, 16, 24, 30]. For example, if a DNN has learned to distinguish airplanes flying in the sky from boats sailing in the ocean, the model will probably use the background as a base for its classification: detecting it instead of learning the vehicle shape is a much simpler task. However, the model does not generalize to scenarios such as a landing seaplane. Differently from domain adaptation [9, 29, 36], where the objective is to learn general features that compensate for the domain shift or to adapt extracted features to different domains, the goal of debiasing is to discourage the learning + +![](images/e3af36cc3de9feb6dfa2ff54a85379eebb5e62f2a86fe3a3418350e1fb6435af.jpg) +Figure 1. Our proposed approach to agnostically remove the bias. + +of spurious correlations. + +Many current debiasing approaches rely on prior information about the bias, such as the existence of an auxiliary label indicating some side information, the presence of bias(es) or their quality [5, 6, 8, 11, 34, 37]. However, obtaining these labels or information on the nature of the bias can be either very costly (due to annotation costs) or very noisy: this is what motivates the development of bias-agnostic approaches. Recent works have shown that bias features are learned "early" [26, 30]; there are bias-target aligned samples, for which the bias is learned, and the performance on the train set increases, and some misaligned ones, for which the prediction is wrong. Since bias-agnostic approaches delve into the biased information from the training set, it is common to amplify the first features learned using Generalized Cross-Entropy [41] and then discourage their learning in an "unbiased" model. However, there is no guarantee that the very first features learned are the biased ones: detecting them agnostically and effectively remains an open question. + +In this work, we propose a method that identifies the best time to extract bias-target alignment information by observing the relative distance of misclassified samples to the Voronoi boundary of the correct target class. We use this information to train an unbiased model, where we give higher weight to bias-misaligned samples, and remove the bias-alignment information from the bottleneck layer (Fig. 1). + +At a glance, our contributions are the following: + +- we propose a bias-agnostic approach that indicates, + +during the training of a vanilla model, when to extract bias-target alignment information. More precisely, we extract it when the distance of misclassified samples to the Voronoi boundary of the target class is maximal (Sec. 3.3); + +- we use the bias alignment information to weight the loss contribution of every single sample: this will favor the learning of misaligned samples (Sec. 3.4.1); +- we propose an approach to eliminate bias information: specifically, we minimize the extractability of bias alignment information at the bottleneck of the DNN, conditioned to bias-target misalignment (Sec. 3.4.2); +- we study the behavior on several datasets typically used for debiasing and compare both supervised and bias-agnostic approaches: although our proposed technique is bias-agnostic, its performance is comparable to that of supervised approaches (Sec. 4.3). + +# 2. Related works + +We will review debiasing approaches below, which can be divided into supervised methods (where we have access to a "bias label"), and unsupervised methods. + +# 2.1. Fairness methods + +While bias can have ethical implications and some debiasing methods can be useful for Fairness, the goals of the two areas of research remain distinct. Fairness aims at minimizing the treatment inequalities between certain groups (according to some ethical principles [12, 14, 22, 39]) generated by classifiers that base their predictions on specific predetermined sets of features or classes (labeled as "sensitive"). Some fairness metrics measure these types of inequalities: Demographic Parity, Equalized Odds, or Equal Opportunity are some representative examples [12, 15, 17] and trying to lead the classifier to optimize them in its learning process can help mitigate unfair discriminations. Debiasing does not necessarily target the protection of specific sample groups or set the "sensitive" features in advance: it aims at promoting the learning of features that will generalize to a real-life distribution. In this work, we tackle debiasing approaches and we will therefore focus on it in the remainder of the article. + +# 2.2. Supervised methods + +Supervised debiasing methods are divided into three categories: pre-processing methods, which modify the dataset before classification; in-processing methods, which modify the learning process of the model; and post-processing methods, which directly modify the output of the DNN. + +Preprocessing methods. Among the most used preprocessing methods in the literature, driven data augmentation plays a prominent role. Generative Adversarial Networks + +(GANs) are widely used to generate realistic images: StyleGANs [10] is indeed one of the mostly used GANs in this context. For example, Kang et al. [23] used it to generate handwritten text in specific styles. In image classification, Geirhos et al. [16] used style transfer to augment ImageNet with texture-bias-conflicting elements to create a more texture-balanced dataset. + +Postprocessing methods. These methods have the advantage of neither re-training models nor requiring additional data for the training. With their Reject Option Classification, for example, Kamiran et al. [21] proposed to take the samples classified with the most uncertainty (outside a predefined confidence margin) and to change their class to decrease the Disparate Impact metric. In this same context, Equalized Odds Postprocessing proposed by Hardt et al. [17] maximizes the Equalized Odds metric. Despite the potential advantages of these approaches, a major drawback lies in the low degrees of freedom for the corrections (since they can only access post-classification information), which limits their practical effectiveness. + +In-processing: debiasing within training. Most of the debiasing methods in the literature work directly on the model, learning from a biased dataset. In general, unbiased elements are weighted more than biased elements. This simple yet effective approach is nowadays very popular in supervised setups [20]. Other methods tackle supervised debiasing by adding regularization terms during the training of the deep model, which is the case of methods such as EnD [34] and FairKL [6]. Another intuitive approach relies upon simply removing the biased features from each sample in the dataset and performing the so-called fairness by blindness. However, the phenomenon known as encoding redundancy [17] states that information is very rarely encoded only once in the data [31], so removing a single value or label is probably not sufficient to remove the effect of the bias on classification. + +# 2.3. Unsupervised methods + +Some recent methods do not rely on bias labels because they can be difficult to obtain on real-life datasets and we will refer to them as "unsupervised" or "bias-agnostic". All of these approaches follow a general scheme, which is typically divided into two phases: bias inference, where a first model, often called "bias capturing", aims to capture biases in the data; and bias mitigation, where a second model is trained to avoid the biases captured by the first model. These approaches rely on prior knowledge, which may be more or less specific to the target task. + +Bias is in the texture. Some work focuses on the bias specifically present in texture, as it is prominent in image classification [16]. Rebias [5], for example, promoted learning with representations that are maximally different from using small receptive fields in convolutional layers. These + +![](images/ee9c3617f456cfb43b62b1e9b0784bbbb5064fd4e2b7ce27aa7596f1d23e6289.jpg) +Figure 2. Overview of the proposed debiasing approach: the bias is first extracted (left) and then the unbiased model is trained (right). Blue arrows represent forward propagation while red arrows represent backpropagation. + +are biased-by-design, toward learning specific textures. For the same texture debiasing task, HEX [37] proposed to use the gray-level co-occurrence matrix and to promote representation independent of colors. + +Bias generates imbalances between groups. Some unsupervised approaches involve finding the bias groups that optimize some fairness metric and train the model to have representations orthogonal to those inferred by the biases. With DebiAN [27], Li et al. for example proposes a method that alternates between the training of bias-capturing and unbiased models, minimizing the Equal Opportunity fairness metric. In EIIL [13], Creager et al. identified biases by finding the groups that maximize violation of an invariance principle measured by the objective function IRMv1 [4]. Similarly, PGI [1] built upon EIIL by minimizing the KL-Divergence of the prediction over these groups. + +Bias is learned early. Some recent methods are based on the assumption that bias features are easy to learn. These features can be extracted at a given point, at the beginning of the training. With LfF [30], Nam et al. proposed a loss reweighing method based on this assumption: they train a biased neural network and amplify its early stages prediction. In parallel, they train a debiased model increasing the weights of "difficult samples". Based on this, with DFA [26], Lee et al. performed data augmentation attempting to disentangle bias features from intrinsic features through latent representations of the bias-capturing and unbiased models. Similarly, with LWBC [25], Kim et al. focus the training of their main classifier on the most "difficult samples" for their classifier committee. With PGD, Ahn et al. [2] use the magnitude of the sample gradient as a metric to increase their importance. + +The closest competing strategy to the one we propose is LfF [30]. Differently from theirs, our main assumption is not that the first features learned by the model are biased: + +we assume that the model, at some point, will adapt to the bias and that it is possible to identify this moment by examining the latent representation of the dataset. This particular point can occur at any time during the training, and so emphasizing the earlier choices of the model can prevent it from efficiently adapting to the bias. Moreover, unlike [30], we do not seek to extract the information from the bias, but its alignment with target classes, which allows our approach to easily scale to multi-biased setups. + +# 3. Proposed Method + +# 3.1. Overview of the proposed method + +Let us consider a supervised learning setup, where we have a dataset $\mathcal{D}$ containing $N$ input samples $(\pmb{x}_1,\dots,\pmb{x}_N)\in \mathcal{X}$ , each associated to a ground truth target label $(\hat{y}_1,\dots,\hat{y}_N)\in \mathcal{Y}$ and an index $n\in \mathcal{N}_{\mathcal{D}}$ . A given deep neural network $\mathcal{M}$ , trained for $e$ epochs, produces $\forall n\in N_{\mathcal{D}}$ an output $\pmb{y}_{e,n}$ given some $\pmb{x}_n$ , and is typically trained to match $\hat{y}_n$ through the minimization of a loss function $\mathcal{L}(\pmb{y}_{e,n},\hat{y}_n)$ . Unfortunately, this learning process does not impose any prior on the specific subset of features that are extracted, which leads to a biased prediction over unseen data. We want to fight this effect. + +Fig. 2 provides an overview of the proposed debiasing approach. First, the bias is inferred by the learning of a vanilla model: at the end of each epoch (or after a few iterations), the target class centroids and the Voronoi boundaries between them are computed from the well-classified samples at the bottleneck layer (Sec. 3.2). The distance of the misclassified samples to the Voronoi boundary is computed to find the epoch $e^{*}$ when the bias-target alignment is maximally learned (Sec. 3.3). Then, a debiasing process follows (Sec. 3.4): from the distances gathered from the previous step, we assign each sample a weight, which will be used + +in the weighted loss (Sec. 3.4.1). In addition, at the bottleneck layer, we minimize the information about bias misalignment: this favors the unbiasedness of the classification head (Sec. 3.4.2). In the rest of this section, we will detail all the steps of our proposed technique. + +# 3.2. Bottleneck latent representation + +The debiasing method we propose stems from the concept of latent representation: the output of each layer of a DNN consists of a representation of the input $\mathbf{x}_n$ . Thus, the classification phase, which takes place just before the output of the model, consists in partitioning the feature space into each of the different classes. Therefore, the output of the bottleneck layer (the output of the backbone) is the compressed representation of the input sample, which is often referred to as latent representation. Therefore, each $\mathbf{x}_n$ has a vector of latent attributes $\mathbf{a}_{e,n} \in \mathbb{R}^K$ (where $K$ is the number of neurons in the bottleneck layer) associated to a specific epoch (or iteration) $e$ for the model $\mathcal{M}$ : this forms its latent bottleneck representation. + +We define $\mathcal{D}_e^{\parallel}$ the set of samples well classified by the model $\mathcal{M}$ at epoch $e$ , and $\mathcal{D}_e^{\perp}$ the misclassified samples. For each $t$ -th target class (of $T$ classes), it is possible to define a class centroid $C_{e,t}$ as the average of the bottleneck representations of each well-classified samples of the $t$ -th target class: + +$$ +C _ {e, t} = \frac {1}{\left| \mathcal {D} _ {e , t} ^ {\parallel} \right|} \sum_ {n \in \mathcal {N} _ {\mathcal {D} _ {e, t} ^ {\parallel}}} \boldsymbol {a} _ {e, n}, \tag {1} +$$ + +where $\mathcal{D}_{e,t}^{\parallel}$ is the subset of correctly classified samples for the $t$ -th class, and $|\cdot|$ denotes the cardinality of a set. Such centroids are proxies for the representations of the correctly classified elements of the class by the model. Let us define Voronoi boundary $H_{e,i,j}$ as the hyperplane equidistant from $C_{e,i}$ and $C_{e,j}$ in the bottleneck representation space of $\mathcal{M}$ : $H_{e,i,j}$ divides the latent space into two Voronoi cells of generators $C_{e,i}$ and $C_{e,j}$ . + +In Fig. 3, we have two target classes (the triangles and the squares) and the bias is pictured as the color (blue and red). The first image ("Initialization") shows the latent representation of the dataset by the model at its initialization: the samples are scattered randomly in the feature space, a first classification occurs, materialized by the Voronoi boundary $H_{0,\Delta,\circ}$ . Ideally, as shown in the picture the furthest to the right ("Ideal classification"), a deep learning model should minimize the intra-class distance and maximize the inter-class one. However, in the presence of bias, another kind of attractor can emerge: the bias-conflicting elements will be attracted by the wrong class. The more the model is biased, the more the sample clusters that form will represent the bias classes more than the target class. For instance, in the second picture, the samples are clustered by color and not by shape: the red triangles have been attracted by the + +circle class that is correlated with the color red. The samples misclassified at that specific moment are bias-target misaligned. If the model is, then, over-parametrized, the biased elements will be attracted as well towards the target centroid (third figure "Epoch $e > e^{*}$ "): although a set of bias-misaligned features are learned, the model still holds biased ones, which leads to a subpar generalization performance: our first goal will be, hence, to detect the $e^{*}$ moment of the learning where it is possible to extract the bias-target misalignment information. + +# 3.3. Bias alignment capture + +To distinguish between bias-misaligned samples and bias-aligned ones, we assume that, after a few learning steps, the farther a misclassified sample is distant from its target Voronoi cell, the more it has been strongly pulled by an attractor. Such an attractor, since it is not its target class centroid, can be considered as resulting from some bias. Hence, when the average distance between the misclassified samples and their target Voronoi cell reaches its maximum, the model has learned bias features. This scenario is visualized in Fig. 3 (second figure "Epoch $e^{*}$ "). To select the exact moment when to extract the bias-target alignment, we are looking for the epoch $e^{*}$ defined by: + +$$ +e ^ {*} = \underset {e} {\operatorname {a r g m a x}} \frac {\sum_ {i} d ^ {*} \left(\boldsymbol {a} _ {e , n}\right)}{\left| \mathcal {D} _ {e} ^ {\perp} \right|}, \tag {2} +$$ + +where + +$$ +\begin{array}{l} d ^ {*} \left(\boldsymbol {a} _ {e, n}\right) = d \left(\boldsymbol {a} _ {e, n}, \boldsymbol {H} _ {e, \operatorname {a r g m a x} \left(\boldsymbol {y} _ {e, n}\right), \hat {\boldsymbol {y}} _ {n}}\right) \tag {3} \\ \cdot \left(1 - \delta_ {\operatorname {a r g m a x} (\boldsymbol {y} _ {e, n}), \hat {y} _ {n}}\right), \\ \end{array} +$$ + +and $d(\pmb{a},\pmb{H})$ indicates the $\ell_2$ distance between $\pmb{a}$ and the closest point of $\pmb{H}$ and $\delta_{\cdot ,\cdot}$ is the Kronecker delta. At this point, we can collect the bias-target alignment information $\mathcal{B}^{*} = (b_{n}^{*})_{n\in \mathcal{N}_{\mathcal{D}}}$ , where $\forall b\in \mathcal{N}_{\mathcal{D}}$ , $b_{n}^{*} = \mathrm{argmax}(\pmb{y}_{e*,n})$ . We can hereby identify the subset of bias-target misaligned samples $\mathcal{D}^{\perp} = \mathcal{D}_{e^{*}}^{\perp}$ , and the set of bias-target aligned ones $\mathcal{D}^{\parallel} = \mathcal{D}_{e^{*}}^{\parallel}$ . Given that vanilla learning strategies employ weight-decay, where the distances tend to diminish when reaching the loss minimum, we propose to modify (3) as + +$$ +\begin{array}{l} d ^ {*} \left(\boldsymbol {a} _ {e, n}\right) = d \left(\boldsymbol {a} _ {e, n}, \boldsymbol {H} _ {e, \operatorname {a r g m a x} \left(\boldsymbol {y} _ {e, n}\right), \hat {\boldsymbol {y}} _ {n}}\right) \\ \cdot \frac {2 \cdot \left(1 - \delta_ {\operatorname* {a r g m a x} \left(\boldsymbol {y} _ {e , n}\right) , \hat {y} _ {n}}\right)}{\| \boldsymbol {C} _ {e , \operatorname* {a r g m a x} \left(\boldsymbol {y} _ {e , n}\right)} \| _ {2} + \| \boldsymbol {C} _ {e , \hat {y} _ {n}} \| _ {2}}, \tag {4} \\ \end{array} +$$ + +where we scale the distance by the averaged $\ell_2$ norm (denoted by $\| \cdot \| _2$ ) of the two considered centroids. + +We highlight that our hypothesis is similar but substantially different, from the one formulated in LfF [30]: here, we are free from the assumption bias features are learned earlier than all the more robust ones by the models, and even more from the assumption that they are the very first features learned by the models. + +![](images/5f8262c6d519db8a50b79d7f460ce2930f0d72b2b58107372f3dbb4b23a1f0a0.jpg) +Figure 3. Representation of latent representations of a dataset at different learning stages. The target classes are shapes and the bias is color. Arrows represent the distance between misclassified elements and the Voronoi boundary. + +![](images/7624e1b67b0f3e4f5cd21f846788d0476b450fb232c4d44f5210ff2a7c0c7512.jpg) + +![](images/704b819a2078f34a43573164c6ed7bec39fd582b19911484ff3c7e7e9f6737ab.jpg) + +![](images/3c21f2c9ef4f99741977bb73c73675467ee09f5a3fe059b3d24568922337297f.jpg) + +# 3.4. Debiasing the model + +Once having extracted the bias alignment labels for each sample, we can start training and debiasing our actual model. In this work, we propose unbiased models having the same architecture and learning parameters as the bias-extracting one, although no explicit constraint forbids us to use different models. Our approach here consists of modifying the objective function optimized during the training of the model with two goals: increasing the weight of the bias-misaligned samples (as they contain relevant information for generalization compared to other representatives of the same class) and moving these samples away from the bias centroid that tends to attract them. + +# 3.4.1 Loss function reweighting + +As shown by LfF [30] and other works like [20], reweighting the loss function to up-weigh the bias-conflicting elements is an efficient method to orient the training in a less biased direction as the correlation bias-target will be less emphasized in the loss. In this work, we assign the weight $r_n$ to the $n$ -th sample according to + +$$ +r _ {n} = \frac {1}{\rho_ {b _ {n} ^ {*}}} \cdot \delta_ {b _ {n} ^ {*}, \hat {y} _ {n}} + \frac {1}{1 - \rho_ {b _ {n} ^ {*}}} \cdot \left(1 - \delta_ {b _ {n} ^ {*}, \hat {y} _ {n}}\right), \tag {5} +$$ + +where we define + +$$ +\rho_ {t} = \frac {\left| \mathcal {D} _ {e ^ {*} , t} ^ {\parallel} \right|}{\left| \mathcal {D} _ {e ^ {*} , t} ^ {\parallel} \cup \mathcal {D} _ {e ^ {*} , t} ^ {\perp} \right|}. \tag {6} +$$ + +In a nutshell, misaligned samples receive a weight that is proportionally inverse to their cardinality in the $t$ -th class. This has the effect of strongly encouraging the learning of bias-misaligned samples, over bias-aligned ones. In the feature space, we can interpret the resulting reweighted loss $\mathcal{L}(r_n,\pmb{y}_{e,n},\hat{y}_n)$ as an attractive force on the bias-misaligned samples, that are being pulled toward their class centroids. + +# 3.4.2 Bias alignment information removal + +Besides having a loss reweighting to favor misaligned sample learning, we can also discourage the model from learning any information related to bias alignment to the target. To estimate how much of this information is learned by the model, at the bottleneck we plug an auxiliary classification head that we call information removal head (IRH). This head is trained to minimize a cross-entropy loss $\mathcal{L}(b_{e,n}, b_n^*)$ . Its performance is an important indicator for us, as it reveals how much the latent space is similar (or different) from the vanilla bias-capturing model, when it was the most fitted to the bias (at epoch $e^*$ ), from the bias-target misalignment perspective. To estimate this similarity more precisely, we compute the mutual information between $\mathcal{B} = (b_{e,n})_{n \in \mathcal{N}_{\mathcal{D}}}^*$ and $\mathcal{B}^*$ under the bias misalignment condition as + +$$ +\mathcal {I} ^ {\perp} = \sum_ {j, k} p _ {\mathcal {B}, \mathcal {B} ^ {*}} ^ {\perp} (j, k) \log_ {T} \left[ \frac {p _ {\mathcal {B} , \mathcal {B} ^ {*}} ^ {\perp} (j , k)}{p _ {\mathcal {B}} ^ {\perp} (j) p _ {\mathcal {B} ^ {*}} ^ {\perp} (k)} \right], \tag {7} +$$ + +where + +$$ +p _ {\mathcal {B}, \mathcal {B} ^ {*}} ^ {\perp} (j, k) = \frac {1}{| \mathcal {D} ^ {\perp} |} \sum_ {n \in \mathcal {N} _ {\mathcal {D}}} \delta_ {j, b _ {n} ^ {*}} \boldsymbol {\sigma} \left(\boldsymbol {b} _ {e, n}\right) _ {k} \left(1 - \delta_ {b _ {n} ^ {*}, \hat {y} _ {n}}\right) \tag {8} +$$ + +is the joint probability between $\mathcal{B}$ and $\mathcal{B}^*$ calculated on the bias-target misaligned samples, $\sigma$ is the softmax function and $p_{\mathcal{B}}^{\perp}, p_{\mathcal{B}^*}^{\perp}$ are the two marginals. (7) is differentiable, as we work with $\sigma(\boldsymbol{b}_{e,n})$ , the softmax-ed output of the IRH. Hence, we are allowed to minimize this term, eventually scaled by a hyper-parameter $\lambda_{\mathcal{I}^{\perp}}$ . + +As displayed in Fig. 2, the mutual information does not contribute to the IRH's update but is propagated directly back to the backbone. Minimizing information over misaligned samples can be seen as a repulsive force, pushing them away from their attractor class. We focus on minimizing conditional mutual information to avoid pushing aligned samples away from their target class, preserving information needed for classification. In the next section, we will test and compare our approach with other state-of-the-art methods. + +# 4. Experiments + +Every result here presented is averaged over three seeds as done in most of the literature, and every algorithm is implemented in Python, using PyTorch 1.13, and trained on GPUs Nvidia GeForce RTX3090 Ti equipped with 24GB RAM. As we compare our method to the other unsupervised state-of-the-art methods, the best-unsupervised accuracies are systematically in bold and the second best are underlined. Besides, we highlight in red the best-overall to see how our method compares even to the supervised ones. + +# 4.1. Datasets + +Here below we describe at a glance the datasets employed for the quantitative evaluation. They were chosen to reflect different problematics bound to biases, from the very simple control case of Biased MNIST to multiple and different biases, synthetic and real-world images. + +Biased MNIST. The first dataset we are using is Biased MNIST, which was first introduced by Bahng et al. [5]. The 60k samples of this dataset consist of a colored version of the famous handwritten digits dataset MNIST with some correlation $\rho$ between the color and the digits. To build it, first one specific color gets assigned to each of the ten digits; then each of the samples gets its background color. We will test on four levels of color-digit correlation $\rho$ : 0.99, 0.995, 0.997, and 0.999. The effect of the bias (namely, the background color) is evaluated by testing the model on a completely unbiased dataset, with $\rho = 0.1$ . + +Multi-Color MNIST. Building on top of Biased MNIST, Li et al. proposed in [27] a bi-colored version to better benchmark the performance of current models on multiple biases at once. Here, the left and the right side of the background have two different colors, with a correlation to the target $\rho_{L}$ for the left background color of the image and $\rho_{R}$ for the right one. We follow their proposed setup, with $\rho_{L} = 0.99$ and $\rho_{R} = 0.95$ . + +CelebA. CelebA [28] is a real-world dataset commonly used to test debiasing performance. It is a face classification dataset provided with 40 attributes for each of the 203k image samples. The task we solve here is to classify "blond" or "not blond" hair, with the main bias lying on the gender, as in the dataset there is a natural bias for "females" to have the "blond" attribute. + +9-class ImageNet. The 9-class ImageNet dataset was proposed by [5], consisting of the extraction of a subset of 9 super-classes from ImageNet-1k, balanced to have each class correlated to a specific texture bias. + +ImageNet-A. ImageNet-A was proposed by Hendrycks et al. in [18] as a subset of cropped images from ImageNet, purposely selected to be very hard to + +Table 1. Results on Balanced Biased MNIST when training with different correlations color-digit $\rho$ . + +
MethodBias agnosticTest accuracy [%] (↑)
ρ=0.999ρ=0.997ρ=0.995ρ=0.99
Vanilla✓11.240.572.488.4
Rubi [8]X13.790.443.093.6
EnD [34]X52.383.793.996.0
BCon+BBal [19]X94.097.397.798.1
HEX [37]BT10.816.619.724.7
ReBias [5]BT26.565.875.488.4
LearnedMixin [11]✓12.150.278.288.3
LfF [30]✓15.363.790.395.1
SoftCon [19]✓65.088.693.195.2
Ours✓58.7±21.892.7±1.295.5±0.897.7±0.3
+ +be classified by state-of-the-art CNNs. They were precisely selected among the subset misclassified by a cluster of ResNet-50 models. Following [5, 6, 19], we use it to test our performance when training on 9-class ImageNet. + +# 4.2. Model architecture and training details + +In our experiments, we consistently employed the same architecture for both the vanilla model and the model used for measuring distances to Voronoi boundaries and debiasing. The architecture details for each dataset are provided below. For the Information Removal Head (IRH), we used SGD optimization with a learning rate of 0.1 for each model and dataset. The cross-entropy loss was used for all our losses, and $\lambda_{\mathcal{I}^{\perp}}$ was set to 2 for all experiments. + +Regarding the experiments on Biased MNIST, we used the same fully convolutional network used for Rebias [5] and Irene [33], of four convolutional layers with $7 \times 7$ kernels, with a batch normalization after each of these layers. For training, we followed the implementation used in [33] of 80 epochs, with an initial learning rate of 0.1 decayed by 0.1 at epochs 40 and 60, and a weight decay of $10^{-4}$ . For Multi-Color MNIST, we employ as architecture the same 3-layer MLP used in [27], trained for 500 epochs (until the model starts overfitting on the training set), using the same optimization strategy as in [27]. For the experiments on CelebA and 9-class ImageNet, we used a pre-trained ResNet-18 and the same optimization strategy as in [19, 30]. + +# 4.3. Discussion + +Here we compare our method to the current state-of-the-art, both supervised and unsupervised, on the multiple datasets presented in Sec. 4.1. In what follows, we divide the supervision level of the method into three categories: bias-agnostic, bias-aware (using an extra ground-truth bias label), and "bias tailored" (BT) where the method does not rely on bias labels, but by construction, it captures specific biases (like the texture [5, 37]). + +Results on Biased MNIST. Our results on Biased MNIST, presented in Table 1, show that our method achieves state-of-the-art performance, even when compared with super + +Table 2. Results on CelebA, targeting the attribute "blond", with a bias towards gender. + +
MethodBias agnosticTest accuracy [%] (↑)
UnbiasedBias-Conflicting
Vanilla✓79.059.0
EnD [34]✗86.976.4
LNL [24]✗80.161.2
DI [38]✗90.986.3
BiasCon + BiasBal [19]✗91.487.2
Group DRO [32]✓85.483.4
LfF [30]✓84.281.2
Ours✓90.2±1.184.5±2.0
+ +vised ones, for not extreme values of $\rho$ : the only method that yields better results on the three lower correlations levels is the use of the associated BiasContrastive and BiasBalanced losses [19]. On the unsupervised field, we get better accuracies than our competitors except for the highest correlation level. We can observe in this case a very high standard deviation because of the high stochastic noise of the gradient: the very few bias-target misaligned (60 in total, constituting $0.1\%$ of the train set) searches for the perfect moment to mark. We hypothesize these difficulties are caused by the large gradients, which make the bias-target alignment information extraction noisy: we tried to perform the bias extraction for this specific setup having a smaller learning rate (0.01), and the performance improved to $72.6\% \pm 11.6$ . Tuning properly the learning rate in extreme scenarios is a key element towards a successful bias-target alignment information extraction. + +Results on Multi-Color MNIST. The Multi-Color MNIST dataset [27] helps us to test the performance of our method on multiple biases at the same time. To differentiate performance in different bias-alignment configurations, we will refer to two distinct partitions of the dataset $\mathcal{D}$ : + +$$ +\mathcal {D} = R ^ {\parallel} \cup R ^ {\perp} = L ^ {\parallel} \cup L ^ {\perp}, \tag {9} +$$ + +where $R^{\parallel}(L^{\parallel})$ is the subset of samples whose right (left) background is aligned with its digit, and $R^{\perp}(L^{\perp})$ when it's not. As previously done in the state-of-the-art [27], we compute separately the accuracies for the four subsets intersections. The average of these four metrics constitutes "unbiased accuracy". The most difficult subset is $R^{\perp} \cap L^{\perp}$ : the performance of the vanilla model is below that of random guessing, and the same is true for three out of five tested debiasing methods. In contrast, every method reaches $100\%$ accuracy or close for samples in $R^{\parallel} \cap L^{\parallel}$ . Even in this case, our method achieves state-of-the-art results for this dataset. More specifically, we record the best-unbiased accuracy, and we improve the best score on the double-conflicting setup by $+8\%$ . For instance, LfF [30], whose main assumption is close to ours, while emphasizing the early choices of its bias-extracting model seems to perform very unevenly regarding the two biases (around $5\%$ accu + +![](images/61f84dcd86bf79a79c81006289e9c427e83c4eb7ea53a1e64691651103d89cd1.jpg) +Figure 4. Evolution of the relative distance to the target Voronoi boundary for the misclassified elements (red curve) and the match between the misclassified samples $\{n|\arg \max (\pmb{y}_{e,n})\neq \hat{y}_n\}$ and the misaligned samples $\{n|\hat{b}_n\neq \hat{y}_n\}$ (blue dashed line). + +racy when for $R^{\perp}$ ). This further strengthens our choice of not extracting a bias label, but the bias-target alignment information, and waiting for the best time to extract it. + +Results on CelebA. On the CelebA dataset, two test setups are employed: the "unbiased", where the average of the scores obtained on each of the target-bias combinations (here blond-male, blond-female, not blond-male and not blond-female) is considered, and the "bias-conflicting" one, where the two bias-aligned combinations are not considered. On both metrics, our approach ranks the best unsupervised $(+4.8\%)$ on the "unbiased" metric), and third overall. + +Results on 9-class ImageNet. When working at debiasing 9-class ImageNet, all other state-of-the-art methods become bias-tailored (BT): indeed, they use BagNet-18 [7] as a bias-extracting model for its known tendency to fit texture (as these datasets are known to be very biased towards texture [16]). If we want to perform bias-agnostic debiasing, we shouldn't rely on that kind of bias-extracting model chosen to fit the bias type of the dataset. However, to compare our method to theirs on an equal footing we tested two configurations: + +- ours (+BagNet), where we extract the bias-conflicting samples from training BagNet-18 and then proceed to debiasing ResNet-18; +- ours, where we extract the bias-conflicting samples directly from the ResNet-18, which makes us the only bias-agnostic method tested on this dataset. + +We obtain comparable results to the state-of-the-art on ImageNet-A (respectively $1.2\%$ and $1.5\%$ below the best-performing method in FairKL [6]) and the two best results overall on 9-class ImageNet. Interestingly, we get state-ofthe-art results with our method, when extracting information directly from ResNet-18. + +Ablation study. We tested the effect of the different modules of our method on Biased MNIST, training with $\rho = 0.99$ . The results in Table 5 show that the use of the reweighted loss function $\mathcal{L}$ yields an average increase in accuracy of $+7.1\%$ and that the use of the IRH further increases it by $+1.7\%$ . Finally, employing a conditional mutual information term (on the bias-target misaligned ele + +Table 3. Test accuracy on four subsets of Multi-Color MNIST. The "Unbiased" accuracy is the average of the four subsets. + +
MethodBias agnosticTest accuracy [%] (↑)
L|| ∩ R||L|| ∩ R↓L↓ ∩ R||L↓ ∩ R↓Unbiased
Vanilla✓100.097.127.55.257.4
LfF [30]✓99.64.798.65.152.0
EIIL [13]✓100.097.270.810.969.7
PGI [1]✓98.682.626.69.554.3
DebiAN [27]✓100.095.676.516.072.0
Ours✓100 ±0.090.9 ±3.577.5 ±2.824.1 ±1.873.1 ±0.9
+ +Table 4. Test accuracy on 9-class ImageNet and ImageNet-A. + +
MethodBias agnosticTest accuracy [%] (↑)
9-class ImageNetImageNet-A
Vanilla✓94.030.5
ReBias [5]X94.030.5
StyllmageNet [16]BT88.424.6
LearnedMixin [11]BT79.219.0
RUBi [8]BT93.931.0
LfF [30]BT91.229.4
SoftCon [19]BT95.334.1
FairKL [6]BT95.135.7
Ours (BagNet [7])BT96.4 ±0.034.5 ±3.4
Ours✓95.5 ±0.234.2 ±0.9
+ +Table 5. Ablation study on Biased MNIST with $\rho = {0.99}$ . + +
Weighted LIRHMisaligned onlyTest accuracy [%](↑)
88.4 ±0.5
✓95.5 ±0.5
✓✓97.2 ±0.4
✓✓✓97.7 ±0.4
+ +ments only) in place of total information removal provides an extra gain in performance. + +We also measured the average relative distances from the misclassified samples at each epoch, comparing it to the match of the extracted bias alignment information $\mathcal{B}$ to the ideal ground truth $\hat{\mathcal{B}} = (\hat{b}_n)_{n\in \mathcal{N}_{\mathcal{D}}}($ (which is provided in Biased MNIST), expressed by + +$$ +\zeta = \frac {1}{| \mathcal {D} ^ {\perp} |} \sum_ {n \in \mathcal {N} _ {\mathcal {D} ^ {\perp}}} \delta_ {\operatorname {a r g m a x} \left(\boldsymbol {y} _ {e, n}\right), \hat {\boldsymbol {b}} _ {n}}. \tag {10} +$$ + +In Fig. 4, we can see a peak in the average distances (marked with $\star$ ) after the first few iterations: the model fits the color bias in less than one epoch of training. As the training continues, the average relative distance decreases as expected: the misclassified samples stay closer to the Voronoi boundary. We observe that the relative average distance is a good proxy for knowing when to learn the optimal bias alignment $\hat{\mathcal{B}}$ , as the two curves show a similar trend. + +General discussion and limitations. Through the conducted experiments, we have observed that our method establishes, in most of the considered setups, a new state-of-the-art for bias-agnostic approaches, and in some cases even + +outperforms supervised methods, such as in 9-class ImageNet and the double-biased Multi-Color MNIST. A limitation of the proposed approach appears when the correlation between bias and target is extremely high ( $\rho = 0.999$ in Biased MNIST). Since it heavily relies on the extraction of these bias-conflicting samples, when the stochastic noise overwhelms the extraction of the bias misalignment information, the proposed method will be sub-optimal. A possible solution to this problem relies upon using a "sufficiently small" learning rate. Finally, our method strongly depends on the existence of these bias-conflicting elements: in a fully-biased dataset, where the alignment bias-target $\rho = 1$ , since we have no information to extract from the training set, our approach is expected to fail. + +# 5. Conclusion + +In this paper, we have presented an unsupervised, bias-agnostic debiasing approach, whose performance is generally of the same order as that of state-of-the-art supervised methods. We proposed a new bias-target alignment extraction method based on the distance between the misclassified samples and the Voronoi boundary separating them from their target class. Based on this distilled information, we proposed a debiasing method composed of two synergetic elements. The first is a reweighted loss, where sample weights reflect the bias-target (mis)alignment. The second is a bias-target alignment information removal term, acting as a regularizer for the latent space. We tested our method on several debiasing benchmarks, recording a new state-of-the-art for unsupervised debiasing in most of the considered scenarios, although no specific hyperparameters tuning was performed. In extreme cases, where the bias-target alignment is extremely high, we observed that the appropriate choice of the vanilla model's learning setup is crucial to the success of the proposed approach, and its exploration is left as future work. + +Acknowledgments. This work was granted access to the HPC resources of IDRIS under the allocation 2023-AD011014080 made by GENCI. + +# References + +[1] Faruk Ahmed, Yoshua Bengio, Harm van Seijen, and Aaron C. Courville. Systematic generalisation with group invariant predictions. In International Conference on Learning Representations, 2021. 3, 8 +[2] Sumyeong Ahn, Seongyoon Kim, and Se-Young Yun. Mitigating dataset bias by using per-sample gradient. 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Distributionally robust neural networks. In International Conference on Learning Representations, 2020. 7 +[33] Enzo Tartaglione. Information removal at the bottleneck in deep neural networks. In 33rd British Machine Vision Conference 2022, {BMVC} 2022, London, UK, November 21-24, 2022, 2022. 6 +[34] Enzo Tartaglione, Carlo Alberto Barbano, and Marco Grangetto. End: Entangling and disentangling deep representations for bias correction. In Proceedings of the IEEE/CVF conference on computer vision and pattern recognition, pages 13508-13517, 2021. 1, 2, 6, 7 +[35] Antonio Torralba and Alexei A Efros. Unbiased look at dataset bias. In CVPR 2011, pages 1521-1528. IEEE, 2011. 1 +[36] Eric Tzeng, Judy Hoffman, N. Zhang, Kate Saenko, and Trevor Darrell. Deep domain confusion: Maximizing for domain invariance. ArXiv, abs/1412.3474, 2014. 1 +[37] Haohan Wang, Zexue He, Zachary L. Lipton, and Eric P. Xing. Learning robust representations by projecting superficial statistics out. 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Advances in neural information processing systems, 31, 2018. 1 \ No newline at end of file diff --git a/2023/Mining bias-target Alignment from Voronoi Cells/images.zip b/2023/Mining bias-target Alignment from Voronoi Cells/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..b7bf94b77e068ad3e9d55d0fb2e59094dce6e4b7 --- /dev/null +++ b/2023/Mining bias-target Alignment from Voronoi Cells/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:409830b679f4f4f850d331b7af0ced533eb6a4f443134935d6cba98599fa905c +size 384625 diff --git a/2023/Mining bias-target Alignment from Voronoi Cells/layout.json b/2023/Mining bias-target Alignment from Voronoi Cells/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..882928ea0e179050cb7373301ea0eb1c32bd77a7 --- /dev/null +++ b/2023/Mining bias-target Alignment from Voronoi Cells/layout.json @@ -0,0 +1,8491 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 144, + 103, + 451, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 144, + 103, + 451, + 121 + ], + "spans": [ + { + "bbox": [ + 144, + 103, + 451, + 121 + ], + "type": "text", + "content": "Mining bias-target Alignment from Voronoi Cells" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 124, + 144, + 466, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 124, + 144, + 466, + 185 + ], + "spans": [ + { + "bbox": [ + 124, + 144, + 466, + 185 + ], + "type": "text", + "content": "Rémi Nahon Van-Tam Nguyen Enzo Tartaglione LTCI, Télecom Paris, Institut Polytechnique de Paris, France {remi.nahon, van-tam.nguyen, enzo tartaglione}@telecom-paris.fr" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "spans": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 239, + 290, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 290, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 290, + 418 + ], + "type": "text", + "content": "Despite significant research efforts, deep neural networks remain vulnerable to biases: this raises concerns about their fairness and limits their generalization. In this paper, we propose a bias-agnostic approach to mitigate the impact of biases in deep neural networks. Unlike traditional debiasing approaches, we rely on a metric to quantify \"bias alignment/misalignment\" on target classes and use this information to discourage the propagation of bias-target alignment information through the network. We conduct experiments on several commonly used datasets for debiasing and compare our method with supervised and bias-specific approaches. Our results indicate that the proposed method achieves comparable performance to state-of-the-art supervised approaches, despite being bias-agnostic, even in the presence of multiple biases in the same sample." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 441, + 128, + 453 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 441, + 128, + 453 + ], + "spans": [ + { + "bbox": [ + 47, + 441, + 128, + 453 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 461, + 287, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 461, + 287, + 581 + ], + "spans": [ + { + "bbox": [ + 46, + 461, + 287, + 581 + ], + "type": "text", + "content": "Today, deep Neural Networks (DNNs) are renowned for their high performance and resilience in many areas of computer vision, such as image classification, semantic segmentation, and object detection, used in fields ranging from self-driving vehicles to face recognition or surgical guidance. However, it is well known that their tendency to rely heavily on any type of correlation present in the training data exposes them to potential pitfalls [3, 16, 40]: some \"spurious correlations\" may be erroneously learned by the DNN. These can act as biases [35]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 582, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 714 + ], + "type": "text", + "content": "Learned biases can reduce the generalization of the DNN [3, 5, 8, 16, 24, 30]. For example, if a DNN has learned to distinguish airplanes flying in the sky from boats sailing in the ocean, the model will probably use the background as a base for its classification: detecting it instead of learning the vehicle shape is a much simpler task. However, the model does not generalize to scenarios such as a landing seaplane. Differently from domain adaptation [9, 29, 36], where the objective is to learn general features that compensate for the domain shift or to adapt extracted features to different domains, the goal of debiasing is to discourage the learning" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 312, + 211, + 541, + 326 + ], + "blocks": [ + { + "bbox": [ + 312, + 211, + 541, + 326 + ], + "lines": [ + { + "bbox": [ + 312, + 211, + 541, + 326 + ], + "spans": [ + { + "bbox": [ + 312, + 211, + 541, + 326 + ], + "type": "image", + "image_path": "e3af36cc3de9feb6dfa2ff54a85379eebb5e62f2a86fe3a3418350e1fb6435af.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 333, + 544, + 345 + ], + "lines": [ + { + "bbox": [ + 306, + 333, + 544, + 345 + ], + "spans": [ + { + "bbox": [ + 306, + 333, + 544, + 345 + ], + "type": "text", + "content": "Figure 1. Our proposed approach to agnostically remove the bias." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 365, + 406, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 365, + 406, + 376 + ], + "spans": [ + { + "bbox": [ + 305, + 365, + 406, + 376 + ], + "type": "text", + "content": "of spurious correlations." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 377, + 546, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 377, + 546, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 377, + 546, + 605 + ], + "type": "text", + "content": "Many current debiasing approaches rely on prior information about the bias, such as the existence of an auxiliary label indicating some side information, the presence of bias(es) or their quality [5, 6, 8, 11, 34, 37]. However, obtaining these labels or information on the nature of the bias can be either very costly (due to annotation costs) or very noisy: this is what motivates the development of bias-agnostic approaches. Recent works have shown that bias features are learned \"early\" [26, 30]; there are bias-target aligned samples, for which the bias is learned, and the performance on the train set increases, and some misaligned ones, for which the prediction is wrong. Since bias-agnostic approaches delve into the biased information from the training set, it is common to amplify the first features learned using Generalized Cross-Entropy [41] and then discourage their learning in an \"unbiased\" model. However, there is no guarantee that the very first features learned are the biased ones: detecting them agnostically and effectively remains an open question." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 605, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 689 + ], + "type": "text", + "content": "In this work, we propose a method that identifies the best time to extract bias-target alignment information by observing the relative distance of misclassified samples to the Voronoi boundary of the correct target class. We use this information to train an unbiased model, where we give higher weight to bias-misaligned samples, and remove the bias-alignment information from the bottleneck layer (Fig. 1)." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 689, + 501, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 501, + 700 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 501, + 700 + ], + "type": "text", + "content": "At a glance, our contributions are the following:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "content": "- we propose a bias-agnostic approach that indicates," + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "4946" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 66, + 72, + 286, + 131 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 72, + 286, + 131 + ], + "spans": [ + { + "bbox": [ + 66, + 72, + 286, + 131 + ], + "type": "text", + "content": "during the training of a vanilla model, when to extract bias-target alignment information. More precisely, we extract it when the distance of misclassified samples to the Voronoi boundary of the target class is maximal (Sec. 3.3);" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 59, + 133, + 286, + 275 + ], + "type": "list", + "angle": 0, + "index": 4, + "blocks": [ + { + "bbox": [ + 59, + 133, + 286, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 133, + 286, + 167 + ], + "spans": [ + { + "bbox": [ + 59, + 133, + 286, + 167 + ], + "type": "text", + "content": "- we use the bias alignment information to weight the loss contribution of every single sample: this will favor the learning of misaligned samples (Sec. 3.4.1);" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 168, + 286, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 168, + 286, + 215 + ], + "spans": [ + { + "bbox": [ + 59, + 168, + 286, + 215 + ], + "type": "text", + "content": "- we propose an approach to eliminate bias information: specifically, we minimize the extractability of bias alignment information at the bottleneck of the DNN, conditioned to bias-target misalignment (Sec. 3.4.2);" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 217, + 286, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 217, + 286, + 275 + ], + "spans": [ + { + "bbox": [ + 59, + 217, + 286, + 275 + ], + "type": "text", + "content": "- we study the behavior on several datasets typically used for debiasing and compare both supervised and bias-agnostic approaches: although our proposed technique is bias-agnostic, its performance is comparable to that of supervised approaches (Sec. 4.3)." + } + ] + } + ], + "index": 3 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 289, + 135, + 300 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 289, + 135, + 300 + ], + "spans": [ + { + "bbox": [ + 47, + 289, + 135, + 300 + ], + "type": "text", + "content": "2. Related works" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 309, + 286, + 344 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 309, + 286, + 344 + ], + "spans": [ + { + "bbox": [ + 47, + 309, + 286, + 344 + ], + "type": "text", + "content": "We will review debiasing approaches below, which can be divided into supervised methods (where we have access to a \"bias label\"), and unsupervised methods." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 354, + 151, + 366 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 354, + 151, + 366 + ], + "spans": [ + { + "bbox": [ + 47, + 354, + 151, + 366 + ], + "type": "text", + "content": "2.1. Fairness methods" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 373, + 286, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 373, + 286, + 588 + ], + "spans": [ + { + "bbox": [ + 47, + 373, + 286, + 588 + ], + "type": "text", + "content": "While bias can have ethical implications and some debiasing methods can be useful for Fairness, the goals of the two areas of research remain distinct. Fairness aims at minimizing the treatment inequalities between certain groups (according to some ethical principles [12, 14, 22, 39]) generated by classifiers that base their predictions on specific predetermined sets of features or classes (labeled as \"sensitive\"). Some fairness metrics measure these types of inequalities: Demographic Parity, Equalized Odds, or Equal Opportunity are some representative examples [12, 15, 17] and trying to lead the classifier to optimize them in its learning process can help mitigate unfair discriminations. Debiasing does not necessarily target the protection of specific sample groups or set the \"sensitive\" features in advance: it aims at promoting the learning of features that will generalize to a real-life distribution. In this work, we tackle debiasing approaches and we will therefore focus on it in the remainder of the article." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 598, + 163, + 611 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 598, + 163, + 611 + ], + "spans": [ + { + "bbox": [ + 47, + 598, + 163, + 611 + ], + "type": "text", + "content": "2.2. Supervised methods" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 618, + 286, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 618, + 286, + 677 + ], + "spans": [ + { + "bbox": [ + 47, + 618, + 286, + 677 + ], + "type": "text", + "content": "Supervised debiasing methods are divided into three categories: pre-processing methods, which modify the dataset before classification; in-processing methods, which modify the learning process of the model; and post-processing methods, which directly modify the output of the DNN." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 678, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 678, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 678, + 286, + 713 + ], + "type": "text", + "content": "Preprocessing methods. Among the most used preprocessing methods in the literature, driven data augmentation plays a prominent role. Generative Adversarial Networks" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 72, + 545, + 155 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 155 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 155 + ], + "type": "text", + "content": "(GANs) are widely used to generate realistic images: StyleGANs [10] is indeed one of the mostly used GANs in this context. For example, Kang et al. [23] used it to generate handwritten text in specific styles. In image classification, Geirhos et al. [16] used style transfer to augment ImageNet with texture-bias-conflicting elements to create a more texture-balanced dataset." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 156, + 545, + 311 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 156, + 545, + 311 + ], + "spans": [ + { + "bbox": [ + 304, + 156, + 545, + 311 + ], + "type": "text", + "content": "Postprocessing methods. These methods have the advantage of neither re-training models nor requiring additional data for the training. With their Reject Option Classification, for example, Kamiran et al. [21] proposed to take the samples classified with the most uncertainty (outside a predefined confidence margin) and to change their class to decrease the Disparate Impact metric. In this same context, Equalized Odds Postprocessing proposed by Hardt et al. [17] maximizes the Equalized Odds metric. Despite the potential advantages of these approaches, a major drawback lies in the low degrees of freedom for the corrections (since they can only access post-classification information), which limits their practical effectiveness." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 312, + 545, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 545, + 502 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 545, + 502 + ], + "type": "text", + "content": "In-processing: debiasing within training. Most of the debiasing methods in the literature work directly on the model, learning from a biased dataset. In general, unbiased elements are weighted more than biased elements. This simple yet effective approach is nowadays very popular in supervised setups [20]. Other methods tackle supervised debiasing by adding regularization terms during the training of the deep model, which is the case of methods such as EnD [34] and FairKL [6]. Another intuitive approach relies upon simply removing the biased features from each sample in the dataset and performing the so-called fairness by blindness. However, the phenomenon known as encoding redundancy [17] states that information is very rarely encoded only once in the data [31], so removing a single value or label is probably not sufficient to remove the effect of the bias on classification." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 514, + 434, + 527 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 514, + 434, + 527 + ], + "spans": [ + { + "bbox": [ + 306, + 514, + 434, + 527 + ], + "type": "text", + "content": "2.3. Unsupervised methods" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 534, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 545, + 653 + ], + "type": "text", + "content": "Some recent methods do not rely on bias labels because they can be difficult to obtain on real-life datasets and we will refer to them as \"unsupervised\" or \"bias-agnostic\". All of these approaches follow a general scheme, which is typically divided into two phases: bias inference, where a first model, often called \"bias capturing\", aims to capture biases in the data; and bias mitigation, where a second model is trained to avoid the biases captured by the first model. These approaches rely on prior knowledge, which may be more or less specific to the target task." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 654, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 712 + ], + "type": "text", + "content": "Bias is in the texture. Some work focuses on the bias specifically present in texture, as it is prominent in image classification [16]. Rebias [5], for example, promoted learning with representations that are maximally different from using small receptive fields in convolutional layers. These" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4947" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 72, + 534, + 240 + ], + "blocks": [ + { + "bbox": [ + 55, + 72, + 534, + 240 + ], + "lines": [ + { + "bbox": [ + 55, + 72, + 534, + 240 + ], + "spans": [ + { + "bbox": [ + 55, + 72, + 534, + 240 + ], + "type": "image", + "image_path": "ee9c3617f456cfb43b62b1e9b0784bbbb5064fd4e2b7ce27aa7596f1d23e6289.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 244, + 546, + 268 + ], + "lines": [ + { + "bbox": [ + 46, + 244, + 546, + 268 + ], + "spans": [ + { + "bbox": [ + 46, + 244, + 546, + 268 + ], + "type": "text", + "content": "Figure 2. Overview of the proposed debiasing approach: the bias is first extracted (left) and then the unbiased model is trained (right). Blue arrows represent forward propagation while red arrows represent backpropagation." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 286, + 287, + 334 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 286, + 287, + 334 + ], + "spans": [ + { + "bbox": [ + 46, + 286, + 287, + 334 + ], + "type": "text", + "content": "are biased-by-design, toward learning specific textures. For the same texture debiasing task, HEX [37] proposed to use the gray-level co-occurrence matrix and to promote representation independent of colors." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 335, + 287, + 477 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 335, + 287, + 477 + ], + "spans": [ + { + "bbox": [ + 46, + 335, + 287, + 477 + ], + "type": "text", + "content": "Bias generates imbalances between groups. Some unsupervised approaches involve finding the bias groups that optimize some fairness metric and train the model to have representations orthogonal to those inferred by the biases. With DebiAN [27], Li et al. for example proposes a method that alternates between the training of bias-capturing and unbiased models, minimizing the Equal Opportunity fairness metric. In EIIL [13], Creager et al. identified biases by finding the groups that maximize violation of an invariance principle measured by the objective function IRMv1 [4]. Similarly, PGI [1] built upon EIIL by minimizing the KL-Divergence of the prediction over these groups." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 478, + 287, + 668 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 478, + 287, + 668 + ], + "spans": [ + { + "bbox": [ + 46, + 478, + 287, + 668 + ], + "type": "text", + "content": "Bias is learned early. Some recent methods are based on the assumption that bias features are easy to learn. These features can be extracted at a given point, at the beginning of the training. With LfF [30], Nam et al. proposed a loss reweighing method based on this assumption: they train a biased neural network and amplify its early stages prediction. In parallel, they train a debiased model increasing the weights of \"difficult samples\". Based on this, with DFA [26], Lee et al. performed data augmentation attempting to disentangle bias features from intrinsic features through latent representations of the bias-capturing and unbiased models. Similarly, with LWBC [25], Kim et al. focus the training of their main classifier on the most \"difficult samples\" for their classifier committee. With PGD, Ahn et al. [2] use the magnitude of the sample gradient as a metric to increase their importance." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 670, + 287, + 704 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 670, + 287, + 704 + ], + "spans": [ + { + "bbox": [ + 46, + 670, + 287, + 704 + ], + "type": "text", + "content": "The closest competing strategy to the one we propose is LfF [30]. Differently from theirs, our main assumption is not that the first features learned by the model are biased:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 286, + 546, + 394 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 286, + 546, + 394 + ], + "spans": [ + { + "bbox": [ + 304, + 286, + 546, + 394 + ], + "type": "text", + "content": "we assume that the model, at some point, will adapt to the bias and that it is possible to identify this moment by examining the latent representation of the dataset. This particular point can occur at any time during the training, and so emphasizing the earlier choices of the model can prevent it from efficiently adapting to the bias. Moreover, unlike [30], we do not seek to extract the information from the bias, but its alignment with target classes, which allows our approach to easily scale to multi-biased setups." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 409, + 411, + 422 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 409, + 411, + 422 + ], + "spans": [ + { + "bbox": [ + 306, + 409, + 411, + 422 + ], + "type": "text", + "content": "3. Proposed Method" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 430, + 486, + 443 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 430, + 486, + 443 + ], + "spans": [ + { + "bbox": [ + 306, + 430, + 486, + 443 + ], + "type": "text", + "content": "3.1. Overview of the proposed method" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": "Let us consider a supervised learning setup, where we have a dataset " + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": " containing " + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": " input samples " + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "inline_equation", + "content": "(\\pmb{x}_1,\\dots,\\pmb{x}_N)\\in \\mathcal{X}" + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": ", each associated to a ground truth target label " + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "inline_equation", + "content": "(\\hat{y}_1,\\dots,\\hat{y}_N)\\in \\mathcal{Y}" + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": " and an index " + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "inline_equation", + "content": "n\\in \\mathcal{N}_{\\mathcal{D}}" + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": ". A given deep neural network " + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathcal{M}" + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": ", trained for " + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": " epochs, produces " + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\forall n\\in N_{\\mathcal{D}}" + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": " an output " + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\pmb{y}_{e,n}" + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": " given some " + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\pmb{x}_n" + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": ", and is typically trained to match " + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\hat{y}_n" + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": " through the minimization of a loss function " + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathcal{L}(\\pmb{y}_{e,n},\\hat{y}_n)" + }, + { + "bbox": [ + 304, + 450, + 545, + 581 + ], + "type": "text", + "content": ". Unfortunately, this learning process does not impose any prior on the specific subset of features that are extracted, which leads to a biased prediction over unseen data. We want to fight this effect." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "type": "text", + "content": "Fig. 2 provides an overview of the proposed debiasing approach. First, the bias is inferred by the learning of a vanilla model: at the end of each epoch (or after a few iterations), the target class centroids and the Voronoi boundaries between them are computed from the well-classified samples at the bottleneck layer (Sec. 3.2). The distance of the misclassified samples to the Voronoi boundary is computed to find the epoch " + }, + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "type": "inline_equation", + "content": "e^{*}" + }, + { + "bbox": [ + 304, + 582, + 546, + 713 + ], + "type": "text", + "content": " when the bias-target alignment is maximally learned (Sec. 3.3). Then, a debiasing process follows (Sec. 3.4): from the distances gathered from the previous step, we assign each sample a weight, which will be used" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4948" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": "in the weighted loss (Sec. 3.4.1). In addition, at the bottleneck layer, we minimize the information about bias misalignment: this favors the unbiasedness of the classification head (Sec. 3.4.2). In the rest of this section, we will detail all the steps of our proposed technique." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 139, + 220, + 152 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 139, + 220, + 152 + ], + "spans": [ + { + "bbox": [ + 47, + 139, + 220, + 152 + ], + "type": "text", + "content": "3.2. Bottleneck latent representation" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "spans": [ + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "text", + "content": "The debiasing method we propose stems from the concept of latent representation: the output of each layer of a DNN consists of a representation of the input " + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_n" + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "text", + "content": ". Thus, the classification phase, which takes place just before the output of the model, consists in partitioning the feature space into each of the different classes. Therefore, the output of the bottleneck layer (the output of the backbone) is the compressed representation of the input sample, which is often referred to as latent representation. Therefore, each " + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_n" + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "text", + "content": " has a vector of latent attributes " + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{a}_{e,n} \\in \\mathbb{R}^K" + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "text", + "content": " (where " + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "text", + "content": " is the number of neurons in the bottleneck layer) associated to a specific epoch (or iteration) " + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "text", + "content": " for the model " + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "inline_equation", + "content": "\\mathcal{M}" + }, + { + "bbox": [ + 46, + 158, + 287, + 312 + ], + "type": "text", + "content": ": this forms its latent bottleneck representation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "spans": [ + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "text", + "content": "We define " + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_e^{\\parallel}" + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "text", + "content": " the set of samples well classified by the model " + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "inline_equation", + "content": "\\mathcal{M}" + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "text", + "content": " at epoch " + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_e^{\\perp}" + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "text", + "content": " the misclassified samples. For each " + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "text", + "content": "-th target class (of " + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "text", + "content": " classes), it is possible to define a class centroid " + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "inline_equation", + "content": "C_{e,t}" + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "text", + "content": " as the average of the bottleneck representations of each well-classified samples of the " + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 47, + 314, + 287, + 375 + ], + "type": "text", + "content": "-th target class:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 108, + 382, + 287, + 418 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 108, + 382, + 287, + 418 + ], + "spans": [ + { + "bbox": [ + 108, + 382, + 287, + 418 + ], + "type": "interline_equation", + "content": "C _ {e, t} = \\frac {1}{\\left| \\mathcal {D} _ {e , t} ^ {\\parallel} \\right|} \\sum_ {n \\in \\mathcal {N} _ {\\mathcal {D} _ {e, t} ^ {\\parallel}}} \\boldsymbol {a} _ {e, n}, \\tag {1}", + "image_path": "ce02e4dcfe16ddd25058429bda9942f5dc9e1e2b95e39bb587ebbda5d6255d6e.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_{e,t}^{\\parallel}" + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "text", + "content": " is the subset of correctly classified samples for the " + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "text", + "content": "-th class, and " + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "inline_equation", + "content": "|\\cdot|" + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "text", + "content": " denotes the cardinality of a set. Such centroids are proxies for the representations of the correctly classified elements of the class by the model. Let us define Voronoi boundary " + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "inline_equation", + "content": "H_{e,i,j}" + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "text", + "content": " as the hyperplane equidistant from " + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "inline_equation", + "content": "C_{e,i}" + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "inline_equation", + "content": "C_{e,j}" + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "text", + "content": " in the bottleneck representation space of " + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "inline_equation", + "content": "\\mathcal{M}" + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "text", + "content": ": " + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "inline_equation", + "content": "H_{e,i,j}" + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "text", + "content": " divides the latent space into two Voronoi cells of generators " + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "inline_equation", + "content": "C_{e,i}" + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "inline_equation", + "content": "C_{e,j}" + }, + { + "bbox": [ + 46, + 425, + 287, + 521 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 522, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 522, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 522, + 287, + 713 + ], + "type": "text", + "content": "In Fig. 3, we have two target classes (the triangles and the squares) and the bias is pictured as the color (blue and red). The first image (\"Initialization\") shows the latent representation of the dataset by the model at its initialization: the samples are scattered randomly in the feature space, a first classification occurs, materialized by the Voronoi boundary " + }, + { + "bbox": [ + 46, + 522, + 287, + 713 + ], + "type": "inline_equation", + "content": "H_{0,\\Delta,\\circ}" + }, + { + "bbox": [ + 46, + 522, + 287, + 713 + ], + "type": "text", + "content": ". Ideally, as shown in the picture the furthest to the right (\"Ideal classification\"), a deep learning model should minimize the intra-class distance and maximize the inter-class one. However, in the presence of bias, another kind of attractor can emerge: the bias-conflicting elements will be attracted by the wrong class. The more the model is biased, the more the sample clusters that form will represent the bias classes more than the target class. For instance, in the second picture, the samples are clustered by color and not by shape: the red triangles have been attracted by the" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "type": "text", + "content": "circle class that is correlated with the color red. The samples misclassified at that specific moment are bias-target misaligned. If the model is, then, over-parametrized, the biased elements will be attracted as well towards the target centroid (third figure \"Epoch " + }, + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "type": "inline_equation", + "content": "e > e^{*}" + }, + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "type": "text", + "content": "\"): although a set of bias-misaligned features are learned, the model still holds biased ones, which leads to a subpar generalization performance: our first goal will be, hence, to detect the " + }, + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "type": "inline_equation", + "content": "e^{*}" + }, + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "type": "text", + "content": " moment of the learning where it is possible to extract the bias-target misalignment information." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 198, + 437, + 211 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 198, + 437, + 211 + ], + "spans": [ + { + "bbox": [ + 306, + 198, + 437, + 211 + ], + "type": "text", + "content": "3.3. Bias alignment capture" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 217, + 545, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 217, + 545, + 361 + ], + "spans": [ + { + "bbox": [ + 304, + 217, + 545, + 361 + ], + "type": "text", + "content": "To distinguish between bias-misaligned samples and bias-aligned ones, we assume that, after a few learning steps, the farther a misclassified sample is distant from its target Voronoi cell, the more it has been strongly pulled by an attractor. Such an attractor, since it is not its target class centroid, can be considered as resulting from some bias. Hence, when the average distance between the misclassified samples and their target Voronoi cell reaches its maximum, the model has learned bias features. This scenario is visualized in Fig. 3 (second figure \"Epoch " + }, + { + "bbox": [ + 304, + 217, + 545, + 361 + ], + "type": "inline_equation", + "content": "e^{*}" + }, + { + "bbox": [ + 304, + 217, + 545, + 361 + ], + "type": "text", + "content": "\"). To select the exact moment when to extract the bias-target alignment, we are looking for the epoch " + }, + { + "bbox": [ + 304, + 217, + 545, + 361 + ], + "type": "inline_equation", + "content": "e^{*}" + }, + { + "bbox": [ + 304, + 217, + 545, + 361 + ], + "type": "text", + "content": " defined by:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 371, + 365, + 545, + 389 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 371, + 365, + 545, + 389 + ], + "spans": [ + { + "bbox": [ + 371, + 365, + 545, + 389 + ], + "type": "interline_equation", + "content": "e ^ {*} = \\underset {e} {\\operatorname {a r g m a x}} \\frac {\\sum_ {i} d ^ {*} \\left(\\boldsymbol {a} _ {e , n}\\right)}{\\left| \\mathcal {D} _ {e} ^ {\\perp} \\right|}, \\tag {2}", + "image_path": "21450299b49408c802f7f8c0dfcb1b61bfe2aa2c2a81966ab75039f43b98ed00.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 394, + 333, + 404 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 394, + 333, + 404 + ], + "spans": [ + { + "bbox": [ + 306, + 394, + 333, + 404 + ], + "type": "text", + "content": "where" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 344, + 411, + 545, + 443 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 344, + 411, + 545, + 443 + ], + "spans": [ + { + "bbox": [ + 344, + 411, + 545, + 443 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} d ^ {*} \\left(\\boldsymbol {a} _ {e, n}\\right) = d \\left(\\boldsymbol {a} _ {e, n}, \\boldsymbol {H} _ {e, \\operatorname {a r g m a x} \\left(\\boldsymbol {y} _ {e, n}\\right), \\hat {\\boldsymbol {y}} _ {n}}\\right) \\tag {3} \\\\ \\cdot \\left(1 - \\delta_ {\\operatorname {a r g m a x} (\\boldsymbol {y} _ {e, n}), \\hat {y} _ {n}}\\right), \\\\ \\end{array}", + "image_path": "8fe55c18247f00a2a7dabde15115440898ed76d193c40884a4dab12318d1cf07.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "spans": [ + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "text", + "content": "and " + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "inline_equation", + "content": "d(\\pmb{a},\\pmb{H})" + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "text", + "content": " indicates the " + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "inline_equation", + "content": "\\ell_2" + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "text", + "content": " distance between " + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "inline_equation", + "content": "\\pmb{a}" + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "text", + "content": " and the closest point of " + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "inline_equation", + "content": "\\pmb{H}" + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "inline_equation", + "content": "\\delta_{\\cdot ,\\cdot}" + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "text", + "content": " is the Kronecker delta. At this point, we can collect the bias-target alignment information " + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "inline_equation", + "content": "\\mathcal{B}^{*} = (b_{n}^{*})_{n\\in \\mathcal{N}_{\\mathcal{D}}}" + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "inline_equation", + "content": "\\forall b\\in \\mathcal{N}_{\\mathcal{D}}" + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "inline_equation", + "content": "b_{n}^{*} = \\mathrm{argmax}(\\pmb{y}_{e*,n})" + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "text", + "content": ". We can hereby identify the subset of bias-target misaligned samples " + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "inline_equation", + "content": "\\mathcal{D}^{\\perp} = \\mathcal{D}_{e^{*}}^{\\perp}" + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "text", + "content": ", and the set of bias-target aligned ones " + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "inline_equation", + "content": "\\mathcal{D}^{\\parallel} = \\mathcal{D}_{e^{*}}^{\\parallel}" + }, + { + "bbox": [ + 304, + 449, + 545, + 559 + ], + "type": "text", + "content": ". Given that vanilla learning strategies employ weight-decay, where the distances tend to diminish when reaching the loss minimum, we propose to modify (3) as" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 330, + 565, + 545, + 611 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 330, + 565, + 545, + 611 + ], + "spans": [ + { + "bbox": [ + 330, + 565, + 545, + 611 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} d ^ {*} \\left(\\boldsymbol {a} _ {e, n}\\right) = d \\left(\\boldsymbol {a} _ {e, n}, \\boldsymbol {H} _ {e, \\operatorname {a r g m a x} \\left(\\boldsymbol {y} _ {e, n}\\right), \\hat {\\boldsymbol {y}} _ {n}}\\right) \\\\ \\cdot \\frac {2 \\cdot \\left(1 - \\delta_ {\\operatorname* {a r g m a x} \\left(\\boldsymbol {y} _ {e , n}\\right) , \\hat {y} _ {n}}\\right)}{\\| \\boldsymbol {C} _ {e , \\operatorname* {a r g m a x} \\left(\\boldsymbol {y} _ {e , n}\\right)} \\| _ {2} + \\| \\boldsymbol {C} _ {e , \\hat {y} _ {n}} \\| _ {2}}, \\tag {4} \\\\ \\end{array}", + "image_path": "2c2dca807baeed043352931c38de500e23b2a2b74617c1e4360853ea0a365d0f.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 617, + 544, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 544, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 544, + 641 + ], + "type": "text", + "content": "where we scale the distance by the averaged " + }, + { + "bbox": [ + 304, + 617, + 544, + 641 + ], + "type": "inline_equation", + "content": "\\ell_2" + }, + { + "bbox": [ + 304, + 617, + 544, + 641 + ], + "type": "text", + "content": " norm (denoted by " + }, + { + "bbox": [ + 304, + 617, + 544, + 641 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\| _2" + }, + { + "bbox": [ + 304, + 617, + 544, + 641 + ], + "type": "text", + "content": ") of the two considered centroids." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "type": "text", + "content": "We highlight that our hypothesis is similar but substantially different, from the one formulated in LfF [30]: here, we are free from the assumption bias features are learned earlier than all the more robust ones by the models, and even more from the assumption that they are the very first features learned by the models." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4949" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 61, + 72, + 175, + 186 + ], + "blocks": [ + { + "bbox": [ + 61, + 72, + 175, + 186 + ], + "lines": [ + { + "bbox": [ + 61, + 72, + 175, + 186 + ], + "spans": [ + { + "bbox": [ + 61, + 72, + 175, + 186 + ], + "type": "image", + "image_path": "5f8262c6d519db8a50b79d7f460ce2930f0d72b2b58107372f3dbb4b23a1f0a0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 198, + 547, + 222 + ], + "lines": [ + { + "bbox": [ + 46, + 198, + 547, + 222 + ], + "spans": [ + { + "bbox": [ + 46, + 198, + 547, + 222 + ], + "type": "text", + "content": "Figure 3. Representation of latent representations of a dataset at different learning stages. The target classes are shapes and the bias is color. Arrows represent the distance between misclassified elements and the Voronoi boundary." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 179, + 72, + 293, + 187 + ], + "blocks": [ + { + "bbox": [ + 179, + 72, + 293, + 187 + ], + "lines": [ + { + "bbox": [ + 179, + 72, + 293, + 187 + ], + "spans": [ + { + "bbox": [ + 179, + 72, + 293, + 187 + ], + "type": "image", + "image_path": "7624e1b67b0f3e4f5cd21f846788d0476b450fb232c4d44f5210ff2a7c0c7512.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 296, + 72, + 411, + 187 + ], + "blocks": [ + { + "bbox": [ + 296, + 72, + 411, + 187 + ], + "lines": [ + { + "bbox": [ + 296, + 72, + 411, + 187 + ], + "spans": [ + { + "bbox": [ + 296, + 72, + 411, + 187 + ], + "type": "image", + "image_path": "704b819a2078f34a43573164c6ed7bec39fd582b19911484ff3c7e7e9f6737ab.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 416, + 72, + 529, + 187 + ], + "blocks": [ + { + "bbox": [ + 416, + 72, + 529, + 187 + ], + "lines": [ + { + "bbox": [ + 416, + 72, + 529, + 187 + ], + "spans": [ + { + "bbox": [ + 416, + 72, + 529, + 187 + ], + "type": "image", + "image_path": "3c21f2c9ef4f99741977bb73c73675467ee09f5a3fe059b3d24568922337297f.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 239, + 165, + 252 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 239, + 165, + 252 + ], + "spans": [ + { + "bbox": [ + 47, + 239, + 165, + 252 + ], + "type": "text", + "content": "3.4. Debiasing the model" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 258, + 290, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 258, + 290, + 403 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 290, + 403 + ], + "type": "text", + "content": "Once having extracted the bias alignment labels for each sample, we can start training and debiasing our actual model. In this work, we propose unbiased models having the same architecture and learning parameters as the bias-extracting one, although no explicit constraint forbids us to use different models. Our approach here consists of modifying the objective function optimized during the training of the model with two goals: increasing the weight of the bias-misaligned samples (as they contain relevant information for generalization compared to other representatives of the same class) and moving these samples away from the bias centroid that tends to attract them." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 422, + 192, + 434 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 422, + 192, + 434 + ], + "spans": [ + { + "bbox": [ + 47, + 422, + 192, + 434 + ], + "type": "text", + "content": "3.4.1 Loss function reweighting" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 441, + 287, + 515 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 441, + 287, + 515 + ], + "spans": [ + { + "bbox": [ + 46, + 441, + 287, + 515 + ], + "type": "text", + "content": "As shown by LfF [30] and other works like [20], reweighting the loss function to up-weigh the bias-conflicting elements is an efficient method to orient the training in a less biased direction as the correlation bias-target will be less emphasized in the loss. In this work, we assign the weight " + }, + { + "bbox": [ + 46, + 441, + 287, + 515 + ], + "type": "inline_equation", + "content": "r_n" + }, + { + "bbox": [ + 46, + 441, + 287, + 515 + ], + "type": "text", + "content": " to the " + }, + { + "bbox": [ + 46, + 441, + 287, + 515 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 441, + 287, + 515 + ], + "type": "text", + "content": "-th sample according to" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 76, + 522, + 287, + 552 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 76, + 522, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 76, + 522, + 287, + 552 + ], + "type": "interline_equation", + "content": "r _ {n} = \\frac {1}{\\rho_ {b _ {n} ^ {*}}} \\cdot \\delta_ {b _ {n} ^ {*}, \\hat {y} _ {n}} + \\frac {1}{1 - \\rho_ {b _ {n} ^ {*}}} \\cdot \\left(1 - \\delta_ {b _ {n} ^ {*}, \\hat {y} _ {n}}\\right), \\tag {5}", + "image_path": "847e876e39eb829b44571081f2d8f2bb7edeaae756d02a787603cefa86fff487.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 559, + 117, + 571 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 559, + 117, + 571 + ], + "spans": [ + { + "bbox": [ + 47, + 559, + 117, + 571 + ], + "type": "text", + "content": "where we define" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 121, + 578, + 287, + 620 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 121, + 578, + 287, + 620 + ], + "spans": [ + { + "bbox": [ + 121, + 578, + 287, + 620 + ], + "type": "interline_equation", + "content": "\\rho_ {t} = \\frac {\\left| \\mathcal {D} _ {e ^ {*} , t} ^ {\\parallel} \\right|}{\\left| \\mathcal {D} _ {e ^ {*} , t} ^ {\\parallel} \\cup \\mathcal {D} _ {e ^ {*} , t} ^ {\\perp} \\right|}. \\tag {6}", + "image_path": "dbd2e34a2fcf375ce2bf5213bfb7a8b551fa69cb2d6035c7e2034afeaced7942.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 629, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 629, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 629, + 288, + 715 + ], + "type": "text", + "content": "In a nutshell, misaligned samples receive a weight that is proportionally inverse to their cardinality in the " + }, + { + "bbox": [ + 47, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 47, + 629, + 288, + 715 + ], + "type": "text", + "content": "-th class. This has the effect of strongly encouraging the learning of bias-misaligned samples, over bias-aligned ones. In the feature space, we can interpret the resulting reweighted loss " + }, + { + "bbox": [ + 47, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}(r_n,\\pmb{y}_{e,n},\\hat{y}_n)" + }, + { + "bbox": [ + 47, + 629, + 288, + 715 + ], + "type": "text", + "content": " as an attractive force on the bias-misaligned samples, that are being pulled toward their class centroids." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 240, + 493, + 252 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 240, + 493, + 252 + ], + "spans": [ + { + "bbox": [ + 306, + 240, + 493, + 252 + ], + "type": "text", + "content": "3.4.2 Bias alignment information removal" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 258, + 547, + 427 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 258, + 547, + 427 + ], + "spans": [ + { + "bbox": [ + 304, + 258, + 547, + 427 + ], + "type": "text", + "content": "Besides having a loss reweighting to favor misaligned sample learning, we can also discourage the model from learning any information related to bias alignment to the target. To estimate how much of this information is learned by the model, at the bottleneck we plug an auxiliary classification head that we call information removal head (IRH). This head is trained to minimize a cross-entropy loss " + }, + { + "bbox": [ + 304, + 258, + 547, + 427 + ], + "type": "inline_equation", + "content": "\\mathcal{L}(b_{e,n}, b_n^*)" + }, + { + "bbox": [ + 304, + 258, + 547, + 427 + ], + "type": "text", + "content": ". Its performance is an important indicator for us, as it reveals how much the latent space is similar (or different) from the vanilla bias-capturing model, when it was the most fitted to the bias (at epoch " + }, + { + "bbox": [ + 304, + 258, + 547, + 427 + ], + "type": "inline_equation", + "content": "e^*" + }, + { + "bbox": [ + 304, + 258, + 547, + 427 + ], + "type": "text", + "content": "), from the bias-target misalignment perspective. To estimate this similarity more precisely, we compute the mutual information between " + }, + { + "bbox": [ + 304, + 258, + 547, + 427 + ], + "type": "inline_equation", + "content": "\\mathcal{B} = (b_{e,n})_{n \\in \\mathcal{N}_{\\mathcal{D}}}^*" + }, + { + "bbox": [ + 304, + 258, + 547, + 427 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 258, + 547, + 427 + ], + "type": "inline_equation", + "content": "\\mathcal{B}^*" + }, + { + "bbox": [ + 304, + 258, + 547, + 427 + ], + "type": "text", + "content": " under the bias misalignment condition as" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 333, + 435, + 545, + 469 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 333, + 435, + 545, + 469 + ], + "spans": [ + { + "bbox": [ + 333, + 435, + 545, + 469 + ], + "type": "interline_equation", + "content": "\\mathcal {I} ^ {\\perp} = \\sum_ {j, k} p _ {\\mathcal {B}, \\mathcal {B} ^ {*}} ^ {\\perp} (j, k) \\log_ {T} \\left[ \\frac {p _ {\\mathcal {B} , \\mathcal {B} ^ {*}} ^ {\\perp} (j , k)}{p _ {\\mathcal {B}} ^ {\\perp} (j) p _ {\\mathcal {B} ^ {*}} ^ {\\perp} (k)} \\right], \\tag {7}", + "image_path": "de95954917127147056dc2b3fdfbf2dfbfc38e0876dd4862ba20f15050a29664.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 479, + 334, + 488 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 479, + 334, + 488 + ], + "spans": [ + { + "bbox": [ + 306, + 479, + 334, + 488 + ], + "type": "text", + "content": "where" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 311, + 496, + 545, + 526 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 496, + 545, + 526 + ], + "spans": [ + { + "bbox": [ + 311, + 496, + 545, + 526 + ], + "type": "interline_equation", + "content": "p _ {\\mathcal {B}, \\mathcal {B} ^ {*}} ^ {\\perp} (j, k) = \\frac {1}{| \\mathcal {D} ^ {\\perp} |} \\sum_ {n \\in \\mathcal {N} _ {\\mathcal {D}}} \\delta_ {j, b _ {n} ^ {*}} \\boldsymbol {\\sigma} \\left(\\boldsymbol {b} _ {e, n}\\right) _ {k} \\left(1 - \\delta_ {b _ {n} ^ {*}, \\hat {y} _ {n}}\\right) \\tag {8}", + "image_path": "586e78c64bfc82b955994990af283a554c63c049b079c49921b1ca36ba5485aa.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "text", + "content": "is the joint probability between " + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "inline_equation", + "content": "\\mathcal{B}" + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "inline_equation", + "content": "\\mathcal{B}^*" + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "text", + "content": " calculated on the bias-target misaligned samples, " + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "text", + "content": " is the softmax function and " + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "inline_equation", + "content": "p_{\\mathcal{B}}^{\\perp}, p_{\\mathcal{B}^*}^{\\perp}" + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "text", + "content": " are the two marginals. (7) is differentiable, as we work with " + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "inline_equation", + "content": "\\sigma(\\boldsymbol{b}_{e,n})" + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "text", + "content": ", the softmax-ed output of the IRH. Hence, we are allowed to minimize this term, eventually scaled by a hyper-parameter " + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathcal{I}^{\\perp}}" + }, + { + "bbox": [ + 304, + 533, + 545, + 605 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 606, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 606, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 606, + 547, + 715 + ], + "type": "text", + "content": "As displayed in Fig. 2, the mutual information does not contribute to the IRH's update but is propagated directly back to the backbone. Minimizing information over misaligned samples can be seen as a repulsive force, pushing them away from their attractor class. We focus on minimizing conditional mutual information to avoid pushing aligned samples away from their target class, preserving information needed for classification. In the next section, we will test and compare our approach with other state-of-the-art methods." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4950" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 128, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 128, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 128, + 85 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 288, + 200 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 288, + 200 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 288, + 200 + ], + "type": "text", + "content": "Every result here presented is averaged over three seeds as done in most of the literature, and every algorithm is implemented in Python, using PyTorch 1.13, and trained on GPUs Nvidia GeForce RTX3090 Ti equipped with 24GB RAM. As we compare our method to the other unsupervised state-of-the-art methods, the best-unsupervised accuracies are systematically in bold and the second best are underlined. Besides, we highlight in red the best-overall to see how our method compares even to the supervised ones." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 209, + 110, + 221 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 209, + 110, + 221 + ], + "spans": [ + { + "bbox": [ + 47, + 209, + 110, + 221 + ], + "type": "text", + "content": "4.1. Datasets" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 228, + 287, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 228, + 287, + 289 + ], + "spans": [ + { + "bbox": [ + 46, + 228, + 287, + 289 + ], + "type": "text", + "content": "Here below we describe at a glance the datasets employed for the quantitative evaluation. They were chosen to reflect different problematics bound to biases, from the very simple control case of Biased MNIST to multiple and different biases, synthetic and real-world images." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 289, + 288, + 419 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 289, + 288, + 419 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 288, + 419 + ], + "type": "text", + "content": "Biased MNIST. The first dataset we are using is Biased MNIST, which was first introduced by Bahng et al. [5]. The 60k samples of this dataset consist of a colored version of the famous handwritten digits dataset MNIST with some correlation " + }, + { + "bbox": [ + 46, + 289, + 288, + 419 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 46, + 289, + 288, + 419 + ], + "type": "text", + "content": " between the color and the digits. To build it, first one specific color gets assigned to each of the ten digits; then each of the samples gets its background color. We will test on four levels of color-digit correlation " + }, + { + "bbox": [ + 46, + 289, + 288, + 419 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 46, + 289, + 288, + 419 + ], + "type": "text", + "content": ": 0.99, 0.995, 0.997, and 0.999. The effect of the bias (namely, the background color) is evaluated by testing the model on a completely unbiased dataset, with " + }, + { + "bbox": [ + 46, + 289, + 288, + 419 + ], + "type": "inline_equation", + "content": "\\rho = 0.1" + }, + { + "bbox": [ + 46, + 289, + 288, + 419 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 419, + 288, + 515 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 419, + 288, + 515 + ], + "spans": [ + { + "bbox": [ + 46, + 419, + 288, + 515 + ], + "type": "text", + "content": "Multi-Color MNIST. Building on top of Biased MNIST, Li et al. proposed in [27] a bi-colored version to better benchmark the performance of current models on multiple biases at once. Here, the left and the right side of the background have two different colors, with a correlation to the target " + }, + { + "bbox": [ + 46, + 419, + 288, + 515 + ], + "type": "inline_equation", + "content": "\\rho_{L}" + }, + { + "bbox": [ + 46, + 419, + 288, + 515 + ], + "type": "text", + "content": " for the left background color of the image and " + }, + { + "bbox": [ + 46, + 419, + 288, + 515 + ], + "type": "inline_equation", + "content": "\\rho_{R}" + }, + { + "bbox": [ + 46, + 419, + 288, + 515 + ], + "type": "text", + "content": " for the right one. We follow their proposed setup, with " + }, + { + "bbox": [ + 46, + 419, + 288, + 515 + ], + "type": "inline_equation", + "content": "\\rho_{L} = 0.99" + }, + { + "bbox": [ + 46, + 419, + 288, + 515 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 419, + 288, + 515 + ], + "type": "inline_equation", + "content": "\\rho_{R} = 0.95" + }, + { + "bbox": [ + 46, + 419, + 288, + 515 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 516, + 287, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 516, + 287, + 598 + ], + "spans": [ + { + "bbox": [ + 46, + 516, + 287, + 598 + ], + "type": "text", + "content": "CelebA. CelebA [28] is a real-world dataset commonly used to test debiasing performance. It is a face classification dataset provided with 40 attributes for each of the 203k image samples. The task we solve here is to classify \"blond\" or \"not blond\" hair, with the main bias lying on the gender, as in the dataset there is a natural bias for \"females\" to have the \"blond\" attribute." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 599, + 288, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 599, + 288, + 647 + ], + "spans": [ + { + "bbox": [ + 46, + 599, + 288, + 647 + ], + "type": "text", + "content": "9-class ImageNet. The 9-class ImageNet dataset was proposed by [5], consisting of the extraction of a subset of 9 super-classes from ImageNet-1k, balanced to have each class correlated to a specific texture bias." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 647, + 288, + 684 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 647, + 288, + 684 + ], + "spans": [ + { + "bbox": [ + 46, + 647, + 288, + 684 + ], + "type": "text", + "content": "ImageNet-A. ImageNet-A was proposed by Hendrycks et al. in [18] as a subset of cropped images from ImageNet, purposely selected to be very hard to" + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 309, + 91, + 545, + 205 + ], + "blocks": [ + { + "bbox": [ + 306, + 69, + 545, + 91 + ], + "lines": [ + { + "bbox": [ + 306, + 69, + 545, + 91 + ], + "spans": [ + { + "bbox": [ + 306, + 69, + 545, + 91 + ], + "type": "text", + "content": "Table 1. Results on Balanced Biased MNIST when training with different correlations color-digit " + }, + { + "bbox": [ + 306, + 69, + 545, + 91 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 306, + 69, + 545, + 91 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 91, + 545, + 205 + ], + "lines": [ + { + "bbox": [ + 309, + 91, + 545, + 205 + ], + "spans": [ + { + "bbox": [ + 309, + 91, + 545, + 205 + ], + "type": "table", + "html": "
MethodBias agnosticTest accuracy [%] (↑)
ρ=0.999ρ=0.997ρ=0.995ρ=0.99
Vanilla✓11.240.572.488.4
Rubi [8]X13.790.443.093.6
EnD [34]X52.383.793.996.0
BCon+BBal [19]X94.097.397.798.1
HEX [37]BT10.816.619.724.7
ReBias [5]BT26.565.875.488.4
LearnedMixin [11]✓12.150.278.288.3
LfF [30]✓15.363.790.395.1
SoftCon [19]✓65.088.693.195.2
Ours✓58.7±21.892.7±1.295.5±0.897.7±0.3
", + "image_path": "ef01dd70096ee2c12c5bb341c83e28b6b6b4f463de3cfc231e8673ebca2fadd5.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 225, + 547, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 225, + 547, + 274 + ], + "spans": [ + { + "bbox": [ + 305, + 225, + 547, + 274 + ], + "type": "text", + "content": "be classified by state-of-the-art CNNs. They were precisely selected among the subset misclassified by a cluster of ResNet-50 models. Following [5, 6, 19], we use it to test our performance when training on 9-class ImageNet." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 283, + 512, + 296 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 283, + 512, + 296 + ], + "spans": [ + { + "bbox": [ + 305, + 283, + 512, + 296 + ], + "type": "text", + "content": "4.2. Model architecture and training details" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 301, + 545, + 397 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 301, + 545, + 397 + ], + "spans": [ + { + "bbox": [ + 304, + 301, + 545, + 397 + ], + "type": "text", + "content": "In our experiments, we consistently employed the same architecture for both the vanilla model and the model used for measuring distances to Voronoi boundaries and debiasing. The architecture details for each dataset are provided below. For the Information Removal Head (IRH), we used SGD optimization with a learning rate of 0.1 for each model and dataset. The cross-entropy loss was used for all our losses, and " + }, + { + "bbox": [ + 304, + 301, + 545, + 397 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathcal{I}^{\\perp}}" + }, + { + "bbox": [ + 304, + 301, + 545, + 397 + ], + "type": "text", + "content": " was set to 2 for all experiments." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 397, + 546, + 554 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 397, + 546, + 554 + ], + "spans": [ + { + "bbox": [ + 304, + 397, + 546, + 554 + ], + "type": "text", + "content": "Regarding the experiments on Biased MNIST, we used the same fully convolutional network used for Rebias [5] and Irene [33], of four convolutional layers with " + }, + { + "bbox": [ + 304, + 397, + 546, + 554 + ], + "type": "inline_equation", + "content": "7 \\times 7" + }, + { + "bbox": [ + 304, + 397, + 546, + 554 + ], + "type": "text", + "content": " kernels, with a batch normalization after each of these layers. For training, we followed the implementation used in [33] of 80 epochs, with an initial learning rate of 0.1 decayed by 0.1 at epochs 40 and 60, and a weight decay of " + }, + { + "bbox": [ + 304, + 397, + 546, + 554 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 304, + 397, + 546, + 554 + ], + "type": "text", + "content": ". For Multi-Color MNIST, we employ as architecture the same 3-layer MLP used in [27], trained for 500 epochs (until the model starts overfitting on the training set), using the same optimization strategy as in [27]. For the experiments on CelebA and 9-class ImageNet, we used a pre-trained ResNet-18 and the same optimization strategy as in [19, 30]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 563, + 378, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 563, + 378, + 574 + ], + "spans": [ + { + "bbox": [ + 306, + 563, + 378, + 574 + ], + "type": "text", + "content": "4.3. Discussion" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 582, + 545, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 677 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 677 + ], + "type": "text", + "content": "Here we compare our method to the current state-of-the-art, both supervised and unsupervised, on the multiple datasets presented in Sec. 4.1. In what follows, we divide the supervision level of the method into three categories: bias-agnostic, bias-aware (using an extra ground-truth bias label), and \"bias tailored\" (BT) where the method does not rely on bias labels, but by construction, it captures specific biases (like the texture [5, 37])." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "type": "text", + "content": "Results on Biased MNIST. Our results on Biased MNIST, presented in Table 1, show that our method achieves state-of-the-art performance, even when compared with super" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 46, + 693, + 299, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 693, + 299, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 693, + 299, + 713 + ], + "type": "text", + "content": "1The source code for our method is available at https://github.com/renahon/mining.bias_target Alignment_from_voronoi.cells/." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 294, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 314, + 757 + ], + "type": "text", + "content": "4951" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 91, + 286, + 198 + ], + "blocks": [ + { + "bbox": [ + 47, + 69, + 287, + 91 + ], + "lines": [ + { + "bbox": [ + 47, + 69, + 287, + 91 + ], + "spans": [ + { + "bbox": [ + 47, + 69, + 287, + 91 + ], + "type": "text", + "content": "Table 2. Results on CelebA, targeting the attribute \"blond\", with a bias towards gender." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 91, + 286, + 198 + ], + "lines": [ + { + "bbox": [ + 48, + 91, + 286, + 198 + ], + "spans": [ + { + "bbox": [ + 48, + 91, + 286, + 198 + ], + "type": "table", + "html": "
MethodBias agnosticTest accuracy [%] (↑)
UnbiasedBias-Conflicting
Vanilla✓79.059.0
EnD [34]✗86.976.4
LNL [24]✗80.161.2
DI [38]✗90.986.3
BiasCon + BiasBal [19]✗91.487.2
Group DRO [32]✓85.483.4
LfF [30]✓84.281.2
Ours✓90.2±1.184.5±2.0
", + "image_path": "a71f012d1bb907ee80d773f60aaf67fe788c0300ece91e57532a2ab2c3331e45.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 217, + 287, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 217, + 287, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 217, + 287, + 418 + ], + "type": "text", + "content": "vised ones, for not extreme values of " + }, + { + "bbox": [ + 46, + 217, + 287, + 418 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 46, + 217, + 287, + 418 + ], + "type": "text", + "content": ": the only method that yields better results on the three lower correlations levels is the use of the associated BiasContrastive and BiasBalanced losses [19]. On the unsupervised field, we get better accuracies than our competitors except for the highest correlation level. We can observe in this case a very high standard deviation because of the high stochastic noise of the gradient: the very few bias-target misaligned (60 in total, constituting " + }, + { + "bbox": [ + 46, + 217, + 287, + 418 + ], + "type": "inline_equation", + "content": "0.1\\%" + }, + { + "bbox": [ + 46, + 217, + 287, + 418 + ], + "type": "text", + "content": " of the train set) searches for the perfect moment to mark. We hypothesize these difficulties are caused by the large gradients, which make the bias-target alignment information extraction noisy: we tried to perform the bias extraction for this specific setup having a smaller learning rate (0.01), and the performance improved to " + }, + { + "bbox": [ + 46, + 217, + 287, + 418 + ], + "type": "inline_equation", + "content": "72.6\\% \\pm 11.6" + }, + { + "bbox": [ + 46, + 217, + 287, + 418 + ], + "type": "text", + "content": ". Tuning properly the learning rate in extreme scenarios is a key element towards a successful bias-target alignment information extraction." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 419, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 419, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 419, + 287, + 479 + ], + "type": "text", + "content": "Results on Multi-Color MNIST. The Multi-Color MNIST dataset [27] helps us to test the performance of our method on multiple biases at the same time. To differentiate performance in different bias-alignment configurations, we will refer to two distinct partitions of the dataset " + }, + { + "bbox": [ + 46, + 419, + 287, + 479 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 46, + 419, + 287, + 479 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 108, + 487, + 287, + 502 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 108, + 487, + 287, + 502 + ], + "spans": [ + { + "bbox": [ + 108, + 487, + 287, + 502 + ], + "type": "interline_equation", + "content": "\\mathcal {D} = R ^ {\\parallel} \\cup R ^ {\\perp} = L ^ {\\parallel} \\cup L ^ {\\perp}, \\tag {9}", + "image_path": "9a7ba22a9319db3fce347796c322fba045eaf5d5c8a84606dcf362b8a7706e8a.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "inline_equation", + "content": "R^{\\parallel}(L^{\\parallel})" + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "text", + "content": " is the subset of samples whose right (left) background is aligned with its digit, and " + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "inline_equation", + "content": "R^{\\perp}(L^{\\perp})" + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "text", + "content": " when it's not. As previously done in the state-of-the-art [27], we compute separately the accuracies for the four subsets intersections. The average of these four metrics constitutes \"unbiased accuracy\". The most difficult subset is " + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "inline_equation", + "content": "R^{\\perp} \\cap L^{\\perp}" + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "text", + "content": ": the performance of the vanilla model is below that of random guessing, and the same is true for three out of five tested debiasing methods. In contrast, every method reaches " + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "text", + "content": " accuracy or close for samples in " + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "inline_equation", + "content": "R^{\\parallel} \\cap L^{\\parallel}" + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "text", + "content": ". Even in this case, our method achieves state-of-the-art results for this dataset. More specifically, we record the best-unbiased accuracy, and we improve the best score on the double-conflicting setup by " + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "inline_equation", + "content": "+8\\%" + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "text", + "content": ". For instance, LfF [30], whose main assumption is close to ours, while emphasizing the early choices of its bias-extracting model seems to perform very unevenly regarding the two biases (around " + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 46, + 509, + 288, + 714 + ], + "type": "text", + "content": " accu" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 310, + 64, + 541, + 165 + ], + "blocks": [ + { + "bbox": [ + 310, + 64, + 541, + 165 + ], + "lines": [ + { + "bbox": [ + 310, + 64, + 541, + 165 + ], + "spans": [ + { + "bbox": [ + 310, + 64, + 541, + 165 + ], + "type": "image", + "image_path": "61f84dcd86bf79a79c81006289e9c427e83c4eb7ea53a1e64691651103d89cd1.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 167, + 547, + 213 + ], + "lines": [ + { + "bbox": [ + 304, + 167, + 547, + 213 + ], + "spans": [ + { + "bbox": [ + 304, + 167, + 547, + 213 + ], + "type": "text", + "content": "Figure 4. Evolution of the relative distance to the target Voronoi boundary for the misclassified elements (red curve) and the match between the misclassified samples " + }, + { + "bbox": [ + 304, + 167, + 547, + 213 + ], + "type": "inline_equation", + "content": "\\{n|\\arg \\max (\\pmb{y}_{e,n})\\neq \\hat{y}_n\\}" + }, + { + "bbox": [ + 304, + 167, + 547, + 213 + ], + "type": "text", + "content": " and the misaligned samples " + }, + { + "bbox": [ + 304, + 167, + 547, + 213 + ], + "type": "inline_equation", + "content": "\\{n|\\hat{b}_n\\neq \\hat{y}_n\\}" + }, + { + "bbox": [ + 304, + 167, + 547, + 213 + ], + "type": "text", + "content": " (blue dashed line)." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 234, + 545, + 269 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 234, + 545, + 269 + ], + "spans": [ + { + "bbox": [ + 304, + 234, + 545, + 269 + ], + "type": "text", + "content": "racy when for " + }, + { + "bbox": [ + 304, + 234, + 545, + 269 + ], + "type": "inline_equation", + "content": "R^{\\perp}" + }, + { + "bbox": [ + 304, + 234, + 545, + 269 + ], + "type": "text", + "content": "). This further strengthens our choice of not extracting a bias label, but the bias-target alignment information, and waiting for the best time to extract it." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 270, + 546, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 270, + 546, + 365 + ], + "spans": [ + { + "bbox": [ + 304, + 270, + 546, + 365 + ], + "type": "text", + "content": "Results on CelebA. On the CelebA dataset, two test setups are employed: the \"unbiased\", where the average of the scores obtained on each of the target-bias combinations (here blond-male, blond-female, not blond-male and not blond-female) is considered, and the \"bias-conflicting\" one, where the two bias-aligned combinations are not considered. On both metrics, our approach ranks the best unsupervised " + }, + { + "bbox": [ + 304, + 270, + 546, + 365 + ], + "type": "inline_equation", + "content": "(+4.8\\%)" + }, + { + "bbox": [ + 304, + 270, + 546, + 365 + ], + "type": "text", + "content": " on the \"unbiased\" metric), and third overall." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 365, + 545, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 365, + 545, + 484 + ], + "spans": [ + { + "bbox": [ + 304, + 365, + 545, + 484 + ], + "type": "text", + "content": "Results on 9-class ImageNet. When working at debiasing 9-class ImageNet, all other state-of-the-art methods become bias-tailored (BT): indeed, they use BagNet-18 [7] as a bias-extracting model for its known tendency to fit texture (as these datasets are known to be very biased towards texture [16]). If we want to perform bias-agnostic debiasing, we shouldn't rely on that kind of bias-extracting model chosen to fit the bias type of the dataset. However, to compare our method to theirs on an equal footing we tested two configurations:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 486, + 545, + 556 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 317, + 486, + 545, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 486, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 317, + 486, + 545, + 521 + ], + "type": "text", + "content": "- ours (+BagNet), where we extract the bias-conflicting samples from training BagNet-18 and then proceed to debiasing ResNet-18;" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 317, + 521, + 545, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 521, + 545, + 556 + ], + "spans": [ + { + "bbox": [ + 317, + 521, + 545, + 556 + ], + "type": "text", + "content": "- ours, where we extract the bias-conflicting samples directly from the ResNet-18, which makes us the only bias-agnostic method tested on this dataset." + } + ] + } + ], + "index": 12 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 558, + 545, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 545, + 629 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 545, + 629 + ], + "type": "text", + "content": "We obtain comparable results to the state-of-the-art on ImageNet-A (respectively " + }, + { + "bbox": [ + 304, + 558, + 545, + 629 + ], + "type": "inline_equation", + "content": "1.2\\%" + }, + { + "bbox": [ + 304, + 558, + 545, + 629 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 558, + 545, + 629 + ], + "type": "inline_equation", + "content": "1.5\\%" + }, + { + "bbox": [ + 304, + 558, + 545, + 629 + ], + "type": "text", + "content": " below the best-performing method in FairKL [6]) and the two best results overall on 9-class ImageNet. Interestingly, we get state-ofthe-art results with our method, when extracting information directly from ResNet-18." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "Ablation study. We tested the effect of the different modules of our method on Biased MNIST, training with " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\rho = 0.99" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": ". The results in Table 5 show that the use of the reweighted loss function " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " yields an average increase in accuracy of " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "+7.1\\%" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " and that the use of the IRH further increases it by " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "+1.7\\%" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": ". Finally, employing a conditional mutual information term (on the bias-target misaligned ele" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4952" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 124, + 81, + 472, + 180 + ], + "blocks": [ + { + "bbox": [ + 75, + 69, + 517, + 80 + ], + "lines": [ + { + "bbox": [ + 75, + 69, + 517, + 80 + ], + "spans": [ + { + "bbox": [ + 75, + 69, + 517, + 80 + ], + "type": "text", + "content": "Table 3. Test accuracy on four subsets of Multi-Color MNIST. The \"Unbiased\" accuracy is the average of the four subsets." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 124, + 81, + 472, + 180 + ], + "lines": [ + { + "bbox": [ + 124, + 81, + 472, + 180 + ], + "spans": [ + { + "bbox": [ + 124, + 81, + 472, + 180 + ], + "type": "table", + "html": "
MethodBias agnosticTest accuracy [%] (↑)
L|| ∩ R||L|| ∩ R↓L↓ ∩ R||L↓ ∩ R↓Unbiased
Vanilla✓100.097.127.55.257.4
LfF [30]✓99.64.798.65.152.0
EIIL [13]✓100.097.270.810.969.7
PGI [1]✓98.682.626.69.554.3
DebiAN [27]✓100.095.676.516.072.0
Ours✓100 ±0.090.9 ±3.577.5 ±2.824.1 ±1.873.1 ±0.9
", + "image_path": "9c0aa69e37a05a27f70b44674ef4b872033c8eecc9cd81e82c76f8b0b2955842.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 48, + 207, + 287, + 346 + ], + "blocks": [ + { + "bbox": [ + 48, + 197, + 270, + 207 + ], + "lines": [ + { + "bbox": [ + 48, + 197, + 270, + 207 + ], + "spans": [ + { + "bbox": [ + 48, + 197, + 270, + 207 + ], + "type": "text", + "content": "Table 4. Test accuracy on 9-class ImageNet and ImageNet-A." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 207, + 287, + 346 + ], + "lines": [ + { + "bbox": [ + 48, + 207, + 287, + 346 + ], + "spans": [ + { + "bbox": [ + 48, + 207, + 287, + 346 + ], + "type": "table", + "html": "
MethodBias agnosticTest accuracy [%] (↑)
9-class ImageNetImageNet-A
Vanilla✓94.030.5
ReBias [5]X94.030.5
StyllmageNet [16]BT88.424.6
LearnedMixin [11]BT79.219.0
RUBi [8]BT93.931.0
LfF [30]BT91.229.4
SoftCon [19]BT95.334.1
FairKL [6]BT95.135.7
Ours (BagNet [7])BT96.4 ±0.034.5 ±3.4
Ours✓95.5 ±0.234.2 ±0.9
", + "image_path": "6e51fe59e4f5ce0b45d4b7542cabcd5285ec3157dfa70e699691aafd45388f6d.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 48, + 364, + 287, + 427 + ], + "blocks": [ + { + "bbox": [ + 60, + 354, + 271, + 364 + ], + "lines": [ + { + "bbox": [ + 60, + 354, + 271, + 364 + ], + "spans": [ + { + "bbox": [ + 60, + 354, + 271, + 364 + ], + "type": "text", + "content": "Table 5. Ablation study on Biased MNIST with " + }, + { + "bbox": [ + 60, + 354, + 271, + 364 + ], + "type": "inline_equation", + "content": "\\rho = {0.99}" + }, + { + "bbox": [ + 60, + 354, + 271, + 364 + ], + "type": "text", + "content": " ." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 364, + 287, + 427 + ], + "lines": [ + { + "bbox": [ + 48, + 364, + 287, + 427 + ], + "spans": [ + { + "bbox": [ + 48, + 364, + 287, + 427 + ], + "type": "table", + "html": "
Weighted LIRHMisaligned onlyTest accuracy [%](↑)
88.4 ±0.5
✓95.5 ±0.5
✓✓97.2 ±0.4
✓✓✓97.7 ±0.4
", + "image_path": "20540aa79828bfc6f48fd5b659c75486dea5172f7008b76ecbb0d225e30db666.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 445, + 287, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 445, + 287, + 468 + ], + "spans": [ + { + "bbox": [ + 46, + 445, + 287, + 468 + ], + "type": "text", + "content": "ments only) in place of total information removal provides an extra gain in performance." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 468, + 287, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 468, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 468, + 287, + 529 + ], + "type": "text", + "content": "We also measured the average relative distances from the misclassified samples at each epoch, comparing it to the match of the extracted bias alignment information " + }, + { + "bbox": [ + 46, + 468, + 287, + 529 + ], + "type": "inline_equation", + "content": "\\mathcal{B}" + }, + { + "bbox": [ + 46, + 468, + 287, + 529 + ], + "type": "text", + "content": " to the ideal ground truth " + }, + { + "bbox": [ + 46, + 468, + 287, + 529 + ], + "type": "inline_equation", + "content": "\\hat{\\mathcal{B}} = (\\hat{b}_n)_{n\\in \\mathcal{N}_{\\mathcal{D}}}(" + }, + { + "bbox": [ + 46, + 468, + 287, + 529 + ], + "type": "text", + "content": " (which is provided in Biased MNIST), expressed by" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 94, + 533, + 287, + 564 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 94, + 533, + 287, + 564 + ], + "spans": [ + { + "bbox": [ + 94, + 533, + 287, + 564 + ], + "type": "interline_equation", + "content": "\\zeta = \\frac {1}{| \\mathcal {D} ^ {\\perp} |} \\sum_ {n \\in \\mathcal {N} _ {\\mathcal {D} ^ {\\perp}}} \\delta_ {\\operatorname {a r g m a x} \\left(\\boldsymbol {y} _ {e, n}\\right), \\hat {\\boldsymbol {b}} _ {n}}. \\tag {10}", + "image_path": "ac6751f218c5dcafee0dfa724441d379c050be8c82e35b3c7de11308df7a6bf1.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": "In Fig. 4, we can see a peak in the average distances (marked with " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "\\star" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": ") after the first few iterations: the model fits the color bias in less than one epoch of training. As the training continues, the average relative distance decreases as expected: the misclassified samples stay closer to the Voronoi boundary. We observe that the relative average distance is a good proxy for knowing when to learn the optimal bias alignment " + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "inline_equation", + "content": "\\hat{\\mathcal{B}}" + }, + { + "bbox": [ + 46, + 570, + 287, + 665 + ], + "type": "text", + "content": ", as the two curves show a similar trend." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": "General discussion and limitations. Through the conducted experiments, we have observed that our method establishes, in most of the considered setups, a new state-of-the-art for bias-agnostic approaches, and in some cases even" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 199, + 545, + 368 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 199, + 545, + 368 + ], + "spans": [ + { + "bbox": [ + 304, + 199, + 545, + 368 + ], + "type": "text", + "content": "outperforms supervised methods, such as in 9-class ImageNet and the double-biased Multi-Color MNIST. A limitation of the proposed approach appears when the correlation between bias and target is extremely high (" + }, + { + "bbox": [ + 304, + 199, + 545, + 368 + ], + "type": "inline_equation", + "content": "\\rho = 0.999" + }, + { + "bbox": [ + 304, + 199, + 545, + 368 + ], + "type": "text", + "content": " in Biased MNIST). Since it heavily relies on the extraction of these bias-conflicting samples, when the stochastic noise overwhelms the extraction of the bias misalignment information, the proposed method will be sub-optimal. A possible solution to this problem relies upon using a \"sufficiently small\" learning rate. Finally, our method strongly depends on the existence of these bias-conflicting elements: in a fully-biased dataset, where the alignment bias-target " + }, + { + "bbox": [ + 304, + 199, + 545, + 368 + ], + "type": "inline_equation", + "content": "\\rho = 1" + }, + { + "bbox": [ + 304, + 199, + 545, + 368 + ], + "type": "text", + "content": ", since we have no information to extract from the training set, our approach is expected to fail." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 403, + 378, + 416 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 403, + 378, + 416 + ], + "spans": [ + { + "bbox": [ + 306, + 403, + 378, + 416 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 433, + 545, + 671 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 433, + 545, + 671 + ], + "spans": [ + { + "bbox": [ + 304, + 433, + 545, + 671 + ], + "type": "text", + "content": "In this paper, we have presented an unsupervised, bias-agnostic debiasing approach, whose performance is generally of the same order as that of state-of-the-art supervised methods. We proposed a new bias-target alignment extraction method based on the distance between the misclassified samples and the Voronoi boundary separating them from their target class. Based on this distilled information, we proposed a debiasing method composed of two synergetic elements. The first is a reweighted loss, where sample weights reflect the bias-target (mis)alignment. The second is a bias-target alignment information removal term, acting as a regularizer for the latent space. We tested our method on several debiasing benchmarks, recording a new state-of-the-art for unsupervised debiasing in most of the considered scenarios, although no specific hyperparameters tuning was performed. In extreme cases, where the bias-target alignment is extremely high, we observed that the appropriate choice of the vanilla model's learning setup is crucial to the success of the proposed approach, and its exploration is left as future work." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 680, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 680, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 680, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgments. 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Advances in neural information processing systems, 31, 2018. 1" + } + ] + } + ], + "index": 13 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "4955" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Misalign, Contrast then Distill_ Rethinking Misalignments in Language-Image Pre-training/8db6862b-91a8-4f4b-b1af-4631b12bd46c_content_list.json b/2023/Misalign, Contrast then Distill_ Rethinking Misalignments in Language-Image Pre-training/8db6862b-91a8-4f4b-b1af-4631b12bd46c_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..732356b4ad2486cd20aaa1ca1b0f6f34af3b7c82 --- /dev/null +++ b/2023/Misalign, Contrast then Distill_ Rethinking Misalignments in Language-Image Pre-training/8db6862b-91a8-4f4b-b1af-4631b12bd46c_content_list.json @@ -0,0 +1,1593 @@ +[ + { + "type": "text", + "text": "Misalign, Contrast then Distill: Rethinking Misalignments in Language-Image Pretraining", + "text_level": 1, + "bbox": [ + 189, + 130, + 782, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Bumsoo Kim* Yeonsik Jo Jinhyung Kim Seunghwan Kim LG AI Research", + "bbox": [ + 230, + 203, + 740, + 244 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 280, + 313, + 296 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Contrastive Language-Image Pretraining has emerged as a prominent approach for training vision and text encoders with uncurated image-text pairs from the web. To enhance data-efficiency, recent efforts have introduced additional supervision terms that involve random-augmented views of the image. However, since the image augmentation process is unaware of its text counterpart, this procedure could cause various degrees of image-text misalignments during training. Prior methods either disregarded this discrepancy or introduced external models to mitigate the impact of misalignments during training. In contrast, we propose a novel metric learning approach that capitalizes on these misalignments as an additional training source, which we term \"Misalign, Contrast then Distill (MCD)\". Unlike previous methods that treat augmented images and their text counterparts as simple positive pairs, MCD predicts the continuous scales of misalignment caused by the augmentation. Our extensive experimental results show that our proposed MCD achieves state-of-the-art transferability in multiple classification and retrieval downstream datasets.", + "bbox": [ + 75, + 311, + 473, + 614 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 657, + 209, + 672 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recent advances in deep learning have shown that image representations trained with large-scale uncurated natural language supervision shows powerful transferability to various downstream tasks [14, 32]. A predominant paradigm in vision-language pre-training is to use a simple contrastive loss that makes the embedding of an image and its matching text description (positive pair) more similar to each other than other arbitrary image-text pairs (negative pairs) [29]. To achieve a more data-efficient training, following works actively capitalized on image random augmentation by: (i) joining language-image pretraining objectives with vision self-supervision terms [3, 5] between the augmented images [27, 23, 18] and (ii) involving more pairs of posi", + "bbox": [ + 75, + 681, + 468, + 878 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/9bca8c2cec6580e92d17e4e65cf7da070a0e7d0fa3cd9392719334c49c10dd13.jpg", + "image_caption": [ + "Figure 1. Conceptual illustration of contrastive language-image objectives of previous works (i.e., InfoNCE) and our MCD for (a) augmentation that doesn't harm the correspondence with its description and (b) augmentation that does. Previous works either disregard these misalignments [23] or leverage external models [18, 9] to mitigate their impact. On the other hand, MCD uses the continuous degree of misalignments caused by random image augmentation as a useful source for training various levels of alignments between images and their text descriptions." + ], + "image_footnote": [], + "bbox": [ + 503, + 284, + 890, + 484 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "tive/negative supervisions between the augmented images and their original text description [23, 18].", + "bbox": [ + 496, + 642, + 890, + 672 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "However, since the random image augmentation process is unaware of its corresponding text, it often results in the augmented image view to be misaligned with its description (see (b) in Fig.1). These misalignments behave as noisy training signals for the contrastive loss in language-image pretraining, thus causing performance degradation if not properly attended [27]. To mitigate this issue, recent works have used additional augmentation embeddings [18] or heavy external off-the-shelf object detectors and summary extractors [9] to match the alignment during training. Though being straightforward and showing strong performance, these works are limited in that they add unnecessary burden in both training and inference.", + "bbox": [ + 496, + 672, + 892, + 869 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Based on this observation, we start with a simple question: \"Instead of treating misalignments as noise to elim", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Correspondence to: bumsoo.kim@lgresearch.ai", + "bbox": [ + 94, + 886, + 397, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "2563", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "inate, can we rather harness them as a training source for language-image pretraining?\". To this end, we propose MCD (i.e., Misalign, Contrast then Distill), a novel training framework that leverages the various levels of misalignments between random augmented images and its text description during training.", + "bbox": [ + 75, + 90, + 468, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "MCD consists of three steps (see Fig 2 for an overview illustration of MCD): First, we conduct random augmentation on the image that causes various levels of misalignments (or not at all) with its text counterpart (Misalign). Then, we project all the participants (image, text, and augmented image) into an unified multimodal space, and learn the distance between all the image-text pairs with a contrastive objective (Contrast). Finally, we use a teacher-student network where the student learns from the \"soft\" distance between the text- original image (i.e., $D(\\bar{I}, T)$ in Fig 2) and text-augmented image (i.e., $D(\\bar{I}', T)$ in Fig 2) of the momentum teacher with a log-ratio loss (Distill). continuous scale of misalignment to the student model, enabling the student to learn from the various levels of misalignment that occur from the random augmentation during training time.", + "bbox": [ + 75, + 181, + 470, + 421 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our contribution of this paper is threefold:", + "bbox": [ + 96, + 422, + 377, + 436 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose MCD, a novel training framework where we learn the continuous level of misalignment as a source for contrastive language-image pretraining.", + "- Our MCD outperforms state-of-the-art models across various single/multi-modal downstream datasets without adding additional parameters for inference or using external models to force the alignment.", + "- We propose three distillation strategies leveraging misalignments: i) misalignment between positive pairs, ii) misalignment between negative pairs, and iii) misalignment between noisy pairs. Extensive experiments show that all three strategies positively contributes to our final performance." + ], + "bbox": [ + 96, + 449, + 468, + 665 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 690, + 218, + 705 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Here, we present brief review of multi-modal representation learning, especially vision-language pre-training.", + "bbox": [ + 76, + 715, + 467, + 746 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Vision-language Pre-training", + "text_level": 1, + "bbox": [ + 76, + 756, + 334, + 772 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Vision-Language Pre-training (VLP) trains a multimodal model to learn joint representation of visual and textual information that can be transfer to various vision-language downstream tasks. The success of VLP primarily relies on large-scale datasets which contains images and their corresponding descriptions, enabling the model to understand the semantic relationship between the pairs. VLP includes two different group of models: 1) single-stream", + "bbox": [ + 75, + 779, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/74c6af92fcd1cd78585077323a6009b7dc5f64f66d7f7ccbc4643c17c207f532.jpg", + "image_caption": [ + "Figure 2. Overview of MCD. Our MCD consist of three steps: (i) text-agnostic random augmentation of the image that causes various levels of misalignment with the corresponding text, (ii) learning the distance between the image/augmented image and text with contrastive objectives then (iii) distill the log-ratio of the image-text distance between the original and the augmented image." + ], + "image_footnote": [], + "bbox": [ + 501, + 90, + 890, + 429 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "models [20, 6, 13, 22, 21, 25, 36] which process an image and its associated text information in a shared backbone network and 2) dual-stream models [14, 32] which has two independent backbone networks for processing each modality. In this work, we focuses on Contrastive Language Image Pretraining (CLIP [32]), which is a type of dual-stream models trained with image-text contrastive loss where the image and its matching text description in the dataset as a positive pair and other unrelated pairs in a batch as negative pairs.", + "bbox": [ + 498, + 542, + 890, + 693 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Misalignments between Image-Text Pairs", + "text_level": 1, + "bbox": [ + 500, + 704, + 851, + 720 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "There are two different sources that cause misalignments in image-text pairs for VLP: misalignment that naturally occurs in image-text paired datasets, and misalignments caused by random image augmentation.", + "bbox": [ + 498, + 728, + 890, + 789 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Misalignment in Image-Text Pairs. Large scale image-text paired datasets for VLP are usually collected from the web thus can contain uncurated and noisy pairs which have weak relations. This inevitably incurs misalignment between positive image-text pairs in the dataset misleading naive contrastive language image objective. Previous", + "bbox": [ + 498, + 809, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "2564", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "studies [19, 24, 1] have attempted to address the problem by knowledge distillation [11] of soft image-text alignment matrix from momentum teacher network to the student network via KL divergence loss. Our proposed method stands apart from previous approaches due to its element-wise log-ratio loss for distillation. Element-wise loss lessens the dependence on training hyperparameters like batch size and temperature for KL loss. Furthermore, it enables the model to harness the various levels of individual misalignments of each sample from random augmentation or label noise.", + "bbox": [ + 75, + 90, + 472, + 243 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Misalignment by Augmentations. View-based self-supervised learning, in which models are trained to represent views or augmentations of the same image similarly, has yielded strong results across a variety of different formulations. Consecutive work of CLIP (i.e., SLIP [27]) initially introduced supervision between random augmented image views (e.g., cropping, gray-scale, jittering, gaussian blur, horizontal flipping, etc.). Since only image-image supervision was given in a separately embedded space, augmentation was not a factor for misalignment. To include more positive/negative pairs for the image-text contrastive objective, following works [23, 18] also introduced InfoNCE loss between the augmented views and the text pairs. However, since the text description is unaware of the random augmentations, there is a high chance that misalignments occur during training. SLIP shows that naïve application of contrastive loss to these misaligned pairs results in suboptimal performance. Previous work have either ignored this misalignment [23] or addressed this issue with an additional encoder that encodes the one-hot information of which augmentation has been applied during training [18]. PyramidCLIP [9] addressed this issue with external off-the-shelf object detectors and summary extractors. HiCLIP [10] captured the hierarchical nature of high-level on unsupervised manner with tree Transformer [39]. MCD incorporate the misalignment information as a source of training via novel log-ratio loss without introducing any external module.", + "bbox": [ + 75, + 268, + 472, + 691 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Preliminary", + "text_level": 1, + "bbox": [ + 76, + 710, + 204, + 728 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In our preliminary, we revisit the basic form of Contrastive Language-Image Pretraining (i.e., CLIP [32]). CLIP features a dual-encoder architecture where the image encoder $f_{I}$ and text encoder $f_{T}$ are jointly trained with a contrastive objective $\\mathcal{L}_{\\mathrm{CLIP}}$ .", + "bbox": [ + 75, + 737, + 468, + 814 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "InfoNCE Loss Given $N$ image-text pairs $\\{(x_i^I, x_i^T)\\}_{i=1}^N$ , we define a similarity matrix $S$ whose $i$ -th row and the $j$ -th column is the cosine similarity between the projected representations of the $i$ -th text $T_i$ and the $j$ -th image $I_j$ (i.e.,", + "bbox": [ + 75, + 838, + 468, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "$T_{i} = f_{T}(x_{i}^{T}),I_{j} = f_{I}(x_{j}^{I}))$ , written as:", + "bbox": [ + 498, + 89, + 764, + 108 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nS _ {i j} = \\operatorname {s i m} \\left(T _ {i}, I _ {j}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 632, + 116, + 890, + 133 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathrm{sim}(\\cdot ,\\cdot)$ is cosine similarity. In CLIP [32], the encoded image features $I$ and text features $T$ are projected to the same dimension where the embeddings for matching image-text pairs are pulled together while embeddings for arbitrary pairs are pushed apart with the InfoNCE loss [29]. Given the similarity matrix $S$ , the InfoNCE loss $\\mathcal{L}_N$ is rewritten as:", + "bbox": [ + 496, + 142, + 893, + 247 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {N} (S) = - \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\log \\frac {\\exp \\left(S _ {i i} / \\tau\\right)}{\\sum_ {j = 1} ^ {N} \\exp \\left(S _ {i j} / \\tau\\right)}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 549, + 255, + 890, + 297 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\tau$ is a learnable temperature variable. The overall loss of clip $\\mathcal{L}_{\\mathrm{CLIP}}$ is written as:", + "bbox": [ + 498, + 305, + 890, + 335 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {C L I P}} = \\frac {1}{2} \\left(\\mathcal {L} _ {N} (S) + \\mathcal {L} _ {N} \\left(S ^ {T}\\right)\\right). \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 345, + 890, + 378 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Augmentations and Misalignment. To include more positive/negative pairs for the contrastive objective, following works [23, 18] introduced InfoNCE loss between the random augmented image views and the text description for the original image. Let $\\mathcal{A}$ a function for random image augmentation that includes randomly applying cropping, gray-scale, jittering, gaussian blur, horizontal flipping following SimCLR [3]. $I_{j'}$ is the encoded image feature of augmented view of $j$ -th image(e.g. $I_{j'} = f_I(\\mathcal{A}(x_j^I))$ ). Let $S_{ij}' = \\mathrm{sim}(T_i, I_{j'})$ represent the similarity between the augmented view of $j$ -th image and $i$ -th text. We denote the matrix of these similarity as $S'$ for concise notation. Then, InfoNCE loss between the augmented image and the text is", + "bbox": [ + 496, + 393, + 890, + 590 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {C L I P}} ^ {\\prime} = \\frac {1}{2} \\left(\\mathcal {L} _ {N} \\left(S ^ {\\prime}\\right) + \\mathcal {L} _ {N} \\left(S ^ {\\prime T}\\right)\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 599, + 890, + 628 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As the random augmentation function $\\mathcal{A}$ is independent to the corresponding text description, the augmented view $I_{j'}$ is likely to exhibit misalignment with text $T_i$ . This hypothesis is consistent with the finding of SLIP [27], which demonstrated that introducing augmentation (particularly resize crop, and flip) to CLIP actually resulted in a performance decrease. Previous works [27, 23] have sidestepped the utilization of augmented view in CLIP by substituting infoNCE with self-supervised learning loss(e.g. SimCLR [3]) between images. These approaches have limitation in fully capturing the essence of multi-modal learning.", + "bbox": [ + 496, + 635, + 890, + 801 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. Method", + "text_level": 1, + "bbox": [ + 500, + 814, + 589, + 830 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we introduce MCD (Misalign, Contrast then Distill), a novel training framework for language-image pretraining using misalignments as continuous labels for learning the distance between image-text pairs.", + "bbox": [ + 496, + 839, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "2565", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4.1. Misalign", + "text_level": 1, + "bbox": [ + 76, + 90, + 181, + 107 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The first step of MCD is to apply text-agnostic random image augmentations (e.g., random crop, random flip, grayscale, etc.) to create various levels of misalignments between the images and its description. Here, we elaborate on three distinct scenarios of misalignment that can arise during the augmentation process, hindering the contrastive loss to learn proper distance between image-text pairs: (i) Text-agnostic random augmentation can cause misalignments in positive image-text pairs. (ii) The random-augmentation can mistakenly cause positive signals between negative pairs. (iii) Misalignments can already exist innately within the original image-text pair. A detailed illustration of each cases are provided in Fig 3.", + "bbox": [ + 75, + 114, + 473, + 311 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. Contrast", + "text_level": 1, + "bbox": [ + 76, + 321, + 181, + 335 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In the second step, MCD initially learns the distance metric between image-text pairs with a contrastive objective. Motivated by [18], we project both image and text modalities to a unified space and use all the positive pairs and negative pairs of both modalities. For an $i$ -th embedding $z_{i}$ in a batch of embeddings $\\{z_i\\}_{i = 1}^{3N}$ that includes $N$ image samples, $N$ text samples, and $N$ random augmented image samples, let $\\mathcal{P}_i$ and $\\mathcal{N}_i$ each denote the set of all positive sample indices of the $i$ -th sample including $i$ itself and the set of all negative sample indices of the $i$ -th sample. Then, the contrastive loss for the multiple positives and multiple negatives for sample $i$ can be written as", + "bbox": [ + 75, + 345, + 472, + 527 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {i} ^ {C} = \\mathbb {E} _ {p \\in \\mathcal {P} _ {i}} \\left[ - \\log \\frac {\\sin \\left(z _ {i} , z _ {p}\\right)}{\\sin \\left(z _ {i} , z _ {p}\\right) + \\sum_ {n \\in \\mathcal {N} _ {i}} \\sin \\left(z _ {i} , z _ {n}\\right)} \\right]. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 537, + 468, + 575 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "However, without encoding augmentation information the image-text contrastive loss is prone to the three aforementioned issues. We address these three issues with a teacher-student model where the continuous distance between the image-text and augmented image-text of the teacher model is distilled to the student model.", + "bbox": [ + 75, + 585, + 468, + 676 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.3. Distill", + "text_level": 1, + "bbox": [ + 76, + 686, + 160, + 702 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Knowledge distillation, introduced by Hinton et al. [11], is a learning paradigm where we train the student network to mimic the \"soft\" labels predicted from the teacher network. In MCD, we train the student network with the continuous image-text distance predicted by the teacher network. Psuedocode for the distillation in MCD is provided in Algorithm 1.", + "bbox": [ + 75, + 710, + 468, + 818 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Log-Ratio Loss for Image-Text Distance. Given a student $f_{I}$ and a momentum teacher $\\bar{f}_{I}$ , we propose to use log-ratio loss [15] on image-text similarities that aims to approximate the ratio of similarity distances by the ratio of", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/dd1a15f3b5c0a06aa990d4bf1ebb85ec39f7ed063c922cd745f600d2bd89d123.jpg", + "image_caption": [ + "Figure 3. MCD loss for various cases of misalignments that occur when applying random image augmentation in language-image pretraining with. In this paper, we elaborate three scenarios: (a) misalignment caused by augmenting the image of an original positive pair, which is addressed by $\\mathcal{L}^{\\mathrm{pos}}$ (b) augmentation that mistakenly cause positive alignment between negative pairs (c) misalignment that already exists within the dataset." + ], + "image_footnote": [], + "bbox": [ + 506, + 87, + 883, + 304 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "image-text misalignments in the learned embedding space. Specifically, we define the loss function as", + "bbox": [ + 498, + 445, + 890, + 476 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\ell_ {l r} (i, j; \\alpha , \\beta) = \\left\\| \\log \\frac {D \\left(I _ {\\alpha} , T _ {\\beta}\\right)}{D \\left(I _ {i} , T _ {j}\\right)} - \\log \\frac {D \\left(\\bar {I} _ {\\alpha} , T _ {\\beta}\\right)}{D \\left(\\bar {I} _ {i} , T _ {j}\\right)} \\right\\| _ {1}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 486, + 890, + 525 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\| \\cdot \\|_1$ is $\\ell_1$ loss, $D(\\cdot, \\cdot)$ is distance function. We utilize Euclidean distance between the projected representations as distance function. Since the embedded vectors comprising the image $I_i, \\bar{I}_i$ and text $T_j$ are L2-normalized, Euclidean distance operates as a proxy for cosine similarity $D(I_i, T_j) = 2(1 - S_{ij})$ . This log-ratio loss approximates the degree of misalignment, which is measured as the ratio of two image-text pairs. By leveraging this measure, we aim to promote a coherent and continuous embedding space. Accordingly, our student encoder is trained under the guidance of the momentum teacher with the incorporation of this degree of misalignment. By establishing these pairs of log-ratio, we enable the handling of diverse forms of misalignment. We present three distinct index setups that correspond to different types of misalignment.", + "bbox": [ + 498, + 534, + 893, + 762 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Misalignment in Positive pairs. First, we define distance pair for misalignment between the original image-text pair. Let $i'$ denote the index of augmented image sample. On Eq.(5), $i'$ -th image sample and $i$ -th text sample serve as positive pair. However, random augmentation can occasionally transform positive pair into negative pair. To account for such transformations, we intend to utilize the log-ratio between original pairs and augmented pairs. This allows us to", + "bbox": [ + 498, + 779, + 893, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "2566", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "code", + "sub_type": "code", + "code_caption": [ + "Algorithm 1 MCD Pseudocode" + ], + "code_body": "# fm, fs: image encoders (teacher, student) \n# ft: text encoder \n# fa: random-augmentation function \n# N : batch size \ndef D(sim): # cosine sim -> L2 distance \nreturn 2 - 2 * sim + 1e-6 \ndef MCD(img, txt): \n# image, text encodings \naug = fa(img) \n# normalized projection embeddings \nzm, zs,zt = fm(img), fs(img), ft(txt) \nzam,zas = fm(aug), fs(aug) # misalign \n# distance (contrast) \ndi_t, di_s = D(zm @ zt.T), D(zs @ zt.T) \nda_t, da_s = D(zam @ zt.T), D(zas @ zt.T) \n# distill \npos_l, neg_l, noise_l = 0, 0, 0 \nfor i in range(N): \n lr_s1 = log(da_s[i,i]/di_s[i,i]) \n lr_t1 = log(da_t[i,i]/di_t[i,i]) \n# positive pairs \npos_l += abs(lr_s1 - lr_t1) / N \nfor j in range(N): \n if i==j: continue \n lr_s2 = log(da_s[i,j]/di_s[i,i]) \n lr_t2 = log(da_t[i,j]/di_t[i,i]) \n# negative pairs \nneg_l += abs(lr_s2 - lr_t2) / (N*(N-1)) \nlr_s3 = log(di_s[j,j]/di_s[i,i]) \nlr_t3 = log(di_t[j,j]/di_t[i,i]) \n# noisy pairs \nnoise_l += abs(lr_s3 - lr_t3) / (N*(N-1)) \nreturn pos_l + neg_l + noise_l", + "guess_lang": "julia", + "bbox": [ + 76, + 114, + 467, + 575 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "capture these shifts and incorporate them into the learning process effectively.", + "bbox": [ + 75, + 606, + 468, + 638 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} ^ {\\mathrm {p o s}} = \\mathbb {E} _ {i = 1, \\dots , N} \\left[ \\ell_ {l r} (i, i; i ^ {\\prime}, i) \\right], \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 650, + 468, + 667 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $i'$ is the index of augmented $i$ -th sample.", + "bbox": [ + 76, + 671, + 392, + 688 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Misalignment in Negative pairs. Augmented images can possess relevance with different text, which would normally be considered negative pairs in Eq.(5). However, the log-ratio obtained by our momentum teacher alleviates our model from mistakenly pushing the embedding of relevant texts away.", + "bbox": [ + 75, + 704, + 468, + 796 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} ^ {\\text {n e g}} = \\underset {i \\neq j} {\\mathbb {E}} _ {i, j = 1, 2, \\dots , N} \\left[ \\ell_ {l r} \\left(i, i; j ^ {\\prime}, i\\right) \\right], \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 803, + 468, + 830 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $j^{\\prime}$ is the index of augmented $j$ -th sample.", + "bbox": [ + 76, + 837, + 395, + 853 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Misalignment in Noisy pairs. Original image-text pairs obtained from the web may contain either noisy images or", + "bbox": [ + 75, + 869, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "descriptions. While these pairs are normally treated as positive pairs under contrastive loss, we propose a loss for noisy pairs where the noisy labels are trained to have larger distance than matching image-text pairs.", + "bbox": [ + 496, + 90, + 892, + 152 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} ^ {\\text {n o i s y}} = \\mathbb {E} _ {i, j = 1, 2, \\dots , N} \\left[ \\ell_ {l r} (i, i; j, j) \\right]. \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 162, + 892, + 191 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Distillation Loss. The full training objective of MCD distillation $\\mathcal{L}^D$ is the sum of the three distillation terms, which is written as", + "bbox": [ + 498, + 208, + 892, + 253 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} ^ {\\mathrm {D}} = \\mathcal {L} ^ {\\text {p o s}} + \\mathcal {L} ^ {\\text {n e g}} + \\mathcal {L} ^ {\\text {n o i s y}}. \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 602, + 265, + 892, + 282 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.4. Training MCD", + "text_level": 1, + "bbox": [ + 500, + 295, + 651, + 311 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we explain the details of MCD training. The training objective for the text encoder and student image encoder for MCD consists of the three objectives: contrastive loss $\\mathcal{L}^C$ in Eq (5) for initial image-text distance learning, distillation loss $\\mathcal{L}^D$ for the three misalignment scenarios, and loss for masked language modeling $\\mathcal{L}^{\\mathrm{MLM}}$ . The parameters for the teacher image encoder are momentum updated.", + "bbox": [ + 496, + 319, + 892, + 441 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "MLM Loss. Following previous work in literature [23, 18, 19], we randomly mask out the input tokens with a probability of $15\\%$ and replace them with the special token $[\\mathrm{MASK}]^{1}$ . Let $p^{\\mathrm{msk}}$ and $y^{\\mathrm{msk}}$ each denote the set of model's predicted probability for the masked tokens and the set of ground-truth vocabulary index for the tokens, respectively. Then, MLM loss is written as:", + "bbox": [ + 496, + 460, + 892, + 566 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} ^ {\\mathrm {M L M}} = \\mathbb {E} _ {p \\in p ^ {\\mathrm {m s k}}, y \\in y ^ {\\mathrm {m s k}}} \\left[ \\mathrm {C E} (p, y) \\right], \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 578, + 578, + 890, + 598 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where CE denotes Cross Entropy loss.", + "bbox": [ + 500, + 609, + 754, + 625 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Momentum Teacher Update. Let $\\theta_{f_I},\\theta_{\\bar{f}_I}$ be the parameter of the student encoder and momentum teacher, respectively. For the $t$ -th step, we update $\\theta_{\\bar{f}_I}^{(t)}$ of the momentum teacher according to the following:", + "bbox": [ + 496, + 645, + 890, + 710 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\theta_ {\\bar {f} I} ^ {(t)} = m \\theta_ {\\bar {f} I} ^ {(t - 1)} + (1 - m) \\theta_ {f I} ^ {(t)}, \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 589, + 720, + 890, + 744 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $m$ denotes the momentum parameter. We use $m = 0.994$ in our experiments, where $m$ grows in a cosine schedule to 1 at the end of training.", + "bbox": [ + 496, + 755, + 890, + 801 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Progressive Distillation. As the training proceeds, InfoNCE loss conflicts with our misalignment loss. InfoNCE", + "bbox": [ + 500, + 821, + 892, + 853 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "$^{1}$ Following BERT, the replacement is done with either the [MASK] token (80%), another random token within the dictionary (10%), or left unchanged (10%).", + "bbox": [ + 496, + 862, + 892, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "2567", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "between pair $I_{j}^{\\prime}$ and $T_{i}$ forces the embedding to pull regardless of its degree of misalignment. In early stages of training, the model needs to learn how to discriminate positive or negative pairs with a hard label. However, as the training progresses, the log-ratio loss delicately models the distance between the various misalignments occurred by augmentations or innately existing in the original image-text pair. Therefore, we progressively diminish the contribution of InfoNCE loss involving augmented views.", + "bbox": [ + 75, + 90, + 472, + 227 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "MCD Loss. The final loss for MCD is written as:", + "bbox": [ + 76, + 246, + 416, + 261 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} ^ {\\mathrm {M C D}} = \\mathcal {L} ^ {\\mathrm {C}} + \\alpha \\cdot \\mathcal {L} ^ {\\mathrm {D}} + \\beta \\cdot \\mathcal {L} ^ {\\mathrm {M L M}}, \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 156, + 271, + 468, + 290 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\alpha = 0$ progressively increases on a cosine schedule to 1, and $\\beta = 0.2$ .", + "bbox": [ + 75, + 301, + 468, + 333 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.5. MCD Inference", + "text_level": 1, + "bbox": [ + 76, + 340, + 235, + 357 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "MCD is based on a teacher-student network, thus the student $f_{I}$ and momentum teacher $\\bar{f}_{I}$ is obtained after training. Unlike previous work in literature that leverage the teacher network for inference [37, 19], we use the student network that is trained with both the contrastive loss and the log-ratio loss for image-text distance learning.", + "bbox": [ + 75, + 364, + 468, + 455 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiment", + "text_level": 1, + "bbox": [ + 76, + 469, + 202, + 486 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this section, we provide implementation details and experimental results with our MCD pretrained on two widely used image-text benchmark datasets (e.g., CC3M, YFCC15M) to validate the effectiveness of our proposed MCD on multiple downstream datasets including classification and image-text retrieval.", + "bbox": [ + 75, + 494, + 468, + 585 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Implementation Details and Datasets", + "text_level": 1, + "bbox": [ + 76, + 595, + 397, + 612 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For implementation details, our work is built on top of the open-source SLIP codebase $[27]^2$ . For DECLIP [23], we follow the implementation details of the official code release. The performance on GPU-machine runs for CLIP and SLIP follows the exact implementation details upon this codebase. Since MCD features both the momentum teacher image encoder $\\bar{f}_I$ and student $f_I$ , we conduct the following experiment section with $\\bar{f}_I$ based on empirical results. All of our models are pretrained in $16\\times$ A100 GPUs. For CC3M, All models are trained with a ViT-B/16 backbone with a learning rate of 5e-4 and weight decay of 0.5. For YFCC15M, we train the model with ViT-B/32 backbone, batch size 4096, learning rate 1e-3, and weight decay 0.2.", + "bbox": [ + 75, + 619, + 470, + 816 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Pretraining Datasets. To validate the effectiveness of MCD, we pretrain MCD on large-scale open-source", + "bbox": [ + 75, + 834, + 470, + 866 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "datasets: YFCC (Yahoo Flickr Creative Commons) 15M [38] and CC (Conceptual Captions) 3M [34].", + "bbox": [ + 500, + 90, + 890, + 122 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Downstream Datasets. Following CLIP [32], we evaluate the transferability of pretrained MCD on 11 widely used downstream datasets for classification (i.e., Oxford Pets [30], CIFAR-10, CIFAR-100 [17], SUN397 [41], Food-101 [2], Flowers [28], Cars [16], Caltech-101 [8], Aircraft [26], DTD [7], ImageNet-1k [33]). We also transfer to image-text retrieval tasks on Flickr30K [31] and MS-COCO Captions [4] datasets. The evaluation settings for each dataset are consistent with CLIP as in the open-source implementation2.", + "bbox": [ + 496, + 140, + 893, + 292 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. MCD Pretraining on YFCC15M Dataset", + "text_level": 1, + "bbox": [ + 498, + 301, + 848, + 316 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "First, we pretrain MCD on YFCC15M and evaluate its transferability in single-modal (e.g., classification) and multi-modal (e.g., image-text retrieval) downstream tasks. We compare the result against other state-of-the-art Contrastive Language-Image Pretraining approaches [32, 27, 23, 18] that utilizes various levels of supervision including vision self-supervision [3, 5], text self-supervision [23], memory queue [23], and augmentation encoding [18]. All models are pretrained with a learning rate 1e-3 for 32 epochs unless mentioned otherwise.", + "bbox": [ + 496, + 324, + 890, + 476 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Zero-shot Classification. We evaluate the zero-shot classification performance on 11 downstream datasets for single-modal experiments. Tab. 1 shows both the zero-shot classification and linear probing accuracy of CLIP variants [32, 27, 23, 18] pretrained on YFCC15M dataset and transferred to downstream classification datasets. In test time, the learned text encoder $f_{T}$ synthesizes a zero-shot linear classifier by embedding the arbitrary categories of the test dataset. As classes are in the form of a single word, we use prompts including the label (e.g., \"a photo of a {label}\") as following CLIP [32]. Our MCD outperforms across a majority of the 11 datasets with a noticeable margin. Note that even without additional augmented-aware network leveraged in UniCLIP [18] or additional supervision terms such as text augmentation [40], masked language modeling [23] and memory queue, our MCD achieves state-of-the-art performance.", + "bbox": [ + 496, + 494, + 890, + 752 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Linear Probing. To implement linear probe evaluation, we follow CLIP [32] to train a logistic regression classifier on the frozen visual features extracted by the image encoder $f_{I}$ . Specifically, we train the logistic regression classifier using L-BFGS algorithm provided by scikit-learn with maximum 1,000 iterations, and report the corresponding metric for each dataset4. Parameters for L2 regularization are", + "bbox": [ + 496, + 771, + 890, + 878 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "4https://github.com/facebookresearch/SLIP/blob/main/mainlinear.py", + "bbox": [ + 516, + 886, + 883, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "$^{2}$ https://github.com/facebookresearch/SLIP", + "bbox": [ + 93, + 873, + 326, + 887 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "3https://github.com/Sense-GVT/DeCLIP", + "bbox": [ + 96, + 887, + 313, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "2568", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/8edb2fc566eb09511cbc309231a8e8a27d84421c64b0d645417045e2295733a0.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodVision EncoderOxford PetsCIFAR-10CIFAR-100SUN397Food-101FlowersCarsCaltech-101AircraftDTDImageNetAverage
OxfordCIFAR-10OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-10Oxford
Zero-shot Classification:
CLIP [32]19.462.333.640.233.76.32.155.41.416.931.327.5
SLIP [27]28.372.245.345.144.76.82.965.91.921.838.333.9
DeCLIP [23]ViT-B/3230.272.139.751.646.97.13.970.12.524.241.235.4
UniCLIP [18]32.578.647.250.448.78.13.473.02.823.342.837.3
MCD (Ours)40.080.349.655.354.07.94.573.23.030.544.740.2
Linear Probing:
CLIP [32]71.289.272.170.171.493.234.984.329.760.961.167.1
SLIP [27]75.490.575.373.577.196.143.087.234.171.168.171.9
DeCLIP [23]ViT-B/3276.588.671.675.979.396.742.688.032.669.169.271.8
UniCLIP [18]83.192.578.277.081.397.149.888.936.272.870.875.2
MCD (Ours)85.692.779.377.681.797.146.989.536.674.171.375.7
", + "bbox": [ + 76, + 88, + 890, + 343 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 1. Zero-shot image classification/linear probing performance on 11 downstream datasets with YFCC15M pretrained models. Note that DeCLIP [23] utilizes an external momentum queue while UniCLIP [18] features the augmentation encoder during training.", + "bbox": [ + 75, + 345, + 890, + 376 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "determined using hyperparameter sweep on the validation sets. Standard cropping and flipping augmentations [35] are used for linear probing. The bottom section of Tab. 1 reports linear classification performances on the 11 downstream datasets. Our proposed approach, MCD, has consistently outperformed previous baseline methods in zero-shot classification across multiple datasets, with only one exception.", + "bbox": [ + 75, + 398, + 472, + 521 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Image-Text Retrieval. For multi-modal evaluations, we test both the zero-shot and fine-tuned image-text (and text-image) retrieval on Flickr30k and COCO Captions benchmarks. Image-text pairs are ranked according to their similarity scores. Tab. 2 shows the performance for image-text retrieval tasks of MCD pretrained on YFCC15M dataset. Our MCD outperforms all state-of-the-art baselines across every measure with a considerable margin. By incorporating a log-ratio loss with metric learning characteristics into the CLIP framework, our proposed approach has achieved significant improvements in image-text retrieval performance.", + "bbox": [ + 75, + 544, + 472, + 724 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Vision-Language Compositionality. To conduct a thorough analysis of multimodal representation learning, we assess the performance of our model using the SugarCrepe [12] dataset. This dataset serves as a de-biased benchmark specifically designed for evaluating the compositionality aspect of vision-language models. SugarCrepe introduces a set of challenging negative captions for COCO image-text pairs by replacing, swapping, or adding certain concepts to the ground truth caption, and gauge the model's capability to discern the positive from its distractor. Tab. 3", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "summarizes the result, showcasing the performance of various models pretrained on the YFCC15M dataset. Our findings demonstrate that the MCD exhibits significantly better compositionality compared to prior methods. This improved performance is attributed to leveraging augmentations with proper handling for misalignment arising from these augmentations. While other methods often show improved performance over CLIP baseline, adopting augmentations without meticulous management of misalignment cannot maximize their utility.", + "bbox": [ + 496, + 398, + 893, + 551 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. MCD Pretraining on CC3M Dataset", + "text_level": 1, + "bbox": [ + 498, + 561, + 816, + 578 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we compare MCD against other state-of-the-art Contrastive Language-Image Pretraining approaches [32, 27, 23]. All models are pretrained on the CC3M dataset with a learning rate 5e-4 for 40 epochs $^{5}$ . Tab. 4 shows the ImageNet zero-shot results of MCD with other CLIP variants. MCD outperforms all CLIP variants without external training sources such as Nearest Neighbor supervision with large memory queues (NNS) or augmentation information during training (AUG). Furthermore, MCD does not require any additional parameters for the SSL projection layer [27, 23] or additional network for augmentation-aware feature embedding [18].", + "bbox": [ + 496, + 585, + 890, + 767 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.4. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 776, + 653, + 792 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "This section presents ablation studies to evaluate the contribution of each component in our proposed approach, MCD, towards the final performance. To this end, we pretrain all models on the YFCC15M dataset and evaluate them using zero-shot learning on the Imagenet-1k validation set.", + "bbox": [ + 496, + 800, + 890, + 878 + ], + "page_idx": 6 + }, + { + "type": "page_footnote", + "text": "5 More detailed training configuration will be provided in supplement.", + "bbox": [ + 514, + 886, + 885, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "2569", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/b01dbb8d35fa4a293d1ed383f47e2e1155c734c101d0404583fa74f7d3919195.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodImage-to-text retrievalText-to-image retrieval
Flickr30kCOCO CaptionsFlickr30kCOCO Captions
R@1R@5R@10R@1R@5R@10R@1R@5R@10R@1R@5R@10
Zero-shot retrieval:
CLIP [32]34.963.975.920.843.955.723.447.258.913.031.742.7
SLIP [27]47.876.585.927.752.663.932.358.768.818.239.251.0
DeCLIP [23]51.480.288.928.353.264.534.360.370.718.439.651.4
UniCLIP [18]52.381.689.032.057.769.234.862.072.020.243.254.4
MCD (Ours)57.682.691.132.358.771.236.464.874.120.743.555.3
Fine-tuned retrieval
CLIP [32]58.384.891.536.165.076.443.171.180.324.951.764.1
SLIP [27]69.690.495.745.074.083.052.179.486.931.659.571.3
DeCLIP [23]75.693.096.648.777.386.257.883.390.334.263.174.6
UniCLIP [18]78.194.997.754.580.989.161.086.091.938.067.278.0
MCD (Ours)79.395.298.055.681.289.563.187.292.338.267.478.5
", + "bbox": [ + 76, + 88, + 893, + 345 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/e0386c05b45026ee1f91d56a746554a12037e8cfb9f2fe578ee30da35eec801c.jpg", + "table_caption": [ + "Table 2. Zero-shot & Fine-tuned image-text retrieval on the test splits of Flickr30k and COCO Captions with models pre-trained on YFCC15M. ViT-B/32 is used for all setup." + ], + "table_footnote": [], + "table_body": "
MethodAug.MisalignReplaceSwapAdd
CLIP [32]N/A73.659.569.4
SLIP [27]✓N/A74.758.669.1
DeCLIP [23]✓Disregard74.558.266.8
UniCLIP [18]✓fA75.558.470.4
MCD (Ours)✓LD76.261.571.7
", + "bbox": [ + 78, + 400, + 470, + 500 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/7f6ca482462e143aa61b1dee8624083b36f6479ddb29b3f158411f3990c1cf5c.jpg", + "table_caption": [ + "Table 3. Evaluation on SugarCrepe [12]. All models were pretrained on YFCC15M with ViT-B/32 backbone. Models except CLIP involve random image augmentations (Aug.) with different schemes for dealing with image-text misalignments (Misalign). While previous methods either disregard the issue [23] or introduce an additional augmentation encoder $(f_{A})$ [18], MCD manages to harness the misalignment for the distillation loss $(\\mathcal{L}_{\\mathrm{D}})$" + ], + "table_footnote": [], + "table_body": "
MethodEncoderSSLEXTTop1(%)
CLIP [32]--19.6
SLIP [27]SimCLR [3]-23.2
DeCLIP [23]ViT-B/16SimSiam [5]NNS25.4
UniCLIP [18]MP-NCE [18]AUG27.8
MCD (Ours)MP-NCE [18]-28.2
", + "bbox": [ + 78, + 614, + 473, + 712 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Specifically, we implement the MP-NCE loss without augmentation encoding, which results in an accuracy of 39.6. Our results in Tab. 5 demonstrate that each loss component in MCD has a positive impact on the final performance, leading to an overall improvement in accuracy. These find", + "bbox": [ + 75, + 824, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/74dc79f7e8c5f73b6de8932772a352475ac9716fca76208dfcc85be1a203a9c1.jpg", + "table_caption": [ + "Table 4. ImageNet-1k Top 1 zero shot accuracy with models pretrained on CC3M dataset. SSL denotes the vision self-supervision term used in each model and EXT denotes external sources involved during training. NNS is nearest neighbor supervision using a separate memory queue, and AUG is the vectorized information of each random augmentation conducted during training." + ], + "table_footnote": [], + "table_body": "
\\( \\mathcal{L}^{\\text{base}} \\)\\( f_A \\)\\( \\mathcal{L}^{\\text{pos}} \\)\\( \\mathcal{L}^{\\text{neg}} \\)\\( \\mathcal{L}^{\\text{noisy}} \\)Top1 Acc (%)
(a)✓39.6
(b)✓✓42.8
(c)✓✓43.9
(d)✓✓✓44.3
(e)✓✓✓✓44.7
", + "bbox": [ + 504, + 400, + 890, + 486 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Ablation study on ImageNet-1k Top 1 zero shot accuracy for vision-language pretraining for each loss components of MCD. All models were pretrained with a ViT-B/32 backbone with a basic contrastive loss $\\mathcal{L}^C$ in Eq (5) and MLM loss in Eq (11), which we abbreviate as $\\mathcal{L}^{\\mathrm{base}}$ . All $\\mathcal{L}^{\\mathrm{pos}}$ , $\\mathcal{L}^{\\mathrm{neg}}$ , $\\mathcal{L}^{\\mathrm{noisy}}$ shows a consistent gain in zero-shot performance. $f_{A}$ denotes the augmentation encoder, making (b) analogous to UniCLIP [18].", + "bbox": [ + 496, + 489, + 893, + 589 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "ings highlight the importance of each component in our proposed approach and validate its effectiveness in improving the zero-shot classification performance. Note that MCD outperforms (b) (i.e., UniCLIP) that explicitly includes the augmentation information during training with only $\\mathcal{L}^{\\mathrm{pos}}$ , showing the effectiveness of harnessing the misalignments that occur during random image augmentation for training.", + "bbox": [ + 496, + 606, + 890, + 714 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 726, + 619, + 742 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We propose MCD, a new training strategy for dealing with misalignments occurred by random image augmentations under visual-language pretraining. Our novel distillation formulation enables data-efficient training under Contrastive Language-Image Pretraining. Future works will include extending MCD frameworks to other modalities.", + "bbox": [ + 496, + 751, + 893, + 843 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "2570", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Alex Andonian, Shixing Chen, and Raffay Hamid. Robust cross-modal representation learning with progressive self-distillation. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, 2022.", + "[2] Lukas Bossard, Matthieu Guillaumin, and Luc Van Gool. Food-101-mining discriminative components with random forests. In European conference on computer vision, pages 446-461. Springer, 2014.", + "[3] Ting Chen, Simon Kornblith, Mohammad Norouzi, and Geoffrey Hinton. 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International Journal of Computer Vision, 119(1):3-22, 2016." + ], + "bbox": [ + 501, + 92, + 890, + 260 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "2572", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Misalign, Contrast then Distill_ Rethinking Misalignments in Language-Image Pre-training/8db6862b-91a8-4f4b-b1af-4631b12bd46c_model.json b/2023/Misalign, Contrast then Distill_ Rethinking Misalignments in Language-Image Pre-training/8db6862b-91a8-4f4b-b1af-4631b12bd46c_model.json new file mode 100644 index 0000000000000000000000000000000000000000..c76c64a6b22fbc79599564d5019d6f7355889972 --- /dev/null +++ b/2023/Misalign, Contrast then Distill_ Rethinking Misalignments in Language-Image Pre-training/8db6862b-91a8-4f4b-b1af-4631b12bd46c_model.json @@ -0,0 +1,2090 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.19, + 0.131, + 0.784, + 0.177 + ], + "angle": 0, + "content": "Misalign, Contrast then Distill: Rethinking Misalignments in Language-Image Pretraining" + }, + { + "type": "text", + "bbox": [ + 0.231, + 0.204, + 0.741, + 0.246 + ], + "angle": 0, + "content": "Bumsoo Kim* Yeonsik Jo Jinhyung Kim Seunghwan Kim LG AI Research" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.281, + 0.314, + 0.297 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.313, + 0.474, + 0.616 + ], + "angle": 0, + "content": "Contrastive Language-Image Pretraining has emerged as a prominent approach for training vision and text encoders with uncurated image-text pairs from the web. To enhance data-efficiency, recent efforts have introduced additional supervision terms that involve random-augmented views of the image. However, since the image augmentation process is unaware of its text counterpart, this procedure could cause various degrees of image-text misalignments during training. Prior methods either disregarded this discrepancy or introduced external models to mitigate the impact of misalignments during training. In contrast, we propose a novel metric learning approach that capitalizes on these misalignments as an additional training source, which we term \"Misalign, Contrast then Distill (MCD)\". Unlike previous methods that treat augmented images and their text counterparts as simple positive pairs, MCD predicts the continuous scales of misalignment caused by the augmentation. Our extensive experimental results show that our proposed MCD achieves state-of-the-art transferability in multiple classification and retrieval downstream datasets." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.658, + 0.21, + 0.673 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.683, + 0.47, + 0.88 + ], + "angle": 0, + "content": "Recent advances in deep learning have shown that image representations trained with large-scale uncurated natural language supervision shows powerful transferability to various downstream tasks [14, 32]. A predominant paradigm in vision-language pre-training is to use a simple contrastive loss that makes the embedding of an image and its matching text description (positive pair) more similar to each other than other arbitrary image-text pairs (negative pairs) [29]. To achieve a more data-efficient training, following works actively capitalized on image random augmentation by: (i) joining language-image pretraining objectives with vision self-supervision terms [3, 5] between the augmented images [27, 23, 18] and (ii) involving more pairs of posi" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.285, + 0.891, + 0.486 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.497, + 0.895, + 0.624 + ], + "angle": 0, + "content": "Figure 1. Conceptual illustration of contrastive language-image objectives of previous works (i.e., InfoNCE) and our MCD for (a) augmentation that doesn't harm the correspondence with its description and (b) augmentation that does. Previous works either disregard these misalignments [23] or leverage external models [18, 9] to mitigate their impact. On the other hand, MCD uses the continuous degree of misalignments caused by random image augmentation as a useful source for training various levels of alignments between images and their text descriptions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.643, + 0.892, + 0.673 + ], + "angle": 0, + "content": "tive/negative supervisions between the augmented images and their original text description [23, 18]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.674, + 0.893, + 0.87 + ], + "angle": 0, + "content": "However, since the random image augmentation process is unaware of its corresponding text, it often results in the augmented image view to be misaligned with its description (see (b) in Fig.1). These misalignments behave as noisy training signals for the contrastive loss in language-image pretraining, thus causing performance degradation if not properly attended [27]. To mitigate this issue, recent works have used additional augmentation embeddings [18] or heavy external off-the-shelf object detectors and summary extractors [9] to match the alignment during training. Though being straightforward and showing strong performance, these works are limited in that they add unnecessary burden in both training and inference." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Based on this observation, we start with a simple question: \"Instead of treating misalignments as noise to elim" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.398, + 0.9 + ], + "angle": 0, + "content": "*Correspondence to: bumsoo.kim@lgresearch.ai" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2563" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.182 + ], + "angle": 0, + "content": "inate, can we rather harness them as a training source for language-image pretraining?\". To this end, we propose MCD (i.e., Misalign, Contrast then Distill), a novel training framework that leverages the various levels of misalignments between random augmented images and its text description during training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.183, + 0.471, + 0.422 + ], + "angle": 0, + "content": "MCD consists of three steps (see Fig 2 for an overview illustration of MCD): First, we conduct random augmentation on the image that causes various levels of misalignments (or not at all) with its text counterpart (Misalign). Then, we project all the participants (image, text, and augmented image) into an unified multimodal space, and learn the distance between all the image-text pairs with a contrastive objective (Contrast). Finally, we use a teacher-student network where the student learns from the \"soft\" distance between the text- original image (i.e., \\( D(\\bar{I}, T) \\) in Fig 2) and text-augmented image (i.e., \\( D(\\bar{I}', T) \\) in Fig 2) of the momentum teacher with a log-ratio loss (Distill). continuous scale of misalignment to the student model, enabling the student to learn from the various levels of misalignment that occur from the random augmentation during training time." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.424, + 0.378, + 0.438 + ], + "angle": 0, + "content": "Our contribution of this paper is threefold:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.45, + 0.469, + 0.495 + ], + "angle": 0, + "content": "- We propose MCD, a novel training framework where we learn the continuous level of misalignment as a source for contrastive language-image pretraining." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.506, + 0.469, + 0.566 + ], + "angle": 0, + "content": "- Our MCD outperforms state-of-the-art models across various single/multi-modal downstream datasets without adding additional parameters for inference or using external models to force the alignment." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.577, + 0.469, + 0.666 + ], + "angle": 0, + "content": "- We propose three distillation strategies leveraging misalignments: i) misalignment between positive pairs, ii) misalignment between negative pairs, and iii) misalignment between noisy pairs. Extensive experiments show that all three strategies positively contributes to our final performance." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.45, + 0.469, + 0.666 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.691, + 0.219, + 0.707 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.717, + 0.468, + 0.747 + ], + "angle": 0, + "content": "Here, we present brief review of multi-modal representation learning, especially vision-language pre-training." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.757, + 0.336, + 0.773 + ], + "angle": 0, + "content": "2.1. Vision-language Pre-training" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Vision-Language Pre-training (VLP) trains a multimodal model to learn joint representation of visual and textual information that can be transfer to various vision-language downstream tasks. The success of VLP primarily relies on large-scale datasets which contains images and their corresponding descriptions, enabling the model to understand the semantic relationship between the pairs. VLP includes two different group of models: 1) single-stream" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.091, + 0.891, + 0.43 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.433, + 0.892, + 0.517 + ], + "angle": 0, + "content": "Figure 2. Overview of MCD. Our MCD consist of three steps: (i) text-agnostic random augmentation of the image that causes various levels of misalignment with the corresponding text, (ii) learning the distance between the image/augmented image and text with contrastive objectives then (iii) distill the log-ratio of the image-text distance between the original and the augmented image." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.543, + 0.892, + 0.694 + ], + "angle": 0, + "content": "models [20, 6, 13, 22, 21, 25, 36] which process an image and its associated text information in a shared backbone network and 2) dual-stream models [14, 32] which has two independent backbone networks for processing each modality. In this work, we focuses on Contrastive Language Image Pretraining (CLIP [32]), which is a type of dual-stream models trained with image-text contrastive loss where the image and its matching text description in the dataset as a positive pair and other unrelated pairs in a batch as negative pairs." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.705, + 0.852, + 0.722 + ], + "angle": 0, + "content": "2.2. Misalignments between Image-Text Pairs" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.729, + 0.891, + 0.79 + ], + "angle": 0, + "content": "There are two different sources that cause misalignments in image-text pairs for VLP: misalignment that naturally occurs in image-text paired datasets, and misalignments caused by random image augmentation." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.81, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Misalignment in Image-Text Pairs. Large scale image-text paired datasets for VLP are usually collected from the web thus can contain uncurated and noisy pairs which have weak relations. This inevitably incurs misalignment between positive image-text pairs in the dataset misleading naive contrastive language image objective. Previous" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2564" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.244 + ], + "angle": 0, + "content": "studies [19, 24, 1] have attempted to address the problem by knowledge distillation [11] of soft image-text alignment matrix from momentum teacher network to the student network via KL divergence loss. Our proposed method stands apart from previous approaches due to its element-wise log-ratio loss for distillation. Element-wise loss lessens the dependence on training hyperparameters like batch size and temperature for KL loss. Furthermore, it enables the model to harness the various levels of individual misalignments of each sample from random augmentation or label noise." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.27, + 0.473, + 0.692 + ], + "angle": 0, + "content": "Misalignment by Augmentations. View-based self-supervised learning, in which models are trained to represent views or augmentations of the same image similarly, has yielded strong results across a variety of different formulations. Consecutive work of CLIP (i.e., SLIP [27]) initially introduced supervision between random augmented image views (e.g., cropping, gray-scale, jittering, gaussian blur, horizontal flipping, etc.). Since only image-image supervision was given in a separately embedded space, augmentation was not a factor for misalignment. To include more positive/negative pairs for the image-text contrastive objective, following works [23, 18] also introduced InfoNCE loss between the augmented views and the text pairs. However, since the text description is unaware of the random augmentations, there is a high chance that misalignments occur during training. SLIP shows that naïve application of contrastive loss to these misaligned pairs results in suboptimal performance. Previous work have either ignored this misalignment [23] or addressed this issue with an additional encoder that encodes the one-hot information of which augmentation has been applied during training [18]. PyramidCLIP [9] addressed this issue with external off-the-shelf object detectors and summary extractors. HiCLIP [10] captured the hierarchical nature of high-level on unsupervised manner with tree Transformer [39]. MCD incorporate the misalignment information as a source of training via novel log-ratio loss without introducing any external module." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.711, + 0.205, + 0.729 + ], + "angle": 0, + "content": "3. Preliminary" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.738, + 0.47, + 0.815 + ], + "angle": 0, + "content": "In our preliminary, we revisit the basic form of Contrastive Language-Image Pretraining (i.e., CLIP [32]). CLIP features a dual-encoder architecture where the image encoder \\( f_{I} \\) and text encoder \\( f_{T} \\) are jointly trained with a contrastive objective \\( \\mathcal{L}_{\\mathrm{CLIP}} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.839, + 0.47, + 0.903 + ], + "angle": 0, + "content": "InfoNCE Loss Given \\( N \\) image-text pairs \\( \\{(x_i^I, x_i^T)\\}_{i=1}^N \\), we define a similarity matrix \\( S \\) whose \\( i \\)-th row and the \\( j \\)-th column is the cosine similarity between the projected representations of the \\( i \\)-th text \\( T_i \\) and the \\( j \\)-th image \\( I_j \\) (i.e.," + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.09, + 0.765, + 0.109 + ], + "angle": 0, + "content": "\\(T_{i} = f_{T}(x_{i}^{T}),I_{j} = f_{I}(x_{j}^{I}))\\) , written as:" + }, + { + "type": "equation", + "bbox": [ + 0.633, + 0.117, + 0.892, + 0.134 + ], + "angle": 0, + "content": "\\[\nS _ {i j} = \\operatorname {s i m} \\left(T _ {i}, I _ {j}\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.143, + 0.894, + 0.248 + ], + "angle": 0, + "content": "where \\(\\mathrm{sim}(\\cdot ,\\cdot)\\) is cosine similarity. In CLIP [32], the encoded image features \\(I\\) and text features \\(T\\) are projected to the same dimension where the embeddings for matching image-text pairs are pulled together while embeddings for arbitrary pairs are pushed apart with the InfoNCE loss [29]. Given the similarity matrix \\(S\\), the InfoNCE loss \\(\\mathcal{L}_N\\) is rewritten as:" + }, + { + "type": "equation", + "bbox": [ + 0.55, + 0.256, + 0.892, + 0.299 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {N} (S) = - \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\log \\frac {\\exp \\left(S _ {i i} / \\tau\\right)}{\\sum_ {j = 1} ^ {N} \\exp \\left(S _ {i j} / \\tau\\right)}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.306, + 0.892, + 0.336 + ], + "angle": 0, + "content": "where \\(\\tau\\) is a learnable temperature variable. The overall loss of clip \\(\\mathcal{L}_{\\mathrm{CLIP}}\\) is written as:" + }, + { + "type": "equation", + "bbox": [ + 0.582, + 0.346, + 0.892, + 0.38 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {C L I P}} = \\frac {1}{2} \\left(\\mathcal {L} _ {N} (S) + \\mathcal {L} _ {N} \\left(S ^ {T}\\right)\\right). \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.394, + 0.892, + 0.591 + ], + "angle": 0, + "content": "Augmentations and Misalignment. To include more positive/negative pairs for the contrastive objective, following works [23, 18] introduced InfoNCE loss between the random augmented image views and the text description for the original image. Let \\(\\mathcal{A}\\) a function for random image augmentation that includes randomly applying cropping, gray-scale, jittering, gaussian blur, horizontal flipping following SimCLR [3]. \\(I_{j'}\\) is the encoded image feature of augmented view of \\(j\\)-th image(e.g. \\(I_{j'} = f_I(\\mathcal{A}(x_j^I))\\)). Let \\(S_{ij}' = \\mathrm{sim}(T_i, I_{j'})\\) represent the similarity between the augmented view of \\(j\\)-th image and \\(i\\)-th text. We denote the matrix of these similarity as \\(S'\\) for concise notation. Then, InfoNCE loss between the augmented image and the text is" + }, + { + "type": "equation", + "bbox": [ + 0.582, + 0.6, + 0.892, + 0.629 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {C L I P}} ^ {\\prime} = \\frac {1}{2} \\left(\\mathcal {L} _ {N} \\left(S ^ {\\prime}\\right) + \\mathcal {L} _ {N} \\left(S ^ {\\prime T}\\right)\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.636, + 0.892, + 0.803 + ], + "angle": 0, + "content": "As the random augmentation function \\(\\mathcal{A}\\) is independent to the corresponding text description, the augmented view \\(I_{j'}\\) is likely to exhibit misalignment with text \\(T_i\\). This hypothesis is consistent with the finding of SLIP [27], which demonstrated that introducing augmentation (particularly resize crop, and flip) to CLIP actually resulted in a performance decrease. Previous works [27, 23] have sidestepped the utilization of augmented view in CLIP by substituting infoNCE with self-supervised learning loss(e.g. SimCLR [3]) between images. These approaches have limitation in fully capturing the essence of multi-modal learning." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.815, + 0.591, + 0.831 + ], + "angle": 0, + "content": "4. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.902 + ], + "angle": 0, + "content": "In this section, we introduce MCD (Misalign, Contrast then Distill), a novel training framework for language-image pretraining using misalignments as continuous labels for learning the distance between image-text pairs." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2565" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.091, + 0.182, + 0.108 + ], + "angle": 0, + "content": "4.1. Misalign" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.115, + 0.474, + 0.313 + ], + "angle": 0, + "content": "The first step of MCD is to apply text-agnostic random image augmentations (e.g., random crop, random flip, grayscale, etc.) to create various levels of misalignments between the images and its description. Here, we elaborate on three distinct scenarios of misalignment that can arise during the augmentation process, hindering the contrastive loss to learn proper distance between image-text pairs: (i) Text-agnostic random augmentation can cause misalignments in positive image-text pairs. (ii) The random-augmentation can mistakenly cause positive signals between negative pairs. (iii) Misalignments can already exist innately within the original image-text pair. A detailed illustration of each cases are provided in Fig 3." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.323, + 0.183, + 0.337 + ], + "angle": 0, + "content": "4.2. Contrast" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.347, + 0.473, + 0.529 + ], + "angle": 0, + "content": "In the second step, MCD initially learns the distance metric between image-text pairs with a contrastive objective. Motivated by [18], we project both image and text modalities to a unified space and use all the positive pairs and negative pairs of both modalities. For an \\(i\\)-th embedding \\(z_{i}\\) in a batch of embeddings \\(\\{z_i\\}_{i = 1}^{3N}\\) that includes \\(N\\) image samples, \\(N\\) text samples, and \\(N\\) random augmented image samples, let \\(\\mathcal{P}_i\\) and \\(\\mathcal{N}_i\\) each denote the set of all positive sample indices of the \\(i\\)-th sample including \\(i\\) itself and the set of all negative sample indices of the \\(i\\)-th sample. Then, the contrastive loss for the multiple positives and multiple negatives for sample \\(i\\) can be written as" + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.539, + 0.47, + 0.577 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {i} ^ {C} = \\mathbb {E} _ {p \\in \\mathcal {P} _ {i}} \\left[ - \\log \\frac {\\sin \\left(z _ {i} , z _ {p}\\right)}{\\sin \\left(z _ {i} , z _ {p}\\right) + \\sum_ {n \\in \\mathcal {N} _ {i}} \\sin \\left(z _ {i} , z _ {n}\\right)} \\right]. \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.587, + 0.47, + 0.678 + ], + "angle": 0, + "content": "However, without encoding augmentation information the image-text contrastive loss is prone to the three aforementioned issues. We address these three issues with a teacher-student model where the continuous distance between the image-text and augmented image-text of the teacher model is distilled to the student model." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.688, + 0.161, + 0.703 + ], + "angle": 0, + "content": "4.3. Distill" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.712, + 0.47, + 0.819 + ], + "angle": 0, + "content": "Knowledge distillation, introduced by Hinton et al. [11], is a learning paradigm where we train the student network to mimic the \"soft\" labels predicted from the teacher network. In MCD, we train the student network with the continuous image-text distance predicted by the teacher network. Psuedocode for the distillation in MCD is provided in Algorithm 1." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Log-Ratio Loss for Image-Text Distance. Given a student \\( f_{I} \\) and a momentum teacher \\( \\bar{f}_{I} \\), we propose to use log-ratio loss [15] on image-text similarities that aims to approximate the ratio of similarity distances by the ratio of" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.088, + 0.885, + 0.305 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.323, + 0.895, + 0.422 + ], + "angle": 0, + "content": "Figure 3. MCD loss for various cases of misalignments that occur when applying random image augmentation in language-image pretraining with. In this paper, we elaborate three scenarios: (a) misalignment caused by augmenting the image of an original positive pair, which is addressed by \\(\\mathcal{L}^{\\mathrm{pos}}\\) (b) augmentation that mistakenly cause positive alignment between negative pairs (c) misalignment that already exists within the dataset." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.446, + 0.892, + 0.477 + ], + "angle": 0, + "content": "image-text misalignments in the learned embedding space. Specifically, we define the loss function as" + }, + { + "type": "equation", + "bbox": [ + 0.508, + 0.487, + 0.892, + 0.526 + ], + "angle": 0, + "content": "\\[\n\\ell_ {l r} (i, j; \\alpha , \\beta) = \\left\\| \\log \\frac {D \\left(I _ {\\alpha} , T _ {\\beta}\\right)}{D \\left(I _ {i} , T _ {j}\\right)} - \\log \\frac {D \\left(\\bar {I} _ {\\alpha} , T _ {\\beta}\\right)}{D \\left(\\bar {I} _ {i} , T _ {j}\\right)} \\right\\| _ {1}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.535, + 0.895, + 0.763 + ], + "angle": 0, + "content": "where \\( \\| \\cdot \\|_1 \\) is \\( \\ell_1 \\) loss, \\( D(\\cdot, \\cdot) \\) is distance function. We utilize Euclidean distance between the projected representations as distance function. Since the embedded vectors comprising the image \\( I_i, \\bar{I}_i \\) and text \\( T_j \\) are L2-normalized, Euclidean distance operates as a proxy for cosine similarity \\( D(I_i, T_j) = 2(1 - S_{ij}) \\). This log-ratio loss approximates the degree of misalignment, which is measured as the ratio of two image-text pairs. By leveraging this measure, we aim to promote a coherent and continuous embedding space. Accordingly, our student encoder is trained under the guidance of the momentum teacher with the incorporation of this degree of misalignment. By establishing these pairs of log-ratio, we enable the handling of diverse forms of misalignment. We present three distinct index setups that correspond to different types of misalignment." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.78, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Misalignment in Positive pairs. First, we define distance pair for misalignment between the original image-text pair. Let \\( i' \\) denote the index of augmented image sample. On Eq.(5), \\( i' \\)-th image sample and \\( i \\)-th text sample serve as positive pair. However, random augmentation can occasionally transform positive pair into negative pair. To account for such transformations, we intend to utilize the log-ratio between original pairs and augmented pairs. This allows us to" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2566" + } + ], + [ + { + "type": "code_caption", + "bbox": [ + 0.08, + 0.092, + 0.292, + 0.106 + ], + "angle": 0, + "content": "Algorithm 1 MCD Pseudocode" + }, + { + "type": "code", + "bbox": [ + 0.078, + 0.115, + 0.468, + 0.576 + ], + "angle": 0, + "content": "# fm, fs: image encoders (teacher, student) \n# ft: text encoder \n# fa: random-augmentation function \n# N : batch size \ndef D(sim): # cosine sim -> L2 distance \nreturn 2 - 2 * sim + 1e-6 \ndef MCD(img, txt): \n# image, text encodings \naug = fa(img) \n# normalized projection embeddings \nzm, zs,zt = fm(img), fs(img), ft(txt) \nzam,zas = fm(aug), fs(aug) # misalign \n# distance (contrast) \ndi_t, di_s = D(zm @ zt.T), D(zs @ zt.T) \nda_t, da_s = D(zam @ zt.T), D(zas @ zt.T) \n# distill \npos_l, neg_l, noise_l = 0, 0, 0 \nfor i in range(N): \n lr_s1 = log(da_s[i,i]/di_s[i,i]) \n lr_t1 = log(da_t[i,i]/di_t[i,i]) \n# positive pairs \npos_l += abs(lr_s1 - lr_t1) / N \nfor j in range(N): \n if i==j: continue \n lr_s2 = log(da_s[i,j]/di_s[i,i]) \n lr_t2 = log(da_t[i,j]/di_t[i,i]) \n# negative pairs \nneg_l += abs(lr_s2 - lr_t2) / (N*(N-1)) \nlr_s3 = log(di_s[j,j]/di_s[i,i]) \nlr_t3 = log(di_t[j,j]/di_t[i,i]) \n# noisy pairs \nnoise_l += abs(lr_s3 - lr_t3) / (N*(N-1)) \nreturn pos_l + neg_l + noise_l" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.607, + 0.47, + 0.639 + ], + "angle": 0, + "content": "capture these shifts and incorporate them into the learning process effectively." + }, + { + "type": "equation", + "bbox": [ + 0.165, + 0.651, + 0.47, + 0.669 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} ^ {\\mathrm {p o s}} = \\mathbb {E} _ {i = 1, \\dots , N} \\left[ \\ell_ {l r} (i, i; i ^ {\\prime}, i) \\right], \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.672, + 0.393, + 0.689 + ], + "angle": 0, + "content": "where \\( i' \\) is the index of augmented \\( i \\)-th sample." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.47, + 0.797 + ], + "angle": 0, + "content": "Misalignment in Negative pairs. Augmented images can possess relevance with different text, which would normally be considered negative pairs in Eq.(5). However, the log-ratio obtained by our momentum teacher alleviates our model from mistakenly pushing the embedding of relevant texts away." + }, + { + "type": "equation", + "bbox": [ + 0.153, + 0.804, + 0.47, + 0.831 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} ^ {\\text {n e g}} = \\underset {i \\neq j} {\\mathbb {E}} _ {i, j = 1, 2, \\dots , N} \\left[ \\ell_ {l r} \\left(i, i; j ^ {\\prime}, i\\right) \\right], \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.838, + 0.396, + 0.854 + ], + "angle": 0, + "content": "where \\(j^{\\prime}\\) is the index of augmented \\(j\\)-th sample." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Misalignment in Noisy pairs. Original image-text pairs obtained from the web may contain either noisy images or" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.893, + 0.153 + ], + "angle": 0, + "content": "descriptions. While these pairs are normally treated as positive pairs under contrastive loss, we propose a loss for noisy pairs where the noisy labels are trained to have larger distance than matching image-text pairs." + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.164, + 0.893, + 0.192 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} ^ {\\text {n o i s y}} = \\mathbb {E} _ {i, j = 1, 2, \\dots , N} \\left[ \\ell_ {l r} (i, i; j, j) \\right]. \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.209, + 0.893, + 0.254 + ], + "angle": 0, + "content": "Distillation Loss. The full training objective of MCD distillation \\(\\mathcal{L}^D\\) is the sum of the three distillation terms, which is written as" + }, + { + "type": "equation", + "bbox": [ + 0.604, + 0.266, + 0.893, + 0.283 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} ^ {\\mathrm {D}} = \\mathcal {L} ^ {\\text {p o s}} + \\mathcal {L} ^ {\\text {n e g}} + \\mathcal {L} ^ {\\text {n o i s y}}. \\tag {10}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.296, + 0.652, + 0.313 + ], + "angle": 0, + "content": "4.4. Training MCD" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.32, + 0.893, + 0.442 + ], + "angle": 0, + "content": "In this section, we explain the details of MCD training. The training objective for the text encoder and student image encoder for MCD consists of the three objectives: contrastive loss \\(\\mathcal{L}^C\\) in Eq (5) for initial image-text distance learning, distillation loss \\(\\mathcal{L}^D\\) for the three misalignment scenarios, and loss for masked language modeling \\(\\mathcal{L}^{\\mathrm{MLM}}\\). The parameters for the teacher image encoder are momentum updated." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.462, + 0.893, + 0.567 + ], + "angle": 0, + "content": "MLM Loss. Following previous work in literature [23, 18, 19], we randomly mask out the input tokens with a probability of \\(15\\%\\) and replace them with the special token \\([\\mathrm{MASK}]^{1}\\). Let \\(p^{\\mathrm{msk}}\\) and \\(y^{\\mathrm{msk}}\\) each denote the set of model's predicted probability for the masked tokens and the set of ground-truth vocabulary index for the tokens, respectively. Then, MLM loss is written as:" + }, + { + "type": "equation", + "bbox": [ + 0.58, + 0.579, + 0.892, + 0.599 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} ^ {\\mathrm {M L M}} = \\mathbb {E} _ {p \\in p ^ {\\mathrm {m s k}}, y \\in y ^ {\\mathrm {m s k}}} \\left[ \\mathrm {C E} (p, y) \\right], \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.61, + 0.755, + 0.626 + ], + "angle": 0, + "content": "where CE denotes Cross Entropy loss." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.646, + 0.892, + 0.711 + ], + "angle": 0, + "content": "Momentum Teacher Update. Let \\(\\theta_{f_I},\\theta_{\\bar{f}_I}\\) be the parameter of the student encoder and momentum teacher, respectively. For the \\(t\\) -th step, we update \\(\\theta_{\\bar{f}_I}^{(t)}\\) of the momentum teacher according to the following:" + }, + { + "type": "equation", + "bbox": [ + 0.59, + 0.721, + 0.892, + 0.746 + ], + "angle": 0, + "content": "\\[\n\\theta_ {\\bar {f} I} ^ {(t)} = m \\theta_ {\\bar {f} I} ^ {(t - 1)} + (1 - m) \\theta_ {f I} ^ {(t)}, \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.756, + 0.892, + 0.802 + ], + "angle": 0, + "content": "where \\( m \\) denotes the momentum parameter. We use \\( m = 0.994 \\) in our experiments, where \\( m \\) grows in a cosine schedule to 1 at the end of training." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.822, + 0.893, + 0.854 + ], + "angle": 0, + "content": "Progressive Distillation. As the training proceeds, InfoNCE loss conflicts with our misalignment loss. InfoNCE" + }, + { + "type": "page_footnote", + "bbox": [ + 0.498, + 0.863, + 0.893, + 0.901 + ], + "angle": 0, + "content": "\\(^{1}\\)Following BERT, the replacement is done with either the [MASK] token (80%), another random token within the dictionary (10%), or left unchanged (10%)." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2567" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.228 + ], + "angle": 0, + "content": "between pair \\( I_{j}^{\\prime} \\) and \\( T_{i} \\) forces the embedding to pull regardless of its degree of misalignment. In early stages of training, the model needs to learn how to discriminate positive or negative pairs with a hard label. However, as the training progresses, the log-ratio loss delicately models the distance between the various misalignments occurred by augmentations or innately existing in the original image-text pair. Therefore, we progressively diminish the contribution of InfoNCE loss involving augmented views." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.247, + 0.418, + 0.262 + ], + "angle": 0, + "content": "MCD Loss. The final loss for MCD is written as:" + }, + { + "type": "equation", + "bbox": [ + 0.157, + 0.272, + 0.47, + 0.291 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} ^ {\\mathrm {M C D}} = \\mathcal {L} ^ {\\mathrm {C}} + \\alpha \\cdot \\mathcal {L} ^ {\\mathrm {D}} + \\beta \\cdot \\mathcal {L} ^ {\\mathrm {M L M}}, \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.303, + 0.47, + 0.334 + ], + "angle": 0, + "content": "where \\(\\alpha = 0\\) progressively increases on a cosine schedule to 1, and \\(\\beta = 0.2\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.342, + 0.236, + 0.358 + ], + "angle": 0, + "content": "4.5. MCD Inference" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.366, + 0.47, + 0.457 + ], + "angle": 0, + "content": "MCD is based on a teacher-student network, thus the student \\( f_{I} \\) and momentum teacher \\( \\bar{f}_{I} \\) is obtained after training. Unlike previous work in literature that leverage the teacher network for inference [37, 19], we use the student network that is trained with both the contrastive loss and the log-ratio loss for image-text distance learning." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.47, + 0.203, + 0.487 + ], + "angle": 0, + "content": "5. Experiment" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.496, + 0.47, + 0.587 + ], + "angle": 0, + "content": "In this section, we provide implementation details and experimental results with our MCD pretrained on two widely used image-text benchmark datasets (e.g., CC3M, YFCC15M) to validate the effectiveness of our proposed MCD on multiple downstream datasets including classification and image-text retrieval." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.597, + 0.398, + 0.613 + ], + "angle": 0, + "content": "5.1. Implementation Details and Datasets" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.62, + 0.471, + 0.817 + ], + "angle": 0, + "content": "For implementation details, our work is built on top of the open-source SLIP codebase \\([27]^2\\). For DECLIP [23], we follow the implementation details of the official code release. The performance on GPU-machine runs for CLIP and SLIP follows the exact implementation details upon this codebase. Since MCD features both the momentum teacher image encoder \\(\\bar{f}_I\\) and student \\(f_I\\), we conduct the following experiment section with \\(\\bar{f}_I\\) based on empirical results. All of our models are pretrained in \\(16\\times\\) A100 GPUs. For CC3M, All models are trained with a ViT-B/16 backbone with a learning rate of 5e-4 and weight decay of 0.5. For YFCC15M, we train the model with ViT-B/32 backbone, batch size 4096, learning rate 1e-3, and weight decay 0.2." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.835, + 0.471, + 0.867 + ], + "angle": 0, + "content": "Pretraining Datasets. To validate the effectiveness of MCD, we pretrain MCD on large-scale open-source" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.892, + 0.123 + ], + "angle": 0, + "content": "datasets: YFCC (Yahoo Flickr Creative Commons) 15M [38] and CC (Conceptual Captions) 3M [34]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.141, + 0.894, + 0.293 + ], + "angle": 0, + "content": "Downstream Datasets. Following CLIP [32], we evaluate the transferability of pretrained MCD on 11 widely used downstream datasets for classification (i.e., Oxford Pets [30], CIFAR-10, CIFAR-100 [17], SUN397 [41], Food-101 [2], Flowers [28], Cars [16], Caltech-101 [8], Aircraft [26], DTD [7], ImageNet-1k [33]). We also transfer to image-text retrieval tasks on Flickr30K [31] and MS-COCO Captions [4] datasets. The evaluation settings for each dataset are consistent with CLIP as in the open-source implementation2." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.302, + 0.849, + 0.318 + ], + "angle": 0, + "content": "5.2. MCD Pretraining on YFCC15M Dataset" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.325, + 0.892, + 0.477 + ], + "angle": 0, + "content": "First, we pretrain MCD on YFCC15M and evaluate its transferability in single-modal (e.g., classification) and multi-modal (e.g., image-text retrieval) downstream tasks. We compare the result against other state-of-the-art Contrastive Language-Image Pretraining approaches [32, 27, 23, 18] that utilizes various levels of supervision including vision self-supervision [3, 5], text self-supervision [23], memory queue [23], and augmentation encoding [18]. All models are pretrained with a learning rate 1e-3 for 32 epochs unless mentioned otherwise." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.495, + 0.892, + 0.753 + ], + "angle": 0, + "content": "Zero-shot Classification. We evaluate the zero-shot classification performance on 11 downstream datasets for single-modal experiments. Tab. 1 shows both the zero-shot classification and linear probing accuracy of CLIP variants [32, 27, 23, 18] pretrained on YFCC15M dataset and transferred to downstream classification datasets. In test time, the learned text encoder \\( f_{T} \\) synthesizes a zero-shot linear classifier by embedding the arbitrary categories of the test dataset. As classes are in the form of a single word, we use prompts including the label (e.g., \"a photo of a {label}\") as following CLIP [32]. Our MCD outperforms across a majority of the 11 datasets with a noticeable margin. Note that even without additional augmented-aware network leveraged in UniCLIP [18] or additional supervision terms such as text augmentation [40], masked language modeling [23] and memory queue, our MCD achieves state-of-the-art performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.772, + 0.892, + 0.879 + ], + "angle": 0, + "content": "Linear Probing. To implement linear probe evaluation, we follow CLIP [32] to train a logistic regression classifier on the frozen visual features extracted by the image encoder \\( f_{I} \\). Specifically, we train the logistic regression classifier using L-BFGS algorithm provided by scikit-learn with maximum 1,000 iterations, and report the corresponding metric for each dataset4. Parameters for L2 regularization are" + }, + { + "type": "page_footnote", + "bbox": [ + 0.517, + 0.887, + 0.885, + 0.902 + ], + "angle": 0, + "content": "4https://github.com/facebookresearch/SLIP/blob/main/mainlinear.py" + }, + { + "type": "page_footnote", + "bbox": [ + 0.094, + 0.874, + 0.327, + 0.888 + ], + "angle": 0, + "content": "\\(^{2}\\)https://github.com/facebookresearch/SLIP" + }, + { + "type": "page_footnote", + "bbox": [ + 0.097, + 0.888, + 0.314, + 0.901 + ], + "angle": 0, + "content": "3https://github.com/Sense-GVT/DeCLIP" + }, + { + "type": "list", + "bbox": [ + 0.094, + 0.874, + 0.327, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2568" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.078, + 0.089, + 0.892, + 0.344 + ], + "angle": 0, + "content": "
MethodVision EncoderOxford PetsCIFAR-10CIFAR-100SUN397Food-101FlowersCarsCaltech-101AircraftDTDImageNetAverage
OxfordCIFAR-10OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-10Oxford
Zero-shot Classification:
CLIP [32]19.462.333.640.233.76.32.155.41.416.931.327.5
SLIP [27]28.372.245.345.144.76.82.965.91.921.838.333.9
DeCLIP [23]ViT-B/3230.272.139.751.646.97.13.970.12.524.241.235.4
UniCLIP [18]32.578.647.250.448.78.13.473.02.823.342.837.3
MCD (Ours)40.080.349.655.354.07.94.573.23.030.544.740.2
Linear Probing:
CLIP [32]71.289.272.170.171.493.234.984.329.760.961.167.1
SLIP [27]75.490.575.373.577.196.143.087.234.171.168.171.9
DeCLIP [23]ViT-B/3276.588.671.675.979.396.742.688.032.669.169.271.8
UniCLIP [18]83.192.578.277.081.397.149.888.936.272.870.875.2
MCD (Ours)85.692.779.377.681.797.146.989.536.674.171.375.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.347, + 0.892, + 0.377 + ], + "angle": 0, + "content": "Table 1. Zero-shot image classification/linear probing performance on 11 downstream datasets with YFCC15M pretrained models. Note that DeCLIP [23] utilizes an external momentum queue while UniCLIP [18] features the augmentation encoder during training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.4, + 0.473, + 0.522 + ], + "angle": 0, + "content": "determined using hyperparameter sweep on the validation sets. Standard cropping and flipping augmentations [35] are used for linear probing. The bottom section of Tab. 1 reports linear classification performances on the 11 downstream datasets. Our proposed approach, MCD, has consistently outperformed previous baseline methods in zero-shot classification across multiple datasets, with only one exception." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.545, + 0.473, + 0.726 + ], + "angle": 0, + "content": "Image-Text Retrieval. For multi-modal evaluations, we test both the zero-shot and fine-tuned image-text (and text-image) retrieval on Flickr30k and COCO Captions benchmarks. Image-text pairs are ranked according to their similarity scores. Tab. 2 shows the performance for image-text retrieval tasks of MCD pretrained on YFCC15M dataset. Our MCD outperforms all state-of-the-art baselines across every measure with a considerable margin. By incorporating a log-ratio loss with metric learning characteristics into the CLIP framework, our proposed approach has achieved significant improvements in image-text retrieval performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Vision-Language Compositionality. To conduct a thorough analysis of multimodal representation learning, we assess the performance of our model using the SugarCrepe [12] dataset. This dataset serves as a de-biased benchmark specifically designed for evaluating the compositionality aspect of vision-language models. SugarCrepe introduces a set of challenging negative captions for COCO image-text pairs by replacing, swapping, or adding certain concepts to the ground truth caption, and gauge the model's capability to discern the positive from its distractor. Tab. 3" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.4, + 0.895, + 0.553 + ], + "angle": 0, + "content": "summarizes the result, showcasing the performance of various models pretrained on the YFCC15M dataset. Our findings demonstrate that the MCD exhibits significantly better compositionality compared to prior methods. This improved performance is attributed to leveraging augmentations with proper handling for misalignment arising from these augmentations. While other methods often show improved performance over CLIP baseline, adopting augmentations without meticulous management of misalignment cannot maximize their utility." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.562, + 0.817, + 0.579 + ], + "angle": 0, + "content": "5.3. MCD Pretraining on CC3M Dataset" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.586, + 0.892, + 0.768 + ], + "angle": 0, + "content": "In this section, we compare MCD against other state-of-the-art Contrastive Language-Image Pretraining approaches [32, 27, 23]. All models are pretrained on the CC3M dataset with a learning rate 5e-4 for 40 epochs\\(^{5}\\). Tab. 4 shows the ImageNet zero-shot results of MCD with other CLIP variants. MCD outperforms all CLIP variants without external training sources such as Nearest Neighbor supervision with large memory queues (NNS) or augmentation information during training (AUG). Furthermore, MCD does not require any additional parameters for the SSL projection layer [27, 23] or additional network for augmentation-aware feature embedding [18]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.777, + 0.655, + 0.794 + ], + "angle": 0, + "content": "5.4. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.801, + 0.892, + 0.879 + ], + "angle": 0, + "content": "This section presents ablation studies to evaluate the contribution of each component in our proposed approach, MCD, towards the final performance. To this end, we pretrain all models on the YFCC15M dataset and evaluate them using zero-shot learning on the Imagenet-1k validation set." + }, + { + "type": "page_footnote", + "bbox": [ + 0.516, + 0.887, + 0.887, + 0.902 + ], + "angle": 0, + "content": "5 More detailed training configuration will be provided in supplement." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2569" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.078, + 0.089, + 0.895, + 0.346 + ], + "angle": 0, + "content": "
MethodImage-to-text retrievalText-to-image retrieval
Flickr30kCOCO CaptionsFlickr30kCOCO Captions
R@1R@5R@10R@1R@5R@10R@1R@5R@10R@1R@5R@10
Zero-shot retrieval:
CLIP [32]34.963.975.920.843.955.723.447.258.913.031.742.7
SLIP [27]47.876.585.927.752.663.932.358.768.818.239.251.0
DeCLIP [23]51.480.288.928.353.264.534.360.370.718.439.651.4
UniCLIP [18]52.381.689.032.057.769.234.862.072.020.243.254.4
MCD (Ours)57.682.691.132.358.771.236.464.874.120.743.555.3
Fine-tuned retrieval
CLIP [32]58.384.891.536.165.076.443.171.180.324.951.764.1
SLIP [27]69.690.495.745.074.083.052.179.486.931.659.571.3
DeCLIP [23]75.693.096.648.777.386.257.883.390.334.263.174.6
UniCLIP [18]78.194.997.754.580.989.161.086.091.938.067.278.0
MCD (Ours)79.395.298.055.681.289.563.187.292.338.267.478.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.35, + 0.895, + 0.38 + ], + "angle": 0, + "content": "Table 2. Zero-shot & Fine-tuned image-text retrieval on the test splits of Flickr30k and COCO Captions with models pre-trained on YFCC15M. ViT-B/32 is used for all setup." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.401, + 0.472, + 0.501 + ], + "angle": 0, + "content": "
MethodAug.MisalignReplaceSwapAdd
CLIP [32]N/A73.659.569.4
SLIP [27]✓N/A74.758.669.1
DeCLIP [23]✓Disregard74.558.266.8
UniCLIP [18]✓fA75.558.470.4
MCD (Ours)✓LD76.261.571.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.505, + 0.472, + 0.604 + ], + "angle": 0, + "content": "Table 3. Evaluation on SugarCrepe [12]. All models were pretrained on YFCC15M with ViT-B/32 backbone. Models except CLIP involve random image augmentations (Aug.) with different schemes for dealing with image-text misalignments (Misalign). While previous methods either disregard the issue [23] or introduce an additional augmentation encoder \\((f_{A})\\) [18], MCD manages to harness the misalignment for the distillation loss \\((\\mathcal{L}_{\\mathrm{D}})\\)" + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.616, + 0.475, + 0.713 + ], + "angle": 0, + "content": "
MethodEncoderSSLEXTTop1(%)
CLIP [32]--19.6
SLIP [27]SimCLR [3]-23.2
DeCLIP [23]ViT-B/16SimSiam [5]NNS25.4
UniCLIP [18]MP-NCE [18]AUG27.8
MCD (Ours)MP-NCE [18]-28.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.717, + 0.47, + 0.801 + ], + "angle": 0, + "content": "Table 4. ImageNet-1k Top 1 zero shot accuracy with models pretrained on CC3M dataset. SSL denotes the vision self-supervision term used in each model and EXT denotes external sources involved during training. NNS is nearest neighbor supervision using a separate memory queue, and AUG is the vectorized information of each random augmentation conducted during training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Specifically, we implement the MP-NCE loss without augmentation encoding, which results in an accuracy of 39.6. Our results in Tab. 5 demonstrate that each loss component in MCD has a positive impact on the final performance, leading to an overall improvement in accuracy. These find" + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.401, + 0.892, + 0.487 + ], + "angle": 0, + "content": "
\\( \\mathcal{L}^{\\text{base}} \\)\\( f_A \\)\\( \\mathcal{L}^{\\text{pos}} \\)\\( \\mathcal{L}^{\\text{neg}} \\)\\( \\mathcal{L}^{\\text{noisy}} \\)Top1 Acc (%)
(a)✓39.6
(b)✓✓42.8
(c)✓✓43.9
(d)✓✓✓44.3
(e)✓✓✓✓44.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.491, + 0.895, + 0.59 + ], + "angle": 0, + "content": "Table 5. Ablation study on ImageNet-1k Top 1 zero shot accuracy for vision-language pretraining for each loss components of MCD. All models were pretrained with a ViT-B/32 backbone with a basic contrastive loss \\(\\mathcal{L}^C\\) in Eq (5) and MLM loss in Eq (11), which we abbreviate as \\(\\mathcal{L}^{\\mathrm{base}}\\). All \\(\\mathcal{L}^{\\mathrm{pos}}\\), \\(\\mathcal{L}^{\\mathrm{neg}}\\), \\(\\mathcal{L}^{\\mathrm{noisy}}\\) shows a consistent gain in zero-shot performance. \\(f_{A}\\) denotes the augmentation encoder, making (b) analogous to UniCLIP [18]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.607, + 0.892, + 0.715 + ], + "angle": 0, + "content": "ings highlight the importance of each component in our proposed approach and validate its effectiveness in improving the zero-shot classification performance. Note that MCD outperforms (b) (i.e., UniCLIP) that explicitly includes the augmentation information during training with only \\(\\mathcal{L}^{\\mathrm{pos}}\\), showing the effectiveness of harnessing the misalignments that occur during random image augmentation for training." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.727, + 0.62, + 0.743 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.752, + 0.894, + 0.844 + ], + "angle": 0, + "content": "We propose MCD, a new training strategy for dealing with misalignments occurred by random image augmentations under visual-language pretraining. Our novel distillation formulation enables data-efficient training under Contrastive Language-Image Pretraining. Future works will include extending MCD frameworks to other modalities." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.957 + ], + "angle": 0, + "content": "2570" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Alex Andonian, Shixing Chen, and Raffay Hamid. Robust cross-modal representation learning with progressive self-distillation. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, 2022." + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.173, + 0.47, + 0.228 + ], + "angle": 0, + "content": "[2] Lukas Bossard, Matthieu Guillaumin, and Luc Van Gool. Food-101-mining discriminative components with random forests. In European conference on computer vision, pages 446-461. 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To enhance data-efficiency, recent efforts have introduced additional supervision terms that involve random-augmented views of the image. However, since the image augmentation process is unaware of its text counterpart, this procedure could cause various degrees of image-text misalignments during training. Prior methods either disregarded this discrepancy or introduced external models to mitigate the impact of misalignments during training. In contrast, we propose a novel metric learning approach that capitalizes on these misalignments as an additional training source, which we term "Misalign, Contrast then Distill (MCD)". Unlike previous methods that treat augmented images and their text counterparts as simple positive pairs, MCD predicts the continuous scales of misalignment caused by the augmentation. Our extensive experimental results show that our proposed MCD achieves state-of-the-art transferability in multiple classification and retrieval downstream datasets. + +# 1. Introduction + +Recent advances in deep learning have shown that image representations trained with large-scale uncurated natural language supervision shows powerful transferability to various downstream tasks [14, 32]. A predominant paradigm in vision-language pre-training is to use a simple contrastive loss that makes the embedding of an image and its matching text description (positive pair) more similar to each other than other arbitrary image-text pairs (negative pairs) [29]. To achieve a more data-efficient training, following works actively capitalized on image random augmentation by: (i) joining language-image pretraining objectives with vision self-supervision terms [3, 5] between the augmented images [27, 23, 18] and (ii) involving more pairs of posi + +![](images/9bca8c2cec6580e92d17e4e65cf7da070a0e7d0fa3cd9392719334c49c10dd13.jpg) +Figure 1. Conceptual illustration of contrastive language-image objectives of previous works (i.e., InfoNCE) and our MCD for (a) augmentation that doesn't harm the correspondence with its description and (b) augmentation that does. Previous works either disregard these misalignments [23] or leverage external models [18, 9] to mitigate their impact. On the other hand, MCD uses the continuous degree of misalignments caused by random image augmentation as a useful source for training various levels of alignments between images and their text descriptions. + +tive/negative supervisions between the augmented images and their original text description [23, 18]. + +However, since the random image augmentation process is unaware of its corresponding text, it often results in the augmented image view to be misaligned with its description (see (b) in Fig.1). These misalignments behave as noisy training signals for the contrastive loss in language-image pretraining, thus causing performance degradation if not properly attended [27]. To mitigate this issue, recent works have used additional augmentation embeddings [18] or heavy external off-the-shelf object detectors and summary extractors [9] to match the alignment during training. Though being straightforward and showing strong performance, these works are limited in that they add unnecessary burden in both training and inference. + +Based on this observation, we start with a simple question: "Instead of treating misalignments as noise to elim + +inate, can we rather harness them as a training source for language-image pretraining?". To this end, we propose MCD (i.e., Misalign, Contrast then Distill), a novel training framework that leverages the various levels of misalignments between random augmented images and its text description during training. + +MCD consists of three steps (see Fig 2 for an overview illustration of MCD): First, we conduct random augmentation on the image that causes various levels of misalignments (or not at all) with its text counterpart (Misalign). Then, we project all the participants (image, text, and augmented image) into an unified multimodal space, and learn the distance between all the image-text pairs with a contrastive objective (Contrast). Finally, we use a teacher-student network where the student learns from the "soft" distance between the text- original image (i.e., $D(\bar{I}, T)$ in Fig 2) and text-augmented image (i.e., $D(\bar{I}', T)$ in Fig 2) of the momentum teacher with a log-ratio loss (Distill). continuous scale of misalignment to the student model, enabling the student to learn from the various levels of misalignment that occur from the random augmentation during training time. + +Our contribution of this paper is threefold: + +- We propose MCD, a novel training framework where we learn the continuous level of misalignment as a source for contrastive language-image pretraining. +- Our MCD outperforms state-of-the-art models across various single/multi-modal downstream datasets without adding additional parameters for inference or using external models to force the alignment. +- We propose three distillation strategies leveraging misalignments: i) misalignment between positive pairs, ii) misalignment between negative pairs, and iii) misalignment between noisy pairs. Extensive experiments show that all three strategies positively contributes to our final performance. + +# 2. Related Work + +Here, we present brief review of multi-modal representation learning, especially vision-language pre-training. + +# 2.1. Vision-language Pre-training + +Vision-Language Pre-training (VLP) trains a multimodal model to learn joint representation of visual and textual information that can be transfer to various vision-language downstream tasks. The success of VLP primarily relies on large-scale datasets which contains images and their corresponding descriptions, enabling the model to understand the semantic relationship between the pairs. VLP includes two different group of models: 1) single-stream + +![](images/74c6af92fcd1cd78585077323a6009b7dc5f64f66d7f7ccbc4643c17c207f532.jpg) +Figure 2. Overview of MCD. Our MCD consist of three steps: (i) text-agnostic random augmentation of the image that causes various levels of misalignment with the corresponding text, (ii) learning the distance between the image/augmented image and text with contrastive objectives then (iii) distill the log-ratio of the image-text distance between the original and the augmented image. + +models [20, 6, 13, 22, 21, 25, 36] which process an image and its associated text information in a shared backbone network and 2) dual-stream models [14, 32] which has two independent backbone networks for processing each modality. In this work, we focuses on Contrastive Language Image Pretraining (CLIP [32]), which is a type of dual-stream models trained with image-text contrastive loss where the image and its matching text description in the dataset as a positive pair and other unrelated pairs in a batch as negative pairs. + +# 2.2. Misalignments between Image-Text Pairs + +There are two different sources that cause misalignments in image-text pairs for VLP: misalignment that naturally occurs in image-text paired datasets, and misalignments caused by random image augmentation. + +Misalignment in Image-Text Pairs. Large scale image-text paired datasets for VLP are usually collected from the web thus can contain uncurated and noisy pairs which have weak relations. This inevitably incurs misalignment between positive image-text pairs in the dataset misleading naive contrastive language image objective. Previous + +studies [19, 24, 1] have attempted to address the problem by knowledge distillation [11] of soft image-text alignment matrix from momentum teacher network to the student network via KL divergence loss. Our proposed method stands apart from previous approaches due to its element-wise log-ratio loss for distillation. Element-wise loss lessens the dependence on training hyperparameters like batch size and temperature for KL loss. Furthermore, it enables the model to harness the various levels of individual misalignments of each sample from random augmentation or label noise. + +Misalignment by Augmentations. View-based self-supervised learning, in which models are trained to represent views or augmentations of the same image similarly, has yielded strong results across a variety of different formulations. Consecutive work of CLIP (i.e., SLIP [27]) initially introduced supervision between random augmented image views (e.g., cropping, gray-scale, jittering, gaussian blur, horizontal flipping, etc.). Since only image-image supervision was given in a separately embedded space, augmentation was not a factor for misalignment. To include more positive/negative pairs for the image-text contrastive objective, following works [23, 18] also introduced InfoNCE loss between the augmented views and the text pairs. However, since the text description is unaware of the random augmentations, there is a high chance that misalignments occur during training. SLIP shows that naïve application of contrastive loss to these misaligned pairs results in suboptimal performance. Previous work have either ignored this misalignment [23] or addressed this issue with an additional encoder that encodes the one-hot information of which augmentation has been applied during training [18]. PyramidCLIP [9] addressed this issue with external off-the-shelf object detectors and summary extractors. HiCLIP [10] captured the hierarchical nature of high-level on unsupervised manner with tree Transformer [39]. MCD incorporate the misalignment information as a source of training via novel log-ratio loss without introducing any external module. + +# 3. Preliminary + +In our preliminary, we revisit the basic form of Contrastive Language-Image Pretraining (i.e., CLIP [32]). CLIP features a dual-encoder architecture where the image encoder $f_{I}$ and text encoder $f_{T}$ are jointly trained with a contrastive objective $\mathcal{L}_{\mathrm{CLIP}}$ . + +InfoNCE Loss Given $N$ image-text pairs $\{(x_i^I, x_i^T)\}_{i=1}^N$ , we define a similarity matrix $S$ whose $i$ -th row and the $j$ -th column is the cosine similarity between the projected representations of the $i$ -th text $T_i$ and the $j$ -th image $I_j$ (i.e., + +$T_{i} = f_{T}(x_{i}^{T}),I_{j} = f_{I}(x_{j}^{I}))$ , written as: + +$$ +S _ {i j} = \operatorname {s i m} \left(T _ {i}, I _ {j}\right), \tag {1} +$$ + +where $\mathrm{sim}(\cdot ,\cdot)$ is cosine similarity. In CLIP [32], the encoded image features $I$ and text features $T$ are projected to the same dimension where the embeddings for matching image-text pairs are pulled together while embeddings for arbitrary pairs are pushed apart with the InfoNCE loss [29]. Given the similarity matrix $S$ , the InfoNCE loss $\mathcal{L}_N$ is rewritten as: + +$$ +\mathcal {L} _ {N} (S) = - \frac {1}{N} \sum_ {i = 1} ^ {N} \log \frac {\exp \left(S _ {i i} / \tau\right)}{\sum_ {j = 1} ^ {N} \exp \left(S _ {i j} / \tau\right)}, \tag {2} +$$ + +where $\tau$ is a learnable temperature variable. The overall loss of clip $\mathcal{L}_{\mathrm{CLIP}}$ is written as: + +$$ +\mathcal {L} _ {\mathrm {C L I P}} = \frac {1}{2} \left(\mathcal {L} _ {N} (S) + \mathcal {L} _ {N} \left(S ^ {T}\right)\right). \tag {3} +$$ + +Augmentations and Misalignment. To include more positive/negative pairs for the contrastive objective, following works [23, 18] introduced InfoNCE loss between the random augmented image views and the text description for the original image. Let $\mathcal{A}$ a function for random image augmentation that includes randomly applying cropping, gray-scale, jittering, gaussian blur, horizontal flipping following SimCLR [3]. $I_{j'}$ is the encoded image feature of augmented view of $j$ -th image(e.g. $I_{j'} = f_I(\mathcal{A}(x_j^I))$ ). Let $S_{ij}' = \mathrm{sim}(T_i, I_{j'})$ represent the similarity between the augmented view of $j$ -th image and $i$ -th text. We denote the matrix of these similarity as $S'$ for concise notation. Then, InfoNCE loss between the augmented image and the text is + +$$ +\mathcal {L} _ {\mathrm {C L I P}} ^ {\prime} = \frac {1}{2} \left(\mathcal {L} _ {N} \left(S ^ {\prime}\right) + \mathcal {L} _ {N} \left(S ^ {\prime T}\right)\right). \tag {4} +$$ + +As the random augmentation function $\mathcal{A}$ is independent to the corresponding text description, the augmented view $I_{j'}$ is likely to exhibit misalignment with text $T_i$ . This hypothesis is consistent with the finding of SLIP [27], which demonstrated that introducing augmentation (particularly resize crop, and flip) to CLIP actually resulted in a performance decrease. Previous works [27, 23] have sidestepped the utilization of augmented view in CLIP by substituting infoNCE with self-supervised learning loss(e.g. SimCLR [3]) between images. These approaches have limitation in fully capturing the essence of multi-modal learning. + +# 4. Method + +In this section, we introduce MCD (Misalign, Contrast then Distill), a novel training framework for language-image pretraining using misalignments as continuous labels for learning the distance between image-text pairs. + +# 4.1. Misalign + +The first step of MCD is to apply text-agnostic random image augmentations (e.g., random crop, random flip, grayscale, etc.) to create various levels of misalignments between the images and its description. Here, we elaborate on three distinct scenarios of misalignment that can arise during the augmentation process, hindering the contrastive loss to learn proper distance between image-text pairs: (i) Text-agnostic random augmentation can cause misalignments in positive image-text pairs. (ii) The random-augmentation can mistakenly cause positive signals between negative pairs. (iii) Misalignments can already exist innately within the original image-text pair. A detailed illustration of each cases are provided in Fig 3. + +# 4.2. Contrast + +In the second step, MCD initially learns the distance metric between image-text pairs with a contrastive objective. Motivated by [18], we project both image and text modalities to a unified space and use all the positive pairs and negative pairs of both modalities. For an $i$ -th embedding $z_{i}$ in a batch of embeddings $\{z_i\}_{i = 1}^{3N}$ that includes $N$ image samples, $N$ text samples, and $N$ random augmented image samples, let $\mathcal{P}_i$ and $\mathcal{N}_i$ each denote the set of all positive sample indices of the $i$ -th sample including $i$ itself and the set of all negative sample indices of the $i$ -th sample. Then, the contrastive loss for the multiple positives and multiple negatives for sample $i$ can be written as + +$$ +\mathcal {L} _ {i} ^ {C} = \mathbb {E} _ {p \in \mathcal {P} _ {i}} \left[ - \log \frac {\sin \left(z _ {i} , z _ {p}\right)}{\sin \left(z _ {i} , z _ {p}\right) + \sum_ {n \in \mathcal {N} _ {i}} \sin \left(z _ {i} , z _ {n}\right)} \right]. \tag {5} +$$ + +However, without encoding augmentation information the image-text contrastive loss is prone to the three aforementioned issues. We address these three issues with a teacher-student model where the continuous distance between the image-text and augmented image-text of the teacher model is distilled to the student model. + +# 4.3. Distill + +Knowledge distillation, introduced by Hinton et al. [11], is a learning paradigm where we train the student network to mimic the "soft" labels predicted from the teacher network. In MCD, we train the student network with the continuous image-text distance predicted by the teacher network. Psuedocode for the distillation in MCD is provided in Algorithm 1. + +Log-Ratio Loss for Image-Text Distance. Given a student $f_{I}$ and a momentum teacher $\bar{f}_{I}$ , we propose to use log-ratio loss [15] on image-text similarities that aims to approximate the ratio of similarity distances by the ratio of + +![](images/dd1a15f3b5c0a06aa990d4bf1ebb85ec39f7ed063c922cd745f600d2bd89d123.jpg) +Figure 3. MCD loss for various cases of misalignments that occur when applying random image augmentation in language-image pretraining with. In this paper, we elaborate three scenarios: (a) misalignment caused by augmenting the image of an original positive pair, which is addressed by $\mathcal{L}^{\mathrm{pos}}$ (b) augmentation that mistakenly cause positive alignment between negative pairs (c) misalignment that already exists within the dataset. + +image-text misalignments in the learned embedding space. Specifically, we define the loss function as + +$$ +\ell_ {l r} (i, j; \alpha , \beta) = \left\| \log \frac {D \left(I _ {\alpha} , T _ {\beta}\right)}{D \left(I _ {i} , T _ {j}\right)} - \log \frac {D \left(\bar {I} _ {\alpha} , T _ {\beta}\right)}{D \left(\bar {I} _ {i} , T _ {j}\right)} \right\| _ {1}, \tag {6} +$$ + +where $\| \cdot \|_1$ is $\ell_1$ loss, $D(\cdot, \cdot)$ is distance function. We utilize Euclidean distance between the projected representations as distance function. Since the embedded vectors comprising the image $I_i, \bar{I}_i$ and text $T_j$ are L2-normalized, Euclidean distance operates as a proxy for cosine similarity $D(I_i, T_j) = 2(1 - S_{ij})$ . This log-ratio loss approximates the degree of misalignment, which is measured as the ratio of two image-text pairs. By leveraging this measure, we aim to promote a coherent and continuous embedding space. Accordingly, our student encoder is trained under the guidance of the momentum teacher with the incorporation of this degree of misalignment. By establishing these pairs of log-ratio, we enable the handling of diverse forms of misalignment. We present three distinct index setups that correspond to different types of misalignment. + +Misalignment in Positive pairs. First, we define distance pair for misalignment between the original image-text pair. Let $i'$ denote the index of augmented image sample. On Eq.(5), $i'$ -th image sample and $i$ -th text sample serve as positive pair. However, random augmentation can occasionally transform positive pair into negative pair. To account for such transformations, we intend to utilize the log-ratio between original pairs and augmented pairs. This allows us to + +Algorithm 1 MCD Pseudocode +```julia +# fm, fs: image encoders (teacher, student) +# ft: text encoder +# fa: random-augmentation function +# N : batch size +def D(sim): # cosine sim -> L2 distance +return 2 - 2 * sim + 1e-6 +def MCD(img, txt): +# image, text encodings +aug = fa(img) +# normalized projection embeddings +zm, zs,zt = fm(img), fs(img), ft(txt) +zam,zas = fm(aug), fs(aug) # misalign +# distance (contrast) +di_t, di_s = D(zm @ zt.T), D(zs @ zt.T) +da_t, da_s = D(zam @ zt.T), D(zas @ zt.T) +# distill +pos_l, neg_l, noise_l = 0, 0, 0 +for i in range(N): + lr_s1 = log(da_s[i,i]/di_s[i,i]) + lr_t1 = log(da_t[i,i]/di_t[i,i]) +# positive pairs +pos_l += abs(lr_s1 - lr_t1) / N +for j in range(N): + if i==j: continue + lr_s2 = log(da_s[i,j]/di_s[i,i]) + lr_t2 = log(da_t[i,j]/di_t[i,i]) +# negative pairs +neg_l += abs(lr_s2 - lr_t2) / (N*(N-1)) +lr_s3 = log(di_s[j,j]/di_s[i,i]) +lr_t3 = log(di_t[j,j]/di_t[i,i]) +# noisy pairs +noise_l += abs(lr_s3 - lr_t3) / (N*(N-1)) +return pos_l + neg_l + noise_l +``` + +capture these shifts and incorporate them into the learning process effectively. + +$$ +\mathcal {L} ^ {\mathrm {p o s}} = \mathbb {E} _ {i = 1, \dots , N} \left[ \ell_ {l r} (i, i; i ^ {\prime}, i) \right], \tag {7} +$$ + +where $i'$ is the index of augmented $i$ -th sample. + +Misalignment in Negative pairs. Augmented images can possess relevance with different text, which would normally be considered negative pairs in Eq.(5). However, the log-ratio obtained by our momentum teacher alleviates our model from mistakenly pushing the embedding of relevant texts away. + +$$ +\mathcal {L} ^ {\text {n e g}} = \underset {i \neq j} {\mathbb {E}} _ {i, j = 1, 2, \dots , N} \left[ \ell_ {l r} \left(i, i; j ^ {\prime}, i\right) \right], \tag {8} +$$ + +where $j^{\prime}$ is the index of augmented $j$ -th sample. + +Misalignment in Noisy pairs. Original image-text pairs obtained from the web may contain either noisy images or + +descriptions. While these pairs are normally treated as positive pairs under contrastive loss, we propose a loss for noisy pairs where the noisy labels are trained to have larger distance than matching image-text pairs. + +$$ +\mathcal {L} ^ {\text {n o i s y}} = \mathbb {E} _ {i, j = 1, 2, \dots , N} \left[ \ell_ {l r} (i, i; j, j) \right]. \tag {9} +$$ + +Distillation Loss. The full training objective of MCD distillation $\mathcal{L}^D$ is the sum of the three distillation terms, which is written as + +$$ +\mathcal {L} ^ {\mathrm {D}} = \mathcal {L} ^ {\text {p o s}} + \mathcal {L} ^ {\text {n e g}} + \mathcal {L} ^ {\text {n o i s y}}. \tag {10} +$$ + +# 4.4. Training MCD + +In this section, we explain the details of MCD training. The training objective for the text encoder and student image encoder for MCD consists of the three objectives: contrastive loss $\mathcal{L}^C$ in Eq (5) for initial image-text distance learning, distillation loss $\mathcal{L}^D$ for the three misalignment scenarios, and loss for masked language modeling $\mathcal{L}^{\mathrm{MLM}}$ . The parameters for the teacher image encoder are momentum updated. + +MLM Loss. Following previous work in literature [23, 18, 19], we randomly mask out the input tokens with a probability of $15\%$ and replace them with the special token $[\mathrm{MASK}]^{1}$ . Let $p^{\mathrm{msk}}$ and $y^{\mathrm{msk}}$ each denote the set of model's predicted probability for the masked tokens and the set of ground-truth vocabulary index for the tokens, respectively. Then, MLM loss is written as: + +$$ +\mathcal {L} ^ {\mathrm {M L M}} = \mathbb {E} _ {p \in p ^ {\mathrm {m s k}}, y \in y ^ {\mathrm {m s k}}} \left[ \mathrm {C E} (p, y) \right], \tag {11} +$$ + +where CE denotes Cross Entropy loss. + +Momentum Teacher Update. Let $\theta_{f_I},\theta_{\bar{f}_I}$ be the parameter of the student encoder and momentum teacher, respectively. For the $t$ -th step, we update $\theta_{\bar{f}_I}^{(t)}$ of the momentum teacher according to the following: + +$$ +\theta_ {\bar {f} I} ^ {(t)} = m \theta_ {\bar {f} I} ^ {(t - 1)} + (1 - m) \theta_ {f I} ^ {(t)}, \tag {12} +$$ + +where $m$ denotes the momentum parameter. We use $m = 0.994$ in our experiments, where $m$ grows in a cosine schedule to 1 at the end of training. + +Progressive Distillation. As the training proceeds, InfoNCE loss conflicts with our misalignment loss. InfoNCE + +between pair $I_{j}^{\prime}$ and $T_{i}$ forces the embedding to pull regardless of its degree of misalignment. In early stages of training, the model needs to learn how to discriminate positive or negative pairs with a hard label. However, as the training progresses, the log-ratio loss delicately models the distance between the various misalignments occurred by augmentations or innately existing in the original image-text pair. Therefore, we progressively diminish the contribution of InfoNCE loss involving augmented views. + +MCD Loss. The final loss for MCD is written as: + +$$ +\mathcal {L} ^ {\mathrm {M C D}} = \mathcal {L} ^ {\mathrm {C}} + \alpha \cdot \mathcal {L} ^ {\mathrm {D}} + \beta \cdot \mathcal {L} ^ {\mathrm {M L M}}, \tag {13} +$$ + +where $\alpha = 0$ progressively increases on a cosine schedule to 1, and $\beta = 0.2$ . + +# 4.5. MCD Inference + +MCD is based on a teacher-student network, thus the student $f_{I}$ and momentum teacher $\bar{f}_{I}$ is obtained after training. Unlike previous work in literature that leverage the teacher network for inference [37, 19], we use the student network that is trained with both the contrastive loss and the log-ratio loss for image-text distance learning. + +# 5. Experiment + +In this section, we provide implementation details and experimental results with our MCD pretrained on two widely used image-text benchmark datasets (e.g., CC3M, YFCC15M) to validate the effectiveness of our proposed MCD on multiple downstream datasets including classification and image-text retrieval. + +# 5.1. Implementation Details and Datasets + +For implementation details, our work is built on top of the open-source SLIP codebase $[27]^2$ . For DECLIP [23], we follow the implementation details of the official code release. The performance on GPU-machine runs for CLIP and SLIP follows the exact implementation details upon this codebase. Since MCD features both the momentum teacher image encoder $\bar{f}_I$ and student $f_I$ , we conduct the following experiment section with $\bar{f}_I$ based on empirical results. All of our models are pretrained in $16\times$ A100 GPUs. For CC3M, All models are trained with a ViT-B/16 backbone with a learning rate of 5e-4 and weight decay of 0.5. For YFCC15M, we train the model with ViT-B/32 backbone, batch size 4096, learning rate 1e-3, and weight decay 0.2. + +Pretraining Datasets. To validate the effectiveness of MCD, we pretrain MCD on large-scale open-source + +datasets: YFCC (Yahoo Flickr Creative Commons) 15M [38] and CC (Conceptual Captions) 3M [34]. + +Downstream Datasets. Following CLIP [32], we evaluate the transferability of pretrained MCD on 11 widely used downstream datasets for classification (i.e., Oxford Pets [30], CIFAR-10, CIFAR-100 [17], SUN397 [41], Food-101 [2], Flowers [28], Cars [16], Caltech-101 [8], Aircraft [26], DTD [7], ImageNet-1k [33]). We also transfer to image-text retrieval tasks on Flickr30K [31] and MS-COCO Captions [4] datasets. The evaluation settings for each dataset are consistent with CLIP as in the open-source implementation2. + +# 5.2. MCD Pretraining on YFCC15M Dataset + +First, we pretrain MCD on YFCC15M and evaluate its transferability in single-modal (e.g., classification) and multi-modal (e.g., image-text retrieval) downstream tasks. We compare the result against other state-of-the-art Contrastive Language-Image Pretraining approaches [32, 27, 23, 18] that utilizes various levels of supervision including vision self-supervision [3, 5], text self-supervision [23], memory queue [23], and augmentation encoding [18]. All models are pretrained with a learning rate 1e-3 for 32 epochs unless mentioned otherwise. + +Zero-shot Classification. We evaluate the zero-shot classification performance on 11 downstream datasets for single-modal experiments. Tab. 1 shows both the zero-shot classification and linear probing accuracy of CLIP variants [32, 27, 23, 18] pretrained on YFCC15M dataset and transferred to downstream classification datasets. In test time, the learned text encoder $f_{T}$ synthesizes a zero-shot linear classifier by embedding the arbitrary categories of the test dataset. As classes are in the form of a single word, we use prompts including the label (e.g., "a photo of a {label}") as following CLIP [32]. Our MCD outperforms across a majority of the 11 datasets with a noticeable margin. Note that even without additional augmented-aware network leveraged in UniCLIP [18] or additional supervision terms such as text augmentation [40], masked language modeling [23] and memory queue, our MCD achieves state-of-the-art performance. + +Linear Probing. To implement linear probe evaluation, we follow CLIP [32] to train a logistic regression classifier on the frozen visual features extracted by the image encoder $f_{I}$ . Specifically, we train the logistic regression classifier using L-BFGS algorithm provided by scikit-learn with maximum 1,000 iterations, and report the corresponding metric for each dataset4. Parameters for L2 regularization are + +
MethodVision EncoderOxford PetsCIFAR-10CIFAR-100SUN397Food-101FlowersCarsCaltech-101AircraftDTDImageNetAverage
OxfordCIFAR-10OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-10Oxford
Zero-shot Classification:
CLIP [32]19.462.333.640.233.76.32.155.41.416.931.327.5
SLIP [27]28.372.245.345.144.76.82.965.91.921.838.333.9
DeCLIP [23]ViT-B/3230.272.139.751.646.97.13.970.12.524.241.235.4
UniCLIP [18]32.578.647.250.448.78.13.473.02.823.342.837.3
MCD (Ours)40.080.349.655.354.07.94.573.23.030.544.740.2
Linear Probing:
CLIP [32]71.289.272.170.171.493.234.984.329.760.961.167.1
SLIP [27]75.490.575.373.577.196.143.087.234.171.168.171.9
DeCLIP [23]ViT-B/3276.588.671.675.979.396.742.688.032.669.169.271.8
UniCLIP [18]83.192.578.277.081.397.149.888.936.272.870.875.2
MCD (Ours)85.692.779.377.681.797.146.989.536.674.171.375.7
+ +Table 1. Zero-shot image classification/linear probing performance on 11 downstream datasets with YFCC15M pretrained models. Note that DeCLIP [23] utilizes an external momentum queue while UniCLIP [18] features the augmentation encoder during training. + +determined using hyperparameter sweep on the validation sets. Standard cropping and flipping augmentations [35] are used for linear probing. The bottom section of Tab. 1 reports linear classification performances on the 11 downstream datasets. Our proposed approach, MCD, has consistently outperformed previous baseline methods in zero-shot classification across multiple datasets, with only one exception. + +Image-Text Retrieval. For multi-modal evaluations, we test both the zero-shot and fine-tuned image-text (and text-image) retrieval on Flickr30k and COCO Captions benchmarks. Image-text pairs are ranked according to their similarity scores. Tab. 2 shows the performance for image-text retrieval tasks of MCD pretrained on YFCC15M dataset. Our MCD outperforms all state-of-the-art baselines across every measure with a considerable margin. By incorporating a log-ratio loss with metric learning characteristics into the CLIP framework, our proposed approach has achieved significant improvements in image-text retrieval performance. + +Vision-Language Compositionality. To conduct a thorough analysis of multimodal representation learning, we assess the performance of our model using the SugarCrepe [12] dataset. This dataset serves as a de-biased benchmark specifically designed for evaluating the compositionality aspect of vision-language models. SugarCrepe introduces a set of challenging negative captions for COCO image-text pairs by replacing, swapping, or adding certain concepts to the ground truth caption, and gauge the model's capability to discern the positive from its distractor. Tab. 3 + +summarizes the result, showcasing the performance of various models pretrained on the YFCC15M dataset. Our findings demonstrate that the MCD exhibits significantly better compositionality compared to prior methods. This improved performance is attributed to leveraging augmentations with proper handling for misalignment arising from these augmentations. While other methods often show improved performance over CLIP baseline, adopting augmentations without meticulous management of misalignment cannot maximize their utility. + +# 5.3. MCD Pretraining on CC3M Dataset + +In this section, we compare MCD against other state-of-the-art Contrastive Language-Image Pretraining approaches [32, 27, 23]. All models are pretrained on the CC3M dataset with a learning rate 5e-4 for 40 epochs $^{5}$ . Tab. 4 shows the ImageNet zero-shot results of MCD with other CLIP variants. MCD outperforms all CLIP variants without external training sources such as Nearest Neighbor supervision with large memory queues (NNS) or augmentation information during training (AUG). Furthermore, MCD does not require any additional parameters for the SSL projection layer [27, 23] or additional network for augmentation-aware feature embedding [18]. + +# 5.4. Ablation Study + +This section presents ablation studies to evaluate the contribution of each component in our proposed approach, MCD, towards the final performance. To this end, we pretrain all models on the YFCC15M dataset and evaluate them using zero-shot learning on the Imagenet-1k validation set. + +
MethodImage-to-text retrievalText-to-image retrieval
Flickr30kCOCO CaptionsFlickr30kCOCO Captions
R@1R@5R@10R@1R@5R@10R@1R@5R@10R@1R@5R@10
Zero-shot retrieval:
CLIP [32]34.963.975.920.843.955.723.447.258.913.031.742.7
SLIP [27]47.876.585.927.752.663.932.358.768.818.239.251.0
DeCLIP [23]51.480.288.928.353.264.534.360.370.718.439.651.4
UniCLIP [18]52.381.689.032.057.769.234.862.072.020.243.254.4
MCD (Ours)57.682.691.132.358.771.236.464.874.120.743.555.3
Fine-tuned retrieval
CLIP [32]58.384.891.536.165.076.443.171.180.324.951.764.1
SLIP [27]69.690.495.745.074.083.052.179.486.931.659.571.3
DeCLIP [23]75.693.096.648.777.386.257.883.390.334.263.174.6
UniCLIP [18]78.194.997.754.580.989.161.086.091.938.067.278.0
MCD (Ours)79.395.298.055.681.289.563.187.292.338.267.478.5
+ +Table 2. Zero-shot & Fine-tuned image-text retrieval on the test splits of Flickr30k and COCO Captions with models pre-trained on YFCC15M. ViT-B/32 is used for all setup. + +
MethodAug.MisalignReplaceSwapAdd
CLIP [32]N/A73.659.569.4
SLIP [27]✓N/A74.758.669.1
DeCLIP [23]✓Disregard74.558.266.8
UniCLIP [18]✓fA75.558.470.4
MCD (Ours)✓LD76.261.571.7
+ +Table 3. Evaluation on SugarCrepe [12]. All models were pretrained on YFCC15M with ViT-B/32 backbone. Models except CLIP involve random image augmentations (Aug.) with different schemes for dealing with image-text misalignments (Misalign). While previous methods either disregard the issue [23] or introduce an additional augmentation encoder $(f_{A})$ [18], MCD manages to harness the misalignment for the distillation loss $(\mathcal{L}_{\mathrm{D}})$ + +
MethodEncoderSSLEXTTop1(%)
CLIP [32]--19.6
SLIP [27]SimCLR [3]-23.2
DeCLIP [23]ViT-B/16SimSiam [5]NNS25.4
UniCLIP [18]MP-NCE [18]AUG27.8
MCD (Ours)MP-NCE [18]-28.2
+ +Specifically, we implement the MP-NCE loss without augmentation encoding, which results in an accuracy of 39.6. Our results in Tab. 5 demonstrate that each loss component in MCD has a positive impact on the final performance, leading to an overall improvement in accuracy. These find + +Table 4. ImageNet-1k Top 1 zero shot accuracy with models pretrained on CC3M dataset. SSL denotes the vision self-supervision term used in each model and EXT denotes external sources involved during training. NNS is nearest neighbor supervision using a separate memory queue, and AUG is the vectorized information of each random augmentation conducted during training. + +
\( \mathcal{L}^{\text{base}} \)\( f_A \)\( \mathcal{L}^{\text{pos}} \)\( \mathcal{L}^{\text{neg}} \)\( \mathcal{L}^{\text{noisy}} \)Top1 Acc (%)
(a)✓39.6
(b)✓✓42.8
(c)✓✓43.9
(d)✓✓✓44.3
(e)✓✓✓✓44.7
+ +Table 5. Ablation study on ImageNet-1k Top 1 zero shot accuracy for vision-language pretraining for each loss components of MCD. All models were pretrained with a ViT-B/32 backbone with a basic contrastive loss $\mathcal{L}^C$ in Eq (5) and MLM loss in Eq (11), which we abbreviate as $\mathcal{L}^{\mathrm{base}}$ . All $\mathcal{L}^{\mathrm{pos}}$ , $\mathcal{L}^{\mathrm{neg}}$ , $\mathcal{L}^{\mathrm{noisy}}$ shows a consistent gain in zero-shot performance. $f_{A}$ denotes the augmentation encoder, making (b) analogous to UniCLIP [18]. + +ings highlight the importance of each component in our proposed approach and validate its effectiveness in improving the zero-shot classification performance. Note that MCD outperforms (b) (i.e., UniCLIP) that explicitly includes the augmentation information during training with only $\mathcal{L}^{\mathrm{pos}}$ , showing the effectiveness of harnessing the misalignments that occur during random image augmentation for training. + +# 6. Conclusion + +We propose MCD, a new training strategy for dealing with misalignments occurred by random image augmentations under visual-language pretraining. Our novel distillation formulation enables data-efficient training under Contrastive Language-Image Pretraining. Future works will include extending MCD frameworks to other modalities. + +# References + +[1] Alex Andonian, Shixing Chen, and Raffay Hamid. Robust cross-modal representation learning with progressive self-distillation. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, 2022. +[2] Lukas Bossard, Matthieu Guillaumin, and Luc Van Gool. Food-101-mining discriminative components with random forests. In European conference on computer vision, pages 446-461. Springer, 2014. +[3] Ting Chen, Simon Kornblith, Mohammad Norouzi, and Geoffrey Hinton. A simple framework for contrastive learning of visual representations. In International conference on machine learning, pages 1597-1607. 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International Journal of Computer Vision, 119(1):3-22, 2016. \ No newline at end of file diff --git a/2023/Misalign, Contrast then Distill_ Rethinking Misalignments in Language-Image Pre-training/images.zip b/2023/Misalign, Contrast then Distill_ Rethinking Misalignments in Language-Image Pre-training/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..3897df181e67d4435bc71505ff7e344ee98f661f --- /dev/null +++ b/2023/Misalign, Contrast then Distill_ Rethinking Misalignments in Language-Image Pre-training/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:4513841692bfa5af6cd73cd6a6bd0a25c70894b416e5332a865ae56014ce147a +size 469668 diff --git a/2023/Misalign, Contrast then Distill_ Rethinking Misalignments in Language-Image Pre-training/layout.json b/2023/Misalign, Contrast then Distill_ Rethinking Misalignments in Language-Image Pre-training/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..27d702123ec834b5d831bc2c977fb3167c4f3152 --- /dev/null +++ b/2023/Misalign, Contrast then Distill_ Rethinking Misalignments in Language-Image Pre-training/layout.json @@ -0,0 +1,8280 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 116, + 103, + 479, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 103, + 479, + 140 + ], + "spans": [ + { + "bbox": [ + 116, + 103, + 479, + 140 + ], + "type": "text", + "content": "Misalign, Contrast then Distill: Rethinking Misalignments in Language-Image Pretraining" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 141, + 161, + 453, + 194 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 141, + 161, + 453, + 194 + ], + "spans": [ + { + "bbox": [ + 141, + 161, + 453, + 194 + ], + "type": "text", + "content": "Bumsoo Kim* Yeonsik Jo Jinhyung Kim Seunghwan Kim LG AI Research" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 222, + 192, + 235 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 222, + 192, + 235 + ], + "spans": [ + { + "bbox": [ + 143, + 222, + 192, + 235 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 247, + 290, + 487 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 247, + 290, + 487 + ], + "spans": [ + { + "bbox": [ + 46, + 247, + 290, + 487 + ], + "type": "text", + "content": "Contrastive Language-Image Pretraining has emerged as a prominent approach for training vision and text encoders with uncurated image-text pairs from the web. To enhance data-efficiency, recent efforts have introduced additional supervision terms that involve random-augmented views of the image. However, since the image augmentation process is unaware of its text counterpart, this procedure could cause various degrees of image-text misalignments during training. Prior methods either disregarded this discrepancy or introduced external models to mitigate the impact of misalignments during training. In contrast, we propose a novel metric learning approach that capitalizes on these misalignments as an additional training source, which we term \"Misalign, Contrast then Distill (MCD)\". Unlike previous methods that treat augmented images and their text counterparts as simple positive pairs, MCD predicts the continuous scales of misalignment caused by the augmentation. Our extensive experimental results show that our proposed MCD achieves state-of-the-art transferability in multiple classification and retrieval downstream datasets." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 521, + 128, + 533 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 521, + 128, + 533 + ], + "spans": [ + { + "bbox": [ + 47, + 521, + 128, + 533 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 540, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 540, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 540, + 287, + 696 + ], + "type": "text", + "content": "Recent advances in deep learning have shown that image representations trained with large-scale uncurated natural language supervision shows powerful transferability to various downstream tasks [14, 32]. A predominant paradigm in vision-language pre-training is to use a simple contrastive loss that makes the embedding of an image and its matching text description (positive pair) more similar to each other than other arbitrary image-text pairs (negative pairs) [29]. To achieve a more data-efficient training, following works actively capitalized on image random augmentation by: (i) joining language-image pretraining objectives with vision self-supervision terms [3, 5] between the augmented images [27, 23, 18] and (ii) involving more pairs of posi" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 308, + 225, + 545, + 384 + ], + "blocks": [ + { + "bbox": [ + 308, + 225, + 545, + 384 + ], + "lines": [ + { + "bbox": [ + 308, + 225, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 308, + 225, + 545, + 384 + ], + "type": "image", + "image_path": "9bca8c2cec6580e92d17e4e65cf7da070a0e7d0fa3cd9392719334c49c10dd13.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 393, + 547, + 494 + ], + "lines": [ + { + "bbox": [ + 304, + 393, + 547, + 494 + ], + "spans": [ + { + "bbox": [ + 304, + 393, + 547, + 494 + ], + "type": "text", + "content": "Figure 1. Conceptual illustration of contrastive language-image objectives of previous works (i.e., InfoNCE) and our MCD for (a) augmentation that doesn't harm the correspondence with its description and (b) augmentation that does. Previous works either disregard these misalignments [23] or leverage external models [18, 9] to mitigate their impact. On the other hand, MCD uses the continuous degree of misalignments caused by random image augmentation as a useful source for training various levels of alignments between images and their text descriptions." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 509, + 545, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 509, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 304, + 509, + 545, + 533 + ], + "type": "text", + "content": "tive/negative supervisions between the augmented images and their original text description [23, 18]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 533, + 546, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 533, + 546, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 533, + 546, + 689 + ], + "type": "text", + "content": "However, since the random image augmentation process is unaware of its corresponding text, it often results in the augmented image view to be misaligned with its description (see (b) in Fig.1). These misalignments behave as noisy training signals for the contrastive loss in language-image pretraining, thus causing performance degradation if not properly attended [27]. To mitigate this issue, recent works have used additional augmentation embeddings [18] or heavy external off-the-shelf object detectors and summary extractors [9] to match the alignment during training. Though being straightforward and showing strong performance, these works are limited in that they add unnecessary burden in both training and inference." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "Based on this observation, we start with a simple question: \"Instead of treating misalignments as noise to elim" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 243, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 243, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 243, + 712 + ], + "type": "text", + "content": "*Correspondence to: bumsoo.kim@lgresearch.ai" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2563" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "inate, can we rather harness them as a training source for language-image pretraining?\". To this end, we propose MCD (i.e., Misalign, Contrast then Distill), a novel training framework that leverages the various levels of misalignments between random augmented images and its text description during training." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 144, + 288, + 334 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 144, + 288, + 334 + ], + "spans": [ + { + "bbox": [ + 46, + 144, + 288, + 334 + ], + "type": "text", + "content": "MCD consists of three steps (see Fig 2 for an overview illustration of MCD): First, we conduct random augmentation on the image that causes various levels of misalignments (or not at all) with its text counterpart (Misalign). Then, we project all the participants (image, text, and augmented image) into an unified multimodal space, and learn the distance between all the image-text pairs with a contrastive objective (Contrast). Finally, we use a teacher-student network where the student learns from the \"soft\" distance between the text- original image (i.e., " + }, + { + "bbox": [ + 46, + 144, + 288, + 334 + ], + "type": "inline_equation", + "content": "D(\\bar{I}, T)" + }, + { + "bbox": [ + 46, + 144, + 288, + 334 + ], + "type": "text", + "content": " in Fig 2) and text-augmented image (i.e., " + }, + { + "bbox": [ + 46, + 144, + 288, + 334 + ], + "type": "inline_equation", + "content": "D(\\bar{I}', T)" + }, + { + "bbox": [ + 46, + 144, + 288, + 334 + ], + "type": "text", + "content": " in Fig 2) of the momentum teacher with a log-ratio loss (Distill). continuous scale of misalignment to the student model, enabling the student to learn from the various levels of misalignment that occur from the random augmentation during training time." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 335, + 231, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 335, + 231, + 346 + ], + "spans": [ + { + "bbox": [ + 59, + 335, + 231, + 346 + ], + "type": "text", + "content": "Our contribution of this paper is threefold:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 356, + 287, + 527 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 59, + 356, + 287, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 356, + 287, + 392 + ], + "spans": [ + { + "bbox": [ + 59, + 356, + 287, + 392 + ], + "type": "text", + "content": "- We propose MCD, a novel training framework where we learn the continuous level of misalignment as a source for contrastive language-image pretraining." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 400, + 287, + 448 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 400, + 287, + 448 + ], + "spans": [ + { + "bbox": [ + 59, + 400, + 287, + 448 + ], + "type": "text", + "content": "- Our MCD outperforms state-of-the-art models across various single/multi-modal downstream datasets without adding additional parameters for inference or using external models to force the alignment." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 456, + 287, + 527 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 456, + 287, + 527 + ], + "spans": [ + { + "bbox": [ + 59, + 456, + 287, + 527 + ], + "type": "text", + "content": "- We propose three distillation strategies leveraging misalignments: i) misalignment between positive pairs, ii) misalignment between negative pairs, and iii) misalignment between noisy pairs. Extensive experiments show that all three strategies positively contributes to our final performance." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 547, + 134, + 559 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 547, + 134, + 559 + ], + "spans": [ + { + "bbox": [ + 47, + 547, + 134, + 559 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 567, + 286, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 567, + 286, + 591 + ], + "spans": [ + { + "bbox": [ + 47, + 567, + 286, + 591 + ], + "type": "text", + "content": "Here, we present brief review of multi-modal representation learning, especially vision-language pre-training." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 599, + 205, + 612 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 599, + 205, + 612 + ], + "spans": [ + { + "bbox": [ + 47, + 599, + 205, + 612 + ], + "type": "text", + "content": "2.1. Vision-language Pre-training" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 617, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 713 + ], + "type": "text", + "content": "Vision-Language Pre-training (VLP) trains a multimodal model to learn joint representation of visual and textual information that can be transfer to various vision-language downstream tasks. The success of VLP primarily relies on large-scale datasets which contains images and their corresponding descriptions, enabling the model to understand the semantic relationship between the pairs. VLP includes two different group of models: 1) single-stream" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 307, + 72, + 545, + 340 + ], + "blocks": [ + { + "bbox": [ + 307, + 72, + 545, + 340 + ], + "lines": [ + { + "bbox": [ + 307, + 72, + 545, + 340 + ], + "spans": [ + { + "bbox": [ + 307, + 72, + 545, + 340 + ], + "type": "image", + "image_path": "74c6af92fcd1cd78585077323a6009b7dc5f64f66d7f7ccbc4643c17c207f532.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 342, + 545, + 409 + ], + "lines": [ + { + "bbox": [ + 305, + 342, + 545, + 409 + ], + "spans": [ + { + "bbox": [ + 305, + 342, + 545, + 409 + ], + "type": "text", + "content": "Figure 2. Overview of MCD. Our MCD consist of three steps: (i) text-agnostic random augmentation of the image that causes various levels of misalignment with the corresponding text, (ii) learning the distance between the image/augmented image and text with contrastive objectives then (iii) distill the log-ratio of the image-text distance between the original and the augmented image." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 430, + 545, + 549 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 430, + 545, + 549 + ], + "spans": [ + { + "bbox": [ + 305, + 430, + 545, + 549 + ], + "type": "text", + "content": "models [20, 6, 13, 22, 21, 25, 36] which process an image and its associated text information in a shared backbone network and 2) dual-stream models [14, 32] which has two independent backbone networks for processing each modality. In this work, we focuses on Contrastive Language Image Pretraining (CLIP [32]), which is a type of dual-stream models trained with image-text contrastive loss where the image and its matching text description in the dataset as a positive pair and other unrelated pairs in a batch as negative pairs." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 558, + 521, + 571 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 558, + 521, + 571 + ], + "spans": [ + { + "bbox": [ + 306, + 558, + 521, + 571 + ], + "type": "text", + "content": "2.2. Misalignments between Image-Text Pairs" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 577, + 545, + 625 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 577, + 545, + 625 + ], + "spans": [ + { + "bbox": [ + 305, + 577, + 545, + 625 + ], + "type": "text", + "content": "There are two different sources that cause misalignments in image-text pairs for VLP: misalignment that naturally occurs in image-text paired datasets, and misalignments caused by random image augmentation." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 641, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 641, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 641, + 545, + 713 + ], + "type": "text", + "content": "Misalignment in Image-Text Pairs. Large scale image-text paired datasets for VLP are usually collected from the web thus can contain uncurated and noisy pairs which have weak relations. This inevitably incurs misalignment between positive image-text pairs in the dataset misleading naive contrastive language image objective. Previous" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2564" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": "studies [19, 24, 1] have attempted to address the problem by knowledge distillation [11] of soft image-text alignment matrix from momentum teacher network to the student network via KL divergence loss. Our proposed method stands apart from previous approaches due to its element-wise log-ratio loss for distillation. Element-wise loss lessens the dependence on training hyperparameters like batch size and temperature for KL loss. Furthermore, it enables the model to harness the various levels of individual misalignments of each sample from random augmentation or label noise." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 213, + 289, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 213, + 289, + 548 + ], + "spans": [ + { + "bbox": [ + 46, + 213, + 289, + 548 + ], + "type": "text", + "content": "Misalignment by Augmentations. View-based self-supervised learning, in which models are trained to represent views or augmentations of the same image similarly, has yielded strong results across a variety of different formulations. Consecutive work of CLIP (i.e., SLIP [27]) initially introduced supervision between random augmented image views (e.g., cropping, gray-scale, jittering, gaussian blur, horizontal flipping, etc.). Since only image-image supervision was given in a separately embedded space, augmentation was not a factor for misalignment. To include more positive/negative pairs for the image-text contrastive objective, following works [23, 18] also introduced InfoNCE loss between the augmented views and the text pairs. However, since the text description is unaware of the random augmentations, there is a high chance that misalignments occur during training. SLIP shows that naïve application of contrastive loss to these misaligned pairs results in suboptimal performance. Previous work have either ignored this misalignment [23] or addressed this issue with an additional encoder that encodes the one-hot information of which augmentation has been applied during training [18]. PyramidCLIP [9] addressed this issue with external off-the-shelf object detectors and summary extractors. HiCLIP [10] captured the hierarchical nature of high-level on unsupervised manner with tree Transformer [39]. MCD incorporate the misalignment information as a source of training via novel log-ratio loss without introducing any external module." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 563, + 125, + 577 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 563, + 125, + 577 + ], + "spans": [ + { + "bbox": [ + 47, + 563, + 125, + 577 + ], + "type": "text", + "content": "3. Preliminary" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 584, + 287, + 645 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 584, + 287, + 645 + ], + "spans": [ + { + "bbox": [ + 46, + 584, + 287, + 645 + ], + "type": "text", + "content": "In our preliminary, we revisit the basic form of Contrastive Language-Image Pretraining (i.e., CLIP [32]). CLIP features a dual-encoder architecture where the image encoder " + }, + { + "bbox": [ + 46, + 584, + 287, + 645 + ], + "type": "inline_equation", + "content": "f_{I}" + }, + { + "bbox": [ + 46, + 584, + 287, + 645 + ], + "type": "text", + "content": " and text encoder " + }, + { + "bbox": [ + 46, + 584, + 287, + 645 + ], + "type": "inline_equation", + "content": "f_{T}" + }, + { + "bbox": [ + 46, + 584, + 287, + 645 + ], + "type": "text", + "content": " are jointly trained with a contrastive objective " + }, + { + "bbox": [ + 46, + 584, + 287, + 645 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{CLIP}}" + }, + { + "bbox": [ + 46, + 584, + 287, + 645 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "text", + "content": "InfoNCE Loss Given " + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "text", + "content": " image-text pairs " + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\{(x_i^I, x_i^T)\\}_{i=1}^N" + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "text", + "content": ", we define a similarity matrix " + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "text", + "content": " whose " + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "text", + "content": "-th row and the " + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "text", + "content": "-th column is the cosine similarity between the projected representations of the " + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "text", + "content": "-th text " + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "inline_equation", + "content": "T_i" + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "text", + "content": " and the " + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "text", + "content": "-th image " + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "inline_equation", + "content": "I_j" + }, + { + "bbox": [ + 46, + 664, + 287, + 715 + ], + "type": "text", + "content": " (i.e.," + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 71, + 468, + 86 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 71, + 468, + 86 + ], + "spans": [ + { + "bbox": [ + 305, + 71, + 468, + 86 + ], + "type": "inline_equation", + "content": "T_{i} = f_{T}(x_{i}^{T}),I_{j} = f_{I}(x_{j}^{I}))" + }, + { + "bbox": [ + 305, + 71, + 468, + 86 + ], + "type": "text", + "content": " , written as:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 387, + 92, + 545, + 106 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 387, + 92, + 545, + 106 + ], + "spans": [ + { + "bbox": [ + 387, + 92, + 545, + 106 + ], + "type": "interline_equation", + "content": "S _ {i j} = \\operatorname {s i m} \\left(T _ {i}, I _ {j}\\right), \\tag {1}", + "image_path": "95b0ed3f536075f59a8b5dc9d375771e482cc748041b80296f8eeb668291a8d9.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "spans": [ + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "type": "inline_equation", + "content": "\\mathrm{sim}(\\cdot ,\\cdot)" + }, + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "type": "text", + "content": " is cosine similarity. In CLIP [32], the encoded image features " + }, + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "type": "text", + "content": " and text features " + }, + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "type": "text", + "content": " are projected to the same dimension where the embeddings for matching image-text pairs are pulled together while embeddings for arbitrary pairs are pushed apart with the InfoNCE loss [29]. Given the similarity matrix " + }, + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "type": "text", + "content": ", the InfoNCE loss " + }, + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_N" + }, + { + "bbox": [ + 304, + 113, + 547, + 196 + ], + "type": "text", + "content": " is rewritten as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 336, + 202, + 545, + 236 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 336, + 202, + 545, + 236 + ], + "spans": [ + { + "bbox": [ + 336, + 202, + 545, + 236 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {N} (S) = - \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\log \\frac {\\exp \\left(S _ {i i} / \\tau\\right)}{\\sum_ {j = 1} ^ {N} \\exp \\left(S _ {i j} / \\tau\\right)}, \\tag {2}", + "image_path": "2ce1e19bd72719db826173b0859fce08ebdbdc11eea993efc65fc187300a7135.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 242, + 545, + 266 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 242, + 545, + 266 + ], + "spans": [ + { + "bbox": [ + 305, + 242, + 545, + 266 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 242, + 545, + 266 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 305, + 242, + 545, + 266 + ], + "type": "text", + "content": " is a learnable temperature variable. The overall loss of clip " + }, + { + "bbox": [ + 305, + 242, + 545, + 266 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{CLIP}}" + }, + { + "bbox": [ + 305, + 242, + 545, + 266 + ], + "type": "text", + "content": " is written as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 356, + 274, + 545, + 300 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 274, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 356, + 274, + 545, + 300 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {C L I P}} = \\frac {1}{2} \\left(\\mathcal {L} _ {N} (S) + \\mathcal {L} _ {N} \\left(S ^ {T}\\right)\\right). \\tag {3}", + "image_path": "a5fd600c822adb589db94971aaad655eada7339e1ac57690b63532219872717d.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "text", + "content": "Augmentations and Misalignment. To include more positive/negative pairs for the contrastive objective, following works [23, 18] introduced InfoNCE loss between the random augmented image views and the text description for the original image. Let " + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "inline_equation", + "content": "\\mathcal{A}" + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "text", + "content": " a function for random image augmentation that includes randomly applying cropping, gray-scale, jittering, gaussian blur, horizontal flipping following SimCLR [3]. " + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "inline_equation", + "content": "I_{j'}" + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "text", + "content": " is the encoded image feature of augmented view of " + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "text", + "content": "-th image(e.g. " + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "inline_equation", + "content": "I_{j'} = f_I(\\mathcal{A}(x_j^I))" + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "text", + "content": "). Let " + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "inline_equation", + "content": "S_{ij}' = \\mathrm{sim}(T_i, I_{j'})" + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "text", + "content": " represent the similarity between the augmented view of " + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "text", + "content": "-th image and " + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "text", + "content": "-th text. We denote the matrix of these similarity as " + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "inline_equation", + "content": "S'" + }, + { + "bbox": [ + 304, + 312, + 545, + 468 + ], + "type": "text", + "content": " for concise notation. Then, InfoNCE loss between the augmented image and the text is" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 356, + 475, + 545, + 498 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 475, + 545, + 498 + ], + "spans": [ + { + "bbox": [ + 356, + 475, + 545, + 498 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {C L I P}} ^ {\\prime} = \\frac {1}{2} \\left(\\mathcal {L} _ {N} \\left(S ^ {\\prime}\\right) + \\mathcal {L} _ {N} \\left(S ^ {\\prime T}\\right)\\right). \\tag {4}", + "image_path": "a6d3a01f2b16ef150a4481a31382a7411de95c6a565b65852678b10085b363f4.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 503, + 545, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 503, + 545, + 635 + ], + "spans": [ + { + "bbox": [ + 304, + 503, + 545, + 635 + ], + "type": "text", + "content": "As the random augmentation function " + }, + { + "bbox": [ + 304, + 503, + 545, + 635 + ], + "type": "inline_equation", + "content": "\\mathcal{A}" + }, + { + "bbox": [ + 304, + 503, + 545, + 635 + ], + "type": "text", + "content": " is independent to the corresponding text description, the augmented view " + }, + { + "bbox": [ + 304, + 503, + 545, + 635 + ], + "type": "inline_equation", + "content": "I_{j'}" + }, + { + "bbox": [ + 304, + 503, + 545, + 635 + ], + "type": "text", + "content": " is likely to exhibit misalignment with text " + }, + { + "bbox": [ + 304, + 503, + 545, + 635 + ], + "type": "inline_equation", + "content": "T_i" + }, + { + "bbox": [ + 304, + 503, + 545, + 635 + ], + "type": "text", + "content": ". This hypothesis is consistent with the finding of SLIP [27], which demonstrated that introducing augmentation (particularly resize crop, and flip) to CLIP actually resulted in a performance decrease. Previous works [27, 23] have sidestepped the utilization of augmented view in CLIP by substituting infoNCE with self-supervised learning loss(e.g. SimCLR [3]) between images. These approaches have limitation in fully capturing the essence of multi-modal learning." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 645, + 361, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 645, + 361, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 645, + 361, + 658 + ], + "type": "text", + "content": "4. Method" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 665, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 714 + ], + "type": "text", + "content": "In this section, we introduce MCD (Misalign, Contrast then Distill), a novel training framework for language-image pretraining using misalignments as continuous labels for learning the distance between image-text pairs." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2565" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 111, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 111, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 111, + 85 + ], + "type": "text", + "content": "4.1. Misalign" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 290, + 247 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 290, + 247 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 290, + 247 + ], + "type": "text", + "content": "The first step of MCD is to apply text-agnostic random image augmentations (e.g., random crop, random flip, grayscale, etc.) to create various levels of misalignments between the images and its description. Here, we elaborate on three distinct scenarios of misalignment that can arise during the augmentation process, hindering the contrastive loss to learn proper distance between image-text pairs: (i) Text-agnostic random augmentation can cause misalignments in positive image-text pairs. (ii) The random-augmentation can mistakenly cause positive signals between negative pairs. (iii) Misalignments can already exist innately within the original image-text pair. A detailed illustration of each cases are provided in Fig 3." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 255, + 111, + 266 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 255, + 111, + 266 + ], + "spans": [ + { + "bbox": [ + 47, + 255, + 111, + 266 + ], + "type": "text", + "content": "4.2. Contrast" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": "In the second step, MCD initially learns the distance metric between image-text pairs with a contrastive objective. Motivated by [18], we project both image and text modalities to a unified space and use all the positive pairs and negative pairs of both modalities. For an " + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": "-th embedding " + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "inline_equation", + "content": "z_{i}" + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": " in a batch of embeddings " + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "inline_equation", + "content": "\\{z_i\\}_{i = 1}^{3N}" + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": " that includes " + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": " image samples, " + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": " text samples, and " + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": " random augmented image samples, let " + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "inline_equation", + "content": "\\mathcal{P}_i" + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "inline_equation", + "content": "\\mathcal{N}_i" + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": " each denote the set of all positive sample indices of the " + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": "-th sample including " + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": " itself and the set of all negative sample indices of the " + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": "-th sample. Then, the contrastive loss for the multiple positives and multiple negatives for sample " + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 274, + 289, + 418 + ], + "type": "text", + "content": " can be written as" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 426, + 287, + 456 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 426, + 287, + 456 + ], + "spans": [ + { + "bbox": [ + 53, + 426, + 287, + 456 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {i} ^ {C} = \\mathbb {E} _ {p \\in \\mathcal {P} _ {i}} \\left[ - \\log \\frac {\\sin \\left(z _ {i} , z _ {p}\\right)}{\\sin \\left(z _ {i} , z _ {p}\\right) + \\sum_ {n \\in \\mathcal {N} _ {i}} \\sin \\left(z _ {i} , z _ {n}\\right)} \\right]. \\tag {5}", + "image_path": "badc8bd87f8051072c6db2b2b58def86bf3740a5e8c034c827cd9d0d69cf20dc.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 464, + 287, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 464, + 287, + 536 + ], + "spans": [ + { + "bbox": [ + 46, + 464, + 287, + 536 + ], + "type": "text", + "content": "However, without encoding augmentation information the image-text contrastive loss is prone to the three aforementioned issues. We address these three issues with a teacher-student model where the continuous distance between the image-text and augmented image-text of the teacher model is distilled to the student model." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 544, + 98, + 556 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 544, + 98, + 556 + ], + "spans": [ + { + "bbox": [ + 47, + 544, + 98, + 556 + ], + "type": "text", + "content": "4.3. Distill" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 563, + 287, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 563, + 287, + 648 + ], + "spans": [ + { + "bbox": [ + 46, + 563, + 287, + 648 + ], + "type": "text", + "content": "Knowledge distillation, introduced by Hinton et al. [11], is a learning paradigm where we train the student network to mimic the \"soft\" labels predicted from the teacher network. In MCD, we train the student network with the continuous image-text distance predicted by the teacher network. Psuedocode for the distillation in MCD is provided in Algorithm 1." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": "Log-Ratio Loss for Image-Text Distance. Given a student " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{I}" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " and a momentum teacher " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\bar{f}_{I}" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": ", we propose to use log-ratio loss [15] on image-text similarities that aims to approximate the ratio of similarity distances by the ratio of" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 310, + 69, + 541, + 241 + ], + "blocks": [ + { + "bbox": [ + 310, + 69, + 541, + 241 + ], + "lines": [ + { + "bbox": [ + 310, + 69, + 541, + 241 + ], + "spans": [ + { + "bbox": [ + 310, + 69, + 541, + 241 + ], + "type": "image", + "image_path": "dd1a15f3b5c0a06aa990d4bf1ebb85ec39f7ed063c922cd745f600d2bd89d123.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 255, + 547, + 334 + ], + "lines": [ + { + "bbox": [ + 305, + 255, + 547, + 334 + ], + "spans": [ + { + "bbox": [ + 305, + 255, + 547, + 334 + ], + "type": "text", + "content": "Figure 3. MCD loss for various cases of misalignments that occur when applying random image augmentation in language-image pretraining with. In this paper, we elaborate three scenarios: (a) misalignment caused by augmenting the image of an original positive pair, which is addressed by " + }, + { + "bbox": [ + 305, + 255, + 547, + 334 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^{\\mathrm{pos}}" + }, + { + "bbox": [ + 305, + 255, + 547, + 334 + ], + "type": "text", + "content": " (b) augmentation that mistakenly cause positive alignment between negative pairs (c) misalignment that already exists within the dataset." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 353, + 545, + 377 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 353, + 545, + 377 + ], + "spans": [ + { + "bbox": [ + 305, + 353, + 545, + 377 + ], + "type": "text", + "content": "image-text misalignments in the learned embedding space. Specifically, we define the loss function as" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 310, + 385, + 545, + 416 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 385, + 545, + 416 + ], + "spans": [ + { + "bbox": [ + 310, + 385, + 545, + 416 + ], + "type": "interline_equation", + "content": "\\ell_ {l r} (i, j; \\alpha , \\beta) = \\left\\| \\log \\frac {D \\left(I _ {\\alpha} , T _ {\\beta}\\right)}{D \\left(I _ {i} , T _ {j}\\right)} - \\log \\frac {D \\left(\\bar {I} _ {\\alpha} , T _ {\\beta}\\right)}{D \\left(\\bar {I} _ {i} , T _ {j}\\right)} \\right\\| _ {1}, \\tag {6}", + "image_path": "1dffa3138386bd9d4070125990ce93a6980f92b0f064394738dd506774d20d61.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "spans": [ + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\|_1" + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "inline_equation", + "content": "\\ell_1" + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "text", + "content": " loss, " + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "inline_equation", + "content": "D(\\cdot, \\cdot)" + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "text", + "content": " is distance function. We utilize Euclidean distance between the projected representations as distance function. Since the embedded vectors comprising the image " + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "inline_equation", + "content": "I_i, \\bar{I}_i" + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "text", + "content": " and text " + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "inline_equation", + "content": "T_j" + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "text", + "content": " are L2-normalized, Euclidean distance operates as a proxy for cosine similarity " + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "inline_equation", + "content": "D(I_i, T_j) = 2(1 - S_{ij})" + }, + { + "bbox": [ + 305, + 423, + 547, + 604 + ], + "type": "text", + "content": ". This log-ratio loss approximates the degree of misalignment, which is measured as the ratio of two image-text pairs. By leveraging this measure, we aim to promote a coherent and continuous embedding space. Accordingly, our student encoder is trained under the guidance of the momentum teacher with the incorporation of this degree of misalignment. By establishing these pairs of log-ratio, we enable the handling of diverse forms of misalignment. We present three distinct index setups that correspond to different types of misalignment." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 617, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 617, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 617, + 547, + 715 + ], + "type": "text", + "content": "Misalignment in Positive pairs. First, we define distance pair for misalignment between the original image-text pair. Let " + }, + { + "bbox": [ + 305, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "i'" + }, + { + "bbox": [ + 305, + 617, + 547, + 715 + ], + "type": "text", + "content": " denote the index of augmented image sample. On Eq.(5), " + }, + { + "bbox": [ + 305, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "i'" + }, + { + "bbox": [ + 305, + 617, + 547, + 715 + ], + "type": "text", + "content": "-th image sample and " + }, + { + "bbox": [ + 305, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 617, + 547, + 715 + ], + "type": "text", + "content": "-th text sample serve as positive pair. However, random augmentation can occasionally transform positive pair into negative pair. To account for such transformations, we intend to utilize the log-ratio between original pairs and augmented pairs. This allows us to" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2566" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "code", + "bbox": [ + 47, + 91, + 286, + 456 + ], + "blocks": [ + { + "bbox": [ + 48, + 72, + 178, + 83 + ], + "lines": [ + { + "bbox": [ + 48, + 72, + 178, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 72, + 178, + 83 + ], + "type": "text", + "content": "Algorithm 1 MCD Pseudocode" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 47, + 91, + 286, + 456 + ], + "lines": [ + { + "bbox": [ + 47, + 91, + 286, + 456 + ], + "spans": [ + { + "bbox": [ + 47, + 91, + 286, + 456 + ], + "type": "text", + "content": "# fm, fs: image encoders (teacher, student) \n# ft: text encoder \n# fa: random-augmentation function \n# N : batch size \ndef D(sim): # cosine sim -> L2 distance \nreturn 2 - 2 * sim + 1e-6 \ndef MCD(img, txt): \n# image, text encodings \naug = fa(img) \n# normalized projection embeddings \nzm, zs,zt = fm(img), fs(img), ft(txt) \nzam,zas = fm(aug), fs(aug) # misalign \n# distance (contrast) \ndi_t, di_s = D(zm @ zt.T), D(zs @ zt.T) \nda_t, da_s = D(zam @ zt.T), D(zas @ zt.T) \n# distill \npos_l, neg_l, noise_l = 0, 0, 0 \nfor i in range(N): \n lr_s1 = log(da_s[i,i]/di_s[i,i]) \n lr_t1 = log(da_t[i,i]/di_t[i,i]) \n# positive pairs \npos_l += abs(lr_s1 - lr_t1) / N \nfor j in range(N): \n if i==j: continue \n lr_s2 = log(da_s[i,j]/di_s[i,i]) \n lr_t2 = log(da_t[i,j]/di_t[i,i]) \n# negative pairs \nneg_l += abs(lr_s2 - lr_t2) / (N*(N-1)) \nlr_s3 = log(di_s[j,j]/di_s[i,i]) \nlr_t3 = log(di_t[j,j]/di_t[i,i]) \n# noisy pairs \nnoise_l += abs(lr_s3 - lr_t3) / (N*(N-1)) \nreturn pos_l + neg_l + noise_l" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "code_body" + } + ], + "index": 1, + "sub_type": "code", + "guess_lang": "julia" + }, + { + "bbox": [ + 46, + 480, + 287, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 480, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 480, + 287, + 506 + ], + "type": "text", + "content": "capture these shifts and incorporate them into the learning process effectively." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 100, + 515, + 287, + 529 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 515, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 100, + 515, + 287, + 529 + ], + "type": "interline_equation", + "content": "\\mathcal {L} ^ {\\mathrm {p o s}} = \\mathbb {E} _ {i = 1, \\dots , N} \\left[ \\ell_ {l r} (i, i; i ^ {\\prime}, i) \\right], \\tag {7}", + "image_path": "aa717b3c70234a5d249cb782394950508e12ea9188559ec7ad9d89124ccbb899.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 532, + 240, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 532, + 240, + 545 + ], + "spans": [ + { + "bbox": [ + 47, + 532, + 240, + 545 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 532, + 240, + 545 + ], + "type": "inline_equation", + "content": "i'" + }, + { + "bbox": [ + 47, + 532, + 240, + 545 + ], + "type": "text", + "content": " is the index of augmented " + }, + { + "bbox": [ + 47, + 532, + 240, + 545 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 47, + 532, + 240, + 545 + ], + "type": "text", + "content": "-th sample." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 558, + 287, + 631 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 287, + 631 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 287, + 631 + ], + "type": "text", + "content": "Misalignment in Negative pairs. Augmented images can possess relevance with different text, which would normally be considered negative pairs in Eq.(5). However, the log-ratio obtained by our momentum teacher alleviates our model from mistakenly pushing the embedding of relevant texts away." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 93, + 636, + 287, + 658 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 636, + 287, + 658 + ], + "spans": [ + { + "bbox": [ + 93, + 636, + 287, + 658 + ], + "type": "interline_equation", + "content": "\\mathcal {L} ^ {\\text {n e g}} = \\underset {i \\neq j} {\\mathbb {E}} _ {i, j = 1, 2, \\dots , N} \\left[ \\ell_ {l r} \\left(i, i; j ^ {\\prime}, i\\right) \\right], \\tag {8}", + "image_path": "a68cadecf2f8a0034977a5ab493c7d6c2c4281dc04064c4715cbda42de971f4f.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 663, + 242, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 663, + 242, + 676 + ], + "spans": [ + { + "bbox": [ + 47, + 663, + 242, + 676 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 663, + 242, + 676 + ], + "type": "inline_equation", + "content": "j^{\\prime}" + }, + { + "bbox": [ + 47, + 663, + 242, + 676 + ], + "type": "text", + "content": " is the index of augmented " + }, + { + "bbox": [ + 47, + 663, + 242, + 676 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 47, + 663, + 242, + 676 + ], + "type": "text", + "content": "-th sample." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 689, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 715 + ], + "type": "text", + "content": "Misalignment in Noisy pairs. Original image-text pairs obtained from the web may contain either noisy images or" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 546, + 121 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 546, + 121 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 546, + 121 + ], + "type": "text", + "content": "descriptions. While these pairs are normally treated as positive pairs under contrastive loss, we propose a loss for noisy pairs where the noisy labels are trained to have larger distance than matching image-text pairs." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 350, + 129, + 546, + 152 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 129, + 546, + 152 + ], + "spans": [ + { + "bbox": [ + 350, + 129, + 546, + 152 + ], + "type": "interline_equation", + "content": "\\mathcal {L} ^ {\\text {n o i s y}} = \\mathbb {E} _ {i, j = 1, 2, \\dots , N} \\left[ \\ell_ {l r} (i, i; j, j) \\right]. \\tag {9}", + "image_path": "85c37ec2cdb698fbedd95094a3f71799a773ad8e84616808d810166816b496a5.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 165, + 546, + 201 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 165, + 546, + 201 + ], + "spans": [ + { + "bbox": [ + 305, + 165, + 546, + 201 + ], + "type": "text", + "content": "Distillation Loss. The full training objective of MCD distillation " + }, + { + "bbox": [ + 305, + 165, + 546, + 201 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^D" + }, + { + "bbox": [ + 305, + 165, + 546, + 201 + ], + "type": "text", + "content": " is the sum of the three distillation terms, which is written as" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 369, + 210, + 546, + 224 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 369, + 210, + 546, + 224 + ], + "spans": [ + { + "bbox": [ + 369, + 210, + 546, + 224 + ], + "type": "interline_equation", + "content": "\\mathcal {L} ^ {\\mathrm {D}} = \\mathcal {L} ^ {\\text {p o s}} + \\mathcal {L} ^ {\\text {n e g}} + \\mathcal {L} ^ {\\text {n o i s y}}. \\tag {10}", + "image_path": "682a4f6d3847e77da9c3fbae3e95ad232c5f8ba057c45142f7673c1abba6b327.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 234, + 399, + 247 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 234, + 399, + 247 + ], + "spans": [ + { + "bbox": [ + 306, + 234, + 399, + 247 + ], + "type": "text", + "content": "4.4. Training MCD" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 253, + 546, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 253, + 546, + 350 + ], + "spans": [ + { + "bbox": [ + 304, + 253, + 546, + 350 + ], + "type": "text", + "content": "In this section, we explain the details of MCD training. The training objective for the text encoder and student image encoder for MCD consists of the three objectives: contrastive loss " + }, + { + "bbox": [ + 304, + 253, + 546, + 350 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^C" + }, + { + "bbox": [ + 304, + 253, + 546, + 350 + ], + "type": "text", + "content": " in Eq (5) for initial image-text distance learning, distillation loss " + }, + { + "bbox": [ + 304, + 253, + 546, + 350 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^D" + }, + { + "bbox": [ + 304, + 253, + 546, + 350 + ], + "type": "text", + "content": " for the three misalignment scenarios, and loss for masked language modeling " + }, + { + "bbox": [ + 304, + 253, + 546, + 350 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^{\\mathrm{MLM}}" + }, + { + "bbox": [ + 304, + 253, + 546, + 350 + ], + "type": "text", + "content": ". The parameters for the teacher image encoder are momentum updated." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 365, + 546, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 365, + 546, + 449 + ], + "spans": [ + { + "bbox": [ + 304, + 365, + 546, + 449 + ], + "type": "text", + "content": "MLM Loss. Following previous work in literature [23, 18, 19], we randomly mask out the input tokens with a probability of " + }, + { + "bbox": [ + 304, + 365, + 546, + 449 + ], + "type": "inline_equation", + "content": "15\\%" + }, + { + "bbox": [ + 304, + 365, + 546, + 449 + ], + "type": "text", + "content": " and replace them with the special token " + }, + { + "bbox": [ + 304, + 365, + 546, + 449 + ], + "type": "inline_equation", + "content": "[\\mathrm{MASK}]^{1}" + }, + { + "bbox": [ + 304, + 365, + 546, + 449 + ], + "type": "text", + "content": ". Let " + }, + { + "bbox": [ + 304, + 365, + 546, + 449 + ], + "type": "inline_equation", + "content": "p^{\\mathrm{msk}}" + }, + { + "bbox": [ + 304, + 365, + 546, + 449 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 365, + 546, + 449 + ], + "type": "inline_equation", + "content": "y^{\\mathrm{msk}}" + }, + { + "bbox": [ + 304, + 365, + 546, + 449 + ], + "type": "text", + "content": " each denote the set of model's predicted probability for the masked tokens and the set of ground-truth vocabulary index for the tokens, respectively. Then, MLM loss is written as:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 354, + 458, + 545, + 474 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 354, + 458, + 545, + 474 + ], + "spans": [ + { + "bbox": [ + 354, + 458, + 545, + 474 + ], + "type": "interline_equation", + "content": "\\mathcal {L} ^ {\\mathrm {M L M}} = \\mathbb {E} _ {p \\in p ^ {\\mathrm {m s k}}, y \\in y ^ {\\mathrm {m s k}}} \\left[ \\mathrm {C E} (p, y) \\right], \\tag {11}", + "image_path": "9f8be531f5af1ef177c9584ce3d20a42c135f2e598e80ac95d126076bc8276a3.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 483, + 462, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 483, + 462, + 495 + ], + "spans": [ + { + "bbox": [ + 306, + 483, + 462, + 495 + ], + "type": "text", + "content": "where CE denotes Cross Entropy loss." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 511, + 545, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 511, + 545, + 563 + ], + "spans": [ + { + "bbox": [ + 304, + 511, + 545, + 563 + ], + "type": "text", + "content": "Momentum Teacher Update. Let " + }, + { + "bbox": [ + 304, + 511, + 545, + 563 + ], + "type": "inline_equation", + "content": "\\theta_{f_I},\\theta_{\\bar{f}_I}" + }, + { + "bbox": [ + 304, + 511, + 545, + 563 + ], + "type": "text", + "content": " be the parameter of the student encoder and momentum teacher, respectively. For the " + }, + { + "bbox": [ + 304, + 511, + 545, + 563 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 511, + 545, + 563 + ], + "type": "text", + "content": " -th step, we update " + }, + { + "bbox": [ + 304, + 511, + 545, + 563 + ], + "type": "inline_equation", + "content": "\\theta_{\\bar{f}_I}^{(t)}" + }, + { + "bbox": [ + 304, + 511, + 545, + 563 + ], + "type": "text", + "content": " of the momentum teacher according to the following:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 361, + 571, + 545, + 590 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 361, + 571, + 545, + 590 + ], + "spans": [ + { + "bbox": [ + 361, + 571, + 545, + 590 + ], + "type": "interline_equation", + "content": "\\theta_ {\\bar {f} I} ^ {(t)} = m \\theta_ {\\bar {f} I} ^ {(t - 1)} + (1 - m) \\theta_ {f I} ^ {(t)}, \\tag {12}", + "image_path": "b7e780888e7fdab3ed3632b18f91f43199d049307d73dbd04e3ae46d96ac18bc.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 598, + 545, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 598, + 545, + 635 + ], + "spans": [ + { + "bbox": [ + 304, + 598, + 545, + 635 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 598, + 545, + 635 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 598, + 545, + 635 + ], + "type": "text", + "content": " denotes the momentum parameter. We use " + }, + { + "bbox": [ + 304, + 598, + 545, + 635 + ], + "type": "inline_equation", + "content": "m = 0.994" + }, + { + "bbox": [ + 304, + 598, + 545, + 635 + ], + "type": "text", + "content": " in our experiments, where " + }, + { + "bbox": [ + 304, + 598, + 545, + 635 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 598, + 545, + 635 + ], + "type": "text", + "content": " grows in a cosine schedule to 1 at the end of training." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 651, + 546, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 651, + 546, + 676 + ], + "spans": [ + { + "bbox": [ + 306, + 651, + 546, + 676 + ], + "type": "text", + "content": "Progressive Distillation. As the training proceeds, InfoNCE loss conflicts with our misalignment loss. InfoNCE" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 304, + 683, + 546, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 683, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 683, + 546, + 713 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 304, + 683, + 546, + 713 + ], + "type": "text", + "content": "Following BERT, the replacement is done with either the [MASK] token (80%), another random token within the dictionary (10%), or left unchanged (10%)." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2567" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "text", + "content": "between pair " + }, + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "inline_equation", + "content": "I_{j}^{\\prime}" + }, + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "inline_equation", + "content": "T_{i}" + }, + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "text", + "content": " forces the embedding to pull regardless of its degree of misalignment. In early stages of training, the model needs to learn how to discriminate positive or negative pairs with a hard label. However, as the training progresses, the log-ratio loss delicately models the distance between the various misalignments occurred by augmentations or innately existing in the original image-text pair. Therefore, we progressively diminish the contribution of InfoNCE loss involving augmented views." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 195, + 255, + 207 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 195, + 255, + 207 + ], + "spans": [ + { + "bbox": [ + 47, + 195, + 255, + 207 + ], + "type": "text", + "content": "MCD Loss. The final loss for MCD is written as:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 96, + 215, + 287, + 230 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 96, + 215, + 287, + 230 + ], + "spans": [ + { + "bbox": [ + 96, + 215, + 287, + 230 + ], + "type": "interline_equation", + "content": "\\mathcal {L} ^ {\\mathrm {M C D}} = \\mathcal {L} ^ {\\mathrm {C}} + \\alpha \\cdot \\mathcal {L} ^ {\\mathrm {D}} + \\beta \\cdot \\mathcal {L} ^ {\\mathrm {M L M}}, \\tag {13}", + "image_path": "334a31bfde4c780fdb0e200878beaa44c7fb8a1138ed92b1947a73a59eb0ca75.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 239, + 287, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 287, + 264 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 287, + 264 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 239, + 287, + 264 + ], + "type": "inline_equation", + "content": "\\alpha = 0" + }, + { + "bbox": [ + 46, + 239, + 287, + 264 + ], + "type": "text", + "content": " progressively increases on a cosine schedule to 1, and " + }, + { + "bbox": [ + 46, + 239, + 287, + 264 + ], + "type": "inline_equation", + "content": "\\beta = 0.2" + }, + { + "bbox": [ + 46, + 239, + 287, + 264 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 270, + 144, + 283 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 270, + 144, + 283 + ], + "spans": [ + { + "bbox": [ + 47, + 270, + 144, + 283 + ], + "type": "text", + "content": "4.5. MCD Inference" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 289, + 287, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 289, + 287, + 361 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 287, + 361 + ], + "type": "text", + "content": "MCD is based on a teacher-student network, thus the student " + }, + { + "bbox": [ + 46, + 289, + 287, + 361 + ], + "type": "inline_equation", + "content": "f_{I}" + }, + { + "bbox": [ + 46, + 289, + 287, + 361 + ], + "type": "text", + "content": " and momentum teacher " + }, + { + "bbox": [ + 46, + 289, + 287, + 361 + ], + "type": "inline_equation", + "content": "\\bar{f}_{I}" + }, + { + "bbox": [ + 46, + 289, + 287, + 361 + ], + "type": "text", + "content": " is obtained after training. Unlike previous work in literature that leverage the teacher network for inference [37, 19], we use the student network that is trained with both the contrastive loss and the log-ratio loss for image-text distance learning." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 372, + 124, + 385 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 372, + 124, + 385 + ], + "spans": [ + { + "bbox": [ + 47, + 372, + 124, + 385 + ], + "type": "text", + "content": "5. Experiment" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 392, + 287, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 392, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 46, + 392, + 287, + 464 + ], + "type": "text", + "content": "In this section, we provide implementation details and experimental results with our MCD pretrained on two widely used image-text benchmark datasets (e.g., CC3M, YFCC15M) to validate the effectiveness of our proposed MCD on multiple downstream datasets including classification and image-text retrieval." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 472, + 243, + 485 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 472, + 243, + 485 + ], + "spans": [ + { + "bbox": [ + 47, + 472, + 243, + 485 + ], + "type": "text", + "content": "5.1. Implementation Details and Datasets" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "spans": [ + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "type": "text", + "content": "For implementation details, our work is built on top of the open-source SLIP codebase " + }, + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "type": "inline_equation", + "content": "[27]^2" + }, + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "type": "text", + "content": ". For DECLIP [23], we follow the implementation details of the official code release. The performance on GPU-machine runs for CLIP and SLIP follows the exact implementation details upon this codebase. Since MCD features both the momentum teacher image encoder " + }, + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "type": "inline_equation", + "content": "\\bar{f}_I" + }, + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "type": "text", + "content": " and student " + }, + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "type": "inline_equation", + "content": "f_I" + }, + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "type": "text", + "content": ", we conduct the following experiment section with " + }, + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "type": "inline_equation", + "content": "\\bar{f}_I" + }, + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "type": "text", + "content": " based on empirical results. All of our models are pretrained in " + }, + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "type": "inline_equation", + "content": "16\\times" + }, + { + "bbox": [ + 46, + 491, + 288, + 647 + ], + "type": "text", + "content": " A100 GPUs. For CC3M, All models are trained with a ViT-B/16 backbone with a learning rate of 5e-4 and weight decay of 0.5. For YFCC15M, we train the model with ViT-B/32 backbone, batch size 4096, learning rate 1e-3, and weight decay 0.2." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 661, + 288, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 661, + 288, + 686 + ], + "spans": [ + { + "bbox": [ + 46, + 661, + 288, + 686 + ], + "type": "text", + "content": "Pretraining Datasets. To validate the effectiveness of MCD, we pretrain MCD on large-scale open-source" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 72, + 545, + 97 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 545, + 97 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 545, + 97 + ], + "type": "text", + "content": "datasets: YFCC (Yahoo Flickr Creative Commons) 15M [38] and CC (Conceptual Captions) 3M [34]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 111, + 547, + 232 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 111, + 547, + 232 + ], + "spans": [ + { + "bbox": [ + 304, + 111, + 547, + 232 + ], + "type": "text", + "content": "Downstream Datasets. Following CLIP [32], we evaluate the transferability of pretrained MCD on 11 widely used downstream datasets for classification (i.e., Oxford Pets [30], CIFAR-10, CIFAR-100 [17], SUN397 [41], Food-101 [2], Flowers [28], Cars [16], Caltech-101 [8], Aircraft [26], DTD [7], ImageNet-1k [33]). We also transfer to image-text retrieval tasks on Flickr30K [31] and MS-COCO Captions [4] datasets. The evaluation settings for each dataset are consistent with CLIP as in the open-source implementation2." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 239, + 519, + 251 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 239, + 519, + 251 + ], + "spans": [ + { + "bbox": [ + 305, + 239, + 519, + 251 + ], + "type": "text", + "content": "5.2. MCD Pretraining on YFCC15M Dataset" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 257, + 545, + 377 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 257, + 545, + 377 + ], + "spans": [ + { + "bbox": [ + 304, + 257, + 545, + 377 + ], + "type": "text", + "content": "First, we pretrain MCD on YFCC15M and evaluate its transferability in single-modal (e.g., classification) and multi-modal (e.g., image-text retrieval) downstream tasks. We compare the result against other state-of-the-art Contrastive Language-Image Pretraining approaches [32, 27, 23, 18] that utilizes various levels of supervision including vision self-supervision [3, 5], text self-supervision [23], memory queue [23], and augmentation encoding [18]. All models are pretrained with a learning rate 1e-3 for 32 epochs unless mentioned otherwise." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 392, + 545, + 596 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 392, + 545, + 596 + ], + "spans": [ + { + "bbox": [ + 304, + 392, + 545, + 596 + ], + "type": "text", + "content": "Zero-shot Classification. We evaluate the zero-shot classification performance on 11 downstream datasets for single-modal experiments. Tab. 1 shows both the zero-shot classification and linear probing accuracy of CLIP variants [32, 27, 23, 18] pretrained on YFCC15M dataset and transferred to downstream classification datasets. In test time, the learned text encoder " + }, + { + "bbox": [ + 304, + 392, + 545, + 596 + ], + "type": "inline_equation", + "content": "f_{T}" + }, + { + "bbox": [ + 304, + 392, + 545, + 596 + ], + "type": "text", + "content": " synthesizes a zero-shot linear classifier by embedding the arbitrary categories of the test dataset. As classes are in the form of a single word, we use prompts including the label (e.g., \"a photo of a {label}\") as following CLIP [32]. Our MCD outperforms across a majority of the 11 datasets with a noticeable margin. Note that even without additional augmented-aware network leveraged in UniCLIP [18] or additional supervision terms such as text augmentation [40], masked language modeling [23] and memory queue, our MCD achieves state-of-the-art performance." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 611, + 545, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 611, + 545, + 696 + ], + "spans": [ + { + "bbox": [ + 304, + 611, + 545, + 696 + ], + "type": "text", + "content": "Linear Probing. To implement linear probe evaluation, we follow CLIP [32] to train a logistic regression classifier on the frozen visual features extracted by the image encoder " + }, + { + "bbox": [ + 304, + 611, + 545, + 696 + ], + "type": "inline_equation", + "content": "f_{I}" + }, + { + "bbox": [ + 304, + 611, + 545, + 696 + ], + "type": "text", + "content": ". Specifically, we train the logistic regression classifier using L-BFGS algorithm provided by scikit-learn with maximum 1,000 iterations, and report the corresponding metric for each dataset4. Parameters for L2 regularization are" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 316, + 702, + 541, + 714 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 702, + 541, + 714 + ], + "spans": [ + { + "bbox": [ + 316, + 702, + 541, + 714 + ], + "type": "text", + "content": "4https://github.com/facebookresearch/SLIP/blob/main/mainlinear.py" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 57, + 692, + 200, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 692, + 200, + 703 + ], + "spans": [ + { + "bbox": [ + 57, + 692, + 200, + 703 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 57, + 692, + 200, + 703 + ], + "type": "text", + "content": "https://github.com/facebookresearch/SLIP" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 59, + 703, + 192, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 703, + 192, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 703, + 192, + 713 + ], + "type": "text", + "content": "3https://github.com/Sense-GVT/DeCLIP" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2568" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 70, + 545, + 272 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 545, + 272 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 545, + 272 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 545, + 272 + ], + "type": "table", + "html": "
MethodVision EncoderOxford PetsCIFAR-10CIFAR-100SUN397Food-101FlowersCarsCaltech-101AircraftDTDImageNetAverage
OxfordCIFAR-10OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-100OxfordCIFAR-10Oxford
Zero-shot Classification:
CLIP [32]19.462.333.640.233.76.32.155.41.416.931.327.5
SLIP [27]28.372.245.345.144.76.82.965.91.921.838.333.9
DeCLIP [23]ViT-B/3230.272.139.751.646.97.13.970.12.524.241.235.4
UniCLIP [18]32.578.647.250.448.78.13.473.02.823.342.837.3
MCD (Ours)40.080.349.655.354.07.94.573.23.030.544.740.2
Linear Probing:
CLIP [32]71.289.272.170.171.493.234.984.329.760.961.167.1
SLIP [27]75.490.575.373.577.196.143.087.234.171.168.171.9
DeCLIP [23]ViT-B/3276.588.671.675.979.396.742.688.032.669.169.271.8
UniCLIP [18]83.192.578.277.081.397.149.888.936.272.870.875.2
MCD (Ours)85.692.779.377.681.797.146.989.536.674.171.375.7
", + "image_path": "8edb2fc566eb09511cbc309231a8e8a27d84421c64b0d645417045e2295733a0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 274, + 545, + 298 + ], + "lines": [ + { + "bbox": [ + 46, + 274, + 545, + 298 + ], + "spans": [ + { + "bbox": [ + 46, + 274, + 545, + 298 + ], + "type": "text", + "content": "Table 1. Zero-shot image classification/linear probing performance on 11 downstream datasets with YFCC15M pretrained models. Note that DeCLIP [23] utilizes an external momentum queue while UniCLIP [18] features the augmentation encoder during training." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 316, + 289, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 316, + 289, + 413 + ], + "spans": [ + { + "bbox": [ + 46, + 316, + 289, + 413 + ], + "type": "text", + "content": "determined using hyperparameter sweep on the validation sets. Standard cropping and flipping augmentations [35] are used for linear probing. The bottom section of Tab. 1 reports linear classification performances on the 11 downstream datasets. Our proposed approach, MCD, has consistently outperformed previous baseline methods in zero-shot classification across multiple datasets, with only one exception." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 431, + 289, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 431, + 289, + 574 + ], + "spans": [ + { + "bbox": [ + 46, + 431, + 289, + 574 + ], + "type": "text", + "content": "Image-Text Retrieval. For multi-modal evaluations, we test both the zero-shot and fine-tuned image-text (and text-image) retrieval on Flickr30k and COCO Captions benchmarks. Image-text pairs are ranked according to their similarity scores. Tab. 2 shows the performance for image-text retrieval tasks of MCD pretrained on YFCC15M dataset. Our MCD outperforms all state-of-the-art baselines across every measure with a considerable margin. By incorporating a log-ratio loss with metric learning characteristics into the CLIP framework, our proposed approach has achieved significant improvements in image-text retrieval performance." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "Vision-Language Compositionality. To conduct a thorough analysis of multimodal representation learning, we assess the performance of our model using the SugarCrepe [12] dataset. This dataset serves as a de-biased benchmark specifically designed for evaluating the compositionality aspect of vision-language models. SugarCrepe introduces a set of challenging negative captions for COCO image-text pairs by replacing, swapping, or adding certain concepts to the ground truth caption, and gauge the model's capability to discern the positive from its distractor. Tab. 3" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 316, + 547, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 316, + 547, + 437 + ], + "spans": [ + { + "bbox": [ + 304, + 316, + 547, + 437 + ], + "type": "text", + "content": "summarizes the result, showcasing the performance of various models pretrained on the YFCC15M dataset. Our findings demonstrate that the MCD exhibits significantly better compositionality compared to prior methods. This improved performance is attributed to leveraging augmentations with proper handling for misalignment arising from these augmentations. While other methods often show improved performance over CLIP baseline, adopting augmentations without meticulous management of misalignment cannot maximize their utility." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 445, + 500, + 458 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 445, + 500, + 458 + ], + "spans": [ + { + "bbox": [ + 305, + 445, + 500, + 458 + ], + "type": "text", + "content": "5.3. MCD Pretraining on CC3M Dataset" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 464, + 545, + 608 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 464, + 545, + 608 + ], + "spans": [ + { + "bbox": [ + 304, + 464, + 545, + 608 + ], + "type": "text", + "content": "In this section, we compare MCD against other state-of-the-art Contrastive Language-Image Pretraining approaches [32, 27, 23]. All models are pretrained on the CC3M dataset with a learning rate 5e-4 for 40 epochs" + }, + { + "bbox": [ + 304, + 464, + 545, + 608 + ], + "type": "inline_equation", + "content": "^{5}" + }, + { + "bbox": [ + 304, + 464, + 545, + 608 + ], + "type": "text", + "content": ". Tab. 4 shows the ImageNet zero-shot results of MCD with other CLIP variants. MCD outperforms all CLIP variants without external training sources such as Nearest Neighbor supervision with large memory queues (NNS) or augmentation information during training (AUG). Furthermore, MCD does not require any additional parameters for the SSL projection layer [27, 23] or additional network for augmentation-aware feature embedding [18]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 615, + 400, + 628 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 615, + 400, + 628 + ], + "spans": [ + { + "bbox": [ + 306, + 615, + 400, + 628 + ], + "type": "text", + "content": "5.4. Ablation Study" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 634, + 545, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 634, + 545, + 696 + ], + "spans": [ + { + "bbox": [ + 304, + 634, + 545, + 696 + ], + "type": "text", + "content": "This section presents ablation studies to evaluate the contribution of each component in our proposed approach, MCD, towards the final performance. To this end, we pretrain all models on the YFCC15M dataset and evaluate them using zero-shot learning on the Imagenet-1k validation set." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 315, + 702, + 542, + 714 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 702, + 542, + 714 + ], + "spans": [ + { + "bbox": [ + 315, + 702, + 542, + 714 + ], + "type": "text", + "content": "5 More detailed training configuration will be provided in supplement." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2569" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 70, + 547, + 274 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 547, + 274 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 547, + 274 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 547, + 274 + ], + "type": "table", + "html": "
MethodImage-to-text retrievalText-to-image retrieval
Flickr30kCOCO CaptionsFlickr30kCOCO Captions
R@1R@5R@10R@1R@5R@10R@1R@5R@10R@1R@5R@10
Zero-shot retrieval:
CLIP [32]34.963.975.920.843.955.723.447.258.913.031.742.7
SLIP [27]47.876.585.927.752.663.932.358.768.818.239.251.0
DeCLIP [23]51.480.288.928.353.264.534.360.370.718.439.651.4
UniCLIP [18]52.381.689.032.057.769.234.862.072.020.243.254.4
MCD (Ours)57.682.691.132.358.771.236.464.874.120.743.555.3
Fine-tuned retrieval
CLIP [32]58.384.891.536.165.076.443.171.180.324.951.764.1
SLIP [27]69.690.495.745.074.083.052.179.486.931.659.571.3
DeCLIP [23]75.693.096.648.777.386.257.883.390.334.263.174.6
UniCLIP [18]78.194.997.754.580.989.161.086.091.938.067.278.0
MCD (Ours)79.395.298.055.681.289.563.187.292.338.267.478.5
", + "image_path": "b01dbb8d35fa4a293d1ed383f47e2e1155c734c101d0404583fa74f7d3919195.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 317, + 288, + 396 + ], + "blocks": [ + { + "bbox": [ + 46, + 277, + 547, + 300 + ], + "lines": [ + { + "bbox": [ + 46, + 277, + 547, + 300 + ], + "spans": [ + { + "bbox": [ + 46, + 277, + 547, + 300 + ], + "type": "text", + "content": "Table 2. Zero-shot & Fine-tuned image-text retrieval on the test splits of Flickr30k and COCO Captions with models pre-trained on YFCC15M. ViT-B/32 is used for all setup." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 317, + 288, + 396 + ], + "lines": [ + { + "bbox": [ + 48, + 317, + 288, + 396 + ], + "spans": [ + { + "bbox": [ + 48, + 317, + 288, + 396 + ], + "type": "table", + "html": "
MethodAug.MisalignReplaceSwapAdd
CLIP [32]N/A73.659.569.4
SLIP [27]✓N/A74.758.669.1
DeCLIP [23]✓Disregard74.558.266.8
UniCLIP [18]✓fA75.558.470.4
MCD (Ours)✓LD76.261.571.7
", + "image_path": "e0386c05b45026ee1f91d56a746554a12037e8cfb9f2fe578ee30da35eec801c.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 48, + 487, + 290, + 564 + ], + "blocks": [ + { + "bbox": [ + 46, + 399, + 288, + 478 + ], + "lines": [ + { + "bbox": [ + 46, + 399, + 288, + 478 + ], + "spans": [ + { + "bbox": [ + 46, + 399, + 288, + 478 + ], + "type": "text", + "content": "Table 3. Evaluation on SugarCrepe [12]. All models were pretrained on YFCC15M with ViT-B/32 backbone. Models except CLIP involve random image augmentations (Aug.) with different schemes for dealing with image-text misalignments (Misalign). While previous methods either disregard the issue [23] or introduce an additional augmentation encoder " + }, + { + "bbox": [ + 46, + 399, + 288, + 478 + ], + "type": "inline_equation", + "content": "(f_{A})" + }, + { + "bbox": [ + 46, + 399, + 288, + 478 + ], + "type": "text", + "content": " [18], MCD manages to harness the misalignment for the distillation loss " + }, + { + "bbox": [ + 46, + 399, + 288, + 478 + ], + "type": "inline_equation", + "content": "(\\mathcal{L}_{\\mathrm{D}})" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 487, + 290, + 564 + ], + "lines": [ + { + "bbox": [ + 48, + 487, + 290, + 564 + ], + "spans": [ + { + "bbox": [ + 48, + 487, + 290, + 564 + ], + "type": "table", + "html": "
MethodEncoderSSLEXTTop1(%)
CLIP [32]--19.6
SLIP [27]SimCLR [3]-23.2
DeCLIP [23]ViT-B/16SimSiam [5]NNS25.4
UniCLIP [18]MP-NCE [18]AUG27.8
MCD (Ours)MP-NCE [18]-28.2
", + "image_path": "7f6ca482462e143aa61b1dee8624083b36f6479ddb29b3f158411f3990c1cf5c.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "content": "Specifically, we implement the MP-NCE loss without augmentation encoding, which results in an accuracy of 39.6. Our results in Tab. 5 demonstrate that each loss component in MCD has a positive impact on the final performance, leading to an overall improvement in accuracy. These find" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 309, + 317, + 545, + 385 + ], + "blocks": [ + { + "bbox": [ + 46, + 567, + 287, + 634 + ], + "lines": [ + { + "bbox": [ + 46, + 567, + 287, + 634 + ], + "spans": [ + { + "bbox": [ + 46, + 567, + 287, + 634 + ], + "type": "text", + "content": "Table 4. ImageNet-1k Top 1 zero shot accuracy with models pretrained on CC3M dataset. SSL denotes the vision self-supervision term used in each model and EXT denotes external sources involved during training. NNS is nearest neighbor supervision using a separate memory queue, and AUG is the vectorized information of each random augmentation conducted during training." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 317, + 545, + 385 + ], + "lines": [ + { + "bbox": [ + 309, + 317, + 545, + 385 + ], + "spans": [ + { + "bbox": [ + 309, + 317, + 545, + 385 + ], + "type": "table", + "html": "
\\( \\mathcal{L}^{\\text{base}} \\)\\( f_A \\)\\( \\mathcal{L}^{\\text{pos}} \\)\\( \\mathcal{L}^{\\text{neg}} \\)\\( \\mathcal{L}^{\\text{noisy}} \\)Top1 Acc (%)
(a)✓39.6
(b)✓✓42.8
(c)✓✓43.9
(d)✓✓✓44.3
(e)✓✓✓✓44.7
", + "image_path": "74dc79f7e8c5f73b6de8932772a352475ac9716fca76208dfcc85be1a203a9c1.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "lines": [ + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "spans": [ + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "text", + "content": "Table 5. Ablation study on ImageNet-1k Top 1 zero shot accuracy for vision-language pretraining for each loss components of MCD. All models were pretrained with a ViT-B/32 backbone with a basic contrastive loss " + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^C" + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "text", + "content": " in Eq (5) and MLM loss in Eq (11), which we abbreviate as " + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^{\\mathrm{base}}" + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "text", + "content": ". All " + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^{\\mathrm{pos}}" + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^{\\mathrm{neg}}" + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^{\\mathrm{noisy}}" + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "text", + "content": " shows a consistent gain in zero-shot performance. " + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "inline_equation", + "content": "f_{A}" + }, + { + "bbox": [ + 304, + 388, + 547, + 467 + ], + "type": "text", + "content": " denotes the augmentation encoder, making (b) analogous to UniCLIP [18]." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 480, + 545, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 480, + 545, + 566 + ], + "spans": [ + { + "bbox": [ + 304, + 480, + 545, + 566 + ], + "type": "text", + "content": "ings highlight the importance of each component in our proposed approach and validate its effectiveness in improving the zero-shot classification performance. Note that MCD outperforms (b) (i.e., UniCLIP) that explicitly includes the augmentation information during training with only " + }, + { + "bbox": [ + 304, + 480, + 545, + 566 + ], + "type": "inline_equation", + "content": "\\mathcal{L}^{\\mathrm{pos}}" + }, + { + "bbox": [ + 304, + 480, + 545, + 566 + ], + "type": "text", + "content": ", showing the effectiveness of harnessing the misalignments that occur during random image augmentation for training." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 575, + 379, + 588 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 575, + 379, + 588 + ], + "spans": [ + { + "bbox": [ + 306, + 575, + 379, + 588 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 595, + 547, + 668 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 595, + 547, + 668 + ], + "spans": [ + { + "bbox": [ + 304, + 595, + 547, + 668 + ], + "type": "text", + "content": "We propose MCD, a new training strategy for dealing with misalignments occurred by random image augmentations under visual-language pretraining. Our novel distillation formulation enables data-efficient training under Contrastive Language-Image Pretraining. Future works will include extending MCD frameworks to other modalities." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "text", + "content": "2570" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Alex Andonian, Shixing Chen, and Raffay Hamid. 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International Journal of Computer Vision, 119(1):3-22, 2016." + } + ] + } + ], + "index": 16 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "2572" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Mitigating Adversarial Vulnerability through Causal Parameter Estimation by Adversarial Double Machine Learning/720877af-e8c3-460a-ab3f-fbddf4379306_content_list.json b/2023/Mitigating Adversarial Vulnerability through Causal Parameter Estimation by Adversarial Double Machine Learning/720877af-e8c3-460a-ab3f-fbddf4379306_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..3e5f919125d85fd54aa5f6a5def1871b7ef88a8b --- /dev/null +++ b/2023/Mitigating Adversarial Vulnerability through Causal Parameter Estimation by Adversarial Double Machine Learning/720877af-e8c3-460a-ab3f-fbddf4379306_content_list.json @@ -0,0 +1,1608 @@ +[ + { + "type": "text", + "text": "Mitigating Adversarial Vulnerability through Causal Parameter Estimation by Adversarial Double Machine Learning", + "text_level": 1, + "bbox": [ + 104, + 128, + 867, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Byung-Kwan Lee\\*, Junho Kim\\*, Yong Man Ro† \nImage and Video Systems Lab, School of Electrical Engineering, KAIST, South Korea \n{leebk, arkimjh, ymro}@kaist.ac.kr", + "bbox": [ + 142, + 202, + 826, + 256 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 291, + 313, + 306 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Adversarial examples derived from deliberately crafted perturbations on visual inputs can easily harm decision process of deep neural networks. To prevent potential threats, various adversarial training-based defense methods have grown rapidly and become a de facto standard approach for robustness. Despite recent competitive achievements, we observe that adversarial vulnerability varies across targets and certain vulnerabilities remain prevalent. Intriguingly, such peculiar phenomenon cannot be relieved even with deeper architectures and advanced defense methods. To address this issue, in this paper, we introduce a causal approach called Adversarial Double Machine Learning (ADML), which allows us to quantify the degree of adversarial vulnerability for network predictions and capture the effect of treatments on outcome of interests. ADML can directly estimate causal parameter of adversarial perturbations per se and mitigate negative effects that can potentially damage robustness, bridging a causal perspective into the adversarial vulnerability. Through extensive experiments on various CNN and Transformer architectures, we corroborate that ADML improves adversarial robustness with large margins and relieve the empirical observation.", + "bbox": [ + 75, + 323, + 473, + 656 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 700, + 209, + 715 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Along with the progressive developments of deep neural networks (DNNs) [17, 10, 2], an aspect of AI safety comes into a prominence in various computer vision research [45, 64, 12, 19]. Especially, adversarial examples [50, 15, 30] are known as potential threats on AI systems. With deliberately crafted perturbations on the visual inputs, adversarial examples are hardly distinguishable to human observers, but they easily result in misleading decision process of DNNs. Such adversarial vulnerability provokes weak reliability of inference process of DNNs and", + "bbox": [ + 75, + 726, + 468, + 877 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ded32df863e6df671fb766df832c0fc85aa35d9430c48613ac2f9185fb117fc0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 500, + 289, + 888, + 419 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b047ba990555ccaa161b87d7b7d8c128369ab598d7220291d8c020397099c8ef.jpg", + "image_caption": [ + "(b) Adversarial Defense Methods", + "Figure 1. The comparison of adversarial robustness along target classes with respect to (a) Network Architectures and (b) Adversarial Defense Methods on CIFAR-10 [27]. Note that, the distribution of adversarial robustness is consistent along both criteria." + ], + "image_footnote": [], + "bbox": [ + 506, + 415, + 875, + 542 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "discourages AI adoption to the safety critical areas [54, 44].", + "bbox": [ + 500, + 625, + 890, + 640 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In order to achieve robust and trustworthy DNNs from adversarial perturbation, previous methods [33, 28, 3, 62, 55, 58, 8] have delved into developing various adversarial attack and defense algorithms in the sense of cat-and-mouse game. As a seminal work, Madry et al. [33] have paved the way for obtaining robust network through adversarial training (AT) regarded as an ultimate augmentation training [52] with respect to adversarial examples. Based on its effectiveness, various subsequent works [62, 55, 58, 63, 39, 25] have investigated it to further enhance adversarial robustness.", + "bbox": [ + 496, + 641, + 892, + 792 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Although several AT-based defense methods have become a de facto standard due to their competitive adversarial robustness, we found an intriguing property of the current defense methods. As in Figure 1, we identify that the adversarial robustness for the each target class significantly varies with a large gap, and this phenomenon equally happens in the course of (a) network architectures and (b)", + "bbox": [ + 496, + 795, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Equal contribution. † Corresponding author.", + "bbox": [ + 94, + 886, + 334, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "4499", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/02dbee48291103d15cd24f8d88fee461f847db0f55d52a5470d18d0b3f6fe53a.jpg", + "image_caption": [ + "(a) AT Causal Diagram" + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 250, + 215 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/99adc6bb6951d2708d06870e307ee30662f0b6aaba9fac10b269bd4e25efd149.jpg", + "image_caption": [ + "(b) Training Robust Network", + "Figure 2. Overview of canonical adversarial training procedure for robust network and its causal diagram." + ], + "image_footnote": [], + "bbox": [ + 263, + 89, + 464, + 218 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "various AT-based defense methods. In addition, we would like to point out that the robustness of particular target is still severely vulnerable than others even with advanced architectures [10, 51, 31] and defense methods [62, 55, 58]. We argue that such phenomenon is derived from the current learning strategies of AT-based defense methods that lacks of understanding causal relations between the visual inputs and predictions. When considering AT methods as the ultimate augmentation [52], current methods rely solely on strengthening the correlation between adversarial examples and target classes through canonical objectives that improve robustness. To fundamentally address such vulnerability and understand the causal relation, we need to quantify the degree of vulnerability (i.e., causal parameter) and should mitigate its direct effects to the network predictions.", + "bbox": [ + 75, + 272, + 468, + 498 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Accordingly, we investigate the AT-based defense methods in a causal viewpoint and propose a way of precisely estimating causal parameter between adversarial examples and their predictions, namely Adversarial Double Machine Learning (ADML). We first represent a causal diagram of AT-based methods and interpret it as a generating process of robust classifiers as illustrated in Figure 2. Regarding standard adversarial training [33] as an optimizing procedure for the robust network parameters $f$ with respect to the worst perturbations $t$ , we can instantiate a generation $g^{1}$ as an adversarial attack of projected gradient descent (PGD) [33] for the given clean examples $x$ .", + "bbox": [ + 75, + 500, + 468, + 680 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Then, our research question is how to quantitatively compute the causal parameter $\\theta$ between the perturbations $t$ and target classes $y$ , and identify the causal effects on outcome of our interests. Through double machine learning (DML) [5], widely studied as a powerful causal estimator [4, 7, 13, 20, 21] for the given two regression models, we can establish an initial research point of estimating causal parameter of adversarial perturbation with theoretical background. However, it is difficult to directly estimate $\\theta$ in the high-dimensional manifolds, especially for DNNs. In this paper, we shed some lights on identifying causal parameter of the perturbations while theoretically bridging the gap be", + "bbox": [ + 75, + 681, + 468, + 863 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tween causal inference and adversarial robustness. Then, by minimizing the magnitude of the estimated causal parameter, we essentially lessen negative causal effects of adversarial vulnerability, and consequently acquire robust network with the aforementioned phenomenon alleviated.", + "bbox": [ + 500, + 90, + 890, + 166 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To corroborate the effectiveness of ADML on adversarial robustness, we set extensive experiments with four publicly available datasets [27, 29, 9]. Our experiments include various convolutional neural network architectures (CNNs), as well as Transformer architectures that have drawn great attention in both vision and language tasks [53, 10, 66, 65] yet relatively lack of being studied in adversarial research.", + "bbox": [ + 496, + 167, + 890, + 271 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our contributions can be summarized as follows:", + "bbox": [ + 517, + 272, + 844, + 285 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We present an empirical evidence that despite the recent advances in AT-based defenses, fundamentally adversarial vulnerability still remains across various architectures and defense algorithms.", + "- Bridging a causal perspective into adversary, we propose Adversarial Double Machine Learning (ADML), estimating causal parameter in adversarial examples and mitigating its causal effects damaging robustness.", + "- Through extensive experiments and analyses on various CNN and Transformer architectures, we corroborate intensive robustness of our proposed method with the phenomenon alleviated." + ], + "bbox": [ + 517, + 287, + 890, + 468 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Background and Related Work", + "text_level": 1, + "bbox": [ + 500, + 481, + 784, + 498 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Notation. We deal with DNNs for classification as in Figure 2, represented by $f: \\mathcal{X} \\to \\mathcal{Y}$ , where $\\mathcal{X}$ and $\\mathcal{Y}$ denote image and probability space, respectively. Let $x \\in \\mathcal{X}$ denote clean images and $y \\in \\mathcal{Y}$ indicate (one-hot) target classes corresponding to the images. Adversarial examples $x_{\\mathrm{adv}}$ are generated by adversarial perturbations $t$ through DNNs, such that $x_{\\mathrm{adv}} = x + t$ . Here, the perturbations are carefully created through the following formulation:", + "bbox": [ + 496, + 506, + 890, + 627 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\n\\max _ {\\| t \\| _ {\\infty} \\leq \\gamma} \\mathcal {L} _ {\\mathrm {C E}} (f (x + t), y), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 609, + 638, + 890, + 662 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{\\mathrm{CE}}$ represents a pre-defined loss such as cross-entropy for classification task. We regard adversarial perturbations $t$ as $l_{\\infty}$ perturbation within $\\gamma$ -ball (i.e., perturbation budget). Here, $\\| \\cdot \\|_{\\infty}$ describes $l_{\\infty}$ perturbation magnitude.", + "bbox": [ + 496, + 672, + 890, + 734 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Adversarial Training", + "text_level": 1, + "bbox": [ + 500, + 741, + 697, + 757 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "After several works [50, 15, 24] have found that human-imperceptible adversarial examples easily break network predictions, Madry et al. [33] have thrown a fundamental question: \"How can we make models robust to adversarial examples with security guarantee?\" To answer it, they have used the concept of empirical risk minimization (ERM) serving as a recipe to obtain classifiers with small population risk. Thanks to its reliable guarantee, they have consolidated it on the purpose of adversarial defense and", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_footnote", + "text": "$^{1}$ Selecting $g$ as proper perturbations varies according to domain specific tasks (e.g., rotations, translations [11], or spatial deformations [59]).", + "bbox": [ + 76, + 875, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "4500", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "accomplished the yardstick of adversarial training. The key factor of its achievement is regarding adversarial training as min-max optimization in a perspective of saddle point problem, which can be written as follows:", + "bbox": [ + 75, + 90, + 468, + 151 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {f} \\mathbb {E} _ {(x, y) \\sim \\mathcal {D}} \\left[ \\max _ {\\| t \\| _ {\\infty} \\leq \\gamma} \\mathcal {L} _ {\\mathrm {C E}} (f (x + t), y) \\right], \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 127, + 159, + 468, + 195 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathcal{D}$ denotes a set of data samples $(x,y)$ . Here, they have presented an adversarial attack based on PGD to powerfully behave inner-maximization on Eq. (2), which is an ultimate first-order adversary with a multi-step variant of fast gradient sign method [28] by adding a random perturbation around the clean images $x$ .", + "bbox": [ + 75, + 203, + 468, + 294 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "According to its impact, various adversarial training methods [33, 62, 55, 58] have grown exponentially and become de facto standards robustifying DNNs against adversarial perturbation. Zhang et al. [62] have pointed out the trade-off between clean accuracy and adversarial robustness, and reduced the gap between clean errors and robust errors. Wang et al. [55] have claimed that all of clean images are used to perform both inner-maximization and outer-minimization process in Eq. (2), irrespective of whether they are correctly classified or not. Thus, they have focused on misclassified clean images prone to be easily overlooked during adversarial training and demonstrated their significant impacts on the robustness by incorporating an explicit regularizer for them. Wu et al. [58] have studied loss landscapes with respect to network parameters and shown a positive correlation between the flatness of the parameter loss landscapes and the robustness. In the end, they have presented a double-perturbation mechanism where clean images are perturbed, while network parameters are simultaneously perturbed as well.", + "bbox": [ + 75, + 294, + 468, + 595 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "On the other hand, we plunge into investigating where adversarial vulnerability comes from and observe that the vulnerability varies along target classes, and it significantly deteriorates network predictions. Further, we find that this phenomenon commonly happens across various network architectures and advanced defense methods. To relieve such peculiarity, we deploy double machine learning (DML) that helps to capture how treatments (i.e., adversarial perturbations) affect outcomes of our interests (i.e., network predictions), which is one of the powerful causal inference methods. After we concisely explicate the necessary background of DML, we will bridge it to the adversary in Sec. (3).", + "bbox": [ + 75, + 597, + 468, + 779 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Double Machine Learning", + "text_level": 1, + "bbox": [ + 76, + 786, + 313, + 803 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In data science and econometrics, one of the fundamental problems is how to measure causality between treatments $t$ and outcomes of our interest $y$ among high-dimensional observational data samples (see Figure 2) to identify data generating process. At a first glance, it seems simple to compute their causality, but we should keep in mind the", + "bbox": [ + 75, + 810, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "possibility for the existence of covariates $x$ affecting both treatments and outcomes. In other words, for example, if one may want to know the causal effects of drug dosage $t$ to blood pressure changes $y$ , one needs to collect observational data with respect to a variety of patients characteristics and their clinical histories $x$ , so as not to fall into biased environment. In reality, though, it is impossible to collect observational data including all covariates concerning treatments and outcomes, so it is not an easy problem to catch genuine causality under the unknown covariates $x$ . Therefore, there has been a growing demand for robustly predicting the unbiased causal relation, despite with the limited data samples.", + "bbox": [ + 496, + 90, + 890, + 271 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Recently, the advent of double machine learning (DML) [5] enables us to clarify the causality between treatments $t$ and outcomes $y$ , when two regression models are given. The formulation of initial DML can be written as:", + "bbox": [ + 496, + 272, + 890, + 333 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ny = f (x) + \\theta t + u, \\quad (\\mathbb {E} [ u \\mid x, t ] = 0) \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 342, + 890, + 366 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nt = g (x) + v, \\quad (\\mathbb {E} [ v \\mid x ] = 0)\n$$\n", + "text_format": "latex", + "bbox": [ + 568, + 361, + 807, + 376 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\theta \\in \\mathbb{R}$ denotes causal parameter representing causal relation between $t \\in \\mathbb{R}^d$ and $y \\in \\mathbb{R}^d$ . In addition, $f$ indicates one regression model projecting covariates to outcome domain, and $g$ denotes another regression model generating treatments $t$ . In the sense that two regression models $f$ and $g$ are not main interest of DML, they are called as nuisance parameters to estimate the causal parameter $\\theta$ . Note that, early DML assumes the problem setup is proceeded in partially linear settings as a shape of Robinson-style [42] described in Eq. (3), where \"partially\" literally means that treatments $t \\in \\mathbb{R}^d$ are linearly connected to outcome $y \\in \\mathbb{R}^d$ , while covariates $x$ are not. In addition, it is supposed that the conditional expected error of $u \\in \\mathbb{R}^d$ and $v \\in \\mathbb{R}^d$ equals to zero vector $0 \\in \\mathbb{R}^d$ .", + "bbox": [ + 496, + 386, + 890, + 595 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To obtain the causal parameter $\\theta$ , Chernozhukov et al. [5] have provided a solution of estimating the causal parameter such that $\\hat{\\theta} = (y - \\mathbb{E}[y \\mid x]) \\cdot v / \\|v\\|^2$ which satisfies Neyman-orthogonality [35, 34]. It makes $\\hat{\\theta}$ invariant to their erroneous of two nuisance parameters with the variance of causal parameter reduced. Furthermore, they have addressed a chronic problem that $\\theta$ is only accessible when the two nuisance parameters are in a class of Donsker condition, where deep neural networks are not included in that condition. They have theoretically demonstrated sample-splitting plus cross-fitting can effectively relax Donsker condition and allow a broad array of modern ML methods [5] to compute unbiased causal parameter $\\theta$ .", + "bbox": [ + 496, + 597, + 890, + 794 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Following the principle, they first split the data samples $\\{\\mathcal{D}_1,\\mathcal{D}_2\\} \\sim \\mathcal{D}$ and divided the process of causal inference into two steps: (a) training two nuisance parameters $f$ and $g$ with $\\mathcal{D}_1$ , (b) estimating unbiased $\\theta$ with $\\mathcal{D}_2$ . Here, data samples $\\mathcal{D}_2$ used to estimate unbiased causal parameters should not be overlapped with $\\mathcal{D}_1$ utilized to train the nuisance parameters. To make copious combinations, they", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "4501", + "bbox": [ + 480, + 944, + 513, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": " swapped the role of partitioned data samples $\\mathcal{D}_1 \\leftrightarrows \\mathcal{D}_2$ or repeatedly split $\\mathcal{D}$ . Subsequently, they have performed cross-fitting (e.g., $k$ -fold cross validation) by averaging the estimated causal parameters from various split samples.", + "bbox": [ + 75, + 90, + 468, + 151 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Along with the success of initial DML in partially linear settings, numerous variants [4, 7, 32, 14, 13, 26, 6] have emerged, and they have extended its initial nature to non-parametric settings with continuous treatments $t$ in order to capture more complicated non-linear causal relations in a debiased state. A non-parametric formulation [4] represents a more general problem setup of DML as follows:", + "bbox": [ + 75, + 152, + 470, + 257 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ny = f (x, t) + u, \\quad (\\mathbb {E} [ u \\mid x, t ] = 0) \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 266, + 468, + 291 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nt = g (x) + v, \\qquad (\\mathbb {E} [ v \\mid x ] = 0)\n$$\n", + "text_format": "latex", + "bbox": [ + 156, + 286, + 380, + 301 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where there is no explicit term for causal parameter $\\theta$ exhibiting causal relation between treatments $t$ and outcomes $y$ , compared to Eq. (3). Colangelo et al. [7] have introduced a way of estimating causal parameter $\\theta$ applicable to non-parametric settings with high-dimensional continuous treatments $t \\in \\mathcal{T}$ , which can be written as:", + "bbox": [ + 75, + 311, + 468, + 401 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\theta} = \\frac {\\partial}{\\partial t} \\mathbb {E} [ y \\mid \\operatorname {d o} (\\mathcal {T} = t) ]. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 189, + 407, + 468, + 439 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "They have utilized do-operator [37] commonly used in graphical causal models and intervened on treatments $t$ to compute an interventional expectation $\\mathbb{E}[y|\\mathrm{do}(\\mathcal{T} = t)]$ . It represents the expected outcome averaged from all the possible covariates for the given fixed treatments $t$ , such that $\\mathbb{E}[y|\\mathrm{do}(\\mathcal{T} = t)] = \\sum_{x\\in \\mathcal{X}}\\mathbb{E}[y|x,t]p(x)$ . Specifically, they have estimated causal parameter $\\theta$ by measuring how much the interventional expectation shifted, once they change the treatments slightly. Since the most important property of DML is Neyman-Orthogonality helping to robustly estimate the causal parameter, the interventional expectation should be also modified to satisfy the property [7, 23] of its invariance to nuisance parameters $f$ and $g$ . Its formulation can be written as follows (see details in Appendix A):", + "bbox": [ + 75, + 446, + 470, + 657 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {E} [ y \\mid \\operatorname {d o} (\\mathcal {T} = t) ] = \\mathbb {E} _ {\\mathcal {D} _ {t}} \\left[ f (x, t) + \\frac {y - f (x , t)}{p (\\mathcal {T} = t \\mid x)} \\right], \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 98, + 676, + 468, + 712 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{D}_t$ denotes a set of observational covariates and outcome samples for a fixed $t\\in \\mathcal{T}$ such that $(x,y)\\sim \\mathcal{D}_t$ , a sub-population of $\\mathcal{D}$ . Note that, $p(\\mathcal{T} = t|x)$ is related to treatment generator $g$ . Here, differentiating Eq. (6) enables us to acquire unbiased causal parameter in non-parametric settings with non-linear causal relation.", + "bbox": [ + 75, + 719, + 468, + 809 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In brief, DML captures unbiased causal relation between treatments $t$ and outcomes $y$ even with finite data samples, of which theoretical ground is (a) Neyman-Orthogonality for robustly estimated causal parameter despite undesirable outputs of nuisance parameters, and (b) sample-splitting plus cross-fitting for debiased causal parameters.", + "bbox": [ + 75, + 810, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3. Adversarial Double Machine Learning", + "text_level": 1, + "bbox": [ + 498, + 89, + 848, + 107 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Adversarial Data Generating Process", + "text_level": 1, + "bbox": [ + 500, + 114, + 821, + 130 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In general deep learning schemes, we have clean visual images $x \\in \\mathbb{R}^{hwc}$ and their corresponding target classes $y \\in \\mathbb{R}^d$ in our hand as a format of dataset, where $h, w, c$ denotes image resolution of height, width, channel, respectively, and $d$ denotes the number of classes. Thus, we do not need additional data generating process. For adversarial training, on the other hand, we need another data, which are adversarial perturbations generated from data samples $(x,y)$ as in Eq. (1). They are normally created by PGD [33] at every training iteration to make DNNs $f$ robust through min-max optimization game according to Eq. (2).", + "bbox": [ + 496, + 137, + 890, + 303 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Though, the more iterations of adversarial training, the fewer perturbations that impair network predictions. In other words, not all of the perturbations can corrupt network predictions among newly generated perturbations. Hence, we do not consider all of the perturbations as treatments but selectively define them as worst perturbations $t$ breaking network predictions, such that it satisfies $y \\neq f(x + t)$ , where we call $x_{\\mathrm{adv}} = x + t$ as worst examples. This is because our major goal is to catch actual adversarial vulnerability of DNNs, so that we do not tackle the perturbations incapable of harming network predictions.", + "bbox": [ + 496, + 304, + 890, + 469 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To access such worst perturbation, we choose perturbation generator $g$ as an adversarial attack of PGD according to standard adversarial training [33]. In addition, we pick the worst perturbations $t$ damaging network predictions among adversarial perturbations from the generator $g$ . In this way, we perform adversarial data generating process.", + "bbox": [ + 496, + 470, + 890, + 561 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Adversarial Problem Setup", + "text_level": 1, + "bbox": [ + 500, + 568, + 745, + 584 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In the nature of adversarial training, the worst perturbations $t$ are explicitly injected to clean images $x$ such that $x_{\\mathrm{adv}} = x + t$ , and these combined images are propagated into DNNs $f$ . Here, through this formulation as: $f(x + t) = f(x,t)$ , we connect DNNs for adversarial training and a nuisance parameter $f$ for non-parametric DML in Eq. (4). Fortunately, once we use Taylor expansion (with scalar-valued function for better understanding) and decompose $f$ by its input component as: $f(x + t) = f(x) + \\sum_{i=1}^{\\infty} t^{i} f^{(i)}(x) / i!$ , where $f^{(i)}$ indicates $i$ -th order derivative function, we can also express partially linear settings described in Eq. (3). That is, since adversarial examples start from the concept of \"additive noise\", both settings can exist at the same time in the scheme of adversarial training. From this reason, we build Adversarial Double Machine Learning (ADML):", + "bbox": [ + 496, + 590, + 890, + 818 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} y = f (x + t) = f (x) + \\theta \\bar {t} + u, \\quad (\\mathbb {E} [ u \\mid x, t ] = 0) \\tag {7} \\\\ t = g (x) + v, \\quad (\\mathbb {E} [ v \\mid x ] = 0) \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 823, + 890, + 859 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\bar{t}$ indicates Taylor-order matrix: $[t, t^2, \\dots]^T$ and $\\theta$ represents Taylor-coefficient matrix $\\left[\\frac{f^{(1)}(x)}{1!}, \\frac{f^{(2)}(x)}{2!}, \\dots\\right]$ (see", + "bbox": [ + 498, + 867, + 890, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "4502", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "strict mathematical verification in Appendix B).", + "bbox": [ + 76, + 90, + 393, + 104 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here, we explain what the conditional expected error of $u$ and $v$ in Eq. (7) means in adversarial training. The former $\\mathbb{E}[u|x,t] = 0$ implies the nature of adversarial training, which can be viewed as an ultimate augmentation robustifying DNNs, when infinite data population of $x$ and $t$ is given. Thus, it means network predictions become invariant in the end, despite the given worst perturbations. To implement it practically, we replace it with a mild assumption as $\\mathbb{E}[u|x,g(x)] = 0$ (see Appendix C) that signifies PGD-based perturbations are used to perform adversarial training. This is because we cannot always acquire worst perturbations $t$ using only PGD. For the latter $\\mathbb{E}[v|x] = 0$ , it represents PGD has capability of producing worst perturbations deviating network predictions during the training.", + "bbox": [ + 75, + 107, + 468, + 318 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Estimating Adversarily Causal Parameter", + "text_level": 1, + "bbox": [ + 76, + 330, + 449, + 345 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Aligned with Eq. (3), an explicit term of $\\theta$ is regarded as the causal parameter in our problem setup of ADML. We can now interpret that $\\theta$ is a causal factor to spur adversarial vulnerability, since its magnitude easily catalyzes the deviations from network predictions of clean images. Here, if it is possible to directly compute $\\theta$ over all data samples, we can finally handle adversarial vulnerability.", + "bbox": [ + 75, + 354, + 468, + 459 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Favorably, ADML follows both partially linear and nonparametric settings due to the concept of additive noise, thus we can employ the way of estimating causal parameter as in Eq. (5). The following formulation represents the estimated causal parameter $\\hat{\\theta}$ in ADML (see Appendix D). Note that, as we emphasized, sample-splitting plus cross-fitting must be applied to estimate unbiased causal parameter.", + "bbox": [ + 75, + 460, + 468, + 566 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\theta} = \\mathbb {E} _ {\\mathcal {D} _ {t}} \\left[ - \\left(\\frac {1}{p (\\mathcal {T} = t \\mid x)} - 1\\right) \\frac {\\partial}{\\partial t} f (x + t) \\right], \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 104, + 578, + 468, + 613 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\frac{\\partial}{\\partial t} f(x + t)$ indicates an input gradient for network predictions with respect to $t$ , and $p(\\mathcal{T} = t|x)$ represents a distribution of worst perturbation given clean images $x$ . Here, we cannot directly handle this distribution due to the presence of multiple unknown parameters required to define it. For that reason, we instead approximate it with the sharpening technique by incorporating the information on attacked confidence such that $p(\\mathcal{T} = t|x) \\approx \\mathbb{E}_{t'|x}[p(y_a|x,t')]$ (see Appendix E), where $y_{a}$ denotes attacked classes for the given worst perturbations $t$ . It implicitly means that the higher the attacked confidence, the higher the probability of finding worst perturbations.", + "bbox": [ + 75, + 625, + 468, + 806 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Aligned with the previous analysis [47] that show increasing magnitude of input gradient increases adversarial vulnerability, the magnitude of our causal parameter $|\\hat{\\theta}|$ also becomes huge due to $|\\hat{\\theta}| \\propto |\\frac{\\partial}{\\partial t} f(x + t)|$ . In parallel, Qin et al. [38] show the more ambiguous confident, the lower robustness (high vulnerability), and interestingly, the mag-", + "bbox": [ + 75, + 809, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/278a81867ac2b1a3578af499f67b14682bb887ab26d13d30433a2034dfa6bb62.jpg", + "table_caption": [ + "Algorithm 1 ADML" + ], + "table_footnote": [], + "table_body": "
Require: Data Samples D, Network f
1: for (x,y) ~ D do▷ Cross-Fitting
2: t' ← g(x)▷ PGD Attack
3: (x1,y1,t1'), (x2,y2,t2') ~ Split(x,y,t')
4: L_a ← L_Delphi(x1,y1,t1';f)▷ Mild Assumption
5: (xt2,yt2,t2) ← Select(y2 ≠ f(x2+t2')) ▷ Worst
6: j* ← arg maxj f_j(xt2+t2)▷ j: Class Index
7: τ ← 1/fj*(xt2+t2)-1▷ Balancing Ratio
8: L_b ← τL_CE(f(xt2+t2),yt2) + L_CE(f(xt2),yt2)
9: L_ADML ← L_a + L_b▷ ADML Loss
10: wf ← wf - α ∂/∂w_f L_ADML ▷ Weight Update (α: lr)
11: end for
", + "bbox": [ + 501, + 107, + 890, + 292 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "nitude of our causal parameter also $|\\hat{\\theta}|$ becomes large due to $|\\hat{\\theta}| \\propto |1 / \\mathbb{E}_{t' | x}[p(y_a | x, t')]|$ .", + "bbox": [ + 500, + 301, + 890, + 335 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Bringing such factors at once, $\\hat{\\theta}$ represents a weighted measurement of attacked confidence and their input gradients. Comprehensively, we can revisit that the network predictions of worst examples are easily flipped due to the following adversarial vulnerability: (a) ambiguous confidence around classification boundaries, or (b) high gradient magnitude amplifying the leverage of the perturbations. To improve the adversarial robustness of DNNs, it is essential to minimize the negative effects of causal parameters, which are combinatorial outcomes of the gradient and confidence.", + "bbox": [ + 496, + 337, + 890, + 488 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Mitigating Adversarial Vulnerability", + "text_level": 1, + "bbox": [ + 500, + 500, + 816, + 517 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "By deploying ADML, we propose a way of estimating causal parameter representing the degree of adversarial vulnerability that disturbs to predict the target classes. Then, our final goal is essentially to lessen its direct causal effect from adversarial perturbations in order to achieve robust networks. In detailed, alleviating their causal effect derived from $\\hat{\\theta}$ is the process of comprehensive reconstruction to focus more on vulnerable samples as we reflect their attacked confidence and gradients effects altogether.", + "bbox": [ + 496, + 523, + 890, + 660 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Accordingly, the very first way is naively reducing the magnitude of $\\hat{\\theta}$ to suppress adversarial vulnerability damaging the robustness. However, calculating $\\hat{\\theta}$ and minimizing its magnitude at every iteration is computationally striking because input gradient has huge dimension of $\\mathbb{R}^{dhwc}$ and getting its gradient inevitably needs to compute second-order gradient with its tremendous dimension. We instead approximate the partial derivative $\\frac{\\partial}{\\partial t}\\mathbb{E}[y|\\mathrm{do}(\\mathcal{T} = t)]$ and minimize its magnitude, which can be written as:", + "bbox": [ + 496, + 662, + 890, + 797 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {f} | \\hat {\\theta} | \\approx \\left| \\frac {\\mathbb {E} [ y \\mid \\operatorname {d o} (\\mathcal {T} = t) ] - \\mathbb {E} [ y \\mid \\operatorname {d o} (\\mathcal {T} = 0) ]}{t - 0} \\right|, \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 522, + 809, + 890, + 844 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where network parameters of DNNs $f$ are only dependent on the numerator, thus we engross the numerator only. Lastly, we redesign $\\mathbb{E}[y|\\mathrm{do}(\\mathcal{T} = t)]$ into the form of loss", + "bbox": [ + 496, + 854, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "4503", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/8ad57b2acbcb8d03d54c261188682ca29695deacf3170f4f81bfd403fc0e4eb2.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodCIFAR-10CIFAR-100Tiny-ImageNet
CleanBIMPGD\\(CW_{\\infty}\\)APDLRAACleanBIMPGD\\(CW_{\\infty}\\)APDLRAACleanBIMPGD\\(CW_{\\infty}\\)APDLRAA
VGG-16AT78.849.448.146.846.446.446.353.926.025.024.123.723.823.756.526.625.425.524.724.624.6
+ADML80.961.861.759.855.054.854.552.231.030.829.927.827.627.355.435.534.932.932.732.432.2
TRADES79.548.647.645.746.446.346.353.325.524.823.523.623.723.256.128.327.326.225.825.825.7
+ADML81.062.662.459.055.355.154.952.231.231.129.827.627.327.355.436.636.034.033.633.433.3
MART78.351.950.648.848.948.848.752.626.626.024.424.324.324.255.727.826.626.025.725.725.6
+ADML80.462.462.260.355.755.355.251.631.631.029.627.827.527.355.136.235.834.934.333.933.7
AWP77.253.952.650.151.451.151.052.130.229.327.528.728.528.356.931.631.029.429.929.829.7
+ADML80.264.764.661.858.057.757.552.333.833.531.329.729.529.054.536.636.134.634.533.833.7
ResNet-18AT83.153.351.950.849.949.749.559.127.126.325.425.325.325.161.531.030.129.528.828.928.8
+ADML84.561.160.858.556.756.255.656.431.630.929.528.428.227.857.335.935.533.534.734.734.6
TRADES83.353.052.050.950.950.850.758.527.626.826.225.925.925.860.432.031.030.229.729.629.5
+ADML84.062.361.959.556.756.655.957.331.731.630.028.828.528.058.437.036.033.335.034.134.0
MART82.554.152.851.351.550.850.858.127.726.725.525.425.125.060.631.030.229.829.029.029.0
+ADML84.163.362.958.756.856.456.257.432.131.730.228.928.828.557.136.636.033.635.133.933.8
AWP81.356.355.553.654.254.054.057.931.430.729.030.030.029.861.434.734.132.433.333.233.1
+ADML84.064.664.561.460.559.959.756.233.932.930.731.130.530.359.838.638.135.937.736.736.6
WideResNet-28-10AT86.755.453.453.451.351.351.261.928.827.427.126.026.025.964.832.731.231.130.130.130.0
+ADML87.561.760.758.856.456.355.858.932.932.631.329.629.229.162.143.543.141.141.940.440.2
TRADES86.055.353.753.651.651.651.461.929.128.527.826.726.826.764.232.531.631.430.029.929.8
+ADML88.562.961.959.657.657.656.661.633.333.031.530.030.129.663.143.542.941.041.440.340.2
MART86.456.054.353.451.651.651.561.628.326.726.425.325.425.364.232.931.831.830.730.530.5
+ADML88.362.160.959.656.756.656.259.633.032.931.630.329.929.661.842.842.640.340.739.038.9
AWP85.960.258.957.256.956.956.862.433.032.231.130.930.930.865.436.936.035.134.834.834.7
+ADML88.267.567.464.263.563.263.162.539.739.336.937.637.136.864.944.644.241.943.342.142.0
WideResNet-70-10AT88.156.654.855.052.853.052.864.128.427.327.426.026.425.665.334.933.433.932.232.232.1
+ADML88.961.561.461.056.556.356.063.330.029.228.826.926.726.461.037.737.436.933.833.032.9
TRADES87.756.354.755.053.453.353.363.328.727.827.926.626.226.065.734.432.633.031.531.531.4
+ADML89.163.963.362.759.059.659.063.431.230.830.327.527.127.061.840.239.538.836.135.535.4
MART88.057.455.555.452.852.852.663.228.727.527.525.826.325.665.433.832.532.431.331.331.2
+ADML88.561.761.360.856.756.856.662.330.130.029.429.329.128.763.241.841.040.237.736.636.5
AWP86.661.860.659.959.159.459.265.233.333.331.731.530.330.066.740.740.040.039.139.038.9
+ADML89.467.066.966.163.463.663.165.341.941.840.938.938.037.665.845.044.543.343.543.142.8
", + "bbox": [ + 94, + 60, + 870, + 460 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. Comparing adversarial robustness of various defence methods whether to the inclusion of ADML for CIFAR-10 [27], CIFAR-100 [27], Tiny-ImageNet [29] trained with VGG-16 [48], ResNet-18 [17], WideResNet-28-10 [61], and WideResNet-70-10 [61].", + "bbox": [ + 76, + 463, + 890, + 493 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "function used in deep learning and finally construct the objective function for ADML, of which formulation can be written as follows (see details in Appendix F):", + "bbox": [ + 75, + 505, + 470, + 551 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {f} \\mathbb {E} _ {\\mathcal {D} _ {t}} [ \\tau \\mathcal {L} _ {\\mathrm {C E}} (f (x + t), y) ] + \\mathbb {E} _ {\\mathcal {D} _ {0}} [ \\mathcal {L} _ {\\mathrm {C E}} (f (x), y) ], \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 560, + 468, + 585 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where we denote $\\tau = \\frac{1}{p(\\mathcal{T} = t|x)} - 1$ as balancing ratio. The current AT-based defenses use an equal weight \"1/n\" to loss for all data samples: $\\frac{1}{n}\\sum_{i=1}^{n}\\mathcal{L}_{\\text{Defense}}(x_i, y_i, t_i; f)$ because they presume all of perturbations have equal causal effect (successful attack) to change targets without realizing vulnerable samples. Whereas, ADML uses the balancing ratio $\\tau$ to adaptively focus on vulnerable samples by reweighting the loss. To realize ADML, we describe Algorithm 1 to explain further details, where $\\mathcal{L}_{\\text{Defense}}(x, y, t; f)$ indicates a main body of the loss function for AT-based defenses.", + "bbox": [ + 75, + 595, + 468, + 750 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiment", + "text_level": 1, + "bbox": [ + 76, + 762, + 202, + 779 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Implementation Details", + "text_level": 1, + "bbox": [ + 76, + 786, + 294, + 801 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Datasets & Networks. We conduct comprehensive experiments on various datasets and networks. For datasets, we use CIFAR-10 [27], CIFAR-100 [27], and two larger datasets: Tiny-[ImageNet [29] and ImageNet [9]. For networks, four CNN architectures: [48, 17, 61] and four Transformer architectures: [10, 51] are used.", + "bbox": [ + 75, + 809, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Adversarial Attacks. We adaptively set perturbation budget $\\gamma$ of adversarial attacks depending on the classification difficulty of the four datasets: 8/255 equally for CIFAR-10 [27] and CIFAR100 [27], 4/255 for Tiny-ImageNet [29], and 2/255 for ImageNet [9]. We prepare three standard attacks: BIM [28], PGD [33], $\\mathrm{CW}_{\\infty}$ [3], and three advanced attacks: AP (Auto-PGD: step size-free), DLR (Auto-DLR: shift and scaling invariant), AA (Auto-Attack: parameter-free), all of which are introduced by Francesco et al. [8]. PGD, AP, DLR have 30 steps with random starts, where PGD has step size $2.3 \\times \\frac{\\gamma}{30}$ , and AP, DLR both have momentum coefficient $\\rho = 0.75$ . $\\mathrm{CW}_{\\infty}$ uses PGD-based gradient clamping for $l_{\\infty}$ with CW objective [3] on $\\kappa = 0$ .", + "bbox": [ + 496, + 505, + 890, + 702 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Adversarial Defenses. We use four defense baselines with a standard baseline: AT [33] and three advanced defense baselines: TRADES [62], MART [55], AWP [58]. To fairly validate experiments, a perturbation generator, PGD [33] is equivalently used to generate adversarial examples for which we use the budget 8/255 and set 10 steps with $2.3 \\times \\frac{\\gamma}{10}$ step size in training. Especially, adversarially training Tiny-ImageNet [29] and ImageNet [9] is a computational burden, thus we employ fast adversarial training [57] with FGSM [15]. For training CNNs, we use SGD [43] with a learning rate of 0.5 scheduled by Cyclic [49] in 120 epochs and use early stopping to prevent overfitting [41]. For training Transformers, we use SGD [43] with a learn", + "bbox": [ + 496, + 703, + 892, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "4504", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/c941ff86c6b96f783b546f39798bbbc40dadc614db8e7d17dd6a9651d1f46929.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodCIFAR-10CIFAR-100Tiny-ImageNet
CleanBIMPGDCWAPDLRAACleanBIMPGDCW∞APDLRAACleanBIMPGDCW∞APDLRAA
VIT-S/16AT83.549.947.346.644.944.844.759.926.625.825.124.624.524.573.835.834.133.531.931.931.8
+ADML88.156.855.153.851.350.750.762.732.430.729.428.427.927.775.647.746.645.645.342.742.6
TRADES85.051.049.448.648.148.047.859.527.326.626.325.825.925.772.938.837.837.436.136.136.0
+ADML87.957.656.255.152.752.051.963.235.034.733.831.631.331.275.349.148.047.145.643.043.0
MART85.752.449.748.946.746.746.660.928.627.927.526.526.526.477.638.637.236.835.235.235.2
+ADML88.057.556.154.751.951.451.462.734.432.731.730.029.329.276.548.947.746.346.042.942.9
AWP84.954.252.351.650.149.949.961.129.629.028.127.727.727.678.141.039.338.737.337.337.2
+ADML88.057.054.353.350.149.649.564.434.834.133.031.330.630.576.647.546.444.944.742.542.4
VIT-B/16AT87.052.850.850.447.847.747.763.330.429.629.228.628.328.372.440.137.737.834.434.334.5
+ADML89.956.154.954.151.651.451.267.138.136.135.434.333.433.179.050.249.748.448.546.946.8
TRADES85.353.852.451.650.950.850.865.732.631.531.029.930.030.073.243.341.241.839.139.039.4
+ADML88.958.657.356.154.754.454.369.438.937.937.034.834.634.779.454.052.251.648.247.347.2
MART87.453.350.650.548.348.448.265.731.930.830.229.229.229.179.341.740.039.636.836.837.1
+ADML89.657.055.654.351.851.551.368.935.433.532.930.530.130.280.150.750.149.048.947.447.0
AWP87.454.952.951.949.849.849.766.833.431.731.330.330.230.278.745.042.242.239.539.439.7
+ADML90.459.156.756.653.853.652.870.037.736.135.633.332.832.979.350.849.748.048.046.045.8
DeT-S/16AT83.549.347.846.745.345.345.259.529.228.527.627.527.527.475.737.435.634.733.133.033.0
+ADML87.756.856.054.952.351.951.963.734.432.931.731.430.530.474.744.943.642.240.839.539.4
TRADES84.150.649.348.848.048.048.061.829.428.827.828.128.028.074.839.038.037.436.436.436.3
+ADML87.957.856.555.353.753.053.266.237.236.435.533.232.332.376.345.244.943.839.538.738.4
MART84.252.350.049.147.847.647.559.831.030.629.329.729.629.674.640.139.138.437.737.637.6
+ADML87.557.555.655.052.652.352.265.337.035.634.732.430.730.775.245.344.243.342.838.438.4
AWP82.353.552.351.550.550.450.460.731.831.430.231.030.030.075.441.740.939.839.039.139.0
+ADML86.755.953.252.650.650.550.564.739.438.136.835.734.534.575.449.447.646.545.742.842.8
DeT-B/16AT84.651.549.548.447.247.147.064.930.329.128.427.527.427.479.138.636.336.134.434.334.0
+ADML89.755.754.853.850.049.749.765.735.434.433.432.230.330.377.646.945.644.744.940.540.5
TRADES85.452.851.750.650.250.250.264.830.029.328.628.428.328.378.343.141.640.540.540.540.4
+ADML90.261.460.459.458.357.657.668.640.539.938.437.436.836.780.845.443.542.743.242.942.7
MART83.954.753.252.051.050.950.764.531.931.130.530.230.130.075.844.643.342.642.642.642.5
+ADML89.660.360.258.955.155.055.065.339.638.537.135.434.634.677.847.746.144.645.544.844.7
AWP83.354.153.152.451.851.651.565.432.331.530.430.230.130.176.642.841.440.742.842.842.7
+ADML88.959.057.356.454.053.853.769.739.438.337.335.234.434.480.351.250.248.949.448.148.0
", + "bbox": [ + 94, + 60, + 870, + 465 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/aa102ca2e3b13ddad21e04b27e2e4d96a5b57765246d90d3a17091462350d75e.jpg", + "table_caption": [ + "Table 2. Comparing adversarial robustness of various defence methods whether to the inclusion of ADML for CIFAR-10 [27], CIFAR-100 [27], Tiny-ImageNet [29] trained with ViT-S/16 [10], ViT-B/16 [10], DeiT-S/16 [51], and DeiT-B/16 [51]." + ], + "table_footnote": [ + "Table 3. Ablation study for the effects of sample-splitting plus cross-fitting (SS+CF) and Worst(W) / Non-Worst(NW) examples." + ], + "table_body": "
SS+CFWNWCIFAR-10Tiny-ImageNet
PGDCW∞DLRAAPGDCW∞DLRAA
VGG-16✓✓X61.759.854.854.434.932.932.432.2
✓✓✓52.349.448.948.825.424.924.224.2
✓X✓48.047.145.845.826.025.824.524.4
X✓X52.650.049.449.428.127.026.426.4
ResNet-18✓✓X60.858.556.255.635.533.534.734.6
✓✓✓51.750.149.549.234.932.432.732.7
✓X✓50.850.549.449.130.029.529.028.9
X✓X53.651.751.451.031.729.730.230.1
", + "bbox": [ + 81, + 506, + 460, + 642 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ing rate of 0.001 on the equal experimental setup of CNNs, where $224 \\times 224$ resolution is applied for all datasets and pretrained parameters on ImageNet-1k models are utilized.", + "bbox": [ + 80, + 679, + 467, + 722 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Training ADML. After the completion of standard adversarial training [33], we apply AT-based defense methods to line 4 in Algorithm 1 for ADML. We then optimize adversarially trained CNNs in 10 epochs using SGD [43] with a learning rate of 0.001 scheduled by Cyclic [49], which allows empirically sufficient convergence to robustness. In addition, adversarially trained Transformers are also optimized with ADML using a learning rate of 0.0001 on the equal experimental setup of CNNs. Note that, we set sample-splitting ratio in half (see Appendix G) for each batch, and cross-fitting is satisfied during training iterations.", + "bbox": [ + 80, + 734, + 467, + 898 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/c875b6ba88e06b2f105ae4a5fee58a08eba419a175c487f85d0f7a47b5871cbd.jpg", + "table_caption": [], + "table_footnote": [ + "Table 4. Comparing adversarial robustness of TRADES [62] using synthetic images: DDPM [18] and EDM [22] whether to the inclusion of ADML for CIFAR-10/100 with WRN-34-10: PORT [46] and WRN-28-10: Gowal [16], HAT [39], SCORE [36], Wang [56]." + ], + "table_body": "
PORT+ADMLGowal+ADMLHAT+ADMLSCORE+ADMLWang+ADML
○Clean87.088.186.087.488.289.588.089.991.491.8
UAA60.666.460.766.861.067.561.168.064.070.5
∞Clean65.965.859.259.962.262.462.062.368.168.2
JAA31.237.930.837.731.237.331.237.135.741.1
", + "bbox": [ + 504, + 507, + 888, + 571 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Robustness Validation on ADML", + "text_level": 1, + "bbox": [ + 503, + 635, + 787, + 647 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Adversarial Robustness. Based on our experimental setups, we have conducted enormous validations of adversarial robustness on CNNs in Table 1 and Transformers in Table 2. As shown in these tables, employing ADML on AT-based defense methods: AT [33], TRADES [62], MART [55], AWP [58] enables to largely improve adversarial robustness, compared with that of each defense method baseline. Bai et al. [1] have argued that Transformers cannot show noticeable adversarial robustness than CNNs, but we want to point out that the robustness of Transformers can be remarkably improved, especially in larger datasets.", + "bbox": [ + 504, + 657, + 888, + 823 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation Study. In Table 3, we conduct ablation studies on the effect of sample-splitting plus cross-fitting on robustness and the effect of considering treatments as worst examples, non-worst examples, or both on robustness, either. According to the results, only considering treatments", + "bbox": [ + 503, + 825, + 888, + 898 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "4505", + "bbox": [ + 483, + 946, + 513, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/55afc6e3c2b8f150b815aa85d03d8b568c6ed32cd30ba9b61f1782618de542dd.jpg", + "image_caption": [ + "(a) CIFAR-10 [27]" + ], + "image_footnote": [], + "bbox": [ + 80, + 60, + 287, + 176 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3ba5f2c4c181843f98b672ee5ad9971a5f0fe96f2ef6eca2eec3cb393a368573.jpg", + "image_caption": [ + "(b) CIFAR-100 [27]" + ], + "image_footnote": [], + "bbox": [ + 292, + 60, + 486, + 176 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/5660746d2778873f77e230c6d29c782f12f370c00323d443c14b51e31ba363d7.jpg", + "image_caption": [ + "(c) Tiny-ImageNet [29]" + ], + "image_footnote": [], + "bbox": [ + 491, + 60, + 686, + 176 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/582191614aa4ad7c3dca3c7d2ba571ff2701dbe9fb3ea4537144174cf1d8e4f2.jpg", + "image_caption": [ + "(d) ImageNet [9]" + ], + "image_footnote": [], + "bbox": [ + 687, + 61, + 882, + 176 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2e011e0eda560ec3b37bd795fb594a5d55b7479cc9d9d7d0940358b3afd065d7.jpg", + "image_caption": [ + "Figure 3. Cumulative distribution with averaged adversarial robustness for bottom-k classes against PGD [33] on four benchmark datasets. Note that, $10\\%$ , $30\\%$ , and $50\\%$ of $k$ values are applied, and perturbation budget is set to $[8/255, 8/255, 4/255, 2/255]$ on each dataset.", + "Figure 4. Distribution of adversarial robustness across whole classes on CIFAR-10. Four methods: AT [33], TRADES [62], MART [55], AWP [58] are integrated on each architecture." + ], + "image_footnote": [], + "bbox": [ + 107, + 223, + 434, + 378 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "as worst examples can catch actual adversarial vulnerability, thereby improving robustness much more than others.", + "bbox": [ + 75, + 430, + 467, + 460 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Utilizing Synthetic Images. Recently, several works [46, 16, 39, 36, 56] have employed TRADES [62] utilizing synthetic images: DDPM [18] and EDM [22] to improve adversarial robustness based on the insight that data augmentation such as CutMix [60] can improve robustness [40]. To further investigate the benefits of ADML, we experiment ADML combined with TRADES on the synthetic images. Table 4 shows ADML can further improve the robustness even on synthetic images, demonstrating its efficacy.", + "bbox": [ + 75, + 460, + 467, + 595 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.3. Causal Analysis on ADML", + "text_level": 1, + "bbox": [ + 76, + 604, + 316, + 619 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Adversarial Vulnerability. To validate the alleviation of adversarial vulnerability existing in certain classes as in Figure 1, we evaluate the averaged adversarial robustness for the cumulative distribution of bottom- $k$ classes with respect to the network prediction. We set the $k$ value as $10\\%$ , $30\\%$ , and $50\\%$ . As in Figure 3, we can observe that AT shows noticeable vulnerability in bottom- $k$ classes, and such tendency pervades in four different datasets and architectures. If we successfully mitigate direct causal parameter of adversarial perturbations on each class, we expect apparent improvements of robustness for bottom- $k$ classes. As in the figure, we can observe the notable robustness of ADML in the vulnerable bottom- $k$ classes and corroborate its effectiveness to alleviate aforementioned phenomenon existing in current AT-based defenses. Further infographic is illustrated in Figure 4 for the integrated distribution of baselines [33, 62, 55, 58] and their corresponding ADML adoptions on each architecture, and it shows further adversarial", + "bbox": [ + 75, + 628, + 468, + 898 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/074a5f4382ba18ac8dfacb449a03c348993ce8bf55a474e6212c54e372ef5afd.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
NetworksCIFAR10Tiny-ImageNet
ρ10ρ30ρ50ρAvgρ10ρ30ρ50ρAvg
ResNet-1853.9856.8952.9767.334.935.395.546.49
WRN-28-1063.6068.7068.2777.866.725.916.6010.74
ViT-B/1676.7885.4580.0384.331.541.731.913.08
DeiT-B/1669.3674.4668.6369.711.151.131.222.05
", + "bbox": [ + 501, + 223, + 885, + 309 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Relative ratio of causal parameter (\\%) in CIFAR-10 and Tiny-ImageNet with four architectures. Note that $k$ is set to 10,30, 50, and Avg indicates average on whole classes in each dataset.", + "bbox": [ + 498, + 311, + 890, + 353 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "robustness in general (Additional results in Appendix H).", + "bbox": [ + 498, + 359, + 877, + 375 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Causal Parameter. By deploying ADML, we present a way of mitigating the magnitude of causal parameter $|\\theta|$ . To numerically calculate $|\\theta|$ , we employ Eq. (8) and measure the average of $|\\theta_{\\mathrm{ADML}}|$ for ADML with respect to the bottom- $k$ and whole classes, respectively. By dividing $|\\theta_{\\mathrm{ADML}}|$ with $|\\theta_{\\mathrm{AT}}|$ , we can obtain relative ratio of causal parameter, $\\rho_k := 100 \\times |\\theta_{\\mathrm{ADML}}| / |\\theta_{\\mathrm{AT}}|$ of adversarial examples in bottom- $k$ classes. This ratio indicates that relative intensity of causal parameter compared to that of AT [33]. As in Table 5, we can observe that ADML shows less intensity of the causal parameter than AT, which means less causal effects of adversarial perturbations on target classes. From combinatorial results of preceding robustness comparison in Sec. 4.2, we corroborate that ADML indeed mitigate the intrinsic causal parameter and alleviate empirical observation in Figure 1, thus results in adversarial robustness.", + "bbox": [ + 496, + 375, + 890, + 616 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 632, + 617, + 647 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we observe adversarial vulnerability varies across targets and still pervades even with deeper architectures and advanced defense methods. To fundamentally address it, we build causal perspective in adversarial examples and propose a way of estimating causal parameter representing the degree of adversarial vulnerability, namely Adversarial Double Machine Learning (ADML). By minimizing causal effects from the estimated vulnerability, ADML can mitigate the empirical phenomenon as well as solidly improve adversarial robustness with other methods.", + "bbox": [ + 496, + 657, + 890, + 808 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments. This work was partially supported by two funds: IITP grant funded by the Korea government (MSIT) (No.2022-0-00984) and Center for Applied Research in Artificial Intelligence (CARAI) grant funded by DAPA and ADD (UD190031RD).", + "bbox": [ + 496, + 824, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "4506", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Yutong Bai, Jieru Mei, Alan L Yuille, and Cihang Xie. Are transformers more robust than cnns? Advances in Neural Information Processing Systems, 2021.", + "[2] Nicolas Carion, Francisco Massa, Gabriel Synnaeve, Nicolas Usunier, Alexander Kirillov, and Sergey Zagoruyko. End-to-end object detection with transformers. 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Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.105, + 0.13, + 0.868, + 0.177 + ], + "angle": 0, + "content": "Mitigating Adversarial Vulnerability through Causal Parameter Estimation by Adversarial Double Machine Learning" + }, + { + "type": "text", + "bbox": [ + 0.143, + 0.203, + 0.827, + 0.257 + ], + "angle": 0, + "content": "Byung-Kwan Lee\\*, Junho Kim\\*, Yong Man Ro† \nImage and Video Systems Lab, School of Electrical Engineering, KAIST, South Korea \n{leebk, arkimjh, ymro}@kaist.ac.kr" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.314, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.324, + 0.474, + 0.657 + ], + "angle": 0, + "content": "Adversarial examples derived from deliberately crafted perturbations on visual inputs can easily harm decision process of deep neural networks. To prevent potential threats, various adversarial training-based defense methods have grown rapidly and become a de facto standard approach for robustness. Despite recent competitive achievements, we observe that adversarial vulnerability varies across targets and certain vulnerabilities remain prevalent. Intriguingly, such peculiar phenomenon cannot be relieved even with deeper architectures and advanced defense methods. To address this issue, in this paper, we introduce a causal approach called Adversarial Double Machine Learning (ADML), which allows us to quantify the degree of adversarial vulnerability for network predictions and capture the effect of treatments on outcome of interests. ADML can directly estimate causal parameter of adversarial perturbations per se and mitigate negative effects that can potentially damage robustness, bridging a causal perspective into the adversarial vulnerability. Through extensive experiments on various CNN and Transformer architectures, we corroborate that ADML improves adversarial robustness with large margins and relieve the empirical observation." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.701, + 0.21, + 0.716 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.727, + 0.47, + 0.878 + ], + "angle": 0, + "content": "Along with the progressive developments of deep neural networks (DNNs) [17, 10, 2], an aspect of AI safety comes into a prominence in various computer vision research [45, 64, 12, 19]. Especially, adversarial examples [50, 15, 30] are known as potential threats on AI systems. With deliberately crafted perturbations on the visual inputs, adversarial examples are hardly distinguishable to human observers, but they easily result in misleading decision process of DNNs. Such adversarial vulnerability provokes weak reliability of inference process of DNNs and" + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.29, + 0.889, + 0.42 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.416, + 0.877, + 0.544 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.591, + 0.545, + 0.81, + 0.557 + ], + "angle": 0, + "content": "(b) Adversarial Defense Methods" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.56, + 0.892, + 0.616 + ], + "angle": 0, + "content": "Figure 1. The comparison of adversarial robustness along target classes with respect to (a) Network Architectures and (b) Adversarial Defense Methods on CIFAR-10 [27]. Note that, the distribution of adversarial robustness is consistent along both criteria." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.625, + 0.892, + 0.641 + ], + "angle": 0, + "content": "discourages AI adoption to the safety critical areas [54, 44]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.642, + 0.893, + 0.793 + ], + "angle": 0, + "content": "In order to achieve robust and trustworthy DNNs from adversarial perturbation, previous methods [33, 28, 3, 62, 55, 58, 8] have delved into developing various adversarial attack and defense algorithms in the sense of cat-and-mouse game. As a seminal work, Madry et al. [33] have paved the way for obtaining robust network through adversarial training (AT) regarded as an ultimate augmentation training [52] with respect to adversarial examples. Based on its effectiveness, various subsequent works [62, 55, 58, 63, 39, 25] have investigated it to further enhance adversarial robustness." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Although several AT-based defense methods have become a de facto standard due to their competitive adversarial robustness, we found an intriguing property of the current defense methods. As in Figure 1, we identify that the adversarial robustness for the each target class significantly varies with a large gap, and this phenomenon equally happens in the course of (a) network architectures and (b)" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.336, + 0.901 + ], + "angle": 0, + "content": "*Equal contribution. † Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4499" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.25, + 0.217 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.088, + 0.223, + 0.242, + 0.237 + ], + "angle": 0, + "content": "(a) AT Causal Diagram" + }, + { + "type": "image", + "bbox": [ + 0.264, + 0.09, + 0.465, + 0.219 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.267, + 0.223, + 0.459, + 0.237 + ], + "angle": 0, + "content": "(b) Training Robust Network" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.24, + 0.47, + 0.268 + ], + "angle": 0, + "content": "Figure 2. Overview of canonical adversarial training procedure for robust network and its causal diagram." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.273, + 0.469, + 0.499 + ], + "angle": 0, + "content": "various AT-based defense methods. In addition, we would like to point out that the robustness of particular target is still severely vulnerable than others even with advanced architectures [10, 51, 31] and defense methods [62, 55, 58]. We argue that such phenomenon is derived from the current learning strategies of AT-based defense methods that lacks of understanding causal relations between the visual inputs and predictions. When considering AT methods as the ultimate augmentation [52], current methods rely solely on strengthening the correlation between adversarial examples and target classes through canonical objectives that improve robustness. To fundamentally address such vulnerability and understand the causal relation, we need to quantify the degree of vulnerability (i.e., causal parameter) and should mitigate its direct effects to the network predictions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.5, + 0.469, + 0.681 + ], + "angle": 0, + "content": "Accordingly, we investigate the AT-based defense methods in a causal viewpoint and propose a way of precisely estimating causal parameter between adversarial examples and their predictions, namely Adversarial Double Machine Learning (ADML). We first represent a causal diagram of AT-based methods and interpret it as a generating process of robust classifiers as illustrated in Figure 2. Regarding standard adversarial training [33] as an optimizing procedure for the robust network parameters \\( f \\) with respect to the worst perturbations \\( t \\), we can instantiate a generation \\( g^{1} \\) as an adversarial attack of projected gradient descent (PGD) [33] for the given clean examples \\( x \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.682, + 0.469, + 0.864 + ], + "angle": 0, + "content": "Then, our research question is how to quantitatively compute the causal parameter \\(\\theta\\) between the perturbations \\(t\\) and target classes \\(y\\), and identify the causal effects on outcome of our interests. Through double machine learning (DML) [5], widely studied as a powerful causal estimator [4, 7, 13, 20, 21] for the given two regression models, we can establish an initial research point of estimating causal parameter of adversarial perturbation with theoretical background. However, it is difficult to directly estimate \\(\\theta\\) in the high-dimensional manifolds, especially for DNNs. In this paper, we shed some lights on identifying causal parameter of the perturbations while theoretically bridging the gap be" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.892, + 0.167 + ], + "angle": 0, + "content": "tween causal inference and adversarial robustness. Then, by minimizing the magnitude of the estimated causal parameter, we essentially lessen negative causal effects of adversarial vulnerability, and consequently acquire robust network with the aforementioned phenomenon alleviated." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.168, + 0.892, + 0.272 + ], + "angle": 0, + "content": "To corroborate the effectiveness of ADML on adversarial robustness, we set extensive experiments with four publicly available datasets [27, 29, 9]. Our experiments include various convolutional neural network architectures (CNNs), as well as Transformer architectures that have drawn great attention in both vision and language tasks [53, 10, 66, 65] yet relatively lack of being studied in adversarial research." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.273, + 0.845, + 0.286 + ], + "angle": 0, + "content": "Our contributions can be summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.288, + 0.891, + 0.348 + ], + "angle": 0, + "content": "- We present an empirical evidence that despite the recent advances in AT-based defenses, fundamentally adversarial vulnerability still remains across various architectures and defense algorithms." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.348, + 0.891, + 0.408 + ], + "angle": 0, + "content": "- Bridging a causal perspective into adversary, we propose Adversarial Double Machine Learning (ADML), estimating causal parameter in adversarial examples and mitigating its causal effects damaging robustness." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.409, + 0.891, + 0.469 + ], + "angle": 0, + "content": "- Through extensive experiments and analyses on various CNN and Transformer architectures, we corroborate intensive robustness of our proposed method with the phenomenon alleviated." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.288, + 0.891, + 0.469 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.482, + 0.785, + 0.499 + ], + "angle": 0, + "content": "2. Background and Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.507, + 0.892, + 0.628 + ], + "angle": 0, + "content": "Notation. We deal with DNNs for classification as in Figure 2, represented by \\( f: \\mathcal{X} \\to \\mathcal{Y} \\), where \\( \\mathcal{X} \\) and \\( \\mathcal{Y} \\) denote image and probability space, respectively. Let \\( x \\in \\mathcal{X} \\) denote clean images and \\( y \\in \\mathcal{Y} \\) indicate (one-hot) target classes corresponding to the images. Adversarial examples \\( x_{\\mathrm{adv}} \\) are generated by adversarial perturbations \\( t \\) through DNNs, such that \\( x_{\\mathrm{adv}} = x + t \\). Here, the perturbations are carefully created through the following formulation:" + }, + { + "type": "equation", + "bbox": [ + 0.61, + 0.639, + 0.891, + 0.663 + ], + "angle": 0, + "content": "\\[\n\\max _ {\\| t \\| _ {\\infty} \\leq \\gamma} \\mathcal {L} _ {\\mathrm {C E}} (f (x + t), y), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.673, + 0.891, + 0.735 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{\\mathrm{CE}}\\) represents a pre-defined loss such as cross-entropy for classification task. We regard adversarial perturbations \\(t\\) as \\(l_{\\infty}\\) perturbation within \\(\\gamma\\)-ball (i.e., perturbation budget). Here, \\(\\| \\cdot \\|_{\\infty}\\) describes \\(l_{\\infty}\\) perturbation magnitude." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.742, + 0.699, + 0.758 + ], + "angle": 0, + "content": "2.1. Adversarial Training" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "After several works [50, 15, 24] have found that human-imperceptible adversarial examples easily break network predictions, Madry et al. [33] have thrown a fundamental question: \"How can we make models robust to adversarial examples with security guarantee?\" To answer it, they have used the concept of empirical risk minimization (ERM) serving as a recipe to obtain classifiers with small population risk. Thanks to its reliable guarantee, they have consolidated it on the purpose of adversarial defense and" + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.875, + 0.469, + 0.901 + ], + "angle": 0, + "content": "\\(^{1}\\)Selecting \\(g\\) as proper perturbations varies according to domain specific tasks (e.g., rotations, translations [11], or spatial deformations [59])." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4500" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "accomplished the yardstick of adversarial training. The key factor of its achievement is regarding adversarial training as min-max optimization in a perspective of saddle point problem, which can be written as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.129, + 0.16, + 0.47, + 0.196 + ], + "angle": 0, + "content": "\\[\n\\min _ {f} \\mathbb {E} _ {(x, y) \\sim \\mathcal {D}} \\left[ \\max _ {\\| t \\| _ {\\infty} \\leq \\gamma} \\mathcal {L} _ {\\mathrm {C E}} (f (x + t), y) \\right], \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.204, + 0.469, + 0.295 + ], + "angle": 0, + "content": "where \\(\\mathcal{D}\\) denotes a set of data samples \\((x,y)\\). Here, they have presented an adversarial attack based on PGD to powerfully behave inner-maximization on Eq. (2), which is an ultimate first-order adversary with a multi-step variant of fast gradient sign method [28] by adding a random perturbation around the clean images \\(x\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.295, + 0.47, + 0.597 + ], + "angle": 0, + "content": "According to its impact, various adversarial training methods [33, 62, 55, 58] have grown exponentially and become de facto standards robustifying DNNs against adversarial perturbation. Zhang et al. [62] have pointed out the trade-off between clean accuracy and adversarial robustness, and reduced the gap between clean errors and robust errors. Wang et al. [55] have claimed that all of clean images are used to perform both inner-maximization and outer-minimization process in Eq. (2), irrespective of whether they are correctly classified or not. Thus, they have focused on misclassified clean images prone to be easily overlooked during adversarial training and demonstrated their significant impacts on the robustness by incorporating an explicit regularizer for them. Wu et al. [58] have studied loss landscapes with respect to network parameters and shown a positive correlation between the flatness of the parameter loss landscapes and the robustness. In the end, they have presented a double-perturbation mechanism where clean images are perturbed, while network parameters are simultaneously perturbed as well." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.598, + 0.469, + 0.78 + ], + "angle": 0, + "content": "On the other hand, we plunge into investigating where adversarial vulnerability comes from and observe that the vulnerability varies along target classes, and it significantly deteriorates network predictions. Further, we find that this phenomenon commonly happens across various network architectures and advanced defense methods. To relieve such peculiarity, we deploy double machine learning (DML) that helps to capture how treatments (i.e., adversarial perturbations) affect outcomes of our interests (i.e., network predictions), which is one of the powerful causal inference methods. After we concisely explicate the necessary background of DML, we will bridge it to the adversary in Sec. (3)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.315, + 0.804 + ], + "angle": 0, + "content": "2.2. Double Machine Learning" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.469, + 0.901 + ], + "angle": 0, + "content": "In data science and econometrics, one of the fundamental problems is how to measure causality between treatments \\( t \\) and outcomes of our interest \\( y \\) among high-dimensional observational data samples (see Figure 2) to identify data generating process. At a first glance, it seems simple to compute their causality, but we should keep in mind the" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.272 + ], + "angle": 0, + "content": "possibility for the existence of covariates \\( x \\) affecting both treatments and outcomes. In other words, for example, if one may want to know the causal effects of drug dosage \\( t \\) to blood pressure changes \\( y \\), one needs to collect observational data with respect to a variety of patients characteristics and their clinical histories \\( x \\), so as not to fall into biased environment. In reality, though, it is impossible to collect observational data including all covariates concerning treatments and outcomes, so it is not an easy problem to catch genuine causality under the unknown covariates \\( x \\). Therefore, there has been a growing demand for robustly predicting the unbiased causal relation, despite with the limited data samples." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.273, + 0.892, + 0.334 + ], + "angle": 0, + "content": "Recently, the advent of double machine learning (DML) [5] enables us to clarify the causality between treatments \\( t \\) and outcomes \\( y \\), when two regression models are given. The formulation of initial DML can be written as:" + }, + { + "type": "equation", + "bbox": [ + 0.567, + 0.343, + 0.892, + 0.367 + ], + "angle": 0, + "content": "\\[\ny = f (x) + \\theta t + u, \\quad (\\mathbb {E} [ u \\mid x, t ] = 0) \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.57, + 0.362, + 0.808, + 0.377 + ], + "angle": 0, + "content": "\\[\nt = g (x) + v, \\quad (\\mathbb {E} [ v \\mid x ] = 0)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.387, + 0.892, + 0.597 + ], + "angle": 0, + "content": "where \\(\\theta \\in \\mathbb{R}\\) denotes causal parameter representing causal relation between \\(t \\in \\mathbb{R}^d\\) and \\(y \\in \\mathbb{R}^d\\). In addition, \\(f\\) indicates one regression model projecting covariates to outcome domain, and \\(g\\) denotes another regression model generating treatments \\(t\\). In the sense that two regression models \\(f\\) and \\(g\\) are not main interest of DML, they are called as nuisance parameters to estimate the causal parameter \\(\\theta\\). Note that, early DML assumes the problem setup is proceeded in partially linear settings as a shape of Robinson-style [42] described in Eq. (3), where \"partially\" literally means that treatments \\(t \\in \\mathbb{R}^d\\) are linearly connected to outcome \\(y \\in \\mathbb{R}^d\\), while covariates \\(x\\) are not. In addition, it is supposed that the conditional expected error of \\(u \\in \\mathbb{R}^d\\) and \\(v \\in \\mathbb{R}^d\\) equals to zero vector \\(0 \\in \\mathbb{R}^d\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.598, + 0.892, + 0.795 + ], + "angle": 0, + "content": "To obtain the causal parameter \\(\\theta\\), Chernozhukov et al. [5] have provided a solution of estimating the causal parameter such that \\(\\hat{\\theta} = (y - \\mathbb{E}[y \\mid x]) \\cdot v / \\|v\\|^2\\) which satisfies Neyman-orthogonality [35, 34]. It makes \\(\\hat{\\theta}\\) invariant to their erroneous of two nuisance parameters with the variance of causal parameter reduced. Furthermore, they have addressed a chronic problem that \\(\\theta\\) is only accessible when the two nuisance parameters are in a class of Donsker condition, where deep neural networks are not included in that condition. They have theoretically demonstrated sample-splitting plus cross-fitting can effectively relax Donsker condition and allow a broad array of modern ML methods [5] to compute unbiased causal parameter \\(\\theta\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Following the principle, they first split the data samples \\(\\{\\mathcal{D}_1,\\mathcal{D}_2\\} \\sim \\mathcal{D}\\) and divided the process of causal inference into two steps: (a) training two nuisance parameters \\(f\\) and \\(g\\) with \\(\\mathcal{D}_1\\), (b) estimating unbiased \\(\\theta\\) with \\(\\mathcal{D}_2\\). Here, data samples \\(\\mathcal{D}_2\\) used to estimate unbiased causal parameters should not be overlapped with \\(\\mathcal{D}_1\\) utilized to train the nuisance parameters. To make copious combinations, they" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "4501" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": " swapped the role of partitioned data samples \\(\\mathcal{D}_1 \\leftrightarrows \\mathcal{D}_2\\) or repeatedly split \\(\\mathcal{D}\\). Subsequently, they have performed cross-fitting (e.g., \\(k\\)-fold cross validation) by averaging the estimated causal parameters from various split samples." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.153, + 0.471, + 0.258 + ], + "angle": 0, + "content": "Along with the success of initial DML in partially linear settings, numerous variants [4, 7, 32, 14, 13, 26, 6] have emerged, and they have extended its initial nature to non-parametric settings with continuous treatments \\( t \\) in order to capture more complicated non-linear causal relations in a debiased state. A non-parametric formulation [4] represents a more general problem setup of DML as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.152, + 0.267, + 0.47, + 0.292 + ], + "angle": 0, + "content": "\\[\ny = f (x, t) + u, \\quad (\\mathbb {E} [ u \\mid x, t ] = 0) \\tag {4}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.157, + 0.287, + 0.381, + 0.303 + ], + "angle": 0, + "content": "\\[\nt = g (x) + v, \\qquad (\\mathbb {E} [ v \\mid x ] = 0)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.312, + 0.47, + 0.402 + ], + "angle": 0, + "content": "where there is no explicit term for causal parameter \\(\\theta\\) exhibiting causal relation between treatments \\(t\\) and outcomes \\(y\\), compared to Eq. (3). Colangelo et al. [7] have introduced a way of estimating causal parameter \\(\\theta\\) applicable to non-parametric settings with high-dimensional continuous treatments \\(t \\in \\mathcal{T}\\), which can be written as:" + }, + { + "type": "equation", + "bbox": [ + 0.191, + 0.409, + 0.47, + 0.44 + ], + "angle": 0, + "content": "\\[\n\\hat {\\theta} = \\frac {\\partial}{\\partial t} \\mathbb {E} [ y \\mid \\operatorname {d o} (\\mathcal {T} = t) ]. \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.447, + 0.471, + 0.658 + ], + "angle": 0, + "content": "They have utilized do-operator [37] commonly used in graphical causal models and intervened on treatments \\( t \\) to compute an interventional expectation \\( \\mathbb{E}[y|\\mathrm{do}(\\mathcal{T} = t)] \\). It represents the expected outcome averaged from all the possible covariates for the given fixed treatments \\( t \\), such that \\( \\mathbb{E}[y|\\mathrm{do}(\\mathcal{T} = t)] = \\sum_{x\\in \\mathcal{X}}\\mathbb{E}[y|x,t]p(x) \\). Specifically, they have estimated causal parameter \\( \\theta \\) by measuring how much the interventional expectation shifted, once they change the treatments slightly. Since the most important property of DML is Neyman-Orthogonality helping to robustly estimate the causal parameter, the interventional expectation should be also modified to satisfy the property [7, 23] of its invariance to nuisance parameters \\( f \\) and \\( g \\). Its formulation can be written as follows (see details in Appendix A):" + }, + { + "type": "equation", + "bbox": [ + 0.099, + 0.678, + 0.47, + 0.713 + ], + "angle": 0, + "content": "\\[\n\\mathbb {E} [ y \\mid \\operatorname {d o} (\\mathcal {T} = t) ] = \\mathbb {E} _ {\\mathcal {D} _ {t}} \\left[ f (x, t) + \\frac {y - f (x , t)}{p (\\mathcal {T} = t \\mid x)} \\right], \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.469, + 0.81 + ], + "angle": 0, + "content": "where \\(\\mathcal{D}_t\\) denotes a set of observational covariates and outcome samples for a fixed \\(t\\in \\mathcal{T}\\) such that \\((x,y)\\sim \\mathcal{D}_t\\), a sub-population of \\(\\mathcal{D}\\). Note that, \\(p(\\mathcal{T} = t|x)\\) is related to treatment generator \\(g\\). Here, differentiating Eq. (6) enables us to acquire unbiased causal parameter in non-parametric settings with non-linear causal relation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.47, + 0.902 + ], + "angle": 0, + "content": "In brief, DML captures unbiased causal relation between treatments \\( t \\) and outcomes \\( y \\) even with finite data samples, of which theoretical ground is (a) Neyman-Orthogonality for robustly estimated causal parameter despite undesirable outputs of nuisance parameters, and (b) sample-splitting plus cross-fitting for debiased causal parameters." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.09, + 0.849, + 0.108 + ], + "angle": 0, + "content": "3. Adversarial Double Machine Learning" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.115, + 0.822, + 0.131 + ], + "angle": 0, + "content": "3.1. Adversarial Data Generating Process" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.138, + 0.892, + 0.304 + ], + "angle": 0, + "content": "In general deep learning schemes, we have clean visual images \\( x \\in \\mathbb{R}^{hwc} \\) and their corresponding target classes \\( y \\in \\mathbb{R}^d \\) in our hand as a format of dataset, where \\( h, w, c \\) denotes image resolution of height, width, channel, respectively, and \\( d \\) denotes the number of classes. Thus, we do not need additional data generating process. For adversarial training, on the other hand, we need another data, which are adversarial perturbations generated from data samples \\( (x,y) \\) as in Eq. (1). They are normally created by PGD [33] at every training iteration to make DNNs \\( f \\) robust through min-max optimization game according to Eq. (2)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.305, + 0.892, + 0.47 + ], + "angle": 0, + "content": "Though, the more iterations of adversarial training, the fewer perturbations that impair network predictions. In other words, not all of the perturbations can corrupt network predictions among newly generated perturbations. Hence, we do not consider all of the perturbations as treatments but selectively define them as worst perturbations \\( t \\) breaking network predictions, such that it satisfies \\( y \\neq f(x + t) \\), where we call \\( x_{\\mathrm{adv}} = x + t \\) as worst examples. This is because our major goal is to catch actual adversarial vulnerability of DNNs, so that we do not tackle the perturbations incapable of harming network predictions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.471, + 0.892, + 0.562 + ], + "angle": 0, + "content": "To access such worst perturbation, we choose perturbation generator \\( g \\) as an adversarial attack of PGD according to standard adversarial training [33]. In addition, we pick the worst perturbations \\( t \\) damaging network predictions among adversarial perturbations from the generator \\( g \\). In this way, we perform adversarial data generating process." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.569, + 0.746, + 0.585 + ], + "angle": 0, + "content": "3.2. Adversarial Problem Setup" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.592, + 0.892, + 0.819 + ], + "angle": 0, + "content": "In the nature of adversarial training, the worst perturbations \\( t \\) are explicitly injected to clean images \\( x \\) such that \\( x_{\\mathrm{adv}} = x + t \\), and these combined images are propagated into DNNs \\( f \\). Here, through this formulation as: \\( f(x + t) = f(x,t) \\), we connect DNNs for adversarial training and a nuisance parameter \\( f \\) for non-parametric DML in Eq. (4). Fortunately, once we use Taylor expansion (with scalar-valued function for better understanding) and decompose \\( f \\) by its input component as: \\( f(x + t) = f(x) + \\sum_{i=1}^{\\infty} t^{i} f^{(i)}(x) / i! \\), where \\( f^{(i)} \\) indicates \\( i \\)-th order derivative function, we can also express partially linear settings described in Eq. (3). That is, since adversarial examples start from the concept of \"additive noise\", both settings can exist at the same time in the scheme of adversarial training. From this reason, we build Adversarial Double Machine Learning (ADML):" + }, + { + "type": "equation", + "bbox": [ + 0.515, + 0.824, + 0.892, + 0.861 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} y = f (x + t) = f (x) + \\theta \\bar {t} + u, \\quad (\\mathbb {E} [ u \\mid x, t ] = 0) \\tag {7} \\\\ t = g (x) + v, \\quad (\\mathbb {E} [ v \\mid x ] = 0) \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.868, + 0.892, + 0.903 + ], + "angle": 0, + "content": "where \\(\\bar{t}\\) indicates Taylor-order matrix: \\([t, t^2, \\dots]^T\\) and \\(\\theta\\) represents Taylor-coefficient matrix \\(\\left[\\frac{f^{(1)}(x)}{1!}, \\frac{f^{(2)}(x)}{2!}, \\dots\\right]\\) (see" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4502" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.395, + 0.106 + ], + "angle": 0, + "content": "strict mathematical verification in Appendix B)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.108, + 0.47, + 0.319 + ], + "angle": 0, + "content": "Here, we explain what the conditional expected error of \\( u \\) and \\( v \\) in Eq. (7) means in adversarial training. The former \\( \\mathbb{E}[u|x,t] = 0 \\) implies the nature of adversarial training, which can be viewed as an ultimate augmentation robustifying DNNs, when infinite data population of \\( x \\) and \\( t \\) is given. Thus, it means network predictions become invariant in the end, despite the given worst perturbations. To implement it practically, we replace it with a mild assumption as \\( \\mathbb{E}[u|x,g(x)] = 0 \\) (see Appendix C) that signifies PGD-based perturbations are used to perform adversarial training. This is because we cannot always acquire worst perturbations \\( t \\) using only PGD. For the latter \\( \\mathbb{E}[v|x] = 0 \\), it represents PGD has capability of producing worst perturbations deviating network predictions during the training." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.331, + 0.45, + 0.347 + ], + "angle": 0, + "content": "3.3. Estimating Adversarily Causal Parameter" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.355, + 0.469, + 0.46 + ], + "angle": 0, + "content": "Aligned with Eq. (3), an explicit term of \\(\\theta\\) is regarded as the causal parameter in our problem setup of ADML. We can now interpret that \\(\\theta\\) is a causal factor to spur adversarial vulnerability, since its magnitude easily catalyzes the deviations from network predictions of clean images. Here, if it is possible to directly compute \\(\\theta\\) over all data samples, we can finally handle adversarial vulnerability." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.461, + 0.469, + 0.567 + ], + "angle": 0, + "content": "Favorably, ADML follows both partially linear and nonparametric settings due to the concept of additive noise, thus we can employ the way of estimating causal parameter as in Eq. (5). The following formulation represents the estimated causal parameter \\(\\hat{\\theta}\\) in ADML (see Appendix D). Note that, as we emphasized, sample-splitting plus cross-fitting must be applied to estimate unbiased causal parameter." + }, + { + "type": "equation", + "bbox": [ + 0.105, + 0.579, + 0.47, + 0.614 + ], + "angle": 0, + "content": "\\[\n\\hat {\\theta} = \\mathbb {E} _ {\\mathcal {D} _ {t}} \\left[ - \\left(\\frac {1}{p (\\mathcal {T} = t \\mid x)} - 1\\right) \\frac {\\partial}{\\partial t} f (x + t) \\right], \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.626, + 0.469, + 0.808 + ], + "angle": 0, + "content": "where \\(\\frac{\\partial}{\\partial t} f(x + t)\\) indicates an input gradient for network predictions with respect to \\(t\\), and \\(p(\\mathcal{T} = t|x)\\) represents a distribution of worst perturbation given clean images \\(x\\). Here, we cannot directly handle this distribution due to the presence of multiple unknown parameters required to define it. For that reason, we instead approximate it with the sharpening technique by incorporating the information on attacked confidence such that \\(p(\\mathcal{T} = t|x) \\approx \\mathbb{E}_{t'|x}[p(y_a|x,t')]\\) (see Appendix E), where \\(y_{a}\\) denotes attacked classes for the given worst perturbations \\(t\\). It implicitly means that the higher the attacked confidence, the higher the probability of finding worst perturbations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Aligned with the previous analysis [47] that show increasing magnitude of input gradient increases adversarial vulnerability, the magnitude of our causal parameter \\( |\\hat{\\theta}| \\) also becomes huge due to \\( |\\hat{\\theta}| \\propto |\\frac{\\partial}{\\partial t} f(x + t)| \\). In parallel, Qin et al. [38] show the more ambiguous confident, the lower robustness (high vulnerability), and interestingly, the mag-" + }, + { + "type": "table_caption", + "bbox": [ + 0.501, + 0.091, + 0.642, + 0.106 + ], + "angle": 0, + "content": "Algorithm 1 ADML" + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.108, + 0.892, + 0.294 + ], + "angle": 0, + "content": "
Require: Data Samples D, Network f
1: for (x,y) ~ D do▷ Cross-Fitting
2: t' ← g(x)▷ PGD Attack
3: (x1,y1,t1'), (x2,y2,t2') ~ Split(x,y,t')
4: L_a ← L_Delphi(x1,y1,t1';f)▷ Mild Assumption
5: (xt2,yt2,t2) ← Select(y2 ≠ f(x2+t2')) ▷ Worst
6: j* ← arg maxj f_j(xt2+t2)▷ j: Class Index
7: τ ← 1/fj*(xt2+t2)-1▷ Balancing Ratio
8: L_b ← τL_CE(f(xt2+t2),yt2) + L_CE(f(xt2),yt2)
9: L_ADML ← L_a + L_b▷ ADML Loss
10: wf ← wf - α ∂/∂w_f L_ADML ▷ Weight Update (α: lr)
11: end for
" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.303, + 0.892, + 0.336 + ], + "angle": 0, + "content": "nitude of our causal parameter also \\( |\\hat{\\theta}| \\) becomes large due to \\( |\\hat{\\theta}| \\propto |1 / \\mathbb{E}_{t' | x}[p(y_a | x, t')]| \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.338, + 0.892, + 0.489 + ], + "angle": 0, + "content": "Bringing such factors at once, \\(\\hat{\\theta}\\) represents a weighted measurement of attacked confidence and their input gradients. Comprehensively, we can revisit that the network predictions of worst examples are easily flipped due to the following adversarial vulnerability: (a) ambiguous confidence around classification boundaries, or (b) high gradient magnitude amplifying the leverage of the perturbations. To improve the adversarial robustness of DNNs, it is essential to minimize the negative effects of causal parameters, which are combinatorial outcomes of the gradient and confidence." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.501, + 0.818, + 0.518 + ], + "angle": 0, + "content": "3.4. Mitigating Adversarial Vulnerability" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.525, + 0.892, + 0.661 + ], + "angle": 0, + "content": "By deploying ADML, we propose a way of estimating causal parameter representing the degree of adversarial vulnerability that disturbs to predict the target classes. Then, our final goal is essentially to lessen its direct causal effect from adversarial perturbations in order to achieve robust networks. In detailed, alleviating their causal effect derived from \\(\\hat{\\theta}\\) is the process of comprehensive reconstruction to focus more on vulnerable samples as we reflect their attacked confidence and gradients effects altogether." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.663, + 0.892, + 0.798 + ], + "angle": 0, + "content": "Accordingly, the very first way is naively reducing the magnitude of \\(\\hat{\\theta}\\) to suppress adversarial vulnerability damaging the robustness. However, calculating \\(\\hat{\\theta}\\) and minimizing its magnitude at every iteration is computationally striking because input gradient has huge dimension of \\(\\mathbb{R}^{dhwc}\\) and getting its gradient inevitably needs to compute second-order gradient with its tremendous dimension. We instead approximate the partial derivative \\(\\frac{\\partial}{\\partial t}\\mathbb{E}[y|\\mathrm{do}(\\mathcal{T} = t)]\\) and minimize its magnitude, which can be written as:" + }, + { + "type": "equation", + "bbox": [ + 0.523, + 0.81, + 0.892, + 0.845 + ], + "angle": 0, + "content": "\\[\n\\min _ {f} | \\hat {\\theta} | \\approx \\left| \\frac {\\mathbb {E} [ y \\mid \\operatorname {d o} (\\mathcal {T} = t) ] - \\mathbb {E} [ y \\mid \\operatorname {d o} (\\mathcal {T} = 0) ]}{t - 0} \\right|, \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.902 + ], + "angle": 0, + "content": "where network parameters of DNNs \\(f\\) are only dependent on the numerator, thus we engross the numerator only. Lastly, we redesign \\(\\mathbb{E}[y|\\mathrm{do}(\\mathcal{T} = t)]\\) into the form of loss" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4503" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.096, + 0.061, + 0.871, + 0.462 + ], + "angle": 0, + "content": "
MethodCIFAR-10CIFAR-100Tiny-ImageNet
CleanBIMPGD\\(CW_{\\infty}\\)APDLRAACleanBIMPGD\\(CW_{\\infty}\\)APDLRAACleanBIMPGD\\(CW_{\\infty}\\)APDLRAA
VGG-16AT78.849.448.146.846.446.446.353.926.025.024.123.723.823.756.526.625.425.524.724.624.6
+ADML80.961.861.759.855.054.854.552.231.030.829.927.827.627.355.435.534.932.932.732.432.2
TRADES79.548.647.645.746.446.346.353.325.524.823.523.623.723.256.128.327.326.225.825.825.7
+ADML81.062.662.459.055.355.154.952.231.231.129.827.627.327.355.436.636.034.033.633.433.3
MART78.351.950.648.848.948.848.752.626.626.024.424.324.324.255.727.826.626.025.725.725.6
+ADML80.462.462.260.355.755.355.251.631.631.029.627.827.527.355.136.235.834.934.333.933.7
AWP77.253.952.650.151.451.151.052.130.229.327.528.728.528.356.931.631.029.429.929.829.7
+ADML80.264.764.661.858.057.757.552.333.833.531.329.729.529.054.536.636.134.634.533.833.7
ResNet-18AT83.153.351.950.849.949.749.559.127.126.325.425.325.325.161.531.030.129.528.828.928.8
+ADML84.561.160.858.556.756.255.656.431.630.929.528.428.227.857.335.935.533.534.734.734.6
TRADES83.353.052.050.950.950.850.758.527.626.826.225.925.925.860.432.031.030.229.729.629.5
+ADML84.062.361.959.556.756.655.957.331.731.630.028.828.528.058.437.036.033.335.034.134.0
MART82.554.152.851.351.550.850.858.127.726.725.525.425.125.060.631.030.229.829.029.029.0
+ADML84.163.362.958.756.856.456.257.432.131.730.228.928.828.557.136.636.033.635.133.933.8
AWP81.356.355.553.654.254.054.057.931.430.729.030.030.029.861.434.734.132.433.333.233.1
+ADML84.064.664.561.460.559.959.756.233.932.930.731.130.530.359.838.638.135.937.736.736.6
WideResNet-28-10AT86.755.453.453.451.351.351.261.928.827.427.126.026.025.964.832.731.231.130.130.130.0
+ADML87.561.760.758.856.456.355.858.932.932.631.329.629.229.162.143.543.141.141.940.440.2
TRADES86.055.353.753.651.651.651.461.929.128.527.826.726.826.764.232.531.631.430.029.929.8
+ADML88.562.961.959.657.657.656.661.633.333.031.530.030.129.663.143.542.941.041.440.340.2
MART86.456.054.353.451.651.651.561.628.326.726.425.325.425.364.232.931.831.830.730.530.5
+ADML88.362.160.959.656.756.656.259.633.032.931.630.329.929.661.842.842.640.340.739.038.9
AWP85.960.258.957.256.956.956.862.433.032.231.130.930.930.865.436.936.035.134.834.834.7
+ADML88.267.567.464.263.563.263.162.539.739.336.937.637.136.864.944.644.241.943.342.142.0
WideResNet-70-10AT88.156.654.855.052.853.052.864.128.427.327.426.026.425.665.334.933.433.932.232.232.1
+ADML88.961.561.461.056.556.356.063.330.029.228.826.926.726.461.037.737.436.933.833.032.9
TRADES87.756.354.755.053.453.353.363.328.727.827.926.626.226.065.734.432.633.031.531.531.4
+ADML89.163.963.362.759.059.659.063.431.230.830.327.527.127.061.840.239.538.836.135.535.4
MART88.057.455.555.452.852.852.663.228.727.527.525.826.325.665.433.832.532.431.331.331.2
+ADML88.561.761.360.856.756.856.662.330.130.029.429.329.128.763.241.841.040.237.736.636.5
AWP86.661.860.659.959.159.459.265.233.333.331.731.530.330.066.740.740.040.039.139.038.9
+ADML89.467.066.966.163.463.663.165.341.941.840.938.938.037.665.845.044.543.343.543.142.8
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.464, + 0.892, + 0.494 + ], + "angle": 0, + "content": "Table 1. Comparing adversarial robustness of various defence methods whether to the inclusion of ADML for CIFAR-10 [27], CIFAR-100 [27], Tiny-ImageNet [29] trained with VGG-16 [48], ResNet-18 [17], WideResNet-28-10 [61], and WideResNet-70-10 [61]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.506, + 0.471, + 0.553 + ], + "angle": 0, + "content": "function used in deep learning and finally construct the objective function for ADML, of which formulation can be written as follows (see details in Appendix F):" + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.561, + 0.47, + 0.586 + ], + "angle": 0, + "content": "\\[\n\\min _ {f} \\mathbb {E} _ {\\mathcal {D} _ {t}} [ \\tau \\mathcal {L} _ {\\mathrm {C E}} (f (x + t), y) ] + \\mathbb {E} _ {\\mathcal {D} _ {0}} [ \\mathcal {L} _ {\\mathrm {C E}} (f (x), y) ], \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.596, + 0.47, + 0.751 + ], + "angle": 0, + "content": "where we denote \\(\\tau = \\frac{1}{p(\\mathcal{T} = t|x)} - 1\\) as balancing ratio. The current AT-based defenses use an equal weight \"1/n\" to loss for all data samples: \\(\\frac{1}{n}\\sum_{i=1}^{n}\\mathcal{L}_{\\text{Defense}}(x_i, y_i, t_i; f)\\) because they presume all of perturbations have equal causal effect (successful attack) to change targets without realizing vulnerable samples. Whereas, ADML uses the balancing ratio \\(\\tau\\) to adaptively focus on vulnerable samples by reweighting the loss. To realize ADML, we describe Algorithm 1 to explain further details, where \\(\\mathcal{L}_{\\text{Defense}}(x, y, t; f)\\) indicates a main body of the loss function for AT-based defenses." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.763, + 0.203, + 0.78 + ], + "angle": 0, + "content": "4. Experiment" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.295, + 0.803 + ], + "angle": 0, + "content": "4.1. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Datasets & Networks. We conduct comprehensive experiments on various datasets and networks. For datasets, we use CIFAR-10 [27], CIFAR-100 [27], and two larger datasets: Tiny-[ImageNet [29] and ImageNet [9]. For networks, four CNN architectures: [48, 17, 61] and four Transformer architectures: [10, 51] are used." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.506, + 0.892, + 0.703 + ], + "angle": 0, + "content": "Adversarial Attacks. We adaptively set perturbation budget \\(\\gamma\\) of adversarial attacks depending on the classification difficulty of the four datasets: 8/255 equally for CIFAR-10 [27] and CIFAR100 [27], 4/255 for Tiny-ImageNet [29], and 2/255 for ImageNet [9]. We prepare three standard attacks: BIM [28], PGD [33], \\(\\mathrm{CW}_{\\infty}\\) [3], and three advanced attacks: AP (Auto-PGD: step size-free), DLR (Auto-DLR: shift and scaling invariant), AA (Auto-Attack: parameter-free), all of which are introduced by Francesco et al. [8]. PGD, AP, DLR have 30 steps with random starts, where PGD has step size \\(2.3 \\times \\frac{\\gamma}{30}\\), and AP, DLR both have momentum coefficient \\(\\rho = 0.75\\). \\(\\mathrm{CW}_{\\infty}\\) uses PGD-based gradient clamping for \\(l_{\\infty}\\) with CW objective [3] on \\(\\kappa = 0\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.893, + 0.902 + ], + "angle": 0, + "content": "Adversarial Defenses. We use four defense baselines with a standard baseline: AT [33] and three advanced defense baselines: TRADES [62], MART [55], AWP [58]. To fairly validate experiments, a perturbation generator, PGD [33] is equivalently used to generate adversarial examples for which we use the budget 8/255 and set 10 steps with \\(2.3 \\times \\frac{\\gamma}{10}\\) step size in training. Especially, adversarially training Tiny-ImageNet [29] and ImageNet [9] is a computational burden, thus we employ fast adversarial training [57] with FGSM [15]. For training CNNs, we use SGD [43] with a learning rate of 0.5 scheduled by Cyclic [49] in 120 epochs and use early stopping to prevent overfitting [41]. For training Transformers, we use SGD [43] with a learn" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4504" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.096, + 0.061, + 0.871, + 0.466 + ], + "angle": 0, + "content": "
MethodCIFAR-10CIFAR-100Tiny-ImageNet
CleanBIMPGDCWAPDLRAACleanBIMPGDCW∞APDLRAACleanBIMPGDCW∞APDLRAA
VIT-S/16AT83.549.947.346.644.944.844.759.926.625.825.124.624.524.573.835.834.133.531.931.931.8
+ADML88.156.855.153.851.350.750.762.732.430.729.428.427.927.775.647.746.645.645.342.742.6
TRADES85.051.049.448.648.148.047.859.527.326.626.325.825.925.772.938.837.837.436.136.136.0
+ADML87.957.656.255.152.752.051.963.235.034.733.831.631.331.275.349.148.047.145.643.043.0
MART85.752.449.748.946.746.746.660.928.627.927.526.526.526.477.638.637.236.835.235.235.2
+ADML88.057.556.154.751.951.451.462.734.432.731.730.029.329.276.548.947.746.346.042.942.9
AWP84.954.252.351.650.149.949.961.129.629.028.127.727.727.678.141.039.338.737.337.337.2
+ADML88.057.054.353.350.149.649.564.434.834.133.031.330.630.576.647.546.444.944.742.542.4
VIT-B/16AT87.052.850.850.447.847.747.763.330.429.629.228.628.328.372.440.137.737.834.434.334.5
+ADML89.956.154.954.151.651.451.267.138.136.135.434.333.433.179.050.249.748.448.546.946.8
TRADES85.353.852.451.650.950.850.865.732.631.531.029.930.030.073.243.341.241.839.139.039.4
+ADML88.958.657.356.154.754.454.369.438.937.937.034.834.634.779.454.052.251.648.247.347.2
MART87.453.350.650.548.348.448.265.731.930.830.229.229.229.179.341.740.039.636.836.837.1
+ADML89.657.055.654.351.851.551.368.935.433.532.930.530.130.280.150.750.149.048.947.447.0
AWP87.454.952.951.949.849.849.766.833.431.731.330.330.230.278.745.042.242.239.539.439.7
+ADML90.459.156.756.653.853.652.870.037.736.135.633.332.832.979.350.849.748.048.046.045.8
DeT-S/16AT83.549.347.846.745.345.345.259.529.228.527.627.527.527.475.737.435.634.733.133.033.0
+ADML87.756.856.054.952.351.951.963.734.432.931.731.430.530.474.744.943.642.240.839.539.4
TRADES84.150.649.348.848.048.048.061.829.428.827.828.128.028.074.839.038.037.436.436.436.3
+ADML87.957.856.555.353.753.053.266.237.236.435.533.232.332.376.345.244.943.839.538.738.4
MART84.252.350.049.147.847.647.559.831.030.629.329.729.629.674.640.139.138.437.737.637.6
+ADML87.557.555.655.052.652.352.265.337.035.634.732.430.730.775.245.344.243.342.838.438.4
AWP82.353.552.351.550.550.450.460.731.831.430.231.030.030.075.441.740.939.839.039.139.0
+ADML86.755.953.252.650.650.550.564.739.438.136.835.734.534.575.449.447.646.545.742.842.8
DeT-B/16AT84.651.549.548.447.247.147.064.930.329.128.427.527.427.479.138.636.336.134.434.334.0
+ADML89.755.754.853.850.049.749.765.735.434.433.432.230.330.377.646.945.644.744.940.540.5
TRADES85.452.851.750.650.250.250.264.830.029.328.628.428.328.378.343.141.640.540.540.540.4
+ADML90.261.460.459.458.357.657.668.640.539.938.437.436.836.780.845.443.542.743.242.942.7
MART83.954.753.252.051.050.950.764.531.931.130.530.230.130.075.844.643.342.642.642.642.5
+ADML89.660.360.258.955.155.055.065.339.638.537.135.434.634.677.847.746.144.645.544.844.7
AWP83.354.153.152.451.851.651.565.432.331.530.430.230.130.176.642.841.440.742.842.842.7
+ADML88.959.057.356.454.053.853.769.739.438.337.335.234.434.480.351.250.248.949.448.148.0
" + }, + { + "type": "table_caption", + "bbox": [ + 0.081, + 0.468, + 0.89, + 0.496 + ], + "angle": 0, + "content": "Table 2. Comparing adversarial robustness of various defence methods whether to the inclusion of ADML for CIFAR-10 [27], CIFAR-100 [27], Tiny-ImageNet [29] trained with ViT-S/16 [10], ViT-B/16 [10], DeiT-S/16 [51], and DeiT-B/16 [51]." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.507, + 0.462, + 0.643 + ], + "angle": 0, + "content": "
SS+CFWNWCIFAR-10Tiny-ImageNet
PGDCW∞DLRAAPGDCW∞DLRAA
VGG-16✓✓X61.759.854.854.434.932.932.432.2
✓✓✓52.349.448.948.825.424.924.224.2
✓X✓48.047.145.845.826.025.824.524.4
X✓X52.650.049.449.428.127.026.426.4
ResNet-18✓✓X60.858.556.255.635.533.534.734.6
✓✓✓51.750.149.549.234.932.432.732.7
✓X✓50.850.549.449.130.029.529.028.9
X✓X53.651.751.451.031.729.730.230.1
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.081, + 0.646, + 0.468, + 0.672 + ], + "angle": 0, + "content": "Table 3. Ablation study for the effects of sample-splitting plus cross-fitting (SS+CF) and Worst(W) / Non-Worst(NW) examples." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.68, + 0.468, + 0.723 + ], + "angle": 0, + "content": "ing rate of 0.001 on the equal experimental setup of CNNs, where \\(224 \\times 224\\) resolution is applied for all datasets and pretrained parameters on ImageNet-1k models are utilized." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.736, + 0.468, + 0.9 + ], + "angle": 0, + "content": "Training ADML. After the completion of standard adversarial training [33], we apply AT-based defense methods to line 4 in Algorithm 1 for ADML. We then optimize adversarially trained CNNs in 10 epochs using SGD [43] with a learning rate of 0.001 scheduled by Cyclic [49], which allows empirically sufficient convergence to robustness. In addition, adversarially trained Transformers are also optimized with ADML using a learning rate of 0.0001 on the equal experimental setup of CNNs. Note that, we set sample-splitting ratio in half (see Appendix G) for each batch, and cross-fitting is satisfied during training iterations." + }, + { + "type": "table", + "bbox": [ + 0.506, + 0.508, + 0.889, + 0.572 + ], + "angle": 0, + "content": "
PORT+ADMLGowal+ADMLHAT+ADMLSCORE+ADMLWang+ADML
○Clean87.088.186.087.488.289.588.089.991.491.8
UAA60.666.460.766.861.067.561.168.064.070.5
∞Clean65.965.859.259.962.262.462.062.368.168.2
JAA31.237.930.837.731.237.331.237.135.741.1
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.504, + 0.575, + 0.89, + 0.629 + ], + "angle": 0, + "content": "Table 4. Comparing adversarial robustness of TRADES [62] using synthetic images: DDPM [18] and EDM [22] whether to the inclusion of ADML for CIFAR-10/100 with WRN-34-10: PORT [46] and WRN-28-10: Gowal [16], HAT [39], SCORE [36], Wang [56]." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.636, + 0.788, + 0.648 + ], + "angle": 0, + "content": "4.2. Robustness Validation on ADML" + }, + { + "type": "text", + "bbox": [ + 0.506, + 0.659, + 0.89, + 0.824 + ], + "angle": 0, + "content": "Adversarial Robustness. Based on our experimental setups, we have conducted enormous validations of adversarial robustness on CNNs in Table 1 and Transformers in Table 2. As shown in these tables, employing ADML on AT-based defense methods: AT [33], TRADES [62], MART [55], AWP [58] enables to largely improve adversarial robustness, compared with that of each defense method baseline. Bai et al. [1] have argued that Transformers cannot show noticeable adversarial robustness than CNNs, but we want to point out that the robustness of Transformers can be remarkably improved, especially in larger datasets." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.827, + 0.89, + 0.899 + ], + "angle": 0, + "content": "Ablation Study. In Table 3, we conduct ablation studies on the effect of sample-splitting plus cross-fitting on robustness and the effect of considering treatments as worst examples, non-worst examples, or both on robustness, either. According to the results, only considering treatments" + }, + { + "type": "page_number", + "bbox": [ + 0.485, + 0.947, + 0.514, + 0.957 + ], + "angle": 0, + "content": "4505" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.061, + 0.288, + 0.177 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.14, + 0.179, + 0.264, + 0.192 + ], + "angle": 0, + "content": "(a) CIFAR-10 [27]" + }, + { + "type": "image", + "bbox": [ + 0.293, + 0.061, + 0.488, + 0.177 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.336, + 0.179, + 0.468, + 0.192 + ], + "angle": 0, + "content": "(b) CIFAR-100 [27]" + }, + { + "type": "image", + "bbox": [ + 0.492, + 0.061, + 0.687, + 0.177 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.521, + 0.179, + 0.676, + 0.192 + ], + "angle": 0, + "content": "(c) Tiny-ImageNet [29]" + }, + { + "type": "image", + "bbox": [ + 0.689, + 0.062, + 0.883, + 0.177 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.74, + 0.179, + 0.851, + 0.192 + ], + "angle": 0, + "content": "(d) ImageNet [9]" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.192, + 0.89, + 0.221 + ], + "angle": 0, + "content": "Figure 3. Cumulative distribution with averaged adversarial robustness for bottom-k classes against PGD [33] on four benchmark datasets. Note that, \\(10\\%\\), \\(30\\%\\), and \\(50\\%\\) of \\(k\\) values are applied, and perturbation budget is set to \\([8/255, 8/255, 4/255, 2/255]\\) on each dataset." + }, + { + "type": "image", + "bbox": [ + 0.108, + 0.224, + 0.436, + 0.38 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.383, + 0.47, + 0.425 + ], + "angle": 0, + "content": "Figure 4. Distribution of adversarial robustness across whole classes on CIFAR-10. Four methods: AT [33], TRADES [62], MART [55], AWP [58] are integrated on each architecture." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.431, + 0.468, + 0.461 + ], + "angle": 0, + "content": "as worst examples can catch actual adversarial vulnerability, thereby improving robustness much more than others." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.461, + 0.468, + 0.597 + ], + "angle": 0, + "content": "Utilizing Synthetic Images. Recently, several works [46, 16, 39, 36, 56] have employed TRADES [62] utilizing synthetic images: DDPM [18] and EDM [22] to improve adversarial robustness based on the insight that data augmentation such as CutMix [60] can improve robustness [40]. To further investigate the benefits of ADML, we experiment ADML combined with TRADES on the synthetic images. Table 4 shows ADML can further improve the robustness even on synthetic images, demonstrating its efficacy." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.606, + 0.318, + 0.621 + ], + "angle": 0, + "content": "4.3. Causal Analysis on ADML" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.47, + 0.9 + ], + "angle": 0, + "content": "Adversarial Vulnerability. To validate the alleviation of adversarial vulnerability existing in certain classes as in Figure 1, we evaluate the averaged adversarial robustness for the cumulative distribution of bottom-\\(k\\) classes with respect to the network prediction. We set the \\(k\\) value as \\(10\\%\\), \\(30\\%\\), and \\(50\\%\\). As in Figure 3, we can observe that AT shows noticeable vulnerability in bottom-\\(k\\) classes, and such tendency pervades in four different datasets and architectures. If we successfully mitigate direct causal parameter of adversarial perturbations on each class, we expect apparent improvements of robustness for bottom-\\(k\\) classes. As in the figure, we can observe the notable robustness of ADML in the vulnerable bottom-\\(k\\) classes and corroborate its effectiveness to alleviate aforementioned phenomenon existing in current AT-based defenses. Further infographic is illustrated in Figure 4 for the integrated distribution of baselines [33, 62, 55, 58] and their corresponding ADML adoptions on each architecture, and it shows further adversarial" + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.224, + 0.886, + 0.31 + ], + "angle": 0, + "content": "
NetworksCIFAR10Tiny-ImageNet
ρ10ρ30ρ50ρAvgρ10ρ30ρ50ρAvg
ResNet-1853.9856.8952.9767.334.935.395.546.49
WRN-28-1063.6068.7068.2777.866.725.916.6010.74
ViT-B/1676.7885.4580.0384.331.541.731.913.08
DeiT-B/1669.3674.4668.6369.711.151.131.222.05
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.312, + 0.892, + 0.354 + ], + "angle": 0, + "content": "Table 5. Relative ratio of causal parameter (\\%) in CIFAR-10 and Tiny-ImageNet with four architectures. Note that \\( k \\) is set to 10,30, 50, and Avg indicates average on whole classes in each dataset." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.36, + 0.878, + 0.375 + ], + "angle": 0, + "content": "robustness in general (Additional results in Appendix H)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.376, + 0.892, + 0.617 + ], + "angle": 0, + "content": "Causal Parameter. By deploying ADML, we present a way of mitigating the magnitude of causal parameter \\( |\\theta| \\). To numerically calculate \\( |\\theta| \\), we employ Eq. (8) and measure the average of \\( |\\theta_{\\mathrm{ADML}}| \\) for ADML with respect to the bottom-\\( k \\) and whole classes, respectively. By dividing \\( |\\theta_{\\mathrm{ADML}}| \\) with \\( |\\theta_{\\mathrm{AT}}| \\), we can obtain relative ratio of causal parameter, \\( \\rho_k := 100 \\times |\\theta_{\\mathrm{ADML}}| / |\\theta_{\\mathrm{AT}}| \\) of adversarial examples in bottom-\\( k \\) classes. This ratio indicates that relative intensity of causal parameter compared to that of AT [33]. As in Table 5, we can observe that ADML shows less intensity of the causal parameter than AT, which means less causal effects of adversarial perturbations on target classes. From combinatorial results of preceding robustness comparison in Sec. 4.2, we corroborate that ADML indeed mitigate the intrinsic causal parameter and alleviate empirical observation in Figure 1, thus results in adversarial robustness." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.633, + 0.619, + 0.648 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.892, + 0.809 + ], + "angle": 0, + "content": "In this paper, we observe adversarial vulnerability varies across targets and still pervades even with deeper architectures and advanced defense methods. To fundamentally address it, we build causal perspective in adversarial examples and propose a way of estimating causal parameter representing the degree of adversarial vulnerability, namely Adversarial Double Machine Learning (ADML). By minimizing causal effects from the estimated vulnerability, ADML can mitigate the empirical phenomenon as well as solidly improve adversarial robustness with other methods." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Acknowledgments. This work was partially supported by two funds: IITP grant funded by the Korea government (MSIT) (No.2022-0-00984) and Center for Applied Research in Artificial Intelligence (CARAI) grant funded by DAPA and ADD (UD190031RD)." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "4506" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.158 + ], + "angle": 0, + "content": "[1] Yutong Bai, Jieru Mei, Alan L Yuille, and Cihang Xie. Are transformers more robust than cnns? Advances in Neural Information Processing Systems, 2021." + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.16, + 0.47, + 0.214 + ], + "angle": 0, + "content": "[2] Nicolas Carion, Francisco Massa, Gabriel Synnaeve, Nicolas Usunier, Alexander Kirillov, and Sergey Zagoruyko. 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To prevent potential threats, various adversarial training-based defense methods have grown rapidly and become a de facto standard approach for robustness. Despite recent competitive achievements, we observe that adversarial vulnerability varies across targets and certain vulnerabilities remain prevalent. Intriguingly, such peculiar phenomenon cannot be relieved even with deeper architectures and advanced defense methods. To address this issue, in this paper, we introduce a causal approach called Adversarial Double Machine Learning (ADML), which allows us to quantify the degree of adversarial vulnerability for network predictions and capture the effect of treatments on outcome of interests. ADML can directly estimate causal parameter of adversarial perturbations per se and mitigate negative effects that can potentially damage robustness, bridging a causal perspective into the adversarial vulnerability. Through extensive experiments on various CNN and Transformer architectures, we corroborate that ADML improves adversarial robustness with large margins and relieve the empirical observation. + +# 1. Introduction + +Along with the progressive developments of deep neural networks (DNNs) [17, 10, 2], an aspect of AI safety comes into a prominence in various computer vision research [45, 64, 12, 19]. Especially, adversarial examples [50, 15, 30] are known as potential threats on AI systems. With deliberately crafted perturbations on the visual inputs, adversarial examples are hardly distinguishable to human observers, but they easily result in misleading decision process of DNNs. Such adversarial vulnerability provokes weak reliability of inference process of DNNs and + +![](images/ded32df863e6df671fb766df832c0fc85aa35d9430c48613ac2f9185fb117fc0.jpg) + +![](images/b047ba990555ccaa161b87d7b7d8c128369ab598d7220291d8c020397099c8ef.jpg) +(b) Adversarial Defense Methods +Figure 1. The comparison of adversarial robustness along target classes with respect to (a) Network Architectures and (b) Adversarial Defense Methods on CIFAR-10 [27]. Note that, the distribution of adversarial robustness is consistent along both criteria. + +discourages AI adoption to the safety critical areas [54, 44]. + +In order to achieve robust and trustworthy DNNs from adversarial perturbation, previous methods [33, 28, 3, 62, 55, 58, 8] have delved into developing various adversarial attack and defense algorithms in the sense of cat-and-mouse game. As a seminal work, Madry et al. [33] have paved the way for obtaining robust network through adversarial training (AT) regarded as an ultimate augmentation training [52] with respect to adversarial examples. Based on its effectiveness, various subsequent works [62, 55, 58, 63, 39, 25] have investigated it to further enhance adversarial robustness. + +Although several AT-based defense methods have become a de facto standard due to their competitive adversarial robustness, we found an intriguing property of the current defense methods. As in Figure 1, we identify that the adversarial robustness for the each target class significantly varies with a large gap, and this phenomenon equally happens in the course of (a) network architectures and (b) + +![](images/02dbee48291103d15cd24f8d88fee461f847db0f55d52a5470d18d0b3f6fe53a.jpg) +(a) AT Causal Diagram + +![](images/99adc6bb6951d2708d06870e307ee30662f0b6aaba9fac10b269bd4e25efd149.jpg) +(b) Training Robust Network +Figure 2. Overview of canonical adversarial training procedure for robust network and its causal diagram. + +various AT-based defense methods. In addition, we would like to point out that the robustness of particular target is still severely vulnerable than others even with advanced architectures [10, 51, 31] and defense methods [62, 55, 58]. We argue that such phenomenon is derived from the current learning strategies of AT-based defense methods that lacks of understanding causal relations between the visual inputs and predictions. When considering AT methods as the ultimate augmentation [52], current methods rely solely on strengthening the correlation between adversarial examples and target classes through canonical objectives that improve robustness. To fundamentally address such vulnerability and understand the causal relation, we need to quantify the degree of vulnerability (i.e., causal parameter) and should mitigate its direct effects to the network predictions. + +Accordingly, we investigate the AT-based defense methods in a causal viewpoint and propose a way of precisely estimating causal parameter between adversarial examples and their predictions, namely Adversarial Double Machine Learning (ADML). We first represent a causal diagram of AT-based methods and interpret it as a generating process of robust classifiers as illustrated in Figure 2. Regarding standard adversarial training [33] as an optimizing procedure for the robust network parameters $f$ with respect to the worst perturbations $t$ , we can instantiate a generation $g^{1}$ as an adversarial attack of projected gradient descent (PGD) [33] for the given clean examples $x$ . + +Then, our research question is how to quantitatively compute the causal parameter $\theta$ between the perturbations $t$ and target classes $y$ , and identify the causal effects on outcome of our interests. Through double machine learning (DML) [5], widely studied as a powerful causal estimator [4, 7, 13, 20, 21] for the given two regression models, we can establish an initial research point of estimating causal parameter of adversarial perturbation with theoretical background. However, it is difficult to directly estimate $\theta$ in the high-dimensional manifolds, especially for DNNs. In this paper, we shed some lights on identifying causal parameter of the perturbations while theoretically bridging the gap be + +tween causal inference and adversarial robustness. Then, by minimizing the magnitude of the estimated causal parameter, we essentially lessen negative causal effects of adversarial vulnerability, and consequently acquire robust network with the aforementioned phenomenon alleviated. + +To corroborate the effectiveness of ADML on adversarial robustness, we set extensive experiments with four publicly available datasets [27, 29, 9]. Our experiments include various convolutional neural network architectures (CNNs), as well as Transformer architectures that have drawn great attention in both vision and language tasks [53, 10, 66, 65] yet relatively lack of being studied in adversarial research. + +Our contributions can be summarized as follows: + +- We present an empirical evidence that despite the recent advances in AT-based defenses, fundamentally adversarial vulnerability still remains across various architectures and defense algorithms. +- Bridging a causal perspective into adversary, we propose Adversarial Double Machine Learning (ADML), estimating causal parameter in adversarial examples and mitigating its causal effects damaging robustness. +- Through extensive experiments and analyses on various CNN and Transformer architectures, we corroborate intensive robustness of our proposed method with the phenomenon alleviated. + +# 2. Background and Related Work + +Notation. We deal with DNNs for classification as in Figure 2, represented by $f: \mathcal{X} \to \mathcal{Y}$ , where $\mathcal{X}$ and $\mathcal{Y}$ denote image and probability space, respectively. Let $x \in \mathcal{X}$ denote clean images and $y \in \mathcal{Y}$ indicate (one-hot) target classes corresponding to the images. Adversarial examples $x_{\mathrm{adv}}$ are generated by adversarial perturbations $t$ through DNNs, such that $x_{\mathrm{adv}} = x + t$ . Here, the perturbations are carefully created through the following formulation: + +$$ +\max _ {\| t \| _ {\infty} \leq \gamma} \mathcal {L} _ {\mathrm {C E}} (f (x + t), y), \tag {1} +$$ + +where $\mathcal{L}_{\mathrm{CE}}$ represents a pre-defined loss such as cross-entropy for classification task. We regard adversarial perturbations $t$ as $l_{\infty}$ perturbation within $\gamma$ -ball (i.e., perturbation budget). Here, $\| \cdot \|_{\infty}$ describes $l_{\infty}$ perturbation magnitude. + +# 2.1. Adversarial Training + +After several works [50, 15, 24] have found that human-imperceptible adversarial examples easily break network predictions, Madry et al. [33] have thrown a fundamental question: "How can we make models robust to adversarial examples with security guarantee?" To answer it, they have used the concept of empirical risk minimization (ERM) serving as a recipe to obtain classifiers with small population risk. Thanks to its reliable guarantee, they have consolidated it on the purpose of adversarial defense and + +accomplished the yardstick of adversarial training. The key factor of its achievement is regarding adversarial training as min-max optimization in a perspective of saddle point problem, which can be written as follows: + +$$ +\min _ {f} \mathbb {E} _ {(x, y) \sim \mathcal {D}} \left[ \max _ {\| t \| _ {\infty} \leq \gamma} \mathcal {L} _ {\mathrm {C E}} (f (x + t), y) \right], \tag {2} +$$ + +where $\mathcal{D}$ denotes a set of data samples $(x,y)$ . Here, they have presented an adversarial attack based on PGD to powerfully behave inner-maximization on Eq. (2), which is an ultimate first-order adversary with a multi-step variant of fast gradient sign method [28] by adding a random perturbation around the clean images $x$ . + +According to its impact, various adversarial training methods [33, 62, 55, 58] have grown exponentially and become de facto standards robustifying DNNs against adversarial perturbation. Zhang et al. [62] have pointed out the trade-off between clean accuracy and adversarial robustness, and reduced the gap between clean errors and robust errors. Wang et al. [55] have claimed that all of clean images are used to perform both inner-maximization and outer-minimization process in Eq. (2), irrespective of whether they are correctly classified or not. Thus, they have focused on misclassified clean images prone to be easily overlooked during adversarial training and demonstrated their significant impacts on the robustness by incorporating an explicit regularizer for them. Wu et al. [58] have studied loss landscapes with respect to network parameters and shown a positive correlation between the flatness of the parameter loss landscapes and the robustness. In the end, they have presented a double-perturbation mechanism where clean images are perturbed, while network parameters are simultaneously perturbed as well. + +On the other hand, we plunge into investigating where adversarial vulnerability comes from and observe that the vulnerability varies along target classes, and it significantly deteriorates network predictions. Further, we find that this phenomenon commonly happens across various network architectures and advanced defense methods. To relieve such peculiarity, we deploy double machine learning (DML) that helps to capture how treatments (i.e., adversarial perturbations) affect outcomes of our interests (i.e., network predictions), which is one of the powerful causal inference methods. After we concisely explicate the necessary background of DML, we will bridge it to the adversary in Sec. (3). + +# 2.2. Double Machine Learning + +In data science and econometrics, one of the fundamental problems is how to measure causality between treatments $t$ and outcomes of our interest $y$ among high-dimensional observational data samples (see Figure 2) to identify data generating process. At a first glance, it seems simple to compute their causality, but we should keep in mind the + +possibility for the existence of covariates $x$ affecting both treatments and outcomes. In other words, for example, if one may want to know the causal effects of drug dosage $t$ to blood pressure changes $y$ , one needs to collect observational data with respect to a variety of patients characteristics and their clinical histories $x$ , so as not to fall into biased environment. In reality, though, it is impossible to collect observational data including all covariates concerning treatments and outcomes, so it is not an easy problem to catch genuine causality under the unknown covariates $x$ . Therefore, there has been a growing demand for robustly predicting the unbiased causal relation, despite with the limited data samples. + +Recently, the advent of double machine learning (DML) [5] enables us to clarify the causality between treatments $t$ and outcomes $y$ , when two regression models are given. The formulation of initial DML can be written as: + +$$ +y = f (x) + \theta t + u, \quad (\mathbb {E} [ u \mid x, t ] = 0) \tag {3} +$$ + +$$ +t = g (x) + v, \quad (\mathbb {E} [ v \mid x ] = 0) +$$ + +where $\theta \in \mathbb{R}$ denotes causal parameter representing causal relation between $t \in \mathbb{R}^d$ and $y \in \mathbb{R}^d$ . In addition, $f$ indicates one regression model projecting covariates to outcome domain, and $g$ denotes another regression model generating treatments $t$ . In the sense that two regression models $f$ and $g$ are not main interest of DML, they are called as nuisance parameters to estimate the causal parameter $\theta$ . Note that, early DML assumes the problem setup is proceeded in partially linear settings as a shape of Robinson-style [42] described in Eq. (3), where "partially" literally means that treatments $t \in \mathbb{R}^d$ are linearly connected to outcome $y \in \mathbb{R}^d$ , while covariates $x$ are not. In addition, it is supposed that the conditional expected error of $u \in \mathbb{R}^d$ and $v \in \mathbb{R}^d$ equals to zero vector $0 \in \mathbb{R}^d$ . + +To obtain the causal parameter $\theta$ , Chernozhukov et al. [5] have provided a solution of estimating the causal parameter such that $\hat{\theta} = (y - \mathbb{E}[y \mid x]) \cdot v / \|v\|^2$ which satisfies Neyman-orthogonality [35, 34]. It makes $\hat{\theta}$ invariant to their erroneous of two nuisance parameters with the variance of causal parameter reduced. Furthermore, they have addressed a chronic problem that $\theta$ is only accessible when the two nuisance parameters are in a class of Donsker condition, where deep neural networks are not included in that condition. They have theoretically demonstrated sample-splitting plus cross-fitting can effectively relax Donsker condition and allow a broad array of modern ML methods [5] to compute unbiased causal parameter $\theta$ . + +Following the principle, they first split the data samples $\{\mathcal{D}_1,\mathcal{D}_2\} \sim \mathcal{D}$ and divided the process of causal inference into two steps: (a) training two nuisance parameters $f$ and $g$ with $\mathcal{D}_1$ , (b) estimating unbiased $\theta$ with $\mathcal{D}_2$ . Here, data samples $\mathcal{D}_2$ used to estimate unbiased causal parameters should not be overlapped with $\mathcal{D}_1$ utilized to train the nuisance parameters. To make copious combinations, they + +swapped the role of partitioned data samples $\mathcal{D}_1 \leftrightarrows \mathcal{D}_2$ or repeatedly split $\mathcal{D}$ . Subsequently, they have performed cross-fitting (e.g., $k$ -fold cross validation) by averaging the estimated causal parameters from various split samples. + +Along with the success of initial DML in partially linear settings, numerous variants [4, 7, 32, 14, 13, 26, 6] have emerged, and they have extended its initial nature to non-parametric settings with continuous treatments $t$ in order to capture more complicated non-linear causal relations in a debiased state. A non-parametric formulation [4] represents a more general problem setup of DML as follows: + +$$ +y = f (x, t) + u, \quad (\mathbb {E} [ u \mid x, t ] = 0) \tag {4} +$$ + +$$ +t = g (x) + v, \qquad (\mathbb {E} [ v \mid x ] = 0) +$$ + +where there is no explicit term for causal parameter $\theta$ exhibiting causal relation between treatments $t$ and outcomes $y$ , compared to Eq. (3). Colangelo et al. [7] have introduced a way of estimating causal parameter $\theta$ applicable to non-parametric settings with high-dimensional continuous treatments $t \in \mathcal{T}$ , which can be written as: + +$$ +\hat {\theta} = \frac {\partial}{\partial t} \mathbb {E} [ y \mid \operatorname {d o} (\mathcal {T} = t) ]. \tag {5} +$$ + +They have utilized do-operator [37] commonly used in graphical causal models and intervened on treatments $t$ to compute an interventional expectation $\mathbb{E}[y|\mathrm{do}(\mathcal{T} = t)]$ . It represents the expected outcome averaged from all the possible covariates for the given fixed treatments $t$ , such that $\mathbb{E}[y|\mathrm{do}(\mathcal{T} = t)] = \sum_{x\in \mathcal{X}}\mathbb{E}[y|x,t]p(x)$ . Specifically, they have estimated causal parameter $\theta$ by measuring how much the interventional expectation shifted, once they change the treatments slightly. Since the most important property of DML is Neyman-Orthogonality helping to robustly estimate the causal parameter, the interventional expectation should be also modified to satisfy the property [7, 23] of its invariance to nuisance parameters $f$ and $g$ . Its formulation can be written as follows (see details in Appendix A): + +$$ +\mathbb {E} [ y \mid \operatorname {d o} (\mathcal {T} = t) ] = \mathbb {E} _ {\mathcal {D} _ {t}} \left[ f (x, t) + \frac {y - f (x , t)}{p (\mathcal {T} = t \mid x)} \right], \tag {6} +$$ + +where $\mathcal{D}_t$ denotes a set of observational covariates and outcome samples for a fixed $t\in \mathcal{T}$ such that $(x,y)\sim \mathcal{D}_t$ , a sub-population of $\mathcal{D}$ . Note that, $p(\mathcal{T} = t|x)$ is related to treatment generator $g$ . Here, differentiating Eq. (6) enables us to acquire unbiased causal parameter in non-parametric settings with non-linear causal relation. + +In brief, DML captures unbiased causal relation between treatments $t$ and outcomes $y$ even with finite data samples, of which theoretical ground is (a) Neyman-Orthogonality for robustly estimated causal parameter despite undesirable outputs of nuisance parameters, and (b) sample-splitting plus cross-fitting for debiased causal parameters. + +# 3. Adversarial Double Machine Learning + +# 3.1. Adversarial Data Generating Process + +In general deep learning schemes, we have clean visual images $x \in \mathbb{R}^{hwc}$ and their corresponding target classes $y \in \mathbb{R}^d$ in our hand as a format of dataset, where $h, w, c$ denotes image resolution of height, width, channel, respectively, and $d$ denotes the number of classes. Thus, we do not need additional data generating process. For adversarial training, on the other hand, we need another data, which are adversarial perturbations generated from data samples $(x,y)$ as in Eq. (1). They are normally created by PGD [33] at every training iteration to make DNNs $f$ robust through min-max optimization game according to Eq. (2). + +Though, the more iterations of adversarial training, the fewer perturbations that impair network predictions. In other words, not all of the perturbations can corrupt network predictions among newly generated perturbations. Hence, we do not consider all of the perturbations as treatments but selectively define them as worst perturbations $t$ breaking network predictions, such that it satisfies $y \neq f(x + t)$ , where we call $x_{\mathrm{adv}} = x + t$ as worst examples. This is because our major goal is to catch actual adversarial vulnerability of DNNs, so that we do not tackle the perturbations incapable of harming network predictions. + +To access such worst perturbation, we choose perturbation generator $g$ as an adversarial attack of PGD according to standard adversarial training [33]. In addition, we pick the worst perturbations $t$ damaging network predictions among adversarial perturbations from the generator $g$ . In this way, we perform adversarial data generating process. + +# 3.2. Adversarial Problem Setup + +In the nature of adversarial training, the worst perturbations $t$ are explicitly injected to clean images $x$ such that $x_{\mathrm{adv}} = x + t$ , and these combined images are propagated into DNNs $f$ . Here, through this formulation as: $f(x + t) = f(x,t)$ , we connect DNNs for adversarial training and a nuisance parameter $f$ for non-parametric DML in Eq. (4). Fortunately, once we use Taylor expansion (with scalar-valued function for better understanding) and decompose $f$ by its input component as: $f(x + t) = f(x) + \sum_{i=1}^{\infty} t^{i} f^{(i)}(x) / i!$ , where $f^{(i)}$ indicates $i$ -th order derivative function, we can also express partially linear settings described in Eq. (3). That is, since adversarial examples start from the concept of "additive noise", both settings can exist at the same time in the scheme of adversarial training. From this reason, we build Adversarial Double Machine Learning (ADML): + +$$ +\begin{array}{l} y = f (x + t) = f (x) + \theta \bar {t} + u, \quad (\mathbb {E} [ u \mid x, t ] = 0) \tag {7} \\ t = g (x) + v, \quad (\mathbb {E} [ v \mid x ] = 0) \\ \end{array} +$$ + +where $\bar{t}$ indicates Taylor-order matrix: $[t, t^2, \dots]^T$ and $\theta$ represents Taylor-coefficient matrix $\left[\frac{f^{(1)}(x)}{1!}, \frac{f^{(2)}(x)}{2!}, \dots\right]$ (see + +strict mathematical verification in Appendix B). + +Here, we explain what the conditional expected error of $u$ and $v$ in Eq. (7) means in adversarial training. The former $\mathbb{E}[u|x,t] = 0$ implies the nature of adversarial training, which can be viewed as an ultimate augmentation robustifying DNNs, when infinite data population of $x$ and $t$ is given. Thus, it means network predictions become invariant in the end, despite the given worst perturbations. To implement it practically, we replace it with a mild assumption as $\mathbb{E}[u|x,g(x)] = 0$ (see Appendix C) that signifies PGD-based perturbations are used to perform adversarial training. This is because we cannot always acquire worst perturbations $t$ using only PGD. For the latter $\mathbb{E}[v|x] = 0$ , it represents PGD has capability of producing worst perturbations deviating network predictions during the training. + +# 3.3. Estimating Adversarily Causal Parameter + +Aligned with Eq. (3), an explicit term of $\theta$ is regarded as the causal parameter in our problem setup of ADML. We can now interpret that $\theta$ is a causal factor to spur adversarial vulnerability, since its magnitude easily catalyzes the deviations from network predictions of clean images. Here, if it is possible to directly compute $\theta$ over all data samples, we can finally handle adversarial vulnerability. + +Favorably, ADML follows both partially linear and nonparametric settings due to the concept of additive noise, thus we can employ the way of estimating causal parameter as in Eq. (5). The following formulation represents the estimated causal parameter $\hat{\theta}$ in ADML (see Appendix D). Note that, as we emphasized, sample-splitting plus cross-fitting must be applied to estimate unbiased causal parameter. + +$$ +\hat {\theta} = \mathbb {E} _ {\mathcal {D} _ {t}} \left[ - \left(\frac {1}{p (\mathcal {T} = t \mid x)} - 1\right) \frac {\partial}{\partial t} f (x + t) \right], \tag {8} +$$ + +where $\frac{\partial}{\partial t} f(x + t)$ indicates an input gradient for network predictions with respect to $t$ , and $p(\mathcal{T} = t|x)$ represents a distribution of worst perturbation given clean images $x$ . Here, we cannot directly handle this distribution due to the presence of multiple unknown parameters required to define it. For that reason, we instead approximate it with the sharpening technique by incorporating the information on attacked confidence such that $p(\mathcal{T} = t|x) \approx \mathbb{E}_{t'|x}[p(y_a|x,t')]$ (see Appendix E), where $y_{a}$ denotes attacked classes for the given worst perturbations $t$ . It implicitly means that the higher the attacked confidence, the higher the probability of finding worst perturbations. + +Aligned with the previous analysis [47] that show increasing magnitude of input gradient increases adversarial vulnerability, the magnitude of our causal parameter $|\hat{\theta}|$ also becomes huge due to $|\hat{\theta}| \propto |\frac{\partial}{\partial t} f(x + t)|$ . In parallel, Qin et al. [38] show the more ambiguous confident, the lower robustness (high vulnerability), and interestingly, the mag- + +Algorithm 1 ADML + +
Require: Data Samples D, Network f
1: for (x,y) ~ D do▷ Cross-Fitting
2: t' ← g(x)▷ PGD Attack
3: (x1,y1,t1'), (x2,y2,t2') ~ Split(x,y,t')
4: L_a ← L_Delphi(x1,y1,t1';f)▷ Mild Assumption
5: (xt2,yt2,t2) ← Select(y2 ≠ f(x2+t2')) ▷ Worst
6: j* ← arg maxj f_j(xt2+t2)▷ j: Class Index
7: τ ← 1/fj*(xt2+t2)-1▷ Balancing Ratio
8: L_b ← τL_CE(f(xt2+t2),yt2) + L_CE(f(xt2),yt2)
9: L_ADML ← L_a + L_b▷ ADML Loss
10: wf ← wf - α ∂/∂w_f L_ADML ▷ Weight Update (α: lr)
11: end for
+ +nitude of our causal parameter also $|\hat{\theta}|$ becomes large due to $|\hat{\theta}| \propto |1 / \mathbb{E}_{t' | x}[p(y_a | x, t')]|$ . + +Bringing such factors at once, $\hat{\theta}$ represents a weighted measurement of attacked confidence and their input gradients. Comprehensively, we can revisit that the network predictions of worst examples are easily flipped due to the following adversarial vulnerability: (a) ambiguous confidence around classification boundaries, or (b) high gradient magnitude amplifying the leverage of the perturbations. To improve the adversarial robustness of DNNs, it is essential to minimize the negative effects of causal parameters, which are combinatorial outcomes of the gradient and confidence. + +# 3.4. Mitigating Adversarial Vulnerability + +By deploying ADML, we propose a way of estimating causal parameter representing the degree of adversarial vulnerability that disturbs to predict the target classes. Then, our final goal is essentially to lessen its direct causal effect from adversarial perturbations in order to achieve robust networks. In detailed, alleviating their causal effect derived from $\hat{\theta}$ is the process of comprehensive reconstruction to focus more on vulnerable samples as we reflect their attacked confidence and gradients effects altogether. + +Accordingly, the very first way is naively reducing the magnitude of $\hat{\theta}$ to suppress adversarial vulnerability damaging the robustness. However, calculating $\hat{\theta}$ and minimizing its magnitude at every iteration is computationally striking because input gradient has huge dimension of $\mathbb{R}^{dhwc}$ and getting its gradient inevitably needs to compute second-order gradient with its tremendous dimension. We instead approximate the partial derivative $\frac{\partial}{\partial t}\mathbb{E}[y|\mathrm{do}(\mathcal{T} = t)]$ and minimize its magnitude, which can be written as: + +$$ +\min _ {f} | \hat {\theta} | \approx \left| \frac {\mathbb {E} [ y \mid \operatorname {d o} (\mathcal {T} = t) ] - \mathbb {E} [ y \mid \operatorname {d o} (\mathcal {T} = 0) ]}{t - 0} \right|, \tag {9} +$$ + +where network parameters of DNNs $f$ are only dependent on the numerator, thus we engross the numerator only. Lastly, we redesign $\mathbb{E}[y|\mathrm{do}(\mathcal{T} = t)]$ into the form of loss + +
MethodCIFAR-10CIFAR-100Tiny-ImageNet
CleanBIMPGD\(CW_{\infty}\)APDLRAACleanBIMPGD\(CW_{\infty}\)APDLRAACleanBIMPGD\(CW_{\infty}\)APDLRAA
VGG-16AT78.849.448.146.846.446.446.353.926.025.024.123.723.823.756.526.625.425.524.724.624.6
+ADML80.961.861.759.855.054.854.552.231.030.829.927.827.627.355.435.534.932.932.732.432.2
TRADES79.548.647.645.746.446.346.353.325.524.823.523.623.723.256.128.327.326.225.825.825.7
+ADML81.062.662.459.055.355.154.952.231.231.129.827.627.327.355.436.636.034.033.633.433.3
MART78.351.950.648.848.948.848.752.626.626.024.424.324.324.255.727.826.626.025.725.725.6
+ADML80.462.462.260.355.755.355.251.631.631.029.627.827.527.355.136.235.834.934.333.933.7
AWP77.253.952.650.151.451.151.052.130.229.327.528.728.528.356.931.631.029.429.929.829.7
+ADML80.264.764.661.858.057.757.552.333.833.531.329.729.529.054.536.636.134.634.533.833.7
ResNet-18AT83.153.351.950.849.949.749.559.127.126.325.425.325.325.161.531.030.129.528.828.928.8
+ADML84.561.160.858.556.756.255.656.431.630.929.528.428.227.857.335.935.533.534.734.734.6
TRADES83.353.052.050.950.950.850.758.527.626.826.225.925.925.860.432.031.030.229.729.629.5
+ADML84.062.361.959.556.756.655.957.331.731.630.028.828.528.058.437.036.033.335.034.134.0
MART82.554.152.851.351.550.850.858.127.726.725.525.425.125.060.631.030.229.829.029.029.0
+ADML84.163.362.958.756.856.456.257.432.131.730.228.928.828.557.136.636.033.635.133.933.8
AWP81.356.355.553.654.254.054.057.931.430.729.030.030.029.861.434.734.132.433.333.233.1
+ADML84.064.664.561.460.559.959.756.233.932.930.731.130.530.359.838.638.135.937.736.736.6
WideResNet-28-10AT86.755.453.453.451.351.351.261.928.827.427.126.026.025.964.832.731.231.130.130.130.0
+ADML87.561.760.758.856.456.355.858.932.932.631.329.629.229.162.143.543.141.141.940.440.2
TRADES86.055.353.753.651.651.651.461.929.128.527.826.726.826.764.232.531.631.430.029.929.8
+ADML88.562.961.959.657.657.656.661.633.333.031.530.030.129.663.143.542.941.041.440.340.2
MART86.456.054.353.451.651.651.561.628.326.726.425.325.425.364.232.931.831.830.730.530.5
+ADML88.362.160.959.656.756.656.259.633.032.931.630.329.929.661.842.842.640.340.739.038.9
AWP85.960.258.957.256.956.956.862.433.032.231.130.930.930.865.436.936.035.134.834.834.7
+ADML88.267.567.464.263.563.263.162.539.739.336.937.637.136.864.944.644.241.943.342.142.0
WideResNet-70-10AT88.156.654.855.052.853.052.864.128.427.327.426.026.425.665.334.933.433.932.232.232.1
+ADML88.961.561.461.056.556.356.063.330.029.228.826.926.726.461.037.737.436.933.833.032.9
TRADES87.756.354.755.053.453.353.363.328.727.827.926.626.226.065.734.432.633.031.531.531.4
+ADML89.163.963.362.759.059.659.063.431.230.830.327.527.127.061.840.239.538.836.135.535.4
MART88.057.455.555.452.852.852.663.228.727.527.525.826.325.665.433.832.532.431.331.331.2
+ADML88.561.761.360.856.756.856.662.330.130.029.429.329.128.763.241.841.040.237.736.636.5
AWP86.661.860.659.959.159.459.265.233.333.331.731.530.330.066.740.740.040.039.139.038.9
+ADML89.467.066.966.163.463.663.165.341.941.840.938.938.037.665.845.044.543.343.543.142.8
+ +Table 1. Comparing adversarial robustness of various defence methods whether to the inclusion of ADML for CIFAR-10 [27], CIFAR-100 [27], Tiny-ImageNet [29] trained with VGG-16 [48], ResNet-18 [17], WideResNet-28-10 [61], and WideResNet-70-10 [61]. + +function used in deep learning and finally construct the objective function for ADML, of which formulation can be written as follows (see details in Appendix F): + +$$ +\min _ {f} \mathbb {E} _ {\mathcal {D} _ {t}} [ \tau \mathcal {L} _ {\mathrm {C E}} (f (x + t), y) ] + \mathbb {E} _ {\mathcal {D} _ {0}} [ \mathcal {L} _ {\mathrm {C E}} (f (x), y) ], \tag {10} +$$ + +where we denote $\tau = \frac{1}{p(\mathcal{T} = t|x)} - 1$ as balancing ratio. The current AT-based defenses use an equal weight "1/n" to loss for all data samples: $\frac{1}{n}\sum_{i=1}^{n}\mathcal{L}_{\text{Defense}}(x_i, y_i, t_i; f)$ because they presume all of perturbations have equal causal effect (successful attack) to change targets without realizing vulnerable samples. Whereas, ADML uses the balancing ratio $\tau$ to adaptively focus on vulnerable samples by reweighting the loss. To realize ADML, we describe Algorithm 1 to explain further details, where $\mathcal{L}_{\text{Defense}}(x, y, t; f)$ indicates a main body of the loss function for AT-based defenses. + +# 4. Experiment + +# 4.1. Implementation Details + +Datasets & Networks. We conduct comprehensive experiments on various datasets and networks. For datasets, we use CIFAR-10 [27], CIFAR-100 [27], and two larger datasets: Tiny-[ImageNet [29] and ImageNet [9]. For networks, four CNN architectures: [48, 17, 61] and four Transformer architectures: [10, 51] are used. + +Adversarial Attacks. We adaptively set perturbation budget $\gamma$ of adversarial attacks depending on the classification difficulty of the four datasets: 8/255 equally for CIFAR-10 [27] and CIFAR100 [27], 4/255 for Tiny-ImageNet [29], and 2/255 for ImageNet [9]. We prepare three standard attacks: BIM [28], PGD [33], $\mathrm{CW}_{\infty}$ [3], and three advanced attacks: AP (Auto-PGD: step size-free), DLR (Auto-DLR: shift and scaling invariant), AA (Auto-Attack: parameter-free), all of which are introduced by Francesco et al. [8]. PGD, AP, DLR have 30 steps with random starts, where PGD has step size $2.3 \times \frac{\gamma}{30}$ , and AP, DLR both have momentum coefficient $\rho = 0.75$ . $\mathrm{CW}_{\infty}$ uses PGD-based gradient clamping for $l_{\infty}$ with CW objective [3] on $\kappa = 0$ . + +Adversarial Defenses. We use four defense baselines with a standard baseline: AT [33] and three advanced defense baselines: TRADES [62], MART [55], AWP [58]. To fairly validate experiments, a perturbation generator, PGD [33] is equivalently used to generate adversarial examples for which we use the budget 8/255 and set 10 steps with $2.3 \times \frac{\gamma}{10}$ step size in training. Especially, adversarially training Tiny-ImageNet [29] and ImageNet [9] is a computational burden, thus we employ fast adversarial training [57] with FGSM [15]. For training CNNs, we use SGD [43] with a learning rate of 0.5 scheduled by Cyclic [49] in 120 epochs and use early stopping to prevent overfitting [41]. For training Transformers, we use SGD [43] with a learn + +
MethodCIFAR-10CIFAR-100Tiny-ImageNet
CleanBIMPGDCWAPDLRAACleanBIMPGDCW∞APDLRAACleanBIMPGDCW∞APDLRAA
VIT-S/16AT83.549.947.346.644.944.844.759.926.625.825.124.624.524.573.835.834.133.531.931.931.8
+ADML88.156.855.153.851.350.750.762.732.430.729.428.427.927.775.647.746.645.645.342.742.6
TRADES85.051.049.448.648.148.047.859.527.326.626.325.825.925.772.938.837.837.436.136.136.0
+ADML87.957.656.255.152.752.051.963.235.034.733.831.631.331.275.349.148.047.145.643.043.0
MART85.752.449.748.946.746.746.660.928.627.927.526.526.526.477.638.637.236.835.235.235.2
+ADML88.057.556.154.751.951.451.462.734.432.731.730.029.329.276.548.947.746.346.042.942.9
AWP84.954.252.351.650.149.949.961.129.629.028.127.727.727.678.141.039.338.737.337.337.2
+ADML88.057.054.353.350.149.649.564.434.834.133.031.330.630.576.647.546.444.944.742.542.4
VIT-B/16AT87.052.850.850.447.847.747.763.330.429.629.228.628.328.372.440.137.737.834.434.334.5
+ADML89.956.154.954.151.651.451.267.138.136.135.434.333.433.179.050.249.748.448.546.946.8
TRADES85.353.852.451.650.950.850.865.732.631.531.029.930.030.073.243.341.241.839.139.039.4
+ADML88.958.657.356.154.754.454.369.438.937.937.034.834.634.779.454.052.251.648.247.347.2
MART87.453.350.650.548.348.448.265.731.930.830.229.229.229.179.341.740.039.636.836.837.1
+ADML89.657.055.654.351.851.551.368.935.433.532.930.530.130.280.150.750.149.048.947.447.0
AWP87.454.952.951.949.849.849.766.833.431.731.330.330.230.278.745.042.242.239.539.439.7
+ADML90.459.156.756.653.853.652.870.037.736.135.633.332.832.979.350.849.748.048.046.045.8
DeT-S/16AT83.549.347.846.745.345.345.259.529.228.527.627.527.527.475.737.435.634.733.133.033.0
+ADML87.756.856.054.952.351.951.963.734.432.931.731.430.530.474.744.943.642.240.839.539.4
TRADES84.150.649.348.848.048.048.061.829.428.827.828.128.028.074.839.038.037.436.436.436.3
+ADML87.957.856.555.353.753.053.266.237.236.435.533.232.332.376.345.244.943.839.538.738.4
MART84.252.350.049.147.847.647.559.831.030.629.329.729.629.674.640.139.138.437.737.637.6
+ADML87.557.555.655.052.652.352.265.337.035.634.732.430.730.775.245.344.243.342.838.438.4
AWP82.353.552.351.550.550.450.460.731.831.430.231.030.030.075.441.740.939.839.039.139.0
+ADML86.755.953.252.650.650.550.564.739.438.136.835.734.534.575.449.447.646.545.742.842.8
DeT-B/16AT84.651.549.548.447.247.147.064.930.329.128.427.527.427.479.138.636.336.134.434.334.0
+ADML89.755.754.853.850.049.749.765.735.434.433.432.230.330.377.646.945.644.744.940.540.5
TRADES85.452.851.750.650.250.250.264.830.029.328.628.428.328.378.343.141.640.540.540.540.4
+ADML90.261.460.459.458.357.657.668.640.539.938.437.436.836.780.845.443.542.743.242.942.7
MART83.954.753.252.051.050.950.764.531.931.130.530.230.130.075.844.643.342.642.642.642.5
+ADML89.660.360.258.955.155.055.065.339.638.537.135.434.634.677.847.746.144.645.544.844.7
AWP83.354.153.152.451.851.651.565.432.331.530.430.230.130.176.642.841.440.742.842.842.7
+ADML88.959.057.356.454.053.853.769.739.438.337.335.234.434.480.351.250.248.949.448.148.0
+ +Table 2. Comparing adversarial robustness of various defence methods whether to the inclusion of ADML for CIFAR-10 [27], CIFAR-100 [27], Tiny-ImageNet [29] trained with ViT-S/16 [10], ViT-B/16 [10], DeiT-S/16 [51], and DeiT-B/16 [51]. + +
SS+CFWNWCIFAR-10Tiny-ImageNet
PGDCW∞DLRAAPGDCW∞DLRAA
VGG-16✓✓X61.759.854.854.434.932.932.432.2
✓✓✓52.349.448.948.825.424.924.224.2
✓X✓48.047.145.845.826.025.824.524.4
X✓X52.650.049.449.428.127.026.426.4
ResNet-18✓✓X60.858.556.255.635.533.534.734.6
✓✓✓51.750.149.549.234.932.432.732.7
✓X✓50.850.549.449.130.029.529.028.9
X✓X53.651.751.451.031.729.730.230.1
+ +Table 3. Ablation study for the effects of sample-splitting plus cross-fitting (SS+CF) and Worst(W) / Non-Worst(NW) examples. + +ing rate of 0.001 on the equal experimental setup of CNNs, where $224 \times 224$ resolution is applied for all datasets and pretrained parameters on ImageNet-1k models are utilized. + +Training ADML. After the completion of standard adversarial training [33], we apply AT-based defense methods to line 4 in Algorithm 1 for ADML. We then optimize adversarially trained CNNs in 10 epochs using SGD [43] with a learning rate of 0.001 scheduled by Cyclic [49], which allows empirically sufficient convergence to robustness. In addition, adversarially trained Transformers are also optimized with ADML using a learning rate of 0.0001 on the equal experimental setup of CNNs. Note that, we set sample-splitting ratio in half (see Appendix G) for each batch, and cross-fitting is satisfied during training iterations. + +
PORT+ADMLGowal+ADMLHAT+ADMLSCORE+ADMLWang+ADML
○Clean87.088.186.087.488.289.588.089.991.491.8
UAA60.666.460.766.861.067.561.168.064.070.5
∞Clean65.965.859.259.962.262.462.062.368.168.2
JAA31.237.930.837.731.237.331.237.135.741.1
+ +Table 4. Comparing adversarial robustness of TRADES [62] using synthetic images: DDPM [18] and EDM [22] whether to the inclusion of ADML for CIFAR-10/100 with WRN-34-10: PORT [46] and WRN-28-10: Gowal [16], HAT [39], SCORE [36], Wang [56]. + +# 4.2. Robustness Validation on ADML + +Adversarial Robustness. Based on our experimental setups, we have conducted enormous validations of adversarial robustness on CNNs in Table 1 and Transformers in Table 2. As shown in these tables, employing ADML on AT-based defense methods: AT [33], TRADES [62], MART [55], AWP [58] enables to largely improve adversarial robustness, compared with that of each defense method baseline. Bai et al. [1] have argued that Transformers cannot show noticeable adversarial robustness than CNNs, but we want to point out that the robustness of Transformers can be remarkably improved, especially in larger datasets. + +Ablation Study. In Table 3, we conduct ablation studies on the effect of sample-splitting plus cross-fitting on robustness and the effect of considering treatments as worst examples, non-worst examples, or both on robustness, either. According to the results, only considering treatments + +![](images/55afc6e3c2b8f150b815aa85d03d8b568c6ed32cd30ba9b61f1782618de542dd.jpg) +(a) CIFAR-10 [27] + +![](images/3ba5f2c4c181843f98b672ee5ad9971a5f0fe96f2ef6eca2eec3cb393a368573.jpg) +(b) CIFAR-100 [27] + +![](images/5660746d2778873f77e230c6d29c782f12f370c00323d443c14b51e31ba363d7.jpg) +(c) Tiny-ImageNet [29] + +![](images/582191614aa4ad7c3dca3c7d2ba571ff2701dbe9fb3ea4537144174cf1d8e4f2.jpg) +(d) ImageNet [9] + +![](images/2e011e0eda560ec3b37bd795fb594a5d55b7479cc9d9d7d0940358b3afd065d7.jpg) +Figure 3. Cumulative distribution with averaged adversarial robustness for bottom-k classes against PGD [33] on four benchmark datasets. Note that, $10\%$ , $30\%$ , and $50\%$ of $k$ values are applied, and perturbation budget is set to $[8/255, 8/255, 4/255, 2/255]$ on each dataset. +Figure 4. Distribution of adversarial robustness across whole classes on CIFAR-10. Four methods: AT [33], TRADES [62], MART [55], AWP [58] are integrated on each architecture. + +as worst examples can catch actual adversarial vulnerability, thereby improving robustness much more than others. + +Utilizing Synthetic Images. Recently, several works [46, 16, 39, 36, 56] have employed TRADES [62] utilizing synthetic images: DDPM [18] and EDM [22] to improve adversarial robustness based on the insight that data augmentation such as CutMix [60] can improve robustness [40]. To further investigate the benefits of ADML, we experiment ADML combined with TRADES on the synthetic images. Table 4 shows ADML can further improve the robustness even on synthetic images, demonstrating its efficacy. + +# 4.3. Causal Analysis on ADML + +Adversarial Vulnerability. To validate the alleviation of adversarial vulnerability existing in certain classes as in Figure 1, we evaluate the averaged adversarial robustness for the cumulative distribution of bottom- $k$ classes with respect to the network prediction. We set the $k$ value as $10\%$ , $30\%$ , and $50\%$ . As in Figure 3, we can observe that AT shows noticeable vulnerability in bottom- $k$ classes, and such tendency pervades in four different datasets and architectures. If we successfully mitigate direct causal parameter of adversarial perturbations on each class, we expect apparent improvements of robustness for bottom- $k$ classes. As in the figure, we can observe the notable robustness of ADML in the vulnerable bottom- $k$ classes and corroborate its effectiveness to alleviate aforementioned phenomenon existing in current AT-based defenses. Further infographic is illustrated in Figure 4 for the integrated distribution of baselines [33, 62, 55, 58] and their corresponding ADML adoptions on each architecture, and it shows further adversarial + +
NetworksCIFAR10Tiny-ImageNet
ρ10ρ30ρ50ρAvgρ10ρ30ρ50ρAvg
ResNet-1853.9856.8952.9767.334.935.395.546.49
WRN-28-1063.6068.7068.2777.866.725.916.6010.74
ViT-B/1676.7885.4580.0384.331.541.731.913.08
DeiT-B/1669.3674.4668.6369.711.151.131.222.05
+ +Table 5. Relative ratio of causal parameter (\%) in CIFAR-10 and Tiny-ImageNet with four architectures. Note that $k$ is set to 10,30, 50, and Avg indicates average on whole classes in each dataset. + +robustness in general (Additional results in Appendix H). + +Causal Parameter. By deploying ADML, we present a way of mitigating the magnitude of causal parameter $|\theta|$ . To numerically calculate $|\theta|$ , we employ Eq. (8) and measure the average of $|\theta_{\mathrm{ADML}}|$ for ADML with respect to the bottom- $k$ and whole classes, respectively. By dividing $|\theta_{\mathrm{ADML}}|$ with $|\theta_{\mathrm{AT}}|$ , we can obtain relative ratio of causal parameter, $\rho_k := 100 \times |\theta_{\mathrm{ADML}}| / |\theta_{\mathrm{AT}}|$ of adversarial examples in bottom- $k$ classes. This ratio indicates that relative intensity of causal parameter compared to that of AT [33]. As in Table 5, we can observe that ADML shows less intensity of the causal parameter than AT, which means less causal effects of adversarial perturbations on target classes. From combinatorial results of preceding robustness comparison in Sec. 4.2, we corroborate that ADML indeed mitigate the intrinsic causal parameter and alleviate empirical observation in Figure 1, thus results in adversarial robustness. + +# 5. Conclusion + +In this paper, we observe adversarial vulnerability varies across targets and still pervades even with deeper architectures and advanced defense methods. To fundamentally address it, we build causal perspective in adversarial examples and propose a way of estimating causal parameter representing the degree of adversarial vulnerability, namely Adversarial Double Machine Learning (ADML). By minimizing causal effects from the estimated vulnerability, ADML can mitigate the empirical phenomenon as well as solidly improve adversarial robustness with other methods. + +Acknowledgments. This work was partially supported by two funds: IITP grant funded by the Korea government (MSIT) (No.2022-0-00984) and Center for Applied Research in Artificial Intelligence (CARAI) grant funded by DAPA and ADD (UD190031RD). + +# References + +[1] Yutong Bai, Jieru Mei, Alan L Yuille, and Cihang Xie. Are transformers more robust than cnns? Advances in Neural Information Processing Systems, 2021. +[2] Nicolas Carion, Francisco Massa, Gabriel Synnaeve, Nicolas Usunier, Alexander Kirillov, and Sergey Zagoruyko. End-to-end object detection with transformers. In European Conference on Computer Vision, pages 213-229, 2020. +[3] Nicholas Carlini and David Wagner. Towards evaluating the robustness of neural networks. In 2017 IEEE Symposium on Security and Privacy, pages 39-57. 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To prevent potential threats, various adversarial training-based defense methods have grown rapidly and become a de facto standard approach for robustness. Despite recent competitive achievements, we observe that adversarial vulnerability varies across targets and certain vulnerabilities remain prevalent. Intriguingly, such peculiar phenomenon cannot be relieved even with deeper architectures and advanced defense methods. To address this issue, in this paper, we introduce a causal approach called Adversarial Double Machine Learning (ADML), which allows us to quantify the degree of adversarial vulnerability for network predictions and capture the effect of treatments on outcome of interests. ADML can directly estimate causal parameter of adversarial perturbations per se and mitigate negative effects that can potentially damage robustness, bridging a causal perspective into the adversarial vulnerability. Through extensive experiments on various CNN and Transformer architectures, we corroborate that ADML improves adversarial robustness with large margins and relieve the empirical observation." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 555, + 128, + 567 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 555, + 128, + 567 + ], + "spans": [ + { + "bbox": [ + 47, + 555, + 128, + 567 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 575, + 287, + 695 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 575, + 287, + 695 + ], + "spans": [ + { + "bbox": [ + 46, + 575, + 287, + 695 + ], + "type": "text", + "content": "Along with the progressive developments of deep neural networks (DNNs) [17, 10, 2], an aspect of AI safety comes into a prominence in various computer vision research [45, 64, 12, 19]. Especially, adversarial examples [50, 15, 30] are known as potential threats on AI systems. With deliberately crafted perturbations on the visual inputs, adversarial examples are hardly distinguishable to human observers, but they easily result in misleading decision process of DNNs. Such adversarial vulnerability provokes weak reliability of inference process of DNNs and" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 306, + 229, + 544, + 332 + ], + "blocks": [ + { + "bbox": [ + 306, + 229, + 544, + 332 + ], + "lines": [ + { + "bbox": [ + 306, + 229, + 544, + 332 + ], + "spans": [ + { + "bbox": [ + 306, + 229, + 544, + 332 + ], + "type": "image", + "image_path": "ded32df863e6df671fb766df832c0fc85aa35d9430c48613ac2f9185fb117fc0.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 310, + 329, + 536, + 430 + ], + "blocks": [ + { + "bbox": [ + 310, + 329, + 536, + 430 + ], + "lines": [ + { + "bbox": [ + 310, + 329, + 536, + 430 + ], + "spans": [ + { + "bbox": [ + 310, + 329, + 536, + 430 + ], + "type": "image", + "image_path": "b047ba990555ccaa161b87d7b7d8c128369ab598d7220291d8c020397099c8ef.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 361, + 431, + 495, + 441 + ], + "lines": [ + { + "bbox": [ + 361, + 431, + 495, + 441 + ], + "spans": [ + { + "bbox": [ + 361, + 431, + 495, + 441 + ], + "type": "text", + "content": "(b) Adversarial Defense Methods" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 443, + 545, + 487 + ], + "lines": [ + { + "bbox": [ + 305, + 443, + 545, + 487 + ], + "spans": [ + { + "bbox": [ + 305, + 443, + 545, + 487 + ], + "type": "text", + "content": "Figure 1. The comparison of adversarial robustness along target classes with respect to (a) Network Architectures and (b) Adversarial Defense Methods on CIFAR-10 [27]. Note that, the distribution of adversarial robustness is consistent along both criteria." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 495, + 545, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 495, + 545, + 507 + ], + "spans": [ + { + "bbox": [ + 306, + 495, + 545, + 507 + ], + "type": "text", + "content": "discourages AI adoption to the safety critical areas [54, 44]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 508, + 546, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 508, + 546, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 508, + 546, + 628 + ], + "type": "text", + "content": "In order to achieve robust and trustworthy DNNs from adversarial perturbation, previous methods [33, 28, 3, 62, 55, 58, 8] have delved into developing various adversarial attack and defense algorithms in the sense of cat-and-mouse game. As a seminal work, Madry et al. [33] have paved the way for obtaining robust network through adversarial training (AT) regarded as an ultimate augmentation training [52] with respect to adversarial examples. Based on its effectiveness, various subsequent works [62, 55, 58, 63, 39, 25] have investigated it to further enhance adversarial robustness." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "content": "Although several AT-based defense methods have become a de facto standard due to their competitive adversarial robustness, we found an intriguing property of the current defense methods. As in Figure 1, we identify that the adversarial robustness for the each target class significantly varies with a large gap, and this phenomenon equally happens in the course of (a) network architectures and (b)" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 205, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 205, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 205, + 713 + ], + "type": "text", + "content": "*Equal contribution. † Corresponding author." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4499" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 70, + 153, + 171 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 153, + 171 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 153, + 171 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 153, + 171 + ], + "type": "image", + "image_path": "02dbee48291103d15cd24f8d88fee461f847db0f55d52a5470d18d0b3f6fe53a.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 53, + 176, + 148, + 187 + ], + "lines": [ + { + "bbox": [ + 53, + 176, + 148, + 187 + ], + "spans": [ + { + "bbox": [ + 53, + 176, + 148, + 187 + ], + "type": "text", + "content": "(a) AT Causal Diagram" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 161, + 71, + 284, + 173 + ], + "blocks": [ + { + "bbox": [ + 161, + 71, + 284, + 173 + ], + "lines": [ + { + "bbox": [ + 161, + 71, + 284, + 173 + ], + "spans": [ + { + "bbox": [ + 161, + 71, + 284, + 173 + ], + "type": "image", + "image_path": "99adc6bb6951d2708d06870e307ee30662f0b6aaba9fac10b269bd4e25efd149.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 163, + 176, + 280, + 187 + ], + "lines": [ + { + "bbox": [ + 163, + 176, + 280, + 187 + ], + "spans": [ + { + "bbox": [ + 163, + 176, + 280, + 187 + ], + "type": "text", + "content": "(b) Training Robust Network" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 47, + 190, + 287, + 212 + ], + "lines": [ + { + "bbox": [ + 47, + 190, + 287, + 212 + ], + "spans": [ + { + "bbox": [ + 47, + 190, + 287, + 212 + ], + "type": "text", + "content": "Figure 2. Overview of canonical adversarial training procedure for robust network and its causal diagram." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 216, + 287, + 395 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 216, + 287, + 395 + ], + "spans": [ + { + "bbox": [ + 46, + 216, + 287, + 395 + ], + "type": "text", + "content": "various AT-based defense methods. In addition, we would like to point out that the robustness of particular target is still severely vulnerable than others even with advanced architectures [10, 51, 31] and defense methods [62, 55, 58]. We argue that such phenomenon is derived from the current learning strategies of AT-based defense methods that lacks of understanding causal relations between the visual inputs and predictions. When considering AT methods as the ultimate augmentation [52], current methods rely solely on strengthening the correlation between adversarial examples and target classes through canonical objectives that improve robustness. To fundamentally address such vulnerability and understand the causal relation, we need to quantify the degree of vulnerability (i.e., causal parameter) and should mitigate its direct effects to the network predictions." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 396, + 287, + 539 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 396, + 287, + 539 + ], + "spans": [ + { + "bbox": [ + 46, + 396, + 287, + 539 + ], + "type": "text", + "content": "Accordingly, we investigate the AT-based defense methods in a causal viewpoint and propose a way of precisely estimating causal parameter between adversarial examples and their predictions, namely Adversarial Double Machine Learning (ADML). We first represent a causal diagram of AT-based methods and interpret it as a generating process of robust classifiers as illustrated in Figure 2. Regarding standard adversarial training [33] as an optimizing procedure for the robust network parameters " + }, + { + "bbox": [ + 46, + 396, + 287, + 539 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 396, + 287, + 539 + ], + "type": "text", + "content": " with respect to the worst perturbations " + }, + { + "bbox": [ + 46, + 396, + 287, + 539 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 396, + 287, + 539 + ], + "type": "text", + "content": ", we can instantiate a generation " + }, + { + "bbox": [ + 46, + 396, + 287, + 539 + ], + "type": "inline_equation", + "content": "g^{1}" + }, + { + "bbox": [ + 46, + 396, + 287, + 539 + ], + "type": "text", + "content": " as an adversarial attack of projected gradient descent (PGD) [33] for the given clean examples " + }, + { + "bbox": [ + 46, + 396, + 287, + 539 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 396, + 287, + 539 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 540, + 287, + 684 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 540, + 287, + 684 + ], + "spans": [ + { + "bbox": [ + 46, + 540, + 287, + 684 + ], + "type": "text", + "content": "Then, our research question is how to quantitatively compute the causal parameter " + }, + { + "bbox": [ + 46, + 540, + 287, + 684 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 540, + 287, + 684 + ], + "type": "text", + "content": " between the perturbations " + }, + { + "bbox": [ + 46, + 540, + 287, + 684 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 540, + 287, + 684 + ], + "type": "text", + "content": " and target classes " + }, + { + "bbox": [ + 46, + 540, + 287, + 684 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 540, + 287, + 684 + ], + "type": "text", + "content": ", and identify the causal effects on outcome of our interests. Through double machine learning (DML) [5], widely studied as a powerful causal estimator [4, 7, 13, 20, 21] for the given two regression models, we can establish an initial research point of estimating causal parameter of adversarial perturbation with theoretical background. However, it is difficult to directly estimate " + }, + { + "bbox": [ + 46, + 540, + 287, + 684 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 540, + 287, + 684 + ], + "type": "text", + "content": " in the high-dimensional manifolds, especially for DNNs. In this paper, we shed some lights on identifying causal parameter of the perturbations while theoretically bridging the gap be" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 72, + 545, + 132 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 545, + 132 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 545, + 132 + ], + "type": "text", + "content": "tween causal inference and adversarial robustness. Then, by minimizing the magnitude of the estimated causal parameter, we essentially lessen negative causal effects of adversarial vulnerability, and consequently acquire robust network with the aforementioned phenomenon alleviated." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 133, + 545, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 133, + 545, + 215 + ], + "spans": [ + { + "bbox": [ + 304, + 133, + 545, + 215 + ], + "type": "text", + "content": "To corroborate the effectiveness of ADML on adversarial robustness, we set extensive experiments with four publicly available datasets [27, 29, 9]. Our experiments include various convolutional neural network architectures (CNNs), as well as Transformer architectures that have drawn great attention in both vision and language tasks [53, 10, 66, 65] yet relatively lack of being studied in adversarial research." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 216, + 517, + 226 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 216, + 517, + 226 + ], + "spans": [ + { + "bbox": [ + 317, + 216, + 517, + 226 + ], + "type": "text", + "content": "Our contributions can be summarized as follows:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 228, + 545, + 371 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 317, + 228, + 545, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 228, + 545, + 275 + ], + "spans": [ + { + "bbox": [ + 317, + 228, + 545, + 275 + ], + "type": "text", + "content": "- We present an empirical evidence that despite the recent advances in AT-based defenses, fundamentally adversarial vulnerability still remains across various architectures and defense algorithms." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 317, + 275, + 545, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 275, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 317, + 275, + 545, + 323 + ], + "type": "text", + "content": "- Bridging a causal perspective into adversary, we propose Adversarial Double Machine Learning (ADML), estimating causal parameter in adversarial examples and mitigating its causal effects damaging robustness." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 317, + 323, + 545, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 323, + 545, + 371 + ], + "spans": [ + { + "bbox": [ + 317, + 323, + 545, + 371 + ], + "type": "text", + "content": "- Through extensive experiments and analyses on various CNN and Transformer architectures, we corroborate intensive robustness of our proposed method with the phenomenon alleviated." + } + ] + } + ], + "index": 13 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 381, + 480, + 395 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 381, + 480, + 395 + ], + "spans": [ + { + "bbox": [ + 306, + 381, + 480, + 395 + ], + "type": "text", + "content": "2. Background and Related Work" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "spans": [ + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "text", + "content": "Notation. We deal with DNNs for classification as in Figure 2, represented by " + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "f: \\mathcal{X} \\to \\mathcal{Y}" + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "\\mathcal{X}" + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "\\mathcal{Y}" + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "text", + "content": " denote image and probability space, respectively. Let " + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "x \\in \\mathcal{X}" + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "text", + "content": " denote clean images and " + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "y \\in \\mathcal{Y}" + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "text", + "content": " indicate (one-hot) target classes corresponding to the images. Adversarial examples " + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "x_{\\mathrm{adv}}" + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "text", + "content": " are generated by adversarial perturbations " + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "text", + "content": " through DNNs, such that " + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "inline_equation", + "content": "x_{\\mathrm{adv}} = x + t" + }, + { + "bbox": [ + 304, + 401, + 545, + 497 + ], + "type": "text", + "content": ". Here, the perturbations are carefully created through the following formulation:" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 373, + 506, + 545, + 525 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 373, + 506, + 545, + 525 + ], + "spans": [ + { + "bbox": [ + 373, + 506, + 545, + 525 + ], + "type": "interline_equation", + "content": "\\max _ {\\| t \\| _ {\\infty} \\leq \\gamma} \\mathcal {L} _ {\\mathrm {C E}} (f (x + t), y), \\tag {1}", + "image_path": "307a688aa6e1d4476d4e07a2eb734520b2fe9efb32a710fd6d287f623890fc5b.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "spans": [ + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{CE}}" + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "text", + "content": " represents a pre-defined loss such as cross-entropy for classification task. We regard adversarial perturbations " + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "inline_equation", + "content": "l_{\\infty}" + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "text", + "content": " perturbation within " + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "text", + "content": "-ball (i.e., perturbation budget). Here, " + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\|_{\\infty}" + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "text", + "content": " describes " + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "inline_equation", + "content": "l_{\\infty}" + }, + { + "bbox": [ + 304, + 533, + 545, + 582 + ], + "type": "text", + "content": " perturbation magnitude." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 587, + 427, + 600 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 587, + 427, + 600 + ], + "spans": [ + { + "bbox": [ + 306, + 587, + 427, + 600 + ], + "type": "text", + "content": "2.1. Adversarial Training" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "After several works [50, 15, 24] have found that human-imperceptible adversarial examples easily break network predictions, Madry et al. [33] have thrown a fundamental question: \"How can we make models robust to adversarial examples with security guarantee?\" To answer it, they have used the concept of empirical risk minimization (ERM) serving as a recipe to obtain classifiers with small population risk. Thanks to its reliable guarantee, they have consolidated it on the purpose of adversarial defense and" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "text", + "content": "Selecting " + }, + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "text", + "content": " as proper perturbations varies according to domain specific tasks (e.g., rotations, translations [11], or spatial deformations [59])." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "4500" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": "accomplished the yardstick of adversarial training. The key factor of its achievement is regarding adversarial training as min-max optimization in a perspective of saddle point problem, which can be written as follows:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 78, + 126, + 287, + 155 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 78, + 126, + 287, + 155 + ], + "spans": [ + { + "bbox": [ + 78, + 126, + 287, + 155 + ], + "type": "interline_equation", + "content": "\\min _ {f} \\mathbb {E} _ {(x, y) \\sim \\mathcal {D}} \\left[ \\max _ {\\| t \\| _ {\\infty} \\leq \\gamma} \\mathcal {L} _ {\\mathrm {C E}} (f (x + t), y) \\right], \\tag {2}", + "image_path": "8dda02687e0483815b819bc4c602c7de6666e77bd1e0e0edf2dc03c5c0c47ef4.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 161, + 287, + 233 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 161, + 287, + 233 + ], + "spans": [ + { + "bbox": [ + 46, + 161, + 287, + 233 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 161, + 287, + 233 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 46, + 161, + 287, + 233 + ], + "type": "text", + "content": " denotes a set of data samples " + }, + { + "bbox": [ + 46, + 161, + 287, + 233 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 46, + 161, + 287, + 233 + ], + "type": "text", + "content": ". Here, they have presented an adversarial attack based on PGD to powerfully behave inner-maximization on Eq. (2), which is an ultimate first-order adversary with a multi-step variant of fast gradient sign method [28] by adding a random perturbation around the clean images " + }, + { + "bbox": [ + 46, + 161, + 287, + 233 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 161, + 287, + 233 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 233, + 287, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 233, + 287, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 233, + 287, + 472 + ], + "type": "text", + "content": "According to its impact, various adversarial training methods [33, 62, 55, 58] have grown exponentially and become de facto standards robustifying DNNs against adversarial perturbation. Zhang et al. [62] have pointed out the trade-off between clean accuracy and adversarial robustness, and reduced the gap between clean errors and robust errors. Wang et al. [55] have claimed that all of clean images are used to perform both inner-maximization and outer-minimization process in Eq. (2), irrespective of whether they are correctly classified or not. Thus, they have focused on misclassified clean images prone to be easily overlooked during adversarial training and demonstrated their significant impacts on the robustness by incorporating an explicit regularizer for them. Wu et al. [58] have studied loss landscapes with respect to network parameters and shown a positive correlation between the flatness of the parameter loss landscapes and the robustness. In the end, they have presented a double-perturbation mechanism where clean images are perturbed, while network parameters are simultaneously perturbed as well." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 473, + 287, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 473, + 287, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 473, + 287, + 617 + ], + "type": "text", + "content": "On the other hand, we plunge into investigating where adversarial vulnerability comes from and observe that the vulnerability varies along target classes, and it significantly deteriorates network predictions. Further, we find that this phenomenon commonly happens across various network architectures and advanced defense methods. To relieve such peculiarity, we deploy double machine learning (DML) that helps to capture how treatments (i.e., adversarial perturbations) affect outcomes of our interests (i.e., network predictions), which is one of the powerful causal inference methods. After we concisely explicate the necessary background of DML, we will bridge it to the adversary in Sec. (3)." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 623, + 192, + 636 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 192, + 636 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 192, + 636 + ], + "type": "text", + "content": "2.2. Double Machine Learning" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": "In data science and econometrics, one of the fundamental problems is how to measure causality between treatments " + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": " and outcomes of our interest " + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": " among high-dimensional observational data samples (see Figure 2) to identify data generating process. At a first glance, it seems simple to compute their causality, but we should keep in mind the" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "content": "possibility for the existence of covariates " + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "content": " affecting both treatments and outcomes. In other words, for example, if one may want to know the causal effects of drug dosage " + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "content": " to blood pressure changes " + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "content": ", one needs to collect observational data with respect to a variety of patients characteristics and their clinical histories " + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "content": ", so as not to fall into biased environment. In reality, though, it is impossible to collect observational data including all covariates concerning treatments and outcomes, so it is not an easy problem to catch genuine causality under the unknown covariates " + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "content": ". Therefore, there has been a growing demand for robustly predicting the unbiased causal relation, despite with the limited data samples." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 216, + 545, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 216, + 545, + 264 + ], + "spans": [ + { + "bbox": [ + 304, + 216, + 545, + 264 + ], + "type": "text", + "content": "Recently, the advent of double machine learning (DML) [5] enables us to clarify the causality between treatments " + }, + { + "bbox": [ + 304, + 216, + 545, + 264 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 216, + 545, + 264 + ], + "type": "text", + "content": " and outcomes " + }, + { + "bbox": [ + 304, + 216, + 545, + 264 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 216, + 545, + 264 + ], + "type": "text", + "content": ", when two regression models are given. The formulation of initial DML can be written as:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 347, + 271, + 545, + 290 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 271, + 545, + 290 + ], + "spans": [ + { + "bbox": [ + 347, + 271, + 545, + 290 + ], + "type": "interline_equation", + "content": "y = f (x) + \\theta t + u, \\quad (\\mathbb {E} [ u \\mid x, t ] = 0) \\tag {3}", + "image_path": "6645dc2751b4f4effcc93916f46a8dcf7cefd238c4d52bfda16d7e3677b71b47.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 348, + 286, + 494, + 298 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 348, + 286, + 494, + 298 + ], + "spans": [ + { + "bbox": [ + 348, + 286, + 494, + 298 + ], + "type": "interline_equation", + "content": "t = g (x) + v, \\quad (\\mathbb {E} [ v \\mid x ] = 0)", + "image_path": "e4b6851e02637d335db3db70be4073ccfbf45b5566f1e5824eff802a486c345f.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "spans": [ + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "\\theta \\in \\mathbb{R}" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": " denotes causal parameter representing causal relation between " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "t \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "y \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": ". In addition, " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": " indicates one regression model projecting covariates to outcome domain, and " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": " denotes another regression model generating treatments " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": ". In the sense that two regression models " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": " are not main interest of DML, they are called as nuisance parameters to estimate the causal parameter " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": ". Note that, early DML assumes the problem setup is proceeded in partially linear settings as a shape of Robinson-style [42] described in Eq. (3), where \"partially\" literally means that treatments " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "t \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": " are linearly connected to outcome " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "y \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": ", while covariates " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": " are not. In addition, it is supposed that the conditional expected error of " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "u \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "v \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": " equals to zero vector " + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "inline_equation", + "content": "0 \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 304, + 306, + 545, + 472 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "spans": [ + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "type": "text", + "content": "To obtain the causal parameter " + }, + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "type": "text", + "content": ", Chernozhukov et al. [5] have provided a solution of estimating the causal parameter such that " + }, + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "type": "inline_equation", + "content": "\\hat{\\theta} = (y - \\mathbb{E}[y \\mid x]) \\cdot v / \\|v\\|^2" + }, + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "type": "text", + "content": " which satisfies Neyman-orthogonality [35, 34]. It makes " + }, + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "type": "inline_equation", + "content": "\\hat{\\theta}" + }, + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "type": "text", + "content": " invariant to their erroneous of two nuisance parameters with the variance of causal parameter reduced. Furthermore, they have addressed a chronic problem that " + }, + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "type": "text", + "content": " is only accessible when the two nuisance parameters are in a class of Donsker condition, where deep neural networks are not included in that condition. They have theoretically demonstrated sample-splitting plus cross-fitting can effectively relax Donsker condition and allow a broad array of modern ML methods [5] to compute unbiased causal parameter " + }, + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 304, + 473, + 545, + 629 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "Following the principle, they first split the data samples " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{D}_1,\\mathcal{D}_2\\} \\sim \\mathcal{D}" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " and divided the process of causal inference into two steps: (a) training two nuisance parameters " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_1" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": ", (b) estimating unbiased " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_2" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": ". Here, data samples " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_2" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " used to estimate unbiased causal parameters should not be overlapped with " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_1" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " utilized to train the nuisance parameters. To make copious combinations, they" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 314, + 757 + ], + "type": "text", + "content": "4501" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": " swapped the role of partitioned data samples " + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_1 \\leftrightarrows \\mathcal{D}_2" + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": " or repeatedly split " + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": ". Subsequently, they have performed cross-fitting (e.g., " + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": "-fold cross validation) by averaging the estimated causal parameters from various split samples." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 121, + 288, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 121, + 288, + 204 + ], + "spans": [ + { + "bbox": [ + 46, + 121, + 288, + 204 + ], + "type": "text", + "content": "Along with the success of initial DML in partially linear settings, numerous variants [4, 7, 32, 14, 13, 26, 6] have emerged, and they have extended its initial nature to non-parametric settings with continuous treatments " + }, + { + "bbox": [ + 46, + 121, + 288, + 204 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 121, + 288, + 204 + ], + "type": "text", + "content": " in order to capture more complicated non-linear causal relations in a debiased state. A non-parametric formulation [4] represents a more general problem setup of DML as follows:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 93, + 211, + 287, + 231 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 211, + 287, + 231 + ], + "spans": [ + { + "bbox": [ + 93, + 211, + 287, + 231 + ], + "type": "interline_equation", + "content": "y = f (x, t) + u, \\quad (\\mathbb {E} [ u \\mid x, t ] = 0) \\tag {4}", + "image_path": "c1e8760870c826426ea25f2022302e5fcd4509d7d8e6422430174d9ff6cb5ea6.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 96, + 227, + 233, + 239 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 96, + 227, + 233, + 239 + ], + "spans": [ + { + "bbox": [ + 96, + 227, + 233, + 239 + ], + "type": "interline_equation", + "content": "t = g (x) + v, \\qquad (\\mathbb {E} [ v \\mid x ] = 0)", + "image_path": "fe1eaa63ea76aad236ecfc49ce4d742a8aff51ebf97619c9ffe1ab95b30f6a7a.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "spans": [ + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "type": "text", + "content": "where there is no explicit term for causal parameter " + }, + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "type": "text", + "content": " exhibiting causal relation between treatments " + }, + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "type": "text", + "content": " and outcomes " + }, + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "type": "text", + "content": ", compared to Eq. (3). Colangelo et al. [7] have introduced a way of estimating causal parameter " + }, + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "type": "text", + "content": " applicable to non-parametric settings with high-dimensional continuous treatments " + }, + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "type": "inline_equation", + "content": "t \\in \\mathcal{T}" + }, + { + "bbox": [ + 46, + 247, + 287, + 318 + ], + "type": "text", + "content": ", which can be written as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 116, + 323, + 287, + 348 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 323, + 287, + 348 + ], + "spans": [ + { + "bbox": [ + 116, + 323, + 287, + 348 + ], + "type": "interline_equation", + "content": "\\hat {\\theta} = \\frac {\\partial}{\\partial t} \\mathbb {E} [ y \\mid \\operatorname {d o} (\\mathcal {T} = t) ]. \\tag {5}", + "image_path": "605a46827e89bd467759c031067291ba0b118988a9db32d2374b5492f8a5c659.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "text", + "content": "They have utilized do-operator [37] commonly used in graphical causal models and intervened on treatments " + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "text", + "content": " to compute an interventional expectation " + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "inline_equation", + "content": "\\mathbb{E}[y|\\mathrm{do}(\\mathcal{T} = t)]" + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "text", + "content": ". It represents the expected outcome averaged from all the possible covariates for the given fixed treatments " + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "text", + "content": ", such that " + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "inline_equation", + "content": "\\mathbb{E}[y|\\mathrm{do}(\\mathcal{T} = t)] = \\sum_{x\\in \\mathcal{X}}\\mathbb{E}[y|x,t]p(x)" + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "text", + "content": ". Specifically, they have estimated causal parameter " + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "text", + "content": " by measuring how much the interventional expectation shifted, once they change the treatments slightly. Since the most important property of DML is Neyman-Orthogonality helping to robustly estimate the causal parameter, the interventional expectation should be also modified to satisfy the property [7, 23] of its invariance to nuisance parameters " + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 46, + 354, + 288, + 521 + ], + "type": "text", + "content": ". Its formulation can be written as follows (see details in Appendix A):" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 60, + 536, + 287, + 564 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 60, + 536, + 287, + 564 + ], + "spans": [ + { + "bbox": [ + 60, + 536, + 287, + 564 + ], + "type": "interline_equation", + "content": "\\mathbb {E} [ y \\mid \\operatorname {d o} (\\mathcal {T} = t) ] = \\mathbb {E} _ {\\mathcal {D} _ {t}} \\left[ f (x, t) + \\frac {y - f (x , t)}{p (\\mathcal {T} = t \\mid x)} \\right], \\tag {6}", + "image_path": "b822aaa0b4201ee67d37b02fa8fb7116850a5601f562ab9afbe4d3dddfa3f45a.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_t" + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "text", + "content": " denotes a set of observational covariates and outcome samples for a fixed " + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "inline_equation", + "content": "t\\in \\mathcal{T}" + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "text", + "content": " such that " + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "inline_equation", + "content": "(x,y)\\sim \\mathcal{D}_t" + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "text", + "content": ", a sub-population of " + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "text", + "content": ". Note that, " + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "inline_equation", + "content": "p(\\mathcal{T} = t|x)" + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "text", + "content": " is related to treatment generator " + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 46, + 570, + 287, + 641 + ], + "type": "text", + "content": ". Here, differentiating Eq. (6) enables us to acquire unbiased causal parameter in non-parametric settings with non-linear causal relation." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "content": "In brief, DML captures unbiased causal relation between treatments " + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "content": " and outcomes " + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "content": " even with finite data samples, of which theoretical ground is (a) Neyman-Orthogonality for robustly estimated causal parameter despite undesirable outputs of nuisance parameters, and (b) sample-splitting plus cross-fitting for debiased causal parameters." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 71, + 519, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 71, + 519, + 85 + ], + "spans": [ + { + "bbox": [ + 305, + 71, + 519, + 85 + ], + "type": "text", + "content": "3. Adversarial Double Machine Learning" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 91, + 503, + 103 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 91, + 503, + 103 + ], + "spans": [ + { + "bbox": [ + 306, + 91, + 503, + 103 + ], + "type": "text", + "content": "3.1. Adversarial Data Generating Process" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "spans": [ + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "text", + "content": "In general deep learning schemes, we have clean visual images " + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "inline_equation", + "content": "x \\in \\mathbb{R}^{hwc}" + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "text", + "content": " and their corresponding target classes " + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "inline_equation", + "content": "y \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "text", + "content": " in our hand as a format of dataset, where " + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "inline_equation", + "content": "h, w, c" + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "text", + "content": " denotes image resolution of height, width, channel, respectively, and " + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "text", + "content": " denotes the number of classes. Thus, we do not need additional data generating process. For adversarial training, on the other hand, we need another data, which are adversarial perturbations generated from data samples " + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "text", + "content": " as in Eq. (1). They are normally created by PGD [33] at every training iteration to make DNNs " + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "text", + "content": " robust through min-max optimization game according to Eq. (2)." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 241, + 545, + 372 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 241, + 545, + 372 + ], + "spans": [ + { + "bbox": [ + 304, + 241, + 545, + 372 + ], + "type": "text", + "content": "Though, the more iterations of adversarial training, the fewer perturbations that impair network predictions. In other words, not all of the perturbations can corrupt network predictions among newly generated perturbations. Hence, we do not consider all of the perturbations as treatments but selectively define them as worst perturbations " + }, + { + "bbox": [ + 304, + 241, + 545, + 372 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 241, + 545, + 372 + ], + "type": "text", + "content": " breaking network predictions, such that it satisfies " + }, + { + "bbox": [ + 304, + 241, + 545, + 372 + ], + "type": "inline_equation", + "content": "y \\neq f(x + t)" + }, + { + "bbox": [ + 304, + 241, + 545, + 372 + ], + "type": "text", + "content": ", where we call " + }, + { + "bbox": [ + 304, + 241, + 545, + 372 + ], + "type": "inline_equation", + "content": "x_{\\mathrm{adv}} = x + t" + }, + { + "bbox": [ + 304, + 241, + 545, + 372 + ], + "type": "text", + "content": " as worst examples. This is because our major goal is to catch actual adversarial vulnerability of DNNs, so that we do not tackle the perturbations incapable of harming network predictions." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 373, + 545, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 373, + 545, + 445 + ], + "spans": [ + { + "bbox": [ + 304, + 373, + 545, + 445 + ], + "type": "text", + "content": "To access such worst perturbation, we choose perturbation generator " + }, + { + "bbox": [ + 304, + 373, + 545, + 445 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 304, + 373, + 545, + 445 + ], + "type": "text", + "content": " as an adversarial attack of PGD according to standard adversarial training [33]. In addition, we pick the worst perturbations " + }, + { + "bbox": [ + 304, + 373, + 545, + 445 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 373, + 545, + 445 + ], + "type": "text", + "content": " damaging network predictions among adversarial perturbations from the generator " + }, + { + "bbox": [ + 304, + 373, + 545, + 445 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 304, + 373, + 545, + 445 + ], + "type": "text", + "content": ". In this way, we perform adversarial data generating process." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 450, + 456, + 463 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 450, + 456, + 463 + ], + "spans": [ + { + "bbox": [ + 306, + 450, + 456, + 463 + ], + "type": "text", + "content": "3.2. Adversarial Problem Setup" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "spans": [ + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "text", + "content": "In the nature of adversarial training, the worst perturbations " + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "text", + "content": " are explicitly injected to clean images " + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "text", + "content": " such that " + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "inline_equation", + "content": "x_{\\mathrm{adv}} = x + t" + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "text", + "content": ", and these combined images are propagated into DNNs " + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "text", + "content": ". Here, through this formulation as: " + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "inline_equation", + "content": "f(x + t) = f(x,t)" + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "text", + "content": ", we connect DNNs for adversarial training and a nuisance parameter " + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "text", + "content": " for non-parametric DML in Eq. (4). Fortunately, once we use Taylor expansion (with scalar-valued function for better understanding) and decompose " + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "text", + "content": " by its input component as: " + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "inline_equation", + "content": "f(x + t) = f(x) + \\sum_{i=1}^{\\infty} t^{i} f^{(i)}(x) / i!" + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "inline_equation", + "content": "f^{(i)}" + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "text", + "content": " indicates " + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 468, + 545, + 648 + ], + "type": "text", + "content": "-th order derivative function, we can also express partially linear settings described in Eq. (3). That is, since adversarial examples start from the concept of \"additive noise\", both settings can exist at the same time in the scheme of adversarial training. From this reason, we build Adversarial Double Machine Learning (ADML):" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 315, + 652, + 545, + 681 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 652, + 545, + 681 + ], + "spans": [ + { + "bbox": [ + 315, + 652, + 545, + 681 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} y = f (x + t) = f (x) + \\theta \\bar {t} + u, \\quad (\\mathbb {E} [ u \\mid x, t ] = 0) \\tag {7} \\\\ t = g (x) + v, \\quad (\\mathbb {E} [ v \\mid x ] = 0) \\\\ \\end{array}", + "image_path": "574d1e07315ec1ef8a2f5d65e9be7655d5b636be136fdc03ecea87f1c9022e38.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 687, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 687, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 687, + 545, + 715 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 687, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\bar{t}" + }, + { + "bbox": [ + 305, + 687, + 545, + 715 + ], + "type": "text", + "content": " indicates Taylor-order matrix: " + }, + { + "bbox": [ + 305, + 687, + 545, + 715 + ], + "type": "inline_equation", + "content": "[t, t^2, \\dots]^T" + }, + { + "bbox": [ + 305, + 687, + 545, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 687, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 305, + 687, + 545, + 715 + ], + "type": "text", + "content": " represents Taylor-coefficient matrix " + }, + { + "bbox": [ + 305, + 687, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\left[\\frac{f^{(1)}(x)}{1!}, \\frac{f^{(2)}(x)}{2!}, \\dots\\right]" + }, + { + "bbox": [ + 305, + 687, + 545, + 715 + ], + "type": "text", + "content": " (see" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "4502" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 241, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 241, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 241, + 83 + ], + "type": "text", + "content": "strict mathematical verification in Appendix B)." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "spans": [ + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "text", + "content": "Here, we explain what the conditional expected error of " + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "inline_equation", + "content": "u" + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "text", + "content": " in Eq. (7) means in adversarial training. The former " + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "inline_equation", + "content": "\\mathbb{E}[u|x,t] = 0" + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "text", + "content": " implies the nature of adversarial training, which can be viewed as an ultimate augmentation robustifying DNNs, when infinite data population of " + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "text", + "content": " is given. Thus, it means network predictions become invariant in the end, despite the given worst perturbations. To implement it practically, we replace it with a mild assumption as " + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "inline_equation", + "content": "\\mathbb{E}[u|x,g(x)] = 0" + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "text", + "content": " (see Appendix C) that signifies PGD-based perturbations are used to perform adversarial training. This is because we cannot always acquire worst perturbations " + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "text", + "content": " using only PGD. For the latter " + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "inline_equation", + "content": "\\mathbb{E}[v|x] = 0" + }, + { + "bbox": [ + 46, + 85, + 287, + 252 + ], + "type": "text", + "content": ", it represents PGD has capability of producing worst perturbations deviating network predictions during the training." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 262, + 275, + 274 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 262, + 275, + 274 + ], + "spans": [ + { + "bbox": [ + 47, + 262, + 275, + 274 + ], + "type": "text", + "content": "3.3. Estimating Adversarily Causal Parameter" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 281, + 287, + 364 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 281, + 287, + 364 + ], + "spans": [ + { + "bbox": [ + 46, + 281, + 287, + 364 + ], + "type": "text", + "content": "Aligned with Eq. (3), an explicit term of " + }, + { + "bbox": [ + 46, + 281, + 287, + 364 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 281, + 287, + 364 + ], + "type": "text", + "content": " is regarded as the causal parameter in our problem setup of ADML. We can now interpret that " + }, + { + "bbox": [ + 46, + 281, + 287, + 364 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 281, + 287, + 364 + ], + "type": "text", + "content": " is a causal factor to spur adversarial vulnerability, since its magnitude easily catalyzes the deviations from network predictions of clean images. Here, if it is possible to directly compute " + }, + { + "bbox": [ + 46, + 281, + 287, + 364 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 281, + 287, + 364 + ], + "type": "text", + "content": " over all data samples, we can finally handle adversarial vulnerability." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "content": "Favorably, ADML follows both partially linear and nonparametric settings due to the concept of additive noise, thus we can employ the way of estimating causal parameter as in Eq. (5). The following formulation represents the estimated causal parameter " + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "inline_equation", + "content": "\\hat{\\theta}" + }, + { + "bbox": [ + 46, + 365, + 287, + 449 + ], + "type": "text", + "content": " in ADML (see Appendix D). Note that, as we emphasized, sample-splitting plus cross-fitting must be applied to estimate unbiased causal parameter." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 64, + 458, + 287, + 486 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 64, + 458, + 287, + 486 + ], + "spans": [ + { + "bbox": [ + 64, + 458, + 287, + 486 + ], + "type": "interline_equation", + "content": "\\hat {\\theta} = \\mathbb {E} _ {\\mathcal {D} _ {t}} \\left[ - \\left(\\frac {1}{p (\\mathcal {T} = t \\mid x)} - 1\\right) \\frac {\\partial}{\\partial t} f (x + t) \\right], \\tag {8}", + "image_path": "5964fa3b004de984c030635d0cc2eda6f005bab480118c648e9b8ac180e06eba.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "spans": [ + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "inline_equation", + "content": "\\frac{\\partial}{\\partial t} f(x + t)" + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "text", + "content": " indicates an input gradient for network predictions with respect to " + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "inline_equation", + "content": "p(\\mathcal{T} = t|x)" + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "text", + "content": " represents a distribution of worst perturbation given clean images " + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "text", + "content": ". Here, we cannot directly handle this distribution due to the presence of multiple unknown parameters required to define it. For that reason, we instead approximate it with the sharpening technique by incorporating the information on attacked confidence such that " + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "inline_equation", + "content": "p(\\mathcal{T} = t|x) \\approx \\mathbb{E}_{t'|x}[p(y_a|x,t')]" + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "text", + "content": " (see Appendix E), where " + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "inline_equation", + "content": "y_{a}" + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "text", + "content": " denotes attacked classes for the given worst perturbations " + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 495, + 287, + 639 + ], + "type": "text", + "content": ". It implicitly means that the higher the attacked confidence, the higher the probability of finding worst perturbations." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": "Aligned with the previous analysis [47] that show increasing magnitude of input gradient increases adversarial vulnerability, the magnitude of our causal parameter " + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "inline_equation", + "content": "|\\hat{\\theta}|" + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": " also becomes huge due to " + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "inline_equation", + "content": "|\\hat{\\theta}| \\propto |\\frac{\\partial}{\\partial t} f(x + t)|" + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": ". In parallel, Qin et al. [38] show the more ambiguous confident, the lower robustness (high vulnerability), and interestingly, the mag-" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 307, + 85, + 545, + 232 + ], + "blocks": [ + { + "bbox": [ + 306, + 72, + 392, + 83 + ], + "lines": [ + { + "bbox": [ + 306, + 72, + 392, + 83 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 392, + 83 + ], + "type": "text", + "content": "Algorithm 1 ADML" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 85, + 545, + 232 + ], + "lines": [ + { + "bbox": [ + 307, + 85, + 545, + 232 + ], + "spans": [ + { + "bbox": [ + 307, + 85, + 545, + 232 + ], + "type": "table", + "html": "
Require: Data Samples D, Network f
1: for (x,y) ~ D do▷ Cross-Fitting
2: t' ← g(x)▷ PGD Attack
3: (x1,y1,t1'), (x2,y2,t2') ~ Split(x,y,t')
4: L_a ← L_Delphi(x1,y1,t1';f)▷ Mild Assumption
5: (xt2,yt2,t2) ← Select(y2 ≠ f(x2+t2')) ▷ Worst
6: j* ← arg maxj f_j(xt2+t2)▷ j: Class Index
7: τ ← 1/fj*(xt2+t2)-1▷ Balancing Ratio
8: L_b ← τL_CE(f(xt2+t2),yt2) + L_CE(f(xt2),yt2)
9: L_ADML ← L_a + L_b▷ ADML Loss
10: wf ← wf - α ∂/∂w_f L_ADML ▷ Weight Update (α: lr)
11: end for
", + "image_path": "278a81867ac2b1a3578af499f67b14682bb887ab26d13d30433a2034dfa6bb62.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 239, + 545, + 266 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 239, + 545, + 266 + ], + "spans": [ + { + "bbox": [ + 306, + 239, + 545, + 266 + ], + "type": "text", + "content": "nitude of our causal parameter also " + }, + { + "bbox": [ + 306, + 239, + 545, + 266 + ], + "type": "inline_equation", + "content": "|\\hat{\\theta}|" + }, + { + "bbox": [ + 306, + 239, + 545, + 266 + ], + "type": "text", + "content": " becomes large due to " + }, + { + "bbox": [ + 306, + 239, + 545, + 266 + ], + "type": "inline_equation", + "content": "|\\hat{\\theta}| \\propto |1 / \\mathbb{E}_{t' | x}[p(y_a | x, t')]|" + }, + { + "bbox": [ + 306, + 239, + 545, + 266 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 267, + 545, + 387 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 267, + 545, + 387 + ], + "spans": [ + { + "bbox": [ + 304, + 267, + 545, + 387 + ], + "type": "text", + "content": "Bringing such factors at once, " + }, + { + "bbox": [ + 304, + 267, + 545, + 387 + ], + "type": "inline_equation", + "content": "\\hat{\\theta}" + }, + { + "bbox": [ + 304, + 267, + 545, + 387 + ], + "type": "text", + "content": " represents a weighted measurement of attacked confidence and their input gradients. Comprehensively, we can revisit that the network predictions of worst examples are easily flipped due to the following adversarial vulnerability: (a) ambiguous confidence around classification boundaries, or (b) high gradient magnitude amplifying the leverage of the perturbations. To improve the adversarial robustness of DNNs, it is essential to minimize the negative effects of causal parameters, which are combinatorial outcomes of the gradient and confidence." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 396, + 500, + 410 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 396, + 500, + 410 + ], + "spans": [ + { + "bbox": [ + 306, + 396, + 500, + 410 + ], + "type": "text", + "content": "3.4. Mitigating Adversarial Vulnerability" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 415, + 545, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 545, + 523 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 545, + 523 + ], + "type": "text", + "content": "By deploying ADML, we propose a way of estimating causal parameter representing the degree of adversarial vulnerability that disturbs to predict the target classes. Then, our final goal is essentially to lessen its direct causal effect from adversarial perturbations in order to achieve robust networks. In detailed, alleviating their causal effect derived from " + }, + { + "bbox": [ + 304, + 415, + 545, + 523 + ], + "type": "inline_equation", + "content": "\\hat{\\theta}" + }, + { + "bbox": [ + 304, + 415, + 545, + 523 + ], + "type": "text", + "content": " is the process of comprehensive reconstruction to focus more on vulnerable samples as we reflect their attacked confidence and gradients effects altogether." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 525, + 545, + 632 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 525, + 545, + 632 + ], + "spans": [ + { + "bbox": [ + 304, + 525, + 545, + 632 + ], + "type": "text", + "content": "Accordingly, the very first way is naively reducing the magnitude of " + }, + { + "bbox": [ + 304, + 525, + 545, + 632 + ], + "type": "inline_equation", + "content": "\\hat{\\theta}" + }, + { + "bbox": [ + 304, + 525, + 545, + 632 + ], + "type": "text", + "content": " to suppress adversarial vulnerability damaging the robustness. However, calculating " + }, + { + "bbox": [ + 304, + 525, + 545, + 632 + ], + "type": "inline_equation", + "content": "\\hat{\\theta}" + }, + { + "bbox": [ + 304, + 525, + 545, + 632 + ], + "type": "text", + "content": " and minimizing its magnitude at every iteration is computationally striking because input gradient has huge dimension of " + }, + { + "bbox": [ + 304, + 525, + 545, + 632 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{dhwc}" + }, + { + "bbox": [ + 304, + 525, + 545, + 632 + ], + "type": "text", + "content": " and getting its gradient inevitably needs to compute second-order gradient with its tremendous dimension. We instead approximate the partial derivative " + }, + { + "bbox": [ + 304, + 525, + 545, + 632 + ], + "type": "inline_equation", + "content": "\\frac{\\partial}{\\partial t}\\mathbb{E}[y|\\mathrm{do}(\\mathcal{T} = t)]" + }, + { + "bbox": [ + 304, + 525, + 545, + 632 + ], + "type": "text", + "content": " and minimize its magnitude, which can be written as:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 320, + 641, + 545, + 669 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 320, + 641, + 545, + 669 + ], + "spans": [ + { + "bbox": [ + 320, + 641, + 545, + 669 + ], + "type": "interline_equation", + "content": "\\min _ {f} | \\hat {\\theta} | \\approx \\left| \\frac {\\mathbb {E} [ y \\mid \\operatorname {d o} (\\mathcal {T} = t) ] - \\mathbb {E} [ y \\mid \\operatorname {d o} (\\mathcal {T} = 0) ]}{t - 0} \\right|, \\tag {9}", + "image_path": "e93e37cea9512dca8e491571de09a23fbe544064706a7be1e615e0b218a6f072.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "content": "where network parameters of DNNs " + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "content": " are only dependent on the numerator, thus we engross the numerator only. Lastly, we redesign " + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathbb{E}[y|\\mathrm{do}(\\mathcal{T} = t)]" + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "content": " into the form of loss" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "4503" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 58, + 48, + 533, + 365 + ], + "blocks": [ + { + "bbox": [ + 58, + 48, + 533, + 365 + ], + "lines": [ + { + "bbox": [ + 58, + 48, + 533, + 365 + ], + "spans": [ + { + "bbox": [ + 58, + 48, + 533, + 365 + ], + "type": "table", + "html": "
MethodCIFAR-10CIFAR-100Tiny-ImageNet
CleanBIMPGD\\(CW_{\\infty}\\)APDLRAACleanBIMPGD\\(CW_{\\infty}\\)APDLRAACleanBIMPGD\\(CW_{\\infty}\\)APDLRAA
VGG-16AT78.849.448.146.846.446.446.353.926.025.024.123.723.823.756.526.625.425.524.724.624.6
+ADML80.961.861.759.855.054.854.552.231.030.829.927.827.627.355.435.534.932.932.732.432.2
TRADES79.548.647.645.746.446.346.353.325.524.823.523.623.723.256.128.327.326.225.825.825.7
+ADML81.062.662.459.055.355.154.952.231.231.129.827.627.327.355.436.636.034.033.633.433.3
MART78.351.950.648.848.948.848.752.626.626.024.424.324.324.255.727.826.626.025.725.725.6
+ADML80.462.462.260.355.755.355.251.631.631.029.627.827.527.355.136.235.834.934.333.933.7
AWP77.253.952.650.151.451.151.052.130.229.327.528.728.528.356.931.631.029.429.929.829.7
+ADML80.264.764.661.858.057.757.552.333.833.531.329.729.529.054.536.636.134.634.533.833.7
ResNet-18AT83.153.351.950.849.949.749.559.127.126.325.425.325.325.161.531.030.129.528.828.928.8
+ADML84.561.160.858.556.756.255.656.431.630.929.528.428.227.857.335.935.533.534.734.734.6
TRADES83.353.052.050.950.950.850.758.527.626.826.225.925.925.860.432.031.030.229.729.629.5
+ADML84.062.361.959.556.756.655.957.331.731.630.028.828.528.058.437.036.033.335.034.134.0
MART82.554.152.851.351.550.850.858.127.726.725.525.425.125.060.631.030.229.829.029.029.0
+ADML84.163.362.958.756.856.456.257.432.131.730.228.928.828.557.136.636.033.635.133.933.8
AWP81.356.355.553.654.254.054.057.931.430.729.030.030.029.861.434.734.132.433.333.233.1
+ADML84.064.664.561.460.559.959.756.233.932.930.731.130.530.359.838.638.135.937.736.736.6
WideResNet-28-10AT86.755.453.453.451.351.351.261.928.827.427.126.026.025.964.832.731.231.130.130.130.0
+ADML87.561.760.758.856.456.355.858.932.932.631.329.629.229.162.143.543.141.141.940.440.2
TRADES86.055.353.753.651.651.651.461.929.128.527.826.726.826.764.232.531.631.430.029.929.8
+ADML88.562.961.959.657.657.656.661.633.333.031.530.030.129.663.143.542.941.041.440.340.2
MART86.456.054.353.451.651.651.561.628.326.726.425.325.425.364.232.931.831.830.730.530.5
+ADML88.362.160.959.656.756.656.259.633.032.931.630.329.929.661.842.842.640.340.739.038.9
AWP85.960.258.957.256.956.956.862.433.032.231.130.930.930.865.436.936.035.134.834.834.7
+ADML88.267.567.464.263.563.263.162.539.739.336.937.637.136.864.944.644.241.943.342.142.0
WideResNet-70-10AT88.156.654.855.052.853.052.864.128.427.327.426.026.425.665.334.933.433.932.232.232.1
+ADML88.961.561.461.056.556.356.063.330.029.228.826.926.726.461.037.737.436.933.833.032.9
TRADES87.756.354.755.053.453.353.363.328.727.827.926.626.226.065.734.432.633.031.531.531.4
+ADML89.163.963.362.759.059.659.063.431.230.830.327.527.127.061.840.239.538.836.135.535.4
MART88.057.455.555.452.852.852.663.228.727.527.525.826.325.665.433.832.532.431.331.331.2
+ADML88.561.761.360.856.756.856.662.330.130.029.429.329.128.763.241.841.040.237.736.636.5
AWP86.661.860.659.959.159.459.265.233.333.331.731.530.330.066.740.740.040.039.139.038.9
+ADML89.467.066.966.163.463.663.165.341.941.840.938.938.037.665.845.044.543.343.543.142.8
", + "image_path": "8ad57b2acbcb8d03d54c261188682ca29695deacf3170f4f81bfd403fc0e4eb2.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 367, + 545, + 391 + ], + "lines": [ + { + "bbox": [ + 47, + 367, + 545, + 391 + ], + "spans": [ + { + "bbox": [ + 47, + 367, + 545, + 391 + ], + "type": "text", + "content": "Table 1. Comparing adversarial robustness of various defence methods whether to the inclusion of ADML for CIFAR-10 [27], CIFAR-100 [27], Tiny-ImageNet [29] trained with VGG-16 [48], ResNet-18 [17], WideResNet-28-10 [61], and WideResNet-70-10 [61]." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 400, + 288, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 400, + 288, + 437 + ], + "spans": [ + { + "bbox": [ + 46, + 400, + 288, + 437 + ], + "type": "text", + "content": "function used in deep learning and finally construct the objective function for ADML, of which formulation can be written as follows (see details in Appendix F):" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 53, + 444, + 287, + 464 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 444, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 53, + 444, + 287, + 464 + ], + "type": "interline_equation", + "content": "\\min _ {f} \\mathbb {E} _ {\\mathcal {D} _ {t}} [ \\tau \\mathcal {L} _ {\\mathrm {C E}} (f (x + t), y) ] + \\mathbb {E} _ {\\mathcal {D} _ {0}} [ \\mathcal {L} _ {\\mathrm {C E}} (f (x), y) ], \\tag {10}", + "image_path": "d72fde635b79e72dd4f7dbe4f0567b203229ed878490fb370d31ae037bf9bf8c.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 472, + 287, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 287, + 594 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 287, + 594 + ], + "type": "text", + "content": "where we denote " + }, + { + "bbox": [ + 46, + 472, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\tau = \\frac{1}{p(\\mathcal{T} = t|x)} - 1" + }, + { + "bbox": [ + 46, + 472, + 287, + 594 + ], + "type": "text", + "content": " as balancing ratio. The current AT-based defenses use an equal weight \"1/n\" to loss for all data samples: " + }, + { + "bbox": [ + 46, + 472, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\frac{1}{n}\\sum_{i=1}^{n}\\mathcal{L}_{\\text{Defense}}(x_i, y_i, t_i; f)" + }, + { + "bbox": [ + 46, + 472, + 287, + 594 + ], + "type": "text", + "content": " because they presume all of perturbations have equal causal effect (successful attack) to change targets without realizing vulnerable samples. Whereas, ADML uses the balancing ratio " + }, + { + "bbox": [ + 46, + 472, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 472, + 287, + 594 + ], + "type": "text", + "content": " to adaptively focus on vulnerable samples by reweighting the loss. To realize ADML, we describe Algorithm 1 to explain further details, where " + }, + { + "bbox": [ + 46, + 472, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\text{Defense}}(x, y, t; f)" + }, + { + "bbox": [ + 46, + 472, + 287, + 594 + ], + "type": "text", + "content": " indicates a main body of the loss function for AT-based defenses." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 604, + 124, + 617 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 604, + 124, + 617 + ], + "spans": [ + { + "bbox": [ + 47, + 604, + 124, + 617 + ], + "type": "text", + "content": "4. Experiment" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 623, + 180, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 180, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 180, + 635 + ], + "type": "text", + "content": "4.1. Implementation Details" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "content": "Datasets & Networks. We conduct comprehensive experiments on various datasets and networks. For datasets, we use CIFAR-10 [27], CIFAR-100 [27], and two larger datasets: Tiny-[ImageNet [29] and ImageNet [9]. For networks, four CNN architectures: [48, 17, 61] and four Transformer architectures: [10, 51] are used." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "spans": [ + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "text", + "content": "Adversarial Attacks. We adaptively set perturbation budget " + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "text", + "content": " of adversarial attacks depending on the classification difficulty of the four datasets: 8/255 equally for CIFAR-10 [27] and CIFAR100 [27], 4/255 for Tiny-ImageNet [29], and 2/255 for ImageNet [9]. We prepare three standard attacks: BIM [28], PGD [33], " + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "inline_equation", + "content": "\\mathrm{CW}_{\\infty}" + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "text", + "content": " [3], and three advanced attacks: AP (Auto-PGD: step size-free), DLR (Auto-DLR: shift and scaling invariant), AA (Auto-Attack: parameter-free), all of which are introduced by Francesco et al. [8]. PGD, AP, DLR have 30 steps with random starts, where PGD has step size " + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "inline_equation", + "content": "2.3 \\times \\frac{\\gamma}{30}" + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "text", + "content": ", and AP, DLR both have momentum coefficient " + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "inline_equation", + "content": "\\rho = 0.75" + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "inline_equation", + "content": "\\mathrm{CW}_{\\infty}" + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "text", + "content": " uses PGD-based gradient clamping for " + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "inline_equation", + "content": "l_{\\infty}" + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "text", + "content": " with CW objective [3] on " + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "inline_equation", + "content": "\\kappa = 0" + }, + { + "bbox": [ + 304, + 400, + 545, + 556 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 557, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 546, + 714 + ], + "type": "text", + "content": "Adversarial Defenses. We use four defense baselines with a standard baseline: AT [33] and three advanced defense baselines: TRADES [62], MART [55], AWP [58]. To fairly validate experiments, a perturbation generator, PGD [33] is equivalently used to generate adversarial examples for which we use the budget 8/255 and set 10 steps with " + }, + { + "bbox": [ + 304, + 557, + 546, + 714 + ], + "type": "inline_equation", + "content": "2.3 \\times \\frac{\\gamma}{10}" + }, + { + "bbox": [ + 304, + 557, + 546, + 714 + ], + "type": "text", + "content": " step size in training. Especially, adversarially training Tiny-ImageNet [29] and ImageNet [9] is a computational burden, thus we employ fast adversarial training [57] with FGSM [15]. For training CNNs, we use SGD [43] with a learning rate of 0.5 scheduled by Cyclic [49] in 120 epochs and use early stopping to prevent overfitting [41]. For training Transformers, we use SGD [43] with a learn" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4504" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 58, + 48, + 533, + 369 + ], + "blocks": [ + { + "bbox": [ + 58, + 48, + 533, + 369 + ], + "lines": [ + { + "bbox": [ + 58, + 48, + 533, + 369 + ], + "spans": [ + { + "bbox": [ + 58, + 48, + 533, + 369 + ], + "type": "table", + "html": "
MethodCIFAR-10CIFAR-100Tiny-ImageNet
CleanBIMPGDCWAPDLRAACleanBIMPGDCW∞APDLRAACleanBIMPGDCW∞APDLRAA
VIT-S/16AT83.549.947.346.644.944.844.759.926.625.825.124.624.524.573.835.834.133.531.931.931.8
+ADML88.156.855.153.851.350.750.762.732.430.729.428.427.927.775.647.746.645.645.342.742.6
TRADES85.051.049.448.648.148.047.859.527.326.626.325.825.925.772.938.837.837.436.136.136.0
+ADML87.957.656.255.152.752.051.963.235.034.733.831.631.331.275.349.148.047.145.643.043.0
MART85.752.449.748.946.746.746.660.928.627.927.526.526.526.477.638.637.236.835.235.235.2
+ADML88.057.556.154.751.951.451.462.734.432.731.730.029.329.276.548.947.746.346.042.942.9
AWP84.954.252.351.650.149.949.961.129.629.028.127.727.727.678.141.039.338.737.337.337.2
+ADML88.057.054.353.350.149.649.564.434.834.133.031.330.630.576.647.546.444.944.742.542.4
VIT-B/16AT87.052.850.850.447.847.747.763.330.429.629.228.628.328.372.440.137.737.834.434.334.5
+ADML89.956.154.954.151.651.451.267.138.136.135.434.333.433.179.050.249.748.448.546.946.8
TRADES85.353.852.451.650.950.850.865.732.631.531.029.930.030.073.243.341.241.839.139.039.4
+ADML88.958.657.356.154.754.454.369.438.937.937.034.834.634.779.454.052.251.648.247.347.2
MART87.453.350.650.548.348.448.265.731.930.830.229.229.229.179.341.740.039.636.836.837.1
+ADML89.657.055.654.351.851.551.368.935.433.532.930.530.130.280.150.750.149.048.947.447.0
AWP87.454.952.951.949.849.849.766.833.431.731.330.330.230.278.745.042.242.239.539.439.7
+ADML90.459.156.756.653.853.652.870.037.736.135.633.332.832.979.350.849.748.048.046.045.8
DeT-S/16AT83.549.347.846.745.345.345.259.529.228.527.627.527.527.475.737.435.634.733.133.033.0
+ADML87.756.856.054.952.351.951.963.734.432.931.731.430.530.474.744.943.642.240.839.539.4
TRADES84.150.649.348.848.048.048.061.829.428.827.828.128.028.074.839.038.037.436.436.436.3
+ADML87.957.856.555.353.753.053.266.237.236.435.533.232.332.376.345.244.943.839.538.738.4
MART84.252.350.049.147.847.647.559.831.030.629.329.729.629.674.640.139.138.437.737.637.6
+ADML87.557.555.655.052.652.352.265.337.035.634.732.430.730.775.245.344.243.342.838.438.4
AWP82.353.552.351.550.550.450.460.731.831.430.231.030.030.075.441.740.939.839.039.139.0
+ADML86.755.953.252.650.650.550.564.739.438.136.835.734.534.575.449.447.646.545.742.842.8
DeT-B/16AT84.651.549.548.447.247.147.064.930.329.128.427.527.427.479.138.636.336.134.434.334.0
+ADML89.755.754.853.850.049.749.765.735.434.433.432.230.330.377.646.945.644.744.940.540.5
TRADES85.452.851.750.650.250.250.264.830.029.328.628.428.328.378.343.141.640.540.540.540.4
+ADML90.261.460.459.458.357.657.668.640.539.938.437.436.836.780.845.443.542.743.242.942.7
MART83.954.753.252.051.050.950.764.531.931.130.530.230.130.075.844.643.342.642.642.642.5
+ADML89.660.360.258.955.155.055.065.339.638.537.135.434.634.677.847.746.144.645.544.844.7
AWP83.354.153.152.451.851.651.565.432.331.530.430.230.130.176.642.841.440.742.842.842.7
+ADML88.959.057.356.454.053.853.769.739.438.337.335.234.434.480.351.250.248.949.448.148.0
", + "image_path": "c941ff86c6b96f783b546f39798bbbc40dadc614db8e7d17dd6a9651d1f46929.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 401, + 282, + 509 + ], + "blocks": [ + { + "bbox": [ + 49, + 370, + 544, + 392 + ], + "lines": [ + { + "bbox": [ + 49, + 370, + 544, + 392 + ], + "spans": [ + { + "bbox": [ + 49, + 370, + 544, + 392 + ], + "type": "text", + "content": "Table 2. Comparing adversarial robustness of various defence methods whether to the inclusion of ADML for CIFAR-10 [27], CIFAR-100 [27], Tiny-ImageNet [29] trained with ViT-S/16 [10], ViT-B/16 [10], DeiT-S/16 [51], and DeiT-B/16 [51]." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 401, + 282, + 509 + ], + "lines": [ + { + "bbox": [ + 50, + 401, + 282, + 509 + ], + "spans": [ + { + "bbox": [ + 50, + 401, + 282, + 509 + ], + "type": "table", + "html": "
SS+CFWNWCIFAR-10Tiny-ImageNet
PGDCW∞DLRAAPGDCW∞DLRAA
VGG-16✓✓X61.759.854.854.434.932.932.432.2
✓✓✓52.349.448.948.825.424.924.224.2
✓X✓48.047.145.845.826.025.824.524.4
X✓X52.650.049.449.428.127.026.426.4
ResNet-18✓✓X60.858.556.255.635.533.534.734.6
✓✓✓51.750.149.549.234.932.432.732.7
✓X✓50.850.549.449.130.029.529.028.9
X✓X53.651.751.451.031.729.730.230.1
", + "image_path": "aa102ca2e3b13ddad21e04b27e2e4d96a5b57765246d90d3a17091462350d75e.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 49, + 511, + 286, + 532 + ], + "lines": [ + { + "bbox": [ + 49, + 511, + 286, + 532 + ], + "spans": [ + { + "bbox": [ + 49, + 511, + 286, + 532 + ], + "type": "text", + "content": "Table 3. Ablation study for the effects of sample-splitting plus cross-fitting (SS+CF) and Worst(W) / Non-Worst(NW) examples." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 2 + }, + { + "bbox": [ + 49, + 538, + 286, + 572 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 538, + 286, + 572 + ], + "spans": [ + { + "bbox": [ + 49, + 538, + 286, + 572 + ], + "type": "text", + "content": "ing rate of 0.001 on the equal experimental setup of CNNs, where " + }, + { + "bbox": [ + 49, + 538, + 286, + 572 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 49, + 538, + 286, + 572 + ], + "type": "text", + "content": " resolution is applied for all datasets and pretrained parameters on ImageNet-1k models are utilized." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 49, + 582, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 582, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 49, + 582, + 286, + 712 + ], + "type": "text", + "content": "Training ADML. After the completion of standard adversarial training [33], we apply AT-based defense methods to line 4 in Algorithm 1 for ADML. We then optimize adversarially trained CNNs in 10 epochs using SGD [43] with a learning rate of 0.001 scheduled by Cyclic [49], which allows empirically sufficient convergence to robustness. In addition, adversarially trained Transformers are also optimized with ADML using a learning rate of 0.0001 on the equal experimental setup of CNNs. Note that, we set sample-splitting ratio in half (see Appendix G) for each batch, and cross-fitting is satisfied during training iterations." + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 309, + 402, + 544, + 453 + ], + "blocks": [ + { + "bbox": [ + 309, + 402, + 544, + 453 + ], + "lines": [ + { + "bbox": [ + 309, + 402, + 544, + 453 + ], + "spans": [ + { + "bbox": [ + 309, + 402, + 544, + 453 + ], + "type": "table", + "html": "
PORT+ADMLGowal+ADMLHAT+ADMLSCORE+ADMLWang+ADML
○Clean87.088.186.087.488.289.588.089.991.491.8
UAA60.666.460.766.861.067.561.168.064.070.5
∞Clean65.965.859.259.962.262.462.062.368.168.2
JAA31.237.930.837.731.237.331.237.135.741.1
", + "image_path": "c875b6ba88e06b2f105ae4a5fee58a08eba419a175c487f85d0f7a47b5871cbd.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 308, + 455, + 544, + 498 + ], + "lines": [ + { + "bbox": [ + 308, + 455, + 544, + 498 + ], + "spans": [ + { + "bbox": [ + 308, + 455, + 544, + 498 + ], + "type": "text", + "content": "Table 4. Comparing adversarial robustness of TRADES [62] using synthetic images: DDPM [18] and EDM [22] whether to the inclusion of ADML for CIFAR-10/100 with WRN-34-10: PORT [46] and WRN-28-10: Gowal [16], HAT [39], SCORE [36], Wang [56]." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 6 + }, + { + "bbox": [ + 308, + 503, + 482, + 513 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 503, + 482, + 513 + ], + "spans": [ + { + "bbox": [ + 308, + 503, + 482, + 513 + ], + "type": "text", + "content": "4.2. Robustness Validation on ADML" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 309, + 521, + 544, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 309, + 521, + 544, + 652 + ], + "spans": [ + { + "bbox": [ + 309, + 521, + 544, + 652 + ], + "type": "text", + "content": "Adversarial Robustness. Based on our experimental setups, we have conducted enormous validations of adversarial robustness on CNNs in Table 1 and Transformers in Table 2. As shown in these tables, employing ADML on AT-based defense methods: AT [33], TRADES [62], MART [55], AWP [58] enables to largely improve adversarial robustness, compared with that of each defense method baseline. Bai et al. [1] have argued that Transformers cannot show noticeable adversarial robustness than CNNs, but we want to point out that the robustness of Transformers can be remarkably improved, especially in larger datasets." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 308, + 654, + 544, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 654, + 544, + 712 + ], + "spans": [ + { + "bbox": [ + 308, + 654, + 544, + 712 + ], + "type": "text", + "content": "Ablation Study. In Table 3, we conduct ablation studies on the effect of sample-splitting plus cross-fitting on robustness and the effect of considering treatments as worst examples, non-worst examples, or both on robustness, either. According to the results, only considering treatments" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 750, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 750, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 750, + 314, + 757 + ], + "type": "text", + "content": "4505" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 48, + 176, + 140 + ], + "blocks": [ + { + "bbox": [ + 49, + 48, + 176, + 140 + ], + "lines": [ + { + "bbox": [ + 49, + 48, + 176, + 140 + ], + "spans": [ + { + "bbox": [ + 49, + 48, + 176, + 140 + ], + "type": "image", + "image_path": "55afc6e3c2b8f150b815aa85d03d8b568c6ed32cd30ba9b61f1782618de542dd.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 85, + 141, + 161, + 152 + ], + "lines": [ + { + "bbox": [ + 85, + 141, + 161, + 152 + ], + "spans": [ + { + "bbox": [ + 85, + 141, + 161, + 152 + ], + "type": "text", + "content": "(a) CIFAR-10 [27]" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 179, + 48, + 298, + 140 + ], + "blocks": [ + { + "bbox": [ + 179, + 48, + 298, + 140 + ], + "lines": [ + { + "bbox": [ + 179, + 48, + 298, + 140 + ], + "spans": [ + { + "bbox": [ + 179, + 48, + 298, + 140 + ], + "type": "image", + "image_path": "3ba5f2c4c181843f98b672ee5ad9971a5f0fe96f2ef6eca2eec3cb393a368573.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 205, + 141, + 286, + 152 + ], + "lines": [ + { + "bbox": [ + 205, + 141, + 286, + 152 + ], + "spans": [ + { + "bbox": [ + 205, + 141, + 286, + 152 + ], + "type": "text", + "content": "(b) CIFAR-100 [27]" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 301, + 48, + 420, + 140 + ], + "blocks": [ + { + "bbox": [ + 301, + 48, + 420, + 140 + ], + "lines": [ + { + "bbox": [ + 301, + 48, + 420, + 140 + ], + "spans": [ + { + "bbox": [ + 301, + 48, + 420, + 140 + ], + "type": "image", + "image_path": "5660746d2778873f77e230c6d29c782f12f370c00323d443c14b51e31ba363d7.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 318, + 141, + 413, + 152 + ], + "lines": [ + { + "bbox": [ + 318, + 141, + 413, + 152 + ], + "spans": [ + { + "bbox": [ + 318, + 141, + 413, + 152 + ], + "type": "text", + "content": "(c) Tiny-ImageNet [29]" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 421, + 49, + 540, + 140 + ], + "blocks": [ + { + "bbox": [ + 421, + 49, + 540, + 140 + ], + "lines": [ + { + "bbox": [ + 421, + 49, + 540, + 140 + ], + "spans": [ + { + "bbox": [ + 421, + 49, + 540, + 140 + ], + "type": "image", + "image_path": "582191614aa4ad7c3dca3c7d2ba571ff2701dbe9fb3ea4537144174cf1d8e4f2.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 452, + 141, + 520, + 152 + ], + "lines": [ + { + "bbox": [ + 452, + 141, + 520, + 152 + ], + "spans": [ + { + "bbox": [ + 452, + 141, + 520, + 152 + ], + "type": "text", + "content": "(d) ImageNet [9]" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 66, + 177, + 266, + 300 + ], + "blocks": [ + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "lines": [ + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "spans": [ + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "type": "text", + "content": "Figure 3. Cumulative distribution with averaged adversarial robustness for bottom-k classes against PGD [33] on four benchmark datasets. Note that, " + }, + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "type": "inline_equation", + "content": "30\\%" + }, + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "type": "text", + "content": " values are applied, and perturbation budget is set to " + }, + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "type": "inline_equation", + "content": "[8/255, 8/255, 4/255, 2/255]" + }, + { + "bbox": [ + 46, + 152, + 544, + 175 + ], + "type": "text", + "content": " on each dataset." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 66, + 177, + 266, + 300 + ], + "lines": [ + { + "bbox": [ + 66, + 177, + 266, + 300 + ], + "spans": [ + { + "bbox": [ + 66, + 177, + 266, + 300 + ], + "type": "image", + "image_path": "2e011e0eda560ec3b37bd795fb594a5d55b7479cc9d9d7d0940358b3afd065d7.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 303, + 287, + 336 + ], + "lines": [ + { + "bbox": [ + 46, + 303, + 287, + 336 + ], + "spans": [ + { + "bbox": [ + 46, + 303, + 287, + 336 + ], + "type": "text", + "content": "Figure 4. Distribution of adversarial robustness across whole classes on CIFAR-10. Four methods: AT [33], TRADES [62], MART [55], AWP [58] are integrated on each architecture." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 341, + 286, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 341, + 286, + 365 + ], + "spans": [ + { + "bbox": [ + 46, + 341, + 286, + 365 + ], + "type": "text", + "content": "as worst examples can catch actual adversarial vulnerability, thereby improving robustness much more than others." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 365, + 286, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 286, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 286, + 472 + ], + "type": "text", + "content": "Utilizing Synthetic Images. Recently, several works [46, 16, 39, 36, 56] have employed TRADES [62] utilizing synthetic images: DDPM [18] and EDM [22] to improve adversarial robustness based on the insight that data augmentation such as CutMix [60] can improve robustness [40]. To further investigate the benefits of ADML, we experiment ADML combined with TRADES on the synthetic images. Table 4 shows ADML can further improve the robustness even on synthetic images, demonstrating its efficacy." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 479, + 194, + 491 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 479, + 194, + 491 + ], + "spans": [ + { + "bbox": [ + 47, + 479, + 194, + 491 + ], + "type": "text", + "content": "4.3. Causal Analysis on ADML" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "text", + "content": "Adversarial Vulnerability. To validate the alleviation of adversarial vulnerability existing in certain classes as in Figure 1, we evaluate the averaged adversarial robustness for the cumulative distribution of bottom-" + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "text", + "content": " classes with respect to the network prediction. We set the " + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "text", + "content": " value as " + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "inline_equation", + "content": "30\\%" + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "text", + "content": ". As in Figure 3, we can observe that AT shows noticeable vulnerability in bottom-" + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "text", + "content": " classes, and such tendency pervades in four different datasets and architectures. If we successfully mitigate direct causal parameter of adversarial perturbations on each class, we expect apparent improvements of robustness for bottom-" + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "text", + "content": " classes. As in the figure, we can observe the notable robustness of ADML in the vulnerable bottom-" + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 498, + 287, + 712 + ], + "type": "text", + "content": " classes and corroborate its effectiveness to alleviate aforementioned phenomenon existing in current AT-based defenses. Further infographic is illustrated in Figure 4 for the integrated distribution of baselines [33, 62, 55, 58] and their corresponding ADML adoptions on each architecture, and it shows further adversarial" + } + ] + } + ], + "index": 14 + }, + { + "type": "table", + "bbox": [ + 307, + 177, + 542, + 245 + ], + "blocks": [ + { + "bbox": [ + 307, + 177, + 542, + 245 + ], + "lines": [ + { + "bbox": [ + 307, + 177, + 542, + 245 + ], + "spans": [ + { + "bbox": [ + 307, + 177, + 542, + 245 + ], + "type": "table", + "html": "
NetworksCIFAR10Tiny-ImageNet
ρ10ρ30ρ50ρAvgρ10ρ30ρ50ρAvg
ResNet-1853.9856.8952.9767.334.935.395.546.49
WRN-28-1063.6068.7068.2777.866.725.916.6010.74
ViT-B/1676.7885.4580.0384.331.541.731.913.08
DeiT-B/1669.3674.4668.6369.711.151.131.222.05
", + "image_path": "074a5f4382ba18ac8dfacb449a03c348993ce8bf55a474e6212c54e372ef5afd.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "table_body" + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 247, + 545, + 280 + ], + "lines": [ + { + "bbox": [ + 305, + 247, + 545, + 280 + ], + "spans": [ + { + "bbox": [ + 305, + 247, + 545, + 280 + ], + "type": "text", + "content": "Table 5. Relative ratio of causal parameter (\\%) in CIFAR-10 and Tiny-ImageNet with four architectures. Note that " + }, + { + "bbox": [ + 305, + 247, + 545, + 280 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 247, + 545, + 280 + ], + "type": "text", + "content": " is set to 10,30, 50, and Avg indicates average on whole classes in each dataset." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 285, + 537, + 297 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 285, + 537, + 297 + ], + "spans": [ + { + "bbox": [ + 305, + 285, + 537, + 297 + ], + "type": "text", + "content": "robustness in general (Additional results in Appendix H)." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "spans": [ + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "text", + "content": "Causal Parameter. By deploying ADML, we present a way of mitigating the magnitude of causal parameter " + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "inline_equation", + "content": "|\\theta|" + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "text", + "content": ". To numerically calculate " + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "inline_equation", + "content": "|\\theta|" + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "text", + "content": ", we employ Eq. (8) and measure the average of " + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "inline_equation", + "content": "|\\theta_{\\mathrm{ADML}}|" + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "text", + "content": " for ADML with respect to the bottom-" + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "text", + "content": " and whole classes, respectively. By dividing " + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "inline_equation", + "content": "|\\theta_{\\mathrm{ADML}}|" + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "inline_equation", + "content": "|\\theta_{\\mathrm{AT}}|" + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "text", + "content": ", we can obtain relative ratio of causal parameter, " + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\rho_k := 100 \\times |\\theta_{\\mathrm{ADML}}| / |\\theta_{\\mathrm{AT}}|" + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "text", + "content": " of adversarial examples in bottom-" + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 297, + 545, + 488 + ], + "type": "text", + "content": " classes. This ratio indicates that relative intensity of causal parameter compared to that of AT [33]. As in Table 5, we can observe that ADML shows less intensity of the causal parameter than AT, which means less causal effects of adversarial perturbations on target classes. From combinatorial results of preceding robustness comparison in Sec. 4.2, we corroborate that ADML indeed mitigate the intrinsic causal parameter and alleviate empirical observation in Figure 1, thus results in adversarial robustness." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 501, + 378, + 513 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 501, + 378, + 513 + ], + "spans": [ + { + "bbox": [ + 306, + 501, + 378, + 513 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 521, + 545, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 640 + ], + "type": "text", + "content": "In this paper, we observe adversarial vulnerability varies across targets and still pervades even with deeper architectures and advanced defense methods. To fundamentally address it, we build causal perspective in adversarial examples and propose a way of estimating causal parameter representing the degree of adversarial vulnerability, namely Adversarial Double Machine Learning (ADML). By minimizing causal effects from the estimated vulnerability, ADML can mitigate the empirical phenomenon as well as solidly improve adversarial robustness with other methods." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 653, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 545, + 712 + ], + "type": "text", + "content": "Acknowledgments. This work was partially supported by two funds: IITP grant funded by the Korea government (MSIT) (No.2022-0-00984) and Center for Applied Research in Artificial Intelligence (CARAI) grant funded by DAPA and ADD (UD190031RD)." + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4506" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 125 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 125 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 125 + ], + "type": "text", + "content": "[1] Yutong Bai, Jieru Mei, Alan L Yuille, and Cihang Xie. 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The video background is clearly a source of static bias, but the video foreground, such as the clothing of the actor, can also provide static bias. In this paper, we empirically verify the existence of foreground static bias by creating test videos with conflicting signals from the static and moving portions of the video. To tackle this issue, we propose a simple yet effective technique, StillMix, to learn robust action representations. Specifically, StillMix identifies bias-inducing video frames using a 2D reference network and mixes them with videos for training, serving as effective bias suppression even when we cannot explicitly extract the source of bias within each video frame or enumerate types of bias. Finally, to precisely evaluate static bias, we synthesize two new benchmarks, SCUBA for static cues in the background, and SCUFO for static cues in the foreground. With extensive experiments, we demonstrate that StillMix mitigates both types of static bias and improves video representations for downstream applications. Code is available at https://github.com/1ihaoxin05/StillMix.", + "bbox": [ + 75, + 325, + 473, + 657 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 691, + 209, + 708 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Traditional computer vision techniques perform well on independent and identically distributed (IID) test data, but often lack out-of-distribution (OOD) generalization [9, 32, 12]. This is intimately tied to the learning of shortcut features [27, 16, 17], which are easy to learn and correlate strongly with IID labels but cause poor OOD generalization [53, 62, 49, 22]. In video action recognition, shortcut features often manifest as static cues. For example, a network may classify a video as golf swinging based on its background, a golf course, even if the motion patterns indicate another action such as walking. While static cues can provide valuable information [74, 11, 77], they often outcom", + "bbox": [ + 75, + 719, + 468, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/633fad13f820924081931ab86d4c72e3ca88a1f0d0bf709c95d557ae0ca047bc.jpg", + "image_caption": [ + "Figure 1: Evaluation of background and foreground static bias. (a) Testing on IID HMDB51 [36] test videos. (b) Testing on SCUBA videos, constructed by replacing the video background with a synthetic sinusoidal stripe image. (c) Testing on videos with conflicting foreground cues, constructed by inserting a random static foreground into the SCUBA video." + ], + "image_footnote": [], + "bbox": [ + 503, + 290, + 890, + 477 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "pete motion features [23, 40, 41, 52, 69] and result in low OOD performance [41, 63, 26]. In contrast to the rich literature on mitigating background static bias (e.g., golf courses for golf swinging) [5, 63, 73, 10, 6], foreground static bias has been underexplored. Examples of foreground bias include swimsuits for swimming and guitars for guitar playing — people can swim without swimsuits or show guitars in the video without playing them.", + "bbox": [ + 496, + 626, + 893, + 747 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The first question we ask is if foreground static bias exists and if it is captured by the representations learned by neural networks. Our investigation technique is to create test videos with conflicting action cues from the moving part and the static part of the video. In the first step, shown in Figure 1(b), we replace the backgrounds of IID HMDB51 [36] test videos by sinusoidal stripe images. These videos have no meaningful backgrounds, so the action information must come from the foreground. Therefore, models overly reliant on background static cues", + "bbox": [ + 496, + 750, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "19911", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/1b1598c41f49d139085ebc9da8ec6d6eb7ec438e6972d1cd71a1c97d98b86de8.jpg", + "image_caption": [ + "Figure 2: An illustration of StillMix. We train a 2D reference network that classifies still frames into actions to capture static bias. With the reference network, we sample frames inducing static bias to construct a biased frame bank. We mix the frames from the bank with a given video to generate an augmented video, which is used to train a 3D main network to mitigate static bias." + ], + "image_footnote": [], + "bbox": [ + 81, + 92, + 483, + 334 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/83a65917ced9f3485739c02e64c3d2754535ed0f8a48e95b69809026390e7666.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 490, + 93, + 887, + 335 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "should perform poorly. A background debiasing technique, FAME [10], coupled with a tiny Video Swin Transformer (Swin-T) [46], works relatively well on this test.", + "bbox": [ + 75, + 441, + 468, + 486 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In the second step, shown in Figure 1(c), from a single frame of a random video, we extract its foreground (mainly human actors), and insert the static foreground into all the frames of the current SCUBA video. The resultant video contains only two action features: a static foreground that indicates one action label and a moving foreground that indicates another action label. Predictions made using the static foreground would be wrong. This design allows the quantification of foreground static bias. More details can be found in Sec. S1 of the Supplementary Material.", + "bbox": [ + 75, + 488, + 468, + 638 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The results clearly show the existence of foreground static bias and its negative effects. On the second test set, both Swin-T and Swin-T+FAME suffer similar degradation and perform $5\\%$ worse than SCUBA videos. FAME works by procedurally isolating the foreground regions from each frame and use those for training. However, it is hard to separate the foreground motion from the static foreground (e.g., clothing, equipment, or other people attributes [40]) in the training videos, since both types of features are strongly tied to the human actors.", + "bbox": [ + 75, + 642, + 468, + 792 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We propose StillMix, a technique that mitigates static bias in both the background and the foreground, without the need to explicitly isolate (or even enumerate [5]) the bias-inducing content within a frame. StillMix identifies bias-inducing frames using a reference network and mixes them with training videos without affecting motion features. The process is illustrated in Figure 2. Unlike FAME, StillMix", + "bbox": [ + 75, + 795, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "could suppress static bias anywhere in a frame, including the background and the foreground. In Figure 1, StillMix outperforms FAME and suffers only $2\\%$ accuracy drop on the second benchmark, highlighting its resilience.", + "bbox": [ + 496, + 441, + 890, + 502 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Evaluating OOD action recognition is challenging as test videos with OOD foregrounds, such as swimming without swimsuits or cycling while carrying a guitar, are rare. To pinpoint the static bias in either the background or the foreground, we create new synthetic sets of OOD benchmarks by altering the static features in IID test videos, as illustrated in Figure 3. Specifically, we retain the foregrounds of actions and replace the backgrounds with diverse natural and synthetic images. This procedure yields a test set that quantifies representation bias toward static cues in the background (SCUBA). Second, we create videos that repeat a single random frame from SCUBA, producing a test set that quantifies representation bias toward static cues in the foreground (SCUFO). As these videos disassociate the backgrounds from the action and contain no motion, their actions can be recognized by only static foreground features. Thus, high accuracy on SCUFO indicates strong foreground static bias.", + "bbox": [ + 496, + 505, + 892, + 775 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "With the synthetic OOD benchmarks, we extensively evaluate several mainstream action recognition methods and make the following observations. First, all examined methods exhibit static bias. Second, existing debiasing methods like ActorCutMix [78] and FAME [10] demonstrate resistance to background static bias, but remain vulnerable to foreground static bias. In contrast, the proposed StillMix consistently boosts performance of action recognition mod", + "bbox": [ + 496, + 779, + 893, + 901 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "19912", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/32fda1929fb10e6a5a95e833e968db77e580056813dedfad3d3198875321de3d.jpg", + "image_caption": [ + "Figure 3: An illustration of OOD benchmark construction. To quantify static cues in the background, we reserve the foreground actions and replace the backgrounds with other images to synthesize SCUBA videos. To quantify static cues in the foreground, we randomly select one frame in the SCUBA video and stack it into a single-frame video without motion, named SCUFO videos." + ], + "image_footnote": [], + "bbox": [ + 84, + 90, + 465, + 252 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "els and compares favorably with the other debiasing techniques on both background and foreground static bias. In addition, StillMix improves the performance of transfer learning and downstream weakly supervised action localization.", + "bbox": [ + 75, + 398, + 467, + 472 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The paper makes the following contributions:", + "bbox": [ + 96, + 474, + 398, + 489 + ], + "page_idx": 2 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Through quantitative experiments, we highlight the importance to address foreground static bias in learning robust action representations.", + "- We propose StillMix, a video data augmentation technique to mitigate static bias in not only the background but also the foreground.", + "- We create new benchmarks to quantitatively evaluate static bias of action representations and pinpoint the source of static bias (backgrounds or foregrounds).", + "- We compare action recognition methods on the created benchmarks to reveal their characteristics and validate the effectiveness of StillMix." + ], + "bbox": [ + 96, + 493, + 468, + 679 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 693, + 218, + 709 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Bias Evaluation. Biases are surface features that are easily learned by neural networks and strongly influence their predictions. Such features perform well on IID data [60, 29] but do not generalize to OOD data [53, 49]. In action recognition, models easily capture static bias [40, 41, 5, 63]. The following methods are used for bias evaluation: (1) Visualization techniques [15, 47] visualize the regions that models focus on to interpret the static bias qualitatively. (2) Proxy data or tasks. Synthetic videos with altered backgrounds [6], videos with white-noise textures [26], dynamic texture videos [21, 3] are used to reveal the bias toward backgrounds or texture. Proxy tasks evaluating temporal", + "bbox": [ + 75, + 719, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "asymmetry, continuity, and causality are designed to show the static bias in video representations [18]. (3) Mutual information. [33] quantifies the static bias using mutual information between representations of different types of videos. Although these works evaluate the static bias in the whole video, they do not specify the source of static bias. In this paper, we create new benchmarks to pinpoint the source of static bias as the background and the foreground.", + "bbox": [ + 496, + 90, + 890, + 210 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Bias Mitigation. Prevalent techniques of mitigating bias in action representations can be broadly classified into four categories. (1) Attribute supervision. [5] uses scene pseudolabels and human masks to discourage models from predicting scenes and recognizing actions without human, but it needs extra attribute labels. (2) Re-weighting. [40, 41] identify videos containing bias and downweight them in training, but [65] suggests merely weight adjustment is insufficient. (3) Context separation. [66] learns to separate action and contexts by collecting samples with similar contexts but different actions. (4) Data augmentation. Similar to the proposed StillMix, a few works utilize augmented videos. BE [63] mixes a frame from a video with other frames in the same video. ActorCutMix [78], FAME [10], ObjectMix [31] and FreqAug [30] carefully carve out the foreground (human actors or regions of motion), and replace the background with other images to create augmented training data. SSVC [73] and MCL [38] focus the models to the dynamic regions. However, these methods have not addressed static cues in the foreground.", + "bbox": [ + 496, + 213, + 892, + 516 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "A particular advantage of StillMix is that it does not require specially designed procedures to carve out the bias-inducing pixels within the frames like ActorCutMix [78] and FAME [10], or even to enumerate the source of bias like [5]. Rather, it automatically identifies bias-inducing frames using a reference network. Consequently, StillMix can suppress static bias in both the background and the foreground.", + "bbox": [ + 496, + 518, + 890, + 625 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "StillMix is also similar to two debiasing techniques designed for image recognition and text classification [48, 44], which use a reference network to identify bias-inducing data instances. However, StillMix exploits the special property of videos that they can be decomposed into individual frames. StillMix identifies bias-inducing components (frames) using 2D networks rather than whole data points as in [48, 44].", + "bbox": [ + 496, + 626, + 890, + 747 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Action Recognition. 3D convolution or decomposed 3D convolutions [28, 58, 4, 61, 59, 42] are popular choices for action recognition. Two-stream architectures employ two modalities to classify actions, such as both RGB frames and optical flow [54, 64], or videos with two different frame rates and resolutions [14]. Multi-scale temporal convolutions or feature fusion are designed for fine-grained actions with strong temporal structures [75, 24, 39, 67]. Transformer networks are proposed to capture the long-range dependencies [1, 2, 46]. However, our understanding of the", + "bbox": [ + 496, + 750, + 892, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "19913", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "representations learned by these models remains limited. In this paper, we create benchmarks to evaluate what features are captured by action models and propose a simple data augmentation method that effectively improves the robustness of action models.", + "bbox": [ + 75, + 90, + 472, + 167 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3. The StillMix Technique", + "text_level": 1, + "bbox": [ + 76, + 183, + 299, + 202 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In order to learn robust and generalizable action representations that are invariant to static cues, we propose a simple but effective video data augmentation technique, StillMix. Instead of using manually designed rules to identify and remove biased data from the training set, as in ActorCutMix [78] and FAME [10], StillMix learns to identify still frames that induce biased representation using a neural network and mitigate static bias through mixing the identified frames with videos. As a result, StillMix offers a flexible bias suppression technique that works for both the background and the foreground.", + "bbox": [ + 75, + 210, + 468, + 376 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We begin with some notations. We denote the $i^{\\mathrm{th}}$ video in the training set as tensor $\\pmb{x}_i\\in \\mathbb{R}^{C\\times T\\times H\\times W}$ , where $C$ , $T$ , $H$ and $W$ are the number of channels, number of frames, height and width of the video, respectively. The associated ground-truth action label is $y_{i}$ . The video $\\pmb{x}_i$ contains a sequence of frames $\\langle \\pmb {z}_{i,j}\\rangle_{j = 1}^{T}$ , $\\pmb {z}_{i,j}\\in \\mathbb{R}^{C\\times H\\times W}$ . The training set contains $N$ training video samples and is written as $\\{(x_i,y_i)\\}_{i = 1}^N$ . The goal of StillMix is to augment a given training sample $(x_{i},y_{i})$ into a transformed sample $(\\tilde{x}_i,\\tilde{y}_i)$ . The procedures of StillMix are illustrated in Figure 2 and introduced as follows.", + "bbox": [ + 75, + 377, + 472, + 544 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Step 1: Training the Reference Network. We identify bias-inducing frames using a 2D reference network that predicts the action label from a still frame of a video. As the still frame contains no motion, we expect the network to rely on static features to make the predictions.", + "bbox": [ + 75, + 551, + 468, + 626 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Specifically, at every epoch we randomly sample a frame $\\mathbf{z}_{i,j} \\in \\mathbb{R}^{C \\times H \\times W}$ from each video $\\mathbf{x}_i$ , and train the reference network $\\mathcal{R}(\\cdot)$ to predict the label $y_i$ . The loss is", + "bbox": [ + 76, + 627, + 468, + 674 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nL _ {r e f} = \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\ell \\left(\\mathcal {R} \\left(\\boldsymbol {z} _ {i, j}\\right), y _ {i}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 686, + 468, + 729 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\ell(\\cdot)$ can be any classification loss, such as the cross-entropy. After training, the reference network $\\mathcal{R}(\\cdot)$ encodes the correlations between static cues within the frames and the action classes.", + "bbox": [ + 75, + 742, + 468, + 801 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Step 2: Identifying Biased Frames. The output of reference network $\\mathcal{R}(\\pmb{z}_{i,j})$ is a categorical distribution over action classes. We take the probability of the predicted class $p_{i,j} = \\max_k P(y = k|\\pmb{z}_{i,j})$ . A high $p_{i,j}$ indicates strong correlation between $\\pmb{z}_{i,j}$ and the action class, which means $\\pmb{z}_{i,j}$ can induce static bias. Therefore, we select frames with", + "bbox": [ + 75, + 809, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "high $p_{i,j}$ to construct the biased frame bank $S$ :", + "bbox": [ + 498, + 90, + 808, + 107 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nS = \\left\\{\\boldsymbol {z} _ {i, j} \\mid p _ {i, j} \\geq p _ {\\tau} \\right\\}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 619, + 117, + 890, + 135 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $p_{\\tau}$ is the $\\tau$ -th percentile value of $p_{i,j}$ . In practice, we perform another round of uniformly random selection to control the size of the biased frame bank.", + "bbox": [ + 498, + 145, + 893, + 190 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Step 3: Mixing Video and Biased Frames. To break the strong correlation between the biased frame and the action class, we mix a video of any action class with different biased frames identified above. Specifically, in each epoch, given a video sample $(x_{i},y_{i})$ , we sample a frame $z^{\\mathrm{biased}}$ from the biased frame bank $S$ and tile it $T$ times along the temporal dimension, yielding a static video with $T$ identical frames. We denote this operation as $\\mathrm{Tile}(z^{\\mathrm{biased}},T)$ . The augmented video sample $\\tilde{x}_i$ is generated by the pixel-wise interpolation of $x_{i}$ and the static video. The augmented video label $\\tilde{y}_i$ is the same as the original action label $y_{i}$ .", + "bbox": [ + 496, + 196, + 890, + 364 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {\\boldsymbol {x}} _ {i} = \\lambda \\boldsymbol {x} _ {i} + (1 - \\lambda) \\operatorname {T i l e} \\left(\\boldsymbol {z} ^ {\\text {b i a s e d}}, T\\right), \\quad \\tilde {y} _ {i} = y _ {i}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 542, + 377, + 890, + 393 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where the scalar $\\lambda$ is sampled from a Beta distribution $\\operatorname{Beta}(\\alpha, \\beta)$ .", + "bbox": [ + 500, + 400, + 890, + 430 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The rationale for keeping the video label unchanged after augmentation is that the static video contains no motion and does not affects the motion patterns in the mixed video, thus it should not contribute to the action label. This setting of StillMix can be intuitively understood as randomly permuting the labels of the static video, so that the network is forced to ignore the correlations between the static cues in the biased frames and actions.", + "bbox": [ + 496, + 431, + 890, + 551 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Training with Augmented Videos. We apply StillMix to each video with a predefined probability $P_{\\mathrm{aug}}$ .", + "bbox": [ + 498, + 556, + 890, + 589 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\boldsymbol {x} _ {i} ^ {*}, y _ {i} ^ {*}\\right) = \\left\\{ \\begin{array}{l l} \\left(\\boldsymbol {x} _ {i}, y _ {i}\\right) & a _ {i} = 0 \\\\ \\left(\\tilde {\\boldsymbol {x}} _ {i}, \\tilde {y} _ {i}\\right) & a _ {i} = 1 \\end{array} , a _ {i} \\sim \\operatorname {B e r} \\left(P _ {\\text {a u g}}\\right), \\right. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 522, + 599, + 890, + 641 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $a$ is a scalar sampled from a Bernoulli distribution $Ber(P_{\\mathrm{aug}})$ . The samples $\\{(x_i^*, y_i^*)\\}_{i=1}^N$ are used to train the main network $\\mathcal{F}(\\cdot)$ using the following loss function:", + "bbox": [ + 500, + 650, + 890, + 696 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nL = \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\ell \\left(\\mathcal {F} \\left(\\boldsymbol {x} _ {i} ^ {*}\\right), y _ {i} ^ {*}\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 606, + 705, + 890, + 748 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\ell (\\cdot)$ could be any classification loss.", + "bbox": [ + 500, + 758, + 782, + 773 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Discussion. StillMix aims to learn robust action representations that generalize to OOD data. One popular formulation of OOD generalization [68, 34, 51, 35, 50] considers shortcut features as features that work under a specific environment but not others. For example, a classifier that excels in well-lit environments may perform terribly in dim environments. To learn robust classifiers, we ought to discover invariant features that work equally well in all environments.", + "bbox": [ + 496, + 779, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "19914", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "More formally, the optimal predictor $\\mathcal{F}^*$ can be found with the bi-level optimization", + "bbox": [ + 76, + 90, + 468, + 121 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {F} ^ {*} = \\underset {\\mathcal {F}} {\\operatorname {a r g m i n}} \\max _ {e} \\mathbb {E} _ {\\boldsymbol {x} ^ {e}, y ^ {e}} [ \\ell (\\mathcal {F} (\\boldsymbol {x} ^ {e}), y ^ {e}) ], \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 142, + 128, + 468, + 154 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the feature-label pair, $(\\pmb{x}^e,y^e)$ , are drawn from the data distribution $P(\\pmb{x},y|e)$ of environment $e$ and $\\ell$ is the per-sample loss. $\\pmb{x}^e$ contains both class features and environment features; a good predictor $\\mathcal{F}$ is sensitive to the former and ignores the latter. The optimization encourages this because if $\\mathcal{F}$ utilizes features that work for environment $e_1$ but not $e_2$ , the loss will increase as the $\\max_e$ operation will select $e_2$ .", + "bbox": [ + 75, + 162, + 468, + 281 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "However, directly optimizing Eq. (6), such as in [51], requires sampling data from all environments, which is impractical due to skewed environment distributions. For example, videos of people playing soccer in tuxedos on beaches are exceedingly rare. Maximizing over all environments is also challenging.", + "bbox": [ + 75, + 282, + 468, + 375 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The mixing operation in StillMix may be understood in the same framework. A static frame $z^{\\mathrm{biased}}$ can be considered as coming from an environment $e'$ which biases predictions toward certain action labels. Mixing $z^{\\mathrm{biased}}$ with $x_{i}$ simulates sampling $x^{e'}$ from the environment $e'$ . StillMix may be considered to optimize the following loss,", + "bbox": [ + 75, + 375, + 468, + 465 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {F} ^ {*} = \\underset {\\mathcal {F}} {\\operatorname {a r g m i n}} \\mathbb {E} _ {e} \\left[ \\mathbb {E} _ {\\boldsymbol {x} ^ {e}, y ^ {e}} [ \\ell (\\mathcal {F} (\\boldsymbol {x} ^ {e}), y ^ {e}) ] \\right], \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 142, + 472, + 468, + 501 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "which replaces the maximization over environments in Eq. (6) with an expectation over environments due to the random sampling of $z^{\\mathrm{biased}}$ .", + "bbox": [ + 76, + 508, + 468, + 554 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. SCUBA and SCUFO: OOD Benchmarks", + "text_level": 1, + "bbox": [ + 76, + 565, + 441, + 580 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To quantitatively evaluate static bias in the background and the foreground, we create OOD benchmarks based on three commonly used video datasets, i.e., HMDB51 [36], UCF101 [55] and Kinetics-400 [4], as detailed below.", + "bbox": [ + 76, + 590, + 468, + 651 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Foreground Masks and Background Images", + "text_level": 1, + "bbox": [ + 76, + 659, + 449, + 676 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Foreground Masks. To extract the foreground area of actions, we use available human-annotated masks of people for UCF101 and HMDB51. There are totally 910 videos in the UCF101 test set and 256 videos in the HMDB51 test set having foreground annotations. Since there is no human-annotated masks for Kinetics-400, we use video segmentation models [57, 56] to generate foreground masks. After filtering out the videos with small foreground masks (likely to be wrong), we obtain totally 10,190 videos in the Kinetics-400 validation set to construct the benchmark.", + "bbox": [ + 75, + 681, + 468, + 832 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Background Images. In order to synthesize diverse test videos, we collect background images from three different image sources: 1) the test set of Place365 [76]. 2) images generated by VQGAN-CLIP [8] from a random scene", + "bbox": [ + 76, + 839, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/e32537a5d83988613f069bec27e332612ffd75abc2bb9813a237f71cf0220241.jpg", + "image_caption": [ + "(a) Place365" + ], + "image_footnote": [], + "bbox": [ + 506, + 87, + 627, + 147 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/f3bdb01d696d78843f7f15aab06bd4cb02b5517749a4b770b17263b3464262ac.jpg", + "image_caption": [ + "Figure 4: Background images from different sources. (a) An image from Place365. (b) An image generated by VQGAN-CLIP from the query \"A painting of a conference room in the style of surreal art\". (c) An image of randomly generated sinusoidal stripes." + ], + "image_footnote": [], + "bbox": [ + 630, + 88, + 754, + 145 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/f46bc9432e2a971c31aa545278859615ec74b415cfbc900d37b4049831255401.jpg", + "image_caption": [ + "(b) VQGAN-CLIP", + "(c) Sinusoid" + ], + "image_footnote": [], + "bbox": [ + 759, + 87, + 883, + 145 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "category of Place365 and a random artistic style. 3) randomly generated images with S-shaped stripes defined by sinusoidal functions. For each image source, we construct a background image pool. In Figure 4, we show three example background images from the three sources. More details are described in Sec. S2 of the Supplementary Material.", + "bbox": [ + 498, + 270, + 890, + 361 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Test Video Synthesis", + "text_level": 1, + "bbox": [ + 500, + 369, + 692, + 383 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Testing for Background Static Cues. Given a video $\\pmb{x}$ with $T$ frames $\\{\\pmb{x}_t\\}_{t=1}^T$ , we create a synthetic video $\\hat{\\pmb{x}}$ by combining the foreground of $\\pmb{x}$ and a background image sampled from a background image pool.", + "bbox": [ + 498, + 392, + 890, + 453 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\boldsymbol {x}} _ {t} = \\boldsymbol {m} _ {t} \\odot \\boldsymbol {x} _ {t} + (1 - \\boldsymbol {m} _ {t}) \\odot \\operatorname {T i l e} (\\boldsymbol {z} ^ {\\mathrm {b g}}, T), \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 549, + 460, + 890, + 478 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $m_t$ is the foreground mask, $\\odot$ denotes pixel-wise multiplication, $z^{\\mathrm{bg}}$ is a background image sampled from the image pool. $\\mathrm{Tile}(z^{\\mathrm{bg}}, T)$ repeats $z^{\\mathrm{bg}}T$ times along the temporal dimension. For each video with foreground masks, we pair it with $m$ randomly selected background images from each of the 3 background image pools to synthesize $3m$ videos. We set $m = 10,5,1$ for HMDB51, UCF101 and Kinetics-400, respectively, since HMDB51 and UCF101 have fewer videos with foreground masks and we would like to increase the diversity of the synthetic videos.", + "bbox": [ + 498, + 486, + 890, + 636 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The generated videos retain the original action foreground, including the human actors and their motion, on new random backgrounds. They are designed to test bias toward static cues from the background, and are named SCUBA videos. We expect models invariant to static backgrounds to obtain high classification accuracy on SCUBA.", + "bbox": [ + 498, + 638, + 890, + 728 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Testing for Foreground Static Cues. In addition, we create another set of videos to test the amount of foreground static bias in the learned representations. Foreground static cues include people and object attributes, such as bicycle helmets for cycling and bows for archery — people can ride a bicycle without helmets or hold bows when not performing archery. As the SCUBA videos contain most foreground elements in the original videos, they cannot distinguish whether models rely on foreground static cues.", + "bbox": [ + 498, + 734, + 890, + 869 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To this end, we create videos that contain only a single frame. Specifically, from each SCUBA video, we ran", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "19915", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/23247d1e9e37859697ce5af328bb5d525f09afaca2dc2846419a4b8e6edbdf06.jpg", + "table_caption": [ + "Table 1: Statistics of the created benchmarks." + ], + "table_footnote": [], + "table_body": "
Video Source# Original VideosBackground Source# Synthetic Videos# Domain Gap of SCUBA# Domain Gap of SCUFO
HMDB51256Place3652,5605.646±0.2765.745±0.290
VQGAN-CLIP2,5608.178±0.6858.307±0.533
Sinusoid2,56011.739±0.44411.998±0.932
UCF101910Place3654,55020.493±2.19920.829±2.093
VQGAN-CLIP4,55051.320±5.79055.202±9.477
Sinusoid4,55052.249±3.52252.534±5.930
Kinetics-40010,190Place36510,1906.094±0.2086.455±0.224
VQGAN-CLIP10,1907.504±0.2968.052±0.273
Sinusoid10,1907.211±0.3117.766±0.148
", + "bbox": [ + 78, + 109, + 470, + 252 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "domly select one frame and repeat it temporally to create a video with zero motion. As these videos quantify the representation bias toward static cues in the foreground, we name them SCUFO videos. In SCUFO videos, the foreground static features are identical to the corresponding SCUBA videos, but the motion information is totally removed. Therefore, a model invariant to foreground static features should obtain low classification accuracy on them.", + "bbox": [ + 75, + 291, + 468, + 412 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We summarize the dataset statistics in Table 1. SCUBA and SCUFO have the same number of videos for each pair of video source and background source. We also report the domain gap between original videos to show their OOD characteristics, as explained in the next section.", + "bbox": [ + 75, + 412, + 468, + 489 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Quality Assessment", + "text_level": 1, + "bbox": [ + 76, + 503, + 264, + 518 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We empirically verify that the SCUBA datasets retain the motion features of the original videos but replace background static features using the following two tests.", + "bbox": [ + 75, + 527, + 468, + 574 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Human Assessment. To test if SCUBA preserves the motion information sufficiently for action recognition, we carry out an experiment on Amazon Mechanical Turk (AMT) to verify if human workers can recognize the actions in SCUBA videos.", + "bbox": [ + 75, + 580, + 468, + 655 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "From the same original video, we randomly sampled one synthetic video and asked the AMT workers if the moving parts in the video show the labeled action. The workers are given three options: yes, no, and can't tell. We also create control questions with original videos to detect random clicking and design control groups to prevent the workers from always answering yes to synthetic videos. The final answer for each video is obtained by majority voting of three workers. Workers who do not reach at least $75\\%$ accuracy on the control questions are rejected. More details are described in Sec. S2 of the Supplementary Material.", + "bbox": [ + 75, + 657, + 468, + 823 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Collectively, the AMT workers were able to correctly recognize the actions in $96.15\\%$ of UCF101-SCUBA, $86.33\\%$ of HMDB51-SCUBA and $85.19\\%$ of Kinetics400-SCUBA videos. We conclude that SCUBA videos preserve sufficient action information for humans to recognize.", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Domain Gaps of the Static Features. To verify if SCUBA and SCUFO have successfully replaced the background static features and qualify as OOD test sets, we test if a classifier based on purely static features trained on IID videos can generalize to SCUBA and SCUFO.", + "bbox": [ + 496, + 90, + 890, + 165 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Using a variation of scene representation bias [5], we define the domain gap $G_{\\text{scene}}$ as", + "bbox": [ + 498, + 167, + 890, + 196 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nG _ {s c e n e} = A c c \\left(D _ {\\text {o r i}}, \\Phi_ {s c e n e}\\right) / A c c \\left(D _ {\\text {s y n}}, \\Phi_ {s c e n e}\\right). \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 545, + 208, + 890, + 223 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Here $\\Phi_{\\text{scene}}$ is the average frame feature extracted from a ResNet-50 pretrained on Place365 [76]. Thus, the extracted feature captures static scene information, mostly from the background. We train a linear classifier on the original video training set and apply it to the original test set $D_{\\text{ori}}$ , obtaining the accuracy $Acc(D_{\\text{ori}}, \\Phi_{\\text{scene}})$ . After that, we apply the same classifier to the synthetic dataset $D_{\\text{syn}}$ , obtaining the accuracy $Acc(D_{\\text{syn}}, \\Phi_{\\text{scene}})$ . A higher ratio indicates greater domain gap with respect to static features.", + "bbox": [ + 496, + 237, + 890, + 375 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In Table 1, we show the means and standard deviations computed from three random repeats of video synthesis. We observe large domain gaps, ranging from 5.6-fold to 52-fold decrease in accuracy on the synthetic test set. This demonstrates the static features of synthetic videos differ substantially from the original videos and the synthetic videos can serve as OOD tests. Moreover, the low standard deviations show that the effects of random sampling are marginal. In later experiments, we use the dataset from one random seed.", + "bbox": [ + 496, + 375, + 890, + 511 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 500, + 529, + 633, + 546 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this section, we compare the performance of several mainstream action recognition methods on IID and OOD test data and validate the effectiveness of StillMix.", + "bbox": [ + 498, + 555, + 890, + 601 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Comparing Methods", + "text_level": 1, + "bbox": [ + 500, + 614, + 694, + 631 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Action Recognition Models. (1) TSM [43], a temporal shift module learning spatiotemporal features with 2D CNN. (2) SlowFast [14], a two-branch 3D CNN learning spatiotemporal signals under two frame rates. (3) Video Swin Transformer [46], an adapted Swin Transformer [45] for videos. We use the tiny version, denoted as Swin-T.", + "bbox": [ + 496, + 638, + 890, + 731 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Video Data Augmentation and Debiasing Methods. We compare the debiasing performance of several video data augmentation and debiasing methods by adapting them to supervised action recognition. (1) Mixup [72] and VideoMix [70]. (2) SDN [5]. (3) BE [63], ActorCutMix[78] and FAME [10]. We adapt these three self-supervised debiasing methods as data augmentations, which carve out the foreground and replace the background as in the original papers. All the data augmentation techniques are applied stochastically as in [19]. More implementation details are described in Sec. S3 of the Supplementary Material.", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "19916", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/93f3c4e89df01ddfdddad11244c6b117f606b3ad923d441281ec94024a25ad8a.jpg", + "table_caption": [ + "Table 2: IID and OOD test accuracy (\\%) of augmentation and debiasing methods on Kinetics-400. † indicates adaptation from self-supervised debiasing methods. ConfI-FG denotes synthetic videos with conflicting foreground cues. All models are pretrained on ImageNet." + ], + "table_footnote": [], + "table_body": "
ModelAugmentation or DebiasingIIDOOD
Avg SCUBA↑Avg SCUFO↓Contra Acc.↑Confl-FG↑ARAS↑
TSMNo71.1337.3917.2222.8020.1557.86
Mixup71.3340.8117.5325.9823.4858.05
VideoMix71.3538.8717.2524.5723.4356.61
SDN69.9936.9516.5522.3820.2955.06
BE†71.3037.8916.0824.3520.1157.47
ActorCutMix†71.0740.4216.2926.5221.4157.09
FAME†71.1340.9118.3425.6324.4157.47
StillMix (Ours)71.2840.485.2336.0725.7359.69
Swin-TNo73.9541.7418.1725.9325.2560.17
Mixup73.9143.9517.9228.2427.6459.59
VideoMix73.8043.1719.2626.4029.3760.95
SDN72.2342.3421.4624.4627.1460.26
BE†73.9343.4019.5626.2826.6759.79
ActorCutMix†73.9745.7019.3928.6429.0261.23
FAME†73.8148.7921.2730.0329.5060.37
StillMix (Ours)73.8644.105.5139.4130.7762.49
", + "bbox": [ + 76, + 176, + 486, + 435 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Evaluation Metrics", + "text_level": 1, + "bbox": [ + 76, + 459, + 261, + 474 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We conduct the following experiments on Kinetics-400, UCF101 and HMDB51. First, we perform IID tests on the original test sets and use the top-1 accuracy as metrics. After that, we perform OOD tests on SCUBA and SCUFO and report the average top-1 accuracy across background image sources. Note that higher accuracy on SCUBA is better (low background static bias), while lower accuracy on SCUFO is better (low foreground static bias).", + "bbox": [ + 75, + 484, + 468, + 604 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To show the performance of utilizing pure foreground motion information, we propose another performance metric called contrasted accuracy (Contra. Acc.). As one SCUFO video is derived from a SCUBA video, we count one correct prediction if the model is correct on the SCUBA but incorrect on the associated SCUFO video.", + "bbox": [ + 75, + 606, + 468, + 696 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We further evaluate on the synthetic videos with conflicting foreground cues (Figure 1). Finally, we also evaluate on ARAS [13], a real-world OOD dataset with rare scenes, to show the performance of scene bias reduction.", + "bbox": [ + 75, + 696, + 468, + 758 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Results on IID and OOD Benchmarks", + "text_level": 1, + "bbox": [ + 76, + 770, + 405, + 786 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2, 3 and 4 compare the IID and OOD performance of different video data augmentation and debiasing methods on Kinetics-400, HMDB51 and UCF101. Given limited computational resources, we ran experiments on Kinetics-400 using a single seed. However, on the smaller HMDB51 and UCF101, we repeated experiments with three seeds. In Sec. S1 of the Supplementary Material, we provide more", + "bbox": [ + 75, + 794, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/917a6061fadc618684aabe51460f0a0175e2d468bef852f939d3595771e12639.jpg", + "table_caption": [ + "Table 3: IID and OOD test accuracy $(\\%)$ of augmentation and debiasing methods on HMDB51. All models are pretrained on Kinetics-400." + ], + "table_footnote": [], + "table_body": "
ModelAugmentation or DebiasingIIDOOD
Avg SCUBA↑Avg SCUFO↓Contra. Acc.↑ConfI-FG↑
TSMNo70.39±0.5138.03±1.3919.23±1.3022.02±0.6425.44±1.31
Mixup72.00±0.4739.76±1.7219.08±1.3723.76±0.8426.94±1.23
VideoMix70.72±0.1235.71±1.5717.48±1.1121.03±0.5522.19±1.47
SDN69.51±0.3037.05±0.7317.60±0.3723.74±0.9528.38±0.87
BE71.22±0.2438.48±1.4219.45±1.0622.39±0.6725.21±1.35
ActorCutMix70.52±0.8238.40±0.5319.61±0.5621.94±0.4026.16±0.36
FAME70.39±0.8847.19±1.5222.33±0.9128.21±0.8933.98±2.09
StillMix71.52±0.3848.23±0.968.43±0.8842.05±0.9936.89±1.09
Swin-TNo73.92±0.7443.93±0.7820.46±0.7127.84±1.2836.58±1.65
Mixup74.58±0.4343.10±1.1321.17±0.6626.09±1.0536.62±2.98
VideoMix73.31±0.5339.39±0.7120.44±0.7323.13±0.5432.68±1.04
SDN74.66±0.8240.02±1.4820.22±1.2422.88±1.0534.87±2.43
BE74.31±0.4143.56±1.3819.96±0.7127.84±1.3235.99±0.67
ActorCutMix74.05±0.6046.79±1.3822.07±0.3628.12±1.2736.97±1.63
FAME73.79±0.2951.40±1.5426.92±0.7129.66±2.1139.61±1.87
StillMix74.82±0.4351.81±1.7813.39±0.7140.28±1.6147.38±1.50
", + "bbox": [ + 501, + 147, + 903, + 367 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/7c9ca6dac70356264042faefa58b77255b0637b7755d4f70b9e2adb5c3d70f24.jpg", + "table_caption": [ + "Table 4: IID and OOD test accuracy $(\\%)$ of augmentation and debiasing methods on UCF101. All models are pretrained on Kinetics-400." + ], + "table_footnote": [], + "table_body": "
ModelAugmentation or DebiasingIIDOOD
Avg SCUBA↑Avg SCUFO↓Contra. Acc.↑ConfI-FG↑
TSMNo94.62±0.0825.60±1.364.21±0.8421.83±1.4827.68±1.35
Mixup94.71±0.1427.80±0.954.04±0.8124.17±1.0030.31±1.10
VideoMix94.50±0.1931.55±1.685.77±0.7426.69±1.3830.69±1.79
SDN93.84±0.2719.91±0.613.10±0.1917.19±0.5120.89±0.36
BE94.49±0.1425.91±1.374.62±0.8421.82±1.3828.06±1.32
ActorCutMix94.47±0.1538.11±1.484.56±0.1633.90±1.5138.12±2.12
FAME93.72±0.0935.72±1.153.67±0.5232.28±1.2834.58±0.93
StillMix94.30±0.1437.18±1.290.79±0.1236.47±1.2440.59±0.80
Swin-TNo96.21±0.1942.31±2.245.78±0.6836.82±2.1244.65±2.10
Mixup96.17±0.1446.16±1.745.93±0.4340.46±1.9647.16±2.82
VideoMix96.00±0.0241.40±1.1113.27±0.8529.37±0.9142.59±1.51
SDN95.76±0.1139.25±2.322.98±0.8836.42±1.7448.47±2.06
BE96.06±0.1143.98±0.805.54±0.9438.62±1.1346.62±0.96
ActorCutMix95.87±0.1958.61±0.4811.92±0.2546.87±0.4556.88±0.39
FAME95.81±0.1540.90±1.576.36±0.7135.14±1.6628.21±1.83
StillMix96.02±0.0858.22±0.413.44±0.5154.90±0.7757.30±0.60
", + "bbox": [ + 501, + 452, + 903, + 672 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "detailed results (e.g., tests on videos with conflicting foreground cues and ARAS [13]).", + "bbox": [ + 498, + 698, + 888, + 729 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "OOD data cause performance degradation. Comparing the performance of TSM and Swin-T on IID and OOD tests, we observe that they perform much worse (more than $20\\%$ ) on SCUBA than IID videos. Given that human workers can recognize the action in more than $85\\%$ of SCUBA videos, the results indicate that the models are not robust to the domain shifts, probably due to the reliance of static background features; when the backgrounds are replaced, performance deterioration ensues.", + "bbox": [ + 496, + 731, + 890, + 866 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "IID tests do not fully reveal representation quality. Comparing the performance of different augmentation and debi", + "bbox": [ + 498, + 869, + 890, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "19917", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "asing methods, we observe that all methods obtain similar accuracies on IID tests, which fall within a $2\\%$ band. However, they show vastly different performance on SCUBA and SCUFO — the maximum difference is larger than $15\\%$ . Therefore, we argue that IID tests alone may not be good indicators of the robustness of action representations.", + "bbox": [ + 75, + 90, + 468, + 181 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In particular, VideoMix, SDN and BE provide little debiasing effects. Mixup leads to inconsistent performance gains. ActorCutMix and FAME consistently improve performance on SCUBA. Nevertheless, they decrease performance (increase accuracy) on SCUFO, which suggests that they improve performance on SCUBA partially by increasing reliance on foreground static features. The action features learned with ActorCutMix and FAME are likely still vulnerable to foreground static bias.", + "bbox": [ + 75, + 183, + 470, + 318 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "StillMix alleviates foreground and background static bias. StillMix boosts the performance on both SCUBA and SCUFO videos and obtains the best contrasted accuracy (Contra. Acc.). The significant improvements on SCUFO indicate that StillMix can suppress static bias from the entire video and not only the background. In addition, StillMix outperforms other methods on videos with conflicting foreground cues as well as ARAS. Overall, these results demonstrate the ability of StillMix to reduce static bias that is difficult to exhaustively name or pixel-wise cut out.", + "bbox": [ + 75, + 325, + 468, + 477 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.4. StillMix Improves Representation Learning", + "text_level": 1, + "bbox": [ + 76, + 489, + 447, + 507 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We further investigate the effects of StillMix on improving representation learning through the following tests.", + "bbox": [ + 76, + 515, + 468, + 546 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Transferring action features across datasets. We evaluate the representations learned with different augmentation and debiasing methods by their capability to transfer to different datasets. We adopt the linear probing protocol, which trains a linear classifier on the target dataset on top of the backbone network trained on the source dataset. Table 5 shows the results of TSM, where StillMix obtains the best performance, especially in transferring across small datasets.", + "bbox": [ + 75, + 551, + 468, + 674 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Downstream weakly supervised action localization. We evaluate the representations learned with StillMix by their ability to improve downstream weakly supervised action localization. We pretrain TSM on Kinetics-400 with StillMix. After that, we extract RGB features for each video segments on THUMOS14 [25] and use the extracted features to train weakly supervised action localization models BaSNet [37] and CoLA [71]. StillMix improves the performance by more than $1.0\\%$ of average mAP for BaSNet and more than $0.5\\%$ of average mAP for CoLA.", + "bbox": [ + 75, + 681, + 468, + 832 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.5. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 845, + 230, + 862 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We conduct ablation study on UCF101 and HMDB51 to examine design choices of StillMix.", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/54ac9c07fd52705ff2f2b1ae298f47d7118b7f9cc777d03b009183d8279cc100.jpg", + "table_caption": [ + "Table 5: Action recognition accuracy (%) of transferring features across Kinetics-400, UCF101, and HMDB51." + ], + "table_footnote": [], + "table_body": "
Augmentation or DebiasingSource→Target
K400→UCFK400→HMDBHMDB→UCFUCF→HMDB
No92.5266.6761.6444.95
Mixup93.0768.6963.5846.60
VideoMix93.5569.2261.4940.33
SDN92.8163.7961.1241.90
BE93.1067.4562.7145.88
ActorCutMix92.7367.3961.6742.92
FAME93.8767.8458.8744.99
StillMix93.8970.0765.6947.99
", + "bbox": [ + 500, + 132, + 903, + 275 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/32e312316be4057688d0f74a620980a362ebcbe01371ef76e5981186e15ae436.jpg", + "table_caption": [ + "Table 6: Weakly supervised action localization performance of features learned by StillMix." + ], + "table_footnote": [], + "table_body": "
MethodFeatureDebiasingAvg mAP@IoU=[0.1:0.9]
BaSNetTSM (RGB)No0.1810
TSM (RGB)StillMix0.1935
CoLATSM (RGB)No0.2380
TSM (RGB)StillMix0.2436
", + "bbox": [ + 526, + 344, + 864, + 426 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Debiasing works the best when the reference network and the main network share the same architecture. We compare the results of StillMix with different network structures in Table 7. When the structures of the reference network and the main network are identical, the OOD performance is the best and the IID performance is very close to the best, indicating good bias mitigation. We hypothesize that networks with same architecture tend to learn the same bias. As a result, using a reference network with the same architecture as the main network could be the most effective at identifying bias-inducing frames.", + "bbox": [ + 496, + 454, + 890, + 621 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Sampling biased frames improves debiasing. We compare three frame sampling strategies when constructing the biased frame bank: (1) No RefNet: the frame bank is uniformly sampled from the whole dataset; (2) RefNet: as in StillMix, we sample frames with high prediction probabilities from the reference network according to Eq. (2); (3) RefNet Inversed: contrary to StillMix, we sample frames with low prediction probabilities from the reference network, $S = \\{z_{i,j}|p_{i,j} < p_{\\tau}\\}$ . Table 8 shows results of ImageNet pretrained TSM and Swin-T. The reference network (RefNet) approach achieves the best OOD performance, whereas RefNet Inversed performs the worst.", + "bbox": [ + 496, + 627, + 890, + 808 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We observe the difference between RefNet and No RefNet is small on UCF101 but is large on HMDB51. We attribute this to the prevalence of bias-inducing frames in UCF101. MMAction2 [7] trained TSN [64] using only three frames per video on UCF101 and achieved $83.03\\%$ classification accuracy but achieved only $48.95\\%$ with 8", + "bbox": [ + 496, + 810, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "19918", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/e69887ada079cd1a3f37a0df137fde67046374dd5fd8697a80cb9c12f8368763.jpg", + "table_caption": [ + "Table 7: Action recognition accuracy (%) of StillMix with different reference network structures. All networks are pretrained on ImageNet." + ], + "table_footnote": [], + "table_body": "
Main NetworkReference NetworkUCF101HMDB51
IIDContra. Acc.IIDContra. Acc.
TSMResNet50-2D87.2924.6054.6633.14
SlowFast-2D87.4422.2055.0330.51
Swin-T-2D86.7223.0855.0531.62
SlowFastResNet50-2D84.8518.8650.7420.89
SlowFast-2D84.9619.7651.5321.21
Swin-T-2D85.1619.1851.8520.28
Swin-TResNet50-2D88.5931.0956.1018.44
SlowFast-2D88.6029.3454.4319.25
Swin-T-2D88.9232.1455.3621.40
", + "bbox": [ + 96, + 145, + 450, + 325 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/b7bb0699cd9ad04bb376610fd1a555a825250e545a42c2a8756a8ad229d7e715.jpg", + "table_caption": [ + "Table 8: Action recognition accuracy (\\%) of StillMix with different frame sampling strategies." + ], + "table_footnote": [], + "table_body": "
Main NetworkSampling StrategyUCF101HMDB51
IIDContra. Acc.IIDContra. Acc.
TSMNo RefNet87.3924.4954.0731.21
RefNet87.2924.6054.6633.14
RefNet Inversed87.3823.5354.7929.17
SlowFastNo RefNet85.0318.9851.7920.94
RefNet84.9619.7651.5321.21
RefNet Inversed84.3318.7750.9418.61
Swin-TNo RefNet88.3731.2455.6218.89
RefNet88.9232.1455.3621.40
RefNet Inversed88.5930.5156.3418.18
", + "bbox": [ + 89, + 392, + 455, + 571 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "frames on HMDB511. This shows many frames in UCF101 contain static cues correlated with the class labels. Random sampling can yield many bias-inducing frames on UCF101 but cannot do so on HMDB51, where the strength of RefNet becomes apparent.", + "bbox": [ + 75, + 594, + 467, + 670 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In Sec. S1 of the Supplementary Material, we provide more ablation studies showing that mixing action labels in StillMix decreases performance and sufficient mixing strength (i.e., small values of $\\lambda$ in Eq. (3)) is necessary for debiasing.", + "bbox": [ + 75, + 670, + 467, + 746 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5.6. Performance on Something-Something-V2", + "text_level": 1, + "bbox": [ + 76, + 755, + 437, + 771 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "To validate the effectiveness of different debiasing methods on recognizing fine-grained actions with strong temporal structures, we perform tests on Something-Something-V2 [20]. In Table 9, we show the performance of different debiasing methods with TSM as the base model. Since SDN", + "bbox": [ + 75, + 777, + 467, + 853 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/14345ebfe0e8c8b1e0d47ac2010ac984d47033d67f00f14f085c8ae7b687af2b.jpg", + "table_caption": [ + "Table 9: Action recognition accuracy (\\%) of different debiasing methods on Something-Something-V2." + ], + "table_footnote": [], + "table_body": "
DebiasingAccuracy
No57.49
Mixup57.86
VideoMix58.23
BE57.68
FAME58.10
StillMix (Ours)58.68
", + "bbox": [ + 589, + 130, + 802, + 253 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "and ActorCutMix require bounding boxes of human, which are time-consuming to extract, we did not include the results of these two methods. The results show that StillMix outperforms other data augmentation methods, illustrating its effectiveness on fine-grained action videos.", + "bbox": [ + 496, + 277, + 890, + 354 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Conclusion and Discussion", + "text_level": 1, + "bbox": [ + 498, + 368, + 746, + 383 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "To learn robust and generalizable action representations, we explore techniques that mitigate static bias in both the background and the foreground. We propose a simple yet effective video data augmentation method, StillMix, and create two new sets of OOD benchmarks, SCUBA and SCUFO, to quantify static bias in the background and the foreground. Through extensive evaluation, we conclude that StillMix mitigates static bias in the background and the foreground and improves the performance of transferring learning and downstream tasks. In contrast, existing debi-asing methods remain vulnerable to foreground static bias despite their robustness to background static bias.", + "bbox": [ + 496, + 393, + 890, + 574 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Despite the strengths of StillMix on mitigating static bias in the background and the foreground, it has the following limitations: (1) additional computational overhead in training the reference network (about $8\\%$ of the training time of the main network); and (2) little improvement (and little degradation) on IID tests.", + "bbox": [ + 496, + 574, + 890, + 662 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "For future work, we believe that evaluating static bias in large pretrained models with the created benchmarks and adapting StillMix to mitigate static bias in such models would be promising directions.", + "bbox": [ + 496, + 664, + 890, + 724 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgments", + "text_level": 1, + "bbox": [ + 500, + 739, + 658, + 756 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work has been supported by the Nanyang Associate Professorship and the National Research Foundation Fellowship (NRF-NRFF13-2021-0006), Singapore. The computational work for this article was partially performed on resources of the National Supercomputing Centre, Singapore (https://www.nscc.sg). Any opinions, findings, conclusions, or recommendations expressed in this material are those of the authors and do not reflect the views of the funding agencies.", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 8 + }, + { + "type": "page_footnote", + "text": "1https://github.com/open-mmlab/mmaction2/blob/02a06bb3180e951b00cccbeb48dab055f95acd1a7/configs/recognition/tsn/README.md", + "bbox": [ + 76, + 862, + 464, + 900 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "19919", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Anurag Arnab, Mostafa Dehghani, Georg Heigold, Chen Sun, Mario Lučić, and Cordelia Schmid. Vivit: A video vision transformer. 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Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.132, + 0.131, + 0.84, + 0.177 + ], + "angle": 0, + "content": "Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground" + }, + { + "type": "text", + "bbox": [ + 0.269, + 0.203, + 0.73, + 0.24 + ], + "angle": 0, + "content": "Haoxin Li\\(^{1}\\), Yuan Liu\\(^{2}\\), Hanwang Zhang\\(^{1}\\), Boyang Li\\(^{1}\\) \nanyang Technological University \\(^{2}\\)Guangzhou University" + }, + { + "type": "text", + "bbox": [ + 0.186, + 0.242, + 0.785, + 0.257 + ], + "angle": 0, + "content": "{haoxin003, hanwangzhang, boyang.li}@ntu.edu.sg, yuanliu@gzhu.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.314, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.326, + 0.474, + 0.658 + ], + "angle": 0, + "content": "In video action recognition, shortcut static features can interfere with the learning of motion features, resulting in poor out-of-distribution (OOD) generalization. The video background is clearly a source of static bias, but the video foreground, such as the clothing of the actor, can also provide static bias. In this paper, we empirically verify the existence of foreground static bias by creating test videos with conflicting signals from the static and moving portions of the video. To tackle this issue, we propose a simple yet effective technique, StillMix, to learn robust action representations. Specifically, StillMix identifies bias-inducing video frames using a 2D reference network and mixes them with videos for training, serving as effective bias suppression even when we cannot explicitly extract the source of bias within each video frame or enumerate types of bias. Finally, to precisely evaluate static bias, we synthesize two new benchmarks, SCUBA for static cues in the background, and SCUFO for static cues in the foreground. With extensive experiments, we demonstrate that StillMix mitigates both types of static bias and improves video representations for downstream applications. Code is available at https://github.com/1ihaoxin05/StillMix." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.692, + 0.21, + 0.709 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Traditional computer vision techniques perform well on independent and identically distributed (IID) test data, but often lack out-of-distribution (OOD) generalization [9, 32, 12]. This is intimately tied to the learning of shortcut features [27, 16, 17], which are easy to learn and correlate strongly with IID labels but cause poor OOD generalization [53, 62, 49, 22]. In video action recognition, shortcut features often manifest as static cues. For example, a network may classify a video as golf swinging based on its background, a golf course, even if the motion patterns indicate another action such as walking. While static cues can provide valuable information [74, 11, 77], they often outcom" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.291, + 0.891, + 0.478 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.489, + 0.895, + 0.596 + ], + "angle": 0, + "content": "Figure 1: Evaluation of background and foreground static bias. (a) Testing on IID HMDB51 [36] test videos. (b) Testing on SCUBA videos, constructed by replacing the video background with a synthetic sinusoidal stripe image. (c) Testing on videos with conflicting foreground cues, constructed by inserting a random static foreground into the SCUBA video." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.627, + 0.894, + 0.748 + ], + "angle": 0, + "content": "pete motion features [23, 40, 41, 52, 69] and result in low OOD performance [41, 63, 26]. In contrast to the rich literature on mitigating background static bias (e.g., golf courses for golf swinging) [5, 63, 73, 10, 6], foreground static bias has been underexplored. Examples of foreground bias include swimsuits for swimming and guitars for guitar playing — people can swim without swimsuits or show guitars in the video without playing them." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.895, + 0.901 + ], + "angle": 0, + "content": "The first question we ask is if foreground static bias exists and if it is captured by the representations learned by neural networks. Our investigation technique is to create test videos with conflicting action cues from the moving part and the static part of the video. In the first step, shown in Figure 1(b), we replace the backgrounds of IID HMDB51 [36] test videos by sinusoidal stripe images. These videos have no meaningful backgrounds, so the action information must come from the foreground. Therefore, models overly reliant on background static cues" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "19911" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.093, + 0.485, + 0.335 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.491, + 0.094, + 0.888, + 0.337 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.354, + 0.895, + 0.414 + ], + "angle": 0, + "content": "Figure 2: An illustration of StillMix. We train a 2D reference network that classifies still frames into actions to capture static bias. With the reference network, we sample frames inducing static bias to construct a biased frame bank. We mix the frames from the bank with a given video to generate an augmented video, which is used to train a 3D main network to mitigate static bias." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.442, + 0.47, + 0.487 + ], + "angle": 0, + "content": "should perform poorly. A background debiasing technique, FAME [10], coupled with a tiny Video Swin Transformer (Swin-T) [46], works relatively well on this test." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.489, + 0.47, + 0.64 + ], + "angle": 0, + "content": "In the second step, shown in Figure 1(c), from a single frame of a random video, we extract its foreground (mainly human actors), and insert the static foreground into all the frames of the current SCUBA video. The resultant video contains only two action features: a static foreground that indicates one action label and a moving foreground that indicates another action label. Predictions made using the static foreground would be wrong. This design allows the quantification of foreground static bias. More details can be found in Sec. S1 of the Supplementary Material." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.643, + 0.47, + 0.793 + ], + "angle": 0, + "content": "The results clearly show the existence of foreground static bias and its negative effects. On the second test set, both Swin-T and Swin-T+FAME suffer similar degradation and perform \\(5\\%\\) worse than SCUBA videos. FAME works by procedurally isolating the foreground regions from each frame and use those for training. However, it is hard to separate the foreground motion from the static foreground (e.g., clothing, equipment, or other people attributes [40]) in the training videos, since both types of features are strongly tied to the human actors." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.47, + 0.903 + ], + "angle": 0, + "content": "We propose StillMix, a technique that mitigates static bias in both the background and the foreground, without the need to explicitly isolate (or even enumerate [5]) the bias-inducing content within a frame. StillMix identifies bias-inducing frames using a reference network and mixes them with training videos without affecting motion features. The process is illustrated in Figure 2. Unlike FAME, StillMix" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.442, + 0.892, + 0.503 + ], + "angle": 0, + "content": "could suppress static bias anywhere in a frame, including the background and the foreground. In Figure 1, StillMix outperforms FAME and suffers only \\(2\\%\\) accuracy drop on the second benchmark, highlighting its resilience." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.506, + 0.893, + 0.776 + ], + "angle": 0, + "content": "Evaluating OOD action recognition is challenging as test videos with OOD foregrounds, such as swimming without swimsuits or cycling while carrying a guitar, are rare. To pinpoint the static bias in either the background or the foreground, we create new synthetic sets of OOD benchmarks by altering the static features in IID test videos, as illustrated in Figure 3. Specifically, we retain the foregrounds of actions and replace the backgrounds with diverse natural and synthetic images. This procedure yields a test set that quantifies representation bias toward static cues in the background (SCUBA). Second, we create videos that repeat a single random frame from SCUBA, producing a test set that quantifies representation bias toward static cues in the foreground (SCUFO). As these videos disassociate the backgrounds from the action and contain no motion, their actions can be recognized by only static foreground features. Thus, high accuracy on SCUFO indicates strong foreground static bias." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.902 + ], + "angle": 0, + "content": "With the synthetic OOD benchmarks, we extensively evaluate several mainstream action recognition methods and make the following observations. First, all examined methods exhibit static bias. Second, existing debiasing methods like ActorCutMix [78] and FAME [10] demonstrate resistance to background static bias, but remain vulnerable to foreground static bias. In contrast, the proposed StillMix consistently boosts performance of action recognition mod" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "19912" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.092, + 0.466, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.267, + 0.47, + 0.371 + ], + "angle": 0, + "content": "Figure 3: An illustration of OOD benchmark construction. To quantify static cues in the background, we reserve the foreground actions and replace the backgrounds with other images to synthesize SCUBA videos. To quantify static cues in the foreground, we randomly select one frame in the SCUBA video and stack it into a single-frame video without motion, named SCUFO videos." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.399, + 0.468, + 0.473 + ], + "angle": 0, + "content": "els and compares favorably with the other debiasing techniques on both background and foreground static bias. In addition, StillMix improves the performance of transfer learning and downstream weakly supervised action localization." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.475, + 0.399, + 0.49 + ], + "angle": 0, + "content": "The paper makes the following contributions:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.494, + 0.469, + 0.539 + ], + "angle": 0, + "content": "- Through quantitative experiments, we highlight the importance to address foreground static bias in learning robust action representations." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.542, + 0.469, + 0.586 + ], + "angle": 0, + "content": "- We propose StillMix, a video data augmentation technique to mitigate static bias in not only the background but also the foreground." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.589, + 0.469, + 0.634 + ], + "angle": 0, + "content": "- We create new benchmarks to quantitatively evaluate static bias of action representations and pinpoint the source of static bias (backgrounds or foregrounds)." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.636, + 0.469, + 0.68 + ], + "angle": 0, + "content": "- We compare action recognition methods on the created benchmarks to reveal their characteristics and validate the effectiveness of StillMix." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.494, + 0.469, + 0.68 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.694, + 0.219, + 0.71 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Bias Evaluation. Biases are surface features that are easily learned by neural networks and strongly influence their predictions. Such features perform well on IID data [60, 29] but do not generalize to OOD data [53, 49]. In action recognition, models easily capture static bias [40, 41, 5, 63]. The following methods are used for bias evaluation: (1) Visualization techniques [15, 47] visualize the regions that models focus on to interpret the static bias qualitatively. (2) Proxy data or tasks. Synthetic videos with altered backgrounds [6], videos with white-noise textures [26], dynamic texture videos [21, 3] are used to reveal the bias toward backgrounds or texture. Proxy tasks evaluating temporal" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.212 + ], + "angle": 0, + "content": "asymmetry, continuity, and causality are designed to show the static bias in video representations [18]. (3) Mutual information. [33] quantifies the static bias using mutual information between representations of different types of videos. Although these works evaluate the static bias in the whole video, they do not specify the source of static bias. In this paper, we create new benchmarks to pinpoint the source of static bias as the background and the foreground." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.214, + 0.893, + 0.517 + ], + "angle": 0, + "content": "Bias Mitigation. Prevalent techniques of mitigating bias in action representations can be broadly classified into four categories. (1) Attribute supervision. [5] uses scene pseudolabels and human masks to discourage models from predicting scenes and recognizing actions without human, but it needs extra attribute labels. (2) Re-weighting. [40, 41] identify videos containing bias and downweight them in training, but [65] suggests merely weight adjustment is insufficient. (3) Context separation. [66] learns to separate action and contexts by collecting samples with similar contexts but different actions. (4) Data augmentation. Similar to the proposed StillMix, a few works utilize augmented videos. BE [63] mixes a frame from a video with other frames in the same video. ActorCutMix [78], FAME [10], ObjectMix [31] and FreqAug [30] carefully carve out the foreground (human actors or regions of motion), and replace the background with other images to create augmented training data. SSVC [73] and MCL [38] focus the models to the dynamic regions. However, these methods have not addressed static cues in the foreground." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.519, + 0.892, + 0.626 + ], + "angle": 0, + "content": "A particular advantage of StillMix is that it does not require specially designed procedures to carve out the bias-inducing pixels within the frames like ActorCutMix [78] and FAME [10], or even to enumerate the source of bias like [5]. Rather, it automatically identifies bias-inducing frames using a reference network. Consequently, StillMix can suppress static bias in both the background and the foreground." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.627, + 0.892, + 0.748 + ], + "angle": 0, + "content": "StillMix is also similar to two debiasing techniques designed for image recognition and text classification [48, 44], which use a reference network to identify bias-inducing data instances. However, StillMix exploits the special property of videos that they can be decomposed into individual frames. StillMix identifies bias-inducing components (frames) using 2D networks rather than whole data points as in [48, 44]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Action Recognition. 3D convolution or decomposed 3D convolutions [28, 58, 4, 61, 59, 42] are popular choices for action recognition. Two-stream architectures employ two modalities to classify actions, such as both RGB frames and optical flow [54, 64], or videos with two different frame rates and resolutions [14]. Multi-scale temporal convolutions or feature fusion are designed for fine-grained actions with strong temporal structures [75, 24, 39, 67]. Transformer networks are proposed to capture the long-range dependencies [1, 2, 46]. However, our understanding of the" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19913" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.168 + ], + "angle": 0, + "content": "representations learned by these models remains limited. In this paper, we create benchmarks to evaluate what features are captured by action models and propose a simple data augmentation method that effectively improves the robustness of action models." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.184, + 0.3, + 0.203 + ], + "angle": 0, + "content": "3. The StillMix Technique" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.211, + 0.47, + 0.377 + ], + "angle": 0, + "content": "In order to learn robust and generalizable action representations that are invariant to static cues, we propose a simple but effective video data augmentation technique, StillMix. Instead of using manually designed rules to identify and remove biased data from the training set, as in ActorCutMix [78] and FAME [10], StillMix learns to identify still frames that induce biased representation using a neural network and mitigate static bias through mixing the identified frames with videos. As a result, StillMix offers a flexible bias suppression technique that works for both the background and the foreground." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.378, + 0.473, + 0.545 + ], + "angle": 0, + "content": "We begin with some notations. We denote the \\(i^{\\mathrm{th}}\\) video in the training set as tensor \\(\\pmb{x}_i\\in \\mathbb{R}^{C\\times T\\times H\\times W}\\), where \\(C\\), \\(T\\), \\(H\\) and \\(W\\) are the number of channels, number of frames, height and width of the video, respectively. The associated ground-truth action label is \\(y_{i}\\). The video \\(\\pmb{x}_i\\) contains a sequence of frames \\(\\langle \\pmb {z}_{i,j}\\rangle_{j = 1}^{T}\\), \\(\\pmb {z}_{i,j}\\in \\mathbb{R}^{C\\times H\\times W}\\). The training set contains \\(N\\) training video samples and is written as \\(\\{(x_i,y_i)\\}_{i = 1}^N\\). The goal of StillMix is to augment a given training sample \\((x_{i},y_{i})\\) into a transformed sample \\((\\tilde{x}_i,\\tilde{y}_i)\\). The procedures of StillMix are illustrated in Figure 2 and introduced as follows." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.552, + 0.47, + 0.627 + ], + "angle": 0, + "content": "Step 1: Training the Reference Network. We identify bias-inducing frames using a 2D reference network that predicts the action label from a still frame of a video. As the still frame contains no motion, we expect the network to rely on static features to make the predictions." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.628, + 0.47, + 0.675 + ], + "angle": 0, + "content": "Specifically, at every epoch we randomly sample a frame \\( \\mathbf{z}_{i,j} \\in \\mathbb{R}^{C \\times H \\times W} \\) from each video \\( \\mathbf{x}_i \\), and train the reference network \\( \\mathcal{R}(\\cdot) \\) to predict the label \\( y_i \\). The loss is" + }, + { + "type": "equation", + "bbox": [ + 0.171, + 0.687, + 0.47, + 0.73 + ], + "angle": 0, + "content": "\\[\nL _ {r e f} = \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\ell \\left(\\mathcal {R} \\left(\\boldsymbol {z} _ {i, j}\\right), y _ {i}\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.743, + 0.47, + 0.803 + ], + "angle": 0, + "content": "where \\(\\ell(\\cdot)\\) can be any classification loss, such as the cross-entropy. After training, the reference network \\(\\mathcal{R}(\\cdot)\\) encodes the correlations between static cues within the frames and the action classes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.904 + ], + "angle": 0, + "content": "Step 2: Identifying Biased Frames. The output of reference network \\(\\mathcal{R}(\\pmb{z}_{i,j})\\) is a categorical distribution over action classes. We take the probability of the predicted class \\(p_{i,j} = \\max_k P(y = k|\\pmb{z}_{i,j})\\). A high \\(p_{i,j}\\) indicates strong correlation between \\(\\pmb{z}_{i,j}\\) and the action class, which means \\(\\pmb{z}_{i,j}\\) can induce static bias. Therefore, we select frames with" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.81, + 0.108 + ], + "angle": 0, + "content": "high \\(p_{i,j}\\) to construct the biased frame bank \\(S\\):" + }, + { + "type": "equation", + "bbox": [ + 0.62, + 0.118, + 0.892, + 0.136 + ], + "angle": 0, + "content": "\\[\nS = \\left\\{\\boldsymbol {z} _ {i, j} \\mid p _ {i, j} \\geq p _ {\\tau} \\right\\}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.146, + 0.894, + 0.191 + ], + "angle": 0, + "content": "where \\( p_{\\tau} \\) is the \\( \\tau \\)-th percentile value of \\( p_{i,j} \\). In practice, we perform another round of uniformly random selection to control the size of the biased frame bank." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.198, + 0.892, + 0.365 + ], + "angle": 0, + "content": "Step 3: Mixing Video and Biased Frames. To break the strong correlation between the biased frame and the action class, we mix a video of any action class with different biased frames identified above. Specifically, in each epoch, given a video sample \\((x_{i},y_{i})\\), we sample a frame \\(z^{\\mathrm{biased}}\\) from the biased frame bank \\(S\\) and tile it \\(T\\) times along the temporal dimension, yielding a static video with \\(T\\) identical frames. We denote this operation as \\(\\mathrm{Tile}(z^{\\mathrm{biased}},T)\\). The augmented video sample \\(\\tilde{x}_i\\) is generated by the pixel-wise interpolation of \\(x_{i}\\) and the static video. The augmented video label \\(\\tilde{y}_i\\) is the same as the original action label \\(y_{i}\\)." + }, + { + "type": "equation", + "bbox": [ + 0.543, + 0.378, + 0.892, + 0.395 + ], + "angle": 0, + "content": "\\[\n\\tilde {\\boldsymbol {x}} _ {i} = \\lambda \\boldsymbol {x} _ {i} + (1 - \\lambda) \\operatorname {T i l e} \\left(\\boldsymbol {z} ^ {\\text {b i a s e d}}, T\\right), \\quad \\tilde {y} _ {i} = y _ {i}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.401, + 0.892, + 0.431 + ], + "angle": 0, + "content": "where the scalar \\(\\lambda\\) is sampled from a Beta distribution \\(\\operatorname{Beta}(\\alpha, \\beta)\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.432, + 0.892, + 0.552 + ], + "angle": 0, + "content": "The rationale for keeping the video label unchanged after augmentation is that the static video contains no motion and does not affects the motion patterns in the mixed video, thus it should not contribute to the action label. This setting of StillMix can be intuitively understood as randomly permuting the labels of the static video, so that the network is forced to ignore the correlations between the static cues in the biased frames and actions." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.558, + 0.892, + 0.59 + ], + "angle": 0, + "content": "Training with Augmented Videos. We apply StillMix to each video with a predefined probability \\( P_{\\mathrm{aug}} \\)." + }, + { + "type": "equation", + "bbox": [ + 0.524, + 0.6, + 0.892, + 0.642 + ], + "angle": 0, + "content": "\\[\n\\left(\\boldsymbol {x} _ {i} ^ {*}, y _ {i} ^ {*}\\right) = \\left\\{ \\begin{array}{l l} \\left(\\boldsymbol {x} _ {i}, y _ {i}\\right) & a _ {i} = 0 \\\\ \\left(\\tilde {\\boldsymbol {x}} _ {i}, \\tilde {y} _ {i}\\right) & a _ {i} = 1 \\end{array} , a _ {i} \\sim \\operatorname {B e r} \\left(P _ {\\text {a u g}}\\right), \\right. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.651, + 0.892, + 0.697 + ], + "angle": 0, + "content": "where \\(a\\) is a scalar sampled from a Bernoulli distribution \\(Ber(P_{\\mathrm{aug}})\\). The samples \\(\\{(x_i^*, y_i^*)\\}_{i=1}^N\\) are used to train the main network \\(\\mathcal{F}(\\cdot)\\) using the following loss function:" + }, + { + "type": "equation", + "bbox": [ + 0.607, + 0.706, + 0.892, + 0.749 + ], + "angle": 0, + "content": "\\[\nL = \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\ell \\left(\\mathcal {F} \\left(\\boldsymbol {x} _ {i} ^ {*}\\right), y _ {i} ^ {*}\\right), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.759, + 0.783, + 0.774 + ], + "angle": 0, + "content": "where \\(\\ell (\\cdot)\\) could be any classification loss." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Discussion. StillMix aims to learn robust action representations that generalize to OOD data. One popular formulation of OOD generalization [68, 34, 51, 35, 50] considers shortcut features as features that work under a specific environment but not others. For example, a classifier that excels in well-lit environments may perform terribly in dim environments. To learn robust classifiers, we ought to discover invariant features that work equally well in all environments." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "19914" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.122 + ], + "angle": 0, + "content": "More formally, the optimal predictor \\(\\mathcal{F}^*\\) can be found with the bi-level optimization" + }, + { + "type": "equation", + "bbox": [ + 0.143, + 0.13, + 0.469, + 0.155 + ], + "angle": 0, + "content": "\\[\n\\mathcal {F} ^ {*} = \\underset {\\mathcal {F}} {\\operatorname {a r g m i n}} \\max _ {e} \\mathbb {E} _ {\\boldsymbol {x} ^ {e}, y ^ {e}} [ \\ell (\\mathcal {F} (\\boldsymbol {x} ^ {e}), y ^ {e}) ], \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.163, + 0.469, + 0.282 + ], + "angle": 0, + "content": "where the feature-label pair, \\((\\pmb{x}^e,y^e)\\), are drawn from the data distribution \\(P(\\pmb{x},y|e)\\) of environment \\(e\\) and \\(\\ell\\) is the per-sample loss. \\(\\pmb{x}^e\\) contains both class features and environment features; a good predictor \\(\\mathcal{F}\\) is sensitive to the former and ignores the latter. The optimization encourages this because if \\(\\mathcal{F}\\) utilizes features that work for environment \\(e_1\\) but not \\(e_2\\), the loss will increase as the \\(\\max_e\\) operation will select \\(e_2\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.284, + 0.469, + 0.375 + ], + "angle": 0, + "content": "However, directly optimizing Eq. (6), such as in [51], requires sampling data from all environments, which is impractical due to skewed environment distributions. For example, videos of people playing soccer in tuxedos on beaches are exceedingly rare. Maximizing over all environments is also challenging." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.375, + 0.469, + 0.466 + ], + "angle": 0, + "content": "The mixing operation in StillMix may be understood in the same framework. A static frame \\( z^{\\mathrm{biased}} \\) can be considered as coming from an environment \\( e' \\) which biases predictions toward certain action labels. Mixing \\( z^{\\mathrm{biased}} \\) with \\( x_{i} \\) simulates sampling \\( x^{e'} \\) from the environment \\( e' \\). StillMix may be considered to optimize the following loss," + }, + { + "type": "equation", + "bbox": [ + 0.143, + 0.473, + 0.469, + 0.502 + ], + "angle": 0, + "content": "\\[\n\\mathcal {F} ^ {*} = \\underset {\\mathcal {F}} {\\operatorname {a r g m i n}} \\mathbb {E} _ {e} \\left[ \\mathbb {E} _ {\\boldsymbol {x} ^ {e}, y ^ {e}} [ \\ell (\\mathcal {F} (\\boldsymbol {x} ^ {e}), y ^ {e}) ] \\right], \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.509, + 0.469, + 0.555 + ], + "angle": 0, + "content": "which replaces the maximization over environments in Eq. (6) with an expectation over environments due to the random sampling of \\( z^{\\mathrm{biased}} \\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.566, + 0.442, + 0.582 + ], + "angle": 0, + "content": "4. SCUBA and SCUFO: OOD Benchmarks" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.592, + 0.469, + 0.652 + ], + "angle": 0, + "content": "To quantitatively evaluate static bias in the background and the foreground, we create OOD benchmarks based on three commonly used video datasets, i.e., HMDB51 [36], UCF101 [55] and Kinetics-400 [4], as detailed below." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.66, + 0.45, + 0.677 + ], + "angle": 0, + "content": "4.1. Foreground Masks and Background Images" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.683, + 0.469, + 0.833 + ], + "angle": 0, + "content": "Foreground Masks. To extract the foreground area of actions, we use available human-annotated masks of people for UCF101 and HMDB51. There are totally 910 videos in the UCF101 test set and 256 videos in the HMDB51 test set having foreground annotations. Since there is no human-annotated masks for Kinetics-400, we use video segmentation models [57, 56] to generate foreground masks. After filtering out the videos with small foreground masks (likely to be wrong), we obtain totally 10,190 videos in the Kinetics-400 validation set to construct the benchmark." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.84, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Background Images. In order to synthesize diverse test videos, we collect background images from three different image sources: 1) the test set of Place365 [76]. 2) images generated by VQGAN-CLIP [8] from a random scene" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.088, + 0.628, + 0.148 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.529, + 0.151, + 0.606, + 0.164 + ], + "angle": 0, + "content": "(a) Place365" + }, + { + "type": "image", + "bbox": [ + 0.632, + 0.089, + 0.756, + 0.146 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.638, + 0.151, + 0.752, + 0.164 + ], + "angle": 0, + "content": "(b) VQGAN-CLIP" + }, + { + "type": "image", + "bbox": [ + 0.76, + 0.088, + 0.884, + 0.146 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.785, + 0.151, + 0.86, + 0.164 + ], + "angle": 0, + "content": "(c) Sinusoid" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.171, + 0.892, + 0.247 + ], + "angle": 0, + "content": "Figure 4: Background images from different sources. (a) An image from Place365. (b) An image generated by VQGAN-CLIP from the query \"A painting of a conference room in the style of surreal art\". (c) An image of randomly generated sinusoidal stripes." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.271, + 0.892, + 0.362 + ], + "angle": 0, + "content": "category of Place365 and a random artistic style. 3) randomly generated images with S-shaped stripes defined by sinusoidal functions. For each image source, we construct a background image pool. In Figure 4, we show three example background images from the three sources. More details are described in Sec. S2 of the Supplementary Material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.37, + 0.693, + 0.385 + ], + "angle": 0, + "content": "4.2. Test Video Synthesis" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.393, + 0.892, + 0.454 + ], + "angle": 0, + "content": "Testing for Background Static Cues. Given a video \\( \\pmb{x} \\) with \\( T \\) frames \\( \\{\\pmb{x}_t\\}_{t=1}^T \\), we create a synthetic video \\( \\hat{\\pmb{x}} \\) by combining the foreground of \\( \\pmb{x} \\) and a background image sampled from a background image pool." + }, + { + "type": "equation", + "bbox": [ + 0.55, + 0.462, + 0.891, + 0.479 + ], + "angle": 0, + "content": "\\[\n\\hat {\\boldsymbol {x}} _ {t} = \\boldsymbol {m} _ {t} \\odot \\boldsymbol {x} _ {t} + (1 - \\boldsymbol {m} _ {t}) \\odot \\operatorname {T i l e} (\\boldsymbol {z} ^ {\\mathrm {b g}}, T), \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.487, + 0.892, + 0.637 + ], + "angle": 0, + "content": "where \\( m_t \\) is the foreground mask, \\( \\odot \\) denotes pixel-wise multiplication, \\( z^{\\mathrm{bg}} \\) is a background image sampled from the image pool. \\( \\mathrm{Tile}(z^{\\mathrm{bg}}, T) \\) repeats \\( z^{\\mathrm{bg}}T \\) times along the temporal dimension. For each video with foreground masks, we pair it with \\( m \\) randomly selected background images from each of the 3 background image pools to synthesize \\( 3m \\) videos. We set \\( m = 10,5,1 \\) for HMDB51, UCF101 and Kinetics-400, respectively, since HMDB51 and UCF101 have fewer videos with foreground masks and we would like to increase the diversity of the synthetic videos." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.639, + 0.892, + 0.729 + ], + "angle": 0, + "content": "The generated videos retain the original action foreground, including the human actors and their motion, on new random backgrounds. They are designed to test bias toward static cues from the background, and are named SCUBA videos. We expect models invariant to static backgrounds to obtain high classification accuracy on SCUBA." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.735, + 0.892, + 0.87 + ], + "angle": 0, + "content": "Testing for Foreground Static Cues. In addition, we create another set of videos to test the amount of foreground static bias in the learned representations. Foreground static cues include people and object attributes, such as bicycle helmets for cycling and bows for archery — people can ride a bicycle without helmets or hold bows when not performing archery. As the SCUBA videos contain most foreground elements in the original videos, they cannot distinguish whether models rely on foreground static cues." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "To this end, we create videos that contain only a single frame. Specifically, from each SCUBA video, we ran" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "19915" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.124, + 0.09, + 0.424, + 0.104 + ], + "angle": 0, + "content": "Table 1: Statistics of the created benchmarks." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.111, + 0.472, + 0.253 + ], + "angle": 0, + "content": "
Video Source# Original VideosBackground Source# Synthetic Videos# Domain Gap of SCUBA# Domain Gap of SCUFO
HMDB51256Place3652,5605.646±0.2765.745±0.290
VQGAN-CLIP2,5608.178±0.6858.307±0.533
Sinusoid2,56011.739±0.44411.998±0.932
UCF101910Place3654,55020.493±2.19920.829±2.093
VQGAN-CLIP4,55051.320±5.79055.202±9.477
Sinusoid4,55052.249±3.52252.534±5.930
Kinetics-40010,190Place36510,1906.094±0.2086.455±0.224
VQGAN-CLIP10,1907.504±0.2968.052±0.273
Sinusoid10,1907.211±0.3117.766±0.148
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.292, + 0.47, + 0.413 + ], + "angle": 0, + "content": "domly select one frame and repeat it temporally to create a video with zero motion. As these videos quantify the representation bias toward static cues in the foreground, we name them SCUFO videos. In SCUFO videos, the foreground static features are identical to the corresponding SCUBA videos, but the motion information is totally removed. Therefore, a model invariant to foreground static features should obtain low classification accuracy on them." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.414, + 0.47, + 0.49 + ], + "angle": 0, + "content": "We summarize the dataset statistics in Table 1. SCUBA and SCUFO have the same number of videos for each pair of video source and background source. We also report the domain gap between original videos to show their OOD characteristics, as explained in the next section." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.504, + 0.266, + 0.52 + ], + "angle": 0, + "content": "4.3. Quality Assessment" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.528, + 0.47, + 0.575 + ], + "angle": 0, + "content": "We empirically verify that the SCUBA datasets retain the motion features of the original videos but replace background static features using the following two tests." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.47, + 0.656 + ], + "angle": 0, + "content": "Human Assessment. To test if SCUBA preserves the motion information sufficiently for action recognition, we carry out an experiment on Amazon Mechanical Turk (AMT) to verify if human workers can recognize the actions in SCUBA videos." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.658, + 0.47, + 0.824 + ], + "angle": 0, + "content": "From the same original video, we randomly sampled one synthetic video and asked the AMT workers if the moving parts in the video show the labeled action. The workers are given three options: yes, no, and can't tell. We also create control questions with original videos to detect random clicking and design control groups to prevent the workers from always answering yes to synthetic videos. The final answer for each video is obtained by majority voting of three workers. Workers who do not reach at least \\(75\\%\\) accuracy on the control questions are rejected. More details are described in Sec. S2 of the Supplementary Material." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Collectively, the AMT workers were able to correctly recognize the actions in \\(96.15\\%\\) of UCF101-SCUBA, \\(86.33\\%\\) of HMDB51-SCUBA and \\(85.19\\%\\) of Kinetics400-SCUBA videos. We conclude that SCUBA videos preserve sufficient action information for humans to recognize." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.166 + ], + "angle": 0, + "content": "Domain Gaps of the Static Features. To verify if SCUBA and SCUFO have successfully replaced the background static features and qualify as OOD test sets, we test if a classifier based on purely static features trained on IID videos can generalize to SCUBA and SCUFO." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.168, + 0.892, + 0.197 + ], + "angle": 0, + "content": "Using a variation of scene representation bias [5], we define the domain gap \\( G_{\\text{scene}} \\) as" + }, + { + "type": "equation", + "bbox": [ + 0.546, + 0.209, + 0.892, + 0.224 + ], + "angle": 0, + "content": "\\[\nG _ {s c e n e} = A c c \\left(D _ {\\text {o r i}}, \\Phi_ {s c e n e}\\right) / A c c \\left(D _ {\\text {s y n}}, \\Phi_ {s c e n e}\\right). \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.238, + 0.892, + 0.375 + ], + "angle": 0, + "content": "Here \\(\\Phi_{\\text{scene}}\\) is the average frame feature extracted from a ResNet-50 pretrained on Place365 [76]. Thus, the extracted feature captures static scene information, mostly from the background. We train a linear classifier on the original video training set and apply it to the original test set \\(D_{\\text{ori}}\\), obtaining the accuracy \\(Acc(D_{\\text{ori}}, \\Phi_{\\text{scene}})\\). After that, we apply the same classifier to the synthetic dataset \\(D_{\\text{syn}}\\), obtaining the accuracy \\(Acc(D_{\\text{syn}}, \\Phi_{\\text{scene}})\\). A higher ratio indicates greater domain gap with respect to static features." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.376, + 0.892, + 0.512 + ], + "angle": 0, + "content": "In Table 1, we show the means and standard deviations computed from three random repeats of video synthesis. We observe large domain gaps, ranging from 5.6-fold to 52-fold decrease in accuracy on the synthetic test set. This demonstrates the static features of synthetic videos differ substantially from the original videos and the synthetic videos can serve as OOD tests. Moreover, the low standard deviations show that the effects of random sampling are marginal. In later experiments, we use the dataset from one random seed." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.53, + 0.634, + 0.547 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.556, + 0.892, + 0.602 + ], + "angle": 0, + "content": "In this section, we compare the performance of several mainstream action recognition methods on IID and OOD test data and validate the effectiveness of StillMix." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.616, + 0.696, + 0.632 + ], + "angle": 0, + "content": "5.1. Comparing Methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.64, + 0.892, + 0.732 + ], + "angle": 0, + "content": "Action Recognition Models. (1) TSM [43], a temporal shift module learning spatiotemporal features with 2D CNN. (2) SlowFast [14], a two-branch 3D CNN learning spatiotemporal signals under two frame rates. (3) Video Swin Transformer [46], an adapted Swin Transformer [45] for videos. We use the tiny version, denoted as Swin-T." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Video Data Augmentation and Debiasing Methods. We compare the debiasing performance of several video data augmentation and debiasing methods by adapting them to supervised action recognition. (1) Mixup [72] and VideoMix [70]. (2) SDN [5]. (3) BE [63], ActorCutMix[78] and FAME [10]. We adapt these three self-supervised debiasing methods as data augmentations, which carve out the foreground and replace the background as in the original papers. All the data augmentation techniques are applied stochastically as in [19]. More implementation details are described in Sec. S3 of the Supplementary Material." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "19916" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.089, + 0.472, + 0.166 + ], + "angle": 0, + "content": "Table 2: IID and OOD test accuracy (\\%) of augmentation and debiasing methods on Kinetics-400. † indicates adaptation from self-supervised debiasing methods. ConfI-FG denotes synthetic videos with conflicting foreground cues. All models are pretrained on ImageNet." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.178, + 0.487, + 0.436 + ], + "angle": 0, + "content": "
ModelAugmentation or DebiasingIIDOOD
Avg SCUBA↑Avg SCUFO↓Contra Acc.↑Confl-FG↑ARAS↑
TSMNo71.1337.3917.2222.8020.1557.86
Mixup71.3340.8117.5325.9823.4858.05
VideoMix71.3538.8717.2524.5723.4356.61
SDN69.9936.9516.5522.3820.2955.06
BE†71.3037.8916.0824.3520.1157.47
ActorCutMix†71.0740.4216.2926.5221.4157.09
FAME†71.1340.9118.3425.6324.4157.47
StillMix (Ours)71.2840.485.2336.0725.7359.69
Swin-TNo73.9541.7418.1725.9325.2560.17
Mixup73.9143.9517.9228.2427.6459.59
VideoMix73.8043.1719.2626.4029.3760.95
SDN72.2342.3421.4624.4627.1460.26
BE†73.9343.4019.5626.2826.6759.79
ActorCutMix†73.9745.7019.3928.6429.0261.23
FAME†73.8148.7921.2730.0329.5060.37
StillMix (Ours)73.8644.105.5139.4130.7762.49
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.46, + 0.262, + 0.475 + ], + "angle": 0, + "content": "5.2. Evaluation Metrics" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.485, + 0.47, + 0.606 + ], + "angle": 0, + "content": "We conduct the following experiments on Kinetics-400, UCF101 and HMDB51. First, we perform IID tests on the original test sets and use the top-1 accuracy as metrics. After that, we perform OOD tests on SCUBA and SCUFO and report the average top-1 accuracy across background image sources. Note that higher accuracy on SCUBA is better (low background static bias), while lower accuracy on SCUFO is better (low foreground static bias)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.607, + 0.47, + 0.697 + ], + "angle": 0, + "content": "To show the performance of utilizing pure foreground motion information, we propose another performance metric called contrasted accuracy (Contra. Acc.). As one SCUFO video is derived from a SCUBA video, we count one correct prediction if the model is correct on the SCUBA but incorrect on the associated SCUFO video." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.697, + 0.47, + 0.759 + ], + "angle": 0, + "content": "We further evaluate on the synthetic videos with conflicting foreground cues (Figure 1). Finally, we also evaluate on ARAS [13], a real-world OOD dataset with rare scenes, to show the performance of scene bias reduction." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.771, + 0.406, + 0.787 + ], + "angle": 0, + "content": "5.3. Results on IID and OOD Benchmarks" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Table 2, 3 and 4 compare the IID and OOD performance of different video data augmentation and debiasing methods on Kinetics-400, HMDB51 and UCF101. Given limited computational resources, we ran experiments on Kinetics-400 using a single seed. However, on the smaller HMDB51 and UCF101, we repeated experiments with three seeds. In Sec. S1 of the Supplementary Material, we provide more" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.089, + 0.892, + 0.135 + ], + "angle": 0, + "content": "Table 3: IID and OOD test accuracy \\((\\%)\\) of augmentation and debiasing methods on HMDB51. All models are pretrained on Kinetics-400." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.148, + 0.905, + 0.368 + ], + "angle": 0, + "content": "
ModelAugmentation or DebiasingIIDOOD
Avg SCUBA↑Avg SCUFO↓Contra. Acc.↑ConfI-FG↑
TSMNo70.39±0.5138.03±1.3919.23±1.3022.02±0.6425.44±1.31
Mixup72.00±0.4739.76±1.7219.08±1.3723.76±0.8426.94±1.23
VideoMix70.72±0.1235.71±1.5717.48±1.1121.03±0.5522.19±1.47
SDN69.51±0.3037.05±0.7317.60±0.3723.74±0.9528.38±0.87
BE71.22±0.2438.48±1.4219.45±1.0622.39±0.6725.21±1.35
ActorCutMix70.52±0.8238.40±0.5319.61±0.5621.94±0.4026.16±0.36
FAME70.39±0.8847.19±1.5222.33±0.9128.21±0.8933.98±2.09
StillMix71.52±0.3848.23±0.968.43±0.8842.05±0.9936.89±1.09
Swin-TNo73.92±0.7443.93±0.7820.46±0.7127.84±1.2836.58±1.65
Mixup74.58±0.4343.10±1.1321.17±0.6626.09±1.0536.62±2.98
VideoMix73.31±0.5339.39±0.7120.44±0.7323.13±0.5432.68±1.04
SDN74.66±0.8240.02±1.4820.22±1.2422.88±1.0534.87±2.43
BE74.31±0.4143.56±1.3819.96±0.7127.84±1.3235.99±0.67
ActorCutMix74.05±0.6046.79±1.3822.07±0.3628.12±1.2736.97±1.63
FAME73.79±0.2951.40±1.5426.92±0.7129.66±2.1139.61±1.87
StillMix74.82±0.4351.81±1.7813.39±0.7140.28±1.6147.38±1.50
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.394, + 0.892, + 0.44 + ], + "angle": 0, + "content": "Table 4: IID and OOD test accuracy \\((\\%)\\) of augmentation and debiasing methods on UCF101. All models are pretrained on Kinetics-400." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.453, + 0.905, + 0.673 + ], + "angle": 0, + "content": "
ModelAugmentation or DebiasingIIDOOD
Avg SCUBA↑Avg SCUFO↓Contra. Acc.↑ConfI-FG↑
TSMNo94.62±0.0825.60±1.364.21±0.8421.83±1.4827.68±1.35
Mixup94.71±0.1427.80±0.954.04±0.8124.17±1.0030.31±1.10
VideoMix94.50±0.1931.55±1.685.77±0.7426.69±1.3830.69±1.79
SDN93.84±0.2719.91±0.613.10±0.1917.19±0.5120.89±0.36
BE94.49±0.1425.91±1.374.62±0.8421.82±1.3828.06±1.32
ActorCutMix94.47±0.1538.11±1.484.56±0.1633.90±1.5138.12±2.12
FAME93.72±0.0935.72±1.153.67±0.5232.28±1.2834.58±0.93
StillMix94.30±0.1437.18±1.290.79±0.1236.47±1.2440.59±0.80
Swin-TNo96.21±0.1942.31±2.245.78±0.6836.82±2.1244.65±2.10
Mixup96.17±0.1446.16±1.745.93±0.4340.46±1.9647.16±2.82
VideoMix96.00±0.0241.40±1.1113.27±0.8529.37±0.9142.59±1.51
SDN95.76±0.1139.25±2.322.98±0.8836.42±1.7448.47±2.06
BE96.06±0.1143.98±0.805.54±0.9438.62±1.1346.62±0.96
ActorCutMix95.87±0.1958.61±0.4811.92±0.2546.87±0.4556.88±0.39
FAME95.81±0.1540.90±1.576.36±0.7135.14±1.6628.21±1.83
StillMix96.02±0.0858.22±0.413.44±0.5154.90±0.7757.30±0.60
" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.699, + 0.89, + 0.73 + ], + "angle": 0, + "content": "detailed results (e.g., tests on videos with conflicting foreground cues and ARAS [13])." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.732, + 0.892, + 0.867 + ], + "angle": 0, + "content": "OOD data cause performance degradation. Comparing the performance of TSM and Swin-T on IID and OOD tests, we observe that they perform much worse (more than \\(20\\%\\)) on SCUBA than IID videos. Given that human workers can recognize the action in more than \\(85\\%\\) of SCUBA videos, the results indicate that the models are not robust to the domain shifts, probably due to the reliance of static background features; when the backgrounds are replaced, performance deterioration ensues." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "IID tests do not fully reveal representation quality. Comparing the performance of different augmentation and debi" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19917" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.182 + ], + "angle": 0, + "content": "asing methods, we observe that all methods obtain similar accuracies on IID tests, which fall within a \\(2\\%\\) band. However, they show vastly different performance on SCUBA and SCUFO — the maximum difference is larger than \\(15\\%\\). Therefore, we argue that IID tests alone may not be good indicators of the robustness of action representations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.184, + 0.471, + 0.319 + ], + "angle": 0, + "content": "In particular, VideoMix, SDN and BE provide little debiasing effects. Mixup leads to inconsistent performance gains. ActorCutMix and FAME consistently improve performance on SCUBA. Nevertheless, they decrease performance (increase accuracy) on SCUFO, which suggests that they improve performance on SCUBA partially by increasing reliance on foreground static features. The action features learned with ActorCutMix and FAME are likely still vulnerable to foreground static bias." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.327, + 0.47, + 0.478 + ], + "angle": 0, + "content": "StillMix alleviates foreground and background static bias. StillMix boosts the performance on both SCUBA and SCUFO videos and obtains the best contrasted accuracy (Contra. Acc.). The significant improvements on SCUFO indicate that StillMix can suppress static bias from the entire video and not only the background. In addition, StillMix outperforms other methods on videos with conflicting foreground cues as well as ARAS. Overall, these results demonstrate the ability of StillMix to reduce static bias that is difficult to exhaustively name or pixel-wise cut out." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.491, + 0.449, + 0.508 + ], + "angle": 0, + "content": "5.4. StillMix Improves Representation Learning" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.516, + 0.469, + 0.547 + ], + "angle": 0, + "content": "We further investigate the effects of StillMix on improving representation learning through the following tests." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.553, + 0.469, + 0.675 + ], + "angle": 0, + "content": "Transferring action features across datasets. We evaluate the representations learned with different augmentation and debiasing methods by their capability to transfer to different datasets. We adopt the linear probing protocol, which trains a linear classifier on the target dataset on top of the backbone network trained on the source dataset. Table 5 shows the results of TSM, where StillMix obtains the best performance, especially in transferring across small datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.682, + 0.469, + 0.833 + ], + "angle": 0, + "content": "Downstream weakly supervised action localization. We evaluate the representations learned with StillMix by their ability to improve downstream weakly supervised action localization. We pretrain TSM on Kinetics-400 with StillMix. After that, we extract RGB features for each video segments on THUMOS14 [25] and use the extracted features to train weakly supervised action localization models BaSNet [37] and CoLA [71]. StillMix improves the performance by more than \\(1.0\\%\\) of average mAP for BaSNet and more than \\(0.5\\%\\) of average mAP for CoLA." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.846, + 0.231, + 0.863 + ], + "angle": 0, + "content": "5.5. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "We conduct ablation study on UCF101 and HMDB51 to examine design choices of StillMix." + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.09, + 0.892, + 0.12 + ], + "angle": 0, + "content": "Table 5: Action recognition accuracy (%) of transferring features across Kinetics-400, UCF101, and HMDB51." + }, + { + "type": "table", + "bbox": [ + 0.501, + 0.133, + 0.905, + 0.276 + ], + "angle": 0, + "content": "
Augmentation or DebiasingSource→Target
K400→UCFK400→HMDBHMDB→UCFUCF→HMDB
No92.5266.6761.6444.95
Mixup93.0768.6963.5846.60
VideoMix93.5569.2261.4940.33
SDN92.8163.7961.1241.90
BE93.1067.4562.7145.88
ActorCutMix92.7367.3961.6742.92
FAME93.8767.8458.8744.99
StillMix93.8970.0765.6947.99
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.303, + 0.892, + 0.334 + ], + "angle": 0, + "content": "Table 6: Weakly supervised action localization performance of features learned by StillMix." + }, + { + "type": "table", + "bbox": [ + 0.527, + 0.345, + 0.866, + 0.428 + ], + "angle": 0, + "content": "
MethodFeatureDebiasingAvg mAP@IoU=[0.1:0.9]
BaSNetTSM (RGB)No0.1810
TSM (RGB)StillMix0.1935
CoLATSM (RGB)No0.2380
TSM (RGB)StillMix0.2436
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.455, + 0.892, + 0.622 + ], + "angle": 0, + "content": "Debiasing works the best when the reference network and the main network share the same architecture. We compare the results of StillMix with different network structures in Table 7. When the structures of the reference network and the main network are identical, the OOD performance is the best and the IID performance is very close to the best, indicating good bias mitigation. We hypothesize that networks with same architecture tend to learn the same bias. As a result, using a reference network with the same architecture as the main network could be the most effective at identifying bias-inducing frames." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.628, + 0.892, + 0.809 + ], + "angle": 0, + "content": "Sampling biased frames improves debiasing. We compare three frame sampling strategies when constructing the biased frame bank: (1) No RefNet: the frame bank is uniformly sampled from the whole dataset; (2) RefNet: as in StillMix, we sample frames with high prediction probabilities from the reference network according to Eq. (2); (3) RefNet Inversed: contrary to StillMix, we sample frames with low prediction probabilities from the reference network, \\( S = \\{z_{i,j}|p_{i,j} < p_{\\tau}\\} \\). Table 8 shows results of ImageNet pretrained TSM and Swin-T. The reference network (RefNet) approach achieves the best OOD performance, whereas RefNet Inversed performs the worst." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We observe the difference between RefNet and No RefNet is small on UCF101 but is large on HMDB51. We attribute this to the prevalence of bias-inducing frames in UCF101. MMAction2 [7] trained TSN [64] using only three frames per video on UCF101 and achieved \\(83.03\\%\\) classification accuracy but achieved only \\(48.95\\%\\) with 8" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19918" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.089, + 0.472, + 0.135 + ], + "angle": 0, + "content": "Table 7: Action recognition accuracy (%) of StillMix with different reference network structures. All networks are pretrained on ImageNet." + }, + { + "type": "table", + "bbox": [ + 0.098, + 0.146, + 0.451, + 0.326 + ], + "angle": 0, + "content": "
Main NetworkReference NetworkUCF101HMDB51
IIDContra. Acc.IIDContra. Acc.
TSMResNet50-2D87.2924.6054.6633.14
SlowFast-2D87.4422.2055.0330.51
Swin-T-2D86.7223.0855.0531.62
SlowFastResNet50-2D84.8518.8650.7420.89
SlowFast-2D84.9619.7651.5321.21
Swin-T-2D85.1619.1851.8520.28
Swin-TResNet50-2D88.5931.0956.1018.44
SlowFast-2D88.6029.3454.4319.25
Swin-T-2D88.9232.1455.3621.40
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.35, + 0.47, + 0.381 + ], + "angle": 0, + "content": "Table 8: Action recognition accuracy (\\%) of StillMix with different frame sampling strategies." + }, + { + "type": "table", + "bbox": [ + 0.091, + 0.393, + 0.457, + 0.572 + ], + "angle": 0, + "content": "
Main NetworkSampling StrategyUCF101HMDB51
IIDContra. Acc.IIDContra. Acc.
TSMNo RefNet87.3924.4954.0731.21
RefNet87.2924.6054.6633.14
RefNet Inversed87.3823.5354.7929.17
SlowFastNo RefNet85.0318.9851.7920.94
RefNet84.9619.7651.5321.21
RefNet Inversed84.3318.7750.9418.61
Swin-TNo RefNet88.3731.2455.6218.89
RefNet88.9232.1455.3621.40
RefNet Inversed88.5930.5156.3418.18
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.595, + 0.468, + 0.671 + ], + "angle": 0, + "content": "frames on HMDB511. This shows many frames in UCF101 contain static cues correlated with the class labels. Random sampling can yield many bias-inducing frames on UCF101 but cannot do so on HMDB51, where the strength of RefNet becomes apparent." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.671, + 0.468, + 0.747 + ], + "angle": 0, + "content": "In Sec. S1 of the Supplementary Material, we provide more ablation studies showing that mixing action labels in StillMix decreases performance and sufficient mixing strength (i.e., small values of \\(\\lambda\\) in Eq. (3)) is necessary for debiasing." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.756, + 0.439, + 0.772 + ], + "angle": 0, + "content": "5.6. Performance on Something-Something-V2" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.779, + 0.468, + 0.854 + ], + "angle": 0, + "content": "To validate the effectiveness of different debiasing methods on recognizing fine-grained actions with strong temporal structures, we perform tests on Something-Something-V2 [20]. In Table 9, we show the performance of different debiasing methods with TSM as the base model. Since SDN" + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.863, + 0.465, + 0.901 + ], + "angle": 0, + "content": "1https://github.com/open-mmlab/mmaction2/blob/02a06bb3180e951b00cccbeb48dab055f95acd1a7/configs/recognition/tsn/README.md" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.089, + 0.892, + 0.12 + ], + "angle": 0, + "content": "Table 9: Action recognition accuracy (\\%) of different debiasing methods on Something-Something-V2." + }, + { + "type": "table", + "bbox": [ + 0.591, + 0.131, + 0.803, + 0.254 + ], + "angle": 0, + "content": "
DebiasingAccuracy
No57.49
Mixup57.86
VideoMix58.23
BE57.68
FAME58.10
StillMix (Ours)58.68
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.279, + 0.892, + 0.355 + ], + "angle": 0, + "content": "and ActorCutMix require bounding boxes of human, which are time-consuming to extract, we did not include the results of these two methods. The results show that StillMix outperforms other data augmentation methods, illustrating its effectiveness on fine-grained action videos." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.369, + 0.747, + 0.384 + ], + "angle": 0, + "content": "6. Conclusion and Discussion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.394, + 0.892, + 0.575 + ], + "angle": 0, + "content": "To learn robust and generalizable action representations, we explore techniques that mitigate static bias in both the background and the foreground. We propose a simple yet effective video data augmentation method, StillMix, and create two new sets of OOD benchmarks, SCUBA and SCUFO, to quantify static bias in the background and the foreground. Through extensive evaluation, we conclude that StillMix mitigates static bias in the background and the foreground and improves the performance of transferring learning and downstream tasks. In contrast, existing debi-asing methods remain vulnerable to foreground static bias despite their robustness to background static bias." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.575, + 0.892, + 0.664 + ], + "angle": 0, + "content": "Despite the strengths of StillMix on mitigating static bias in the background and the foreground, it has the following limitations: (1) additional computational overhead in training the reference network (about \\(8\\%\\) of the training time of the main network); and (2) little improvement (and little degradation) on IID tests." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.665, + 0.892, + 0.726 + ], + "angle": 0, + "content": "For future work, we believe that evaluating static bias in large pretrained models with the created benchmarks and adapting StillMix to mitigate static bias in such models would be promising directions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.74, + 0.66, + 0.757 + ], + "angle": 0, + "content": "Acknowledgments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This work has been supported by the Nanyang Associate Professorship and the National Research Foundation Fellowship (NRF-NRFF13-2021-0006), Singapore. The computational work for this article was partially performed on resources of the National Supercomputing Centre, Singapore (https://www.nscc.sg). Any opinions, findings, conclusions, or recommendations expressed in this material are those of the authors and do not reflect the views of the funding agencies." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19919" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.105 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Anurag Arnab, Mostafa Dehghani, Georg Heigold, Chen Sun, Mario Lučić, and Cordelia Schmid. Vivit: A video vision transformer. 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Learning representational invariances for data-efficient action recognition. arXiv preprint arXiv:2103.16565, 2021. 2, 3, 4, 6" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.389 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.956 + ], + "angle": 0, + "content": "19923" + } + ] +] \ No newline at end of file diff --git a/2023/Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground/6ba02bea-6b1d-48df-8380-8f905fcf7514_origin.pdf b/2023/Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground/6ba02bea-6b1d-48df-8380-8f905fcf7514_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..4379dc6eee9593761d33780dd637218816f9a1dc --- /dev/null +++ b/2023/Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground/6ba02bea-6b1d-48df-8380-8f905fcf7514_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:c196c3b3ec9b28b669e0702c9710b6e688f3e99421af6d28e4a37c2d5aeffe24 +size 1179522 diff --git a/2023/Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground/full.md b/2023/Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground/full.md new file mode 100644 index 0000000000000000000000000000000000000000..78f7413ba4833f7d404d91ffa3b3558060add9f4 --- /dev/null +++ b/2023/Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground/full.md @@ -0,0 +1,402 @@ +# Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground + +Haoxin Li $^{1}$ , Yuan Liu $^{2}$ , Hanwang Zhang $^{1}$ , Boyang Li $^{1}$ +anyang Technological University $^{2}$ Guangzhou University + +{haoxin003, hanwangzhang, boyang.li}@ntu.edu.sg, yuanliu@gzhu.edu.cn + +# Abstract + +In video action recognition, shortcut static features can interfere with the learning of motion features, resulting in poor out-of-distribution (OOD) generalization. The video background is clearly a source of static bias, but the video foreground, such as the clothing of the actor, can also provide static bias. In this paper, we empirically verify the existence of foreground static bias by creating test videos with conflicting signals from the static and moving portions of the video. To tackle this issue, we propose a simple yet effective technique, StillMix, to learn robust action representations. Specifically, StillMix identifies bias-inducing video frames using a 2D reference network and mixes them with videos for training, serving as effective bias suppression even when we cannot explicitly extract the source of bias within each video frame or enumerate types of bias. Finally, to precisely evaluate static bias, we synthesize two new benchmarks, SCUBA for static cues in the background, and SCUFO for static cues in the foreground. With extensive experiments, we demonstrate that StillMix mitigates both types of static bias and improves video representations for downstream applications. Code is available at https://github.com/1ihaoxin05/StillMix. + +# 1. Introduction + +Traditional computer vision techniques perform well on independent and identically distributed (IID) test data, but often lack out-of-distribution (OOD) generalization [9, 32, 12]. This is intimately tied to the learning of shortcut features [27, 16, 17], which are easy to learn and correlate strongly with IID labels but cause poor OOD generalization [53, 62, 49, 22]. In video action recognition, shortcut features often manifest as static cues. For example, a network may classify a video as golf swinging based on its background, a golf course, even if the motion patterns indicate another action such as walking. While static cues can provide valuable information [74, 11, 77], they often outcom + +![](images/633fad13f820924081931ab86d4c72e3ca88a1f0d0bf709c95d557ae0ca047bc.jpg) +Figure 1: Evaluation of background and foreground static bias. (a) Testing on IID HMDB51 [36] test videos. (b) Testing on SCUBA videos, constructed by replacing the video background with a synthetic sinusoidal stripe image. (c) Testing on videos with conflicting foreground cues, constructed by inserting a random static foreground into the SCUBA video. + +pete motion features [23, 40, 41, 52, 69] and result in low OOD performance [41, 63, 26]. In contrast to the rich literature on mitigating background static bias (e.g., golf courses for golf swinging) [5, 63, 73, 10, 6], foreground static bias has been underexplored. Examples of foreground bias include swimsuits for swimming and guitars for guitar playing — people can swim without swimsuits or show guitars in the video without playing them. + +The first question we ask is if foreground static bias exists and if it is captured by the representations learned by neural networks. Our investigation technique is to create test videos with conflicting action cues from the moving part and the static part of the video. In the first step, shown in Figure 1(b), we replace the backgrounds of IID HMDB51 [36] test videos by sinusoidal stripe images. These videos have no meaningful backgrounds, so the action information must come from the foreground. Therefore, models overly reliant on background static cues + +![](images/1b1598c41f49d139085ebc9da8ec6d6eb7ec438e6972d1cd71a1c97d98b86de8.jpg) +Figure 2: An illustration of StillMix. We train a 2D reference network that classifies still frames into actions to capture static bias. With the reference network, we sample frames inducing static bias to construct a biased frame bank. We mix the frames from the bank with a given video to generate an augmented video, which is used to train a 3D main network to mitigate static bias. + +![](images/83a65917ced9f3485739c02e64c3d2754535ed0f8a48e95b69809026390e7666.jpg) + +should perform poorly. A background debiasing technique, FAME [10], coupled with a tiny Video Swin Transformer (Swin-T) [46], works relatively well on this test. + +In the second step, shown in Figure 1(c), from a single frame of a random video, we extract its foreground (mainly human actors), and insert the static foreground into all the frames of the current SCUBA video. The resultant video contains only two action features: a static foreground that indicates one action label and a moving foreground that indicates another action label. Predictions made using the static foreground would be wrong. This design allows the quantification of foreground static bias. More details can be found in Sec. S1 of the Supplementary Material. + +The results clearly show the existence of foreground static bias and its negative effects. On the second test set, both Swin-T and Swin-T+FAME suffer similar degradation and perform $5\%$ worse than SCUBA videos. FAME works by procedurally isolating the foreground regions from each frame and use those for training. However, it is hard to separate the foreground motion from the static foreground (e.g., clothing, equipment, or other people attributes [40]) in the training videos, since both types of features are strongly tied to the human actors. + +We propose StillMix, a technique that mitigates static bias in both the background and the foreground, without the need to explicitly isolate (or even enumerate [5]) the bias-inducing content within a frame. StillMix identifies bias-inducing frames using a reference network and mixes them with training videos without affecting motion features. The process is illustrated in Figure 2. Unlike FAME, StillMix + +could suppress static bias anywhere in a frame, including the background and the foreground. In Figure 1, StillMix outperforms FAME and suffers only $2\%$ accuracy drop on the second benchmark, highlighting its resilience. + +Evaluating OOD action recognition is challenging as test videos with OOD foregrounds, such as swimming without swimsuits or cycling while carrying a guitar, are rare. To pinpoint the static bias in either the background or the foreground, we create new synthetic sets of OOD benchmarks by altering the static features in IID test videos, as illustrated in Figure 3. Specifically, we retain the foregrounds of actions and replace the backgrounds with diverse natural and synthetic images. This procedure yields a test set that quantifies representation bias toward static cues in the background (SCUBA). Second, we create videos that repeat a single random frame from SCUBA, producing a test set that quantifies representation bias toward static cues in the foreground (SCUFO). As these videos disassociate the backgrounds from the action and contain no motion, their actions can be recognized by only static foreground features. Thus, high accuracy on SCUFO indicates strong foreground static bias. + +With the synthetic OOD benchmarks, we extensively evaluate several mainstream action recognition methods and make the following observations. First, all examined methods exhibit static bias. Second, existing debiasing methods like ActorCutMix [78] and FAME [10] demonstrate resistance to background static bias, but remain vulnerable to foreground static bias. In contrast, the proposed StillMix consistently boosts performance of action recognition mod + +![](images/32fda1929fb10e6a5a95e833e968db77e580056813dedfad3d3198875321de3d.jpg) +Figure 3: An illustration of OOD benchmark construction. To quantify static cues in the background, we reserve the foreground actions and replace the backgrounds with other images to synthesize SCUBA videos. To quantify static cues in the foreground, we randomly select one frame in the SCUBA video and stack it into a single-frame video without motion, named SCUFO videos. + +els and compares favorably with the other debiasing techniques on both background and foreground static bias. In addition, StillMix improves the performance of transfer learning and downstream weakly supervised action localization. + +The paper makes the following contributions: + +- Through quantitative experiments, we highlight the importance to address foreground static bias in learning robust action representations. +- We propose StillMix, a video data augmentation technique to mitigate static bias in not only the background but also the foreground. +- We create new benchmarks to quantitatively evaluate static bias of action representations and pinpoint the source of static bias (backgrounds or foregrounds). +- We compare action recognition methods on the created benchmarks to reveal their characteristics and validate the effectiveness of StillMix. + +# 2. Related Work + +Bias Evaluation. Biases are surface features that are easily learned by neural networks and strongly influence their predictions. Such features perform well on IID data [60, 29] but do not generalize to OOD data [53, 49]. In action recognition, models easily capture static bias [40, 41, 5, 63]. The following methods are used for bias evaluation: (1) Visualization techniques [15, 47] visualize the regions that models focus on to interpret the static bias qualitatively. (2) Proxy data or tasks. Synthetic videos with altered backgrounds [6], videos with white-noise textures [26], dynamic texture videos [21, 3] are used to reveal the bias toward backgrounds or texture. Proxy tasks evaluating temporal + +asymmetry, continuity, and causality are designed to show the static bias in video representations [18]. (3) Mutual information. [33] quantifies the static bias using mutual information between representations of different types of videos. Although these works evaluate the static bias in the whole video, they do not specify the source of static bias. In this paper, we create new benchmarks to pinpoint the source of static bias as the background and the foreground. + +Bias Mitigation. Prevalent techniques of mitigating bias in action representations can be broadly classified into four categories. (1) Attribute supervision. [5] uses scene pseudolabels and human masks to discourage models from predicting scenes and recognizing actions without human, but it needs extra attribute labels. (2) Re-weighting. [40, 41] identify videos containing bias and downweight them in training, but [65] suggests merely weight adjustment is insufficient. (3) Context separation. [66] learns to separate action and contexts by collecting samples with similar contexts but different actions. (4) Data augmentation. Similar to the proposed StillMix, a few works utilize augmented videos. BE [63] mixes a frame from a video with other frames in the same video. ActorCutMix [78], FAME [10], ObjectMix [31] and FreqAug [30] carefully carve out the foreground (human actors or regions of motion), and replace the background with other images to create augmented training data. SSVC [73] and MCL [38] focus the models to the dynamic regions. However, these methods have not addressed static cues in the foreground. + +A particular advantage of StillMix is that it does not require specially designed procedures to carve out the bias-inducing pixels within the frames like ActorCutMix [78] and FAME [10], or even to enumerate the source of bias like [5]. Rather, it automatically identifies bias-inducing frames using a reference network. Consequently, StillMix can suppress static bias in both the background and the foreground. + +StillMix is also similar to two debiasing techniques designed for image recognition and text classification [48, 44], which use a reference network to identify bias-inducing data instances. However, StillMix exploits the special property of videos that they can be decomposed into individual frames. StillMix identifies bias-inducing components (frames) using 2D networks rather than whole data points as in [48, 44]. + +Action Recognition. 3D convolution or decomposed 3D convolutions [28, 58, 4, 61, 59, 42] are popular choices for action recognition. Two-stream architectures employ two modalities to classify actions, such as both RGB frames and optical flow [54, 64], or videos with two different frame rates and resolutions [14]. Multi-scale temporal convolutions or feature fusion are designed for fine-grained actions with strong temporal structures [75, 24, 39, 67]. Transformer networks are proposed to capture the long-range dependencies [1, 2, 46]. However, our understanding of the + +representations learned by these models remains limited. In this paper, we create benchmarks to evaluate what features are captured by action models and propose a simple data augmentation method that effectively improves the robustness of action models. + +# 3. The StillMix Technique + +In order to learn robust and generalizable action representations that are invariant to static cues, we propose a simple but effective video data augmentation technique, StillMix. Instead of using manually designed rules to identify and remove biased data from the training set, as in ActorCutMix [78] and FAME [10], StillMix learns to identify still frames that induce biased representation using a neural network and mitigate static bias through mixing the identified frames with videos. As a result, StillMix offers a flexible bias suppression technique that works for both the background and the foreground. + +We begin with some notations. We denote the $i^{\mathrm{th}}$ video in the training set as tensor $\pmb{x}_i\in \mathbb{R}^{C\times T\times H\times W}$ , where $C$ , $T$ , $H$ and $W$ are the number of channels, number of frames, height and width of the video, respectively. The associated ground-truth action label is $y_{i}$ . The video $\pmb{x}_i$ contains a sequence of frames $\langle \pmb {z}_{i,j}\rangle_{j = 1}^{T}$ , $\pmb {z}_{i,j}\in \mathbb{R}^{C\times H\times W}$ . The training set contains $N$ training video samples and is written as $\{(x_i,y_i)\}_{i = 1}^N$ . The goal of StillMix is to augment a given training sample $(x_{i},y_{i})$ into a transformed sample $(\tilde{x}_i,\tilde{y}_i)$ . The procedures of StillMix are illustrated in Figure 2 and introduced as follows. + +Step 1: Training the Reference Network. We identify bias-inducing frames using a 2D reference network that predicts the action label from a still frame of a video. As the still frame contains no motion, we expect the network to rely on static features to make the predictions. + +Specifically, at every epoch we randomly sample a frame $\mathbf{z}_{i,j} \in \mathbb{R}^{C \times H \times W}$ from each video $\mathbf{x}_i$ , and train the reference network $\mathcal{R}(\cdot)$ to predict the label $y_i$ . The loss is + +$$ +L _ {r e f} = \frac {1}{N} \sum_ {i = 1} ^ {N} \ell \left(\mathcal {R} \left(\boldsymbol {z} _ {i, j}\right), y _ {i}\right), \tag {1} +$$ + +where $\ell(\cdot)$ can be any classification loss, such as the cross-entropy. After training, the reference network $\mathcal{R}(\cdot)$ encodes the correlations between static cues within the frames and the action classes. + +Step 2: Identifying Biased Frames. The output of reference network $\mathcal{R}(\pmb{z}_{i,j})$ is a categorical distribution over action classes. We take the probability of the predicted class $p_{i,j} = \max_k P(y = k|\pmb{z}_{i,j})$ . A high $p_{i,j}$ indicates strong correlation between $\pmb{z}_{i,j}$ and the action class, which means $\pmb{z}_{i,j}$ can induce static bias. Therefore, we select frames with + +high $p_{i,j}$ to construct the biased frame bank $S$ : + +$$ +S = \left\{\boldsymbol {z} _ {i, j} \mid p _ {i, j} \geq p _ {\tau} \right\}, \tag {2} +$$ + +where $p_{\tau}$ is the $\tau$ -th percentile value of $p_{i,j}$ . In practice, we perform another round of uniformly random selection to control the size of the biased frame bank. + +Step 3: Mixing Video and Biased Frames. To break the strong correlation between the biased frame and the action class, we mix a video of any action class with different biased frames identified above. Specifically, in each epoch, given a video sample $(x_{i},y_{i})$ , we sample a frame $z^{\mathrm{biased}}$ from the biased frame bank $S$ and tile it $T$ times along the temporal dimension, yielding a static video with $T$ identical frames. We denote this operation as $\mathrm{Tile}(z^{\mathrm{biased}},T)$ . The augmented video sample $\tilde{x}_i$ is generated by the pixel-wise interpolation of $x_{i}$ and the static video. The augmented video label $\tilde{y}_i$ is the same as the original action label $y_{i}$ . + +$$ +\tilde {\boldsymbol {x}} _ {i} = \lambda \boldsymbol {x} _ {i} + (1 - \lambda) \operatorname {T i l e} \left(\boldsymbol {z} ^ {\text {b i a s e d}}, T\right), \quad \tilde {y} _ {i} = y _ {i}, \tag {3} +$$ + +where the scalar $\lambda$ is sampled from a Beta distribution $\operatorname{Beta}(\alpha, \beta)$ . + +The rationale for keeping the video label unchanged after augmentation is that the static video contains no motion and does not affects the motion patterns in the mixed video, thus it should not contribute to the action label. This setting of StillMix can be intuitively understood as randomly permuting the labels of the static video, so that the network is forced to ignore the correlations between the static cues in the biased frames and actions. + +Training with Augmented Videos. We apply StillMix to each video with a predefined probability $P_{\mathrm{aug}}$ . + +$$ +\left(\boldsymbol {x} _ {i} ^ {*}, y _ {i} ^ {*}\right) = \left\{ \begin{array}{l l} \left(\boldsymbol {x} _ {i}, y _ {i}\right) & a _ {i} = 0 \\ \left(\tilde {\boldsymbol {x}} _ {i}, \tilde {y} _ {i}\right) & a _ {i} = 1 \end{array} , a _ {i} \sim \operatorname {B e r} \left(P _ {\text {a u g}}\right), \right. \tag {4} +$$ + +where $a$ is a scalar sampled from a Bernoulli distribution $Ber(P_{\mathrm{aug}})$ . The samples $\{(x_i^*, y_i^*)\}_{i=1}^N$ are used to train the main network $\mathcal{F}(\cdot)$ using the following loss function: + +$$ +L = \frac {1}{N} \sum_ {i = 1} ^ {N} \ell \left(\mathcal {F} \left(\boldsymbol {x} _ {i} ^ {*}\right), y _ {i} ^ {*}\right), \tag {5} +$$ + +where $\ell (\cdot)$ could be any classification loss. + +Discussion. StillMix aims to learn robust action representations that generalize to OOD data. One popular formulation of OOD generalization [68, 34, 51, 35, 50] considers shortcut features as features that work under a specific environment but not others. For example, a classifier that excels in well-lit environments may perform terribly in dim environments. To learn robust classifiers, we ought to discover invariant features that work equally well in all environments. + +More formally, the optimal predictor $\mathcal{F}^*$ can be found with the bi-level optimization + +$$ +\mathcal {F} ^ {*} = \underset {\mathcal {F}} {\operatorname {a r g m i n}} \max _ {e} \mathbb {E} _ {\boldsymbol {x} ^ {e}, y ^ {e}} [ \ell (\mathcal {F} (\boldsymbol {x} ^ {e}), y ^ {e}) ], \tag {6} +$$ + +where the feature-label pair, $(\pmb{x}^e,y^e)$ , are drawn from the data distribution $P(\pmb{x},y|e)$ of environment $e$ and $\ell$ is the per-sample loss. $\pmb{x}^e$ contains both class features and environment features; a good predictor $\mathcal{F}$ is sensitive to the former and ignores the latter. The optimization encourages this because if $\mathcal{F}$ utilizes features that work for environment $e_1$ but not $e_2$ , the loss will increase as the $\max_e$ operation will select $e_2$ . + +However, directly optimizing Eq. (6), such as in [51], requires sampling data from all environments, which is impractical due to skewed environment distributions. For example, videos of people playing soccer in tuxedos on beaches are exceedingly rare. Maximizing over all environments is also challenging. + +The mixing operation in StillMix may be understood in the same framework. A static frame $z^{\mathrm{biased}}$ can be considered as coming from an environment $e'$ which biases predictions toward certain action labels. Mixing $z^{\mathrm{biased}}$ with $x_{i}$ simulates sampling $x^{e'}$ from the environment $e'$ . StillMix may be considered to optimize the following loss, + +$$ +\mathcal {F} ^ {*} = \underset {\mathcal {F}} {\operatorname {a r g m i n}} \mathbb {E} _ {e} \left[ \mathbb {E} _ {\boldsymbol {x} ^ {e}, y ^ {e}} [ \ell (\mathcal {F} (\boldsymbol {x} ^ {e}), y ^ {e}) ] \right], \tag {7} +$$ + +which replaces the maximization over environments in Eq. (6) with an expectation over environments due to the random sampling of $z^{\mathrm{biased}}$ . + +# 4. SCUBA and SCUFO: OOD Benchmarks + +To quantitatively evaluate static bias in the background and the foreground, we create OOD benchmarks based on three commonly used video datasets, i.e., HMDB51 [36], UCF101 [55] and Kinetics-400 [4], as detailed below. + +# 4.1. Foreground Masks and Background Images + +Foreground Masks. To extract the foreground area of actions, we use available human-annotated masks of people for UCF101 and HMDB51. There are totally 910 videos in the UCF101 test set and 256 videos in the HMDB51 test set having foreground annotations. Since there is no human-annotated masks for Kinetics-400, we use video segmentation models [57, 56] to generate foreground masks. After filtering out the videos with small foreground masks (likely to be wrong), we obtain totally 10,190 videos in the Kinetics-400 validation set to construct the benchmark. + +Background Images. In order to synthesize diverse test videos, we collect background images from three different image sources: 1) the test set of Place365 [76]. 2) images generated by VQGAN-CLIP [8] from a random scene + +![](images/e32537a5d83988613f069bec27e332612ffd75abc2bb9813a237f71cf0220241.jpg) +(a) Place365 + +![](images/f3bdb01d696d78843f7f15aab06bd4cb02b5517749a4b770b17263b3464262ac.jpg) +Figure 4: Background images from different sources. (a) An image from Place365. (b) An image generated by VQGAN-CLIP from the query "A painting of a conference room in the style of surreal art". (c) An image of randomly generated sinusoidal stripes. + +![](images/f46bc9432e2a971c31aa545278859615ec74b415cfbc900d37b4049831255401.jpg) +(b) VQGAN-CLIP +(c) Sinusoid + +category of Place365 and a random artistic style. 3) randomly generated images with S-shaped stripes defined by sinusoidal functions. For each image source, we construct a background image pool. In Figure 4, we show three example background images from the three sources. More details are described in Sec. S2 of the Supplementary Material. + +# 4.2. Test Video Synthesis + +Testing for Background Static Cues. Given a video $\pmb{x}$ with $T$ frames $\{\pmb{x}_t\}_{t=1}^T$ , we create a synthetic video $\hat{\pmb{x}}$ by combining the foreground of $\pmb{x}$ and a background image sampled from a background image pool. + +$$ +\hat {\boldsymbol {x}} _ {t} = \boldsymbol {m} _ {t} \odot \boldsymbol {x} _ {t} + (1 - \boldsymbol {m} _ {t}) \odot \operatorname {T i l e} (\boldsymbol {z} ^ {\mathrm {b g}}, T), \tag {8} +$$ + +where $m_t$ is the foreground mask, $\odot$ denotes pixel-wise multiplication, $z^{\mathrm{bg}}$ is a background image sampled from the image pool. $\mathrm{Tile}(z^{\mathrm{bg}}, T)$ repeats $z^{\mathrm{bg}}T$ times along the temporal dimension. For each video with foreground masks, we pair it with $m$ randomly selected background images from each of the 3 background image pools to synthesize $3m$ videos. We set $m = 10,5,1$ for HMDB51, UCF101 and Kinetics-400, respectively, since HMDB51 and UCF101 have fewer videos with foreground masks and we would like to increase the diversity of the synthetic videos. + +The generated videos retain the original action foreground, including the human actors and their motion, on new random backgrounds. They are designed to test bias toward static cues from the background, and are named SCUBA videos. We expect models invariant to static backgrounds to obtain high classification accuracy on SCUBA. + +Testing for Foreground Static Cues. In addition, we create another set of videos to test the amount of foreground static bias in the learned representations. Foreground static cues include people and object attributes, such as bicycle helmets for cycling and bows for archery — people can ride a bicycle without helmets or hold bows when not performing archery. As the SCUBA videos contain most foreground elements in the original videos, they cannot distinguish whether models rely on foreground static cues. + +To this end, we create videos that contain only a single frame. Specifically, from each SCUBA video, we ran + +Table 1: Statistics of the created benchmarks. + +
Video Source# Original VideosBackground Source# Synthetic Videos# Domain Gap of SCUBA# Domain Gap of SCUFO
HMDB51256Place3652,5605.646±0.2765.745±0.290
VQGAN-CLIP2,5608.178±0.6858.307±0.533
Sinusoid2,56011.739±0.44411.998±0.932
UCF101910Place3654,55020.493±2.19920.829±2.093
VQGAN-CLIP4,55051.320±5.79055.202±9.477
Sinusoid4,55052.249±3.52252.534±5.930
Kinetics-40010,190Place36510,1906.094±0.2086.455±0.224
VQGAN-CLIP10,1907.504±0.2968.052±0.273
Sinusoid10,1907.211±0.3117.766±0.148
+ +domly select one frame and repeat it temporally to create a video with zero motion. As these videos quantify the representation bias toward static cues in the foreground, we name them SCUFO videos. In SCUFO videos, the foreground static features are identical to the corresponding SCUBA videos, but the motion information is totally removed. Therefore, a model invariant to foreground static features should obtain low classification accuracy on them. + +We summarize the dataset statistics in Table 1. SCUBA and SCUFO have the same number of videos for each pair of video source and background source. We also report the domain gap between original videos to show their OOD characteristics, as explained in the next section. + +# 4.3. Quality Assessment + +We empirically verify that the SCUBA datasets retain the motion features of the original videos but replace background static features using the following two tests. + +Human Assessment. To test if SCUBA preserves the motion information sufficiently for action recognition, we carry out an experiment on Amazon Mechanical Turk (AMT) to verify if human workers can recognize the actions in SCUBA videos. + +From the same original video, we randomly sampled one synthetic video and asked the AMT workers if the moving parts in the video show the labeled action. The workers are given three options: yes, no, and can't tell. We also create control questions with original videos to detect random clicking and design control groups to prevent the workers from always answering yes to synthetic videos. The final answer for each video is obtained by majority voting of three workers. Workers who do not reach at least $75\%$ accuracy on the control questions are rejected. More details are described in Sec. S2 of the Supplementary Material. + +Collectively, the AMT workers were able to correctly recognize the actions in $96.15\%$ of UCF101-SCUBA, $86.33\%$ of HMDB51-SCUBA and $85.19\%$ of Kinetics400-SCUBA videos. We conclude that SCUBA videos preserve sufficient action information for humans to recognize. + +Domain Gaps of the Static Features. To verify if SCUBA and SCUFO have successfully replaced the background static features and qualify as OOD test sets, we test if a classifier based on purely static features trained on IID videos can generalize to SCUBA and SCUFO. + +Using a variation of scene representation bias [5], we define the domain gap $G_{\text{scene}}$ as + +$$ +G _ {s c e n e} = A c c \left(D _ {\text {o r i}}, \Phi_ {s c e n e}\right) / A c c \left(D _ {\text {s y n}}, \Phi_ {s c e n e}\right). \tag {9} +$$ + +Here $\Phi_{\text{scene}}$ is the average frame feature extracted from a ResNet-50 pretrained on Place365 [76]. Thus, the extracted feature captures static scene information, mostly from the background. We train a linear classifier on the original video training set and apply it to the original test set $D_{\text{ori}}$ , obtaining the accuracy $Acc(D_{\text{ori}}, \Phi_{\text{scene}})$ . After that, we apply the same classifier to the synthetic dataset $D_{\text{syn}}$ , obtaining the accuracy $Acc(D_{\text{syn}}, \Phi_{\text{scene}})$ . A higher ratio indicates greater domain gap with respect to static features. + +In Table 1, we show the means and standard deviations computed from three random repeats of video synthesis. We observe large domain gaps, ranging from 5.6-fold to 52-fold decrease in accuracy on the synthetic test set. This demonstrates the static features of synthetic videos differ substantially from the original videos and the synthetic videos can serve as OOD tests. Moreover, the low standard deviations show that the effects of random sampling are marginal. In later experiments, we use the dataset from one random seed. + +# 5. Experiments + +In this section, we compare the performance of several mainstream action recognition methods on IID and OOD test data and validate the effectiveness of StillMix. + +# 5.1. Comparing Methods + +Action Recognition Models. (1) TSM [43], a temporal shift module learning spatiotemporal features with 2D CNN. (2) SlowFast [14], a two-branch 3D CNN learning spatiotemporal signals under two frame rates. (3) Video Swin Transformer [46], an adapted Swin Transformer [45] for videos. We use the tiny version, denoted as Swin-T. + +Video Data Augmentation and Debiasing Methods. We compare the debiasing performance of several video data augmentation and debiasing methods by adapting them to supervised action recognition. (1) Mixup [72] and VideoMix [70]. (2) SDN [5]. (3) BE [63], ActorCutMix[78] and FAME [10]. We adapt these three self-supervised debiasing methods as data augmentations, which carve out the foreground and replace the background as in the original papers. All the data augmentation techniques are applied stochastically as in [19]. More implementation details are described in Sec. S3 of the Supplementary Material. + +Table 2: IID and OOD test accuracy (\%) of augmentation and debiasing methods on Kinetics-400. † indicates adaptation from self-supervised debiasing methods. ConfI-FG denotes synthetic videos with conflicting foreground cues. All models are pretrained on ImageNet. + +
ModelAugmentation or DebiasingIIDOOD
Avg SCUBA↑Avg SCUFO↓Contra Acc.↑Confl-FG↑ARAS↑
TSMNo71.1337.3917.2222.8020.1557.86
Mixup71.3340.8117.5325.9823.4858.05
VideoMix71.3538.8717.2524.5723.4356.61
SDN69.9936.9516.5522.3820.2955.06
BE†71.3037.8916.0824.3520.1157.47
ActorCutMix†71.0740.4216.2926.5221.4157.09
FAME†71.1340.9118.3425.6324.4157.47
StillMix (Ours)71.2840.485.2336.0725.7359.69
Swin-TNo73.9541.7418.1725.9325.2560.17
Mixup73.9143.9517.9228.2427.6459.59
VideoMix73.8043.1719.2626.4029.3760.95
SDN72.2342.3421.4624.4627.1460.26
BE†73.9343.4019.5626.2826.6759.79
ActorCutMix†73.9745.7019.3928.6429.0261.23
FAME†73.8148.7921.2730.0329.5060.37
StillMix (Ours)73.8644.105.5139.4130.7762.49
+ +# 5.2. Evaluation Metrics + +We conduct the following experiments on Kinetics-400, UCF101 and HMDB51. First, we perform IID tests on the original test sets and use the top-1 accuracy as metrics. After that, we perform OOD tests on SCUBA and SCUFO and report the average top-1 accuracy across background image sources. Note that higher accuracy on SCUBA is better (low background static bias), while lower accuracy on SCUFO is better (low foreground static bias). + +To show the performance of utilizing pure foreground motion information, we propose another performance metric called contrasted accuracy (Contra. Acc.). As one SCUFO video is derived from a SCUBA video, we count one correct prediction if the model is correct on the SCUBA but incorrect on the associated SCUFO video. + +We further evaluate on the synthetic videos with conflicting foreground cues (Figure 1). Finally, we also evaluate on ARAS [13], a real-world OOD dataset with rare scenes, to show the performance of scene bias reduction. + +# 5.3. Results on IID and OOD Benchmarks + +Table 2, 3 and 4 compare the IID and OOD performance of different video data augmentation and debiasing methods on Kinetics-400, HMDB51 and UCF101. Given limited computational resources, we ran experiments on Kinetics-400 using a single seed. However, on the smaller HMDB51 and UCF101, we repeated experiments with three seeds. In Sec. S1 of the Supplementary Material, we provide more + +Table 3: IID and OOD test accuracy $(\%)$ of augmentation and debiasing methods on HMDB51. All models are pretrained on Kinetics-400. + +
ModelAugmentation or DebiasingIIDOOD
Avg SCUBA↑Avg SCUFO↓Contra. Acc.↑ConfI-FG↑
TSMNo70.39±0.5138.03±1.3919.23±1.3022.02±0.6425.44±1.31
Mixup72.00±0.4739.76±1.7219.08±1.3723.76±0.8426.94±1.23
VideoMix70.72±0.1235.71±1.5717.48±1.1121.03±0.5522.19±1.47
SDN69.51±0.3037.05±0.7317.60±0.3723.74±0.9528.38±0.87
BE71.22±0.2438.48±1.4219.45±1.0622.39±0.6725.21±1.35
ActorCutMix70.52±0.8238.40±0.5319.61±0.5621.94±0.4026.16±0.36
FAME70.39±0.8847.19±1.5222.33±0.9128.21±0.8933.98±2.09
StillMix71.52±0.3848.23±0.968.43±0.8842.05±0.9936.89±1.09
Swin-TNo73.92±0.7443.93±0.7820.46±0.7127.84±1.2836.58±1.65
Mixup74.58±0.4343.10±1.1321.17±0.6626.09±1.0536.62±2.98
VideoMix73.31±0.5339.39±0.7120.44±0.7323.13±0.5432.68±1.04
SDN74.66±0.8240.02±1.4820.22±1.2422.88±1.0534.87±2.43
BE74.31±0.4143.56±1.3819.96±0.7127.84±1.3235.99±0.67
ActorCutMix74.05±0.6046.79±1.3822.07±0.3628.12±1.2736.97±1.63
FAME73.79±0.2951.40±1.5426.92±0.7129.66±2.1139.61±1.87
StillMix74.82±0.4351.81±1.7813.39±0.7140.28±1.6147.38±1.50
+ +Table 4: IID and OOD test accuracy $(\%)$ of augmentation and debiasing methods on UCF101. All models are pretrained on Kinetics-400. + +
ModelAugmentation or DebiasingIIDOOD
Avg SCUBA↑Avg SCUFO↓Contra. Acc.↑ConfI-FG↑
TSMNo94.62±0.0825.60±1.364.21±0.8421.83±1.4827.68±1.35
Mixup94.71±0.1427.80±0.954.04±0.8124.17±1.0030.31±1.10
VideoMix94.50±0.1931.55±1.685.77±0.7426.69±1.3830.69±1.79
SDN93.84±0.2719.91±0.613.10±0.1917.19±0.5120.89±0.36
BE94.49±0.1425.91±1.374.62±0.8421.82±1.3828.06±1.32
ActorCutMix94.47±0.1538.11±1.484.56±0.1633.90±1.5138.12±2.12
FAME93.72±0.0935.72±1.153.67±0.5232.28±1.2834.58±0.93
StillMix94.30±0.1437.18±1.290.79±0.1236.47±1.2440.59±0.80
Swin-TNo96.21±0.1942.31±2.245.78±0.6836.82±2.1244.65±2.10
Mixup96.17±0.1446.16±1.745.93±0.4340.46±1.9647.16±2.82
VideoMix96.00±0.0241.40±1.1113.27±0.8529.37±0.9142.59±1.51
SDN95.76±0.1139.25±2.322.98±0.8836.42±1.7448.47±2.06
BE96.06±0.1143.98±0.805.54±0.9438.62±1.1346.62±0.96
ActorCutMix95.87±0.1958.61±0.4811.92±0.2546.87±0.4556.88±0.39
FAME95.81±0.1540.90±1.576.36±0.7135.14±1.6628.21±1.83
StillMix96.02±0.0858.22±0.413.44±0.5154.90±0.7757.30±0.60
+ +detailed results (e.g., tests on videos with conflicting foreground cues and ARAS [13]). + +OOD data cause performance degradation. Comparing the performance of TSM and Swin-T on IID and OOD tests, we observe that they perform much worse (more than $20\%$ ) on SCUBA than IID videos. Given that human workers can recognize the action in more than $85\%$ of SCUBA videos, the results indicate that the models are not robust to the domain shifts, probably due to the reliance of static background features; when the backgrounds are replaced, performance deterioration ensues. + +IID tests do not fully reveal representation quality. Comparing the performance of different augmentation and debi + +asing methods, we observe that all methods obtain similar accuracies on IID tests, which fall within a $2\%$ band. However, they show vastly different performance on SCUBA and SCUFO — the maximum difference is larger than $15\%$ . Therefore, we argue that IID tests alone may not be good indicators of the robustness of action representations. + +In particular, VideoMix, SDN and BE provide little debiasing effects. Mixup leads to inconsistent performance gains. ActorCutMix and FAME consistently improve performance on SCUBA. Nevertheless, they decrease performance (increase accuracy) on SCUFO, which suggests that they improve performance on SCUBA partially by increasing reliance on foreground static features. The action features learned with ActorCutMix and FAME are likely still vulnerable to foreground static bias. + +StillMix alleviates foreground and background static bias. StillMix boosts the performance on both SCUBA and SCUFO videos and obtains the best contrasted accuracy (Contra. Acc.). The significant improvements on SCUFO indicate that StillMix can suppress static bias from the entire video and not only the background. In addition, StillMix outperforms other methods on videos with conflicting foreground cues as well as ARAS. Overall, these results demonstrate the ability of StillMix to reduce static bias that is difficult to exhaustively name or pixel-wise cut out. + +# 5.4. StillMix Improves Representation Learning + +We further investigate the effects of StillMix on improving representation learning through the following tests. + +Transferring action features across datasets. We evaluate the representations learned with different augmentation and debiasing methods by their capability to transfer to different datasets. We adopt the linear probing protocol, which trains a linear classifier on the target dataset on top of the backbone network trained on the source dataset. Table 5 shows the results of TSM, where StillMix obtains the best performance, especially in transferring across small datasets. + +Downstream weakly supervised action localization. We evaluate the representations learned with StillMix by their ability to improve downstream weakly supervised action localization. We pretrain TSM on Kinetics-400 with StillMix. After that, we extract RGB features for each video segments on THUMOS14 [25] and use the extracted features to train weakly supervised action localization models BaSNet [37] and CoLA [71]. StillMix improves the performance by more than $1.0\%$ of average mAP for BaSNet and more than $0.5\%$ of average mAP for CoLA. + +# 5.5. Ablation Study + +We conduct ablation study on UCF101 and HMDB51 to examine design choices of StillMix. + +Table 5: Action recognition accuracy (%) of transferring features across Kinetics-400, UCF101, and HMDB51. + +
Augmentation or DebiasingSource→Target
K400→UCFK400→HMDBHMDB→UCFUCF→HMDB
No92.5266.6761.6444.95
Mixup93.0768.6963.5846.60
VideoMix93.5569.2261.4940.33
SDN92.8163.7961.1241.90
BE93.1067.4562.7145.88
ActorCutMix92.7367.3961.6742.92
FAME93.8767.8458.8744.99
StillMix93.8970.0765.6947.99
+ +Table 6: Weakly supervised action localization performance of features learned by StillMix. + +
MethodFeatureDebiasingAvg mAP@IoU=[0.1:0.9]
BaSNetTSM (RGB)No0.1810
TSM (RGB)StillMix0.1935
CoLATSM (RGB)No0.2380
TSM (RGB)StillMix0.2436
+ +Debiasing works the best when the reference network and the main network share the same architecture. We compare the results of StillMix with different network structures in Table 7. When the structures of the reference network and the main network are identical, the OOD performance is the best and the IID performance is very close to the best, indicating good bias mitigation. We hypothesize that networks with same architecture tend to learn the same bias. As a result, using a reference network with the same architecture as the main network could be the most effective at identifying bias-inducing frames. + +Sampling biased frames improves debiasing. We compare three frame sampling strategies when constructing the biased frame bank: (1) No RefNet: the frame bank is uniformly sampled from the whole dataset; (2) RefNet: as in StillMix, we sample frames with high prediction probabilities from the reference network according to Eq. (2); (3) RefNet Inversed: contrary to StillMix, we sample frames with low prediction probabilities from the reference network, $S = \{z_{i,j}|p_{i,j} < p_{\tau}\}$ . Table 8 shows results of ImageNet pretrained TSM and Swin-T. The reference network (RefNet) approach achieves the best OOD performance, whereas RefNet Inversed performs the worst. + +We observe the difference between RefNet and No RefNet is small on UCF101 but is large on HMDB51. We attribute this to the prevalence of bias-inducing frames in UCF101. MMAction2 [7] trained TSN [64] using only three frames per video on UCF101 and achieved $83.03\%$ classification accuracy but achieved only $48.95\%$ with 8 + +Table 7: Action recognition accuracy (%) of StillMix with different reference network structures. All networks are pretrained on ImageNet. + +
Main NetworkReference NetworkUCF101HMDB51
IIDContra. Acc.IIDContra. Acc.
TSMResNet50-2D87.2924.6054.6633.14
SlowFast-2D87.4422.2055.0330.51
Swin-T-2D86.7223.0855.0531.62
SlowFastResNet50-2D84.8518.8650.7420.89
SlowFast-2D84.9619.7651.5321.21
Swin-T-2D85.1619.1851.8520.28
Swin-TResNet50-2D88.5931.0956.1018.44
SlowFast-2D88.6029.3454.4319.25
Swin-T-2D88.9232.1455.3621.40
+ +Table 8: Action recognition accuracy (\%) of StillMix with different frame sampling strategies. + +
Main NetworkSampling StrategyUCF101HMDB51
IIDContra. Acc.IIDContra. Acc.
TSMNo RefNet87.3924.4954.0731.21
RefNet87.2924.6054.6633.14
RefNet Inversed87.3823.5354.7929.17
SlowFastNo RefNet85.0318.9851.7920.94
RefNet84.9619.7651.5321.21
RefNet Inversed84.3318.7750.9418.61
Swin-TNo RefNet88.3731.2455.6218.89
RefNet88.9232.1455.3621.40
RefNet Inversed88.5930.5156.3418.18
+ +frames on HMDB511. This shows many frames in UCF101 contain static cues correlated with the class labels. Random sampling can yield many bias-inducing frames on UCF101 but cannot do so on HMDB51, where the strength of RefNet becomes apparent. + +In Sec. S1 of the Supplementary Material, we provide more ablation studies showing that mixing action labels in StillMix decreases performance and sufficient mixing strength (i.e., small values of $\lambda$ in Eq. (3)) is necessary for debiasing. + +# 5.6. Performance on Something-Something-V2 + +To validate the effectiveness of different debiasing methods on recognizing fine-grained actions with strong temporal structures, we perform tests on Something-Something-V2 [20]. In Table 9, we show the performance of different debiasing methods with TSM as the base model. Since SDN + +Table 9: Action recognition accuracy (\%) of different debiasing methods on Something-Something-V2. + +
DebiasingAccuracy
No57.49
Mixup57.86
VideoMix58.23
BE57.68
FAME58.10
StillMix (Ours)58.68
+ +and ActorCutMix require bounding boxes of human, which are time-consuming to extract, we did not include the results of these two methods. The results show that StillMix outperforms other data augmentation methods, illustrating its effectiveness on fine-grained action videos. + +# 6. Conclusion and Discussion + +To learn robust and generalizable action representations, we explore techniques that mitigate static bias in both the background and the foreground. We propose a simple yet effective video data augmentation method, StillMix, and create two new sets of OOD benchmarks, SCUBA and SCUFO, to quantify static bias in the background and the foreground. Through extensive evaluation, we conclude that StillMix mitigates static bias in the background and the foreground and improves the performance of transferring learning and downstream tasks. In contrast, existing debi-asing methods remain vulnerable to foreground static bias despite their robustness to background static bias. + +Despite the strengths of StillMix on mitigating static bias in the background and the foreground, it has the following limitations: (1) additional computational overhead in training the reference network (about $8\%$ of the training time of the main network); and (2) little improvement (and little degradation) on IID tests. + +For future work, we believe that evaluating static bias in large pretrained models with the created benchmarks and adapting StillMix to mitigate static bias in such models would be promising directions. + +# Acknowledgments + +This work has been supported by the Nanyang Associate Professorship and the National Research Foundation Fellowship (NRF-NRFF13-2021-0006), Singapore. The computational work for this article was partially performed on resources of the National Supercomputing Centre, Singapore (https://www.nscc.sg). 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Learning representational invariances for data-efficient action recognition. arXiv preprint arXiv:2103.16565, 2021. 2, 3, 4, 6 \ No newline at end of file diff --git a/2023/Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground/images.zip b/2023/Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..e8661b5a435547dbaadb177a2d35de51756392ab --- /dev/null +++ b/2023/Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:6e2ad72d532b152b90911bab644c90ad4c95fdd04bddda59aa99b7f1d1e34a8c +size 708886 diff --git a/2023/Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground/layout.json b/2023/Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..69aa7093a22e020750c960dfb4516bcf85573fc9 --- /dev/null +++ b/2023/Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground/layout.json @@ -0,0 +1,10921 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 80, + 103, + 514, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 103, + 514, + 140 + ], + "spans": [ + { + "bbox": [ + 80, + 103, + 514, + 140 + ], + "type": "text", + "content": "Mitigating and Evaluating Static Bias of Action Representations in the Background and the Foreground" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "spans": [ + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "type": "text", + "content": "Haoxin Li" + }, + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "type": "text", + "content": ", Yuan Liu" + }, + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "type": "text", + "content": ", Hanwang Zhang" + }, + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "type": "text", + "content": ", Boyang Li" + }, + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "type": "text", + "content": " \nanyang Technological University " + }, + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 164, + 160, + 446, + 190 + ], + "type": "text", + "content": "Guangzhou University" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 113, + 191, + 480, + 203 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 113, + 191, + 480, + 203 + ], + "spans": [ + { + "bbox": [ + 113, + 191, + 480, + 203 + ], + "type": "text", + "content": "{haoxin003, hanwangzhang, boyang.li}@ntu.edu.sg, yuanliu@gzhu.edu.cn" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "spans": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 258, + 290, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 258, + 290, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 290, + 521 + ], + "type": "text", + "content": "In video action recognition, shortcut static features can interfere with the learning of motion features, resulting in poor out-of-distribution (OOD) generalization. The video background is clearly a source of static bias, but the video foreground, such as the clothing of the actor, can also provide static bias. In this paper, we empirically verify the existence of foreground static bias by creating test videos with conflicting signals from the static and moving portions of the video. To tackle this issue, we propose a simple yet effective technique, StillMix, to learn robust action representations. Specifically, StillMix identifies bias-inducing video frames using a 2D reference network and mixes them with videos for training, serving as effective bias suppression even when we cannot explicitly extract the source of bias within each video frame or enumerate types of bias. Finally, to precisely evaluate static bias, we synthesize two new benchmarks, SCUBA for static cues in the background, and SCUFO for static cues in the foreground. With extensive experiments, we demonstrate that StillMix mitigates both types of static bias and improves video representations for downstream applications. Code is available at https://github.com/1ihaoxin05/StillMix." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 548, + 128, + 561 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 548, + 128, + 561 + ], + "spans": [ + { + "bbox": [ + 47, + 548, + 128, + 561 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 570, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 714 + ], + "type": "text", + "content": "Traditional computer vision techniques perform well on independent and identically distributed (IID) test data, but often lack out-of-distribution (OOD) generalization [9, 32, 12]. This is intimately tied to the learning of shortcut features [27, 16, 17], which are easy to learn and correlate strongly with IID labels but cause poor OOD generalization [53, 62, 49, 22]. In video action recognition, shortcut features often manifest as static cues. For example, a network may classify a video as golf swinging based on its background, a golf course, even if the motion patterns indicate another action such as walking. While static cues can provide valuable information [74, 11, 77], they often outcom" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 308, + 230, + 545, + 378 + ], + "blocks": [ + { + "bbox": [ + 308, + 230, + 545, + 378 + ], + "lines": [ + { + "bbox": [ + 308, + 230, + 545, + 378 + ], + "spans": [ + { + "bbox": [ + 308, + 230, + 545, + 378 + ], + "type": "image", + "image_path": "633fad13f820924081931ab86d4c72e3ca88a1f0d0bf709c95d557ae0ca047bc.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 387, + 547, + 472 + ], + "lines": [ + { + "bbox": [ + 304, + 387, + 547, + 472 + ], + "spans": [ + { + "bbox": [ + 304, + 387, + 547, + 472 + ], + "type": "text", + "content": "Figure 1: Evaluation of background and foreground static bias. (a) Testing on IID HMDB51 [36] test videos. (b) Testing on SCUBA videos, constructed by replacing the video background with a synthetic sinusoidal stripe image. (c) Testing on videos with conflicting foreground cues, constructed by inserting a random static foreground into the SCUBA video." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 496, + 547, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 496, + 547, + 592 + ], + "spans": [ + { + "bbox": [ + 304, + 496, + 547, + 592 + ], + "type": "text", + "content": "pete motion features [23, 40, 41, 52, 69] and result in low OOD performance [41, 63, 26]. In contrast to the rich literature on mitigating background static bias (e.g., golf courses for golf swinging) [5, 63, 73, 10, 6], foreground static bias has been underexplored. Examples of foreground bias include swimsuits for swimming and guitars for guitar playing — people can swim without swimsuits or show guitars in the video without playing them." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": "The first question we ask is if foreground static bias exists and if it is captured by the representations learned by neural networks. Our investigation technique is to create test videos with conflicting action cues from the moving part and the static part of the video. In the first step, shown in Figure 1(b), we replace the backgrounds of IID HMDB51 [36] test videos by sinusoidal stripe images. These videos have no meaningful backgrounds, so the action information must come from the foreground. Therefore, models overly reliant on background static cues" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19911" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 73, + 296, + 265 + ], + "blocks": [ + { + "bbox": [ + 50, + 73, + 296, + 265 + ], + "lines": [ + { + "bbox": [ + 50, + 73, + 296, + 265 + ], + "spans": [ + { + "bbox": [ + 50, + 73, + 296, + 265 + ], + "type": "image", + "image_path": "1b1598c41f49d139085ebc9da8ec6d6eb7ec438e6972d1cd71a1c97d98b86de8.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 280, + 547, + 327 + ], + "lines": [ + { + "bbox": [ + 46, + 280, + 547, + 327 + ], + "spans": [ + { + "bbox": [ + 46, + 280, + 547, + 327 + ], + "type": "text", + "content": "Figure 2: An illustration of StillMix. We train a 2D reference network that classifies still frames into actions to capture static bias. With the reference network, we sample frames inducing static bias to construct a biased frame bank. We mix the frames from the bank with a given video to generate an augmented video, which is used to train a 3D main network to mitigate static bias." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 300, + 74, + 543, + 266 + ], + "blocks": [ + { + "bbox": [ + 300, + 74, + 543, + 266 + ], + "lines": [ + { + "bbox": [ + 300, + 74, + 543, + 266 + ], + "spans": [ + { + "bbox": [ + 300, + 74, + 543, + 266 + ], + "type": "image", + "image_path": "83a65917ced9f3485739c02e64c3d2754535ed0f8a48e95b69809026390e7666.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 350, + 287, + 385 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 350, + 287, + 385 + ], + "spans": [ + { + "bbox": [ + 46, + 350, + 287, + 385 + ], + "type": "text", + "content": "should perform poorly. A background debiasing technique, FAME [10], coupled with a tiny Video Swin Transformer (Swin-T) [46], works relatively well on this test." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 387, + 287, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 387, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 387, + 287, + 506 + ], + "type": "text", + "content": "In the second step, shown in Figure 1(c), from a single frame of a random video, we extract its foreground (mainly human actors), and insert the static foreground into all the frames of the current SCUBA video. The resultant video contains only two action features: a static foreground that indicates one action label and a moving foreground that indicates another action label. Predictions made using the static foreground would be wrong. This design allows the quantification of foreground static bias. More details can be found in Sec. S1 of the Supplementary Material." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "text", + "content": "The results clearly show the existence of foreground static bias and its negative effects. On the second test set, both Swin-T and Swin-T+FAME suffer similar degradation and perform " + }, + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 46, + 509, + 287, + 628 + ], + "type": "text", + "content": " worse than SCUBA videos. FAME works by procedurally isolating the foreground regions from each frame and use those for training. However, it is hard to separate the foreground motion from the static foreground (e.g., clothing, equipment, or other people attributes [40]) in the training videos, since both types of features are strongly tied to the human actors." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 287, + 715 + ], + "type": "text", + "content": "We propose StillMix, a technique that mitigates static bias in both the background and the foreground, without the need to explicitly isolate (or even enumerate [5]) the bias-inducing content within a frame. StillMix identifies bias-inducing frames using a reference network and mixes them with training videos without affecting motion features. The process is illustrated in Figure 2. Unlike FAME, StillMix" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 350, + 545, + 398 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 350, + 545, + 398 + ], + "spans": [ + { + "bbox": [ + 304, + 350, + 545, + 398 + ], + "type": "text", + "content": "could suppress static bias anywhere in a frame, including the background and the foreground. In Figure 1, StillMix outperforms FAME and suffers only " + }, + { + "bbox": [ + 304, + 350, + 545, + 398 + ], + "type": "inline_equation", + "content": "2\\%" + }, + { + "bbox": [ + 304, + 350, + 545, + 398 + ], + "type": "text", + "content": " accuracy drop on the second benchmark, highlighting its resilience." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 400, + 546, + 614 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 400, + 546, + 614 + ], + "spans": [ + { + "bbox": [ + 304, + 400, + 546, + 614 + ], + "type": "text", + "content": "Evaluating OOD action recognition is challenging as test videos with OOD foregrounds, such as swimming without swimsuits or cycling while carrying a guitar, are rare. To pinpoint the static bias in either the background or the foreground, we create new synthetic sets of OOD benchmarks by altering the static features in IID test videos, as illustrated in Figure 3. Specifically, we retain the foregrounds of actions and replace the backgrounds with diverse natural and synthetic images. This procedure yields a test set that quantifies representation bias toward static cues in the background (SCUBA). Second, we create videos that repeat a single random frame from SCUBA, producing a test set that quantifies representation bias toward static cues in the foreground (SCUFO). As these videos disassociate the backgrounds from the action and contain no motion, their actions can be recognized by only static foreground features. Thus, high accuracy on SCUFO indicates strong foreground static bias." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 617, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 714 + ], + "type": "text", + "content": "With the synthetic OOD benchmarks, we extensively evaluate several mainstream action recognition methods and make the following observations. First, all examined methods exhibit static bias. Second, existing debiasing methods like ActorCutMix [78] and FAME [10] demonstrate resistance to background static bias, but remain vulnerable to foreground static bias. In contrast, the proposed StillMix consistently boosts performance of action recognition mod" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "19912" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 72, + 285, + 200 + ], + "blocks": [ + { + "bbox": [ + 52, + 72, + 285, + 200 + ], + "lines": [ + { + "bbox": [ + 52, + 72, + 285, + 200 + ], + "spans": [ + { + "bbox": [ + 52, + 72, + 285, + 200 + ], + "type": "image", + "image_path": "32fda1929fb10e6a5a95e833e968db77e580056813dedfad3d3198875321de3d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 211, + 287, + 293 + ], + "lines": [ + { + "bbox": [ + 46, + 211, + 287, + 293 + ], + "spans": [ + { + "bbox": [ + 46, + 211, + 287, + 293 + ], + "type": "text", + "content": "Figure 3: An illustration of OOD benchmark construction. To quantify static cues in the background, we reserve the foreground actions and replace the backgrounds with other images to synthesize SCUBA videos. To quantify static cues in the foreground, we randomly select one frame in the SCUBA video and stack it into a single-frame video without motion, named SCUFO videos." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 316, + 286, + 374 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 316, + 286, + 374 + ], + "spans": [ + { + "bbox": [ + 46, + 316, + 286, + 374 + ], + "type": "text", + "content": "els and compares favorably with the other debiasing techniques on both background and foreground static bias. In addition, StillMix improves the performance of transfer learning and downstream weakly supervised action localization." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 376, + 244, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 376, + 244, + 388 + ], + "spans": [ + { + "bbox": [ + 59, + 376, + 244, + 388 + ], + "type": "text", + "content": "The paper makes the following contributions:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 391, + 287, + 538 + ], + "type": "list", + "angle": 0, + "index": 8, + "blocks": [ + { + "bbox": [ + 59, + 391, + 287, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 391, + 287, + 426 + ], + "spans": [ + { + "bbox": [ + 59, + 391, + 287, + 426 + ], + "type": "text", + "content": "- Through quantitative experiments, we highlight the importance to address foreground static bias in learning robust action representations." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 429, + 287, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 429, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 59, + 429, + 287, + 464 + ], + "type": "text", + "content": "- We propose StillMix, a video data augmentation technique to mitigate static bias in not only the background but also the foreground." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 59, + 466, + 287, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 466, + 287, + 502 + ], + "spans": [ + { + "bbox": [ + 59, + 466, + 287, + 502 + ], + "type": "text", + "content": "- We create new benchmarks to quantitatively evaluate static bias of action representations and pinpoint the source of static bias (backgrounds or foregrounds)." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 59, + 503, + 287, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 503, + 287, + 538 + ], + "spans": [ + { + "bbox": [ + 59, + 503, + 287, + 538 + ], + "type": "text", + "content": "- We compare action recognition methods on the created benchmarks to reveal their characteristics and validate the effectiveness of StillMix." + } + ] + } + ], + "index": 7 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 549, + 134, + 562 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 549, + 134, + 562 + ], + "spans": [ + { + "bbox": [ + 47, + 549, + 134, + 562 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": "Bias Evaluation. Biases are surface features that are easily learned by neural networks and strongly influence their predictions. Such features perform well on IID data [60, 29] but do not generalize to OOD data [53, 49]. In action recognition, models easily capture static bias [40, 41, 5, 63]. The following methods are used for bias evaluation: (1) Visualization techniques [15, 47] visualize the regions that models focus on to interpret the static bias qualitatively. (2) Proxy data or tasks. Synthetic videos with altered backgrounds [6], videos with white-noise textures [26], dynamic texture videos [21, 3] are used to reveal the bias toward backgrounds or texture. Proxy tasks evaluating temporal" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": "asymmetry, continuity, and causality are designed to show the static bias in video representations [18]. (3) Mutual information. [33] quantifies the static bias using mutual information between representations of different types of videos. Although these works evaluate the static bias in the whole video, they do not specify the source of static bias. In this paper, we create new benchmarks to pinpoint the source of static bias as the background and the foreground." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 169, + 546, + 409 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 169, + 546, + 409 + ], + "spans": [ + { + "bbox": [ + 304, + 169, + 546, + 409 + ], + "type": "text", + "content": "Bias Mitigation. Prevalent techniques of mitigating bias in action representations can be broadly classified into four categories. (1) Attribute supervision. [5] uses scene pseudolabels and human masks to discourage models from predicting scenes and recognizing actions without human, but it needs extra attribute labels. (2) Re-weighting. [40, 41] identify videos containing bias and downweight them in training, but [65] suggests merely weight adjustment is insufficient. (3) Context separation. [66] learns to separate action and contexts by collecting samples with similar contexts but different actions. (4) Data augmentation. Similar to the proposed StillMix, a few works utilize augmented videos. BE [63] mixes a frame from a video with other frames in the same video. ActorCutMix [78], FAME [10], ObjectMix [31] and FreqAug [30] carefully carve out the foreground (human actors or regions of motion), and replace the background with other images to create augmented training data. SSVC [73] and MCL [38] focus the models to the dynamic regions. However, these methods have not addressed static cues in the foreground." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 411, + 545, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 411, + 545, + 495 + ], + "spans": [ + { + "bbox": [ + 304, + 411, + 545, + 495 + ], + "type": "text", + "content": "A particular advantage of StillMix is that it does not require specially designed procedures to carve out the bias-inducing pixels within the frames like ActorCutMix [78] and FAME [10], or even to enumerate the source of bias like [5]. Rather, it automatically identifies bias-inducing frames using a reference network. Consequently, StillMix can suppress static bias in both the background and the foreground." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 496, + 545, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 496, + 545, + 592 + ], + "spans": [ + { + "bbox": [ + 304, + 496, + 545, + 592 + ], + "type": "text", + "content": "StillMix is also similar to two debiasing techniques designed for image recognition and text classification [48, 44], which use a reference network to identify bias-inducing data instances. However, StillMix exploits the special property of videos that they can be decomposed into individual frames. StillMix identifies bias-inducing components (frames) using 2D networks rather than whole data points as in [48, 44]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "text", + "content": "Action Recognition. 3D convolution or decomposed 3D convolutions [28, 58, 4, 61, 59, 42] are popular choices for action recognition. Two-stream architectures employ two modalities to classify actions, such as both RGB frames and optical flow [54, 64], or videos with two different frame rates and resolutions [14]. Multi-scale temporal convolutions or feature fusion are designed for fine-grained actions with strong temporal structures [75, 24, 39, 67]. Transformer networks are proposed to capture the long-range dependencies [1, 2, 46]. However, our understanding of the" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19913" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "content": "representations learned by these models remains limited. In this paper, we create benchmarks to evaluate what features are captured by action models and propose a simple data augmentation method that effectively improves the robustness of action models." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 145, + 183, + 160 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 145, + 183, + 160 + ], + "spans": [ + { + "bbox": [ + 47, + 145, + 183, + 160 + ], + "type": "text", + "content": "3. The StillMix Technique" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 167, + 287, + 298 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 167, + 287, + 298 + ], + "spans": [ + { + "bbox": [ + 46, + 167, + 287, + 298 + ], + "type": "text", + "content": "In order to learn robust and generalizable action representations that are invariant to static cues, we propose a simple but effective video data augmentation technique, StillMix. Instead of using manually designed rules to identify and remove biased data from the training set, as in ActorCutMix [78] and FAME [10], StillMix learns to identify still frames that induce biased representation using a neural network and mitigate static bias through mixing the identified frames with videos. As a result, StillMix offers a flexible bias suppression technique that works for both the background and the foreground." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "spans": [ + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": "We begin with some notations. We denote the " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "i^{\\mathrm{th}}" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": " video in the training set as tensor " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "\\pmb{x}_i\\in \\mathbb{R}^{C\\times T\\times H\\times W}" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": " are the number of channels, number of frames, height and width of the video, respectively. The associated ground-truth action label is " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "y_{i}" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": ". The video " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "\\pmb{x}_i" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": " contains a sequence of frames " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "\\langle \\pmb {z}_{i,j}\\rangle_{j = 1}^{T}" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "\\pmb {z}_{i,j}\\in \\mathbb{R}^{C\\times H\\times W}" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": ". The training set contains " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": " training video samples and is written as " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "\\{(x_i,y_i)\\}_{i = 1}^N" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": ". The goal of StillMix is to augment a given training sample " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "(x_{i},y_{i})" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": " into a transformed sample " + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "inline_equation", + "content": "(\\tilde{x}_i,\\tilde{y}_i)" + }, + { + "bbox": [ + 46, + 299, + 289, + 431 + ], + "type": "text", + "content": ". The procedures of StillMix are illustrated in Figure 2 and introduced as follows." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 437, + 287, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 496 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 496 + ], + "type": "text", + "content": "Step 1: Training the Reference Network. We identify bias-inducing frames using a 2D reference network that predicts the action label from a still frame of a video. As the still frame contains no motion, we expect the network to rely on static features to make the predictions." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 497, + 287, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 497, + 287, + 534 + ], + "spans": [ + { + "bbox": [ + 47, + 497, + 287, + 534 + ], + "type": "text", + "content": "Specifically, at every epoch we randomly sample a frame " + }, + { + "bbox": [ + 47, + 497, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_{i,j} \\in \\mathbb{R}^{C \\times H \\times W}" + }, + { + "bbox": [ + 47, + 497, + 287, + 534 + ], + "type": "text", + "content": " from each video " + }, + { + "bbox": [ + 47, + 497, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i" + }, + { + "bbox": [ + 47, + 497, + 287, + 534 + ], + "type": "text", + "content": ", and train the reference network " + }, + { + "bbox": [ + 47, + 497, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathcal{R}(\\cdot)" + }, + { + "bbox": [ + 47, + 497, + 287, + 534 + ], + "type": "text", + "content": " to predict the label " + }, + { + "bbox": [ + 47, + 497, + 287, + 534 + ], + "type": "inline_equation", + "content": "y_i" + }, + { + "bbox": [ + 47, + 497, + 287, + 534 + ], + "type": "text", + "content": ". The loss is" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 104, + 544, + 287, + 578 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 544, + 287, + 578 + ], + "spans": [ + { + "bbox": [ + 104, + 544, + 287, + 578 + ], + "type": "interline_equation", + "content": "L _ {r e f} = \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\ell \\left(\\mathcal {R} \\left(\\boldsymbol {z} _ {i, j}\\right), y _ {i}\\right), \\tag {1}", + "image_path": "3c997c8f70cdbaeea0d5dc122f3fb95cde4f40b2d480928abd981ae0549e6297.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "inline_equation", + "content": "\\ell(\\cdot)" + }, + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "text", + "content": " can be any classification loss, such as the cross-entropy. After training, the reference network " + }, + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "inline_equation", + "content": "\\mathcal{R}(\\cdot)" + }, + { + "bbox": [ + 46, + 588, + 287, + 635 + ], + "type": "text", + "content": " encodes the correlations between static cues within the frames and the action classes." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "content": "Step 2: Identifying Biased Frames. The output of reference network " + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{R}(\\pmb{z}_{i,j})" + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "content": " is a categorical distribution over action classes. We take the probability of the predicted class " + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "inline_equation", + "content": "p_{i,j} = \\max_k P(y = k|\\pmb{z}_{i,j})" + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "content": ". A high " + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "inline_equation", + "content": "p_{i,j}" + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "content": " indicates strong correlation between " + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\pmb{z}_{i,j}" + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "content": " and the action class, which means " + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\pmb{z}_{i,j}" + }, + { + "bbox": [ + 46, + 641, + 288, + 715 + ], + "type": "text", + "content": " can induce static bias. Therefore, we select frames with" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 72, + 495, + 85 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 495, + 85 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 495, + 85 + ], + "type": "text", + "content": "high " + }, + { + "bbox": [ + 305, + 72, + 495, + 85 + ], + "type": "inline_equation", + "content": "p_{i,j}" + }, + { + "bbox": [ + 305, + 72, + 495, + 85 + ], + "type": "text", + "content": " to construct the biased frame bank " + }, + { + "bbox": [ + 305, + 72, + 495, + 85 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 305, + 72, + 495, + 85 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 379, + 93, + 545, + 107 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 379, + 93, + 545, + 107 + ], + "spans": [ + { + "bbox": [ + 379, + 93, + 545, + 107 + ], + "type": "interline_equation", + "content": "S = \\left\\{\\boldsymbol {z} _ {i, j} \\mid p _ {i, j} \\geq p _ {\\tau} \\right\\}, \\tag {2}", + "image_path": "5dc82c22fe3496746c28d3186d7a2384a56cf4caf615536bcea8994b848a16e6.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 115, + 547, + 151 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 115, + 547, + 151 + ], + "spans": [ + { + "bbox": [ + 305, + 115, + 547, + 151 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 115, + 547, + 151 + ], + "type": "inline_equation", + "content": "p_{\\tau}" + }, + { + "bbox": [ + 305, + 115, + 547, + 151 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 305, + 115, + 547, + 151 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 305, + 115, + 547, + 151 + ], + "type": "text", + "content": "-th percentile value of " + }, + { + "bbox": [ + 305, + 115, + 547, + 151 + ], + "type": "inline_equation", + "content": "p_{i,j}" + }, + { + "bbox": [ + 305, + 115, + 547, + 151 + ], + "type": "text", + "content": ". In practice, we perform another round of uniformly random selection to control the size of the biased frame bank." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "spans": [ + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "text", + "content": "Step 3: Mixing Video and Biased Frames. To break the strong correlation between the biased frame and the action class, we mix a video of any action class with different biased frames identified above. Specifically, in each epoch, given a video sample " + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "inline_equation", + "content": "(x_{i},y_{i})" + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "text", + "content": ", we sample a frame " + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "inline_equation", + "content": "z^{\\mathrm{biased}}" + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "text", + "content": " from the biased frame bank " + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "text", + "content": " and tile it " + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "text", + "content": " times along the temporal dimension, yielding a static video with " + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "text", + "content": " identical frames. We denote this operation as " + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "inline_equation", + "content": "\\mathrm{Tile}(z^{\\mathrm{biased}},T)" + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "text", + "content": ". The augmented video sample " + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "inline_equation", + "content": "\\tilde{x}_i" + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "text", + "content": " is generated by the pixel-wise interpolation of " + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "inline_equation", + "content": "x_{i}" + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "text", + "content": " and the static video. The augmented video label " + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "inline_equation", + "content": "\\tilde{y}_i" + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "text", + "content": " is the same as the original action label " + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "inline_equation", + "content": "y_{i}" + }, + { + "bbox": [ + 304, + 156, + 545, + 289 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 332, + 299, + 545, + 312 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 332, + 299, + 545, + 312 + ], + "spans": [ + { + "bbox": [ + 332, + 299, + 545, + 312 + ], + "type": "interline_equation", + "content": "\\tilde {\\boldsymbol {x}} _ {i} = \\lambda \\boldsymbol {x} _ {i} + (1 - \\lambda) \\operatorname {T i l e} \\left(\\boldsymbol {z} ^ {\\text {b i a s e d}}, T\\right), \\quad \\tilde {y} _ {i} = y _ {i}, \\tag {3}", + "image_path": "66f5f1a99f573e4083c84578c6f349f3dcdb54c605fee5efe4a8ea7719bb1cdf.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 317, + 545, + 341 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 317, + 545, + 341 + ], + "spans": [ + { + "bbox": [ + 306, + 317, + 545, + 341 + ], + "type": "text", + "content": "where the scalar " + }, + { + "bbox": [ + 306, + 317, + 545, + 341 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 306, + 317, + 545, + 341 + ], + "type": "text", + "content": " is sampled from a Beta distribution " + }, + { + "bbox": [ + 306, + 317, + 545, + 341 + ], + "type": "inline_equation", + "content": "\\operatorname{Beta}(\\alpha, \\beta)" + }, + { + "bbox": [ + 306, + 317, + 545, + 341 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 342, + 545, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 342, + 545, + 437 + ], + "spans": [ + { + "bbox": [ + 304, + 342, + 545, + 437 + ], + "type": "text", + "content": "The rationale for keeping the video label unchanged after augmentation is that the static video contains no motion and does not affects the motion patterns in the mixed video, thus it should not contribute to the action label. This setting of StillMix can be intuitively understood as randomly permuting the labels of the static video, so that the network is forced to ignore the correlations between the static cues in the biased frames and actions." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 441, + 545, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 441, + 545, + 467 + ], + "spans": [ + { + "bbox": [ + 305, + 441, + 545, + 467 + ], + "type": "text", + "content": "Training with Augmented Videos. We apply StillMix to each video with a predefined probability " + }, + { + "bbox": [ + 305, + 441, + 545, + 467 + ], + "type": "inline_equation", + "content": "P_{\\mathrm{aug}}" + }, + { + "bbox": [ + 305, + 441, + 545, + 467 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 320, + 475, + 545, + 508 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 320, + 475, + 545, + 508 + ], + "spans": [ + { + "bbox": [ + 320, + 475, + 545, + 508 + ], + "type": "interline_equation", + "content": "\\left(\\boldsymbol {x} _ {i} ^ {*}, y _ {i} ^ {*}\\right) = \\left\\{ \\begin{array}{l l} \\left(\\boldsymbol {x} _ {i}, y _ {i}\\right) & a _ {i} = 0 \\\\ \\left(\\tilde {\\boldsymbol {x}} _ {i}, \\tilde {y} _ {i}\\right) & a _ {i} = 1 \\end{array} , a _ {i} \\sim \\operatorname {B e r} \\left(P _ {\\text {a u g}}\\right), \\right. \\tag {4}", + "image_path": "9cceb4aecf1980b57517e2d30212357ff492e6f677221ffd1acf440b08b37764.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 515, + 545, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 515, + 545, + 552 + ], + "spans": [ + { + "bbox": [ + 306, + 515, + 545, + 552 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 515, + 545, + 552 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 306, + 515, + 545, + 552 + ], + "type": "text", + "content": " is a scalar sampled from a Bernoulli distribution " + }, + { + "bbox": [ + 306, + 515, + 545, + 552 + ], + "type": "inline_equation", + "content": "Ber(P_{\\mathrm{aug}})" + }, + { + "bbox": [ + 306, + 515, + 545, + 552 + ], + "type": "text", + "content": ". The samples " + }, + { + "bbox": [ + 306, + 515, + 545, + 552 + ], + "type": "inline_equation", + "content": "\\{(x_i^*, y_i^*)\\}_{i=1}^N" + }, + { + "bbox": [ + 306, + 515, + 545, + 552 + ], + "type": "text", + "content": " are used to train the main network " + }, + { + "bbox": [ + 306, + 515, + 545, + 552 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 306, + 515, + 545, + 552 + ], + "type": "text", + "content": " using the following loss function:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 371, + 559, + 545, + 593 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 371, + 559, + 545, + 593 + ], + "spans": [ + { + "bbox": [ + 371, + 559, + 545, + 593 + ], + "type": "interline_equation", + "content": "L = \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\ell \\left(\\mathcal {F} \\left(\\boldsymbol {x} _ {i} ^ {*}\\right), y _ {i} ^ {*}\\right), \\tag {5}", + "image_path": "e45b85cf69d61c8024874aeebcedca7e9b542de8cefd686bd33bc3a51548a56b.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 601, + 479, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 601, + 479, + 613 + ], + "spans": [ + { + "bbox": [ + 306, + 601, + 479, + 613 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 601, + 479, + 613 + ], + "type": "inline_equation", + "content": "\\ell (\\cdot)" + }, + { + "bbox": [ + 306, + 601, + 479, + 613 + ], + "type": "text", + "content": " could be any classification loss." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": "Discussion. StillMix aims to learn robust action representations that generalize to OOD data. One popular formulation of OOD generalization [68, 34, 51, 35, 50] considers shortcut features as features that work under a specific environment but not others. For example, a classifier that excels in well-lit environments may perform terribly in dim environments. To learn robust classifiers, we ought to discover invariant features that work equally well in all environments." + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "19914" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "content": "More formally, the optimal predictor " + }, + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "inline_equation", + "content": "\\mathcal{F}^*" + }, + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "content": " can be found with the bi-level optimization" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 87, + 102, + 287, + 122 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 87, + 102, + 287, + 122 + ], + "spans": [ + { + "bbox": [ + 87, + 102, + 287, + 122 + ], + "type": "interline_equation", + "content": "\\mathcal {F} ^ {*} = \\underset {\\mathcal {F}} {\\operatorname {a r g m i n}} \\max _ {e} \\mathbb {E} _ {\\boldsymbol {x} ^ {e}, y ^ {e}} [ \\ell (\\mathcal {F} (\\boldsymbol {x} ^ {e}), y ^ {e}) ], \\tag {6}", + "image_path": "bf4bc26338e15100e6bbcda70f8179291710c3b38827a91a03a00a660af34887.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "spans": [ + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "content": "where the feature-label pair, " + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "inline_equation", + "content": "(\\pmb{x}^e,y^e)" + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "content": ", are drawn from the data distribution " + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "inline_equation", + "content": "P(\\pmb{x},y|e)" + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "content": " of environment " + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "inline_equation", + "content": "\\ell" + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "content": " is the per-sample loss. " + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "inline_equation", + "content": "\\pmb{x}^e" + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "content": " contains both class features and environment features; a good predictor " + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "content": " is sensitive to the former and ignores the latter. The optimization encourages this because if " + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "content": " utilizes features that work for environment " + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "inline_equation", + "content": "e_1" + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "content": " but not " + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "inline_equation", + "content": "e_2" + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "content": ", the loss will increase as the " + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "inline_equation", + "content": "\\max_e" + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "content": " operation will select " + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "inline_equation", + "content": "e_2" + }, + { + "bbox": [ + 46, + 129, + 287, + 223 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 224, + 287, + 297 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 224, + 287, + 297 + ], + "spans": [ + { + "bbox": [ + 46, + 224, + 287, + 297 + ], + "type": "text", + "content": "However, directly optimizing Eq. (6), such as in [51], requires sampling data from all environments, which is impractical due to skewed environment distributions. For example, videos of people playing soccer in tuxedos on beaches are exceedingly rare. Maximizing over all environments is also challenging." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "spans": [ + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "text", + "content": "The mixing operation in StillMix may be understood in the same framework. A static frame " + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "inline_equation", + "content": "z^{\\mathrm{biased}}" + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "text", + "content": " can be considered as coming from an environment " + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "inline_equation", + "content": "e'" + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "text", + "content": " which biases predictions toward certain action labels. Mixing " + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "inline_equation", + "content": "z^{\\mathrm{biased}}" + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "inline_equation", + "content": "x_{i}" + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "text", + "content": " simulates sampling " + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "inline_equation", + "content": "x^{e'}" + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "text", + "content": " from the environment " + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "inline_equation", + "content": "e'" + }, + { + "bbox": [ + 46, + 297, + 287, + 369 + ], + "type": "text", + "content": ". StillMix may be considered to optimize the following loss," + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 87, + 374, + 287, + 397 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 87, + 374, + 287, + 397 + ], + "spans": [ + { + "bbox": [ + 87, + 374, + 287, + 397 + ], + "type": "interline_equation", + "content": "\\mathcal {F} ^ {*} = \\underset {\\mathcal {F}} {\\operatorname {a r g m i n}} \\mathbb {E} _ {e} \\left[ \\mathbb {E} _ {\\boldsymbol {x} ^ {e}, y ^ {e}} [ \\ell (\\mathcal {F} (\\boldsymbol {x} ^ {e}), y ^ {e}) ] \\right], \\tag {7}", + "image_path": "236d1d3c4dc345072171a4eb44092e3487ac648d28aa7138fca5bdfed3577c0b.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 403, + 287, + 439 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 403, + 287, + 439 + ], + "spans": [ + { + "bbox": [ + 47, + 403, + 287, + 439 + ], + "type": "text", + "content": "which replaces the maximization over environments in Eq. (6) with an expectation over environments due to the random sampling of " + }, + { + "bbox": [ + 47, + 403, + 287, + 439 + ], + "type": "inline_equation", + "content": "z^{\\mathrm{biased}}" + }, + { + "bbox": [ + 47, + 403, + 287, + 439 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 448, + 270, + 460 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 448, + 270, + 460 + ], + "spans": [ + { + "bbox": [ + 47, + 448, + 270, + 460 + ], + "type": "text", + "content": "4. SCUBA and SCUFO: OOD Benchmarks" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 468, + 287, + 516 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 468, + 287, + 516 + ], + "spans": [ + { + "bbox": [ + 47, + 468, + 287, + 516 + ], + "type": "text", + "content": "To quantitatively evaluate static bias in the background and the foreground, we create OOD benchmarks based on three commonly used video datasets, i.e., HMDB51 [36], UCF101 [55] and Kinetics-400 [4], as detailed below." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 522, + 275, + 536 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 522, + 275, + 536 + ], + "spans": [ + { + "bbox": [ + 47, + 522, + 275, + 536 + ], + "type": "text", + "content": "4.1. Foreground Masks and Background Images" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 540, + 287, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 540, + 287, + 659 + ], + "spans": [ + { + "bbox": [ + 46, + 540, + 287, + 659 + ], + "type": "text", + "content": "Foreground Masks. To extract the foreground area of actions, we use available human-annotated masks of people for UCF101 and HMDB51. There are totally 910 videos in the UCF101 test set and 256 videos in the HMDB51 test set having foreground annotations. Since there is no human-annotated masks for Kinetics-400, we use video segmentation models [57, 56] to generate foreground masks. After filtering out the videos with small foreground masks (likely to be wrong), we obtain totally 10,190 videos in the Kinetics-400 validation set to construct the benchmark." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 665, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 665, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 665, + 287, + 713 + ], + "type": "text", + "content": "Background Images. In order to synthesize diverse test videos, we collect background images from three different image sources: 1) the test set of Place365 [76]. 2) images generated by VQGAN-CLIP [8] from a random scene" + } + ] + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 310, + 69, + 384, + 117 + ], + "blocks": [ + { + "bbox": [ + 310, + 69, + 384, + 117 + ], + "lines": [ + { + "bbox": [ + 310, + 69, + 384, + 117 + ], + "spans": [ + { + "bbox": [ + 310, + 69, + 384, + 117 + ], + "type": "image", + "image_path": "e32537a5d83988613f069bec27e332612ffd75abc2bb9813a237f71cf0220241.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 323, + 119, + 370, + 129 + ], + "lines": [ + { + "bbox": [ + 323, + 119, + 370, + 129 + ], + "spans": [ + { + "bbox": [ + 323, + 119, + 370, + 129 + ], + "type": "text", + "content": "(a) Place365" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 386, + 70, + 462, + 115 + ], + "blocks": [ + { + "bbox": [ + 386, + 70, + 462, + 115 + ], + "lines": [ + { + "bbox": [ + 386, + 70, + 462, + 115 + ], + "spans": [ + { + "bbox": [ + 386, + 70, + 462, + 115 + ], + "type": "image", + "image_path": "f3bdb01d696d78843f7f15aab06bd4cb02b5517749a4b770b17263b3464262ac.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 135, + 545, + 195 + ], + "lines": [ + { + "bbox": [ + 305, + 135, + 545, + 195 + ], + "spans": [ + { + "bbox": [ + 305, + 135, + 545, + 195 + ], + "type": "text", + "content": "Figure 4: Background images from different sources. (a) An image from Place365. (b) An image generated by VQGAN-CLIP from the query \"A painting of a conference room in the style of surreal art\". (c) An image of randomly generated sinusoidal stripes." + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 465, + 69, + 541, + 115 + ], + "blocks": [ + { + "bbox": [ + 390, + 119, + 460, + 129 + ], + "lines": [ + { + "bbox": [ + 390, + 119, + 460, + 129 + ], + "spans": [ + { + "bbox": [ + 390, + 119, + 460, + 129 + ], + "type": "text", + "content": "(b) VQGAN-CLIP" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 465, + 69, + 541, + 115 + ], + "lines": [ + { + "bbox": [ + 465, + 69, + 541, + 115 + ], + "spans": [ + { + "bbox": [ + 465, + 69, + 541, + 115 + ], + "type": "image", + "image_path": "f46bc9432e2a971c31aa545278859615ec74b415cfbc900d37b4049831255401.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 480, + 119, + 526, + 129 + ], + "lines": [ + { + "bbox": [ + 480, + 119, + 526, + 129 + ], + "spans": [ + { + "bbox": [ + 480, + 119, + 526, + 129 + ], + "type": "text", + "content": "(c) Sinusoid" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 214, + 545, + 286 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 214, + 545, + 286 + ], + "spans": [ + { + "bbox": [ + 305, + 214, + 545, + 286 + ], + "type": "text", + "content": "category of Place365 and a random artistic style. 3) randomly generated images with S-shaped stripes defined by sinusoidal functions. For each image source, we construct a background image pool. In Figure 4, we show three example background images from the three sources. More details are described in Sec. S2 of the Supplementary Material." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 293, + 424, + 304 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 293, + 424, + 304 + ], + "spans": [ + { + "bbox": [ + 306, + 293, + 424, + 304 + ], + "type": "text", + "content": "4.2. Test Video Synthesis" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "spans": [ + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "type": "text", + "content": "Testing for Background Static Cues. Given a video " + }, + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "type": "inline_equation", + "content": "\\pmb{x}" + }, + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "type": "text", + "content": " frames " + }, + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "type": "inline_equation", + "content": "\\{\\pmb{x}_t\\}_{t=1}^T" + }, + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "type": "text", + "content": ", we create a synthetic video " + }, + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{x}}" + }, + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "type": "text", + "content": " by combining the foreground of " + }, + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "type": "inline_equation", + "content": "\\pmb{x}" + }, + { + "bbox": [ + 305, + 311, + 545, + 359 + ], + "type": "text", + "content": " and a background image sampled from a background image pool." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 336, + 365, + 545, + 379 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 336, + 365, + 545, + 379 + ], + "spans": [ + { + "bbox": [ + 336, + 365, + 545, + 379 + ], + "type": "interline_equation", + "content": "\\hat {\\boldsymbol {x}} _ {t} = \\boldsymbol {m} _ {t} \\odot \\boldsymbol {x} _ {t} + (1 - \\boldsymbol {m} _ {t}) \\odot \\operatorname {T i l e} (\\boldsymbol {z} ^ {\\mathrm {b g}}, T), \\tag {8}", + "image_path": "d792ba39f4f060ff56e172bd89dad9dad457b39f10163c02fc4b3347df80684b.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "spans": [ + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "inline_equation", + "content": "m_t" + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "text", + "content": " is the foreground mask, " + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "text", + "content": " denotes pixel-wise multiplication, " + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "inline_equation", + "content": "z^{\\mathrm{bg}}" + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "text", + "content": " is a background image sampled from the image pool. " + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "inline_equation", + "content": "\\mathrm{Tile}(z^{\\mathrm{bg}}, T)" + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "text", + "content": " repeats " + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "inline_equation", + "content": "z^{\\mathrm{bg}}T" + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "text", + "content": " times along the temporal dimension. For each video with foreground masks, we pair it with " + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "text", + "content": " randomly selected background images from each of the 3 background image pools to synthesize " + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "inline_equation", + "content": "3m" + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "text", + "content": " videos. We set " + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "inline_equation", + "content": "m = 10,5,1" + }, + { + "bbox": [ + 305, + 385, + 545, + 504 + ], + "type": "text", + "content": " for HMDB51, UCF101 and Kinetics-400, respectively, since HMDB51 and UCF101 have fewer videos with foreground masks and we would like to increase the diversity of the synthetic videos." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 305, + 506, + 545, + 577 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 506, + 545, + 577 + ], + "spans": [ + { + "bbox": [ + 305, + 506, + 545, + 577 + ], + "type": "text", + "content": "The generated videos retain the original action foreground, including the human actors and their motion, on new random backgrounds. They are designed to test bias toward static cues from the background, and are named SCUBA videos. We expect models invariant to static backgrounds to obtain high classification accuracy on SCUBA." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 305, + 582, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 582, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 305, + 582, + 545, + 689 + ], + "type": "text", + "content": "Testing for Foreground Static Cues. In addition, we create another set of videos to test the amount of foreground static bias in the learned representations. Foreground static cues include people and object attributes, such as bicycle helmets for cycling and bows for archery — people can ride a bicycle without helmets or hold bows when not performing archery. As the SCUBA videos contain most foreground elements in the original videos, they cannot distinguish whether models rely on foreground static cues." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "To this end, we create videos that contain only a single frame. Specifically, from each SCUBA video, we ran" + } + ] + } + ], + "index": 26 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19915" + } + ] + } + ], + "index": 27 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 87, + 288, + 200 + ], + "blocks": [ + { + "bbox": [ + 75, + 71, + 259, + 82 + ], + "lines": [ + { + "bbox": [ + 75, + 71, + 259, + 82 + ], + "spans": [ + { + "bbox": [ + 75, + 71, + 259, + 82 + ], + "type": "text", + "content": "Table 1: Statistics of the created benchmarks." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 87, + 288, + 200 + ], + "lines": [ + { + "bbox": [ + 48, + 87, + 288, + 200 + ], + "spans": [ + { + "bbox": [ + 48, + 87, + 288, + 200 + ], + "type": "table", + "html": "
Video Source# Original VideosBackground Source# Synthetic Videos# Domain Gap of SCUBA# Domain Gap of SCUFO
HMDB51256Place3652,5605.646±0.2765.745±0.290
VQGAN-CLIP2,5608.178±0.6858.307±0.533
Sinusoid2,56011.739±0.44411.998±0.932
UCF101910Place3654,55020.493±2.19920.829±2.093
VQGAN-CLIP4,55051.320±5.79055.202±9.477
Sinusoid4,55052.249±3.52252.534±5.930
Kinetics-40010,190Place36510,1906.094±0.2086.455±0.224
VQGAN-CLIP10,1907.504±0.2968.052±0.273
Sinusoid10,1907.211±0.3117.766±0.148
", + "image_path": "23247d1e9e37859697ce5af328bb5d525f09afaca2dc2846419a4b8e6edbdf06.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 231, + 287, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 231, + 287, + 327 + ], + "spans": [ + { + "bbox": [ + 46, + 231, + 287, + 327 + ], + "type": "text", + "content": "domly select one frame and repeat it temporally to create a video with zero motion. As these videos quantify the representation bias toward static cues in the foreground, we name them SCUFO videos. In SCUFO videos, the foreground static features are identical to the corresponding SCUBA videos, but the motion information is totally removed. Therefore, a model invariant to foreground static features should obtain low classification accuracy on them." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 327, + 287, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 327, + 287, + 388 + ], + "spans": [ + { + "bbox": [ + 46, + 327, + 287, + 388 + ], + "type": "text", + "content": "We summarize the dataset statistics in Table 1. SCUBA and SCUFO have the same number of videos for each pair of video source and background source. We also report the domain gap between original videos to show their OOD characteristics, as explained in the next section." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 399, + 162, + 411 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 399, + 162, + 411 + ], + "spans": [ + { + "bbox": [ + 47, + 399, + 162, + 411 + ], + "type": "text", + "content": "4.3. Quality Assessment" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 418, + 287, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 418, + 287, + 455 + ], + "spans": [ + { + "bbox": [ + 46, + 418, + 287, + 455 + ], + "type": "text", + "content": "We empirically verify that the SCUBA datasets retain the motion features of the original videos but replace background static features using the following two tests." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "text", + "content": "Human Assessment. To test if SCUBA preserves the motion information sufficiently for action recognition, we carry out an experiment on Amazon Mechanical Turk (AMT) to verify if human workers can recognize the actions in SCUBA videos." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 521, + 287, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 652 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 652 + ], + "type": "text", + "content": "From the same original video, we randomly sampled one synthetic video and asked the AMT workers if the moving parts in the video show the labeled action. The workers are given three options: yes, no, and can't tell. We also create control questions with original videos to detect random clicking and design control groups to prevent the workers from always answering yes to synthetic videos. The final answer for each video is obtained by majority voting of three workers. Workers who do not reach at least " + }, + { + "bbox": [ + 46, + 521, + 287, + 652 + ], + "type": "inline_equation", + "content": "75\\%" + }, + { + "bbox": [ + 46, + 521, + 287, + 652 + ], + "type": "text", + "content": " accuracy on the control questions are rejected. More details are described in Sec. S2 of the Supplementary Material." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "Collectively, the AMT workers were able to correctly recognize the actions in " + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "inline_equation", + "content": "96.15\\%" + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": " of UCF101-SCUBA, " + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "inline_equation", + "content": "86.33\\%" + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": " of HMDB51-SCUBA and " + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "inline_equation", + "content": "85.19\\%" + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": " of Kinetics400-SCUBA videos. We conclude that SCUBA videos preserve sufficient action information for humans to recognize." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 545, + 131 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 131 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 131 + ], + "type": "text", + "content": "Domain Gaps of the Static Features. To verify if SCUBA and SCUFO have successfully replaced the background static features and qualify as OOD test sets, we test if a classifier based on purely static features trained on IID videos can generalize to SCUBA and SCUFO." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 133, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 133, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 305, + 133, + 545, + 156 + ], + "type": "text", + "content": "Using a variation of scene representation bias [5], we define the domain gap " + }, + { + "bbox": [ + 305, + 133, + 545, + 156 + ], + "type": "inline_equation", + "content": "G_{\\text{scene}}" + }, + { + "bbox": [ + 305, + 133, + 545, + 156 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 334, + 165, + 545, + 177 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 334, + 165, + 545, + 177 + ], + "spans": [ + { + "bbox": [ + 334, + 165, + 545, + 177 + ], + "type": "interline_equation", + "content": "G _ {s c e n e} = A c c \\left(D _ {\\text {o r i}}, \\Phi_ {s c e n e}\\right) / A c c \\left(D _ {\\text {s y n}}, \\Phi_ {s c e n e}\\right). \\tag {9}", + "image_path": "c3378c6332ab8d284616b6f2473b64fc9633b802f5f3d53e82348f0f3adbd026.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "spans": [ + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "type": "text", + "content": "Here " + }, + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "type": "inline_equation", + "content": "\\Phi_{\\text{scene}}" + }, + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "type": "text", + "content": " is the average frame feature extracted from a ResNet-50 pretrained on Place365 [76]. Thus, the extracted feature captures static scene information, mostly from the background. We train a linear classifier on the original video training set and apply it to the original test set " + }, + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "type": "inline_equation", + "content": "D_{\\text{ori}}" + }, + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "type": "text", + "content": ", obtaining the accuracy " + }, + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "type": "inline_equation", + "content": "Acc(D_{\\text{ori}}, \\Phi_{\\text{scene}})" + }, + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "type": "text", + "content": ". After that, we apply the same classifier to the synthetic dataset " + }, + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "type": "inline_equation", + "content": "D_{\\text{syn}}" + }, + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "type": "text", + "content": ", obtaining the accuracy " + }, + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "type": "inline_equation", + "content": "Acc(D_{\\text{syn}}, \\Phi_{\\text{scene}})" + }, + { + "bbox": [ + 304, + 188, + 545, + 297 + ], + "type": "text", + "content": ". A higher ratio indicates greater domain gap with respect to static features." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 297, + 545, + 405 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 297, + 545, + 405 + ], + "spans": [ + { + "bbox": [ + 304, + 297, + 545, + 405 + ], + "type": "text", + "content": "In Table 1, we show the means and standard deviations computed from three random repeats of video synthesis. We observe large domain gaps, ranging from 5.6-fold to 52-fold decrease in accuracy on the synthetic test set. This demonstrates the static features of synthetic videos differ substantially from the original videos and the synthetic videos can serve as OOD tests. Moreover, the low standard deviations show that the effects of random sampling are marginal. In later experiments, we use the dataset from one random seed." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 419, + 388, + 433 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 419, + 388, + 433 + ], + "spans": [ + { + "bbox": [ + 306, + 419, + 388, + 433 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 440, + 545, + 476 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 440, + 545, + 476 + ], + "spans": [ + { + "bbox": [ + 305, + 440, + 545, + 476 + ], + "type": "text", + "content": "In this section, we compare the performance of several mainstream action recognition methods on IID and OOD test data and validate the effectiveness of StillMix." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 487, + 425, + 500 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 487, + 425, + 500 + ], + "spans": [ + { + "bbox": [ + 306, + 487, + 425, + 500 + ], + "type": "text", + "content": "5.1. Comparing Methods" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 506, + 545, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 506, + 545, + 579 + ], + "spans": [ + { + "bbox": [ + 304, + 506, + 545, + 579 + ], + "type": "text", + "content": "Action Recognition Models. (1) TSM [43], a temporal shift module learning spatiotemporal features with 2D CNN. (2) SlowFast [14], a two-branch 3D CNN learning spatiotemporal signals under two frame rates. (3) Video Swin Transformer [46], an adapted Swin Transformer [45] for videos. We use the tiny version, denoted as Swin-T." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "Video Data Augmentation and Debiasing Methods. We compare the debiasing performance of several video data augmentation and debiasing methods by adapting them to supervised action recognition. (1) Mixup [72] and VideoMix [70]. (2) SDN [5]. (3) BE [63], ActorCutMix[78] and FAME [10]. We adapt these three self-supervised debiasing methods as data augmentations, which carve out the foreground and replace the background as in the original papers. All the data augmentation techniques are applied stochastically as in [19]. More implementation details are described in Sec. S3 of the Supplementary Material." + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "19916" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 140, + 298, + 345 + ], + "blocks": [ + { + "bbox": [ + 46, + 70, + 288, + 131 + ], + "lines": [ + { + "bbox": [ + 46, + 70, + 288, + 131 + ], + "spans": [ + { + "bbox": [ + 46, + 70, + 288, + 131 + ], + "type": "text", + "content": "Table 2: IID and OOD test accuracy (\\%) of augmentation and debiasing methods on Kinetics-400. † indicates adaptation from self-supervised debiasing methods. ConfI-FG denotes synthetic videos with conflicting foreground cues. All models are pretrained on ImageNet." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 47, + 140, + 298, + 345 + ], + "lines": [ + { + "bbox": [ + 47, + 140, + 298, + 345 + ], + "spans": [ + { + "bbox": [ + 47, + 140, + 298, + 345 + ], + "type": "table", + "html": "
ModelAugmentation or DebiasingIIDOOD
Avg SCUBA↑Avg SCUFO↓Contra Acc.↑Confl-FG↑ARAS↑
TSMNo71.1337.3917.2222.8020.1557.86
Mixup71.3340.8117.5325.9823.4858.05
VideoMix71.3538.8717.2524.5723.4356.61
SDN69.9936.9516.5522.3820.2955.06
BE†71.3037.8916.0824.3520.1157.47
ActorCutMix†71.0740.4216.2926.5221.4157.09
FAME†71.1340.9118.3425.6324.4157.47
StillMix (Ours)71.2840.485.2336.0725.7359.69
Swin-TNo73.9541.7418.1725.9325.2560.17
Mixup73.9143.9517.9228.2427.6459.59
VideoMix73.8043.1719.2626.4029.3760.95
SDN72.2342.3421.4624.4627.1460.26
BE†73.9343.4019.5626.2826.6759.79
ActorCutMix†73.9745.7019.3928.6429.0261.23
FAME†73.8148.7921.2730.0329.5060.37
StillMix (Ours)73.8644.105.5139.4130.7762.49
", + "image_path": "93f3c4e89df01ddfdddad11244c6b117f606b3ad923d441281ec94024a25ad8a.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 364, + 160, + 376 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 364, + 160, + 376 + ], + "spans": [ + { + "bbox": [ + 47, + 364, + 160, + 376 + ], + "type": "text", + "content": "5.2. Evaluation Metrics" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 384, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 384, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 384, + 287, + 479 + ], + "type": "text", + "content": "We conduct the following experiments on Kinetics-400, UCF101 and HMDB51. First, we perform IID tests on the original test sets and use the top-1 accuracy as metrics. After that, we perform OOD tests on SCUBA and SCUFO and report the average top-1 accuracy across background image sources. Note that higher accuracy on SCUBA is better (low background static bias), while lower accuracy on SCUFO is better (low foreground static bias)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 480, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 480, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 480, + 287, + 552 + ], + "type": "text", + "content": "To show the performance of utilizing pure foreground motion information, we propose another performance metric called contrasted accuracy (Contra. Acc.). As one SCUFO video is derived from a SCUBA video, we count one correct prediction if the model is correct on the SCUBA but incorrect on the associated SCUFO video." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 552, + 287, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 552, + 287, + 601 + ], + "spans": [ + { + "bbox": [ + 46, + 552, + 287, + 601 + ], + "type": "text", + "content": "We further evaluate on the synthetic videos with conflicting foreground cues (Figure 1). Finally, we also evaluate on ARAS [13], a real-world OOD dataset with rare scenes, to show the performance of scene bias reduction." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 610, + 248, + 623 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 610, + 248, + 623 + ], + "spans": [ + { + "bbox": [ + 47, + 610, + 248, + 623 + ], + "type": "text", + "content": "5.3. Results on IID and OOD Benchmarks" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": "Table 2, 3 and 4 compare the IID and OOD performance of different video data augmentation and debiasing methods on Kinetics-400, HMDB51 and UCF101. Given limited computational resources, we ran experiments on Kinetics-400 using a single seed. However, on the smaller HMDB51 and UCF101, we repeated experiments with three seeds. In Sec. S1 of the Supplementary Material, we provide more" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 307, + 117, + 553, + 291 + ], + "blocks": [ + { + "bbox": [ + 305, + 70, + 545, + 106 + ], + "lines": [ + { + "bbox": [ + 305, + 70, + 545, + 106 + ], + "spans": [ + { + "bbox": [ + 305, + 70, + 545, + 106 + ], + "type": "text", + "content": "Table 3: IID and OOD test accuracy " + }, + { + "bbox": [ + 305, + 70, + 545, + 106 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 305, + 70, + 545, + 106 + ], + "type": "text", + "content": " of augmentation and debiasing methods on HMDB51. All models are pretrained on Kinetics-400." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 117, + 553, + 291 + ], + "lines": [ + { + "bbox": [ + 307, + 117, + 553, + 291 + ], + "spans": [ + { + "bbox": [ + 307, + 117, + 553, + 291 + ], + "type": "table", + "html": "
ModelAugmentation or DebiasingIIDOOD
Avg SCUBA↑Avg SCUFO↓Contra. Acc.↑ConfI-FG↑
TSMNo70.39±0.5138.03±1.3919.23±1.3022.02±0.6425.44±1.31
Mixup72.00±0.4739.76±1.7219.08±1.3723.76±0.8426.94±1.23
VideoMix70.72±0.1235.71±1.5717.48±1.1121.03±0.5522.19±1.47
SDN69.51±0.3037.05±0.7317.60±0.3723.74±0.9528.38±0.87
BE71.22±0.2438.48±1.4219.45±1.0622.39±0.6725.21±1.35
ActorCutMix70.52±0.8238.40±0.5319.61±0.5621.94±0.4026.16±0.36
FAME70.39±0.8847.19±1.5222.33±0.9128.21±0.8933.98±2.09
StillMix71.52±0.3848.23±0.968.43±0.8842.05±0.9936.89±1.09
Swin-TNo73.92±0.7443.93±0.7820.46±0.7127.84±1.2836.58±1.65
Mixup74.58±0.4343.10±1.1321.17±0.6626.09±1.0536.62±2.98
VideoMix73.31±0.5339.39±0.7120.44±0.7323.13±0.5432.68±1.04
SDN74.66±0.8240.02±1.4820.22±1.2422.88±1.0534.87±2.43
BE74.31±0.4143.56±1.3819.96±0.7127.84±1.3235.99±0.67
ActorCutMix74.05±0.6046.79±1.3822.07±0.3628.12±1.2736.97±1.63
FAME73.79±0.2951.40±1.5426.92±0.7129.66±2.1139.61±1.87
StillMix74.82±0.4351.81±1.7813.39±0.7140.28±1.6147.38±1.50
", + "image_path": "917a6061fadc618684aabe51460f0a0175e2d468bef852f939d3595771e12639.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 307, + 358, + 553, + 533 + ], + "blocks": [ + { + "bbox": [ + 305, + 312, + 545, + 348 + ], + "lines": [ + { + "bbox": [ + 305, + 312, + 545, + 348 + ], + "spans": [ + { + "bbox": [ + 305, + 312, + 545, + 348 + ], + "type": "text", + "content": "Table 4: IID and OOD test accuracy " + }, + { + "bbox": [ + 305, + 312, + 545, + 348 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 305, + 312, + 545, + 348 + ], + "type": "text", + "content": " of augmentation and debiasing methods on UCF101. All models are pretrained on Kinetics-400." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 358, + 553, + 533 + ], + "lines": [ + { + "bbox": [ + 307, + 358, + 553, + 533 + ], + "spans": [ + { + "bbox": [ + 307, + 358, + 553, + 533 + ], + "type": "table", + "html": "
ModelAugmentation or DebiasingIIDOOD
Avg SCUBA↑Avg SCUFO↓Contra. Acc.↑ConfI-FG↑
TSMNo94.62±0.0825.60±1.364.21±0.8421.83±1.4827.68±1.35
Mixup94.71±0.1427.80±0.954.04±0.8124.17±1.0030.31±1.10
VideoMix94.50±0.1931.55±1.685.77±0.7426.69±1.3830.69±1.79
SDN93.84±0.2719.91±0.613.10±0.1917.19±0.5120.89±0.36
BE94.49±0.1425.91±1.374.62±0.8421.82±1.3828.06±1.32
ActorCutMix94.47±0.1538.11±1.484.56±0.1633.90±1.5138.12±2.12
FAME93.72±0.0935.72±1.153.67±0.5232.28±1.2834.58±0.93
StillMix94.30±0.1437.18±1.290.79±0.1236.47±1.2440.59±0.80
Swin-TNo96.21±0.1942.31±2.245.78±0.6836.82±2.1244.65±2.10
Mixup96.17±0.1446.16±1.745.93±0.4340.46±1.9647.16±2.82
VideoMix96.00±0.0241.40±1.1113.27±0.8529.37±0.9142.59±1.51
SDN95.76±0.1139.25±2.322.98±0.8836.42±1.7448.47±2.06
BE96.06±0.1143.98±0.805.54±0.9438.62±1.1346.62±0.96
ActorCutMix95.87±0.1958.61±0.4811.92±0.2546.87±0.4556.88±0.39
FAME95.81±0.1540.90±1.576.36±0.7135.14±1.6628.21±1.83
StillMix96.02±0.0858.22±0.413.44±0.5154.90±0.7757.30±0.60
", + "image_path": "7c9ca6dac70356264042faefa58b77255b0637b7755d4f70b9e2adb5c3d70f24.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 553, + 544, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 553, + 544, + 578 + ], + "spans": [ + { + "bbox": [ + 305, + 553, + 544, + 578 + ], + "type": "text", + "content": "detailed results (e.g., tests on videos with conflicting foreground cues and ARAS [13])." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 579, + 545, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 579, + 545, + 686 + ], + "spans": [ + { + "bbox": [ + 304, + 579, + 545, + 686 + ], + "type": "text", + "content": "OOD data cause performance degradation. Comparing the performance of TSM and Swin-T on IID and OOD tests, we observe that they perform much worse (more than " + }, + { + "bbox": [ + 304, + 579, + 545, + 686 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 304, + 579, + 545, + 686 + ], + "type": "text", + "content": ") on SCUBA than IID videos. Given that human workers can recognize the action in more than " + }, + { + "bbox": [ + 304, + 579, + 545, + 686 + ], + "type": "inline_equation", + "content": "85\\%" + }, + { + "bbox": [ + 304, + 579, + 545, + 686 + ], + "type": "text", + "content": " of SCUBA videos, the results indicate that the models are not robust to the domain shifts, probably due to the reliance of static background features; when the backgrounds are replaced, performance deterioration ensues." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "content": "IID tests do not fully reveal representation quality. Comparing the performance of different augmentation and debi" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19917" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "asing methods, we observe that all methods obtain similar accuracies on IID tests, which fall within a " + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "inline_equation", + "content": "2\\%" + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": " band. However, they show vastly different performance on SCUBA and SCUFO — the maximum difference is larger than " + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "inline_equation", + "content": "15\\%" + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": ". Therefore, we argue that IID tests alone may not be good indicators of the robustness of action representations." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 145, + 288, + 252 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 145, + 288, + 252 + ], + "spans": [ + { + "bbox": [ + 46, + 145, + 288, + 252 + ], + "type": "text", + "content": "In particular, VideoMix, SDN and BE provide little debiasing effects. Mixup leads to inconsistent performance gains. ActorCutMix and FAME consistently improve performance on SCUBA. Nevertheless, they decrease performance (increase accuracy) on SCUFO, which suggests that they improve performance on SCUBA partially by increasing reliance on foreground static features. The action features learned with ActorCutMix and FAME are likely still vulnerable to foreground static bias." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 258, + 287, + 378 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 258, + 287, + 378 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 287, + 378 + ], + "type": "text", + "content": "StillMix alleviates foreground and background static bias. StillMix boosts the performance on both SCUBA and SCUFO videos and obtains the best contrasted accuracy (Contra. Acc.). The significant improvements on SCUFO indicate that StillMix can suppress static bias from the entire video and not only the background. In addition, StillMix outperforms other methods on videos with conflicting foreground cues as well as ARAS. Overall, these results demonstrate the ability of StillMix to reduce static bias that is difficult to exhaustively name or pixel-wise cut out." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 388, + 274, + 402 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 388, + 274, + 402 + ], + "spans": [ + { + "bbox": [ + 47, + 388, + 274, + 402 + ], + "type": "text", + "content": "5.4. StillMix Improves Representation Learning" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 408, + 287, + 433 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 408, + 287, + 433 + ], + "spans": [ + { + "bbox": [ + 47, + 408, + 287, + 433 + ], + "type": "text", + "content": "We further investigate the effects of StillMix on improving representation learning through the following tests." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 437, + 287, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 534 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 534 + ], + "type": "text", + "content": "Transferring action features across datasets. We evaluate the representations learned with different augmentation and debiasing methods by their capability to transfer to different datasets. We adopt the linear probing protocol, which trains a linear classifier on the target dataset on top of the backbone network trained on the source dataset. Table 5 shows the results of TSM, where StillMix obtains the best performance, especially in transferring across small datasets." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 540, + 287, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 540, + 287, + 659 + ], + "spans": [ + { + "bbox": [ + 46, + 540, + 287, + 659 + ], + "type": "text", + "content": "Downstream weakly supervised action localization. We evaluate the representations learned with StillMix by their ability to improve downstream weakly supervised action localization. We pretrain TSM on Kinetics-400 with StillMix. After that, we extract RGB features for each video segments on THUMOS14 [25] and use the extracted features to train weakly supervised action localization models BaSNet [37] and CoLA [71]. StillMix improves the performance by more than " + }, + { + "bbox": [ + 46, + 540, + 287, + 659 + ], + "type": "inline_equation", + "content": "1.0\\%" + }, + { + "bbox": [ + 46, + 540, + 287, + 659 + ], + "type": "text", + "content": " of average mAP for BaSNet and more than " + }, + { + "bbox": [ + 46, + 540, + 287, + 659 + ], + "type": "inline_equation", + "content": "0.5\\%" + }, + { + "bbox": [ + 46, + 540, + 287, + 659 + ], + "type": "text", + "content": " of average mAP for CoLA." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 670, + 141, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 670, + 141, + 683 + ], + "spans": [ + { + "bbox": [ + 47, + 670, + 141, + 683 + ], + "type": "text", + "content": "5.5. Ablation Study" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "We conduct ablation study on UCF101 and HMDB51 to examine design choices of StillMix." + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 306, + 105, + 553, + 218 + ], + "blocks": [ + { + "bbox": [ + 305, + 71, + 545, + 95 + ], + "lines": [ + { + "bbox": [ + 305, + 71, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 305, + 71, + 545, + 95 + ], + "type": "text", + "content": "Table 5: Action recognition accuracy (%) of transferring features across Kinetics-400, UCF101, and HMDB51." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 306, + 105, + 553, + 218 + ], + "lines": [ + { + "bbox": [ + 306, + 105, + 553, + 218 + ], + "spans": [ + { + "bbox": [ + 306, + 105, + 553, + 218 + ], + "type": "table", + "html": "
Augmentation or DebiasingSource→Target
K400→UCFK400→HMDBHMDB→UCFUCF→HMDB
No92.5266.6761.6444.95
Mixup93.0768.6963.5846.60
VideoMix93.5569.2261.4940.33
SDN92.8163.7961.1241.90
BE93.1067.4562.7145.88
ActorCutMix92.7367.3961.6742.92
FAME93.8767.8458.8744.99
StillMix93.8970.0765.6947.99
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MethodFeatureDebiasingAvg mAP@IoU=[0.1:0.9]
BaSNetTSM (RGB)No0.1810
TSM (RGB)StillMix0.1935
CoLATSM (RGB)No0.2380
TSM (RGB)StillMix0.2436
", + "image_path": "32e312316be4057688d0f74a620980a362ebcbe01371ef76e5981186e15ae436.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 360, + 545, + 492 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 360, + 545, + 492 + ], + "spans": [ + { + "bbox": [ + 304, + 360, + 545, + 492 + ], + "type": "text", + "content": "Debiasing works the best when the reference network and the main network share the same architecture. We compare the results of StillMix with different network structures in Table 7. When the structures of the reference network and the main network are identical, the OOD performance is the best and the IID performance is very close to the best, indicating good bias mitigation. We hypothesize that networks with same architecture tend to learn the same bias. As a result, using a reference network with the same architecture as the main network could be the most effective at identifying bias-inducing frames." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 497, + 545, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 497, + 545, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 497, + 545, + 640 + ], + "type": "text", + "content": "Sampling biased frames improves debiasing. We compare three frame sampling strategies when constructing the biased frame bank: (1) No RefNet: the frame bank is uniformly sampled from the whole dataset; (2) RefNet: as in StillMix, we sample frames with high prediction probabilities from the reference network according to Eq. (2); (3) RefNet Inversed: contrary to StillMix, we sample frames with low prediction probabilities from the reference network, " + }, + { + "bbox": [ + 304, + 497, + 545, + 640 + ], + "type": "inline_equation", + "content": "S = \\{z_{i,j}|p_{i,j} < p_{\\tau}\\}" + }, + { + "bbox": [ + 304, + 497, + 545, + 640 + ], + "type": "text", + "content": ". Table 8 shows results of ImageNet pretrained TSM and Swin-T. The reference network (RefNet) approach achieves the best OOD performance, whereas RefNet Inversed performs the worst." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": "We observe the difference between RefNet and No RefNet is small on UCF101 but is large on HMDB51. We attribute this to the prevalence of bias-inducing frames in UCF101. MMAction2 [7] trained TSN [64] using only three frames per video on UCF101 and achieved " + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "inline_equation", + "content": "83.03\\%" + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": " classification accuracy but achieved only " + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "inline_equation", + "content": "48.95\\%" + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": " with 8" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19918" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 59, + 115, + 276, + 258 + ], + "blocks": [ + { + "bbox": [ + 46, + 70, + 288, + 106 + ], + "lines": [ + { + "bbox": [ + 46, + 70, + 288, + 106 + ], + "spans": [ + { + "bbox": [ + 46, + 70, + 288, + 106 + ], + "type": "text", + "content": "Table 7: Action recognition accuracy (%) of StillMix with different reference network structures. All networks are pretrained on ImageNet." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 59, + 115, + 276, + 258 + ], + "lines": [ + { + "bbox": [ + 59, + 115, + 276, + 258 + ], + "spans": [ + { + "bbox": [ + 59, + 115, + 276, + 258 + ], + "type": "table", + "html": "
Main NetworkReference NetworkUCF101HMDB51
IIDContra. Acc.IIDContra. Acc.
TSMResNet50-2D87.2924.6054.6633.14
SlowFast-2D87.4422.2055.0330.51
Swin-T-2D86.7223.0855.0531.62
SlowFastResNet50-2D84.8518.8650.7420.89
SlowFast-2D84.9619.7651.5321.21
Swin-T-2D85.1619.1851.8520.28
Swin-TResNet50-2D88.5931.0956.1018.44
SlowFast-2D88.6029.3454.4319.25
Swin-T-2D88.9232.1455.3621.40
", + "image_path": "e69887ada079cd1a3f37a0df137fde67046374dd5fd8697a80cb9c12f8368763.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 55, + 311, + 279, + 453 + ], + "blocks": [ + { + "bbox": [ + 46, + 277, + 287, + 301 + ], + "lines": [ + { + "bbox": [ + 46, + 277, + 287, + 301 + ], + "spans": [ + { + "bbox": [ + 46, + 277, + 287, + 301 + ], + "type": "text", + "content": "Table 8: Action recognition accuracy (\\%) of StillMix with different frame sampling strategies." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 55, + 311, + 279, + 453 + ], + "lines": [ + { + "bbox": [ + 55, + 311, + 279, + 453 + ], + "spans": [ + { + "bbox": [ + 55, + 311, + 279, + 453 + ], + "type": "table", + "html": "
Main NetworkSampling StrategyUCF101HMDB51
IIDContra. Acc.IIDContra. Acc.
TSMNo RefNet87.3924.4954.0731.21
RefNet87.2924.6054.6633.14
RefNet Inversed87.3823.5354.7929.17
SlowFastNo RefNet85.0318.9851.7920.94
RefNet84.9619.7651.5321.21
RefNet Inversed84.3318.7750.9418.61
Swin-TNo RefNet88.3731.2455.6218.89
RefNet88.9232.1455.3621.40
RefNet Inversed88.5930.5156.3418.18
", + "image_path": "b7bb0699cd9ad04bb376610fd1a555a825250e545a42c2a8756a8ad229d7e715.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 471, + 286, + 531 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 471, + 286, + 531 + ], + "spans": [ + { + "bbox": [ + 46, + 471, + 286, + 531 + ], + "type": "text", + "content": "frames on HMDB511. This shows many frames in UCF101 contain static cues correlated with the class labels. Random sampling can yield many bias-inducing frames on UCF101 but cannot do so on HMDB51, where the strength of RefNet becomes apparent." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 531, + 286, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 531, + 286, + 591 + ], + "spans": [ + { + "bbox": [ + 46, + 531, + 286, + 591 + ], + "type": "text", + "content": "In Sec. S1 of the Supplementary Material, we provide more ablation studies showing that mixing action labels in StillMix decreases performance and sufficient mixing strength (i.e., small values of " + }, + { + "bbox": [ + 46, + 531, + 286, + 591 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 531, + 286, + 591 + ], + "type": "text", + "content": " in Eq. (3)) is necessary for debiasing." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 598, + 268, + 611 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 598, + 268, + 611 + ], + "spans": [ + { + "bbox": [ + 47, + 598, + 268, + 611 + ], + "type": "text", + "content": "5.6. Performance on Something-Something-V2" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 616, + 286, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 616, + 286, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 616, + 286, + 676 + ], + "type": "text", + "content": "To validate the effectiveness of different debiasing methods on recognizing fine-grained actions with strong temporal structures, we perform tests on Something-Something-V2 [20]. In Table 9, we show the performance of different debiasing methods with TSM as the base model. Since SDN" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 361, + 103, + 491, + 201 + ], + "blocks": [ + { + "bbox": [ + 305, + 70, + 545, + 95 + ], + "lines": [ + { + "bbox": [ + 305, + 70, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 305, + 70, + 545, + 95 + ], + "type": "text", + "content": "Table 9: Action recognition accuracy (\\%) of different debiasing methods on Something-Something-V2." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 361, + 103, + 491, + 201 + ], + "lines": [ + { + "bbox": [ + 361, + 103, + 491, + 201 + ], + "spans": [ + { + "bbox": [ + 361, + 103, + 491, + 201 + ], + "type": "table", + "html": "
DebiasingAccuracy
No57.49
Mixup57.86
VideoMix58.23
BE57.68
FAME58.10
StillMix (Ours)58.68
", + "image_path": "14345ebfe0e8c8b1e0d47ac2010ac984d47033d67f00f14f085c8ae7b687af2b.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 220, + 545, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 220, + 545, + 281 + ], + "spans": [ + { + "bbox": [ + 304, + 220, + 545, + 281 + ], + "type": "text", + "content": "and ActorCutMix require bounding boxes of human, which are time-consuming to extract, we did not include the results of these two methods. The results show that StillMix outperforms other data augmentation methods, illustrating its effectiveness on fine-grained action videos." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 292, + 457, + 304 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 292, + 457, + 304 + ], + "spans": [ + { + "bbox": [ + 305, + 292, + 457, + 304 + ], + "type": "text", + "content": "6. Conclusion and Discussion" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 312, + 545, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 545, + 455 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 545, + 455 + ], + "type": "text", + "content": "To learn robust and generalizable action representations, we explore techniques that mitigate static bias in both the background and the foreground. We propose a simple yet effective video data augmentation method, StillMix, and create two new sets of OOD benchmarks, SCUBA and SCUFO, to quantify static bias in the background and the foreground. Through extensive evaluation, we conclude that StillMix mitigates static bias in the background and the foreground and improves the performance of transferring learning and downstream tasks. In contrast, existing debi-asing methods remain vulnerable to foreground static bias despite their robustness to background static bias." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 455, + 545, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 455, + 545, + 525 + ], + "spans": [ + { + "bbox": [ + 304, + 455, + 545, + 525 + ], + "type": "text", + "content": "Despite the strengths of StillMix on mitigating static bias in the background and the foreground, it has the following limitations: (1) additional computational overhead in training the reference network (about " + }, + { + "bbox": [ + 304, + 455, + 545, + 525 + ], + "type": "inline_equation", + "content": "8\\%" + }, + { + "bbox": [ + 304, + 455, + 545, + 525 + ], + "type": "text", + "content": " of the training time of the main network); and (2) little improvement (and little degradation) on IID tests." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 526, + 545, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 526, + 545, + 574 + ], + "spans": [ + { + "bbox": [ + 304, + 526, + 545, + 574 + ], + "type": "text", + "content": "For future work, we believe that evaluating static bias in large pretrained models with the created benchmarks and adapting StillMix to mitigate static bias in such models would be promising directions." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 586, + 403, + 599 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 586, + 403, + 599 + ], + "spans": [ + { + "bbox": [ + 306, + 586, + 403, + 599 + ], + "type": "text", + "content": "Acknowledgments" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "This work has been supported by the Nanyang Associate Professorship and the National Research Foundation Fellowship (NRF-NRFF13-2021-0006), Singapore. The computational work for this article was partially performed on resources of the National Supercomputing Centre, Singapore (https://www.nscc.sg). Any opinions, findings, conclusions, or recommendations expressed in this material are those of the authors and do not reflect the views of the funding agencies." + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 683, + 284, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 683, + 284, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 683, + 284, + 713 + ], + "type": "text", + "content": "1https://github.com/open-mmlab/mmaction2/blob/02a06bb3180e951b00cccbeb48dab055f95acd1a7/configs/recognition/tsn/README.md" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19919" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 289, + 714 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Anurag Arnab, Mostafa Dehghani, Georg Heigold, Chen Sun, Mario Lučić, and Cordelia Schmid. 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Learning representational invariances for data-efficient action recognition. arXiv preprint arXiv:2103.16565, 2021. 2, 3, 4, 6" + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19923" + } + ] + } + ], + "index": 6 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 12 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/c288d48a-0e97-49d8-951a-99b2d027811b_content_list.json b/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/c288d48a-0e97-49d8-951a-99b2d027811b_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..f0b6a0b66706217c62dbb03a6a5c59e21c4b6aed --- /dev/null +++ b/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/c288d48a-0e97-49d8-951a-99b2d027811b_content_list.json @@ -0,0 +1,1576 @@ +[ + { + "type": "text", + "text": "MixBag: Bag-Level Data Augmentation for Learning from Label Proportions", + "text_level": 1, + "bbox": [ + 94, + 130, + 875, + 154 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Takanori Asanomi1, Shinnosuke Matsuo1, Daiki Suehiro1,2, Ryoma Bise1 \n1Kyushu University, Fukuoka, Japan \n2RIKEN AIP, Japan", + "bbox": [ + 192, + 179, + 772, + 219 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{takanori.asanomi@human., shinnosuke.matsuo@human., suehiro@, bise@}ait.kyushu-u.ac.jp", + "bbox": [ + 104, + 219, + 864, + 234 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Learning from label proportions (LLP) is a promising weakly supervised learning problem. In LPP, a set of instances (bag) has label proportions, but no instance-level labels are given. LPP aims to train an instance-level classifier by using the label proportions of the bag. In this paper, we propose a bag-level data augmentation method for LPP called MixBag, based on the key observation from our preliminary experiments; that the instance-level classification accuracy improves as the number of labeled bags increases even though the total number of instances is fixed. We also propose a confidence interval loss designed based on statistical theory to use the augmented bags effectively. To the best of our knowledge, this is the first attempt to propose bag-level data augmentation for LPP. The advantage of MixBag is that it can be applied to instance-level data augmentation techniques and any LPP method that uses the proportion loss. Experimental results demonstrate this advantage and the effectiveness of our method.", + "bbox": [ + 73, + 300, + 473, + 574 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 602, + 209, + 618 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In general classification tasks, a model is trained on datasets where each piece of data (instance) has class labels. However, instance-level annotations cost a lot, and there are many cases in which instance-level annotation cannot be disclosed to the public for privacy reasons [23]. In such a situation, we only know the label proportions given to a set of instances (bag) and must train a model from these label proportions to classify each instance. This problem setting is known as learning from label proportions (LLP) [1].", + "bbox": [ + 75, + 628, + 468, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Figure 1 illustrates the problem setup of LLP. A bag $B$ consists of instances (e.g., images). Bag-level labels are given as training data instead of instance-level labels (class labels of each instance $x$ are unknown). The label proportion $\\mathbf{p}^i$ of bag $B^i$ is given as a bag-level label. For example, if a bag $B^0$ contains 60, 100, and 40 instances of class 1, 2, and 3, respectively, $\\mathbf{p}^i = (0.3, 0.5, 0.2)^{\\mathrm{T}}$ . LLP aims to train an instance-level classifier by using the label proportions of a bag. It is a weakly supervised learning task.", + "bbox": [ + 75, + 763, + 470, + 902 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/29b2be03f814735205653ecffdf7aa9552c9466c46f69a0596f89fd816f90fcd.jpg", + "image_caption": [ + "Figure 1. Illustration of learning from label proportions. LLP aims to train an instance-level classifier by using label proportions of a bag as training data instead of instance-level labels." + ], + "image_footnote": [], + "bbox": [ + 501, + 270, + 893, + 479 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Many LLP methods have been proposed to address this challenging task [1, 24, 28, 27, 18, 19]. Most of them are based on the proportion loss, which evaluates the difference between the given proportion $\\mathbf{p}^i$ and the estimated proportion $\\hat{\\mathbf{p}}^i$ , and can be calculated by taking the average of the class probabilities of the instances in a bag. The methods based on the proportion loss work well when bag-level labels (label proportions) are sufficient. However, the accuracy decreases as the number of labeled bags decreases, i.e., insufficient labeled data causes difficulty in training a network, which is known in machine learning tasks.", + "bbox": [ + 496, + 561, + 893, + 728 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In such cases, instance-level data augmentation is often an effective way to improve accuracy. Many instance-level data augmentation techniques, such as perturbation, for general classification tasks have been proposed, and their effectiveness has been demonstrated [25]. Instance-level data augmentation may improve the accuracy in LLP. However, it does not increase the number of labeled bags from the original one, and it is difficult to generate various bags with different proportions without using instance-level labels (these are unknown in LLP).", + "bbox": [ + 496, + 729, + 893, + 882 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "This paper proposes a bag-level data augmentation for", + "bbox": [ + 519, + 885, + 890, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "16570", + "bbox": [ + 480, + 924, + 519, + 936 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "LLP that can generate new bags with various label proportions. To design an effective bag-level data augmentation technique, we conducted a detailed analysis of what situation can improve the accuracy in LLP. As a result, we found an important observation that the accuracy improves as the number of labeled bags increases, even though the total number of instances is fixed, i.e., different bags overlap each other as shown in Figure 2 (Right). On the basis of this observation, we propose a bag-level data augmentation called MixBag. MixBag increases the number of labeled bags artificially by sampling instances from a pair of original bags and mixing them: this operation mimics the above observations. The expected label proportion of a generated mixed bag can be calculated by those of the original bags. However, it may have a gap from the actual proportion of the mixed bag because randomly selected instances do not follow the proportion of the original ones. This gap adversely affects the training.", + "bbox": [ + 75, + 90, + 472, + 362 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We thus introduce a confidence interval loss that helps to train a classification network by using the generated bags while avoiding this adverse effect by a proportion gap; it is statistically guaranteed. To the best of our knowledge, this is the first attempt to propose bag-level data augmentation for LLP. Experiments using eight datasets demonstrate the effectiveness of our method in various cases; our method improved the classification accuracy on all datasets. Our main contributions are summarized as follows.", + "bbox": [ + 75, + 363, + 472, + 498 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We examined how the number of labeled bags and the bag size affect the performance in LLP. From the preliminary experiments, we concluded that the accuracy improves as the number of labeled bags increases, even though the total number of instances is fixed.", + "- We proposed MixBag with a confidence interval loss. This method artificially increases the number of labeled bags, and the confidence interval loss helps train a classification network using the generated bags.", + "- We demonstrated that MixBag can be applied to any of the current LLP methods and any of the instance-level augmentation methods. Experimental results show that our method improved classification accuracy on various datasets." + ], + "bbox": [ + 96, + 505, + 468, + 734 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 76, + 746, + 215, + 762 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Learning from Label Proportion (LLP)", + "text_level": 1, + "bbox": [ + 76, + 771, + 413, + 787 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Proportion loss [1] is the most common approach to LLP. To compute the proportion loss, the average of the output probability in a bag is calculated as a proportion estimation, and then the bag-level cross-entropy between the true label proportion and the estimated proportion is used as the loss.", + "bbox": [ + 75, + 794, + 468, + 869 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The proportion loss has been extended in many methods; e.g., introducing regularization terms [33, 1, 8, 28, 30, 17,", + "bbox": [ + 75, + 869, + 468, + 901 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/14764b48d3c88aea555ea6770fdab8d130813c39af571648e8df54817e47cab0.jpg", + "image_caption": [ + "Figure 2. Illustration of overlap and non-overlap situations. (a) Original bags. (b) New bags (yellow) are added with non-overlap, i.e., the total number of instances increases. (c) New bags overlap with the original ones, i.e., the total number of instances is fixed." + ], + "image_footnote": [], + "bbox": [ + 500, + 90, + 893, + 224 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "18]. Tsai et al. [28] incorporated a consistency regularization into the proportion loss, which forces the network predictions to be consistent when its input is perturbed. Yang et al. [30] use contrastive learning for pre-training in a self-supervised learning manner and then train the model by using the proportion loss. LLP-GAN [17] introduces the generative adversarial network (GAN) to LLP. The fake instances created by the generator encourage the discriminator to distinguish real or fake and classify the real instances. This method also uses the proportion loss to train the classifier. Two-stage LLP [18] introduces pseudo-labeling after pre-training by using a proportion loss.", + "bbox": [ + 496, + 309, + 890, + 491 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "It is known that the classification accuracy decreases when the labeled data is insufficient in machine learning. To deal with this issue, data augmentation is a standard approach. However, bag-level data augmentation for LLP is still an unexplored area. This paper proposes a simple but effective bag-level data augmentation method. One of the advantages of our method is that any LLP method can be applied after our bag-level augmentation.", + "bbox": [ + 496, + 491, + 890, + 612 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Instance-level data Augmentation", + "text_level": 1, + "bbox": [ + 500, + 619, + 794, + 636 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Data augmentation is a standard way to address the problem of inadequately labeled data. Many instance-level data augmentation techniques have been proposed. Basic data augmentation involves adding perturbations to the original images, such as by flipping the image [25], adding noise [25], and erasing parts of an image [7, 2, 14]. Image mix [11, 35, 34, 10] is another approach, where methods such as MixUP [35] and CutMix [34] mix together two original images. GAN-based augmentation methods [22, 36, 26] represent data distributions and generate new images based on these distributions. Auto augment [3, 16, 4] automatically searches for suitable augmentation approaches that improved performance. The above methods are instance-level data augmentations. It is not a simple task to generate various bags that have different proportions without using instance-level labels. For example, CutMix and MixUp require the labels of the original im", + "bbox": [ + 496, + 643, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "16571", + "bbox": [ + 480, + 924, + 517, + 936 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ages (instances) in order to prepare the label proportions of a generated new bag. Since simple perturbation methods do not require the ground truth of the image label for augmentation, they can be used to add perturbations to each instance in a bag. However, these methods are not designed for bag-level data augmentation.", + "bbox": [ + 75, + 90, + 472, + 183 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Bag-Level data augmentation for MIL", + "text_level": 1, + "bbox": [ + 76, + 190, + 406, + 207 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Few bag-level data augmentation methods have been proposed for multiple instance learning (MIL), which trains a classifier from bag-level class labels (positive or negative). Li et al. [15] proposed a MIL-based method that uses bag-level augmentation for COVID-19 severity assessment. This method takes a pseudo-labeling approach, where positive and negative instances are taken from positive bags based on the estimated confidence of the instance class and used to make a new bag. Yang et al. [31] proposed a MIL method for segmenting pathology images. This method generates new bags by clustering instances. It is reasonable for MIL to make a positive or negative bag from high confidence positive or negative instances. However, it is difficult to make a proportion label from pseudo labeling since all of the pseudo labels have to be accurate to calculate the correct proportion. So in order to improve the performance of LLP, appropriately designing a bag-level data augmentation is required.", + "bbox": [ + 75, + 214, + 473, + 487 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Preliminary: LLP and Proportion Loss", + "text_level": 1, + "bbox": [ + 76, + 500, + 429, + 517 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In LLP, the training set contains $n$ bags, $B^1, \\ldots, B^n$ . Each bag $B^i$ consists of a set of instances, i.e., $B^i = \\{x_j^i\\}_{j=1}^{|B^i|}$ , and a vector of label proportions $\\mathbf{p}^i = (p_1^i, \\ldots, p_c^i, \\ldots, p_C^i)^T$ is attached to each bag as training label, where $C$ is the number of classes. This label indicates that $p_c^i \\times |B^i|$ instances in the $i$ -th bag belong to the class $c$ for any $c \\in \\{1, \\ldots, C\\}$ . The goal of LLP is to train a network that estimates the class label of each instance by using only the proportion labels of the bags. Proportion loss [1] is a standard approach to this challenging task, and many methods are based on it.", + "bbox": [ + 75, + 523, + 468, + 696 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given training data with label proportions, the standard proportion loss is a bag-level cross-entropy between the ground-truth of the label proportion $\\mathbf{p}^i$ and the predicted proportion $\\hat{\\mathbf{p}}^i$ , which is the average of the output class probabilities in a bag. It is defined as:", + "bbox": [ + 75, + 696, + 470, + 772 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\ell_ {\\text {p r o p}} \\left(B ^ {i}, \\mathbf {p} ^ {i}, f\\right) = - \\sum_ {c = 1} ^ {C} p _ {c} ^ {i} \\log \\hat {p} _ {c} ^ {i}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 153, + 782, + 468, + 825 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {p} _ {c} ^ {i} = \\frac {1}{| B ^ {i} |} \\sum_ {j = 1} ^ {| B ^ {i} |} f \\left(x _ {j} ^ {i}\\right) _ {c}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 236, + 828, + 468, + 873 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $f(x_{j}^{i})_{c}$ is the output probability that $x_{j}^{i}$ belongs to $c$ .", + "bbox": [ + 76, + 883, + 467, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. Preliminary Empirical Analysis of LLP", + "text_level": 1, + "bbox": [ + 500, + 89, + 854, + 108 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In previous works, the relationship between the number of labeled bags, bag sizes, and accuracy in LLP has not been analyzed well. Some papers [17, 8] reported that the accuracy increased as the larger bag size in their experiments. However, the reason was not discussed well. In their experiments, they changed the bag size while the total number of instances was fixed. Since an instance generally does not belong to two bags (i.e., bags does not overlap each other) in LLP, it indicates that the bag size and the number of labeled bags have a trade-off; when the bag size increases, the number of labeled bags decreases.", + "bbox": [ + 496, + 116, + 890, + 282 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we further empirically analyze the relationships among the number of labeled bags, bag sizes, and accuracy by using the proportion loss on various public datasets. First, we conducted experiments on whether the number of labeled bags or the bag size has more influence on the classification accuracy in a general setup of LLP, where different bags do not contain the same instance (no overlap), as shown in Figure 2 (b). To avoid the tradeoff between the number of labeled bags and the bag size, we fixed the number of labeled bags to analyze the effect for accuracy by the number of labeled bags, and vice versa. In the experiments, the total number of instances changed. We speculated that this analysis may give clues for developing a new method in LLP.", + "bbox": [ + 496, + 282, + 892, + 494 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Datasets and experimental settings: We used eight datasets in our experiments1: 1) CIFAR10 [12], which is commonly used in classification tasks. The dataset contains ten classes, such as vehicles and animals; 2) SVHN [20], which is a house-number-images dataset, and a character-level label is given like in MNIST [6]; 3) OCT, which contains four classes of Retinal OCT images; 4) BLOOD, which contains eight classes of Blood Cell Microscope images; 5) ORGAN, 6) ORGANC, 7) ORGANS, which contain eleven classes of abdominal CT images. The difference is the view of the image and its sizes, and 8) PATH, which contains nine classes of colon pathology images. Note that 3) to 8) are datasets in MedMNIST [32], and we did not use the small datasets in [32] since they cannot be used to prepare enough bags for LLP.", + "bbox": [ + 496, + 502, + 892, + 729 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To prepare a bag, the proportions of each class were randomly selected from a Gaussian distribution; the decided proportion was used as the label of the bag. Then, samples were randomly selected from each class, in which the number of samples for each class followed the proportion of the class. In real applications, different bags do not contain the same instance; i.e., they do not overlap. We thus generated bags without overlap in these experiments.", + "bbox": [ + 496, + 729, + 890, + 851 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Performance when changing the number of labeled bags", + "text_level": 1, + "bbox": [ + 500, + 858, + 890, + 875 + ], + "page_idx": 2 + }, + { + "type": "page_footnote", + "text": "1Almost all papers on LLP use CIFAR10 and SVHN", + "bbox": [ + 517, + 886, + 797, + 898 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "16572", + "bbox": [ + 480, + 924, + 517, + 936 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/0099fcb638333b2d61d6a625b9b0140ba4f083ed6a2770a4bddb834a1cc7a997.jpg", + "image_caption": [ + "Figure 3. Relationship among the number of labeled bags, bag sizes, and accuracy in a general setup of LLP, where different bags do not contain the same instance (no overlap). Left: Accuracy improvement when increasing the number of labeled bags (bag size is fixed). Right: Accuracy improvement when increasing the bag size (the number of labeled bags is fixed)." + ], + "image_footnote": [], + "bbox": [ + 81, + 90, + 467, + 213 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "in the general setup of LLP (no overlap): We examined how the number of labeled bags affects the instance-level classification accuracy for the standard proportion loss. We varied the number of labeled bags (64, 128, 256, 512) while keeping the bag size fixed at 10. In this experiment, we follow the general setup of LLP; different bags do not overlap, i.e., the number of instances changed when the number of labeled bags was changed. As shown in Figure3 (Left), the accuracy improved due to increasing the number of labeled bags in all datasets. This is reasonable because the number of labeled bags indicates the number of proportion labels; more labeled data for training is expected to improve accuracy in machine learning.", + "bbox": [ + 75, + 327, + 468, + 523 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Performance when changing the bag size in the general setup of LLP (no overlap): We analyzed how the bag size affects the accuracy in the general setup of LLP. In this experiment, we changed the bag size (64, 128, 256, 512) but fixed the number of labeled bags at 10. As shown in Figure 3 (Right), the accuracy did not vary significantly with the bag size in six of the datasets, while it improved in two datasets. This result shows that increasing the number of instances without increasing the labels does not effectively improve accuracy.", + "bbox": [ + 75, + 531, + 468, + 681 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Performance when changing the number of labeled bags in the case of overlap: The above observations indicate that increasing the number of labeled bags is important to improving accuracy. Another factor that might have improved the accuracy is increasing the total number of 'instances,' which occurs when the number of labeled bags increases. To confirm whether the number of labeled bags or the total number of instances affects accuracy, we performed experiments on how the number of labeled bags affects the accuracy in the case of overlap, i.e., when the total number of instances was fixed. The initial bags were prepared, where the number of labeled bags was 64, and the bag size was 10. To increase the number of labeled bags, we then incrementally added new bags (64, 128, 256), where the new", + "bbox": [ + 75, + 688, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/37623f6381952cfeed9fd96eb9e80ac9cbd66c8b8f4dbf9f61efb323e2c84303.jpg", + "image_caption": [ + "Figure 4. Experimental results on how the number of labeled bags affects the accuracy in the case of overlap, i.e., when the total number of instances was fixed." + ], + "image_footnote": [], + "bbox": [ + 584, + 90, + 808, + 212 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "bags were generated from the initial instances that belong to the initial bags, i.e., generated bags overlap with the initial ones, as shown in Figure 2 (c). As shown in Figure4, the accuracy improves as the number of labeled bags increases in all datasets. This observation is important for our bag-level data augmentation. If we were to mimic this situation where the number of labeled bags increases and the total number of instances is fixed, it should improve accuracy, even though a situation with bags having overlaps is unnatural in actual applications. However, we can make this situation by generating new bags from the original ones.", + "bbox": [ + 496, + 281, + 890, + 448 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "5. MixBag with confidence interval loss", + "text_level": 1, + "bbox": [ + 500, + 460, + 831, + 479 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To mimic the situation of increasing the number of labeled bags and allowing their overlap, we propose MixBag, which is a bag-level data augmentation technique.", + "bbox": [ + 498, + 487, + 890, + 532 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "5.1. MixBag", + "text_level": 1, + "bbox": [ + 500, + 541, + 598, + 558 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Figure 5 (Left) shows an overview of MixBag. Given two randomly selected bags $\\{B^i, B^j\\}$ where each bag is labeled with a proportion, $\\mathbf{p}_i$ or $\\mathbf{p}_j$ , mix the two bags to generate a new bag. More precisely, $n_i = |B^i| \\times \\gamma$ and $n_j = |B^j| \\times (1 - \\gamma)$ instances are randomly sampled from $B^i$ and $B^j$ , respectively, where $\\gamma \\in [0,1]$ is a random variable, and the sampled sub-bags are denoted as $S^i$ and $S^j$ . Then, these two sub-bags are combined to generate a mixed bag, $B^k = S^i \\cup S^j$ . This generated mixed bag overlaps with the original bags while the total number of instances is fixed, and the number of labeled bags is increased by the generated bags. It can be considered to mimic the third preliminary experiment (Figure 2 (c)).", + "bbox": [ + 496, + 565, + 890, + 762 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "5.2. Confidence interval loss", + "text_level": 1, + "bbox": [ + 500, + 771, + 718, + 786 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The sampled sub-bags $S^i$ , $S^j$ are expected to have almost the same proportions as the original ones, $\\mathbf{p}^i$ and $\\mathbf{p}^j$ , if the randomly selected instances follow the proportion of the original bags. In this case, the expected proportion of the generated new bag $B^k$ is $\\mathbf{p}^k = \\gamma \\mathbf{p}^i + (1 - \\gamma) \\mathbf{p}^j$ . However, in practice, the actual proportion of randomly sampled instances may have some gaps from that of the original bag", + "bbox": [ + 496, + 794, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "16573", + "bbox": [ + 480, + 924, + 517, + 936 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/1ad0c9007d47146a42ca707d8e7d7a7451f1a385b987556d31981868ba61036b.jpg", + "image_caption": [ + "Figure 5. Overview of our method. Left: the way to create mixed bags and illustration of label proportion's probability. Right: confidence interval" + ], + "image_footnote": [], + "bbox": [ + 84, + 90, + 558, + 262 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/4db93041b724b2e6dc4a52c0a26c1e2388ade4397e54c597b28eabe5c38d0179.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 571, + 90, + 883, + 257 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "because the number of sampled instances in each class does not always follow the original proportion. This gap can be estimated by calculating the confidence interval (CI) for a population proportion.", + "bbox": [ + 75, + 319, + 468, + 380 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Let us denote the proportion of a class $c$ in the $i$ -th bag as $p_c^i$ . The standard deviation of the class $c$ proportion of the sampled sub-bag $S^i$ is defined as:", + "bbox": [ + 76, + 380, + 470, + 425 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\sigma_ {c} ^ {i} = \\sqrt {\\frac {p _ {c} ^ {i} \\left(1 - p _ {c} ^ {i}\\right)}{n _ {i}}}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 202, + 438, + 468, + 479 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $n_i = |B^i| \\times \\gamma$ is the number of instances randomly sampled from $B^i$ . This equation is well-known in statistics; it can be derived using the central limit theorem.", + "bbox": [ + 76, + 491, + 468, + 537 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The CI for the truth proportion $\\tilde{p}_c^i$ of the sub-bag $S^i$ is formulated as:", + "bbox": [ + 76, + 537, + 468, + 566 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\np _ {c} ^ {i} - \\alpha \\sigma_ {c} ^ {i} \\leq \\tilde {p} _ {c} ^ {i} \\leq p _ {c} ^ {i} + \\alpha \\sigma_ {c} ^ {i}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 176, + 579, + 468, + 598 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\alpha$ is set according to the desired degree of confidence, e.g., $95\\%$ . If we set the confidence to a higher value, $\\alpha$ becomes higher values. For the other sub-bag $S_{j}$ , the CI for the population proportion of $\\tilde{p}_c^j$ is formulated in the same manner.", + "bbox": [ + 75, + 609, + 468, + 683 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The CI for $\\tilde{p}_c^k$ , which is the proportion of the newly generated bag $B^{k}$ , is defined as:", + "bbox": [ + 75, + 685, + 468, + 715 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\np _ {c} ^ {k} - \\alpha \\sigma_ {c} ^ {k} \\leq \\tilde {p} _ {c} ^ {k} \\leq p _ {c} ^ {k} + \\alpha \\sigma_ {c} ^ {k}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 227, + 726, + 468, + 746 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\np _ {c} ^ {k} = \\gamma p _ {c} ^ {i} + (1 - \\gamma) p _ {c} ^ {j}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 269, + 747, + 468, + 767 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\gamma = \\frac {n _ {i}}{n _ {i} + n _ {j}}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 331, + 768, + 468, + 799 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\sigma_ {c} ^ {k} = \\gamma \\sqrt {\\frac {p _ {c} ^ {i} \\left(1 - p _ {c} ^ {i}\\right)}{n _ {i}}} + (1 - \\gamma) \\sqrt {\\frac {p _ {c} ^ {j} \\left(1 - p _ {c} ^ {j}\\right)}{n _ {j}}}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 117, + 801, + 468, + 842 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $p_c^k$ is the expected proportion of the generated mixed bag, which is directly computed from the proportions of the original bags $B^{i}$ , $B^{j}$ , and the standard deviation $\\sigma_c^k$ of the", + "bbox": [ + 76, + 854, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "mixed bag can be calculated by using the standard deviation of the sub-bags with the ratio $\\gamma$ .", + "bbox": [ + 498, + 319, + 890, + 349 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "This confidence interval (Eq.5) indicates that the actual proportion of the mixed bag has a gap from the expected proportion. If we directly use the proportion $\\mathbf{p}^k$ (Eq.6) for the mixed bag as augmented data and use it for the proportion loss, the gap from the actual proportion may adversely affect the training of the network since the gap causes a label noise.", + "bbox": [ + 496, + 349, + 890, + 454 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To avoid this adverse effect caused by gaps (label noise), we propose a confidence interval loss (CI loss) for generated mixed bags. The CI loss is based on the proportion loss [1]. In contrast to the standard proportion loss, the CI loss ignores a loss when the estimated proportion $\\hat{p}_c^k$ is in the confidence interval $[p_c^k -\\alpha \\sigma_c^k,p_c^k +\\alpha \\sigma_c^k ]$ since gaps in the CI often occur.", + "bbox": [ + 496, + 455, + 890, + 560 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Given the degree of confidence $\\alpha \\%$ (the corresponding value is set to $\\alpha$ ), such as when the degree of confidence is $95\\%$ , $\\alpha = 1.96$ , the CI loss is defined as:", + "bbox": [ + 498, + 561, + 890, + 606 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\ell_ {\\mathrm {C I}} \\left(B ^ {k}, \\mathbf {p} ^ {k}, f\\right) = - \\sum_ {c = 1} ^ {C} \\mathbf {1} \\left(p _ {c} ^ {k}, \\hat {p} _ {c} ^ {k}\\right) p _ {c} ^ {k} \\log \\hat {p} _ {c} ^ {k}, \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 542, + 614, + 890, + 656 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {p} _ {c} ^ {k} = \\frac {1}{| B ^ {k} |} \\sum_ {j = 1} ^ {| B ^ {k} |} f \\left(x _ {j} ^ {k}\\right) _ {c}, \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 674, + 659, + 890, + 704 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {1} \\left(p, p ^ {\\prime}\\right) = \\left\\{ \\begin{array}{l l} 0 & \\text {i f} p - \\alpha \\sigma \\leq p ^ {\\prime} \\leq p + \\alpha \\sigma \\\\ 1 & \\text {o t h e r w i s e} \\end{array} , \\right. \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 529, + 707, + 890, + 739 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{1}$ is the indicator function, which outputs 0 if $p'$ is in the confidence interval, and 1 otherwise. This CI loss updates the network parameters if the difference between the estimated proportion $\\hat{p}_c^k$ and the expected proportion $p_c^k$ calculated by Eq.6 is significant. Using this loss, we can accelerate the training by using the augmented bags without any adverse effects from proportion gaps.", + "bbox": [ + 496, + 750, + 890, + 854 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In training, mixed bags are randomly generated in each batch. It indicates that the number of generated bags will increase with iteration. We stop training based on the propor", + "bbox": [ + 496, + 854, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "16574", + "bbox": [ + 480, + 924, + 517, + 936 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/b4f1f32156b548e24b1dfb69b4c6fcc588070df698066c712a833d9f10f5adb7.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodCIFAR10AccuracySVHNAccuracyPATHAccuracyOCTAccuracyBLOODAccuracyORGANACuracyORGANCuracyORGANSAccuracyAverageAccuracy
LLP [1]0.45380.30090.78430.43360.88690.76350.78980.53720.6187
LLP + Ours(w/o CI)0.45820.29710.78840.4250.88980.78310.81890.5630.6280
LLP + Ours0.52560.37420.78610.43470.90170.79710.80990.61970.6561
LLP + Ours(supervised)0.65940.77810.81180.53960.89470.82220.82330.66740.7234
LLP-VAT [28]0.47400.31190.89150.41240.89150.79360.80600.58370.6455
LLP-VAT + Ours(w/o CI)0.52030.43020.87790.45030.87790.78470.76560.58490.6614
LLP-VAT + Ours0.52830.41110.89440.43660.89440.81550.82280.63760.6800
LLP-VAT + Ours(supervised)0.59630.59760.89970.47770.89970.82300.83130.66220.7234
LLP-PI [13]0.47020.30110.88860.42240.88620.78100.79620.59170.6421
LLP-PI + Ours(w/o CI)0.47940.52090.86880.43500.85730.75950.75700.57410.6565
LLP-PI + Ours0.52900.38650.88410.43660.88410.80130.79890.62360.6680
LLP-PI + Ours(supervised)0.58960.77210.89180.47200.89180.81010.81840.65770.7379
", + "bbox": [ + 78, + 88, + 888, + 271 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/ad34867050f3d05d0eb74eb6b2244c7c760ab8766e4998f5682147a175c7d1b4.jpg", + "table_caption": [ + "Table 1. Instance-level classification accuracy when our method was applied to three baseline methods; LLP [1], LLP-VAT [28] and LLP-PI [13]. Each value is the average of five-fold cross-validation results. Here, 'CI' means the confident interval, and 'supervised' indicates the case when a ground-truth proportion to the generated mixed bag is given." + ], + "table_footnote": [], + "table_body": "
MethodCIFAR10 AccuracySVHN AccuracyPATH AccuracyOCT AccuracyBLOOD AccuracyORGANA AccuracyORGANC AccuracyORGANS AccuracyAverage Accuracy
LLP [1]0.45380.30090.78430.43360.88690.76350.78980.53720.6187
LLP + Ours0.52560.37420.78610.43470.90170.79710.80990.61970.6561
LLP + Flip0.57770.38840.82990.47930.92650.65270.69040.62930.6467
LLP + Flip + Ours0.57640.41240.80050.55040.91550.67180.67170.62800.6533
LLP + Erase0.55510.35000.80970.44140.90940.83930.84470.65780.6759
LLP + Erase + Ours0.56710.42690.79340.42910.90210.82660.83130.65940.6794
LLP + Invert0.52580.67630.77750.43940.87900.77790.82150.62550.6899
LLP + Invert + Ours0.57840.77610.74210.45800.87360.78450.83230.63290.7097
LLP + Gaussianblur0.47660.36860.76390.41450.88750.79060.83180.63250.6457
LLP + Gaussianblur + Ours0.51350.40360.75550.43000.87890.79620.79890.67090.6559
LLP + Perspective0.56750.54410.78920.46780.89680.83090.84400.66890.7011
LLP + Perspective + Ours0.57500.57150.77450.49620.90640.81800.84040.68950.7089
", + "bbox": [ + 81, + 330, + 888, + 517 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2. Instance-level classification accuracy when our method was applied after various instance-level augmentation methods.", + "bbox": [ + 102, + 522, + 857, + 537 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "tion loss in validation data. Note that instance-level labels cannot be used for validation in LLP.", + "bbox": [ + 75, + 561, + 468, + 592 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "6. Experiments", + "text_level": 1, + "bbox": [ + 76, + 604, + 209, + 622 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "6.1. Datasets and experimental settings", + "text_level": 1, + "bbox": [ + 76, + 628, + 380, + 646 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Preparation of bags: The eight datasets used in these experiments were the same as those used in the preliminary experiments. The way of generating bags was also the same as in the preliminary experiments. Although some of the related studies generated bags by allowing overlaps to increase the number of labeled bags, we did not allow overlaps since this situation is unnatural in actual applications. To keep the experiment setups the same in all datasets, we set the number of labeled bags as 512 and the bag size as 10 based on the smallest dataset. This small bag size can be considered a challenging scenario for MixBag since the number of samplings for sub-bags decreases, and it increases the confidence interval. We also evaluated our method using different bag sizes to demonstrate the effectiveness of our method in various situations.", + "bbox": [ + 75, + 652, + 468, + 878 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation: We implemented our method by using", + "bbox": [ + 76, + 885, + 468, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Pytorch [21]. The network model was ResNet18 [9] pretrained on the ImageNet dataset [5]. To train our network, we also used the Adam Optimizer [9] with a learning rate of 3e-4, epoch= 1000, mini-batch size = 32, early stopping = 10 and trained on an NVIDIA GeForce 3090 GPU. We set the confidence degree as '99%' and selected $\\gamma$ randomly from a uniform distribution [0, 1].", + "bbox": [ + 496, + 561, + 890, + 669 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation metric: We evaluated the model performance by the instance-level classification accuracies, which were calculated by using the confusion matrix. To compute the metric, we performed a five-fold cross-validation in all our experiments. The accuracies listed in the tables are the average values of the five-fold cross-validation.", + "bbox": [ + 496, + 676, + 890, + 767 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "6.2. Comparison", + "text_level": 1, + "bbox": [ + 500, + 784, + 632, + 800 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparison with current methods: Our method MixBag can be applied to any proportion loss-based method since MixBag is a data augmentation method, in which any method can be applied after data augmentation with the CI loss. Most current LLP methods incorporate self-supervised learning, such as consistency, into the proportion loss. We", + "bbox": [ + 496, + 809, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "16575", + "bbox": [ + 478, + 924, + 517, + 936 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/4e451e5ae3f1c64770f5f5cbaa33403df58106982fd3f8c256791f1dae54288e.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Methodγ-samplingAverage Accuracy
LLP [1]-0.6187
LLP + Oursuniform0.6561
LLP + OursGauss0.6512
LLP + Ourshalf0.6524
", + "bbox": [ + 125, + 88, + 415, + 159 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/4496a56f33b4a2674595241e64b61243e81419ed2f5a781e9e792bb2520dbced.jpg", + "table_caption": [ + "Table 3. Average accuracy on eight datasets when changing a sampling method for $\\gamma$ ." + ], + "table_footnote": [], + "table_body": "
MethodCIAverage Accuracy
LLP [1]0.6187
LLP + Ours(99%)✓0.6561
LLP + Ours(95%)✓0.6519
LLP + Ours(80%)✓0.6531
LLP + Ours(50%)✓0.6243
", + "bbox": [ + 138, + 205, + 405, + 287 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "thus applied our method in three methods: 1) LLP [1], which is the method of the original paper on using the proportion loss; 2) LLP-VAT [28], which introduces the consistency regularization into the proportion loss; and 3) LLP-PI [13], which uses the additive Gaussian noise for making perturbed examples. The LLP-VAT is one of the state-of-the-art LLP methods using the proportion loss, and its implementations are publicly available.", + "bbox": [ + 75, + 347, + 467, + 468 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We compared the baseline methods as an ablation study. The first was 'LLP', which uses the standard proportion loss; the second was 'LLP+Ours(w/o CI)' which uses the MixBag without using the CI loss, where the proportion is directly calculated from the original bags (and may contain noise) was used as the label for the generated mixed bag. The third was 'LLP+Ours(supervised)', which uses the ground-truth proportions of the mixed bags. Note that the proportion would be unknown in real cases.", + "bbox": [ + 75, + 469, + 467, + 604 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 1 shows the accuracy of each method, where the gray color field indicates the proposed methods in each baseline method. 'LLP+Ours(w/o CI)' improved the accuracies in some datasets and slightly improved them on average from the baselines. However, the improvement was limited by the noisy proportions. MixBag improved the accuracy of every baseline method on all datasets, and the improvement was 3 to 4 points on average.", + "bbox": [ + 75, + 606, + 467, + 728 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Introducing MixBag with instance-level augmentation: Next, we introduced our method to the instance-level augmentation methods. We used standard augmentation techniques: 'Flip' randomly flips the image horizontally and upside down. 'Erase' removes a randomly selected area from an original image. 'Invert' randomly changes the colors of the image by inversion. 'Gaussianblur' blurs an image by adding a randomly chosen Gaussian blur. 'Perspective' performs a random projective transformation on an image. To generate a bag by instance-level augmentation, we added perturbations into instances randomly selected from", + "bbox": [ + 75, + 734, + 467, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/52c0b2f9fadd78f2513a00f1d859f9a51da918a02f2157d28d83fa52f54228a2.jpg", + "table_caption": [ + "Table 4. Average accuracy on eight datasets when changing the degree of confidence interval (50%, 80%, 95%, 99%)." + ], + "table_footnote": [], + "table_body": "
MethodSizeNumAverage Accuracy
LLP [1]105120.6187
LLP + Ours(w/o CI)105120.6280
LLP + Ours105120.6561
LLP [1]202560.5441
LLP + Ours(w/o CI)202560.5496
LLP + Ours202560.5667
LLP [1]401280.4746
LLP + Ours(w/o CI)401280.4600
LLP + Ours401280.5058
", + "bbox": [ + 557, + 88, + 826, + 224 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 5. Average accuracy on eight datasets when changing the number of labeled bags and bag size. 'Size' means the bag size. 'Num' means the number of labeled bags.", + "bbox": [ + 500, + 229, + 890, + 272 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "an original bag; i.e., an augmented bag contains the perturbed instances and original instances, where this augmentation has not been reported in previous papers. In $\\mathrm{LLP} +$ instance-level $^+$ MixBag, the mixed bag was created from the original and instance-level augmented bags. Table 2 shows the accuracies of the baseline and our methods. The instance-level data augmentation improved the performance from the baseline. Our method further improved the accuracies of every instance-level augmentation method.", + "bbox": [ + 498, + 296, + 890, + 434 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.3. Performance in various situations", + "text_level": 1, + "bbox": [ + 500, + 441, + 794, + 455 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Performance with different $\\gamma$ sampling methods: We evaluated our method with three different $\\gamma$ sampling methods, i.e., three different ways to determine the mixing rate $\\gamma$ of the two sub-bags $S^i, S^j$ : 'uniform' selects $\\gamma$ randomly from a uniform distribution; 'Gauss' selects $\\gamma$ randomly from a Gaussian distribution $\\mathcal{N}(0.5, 0.25)$ ; 'half' always set $\\gamma$ to 0.5. Table 3 shows the average accuracies of all datasets. All sampling methods outperformed the performance compared to the baseline method (LLP); 'uniform' was marginally better than other methods.", + "bbox": [ + 498, + 465, + 890, + 616 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Performance with different confidence intervals: We conducted experiments with four different confidence intervals, $99\\%$ , $95\\%$ , $80\\%$ , and $50\\%$ . Table 4 shows the average accuracies of all datasets. For all confidence interval settings, our method improved the accuracy on all datasets and in all cases. When the confidence interval took high values $(99\\%, 95\\%, 80\\%)$ , our method worked well since the worst effects of noisy labels were mitigated by the CI loss. Even when the confidence interval was low $(50\\%)$ , the accuracy improved from the baseline method. The case of $99\\%$ was the best on average. We consider that a larger confidence interval avoids the adverse effects of noisy proportions and makes the training more stable.", + "bbox": [ + 498, + 622, + 890, + 818 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Performance when changing the number of labeled bags and bag size: To show the effectiveness of our method in various situations, we conducted experiments with different bag sizes (512, 256, 128) and different numbers of labeled bags (10, 20, 40), where the bag size and the number of", + "bbox": [ + 498, + 825, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "16576", + "bbox": [ + 480, + 924, + 517, + 936 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/a86d6c66e6da2e001beec176729b763c5aa5105a3893b90906df2d15ba9b0c87.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodBag-GenerationCIAverage Accuracy
LLP [1]--0.6187
LLP + Ours(w/o CI)Union-0.6226
LLP + Ours(w/o CI)Sub-bag0.4956
LLP + Ours(with CI)Sub-bag✓0.6364
LLP + Ours(w/o CI)MixBag0.6280
LLP + Ours(with CI)MixBag✓0.6561
", + "bbox": [ + 114, + 88, + 426, + 186 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 6. Average accuracy on eight datasets in different bag-generation methods.", + "bbox": [ + 76, + 191, + 468, + 219 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "labeled bags have a trade-off since the total number of instances is fixed. Table 5 shows the average accuracies on all datasets with various setups. Our method improved the accuracy from the baseline methods on average in all cases. This demonstrates the robustness of our method.", + "bbox": [ + 76, + 243, + 467, + 316 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Performance with different bag generations: To confirm the effectiveness of the 'Mix' approach, we compared MixBag with two other bag generation methods. 1) 'union' directly combines any two bags $(B^i, B^j)$ without sampling. In this case, the proportion of a generated bag can be directly calculated from those of the original bags; i.e., there is no noise for the combined proportions by taking the union of two bags. Therefore, the CI loss was not used for this method. 2) 'sub-bag' randomly samples instances from a single bag $B^i$ . It can be considered as a sub-bag of the original bag $B^i$ . In this case, the label proportions of the sub-bag may have a gap from the original one, and thus, we evaluated two cases; 'sub-bag' without and with the CI loss. 3) 'MixBag' is our method, which mixes two bags. We also evaluated two cases; Mixbag with and without CI loss.", + "bbox": [ + 75, + 325, + 467, + 549 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 6 shows the average of the instance-level accuracies of the comparative methods on the eight datasets. Since 'sub-bag with CI' and union' can increase the number of labeled bags, these methods had slightly improved accuracy from that of baseline method LLP [1]. Our method, 'MixBag with CI' further improved the accuracy compared with these other bag generation methods. We consider that our method has two characteristics of 'sub-bag' and 'union', where MixBag first makes sub-bags from original bags and then takes the union of these sub-bags. In addition, MixBag can generate various proportions of the mixed bag compared to 'sub-bag' and 'union'. Therefore, MixBag was better than them.", + "bbox": [ + 75, + 551, + 467, + 746 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6.4. Detailed Analysis", + "text_level": 1, + "bbox": [ + 76, + 756, + 246, + 772 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Distribution of proportion vectors in the space of proportion labels: Figure 6 shows distributions of the original proportion vectors $\\{\\mathbf{p}^i\\}_{i=1}^n$ (blue) and the generated mixed bag's proportion vectors $\\{\\mathbf{r}^i\\}_{i=1}^m$ (orange) in the 'ORGANS' dataset, in which the dimension was compressed to 2D by PCA [29]. Here, the number of mixed bags is the same as that of the original bags. We can see that the MixBag proportion vectors do not overlap with the orig-", + "bbox": [ + 75, + 779, + 467, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a35aa66f6a3c7a4c2feb5c6879cda2491d3ed532a7212fe31e4ded9388b3dc8f.jpg", + "image_caption": [ + "Figure 6. Distribution of proportion vectors. Blue: Original bag's proportion. Orange: Mixed bag's proportion." + ], + "image_footnote": [], + "bbox": [ + 511, + 104, + 684, + 224 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8aea3cb7fe3f5113ce626775fd52aa264bdb32faaef10865ddf5e036256a3066.jpg", + "image_caption": [ + "Figure 7. Relationship between confidence interval and actual gaps. Blue: proportion vector of a bag." + ], + "image_footnote": [], + "bbox": [ + 722, + 103, + 892, + 224 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "inal ones, i.e., new proportion labels were generated, and the distribution of mixed bag proportions covers the original distribution by interpolating pairs of the original bags. This result shows that MixBag adds diversity to the training dataset, which facilitates an improvement in the instance-level classification accuracy.", + "bbox": [ + 496, + 319, + 890, + 409 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Relationship between confidence interval and ground-truth proportion: Figure 7 shows how well the confidence interval works. The horizontal axis indicates the difference $(\\| \\mathbf{p} - \\hat{\\mathbf{p}} \\|_1)$ between the ground-truth proportion $\\mathbf{p}$ and the estimated proportion $\\hat{\\mathbf{p}}$ of a mixed bag. The vertical axis indicates the difference $(\\alpha \\sigma^k)$ between the upper bounds of the confidence interval and $\\mathbf{p}$ , where we set the degree of confidence as $99\\%$ . Each blue point indicates the proportion vector of a mixed bag. Almost all points are under the straight line in the figure. This indicates that the actual proportion gaps from the ground truth were less than the confidence interval, and thus the proposed CI loss works properly.", + "bbox": [ + 496, + 417, + 890, + 616 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "7. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 632, + 617, + 647 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we examined how the number of labeled bags and the bag size affects the performance in LLP. As a result, we found that the accuracy improves as the number of labeled bags increases, even when the total number of instances is fixed. Then, based on this observation, we propose a simple but effective bag-level data augmentation method. In addition, we also proposed a confidence interval loss that effectively trains a classification network by using the generated bags while avoiding the adverse effects caused by noisy proportions. To the best of our knowledge, this is the first attempt to propose bag-level data augmentation for LLP. The experiments using eight datasets demonstrated the effectiveness of our method in various cases. Additionally, MixBag can be applied to instance-level data augmentation techniques and any LLP method that uses a standard proportion loss.", + "bbox": [ + 496, + 657, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "16577", + "bbox": [ + 478, + 924, + 517, + 935 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements: This work was supported by JSPS KAKENHI Grant Number JP20H04211 and JP23K18509, and JST, ACT-X Grant Number JPMJAX200G, Japan.", + "bbox": [ + 76, + 90, + 468, + 137 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 165, + 171, + 180 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Ehsan Mohammady Ardehaly and Aron Culotta. Co-training for demographic classification using deep learning from label proportions. 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In Proceedings of the IEEE international conference on computer vision, pages 2223-2232, 2017." + ], + "bbox": [ + 78, + 90, + 468, + 541 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "16579", + "bbox": [ + 480, + 924, + 517, + 936 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/c288d48a-0e97-49d8-951a-99b2d027811b_model.json b/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/c288d48a-0e97-49d8-951a-99b2d027811b_model.json new file mode 100644 index 0000000000000000000000000000000000000000..7729ffe9877f1fda62d0df8a6a4faaa7d8801523 --- /dev/null +++ b/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/c288d48a-0e97-49d8-951a-99b2d027811b_model.json @@ -0,0 +1,2013 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.096, + 0.131, + 0.877, + 0.155 + ], + "angle": 0, + "content": "MixBag: Bag-Level Data Augmentation for Learning from Label Proportions" + }, + { + "type": "text", + "bbox": [ + 0.194, + 0.18, + 0.774, + 0.22 + ], + "angle": 0, + "content": "Takanori Asanomi1, Shinnosuke Matsuo1, Daiki Suehiro1,2, Ryoma Bise1 \n1Kyushu University, Fukuoka, Japan \n2RIKEN AIP, Japan" + }, + { + "type": "text", + "bbox": [ + 0.106, + 0.22, + 0.865, + 0.235 + ], + "angle": 0, + "content": "{takanori.asanomi@human., shinnosuke.matsuo@human., suehiro@, bise@}ait.kyushu-u.ac.jp" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.301, + 0.474, + 0.575 + ], + "angle": 0, + "content": "Learning from label proportions (LLP) is a promising weakly supervised learning problem. In LPP, a set of instances (bag) has label proportions, but no instance-level labels are given. LPP aims to train an instance-level classifier by using the label proportions of the bag. In this paper, we propose a bag-level data augmentation method for LPP called MixBag, based on the key observation from our preliminary experiments; that the instance-level classification accuracy improves as the number of labeled bags increases even though the total number of instances is fixed. We also propose a confidence interval loss designed based on statistical theory to use the augmented bags effectively. To the best of our knowledge, this is the first attempt to propose bag-level data augmentation for LPP. The advantage of MixBag is that it can be applied to instance-level data augmentation techniques and any LPP method that uses the proportion loss. Experimental results demonstrate this advantage and the effectiveness of our method." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.603, + 0.21, + 0.619 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.47, + 0.765 + ], + "angle": 0, + "content": "In general classification tasks, a model is trained on datasets where each piece of data (instance) has class labels. However, instance-level annotations cost a lot, and there are many cases in which instance-level annotation cannot be disclosed to the public for privacy reasons [23]. In such a situation, we only know the label proportions given to a set of instances (bag) and must train a model from these label proportions to classify each instance. This problem setting is known as learning from label proportions (LLP) [1]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Figure 1 illustrates the problem setup of LLP. A bag \\( B \\) consists of instances (e.g., images). Bag-level labels are given as training data instead of instance-level labels (class labels of each instance \\( x \\) are unknown). The label proportion \\( \\mathbf{p}^i \\) of bag \\( B^i \\) is given as a bag-level label. For example, if a bag \\( B^0 \\) contains 60, 100, and 40 instances of class 1, 2, and 3, respectively, \\( \\mathbf{p}^i = (0.3, 0.5, 0.2)^{\\mathrm{T}} \\). LLP aims to train an instance-level classifier by using the label proportions of a bag. It is a weakly supervised learning task." + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.271, + 0.895, + 0.481 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.488, + 0.895, + 0.531 + ], + "angle": 0, + "content": "Figure 1. Illustration of learning from label proportions. LLP aims to train an instance-level classifier by using label proportions of a bag as training data instead of instance-level labels." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.562, + 0.895, + 0.729 + ], + "angle": 0, + "content": "Many LLP methods have been proposed to address this challenging task [1, 24, 28, 27, 18, 19]. Most of them are based on the proportion loss, which evaluates the difference between the given proportion \\(\\mathbf{p}^i\\) and the estimated proportion \\(\\hat{\\mathbf{p}}^i\\), and can be calculated by taking the average of the class probabilities of the instances in a bag. The methods based on the proportion loss work well when bag-level labels (label proportions) are sufficient. However, the accuracy decreases as the number of labeled bags decreases, i.e., insufficient labeled data causes difficulty in training a network, which is known in machine learning tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.731, + 0.895, + 0.883 + ], + "angle": 0, + "content": "In such cases, instance-level data augmentation is often an effective way to improve accuracy. Many instance-level data augmentation techniques, such as perturbation, for general classification tasks have been proposed, and their effectiveness has been demonstrated [25]. Instance-level data augmentation may improve the accuracy in LLP. However, it does not increase the number of labeled bags from the original one, and it is difficult to generate various bags with different proportions without using instance-level labels (these are unknown in LLP)." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "This paper proposes a bag-level data augmentation for" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.925, + 0.52, + 0.937 + ], + "angle": 0, + "content": "16570" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.363 + ], + "angle": 0, + "content": "LLP that can generate new bags with various label proportions. To design an effective bag-level data augmentation technique, we conducted a detailed analysis of what situation can improve the accuracy in LLP. As a result, we found an important observation that the accuracy improves as the number of labeled bags increases, even though the total number of instances is fixed, i.e., different bags overlap each other as shown in Figure 2 (Right). On the basis of this observation, we propose a bag-level data augmentation called MixBag. MixBag increases the number of labeled bags artificially by sampling instances from a pair of original bags and mixing them: this operation mimics the above observations. The expected label proportion of a generated mixed bag can be calculated by those of the original bags. However, it may have a gap from the actual proportion of the mixed bag because randomly selected instances do not follow the proportion of the original ones. This gap adversely affects the training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.364, + 0.473, + 0.499 + ], + "angle": 0, + "content": "We thus introduce a confidence interval loss that helps to train a classification network by using the generated bags while avoiding this adverse effect by a proportion gap; it is statistically guaranteed. To the best of our knowledge, this is the first attempt to propose bag-level data augmentation for LLP. Experiments using eight datasets demonstrate the effectiveness of our method in various cases; our method improved the classification accuracy on all datasets. Our main contributions are summarized as follows." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.506, + 0.47, + 0.582 + ], + "angle": 0, + "content": "- We examined how the number of labeled bags and the bag size affect the performance in LLP. From the preliminary experiments, we concluded that the accuracy improves as the number of labeled bags increases, even though the total number of instances is fixed." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.59, + 0.47, + 0.652 + ], + "angle": 0, + "content": "- We proposed MixBag with a confidence interval loss. This method artificially increases the number of labeled bags, and the confidence interval loss helps train a classification network using the generated bags." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.66, + 0.47, + 0.735 + ], + "angle": 0, + "content": "- We demonstrated that MixBag can be applied to any of the current LLP methods and any of the instance-level augmentation methods. Experimental results show that our method improved classification accuracy on various datasets." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.506, + 0.47, + 0.735 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.747, + 0.216, + 0.763 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.772, + 0.415, + 0.789 + ], + "angle": 0, + "content": "2.1. Learning from Label Proportion (LLP)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.469, + 0.871 + ], + "angle": 0, + "content": "Proportion loss [1] is the most common approach to LLP. To compute the proportion loss, the average of the output probability in a bag is calculated as a proportion estimation, and then the bag-level cross-entropy between the true label proportion and the estimated proportion is used as the loss." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "The proportion loss has been extended in many methods; e.g., introducing regularization terms [33, 1, 8, 28, 30, 17," + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.091, + 0.895, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.232, + 0.894, + 0.288 + ], + "angle": 0, + "content": "Figure 2. Illustration of overlap and non-overlap situations. (a) Original bags. (b) New bags (yellow) are added with non-overlap, i.e., the total number of instances increases. (c) New bags overlap with the original ones, i.e., the total number of instances is fixed." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.31, + 0.892, + 0.492 + ], + "angle": 0, + "content": "18]. Tsai et al. [28] incorporated a consistency regularization into the proportion loss, which forces the network predictions to be consistent when its input is perturbed. Yang et al. [30] use contrastive learning for pre-training in a self-supervised learning manner and then train the model by using the proportion loss. LLP-GAN [17] introduces the generative adversarial network (GAN) to LLP. The fake instances created by the generator encourage the discriminator to distinguish real or fake and classify the real instances. This method also uses the proportion loss to train the classifier. Two-stage LLP [18] introduces pseudo-labeling after pre-training by using a proportion loss." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.492, + 0.892, + 0.613 + ], + "angle": 0, + "content": "It is known that the classification accuracy decreases when the labeled data is insufficient in machine learning. To deal with this issue, data augmentation is a standard approach. However, bag-level data augmentation for LLP is still an unexplored area. This paper proposes a simple but effective bag-level data augmentation method. One of the advantages of our method is that any LLP method can be applied after our bag-level augmentation." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.621, + 0.795, + 0.637 + ], + "angle": 0, + "content": "2.2. Instance-level data Augmentation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.645, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Data augmentation is a standard way to address the problem of inadequately labeled data. Many instance-level data augmentation techniques have been proposed. Basic data augmentation involves adding perturbations to the original images, such as by flipping the image [25], adding noise [25], and erasing parts of an image [7, 2, 14]. Image mix [11, 35, 34, 10] is another approach, where methods such as MixUP [35] and CutMix [34] mix together two original images. GAN-based augmentation methods [22, 36, 26] represent data distributions and generate new images based on these distributions. Auto augment [3, 16, 4] automatically searches for suitable augmentation approaches that improved performance. The above methods are instance-level data augmentations. It is not a simple task to generate various bags that have different proportions without using instance-level labels. For example, CutMix and MixUp require the labels of the original im" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.925, + 0.518, + 0.937 + ], + "angle": 0, + "content": "16571" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.184 + ], + "angle": 0, + "content": "ages (instances) in order to prepare the label proportions of a generated new bag. Since simple perturbation methods do not require the ground truth of the image label for augmentation, they can be used to add perturbations to each instance in a bag. However, these methods are not designed for bag-level data augmentation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.191, + 0.408, + 0.208 + ], + "angle": 0, + "content": "2.3. Bag-Level data augmentation for MIL" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.215, + 0.474, + 0.488 + ], + "angle": 0, + "content": "Few bag-level data augmentation methods have been proposed for multiple instance learning (MIL), which trains a classifier from bag-level class labels (positive or negative). Li et al. [15] proposed a MIL-based method that uses bag-level augmentation for COVID-19 severity assessment. This method takes a pseudo-labeling approach, where positive and negative instances are taken from positive bags based on the estimated confidence of the instance class and used to make a new bag. Yang et al. [31] proposed a MIL method for segmenting pathology images. This method generates new bags by clustering instances. It is reasonable for MIL to make a positive or negative bag from high confidence positive or negative instances. However, it is difficult to make a proportion label from pseudo labeling since all of the pseudo labels have to be accurate to calculate the correct proportion. So in order to improve the performance of LLP, appropriately designing a bag-level data augmentation is required." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.5, + 0.431, + 0.518 + ], + "angle": 0, + "content": "3. Preliminary: LLP and Proportion Loss" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.525, + 0.47, + 0.697 + ], + "angle": 0, + "content": "In LLP, the training set contains \\( n \\) bags, \\( B^1, \\ldots, B^n \\). Each bag \\( B^i \\) consists of a set of instances, i.e., \\( B^i = \\{x_j^i\\}_{j=1}^{|B^i|} \\), and a vector of label proportions \\( \\mathbf{p}^i = (p_1^i, \\ldots, p_c^i, \\ldots, p_C^i)^T \\) is attached to each bag as training label, where \\( C \\) is the number of classes. This label indicates that \\( p_c^i \\times |B^i| \\) instances in the \\( i \\)-th bag belong to the class \\( c \\) for any \\( c \\in \\{1, \\ldots, C\\} \\). The goal of LLP is to train a network that estimates the class label of each instance by using only the proportion labels of the bags. Proportion loss [1] is a standard approach to this challenging task, and many methods are based on it." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.697, + 0.471, + 0.773 + ], + "angle": 0, + "content": "Given training data with label proportions, the standard proportion loss is a bag-level cross-entropy between the ground-truth of the label proportion \\(\\mathbf{p}^i\\) and the predicted proportion \\(\\hat{\\mathbf{p}}^i\\), which is the average of the output class probabilities in a bag. It is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.154, + 0.784, + 0.47, + 0.826 + ], + "angle": 0, + "content": "\\[\n\\ell_ {\\text {p r o p}} \\left(B ^ {i}, \\mathbf {p} ^ {i}, f\\right) = - \\sum_ {c = 1} ^ {C} p _ {c} ^ {i} \\log \\hat {p} _ {c} ^ {i}, \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.237, + 0.829, + 0.469, + 0.874 + ], + "angle": 0, + "content": "\\[\n\\hat {p} _ {c} ^ {i} = \\frac {1}{| B ^ {i} |} \\sum_ {j = 1} ^ {| B ^ {i} |} f \\left(x _ {j} ^ {i}\\right) _ {c}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.885, + 0.468, + 0.904 + ], + "angle": 0, + "content": "where \\( f(x_{j}^{i})_{c} \\) is the output probability that \\( x_{j}^{i} \\) belongs to \\( c \\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.09, + 0.855, + 0.109 + ], + "angle": 0, + "content": "4. Preliminary Empirical Analysis of LLP" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.117, + 0.892, + 0.283 + ], + "angle": 0, + "content": "In previous works, the relationship between the number of labeled bags, bag sizes, and accuracy in LLP has not been analyzed well. Some papers [17, 8] reported that the accuracy increased as the larger bag size in their experiments. However, the reason was not discussed well. In their experiments, they changed the bag size while the total number of instances was fixed. Since an instance generally does not belong to two bags (i.e., bags does not overlap each other) in LLP, it indicates that the bag size and the number of labeled bags have a trade-off; when the bag size increases, the number of labeled bags decreases." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.284, + 0.893, + 0.495 + ], + "angle": 0, + "content": "In this section, we further empirically analyze the relationships among the number of labeled bags, bag sizes, and accuracy by using the proportion loss on various public datasets. First, we conducted experiments on whether the number of labeled bags or the bag size has more influence on the classification accuracy in a general setup of LLP, where different bags do not contain the same instance (no overlap), as shown in Figure 2 (b). To avoid the tradeoff between the number of labeled bags and the bag size, we fixed the number of labeled bags to analyze the effect for accuracy by the number of labeled bags, and vice versa. In the experiments, the total number of instances changed. We speculated that this analysis may give clues for developing a new method in LLP." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.503, + 0.893, + 0.73 + ], + "angle": 0, + "content": "Datasets and experimental settings: We used eight datasets in our experiments1: 1) CIFAR10 [12], which is commonly used in classification tasks. The dataset contains ten classes, such as vehicles and animals; 2) SVHN [20], which is a house-number-images dataset, and a character-level label is given like in MNIST [6]; 3) OCT, which contains four classes of Retinal OCT images; 4) BLOOD, which contains eight classes of Blood Cell Microscope images; 5) ORGAN, 6) ORGANC, 7) ORGANS, which contain eleven classes of abdominal CT images. The difference is the view of the image and its sizes, and 8) PATH, which contains nine classes of colon pathology images. Note that 3) to 8) are datasets in MedMNIST [32], and we did not use the small datasets in [32] since they cannot be used to prepare enough bags for LLP." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.731, + 0.892, + 0.852 + ], + "angle": 0, + "content": "To prepare a bag, the proportions of each class were randomly selected from a Gaussian distribution; the decided proportion was used as the label of the bag. Then, samples were randomly selected from each class, in which the number of samples for each class followed the proportion of the class. In real applications, different bags do not contain the same instance; i.e., they do not overlap. We thus generated bags without overlap in these experiments." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.859, + 0.892, + 0.875 + ], + "angle": 0, + "content": "Performance when changing the number of labeled bags" + }, + { + "type": "page_footnote", + "bbox": [ + 0.518, + 0.887, + 0.799, + 0.9 + ], + "angle": 0, + "content": "1Almost all papers on LLP use CIFAR10 and SVHN" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.925, + 0.519, + 0.937 + ], + "angle": 0, + "content": "16572" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.092, + 0.468, + 0.214 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.218, + 0.47, + 0.302 + ], + "angle": 0, + "content": "Figure 3. Relationship among the number of labeled bags, bag sizes, and accuracy in a general setup of LLP, where different bags do not contain the same instance (no overlap). Left: Accuracy improvement when increasing the number of labeled bags (bag size is fixed). Right: Accuracy improvement when increasing the bag size (the number of labeled bags is fixed)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.328, + 0.47, + 0.525 + ], + "angle": 0, + "content": "in the general setup of LLP (no overlap): We examined how the number of labeled bags affects the instance-level classification accuracy for the standard proportion loss. We varied the number of labeled bags (64, 128, 256, 512) while keeping the bag size fixed at 10. In this experiment, we follow the general setup of LLP; different bags do not overlap, i.e., the number of instances changed when the number of labeled bags was changed. As shown in Figure3 (Left), the accuracy improved due to increasing the number of labeled bags in all datasets. This is reasonable because the number of labeled bags indicates the number of proportion labels; more labeled data for training is expected to improve accuracy in machine learning." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.532, + 0.47, + 0.683 + ], + "angle": 0, + "content": "Performance when changing the bag size in the general setup of LLP (no overlap): We analyzed how the bag size affects the accuracy in the general setup of LLP. In this experiment, we changed the bag size (64, 128, 256, 512) but fixed the number of labeled bags at 10. As shown in Figure 3 (Right), the accuracy did not vary significantly with the bag size in six of the datasets, while it improved in two datasets. This result shows that increasing the number of instances without increasing the labels does not effectively improve accuracy." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Performance when changing the number of labeled bags in the case of overlap: The above observations indicate that increasing the number of labeled bags is important to improving accuracy. Another factor that might have improved the accuracy is increasing the total number of 'instances,' which occurs when the number of labeled bags increases. To confirm whether the number of labeled bags or the total number of instances affects accuracy, we performed experiments on how the number of labeled bags affects the accuracy in the case of overlap, i.e., when the total number of instances was fixed. The initial bags were prepared, where the number of labeled bags was 64, and the bag size was 10. To increase the number of labeled bags, we then incrementally added new bags (64, 128, 256), where the new" + }, + { + "type": "image", + "bbox": [ + 0.585, + 0.092, + 0.81, + 0.213 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.217, + 0.892, + 0.259 + ], + "angle": 0, + "content": "Figure 4. Experimental results on how the number of labeled bags affects the accuracy in the case of overlap, i.e., when the total number of instances was fixed." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.282, + 0.892, + 0.449 + ], + "angle": 0, + "content": "bags were generated from the initial instances that belong to the initial bags, i.e., generated bags overlap with the initial ones, as shown in Figure 2 (c). As shown in Figure4, the accuracy improves as the number of labeled bags increases in all datasets. This observation is important for our bag-level data augmentation. If we were to mimic this situation where the number of labeled bags increases and the total number of instances is fixed, it should improve accuracy, even though a situation with bags having overlaps is unnatural in actual applications. However, we can make this situation by generating new bags from the original ones." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.462, + 0.833, + 0.48 + ], + "angle": 0, + "content": "5. MixBag with confidence interval loss" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.488, + 0.892, + 0.534 + ], + "angle": 0, + "content": "To mimic the situation of increasing the number of labeled bags and allowing their overlap, we propose MixBag, which is a bag-level data augmentation technique." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.542, + 0.599, + 0.559 + ], + "angle": 0, + "content": "5.1. MixBag" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.566, + 0.892, + 0.763 + ], + "angle": 0, + "content": "Figure 5 (Left) shows an overview of MixBag. Given two randomly selected bags \\(\\{B^i, B^j\\}\\) where each bag is labeled with a proportion, \\(\\mathbf{p}_i\\) or \\(\\mathbf{p}_j\\), mix the two bags to generate a new bag. More precisely, \\(n_i = |B^i| \\times \\gamma\\) and \\(n_j = |B^j| \\times (1 - \\gamma)\\) instances are randomly sampled from \\(B^i\\) and \\(B^j\\), respectively, where \\(\\gamma \\in [0,1]\\) is a random variable, and the sampled sub-bags are denoted as \\(S^i\\) and \\(S^j\\). Then, these two sub-bags are combined to generate a mixed bag, \\(B^k = S^i \\cup S^j\\). This generated mixed bag overlaps with the original bags while the total number of instances is fixed, and the number of labeled bags is increased by the generated bags. It can be considered to mimic the third preliminary experiment (Figure 2 (c))." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.772, + 0.72, + 0.787 + ], + "angle": 0, + "content": "5.2. Confidence interval loss" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The sampled sub-bags \\( S^i \\), \\( S^j \\) are expected to have almost the same proportions as the original ones, \\( \\mathbf{p}^i \\) and \\( \\mathbf{p}^j \\), if the randomly selected instances follow the proportion of the original bags. In this case, the expected proportion of the generated new bag \\( B^k \\) is \\( \\mathbf{p}^k = \\gamma \\mathbf{p}^i + (1 - \\gamma) \\mathbf{p}^j \\). However, in practice, the actual proportion of randomly sampled instances may have some gaps from that of the original bag" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.925, + 0.519, + 0.937 + ], + "angle": 0, + "content": "16573" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.085, + 0.092, + 0.56, + 0.263 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.572, + 0.092, + 0.885, + 0.258 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.269, + 0.893, + 0.299 + ], + "angle": 0, + "content": "Figure 5. Overview of our method. Left: the way to create mixed bags and illustration of label proportion's probability. Right: confidence interval" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.32, + 0.47, + 0.381 + ], + "angle": 0, + "content": "because the number of sampled instances in each class does not always follow the original proportion. This gap can be estimated by calculating the confidence interval (CI) for a population proportion." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.381, + 0.471, + 0.426 + ], + "angle": 0, + "content": "Let us denote the proportion of a class \\(c\\) in the \\(i\\)-th bag as \\(p_c^i\\). The standard deviation of the class \\(c\\) proportion of the sampled sub-bag \\(S^i\\) is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.203, + 0.439, + 0.47, + 0.48 + ], + "angle": 0, + "content": "\\[\n\\sigma_ {c} ^ {i} = \\sqrt {\\frac {p _ {c} ^ {i} \\left(1 - p _ {c} ^ {i}\\right)}{n _ {i}}}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.492, + 0.469, + 0.538 + ], + "angle": 0, + "content": "where \\( n_i = |B^i| \\times \\gamma \\) is the number of instances randomly sampled from \\( B^i \\). This equation is well-known in statistics; it can be derived using the central limit theorem." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.538, + 0.47, + 0.567 + ], + "angle": 0, + "content": "The CI for the truth proportion \\(\\tilde{p}_c^i\\) of the sub-bag \\(S^i\\) is formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.177, + 0.58, + 0.469, + 0.599 + ], + "angle": 0, + "content": "\\[\np _ {c} ^ {i} - \\alpha \\sigma_ {c} ^ {i} \\leq \\tilde {p} _ {c} ^ {i} \\leq p _ {c} ^ {i} + \\alpha \\sigma_ {c} ^ {i}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.611, + 0.469, + 0.684 + ], + "angle": 0, + "content": "where \\(\\alpha\\) is set according to the desired degree of confidence, e.g., \\(95\\%\\). If we set the confidence to a higher value, \\(\\alpha\\) becomes higher values. For the other sub-bag \\(S_{j}\\), the CI for the population proportion of \\(\\tilde{p}_c^j\\) is formulated in the same manner." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.686, + 0.469, + 0.716 + ], + "angle": 0, + "content": "The CI for \\(\\tilde{p}_c^k\\), which is the proportion of the newly generated bag \\(B^{k}\\), is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.228, + 0.727, + 0.469, + 0.747 + ], + "angle": 0, + "content": "\\[\np _ {c} ^ {k} - \\alpha \\sigma_ {c} ^ {k} \\leq \\tilde {p} _ {c} ^ {k} \\leq p _ {c} ^ {k} + \\alpha \\sigma_ {c} ^ {k}, \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.271, + 0.748, + 0.469, + 0.768 + ], + "angle": 0, + "content": "\\[\np _ {c} ^ {k} = \\gamma p _ {c} ^ {i} + (1 - \\gamma) p _ {c} ^ {j}, \\tag {6}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.332, + 0.769, + 0.469, + 0.8 + ], + "angle": 0, + "content": "\\[\n\\gamma = \\frac {n _ {i}}{n _ {i} + n _ {j}}, \\tag {7}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.118, + 0.802, + 0.469, + 0.843 + ], + "angle": 0, + "content": "\\[\n\\sigma_ {c} ^ {k} = \\gamma \\sqrt {\\frac {p _ {c} ^ {i} \\left(1 - p _ {c} ^ {i}\\right)}{n _ {i}}} + (1 - \\gamma) \\sqrt {\\frac {p _ {c} ^ {j} \\left(1 - p _ {c} ^ {j}\\right)}{n _ {j}}}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.855, + 0.47, + 0.902 + ], + "angle": 0, + "content": "where \\(p_c^k\\) is the expected proportion of the generated mixed bag, which is directly computed from the proportions of the original bags \\(B^{i}\\), \\(B^{j}\\), and the standard deviation \\(\\sigma_c^k\\) of the" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.32, + 0.891, + 0.35 + ], + "angle": 0, + "content": "mixed bag can be calculated by using the standard deviation of the sub-bags with the ratio \\(\\gamma\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.351, + 0.892, + 0.455 + ], + "angle": 0, + "content": "This confidence interval (Eq.5) indicates that the actual proportion of the mixed bag has a gap from the expected proportion. If we directly use the proportion \\(\\mathbf{p}^k\\) (Eq.6) for the mixed bag as augmented data and use it for the proportion loss, the gap from the actual proportion may adversely affect the training of the network since the gap causes a label noise." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.456, + 0.892, + 0.561 + ], + "angle": 0, + "content": "To avoid this adverse effect caused by gaps (label noise), we propose a confidence interval loss (CI loss) for generated mixed bags. The CI loss is based on the proportion loss [1]. In contrast to the standard proportion loss, the CI loss ignores a loss when the estimated proportion \\(\\hat{p}_c^k\\) is in the confidence interval \\([p_c^k -\\alpha \\sigma_c^k,p_c^k +\\alpha \\sigma_c^k ]\\) since gaps in the CI often occur." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.562, + 0.892, + 0.607 + ], + "angle": 0, + "content": "Given the degree of confidence \\(\\alpha \\%\\) (the corresponding value is set to \\(\\alpha\\)), such as when the degree of confidence is \\(95\\%\\), \\(\\alpha = 1.96\\), the CI loss is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.543, + 0.616, + 0.892, + 0.657 + ], + "angle": 0, + "content": "\\[\n\\ell_ {\\mathrm {C I}} \\left(B ^ {k}, \\mathbf {p} ^ {k}, f\\right) = - \\sum_ {c = 1} ^ {C} \\mathbf {1} \\left(p _ {c} ^ {k}, \\hat {p} _ {c} ^ {k}\\right) p _ {c} ^ {k} \\log \\hat {p} _ {c} ^ {k}, \\tag {9}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.675, + 0.66, + 0.891, + 0.705 + ], + "angle": 0, + "content": "\\[\n\\hat {p} _ {c} ^ {k} = \\frac {1}{| B ^ {k} |} \\sum_ {j = 1} ^ {| B ^ {k} |} f \\left(x _ {j} ^ {k}\\right) _ {c}, \\tag {10}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.53, + 0.708, + 0.891, + 0.741 + ], + "angle": 0, + "content": "\\[\n\\mathbf {1} \\left(p, p ^ {\\prime}\\right) = \\left\\{ \\begin{array}{l l} 0 & \\text {i f} p - \\alpha \\sigma \\leq p ^ {\\prime} \\leq p + \\alpha \\sigma \\\\ 1 & \\text {o t h e r w i s e} \\end{array} , \\right. \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.856 + ], + "angle": 0, + "content": "where \\(\\mathbf{1}\\) is the indicator function, which outputs 0 if \\(p'\\) is in the confidence interval, and 1 otherwise. This CI loss updates the network parameters if the difference between the estimated proportion \\(\\hat{p}_c^k\\) and the expected proportion \\(p_c^k\\) calculated by Eq.6 is significant. Using this loss, we can accelerate the training by using the augmented bags without any adverse effects from proportion gaps." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.902 + ], + "angle": 0, + "content": "In training, mixed bags are randomly generated in each batch. It indicates that the number of generated bags will increase with iteration. We stop training based on the propor" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.925, + 0.519, + 0.937 + ], + "angle": 0, + "content": "16574" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.08, + 0.089, + 0.89, + 0.272 + ], + "angle": 0, + "content": "
MethodCIFAR10AccuracySVHNAccuracyPATHAccuracyOCTAccuracyBLOODAccuracyORGANACuracyORGANCuracyORGANSAccuracyAverageAccuracy
LLP [1]0.45380.30090.78430.43360.88690.76350.78980.53720.6187
LLP + Ours(w/o CI)0.45820.29710.78840.4250.88980.78310.81890.5630.6280
LLP + Ours0.52560.37420.78610.43470.90170.79710.80990.61970.6561
LLP + Ours(supervised)0.65940.77810.81180.53960.89470.82220.82330.66740.7234
LLP-VAT [28]0.47400.31190.89150.41240.89150.79360.80600.58370.6455
LLP-VAT + Ours(w/o CI)0.52030.43020.87790.45030.87790.78470.76560.58490.6614
LLP-VAT + Ours0.52830.41110.89440.43660.89440.81550.82280.63760.6800
LLP-VAT + Ours(supervised)0.59630.59760.89970.47770.89970.82300.83130.66220.7234
LLP-PI [13]0.47020.30110.88860.42240.88620.78100.79620.59170.6421
LLP-PI + Ours(w/o CI)0.47940.52090.86880.43500.85730.75950.75700.57410.6565
LLP-PI + Ours0.52900.38650.88410.43660.88410.80130.79890.62360.6680
LLP-PI + Ours(supervised)0.58960.77210.89180.47200.89180.81010.81840.65770.7379
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.278, + 0.893, + 0.322 + ], + "angle": 0, + "content": "Table 1. Instance-level classification accuracy when our method was applied to three baseline methods; LLP [1], LLP-VAT [28] and LLP-PI [13]. Each value is the average of five-fold cross-validation results. Here, 'CI' means the confident interval, and 'supervised' indicates the case when a ground-truth proportion to the generated mixed bag is given." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.332, + 0.89, + 0.518 + ], + "angle": 0, + "content": "
MethodCIFAR10 AccuracySVHN AccuracyPATH AccuracyOCT AccuracyBLOOD AccuracyORGANA AccuracyORGANC AccuracyORGANS AccuracyAverage Accuracy
LLP [1]0.45380.30090.78430.43360.88690.76350.78980.53720.6187
LLP + Ours0.52560.37420.78610.43470.90170.79710.80990.61970.6561
LLP + Flip0.57770.38840.82990.47930.92650.65270.69040.62930.6467
LLP + Flip + Ours0.57640.41240.80050.55040.91550.67180.67170.62800.6533
LLP + Erase0.55510.35000.80970.44140.90940.83930.84470.65780.6759
LLP + Erase + Ours0.56710.42690.79340.42910.90210.82660.83130.65940.6794
LLP + Invert0.52580.67630.77750.43940.87900.77790.82150.62550.6899
LLP + Invert + Ours0.57840.77610.74210.45800.87360.78450.83230.63290.7097
LLP + Gaussianblur0.47660.36860.76390.41450.88750.79060.83180.63250.6457
LLP + Gaussianblur + Ours0.51350.40360.75550.43000.87890.79620.79890.67090.6559
LLP + Perspective0.56750.54410.78920.46780.89680.83090.84400.66890.7011
LLP + Perspective + Ours0.57500.57150.77450.49620.90640.81800.84040.68950.7089
" + }, + { + "type": "table_caption", + "bbox": [ + 0.104, + 0.523, + 0.859, + 0.538 + ], + "angle": 0, + "content": "Table 2. Instance-level classification accuracy when our method was applied after various instance-level augmentation methods." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.563, + 0.47, + 0.593 + ], + "angle": 0, + "content": "tion loss in validation data. Note that instance-level labels cannot be used for validation in LLP." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.606, + 0.21, + 0.623 + ], + "angle": 0, + "content": "6. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.63, + 0.381, + 0.647 + ], + "angle": 0, + "content": "6.1. Datasets and experimental settings" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.653, + 0.47, + 0.879 + ], + "angle": 0, + "content": "Preparation of bags: The eight datasets used in these experiments were the same as those used in the preliminary experiments. The way of generating bags was also the same as in the preliminary experiments. Although some of the related studies generated bags by allowing overlaps to increase the number of labeled bags, we did not allow overlaps since this situation is unnatural in actual applications. To keep the experiment setups the same in all datasets, we set the number of labeled bags as 512 and the bag size as 10 based on the smallest dataset. This small bag size can be considered a challenging scenario for MixBag since the number of samplings for sub-bags decreases, and it increases the confidence interval. We also evaluated our method using different bag sizes to demonstrate the effectiveness of our method in various situations." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.886, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Implementation: We implemented our method by using" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.563, + 0.892, + 0.67 + ], + "angle": 0, + "content": "Pytorch [21]. The network model was ResNet18 [9] pretrained on the ImageNet dataset [5]. To train our network, we also used the Adam Optimizer [9] with a learning rate of 3e-4, epoch= 1000, mini-batch size = 32, early stopping = 10 and trained on an NVIDIA GeForce 3090 GPU. We set the confidence degree as '99%' and selected \\(\\gamma\\) randomly from a uniform distribution [0, 1]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.677, + 0.892, + 0.768 + ], + "angle": 0, + "content": "Evaluation metric: We evaluated the model performance by the instance-level classification accuracies, which were calculated by using the confusion matrix. To compute the metric, we performed a five-fold cross-validation in all our experiments. The accuracies listed in the tables are the average values of the five-fold cross-validation." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.785, + 0.633, + 0.801 + ], + "angle": 0, + "content": "6.2. Comparison" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Comparison with current methods: Our method MixBag can be applied to any proportion loss-based method since MixBag is a data augmentation method, in which any method can be applied after data augmentation with the CI loss. Most current LLP methods incorporate self-supervised learning, such as consistency, into the proportion loss. We" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.925, + 0.519, + 0.937 + ], + "angle": 0, + "content": "16575" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.126, + 0.089, + 0.416, + 0.16 + ], + "angle": 0, + "content": "
Methodγ-samplingAverage Accuracy
LLP [1]-0.6187
LLP + Oursuniform0.6561
LLP + OursGauss0.6512
LLP + Ourshalf0.6524
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.165, + 0.47, + 0.193 + ], + "angle": 0, + "content": "Table 3. Average accuracy on eight datasets when changing a sampling method for \\(\\gamma\\)." + }, + { + "type": "table", + "bbox": [ + 0.139, + 0.207, + 0.406, + 0.289 + ], + "angle": 0, + "content": "
MethodCIAverage Accuracy
LLP [1]0.6187
LLP + Ours(99%)✓0.6561
LLP + Ours(95%)✓0.6519
LLP + Ours(80%)✓0.6531
LLP + Ours(50%)✓0.6243
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.294, + 0.468, + 0.322 + ], + "angle": 0, + "content": "Table 4. Average accuracy on eight datasets when changing the degree of confidence interval (50%, 80%, 95%, 99%)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.348, + 0.468, + 0.469 + ], + "angle": 0, + "content": "thus applied our method in three methods: 1) LLP [1], which is the method of the original paper on using the proportion loss; 2) LLP-VAT [28], which introduces the consistency regularization into the proportion loss; and 3) LLP-PI [13], which uses the additive Gaussian noise for making perturbed examples. The LLP-VAT is one of the state-of-the-art LLP methods using the proportion loss, and its implementations are publicly available." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.47, + 0.468, + 0.606 + ], + "angle": 0, + "content": "We compared the baseline methods as an ablation study. The first was 'LLP', which uses the standard proportion loss; the second was 'LLP+Ours(w/o CI)' which uses the MixBag without using the CI loss, where the proportion is directly calculated from the original bags (and may contain noise) was used as the label for the generated mixed bag. The third was 'LLP+Ours(supervised)', which uses the ground-truth proportions of the mixed bags. Note that the proportion would be unknown in real cases." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.607, + 0.468, + 0.729 + ], + "angle": 0, + "content": "Table 1 shows the accuracy of each method, where the gray color field indicates the proposed methods in each baseline method. 'LLP+Ours(w/o CI)' improved the accuracies in some datasets and slightly improved them on average from the baselines. However, the improvement was limited by the noisy proportions. MixBag improved the accuracy of every baseline method on all datasets, and the improvement was 3 to 4 points on average." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Introducing MixBag with instance-level augmentation: Next, we introduced our method to the instance-level augmentation methods. We used standard augmentation techniques: 'Flip' randomly flips the image horizontally and upside down. 'Erase' removes a randomly selected area from an original image. 'Invert' randomly changes the colors of the image by inversion. 'Gaussianblur' blurs an image by adding a randomly chosen Gaussian blur. 'Perspective' performs a random projective transformation on an image. To generate a bag by instance-level augmentation, we added perturbations into instances randomly selected from" + }, + { + "type": "table", + "bbox": [ + 0.558, + 0.089, + 0.828, + 0.226 + ], + "angle": 0, + "content": "
MethodSizeNumAverage Accuracy
LLP [1]105120.6187
LLP + Ours(w/o CI)105120.6280
LLP + Ours105120.6561
LLP [1]202560.5441
LLP + Ours(w/o CI)202560.5496
LLP + Ours202560.5667
LLP [1]401280.4746
LLP + Ours(w/o CI)401280.4600
LLP + Ours401280.5058
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.231, + 0.892, + 0.273 + ], + "angle": 0, + "content": "Table 5. Average accuracy on eight datasets when changing the number of labeled bags and bag size. 'Size' means the bag size. 'Num' means the number of labeled bags." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.297, + 0.892, + 0.435 + ], + "angle": 0, + "content": "an original bag; i.e., an augmented bag contains the perturbed instances and original instances, where this augmentation has not been reported in previous papers. In \\(\\mathrm{LLP} +\\) instance-level \\(^+\\) MixBag, the mixed bag was created from the original and instance-level augmented bags. Table 2 shows the accuracies of the baseline and our methods. The instance-level data augmentation improved the performance from the baseline. Our method further improved the accuracies of every instance-level augmentation method." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.443, + 0.795, + 0.457 + ], + "angle": 0, + "content": "6.3. Performance in various situations" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.466, + 0.892, + 0.617 + ], + "angle": 0, + "content": "Performance with different \\(\\gamma\\) sampling methods: We evaluated our method with three different \\(\\gamma\\) sampling methods, i.e., three different ways to determine the mixing rate \\(\\gamma\\) of the two sub-bags \\(S^i, S^j\\): 'uniform' selects \\(\\gamma\\) randomly from a uniform distribution; 'Gauss' selects \\(\\gamma\\) randomly from a Gaussian distribution \\(\\mathcal{N}(0.5, 0.25)\\); 'half' always set \\(\\gamma\\) to 0.5. Table 3 shows the average accuracies of all datasets. All sampling methods outperformed the performance compared to the baseline method (LLP); 'uniform' was marginally better than other methods." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.623, + 0.892, + 0.819 + ], + "angle": 0, + "content": "Performance with different confidence intervals: We conducted experiments with four different confidence intervals, \\(99\\%\\), \\(95\\%\\), \\(80\\%\\), and \\(50\\%\\). Table 4 shows the average accuracies of all datasets. For all confidence interval settings, our method improved the accuracy on all datasets and in all cases. When the confidence interval took high values \\((99\\%, 95\\%, 80\\%)\\), our method worked well since the worst effects of noisy labels were mitigated by the CI loss. Even when the confidence interval was low \\((50\\%)\\), the accuracy improved from the baseline method. The case of \\(99\\%\\) was the best on average. We consider that a larger confidence interval avoids the adverse effects of noisy proportions and makes the training more stable." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.826, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Performance when changing the number of labeled bags and bag size: To show the effectiveness of our method in various situations, we conducted experiments with different bag sizes (512, 256, 128) and different numbers of labeled bags (10, 20, 40), where the bag size and the number of" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.925, + 0.519, + 0.937 + ], + "angle": 0, + "content": "16576" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.116, + 0.089, + 0.428, + 0.187 + ], + "angle": 0, + "content": "
MethodBag-GenerationCIAverage Accuracy
LLP [1]--0.6187
LLP + Ours(w/o CI)Union-0.6226
LLP + Ours(w/o CI)Sub-bag0.4956
LLP + Ours(with CI)Sub-bag✓0.6364
LLP + Ours(w/o CI)MixBag0.6280
LLP + Ours(with CI)MixBag✓0.6561
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.192, + 0.47, + 0.22 + ], + "angle": 0, + "content": "Table 6. Average accuracy on eight datasets in different bag-generation methods." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.244, + 0.468, + 0.318 + ], + "angle": 0, + "content": "labeled bags have a trade-off since the total number of instances is fixed. Table 5 shows the average accuracies on all datasets with various setups. Our method improved the accuracy from the baseline methods on average in all cases. This demonstrates the robustness of our method." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.326, + 0.468, + 0.55 + ], + "angle": 0, + "content": "Performance with different bag generations: To confirm the effectiveness of the 'Mix' approach, we compared MixBag with two other bag generation methods. 1) 'union' directly combines any two bags \\((B^i, B^j)\\) without sampling. In this case, the proportion of a generated bag can be directly calculated from those of the original bags; i.e., there is no noise for the combined proportions by taking the union of two bags. Therefore, the CI loss was not used for this method. 2) 'sub-bag' randomly samples instances from a single bag \\(B^i\\). It can be considered as a sub-bag of the original bag \\(B^i\\). In this case, the label proportions of the sub-bag may have a gap from the original one, and thus, we evaluated two cases; 'sub-bag' without and with the CI loss. 3) 'MixBag' is our method, which mixes two bags. We also evaluated two cases; Mixbag with and without CI loss." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.552, + 0.468, + 0.747 + ], + "angle": 0, + "content": "Table 6 shows the average of the instance-level accuracies of the comparative methods on the eight datasets. Since 'sub-bag with CI' and union' can increase the number of labeled bags, these methods had slightly improved accuracy from that of baseline method LLP [1]. Our method, 'MixBag with CI' further improved the accuracy compared with these other bag generation methods. We consider that our method has two characteristics of 'sub-bag' and 'union', where MixBag first makes sub-bags from original bags and then takes the union of these sub-bags. In addition, MixBag can generate various proportions of the mixed bag compared to 'sub-bag' and 'union'. Therefore, MixBag was better than them." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.757, + 0.248, + 0.773 + ], + "angle": 0, + "content": "6.4. Detailed Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Distribution of proportion vectors in the space of proportion labels: Figure 6 shows distributions of the original proportion vectors \\(\\{\\mathbf{p}^i\\}_{i=1}^n\\) (blue) and the generated mixed bag's proportion vectors \\(\\{\\mathbf{r}^i\\}_{i=1}^m\\) (orange) in the 'ORGANS' dataset, in which the dimension was compressed to 2D by PCA [29]. Here, the number of mixed bags is the same as that of the original bags. We can see that the MixBag proportion vectors do not overlap with the orig-" + }, + { + "type": "image", + "bbox": [ + 0.513, + 0.105, + 0.685, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.509, + 0.237, + 0.7, + 0.293 + ], + "angle": 0, + "content": "Figure 6. Distribution of proportion vectors. Blue: Original bag's proportion. Orange: Mixed bag's proportion." + }, + { + "type": "image", + "bbox": [ + 0.723, + 0.104, + 0.893, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.715, + 0.237, + 0.906, + 0.293 + ], + "angle": 0, + "content": "Figure 7. Relationship between confidence interval and actual gaps. Blue: proportion vector of a bag." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.32, + 0.892, + 0.41 + ], + "angle": 0, + "content": "inal ones, i.e., new proportion labels were generated, and the distribution of mixed bag proportions covers the original distribution by interpolating pairs of the original bags. This result shows that MixBag adds diversity to the training dataset, which facilitates an improvement in the instance-level classification accuracy." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.419, + 0.892, + 0.617 + ], + "angle": 0, + "content": "Relationship between confidence interval and ground-truth proportion: Figure 7 shows how well the confidence interval works. The horizontal axis indicates the difference \\((\\| \\mathbf{p} - \\hat{\\mathbf{p}} \\|_1)\\) between the ground-truth proportion \\(\\mathbf{p}\\) and the estimated proportion \\(\\hat{\\mathbf{p}}\\) of a mixed bag. The vertical axis indicates the difference \\((\\alpha \\sigma^k)\\) between the upper bounds of the confidence interval and \\(\\mathbf{p}\\), where we set the degree of confidence as \\(99\\%\\). Each blue point indicates the proportion vector of a mixed bag. Almost all points are under the straight line in the figure. This indicates that the actual proportion gaps from the ground truth were less than the confidence interval, and thus the proposed CI loss works properly." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.633, + 0.619, + 0.648 + ], + "angle": 0, + "content": "7. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this paper, we examined how the number of labeled bags and the bag size affects the performance in LLP. As a result, we found that the accuracy improves as the number of labeled bags increases, even when the total number of instances is fixed. Then, based on this observation, we propose a simple but effective bag-level data augmentation method. In addition, we also proposed a confidence interval loss that effectively trains a classification network by using the generated bags while avoiding the adverse effects caused by noisy proportions. To the best of our knowledge, this is the first attempt to propose bag-level data augmentation for LLP. The experiments using eight datasets demonstrated the effectiveness of our method in various cases. Additionally, MixBag can be applied to instance-level data augmentation techniques and any LLP method that uses a standard proportion loss." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.925, + 0.518, + 0.936 + ], + "angle": 0, + "content": "16577" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.092, + 0.47, + 0.138 + ], + "angle": 0, + "content": "Acknowledgements: This work was supported by JSPS KAKENHI Grant Number JP20H04211 and JP23K18509, and JST, ACT-X Grant Number JPMJAX200G, Japan." + }, + { + "type": "title", + "bbox": [ + 0.08, + 0.166, + 0.173, + 0.181 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.19, + 0.47, + 0.246 + ], + "angle": 0, + "content": "[1] Ehsan Mohammady Ardehaly and Aron Culotta. 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In Proceedings of the IEEE international conference on computer vision, pages 2223-2232, 2017." + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.542 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.925, + 0.519, + 0.937 + ], + "angle": 0, + "content": "16579" + } + ] +] \ No newline at end of file diff --git a/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/c288d48a-0e97-49d8-951a-99b2d027811b_origin.pdf b/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/c288d48a-0e97-49d8-951a-99b2d027811b_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..05c52f8eb3f0a8e041424407a8ce6224b43de76c --- /dev/null +++ b/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/c288d48a-0e97-49d8-951a-99b2d027811b_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:724c8bd393276590d3dbcaa9c7fb804ca6a854c9d26f4aef5afbb3eefe4ca33f +size 493692 diff --git a/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/full.md b/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/full.md new file mode 100644 index 0000000000000000000000000000000000000000..60c8febe380b9bbde8b81a9d6084cb7c9ca676f2 --- /dev/null +++ b/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/full.md @@ -0,0 +1,308 @@ +# MixBag: Bag-Level Data Augmentation for Learning from Label Proportions + +Takanori Asanomi1, Shinnosuke Matsuo1, Daiki Suehiro1,2, Ryoma Bise1 +1Kyushu University, Fukuoka, Japan +2RIKEN AIP, Japan + +{takanori.asanomi@human., shinnosuke.matsuo@human., suehiro@, bise@}ait.kyushu-u.ac.jp + +# Abstract + +Learning from label proportions (LLP) is a promising weakly supervised learning problem. In LPP, a set of instances (bag) has label proportions, but no instance-level labels are given. LPP aims to train an instance-level classifier by using the label proportions of the bag. In this paper, we propose a bag-level data augmentation method for LPP called MixBag, based on the key observation from our preliminary experiments; that the instance-level classification accuracy improves as the number of labeled bags increases even though the total number of instances is fixed. We also propose a confidence interval loss designed based on statistical theory to use the augmented bags effectively. To the best of our knowledge, this is the first attempt to propose bag-level data augmentation for LPP. The advantage of MixBag is that it can be applied to instance-level data augmentation techniques and any LPP method that uses the proportion loss. Experimental results demonstrate this advantage and the effectiveness of our method. + +# 1. Introduction + +In general classification tasks, a model is trained on datasets where each piece of data (instance) has class labels. However, instance-level annotations cost a lot, and there are many cases in which instance-level annotation cannot be disclosed to the public for privacy reasons [23]. In such a situation, we only know the label proportions given to a set of instances (bag) and must train a model from these label proportions to classify each instance. This problem setting is known as learning from label proportions (LLP) [1]. + +Figure 1 illustrates the problem setup of LLP. A bag $B$ consists of instances (e.g., images). Bag-level labels are given as training data instead of instance-level labels (class labels of each instance $x$ are unknown). The label proportion $\mathbf{p}^i$ of bag $B^i$ is given as a bag-level label. For example, if a bag $B^0$ contains 60, 100, and 40 instances of class 1, 2, and 3, respectively, $\mathbf{p}^i = (0.3, 0.5, 0.2)^{\mathrm{T}}$ . LLP aims to train an instance-level classifier by using the label proportions of a bag. It is a weakly supervised learning task. + +![](images/29b2be03f814735205653ecffdf7aa9552c9466c46f69a0596f89fd816f90fcd.jpg) +Figure 1. Illustration of learning from label proportions. LLP aims to train an instance-level classifier by using label proportions of a bag as training data instead of instance-level labels. + +Many LLP methods have been proposed to address this challenging task [1, 24, 28, 27, 18, 19]. Most of them are based on the proportion loss, which evaluates the difference between the given proportion $\mathbf{p}^i$ and the estimated proportion $\hat{\mathbf{p}}^i$ , and can be calculated by taking the average of the class probabilities of the instances in a bag. The methods based on the proportion loss work well when bag-level labels (label proportions) are sufficient. However, the accuracy decreases as the number of labeled bags decreases, i.e., insufficient labeled data causes difficulty in training a network, which is known in machine learning tasks. + +In such cases, instance-level data augmentation is often an effective way to improve accuracy. Many instance-level data augmentation techniques, such as perturbation, for general classification tasks have been proposed, and their effectiveness has been demonstrated [25]. Instance-level data augmentation may improve the accuracy in LLP. However, it does not increase the number of labeled bags from the original one, and it is difficult to generate various bags with different proportions without using instance-level labels (these are unknown in LLP). + +This paper proposes a bag-level data augmentation for + +LLP that can generate new bags with various label proportions. To design an effective bag-level data augmentation technique, we conducted a detailed analysis of what situation can improve the accuracy in LLP. As a result, we found an important observation that the accuracy improves as the number of labeled bags increases, even though the total number of instances is fixed, i.e., different bags overlap each other as shown in Figure 2 (Right). On the basis of this observation, we propose a bag-level data augmentation called MixBag. MixBag increases the number of labeled bags artificially by sampling instances from a pair of original bags and mixing them: this operation mimics the above observations. The expected label proportion of a generated mixed bag can be calculated by those of the original bags. However, it may have a gap from the actual proportion of the mixed bag because randomly selected instances do not follow the proportion of the original ones. This gap adversely affects the training. + +We thus introduce a confidence interval loss that helps to train a classification network by using the generated bags while avoiding this adverse effect by a proportion gap; it is statistically guaranteed. To the best of our knowledge, this is the first attempt to propose bag-level data augmentation for LLP. Experiments using eight datasets demonstrate the effectiveness of our method in various cases; our method improved the classification accuracy on all datasets. Our main contributions are summarized as follows. + +- We examined how the number of labeled bags and the bag size affect the performance in LLP. From the preliminary experiments, we concluded that the accuracy improves as the number of labeled bags increases, even though the total number of instances is fixed. +- We proposed MixBag with a confidence interval loss. This method artificially increases the number of labeled bags, and the confidence interval loss helps train a classification network using the generated bags. +- We demonstrated that MixBag can be applied to any of the current LLP methods and any of the instance-level augmentation methods. Experimental results show that our method improved classification accuracy on various datasets. + +# 2. Related work + +# 2.1. Learning from Label Proportion (LLP) + +Proportion loss [1] is the most common approach to LLP. To compute the proportion loss, the average of the output probability in a bag is calculated as a proportion estimation, and then the bag-level cross-entropy between the true label proportion and the estimated proportion is used as the loss. + +The proportion loss has been extended in many methods; e.g., introducing regularization terms [33, 1, 8, 28, 30, 17, + +![](images/14764b48d3c88aea555ea6770fdab8d130813c39af571648e8df54817e47cab0.jpg) +Figure 2. Illustration of overlap and non-overlap situations. (a) Original bags. (b) New bags (yellow) are added with non-overlap, i.e., the total number of instances increases. (c) New bags overlap with the original ones, i.e., the total number of instances is fixed. + +18]. Tsai et al. [28] incorporated a consistency regularization into the proportion loss, which forces the network predictions to be consistent when its input is perturbed. Yang et al. [30] use contrastive learning for pre-training in a self-supervised learning manner and then train the model by using the proportion loss. LLP-GAN [17] introduces the generative adversarial network (GAN) to LLP. The fake instances created by the generator encourage the discriminator to distinguish real or fake and classify the real instances. This method also uses the proportion loss to train the classifier. Two-stage LLP [18] introduces pseudo-labeling after pre-training by using a proportion loss. + +It is known that the classification accuracy decreases when the labeled data is insufficient in machine learning. To deal with this issue, data augmentation is a standard approach. However, bag-level data augmentation for LLP is still an unexplored area. This paper proposes a simple but effective bag-level data augmentation method. One of the advantages of our method is that any LLP method can be applied after our bag-level augmentation. + +# 2.2. Instance-level data Augmentation + +Data augmentation is a standard way to address the problem of inadequately labeled data. Many instance-level data augmentation techniques have been proposed. Basic data augmentation involves adding perturbations to the original images, such as by flipping the image [25], adding noise [25], and erasing parts of an image [7, 2, 14]. Image mix [11, 35, 34, 10] is another approach, where methods such as MixUP [35] and CutMix [34] mix together two original images. GAN-based augmentation methods [22, 36, 26] represent data distributions and generate new images based on these distributions. Auto augment [3, 16, 4] automatically searches for suitable augmentation approaches that improved performance. The above methods are instance-level data augmentations. It is not a simple task to generate various bags that have different proportions without using instance-level labels. For example, CutMix and MixUp require the labels of the original im + +ages (instances) in order to prepare the label proportions of a generated new bag. Since simple perturbation methods do not require the ground truth of the image label for augmentation, they can be used to add perturbations to each instance in a bag. However, these methods are not designed for bag-level data augmentation. + +# 2.3. Bag-Level data augmentation for MIL + +Few bag-level data augmentation methods have been proposed for multiple instance learning (MIL), which trains a classifier from bag-level class labels (positive or negative). Li et al. [15] proposed a MIL-based method that uses bag-level augmentation for COVID-19 severity assessment. This method takes a pseudo-labeling approach, where positive and negative instances are taken from positive bags based on the estimated confidence of the instance class and used to make a new bag. Yang et al. [31] proposed a MIL method for segmenting pathology images. This method generates new bags by clustering instances. It is reasonable for MIL to make a positive or negative bag from high confidence positive or negative instances. However, it is difficult to make a proportion label from pseudo labeling since all of the pseudo labels have to be accurate to calculate the correct proportion. So in order to improve the performance of LLP, appropriately designing a bag-level data augmentation is required. + +# 3. Preliminary: LLP and Proportion Loss + +In LLP, the training set contains $n$ bags, $B^1, \ldots, B^n$ . Each bag $B^i$ consists of a set of instances, i.e., $B^i = \{x_j^i\}_{j=1}^{|B^i|}$ , and a vector of label proportions $\mathbf{p}^i = (p_1^i, \ldots, p_c^i, \ldots, p_C^i)^T$ is attached to each bag as training label, where $C$ is the number of classes. This label indicates that $p_c^i \times |B^i|$ instances in the $i$ -th bag belong to the class $c$ for any $c \in \{1, \ldots, C\}$ . The goal of LLP is to train a network that estimates the class label of each instance by using only the proportion labels of the bags. Proportion loss [1] is a standard approach to this challenging task, and many methods are based on it. + +Given training data with label proportions, the standard proportion loss is a bag-level cross-entropy between the ground-truth of the label proportion $\mathbf{p}^i$ and the predicted proportion $\hat{\mathbf{p}}^i$ , which is the average of the output class probabilities in a bag. It is defined as: + +$$ +\ell_ {\text {p r o p}} \left(B ^ {i}, \mathbf {p} ^ {i}, f\right) = - \sum_ {c = 1} ^ {C} p _ {c} ^ {i} \log \hat {p} _ {c} ^ {i}, \tag {1} +$$ + +$$ +\hat {p} _ {c} ^ {i} = \frac {1}{| B ^ {i} |} \sum_ {j = 1} ^ {| B ^ {i} |} f \left(x _ {j} ^ {i}\right) _ {c}, \tag {2} +$$ + +where $f(x_{j}^{i})_{c}$ is the output probability that $x_{j}^{i}$ belongs to $c$ . + +# 4. Preliminary Empirical Analysis of LLP + +In previous works, the relationship between the number of labeled bags, bag sizes, and accuracy in LLP has not been analyzed well. Some papers [17, 8] reported that the accuracy increased as the larger bag size in their experiments. However, the reason was not discussed well. In their experiments, they changed the bag size while the total number of instances was fixed. Since an instance generally does not belong to two bags (i.e., bags does not overlap each other) in LLP, it indicates that the bag size and the number of labeled bags have a trade-off; when the bag size increases, the number of labeled bags decreases. + +In this section, we further empirically analyze the relationships among the number of labeled bags, bag sizes, and accuracy by using the proportion loss on various public datasets. First, we conducted experiments on whether the number of labeled bags or the bag size has more influence on the classification accuracy in a general setup of LLP, where different bags do not contain the same instance (no overlap), as shown in Figure 2 (b). To avoid the tradeoff between the number of labeled bags and the bag size, we fixed the number of labeled bags to analyze the effect for accuracy by the number of labeled bags, and vice versa. In the experiments, the total number of instances changed. We speculated that this analysis may give clues for developing a new method in LLP. + +Datasets and experimental settings: We used eight datasets in our experiments1: 1) CIFAR10 [12], which is commonly used in classification tasks. The dataset contains ten classes, such as vehicles and animals; 2) SVHN [20], which is a house-number-images dataset, and a character-level label is given like in MNIST [6]; 3) OCT, which contains four classes of Retinal OCT images; 4) BLOOD, which contains eight classes of Blood Cell Microscope images; 5) ORGAN, 6) ORGANC, 7) ORGANS, which contain eleven classes of abdominal CT images. The difference is the view of the image and its sizes, and 8) PATH, which contains nine classes of colon pathology images. Note that 3) to 8) are datasets in MedMNIST [32], and we did not use the small datasets in [32] since they cannot be used to prepare enough bags for LLP. + +To prepare a bag, the proportions of each class were randomly selected from a Gaussian distribution; the decided proportion was used as the label of the bag. Then, samples were randomly selected from each class, in which the number of samples for each class followed the proportion of the class. In real applications, different bags do not contain the same instance; i.e., they do not overlap. We thus generated bags without overlap in these experiments. + +# Performance when changing the number of labeled bags + +![](images/0099fcb638333b2d61d6a625b9b0140ba4f083ed6a2770a4bddb834a1cc7a997.jpg) +Figure 3. Relationship among the number of labeled bags, bag sizes, and accuracy in a general setup of LLP, where different bags do not contain the same instance (no overlap). Left: Accuracy improvement when increasing the number of labeled bags (bag size is fixed). Right: Accuracy improvement when increasing the bag size (the number of labeled bags is fixed). + +in the general setup of LLP (no overlap): We examined how the number of labeled bags affects the instance-level classification accuracy for the standard proportion loss. We varied the number of labeled bags (64, 128, 256, 512) while keeping the bag size fixed at 10. In this experiment, we follow the general setup of LLP; different bags do not overlap, i.e., the number of instances changed when the number of labeled bags was changed. As shown in Figure3 (Left), the accuracy improved due to increasing the number of labeled bags in all datasets. This is reasonable because the number of labeled bags indicates the number of proportion labels; more labeled data for training is expected to improve accuracy in machine learning. + +Performance when changing the bag size in the general setup of LLP (no overlap): We analyzed how the bag size affects the accuracy in the general setup of LLP. In this experiment, we changed the bag size (64, 128, 256, 512) but fixed the number of labeled bags at 10. As shown in Figure 3 (Right), the accuracy did not vary significantly with the bag size in six of the datasets, while it improved in two datasets. This result shows that increasing the number of instances without increasing the labels does not effectively improve accuracy. + +Performance when changing the number of labeled bags in the case of overlap: The above observations indicate that increasing the number of labeled bags is important to improving accuracy. Another factor that might have improved the accuracy is increasing the total number of 'instances,' which occurs when the number of labeled bags increases. To confirm whether the number of labeled bags or the total number of instances affects accuracy, we performed experiments on how the number of labeled bags affects the accuracy in the case of overlap, i.e., when the total number of instances was fixed. The initial bags were prepared, where the number of labeled bags was 64, and the bag size was 10. To increase the number of labeled bags, we then incrementally added new bags (64, 128, 256), where the new + +![](images/37623f6381952cfeed9fd96eb9e80ac9cbd66c8b8f4dbf9f61efb323e2c84303.jpg) +Figure 4. Experimental results on how the number of labeled bags affects the accuracy in the case of overlap, i.e., when the total number of instances was fixed. + +bags were generated from the initial instances that belong to the initial bags, i.e., generated bags overlap with the initial ones, as shown in Figure 2 (c). As shown in Figure4, the accuracy improves as the number of labeled bags increases in all datasets. This observation is important for our bag-level data augmentation. If we were to mimic this situation where the number of labeled bags increases and the total number of instances is fixed, it should improve accuracy, even though a situation with bags having overlaps is unnatural in actual applications. However, we can make this situation by generating new bags from the original ones. + +# 5. MixBag with confidence interval loss + +To mimic the situation of increasing the number of labeled bags and allowing their overlap, we propose MixBag, which is a bag-level data augmentation technique. + +# 5.1. MixBag + +Figure 5 (Left) shows an overview of MixBag. Given two randomly selected bags $\{B^i, B^j\}$ where each bag is labeled with a proportion, $\mathbf{p}_i$ or $\mathbf{p}_j$ , mix the two bags to generate a new bag. More precisely, $n_i = |B^i| \times \gamma$ and $n_j = |B^j| \times (1 - \gamma)$ instances are randomly sampled from $B^i$ and $B^j$ , respectively, where $\gamma \in [0,1]$ is a random variable, and the sampled sub-bags are denoted as $S^i$ and $S^j$ . Then, these two sub-bags are combined to generate a mixed bag, $B^k = S^i \cup S^j$ . This generated mixed bag overlaps with the original bags while the total number of instances is fixed, and the number of labeled bags is increased by the generated bags. It can be considered to mimic the third preliminary experiment (Figure 2 (c)). + +# 5.2. Confidence interval loss + +The sampled sub-bags $S^i$ , $S^j$ are expected to have almost the same proportions as the original ones, $\mathbf{p}^i$ and $\mathbf{p}^j$ , if the randomly selected instances follow the proportion of the original bags. In this case, the expected proportion of the generated new bag $B^k$ is $\mathbf{p}^k = \gamma \mathbf{p}^i + (1 - \gamma) \mathbf{p}^j$ . However, in practice, the actual proportion of randomly sampled instances may have some gaps from that of the original bag + +![](images/1ad0c9007d47146a42ca707d8e7d7a7451f1a385b987556d31981868ba61036b.jpg) +Figure 5. Overview of our method. Left: the way to create mixed bags and illustration of label proportion's probability. Right: confidence interval + +![](images/4db93041b724b2e6dc4a52c0a26c1e2388ade4397e54c597b28eabe5c38d0179.jpg) + +because the number of sampled instances in each class does not always follow the original proportion. This gap can be estimated by calculating the confidence interval (CI) for a population proportion. + +Let us denote the proportion of a class $c$ in the $i$ -th bag as $p_c^i$ . The standard deviation of the class $c$ proportion of the sampled sub-bag $S^i$ is defined as: + +$$ +\sigma_ {c} ^ {i} = \sqrt {\frac {p _ {c} ^ {i} \left(1 - p _ {c} ^ {i}\right)}{n _ {i}}}, \tag {3} +$$ + +where $n_i = |B^i| \times \gamma$ is the number of instances randomly sampled from $B^i$ . This equation is well-known in statistics; it can be derived using the central limit theorem. + +The CI for the truth proportion $\tilde{p}_c^i$ of the sub-bag $S^i$ is formulated as: + +$$ +p _ {c} ^ {i} - \alpha \sigma_ {c} ^ {i} \leq \tilde {p} _ {c} ^ {i} \leq p _ {c} ^ {i} + \alpha \sigma_ {c} ^ {i}, \tag {4} +$$ + +where $\alpha$ is set according to the desired degree of confidence, e.g., $95\%$ . If we set the confidence to a higher value, $\alpha$ becomes higher values. For the other sub-bag $S_{j}$ , the CI for the population proportion of $\tilde{p}_c^j$ is formulated in the same manner. + +The CI for $\tilde{p}_c^k$ , which is the proportion of the newly generated bag $B^{k}$ , is defined as: + +$$ +p _ {c} ^ {k} - \alpha \sigma_ {c} ^ {k} \leq \tilde {p} _ {c} ^ {k} \leq p _ {c} ^ {k} + \alpha \sigma_ {c} ^ {k}, \tag {5} +$$ + +$$ +p _ {c} ^ {k} = \gamma p _ {c} ^ {i} + (1 - \gamma) p _ {c} ^ {j}, \tag {6} +$$ + +$$ +\gamma = \frac {n _ {i}}{n _ {i} + n _ {j}}, \tag {7} +$$ + +$$ +\sigma_ {c} ^ {k} = \gamma \sqrt {\frac {p _ {c} ^ {i} \left(1 - p _ {c} ^ {i}\right)}{n _ {i}}} + (1 - \gamma) \sqrt {\frac {p _ {c} ^ {j} \left(1 - p _ {c} ^ {j}\right)}{n _ {j}}}, \tag {8} +$$ + +where $p_c^k$ is the expected proportion of the generated mixed bag, which is directly computed from the proportions of the original bags $B^{i}$ , $B^{j}$ , and the standard deviation $\sigma_c^k$ of the + +mixed bag can be calculated by using the standard deviation of the sub-bags with the ratio $\gamma$ . + +This confidence interval (Eq.5) indicates that the actual proportion of the mixed bag has a gap from the expected proportion. If we directly use the proportion $\mathbf{p}^k$ (Eq.6) for the mixed bag as augmented data and use it for the proportion loss, the gap from the actual proportion may adversely affect the training of the network since the gap causes a label noise. + +To avoid this adverse effect caused by gaps (label noise), we propose a confidence interval loss (CI loss) for generated mixed bags. The CI loss is based on the proportion loss [1]. In contrast to the standard proportion loss, the CI loss ignores a loss when the estimated proportion $\hat{p}_c^k$ is in the confidence interval $[p_c^k -\alpha \sigma_c^k,p_c^k +\alpha \sigma_c^k ]$ since gaps in the CI often occur. + +Given the degree of confidence $\alpha \%$ (the corresponding value is set to $\alpha$ ), such as when the degree of confidence is $95\%$ , $\alpha = 1.96$ , the CI loss is defined as: + +$$ +\ell_ {\mathrm {C I}} \left(B ^ {k}, \mathbf {p} ^ {k}, f\right) = - \sum_ {c = 1} ^ {C} \mathbf {1} \left(p _ {c} ^ {k}, \hat {p} _ {c} ^ {k}\right) p _ {c} ^ {k} \log \hat {p} _ {c} ^ {k}, \tag {9} +$$ + +$$ +\hat {p} _ {c} ^ {k} = \frac {1}{| B ^ {k} |} \sum_ {j = 1} ^ {| B ^ {k} |} f \left(x _ {j} ^ {k}\right) _ {c}, \tag {10} +$$ + +$$ +\mathbf {1} \left(p, p ^ {\prime}\right) = \left\{ \begin{array}{l l} 0 & \text {i f} p - \alpha \sigma \leq p ^ {\prime} \leq p + \alpha \sigma \\ 1 & \text {o t h e r w i s e} \end{array} , \right. \tag {11} +$$ + +where $\mathbf{1}$ is the indicator function, which outputs 0 if $p'$ is in the confidence interval, and 1 otherwise. This CI loss updates the network parameters if the difference between the estimated proportion $\hat{p}_c^k$ and the expected proportion $p_c^k$ calculated by Eq.6 is significant. Using this loss, we can accelerate the training by using the augmented bags without any adverse effects from proportion gaps. + +In training, mixed bags are randomly generated in each batch. It indicates that the number of generated bags will increase with iteration. We stop training based on the propor + +
MethodCIFAR10AccuracySVHNAccuracyPATHAccuracyOCTAccuracyBLOODAccuracyORGANACuracyORGANCuracyORGANSAccuracyAverageAccuracy
LLP [1]0.45380.30090.78430.43360.88690.76350.78980.53720.6187
LLP + Ours(w/o CI)0.45820.29710.78840.4250.88980.78310.81890.5630.6280
LLP + Ours0.52560.37420.78610.43470.90170.79710.80990.61970.6561
LLP + Ours(supervised)0.65940.77810.81180.53960.89470.82220.82330.66740.7234
LLP-VAT [28]0.47400.31190.89150.41240.89150.79360.80600.58370.6455
LLP-VAT + Ours(w/o CI)0.52030.43020.87790.45030.87790.78470.76560.58490.6614
LLP-VAT + Ours0.52830.41110.89440.43660.89440.81550.82280.63760.6800
LLP-VAT + Ours(supervised)0.59630.59760.89970.47770.89970.82300.83130.66220.7234
LLP-PI [13]0.47020.30110.88860.42240.88620.78100.79620.59170.6421
LLP-PI + Ours(w/o CI)0.47940.52090.86880.43500.85730.75950.75700.57410.6565
LLP-PI + Ours0.52900.38650.88410.43660.88410.80130.79890.62360.6680
LLP-PI + Ours(supervised)0.58960.77210.89180.47200.89180.81010.81840.65770.7379
+ +Table 1. Instance-level classification accuracy when our method was applied to three baseline methods; LLP [1], LLP-VAT [28] and LLP-PI [13]. Each value is the average of five-fold cross-validation results. Here, 'CI' means the confident interval, and 'supervised' indicates the case when a ground-truth proportion to the generated mixed bag is given. + +
MethodCIFAR10 AccuracySVHN AccuracyPATH AccuracyOCT AccuracyBLOOD AccuracyORGANA AccuracyORGANC AccuracyORGANS AccuracyAverage Accuracy
LLP [1]0.45380.30090.78430.43360.88690.76350.78980.53720.6187
LLP + Ours0.52560.37420.78610.43470.90170.79710.80990.61970.6561
LLP + Flip0.57770.38840.82990.47930.92650.65270.69040.62930.6467
LLP + Flip + Ours0.57640.41240.80050.55040.91550.67180.67170.62800.6533
LLP + Erase0.55510.35000.80970.44140.90940.83930.84470.65780.6759
LLP + Erase + Ours0.56710.42690.79340.42910.90210.82660.83130.65940.6794
LLP + Invert0.52580.67630.77750.43940.87900.77790.82150.62550.6899
LLP + Invert + Ours0.57840.77610.74210.45800.87360.78450.83230.63290.7097
LLP + Gaussianblur0.47660.36860.76390.41450.88750.79060.83180.63250.6457
LLP + Gaussianblur + Ours0.51350.40360.75550.43000.87890.79620.79890.67090.6559
LLP + Perspective0.56750.54410.78920.46780.89680.83090.84400.66890.7011
LLP + Perspective + Ours0.57500.57150.77450.49620.90640.81800.84040.68950.7089
+ +Table 2. Instance-level classification accuracy when our method was applied after various instance-level augmentation methods. + +tion loss in validation data. Note that instance-level labels cannot be used for validation in LLP. + +# 6. Experiments + +# 6.1. Datasets and experimental settings + +Preparation of bags: The eight datasets used in these experiments were the same as those used in the preliminary experiments. The way of generating bags was also the same as in the preliminary experiments. Although some of the related studies generated bags by allowing overlaps to increase the number of labeled bags, we did not allow overlaps since this situation is unnatural in actual applications. To keep the experiment setups the same in all datasets, we set the number of labeled bags as 512 and the bag size as 10 based on the smallest dataset. This small bag size can be considered a challenging scenario for MixBag since the number of samplings for sub-bags decreases, and it increases the confidence interval. We also evaluated our method using different bag sizes to demonstrate the effectiveness of our method in various situations. + +Implementation: We implemented our method by using + +Pytorch [21]. The network model was ResNet18 [9] pretrained on the ImageNet dataset [5]. To train our network, we also used the Adam Optimizer [9] with a learning rate of 3e-4, epoch= 1000, mini-batch size = 32, early stopping = 10 and trained on an NVIDIA GeForce 3090 GPU. We set the confidence degree as '99%' and selected $\gamma$ randomly from a uniform distribution [0, 1]. + +Evaluation metric: We evaluated the model performance by the instance-level classification accuracies, which were calculated by using the confusion matrix. To compute the metric, we performed a five-fold cross-validation in all our experiments. The accuracies listed in the tables are the average values of the five-fold cross-validation. + +# 6.2. Comparison + +Comparison with current methods: Our method MixBag can be applied to any proportion loss-based method since MixBag is a data augmentation method, in which any method can be applied after data augmentation with the CI loss. Most current LLP methods incorporate self-supervised learning, such as consistency, into the proportion loss. We + +
Methodγ-samplingAverage Accuracy
LLP [1]-0.6187
LLP + Oursuniform0.6561
LLP + OursGauss0.6512
LLP + Ourshalf0.6524
+ +Table 3. Average accuracy on eight datasets when changing a sampling method for $\gamma$ . + +
MethodCIAverage Accuracy
LLP [1]0.6187
LLP + Ours(99%)✓0.6561
LLP + Ours(95%)✓0.6519
LLP + Ours(80%)✓0.6531
LLP + Ours(50%)✓0.6243
+ +thus applied our method in three methods: 1) LLP [1], which is the method of the original paper on using the proportion loss; 2) LLP-VAT [28], which introduces the consistency regularization into the proportion loss; and 3) LLP-PI [13], which uses the additive Gaussian noise for making perturbed examples. The LLP-VAT is one of the state-of-the-art LLP methods using the proportion loss, and its implementations are publicly available. + +We compared the baseline methods as an ablation study. The first was 'LLP', which uses the standard proportion loss; the second was 'LLP+Ours(w/o CI)' which uses the MixBag without using the CI loss, where the proportion is directly calculated from the original bags (and may contain noise) was used as the label for the generated mixed bag. The third was 'LLP+Ours(supervised)', which uses the ground-truth proportions of the mixed bags. Note that the proportion would be unknown in real cases. + +Table 1 shows the accuracy of each method, where the gray color field indicates the proposed methods in each baseline method. 'LLP+Ours(w/o CI)' improved the accuracies in some datasets and slightly improved them on average from the baselines. However, the improvement was limited by the noisy proportions. MixBag improved the accuracy of every baseline method on all datasets, and the improvement was 3 to 4 points on average. + +Introducing MixBag with instance-level augmentation: Next, we introduced our method to the instance-level augmentation methods. We used standard augmentation techniques: 'Flip' randomly flips the image horizontally and upside down. 'Erase' removes a randomly selected area from an original image. 'Invert' randomly changes the colors of the image by inversion. 'Gaussianblur' blurs an image by adding a randomly chosen Gaussian blur. 'Perspective' performs a random projective transformation on an image. To generate a bag by instance-level augmentation, we added perturbations into instances randomly selected from + +Table 4. Average accuracy on eight datasets when changing the degree of confidence interval (50%, 80%, 95%, 99%). + +
MethodSizeNumAverage Accuracy
LLP [1]105120.6187
LLP + Ours(w/o CI)105120.6280
LLP + Ours105120.6561
LLP [1]202560.5441
LLP + Ours(w/o CI)202560.5496
LLP + Ours202560.5667
LLP [1]401280.4746
LLP + Ours(w/o CI)401280.4600
LLP + Ours401280.5058
+ +Table 5. Average accuracy on eight datasets when changing the number of labeled bags and bag size. 'Size' means the bag size. 'Num' means the number of labeled bags. + +an original bag; i.e., an augmented bag contains the perturbed instances and original instances, where this augmentation has not been reported in previous papers. In $\mathrm{LLP} +$ instance-level $^+$ MixBag, the mixed bag was created from the original and instance-level augmented bags. Table 2 shows the accuracies of the baseline and our methods. The instance-level data augmentation improved the performance from the baseline. Our method further improved the accuracies of every instance-level augmentation method. + +# 6.3. Performance in various situations + +Performance with different $\gamma$ sampling methods: We evaluated our method with three different $\gamma$ sampling methods, i.e., three different ways to determine the mixing rate $\gamma$ of the two sub-bags $S^i, S^j$ : 'uniform' selects $\gamma$ randomly from a uniform distribution; 'Gauss' selects $\gamma$ randomly from a Gaussian distribution $\mathcal{N}(0.5, 0.25)$ ; 'half' always set $\gamma$ to 0.5. Table 3 shows the average accuracies of all datasets. All sampling methods outperformed the performance compared to the baseline method (LLP); 'uniform' was marginally better than other methods. + +Performance with different confidence intervals: We conducted experiments with four different confidence intervals, $99\%$ , $95\%$ , $80\%$ , and $50\%$ . Table 4 shows the average accuracies of all datasets. For all confidence interval settings, our method improved the accuracy on all datasets and in all cases. When the confidence interval took high values $(99\%, 95\%, 80\%)$ , our method worked well since the worst effects of noisy labels were mitigated by the CI loss. Even when the confidence interval was low $(50\%)$ , the accuracy improved from the baseline method. The case of $99\%$ was the best on average. We consider that a larger confidence interval avoids the adverse effects of noisy proportions and makes the training more stable. + +Performance when changing the number of labeled bags and bag size: To show the effectiveness of our method in various situations, we conducted experiments with different bag sizes (512, 256, 128) and different numbers of labeled bags (10, 20, 40), where the bag size and the number of + +
MethodBag-GenerationCIAverage Accuracy
LLP [1]--0.6187
LLP + Ours(w/o CI)Union-0.6226
LLP + Ours(w/o CI)Sub-bag0.4956
LLP + Ours(with CI)Sub-bag✓0.6364
LLP + Ours(w/o CI)MixBag0.6280
LLP + Ours(with CI)MixBag✓0.6561
+ +Table 6. Average accuracy on eight datasets in different bag-generation methods. + +labeled bags have a trade-off since the total number of instances is fixed. Table 5 shows the average accuracies on all datasets with various setups. Our method improved the accuracy from the baseline methods on average in all cases. This demonstrates the robustness of our method. + +Performance with different bag generations: To confirm the effectiveness of the 'Mix' approach, we compared MixBag with two other bag generation methods. 1) 'union' directly combines any two bags $(B^i, B^j)$ without sampling. In this case, the proportion of a generated bag can be directly calculated from those of the original bags; i.e., there is no noise for the combined proportions by taking the union of two bags. Therefore, the CI loss was not used for this method. 2) 'sub-bag' randomly samples instances from a single bag $B^i$ . It can be considered as a sub-bag of the original bag $B^i$ . In this case, the label proportions of the sub-bag may have a gap from the original one, and thus, we evaluated two cases; 'sub-bag' without and with the CI loss. 3) 'MixBag' is our method, which mixes two bags. We also evaluated two cases; Mixbag with and without CI loss. + +Table 6 shows the average of the instance-level accuracies of the comparative methods on the eight datasets. Since 'sub-bag with CI' and union' can increase the number of labeled bags, these methods had slightly improved accuracy from that of baseline method LLP [1]. Our method, 'MixBag with CI' further improved the accuracy compared with these other bag generation methods. We consider that our method has two characteristics of 'sub-bag' and 'union', where MixBag first makes sub-bags from original bags and then takes the union of these sub-bags. In addition, MixBag can generate various proportions of the mixed bag compared to 'sub-bag' and 'union'. Therefore, MixBag was better than them. + +# 6.4. Detailed Analysis + +Distribution of proportion vectors in the space of proportion labels: Figure 6 shows distributions of the original proportion vectors $\{\mathbf{p}^i\}_{i=1}^n$ (blue) and the generated mixed bag's proportion vectors $\{\mathbf{r}^i\}_{i=1}^m$ (orange) in the 'ORGANS' dataset, in which the dimension was compressed to 2D by PCA [29]. Here, the number of mixed bags is the same as that of the original bags. We can see that the MixBag proportion vectors do not overlap with the orig- + +![](images/a35aa66f6a3c7a4c2feb5c6879cda2491d3ed532a7212fe31e4ded9388b3dc8f.jpg) +Figure 6. Distribution of proportion vectors. Blue: Original bag's proportion. Orange: Mixed bag's proportion. + +![](images/8aea3cb7fe3f5113ce626775fd52aa264bdb32faaef10865ddf5e036256a3066.jpg) +Figure 7. Relationship between confidence interval and actual gaps. Blue: proportion vector of a bag. + +inal ones, i.e., new proportion labels were generated, and the distribution of mixed bag proportions covers the original distribution by interpolating pairs of the original bags. This result shows that MixBag adds diversity to the training dataset, which facilitates an improvement in the instance-level classification accuracy. + +Relationship between confidence interval and ground-truth proportion: Figure 7 shows how well the confidence interval works. The horizontal axis indicates the difference $(\| \mathbf{p} - \hat{\mathbf{p}} \|_1)$ between the ground-truth proportion $\mathbf{p}$ and the estimated proportion $\hat{\mathbf{p}}$ of a mixed bag. The vertical axis indicates the difference $(\alpha \sigma^k)$ between the upper bounds of the confidence interval and $\mathbf{p}$ , where we set the degree of confidence as $99\%$ . Each blue point indicates the proportion vector of a mixed bag. Almost all points are under the straight line in the figure. This indicates that the actual proportion gaps from the ground truth were less than the confidence interval, and thus the proposed CI loss works properly. + +# 7. Conclusion + +In this paper, we examined how the number of labeled bags and the bag size affects the performance in LLP. As a result, we found that the accuracy improves as the number of labeled bags increases, even when the total number of instances is fixed. Then, based on this observation, we propose a simple but effective bag-level data augmentation method. In addition, we also proposed a confidence interval loss that effectively trains a classification network by using the generated bags while avoiding the adverse effects caused by noisy proportions. To the best of our knowledge, this is the first attempt to propose bag-level data augmentation for LLP. The experiments using eight datasets demonstrated the effectiveness of our method in various cases. 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In Proceedings of the IEEE/CVF international conference on computer vision, pages 6023-6032, 2019. +[35] Hongyi Zhang, Moustapha Cisse, Yann N Dauphin, and David Lopez-Paz. mixup: Beyond empirical risk minimization. arXiv preprint arXiv:1710.09412, 2017. +[36] Jun-Yan Zhu, Taesung Park, Phillip Isola, and Alexei A Efros. Unpaired image-to-image translation using cycle-consistent adversarial networks. In Proceedings of the IEEE international conference on computer vision, pages 2223-2232, 2017. \ No newline at end of file diff --git a/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/images.zip b/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..33d01fc4dca9061c03fab780ab61667a51a71094 --- /dev/null +++ b/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:58d5bc87c1f683653dcdc13d63fc7a73064dd80dc1ee7d9b2d48a91f809e3528 +size 582399 diff --git a/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/layout.json b/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..784f3b03d6b24ebcdd280c809c771e3762ba91fa --- /dev/null +++ b/2023/MixBag_ Bag-Level Data Augmentation for Learning from Label Proportions/layout.json @@ -0,0 +1,8238 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 58, + 103, + 536, + 122 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 103, + 536, + 122 + ], + "spans": [ + { + "bbox": [ + 58, + 103, + 536, + 122 + ], + "type": "text", + "content": "MixBag: Bag-Level Data Augmentation for Learning from Label Proportions" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 118, + 142, + 473, + 174 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 118, + 142, + 473, + 174 + ], + "spans": [ + { + "bbox": [ + 118, + 142, + 473, + 174 + ], + "type": "text", + "content": "Takanori Asanomi1, Shinnosuke Matsuo1, Daiki Suehiro1,2, Ryoma Bise1 \n1Kyushu University, Fukuoka, Japan \n2RIKEN AIP, Japan" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 64, + 174, + 529, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 64, + 174, + 529, + 186 + ], + "spans": [ + { + "bbox": [ + 64, + 174, + 529, + 186 + ], + "type": "text", + "content": "{takanori.asanomi@human., shinnosuke.matsuo@human., suehiro@, bise@}ait.kyushu-u.ac.jp" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "spans": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 238, + 290, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 238, + 290, + 455 + ], + "spans": [ + { + "bbox": [ + 45, + 238, + 290, + 455 + ], + "type": "text", + "content": "Learning from label proportions (LLP) is a promising weakly supervised learning problem. In LPP, a set of instances (bag) has label proportions, but no instance-level labels are given. LPP aims to train an instance-level classifier by using the label proportions of the bag. In this paper, we propose a bag-level data augmentation method for LPP called MixBag, based on the key observation from our preliminary experiments; that the instance-level classification accuracy improves as the number of labeled bags increases even though the total number of instances is fixed. We also propose a confidence interval loss designed based on statistical theory to use the augmented bags effectively. To the best of our knowledge, this is the first attempt to propose bag-level data augmentation for LPP. The advantage of MixBag is that it can be applied to instance-level data augmentation techniques and any LPP method that uses the proportion loss. Experimental results demonstrate this advantage and the effectiveness of our method." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 477, + 128, + 490 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 477, + 128, + 490 + ], + "spans": [ + { + "bbox": [ + 47, + 477, + 128, + 490 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 498, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 287, + 605 + ], + "type": "text", + "content": "In general classification tasks, a model is trained on datasets where each piece of data (instance) has class labels. However, instance-level annotations cost a lot, and there are many cases in which instance-level annotation cannot be disclosed to the public for privacy reasons [23]. In such a situation, we only know the label proportions given to a set of instances (bag) and must train a model from these label proportions to classify each instance. This problem setting is known as learning from label proportions (LLP) [1]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "Figure 1 illustrates the problem setup of LLP. A bag " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " consists of instances (e.g., images). 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It is a weakly supervised learning task." + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 307, + 214, + 547, + 380 + ], + "blocks": [ + { + "bbox": [ + 307, + 214, + 547, + 380 + ], + "lines": [ + { + "bbox": [ + 307, + 214, + 547, + 380 + ], + "spans": [ + { + "bbox": [ + 307, + 214, + 547, + 380 + ], + "type": "image", + "image_path": "29b2be03f814735205653ecffdf7aa9552c9466c46f69a0596f89fd816f90fcd.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 386, + 547, + 420 + ], + "lines": [ + { + "bbox": [ + 305, + 386, + 547, + 420 + ], + "spans": [ + { + "bbox": [ + 305, + 386, + 547, + 420 + ], + "type": "text", + "content": "Figure 1. Illustration of learning from label proportions. LLP aims to train an instance-level classifier by using label proportions of a bag as training data instead of instance-level labels." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 445, + 547, + 577 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 445, + 547, + 577 + ], + "spans": [ + { + "bbox": [ + 304, + 445, + 547, + 577 + ], + "type": "text", + "content": "Many LLP methods have been proposed to address this challenging task [1, 24, 28, 27, 18, 19]. Most of them are based on the proportion loss, which evaluates the difference between the given proportion " + }, + { + "bbox": [ + 304, + 445, + 547, + 577 + ], + "type": "inline_equation", + "content": "\\mathbf{p}^i" + }, + { + "bbox": [ + 304, + 445, + 547, + 577 + ], + "type": "text", + "content": " and the estimated proportion " + }, + { + "bbox": [ + 304, + 445, + 547, + 577 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{p}}^i" + }, + { + "bbox": [ + 304, + 445, + 547, + 577 + ], + "type": "text", + "content": ", and can be calculated by taking the average of the class probabilities of the instances in a bag. The methods based on the proportion loss work well when bag-level labels (label proportions) are sufficient. However, the accuracy decreases as the number of labeled bags decreases, i.e., insufficient labeled data causes difficulty in training a network, which is known in machine learning tasks." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 578, + 547, + 699 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 578, + 547, + 699 + ], + "spans": [ + { + "bbox": [ + 304, + 578, + 547, + 699 + ], + "type": "text", + "content": "In such cases, instance-level data augmentation is often an effective way to improve accuracy. Many instance-level data augmentation techniques, such as perturbation, for general classification tasks have been proposed, and their effectiveness has been demonstrated [25]. Instance-level data augmentation may improve the accuracy in LLP. However, it does not increase the number of labeled bags from the original one, and it is difficult to generate various bags with different proportions without using instance-level labels (these are unknown in LLP)." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 318, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 318, + 701, + 545, + 714 + ], + "type": "text", + "content": "This paper proposes a bag-level data augmentation for" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 732, + 318, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 732, + 318, + 742 + ], + "spans": [ + { + "bbox": [ + 294, + 732, + 318, + 742 + ], + "type": "text", + "content": "16570" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 287 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 287 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 287 + ], + "type": "text", + "content": "LLP that can generate new bags with various label proportions. To design an effective bag-level data augmentation technique, we conducted a detailed analysis of what situation can improve the accuracy in LLP. As a result, we found an important observation that the accuracy improves as the number of labeled bags increases, even though the total number of instances is fixed, i.e., different bags overlap each other as shown in Figure 2 (Right). On the basis of this observation, we propose a bag-level data augmentation called MixBag. MixBag increases the number of labeled bags artificially by sampling instances from a pair of original bags and mixing them: this operation mimics the above observations. The expected label proportion of a generated mixed bag can be calculated by those of the original bags. However, it may have a gap from the actual proportion of the mixed bag because randomly selected instances do not follow the proportion of the original ones. This gap adversely affects the training." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 288, + 289, + 395 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 288, + 289, + 395 + ], + "spans": [ + { + "bbox": [ + 46, + 288, + 289, + 395 + ], + "type": "text", + "content": "We thus introduce a confidence interval loss that helps to train a classification network by using the generated bags while avoiding this adverse effect by a proportion gap; it is statistically guaranteed. To the best of our knowledge, this is the first attempt to propose bag-level data augmentation for LLP. Experiments using eight datasets demonstrate the effectiveness of our method in various cases; our method improved the classification accuracy on all datasets. Our main contributions are summarized as follows." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 400, + 287, + 582 + ], + "type": "list", + "angle": 0, + "index": 5, + "blocks": [ + { + "bbox": [ + 59, + 400, + 287, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 400, + 287, + 460 + ], + "spans": [ + { + "bbox": [ + 59, + 400, + 287, + 460 + ], + "type": "text", + "content": "- We examined how the number of labeled bags and the bag size affect the performance in LLP. From the preliminary experiments, we concluded that the accuracy improves as the number of labeled bags increases, even though the total number of instances is fixed." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 467, + 287, + 516 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 467, + 287, + 516 + ], + "spans": [ + { + "bbox": [ + 59, + 467, + 287, + 516 + ], + "type": "text", + "content": "- We proposed MixBag with a confidence interval loss. This method artificially increases the number of labeled bags, and the confidence interval loss helps train a classification network using the generated bags." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 522, + 287, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 522, + 287, + 582 + ], + "spans": [ + { + "bbox": [ + 59, + 522, + 287, + 582 + ], + "type": "text", + "content": "- We demonstrated that MixBag can be applied to any of the current LLP methods and any of the instance-level augmentation methods. Experimental results show that our method improved classification accuracy on various datasets." + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 591, + 132, + 604 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 591, + 132, + 604 + ], + "spans": [ + { + "bbox": [ + 47, + 591, + 132, + 604 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 611, + 253, + 624 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 611, + 253, + 624 + ], + "spans": [ + { + "bbox": [ + 47, + 611, + 253, + 624 + ], + "type": "text", + "content": "2.1. Learning from Label Proportion (LLP)" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 629, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 689 + ], + "type": "text", + "content": "Proportion loss [1] is the most common approach to LLP. To compute the proportion loss, the average of the output probability in a bag is calculated as a proportion estimation, and then the bag-level cross-entropy between the true label proportion and the estimated proportion is used as the loss." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "content": "The proportion loss has been extended in many methods; e.g., introducing regularization terms [33, 1, 8, 28, 30, 17," + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 306, + 72, + 547, + 178 + ], + "blocks": [ + { + "bbox": [ + 306, + 72, + 547, + 178 + ], + "lines": [ + { + "bbox": [ + 306, + 72, + 547, + 178 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 547, + 178 + ], + "type": "image", + "image_path": "14764b48d3c88aea555ea6770fdab8d130813c39af571648e8df54817e47cab0.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 183, + 547, + 228 + ], + "lines": [ + { + "bbox": [ + 304, + 183, + 547, + 228 + ], + "spans": [ + { + "bbox": [ + 304, + 183, + 547, + 228 + ], + "type": "text", + "content": "Figure 2. Illustration of overlap and non-overlap situations. (a) Original bags. (b) New bags (yellow) are added with non-overlap, i.e., the total number of instances increases. (c) New bags overlap with the original ones, i.e., the total number of instances is fixed." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 245, + 545, + 389 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 245, + 545, + 389 + ], + "spans": [ + { + "bbox": [ + 304, + 245, + 545, + 389 + ], + "type": "text", + "content": "18]. Tsai et al. [28] incorporated a consistency regularization into the proportion loss, which forces the network predictions to be consistent when its input is perturbed. Yang et al. [30] use contrastive learning for pre-training in a self-supervised learning manner and then train the model by using the proportion loss. LLP-GAN [17] introduces the generative adversarial network (GAN) to LLP. The fake instances created by the generator encourage the discriminator to distinguish real or fake and classify the real instances. This method also uses the proportion loss to train the classifier. Two-stage LLP [18] introduces pseudo-labeling after pre-training by using a proportion loss." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 389, + 545, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 389, + 545, + 485 + ], + "spans": [ + { + "bbox": [ + 304, + 389, + 545, + 485 + ], + "type": "text", + "content": "It is known that the classification accuracy decreases when the labeled data is insufficient in machine learning. To deal with this issue, data augmentation is a standard approach. However, bag-level data augmentation for LLP is still an unexplored area. This paper proposes a simple but effective bag-level data augmentation method. One of the advantages of our method is that any LLP method can be applied after our bag-level augmentation." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 491, + 486, + 504 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 491, + 486, + 504 + ], + "spans": [ + { + "bbox": [ + 306, + 491, + 486, + 504 + ], + "type": "text", + "content": "2.2. Instance-level data Augmentation" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "content": "Data augmentation is a standard way to address the problem of inadequately labeled data. Many instance-level data augmentation techniques have been proposed. Basic data augmentation involves adding perturbations to the original images, such as by flipping the image [25], adding noise [25], and erasing parts of an image [7, 2, 14]. Image mix [11, 35, 34, 10] is another approach, where methods such as MixUP [35] and CutMix [34] mix together two original images. GAN-based augmentation methods [22, 36, 26] represent data distributions and generate new images based on these distributions. Auto augment [3, 16, 4] automatically searches for suitable augmentation approaches that improved performance. The above methods are instance-level data augmentations. It is not a simple task to generate various bags that have different proportions without using instance-level labels. For example, CutMix and MixUp require the labels of the original im" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "spans": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "type": "text", + "content": "16571" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": "ages (instances) in order to prepare the label proportions of a generated new bag. Since simple perturbation methods do not require the ground truth of the image label for augmentation, they can be used to add perturbations to each instance in a bag. However, these methods are not designed for bag-level data augmentation." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 151, + 249, + 164 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 151, + 249, + 164 + ], + "spans": [ + { + "bbox": [ + 47, + 151, + 249, + 164 + ], + "type": "text", + "content": "2.3. Bag-Level data augmentation for MIL" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 170, + 290, + 386 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 170, + 290, + 386 + ], + "spans": [ + { + "bbox": [ + 46, + 170, + 290, + 386 + ], + "type": "text", + "content": "Few bag-level data augmentation methods have been proposed for multiple instance learning (MIL), which trains a classifier from bag-level class labels (positive or negative). Li et al. [15] proposed a MIL-based method that uses bag-level augmentation for COVID-19 severity assessment. This method takes a pseudo-labeling approach, where positive and negative instances are taken from positive bags based on the estimated confidence of the instance class and used to make a new bag. Yang et al. [31] proposed a MIL method for segmenting pathology images. This method generates new bags by clustering instances. It is reasonable for MIL to make a positive or negative bag from high confidence positive or negative instances. However, it is difficult to make a proportion label from pseudo labeling since all of the pseudo labels have to be accurate to calculate the correct proportion. So in order to improve the performance of LLP, appropriately designing a bag-level data augmentation is required." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 396, + 263, + 410 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 396, + 263, + 410 + ], + "spans": [ + { + "bbox": [ + 47, + 396, + 263, + 410 + ], + "type": "text", + "content": "3. Preliminary: LLP and Proportion Loss" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "text", + "content": "In LLP, the training set contains " + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "text", + "content": " bags, " + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "inline_equation", + "content": "B^1, \\ldots, B^n" + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "text", + "content": ". Each bag " + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "inline_equation", + "content": "B^i" + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "text", + "content": " consists of a set of instances, i.e., " + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "inline_equation", + "content": "B^i = \\{x_j^i\\}_{j=1}^{|B^i|}" + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "text", + "content": ", and a vector of label proportions " + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "inline_equation", + "content": "\\mathbf{p}^i = (p_1^i, \\ldots, p_c^i, \\ldots, p_C^i)^T" + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "text", + "content": " is attached to each bag as training label, where " + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "text", + "content": " is the number of classes. This label indicates that " + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "inline_equation", + "content": "p_c^i \\times |B^i|" + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "text", + "content": " instances in the " + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "text", + "content": "-th bag belong to the class " + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "text", + "content": " for any " + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "inline_equation", + "content": "c \\in \\{1, \\ldots, C\\}" + }, + { + "bbox": [ + 46, + 415, + 287, + 552 + ], + "type": "text", + "content": ". The goal of LLP is to train a network that estimates the class label of each instance by using only the proportion labels of the bags. Proportion loss [1] is a standard approach to this challenging task, and many methods are based on it." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 552, + 288, + 612 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 552, + 288, + 612 + ], + "spans": [ + { + "bbox": [ + 46, + 552, + 288, + 612 + ], + "type": "text", + "content": "Given training data with label proportions, the standard proportion loss is a bag-level cross-entropy between the ground-truth of the label proportion " + }, + { + "bbox": [ + 46, + 552, + 288, + 612 + ], + "type": "inline_equation", + "content": "\\mathbf{p}^i" + }, + { + "bbox": [ + 46, + 552, + 288, + 612 + ], + "type": "text", + "content": " and the predicted proportion " + }, + { + "bbox": [ + 46, + 552, + 288, + 612 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{p}}^i" + }, + { + "bbox": [ + 46, + 552, + 288, + 612 + ], + "type": "text", + "content": ", which is the average of the output class probabilities in a bag. It is defined as:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 94, + 620, + 287, + 654 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 94, + 620, + 287, + 654 + ], + "spans": [ + { + "bbox": [ + 94, + 620, + 287, + 654 + ], + "type": "interline_equation", + "content": "\\ell_ {\\text {p r o p}} \\left(B ^ {i}, \\mathbf {p} ^ {i}, f\\right) = - \\sum_ {c = 1} ^ {C} p _ {c} ^ {i} \\log \\hat {p} _ {c} ^ {i}, \\tag {1}", + "image_path": "ffa220a65f6bb032fcf5dff1a5bf743419730a372ecc9166ed3ac7462314e5c5.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 145, + 656, + 287, + 692 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 145, + 656, + 287, + 692 + ], + "spans": [ + { + "bbox": [ + 145, + 656, + 287, + 692 + ], + "type": "interline_equation", + "content": "\\hat {p} _ {c} ^ {i} = \\frac {1}{| B ^ {i} |} \\sum_ {j = 1} ^ {| B ^ {i} |} f \\left(x _ {j} ^ {i}\\right) _ {c}, \\tag {2}", + "image_path": "e8152d3596768a7b4a2fa62b9a03b69e2caa469e9819394e45fc95b790a33f40.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 700, + 286, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 700, + 286, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 700, + 286, + 715 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 700, + 286, + 715 + ], + "type": "inline_equation", + "content": "f(x_{j}^{i})_{c}" + }, + { + "bbox": [ + 47, + 700, + 286, + 715 + ], + "type": "text", + "content": " is the output probability that " + }, + { + "bbox": [ + 47, + 700, + 286, + 715 + ], + "type": "inline_equation", + "content": "x_{j}^{i}" + }, + { + "bbox": [ + 47, + 700, + 286, + 715 + ], + "type": "text", + "content": " belongs to " + }, + { + "bbox": [ + 47, + 700, + 286, + 715 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 47, + 700, + 286, + 715 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 71, + 523, + 86 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 71, + 523, + 86 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 523, + 86 + ], + "type": "text", + "content": "4. Preliminary Empirical Analysis of LLP" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 92, + 545, + 224 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 92, + 545, + 224 + ], + "spans": [ + { + "bbox": [ + 304, + 92, + 545, + 224 + ], + "type": "text", + "content": "In previous works, the relationship between the number of labeled bags, bag sizes, and accuracy in LLP has not been analyzed well. Some papers [17, 8] reported that the accuracy increased as the larger bag size in their experiments. However, the reason was not discussed well. In their experiments, they changed the bag size while the total number of instances was fixed. Since an instance generally does not belong to two bags (i.e., bags does not overlap each other) in LLP, it indicates that the bag size and the number of labeled bags have a trade-off; when the bag size increases, the number of labeled bags decreases." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 224, + 546, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 224, + 546, + 392 + ], + "spans": [ + { + "bbox": [ + 304, + 224, + 546, + 392 + ], + "type": "text", + "content": "In this section, we further empirically analyze the relationships among the number of labeled bags, bag sizes, and accuracy by using the proportion loss on various public datasets. First, we conducted experiments on whether the number of labeled bags or the bag size has more influence on the classification accuracy in a general setup of LLP, where different bags do not contain the same instance (no overlap), as shown in Figure 2 (b). To avoid the tradeoff between the number of labeled bags and the bag size, we fixed the number of labeled bags to analyze the effect for accuracy by the number of labeled bags, and vice versa. In the experiments, the total number of instances changed. We speculated that this analysis may give clues for developing a new method in LLP." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 398, + 546, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 398, + 546, + 578 + ], + "spans": [ + { + "bbox": [ + 304, + 398, + 546, + 578 + ], + "type": "text", + "content": "Datasets and experimental settings: We used eight datasets in our experiments1: 1) CIFAR10 [12], which is commonly used in classification tasks. The dataset contains ten classes, such as vehicles and animals; 2) SVHN [20], which is a house-number-images dataset, and a character-level label is given like in MNIST [6]; 3) OCT, which contains four classes of Retinal OCT images; 4) BLOOD, which contains eight classes of Blood Cell Microscope images; 5) ORGAN, 6) ORGANC, 7) ORGANS, which contain eleven classes of abdominal CT images. The difference is the view of the image and its sizes, and 8) PATH, which contains nine classes of colon pathology images. Note that 3) to 8) are datasets in MedMNIST [32], and we did not use the small datasets in [32] since they cannot be used to prepare enough bags for LLP." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 578, + 545, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 578, + 545, + 674 + ], + "spans": [ + { + "bbox": [ + 304, + 578, + 545, + 674 + ], + "type": "text", + "content": "To prepare a bag, the proportions of each class were randomly selected from a Gaussian distribution; the decided proportion was used as the label of the bag. Then, samples were randomly selected from each class, in which the number of samples for each class followed the proportion of the class. In real applications, different bags do not contain the same instance; i.e., they do not overlap. We thus generated bags without overlap in these experiments." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 680, + 545, + 693 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 680, + 545, + 693 + ], + "spans": [ + { + "bbox": [ + 306, + 680, + 545, + 693 + ], + "type": "text", + "content": "Performance when changing the number of labeled bags" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 317, + 702, + 488, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 702, + 488, + 712 + ], + "spans": [ + { + "bbox": [ + 317, + 702, + 488, + 712 + ], + "type": "text", + "content": "1Almost all papers on LLP use CIFAR10 and SVHN" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "spans": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "type": "text", + "content": "16572" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 72, + 286, + 169 + ], + "blocks": [ + { + "bbox": [ + 50, + 72, + 286, + 169 + ], + "lines": [ + { + "bbox": [ + 50, + 72, + 286, + 169 + ], + "spans": [ + { + "bbox": [ + 50, + 72, + 286, + 169 + ], + "type": "image", + "image_path": "0099fcb638333b2d61d6a625b9b0140ba4f083ed6a2770a4bddb834a1cc7a997.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 172, + 287, + 239 + ], + "lines": [ + { + "bbox": [ + 46, + 172, + 287, + 239 + ], + "spans": [ + { + "bbox": [ + 46, + 172, + 287, + 239 + ], + "type": "text", + "content": "Figure 3. Relationship among the number of labeled bags, bag sizes, and accuracy in a general setup of LLP, where different bags do not contain the same instance (no overlap). Left: Accuracy improvement when increasing the number of labeled bags (bag size is fixed). Right: Accuracy improvement when increasing the bag size (the number of labeled bags is fixed)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 259, + 287, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 259, + 287, + 415 + ], + "spans": [ + { + "bbox": [ + 46, + 259, + 287, + 415 + ], + "type": "text", + "content": "in the general setup of LLP (no overlap): We examined how the number of labeled bags affects the instance-level classification accuracy for the standard proportion loss. We varied the number of labeled bags (64, 128, 256, 512) while keeping the bag size fixed at 10. In this experiment, we follow the general setup of LLP; different bags do not overlap, i.e., the number of instances changed when the number of labeled bags was changed. As shown in Figure3 (Left), the accuracy improved due to increasing the number of labeled bags in all datasets. This is reasonable because the number of labeled bags indicates the number of proportion labels; more labeled data for training is expected to improve accuracy in machine learning." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 421, + 287, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 421, + 287, + 540 + ], + "spans": [ + { + "bbox": [ + 46, + 421, + 287, + 540 + ], + "type": "text", + "content": "Performance when changing the bag size in the general setup of LLP (no overlap): We analyzed how the bag size affects the accuracy in the general setup of LLP. In this experiment, we changed the bag size (64, 128, 256, 512) but fixed the number of labeled bags at 10. As shown in Figure 3 (Right), the accuracy did not vary significantly with the bag size in six of the datasets, while it improved in two datasets. This result shows that increasing the number of instances without increasing the labels does not effectively improve accuracy." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 545, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 713 + ], + "type": "text", + "content": "Performance when changing the number of labeled bags in the case of overlap: The above observations indicate that increasing the number of labeled bags is important to improving accuracy. Another factor that might have improved the accuracy is increasing the total number of 'instances,' which occurs when the number of labeled bags increases. To confirm whether the number of labeled bags or the total number of instances affects accuracy, we performed experiments on how the number of labeled bags affects the accuracy in the case of overlap, i.e., when the total number of instances was fixed. The initial bags were prepared, where the number of labeled bags was 64, and the bag size was 10. To increase the number of labeled bags, we then incrementally added new bags (64, 128, 256), where the new" + } + ] + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 358, + 72, + 495, + 168 + ], + "blocks": [ + { + "bbox": [ + 358, + 72, + 495, + 168 + ], + "lines": [ + { + "bbox": [ + 358, + 72, + 495, + 168 + ], + "spans": [ + { + "bbox": [ + 358, + 72, + 495, + 168 + ], + "type": "image", + "image_path": "37623f6381952cfeed9fd96eb9e80ac9cbd66c8b8f4dbf9f61efb323e2c84303.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 171, + 545, + 205 + ], + "lines": [ + { + "bbox": [ + 305, + 171, + 545, + 205 + ], + "spans": [ + { + "bbox": [ + 305, + 171, + 545, + 205 + ], + "type": "text", + "content": "Figure 4. Experimental results on how the number of labeled bags affects the accuracy in the case of overlap, i.e., when the total number of instances was fixed." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 223, + 545, + 355 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 223, + 545, + 355 + ], + "spans": [ + { + "bbox": [ + 304, + 223, + 545, + 355 + ], + "type": "text", + "content": "bags were generated from the initial instances that belong to the initial bags, i.e., generated bags overlap with the initial ones, as shown in Figure 2 (c). As shown in Figure4, the accuracy improves as the number of labeled bags increases in all datasets. This observation is important for our bag-level data augmentation. If we were to mimic this situation where the number of labeled bags increases and the total number of instances is fixed, it should improve accuracy, even though a situation with bags having overlaps is unnatural in actual applications. However, we can make this situation by generating new bags from the original ones." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 365, + 509, + 380 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 365, + 509, + 380 + ], + "spans": [ + { + "bbox": [ + 306, + 365, + 509, + 380 + ], + "type": "text", + "content": "5. MixBag with confidence interval loss" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 386, + 545, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 386, + 545, + 422 + ], + "spans": [ + { + "bbox": [ + 305, + 386, + 545, + 422 + ], + "type": "text", + "content": "To mimic the situation of increasing the number of labeled bags and allowing their overlap, we propose MixBag, which is a bag-level data augmentation technique." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 429, + 366, + 442 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 429, + 366, + 442 + ], + "spans": [ + { + "bbox": [ + 306, + 429, + 366, + 442 + ], + "type": "text", + "content": "5.1. MixBag" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": "Figure 5 (Left) shows an overview of MixBag. Given two randomly selected bags " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "\\{B^i, B^j\\}" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " where each bag is labeled with a proportion, " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "\\mathbf{p}_i" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "\\mathbf{p}_j" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": ", mix the two bags to generate a new bag. More precisely, " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "n_i = |B^i| \\times \\gamma" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "n_j = |B^j| \\times (1 - \\gamma)" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " instances are randomly sampled from " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "B^i" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "B^j" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": ", respectively, where " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "\\gamma \\in [0,1]" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " is a random variable, and the sampled sub-bags are denoted as " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "S^i" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "S^j" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": ". Then, these two sub-bags are combined to generate a mixed bag, " + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "inline_equation", + "content": "B^k = S^i \\cup S^j" + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": ". This generated mixed bag overlaps with the original bags while the total number of instances is fixed, and the number of labeled bags is increased by the generated bags. It can be considered to mimic the third preliminary experiment (Figure 2 (c))." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 611, + 440, + 623 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 611, + 440, + 623 + ], + "spans": [ + { + "bbox": [ + 306, + 611, + 440, + 623 + ], + "type": "text", + "content": "5.2. Confidence interval loss" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": "The sampled sub-bags " + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "inline_equation", + "content": "S^i" + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "inline_equation", + "content": "S^j" + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": " are expected to have almost the same proportions as the original ones, " + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{p}^i" + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{p}^j" + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": ", if the randomly selected instances follow the proportion of the original bags. In this case, the expected proportion of the generated new bag " + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "inline_equation", + "content": "B^k" + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{p}^k = \\gamma \\mathbf{p}^i + (1 - \\gamma) \\mathbf{p}^j" + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": ". However, in practice, the actual proportion of randomly sampled instances may have some gaps from that of the original bag" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "spans": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "type": "text", + "content": "16573" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 72, + 342, + 208 + ], + "blocks": [ + { + "bbox": [ + 52, + 72, + 342, + 208 + ], + "lines": [ + { + "bbox": [ + 52, + 72, + 342, + 208 + ], + "spans": [ + { + "bbox": [ + 52, + 72, + 342, + 208 + ], + "type": "image", + "image_path": "1ad0c9007d47146a42ca707d8e7d7a7451f1a385b987556d31981868ba61036b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 213, + 546, + 236 + ], + "lines": [ + { + "bbox": [ + 46, + 213, + 546, + 236 + ], + "spans": [ + { + "bbox": [ + 46, + 213, + 546, + 236 + ], + "type": "text", + "content": "Figure 5. Overview of our method. Left: the way to create mixed bags and illustration of label proportion's probability. Right: confidence interval" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 350, + 72, + 541, + 204 + ], + "blocks": [ + { + "bbox": [ + 350, + 72, + 541, + 204 + ], + "lines": [ + { + "bbox": [ + 350, + 72, + 541, + 204 + ], + "spans": [ + { + "bbox": [ + 350, + 72, + 541, + 204 + ], + "type": "image", + "image_path": "4db93041b724b2e6dc4a52c0a26c1e2388ade4397e54c597b28eabe5c38d0179.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 253, + 287, + 301 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 253, + 287, + 301 + ], + "spans": [ + { + "bbox": [ + 46, + 253, + 287, + 301 + ], + "type": "text", + "content": "because the number of sampled instances in each class does not always follow the original proportion. This gap can be estimated by calculating the confidence interval (CI) for a population proportion." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "spans": [ + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "type": "text", + "content": "Let us denote the proportion of a class " + }, + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "type": "text", + "content": " in the " + }, + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "type": "text", + "content": "-th bag as " + }, + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "type": "inline_equation", + "content": "p_c^i" + }, + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "type": "text", + "content": ". The standard deviation of the class " + }, + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "type": "text", + "content": " proportion of the sampled sub-bag " + }, + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "type": "inline_equation", + "content": "S^i" + }, + { + "bbox": [ + 47, + 301, + 288, + 337 + ], + "type": "text", + "content": " is defined as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 124, + 347, + 287, + 380 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 124, + 347, + 287, + 380 + ], + "spans": [ + { + "bbox": [ + 124, + 347, + 287, + 380 + ], + "type": "interline_equation", + "content": "\\sigma_ {c} ^ {i} = \\sqrt {\\frac {p _ {c} ^ {i} \\left(1 - p _ {c} ^ {i}\\right)}{n _ {i}}}, \\tag {3}", + "image_path": "9149b1f26f029a18def33a91fff87f7204dbd308514e9817c72129b90c82f8a9.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 389, + 287, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 389, + 287, + 426 + ], + "spans": [ + { + "bbox": [ + 47, + 389, + 287, + 426 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 389, + 287, + 426 + ], + "type": "inline_equation", + "content": "n_i = |B^i| \\times \\gamma" + }, + { + "bbox": [ + 47, + 389, + 287, + 426 + ], + "type": "text", + "content": " is the number of instances randomly sampled from " + }, + { + "bbox": [ + 47, + 389, + 287, + 426 + ], + "type": "inline_equation", + "content": "B^i" + }, + { + "bbox": [ + 47, + 389, + 287, + 426 + ], + "type": "text", + "content": ". This equation is well-known in statistics; it can be derived using the central limit theorem." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 426, + 287, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 426, + 287, + 449 + ], + "spans": [ + { + "bbox": [ + 47, + 426, + 287, + 449 + ], + "type": "text", + "content": "The CI for the truth proportion " + }, + { + "bbox": [ + 47, + 426, + 287, + 449 + ], + "type": "inline_equation", + "content": "\\tilde{p}_c^i" + }, + { + "bbox": [ + 47, + 426, + 287, + 449 + ], + "type": "text", + "content": " of the sub-bag " + }, + { + "bbox": [ + 47, + 426, + 287, + 449 + ], + "type": "inline_equation", + "content": "S^i" + }, + { + "bbox": [ + 47, + 426, + 287, + 449 + ], + "type": "text", + "content": " is formulated as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 108, + 459, + 287, + 474 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 108, + 459, + 287, + 474 + ], + "spans": [ + { + "bbox": [ + 108, + 459, + 287, + 474 + ], + "type": "interline_equation", + "content": "p _ {c} ^ {i} - \\alpha \\sigma_ {c} ^ {i} \\leq \\tilde {p} _ {c} ^ {i} \\leq p _ {c} ^ {i} + \\alpha \\sigma_ {c} ^ {i}, \\tag {4}", + "image_path": "e0bc2e779f17be4917f003b57cb3729468107a225a7c2e757afbd9bab22d8789.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "spans": [ + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "type": "text", + "content": " is set according to the desired degree of confidence, e.g., " + }, + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "type": "inline_equation", + "content": "95\\%" + }, + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "type": "text", + "content": ". If we set the confidence to a higher value, " + }, + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "type": "text", + "content": " becomes higher values. For the other sub-bag " + }, + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "type": "inline_equation", + "content": "S_{j}" + }, + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "type": "text", + "content": ", the CI for the population proportion of " + }, + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "type": "inline_equation", + "content": "\\tilde{p}_c^j" + }, + { + "bbox": [ + 46, + 483, + 287, + 541 + ], + "type": "text", + "content": " is formulated in the same manner." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 543, + 287, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 543, + 287, + 567 + ], + "spans": [ + { + "bbox": [ + 46, + 543, + 287, + 567 + ], + "type": "text", + "content": "The CI for " + }, + { + "bbox": [ + 46, + 543, + 287, + 567 + ], + "type": "inline_equation", + "content": "\\tilde{p}_c^k" + }, + { + "bbox": [ + 46, + 543, + 287, + 567 + ], + "type": "text", + "content": ", which is the proportion of the newly generated bag " + }, + { + "bbox": [ + 46, + 543, + 287, + 567 + ], + "type": "inline_equation", + "content": "B^{k}" + }, + { + "bbox": [ + 46, + 543, + 287, + 567 + ], + "type": "text", + "content": ", is defined as:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 139, + 575, + 287, + 591 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 139, + 575, + 287, + 591 + ], + "spans": [ + { + "bbox": [ + 139, + 575, + 287, + 591 + ], + "type": "interline_equation", + "content": "p _ {c} ^ {k} - \\alpha \\sigma_ {c} ^ {k} \\leq \\tilde {p} _ {c} ^ {k} \\leq p _ {c} ^ {k} + \\alpha \\sigma_ {c} ^ {k}, \\tag {5}", + "image_path": "3c6ceb0e2fd2cc344b738f9e9ab830996ea510184d0fb0a3b46f4c41f5d60f04.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 165, + 592, + 287, + 608 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 165, + 592, + 287, + 608 + ], + "spans": [ + { + "bbox": [ + 165, + 592, + 287, + 608 + ], + "type": "interline_equation", + "content": "p _ {c} ^ {k} = \\gamma p _ {c} ^ {i} + (1 - \\gamma) p _ {c} ^ {j}, \\tag {6}", + "image_path": "b7042e0024761e577f41390e97277e6ec8865a0ddfca7ac5dba2e1e64936f5a6.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 203, + 609, + 287, + 633 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 203, + 609, + 287, + 633 + ], + "spans": [ + { + "bbox": [ + 203, + 609, + 287, + 633 + ], + "type": "interline_equation", + "content": "\\gamma = \\frac {n _ {i}}{n _ {i} + n _ {j}}, \\tag {7}", + "image_path": "ab7e174e9616bd9cc7b8102e15d512fda9281346a4b681aeda710360ecde993b.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 72, + 635, + 287, + 667 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 72, + 635, + 287, + 667 + ], + "spans": [ + { + "bbox": [ + 72, + 635, + 287, + 667 + ], + "type": "interline_equation", + "content": "\\sigma_ {c} ^ {k} = \\gamma \\sqrt {\\frac {p _ {c} ^ {i} \\left(1 - p _ {c} ^ {i}\\right)}{n _ {i}}} + (1 - \\gamma) \\sqrt {\\frac {p _ {c} ^ {j} \\left(1 - p _ {c} ^ {j}\\right)}{n _ {j}}}, \\tag {8}", + "image_path": "814ee93825c1b9b6a16b37084abb3e807460d3ef392ec9fa0a7cf4c8662342e0.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "p_c^k" + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "text", + "content": " is the expected proportion of the generated mixed bag, which is directly computed from the proportions of the original bags " + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "B^{i}" + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "B^{j}" + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "text", + "content": ", and the standard deviation " + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\sigma_c^k" + }, + { + "bbox": [ + 47, + 677, + 287, + 714 + ], + "type": "text", + "content": " of the" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 253, + 545, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 253, + 545, + 277 + ], + "spans": [ + { + "bbox": [ + 305, + 253, + 545, + 277 + ], + "type": "text", + "content": "mixed bag can be calculated by using the standard deviation of the sub-bags with the ratio " + }, + { + "bbox": [ + 305, + 253, + 545, + 277 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 305, + 253, + 545, + 277 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 277, + 545, + 360 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 277, + 545, + 360 + ], + "spans": [ + { + "bbox": [ + 304, + 277, + 545, + 360 + ], + "type": "text", + "content": "This confidence interval (Eq.5) indicates that the actual proportion of the mixed bag has a gap from the expected proportion. If we directly use the proportion " + }, + { + "bbox": [ + 304, + 277, + 545, + 360 + ], + "type": "inline_equation", + "content": "\\mathbf{p}^k" + }, + { + "bbox": [ + 304, + 277, + 545, + 360 + ], + "type": "text", + "content": " (Eq.6) for the mixed bag as augmented data and use it for the proportion loss, the gap from the actual proportion may adversely affect the training of the network since the gap causes a label noise." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 361, + 545, + 444 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 361, + 545, + 444 + ], + "spans": [ + { + "bbox": [ + 304, + 361, + 545, + 444 + ], + "type": "text", + "content": "To avoid this adverse effect caused by gaps (label noise), we propose a confidence interval loss (CI loss) for generated mixed bags. The CI loss is based on the proportion loss [1]. In contrast to the standard proportion loss, the CI loss ignores a loss when the estimated proportion " + }, + { + "bbox": [ + 304, + 361, + 545, + 444 + ], + "type": "inline_equation", + "content": "\\hat{p}_c^k" + }, + { + "bbox": [ + 304, + 361, + 545, + 444 + ], + "type": "text", + "content": " is in the confidence interval " + }, + { + "bbox": [ + 304, + 361, + 545, + 444 + ], + "type": "inline_equation", + "content": "[p_c^k -\\alpha \\sigma_c^k,p_c^k +\\alpha \\sigma_c^k ]" + }, + { + "bbox": [ + 304, + 361, + 545, + 444 + ], + "type": "text", + "content": " since gaps in the CI often occur." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 445, + 545, + 480 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 445, + 545, + 480 + ], + "spans": [ + { + "bbox": [ + 305, + 445, + 545, + 480 + ], + "type": "text", + "content": "Given the degree of confidence " + }, + { + "bbox": [ + 305, + 445, + 545, + 480 + ], + "type": "inline_equation", + "content": "\\alpha \\%" + }, + { + "bbox": [ + 305, + 445, + 545, + 480 + ], + "type": "text", + "content": " (the corresponding value is set to " + }, + { + "bbox": [ + 305, + 445, + 545, + 480 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 305, + 445, + 545, + 480 + ], + "type": "text", + "content": "), such as when the degree of confidence is " + }, + { + "bbox": [ + 305, + 445, + 545, + 480 + ], + "type": "inline_equation", + "content": "95\\%" + }, + { + "bbox": [ + 305, + 445, + 545, + 480 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 445, + 545, + 480 + ], + "type": "inline_equation", + "content": "\\alpha = 1.96" + }, + { + "bbox": [ + 305, + 445, + 545, + 480 + ], + "type": "text", + "content": ", the CI loss is defined as:" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 332, + 487, + 545, + 520 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 332, + 487, + 545, + 520 + ], + "spans": [ + { + "bbox": [ + 332, + 487, + 545, + 520 + ], + "type": "interline_equation", + "content": "\\ell_ {\\mathrm {C I}} \\left(B ^ {k}, \\mathbf {p} ^ {k}, f\\right) = - \\sum_ {c = 1} ^ {C} \\mathbf {1} \\left(p _ {c} ^ {k}, \\hat {p} _ {c} ^ {k}\\right) p _ {c} ^ {k} \\log \\hat {p} _ {c} ^ {k}, \\tag {9}", + "image_path": "56817e7af547b156dd610fd15155ea874dca2a9664e145373a1cedc8bcd55ecd.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 413, + 522, + 545, + 558 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 413, + 522, + 545, + 558 + ], + "spans": [ + { + "bbox": [ + 413, + 522, + 545, + 558 + ], + "type": "interline_equation", + "content": "\\hat {p} _ {c} ^ {k} = \\frac {1}{| B ^ {k} |} \\sum_ {j = 1} ^ {| B ^ {k} |} f \\left(x _ {j} ^ {k}\\right) _ {c}, \\tag {10}", + "image_path": "f16576cf1f4d017444b6a58a459d9e8c96a723fdff34151e53d62627d27782f8.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 324, + 560, + 545, + 586 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 324, + 560, + 545, + 586 + ], + "spans": [ + { + "bbox": [ + 324, + 560, + 545, + 586 + ], + "type": "interline_equation", + "content": "\\mathbf {1} \\left(p, p ^ {\\prime}\\right) = \\left\\{ \\begin{array}{l l} 0 & \\text {i f} p - \\alpha \\sigma \\leq p ^ {\\prime} \\leq p + \\alpha \\sigma \\\\ 1 & \\text {o t h e r w i s e} \\end{array} , \\right. \\tag {11}", + "image_path": "cddc04f3b3681d01f1145e2ec9efa95d9587be8e8fd3c8ddbba7eef0574dd5ad.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{1}" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": " is the indicator function, which outputs 0 if " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "p'" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": " is in the confidence interval, and 1 otherwise. This CI loss updates the network parameters if the difference between the estimated proportion " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "\\hat{p}_c^k" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": " and the expected proportion " + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "inline_equation", + "content": "p_c^k" + }, + { + "bbox": [ + 304, + 594, + 545, + 677 + ], + "type": "text", + "content": " calculated by Eq.6 is significant. Using this loss, we can accelerate the training by using the augmented bags without any adverse effects from proportion gaps." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "content": "In training, mixed bags are randomly generated in each batch. It indicates that the number of generated bags will increase with iteration. We stop training based on the propor" + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "spans": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "type": "text", + "content": "16574" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 70, + 544, + 215 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 544, + 215 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 544, + 215 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 544, + 215 + ], + "type": "table", + "html": "
MethodCIFAR10AccuracySVHNAccuracyPATHAccuracyOCTAccuracyBLOODAccuracyORGANACuracyORGANCuracyORGANSAccuracyAverageAccuracy
LLP [1]0.45380.30090.78430.43360.88690.76350.78980.53720.6187
LLP + Ours(w/o CI)0.45820.29710.78840.4250.88980.78310.81890.5630.6280
LLP + Ours0.52560.37420.78610.43470.90170.79710.80990.61970.6561
LLP + Ours(supervised)0.65940.77810.81180.53960.89470.82220.82330.66740.7234
LLP-VAT [28]0.47400.31190.89150.41240.89150.79360.80600.58370.6455
LLP-VAT + Ours(w/o CI)0.52030.43020.87790.45030.87790.78470.76560.58490.6614
LLP-VAT + Ours0.52830.41110.89440.43660.89440.81550.82280.63760.6800
LLP-VAT + Ours(supervised)0.59630.59760.89970.47770.89970.82300.83130.66220.7234
LLP-PI [13]0.47020.30110.88860.42240.88620.78100.79620.59170.6421
LLP-PI + Ours(w/o CI)0.47940.52090.86880.43500.85730.75950.75700.57410.6565
LLP-PI + Ours0.52900.38650.88410.43660.88410.80130.79890.62360.6680
LLP-PI + Ours(supervised)0.58960.77210.89180.47200.89180.81010.81840.65770.7379
", + "image_path": "b4f1f32156b548e24b1dfb69b4c6fcc588070df698066c712a833d9f10f5adb7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 262, + 544, + 410 + ], + "blocks": [ + { + "bbox": [ + 46, + 220, + 546, + 255 + ], + "lines": [ + { + "bbox": [ + 46, + 220, + 546, + 255 + ], + "spans": [ + { + "bbox": [ + 46, + 220, + 546, + 255 + ], + "type": "text", + "content": "Table 1. Instance-level classification accuracy when our method was applied to three baseline methods; LLP [1], LLP-VAT [28] and LLP-PI [13]. Each value is the average of five-fold cross-validation results. Here, 'CI' means the confident interval, and 'supervised' indicates the case when a ground-truth proportion to the generated mixed bag is given." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 262, + 544, + 410 + ], + "lines": [ + { + "bbox": [ + 50, + 262, + 544, + 410 + ], + "spans": [ + { + "bbox": [ + 50, + 262, + 544, + 410 + ], + "type": "table", + "html": "
MethodCIFAR10 AccuracySVHN AccuracyPATH AccuracyOCT AccuracyBLOOD AccuracyORGANA AccuracyORGANC AccuracyORGANS AccuracyAverage Accuracy
LLP [1]0.45380.30090.78430.43360.88690.76350.78980.53720.6187
LLP + Ours0.52560.37420.78610.43470.90170.79710.80990.61970.6561
LLP + Flip0.57770.38840.82990.47930.92650.65270.69040.62930.6467
LLP + Flip + Ours0.57640.41240.80050.55040.91550.67180.67170.62800.6533
LLP + Erase0.55510.35000.80970.44140.90940.83930.84470.65780.6759
LLP + Erase + Ours0.56710.42690.79340.42910.90210.82660.83130.65940.6794
LLP + Invert0.52580.67630.77750.43940.87900.77790.82150.62550.6899
LLP + Invert + Ours0.57840.77610.74210.45800.87360.78450.83230.63290.7097
LLP + Gaussianblur0.47660.36860.76390.41450.88750.79060.83180.63250.6457
LLP + Gaussianblur + Ours0.51350.40360.75550.43000.87890.79620.79890.67090.6559
LLP + Perspective0.56750.54410.78920.46780.89680.83090.84400.66890.7011
LLP + Perspective + Ours0.57500.57150.77450.49620.90640.81800.84040.68950.7089
", + "image_path": "ad34867050f3d05d0eb74eb6b2244c7c760ab8766e4998f5682147a175c7d1b4.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 63, + 414, + 525, + 426 + ], + "lines": [ + { + "bbox": [ + 63, + 414, + 525, + 426 + ], + "spans": [ + { + "bbox": [ + 63, + 414, + 525, + 426 + ], + "type": "text", + "content": "Table 2. Instance-level classification accuracy when our method was applied after various instance-level augmentation methods." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 445, + 287, + 469 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 445, + 287, + 469 + ], + "spans": [ + { + "bbox": [ + 46, + 445, + 287, + 469 + ], + "type": "text", + "content": "tion loss in validation data. Note that instance-level labels cannot be used for validation in LLP." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 479, + 128, + 493 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 479, + 128, + 493 + ], + "spans": [ + { + "bbox": [ + 47, + 479, + 128, + 493 + ], + "type": "text", + "content": "6. Experiments" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 498, + 233, + 512 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 498, + 233, + 512 + ], + "spans": [ + { + "bbox": [ + 47, + 498, + 233, + 512 + ], + "type": "text", + "content": "6.1. Datasets and experimental settings" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 517, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 517, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 517, + 287, + 696 + ], + "type": "text", + "content": "Preparation of bags: The eight datasets used in these experiments were the same as those used in the preliminary experiments. The way of generating bags was also the same as in the preliminary experiments. Although some of the related studies generated bags by allowing overlaps to increase the number of labeled bags, we did not allow overlaps since this situation is unnatural in actual applications. To keep the experiment setups the same in all datasets, we set the number of labeled bags as 512 and the bag size as 10 based on the smallest dataset. This small bag size can be considered a challenging scenario for MixBag since the number of samplings for sub-bags decreases, and it increases the confidence interval. We also evaluated our method using different bag sizes to demonstrate the effectiveness of our method in various situations." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 701, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 701, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 701, + 287, + 714 + ], + "type": "text", + "content": "Implementation: We implemented our method by using" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 445, + 545, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 445, + 545, + 530 + ], + "spans": [ + { + "bbox": [ + 304, + 445, + 545, + 530 + ], + "type": "text", + "content": "Pytorch [21]. The network model was ResNet18 [9] pretrained on the ImageNet dataset [5]. To train our network, we also used the Adam Optimizer [9] with a learning rate of 3e-4, epoch= 1000, mini-batch size = 32, early stopping = 10 and trained on an NVIDIA GeForce 3090 GPU. We set the confidence degree as '99%' and selected " + }, + { + "bbox": [ + 304, + 445, + 545, + 530 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 445, + 545, + 530 + ], + "type": "text", + "content": " randomly from a uniform distribution [0, 1]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 536, + 545, + 608 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 536, + 545, + 608 + ], + "spans": [ + { + "bbox": [ + 304, + 536, + 545, + 608 + ], + "type": "text", + "content": "Evaluation metric: We evaluated the model performance by the instance-level classification accuracies, which were calculated by using the confusion matrix. To compute the metric, we performed a five-fold cross-validation in all our experiments. The accuracies listed in the tables are the average values of the five-fold cross-validation." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 621, + 387, + 634 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 621, + 387, + 634 + ], + "spans": [ + { + "bbox": [ + 306, + 621, + 387, + 634 + ], + "type": "text", + "content": "6.2. Comparison" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": "Comparison with current methods: Our method MixBag can be applied to any proportion loss-based method since MixBag is a data augmentation method, in which any method can be applied after data augmentation with the CI loss. Most current LLP methods incorporate self-supervised learning, such as consistency, into the proportion loss. We" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "spans": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "type": "text", + "content": "16575" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 77, + 70, + 254, + 126 + ], + "blocks": [ + { + "bbox": [ + 77, + 70, + 254, + 126 + ], + "lines": [ + { + "bbox": [ + 77, + 70, + 254, + 126 + ], + "spans": [ + { + "bbox": [ + 77, + 70, + 254, + 126 + ], + "type": "table", + "html": "
Methodγ-samplingAverage Accuracy
LLP [1]-0.6187
LLP + Oursuniform0.6561
LLP + OursGauss0.6512
LLP + Ourshalf0.6524
", + "image_path": "4e451e5ae3f1c64770f5f5cbaa33403df58106982fd3f8c256791f1dae54288e.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 85, + 163, + 248, + 228 + ], + "blocks": [ + { + "bbox": [ + 47, + 130, + 287, + 152 + ], + "lines": [ + { + "bbox": [ + 47, + 130, + 287, + 152 + ], + "spans": [ + { + "bbox": [ + 47, + 130, + 287, + 152 + ], + "type": "text", + "content": "Table 3. Average accuracy on eight datasets when changing a sampling method for " + }, + { + "bbox": [ + 47, + 130, + 287, + 152 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 47, + 130, + 287, + 152 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 85, + 163, + 248, + 228 + ], + "lines": [ + { + "bbox": [ + 85, + 163, + 248, + 228 + ], + "spans": [ + { + "bbox": [ + 85, + 163, + 248, + 228 + ], + "type": "table", + "html": "
MethodCIAverage Accuracy
LLP [1]0.6187
LLP + Ours(99%)✓0.6561
LLP + Ours(95%)✓0.6519
LLP + Ours(80%)✓0.6531
LLP + Ours(50%)✓0.6243
", + "image_path": "4496a56f33b4a2674595241e64b61243e81419ed2f5a781e9e792bb2520dbced.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 275, + 286, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 275, + 286, + 371 + ], + "spans": [ + { + "bbox": [ + 46, + 275, + 286, + 371 + ], + "type": "text", + "content": "thus applied our method in three methods: 1) LLP [1], which is the method of the original paper on using the proportion loss; 2) LLP-VAT [28], which introduces the consistency regularization into the proportion loss; and 3) LLP-PI [13], which uses the additive Gaussian noise for making perturbed examples. The LLP-VAT is one of the state-of-the-art LLP methods using the proportion loss, and its implementations are publicly available." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 372, + 286, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 372, + 286, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 372, + 286, + 479 + ], + "type": "text", + "content": "We compared the baseline methods as an ablation study. The first was 'LLP', which uses the standard proportion loss; the second was 'LLP+Ours(w/o CI)' which uses the MixBag without using the CI loss, where the proportion is directly calculated from the original bags (and may contain noise) was used as the label for the generated mixed bag. The third was 'LLP+Ours(supervised)', which uses the ground-truth proportions of the mixed bags. Note that the proportion would be unknown in real cases." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 480, + 286, + 577 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 480, + 286, + 577 + ], + "spans": [ + { + "bbox": [ + 46, + 480, + 286, + 577 + ], + "type": "text", + "content": "Table 1 shows the accuracy of each method, where the gray color field indicates the proposed methods in each baseline method. 'LLP+Ours(w/o CI)' improved the accuracies in some datasets and slightly improved them on average from the baselines. However, the improvement was limited by the noisy proportions. MixBag improved the accuracy of every baseline method on all datasets, and the improvement was 3 to 4 points on average." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "content": "Introducing MixBag with instance-level augmentation: Next, we introduced our method to the instance-level augmentation methods. We used standard augmentation techniques: 'Flip' randomly flips the image horizontally and upside down. 'Erase' removes a randomly selected area from an original image. 'Invert' randomly changes the colors of the image by inversion. 'Gaussianblur' blurs an image by adding a randomly chosen Gaussian blur. 'Perspective' performs a random projective transformation on an image. To generate a bag by instance-level augmentation, we added perturbations into instances randomly selected from" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 341, + 70, + 506, + 178 + ], + "blocks": [ + { + "bbox": [ + 47, + 232, + 286, + 255 + ], + "lines": [ + { + "bbox": [ + 47, + 232, + 286, + 255 + ], + "spans": [ + { + "bbox": [ + 47, + 232, + 286, + 255 + ], + "type": "text", + "content": "Table 4. Average accuracy on eight datasets when changing the degree of confidence interval (50%, 80%, 95%, 99%)." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 341, + 70, + 506, + 178 + ], + "lines": [ + { + "bbox": [ + 341, + 70, + 506, + 178 + ], + "spans": [ + { + "bbox": [ + 341, + 70, + 506, + 178 + ], + "type": "table", + "html": "
MethodSizeNumAverage Accuracy
LLP [1]105120.6187
LLP + Ours(w/o CI)105120.6280
LLP + Ours105120.6561
LLP [1]202560.5441
LLP + Ours(w/o CI)202560.5496
LLP + Ours202560.5667
LLP [1]401280.4746
LLP + Ours(w/o CI)401280.4600
LLP + Ours401280.5058
", + "image_path": "52c0b2f9fadd78f2513a00f1d859f9a51da918a02f2157d28d83fa52f54228a2.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 182, + 545, + 216 + ], + "lines": [ + { + "bbox": [ + 306, + 182, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 306, + 182, + 545, + 216 + ], + "type": "text", + "content": "Table 5. Average accuracy on eight datasets when changing the number of labeled bags and bag size. 'Size' means the bag size. 'Num' means the number of labeled bags." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 235, + 545, + 344 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 235, + 545, + 344 + ], + "spans": [ + { + "bbox": [ + 305, + 235, + 545, + 344 + ], + "type": "text", + "content": "an original bag; i.e., an augmented bag contains the perturbed instances and original instances, where this augmentation has not been reported in previous papers. In " + }, + { + "bbox": [ + 305, + 235, + 545, + 344 + ], + "type": "inline_equation", + "content": "\\mathrm{LLP} +" + }, + { + "bbox": [ + 305, + 235, + 545, + 344 + ], + "type": "text", + "content": " instance-level " + }, + { + "bbox": [ + 305, + 235, + 545, + 344 + ], + "type": "inline_equation", + "content": "^+" + }, + { + "bbox": [ + 305, + 235, + 545, + 344 + ], + "type": "text", + "content": " MixBag, the mixed bag was created from the original and instance-level augmented bags. Table 2 shows the accuracies of the baseline and our methods. The instance-level data augmentation improved the performance from the baseline. Our method further improved the accuracies of every instance-level augmentation method." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 350, + 486, + 361 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 350, + 486, + 361 + ], + "spans": [ + { + "bbox": [ + 306, + 350, + 486, + 361 + ], + "type": "text", + "content": "6.3. Performance in various situations" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "spans": [ + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "text", + "content": "Performance with different " + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "text", + "content": " sampling methods: We evaluated our method with three different " + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "text", + "content": " sampling methods, i.e., three different ways to determine the mixing rate " + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "text", + "content": " of the two sub-bags " + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "inline_equation", + "content": "S^i, S^j" + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "text", + "content": ": 'uniform' selects " + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "text", + "content": " randomly from a uniform distribution; 'Gauss' selects " + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "text", + "content": " randomly from a Gaussian distribution " + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\mathcal{N}(0.5, 0.25)" + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "text", + "content": "; 'half' always set " + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 305, + 369, + 545, + 488 + ], + "type": "text", + "content": " to 0.5. Table 3 shows the average accuracies of all datasets. All sampling methods outperformed the performance compared to the baseline method (LLP); 'uniform' was marginally better than other methods." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "spans": [ + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "text", + "content": "Performance with different confidence intervals: We conducted experiments with four different confidence intervals, " + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "inline_equation", + "content": "99\\%" + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "inline_equation", + "content": "95\\%" + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "inline_equation", + "content": "80\\%" + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "text", + "content": ". Table 4 shows the average accuracies of all datasets. For all confidence interval settings, our method improved the accuracy on all datasets and in all cases. When the confidence interval took high values " + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "inline_equation", + "content": "(99\\%, 95\\%, 80\\%)" + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "text", + "content": ", our method worked well since the worst effects of noisy labels were mitigated by the CI loss. Even when the confidence interval was low " + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "inline_equation", + "content": "(50\\%)" + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "text", + "content": ", the accuracy improved from the baseline method. The case of " + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "inline_equation", + "content": "99\\%" + }, + { + "bbox": [ + 305, + 493, + 545, + 648 + ], + "type": "text", + "content": " was the best on average. We consider that a larger confidence interval avoids the adverse effects of noisy proportions and makes the training more stable." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 654, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 654, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 654, + 545, + 713 + ], + "type": "text", + "content": "Performance when changing the number of labeled bags and bag size: To show the effectiveness of our method in various situations, we conducted experiments with different bag sizes (512, 256, 128) and different numbers of labeled bags (10, 20, 40), where the bag size and the number of" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "spans": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "type": "text", + "content": "16576" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 70, + 70, + 261, + 148 + ], + "blocks": [ + { + "bbox": [ + 70, + 70, + 261, + 148 + ], + "lines": [ + { + "bbox": [ + 70, + 70, + 261, + 148 + ], + "spans": [ + { + "bbox": [ + 70, + 70, + 261, + 148 + ], + "type": "table", + "html": "
MethodBag-GenerationCIAverage Accuracy
LLP [1]--0.6187
LLP + Ours(w/o CI)Union-0.6226
LLP + Ours(w/o CI)Sub-bag0.4956
LLP + Ours(with CI)Sub-bag✓0.6364
LLP + Ours(w/o CI)MixBag0.6280
LLP + Ours(with CI)MixBag✓0.6561
", + "image_path": "a86d6c66e6da2e001beec176729b763c5aa5105a3893b90906df2d15ba9b0c87.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 152, + 287, + 174 + ], + "lines": [ + { + "bbox": [ + 47, + 152, + 287, + 174 + ], + "spans": [ + { + "bbox": [ + 47, + 152, + 287, + 174 + ], + "type": "text", + "content": "Table 6. Average accuracy on eight datasets in different bag-generation methods." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 193, + 286, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 193, + 286, + 251 + ], + "spans": [ + { + "bbox": [ + 47, + 193, + 286, + 251 + ], + "type": "text", + "content": "labeled bags have a trade-off since the total number of instances is fixed. Table 5 shows the average accuracies on all datasets with various setups. Our method improved the accuracy from the baseline methods on average in all cases. This demonstrates the robustness of our method." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 258, + 286, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 258, + 286, + 435 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 286, + 435 + ], + "type": "text", + "content": "Performance with different bag generations: To confirm the effectiveness of the 'Mix' approach, we compared MixBag with two other bag generation methods. 1) 'union' directly combines any two bags " + }, + { + "bbox": [ + 46, + 258, + 286, + 435 + ], + "type": "inline_equation", + "content": "(B^i, B^j)" + }, + { + "bbox": [ + 46, + 258, + 286, + 435 + ], + "type": "text", + "content": " without sampling. In this case, the proportion of a generated bag can be directly calculated from those of the original bags; i.e., there is no noise for the combined proportions by taking the union of two bags. Therefore, the CI loss was not used for this method. 2) 'sub-bag' randomly samples instances from a single bag " + }, + { + "bbox": [ + 46, + 258, + 286, + 435 + ], + "type": "inline_equation", + "content": "B^i" + }, + { + "bbox": [ + 46, + 258, + 286, + 435 + ], + "type": "text", + "content": ". It can be considered as a sub-bag of the original bag " + }, + { + "bbox": [ + 46, + 258, + 286, + 435 + ], + "type": "inline_equation", + "content": "B^i" + }, + { + "bbox": [ + 46, + 258, + 286, + 435 + ], + "type": "text", + "content": ". In this case, the label proportions of the sub-bag may have a gap from the original one, and thus, we evaluated two cases; 'sub-bag' without and with the CI loss. 3) 'MixBag' is our method, which mixes two bags. We also evaluated two cases; Mixbag with and without CI loss." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 437, + 286, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 286, + 591 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 286, + 591 + ], + "type": "text", + "content": "Table 6 shows the average of the instance-level accuracies of the comparative methods on the eight datasets. Since 'sub-bag with CI' and union' can increase the number of labeled bags, these methods had slightly improved accuracy from that of baseline method LLP [1]. Our method, 'MixBag with CI' further improved the accuracy compared with these other bag generation methods. We consider that our method has two characteristics of 'sub-bag' and 'union', where MixBag first makes sub-bags from original bags and then takes the union of these sub-bags. In addition, MixBag can generate various proportions of the mixed bag compared to 'sub-bag' and 'union'. Therefore, MixBag was better than them." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 599, + 151, + 612 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 599, + 151, + 612 + ], + "spans": [ + { + "bbox": [ + 47, + 599, + 151, + 612 + ], + "type": "text", + "content": "6.4. Detailed Analysis" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "content": "Distribution of proportion vectors in the space of proportion labels: Figure 6 shows distributions of the original proportion vectors " + }, + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{p}^i\\}_{i=1}^n" + }, + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "content": " (blue) and the generated mixed bag's proportion vectors " + }, + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{r}^i\\}_{i=1}^m" + }, + { + "bbox": [ + 46, + 617, + 286, + 713 + ], + "type": "text", + "content": " (orange) in the 'ORGANS' dataset, in which the dimension was compressed to 2D by PCA [29]. Here, the number of mixed bags is the same as that of the original bags. We can see that the MixBag proportion vectors do not overlap with the orig-" + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 313, + 83, + 419, + 178 + ], + "blocks": [ + { + "bbox": [ + 313, + 83, + 419, + 178 + ], + "lines": [ + { + "bbox": [ + 313, + 83, + 419, + 178 + ], + "spans": [ + { + "bbox": [ + 313, + 83, + 419, + 178 + ], + "type": "image", + "image_path": "a35aa66f6a3c7a4c2feb5c6879cda2491d3ed532a7212fe31e4ded9388b3dc8f.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 311, + 187, + 428, + 232 + ], + "lines": [ + { + "bbox": [ + 311, + 187, + 428, + 232 + ], + "spans": [ + { + "bbox": [ + 311, + 187, + 428, + 232 + ], + "type": "text", + "content": "Figure 6. Distribution of proportion vectors. Blue: Original bag's proportion. Orange: Mixed bag's proportion." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 442, + 82, + 546, + 178 + ], + "blocks": [ + { + "bbox": [ + 442, + 82, + 546, + 178 + ], + "lines": [ + { + "bbox": [ + 442, + 82, + 546, + 178 + ], + "spans": [ + { + "bbox": [ + 442, + 82, + 546, + 178 + ], + "type": "image", + "image_path": "8aea3cb7fe3f5113ce626775fd52aa264bdb32faaef10865ddf5e036256a3066.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 437, + 187, + 554, + 232 + ], + "lines": [ + { + "bbox": [ + 437, + 187, + 554, + 232 + ], + "spans": [ + { + "bbox": [ + 437, + 187, + 554, + 232 + ], + "type": "text", + "content": "Figure 7. Relationship between confidence interval and actual gaps. Blue: proportion vector of a bag." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 253, + 545, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 253, + 545, + 324 + ], + "spans": [ + { + "bbox": [ + 304, + 253, + 545, + 324 + ], + "type": "text", + "content": "inal ones, i.e., new proportion labels were generated, and the distribution of mixed bag proportions covers the original distribution by interpolating pairs of the original bags. This result shows that MixBag adds diversity to the training dataset, which facilitates an improvement in the instance-level classification accuracy." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "spans": [ + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "text", + "content": "Relationship between confidence interval and ground-truth proportion: Figure 7 shows how well the confidence interval works. The horizontal axis indicates the difference " + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "inline_equation", + "content": "(\\| \\mathbf{p} - \\hat{\\mathbf{p}} \\|_1)" + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "text", + "content": " between the ground-truth proportion " + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\mathbf{p}" + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "text", + "content": " and the estimated proportion " + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{p}}" + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "text", + "content": " of a mixed bag. The vertical axis indicates the difference " + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "inline_equation", + "content": "(\\alpha \\sigma^k)" + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "text", + "content": " between the upper bounds of the confidence interval and " + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\mathbf{p}" + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "text", + "content": ", where we set the degree of confidence as " + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "inline_equation", + "content": "99\\%" + }, + { + "bbox": [ + 304, + 331, + 545, + 488 + ], + "type": "text", + "content": ". Each blue point indicates the proportion vector of a mixed bag. Almost all points are under the straight line in the figure. This indicates that the actual proportion gaps from the ground truth were less than the confidence interval, and thus the proposed CI loss works properly." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 501, + 378, + 513 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 501, + 378, + 513 + ], + "spans": [ + { + "bbox": [ + 306, + 501, + 378, + 513 + ], + "type": "text", + "content": "7. Conclusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 521, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 713 + ], + "type": "text", + "content": "In this paper, we examined how the number of labeled bags and the bag size affects the performance in LLP. As a result, we found that the accuracy improves as the number of labeled bags increases, even when the total number of instances is fixed. Then, based on this observation, we propose a simple but effective bag-level data augmentation method. In addition, we also proposed a confidence interval loss that effectively trains a classification network by using the generated bags while avoiding the adverse effects caused by noisy proportions. To the best of our knowledge, this is the first attempt to propose bag-level data augmentation for LLP. The experiments using eight datasets demonstrated the effectiveness of our method in various cases. Additionally, MixBag can be applied to instance-level data augmentation techniques and any LLP method that uses a standard proportion loss." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 732, + 317, + 741 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 732, + 317, + 741 + ], + "spans": [ + { + "bbox": [ + 293, + 732, + 317, + 741 + ], + "type": "text", + "content": "16577" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "content": "Acknowledgements: This work was supported by JSPS KAKENHI Grant Number JP20H04211 and JP23K18509, and JST, ACT-X Grant Number JPMJAX200G, Japan." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 131, + 105, + 143 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 131, + 105, + 143 + ], + "spans": [ + { + "bbox": [ + 48, + 131, + 105, + 143 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 150, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 53, + 150, + 287, + 194 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 150, + 287, + 194 + ], + "spans": [ + { + "bbox": [ + 53, + 150, + 287, + 194 + ], + "type": "text", + "content": "[1] Ehsan Mohammady Ardehaly and Aron Culotta. 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In Proceedings of the IEEE international conference on computer vision, pages 2223-2232, 2017." + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "spans": [ + { + "bbox": [ + 294, + 732, + 317, + 742 + ], + "type": "text", + "content": "16579" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/MixCycle_ Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency/1f3580cb-fdbe-4e7d-96d7-32968d08a569_content_list.json b/2023/MixCycle_ Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency/1f3580cb-fdbe-4e7d-96d7-32968d08a569_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..c8b93bdb705fe96fd246a89e6dd62271d572bd22 --- /dev/null +++ b/2023/MixCycle_ Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency/1f3580cb-fdbe-4e7d-96d7-32968d08a569_content_list.json @@ -0,0 +1,1559 @@ +[ + { + "type": "text", + "text": "MixCycle: Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency", + "text_level": 1, + "bbox": [ + 101, + 128, + 870, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Qiao Wu $^{1}$ Jiaqi Yang $^{1*}$ Kun Sun $^{2}$ Chu'ai Zhang $^{1}$ Yanning Zhang $^{1}$ Mathieu Salzmann $^{3}$", + "bbox": [ + 132, + 202, + 836, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1 Northwestern Polytechnical University 2 China University of Geosciences, Wuhan 3 École Polytechnique Fédérale de Lausanne", + "bbox": [ + 151, + 220, + 818, + 258 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "qiaowu@mail.nwpu.edu.cn; jqyang@nwpu.edu.cn; sunkun@cug.edu.cn;", + "bbox": [ + 204, + 261, + 763, + 275 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "cazhang@mail.nwpu.edu.cn; ynzhang@nwpu.edu.cn; mathieu.salzmann@epfl.ch", + "bbox": [ + 169, + 279, + 797, + 292 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 327, + 313, + 343 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "3D single object tracking (SOT) is an indispensable part of automated driving. Existing approaches rely heavily on large, densely labeled datasets. However, annotating point clouds is both costly and time-consuming. Inspired by the great success of cycle tracking in unsupervised 2D SOT, we introduce the first semi-supervised approach to 3D SOT. Specifically, we introduce two cycle-consistency strategies for supervision: 1) Self tracking cycles, which leverage labels to help the model converge better in the early stages of training; 2) forward-backward cycles, which strengthen the tracker's robustness to motion variations and the template noise caused by the template update strategy. Furthermore, we propose a data augmentation strategy named SOT-Mixup to improve the tracker's robustness to point cloud diversity. SOTMixup generates training samples by sampling points in two point clouds with a mixing rate and assigns a reasonable loss weight for training according to the mixing rate. The resulting MixCycle approach generalizes to appearance matching-based trackers. On the KITTI benchmark, based on the P2B tracker [16], MixCycle trained with $10\\%$ labels outperforms P2B trained with $100\\%$ labels, and achieves a $28.4\\%$ precision improvement when using $1\\%$ labels. Our code will be released at https://github.com/Mumuqiao/MixCycle.", + "bbox": [ + 75, + 359, + 473, + 724 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 748, + 209, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "3D single object tracking (SOT) plays a critical role in the field of autonomous driving. For example, given object detection [15, 33] results as input, it can output the necessary information for trajectory prediction [8]. The goal of SOT is to regress the center position and 3D bounding-box (BBox) of an object of interest in a search area, given the point cloud (PC) patch and BBox of the object template.", + "bbox": [ + 75, + 773, + 470, + 881 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/afbf5385e08d25e08f66aaa42b4e185ffc675c5b6fd4d1cf8c31311736305a18.jpg", + "image_caption": [ + "Figure 1. Comparison of MixCycle and fully-supervised methods [16, 25, 34], all trained with $1\\%$ labels on KITTI [5]. 'Succ.' and 'Prec.' represent Success and Precision, respectively." + ], + "image_footnote": [], + "bbox": [ + 501, + 325, + 893, + 518 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "This is a very challenging task because (i) point clouds obtained with, e.g., LiDAR sensors, suffer from occlusions and point sparsity, complicating the tracker's task of finding the object of interest; (ii) the point distribution for an object may vary significantly, making it difficult for the model to learn discriminative object features.", + "bbox": [ + 496, + 593, + 893, + 684 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To tackle the above challenges, existing 3D SOT models [6, 16, 4, 9, 10, 25, 34, 18, 35] rely on large scale annotated point cloud datasets for training. Unfortunately, obtaining annotations for this task, as for many 3D tasks, is extremely time-consuming. Furthermore, as shown in Fig. 1, the performance of these methods degrades dramatically as the number of labeled samples decreases. Nevertheless, no semi-supervised or unsupervised methods have been explored so far in 3D SOT.", + "bbox": [ + 496, + 686, + 893, + 821 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "As shown in Fig. 2, the matching-based tracker of [34] can still track the target at the very beginning of a sequence by predicting a motion offset relative to the reference coordinate, even though there are no points in the template for appearance matching. This indicates that the appearance", + "bbox": [ + 496, + 824, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author", + "bbox": [ + 94, + 886, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "13956", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ddf3e0f5b35c2a741dac34bfce18a8377279aad272d234ce75975f9b529f2f3b.jpg", + "image_caption": [ + "Ground Truth" + ], + "image_footnote": [], + "bbox": [ + 81, + 89, + 467, + 176 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/2dcdfb205a088ddb3cee58189a8e7ec6d577e15510266212f5a61f82b34c410f.jpg", + "image_caption": [ + "Matching-Based Tracker", + "Figure 2. We observe that appearance matching-based trackers can learn the objects motion distribution and track them even in the absence of points for appearance matching. For instance, BAT [34] manages to track objects in extremely sparse point clouds." + ], + "image_footnote": [], + "bbox": [ + 276, + 181, + 308, + 194 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "matching-based trackers can learn motion information. By contrast, in 2D SOT, many trackers [23, 24, 36, 29] employ cycle consistency to leverage unsupervised data. Specifically, they encourage forward and backward tracking to produce consistent motions. In principle, we expect to apply this idea to 3D SOT and make trackers to learn the object's motion distribution in unlabeled data. However, transferring these 2D methods directly to 3D is challenging. First, since the point cloud is sparse and the environment is cluttered with objects, it is hard to find meaningful patches to use as pseudo labels for training. Second, unsupervised 2D SOT methods rely on the assumption that the target appears in every frame of the sequence. Unfortunately, this assumption is not always satisfied in point cloud datasets such as KITTI [5], NuScenes [1], and Waymo [20]. This is because they are built for the multi-object tracking task, and cannot guarantee that the tracking object exists in the whole sequence.", + "bbox": [ + 75, + 280, + 468, + 551 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we introduce a label-efficient way to train 3D SOT trackers. We call it MixCycle - a 3D SOT approach based on a novel SOTMixup data augmentation strategy for semi-supervised Cycle tracking. Specifically, we first develop a tracking framework exploiting both self and forward-backward tracking cycles. Self tracking consistency is performed to cover the object point cloud appearance variation, and forward-backward consistency is built for learning the object's motion distribution. Second, we present a data augmentation method for 3D SOT called SOTMixup, which is inspired by the success of mixup [31] and Manifold mixup [22]. Without changing the total number of points in the search area, SOTMixup samples points in a random point cloud and the search area point cloud according to the mixing rate and generates training samples. Specifically, the random point cloud is sampled from the labeled training set. SOTMixup thus increases the tracker's robustness to point cloud variations. We evaluate MixCycle on KITTI, NuScenes, and Waymo. As shown in Fig. 1, our experiments clearly demonstrate the label efficiency, generalization and remarkable performance of our method on the 3D SOT task.", + "bbox": [ + 75, + 553, + 468, + 883 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Contributions: (i) We propose the first semi-supervised", + "bbox": [ + 76, + 885, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3D SOT framework. It exploits self and forward-backward consistency as supervision and generalizes to appearance matching-based trackers. (ii) We introduce a SOTMixup augmentation strategy that increases the tracker's robustness to point distribution variations and allows it to learn motion information in extreme situations. (iii) Our framework demonstrates a remarkable performance in terms of label efficiency, achieving better results than existing supervised methods in our experiments on KITTI NuScenes, and Waymo when using fewer labels. In particular, we surpass P2B [16] trained on $100\\%$ labels while only using $10\\%$ labels.", + "bbox": [ + 496, + 90, + 890, + 271 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 286, + 640, + 301 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3D Single Object Tracking. Since LiDAR is insensitive to illumination, the appearance matching model has become the main choice in the field of 3D single object tracking. Giancola et al. [6] proposed SC3D which is the first method using a Siamese network to deal with this problem. However, it is very time-consuming and inaccurate due to heuristic matching. Zarzar et al. [30] built an end-to-end tracker by using 2D RPN in 2D bird's eyes view (BEV). Unfortunately, the lack of information in one dimension leads to limited accuracy. The point-to-box (P2B) network [16] employs VoteNet[15] as object regression module to construct a point-based tracker. A number of works [4, 9, 10, 25, 34, 18] investigate different architectures of trackers based on P2B [16]. Zheng et al. [34] depicted an object using the point-to-box relation and proposed BoxCloud, which enables the model to better sense the size of objects. Hui et al. [9] discovered the priori information of object shapes in the dataset to obtain dense representations of objects from sparse point clouds. Zheng et al. [35] presented a motion centric method $M^2$ -Track, which is appearance matching-free and has made great progress in dealing with the sparse point cloud tracking problem. However, $M^2$ -track is limited by the LiDAR frequency of datasets as object motion in adjacent frames varies with the LiDAR sampling frequency.", + "bbox": [ + 496, + 311, + 890, + 688 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "All the above methods rely on large-scale labeled datasets. Unfortunately, 3D point cloud annotation is labor- and time-consuming. To overcome this, we propose MixCycle, a semi-supervised tracking method based on cycle consistency constraints with SOTMixup data augmentation. Label-Efficient Visual Tracking. Wang et al. [23] proposed unsupervised deep tracking (UDT) with cycle consistency, based on a Siamese correlation filter backbone network. UDT achieved remarkable performance, revealing the potential of unsupervised learning in visual tracking. Yuan et al. [29] improved the UDT approach to make the target features passed forward and backward as similar as possible. The self-supervised fully convolutional Siamese network [19] uses only spatially supervised learning of tar", + "bbox": [ + 496, + 688, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "13957", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/f79febe5b5c4ce3e41316e7de7fe6b46f8f668debebe7525810aab10a7d17897.jpg", + "image_caption": [ + "Figure 3. MixCycle framework. The label is only contained in $P_0^s$ of point cloud (PC) sequence $\\{P_0^s, P_1^s, \\ldots, P_n^s\\}$ . 1) Self tracking cycle: we first sample a PC $P_r^s$ from the labeled training set. Then, we generate pseudo labels by applying SOTMixup and random rigid transformation (Trans.) to $P_0^s$ and $P_r^s$ . SOTMixup directly mixes $P_r^s$ and $P_0^s$ based on the number of points with a mixing rate, assigning a reasonable loss weight corresponding to the mixing rate. We employ the consistency between self tracking proposals and pseudo labels to formulate the loss $\\mathcal{L}_{self}$ . 2) Forward-backward tracking cycle: we leverage forward tracking proposals as pseudo labels and apply a random rigid transformation to them. Then, we employ the consistency between ground truth (GT)/pseudo labels and backward tracking proposals to formulate the losses $\\mathcal{L}_{con0} / \\{\\mathcal{L}_{con1}, \\ldots, \\mathcal{L}_{con(n-1)}\\}$ ." + ], + "image_footnote": [], + "bbox": [ + 76, + 85, + 893, + 295 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "get correspondences in still video frames. Wu et al. [26] proposed a progressive unsupervised learning (PUL) network, which distinguishes the background by contrastive learning and models the regression result noise. PUL thus makes the tracker robust in long-time tracking. Unsupervised single object tracker [36] consists of an online-updating tracker with a novel memory learning scheme.", + "bbox": [ + 75, + 424, + 468, + 530 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In essence, the above unsupervised trackers all make the implicit assumption that the tracked target exists in every frame of the sequence. Unfortunately, this is not necessarily true in KITTI [5], NuScenes [1], and Waymo [20]. Therefore, the above methods are not directly applicable to 3D SOT.", + "bbox": [ + 75, + 532, + 470, + 622 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Mixup Data Augmentation. Data augmentation has become a crucial pre-processing step for many deep learning models. Zhang et al. [31] introduced a data augmentation method called mixup, which linearly interpolates two image samples, and Manifold mixup [22] transfers this idea to high-dimensional feature spaces. By interpolating a new sample, PointMixup [2] extends mixup to point clouds. Mix3D [14] introduces a scene-aware mixup by taking the union of two 3D scenes and their labels after random transformations. Lu et al. [13] developed a directed mixup based on the pixel values. Additionally, a variety of region mixup techniques have been proposed [32, 12, 21, 11]. In the case of outdoor scenes, Xiao et al. [28] combined two images using random rotation. CosMix[17] and structure aware fusion [7] combine point clouds using semantic structures. Fang et al. [3] turned a CAD into a point cloud to combat object occlusion.", + "bbox": [ + 75, + 626, + 472, + 883 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "However, the above-mentioned methods are made for the", + "bbox": [ + 96, + 885, + 468, + 898 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "multi-class classification scenario and are not suitable for SOT, which only contains a positive and negative sample.", + "bbox": [ + 498, + 424, + 890, + 455 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 468, + 591, + 484 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overview", + "text_level": 1, + "bbox": [ + 500, + 493, + 609, + 508 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The purpose of 3D SOT is to continually locate the target in the search area point cloud sequence $\\mathbf{P}^s = \\{P_0^s,\\dots ,P_k^s,\\dots ,P_n^s |P_k^s\\in \\mathbb{R}^{N_s\\times 3}\\}$ given the tracking object template point cloud $P_0^o\\in \\mathbb{R}^{N_t\\times 3}$ and the 3D BBox $B_{0}\\in \\mathbb{R}^{7}$ in the initial frame. This can be described as", + "bbox": [ + 498, + 516, + 890, + 592 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\widetilde {P} _ {k + 1} ^ {o}, \\widetilde {B} _ {k + 1}\\right) = \\mathcal {F} \\left(P _ {k + 1} ^ {s}, \\widetilde {P} _ {k} ^ {o}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 586, + 604, + 890, + 625 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\widetilde{P}_k^o$ , $\\widetilde{P}_{k + 1}^o$ and $\\widetilde{B}_{k + 1}$ are the predicted target point cloud and 3D BBox in frame $k$ and $k + 1$ , respectively. By referring to P2B [16] and its follow-ups [4, 9, 10, 18, 25, 34], we summarize the typically 3D SOT loss as", + "bbox": [ + 496, + 630, + 893, + 694 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\rho_ {1} \\cdot \\mathcal {L} _ {c l a} + \\rho_ {2} \\cdot \\mathcal {L} _ {p r o p} + \\rho_ {3} \\cdot \\mathcal {L} _ {r e g} + \\rho_ {4} \\cdot \\mathcal {L} _ {b o x}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 513, + 705, + 890, + 723 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\rho$ is the manually-tuned hyperparameter, $\\mathcal{L}_{\\text{cla}}$ , $\\mathcal{L}_{\\text{prop}}$ , $\\mathcal{L}_{\\text{reg}}$ and $\\mathcal{L}_{\\text{box}}$ are the losses for foreground-background classification, confidences for the BBox proposals, voting offsets of the seed points, and offsets of the BBox proposals, respectively.", + "bbox": [ + 496, + 734, + 890, + 809 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To address this task, we propose MixCycle, a novel semi-supervised framework for 3D SOT. Illustrated in Fig. 3, MixCycle relies on a SOTMixup data augmentation strategy to tackle data sparsity and diversity (Sec. 3.2). Further, it utilizes self and forward-backward cycle consistencies as sources of supervision to cover the object appear", + "bbox": [ + 496, + 810, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "13958", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ance and motion variation (Sec. 3.3). Additionally, we apply rigid transformations to ground truth (GT) labels to generate search areas in unlabeled data (Sec. 3.4).", + "bbox": [ + 75, + 90, + 468, + 136 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. SOTMixup", + "text_level": 1, + "bbox": [ + 76, + 145, + 200, + 162 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Inspired by the great success of mixup [31], we develop SOTMixup to supply diverse training samples and deal with the point cloud diversity problem, providing a solution for the mixup application in binary classification in SOT task. With two image samples $(I_A, I_B)$ , mixup can be simply describe as creating an image", + "bbox": [ + 75, + 169, + 468, + 260 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nI _ {A} ^ {m} = \\lambda I _ {A} + (1 - \\lambda) I _ {B}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 187, + 270, + 468, + 287 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ny _ {A} ^ {m} = \\lambda y _ {A} + (1 - \\lambda) y _ {B}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 184, + 313, + 468, + 330 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\lambda \\in [0,1]$ is the mixing rate, and $(y_A,y_B)$ are the image labels. Typically, $\\lambda$ follows a Beta distribution $\\beta (\\eta ,\\eta)$ . A multi-class loss is then calculated as", + "bbox": [ + 75, + 335, + 468, + 380 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {m u t i - c a l}} = \\lambda \\cdot \\mathcal {C} (\\widetilde {y}, y _ {A}) + (1 - \\lambda) \\cdot \\mathcal {C} (\\widetilde {y}, y _ {B}), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 116, + 393, + 468, + 409 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\widetilde{y}$ is the predicted label, and $\\mathcal{C}$ is the criterion (usually being the cross-entropy loss). Vanilla mixup applies linear interpolation in aligned pixel space. However, this operation is not suitable to unordered point clouds. Furthermore, one of the key challenges for the SOT task is to determine whether the proposal is positive or negative. Multi-class label interpolation approach in mixup cannot be directly applied. Specifically, given the search area PC $P_A$ and a random PC $P_B$ sampled in the training set, we employ mixup to generate a foreground and background label pair $(\\lambda \\cdot y_A, (1 - \\lambda) \\cdot y_B)$ . In practice, this label pair should be set to $(y_A, 0)$ , as the points in $P_B$ mismatch the template and should be considered as background.", + "bbox": [ + 75, + 419, + 468, + 617 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We therefore develop a point cloud mixup strategy for SOT based on the number of points, called SOTMixup. As shown in Fig. 4, SOTMixup generates new samples and minimizes the gap between the generated samples and the real sample distribution. Specifically, SOTMixup mixes a point cloud randomly sampled from the training set and the search area point cloud by sampling points using a mixing rate, without changing the total number of points in the search area. First, given point cloud pair $(P_A, P_B)$ , corresponding binary classification labels $(y_A, y_B)$ , and a mixing rate $\\lambda$ , we separate the backgrounds and object points in $P_A$ and $P_B$ and obtain $(P_A^b, P_A^o, P_B^b, P_B^o)$ , where $P_A^o \\in \\mathbb{R}^{N_A^o \\times 3}$ and $P_B^o \\in \\mathbb{R}^{N_B^o \\times 3}$ . Second, we generate $\\hat{P}_A^o$ and $\\hat{P}_B^o$ by randomly sampling $\\lambda \\times N_A^o$ and $(1 - \\lambda) \\times N_A^o$ points from $P_A^o$ and $P_B^o$ , respectively. We then perform SOTMixup as", + "bbox": [ + 75, + 617, + 468, + 845 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nP _ {A} ^ {m} = P _ {A} ^ {b} + \\hat {P} _ {A} ^ {o} + \\hat {P} _ {B} ^ {o}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 192, + 856, + 468, + 875 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $^{\\prime} + ^{\\prime}$ represents the concatenation operation.", + "bbox": [ + 76, + 885, + 406, + 900 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/392cc2a2f5afe57ede32399f731ecda0c8f8519d165c3254767ef68db05a4f05.jpg", + "image_caption": [ + "Figure 4. SOTMixup. First, the search area point cloud (PC) and a point cloud randomly sampled from the labeled training set are segmented into foreground and background, respectively. Second, a mixing rate $\\lambda$ is applied to sample two object PCs. Finally, we concatenate the sampled object PCs and search area background to generate the mixed search area." + ], + "image_footnote": [], + "bbox": [ + 500, + 87, + 893, + 282 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Usually, we consider the distance between the predicted object center and the ground truth to be positive if it is less than 0.3 meters, and negative if it is greater than 0.6 meters. The binary cross entropy loss for regression and foreground classification in SOTMixup can be written as", + "bbox": [ + 498, + 395, + 890, + 470 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {p r o p . m i x}} = - \\left(\\lambda \\cdot y _ {A} \\cdot \\log \\left(s _ {i} ^ {p}\\right) + \\left(1 - y _ {A}\\right) \\cdot \\log \\left(1 - s _ {i} ^ {p}\\right)\\right), \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 482, + 890, + 500 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {c l a - m i x}} = - \\left(\\lambda \\cdot y _ {A} \\cdot \\log \\left(b _ {j} ^ {p}\\right) + (1 - y _ {A}) \\cdot \\log \\left(1 - b _ {j} ^ {p}\\right)\\right), \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 537, + 890, + 556 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{prop\\_ mix}$ and $\\mathcal{L}_{cla\\_ mix}$ are the proposal confidence loss and foreground-background classification loss, respectively. $s_i^p$ is the confidence score of proposal $i$ , and $b_j^p$ is the predicted foreground probability of point $j$ in search area $P^s$ . We replace losses $\\mathcal{L}_{prop}$ and $\\mathcal{L}_{cla}$ with $\\mathcal{L}_{prop\\_ mix} = \\lambda \\cdot \\mathcal{L}_{prop}$ and $\\mathcal{L}_{cla\\_ mix} = \\lambda \\cdot \\mathcal{L}_{cla}$ . SOTMixup applies a loss weight $\\lambda$ to the positive proposals and foreground points, but does not change the loss weight of the negative proposals and background points. We reduce the loss penalty on the positive sample prediction scores to lessen the influence on the appearance matching ability of the tracker. We leave the loss weight unchanged for the negative samples. Because we intend the trackers to predict the motion offset of the object even if the object point cloud in the search area has dramatically changed.", + "bbox": [ + 498, + 566, + 892, + 792 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Cycle Tracking", + "text_level": 1, + "bbox": [ + 500, + 801, + 653, + 816 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Self Tracking Cycle. In contrast with existing 2D cycle trackers [23, 24, 36, 29], which only consider forward-backward cycle consistency, we propose to create the self tracking cycle. The motivation is to leverage virtually infinite supervision information contained in the initial frame", + "bbox": [ + 498, + 824, + 890, + 898 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "13959", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "itself. To this end, we first randomly sample a search area point cloud $P_r^s$ and object 3D BBox $B_r$ from the labeled training set. SOTMixup is then applied to generate the mixed point cloud", + "bbox": [ + 75, + 90, + 468, + 151 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nP _ {0} ^ {m} = S O T M i x u p \\left(P _ {0} ^ {s}, B _ {0}, P _ {r} ^ {s}, B _ {r}, \\lambda\\right), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 161, + 468, + 180 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\lambda \\in [0,1]$ is the mixing rate. Inspired by SC3D [6], we apply a random rigid transformation $\\mathcal{T}$ to $\\{P_0^m,B_0\\}$ and generate pseudo labels", + "bbox": [ + 76, + 186, + 468, + 234 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left(P _ {0} ^ {m t}, B _ {0} ^ {t}\\right) = \\mathcal {T} \\left(P _ {0} ^ {m}, B _ {0}, \\alpha\\right), \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 173, + 243, + 468, + 262 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $P_0^{mt}$ is the search area PC generated by applying SOTMixup and a rigid transformation on $P_0^s$ and $\\alpha = (\\Delta x, \\Delta y, \\Delta z, \\Delta \\theta)$ is a transformation parameter with a coordinate offset $(\\Delta x, \\Delta y, \\Delta z)$ and a rotation degree $\\Delta \\theta$ around the up-axis. This creates a self tracking cycle", + "bbox": [ + 76, + 271, + 468, + 348 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\widetilde {P} _ {0} ^ {o t}, \\widetilde {B} _ {0} ^ {t}\\right) = \\mathcal {F} \\left(P _ {0} ^ {m t}, P _ {0} ^ {o}\\right), \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 181, + 354, + 468, + 375 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\widetilde{B}_0^t$ is the predicted result on $P_0^{mt}$ and $P_0^o$ is the object template PC cropped from $P_0^s$ . We then calculate the self consistency loss $\\mathcal{L}_{self}$ between $\\widetilde{B}_0^t$ and $B_0^t$ . $\\mathcal{L}_{self}$ has the same setting with $\\mathcal{L}$ of Eq. (2) while corresponding loss with $\\mathcal{L}_{cal\\_ mix}$ and $\\mathcal{L}_{prop\\_ mix}$ .", + "bbox": [ + 75, + 383, + 468, + 463 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In the self tracking cycle, the loss weight can be automatically quantified by the mixing rate in SOTMixup. This provides the tracker with simple training samples to make it converge faster in the early stage of training with a high mixing rate, and also allows us to improve the tracker's robustness to point cloud variations using a low mixing rate.", + "bbox": [ + 75, + 463, + 468, + 551 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Forward-Backward Tracking Cycle. In addition to self tracking cycles, we also use forward-backward consistency. Hence, we forward track the object in the given search area sequence $\\mathbf{P}^{\\mathrm{s}}$ , which can be written as", + "bbox": [ + 75, + 551, + 468, + 612 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\widetilde {P} _ {1} ^ {o}, \\widetilde {B} _ {1}\\right) = \\mathcal {F} \\left(P _ {1} ^ {s}, P _ {0} ^ {o}\\right), \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 189, + 621, + 468, + 642 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\widetilde {P} _ {2} ^ {o}, \\widetilde {B} _ {2}\\right) = \\mathcal {F} \\left(P _ {2} ^ {s}, \\widetilde {P} _ {1} ^ {o}\\right), \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 189, + 662, + 468, + 681 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\{\\widetilde{P}_1^o,\\widetilde{P}_2^o\\}$ and $\\{\\widetilde{B}_1,\\widetilde{B}_0\\}$ are the predicted forward tracking object point clouds and 3D BBoxes of $P_{1}^{s}$ and $P_2^s$ respectively. Following this strategy lets us further predict $\\{\\widetilde{P}_3^o,\\dots ,\\widetilde{P}_n^o\\}$ and $\\{\\widetilde{B}_3,\\dots ,\\widetilde{B}_n\\}$ in $\\{P_3^s,\\ldots ,P_n^s\\}$ .", + "bbox": [ + 76, + 686, + 468, + 750 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Then, we reverse the tracking sequence and perform backward tracking while applying random rigid transformations. This can be expressed as", + "bbox": [ + 75, + 750, + 468, + 794 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\widetilde {P} _ {1} ^ {o \\prime}, \\widetilde {B} _ {1} ^ {\\prime}\\right) = \\mathcal {F} \\left(\\mathcal {T} \\left(P _ {1} ^ {s}, \\widetilde {B} _ {1}, \\alpha\\right), \\widetilde {P} _ {2} ^ {o \\prime}\\right), \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 801, + 468, + 821 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\widetilde {P} _ {0} ^ {o \\prime}, \\widetilde {B} _ {0} ^ {\\prime}\\right) = \\mathcal {F} \\left(\\mathcal {T} \\left(P _ {0} ^ {s}, B _ {0}, \\alpha\\right), \\widetilde {P} _ {1} ^ {o \\prime}\\right), \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 844, + 468, + 864 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\{\\widetilde{P}_0^{o'},\\widetilde{P}_1^{o'},\\widetilde{P}_2^{o'}\\}$ and $\\{\\widetilde{B}_1',\\widetilde{B}_0'\\}$ are the predicted backward tracking object point clouds and 3D BBoxes.", + "bbox": [ + 75, + 868, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We then measure the consistency losses $\\mathcal{L}_{con1}$ and $\\mathcal{L}_{con0}$ between $\\widetilde{B}_1^{\\prime}$ and $\\widetilde{B}_1$ , as well as between $\\widetilde{B}_0^{\\prime}$ and $B_0$ . Similarly, we can measure the consistency losses $\\{\\mathcal{L}_{con2},\\dots,\\mathcal{L}_{con(n - 1)}\\}$ . $\\mathcal{L}_{con}$ has the same setting with $\\mathcal{L}$ of Eq. (2).", + "bbox": [ + 500, + 90, + 890, + 167 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The forward-backward tracking cycle provides real and diverse motion consistency, leading trackers to learn the object's motion distribution between two neighboring frames. Furthermore, the tracker's robustness is increased by training with a disturbed template generated by the template update strategy (Sec. 3.4).", + "bbox": [ + 496, + 178, + 890, + 268 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Implementation Details", + "text_level": 1, + "bbox": [ + 500, + 313, + 718, + 330 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Training & Testing. We train MixCycle using the SGD optimizer with a batch size of 48 and an initial learning rate of 0.01 with a decay rate of $5e - 5$ at each epoch. All experiments are conducted using NVIDIA RTX-3090 GPUs. We set $n = 2$ and only measure the self and forward-backward cycle consistency losses $\\mathcal{L}_{self}$ and $\\mathcal{L}_{con0}$ for $P_0^s$ due to the GPU memory limit. At test time, we track the object frame by frame in a point cloud sequence with labels in the first frame. For both training and testing, our default setting for the template update strategy is to merge the target in the first frame with the predicted previous result.", + "bbox": [ + 496, + 348, + 890, + 513 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Input & Data Augmentation. Our MixCycle takes three frames $f$ , $f + 1$ and $f + 2$ as input. For the initial frame $f$ , we transform the BBox and point clouds to the object coordinate system. For the other frames in the tracking cycle, we transform the BBox and point clouds to the predicted object coordinate system in the last frame. We assume that the motion of the objects across neighboring frames is not significant. We apply random rigid transformations to BBoxes in labeled frames and use them to crop out search areas in the neighboring frames. Only the area within 2 meters around the reference object BBox is considered as input (search area) since we are only interested in the area where the target is expected to appear. The random rigid transformation parameter $\\alpha$ is set to $(0.3, 0.3, 0.0, 5.0^{\\circ})$ , and the $\\beta$ distribution parameter is set to $\\eta = 0.5$ .", + "bbox": [ + 496, + 526, + 890, + 752 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Loss Function. The loss function of MixCycle is defined as $\\mathcal{L}_{MixCycle} = \\gamma_1\\mathcal{L}_{self} + \\gamma_2\\mathcal{L}_{con0}$ containing self tracking cycle losses and forward-backward tracking cycle losses. Each of our cycle losses is set according to the original loss setting of the tracker to which we apply MixCycle. Additionally, the corresponding losses are replaced with $\\mathcal{L}_{prop\\_ mix}$ and $\\mathcal{L}_{cla\\_ mix}$ . We empirically set $\\gamma_1 = 1.0$ and $\\gamma_2 = 2.0$ , as we expect the tracker to focus more on learning the motion distribution of the object.", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "13960", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/c84afc59edfbfc51fb671149dc74b7f105c8de22132a27d411c34577d8be5032.jpg", + "table_caption": [ + "Table 1. Overall performance comparison between our MixCycle and the fully-supervised methods on the KITTI (left) and NuScenes (right) datasets, where the percentage of labels used for training is shown under the dataset names. Improvements based on the same tracker are shown in green. Bold and underline denote the best and the second-best performance, respectively." + ], + "table_footnote": [], + "table_body": "
DatasetKITTINuScenes
Sampling Rate1%5%10%0.1%0.5%1%
SuccessP2B [16]6.125.534.315.223.024.3
MLVSNet [25]25.035.536.621.529.934.0
BAT [34]10.121.634.917.526.430.6
Ours(P2B)20.314.2↑36.711.2↑43.89.5↑23.27.9↑34.311.3↑34.310.0↑
Ours(MLVSNet)32.47.4↑38.83.3↑42.66↑31.49.9↑34.54.7↑41.97.9↑
Ours(BAT)19.79.6↑42.220.6↑46.211.3↑24.46.9↑32.86.4↑34.43.8↑
PrecisionP2B [16]5.039.552.713.021.222.6
MLVSNet [25]36.353.254.719.530.435.3
BAT [34]12.335.352.715.225.730.6
Ours(P2B)33.428.4↑55.315.8↑64.211.5↑21.98.9↑34.213↑34.011.4↑
Ours(MLVSNet)49.212.9↑56.63.4↑61.46.7↑31.111.6↑35.24.8↑43.68.3↑
Ours(BAT)27.014.7↑62.327.0↑67.815.1↑22.77.5↑31.96.2↑34.13.5↑
", + "bbox": [ + 153, + 128, + 818, + 306 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/f5be33705bb86a754aabb83ca3eac4ae87f7da9aa637dde75fd88911c14f6044.jpg", + "table_caption": [ + "Table 2. Comparison of MixCycle against fully-supervised methods on each category. We train the models with $1\\% /0.1\\%$ sampling rate on KITTI/NuScenes. Improvements and decreases based on the same tracker are shown in green and red, respectively." + ], + "table_footnote": [], + "table_body": "
DatasetKITTI(1%)Nuscenes(0.1%)
Category Frame NumberCar 6424Pedestrian 6088Van 1248Cyclist 308Mean 14068Car 64159Truck 13587Trailer 3352Bus 2953Mean 84051
SuccessP2B [16]8.13.68.15.66.115.813.112.816.115.2
MLVSNet [25]35.315.222.912.825.021.025.222.513.521.5
BAT [34]16.73.87.26.810.117.517.820.414.417.5
Ours(P2B)20.612.5↑22.819.2↑8.00.1↓16.611.0↑20.314.2↑23.07.2↑25.212.1↑22.49.6↑17.71.5↑23.27.9↑
Ours(MLVSNet)43.88.5↑20.75.5↑28.25.3↑43.731.0↑32.47.4↑29.78.7↑42.417.3↑31.38.9↑19.25.7↑31.49.9↑
Ours(BAT)32.615.9↑6.12.3↑16.39.2↑34.127.4↑19.79.6↑24.36.9↑26.99.1↑23.73.2↑16.92.5↑24.46.9↑
PrecisionP2B [16]7.42.26.14.45.014.58.26.88.413.0
MLVSNet [25]46.528.825.416.636.320.520.011.36.419.5
BAT [34]22.72.95.99.512.316.312.29.212.215.2
Ours(P2B)30.022.6↑43.741.5↑6.10.011.16.7↑33.428.4↑23.59.0↑18.910.7↑11.24.4↑14.05.6↑21.98.9↑
Ours(MLVSNet)59.212.7↑40.711.9↑31.15.7↑79.062.4↑49.212.8↑31.110.6↑38.618.6↑19.58.1↑11.55.2↑31.111.6↑
Ours(BAT)43.921.2↑9.36.4↑19.213.2↑57.347.8↑27.014.7↑24.17.8↑21.18.9↑13.84.6↑9.72.6↓22.77.5↑
", + "bbox": [ + 80, + 345, + 893, + 518 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 542, + 209, + 559 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Datasets", + "text_level": 1, + "bbox": [ + 76, + 570, + 179, + 584 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We evaluate our MixCycle on the challenging 3D visual tracking benchmarks of KITTI [5], NuScenes [1] and Waymo [20] for semi-supervised 3D single object tracking. Semi-supervision labels are generated by applying random sampling to the training set.", + "bbox": [ + 75, + 595, + 468, + 672 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The KITTI tracking dataset contains 21 training sequences and 29 test sequences with 8 types of objects. Following previous works [6, 16, 34, 25], we split the training set into training/validation/testing: Sequences 0-16 are used for training, 17-18 for validation, and 19-20 for testing. The NuScenes dataset contains 1000 scenes and annotations for 23 object classes with accurate 3D BBoxes. NuScenes is officially divided into $700 / 150 / 150$ scenes for training/validation/testing. Following the setting in [34], we train our MixCycle on the subset \"training_track\" of the training set, and test it on the validation set. Waymo includes 1150 scenes, $798 / 202 / 150$ scenes for training/validation/testing. Following the setting in [35], we test trackers in the validation set. Compared to KITTI, NuScenes, and Waymo include larger data volumes and", + "bbox": [ + 75, + 674, + 470, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "more complex scenarios.", + "bbox": [ + 500, + 545, + 666, + 559 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation Metrics. In this paper, we use One Pass Evaluation (OPE) [27] to evaluate the Success (Succ.) and Precision (Prec.) of different methods. Success is calculated as the overlap (Intersection Over Union, IoU) between the proposal BBox and the ground truth (GT) BBox. Precision represents the AUC of distance error between the centers of two BBoxes from 0 to 2 meters.", + "bbox": [ + 496, + 560, + 893, + 666 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison with Fully-supervised Methods", + "text_level": 1, + "bbox": [ + 498, + 679, + 872, + 696 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To the best of our knowledge, no other 3D single object trackers work in a semi-supervision fashion. Therefore, we choose P2B [16], the multi-level voting Siamese network (MLVSNet) [25] and the box-aware tracker (BAT) [34] to validate our method by sharing the same network backbone. Note that BAT is the state-of-the-art (SOTA) method in appearance matching-based trackers, and we regard it as our upper bound. The fully-supervised methods will be trained with labeled data, as their original approaches. We train MixCycle in a semi-supervised way, which uses both labeled and unlabeled data. We do not evaluate the motion-based tracker [35] since it requires 2 consecutive labeled point clouds for training and is not suitable for our training", + "bbox": [ + 496, + 704, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "13961", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/f73cfab07c930279763bad7c5664c6dd9e09c658c4e71394ab579735cb30e41d.jpg", + "table_caption": [ + "Table 3. Overall performance comparison on KITTI/NuScenes between our MixCycle with $10\\% /1\\%$ sampling rates and the fully-supervised methods with $100\\%$ sampling rate." + ], + "table_footnote": [], + "table_body": "
DatasetMethodSuccessPrecision
KITTIP2B(100%) [16] vs Ours(10%)42.4 vs 43.81.4↑60.0 vs 64.24.2↑
MLVSNet(100%) [25] vs Ours(10%)45.7 vs 42.63.1↓66.6 vs 61.45.2↓
BAT(100%) [34] vs Ours(10%)51.2 vs 46.25.0↓72.8 vs 67.85.0↓
NuScenesP2B(100%) [16] vs Ours(1%)39.7 vs 34.35.4↓42.2 vs 34.08.2↓
MLVSNet(100%) [25] vs Ours(1%)45.7 vs 41.93.8↓47.9 vs 43.64.3↓
BAT(100%) [34] vs Ours(1%)41.8 vs 34.47.4↓42.7 vs 34.18.6↓
", + "bbox": [ + 80, + 128, + 468, + 210 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/013fe6f6dac3aa88a0b8281d827e1484c2dd475f75682bcb3b278ee34bd9c7f5.jpg", + "table_caption": [ + "Table 4. Comparison of MixCycle against BAT on Car in KITTI for different sampling rates. 'Improv.' denotes Improvement." + ], + "table_footnote": [], + "table_body": "
Sampling Rate1%5%10%30%50%70%100%
Succ.BAT [34]16.724.344.048.048.755.560.5
Ours(BAT)32.649.255.256.256.660.964.7
Improv.15.9↑24.9↑11.2↑8.2↑7.9↑5.4↑4.2↑
Prec.BAT [34]22.734.857.363.165.369.577.7
Ours(BAT)43.962.170.070.570.375.777.9
Improv.21.2↑27.3↑12.7↑7.4↑5.0↑6.2↑0.2↑
", + "bbox": [ + 81, + 253, + 467, + 354 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "set generation strategy. We employ different sampling rates for the two datasets. The first reason is that we account for the different scales of the dataset. The second season is that the case of very limited labels is more practical in real applications, and we attempt to set the sampling rate as low as possible within the trainable range.", + "bbox": [ + 75, + 383, + 467, + 474 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results on KITTI. 1) We evaluate our MixCycle in 4 categories (Car, Pedestrian, Van and Cyclist) and compare it using 3 sampling rates: $1\\%$ , $5\\%$ and $10\\%$ . As shown in Tab. 1, our method outperforms the fully-supervised approaches under all sampling rates by a large margin. This confirms the high label efficiency of our proposed semi-supervised framework.", + "bbox": [ + 75, + 476, + 467, + 582 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The performance gap between our MixCycle and the fully-supervised P2B becomes larger as the proportion of labeled samples decreases. In particular, in the extreme case of $1\\%$ labels usage, we achieve $14.2\\%$ and $28.4\\%$ improvement in success and precision, respectively, demonstrating the impact of our approach on the baseline method. Interestingly, our MixCycle based on the SOTA fully-supervised method BAT achieves the best results $(42.2\\%, 46.2\\%) / (62.3\\%, 67.8\\%)$ in succ./prec.) with $5\\%$ and $10\\%$ sampling rates, but the MLVSNet based MixCycle takes the first place $(32.4\\% / 49.2\\%)$ in succ./prec.) with $1\\%$ sampling rate. We believe this is because the multiscale approach in MLVSNet effectively enhances the robustness of its feature representation. The BoxCloud proposed by BAT further strengthens the reliance on labels, leading to a degradation of BAT and MixCycle performance at $1\\%$ sampling rate. 2) We further present the test results on each category with $1\\%$ sampling rate in Tab. 2. We achieve better performance in all categories, except Van on P2B. We assume this to be caused by the less labeled, huge, and moving fast feature of Van, which leads the tracker hard", + "bbox": [ + 75, + 583, + 467, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/2f4a327ec433721f8a16cafa24fc234d891bd820d6c3754788061d9983993432.jpg", + "table_caption": [ + "Table 5. Comparison of MixCycle against BAT on Waymo. MixCycle(BAT) is trained only on KITTI with a $10\\%$ sampling rate; BAT* represents BAT trained on Waymo using all the labels." + ], + "table_footnote": [], + "table_body": "
Category Frame Number MetricsVehicle 1057651 Succ.Pedestrian 510533 Prec.Mean 1568184 Succ.Prec.
BAT [34]26.528.216.531.1
Ours(BAT)31.133.525.546.4
BAT* [34]35.644.222.136.8
", + "bbox": [ + 504, + 128, + 890, + 229 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "to predict a precise motion. The improvements on Cyclist $(31.0\\% /62.4\\%)$ and $27.4\\% /47.8\\%$ in succ./prec. for P2B and BAT, respectively) and Pedestrian $(19.2\\% /41.5\\%)$ in succ./prec. on P2B) reveal the robustness of MixCycle to point cloud variations. As pedestrians and cyclists are usually considered to have the largest point cloud variations due to their small object sizes and the diversity of body motion. 3) In Tab. 3, we compare the performance between fully-supervised methods trained with $100\\%$ labels and MixCycle trained with $10\\%$ labels. Although our performance decreases slightly on MLVSNet and BAT, MixCycle still shows a remarkable result (43.8/64.2 in succ./prec.) on P2B. With only $10\\%$ of the labels, MixCycle based on P2B outperforms the fully-supervised method $(1.4\\% /4.2\\%)$ improvement in succ./prec.) using $100\\%$ of the labels. This confirms the strong ability of our approach to leverage data information and highlights its promise for future developments. 4) We provide the comparison of MixCycle against BAT on Car from KITTI with more sampling rates in Tab. 4. Our Mixcycle not only achieves great improvements in low sampling rates, but also boosts the tracker's performance in the fully-supervised training $(4.2 / 0.2$ in succ./prec.). 5) In Fig. 5, we compare MixCycle with BAT trained with $10\\%$ labels. MixCycle achieves a better performance in both extremely sparse and complex point clouds.", + "bbox": [ + 496, + 262, + 890, + 641 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results on NuScenes. Following the setting in BAT [34], we test our MixCycle in 4 categories (Car, Truck, Trailer and Bus). The results of P2B [16], MLVSNet [25] and BAT [34] on NuScenes are provided by $M^2$ -Track [35] and BAT [34]. 1) We use the published codes of the competitors to obtain results for each sampling rate. We compare them on 3 sampling rates: $0.1\\%$ , $0.5\\%$ and $1\\%$ , as NuScenes is larger than KITTI. As shown in Tab. 1, MixCycle still outperforms the fully-supervised approaches under all sampling rates. 2) Observing the individual categories in Tab. 2 evidences that MixCycle yields a remarkable improvement on Truck $(17.3\\% / 18.6\\%)$ and $12.1\\% / 10.7\\%$ in succ./prec. on MLVSNet and P2B, respectively) and Car $(8.7\\% / 10.6\\%)$ in succ./prec. on MLVSNet). However, MixCycle drops by $2.6\\%$ in precision on Bus, which has fewer labels, a greater size, and high velocity. 3) Moreover, in Tab. 3, we compare the performance of MixCycle trained with $1\\%$ labels and", + "bbox": [ + 496, + 643, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "13962", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e96cb02350fe3a31df26d62b9a84cb5983e06d61e24d6650528e772a9337859e.jpg", + "image_caption": [ + "Figure 5. Visualization. Car&Van: Extremely sparse cases. Pedestrian: Medium density cases. Cyclist: complex environment cases." + ], + "image_footnote": [], + "bbox": [ + 117, + 88, + 854, + 425 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "fully-supervised methods trained with $100\\%$ labels. Our MixCycle based on MLVSNet surpasses the SOTA method BAT despite using significantly fewer labels. On such a challenging dataset with pervasive distractors and drastic appearance changes, our method exhibits even more competitive performance when using few labels.", + "bbox": [ + 75, + 468, + 468, + 558 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Result on Waymo. Following the setting in [35], we test MixCycle in Vehicle and Pedestrian. We use the BAT backbone, and MixCycle(BAT) is only trained on KITTI with a $10\\%$ sampling rate. As shown in Tab. 5, MixCycle(BAT) outperforms BAT by $6.1\\%$ and $8.6\\%$ in terms of mean 'succ.' and 'prec.' values, respectively. More impressively, our performance is close to the fully supervised BAT trained on Waymo (31.2%/41.75% in succ./prec. reported in [34]). To summarize, our MixCycle still delivers excellent results on large-scale datasets.", + "bbox": [ + 75, + 560, + 470, + 710 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.3. Analysis Experiments", + "text_level": 1, + "bbox": [ + 76, + 724, + 282, + 739 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this section, we extensively analyze MixCycle with a series of experiments. First, we study the effectiveness of each component in MixCycle. Second, we further analyze the influence of forward-backward cycle step sizes. Finally, we compare the various application ways of SOT-Mixup. All the experiments are conducted on KITTI with $10\\%$ sampling rate and with BAT as the backbone network, unless otherwise stated.", + "bbox": [ + 75, + 748, + 468, + 867 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Ablation Study. We conduct experiments to analyze the effectiveness of different modules in MixCycle. First, we ver", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "if our assumption that appearance matching-based trackers can learn the object's motion distribution. As shown in Tab. 6, the cycle tracking framework yields better performance when using only forward-backward cycle than when using only self cycle (3.5%/5.4% improvement in succ./prec.). Additionally, this supports the intuition that real and diverse motion information is helpful to appearance trackers. Furthermore, combining them boosts the results. Note that the random rigid transformation is necessary for self cycle, otherwise the GT BBox will always be fixed at the origin of the coordinate system. Second, we evaluate the effectiveness of random rigid transformation and SOTMixup in the framework. The performance grows significantly after applying SOTMixup (5.1%/6% improvement in succ./prec.), demonstrating the importance of SOTMixup in semi-supervised tasks. Random rigid transformation plays a negative role in the cycle tracking framework but is practical in MixCycle. We conjecture this to be due to the missing target in the search area caused by random rigid transformation. This phenomenon may occur when the target moves rapidly and the model makes wrong predictions. Applying SOTMixup to the cycle tracking framework can significantly improve the model's tracking capabilities and address this issue.", + "bbox": [ + 496, + 468, + 890, + 830 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Flexibility of MixCycle. We further explore the effect of forward-backward tacking cycle step size. As shown in Tab. 7, we conduct experiments with 2 and 3 step cycles, respectively. Compared to the 2 step cycle, 3 step cycle", + "bbox": [ + 496, + 839, + 892, + 902 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "13963", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/da122e3330b09a154f16ae10dbedb570b028ed13a4d1cb7a73d3e3385641bac5.jpg", + "table_caption": [ + "Table 6. Results of MixCycle when different modules are ablated. 'Self', 'F.-B. Cycle' and 'Trans.' stand for self cycle, forward-backward cycle and random rigid transformation in the forward-backward cycle, respectively." + ], + "table_footnote": [], + "table_body": "
SelfF.-B. CycleTrans.SOTMixupSuccessPrecision
✓34.911.3↓52.715.1↓
✓38.47.8↓58.19.7↓
✓✓39.56.7↓59.28.6↓
✓✓✓38.87.4↓59.38.5↓
✓✓✓44.61.6↓65.22.6↓
✓✓✓✓46.267.8
", + "bbox": [ + 81, + 142, + 467, + 234 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/5affe42bd37b551c11bea17d37e0ae819dafff055c9a7b522e6d62ecd5232acf.jpg", + "table_caption": [ + "Table 7. Analysis of the forward-backward cycle step size." + ], + "table_footnote": [], + "table_body": "
SuccessPrecision
2 Steps45.866.6
3 Steps46.267.8
Improvement0.4↑1.2↑
", + "bbox": [ + 161, + 268, + 383, + 337 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/aebe9be2c10ac556c81786b8dbed58278e3c29a994c0c525ae07594339b9b13a.jpg", + "table_caption": [ + "Table 8. Results of SOTMixup with different settings. 'Template' and 'Search Area' indicate we apply SOTMixup with different inputs. 'Self' indicates we apply SOTMixup in the self cycle. 'Backward' means we apply SOTMixup in backward tracking $P_1^s$ to $P_0^s$ ." + ], + "table_footnote": [], + "table_body": "
SelfBackwardTemplateSearch AreaSuccessPrecision
✓✓44.71.5↓64.73.1↓
✓✓✓45.40.8↓67.60.2↓
✓✓42.33.9↓634.8↓
✓✓✓44.51.7↓66.11.7↓
✓✓46.267.8
", + "bbox": [ + 81, + 414, + 467, + 497 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "achieves a better performance in both success and precision. This experiment demonstrates the potential of MixCycle for further growth in step size. We believe that larger step sizes can provide a template point cloud disturbed in long sequence tracking, leading to improved model robustness. Furthermore, according to [24], a larger step size more effectively penalizes inaccurate localization.", + "bbox": [ + 75, + 532, + 467, + 638 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Influence of SOTMixup. In Tab. 8, we compare SOTMixup with different settings. First, we analyze the effect of applying SOTMixup to different inputs (Template and Search Area) while only using it in self cycle. The performance drops when we apply it to the template and to both the template and search area. We consider this to be due to the mismatch with real tracking. As the template is usually accurate while the search area point cloud varies significantly. Note that we share the same $\\lambda$ when taking SOTMixup in both the template and search area, and set $\\lambda = 1$ in the SOTMixup loss. Second, we explore various ways of exploiting SOTMixup in MixCycle. SOTMixup leads to performance degradation when we apply it to backward tracking. This is caused by the disturbance of the template point cloud in backward tracking, making the loss weights misaligned. This further proves that the loss weights provided by SOTMixup are reliable.", + "bbox": [ + 75, + 643, + 467, + 900 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 89, + 617, + 104 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this paper, we have presented the first semi-supervised framework, MixCycle, for 3D SOT. Its three main components, self tracking cycle, forward-backward tracking cycle and SOTMixup, have been proposed to achieve robustness to point cloud variations and percept object's motion distribution. Our experiments have demonstrated that MixCycle yields high label efficiency and outperforming fully-supervised approaches using scarce labels.", + "bbox": [ + 496, + 114, + 890, + 234 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In the future, we plan to develop a more robust tracking network backbone for MixCycle, and thus further enhance its 3D SOT performance.", + "bbox": [ + 496, + 236, + 890, + 280 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgments. This work is supported in part by the National Natural Science Foundation of China (No. 62176242 and 62002295), and NWPU international cooperation and exchange promotion projects (No. 02100-23GH0501). Thank Haozhe Qi for the discussion and preliminary exploration.", + "bbox": [ + 496, + 281, + 890, + 372 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "13964", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Holger Caesar, Varun Bankiti, Alex H. Lang, Sourabh Vora, Venice Erin Liong, Qiang Xu, Anush Krishnan, Yu Pan, Giancarlo Baldan, and Oscar Beijbom. nuscenes: A multimodal dataset for autonomous driving. arXiv preprint arXiv:1903.11027, 2019. 2, 3, 6", + "[2] Yunlu Chen, Vincent Tao Hu, Efstratos Gavves, Thomas Mensink, Pascal Mettes, Pengwan Yang, and Cees GM Snoek. Pointmixup: Augmentation for point clouds. 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In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 13546-13555, 2021. 2, 3, 4" + ], + "bbox": [ + 78, + 90, + 468, + 784 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "13966", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/MixCycle_ Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency/1f3580cb-fdbe-4e7d-96d7-32968d08a569_model.json b/2023/MixCycle_ Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency/1f3580cb-fdbe-4e7d-96d7-32968d08a569_model.json new file mode 100644 index 0000000000000000000000000000000000000000..53c533b1aa4aeb4c173cf4c7ee3f831b5962aa9a --- /dev/null +++ b/2023/MixCycle_ Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency/1f3580cb-fdbe-4e7d-96d7-32968d08a569_model.json @@ -0,0 +1,2015 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.102, + 0.13, + 0.872, + 0.178 + ], + "angle": 0, + "content": "MixCycle: Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency" + }, + { + "type": "text", + "bbox": [ + 0.133, + 0.203, + 0.837, + 0.221 + ], + "angle": 0, + "content": "Qiao Wu\\(^{1}\\) Jiaqi Yang\\(^{1*}\\) Kun Sun\\(^{2}\\) Chu'ai Zhang\\(^{1}\\) Yanning Zhang\\(^{1}\\) Mathieu Salzmann\\(^{3}\\)" + }, + { + "type": "text", + "bbox": [ + 0.153, + 0.222, + 0.819, + 0.259 + ], + "angle": 0, + "content": "1 Northwestern Polytechnical University 2 China University of Geosciences, Wuhan 3 École Polytechnique Fédérale de Lausanne" + }, + { + "type": "text", + "bbox": [ + 0.205, + 0.262, + 0.764, + 0.276 + ], + "angle": 0, + "content": "qiaowu@mail.nwpu.edu.cn; jqyang@nwpu.edu.cn; sunkun@cug.edu.cn;" + }, + { + "type": "text", + "bbox": [ + 0.17, + 0.28, + 0.799, + 0.294 + ], + "angle": 0, + "content": "cazhang@mail.nwpu.edu.cn; ynzhang@nwpu.edu.cn; mathieu.salzmann@epfl.ch" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.328, + 0.314, + 0.344 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.36, + 0.474, + 0.725 + ], + "angle": 0, + "content": "3D single object tracking (SOT) is an indispensable part of automated driving. Existing approaches rely heavily on large, densely labeled datasets. However, annotating point clouds is both costly and time-consuming. Inspired by the great success of cycle tracking in unsupervised 2D SOT, we introduce the first semi-supervised approach to 3D SOT. Specifically, we introduce two cycle-consistency strategies for supervision: 1) Self tracking cycles, which leverage labels to help the model converge better in the early stages of training; 2) forward-backward cycles, which strengthen the tracker's robustness to motion variations and the template noise caused by the template update strategy. Furthermore, we propose a data augmentation strategy named SOT-Mixup to improve the tracker's robustness to point cloud diversity. SOTMixup generates training samples by sampling points in two point clouds with a mixing rate and assigns a reasonable loss weight for training according to the mixing rate. The resulting MixCycle approach generalizes to appearance matching-based trackers. On the KITTI benchmark, based on the P2B tracker [16], MixCycle trained with \\(10\\%\\) labels outperforms P2B trained with \\(100\\%\\) labels, and achieves a \\(28.4\\%\\) precision improvement when using \\(1\\%\\) labels. Our code will be released at https://github.com/Mumuqiao/MixCycle." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.749, + 0.21, + 0.765 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.774, + 0.471, + 0.882 + ], + "angle": 0, + "content": "3D single object tracking (SOT) plays a critical role in the field of autonomous driving. For example, given object detection [15, 33] results as input, it can output the necessary information for trajectory prediction [8]. The goal of SOT is to regress the center position and 3D bounding-box (BBox) of an object of interest in a search area, given the point cloud (PC) patch and BBox of the object template." + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.326, + 0.895, + 0.52 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.522, + 0.895, + 0.566 + ], + "angle": 0, + "content": "Figure 1. Comparison of MixCycle and fully-supervised methods [16, 25, 34], all trained with \\(1\\%\\) labels on KITTI [5]. 'Succ.' and 'Prec.' represent Success and Precision, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.594, + 0.895, + 0.685 + ], + "angle": 0, + "content": "This is a very challenging task because (i) point clouds obtained with, e.g., LiDAR sensors, suffer from occlusions and point sparsity, complicating the tracker's task of finding the object of interest; (ii) the point distribution for an object may vary significantly, making it difficult for the model to learn discriminative object features." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.687, + 0.895, + 0.822 + ], + "angle": 0, + "content": "To tackle the above challenges, existing 3D SOT models [6, 16, 4, 9, 10, 25, 34, 18, 35] rely on large scale annotated point cloud datasets for training. Unfortunately, obtaining annotations for this task, as for many 3D tasks, is extremely time-consuming. Furthermore, as shown in Fig. 1, the performance of these methods degrades dramatically as the number of labeled samples decreases. Nevertheless, no semi-supervised or unsupervised methods have been explored so far in 3D SOT." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.895, + 0.903 + ], + "angle": 0, + "content": "As shown in Fig. 2, the matching-based tracker of [34] can still track the target at the very beginning of a sequence by predicting a motion offset relative to the reference coordinate, even though there are no points in the template for appearance matching. This indicates that the appearance" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.221, + 0.9 + ], + "angle": 0, + "content": "*Corresponding author" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "13956" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.09, + 0.468, + 0.177 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.111, + 0.183, + 0.221, + 0.195 + ], + "angle": 0, + "content": "Ground Truth" + }, + { + "type": "image", + "bbox": [ + 0.277, + 0.183, + 0.309, + 0.195 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.315, + 0.184, + 0.447, + 0.196 + ], + "angle": 0, + "content": "Matching-Based Tracker" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.2, + 0.47, + 0.256 + ], + "angle": 0, + "content": "Figure 2. We observe that appearance matching-based trackers can learn the objects motion distribution and track them even in the absence of points for appearance matching. For instance, BAT [34] manages to track objects in extremely sparse point clouds." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.281, + 0.47, + 0.553 + ], + "angle": 0, + "content": "matching-based trackers can learn motion information. By contrast, in 2D SOT, many trackers [23, 24, 36, 29] employ cycle consistency to leverage unsupervised data. Specifically, they encourage forward and backward tracking to produce consistent motions. In principle, we expect to apply this idea to 3D SOT and make trackers to learn the object's motion distribution in unlabeled data. However, transferring these 2D methods directly to 3D is challenging. First, since the point cloud is sparse and the environment is cluttered with objects, it is hard to find meaningful patches to use as pseudo labels for training. Second, unsupervised 2D SOT methods rely on the assumption that the target appears in every frame of the sequence. Unfortunately, this assumption is not always satisfied in point cloud datasets such as KITTI [5], NuScenes [1], and Waymo [20]. This is because they are built for the multi-object tracking task, and cannot guarantee that the tracking object exists in the whole sequence." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.554, + 0.47, + 0.884 + ], + "angle": 0, + "content": "In this paper, we introduce a label-efficient way to train 3D SOT trackers. We call it MixCycle - a 3D SOT approach based on a novel SOTMixup data augmentation strategy for semi-supervised Cycle tracking. Specifically, we first develop a tracking framework exploiting both self and forward-backward tracking cycles. Self tracking consistency is performed to cover the object point cloud appearance variation, and forward-backward consistency is built for learning the object's motion distribution. Second, we present a data augmentation method for 3D SOT called SOTMixup, which is inspired by the success of mixup [31] and Manifold mixup [22]. Without changing the total number of points in the search area, SOTMixup samples points in a random point cloud and the search area point cloud according to the mixing rate and generates training samples. Specifically, the random point cloud is sampled from the labeled training set. SOTMixup thus increases the tracker's robustness to point cloud variations. We evaluate MixCycle on KITTI, NuScenes, and Waymo. As shown in Fig. 1, our experiments clearly demonstrate the label efficiency, generalization and remarkable performance of our method on the 3D SOT task." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.886, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Contributions: (i) We propose the first semi-supervised" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.272 + ], + "angle": 0, + "content": "3D SOT framework. It exploits self and forward-backward consistency as supervision and generalizes to appearance matching-based trackers. (ii) We introduce a SOTMixup augmentation strategy that increases the tracker's robustness to point distribution variations and allows it to learn motion information in extreme situations. (iii) Our framework demonstrates a remarkable performance in terms of label efficiency, achieving better results than existing supervised methods in our experiments on KITTI NuScenes, and Waymo when using fewer labels. In particular, we surpass P2B [16] trained on \\(100\\%\\) labels while only using \\(10\\%\\) labels." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.287, + 0.642, + 0.303 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.312, + 0.892, + 0.689 + ], + "angle": 0, + "content": "3D Single Object Tracking. Since LiDAR is insensitive to illumination, the appearance matching model has become the main choice in the field of 3D single object tracking. Giancola et al. [6] proposed SC3D which is the first method using a Siamese network to deal with this problem. However, it is very time-consuming and inaccurate due to heuristic matching. Zarzar et al. [30] built an end-to-end tracker by using 2D RPN in 2D bird's eyes view (BEV). Unfortunately, the lack of information in one dimension leads to limited accuracy. The point-to-box (P2B) network [16] employs VoteNet[15] as object regression module to construct a point-based tracker. A number of works [4, 9, 10, 25, 34, 18] investigate different architectures of trackers based on P2B [16]. Zheng et al. [34] depicted an object using the point-to-box relation and proposed BoxCloud, which enables the model to better sense the size of objects. Hui et al. [9] discovered the priori information of object shapes in the dataset to obtain dense representations of objects from sparse point clouds. Zheng et al. [35] presented a motion centric method \\( M^2 \\)-Track, which is appearance matching-free and has made great progress in dealing with the sparse point cloud tracking problem. However, \\( M^2 \\)-track is limited by the LiDAR frequency of datasets as object motion in adjacent frames varies with the LiDAR sampling frequency." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.892, + 0.901 + ], + "angle": 0, + "content": "All the above methods rely on large-scale labeled datasets. Unfortunately, 3D point cloud annotation is labor- and time-consuming. To overcome this, we propose MixCycle, a semi-supervised tracking method based on cycle consistency constraints with SOTMixup data augmentation. Label-Efficient Visual Tracking. Wang et al. [23] proposed unsupervised deep tracking (UDT) with cycle consistency, based on a Siamese correlation filter backbone network. UDT achieved remarkable performance, revealing the potential of unsupervised learning in visual tracking. Yuan et al. [29] improved the UDT approach to make the target features passed forward and backward as similar as possible. The self-supervised fully convolutional Siamese network [19] uses only spatially supervised learning of tar" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13957" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.086, + 0.895, + 0.296 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.075, + 0.301, + 0.895, + 0.402 + ], + "angle": 0, + "content": "Figure 3. MixCycle framework. The label is only contained in \\( P_0^s \\) of point cloud (PC) sequence \\( \\{P_0^s, P_1^s, \\ldots, P_n^s\\} \\). 1) Self tracking cycle: we first sample a PC \\( P_r^s \\) from the labeled training set. Then, we generate pseudo labels by applying SOTMixup and random rigid transformation (Trans.) to \\( P_0^s \\) and \\( P_r^s \\). SOTMixup directly mixes \\( P_r^s \\) and \\( P_0^s \\) based on the number of points with a mixing rate, assigning a reasonable loss weight corresponding to the mixing rate. We employ the consistency between self tracking proposals and pseudo labels to formulate the loss \\( \\mathcal{L}_{self} \\). 2) Forward-backward tracking cycle: we leverage forward tracking proposals as pseudo labels and apply a random rigid transformation to them. Then, we employ the consistency between ground truth (GT)/pseudo labels and backward tracking proposals to formulate the losses \\( \\mathcal{L}_{con0} / \\{\\mathcal{L}_{con1}, \\ldots, \\mathcal{L}_{con(n-1)}\\} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.425, + 0.47, + 0.531 + ], + "angle": 0, + "content": "get correspondences in still video frames. Wu et al. [26] proposed a progressive unsupervised learning (PUL) network, which distinguishes the background by contrastive learning and models the regression result noise. PUL thus makes the tracker robust in long-time tracking. Unsupervised single object tracker [36] consists of an online-updating tracker with a novel memory learning scheme." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.533, + 0.471, + 0.623 + ], + "angle": 0, + "content": "In essence, the above unsupervised trackers all make the implicit assumption that the tracked target exists in every frame of the sequence. Unfortunately, this is not necessarily true in KITTI [5], NuScenes [1], and Waymo [20]. Therefore, the above methods are not directly applicable to 3D SOT." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.627, + 0.473, + 0.884 + ], + "angle": 0, + "content": "Mixup Data Augmentation. Data augmentation has become a crucial pre-processing step for many deep learning models. Zhang et al. [31] introduced a data augmentation method called mixup, which linearly interpolates two image samples, and Manifold mixup [22] transfers this idea to high-dimensional feature spaces. By interpolating a new sample, PointMixup [2] extends mixup to point clouds. Mix3D [14] introduces a scene-aware mixup by taking the union of two 3D scenes and their labels after random transformations. Lu et al. [13] developed a directed mixup based on the pixel values. Additionally, a variety of region mixup techniques have been proposed [32, 12, 21, 11]. In the case of outdoor scenes, Xiao et al. [28] combined two images using random rotation. CosMix[17] and structure aware fusion [7] combine point clouds using semantic structures. Fang et al. [3] turned a CAD into a point cloud to combat object occlusion." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.47, + 0.9 + ], + "angle": 0, + "content": "However, the above-mentioned methods are made for the" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.425, + 0.892, + 0.457 + ], + "angle": 0, + "content": "multi-class classification scenario and are not suitable for SOT, which only contains a positive and negative sample." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.469, + 0.593, + 0.485 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.494, + 0.611, + 0.509 + ], + "angle": 0, + "content": "3.1. Overview" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.517, + 0.892, + 0.593 + ], + "angle": 0, + "content": "The purpose of 3D SOT is to continually locate the target in the search area point cloud sequence \\(\\mathbf{P}^s = \\{P_0^s,\\dots ,P_k^s,\\dots ,P_n^s |P_k^s\\in \\mathbb{R}^{N_s\\times 3}\\}\\) given the tracking object template point cloud \\(P_0^o\\in \\mathbb{R}^{N_t\\times 3}\\) and the 3D BBox \\(B_{0}\\in \\mathbb{R}^{7}\\) in the initial frame. This can be described as" + }, + { + "type": "equation", + "bbox": [ + 0.588, + 0.605, + 0.892, + 0.626 + ], + "angle": 0, + "content": "\\[\n\\left(\\widetilde {P} _ {k + 1} ^ {o}, \\widetilde {B} _ {k + 1}\\right) = \\mathcal {F} \\left(P _ {k + 1} ^ {s}, \\widetilde {P} _ {k} ^ {o}\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.631, + 0.894, + 0.695 + ], + "angle": 0, + "content": "where \\(\\widetilde{P}_k^o\\), \\(\\widetilde{P}_{k + 1}^o\\) and \\(\\widetilde{B}_{k + 1}\\) are the predicted target point cloud and 3D BBox in frame \\(k\\) and \\(k + 1\\), respectively. By referring to P2B [16] and its follow-ups [4, 9, 10, 18, 25, 34], we summarize the typically 3D SOT loss as" + }, + { + "type": "equation", + "bbox": [ + 0.514, + 0.707, + 0.892, + 0.724 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\rho_ {1} \\cdot \\mathcal {L} _ {c l a} + \\rho_ {2} \\cdot \\mathcal {L} _ {p r o p} + \\rho_ {3} \\cdot \\mathcal {L} _ {r e g} + \\rho_ {4} \\cdot \\mathcal {L} _ {b o x}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.81 + ], + "angle": 0, + "content": "where \\(\\rho\\) is the manually-tuned hyperparameter, \\(\\mathcal{L}_{\\text{cla}}\\), \\(\\mathcal{L}_{\\text{prop}}\\), \\(\\mathcal{L}_{\\text{reg}}\\) and \\(\\mathcal{L}_{\\text{box}}\\) are the losses for foreground-background classification, confidences for the BBox proposals, voting offsets of the seed points, and offsets of the BBox proposals, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.902 + ], + "angle": 0, + "content": "To address this task, we propose MixCycle, a novel semi-supervised framework for 3D SOT. Illustrated in Fig. 3, MixCycle relies on a SOTMixup data augmentation strategy to tackle data sparsity and diversity (Sec. 3.2). Further, it utilizes self and forward-backward cycle consistencies as sources of supervision to cover the object appear" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13958" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.137 + ], + "angle": 0, + "content": "ance and motion variation (Sec. 3.3). Additionally, we apply rigid transformations to ground truth (GT) labels to generate search areas in unlabeled data (Sec. 3.4)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.146, + 0.201, + 0.163 + ], + "angle": 0, + "content": "3.2. SOTMixup" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.17, + 0.469, + 0.261 + ], + "angle": 0, + "content": "Inspired by the great success of mixup [31], we develop SOTMixup to supply diverse training samples and deal with the point cloud diversity problem, providing a solution for the mixup application in binary classification in SOT task. With two image samples \\((I_A, I_B)\\), mixup can be simply describe as creating an image" + }, + { + "type": "equation", + "bbox": [ + 0.188, + 0.271, + 0.469, + 0.288 + ], + "angle": 0, + "content": "\\[\nI _ {A} ^ {m} = \\lambda I _ {A} + (1 - \\lambda) I _ {B}, \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.186, + 0.314, + 0.469, + 0.331 + ], + "angle": 0, + "content": "\\[\ny _ {A} ^ {m} = \\lambda y _ {A} + (1 - \\lambda) y _ {B}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.336, + 0.469, + 0.381 + ], + "angle": 0, + "content": "where \\(\\lambda \\in [0,1]\\) is the mixing rate, and \\((y_A,y_B)\\) are the image labels. Typically, \\(\\lambda\\) follows a Beta distribution \\(\\beta (\\eta ,\\eta)\\). A multi-class loss is then calculated as" + }, + { + "type": "equation", + "bbox": [ + 0.117, + 0.394, + 0.469, + 0.41 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {m u t i - c a l}} = \\lambda \\cdot \\mathcal {C} (\\widetilde {y}, y _ {A}) + (1 - \\lambda) \\cdot \\mathcal {C} (\\widetilde {y}, y _ {B}), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.42, + 0.469, + 0.618 + ], + "angle": 0, + "content": "where \\(\\widetilde{y}\\) is the predicted label, and \\(\\mathcal{C}\\) is the criterion (usually being the cross-entropy loss). Vanilla mixup applies linear interpolation in aligned pixel space. However, this operation is not suitable to unordered point clouds. Furthermore, one of the key challenges for the SOT task is to determine whether the proposal is positive or negative. Multi-class label interpolation approach in mixup cannot be directly applied. Specifically, given the search area PC \\(P_A\\) and a random PC \\(P_B\\) sampled in the training set, we employ mixup to generate a foreground and background label pair \\((\\lambda \\cdot y_A, (1 - \\lambda) \\cdot y_B)\\). In practice, this label pair should be set to \\((y_A, 0)\\), as the points in \\(P_B\\) mismatch the template and should be considered as background." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.618, + 0.47, + 0.846 + ], + "angle": 0, + "content": "We therefore develop a point cloud mixup strategy for SOT based on the number of points, called SOTMixup. As shown in Fig. 4, SOTMixup generates new samples and minimizes the gap between the generated samples and the real sample distribution. Specifically, SOTMixup mixes a point cloud randomly sampled from the training set and the search area point cloud by sampling points using a mixing rate, without changing the total number of points in the search area. First, given point cloud pair \\((P_A, P_B)\\), corresponding binary classification labels \\((y_A, y_B)\\), and a mixing rate \\(\\lambda\\), we separate the backgrounds and object points in \\(P_A\\) and \\(P_B\\) and obtain \\((P_A^b, P_A^o, P_B^b, P_B^o)\\), where \\(P_A^o \\in \\mathbb{R}^{N_A^o \\times 3}\\) and \\(P_B^o \\in \\mathbb{R}^{N_B^o \\times 3}\\). Second, we generate \\(\\hat{P}_A^o\\) and \\(\\hat{P}_B^o\\) by randomly sampling \\(\\lambda \\times N_A^o\\) and \\((1 - \\lambda) \\times N_A^o\\) points from \\(P_A^o\\) and \\(P_B^o\\), respectively. We then perform SOTMixup as" + }, + { + "type": "equation", + "bbox": [ + 0.193, + 0.857, + 0.469, + 0.876 + ], + "angle": 0, + "content": "\\[\nP _ {A} ^ {m} = P _ {A} ^ {b} + \\hat {P} _ {A} ^ {o} + \\hat {P} _ {B} ^ {o}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.886, + 0.408, + 0.901 + ], + "angle": 0, + "content": "where \\(^{\\prime} + ^{\\prime}\\) represents the concatenation operation." + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.088, + 0.895, + 0.284 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.288, + 0.892, + 0.371 + ], + "angle": 0, + "content": "Figure 4. SOTMixup. First, the search area point cloud (PC) and a point cloud randomly sampled from the labeled training set are segmented into foreground and background, respectively. Second, a mixing rate \\(\\lambda\\) is applied to sample two object PCs. Finally, we concatenate the sampled object PCs and search area background to generate the mixed search area." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.396, + 0.892, + 0.472 + ], + "angle": 0, + "content": "Usually, we consider the distance between the predicted object center and the ground truth to be positive if it is less than 0.3 meters, and negative if it is greater than 0.6 meters. The binary cross entropy loss for regression and foreground classification in SOTMixup can be written as" + }, + { + "type": "equation", + "bbox": [ + 0.508, + 0.483, + 0.892, + 0.501 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {p r o p . m i x}} = - \\left(\\lambda \\cdot y _ {A} \\cdot \\log \\left(s _ {i} ^ {p}\\right) + \\left(1 - y _ {A}\\right) \\cdot \\log \\left(1 - s _ {i} ^ {p}\\right)\\right), \\tag {7}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.508, + 0.538, + 0.892, + 0.557 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {c l a - m i x}} = - \\left(\\lambda \\cdot y _ {A} \\cdot \\log \\left(b _ {j} ^ {p}\\right) + (1 - y _ {A}) \\cdot \\log \\left(1 - b _ {j} ^ {p}\\right)\\right), \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.567, + 0.893, + 0.793 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{prop\\_ mix}\\) and \\(\\mathcal{L}_{cla\\_ mix}\\) are the proposal confidence loss and foreground-background classification loss, respectively. \\(s_i^p\\) is the confidence score of proposal \\(i\\), and \\(b_j^p\\) is the predicted foreground probability of point \\(j\\) in search area \\(P^s\\). We replace losses \\(\\mathcal{L}_{prop}\\) and \\(\\mathcal{L}_{cla}\\) with \\(\\mathcal{L}_{prop\\_ mix} = \\lambda \\cdot \\mathcal{L}_{prop}\\) and \\(\\mathcal{L}_{cla\\_ mix} = \\lambda \\cdot \\mathcal{L}_{cla}\\). SOTMixup applies a loss weight \\(\\lambda\\) to the positive proposals and foreground points, but does not change the loss weight of the negative proposals and background points. We reduce the loss penalty on the positive sample prediction scores to lessen the influence on the appearance matching ability of the tracker. We leave the loss weight unchanged for the negative samples. Because we intend the trackers to predict the motion offset of the object even if the object point cloud in the search area has dramatically changed." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.802, + 0.655, + 0.818 + ], + "angle": 0, + "content": "3.3. Cycle Tracking" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.825, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Self Tracking Cycle. In contrast with existing 2D cycle trackers [23, 24, 36, 29], which only consider forward-backward cycle consistency, we propose to create the self tracking cycle. The motivation is to leverage virtually infinite supervision information contained in the initial frame" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13959" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "itself. To this end, we first randomly sample a search area point cloud \\( P_r^s \\) and object 3D BBox \\( B_r \\) from the labeled training set. SOTMixup is then applied to generate the mixed point cloud" + }, + { + "type": "equation", + "bbox": [ + 0.137, + 0.162, + 0.469, + 0.181 + ], + "angle": 0, + "content": "\\[\nP _ {0} ^ {m} = S O T M i x u p \\left(P _ {0} ^ {s}, B _ {0}, P _ {r} ^ {s}, B _ {r}, \\lambda\\right), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.188, + 0.47, + 0.235 + ], + "angle": 0, + "content": "where \\(\\lambda \\in [0,1]\\) is the mixing rate. Inspired by SC3D [6], we apply a random rigid transformation \\(\\mathcal{T}\\) to \\(\\{P_0^m,B_0\\}\\) and generate pseudo labels" + }, + { + "type": "equation", + "bbox": [ + 0.174, + 0.244, + 0.469, + 0.263 + ], + "angle": 0, + "content": "\\[\n\\left(P _ {0} ^ {m t}, B _ {0} ^ {t}\\right) = \\mathcal {T} \\left(P _ {0} ^ {m}, B _ {0}, \\alpha\\right), \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.272, + 0.47, + 0.349 + ], + "angle": 0, + "content": "where \\(P_0^{mt}\\) is the search area PC generated by applying SOTMixup and a rigid transformation on \\(P_0^s\\) and \\(\\alpha = (\\Delta x, \\Delta y, \\Delta z, \\Delta \\theta)\\) is a transformation parameter with a coordinate offset \\((\\Delta x, \\Delta y, \\Delta z)\\) and a rotation degree \\(\\Delta \\theta\\) around the up-axis. This creates a self tracking cycle" + }, + { + "type": "equation", + "bbox": [ + 0.182, + 0.355, + 0.469, + 0.375 + ], + "angle": 0, + "content": "\\[\n\\left(\\widetilde {P} _ {0} ^ {o t}, \\widetilde {B} _ {0} ^ {t}\\right) = \\mathcal {F} \\left(P _ {0} ^ {m t}, P _ {0} ^ {o}\\right), \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.385, + 0.469, + 0.464 + ], + "angle": 0, + "content": "where \\(\\widetilde{B}_0^t\\) is the predicted result on \\(P_0^{mt}\\) and \\(P_0^o\\) is the object template PC cropped from \\(P_0^s\\). We then calculate the self consistency loss \\(\\mathcal{L}_{self}\\) between \\(\\widetilde{B}_0^t\\) and \\(B_0^t\\). \\(\\mathcal{L}_{self}\\) has the same setting with \\(\\mathcal{L}\\) of Eq. (2) while corresponding loss with \\(\\mathcal{L}_{cal\\_ mix}\\) and \\(\\mathcal{L}_{prop\\_ mix}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.464, + 0.469, + 0.553 + ], + "angle": 0, + "content": "In the self tracking cycle, the loss weight can be automatically quantified by the mixing rate in SOTMixup. This provides the tracker with simple training samples to make it converge faster in the early stage of training with a high mixing rate, and also allows us to improve the tracker's robustness to point cloud variations using a low mixing rate." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.553, + 0.469, + 0.613 + ], + "angle": 0, + "content": "Forward-Backward Tracking Cycle. In addition to self tracking cycles, we also use forward-backward consistency. Hence, we forward track the object in the given search area sequence \\(\\mathbf{P}^{\\mathrm{s}}\\), which can be written as" + }, + { + "type": "equation", + "bbox": [ + 0.19, + 0.622, + 0.469, + 0.643 + ], + "angle": 0, + "content": "\\[\n\\left(\\widetilde {P} _ {1} ^ {o}, \\widetilde {B} _ {1}\\right) = \\mathcal {F} \\left(P _ {1} ^ {s}, P _ {0} ^ {o}\\right), \\tag {12}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.19, + 0.663, + 0.469, + 0.683 + ], + "angle": 0, + "content": "\\[\n\\left(\\widetilde {P} _ {2} ^ {o}, \\widetilde {B} _ {2}\\right) = \\mathcal {F} \\left(P _ {2} ^ {s}, \\widetilde {P} _ {1} ^ {o}\\right), \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.687, + 0.469, + 0.751 + ], + "angle": 0, + "content": "where \\(\\{\\widetilde{P}_1^o,\\widetilde{P}_2^o\\}\\) and \\(\\{\\widetilde{B}_1,\\widetilde{B}_0\\}\\) are the predicted forward tracking object point clouds and 3D BBoxes of \\(P_{1}^{s}\\) and \\(P_2^s\\) respectively. Following this strategy lets us further predict \\(\\{\\widetilde{P}_3^o,\\dots ,\\widetilde{P}_n^o\\}\\) and \\(\\{\\widetilde{B}_3,\\dots ,\\widetilde{B}_n\\}\\) in \\(\\{P_3^s,\\ldots ,P_n^s\\}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.751, + 0.469, + 0.795 + ], + "angle": 0, + "content": "Then, we reverse the tracking sequence and perform backward tracking while applying random rigid transformations. This can be expressed as" + }, + { + "type": "equation", + "bbox": [ + 0.152, + 0.803, + 0.469, + 0.823 + ], + "angle": 0, + "content": "\\[\n\\left(\\widetilde {P} _ {1} ^ {o \\prime}, \\widetilde {B} _ {1} ^ {\\prime}\\right) = \\mathcal {F} \\left(\\mathcal {T} \\left(P _ {1} ^ {s}, \\widetilde {B} _ {1}, \\alpha\\right), \\widetilde {P} _ {2} ^ {o \\prime}\\right), \\tag {14}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.152, + 0.845, + 0.469, + 0.865 + ], + "angle": 0, + "content": "\\[\n\\left(\\widetilde {P} _ {0} ^ {o \\prime}, \\widetilde {B} _ {0} ^ {\\prime}\\right) = \\mathcal {F} \\left(\\mathcal {T} \\left(P _ {0} ^ {s}, B _ {0}, \\alpha\\right), \\widetilde {P} _ {1} ^ {o \\prime}\\right), \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.869, + 0.469, + 0.901 + ], + "angle": 0, + "content": "where \\(\\{\\widetilde{P}_0^{o'},\\widetilde{P}_1^{o'},\\widetilde{P}_2^{o'}\\}\\) and \\(\\{\\widetilde{B}_1',\\widetilde{B}_0'\\}\\) are the predicted backward tracking object point clouds and 3D BBoxes." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.892, + 0.168 + ], + "angle": 0, + "content": "We then measure the consistency losses \\(\\mathcal{L}_{con1}\\) and \\(\\mathcal{L}_{con0}\\) between \\(\\widetilde{B}_1^{\\prime}\\) and \\(\\widetilde{B}_1\\), as well as between \\(\\widetilde{B}_0^{\\prime}\\) and \\(B_0\\). Similarly, we can measure the consistency losses \\(\\{\\mathcal{L}_{con2},\\dots,\\mathcal{L}_{con(n - 1)}\\}\\). \\(\\mathcal{L}_{con}\\) has the same setting with \\(\\mathcal{L}\\) of Eq. (2)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.179, + 0.892, + 0.27 + ], + "angle": 0, + "content": "The forward-backward tracking cycle provides real and diverse motion consistency, leading trackers to learn the object's motion distribution between two neighboring frames. Furthermore, the tracker's robustness is increased by training with a disturbed template generated by the template update strategy (Sec. 3.4)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.314, + 0.719, + 0.331 + ], + "angle": 0, + "content": "3.4. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.349, + 0.892, + 0.515 + ], + "angle": 0, + "content": "Training & Testing. We train MixCycle using the SGD optimizer with a batch size of 48 and an initial learning rate of 0.01 with a decay rate of \\(5e - 5\\) at each epoch. All experiments are conducted using NVIDIA RTX-3090 GPUs. We set \\(n = 2\\) and only measure the self and forward-backward cycle consistency losses \\(\\mathcal{L}_{self}\\) and \\(\\mathcal{L}_{con0}\\) for \\(P_0^s\\) due to the GPU memory limit. At test time, we track the object frame by frame in a point cloud sequence with labels in the first frame. For both training and testing, our default setting for the template update strategy is to merge the target in the first frame with the predicted previous result." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.527, + 0.892, + 0.753 + ], + "angle": 0, + "content": "Input & Data Augmentation. Our MixCycle takes three frames \\( f \\), \\( f + 1 \\) and \\( f + 2 \\) as input. For the initial frame \\( f \\), we transform the BBox and point clouds to the object coordinate system. For the other frames in the tracking cycle, we transform the BBox and point clouds to the predicted object coordinate system in the last frame. We assume that the motion of the objects across neighboring frames is not significant. We apply random rigid transformations to BBoxes in labeled frames and use them to crop out search areas in the neighboring frames. Only the area within 2 meters around the reference object BBox is considered as input (search area) since we are only interested in the area where the target is expected to appear. The random rigid transformation parameter \\( \\alpha \\) is set to \\( (0.3, 0.3, 0.0, 5.0^{\\circ}) \\), and the \\( \\beta \\) distribution parameter is set to \\( \\eta = 0.5 \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Loss Function. The loss function of MixCycle is defined as \\(\\mathcal{L}_{MixCycle} = \\gamma_1\\mathcal{L}_{self} + \\gamma_2\\mathcal{L}_{con0}\\) containing self tracking cycle losses and forward-backward tracking cycle losses. Each of our cycle losses is set according to the original loss setting of the tracker to which we apply MixCycle. Additionally, the corresponding losses are replaced with \\(\\mathcal{L}_{prop\\_ mix}\\) and \\(\\mathcal{L}_{cla\\_ mix}\\). We empirically set \\(\\gamma_1 = 1.0\\) and \\(\\gamma_2 = 2.0\\), as we expect the tracker to focus more on learning the motion distribution of the object." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "13960" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.088, + 0.894, + 0.129 + ], + "angle": 0, + "content": "Table 1. Overall performance comparison between our MixCycle and the fully-supervised methods on the KITTI (left) and NuScenes (right) datasets, where the percentage of labels used for training is shown under the dataset names. Improvements based on the same tracker are shown in green. Bold and underline denote the best and the second-best performance, respectively." + }, + { + "type": "table", + "bbox": [ + 0.155, + 0.13, + 0.819, + 0.307 + ], + "angle": 0, + "content": "
DatasetKITTINuScenes
Sampling Rate1%5%10%0.1%0.5%1%
SuccessP2B [16]6.125.534.315.223.024.3
MLVSNet [25]25.035.536.621.529.934.0
BAT [34]10.121.634.917.526.430.6
Ours(P2B)20.314.2↑36.711.2↑43.89.5↑23.27.9↑34.311.3↑34.310.0↑
Ours(MLVSNet)32.47.4↑38.83.3↑42.66↑31.49.9↑34.54.7↑41.97.9↑
Ours(BAT)19.79.6↑42.220.6↑46.211.3↑24.46.9↑32.86.4↑34.43.8↑
PrecisionP2B [16]5.039.552.713.021.222.6
MLVSNet [25]36.353.254.719.530.435.3
BAT [34]12.335.352.715.225.730.6
Ours(P2B)33.428.4↑55.315.8↑64.211.5↑21.98.9↑34.213↑34.011.4↑
Ours(MLVSNet)49.212.9↑56.63.4↑61.46.7↑31.111.6↑35.24.8↑43.68.3↑
Ours(BAT)27.014.7↑62.327.0↑67.815.1↑22.77.5↑31.96.2↑34.13.5↑
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.318, + 0.893, + 0.346 + ], + "angle": 0, + "content": "Table 2. Comparison of MixCycle against fully-supervised methods on each category. We train the models with \\(1\\% /0.1\\%\\) sampling rate on KITTI/NuScenes. Improvements and decreases based on the same tracker are shown in green and red, respectively." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.346, + 0.894, + 0.519 + ], + "angle": 0, + "content": "
DatasetKITTI(1%)Nuscenes(0.1%)
Category Frame NumberCar 6424Pedestrian 6088Van 1248Cyclist 308Mean 14068Car 64159Truck 13587Trailer 3352Bus 2953Mean 84051
SuccessP2B [16]8.13.68.15.66.115.813.112.816.115.2
MLVSNet [25]35.315.222.912.825.021.025.222.513.521.5
BAT [34]16.73.87.26.810.117.517.820.414.417.5
Ours(P2B)20.612.5↑22.819.2↑8.00.1↓16.611.0↑20.314.2↑23.07.2↑25.212.1↑22.49.6↑17.71.5↑23.27.9↑
Ours(MLVSNet)43.88.5↑20.75.5↑28.25.3↑43.731.0↑32.47.4↑29.78.7↑42.417.3↑31.38.9↑19.25.7↑31.49.9↑
Ours(BAT)32.615.9↑6.12.3↑16.39.2↑34.127.4↑19.79.6↑24.36.9↑26.99.1↑23.73.2↑16.92.5↑24.46.9↑
PrecisionP2B [16]7.42.26.14.45.014.58.26.88.413.0
MLVSNet [25]46.528.825.416.636.320.520.011.36.419.5
BAT [34]22.72.95.99.512.316.312.29.212.215.2
Ours(P2B)30.022.6↑43.741.5↑6.10.011.16.7↑33.428.4↑23.59.0↑18.910.7↑11.24.4↑14.05.6↑21.98.9↑
Ours(MLVSNet)59.212.7↑40.711.9↑31.15.7↑79.062.4↑49.212.8↑31.110.6↑38.618.6↑19.58.1↑11.55.2↑31.111.6↑
Ours(BAT)43.921.2↑9.36.4↑19.213.2↑57.347.8↑27.014.7↑24.17.8↑21.18.9↑13.84.6↑9.72.6↓22.77.5↑
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.544, + 0.21, + 0.56 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.571, + 0.18, + 0.585 + ], + "angle": 0, + "content": "4.1. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.597, + 0.47, + 0.673 + ], + "angle": 0, + "content": "We evaluate our MixCycle on the challenging 3D visual tracking benchmarks of KITTI [5], NuScenes [1] and Waymo [20] for semi-supervised 3D single object tracking. Semi-supervision labels are generated by applying random sampling to the training set." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.675, + 0.471, + 0.902 + ], + "angle": 0, + "content": "The KITTI tracking dataset contains 21 training sequences and 29 test sequences with 8 types of objects. Following previous works [6, 16, 34, 25], we split the training set into training/validation/testing: Sequences 0-16 are used for training, 17-18 for validation, and 19-20 for testing. The NuScenes dataset contains 1000 scenes and annotations for 23 object classes with accurate 3D BBoxes. NuScenes is officially divided into \\(700 / 150 / 150\\) scenes for training/validation/testing. Following the setting in [34], we train our MixCycle on the subset \"training_track\" of the training set, and test it on the validation set. Waymo includes 1150 scenes, \\(798 / 202 / 150\\) scenes for training/validation/testing. Following the setting in [35], we test trackers in the validation set. Compared to KITTI, NuScenes, and Waymo include larger data volumes and" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.546, + 0.668, + 0.56 + ], + "angle": 0, + "content": "more complex scenarios." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.561, + 0.894, + 0.667 + ], + "angle": 0, + "content": "Evaluation Metrics. In this paper, we use One Pass Evaluation (OPE) [27] to evaluate the Success (Succ.) and Precision (Prec.) of different methods. Success is calculated as the overlap (Intersection Over Union, IoU) between the proposal BBox and the ground truth (GT) BBox. Precision represents the AUC of distance error between the centers of two BBoxes from 0 to 2 meters." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.68, + 0.874, + 0.697 + ], + "angle": 0, + "content": "4.2. Comparison with Fully-supervised Methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.895, + 0.903 + ], + "angle": 0, + "content": "To the best of our knowledge, no other 3D single object trackers work in a semi-supervision fashion. Therefore, we choose P2B [16], the multi-level voting Siamese network (MLVSNet) [25] and the box-aware tracker (BAT) [34] to validate our method by sharing the same network backbone. Note that BAT is the state-of-the-art (SOTA) method in appearance matching-based trackers, and we regard it as our upper bound. The fully-supervised methods will be trained with labeled data, as their original approaches. We train MixCycle in a semi-supervised way, which uses both labeled and unlabeled data. We do not evaluate the motion-based tracker [35] since it requires 2 consecutive labeled point clouds for training and is not suitable for our training" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "13961" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.088, + 0.47, + 0.129 + ], + "angle": 0, + "content": "Table 3. Overall performance comparison on KITTI/NuScenes between our MixCycle with \\(10\\% /1\\%\\) sampling rates and the fully-supervised methods with \\(100\\%\\) sampling rate." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.13, + 0.47, + 0.212 + ], + "angle": 0, + "content": "
DatasetMethodSuccessPrecision
KITTIP2B(100%) [16] vs Ours(10%)42.4 vs 43.81.4↑60.0 vs 64.24.2↑
MLVSNet(100%) [25] vs Ours(10%)45.7 vs 42.63.1↓66.6 vs 61.45.2↓
BAT(100%) [34] vs Ours(10%)51.2 vs 46.25.0↓72.8 vs 67.85.0↓
NuScenesP2B(100%) [16] vs Ours(1%)39.7 vs 34.35.4↓42.2 vs 34.08.2↓
MLVSNet(100%) [25] vs Ours(1%)45.7 vs 41.93.8↓47.9 vs 43.64.3↓
BAT(100%) [34] vs Ours(1%)41.8 vs 34.47.4↓42.7 vs 34.18.6↓
" + }, + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.227, + 0.468, + 0.254 + ], + "angle": 0, + "content": "Table 4. Comparison of MixCycle against BAT on Car in KITTI for different sampling rates. 'Improv.' denotes Improvement." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.254, + 0.468, + 0.355 + ], + "angle": 0, + "content": "
Sampling Rate1%5%10%30%50%70%100%
Succ.BAT [34]16.724.344.048.048.755.560.5
Ours(BAT)32.649.255.256.256.660.964.7
Improv.15.9↑24.9↑11.2↑8.2↑7.9↑5.4↑4.2↑
Prec.BAT [34]22.734.857.363.165.369.577.7
Ours(BAT)43.962.170.070.570.375.777.9
Improv.21.2↑27.3↑12.7↑7.4↑5.0↑6.2↑0.2↑
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.384, + 0.468, + 0.476 + ], + "angle": 0, + "content": "set generation strategy. We employ different sampling rates for the two datasets. The first reason is that we account for the different scales of the dataset. The second season is that the case of very limited labels is more practical in real applications, and we attempt to set the sampling rate as low as possible within the trainable range." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.477, + 0.468, + 0.583 + ], + "angle": 0, + "content": "Results on KITTI. 1) We evaluate our MixCycle in 4 categories (Car, Pedestrian, Van and Cyclist) and compare it using 3 sampling rates: \\(1\\%\\), \\(5\\%\\) and \\(10\\%\\). As shown in Tab. 1, our method outperforms the fully-supervised approaches under all sampling rates by a large margin. This confirms the high label efficiency of our proposed semi-supervised framework." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.468, + 0.901 + ], + "angle": 0, + "content": "The performance gap between our MixCycle and the fully-supervised P2B becomes larger as the proportion of labeled samples decreases. In particular, in the extreme case of \\(1\\%\\) labels usage, we achieve \\(14.2\\%\\) and \\(28.4\\%\\) improvement in success and precision, respectively, demonstrating the impact of our approach on the baseline method. Interestingly, our MixCycle based on the SOTA fully-supervised method BAT achieves the best results \\((42.2\\%, 46.2\\%) / (62.3\\%, 67.8\\%)\\) in succ./prec.) with \\(5\\%\\) and \\(10\\%\\) sampling rates, but the MLVSNet based MixCycle takes the first place \\((32.4\\% / 49.2\\%)\\) in succ./prec.) with \\(1\\%\\) sampling rate. We believe this is because the multiscale approach in MLVSNet effectively enhances the robustness of its feature representation. The BoxCloud proposed by BAT further strengthens the reliance on labels, leading to a degradation of BAT and MixCycle performance at \\(1\\%\\) sampling rate. 2) We further present the test results on each category with \\(1\\%\\) sampling rate in Tab. 2. We achieve better performance in all categories, except Van on P2B. We assume this to be caused by the less labeled, huge, and moving fast feature of Van, which leads the tracker hard" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.087, + 0.892, + 0.129 + ], + "angle": 0, + "content": "Table 5. Comparison of MixCycle against BAT on Waymo. MixCycle(BAT) is trained only on KITTI with a \\(10\\%\\) sampling rate; BAT* represents BAT trained on Waymo using all the labels." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.13, + 0.892, + 0.231 + ], + "angle": 0, + "content": "
Category Frame Number MetricsVehicle 1057651 Succ.Pedestrian 510533 Prec.Mean 1568184 Succ.Prec.
BAT [34]26.528.216.531.1
Ours(BAT)31.133.525.546.4
BAT* [34]35.644.222.136.8
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.263, + 0.892, + 0.642 + ], + "angle": 0, + "content": "to predict a precise motion. The improvements on Cyclist \\((31.0\\% /62.4\\%)\\) and \\(27.4\\% /47.8\\%\\) in succ./prec. for P2B and BAT, respectively) and Pedestrian \\((19.2\\% /41.5\\%)\\) in succ./prec. on P2B) reveal the robustness of MixCycle to point cloud variations. As pedestrians and cyclists are usually considered to have the largest point cloud variations due to their small object sizes and the diversity of body motion. 3) In Tab. 3, we compare the performance between fully-supervised methods trained with \\(100\\%\\) labels and MixCycle trained with \\(10\\%\\) labels. Although our performance decreases slightly on MLVSNet and BAT, MixCycle still shows a remarkable result (43.8/64.2 in succ./prec.) on P2B. With only \\(10\\%\\) of the labels, MixCycle based on P2B outperforms the fully-supervised method \\((1.4\\% /4.2\\%)\\) improvement in succ./prec.) using \\(100\\%\\) of the labels. This confirms the strong ability of our approach to leverage data information and highlights its promise for future developments. 4) We provide the comparison of MixCycle against BAT on Car from KITTI with more sampling rates in Tab. 4. Our Mixcycle not only achieves great improvements in low sampling rates, but also boosts the tracker's performance in the fully-supervised training \\((4.2 / 0.2\\) in succ./prec.). 5) In Fig. 5, we compare MixCycle with BAT trained with \\(10\\%\\) labels. MixCycle achieves a better performance in both extremely sparse and complex point clouds." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Results on NuScenes. Following the setting in BAT [34], we test our MixCycle in 4 categories (Car, Truck, Trailer and Bus). The results of P2B [16], MLVSNet [25] and BAT [34] on NuScenes are provided by \\(M^2\\)-Track [35] and BAT [34]. 1) We use the published codes of the competitors to obtain results for each sampling rate. We compare them on 3 sampling rates: \\(0.1\\%\\), \\(0.5\\%\\) and \\(1\\%\\), as NuScenes is larger than KITTI. As shown in Tab. 1, MixCycle still outperforms the fully-supervised approaches under all sampling rates. 2) Observing the individual categories in Tab. 2 evidences that MixCycle yields a remarkable improvement on Truck \\((17.3\\% / 18.6\\%)\\) and \\(12.1\\% / 10.7\\%\\) in succ./prec. on MLVSNet and P2B, respectively) and Car \\((8.7\\% / 10.6\\%)\\) in succ./prec. on MLVSNet). However, MixCycle drops by \\(2.6\\%\\) in precision on Bus, which has fewer labels, a greater size, and high velocity. 3) Moreover, in Tab. 3, we compare the performance of MixCycle trained with \\(1\\%\\) labels and" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13962" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.118, + 0.089, + 0.855, + 0.426 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.429, + 0.871, + 0.445 + ], + "angle": 0, + "content": "Figure 5. Visualization. Car&Van: Extremely sparse cases. Pedestrian: Medium density cases. Cyclist: complex environment cases." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.469, + 0.47, + 0.559 + ], + "angle": 0, + "content": "fully-supervised methods trained with \\(100\\%\\) labels. Our MixCycle based on MLVSNet surpasses the SOTA method BAT despite using significantly fewer labels. On such a challenging dataset with pervasive distractors and drastic appearance changes, our method exhibits even more competitive performance when using few labels." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.561, + 0.471, + 0.712 + ], + "angle": 0, + "content": "Result on Waymo. Following the setting in [35], we test MixCycle in Vehicle and Pedestrian. We use the BAT backbone, and MixCycle(BAT) is only trained on KITTI with a \\(10\\%\\) sampling rate. As shown in Tab. 5, MixCycle(BAT) outperforms BAT by \\(6.1\\%\\) and \\(8.6\\%\\) in terms of mean 'succ.' and 'prec.' values, respectively. More impressively, our performance is close to the fully supervised BAT trained on Waymo (31.2%/41.75% in succ./prec. reported in [34]). To summarize, our MixCycle still delivers excellent results on large-scale datasets." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.725, + 0.283, + 0.74 + ], + "angle": 0, + "content": "4.3. Analysis Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.749, + 0.469, + 0.868 + ], + "angle": 0, + "content": "In this section, we extensively analyze MixCycle with a series of experiments. First, we study the effectiveness of each component in MixCycle. Second, we further analyze the influence of forward-backward cycle step sizes. Finally, we compare the various application ways of SOT-Mixup. All the experiments are conducted on KITTI with \\(10\\%\\) sampling rate and with BAT as the backbone network, unless otherwise stated." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Ablation Study. We conduct experiments to analyze the effectiveness of different modules in MixCycle. First, we ver" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.469, + 0.892, + 0.832 + ], + "angle": 0, + "content": "if our assumption that appearance matching-based trackers can learn the object's motion distribution. As shown in Tab. 6, the cycle tracking framework yields better performance when using only forward-backward cycle than when using only self cycle (3.5%/5.4% improvement in succ./prec.). Additionally, this supports the intuition that real and diverse motion information is helpful to appearance trackers. Furthermore, combining them boosts the results. Note that the random rigid transformation is necessary for self cycle, otherwise the GT BBox will always be fixed at the origin of the coordinate system. Second, we evaluate the effectiveness of random rigid transformation and SOTMixup in the framework. The performance grows significantly after applying SOTMixup (5.1%/6% improvement in succ./prec.), demonstrating the importance of SOTMixup in semi-supervised tasks. Random rigid transformation plays a negative role in the cycle tracking framework but is practical in MixCycle. We conjecture this to be due to the missing target in the search area caused by random rigid transformation. This phenomenon may occur when the target moves rapidly and the model makes wrong predictions. Applying SOTMixup to the cycle tracking framework can significantly improve the model's tracking capabilities and address this issue." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.893, + 0.903 + ], + "angle": 0, + "content": "Flexibility of MixCycle. We further explore the effect of forward-backward tacking cycle step size. As shown in Tab. 7, we conduct experiments with 2 and 3 step cycles, respectively. Compared to the 2 step cycle, 3 step cycle" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13963" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.088, + 0.468, + 0.142 + ], + "angle": 0, + "content": "Table 6. Results of MixCycle when different modules are ablated. 'Self', 'F.-B. Cycle' and 'Trans.' stand for self cycle, forward-backward cycle and random rigid transformation in the forward-backward cycle, respectively." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.143, + 0.468, + 0.235 + ], + "angle": 0, + "content": "
SelfF.-B. CycleTrans.SOTMixupSuccessPrecision
✓34.911.3↓52.715.1↓
✓38.47.8↓58.19.7↓
✓✓39.56.7↓59.28.6↓
✓✓✓38.87.4↓59.38.5↓
✓✓✓44.61.6↓65.22.6↓
✓✓✓✓46.267.8
" + }, + { + "type": "table_caption", + "bbox": [ + 0.1, + 0.256, + 0.446, + 0.27 + ], + "angle": 0, + "content": "Table 7. Analysis of the forward-backward cycle step size." + }, + { + "type": "table", + "bbox": [ + 0.163, + 0.27, + 0.385, + 0.338 + ], + "angle": 0, + "content": "
SuccessPrecision
2 Steps45.866.6
3 Steps46.267.8
Improvement0.4↑1.2↑
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.358, + 0.468, + 0.414 + ], + "angle": 0, + "content": "Table 8. Results of SOTMixup with different settings. 'Template' and 'Search Area' indicate we apply SOTMixup with different inputs. 'Self' indicates we apply SOTMixup in the self cycle. 'Backward' means we apply SOTMixup in backward tracking \\( P_1^s \\) to \\( P_0^s \\)." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.415, + 0.468, + 0.498 + ], + "angle": 0, + "content": "
SelfBackwardTemplateSearch AreaSuccessPrecision
✓✓44.71.5↓64.73.1↓
✓✓✓45.40.8↓67.60.2↓
✓✓42.33.9↓634.8↓
✓✓✓44.51.7↓66.11.7↓
✓✓46.267.8
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.534, + 0.468, + 0.64 + ], + "angle": 0, + "content": "achieves a better performance in both success and precision. This experiment demonstrates the potential of MixCycle for further growth in step size. We believe that larger step sizes can provide a template point cloud disturbed in long sequence tracking, leading to improved model robustness. Furthermore, according to [24], a larger step size more effectively penalizes inaccurate localization." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Influence of SOTMixup. In Tab. 8, we compare SOTMixup with different settings. First, we analyze the effect of applying SOTMixup to different inputs (Template and Search Area) while only using it in self cycle. The performance drops when we apply it to the template and to both the template and search area. We consider this to be due to the mismatch with real tracking. As the template is usually accurate while the search area point cloud varies significantly. Note that we share the same \\(\\lambda\\) when taking SOTMixup in both the template and search area, and set \\(\\lambda = 1\\) in the SOTMixup loss. Second, we explore various ways of exploiting SOTMixup in MixCycle. SOTMixup leads to performance degradation when we apply it to backward tracking. This is caused by the disturbance of the template point cloud in backward tracking, making the loss weights misaligned. This further proves that the loss weights provided by SOTMixup are reliable." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.09, + 0.619, + 0.106 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.115, + 0.892, + 0.236 + ], + "angle": 0, + "content": "In this paper, we have presented the first semi-supervised framework, MixCycle, for 3D SOT. Its three main components, self tracking cycle, forward-backward tracking cycle and SOTMixup, have been proposed to achieve robustness to point cloud variations and percept object's motion distribution. Our experiments have demonstrated that MixCycle yields high label efficiency and outperforming fully-supervised approaches using scarce labels." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.237, + 0.892, + 0.281 + ], + "angle": 0, + "content": "In the future, we plan to develop a more robust tracking network backbone for MixCycle, and thus further enhance its 3D SOT performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.282, + 0.892, + 0.373 + ], + "angle": 0, + "content": "Acknowledgments. This work is supported in part by the National Natural Science Foundation of China (No. 62176242 and 62002295), and NWPU international cooperation and exchange promotion projects (No. 02100-23GH0501). Thank Haozhe Qi for the discussion and preliminary exploration." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13964" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.185 + ], + "angle": 0, + "content": "[1] Holger Caesar, Varun Bankiti, Alex H. Lang, Sourabh Vora, Venice Erin Liong, Qiang Xu, Anush Krishnan, Yu Pan, Giancarlo Baldan, and Oscar Beijbom. nuscenes: A multimodal dataset for autonomous driving. arXiv preprint arXiv:1903.11027, 2019. 2, 3, 6" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.187, + 0.472, + 0.257 + ], + "angle": 0, + "content": "[2] Yunlu Chen, Vincent Tao Hu, Efstratos Gavves, Thomas Mensink, Pascal Mettes, Pengwan Yang, and Cees GM Snoek. Pointmixup: Augmentation for point clouds. 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In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 13546-13555, 2021. 2, 3, 4" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.785 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.956 + ], + "angle": 0, + "content": "13966" + } + ] +] \ No newline at end of file diff --git a/2023/MixCycle_ Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency/1f3580cb-fdbe-4e7d-96d7-32968d08a569_origin.pdf b/2023/MixCycle_ Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency/1f3580cb-fdbe-4e7d-96d7-32968d08a569_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..80a039d7e492f5a4d640f6d1722f5954e3af5d77 --- /dev/null +++ b/2023/MixCycle_ Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency/1f3580cb-fdbe-4e7d-96d7-32968d08a569_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:6e7ac28c4ad52187bbc540a445dc7804390886a4bcc16d2e4b11e02705d1ccef +size 1410657 diff --git a/2023/MixCycle_ Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency/full.md b/2023/MixCycle_ Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency/full.md new file mode 100644 index 0000000000000000000000000000000000000000..771035782eaa92b5fe21b8453f8c069b4f31f560 --- /dev/null +++ b/2023/MixCycle_ Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency/full.md @@ -0,0 +1,316 @@ +# MixCycle: Mixup Assisted Semi-Supervised 3D Single Object Tracking with Cycle Consistency + +Qiao Wu $^{1}$ Jiaqi Yang $^{1*}$ Kun Sun $^{2}$ Chu'ai Zhang $^{1}$ Yanning Zhang $^{1}$ Mathieu Salzmann $^{3}$ + +1 Northwestern Polytechnical University 2 China University of Geosciences, Wuhan 3 École Polytechnique Fédérale de Lausanne + +qiaowu@mail.nwpu.edu.cn; jqyang@nwpu.edu.cn; sunkun@cug.edu.cn; + +cazhang@mail.nwpu.edu.cn; ynzhang@nwpu.edu.cn; mathieu.salzmann@epfl.ch + +# Abstract + +3D single object tracking (SOT) is an indispensable part of automated driving. Existing approaches rely heavily on large, densely labeled datasets. However, annotating point clouds is both costly and time-consuming. Inspired by the great success of cycle tracking in unsupervised 2D SOT, we introduce the first semi-supervised approach to 3D SOT. Specifically, we introduce two cycle-consistency strategies for supervision: 1) Self tracking cycles, which leverage labels to help the model converge better in the early stages of training; 2) forward-backward cycles, which strengthen the tracker's robustness to motion variations and the template noise caused by the template update strategy. Furthermore, we propose a data augmentation strategy named SOT-Mixup to improve the tracker's robustness to point cloud diversity. SOTMixup generates training samples by sampling points in two point clouds with a mixing rate and assigns a reasonable loss weight for training according to the mixing rate. The resulting MixCycle approach generalizes to appearance matching-based trackers. On the KITTI benchmark, based on the P2B tracker [16], MixCycle trained with $10\%$ labels outperforms P2B trained with $100\%$ labels, and achieves a $28.4\%$ precision improvement when using $1\%$ labels. Our code will be released at https://github.com/Mumuqiao/MixCycle. + +# 1. Introduction + +3D single object tracking (SOT) plays a critical role in the field of autonomous driving. For example, given object detection [15, 33] results as input, it can output the necessary information for trajectory prediction [8]. The goal of SOT is to regress the center position and 3D bounding-box (BBox) of an object of interest in a search area, given the point cloud (PC) patch and BBox of the object template. + +![](images/afbf5385e08d25e08f66aaa42b4e185ffc675c5b6fd4d1cf8c31311736305a18.jpg) +Figure 1. Comparison of MixCycle and fully-supervised methods [16, 25, 34], all trained with $1\%$ labels on KITTI [5]. 'Succ.' and 'Prec.' represent Success and Precision, respectively. + +This is a very challenging task because (i) point clouds obtained with, e.g., LiDAR sensors, suffer from occlusions and point sparsity, complicating the tracker's task of finding the object of interest; (ii) the point distribution for an object may vary significantly, making it difficult for the model to learn discriminative object features. + +To tackle the above challenges, existing 3D SOT models [6, 16, 4, 9, 10, 25, 34, 18, 35] rely on large scale annotated point cloud datasets for training. Unfortunately, obtaining annotations for this task, as for many 3D tasks, is extremely time-consuming. Furthermore, as shown in Fig. 1, the performance of these methods degrades dramatically as the number of labeled samples decreases. Nevertheless, no semi-supervised or unsupervised methods have been explored so far in 3D SOT. + +As shown in Fig. 2, the matching-based tracker of [34] can still track the target at the very beginning of a sequence by predicting a motion offset relative to the reference coordinate, even though there are no points in the template for appearance matching. This indicates that the appearance + +![](images/ddf3e0f5b35c2a741dac34bfce18a8377279aad272d234ce75975f9b529f2f3b.jpg) +Ground Truth + +![](images/2dcdfb205a088ddb3cee58189a8e7ec6d577e15510266212f5a61f82b34c410f.jpg) +Matching-Based Tracker +Figure 2. We observe that appearance matching-based trackers can learn the objects motion distribution and track them even in the absence of points for appearance matching. For instance, BAT [34] manages to track objects in extremely sparse point clouds. + +matching-based trackers can learn motion information. By contrast, in 2D SOT, many trackers [23, 24, 36, 29] employ cycle consistency to leverage unsupervised data. Specifically, they encourage forward and backward tracking to produce consistent motions. In principle, we expect to apply this idea to 3D SOT and make trackers to learn the object's motion distribution in unlabeled data. However, transferring these 2D methods directly to 3D is challenging. First, since the point cloud is sparse and the environment is cluttered with objects, it is hard to find meaningful patches to use as pseudo labels for training. Second, unsupervised 2D SOT methods rely on the assumption that the target appears in every frame of the sequence. Unfortunately, this assumption is not always satisfied in point cloud datasets such as KITTI [5], NuScenes [1], and Waymo [20]. This is because they are built for the multi-object tracking task, and cannot guarantee that the tracking object exists in the whole sequence. + +In this paper, we introduce a label-efficient way to train 3D SOT trackers. We call it MixCycle - a 3D SOT approach based on a novel SOTMixup data augmentation strategy for semi-supervised Cycle tracking. Specifically, we first develop a tracking framework exploiting both self and forward-backward tracking cycles. Self tracking consistency is performed to cover the object point cloud appearance variation, and forward-backward consistency is built for learning the object's motion distribution. Second, we present a data augmentation method for 3D SOT called SOTMixup, which is inspired by the success of mixup [31] and Manifold mixup [22]. Without changing the total number of points in the search area, SOTMixup samples points in a random point cloud and the search area point cloud according to the mixing rate and generates training samples. Specifically, the random point cloud is sampled from the labeled training set. SOTMixup thus increases the tracker's robustness to point cloud variations. We evaluate MixCycle on KITTI, NuScenes, and Waymo. As shown in Fig. 1, our experiments clearly demonstrate the label efficiency, generalization and remarkable performance of our method on the 3D SOT task. + +Contributions: (i) We propose the first semi-supervised + +3D SOT framework. It exploits self and forward-backward consistency as supervision and generalizes to appearance matching-based trackers. (ii) We introduce a SOTMixup augmentation strategy that increases the tracker's robustness to point distribution variations and allows it to learn motion information in extreme situations. (iii) Our framework demonstrates a remarkable performance in terms of label efficiency, achieving better results than existing supervised methods in our experiments on KITTI NuScenes, and Waymo when using fewer labels. In particular, we surpass P2B [16] trained on $100\%$ labels while only using $10\%$ labels. + +# 2. Related Work + +3D Single Object Tracking. Since LiDAR is insensitive to illumination, the appearance matching model has become the main choice in the field of 3D single object tracking. Giancola et al. [6] proposed SC3D which is the first method using a Siamese network to deal with this problem. However, it is very time-consuming and inaccurate due to heuristic matching. Zarzar et al. [30] built an end-to-end tracker by using 2D RPN in 2D bird's eyes view (BEV). Unfortunately, the lack of information in one dimension leads to limited accuracy. The point-to-box (P2B) network [16] employs VoteNet[15] as object regression module to construct a point-based tracker. A number of works [4, 9, 10, 25, 34, 18] investigate different architectures of trackers based on P2B [16]. Zheng et al. [34] depicted an object using the point-to-box relation and proposed BoxCloud, which enables the model to better sense the size of objects. Hui et al. [9] discovered the priori information of object shapes in the dataset to obtain dense representations of objects from sparse point clouds. Zheng et al. [35] presented a motion centric method $M^2$ -Track, which is appearance matching-free and has made great progress in dealing with the sparse point cloud tracking problem. However, $M^2$ -track is limited by the LiDAR frequency of datasets as object motion in adjacent frames varies with the LiDAR sampling frequency. + +All the above methods rely on large-scale labeled datasets. Unfortunately, 3D point cloud annotation is labor- and time-consuming. To overcome this, we propose MixCycle, a semi-supervised tracking method based on cycle consistency constraints with SOTMixup data augmentation. Label-Efficient Visual Tracking. Wang et al. [23] proposed unsupervised deep tracking (UDT) with cycle consistency, based on a Siamese correlation filter backbone network. UDT achieved remarkable performance, revealing the potential of unsupervised learning in visual tracking. Yuan et al. [29] improved the UDT approach to make the target features passed forward and backward as similar as possible. The self-supervised fully convolutional Siamese network [19] uses only spatially supervised learning of tar + +![](images/f79febe5b5c4ce3e41316e7de7fe6b46f8f668debebe7525810aab10a7d17897.jpg) +Figure 3. MixCycle framework. The label is only contained in $P_0^s$ of point cloud (PC) sequence $\{P_0^s, P_1^s, \ldots, P_n^s\}$ . 1) Self tracking cycle: we first sample a PC $P_r^s$ from the labeled training set. Then, we generate pseudo labels by applying SOTMixup and random rigid transformation (Trans.) to $P_0^s$ and $P_r^s$ . SOTMixup directly mixes $P_r^s$ and $P_0^s$ based on the number of points with a mixing rate, assigning a reasonable loss weight corresponding to the mixing rate. We employ the consistency between self tracking proposals and pseudo labels to formulate the loss $\mathcal{L}_{self}$ . 2) Forward-backward tracking cycle: we leverage forward tracking proposals as pseudo labels and apply a random rigid transformation to them. Then, we employ the consistency between ground truth (GT)/pseudo labels and backward tracking proposals to formulate the losses $\mathcal{L}_{con0} / \{\mathcal{L}_{con1}, \ldots, \mathcal{L}_{con(n-1)}\}$ . + +get correspondences in still video frames. Wu et al. [26] proposed a progressive unsupervised learning (PUL) network, which distinguishes the background by contrastive learning and models the regression result noise. PUL thus makes the tracker robust in long-time tracking. Unsupervised single object tracker [36] consists of an online-updating tracker with a novel memory learning scheme. + +In essence, the above unsupervised trackers all make the implicit assumption that the tracked target exists in every frame of the sequence. Unfortunately, this is not necessarily true in KITTI [5], NuScenes [1], and Waymo [20]. Therefore, the above methods are not directly applicable to 3D SOT. + +Mixup Data Augmentation. Data augmentation has become a crucial pre-processing step for many deep learning models. Zhang et al. [31] introduced a data augmentation method called mixup, which linearly interpolates two image samples, and Manifold mixup [22] transfers this idea to high-dimensional feature spaces. By interpolating a new sample, PointMixup [2] extends mixup to point clouds. Mix3D [14] introduces a scene-aware mixup by taking the union of two 3D scenes and their labels after random transformations. Lu et al. [13] developed a directed mixup based on the pixel values. Additionally, a variety of region mixup techniques have been proposed [32, 12, 21, 11]. In the case of outdoor scenes, Xiao et al. [28] combined two images using random rotation. CosMix[17] and structure aware fusion [7] combine point clouds using semantic structures. Fang et al. [3] turned a CAD into a point cloud to combat object occlusion. + +However, the above-mentioned methods are made for the + +multi-class classification scenario and are not suitable for SOT, which only contains a positive and negative sample. + +# 3. Method + +# 3.1. Overview + +The purpose of 3D SOT is to continually locate the target in the search area point cloud sequence $\mathbf{P}^s = \{P_0^s,\dots ,P_k^s,\dots ,P_n^s |P_k^s\in \mathbb{R}^{N_s\times 3}\}$ given the tracking object template point cloud $P_0^o\in \mathbb{R}^{N_t\times 3}$ and the 3D BBox $B_{0}\in \mathbb{R}^{7}$ in the initial frame. This can be described as + +$$ +\left(\widetilde {P} _ {k + 1} ^ {o}, \widetilde {B} _ {k + 1}\right) = \mathcal {F} \left(P _ {k + 1} ^ {s}, \widetilde {P} _ {k} ^ {o}\right), \tag {1} +$$ + +where $\widetilde{P}_k^o$ , $\widetilde{P}_{k + 1}^o$ and $\widetilde{B}_{k + 1}$ are the predicted target point cloud and 3D BBox in frame $k$ and $k + 1$ , respectively. By referring to P2B [16] and its follow-ups [4, 9, 10, 18, 25, 34], we summarize the typically 3D SOT loss as + +$$ +\mathcal {L} = \rho_ {1} \cdot \mathcal {L} _ {c l a} + \rho_ {2} \cdot \mathcal {L} _ {p r o p} + \rho_ {3} \cdot \mathcal {L} _ {r e g} + \rho_ {4} \cdot \mathcal {L} _ {b o x}, \tag {2} +$$ + +where $\rho$ is the manually-tuned hyperparameter, $\mathcal{L}_{\text{cla}}$ , $\mathcal{L}_{\text{prop}}$ , $\mathcal{L}_{\text{reg}}$ and $\mathcal{L}_{\text{box}}$ are the losses for foreground-background classification, confidences for the BBox proposals, voting offsets of the seed points, and offsets of the BBox proposals, respectively. + +To address this task, we propose MixCycle, a novel semi-supervised framework for 3D SOT. Illustrated in Fig. 3, MixCycle relies on a SOTMixup data augmentation strategy to tackle data sparsity and diversity (Sec. 3.2). Further, it utilizes self and forward-backward cycle consistencies as sources of supervision to cover the object appear + +ance and motion variation (Sec. 3.3). Additionally, we apply rigid transformations to ground truth (GT) labels to generate search areas in unlabeled data (Sec. 3.4). + +# 3.2. SOTMixup + +Inspired by the great success of mixup [31], we develop SOTMixup to supply diverse training samples and deal with the point cloud diversity problem, providing a solution for the mixup application in binary classification in SOT task. With two image samples $(I_A, I_B)$ , mixup can be simply describe as creating an image + +$$ +I _ {A} ^ {m} = \lambda I _ {A} + (1 - \lambda) I _ {B}, \tag {3} +$$ + +$$ +y _ {A} ^ {m} = \lambda y _ {A} + (1 - \lambda) y _ {B}, \tag {4} +$$ + +where $\lambda \in [0,1]$ is the mixing rate, and $(y_A,y_B)$ are the image labels. Typically, $\lambda$ follows a Beta distribution $\beta (\eta ,\eta)$ . A multi-class loss is then calculated as + +$$ +\mathcal {L} _ {\text {m u t i - c a l}} = \lambda \cdot \mathcal {C} (\widetilde {y}, y _ {A}) + (1 - \lambda) \cdot \mathcal {C} (\widetilde {y}, y _ {B}), \tag {5} +$$ + +where $\widetilde{y}$ is the predicted label, and $\mathcal{C}$ is the criterion (usually being the cross-entropy loss). Vanilla mixup applies linear interpolation in aligned pixel space. However, this operation is not suitable to unordered point clouds. Furthermore, one of the key challenges for the SOT task is to determine whether the proposal is positive or negative. Multi-class label interpolation approach in mixup cannot be directly applied. Specifically, given the search area PC $P_A$ and a random PC $P_B$ sampled in the training set, we employ mixup to generate a foreground and background label pair $(\lambda \cdot y_A, (1 - \lambda) \cdot y_B)$ . In practice, this label pair should be set to $(y_A, 0)$ , as the points in $P_B$ mismatch the template and should be considered as background. + +We therefore develop a point cloud mixup strategy for SOT based on the number of points, called SOTMixup. As shown in Fig. 4, SOTMixup generates new samples and minimizes the gap between the generated samples and the real sample distribution. Specifically, SOTMixup mixes a point cloud randomly sampled from the training set and the search area point cloud by sampling points using a mixing rate, without changing the total number of points in the search area. First, given point cloud pair $(P_A, P_B)$ , corresponding binary classification labels $(y_A, y_B)$ , and a mixing rate $\lambda$ , we separate the backgrounds and object points in $P_A$ and $P_B$ and obtain $(P_A^b, P_A^o, P_B^b, P_B^o)$ , where $P_A^o \in \mathbb{R}^{N_A^o \times 3}$ and $P_B^o \in \mathbb{R}^{N_B^o \times 3}$ . Second, we generate $\hat{P}_A^o$ and $\hat{P}_B^o$ by randomly sampling $\lambda \times N_A^o$ and $(1 - \lambda) \times N_A^o$ points from $P_A^o$ and $P_B^o$ , respectively. We then perform SOTMixup as + +$$ +P _ {A} ^ {m} = P _ {A} ^ {b} + \hat {P} _ {A} ^ {o} + \hat {P} _ {B} ^ {o}, \tag {6} +$$ + +where $^{\prime} + ^{\prime}$ represents the concatenation operation. + +![](images/392cc2a2f5afe57ede32399f731ecda0c8f8519d165c3254767ef68db05a4f05.jpg) +Figure 4. SOTMixup. First, the search area point cloud (PC) and a point cloud randomly sampled from the labeled training set are segmented into foreground and background, respectively. Second, a mixing rate $\lambda$ is applied to sample two object PCs. Finally, we concatenate the sampled object PCs and search area background to generate the mixed search area. + +Usually, we consider the distance between the predicted object center and the ground truth to be positive if it is less than 0.3 meters, and negative if it is greater than 0.6 meters. The binary cross entropy loss for regression and foreground classification in SOTMixup can be written as + +$$ +\mathcal {L} _ {\text {p r o p . m i x}} = - \left(\lambda \cdot y _ {A} \cdot \log \left(s _ {i} ^ {p}\right) + \left(1 - y _ {A}\right) \cdot \log \left(1 - s _ {i} ^ {p}\right)\right), \tag {7} +$$ + +$$ +\mathcal {L} _ {\text {c l a - m i x}} = - \left(\lambda \cdot y _ {A} \cdot \log \left(b _ {j} ^ {p}\right) + (1 - y _ {A}) \cdot \log \left(1 - b _ {j} ^ {p}\right)\right), \tag {8} +$$ + +where $\mathcal{L}_{prop\_ mix}$ and $\mathcal{L}_{cla\_ mix}$ are the proposal confidence loss and foreground-background classification loss, respectively. $s_i^p$ is the confidence score of proposal $i$ , and $b_j^p$ is the predicted foreground probability of point $j$ in search area $P^s$ . We replace losses $\mathcal{L}_{prop}$ and $\mathcal{L}_{cla}$ with $\mathcal{L}_{prop\_ mix} = \lambda \cdot \mathcal{L}_{prop}$ and $\mathcal{L}_{cla\_ mix} = \lambda \cdot \mathcal{L}_{cla}$ . SOTMixup applies a loss weight $\lambda$ to the positive proposals and foreground points, but does not change the loss weight of the negative proposals and background points. We reduce the loss penalty on the positive sample prediction scores to lessen the influence on the appearance matching ability of the tracker. We leave the loss weight unchanged for the negative samples. Because we intend the trackers to predict the motion offset of the object even if the object point cloud in the search area has dramatically changed. + +# 3.3. Cycle Tracking + +Self Tracking Cycle. In contrast with existing 2D cycle trackers [23, 24, 36, 29], which only consider forward-backward cycle consistency, we propose to create the self tracking cycle. The motivation is to leverage virtually infinite supervision information contained in the initial frame + +itself. To this end, we first randomly sample a search area point cloud $P_r^s$ and object 3D BBox $B_r$ from the labeled training set. SOTMixup is then applied to generate the mixed point cloud + +$$ +P _ {0} ^ {m} = S O T M i x u p \left(P _ {0} ^ {s}, B _ {0}, P _ {r} ^ {s}, B _ {r}, \lambda\right), \tag {9} +$$ + +where $\lambda \in [0,1]$ is the mixing rate. Inspired by SC3D [6], we apply a random rigid transformation $\mathcal{T}$ to $\{P_0^m,B_0\}$ and generate pseudo labels + +$$ +\left(P _ {0} ^ {m t}, B _ {0} ^ {t}\right) = \mathcal {T} \left(P _ {0} ^ {m}, B _ {0}, \alpha\right), \tag {10} +$$ + +where $P_0^{mt}$ is the search area PC generated by applying SOTMixup and a rigid transformation on $P_0^s$ and $\alpha = (\Delta x, \Delta y, \Delta z, \Delta \theta)$ is a transformation parameter with a coordinate offset $(\Delta x, \Delta y, \Delta z)$ and a rotation degree $\Delta \theta$ around the up-axis. This creates a self tracking cycle + +$$ +\left(\widetilde {P} _ {0} ^ {o t}, \widetilde {B} _ {0} ^ {t}\right) = \mathcal {F} \left(P _ {0} ^ {m t}, P _ {0} ^ {o}\right), \tag {11} +$$ + +where $\widetilde{B}_0^t$ is the predicted result on $P_0^{mt}$ and $P_0^o$ is the object template PC cropped from $P_0^s$ . We then calculate the self consistency loss $\mathcal{L}_{self}$ between $\widetilde{B}_0^t$ and $B_0^t$ . $\mathcal{L}_{self}$ has the same setting with $\mathcal{L}$ of Eq. (2) while corresponding loss with $\mathcal{L}_{cal\_ mix}$ and $\mathcal{L}_{prop\_ mix}$ . + +In the self tracking cycle, the loss weight can be automatically quantified by the mixing rate in SOTMixup. This provides the tracker with simple training samples to make it converge faster in the early stage of training with a high mixing rate, and also allows us to improve the tracker's robustness to point cloud variations using a low mixing rate. + +Forward-Backward Tracking Cycle. In addition to self tracking cycles, we also use forward-backward consistency. Hence, we forward track the object in the given search area sequence $\mathbf{P}^{\mathrm{s}}$ , which can be written as + +$$ +\left(\widetilde {P} _ {1} ^ {o}, \widetilde {B} _ {1}\right) = \mathcal {F} \left(P _ {1} ^ {s}, P _ {0} ^ {o}\right), \tag {12} +$$ + +$$ +\left(\widetilde {P} _ {2} ^ {o}, \widetilde {B} _ {2}\right) = \mathcal {F} \left(P _ {2} ^ {s}, \widetilde {P} _ {1} ^ {o}\right), \tag {13} +$$ + +where $\{\widetilde{P}_1^o,\widetilde{P}_2^o\}$ and $\{\widetilde{B}_1,\widetilde{B}_0\}$ are the predicted forward tracking object point clouds and 3D BBoxes of $P_{1}^{s}$ and $P_2^s$ respectively. Following this strategy lets us further predict $\{\widetilde{P}_3^o,\dots ,\widetilde{P}_n^o\}$ and $\{\widetilde{B}_3,\dots ,\widetilde{B}_n\}$ in $\{P_3^s,\ldots ,P_n^s\}$ . + +Then, we reverse the tracking sequence and perform backward tracking while applying random rigid transformations. This can be expressed as + +$$ +\left(\widetilde {P} _ {1} ^ {o \prime}, \widetilde {B} _ {1} ^ {\prime}\right) = \mathcal {F} \left(\mathcal {T} \left(P _ {1} ^ {s}, \widetilde {B} _ {1}, \alpha\right), \widetilde {P} _ {2} ^ {o \prime}\right), \tag {14} +$$ + +$$ +\left(\widetilde {P} _ {0} ^ {o \prime}, \widetilde {B} _ {0} ^ {\prime}\right) = \mathcal {F} \left(\mathcal {T} \left(P _ {0} ^ {s}, B _ {0}, \alpha\right), \widetilde {P} _ {1} ^ {o \prime}\right), \tag {15} +$$ + +where $\{\widetilde{P}_0^{o'},\widetilde{P}_1^{o'},\widetilde{P}_2^{o'}\}$ and $\{\widetilde{B}_1',\widetilde{B}_0'\}$ are the predicted backward tracking object point clouds and 3D BBoxes. + +We then measure the consistency losses $\mathcal{L}_{con1}$ and $\mathcal{L}_{con0}$ between $\widetilde{B}_1^{\prime}$ and $\widetilde{B}_1$ , as well as between $\widetilde{B}_0^{\prime}$ and $B_0$ . Similarly, we can measure the consistency losses $\{\mathcal{L}_{con2},\dots,\mathcal{L}_{con(n - 1)}\}$ . $\mathcal{L}_{con}$ has the same setting with $\mathcal{L}$ of Eq. (2). + +The forward-backward tracking cycle provides real and diverse motion consistency, leading trackers to learn the object's motion distribution between two neighboring frames. Furthermore, the tracker's robustness is increased by training with a disturbed template generated by the template update strategy (Sec. 3.4). + +# 3.4. Implementation Details + +Training & Testing. We train MixCycle using the SGD optimizer with a batch size of 48 and an initial learning rate of 0.01 with a decay rate of $5e - 5$ at each epoch. All experiments are conducted using NVIDIA RTX-3090 GPUs. We set $n = 2$ and only measure the self and forward-backward cycle consistency losses $\mathcal{L}_{self}$ and $\mathcal{L}_{con0}$ for $P_0^s$ due to the GPU memory limit. At test time, we track the object frame by frame in a point cloud sequence with labels in the first frame. For both training and testing, our default setting for the template update strategy is to merge the target in the first frame with the predicted previous result. + +Input & Data Augmentation. Our MixCycle takes three frames $f$ , $f + 1$ and $f + 2$ as input. For the initial frame $f$ , we transform the BBox and point clouds to the object coordinate system. For the other frames in the tracking cycle, we transform the BBox and point clouds to the predicted object coordinate system in the last frame. We assume that the motion of the objects across neighboring frames is not significant. We apply random rigid transformations to BBoxes in labeled frames and use them to crop out search areas in the neighboring frames. Only the area within 2 meters around the reference object BBox is considered as input (search area) since we are only interested in the area where the target is expected to appear. The random rigid transformation parameter $\alpha$ is set to $(0.3, 0.3, 0.0, 5.0^{\circ})$ , and the $\beta$ distribution parameter is set to $\eta = 0.5$ . + +Loss Function. The loss function of MixCycle is defined as $\mathcal{L}_{MixCycle} = \gamma_1\mathcal{L}_{self} + \gamma_2\mathcal{L}_{con0}$ containing self tracking cycle losses and forward-backward tracking cycle losses. Each of our cycle losses is set according to the original loss setting of the tracker to which we apply MixCycle. Additionally, the corresponding losses are replaced with $\mathcal{L}_{prop\_ mix}$ and $\mathcal{L}_{cla\_ mix}$ . We empirically set $\gamma_1 = 1.0$ and $\gamma_2 = 2.0$ , as we expect the tracker to focus more on learning the motion distribution of the object. + +Table 1. Overall performance comparison between our MixCycle and the fully-supervised methods on the KITTI (left) and NuScenes (right) datasets, where the percentage of labels used for training is shown under the dataset names. Improvements based on the same tracker are shown in green. Bold and underline denote the best and the second-best performance, respectively. + +
DatasetKITTINuScenes
Sampling Rate1%5%10%0.1%0.5%1%
SuccessP2B [16]6.125.534.315.223.024.3
MLVSNet [25]25.035.536.621.529.934.0
BAT [34]10.121.634.917.526.430.6
Ours(P2B)20.314.2↑36.711.2↑43.89.5↑23.27.9↑34.311.3↑34.310.0↑
Ours(MLVSNet)32.47.4↑38.83.3↑42.66↑31.49.9↑34.54.7↑41.97.9↑
Ours(BAT)19.79.6↑42.220.6↑46.211.3↑24.46.9↑32.86.4↑34.43.8↑
PrecisionP2B [16]5.039.552.713.021.222.6
MLVSNet [25]36.353.254.719.530.435.3
BAT [34]12.335.352.715.225.730.6
Ours(P2B)33.428.4↑55.315.8↑64.211.5↑21.98.9↑34.213↑34.011.4↑
Ours(MLVSNet)49.212.9↑56.63.4↑61.46.7↑31.111.6↑35.24.8↑43.68.3↑
Ours(BAT)27.014.7↑62.327.0↑67.815.1↑22.77.5↑31.96.2↑34.13.5↑
+ +Table 2. Comparison of MixCycle against fully-supervised methods on each category. We train the models with $1\% /0.1\%$ sampling rate on KITTI/NuScenes. Improvements and decreases based on the same tracker are shown in green and red, respectively. + +
DatasetKITTI(1%)Nuscenes(0.1%)
Category Frame NumberCar 6424Pedestrian 6088Van 1248Cyclist 308Mean 14068Car 64159Truck 13587Trailer 3352Bus 2953Mean 84051
SuccessP2B [16]8.13.68.15.66.115.813.112.816.115.2
MLVSNet [25]35.315.222.912.825.021.025.222.513.521.5
BAT [34]16.73.87.26.810.117.517.820.414.417.5
Ours(P2B)20.612.5↑22.819.2↑8.00.1↓16.611.0↑20.314.2↑23.07.2↑25.212.1↑22.49.6↑17.71.5↑23.27.9↑
Ours(MLVSNet)43.88.5↑20.75.5↑28.25.3↑43.731.0↑32.47.4↑29.78.7↑42.417.3↑31.38.9↑19.25.7↑31.49.9↑
Ours(BAT)32.615.9↑6.12.3↑16.39.2↑34.127.4↑19.79.6↑24.36.9↑26.99.1↑23.73.2↑16.92.5↑24.46.9↑
PrecisionP2B [16]7.42.26.14.45.014.58.26.88.413.0
MLVSNet [25]46.528.825.416.636.320.520.011.36.419.5
BAT [34]22.72.95.99.512.316.312.29.212.215.2
Ours(P2B)30.022.6↑43.741.5↑6.10.011.16.7↑33.428.4↑23.59.0↑18.910.7↑11.24.4↑14.05.6↑21.98.9↑
Ours(MLVSNet)59.212.7↑40.711.9↑31.15.7↑79.062.4↑49.212.8↑31.110.6↑38.618.6↑19.58.1↑11.55.2↑31.111.6↑
Ours(BAT)43.921.2↑9.36.4↑19.213.2↑57.347.8↑27.014.7↑24.17.8↑21.18.9↑13.84.6↑9.72.6↓22.77.5↑
+ +# 4. Experiments + +# 4.1. Datasets + +We evaluate our MixCycle on the challenging 3D visual tracking benchmarks of KITTI [5], NuScenes [1] and Waymo [20] for semi-supervised 3D single object tracking. Semi-supervision labels are generated by applying random sampling to the training set. + +The KITTI tracking dataset contains 21 training sequences and 29 test sequences with 8 types of objects. Following previous works [6, 16, 34, 25], we split the training set into training/validation/testing: Sequences 0-16 are used for training, 17-18 for validation, and 19-20 for testing. The NuScenes dataset contains 1000 scenes and annotations for 23 object classes with accurate 3D BBoxes. NuScenes is officially divided into $700 / 150 / 150$ scenes for training/validation/testing. Following the setting in [34], we train our MixCycle on the subset "training_track" of the training set, and test it on the validation set. Waymo includes 1150 scenes, $798 / 202 / 150$ scenes for training/validation/testing. Following the setting in [35], we test trackers in the validation set. Compared to KITTI, NuScenes, and Waymo include larger data volumes and + +more complex scenarios. + +Evaluation Metrics. In this paper, we use One Pass Evaluation (OPE) [27] to evaluate the Success (Succ.) and Precision (Prec.) of different methods. Success is calculated as the overlap (Intersection Over Union, IoU) between the proposal BBox and the ground truth (GT) BBox. Precision represents the AUC of distance error between the centers of two BBoxes from 0 to 2 meters. + +# 4.2. Comparison with Fully-supervised Methods + +To the best of our knowledge, no other 3D single object trackers work in a semi-supervision fashion. Therefore, we choose P2B [16], the multi-level voting Siamese network (MLVSNet) [25] and the box-aware tracker (BAT) [34] to validate our method by sharing the same network backbone. Note that BAT is the state-of-the-art (SOTA) method in appearance matching-based trackers, and we regard it as our upper bound. The fully-supervised methods will be trained with labeled data, as their original approaches. We train MixCycle in a semi-supervised way, which uses both labeled and unlabeled data. We do not evaluate the motion-based tracker [35] since it requires 2 consecutive labeled point clouds for training and is not suitable for our training + +Table 3. Overall performance comparison on KITTI/NuScenes between our MixCycle with $10\% /1\%$ sampling rates and the fully-supervised methods with $100\%$ sampling rate. + +
DatasetMethodSuccessPrecision
KITTIP2B(100%) [16] vs Ours(10%)42.4 vs 43.81.4↑60.0 vs 64.24.2↑
MLVSNet(100%) [25] vs Ours(10%)45.7 vs 42.63.1↓66.6 vs 61.45.2↓
BAT(100%) [34] vs Ours(10%)51.2 vs 46.25.0↓72.8 vs 67.85.0↓
NuScenesP2B(100%) [16] vs Ours(1%)39.7 vs 34.35.4↓42.2 vs 34.08.2↓
MLVSNet(100%) [25] vs Ours(1%)45.7 vs 41.93.8↓47.9 vs 43.64.3↓
BAT(100%) [34] vs Ours(1%)41.8 vs 34.47.4↓42.7 vs 34.18.6↓
+ +Table 4. Comparison of MixCycle against BAT on Car in KITTI for different sampling rates. 'Improv.' denotes Improvement. + +
Sampling Rate1%5%10%30%50%70%100%
Succ.BAT [34]16.724.344.048.048.755.560.5
Ours(BAT)32.649.255.256.256.660.964.7
Improv.15.9↑24.9↑11.2↑8.2↑7.9↑5.4↑4.2↑
Prec.BAT [34]22.734.857.363.165.369.577.7
Ours(BAT)43.962.170.070.570.375.777.9
Improv.21.2↑27.3↑12.7↑7.4↑5.0↑6.2↑0.2↑
+ +set generation strategy. We employ different sampling rates for the two datasets. The first reason is that we account for the different scales of the dataset. The second season is that the case of very limited labels is more practical in real applications, and we attempt to set the sampling rate as low as possible within the trainable range. + +Results on KITTI. 1) We evaluate our MixCycle in 4 categories (Car, Pedestrian, Van and Cyclist) and compare it using 3 sampling rates: $1\%$ , $5\%$ and $10\%$ . As shown in Tab. 1, our method outperforms the fully-supervised approaches under all sampling rates by a large margin. This confirms the high label efficiency of our proposed semi-supervised framework. + +The performance gap between our MixCycle and the fully-supervised P2B becomes larger as the proportion of labeled samples decreases. In particular, in the extreme case of $1\%$ labels usage, we achieve $14.2\%$ and $28.4\%$ improvement in success and precision, respectively, demonstrating the impact of our approach on the baseline method. Interestingly, our MixCycle based on the SOTA fully-supervised method BAT achieves the best results $(42.2\%, 46.2\%) / (62.3\%, 67.8\%)$ in succ./prec.) with $5\%$ and $10\%$ sampling rates, but the MLVSNet based MixCycle takes the first place $(32.4\% / 49.2\%)$ in succ./prec.) with $1\%$ sampling rate. We believe this is because the multiscale approach in MLVSNet effectively enhances the robustness of its feature representation. The BoxCloud proposed by BAT further strengthens the reliance on labels, leading to a degradation of BAT and MixCycle performance at $1\%$ sampling rate. 2) We further present the test results on each category with $1\%$ sampling rate in Tab. 2. We achieve better performance in all categories, except Van on P2B. We assume this to be caused by the less labeled, huge, and moving fast feature of Van, which leads the tracker hard + +Table 5. Comparison of MixCycle against BAT on Waymo. MixCycle(BAT) is trained only on KITTI with a $10\%$ sampling rate; BAT* represents BAT trained on Waymo using all the labels. + +
Category Frame Number MetricsVehicle 1057651 Succ.Pedestrian 510533 Prec.Mean 1568184 Succ.Prec.
BAT [34]26.528.216.531.1
Ours(BAT)31.133.525.546.4
BAT* [34]35.644.222.136.8
+ +to predict a precise motion. The improvements on Cyclist $(31.0\% /62.4\%)$ and $27.4\% /47.8\%$ in succ./prec. for P2B and BAT, respectively) and Pedestrian $(19.2\% /41.5\%)$ in succ./prec. on P2B) reveal the robustness of MixCycle to point cloud variations. As pedestrians and cyclists are usually considered to have the largest point cloud variations due to their small object sizes and the diversity of body motion. 3) In Tab. 3, we compare the performance between fully-supervised methods trained with $100\%$ labels and MixCycle trained with $10\%$ labels. Although our performance decreases slightly on MLVSNet and BAT, MixCycle still shows a remarkable result (43.8/64.2 in succ./prec.) on P2B. With only $10\%$ of the labels, MixCycle based on P2B outperforms the fully-supervised method $(1.4\% /4.2\%)$ improvement in succ./prec.) using $100\%$ of the labels. This confirms the strong ability of our approach to leverage data information and highlights its promise for future developments. 4) We provide the comparison of MixCycle against BAT on Car from KITTI with more sampling rates in Tab. 4. Our Mixcycle not only achieves great improvements in low sampling rates, but also boosts the tracker's performance in the fully-supervised training $(4.2 / 0.2$ in succ./prec.). 5) In Fig. 5, we compare MixCycle with BAT trained with $10\%$ labels. MixCycle achieves a better performance in both extremely sparse and complex point clouds. + +Results on NuScenes. Following the setting in BAT [34], we test our MixCycle in 4 categories (Car, Truck, Trailer and Bus). The results of P2B [16], MLVSNet [25] and BAT [34] on NuScenes are provided by $M^2$ -Track [35] and BAT [34]. 1) We use the published codes of the competitors to obtain results for each sampling rate. We compare them on 3 sampling rates: $0.1\%$ , $0.5\%$ and $1\%$ , as NuScenes is larger than KITTI. As shown in Tab. 1, MixCycle still outperforms the fully-supervised approaches under all sampling rates. 2) Observing the individual categories in Tab. 2 evidences that MixCycle yields a remarkable improvement on Truck $(17.3\% / 18.6\%)$ and $12.1\% / 10.7\%$ in succ./prec. on MLVSNet and P2B, respectively) and Car $(8.7\% / 10.6\%)$ in succ./prec. on MLVSNet). However, MixCycle drops by $2.6\%$ in precision on Bus, which has fewer labels, a greater size, and high velocity. 3) Moreover, in Tab. 3, we compare the performance of MixCycle trained with $1\%$ labels and + +![](images/e96cb02350fe3a31df26d62b9a84cb5983e06d61e24d6650528e772a9337859e.jpg) +Figure 5. Visualization. Car&Van: Extremely sparse cases. Pedestrian: Medium density cases. Cyclist: complex environment cases. + +fully-supervised methods trained with $100\%$ labels. Our MixCycle based on MLVSNet surpasses the SOTA method BAT despite using significantly fewer labels. On such a challenging dataset with pervasive distractors and drastic appearance changes, our method exhibits even more competitive performance when using few labels. + +Result on Waymo. Following the setting in [35], we test MixCycle in Vehicle and Pedestrian. We use the BAT backbone, and MixCycle(BAT) is only trained on KITTI with a $10\%$ sampling rate. As shown in Tab. 5, MixCycle(BAT) outperforms BAT by $6.1\%$ and $8.6\%$ in terms of mean 'succ.' and 'prec.' values, respectively. More impressively, our performance is close to the fully supervised BAT trained on Waymo (31.2%/41.75% in succ./prec. reported in [34]). To summarize, our MixCycle still delivers excellent results on large-scale datasets. + +# 4.3. Analysis Experiments + +In this section, we extensively analyze MixCycle with a series of experiments. First, we study the effectiveness of each component in MixCycle. Second, we further analyze the influence of forward-backward cycle step sizes. Finally, we compare the various application ways of SOT-Mixup. All the experiments are conducted on KITTI with $10\%$ sampling rate and with BAT as the backbone network, unless otherwise stated. + +Ablation Study. We conduct experiments to analyze the effectiveness of different modules in MixCycle. First, we ver + +if our assumption that appearance matching-based trackers can learn the object's motion distribution. As shown in Tab. 6, the cycle tracking framework yields better performance when using only forward-backward cycle than when using only self cycle (3.5%/5.4% improvement in succ./prec.). Additionally, this supports the intuition that real and diverse motion information is helpful to appearance trackers. Furthermore, combining them boosts the results. Note that the random rigid transformation is necessary for self cycle, otherwise the GT BBox will always be fixed at the origin of the coordinate system. Second, we evaluate the effectiveness of random rigid transformation and SOTMixup in the framework. The performance grows significantly after applying SOTMixup (5.1%/6% improvement in succ./prec.), demonstrating the importance of SOTMixup in semi-supervised tasks. Random rigid transformation plays a negative role in the cycle tracking framework but is practical in MixCycle. We conjecture this to be due to the missing target in the search area caused by random rigid transformation. This phenomenon may occur when the target moves rapidly and the model makes wrong predictions. Applying SOTMixup to the cycle tracking framework can significantly improve the model's tracking capabilities and address this issue. + +Flexibility of MixCycle. We further explore the effect of forward-backward tacking cycle step size. As shown in Tab. 7, we conduct experiments with 2 and 3 step cycles, respectively. Compared to the 2 step cycle, 3 step cycle + +Table 6. Results of MixCycle when different modules are ablated. 'Self', 'F.-B. Cycle' and 'Trans.' stand for self cycle, forward-backward cycle and random rigid transformation in the forward-backward cycle, respectively. + +
SelfF.-B. CycleTrans.SOTMixupSuccessPrecision
✓34.911.3↓52.715.1↓
✓38.47.8↓58.19.7↓
✓✓39.56.7↓59.28.6↓
✓✓✓38.87.4↓59.38.5↓
✓✓✓44.61.6↓65.22.6↓
✓✓✓✓46.267.8
+ +Table 7. Analysis of the forward-backward cycle step size. + +
SuccessPrecision
2 Steps45.866.6
3 Steps46.267.8
Improvement0.4↑1.2↑
+ +Table 8. Results of SOTMixup with different settings. 'Template' and 'Search Area' indicate we apply SOTMixup with different inputs. 'Self' indicates we apply SOTMixup in the self cycle. 'Backward' means we apply SOTMixup in backward tracking $P_1^s$ to $P_0^s$ . + +
SelfBackwardTemplateSearch AreaSuccessPrecision
✓✓44.71.5↓64.73.1↓
✓✓✓45.40.8↓67.60.2↓
✓✓42.33.9↓634.8↓
✓✓✓44.51.7↓66.11.7↓
✓✓46.267.8
+ +achieves a better performance in both success and precision. This experiment demonstrates the potential of MixCycle for further growth in step size. We believe that larger step sizes can provide a template point cloud disturbed in long sequence tracking, leading to improved model robustness. Furthermore, according to [24], a larger step size more effectively penalizes inaccurate localization. + +Influence of SOTMixup. In Tab. 8, we compare SOTMixup with different settings. First, we analyze the effect of applying SOTMixup to different inputs (Template and Search Area) while only using it in self cycle. The performance drops when we apply it to the template and to both the template and search area. We consider this to be due to the mismatch with real tracking. As the template is usually accurate while the search area point cloud varies significantly. Note that we share the same $\lambda$ when taking SOTMixup in both the template and search area, and set $\lambda = 1$ in the SOTMixup loss. Second, we explore various ways of exploiting SOTMixup in MixCycle. SOTMixup leads to performance degradation when we apply it to backward tracking. This is caused by the disturbance of the template point cloud in backward tracking, making the loss weights misaligned. This further proves that the loss weights provided by SOTMixup are reliable. + +# 5. Conclusion + +In this paper, we have presented the first semi-supervised framework, MixCycle, for 3D SOT. Its three main components, self tracking cycle, forward-backward tracking cycle and SOTMixup, have been proposed to achieve robustness to point cloud variations and percept object's motion distribution. Our experiments have demonstrated that MixCycle yields high label efficiency and outperforming fully-supervised approaches using scarce labels. + +In the future, we plan to develop a more robust tracking network backbone for MixCycle, and thus further enhance its 3D SOT performance. + +Acknowledgments. This work is supported in part by the National Natural Science Foundation of China (No. 62176242 and 62002295), and NWPU international cooperation and exchange promotion projects (No. 02100-23GH0501). Thank Haozhe Qi for the discussion and preliminary exploration. + +# References + +[1] Holger Caesar, Varun Bankiti, Alex H. Lang, Sourabh Vora, Venice Erin Liong, Qiang Xu, Anush Krishnan, Yu Pan, Giancarlo Baldan, and Oscar Beijbom. nuscenes: A multimodal dataset for autonomous driving. arXiv preprint arXiv:1903.11027, 2019. 2, 3, 6 +[2] Yunlu Chen, Vincent Tao Hu, Efstratos Gavves, Thomas Mensink, Pascal Mettes, Pengwan Yang, and Cees GM Snoek. Pointmixup: Augmentation for point clouds. 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Existing approaches rely heavily on large, densely labeled datasets. However, annotating point clouds is both costly and time-consuming. Inspired by the great success of cycle tracking in unsupervised 2D SOT, we introduce the first semi-supervised approach to 3D SOT. Specifically, we introduce two cycle-consistency strategies for supervision: 1) Self tracking cycles, which leverage labels to help the model converge better in the early stages of training; 2) forward-backward cycles, which strengthen the tracker's robustness to motion variations and the template noise caused by the template update strategy. Furthermore, we propose a data augmentation strategy named SOT-Mixup to improve the tracker's robustness to point cloud diversity. SOTMixup generates training samples by sampling points in two point clouds with a mixing rate and assigns a reasonable loss weight for training according to the mixing rate. 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The goal of SOT is to regress the center position and 3D bounding-box (BBox) of an object of interest in a search area, given the point cloud (PC) patch and BBox of the object template." + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 307, + 258, + 547, + 411 + ], + "blocks": [ + { + "bbox": [ + 307, + 258, + 547, + 411 + ], + "lines": [ + { + "bbox": [ + 307, + 258, + 547, + 411 + ], + "spans": [ + { + "bbox": [ + 307, + 258, + 547, + 411 + ], + "type": "image", + "image_path": "afbf5385e08d25e08f66aaa42b4e185ffc675c5b6fd4d1cf8c31311736305a18.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 413, + 547, + 448 + ], + "lines": [ + { + "bbox": [ + 305, + 413, + 547, + 448 + ], + "spans": [ + { + "bbox": [ + 305, + 413, + 547, + 448 + ], + "type": "text", + "content": "Figure 1. Comparison of MixCycle and fully-supervised methods [16, 25, 34], all trained with " + }, + { + "bbox": [ + 305, + 413, + 547, + 448 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 305, + 413, + 547, + 448 + ], + "type": "text", + "content": " labels on KITTI [5]. 'Succ.' and 'Prec.' represent Success and Precision, respectively." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 470, + 547, + 542 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 470, + 547, + 542 + ], + "spans": [ + { + "bbox": [ + 304, + 470, + 547, + 542 + ], + "type": "text", + "content": "This is a very challenging task because (i) point clouds obtained with, e.g., LiDAR sensors, suffer from occlusions and point sparsity, complicating the tracker's task of finding the object of interest; (ii) the point distribution for an object may vary significantly, making it difficult for the model to learn discriminative object features." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 544, + 547, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 544, + 547, + 651 + ], + "spans": [ + { + "bbox": [ + 304, + 544, + 547, + 651 + ], + "type": "text", + "content": "To tackle the above challenges, existing 3D SOT models [6, 16, 4, 9, 10, 25, 34, 18, 35] rely on large scale annotated point cloud datasets for training. Unfortunately, obtaining annotations for this task, as for many 3D tasks, is extremely time-consuming. Furthermore, as shown in Fig. 1, the performance of these methods degrades dramatically as the number of labeled samples decreases. Nevertheless, no semi-supervised or unsupervised methods have been explored so far in 3D SOT." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "content": "As shown in Fig. 2, the matching-based tracker of [34] can still track the target at the very beginning of a sequence by predicting a motion offset relative to the reference coordinate, even though there are no points in the template for appearance matching. This indicates that the appearance" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "text", + "content": "*Corresponding author" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "13956" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 71, + 286, + 140 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 286, + 140 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 286, + 140 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 286, + 140 + ], + "type": "image", + "image_path": "ddf3e0f5b35c2a741dac34bfce18a8377279aad272d234ce75975f9b529f2f3b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 67, + 144, + 135, + 154 + ], + "lines": [ + { + "bbox": [ + 67, + 144, + 135, + 154 + ], + "spans": [ + { + "bbox": [ + 67, + 144, + 135, + 154 + ], + "type": "text", + "content": "Ground Truth" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 169, + 144, + 189, + 154 + ], + "blocks": [ + { + "bbox": [ + 169, + 144, + 189, + 154 + ], + "lines": [ + { + "bbox": [ + 169, + 144, + 189, + 154 + ], + "spans": [ + { + "bbox": [ + 169, + 144, + 189, + 154 + ], + "type": "image", + "image_path": "2dcdfb205a088ddb3cee58189a8e7ec6d577e15510266212f5a61f82b34c410f.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 192, + 145, + 273, + 155 + ], + "lines": [ + { + "bbox": [ + 192, + 145, + 273, + 155 + ], + "spans": [ + { + "bbox": [ + 192, + 145, + 273, + 155 + ], + "type": "text", + "content": "Matching-Based Tracker" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 158, + 287, + 202 + ], + "lines": [ + { + "bbox": [ + 46, + 158, + 287, + 202 + ], + "spans": [ + { + "bbox": [ + 46, + 158, + 287, + 202 + ], + "type": "text", + "content": "Figure 2. We observe that appearance matching-based trackers can learn the objects motion distribution and track them even in the absence of points for appearance matching. For instance, BAT [34] manages to track objects in extremely sparse point clouds." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 222, + 287, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 222, + 287, + 437 + ], + "spans": [ + { + "bbox": [ + 46, + 222, + 287, + 437 + ], + "type": "text", + "content": "matching-based trackers can learn motion information. By contrast, in 2D SOT, many trackers [23, 24, 36, 29] employ cycle consistency to leverage unsupervised data. Specifically, they encourage forward and backward tracking to produce consistent motions. In principle, we expect to apply this idea to 3D SOT and make trackers to learn the object's motion distribution in unlabeled data. However, transferring these 2D methods directly to 3D is challenging. First, since the point cloud is sparse and the environment is cluttered with objects, it is hard to find meaningful patches to use as pseudo labels for training. Second, unsupervised 2D SOT methods rely on the assumption that the target appears in every frame of the sequence. Unfortunately, this assumption is not always satisfied in point cloud datasets such as KITTI [5], NuScenes [1], and Waymo [20]. This is because they are built for the multi-object tracking task, and cannot guarantee that the tracking object exists in the whole sequence." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 438, + 287, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 438, + 287, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 438, + 287, + 700 + ], + "type": "text", + "content": "In this paper, we introduce a label-efficient way to train 3D SOT trackers. We call it MixCycle - a 3D SOT approach based on a novel SOTMixup data augmentation strategy for semi-supervised Cycle tracking. Specifically, we first develop a tracking framework exploiting both self and forward-backward tracking cycles. Self tracking consistency is performed to cover the object point cloud appearance variation, and forward-backward consistency is built for learning the object's motion distribution. Second, we present a data augmentation method for 3D SOT called SOTMixup, which is inspired by the success of mixup [31] and Manifold mixup [22]. Without changing the total number of points in the search area, SOTMixup samples points in a random point cloud and the search area point cloud according to the mixing rate and generates training samples. Specifically, the random point cloud is sampled from the labeled training set. SOTMixup thus increases the tracker's robustness to point cloud variations. We evaluate MixCycle on KITTI, NuScenes, and Waymo. As shown in Fig. 1, our experiments clearly demonstrate the label efficiency, generalization and remarkable performance of our method on the 3D SOT task." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 701, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 701, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 701, + 287, + 713 + ], + "type": "text", + "content": "Contributions: (i) We propose the first semi-supervised" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "content": "3D SOT framework. It exploits self and forward-backward consistency as supervision and generalizes to appearance matching-based trackers. (ii) We introduce a SOTMixup augmentation strategy that increases the tracker's robustness to point distribution variations and allows it to learn motion information in extreme situations. (iii) Our framework demonstrates a remarkable performance in terms of label efficiency, achieving better results than existing supervised methods in our experiments on KITTI NuScenes, and Waymo when using fewer labels. In particular, we surpass P2B [16] trained on " + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "content": " labels while only using " + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "content": " labels." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 227, + 392, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 227, + 392, + 239 + ], + "spans": [ + { + "bbox": [ + 306, + 227, + 392, + 239 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 247, + 545, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 247, + 545, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 247, + 545, + 545 + ], + "type": "text", + "content": "3D Single Object Tracking. Since LiDAR is insensitive to illumination, the appearance matching model has become the main choice in the field of 3D single object tracking. Giancola et al. [6] proposed SC3D which is the first method using a Siamese network to deal with this problem. However, it is very time-consuming and inaccurate due to heuristic matching. Zarzar et al. [30] built an end-to-end tracker by using 2D RPN in 2D bird's eyes view (BEV). Unfortunately, the lack of information in one dimension leads to limited accuracy. The point-to-box (P2B) network [16] employs VoteNet[15] as object regression module to construct a point-based tracker. A number of works [4, 9, 10, 25, 34, 18] investigate different architectures of trackers based on P2B [16]. Zheng et al. [34] depicted an object using the point-to-box relation and proposed BoxCloud, which enables the model to better sense the size of objects. Hui et al. [9] discovered the priori information of object shapes in the dataset to obtain dense representations of objects from sparse point clouds. Zheng et al. [35] presented a motion centric method " + }, + { + "bbox": [ + 304, + 247, + 545, + 545 + ], + "type": "inline_equation", + "content": "M^2" + }, + { + "bbox": [ + 304, + 247, + 545, + 545 + ], + "type": "text", + "content": "-Track, which is appearance matching-free and has made great progress in dealing with the sparse point cloud tracking problem. However, " + }, + { + "bbox": [ + 304, + 247, + 545, + 545 + ], + "type": "inline_equation", + "content": "M^2" + }, + { + "bbox": [ + 304, + 247, + 545, + 545 + ], + "type": "text", + "content": "-track is limited by the LiDAR frequency of datasets as object motion in adjacent frames varies with the LiDAR sampling frequency." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "text", + "content": "All the above methods rely on large-scale labeled datasets. Unfortunately, 3D point cloud annotation is labor- and time-consuming. To overcome this, we propose MixCycle, a semi-supervised tracking method based on cycle consistency constraints with SOTMixup data augmentation. Label-Efficient Visual Tracking. Wang et al. [23] proposed unsupervised deep tracking (UDT) with cycle consistency, based on a Siamese correlation filter backbone network. UDT achieved remarkable performance, revealing the potential of unsupervised learning in visual tracking. Yuan et al. [29] improved the UDT approach to make the target features passed forward and backward as similar as possible. The self-supervised fully convolutional Siamese network [19] uses only spatially supervised learning of tar" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13957" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 68, + 547, + 234 + ], + "blocks": [ + { + "bbox": [ + 47, + 68, + 547, + 234 + ], + "lines": [ + { + "bbox": [ + 47, + 68, + 547, + 234 + ], + "spans": [ + { + "bbox": [ + 47, + 68, + 547, + 234 + ], + "type": "image", + "image_path": "f79febe5b5c4ce3e41316e7de7fe6b46f8f668debebe7525810aab10a7d17897.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "lines": [ + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "spans": [ + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "text", + "content": "Figure 3. MixCycle framework. The label is only contained in " + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "inline_equation", + "content": "P_0^s" + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "text", + "content": " of point cloud (PC) sequence " + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "inline_equation", + "content": "\\{P_0^s, P_1^s, \\ldots, P_n^s\\}" + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "text", + "content": ". 1) Self tracking cycle: we first sample a PC " + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "inline_equation", + "content": "P_r^s" + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "text", + "content": " from the labeled training set. Then, we generate pseudo labels by applying SOTMixup and random rigid transformation (Trans.) to " + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "inline_equation", + "content": "P_0^s" + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "inline_equation", + "content": "P_r^s" + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "text", + "content": ". SOTMixup directly mixes " + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "inline_equation", + "content": "P_r^s" + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "inline_equation", + "content": "P_0^s" + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "text", + "content": " based on the number of points with a mixing rate, assigning a reasonable loss weight corresponding to the mixing rate. We employ the consistency between self tracking proposals and pseudo labels to formulate the loss " + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{self}" + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "text", + "content": ". 2) Forward-backward tracking cycle: we leverage forward tracking proposals as pseudo labels and apply a random rigid transformation to them. Then, we employ the consistency between ground truth (GT)/pseudo labels and backward tracking proposals to formulate the losses " + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{con0} / \\{\\mathcal{L}_{con1}, \\ldots, \\mathcal{L}_{con(n-1)}\\}" + }, + { + "bbox": [ + 45, + 238, + 547, + 318 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 336, + 287, + 420 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 336, + 287, + 420 + ], + "spans": [ + { + "bbox": [ + 46, + 336, + 287, + 420 + ], + "type": "text", + "content": "get correspondences in still video frames. Wu et al. [26] proposed a progressive unsupervised learning (PUL) network, which distinguishes the background by contrastive learning and models the regression result noise. PUL thus makes the tracker robust in long-time tracking. Unsupervised single object tracker [36] consists of an online-updating tracker with a novel memory learning scheme." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 422, + 288, + 493 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 422, + 288, + 493 + ], + "spans": [ + { + "bbox": [ + 46, + 422, + 288, + 493 + ], + "type": "text", + "content": "In essence, the above unsupervised trackers all make the implicit assumption that the tracked target exists in every frame of the sequence. Unfortunately, this is not necessarily true in KITTI [5], NuScenes [1], and Waymo [20]. Therefore, the above methods are not directly applicable to 3D SOT." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 496, + 289, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 496, + 289, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 496, + 289, + 700 + ], + "type": "text", + "content": "Mixup Data Augmentation. Data augmentation has become a crucial pre-processing step for many deep learning models. Zhang et al. [31] introduced a data augmentation method called mixup, which linearly interpolates two image samples, and Manifold mixup [22] transfers this idea to high-dimensional feature spaces. By interpolating a new sample, PointMixup [2] extends mixup to point clouds. Mix3D [14] introduces a scene-aware mixup by taking the union of two 3D scenes and their labels after random transformations. Lu et al. [13] developed a directed mixup based on the pixel values. Additionally, a variety of region mixup techniques have been proposed [32, 12, 21, 11]. In the case of outdoor scenes, Xiao et al. [28] combined two images using random rotation. CosMix[17] and structure aware fusion [7] combine point clouds using semantic structures. Fang et al. [3] turned a CAD into a point cloud to combat object occlusion." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 701, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 712 + ], + "type": "text", + "content": "However, the above-mentioned methods are made for the" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 336, + 545, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 336, + 545, + 361 + ], + "spans": [ + { + "bbox": [ + 305, + 336, + 545, + 361 + ], + "type": "text", + "content": "multi-class classification scenario and are not suitable for SOT, which only contains a positive and negative sample." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 371, + 362, + 384 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 371, + 362, + 384 + ], + "spans": [ + { + "bbox": [ + 306, + 371, + 362, + 384 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 391, + 373, + 403 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 391, + 373, + 403 + ], + "spans": [ + { + "bbox": [ + 306, + 391, + 373, + 403 + ], + "type": "text", + "content": "3.1. Overview" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 409, + 545, + 469 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 409, + 545, + 469 + ], + "spans": [ + { + "bbox": [ + 305, + 409, + 545, + 469 + ], + "type": "text", + "content": "The purpose of 3D SOT is to continually locate the target in the search area point cloud sequence " + }, + { + "bbox": [ + 305, + 409, + 545, + 469 + ], + "type": "inline_equation", + "content": "\\mathbf{P}^s = \\{P_0^s,\\dots ,P_k^s,\\dots ,P_n^s |P_k^s\\in \\mathbb{R}^{N_s\\times 3}\\}" + }, + { + "bbox": [ + 305, + 409, + 545, + 469 + ], + "type": "text", + "content": " given the tracking object template point cloud " + }, + { + "bbox": [ + 305, + 409, + 545, + 469 + ], + "type": "inline_equation", + "content": "P_0^o\\in \\mathbb{R}^{N_t\\times 3}" + }, + { + "bbox": [ + 305, + 409, + 545, + 469 + ], + "type": "text", + "content": " and the 3D BBox " + }, + { + "bbox": [ + 305, + 409, + 545, + 469 + ], + "type": "inline_equation", + "content": "B_{0}\\in \\mathbb{R}^{7}" + }, + { + "bbox": [ + 305, + 409, + 545, + 469 + ], + "type": "text", + "content": " in the initial frame. This can be described as" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 359, + 479, + 545, + 495 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 359, + 479, + 545, + 495 + ], + "spans": [ + { + "bbox": [ + 359, + 479, + 545, + 495 + ], + "type": "interline_equation", + "content": "\\left(\\widetilde {P} _ {k + 1} ^ {o}, \\widetilde {B} _ {k + 1}\\right) = \\mathcal {F} \\left(P _ {k + 1} ^ {s}, \\widetilde {P} _ {k} ^ {o}\\right), \\tag {1}", + "image_path": "c47e4ef8075ef0d657d8df838071601ca8e266fbdf52c38d1d2e1bd39760f1eb.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "spans": [ + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "type": "inline_equation", + "content": "\\widetilde{P}_k^o" + }, + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "type": "inline_equation", + "content": "\\widetilde{P}_{k + 1}^o" + }, + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "type": "inline_equation", + "content": "\\widetilde{B}_{k + 1}" + }, + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "type": "text", + "content": " are the predicted target point cloud and 3D BBox in frame " + }, + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "type": "inline_equation", + "content": "k + 1" + }, + { + "bbox": [ + 304, + 499, + 547, + 550 + ], + "type": "text", + "content": ", respectively. By referring to P2B [16] and its follow-ups [4, 9, 10, 18, 25, 34], we summarize the typically 3D SOT loss as" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 314, + 559, + 545, + 573 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 314, + 559, + 545, + 573 + ], + "spans": [ + { + "bbox": [ + 314, + 559, + 545, + 573 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\rho_ {1} \\cdot \\mathcal {L} _ {c l a} + \\rho_ {2} \\cdot \\mathcal {L} _ {p r o p} + \\rho_ {3} \\cdot \\mathcal {L} _ {r e g} + \\rho_ {4} \\cdot \\mathcal {L} _ {b o x}, \\tag {2}", + "image_path": "e0ad59dd492f079a1086303910c2ab984d9c6118f8dea741017f4071c24dbe84.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "type": "text", + "content": " is the manually-tuned hyperparameter, " + }, + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\text{cla}}" + }, + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\text{prop}}" + }, + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\text{reg}}" + }, + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\text{box}}" + }, + { + "bbox": [ + 304, + 582, + 545, + 641 + ], + "type": "text", + "content": " are the losses for foreground-background classification, confidences for the BBox proposals, voting offsets of the seed points, and offsets of the BBox proposals, respectively." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 642, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 714 + ], + "type": "text", + "content": "To address this task, we propose MixCycle, a novel semi-supervised framework for 3D SOT. Illustrated in Fig. 3, MixCycle relies on a SOTMixup data augmentation strategy to tackle data sparsity and diversity (Sec. 3.2). Further, it utilizes self and forward-backward cycle consistencies as sources of supervision to cover the object appear" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13958" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "content": "ance and motion variation (Sec. 3.3). Additionally, we apply rigid transformations to ground truth (GT) labels to generate search areas in unlabeled data (Sec. 3.4)." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 115, + 123, + 129 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 115, + 123, + 129 + ], + "spans": [ + { + "bbox": [ + 47, + 115, + 123, + 129 + ], + "type": "text", + "content": "3.2. SOTMixup" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 134, + 287, + 206 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 134, + 287, + 206 + ], + "spans": [ + { + "bbox": [ + 46, + 134, + 287, + 206 + ], + "type": "text", + "content": "Inspired by the great success of mixup [31], we develop SOTMixup to supply diverse training samples and deal with the point cloud diversity problem, providing a solution for the mixup application in binary classification in SOT task. With two image samples " + }, + { + "bbox": [ + 46, + 134, + 287, + 206 + ], + "type": "inline_equation", + "content": "(I_A, I_B)" + }, + { + "bbox": [ + 46, + 134, + 287, + 206 + ], + "type": "text", + "content": ", mixup can be simply describe as creating an image" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 115, + 214, + 287, + 228 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 115, + 214, + 287, + 228 + ], + "spans": [ + { + "bbox": [ + 115, + 214, + 287, + 228 + ], + "type": "interline_equation", + "content": "I _ {A} ^ {m} = \\lambda I _ {A} + (1 - \\lambda) I _ {B}, \\tag {3}", + "image_path": "5fed01d4263bf299b8dd3ee735663e9a779335db272d4f5ed36e7074ac1c17d5.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 113, + 248, + 287, + 262 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 113, + 248, + 287, + 262 + ], + "spans": [ + { + "bbox": [ + 113, + 248, + 287, + 262 + ], + "type": "interline_equation", + "content": "y _ {A} ^ {m} = \\lambda y _ {A} + (1 - \\lambda) y _ {B}, \\tag {4}", + "image_path": "6bf20559f813bbc07b25c016729bf00566d0dbfc8bbf082d87cffcf85ce25b22.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 266, + 287, + 301 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 266, + 287, + 301 + ], + "spans": [ + { + "bbox": [ + 46, + 266, + 287, + 301 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 266, + 287, + 301 + ], + "type": "inline_equation", + "content": "\\lambda \\in [0,1]" + }, + { + "bbox": [ + 46, + 266, + 287, + 301 + ], + "type": "text", + "content": " is the mixing rate, and " + }, + { + "bbox": [ + 46, + 266, + 287, + 301 + ], + "type": "inline_equation", + "content": "(y_A,y_B)" + }, + { + "bbox": [ + 46, + 266, + 287, + 301 + ], + "type": "text", + "content": " are the image labels. Typically, " + }, + { + "bbox": [ + 46, + 266, + 287, + 301 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 266, + 287, + 301 + ], + "type": "text", + "content": " follows a Beta distribution " + }, + { + "bbox": [ + 46, + 266, + 287, + 301 + ], + "type": "inline_equation", + "content": "\\beta (\\eta ,\\eta)" + }, + { + "bbox": [ + 46, + 266, + 287, + 301 + ], + "type": "text", + "content": ". A multi-class loss is then calculated as" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 71, + 312, + 287, + 324 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 71, + 312, + 287, + 324 + ], + "spans": [ + { + "bbox": [ + 71, + 312, + 287, + 324 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {m u t i - c a l}} = \\lambda \\cdot \\mathcal {C} (\\widetilde {y}, y _ {A}) + (1 - \\lambda) \\cdot \\mathcal {C} (\\widetilde {y}, y _ {B}), \\tag {5}", + "image_path": "42132aa0b8a961cb2c60db2249fcb36bfc493cfc6946dfef59f1b9565430f14f.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "spans": [ + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "inline_equation", + "content": "\\widetilde{y}" + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "text", + "content": " is the predicted label, and " + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "inline_equation", + "content": "\\mathcal{C}" + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "text", + "content": " is the criterion (usually being the cross-entropy loss). Vanilla mixup applies linear interpolation in aligned pixel space. However, this operation is not suitable to unordered point clouds. Furthermore, one of the key challenges for the SOT task is to determine whether the proposal is positive or negative. Multi-class label interpolation approach in mixup cannot be directly applied. Specifically, given the search area PC " + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "inline_equation", + "content": "P_A" + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "text", + "content": " and a random PC " + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "inline_equation", + "content": "P_B" + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "text", + "content": " sampled in the training set, we employ mixup to generate a foreground and background label pair " + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "inline_equation", + "content": "(\\lambda \\cdot y_A, (1 - \\lambda) \\cdot y_B)" + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "text", + "content": ". In practice, this label pair should be set to " + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "inline_equation", + "content": "(y_A, 0)" + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "text", + "content": ", as the points in " + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "inline_equation", + "content": "P_B" + }, + { + "bbox": [ + 46, + 332, + 287, + 489 + ], + "type": "text", + "content": " mismatch the template and should be considered as background." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "spans": [ + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": "We therefore develop a point cloud mixup strategy for SOT based on the number of points, called SOTMixup. As shown in Fig. 4, SOTMixup generates new samples and minimizes the gap between the generated samples and the real sample distribution. Specifically, SOTMixup mixes a point cloud randomly sampled from the training set and the search area point cloud by sampling points using a mixing rate, without changing the total number of points in the search area. First, given point cloud pair " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "(P_A, P_B)" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": ", corresponding binary classification labels " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "(y_A, y_B)" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": ", and a mixing rate " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": ", we separate the backgrounds and object points in " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "P_A" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "P_B" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": " and obtain " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "(P_A^b, P_A^o, P_B^b, P_B^o)" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "P_A^o \\in \\mathbb{R}^{N_A^o \\times 3}" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "P_B^o \\in \\mathbb{R}^{N_B^o \\times 3}" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": ". Second, we generate " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "\\hat{P}_A^o" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "\\hat{P}_B^o" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": " by randomly sampling " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "\\lambda \\times N_A^o" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "(1 - \\lambda) \\times N_A^o" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": " points from " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "P_A^o" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "inline_equation", + "content": "P_B^o" + }, + { + "bbox": [ + 46, + 489, + 287, + 670 + ], + "type": "text", + "content": ", respectively. We then perform SOTMixup as" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 118, + 678, + 287, + 693 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 118, + 678, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 118, + 678, + 287, + 693 + ], + "type": "interline_equation", + "content": "P _ {A} ^ {m} = P _ {A} ^ {b} + \\hat {P} _ {A} ^ {o} + \\hat {P} _ {B} ^ {o}, \\tag {6}", + "image_path": "ccc33175567fdea76a0ba0d09679c44725b422ea4c7a3695662f732bb910c989.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 701, + 249, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 701, + 249, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 701, + 249, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 701, + 249, + 713 + ], + "type": "inline_equation", + "content": "^{\\prime} + ^{\\prime}" + }, + { + "bbox": [ + 47, + 701, + 249, + 713 + ], + "type": "text", + "content": " represents the concatenation operation." + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 306, + 69, + 547, + 224 + ], + "blocks": [ + { + "bbox": [ + 306, + 69, + 547, + 224 + ], + "lines": [ + { + "bbox": [ + 306, + 69, + 547, + 224 + ], + "spans": [ + { + "bbox": [ + 306, + 69, + 547, + 224 + ], + "type": "image", + "image_path": "392cc2a2f5afe57ede32399f731ecda0c8f8519d165c3254767ef68db05a4f05.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 228, + 545, + 293 + ], + "lines": [ + { + "bbox": [ + 305, + 228, + 545, + 293 + ], + "spans": [ + { + "bbox": [ + 305, + 228, + 545, + 293 + ], + "type": "text", + "content": "Figure 4. SOTMixup. First, the search area point cloud (PC) and a point cloud randomly sampled from the labeled training set are segmented into foreground and background, respectively. Second, a mixing rate " + }, + { + "bbox": [ + 305, + 228, + 545, + 293 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 305, + 228, + 545, + 293 + ], + "type": "text", + "content": " is applied to sample two object PCs. Finally, we concatenate the sampled object PCs and search area background to generate the mixed search area." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 313, + 545, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 313, + 545, + 373 + ], + "spans": [ + { + "bbox": [ + 305, + 313, + 545, + 373 + ], + "type": "text", + "content": "Usually, we consider the distance between the predicted object center and the ground truth to be positive if it is less than 0.3 meters, and negative if it is greater than 0.6 meters. The binary cross entropy loss for regression and foreground classification in SOTMixup can be written as" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 310, + 382, + 545, + 396 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 382, + 545, + 396 + ], + "spans": [ + { + "bbox": [ + 310, + 382, + 545, + 396 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {p r o p . m i x}} = - \\left(\\lambda \\cdot y _ {A} \\cdot \\log \\left(s _ {i} ^ {p}\\right) + \\left(1 - y _ {A}\\right) \\cdot \\log \\left(1 - s _ {i} ^ {p}\\right)\\right), \\tag {7}", + "image_path": "cadbe2a1dc4f746e8076490649c158220aaf645a24021e3ff605cef5d4681d16.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 310, + 426, + 545, + 441 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 426, + 545, + 441 + ], + "spans": [ + { + "bbox": [ + 310, + 426, + 545, + 441 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {c l a - m i x}} = - \\left(\\lambda \\cdot y _ {A} \\cdot \\log \\left(b _ {j} ^ {p}\\right) + (1 - y _ {A}) \\cdot \\log \\left(1 - b _ {j} ^ {p}\\right)\\right), \\tag {8}", + "image_path": "9b4efbf38ff012cb4d8737de38d97bc8cf974545bf5ad2f4d6b3151557c1201a.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "spans": [ + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{prop\\_ mix}" + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{cla\\_ mix}" + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": " are the proposal confidence loss and foreground-background classification loss, respectively. " + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "inline_equation", + "content": "s_i^p" + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": " is the confidence score of proposal " + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "inline_equation", + "content": "b_j^p" + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": " is the predicted foreground probability of point " + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": " in search area " + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "inline_equation", + "content": "P^s" + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": ". We replace losses " + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{prop}" + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{cla}" + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{prop\\_ mix} = \\lambda \\cdot \\mathcal{L}_{prop}" + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{cla\\_ mix} = \\lambda \\cdot \\mathcal{L}_{cla}" + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": ". SOTMixup applies a loss weight " + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 305, + 449, + 546, + 628 + ], + "type": "text", + "content": " to the positive proposals and foreground points, but does not change the loss weight of the negative proposals and background points. We reduce the loss penalty on the positive sample prediction scores to lessen the influence on the appearance matching ability of the tracker. We leave the loss weight unchanged for the negative samples. Because we intend the trackers to predict the motion offset of the object even if the object point cloud in the search area has dramatically changed." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 635, + 400, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 635, + 400, + 647 + ], + "spans": [ + { + "bbox": [ + 306, + 635, + 400, + 647 + ], + "type": "text", + "content": "3.3. Cycle Tracking" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 653, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 653, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 305, + 653, + 545, + 712 + ], + "type": "text", + "content": "Self Tracking Cycle. In contrast with existing 2D cycle trackers [23, 24, 36, 29], which only consider forward-backward cycle consistency, we propose to create the self tracking cycle. The motivation is to leverage virtually infinite supervision information contained in the initial frame" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13959" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": "itself. To this end, we first randomly sample a search area point cloud " + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "P_r^s" + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": " and object 3D BBox " + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "B_r" + }, + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": " from the labeled training set. SOTMixup is then applied to generate the mixed point cloud" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 83, + 128, + 287, + 143 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 128, + 287, + 143 + ], + "spans": [ + { + "bbox": [ + 83, + 128, + 287, + 143 + ], + "type": "interline_equation", + "content": "P _ {0} ^ {m} = S O T M i x u p \\left(P _ {0} ^ {s}, B _ {0}, P _ {r} ^ {s}, B _ {r}, \\lambda\\right), \\tag {9}", + "image_path": "818544a712d973909c7d955b3a11b538a8d515761935dd838ae34b288b699db7.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 148, + 287, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 148, + 287, + 186 + ], + "spans": [ + { + "bbox": [ + 47, + 148, + 287, + 186 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 148, + 287, + 186 + ], + "type": "inline_equation", + "content": "\\lambda \\in [0,1]" + }, + { + "bbox": [ + 47, + 148, + 287, + 186 + ], + "type": "text", + "content": " is the mixing rate. Inspired by SC3D [6], we apply a random rigid transformation " + }, + { + "bbox": [ + 47, + 148, + 287, + 186 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 47, + 148, + 287, + 186 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 47, + 148, + 287, + 186 + ], + "type": "inline_equation", + "content": "\\{P_0^m,B_0\\}" + }, + { + "bbox": [ + 47, + 148, + 287, + 186 + ], + "type": "text", + "content": " and generate pseudo labels" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 106, + 193, + 287, + 208 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 106, + 193, + 287, + 208 + ], + "spans": [ + { + "bbox": [ + 106, + 193, + 287, + 208 + ], + "type": "interline_equation", + "content": "\\left(P _ {0} ^ {m t}, B _ {0} ^ {t}\\right) = \\mathcal {T} \\left(P _ {0} ^ {m}, B _ {0}, \\alpha\\right), \\tag {10}", + "image_path": "de28da2673cfc694bd23d163b8daab872ede2d8a18ecec01420d33a7d25494af.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "spans": [ + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "type": "inline_equation", + "content": "P_0^{mt}" + }, + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "type": "text", + "content": " is the search area PC generated by applying SOTMixup and a rigid transformation on " + }, + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "type": "inline_equation", + "content": "P_0^s" + }, + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "type": "inline_equation", + "content": "\\alpha = (\\Delta x, \\Delta y, \\Delta z, \\Delta \\theta)" + }, + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "type": "text", + "content": " is a transformation parameter with a coordinate offset " + }, + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "type": "inline_equation", + "content": "(\\Delta x, \\Delta y, \\Delta z)" + }, + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "type": "text", + "content": " and a rotation degree " + }, + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "type": "inline_equation", + "content": "\\Delta \\theta" + }, + { + "bbox": [ + 47, + 215, + 287, + 276 + ], + "type": "text", + "content": " around the up-axis. This creates a self tracking cycle" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 111, + 281, + 287, + 297 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 281, + 287, + 297 + ], + "spans": [ + { + "bbox": [ + 111, + 281, + 287, + 297 + ], + "type": "interline_equation", + "content": "\\left(\\widetilde {P} _ {0} ^ {o t}, \\widetilde {B} _ {0} ^ {t}\\right) = \\mathcal {F} \\left(P _ {0} ^ {m t}, P _ {0} ^ {o}\\right), \\tag {11}", + "image_path": "bfa22160fe7fc3fe3c238fb2f67bcfdb3537c373304175d5584f38d0302a2b08.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "inline_equation", + "content": "\\widetilde{B}_0^t" + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "content": " is the predicted result on " + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "inline_equation", + "content": "P_0^{mt}" + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "inline_equation", + "content": "P_0^o" + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "content": " is the object template PC cropped from " + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "inline_equation", + "content": "P_0^s" + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "content": ". We then calculate the self consistency loss " + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{self}" + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "content": " between " + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "inline_equation", + "content": "\\widetilde{B}_0^t" + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "inline_equation", + "content": "B_0^t" + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{self}" + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "content": " has the same setting with " + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "inline_equation", + "content": "\\mathcal{L}" + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "content": " of Eq. (2) while corresponding loss with " + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{cal\\_ mix}" + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{prop\\_ mix}" + }, + { + "bbox": [ + 46, + 304, + 287, + 367 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 367, + 287, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 367, + 287, + 437 + ], + "spans": [ + { + "bbox": [ + 46, + 367, + 287, + 437 + ], + "type": "text", + "content": "In the self tracking cycle, the loss weight can be automatically quantified by the mixing rate in SOTMixup. This provides the tracker with simple training samples to make it converge faster in the early stage of training with a high mixing rate, and also allows us to improve the tracker's robustness to point cloud variations using a low mixing rate." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 437, + 287, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 485 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 485 + ], + "type": "text", + "content": "Forward-Backward Tracking Cycle. In addition to self tracking cycles, we also use forward-backward consistency. Hence, we forward track the object in the given search area sequence " + }, + { + "bbox": [ + 46, + 437, + 287, + 485 + ], + "type": "inline_equation", + "content": "\\mathbf{P}^{\\mathrm{s}}" + }, + { + "bbox": [ + 46, + 437, + 287, + 485 + ], + "type": "text", + "content": ", which can be written as" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 116, + 492, + 287, + 509 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 492, + 287, + 509 + ], + "spans": [ + { + "bbox": [ + 116, + 492, + 287, + 509 + ], + "type": "interline_equation", + "content": "\\left(\\widetilde {P} _ {1} ^ {o}, \\widetilde {B} _ {1}\\right) = \\mathcal {F} \\left(P _ {1} ^ {s}, P _ {0} ^ {o}\\right), \\tag {12}", + "image_path": "28d44abae3bfd19a280f2416c7509b022bc62e08310e07c1f97572a5715ff66c.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 116, + 525, + 287, + 540 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 525, + 287, + 540 + ], + "spans": [ + { + "bbox": [ + 116, + 525, + 287, + 540 + ], + "type": "interline_equation", + "content": "\\left(\\widetilde {P} _ {2} ^ {o}, \\widetilde {B} _ {2}\\right) = \\mathcal {F} \\left(P _ {2} ^ {s}, \\widetilde {P} _ {1} ^ {o}\\right), \\tag {13}", + "image_path": "783d168f46eb7de0fbada48214436667a0ef66263d14831478aa486012ce0f28.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "spans": [ + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\{\\widetilde{P}_1^o,\\widetilde{P}_2^o\\}" + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\{\\widetilde{B}_1,\\widetilde{B}_0\\}" + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "text", + "content": " are the predicted forward tracking object point clouds and 3D BBoxes of " + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "inline_equation", + "content": "P_{1}^{s}" + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "inline_equation", + "content": "P_2^s" + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "text", + "content": " respectively. Following this strategy lets us further predict " + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\{\\widetilde{P}_3^o,\\dots ,\\widetilde{P}_n^o\\}" + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\{\\widetilde{B}_3,\\dots ,\\widetilde{B}_n\\}" + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\{P_3^s,\\ldots ,P_n^s\\}" + }, + { + "bbox": [ + 47, + 544, + 287, + 594 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 594, + 287, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 287, + 629 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 287, + 629 + ], + "type": "text", + "content": "Then, we reverse the tracking sequence and perform backward tracking while applying random rigid transformations. This can be expressed as" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 93, + 635, + 287, + 651 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 635, + 287, + 651 + ], + "spans": [ + { + "bbox": [ + 93, + 635, + 287, + 651 + ], + "type": "interline_equation", + "content": "\\left(\\widetilde {P} _ {1} ^ {o \\prime}, \\widetilde {B} _ {1} ^ {\\prime}\\right) = \\mathcal {F} \\left(\\mathcal {T} \\left(P _ {1} ^ {s}, \\widetilde {B} _ {1}, \\alpha\\right), \\widetilde {P} _ {2} ^ {o \\prime}\\right), \\tag {14}", + "image_path": "2339fbc9ba6b696e2a68dcfc9f704aa04aee984b767993b71711bce29658ed4f.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 93, + 669, + 287, + 685 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 669, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 93, + 669, + 287, + 685 + ], + "type": "interline_equation", + "content": "\\left(\\widetilde {P} _ {0} ^ {o \\prime}, \\widetilde {B} _ {0} ^ {\\prime}\\right) = \\mathcal {F} \\left(\\mathcal {T} \\left(P _ {0} ^ {s}, B _ {0}, \\alpha\\right), \\widetilde {P} _ {1} ^ {o \\prime}\\right), \\tag {15}", + "image_path": "c2225603a551ae5d8659406abcef92e2f916e4fd94ffc49d8c74a3ec03ad9855.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 688, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 688, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 688, + 287, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 688, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\{\\widetilde{P}_0^{o'},\\widetilde{P}_1^{o'},\\widetilde{P}_2^{o'}\\}" + }, + { + "bbox": [ + 46, + 688, + 287, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 688, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\{\\widetilde{B}_1',\\widetilde{B}_0'\\}" + }, + { + "bbox": [ + 46, + 688, + 287, + 713 + ], + "type": "text", + "content": " are the predicted backward tracking object point clouds and 3D BBoxes." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "text", + "content": "We then measure the consistency losses " + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{con1}" + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{con0}" + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "text", + "content": " between " + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\widetilde{B}_1^{\\prime}" + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\widetilde{B}_1" + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "text", + "content": ", as well as between " + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\widetilde{B}_0^{\\prime}" + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "B_0" + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "text", + "content": ". Similarly, we can measure the consistency losses " + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{L}_{con2},\\dots,\\mathcal{L}_{con(n - 1)}\\}" + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{con}" + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "text", + "content": " has the same setting with " + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\mathcal{L}" + }, + { + "bbox": [ + 306, + 72, + 545, + 133 + ], + "type": "text", + "content": " of Eq. (2)." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 141, + 545, + 213 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 141, + 545, + 213 + ], + "spans": [ + { + "bbox": [ + 304, + 141, + 545, + 213 + ], + "type": "text", + "content": "The forward-backward tracking cycle provides real and diverse motion consistency, leading trackers to learn the object's motion distribution between two neighboring frames. Furthermore, the tracker's robustness is increased by training with a disturbed template generated by the template update strategy (Sec. 3.4)." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 248, + 440, + 262 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 248, + 440, + 262 + ], + "spans": [ + { + "bbox": [ + 306, + 248, + 440, + 262 + ], + "type": "text", + "content": "3.4. Implementation Details" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "spans": [ + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "type": "text", + "content": "Training & Testing. We train MixCycle using the SGD optimizer with a batch size of 48 and an initial learning rate of 0.01 with a decay rate of " + }, + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "type": "inline_equation", + "content": "5e - 5" + }, + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "type": "text", + "content": " at each epoch. All experiments are conducted using NVIDIA RTX-3090 GPUs. We set " + }, + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "type": "inline_equation", + "content": "n = 2" + }, + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "type": "text", + "content": " and only measure the self and forward-backward cycle consistency losses " + }, + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{self}" + }, + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{con0}" + }, + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "type": "inline_equation", + "content": "P_0^s" + }, + { + "bbox": [ + 304, + 276, + 545, + 407 + ], + "type": "text", + "content": " due to the GPU memory limit. At test time, we track the object frame by frame in a point cloud sequence with labels in the first frame. For both training and testing, our default setting for the template update strategy is to merge the target in the first frame with the predicted previous result." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "spans": [ + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "text", + "content": "Input & Data Augmentation. Our MixCycle takes three frames " + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "inline_equation", + "content": "f + 1" + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "inline_equation", + "content": "f + 2" + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "text", + "content": " as input. For the initial frame " + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "text", + "content": ", we transform the BBox and point clouds to the object coordinate system. For the other frames in the tracking cycle, we transform the BBox and point clouds to the predicted object coordinate system in the last frame. We assume that the motion of the objects across neighboring frames is not significant. We apply random rigid transformations to BBoxes in labeled frames and use them to crop out search areas in the neighboring frames. Only the area within 2 meters around the reference object BBox is considered as input (search area) since we are only interested in the area where the target is expected to appear. The random rigid transformation parameter " + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "text", + "content": " is set to " + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "inline_equation", + "content": "(0.3, 0.3, 0.0, 5.0^{\\circ})" + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "text", + "content": ", and the " + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "text", + "content": " distribution parameter is set to " + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "inline_equation", + "content": "\\eta = 0.5" + }, + { + "bbox": [ + 304, + 417, + 545, + 596 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Loss Function. The loss function of MixCycle is defined as " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{MixCycle} = \\gamma_1\\mathcal{L}_{self} + \\gamma_2\\mathcal{L}_{con0}" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " containing self tracking cycle losses and forward-backward tracking cycle losses. Each of our cycle losses is set according to the original loss setting of the tracker to which we apply MixCycle. Additionally, the corresponding losses are replaced with " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{prop\\_ mix}" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{cla\\_ mix}" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ". We empirically set " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\gamma_1 = 1.0" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\gamma_2 = 2.0" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ", as we expect the tracker to focus more on learning the motion distribution of the object." + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "13960" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 94, + 102, + 501, + 243 + ], + "blocks": [ + { + "bbox": [ + 46, + 69, + 547, + 102 + ], + "lines": [ + { + "bbox": [ + 46, + 69, + 547, + 102 + ], + "spans": [ + { + "bbox": [ + 46, + 69, + 547, + 102 + ], + "type": "text", + "content": "Table 1. Overall performance comparison between our MixCycle and the fully-supervised methods on the KITTI (left) and NuScenes (right) datasets, where the percentage of labels used for training is shown under the dataset names. Improvements based on the same tracker are shown in green. Bold and underline denote the best and the second-best performance, respectively." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 94, + 102, + 501, + 243 + ], + "lines": [ + { + "bbox": [ + 94, + 102, + 501, + 243 + ], + "spans": [ + { + "bbox": [ + 94, + 102, + 501, + 243 + ], + "type": "table", + "html": "
DatasetKITTINuScenes
Sampling Rate1%5%10%0.1%0.5%1%
SuccessP2B [16]6.125.534.315.223.024.3
MLVSNet [25]25.035.536.621.529.934.0
BAT [34]10.121.634.917.526.430.6
Ours(P2B)20.314.2↑36.711.2↑43.89.5↑23.27.9↑34.311.3↑34.310.0↑
Ours(MLVSNet)32.47.4↑38.83.3↑42.66↑31.49.9↑34.54.7↑41.97.9↑
Ours(BAT)19.79.6↑42.220.6↑46.211.3↑24.46.9↑32.86.4↑34.43.8↑
PrecisionP2B [16]5.039.552.713.021.222.6
MLVSNet [25]36.353.254.719.530.435.3
BAT [34]12.335.352.715.225.730.6
Ours(P2B)33.428.4↑55.315.8↑64.211.5↑21.98.9↑34.213↑34.011.4↑
Ours(MLVSNet)49.212.9↑56.63.4↑61.46.7↑31.111.6↑35.24.8↑43.68.3↑
Ours(BAT)27.014.7↑62.327.0↑67.815.1↑22.77.5↑31.96.2↑34.13.5↑
", + "image_path": "c84afc59edfbfc51fb671149dc74b7f105c8de22132a27d411c34577d8be5032.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 49, + 274, + 547, + 411 + ], + "blocks": [ + { + "bbox": [ + 46, + 251, + 546, + 274 + ], + "lines": [ + { + "bbox": [ + 46, + 251, + 546, + 274 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 546, + 274 + ], + "type": "text", + "content": "Table 2. Comparison of MixCycle against fully-supervised methods on each category. We train the models with " + }, + { + "bbox": [ + 46, + 251, + 546, + 274 + ], + "type": "inline_equation", + "content": "1\\% /0.1\\%" + }, + { + "bbox": [ + 46, + 251, + 546, + 274 + ], + "type": "text", + "content": " sampling rate on KITTI/NuScenes. Improvements and decreases based on the same tracker are shown in green and red, respectively." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 274, + 547, + 411 + ], + "lines": [ + { + "bbox": [ + 49, + 274, + 547, + 411 + ], + "spans": [ + { + "bbox": [ + 49, + 274, + 547, + 411 + ], + "type": "table", + "html": "
DatasetKITTI(1%)Nuscenes(0.1%)
Category Frame NumberCar 6424Pedestrian 6088Van 1248Cyclist 308Mean 14068Car 64159Truck 13587Trailer 3352Bus 2953Mean 84051
SuccessP2B [16]8.13.68.15.66.115.813.112.816.115.2
MLVSNet [25]35.315.222.912.825.021.025.222.513.521.5
BAT [34]16.73.87.26.810.117.517.820.414.417.5
Ours(P2B)20.612.5↑22.819.2↑8.00.1↓16.611.0↑20.314.2↑23.07.2↑25.212.1↑22.49.6↑17.71.5↑23.27.9↑
Ours(MLVSNet)43.88.5↑20.75.5↑28.25.3↑43.731.0↑32.47.4↑29.78.7↑42.417.3↑31.38.9↑19.25.7↑31.49.9↑
Ours(BAT)32.615.9↑6.12.3↑16.39.2↑34.127.4↑19.79.6↑24.36.9↑26.99.1↑23.73.2↑16.92.5↑24.46.9↑
PrecisionP2B [16]7.42.26.14.45.014.58.26.88.413.0
MLVSNet [25]46.528.825.416.636.320.520.011.36.419.5
BAT [34]22.72.95.99.512.316.312.29.212.215.2
Ours(P2B)30.022.6↑43.741.5↑6.10.011.16.7↑33.428.4↑23.59.0↑18.910.7↑11.24.4↑14.05.6↑21.98.9↑
Ours(MLVSNet)59.212.7↑40.711.9↑31.15.7↑79.062.4↑49.212.8↑31.110.6↑38.618.6↑19.58.1↑11.55.2↑31.111.6↑
Ours(BAT)43.921.2↑9.36.4↑19.213.2↑57.347.8↑27.014.7↑24.17.8↑21.18.9↑13.84.6↑9.72.6↓22.77.5↑
", + "image_path": "f5be33705bb86a754aabb83ca3eac4ae87f7da9aa637dde75fd88911c14f6044.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 430, + 128, + 443 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 430, + 128, + 443 + ], + "spans": [ + { + "bbox": [ + 47, + 430, + 128, + 443 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 452, + 110, + 463 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 452, + 110, + 463 + ], + "spans": [ + { + "bbox": [ + 47, + 452, + 110, + 463 + ], + "type": "text", + "content": "4.1. Datasets" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 472, + 287, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 287, + 533 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 287, + 533 + ], + "type": "text", + "content": "We evaluate our MixCycle on the challenging 3D visual tracking benchmarks of KITTI [5], NuScenes [1] and Waymo [20] for semi-supervised 3D single object tracking. Semi-supervision labels are generated by applying random sampling to the training set." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 534, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 534, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 534, + 288, + 714 + ], + "type": "text", + "content": "The KITTI tracking dataset contains 21 training sequences and 29 test sequences with 8 types of objects. Following previous works [6, 16, 34, 25], we split the training set into training/validation/testing: Sequences 0-16 are used for training, 17-18 for validation, and 19-20 for testing. The NuScenes dataset contains 1000 scenes and annotations for 23 object classes with accurate 3D BBoxes. NuScenes is officially divided into " + }, + { + "bbox": [ + 46, + 534, + 288, + 714 + ], + "type": "inline_equation", + "content": "700 / 150 / 150" + }, + { + "bbox": [ + 46, + 534, + 288, + 714 + ], + "type": "text", + "content": " scenes for training/validation/testing. Following the setting in [34], we train our MixCycle on the subset \"training_track\" of the training set, and test it on the validation set. Waymo includes 1150 scenes, " + }, + { + "bbox": [ + 46, + 534, + 288, + 714 + ], + "type": "inline_equation", + "content": "798 / 202 / 150" + }, + { + "bbox": [ + 46, + 534, + 288, + 714 + ], + "type": "text", + "content": " scenes for training/validation/testing. Following the setting in [35], we test trackers in the validation set. Compared to KITTI, NuScenes, and Waymo include larger data volumes and" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 432, + 408, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 432, + 408, + 443 + ], + "spans": [ + { + "bbox": [ + 306, + 432, + 408, + 443 + ], + "type": "text", + "content": "more complex scenarios." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 444, + 547, + 528 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 444, + 547, + 528 + ], + "spans": [ + { + "bbox": [ + 304, + 444, + 547, + 528 + ], + "type": "text", + "content": "Evaluation Metrics. In this paper, we use One Pass Evaluation (OPE) [27] to evaluate the Success (Succ.) and Precision (Prec.) of different methods. Success is calculated as the overlap (Intersection Over Union, IoU) between the proposal BBox and the ground truth (GT) BBox. Precision represents the AUC of distance error between the centers of two BBoxes from 0 to 2 meters." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 538, + 534, + 552 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 538, + 534, + 552 + ], + "spans": [ + { + "bbox": [ + 305, + 538, + 534, + 552 + ], + "type": "text", + "content": "4.2. Comparison with Fully-supervised Methods" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 558, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 547, + 715 + ], + "type": "text", + "content": "To the best of our knowledge, no other 3D single object trackers work in a semi-supervision fashion. Therefore, we choose P2B [16], the multi-level voting Siamese network (MLVSNet) [25] and the box-aware tracker (BAT) [34] to validate our method by sharing the same network backbone. Note that BAT is the state-of-the-art (SOTA) method in appearance matching-based trackers, and we regard it as our upper bound. The fully-supervised methods will be trained with labeled data, as their original approaches. We train MixCycle in a semi-supervised way, which uses both labeled and unlabeled data. We do not evaluate the motion-based tracker [35] since it requires 2 consecutive labeled point clouds for training and is not suitable for our training" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "13961" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 102, + 287, + 167 + ], + "blocks": [ + { + "bbox": [ + 47, + 69, + 287, + 102 + ], + "lines": [ + { + "bbox": [ + 47, + 69, + 287, + 102 + ], + "spans": [ + { + "bbox": [ + 47, + 69, + 287, + 102 + ], + "type": "text", + "content": "Table 3. Overall performance comparison on KITTI/NuScenes between our MixCycle with " + }, + { + "bbox": [ + 47, + 69, + 287, + 102 + ], + "type": "inline_equation", + "content": "10\\% /1\\%" + }, + { + "bbox": [ + 47, + 69, + 287, + 102 + ], + "type": "text", + "content": " sampling rates and the fully-supervised methods with " + }, + { + "bbox": [ + 47, + 69, + 287, + 102 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 47, + 69, + 287, + 102 + ], + "type": "text", + "content": " sampling rate." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 102, + 287, + 167 + ], + "lines": [ + { + "bbox": [ + 49, + 102, + 287, + 167 + ], + "spans": [ + { + "bbox": [ + 49, + 102, + 287, + 167 + ], + "type": "table", + "html": "
DatasetMethodSuccessPrecision
KITTIP2B(100%) [16] vs Ours(10%)42.4 vs 43.81.4↑60.0 vs 64.24.2↑
MLVSNet(100%) [25] vs Ours(10%)45.7 vs 42.63.1↓66.6 vs 61.45.2↓
BAT(100%) [34] vs Ours(10%)51.2 vs 46.25.0↓72.8 vs 67.85.0↓
NuScenesP2B(100%) [16] vs Ours(1%)39.7 vs 34.35.4↓42.2 vs 34.08.2↓
MLVSNet(100%) [25] vs Ours(1%)45.7 vs 41.93.8↓47.9 vs 43.64.3↓
BAT(100%) [34] vs Ours(1%)41.8 vs 34.47.4↓42.7 vs 34.18.6↓
", + "image_path": "f73cfab07c930279763bad7c5664c6dd9e09c658c4e71394ab579735cb30e41d.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 50, + 201, + 286, + 281 + ], + "blocks": [ + { + "bbox": [ + 47, + 179, + 286, + 201 + ], + "lines": [ + { + "bbox": [ + 47, + 179, + 286, + 201 + ], + "spans": [ + { + "bbox": [ + 47, + 179, + 286, + 201 + ], + "type": "text", + "content": "Table 4. Comparison of MixCycle against BAT on Car in KITTI for different sampling rates. 'Improv.' denotes Improvement." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 201, + 286, + 281 + ], + "lines": [ + { + "bbox": [ + 50, + 201, + 286, + 281 + ], + "spans": [ + { + "bbox": [ + 50, + 201, + 286, + 281 + ], + "type": "table", + "html": "
Sampling Rate1%5%10%30%50%70%100%
Succ.BAT [34]16.724.344.048.048.755.560.5
Ours(BAT)32.649.255.256.256.660.964.7
Improv.15.9↑24.9↑11.2↑8.2↑7.9↑5.4↑4.2↑
Prec.BAT [34]22.734.857.363.165.369.577.7
Ours(BAT)43.962.170.070.570.375.777.9
Improv.21.2↑27.3↑12.7↑7.4↑5.0↑6.2↑0.2↑
", + "image_path": "013fe6f6dac3aa88a0b8281d827e1484c2dd475f75682bcb3b278ee34bd9c7f5.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 304, + 286, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 286, + 376 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 286, + 376 + ], + "type": "text", + "content": "set generation strategy. We employ different sampling rates for the two datasets. The first reason is that we account for the different scales of the dataset. The second season is that the case of very limited labels is more practical in real applications, and we attempt to set the sampling rate as low as possible within the trainable range." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 377, + 286, + 461 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 377, + 286, + 461 + ], + "spans": [ + { + "bbox": [ + 46, + 377, + 286, + 461 + ], + "type": "text", + "content": "Results on KITTI. 1) We evaluate our MixCycle in 4 categories (Car, Pedestrian, Van and Cyclist) and compare it using 3 sampling rates: " + }, + { + "bbox": [ + 46, + 377, + 286, + 461 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 46, + 377, + 286, + 461 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 377, + 286, + 461 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 46, + 377, + 286, + 461 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 377, + 286, + 461 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 377, + 286, + 461 + ], + "type": "text", + "content": ". As shown in Tab. 1, our method outperforms the fully-supervised approaches under all sampling rates by a large margin. This confirms the high label efficiency of our proposed semi-supervised framework." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "text", + "content": "The performance gap between our MixCycle and the fully-supervised P2B becomes larger as the proportion of labeled samples decreases. In particular, in the extreme case of " + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "text", + "content": " labels usage, we achieve " + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "inline_equation", + "content": "14.2\\%" + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "inline_equation", + "content": "28.4\\%" + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "text", + "content": " improvement in success and precision, respectively, demonstrating the impact of our approach on the baseline method. Interestingly, our MixCycle based on the SOTA fully-supervised method BAT achieves the best results " + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "inline_equation", + "content": "(42.2\\%, 46.2\\%) / (62.3\\%, 67.8\\%)" + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "text", + "content": " in succ./prec.) with " + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "text", + "content": " sampling rates, but the MLVSNet based MixCycle takes the first place " + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "inline_equation", + "content": "(32.4\\% / 49.2\\%)" + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "text", + "content": " in succ./prec.) with " + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "text", + "content": " sampling rate. We believe this is because the multiscale approach in MLVSNet effectively enhances the robustness of its feature representation. The BoxCloud proposed by BAT further strengthens the reliance on labels, leading to a degradation of BAT and MixCycle performance at " + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "text", + "content": " sampling rate. 2) We further present the test results on each category with " + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 46, + 462, + 286, + 713 + ], + "type": "text", + "content": " sampling rate in Tab. 2. We achieve better performance in all categories, except Van on P2B. We assume this to be caused by the less labeled, huge, and moving fast feature of Van, which leads the tracker hard" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 309, + 102, + 545, + 182 + ], + "blocks": [ + { + "bbox": [ + 305, + 68, + 545, + 102 + ], + "lines": [ + { + "bbox": [ + 305, + 68, + 545, + 102 + ], + "spans": [ + { + "bbox": [ + 305, + 68, + 545, + 102 + ], + "type": "text", + "content": "Table 5. Comparison of MixCycle against BAT on Waymo. MixCycle(BAT) is trained only on KITTI with a " + }, + { + "bbox": [ + 305, + 68, + 545, + 102 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 305, + 68, + 545, + 102 + ], + "type": "text", + "content": " sampling rate; BAT* represents BAT trained on Waymo using all the labels." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 102, + 545, + 182 + ], + "lines": [ + { + "bbox": [ + 309, + 102, + 545, + 182 + ], + "spans": [ + { + "bbox": [ + 309, + 102, + 545, + 182 + ], + "type": "table", + "html": "
Category Frame Number MetricsVehicle 1057651 Succ.Pedestrian 510533 Prec.Mean 1568184 Succ.Prec.
BAT [34]26.528.216.531.1
Ours(BAT)31.133.525.546.4
BAT* [34]35.644.222.136.8
", + "image_path": "2f4a327ec433721f8a16cafa24fc234d891bd820d6c3754788061d9983993432.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "spans": [ + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "text", + "content": "to predict a precise motion. The improvements on Cyclist " + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "inline_equation", + "content": "(31.0\\% /62.4\\%)" + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "inline_equation", + "content": "27.4\\% /47.8\\%" + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "text", + "content": " in succ./prec. for P2B and BAT, respectively) and Pedestrian " + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "inline_equation", + "content": "(19.2\\% /41.5\\%)" + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "text", + "content": " in succ./prec. on P2B) reveal the robustness of MixCycle to point cloud variations. As pedestrians and cyclists are usually considered to have the largest point cloud variations due to their small object sizes and the diversity of body motion. 3) In Tab. 3, we compare the performance between fully-supervised methods trained with " + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "text", + "content": " labels and MixCycle trained with " + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "text", + "content": " labels. Although our performance decreases slightly on MLVSNet and BAT, MixCycle still shows a remarkable result (43.8/64.2 in succ./prec.) on P2B. With only " + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "text", + "content": " of the labels, MixCycle based on P2B outperforms the fully-supervised method " + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "inline_equation", + "content": "(1.4\\% /4.2\\%)" + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "text", + "content": " improvement in succ./prec.) using " + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "text", + "content": " of the labels. This confirms the strong ability of our approach to leverage data information and highlights its promise for future developments. 4) We provide the comparison of MixCycle against BAT on Car from KITTI with more sampling rates in Tab. 4. Our Mixcycle not only achieves great improvements in low sampling rates, but also boosts the tracker's performance in the fully-supervised training " + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "inline_equation", + "content": "(4.2 / 0.2" + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "text", + "content": " in succ./prec.). 5) In Fig. 5, we compare MixCycle with BAT trained with " + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 304, + 208, + 545, + 508 + ], + "type": "text", + "content": " labels. MixCycle achieves a better performance in both extremely sparse and complex point clouds." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "content": "Results on NuScenes. Following the setting in BAT [34], we test our MixCycle in 4 categories (Car, Truck, Trailer and Bus). The results of P2B [16], MLVSNet [25] and BAT [34] on NuScenes are provided by " + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "inline_equation", + "content": "M^2" + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "content": "-Track [35] and BAT [34]. 1) We use the published codes of the competitors to obtain results for each sampling rate. We compare them on 3 sampling rates: " + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "inline_equation", + "content": "0.1\\%" + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "inline_equation", + "content": "0.5\\%" + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "content": ", as NuScenes is larger than KITTI. As shown in Tab. 1, MixCycle still outperforms the fully-supervised approaches under all sampling rates. 2) Observing the individual categories in Tab. 2 evidences that MixCycle yields a remarkable improvement on Truck " + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "inline_equation", + "content": "(17.3\\% / 18.6\\%)" + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "inline_equation", + "content": "12.1\\% / 10.7\\%" + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "content": " in succ./prec. on MLVSNet and P2B, respectively) and Car " + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "inline_equation", + "content": "(8.7\\% / 10.6\\%)" + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "content": " in succ./prec. on MLVSNet). However, MixCycle drops by " + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "inline_equation", + "content": "2.6\\%" + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "content": " in precision on Bus, which has fewer labels, a greater size, and high velocity. 3) Moreover, in Tab. 3, we compare the performance of MixCycle trained with " + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 304, + 510, + 545, + 713 + ], + "type": "text", + "content": " labels and" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13962" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 72, + 70, + 523, + 337 + ], + "blocks": [ + { + "bbox": [ + 72, + 70, + 523, + 337 + ], + "lines": [ + { + "bbox": [ + 72, + 70, + 523, + 337 + ], + "spans": [ + { + "bbox": [ + 72, + 70, + 523, + 337 + ], + "type": "image", + "image_path": "e96cb02350fe3a31df26d62b9a84cb5983e06d61e24d6650528e772a9337859e.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 339, + 533, + 352 + ], + "lines": [ + { + "bbox": [ + 47, + 339, + 533, + 352 + ], + "spans": [ + { + "bbox": [ + 47, + 339, + 533, + 352 + ], + "type": "text", + "content": "Figure 5. Visualization. Car&Van: Extremely sparse cases. Pedestrian: Medium density cases. Cyclist: complex environment cases." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 371, + 287, + 442 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 371, + 287, + 442 + ], + "spans": [ + { + "bbox": [ + 46, + 371, + 287, + 442 + ], + "type": "text", + "content": "fully-supervised methods trained with " + }, + { + "bbox": [ + 46, + 371, + 287, + 442 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 46, + 371, + 287, + 442 + ], + "type": "text", + "content": " labels. Our MixCycle based on MLVSNet surpasses the SOTA method BAT despite using significantly fewer labels. On such a challenging dataset with pervasive distractors and drastic appearance changes, our method exhibits even more competitive performance when using few labels." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 444, + 288, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 444, + 288, + 563 + ], + "spans": [ + { + "bbox": [ + 46, + 444, + 288, + 563 + ], + "type": "text", + "content": "Result on Waymo. Following the setting in [35], we test MixCycle in Vehicle and Pedestrian. We use the BAT backbone, and MixCycle(BAT) is only trained on KITTI with a " + }, + { + "bbox": [ + 46, + 444, + 288, + 563 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 444, + 288, + 563 + ], + "type": "text", + "content": " sampling rate. As shown in Tab. 5, MixCycle(BAT) outperforms BAT by " + }, + { + "bbox": [ + 46, + 444, + 288, + 563 + ], + "type": "inline_equation", + "content": "6.1\\%" + }, + { + "bbox": [ + 46, + 444, + 288, + 563 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 444, + 288, + 563 + ], + "type": "inline_equation", + "content": "8.6\\%" + }, + { + "bbox": [ + 46, + 444, + 288, + 563 + ], + "type": "text", + "content": " in terms of mean 'succ.' and 'prec.' values, respectively. More impressively, our performance is close to the fully supervised BAT trained on Waymo (31.2%/41.75% in succ./prec. reported in [34]). To summarize, our MixCycle still delivers excellent results on large-scale datasets." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 574, + 173, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 574, + 173, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 574, + 173, + 586 + ], + "type": "text", + "content": "4.3. Analysis Experiments" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 593, + 287, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 593, + 287, + 687 + ], + "spans": [ + { + "bbox": [ + 46, + 593, + 287, + 687 + ], + "type": "text", + "content": "In this section, we extensively analyze MixCycle with a series of experiments. First, we study the effectiveness of each component in MixCycle. Second, we further analyze the influence of forward-backward cycle step sizes. Finally, we compare the various application ways of SOT-Mixup. All the experiments are conducted on KITTI with " + }, + { + "bbox": [ + 46, + 593, + 287, + 687 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 593, + 287, + 687 + ], + "type": "text", + "content": " sampling rate and with BAT as the backbone network, unless otherwise stated." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "Ablation Study. We conduct experiments to analyze the effectiveness of different modules in MixCycle. First, we ver" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 371, + 545, + 658 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 371, + 545, + 658 + ], + "spans": [ + { + "bbox": [ + 304, + 371, + 545, + 658 + ], + "type": "text", + "content": "if our assumption that appearance matching-based trackers can learn the object's motion distribution. As shown in Tab. 6, the cycle tracking framework yields better performance when using only forward-backward cycle than when using only self cycle (3.5%/5.4% improvement in succ./prec.). Additionally, this supports the intuition that real and diverse motion information is helpful to appearance trackers. Furthermore, combining them boosts the results. Note that the random rigid transformation is necessary for self cycle, otherwise the GT BBox will always be fixed at the origin of the coordinate system. Second, we evaluate the effectiveness of random rigid transformation and SOTMixup in the framework. The performance grows significantly after applying SOTMixup (5.1%/6% improvement in succ./prec.), demonstrating the importance of SOTMixup in semi-supervised tasks. Random rigid transformation plays a negative role in the cycle tracking framework but is practical in MixCycle. We conjecture this to be due to the missing target in the search area caused by random rigid transformation. This phenomenon may occur when the target moves rapidly and the model makes wrong predictions. Applying SOTMixup to the cycle tracking framework can significantly improve the model's tracking capabilities and address this issue." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 665, + 546, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 546, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 546, + 715 + ], + "type": "text", + "content": "Flexibility of MixCycle. We further explore the effect of forward-backward tacking cycle step size. As shown in Tab. 7, we conduct experiments with 2 and 3 step cycles, respectively. Compared to the 2 step cycle, 3 step cycle" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13963" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 113, + 286, + 186 + ], + "blocks": [ + { + "bbox": [ + 47, + 69, + 286, + 112 + ], + "lines": [ + { + "bbox": [ + 47, + 69, + 286, + 112 + ], + "spans": [ + { + "bbox": [ + 47, + 69, + 286, + 112 + ], + "type": "text", + "content": "Table 6. Results of MixCycle when different modules are ablated. 'Self', 'F.-B. Cycle' and 'Trans.' stand for self cycle, forward-backward cycle and random rigid transformation in the forward-backward cycle, respectively." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 113, + 286, + 186 + ], + "lines": [ + { + "bbox": [ + 50, + 113, + 286, + 186 + ], + "spans": [ + { + "bbox": [ + 50, + 113, + 286, + 186 + ], + "type": "table", + "html": "
SelfF.-B. CycleTrans.SOTMixupSuccessPrecision
✓34.911.3↓52.715.1↓
✓38.47.8↓58.19.7↓
✓✓39.56.7↓59.28.6↓
✓✓✓38.87.4↓59.38.5↓
✓✓✓44.61.6↓65.22.6↓
✓✓✓✓46.267.8
", + "image_path": "da122e3330b09a154f16ae10dbedb570b028ed13a4d1cb7a73d3e3385641bac5.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 99, + 213, + 235, + 267 + ], + "blocks": [ + { + "bbox": [ + 61, + 202, + 272, + 213 + ], + "lines": [ + { + "bbox": [ + 61, + 202, + 272, + 213 + ], + "spans": [ + { + "bbox": [ + 61, + 202, + 272, + 213 + ], + "type": "text", + "content": "Table 7. Analysis of the forward-backward cycle step size." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 99, + 213, + 235, + 267 + ], + "lines": [ + { + "bbox": [ + 99, + 213, + 235, + 267 + ], + "spans": [ + { + "bbox": [ + 99, + 213, + 235, + 267 + ], + "type": "table", + "html": "
SuccessPrecision
2 Steps45.866.6
3 Steps46.267.8
Improvement0.4↑1.2↑
", + "image_path": "5affe42bd37b551c11bea17d37e0ae819dafff055c9a7b522e6d62ecd5232acf.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 50, + 328, + 286, + 394 + ], + "blocks": [ + { + "bbox": [ + 47, + 283, + 286, + 327 + ], + "lines": [ + { + "bbox": [ + 47, + 283, + 286, + 327 + ], + "spans": [ + { + "bbox": [ + 47, + 283, + 286, + 327 + ], + "type": "text", + "content": "Table 8. Results of SOTMixup with different settings. 'Template' and 'Search Area' indicate we apply SOTMixup with different inputs. 'Self' indicates we apply SOTMixup in the self cycle. 'Backward' means we apply SOTMixup in backward tracking " + }, + { + "bbox": [ + 47, + 283, + 286, + 327 + ], + "type": "inline_equation", + "content": "P_1^s" + }, + { + "bbox": [ + 47, + 283, + 286, + 327 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 47, + 283, + 286, + 327 + ], + "type": "inline_equation", + "content": "P_0^s" + }, + { + "bbox": [ + 47, + 283, + 286, + 327 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 328, + 286, + 394 + ], + "lines": [ + { + "bbox": [ + 50, + 328, + 286, + 394 + ], + "spans": [ + { + "bbox": [ + 50, + 328, + 286, + 394 + ], + "type": "table", + "html": "
SelfBackwardTemplateSearch AreaSuccessPrecision
✓✓44.71.5↓64.73.1↓
✓✓✓45.40.8↓67.60.2↓
✓✓42.33.9↓634.8↓
✓✓✓44.51.7↓66.11.7↓
✓✓46.267.8
", + "image_path": "aebe9be2c10ac556c81786b8dbed58278e3c29a994c0c525ae07594339b9b13a.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 422, + 286, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 422, + 286, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 422, + 286, + 506 + ], + "type": "text", + "content": "achieves a better performance in both success and precision. This experiment demonstrates the potential of MixCycle for further growth in step size. We believe that larger step sizes can provide a template point cloud disturbed in long sequence tracking, leading to improved model robustness. Furthermore, according to [24], a larger step size more effectively penalizes inaccurate localization." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 510, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 286, + 713 + ], + "type": "text", + "content": "Influence of SOTMixup. In Tab. 8, we compare SOTMixup with different settings. First, we analyze the effect of applying SOTMixup to different inputs (Template and Search Area) while only using it in self cycle. The performance drops when we apply it to the template and to both the template and search area. We consider this to be due to the mismatch with real tracking. As the template is usually accurate while the search area point cloud varies significantly. Note that we share the same " + }, + { + "bbox": [ + 46, + 510, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 510, + 286, + 713 + ], + "type": "text", + "content": " when taking SOTMixup in both the template and search area, and set " + }, + { + "bbox": [ + 46, + 510, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\lambda = 1" + }, + { + "bbox": [ + 46, + 510, + 286, + 713 + ], + "type": "text", + "content": " in the SOTMixup loss. Second, we explore various ways of exploiting SOTMixup in MixCycle. SOTMixup leads to performance degradation when we apply it to backward tracking. This is caused by the disturbance of the template point cloud in backward tracking, making the loss weights misaligned. This further proves that the loss weights provided by SOTMixup are reliable." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 71, + 378, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 71, + 378, + 83 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 378, + 83 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 91, + 545, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 91, + 545, + 186 + ], + "spans": [ + { + "bbox": [ + 304, + 91, + 545, + 186 + ], + "type": "text", + "content": "In this paper, we have presented the first semi-supervised framework, MixCycle, for 3D SOT. Its three main components, self tracking cycle, forward-backward tracking cycle and SOTMixup, have been proposed to achieve robustness to point cloud variations and percept object's motion distribution. Our experiments have demonstrated that MixCycle yields high label efficiency and outperforming fully-supervised approaches using scarce labels." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 187, + 545, + 222 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 187, + 545, + 222 + ], + "spans": [ + { + "bbox": [ + 304, + 187, + 545, + 222 + ], + "type": "text", + "content": "In the future, we plan to develop a more robust tracking network backbone for MixCycle, and thus further enhance its 3D SOT performance." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "spans": [ + { + "bbox": [ + 304, + 223, + 545, + 295 + ], + "type": "text", + "content": "Acknowledgments. This work is supported in part by the National Natural Science Foundation of China (No. 62176242 and 62002295), and NWPU international cooperation and exchange promotion projects (No. 02100-23GH0501). Thank Haozhe Qi for the discussion and preliminary exploration." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13964" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 146 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 146 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 146 + ], + "type": "text", + "content": "[1] Holger Caesar, Varun Bankiti, Alex H. 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In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 13546-13555, 2021. 2, 3, 4" + } + ] + } + ], + "index": 11 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "13966" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/7b5c5fe0-450e-42c0-9209-d2128ddb12f9_content_list.json b/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/7b5c5fe0-450e-42c0-9209-d2128ddb12f9_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..fd09fdf86c3c2a5a9291e90d4113b3e818b7f94a --- /dev/null +++ b/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/7b5c5fe0-450e-42c0-9209-d2128ddb12f9_content_list.json @@ -0,0 +1,1859 @@ +[ + { + "type": "text", + "text": "MixPath: A Unified Approach for One-shot Neural Architecture Search", + "text_level": 1, + "bbox": [ + 122, + 130, + 846, + 151 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Xiangxiang Chu Shun Lu Xudong Li Bo Zhang", + "bbox": [ + 264, + 181, + 702, + 199 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "cxxgtxy@gmail.com, lushun19s@ict.ac.cn, lixudong16@mails.ucas.edu.cn, zhangboyd@qq.com", + "bbox": [ + 192, + 200, + 772, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 251, + 313, + 266 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Blending multiple convolutional kernels is proved advantageous in neural architecture design. However, current two-stage neural architecture search methods are mainly limited to single-path search spaces. How to efficiently search models of multi-path structures remains a difficult problem. In this paper, we are motivated to train a one-shot multi-path supernet to accurately evaluate the candidate architectures. Specifically, we discover that in the studied search spaces, feature vectors summed from multiple paths are nearly multiples of those from a single path. Such disparity perturbs the supernet training and its ranking ability. Therefore, we propose a novel mechanism called Shadow Batch Normalization (SBN) to regularize the disparate feature statistics. Extensive experiments prove that SBNs are capable of stabilizing the optimization and improving ranking performance. We call our unified multi-path one-shot approach as MixPath, which generates a series of models that achieve state-of-the-art results on ImageNet.", + "bbox": [ + 75, + 282, + 473, + 555 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 585, + 209, + 602 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Complete automation in neural network design is one of the most important research directions of automated machine learning [32, 22]. Among various mainstream paradigms, one-shot approaches [13, 8, 19] make use of a weight-sharing mechanism that reduces a large amount of computational cost, but these approaches mainly focus on searching for single-path networks. Observing that a multi-path structure is beneficial for model performance as in Inception [30] and ResNeXT [37], it is necessary to incorporate multi-path structure into the search space. Noticeably, exploring multipath search space is made possible in one-stage approaches like [9] and [26]. However, it poses a challenge for two-stage methods to train a one-shot supernet that can accurately predict the performance of its multi-path submodels.", + "bbox": [ + 75, + 612, + 470, + 824 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Although FairNAS [8] largely alleviates the ranking difficulty in the single-path case with a fairness strategy, it is inherently difficult to apply the same method in a multi-path scenario. It should be emphasized that the most critical point of the two-stage NAS is that the supernet can rank submod", + "bbox": [ + 75, + 824, + 472, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3981cbfa5dcf96d9d90d7aca7f490e595dac55b7ffab4d595c10c2b39f610127.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 531, + 250, + 700, + 362 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/0921f6b56f614797a5ad32638055cc8d2942c90a47b3db9b872f4744c8a1dca3.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 704, + 251, + 862, + 361 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/18ef9506347d71c0f1dba0139e93800a643f15bc04c56a671e2296af7832314d.jpg", + "image_caption": [ + "Figure 1: Top Left: Options in a demo block, where at most $m$ paths can be chosen. Bottom: An example of MixPath supernet training with Shadow Batch Normalizations (SBNs). Note 1x1 Conv is not a must. SBNs are standard BNs, except that SBNs are applied w.r.t the number of activated paths. E.g., $SBN_{1}$ is used whenever only $m' = 1$ path is activated, $SBN_{2}$ for $m' = 2$ paths. Top Right: SBNs catch each of the statistics in two modes (red for $m' = 1$ , green for $m' = 2$ ), however, a single BN (black) can't capture both." + ], + "image_footnote": [], + "bbox": [ + 532, + 363, + 691, + 473 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/824b1db173b9aeb4c47f838c114a9dc3c35f0a35c357dcbc54e10f795797f878.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 692, + 363, + 857, + 473 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "els as accurately as possible. However, we find that a vanilla training of a multi-path supernet (e.g. randomly pick a multipath submodel to train at each step) is not stable to provide a confident ranking because of changing statistics during the sampling process. Therefore, we dive into its real causes and undertake a unified approach to tackle this issue. Our contributions can be summarized as follows.", + "bbox": [ + 496, + 648, + 893, + 753 + ], + "page_idx": 0 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a unified approach for multi-path (say at most $m$ paths are allowed) one-shot NAS, as opposed to the current single-path methods. From this perspective, current one-shot methods [13, 8] become one of our special cases when $m = 1$ .", + "- We disclose why a vanilla multi-path training fails, and we propose a novel yet lightweight mechanism, called shadow batch normalization (SBN, see Fig. 1), to stabi" + ], + "bbox": [ + 517, + 768, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "5972", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "lize the supernet with a negligible cost. By exploiting feature similarity from different paths, we further reduce the number of SBNs to be $m$ , otherwise it would be exponential.", + "bbox": [ + 107, + 90, + 470, + 151 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We reveal that our multi-path supernet is trained with stability due to SBNs. It also comes with boosted ranking performance. Together with post BN calibration, it obtains a high Kendall tau (0.597) on a subset of NAS-Bench-101 [40].", + "- We use extensive experiments to verify the validity of our method across 4 spaces. We search proxely on ImageNet using 10 GPU days. The searched models obtain state-of-the-art performances, which are comparable with MixNet [34] models searched with $200 \\times$ more computing powers. Moreover, our MixPath-B makes use of multi-branch feature aggregation and reaches higher accuracy than EfficientNet-B0 with fewer FLOPS and parameters." + ], + "bbox": [ + 96, + 160, + 472, + 381 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 76, + 391, + 215, + 407 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Conditional batch normalization Batch Normalization (BN) [16] has greatly facilitated the training of neural networks by normalizing layer inputs to have fixed means and variances. Slimmable neural networks[42] introduces a shared supernet that can run with switchable channels at four different scales $(1\\times, 0.75\\times, 0.5\\times, 0.25\\times)$ . Due to feature inconsistency, independent BNs are applied for each switch configuration to encode conditional statistics. However, it is impractical because it requires an increased number of BNs when it has arbitrary channel widths. BatchQuant [1] utilizes BNs to stabilize the mixed-precision supernet training in a single-path MobileNetV3 search space.", + "bbox": [ + 75, + 417, + 468, + 598 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Model ranking correlation It should be emphasized that the ranking ability for the family of two-stage algorithms is of the uttermost importance [2], whose sole purpose is to evaluate networks. To quantitatively analyze their ranking ability, previous works like [43, 8, 20, 46] have applied a Kendall tau measure [17]. To this end, various proxies [32, 47, 48], explicit or implicit performance predictors [23, 21] are developed to avoid the intractable evaluation. Recent one-shot approaches [2, 13, 8] utilize a subnet where each submodel can be rapidly assessed with inherited weights. One-Shot [2] uses dropout (a very sensitive hyperparameter) to simulate sampling and evaluating submodel using a subnet. However, its poor ranking performance prevents it from robustly finding good models [8].", + "bbox": [ + 75, + 598, + 470, + 811 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. MixPath: a unified approach", + "text_level": 1, + "bbox": [ + 76, + 821, + 344, + 839 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3.1. Motivation", + "text_level": 1, + "bbox": [ + 76, + 847, + 199, + 861 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "There is a call for an efficient multi-path one-shot approach. Informally, existing weight-sharing approaches", + "bbox": [ + 76, + 869, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "[22, 9, 13, 8] can be classified into four categories based on two dimensions: stage levels and multi-path support, as shown in Fig. 2. Specifically, DARTS [22] and Fair DARTS [9] both are one-stage methods while the latter allows multiple paths between any two nodes. One-shot methods [13, 8] typically train a supernet in the first stage and evaluate sub-models in the second stage for model selection. So far, the two-stage one-shot methods mainly consider a single-path search space except [2] which involves strong regularization and careful hyper-parameter tuning for supernet training. It is thus natural to study this multi-path counterpart further. MPNAS [35] resorts to reinforcement learning as in [26] for a multi-path searching but verified only on small datasets. ScaleNAS [6] adopts an evolutionary algorithm in a multiscale search space but it is designed for downstream tasks like segmentations and human pose estimation.", + "bbox": [ + 496, + 90, + 893, + 332 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Moreover, it's reasonable to design such a search space regarding two factors. First, multi-path feature aggregation is proven to be useful, such as Inception series [30, 16, 31, 29] and ResNeXt [37]. Second, it has the potential to balance the trade-off between performance and cost.", + "bbox": [ + 496, + 333, + 893, + 409 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/221cc0c0678a59359bf64ec5273cbd8f5f448b956c3bbf2ec670329ca01c9548.jpg", + "image_caption": [ + "Figure 2: A brief taxonomy of weight-sharing NAS. MixPath fills the empty space of two-stage multiple-path methods." + ], + "image_footnote": [], + "bbox": [ + 524, + 421, + 864, + 566 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Without loss of generality, say an inverted bottleneck has an input feature of $C_{in} \\times H \\times W$ , whose number of intermediate and output channels are $C_{mid}$ and $C_{out}$ (same as $C_{in}$ ) respectively. Its computational cost can be formulated as $c_{total} = 2HWC_{in}C_{mid} + k^2HWC_{mid} = 2HWC_{mid}(C_{in} + \\frac{k^2}{2})$ , where $k$ is the kernel size of the depthwise convolution. Usually, the value of $k$ is set to 3 or 5. Since $C_{in}$ typically dominates $\\frac{k^2}{2}$ , we can boost the representative power of depthwise transformation by mixing more kernels with a neglectable increased cost. This design can be regarded as a straightforward combination of MixConv [34] and ResNeXt [37].", + "bbox": [ + 496, + 626, + 893, + 808 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-path supernet is very hard to train. Vanilla training of the multi-path supernet suffers from severe training difficulties. We can simply train a multi-path supernet by randomly activating a multi-path model at a single step. Here we randomly activate or deactivate each operation. However, this training process is very unstable according to our pi-", + "bbox": [ + 496, + 810, + 895, + 901 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "5973", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "lot experiments conducted with the MixPath supernet on ImageNet [11], shown by the blue line in Fig. 3 (a).", + "bbox": [ + 76, + 90, + 468, + 121 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/35f721875880855b31ae6e02d93a7d2ffbf39b2c6407a07d6f48249c00085e84.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 109, + 150, + 437, + 314 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/aece7b0da3d73268f21ba4ecacd039220a721148951484d2e333026e4ca382b0.jpg", + "image_caption": [ + "(a)" + ], + "image_footnote": [], + "bbox": [ + 81, + 340, + 272, + 455 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/a17b506732165f5c3448457dd3d84bdb0436017bc7f1d86c8e30a3578d767aac.jpg", + "image_caption": [ + "(b)", + "Figure 3: (a) Average one-shot validation accuracies (solid line) and their variances (shade) when training the MixPath supernet in $S_{2}$ (activating at most $m = 2$ paths in each MixPath block) on ImageNet. Twenty models are randomly sampled every two epochs. (b) Histogram of accuracies of randomly sampled 3k one-shot models. One-shot models generally come with good performance when SBNs are enabled during supernet training." + ], + "image_footnote": [], + "bbox": [ + 272, + 340, + 465, + 457 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "What might have caused such a problem? It has been pointed out that high cosine similarity of features from different operations is important for training stability [8]. To verify the issue, we draw the cosine similarity matrix of different features from our trained supernet in the top row of Fig. 4 (a). Surprisingly, not only are the features from single-path similar to each other, but also the multi-path features where they get added up. We discover that cosine similarity is limited because it measures the orientation only. The addition of high-dimensional feature vectors does not change their angles too much (as they are similar), but their magnitudes get scaled up, see blue arrows in Fig.4 (b). We can further make a bold postulation that a simple superposition of multiple vectors renders very dynamic statistics, hence it causes training instability. With this motivation in mind, we next scale the feature vectors down to the same magnitude to verify if we can make it stabilized.", + "bbox": [ + 75, + 643, + 472, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Regularizing Multi-path Supernet", + "text_level": 1, + "bbox": [ + 500, + 90, + 797, + 107 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "First of all, we can think of using a large amount of BNs to track the changing statistics. For a thorough regularization, we adopt multiple standard BNs to regularize feature statistics from different combinations of $m$ paths. We call them shadow batch normalizations (SBNs) since they follow the activated paths combinations as shadows. Strictly speaking, in order to regularize all feature combinations in a multi-path setting, the number of SBNs has to grow exponentially. $^{1}$", + "bbox": [ + 496, + 113, + 893, + 234 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2.1 Reduce the complexity from $2^{m}$ to $m$ .", + "text_level": 1, + "bbox": [ + 498, + 253, + 815, + 268 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The above regularization is too costly. As [8] indicates for the single path case, the outputs of different operations at the same layer have higher similarities. It motivates us to reduce the number of shadow BN by diving into the underlying mechanisms further. Informally, if the features of every single path are similar (both magnitude and angles), we can derive that their combinations have similar statistics too, then the number of BNs can be reduced to $m$ . Formally, this can be formulated as follows.", + "bbox": [ + 496, + 277, + 890, + 412 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Definition 1. Zero-order condition: Let two high-dimensional random variables $\\mathbf{y} = \\mathbf{f}(\\mathbf{x}) \\in \\mathbf{R}^{\\mathbf{M} \\times \\mathbf{d}_1}$ and $\\mathbf{z} = \\mathbf{g}(\\mathbf{x}) \\in \\mathbf{R}^{\\mathbf{M} \\times \\mathbf{d}_1}$ , we say that $\\mathbf{y}$ and $\\mathbf{z}$ satisfy the zero-order condition if $|\\mathbf{y} - \\mathbf{z}|_2 \\leq \\epsilon$ for any valid sample $\\mathbf{x} \\in \\mathbf{R}^{\\mathbf{N} \\times \\mathbf{d}}$ , where $\\epsilon$ is a very small positive float number.", + "bbox": [ + 496, + 422, + 893, + 500 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Lemma 3.1. Let $\\mathbf{m}$ be the maximum number of the activable paths, and each pair of operations satisfy the zero-order condition, we can use $\\mathbf{m}$ kinds of expectation and variance to approximate all combinations $(2^{m})$ .", + "bbox": [ + 496, + 508, + 890, + 570 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The proof is provided in A.1 (appendix). Note that the magnitude of $\\epsilon$ largely affects the approximation error. It is pretty straightforward as the expectations and variances are simply scaled up according to the number of additions. For instance, $\\mathbb{E}[\\mathbf{y} + \\mathbf{z}] \\approx \\mathbb{E}[\\mathbf{u} + \\mathbf{v}] \\approx 2\\mathbb{E}[\\mathbf{y}]$ . Lemma 3.1 assures us that we can take $SBN_{i}(i = 1,2,\\dots,m)$ to track the combination that contains $i$ paths. For the multi-path setting, we can observe similar results in Figure 4, which means the requirement of Definition 1 is also satisfied.", + "bbox": [ + 496, + 579, + 890, + 714 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Statistical analysis of Shadow Batch Normalization. We look into the statistics from the supernet trained on CIFAR- $10^{2}$ in search space $S_{1}$ (elaborated later in Section 4.3) (appendix). Without loss of generality, we set $m = 2$ and collect statistics of the four parameters of SBNs across all channels for the first choice block in Fig. 5. Note $SBN_{1}$ captures the statistics of one path, so does $SBN_{2}$ for two paths. Based on the theoretical analysis of Section 3.2, we should have $\\mu_{bn_1} \\approx 0.5\\mu_{bn_2}$ and $\\sigma_{bn_1}^2 \\approx 0.25\\sigma_{bn_2}^2$ . This", + "bbox": [ + 496, + 715, + 893, + 853 + ], + "page_idx": 2 + }, + { + "type": "page_footnote", + "text": "${}^{1}{C}_{m}^{1} + {C}_{m}^{2} + \\cdots + {C}_{m}^{m} = {2}^{m} - 1$", + "bbox": [ + 517, + 861, + 720, + 876 + ], + "page_idx": 2 + }, + { + "type": "page_footnote", + "text": "2It's cheaper to train the supernet on CIFAR-10, and similar observations are also reproducible on ImageNet.", + "bbox": [ + 501, + 876, + 890, + 898 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "5974", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/797186a47f6331dfabc1bab202eb72e45677fc55fdda8adb7492686b4097b365.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 122, + 90, + 197, + 143 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/ba5bda16ef6d8379d36e93abaf208962479a79ac9946a78d2f8650f34aa884b7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 205, + 90, + 279, + 143 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/cb3e842a39b1f1c8998ccfab92563d20ef757a5e8fba3d5812e45162280ab18f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 290, + 90, + 364, + 143 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/36aa0bb4f946faf1a915e717050c79f594927d258f0da86e0c997130c6586dfb.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 372, + 90, + 447, + 143 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/c040e57756835bbd33ef7bf58b392935600ec35a9fbcff1f92faad4834b8a2af.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 454, + 90, + 558, + 152 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/16d2305ff8760c6021d9b818f2f052e8957531524896fd49a593ff4b405c5427.jpg", + "image_caption": [ + "(a) Similarity of multi-path feature vectors" + ], + "image_footnote": [], + "bbox": [ + 205, + 156, + 279, + 208 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/dd0ffb70a22adf4e45115d50375aeac2f7fe4b4eaa15ce8d3d76d4591a964d85.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 290, + 156, + 364, + 207 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/468fba8f263b9b6c1a2178a4c03fef696d618f573a73947f1f78ed635f1e4cf7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 372, + 156, + 447, + 207 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/b1aab83e556bc76a724c567de44caa661fb4c80b960c2af3e3268642658157f9.jpg", + "image_caption": [ + "Figure 4: (a) Features from various path combinations are quite alike (w/ and w/o SBNs). Shown here is the cosine similarity map of first-block feature vectors from the supernets (in $S_{1}$ ). Darker means higher similarity. (b) SBNs regularize the magnitudes of feature vectors (projected into 2-dimensional space here) while vanilla BN cannot. Blue arrows represent the feature vectors obtained before SBNs or a single BN, and red ones after them. Here SBNs transform the magnitudes (19.6, 37.2, 53.7, 68.7) to around 32. BN normalized magnitudes (32.6, 36.6, 50.6, 66.7) are still diverse." + ], + "image_footnote": [], + "bbox": [ + 454, + 156, + 552, + 215 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/f18de9bfc50b4dfbcdeb1d8ca13ebd0f262bb70dcff72bac4b9c6ae8a274383b.jpg", + "image_caption": [ + "(b) Feature vectors projected to 2d space" + ], + "image_footnote": [], + "bbox": [ + 571, + 112, + 694, + 196 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/0d772ced865d7dc66c626d1c5409c8a78fb8b71d6825b14fdcd5991640392862.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 702, + 111, + 825, + 196 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "is consistently observed in the first two columns of Fig. 5. It's also interesting to see that the other two learnable parameters $\\beta$ and $\\gamma$ are quite similar for $SBN_{1}$ and $SBN_{2}$ . This is explainable as SBNs have transformed different statistics to a similar distribution, the parameters of $\\beta$ and $\\gamma$ become very close. Similar results are observed when $m = 3,4$ and in different layers in Fig. 3 and Fig. 4 in C.6 (appendix).", + "bbox": [ + 75, + 353, + 472, + 460 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. MixPath Neural Architecture Search", + "text_level": 1, + "bbox": [ + 76, + 468, + 395, + 483 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Based on the above analysis, we train our multi-path supernet with shadow batch normalizations, which we call the MixPath supernet. Following One-Shot [2], the supernet is used to evaluate models in the predefined search space, which makes our approach a two-stage pipeline: 1) training supernet with SBNs and 2) searching for competitive models. Specifically, in the training stage, we apply random sampling so that multiple paths can be activated at each step, where they add up to a mixed output. We then attach a corresponding SBN to the current path combination. This process is detailed in Algorithm 1 (appendix). Next, similar to [9], we progress with a well-known evolutionary algorithm NSGA-II [10] for searching. In particular, our objectives are to maximize classification accuracy while minimizing the FLOPS. In addition, batch normalization calibration [2, 13, 25], as an orthogonal post-processing trick, is verified effective to further improve the ranking ability.", + "bbox": [ + 75, + 491, + 473, + 750 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 762, + 209, + 779 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Search spaces", + "text_level": 1, + "bbox": [ + 76, + 786, + 218, + 801 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We investigate four search spaces in this paper, from $S_{1}$ to $S_{4}$ . For searching on CIFAR-10, we use $S_{1}$ that contains 12 inverted bottleneck blocks. For ImageNet, we search in $S_{2}$ and $S_{3}$ that are similar to MnasNet [32] and MixNet [34]. For Kendall Tau analysis, we devise a subset of a common benchmark NAS-Bench-101 [40], denoted as $S_{4}$ . The details", + "bbox": [ + 75, + 809, + 470, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Algorithm 1: Stage 1 Supernet training with SBN.", + "bbox": [ + 501, + 353, + 841, + 369 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Input: search space $S_{(n,L)}$ with $n$ choice paths per layer and $L$ layers in total, maximum optional paths $m$ , supernet parameters $\\Theta (n,L)$ , training epochs $N$ , training data loader $D$ , loss function $Loss$ .", + "bbox": [ + 514, + 372, + 893, + 431 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Initialize every $\\theta_{j,l}$ in $\\Theta_{(m,L)}$ , SBN set $\\{SBN_1, SBN_2, \\dots, SBN_n\\}$ in each layer.", + "bbox": [ + 516, + 433, + 890, + 463 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "for $i = 1$ to $N$ do", + "bbox": [ + 517, + 464, + 640, + 477 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "for data, labels in $D$ do", + "bbox": [ + 532, + 478, + 699, + 492 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "for $l = 1$ to $L$ do", + "bbox": [ + 549, + 494, + 666, + 507 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Randomly sample a number $m^{\\prime}$ between 1 and $m$ , then randomly sample $m^{\\prime}$ paths without replacement, where each has output $\\mathbf{o}_i^l$ , and use $SBN_{m^{\\prime}}$ to act on the sum of outputs: $\\mathbf{o}^{l} = SBN_{m^{\\prime}}\\left(\\sum_{i}\\mathbf{o}_{i}^{l}\\right)$", + "bbox": [ + 563, + 508, + 893, + 585 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "end for", + "bbox": [ + 550, + 585, + 602, + 597 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Select model from above sampled index.", + "bbox": [ + 549, + 599, + 820, + 613 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Clear gradients recorder for all parameters.", + "bbox": [ + 549, + 614, + 833, + 628 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Calculate gradients for model based on Loss, data, labels, update $\\theta_{(m,L)}$ by gradients.", + "bbox": [ + 549, + 628, + 893, + 660 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "end for", + "bbox": [ + 532, + 660, + 586, + 672 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "end for", + "bbox": [ + 517, + 675, + 571, + 686 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "of these search spaces are listed in Table 1 (appendix).", + "bbox": [ + 500, + 717, + 857, + 732 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. Ranking ability analysis on NAS-Bench-101", + "text_level": 1, + "bbox": [ + 500, + 741, + 870, + 757 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To show that SBNs can stabilize the supernet training and improve its ranking, we score our method on a subset of a NAS-Bench-101 [40]. Each model is stacked by 9 cells, and every cell has at most 5 internal nodes. We make some adaptations to our method. The first 4 nodes are used to make candidate paths, each has 3 possible operations: $1 \\times 1$ Conv, $3 \\times 3$ Conv, and $3 \\times 3$ Maxpool. The outputs of selected paths are summed up to give input to the fifth node (assigned as $1 \\times 1$ Conv), after which the proposed SBNs are used.", + "bbox": [ + 496, + 763, + 893, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "5975", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/8e6362b0398cf9a12e3c3cd5c0fc0f351429b3effb9e667df36dbab3099259db.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 96, + 88, + 294, + 188 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/99080b0c074231527751d06926dc36fbf1d078b35ac10b4604ee7ca50bde837c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 292, + 90, + 486, + 188 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/69343a9f012e530df428f07655c97cad2102bc991f75f27f76c1937054f2e5d0.jpg", + "image_caption": [ + "Figure 5: Top: Parameters $(\\mu, \\sigma^2, \\gamma, \\beta)$ of the first-layer SBNs in MixPath supernet trained on CIFAR-10 when at most $m = 2$ paths are activated. Specifically, $SBN_1$ and $SBN_2$ represent SBNs for a single path and two paths. Bottom: Histogram of ratios $(SBN_1 / SBN_2)$ for each BN parameter. They center around (0.5, 0.25, 1, 1). Note the mean of $SBN_2$ is roughly twice as that of $SBN_1$ . It's interesting that we have previously forecasted this result." + ], + "image_footnote": [], + "bbox": [ + 101, + 189, + 292, + 252 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/a880fbf4ab6dc9a37fa2a76368bcc8e273058692ab17265201ae3d30e836091f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 295, + 189, + 485, + 252 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/dd63aab65b8c23c26469f598c32c5d5d82db3604b968c37c785db9124c7f45b7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 490, + 90, + 679, + 188 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/2673c26acc7f1e51fddd494aba89813ecdd5fb6bd334b2a94f0fbbe919a419e2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 684, + 90, + 872, + 188 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/455156ffa125b12515d31ebcc4c5725b40ef6a838cef6bacbf2adefe3ccecb18.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 491, + 189, + 679, + 252 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/6d7e50ddd5f6e8be1290a7a95671f55447e9158c0aeff3f11e9c12e3e42e66a0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 684, + 189, + 872, + 251 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The designed cell space is shown in Fig. 6.", + "bbox": [ + 76, + 353, + 359, + 369 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/10a33c9c44153f2623106ab9b18311fa9c7a7694169f8d7ecbf73caf69259e83.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 114, + 388, + 431, + 584 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/72f09e3c57b15d534c45647925a9da8a50dc9cde3c42287154738dd9158048f1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 114, + 594, + 259, + 675 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/2286a72ac9538e72c1266516257a7addbab831e0e5668b92491184fd415fd07d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 272, + 594, + 415, + 675 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/9142a620a7feffb69c8ed80e7f1fdd9ad31fbeaae5ca83c25352752a3d0ca378.jpg", + "image_caption": [ + "Figure 6: (a) Cell space with SBNs in NAS-Bench-101 [40] (b) Ground truth accuracies vs. predictions by one-shot MixPath supernets ( $m = 4$ ) trained with various strategies. We sample 70 models in NAS-Bench-101 [40] (sampling one time) to get the ground-truth. The supernet trained SBN with post BN calibration (top right) gives the best prediction. A vanilla BN alone (w/ SBNs) wrongly pushes models into a narrow range under 0.2." + ], + "image_footnote": [], + "bbox": [ + 116, + 681, + 259, + 762 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/39a6de23efae5e28d808a2c78526cad4c2a3e3985b3279051677cf90b9415fde.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 272, + 681, + 415, + 762 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Firstly, we conduct the baseline experiments on NAS-Bench-101 [40], training with and without SBNs. For the latter, the features from the multi-path are summed up and then divided by the number of activated paths, following a $1 \\times 1$ Conv-BN-ReLU (i.e., a single BN).", + "bbox": [ + 500, + 353, + 893, + 428 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To deeply analyze the model ranking capacity of our method and to understand the effects of SBNs, we conduct two pairs of experiments: (i) vanilla BN vs. SBN (ii) post-calibrated vanilla BN vs. post-calibrated SBN. For all experiments, we train the supernet for 100 epochs with a batch size of 96 and a learning rate of 0.025 on three different seeds. We randomly sample 70 models to find their ground-truth top-1 accuracy from NAS-Bench-101 to obtain Kendall tau [17]. Compared with FairNAS [8] and SGAS [20] utilizing about 10-20 models to calculate Kendall-tau, 70 models are adequate enough to evaluate the ranking performance. We use $m = 4$ in this section. The results are shown in Table 1 and Fig. 6 (b).", + "bbox": [ + 496, + 429, + 893, + 625 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/b80e95382baf0ba73474c054d28937ab650024dfa1dbec3e1f370611b24184fb.jpg", + "table_caption": [ + "Table 1: Comparison of Kendall taus between MixPath supernets ( $m = 4$ ) trained with various strategies. For each control group, we sampled 70 models from NAS-Bench-101 [40] and repeated it 3 times on different seeds. $\\dagger$ : after BN calibration." + ], + "table_footnote": [], + "table_body": "
Strategyw/o Calibrationw/ Calibration
w/o SBN0.117±0.0270.382±0.007
w/ SBN0.393±0.0370.597±0.037
", + "bbox": [ + 535, + 728, + 857, + 781 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Notably, BN post-calibration can boost Kendall tau in each case, which confirms the validity of this post-processing trick [2, 13, 25]. Compared with baseline experiments, the supernet trained with SBNs has a much stronger ranking capacity. Even without calibration, the proposed method", + "bbox": [ + 496, + 797, + 893, + 875 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "3We place $m = 3$ case in ablation study.", + "bbox": [ + 514, + 886, + 735, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "5976", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "still ranks architectures better than the calibrated vanilla BN $(+0.011)$ . The composition of two tricks can further boost the final score to 0.597. Next, we will search for models in the search space commonly used for CIFAR-10 [18] and ImageNet [11] dataset respectively.", + "bbox": [ + 75, + 90, + 470, + 167 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Search on CIFAR-10", + "text_level": 1, + "bbox": [ + 76, + 176, + 272, + 191 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We conduct experiments on CIFAR-10 dataset [18] with a designed search space $S_{1}$ containing 12 inverted bottlenecks [27], each of which has four choices of kernel size (3, 5, 7, 9) for the depthwise layer and two choices (3, 6) for expansion rates. Hence, the size of search space $S_{1}$ ranges from $8^{12}$ ( $m = 1$ ) to $162^{12}$ ( $m = 4$ ). For each case, we train the supernet on CIFAR-10 for 200 epochs. The batch size is set to 96 and we use the SGD optimizer with a momentum of 0.9 and $3 \\times 10^{-4}$ weight decay. We also use a cosine scheduler for the learning rate strategy with an initial value of 0.025. It only takes about 6 GPU hours on a single Tesla V100 GPU in total. The comparison with recent state-of-the-art models is listed in Table 2. Our searched model MixPath-c obtains $97.4\\%$ top-1 accuracy using 493M FLOPS on CIFAR-10, whose architecture is shown in Fig. 5 in C.8 (appendix).", + "bbox": [ + 75, + 200, + 470, + 429 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/e50afc740f7ffd948999a2150d91ceeb9e7c233c368c898fd0ac00d02f0e39c5.jpg", + "table_caption": [ + "Table 2: Comparison on CIFAR-10. †: MultAdds computed from the provided code. *: transferred from ImageNet (search cost is on ImageNet). RL: Reinforcement learning, GD: Gradient-based, OS: one-shot, TF: Transferred." + ], + "table_footnote": [], + "table_body": "
ModelsParams (M)×+ (M)Top-1 (%)TypeCost G·d
NASNet-A [48]3.360897.4RL1800
NASNet-A Large [48]*85.01203098.0TF1800
ENAS [26]4.6626†97.1RL0.5
DARTS [22]3.352897.1GD0.4
RDARTS [44]--97.1GD1.6
SNAS [38]2.942297.0GD1.5
GDAS [12]3.451997.1GD0.2
P-DARTS [5]3.453297.5GD0.3
PC-DARTS [39]3.655897.4GD0.1
DARTS- [7]3.556897.5GD0.4
Few-shot DARTS [45]3.8-97.6GD1.3
MixPath-c (ours)5.449397.4OS0.25
MixNet-M [34]*3.536097.9TF≈3k
MixPath-a (ours)*3.534898.1TF10
MixPath-b (ours)*3.637798.2TF10
", + "bbox": [ + 91, + 515, + 450, + 758 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Proxyless Search on ImageNet", + "text_level": 1, + "bbox": [ + 76, + 786, + 344, + 801 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We search proxelyssly on ImageNet [11] in the search space of MnasNet [32], as this layer-wise search space with inverted bottleneck blocks [27] is also very commonly used [32, 33, 36, 8, 34]. We fix the expansion rate as in [34] and search for the combinations of various depthwise convolutions. Specifically, we search from the kernel sizes (3, 5,", + "bbox": [ + 75, + 809, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "7, 9) and their combinations. We call this search space $S_{2}$ . Moreover, we also construct a search space $S_{3}$ to incorporate architectures like MixNet [34], where we evenly divide the channel dimension of the depthwise layer into 4 groups and search from the kernel sizes (3, 5, 7, 9) for each group. We set $m = 2$ (in $S_{2}$ ) and $m = 1$ (in $S_{3}$ ). In each case, we utilize the same hyper-parameters: a batch size of 1024 and the SGD optimizer with 0.9 momentum and a weight decay of $10^{-5}$ . The initial learning rate is 0.1 with cosine decay and it decreases to 0 within 120 epochs. This takes about 150k times of backpropagation (10 GPU days on Tesla V100). Once the supernet is trained, we adopt NSGA-II [10] for model selection.", + "bbox": [ + 496, + 90, + 893, + 286 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "As per training stand-alone models, we use the same tricks as MixNet-M [34], the results are listed in Table 3. To make fair comparisons, we disable distillation in NAS approaches because it can marginally boost the performance of found models. Our cost in Table 3 includes training supernet (10 GPU days) and NSGA-II (0.3 GPU day). MixPath-A, sampled from the Pareto front in $S_{3}$ (so is MixNet), uses 349M multiply-adds to obtain $76.9\\%$ accuracy on ImageNet. MixPath-B, in $S_{2}$ , uses fewer FLOPS and parameters w.r.t EfficientNet-B0 to obtain $77.2\\%$ . Note SPOS, FBNet, ProxylessNAS are also in $S_{2}$ or similar. In the appendix we list the detailed structures of two models in Fig. 5 of C.8.", + "bbox": [ + 496, + 287, + 893, + 468 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Transferability. We also transfer these models to CIFAR-10 and COCO detection, please refer to Table 2 and C.4.", + "bbox": [ + 498, + 488, + 893, + 518 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Ablation Study and Discussions", + "text_level": 1, + "bbox": [ + 500, + 534, + 790, + 550 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Supernet ranking with different strategies", + "text_level": 1, + "bbox": [ + 500, + 559, + 856, + 575 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To study the individual contribution of SBN and BN postcalibration, we profit from NAS-Bench-101 [40] for ranking calculation since it provides ground truths for all models. Moreover, it allows a fair comparison with other approaches in the same search space. Specifically, we investigate the case $m = 3$ and report the result of each control group using 3 different seeds. Kendall tau [17] is calculated by randomly sampled 70 models.", + "bbox": [ + 496, + 582, + 893, + 702 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Supernet with and without SBNs. Table 4 shows that the supernet trained without SBN is inadequate to evaluate sampled models ( $\\tau = 0.05$ ), which is much lower than the one with a linear number of SBNs ( $\\tau = 0.32$ ). We further quantify the effect of the additional post BN calibration, and both taus can be boosted. Particularly for SBN, it's improved to $0.59(+0.27)$ . Therefore, the combination of SBN and post BN calibration delivers the best ranking performance.", + "bbox": [ + 496, + 704, + 893, + 824 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Linear number of SBNs vs. exponential. Through theoretical analysis, we conclude that a linear number of SBNs are enough to match all the combinations of activable paths, while we can still use its exponential counterpart where every single combination follows an SBN. Table 4 shows that", + "bbox": [ + 496, + 825, + 893, + 898 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "5977", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/162b67c9b7432a9fa8567c4b34090107e1d58a33aa285faf5bd1d872478caa47.jpg", + "table_caption": [ + "Table 3: Comparison with state-of-the-art models on ImageNet. For fair comparisons, we disable distillations for all methods. Search cost is computed by GPU days. $\\dagger$ : TPU days. $\\ddagger$ : w/ distillation." + ], + "table_footnote": [], + "table_body": "
Models×+ (M)#P (M)Top-1 (%)Top-5 (%)Cost G·d
MobileNetV2 [27]3003.472.091.0-
ShuffleNetV2 [24]2993.572.6--
GhostNet 1.3× [14]2267.375.792.7-
DARTS [22]5744.773.3-0.5
P-DARTS[5]5574.975.692.60.3
PC-DARTS [39]5865.374.992.20.1
SGAS (Cri.2 best) [20]5985.475.992.70.25
FairDARTS-C [9]3804.275.192.40.4
MnasNet-A2 [32]3404.875.692.7≈4k
One-Shot Small (F=32) [2]-5.174.2-4†
FBNet-B [36]2954.574.1-9
MobileNetV3 [15]2195.475.292.2≈3k
Proxyless-R [4]3204.074.692.28.3
FairNAS-A [8]3884.675.392.412
Single Path One Shot [13]3283.474.992.012
Single-Path NAS [28]3654.375.092.21.25
OFA w/o PS [3]2354.472.4-50
OFA‡n [3]230-76.0-50
BigNAS-M‡[41]4185.577.493.5-
MixNet-M [34]3605.077.093.3≈3k
MixPath-A (ours)3495.076.993.410.3
MixPath-B (ours)3785.177.293.510.3
", + "bbox": [ + 81, + 165, + 457, + 506 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/93a74018fbc52ca07a24ed77a6d1e1e9a257d237beeb74729d5446b966801d62.jpg", + "table_caption": [ + "Table 4: Kendall taus' comparison between MixPath supernets ( $m = 3$ ) trained with multiple strategies. (same settings as Table 1). ESBN: Exponential SBNs, LSBN: Linear SBNs" + ], + "table_footnote": [], + "table_body": "
τw/o SBNESBNLSBN
w/o Calibration0.05±0.060.37±0.060.32±0.03
w/ Calibration0.43±0.030.34±0.080.59±0.02
", + "bbox": [ + 109, + 582, + 436, + 632 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "linear SBN with BN calibration works best (with the highest $\\tau$ ), while Exp SBN (exponential) performs best if no calibration is applied. Why is it so? Linear SBNs make use of the zero-order condition which is an approximate relationship. Exp SBNs are more accurate since they catch statistics from each of the combinations. However, this makes a wider distribution of learnable parameters $\\gamma, \\beta$ , which is difficult for BN calibration to fit them well. Therefore, we choose Linear SBNs with BN calibration instead. Regarding the Occam's Razor, the linear growing BN generalizes better than the exponential counterpart.", + "bbox": [ + 75, + 657, + 468, + 824 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "One-shot accuracy distribution of candidate models w.r.t. $m$ We run four experiments with $m = 1,2,3,4$ to investigate the effect of SBNs in $S_{1}$ , other settings are kept the same. In total, 1k models are randomly sampled to plot their test accuracy distributions on CIFAR-10 for each $m$", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "in Fig. 7. When $m = 1$ , MixPath falls back to single path. Whereas, SBN begins to demonstrate its power for $m > 1$ , whose absence leads to a bad supernet with lower predicted accuracies and a much larger gap. This indicates the supernet without SBNs severely underestimates the performance of a large proportion of architectures.", + "bbox": [ + 496, + 90, + 893, + 181 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Simple scaling vs. SBNs. Intuitively from the above motivation, simply scaling the magnitudes of all features to the same level in each block could also stabilize the supernet training. We hereby treat simple scaling as a baseline experiment. However, it is somewhat limited because it adjusts magnitudes only. We find that ranking ability after the calibration of the simple scaling case is higher than that of vanilla BNs and exponential SBNs, but it is lower than that of linear SBNs. This is consistent with the baseline experiment in Table 5. Our proposed method with linear SBNs is still the best among all the compared strategies. Note that the simple scaling approach can only roughly scale the magnitudes of the output. In contrast, SBNs can adjust the magnitudes and angles together to better capture the changing distributions.", + "bbox": [ + 496, + 183, + 893, + 395 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/16999e7d24ff9f8d803d523b44df476de69f0e0473e875500de1758fe3e943fb.jpg", + "table_caption": [ + "Table 5: Comparison of Kendall taus between MixPath supernets ( $m = 4$ ) trained with various strategies. We sampled 70 models from NAS-Bench-101 [40] and repeated it 3 times on different seeds. $\\dagger$ : after BN calibration" + ], + "table_footnote": [], + "table_body": "
StrategySimple Scalingw/ SBNs
w/o Calibration0.293±0.0160.393±0.017
Calibration0.472±0.0210.597±0.037
", + "bbox": [ + 535, + 488, + 857, + 537 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Applying SPOS on multi-path search space. We design a \"branch composition\" experiment $m = 4$ in NAS-Bench-101 with 3 candidate operations, leading to 34 possible blocks. We use SPOS [13] to train this supernet with the same hyper-parameters as ours, but we only get a Kendall tau of -0.225 while our method obtains 0.504 in terms of ranking the same sub-models (see Fig. 8). This result is not surprising. We blame the failure of the former approach for the use of an excessive number of blocks, which brings nearly $4 \\times$ more trainable parameters in the supernet (199.7M vs. ours 52.9M). In this case, it's impractical and infeasible for SPOS to work under such setting because it's hard to make candidate blocks fully optimized. In effect, thus-trained supernet is unable to ensure a reliable rank. For example, on average, one block receives an update every 34 iterations, resulting in poor ranking performance. Besides, this approach will encounter memory explosion at a growing $m$ . Even if we can solve the ranking issue, it requires much more GPU memory to save the trainable parameters, which prevents proxyless search on large datasets or big models. In contrast, our method doesn't suffer from these issues.", + "bbox": [ + 496, + 583, + 893, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "5978", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/4660e03161ed6269f9b2493e8618552f01332d097d1a88586d596818f7095f1e.jpg", + "image_caption": [ + "Figure 7: Histogram of one-shot model accuracies sampled from MixPath supernets trained on CIFAR-10 in $S_{1}$ , activating at most $m = 1,2,3,4$ paths respectively. In all cases, the supernet trained without SBNs severely underestimates a large proportion of candidate architectures. Note when $m = 1$ it falls back to a vanilla BN." + ], + "image_footnote": [], + "bbox": [ + 96, + 89, + 292, + 198 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/68c9059767e1eec82a94620aa8c73de79444f2c30472e6b48319937a993fcb80.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 292, + 90, + 486, + 196 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4136c10840931dc6d1d497d01f06fa0753c989d241b6530dc84ff16432ccb408.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 486, + 90, + 679, + 196 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4ae382bd15d9c7f0aaa4c137ee1c707ecf4530ece762b6c900382f341eb42780.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 679, + 90, + 872, + 198 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/609139b758c0d7a3c80dbf27c47b996164d5aef934b5b8933f6a82c066849d7d.jpg", + "image_caption": [ + "Figure 8: Rank performance comparison between 'enumerating all compositions' and our method." + ], + "image_footnote": [], + "bbox": [ + 89, + 277, + 274, + 401 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/663209b5c32a527c99d9a2a13c6b4fe46a48d45a6f78d58a0d8287131cd87339.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 282, + 277, + 467, + 400 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.2. Comparison of search strategies", + "text_level": 1, + "bbox": [ + 76, + 478, + 359, + 494 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We use the search space $S_{3}$ on ImageNet to compare the adopted NSGA-II search algorithm [10] with random search by charting the Pareto-front of models found by both methods in Fig. 1 (appendix). NSGA-II has an advantage that the elite models have higher accuracies and fewer FLOPs.", + "bbox": [ + 75, + 502, + 470, + 578 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.3. Pipeline component analysis", + "text_level": 1, + "bbox": [ + 76, + 587, + 330, + 603 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Apart from the ablation studies on NAS-Bench-101 [40], we make a component analysis of our pipeline in $S_{1}$ . We focus on the supernet training with and without SBN by fixing the second-stage searching algorithm. Each pipeline is run three times on different random seeds. Our goal is to find the best models under 500M FLOPS. As a result, with SBN enabled, we obtain $97.44\\%$ top-1 accuracy, higher than the best $97.12\\%$ when SBN is disabled. This confirms that it mainly benefits from our novel training mechanism.", + "bbox": [ + 75, + 609, + 468, + 746 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.4. Discussions", + "text_level": 1, + "bbox": [ + 76, + 756, + 200, + 770 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Why can SBNs stabilize supernet training and improve ranking ability? We have verified that high cosine similarity is not the only factor that guarantees the stable training of a multi-path supernet. It is more important to ensure that the feature distributions are consistent. Otherwise, the training is disrupted because a single BN is not enough to capture changing statistics from multiple paths. The proposed SBNs are able to track a variety of distribu", + "bbox": [ + 75, + 779, + 472, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "tions, alleviating this instability. Empirically, better training of the supernet also gives more appropriate weights for each subnetwork, with which we can better estimate the ground-truth performance of the stand-alone models.", + "bbox": [ + 496, + 273, + 893, + 333 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Why can SBNs work together with BN postcalibration? According to the analysis in Section 3.2, the parameters $\\mu, \\sigma$ of SBNs that follow a multi-path combination are multiples of those of a single-path, as shown in Fig. 5. But not all the parameters fit well into this relationship, post BN calibration can then readjust the mean and variance of the inputs to fit the learned parameters $\\gamma$ and $\\beta$ . To some extent, it can make up for the gap from the supernet to submodels. Noticeably, SBN is a type of regularization technique during the supernet training, while BN calibration is a post-processing trick. They can work in an orthogonal way and both contribute to the ranking.", + "bbox": [ + 496, + 334, + 893, + 515 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Comparison with Switchable Batch Normalization Switchable BN [42] is only applied to learn the statistics of a limited number $(K)$ of sub-architectures with $K = \\{4,8\\}$ channel configurations. Our SBN is designed to match the changing feature statistics from a more flexible combination of different choice paths, while the number of channels is fixed. The former is used for network pruning while our SBN is to stabilize the training of the multi-path supernet.", + "bbox": [ + 496, + 515, + 893, + 636 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 648, + 617, + 664 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose a unified approach for two-stage one-shot neural architecture search, with a multi-path search space enabled. Existing single-path approaches can thus be regarded as a special case. The proposed method uses SBNs to catch the changing features from various branch combinations, which successfully solves two difficulties of vanilla multi-path methods: the unstable training of supernet and the unbearable weakness of model ranking. Moreover, by exploiting feature similarities from different path combinations, we reduced the number of required exponential SBNs to $m$ , identical to the number of allowed paths. Our method can enjoy the model ranking capacity of the one-shot supernet and robustly search good models across various benchmarks.", + "bbox": [ + 496, + 674, + 893, + 869 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement: This work was supported by National Key R&D Program of China (No. 2022ZD0118700).", + "bbox": [ + 498, + 869, + 893, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "5979", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Haoping Bai, Meng Cao, Ping Huang, and Jiulong Shan. Batchquant: Quantized-for-all architecture search with robust quantizer. 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In CVPR, volume 2, 2018. 2, 6" + ], + "bbox": [ + 78, + 92, + 470, + 893 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "5981", + "bbox": [ + 482, + 945, + 513, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/7b5c5fe0-450e-42c0-9209-d2128ddb12f9_model.json b/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/7b5c5fe0-450e-42c0-9209-d2128ddb12f9_model.json new file mode 100644 index 0000000000000000000000000000000000000000..939fcdadcb2de1790cf8eadf51c0e71ffac2c506 --- /dev/null +++ b/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/7b5c5fe0-450e-42c0-9209-d2128ddb12f9_model.json @@ -0,0 +1,2442 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.124, + 0.131, + 0.848, + 0.152 + ], + "angle": 0, + "content": "MixPath: A Unified Approach for One-shot Neural Architecture Search" + }, + { + "type": "text", + "bbox": [ + 0.266, + 0.182, + 0.704, + 0.2 + ], + "angle": 0, + "content": "Xiangxiang Chu Shun Lu Xudong Li Bo Zhang" + }, + { + "type": "text", + "bbox": [ + 0.194, + 0.202, + 0.773, + 0.217 + ], + "angle": 0, + "content": "cxxgtxy@gmail.com, lushun19s@ict.ac.cn, lixudong16@mails.ucas.edu.cn, zhangboyd@qq.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.252, + 0.314, + 0.267 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.284, + 0.474, + 0.556 + ], + "angle": 0, + "content": "Blending multiple convolutional kernels is proved advantageous in neural architecture design. However, current two-stage neural architecture search methods are mainly limited to single-path search spaces. How to efficiently search models of multi-path structures remains a difficult problem. In this paper, we are motivated to train a one-shot multi-path supernet to accurately evaluate the candidate architectures. Specifically, we discover that in the studied search spaces, feature vectors summed from multiple paths are nearly multiples of those from a single path. Such disparity perturbs the supernet training and its ranking ability. Therefore, we propose a novel mechanism called Shadow Batch Normalization (SBN) to regularize the disparate feature statistics. Extensive experiments prove that SBNs are capable of stabilizing the optimization and improving ranking performance. We call our unified multi-path one-shot approach as MixPath, which generates a series of models that achieve state-of-the-art results on ImageNet." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.587, + 0.21, + 0.603 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.613, + 0.471, + 0.825 + ], + "angle": 0, + "content": "Complete automation in neural network design is one of the most important research directions of automated machine learning [32, 22]. Among various mainstream paradigms, one-shot approaches [13, 8, 19] make use of a weight-sharing mechanism that reduces a large amount of computational cost, but these approaches mainly focus on searching for single-path networks. Observing that a multi-path structure is beneficial for model performance as in Inception [30] and ResNeXT [37], it is necessary to incorporate multi-path structure into the search space. Noticeably, exploring multipath search space is made possible in one-stage approaches like [9] and [26]. However, it poses a challenge for two-stage methods to train a one-shot supernet that can accurately predict the performance of its multi-path submodels." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.473, + 0.902 + ], + "angle": 0, + "content": "Although FairNAS [8] largely alleviates the ranking difficulty in the single-path case with a fairness strategy, it is inherently difficult to apply the same method in a multi-path scenario. It should be emphasized that the most critical point of the two-stage NAS is that the supernet can rank submod" + }, + { + "type": "image", + "bbox": [ + 0.532, + 0.251, + 0.701, + 0.363 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.705, + 0.252, + 0.864, + 0.362 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.533, + 0.364, + 0.692, + 0.474 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.693, + 0.364, + 0.858, + 0.474 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.485, + 0.896, + 0.622 + ], + "angle": 0, + "content": "Figure 1: Top Left: Options in a demo block, where at most \\( m \\) paths can be chosen. Bottom: An example of MixPath supernet training with Shadow Batch Normalizations (SBNs). Note 1x1 Conv is not a must. SBNs are standard BNs, except that SBNs are applied w.r.t the number of activated paths. E.g., \\( SBN_{1} \\) is used whenever only \\( m' = 1 \\) path is activated, \\( SBN_{2} \\) for \\( m' = 2 \\) paths. Top Right: SBNs catch each of the statistics in two modes (red for \\( m' = 1 \\), green for \\( m' = 2 \\)), however, a single BN (black) can't capture both." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.649, + 0.895, + 0.754 + ], + "angle": 0, + "content": "els as accurately as possible. However, we find that a vanilla training of a multi-path supernet (e.g. randomly pick a multipath submodel to train at each step) is not stable to provide a confident ranking because of changing statistics during the sampling process. Therefore, we dive into its real causes and undertake a unified approach to tackle this issue. Our contributions can be summarized as follows." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.769, + 0.894, + 0.844 + ], + "angle": 0, + "content": "- We propose a unified approach for multi-path (say at most \\( m \\) paths are allowed) one-shot NAS, as opposed to the current single-path methods. From this perspective, current one-shot methods [13, 8] become one of our special cases when \\( m = 1 \\)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.856, + 0.895, + 0.901 + ], + "angle": 0, + "content": "- We disclose why a vanilla multi-path training fails, and we propose a novel yet lightweight mechanism, called shadow batch normalization (SBN, see Fig. 1), to stabi" + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.769, + 0.895, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5972" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.108, + 0.092, + 0.471, + 0.152 + ], + "angle": 0, + "content": "lize the supernet with a negligible cost. By exploiting feature similarity from different paths, we further reduce the number of SBNs to be \\( m \\), otherwise it would be exponential." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.161, + 0.472, + 0.237 + ], + "angle": 0, + "content": "- We reveal that our multi-path supernet is trained with stability due to SBNs. It also comes with boosted ranking performance. Together with post BN calibration, it obtains a high Kendall tau (0.597) on a subset of NAS-Bench-101 [40]." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.245, + 0.473, + 0.382 + ], + "angle": 0, + "content": "- We use extensive experiments to verify the validity of our method across 4 spaces. We search proxely on ImageNet using 10 GPU days. The searched models obtain state-of-the-art performances, which are comparable with MixNet [34] models searched with \\(200 \\times\\) more computing powers. Moreover, our MixPath-B makes use of multi-branch feature aggregation and reaches higher accuracy than EfficientNet-B0 with fewer FLOPS and parameters." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.161, + 0.473, + 0.382 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.392, + 0.216, + 0.408 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.418, + 0.47, + 0.599 + ], + "angle": 0, + "content": "Conditional batch normalization Batch Normalization (BN) [16] has greatly facilitated the training of neural networks by normalizing layer inputs to have fixed means and variances. Slimmable neural networks[42] introduces a shared supernet that can run with switchable channels at four different scales \\((1\\times, 0.75\\times, 0.5\\times, 0.25\\times)\\). Due to feature inconsistency, independent BNs are applied for each switch configuration to encode conditional statistics. However, it is impractical because it requires an increased number of BNs when it has arbitrary channel widths. BatchQuant [1] utilizes BNs to stabilize the mixed-precision supernet training in a single-path MobileNetV3 search space." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.599, + 0.471, + 0.812 + ], + "angle": 0, + "content": "Model ranking correlation It should be emphasized that the ranking ability for the family of two-stage algorithms is of the uttermost importance [2], whose sole purpose is to evaluate networks. To quantitatively analyze their ranking ability, previous works like [43, 8, 20, 46] have applied a Kendall tau measure [17]. To this end, various proxies [32, 47, 48], explicit or implicit performance predictors [23, 21] are developed to avoid the intractable evaluation. Recent one-shot approaches [2, 13, 8] utilize a subnet where each submodel can be rapidly assessed with inherited weights. One-Shot [2] uses dropout (a very sensitive hyperparameter) to simulate sampling and evaluating submodel using a subnet. However, its poor ranking performance prevents it from robustly finding good models [8]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.822, + 0.345, + 0.84 + ], + "angle": 0, + "content": "3. MixPath: a unified approach" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.848, + 0.2, + 0.862 + ], + "angle": 0, + "content": "3.1. Motivation" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.473, + 0.903 + ], + "angle": 0, + "content": "There is a call for an efficient multi-path one-shot approach. Informally, existing weight-sharing approaches" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.333 + ], + "angle": 0, + "content": "[22, 9, 13, 8] can be classified into four categories based on two dimensions: stage levels and multi-path support, as shown in Fig. 2. Specifically, DARTS [22] and Fair DARTS [9] both are one-stage methods while the latter allows multiple paths between any two nodes. One-shot methods [13, 8] typically train a supernet in the first stage and evaluate sub-models in the second stage for model selection. So far, the two-stage one-shot methods mainly consider a single-path search space except [2] which involves strong regularization and careful hyper-parameter tuning for supernet training. It is thus natural to study this multi-path counterpart further. MPNAS [35] resorts to reinforcement learning as in [26] for a multi-path searching but verified only on small datasets. ScaleNAS [6] adopts an evolutionary algorithm in a multiscale search space but it is designed for downstream tasks like segmentations and human pose estimation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.334, + 0.895, + 0.41 + ], + "angle": 0, + "content": "Moreover, it's reasonable to design such a search space regarding two factors. First, multi-path feature aggregation is proven to be useful, such as Inception series [30, 16, 31, 29] and ResNeXt [37]. Second, it has the potential to balance the trade-off between performance and cost." + }, + { + "type": "image", + "bbox": [ + 0.526, + 0.422, + 0.866, + 0.567 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.578, + 0.892, + 0.609 + ], + "angle": 0, + "content": "Figure 2: A brief taxonomy of weight-sharing NAS. MixPath fills the empty space of two-stage multiple-path methods." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.627, + 0.895, + 0.809 + ], + "angle": 0, + "content": "Without loss of generality, say an inverted bottleneck has an input feature of \\( C_{in} \\times H \\times W \\), whose number of intermediate and output channels are \\( C_{mid} \\) and \\( C_{out} \\) (same as \\( C_{in} \\)) respectively. Its computational cost can be formulated as \\( c_{total} = 2HWC_{in}C_{mid} + k^2HWC_{mid} = 2HWC_{mid}(C_{in} + \\frac{k^2}{2}) \\), where \\( k \\) is the kernel size of the depthwise convolution. Usually, the value of \\( k \\) is set to 3 or 5. Since \\( C_{in} \\) typically dominates \\( \\frac{k^2}{2} \\), we can boost the representative power of depthwise transformation by mixing more kernels with a neglectable increased cost. This design can be regarded as a straightforward combination of MixConv [34] and ResNeXt [37]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.897, + 0.902 + ], + "angle": 0, + "content": "Multi-path supernet is very hard to train. Vanilla training of the multi-path supernet suffers from severe training difficulties. We can simply train a multi-path supernet by randomly activating a multi-path model at a single step. Here we randomly activate or deactivate each operation. However, this training process is very unstable according to our pi-" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5973" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.122 + ], + "angle": 0, + "content": "lot experiments conducted with the MixPath supernet on ImageNet [11], shown by the blue line in Fig. 3 (a)." + }, + { + "type": "image", + "bbox": [ + 0.11, + 0.151, + 0.439, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.264, + 0.326, + 0.283, + 0.338 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.342, + 0.273, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.274, + 0.342, + 0.466, + 0.458 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.264, + 0.468, + 0.283, + 0.48 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.493, + 0.471, + 0.614 + ], + "angle": 0, + "content": "Figure 3: (a) Average one-shot validation accuracies (solid line) and their variances (shade) when training the MixPath supernet in \\( S_{2} \\) (activating at most \\( m = 2 \\) paths in each MixPath block) on ImageNet. Twenty models are randomly sampled every two epochs. (b) Histogram of accuracies of randomly sampled 3k one-shot models. One-shot models generally come with good performance when SBNs are enabled during supernet training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.473, + 0.902 + ], + "angle": 0, + "content": "What might have caused such a problem? It has been pointed out that high cosine similarity of features from different operations is important for training stability [8]. To verify the issue, we draw the cosine similarity matrix of different features from our trained supernet in the top row of Fig. 4 (a). Surprisingly, not only are the features from single-path similar to each other, but also the multi-path features where they get added up. We discover that cosine similarity is limited because it measures the orientation only. The addition of high-dimensional feature vectors does not change their angles too much (as they are similar), but their magnitudes get scaled up, see blue arrows in Fig.4 (b). We can further make a bold postulation that a simple superposition of multiple vectors renders very dynamic statistics, hence it causes training instability. With this motivation in mind, we next scale the feature vectors down to the same magnitude to verify if we can make it stabilized." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.799, + 0.108 + ], + "angle": 0, + "content": "3.2. Regularizing Multi-path Supernet" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.114, + 0.895, + 0.236 + ], + "angle": 0, + "content": "First of all, we can think of using a large amount of BNs to track the changing statistics. For a thorough regularization, we adopt multiple standard BNs to regularize feature statistics from different combinations of \\( m \\) paths. We call them shadow batch normalizations (SBNs) since they follow the activated paths combinations as shadows. Strictly speaking, in order to regularize all feature combinations in a multi-path setting, the number of SBNs has to grow exponentially.\\(^{1}\\)" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.254, + 0.816, + 0.269 + ], + "angle": 0, + "content": "3.2.1 Reduce the complexity from \\( 2^{m} \\) to \\( m \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.278, + 0.892, + 0.413 + ], + "angle": 0, + "content": "The above regularization is too costly. As [8] indicates for the single path case, the outputs of different operations at the same layer have higher similarities. It motivates us to reduce the number of shadow BN by diving into the underlying mechanisms further. Informally, if the features of every single path are similar (both magnitude and angles), we can derive that their combinations have similar statistics too, then the number of BNs can be reduced to \\( m \\). Formally, this can be formulated as follows." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.424, + 0.894, + 0.5 + ], + "angle": 0, + "content": "Definition 1. Zero-order condition: Let two high-dimensional random variables \\(\\mathbf{y} = \\mathbf{f}(\\mathbf{x}) \\in \\mathbf{R}^{\\mathbf{M} \\times \\mathbf{d}_1}\\) and \\(\\mathbf{z} = \\mathbf{g}(\\mathbf{x}) \\in \\mathbf{R}^{\\mathbf{M} \\times \\mathbf{d}_1}\\), we say that \\(\\mathbf{y}\\) and \\(\\mathbf{z}\\) satisfy the zero-order condition if \\(|\\mathbf{y} - \\mathbf{z}|_2 \\leq \\epsilon\\) for any valid sample \\(\\mathbf{x} \\in \\mathbf{R}^{\\mathbf{N} \\times \\mathbf{d}}\\), where \\(\\epsilon\\) is a very small positive float number." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.51, + 0.892, + 0.571 + ], + "angle": 0, + "content": "Lemma 3.1. Let \\(\\mathbf{m}\\) be the maximum number of the activable paths, and each pair of operations satisfy the zero-order condition, we can use \\(\\mathbf{m}\\) kinds of expectation and variance to approximate all combinations \\((2^{m})\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.58, + 0.892, + 0.715 + ], + "angle": 0, + "content": "The proof is provided in A.1 (appendix). Note that the magnitude of \\(\\epsilon\\) largely affects the approximation error. It is pretty straightforward as the expectations and variances are simply scaled up according to the number of additions. For instance, \\(\\mathbb{E}[\\mathbf{y} + \\mathbf{z}] \\approx \\mathbb{E}[\\mathbf{u} + \\mathbf{v}] \\approx 2\\mathbb{E}[\\mathbf{y}]\\). Lemma 3.1 assures us that we can take \\(SBN_{i}(i = 1,2,\\dots,m)\\) to track the combination that contains \\(i\\) paths. For the multi-path setting, we can observe similar results in Figure 4, which means the requirement of Definition 1 is also satisfied." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.716, + 0.895, + 0.854 + ], + "angle": 0, + "content": "Statistical analysis of Shadow Batch Normalization. We look into the statistics from the supernet trained on CIFAR- \\(10^{2}\\) in search space \\(S_{1}\\) (elaborated later in Section 4.3) (appendix). Without loss of generality, we set \\(m = 2\\) and collect statistics of the four parameters of SBNs across all channels for the first choice block in Fig. 5. Note \\(SBN_{1}\\) captures the statistics of one path, so does \\(SBN_{2}\\) for two paths. Based on the theoretical analysis of Section 3.2, we should have \\(\\mu_{bn_1} \\approx 0.5\\mu_{bn_2}\\) and \\(\\sigma_{bn_1}^2 \\approx 0.25\\sigma_{bn_2}^2\\). This" + }, + { + "type": "page_footnote", + "bbox": [ + 0.518, + 0.862, + 0.721, + 0.877 + ], + "angle": 0, + "content": "\\( {}^{1}{C}_{m}^{1} + {C}_{m}^{2} + \\cdots + {C}_{m}^{m} = {2}^{m} - 1 \\)" + }, + { + "type": "page_footnote", + "bbox": [ + 0.502, + 0.877, + 0.892, + 0.9 + ], + "angle": 0, + "content": "2It's cheaper to train the supernet on CIFAR-10, and similar observations are also reproducible on ImageNet." + }, + { + "type": "list", + "bbox": [ + 0.502, + 0.862, + 0.892, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5974" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.123, + 0.092, + 0.198, + 0.145 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.207, + 0.092, + 0.281, + 0.145 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.291, + 0.092, + 0.365, + 0.145 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.374, + 0.092, + 0.448, + 0.145 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.455, + 0.092, + 0.559, + 0.153 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.206, + 0.157, + 0.28, + 0.209 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.291, + 0.157, + 0.365, + 0.208 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.374, + 0.157, + 0.448, + 0.208 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.455, + 0.157, + 0.553, + 0.217 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.214, + 0.226, + 0.468, + 0.24 + ], + "angle": 0, + "content": "(a) Similarity of multi-path feature vectors" + }, + { + "type": "image", + "bbox": [ + 0.573, + 0.113, + 0.695, + 0.197 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.704, + 0.112, + 0.826, + 0.197 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.589, + 0.204, + 0.83, + 0.219 + ], + "angle": 0, + "content": "(b) Feature vectors projected to 2d space" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.252, + 0.895, + 0.327 + ], + "angle": 0, + "content": "Figure 4: (a) Features from various path combinations are quite alike (w/ and w/o SBNs). Shown here is the cosine similarity map of first-block feature vectors from the supernets (in \\(S_{1}\\)). Darker means higher similarity. (b) SBNs regularize the magnitudes of feature vectors (projected into 2-dimensional space here) while vanilla BN cannot. Blue arrows represent the feature vectors obtained before SBNs or a single BN, and red ones after them. Here SBNs transform the magnitudes (19.6, 37.2, 53.7, 68.7) to around 32. BN normalized magnitudes (32.6, 36.6, 50.6, 66.7) are still diverse." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.354, + 0.473, + 0.462 + ], + "angle": 0, + "content": "is consistently observed in the first two columns of Fig. 5. It's also interesting to see that the other two learnable parameters \\(\\beta\\) and \\(\\gamma\\) are quite similar for \\(SBN_{1}\\) and \\(SBN_{2}\\). This is explainable as SBNs have transformed different statistics to a similar distribution, the parameters of \\(\\beta\\) and \\(\\gamma\\) become very close. Similar results are observed when \\(m = 3,4\\) and in different layers in Fig. 3 and Fig. 4 in C.6 (appendix)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.469, + 0.396, + 0.484 + ], + "angle": 0, + "content": "3.3. MixPath Neural Architecture Search" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.492, + 0.474, + 0.75 + ], + "angle": 0, + "content": "Based on the above analysis, we train our multi-path supernet with shadow batch normalizations, which we call the MixPath supernet. Following One-Shot [2], the supernet is used to evaluate models in the predefined search space, which makes our approach a two-stage pipeline: 1) training supernet with SBNs and 2) searching for competitive models. Specifically, in the training stage, we apply random sampling so that multiple paths can be activated at each step, where they add up to a mixed output. We then attach a corresponding SBN to the current path combination. This process is detailed in Algorithm 1 (appendix). Next, similar to [9], we progress with a well-known evolutionary algorithm NSGA-II [10] for searching. In particular, our objectives are to maximize classification accuracy while minimizing the FLOPS. In addition, batch normalization calibration [2, 13, 25], as an orthogonal post-processing trick, is verified effective to further improve the ranking ability." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.763, + 0.21, + 0.78 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.22, + 0.803 + ], + "angle": 0, + "content": "4.1. Search spaces" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.901 + ], + "angle": 0, + "content": "We investigate four search spaces in this paper, from \\( S_{1} \\) to \\( S_{4} \\). For searching on CIFAR-10, we use \\( S_{1} \\) that contains 12 inverted bottleneck blocks. For ImageNet, we search in \\( S_{2} \\) and \\( S_{3} \\) that are similar to MnasNet [32] and MixNet [34]. For Kendall Tau analysis, we devise a subset of a common benchmark NAS-Bench-101 [40], denoted as \\( S_{4} \\). The details" + }, + { + "type": "code_caption", + "bbox": [ + 0.503, + 0.354, + 0.843, + 0.37 + ], + "angle": 0, + "content": "Algorithm 1: Stage 1 Supernet training with SBN." + }, + { + "type": "text", + "bbox": [ + 0.515, + 0.373, + 0.895, + 0.432 + ], + "angle": 0, + "content": "Input: search space \\( S_{(n,L)} \\) with \\( n \\) choice paths per layer and \\( L \\) layers in total, maximum optional paths \\( m \\), supernet parameters \\( \\Theta (n,L) \\), training epochs \\( N \\), training data loader \\( D \\), loss function \\( Loss \\)." + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.434, + 0.892, + 0.464 + ], + "angle": 0, + "content": "Initialize every \\(\\theta_{j,l}\\) in \\(\\Theta_{(m,L)}\\), SBN set \\(\\{SBN_1, SBN_2, \\dots, SBN_n\\}\\) in each layer." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.465, + 0.641, + 0.478 + ], + "angle": 0, + "content": "for \\(i = 1\\) to \\(N\\) do" + }, + { + "type": "text", + "bbox": [ + 0.534, + 0.479, + 0.7, + 0.493 + ], + "angle": 0, + "content": "for data, labels in \\(D\\) do" + }, + { + "type": "text", + "bbox": [ + 0.55, + 0.495, + 0.668, + 0.508 + ], + "angle": 0, + "content": "for \\(l = 1\\) to \\(L\\) do" + }, + { + "type": "text", + "bbox": [ + 0.565, + 0.509, + 0.895, + 0.586 + ], + "angle": 0, + "content": "Randomly sample a number \\(m^{\\prime}\\) between 1 and \\(m\\) , then randomly sample \\(m^{\\prime}\\) paths without replacement, where each has output \\(\\mathbf{o}_i^l\\) , and use \\(SBN_{m^{\\prime}}\\) to act on the sum of outputs: \\(\\mathbf{o}^{l} = SBN_{m^{\\prime}}\\left(\\sum_{i}\\mathbf{o}_{i}^{l}\\right)\\)" + }, + { + "type": "text", + "bbox": [ + 0.551, + 0.586, + 0.604, + 0.598 + ], + "angle": 0, + "content": "end for" + }, + { + "type": "text", + "bbox": [ + 0.55, + 0.6, + 0.821, + 0.614 + ], + "angle": 0, + "content": "Select model from above sampled index." + }, + { + "type": "text", + "bbox": [ + 0.55, + 0.615, + 0.834, + 0.63 + ], + "angle": 0, + "content": "Clear gradients recorder for all parameters." + }, + { + "type": "text", + "bbox": [ + 0.55, + 0.63, + 0.894, + 0.661 + ], + "angle": 0, + "content": "Calculate gradients for model based on Loss, data, labels, update \\(\\theta_{(m,L)}\\) by gradients." + }, + { + "type": "text", + "bbox": [ + 0.534, + 0.661, + 0.588, + 0.673 + ], + "angle": 0, + "content": "end for" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.676, + 0.572, + 0.688 + ], + "angle": 0, + "content": "end for" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.718, + 0.859, + 0.733 + ], + "angle": 0, + "content": "of these search spaces are listed in Table 1 (appendix)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.742, + 0.871, + 0.758 + ], + "angle": 0, + "content": "4.2. Ranking ability analysis on NAS-Bench-101" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.901 + ], + "angle": 0, + "content": "To show that SBNs can stabilize the supernet training and improve its ranking, we score our method on a subset of a NAS-Bench-101 [40]. Each model is stacked by 9 cells, and every cell has at most 5 internal nodes. We make some adaptations to our method. The first 4 nodes are used to make candidate paths, each has 3 possible operations: \\( 1 \\times 1 \\) Conv, \\( 3 \\times 3 \\) Conv, and \\( 3 \\times 3 \\) Maxpool. The outputs of selected paths are summed up to give input to the fifth node (assigned as \\( 1 \\times 1 \\) Conv), after which the proposed SBNs are used." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5975" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.097, + 0.089, + 0.295, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.293, + 0.092, + 0.487, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.102, + 0.19, + 0.294, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.296, + 0.19, + 0.486, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.491, + 0.092, + 0.681, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.685, + 0.092, + 0.874, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.492, + 0.19, + 0.68, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.686, + 0.19, + 0.874, + 0.252 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.266, + 0.895, + 0.327 + ], + "angle": 0, + "content": "Figure 5: Top: Parameters \\((\\mu, \\sigma^2, \\gamma, \\beta)\\) of the first-layer SBNs in MixPath supernet trained on CIFAR-10 when at most \\(m = 2\\) paths are activated. Specifically, \\(SBN_1\\) and \\(SBN_2\\) represent SBNs for a single path and two paths. Bottom: Histogram of ratios \\((SBN_1 / SBN_2)\\) for each BN parameter. They center around (0.5, 0.25, 1, 1). Note the mean of \\(SBN_2\\) is roughly twice as that of \\(SBN_1\\). It's interesting that we have previously forecasted this result." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.354, + 0.361, + 0.37 + ], + "angle": 0, + "content": "The designed cell space is shown in Fig. 6." + }, + { + "type": "image", + "bbox": [ + 0.116, + 0.389, + 0.432, + 0.585 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.116, + 0.595, + 0.26, + 0.676 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.274, + 0.595, + 0.416, + 0.676 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.117, + 0.683, + 0.26, + 0.763 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.274, + 0.683, + 0.416, + 0.763 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.776, + 0.473, + 0.897 + ], + "angle": 0, + "content": "Figure 6: (a) Cell space with SBNs in NAS-Bench-101 [40] (b) Ground truth accuracies vs. predictions by one-shot MixPath supernets (\\(m = 4\\)) trained with various strategies. We sample 70 models in NAS-Bench-101 [40] (sampling one time) to get the ground-truth. The supernet trained SBN with post BN calibration (top right) gives the best prediction. A vanilla BN alone (w/ SBNs) wrongly pushes models into a narrow range under 0.2." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.354, + 0.894, + 0.429 + ], + "angle": 0, + "content": "Firstly, we conduct the baseline experiments on NAS-Bench-101 [40], training with and without SBNs. For the latter, the features from the multi-path are summed up and then divided by the number of activated paths, following a \\( 1 \\times 1 \\) Conv-BN-ReLU (i.e., a single BN)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.43, + 0.895, + 0.626 + ], + "angle": 0, + "content": "To deeply analyze the model ranking capacity of our method and to understand the effects of SBNs, we conduct two pairs of experiments: (i) vanilla BN vs. SBN (ii) post-calibrated vanilla BN vs. post-calibrated SBN. For all experiments, we train the supernet for 100 epochs with a batch size of 96 and a learning rate of 0.025 on three different seeds. We randomly sample 70 models to find their ground-truth top-1 accuracy from NAS-Bench-101 to obtain Kendall tau [17]. Compared with FairNAS [8] and SGAS [20] utilizing about 10-20 models to calculate Kendall-tau, 70 models are adequate enough to evaluate the ranking performance. We use \\( m = 4 \\) in this section. The results are shown in Table 1 and Fig. 6 (b)." + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.642, + 0.894, + 0.716 + ], + "angle": 0, + "content": "Table 1: Comparison of Kendall taus between MixPath supernets (\\(m = 4\\)) trained with various strategies. For each control group, we sampled 70 models from NAS-Bench-101 [40] and repeated it 3 times on different seeds. \\(\\dagger\\): after BN calibration." + }, + { + "type": "table", + "bbox": [ + 0.536, + 0.729, + 0.858, + 0.782 + ], + "angle": 0, + "content": "
Strategyw/o Calibrationw/ Calibration
w/o SBN0.117±0.0270.382±0.007
w/ SBN0.393±0.0370.597±0.037
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.799, + 0.894, + 0.875 + ], + "angle": 0, + "content": "Notably, BN post-calibration can boost Kendall tau in each case, which confirms the validity of this post-processing trick [2, 13, 25]. Compared with baseline experiments, the supernet trained with SBNs has a much stronger ranking capacity. Even without calibration, the proposed method" + }, + { + "type": "page_footnote", + "bbox": [ + 0.516, + 0.887, + 0.736, + 0.901 + ], + "angle": 0, + "content": "3We place \\(m = 3\\) case in ablation study." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5976" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.168 + ], + "angle": 0, + "content": "still ranks architectures better than the calibrated vanilla BN \\((+0.011)\\). The composition of two tricks can further boost the final score to 0.597. Next, we will search for models in the search space commonly used for CIFAR-10 [18] and ImageNet [11] dataset respectively." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.178, + 0.274, + 0.193 + ], + "angle": 0, + "content": "4.3. Search on CIFAR-10" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.202, + 0.471, + 0.43 + ], + "angle": 0, + "content": "We conduct experiments on CIFAR-10 dataset [18] with a designed search space \\( S_{1} \\) containing 12 inverted bottlenecks [27], each of which has four choices of kernel size (3, 5, 7, 9) for the depthwise layer and two choices (3, 6) for expansion rates. Hence, the size of search space \\( S_{1} \\) ranges from \\( 8^{12} \\) (\\( m = 1 \\)) to \\( 162^{12} \\) (\\( m = 4 \\)). For each case, we train the supernet on CIFAR-10 for 200 epochs. The batch size is set to 96 and we use the SGD optimizer with a momentum of 0.9 and \\( 3 \\times 10^{-4} \\) weight decay. We also use a cosine scheduler for the learning rate strategy with an initial value of 0.025. It only takes about 6 GPU hours on a single Tesla V100 GPU in total. The comparison with recent state-of-the-art models is listed in Table 2. Our searched model MixPath-c obtains \\( 97.4\\% \\) top-1 accuracy using 493M FLOPS on CIFAR-10, whose architecture is shown in Fig. 5 in C.8 (appendix)." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.443, + 0.472, + 0.504 + ], + "angle": 0, + "content": "Table 2: Comparison on CIFAR-10. †: MultAdds computed from the provided code. *: transferred from ImageNet (search cost is on ImageNet). RL: Reinforcement learning, GD: Gradient-based, OS: one-shot, TF: Transferred." + }, + { + "type": "table", + "bbox": [ + 0.093, + 0.516, + 0.451, + 0.759 + ], + "angle": 0, + "content": "
ModelsParams (M)×+ (M)Top-1 (%)TypeCost G·d
NASNet-A [48]3.360897.4RL1800
NASNet-A Large [48]*85.01203098.0TF1800
ENAS [26]4.6626†97.1RL0.5
DARTS [22]3.352897.1GD0.4
RDARTS [44]--97.1GD1.6
SNAS [38]2.942297.0GD1.5
GDAS [12]3.451997.1GD0.2
P-DARTS [5]3.453297.5GD0.3
PC-DARTS [39]3.655897.4GD0.1
DARTS- [7]3.556897.5GD0.4
Few-shot DARTS [45]3.8-97.6GD1.3
MixPath-c (ours)5.449397.4OS0.25
MixNet-M [34]*3.536097.9TF≈3k
MixPath-a (ours)*3.534898.1TF10
MixPath-b (ours)*3.637798.2TF10
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.345, + 0.803 + ], + "angle": 0, + "content": "4.4. Proxyless Search on ImageNet" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.901 + ], + "angle": 0, + "content": "We search proxelyssly on ImageNet [11] in the search space of MnasNet [32], as this layer-wise search space with inverted bottleneck blocks [27] is also very commonly used [32, 33, 36, 8, 34]. We fix the expansion rate as in [34] and search for the combinations of various depthwise convolutions. Specifically, we search from the kernel sizes (3, 5," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.894, + 0.287 + ], + "angle": 0, + "content": "7, 9) and their combinations. We call this search space \\( S_{2} \\). Moreover, we also construct a search space \\( S_{3} \\) to incorporate architectures like MixNet [34], where we evenly divide the channel dimension of the depthwise layer into 4 groups and search from the kernel sizes (3, 5, 7, 9) for each group. We set \\( m = 2 \\) (in \\( S_{2} \\)) and \\( m = 1 \\) (in \\( S_{3} \\)). In each case, we utilize the same hyper-parameters: a batch size of 1024 and the SGD optimizer with 0.9 momentum and a weight decay of \\( 10^{-5} \\). The initial learning rate is 0.1 with cosine decay and it decreases to 0 within 120 epochs. This takes about 150k times of backpropagation (10 GPU days on Tesla V100). Once the supernet is trained, we adopt NSGA-II [10] for model selection." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.288, + 0.895, + 0.469 + ], + "angle": 0, + "content": "As per training stand-alone models, we use the same tricks as MixNet-M [34], the results are listed in Table 3. To make fair comparisons, we disable distillation in NAS approaches because it can marginally boost the performance of found models. Our cost in Table 3 includes training supernet (10 GPU days) and NSGA-II (0.3 GPU day). MixPath-A, sampled from the Pareto front in \\( S_{3} \\) (so is MixNet), uses 349M multiply-adds to obtain \\( 76.9\\% \\) accuracy on ImageNet. MixPath-B, in \\( S_{2} \\), uses fewer FLOPS and parameters w.r.t EfficientNet-B0 to obtain \\( 77.2\\% \\). Note SPOS, FBNet, ProxylessNAS are also in \\( S_{2} \\) or similar. In the appendix we list the detailed structures of two models in Fig. 5 of C.8." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.489, + 0.894, + 0.52 + ], + "angle": 0, + "content": "Transferability. We also transfer these models to CIFAR-10 and COCO detection, please refer to Table 2 and C.4." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.535, + 0.791, + 0.551 + ], + "angle": 0, + "content": "5. Ablation Study and Discussions" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.56, + 0.857, + 0.576 + ], + "angle": 0, + "content": "5.1. Supernet ranking with different strategies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.583, + 0.894, + 0.703 + ], + "angle": 0, + "content": "To study the individual contribution of SBN and BN postcalibration, we profit from NAS-Bench-101 [40] for ranking calculation since it provides ground truths for all models. Moreover, it allows a fair comparison with other approaches in the same search space. Specifically, we investigate the case \\( m = 3 \\) and report the result of each control group using 3 different seeds. Kendall tau [17] is calculated by randomly sampled 70 models." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.894, + 0.825 + ], + "angle": 0, + "content": "Supernet with and without SBNs. Table 4 shows that the supernet trained without SBN is inadequate to evaluate sampled models (\\(\\tau = 0.05\\)), which is much lower than the one with a linear number of SBNs (\\(\\tau = 0.32\\)). We further quantify the effect of the additional post BN calibration, and both taus can be boosted. Particularly for SBN, it's improved to \\(0.59(+0.27)\\). Therefore, the combination of SBN and post BN calibration delivers the best ranking performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.894, + 0.9 + ], + "angle": 0, + "content": "Linear number of SBNs vs. exponential. Through theoretical analysis, we conclude that a linear number of SBNs are enough to match all the combinations of activable paths, while we can still use its exponential counterpart where every single combination follows an SBN. Table 4 shows that" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5977" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.089, + 0.472, + 0.151 + ], + "angle": 0, + "content": "Table 3: Comparison with state-of-the-art models on ImageNet. For fair comparisons, we disable distillations for all methods. Search cost is computed by GPU days. \\(\\dagger\\): TPU days. \\(\\ddagger\\): w/ distillation." + }, + { + "type": "table", + "bbox": [ + 0.083, + 0.166, + 0.459, + 0.507 + ], + "angle": 0, + "content": "
Models×+ (M)#P (M)Top-1 (%)Top-5 (%)Cost G·d
MobileNetV2 [27]3003.472.091.0-
ShuffleNetV2 [24]2993.572.6--
GhostNet 1.3× [14]2267.375.792.7-
DARTS [22]5744.773.3-0.5
P-DARTS[5]5574.975.692.60.3
PC-DARTS [39]5865.374.992.20.1
SGAS (Cri.2 best) [20]5985.475.992.70.25
FairDARTS-C [9]3804.275.192.40.4
MnasNet-A2 [32]3404.875.692.7≈4k
One-Shot Small (F=32) [2]-5.174.2-4†
FBNet-B [36]2954.574.1-9
MobileNetV3 [15]2195.475.292.2≈3k
Proxyless-R [4]3204.074.692.28.3
FairNAS-A [8]3884.675.392.412
Single Path One Shot [13]3283.474.992.012
Single-Path NAS [28]3654.375.092.21.25
OFA w/o PS [3]2354.472.4-50
OFA‡n [3]230-76.0-50
BigNAS-M‡[41]4185.577.493.5-
MixNet-M [34]3605.077.093.3≈3k
MixPath-A (ours)3495.076.993.410.3
MixPath-B (ours)3785.177.293.510.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.522, + 0.472, + 0.568 + ], + "angle": 0, + "content": "Table 4: Kendall taus' comparison between MixPath supernets (\\( m = 3 \\)) trained with multiple strategies. (same settings as Table 1). ESBN: Exponential SBNs, LSBN: Linear SBNs" + }, + { + "type": "table", + "bbox": [ + 0.111, + 0.583, + 0.437, + 0.633 + ], + "angle": 0, + "content": "
τw/o SBNESBNLSBN
w/o Calibration0.05±0.060.37±0.060.32±0.03
w/ Calibration0.43±0.030.34±0.080.59±0.02
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.658, + 0.47, + 0.825 + ], + "angle": 0, + "content": "linear SBN with BN calibration works best (with the highest \\(\\tau\\)), while Exp SBN (exponential) performs best if no calibration is applied. Why is it so? Linear SBNs make use of the zero-order condition which is an approximate relationship. Exp SBNs are more accurate since they catch statistics from each of the combinations. However, this makes a wider distribution of learnable parameters \\(\\gamma, \\beta\\), which is difficult for BN calibration to fit them well. Therefore, we choose Linear SBNs with BN calibration instead. Regarding the Occam's Razor, the linear growing BN generalizes better than the exponential counterpart." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "One-shot accuracy distribution of candidate models w.r.t. \\( m \\) We run four experiments with \\( m = 1,2,3,4 \\) to investigate the effect of SBNs in \\( S_{1} \\), other settings are kept the same. In total, 1k models are randomly sampled to plot their test accuracy distributions on CIFAR-10 for each \\( m \\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.894, + 0.182 + ], + "angle": 0, + "content": "in Fig. 7. When \\( m = 1 \\), MixPath falls back to single path. Whereas, SBN begins to demonstrate its power for \\( m > 1 \\), whose absence leads to a bad supernet with lower predicted accuracies and a much larger gap. This indicates the supernet without SBNs severely underestimates the performance of a large proportion of architectures." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.184, + 0.895, + 0.396 + ], + "angle": 0, + "content": "Simple scaling vs. SBNs. Intuitively from the above motivation, simply scaling the magnitudes of all features to the same level in each block could also stabilize the supernet training. We hereby treat simple scaling as a baseline experiment. However, it is somewhat limited because it adjusts magnitudes only. We find that ranking ability after the calibration of the simple scaling case is higher than that of vanilla BNs and exponential SBNs, but it is lower than that of linear SBNs. This is consistent with the baseline experiment in Table 5. Our proposed method with linear SBNs is still the best among all the compared strategies. Note that the simple scaling approach can only roughly scale the magnitudes of the output. In contrast, SBNs can adjust the magnitudes and angles together to better capture the changing distributions." + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.412, + 0.894, + 0.473 + ], + "angle": 0, + "content": "Table 5: Comparison of Kendall taus between MixPath supernets (\\(m = 4\\)) trained with various strategies. We sampled 70 models from NAS-Bench-101 [40] and repeated it 3 times on different seeds. \\(\\dagger\\): after BN calibration" + }, + { + "type": "table", + "bbox": [ + 0.536, + 0.489, + 0.859, + 0.538 + ], + "angle": 0, + "content": "
StrategySimple Scalingw/ SBNs
w/o Calibration0.293±0.0160.393±0.017
Calibration0.472±0.0210.597±0.037
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.584, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Applying SPOS on multi-path search space. We design a \"branch composition\" experiment \\( m = 4 \\) in NAS-Bench-101 with 3 candidate operations, leading to 34 possible blocks. We use SPOS [13] to train this supernet with the same hyper-parameters as ours, but we only get a Kendall tau of -0.225 while our method obtains 0.504 in terms of ranking the same sub-models (see Fig. 8). This result is not surprising. We blame the failure of the former approach for the use of an excessive number of blocks, which brings nearly \\( 4 \\times \\) more trainable parameters in the supernet (199.7M vs. ours 52.9M). In this case, it's impractical and infeasible for SPOS to work under such setting because it's hard to make candidate blocks fully optimized. In effect, thus-trained supernet is unable to ensure a reliable rank. For example, on average, one block receives an update every 34 iterations, resulting in poor ranking performance. Besides, this approach will encounter memory explosion at a growing \\( m \\). Even if we can solve the ranking issue, it requires much more GPU memory to save the trainable parameters, which prevents proxyless search on large datasets or big models. In contrast, our method doesn't suffer from these issues." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5978" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.097, + 0.09, + 0.293, + 0.199 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.293, + 0.091, + 0.487, + 0.198 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.487, + 0.091, + 0.681, + 0.198 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.68, + 0.091, + 0.874, + 0.199 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.211, + 0.895, + 0.258 + ], + "angle": 0, + "content": "Figure 7: Histogram of one-shot model accuracies sampled from MixPath supernets trained on CIFAR-10 in \\( S_{1} \\), activating at most \\( m = 1,2,3,4 \\) paths respectively. In all cases, the supernet trained without SBNs severely underestimates a large proportion of candidate architectures. Note when \\( m = 1 \\) it falls back to a vanilla BN." + }, + { + "type": "image", + "bbox": [ + 0.091, + 0.279, + 0.276, + 0.402 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.283, + 0.279, + 0.468, + 0.401 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.422, + 0.473, + 0.455 + ], + "angle": 0, + "content": "Figure 8: Rank performance comparison between 'enumerating all compositions' and our method." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.479, + 0.36, + 0.496 + ], + "angle": 0, + "content": "5.2. Comparison of search strategies" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.503, + 0.471, + 0.579 + ], + "angle": 0, + "content": "We use the search space \\( S_{3} \\) on ImageNet to compare the adopted NSGA-II search algorithm [10] with random search by charting the Pareto-front of models found by both methods in Fig. 1 (appendix). NSGA-II has an advantage that the elite models have higher accuracies and fewer FLOPs." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.588, + 0.331, + 0.604 + ], + "angle": 0, + "content": "5.3. Pipeline component analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.611, + 0.47, + 0.747 + ], + "angle": 0, + "content": "Apart from the ablation studies on NAS-Bench-101 [40], we make a component analysis of our pipeline in \\( S_{1} \\). We focus on the supernet training with and without SBN by fixing the second-stage searching algorithm. Each pipeline is run three times on different random seeds. Our goal is to find the best models under 500M FLOPS. As a result, with SBN enabled, we obtain \\( 97.44\\% \\) top-1 accuracy, higher than the best \\( 97.12\\% \\) when SBN is disabled. This confirms that it mainly benefits from our novel training mechanism." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.757, + 0.202, + 0.771 + ], + "angle": 0, + "content": "5.4. Discussions" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.473, + 0.901 + ], + "angle": 0, + "content": "Why can SBNs stabilize supernet training and improve ranking ability? We have verified that high cosine similarity is not the only factor that guarantees the stable training of a multi-path supernet. It is more important to ensure that the feature distributions are consistent. Otherwise, the training is disrupted because a single BN is not enough to capture changing statistics from multiple paths. The proposed SBNs are able to track a variety of distribu" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.274, + 0.895, + 0.334 + ], + "angle": 0, + "content": "tions, alleviating this instability. Empirically, better training of the supernet also gives more appropriate weights for each subnetwork, with which we can better estimate the ground-truth performance of the stand-alone models." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.335, + 0.895, + 0.516 + ], + "angle": 0, + "content": "Why can SBNs work together with BN postcalibration? According to the analysis in Section 3.2, the parameters \\(\\mu, \\sigma\\) of SBNs that follow a multi-path combination are multiples of those of a single-path, as shown in Fig. 5. But not all the parameters fit well into this relationship, post BN calibration can then readjust the mean and variance of the inputs to fit the learned parameters \\(\\gamma\\) and \\(\\beta\\). To some extent, it can make up for the gap from the supernet to submodels. Noticeably, SBN is a type of regularization technique during the supernet training, while BN calibration is a post-processing trick. They can work in an orthogonal way and both contribute to the ranking." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.516, + 0.894, + 0.637 + ], + "angle": 0, + "content": "Comparison with Switchable Batch Normalization Switchable BN [42] is only applied to learn the statistics of a limited number \\((K)\\) of sub-architectures with \\(K = \\{4,8\\}\\) channel configurations. Our SBN is designed to match the changing feature statistics from a more flexible combination of different choice paths, while the number of channels is fixed. The former is used for network pruning while our SBN is to stabilize the training of the multi-path supernet." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.649, + 0.619, + 0.665 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.895, + 0.87 + ], + "angle": 0, + "content": "In this paper, we propose a unified approach for two-stage one-shot neural architecture search, with a multi-path search space enabled. Existing single-path approaches can thus be regarded as a special case. The proposed method uses SBNs to catch the changing features from various branch combinations, which successfully solves two difficulties of vanilla multi-path methods: the unstable training of supernet and the unbearable weakness of model ranking. Moreover, by exploiting feature similarities from different path combinations, we reduced the number of required exponential SBNs to \\( m \\), identical to the number of allowed paths. Our method can enjoy the model ranking capacity of the one-shot supernet and robustly search good models across various benchmarks." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Acknowledgement: This work was supported by National Key R&D Program of China (No. 2022ZD0118700)." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5979" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.472, + 0.171 + ], + "angle": 0, + "content": "[1] Haoping Bai, Meng Cao, Ping Huang, and Jiulong Shan. Batchquant: Quantized-for-all architecture search with robust quantizer. 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In CVPR, volume 2, 2018. 2, 6" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.093, + 0.471, + 0.894 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.514, + 0.957 + ], + "angle": 0, + "content": "5981" + } + ] +] \ No newline at end of file diff --git a/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/7b5c5fe0-450e-42c0-9209-d2128ddb12f9_origin.pdf b/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/7b5c5fe0-450e-42c0-9209-d2128ddb12f9_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..ed6efb9cfc086f06006e80b72d49d69c7636c907 --- /dev/null +++ b/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/7b5c5fe0-450e-42c0-9209-d2128ddb12f9_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:12abaf2f2cf811aa46d4c8b526f14d6f8cb409f4d38e51cb7cd2adc00474fc3d +size 1247846 diff --git a/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/full.md b/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/full.md new file mode 100644 index 0000000000000000000000000000000000000000..015d5b1724ec0e20c5e506af998e479bf9f63146 --- /dev/null +++ b/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/full.md @@ -0,0 +1,338 @@ +# MixPath: A Unified Approach for One-shot Neural Architecture Search + +Xiangxiang Chu Shun Lu Xudong Li Bo Zhang + +cxxgtxy@gmail.com, lushun19s@ict.ac.cn, lixudong16@mails.ucas.edu.cn, zhangboyd@qq.com + +# Abstract + +Blending multiple convolutional kernels is proved advantageous in neural architecture design. However, current two-stage neural architecture search methods are mainly limited to single-path search spaces. How to efficiently search models of multi-path structures remains a difficult problem. In this paper, we are motivated to train a one-shot multi-path supernet to accurately evaluate the candidate architectures. Specifically, we discover that in the studied search spaces, feature vectors summed from multiple paths are nearly multiples of those from a single path. Such disparity perturbs the supernet training and its ranking ability. Therefore, we propose a novel mechanism called Shadow Batch Normalization (SBN) to regularize the disparate feature statistics. Extensive experiments prove that SBNs are capable of stabilizing the optimization and improving ranking performance. We call our unified multi-path one-shot approach as MixPath, which generates a series of models that achieve state-of-the-art results on ImageNet. + +# 1. Introduction + +Complete automation in neural network design is one of the most important research directions of automated machine learning [32, 22]. Among various mainstream paradigms, one-shot approaches [13, 8, 19] make use of a weight-sharing mechanism that reduces a large amount of computational cost, but these approaches mainly focus on searching for single-path networks. Observing that a multi-path structure is beneficial for model performance as in Inception [30] and ResNeXT [37], it is necessary to incorporate multi-path structure into the search space. Noticeably, exploring multipath search space is made possible in one-stage approaches like [9] and [26]. However, it poses a challenge for two-stage methods to train a one-shot supernet that can accurately predict the performance of its multi-path submodels. + +Although FairNAS [8] largely alleviates the ranking difficulty in the single-path case with a fairness strategy, it is inherently difficult to apply the same method in a multi-path scenario. It should be emphasized that the most critical point of the two-stage NAS is that the supernet can rank submod + +![](images/3981cbfa5dcf96d9d90d7aca7f490e595dac55b7ffab4d595c10c2b39f610127.jpg) + +![](images/0921f6b56f614797a5ad32638055cc8d2942c90a47b3db9b872f4744c8a1dca3.jpg) + +![](images/18ef9506347d71c0f1dba0139e93800a643f15bc04c56a671e2296af7832314d.jpg) +Figure 1: Top Left: Options in a demo block, where at most $m$ paths can be chosen. Bottom: An example of MixPath supernet training with Shadow Batch Normalizations (SBNs). Note 1x1 Conv is not a must. SBNs are standard BNs, except that SBNs are applied w.r.t the number of activated paths. E.g., $SBN_{1}$ is used whenever only $m' = 1$ path is activated, $SBN_{2}$ for $m' = 2$ paths. Top Right: SBNs catch each of the statistics in two modes (red for $m' = 1$ , green for $m' = 2$ ), however, a single BN (black) can't capture both. + +![](images/824b1db173b9aeb4c47f838c114a9dc3c35f0a35c357dcbc54e10f795797f878.jpg) + +els as accurately as possible. However, we find that a vanilla training of a multi-path supernet (e.g. randomly pick a multipath submodel to train at each step) is not stable to provide a confident ranking because of changing statistics during the sampling process. Therefore, we dive into its real causes and undertake a unified approach to tackle this issue. Our contributions can be summarized as follows. + +- We propose a unified approach for multi-path (say at most $m$ paths are allowed) one-shot NAS, as opposed to the current single-path methods. From this perspective, current one-shot methods [13, 8] become one of our special cases when $m = 1$ . +- We disclose why a vanilla multi-path training fails, and we propose a novel yet lightweight mechanism, called shadow batch normalization (SBN, see Fig. 1), to stabi + +lize the supernet with a negligible cost. By exploiting feature similarity from different paths, we further reduce the number of SBNs to be $m$ , otherwise it would be exponential. + +- We reveal that our multi-path supernet is trained with stability due to SBNs. It also comes with boosted ranking performance. Together with post BN calibration, it obtains a high Kendall tau (0.597) on a subset of NAS-Bench-101 [40]. +- We use extensive experiments to verify the validity of our method across 4 spaces. We search proxely on ImageNet using 10 GPU days. The searched models obtain state-of-the-art performances, which are comparable with MixNet [34] models searched with $200 \times$ more computing powers. Moreover, our MixPath-B makes use of multi-branch feature aggregation and reaches higher accuracy than EfficientNet-B0 with fewer FLOPS and parameters. + +# 2. Related work + +Conditional batch normalization Batch Normalization (BN) [16] has greatly facilitated the training of neural networks by normalizing layer inputs to have fixed means and variances. Slimmable neural networks[42] introduces a shared supernet that can run with switchable channels at four different scales $(1\times, 0.75\times, 0.5\times, 0.25\times)$ . Due to feature inconsistency, independent BNs are applied for each switch configuration to encode conditional statistics. However, it is impractical because it requires an increased number of BNs when it has arbitrary channel widths. BatchQuant [1] utilizes BNs to stabilize the mixed-precision supernet training in a single-path MobileNetV3 search space. + +Model ranking correlation It should be emphasized that the ranking ability for the family of two-stage algorithms is of the uttermost importance [2], whose sole purpose is to evaluate networks. To quantitatively analyze their ranking ability, previous works like [43, 8, 20, 46] have applied a Kendall tau measure [17]. To this end, various proxies [32, 47, 48], explicit or implicit performance predictors [23, 21] are developed to avoid the intractable evaluation. Recent one-shot approaches [2, 13, 8] utilize a subnet where each submodel can be rapidly assessed with inherited weights. One-Shot [2] uses dropout (a very sensitive hyperparameter) to simulate sampling and evaluating submodel using a subnet. However, its poor ranking performance prevents it from robustly finding good models [8]. + +# 3. MixPath: a unified approach + +# 3.1. Motivation + +There is a call for an efficient multi-path one-shot approach. Informally, existing weight-sharing approaches + +[22, 9, 13, 8] can be classified into four categories based on two dimensions: stage levels and multi-path support, as shown in Fig. 2. Specifically, DARTS [22] and Fair DARTS [9] both are one-stage methods while the latter allows multiple paths between any two nodes. One-shot methods [13, 8] typically train a supernet in the first stage and evaluate sub-models in the second stage for model selection. So far, the two-stage one-shot methods mainly consider a single-path search space except [2] which involves strong regularization and careful hyper-parameter tuning for supernet training. It is thus natural to study this multi-path counterpart further. MPNAS [35] resorts to reinforcement learning as in [26] for a multi-path searching but verified only on small datasets. ScaleNAS [6] adopts an evolutionary algorithm in a multiscale search space but it is designed for downstream tasks like segmentations and human pose estimation. + +Moreover, it's reasonable to design such a search space regarding two factors. First, multi-path feature aggregation is proven to be useful, such as Inception series [30, 16, 31, 29] and ResNeXt [37]. Second, it has the potential to balance the trade-off between performance and cost. + +![](images/221cc0c0678a59359bf64ec5273cbd8f5f448b956c3bbf2ec670329ca01c9548.jpg) +Figure 2: A brief taxonomy of weight-sharing NAS. MixPath fills the empty space of two-stage multiple-path methods. + +Without loss of generality, say an inverted bottleneck has an input feature of $C_{in} \times H \times W$ , whose number of intermediate and output channels are $C_{mid}$ and $C_{out}$ (same as $C_{in}$ ) respectively. Its computational cost can be formulated as $c_{total} = 2HWC_{in}C_{mid} + k^2HWC_{mid} = 2HWC_{mid}(C_{in} + \frac{k^2}{2})$ , where $k$ is the kernel size of the depthwise convolution. Usually, the value of $k$ is set to 3 or 5. Since $C_{in}$ typically dominates $\frac{k^2}{2}$ , we can boost the representative power of depthwise transformation by mixing more kernels with a neglectable increased cost. This design can be regarded as a straightforward combination of MixConv [34] and ResNeXt [37]. + +Multi-path supernet is very hard to train. Vanilla training of the multi-path supernet suffers from severe training difficulties. We can simply train a multi-path supernet by randomly activating a multi-path model at a single step. Here we randomly activate or deactivate each operation. However, this training process is very unstable according to our pi- + +lot experiments conducted with the MixPath supernet on ImageNet [11], shown by the blue line in Fig. 3 (a). + +![](images/35f721875880855b31ae6e02d93a7d2ffbf39b2c6407a07d6f48249c00085e84.jpg) + +![](images/aece7b0da3d73268f21ba4ecacd039220a721148951484d2e333026e4ca382b0.jpg) +(a) + +![](images/a17b506732165f5c3448457dd3d84bdb0436017bc7f1d86c8e30a3578d767aac.jpg) +(b) +Figure 3: (a) Average one-shot validation accuracies (solid line) and their variances (shade) when training the MixPath supernet in $S_{2}$ (activating at most $m = 2$ paths in each MixPath block) on ImageNet. Twenty models are randomly sampled every two epochs. (b) Histogram of accuracies of randomly sampled 3k one-shot models. One-shot models generally come with good performance when SBNs are enabled during supernet training. + +What might have caused such a problem? It has been pointed out that high cosine similarity of features from different operations is important for training stability [8]. To verify the issue, we draw the cosine similarity matrix of different features from our trained supernet in the top row of Fig. 4 (a). Surprisingly, not only are the features from single-path similar to each other, but also the multi-path features where they get added up. We discover that cosine similarity is limited because it measures the orientation only. The addition of high-dimensional feature vectors does not change their angles too much (as they are similar), but their magnitudes get scaled up, see blue arrows in Fig.4 (b). We can further make a bold postulation that a simple superposition of multiple vectors renders very dynamic statistics, hence it causes training instability. With this motivation in mind, we next scale the feature vectors down to the same magnitude to verify if we can make it stabilized. + +# 3.2. Regularizing Multi-path Supernet + +First of all, we can think of using a large amount of BNs to track the changing statistics. For a thorough regularization, we adopt multiple standard BNs to regularize feature statistics from different combinations of $m$ paths. We call them shadow batch normalizations (SBNs) since they follow the activated paths combinations as shadows. Strictly speaking, in order to regularize all feature combinations in a multi-path setting, the number of SBNs has to grow exponentially. $^{1}$ + +# 3.2.1 Reduce the complexity from $2^{m}$ to $m$ . + +The above regularization is too costly. As [8] indicates for the single path case, the outputs of different operations at the same layer have higher similarities. It motivates us to reduce the number of shadow BN by diving into the underlying mechanisms further. Informally, if the features of every single path are similar (both magnitude and angles), we can derive that their combinations have similar statistics too, then the number of BNs can be reduced to $m$ . Formally, this can be formulated as follows. + +Definition 1. Zero-order condition: Let two high-dimensional random variables $\mathbf{y} = \mathbf{f}(\mathbf{x}) \in \mathbf{R}^{\mathbf{M} \times \mathbf{d}_1}$ and $\mathbf{z} = \mathbf{g}(\mathbf{x}) \in \mathbf{R}^{\mathbf{M} \times \mathbf{d}_1}$ , we say that $\mathbf{y}$ and $\mathbf{z}$ satisfy the zero-order condition if $|\mathbf{y} - \mathbf{z}|_2 \leq \epsilon$ for any valid sample $\mathbf{x} \in \mathbf{R}^{\mathbf{N} \times \mathbf{d}}$ , where $\epsilon$ is a very small positive float number. + +Lemma 3.1. Let $\mathbf{m}$ be the maximum number of the activable paths, and each pair of operations satisfy the zero-order condition, we can use $\mathbf{m}$ kinds of expectation and variance to approximate all combinations $(2^{m})$ . + +The proof is provided in A.1 (appendix). Note that the magnitude of $\epsilon$ largely affects the approximation error. It is pretty straightforward as the expectations and variances are simply scaled up according to the number of additions. For instance, $\mathbb{E}[\mathbf{y} + \mathbf{z}] \approx \mathbb{E}[\mathbf{u} + \mathbf{v}] \approx 2\mathbb{E}[\mathbf{y}]$ . Lemma 3.1 assures us that we can take $SBN_{i}(i = 1,2,\dots,m)$ to track the combination that contains $i$ paths. For the multi-path setting, we can observe similar results in Figure 4, which means the requirement of Definition 1 is also satisfied. + +Statistical analysis of Shadow Batch Normalization. We look into the statistics from the supernet trained on CIFAR- $10^{2}$ in search space $S_{1}$ (elaborated later in Section 4.3) (appendix). Without loss of generality, we set $m = 2$ and collect statistics of the four parameters of SBNs across all channels for the first choice block in Fig. 5. Note $SBN_{1}$ captures the statistics of one path, so does $SBN_{2}$ for two paths. Based on the theoretical analysis of Section 3.2, we should have $\mu_{bn_1} \approx 0.5\mu_{bn_2}$ and $\sigma_{bn_1}^2 \approx 0.25\sigma_{bn_2}^2$ . This + +![](images/797186a47f6331dfabc1bab202eb72e45677fc55fdda8adb7492686b4097b365.jpg) + +![](images/ba5bda16ef6d8379d36e93abaf208962479a79ac9946a78d2f8650f34aa884b7.jpg) + +![](images/cb3e842a39b1f1c8998ccfab92563d20ef757a5e8fba3d5812e45162280ab18f.jpg) + +![](images/36aa0bb4f946faf1a915e717050c79f594927d258f0da86e0c997130c6586dfb.jpg) + +![](images/c040e57756835bbd33ef7bf58b392935600ec35a9fbcff1f92faad4834b8a2af.jpg) + +![](images/16d2305ff8760c6021d9b818f2f052e8957531524896fd49a593ff4b405c5427.jpg) +(a) Similarity of multi-path feature vectors + +![](images/dd0ffb70a22adf4e45115d50375aeac2f7fe4b4eaa15ce8d3d76d4591a964d85.jpg) + +![](images/468fba8f263b9b6c1a2178a4c03fef696d618f573a73947f1f78ed635f1e4cf7.jpg) + +![](images/b1aab83e556bc76a724c567de44caa661fb4c80b960c2af3e3268642658157f9.jpg) +Figure 4: (a) Features from various path combinations are quite alike (w/ and w/o SBNs). Shown here is the cosine similarity map of first-block feature vectors from the supernets (in $S_{1}$ ). Darker means higher similarity. (b) SBNs regularize the magnitudes of feature vectors (projected into 2-dimensional space here) while vanilla BN cannot. Blue arrows represent the feature vectors obtained before SBNs or a single BN, and red ones after them. Here SBNs transform the magnitudes (19.6, 37.2, 53.7, 68.7) to around 32. BN normalized magnitudes (32.6, 36.6, 50.6, 66.7) are still diverse. + +![](images/f18de9bfc50b4dfbcdeb1d8ca13ebd0f262bb70dcff72bac4b9c6ae8a274383b.jpg) +(b) Feature vectors projected to 2d space + +![](images/0d772ced865d7dc66c626d1c5409c8a78fb8b71d6825b14fdcd5991640392862.jpg) + +is consistently observed in the first two columns of Fig. 5. It's also interesting to see that the other two learnable parameters $\beta$ and $\gamma$ are quite similar for $SBN_{1}$ and $SBN_{2}$ . This is explainable as SBNs have transformed different statistics to a similar distribution, the parameters of $\beta$ and $\gamma$ become very close. Similar results are observed when $m = 3,4$ and in different layers in Fig. 3 and Fig. 4 in C.6 (appendix). + +# 3.3. MixPath Neural Architecture Search + +Based on the above analysis, we train our multi-path supernet with shadow batch normalizations, which we call the MixPath supernet. Following One-Shot [2], the supernet is used to evaluate models in the predefined search space, which makes our approach a two-stage pipeline: 1) training supernet with SBNs and 2) searching for competitive models. Specifically, in the training stage, we apply random sampling so that multiple paths can be activated at each step, where they add up to a mixed output. We then attach a corresponding SBN to the current path combination. This process is detailed in Algorithm 1 (appendix). Next, similar to [9], we progress with a well-known evolutionary algorithm NSGA-II [10] for searching. In particular, our objectives are to maximize classification accuracy while minimizing the FLOPS. In addition, batch normalization calibration [2, 13, 25], as an orthogonal post-processing trick, is verified effective to further improve the ranking ability. + +# 4. Experiments + +# 4.1. Search spaces + +We investigate four search spaces in this paper, from $S_{1}$ to $S_{4}$ . For searching on CIFAR-10, we use $S_{1}$ that contains 12 inverted bottleneck blocks. For ImageNet, we search in $S_{2}$ and $S_{3}$ that are similar to MnasNet [32] and MixNet [34]. For Kendall Tau analysis, we devise a subset of a common benchmark NAS-Bench-101 [40], denoted as $S_{4}$ . The details + +Algorithm 1: Stage 1 Supernet training with SBN. + +Input: search space $S_{(n,L)}$ with $n$ choice paths per layer and $L$ layers in total, maximum optional paths $m$ , supernet parameters $\Theta (n,L)$ , training epochs $N$ , training data loader $D$ , loss function $Loss$ . + +Initialize every $\theta_{j,l}$ in $\Theta_{(m,L)}$ , SBN set $\{SBN_1, SBN_2, \dots, SBN_n\}$ in each layer. + +for $i = 1$ to $N$ do + +for data, labels in $D$ do + +for $l = 1$ to $L$ do + +Randomly sample a number $m^{\prime}$ between 1 and $m$ , then randomly sample $m^{\prime}$ paths without replacement, where each has output $\mathbf{o}_i^l$ , and use $SBN_{m^{\prime}}$ to act on the sum of outputs: $\mathbf{o}^{l} = SBN_{m^{\prime}}\left(\sum_{i}\mathbf{o}_{i}^{l}\right)$ + +end for + +Select model from above sampled index. + +Clear gradients recorder for all parameters. + +Calculate gradients for model based on Loss, data, labels, update $\theta_{(m,L)}$ by gradients. + +end for + +end for + +of these search spaces are listed in Table 1 (appendix). + +# 4.2. Ranking ability analysis on NAS-Bench-101 + +To show that SBNs can stabilize the supernet training and improve its ranking, we score our method on a subset of a NAS-Bench-101 [40]. Each model is stacked by 9 cells, and every cell has at most 5 internal nodes. We make some adaptations to our method. The first 4 nodes are used to make candidate paths, each has 3 possible operations: $1 \times 1$ Conv, $3 \times 3$ Conv, and $3 \times 3$ Maxpool. The outputs of selected paths are summed up to give input to the fifth node (assigned as $1 \times 1$ Conv), after which the proposed SBNs are used. + +![](images/8e6362b0398cf9a12e3c3cd5c0fc0f351429b3effb9e667df36dbab3099259db.jpg) + +![](images/99080b0c074231527751d06926dc36fbf1d078b35ac10b4604ee7ca50bde837c.jpg) + +![](images/69343a9f012e530df428f07655c97cad2102bc991f75f27f76c1937054f2e5d0.jpg) +Figure 5: Top: Parameters $(\mu, \sigma^2, \gamma, \beta)$ of the first-layer SBNs in MixPath supernet trained on CIFAR-10 when at most $m = 2$ paths are activated. Specifically, $SBN_1$ and $SBN_2$ represent SBNs for a single path and two paths. Bottom: Histogram of ratios $(SBN_1 / SBN_2)$ for each BN parameter. They center around (0.5, 0.25, 1, 1). Note the mean of $SBN_2$ is roughly twice as that of $SBN_1$ . It's interesting that we have previously forecasted this result. + +![](images/a880fbf4ab6dc9a37fa2a76368bcc8e273058692ab17265201ae3d30e836091f.jpg) + +![](images/dd63aab65b8c23c26469f598c32c5d5d82db3604b968c37c785db9124c7f45b7.jpg) + +![](images/2673c26acc7f1e51fddd494aba89813ecdd5fb6bd334b2a94f0fbbe919a419e2.jpg) + +![](images/455156ffa125b12515d31ebcc4c5725b40ef6a838cef6bacbf2adefe3ccecb18.jpg) + +![](images/6d7e50ddd5f6e8be1290a7a95671f55447e9158c0aeff3f11e9c12e3e42e66a0.jpg) + +The designed cell space is shown in Fig. 6. + +![](images/10a33c9c44153f2623106ab9b18311fa9c7a7694169f8d7ecbf73caf69259e83.jpg) + +![](images/72f09e3c57b15d534c45647925a9da8a50dc9cde3c42287154738dd9158048f1.jpg) + +![](images/2286a72ac9538e72c1266516257a7addbab831e0e5668b92491184fd415fd07d.jpg) + +![](images/9142a620a7feffb69c8ed80e7f1fdd9ad31fbeaae5ca83c25352752a3d0ca378.jpg) +Figure 6: (a) Cell space with SBNs in NAS-Bench-101 [40] (b) Ground truth accuracies vs. predictions by one-shot MixPath supernets ( $m = 4$ ) trained with various strategies. We sample 70 models in NAS-Bench-101 [40] (sampling one time) to get the ground-truth. The supernet trained SBN with post BN calibration (top right) gives the best prediction. A vanilla BN alone (w/ SBNs) wrongly pushes models into a narrow range under 0.2. + +![](images/39a6de23efae5e28d808a2c78526cad4c2a3e3985b3279051677cf90b9415fde.jpg) + +Firstly, we conduct the baseline experiments on NAS-Bench-101 [40], training with and without SBNs. For the latter, the features from the multi-path are summed up and then divided by the number of activated paths, following a $1 \times 1$ Conv-BN-ReLU (i.e., a single BN). + +To deeply analyze the model ranking capacity of our method and to understand the effects of SBNs, we conduct two pairs of experiments: (i) vanilla BN vs. SBN (ii) post-calibrated vanilla BN vs. post-calibrated SBN. For all experiments, we train the supernet for 100 epochs with a batch size of 96 and a learning rate of 0.025 on three different seeds. We randomly sample 70 models to find their ground-truth top-1 accuracy from NAS-Bench-101 to obtain Kendall tau [17]. Compared with FairNAS [8] and SGAS [20] utilizing about 10-20 models to calculate Kendall-tau, 70 models are adequate enough to evaluate the ranking performance. We use $m = 4$ in this section. The results are shown in Table 1 and Fig. 6 (b). + +Table 1: Comparison of Kendall taus between MixPath supernets ( $m = 4$ ) trained with various strategies. For each control group, we sampled 70 models from NAS-Bench-101 [40] and repeated it 3 times on different seeds. $\dagger$ : after BN calibration. + +
Strategyw/o Calibrationw/ Calibration
w/o SBN0.117±0.0270.382±0.007
w/ SBN0.393±0.0370.597±0.037
+ +Notably, BN post-calibration can boost Kendall tau in each case, which confirms the validity of this post-processing trick [2, 13, 25]. Compared with baseline experiments, the supernet trained with SBNs has a much stronger ranking capacity. Even without calibration, the proposed method + +still ranks architectures better than the calibrated vanilla BN $(+0.011)$ . The composition of two tricks can further boost the final score to 0.597. Next, we will search for models in the search space commonly used for CIFAR-10 [18] and ImageNet [11] dataset respectively. + +# 4.3. Search on CIFAR-10 + +We conduct experiments on CIFAR-10 dataset [18] with a designed search space $S_{1}$ containing 12 inverted bottlenecks [27], each of which has four choices of kernel size (3, 5, 7, 9) for the depthwise layer and two choices (3, 6) for expansion rates. Hence, the size of search space $S_{1}$ ranges from $8^{12}$ ( $m = 1$ ) to $162^{12}$ ( $m = 4$ ). For each case, we train the supernet on CIFAR-10 for 200 epochs. The batch size is set to 96 and we use the SGD optimizer with a momentum of 0.9 and $3 \times 10^{-4}$ weight decay. We also use a cosine scheduler for the learning rate strategy with an initial value of 0.025. It only takes about 6 GPU hours on a single Tesla V100 GPU in total. The comparison with recent state-of-the-art models is listed in Table 2. Our searched model MixPath-c obtains $97.4\%$ top-1 accuracy using 493M FLOPS on CIFAR-10, whose architecture is shown in Fig. 5 in C.8 (appendix). + +Table 2: Comparison on CIFAR-10. †: MultAdds computed from the provided code. *: transferred from ImageNet (search cost is on ImageNet). RL: Reinforcement learning, GD: Gradient-based, OS: one-shot, TF: Transferred. + +
ModelsParams (M)×+ (M)Top-1 (%)TypeCost G·d
NASNet-A [48]3.360897.4RL1800
NASNet-A Large [48]*85.01203098.0TF1800
ENAS [26]4.6626†97.1RL0.5
DARTS [22]3.352897.1GD0.4
RDARTS [44]--97.1GD1.6
SNAS [38]2.942297.0GD1.5
GDAS [12]3.451997.1GD0.2
P-DARTS [5]3.453297.5GD0.3
PC-DARTS [39]3.655897.4GD0.1
DARTS- [7]3.556897.5GD0.4
Few-shot DARTS [45]3.8-97.6GD1.3
MixPath-c (ours)5.449397.4OS0.25
MixNet-M [34]*3.536097.9TF≈3k
MixPath-a (ours)*3.534898.1TF10
MixPath-b (ours)*3.637798.2TF10
+ +# 4.4. Proxyless Search on ImageNet + +We search proxelyssly on ImageNet [11] in the search space of MnasNet [32], as this layer-wise search space with inverted bottleneck blocks [27] is also very commonly used [32, 33, 36, 8, 34]. We fix the expansion rate as in [34] and search for the combinations of various depthwise convolutions. Specifically, we search from the kernel sizes (3, 5, + +7, 9) and their combinations. We call this search space $S_{2}$ . Moreover, we also construct a search space $S_{3}$ to incorporate architectures like MixNet [34], where we evenly divide the channel dimension of the depthwise layer into 4 groups and search from the kernel sizes (3, 5, 7, 9) for each group. We set $m = 2$ (in $S_{2}$ ) and $m = 1$ (in $S_{3}$ ). In each case, we utilize the same hyper-parameters: a batch size of 1024 and the SGD optimizer with 0.9 momentum and a weight decay of $10^{-5}$ . The initial learning rate is 0.1 with cosine decay and it decreases to 0 within 120 epochs. This takes about 150k times of backpropagation (10 GPU days on Tesla V100). Once the supernet is trained, we adopt NSGA-II [10] for model selection. + +As per training stand-alone models, we use the same tricks as MixNet-M [34], the results are listed in Table 3. To make fair comparisons, we disable distillation in NAS approaches because it can marginally boost the performance of found models. Our cost in Table 3 includes training supernet (10 GPU days) and NSGA-II (0.3 GPU day). MixPath-A, sampled from the Pareto front in $S_{3}$ (so is MixNet), uses 349M multiply-adds to obtain $76.9\%$ accuracy on ImageNet. MixPath-B, in $S_{2}$ , uses fewer FLOPS and parameters w.r.t EfficientNet-B0 to obtain $77.2\%$ . Note SPOS, FBNet, ProxylessNAS are also in $S_{2}$ or similar. In the appendix we list the detailed structures of two models in Fig. 5 of C.8. + +Transferability. We also transfer these models to CIFAR-10 and COCO detection, please refer to Table 2 and C.4. + +# 5. Ablation Study and Discussions + +# 5.1. Supernet ranking with different strategies + +To study the individual contribution of SBN and BN postcalibration, we profit from NAS-Bench-101 [40] for ranking calculation since it provides ground truths for all models. Moreover, it allows a fair comparison with other approaches in the same search space. Specifically, we investigate the case $m = 3$ and report the result of each control group using 3 different seeds. Kendall tau [17] is calculated by randomly sampled 70 models. + +Supernet with and without SBNs. Table 4 shows that the supernet trained without SBN is inadequate to evaluate sampled models ( $\tau = 0.05$ ), which is much lower than the one with a linear number of SBNs ( $\tau = 0.32$ ). We further quantify the effect of the additional post BN calibration, and both taus can be boosted. Particularly for SBN, it's improved to $0.59(+0.27)$ . Therefore, the combination of SBN and post BN calibration delivers the best ranking performance. + +Linear number of SBNs vs. exponential. Through theoretical analysis, we conclude that a linear number of SBNs are enough to match all the combinations of activable paths, while we can still use its exponential counterpart where every single combination follows an SBN. Table 4 shows that + +Table 3: Comparison with state-of-the-art models on ImageNet. For fair comparisons, we disable distillations for all methods. Search cost is computed by GPU days. $\dagger$ : TPU days. $\ddagger$ : w/ distillation. + +
Models×+ (M)#P (M)Top-1 (%)Top-5 (%)Cost G·d
MobileNetV2 [27]3003.472.091.0-
ShuffleNetV2 [24]2993.572.6--
GhostNet 1.3× [14]2267.375.792.7-
DARTS [22]5744.773.3-0.5
P-DARTS[5]5574.975.692.60.3
PC-DARTS [39]5865.374.992.20.1
SGAS (Cri.2 best) [20]5985.475.992.70.25
FairDARTS-C [9]3804.275.192.40.4
MnasNet-A2 [32]3404.875.692.7≈4k
One-Shot Small (F=32) [2]-5.174.2-4†
FBNet-B [36]2954.574.1-9
MobileNetV3 [15]2195.475.292.2≈3k
Proxyless-R [4]3204.074.692.28.3
FairNAS-A [8]3884.675.392.412
Single Path One Shot [13]3283.474.992.012
Single-Path NAS [28]3654.375.092.21.25
OFA w/o PS [3]2354.472.4-50
OFA‡n [3]230-76.0-50
BigNAS-M‡[41]4185.577.493.5-
MixNet-M [34]3605.077.093.3≈3k
MixPath-A (ours)3495.076.993.410.3
MixPath-B (ours)3785.177.293.510.3
+ +Table 4: Kendall taus' comparison between MixPath supernets ( $m = 3$ ) trained with multiple strategies. (same settings as Table 1). ESBN: Exponential SBNs, LSBN: Linear SBNs + +
τw/o SBNESBNLSBN
w/o Calibration0.05±0.060.37±0.060.32±0.03
w/ Calibration0.43±0.030.34±0.080.59±0.02
+ +linear SBN with BN calibration works best (with the highest $\tau$ ), while Exp SBN (exponential) performs best if no calibration is applied. Why is it so? Linear SBNs make use of the zero-order condition which is an approximate relationship. Exp SBNs are more accurate since they catch statistics from each of the combinations. However, this makes a wider distribution of learnable parameters $\gamma, \beta$ , which is difficult for BN calibration to fit them well. Therefore, we choose Linear SBNs with BN calibration instead. Regarding the Occam's Razor, the linear growing BN generalizes better than the exponential counterpart. + +One-shot accuracy distribution of candidate models w.r.t. $m$ We run four experiments with $m = 1,2,3,4$ to investigate the effect of SBNs in $S_{1}$ , other settings are kept the same. In total, 1k models are randomly sampled to plot their test accuracy distributions on CIFAR-10 for each $m$ + +in Fig. 7. When $m = 1$ , MixPath falls back to single path. Whereas, SBN begins to demonstrate its power for $m > 1$ , whose absence leads to a bad supernet with lower predicted accuracies and a much larger gap. This indicates the supernet without SBNs severely underestimates the performance of a large proportion of architectures. + +Simple scaling vs. SBNs. Intuitively from the above motivation, simply scaling the magnitudes of all features to the same level in each block could also stabilize the supernet training. We hereby treat simple scaling as a baseline experiment. However, it is somewhat limited because it adjusts magnitudes only. We find that ranking ability after the calibration of the simple scaling case is higher than that of vanilla BNs and exponential SBNs, but it is lower than that of linear SBNs. This is consistent with the baseline experiment in Table 5. Our proposed method with linear SBNs is still the best among all the compared strategies. Note that the simple scaling approach can only roughly scale the magnitudes of the output. In contrast, SBNs can adjust the magnitudes and angles together to better capture the changing distributions. + +Table 5: Comparison of Kendall taus between MixPath supernets ( $m = 4$ ) trained with various strategies. We sampled 70 models from NAS-Bench-101 [40] and repeated it 3 times on different seeds. $\dagger$ : after BN calibration + +
StrategySimple Scalingw/ SBNs
w/o Calibration0.293±0.0160.393±0.017
Calibration0.472±0.0210.597±0.037
+ +Applying SPOS on multi-path search space. We design a "branch composition" experiment $m = 4$ in NAS-Bench-101 with 3 candidate operations, leading to 34 possible blocks. We use SPOS [13] to train this supernet with the same hyper-parameters as ours, but we only get a Kendall tau of -0.225 while our method obtains 0.504 in terms of ranking the same sub-models (see Fig. 8). This result is not surprising. We blame the failure of the former approach for the use of an excessive number of blocks, which brings nearly $4 \times$ more trainable parameters in the supernet (199.7M vs. ours 52.9M). In this case, it's impractical and infeasible for SPOS to work under such setting because it's hard to make candidate blocks fully optimized. In effect, thus-trained supernet is unable to ensure a reliable rank. For example, on average, one block receives an update every 34 iterations, resulting in poor ranking performance. Besides, this approach will encounter memory explosion at a growing $m$ . Even if we can solve the ranking issue, it requires much more GPU memory to save the trainable parameters, which prevents proxyless search on large datasets or big models. In contrast, our method doesn't suffer from these issues. + +![](images/4660e03161ed6269f9b2493e8618552f01332d097d1a88586d596818f7095f1e.jpg) +Figure 7: Histogram of one-shot model accuracies sampled from MixPath supernets trained on CIFAR-10 in $S_{1}$ , activating at most $m = 1,2,3,4$ paths respectively. In all cases, the supernet trained without SBNs severely underestimates a large proportion of candidate architectures. Note when $m = 1$ it falls back to a vanilla BN. + +![](images/68c9059767e1eec82a94620aa8c73de79444f2c30472e6b48319937a993fcb80.jpg) + +![](images/4136c10840931dc6d1d497d01f06fa0753c989d241b6530dc84ff16432ccb408.jpg) + +![](images/4ae382bd15d9c7f0aaa4c137ee1c707ecf4530ece762b6c900382f341eb42780.jpg) + +![](images/609139b758c0d7a3c80dbf27c47b996164d5aef934b5b8933f6a82c066849d7d.jpg) +Figure 8: Rank performance comparison between 'enumerating all compositions' and our method. + +![](images/663209b5c32a527c99d9a2a13c6b4fe46a48d45a6f78d58a0d8287131cd87339.jpg) + +# 5.2. Comparison of search strategies + +We use the search space $S_{3}$ on ImageNet to compare the adopted NSGA-II search algorithm [10] with random search by charting the Pareto-front of models found by both methods in Fig. 1 (appendix). NSGA-II has an advantage that the elite models have higher accuracies and fewer FLOPs. + +# 5.3. Pipeline component analysis + +Apart from the ablation studies on NAS-Bench-101 [40], we make a component analysis of our pipeline in $S_{1}$ . We focus on the supernet training with and without SBN by fixing the second-stage searching algorithm. Each pipeline is run three times on different random seeds. Our goal is to find the best models under 500M FLOPS. As a result, with SBN enabled, we obtain $97.44\%$ top-1 accuracy, higher than the best $97.12\%$ when SBN is disabled. This confirms that it mainly benefits from our novel training mechanism. + +# 5.4. Discussions + +Why can SBNs stabilize supernet training and improve ranking ability? We have verified that high cosine similarity is not the only factor that guarantees the stable training of a multi-path supernet. It is more important to ensure that the feature distributions are consistent. Otherwise, the training is disrupted because a single BN is not enough to capture changing statistics from multiple paths. The proposed SBNs are able to track a variety of distribu + +tions, alleviating this instability. Empirically, better training of the supernet also gives more appropriate weights for each subnetwork, with which we can better estimate the ground-truth performance of the stand-alone models. + +Why can SBNs work together with BN postcalibration? According to the analysis in Section 3.2, the parameters $\mu, \sigma$ of SBNs that follow a multi-path combination are multiples of those of a single-path, as shown in Fig. 5. But not all the parameters fit well into this relationship, post BN calibration can then readjust the mean and variance of the inputs to fit the learned parameters $\gamma$ and $\beta$ . To some extent, it can make up for the gap from the supernet to submodels. Noticeably, SBN is a type of regularization technique during the supernet training, while BN calibration is a post-processing trick. They can work in an orthogonal way and both contribute to the ranking. + +Comparison with Switchable Batch Normalization Switchable BN [42] is only applied to learn the statistics of a limited number $(K)$ of sub-architectures with $K = \{4,8\}$ channel configurations. Our SBN is designed to match the changing feature statistics from a more flexible combination of different choice paths, while the number of channels is fixed. The former is used for network pruning while our SBN is to stabilize the training of the multi-path supernet. + +# 6. Conclusion + +In this paper, we propose a unified approach for two-stage one-shot neural architecture search, with a multi-path search space enabled. Existing single-path approaches can thus be regarded as a special case. The proposed method uses SBNs to catch the changing features from various branch combinations, which successfully solves two difficulties of vanilla multi-path methods: the unstable training of supernet and the unbearable weakness of model ranking. Moreover, by exploiting feature similarities from different path combinations, we reduced the number of required exponential SBNs to $m$ , identical to the number of allowed paths. Our method can enjoy the model ranking capacity of the one-shot supernet and robustly search good models across various benchmarks. + +Acknowledgement: This work was supported by National Key R&D Program of China (No. 2022ZD0118700). + +# References + +[1] Haoping Bai, Meng Cao, Ping Huang, and Jiulong Shan. Batchquant: Quantized-for-all architecture search with robust quantizer. Advances in Neural Information Processing Systems, 34:1074-1085, 2021. 2 +[2] Gabriel Bender, Pieter-Jan Kindermans, Barret Zoph, Vijay Vasudevan, and Quoc Le. 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In CVPR, volume 2, 2018. 2, 6 \ No newline at end of file diff --git a/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/images.zip b/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..567e249a41fcb5383c7ceab74f4663ae601b1bc0 --- /dev/null +++ b/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:d693d534011207a0c559b533c07cfd43c0f418330625b2ec947fe38c14b0a869 +size 551675 diff --git a/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/layout.json b/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..135e4cd234afe0fd69457f7315b27d4308520128 --- /dev/null +++ b/2023/MixPath_ A Unified Approach for One-shot Neural Architecture Search/layout.json @@ -0,0 +1,10879 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 75, + 103, + 518, + 120 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 75, + 103, + 518, + 120 + ], + "spans": [ + { + "bbox": [ + 75, + 103, + 518, + 120 + ], + "type": "text", + "content": "MixPath: A Unified Approach for One-shot Neural Architecture Search" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 162, + 144, + 430, + 158 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 162, + 144, + 430, + 158 + ], + "spans": [ + { + "bbox": [ + 162, + 144, + 430, + 158 + ], + "type": "text", + "content": "Xiangxiang Chu Shun Lu Xudong Li Bo Zhang" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 118, + 159, + 473, + 171 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 118, + 159, + 473, + 171 + ], + "spans": [ + { + "bbox": [ + 118, + 159, + 473, + 171 + ], + "type": "text", + "content": "cxxgtxy@gmail.com, lushun19s@ict.ac.cn, lixudong16@mails.ucas.edu.cn, zhangboyd@qq.com" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 199, + 192, + 211 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 199, + 192, + 211 + ], + "spans": [ + { + "bbox": [ + 143, + 199, + 192, + 211 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 224, + 290, + 440 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 224, + 290, + 440 + ], + "spans": [ + { + "bbox": [ + 46, + 224, + 290, + 440 + ], + "type": "text", + "content": "Blending multiple convolutional kernels is proved advantageous in neural architecture design. However, current two-stage neural architecture search methods are mainly limited to single-path search spaces. How to efficiently search models of multi-path structures remains a difficult problem. In this paper, we are motivated to train a one-shot multi-path supernet to accurately evaluate the candidate architectures. Specifically, we discover that in the studied search spaces, feature vectors summed from multiple paths are nearly multiples of those from a single path. Such disparity perturbs the supernet training and its ranking ability. Therefore, we propose a novel mechanism called Shadow Batch Normalization (SBN) to regularize the disparate feature statistics. Extensive experiments prove that SBNs are capable of stabilizing the optimization and improving ranking performance. We call our unified multi-path one-shot approach as MixPath, which generates a series of models that achieve state-of-the-art results on ImageNet." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 464, + 128, + 477 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 464, + 128, + 477 + ], + "spans": [ + { + "bbox": [ + 47, + 464, + 128, + 477 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 485, + 288, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 485, + 288, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 485, + 288, + 653 + ], + "type": "text", + "content": "Complete automation in neural network design is one of the most important research directions of automated machine learning [32, 22]. Among various mainstream paradigms, one-shot approaches [13, 8, 19] make use of a weight-sharing mechanism that reduces a large amount of computational cost, but these approaches mainly focus on searching for single-path networks. Observing that a multi-path structure is beneficial for model performance as in Inception [30] and ResNeXT [37], it is necessary to incorporate multi-path structure into the search space. Noticeably, exploring multipath search space is made possible in one-stage approaches like [9] and [26]. However, it poses a challenge for two-stage methods to train a one-shot supernet that can accurately predict the performance of its multi-path submodels." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 653, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 289, + 714 + ], + "type": "text", + "content": "Although FairNAS [8] largely alleviates the ranking difficulty in the single-path case with a fairness strategy, it is inherently difficult to apply the same method in a multi-path scenario. 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Bottom: An example of MixPath supernet training with Shadow Batch Normalizations (SBNs). Note 1x1 Conv is not a must. SBNs are standard BNs, except that SBNs are applied w.r.t the number of activated paths. E.g., " + }, + { + "bbox": [ + 305, + 384, + 548, + 492 + ], + "type": "inline_equation", + "content": "SBN_{1}" + }, + { + "bbox": [ + 305, + 384, + 548, + 492 + ], + "type": "text", + "content": " is used whenever only " + }, + { + "bbox": [ + 305, + 384, + 548, + 492 + ], + "type": "inline_equation", + "content": "m' = 1" + }, + { + "bbox": [ + 305, + 384, + 548, + 492 + ], + "type": "text", + "content": " path is activated, " + }, + { + "bbox": [ + 305, + 384, + 548, + 492 + ], + "type": "inline_equation", + "content": "SBN_{2}" + }, + { + "bbox": [ + 305, + 384, + 548, + 492 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 305, + 384, + 548, + 492 + ], + "type": "inline_equation", + "content": "m' = 2" + }, + { + "bbox": [ + 305, + 384, + 548, + 492 + ], + "type": "text", + "content": " paths. Top Right: SBNs catch each of the statistics in two modes (red for " + }, + { + "bbox": [ + 305, + 384, + 548, + 492 + ], + "type": "inline_equation", + "content": "m' = 1" + }, + { + "bbox": [ + 305, + 384, + 548, + 492 + ], + "type": "text", + "content": ", green for " + }, + { + "bbox": [ + 305, + 384, + 548, + 492 + ], + "type": "inline_equation", + "content": "m' = 2" + }, + { + "bbox": [ + 305, + 384, + 548, + 492 + ], + "type": "text", + "content": "), however, a single BN (black) can't capture both." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 424, + 288, + 525, + 375 + ], + "blocks": [ + { + "bbox": [ + 424, + 288, + 525, + 375 + ], + "lines": [ + { + "bbox": [ + 424, + 288, + 525, + 375 + ], + "spans": [ + { + "bbox": [ + 424, + 288, + 525, + 375 + ], + "type": "image", + "image_path": "824b1db173b9aeb4c47f838c114a9dc3c35f0a35c357dcbc54e10f795797f878.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 514, + 547, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 514, + 547, + 597 + ], + "spans": [ + { + "bbox": [ + 304, + 514, + 547, + 597 + ], + "type": "text", + "content": "els as accurately as possible. However, we find that a vanilla training of a multi-path supernet (e.g. randomly pick a multipath submodel to train at each step) is not stable to provide a confident ranking because of changing statistics during the sampling process. Therefore, we dive into its real causes and undertake a unified approach to tackle this issue. Our contributions can be summarized as follows." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 317, + 609, + 547, + 713 + ], + "type": "list", + "angle": 0, + "index": 18, + "blocks": [ + { + "bbox": [ + 317, + 609, + 547, + 668 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 609, + 547, + 668 + ], + "spans": [ + { + "bbox": [ + 317, + 609, + 547, + 668 + ], + "type": "text", + "content": "- We propose a unified approach for multi-path (say at most " + }, + { + "bbox": [ + 317, + 609, + 547, + 668 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 317, + 609, + 547, + 668 + ], + "type": "text", + "content": " paths are allowed) one-shot NAS, as opposed to the current single-path methods. From this perspective, current one-shot methods [13, 8] become one of our special cases when " + }, + { + "bbox": [ + 317, + 609, + 547, + 668 + ], + "type": "inline_equation", + "content": "m = 1" + }, + { + "bbox": [ + 317, + 609, + 547, + 668 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 317, + 677, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 677, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 317, + 677, + 547, + 713 + ], + "type": "text", + "content": "- We disclose why a vanilla multi-path training fails, and we propose a novel yet lightweight mechanism, called shadow batch normalization (SBN, see Fig. 1), to stabi" + } + ] + } + ], + "index": 17 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5972" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 66, + 72, + 288, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 72, + 288, + 120 + ], + "spans": [ + { + "bbox": [ + 66, + 72, + 288, + 120 + ], + "type": "text", + "content": "lize the supernet with a negligible cost. By exploiting feature similarity from different paths, we further reduce the number of SBNs to be " + }, + { + "bbox": [ + 66, + 72, + 288, + 120 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 66, + 72, + 288, + 120 + ], + "type": "text", + "content": ", otherwise it would be exponential." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 59, + 127, + 289, + 302 + ], + "type": "list", + "angle": 0, + "index": 3, + "blocks": [ + { + "bbox": [ + 59, + 127, + 288, + 187 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 127, + 288, + 187 + ], + "spans": [ + { + "bbox": [ + 59, + 127, + 288, + 187 + ], + "type": "text", + "content": "- We reveal that our multi-path supernet is trained with stability due to SBNs. It also comes with boosted ranking performance. Together with post BN calibration, it obtains a high Kendall tau (0.597) on a subset of NAS-Bench-101 [40]." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 194, + 289, + 302 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 194, + 289, + 302 + ], + "spans": [ + { + "bbox": [ + 59, + 194, + 289, + 302 + ], + "type": "text", + "content": "- We use extensive experiments to verify the validity of our method across 4 spaces. We search proxely on ImageNet using 10 GPU days. The searched models obtain state-of-the-art performances, which are comparable with MixNet [34] models searched with " + }, + { + "bbox": [ + 59, + 194, + 289, + 302 + ], + "type": "inline_equation", + "content": "200 \\times" + }, + { + "bbox": [ + 59, + 194, + 289, + 302 + ], + "type": "text", + "content": " more computing powers. Moreover, our MixPath-B makes use of multi-branch feature aggregation and reaches higher accuracy than EfficientNet-B0 with fewer FLOPS and parameters." + } + ] + } + ], + "index": 2 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 310, + 132, + 323 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 310, + 132, + 323 + ], + "spans": [ + { + "bbox": [ + 47, + 310, + 132, + 323 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 331, + 287, + 474 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 331, + 287, + 474 + ], + "spans": [ + { + "bbox": [ + 46, + 331, + 287, + 474 + ], + "type": "text", + "content": "Conditional batch normalization Batch Normalization (BN) [16] has greatly facilitated the training of neural networks by normalizing layer inputs to have fixed means and variances. Slimmable neural networks[42] introduces a shared supernet that can run with switchable channels at four different scales " + }, + { + "bbox": [ + 46, + 331, + 287, + 474 + ], + "type": "inline_equation", + "content": "(1\\times, 0.75\\times, 0.5\\times, 0.25\\times)" + }, + { + "bbox": [ + 46, + 331, + 287, + 474 + ], + "type": "text", + "content": ". Due to feature inconsistency, independent BNs are applied for each switch configuration to encode conditional statistics. However, it is impractical because it requires an increased number of BNs when it has arbitrary channel widths. BatchQuant [1] utilizes BNs to stabilize the mixed-precision supernet training in a single-path MobileNetV3 search space." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 474, + 288, + 643 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 474, + 288, + 643 + ], + "spans": [ + { + "bbox": [ + 46, + 474, + 288, + 643 + ], + "type": "text", + "content": "Model ranking correlation It should be emphasized that the ranking ability for the family of two-stage algorithms is of the uttermost importance [2], whose sole purpose is to evaluate networks. To quantitatively analyze their ranking ability, previous works like [43, 8, 20, 46] have applied a Kendall tau measure [17]. To this end, various proxies [32, 47, 48], explicit or implicit performance predictors [23, 21] are developed to avoid the intractable evaluation. Recent one-shot approaches [2, 13, 8] utilize a subnet where each submodel can be rapidly assessed with inherited weights. One-Shot [2] uses dropout (a very sensitive hyperparameter) to simulate sampling and evaluating submodel using a subnet. However, its poor ranking performance prevents it from robustly finding good models [8]." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 651, + 211, + 665 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 651, + 211, + 665 + ], + "spans": [ + { + "bbox": [ + 47, + 651, + 211, + 665 + ], + "type": "text", + "content": "3. MixPath: a unified approach" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 671, + 122, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 122, + 682 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 122, + 682 + ], + "type": "text", + "content": "3.1. Motivation" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 689, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 289, + 715 + ], + "type": "text", + "content": "There is a call for an efficient multi-path one-shot approach. Informally, existing weight-sharing approaches" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 547, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 263 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 263 + ], + "type": "text", + "content": "[22, 9, 13, 8] can be classified into four categories based on two dimensions: stage levels and multi-path support, as shown in Fig. 2. Specifically, DARTS [22] and Fair DARTS [9] both are one-stage methods while the latter allows multiple paths between any two nodes. One-shot methods [13, 8] typically train a supernet in the first stage and evaluate sub-models in the second stage for model selection. So far, the two-stage one-shot methods mainly consider a single-path search space except [2] which involves strong regularization and careful hyper-parameter tuning for supernet training. It is thus natural to study this multi-path counterpart further. MPNAS [35] resorts to reinforcement learning as in [26] for a multi-path searching but verified only on small datasets. ScaleNAS [6] adopts an evolutionary algorithm in a multiscale search space but it is designed for downstream tasks like segmentations and human pose estimation." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 264, + 547, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 264, + 547, + 324 + ], + "spans": [ + { + "bbox": [ + 304, + 264, + 547, + 324 + ], + "type": "text", + "content": "Moreover, it's reasonable to design such a search space regarding two factors. First, multi-path feature aggregation is proven to be useful, such as Inception series [30, 16, 31, 29] and ResNeXt [37]. Second, it has the potential to balance the trade-off between performance and cost." + } + ] + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 321, + 334, + 529, + 449 + ], + "blocks": [ + { + "bbox": [ + 321, + 334, + 529, + 449 + ], + "lines": [ + { + "bbox": [ + 321, + 334, + 529, + 449 + ], + "spans": [ + { + "bbox": [ + 321, + 334, + 529, + 449 + ], + "type": "image", + "image_path": "221cc0c0678a59359bf64ec5273cbd8f5f448b956c3bbf2ec670329ca01c9548.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 457, + 545, + 482 + ], + "lines": [ + { + "bbox": [ + 305, + 457, + 545, + 482 + ], + "spans": [ + { + "bbox": [ + 305, + 457, + 545, + 482 + ], + "type": "text", + "content": "Figure 2: A brief taxonomy of weight-sharing NAS. MixPath fills the empty space of two-stage multiple-path methods." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "text", + "content": "Without loss of generality, say an inverted bottleneck has an input feature of " + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "inline_equation", + "content": "C_{in} \\times H \\times W" + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "text", + "content": ", whose number of intermediate and output channels are " + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "inline_equation", + "content": "C_{mid}" + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "inline_equation", + "content": "C_{out}" + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "text", + "content": " (same as " + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "inline_equation", + "content": "C_{in}" + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "text", + "content": ") respectively. Its computational cost can be formulated as " + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "inline_equation", + "content": "c_{total} = 2HWC_{in}C_{mid} + k^2HWC_{mid} = 2HWC_{mid}(C_{in} + \\frac{k^2}{2})" + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "text", + "content": " is the kernel size of the depthwise convolution. Usually, the value of " + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "text", + "content": " is set to 3 or 5. Since " + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "inline_equation", + "content": "C_{in}" + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "text", + "content": " typically dominates " + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "inline_equation", + "content": "\\frac{k^2}{2}" + }, + { + "bbox": [ + 304, + 496, + 547, + 640 + ], + "type": "text", + "content": ", we can boost the representative power of depthwise transformation by mixing more kernels with a neglectable increased cost. This design can be regarded as a straightforward combination of MixConv [34] and ResNeXt [37]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 642, + 548, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 548, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 548, + 714 + ], + "type": "text", + "content": "Multi-path supernet is very hard to train. Vanilla training of the multi-path supernet suffers from severe training difficulties. We can simply train a multi-path supernet by randomly activating a multi-path model at a single step. Here we randomly activate or deactivate each operation. However, this training process is very unstable according to our pi-" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5973" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "content": "lot experiments conducted with the MixPath supernet on ImageNet [11], shown by the blue line in Fig. 3 (a)." + } + ] + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 67, + 119, + 268, + 249 + ], + "blocks": [ + { + "bbox": [ + 67, + 119, + 268, + 249 + ], + "lines": [ + { + "bbox": [ + 67, + 119, + 268, + 249 + ], + "spans": [ + { + "bbox": [ + 67, + 119, + 268, + 249 + ], + "type": "image", + "image_path": "35f721875880855b31ae6e02d93a7d2ffbf39b2c6407a07d6f48249c00085e84.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 50, + 270, + 167, + 361 + ], + "blocks": [ + { + "bbox": [ + 161, + 258, + 173, + 267 + ], + "lines": [ + { + "bbox": [ + 161, + 258, + 173, + 267 + ], + "spans": [ + { + "bbox": [ + 161, + 258, + 173, + 267 + ], + "type": "text", + "content": "(a)" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 50, + 270, + 167, + 361 + ], + "lines": [ + { + "bbox": [ + 50, + 270, + 167, + 361 + ], + "spans": [ + { + "bbox": [ + 50, + 270, + 167, + 361 + ], + "type": "image", + "image_path": "aece7b0da3d73268f21ba4ecacd039220a721148951484d2e333026e4ca382b0.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 167, + 270, + 285, + 362 + ], + "blocks": [ + { + "bbox": [ + 167, + 270, + 285, + 362 + ], + "lines": [ + { + "bbox": [ + 167, + 270, + 285, + 362 + ], + "spans": [ + { + "bbox": [ + 167, + 270, + 285, + 362 + ], + "type": "image", + "image_path": "a17b506732165f5c3448457dd3d84bdb0436017bc7f1d86c8e30a3578d767aac.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 161, + 370, + 173, + 380 + ], + "lines": [ + { + "bbox": [ + 161, + 370, + 173, + 380 + ], + "spans": [ + { + "bbox": [ + 161, + 370, + 173, + 380 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 390, + 288, + 486 + ], + "lines": [ + { + "bbox": [ + 46, + 390, + 288, + 486 + ], + "spans": [ + { + "bbox": [ + 46, + 390, + 288, + 486 + ], + "type": "text", + "content": "Figure 3: (a) Average one-shot validation accuracies (solid line) and their variances (shade) when training the MixPath supernet in " + }, + { + "bbox": [ + 46, + 390, + 288, + 486 + ], + "type": "inline_equation", + "content": "S_{2}" + }, + { + "bbox": [ + 46, + 390, + 288, + 486 + ], + "type": "text", + "content": " (activating at most " + }, + { + "bbox": [ + 46, + 390, + 288, + 486 + ], + "type": "inline_equation", + "content": "m = 2" + }, + { + "bbox": [ + 46, + 390, + 288, + 486 + ], + "type": "text", + "content": " paths in each MixPath block) on ImageNet. Twenty models are randomly sampled every two epochs. (b) Histogram of accuracies of randomly sampled 3k one-shot models. One-shot models generally come with good performance when SBNs are enabled during supernet training." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 510, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 289, + 714 + ], + "type": "text", + "content": "What might have caused such a problem? It has been pointed out that high cosine similarity of features from different operations is important for training stability [8]. To verify the issue, we draw the cosine similarity matrix of different features from our trained supernet in the top row of Fig. 4 (a). Surprisingly, not only are the features from single-path similar to each other, but also the multi-path features where they get added up. We discover that cosine similarity is limited because it measures the orientation only. The addition of high-dimensional feature vectors does not change their angles too much (as they are similar), but their magnitudes get scaled up, see blue arrows in Fig.4 (b). We can further make a bold postulation that a simple superposition of multiple vectors renders very dynamic statistics, hence it causes training instability. With this motivation in mind, we next scale the feature vectors down to the same magnitude to verify if we can make it stabilized." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 72, + 488, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 488, + 85 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 488, + 85 + ], + "type": "text", + "content": "3.2. Regularizing Multi-path Supernet" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 90, + 547, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 90, + 547, + 186 + ], + "spans": [ + { + "bbox": [ + 304, + 90, + 547, + 186 + ], + "type": "text", + "content": "First of all, we can think of using a large amount of BNs to track the changing statistics. For a thorough regularization, we adopt multiple standard BNs to regularize feature statistics from different combinations of " + }, + { + "bbox": [ + 304, + 90, + 547, + 186 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 90, + 547, + 186 + ], + "type": "text", + "content": " paths. We call them shadow batch normalizations (SBNs) since they follow the activated paths combinations as shadows. Strictly speaking, in order to regularize all feature combinations in a multi-path setting, the number of SBNs has to grow exponentially." + }, + { + "bbox": [ + 304, + 90, + 547, + 186 + ], + "type": "inline_equation", + "content": "^{1}" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 201, + 499, + 213 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 201, + 499, + 213 + ], + "spans": [ + { + "bbox": [ + 305, + 201, + 499, + 213 + ], + "type": "text", + "content": "3.2.1 Reduce the complexity from " + }, + { + "bbox": [ + 305, + 201, + 499, + 213 + ], + "type": "inline_equation", + "content": "2^{m}" + }, + { + "bbox": [ + 305, + 201, + 499, + 213 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 305, + 201, + 499, + 213 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 305, + 201, + 499, + 213 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 220, + 545, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 220, + 545, + 327 + ], + "spans": [ + { + "bbox": [ + 304, + 220, + 545, + 327 + ], + "type": "text", + "content": "The above regularization is too costly. As [8] indicates for the single path case, the outputs of different operations at the same layer have higher similarities. It motivates us to reduce the number of shadow BN by diving into the underlying mechanisms further. Informally, if the features of every single path are similar (both magnitude and angles), we can derive that their combinations have similar statistics too, then the number of BNs can be reduced to " + }, + { + "bbox": [ + 304, + 220, + 545, + 327 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 220, + 545, + 327 + ], + "type": "text", + "content": ". Formally, this can be formulated as follows." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "spans": [ + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "text", + "content": "Definition 1. Zero-order condition: Let two high-dimensional random variables " + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "inline_equation", + "content": "\\mathbf{y} = \\mathbf{f}(\\mathbf{x}) \\in \\mathbf{R}^{\\mathbf{M} \\times \\mathbf{d}_1}" + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "inline_equation", + "content": "\\mathbf{z} = \\mathbf{g}(\\mathbf{x}) \\in \\mathbf{R}^{\\mathbf{M} \\times \\mathbf{d}_1}" + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "text", + "content": ", we say that " + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "inline_equation", + "content": "\\mathbf{z}" + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "text", + "content": " satisfy the zero-order condition if " + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "inline_equation", + "content": "|\\mathbf{y} - \\mathbf{z}|_2 \\leq \\epsilon" + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "text", + "content": " for any valid sample " + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "inline_equation", + "content": "\\mathbf{x} \\in \\mathbf{R}^{\\mathbf{N} \\times \\mathbf{d}}" + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 304, + 335, + 547, + 396 + ], + "type": "text", + "content": " is a very small positive float number." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 403, + 545, + 452 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 545, + 452 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 545, + 452 + ], + "type": "text", + "content": "Lemma 3.1. Let " + }, + { + "bbox": [ + 304, + 403, + 545, + 452 + ], + "type": "inline_equation", + "content": "\\mathbf{m}" + }, + { + "bbox": [ + 304, + 403, + 545, + 452 + ], + "type": "text", + "content": " be the maximum number of the activable paths, and each pair of operations satisfy the zero-order condition, we can use " + }, + { + "bbox": [ + 304, + 403, + 545, + 452 + ], + "type": "inline_equation", + "content": "\\mathbf{m}" + }, + { + "bbox": [ + 304, + 403, + 545, + 452 + ], + "type": "text", + "content": " kinds of expectation and variance to approximate all combinations " + }, + { + "bbox": [ + 304, + 403, + 545, + 452 + ], + "type": "inline_equation", + "content": "(2^{m})" + }, + { + "bbox": [ + 304, + 403, + 545, + 452 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 459, + 545, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 459, + 545, + 566 + ], + "spans": [ + { + "bbox": [ + 304, + 459, + 545, + 566 + ], + "type": "text", + "content": "The proof is provided in A.1 (appendix). Note that the magnitude of " + }, + { + "bbox": [ + 304, + 459, + 545, + 566 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 304, + 459, + 545, + 566 + ], + "type": "text", + "content": " largely affects the approximation error. It is pretty straightforward as the expectations and variances are simply scaled up according to the number of additions. For instance, " + }, + { + "bbox": [ + 304, + 459, + 545, + 566 + ], + "type": "inline_equation", + "content": "\\mathbb{E}[\\mathbf{y} + \\mathbf{z}] \\approx \\mathbb{E}[\\mathbf{u} + \\mathbf{v}] \\approx 2\\mathbb{E}[\\mathbf{y}]" + }, + { + "bbox": [ + 304, + 459, + 545, + 566 + ], + "type": "text", + "content": ". Lemma 3.1 assures us that we can take " + }, + { + "bbox": [ + 304, + 459, + 545, + 566 + ], + "type": "inline_equation", + "content": "SBN_{i}(i = 1,2,\\dots,m)" + }, + { + "bbox": [ + 304, + 459, + 545, + 566 + ], + "type": "text", + "content": " to track the combination that contains " + }, + { + "bbox": [ + 304, + 459, + 545, + 566 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 459, + 545, + 566 + ], + "type": "text", + "content": " paths. For the multi-path setting, we can observe similar results in Figure 4, which means the requirement of Definition 1 is also satisfied." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "text", + "content": "Statistical analysis of Shadow Batch Normalization. We look into the statistics from the supernet trained on CIFAR- " + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "inline_equation", + "content": "10^{2}" + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "text", + "content": " in search space " + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "inline_equation", + "content": "S_{1}" + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "text", + "content": " (elaborated later in Section 4.3) (appendix). Without loss of generality, we set " + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "inline_equation", + "content": "m = 2" + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "text", + "content": " and collect statistics of the four parameters of SBNs across all channels for the first choice block in Fig. 5. Note " + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "inline_equation", + "content": "SBN_{1}" + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "text", + "content": " captures the statistics of one path, so does " + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "inline_equation", + "content": "SBN_{2}" + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "text", + "content": " for two paths. Based on the theoretical analysis of Section 3.2, we should have " + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "inline_equation", + "content": "\\mu_{bn_1} \\approx 0.5\\mu_{bn_2}" + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "inline_equation", + "content": "\\sigma_{bn_1}^2 \\approx 0.25\\sigma_{bn_2}^2" + }, + { + "bbox": [ + 304, + 567, + 547, + 676 + ], + "type": "text", + "content": ". This" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 317, + 682, + 441, + 694 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 682, + 441, + 694 + ], + "spans": [ + { + "bbox": [ + 317, + 682, + 441, + 694 + ], + "type": "inline_equation", + "content": "{}^{1}{C}_{m}^{1} + {C}_{m}^{2} + \\cdots + {C}_{m}^{m} = {2}^{m} - 1" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 307, + 694, + 545, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 694, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 307, + 694, + 545, + 712 + ], + "type": "text", + "content": "2It's cheaper to train the supernet on CIFAR-10, and similar observations are also reproducible on ImageNet." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 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178, + 286, + 190 + ], + "type": "text", + "content": "(a) Similarity of multi-path feature vectors" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 178, + 124, + 223, + 164 + ], + "blocks": [ + { + "bbox": [ + 178, + 124, + 223, + 164 + ], + "lines": [ + { + "bbox": [ + 178, + 124, + 223, + 164 + ], + "spans": [ + { + "bbox": [ + 178, + 124, + 223, + 164 + ], + "type": "image", + "image_path": "dd0ffb70a22adf4e45115d50375aeac2f7fe4b4eaa15ce8d3d76d4591a964d85.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 228, + 124, + 274, + 164 + ], + "blocks": [ + { + "bbox": [ + 228, + 124, + 274, + 164 + ], + "lines": [ + { + "bbox": [ + 228, + 124, + 274, + 164 + ], + "spans": [ + { + "bbox": [ + 228, + 124, + 274, + 164 + ], + "type": "image", + "image_path": "468fba8f263b9b6c1a2178a4c03fef696d618f573a73947f1f78ed635f1e4cf7.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 278, + 124, + 338, + 171 + ], + "blocks": [ + { + "bbox": [ + 278, + 124, + 338, + 171 + ], + "lines": [ + { + "bbox": [ + 278, + 124, + 338, + 171 + ], + "spans": [ + { + "bbox": [ + 278, + 124, + 338, + 171 + ], + "type": "image", + "image_path": "b1aab83e556bc76a724c567de44caa661fb4c80b960c2af3e3268642658157f9.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 199, + 547, + 258 + ], + "lines": [ + { + "bbox": [ + 46, + 199, + 547, + 258 + ], + "spans": [ + { + "bbox": [ + 46, + 199, + 547, + 258 + ], + "type": "text", + "content": "Figure 4: (a) Features from various path combinations are quite alike (w/ and w/o SBNs). Shown here is the cosine similarity map of first-block feature vectors from the supernets (in " + }, + { + "bbox": [ + 46, + 199, + 547, + 258 + ], + "type": "inline_equation", + "content": "S_{1}" + }, + { + "bbox": [ + 46, + 199, + 547, + 258 + ], + "type": "text", + "content": "). Darker means higher similarity. (b) SBNs regularize the magnitudes of feature vectors (projected into 2-dimensional space here) while vanilla BN cannot. Blue arrows represent the feature vectors obtained before SBNs or a single BN, and red ones after them. Here SBNs transform the magnitudes (19.6, 37.2, 53.7, 68.7) to around 32. BN normalized magnitudes (32.6, 36.6, 50.6, 66.7) are still diverse." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 350, + 89, + 425, + 156 + ], + "blocks": [ + { + "bbox": [ + 350, + 89, + 425, + 156 + ], + "lines": [ + { + "bbox": [ + 350, + 89, + 425, + 156 + ], + "spans": [ + { + "bbox": [ + 350, + 89, + 425, + 156 + ], + "type": "image", + "image_path": "f18de9bfc50b4dfbcdeb1d8ca13ebd0f262bb70dcff72bac4b9c6ae8a274383b.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 360, + 161, + 507, + 173 + ], + "lines": [ + { + "bbox": [ + 360, + 161, + 507, + 173 + ], + "spans": [ + { + "bbox": [ + 360, + 161, + 507, + 173 + ], + "type": "text", + "content": "(b) Feature vectors projected to 2d space" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 430, + 88, + 505, + 156 + ], + "blocks": [ + { + "bbox": [ + 430, + 88, + 505, + 156 + ], + "lines": [ + { + "bbox": [ + 430, + 88, + 505, + 156 + ], + "spans": [ + { + "bbox": [ + 430, + 88, + 505, + 156 + ], + "type": "image", + "image_path": "0d772ced865d7dc66c626d1c5409c8a78fb8b71d6825b14fdcd5991640392862.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "spans": [ + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "text", + "content": "is consistently observed in the first two columns of Fig. 5. It's also interesting to see that the other two learnable parameters " + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "text", + "content": " are quite similar for " + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "inline_equation", + "content": "SBN_{1}" + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "inline_equation", + "content": "SBN_{2}" + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "text", + "content": ". This is explainable as SBNs have transformed different statistics to a similar distribution, the parameters of " + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "text", + "content": " become very close. Similar results are observed when " + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "inline_equation", + "content": "m = 3,4" + }, + { + "bbox": [ + 46, + 280, + 289, + 365 + ], + "type": "text", + "content": " and in different layers in Fig. 3 and Fig. 4 in C.6 (appendix)." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 47, + 371, + 242, + 383 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 371, + 242, + 383 + ], + "spans": [ + { + "bbox": [ + 47, + 371, + 242, + 383 + ], + "type": "text", + "content": "3.3. MixPath Neural Architecture Search" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 46, + 389, + 290, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 389, + 290, + 594 + ], + "spans": [ + { + "bbox": [ + 46, + 389, + 290, + 594 + ], + "type": "text", + "content": "Based on the above analysis, we train our multi-path supernet with shadow batch normalizations, which we call the MixPath supernet. Following One-Shot [2], the supernet is used to evaluate models in the predefined search space, which makes our approach a two-stage pipeline: 1) training supernet with SBNs and 2) searching for competitive models. Specifically, in the training stage, we apply random sampling so that multiple paths can be activated at each step, where they add up to a mixed output. We then attach a corresponding SBN to the current path combination. This process is detailed in Algorithm 1 (appendix). Next, similar to [9], we progress with a well-known evolutionary algorithm NSGA-II [10] for searching. In particular, our objectives are to maximize classification accuracy while minimizing the FLOPS. In addition, batch normalization calibration [2, 13, 25], as an orthogonal post-processing trick, is verified effective to further improve the ranking ability." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 47, + 604, + 128, + 617 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 604, + 128, + 617 + ], + "spans": [ + { + "bbox": [ + 47, + 604, + 128, + 617 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 47, + 623, + 134, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 134, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 134, + 635 + ], + "type": "text", + "content": "4.1. Search spaces" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "text", + "content": "We investigate four search spaces in this paper, from " + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "inline_equation", + "content": "S_{1}" + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "inline_equation", + "content": "S_{4}" + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "text", + "content": ". For searching on CIFAR-10, we use " + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "inline_equation", + "content": "S_{1}" + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "text", + "content": " that contains 12 inverted bottleneck blocks. For ImageNet, we search in " + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "inline_equation", + "content": "S_{2}" + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "inline_equation", + "content": "S_{3}" + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "text", + "content": " that are similar to MnasNet [32] and MixNet [34]. For Kendall Tau analysis, we devise a subset of a common benchmark NAS-Bench-101 [40], denoted as " + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "inline_equation", + "content": "S_{4}" + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "text", + "content": ". The details" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 307, + 280, + 515, + 293 + ], + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 280, + 515, + 293 + ], + "spans": [ + { + "bbox": [ + 307, + 280, + 515, + 293 + ], + "type": "text", + "content": "Algorithm 1: Stage 1 Supernet training with SBN." + } + ] + } + ], + "index": 20, + "type": "text" + }, + { + "bbox": [ + 315, + 295, + 547, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 295, + 547, + 342 + ], + "spans": [ + { + "bbox": [ + 315, + 295, + 547, + 342 + ], + "type": "text", + "content": "Input: search space " + }, + { + "bbox": [ + 315, + 295, + 547, + 342 + ], + "type": "inline_equation", + "content": "S_{(n,L)}" + }, + { + "bbox": [ + 315, + 295, + 547, + 342 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 315, + 295, + 547, + 342 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 315, + 295, + 547, + 342 + ], + "type": "text", + 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The first 4 nodes are used to make candidate paths, each has 3 possible operations: " + }, + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "type": "text", + "content": " Conv, " + }, + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "type": "text", + "content": " Conv, and " + }, + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 304, + 605, + 547, + 713 + ], + "type": "text", + "content": " Maxpool. 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"type": "text", + "content": ") trained with various strategies. We sample 70 models in NAS-Bench-101 [40] (sampling one time) to get the ground-truth. The supernet trained SBN with post BN calibration (top right) gives the best prediction. A vanilla BN alone (w/ SBNs) wrongly pushes models into a narrow range under 0.2." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 167, + 540, + 254, + 604 + ], + "blocks": [ + { + "bbox": [ + 167, + 540, + 254, + 604 + ], + "lines": [ + { + "bbox": [ + 167, + 540, + 254, + 604 + ], + "spans": [ + { + "bbox": [ + 167, + 540, + 254, + 604 + ], + "type": "image", + "image_path": "39a6de23efae5e28d808a2c78526cad4c2a3e3985b3279051677cf90b9415fde.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 280, + 547, + 339 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 280, + 547, + 339 + ], + "spans": [ + { + "bbox": [ + 306, + 280, + 547, + 339 + ], + "type": "text", + "content": "Firstly, we conduct the baseline experiments on NAS-Bench-101 [40], training with and without SBNs. For the latter, the features from the multi-path are summed up and then divided by the number of activated paths, following a " + }, + { + "bbox": [ + 306, + 280, + 547, + 339 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 306, + 280, + 547, + 339 + ], + "type": "text", + "content": " Conv-BN-ReLU (i.e., a single BN)." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 340, + 547, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 340, + 547, + 495 + ], + "spans": [ + { + "bbox": [ + 304, + 340, + 547, + 495 + ], + "type": "text", + "content": "To deeply analyze the model ranking capacity of our method and to understand the effects of SBNs, we conduct two pairs of experiments: (i) vanilla BN vs. SBN (ii) post-calibrated vanilla BN vs. post-calibrated SBN. For all experiments, we train the supernet for 100 epochs with a batch size of 96 and a learning rate of 0.025 on three different seeds. We randomly sample 70 models to find their ground-truth top-1 accuracy from NAS-Bench-101 to obtain Kendall tau [17]. Compared with FairNAS [8] and SGAS [20] utilizing about 10-20 models to calculate Kendall-tau, 70 models are adequate enough to evaluate the ranking performance. We use " + }, + { + "bbox": [ + 304, + 340, + 547, + 495 + ], + "type": "inline_equation", + "content": "m = 4" + }, + { + "bbox": [ + 304, + 340, + 547, + 495 + ], + "type": "text", + "content": " in this section. The results are shown in Table 1 and Fig. 6 (b)." + } + ] + } + ], + "index": 17 + }, + { + "type": "table", + "bbox": [ + 328, + 577, + 525, + 619 + ], + "blocks": [ + { + "bbox": [ + 304, + 508, + 547, + 567 + ], + "lines": [ + { + "bbox": [ + 304, + 508, + 547, + 567 + ], + "spans": [ + { + "bbox": [ + 304, + 508, + 547, + 567 + ], + "type": "text", + "content": "Table 1: Comparison of Kendall taus between MixPath supernets (" + }, + { + "bbox": [ + 304, + 508, + 547, + 567 + ], + "type": "inline_equation", + "content": "m = 4" + }, + { + "bbox": [ + 304, + 508, + 547, + 567 + ], + "type": "text", + "content": ") trained with various strategies. For each control group, we sampled 70 models from NAS-Bench-101 [40] and repeated it 3 times on different seeds. " + }, + { + "bbox": [ + 304, + 508, + 547, + 567 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 304, + 508, + 547, + 567 + ], + "type": "text", + "content": ": after BN calibration." + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 328, + 577, + 525, + 619 + ], + "lines": [ + { + "bbox": [ + 328, + 577, + 525, + 619 + ], + "spans": [ + { + "bbox": [ + 328, + 577, + 525, + 619 + ], + "type": "table", + "html": "
Strategyw/o Calibrationw/ Calibration
w/o SBN0.117±0.0270.382±0.007
w/ SBN0.393±0.0370.597±0.037
", + "image_path": "b80e95382baf0ba73474c054d28937ab650024dfa1dbec3e1f370611b24184fb.jpg" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "table_body" + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 632, + 547, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 632, + 547, + 693 + ], + "spans": [ + { + "bbox": [ + 304, + 632, + 547, + 693 + ], + "type": "text", + "content": "Notably, BN post-calibration can boost Kendall tau in each case, which confirms the validity of this post-processing trick [2, 13, 25]. Compared with baseline experiments, the supernet trained with SBNs has a much stronger ranking capacity. Even without calibration, the proposed method" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 315, + 702, + 450, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 702, + 450, + 713 + ], + "spans": [ + { + "bbox": [ + 315, + 702, + 450, + 713 + ], + "type": "text", + "content": "3We place " + }, + { + "bbox": [ + 315, + 702, + 450, + 713 + ], + "type": "inline_equation", + "content": "m = 3" + }, + { + "bbox": [ + 315, + 702, + 450, + 713 + ], + "type": "text", + "content": " case in ablation study." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5976" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 133 + ], + "type": "text", + "content": "still ranks architectures better than the calibrated vanilla BN " + }, + { + "bbox": [ + 46, + 72, + 288, + 133 + ], + "type": "inline_equation", + "content": "(+0.011)" + }, + { + "bbox": [ + 46, + 72, + 288, + 133 + ], + "type": "text", + "content": ". The composition of two tricks can further boost the final score to 0.597. Next, we will search for models in the search space commonly used for CIFAR-10 [18] and ImageNet [11] dataset respectively." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 140, + 167, + 152 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 140, + 167, + 152 + ], + "spans": [ + { + "bbox": [ + 47, + 140, + 167, + 152 + ], + "type": "text", + "content": "4.3. Search on CIFAR-10" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "spans": [ + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "text", + "content": "We conduct experiments on CIFAR-10 dataset [18] with a designed search space " + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "inline_equation", + "content": "S_{1}" + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "text", + "content": " containing 12 inverted bottlenecks [27], each of which has four choices of kernel size (3, 5, 7, 9) for the depthwise layer and two choices (3, 6) for expansion rates. Hence, the size of search space " + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "inline_equation", + "content": "S_{1}" + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "text", + "content": " ranges from " + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "inline_equation", + "content": "8^{12}" + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "inline_equation", + "content": "m = 1" + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "text", + "content": ") to " + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "inline_equation", + "content": "162^{12}" + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "inline_equation", + "content": "m = 4" + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "text", + "content": "). For each case, we train the supernet on CIFAR-10 for 200 epochs. The batch size is set to 96 and we use the SGD optimizer with a momentum of 0.9 and " + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "inline_equation", + "content": "3 \\times 10^{-4}" + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "text", + "content": " weight decay. We also use a cosine scheduler for the learning rate strategy with an initial value of 0.025. It only takes about 6 GPU hours on a single Tesla V100 GPU in total. The comparison with recent state-of-the-art models is listed in Table 2. Our searched model MixPath-c obtains " + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "inline_equation", + "content": "97.4\\%" + }, + { + "bbox": [ + 46, + 159, + 288, + 340 + ], + "type": "text", + "content": " top-1 accuracy using 493M FLOPS on CIFAR-10, whose architecture is shown in Fig. 5 in C.8 (appendix)." + } + ] + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 56, + 408, + 276, + 601 + ], + "blocks": [ + { + "bbox": [ + 46, + 350, + 288, + 399 + ], + "lines": [ + { + "bbox": [ + 46, + 350, + 288, + 399 + ], + "spans": [ + { + "bbox": [ + 46, + 350, + 288, + 399 + ], + "type": "text", + "content": "Table 2: Comparison on CIFAR-10. †: MultAdds computed from the provided code. *: transferred from ImageNet (search cost is on ImageNet). RL: Reinforcement learning, GD: Gradient-based, OS: one-shot, TF: Transferred." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 56, + 408, + 276, + 601 + ], + "lines": [ + { + "bbox": [ + 56, + 408, + 276, + 601 + ], + "spans": [ + { + "bbox": [ + 56, + 408, + 276, + 601 + ], + "type": "table", + "html": "
ModelsParams (M)×+ (M)Top-1 (%)TypeCost G·d
NASNet-A [48]3.360897.4RL1800
NASNet-A Large [48]*85.01203098.0TF1800
ENAS [26]4.6626†97.1RL0.5
DARTS [22]3.352897.1GD0.4
RDARTS [44]--97.1GD1.6
SNAS [38]2.942297.0GD1.5
GDAS [12]3.451997.1GD0.2
P-DARTS [5]3.453297.5GD0.3
PC-DARTS [39]3.655897.4GD0.1
DARTS- [7]3.556897.5GD0.4
Few-shot DARTS [45]3.8-97.6GD1.3
MixPath-c (ours)5.449397.4OS0.25
MixNet-M [34]*3.536097.9TF≈3k
MixPath-a (ours)*3.534898.1TF10
MixPath-b (ours)*3.637798.2TF10
", + "image_path": "e50afc740f7ffd948999a2150d91ceeb9e7c233c368c898fd0ac00d02f0e39c5.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 623, + 211, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 211, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 211, + 635 + ], + "type": "text", + "content": "4.4. Proxyless Search on ImageNet" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "text", + "content": "We search proxelyssly on ImageNet [11] in the search space of MnasNet [32], as this layer-wise search space with inverted bottleneck blocks [27] is also very commonly used [32, 33, 36, 8, 34]. We fix the expansion rate as in [34] and search for the combinations of various depthwise convolutions. Specifically, we search from the kernel sizes (3, 5," + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "text", + "content": "7, 9) and their combinations. We call this search space " + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "inline_equation", + "content": "S_{2}" + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "text", + "content": ". Moreover, we also construct a search space " + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "inline_equation", + "content": "S_{3}" + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "text", + "content": " to incorporate architectures like MixNet [34], where we evenly divide the channel dimension of the depthwise layer into 4 groups and search from the kernel sizes (3, 5, 7, 9) for each group. We set " + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "inline_equation", + "content": "m = 2" + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "text", + "content": " (in " + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "inline_equation", + "content": "S_{2}" + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "text", + "content": ") and " + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "inline_equation", + "content": "m = 1" + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "text", + "content": " (in " + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "inline_equation", + "content": "S_{3}" + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "text", + "content": "). In each case, we utilize the same hyper-parameters: a batch size of 1024 and the SGD optimizer with 0.9 momentum and a weight decay of " + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "inline_equation", + "content": "10^{-5}" + }, + { + "bbox": [ + 304, + 72, + 547, + 227 + ], + "type": "text", + "content": ". The initial learning rate is 0.1 with cosine decay and it decreases to 0 within 120 epochs. This takes about 150k times of backpropagation (10 GPU days on Tesla V100). Once the supernet is trained, we adopt NSGA-II [10] for model selection." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "spans": [ + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "type": "text", + "content": "As per training stand-alone models, we use the same tricks as MixNet-M [34], the results are listed in Table 3. To make fair comparisons, we disable distillation in NAS approaches because it can marginally boost the performance of found models. Our cost in Table 3 includes training supernet (10 GPU days) and NSGA-II (0.3 GPU day). MixPath-A, sampled from the Pareto front in " + }, + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "type": "inline_equation", + "content": "S_{3}" + }, + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "type": "text", + "content": " (so is MixNet), uses 349M multiply-adds to obtain " + }, + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "type": "inline_equation", + "content": "76.9\\%" + }, + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "type": "text", + "content": " accuracy on ImageNet. MixPath-B, in " + }, + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "type": "inline_equation", + "content": "S_{2}" + }, + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "type": "text", + "content": ", uses fewer FLOPS and parameters w.r.t EfficientNet-B0 to obtain " + }, + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "type": "inline_equation", + "content": "77.2\\%" + }, + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "type": "text", + "content": ". Note SPOS, FBNet, ProxylessNAS are also in " + }, + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "type": "inline_equation", + "content": "S_{2}" + }, + { + "bbox": [ + 304, + 228, + 547, + 371 + ], + "type": "text", + "content": " or similar. In the appendix we list the detailed structures of two models in Fig. 5 of C.8." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 387, + 547, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 387, + 547, + 411 + ], + "spans": [ + { + "bbox": [ + 305, + 387, + 547, + 411 + ], + "type": "text", + "content": "Transferability. We also transfer these models to CIFAR-10 and COCO detection, please refer to Table 2 and C.4." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 423, + 484, + 436 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 423, + 484, + 436 + ], + "spans": [ + { + "bbox": [ + 306, + 423, + 484, + 436 + ], + "type": "text", + "content": "5. Ablation Study and Discussions" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 443, + 524, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 443, + 524, + 456 + ], + "spans": [ + { + "bbox": [ + 306, + 443, + 524, + 456 + ], + "type": "text", + "content": "5.1. Supernet ranking with different strategies" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 461, + 547, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 461, + 547, + 556 + ], + "spans": [ + { + "bbox": [ + 304, + 461, + 547, + 556 + ], + "type": "text", + "content": "To study the individual contribution of SBN and BN postcalibration, we profit from NAS-Bench-101 [40] for ranking calculation since it provides ground truths for all models. Moreover, it allows a fair comparison with other approaches in the same search space. Specifically, we investigate the case " + }, + { + "bbox": [ + 304, + 461, + 547, + 556 + ], + "type": "inline_equation", + "content": "m = 3" + }, + { + "bbox": [ + 304, + 461, + 547, + 556 + ], + "type": "text", + "content": " and report the result of each control group using 3 different seeds. Kendall tau [17] is calculated by randomly sampled 70 models." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 558, + 547, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 547, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 547, + 653 + ], + "type": "text", + "content": "Supernet with and without SBNs. Table 4 shows that the supernet trained without SBN is inadequate to evaluate sampled models (" + }, + { + "bbox": [ + 304, + 558, + 547, + 653 + ], + "type": "inline_equation", + "content": "\\tau = 0.05" + }, + { + "bbox": [ + 304, + 558, + 547, + 653 + ], + "type": "text", + "content": "), which is much lower than the one with a linear number of SBNs (" + }, + { + "bbox": [ + 304, + 558, + 547, + 653 + ], + "type": "inline_equation", + "content": "\\tau = 0.32" + }, + { + "bbox": [ + 304, + 558, + 547, + 653 + ], + "type": "text", + "content": "). We further quantify the effect of the additional post BN calibration, and both taus can be boosted. Particularly for SBN, it's improved to " + }, + { + "bbox": [ + 304, + 558, + 547, + 653 + ], + "type": "inline_equation", + "content": "0.59(+0.27)" + }, + { + "bbox": [ + 304, + 558, + 547, + 653 + ], + "type": "text", + "content": ". Therefore, the combination of SBN and post BN calibration delivers the best ranking performance." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 654, + 547, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 712 + ], + "type": "text", + "content": "Linear number of SBNs vs. exponential. Through theoretical analysis, we conclude that a linear number of SBNs are enough to match all the combinations of activable paths, while we can still use its exponential counterpart where every single combination follows an SBN. Table 4 shows that" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5977" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 131, + 280, + 401 + ], + "blocks": [ + { + "bbox": [ + 46, + 70, + 288, + 119 + ], + "lines": [ + { + "bbox": [ + 46, + 70, + 288, + 119 + ], + "spans": [ + { + "bbox": [ + 46, + 70, + 288, + 119 + ], + "type": "text", + "content": "Table 3: Comparison with state-of-the-art models on ImageNet. For fair comparisons, we disable distillations for all methods. Search cost is computed by GPU days. " + }, + { + "bbox": [ + 46, + 70, + 288, + 119 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 46, + 70, + 288, + 119 + ], + "type": "text", + "content": ": TPU days. " + }, + { + "bbox": [ + 46, + 70, + 288, + 119 + ], + "type": "inline_equation", + "content": "\\ddagger" + }, + { + "bbox": [ + 46, + 70, + 288, + 119 + ], + "type": "text", + "content": ": w/ distillation." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 131, + 280, + 401 + ], + "lines": [ + { + "bbox": [ + 50, + 131, + 280, + 401 + ], + "spans": [ + { + "bbox": [ + 50, + 131, + 280, + 401 + ], + "type": "table", + "html": "
Models×+ (M)#P (M)Top-1 (%)Top-5 (%)Cost G·d
MobileNetV2 [27]3003.472.091.0-
ShuffleNetV2 [24]2993.572.6--
GhostNet 1.3× [14]2267.375.792.7-
DARTS [22]5744.773.3-0.5
P-DARTS[5]5574.975.692.60.3
PC-DARTS [39]5865.374.992.20.1
SGAS (Cri.2 best) [20]5985.475.992.70.25
FairDARTS-C [9]3804.275.192.40.4
MnasNet-A2 [32]3404.875.692.7≈4k
One-Shot Small (F=32) [2]-5.174.2-4†
FBNet-B [36]2954.574.1-9
MobileNetV3 [15]2195.475.292.2≈3k
Proxyless-R [4]3204.074.692.28.3
FairNAS-A [8]3884.675.392.412
Single Path One Shot [13]3283.474.992.012
Single-Path NAS [28]3654.375.092.21.25
OFA w/o PS [3]2354.472.4-50
OFA‡n [3]230-76.0-50
BigNAS-M‡[41]4185.577.493.5-
MixNet-M [34]3605.077.093.3≈3k
MixPath-A (ours)3495.076.993.410.3
MixPath-B (ours)3785.177.293.510.3
", + "image_path": "162b67c9b7432a9fa8567c4b34090107e1d58a33aa285faf5bd1d872478caa47.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 67, + 461, + 267, + 501 + ], + "blocks": [ + { + "bbox": [ + 46, + 413, + 288, + 449 + ], + "lines": [ + { + "bbox": [ + 46, + 413, + 288, + 449 + ], + "spans": [ + { + "bbox": [ + 46, + 413, + 288, + 449 + ], + "type": "text", + "content": "Table 4: Kendall taus' comparison between MixPath supernets (" + }, + { + "bbox": [ + 46, + 413, + 288, + 449 + ], + "type": "inline_equation", + "content": "m = 3" + }, + { + "bbox": [ + 46, + 413, + 288, + 449 + ], + "type": "text", + "content": ") trained with multiple strategies. (same settings as Table 1). ESBN: Exponential SBNs, LSBN: Linear SBNs" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 67, + 461, + 267, + 501 + ], + "lines": [ + { + "bbox": [ + 67, + 461, + 267, + 501 + ], + "spans": [ + { + "bbox": [ + 67, + 461, + 267, + 501 + ], + "type": "table", + "html": "
τw/o SBNESBNLSBN
w/o Calibration0.05±0.060.37±0.060.32±0.03
w/ Calibration0.43±0.030.34±0.080.59±0.02
", + "image_path": "93a74018fbc52ca07a24ed77a6d1e1e9a257d237beeb74729d5446b966801d62.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 521, + 287, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 653 + ], + "type": "text", + "content": "linear SBN with BN calibration works best (with the highest " + }, + { + "bbox": [ + 46, + 521, + 287, + 653 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 521, + 287, + 653 + ], + "type": "text", + "content": "), while Exp SBN (exponential) performs best if no calibration is applied. Why is it so? Linear SBNs make use of the zero-order condition which is an approximate relationship. Exp SBNs are more accurate since they catch statistics from each of the combinations. However, this makes a wider distribution of learnable parameters " + }, + { + "bbox": [ + 46, + 521, + 287, + 653 + ], + "type": "inline_equation", + "content": "\\gamma, \\beta" + }, + { + "bbox": [ + 46, + 521, + 287, + 653 + ], + "type": "text", + "content": ", which is difficult for BN calibration to fit them well. Therefore, we choose Linear SBNs with BN calibration instead. Regarding the Occam's Razor, the linear growing BN generalizes better than the exponential counterpart." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "One-shot accuracy distribution of candidate models w.r.t. " + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": " We run four experiments with " + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "inline_equation", + "content": "m = 1,2,3,4" + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": " to investigate the effect of SBNs in " + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "inline_equation", + "content": "S_{1}" + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": ", other settings are kept the same. In total, 1k models are randomly sampled to plot their test accuracy distributions on CIFAR-10 for each " + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "inline_equation", + "content": "m" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "type": "text", + "content": "in Fig. 7. When " + }, + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "type": "inline_equation", + "content": "m = 1" + }, + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "type": "text", + "content": ", MixPath falls back to single path. Whereas, SBN begins to demonstrate its power for " + }, + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "type": "inline_equation", + "content": "m > 1" + }, + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "type": "text", + "content": ", whose absence leads to a bad supernet with lower predicted accuracies and a much larger gap. This indicates the supernet without SBNs severely underestimates the performance of a large proportion of architectures." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 145, + 547, + 313 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 145, + 547, + 313 + ], + "spans": [ + { + "bbox": [ + 304, + 145, + 547, + 313 + ], + "type": "text", + "content": "Simple scaling vs. SBNs. Intuitively from the above motivation, simply scaling the magnitudes of all features to the same level in each block could also stabilize the supernet training. We hereby treat simple scaling as a baseline experiment. However, it is somewhat limited because it adjusts magnitudes only. We find that ranking ability after the calibration of the simple scaling case is higher than that of vanilla BNs and exponential SBNs, but it is lower than that of linear SBNs. This is consistent with the baseline experiment in Table 5. Our proposed method with linear SBNs is still the best among all the compared strategies. Note that the simple scaling approach can only roughly scale the magnitudes of the output. In contrast, SBNs can adjust the magnitudes and angles together to better capture the changing distributions." + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 328, + 387, + 525, + 426 + ], + "blocks": [ + { + "bbox": [ + 304, + 326, + 547, + 374 + ], + "lines": [ + { + "bbox": [ + 304, + 326, + 547, + 374 + ], + "spans": [ + { + "bbox": [ + 304, + 326, + 547, + 374 + ], + "type": "text", + "content": "Table 5: Comparison of Kendall taus between MixPath supernets (" + }, + { + "bbox": [ + 304, + 326, + 547, + 374 + ], + "type": "inline_equation", + "content": "m = 4" + }, + { + "bbox": [ + 304, + 326, + 547, + 374 + ], + "type": "text", + "content": ") trained with various strategies. We sampled 70 models from NAS-Bench-101 [40] and repeated it 3 times on different seeds. " + }, + { + "bbox": [ + 304, + 326, + 547, + 374 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 304, + 326, + 547, + 374 + ], + "type": "text", + "content": ": after BN calibration" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 328, + 387, + 525, + 426 + ], + "lines": [ + { + "bbox": [ + 328, + 387, + 525, + 426 + ], + "spans": [ + { + "bbox": [ + 328, + 387, + 525, + 426 + ], + "type": "table", + "html": "
StrategySimple Scalingw/ SBNs
w/o Calibration0.293±0.0160.393±0.017
Calibration0.472±0.0210.597±0.037
", + "image_path": "16999e7d24ff9f8d803d523b44df476de69f0e0473e875500de1758fe3e943fb.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 462, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 462, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 462, + 547, + 713 + ], + "type": "text", + "content": "Applying SPOS on multi-path search space. We design a \"branch composition\" experiment " + }, + { + "bbox": [ + 304, + 462, + 547, + 713 + ], + "type": "inline_equation", + "content": "m = 4" + }, + { + "bbox": [ + 304, + 462, + 547, + 713 + ], + "type": "text", + "content": " in NAS-Bench-101 with 3 candidate operations, leading to 34 possible blocks. We use SPOS [13] to train this supernet with the same hyper-parameters as ours, but we only get a Kendall tau of -0.225 while our method obtains 0.504 in terms of ranking the same sub-models (see Fig. 8). This result is not surprising. We blame the failure of the former approach for the use of an excessive number of blocks, which brings nearly " + }, + { + "bbox": [ + 304, + 462, + 547, + 713 + ], + "type": "inline_equation", + "content": "4 \\times" + }, + { + "bbox": [ + 304, + 462, + 547, + 713 + ], + "type": "text", + "content": " more trainable parameters in the supernet (199.7M vs. ours 52.9M). In this case, it's impractical and infeasible for SPOS to work under such setting because it's hard to make candidate blocks fully optimized. In effect, thus-trained supernet is unable to ensure a reliable rank. For example, on average, one block receives an update every 34 iterations, resulting in poor ranking performance. Besides, this approach will encounter memory explosion at a growing " + }, + { + "bbox": [ + 304, + 462, + 547, + 713 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 462, + 547, + 713 + ], + "type": "text", + "content": ". Even if we can solve the ranking issue, it requires much more GPU memory to save the trainable parameters, which prevents proxyless search on large datasets or big models. In contrast, our method doesn't suffer from these issues." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5978" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 59, + 71, + 179, + 157 + ], + "blocks": [ + { + "bbox": [ + 59, + 71, + 179, + 157 + ], + "lines": [ + { + "bbox": [ + 59, + 71, + 179, + 157 + ], + "spans": [ + { + "bbox": [ + 59, + 71, + 179, + 157 + ], + "type": "image", + "image_path": "4660e03161ed6269f9b2493e8618552f01332d097d1a88586d596818f7095f1e.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 167, + 547, + 204 + ], + "lines": [ + { + "bbox": [ + 46, + 167, + 547, + 204 + ], + "spans": [ + { + "bbox": [ + 46, + 167, + 547, + 204 + ], + "type": "text", + "content": "Figure 7: Histogram of one-shot model accuracies sampled from MixPath supernets trained on CIFAR-10 in " + }, + { + "bbox": [ + 46, + 167, + 547, + 204 + ], + "type": "inline_equation", + "content": "S_{1}" + }, + { + "bbox": [ + 46, + 167, + 547, + 204 + ], + "type": "text", + "content": ", activating at most " + }, + { + "bbox": [ + 46, + 167, + 547, + 204 + ], + "type": "inline_equation", + "content": "m = 1,2,3,4" + }, + { + "bbox": [ + 46, + 167, + 547, + 204 + ], + "type": "text", + "content": " paths respectively. In all cases, the supernet trained without SBNs severely underestimates a large proportion of candidate architectures. Note when " + }, + { + "bbox": [ + 46, + 167, + 547, + 204 + ], + "type": "inline_equation", + "content": "m = 1" + }, + { + "bbox": [ + 46, + 167, + 547, + 204 + ], + "type": "text", + "content": " it falls back to a vanilla BN." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 179, + 72, + 298, + 156 + ], + "blocks": [ + { + "bbox": [ + 179, + 72, + 298, + 156 + ], + "lines": [ + { + "bbox": [ + 179, + 72, + 298, + 156 + ], + "spans": [ + { + "bbox": [ + 179, + 72, + 298, + 156 + ], + "type": "image", + "image_path": "68c9059767e1eec82a94620aa8c73de79444f2c30472e6b48319937a993fcb80.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 298, + 72, + 416, + 156 + ], + "blocks": [ + { + "bbox": [ + 298, + 72, + 416, + 156 + ], + "lines": [ + { + "bbox": [ + 298, + 72, + 416, + 156 + ], + "spans": [ + { + "bbox": [ + 298, + 72, + 416, + 156 + ], + "type": "image", + "image_path": "4136c10840931dc6d1d497d01f06fa0753c989d241b6530dc84ff16432ccb408.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 416, + 72, + 534, + 157 + ], + "blocks": [ + { + "bbox": [ + 416, + 72, + 534, + 157 + ], + "lines": [ + { + "bbox": [ + 416, + 72, + 534, + 157 + ], + "spans": [ + { + "bbox": [ + 416, + 72, + 534, + 157 + ], + "type": "image", + "image_path": "4ae382bd15d9c7f0aaa4c137ee1c707ecf4530ece762b6c900382f341eb42780.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 55, + 220, + 168, + 318 + ], + "blocks": [ + { + "bbox": [ + 55, + 220, + 168, + 318 + ], + "lines": [ + { + "bbox": [ + 55, + 220, + 168, + 318 + ], + "spans": [ + { + "bbox": [ + 55, + 220, + 168, + 318 + ], + "type": "image", + "image_path": "609139b758c0d7a3c80dbf27c47b996164d5aef934b5b8933f6a82c066849d7d.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 334, + 289, + 360 + ], + "lines": [ + { + "bbox": [ + 46, + 334, + 289, + 360 + ], + "spans": [ + { + "bbox": [ + 46, + 334, + 289, + 360 + ], + "type": "text", + "content": "Figure 8: Rank performance comparison between 'enumerating all compositions' and our method." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 173, + 220, + 286, + 317 + ], + "blocks": [ + { + "bbox": [ + 173, + 220, + 286, + 317 + ], + "lines": [ + { + "bbox": [ + 173, + 220, + 286, + 317 + ], + "spans": [ + { + "bbox": [ + 173, + 220, + 286, + 317 + ], + "type": "image", + "image_path": "663209b5c32a527c99d9a2a13c6b4fe46a48d45a6f78d58a0d8287131cd87339.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 379, + 220, + 392 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 379, + 220, + 392 + ], + "spans": [ + { + "bbox": [ + 47, + 379, + 220, + 392 + ], + "type": "text", + "content": "5.2. Comparison of search strategies" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 398, + 288, + 458 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 398, + 288, + 458 + ], + "spans": [ + { + "bbox": [ + 46, + 398, + 288, + 458 + ], + "type": "text", + "content": "We use the search space " + }, + { + "bbox": [ + 46, + 398, + 288, + 458 + ], + "type": "inline_equation", + "content": "S_{3}" + }, + { + "bbox": [ + 46, + 398, + 288, + 458 + ], + "type": "text", + "content": " on ImageNet to compare the adopted NSGA-II search algorithm [10] with random search by charting the Pareto-front of models found by both methods in Fig. 1 (appendix). NSGA-II has an advantage that the elite models have higher accuracies and fewer FLOPs." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 465, + 202, + 478 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 465, + 202, + 478 + ], + "spans": [ + { + "bbox": [ + 47, + 465, + 202, + 478 + ], + "type": "text", + "content": "5.3. Pipeline component analysis" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 483, + 287, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 483, + 287, + 591 + ], + "spans": [ + { + "bbox": [ + 46, + 483, + 287, + 591 + ], + "type": "text", + "content": "Apart from the ablation studies on NAS-Bench-101 [40], we make a component analysis of our pipeline in " + }, + { + "bbox": [ + 46, + 483, + 287, + 591 + ], + "type": "inline_equation", + "content": "S_{1}" + }, + { + "bbox": [ + 46, + 483, + 287, + 591 + ], + "type": "text", + "content": ". We focus on the supernet training with and without SBN by fixing the second-stage searching algorithm. Each pipeline is run three times on different random seeds. Our goal is to find the best models under 500M FLOPS. As a result, with SBN enabled, we obtain " + }, + { + "bbox": [ + 46, + 483, + 287, + 591 + ], + "type": "inline_equation", + "content": "97.44\\%" + }, + { + "bbox": [ + 46, + 483, + 287, + 591 + ], + "type": "text", + "content": " top-1 accuracy, higher than the best " + }, + { + "bbox": [ + 46, + 483, + 287, + 591 + ], + "type": "inline_equation", + "content": "97.12\\%" + }, + { + "bbox": [ + 46, + 483, + 287, + 591 + ], + "type": "text", + "content": " when SBN is disabled. This confirms that it mainly benefits from our novel training mechanism." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 599, + 123, + 610 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 599, + 123, + 610 + ], + "spans": [ + { + "bbox": [ + 47, + 599, + 123, + 610 + ], + "type": "text", + "content": "5.4. Discussions" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 617, + 289, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 289, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 289, + 713 + ], + "type": "text", + "content": "Why can SBNs stabilize supernet training and improve ranking ability? We have verified that high cosine similarity is not the only factor that guarantees the stable training of a multi-path supernet. It is more important to ensure that the feature distributions are consistent. Otherwise, the training is disrupted because a single BN is not enough to capture changing statistics from multiple paths. The proposed SBNs are able to track a variety of distribu" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 217, + 547, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 217, + 547, + 264 + ], + "spans": [ + { + "bbox": [ + 304, + 217, + 547, + 264 + ], + "type": "text", + "content": "tions, alleviating this instability. Empirically, better training of the supernet also gives more appropriate weights for each subnetwork, with which we can better estimate the ground-truth performance of the stand-alone models." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 265, + 547, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 265, + 547, + 408 + ], + "spans": [ + { + "bbox": [ + 304, + 265, + 547, + 408 + ], + "type": "text", + "content": "Why can SBNs work together with BN postcalibration? According to the analysis in Section 3.2, the parameters " + }, + { + "bbox": [ + 304, + 265, + 547, + 408 + ], + "type": "inline_equation", + "content": "\\mu, \\sigma" + }, + { + "bbox": [ + 304, + 265, + 547, + 408 + ], + "type": "text", + "content": " of SBNs that follow a multi-path combination are multiples of those of a single-path, as shown in Fig. 5. But not all the parameters fit well into this relationship, post BN calibration can then readjust the mean and variance of the inputs to fit the learned parameters " + }, + { + "bbox": [ + 304, + 265, + 547, + 408 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 265, + 547, + 408 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 265, + 547, + 408 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 304, + 265, + 547, + 408 + ], + "type": "text", + "content": ". To some extent, it can make up for the gap from the supernet to submodels. Noticeably, SBN is a type of regularization technique during the supernet training, while BN calibration is a post-processing trick. They can work in an orthogonal way and both contribute to the ranking." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 408, + 547, + 504 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 408, + 547, + 504 + ], + "spans": [ + { + "bbox": [ + 304, + 408, + 547, + 504 + ], + "type": "text", + "content": "Comparison with Switchable Batch Normalization Switchable BN [42] is only applied to learn the statistics of a limited number " + }, + { + "bbox": [ + 304, + 408, + 547, + 504 + ], + "type": "inline_equation", + "content": "(K)" + }, + { + "bbox": [ + 304, + 408, + 547, + 504 + ], + "type": "text", + "content": " of sub-architectures with " + }, + { + "bbox": [ + 304, + 408, + 547, + 504 + ], + "type": "inline_equation", + "content": "K = \\{4,8\\}" + }, + { + "bbox": [ + 304, + 408, + 547, + 504 + ], + "type": "text", + "content": " channel configurations. Our SBN is designed to match the changing feature statistics from a more flexible combination of different choice paths, while the number of channels is fixed. The former is used for network pruning while our SBN is to stabilize the training of the multi-path supernet." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 514, + 378, + 526 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 514, + 378, + 526 + ], + "spans": [ + { + "bbox": [ + 306, + 514, + 378, + 526 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 534, + 547, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 547, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 547, + 689 + ], + "type": "text", + "content": "In this paper, we propose a unified approach for two-stage one-shot neural architecture search, with a multi-path search space enabled. Existing single-path approaches can thus be regarded as a special case. The proposed method uses SBNs to catch the changing features from various branch combinations, which successfully solves two difficulties of vanilla multi-path methods: the unstable training of supernet and the unbearable weakness of model ranking. Moreover, by exploiting feature similarities from different path combinations, we reduced the number of required exponential SBNs to " + }, + { + "bbox": [ + 304, + 534, + 547, + 689 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 534, + 547, + 689 + ], + "type": "text", + "content": ", identical to the number of allowed paths. Our method can enjoy the model ranking capacity of the one-shot supernet and robustly search good models across various benchmarks." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 689, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 547, + 713 + ], + "type": "text", + "content": "Acknowledgement: This work was supported by National Key R&D Program of China (No. 2022ZD0118700)." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5979" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 16, + "blocks": [ + { + "bbox": [ + 53, + 91, + 288, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 288, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 288, + 135 + ], + "type": "text", + "content": "[1] Haoping Bai, Meng Cao, Ping Huang, and Jiulong Shan. 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However, these models still face difficulties in learning fine-grained semantic alignment at the pixel level and predicting accurate object masks. To address this issue, we propose MixReorg, a novel and straightforward pre-training paradigm for semantic segmentation that enhances a model's ability to reorganize patches mixed across images, exploring both local visual relevance and global semantic coherence. Our approach involves generating fine-grained patch-text pairs data by mixing image patches while preserving the correspondence between patches and text. The model is then trained to minimize the segmentation loss of the mixed images and the two contrastive losses of the original and restored features. With MixReorg as a mask learner, conventional text-supervised semantic segmentation models can achieve highly generalizable pixel-semantic alignment ability, which is crucial for open-world segmentation. After training with large-scale image-text data, MixReorg models can be applied directly to segment visual objects of arbitrary categories, without the need for further fine-tuning. Our proposed framework demonstrates strong performance on popular zero-shot semantic segmentation benchmarks, outperforming GroupViT by significant margins of $5.0\\%$ , $6.2\\%$ , $2.5\\%$ , and $3.4\\%$ mIoU on PASCAL VOC2012, PASCAL Context, MS COCO, and ADE20K, respectively.", + "bbox": [ + 75, + 376, + 473, + 785 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 811, + 209, + 825 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Image segmentation has important applications in scenarios such as virtual presence, virtual try-on, movie post", + "bbox": [ + 76, + 837, + 468, + 867 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ca005d1882d9048c71d9dfe274aab06f15f4429662c50a1c4b1799d00c21d46d.jpg", + "image_caption": [ + "Figure 1: Comparison between GroupViT [38] and MixReorg. (a) GroupViT obtains image segmentation implicitly from image-text pairs to achieve cross-modal semantic alignment. (b) MixReorg explicitly constructs the fine-grained patch-text pairs data from the image-text pairs for free by mixing the patches from different images and preserving the correspondence between patches and text." + ], + "image_footnote": [], + "bbox": [ + 506, + 344, + 890, + 525 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "production, and autonomous driving. Currently, state-of-the-art semantic segmentation methods [35, 30, 6] benefit from a large number of densely annotated data. However, the assumption of this closed-world setting requires that all categories of objects that appear in the test set are included in the training set. This heavy dependence on annotations limits that they can only work well in closed-set settings. However, considering ubiquitous new concepts in real-world scenarios, learning an open-world segmentation model is more practical, but it is also more challenging. The open-world segmentation model is required to segment all entities and objects class-agnostically and exhaustively during training and be highly generalizable for aligning pixels with new semantics during testing.", + "bbox": [ + 496, + 625, + 893, + 837 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Early methods achieve open-world semantic segmentation through few-shot learning [3] or unsupervised clustering [26]. The former actually still assumes that the training and testing classes are in the same latent feature space,", + "bbox": [ + 496, + 839, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Equal contribution.", + "bbox": [ + 94, + 875, + 207, + 887 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Corresponding author.", + "bbox": [ + 96, + 887, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "1196", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/503e2d745a5c7ef6bc217368896d2fa26169737700839cfc9bfccc478ebb53f7.jpg", + "image_caption": [ + "Figure 2: Visual comparison between MixReorg and GroupViT [38] on images from the network. Our method can better handle open-world classes for segmentation task." + ], + "image_footnote": [], + "bbox": [ + 84, + 88, + 468, + 209 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "while the latter cannot guarantee the consistency of segmentation semantics. Recently, GroupViT [38] achieves state-of-the-art open-world segmentation performance using only text supervision. It realizes the automatic grouping of image patches by vision-language contrastive learning (Figure 1 (a)). ViL-Seg [22] implements image segmentation by introducing additional online clustering of visual embeddings for vision-language contrast. Massive image-text pairs provide rich visual and textual semantics for open-world scenarios. Similar to other CLIP-based [28] vision-language pre-training models (VLM) [32, 41, 19], although these methods achieve local information alignment of different modalities to a certain extent, they are still a computationally-based implicit matching strategy (fine-grained matching is learned by computing patch-text [32] or token-wise [41] similarity matrices). Therefore, how to learn more fine-grained semantic alignment from image-text pair data becomes a key challenge for text-based supervised open-world segmentation tasks.", + "bbox": [ + 75, + 273, + 472, + 561 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Inspired by the related work of mixed image modeling [27, 21], we propose a simple and novel cross-modal mixed image reconstruction mask learner. Specifically, as shown in Figure 1 (b), MixReorg mixes patches from different images to generate mixed images. Unlike previous methods for jigsaw puzzle [27] or mixed image reconstruction [21] in the single visual modality, MixReorg's mixed patch reorganization is a cross-modal mask learner designed for semantic segmentation. MixReorg preserves the correspondence between each patch and text when mixing image patches (the legend of Figure 1 (b)). In this way, we can obtain fine-grained patch-text pairs from the image-text data for free.", + "bbox": [ + 75, + 563, + 468, + 744 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "However, there are still two challenges: (i) the mixed image segmentation is easily disturbed by low-level features, which makes the model unable to realize patch reorganization of mixed images by high-level semantics; (ii) each patch in mixed images are easily interfered by irrelevant patches from different images in the transformer layers, which may cause the image semantics to be difficult to match with the corresponding text.", + "bbox": [ + 75, + 746, + 468, + 867 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "For the first challenge, we propose two strategies of contextual mixing and progressive mixing to solve this prob", + "bbox": [ + 76, + 869, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "lem. The contextual mixing strategy allows each patch in the mixed image to obtain the global semantics of its original image in advance by adding a transformer layer before the mixing operation, thereby forcing the model to learn the mixed image reorganization from high-level semantics. Furthermore, to further enhance the global information in the mixed image features, we propose to use the original image features to enhance the global semantics in the mixed image features. For the second challenge, we present a mixing restoration strategy. It guarantees the semantic association of each patch token in the mixed image with the text through contrastive learning between the image recovered from mixed image and the text. In this way, the mutual interference between patches from different images in the mixed image can be effectively suppressed.", + "bbox": [ + 496, + 90, + 890, + 316 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In general, MixReorg constructs a set of fine-grained patch-text pairs for free from image-text pair data, and successfully builds a cross-modal mixed image patch reorganization mask learner for open-world segmentation tasks. The proposed MixReorg as a good mask learner also shows strong performance compared with the popular zero-shot semantic segmentation baselines, achieving the performance of $50.5\\%$ , $25.4\\%$ , $23.6\\%$ and $10.1\\%$ mIoU on multiscale evaluations on PASCAL VOC2012, PASCAL Context, MS COCO and ADE20K, respectively. The visualization in Figure 2 shows that MixReorg significantly outperforms GroupViT [38] on open-world segmentation. Our contributions can be summarized as follows:", + "bbox": [ + 496, + 316, + 892, + 512 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a novel and simple method that can easily construct patch-text data with fine-grained matching relationships from image-text data, thereby providing densely supervised information for open-world segmentation.", + "- For the constructed patch-text data, we propose a cross-modal mixed patch reorganization method. It successfully addresses the challenge of model failure due to mixed image segmentation susceptible to low-level features and irrelevant patches.", + "- The proposed MixReorg exhibits strong open-world segmentation performance and significantly outperforms current state-of-the-art zero-shot segmentation baselines." + ], + "bbox": [ + 517, + 513, + 890, + 741 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 753, + 640, + 768 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "VLM and Segmentation. Recently, vision-language pretraining models [28, 17] have achieved great success. The models [8, 28, 38, 40] trained with VLM are flexible and versatile, and can adapt to visual [38, 25, 28, 32] and multimodal [37, 16, 42] upstream and downstream tasks only by using the matching relationship of image-text data. This success has also been found in segmentation and has attracted the attention of lots of researchers [38, 32, 39, 44].", + "bbox": [ + 496, + 779, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "1197", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Because traditional semantic segmentation is limited by expensive manual dense annotation, VLMs are expected to break this limitation. Although the above methods achieve promising performance, using image-text sample-level matching relations to learn segmentation masks still faces the challenge of lacking local dense supervision information. In addition, there are some works [41, 32, 19] that explore the alignment of multi-modal local information, but they are still computationally-dominated pseudolocal information correspondence without hard fine-grained supervision from the data level. Therefore, how to obtain finer-grained local supervision information from image-text data through data-level improvement is in great demand for semantic segmentation.", + "bbox": [ + 75, + 90, + 472, + 303 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Self-Supervision Strategies. Self-supervision is an effective way to avoid the limitation of expensive manual annotations. It builds a self-supervised pipeline by fully mining the properties of the data itself. For example, self-supervision strategies such as masked image reconstruction [12, 21, 18], jigsaw puzzles [27], multi-view contrast [2, 45, 5] and angle recognition [11] are widely adopted in the vision domain. Similar self-supervision strategies have been widely and successfully applied in natural language processing [7, 34]. But the above methods are all designed for the single modality. In contrast, semantic segmentation not only needs to consider the representation and segmentation of image features but also needs to consider cross-modal semantic alignment. Therefore, how to draw more supervised information from image-text data by borrowing self-supervision strategies from the vision domain is very beneficial for semantic segmentation. Especially for the extraction of cross-modal fine-grained supervision information.", + "bbox": [ + 75, + 306, + 472, + 580 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Open-World Segmentation. The open-world problem has been studied in the context of recognition [1, 23], namely how to get a model trained only on a given closed-world dataset to also recognize new classes of objects. Similar settings are also used in object detection [36, 15] and segmentation [3, 26, 38]. For example, [26] proposes an unsupervised open-world semantic segmentation; however, it obtains the mask of the image by a clustering method without any network parameter update. On the other hand, VLMs [28, 19, 8] exhibit strong performance and generalization ability with the help of massive image-text pair data. Inspired by this, TSEG [32] and ICILP [19] attempt to obtain fine-grained semantic alignment from image-text pairs to achieve image segmentation. Similarly, GroupViT [38] introduces a set of learnable group tokens for ViT to group patches and uses the generated segment tokens to align with text embeddings. The massively available image-text pair data provides rich visual and textual semantics for open-world scenarios [40]. Therefore, open-world semantic segmentation based on text supervision can achieve more refined segmentation results at a lower cost of annotation.", + "bbox": [ + 75, + 583, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Based on the above observations, this paper follows the open-world semantic segmentation setting based on text supervision to further improve the performance of semantic segmentation.", + "bbox": [ + 496, + 90, + 893, + 151 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 498, + 167, + 635, + 186 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The overall framework of the MixReorg mask learner is shown in Figure 3. MixReorg is CLIP-based [28] and mainly consists of an image encoder and a text encoder. We use the text encoder from CLIP [28]. MixReorg's image encoder mainly has three stages: contextual mixing, progressive mixing, and mixing restoration (Sec. 3.1). Then, the loss composition of MixReorg is described in detail in Sec. 3.2. Finally, the total loss is introduced in Sec. 3.3.", + "bbox": [ + 496, + 194, + 893, + 316 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. MixReorg", + "text_level": 1, + "bbox": [ + 498, + 327, + 616, + 343 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Contextual Mixing. As shown in Figure 3(a), in the contextual image patch mixing stage, patches from different images are randomly mixed to construct a set of mixed images with known segmentation masks. According to the original image-text pairs, the patch-text correspondence of the mixed images is preserved, and the mixed image masks are used as the semantic segmentation labels of the mixed images. Similar to [21], the mixed images only have randomly mixed patch tokens from different images at their same locations. Specially, unlike [21], MixReorg adopts a contextual information image patch mixing strategy. We add a transformer layer before the image patch mixing operation to provide each patch the global image semantic which is closer to the text to create the coherence between patch and text. Meanwhile, it can preliminarily force the model to learn the mixed image patch reorganization from high-level features, thus effectively avoiding the interference of low-level features with the semantic learning of the model.", + "bbox": [ + 496, + 347, + 893, + 619 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Specifically, given a batch of image-text pairs $\\{(x_i^I,x_i^T)\\}_{i = 1}^B$ . Following the design in ViT [9], we first split each input image into $N$ non-overlapping patches and linearly project each patch into a latent space. These projected patches are denoted as $\\{\\mathrm{p}_i\\}_{i = 1}^N$ . For $M$ image-text pairs $\\{(x_i^I,x_i^T)\\}_{i = 1}^M$ , MixReorg randomly mixes the patches from $M$ different images to construct $M$ mixed images, and the corresponding patch composition of $M$ mixed images can be denoted as", + "bbox": [ + 496, + 619, + 893, + 757 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {m i x} \\left(\\left\\{\\left\\{\\mathrm {p} _ {i} \\right\\} _ {i = 1} ^ {N} \\right\\} _ {m = 1} ^ {M}\\right) = \\left\\{ \\right.\\left.\\left.\\left. \\mathrm {p} _ {m, i} ^ {j} \\right\\} _ {i = 1} ^ {N} \\right\\} _ {m = 1} ^ {M}, 1 \\leq j \\leq M, \\right. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 511, + 762, + 890, + 795 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathrm{p}_{m,i}^{j}$ denotes that the $i$ -th patch of the $m$ -th mixed image comes from the $j$ -th image. Correspondingly, we keep the correspondence between each image patch and the text corresponding to the original image, resulting in a semantic segmentation dataset with patch-text correspondence. The patch-text correspondence of the $m$ -th mixed image can be expressed as $\\{\\mathrm{p}_{m,i}^{j}, x_{j}^{T}\\}_{i=1}^{N}$ . Therefore, we obtain a set of", + "bbox": [ + 496, + 794, + 893, + 905 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "1198", + "bbox": [ + 482, + 944, + 517, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/8721a114592d9a12bc2a0a5203c3358b42dced1f71ed32dd6464c5f771aff449.jpg", + "image_caption": [ + "Figure 3: The training pipeline and framework of MixReorg (take two images as an example). MixReorg's image encoder can be divided into three stages: (a) contextual mixing stage: a set of additional patch-text pairs with known segmentation mask is obtained by randomly mixing contextual patches from different images; (b) progressive mixing stage: the original image features are used to enhance the global information of the mixed image features after mixing; (c) mixing restoration stage: the original features, mixed features, and restored features are segmented through a two-stage grouping block [38], and the corresponding segment tokens are obtained. Note that we omit group tokens in the forward process for simplicity. During testing, MixReorg only needs to execute the original image branch." + ], + "image_footnote": [], + "bbox": [ + 117, + 85, + 851, + 315 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "sample-level image-text pairs $\\{(x_i^I,x_i^T)\\}_{i = 1}^B$ and a set of patch-level patch-text pairs $\\{\\{\\mathrm{p}_{m,i}^{j},x_{j}^{T}\\}_{i = 1}^{N}\\}_{m = 1}^{M}$", + "bbox": [ + 75, + 409, + 468, + 444 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Progressive Mixing. Mixed patches' features cannot improve after Contextual Mixing because of the semantic mixing in mixed images. Since more layers in Contextual Mixing will lead to more parameters, we propose Progressive Mixing to enhance mixed features without additional parameters. As shown in Figure 3(b), in the progressive mixing phase, the patch tokens of normal and mixed images are concatenated with $s_1$ learnable group tokens $\\{g_i\\}_{i=1}^{s_1}$ respectively and fed to the multi-layer transformers independently. At the same time, the original features are used to enhance the contextual information of the mixed features. The above process of an original image going through the $l$ -th transformer layer can be represented as", + "bbox": [ + 75, + 441, + 468, + 638 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{\\left\\{\\hat {g} _ {i} \\right\\} _ {i = 1} ^ {s _ {1}}, \\left\\{\\hat {\\mathrm {p}} _ {i} \\right\\} _ {i = 1} ^ {N} \\right\\} = \\operatorname {T r a n s} _ {l} \\left(\\left[ \\left\\{g _ {i} \\right\\} _ {i = 1} ^ {s _ {1}}; \\left\\{\\mathrm {p} _ {i} \\right\\} _ {i = 1} ^ {N} \\right]\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 96, + 641, + 468, + 662 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $[ ; ]$ denotes the concatenation operator. Similarly, the output of the $m$ -th mixed image through the $l$ -th transformer layer can be expressed as", + "bbox": [ + 75, + 664, + 468, + 709 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{r l} & {\\{\\{\\hat {g} _ {i} \\} _ {i = 1} ^ {s _ {1}}, \\{\\hat {\\mathrm {p}} _ {m, i} ^ {j} \\} _ {i = 1} ^ {N} \\} = \\operatorname {T r a n s} _ {l} \\left(\\left[ \\left\\{g _ {i} \\right\\} _ {i = 1} ^ {s _ {1}}; \\left\\{\\mathrm {p} _ {m, i} ^ {j} \\right\\} _ {i = 1} ^ {N} + \\right. \\right.} \\\\ & {\\qquad \\left. \\operatorname {m i x} \\left(\\left\\{\\left\\{\\left\\{\\mathrm {p} _ {i} \\right\\} _ {i = 1} ^ {N} \\right\\} _ {m = 1} ^ {M} \\right\\rbrace_ {l - 1}\\right) _ {m} \\right].} \\end{array} \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 713, + 468, + 768 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Mixing Restoration. Although we can achieve patch-text alignment by mixed images, there are a lot of different semantics in one mixed image which will interfere with each other. Therefore, this requires the patches from different images in a mixed image still need to maintain a semantic match with the corresponding text.", + "bbox": [ + 75, + 779, + 468, + 869 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To this end, as shown in Figure 3(c), in the mixing restoration phase, MixReorg also restores the mixed image", + "bbox": [ + 75, + 869, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "according to the patch position of the image before mixing. The original features $\\{\\mathrm{p}_i\\}_{i = 1}^N$ , mixed features $\\{\\mathrm{p}_{m,i}^{j}\\}_{i = 1}^{N}$ and restored features $r e(\\{\\mathrm{p}_{m,i}^{j}\\}_{i = 1}^{N})$ are segmented through a two-stage grouping block [38], and the corresponding segment tokens $\\{\\mathrm{seg}_i\\}_{i = 1}^{s_2}$ are obtained. These segment tokens are fed into multiple transformer layers and then projected to the same dimensionality $D$ as text embeddings $Z^{T}\\in \\mathbb{R}^{B\\times D}$ through an MLP.", + "bbox": [ + 498, + 410, + 890, + 534 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Cross-Modal Mixed Patch Reorganization Loss", + "text_level": 1, + "bbox": [ + 498, + 554, + 890, + 570 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Mixed Segmentation Loss. Cross-modal mixed patch reorganization is a core module designed in MixReorg for semantic segmentation. It provides the model with more refined local alignment information by using a constructed mixed image dataset with patch-text correspondence. We expect the model to learn more fine-grained semantic alignment with the help of the constructed patch-text pairs. And the calculation process of the mixed image segmentation mask is shown in Figure 4, where every $B_{I}$ (e.g., $B_{I} = M$ ) images are mixed. The mixed image segment tokens and the text embeddings of the whole batch are used to compute the similarity $S \\in \\mathbb{R}^{B_I \\times s_2 \\times B}$ for the text, where $\\otimes$ denotes matrix multiplication. Since we adopt a two-stage grouping block [38], we have the attention map $A \\in \\mathbb{R}^{B_I \\times HW \\times s_2}$ ( $HW = N$ ), which contains the grouping relationship between $HW$ patches and $s_2$ segment tokens. Further, by $A \\otimes S$ , we can predict the segmentation mask $M_p \\in \\mathbb{R}^{B_I \\times HW \\times B}$ of the mixed image. Finally, we compute the cross-entropy loss between the mixed image masks $M_{mix}$ and the prediction masks $M_p$ , formulated as", + "bbox": [ + 496, + 577, + 890, + 878 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {s e g}} = \\mathcal {L} _ {C E} \\left(M _ {p}, M _ {\\text {m i x}}\\right), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 606, + 885, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "1199", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/445400a731bc889e5b512d6d4dbd90efedac1b7f752d88827f2e20aa3ebf40ee.jpg", + "image_caption": [ + "Figure 4: Cross-modal mixed patch reorganization, which combines attention maps and segmentation tokens from the image encoder, and text embeddings to reorganize and predict segmentation masks for mixed images. Where $B_{I} = M$ means that every $B_{I}$ images are mixed. For simplicity, we take a mixed image generated by mixing two images as an example." + ], + "image_footnote": [], + "bbox": [ + 81, + 89, + 472, + 247 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{CE}(\\pmb {p},\\pmb {q}) = -\\sum_{i}\\pmb{q}_{i}\\log (\\pmb{p}_{i})$ is the cross-entropy loss of output $\\pmb{p}$ and target $\\pmb{q}$ .", + "bbox": [ + 75, + 349, + 468, + 380 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Restoration Contrastive Loss. Furthermore, we consider cross-modal semantic contrastive learning of mixing restoration features and text embeddings. Specifically, in order to take full advantage of the correspondence provided by the image-text pair and enhance the model's ability to align semantically across modalities, MixReorg computes the contrastive loss and the multi-label image-text contrastive loss [38] between the output of the restored features branch and the text embeddings, respectively. The calculation of the total image-text contrastive loss is as follows", + "bbox": [ + 75, + 382, + 468, + 532 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {I \\leftrightarrow T} ^ {r e} = \\mathcal {L} _ {I \\rightarrow T} ^ {r e} + \\mathcal {L} _ {I \\leftarrow T} ^ {r e}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 186, + 542, + 468, + 559 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the image-to-text contrastive loss is defined as", + "bbox": [ + 76, + 561, + 426, + 575 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {I \\rightarrow T} ^ {r e} = - \\frac {1}{B} \\sum_ {i = 1} ^ {B} \\log \\frac {\\exp \\left(z _ {i} ^ {I} \\cdot z _ {i} ^ {T} / \\tau\\right)}{\\sum_ {j = 1} ^ {B} \\exp \\left(z _ {i} ^ {I} \\cdot z _ {j} ^ {T} / \\tau\\right)}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 119, + 582, + 468, + 625 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "and the text-to-image contrastive loss is defined as", + "bbox": [ + 76, + 628, + 410, + 643 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {I \\leftarrow T} ^ {r e} = - \\frac {1}{B} \\sum_ {i = 1} ^ {B} \\log \\frac {\\exp \\left(z _ {i} ^ {T} \\cdot z _ {i} ^ {I} / \\tau\\right)}{\\sum_ {j = 1} ^ {B} \\exp \\left(z _ {i} ^ {T} \\cdot z _ {j} ^ {I} / \\tau\\right)}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 119, + 650, + 468, + 691 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\tau$ is a learnable temperature parameter, and $z_{i}^{I}$ and $z_{i}^{T}$ are image and text embedding for image-text pairs $\\{(x_i^I,x_i^T)\\}_{i = 1}^B$ . In addition, we calculate the multi-label contrastive loss of the restored features branch as follows", + "bbox": [ + 76, + 698, + 468, + 758 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {I \\leftrightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e} = \\mathcal {L} _ {I \\rightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e} + \\mathcal {L} _ {I \\leftarrow \\{T _ {k} \\} _ {k = 1} ^ {K}}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 125, + 768, + 468, + 789 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\{T_k\\}_{k=1}^K$ is an additional $K$ text labels generated using the \"prompting engineering\" mechanism in [28],", + "bbox": [ + 76, + 791, + 468, + 821 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {I \\rightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e} = - \\frac {1}{B} \\sum_ {i = 1} ^ {B} \\log \\frac {\\sum_ {k = 1} ^ {K} \\exp \\left(z _ {i} ^ {I} \\cdot z _ {i} ^ {T _ {k}} / \\tau\\right)}{\\sum_ {k = 1} ^ {K} \\sum_ {j = 1} ^ {B} \\exp \\left(z _ {i} ^ {I} \\cdot z _ {j} ^ {T _ {k}} / \\tau\\right)} \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 828, + 472, + 890 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "and", + "bbox": [ + 78, + 886, + 104, + 898 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/bd491be1289fc16364185835df56c362fca610fa20ae503f14b2228725b8c0c9.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Arch.MethodMask mIoU (%)
ViT [9]*pixel-wise20.1
K-means25.0
Mean-shift20.7
Spectral clustering19.7
GroupViT [38]-41.1
ViewCo [31]-45.7
MixReorg (ours)-47.9
", + "bbox": [ + 513, + 88, + 875, + 228 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1: Comparison with zero-shot semantic segmentation baselines on PASCAL VOC. GroupViT[38] and MixReorg are trained on CC12M. The superscript * means the results are from [38].", + "bbox": [ + 498, + 233, + 890, + 275 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {I \\leftarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e} = - \\frac {1}{K B} \\sum_ {k = 1} ^ {K} \\sum_ {i = 1} ^ {B} \\log \\frac {\\exp \\left(z _ {i} ^ {T _ {k}} \\cdot z _ {i} ^ {I} / \\tau\\right)}{\\sum_ {j = 1} ^ {B} \\exp \\left(z _ {i} ^ {T _ {k}} \\cdot z _ {j} ^ {I} / \\tau\\right)}. \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 500, + 282, + 895, + 340 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The total contrastive loss of the restored features and the text embeddings is as follows", + "bbox": [ + 498, + 339, + 890, + 369 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {r e} = \\mathcal {L} _ {I \\leftrightarrow T} ^ {r e} + \\mathcal {L} _ {I \\leftrightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e}. \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 596, + 375, + 890, + 393 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In summary, the total cross-modal mixed image patch reorganization loss is as follows", + "bbox": [ + 498, + 397, + 890, + 426 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {m i x e d}} = \\mathcal {L} _ {\\text {s e g}} + \\mathcal {L} _ {\\text {r e}}. \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 617, + 433, + 890, + 449 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Overall Loss Function", + "text_level": 1, + "bbox": [ + 500, + 455, + 705, + 470 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Similar to Eq. (11), the total contrastive loss between the original image features and the text embeddings is as follows", + "bbox": [ + 498, + 476, + 890, + 518 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {o r i}} = \\mathcal {L} _ {I \\leftrightarrow T} ^ {\\text {o r i}} + \\mathcal {L} _ {I \\leftrightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {\\text {o r i}}. \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 594, + 520, + 890, + 540 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Finally, the total loss of MixReorg is", + "bbox": [ + 500, + 539, + 743, + 554 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathcal {L} _ {\\text {m i x e d}} + \\mathcal {L} _ {\\text {o r i}}. \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 625, + 559, + 890, + 574 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "When testing, MixReorg only needs to execute the original image branch (the solid black line in Figure 3), so it does not add any extra testing time.", + "bbox": [ + 498, + 574, + 890, + 619 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 632, + 632, + 648 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Implementation Details", + "text_level": 1, + "bbox": [ + 500, + 657, + 715, + 672 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Architecture. The image encoder of MixReorg is based on a 2-stage GroupViT [38] with 12 transformer layers, while adding one transformer layer before the mix operation. The size of the input image is $224 \\times 224$ , the patch size is $16 \\times 16$ and the hidden dimensionality is 384. The model outputs 32 segment tokens (i.e., $s_2 = 32$ and $s_1 = 64$ ). Following [28, 38], the text encoder of MixReorg consists of 12 layers of transformer with the hidden feature dimensionality of 256.", + "bbox": [ + 498, + 674, + 890, + 794 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Training and Inference. During the training phase, we use CC12M [4] as the training dataset, which contains 12M image-text pairs. We apply the mix operation for every 16 images (i.e., $M = 16$ ). Following [38, 28], our batch size is 4096. We set the weight for each loss function to 1. During the inference phase, only the original image branch is executed. More details can be seen in Appendix.", + "bbox": [ + 498, + 795, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "1200", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/6866d7eba59bef2380a2dbd13daebfcb3189b7a829b2eb501585dd24629ca7ed.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Pre-trainingTransfer (mIoU (%))
Arch.ModelDatasetSupervisionZero-ShotPASCAL VOCPASCAL Context
ViTDeiT [33]ImageNetclassX53.035.9
DINO [2]ImageNetselfX39.120.4
DINOCC12M+YFCCselfX37.622.8
MoCo [13]ImageNetselfX34.321.3
MoCoCC12M+YFCCselfX36.123.0
CLIPSLIP* [25]LAION-20Mtext & self✓-12.3
CLIP-MAE* [8]LAION-20Mtext & self✓-16.8
MaskCLIP [8]LAION-20Mtext & self✓-17.7
ViewCo [31]CC12Mtext & self✓45.720.8
MaskCLIP [44]CLIP-400Mtext✓-21.7
CLIP* [28]LAION-20Mtext✓-13.5
GroupViT[38]CC12M+YFCCtext✓51.222.3
GroupViTCC12Mtext✓41.1 45.5†18.2 19.2†
MixReorg (ours)CC12Mtext✓47.9 (6.8 ↑) 50.5†(5.0 ↑)23.9 (5.7 ↑) 25.4†(6.2 ↑)
", + "bbox": [ + 133, + 88, + 831, + 409 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/29249a083e9774262369c87a6c060828d94f34869a327d8a2b9fc94129e0041d.jpg", + "table_caption": [ + "Table 2: Performance comparison on PASCAL VOC [10] and PASCAL Context [24]. Zero-shot means that the model is directly transferred to the semantic segmentation task without any fine-tuning on the target dataset. The superscript * denote the results are from [8]. † indicates the results of the multi-scale evaluation." + ], + "table_footnote": [], + "table_body": "
ModelPre-training DatasetTransfer mIoU (%)
ViewCo [31]CC12M20.6
GroupViT [38]CC12M+YFCC20.9
GroupViTCC12M18.4 21.1†
MixReorg (ours)CC12M21.3 (2.9 ↑) 23.6† (2.5 ↑)
", + "bbox": [ + 89, + 455, + 450, + 583 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Open-World Semantic Segmentation. We evaluate the performance of MixReorg on the open-world segmentation task on four commonly used open semantic segmentation datasets PASCAL VOC 2012 [10], PASCAL Context [24], COCO [20], and ADE20K [43]. They contain 20, 59, 80, and 150 foreground classes, respectively, with validation images of 1.5K, 5K, 5K, and 2K, respectively. MixReorg is transferred to the target dataset in a zero-shot manner without any fine-tuning. Following GroupViT [38], MixReorg obtains the corresponding segmentation of the image through the learned group token.", + "bbox": [ + 75, + 617, + 467, + 782 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparisons with Existing Methods", + "text_level": 1, + "bbox": [ + 75, + 792, + 390, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparison with Zero-Shot Baselines. In Table 1, we present a comparison of four ViT-based baselines, which utilize the image-text contrastive loss defined in CLIP [28] to train the vision and text encoders. These baselines employ pixel-wise, k-means, mean-shift, and spectral clustering strategies, respectively. Additionally, we in", + "bbox": [ + 75, + 810, + 467, + 900 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/7e4af9255e014e02931832468208058dcb615162e1996ee8461bdd642b9e4161.jpg", + "table_caption": [ + "Table 3: Performance comparison on COCO [20]. $\\dagger$ indicates the results of the multi-scale evaluation." + ], + "table_footnote": [], + "table_body": "
ModelPre-training DatasetTransfer mIoU (%)
ALIGNa[14]ALIGN-1800M9.7
ALIGNaHQITP-134M7.5
CLIPA[28]HQITP-134M5.1
CLIPCLIP-400M5.8
CLIPbLAION-20M7.7
SLIPb[25]LAION-20M6.8
GroupViT [38]CC12M5.8
6.7
MixReorg (ours)CC12M8.7 (2.9 ↑)
10.1† (3.4 ↑)
", + "bbox": [ + 514, + 455, + 874, + 642 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 4: Performance comparison on ADE20K [43]. The superscript ${}^{a}$ and ${}^{b}$ denote the results are from [29] and [8],respectively.", + "bbox": [ + 498, + 647, + 890, + 676 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "clude GroupViT [38], which employs a bottom-up grouping method. The results in Table 1 demonstrate that MixReorg outperforms both the ViT baselines and GroupViT (41.1% vs. 47.9%), indicating that MixReorg is effective in enhancing the segmentation ability of the model.", + "bbox": [ + 498, + 685, + 890, + 760 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparison with SoTA Methods. We conduct a comprehensive evaluation of MixReorg against fully-supervised methods [33], self-supervised methods [2, 13], vision-language contrastive learning baselines [44, 28, 38], and baselines combining vision-language contrastive learning with self-supervised learning [25, 8, 31]. Table 2 and Table 3 summarizes the comparison results on PASCAL VOC, PASCAL Context, and COCO datasets, both in single-scale and multi-scale evaluation settings. The results show that", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "1201", + "bbox": [ + 483, + 944, + 513, + 955 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "MixReorg outperforms all the methods by a significant margin, demonstrating its effectiveness in semantic segmentation. In comparison to GroupViT, MixReorg that pre-trains on CC12M yields substantial performance improvements of $6.8\\%$ mIoU, $5.7\\%$ mIoU, and $2.9\\%$ mIoU for single-scale evaluation, and $5.0\\%$ mIoU, $6.2\\%$ mIoU, and $2.5\\%$ mIoU for multi-scale evaluation on PASCAL VOC, PASCAL Context, and COCO, respectively. MixReorg also outperforms GroupViT which pre-trains on CC12M and YFCC with less data. Additionally, MixReorg has a clear advantage over the methods which rely on additional supervision information in the vision branch. Furthermore, we evaluate the performance of MixReorg on the ADE20K dataset, as shown in Table 4. MixReorg outperforms GroupViT by a significant margin (8.7% vs. 5.8%), demonstrating its superior performance in complex segmentation tasks.", + "bbox": [ + 75, + 90, + 472, + 332 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Image Classification. We evaluate the zero-shot classification performance of MixReorg on ImageNet. As shown in Table 5, MixReorg significantly outperforms GroupViT, indicating that MixReorg achieves better image-text alignment through fine-grained mask learning.", + "bbox": [ + 75, + 332, + 470, + 407 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/21b2b7673af0ad8368174ab216219a3e6a7462b68230d48551b713ce49f83bad.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Arch.Zero-shot
Acc@1 (%)Acc@5 (%)
GroupViT [38]37.565.5
MixReorg(ours)38.866.7
", + "bbox": [ + 109, + 407, + 434, + 472 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 491, + 230, + 507 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Contextual Mixing. In Table 6, we perform ablation on contextual mixing (CM) strategies. Specifically, we first ablate the parameter variation of the model. As the results show, by adding a transformer layer to GroupViT's image encoder (i.e., GroupViT+), the performance of the model remains consistent (18.4% vs. 18.2%). This shows that simply increasing the number of parameters does not improve the performance of the model. Further, we also compared MixReorg with only CM (i.e., row 3) and GroupViT+. They have the same amount of parameters, but MixReorg significantly outperforms GroupViT+ with the help of CM (19.3% vs. 18.2%). This shows that it is beneficial to help the model obtain more global semantic information in the early stage of the model. For MixReorg, it can be found that MixReorg without CM assistance (row 4) will degenerate to a similar performance to GroupViT, which indicates that CM plays a crucial role in MixReorg's mixed segmentation module (19.3% vs. 18.0% vs. 18.4%). This is mainly because CM can help MixReorg acquire global semantic information early in the model, thus forcing the model to learn mixed image reorganization from high-level semantic, which frees the model from low-level semantic information (e.g., texture and color, etc.) to obtain trivial solutions.", + "bbox": [ + 75, + 507, + 472, + 854 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation of Losses. In Table 6, we also conduct an ablation study on each loss that MixReorg uses. Specifically, $\\mathcal{L}_{seg}$ improves the performance by $1.2\\%$ mIoU ( $20.5\\%$ vs.", + "bbox": [ + 76, + 854, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/30cc0ac14daf0a67d79d51f76901acf1ca34e4757bf37867caf3ad238e040ef7.jpg", + "table_caption": [ + "Table 5: Zero-shot classification performance on ImageNet." + ], + "table_footnote": [], + "table_body": "
MethodCM\\( \\mathcal{L}_{seg} \\)\\( \\mathcal{L}_{re} \\)mIoU (%)
GroupViT---18.4
GroupViT+---18.2
MixReorg✓19.3
✓18.0
✓✓20.5
✓✓20.3
✓✓✓21.3
", + "bbox": [ + 531, + 82, + 859, + 207 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 6: On COCO, MixReorg's ablation study on contextual mixing (CM) and the loss functions. GroupViT+ means adding one transformer layer at the 1-st stage of GroupViT. For MixReorg, without CM means images are mixed prior to passing through the transformer layer that we add.", + "bbox": [ + 496, + 210, + 893, + 279 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/5738bd6c71bd12577e3c4908e9f4df7b86604d2a5ba65aeb72101bc60e5f70d8.jpg", + "image_caption": [ + "Figure 5: On COCO, MixReorg's ablation study on the number of progressive mixings and the number of images for the contextual mixing operation. (a) Yellow line: Ablation study on the number $P$ of the progressive mixing modules. We replace one progressive mixing module with one transformer layer to maintain the model size. (b) Red line: Ablation study on the number $M$ of images for each contextual mixing operation." + ], + "image_footnote": [], + "bbox": [ + 501, + 279, + 888, + 402 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "19.3%). This means that $\\mathcal{L}_{seg}$ plays a significant role. The model learns to distinguish different semantics in the image through $\\mathcal{L}_{seg}$ . Additionally, $\\mathcal{L}_{re}$ improves the performance of the model (20.3% vs. 19.3%). It helps the patches of the mixed image to maintain consistency between its original image semantics and corresponding text. Furthermore, by combining $\\mathcal{L}_{seg}$ and $\\mathcal{L}_{re}$ based on CM, the performance of MixReorg can be further improved (21.3% vs. 20.5% vs. 20.3%), which illustrates that CM and two loss functions are strongly related. CM is fundamental to achieving patch-text alignment since it provides global information to each patch, while $\\mathcal{L}_{seg}$ provides fine-grained semantic alignment ability and $\\mathcal{L}_{re}$ assisting $\\mathcal{L}_{seg}$ keeping the patches' original semantic, free from the interference from different images.", + "bbox": [ + 496, + 508, + 893, + 719 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Number of Images for Mixing. In Figure 5 (red line), we observe the performance impact of the number of images $M$ used for contextual mixing operation. It can be observed that $M = 16$ is optimal. As $M$ increases, mixed images contain more semantic categories, which is helpful for the model in learning semantic grouping (20.5% vs. 17.1%). However, increasing $M$ beyond a certain threshold (e.g.: $M = 32$ ) causes semantic representation in the mixed image to be insufficient due to resolution constraints, thereby interfering with model learning (20.5% vs. 18.2%).", + "bbox": [ + 496, + 719, + 893, + 869 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Progressive Mixing Module. In Figure 5 (yellow line), we study the number $P$ of the progressive mixing modules. We", + "bbox": [ + 498, + 869, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "1202", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/995491eab91c51e579d1793dc8cd1ffdc957808fd75110e8bc925672e0759dd5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 117, + 83, + 848, + 290 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "add one transformer layer when removing one progressive mixing module to maintain the model size. It can be seen that the model is optimal when the number $P$ of the progressive mixing modules is 6. The progressive mixing improves over $P = 0$ by about $7\\%$ mIoU ( $P = 3$ vs. $P = 0$ ). When $P = 0$ , the original image is not used to enhance the mixed image after the mixing operation. In this case, the lack of global information on the original image hinders the learning of the model. Obviously, with the increase of the progressive mixing modules, the semantics of the mixed image features become clearer, which is thus more conducive for model learning to distinguish different semantics, thus improving the model segmentation ability.", + "bbox": [ + 75, + 311, + 473, + 508 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Visualization", + "text_level": 1, + "bbox": [ + 76, + 513, + 215, + 527 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Qualitative Results. In Figure 6, we illustrate zero-shot semantic segmentation examples predicted by GroupViT and MixReorg to verify the segmentation capability of our method. As shown in Figure 6(a), MixReorg can handle more complex segmentation examples which have different classes in one image, showing that our method can better perceive fine-grained semantics. In addition, as shown in Figure 6(b), MixReorg's segmentation quality of stuff classes is significantly better than GroupViT. In a word, MixReorg has a stronger ability of high-level semantic understanding and segmentation.", + "bbox": [ + 75, + 530, + 468, + 696 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Mixed Patch Reorganization. We visualize the reorganized images from mixed images according to the mask predictions from two mixed images in Figure 7(a). It can be seen that except for a few patches, MixReorg can correctly segment most image patches into their corresponding original semantics. In Figure 7(b), the confusion matrix of the prediction for one mixed image indicates that MixReorg can effectively align patches with text.", + "bbox": [ + 75, + 696, + 470, + 818 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Discussion", + "text_level": 1, + "bbox": [ + 76, + 820, + 191, + 835 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Conclusion. We propose a patch-text data construction method with dense matching for image-text data and a cross-modal mixed image patch reorganization mask learner for mixed images to achieve fine-grained semantic", + "bbox": [ + 75, + 839, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e645c8eed64ac0ed5b18a83f4c5d66e9be27df84f0b72550f5c44e4d4e76949b.jpg", + "image_caption": [ + "Figure 7: Mixed image reorganization and the confusion matrix. (a) We use the segmentation mask predicted by MixReorg on the mixed image to obtain the reorganized image. (b) Taking $M = 16$ as an example, the confusion matrix $CM$ of the patch segmentation of the mixed images. $CM_{ij}$ represents the proportion of patches belonging to the $i$ -th image in the mixed image that are classified into the $j$ -th image category." + ], + "image_footnote": [], + "bbox": [ + 504, + 311, + 679, + 465 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/de40525f0b6c457058c9279d0392bca683837eb869c824e2d7bb8cf89c11788e.jpg", + "image_caption": [ + "Figure 6: Comparison of semantic segmentation results on PASCAL VOC 2012 and PASCAL Context." + ], + "image_footnote": [], + "bbox": [ + 687, + 310, + 887, + 464 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "alignment in open-world segmentation. MixReorg shows superior performance in open-world scenarios.", + "bbox": [ + 496, + 563, + 890, + 592 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitations. There are two issues that we should explore to improve MixReorg. First, since we use contextual mixing to create additional dat, the computational budget is increased during the training phase. Second, although Mixreorg successfully constructs patch-text data for semantic segmentation, there is still a gap between it with pixel-level data.", + "bbox": [ + 496, + 593, + 890, + 684 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Acknowledgment", + "text_level": 1, + "bbox": [ + 500, + 691, + 669, + 707 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work was supported in part by National Key R&D Program of China under Grant No. 2020AAA0109700, Guangdong Outstanding Youth Fund (Grant No. 2021B1515020061), Shenzhen Science and Technology Program (Grant No. RCYX20200714114642083), Shenzhen Fundamental Research Program (Grant No. JCYJ20190807154211365), Nansha Key RD Program under Grant No.2022ZD014 and Sun Yat-sen University under Grant No. 22lgqb38 and 76160-12220011. We thank MindSpore for the partial support of this work, which is a new deep learning computing framework*.", + "bbox": [ + 496, + 709, + 890, + 876 + ], + "page_idx": 7 + }, + { + "type": "page_footnote", + "text": "*https://www.mindspore.cn/", + "bbox": [ + 517, + 887, + 669, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "1203", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Abhijit Bendale and Terrance Boult. Towards open world recognition. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 1893-1902, 2015. 3", + "[2] Mathilde Caron, Hugo Touvron, Ishan Misra, Hervé Jégou, Julien Mairal, Piotr Bojanowski, and Armand Joulin. Emerging properties in self-supervised vision transformers. 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In Proceedings of the European Conference on Computer Vision, pages 696-712, 2022. 2, 6", + "[45] Jinghao Zhou, Chen Wei, Huiyu Wang, Wei Shen, Cihang Xie, Alan Yuille, and Tao Kong. ibot: Image bert pre-training with online tokenizer. arXiv preprint arXiv:2111.07832, 2021. 3" + ], + "bbox": [ + 501, + 92, + 890, + 667 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "1205", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/MixReorg_ Cross-Modal Mixed Patch Reorganization is a Good Mask Learner for Open-World Semantic Segmentation/b98d5aa5-34b5-4693-a5bc-bc45e3fb8dcd_model.json b/2023/MixReorg_ Cross-Modal Mixed Patch Reorganization is a Good Mask Learner for Open-World Semantic Segmentation/b98d5aa5-34b5-4693-a5bc-bc45e3fb8dcd_model.json new file mode 100644 index 0000000000000000000000000000000000000000..51ba4a753bef7c413e777c41f9ae9ff27f627aa9 --- /dev/null +++ b/2023/MixReorg_ Cross-Modal Mixed Patch Reorganization is a Good Mask Learner for Open-World Semantic Segmentation/b98d5aa5-34b5-4693-a5bc-bc45e3fb8dcd_model.json @@ -0,0 +1,2101 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.089, + 0.13, + 0.882, + 0.177 + ], + "angle": 0, + "content": "MixReorg: Cross-Modal Mixed Patch Reorganization is a Good Mask Learner for Open-World Semantic Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.2, + 0.203, + 0.786, + 0.24 + ], + "angle": 0, + "content": "Kaixin Cai\\(^{1*}\\) Pengzhen Ren\\(^{1*}\\) Yi Zhu\\(^{2}\\) Hang Xu\\(^{2}\\) Jianzhuang Liu\\(^{2}\\) Changlin Li\\(^{3}\\) Guangrun Wang\\(^{4}\\) Xiaodan Liang\\(^{1,5,6\\dagger}\\)" + }, + { + "type": "text", + "bbox": [ + 0.125, + 0.24, + 0.864, + 0.258 + ], + "angle": 0, + "content": "1Shenzhen Campus of Sun Yat-sen University 2Huawei Noah's Ark Lab 3University of Technology Sydney" + }, + { + "type": "text", + "bbox": [ + 0.281, + 0.258, + 0.708, + 0.275 + ], + "angle": 0, + "content": "\\(^{4}\\)University of Oxford \\(^{5}\\)MBZUAI \\(^{6}\\)DarkMatter AI Research" + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.277, + 0.897, + 0.293 + ], + "angle": 0, + "content": "caikx7@mail2.sysu.edu.cn, pzhren@foxmail.com, {zhuyi36, xuHang, liu.jianzhuang}@huawei.com," + }, + { + "type": "text", + "bbox": [ + 0.286, + 0.296, + 0.702, + 0.31 + ], + "angle": 0, + "content": "{changlinli.ai, wanggrun, xdliang328}@gmail.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.345, + 0.314, + 0.361 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.377, + 0.474, + 0.786 + ], + "angle": 0, + "content": "Recently, semantic segmentation models trained with image-level text supervision have shown promising results in challenging open-world scenarios. However, these models still face difficulties in learning fine-grained semantic alignment at the pixel level and predicting accurate object masks. To address this issue, we propose MixReorg, a novel and straightforward pre-training paradigm for semantic segmentation that enhances a model's ability to reorganize patches mixed across images, exploring both local visual relevance and global semantic coherence. Our approach involves generating fine-grained patch-text pairs data by mixing image patches while preserving the correspondence between patches and text. The model is then trained to minimize the segmentation loss of the mixed images and the two contrastive losses of the original and restored features. With MixReorg as a mask learner, conventional text-supervised semantic segmentation models can achieve highly generalizable pixel-semantic alignment ability, which is crucial for open-world segmentation. After training with large-scale image-text data, MixReorg models can be applied directly to segment visual objects of arbitrary categories, without the need for further fine-tuning. Our proposed framework demonstrates strong performance on popular zero-shot semantic segmentation benchmarks, outperforming GroupViT by significant margins of \\(5.0\\%\\), \\(6.2\\%\\), \\(2.5\\%\\), and \\(3.4\\%\\) mIoU on PASCAL VOC2012, PASCAL Context, MS COCO, and ADE20K, respectively." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.812, + 0.21, + 0.827 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.838, + 0.47, + 0.868 + ], + "angle": 0, + "content": "Image segmentation has important applications in scenarios such as virtual presence, virtual try-on, movie post" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.345, + 0.891, + 0.526 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.527, + 0.895, + 0.612 + ], + "angle": 0, + "content": "Figure 1: Comparison between GroupViT [38] and MixReorg. (a) GroupViT obtains image segmentation implicitly from image-text pairs to achieve cross-modal semantic alignment. (b) MixReorg explicitly constructs the fine-grained patch-text pairs data from the image-text pairs for free by mixing the patches from different images and preserving the correspondence between patches and text." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.626, + 0.895, + 0.838 + ], + "angle": 0, + "content": "production, and autonomous driving. Currently, state-of-the-art semantic segmentation methods [35, 30, 6] benefit from a large number of densely annotated data. However, the assumption of this closed-world setting requires that all categories of objects that appear in the test set are included in the training set. This heavy dependence on annotations limits that they can only work well in closed-set settings. However, considering ubiquitous new concepts in real-world scenarios, learning an open-world segmentation model is more practical, but it is also more challenging. The open-world segmentation model is required to segment all entities and objects class-agnostically and exhaustively during training and be highly generalizable for aligning pixels with new semantics during testing." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Early methods achieve open-world semantic segmentation through few-shot learning [3] or unsupervised clustering [26]. The former actually still assumes that the training and testing classes are in the same latent feature space," + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.875, + 0.208, + 0.888 + ], + "angle": 0, + "content": "*Equal contribution." + }, + { + "type": "page_footnote", + "bbox": [ + 0.097, + 0.888, + 0.222, + 0.9 + ], + "angle": 0, + "content": "† Corresponding author." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.875, + 0.222, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.957 + ], + "angle": 0, + "content": "1196" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.089, + 0.47, + 0.21 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.219, + 0.47, + 0.262 + ], + "angle": 0, + "content": "Figure 2: Visual comparison between MixReorg and GroupViT [38] on images from the network. Our method can better handle open-world classes for segmentation task." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.274, + 0.473, + 0.562 + ], + "angle": 0, + "content": "while the latter cannot guarantee the consistency of segmentation semantics. Recently, GroupViT [38] achieves state-of-the-art open-world segmentation performance using only text supervision. It realizes the automatic grouping of image patches by vision-language contrastive learning (Figure 1 (a)). ViL-Seg [22] implements image segmentation by introducing additional online clustering of visual embeddings for vision-language contrast. Massive image-text pairs provide rich visual and textual semantics for open-world scenarios. Similar to other CLIP-based [28] vision-language pre-training models (VLM) [32, 41, 19], although these methods achieve local information alignment of different modalities to a certain extent, they are still a computationally-based implicit matching strategy (fine-grained matching is learned by computing patch-text [32] or token-wise [41] similarity matrices). Therefore, how to learn more fine-grained semantic alignment from image-text pair data becomes a key challenge for text-based supervised open-world segmentation tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.564, + 0.47, + 0.745 + ], + "angle": 0, + "content": "Inspired by the related work of mixed image modeling [27, 21], we propose a simple and novel cross-modal mixed image reconstruction mask learner. Specifically, as shown in Figure 1 (b), MixReorg mixes patches from different images to generate mixed images. Unlike previous methods for jigsaw puzzle [27] or mixed image reconstruction [21] in the single visual modality, MixReorg's mixed patch reorganization is a cross-modal mask learner designed for semantic segmentation. MixReorg preserves the correspondence between each patch and text when mixing image patches (the legend of Figure 1 (b)). In this way, we can obtain fine-grained patch-text pairs from the image-text data for free." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.747, + 0.47, + 0.868 + ], + "angle": 0, + "content": "However, there are still two challenges: (i) the mixed image segmentation is easily disturbed by low-level features, which makes the model unable to realize patch reorganization of mixed images by high-level semantics; (ii) each patch in mixed images are easily interfered by irrelevant patches from different images in the transformer layers, which may cause the image semantics to be difficult to match with the corresponding text." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.903 + ], + "angle": 0, + "content": "For the first challenge, we propose two strategies of contextual mixing and progressive mixing to solve this prob" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.318 + ], + "angle": 0, + "content": "lem. The contextual mixing strategy allows each patch in the mixed image to obtain the global semantics of its original image in advance by adding a transformer layer before the mixing operation, thereby forcing the model to learn the mixed image reorganization from high-level semantics. Furthermore, to further enhance the global information in the mixed image features, we propose to use the original image features to enhance the global semantics in the mixed image features. For the second challenge, we present a mixing restoration strategy. It guarantees the semantic association of each patch token in the mixed image with the text through contrastive learning between the image recovered from mixed image and the text. In this way, the mutual interference between patches from different images in the mixed image can be effectively suppressed." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.318, + 0.893, + 0.513 + ], + "angle": 0, + "content": "In general, MixReorg constructs a set of fine-grained patch-text pairs for free from image-text pair data, and successfully builds a cross-modal mixed image patch reorganization mask learner for open-world segmentation tasks. The proposed MixReorg as a good mask learner also shows strong performance compared with the popular zero-shot semantic segmentation baselines, achieving the performance of \\(50.5\\%\\), \\(25.4\\%\\), \\(23.6\\%\\) and \\(10.1\\%\\) mIoU on multiscale evaluations on PASCAL VOC2012, PASCAL Context, MS COCO and ADE20K, respectively. The visualization in Figure 2 shows that MixReorg significantly outperforms GroupViT [38] on open-world segmentation. Our contributions can be summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.515, + 0.892, + 0.59 + ], + "angle": 0, + "content": "- We propose a novel and simple method that can easily construct patch-text data with fine-grained matching relationships from image-text data, thereby providing densely supervised information for open-world segmentation." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.599, + 0.892, + 0.675 + ], + "angle": 0, + "content": "- For the constructed patch-text data, we propose a cross-modal mixed patch reorganization method. It successfully addresses the challenge of model failure due to mixed image segmentation susceptible to low-level features and irrelevant patches." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.683, + 0.892, + 0.742 + ], + "angle": 0, + "content": "- The proposed MixReorg exhibits strong open-world segmentation performance and significantly outperforms current state-of-the-art zero-shot segmentation baselines." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.515, + 0.892, + 0.742 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.755, + 0.642, + 0.77 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "VLM and Segmentation. Recently, vision-language pretraining models [28, 17] have achieved great success. The models [8, 28, 38, 40] trained with VLM are flexible and versatile, and can adapt to visual [38, 25, 28, 32] and multimodal [37, 16, 42] upstream and downstream tasks only by using the matching relationship of image-text data. This success has also been found in segmentation and has attracted the attention of lots of researchers [38, 32, 39, 44]." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1197" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.304 + ], + "angle": 0, + "content": "Because traditional semantic segmentation is limited by expensive manual dense annotation, VLMs are expected to break this limitation. Although the above methods achieve promising performance, using image-text sample-level matching relations to learn segmentation masks still faces the challenge of lacking local dense supervision information. In addition, there are some works [41, 32, 19] that explore the alignment of multi-modal local information, but they are still computationally-dominated pseudolocal information correspondence without hard fine-grained supervision from the data level. Therefore, how to obtain finer-grained local supervision information from image-text data through data-level improvement is in great demand for semantic segmentation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.307, + 0.473, + 0.581 + ], + "angle": 0, + "content": "Self-Supervision Strategies. Self-supervision is an effective way to avoid the limitation of expensive manual annotations. It builds a self-supervised pipeline by fully mining the properties of the data itself. For example, self-supervision strategies such as masked image reconstruction [12, 21, 18], jigsaw puzzles [27], multi-view contrast [2, 45, 5] and angle recognition [11] are widely adopted in the vision domain. Similar self-supervision strategies have been widely and successfully applied in natural language processing [7, 34]. But the above methods are all designed for the single modality. In contrast, semantic segmentation not only needs to consider the representation and segmentation of image features but also needs to consider cross-modal semantic alignment. Therefore, how to draw more supervised information from image-text data by borrowing self-supervision strategies from the vision domain is very beneficial for semantic segmentation. Especially for the extraction of cross-modal fine-grained supervision information." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Open-World Segmentation. The open-world problem has been studied in the context of recognition [1, 23], namely how to get a model trained only on a given closed-world dataset to also recognize new classes of objects. Similar settings are also used in object detection [36, 15] and segmentation [3, 26, 38]. For example, [26] proposes an unsupervised open-world semantic segmentation; however, it obtains the mask of the image by a clustering method without any network parameter update. On the other hand, VLMs [28, 19, 8] exhibit strong performance and generalization ability with the help of massive image-text pair data. Inspired by this, TSEG [32] and ICILP [19] attempt to obtain fine-grained semantic alignment from image-text pairs to achieve image segmentation. Similarly, GroupViT [38] introduces a set of learnable group tokens for ViT to group patches and uses the generated segment tokens to align with text embeddings. The massively available image-text pair data provides rich visual and textual semantics for open-world scenarios [40]. Therefore, open-world semantic segmentation based on text supervision can achieve more refined segmentation results at a lower cost of annotation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.152 + ], + "angle": 0, + "content": "Based on the above observations, this paper follows the open-world semantic segmentation setting based on text supervision to further improve the performance of semantic segmentation." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.169, + 0.637, + 0.187 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.195, + 0.895, + 0.318 + ], + "angle": 0, + "content": "The overall framework of the MixReorg mask learner is shown in Figure 3. MixReorg is CLIP-based [28] and mainly consists of an image encoder and a text encoder. We use the text encoder from CLIP [28]. MixReorg's image encoder mainly has three stages: contextual mixing, progressive mixing, and mixing restoration (Sec. 3.1). Then, the loss composition of MixReorg is described in detail in Sec. 3.2. Finally, the total loss is introduced in Sec. 3.3." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.328, + 0.617, + 0.344 + ], + "angle": 0, + "content": "3.1. MixReorg" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.348, + 0.895, + 0.621 + ], + "angle": 0, + "content": "Contextual Mixing. As shown in Figure 3(a), in the contextual image patch mixing stage, patches from different images are randomly mixed to construct a set of mixed images with known segmentation masks. According to the original image-text pairs, the patch-text correspondence of the mixed images is preserved, and the mixed image masks are used as the semantic segmentation labels of the mixed images. Similar to [21], the mixed images only have randomly mixed patch tokens from different images at their same locations. Specially, unlike [21], MixReorg adopts a contextual information image patch mixing strategy. We add a transformer layer before the image patch mixing operation to provide each patch the global image semantic which is closer to the text to create the coherence between patch and text. Meanwhile, it can preliminarily force the model to learn the mixed image patch reorganization from high-level features, thus effectively avoiding the interference of low-level features with the semantic learning of the model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.621, + 0.895, + 0.758 + ], + "angle": 0, + "content": "Specifically, given a batch of image-text pairs \\(\\{(x_i^I,x_i^T)\\}_{i = 1}^B\\). Following the design in ViT [9], we first split each input image into \\(N\\) non-overlapping patches and linearly project each patch into a latent space. These projected patches are denoted as \\(\\{\\mathrm{p}_i\\}_{i = 1}^N\\). For \\(M\\) image-text pairs \\(\\{(x_i^I,x_i^T)\\}_{i = 1}^M\\), MixReorg randomly mixes the patches from \\(M\\) different images to construct \\(M\\) mixed images, and the corresponding patch composition of \\(M\\) mixed images can be denoted as" + }, + { + "type": "equation", + "bbox": [ + 0.512, + 0.763, + 0.892, + 0.796 + ], + "angle": 0, + "content": "\\[\n\\operatorname {m i x} \\left(\\left\\{\\left\\{\\mathrm {p} _ {i} \\right\\} _ {i = 1} ^ {N} \\right\\} _ {m = 1} ^ {M}\\right) = \\left\\{ \\right.\\left.\\left.\\left. \\mathrm {p} _ {m, i} ^ {j} \\right\\} _ {i = 1} ^ {N} \\right\\} _ {m = 1} ^ {M}, 1 \\leq j \\leq M, \\right. \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.895, + 0.906 + ], + "angle": 0, + "content": "where \\(\\mathrm{p}_{m,i}^{j}\\) denotes that the \\(i\\)-th patch of the \\(m\\)-th mixed image comes from the \\(j\\)-th image. Correspondingly, we keep the correspondence between each image patch and the text corresponding to the original image, resulting in a semantic segmentation dataset with patch-text correspondence. The patch-text correspondence of the \\(m\\)-th mixed image can be expressed as \\(\\{\\mathrm{p}_{m,i}^{j}, x_{j}^{T}\\}_{i=1}^{N}\\). Therefore, we obtain a set of" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.518, + 0.958 + ], + "angle": 0, + "content": "1198" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.118, + 0.086, + 0.852, + 0.316 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.322, + 0.892, + 0.406 + ], + "angle": 0, + "content": "Figure 3: The training pipeline and framework of MixReorg (take two images as an example). MixReorg's image encoder can be divided into three stages: (a) contextual mixing stage: a set of additional patch-text pairs with known segmentation mask is obtained by randomly mixing contextual patches from different images; (b) progressive mixing stage: the original image features are used to enhance the global information of the mixed image features after mixing; (c) mixing restoration stage: the original features, mixed features, and restored features are segmented through a two-stage grouping block [38], and the corresponding segment tokens are obtained. Note that we omit group tokens in the forward process for simplicity. During testing, MixReorg only needs to execute the original image branch." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.41, + 0.47, + 0.445 + ], + "angle": 0, + "content": "sample-level image-text pairs \\(\\{(x_i^I,x_i^T)\\}_{i = 1}^B\\) and a set of patch-level patch-text pairs \\(\\{\\{\\mathrm{p}_{m,i}^{j},x_{j}^{T}\\}_{i = 1}^{N}\\}_{m = 1}^{M}\\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.442, + 0.47, + 0.639 + ], + "angle": 0, + "content": "Progressive Mixing. Mixed patches' features cannot improve after Contextual Mixing because of the semantic mixing in mixed images. Since more layers in Contextual Mixing will lead to more parameters, we propose Progressive Mixing to enhance mixed features without additional parameters. As shown in Figure 3(b), in the progressive mixing phase, the patch tokens of normal and mixed images are concatenated with \\( s_1 \\) learnable group tokens \\( \\{g_i\\}_{i=1}^{s_1} \\) respectively and fed to the multi-layer transformers independently. At the same time, the original features are used to enhance the contextual information of the mixed features. The above process of an original image going through the \\( l \\)-th transformer layer can be represented as" + }, + { + "type": "equation", + "bbox": [ + 0.097, + 0.642, + 0.469, + 0.663 + ], + "angle": 0, + "content": "\\[\n\\left\\{\\left\\{\\hat {g} _ {i} \\right\\} _ {i = 1} ^ {s _ {1}}, \\left\\{\\hat {\\mathrm {p}} _ {i} \\right\\} _ {i = 1} ^ {N} \\right\\} = \\operatorname {T r a n s} _ {l} \\left(\\left[ \\left\\{g _ {i} \\right\\} _ {i = 1} ^ {s _ {1}}; \\left\\{\\mathrm {p} _ {i} \\right\\} _ {i = 1} ^ {N} \\right]\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.665, + 0.469, + 0.71 + ], + "angle": 0, + "content": "where \\([ ; ]\\) denotes the concatenation operator. Similarly, the output of the \\(m\\)-th mixed image through the \\(l\\)-th transformer layer can be expressed as" + }, + { + "type": "equation", + "bbox": [ + 0.09, + 0.714, + 0.47, + 0.769 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{r l} & {\\{\\{\\hat {g} _ {i} \\} _ {i = 1} ^ {s _ {1}}, \\{\\hat {\\mathrm {p}} _ {m, i} ^ {j} \\} _ {i = 1} ^ {N} \\} = \\operatorname {T r a n s} _ {l} \\left(\\left[ \\left\\{g _ {i} \\right\\} _ {i = 1} ^ {s _ {1}}; \\left\\{\\mathrm {p} _ {m, i} ^ {j} \\right\\} _ {i = 1} ^ {N} + \\right. \\right.} \\\\ & {\\qquad \\left. \\operatorname {m i x} \\left(\\left\\{\\left\\{\\left\\{\\mathrm {p} _ {i} \\right\\} _ {i = 1} ^ {N} \\right\\} _ {m = 1} ^ {M} \\right\\rbrace_ {l - 1}\\right) _ {m} \\right].} \\end{array} \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.469, + 0.87 + ], + "angle": 0, + "content": "Mixing Restoration. Although we can achieve patch-text alignment by mixed images, there are a lot of different semantics in one mixed image which will interfere with each other. Therefore, this requires the patches from different images in a mixed image still need to maintain a semantic match with the corresponding text." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "To this end, as shown in Figure 3(c), in the mixing restoration phase, MixReorg also restores the mixed image" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.411, + 0.892, + 0.535 + ], + "angle": 0, + "content": "according to the patch position of the image before mixing. The original features \\(\\{\\mathrm{p}_i\\}_{i = 1}^N\\), mixed features \\(\\{\\mathrm{p}_{m,i}^{j}\\}_{i = 1}^{N}\\) and restored features \\(r e(\\{\\mathrm{p}_{m,i}^{j}\\}_{i = 1}^{N})\\) are segmented through a two-stage grouping block [38], and the corresponding segment tokens \\(\\{\\mathrm{seg}_i\\}_{i = 1}^{s_2}\\) are obtained. These segment tokens are fed into multiple transformer layers and then projected to the same dimensionality \\(D\\) as text embeddings \\(Z^{T}\\in \\mathbb{R}^{B\\times D}\\) through an MLP." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.555, + 0.892, + 0.571 + ], + "angle": 0, + "content": "3.2. Cross-Modal Mixed Patch Reorganization Loss" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.578, + 0.892, + 0.88 + ], + "angle": 0, + "content": "Mixed Segmentation Loss. Cross-modal mixed patch reorganization is a core module designed in MixReorg for semantic segmentation. It provides the model with more refined local alignment information by using a constructed mixed image dataset with patch-text correspondence. We expect the model to learn more fine-grained semantic alignment with the help of the constructed patch-text pairs. And the calculation process of the mixed image segmentation mask is shown in Figure 4, where every \\( B_{I} \\) (e.g., \\( B_{I} = M \\)) images are mixed. The mixed image segment tokens and the text embeddings of the whole batch are used to compute the similarity \\( S \\in \\mathbb{R}^{B_I \\times s_2 \\times B} \\) for the text, where \\( \\otimes \\) denotes matrix multiplication. Since we adopt a two-stage grouping block [38], we have the attention map \\( A \\in \\mathbb{R}^{B_I \\times HW \\times s_2} \\) (\\( HW = N \\)), which contains the grouping relationship between \\( HW \\) patches and \\( s_2 \\) segment tokens. Further, by \\( A \\otimes S \\), we can predict the segmentation mask \\( M_p \\in \\mathbb{R}^{B_I \\times HW \\times B} \\) of the mixed image. Finally, we compute the cross-entropy loss between the mixed image masks \\( M_{mix} \\) and the prediction masks \\( M_p \\), formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.607, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {s e g}} = \\mathcal {L} _ {C E} \\left(M _ {p}, M _ {\\text {m i x}}\\right), \\tag {4}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1199" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.09, + 0.473, + 0.248 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.259, + 0.47, + 0.343 + ], + "angle": 0, + "content": "Figure 4: Cross-modal mixed patch reorganization, which combines attention maps and segmentation tokens from the image encoder, and text embeddings to reorganize and predict segmentation masks for mixed images. Where \\( B_{I} = M \\) means that every \\( B_{I} \\) images are mixed. For simplicity, we take a mixed image generated by mixing two images as an example." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.351, + 0.469, + 0.381 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{CE}(\\pmb {p},\\pmb {q}) = -\\sum_{i}\\pmb{q}_{i}\\log (\\pmb{p}_{i})\\) is the cross-entropy loss of output \\(\\pmb{p}\\) and target \\(\\pmb{q}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.383, + 0.47, + 0.534 + ], + "angle": 0, + "content": "Restoration Contrastive Loss. Furthermore, we consider cross-modal semantic contrastive learning of mixing restoration features and text embeddings. Specifically, in order to take full advantage of the correspondence provided by the image-text pair and enhance the model's ability to align semantically across modalities, MixReorg computes the contrastive loss and the multi-label image-text contrastive loss [38] between the output of the restored features branch and the text embeddings, respectively. The calculation of the total image-text contrastive loss is as follows" + }, + { + "type": "equation", + "bbox": [ + 0.187, + 0.543, + 0.469, + 0.56 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {I \\leftrightarrow T} ^ {r e} = \\mathcal {L} _ {I \\rightarrow T} ^ {r e} + \\mathcal {L} _ {I \\leftarrow T} ^ {r e}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.562, + 0.428, + 0.576 + ], + "angle": 0, + "content": "where the image-to-text contrastive loss is defined as" + }, + { + "type": "equation", + "bbox": [ + 0.12, + 0.583, + 0.469, + 0.625 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {I \\rightarrow T} ^ {r e} = - \\frac {1}{B} \\sum_ {i = 1} ^ {B} \\log \\frac {\\exp \\left(z _ {i} ^ {I} \\cdot z _ {i} ^ {T} / \\tau\\right)}{\\sum_ {j = 1} ^ {B} \\exp \\left(z _ {i} ^ {I} \\cdot z _ {j} ^ {T} / \\tau\\right)}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.63, + 0.411, + 0.644 + ], + "angle": 0, + "content": "and the text-to-image contrastive loss is defined as" + }, + { + "type": "equation", + "bbox": [ + 0.12, + 0.651, + 0.469, + 0.693 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {I \\leftarrow T} ^ {r e} = - \\frac {1}{B} \\sum_ {i = 1} ^ {B} \\log \\frac {\\exp \\left(z _ {i} ^ {T} \\cdot z _ {i} ^ {I} / \\tau\\right)}{\\sum_ {j = 1} ^ {B} \\exp \\left(z _ {i} ^ {T} \\cdot z _ {j} ^ {I} / \\tau\\right)}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.699, + 0.47, + 0.759 + ], + "angle": 0, + "content": "where \\(\\tau\\) is a learnable temperature parameter, and \\(z_{i}^{I}\\) and \\(z_{i}^{T}\\) are image and text embedding for image-text pairs \\(\\{(x_i^I,x_i^T)\\}_{i = 1}^B\\). In addition, we calculate the multi-label contrastive loss of the restored features branch as follows" + }, + { + "type": "equation", + "bbox": [ + 0.127, + 0.77, + 0.469, + 0.79 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {I \\leftrightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e} = \\mathcal {L} _ {I \\rightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e} + \\mathcal {L} _ {I \\leftarrow \\{T _ {k} \\} _ {k = 1} ^ {K}}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.792, + 0.469, + 0.823 + ], + "angle": 0, + "content": "where \\(\\{T_k\\}_{k=1}^K\\) is an additional \\(K\\) text labels generated using the \"prompting engineering\" mechanism in [28]," + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.829, + 0.473, + 0.891 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {I \\rightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e} = - \\frac {1}{B} \\sum_ {i = 1} ^ {B} \\log \\frac {\\sum_ {k = 1} ^ {K} \\exp \\left(z _ {i} ^ {I} \\cdot z _ {i} ^ {T _ {k}} / \\tau\\right)}{\\sum_ {k = 1} ^ {K} \\sum_ {j = 1} ^ {B} \\exp \\left(z _ {i} ^ {I} \\cdot z _ {j} ^ {T _ {k}} / \\tau\\right)} \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.079, + 0.887, + 0.105, + 0.899 + ], + "angle": 0, + "content": "and" + }, + { + "type": "table", + "bbox": [ + 0.514, + 0.089, + 0.877, + 0.229 + ], + "angle": 0, + "content": "
Arch.MethodMask mIoU (%)
ViT [9]*pixel-wise20.1
K-means25.0
Mean-shift20.7
Spectral clustering19.7
GroupViT [38]-41.1
ViewCo [31]-45.7
MixReorg (ours)-47.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.234, + 0.892, + 0.276 + ], + "angle": 0, + "content": "Table 1: Comparison with zero-shot semantic segmentation baselines on PASCAL VOC. GroupViT[38] and MixReorg are trained on CC12M. The superscript * means the results are from [38]." + }, + { + "type": "equation", + "bbox": [ + 0.5, + 0.283, + 0.897, + 0.342 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {I \\leftarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e} = - \\frac {1}{K B} \\sum_ {k = 1} ^ {K} \\sum_ {i = 1} ^ {B} \\log \\frac {\\exp \\left(z _ {i} ^ {T _ {k}} \\cdot z _ {i} ^ {I} / \\tau\\right)}{\\sum_ {j = 1} ^ {B} \\exp \\left(z _ {i} ^ {T _ {k}} \\cdot z _ {j} ^ {I} / \\tau\\right)}. \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.34, + 0.892, + 0.37 + ], + "angle": 0, + "content": "The total contrastive loss of the restored features and the text embeddings is as follows" + }, + { + "type": "equation", + "bbox": [ + 0.598, + 0.375, + 0.891, + 0.395 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {r e} = \\mathcal {L} _ {I \\leftrightarrow T} ^ {r e} + \\mathcal {L} _ {I \\leftrightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e}. \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.398, + 0.891, + 0.428 + ], + "angle": 0, + "content": "In summary, the total cross-modal mixed image patch reorganization loss is as follows" + }, + { + "type": "equation", + "bbox": [ + 0.618, + 0.434, + 0.891, + 0.45 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {m i x e d}} = \\mathcal {L} _ {\\text {s e g}} + \\mathcal {L} _ {\\text {r e}}. \\tag {12}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.457, + 0.707, + 0.471 + ], + "angle": 0, + "content": "3.3. Overall Loss Function" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.477, + 0.891, + 0.519 + ], + "angle": 0, + "content": "Similar to Eq. (11), the total contrastive loss between the original image features and the text embeddings is as follows" + }, + { + "type": "equation", + "bbox": [ + 0.595, + 0.521, + 0.891, + 0.541 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {o r i}} = \\mathcal {L} _ {I \\leftrightarrow T} ^ {\\text {o r i}} + \\mathcal {L} _ {I \\leftrightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {\\text {o r i}}. \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.54, + 0.745, + 0.555 + ], + "angle": 0, + "content": "Finally, the total loss of MixReorg is" + }, + { + "type": "equation", + "bbox": [ + 0.627, + 0.56, + 0.891, + 0.575 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathcal {L} _ {\\text {m i x e d}} + \\mathcal {L} _ {\\text {o r i}}. \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.575, + 0.891, + 0.62 + ], + "angle": 0, + "content": "When testing, MixReorg only needs to execute the original image branch (the solid black line in Figure 3), so it does not add any extra testing time." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.633, + 0.633, + 0.65 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.658, + 0.717, + 0.673 + ], + "angle": 0, + "content": "4.1. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.675, + 0.892, + 0.795 + ], + "angle": 0, + "content": "Architecture. The image encoder of MixReorg is based on a 2-stage GroupViT [38] with 12 transformer layers, while adding one transformer layer before the mix operation. The size of the input image is \\(224 \\times 224\\), the patch size is \\(16 \\times 16\\) and the hidden dimensionality is 384. The model outputs 32 segment tokens (i.e., \\(s_2 = 32\\) and \\(s_1 = 64\\)). Following [28, 38], the text encoder of MixReorg consists of 12 layers of transformer with the hidden feature dimensionality of 256." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Training and Inference. During the training phase, we use CC12M [4] as the training dataset, which contains 12M image-text pairs. We apply the mix operation for every 16 images (i.e., \\( M = 16 \\)). Following [38, 28], our batch size is 4096. We set the weight for each loss function to 1. During the inference phase, only the original image branch is executed. More details can be seen in Appendix." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1200" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.134, + 0.089, + 0.833, + 0.41 + ], + "angle": 0, + "content": "
Pre-trainingTransfer (mIoU (%))
Arch.ModelDatasetSupervisionZero-ShotPASCAL VOCPASCAL Context
ViTDeiT [33]ImageNetclassX53.035.9
DINO [2]ImageNetselfX39.120.4
DINOCC12M+YFCCselfX37.622.8
MoCo [13]ImageNetselfX34.321.3
MoCoCC12M+YFCCselfX36.123.0
CLIPSLIP* [25]LAION-20Mtext & self✓-12.3
CLIP-MAE* [8]LAION-20Mtext & self✓-16.8
MaskCLIP [8]LAION-20Mtext & self✓-17.7
ViewCo [31]CC12Mtext & self✓45.720.8
MaskCLIP [44]CLIP-400Mtext✓-21.7
CLIP* [28]LAION-20Mtext✓-13.5
GroupViT[38]CC12M+YFCCtext✓51.222.3
GroupViTCC12Mtext✓41.1 45.5†18.2 19.2†
MixReorg (ours)CC12Mtext✓47.9 (6.8 ↑) 50.5†(5.0 ↑)23.9 (5.7 ↑) 25.4†(6.2 ↑)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.416, + 0.892, + 0.457 + ], + "angle": 0, + "content": "Table 2: Performance comparison on PASCAL VOC [10] and PASCAL Context [24]. Zero-shot means that the model is directly transferred to the semantic segmentation task without any fine-tuning on the target dataset. The superscript * denote the results are from [8]. † indicates the results of the multi-scale evaluation." + }, + { + "type": "table", + "bbox": [ + 0.091, + 0.457, + 0.452, + 0.584 + ], + "angle": 0, + "content": "
ModelPre-training DatasetTransfer mIoU (%)
ViewCo [31]CC12M20.6
GroupViT [38]CC12M+YFCC20.9
GroupViTCC12M18.4 21.1†
MixReorg (ours)CC12M21.3 (2.9 ↑) 23.6† (2.5 ↑)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.587, + 0.468, + 0.614 + ], + "angle": 0, + "content": "Table 3: Performance comparison on COCO [20]. \\(\\dagger\\) indicates the results of the multi-scale evaluation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.618, + 0.468, + 0.784 + ], + "angle": 0, + "content": "Open-World Semantic Segmentation. We evaluate the performance of MixReorg on the open-world segmentation task on four commonly used open semantic segmentation datasets PASCAL VOC 2012 [10], PASCAL Context [24], COCO [20], and ADE20K [43]. They contain 20, 59, 80, and 150 foreground classes, respectively, with validation images of 1.5K, 5K, 5K, and 2K, respectively. MixReorg is transferred to the target dataset in a zero-shot manner without any fine-tuning. Following GroupViT [38], MixReorg obtains the corresponding segmentation of the image through the learned group token." + }, + { + "type": "title", + "bbox": [ + 0.076, + 0.793, + 0.392, + 0.809 + ], + "angle": 0, + "content": "4.2. Comparisons with Existing Methods" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Comparison with Zero-Shot Baselines. In Table 1, we present a comparison of four ViT-based baselines, which utilize the image-text contrastive loss defined in CLIP [28] to train the vision and text encoders. These baselines employ pixel-wise, k-means, mean-shift, and spectral clustering strategies, respectively. Additionally, we in" + }, + { + "type": "table", + "bbox": [ + 0.515, + 0.457, + 0.875, + 0.643 + ], + "angle": 0, + "content": "
ModelPre-training DatasetTransfer mIoU (%)
ALIGNa[14]ALIGN-1800M9.7
ALIGNaHQITP-134M7.5
CLIPA[28]HQITP-134M5.1
CLIPCLIP-400M5.8
CLIPbLAION-20M7.7
SLIPb[25]LAION-20M6.8
GroupViT [38]CC12M5.8
6.7
MixReorg (ours)CC12M8.7 (2.9 ↑)
10.1† (3.4 ↑)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.648, + 0.892, + 0.677 + ], + "angle": 0, + "content": "Table 4: Performance comparison on ADE20K [43]. The superscript \\( {}^{a} \\) and \\( {}^{b} \\) denote the results are from [29] and [8],respectively." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.686, + 0.892, + 0.761 + ], + "angle": 0, + "content": "clude GroupViT [38], which employs a bottom-up grouping method. The results in Table 1 demonstrate that MixReorg outperforms both the ViT baselines and GroupViT (41.1% vs. 47.9%), indicating that MixReorg is effective in enhancing the segmentation ability of the model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Comparison with SoTA Methods. We conduct a comprehensive evaluation of MixReorg against fully-supervised methods [33], self-supervised methods [2, 13], vision-language contrastive learning baselines [44, 28, 38], and baselines combining vision-language contrastive learning with self-supervised learning [25, 8, 31]. Table 2 and Table 3 summarizes the comparison results on PASCAL VOC, PASCAL Context, and COCO datasets, both in single-scale and multi-scale evaluation settings. The results show that" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "1201" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.333 + ], + "angle": 0, + "content": "MixReorg outperforms all the methods by a significant margin, demonstrating its effectiveness in semantic segmentation. In comparison to GroupViT, MixReorg that pre-trains on CC12M yields substantial performance improvements of \\(6.8\\%\\) mIoU, \\(5.7\\%\\) mIoU, and \\(2.9\\%\\) mIoU for single-scale evaluation, and \\(5.0\\%\\) mIoU, \\(6.2\\%\\) mIoU, and \\(2.5\\%\\) mIoU for multi-scale evaluation on PASCAL VOC, PASCAL Context, and COCO, respectively. MixReorg also outperforms GroupViT which pre-trains on CC12M and YFCC with less data. Additionally, MixReorg has a clear advantage over the methods which rely on additional supervision information in the vision branch. Furthermore, we evaluate the performance of MixReorg on the ADE20K dataset, as shown in Table 4. MixReorg outperforms GroupViT by a significant margin (8.7% vs. 5.8%), demonstrating its superior performance in complex segmentation tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.333, + 0.472, + 0.409 + ], + "angle": 0, + "content": "Image Classification. We evaluate the zero-shot classification performance of MixReorg on ImageNet. As shown in Table 5, MixReorg significantly outperforms GroupViT, indicating that MixReorg achieves better image-text alignment through fine-grained mask learning." + }, + { + "type": "table", + "bbox": [ + 0.11, + 0.409, + 0.436, + 0.473 + ], + "angle": 0, + "content": "
Arch.Zero-shot
Acc@1 (%)Acc@5 (%)
GroupViT [38]37.565.5
MixReorg(ours)38.866.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.095, + 0.477, + 0.45, + 0.491 + ], + "angle": 0, + "content": "Table 5: Zero-shot classification performance on ImageNet." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.492, + 0.231, + 0.508 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.508, + 0.473, + 0.856 + ], + "angle": 0, + "content": "Contextual Mixing. In Table 6, we perform ablation on contextual mixing (CM) strategies. Specifically, we first ablate the parameter variation of the model. As the results show, by adding a transformer layer to GroupViT's image encoder (i.e., GroupViT+), the performance of the model remains consistent (18.4% vs. 18.2%). This shows that simply increasing the number of parameters does not improve the performance of the model. Further, we also compared MixReorg with only CM (i.e., row 3) and GroupViT+. They have the same amount of parameters, but MixReorg significantly outperforms GroupViT+ with the help of CM (19.3% vs. 18.2%). This shows that it is beneficial to help the model obtain more global semantic information in the early stage of the model. For MixReorg, it can be found that MixReorg without CM assistance (row 4) will degenerate to a similar performance to GroupViT, which indicates that CM plays a crucial role in MixReorg's mixed segmentation module (19.3% vs. 18.0% vs. 18.4%). This is mainly because CM can help MixReorg acquire global semantic information early in the model, thus forcing the model to learn mixed image reorganization from high-level semantic, which frees the model from low-level semantic information (e.g., texture and color, etc.) to obtain trivial solutions." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.472, + 0.903 + ], + "angle": 0, + "content": "Ablation of Losses. In Table 6, we also conduct an ablation study on each loss that MixReorg uses. Specifically, \\(\\mathcal{L}_{seg}\\) improves the performance by \\(1.2\\%\\) mIoU (\\(20.5\\%\\) vs." + }, + { + "type": "table", + "bbox": [ + 0.532, + 0.083, + 0.86, + 0.208 + ], + "angle": 0, + "content": "
MethodCM\\( \\mathcal{L}_{seg} \\)\\( \\mathcal{L}_{re} \\)mIoU (%)
GroupViT---18.4
GroupViT+---18.2
MixReorg✓19.3
✓18.0
✓✓20.5
✓✓20.3
✓✓✓21.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.212, + 0.895, + 0.28 + ], + "angle": 0, + "content": "Table 6: On COCO, MixReorg's ablation study on contextual mixing (CM) and the loss functions. GroupViT+ means adding one transformer layer at the 1-st stage of GroupViT. For MixReorg, without CM means images are mixed prior to passing through the transformer layer that we add." + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.28, + 0.89, + 0.404 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.41, + 0.895, + 0.508 + ], + "angle": 0, + "content": "Figure 5: On COCO, MixReorg's ablation study on the number of progressive mixings and the number of images for the contextual mixing operation. (a) Yellow line: Ablation study on the number \\( P \\) of the progressive mixing modules. We replace one progressive mixing module with one transformer layer to maintain the model size. (b) Red line: Ablation study on the number \\( M \\) of images for each contextual mixing operation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.509, + 0.895, + 0.72 + ], + "angle": 0, + "content": "19.3%). This means that \\(\\mathcal{L}_{seg}\\) plays a significant role. The model learns to distinguish different semantics in the image through \\(\\mathcal{L}_{seg}\\). Additionally, \\(\\mathcal{L}_{re}\\) improves the performance of the model (20.3% vs. 19.3%). It helps the patches of the mixed image to maintain consistency between its original image semantics and corresponding text. Furthermore, by combining \\(\\mathcal{L}_{seg}\\) and \\(\\mathcal{L}_{re}\\) based on CM, the performance of MixReorg can be further improved (21.3% vs. 20.5% vs. 20.3%), which illustrates that CM and two loss functions are strongly related. CM is fundamental to achieving patch-text alignment since it provides global information to each patch, while \\(\\mathcal{L}_{seg}\\) provides fine-grained semantic alignment ability and \\(\\mathcal{L}_{re}\\) assisting \\(\\mathcal{L}_{seg}\\) keeping the patches' original semantic, free from the interference from different images." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.871 + ], + "angle": 0, + "content": "Number of Images for Mixing. In Figure 5 (red line), we observe the performance impact of the number of images \\( M \\) used for contextual mixing operation. It can be observed that \\( M = 16 \\) is optimal. As \\( M \\) increases, mixed images contain more semantic categories, which is helpful for the model in learning semantic grouping (20.5% vs. 17.1%). However, increasing \\( M \\) beyond a certain threshold (e.g.: \\( M = 32 \\)) causes semantic representation in the mixed image to be insufficient due to resolution constraints, thereby interfering with model learning (20.5% vs. 18.2%)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Progressive Mixing Module. In Figure 5 (yellow line), we study the number \\( P \\) of the progressive mixing modules. We" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1202" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.118, + 0.084, + 0.849, + 0.291 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.178, + 0.296, + 0.79, + 0.31 + ], + "angle": 0, + "content": "Figure 6: Comparison of semantic segmentation results on PASCAL VOC 2012 and PASCAL Context." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.313, + 0.474, + 0.51 + ], + "angle": 0, + "content": "add one transformer layer when removing one progressive mixing module to maintain the model size. It can be seen that the model is optimal when the number \\( P \\) of the progressive mixing modules is 6. The progressive mixing improves over \\( P = 0 \\) by about \\( 7\\% \\) mIoU (\\( P = 3 \\) vs. \\( P = 0 \\)). When \\( P = 0 \\), the original image is not used to enhance the mixed image after the mixing operation. In this case, the lack of global information on the original image hinders the learning of the model. Obviously, with the increase of the progressive mixing modules, the semantics of the mixed image features become clearer, which is thus more conducive for model learning to distinguish different semantics, thus improving the model segmentation ability." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.514, + 0.216, + 0.528 + ], + "angle": 0, + "content": "4.4. Visualization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.531, + 0.47, + 0.697 + ], + "angle": 0, + "content": "Qualitative Results. In Figure 6, we illustrate zero-shot semantic segmentation examples predicted by GroupViT and MixReorg to verify the segmentation capability of our method. As shown in Figure 6(a), MixReorg can handle more complex segmentation examples which have different classes in one image, showing that our method can better perceive fine-grained semantics. In addition, as shown in Figure 6(b), MixReorg's segmentation quality of stuff classes is significantly better than GroupViT. In a word, MixReorg has a stronger ability of high-level semantic understanding and segmentation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.698, + 0.471, + 0.819 + ], + "angle": 0, + "content": "Mixed Patch Reorganization. We visualize the reorganized images from mixed images according to the mask predictions from two mixed images in Figure 7(a). It can be seen that except for a few patches, MixReorg can correctly segment most image patches into their corresponding original semantics. In Figure 7(b), the confusion matrix of the prediction for one mixed image indicates that MixReorg can effectively align patches with text." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.821, + 0.192, + 0.836 + ], + "angle": 0, + "content": "5. Discussion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Conclusion. We propose a patch-text data construction method with dense matching for image-text data and a cross-modal mixed image patch reorganization mask learner for mixed images to achieve fine-grained semantic" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.312, + 0.681, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.689, + 0.311, + 0.888, + 0.465 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.465, + 0.892, + 0.562 + ], + "angle": 0, + "content": "Figure 7: Mixed image reorganization and the confusion matrix. (a) We use the segmentation mask predicted by MixReorg on the mixed image to obtain the reorganized image. (b) Taking \\( M = 16 \\) as an example, the confusion matrix \\( CM \\) of the patch segmentation of the mixed images. \\( CM_{ij} \\) represents the proportion of patches belonging to the \\( i \\)-th image in the mixed image that are classified into the \\( j \\)-th image category." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.564, + 0.892, + 0.593 + ], + "angle": 0, + "content": "alignment in open-world segmentation. MixReorg shows superior performance in open-world scenarios." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.594, + 0.892, + 0.685 + ], + "angle": 0, + "content": "Limitations. There are two issues that we should explore to improve MixReorg. First, since we use contextual mixing to create additional dat, the computational budget is increased during the training phase. Second, although Mixreorg successfully constructs patch-text data for semantic segmentation, there is still a gap between it with pixel-level data." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.692, + 0.671, + 0.708 + ], + "angle": 0, + "content": "6. Acknowledgment" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.71, + 0.892, + 0.877 + ], + "angle": 0, + "content": "This work was supported in part by National Key R&D Program of China under Grant No. 2020AAA0109700, Guangdong Outstanding Youth Fund (Grant No. 2021B1515020061), Shenzhen Science and Technology Program (Grant No. RCYX20200714114642083), Shenzhen Fundamental Research Program (Grant No. JCYJ20190807154211365), Nansha Key RD Program under Grant No.2022ZD014 and Sun Yat-sen University under Grant No. 22lgqb38 and 76160-12220011. We thank MindSpore for the partial support of this work, which is a new deep learning computing framework*." + }, + { + "type": "page_footnote", + "bbox": [ + 0.518, + 0.888, + 0.671, + 0.901 + ], + "angle": 0, + "content": "*https://www.mindspore.cn/" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1203" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.17 + ], + "angle": 0, + "content": "[1] Abhijit Bendale and Terrance Boult. Towards open world recognition. 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However, these models still face difficulties in learning fine-grained semantic alignment at the pixel level and predicting accurate object masks. To address this issue, we propose MixReorg, a novel and straightforward pre-training paradigm for semantic segmentation that enhances a model's ability to reorganize patches mixed across images, exploring both local visual relevance and global semantic coherence. Our approach involves generating fine-grained patch-text pairs data by mixing image patches while preserving the correspondence between patches and text. The model is then trained to minimize the segmentation loss of the mixed images and the two contrastive losses of the original and restored features. With MixReorg as a mask learner, conventional text-supervised semantic segmentation models can achieve highly generalizable pixel-semantic alignment ability, which is crucial for open-world segmentation. After training with large-scale image-text data, MixReorg models can be applied directly to segment visual objects of arbitrary categories, without the need for further fine-tuning. Our proposed framework demonstrates strong performance on popular zero-shot semantic segmentation benchmarks, outperforming GroupViT by significant margins of $5.0\%$ , $6.2\%$ , $2.5\%$ , and $3.4\%$ mIoU on PASCAL VOC2012, PASCAL Context, MS COCO, and ADE20K, respectively. + +# 1. Introduction + +Image segmentation has important applications in scenarios such as virtual presence, virtual try-on, movie post + +![](images/ca005d1882d9048c71d9dfe274aab06f15f4429662c50a1c4b1799d00c21d46d.jpg) +Figure 1: Comparison between GroupViT [38] and MixReorg. (a) GroupViT obtains image segmentation implicitly from image-text pairs to achieve cross-modal semantic alignment. (b) MixReorg explicitly constructs the fine-grained patch-text pairs data from the image-text pairs for free by mixing the patches from different images and preserving the correspondence between patches and text. + +production, and autonomous driving. Currently, state-of-the-art semantic segmentation methods [35, 30, 6] benefit from a large number of densely annotated data. However, the assumption of this closed-world setting requires that all categories of objects that appear in the test set are included in the training set. This heavy dependence on annotations limits that they can only work well in closed-set settings. However, considering ubiquitous new concepts in real-world scenarios, learning an open-world segmentation model is more practical, but it is also more challenging. The open-world segmentation model is required to segment all entities and objects class-agnostically and exhaustively during training and be highly generalizable for aligning pixels with new semantics during testing. + +Early methods achieve open-world semantic segmentation through few-shot learning [3] or unsupervised clustering [26]. The former actually still assumes that the training and testing classes are in the same latent feature space, + +![](images/503e2d745a5c7ef6bc217368896d2fa26169737700839cfc9bfccc478ebb53f7.jpg) +Figure 2: Visual comparison between MixReorg and GroupViT [38] on images from the network. Our method can better handle open-world classes for segmentation task. + +while the latter cannot guarantee the consistency of segmentation semantics. Recently, GroupViT [38] achieves state-of-the-art open-world segmentation performance using only text supervision. It realizes the automatic grouping of image patches by vision-language contrastive learning (Figure 1 (a)). ViL-Seg [22] implements image segmentation by introducing additional online clustering of visual embeddings for vision-language contrast. Massive image-text pairs provide rich visual and textual semantics for open-world scenarios. Similar to other CLIP-based [28] vision-language pre-training models (VLM) [32, 41, 19], although these methods achieve local information alignment of different modalities to a certain extent, they are still a computationally-based implicit matching strategy (fine-grained matching is learned by computing patch-text [32] or token-wise [41] similarity matrices). Therefore, how to learn more fine-grained semantic alignment from image-text pair data becomes a key challenge for text-based supervised open-world segmentation tasks. + +Inspired by the related work of mixed image modeling [27, 21], we propose a simple and novel cross-modal mixed image reconstruction mask learner. Specifically, as shown in Figure 1 (b), MixReorg mixes patches from different images to generate mixed images. Unlike previous methods for jigsaw puzzle [27] or mixed image reconstruction [21] in the single visual modality, MixReorg's mixed patch reorganization is a cross-modal mask learner designed for semantic segmentation. MixReorg preserves the correspondence between each patch and text when mixing image patches (the legend of Figure 1 (b)). In this way, we can obtain fine-grained patch-text pairs from the image-text data for free. + +However, there are still two challenges: (i) the mixed image segmentation is easily disturbed by low-level features, which makes the model unable to realize patch reorganization of mixed images by high-level semantics; (ii) each patch in mixed images are easily interfered by irrelevant patches from different images in the transformer layers, which may cause the image semantics to be difficult to match with the corresponding text. + +For the first challenge, we propose two strategies of contextual mixing and progressive mixing to solve this prob + +lem. The contextual mixing strategy allows each patch in the mixed image to obtain the global semantics of its original image in advance by adding a transformer layer before the mixing operation, thereby forcing the model to learn the mixed image reorganization from high-level semantics. Furthermore, to further enhance the global information in the mixed image features, we propose to use the original image features to enhance the global semantics in the mixed image features. For the second challenge, we present a mixing restoration strategy. It guarantees the semantic association of each patch token in the mixed image with the text through contrastive learning between the image recovered from mixed image and the text. In this way, the mutual interference between patches from different images in the mixed image can be effectively suppressed. + +In general, MixReorg constructs a set of fine-grained patch-text pairs for free from image-text pair data, and successfully builds a cross-modal mixed image patch reorganization mask learner for open-world segmentation tasks. The proposed MixReorg as a good mask learner also shows strong performance compared with the popular zero-shot semantic segmentation baselines, achieving the performance of $50.5\%$ , $25.4\%$ , $23.6\%$ and $10.1\%$ mIoU on multiscale evaluations on PASCAL VOC2012, PASCAL Context, MS COCO and ADE20K, respectively. The visualization in Figure 2 shows that MixReorg significantly outperforms GroupViT [38] on open-world segmentation. Our contributions can be summarized as follows: + +- We propose a novel and simple method that can easily construct patch-text data with fine-grained matching relationships from image-text data, thereby providing densely supervised information for open-world segmentation. +- For the constructed patch-text data, we propose a cross-modal mixed patch reorganization method. It successfully addresses the challenge of model failure due to mixed image segmentation susceptible to low-level features and irrelevant patches. +- The proposed MixReorg exhibits strong open-world segmentation performance and significantly outperforms current state-of-the-art zero-shot segmentation baselines. + +# 2. Related Work + +VLM and Segmentation. Recently, vision-language pretraining models [28, 17] have achieved great success. The models [8, 28, 38, 40] trained with VLM are flexible and versatile, and can adapt to visual [38, 25, 28, 32] and multimodal [37, 16, 42] upstream and downstream tasks only by using the matching relationship of image-text data. This success has also been found in segmentation and has attracted the attention of lots of researchers [38, 32, 39, 44]. + +Because traditional semantic segmentation is limited by expensive manual dense annotation, VLMs are expected to break this limitation. Although the above methods achieve promising performance, using image-text sample-level matching relations to learn segmentation masks still faces the challenge of lacking local dense supervision information. In addition, there are some works [41, 32, 19] that explore the alignment of multi-modal local information, but they are still computationally-dominated pseudolocal information correspondence without hard fine-grained supervision from the data level. Therefore, how to obtain finer-grained local supervision information from image-text data through data-level improvement is in great demand for semantic segmentation. + +Self-Supervision Strategies. Self-supervision is an effective way to avoid the limitation of expensive manual annotations. It builds a self-supervised pipeline by fully mining the properties of the data itself. For example, self-supervision strategies such as masked image reconstruction [12, 21, 18], jigsaw puzzles [27], multi-view contrast [2, 45, 5] and angle recognition [11] are widely adopted in the vision domain. Similar self-supervision strategies have been widely and successfully applied in natural language processing [7, 34]. But the above methods are all designed for the single modality. In contrast, semantic segmentation not only needs to consider the representation and segmentation of image features but also needs to consider cross-modal semantic alignment. Therefore, how to draw more supervised information from image-text data by borrowing self-supervision strategies from the vision domain is very beneficial for semantic segmentation. Especially for the extraction of cross-modal fine-grained supervision information. + +Open-World Segmentation. The open-world problem has been studied in the context of recognition [1, 23], namely how to get a model trained only on a given closed-world dataset to also recognize new classes of objects. Similar settings are also used in object detection [36, 15] and segmentation [3, 26, 38]. For example, [26] proposes an unsupervised open-world semantic segmentation; however, it obtains the mask of the image by a clustering method without any network parameter update. On the other hand, VLMs [28, 19, 8] exhibit strong performance and generalization ability with the help of massive image-text pair data. Inspired by this, TSEG [32] and ICILP [19] attempt to obtain fine-grained semantic alignment from image-text pairs to achieve image segmentation. Similarly, GroupViT [38] introduces a set of learnable group tokens for ViT to group patches and uses the generated segment tokens to align with text embeddings. The massively available image-text pair data provides rich visual and textual semantics for open-world scenarios [40]. Therefore, open-world semantic segmentation based on text supervision can achieve more refined segmentation results at a lower cost of annotation. + +Based on the above observations, this paper follows the open-world semantic segmentation setting based on text supervision to further improve the performance of semantic segmentation. + +# 3. Methodology + +The overall framework of the MixReorg mask learner is shown in Figure 3. MixReorg is CLIP-based [28] and mainly consists of an image encoder and a text encoder. We use the text encoder from CLIP [28]. MixReorg's image encoder mainly has three stages: contextual mixing, progressive mixing, and mixing restoration (Sec. 3.1). Then, the loss composition of MixReorg is described in detail in Sec. 3.2. Finally, the total loss is introduced in Sec. 3.3. + +# 3.1. MixReorg + +Contextual Mixing. As shown in Figure 3(a), in the contextual image patch mixing stage, patches from different images are randomly mixed to construct a set of mixed images with known segmentation masks. According to the original image-text pairs, the patch-text correspondence of the mixed images is preserved, and the mixed image masks are used as the semantic segmentation labels of the mixed images. Similar to [21], the mixed images only have randomly mixed patch tokens from different images at their same locations. Specially, unlike [21], MixReorg adopts a contextual information image patch mixing strategy. We add a transformer layer before the image patch mixing operation to provide each patch the global image semantic which is closer to the text to create the coherence between patch and text. Meanwhile, it can preliminarily force the model to learn the mixed image patch reorganization from high-level features, thus effectively avoiding the interference of low-level features with the semantic learning of the model. + +Specifically, given a batch of image-text pairs $\{(x_i^I,x_i^T)\}_{i = 1}^B$ . Following the design in ViT [9], we first split each input image into $N$ non-overlapping patches and linearly project each patch into a latent space. These projected patches are denoted as $\{\mathrm{p}_i\}_{i = 1}^N$ . For $M$ image-text pairs $\{(x_i^I,x_i^T)\}_{i = 1}^M$ , MixReorg randomly mixes the patches from $M$ different images to construct $M$ mixed images, and the corresponding patch composition of $M$ mixed images can be denoted as + +$$ +\operatorname {m i x} \left(\left\{\left\{\mathrm {p} _ {i} \right\} _ {i = 1} ^ {N} \right\} _ {m = 1} ^ {M}\right) = \left\{ \right.\left.\left.\left. \mathrm {p} _ {m, i} ^ {j} \right\} _ {i = 1} ^ {N} \right\} _ {m = 1} ^ {M}, 1 \leq j \leq M, \right. \tag {1} +$$ + +where $\mathrm{p}_{m,i}^{j}$ denotes that the $i$ -th patch of the $m$ -th mixed image comes from the $j$ -th image. Correspondingly, we keep the correspondence between each image patch and the text corresponding to the original image, resulting in a semantic segmentation dataset with patch-text correspondence. The patch-text correspondence of the $m$ -th mixed image can be expressed as $\{\mathrm{p}_{m,i}^{j}, x_{j}^{T}\}_{i=1}^{N}$ . Therefore, we obtain a set of + +![](images/8721a114592d9a12bc2a0a5203c3358b42dced1f71ed32dd6464c5f771aff449.jpg) +Figure 3: The training pipeline and framework of MixReorg (take two images as an example). MixReorg's image encoder can be divided into three stages: (a) contextual mixing stage: a set of additional patch-text pairs with known segmentation mask is obtained by randomly mixing contextual patches from different images; (b) progressive mixing stage: the original image features are used to enhance the global information of the mixed image features after mixing; (c) mixing restoration stage: the original features, mixed features, and restored features are segmented through a two-stage grouping block [38], and the corresponding segment tokens are obtained. Note that we omit group tokens in the forward process for simplicity. During testing, MixReorg only needs to execute the original image branch. + +sample-level image-text pairs $\{(x_i^I,x_i^T)\}_{i = 1}^B$ and a set of patch-level patch-text pairs $\{\{\mathrm{p}_{m,i}^{j},x_{j}^{T}\}_{i = 1}^{N}\}_{m = 1}^{M}$ + +Progressive Mixing. Mixed patches' features cannot improve after Contextual Mixing because of the semantic mixing in mixed images. Since more layers in Contextual Mixing will lead to more parameters, we propose Progressive Mixing to enhance mixed features without additional parameters. As shown in Figure 3(b), in the progressive mixing phase, the patch tokens of normal and mixed images are concatenated with $s_1$ learnable group tokens $\{g_i\}_{i=1}^{s_1}$ respectively and fed to the multi-layer transformers independently. At the same time, the original features are used to enhance the contextual information of the mixed features. The above process of an original image going through the $l$ -th transformer layer can be represented as + +$$ +\left\{\left\{\hat {g} _ {i} \right\} _ {i = 1} ^ {s _ {1}}, \left\{\hat {\mathrm {p}} _ {i} \right\} _ {i = 1} ^ {N} \right\} = \operatorname {T r a n s} _ {l} \left(\left[ \left\{g _ {i} \right\} _ {i = 1} ^ {s _ {1}}; \left\{\mathrm {p} _ {i} \right\} _ {i = 1} ^ {N} \right]\right), \tag {2} +$$ + +where $[ ; ]$ denotes the concatenation operator. Similarly, the output of the $m$ -th mixed image through the $l$ -th transformer layer can be expressed as + +$$ +\begin{array}{r l} & {\{\{\hat {g} _ {i} \} _ {i = 1} ^ {s _ {1}}, \{\hat {\mathrm {p}} _ {m, i} ^ {j} \} _ {i = 1} ^ {N} \} = \operatorname {T r a n s} _ {l} \left(\left[ \left\{g _ {i} \right\} _ {i = 1} ^ {s _ {1}}; \left\{\mathrm {p} _ {m, i} ^ {j} \right\} _ {i = 1} ^ {N} + \right. \right.} \\ & {\qquad \left. \operatorname {m i x} \left(\left\{\left\{\left\{\mathrm {p} _ {i} \right\} _ {i = 1} ^ {N} \right\} _ {m = 1} ^ {M} \right\rbrace_ {l - 1}\right) _ {m} \right].} \end{array} \tag {3} +$$ + +Mixing Restoration. Although we can achieve patch-text alignment by mixed images, there are a lot of different semantics in one mixed image which will interfere with each other. Therefore, this requires the patches from different images in a mixed image still need to maintain a semantic match with the corresponding text. + +To this end, as shown in Figure 3(c), in the mixing restoration phase, MixReorg also restores the mixed image + +according to the patch position of the image before mixing. The original features $\{\mathrm{p}_i\}_{i = 1}^N$ , mixed features $\{\mathrm{p}_{m,i}^{j}\}_{i = 1}^{N}$ and restored features $r e(\{\mathrm{p}_{m,i}^{j}\}_{i = 1}^{N})$ are segmented through a two-stage grouping block [38], and the corresponding segment tokens $\{\mathrm{seg}_i\}_{i = 1}^{s_2}$ are obtained. These segment tokens are fed into multiple transformer layers and then projected to the same dimensionality $D$ as text embeddings $Z^{T}\in \mathbb{R}^{B\times D}$ through an MLP. + +# 3.2. Cross-Modal Mixed Patch Reorganization Loss + +Mixed Segmentation Loss. Cross-modal mixed patch reorganization is a core module designed in MixReorg for semantic segmentation. It provides the model with more refined local alignment information by using a constructed mixed image dataset with patch-text correspondence. We expect the model to learn more fine-grained semantic alignment with the help of the constructed patch-text pairs. And the calculation process of the mixed image segmentation mask is shown in Figure 4, where every $B_{I}$ (e.g., $B_{I} = M$ ) images are mixed. The mixed image segment tokens and the text embeddings of the whole batch are used to compute the similarity $S \in \mathbb{R}^{B_I \times s_2 \times B}$ for the text, where $\otimes$ denotes matrix multiplication. Since we adopt a two-stage grouping block [38], we have the attention map $A \in \mathbb{R}^{B_I \times HW \times s_2}$ ( $HW = N$ ), which contains the grouping relationship between $HW$ patches and $s_2$ segment tokens. Further, by $A \otimes S$ , we can predict the segmentation mask $M_p \in \mathbb{R}^{B_I \times HW \times B}$ of the mixed image. Finally, we compute the cross-entropy loss between the mixed image masks $M_{mix}$ and the prediction masks $M_p$ , formulated as + +$$ +\mathcal {L} _ {\text {s e g}} = \mathcal {L} _ {C E} \left(M _ {p}, M _ {\text {m i x}}\right), \tag {4} +$$ + +![](images/445400a731bc889e5b512d6d4dbd90efedac1b7f752d88827f2e20aa3ebf40ee.jpg) +Figure 4: Cross-modal mixed patch reorganization, which combines attention maps and segmentation tokens from the image encoder, and text embeddings to reorganize and predict segmentation masks for mixed images. Where $B_{I} = M$ means that every $B_{I}$ images are mixed. For simplicity, we take a mixed image generated by mixing two images as an example. + +where $\mathcal{L}_{CE}(\pmb {p},\pmb {q}) = -\sum_{i}\pmb{q}_{i}\log (\pmb{p}_{i})$ is the cross-entropy loss of output $\pmb{p}$ and target $\pmb{q}$ . + +Restoration Contrastive Loss. Furthermore, we consider cross-modal semantic contrastive learning of mixing restoration features and text embeddings. Specifically, in order to take full advantage of the correspondence provided by the image-text pair and enhance the model's ability to align semantically across modalities, MixReorg computes the contrastive loss and the multi-label image-text contrastive loss [38] between the output of the restored features branch and the text embeddings, respectively. The calculation of the total image-text contrastive loss is as follows + +$$ +\mathcal {L} _ {I \leftrightarrow T} ^ {r e} = \mathcal {L} _ {I \rightarrow T} ^ {r e} + \mathcal {L} _ {I \leftarrow T} ^ {r e}, \tag {5} +$$ + +where the image-to-text contrastive loss is defined as + +$$ +\mathcal {L} _ {I \rightarrow T} ^ {r e} = - \frac {1}{B} \sum_ {i = 1} ^ {B} \log \frac {\exp \left(z _ {i} ^ {I} \cdot z _ {i} ^ {T} / \tau\right)}{\sum_ {j = 1} ^ {B} \exp \left(z _ {i} ^ {I} \cdot z _ {j} ^ {T} / \tau\right)}, \tag {6} +$$ + +and the text-to-image contrastive loss is defined as + +$$ +\mathcal {L} _ {I \leftarrow T} ^ {r e} = - \frac {1}{B} \sum_ {i = 1} ^ {B} \log \frac {\exp \left(z _ {i} ^ {T} \cdot z _ {i} ^ {I} / \tau\right)}{\sum_ {j = 1} ^ {B} \exp \left(z _ {i} ^ {T} \cdot z _ {j} ^ {I} / \tau\right)}, \tag {7} +$$ + +where $\tau$ is a learnable temperature parameter, and $z_{i}^{I}$ and $z_{i}^{T}$ are image and text embedding for image-text pairs $\{(x_i^I,x_i^T)\}_{i = 1}^B$ . In addition, we calculate the multi-label contrastive loss of the restored features branch as follows + +$$ +\mathcal {L} _ {I \leftrightarrow \{T _ {k} \} _ {k = 1} ^ {K}} ^ {r e} = \mathcal {L} _ {I \rightarrow \{T _ {k} \} _ {k = 1} ^ {K}} ^ {r e} + \mathcal {L} _ {I \leftarrow \{T _ {k} \} _ {k = 1} ^ {K}}, \tag {8} +$$ + +where $\{T_k\}_{k=1}^K$ is an additional $K$ text labels generated using the "prompting engineering" mechanism in [28], + +$$ +\mathcal {L} _ {I \rightarrow \{T _ {k} \} _ {k = 1} ^ {K}} ^ {r e} = - \frac {1}{B} \sum_ {i = 1} ^ {B} \log \frac {\sum_ {k = 1} ^ {K} \exp \left(z _ {i} ^ {I} \cdot z _ {i} ^ {T _ {k}} / \tau\right)}{\sum_ {k = 1} ^ {K} \sum_ {j = 1} ^ {B} \exp \left(z _ {i} ^ {I} \cdot z _ {j} ^ {T _ {k}} / \tau\right)} \tag {9} +$$ + +and + +
Arch.MethodMask mIoU (%)
ViT [9]*pixel-wise20.1
K-means25.0
Mean-shift20.7
Spectral clustering19.7
GroupViT [38]-41.1
ViewCo [31]-45.7
MixReorg (ours)-47.9
+ +Table 1: Comparison with zero-shot semantic segmentation baselines on PASCAL VOC. GroupViT[38] and MixReorg are trained on CC12M. The superscript * means the results are from [38]. + +$$ +\mathcal {L} _ {I \leftarrow \{T _ {k} \} _ {k = 1} ^ {K}} ^ {r e} = - \frac {1}{K B} \sum_ {k = 1} ^ {K} \sum_ {i = 1} ^ {B} \log \frac {\exp \left(z _ {i} ^ {T _ {k}} \cdot z _ {i} ^ {I} / \tau\right)}{\sum_ {j = 1} ^ {B} \exp \left(z _ {i} ^ {T _ {k}} \cdot z _ {j} ^ {I} / \tau\right)}. \tag {10} +$$ + +The total contrastive loss of the restored features and the text embeddings is as follows + +$$ +\mathcal {L} _ {r e} = \mathcal {L} _ {I \leftrightarrow T} ^ {r e} + \mathcal {L} _ {I \leftrightarrow \{T _ {k} \} _ {k = 1} ^ {K}} ^ {r e}. \tag {11} +$$ + +In summary, the total cross-modal mixed image patch reorganization loss is as follows + +$$ +\mathcal {L} _ {\text {m i x e d}} = \mathcal {L} _ {\text {s e g}} + \mathcal {L} _ {\text {r e}}. \tag {12} +$$ + +# 3.3. Overall Loss Function + +Similar to Eq. (11), the total contrastive loss between the original image features and the text embeddings is as follows + +$$ +\mathcal {L} _ {\text {o r i}} = \mathcal {L} _ {I \leftrightarrow T} ^ {\text {o r i}} + \mathcal {L} _ {I \leftrightarrow \{T _ {k} \} _ {k = 1} ^ {K}} ^ {\text {o r i}}. \tag {13} +$$ + +Finally, the total loss of MixReorg is + +$$ +\mathcal {L} = \mathcal {L} _ {\text {m i x e d}} + \mathcal {L} _ {\text {o r i}}. \tag {14} +$$ + +When testing, MixReorg only needs to execute the original image branch (the solid black line in Figure 3), so it does not add any extra testing time. + +# 4. Experiments + +# 4.1. Implementation Details + +Architecture. The image encoder of MixReorg is based on a 2-stage GroupViT [38] with 12 transformer layers, while adding one transformer layer before the mix operation. The size of the input image is $224 \times 224$ , the patch size is $16 \times 16$ and the hidden dimensionality is 384. The model outputs 32 segment tokens (i.e., $s_2 = 32$ and $s_1 = 64$ ). Following [28, 38], the text encoder of MixReorg consists of 12 layers of transformer with the hidden feature dimensionality of 256. + +Training and Inference. During the training phase, we use CC12M [4] as the training dataset, which contains 12M image-text pairs. We apply the mix operation for every 16 images (i.e., $M = 16$ ). Following [38, 28], our batch size is 4096. We set the weight for each loss function to 1. During the inference phase, only the original image branch is executed. More details can be seen in Appendix. + +
Pre-trainingTransfer (mIoU (%))
Arch.ModelDatasetSupervisionZero-ShotPASCAL VOCPASCAL Context
ViTDeiT [33]ImageNetclassX53.035.9
DINO [2]ImageNetselfX39.120.4
DINOCC12M+YFCCselfX37.622.8
MoCo [13]ImageNetselfX34.321.3
MoCoCC12M+YFCCselfX36.123.0
CLIPSLIP* [25]LAION-20Mtext & self✓-12.3
CLIP-MAE* [8]LAION-20Mtext & self✓-16.8
MaskCLIP [8]LAION-20Mtext & self✓-17.7
ViewCo [31]CC12Mtext & self✓45.720.8
MaskCLIP [44]CLIP-400Mtext✓-21.7
CLIP* [28]LAION-20Mtext✓-13.5
GroupViT[38]CC12M+YFCCtext✓51.222.3
GroupViTCC12Mtext✓41.1 45.5†18.2 19.2†
MixReorg (ours)CC12Mtext✓47.9 (6.8 ↑) 50.5†(5.0 ↑)23.9 (5.7 ↑) 25.4†(6.2 ↑)
+ +Table 2: Performance comparison on PASCAL VOC [10] and PASCAL Context [24]. Zero-shot means that the model is directly transferred to the semantic segmentation task without any fine-tuning on the target dataset. The superscript * denote the results are from [8]. † indicates the results of the multi-scale evaluation. + +
ModelPre-training DatasetTransfer mIoU (%)
ViewCo [31]CC12M20.6
GroupViT [38]CC12M+YFCC20.9
GroupViTCC12M18.4 21.1†
MixReorg (ours)CC12M21.3 (2.9 ↑) 23.6† (2.5 ↑)
+ +Open-World Semantic Segmentation. We evaluate the performance of MixReorg on the open-world segmentation task on four commonly used open semantic segmentation datasets PASCAL VOC 2012 [10], PASCAL Context [24], COCO [20], and ADE20K [43]. They contain 20, 59, 80, and 150 foreground classes, respectively, with validation images of 1.5K, 5K, 5K, and 2K, respectively. MixReorg is transferred to the target dataset in a zero-shot manner without any fine-tuning. Following GroupViT [38], MixReorg obtains the corresponding segmentation of the image through the learned group token. + +# 4.2. Comparisons with Existing Methods + +Comparison with Zero-Shot Baselines. In Table 1, we present a comparison of four ViT-based baselines, which utilize the image-text contrastive loss defined in CLIP [28] to train the vision and text encoders. These baselines employ pixel-wise, k-means, mean-shift, and spectral clustering strategies, respectively. Additionally, we in + +Table 3: Performance comparison on COCO [20]. $\dagger$ indicates the results of the multi-scale evaluation. + +
ModelPre-training DatasetTransfer mIoU (%)
ALIGNa[14]ALIGN-1800M9.7
ALIGNaHQITP-134M7.5
CLIPA[28]HQITP-134M5.1
CLIPCLIP-400M5.8
CLIPbLAION-20M7.7
SLIPb[25]LAION-20M6.8
GroupViT [38]CC12M5.8
6.7
MixReorg (ours)CC12M8.7 (2.9 ↑)
10.1† (3.4 ↑)
+ +Table 4: Performance comparison on ADE20K [43]. The superscript ${}^{a}$ and ${}^{b}$ denote the results are from [29] and [8],respectively. + +clude GroupViT [38], which employs a bottom-up grouping method. The results in Table 1 demonstrate that MixReorg outperforms both the ViT baselines and GroupViT (41.1% vs. 47.9%), indicating that MixReorg is effective in enhancing the segmentation ability of the model. + +Comparison with SoTA Methods. We conduct a comprehensive evaluation of MixReorg against fully-supervised methods [33], self-supervised methods [2, 13], vision-language contrastive learning baselines [44, 28, 38], and baselines combining vision-language contrastive learning with self-supervised learning [25, 8, 31]. Table 2 and Table 3 summarizes the comparison results on PASCAL VOC, PASCAL Context, and COCO datasets, both in single-scale and multi-scale evaluation settings. The results show that + +MixReorg outperforms all the methods by a significant margin, demonstrating its effectiveness in semantic segmentation. In comparison to GroupViT, MixReorg that pre-trains on CC12M yields substantial performance improvements of $6.8\%$ mIoU, $5.7\%$ mIoU, and $2.9\%$ mIoU for single-scale evaluation, and $5.0\%$ mIoU, $6.2\%$ mIoU, and $2.5\%$ mIoU for multi-scale evaluation on PASCAL VOC, PASCAL Context, and COCO, respectively. MixReorg also outperforms GroupViT which pre-trains on CC12M and YFCC with less data. Additionally, MixReorg has a clear advantage over the methods which rely on additional supervision information in the vision branch. Furthermore, we evaluate the performance of MixReorg on the ADE20K dataset, as shown in Table 4. MixReorg outperforms GroupViT by a significant margin (8.7% vs. 5.8%), demonstrating its superior performance in complex segmentation tasks. + +Image Classification. We evaluate the zero-shot classification performance of MixReorg on ImageNet. As shown in Table 5, MixReorg significantly outperforms GroupViT, indicating that MixReorg achieves better image-text alignment through fine-grained mask learning. + +
Arch.Zero-shot
Acc@1 (%)Acc@5 (%)
GroupViT [38]37.565.5
MixReorg(ours)38.866.7
+ +# 4.3. Ablation Study + +Contextual Mixing. In Table 6, we perform ablation on contextual mixing (CM) strategies. Specifically, we first ablate the parameter variation of the model. As the results show, by adding a transformer layer to GroupViT's image encoder (i.e., GroupViT+), the performance of the model remains consistent (18.4% vs. 18.2%). This shows that simply increasing the number of parameters does not improve the performance of the model. Further, we also compared MixReorg with only CM (i.e., row 3) and GroupViT+. They have the same amount of parameters, but MixReorg significantly outperforms GroupViT+ with the help of CM (19.3% vs. 18.2%). This shows that it is beneficial to help the model obtain more global semantic information in the early stage of the model. For MixReorg, it can be found that MixReorg without CM assistance (row 4) will degenerate to a similar performance to GroupViT, which indicates that CM plays a crucial role in MixReorg's mixed segmentation module (19.3% vs. 18.0% vs. 18.4%). This is mainly because CM can help MixReorg acquire global semantic information early in the model, thus forcing the model to learn mixed image reorganization from high-level semantic, which frees the model from low-level semantic information (e.g., texture and color, etc.) to obtain trivial solutions. + +Ablation of Losses. In Table 6, we also conduct an ablation study on each loss that MixReorg uses. Specifically, $\mathcal{L}_{seg}$ improves the performance by $1.2\%$ mIoU ( $20.5\%$ vs. + +Table 5: Zero-shot classification performance on ImageNet. + +
MethodCM\( \mathcal{L}_{seg} \)\( \mathcal{L}_{re} \)mIoU (%)
GroupViT---18.4
GroupViT+---18.2
MixReorg✓19.3
✓18.0
✓✓20.5
✓✓20.3
✓✓✓21.3
+ +Table 6: On COCO, MixReorg's ablation study on contextual mixing (CM) and the loss functions. GroupViT+ means adding one transformer layer at the 1-st stage of GroupViT. For MixReorg, without CM means images are mixed prior to passing through the transformer layer that we add. + +![](images/5738bd6c71bd12577e3c4908e9f4df7b86604d2a5ba65aeb72101bc60e5f70d8.jpg) +Figure 5: On COCO, MixReorg's ablation study on the number of progressive mixings and the number of images for the contextual mixing operation. (a) Yellow line: Ablation study on the number $P$ of the progressive mixing modules. We replace one progressive mixing module with one transformer layer to maintain the model size. (b) Red line: Ablation study on the number $M$ of images for each contextual mixing operation. + +19.3%). This means that $\mathcal{L}_{seg}$ plays a significant role. The model learns to distinguish different semantics in the image through $\mathcal{L}_{seg}$ . Additionally, $\mathcal{L}_{re}$ improves the performance of the model (20.3% vs. 19.3%). It helps the patches of the mixed image to maintain consistency between its original image semantics and corresponding text. Furthermore, by combining $\mathcal{L}_{seg}$ and $\mathcal{L}_{re}$ based on CM, the performance of MixReorg can be further improved (21.3% vs. 20.5% vs. 20.3%), which illustrates that CM and two loss functions are strongly related. CM is fundamental to achieving patch-text alignment since it provides global information to each patch, while $\mathcal{L}_{seg}$ provides fine-grained semantic alignment ability and $\mathcal{L}_{re}$ assisting $\mathcal{L}_{seg}$ keeping the patches' original semantic, free from the interference from different images. + +Number of Images for Mixing. In Figure 5 (red line), we observe the performance impact of the number of images $M$ used for contextual mixing operation. It can be observed that $M = 16$ is optimal. As $M$ increases, mixed images contain more semantic categories, which is helpful for the model in learning semantic grouping (20.5% vs. 17.1%). However, increasing $M$ beyond a certain threshold (e.g.: $M = 32$ ) causes semantic representation in the mixed image to be insufficient due to resolution constraints, thereby interfering with model learning (20.5% vs. 18.2%). + +Progressive Mixing Module. In Figure 5 (yellow line), we study the number $P$ of the progressive mixing modules. We + +![](images/995491eab91c51e579d1793dc8cd1ffdc957808fd75110e8bc925672e0759dd5.jpg) + +add one transformer layer when removing one progressive mixing module to maintain the model size. It can be seen that the model is optimal when the number $P$ of the progressive mixing modules is 6. The progressive mixing improves over $P = 0$ by about $7\%$ mIoU ( $P = 3$ vs. $P = 0$ ). When $P = 0$ , the original image is not used to enhance the mixed image after the mixing operation. In this case, the lack of global information on the original image hinders the learning of the model. Obviously, with the increase of the progressive mixing modules, the semantics of the mixed image features become clearer, which is thus more conducive for model learning to distinguish different semantics, thus improving the model segmentation ability. + +# 4.4. Visualization + +Qualitative Results. In Figure 6, we illustrate zero-shot semantic segmentation examples predicted by GroupViT and MixReorg to verify the segmentation capability of our method. As shown in Figure 6(a), MixReorg can handle more complex segmentation examples which have different classes in one image, showing that our method can better perceive fine-grained semantics. In addition, as shown in Figure 6(b), MixReorg's segmentation quality of stuff classes is significantly better than GroupViT. In a word, MixReorg has a stronger ability of high-level semantic understanding and segmentation. + +Mixed Patch Reorganization. We visualize the reorganized images from mixed images according to the mask predictions from two mixed images in Figure 7(a). It can be seen that except for a few patches, MixReorg can correctly segment most image patches into their corresponding original semantics. In Figure 7(b), the confusion matrix of the prediction for one mixed image indicates that MixReorg can effectively align patches with text. + +# 5. Discussion + +Conclusion. We propose a patch-text data construction method with dense matching for image-text data and a cross-modal mixed image patch reorganization mask learner for mixed images to achieve fine-grained semantic + +![](images/e645c8eed64ac0ed5b18a83f4c5d66e9be27df84f0b72550f5c44e4d4e76949b.jpg) +Figure 7: Mixed image reorganization and the confusion matrix. (a) We use the segmentation mask predicted by MixReorg on the mixed image to obtain the reorganized image. (b) Taking $M = 16$ as an example, the confusion matrix $CM$ of the patch segmentation of the mixed images. $CM_{ij}$ represents the proportion of patches belonging to the $i$ -th image in the mixed image that are classified into the $j$ -th image category. + +![](images/de40525f0b6c457058c9279d0392bca683837eb869c824e2d7bb8cf89c11788e.jpg) +Figure 6: Comparison of semantic segmentation results on PASCAL VOC 2012 and PASCAL Context. + +alignment in open-world segmentation. MixReorg shows superior performance in open-world scenarios. + +Limitations. There are two issues that we should explore to improve MixReorg. First, since we use contextual mixing to create additional dat, the computational budget is increased during the training phase. Second, although Mixreorg successfully constructs patch-text data for semantic segmentation, there is still a gap between it with pixel-level data. + +# 6. Acknowledgment + +This work was supported in part by National Key R&D Program of China under Grant No. 2020AAA0109700, Guangdong Outstanding Youth Fund (Grant No. 2021B1515020061), Shenzhen Science and Technology Program (Grant No. RCYX20200714114642083), Shenzhen Fundamental Research Program (Grant No. JCYJ20190807154211365), Nansha Key RD Program under Grant No.2022ZD014 and Sun Yat-sen University under Grant No. 22lgqb38 and 76160-12220011. We thank MindSpore for the partial support of this work, which is a new deep learning computing framework*. + +# References + +[1] Abhijit Bendale and Terrance Boult. Towards open world recognition. 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In Proceedings of the European Conference on Computer Vision, pages 696-712, 2022. 2, 6 +[45] Jinghao Zhou, Chen Wei, Huiyu Wang, Wei Shen, Cihang Xie, Alan Yuille, and Tao Kong. ibot: Image bert pre-training with online tokenizer. arXiv preprint arXiv:2111.07832, 2021. 3 \ No newline at end of file diff --git a/2023/MixReorg_ Cross-Modal Mixed Patch Reorganization is a Good Mask Learner for Open-World Semantic Segmentation/images.zip b/2023/MixReorg_ Cross-Modal Mixed Patch Reorganization is a Good Mask Learner for Open-World Semantic Segmentation/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..2cc6f0c4813301043a768c00440c555fddab02ff --- /dev/null +++ b/2023/MixReorg_ Cross-Modal Mixed Patch Reorganization is a Good Mask Learner for Open-World Semantic Segmentation/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:70ded15442d02a00cddda2d2a73abc2e440ae5ed5bcee330837802842bfc0a52 +size 653980 diff --git a/2023/MixReorg_ 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However, these models still face difficulties in learning fine-grained semantic alignment at the pixel level and predicting accurate object masks. To address this issue, we propose MixReorg, a novel and straightforward pre-training paradigm for semantic segmentation that enhances a model's ability to reorganize patches mixed across images, exploring both local visual relevance and global semantic coherence. Our approach involves generating fine-grained patch-text pairs data by mixing image patches while preserving the correspondence between patches and text. The model is then trained to minimize the segmentation loss of the mixed images and the two contrastive losses of the original and restored features. With MixReorg as a mask learner, conventional text-supervised semantic segmentation models can achieve highly generalizable pixel-semantic alignment ability, which is crucial for open-world segmentation. 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Introduction" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 663, + 287, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 663, + 287, + 687 + ], + "spans": [ + { + "bbox": [ + 47, + 663, + 287, + 687 + ], + "type": "text", + "content": "Image segmentation has important applications in scenarios such as virtual presence, virtual try-on, movie post" + } + ] + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 310, + 273, + 545, + 416 + ], + "blocks": [ + { + "bbox": [ + 310, + 273, + 545, + 416 + ], + "lines": [ + { + "bbox": [ + 310, + 273, + 545, + 416 + ], + "spans": [ + { + "bbox": [ + 310, + 273, + 545, + 416 + ], + "type": "image", + "image_path": "ca005d1882d9048c71d9dfe274aab06f15f4429662c50a1c4b1799d00c21d46d.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 417, + 547, + 484 + ], + "lines": [ + { + "bbox": [ + 304, + 417, + 547, + 484 + ], + "spans": [ + { + "bbox": [ + 304, + 417, + 547, + 484 + ], + "type": "text", + "content": "Figure 1: Comparison between GroupViT [38] and MixReorg. (a) GroupViT obtains image segmentation implicitly from image-text pairs to achieve cross-modal semantic alignment. (b) MixReorg explicitly constructs the fine-grained patch-text pairs data from the image-text pairs for free by mixing the patches from different images and preserving the correspondence between patches and text." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 495, + 547, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 547, + 663 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 547, + 663 + ], + "type": "text", + "content": "production, and autonomous driving. Currently, state-of-the-art semantic segmentation methods [35, 30, 6] benefit from a large number of densely annotated data. However, the assumption of this closed-world setting requires that all categories of objects that appear in the test set are included in the training set. This heavy dependence on annotations limits that they can only work well in closed-set settings. However, considering ubiquitous new concepts in real-world scenarios, learning an open-world segmentation model is more practical, but it is also more challenging. The open-world segmentation model is required to segment all entities and objects class-agnostically and exhaustively during training and be highly generalizable for aligning pixels with new semantics during testing." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "content": "Early methods achieve open-world semantic segmentation through few-shot learning [3] or unsupervised clustering [26]. The former actually still assumes that the training and testing classes are in the same latent feature space," + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 693, + 127, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 693, + 127, + 703 + ], + "spans": [ + { + "bbox": [ + 58, + 693, + 127, + 703 + ], + "type": "text", + "content": "*Equal contribution." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 59, + 703, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 703, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 59, + 703, + 135, + 712 + ], + "type": "text", + "content": "† Corresponding author." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "text", + "content": "1196" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 70, + 287, + 166 + ], + "blocks": [ + { + "bbox": [ + 52, + 70, + 287, + 166 + ], + "lines": [ + { + "bbox": [ + 52, + 70, + 287, + 166 + ], + "spans": [ + { + "bbox": [ + 52, + 70, + 287, + 166 + ], + "type": "image", + "image_path": "503e2d745a5c7ef6bc217368896d2fa26169737700839cfc9bfccc478ebb53f7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 173, + 287, + 207 + ], + "lines": [ + { + "bbox": [ + 46, + 173, + 287, + 207 + ], + "spans": [ + { + "bbox": [ + 46, + 173, + 287, + 207 + ], + "type": "text", + "content": "Figure 2: Visual comparison between MixReorg and GroupViT [38] on images from the network. Our method can better handle open-world classes for segmentation task." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 217, + 289, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 217, + 289, + 445 + ], + "spans": [ + { + "bbox": [ + 46, + 217, + 289, + 445 + ], + "type": "text", + "content": "while the latter cannot guarantee the consistency of segmentation semantics. Recently, GroupViT [38] achieves state-of-the-art open-world segmentation performance using only text supervision. It realizes the automatic grouping of image patches by vision-language contrastive learning (Figure 1 (a)). ViL-Seg [22] implements image segmentation by introducing additional online clustering of visual embeddings for vision-language contrast. Massive image-text pairs provide rich visual and textual semantics for open-world scenarios. Similar to other CLIP-based [28] vision-language pre-training models (VLM) [32, 41, 19], although these methods achieve local information alignment of different modalities to a certain extent, they are still a computationally-based implicit matching strategy (fine-grained matching is learned by computing patch-text [32] or token-wise [41] similarity matrices). Therefore, how to learn more fine-grained semantic alignment from image-text pair data becomes a key challenge for text-based supervised open-world segmentation tasks." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 446, + 287, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 446, + 287, + 590 + ], + "spans": [ + { + "bbox": [ + 46, + 446, + 287, + 590 + ], + "type": "text", + "content": "Inspired by the related work of mixed image modeling [27, 21], we propose a simple and novel cross-modal mixed image reconstruction mask learner. Specifically, as shown in Figure 1 (b), MixReorg mixes patches from different images to generate mixed images. Unlike previous methods for jigsaw puzzle [27] or mixed image reconstruction [21] in the single visual modality, MixReorg's mixed patch reorganization is a cross-modal mask learner designed for semantic segmentation. MixReorg preserves the correspondence between each patch and text when mixing image patches (the legend of Figure 1 (b)). In this way, we can obtain fine-grained patch-text pairs from the image-text data for free." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 591, + 287, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 591, + 287, + 687 + ], + "spans": [ + { + "bbox": [ + 46, + 591, + 287, + 687 + ], + "type": "text", + "content": "However, there are still two challenges: (i) the mixed image segmentation is easily disturbed by low-level features, which makes the model unable to realize patch reorganization of mixed images by high-level semantics; (ii) each patch in mixed images are easily interfered by irrelevant patches from different images in the transformer layers, which may cause the image semantics to be difficult to match with the corresponding text." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": "For the first challenge, we propose two strategies of contextual mixing and progressive mixing to solve this prob" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 251 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 251 + ], + "type": "text", + "content": "lem. The contextual mixing strategy allows each patch in the mixed image to obtain the global semantics of its original image in advance by adding a transformer layer before the mixing operation, thereby forcing the model to learn the mixed image reorganization from high-level semantics. Furthermore, to further enhance the global information in the mixed image features, we propose to use the original image features to enhance the global semantics in the mixed image features. For the second challenge, we present a mixing restoration strategy. It guarantees the semantic association of each patch token in the mixed image with the text through contrastive learning between the image recovered from mixed image and the text. In this way, the mutual interference between patches from different images in the mixed image can be effectively suppressed." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 251, + 546, + 406 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 251, + 546, + 406 + ], + "spans": [ + { + "bbox": [ + 304, + 251, + 546, + 406 + ], + "type": "text", + "content": "In general, MixReorg constructs a set of fine-grained patch-text pairs for free from image-text pair data, and successfully builds a cross-modal mixed image patch reorganization mask learner for open-world segmentation tasks. The proposed MixReorg as a good mask learner also shows strong performance compared with the popular zero-shot semantic segmentation baselines, achieving the performance of " + }, + { + "bbox": [ + 304, + 251, + 546, + 406 + ], + "type": "inline_equation", + "content": "50.5\\%" + }, + { + "bbox": [ + 304, + 251, + 546, + 406 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 251, + 546, + 406 + ], + "type": "inline_equation", + "content": "25.4\\%" + }, + { + "bbox": [ + 304, + 251, + 546, + 406 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 251, + 546, + 406 + ], + "type": "inline_equation", + "content": "23.6\\%" + }, + { + "bbox": [ + 304, + 251, + 546, + 406 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 251, + 546, + 406 + ], + "type": "inline_equation", + "content": "10.1\\%" + }, + { + "bbox": [ + 304, + 251, + 546, + 406 + ], + "type": "text", + "content": " mIoU on multiscale evaluations on PASCAL VOC2012, PASCAL Context, MS COCO and ADE20K, respectively. The visualization in Figure 2 shows that MixReorg significantly outperforms GroupViT [38] on open-world segmentation. Our contributions can be summarized as follows:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 407, + 545, + 587 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 317, + 407, + 545, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 407, + 545, + 467 + ], + "spans": [ + { + "bbox": [ + 317, + 407, + 545, + 467 + ], + "type": "text", + "content": "- We propose a novel and simple method that can easily construct patch-text data with fine-grained matching relationships from image-text data, thereby providing densely supervised information for open-world segmentation." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 317, + 474, + 545, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 474, + 545, + 534 + ], + "spans": [ + { + "bbox": [ + 317, + 474, + 545, + 534 + ], + "type": "text", + "content": "- For the constructed patch-text data, we propose a cross-modal mixed patch reorganization method. It successfully addresses the challenge of model failure due to mixed image segmentation susceptible to low-level features and irrelevant patches." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 540, + 545, + 587 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 540, + 545, + 587 + ], + "spans": [ + { + "bbox": [ + 317, + 540, + 545, + 587 + ], + "type": "text", + "content": "- The proposed MixReorg exhibits strong open-world segmentation performance and significantly outperforms current state-of-the-art zero-shot segmentation baselines." + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 597, + 392, + 609 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 597, + 392, + 609 + ], + "spans": [ + { + "bbox": [ + 306, + 597, + 392, + 609 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": "VLM and Segmentation. Recently, vision-language pretraining models [28, 17] have achieved great success. The models [8, 28, 38, 40] trained with VLM are flexible and versatile, and can adapt to visual [38, 25, 28, 32] and multimodal [37, 16, 42] upstream and downstream tasks only by using the matching relationship of image-text data. This success has also been found in segmentation and has attracted the attention of lots of researchers [38, 32, 39, 44]." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "1197" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": "Because traditional semantic segmentation is limited by expensive manual dense annotation, VLMs are expected to break this limitation. Although the above methods achieve promising performance, using image-text sample-level matching relations to learn segmentation masks still faces the challenge of lacking local dense supervision information. In addition, there are some works [41, 32, 19] that explore the alignment of multi-modal local information, but they are still computationally-dominated pseudolocal information correspondence without hard fine-grained supervision from the data level. Therefore, how to obtain finer-grained local supervision information from image-text data through data-level improvement is in great demand for semantic segmentation." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 243, + 289, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 243, + 289, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 243, + 289, + 460 + ], + "type": "text", + "content": "Self-Supervision Strategies. Self-supervision is an effective way to avoid the limitation of expensive manual annotations. It builds a self-supervised pipeline by fully mining the properties of the data itself. For example, self-supervision strategies such as masked image reconstruction [12, 21, 18], jigsaw puzzles [27], multi-view contrast [2, 45, 5] and angle recognition [11] are widely adopted in the vision domain. Similar self-supervision strategies have been widely and successfully applied in natural language processing [7, 34]. But the above methods are all designed for the single modality. In contrast, semantic segmentation not only needs to consider the representation and segmentation of image features but also needs to consider cross-modal semantic alignment. Therefore, how to draw more supervised information from image-text data by borrowing self-supervision strategies from the vision domain is very beneficial for semantic segmentation. Especially for the extraction of cross-modal fine-grained supervision information." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "content": "Open-World Segmentation. The open-world problem has been studied in the context of recognition [1, 23], namely how to get a model trained only on a given closed-world dataset to also recognize new classes of objects. Similar settings are also used in object detection [36, 15] and segmentation [3, 26, 38]. For example, [26] proposes an unsupervised open-world semantic segmentation; however, it obtains the mask of the image by a clustering method without any network parameter update. On the other hand, VLMs [28, 19, 8] exhibit strong performance and generalization ability with the help of massive image-text pair data. Inspired by this, TSEG [32] and ICILP [19] attempt to obtain fine-grained semantic alignment from image-text pairs to achieve image segmentation. Similarly, GroupViT [38] introduces a set of learnable group tokens for ViT to group patches and uses the generated segment tokens to align with text embeddings. The massively available image-text pair data provides rich visual and textual semantics for open-world scenarios [40]. Therefore, open-world semantic segmentation based on text supervision can achieve more refined segmentation results at a lower cost of annotation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 304, + 72, + 547, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 120 + ], + "type": "text", + "content": "Based on the above observations, this paper follows the open-world semantic segmentation setting based on text supervision to further improve the performance of semantic segmentation." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 305, + 133, + 389, + 148 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 133, + 389, + 148 + ], + "spans": [ + { + "bbox": [ + 305, + 133, + 389, + 148 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 154, + 547, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 154, + 547, + 251 + ], + "spans": [ + { + "bbox": [ + 304, + 154, + 547, + 251 + ], + "type": "text", + "content": "The overall framework of the MixReorg mask learner is shown in Figure 3. MixReorg is CLIP-based [28] and mainly consists of an image encoder and a text encoder. We use the text encoder from CLIP [28]. MixReorg's image encoder mainly has three stages: contextual mixing, progressive mixing, and mixing restoration (Sec. 3.1). Then, the loss composition of MixReorg is described in detail in Sec. 3.2. Finally, the total loss is introduced in Sec. 3.3." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 259, + 377, + 272 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 259, + 377, + 272 + ], + "spans": [ + { + "bbox": [ + 305, + 259, + 377, + 272 + ], + "type": "text", + "content": "3.1. MixReorg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 275, + 547, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 275, + 547, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 275, + 547, + 491 + ], + "type": "text", + "content": "Contextual Mixing. As shown in Figure 3(a), in the contextual image patch mixing stage, patches from different images are randomly mixed to construct a set of mixed images with known segmentation masks. According to the original image-text pairs, the patch-text correspondence of the mixed images is preserved, and the mixed image masks are used as the semantic segmentation labels of the mixed images. Similar to [21], the mixed images only have randomly mixed patch tokens from different images at their same locations. Specially, unlike [21], MixReorg adopts a contextual information image patch mixing strategy. We add a transformer layer before the image patch mixing operation to provide each patch the global image semantic which is closer to the text to create the coherence between patch and text. Meanwhile, it can preliminarily force the model to learn the mixed image patch reorganization from high-level features, thus effectively avoiding the interference of low-level features with the semantic learning of the model." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "spans": [ + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "text", + "content": "Specifically, given a batch of image-text pairs " + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "inline_equation", + "content": "\\{(x_i^I,x_i^T)\\}_{i = 1}^B" + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "text", + "content": ". Following the design in ViT [9], we first split each input image into " + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "text", + "content": " non-overlapping patches and linearly project each patch into a latent space. These projected patches are denoted as " + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "inline_equation", + "content": "\\{\\mathrm{p}_i\\}_{i = 1}^N" + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "text", + "content": ". For " + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "text", + "content": " image-text pairs " + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "inline_equation", + "content": "\\{(x_i^I,x_i^T)\\}_{i = 1}^M" + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "text", + "content": ", MixReorg randomly mixes the patches from " + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "text", + "content": " different images to construct " + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "text", + "content": " mixed images, and the corresponding patch composition of " + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 491, + 547, + 600 + ], + "type": "text", + "content": " mixed images can be denoted as" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 313, + 604, + 545, + 630 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 604, + 545, + 630 + ], + "spans": [ + { + "bbox": [ + 313, + 604, + 545, + 630 + ], + "type": "interline_equation", + "content": "\\operatorname {m i x} \\left(\\left\\{\\left\\{\\mathrm {p} _ {i} \\right\\} _ {i = 1} ^ {N} \\right\\} _ {m = 1} ^ {M}\\right) = \\left\\{ \\right.\\left.\\left.\\left. \\mathrm {p} _ {m, i} ^ {j} \\right\\} _ {i = 1} ^ {N} \\right\\} _ {m = 1} ^ {M}, 1 \\leq j \\leq M, \\right. \\tag {1}", + "image_path": "51d7b096847d7cfb592c85e87ac65b67e2a21e0f0b73de3eab156ed8e55ed5a2.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "inline_equation", + "content": "\\mathrm{p}_{m,i}^{j}" + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "text", + "content": " denotes that the " + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "text", + "content": "-th patch of the " + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "text", + "content": "-th mixed image comes from the " + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "text", + "content": "-th image. Correspondingly, we keep the correspondence between each image patch and the text corresponding to the original image, resulting in a semantic segmentation dataset with patch-text correspondence. The patch-text correspondence of the " + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "text", + "content": "-th mixed image can be expressed as " + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "inline_equation", + "content": "\\{\\mathrm{p}_{m,i}^{j}, x_{j}^{T}\\}_{i=1}^{N}" + }, + { + "bbox": [ + 304, + 629, + 547, + 717 + ], + "type": "text", + "content": ". Therefore, we obtain a set of" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 317, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 317, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 317, + 758 + ], + "type": "text", + "content": "1198" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 72, + 68, + 521, + 250 + ], + "blocks": [ + { + "bbox": [ + 72, + 68, + 521, + 250 + ], + "lines": [ + { + "bbox": [ + 72, + 68, + 521, + 250 + ], + "spans": [ + { + "bbox": [ + 72, + 68, + 521, + 250 + ], + "type": "image", + "image_path": "8721a114592d9a12bc2a0a5203c3358b42dced1f71ed32dd6464c5f771aff449.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 255, + 545, + 321 + ], + "lines": [ + { + "bbox": [ + 46, + 255, + 545, + 321 + ], + "spans": [ + { + "bbox": [ + 46, + 255, + 545, + 321 + ], + "type": "text", + "content": "Figure 3: The training pipeline and framework of MixReorg (take two images as an example). MixReorg's image encoder can be divided into three stages: (a) contextual mixing stage: a set of additional patch-text pairs with known segmentation mask is obtained by randomly mixing contextual patches from different images; (b) progressive mixing stage: the original image features are used to enhance the global information of the mixed image features after mixing; (c) mixing restoration stage: the original features, mixed features, and restored features are segmented through a two-stage grouping block [38], and the corresponding segment tokens are obtained. Note that we omit group tokens in the forward process for simplicity. During testing, MixReorg only needs to execute the original image branch." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 324, + 287, + 352 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 324, + 287, + 352 + ], + "spans": [ + { + "bbox": [ + 46, + 324, + 287, + 352 + ], + "type": "text", + "content": "sample-level image-text pairs " + }, + { + "bbox": [ + 46, + 324, + 287, + 352 + ], + "type": "inline_equation", + "content": "\\{(x_i^I,x_i^T)\\}_{i = 1}^B" + }, + { + "bbox": [ + 46, + 324, + 287, + 352 + ], + "type": "text", + "content": " and a set of patch-level patch-text pairs " + }, + { + "bbox": [ + 46, + 324, + 287, + 352 + ], + "type": "inline_equation", + "content": "\\{\\{\\mathrm{p}_{m,i}^{j},x_{j}^{T}\\}_{i = 1}^{N}\\}_{m = 1}^{M}" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 350, + 287, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 350, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 350, + 287, + 506 + ], + "type": "text", + "content": "Progressive Mixing. Mixed patches' features cannot improve after Contextual Mixing because of the semantic mixing in mixed images. Since more layers in Contextual Mixing will lead to more parameters, we propose Progressive Mixing to enhance mixed features without additional parameters. As shown in Figure 3(b), in the progressive mixing phase, the patch tokens of normal and mixed images are concatenated with " + }, + { + "bbox": [ + 46, + 350, + 287, + 506 + ], + "type": "inline_equation", + "content": "s_1" + }, + { + "bbox": [ + 46, + 350, + 287, + 506 + ], + "type": "text", + "content": " learnable group tokens " + }, + { + "bbox": [ + 46, + 350, + 287, + 506 + ], + "type": "inline_equation", + "content": "\\{g_i\\}_{i=1}^{s_1}" + }, + { + "bbox": [ + 46, + 350, + 287, + 506 + ], + "type": "text", + "content": " respectively and fed to the multi-layer transformers independently. At the same time, the original features are used to enhance the contextual information of the mixed features. The above process of an original image going through the " + }, + { + "bbox": [ + 46, + 350, + 287, + 506 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 46, + 350, + 287, + 506 + ], + "type": "text", + "content": "-th transformer layer can be represented as" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 508, + 287, + 525 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 508, + 287, + 525 + ], + "spans": [ + { + "bbox": [ + 59, + 508, + 287, + 525 + ], + "type": "interline_equation", + "content": "\\left\\{\\left\\{\\hat {g} _ {i} \\right\\} _ {i = 1} ^ {s _ {1}}, \\left\\{\\hat {\\mathrm {p}} _ {i} \\right\\} _ {i = 1} ^ {N} \\right\\} = \\operatorname {T r a n s} _ {l} \\left(\\left[ \\left\\{g _ {i} \\right\\} _ {i = 1} ^ {s _ {1}}; \\left\\{\\mathrm {p} _ {i} \\right\\} _ {i = 1} ^ {N} \\right]\\right), \\tag {2}", + "image_path": "0f73bc29866e7bb47132a145858b6d628afa8ec901efc5170b621f0943e06b96.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 526, + 287, + 562 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 526, + 287, + 562 + ], + "spans": [ + { + "bbox": [ + 46, + 526, + 287, + 562 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 526, + 287, + 562 + ], + "type": "inline_equation", + "content": "[ ; ]" + }, + { + "bbox": [ + 46, + 526, + 287, + 562 + ], + "type": "text", + "content": " denotes the concatenation operator. Similarly, the output of the " + }, + { + "bbox": [ + 46, + 526, + 287, + 562 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 46, + 526, + 287, + 562 + ], + "type": "text", + "content": "-th mixed image through the " + }, + { + "bbox": [ + 46, + 526, + 287, + 562 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 46, + 526, + 287, + 562 + ], + "type": "text", + "content": "-th transformer layer can be expressed as" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 55, + 565, + 287, + 609 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 565, + 287, + 609 + ], + "spans": [ + { + "bbox": [ + 55, + 565, + 287, + 609 + ], + "type": "interline_equation", + "content": "\\begin{array}{r l} & {\\{\\{\\hat {g} _ {i} \\} _ {i = 1} ^ {s _ {1}}, \\{\\hat {\\mathrm {p}} _ {m, i} ^ {j} \\} _ {i = 1} ^ {N} \\} = \\operatorname {T r a n s} _ {l} \\left(\\left[ \\left\\{g _ {i} \\right\\} _ {i = 1} ^ {s _ {1}}; \\left\\{\\mathrm {p} _ {m, i} ^ {j} \\right\\} _ {i = 1} ^ {N} + \\right. \\right.} \\\\ & {\\qquad \\left. \\operatorname {m i x} \\left(\\left\\{\\left\\{\\left\\{\\mathrm {p} _ {i} \\right\\} _ {i = 1} ^ {N} \\right\\} _ {m = 1} ^ {M} \\right\\rbrace_ {l - 1}\\right) _ {m} \\right].} \\end{array} \\tag {3}", + "image_path": "f38853ffdddc9e36d7edbaa99af1ae74b1658ba07931d1533005791554d4f39e.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "text", + "content": "Mixing Restoration. Although we can achieve patch-text alignment by mixed images, there are a lot of different semantics in one mixed image which will interfere with each other. Therefore, this requires the patches from different images in a mixed image still need to maintain a semantic match with the corresponding text." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "content": "To this end, as shown in Figure 3(c), in the mixing restoration phase, MixReorg also restores the mixed image" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "spans": [ + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "text", + "content": "according to the patch position of the image before mixing. The original features " + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "inline_equation", + "content": "\\{\\mathrm{p}_i\\}_{i = 1}^N" + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "text", + "content": ", mixed features " + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "inline_equation", + "content": "\\{\\mathrm{p}_{m,i}^{j}\\}_{i = 1}^{N}" + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "text", + "content": " and restored features " + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "inline_equation", + "content": "r e(\\{\\mathrm{p}_{m,i}^{j}\\}_{i = 1}^{N})" + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "text", + "content": " are segmented through a two-stage grouping block [38], and the corresponding segment tokens " + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "inline_equation", + "content": "\\{\\mathrm{seg}_i\\}_{i = 1}^{s_2}" + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "text", + "content": " are obtained. These segment tokens are fed into multiple transformer layers and then projected to the same dimensionality " + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "text", + "content": " as text embeddings " + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "inline_equation", + "content": "Z^{T}\\in \\mathbb{R}^{B\\times D}" + }, + { + "bbox": [ + 305, + 325, + 545, + 423 + ], + "type": "text", + "content": " through an MLP." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 439, + 545, + 452 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 439, + 545, + 452 + ], + "spans": [ + { + "bbox": [ + 305, + 439, + 545, + 452 + ], + "type": "text", + "content": "3.2. Cross-Modal Mixed Patch Reorganization Loss" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "spans": [ + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": "Mixed Segmentation Loss. Cross-modal mixed patch reorganization is a core module designed in MixReorg for semantic segmentation. It provides the model with more refined local alignment information by using a constructed mixed image dataset with patch-text correspondence. We expect the model to learn more fine-grained semantic alignment with the help of the constructed patch-text pairs. And the calculation process of the mixed image segmentation mask is shown in Figure 4, where every " + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "inline_equation", + "content": "B_{I}" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": " (e.g., " + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "inline_equation", + "content": "B_{I} = M" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": ") images are mixed. The mixed image segment tokens and the text embeddings of the whole batch are used to compute the similarity " + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "inline_equation", + "content": "S \\in \\mathbb{R}^{B_I \\times s_2 \\times B}" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": " for the text, where " + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "inline_equation", + "content": "\\otimes" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": " denotes matrix multiplication. Since we adopt a two-stage grouping block [38], we have the attention map " + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "inline_equation", + "content": "A \\in \\mathbb{R}^{B_I \\times HW \\times s_2}" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "inline_equation", + "content": "HW = N" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": "), which contains the grouping relationship between " + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "inline_equation", + "content": "HW" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": " patches and " + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "inline_equation", + "content": "s_2" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": " segment tokens. Further, by " + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "inline_equation", + "content": "A \\otimes S" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": ", we can predict the segmentation mask " + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "inline_equation", + "content": "M_p \\in \\mathbb{R}^{B_I \\times HW \\times B}" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": " of the mixed image. Finally, we compute the cross-entropy loss between the mixed image masks " + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "inline_equation", + "content": "M_{mix}" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": " and the prediction masks " + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "inline_equation", + "content": "M_p" + }, + { + "bbox": [ + 304, + 457, + 545, + 696 + ], + "type": "text", + "content": ", formulated as" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 371, + 701, + 545, + 714 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 371, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 371, + 701, + 545, + 714 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {s e g}} = \\mathcal {L} _ {C E} \\left(M _ {p}, M _ {\\text {m i x}}\\right), \\tag {4}", + "image_path": "97aaa37b9ce92c342d4f560d265b1178e44129d6881a2ad042b6b87466b61838.jpg" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1199" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 71, + 289, + 196 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 289, + 196 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 289, + 196 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 289, + 196 + ], + "type": "image", + "image_path": "445400a731bc889e5b512d6d4dbd90efedac1b7f752d88827f2e20aa3ebf40ee.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 205, + 287, + 271 + ], + "lines": [ + { + "bbox": [ + 46, + 205, + 287, + 271 + ], + "spans": [ + { + "bbox": [ + 46, + 205, + 287, + 271 + ], + "type": "text", + "content": "Figure 4: Cross-modal mixed patch reorganization, which combines attention maps and segmentation tokens from the image encoder, and text embeddings to reorganize and predict segmentation masks for mixed images. Where " + }, + { + "bbox": [ + 46, + 205, + 287, + 271 + ], + "type": "inline_equation", + "content": "B_{I} = M" + }, + { + "bbox": [ + 46, + 205, + 287, + 271 + ], + "type": "text", + "content": " means that every " + }, + { + "bbox": [ + 46, + 205, + 287, + 271 + ], + "type": "inline_equation", + "content": "B_{I}" + }, + { + "bbox": [ + 46, + 205, + 287, + 271 + ], + "type": "text", + "content": " images are mixed. For simplicity, we take a mixed image generated by mixing two images as an example." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 277, + 287, + 301 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 277, + 287, + 301 + ], + "spans": [ + { + "bbox": [ + 46, + 277, + 287, + 301 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 277, + 287, + 301 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{CE}(\\pmb {p},\\pmb {q}) = -\\sum_{i}\\pmb{q}_{i}\\log (\\pmb{p}_{i})" + }, + { + "bbox": [ + 46, + 277, + 287, + 301 + ], + "type": "text", + "content": " is the cross-entropy loss of output " + }, + { + "bbox": [ + 46, + 277, + 287, + 301 + ], + "type": "inline_equation", + "content": "\\pmb{p}" + }, + { + "bbox": [ + 46, + 277, + 287, + 301 + ], + "type": "text", + "content": " and target " + }, + { + "bbox": [ + 46, + 277, + 287, + 301 + ], + "type": "inline_equation", + "content": "\\pmb{q}" + }, + { + "bbox": [ + 46, + 277, + 287, + 301 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 303, + 287, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 303, + 287, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 303, + 287, + 422 + ], + "type": "text", + "content": "Restoration Contrastive Loss. Furthermore, we consider cross-modal semantic contrastive learning of mixing restoration features and text embeddings. Specifically, in order to take full advantage of the correspondence provided by the image-text pair and enhance the model's ability to align semantically across modalities, MixReorg computes the contrastive loss and the multi-label image-text contrastive loss [38] between the output of the restored features branch and the text embeddings, respectively. The calculation of the total image-text contrastive loss is as follows" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 114, + 430, + 287, + 443 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 114, + 430, + 287, + 443 + ], + "spans": [ + { + "bbox": [ + 114, + 430, + 287, + 443 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {I \\leftrightarrow T} ^ {r e} = \\mathcal {L} _ {I \\rightarrow T} ^ {r e} + \\mathcal {L} _ {I \\leftarrow T} ^ {r e}, \\tag {5}", + "image_path": "63d351e54a61239fd4ff1da90e624ec447d08bb813fc8bfe26156558ffc84ae0.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 445, + 261, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 445, + 261, + 456 + ], + "spans": [ + { + "bbox": [ + 47, + 445, + 261, + 456 + ], + "type": "text", + "content": "where the image-to-text contrastive loss is defined as" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 73, + 461, + 287, + 495 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 73, + 461, + 287, + 495 + ], + "spans": [ + { + "bbox": [ + 73, + 461, + 287, + 495 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {I \\rightarrow T} ^ {r e} = - \\frac {1}{B} \\sum_ {i = 1} ^ {B} \\log \\frac {\\exp \\left(z _ {i} ^ {I} \\cdot z _ {i} ^ {T} / \\tau\\right)}{\\sum_ {j = 1} ^ {B} \\exp \\left(z _ {i} ^ {I} \\cdot z _ {j} ^ {T} / \\tau\\right)}, \\tag {6}", + "image_path": "fe596748a244ef6667912803d3b8a22a3a626facd075792d13c713f7e46f25da.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 498, + 251, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 498, + 251, + 510 + ], + "spans": [ + { + "bbox": [ + 47, + 498, + 251, + 510 + ], + "type": "text", + "content": "and the text-to-image contrastive loss is defined as" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 73, + 515, + 287, + 548 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 73, + 515, + 287, + 548 + ], + "spans": [ + { + "bbox": [ + 73, + 515, + 287, + 548 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {I \\leftarrow T} ^ {r e} = - \\frac {1}{B} \\sum_ {i = 1} ^ {B} \\log \\frac {\\exp \\left(z _ {i} ^ {T} \\cdot z _ {i} ^ {I} / \\tau\\right)}{\\sum_ {j = 1} ^ {B} \\exp \\left(z _ {i} ^ {T} \\cdot z _ {j} ^ {I} / \\tau\\right)}, \\tag {7}", + "image_path": "c474fef58854f31bcc93a75f9077748175a6ea23bde27b18f8d328625f66a257.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 553, + 287, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 553, + 287, + 601 + ], + "spans": [ + { + "bbox": [ + 47, + 553, + 287, + 601 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 553, + 287, + 601 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 47, + 553, + 287, + 601 + ], + "type": "text", + "content": " is a learnable temperature parameter, and " + }, + { + "bbox": [ + 47, + 553, + 287, + 601 + ], + "type": "inline_equation", + "content": "z_{i}^{I}" + }, + { + "bbox": [ + 47, + 553, + 287, + 601 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 553, + 287, + 601 + ], + "type": "inline_equation", + "content": "z_{i}^{T}" + }, + { + "bbox": [ + 47, + 553, + 287, + 601 + ], + "type": "text", + "content": " are image and text embedding for image-text pairs " + }, + { + "bbox": [ + 47, + 553, + 287, + 601 + ], + "type": "inline_equation", + "content": "\\{(x_i^I,x_i^T)\\}_{i = 1}^B" + }, + { + "bbox": [ + 47, + 553, + 287, + 601 + ], + "type": "text", + "content": ". In addition, we calculate the multi-label contrastive loss of the restored features branch as follows" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 77, + 609, + 287, + 625 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 609, + 287, + 625 + ], + "spans": [ + { + "bbox": [ + 77, + 609, + 287, + 625 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {I \\leftrightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e} = \\mathcal {L} _ {I \\rightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e} + \\mathcal {L} _ {I \\leftarrow \\{T _ {k} \\} _ {k = 1} ^ {K}}, \\tag {8}", + "image_path": "7c6c8d46b0ad228c801870ba4d65c4dfb4603b37ae82154696608f5619a3ecbc.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 627, + 287, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 627, + 287, + 651 + ], + "spans": [ + { + "bbox": [ + 47, + 627, + 287, + 651 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 627, + 287, + 651 + ], + "type": "inline_equation", + "content": "\\{T_k\\}_{k=1}^K" + }, + { + "bbox": [ + 47, + 627, + 287, + 651 + ], + "type": "text", + "content": " is an additional " + }, + { + "bbox": [ + 47, + 627, + 287, + 651 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 47, + 627, + 287, + 651 + ], + "type": "text", + "content": " text labels generated using the \"prompting engineering\" mechanism in [28]," + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 656, + 289, + 705 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 656, + 289, + 705 + ], + "spans": [ + { + "bbox": [ + 47, + 656, + 289, + 705 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {I \\rightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e} = - \\frac {1}{B} \\sum_ {i = 1} ^ {B} \\log \\frac {\\sum_ {k = 1} ^ {K} \\exp \\left(z _ {i} ^ {I} \\cdot z _ {i} ^ {T _ {k}} / \\tau\\right)}{\\sum_ {k = 1} ^ {K} \\sum_ {j = 1} ^ {B} \\exp \\left(z _ {i} ^ {I} \\cdot z _ {j} ^ {T _ {k}} / \\tau\\right)} \\tag {9}", + "image_path": "6dd910f8d188805b3ed2b3a461614c9adb90d106db52a3c09acb38e2a55a8997.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 48, + 702, + 64, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 702, + 64, + 712 + ], + "spans": [ + { + "bbox": [ + 48, + 702, + 64, + 712 + ], + "type": "text", + "content": "and" + } + ] + } + ], + "index": 13 + }, + { + "type": "table", + "bbox": [ + 314, + 70, + 536, + 181 + ], + "blocks": [ + { + "bbox": [ + 314, + 70, + 536, + 181 + ], + "lines": [ + { + "bbox": [ + 314, + 70, + 536, + 181 + ], + "spans": [ + { + "bbox": [ + 314, + 70, + 536, + 181 + ], + "type": "table", + "html": "
Arch.MethodMask mIoU (%)
ViT [9]*pixel-wise20.1
K-means25.0
Mean-shift20.7
Spectral clustering19.7
GroupViT [38]-41.1
ViewCo [31]-45.7
MixReorg (ours)-47.9
", + "image_path": "bd491be1289fc16364185835df56c362fca610fa20ae503f14b2228725b8c0c9.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 185, + 545, + 218 + ], + "lines": [ + { + "bbox": [ + 305, + 185, + 545, + 218 + ], + "spans": [ + { + "bbox": [ + 305, + 185, + 545, + 218 + ], + "type": "text", + "content": "Table 1: Comparison with zero-shot semantic segmentation baselines on PASCAL VOC. GroupViT[38] and MixReorg are trained on CC12M. The superscript * means the results are from [38]." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 224, + 548, + 270 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 224, + 548, + 270 + ], + "spans": [ + { + "bbox": [ + 306, + 224, + 548, + 270 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {I \\leftarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e} = - \\frac {1}{K B} \\sum_ {k = 1} ^ {K} \\sum_ {i = 1} ^ {B} \\log \\frac {\\exp \\left(z _ {i} ^ {T _ {k}} \\cdot z _ {i} ^ {I} / \\tau\\right)}{\\sum_ {j = 1} ^ {B} \\exp \\left(z _ {i} ^ {T _ {k}} \\cdot z _ {j} ^ {I} / \\tau\\right)}. \\tag {10}", + "image_path": "98962012b3d77a83972691dc6a4048e9847e2a7d5eefdefa9cf54a5830fd6f15.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 269, + 545, + 293 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 269, + 545, + 293 + ], + "spans": [ + { + "bbox": [ + 305, + 269, + 545, + 293 + ], + "type": "text", + "content": "The total contrastive loss of the restored features and the text embeddings is as follows" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 365, + 297, + 545, + 312 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 365, + 297, + 545, + 312 + ], + "spans": [ + { + "bbox": [ + 365, + 297, + 545, + 312 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {r e} = \\mathcal {L} _ {I \\leftrightarrow T} ^ {r e} + \\mathcal {L} _ {I \\leftrightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {r e}. \\tag {11}", + "image_path": "d86575f1a973b73569f1269bd49346598c7c691653c91f272be98ddd09305766.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 315, + 545, + 338 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 315, + 545, + 338 + ], + "spans": [ + { + "bbox": [ + 305, + 315, + 545, + 338 + ], + "type": "text", + "content": "In summary, the total cross-modal mixed image patch reorganization loss is as follows" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 378, + 343, + 545, + 356 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 378, + 343, + 545, + 356 + ], + "spans": [ + { + "bbox": [ + 378, + 343, + 545, + 356 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {m i x e d}} = \\mathcal {L} _ {\\text {s e g}} + \\mathcal {L} _ {\\text {r e}}. \\tag {12}", + "image_path": "0cf34a3ffc14327132da40d0d173139aa5356c9d962fb0d8d4a387b2120302f3.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 361, + 432, + 373 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 361, + 432, + 373 + ], + "spans": [ + { + "bbox": [ + 306, + 361, + 432, + 373 + ], + "type": "text", + "content": "3.3. Overall Loss Function" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 377, + 545, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 377, + 545, + 411 + ], + "spans": [ + { + "bbox": [ + 305, + 377, + 545, + 411 + ], + "type": "text", + "content": "Similar to Eq. (11), the total contrastive loss between the original image features and the text embeddings is as follows" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 364, + 412, + 545, + 428 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 364, + 412, + 545, + 428 + ], + "spans": [ + { + "bbox": [ + 364, + 412, + 545, + 428 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {o r i}} = \\mathcal {L} _ {I \\leftrightarrow T} ^ {\\text {o r i}} + \\mathcal {L} _ {I \\leftrightarrow \\{T _ {k} \\} _ {k = 1} ^ {K}} ^ {\\text {o r i}}. \\tag {13}", + "image_path": "6b6e031b1f4858156de6daa6efaffe28b46798208d58d1f89b60deac0979ab30.jpg" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 427, + 455, + 439 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 427, + 455, + 439 + ], + "spans": [ + { + "bbox": [ + 306, + 427, + 455, + 439 + ], + "type": "text", + "content": "Finally, the total loss of MixReorg is" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 383, + 443, + 545, + 455 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 383, + 443, + 545, + 455 + ], + "spans": [ + { + "bbox": [ + 383, + 443, + 545, + 455 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathcal {L} _ {\\text {m i x e d}} + \\mathcal {L} _ {\\text {o r i}}. \\tag {14}", + "image_path": "404c9b94ce6d28768fb26338406b40de9894c12fe68049cc781f1a60aed2d257.jpg" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 305, + 455, + 545, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 455, + 545, + 491 + ], + "spans": [ + { + "bbox": [ + 305, + 455, + 545, + 491 + ], + "type": "text", + "content": "When testing, MixReorg only needs to execute the original image branch (the solid black line in Figure 3), so it does not add any extra testing time." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 306, + 501, + 387, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 501, + 387, + 514 + ], + "spans": [ + { + "bbox": [ + 306, + 501, + 387, + 514 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 306, + 521, + 438, + 533 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 521, + 438, + 533 + ], + "spans": [ + { + "bbox": [ + 306, + 521, + 438, + 533 + ], + "type": "text", + "content": "4.1. Implementation Details" + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 305, + 534, + 545, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 534, + 545, + 629 + ], + "spans": [ + { + "bbox": [ + 305, + 534, + 545, + 629 + ], + "type": "text", + "content": "Architecture. The image encoder of MixReorg is based on a 2-stage GroupViT [38] with 12 transformer layers, while adding one transformer layer before the mix operation. The size of the input image is " + }, + { + "bbox": [ + 305, + 534, + 545, + 629 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 305, + 534, + 545, + 629 + ], + "type": "text", + "content": ", the patch size is " + }, + { + "bbox": [ + 305, + 534, + 545, + 629 + ], + "type": "inline_equation", + "content": "16 \\times 16" + }, + { + "bbox": [ + 305, + 534, + 545, + 629 + ], + "type": "text", + "content": " and the hidden dimensionality is 384. The model outputs 32 segment tokens (i.e., " + }, + { + "bbox": [ + 305, + 534, + 545, + 629 + ], + "type": "inline_equation", + "content": "s_2 = 32" + }, + { + "bbox": [ + 305, + 534, + 545, + 629 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 534, + 545, + 629 + ], + "type": "inline_equation", + "content": "s_1 = 64" + }, + { + "bbox": [ + 305, + 534, + 545, + 629 + ], + "type": "text", + "content": "). Following [28, 38], the text encoder of MixReorg consists of 12 layers of transformer with the hidden feature dimensionality of 256." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 305, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 630, + 545, + 713 + ], + "type": "text", + "content": "Training and Inference. During the training phase, we use CC12M [4] as the training dataset, which contains 12M image-text pairs. We apply the mix operation for every 16 images (i.e., " + }, + { + "bbox": [ + 305, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "M = 16" + }, + { + "bbox": [ + 305, + 630, + 545, + 713 + ], + "type": "text", + "content": "). Following [38, 28], our batch size is 4096. We set the weight for each loss function to 1. During the inference phase, only the original image branch is executed. More details can be seen in Appendix." + } + ] + } + ], + "index": 30 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1200" + } + ] + } + ], + "index": 31 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 82, + 70, + 509, + 324 + ], + "blocks": [ + { + "bbox": [ + 82, + 70, + 509, + 324 + ], + "lines": [ + { + "bbox": [ + 82, + 70, + 509, + 324 + ], + "spans": [ + { + "bbox": [ + 82, + 70, + 509, + 324 + ], + "type": "table", + "html": "
Pre-trainingTransfer (mIoU (%))
Arch.ModelDatasetSupervisionZero-ShotPASCAL VOCPASCAL Context
ViTDeiT [33]ImageNetclassX53.035.9
DINO [2]ImageNetselfX39.120.4
DINOCC12M+YFCCselfX37.622.8
MoCo [13]ImageNetselfX34.321.3
MoCoCC12M+YFCCselfX36.123.0
CLIPSLIP* [25]LAION-20Mtext & self✓-12.3
CLIP-MAE* [8]LAION-20Mtext & self✓-16.8
MaskCLIP [8]LAION-20Mtext & self✓-17.7
ViewCo [31]CC12Mtext & self✓45.720.8
MaskCLIP [44]CLIP-400Mtext✓-21.7
CLIP* [28]LAION-20Mtext✓-13.5
GroupViT[38]CC12M+YFCCtext✓51.222.3
GroupViTCC12Mtext✓41.1 45.5†18.2 19.2†
MixReorg (ours)CC12Mtext✓47.9 (6.8 ↑) 50.5†(5.0 ↑)23.9 (5.7 ↑) 25.4†(6.2 ↑)
", + "image_path": "6866d7eba59bef2380a2dbd13daebfcb3189b7a829b2eb501585dd24629ca7ed.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 55, + 361, + 276, + 462 + ], + "blocks": [ + { + "bbox": [ + 46, + 329, + 545, + 361 + ], + "lines": [ + { + "bbox": [ + 46, + 329, + 545, + 361 + ], + "spans": [ + { + "bbox": [ + 46, + 329, + 545, + 361 + ], + "type": "text", + "content": "Table 2: Performance comparison on PASCAL VOC [10] and PASCAL Context [24]. Zero-shot means that the model is directly transferred to the semantic segmentation task without any fine-tuning on the target dataset. The superscript * denote the results are from [8]. † indicates the results of the multi-scale evaluation." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 55, + 361, + 276, + 462 + ], + "lines": [ + { + "bbox": [ + 55, + 361, + 276, + 462 + ], + "spans": [ + { + "bbox": [ + 55, + 361, + 276, + 462 + ], + "type": "table", + "html": "
ModelPre-training DatasetTransfer mIoU (%)
ViewCo [31]CC12M20.6
GroupViT [38]CC12M+YFCC20.9
GroupViTCC12M18.4 21.1†
MixReorg (ours)CC12M21.3 (2.9 ↑) 23.6† (2.5 ↑)
", + "image_path": "29249a083e9774262369c87a6c060828d94f34869a327d8a2b9fc94129e0041d.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 489, + 286, + 620 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 489, + 286, + 620 + ], + "spans": [ + { + "bbox": [ + 46, + 489, + 286, + 620 + ], + "type": "text", + "content": "Open-World Semantic Segmentation. We evaluate the performance of MixReorg on the open-world segmentation task on four commonly used open semantic segmentation datasets PASCAL VOC 2012 [10], PASCAL Context [24], COCO [20], and ADE20K [43]. They contain 20, 59, 80, and 150 foreground classes, respectively, with validation images of 1.5K, 5K, 5K, and 2K, respectively. MixReorg is transferred to the target dataset in a zero-shot manner without any fine-tuning. Following GroupViT [38], MixReorg obtains the corresponding segmentation of the image through the learned group token." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 628, + 239, + 640 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 628, + 239, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 628, + 239, + 640 + ], + "type": "text", + "content": "4.2. Comparisons with Existing Methods" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 642, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 286, + 713 + ], + "type": "text", + "content": "Comparison with Zero-Shot Baselines. In Table 1, we present a comparison of four ViT-based baselines, which utilize the image-text contrastive loss defined in CLIP [28] to train the vision and text encoders. These baselines employ pixel-wise, k-means, mean-shift, and spectral clustering strategies, respectively. Additionally, we in" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 315, + 361, + 535, + 509 + ], + "blocks": [ + { + "bbox": [ + 46, + 464, + 286, + 486 + ], + "lines": [ + { + "bbox": [ + 46, + 464, + 286, + 486 + ], + "spans": [ + { + "bbox": [ + 46, + 464, + 286, + 486 + ], + "type": "text", + "content": "Table 3: Performance comparison on COCO [20]. " + }, + { + "bbox": [ + 46, + 464, + 286, + 486 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 46, + 464, + 286, + 486 + ], + "type": "text", + "content": " indicates the results of the multi-scale evaluation." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 315, + 361, + 535, + 509 + ], + "lines": [ + { + "bbox": [ + 315, + 361, + 535, + 509 + ], + "spans": [ + { + "bbox": [ + 315, + 361, + 535, + 509 + ], + "type": "table", + "html": "
ModelPre-training DatasetTransfer mIoU (%)
ALIGNa[14]ALIGN-1800M9.7
ALIGNaHQITP-134M7.5
CLIPA[28]HQITP-134M5.1
CLIPCLIP-400M5.8
CLIPbLAION-20M7.7
SLIPb[25]LAION-20M6.8
GroupViT [38]CC12M5.8
6.7
MixReorg (ours)CC12M8.7 (2.9 ↑)
10.1† (3.4 ↑)
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The superscript " + }, + { + "bbox": [ + 305, + 513, + 545, + 536 + ], + "type": "inline_equation", + "content": "{}^{a}" + }, + { + "bbox": [ + 305, + 513, + 545, + 536 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 513, + 545, + 536 + ], + "type": "inline_equation", + "content": "{}^{b}" + }, + { + "bbox": [ + 305, + 513, + 545, + 536 + ], + "type": "text", + "content": " denote the results are from [29] and [8],respectively." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 543, + 545, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 543, + 545, + 602 + ], + "spans": [ + { + "bbox": [ + 305, + 543, + 545, + 602 + ], + "type": "text", + "content": "clude GroupViT [38], which employs a bottom-up grouping method. The results in Table 1 demonstrate that MixReorg outperforms both the ViT baselines and GroupViT (41.1% vs. 47.9%), indicating that MixReorg is effective in enhancing the segmentation ability of the model." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Comparison with SoTA Methods. We conduct a comprehensive evaluation of MixReorg against fully-supervised methods [33], self-supervised methods [2, 13], vision-language contrastive learning baselines [44, 28, 38], and baselines combining vision-language contrastive learning with self-supervised learning [25, 8, 31]. Table 2 and Table 3 summarizes the comparison results on PASCAL VOC, PASCAL Context, and COCO datasets, both in single-scale and multi-scale evaluation settings. The results show that" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 314, + 757 + ], + "type": "text", + "content": "1201" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": "MixReorg outperforms all the methods by a significant margin, demonstrating its effectiveness in semantic segmentation. In comparison to GroupViT, MixReorg that pre-trains on CC12M yields substantial performance improvements of " + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "inline_equation", + "content": "6.8\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": " mIoU, " + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "inline_equation", + "content": "5.7\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": " mIoU, and " + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "inline_equation", + "content": "2.9\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": " mIoU for single-scale evaluation, and " + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "inline_equation", + "content": "5.0\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": " mIoU, " + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "inline_equation", + "content": "6.2\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": " mIoU, and " + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "inline_equation", + "content": "2.5\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": " mIoU for multi-scale evaluation on PASCAL VOC, PASCAL Context, and COCO, respectively. MixReorg also outperforms GroupViT which pre-trains on CC12M and YFCC with less data. Additionally, MixReorg has a clear advantage over the methods which rely on additional supervision information in the vision branch. Furthermore, we evaluate the performance of MixReorg on the ADE20K dataset, as shown in Table 4. MixReorg outperforms GroupViT by a significant margin (8.7% vs. 5.8%), demonstrating its superior performance in complex segmentation tasks." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 263, + 288, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 263, + 288, + 323 + ], + "spans": [ + { + "bbox": [ + 46, + 263, + 288, + 323 + ], + "type": "text", + "content": "Image Classification. We evaluate the zero-shot classification performance of MixReorg on ImageNet. As shown in Table 5, MixReorg significantly outperforms GroupViT, indicating that MixReorg achieves better image-text alignment through fine-grained mask learning." + } + ] + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 67, + 323, + 266, + 374 + ], + "blocks": [ + { + "bbox": [ + 67, + 323, + 266, + 374 + ], + "lines": [ + { + "bbox": [ + 67, + 323, + 266, + 374 + ], + "spans": [ + { + "bbox": [ + 67, + 323, + 266, + 374 + ], + "type": "table", + "html": "
Arch.Zero-shot
Acc@1 (%)Acc@5 (%)
GroupViT [38]37.565.5
MixReorg(ours)38.866.7
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MethodCM\\( \\mathcal{L}_{seg} \\)\\( \\mathcal{L}_{re} \\)mIoU (%)
GroupViT---18.4
GroupViT+---18.2
MixReorg✓19.3
✓18.0
✓✓20.5
✓✓20.3
✓✓✓21.3
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For MixReorg, without CM means images are mixed prior to passing through the transformer layer that we add." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 307, + 221, + 544, + 319 + ], + "blocks": [ + { + "bbox": [ + 307, + 221, + 544, + 319 + ], + "lines": [ + { + "bbox": [ + 307, + 221, + 544, + 319 + ], + "spans": [ + { + "bbox": [ + 307, + 221, + 544, + 319 + ], + "type": "image", + "image_path": "5738bd6c71bd12577e3c4908e9f4df7b86604d2a5ba65aeb72101bc60e5f70d8.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 324, + 547, + 402 + ], + "lines": [ + { + "bbox": [ + 304, + 324, + 547, + 402 + ], + "spans": [ + { + "bbox": [ + 304, + 324, + 547, + 402 + ], + "type": "text", + "content": "Figure 5: On COCO, MixReorg's ablation study on the number of progressive mixings and the number of images for the contextual mixing operation. (a) Yellow line: Ablation study on the number " + }, + { + "bbox": [ + 304, + 324, + 547, + 402 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 304, + 324, + 547, + 402 + ], + "type": "text", + "content": " of the progressive mixing modules. We replace one progressive mixing module with one transformer layer to maintain the model size. (b) Red line: Ablation study on the number " + }, + { + "bbox": [ + 304, + 324, + 547, + 402 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 324, + 547, + 402 + ], + "type": "text", + "content": " of images for each contextual mixing operation." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "text", + "content": "19.3%). This means that " + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{seg}" + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "text", + "content": " plays a significant role. The model learns to distinguish different semantics in the image through " + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{seg}" + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "text", + "content": ". Additionally, " + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{re}" + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "text", + "content": " improves the performance of the model (20.3% vs. 19.3%). It helps the patches of the mixed image to maintain consistency between its original image semantics and corresponding text. Furthermore, by combining " + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{seg}" + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{re}" + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "text", + "content": " based on CM, the performance of MixReorg can be further improved (21.3% vs. 20.5% vs. 20.3%), which illustrates that CM and two loss functions are strongly related. CM is fundamental to achieving patch-text alignment since it provides global information to each patch, while " + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{seg}" + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "text", + "content": " provides fine-grained semantic alignment ability and " + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{re}" + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "text", + "content": " assisting " + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{seg}" + }, + { + "bbox": [ + 304, + 403, + 547, + 570 + ], + "type": "text", + "content": " keeping the patches' original semantic, free from the interference from different images." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": "Number of Images for Mixing. In Figure 5 (red line), we observe the performance impact of the number of images " + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": " used for contextual mixing operation. It can be observed that " + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "inline_equation", + "content": "M = 16" + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": " is optimal. As " + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": " increases, mixed images contain more semantic categories, which is helpful for the model in learning semantic grouping (20.5% vs. 17.1%). However, increasing " + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": " beyond a certain threshold (e.g.: " + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "inline_equation", + "content": "M = 32" + }, + { + "bbox": [ + 304, + 570, + 547, + 689 + ], + "type": "text", + "content": ") causes semantic representation in the mixed image to be insufficient due to resolution constraints, thereby interfering with model learning (20.5% vs. 18.2%)." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "type": "text", + "content": "Progressive Mixing Module. In Figure 5 (yellow line), we study the number " + }, + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "type": "text", + "content": " of the progressive mixing modules. We" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1202" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 72, + 66, + 519, + 230 + ], + "blocks": [ + { + "bbox": [ + 72, + 66, + 519, + 230 + ], + "lines": [ + { + "bbox": [ + 72, + 66, + 519, + 230 + ], + "spans": [ + { + "bbox": [ + 72, + 66, + 519, + 230 + ], + "type": "image", + "image_path": "995491eab91c51e579d1793dc8cd1ffdc957808fd75110e8bc925672e0759dd5.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "spans": [ + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "text", + "content": "add one transformer layer when removing one progressive mixing module to maintain the model size. It can be seen that the model is optimal when the number " + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "text", + "content": " of the progressive mixing modules is 6. The progressive mixing improves over " + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "inline_equation", + "content": "P = 0" + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "text", + "content": " by about " + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "inline_equation", + "content": "7\\%" + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "text", + "content": " mIoU (" + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "inline_equation", + "content": "P = 3" + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "text", + "content": " vs. " + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "inline_equation", + "content": "P = 0" + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "text", + "content": "). When " + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "inline_equation", + "content": "P = 0" + }, + { + "bbox": [ + 46, + 247, + 290, + 403 + ], + "type": "text", + "content": ", the original image is not used to enhance the mixed image after the mixing operation. In this case, the lack of global information on the original image hinders the learning of the model. Obviously, with the increase of the progressive mixing modules, the semantics of the mixed image features become clearer, which is thus more conducive for model learning to distinguish different semantics, thus improving the model segmentation ability." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 407, + 132, + 418 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 407, + 132, + 418 + ], + "spans": [ + { + "bbox": [ + 47, + 407, + 132, + 418 + ], + "type": "text", + "content": "4.4. Visualization" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 420, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 420, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 420, + 287, + 552 + ], + "type": "text", + "content": "Qualitative Results. In Figure 6, we illustrate zero-shot semantic segmentation examples predicted by GroupViT and MixReorg to verify the segmentation capability of our method. As shown in Figure 6(a), MixReorg can handle more complex segmentation examples which have different classes in one image, showing that our method can better perceive fine-grained semantics. In addition, as shown in Figure 6(b), MixReorg's segmentation quality of stuff classes is significantly better than GroupViT. In a word, MixReorg has a stronger ability of high-level semantic understanding and segmentation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 552, + 288, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 552, + 288, + 648 + ], + "spans": [ + { + "bbox": [ + 46, + 552, + 288, + 648 + ], + "type": "text", + "content": "Mixed Patch Reorganization. We visualize the reorganized images from mixed images according to the mask predictions from two mixed images in Figure 7(a). It can be seen that except for a few patches, MixReorg can correctly segment most image patches into their corresponding original semantics. In Figure 7(b), the confusion matrix of the prediction for one mixed image indicates that MixReorg can effectively align patches with text." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 650, + 117, + 662 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 650, + 117, + 662 + ], + "spans": [ + { + "bbox": [ + 47, + 650, + 117, + 662 + ], + "type": "text", + "content": "5. Discussion" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "content": "Conclusion. We propose a patch-text data construction method with dense matching for image-text data and a cross-modal mixed image patch reorganization mask learner for mixed images to achieve fine-grained semantic" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 309, + 247, + 416, + 369 + ], + "blocks": [ + { + "bbox": [ + 309, + 247, + 416, + 369 + ], + "lines": [ + { + "bbox": [ + 309, + 247, + 416, + 369 + ], + "spans": [ + { + "bbox": [ + 309, + 247, + 416, + 369 + ], + "type": "image", + "image_path": "e645c8eed64ac0ed5b18a83f4c5d66e9be27df84f0b72550f5c44e4d4e76949b.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "lines": [ + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "spans": [ + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "type": "text", + "content": "Figure 7: Mixed image reorganization and the confusion matrix. (a) We use the segmentation mask predicted by MixReorg on the mixed image to obtain the reorganized image. (b) Taking " + }, + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "type": "inline_equation", + "content": "M = 16" + }, + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "type": "text", + "content": " as an example, the confusion matrix " + }, + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "type": "inline_equation", + "content": "CM" + }, + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "type": "text", + "content": " of the patch segmentation of the mixed images. " + }, + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "type": "inline_equation", + "content": "CM_{ij}" + }, + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "type": "text", + "content": " represents the proportion of patches belonging to the " + }, + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "type": "text", + "content": "-th image in the mixed image that are classified into the " + }, + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 368, + 545, + 445 + ], + "type": "text", + "content": "-th image category." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 421, + 246, + 543, + 368 + ], + "blocks": [ + { + "bbox": [ + 108, + 234, + 483, + 245 + ], + "lines": [ + { + "bbox": [ + 108, + 234, + 483, + 245 + ], + "spans": [ + { + "bbox": [ + 108, + 234, + 483, + 245 + ], + "type": "text", + "content": "Figure 6: Comparison of semantic segmentation results on PASCAL VOC 2012 and PASCAL Context." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 421, + 246, + 543, + 368 + ], + "lines": [ + { + "bbox": [ + 421, + 246, + 543, + 368 + ], + "spans": [ + { + "bbox": [ + 421, + 246, + 543, + 368 + ], + "type": "image", + "image_path": "de40525f0b6c457058c9279d0392bca683837eb869c824e2d7bb8cf89c11788e.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 446, + 545, + 469 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 446, + 545, + 469 + ], + "spans": [ + { + "bbox": [ + 304, + 446, + 545, + 469 + ], + "type": "text", + "content": "alignment in open-world segmentation. MixReorg shows superior performance in open-world scenarios." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 470, + 545, + 542 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 470, + 545, + 542 + ], + "spans": [ + { + "bbox": [ + 304, + 470, + 545, + 542 + ], + "type": "text", + "content": "Limitations. There are two issues that we should explore to improve MixReorg. First, since we use contextual mixing to create additional dat, the computational budget is increased during the training phase. Second, although Mixreorg successfully constructs patch-text data for semantic segmentation, there is still a gap between it with pixel-level data." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 548, + 410, + 560 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 548, + 410, + 560 + ], + "spans": [ + { + "bbox": [ + 306, + 548, + 410, + 560 + ], + "type": "text", + "content": "6. Acknowledgment" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 562, + 545, + 694 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 562, + 545, + 694 + ], + "spans": [ + { + "bbox": [ + 304, + 562, + 545, + 694 + ], + "type": "text", + "content": "This work was supported in part by National Key R&D Program of China under Grant No. 2020AAA0109700, Guangdong Outstanding Youth Fund (Grant No. 2021B1515020061), Shenzhen Science and Technology Program (Grant No. RCYX20200714114642083), Shenzhen Fundamental Research Program (Grant No. JCYJ20190807154211365), Nansha Key RD Program under Grant No.2022ZD014 and Sun Yat-sen University under Grant No. 22lgqb38 and 76160-12220011. 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However, despite researchers exploring cross-lingual translation techniques such as machine translation and audio speech translation to overcome language barriers, there is still a shortage of cross-lingual studies on visual speech. This lack of research is mainly due to the absence of datasets containing visual speech and translated text pairs. In this paper, we present AVMuST-TED, the first dataset for Audio-Visual Multilingual Speech Translation, derived from TED talks. Nonetheless, visual speech is not as distinguishable as audio speech, making it difficult to develop a mapping from source speech phonemes to the target language text. To address this issue, we propose MixSpeech, a cross-modality self-learning framework that utilizes audio speech to regularize the training of visual speech tasks. To further minimize the cross-modality gap and its impact on knowledge transfer, we suggest adopting mixed speech, which is created by interpolating audio and visual streams, along with a curriculum learning strategy to adjust the mixing ratio as needed. MixSpeech enhances speech translation in noisy environments, improving BLEU scores for four languages on AVMuST-TED by $+1.4$ to $+4.2$ . Moreover, it achieves state-of-the-art performance in lip reading on CMLR $(11.1\\%)$ , LRS2 $(25.5\\%)$ , and LRS3 $(28.0\\%)$ .", + "bbox": [ + 76, + 340, + 473, + 704 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 733, + 209, + 750 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Multi-media techniques, including Audio-Visual Speech Recognition (AVSR) [4, 1, 2, 53], Audio-Visual Speech Translation (AVST) [8, 38, 61], and Audio-Visual Speech Generation (AVSG) [48, 32, 24], are commonly employed in various online communication scenarios, such as conferences, education, and healthcare. As a tool for ultra-remote communication, many online interactions involve multiple", + "bbox": [ + 75, + 758, + 468, + 864 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/9e335c4f0355b0c07d0ce08b0bcae93eb7596c8a0e96b9b4080f4064649ec260.jpg", + "image_caption": [ + "Figure 1. Diagram of speech tasks. Audio speech and visual speech are paired parallel speech streams which can be employed for speech recognition and speech translation. However, only Lip-Translation remains unexplored." + ], + "image_footnote": [], + "bbox": [ + 509, + 325, + 736, + 448 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "En: Hello, beautiful world.", + "bbox": [ + 746, + 333, + 877, + 345 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Es: Hola, hermoso mundo.", + "bbox": [ + 746, + 377, + 880, + 388 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Fr: Bonjour, beau monde.", + "bbox": [ + 746, + 393, + 880, + 404 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "It : Ciao, bel mondo.", + "bbox": [ + 746, + 407, + 856, + 420 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Pt: Olá, belo mundo.", + "bbox": [ + 746, + 424, + 856, + 436 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "···", + "bbox": [ + 746, + 439, + 782, + 446 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "languages, prompting the need for addressing cross-lingual challenges. Several works have attempted to tackle these challenges, including Machine Translation (MT) [9, 37, 15] for text utterance, Speech Translation (ST) [58, 19] for audio utterance, and Speech-to-Speech Translation (S2ST) [58, 19, 17, 33, 29] for simultaneous interpretation. However, research on cross-lingual visual speech is still limited, as illustrated in Figure 1. As an essential component of multi-media speech, visual speech can be combined with audio to enhance the recognition and understanding of speech content as audio-visual speech [1, 2, 54], and is the unique resource for speech content understanding in audio-disabled scenarios [36].", + "bbox": [ + 496, + 549, + 893, + 744 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Visual speech translation has never been studied, mainly for the lack of visual speech datasets with translated texts in different languages. The few remaining works [57, 60, 44] also cannot be quantitatively verified for this reason, making them unconvincing. The available visual speech corpus is often very scarce compared to audio speech owing to the high demands of visual speech for model training, which requires mostly-frontal and high-resolution videos with a sufficiently high frame rate, such that motions around the lip area are clearly captured [23]. In this paper, we propose the", + "bbox": [ + 496, + 750, + 895, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Equal contribution.", + "bbox": [ + 94, + 875, + 207, + 887 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Corresponding author.", + "bbox": [ + 96, + 887, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "15735", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "first Audio-Visual Multilingual Speech Translation dataset, AVMuST-TED. During the process of acquisition, we first screen out videos with professional translations in four different languages from TED talk which performs strict translation and review processes, and then determine the real speaker's talking head by checking whether each pair of visual speech (i.e., talking head) and audio speech matches in the manner of [1, 2]. Incidentally, this dataset can also be used for quantitative evaluation of other multi-modality translation tasks, such as cross-lingua audio-visual speech generation [51, 60].", + "bbox": [ + 75, + 90, + 472, + 256 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The cascaded model comprising of a speech recognition model and a machine translation model can handle speech translation tasks but suffers from error accumulation due to model cascades and cannot process languages without text (e.g., Minnan). Our proposed end-to-end model, which can translate directly from source speech to target text, addresses the above issues. However, visual speech is less distinguishable than audio speech, making it difficult to develop a mapping from source speech phonemes to the target language text. To address this, we introduce MixSpeech, a method that first pretrains the decoder using high-discrimination audio speech to obtain a mapping from speech phonemes to text and then generalizes this mapping to the visual speech task through cross-modality self-learning. Furthermore, since audio speech and visual speech are two distinct modalities of speech, there is a significant modality gap between them that hinders knowledge transfer. To narrow this gap and improve knowledge transfer, we propose mixed speech, which is created by interpolating audio and visual streams, rather than relying solely on audio speech. We also propose a curriculum-learning [7] based strategy to adjust the mixing ratio as the training progresses and cross-modality integration deepens.", + "bbox": [ + 75, + 258, + 472, + 604 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The code and dataset are available1, the main contributions of this paper are as follows:", + "bbox": [ + 76, + 606, + 468, + 638 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We present the first lip-translation baseline and introduce the Audio-Visual Multilingual Speech Translation dataset, AVMuST-TED.", + "- We present a cross-modality self-learning framework that leverages distinguishable audio speech translation to regularize visual speech translation for effective cross-modality knowledge transfer.", + "- We present to adopt the mixed speech, interpolated from audio and visual speeches, and a curriculum-learning based mixing ratio adjustment strategy to reduce the inter-modality gap during knowledge transfer.", + "- We achieve state-of-the-art performance in lip translation for four languages on AVMuST-TED, with a +1.4 to +4.2 boost in BLEU scores and in lip reading on CMLR (11.1%), LRS2 (25.5%) and LRS3 (28.0%)." + ], + "bbox": [ + 94, + 650, + 467, + 875 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 500, + 89, + 637, + 104 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Audio-Visual Speech", + "text_level": 1, + "bbox": [ + 500, + 114, + 694, + 131 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Audio and visual speeches are two separate modalities that convey speech content. Numerous works [45, 13, 1, 2, 47, 25, 28, 26, 34, 11] have explored ways to extract information from speech using these modalities. Speech recognition [45, 6, 22] is widely used in online meetings and social applications to recognize speech content. Speech translation [58, 66, 19] is commonly used in simultaneous interpretation applications for cross-lingual communication in cross-border travel and meetings. Keyword spotting [5, 52, 30] is employed in short video applications to quickly retrieve relevant content. Additionally, in noisy scenarios, relevant speech tasks [14, 21, 47, 42] rely on visual speech to avoid interference from surrounding speech and background noise. Despite the growing interest in speech tasks that rely on visual speech, researches [57, 60] on visual speech translation are limited and lacks validation due to the lack of multilingual audio-visual speech transcription datasets. This paper proposes a baseline for visual speech translation and introduces the first large-scale audio-visual multilingual translation dataset, AVMuST-TED, which includes 706 hours of audio-visual speech and translation pairs in Spanish, French, Italian, and Portuguese. AVMuST-TED lays a solid foundation or future cross-lingual audio-visual translation tasks, such as Cross-Lingual Talking Head Generation [44].", + "bbox": [ + 496, + 138, + 893, + 517 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Transfer learning from Audio to Visual", + "text_level": 1, + "bbox": [ + 500, + 529, + 834, + 545 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Many researchers [50, 53, 39, 64] attempt to enhance the representation of visual speech by leveraging corresponding audio speech, as the two are paired parallel speech streams. Some [50, 53, 39] use knowledge distillation to bootstrap the training of visual speech models using audio speech models, while others [71, 39] have proposed various distillation strategies to optimize the representation of visual speech by mining the intrinsic connection between audio and visual speeches. Some [53] also use self-supervised learning, with audio as auxiliary supervision for visual utterances, to obtain fine-grained visual representations. The success of these works demonstrates the critical role of audio speech, which has a higher discrimination compared to visual speech, in training visual speech models. However, previous works face the modality shift problem during knowledge transfer because they start directly from speeches of two different modalities, audio and visual speeches, with a significant modality gap. In this paper, we propose an cross-modality self-learning framework MixSpeech, that uses synthetic mixed speech to regularize visual speech translation for effective cross-modality knowledge transfer, reducing the gap between the two modalities during knowledge transfer.", + "bbox": [ + 496, + 553, + 890, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_footnote", + "text": "1https://github.com/Exgc/AVMuST-TED", + "bbox": [ + 94, + 886, + 372, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "15736", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/56481ff7c2a3680be8b6588f69136433f2587497b78a9400fdcd92ab4bfa1fa0.jpg", + "image_caption": [ + "Figure 2. Illustration of our proposed MixSpeech. We first pretrain the model with audio speech translation as shown in the dashed boxed, and then train the visual speech translation with mixed speech regularization. The blank dashed boxes denote the modality missing speech." + ], + "image_footnote": [], + "bbox": [ + 133, + 87, + 851, + 458 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Mixup for Cross-Modality Transfer", + "text_level": 1, + "bbox": [ + 76, + 517, + 387, + 534 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Many works [68, 20, 63, 19, 24] bridge the gap between modalities with mixup. [67] proposes mixup for data augmentation to improve model robustness. [10] suggests mixing at the representation-level to mine implicit associations between labeled and non-labeled sentences. Other works [63, 59, 18, 27] also use mixing to build bridges between different modalities. Some [63, 18] use CLIP [49] to retrieve semantically consistent images with text tokens and synthesize mixed sentences for text-visual consistency representation training. Others [59, 19] construct manifold mixup interpolations based on semantic consistency between audio and text to enhance understanding of audio with textual datasets. By implementing the mixup strategy, these studies have shown notable improvements across a range of tasks, highlighting its potential to facilitate knowledge transfer between different modalities. However, previous works use fixed hyperparameters [67] or mapping functions [19] for mixing ratios, which are typically not optimal and cannot be adapted to the training situation. In this paper, we propose an uncertainty-based [43] curriculum learning [7] strategy that gradually adjusts mixing ratios and apply mixup strategy for cross-modality knowledge transfer between audio and visual speeches for the first time.", + "bbox": [ + 75, + 553, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 516, + 591, + 531 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Task Formulation", + "text_level": 1, + "bbox": [ + 500, + 541, + 671, + 556 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As the twin task of speech recognition, speech translation involves translating source language speech into target language text. The speech translation model takes audio speech utterance $\\mathbf{A} = \\{\\mathbf{A}_t\\}_{t=1}^T \\in \\mathbb{R}^{T \\times D}$ or visual speech utterance $\\mathbf{V} = \\{\\mathbf{V}_t\\}_{t=1}^T \\in \\mathbb{R}^{T \\times D}$ as input and generates the target language text $\\mathbf{w} = \\{\\mathbf{w}_i\\}_{i=0}^s$ , where $\\mathbf{A}_t$ and $\\mathbf{V}_t$ represent the $t$ -th features in the audio and visual speeches, and $\\mathbf{w}_i$ represents the $i$ -th word in the target language translation with a total length of $S$ . Note that, we stack 4 adjacent acoustic frames together forSyncing with visual speech, both with $T$ frames.", + "bbox": [ + 496, + 564, + 890, + 733 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Overview", + "text_level": 1, + "bbox": [ + 500, + 741, + 609, + 756 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We propose a cross-modal self-learning framework for visual speech translation with audio speech regularization, named MixSpeech, as illustrated in Figure 2. This model consists of three modules - a feature extractor for extracting speech embeddings, a speech encoder for attending to the contextual dependencies of speech, and a target language-oriented translation decoder. We utilize the pre-trained feature extractor (AV-Encoder) and speech encoder (Speech-Encoder) from the AV-Hubert [53]", + "bbox": [ + 496, + 763, + 890, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "15737", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "to extract speech representations from both audio and visual speech utterances. Additionally, a randomly initialized translation decoder (Trans-Decoder) is used to autoregressively decode the speech representation into the target language text. MixSpeech is a two-stage training process: 1) Pretraining the translation decoder with high-discrimination audio speech utterances to learn inter-lingual mapping relations between source language phonemes and target language text, as detailed in subsection 3.3. 2) Aligning visual speech with audio speech to transfer the inter-lingual mapping from audio speech to visual in 3.5. The mixed speech 3.4 is synthesized by interpolating audio speech with visual speech in MixupSpeech, bridging the modality gap and enhancing knowledge transfer.", + "bbox": [ + 75, + 90, + 472, + 303 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Pretraining with Audio Speech", + "text_level": 1, + "bbox": [ + 76, + 314, + 349, + 330 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For uni-modality audio speech $\\mathbf{A} \\in \\mathbb{R}^{T \\times D}$ or visual speech $\\mathbf{V} \\in \\mathbb{R}^{T \\times D}$ , the uni-modality audio-visual feature $\\mathbf{e}^u = \\{\\mathbf{e}_t^u\\}_{t=1}^T \\in \\mathbb{R}^{T \\times 2D}$ fed into feature extractor can be defined as:", + "bbox": [ + 76, + 338, + 468, + 398 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {e} _ {t} ^ {u} = \\left\\{ \\begin{array}{l l} \\operatorname {c o n c a t} \\left(\\mathbf {0} _ {D}, \\mathbf {V} _ {t}\\right), & \\mathbf {V} _ {t} \\neq \\text {N o n e}, \\\\ \\operatorname {c o n c a t} \\left(\\mathbf {A} _ {t}, \\mathbf {0} _ {D}\\right), & \\mathbf {A} _ {t} \\neq \\text {N o n e}, \\end{array} \\right. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 130, + 414, + 468, + 454 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbf{0}_D$ denotes the feature of missing modality, following the practice of [53]. And then, we obtain the audiovisual fusion feature $\\mathbf{e}^f\\in \\mathbb{R}^{T\\times D}$ with AV-Encoder. The transformer-based Speech-Encoder allows us to obtain the phoneme embedding $\\mathbf{e}^p\\in \\mathbb{R}^{T\\times D}$ with the contextual speech details. A target language oriented translation decoder Trans-Decoder is appended to autoregressively decode the phoneme embedding $\\mathbf{e}^p$ into the target probabilities $P^u$ , where $P^u = \\{P_t^u\\}_{t = 1}^S = \\{p(\\mathbf{w}_t|\\{\\mathbf{w}_i\\}_{i = 1}^{t - 1},\\mathbf{e}^p)\\}_{t = 1}^S$ represents the probability of the $t$ -th word being $\\mathbf{w}_t$ when the previous $t - 1$ predictions are $\\{\\mathbf{w}_i\\}_{i = 1}^{t - 1}$ and $s$ is the length of the target language translation. During the pretraining, the overall model is trained on audio speech with cross-entropy loss:", + "bbox": [ + 75, + 462, + 472, + 671 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {C E} = - \\sum_ {t = 1} ^ {S} \\log p \\left(w _ {t} \\mid \\left\\{w _ {i} \\right\\} _ {i = 1} ^ {t - 1}, \\mathbf {e} ^ {p}\\right). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 150, + 672, + 468, + 714 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Audio-Visual Speech Mixing", + "text_level": 1, + "bbox": [ + 76, + 724, + 333, + 742 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Audio and visual speeches have a huge modality gap, which greatly impacts knowledge transfer across modalities. We attempt to employ mixed speech to bridge two different modalities of speech. Since the pair of audio and visual speeches is strictly temporally synchronous, we take advantage of this property to interpolate the mixed speech. For a pair of synchronized audio and video speech $(\\mathbf{A},\\mathbf{V})\\in \\mathbb{R}^{2\\times T\\times D}$ , each visual feature $\\mathbf{V}_t$ at $t$ -th frame has its corresponding audio feature $\\mathbf{A}_t$ , representing the same phonetic content. We interpolate with probability $\\phi$", + "bbox": [ + 75, + 750, + 472, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "to obtain a mixed speech $\\mathbf{e}^m = \\{\\mathbf{e}_t^m\\}_{t=1}^T \\in \\mathbb{R}^{T \\times 2D}$ derived partly from audio speech and partly from visual speech:", + "bbox": [ + 498, + 89, + 893, + 122 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {e} _ {t} ^ {m} = \\left\\{ \\begin{array}{l l} \\operatorname {c o n c a t} \\left(\\mathbf {0} _ {D}, \\mathbf {V} _ {t}\\right), & p < \\phi , \\\\ \\operatorname {c o n c a t} \\left(\\mathbf {A} _ {t}, \\mathbf {0} _ {D}\\right), & p \\geq \\phi , \\end{array} \\right. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 570, + 132, + 890, + 172 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $p$ is sampled from the uniform distribution $U(0,1)$ and $\\phi$ is the ratio of speech mixing. In particular, we propose a curriculum learning [7] based mixing ratio adjustment method that adapts the appropriate $\\phi$ as the training progresses. The prediction uncertainty [43] indicates the confidence of the prediction (smaller is better), and we take it as a signal to adjust the mixing ratio:", + "bbox": [ + 496, + 176, + 893, + 284 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {u} = \\frac {1}{S} \\sum_ {t = 1} ^ {S} \\operatorname {E n t r o p y} \\left(P _ {t}\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 602, + 292, + 890, + 334 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "If the discrimination of mixed speech is insufficient to regularize visual speech translation and maintain $n$ steps $(\\Delta \\mathbf{u} = \\mathbf{u}^v - \\mathbf{u}^m < k\\mathbf{u}^v$ , where $\\mathbf{u}^v$ and $\\mathbf{u}^m$ represent the uncertainty of uni-modality (visual) and mixed speech, respectively, and the threshold hyperparameter $k$ is set to 0.05 with $n$ set to 20 in our work), we gradually increase the proportion of audio at a rate of $\\alpha$ $(\\phi' = \\alpha \\phi)$ . We initialize $\\phi = 0.1$ to prevent excessive initial modality gap and maintain $\\phi \\in [0.1, 0.9]$ throughout the training process.", + "bbox": [ + 496, + 340, + 890, + 479 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.5. Cross-Modality Self-Learning for Speech", + "text_level": 1, + "bbox": [ + 500, + 486, + 851, + 503 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Since audio speech is more distinguished compared to visual speech, we intend to boost visual speech translation with the knowledge from audio speech. And the mixed speech bridges the gap between audio speech and visual speech, allowing us to boost cross-modality knowledge transfer with it. With audio speech feature $\\mathbf{A} \\in \\mathbb{R}^{T \\times D}$ and visual speech feature $\\mathbf{V} \\in \\mathbb{R}^{T \\times D}$ fed into the modules with shared parameters, the uni-modality visual speech feature $\\mathbf{e}^u$ and the mixed speech feature $\\mathbf{e}^m$ are decoded into the target probabilities $P^u$ and $P^m$ , respectively.", + "bbox": [ + 496, + 508, + 890, + 660 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "After the pre-training with audio speech translation, the model is promising enough for mixed speech containing partial audio speech, we adopt the Jensen-Shannon Divergence (JSD) [41] to regularize the probabilities of these two different speeches:", + "bbox": [ + 496, + 660, + 890, + 736 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {J S D} = \\sum_ {t = 1} ^ {S} J S D \\left(P _ {t} ^ {m} \\| P _ {t} ^ {u}\\right). \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 594, + 744, + 890, + 786 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As this probability is across the entire training vocabulary, we are able to perform fine-grained regularization to enhance the training of visual speech. Meanwhile, we also minimize the cross-entropy loss between two speech translations and the real translation, $\\mathcal{L} = \\mathcal{L}_{CE}^{uni} + \\lambda_1\\mathcal{L}_{CE}^{mix} + \\lambda_2\\mathcal{L}_{JSD}$ , where $\\lambda_{1}$ and $\\lambda_{2}$ are hyperparameters of loss weights, while $\\lambda_{1} = \\lambda_{2} = 1.0$ in this work.", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "15738", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/3415b3308ea40d81f36e48b816e15ac5327af73368106f3dc1c03212b707402d.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DatasetTarget Language Hours# Lang# Σ Hrs# Σ Sents# Σ Tokens
EnEsFrItPtsrctgt
Audio-Only
LibriSpeech [45]960h----1960h180K5.9M5.9M
MuST-C [16]-504h492h465h385h83617h2016K38.1M35.8M
VoxPopuli [62]543h441h427h461h-165967h2045K65.0M60.1M
Audio-Visual
LRS2 [1]224h----1224h143K2.3M2.3M
LRS3 [2]433h----1433h151K4.2M4.2M
AVMuST-TED (ours)-198h185h165h158h4706h925K7.3M7.0M
", + "bbox": [ + 101, + 88, + 872, + 268 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 330, + 209, + 348 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Datasets", + "text_level": 1, + "bbox": [ + 76, + 357, + 181, + 372 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "AVMuST-TED. To obtain a corpus for AVST, we screened a set of TED and TEDx talks with multilingual subtitles as the data source. All transcriptions and translations are performed strictly following the TED Translation Guidelines and require collaboration between at least one translator (or transcriber) and one reviewer. The prior lip-reading dataset acquisition pipeline is followed to crop face-tracks, and an audio-visual alignment network, SyncNet, is adopted for speaker proofreading. Table 1 compares AVMuST-TED with related datasets, and it is the first audio-visual speech translation dataset containing translations from English (En) to four target languages: Spanish (Es), French (Fr), Italian (It), and Portuguese (Pt). These four languages have the most translated subtitles in TED, and 1024/1536 pieces of data are randomly sampled for each language as the test/validation set. The information about AVMuST-TED is detailed in Appendix A.", + "bbox": [ + 75, + 382, + 470, + 640 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "LRS2&3 [1, 2], two commonly used publicly available English wild audio-visual speech recognition datasets, are adopted to demonstrate the lip-reading performance, containing 224 hours of video from BBC television shows and 433 hours of video from TED and TEDx talks. The training data in both datasets is divided into two partitions, namely Pretrain and Train, both of which are transcribed from videos to text at the sentence level. The only difference is that the video clips in the Pretrain partition are not strictly trimmed and sometimes longer than the corresponding text. In our experiments, we employ different amounts of training data from LRS2 and LRS3, including Pretrain+Train (224/433h) for high resource and Train (29/30h) for low resource.", + "bbox": [ + 75, + 641, + 468, + 851 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "CMLR [70], widely used dataset for Mandarin audio-visual speech recognition, contains 61 hours audio-visual speech utterances collected from Chinese TV stations. In", + "bbox": [ + 75, + 854, + 470, + 902 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/238ae6de05da00bb08371960db027898b0fe1e7da86a50365ee01572a50ed247.jpg", + "table_caption": [ + "Table 1. Comparison of audio-visual speech recognition/translation datasets. #Lang denotes the number of target languages. #∑Hrs denotes the overall duration of speech in the dataset, #Sents and #Tokens denote the overall sentences and the overall token, respectively." + ], + "table_footnote": [], + "table_body": "
MethodMBLEU↑
En-EsEn-FrEn-ItEn-Pt
CascadedV12.711.311.513.2
AV-Hubert [53]V14.212.612.914.8
CascadedA(+Noise)16.012.912.615.5
AV-Hubert [53]A(+Noise)17.614.514.117.1
MixSpeech(ours)V18.515.114.317.2
", + "bbox": [ + 500, + 328, + 893, + 459 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 2. Comparison of the performances of visual speech translation on AVMuST-TED with those of the noisy audio speech translation. The results of noisy audio speech translation are the mean value at five SNRs $\\{-20, -10, 0, 10, 20\\}$ db.", + "bbox": [ + 498, + 467, + 892, + 523 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "our experiments, we adopt this dataset to demonstrate the performance of our proposed MixSpeech in low-resource languages such as Mandarin. Additionally, we sample a training set containing only 12 hours of utterances in the manner of [71] for low resource scenario.", + "bbox": [ + 496, + 547, + 890, + 625 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Evaluation and Implementation Details", + "text_level": 1, + "bbox": [ + 498, + 633, + 839, + 648 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this paper, we measure the performance of MixSpeech on two speech tasks, speech recognition and speech translation. For speech recognition, word error rate (WER) is adopted as the evaluation metric, which is defined as $\\mathrm{WER} = (S + D + I) / M$ , where $S, D, I, M$ represent the number of words replaced, deleted, inserted, and referenced. As for speech translation, the case-sensitive detokenized BLEU score is computed using SACREBLEU [46], following the same evaluation methodology as in previous speech translation works [16, 62]. The implementation details are provided in Appendix B due to page limitations.", + "bbox": [ + 496, + 656, + 890, + 824 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Performance of Speech Translation", + "text_level": 1, + "bbox": [ + 498, + 832, + 807, + 848 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "End-To-End Models VS. Cascaded Models. Table 2 presents a comparison of the lip translation performance between two representative methods: 1) an end-to-end model,", + "bbox": [ + 496, + 854, + 892, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "15739", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "implemented based on the state-of-the-art AV-Hubert [53] method for visual speech-related tasks, and 2) a cascaded model, combining a speech recognition model (i.e., Lip-Reading or ASR) with a machine translation model. In the cascaded model, we use the speech recognition model trained by AV-Hubert on LRS3, which achieve the best lip-reading performance to date, and a transformer-based machine translation model trained on the paired translated text corpus in AVMuST-TED. Comparing the lip translation performance of the end-to-end model and the cascade model, we find that the BLEU score of the end-to-end model improved by $+1.3$ to $+1.6$ . This result demonstrates that the end-to-end trained model can effectively prevent the accumulation of errors caused by the model cascade, and that lip translation cannot be simply disassembled as the superposition of lip reading and machine translation.", + "bbox": [ + 75, + 90, + 472, + 332 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "MixSpeech VS. Prior Methods. Due to the discrimination of speech between modalities, visual speech models are not able to translate speech content as accurately as audio speech models. To address the issue of low discrimination in visual speech, we propose MixSpeech, which is a cross-modality self-learning framework that employs mixed speech to transfer knowledge obtained from audio speech pre-training into the visual speech model. Our proposed MixSpeech significantly improves the BLEU score by another $+1.4$ to $+4.3$ . Furthermore, the improvement from MixSpeech is related to the discrepancy in speech translation between audio and visual modalities. For example, En-Es exhibits a larger discrepancy of 14.7 between audio and visual speech translation, ranging from 28.9 to 14.2, and MixSpeech significantly improves it by $+4.3$ . Conversely, Italian shows a smaller discrepancy of 10.9, ranging from 23.8 to 12.9, and improves only by $+1.4$ . This highlights that the improvement in lip translation stems from the knowledge acquired from audio speech translation.", + "bbox": [ + 75, + 335, + 472, + 625 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Visual Speech VS. Noisy Audio Speech. We also evaluate the performance of audio speech translation in noisy environments, by adding noise sampled from MUSAN [55] to the audio speech and measuring the performance at five SNR levels $\\{-20, -10, 0, 10, 20\\}$ db. We compare the average BLEU scores of different SNRs and present the detailed performance in Appendix C.1. Our experiments show that although noisy audio speech performs better than visual speech, the translation performance is still significantly lower compared to noiseless audio speech. In contrast, MixSpeech, which fully leverages the knowledge of audio speech, greatly improves the visual speech translation performance, making it more reliable in noisy scenes. We also provide a comparison of translation with audio speech and audio-visual speech, demonstrating that visual speech enhances the ceiling and robustness of speech translation, but the details are only available in the Appendix C.1 since audio-visual speech does not require the cross-modality", + "bbox": [ + 75, + 628, + 472, + 902 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/bd5f9cb5cbe5560625d678642c6aab01064533c40b6a90584ba140136f0fd166.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
# RESMethodWER(Labeled Visual Utts Hrs) ↓
CMLRLRS2LRS3
HighWAS [56]38.9(61)70.4(224)-
TM-seq2seq [1]-49.8(698)59.9(698)
CSSMCM [70]32.5(61)--
Conv-seq2seq [69]-51.7(698)60.1(698)
CTC+KD [3]-51.3(224)58.9(433)
LIBS [71]31.3(61)65.3(698)-
CTCH [40]22.0(61)--
Master [50]-49.2(698)59.0(698)
Sub-Word [47]-28.9(698)40.6(698)
†AV-Hubert [53]12.7(61)28.7(224)28.6(433)
MixSpeech(ours)11.1(61)25.5(224)28.0(433)
LowLIBS [71]50.5(12)--
†AV-Hubert [53]25.8(12)31.4(29)32.5(30)
MixSpeech(ours)18.5(12)26.9(29)28.6(30)
", + "bbox": [ + 501, + 89, + 893, + 361 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 3. Comparison of lip reading methods under different resource conditions. # RES represents the amount of resources. (Hours) highlighted in blue are used for low resources. † For better comparison, we reproduce AV-Hubert on CMLR and LRS2.", + "bbox": [ + 498, + 369, + 893, + 428 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "knowledge transfer proposed in this paper.", + "bbox": [ + 500, + 454, + 782, + 470 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Performance of Speech Recognition", + "text_level": 1, + "bbox": [ + 500, + 483, + 808, + 500 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "As shown in Table 3, we compare the performance of MixSpeech on another visual speech task, lip reading (i.e., Visual Speech Recognition), to highlight the mixspeech from more perspectives. MixSpeech obtain state-of-the-art performance on three datasets, two for English (25.5% on LRS2 and 28.0% on LRS3) and one for Chinese (11.1% on CMLR), demonstrating that this cross-modality self-learning framework can be applied for different languages to capture the intrinsic association between audio and visual speeches and thus effectively improve the understanding of visual speech. Since visual speech is relatively low-resource, we verify whether MixSpeech can effectively improve the performance of visual speech tasks in low-resource with audio speech. Compared with previous methods, MixSpeech boosts the WER of lip-reading by -3.9% to -7.3%, highlighting the critical role of high-resource audio speech in low-resource visual speech tasks. Specifically, on LRS2 and LRS3, the performance of Mixspeech in the low-resource scenario (26.9%/28.6% WER obtained with only 29h/30h visual utterances) outperforms the performances of prior methods in the high-resource scenario (28.7%/28.6% obtained with 224h/433h or even more visual utterances). Even though with only limited labeled visual corpus, our proposed MixSpeech performs no less than works with more. It is the bridge between two modalities of speech, which helps visual speech to access the knowl", + "bbox": [ + 496, + 508, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "15740", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "edge stored in high-resource and high-discrimination audio speech without barriers.", + "bbox": [ + 75, + 90, + 468, + 121 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5. Can MixSpeech bridge cross-modality speech?", + "text_level": 1, + "bbox": [ + 76, + 130, + 467, + 147 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Our proposed MixSpeech builds a bridge between cross-modality speech through cross-modality self-learning, with the properly mixes speech. The details are as follows:", + "bbox": [ + 75, + 154, + 468, + 199 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Cross-Modality Self-Learning for Knowledge Transfer. The experiments in Figure 3 provide a positive answer to the question of whether MixSpeech can contribute to achieving knowledge transfer between audio and visual speeches. We evaluate the performance of visual speech translation with different regularization strategies: no audio speech regularization (i.e., $\\phi = 0$ ), mixed speech regularization with different mixing ratios (i.e., $\\phi \\in (0,1)$ , audio speech regularization (i.e., $\\phi = 1$ ), and mixing ratio adjustable mixed speech regularization (i.e., dashed lines). It is evident that the cross-modality self-learning framework significantly enhances visual speech translation, as all performances with audio speech regularization are noticeably better than those without self-learning ( $\\phi = 0$ ), demonstrating the effectiveness of our proposed MixSpeech.", + "bbox": [ + 75, + 200, + 468, + 425 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Narrow the Cross-Modality Distance with Properly Mixed Speech. Moreover, the introduction of mixed speech facilitates smoother cross-modality knowledge transfer by narrowing the modality gap between speeches. Some segments in the mixed speech come from the visual speech, making it much closer to visual speech in terms of modality distance than audio speech. When regularizing with mixed speech in En-Es, the translation performance of visual speech improves further by $+0.3$ to $+0.8$ compared to audio speech regularization alone. Among them, bootstrap", + "bbox": [ + 75, + 426, + 468, + 578 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c9e977e77f4aa403e23c47c220b00ee197026506ec91d8c1244467fe37b10735.jpg", + "image_caption": [ + "Figure 3. BLEU scores of MixSpeech with different speech regularization on En-Es and En-Fr. $\\phi = 0$ : no audio speech regularization, $\\phi \\in (0,1)$ : mixed speech regularization, $\\phi = 1$ : only audio speech regularization. The dashed lines represent the adjustable mixing ratio strategy based on curriculum learning." + ], + "image_footnote": [], + "bbox": [ + 81, + 599, + 464, + 824 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ping with mixed speech of mixing ratio $\\phi = 0.5$ achieves the highest BLEU score of 18.3. This demonstrates that a reasonably mixed ratio ensures that it is neither overly biased towards visual speech, leading to a lack of knowledge of audio speech, nor overly biased towards audio speech, leading to excessive cross-modality distances that affect knowledge transfer. The adjustable mixing ratio strategy based on curriculum learning further increases the applicability of mixed speech to cross-modality self-learning training, thereby boosting visual speech translation performance again.", + "bbox": [ + 496, + 90, + 890, + 257 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/b7eb1ca96eaf58088cecc6bd974db06ec46ec1344d35972b75101ad9dfc02ff8.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
IDMethodBLEU ↑
LmonCELmixCELJSDEn-EsEn-FrEn-ItEn-Pt
#1✓14.212.612.914.8
#2✓✓17.514.313.616.5
#3✓✓18.114.814.116.9
#4✓✓✓18.515.114.317.2
", + "bbox": [ + 509, + 267, + 880, + 380 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4. BLEU of different module combinations in MixSpeech.", + "bbox": [ + 500, + 390, + 880, + 405 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.6. What role does each part play in MixSpeech?", + "text_level": 1, + "bbox": [ + 500, + 424, + 883, + 441 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The effectiveness of MixSpeech, which is a cross-modality self-learning framework designed to improve visual translation performance, has been demonstrated. In this study, we investigate the role of each component in detail and present relevant experiments in Table 4:", + "bbox": [ + 496, + 446, + 890, + 521 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Bridging the cross-modality gaps. We observe a significant improvement in the lip translation performance with the inclusion of $\\mathcal{L}_{JSD}$ (ID: #3, #4) for regularizing the probabilities of visual speech and mixed speech, compared to without (ID: #1, #2). Specifically, experiment #3 with $\\mathcal{L}_{JSD}$ outperform experiment #2 with $\\mathcal{L}_{CE}^{mix}$ by $+0.6$ in lip translation performance on En-Es. This demonstrates that $\\mathcal{L}_{JSD}$ is the main contributor to achieving cross-modality knowledge transfer by building a bridge between the two speeches and performing fine-grained regularization across the probability of each word.", + "bbox": [ + 496, + 523, + 890, + 688 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Maintaining knowledge of audio speech. It is also important to note that during the regularization process, the representation of audio speech is also affected by visual speech, which can interfere with the knowledge of audio speech and ultimately harm the lip translation performance of MixSpeech. As evidenced by experiment #2, the lip translation performance on En-Es decrease by -0.4 compared to experiment #3 when $\\mathcal{L}_{CE}^{mix}$ is not applied. To address this issue, $\\mathcal{L}_{CE}^{mix}$ is introduced to enhance the training ceiling of the cross-modality self-learning framework. By maintaining the translation performance of mixed speech and preventing the excessive disturbance to audio speech knowledge, $\\mathcal{L}_{CE}^{mix}$ helps to improve the overall performance of MixSpeech.", + "bbox": [ + 496, + 689, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "15741", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/29845b784ea69738221c57fbdadb394d9accb123fcee2958b33841140671eac9.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
En-EsTranscription: and always as a child I had this fantasy that somebody would come and rescue me\nMixSpeech: and always as a child I had this fantasy that somebody would come and rescue me
Ground Truth: y de niña siempre tenía la fantasía de que alguien vendrá a salvar me de\nMixSpeech: y de (desde) niña niño siempre tenía la esta fantasía de que alguien vendrá a salvar me (rescató) de
En-FrTranscription: and solutions create new problems which have to be solved in their turn\nMixSpeech: and solutions to create new problems which have to be solved in their turn this year
Ground Truth: et les solutions créent de nouveaux problèmes devant être résolus à leur tour\nMixSpeech: et les (des) solutions pour creer de nouveaux problèmes devant qui doivent être résolus à leur tour
En-ItTranscription: one of the last 10,000 years, and the other certainly of the last 25 years\nMixSpeech: one of the last 10,000 years and the other certainly assistancee of the last 25 years
Ground Truth: uno presente negli ultimi diecimila anni e l'alto certamente negli ultimi 25 anni\nMixSpeech: uno presente negli ultimi diecimila (10000) anni e l'alto certamente negli ultimi 25 anni
En-PtTranscription: has around 2,000 people descending on MIT's campus\nMixSpeech: has around 2,000 people descending on MIT's campus
Ground Truth: congregamerca de 2000 pessoas no campus do mit\nMixSpeech: congregam de circa de 2000 pessoas a estudar no campus do mit
", + "bbox": [ + 76, + 89, + 898, + 481 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Qualitative performance of Visual Speech Recognition and Translation on AVMuST-TED. Red Strikeout Words: mistranslated words with opposite meaning, (Blue Words in parentheses): mistranslated words with similar meaning, Gray Words: the absent words.", + "bbox": [ + 75, + 488, + 892, + 517 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.7. Qualitative results", + "text_level": 1, + "bbox": [ + 76, + 541, + 254, + 556 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We present several examples of lip translation in Table 5 to qualitatively evaluate the translation quality of MixSpeech. The translation results are very close to the ground truth, and the semantics are consistent. We observe two types of words that differ in translation: synonyms and context-sensitive translations. Synonyms that have different spellings but the same meaning, such as salvar and rescató in Spanish, both meaning 'rescue', and diecimila and 10000 in Italian, both meaning 'ten thousand', are commonly found in translation tasks and can affect translation consistency. Additionally, there are translations that require context information, such as when the speaker refers to themselves as a child, and the translation in Spanish needs to take into account the speaker's gender to choose between niña for girl' or Niño for boy' and 'child'. The qualitative translation results of MixSpeech demonstrate its capability to achieve reliable cross-lingua lip translation. In Appendix C.2, we also provide translation results of noisy audio speech translation with visual speech translation and audio speech translation with audiovisual speech translation to highlight the importance of visual speech in speech translation.", + "bbox": [ + 75, + 568, + 472, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 540, + 617, + 556 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "With the advancement of online technologies, such as online healthcare and sales, language barriers often prevent these tools from reaching and benefiting disadvantaged areas. In light of this, we focus on visual speech, a branch of the speech stream, and aim to translate visual speech from source languages to other target languages for cross-linguistic communication, specifically through lip translation. We meticulously curate the AVMuST-TED dataset, consisting of 706 hours of speech clips with professional translations from TED, to facilitate cross-linguistic research on visual speech. We also introduce MixSpeech, a cross-modality self-learning framework that utilizes mixed speech to regularize visual speech translation and achieves state-of-the-art performance in lip translation on AVMuST-TED and lip reading on LRS2, LRS3, and CMLR datasets.", + "bbox": [ + 496, + 566, + 890, + 792 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Moreover, our work on visual speech and AVMuSTED lay a solid foundation for further research on visual speech in cross-lingual fields. There are numerous related tasks with great potential for practical applications, such as Cross-Lingual Talking Head Generation [44]. These tasks hold immense promise for breaking down language barriers and promoting communication across diverse communities.", + "bbox": [ + 496, + 794, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "15742", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements", + "text_level": 1, + "bbox": [ + 78, + 90, + 243, + 107 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was supported in part by National Key R&D Program of China under Grant No.2022ZD0162000, National Natural Science Foundation of China under Grant No.62222211, Grant No.61836002 and Grant No.62072397.", + "bbox": [ + 76, + 114, + 468, + 189 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 203, + 171, + 218 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Triantafyllos Afouras, Joon Son Chung, Andrew Senior, Oriol Vinyals, and Andrew Zisserman. 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Vlmixer: Unpaired vision-language pre-training via cross-modal cutmix. In International Conference on Machine Learning, pages 22680-22690. PMLR, 2022. 3", + "[64] Zehan Wang, Yang Zhao, Xize Cheng, Haifeng Huang, Jiageng Liu, Li Tang, Linjun Li, Yongqi Wang, Aoxiong Yin, Zhang Zhang, et al. Connecting multi-modal contrastive representations. arXiv preprint arXiv:2305.14381, 2023. 2", + "[65] Shuang Yang, Yuanhang Zhang, Dalu Feng, Mingmin Yang, Chenhao Wang, Jingyun Xiao, Keyu Long, Shiguang Shan, and Xilin Chen. Lrw-1000: A naturally-distributed large-scale benchmark for lip reading in the wild. In 2019 14th IEEE international conference on automatic face & gesture recognition (FG 2019), pages 1–8. IEEE, 2019. 12" + ], + "bbox": [ + 78, + 90, + 467, + 898 + ], + "page_idx": 10 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[66] Rong Ye, Mingxuan Wang, and Lei Li. End-to-end speech translation via cross-modal progressive training. arXiv preprint arXiv:2104.10380, 2021. 2", + "[67] Hongyi Zhang, Moustapha Cisse, Yann N Dauphin, and David Lopez-Paz. mixup: Beyond empirical risk minimization. arXiv preprint arXiv:1710.09412, 2017. 3", + "[68] Linjun Zhang, Zhun Deng, Kenji Kawaguchi, Amirata Ghorbani, and James Zou. How does mixup help with robustness and generalization? arXiv preprint arXiv:2010.04819, 2020. 3", + "[69] Xingxuan Zhang, Feng Cheng, and Shilin Wang. Spatiotemporal fusion based convolutional sequence learning for lip reading. In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 713-722, 2019. 6", + "[70] Ya Zhao, Rui Xu, and Mingli Song. A cascade sequence-to-sequence model for chinese mandarin lip reading. In Proceedings of the ACM Multimedia Asia, pages 1-6. 2019. 5, 6", + "[71] Ya Zhao, Rui Xu, Xinchao Wang, Peng Hou, Haihong Tang, and Mingli Song. Hearing lips: Improving lip reading by distilling speech recognizers. In Proceedings of the AAAI Conference on Artificial Intelligence, volume 34, pages 6917-6924, 2020. 2, 5, 6" + ], + "bbox": [ + 501, + 92, + 890, + 415 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "15745", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/8115edb8-8391-4f40-bf06-0cd9421711d5_model.json b/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/8115edb8-8391-4f40-bf06-0cd9421711d5_model.json new file mode 100644 index 0000000000000000000000000000000000000000..a2936c35c83078cebb56991805b8d7999cd3396c --- /dev/null +++ b/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/8115edb8-8391-4f40-bf06-0cd9421711d5_model.json @@ -0,0 +1,2191 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.102, + 0.13, + 0.87, + 0.177 + ], + "angle": 0, + "content": "MixSpeech: Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition" + }, + { + "type": "text", + "bbox": [ + 0.184, + 0.204, + 0.793, + 0.275 + ], + "angle": 0, + "content": "Xize Cheng*, Tao Jin*, Rongjie Huang*, Linjun Li \nWang Lin, Zehan Wang, Ye Wang, Huadai Liu, Aoxiong Yin, Zhou Zhao† \nZhejiang University \n{chengxize, jint.zju, rongjiehuang, zhaozhou}@zju.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.309, + 0.314, + 0.327 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.342, + 0.474, + 0.705 + ], + "angle": 0, + "content": "Multi-media communications facilitate global interaction among people. However, despite researchers exploring cross-lingual translation techniques such as machine translation and audio speech translation to overcome language barriers, there is still a shortage of cross-lingual studies on visual speech. This lack of research is mainly due to the absence of datasets containing visual speech and translated text pairs. In this paper, we present AVMuST-TED, the first dataset for Audio-Visual Multilingual Speech Translation, derived from TED talks. Nonetheless, visual speech is not as distinguishable as audio speech, making it difficult to develop a mapping from source speech phonemes to the target language text. To address this issue, we propose MixSpeech, a cross-modality self-learning framework that utilizes audio speech to regularize the training of visual speech tasks. To further minimize the cross-modality gap and its impact on knowledge transfer, we suggest adopting mixed speech, which is created by interpolating audio and visual streams, along with a curriculum learning strategy to adjust the mixing ratio as needed. MixSpeech enhances speech translation in noisy environments, improving BLEU scores for four languages on AVMuST-TED by \\(+1.4\\) to \\(+4.2\\). Moreover, it achieves state-of-the-art performance in lip reading on CMLR \\((11.1\\%)\\), LRS2 \\((25.5\\%)\\), and LRS3 \\((28.0\\%)\\)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.734, + 0.21, + 0.75 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.759, + 0.47, + 0.866 + ], + "angle": 0, + "content": "Multi-media techniques, including Audio-Visual Speech Recognition (AVSR) [4, 1, 2, 53], Audio-Visual Speech Translation (AVST) [8, 38, 61], and Audio-Visual Speech Generation (AVSG) [48, 32, 24], are commonly employed in various online communication scenarios, such as conferences, education, and healthcare. As a tool for ultra-remote communication, many online interactions involve multiple" + }, + { + "type": "image", + "bbox": [ + 0.511, + 0.326, + 0.738, + 0.449 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.747, + 0.334, + 0.879, + 0.346 + ], + "angle": 0, + "content": "En: Hello, beautiful world." + }, + { + "type": "text", + "bbox": [ + 0.747, + 0.378, + 0.882, + 0.39 + ], + "angle": 0, + "content": "Es: Hola, hermoso mundo." + }, + { + "type": "text", + "bbox": [ + 0.747, + 0.394, + 0.881, + 0.405 + ], + "angle": 0, + "content": "Fr: Bonjour, beau monde." + }, + { + "type": "text", + "bbox": [ + 0.747, + 0.409, + 0.857, + 0.421 + ], + "angle": 0, + "content": "It : Ciao, bel mondo." + }, + { + "type": "text", + "bbox": [ + 0.747, + 0.425, + 0.857, + 0.437 + ], + "angle": 0, + "content": "Pt: Olá, belo mundo." + }, + { + "type": "text", + "bbox": [ + 0.747, + 0.44, + 0.783, + 0.448 + ], + "angle": 0, + "content": "···" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.462, + 0.895, + 0.518 + ], + "angle": 0, + "content": "Figure 1. Diagram of speech tasks. Audio speech and visual speech are paired parallel speech streams which can be employed for speech recognition and speech translation. However, only Lip-Translation remains unexplored." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.55, + 0.895, + 0.746 + ], + "angle": 0, + "content": "languages, prompting the need for addressing cross-lingual challenges. Several works have attempted to tackle these challenges, including Machine Translation (MT) [9, 37, 15] for text utterance, Speech Translation (ST) [58, 19] for audio utterance, and Speech-to-Speech Translation (S2ST) [58, 19, 17, 33, 29] for simultaneous interpretation. However, research on cross-lingual visual speech is still limited, as illustrated in Figure 1. As an essential component of multi-media speech, visual speech can be combined with audio to enhance the recognition and understanding of speech content as audio-visual speech [1, 2, 54], and is the unique resource for speech content understanding in audio-disabled scenarios [36]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.896, + 0.903 + ], + "angle": 0, + "content": "Visual speech translation has never been studied, mainly for the lack of visual speech datasets with translated texts in different languages. The few remaining works [57, 60, 44] also cannot be quantitatively verified for this reason, making them unconvincing. The available visual speech corpus is often very scarce compared to audio speech owing to the high demands of visual speech for model training, which requires mostly-frontal and high-resolution videos with a sufficiently high frame rate, such that motions around the lip area are clearly captured [23]. In this paper, we propose the" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.875, + 0.208, + 0.888 + ], + "angle": 0, + "content": "*Equal contribution." + }, + { + "type": "page_footnote", + "bbox": [ + 0.097, + 0.888, + 0.222, + 0.9 + ], + "angle": 0, + "content": "† Corresponding author." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.875, + 0.222, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15735" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.257 + ], + "angle": 0, + "content": "first Audio-Visual Multilingual Speech Translation dataset, AVMuST-TED. During the process of acquisition, we first screen out videos with professional translations in four different languages from TED talk which performs strict translation and review processes, and then determine the real speaker's talking head by checking whether each pair of visual speech (i.e., talking head) and audio speech matches in the manner of [1, 2]. Incidentally, this dataset can also be used for quantitative evaluation of other multi-modality translation tasks, such as cross-lingua audio-visual speech generation [51, 60]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.259, + 0.473, + 0.606 + ], + "angle": 0, + "content": "The cascaded model comprising of a speech recognition model and a machine translation model can handle speech translation tasks but suffers from error accumulation due to model cascades and cannot process languages without text (e.g., Minnan). Our proposed end-to-end model, which can translate directly from source speech to target text, addresses the above issues. However, visual speech is less distinguishable than audio speech, making it difficult to develop a mapping from source speech phonemes to the target language text. To address this, we introduce MixSpeech, a method that first pretrains the decoder using high-discrimination audio speech to obtain a mapping from speech phonemes to text and then generalizes this mapping to the visual speech task through cross-modality self-learning. Furthermore, since audio speech and visual speech are two distinct modalities of speech, there is a significant modality gap between them that hinders knowledge transfer. To narrow this gap and improve knowledge transfer, we propose mixed speech, which is created by interpolating audio and visual streams, rather than relying solely on audio speech. We also propose a curriculum-learning [7] based strategy to adjust the mixing ratio as the training progresses and cross-modality integration deepens." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.607, + 0.47, + 0.639 + ], + "angle": 0, + "content": "The code and dataset are available1, the main contributions of this paper are as follows:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.651, + 0.468, + 0.695 + ], + "angle": 0, + "content": "- We present the first lip-translation baseline and introduce the Audio-Visual Multilingual Speech Translation dataset, AVMuST-TED." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.696, + 0.468, + 0.755 + ], + "angle": 0, + "content": "- We present a cross-modality self-learning framework that leverages distinguishable audio speech translation to regularize visual speech translation for effective cross-modality knowledge transfer." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.757, + 0.468, + 0.816 + ], + "angle": 0, + "content": "- We present to adopt the mixed speech, interpolated from audio and visual speeches, and a curriculum-learning based mixing ratio adjustment strategy to reduce the inter-modality gap during knowledge transfer." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.817, + 0.468, + 0.876 + ], + "angle": 0, + "content": "- We achieve state-of-the-art performance in lip translation for four languages on AVMuST-TED, with a +1.4 to +4.2 boost in BLEU scores and in lip reading on CMLR (11.1%), LRS2 (25.5%) and LRS3 (28.0%)." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.651, + 0.468, + 0.876 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.09, + 0.638, + 0.105 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.115, + 0.695, + 0.132 + ], + "angle": 0, + "content": "2.1. Audio-Visual Speech" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.14, + 0.895, + 0.518 + ], + "angle": 0, + "content": "Audio and visual speeches are two separate modalities that convey speech content. Numerous works [45, 13, 1, 2, 47, 25, 28, 26, 34, 11] have explored ways to extract information from speech using these modalities. Speech recognition [45, 6, 22] is widely used in online meetings and social applications to recognize speech content. Speech translation [58, 66, 19] is commonly used in simultaneous interpretation applications for cross-lingual communication in cross-border travel and meetings. Keyword spotting [5, 52, 30] is employed in short video applications to quickly retrieve relevant content. Additionally, in noisy scenarios, relevant speech tasks [14, 21, 47, 42] rely on visual speech to avoid interference from surrounding speech and background noise. Despite the growing interest in speech tasks that rely on visual speech, researches [57, 60] on visual speech translation are limited and lacks validation due to the lack of multilingual audio-visual speech transcription datasets. This paper proposes a baseline for visual speech translation and introduces the first large-scale audio-visual multilingual translation dataset, AVMuST-TED, which includes 706 hours of audio-visual speech and translation pairs in Spanish, French, Italian, and Portuguese. AVMuST-TED lays a solid foundation or future cross-lingual audio-visual translation tasks, such as Cross-Lingual Talking Head Generation [44]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.53, + 0.836, + 0.546 + ], + "angle": 0, + "content": "2.2. Transfer learning from Audio to Visual" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.554, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Many researchers [50, 53, 39, 64] attempt to enhance the representation of visual speech by leveraging corresponding audio speech, as the two are paired parallel speech streams. Some [50, 53, 39] use knowledge distillation to bootstrap the training of visual speech models using audio speech models, while others [71, 39] have proposed various distillation strategies to optimize the representation of visual speech by mining the intrinsic connection between audio and visual speeches. Some [53] also use self-supervised learning, with audio as auxiliary supervision for visual utterances, to obtain fine-grained visual representations. The success of these works demonstrates the critical role of audio speech, which has a higher discrimination compared to visual speech, in training visual speech models. However, previous works face the modality shift problem during knowledge transfer because they start directly from speeches of two different modalities, audio and visual speeches, with a significant modality gap. In this paper, we propose an cross-modality self-learning framework MixSpeech, that uses synthetic mixed speech to regularize visual speech translation for effective cross-modality knowledge transfer, reducing the gap between the two modalities during knowledge transfer." + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.374, + 0.9 + ], + "angle": 0, + "content": "1https://github.com/Exgc/AVMuST-TED" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "15736" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.134, + 0.088, + 0.852, + 0.459 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.465, + 0.895, + 0.496 + ], + "angle": 0, + "content": "Figure 2. Illustration of our proposed MixSpeech. We first pretrain the model with audio speech translation as shown in the dashed boxed, and then train the visual speech translation with mixed speech regularization. The blank dashed boxes denote the modality missing speech." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.518, + 0.388, + 0.535 + ], + "angle": 0, + "content": "2.3. Mixup for Cross-Modality Transfer" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.554, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Many works [68, 20, 63, 19, 24] bridge the gap between modalities with mixup. [67] proposes mixup for data augmentation to improve model robustness. [10] suggests mixing at the representation-level to mine implicit associations between labeled and non-labeled sentences. Other works [63, 59, 18, 27] also use mixing to build bridges between different modalities. Some [63, 18] use CLIP [49] to retrieve semantically consistent images with text tokens and synthesize mixed sentences for text-visual consistency representation training. Others [59, 19] construct manifold mixup interpolations based on semantic consistency between audio and text to enhance understanding of audio with textual datasets. By implementing the mixup strategy, these studies have shown notable improvements across a range of tasks, highlighting its potential to facilitate knowledge transfer between different modalities. However, previous works use fixed hyperparameters [67] or mapping functions [19] for mixing ratios, which are typically not optimal and cannot be adapted to the training situation. In this paper, we propose an uncertainty-based [43] curriculum learning [7] strategy that gradually adjusts mixing ratios and apply mixup strategy for cross-modality knowledge transfer between audio and visual speeches for the first time." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.517, + 0.592, + 0.532 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.542, + 0.673, + 0.557 + ], + "angle": 0, + "content": "3.1. Task Formulation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.565, + 0.892, + 0.734 + ], + "angle": 0, + "content": "As the twin task of speech recognition, speech translation involves translating source language speech into target language text. The speech translation model takes audio speech utterance \\(\\mathbf{A} = \\{\\mathbf{A}_t\\}_{t=1}^T \\in \\mathbb{R}^{T \\times D}\\) or visual speech utterance \\(\\mathbf{V} = \\{\\mathbf{V}_t\\}_{t=1}^T \\in \\mathbb{R}^{T \\times D}\\) as input and generates the target language text \\(\\mathbf{w} = \\{\\mathbf{w}_i\\}_{i=0}^s\\), where \\(\\mathbf{A}_t\\) and \\(\\mathbf{V}_t\\) represent the \\(t\\)-th features in the audio and visual speeches, and \\(\\mathbf{w}_i\\) represents the \\(i\\)-th word in the target language translation with a total length of \\(S\\). Note that, we stack 4 adjacent acoustic frames together forSyncing with visual speech, both with \\(T\\) frames." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.742, + 0.611, + 0.757 + ], + "angle": 0, + "content": "3.2. Overview" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.903 + ], + "angle": 0, + "content": "We propose a cross-modal self-learning framework for visual speech translation with audio speech regularization, named MixSpeech, as illustrated in Figure 2. This model consists of three modules - a feature extractor for extracting speech embeddings, a speech encoder for attending to the contextual dependencies of speech, and a target language-oriented translation decoder. We utilize the pre-trained feature extractor (AV-Encoder) and speech encoder (Speech-Encoder) from the AV-Hubert [53]" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15737" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.304 + ], + "angle": 0, + "content": "to extract speech representations from both audio and visual speech utterances. Additionally, a randomly initialized translation decoder (Trans-Decoder) is used to autoregressively decode the speech representation into the target language text. MixSpeech is a two-stage training process: 1) Pretraining the translation decoder with high-discrimination audio speech utterances to learn inter-lingual mapping relations between source language phonemes and target language text, as detailed in subsection 3.3. 2) Aligning visual speech with audio speech to transfer the inter-lingual mapping from audio speech to visual in 3.5. The mixed speech 3.4 is synthesized by interpolating audio speech with visual speech in MixupSpeech, bridging the modality gap and enhancing knowledge transfer." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.315, + 0.351, + 0.332 + ], + "angle": 0, + "content": "3.3. Pretraining with Audio Speech" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.339, + 0.47, + 0.399 + ], + "angle": 0, + "content": "For uni-modality audio speech \\(\\mathbf{A} \\in \\mathbb{R}^{T \\times D}\\) or visual speech \\(\\mathbf{V} \\in \\mathbb{R}^{T \\times D}\\), the uni-modality audio-visual feature \\(\\mathbf{e}^u = \\{\\mathbf{e}_t^u\\}_{t=1}^T \\in \\mathbb{R}^{T \\times 2D}\\) fed into feature extractor can be defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.131, + 0.415, + 0.47, + 0.455 + ], + "angle": 0, + "content": "\\[\n\\mathbf {e} _ {t} ^ {u} = \\left\\{ \\begin{array}{l l} \\operatorname {c o n c a t} \\left(\\mathbf {0} _ {D}, \\mathbf {V} _ {t}\\right), & \\mathbf {V} _ {t} \\neq \\text {N o n e}, \\\\ \\operatorname {c o n c a t} \\left(\\mathbf {A} _ {t}, \\mathbf {0} _ {D}\\right), & \\mathbf {A} _ {t} \\neq \\text {N o n e}, \\end{array} \\right. \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.463, + 0.473, + 0.672 + ], + "angle": 0, + "content": "where \\(\\mathbf{0}_D\\) denotes the feature of missing modality, following the practice of [53]. And then, we obtain the audiovisual fusion feature \\(\\mathbf{e}^f\\in \\mathbb{R}^{T\\times D}\\) with AV-Encoder. The transformer-based Speech-Encoder allows us to obtain the phoneme embedding \\(\\mathbf{e}^p\\in \\mathbb{R}^{T\\times D}\\) with the contextual speech details. A target language oriented translation decoder Trans-Decoder is appended to autoregressively decode the phoneme embedding \\(\\mathbf{e}^p\\) into the target probabilities \\(P^u\\), where \\(P^u = \\{P_t^u\\}_{t = 1}^S = \\{p(\\mathbf{w}_t|\\{\\mathbf{w}_i\\}_{i = 1}^{t - 1},\\mathbf{e}^p)\\}_{t = 1}^S\\) represents the probability of the \\(t\\)-th word being \\(\\mathbf{w}_t\\) when the previous \\(t - 1\\) predictions are \\(\\{\\mathbf{w}_i\\}_{i = 1}^{t - 1}\\) and \\(s\\) is the length of the target language translation. During the pretraining, the overall model is trained on audio speech with cross-entropy loss:" + }, + { + "type": "equation", + "bbox": [ + 0.151, + 0.674, + 0.47, + 0.715 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {C E} = - \\sum_ {t = 1} ^ {S} \\log p \\left(w _ {t} \\mid \\left\\{w _ {i} \\right\\} _ {i = 1} ^ {t - 1}, \\mathbf {e} ^ {p}\\right). \\tag {2}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.726, + 0.334, + 0.743 + ], + "angle": 0, + "content": "3.4. Audio-Visual Speech Mixing" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.902 + ], + "angle": 0, + "content": "Audio and visual speeches have a huge modality gap, which greatly impacts knowledge transfer across modalities. We attempt to employ mixed speech to bridge two different modalities of speech. Since the pair of audio and visual speeches is strictly temporally synchronous, we take advantage of this property to interpolate the mixed speech. For a pair of synchronized audio and video speech \\((\\mathbf{A},\\mathbf{V})\\in \\mathbb{R}^{2\\times T\\times D}\\), each visual feature \\(\\mathbf{V}_t\\) at \\(t\\)-th frame has its corresponding audio feature \\(\\mathbf{A}_t\\), representing the same phonetic content. We interpolate with probability \\(\\phi\\)" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.09, + 0.894, + 0.123 + ], + "angle": 0, + "content": "to obtain a mixed speech \\(\\mathbf{e}^m = \\{\\mathbf{e}_t^m\\}_{t=1}^T \\in \\mathbb{R}^{T \\times 2D}\\) derived partly from audio speech and partly from visual speech:" + }, + { + "type": "equation", + "bbox": [ + 0.571, + 0.133, + 0.892, + 0.173 + ], + "angle": 0, + "content": "\\[\n\\mathbf {e} _ {t} ^ {m} = \\left\\{ \\begin{array}{l l} \\operatorname {c o n c a t} \\left(\\mathbf {0} _ {D}, \\mathbf {V} _ {t}\\right), & p < \\phi , \\\\ \\operatorname {c o n c a t} \\left(\\mathbf {A} _ {t}, \\mathbf {0} _ {D}\\right), & p \\geq \\phi , \\end{array} \\right. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.178, + 0.894, + 0.285 + ], + "angle": 0, + "content": "where \\( p \\) is sampled from the uniform distribution \\( U(0,1) \\) and \\( \\phi \\) is the ratio of speech mixing. In particular, we propose a curriculum learning [7] based mixing ratio adjustment method that adapts the appropriate \\( \\phi \\) as the training progresses. The prediction uncertainty [43] indicates the confidence of the prediction (smaller is better), and we take it as a signal to adjust the mixing ratio:" + }, + { + "type": "equation", + "bbox": [ + 0.604, + 0.293, + 0.892, + 0.335 + ], + "angle": 0, + "content": "\\[\n\\mathbf {u} = \\frac {1}{S} \\sum_ {t = 1} ^ {S} \\operatorname {E n t r o p y} \\left(P _ {t}\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.342, + 0.892, + 0.48 + ], + "angle": 0, + "content": "If the discrimination of mixed speech is insufficient to regularize visual speech translation and maintain \\( n \\) steps \\( (\\Delta \\mathbf{u} = \\mathbf{u}^v - \\mathbf{u}^m < k\\mathbf{u}^v \\), where \\( \\mathbf{u}^v \\) and \\( \\mathbf{u}^m \\) represent the uncertainty of uni-modality (visual) and mixed speech, respectively, and the threshold hyperparameter \\( k \\) is set to 0.05 with \\( n \\) set to 20 in our work), we gradually increase the proportion of audio at a rate of \\( \\alpha \\) \\( (\\phi' = \\alpha \\phi) \\). We initialize \\( \\phi = 0.1 \\) to prevent excessive initial modality gap and maintain \\( \\phi \\in [0.1, 0.9] \\) throughout the training process." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.487, + 0.852, + 0.504 + ], + "angle": 0, + "content": "3.5. Cross-Modality Self-Learning for Speech" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.51, + 0.892, + 0.661 + ], + "angle": 0, + "content": "Since audio speech is more distinguished compared to visual speech, we intend to boost visual speech translation with the knowledge from audio speech. And the mixed speech bridges the gap between audio speech and visual speech, allowing us to boost cross-modality knowledge transfer with it. With audio speech feature \\(\\mathbf{A} \\in \\mathbb{R}^{T \\times D}\\) and visual speech feature \\(\\mathbf{V} \\in \\mathbb{R}^{T \\times D}\\) fed into the modules with shared parameters, the uni-modality visual speech feature \\(\\mathbf{e}^u\\) and the mixed speech feature \\(\\mathbf{e}^m\\) are decoded into the target probabilities \\(P^u\\) and \\(P^m\\), respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.661, + 0.892, + 0.737 + ], + "angle": 0, + "content": "After the pre-training with audio speech translation, the model is promising enough for mixed speech containing partial audio speech, we adopt the Jensen-Shannon Divergence (JSD) [41] to regularize the probabilities of these two different speeches:" + }, + { + "type": "equation", + "bbox": [ + 0.596, + 0.746, + 0.892, + 0.787 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {J S D} = \\sum_ {t = 1} ^ {S} J S D \\left(P _ {t} ^ {m} \\| P _ {t} ^ {u}\\right). \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "As this probability is across the entire training vocabulary, we are able to perform fine-grained regularization to enhance the training of visual speech. Meanwhile, we also minimize the cross-entropy loss between two speech translations and the real translation, \\(\\mathcal{L} = \\mathcal{L}_{CE}^{uni} + \\lambda_1\\mathcal{L}_{CE}^{mix} + \\lambda_2\\mathcal{L}_{JSD}\\), where \\(\\lambda_{1}\\) and \\(\\lambda_{2}\\) are hyperparameters of loss weights, while \\(\\lambda_{1} = \\lambda_{2} = 1.0\\) in this work." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15738" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.102, + 0.089, + 0.873, + 0.27 + ], + "angle": 0, + "content": "
DatasetTarget Language Hours# Lang# Σ Hrs# Σ Sents# Σ Tokens
EnEsFrItPtsrctgt
Audio-Only
LibriSpeech [45]960h----1960h180K5.9M5.9M
MuST-C [16]-504h492h465h385h83617h2016K38.1M35.8M
VoxPopuli [62]543h441h427h461h-165967h2045K65.0M60.1M
Audio-Visual
LRS2 [1]224h----1224h143K2.3M2.3M
LRS3 [2]433h----1433h151K4.2M4.2M
AVMuST-TED (ours)-198h185h165h158h4706h925K7.3M7.0M
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.279, + 0.893, + 0.31 + ], + "angle": 0, + "content": "Table 1. Comparison of audio-visual speech recognition/translation datasets. #Lang denotes the number of target languages. #∑Hrs denotes the overall duration of speech in the dataset, #Sents and #Tokens denote the overall sentences and the overall token, respectively." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.331, + 0.21, + 0.349 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.358, + 0.182, + 0.373 + ], + "angle": 0, + "content": "4.1. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.383, + 0.471, + 0.641 + ], + "angle": 0, + "content": "AVMuST-TED. To obtain a corpus for AVST, we screened a set of TED and TEDx talks with multilingual subtitles as the data source. All transcriptions and translations are performed strictly following the TED Translation Guidelines and require collaboration between at least one translator (or transcriber) and one reviewer. The prior lip-reading dataset acquisition pipeline is followed to crop face-tracks, and an audio-visual alignment network, SyncNet, is adopted for speaker proofreading. Table 1 compares AVMuST-TED with related datasets, and it is the first audio-visual speech translation dataset containing translations from English (En) to four target languages: Spanish (Es), French (Fr), Italian (It), and Portuguese (Pt). These four languages have the most translated subtitles in TED, and 1024/1536 pieces of data are randomly sampled for each language as the test/validation set. The information about AVMuST-TED is detailed in Appendix A." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.642, + 0.47, + 0.852 + ], + "angle": 0, + "content": "LRS2&3 [1, 2], two commonly used publicly available English wild audio-visual speech recognition datasets, are adopted to demonstrate the lip-reading performance, containing 224 hours of video from BBC television shows and 433 hours of video from TED and TEDx talks. The training data in both datasets is divided into two partitions, namely Pretrain and Train, both of which are transcribed from videos to text at the sentence level. The only difference is that the video clips in the Pretrain partition are not strictly trimmed and sometimes longer than the corresponding text. In our experiments, we employ different amounts of training data from LRS2 and LRS3, including Pretrain+Train (224/433h) for high resource and Train (29/30h) for low resource." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.855, + 0.471, + 0.903 + ], + "angle": 0, + "content": "CMLR [70], widely used dataset for Mandarin audio-visual speech recognition, contains 61 hours audio-visual speech utterances collected from Chinese TV stations. In" + }, + { + "type": "table", + "bbox": [ + 0.501, + 0.329, + 0.895, + 0.46 + ], + "angle": 0, + "content": "
MethodMBLEU↑
En-EsEn-FrEn-ItEn-Pt
CascadedV12.711.311.513.2
AV-Hubert [53]V14.212.612.914.8
CascadedA(+Noise)16.012.912.615.5
AV-Hubert [53]A(+Noise)17.614.514.117.1
MixSpeech(ours)V18.515.114.317.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.468, + 0.893, + 0.525 + ], + "angle": 0, + "content": "Table 2. Comparison of the performances of visual speech translation on AVMuST-TED with those of the noisy audio speech translation. The results of noisy audio speech translation are the mean value at five SNRs \\(\\{-20, -10, 0, 10, 20\\}\\) db." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.549, + 0.892, + 0.626 + ], + "angle": 0, + "content": "our experiments, we adopt this dataset to demonstrate the performance of our proposed MixSpeech in low-resource languages such as Mandarin. Additionally, we sample a training set containing only 12 hours of utterances in the manner of [71] for low resource scenario." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.634, + 0.84, + 0.65 + ], + "angle": 0, + "content": "4.2. Evaluation and Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.657, + 0.892, + 0.825 + ], + "angle": 0, + "content": "In this paper, we measure the performance of MixSpeech on two speech tasks, speech recognition and speech translation. For speech recognition, word error rate (WER) is adopted as the evaluation metric, which is defined as \\( \\mathrm{WER} = (S + D + I) / M \\), where \\( S, D, I, M \\) represent the number of words replaced, deleted, inserted, and referenced. As for speech translation, the case-sensitive detokenized BLEU score is computed using SACREBLEU [46], following the same evaluation methodology as in previous speech translation works [16, 62]. The implementation details are provided in Appendix B due to page limitations." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.833, + 0.808, + 0.849 + ], + "angle": 0, + "content": "4.3. Performance of Speech Translation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.893, + 0.903 + ], + "angle": 0, + "content": "End-To-End Models VS. Cascaded Models. Table 2 presents a comparison of the lip translation performance between two representative methods: 1) an end-to-end model," + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "15739" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.333 + ], + "angle": 0, + "content": "implemented based on the state-of-the-art AV-Hubert [53] method for visual speech-related tasks, and 2) a cascaded model, combining a speech recognition model (i.e., Lip-Reading or ASR) with a machine translation model. In the cascaded model, we use the speech recognition model trained by AV-Hubert on LRS3, which achieve the best lip-reading performance to date, and a transformer-based machine translation model trained on the paired translated text corpus in AVMuST-TED. Comparing the lip translation performance of the end-to-end model and the cascade model, we find that the BLEU score of the end-to-end model improved by \\(+1.3\\) to \\(+1.6\\). This result demonstrates that the end-to-end trained model can effectively prevent the accumulation of errors caused by the model cascade, and that lip translation cannot be simply disassembled as the superposition of lip reading and machine translation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.337, + 0.473, + 0.626 + ], + "angle": 0, + "content": "MixSpeech VS. Prior Methods. Due to the discrimination of speech between modalities, visual speech models are not able to translate speech content as accurately as audio speech models. To address the issue of low discrimination in visual speech, we propose MixSpeech, which is a cross-modality self-learning framework that employs mixed speech to transfer knowledge obtained from audio speech pre-training into the visual speech model. Our proposed MixSpeech significantly improves the BLEU score by another \\(+1.4\\) to \\(+4.3\\). Furthermore, the improvement from MixSpeech is related to the discrepancy in speech translation between audio and visual modalities. For example, En-Es exhibits a larger discrepancy of 14.7 between audio and visual speech translation, ranging from 28.9 to 14.2, and MixSpeech significantly improves it by \\(+4.3\\). Conversely, Italian shows a smaller discrepancy of 10.9, ranging from 23.8 to 12.9, and improves only by \\(+1.4\\). This highlights that the improvement in lip translation stems from the knowledge acquired from audio speech translation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Visual Speech VS. Noisy Audio Speech. We also evaluate the performance of audio speech translation in noisy environments, by adding noise sampled from MUSAN [55] to the audio speech and measuring the performance at five SNR levels \\(\\{-20, -10, 0, 10, 20\\}\\) db. We compare the average BLEU scores of different SNRs and present the detailed performance in Appendix C.1. Our experiments show that although noisy audio speech performs better than visual speech, the translation performance is still significantly lower compared to noiseless audio speech. In contrast, MixSpeech, which fully leverages the knowledge of audio speech, greatly improves the visual speech translation performance, making it more reliable in noisy scenes. We also provide a comparison of translation with audio speech and audio-visual speech, demonstrating that visual speech enhances the ceiling and robustness of speech translation, but the details are only available in the Appendix C.1 since audio-visual speech does not require the cross-modality" + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.09, + 0.895, + 0.362 + ], + "angle": 0, + "content": "
# RESMethodWER(Labeled Visual Utts Hrs) ↓
CMLRLRS2LRS3
HighWAS [56]38.9(61)70.4(224)-
TM-seq2seq [1]-49.8(698)59.9(698)
CSSMCM [70]32.5(61)--
Conv-seq2seq [69]-51.7(698)60.1(698)
CTC+KD [3]-51.3(224)58.9(433)
LIBS [71]31.3(61)65.3(698)-
CTCH [40]22.0(61)--
Master [50]-49.2(698)59.0(698)
Sub-Word [47]-28.9(698)40.6(698)
†AV-Hubert [53]12.7(61)28.7(224)28.6(433)
MixSpeech(ours)11.1(61)25.5(224)28.0(433)
LowLIBS [71]50.5(12)--
†AV-Hubert [53]25.8(12)31.4(29)32.5(30)
MixSpeech(ours)18.5(12)26.9(29)28.6(30)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.371, + 0.895, + 0.429 + ], + "angle": 0, + "content": "Table 3. Comparison of lip reading methods under different resource conditions. # RES represents the amount of resources. (Hours) highlighted in blue are used for low resources. † For better comparison, we reproduce AV-Hubert on CMLR and LRS2." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.455, + 0.783, + 0.471 + ], + "angle": 0, + "content": "knowledge transfer proposed in this paper." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.484, + 0.81, + 0.501 + ], + "angle": 0, + "content": "4.4. Performance of Speech Recognition" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.509, + 0.895, + 0.903 + ], + "angle": 0, + "content": "As shown in Table 3, we compare the performance of MixSpeech on another visual speech task, lip reading (i.e., Visual Speech Recognition), to highlight the mixspeech from more perspectives. MixSpeech obtain state-of-the-art performance on three datasets, two for English (25.5% on LRS2 and 28.0% on LRS3) and one for Chinese (11.1% on CMLR), demonstrating that this cross-modality self-learning framework can be applied for different languages to capture the intrinsic association between audio and visual speeches and thus effectively improve the understanding of visual speech. Since visual speech is relatively low-resource, we verify whether MixSpeech can effectively improve the performance of visual speech tasks in low-resource with audio speech. Compared with previous methods, MixSpeech boosts the WER of lip-reading by -3.9% to -7.3%, highlighting the critical role of high-resource audio speech in low-resource visual speech tasks. Specifically, on LRS2 and LRS3, the performance of Mixspeech in the low-resource scenario (26.9%/28.6% WER obtained with only 29h/30h visual utterances) outperforms the performances of prior methods in the high-resource scenario (28.7%/28.6% obtained with 224h/433h or even more visual utterances). Even though with only limited labeled visual corpus, our proposed MixSpeech performs no less than works with more. It is the bridge between two modalities of speech, which helps visual speech to access the knowl" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "15740" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.122 + ], + "angle": 0, + "content": "edge stored in high-resource and high-discrimination audio speech without barriers." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.131, + 0.468, + 0.148 + ], + "angle": 0, + "content": "4.5. Can MixSpeech bridge cross-modality speech?" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.155, + 0.469, + 0.2 + ], + "angle": 0, + "content": "Our proposed MixSpeech builds a bridge between cross-modality speech through cross-modality self-learning, with the properly mixes speech. The details are as follows:" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.201, + 0.469, + 0.426 + ], + "angle": 0, + "content": "Cross-Modality Self-Learning for Knowledge Transfer. The experiments in Figure 3 provide a positive answer to the question of whether MixSpeech can contribute to achieving knowledge transfer between audio and visual speeches. We evaluate the performance of visual speech translation with different regularization strategies: no audio speech regularization (i.e., \\(\\phi = 0\\)), mixed speech regularization with different mixing ratios (i.e., \\(\\phi \\in (0,1)\\), audio speech regularization (i.e., \\(\\phi = 1\\)), and mixing ratio adjustable mixed speech regularization (i.e., dashed lines). It is evident that the cross-modality self-learning framework significantly enhances visual speech translation, as all performances with audio speech regularization are noticeably better than those without self-learning (\\(\\phi = 0\\)), demonstrating the effectiveness of our proposed MixSpeech." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.427, + 0.469, + 0.579 + ], + "angle": 0, + "content": "Narrow the Cross-Modality Distance with Properly Mixed Speech. Moreover, the introduction of mixed speech facilitates smoother cross-modality knowledge transfer by narrowing the modality gap between speeches. Some segments in the mixed speech come from the visual speech, making it much closer to visual speech in terms of modality distance than audio speech. When regularizing with mixed speech in En-Es, the translation performance of visual speech improves further by \\(+0.3\\) to \\(+0.8\\) compared to audio speech regularization alone. Among them, bootstrap" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.6, + 0.465, + 0.825 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.829, + 0.47, + 0.899 + ], + "angle": 0, + "content": "Figure 3. BLEU scores of MixSpeech with different speech regularization on En-Es and En-Fr. \\(\\phi = 0\\): no audio speech regularization, \\(\\phi \\in (0,1)\\): mixed speech regularization, \\(\\phi = 1\\): only audio speech regularization. The dashed lines represent the adjustable mixing ratio strategy based on curriculum learning." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.258 + ], + "angle": 0, + "content": "ping with mixed speech of mixing ratio \\(\\phi = 0.5\\) achieves the highest BLEU score of 18.3. This demonstrates that a reasonably mixed ratio ensures that it is neither overly biased towards visual speech, leading to a lack of knowledge of audio speech, nor overly biased towards audio speech, leading to excessive cross-modality distances that affect knowledge transfer. The adjustable mixing ratio strategy based on curriculum learning further increases the applicability of mixed speech to cross-modality self-learning training, thereby boosting visual speech translation performance again." + }, + { + "type": "table", + "bbox": [ + 0.511, + 0.268, + 0.882, + 0.381 + ], + "angle": 0, + "content": "
IDMethodBLEU ↑
LmonCELmixCELJSDEn-EsEn-FrEn-ItEn-Pt
#1✓14.212.612.914.8
#2✓✓17.514.313.616.5
#3✓✓18.114.814.116.9
#4✓✓✓18.515.114.317.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.391, + 0.882, + 0.406 + ], + "angle": 0, + "content": "Table 4. BLEU of different module combinations in MixSpeech." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.425, + 0.884, + 0.442 + ], + "angle": 0, + "content": "4.6. What role does each part play in MixSpeech?" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.448, + 0.892, + 0.522 + ], + "angle": 0, + "content": "The effectiveness of MixSpeech, which is a cross-modality self-learning framework designed to improve visual translation performance, has been demonstrated. In this study, we investigate the role of each component in detail and present relevant experiments in Table 4:" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.524, + 0.892, + 0.689 + ], + "angle": 0, + "content": "Bridging the cross-modality gaps. We observe a significant improvement in the lip translation performance with the inclusion of \\(\\mathcal{L}_{JSD}\\) (ID: #3, #4) for regularizing the probabilities of visual speech and mixed speech, compared to without (ID: #1, #2). Specifically, experiment #3 with \\(\\mathcal{L}_{JSD}\\) outperform experiment #2 with \\(\\mathcal{L}_{CE}^{mix}\\) by \\(+0.6\\) in lip translation performance on En-Es. This demonstrates that \\(\\mathcal{L}_{JSD}\\) is the main contributor to achieving cross-modality knowledge transfer by building a bridge between the two speeches and performing fine-grained regularization across the probability of each word." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.69, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Maintaining knowledge of audio speech. It is also important to note that during the regularization process, the representation of audio speech is also affected by visual speech, which can interfere with the knowledge of audio speech and ultimately harm the lip translation performance of MixSpeech. As evidenced by experiment #2, the lip translation performance on En-Es decrease by -0.4 compared to experiment #3 when \\(\\mathcal{L}_{CE}^{mix}\\) is not applied. To address this issue, \\(\\mathcal{L}_{CE}^{mix}\\) is introduced to enhance the training ceiling of the cross-modality self-learning framework. By maintaining the translation performance of mixed speech and preventing the excessive disturbance to audio speech knowledge, \\(\\mathcal{L}_{CE}^{mix}\\) helps to improve the overall performance of MixSpeech." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "15741" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.078, + 0.09, + 0.899, + 0.482 + ], + "angle": 0, + "content": "
En-EsTranscription: and always as a child I had this fantasy that somebody would come and rescue me\nMixSpeech: and always as a child I had this fantasy that somebody would come and rescue me
Ground Truth: y de niña siempre tenía la fantasía de que alguien vendrá a salvar me de\nMixSpeech: y de (desde) niña niño siempre tenía la esta fantasía de que alguien vendrá a salvar me (rescató) de
En-FrTranscription: and solutions create new problems which have to be solved in their turn\nMixSpeech: and solutions to create new problems which have to be solved in their turn this year
Ground Truth: et les solutions créent de nouveaux problèmes devant être résolus à leur tour\nMixSpeech: et les (des) solutions pour creer de nouveaux problèmes devant qui doivent être résolus à leur tour
En-ItTranscription: one of the last 10,000 years, and the other certainly of the last 25 years\nMixSpeech: one of the last 10,000 years and the other certainly assistancee of the last 25 years
Ground Truth: uno presente negli ultimi diecimila anni e l'alto certamente negli ultimi 25 anni\nMixSpeech: uno presente negli ultimi diecimila (10000) anni e l'alto certamente negli ultimi 25 anni
En-PtTranscription: has around 2,000 people descending on MIT's campus\nMixSpeech: has around 2,000 people descending on MIT's campus
Ground Truth: congregamerca de 2000 pessoas no campus do mit\nMixSpeech: congregam de circa de 2000 pessoas a estudar no campus do mit
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.489, + 0.893, + 0.518 + ], + "angle": 0, + "content": "Table 5. Qualitative performance of Visual Speech Recognition and Translation on AVMuST-TED. Red Strikeout Words: mistranslated words with opposite meaning, (Blue Words in parentheses): mistranslated words with similar meaning, Gray Words: the absent words." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.542, + 0.255, + 0.558 + ], + "angle": 0, + "content": "4.7. Qualitative results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.569, + 0.473, + 0.903 + ], + "angle": 0, + "content": "We present several examples of lip translation in Table 5 to qualitatively evaluate the translation quality of MixSpeech. The translation results are very close to the ground truth, and the semantics are consistent. We observe two types of words that differ in translation: synonyms and context-sensitive translations. Synonyms that have different spellings but the same meaning, such as salvar and rescató in Spanish, both meaning 'rescue', and diecimila and 10000 in Italian, both meaning 'ten thousand', are commonly found in translation tasks and can affect translation consistency. Additionally, there are translations that require context information, such as when the speaker refers to themselves as a child, and the translation in Spanish needs to take into account the speaker's gender to choose between niña for girl' or Niño for boy' and 'child'. The qualitative translation results of MixSpeech demonstrate its capability to achieve reliable cross-lingua lip translation. In Appendix C.2, we also provide translation results of noisy audio speech translation with visual speech translation and audio speech translation with audiovisual speech translation to highlight the importance of visual speech in speech translation." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.541, + 0.619, + 0.557 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.568, + 0.892, + 0.794 + ], + "angle": 0, + "content": "With the advancement of online technologies, such as online healthcare and sales, language barriers often prevent these tools from reaching and benefiting disadvantaged areas. In light of this, we focus on visual speech, a branch of the speech stream, and aim to translate visual speech from source languages to other target languages for cross-linguistic communication, specifically through lip translation. We meticulously curate the AVMuST-TED dataset, consisting of 706 hours of speech clips with professional translations from TED, to facilitate cross-linguistic research on visual speech. We also introduce MixSpeech, a cross-modality self-learning framework that utilizes mixed speech to regularize visual speech translation and achieves state-of-the-art performance in lip translation on AVMuST-TED and lip reading on LRS2, LRS3, and CMLR datasets." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Moreover, our work on visual speech and AVMuSTED lay a solid foundation for further research on visual speech in cross-lingual fields. There are numerous related tasks with great potential for practical applications, such as Cross-Lingual Talking Head Generation [44]. These tasks hold immense promise for breaking down language barriers and promoting communication across diverse communities." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15742" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.079, + 0.091, + 0.245, + 0.108 + ], + "angle": 0, + "content": "Acknowledgements" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.115, + 0.47, + 0.19 + ], + "angle": 0, + "content": "This work was supported in part by National Key R&D Program of China under Grant No.2022ZD0162000, National Natural Science Foundation of China under Grant No.62222211, Grant No.61836002 and Grant No.62072397." + }, + { + "type": "title", + "bbox": [ + 0.08, + 0.204, + 0.173, + 0.219 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.228, + 0.469, + 0.284 + ], + "angle": 0, + "content": "[1] Triantafyllos Afouras, Joon Son Chung, Andrew Senior, Oriol Vinyals, and Andrew Zisserman. 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In Proceedings of the AAAI Conference on Artificial Intelligence, volume 34, pages 6917-6924, 2020. 2, 5, 6" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.416 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15745" + } + ] +] \ No newline at end of file diff --git a/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/8115edb8-8391-4f40-bf06-0cd9421711d5_origin.pdf b/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/8115edb8-8391-4f40-bf06-0cd9421711d5_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..ab4ce4f47ae32446641dd203d2d01671bd8b3da0 --- /dev/null +++ b/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/8115edb8-8391-4f40-bf06-0cd9421711d5_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:1d2fa4f5932f550b8e359a9a8ac761e7b6734b2a1393cfa388ddd328afe425aa +size 1408727 diff --git a/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/full.md b/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/full.md new file mode 100644 index 0000000000000000000000000000000000000000..86aa7df5b3ab03688422803e26585ec2679abfae --- /dev/null +++ b/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/full.md @@ -0,0 +1,294 @@ +# MixSpeech: Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition + +Xize Cheng*, Tao Jin*, Rongjie Huang*, Linjun Li +Wang Lin, Zehan Wang, Ye Wang, Huadai Liu, Aoxiong Yin, Zhou Zhao† +Zhejiang University +{chengxize, jint.zju, rongjiehuang, zhaozhou}@zju.edu.cn + +# Abstract + +Multi-media communications facilitate global interaction among people. However, despite researchers exploring cross-lingual translation techniques such as machine translation and audio speech translation to overcome language barriers, there is still a shortage of cross-lingual studies on visual speech. This lack of research is mainly due to the absence of datasets containing visual speech and translated text pairs. In this paper, we present AVMuST-TED, the first dataset for Audio-Visual Multilingual Speech Translation, derived from TED talks. Nonetheless, visual speech is not as distinguishable as audio speech, making it difficult to develop a mapping from source speech phonemes to the target language text. To address this issue, we propose MixSpeech, a cross-modality self-learning framework that utilizes audio speech to regularize the training of visual speech tasks. To further minimize the cross-modality gap and its impact on knowledge transfer, we suggest adopting mixed speech, which is created by interpolating audio and visual streams, along with a curriculum learning strategy to adjust the mixing ratio as needed. MixSpeech enhances speech translation in noisy environments, improving BLEU scores for four languages on AVMuST-TED by $+1.4$ to $+4.2$ . Moreover, it achieves state-of-the-art performance in lip reading on CMLR $(11.1\%)$ , LRS2 $(25.5\%)$ , and LRS3 $(28.0\%)$ . + +# 1. Introduction + +Multi-media techniques, including Audio-Visual Speech Recognition (AVSR) [4, 1, 2, 53], Audio-Visual Speech Translation (AVST) [8, 38, 61], and Audio-Visual Speech Generation (AVSG) [48, 32, 24], are commonly employed in various online communication scenarios, such as conferences, education, and healthcare. As a tool for ultra-remote communication, many online interactions involve multiple + +![](images/9e335c4f0355b0c07d0ce08b0bcae93eb7596c8a0e96b9b4080f4064649ec260.jpg) +Figure 1. Diagram of speech tasks. Audio speech and visual speech are paired parallel speech streams which can be employed for speech recognition and speech translation. However, only Lip-Translation remains unexplored. + +En: Hello, beautiful world. + +Es: Hola, hermoso mundo. + +Fr: Bonjour, beau monde. + +It : Ciao, bel mondo. + +Pt: Olá, belo mundo. + +··· + +languages, prompting the need for addressing cross-lingual challenges. Several works have attempted to tackle these challenges, including Machine Translation (MT) [9, 37, 15] for text utterance, Speech Translation (ST) [58, 19] for audio utterance, and Speech-to-Speech Translation (S2ST) [58, 19, 17, 33, 29] for simultaneous interpretation. However, research on cross-lingual visual speech is still limited, as illustrated in Figure 1. As an essential component of multi-media speech, visual speech can be combined with audio to enhance the recognition and understanding of speech content as audio-visual speech [1, 2, 54], and is the unique resource for speech content understanding in audio-disabled scenarios [36]. + +Visual speech translation has never been studied, mainly for the lack of visual speech datasets with translated texts in different languages. The few remaining works [57, 60, 44] also cannot be quantitatively verified for this reason, making them unconvincing. The available visual speech corpus is often very scarce compared to audio speech owing to the high demands of visual speech for model training, which requires mostly-frontal and high-resolution videos with a sufficiently high frame rate, such that motions around the lip area are clearly captured [23]. In this paper, we propose the + +first Audio-Visual Multilingual Speech Translation dataset, AVMuST-TED. During the process of acquisition, we first screen out videos with professional translations in four different languages from TED talk which performs strict translation and review processes, and then determine the real speaker's talking head by checking whether each pair of visual speech (i.e., talking head) and audio speech matches in the manner of [1, 2]. Incidentally, this dataset can also be used for quantitative evaluation of other multi-modality translation tasks, such as cross-lingua audio-visual speech generation [51, 60]. + +The cascaded model comprising of a speech recognition model and a machine translation model can handle speech translation tasks but suffers from error accumulation due to model cascades and cannot process languages without text (e.g., Minnan). Our proposed end-to-end model, which can translate directly from source speech to target text, addresses the above issues. However, visual speech is less distinguishable than audio speech, making it difficult to develop a mapping from source speech phonemes to the target language text. To address this, we introduce MixSpeech, a method that first pretrains the decoder using high-discrimination audio speech to obtain a mapping from speech phonemes to text and then generalizes this mapping to the visual speech task through cross-modality self-learning. Furthermore, since audio speech and visual speech are two distinct modalities of speech, there is a significant modality gap between them that hinders knowledge transfer. To narrow this gap and improve knowledge transfer, we propose mixed speech, which is created by interpolating audio and visual streams, rather than relying solely on audio speech. We also propose a curriculum-learning [7] based strategy to adjust the mixing ratio as the training progresses and cross-modality integration deepens. + +The code and dataset are available1, the main contributions of this paper are as follows: + +- We present the first lip-translation baseline and introduce the Audio-Visual Multilingual Speech Translation dataset, AVMuST-TED. +- We present a cross-modality self-learning framework that leverages distinguishable audio speech translation to regularize visual speech translation for effective cross-modality knowledge transfer. +- We present to adopt the mixed speech, interpolated from audio and visual speeches, and a curriculum-learning based mixing ratio adjustment strategy to reduce the inter-modality gap during knowledge transfer. +- We achieve state-of-the-art performance in lip translation for four languages on AVMuST-TED, with a +1.4 to +4.2 boost in BLEU scores and in lip reading on CMLR (11.1%), LRS2 (25.5%) and LRS3 (28.0%). + +# 2. Related work + +# 2.1. Audio-Visual Speech + +Audio and visual speeches are two separate modalities that convey speech content. Numerous works [45, 13, 1, 2, 47, 25, 28, 26, 34, 11] have explored ways to extract information from speech using these modalities. Speech recognition [45, 6, 22] is widely used in online meetings and social applications to recognize speech content. Speech translation [58, 66, 19] is commonly used in simultaneous interpretation applications for cross-lingual communication in cross-border travel and meetings. Keyword spotting [5, 52, 30] is employed in short video applications to quickly retrieve relevant content. Additionally, in noisy scenarios, relevant speech tasks [14, 21, 47, 42] rely on visual speech to avoid interference from surrounding speech and background noise. Despite the growing interest in speech tasks that rely on visual speech, researches [57, 60] on visual speech translation are limited and lacks validation due to the lack of multilingual audio-visual speech transcription datasets. This paper proposes a baseline for visual speech translation and introduces the first large-scale audio-visual multilingual translation dataset, AVMuST-TED, which includes 706 hours of audio-visual speech and translation pairs in Spanish, French, Italian, and Portuguese. AVMuST-TED lays a solid foundation or future cross-lingual audio-visual translation tasks, such as Cross-Lingual Talking Head Generation [44]. + +# 2.2. Transfer learning from Audio to Visual + +Many researchers [50, 53, 39, 64] attempt to enhance the representation of visual speech by leveraging corresponding audio speech, as the two are paired parallel speech streams. Some [50, 53, 39] use knowledge distillation to bootstrap the training of visual speech models using audio speech models, while others [71, 39] have proposed various distillation strategies to optimize the representation of visual speech by mining the intrinsic connection between audio and visual speeches. Some [53] also use self-supervised learning, with audio as auxiliary supervision for visual utterances, to obtain fine-grained visual representations. The success of these works demonstrates the critical role of audio speech, which has a higher discrimination compared to visual speech, in training visual speech models. However, previous works face the modality shift problem during knowledge transfer because they start directly from speeches of two different modalities, audio and visual speeches, with a significant modality gap. In this paper, we propose an cross-modality self-learning framework MixSpeech, that uses synthetic mixed speech to regularize visual speech translation for effective cross-modality knowledge transfer, reducing the gap between the two modalities during knowledge transfer. + +![](images/56481ff7c2a3680be8b6588f69136433f2587497b78a9400fdcd92ab4bfa1fa0.jpg) +Figure 2. Illustration of our proposed MixSpeech. We first pretrain the model with audio speech translation as shown in the dashed boxed, and then train the visual speech translation with mixed speech regularization. The blank dashed boxes denote the modality missing speech. + +# 2.3. Mixup for Cross-Modality Transfer + +Many works [68, 20, 63, 19, 24] bridge the gap between modalities with mixup. [67] proposes mixup for data augmentation to improve model robustness. [10] suggests mixing at the representation-level to mine implicit associations between labeled and non-labeled sentences. Other works [63, 59, 18, 27] also use mixing to build bridges between different modalities. Some [63, 18] use CLIP [49] to retrieve semantically consistent images with text tokens and synthesize mixed sentences for text-visual consistency representation training. Others [59, 19] construct manifold mixup interpolations based on semantic consistency between audio and text to enhance understanding of audio with textual datasets. By implementing the mixup strategy, these studies have shown notable improvements across a range of tasks, highlighting its potential to facilitate knowledge transfer between different modalities. However, previous works use fixed hyperparameters [67] or mapping functions [19] for mixing ratios, which are typically not optimal and cannot be adapted to the training situation. In this paper, we propose an uncertainty-based [43] curriculum learning [7] strategy that gradually adjusts mixing ratios and apply mixup strategy for cross-modality knowledge transfer between audio and visual speeches for the first time. + +# 3. Method + +# 3.1. Task Formulation + +As the twin task of speech recognition, speech translation involves translating source language speech into target language text. The speech translation model takes audio speech utterance $\mathbf{A} = \{\mathbf{A}_t\}_{t=1}^T \in \mathbb{R}^{T \times D}$ or visual speech utterance $\mathbf{V} = \{\mathbf{V}_t\}_{t=1}^T \in \mathbb{R}^{T \times D}$ as input and generates the target language text $\mathbf{w} = \{\mathbf{w}_i\}_{i=0}^s$ , where $\mathbf{A}_t$ and $\mathbf{V}_t$ represent the $t$ -th features in the audio and visual speeches, and $\mathbf{w}_i$ represents the $i$ -th word in the target language translation with a total length of $S$ . Note that, we stack 4 adjacent acoustic frames together forSyncing with visual speech, both with $T$ frames. + +# 3.2. Overview + +We propose a cross-modal self-learning framework for visual speech translation with audio speech regularization, named MixSpeech, as illustrated in Figure 2. This model consists of three modules - a feature extractor for extracting speech embeddings, a speech encoder for attending to the contextual dependencies of speech, and a target language-oriented translation decoder. We utilize the pre-trained feature extractor (AV-Encoder) and speech encoder (Speech-Encoder) from the AV-Hubert [53] + +to extract speech representations from both audio and visual speech utterances. Additionally, a randomly initialized translation decoder (Trans-Decoder) is used to autoregressively decode the speech representation into the target language text. MixSpeech is a two-stage training process: 1) Pretraining the translation decoder with high-discrimination audio speech utterances to learn inter-lingual mapping relations between source language phonemes and target language text, as detailed in subsection 3.3. 2) Aligning visual speech with audio speech to transfer the inter-lingual mapping from audio speech to visual in 3.5. The mixed speech 3.4 is synthesized by interpolating audio speech with visual speech in MixupSpeech, bridging the modality gap and enhancing knowledge transfer. + +# 3.3. Pretraining with Audio Speech + +For uni-modality audio speech $\mathbf{A} \in \mathbb{R}^{T \times D}$ or visual speech $\mathbf{V} \in \mathbb{R}^{T \times D}$ , the uni-modality audio-visual feature $\mathbf{e}^u = \{\mathbf{e}_t^u\}_{t=1}^T \in \mathbb{R}^{T \times 2D}$ fed into feature extractor can be defined as: + +$$ +\mathbf {e} _ {t} ^ {u} = \left\{ \begin{array}{l l} \operatorname {c o n c a t} \left(\mathbf {0} _ {D}, \mathbf {V} _ {t}\right), & \mathbf {V} _ {t} \neq \text {N o n e}, \\ \operatorname {c o n c a t} \left(\mathbf {A} _ {t}, \mathbf {0} _ {D}\right), & \mathbf {A} _ {t} \neq \text {N o n e}, \end{array} \right. \tag {1} +$$ + +where $\mathbf{0}_D$ denotes the feature of missing modality, following the practice of [53]. And then, we obtain the audiovisual fusion feature $\mathbf{e}^f\in \mathbb{R}^{T\times D}$ with AV-Encoder. The transformer-based Speech-Encoder allows us to obtain the phoneme embedding $\mathbf{e}^p\in \mathbb{R}^{T\times D}$ with the contextual speech details. A target language oriented translation decoder Trans-Decoder is appended to autoregressively decode the phoneme embedding $\mathbf{e}^p$ into the target probabilities $P^u$ , where $P^u = \{P_t^u\}_{t = 1}^S = \{p(\mathbf{w}_t|\{\mathbf{w}_i\}_{i = 1}^{t - 1},\mathbf{e}^p)\}_{t = 1}^S$ represents the probability of the $t$ -th word being $\mathbf{w}_t$ when the previous $t - 1$ predictions are $\{\mathbf{w}_i\}_{i = 1}^{t - 1}$ and $s$ is the length of the target language translation. During the pretraining, the overall model is trained on audio speech with cross-entropy loss: + +$$ +\mathcal {L} _ {C E} = - \sum_ {t = 1} ^ {S} \log p \left(w _ {t} \mid \left\{w _ {i} \right\} _ {i = 1} ^ {t - 1}, \mathbf {e} ^ {p}\right). \tag {2} +$$ + +# 3.4. Audio-Visual Speech Mixing + +Audio and visual speeches have a huge modality gap, which greatly impacts knowledge transfer across modalities. We attempt to employ mixed speech to bridge two different modalities of speech. Since the pair of audio and visual speeches is strictly temporally synchronous, we take advantage of this property to interpolate the mixed speech. For a pair of synchronized audio and video speech $(\mathbf{A},\mathbf{V})\in \mathbb{R}^{2\times T\times D}$ , each visual feature $\mathbf{V}_t$ at $t$ -th frame has its corresponding audio feature $\mathbf{A}_t$ , representing the same phonetic content. We interpolate with probability $\phi$ + +to obtain a mixed speech $\mathbf{e}^m = \{\mathbf{e}_t^m\}_{t=1}^T \in \mathbb{R}^{T \times 2D}$ derived partly from audio speech and partly from visual speech: + +$$ +\mathbf {e} _ {t} ^ {m} = \left\{ \begin{array}{l l} \operatorname {c o n c a t} \left(\mathbf {0} _ {D}, \mathbf {V} _ {t}\right), & p < \phi , \\ \operatorname {c o n c a t} \left(\mathbf {A} _ {t}, \mathbf {0} _ {D}\right), & p \geq \phi , \end{array} \right. \tag {3} +$$ + +where $p$ is sampled from the uniform distribution $U(0,1)$ and $\phi$ is the ratio of speech mixing. In particular, we propose a curriculum learning [7] based mixing ratio adjustment method that adapts the appropriate $\phi$ as the training progresses. The prediction uncertainty [43] indicates the confidence of the prediction (smaller is better), and we take it as a signal to adjust the mixing ratio: + +$$ +\mathbf {u} = \frac {1}{S} \sum_ {t = 1} ^ {S} \operatorname {E n t r o p y} \left(P _ {t}\right). \tag {4} +$$ + +If the discrimination of mixed speech is insufficient to regularize visual speech translation and maintain $n$ steps $(\Delta \mathbf{u} = \mathbf{u}^v - \mathbf{u}^m < k\mathbf{u}^v$ , where $\mathbf{u}^v$ and $\mathbf{u}^m$ represent the uncertainty of uni-modality (visual) and mixed speech, respectively, and the threshold hyperparameter $k$ is set to 0.05 with $n$ set to 20 in our work), we gradually increase the proportion of audio at a rate of $\alpha$ $(\phi' = \alpha \phi)$ . We initialize $\phi = 0.1$ to prevent excessive initial modality gap and maintain $\phi \in [0.1, 0.9]$ throughout the training process. + +# 3.5. Cross-Modality Self-Learning for Speech + +Since audio speech is more distinguished compared to visual speech, we intend to boost visual speech translation with the knowledge from audio speech. And the mixed speech bridges the gap between audio speech and visual speech, allowing us to boost cross-modality knowledge transfer with it. With audio speech feature $\mathbf{A} \in \mathbb{R}^{T \times D}$ and visual speech feature $\mathbf{V} \in \mathbb{R}^{T \times D}$ fed into the modules with shared parameters, the uni-modality visual speech feature $\mathbf{e}^u$ and the mixed speech feature $\mathbf{e}^m$ are decoded into the target probabilities $P^u$ and $P^m$ , respectively. + +After the pre-training with audio speech translation, the model is promising enough for mixed speech containing partial audio speech, we adopt the Jensen-Shannon Divergence (JSD) [41] to regularize the probabilities of these two different speeches: + +$$ +\mathcal {L} _ {J S D} = \sum_ {t = 1} ^ {S} J S D \left(P _ {t} ^ {m} \| P _ {t} ^ {u}\right). \tag {5} +$$ + +As this probability is across the entire training vocabulary, we are able to perform fine-grained regularization to enhance the training of visual speech. Meanwhile, we also minimize the cross-entropy loss between two speech translations and the real translation, $\mathcal{L} = \mathcal{L}_{CE}^{uni} + \lambda_1\mathcal{L}_{CE}^{mix} + \lambda_2\mathcal{L}_{JSD}$ , where $\lambda_{1}$ and $\lambda_{2}$ are hyperparameters of loss weights, while $\lambda_{1} = \lambda_{2} = 1.0$ in this work. + +
DatasetTarget Language Hours# Lang# Σ Hrs# Σ Sents# Σ Tokens
EnEsFrItPtsrctgt
Audio-Only
LibriSpeech [45]960h----1960h180K5.9M5.9M
MuST-C [16]-504h492h465h385h83617h2016K38.1M35.8M
VoxPopuli [62]543h441h427h461h-165967h2045K65.0M60.1M
Audio-Visual
LRS2 [1]224h----1224h143K2.3M2.3M
LRS3 [2]433h----1433h151K4.2M4.2M
AVMuST-TED (ours)-198h185h165h158h4706h925K7.3M7.0M
+ +# 4. Experiments + +# 4.1. Datasets + +AVMuST-TED. To obtain a corpus for AVST, we screened a set of TED and TEDx talks with multilingual subtitles as the data source. All transcriptions and translations are performed strictly following the TED Translation Guidelines and require collaboration between at least one translator (or transcriber) and one reviewer. The prior lip-reading dataset acquisition pipeline is followed to crop face-tracks, and an audio-visual alignment network, SyncNet, is adopted for speaker proofreading. Table 1 compares AVMuST-TED with related datasets, and it is the first audio-visual speech translation dataset containing translations from English (En) to four target languages: Spanish (Es), French (Fr), Italian (It), and Portuguese (Pt). These four languages have the most translated subtitles in TED, and 1024/1536 pieces of data are randomly sampled for each language as the test/validation set. The information about AVMuST-TED is detailed in Appendix A. + +LRS2&3 [1, 2], two commonly used publicly available English wild audio-visual speech recognition datasets, are adopted to demonstrate the lip-reading performance, containing 224 hours of video from BBC television shows and 433 hours of video from TED and TEDx talks. The training data in both datasets is divided into two partitions, namely Pretrain and Train, both of which are transcribed from videos to text at the sentence level. The only difference is that the video clips in the Pretrain partition are not strictly trimmed and sometimes longer than the corresponding text. In our experiments, we employ different amounts of training data from LRS2 and LRS3, including Pretrain+Train (224/433h) for high resource and Train (29/30h) for low resource. + +CMLR [70], widely used dataset for Mandarin audio-visual speech recognition, contains 61 hours audio-visual speech utterances collected from Chinese TV stations. In + +Table 1. Comparison of audio-visual speech recognition/translation datasets. #Lang denotes the number of target languages. #∑Hrs denotes the overall duration of speech in the dataset, #Sents and #Tokens denote the overall sentences and the overall token, respectively. + +
MethodMBLEU↑
En-EsEn-FrEn-ItEn-Pt
CascadedV12.711.311.513.2
AV-Hubert [53]V14.212.612.914.8
CascadedA(+Noise)16.012.912.615.5
AV-Hubert [53]A(+Noise)17.614.514.117.1
MixSpeech(ours)V18.515.114.317.2
+ +Table 2. Comparison of the performances of visual speech translation on AVMuST-TED with those of the noisy audio speech translation. The results of noisy audio speech translation are the mean value at five SNRs $\{-20, -10, 0, 10, 20\}$ db. + +our experiments, we adopt this dataset to demonstrate the performance of our proposed MixSpeech in low-resource languages such as Mandarin. Additionally, we sample a training set containing only 12 hours of utterances in the manner of [71] for low resource scenario. + +# 4.2. Evaluation and Implementation Details + +In this paper, we measure the performance of MixSpeech on two speech tasks, speech recognition and speech translation. For speech recognition, word error rate (WER) is adopted as the evaluation metric, which is defined as $\mathrm{WER} = (S + D + I) / M$ , where $S, D, I, M$ represent the number of words replaced, deleted, inserted, and referenced. As for speech translation, the case-sensitive detokenized BLEU score is computed using SACREBLEU [46], following the same evaluation methodology as in previous speech translation works [16, 62]. The implementation details are provided in Appendix B due to page limitations. + +# 4.3. Performance of Speech Translation + +End-To-End Models VS. Cascaded Models. Table 2 presents a comparison of the lip translation performance between two representative methods: 1) an end-to-end model, + +implemented based on the state-of-the-art AV-Hubert [53] method for visual speech-related tasks, and 2) a cascaded model, combining a speech recognition model (i.e., Lip-Reading or ASR) with a machine translation model. In the cascaded model, we use the speech recognition model trained by AV-Hubert on LRS3, which achieve the best lip-reading performance to date, and a transformer-based machine translation model trained on the paired translated text corpus in AVMuST-TED. Comparing the lip translation performance of the end-to-end model and the cascade model, we find that the BLEU score of the end-to-end model improved by $+1.3$ to $+1.6$ . This result demonstrates that the end-to-end trained model can effectively prevent the accumulation of errors caused by the model cascade, and that lip translation cannot be simply disassembled as the superposition of lip reading and machine translation. + +MixSpeech VS. Prior Methods. Due to the discrimination of speech between modalities, visual speech models are not able to translate speech content as accurately as audio speech models. To address the issue of low discrimination in visual speech, we propose MixSpeech, which is a cross-modality self-learning framework that employs mixed speech to transfer knowledge obtained from audio speech pre-training into the visual speech model. Our proposed MixSpeech significantly improves the BLEU score by another $+1.4$ to $+4.3$ . Furthermore, the improvement from MixSpeech is related to the discrepancy in speech translation between audio and visual modalities. For example, En-Es exhibits a larger discrepancy of 14.7 between audio and visual speech translation, ranging from 28.9 to 14.2, and MixSpeech significantly improves it by $+4.3$ . Conversely, Italian shows a smaller discrepancy of 10.9, ranging from 23.8 to 12.9, and improves only by $+1.4$ . This highlights that the improvement in lip translation stems from the knowledge acquired from audio speech translation. + +Visual Speech VS. Noisy Audio Speech. We also evaluate the performance of audio speech translation in noisy environments, by adding noise sampled from MUSAN [55] to the audio speech and measuring the performance at five SNR levels $\{-20, -10, 0, 10, 20\}$ db. We compare the average BLEU scores of different SNRs and present the detailed performance in Appendix C.1. Our experiments show that although noisy audio speech performs better than visual speech, the translation performance is still significantly lower compared to noiseless audio speech. In contrast, MixSpeech, which fully leverages the knowledge of audio speech, greatly improves the visual speech translation performance, making it more reliable in noisy scenes. We also provide a comparison of translation with audio speech and audio-visual speech, demonstrating that visual speech enhances the ceiling and robustness of speech translation, but the details are only available in the Appendix C.1 since audio-visual speech does not require the cross-modality + +
# RESMethodWER(Labeled Visual Utts Hrs) ↓
CMLRLRS2LRS3
HighWAS [56]38.9(61)70.4(224)-
TM-seq2seq [1]-49.8(698)59.9(698)
CSSMCM [70]32.5(61)--
Conv-seq2seq [69]-51.7(698)60.1(698)
CTC+KD [3]-51.3(224)58.9(433)
LIBS [71]31.3(61)65.3(698)-
CTCH [40]22.0(61)--
Master [50]-49.2(698)59.0(698)
Sub-Word [47]-28.9(698)40.6(698)
†AV-Hubert [53]12.7(61)28.7(224)28.6(433)
MixSpeech(ours)11.1(61)25.5(224)28.0(433)
LowLIBS [71]50.5(12)--
†AV-Hubert [53]25.8(12)31.4(29)32.5(30)
MixSpeech(ours)18.5(12)26.9(29)28.6(30)
+ +Table 3. Comparison of lip reading methods under different resource conditions. # RES represents the amount of resources. (Hours) highlighted in blue are used for low resources. † For better comparison, we reproduce AV-Hubert on CMLR and LRS2. + +knowledge transfer proposed in this paper. + +# 4.4. Performance of Speech Recognition + +As shown in Table 3, we compare the performance of MixSpeech on another visual speech task, lip reading (i.e., Visual Speech Recognition), to highlight the mixspeech from more perspectives. MixSpeech obtain state-of-the-art performance on three datasets, two for English (25.5% on LRS2 and 28.0% on LRS3) and one for Chinese (11.1% on CMLR), demonstrating that this cross-modality self-learning framework can be applied for different languages to capture the intrinsic association between audio and visual speeches and thus effectively improve the understanding of visual speech. Since visual speech is relatively low-resource, we verify whether MixSpeech can effectively improve the performance of visual speech tasks in low-resource with audio speech. Compared with previous methods, MixSpeech boosts the WER of lip-reading by -3.9% to -7.3%, highlighting the critical role of high-resource audio speech in low-resource visual speech tasks. Specifically, on LRS2 and LRS3, the performance of Mixspeech in the low-resource scenario (26.9%/28.6% WER obtained with only 29h/30h visual utterances) outperforms the performances of prior methods in the high-resource scenario (28.7%/28.6% obtained with 224h/433h or even more visual utterances). Even though with only limited labeled visual corpus, our proposed MixSpeech performs no less than works with more. It is the bridge between two modalities of speech, which helps visual speech to access the knowl + +edge stored in high-resource and high-discrimination audio speech without barriers. + +# 4.5. Can MixSpeech bridge cross-modality speech? + +Our proposed MixSpeech builds a bridge between cross-modality speech through cross-modality self-learning, with the properly mixes speech. The details are as follows: + +Cross-Modality Self-Learning for Knowledge Transfer. The experiments in Figure 3 provide a positive answer to the question of whether MixSpeech can contribute to achieving knowledge transfer between audio and visual speeches. We evaluate the performance of visual speech translation with different regularization strategies: no audio speech regularization (i.e., $\phi = 0$ ), mixed speech regularization with different mixing ratios (i.e., $\phi \in (0,1)$ , audio speech regularization (i.e., $\phi = 1$ ), and mixing ratio adjustable mixed speech regularization (i.e., dashed lines). It is evident that the cross-modality self-learning framework significantly enhances visual speech translation, as all performances with audio speech regularization are noticeably better than those without self-learning ( $\phi = 0$ ), demonstrating the effectiveness of our proposed MixSpeech. + +Narrow the Cross-Modality Distance with Properly Mixed Speech. Moreover, the introduction of mixed speech facilitates smoother cross-modality knowledge transfer by narrowing the modality gap between speeches. Some segments in the mixed speech come from the visual speech, making it much closer to visual speech in terms of modality distance than audio speech. When regularizing with mixed speech in En-Es, the translation performance of visual speech improves further by $+0.3$ to $+0.8$ compared to audio speech regularization alone. Among them, bootstrap + +![](images/c9e977e77f4aa403e23c47c220b00ee197026506ec91d8c1244467fe37b10735.jpg) +Figure 3. BLEU scores of MixSpeech with different speech regularization on En-Es and En-Fr. $\phi = 0$ : no audio speech regularization, $\phi \in (0,1)$ : mixed speech regularization, $\phi = 1$ : only audio speech regularization. The dashed lines represent the adjustable mixing ratio strategy based on curriculum learning. + +ping with mixed speech of mixing ratio $\phi = 0.5$ achieves the highest BLEU score of 18.3. This demonstrates that a reasonably mixed ratio ensures that it is neither overly biased towards visual speech, leading to a lack of knowledge of audio speech, nor overly biased towards audio speech, leading to excessive cross-modality distances that affect knowledge transfer. The adjustable mixing ratio strategy based on curriculum learning further increases the applicability of mixed speech to cross-modality self-learning training, thereby boosting visual speech translation performance again. + +
IDMethodBLEU ↑
LmonCELmixCELJSDEn-EsEn-FrEn-ItEn-Pt
#1✓14.212.612.914.8
#2✓✓17.514.313.616.5
#3✓✓18.114.814.116.9
#4✓✓✓18.515.114.317.2
+ +Table 4. BLEU of different module combinations in MixSpeech. + +# 4.6. What role does each part play in MixSpeech? + +The effectiveness of MixSpeech, which is a cross-modality self-learning framework designed to improve visual translation performance, has been demonstrated. In this study, we investigate the role of each component in detail and present relevant experiments in Table 4: + +Bridging the cross-modality gaps. We observe a significant improvement in the lip translation performance with the inclusion of $\mathcal{L}_{JSD}$ (ID: #3, #4) for regularizing the probabilities of visual speech and mixed speech, compared to without (ID: #1, #2). Specifically, experiment #3 with $\mathcal{L}_{JSD}$ outperform experiment #2 with $\mathcal{L}_{CE}^{mix}$ by $+0.6$ in lip translation performance on En-Es. This demonstrates that $\mathcal{L}_{JSD}$ is the main contributor to achieving cross-modality knowledge transfer by building a bridge between the two speeches and performing fine-grained regularization across the probability of each word. + +Maintaining knowledge of audio speech. It is also important to note that during the regularization process, the representation of audio speech is also affected by visual speech, which can interfere with the knowledge of audio speech and ultimately harm the lip translation performance of MixSpeech. As evidenced by experiment #2, the lip translation performance on En-Es decrease by -0.4 compared to experiment #3 when $\mathcal{L}_{CE}^{mix}$ is not applied. To address this issue, $\mathcal{L}_{CE}^{mix}$ is introduced to enhance the training ceiling of the cross-modality self-learning framework. By maintaining the translation performance of mixed speech and preventing the excessive disturbance to audio speech knowledge, $\mathcal{L}_{CE}^{mix}$ helps to improve the overall performance of MixSpeech. + +
En-EsTranscription: and always as a child I had this fantasy that somebody would come and rescue me +MixSpeech: and always as a child I had this fantasy that somebody would come and rescue me
Ground Truth: y de niña siempre tenía la fantasía de que alguien vendrá a salvar me de +MixSpeech: y de (desde) niña niño siempre tenía la esta fantasía de que alguien vendrá a salvar me (rescató) de
En-FrTranscription: and solutions create new problems which have to be solved in their turn +MixSpeech: and solutions to create new problems which have to be solved in their turn this year
Ground Truth: et les solutions créent de nouveaux problèmes devant être résolus à leur tour +MixSpeech: et les (des) solutions pour creer de nouveaux problèmes devant qui doivent être résolus à leur tour
En-ItTranscription: one of the last 10,000 years, and the other certainly of the last 25 years +MixSpeech: one of the last 10,000 years and the other certainly assistancee of the last 25 years
Ground Truth: uno presente negli ultimi diecimila anni e l'alto certamente negli ultimi 25 anni +MixSpeech: uno presente negli ultimi diecimila (10000) anni e l'alto certamente negli ultimi 25 anni
En-PtTranscription: has around 2,000 people descending on MIT's campus +MixSpeech: has around 2,000 people descending on MIT's campus
Ground Truth: congregamerca de 2000 pessoas no campus do mit +MixSpeech: congregam de circa de 2000 pessoas a estudar no campus do mit
+ +Table 5. Qualitative performance of Visual Speech Recognition and Translation on AVMuST-TED. Red Strikeout Words: mistranslated words with opposite meaning, (Blue Words in parentheses): mistranslated words with similar meaning, Gray Words: the absent words. + +# 4.7. Qualitative results + +We present several examples of lip translation in Table 5 to qualitatively evaluate the translation quality of MixSpeech. The translation results are very close to the ground truth, and the semantics are consistent. We observe two types of words that differ in translation: synonyms and context-sensitive translations. Synonyms that have different spellings but the same meaning, such as salvar and rescató in Spanish, both meaning 'rescue', and diecimila and 10000 in Italian, both meaning 'ten thousand', are commonly found in translation tasks and can affect translation consistency. Additionally, there are translations that require context information, such as when the speaker refers to themselves as a child, and the translation in Spanish needs to take into account the speaker's gender to choose between niña for girl' or Niño for boy' and 'child'. The qualitative translation results of MixSpeech demonstrate its capability to achieve reliable cross-lingua lip translation. In Appendix C.2, we also provide translation results of noisy audio speech translation with visual speech translation and audio speech translation with audiovisual speech translation to highlight the importance of visual speech in speech translation. + +# 5. Conclusion + +With the advancement of online technologies, such as online healthcare and sales, language barriers often prevent these tools from reaching and benefiting disadvantaged areas. In light of this, we focus on visual speech, a branch of the speech stream, and aim to translate visual speech from source languages to other target languages for cross-linguistic communication, specifically through lip translation. We meticulously curate the AVMuST-TED dataset, consisting of 706 hours of speech clips with professional translations from TED, to facilitate cross-linguistic research on visual speech. We also introduce MixSpeech, a cross-modality self-learning framework that utilizes mixed speech to regularize visual speech translation and achieves state-of-the-art performance in lip translation on AVMuST-TED and lip reading on LRS2, LRS3, and CMLR datasets. + +Moreover, our work on visual speech and AVMuSTED lay a solid foundation for further research on visual speech in cross-lingual fields. There are numerous related tasks with great potential for practical applications, such as Cross-Lingual Talking Head Generation [44]. These tasks hold immense promise for breaking down language barriers and promoting communication across diverse communities. + +# Acknowledgements + +This work was supported in part by National Key R&D Program of China under Grant No.2022ZD0162000, National Natural Science Foundation of China under Grant No.62222211, Grant No.61836002 and Grant No.62072397. + +# References + +[1] Triantafyllos Afouras, Joon Son Chung, Andrew Senior, Oriol Vinyals, and Andrew Zisserman. Deep audio-visual speech recognition. IEEE transactions on pattern analysis and machine intelligence, 2018. 1, 2, 5, 6, 12, 13 +[2] Triantafyllos Afouras, Joon Son Chung, and Andrew Zisserman. Lrs3-ted: a large-scale dataset for visual speech recognition. arXiv preprint arXiv:1809.00496, 2018. 1, 2, 5, 12, 13 +[3] Triantafyllos Afouras, Joon Son Chung, and Andrew Zisserman. Asr is all you need: Cross-modal distillation for lip reading. 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Connecting multi-modal contrastive representations. arXiv preprint arXiv:2305.14381, 2023. 2 +[65] Shuang Yang, Yuanhang Zhang, Dalu Feng, Mingmin Yang, Chenhao Wang, Jingyun Xiao, Keyu Long, Shiguang Shan, and Xilin Chen. Lrw-1000: A naturally-distributed large-scale benchmark for lip reading in the wild. In 2019 14th IEEE international conference on automatic face & gesture recognition (FG 2019), pages 1–8. IEEE, 2019. 12 + +[66] Rong Ye, Mingxuan Wang, and Lei Li. End-to-end speech translation via cross-modal progressive training. arXiv preprint arXiv:2104.10380, 2021. 2 +[67] Hongyi Zhang, Moustapha Cisse, Yann N Dauphin, and David Lopez-Paz. mixup: Beyond empirical risk minimization. arXiv preprint arXiv:1710.09412, 2017. 3 +[68] Linjun Zhang, Zhun Deng, Kenji Kawaguchi, Amirata Ghorbani, and James Zou. How does mixup help with robustness and generalization? arXiv preprint arXiv:2010.04819, 2020. 3 +[69] Xingxuan Zhang, Feng Cheng, and Shilin Wang. 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In Proceedings of the AAAI Conference on Artificial Intelligence, volume 34, pages 6917-6924, 2020. 2, 5, 6 \ No newline at end of file diff --git a/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/images.zip b/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..686b50d6c9ae6d914faabebef8a4c39fefc5e3a4 --- /dev/null +++ b/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:b54d728bf01fab52a3bd02680780b03ad5850350f9d5407087ac6df21898e8ed +size 620058 diff --git a/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/layout.json b/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..9c29705f40c3b16ab8c38616fe0de4ec675d1fc0 --- /dev/null +++ b/2023/MixSpeech_ Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition/layout.json @@ -0,0 +1,8288 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 62, + 102, + 532, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 62, + 102, + 532, + 140 + ], + "spans": [ + { + "bbox": [ + 62, + 102, + 532, + 140 + ], + "type": "text", + "content": "MixSpeech: Cross-Modality Self-Learning with Audio-Visual Stream Mixup for Visual Speech Translation and Recognition" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 112, + 161, + 485, + 217 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 112, + 161, + 485, + 217 + ], + "spans": [ + { + "bbox": [ + 112, + 161, + 485, + 217 + ], + "type": "text", + "content": "Xize Cheng*, Tao Jin*, Rongjie Huang*, Linjun Li \nWang Lin, Zehan Wang, Ye Wang, Huadai Liu, Aoxiong Yin, Zhou Zhao† \nZhejiang University \n{chengxize, jint.zju, rongjiehuang, zhaozhou}@zju.edu.cn" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 244, + 192, + 258 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 244, + 192, + 258 + ], + "spans": [ + { + "bbox": [ + 143, + 244, + 192, + 258 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "spans": [ + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "type": "text", + "content": "Multi-media communications facilitate global interaction among people. However, despite researchers exploring cross-lingual translation techniques such as machine translation and audio speech translation to overcome language barriers, there is still a shortage of cross-lingual studies on visual speech. This lack of research is mainly due to the absence of datasets containing visual speech and translated text pairs. In this paper, we present AVMuST-TED, the first dataset for Audio-Visual Multilingual Speech Translation, derived from TED talks. Nonetheless, visual speech is not as distinguishable as audio speech, making it difficult to develop a mapping from source speech phonemes to the target language text. To address this issue, we propose MixSpeech, a cross-modality self-learning framework that utilizes audio speech to regularize the training of visual speech tasks. To further minimize the cross-modality gap and its impact on knowledge transfer, we suggest adopting mixed speech, which is created by interpolating audio and visual streams, along with a curriculum learning strategy to adjust the mixing ratio as needed. MixSpeech enhances speech translation in noisy environments, improving BLEU scores for four languages on AVMuST-TED by " + }, + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "type": "inline_equation", + "content": "+1.4" + }, + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "type": "inline_equation", + "content": "+4.2" + }, + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "type": "text", + "content": ". Moreover, it achieves state-of-the-art performance in lip reading on CMLR " + }, + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "type": "inline_equation", + "content": "(11.1\\%)" + }, + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "type": "text", + "content": ", LRS2 " + }, + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "type": "inline_equation", + "content": "(25.5\\%)" + }, + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "type": "text", + "content": ", and LRS3 " + }, + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "type": "inline_equation", + "content": "(28.0\\%)" + }, + { + "bbox": [ + 47, + 270, + 290, + 558 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 581, + 128, + 594 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 581, + 128, + 594 + ], + "spans": [ + { + "bbox": [ + 47, + 581, + 128, + 594 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "type": "text", + "content": "Multi-media techniques, including Audio-Visual Speech Recognition (AVSR) [4, 1, 2, 53], Audio-Visual Speech Translation (AVST) [8, 38, 61], and Audio-Visual Speech Generation (AVSG) [48, 32, 24], are commonly employed in various online communication scenarios, such as conferences, education, and healthcare. As a tool for ultra-remote communication, many online interactions involve multiple" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 312, + 258, + 451, + 355 + ], + "blocks": [ + { + "bbox": [ + 312, + 258, + 451, + 355 + ], + "lines": [ + { + "bbox": [ + 312, + 258, + 451, + 355 + ], + "spans": [ + { + "bbox": [ + 312, + 258, + 451, + 355 + ], + "type": "image", + "image_path": "9e335c4f0355b0c07d0ce08b0bcae93eb7596c8a0e96b9b4080f4064649ec260.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 365, + 547, + 410 + ], + "lines": [ + { + "bbox": [ + 304, + 365, + 547, + 410 + ], + "spans": [ + { + "bbox": [ + 304, + 365, + 547, + 410 + ], + "type": "text", + "content": "Figure 1. Diagram of speech tasks. Audio speech and visual speech are paired parallel speech streams which can be employed for speech recognition and speech translation. However, only Lip-Translation remains unexplored." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 457, + 264, + 537, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 457, + 264, + 537, + 274 + ], + "spans": [ + { + "bbox": [ + 457, + 264, + 537, + 274 + ], + "type": "text", + "content": "En: Hello, beautiful world." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 457, + 299, + 539, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 457, + 299, + 539, + 308 + ], + "spans": [ + { + "bbox": [ + 457, + 299, + 539, + 308 + ], + "type": "text", + "content": "Es: Hola, hermoso mundo." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 457, + 312, + 539, + 320 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 457, + 312, + 539, + 320 + ], + "spans": [ + { + "bbox": [ + 457, + 312, + 539, + 320 + ], + "type": "text", + "content": "Fr: Bonjour, beau monde." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 457, + 323, + 524, + 333 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 457, + 323, + 524, + 333 + ], + "spans": [ + { + "bbox": [ + 457, + 323, + 524, + 333 + ], + "type": "text", + "content": "It : Ciao, bel mondo." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 457, + 336, + 524, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 457, + 336, + 524, + 346 + ], + "spans": [ + { + "bbox": [ + 457, + 336, + 524, + 346 + ], + "type": "text", + "content": "Pt: Olá, belo mundo." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 457, + 348, + 479, + 354 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 457, + 348, + 479, + 354 + ], + "spans": [ + { + "bbox": [ + 457, + 348, + 479, + 354 + ], + "type": "text", + "content": "···" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 435, + 547, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 435, + 547, + 590 + ], + "spans": [ + { + "bbox": [ + 304, + 435, + 547, + 590 + ], + "type": "text", + "content": "languages, prompting the need for addressing cross-lingual challenges. Several works have attempted to tackle these challenges, including Machine Translation (MT) [9, 37, 15] for text utterance, Speech Translation (ST) [58, 19] for audio utterance, and Speech-to-Speech Translation (S2ST) [58, 19, 17, 33, 29] for simultaneous interpretation. However, research on cross-lingual visual speech is still limited, as illustrated in Figure 1. As an essential component of multi-media speech, visual speech can be combined with audio to enhance the recognition and understanding of speech content as audio-visual speech [1, 2, 54], and is the unique resource for speech content understanding in audio-disabled scenarios [36]." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 594, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 548, + 715 + ], + "type": "text", + "content": "Visual speech translation has never been studied, mainly for the lack of visual speech datasets with translated texts in different languages. The few remaining works [57, 60, 44] also cannot be quantitatively verified for this reason, making them unconvincing. The available visual speech corpus is often very scarce compared to audio speech owing to the high demands of visual speech for model training, which requires mostly-frontal and high-resolution videos with a sufficiently high frame rate, such that motions around the lip area are clearly captured [23]. In this paper, we propose the" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 693, + 127, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 693, + 127, + 703 + ], + "spans": [ + { + "bbox": [ + 58, + 693, + 127, + 703 + ], + "type": "text", + "content": "*Equal contribution." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 59, + 703, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 703, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 59, + 703, + 135, + 712 + ], + "type": "text", + "content": "† Corresponding author." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15735" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 203 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 203 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 203 + ], + "type": "text", + "content": "first Audio-Visual Multilingual Speech Translation dataset, AVMuST-TED. During the process of acquisition, we first screen out videos with professional translations in four different languages from TED talk which performs strict translation and review processes, and then determine the real speaker's talking head by checking whether each pair of visual speech (i.e., talking head) and audio speech matches in the manner of [1, 2]. Incidentally, this dataset can also be used for quantitative evaluation of other multi-modality translation tasks, such as cross-lingua audio-visual speech generation [51, 60]." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 205, + 289, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 205, + 289, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 205, + 289, + 479 + ], + "type": "text", + "content": "The cascaded model comprising of a speech recognition model and a machine translation model can handle speech translation tasks but suffers from error accumulation due to model cascades and cannot process languages without text (e.g., Minnan). Our proposed end-to-end model, which can translate directly from source speech to target text, addresses the above issues. However, visual speech is less distinguishable than audio speech, making it difficult to develop a mapping from source speech phonemes to the target language text. To address this, we introduce MixSpeech, a method that first pretrains the decoder using high-discrimination audio speech to obtain a mapping from speech phonemes to text and then generalizes this mapping to the visual speech task through cross-modality self-learning. Furthermore, since audio speech and visual speech are two distinct modalities of speech, there is a significant modality gap between them that hinders knowledge transfer. To narrow this gap and improve knowledge transfer, we propose mixed speech, which is created by interpolating audio and visual streams, rather than relying solely on audio speech. We also propose a curriculum-learning [7] based strategy to adjust the mixing ratio as the training progresses and cross-modality integration deepens." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 480, + 287, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 480, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 47, + 480, + 287, + 506 + ], + "type": "text", + "content": "The code and dataset are available1, the main contributions of this paper are as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 515, + 286, + 693 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 58, + 515, + 286, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 515, + 286, + 550 + ], + "spans": [ + { + "bbox": [ + 58, + 515, + 286, + 550 + ], + "type": "text", + "content": "- We present the first lip-translation baseline and introduce the Audio-Visual Multilingual Speech Translation dataset, AVMuST-TED." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 551, + 286, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 551, + 286, + 597 + ], + "spans": [ + { + "bbox": [ + 58, + 551, + 286, + 597 + ], + "type": "text", + "content": "- We present a cross-modality self-learning framework that leverages distinguishable audio speech translation to regularize visual speech translation for effective cross-modality knowledge transfer." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 599, + 286, + 646 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 599, + 286, + 646 + ], + "spans": [ + { + "bbox": [ + 58, + 599, + 286, + 646 + ], + "type": "text", + "content": "- We present to adopt the mixed speech, interpolated from audio and visual speeches, and a curriculum-learning based mixing ratio adjustment strategy to reduce the inter-modality gap during knowledge transfer." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 58, + 647, + 286, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 647, + 286, + 693 + ], + "spans": [ + { + "bbox": [ + 58, + 647, + 286, + 693 + ], + "type": "text", + "content": "- We achieve state-of-the-art performance in lip translation for four languages on AVMuST-TED, with a +1.4 to +4.2 boost in BLEU scores and in lip reading on CMLR (11.1%), LRS2 (25.5%) and LRS3 (28.0%)." + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 71, + 390, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 71, + 390, + 83 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 390, + 83 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 91, + 425, + 104 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 91, + 425, + 104 + ], + "spans": [ + { + "bbox": [ + 306, + 91, + 425, + 104 + ], + "type": "text", + "content": "2.1. Audio-Visual Speech" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 110, + 547, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 110, + 547, + 410 + ], + "spans": [ + { + "bbox": [ + 304, + 110, + 547, + 410 + ], + "type": "text", + "content": "Audio and visual speeches are two separate modalities that convey speech content. Numerous works [45, 13, 1, 2, 47, 25, 28, 26, 34, 11] have explored ways to extract information from speech using these modalities. Speech recognition [45, 6, 22] is widely used in online meetings and social applications to recognize speech content. Speech translation [58, 66, 19] is commonly used in simultaneous interpretation applications for cross-lingual communication in cross-border travel and meetings. Keyword spotting [5, 52, 30] is employed in short video applications to quickly retrieve relevant content. Additionally, in noisy scenarios, relevant speech tasks [14, 21, 47, 42] rely on visual speech to avoid interference from surrounding speech and background noise. Despite the growing interest in speech tasks that rely on visual speech, researches [57, 60] on visual speech translation are limited and lacks validation due to the lack of multilingual audio-visual speech transcription datasets. This paper proposes a baseline for visual speech translation and introduces the first large-scale audio-visual multilingual translation dataset, AVMuST-TED, which includes 706 hours of audio-visual speech and translation pairs in Spanish, French, Italian, and Portuguese. AVMuST-TED lays a solid foundation or future cross-lingual audio-visual translation tasks, such as Cross-Lingual Talking Head Generation [44]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 419, + 511, + 432 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 419, + 511, + 432 + ], + "spans": [ + { + "bbox": [ + 306, + 419, + 511, + 432 + ], + "type": "text", + "content": "2.2. Transfer learning from Audio to Visual" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 438, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 438, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 438, + 545, + 715 + ], + "type": "text", + "content": "Many researchers [50, 53, 39, 64] attempt to enhance the representation of visual speech by leveraging corresponding audio speech, as the two are paired parallel speech streams. Some [50, 53, 39] use knowledge distillation to bootstrap the training of visual speech models using audio speech models, while others [71, 39] have proposed various distillation strategies to optimize the representation of visual speech by mining the intrinsic connection between audio and visual speeches. Some [53] also use self-supervised learning, with audio as auxiliary supervision for visual utterances, to obtain fine-grained visual representations. The success of these works demonstrates the critical role of audio speech, which has a higher discrimination compared to visual speech, in training visual speech models. However, previous works face the modality shift problem during knowledge transfer because they start directly from speeches of two different modalities, audio and visual speeches, with a significant modality gap. In this paper, we propose an cross-modality self-learning framework MixSpeech, that uses synthetic mixed speech to regularize visual speech translation for effective cross-modality knowledge transfer, reducing the gap between the two modalities during knowledge transfer." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 58, + 702, + 228, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 228, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 228, + 712 + ], + "type": "text", + "content": "1https://github.com/Exgc/AVMuST-TED" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "15736" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 82, + 69, + 521, + 363 + ], + "blocks": [ + { + "bbox": [ + 82, + 69, + 521, + 363 + ], + "lines": [ + { + "bbox": [ + 82, + 69, + 521, + 363 + ], + "spans": [ + { + "bbox": [ + 82, + 69, + 521, + 363 + ], + "type": "image", + "image_path": "56481ff7c2a3680be8b6588f69136433f2587497b78a9400fdcd92ab4bfa1fa0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 368, + 547, + 392 + ], + "lines": [ + { + "bbox": [ + 46, + 368, + 547, + 392 + ], + "spans": [ + { + "bbox": [ + 46, + 368, + 547, + 392 + ], + "type": "text", + "content": "Figure 2. Illustration of our proposed MixSpeech. We first pretrain the model with audio speech translation as shown in the dashed boxed, and then train the visual speech translation with mixed speech regularization. The blank dashed boxes denote the modality missing speech." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 410, + 237, + 423 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 410, + 237, + 423 + ], + "spans": [ + { + "bbox": [ + 47, + 410, + 237, + 423 + ], + "type": "text", + "content": "2.3. Mixup for Cross-Modality Transfer" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 438, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 438, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 438, + 289, + 715 + ], + "type": "text", + "content": "Many works [68, 20, 63, 19, 24] bridge the gap between modalities with mixup. [67] proposes mixup for data augmentation to improve model robustness. [10] suggests mixing at the representation-level to mine implicit associations between labeled and non-labeled sentences. Other works [63, 59, 18, 27] also use mixing to build bridges between different modalities. Some [63, 18] use CLIP [49] to retrieve semantically consistent images with text tokens and synthesize mixed sentences for text-visual consistency representation training. Others [59, 19] construct manifold mixup interpolations based on semantic consistency between audio and text to enhance understanding of audio with textual datasets. By implementing the mixup strategy, these studies have shown notable improvements across a range of tasks, highlighting its potential to facilitate knowledge transfer between different modalities. However, previous works use fixed hyperparameters [67] or mapping functions [19] for mixing ratios, which are typically not optimal and cannot be adapted to the training situation. In this paper, we propose an uncertainty-based [43] curriculum learning [7] strategy that gradually adjusts mixing ratios and apply mixup strategy for cross-modality knowledge transfer between audio and visual speeches for the first time." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 306, + 409, + 362, + 421 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 409, + 362, + 421 + ], + "spans": [ + { + "bbox": [ + 306, + 409, + 362, + 421 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 429, + 411, + 441 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 429, + 411, + 441 + ], + "spans": [ + { + "bbox": [ + 306, + 429, + 411, + 441 + ], + "type": "text", + "content": "3.1. Task Formulation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "text", + "content": "As the twin task of speech recognition, speech translation involves translating source language speech into target language text. The speech translation model takes audio speech utterance " + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathbf{A} = \\{\\mathbf{A}_t\\}_{t=1}^T \\in \\mathbb{R}^{T \\times D}" + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "text", + "content": " or visual speech utterance " + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathbf{V} = \\{\\mathbf{V}_t\\}_{t=1}^T \\in \\mathbb{R}^{T \\times D}" + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "text", + "content": " as input and generates the target language text " + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathbf{w} = \\{\\mathbf{w}_i\\}_{i=0}^s" + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_t" + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathbf{V}_t" + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "text", + "content": " represent the " + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "text", + "content": "-th features in the audio and visual speeches, and " + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathbf{w}_i" + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "text", + "content": " represents the " + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "text", + "content": "-th word in the target language translation with a total length of " + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "text", + "content": ". Note that, we stack 4 adjacent acoustic frames together forSyncing with visual speech, both with " + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 447, + 545, + 581 + ], + "type": "text", + "content": " frames." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 587, + 373, + 599 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 587, + 373, + 599 + ], + "spans": [ + { + "bbox": [ + 306, + 587, + 373, + 599 + ], + "type": "text", + "content": "3.2. Overview" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "content": "We propose a cross-modal self-learning framework for visual speech translation with audio speech regularization, named MixSpeech, as illustrated in Figure 2. This model consists of three modules - a feature extractor for extracting speech embeddings, a speech encoder for attending to the contextual dependencies of speech, and a target language-oriented translation decoder. We utilize the pre-trained feature extractor (AV-Encoder) and speech encoder (Speech-Encoder) from the AV-Hubert [53]" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15737" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": "to extract speech representations from both audio and visual speech utterances. Additionally, a randomly initialized translation decoder (Trans-Decoder) is used to autoregressively decode the speech representation into the target language text. MixSpeech is a two-stage training process: 1) Pretraining the translation decoder with high-discrimination audio speech utterances to learn inter-lingual mapping relations between source language phonemes and target language text, as detailed in subsection 3.3. 2) Aligning visual speech with audio speech to transfer the inter-lingual mapping from audio speech to visual in 3.5. The mixed speech 3.4 is synthesized by interpolating audio speech with visual speech in MixupSpeech, bridging the modality gap and enhancing knowledge transfer." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 249, + 214, + 262 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 249, + 214, + 262 + ], + "spans": [ + { + "bbox": [ + 47, + 249, + 214, + 262 + ], + "type": "text", + "content": "3.3. Pretraining with Audio Speech" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 268, + 287, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 268, + 287, + 316 + ], + "spans": [ + { + "bbox": [ + 47, + 268, + 287, + 316 + ], + "type": "text", + "content": "For uni-modality audio speech " + }, + { + "bbox": [ + 47, + 268, + 287, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{A} \\in \\mathbb{R}^{T \\times D}" + }, + { + "bbox": [ + 47, + 268, + 287, + 316 + ], + "type": "text", + "content": " or visual speech " + }, + { + "bbox": [ + 47, + 268, + 287, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{V} \\in \\mathbb{R}^{T \\times D}" + }, + { + "bbox": [ + 47, + 268, + 287, + 316 + ], + "type": "text", + "content": ", the uni-modality audio-visual feature " + }, + { + "bbox": [ + 47, + 268, + 287, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{e}^u = \\{\\mathbf{e}_t^u\\}_{t=1}^T \\in \\mathbb{R}^{T \\times 2D}" + }, + { + "bbox": [ + 47, + 268, + 287, + 316 + ], + "type": "text", + "content": " fed into feature extractor can be defined as:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 80, + 328, + 287, + 360 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 328, + 287, + 360 + ], + "spans": [ + { + "bbox": [ + 80, + 328, + 287, + 360 + ], + "type": "interline_equation", + "content": "\\mathbf {e} _ {t} ^ {u} = \\left\\{ \\begin{array}{l l} \\operatorname {c o n c a t} \\left(\\mathbf {0} _ {D}, \\mathbf {V} _ {t}\\right), & \\mathbf {V} _ {t} \\neq \\text {N o n e}, \\\\ \\operatorname {c o n c a t} \\left(\\mathbf {A} _ {t}, \\mathbf {0} _ {D}\\right), & \\mathbf {A} _ {t} \\neq \\text {N o n e}, \\end{array} \\right. \\tag {1}", + "image_path": "27b9acd83c16e3674906b33e1d045b16ab3573c7c35b7e511b31412a2d592e61.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "spans": [ + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "inline_equation", + "content": "\\mathbf{0}_D" + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "content": " denotes the feature of missing modality, following the practice of [53]. And then, we obtain the audiovisual fusion feature " + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "inline_equation", + "content": "\\mathbf{e}^f\\in \\mathbb{R}^{T\\times D}" + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "content": " with AV-Encoder. The transformer-based Speech-Encoder allows us to obtain the phoneme embedding " + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "inline_equation", + "content": "\\mathbf{e}^p\\in \\mathbb{R}^{T\\times D}" + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "content": " with the contextual speech details. A target language oriented translation decoder Trans-Decoder is appended to autoregressively decode the phoneme embedding " + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "inline_equation", + "content": "\\mathbf{e}^p" + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "content": " into the target probabilities " + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "inline_equation", + "content": "P^u" + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "inline_equation", + "content": "P^u = \\{P_t^u\\}_{t = 1}^S = \\{p(\\mathbf{w}_t|\\{\\mathbf{w}_i\\}_{i = 1}^{t - 1},\\mathbf{e}^p)\\}_{t = 1}^S" + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "content": " represents the probability of the " + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "content": "-th word being " + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "inline_equation", + "content": "\\mathbf{w}_t" + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "content": " when the previous " + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "inline_equation", + "content": "t - 1" + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "content": " predictions are " + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{w}_i\\}_{i = 1}^{t - 1}" + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 366, + 289, + 532 + ], + "type": "text", + "content": " is the length of the target language translation. During the pretraining, the overall model is trained on audio speech with cross-entropy loss:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 92, + 533, + 287, + 566 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 92, + 533, + 287, + 566 + ], + "spans": [ + { + "bbox": [ + 92, + 533, + 287, + 566 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {C E} = - \\sum_ {t = 1} ^ {S} \\log p \\left(w _ {t} \\mid \\left\\{w _ {i} \\right\\} _ {i = 1} ^ {t - 1}, \\mathbf {e} ^ {p}\\right). \\tag {2}", + "image_path": "95f12d1d9aef1c241699b338ab4f5c773961fa0650425e6f5702d6bbf2c7f11f.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 574, + 204, + 588 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 574, + 204, + 588 + ], + "spans": [ + { + "bbox": [ + 47, + 574, + 204, + 588 + ], + "type": "text", + "content": "3.4. Audio-Visual Speech Mixing" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": "Audio and visual speeches have a huge modality gap, which greatly impacts knowledge transfer across modalities. We attempt to employ mixed speech to bridge two different modalities of speech. Since the pair of audio and visual speeches is strictly temporally synchronous, we take advantage of this property to interpolate the mixed speech. For a pair of synchronized audio and video speech " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "(\\mathbf{A},\\mathbf{V})\\in \\mathbb{R}^{2\\times T\\times D}" + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": ", each visual feature " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{V}_t" + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": "-th frame has its corresponding audio feature " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_t" + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": ", representing the same phonetic content. We interpolate with probability " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\phi" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 71, + 547, + 97 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 71, + 547, + 97 + ], + "spans": [ + { + "bbox": [ + 305, + 71, + 547, + 97 + ], + "type": "text", + "content": "to obtain a mixed speech " + }, + { + "bbox": [ + 305, + 71, + 547, + 97 + ], + "type": "inline_equation", + "content": "\\mathbf{e}^m = \\{\\mathbf{e}_t^m\\}_{t=1}^T \\in \\mathbb{R}^{T \\times 2D}" + }, + { + "bbox": [ + 305, + 71, + 547, + 97 + ], + "type": "text", + "content": " derived partly from audio speech and partly from visual speech:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 349, + 105, + 545, + 137 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 349, + 105, + 545, + 137 + ], + "spans": [ + { + "bbox": [ + 349, + 105, + 545, + 137 + ], + "type": "interline_equation", + "content": "\\mathbf {e} _ {t} ^ {m} = \\left\\{ \\begin{array}{l l} \\operatorname {c o n c a t} \\left(\\mathbf {0} _ {D}, \\mathbf {V} _ {t}\\right), & p < \\phi , \\\\ \\operatorname {c o n c a t} \\left(\\mathbf {A} _ {t}, \\mathbf {0} _ {D}\\right), & p \\geq \\phi , \\end{array} \\right. \\tag {3}", + "image_path": "24a19493855e4d54e957f658201078025b5d113ca4166df7e14da3dbbfcb8f30.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 140, + 547, + 225 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 140, + 547, + 225 + ], + "spans": [ + { + "bbox": [ + 304, + 140, + 547, + 225 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 140, + 547, + 225 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 140, + 547, + 225 + ], + "type": "text", + "content": " is sampled from the uniform distribution " + }, + { + "bbox": [ + 304, + 140, + 547, + 225 + ], + "type": "inline_equation", + "content": "U(0,1)" + }, + { + "bbox": [ + 304, + 140, + 547, + 225 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 140, + 547, + 225 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 304, + 140, + 547, + 225 + ], + "type": "text", + "content": " is the ratio of speech mixing. In particular, we propose a curriculum learning [7] based mixing ratio adjustment method that adapts the appropriate " + }, + { + "bbox": [ + 304, + 140, + 547, + 225 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 304, + 140, + 547, + 225 + ], + "type": "text", + "content": " as the training progresses. The prediction uncertainty [43] indicates the confidence of the prediction (smaller is better), and we take it as a signal to adjust the mixing ratio:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 369, + 232, + 545, + 265 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 369, + 232, + 545, + 265 + ], + "spans": [ + { + "bbox": [ + 369, + 232, + 545, + 265 + ], + "type": "interline_equation", + "content": "\\mathbf {u} = \\frac {1}{S} \\sum_ {t = 1} ^ {S} \\operatorname {E n t r o p y} \\left(P _ {t}\\right). \\tag {4}", + "image_path": "fd5031b79ce6e57e5e540bf45a8a532819d45f7dd3c371e8b9ea9a68827ffad2.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "spans": [ + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "text", + "content": "If the discrimination of mixed speech is insufficient to regularize visual speech translation and maintain " + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "text", + "content": " steps " + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "inline_equation", + "content": "(\\Delta \\mathbf{u} = \\mathbf{u}^v - \\mathbf{u}^m < k\\mathbf{u}^v" + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "inline_equation", + "content": "\\mathbf{u}^v" + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "inline_equation", + "content": "\\mathbf{u}^m" + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "text", + "content": " represent the uncertainty of uni-modality (visual) and mixed speech, respectively, and the threshold hyperparameter " + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "text", + "content": " is set to 0.05 with " + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "text", + "content": " set to 20 in our work), we gradually increase the proportion of audio at a rate of " + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "inline_equation", + "content": "(\\phi' = \\alpha \\phi)" + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "text", + "content": ". We initialize " + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "inline_equation", + "content": "\\phi = 0.1" + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "text", + "content": " to prevent excessive initial modality gap and maintain " + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "inline_equation", + "content": "\\phi \\in [0.1, 0.9]" + }, + { + "bbox": [ + 304, + 270, + 545, + 380 + ], + "type": "text", + "content": " throughout the training process." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 385, + 521, + 399 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 385, + 521, + 399 + ], + "spans": [ + { + "bbox": [ + 306, + 385, + 521, + 399 + ], + "type": "text", + "content": "3.5. Cross-Modality Self-Learning for Speech" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "text", + "content": "Since audio speech is more distinguished compared to visual speech, we intend to boost visual speech translation with the knowledge from audio speech. And the mixed speech bridges the gap between audio speech and visual speech, allowing us to boost cross-modality knowledge transfer with it. With audio speech feature " + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "inline_equation", + "content": "\\mathbf{A} \\in \\mathbb{R}^{T \\times D}" + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "text", + "content": " and visual speech feature " + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "inline_equation", + "content": "\\mathbf{V} \\in \\mathbb{R}^{T \\times D}" + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "text", + "content": " fed into the modules with shared parameters, the uni-modality visual speech feature " + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "inline_equation", + "content": "\\mathbf{e}^u" + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "text", + "content": " and the mixed speech feature " + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "inline_equation", + "content": "\\mathbf{e}^m" + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "text", + "content": " are decoded into the target probabilities " + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "inline_equation", + "content": "P^u" + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "inline_equation", + "content": "P^m" + }, + { + "bbox": [ + 304, + 403, + 545, + 523 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 523, + 545, + 583 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 523, + 545, + 583 + ], + "spans": [ + { + "bbox": [ + 304, + 523, + 545, + 583 + ], + "type": "text", + "content": "After the pre-training with audio speech translation, the model is promising enough for mixed speech containing partial audio speech, we adopt the Jensen-Shannon Divergence (JSD) [41] to regularize the probabilities of these two different speeches:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 364, + 590, + 545, + 623 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 364, + 590, + 545, + 623 + ], + "spans": [ + { + "bbox": [ + 364, + 590, + 545, + 623 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {J S D} = \\sum_ {t = 1} ^ {S} J S D \\left(P _ {t} ^ {m} \\| P _ {t} ^ {u}\\right). \\tag {5}", + "image_path": "67f67133344d08b121ba8ee29b62ab8ff795c6d1bfa82a5b7d86928b0a968313.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "As this probability is across the entire training vocabulary, we are able to perform fine-grained regularization to enhance the training of visual speech. Meanwhile, we also minimize the cross-entropy loss between two speech translations and the real translation, " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L} = \\mathcal{L}_{CE}^{uni} + \\lambda_1\\mathcal{L}_{CE}^{mix} + \\lambda_2\\mathcal{L}_{JSD}" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{1}" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{2}" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " are hyperparameters of loss weights, while " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{1} = \\lambda_{2} = 1.0" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": " in this work." + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15738" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 62, + 70, + 534, + 213 + ], + "blocks": [ + { + "bbox": [ + 62, + 70, + 534, + 213 + ], + "lines": [ + { + "bbox": [ + 62, + 70, + 534, + 213 + ], + "spans": [ + { + "bbox": [ + 62, + 70, + 534, + 213 + ], + "type": "table", + "html": "
DatasetTarget Language Hours# Lang# Σ Hrs# Σ Sents# Σ Tokens
EnEsFrItPtsrctgt
Audio-Only
LibriSpeech [45]960h----1960h180K5.9M5.9M
MuST-C [16]-504h492h465h385h83617h2016K38.1M35.8M
VoxPopuli [62]543h441h427h461h-165967h2045K65.0M60.1M
Audio-Visual
LRS2 [1]224h----1224h143K2.3M2.3M
LRS3 [2]433h----1433h151K4.2M4.2M
AVMuST-TED (ours)-198h185h165h158h4706h925K7.3M7.0M
", + "image_path": "3415b3308ea40d81f36e48b816e15ac5327af73368106f3dc1c03212b707402d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 262, + 128, + 276 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 262, + 128, + 276 + ], + "spans": [ + { + "bbox": [ + 47, + 262, + 128, + 276 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 283, + 111, + 295 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 283, + 111, + 295 + ], + "spans": [ + { + "bbox": [ + 47, + 283, + 111, + 295 + ], + "type": "text", + "content": "4.1. Datasets" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 303, + 288, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 303, + 288, + 507 + ], + "spans": [ + { + "bbox": [ + 46, + 303, + 288, + 507 + ], + "type": "text", + "content": "AVMuST-TED. To obtain a corpus for AVST, we screened a set of TED and TEDx talks with multilingual subtitles as the data source. All transcriptions and translations are performed strictly following the TED Translation Guidelines and require collaboration between at least one translator (or transcriber) and one reviewer. The prior lip-reading dataset acquisition pipeline is followed to crop face-tracks, and an audio-visual alignment network, SyncNet, is adopted for speaker proofreading. Table 1 compares AVMuST-TED with related datasets, and it is the first audio-visual speech translation dataset containing translations from English (En) to four target languages: Spanish (Es), French (Fr), Italian (It), and Portuguese (Pt). These four languages have the most translated subtitles in TED, and 1024/1536 pieces of data are randomly sampled for each language as the test/validation set. The information about AVMuST-TED is detailed in Appendix A." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 508, + 287, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 508, + 287, + 674 + ], + "spans": [ + { + "bbox": [ + 46, + 508, + 287, + 674 + ], + "type": "text", + "content": "LRS2&3 [1, 2], two commonly used publicly available English wild audio-visual speech recognition datasets, are adopted to demonstrate the lip-reading performance, containing 224 hours of video from BBC television shows and 433 hours of video from TED and TEDx talks. The training data in both datasets is divided into two partitions, namely Pretrain and Train, both of which are transcribed from videos to text at the sentence level. The only difference is that the video clips in the Pretrain partition are not strictly trimmed and sometimes longer than the corresponding text. In our experiments, we employ different amounts of training data from LRS2 and LRS3, including Pretrain+Train (224/433h) for high resource and Train (29/30h) for low resource." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": "CMLR [70], widely used dataset for Mandarin audio-visual speech recognition, contains 61 hours audio-visual speech utterances collected from Chinese TV stations. In" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 306, + 260, + 547, + 364 + ], + "blocks": [ + { + "bbox": [ + 46, + 220, + 546, + 245 + ], + "lines": [ + { + "bbox": [ + 46, + 220, + 546, + 245 + ], + "spans": [ + { + "bbox": [ + 46, + 220, + 546, + 245 + ], + "type": "text", + "content": "Table 1. Comparison of audio-visual speech recognition/translation datasets. #Lang denotes the number of target languages. #∑Hrs denotes the overall duration of speech in the dataset, #Sents and #Tokens denote the overall sentences and the overall token, respectively." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 306, + 260, + 547, + 364 + ], + "lines": [ + { + "bbox": [ + 306, + 260, + 547, + 364 + ], + "spans": [ + { + "bbox": [ + 306, + 260, + 547, + 364 + ], + "type": "table", + "html": "
MethodMBLEU↑
En-EsEn-FrEn-ItEn-Pt
CascadedV12.711.311.513.2
AV-Hubert [53]V14.212.612.914.8
CascadedA(+Noise)16.012.912.615.5
AV-Hubert [53]A(+Noise)17.614.514.117.1
MixSpeech(ours)V18.515.114.317.2
", + "image_path": "238ae6de05da00bb08371960db027898b0fe1e7da86a50365ee01572a50ed247.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 370, + 546, + 415 + ], + "lines": [ + { + "bbox": [ + 305, + 370, + 546, + 415 + ], + "spans": [ + { + "bbox": [ + 305, + 370, + 546, + 415 + ], + "type": "text", + "content": "Table 2. Comparison of the performances of visual speech translation on AVMuST-TED with those of the noisy audio speech translation. The results of noisy audio speech translation are the mean value at five SNRs " + }, + { + "bbox": [ + 305, + 370, + 546, + 415 + ], + "type": "inline_equation", + "content": "\\{-20, -10, 0, 10, 20\\}" + }, + { + "bbox": [ + 305, + 370, + 546, + 415 + ], + "type": "text", + "content": " db." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 434, + 545, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 434, + 545, + 495 + ], + "spans": [ + { + "bbox": [ + 304, + 434, + 545, + 495 + ], + "type": "text", + "content": "our experiments, we adopt this dataset to demonstrate the performance of our proposed MixSpeech in low-resource languages such as Mandarin. Additionally, we sample a training set containing only 12 hours of utterances in the manner of [71] for low resource scenario." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 502, + 514, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 502, + 514, + 514 + ], + "spans": [ + { + "bbox": [ + 305, + 502, + 514, + 514 + ], + "type": "text", + "content": "4.2. Evaluation and Implementation Details" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 520, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 520, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 520, + 545, + 653 + ], + "type": "text", + "content": "In this paper, we measure the performance of MixSpeech on two speech tasks, speech recognition and speech translation. For speech recognition, word error rate (WER) is adopted as the evaluation metric, which is defined as " + }, + { + "bbox": [ + 304, + 520, + 545, + 653 + ], + "type": "inline_equation", + "content": "\\mathrm{WER} = (S + D + I) / M" + }, + { + "bbox": [ + 304, + 520, + 545, + 653 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 520, + 545, + 653 + ], + "type": "inline_equation", + "content": "S, D, I, M" + }, + { + "bbox": [ + 304, + 520, + 545, + 653 + ], + "type": "text", + "content": " represent the number of words replaced, deleted, inserted, and referenced. As for speech translation, the case-sensitive detokenized BLEU score is computed using SACREBLEU [46], following the same evaluation methodology as in previous speech translation works [16, 62]. The implementation details are provided in Appendix B due to page limitations." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 659, + 494, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 659, + 494, + 672 + ], + "spans": [ + { + "bbox": [ + 305, + 659, + 494, + 672 + ], + "type": "text", + "content": "4.3. Performance of Speech Translation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 677, + 546, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 546, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 546, + 715 + ], + "type": "text", + "content": "End-To-End Models VS. Cascaded Models. Table 2 presents a comparison of the lip translation performance between two representative methods: 1) an end-to-end model," + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "15739" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": "implemented based on the state-of-the-art AV-Hubert [53] method for visual speech-related tasks, and 2) a cascaded model, combining a speech recognition model (i.e., Lip-Reading or ASR) with a machine translation model. In the cascaded model, we use the speech recognition model trained by AV-Hubert on LRS3, which achieve the best lip-reading performance to date, and a transformer-based machine translation model trained on the paired translated text corpus in AVMuST-TED. Comparing the lip translation performance of the end-to-end model and the cascade model, we find that the BLEU score of the end-to-end model improved by " + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "inline_equation", + "content": "+1.3" + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "inline_equation", + "content": "+1.6" + }, + { + "bbox": [ + 46, + 72, + 289, + 263 + ], + "type": "text", + "content": ". This result demonstrates that the end-to-end trained model can effectively prevent the accumulation of errors caused by the model cascade, and that lip translation cannot be simply disassembled as the superposition of lip reading and machine translation." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 266, + 289, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 266, + 289, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 266, + 289, + 495 + ], + "type": "text", + "content": "MixSpeech VS. Prior Methods. Due to the discrimination of speech between modalities, visual speech models are not able to translate speech content as accurately as audio speech models. To address the issue of low discrimination in visual speech, we propose MixSpeech, which is a cross-modality self-learning framework that employs mixed speech to transfer knowledge obtained from audio speech pre-training into the visual speech model. Our proposed MixSpeech significantly improves the BLEU score by another " + }, + { + "bbox": [ + 46, + 266, + 289, + 495 + ], + "type": "inline_equation", + "content": "+1.4" + }, + { + "bbox": [ + 46, + 266, + 289, + 495 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 266, + 289, + 495 + ], + "type": "inline_equation", + "content": "+4.3" + }, + { + "bbox": [ + 46, + 266, + 289, + 495 + ], + "type": "text", + "content": ". Furthermore, the improvement from MixSpeech is related to the discrepancy in speech translation between audio and visual modalities. For example, En-Es exhibits a larger discrepancy of 14.7 between audio and visual speech translation, ranging from 28.9 to 14.2, and MixSpeech significantly improves it by " + }, + { + "bbox": [ + 46, + 266, + 289, + 495 + ], + "type": "inline_equation", + "content": "+4.3" + }, + { + "bbox": [ + 46, + 266, + 289, + 495 + ], + "type": "text", + "content": ". Conversely, Italian shows a smaller discrepancy of 10.9, ranging from 23.8 to 12.9, and improves only by " + }, + { + "bbox": [ + 46, + 266, + 289, + 495 + ], + "type": "inline_equation", + "content": "+1.4" + }, + { + "bbox": [ + 46, + 266, + 289, + 495 + ], + "type": "text", + "content": ". This highlights that the improvement in lip translation stems from the knowledge acquired from audio speech translation." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 498, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 289, + 715 + ], + "type": "text", + "content": "Visual Speech VS. Noisy Audio Speech. We also evaluate the performance of audio speech translation in noisy environments, by adding noise sampled from MUSAN [55] to the audio speech and measuring the performance at five SNR levels " + }, + { + "bbox": [ + 46, + 498, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\{-20, -10, 0, 10, 20\\}" + }, + { + "bbox": [ + 46, + 498, + 289, + 715 + ], + "type": "text", + "content": " db. We compare the average BLEU scores of different SNRs and present the detailed performance in Appendix C.1. Our experiments show that although noisy audio speech performs better than visual speech, the translation performance is still significantly lower compared to noiseless audio speech. In contrast, MixSpeech, which fully leverages the knowledge of audio speech, greatly improves the visual speech translation performance, making it more reliable in noisy scenes. We also provide a comparison of translation with audio speech and audio-visual speech, demonstrating that visual speech enhances the ceiling and robustness of speech translation, but the details are only available in the Appendix C.1 since audio-visual speech does not require the cross-modality" + } + ] + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 307, + 71, + 547, + 286 + ], + "blocks": [ + { + "bbox": [ + 307, + 71, + 547, + 286 + ], + "lines": [ + { + "bbox": [ + 307, + 71, + 547, + 286 + ], + "spans": [ + { + "bbox": [ + 307, + 71, + 547, + 286 + ], + "type": "table", + "html": "
# RESMethodWER(Labeled Visual Utts Hrs) ↓
CMLRLRS2LRS3
HighWAS [56]38.9(61)70.4(224)-
TM-seq2seq [1]-49.8(698)59.9(698)
CSSMCM [70]32.5(61)--
Conv-seq2seq [69]-51.7(698)60.1(698)
CTC+KD [3]-51.3(224)58.9(433)
LIBS [71]31.3(61)65.3(698)-
CTCH [40]22.0(61)--
Master [50]-49.2(698)59.0(698)
Sub-Word [47]-28.9(698)40.6(698)
†AV-Hubert [53]12.7(61)28.7(224)28.6(433)
MixSpeech(ours)11.1(61)25.5(224)28.0(433)
LowLIBS [71]50.5(12)--
†AV-Hubert [53]25.8(12)31.4(29)32.5(30)
MixSpeech(ours)18.5(12)26.9(29)28.6(30)
", + "image_path": "bd5f9cb5cbe5560625d678642c6aab01064533c40b6a90584ba140136f0fd166.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 305, + 293, + 547, + 339 + ], + "lines": [ + { + "bbox": [ + 305, + 293, + 547, + 339 + ], + "spans": [ + { + "bbox": [ + 305, + 293, + 547, + 339 + ], + "type": "text", + "content": "Table 3. Comparison of lip reading methods under different resource conditions. # RES represents the amount of resources. (Hours) highlighted in blue are used for low resources. † For better comparison, we reproduce AV-Hubert on CMLR and LRS2." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 360, + 479, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 360, + 479, + 373 + ], + "spans": [ + { + "bbox": [ + 306, + 360, + 479, + 373 + ], + "type": "text", + "content": "knowledge transfer proposed in this paper." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 383, + 495, + 396 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 383, + 495, + 396 + ], + "spans": [ + { + "bbox": [ + 306, + 383, + 495, + 396 + ], + "type": "text", + "content": "4.4. Performance of Speech Recognition" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 403, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 547, + 715 + ], + "type": "text", + "content": "As shown in Table 3, we compare the performance of MixSpeech on another visual speech task, lip reading (i.e., Visual Speech Recognition), to highlight the mixspeech from more perspectives. MixSpeech obtain state-of-the-art performance on three datasets, two for English (25.5% on LRS2 and 28.0% on LRS3) and one for Chinese (11.1% on CMLR), demonstrating that this cross-modality self-learning framework can be applied for different languages to capture the intrinsic association between audio and visual speeches and thus effectively improve the understanding of visual speech. Since visual speech is relatively low-resource, we verify whether MixSpeech can effectively improve the performance of visual speech tasks in low-resource with audio speech. Compared with previous methods, MixSpeech boosts the WER of lip-reading by -3.9% to -7.3%, highlighting the critical role of high-resource audio speech in low-resource visual speech tasks. Specifically, on LRS2 and LRS3, the performance of Mixspeech in the low-resource scenario (26.9%/28.6% WER obtained with only 29h/30h visual utterances) outperforms the performances of prior methods in the high-resource scenario (28.7%/28.6% obtained with 224h/433h or even more visual utterances). Even though with only limited labeled visual corpus, our proposed MixSpeech performs no less than works with more. It is the bridge between two modalities of speech, which helps visual speech to access the knowl" + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "15740" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "type": "text", + "content": "edge stored in high-resource and high-discrimination audio speech without barriers." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 103, + 286, + 117 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 103, + 286, + 117 + ], + "spans": [ + { + "bbox": [ + 47, + 103, + 286, + 117 + ], + "type": "text", + "content": "4.5. Can MixSpeech bridge cross-modality speech?" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 122, + 287, + 158 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 122, + 287, + 158 + ], + "spans": [ + { + "bbox": [ + 46, + 122, + 287, + 158 + ], + "type": "text", + "content": "Our proposed MixSpeech builds a bridge between cross-modality speech through cross-modality self-learning, with the properly mixes speech. The details are as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 159, + 287, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 159, + 287, + 337 + ], + "spans": [ + { + "bbox": [ + 46, + 159, + 287, + 337 + ], + "type": "text", + "content": "Cross-Modality Self-Learning for Knowledge Transfer. The experiments in Figure 3 provide a positive answer to the question of whether MixSpeech can contribute to achieving knowledge transfer between audio and visual speeches. We evaluate the performance of visual speech translation with different regularization strategies: no audio speech regularization (i.e., " + }, + { + "bbox": [ + 46, + 159, + 287, + 337 + ], + "type": "inline_equation", + "content": "\\phi = 0" + }, + { + "bbox": [ + 46, + 159, + 287, + 337 + ], + "type": "text", + "content": "), mixed speech regularization with different mixing ratios (i.e., " + }, + { + "bbox": [ + 46, + 159, + 287, + 337 + ], + "type": "inline_equation", + "content": "\\phi \\in (0,1)" + }, + { + "bbox": [ + 46, + 159, + 287, + 337 + ], + "type": "text", + "content": ", audio speech regularization (i.e., " + }, + { + "bbox": [ + 46, + 159, + 287, + 337 + ], + "type": "inline_equation", + "content": "\\phi = 1" + }, + { + "bbox": [ + 46, + 159, + 287, + 337 + ], + "type": "text", + "content": "), and mixing ratio adjustable mixed speech regularization (i.e., dashed lines). It is evident that the cross-modality self-learning framework significantly enhances visual speech translation, as all performances with audio speech regularization are noticeably better than those without self-learning (" + }, + { + "bbox": [ + 46, + 159, + 287, + 337 + ], + "type": "inline_equation", + "content": "\\phi = 0" + }, + { + "bbox": [ + 46, + 159, + 287, + 337 + ], + "type": "text", + "content": "), demonstrating the effectiveness of our proposed MixSpeech." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 338, + 287, + 458 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 338, + 287, + 458 + ], + "spans": [ + { + "bbox": [ + 46, + 338, + 287, + 458 + ], + "type": "text", + "content": "Narrow the Cross-Modality Distance with Properly Mixed Speech. Moreover, the introduction of mixed speech facilitates smoother cross-modality knowledge transfer by narrowing the modality gap between speeches. Some segments in the mixed speech come from the visual speech, making it much closer to visual speech in terms of modality distance than audio speech. When regularizing with mixed speech in En-Es, the translation performance of visual speech improves further by " + }, + { + "bbox": [ + 46, + 338, + 287, + 458 + ], + "type": "inline_equation", + "content": "+0.3" + }, + { + "bbox": [ + 46, + 338, + 287, + 458 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 338, + 287, + 458 + ], + "type": "inline_equation", + "content": "+0.8" + }, + { + "bbox": [ + 46, + 338, + 287, + 458 + ], + "type": "text", + "content": " compared to audio speech regularization alone. Among them, bootstrap" + } + ] + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 50, + 475, + 284, + 653 + ], + "blocks": [ + { + "bbox": [ + 50, + 475, + 284, + 653 + ], + "lines": [ + { + "bbox": [ + 50, + 475, + 284, + 653 + ], + "spans": [ + { + "bbox": [ + 50, + 475, + 284, + 653 + ], + "type": "image", + "image_path": "c9e977e77f4aa403e23c47c220b00ee197026506ec91d8c1244467fe37b10735.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 656, + 287, + 712 + ], + "lines": [ + { + "bbox": [ + 46, + 656, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 656, + 287, + 712 + ], + "type": "text", + "content": "Figure 3. BLEU scores of MixSpeech with different speech regularization on En-Es and En-Fr. " + }, + { + "bbox": [ + 46, + 656, + 287, + 712 + ], + "type": "inline_equation", + "content": "\\phi = 0" + }, + { + "bbox": [ + 46, + 656, + 287, + 712 + ], + "type": "text", + "content": ": no audio speech regularization, " + }, + { + "bbox": [ + 46, + 656, + 287, + 712 + ], + "type": "inline_equation", + "content": "\\phi \\in (0,1)" + }, + { + "bbox": [ + 46, + 656, + 287, + 712 + ], + "type": "text", + "content": ": mixed speech regularization, " + }, + { + "bbox": [ + 46, + 656, + 287, + 712 + ], + "type": "inline_equation", + "content": "\\phi = 1" + }, + { + "bbox": [ + 46, + 656, + 287, + 712 + ], + "type": "text", + "content": ": only audio speech regularization. The dashed lines represent the adjustable mixing ratio strategy based on curriculum learning." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": "ping with mixed speech of mixing ratio " + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "inline_equation", + "content": "\\phi = 0.5" + }, + { + "bbox": [ + 304, + 72, + 545, + 204 + ], + "type": "text", + "content": " achieves the highest BLEU score of 18.3. This demonstrates that a reasonably mixed ratio ensures that it is neither overly biased towards visual speech, leading to a lack of knowledge of audio speech, nor overly biased towards audio speech, leading to excessive cross-modality distances that affect knowledge transfer. The adjustable mixing ratio strategy based on curriculum learning further increases the applicability of mixed speech to cross-modality self-learning training, thereby boosting visual speech translation performance again." + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 312, + 212, + 539, + 301 + ], + "blocks": [ + { + "bbox": [ + 312, + 212, + 539, + 301 + ], + "lines": [ + { + "bbox": [ + 312, + 212, + 539, + 301 + ], + "spans": [ + { + "bbox": [ + 312, + 212, + 539, + 301 + ], + "type": "table", + "html": "
IDMethodBLEU ↑
LmonCELmixCELJSDEn-EsEn-FrEn-ItEn-Pt
#1✓14.212.612.914.8
#2✓✓17.514.313.616.5
#3✓✓18.114.814.116.9
#4✓✓✓18.515.114.317.2
", + "image_path": "b7eb1ca96eaf58088cecc6bd974db06ec46ec1344d35972b75101ad9dfc02ff8.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 309, + 539, + 321 + ], + "lines": [ + { + "bbox": [ + 306, + 309, + 539, + 321 + ], + "spans": [ + { + "bbox": [ + 306, + 309, + 539, + 321 + ], + "type": "text", + "content": "Table 4. BLEU of different module combinations in MixSpeech." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 336, + 541, + 350 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 336, + 541, + 350 + ], + "spans": [ + { + "bbox": [ + 306, + 336, + 541, + 350 + ], + "type": "text", + "content": "4.6. What role does each part play in MixSpeech?" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 354, + 545, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 354, + 545, + 413 + ], + "spans": [ + { + "bbox": [ + 304, + 354, + 545, + 413 + ], + "type": "text", + "content": "The effectiveness of MixSpeech, which is a cross-modality self-learning framework designed to improve visual translation performance, has been demonstrated. In this study, we investigate the role of each component in detail and present relevant experiments in Table 4:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "type": "text", + "content": "Bridging the cross-modality gaps. We observe a significant improvement in the lip translation performance with the inclusion of " + }, + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{JSD}" + }, + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "type": "text", + "content": " (ID: #3, #4) for regularizing the probabilities of visual speech and mixed speech, compared to without (ID: #1, #2). Specifically, experiment #3 with " + }, + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{JSD}" + }, + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "type": "text", + "content": " outperform experiment #2 with " + }, + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{CE}^{mix}" + }, + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "type": "text", + "content": " by " + }, + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "type": "inline_equation", + "content": "+0.6" + }, + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "type": "text", + "content": " in lip translation performance on En-Es. This demonstrates that " + }, + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{JSD}" + }, + { + "bbox": [ + 304, + 415, + 545, + 545 + ], + "type": "text", + "content": " is the main contributor to achieving cross-modality knowledge transfer by building a bridge between the two speeches and performing fine-grained regularization across the probability of each word." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "text", + "content": "Maintaining knowledge of audio speech. It is also important to note that during the regularization process, the representation of audio speech is also affected by visual speech, which can interfere with the knowledge of audio speech and ultimately harm the lip translation performance of MixSpeech. As evidenced by experiment #2, the lip translation performance on En-Es decrease by -0.4 compared to experiment #3 when " + }, + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{CE}^{mix}" + }, + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "text", + "content": " is not applied. To address this issue, " + }, + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{CE}^{mix}" + }, + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "text", + "content": " is introduced to enhance the training ceiling of the cross-modality self-learning framework. By maintaining the translation performance of mixed speech and preventing the excessive disturbance to audio speech knowledge, " + }, + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{CE}^{mix}" + }, + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "text", + "content": " helps to improve the overall performance of MixSpeech." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15741" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 71, + 550, + 381 + ], + "blocks": [ + { + "bbox": [ + 47, + 71, + 550, + 381 + ], + "lines": [ + { + "bbox": [ + 47, + 71, + 550, + 381 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 550, + 381 + ], + "type": "table", + "html": "
En-EsTranscription: and always as a child I had this fantasy that somebody would come and rescue me\nMixSpeech: and always as a child I had this fantasy that somebody would come and rescue me
Ground Truth: y de niña siempre tenía la fantasía de que alguien vendrá a salvar me de\nMixSpeech: y de (desde) niña niño siempre tenía la esta fantasía de que alguien vendrá a salvar me (rescató) de
En-FrTranscription: and solutions create new problems which have to be solved in their turn\nMixSpeech: and solutions to create new problems which have to be solved in their turn this year
Ground Truth: et les solutions créent de nouveaux problèmes devant être résolus à leur tour\nMixSpeech: et les (des) solutions pour creer de nouveaux problèmes devant qui doivent être résolus à leur tour
En-ItTranscription: one of the last 10,000 years, and the other certainly of the last 25 years\nMixSpeech: one of the last 10,000 years and the other certainly assistancee of the last 25 years
Ground Truth: uno presente negli ultimi diecimila anni e l'alto certamente negli ultimi 25 anni\nMixSpeech: uno presente negli ultimi diecimila (10000) anni e l'alto certamente negli ultimi 25 anni
En-PtTranscription: has around 2,000 people descending on MIT's campus\nMixSpeech: has around 2,000 people descending on MIT's campus
Ground Truth: congregamerca de 2000 pessoas no campus do mit\nMixSpeech: congregam de circa de 2000 pessoas a estudar no campus do mit
", + "image_path": "29845b784ea69738221c57fbdadb394d9accb123fcee2958b33841140671eac9.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 387, + 546, + 410 + ], + "lines": [ + { + "bbox": [ + 46, + 387, + 546, + 410 + ], + "spans": [ + { + "bbox": [ + 46, + 387, + 546, + 410 + ], + "type": "text", + "content": "Table 5. Qualitative performance of Visual Speech Recognition and Translation on AVMuST-TED. Red Strikeout Words: mistranslated words with opposite meaning, (Blue Words in parentheses): mistranslated words with similar meaning, Gray Words: the absent words." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 429, + 156, + 441 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 429, + 156, + 441 + ], + "spans": [ + { + "bbox": [ + 47, + 429, + 156, + 441 + ], + "type": "text", + "content": "4.7. Qualitative results" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "type": "text", + "content": "We present several examples of lip translation in Table 5 to qualitatively evaluate the translation quality of MixSpeech. The translation results are very close to the ground truth, and the semantics are consistent. We observe two types of words that differ in translation: synonyms and context-sensitive translations. Synonyms that have different spellings but the same meaning, such as salvar and rescató in Spanish, both meaning 'rescue', and diecimila and 10000 in Italian, both meaning 'ten thousand', are commonly found in translation tasks and can affect translation consistency. Additionally, there are translations that require context information, such as when the speaker refers to themselves as a child, and the translation in Spanish needs to take into account the speaker's gender to choose between niña for girl' or Niño for boy' and 'child'. The qualitative translation results of MixSpeech demonstrate its capability to achieve reliable cross-lingua lip translation. In Appendix C.2, we also provide translation results of noisy audio speech translation with visual speech translation and audio speech translation with audiovisual speech translation to highlight the importance of visual speech in speech translation." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 306, + 428, + 378, + 441 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 428, + 378, + 441 + ], + "spans": [ + { + "bbox": [ + 306, + 428, + 378, + 441 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 449, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 449, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 449, + 545, + 628 + ], + "type": "text", + "content": "With the advancement of online technologies, such as online healthcare and sales, language barriers often prevent these tools from reaching and benefiting disadvantaged areas. In light of this, we focus on visual speech, a branch of the speech stream, and aim to translate visual speech from source languages to other target languages for cross-linguistic communication, specifically through lip translation. We meticulously curate the AVMuST-TED dataset, consisting of 706 hours of speech clips with professional translations from TED, to facilitate cross-linguistic research on visual speech. We also introduce MixSpeech, a cross-modality self-learning framework that utilizes mixed speech to regularize visual speech translation and achieves state-of-the-art performance in lip translation on AVMuST-TED and lip reading on LRS2, LRS3, and CMLR datasets." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": "Moreover, our work on visual speech and AVMuSTED lay a solid foundation for further research on visual speech in cross-lingual fields. There are numerous related tasks with great potential for practical applications, such as Cross-Lingual Talking Head Generation [44]. These tasks hold immense promise for breaking down language barriers and promoting communication across diverse communities." + } + ] + } + ], + "index": 6 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15742" + } + ] + } + ], + "index": 7 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 72, + 149, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 72, + 149, + 85 + ], + "spans": [ + { + "bbox": [ + 48, + 72, + 149, + 85 + ], + "type": "text", + "content": "Acknowledgements" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 91, + 287, + 150 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 91, + 287, + 150 + ], + "spans": [ + { + "bbox": [ + 47, + 91, + 287, + 150 + ], + "type": "text", + "content": "This work was supported in part by National Key R&D Program of China under Grant No.2022ZD0162000, National Natural Science Foundation of China under Grant No.62222211, Grant No.61836002 and Grant No.62072397." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 48, + 161, + 105, + 173 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 161, + 105, + 173 + ], + "spans": [ + { + "bbox": [ + 48, + 161, + 105, + 173 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 48, + 180, + 287, + 712 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 180, + 287, + 224 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 180, + 287, + 224 + ], + "spans": [ + { + "bbox": [ + 53, + 180, + 287, + 224 + ], + "type": "text", + "content": "[1] Triantafyllos Afouras, Joon Son Chung, Andrew Senior, Oriol Vinyals, and Andrew Zisserman. 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In Proceedings of the AAAI Conference on Artificial Intelligence, volume 34, pages 6917-6924, 2020. 2, 5, 6" + } + ] + } + ], + "index": 18 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "15745" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/846dbe02-0b5b-4bf4-a391-96d12e988697_content_list.json b/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/846dbe02-0b5b-4bf4-a391-96d12e988697_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..411d412fc1808e2b4200e5cd48ab6d37b9006a46 --- /dev/null +++ b/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/846dbe02-0b5b-4bf4-a391-96d12e988697_content_list.json @@ -0,0 +1,1746 @@ +[ + { + "type": "text", + "text": "MixSynthFormer: A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation", + "text_level": 1, + "bbox": [ + 84, + 130, + 883, + 174 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yuran Sun, Alan William Dougherty, Zhuoying Zhang, Yi King Choi, Chuan Wu The University of Hong Kong", + "bbox": [ + 165, + 203, + 805, + 239 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "yuransun@connect.hku.hk,{alanwd,tinawork}@hku.hk,{ykchoi,cwu}@cs.hku.hk", + "bbox": [ + 171, + 241, + 795, + 257 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 291, + 313, + 306 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Human pose estimation in videos has wide-ranging practical applications across various fields, many of which require fast inference on resource-scarce devices, necessitating the development of efficient and accurate algorithms. Previous works have demonstrated the feasibility of exploiting motion continuity to conduct pose estimation using sparsely sampled frames with transformer-based models. However, these methods only consider the temporal relation while neglecting spatial attention, and the complexity of dot product self-attention calculations in transformers are quadratically proportional to the embedding size. To address these limitations, we propose MixSynthFormer, a transformer encoder-like model with MLP-based mixed synthetic attention. By mixing synthesized spatial and temporal attentions, our model incorporates inter-joint and inter-frame importance and can accurately estimate human poses in an entire video sequence from sparsely sampled frames. Additionally, the flexible design of our model makes it versatile for other motion synthesis tasks. Our extensive experiments on 2D/3D pose estimation, body mesh recovery, and motion prediction validate the effectiveness and efficiency of MixSynthFormer. The code is available at https://github.com/irenesesun/MixSynthFormer.git", + "bbox": [ + 75, + 325, + 473, + 688 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 722, + 209, + 738 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Human pose estimation is a crucial task in computer vision which aims to estimate the keypoint locations of a human body from visual inputs. It has a wide range of applications in virtual/augmented reality, healthcare, and security surveillance [23, 5]. In recent years, there has been a growing demand for real-time pose estimation in many of these applications. However, the computational burden of deep learning models makes their real-time estimation on resource-constrained devices (e.g., CPU, mobile devices) challenging. How to estimate human poses in videos ef", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e8bd756ea35c49dc38310397c312f3996facd74f6e24c1b8465e944151b606af.jpg", + "image_caption": [ + "(a) Feature-based Keyframe Selector" + ], + "image_footnote": [], + "bbox": [ + 517, + 290, + 877, + 340 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/63913df22c7377e0faec804750e093645a5dc651c436b520cf7faf4b3659db39.jpg", + "image_caption": [ + "(b) Sampling-based Keyframe Selector" + ], + "image_footnote": [], + "bbox": [ + 537, + 368, + 856, + 412 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/7521788d817b6f1540170364e75a89536f202e321c2d7eb40ddba898157e6dd7.jpg", + "image_caption": [ + "(c) Ours", + "Figure 1: Pipelines of keyframe-based pose estimation frameworks. The recover process is similar to interpolation. (a) is the feature-based pipeline [40, 7], which selects $30\\%$ to $40\\%$ of frames based on input features and recovers the whole sequence. (b) is the existing sampling-based pipeline [38], which uses a sampler to select frames and conducts keyframe refinement, whole sequence recovery and whole sequence refinement. (c) is our proposed simplified sampling-based pipeline excluding keyframe refinement." + ], + "image_footnote": [], + "bbox": [ + 557, + 435, + 836, + 479 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "frequently remains an open research problem.", + "bbox": [ + 500, + 628, + 790, + 643 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Conventional pose estimators [3, 22, 41, 29, 4, 37, 27] estimate poses frame-by-frame, and the efficiency depends on the model design. Recent methods [40, 7, 38] have proven the viability of estimating poses in sequences based solely on keyframes. By leveraging the temporal redundancy in videos, poses in the remaining frames can be reconstructed from keyframe poses, similar to motion completion, which can significantly reduce the cost of resource-intensive pose estimators.", + "bbox": [ + 496, + 643, + 893, + 777 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In current keyframe-based pose estimation frameworks, keyframes are selected using a feature-based selector or a sampler, as illustrated in Figures 1a and 1b. Feature-based keyframe selectors [40, 7] select \"good\" frames based on features extracted from inputs. The final poses in the whole sequence are recovered from the estimated poses in those frames without further refinements. A more effective approach is to sample a portion of frames directly from inputs", + "bbox": [ + 496, + 779, + 895, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "14884", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "[38]. Without knowing the quality of selected frames in advance, poses detected from them may be noisy. To tackle this issue, the current design employs a refine-recover-refine pipeline to obtain the final pose sequence.", + "bbox": [ + 76, + 90, + 467, + 151 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Is there a way to simplify the pipeline and further reduce the computational cost? The two refinement modules for keyframe poses and recovered poses appear repetitive and unnecessary, as the poses in keyframes are refined twice. To address this, we propose a simplified recover-refine pipeline, as shown in Figure 1c. Within our framework, keyframes are selected using a sampler, and the pose sequence is recovered from detected poses in keyframes using an interpolator. The rough sequence is then refined using a single refinement module.", + "bbox": [ + 75, + 152, + 467, + 303 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We present a novel framework for sampling-based pose estimation utilizing a lightweight transformer encoder-like structure. The scaled dot product self-attention mechanism in the transformer network [34] is used to determine the relative importance of a token with respect to other tokens. However, the computational cost can be prohibitively high when using a large embedding size. To mitigate this problem, we replace the standard key-query attention with a synthetic self-attention module that generates attention weights using linear layers. To improve the quality of refinements, we synthesize both spatial and temporal attention matrices, which dynamically capture the inter-joint and inter-frame relationships. The features from both dimensions are combined and passed forward for further processing. We name our model MixSynthFormer. The main contributions of this work are summarized as follows:", + "bbox": [ + 75, + 306, + 467, + 546 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "$\\triangleright$ We propose a highly-efficient keyframe-based pose estimation model MixSynthFormer following the transformer encoder structure. It can effectively estimate poses from sampled keyframe poses in a recover-refine pipeline.", + "bbox": [ + 76, + 549, + 467, + 609 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "$\\triangleright$ We design an MLP-based mixed synthetic attention matrix generation module, MixSynth Attention, which generates attention matrices spatially and temporally from input representations. This design enables our model to dynamically fuse channel-wise and token-wise features and refine poses effectively. To speed up the computation, we introduce a reduction factor in the attention matrix generation, which further saves computation without compromising performance.", + "bbox": [ + 75, + 611, + 467, + 746 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "$\\triangleright$ We validate our model on 2D and 3D pose estimation and body recovery tasks with four datasets and five estimators. Experimental results demonstrate that our model outperforms all keyframe-based pose estimation frameworks in terms of accuracy and efficiency. Additionally, our model can adapt to other motion synthesis tasks by indicating different keyframes. We conduct experiments on short-term motion prediction as a sub-task, and results show that it is also competitive compared to state-of-the-art motion prediction models.", + "bbox": [ + 75, + 750, + 467, + 898 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 89, + 640, + 104 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Human Pose Estimation", + "text_level": 1, + "bbox": [ + 500, + 114, + 720, + 130 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Pose estimation models can be categorized into two types based on how frames are fed into the model: frame-by-frame and keyframe-based estimators. Common pose estimation frameworks estimate poses in every frame and optimize efficiency through knowledge distillation [22, 27] or model structure design [3, 41, 29, 4, 37]. However, the computational costs are still high due to the frame-by-frame estimation. Besides, these methods are sensitive to occlusion cases in which partial joints are invisible in the camera view due to complex poses or interactions with environments, resulting in incoherent poses regardless of incorporating temporal information. In contrast, keyframe-based pose estimation frameworks exploit human motion continuity and can produce smoother sequences. Only keyframes are used for heavy single-frame estimation, while poses in the rest of the frames are recovered by a lightweight module. Thus, they can boost the efficiency of single-frame pose estimators in different tasks, such as SimplePose [36] for 2D poses, FCN [25] for 3D poses, and SPIN [20], PARE [19] and EFT [17] for body recovery.", + "bbox": [ + 496, + 138, + 890, + 441 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Keyframe-based methods can be further divided into two categories depending on how the keyframes are selected: feature-based and sampling-based. Feature-based methods [40, 7] select \"good\" keyframes relying on intermediate feature representations and recover the whole sequence without refinement. KFPN [40] selects frames that capture global context based on image features extracted from inputs. MAPN [7] uses the internal motion signals and residual errors to determine whether the heavy pose estimation needs to be conducted on a frame. Nevertheless, the cost of feature extraction cannot be ignored.", + "bbox": [ + 496, + 441, + 890, + 607 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Sampling-based methods [38] select keyframes using a uniform, random or customized sampling strategy. As selected frame may not be \"good\", these frameworks add a refinement module to clean noisy poses. Deciwatch [38] uses a standard transformer encoder to refine the uniformly sampled poses and a decoder to refine the recovered pose sequence based on denoised poses. The refinement on sampled keyframe poses is redundant and can be merged with the subsequent refinement module in the decoder. Moreover, Deciwatch [38] focuses on the temporal aspects and does not take spatial dependencies into consideration, which reflect interdependence among joints. Understanding the patterns of how joints are moving together can facilitate the refinement of incorrectly estimated joints.", + "bbox": [ + 496, + 608, + 890, + 819 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Motion Completion and Prediction", + "text_level": 1, + "bbox": [ + 500, + 830, + 803, + 847 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Motion completion aims to fill the motion of missing frames with specified keyframe constraints, presenting both past and future frames. Traditional methods utilize lin", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "14885", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/901c1b48819d0e6a06a8ed5090a62be210b9b844d091b6db34c3ba83b1857d9f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 106, + 93, + 421, + 351 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/12957400a5b7ec853386d7cdcce8ef0746b514da3291f8c96551761a067b5473.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 437, + 95, + 633, + 333 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/3c12733e75330dca013e530acd8e31ab4bd719562922a430ec766c729fb258f9.jpg", + "image_caption": [ + "Figure 2: Overview of MixSynthFormer. MixSynthFormer recovers and refines poses from sparsely sampled keyframes. It consists of $L$ blocks of MixSynthEncoder blocks and two linear projection layers. MixSynthEncoder follows a standard transformer encoder structure but replaces multi-head self-attention with MixSynth Attention. MixSynth Attention synthesizes spatial and temporal attention via SynthAttention operations (depicted in Figure 3). The output from the two branches are combined and forwarded to a linear layer for feature fusion. (Detected poses in keyframes are colored, and recovered poses by interpolators are in gray.)" + ], + "image_footnote": [], + "bbox": [ + 651, + 95, + 867, + 354 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ear, cubic-spline, Lagrange, and low-rank matrix completion, producing smooth transitions but lacking details [13]. Early learning-based methods employ RNN [9, 10] and convolutional models [12, 18]. Transformer-based models [6, 28, 30] are also adopted due to their exceptional performance in sequence-to-sequence problems. The aforementioned motion completion models are prevalent in the animation field and utilize ground-truth joint rotations and positions. However, in our case, the inputs are detected poses that can be noisy and aperiodic.", + "bbox": [ + 75, + 440, + 468, + 590 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Motion prediction generates future motion given only historical frames. RNN [8, 24] and transformer-based [2, 1] methods are proposed to capture temporal dynamics. GCN-based methods, such as STSGCN [31] and STGAGCN [42], further model the spatial relationships among joints, obtaining high performance by closely combining spatio-temporal modeling.", + "bbox": [ + 75, + 592, + 468, + 696 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Despite a range of frameworks, none of them treat motion completion and prediction as two mutually dependent tasks. Rather, each approach is specialized for one particular motion synthesis task. Notably, the sole distinction between motion completion and motion prediction pertains to the keyframe constraints. In this work, our model can handle both tasks with a unified structure.", + "bbox": [ + 75, + 696, + 468, + 801 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 814, + 168, + 829 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Problem Definition. Given an input video of $T$ frames, a sampler samples one frame out of every $K$ frames ( $T$ is a multiple of $K$ ). The sampled frames are regarded as keyframes where poses will be estimated by a pose esti", + "bbox": [ + 75, + 839, + 468, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "mator. The detected poses from sampled frames may be unreliable due to complex poses or occlusion. We denote poses detected from sampled frames as $\\hat{\\mathbf{X}}_{\\text{noisy}}^{\\text{sampled}} \\in \\mathbb{R}^{\\frac{T}{K} \\times P}$ which serves as the input to our framework. $P$ is the number of pose parameters, which can denote joint positions (2D/3D) or rotations (6D) and may vary depending on the dataset and body representation. The objective of sampling-based pose estimation is to recover all the poses $\\hat{\\mathbf{X}} \\in \\mathbb{R}^{T \\times P}$ in the original sequence from detected poses $\\hat{\\mathbf{X}}_{\\text{noisy}}^{\\text{sampled}}$ in the sampled frames (referred to as sampled detected poses).", + "bbox": [ + 496, + 440, + 890, + 592 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Model Overview. Figure 2 provides an overview of our proposed model. The goal of MixSynthFormer is to recover and refine the poses to obtain accurate estimations efficiently. Initially, the entire pose sequence is recovered through linear interpolation or a linear layer from the sampled detected poses. Those recovered poses are transformed into pose embeddings using linear projection and are fed into $L$ blocks of MixSynthEncoder. Each MixSynthEncoder comprises an attention block and a feed-forward network with residual connection, followed by a layer normalization layer. The attention block MixSynth Attention synthesizes spatial and temporal attention matrices concurrently. By integrating the spatial and temporal information, our model can refine the entire pose sequence in a simultaneous manner. Finally, the recovered poses are output via another linear layer.", + "bbox": [ + 496, + 595, + 892, + 837 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We next present details of MixSynthFormer, starting with an overview of the structure and then proceeding to the design of MixSynth Attention and the detailed operations within it. Finally, we describe the settings of using our", + "bbox": [ + 496, + 839, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "14886", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "model on motion prediction tasks, showcasing its adaptability to other motion synthesis tasks.", + "bbox": [ + 76, + 90, + 468, + 121 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Design of MixSynthFormer", + "text_level": 1, + "bbox": [ + 76, + 130, + 323, + 146 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We adopt a recover-refine pipeline in our framework. The whole pose sequence is preliminarily recovered along the temporal dimension by a traditional or a learned interpolator based on the detected poses $\\hat{\\mathbf{X}}_{\\text{noise}}^{\\text{sample}}$ in keyframes, denoted as $\\hat{\\mathbf{X}}_{\\text{noise}}^{\\text{recover}} \\in \\mathbb{R}^{T \\times P}$ :", + "bbox": [ + 76, + 152, + 467, + 234 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {X}} _ {n o i s y} ^ {r e c o v e r} = I n t e r p (\\hat {\\mathbf {X}} _ {n o i s y} ^ {s a m p l e d}) \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 243, + 468, + 266 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Recovering poses from sparse and noisy inputs results in inaccurate estimates, which necessitates additional processing to obtain a clean output. Moreover, traditional interpolation methods tend to produce overly smooth motion sequences that lack details. Hence, a refinement step is necessary to generate a more precise pose sequence, which can be formulated as a sequence-to-sequence problem. Transformers have shown remarkable success in solving such problems owing to their ability to capture global correlations among tokens. We design MixSynthFormer following the workflow of a standard transformer encoder, except for replacing the self-attention module with MixSynth Attention. Following are the high-level operations of MixSynthFormer.", + "bbox": [ + 75, + 273, + 468, + 468 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "All poses in $\\hat{\\mathbf{X}}_{\\text {noisy }}^{\\text {recover }}$ are transformed to the pose embeddings $\\mathbf{Z}_0 \\in \\mathbb{R}^{T \\times C}$ through a linear layer with weights $\\mathbf{W}_0 \\in \\mathbb{R}^{P \\times C}$ , where $C$ is the dimension of the embedding space. Attention layers in transformers need position embeddings to specify the locations of input tokens, whereas our MLP-based MixSynth Attention is sensitive to the order of tokens in temporal attention synthesis like [33] and does not require additional position embeddings.", + "bbox": [ + 75, + 469, + 468, + 592 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Z} _ {0} = \\hat {\\mathbf {X}} _ {\\text {n o i s y}} ^ {\\text {r e c o v e r}} \\mathbf {W} _ {0} \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 205, + 604, + 468, + 625 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The pose embeddings are then passed to $L$ blocks of MixSynthEncoder. The model conforms to the conventional transformer encoder design, consisting of stacked MixSynth Attention module and feed-forward network (FFN) which is a two-layer point-wise fully connected layer with GELU activation [11]. Residual connection and layer normalization $(LN)$ are applied sequentially after every block.", + "bbox": [ + 75, + 628, + 468, + 734 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {Z}} _ {l} = L N \\left(M i x S y n t h A t t \\left(\\mathbf {Z} _ {l - 1}\\right) + \\mathbf {Z} _ {l - 1}\\right) \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 130, + 744, + 468, + 762 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Z} _ {l} = L N \\left(F F N \\left(\\hat {\\mathbf {Z}} _ {l}\\right) + \\hat {\\mathbf {Z}} _ {l}\\right) \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 178, + 785, + 468, + 804 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here $l \\in [1, L]$ denotes the $l$ -th block. $\\mathbf{Z}_{l-1}$ is the output from the previous encoder block, $\\hat{\\mathbf{Z}}_l$ is the intermediate representation and $\\mathbf{Z}_l$ is the output of the current encoder block. $\\mathbf{Z}_l$ and $\\hat{\\mathbf{Z}}_l$ have the same dimension in $\\mathbb{R}^{T \\times C}$ .", + "bbox": [ + 75, + 809, + 468, + 869 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "After $L$ blocks of operations, the features in the embedding space $\\mathbf{Z}_L$ are transformed back to the pose dimension", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "via another linear layer with weights $\\mathbf{W}_p\\in \\mathbb{R}^{C\\times P}$ . The use of the residual connection can expedite model convergence and yield more stable results. The final recovered pose sequence $\\hat{\\mathbf{X}}$ is thereby the summation of the output from MixSynthEncoder blocks and the preliminarily recovered noisy poses $\\hat{\\mathbf{X}}_{noisy}^{recover}$ :", + "bbox": [ + 496, + 90, + 890, + 184 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {X}} = \\left(L N (\\mathbf {Z} _ {L})\\right) \\mathbf {W} _ {p} + \\hat {\\mathbf {X}} _ {n o i s y} ^ {r e c o v e r} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 584, + 194, + 890, + 215 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. MixSynth Attention", + "text_level": 1, + "bbox": [ + 500, + 223, + 689, + 239 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Transformers are effective in capturing global correlations among tokens, but they may not be sufficient for refining noisy sequences. Token-wise attention primarily focuses on the temporal aspect, while local attention that captures the correlation among joints is also essential, particularly for recovering complex motions. To learn both global and local features, we propose MixSynth Attention, which mixes spatial and temporal synthetic attention matrices. The weights in these matrices reflect the relative inter-joint and inter-frame importance. The spatial matrix reveals the correlation among joints. When performing some motion patterns, joints that move together are highly correlated. It is helpful in locating a wrongly-detected joint from its related joints with accurate detection. The temporal matrix determines the impact of a frame with respect to other frames in the sequence, signifying the extent to which a frame affects the remaining frames.", + "bbox": [ + 496, + 247, + 890, + 502 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We explain the MixSynth Attention operations in detail. For simplicity, we eliminate the block index $l$ in the following explanation. The synthetic attention operation (SynthAttenOP) operates on $\\mathbf{Z} \\in \\mathbb{R}^{T \\times C}$ and outputs feature $\\mathbf{Y}_i \\in \\mathbb{R}^{T \\times C}$ , which can be spatial or temporal, denoted as $\\mathbf{Y}_s$ and $\\mathbf{Y}_t$ , respectively.", + "bbox": [ + 496, + 503, + 890, + 594 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Y} _ {i} = \\operatorname {S y n t h A t t e n O P} _ {i} (\\mathbf {Z}), i \\in \\{s, t \\} \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 606, + 890, + 623 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The spatially and temporally attended features are generated simultaneously. Inspired by [39], we apply split attention to re-balance the contribution of the two branches. Different motions may have different emphases. Inter-joint relations are more important for certain motions, while others may be more influenced by inter-frame relations. The weights $\\mathbf{A}_y\\in \\mathbb{R}^{2\\times C}$ of $\\mathbf{Y}_s$ and $\\mathbf{Y}_t$ are calculated as", + "bbox": [ + 496, + 633, + 890, + 741 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {A} _ {y} = \\operatorname {S o f t m a x} (F F N (G A P (\\mathbf {Y} _ {s} + \\mathbf {Y} _ {t}))) \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 549, + 751, + 890, + 768 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $GAP$ denotes the global average pooling function, $FFN$ contains two fully connected layers with ReLU activation [26] and Softmax is for normalization. The weighted sum $\\mathbf{Y}_{out} \\in \\mathbb{R}^{T \\times C}$ is the summation of the element-wise product of the concatenated representations from two branches with the re-balancing weights $\\mathbf{A}_y$ :", + "bbox": [ + 496, + 779, + 890, + 871 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Y} _ {\\text {o u t}} = \\operatorname {S u m} \\left(\\mathbf {A} _ {y} \\circ \\left[ \\mathbf {Y} _ {s}; \\mathbf {Y} _ {t} \\right]\\right) \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 594, + 883, + 890, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "14887", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The output of the MixSynth Attention block is attained by linearly transforming $\\mathbf{Y}_{out}$ with weights $\\mathbf{W}_o\\in \\mathbb{R}^{C\\times C}$ :", + "bbox": [ + 76, + 90, + 468, + 122 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nM i x S y n t h A t t (\\mathbf {Z}) = \\mathbf {Y} _ {o u t} \\mathbf {W} _ {o} \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 131, + 468, + 148 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. SynthAttention Operation", + "text_level": 1, + "bbox": [ + 76, + 156, + 316, + 174 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The self-attention module in transformers utilizes the pairwise dot product to calculate attention weights. The computation of the query-key matrix multiplication expands quadratically as the embedding size increases. To alleviate the impact of embedding size on computational cost, we propose synthetic attention operation (SynthAttenOp), whose computation grows linearly with the increase of embedding size, as a substitute for the standard attention. We discuss this part in detail in supplementary materials. SynthAttenOp generates attention matrices using linear layers. Details of its operation are described below.", + "bbox": [ + 75, + 180, + 468, + 345 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "SynthAttenOp operates spatially and temporally. In spatial attention synthesis, input and output are transposed. Here we use $\\mathbf{Z} \\in \\mathbb{R}^{N \\times D}$ to illustrate the general case, where $N$ and $D$ can be substituted with either $C$ or $T$ . The coarse synthetic attention matrix $\\mathbf{A}_s \\in \\mathbb{R}^{N \\times N}$ is generated by a linear layer with weights $\\mathbf{W}_z \\in \\mathbb{R}^{D \\times N}$ :", + "bbox": [ + 75, + 345, + 468, + 436 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {A} _ {s} = \\mathbf {Z W} _ {z} \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 228, + 446, + 468, + 463 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As different frames or joints have different contributions, we apply the Squeeze-and-Excitation layer (SELayer) [14] to regulate the influence. It can amplify critical channels while mitigating the effect of less important ones. The fine-grained attention matrix $\\mathbf{A}_{\\text {synth }} \\in \\mathbb{R}^{N \\times N}$ is obtained by", + "bbox": [ + 76, + 473, + 468, + 550 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {S E L a y e r} \\left(\\mathbf {A} _ {s}\\right) = \\mathbf {A} _ {s} \\circ \\sigma \\left(\\mathbf {W} _ {e} \\delta \\left(\\mathbf {W} _ {s} G A P \\left(\\mathbf {A} _ {s}\\right)\\right)\\right) \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 93, + 570, + 468, + 587 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {A} _ {\\text {s y n t h}} = \\operatorname {S o f t m a x} (\\operatorname {S E L a y e r} (\\mathbf {A} _ {s})) \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 143, + 611, + 468, + 628 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where GAP denotes global average pooling and $GAP(\\mathbf{A}) \\in \\mathbb{R}^N$ , $\\delta$ and $\\sigma$ are Sigmoid activation and ReLU functions [26]. The reduction ratio $(r_{se})$ is an empirically found hyperparameter that limits model complexity [14]. $\\mathbf{W}_s \\in \\mathbb{R}^{\\frac{N}{r_{se}} \\times N}$ is for dimension reduction, and $\\mathbf{W}_e \\in \\mathbb{R}^{N \\times \\frac{N}{r_{se}}}$ is for expanding to the original dimension. The output of SELayer is a re-scaled input after channelwise multiplication with calculated weights. Softmax is inherited from the standard transformer, which normalizes the attention weights.", + "bbox": [ + 76, + 633, + 468, + 787 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In alignment with the standard transformer encoder, the output is the product of the attention matrix and the value:", + "bbox": [ + 76, + 789, + 468, + 818 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Y} = \\mathbf {A} _ {\\text {s y n t h}} \\mathbf {V} \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 218, + 829, + 468, + 845 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{V} = \\mathbf{Z}\\in \\mathbb{R}^{N\\times D}$ and $\\mathbf{Y}\\in \\mathbb{R}^{N\\times D}$ .", + "bbox": [ + 76, + 853, + 359, + 869 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The method described above is applicable for cases when $N$ is relatively small. When $N$ is large, the computation", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/8a97663b6eccb8f6b299245b3ad8871f839592586046d9a46967aedc9c04cc0d.jpg", + "image_caption": [ + "Figure 3: The procedure of reduced SynthAttenOp" + ], + "image_footnote": [], + "bbox": [ + 501, + 90, + 890, + 150 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "cost grows quadratically owing to the matrix multiplication in Eqn. 13. We apply a reduction factor $r$ to the last dimension $D$ , saving the computation in Eqn. 13 by $r^2$ times. We denote the reduced dimension as $d = \\lfloor N / r \\rfloor$ . Figure 3 shows the process of reduced attention matrix generation and feature fusion. The reduced coarse attention matrix $\\mathbf{A}_s^r \\in \\mathbb{R}^{N \\times d}$ and reduced value $\\mathbf{V}^r \\in \\mathbb{R}^{d \\times D}$ are obtained through", + "bbox": [ + 496, + 188, + 890, + 309 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {A} _ {s} ^ {r} = \\mathbf {Z} \\mathbf {W} _ {z} ^ {r}, \\mathbf {V} ^ {r} = \\mathbf {W} _ {v} \\mathbf {Z} \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 607, + 324, + 890, + 340 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where weights for reduced attention matrix generation and for reducing the value are $\\mathbf{W}_z^r\\in \\mathbb{R}^{D\\times d}$ and $\\mathbf{W}_v\\in \\mathbb{R}^{d\\times N}$ , respectively.", + "bbox": [ + 496, + 345, + 890, + 391 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Efficiency Calculation", + "text_level": 1, + "bbox": [ + 500, + 400, + 705, + 416 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The overall cost of the model per frame combines the cost of a pose estimator and the cost of MixSynthFormer:", + "bbox": [ + 498, + 422, + 890, + 453 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nF L O P s = \\frac {1}{K} * f (E s t.) + f (M S F) \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 460, + 890, + 491 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$f(\\cdot)$ evaluates the FLOPs of a model per frame. As one frame out of $K$ frames is sampled for estimation, the per-frame cost of the estimator is $\\frac{1}{K} * f(Ext.$ . MixSynthFormer operates on every frame, recovering and refining poses on the whole sequence, and its FLOPs per frame is $f(MSF)$ . In particular, $f(MSF)$ is at least $10^{4}$ times smaller than $f(Ext.$ and is negligible compared to the heavy pose estimator. With $10\\%$ sampling ratio ( $K = 10$ ), our framework can speed up the computation by ten times.", + "bbox": [ + 496, + 500, + 890, + 635 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.5. Loss Function", + "text_level": 1, + "bbox": [ + 500, + 643, + 643, + 657 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Following [38], we apply L1 loss to minimize the error between the finely recovered pose sequence $\\hat{\\mathbf{X}}$ and the ground-truth pose sequence $\\mathbf{X}$ :", + "bbox": [ + 496, + 667, + 890, + 713 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\frac {1}{T} \\sum_ {t = 1} ^ {T} | \\hat {\\mathbf {X}} ^ {t} - \\mathbf {X} ^ {t} | \\tag {16}\n$$\n", + "text_format": "latex", + "bbox": [ + 619, + 722, + 890, + 762 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.6. Motion Prediction Setting", + "text_level": 1, + "bbox": [ + 500, + 771, + 735, + 787 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Motion prediction and motion completion are two subfields in conditional motion generation with the only difference lying in the keyframe constraints. We include short-term motion prediction as a sub-task and demonstrate the versatility of our model on this task.", + "bbox": [ + 496, + 795, + 890, + 869 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The input of motion prediction to our model is a historical ground-truth motion sequence $\\mathbf{X}_{1:T_h} \\in \\mathbb{R}^{T_h \\times P}$ , where", + "bbox": [ + 498, + 869, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "14888", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$T_{h}$ is the number of consecutive historical frames and $P$ is the size of pose parameters (i.e., 3D positions of human body joints). The goal is to predict the future sequence $\\mathbf{X}_{T_h + 1:T_h + T_f} \\in \\mathbb{R}^{T_f \\times P}$ given $\\mathbf{X}_{1:T_h}$ , where $T_{f}$ is the number of frames to be predicted. Similar to the pose estimation settings, the future poses are coarsely generated by interpolation, and then MixSynthFormer refines and outputs the future poses.", + "bbox": [ + 75, + 90, + 468, + 210 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We adopt the L2-norm between the predicted sequence and the ground-truth sequence calculated only on future frames as the loss function, which is equivalent to the Mean Per Joint Position Error (MPJPE) in [31, 42]:", + "bbox": [ + 75, + 212, + 468, + 272 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {f} = \\frac {1}{T _ {f}} \\sum_ {t = T _ {h} + 1} ^ {T _ {h} + T _ {f}} | | \\hat {\\mathbf {X}} ^ {t} - \\mathbf {X} ^ {t} | | _ {2} \\tag {17}\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 281, + 468, + 325 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We will test the above model in experiments, which showcases our model's adaptability to other synthesis tasks.", + "bbox": [ + 76, + 334, + 468, + 364 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 377, + 209, + 393 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Datasets. We evaluate MixSynthFormer on four datasets for three tasks. For 2D pose estimation (to locate the 2D coordinates of joints from images), we use the Sub-JHMDB dataset [16] that contains daily and sports actions. For 3D pose estimation (to extend 2D pose data with depth information prediction), we use the widely-used Human3.6M indoor dataset [15]. For 3D body recovery (to estimate human shape and joint angles), we use the in-the-wild dataset 3DPW which includes videos taken by a moving phone camera [35] and AIST++ [21] with diverse dancing actions shot indoors.", + "bbox": [ + 75, + 402, + 468, + 566 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation Metrics. We adopt the same evaluation metrics as in [38]. For 2D pose estimation, Percentage of the Correct Keypoints (PCK) is used, and three thresholds $(20\\%, 10\\%$ and $5\\%$ of the bounding box size under the pixel level) are set. For 3D tasks, Mean Per Joint Position Error (MPJPE) is utilized to report distance error and the mean Acceleration error (Accel) is adopted to reflect the smoothness of the estimated pose sequence. Mean Floating Point Operations (FLOPs (G)) per frame are also reported to show the computation costs.", + "bbox": [ + 75, + 568, + 468, + 717 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation Details. We use the same single-frame pose estimators and sampling strategy as in [38]. The uniform sampling ratio is set to $10\\%$ ( $K = 10$ ) in all experiments. The presence of the first and last frames is vital in recovery. In practice, we sample $Q$ frames with index $K \\times q$ , $q \\in [0, \\dots, Q - 1]$ from the input of length $K \\times Q + 1$ and additionally include the last frame of the input sequence as keyframes. The number of keyframes $Q$ , the embedding dimension $C$ and the number of MixSynthEncoder blocks $L$ vary among datasets and tasks. We train the model on a single A100 GPU with testing performed on an 8-core CPU Apple M1 Pro chip to obtain the inference time. Due to", + "bbox": [ + 75, + 719, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "page limit, other detailed training settings and qualitative results are provided in supplementary materials.", + "bbox": [ + 498, + 90, + 890, + 121 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Comparison on 2D Pose Estimation", + "text_level": 1, + "bbox": [ + 498, + 132, + 807, + 148 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Existing keyframe-based pose estimation methods use SimplePose [36] as the pose estimator. We follow the same experiment settings as in [40, 7, 38]. Table 1 presents the detailed PCK@0.2 results of each joint, the average performance of all three metrics and computation costs.", + "bbox": [ + 496, + 155, + 890, + 229 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Compared with feature-based methods, KFP [40] and MAPN [7], our method improves the accuracy by over $4.6\\%$ in PCK@0.2. The improvements on fast-moving joints, such as elbows, wrists and ankles, are significant with a maximum increase of $14.8\\%$ . Those joints often cause image blur, leading to wrong detection results. Our sampling-based method incorporates a refinement module and can mitigate the effects of incorrect detection.", + "bbox": [ + 496, + 231, + 890, + 349 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Compared to the sampling-based model DeciWatch [38], our model features a lighter design with 0.4M FLOPs computation, yet achieving a superior accuracy of $99.3\\%$ under PCK@0.2. Notably, our model achieves almost $100\\%$ in predicting the head and torso positions, which can be attributed to the integration of spatial dependencies. While the attention mechanism in [38] only considers inter-frame relations, our method also leverages inter-joint relations, which is particularly useful for limb position estimation. The accuracy of ankle increases from $96.5\\%$ to $97.8\\%$ . By fusing information from highly-correlated joints, our model also outperforms DeciWatch in strict metrics PCK@0.1 by $1\\%$ and PCK@0.05 by $1.3\\%$ .", + "bbox": [ + 496, + 352, + 890, + 547 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison on 3D Pose Estimation", + "text_level": 1, + "bbox": [ + 498, + 559, + 807, + 574 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We next compare our method on 3D keypoint estimation and body recovery tasks against single-frame estimators [25, 20, 19, 17] and the sampling-based model DeciWatch [38]. Results on localization error and acceleration error are in Table 2.", + "bbox": [ + 496, + 582, + 890, + 656 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Compared with DeciWatch [38], our model is significantly smaller with no performance degradation, thanks to SynthAttention. Our model achieves a 1-2mm reduction in MPJPE on Human3.6M and 3DPW without compromising smoothness. Notably, the FLOPs of the model trained on 3DPW are 0.03M, which is more than ten times smaller than DeciWatch. The inference time is less than 0.1 ms per frame on CPU. There are two main reasons for this: first, we only do refinements once; second, the attention matrix in our model is generated by the cost-efficient SynthAttenOp.", + "bbox": [ + 496, + 657, + 890, + 809 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "On AIST++, our model reduces the acceleration error by $33\\%$ compared to DeciWatch and $86\\%$ compared to the single-frame estimator SPIN. We attribute the acceleration reduction to the integration of spatial and temporal attention. AIST++ contains poses with fast movements and diverse dancing actions. Due to the complexity of these poses,", + "bbox": [ + 496, + 810, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "14889", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/79dc8f94be3cd51022fdafa4648a2583e80b8a4370be98329578526036851c42.jpg", + "table_caption": [ + "Table 1: Comparison with keyframe-based pose estimation methods on Sub-JHMDB dataset [16] for 2D pose estimation. R means ResNet [39]. Ratio represents the sampling ratio. Sho., Elb., Wri., Ank., Avg. stand for shoulder, elbow, wrist, ankle and average PCK, respectively." + ], + "table_footnote": [], + "table_body": "
Sub-JHMDB dataset - 2D Pose Estimation PCK@0.2PCK@0.1PCK@0.05
MethodsHeadSho.Elb.Wri.HipKneeAnk.Avg.FLOPs(G)Ratio
KFP(R18) [40]94.796.395.290.296.495.593.294.57.1940.8%--
MAPN(R18) [7]98.297.491.785.299.296.792.294.72.7035.2%--
SimplePose [36]98.697.396.598.690.395.486.594.011.96100%81.657.3
DeciWatch [38]99.899.599.799.798.799.496.598.81.196+0.000510.0%94.179.4
Ours99.999.999.8100.099.299.997.899.31.196+0.000410.0%95.180.7
", + "bbox": [ + 86, + 121, + 879, + 241 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/0cbd315f82e9b9842749d6badd2903cc14db7572d95dd4a9cbc1e9f044d1ce42.jpg", + "table_caption": [ + "Table 2: Comparison for 3D pose estimation and body recovery on Human3.6M [15], 3DPW [35] and AIST++ [21]. The estimators in keyframe-based frameworks are the same as the corresponding single-frame pose models." + ], + "table_footnote": [], + "table_body": "
MethodsMPJPEAccelFLOPs(G)
Human3.6M - 3D Pose Estimation
FCN [25]54.619.26.21
DeciWatch [38]52.81.50.621+0.0007
Ours50.91.50.621+0.0001
3DPW - 3D Body Recovery
SPIN [20]96.634.74.13
DeciWatch [38]93.37.10.413+0.0004
Ours91.26.80.413+0.00003
EFT [17]90.332.84.13
DeciWatch [38]89.06.80.413+0.0004
Ours88.16.30.413+0.00003
PARE [19]78.925.715.51
DeciWatch [38]77.26.91.551+0.0004
Ours76.56.71.551+0.00003
AIST++ - 3D Body Recovery
SPIN [20]107.733.84.13
DeciWatch [38]71.37.10.413+0.0007
Ours71.24.70.413+0.0005
", + "bbox": [ + 99, + 316, + 444, + 628 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "original detections may contain erroneous estimations. By mixing spatial and temporal attention, we can effectively refine incorrect joints while maintaining the smoothness.", + "bbox": [ + 75, + 650, + 468, + 696 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Comparison on Motion Completion", + "text_level": 1, + "bbox": [ + 76, + 709, + 387, + 726 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Our model recovers and refines poses in a completion-like manner. We compare our model with traditional interpolation methods and a transformer-encoder based Motion Completion Model (MCT) [6] from the animation field. MCT can handle different motion completion tasks, and uses the concatenation of positional and rotational data as input. To be consistent with the pose estimation task, we re-implement the MCT model and tune it on our datasets. Our recover-refine process is similar to the in-filling task in MCT. Both are to recover missing poses from uniformly sampled keyframes.", + "bbox": [ + 75, + 734, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/6feaf09ac45ddda717800559d315440d551b9536663fdf67cdc82d2fd3ea11fb.jpg", + "table_caption": [ + "Table 3: Comparison with motion completion methods on Human3.6M [15], 3DPW [35] and AIST++ [21] with estimators stated inside brackets. Nearest, linear, quadratic, cubic-spline methods are used for traditional interpolation. MPJPE (Accel) of different recovery methods are reported. The results from traditional interpolators with the lowest MPJPE are underlined." + ], + "table_footnote": [], + "table_body": "
DataNea.Lin.Qua.Cub.MCTOurs
H36M (FCN)57.054.854.654.654.550.9
(10.2)(1.9)(1.6)(1.5)(2.1)(1.5)
3DPW (SPIN)100.597.297.597.791.991.2
(19.9)(6.7)(6.2)(6.3)(8.0)(6.8)
AIST (SPIN)114.7105.9107.1107.672.071.2
(28.5)(5.7)(4.6)(4.6)(6.9)(4.7)
", + "bbox": [ + 506, + 345, + 880, + 459 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The results are presented in Table 3. Traditional interpolators tend to smooth the sequence but lack the ability to correct noisy poses, resulting in low acceleration errors and high position errors. MCT can reduce position errors at the expense of reduced smoothness. Our model surpasses all other methods. It can produce smooth sequences like interpolation but with more detailed and accurate motions. Specifically, when applied to Human3.6M, our model achieves the same smoothness as cubic-spline interpolation and decrease MPJPE by $7\\%$ . When evaluated on AIST++, our model reduces MPJPE by over $30\\%$ . The significant improvement in position errors without tradeoffs in smoothness shows the superiority of MixSynthFormer in recovering noisy sequences.", + "bbox": [ + 496, + 481, + 890, + 693 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Comparison with Motion Prediction Methods", + "text_level": 1, + "bbox": [ + 498, + 707, + 885, + 724 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We evaluate our model on the sub-task short-term motion prediction (Sec. 3.6) under four testing intervals ranging from $80~\\mathrm{ms}$ to $400~\\mathrm{ms}$ , using $400~\\mathrm{ms}$ input sequences. Table 4 gives the results.", + "bbox": [ + 496, + 732, + 890, + 792 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Our model outperforms STSGCN [31] and STGAGCN [42]. Taking advantage of motion continuity, our model can predict short-term poses that conform to the motion pattern of the historical input poses. It reduces error by $17\\%$ in an 80 ms interval while the improvement is less than $3\\%$ in a 400 ms interval. Limited by refinement on the overly-smoothed interpolation results, our model cannot learn spe", + "bbox": [ + 496, + 794, + 890, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "14890", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/f7014c8829f4f42f2b62f48493daa5858f6dd08e2f0e0a3c30cd5ed1a7b09333.jpg", + "table_caption": [ + "Table 4: Comparison for short-term motion prediction. Average MPJPE across frames on Human3.6M [15] are reported." + ], + "table_footnote": [], + "table_body": "
Methods80160320400
STSGCN [31]10.117.133.138.3
STGAGCN [42]10.116.932.538.5
Ours8.415.830.537.4
", + "bbox": [ + 120, + 122, + 423, + 193 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/1673e324178d5f7348749fbd02c116d5df3baab13218d514467bfc4f71a2744f.jpg", + "table_caption": [ + "Table 5: Comparison with different attention matrix generation methods on 3DPW [35]" + ], + "table_footnote": [], + "table_body": "
MethodsMPJPEAccel#ParamFLOPs
Vanilla92.66.80.14M0.12M
Random92.66.90.12M0.09M
Dense92.56.80.13M0.11M
Ours92.16.80.10M0.09M
", + "bbox": [ + 112, + 232, + 431, + 318 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "cific periodic motion patterns and high-frequency motions. The uncertainty of human motions grows as the prediction interval increases, leading to a downgraded performance in longer intervals. Nevertheless, it yields improvements on complex actions or actions with occlusion like sitting and taking photos. Action-wise results are reported in supplementary materials.", + "bbox": [ + 75, + 337, + 467, + 443 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 453, + 230, + 469 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We conduct the ablation study on attention matrix generation, reduction factor $r$ and model structure. The input sequences are linearly interpolated from keyframe poses.", + "bbox": [ + 75, + 477, + 468, + 521 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Attention Matrix Generation. The attention matrix in our model is generated by a linear layer followed by a SELayer. It can also be generated by a FFN or is a learnable matrix as proposed in [32], referred to as Dense and Random. We compare our generation method with these two methods, together with the vanilla self-attention in transformers. To ensure a fair evaluation, we exclusively focus on the temporal attention matrix. Table 5 presents a comparative analysis of various attention methods, among which our generation approach stands out with the lowest number of parameters (0.1M) and minimum FLOPs (0.09M), owing to the reduction factor. Importantly, our method achieves the lowest MPJPE of $92.1\\mathrm{mm}$ .", + "bbox": [ + 75, + 522, + 468, + 717 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effect of Reduction Factor. We examine the impact of the reduction factor $r$ which is introduced for computation saving in SynthAttention. Specifically, we investigate how $r$ in spatial $(r_s)$ and temporal $(r_t)$ dimensions affects the model size and its performance. As shown in Table 6, overall, applying $r$ on one dimension saves $8\\%$ of the computation and up to $25\\%$ of parameters. When $r$ is applied in temporal attention synthesis, we observe a smoother motion sequence with a decrease in MPJPE by $0.8 \\mathrm{~mm}$ . Applying reduction on both dimensions further reduces the model parameters by $30\\%$ compared to a non-reduced one at the expense of slightly increased MPJPE.", + "bbox": [ + 75, + 719, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/f427103372013bed38b6fc5fd54455201c5b823ff88d40352a809e4b650d95d3.jpg", + "table_caption": [ + "Table 6: Effects of the reduction factor $r$ on Human3.6M [15]" + ], + "table_footnote": [], + "table_body": "
rtrsMPJPEAccel#ParamFLOPs
1152.21.70.26M0.13M
4151.41.60.21M0.12M
1451.81.70.23M0.12M
4451.81.60.18M0.11M
", + "bbox": [ + 537, + 108, + 851, + 193 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/2483ca05eb7f61b0ca6bc284f25fd565f7e3c9413dd528228215de440f0066e9.jpg", + "table_caption": [ + "Table 7: Effects of components in MixSynth Attention block on Sub-JHMDB [16]. w/o means that the component is removed." + ], + "table_footnote": [], + "table_body": "
PCK@0.2PCK@0.1
Ours99.395.1
w/o SE Layer99.094.2
w/o weighted sum98.994.7
w/o temporal attention98.894.4
w/o spatial attention98.692.9
", + "bbox": [ + 535, + 231, + 854, + 330 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Components in MixSynth Attention Block. MixSynth Attention blocks mix synthesized spatial and temporal attention. SELayer is incorporated to augment feature efficacy by emphasizing salient features while suppressing uninformative ones during attention matrix generation. The final output is the weighted sum of spatial and temporal representations. To evaluate the contribution of each component, we conduct ablation experiments by removing one of the components.", + "bbox": [ + 496, + 348, + 890, + 484 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Results under different settings are summarized in Table 7. Removing any component in MixSynth Attention leads to worse performance. When SELayer is removed, PCK@0.1 decreases by $0.9\\%$ , indicating its crucial role in re-calibrating attention weights. The most significant performance decrease is observed when the spatial attention component is excluded: PCK@0.1 drops from $95.1\\%$ to $92.9\\%$ . This finding highlights the usefulness of the inter-joint relation from spatial attention generation in refinement. Moreover, combining spatial and temporal attention through a weighted sum further improves the performance by $0.4\\%$ . These results demonstrate the effectiveness of all components in MixSynth Attention.", + "bbox": [ + 496, + 484, + 892, + 680 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 694, + 617, + 709 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose MixSynthFormer, a transformer encoder-like structure with mixed synthetic attention for efficient human pose estimation in videos. The MLP-based synthetic attention module generates spatial and temporal matrices simultaneously, allowing fast and accurate recovery and refinement. The flexible model design also enables it to easily adapt to other motion synthesis tasks such as short-term motion prediction. Comprehensive experiments demonstrate the superior performance of our model in 2D/3D pose estimation, body mesh recovery, and motion prediction tasks, making it a promising solution for practical use cases.", + "bbox": [ + 496, + 719, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "14891", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 6447–6456, 2022. 3, 6, 7, 8" + ], + "bbox": [ + 501, + 90, + 892, + 359 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "14893", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/846dbe02-0b5b-4bf4-a391-96d12e988697_model.json b/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/846dbe02-0b5b-4bf4-a391-96d12e988697_model.json new file mode 100644 index 0000000000000000000000000000000000000000..b1e0b1a68a0f0409d674511f531cff99ec8c3366 --- /dev/null +++ b/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/846dbe02-0b5b-4bf4-a391-96d12e988697_model.json @@ -0,0 +1,2233 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.085, + 0.131, + 0.885, + 0.175 + ], + "angle": 0, + "content": "MixSynthFormer: A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation" + }, + { + "type": "text", + "bbox": [ + 0.166, + 0.204, + 0.806, + 0.24 + ], + "angle": 0, + "content": "Yuran Sun, Alan William Dougherty, Zhuoying Zhang, Yi King Choi, Chuan Wu The University of Hong Kong" + }, + { + "type": "text", + "bbox": [ + 0.172, + 0.242, + 0.797, + 0.258 + ], + "angle": 0, + "content": "yuransun@connect.hku.hk,{alanwd,tinawork}@hku.hk,{ykchoi,cwu}@cs.hku.hk" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.314, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.326, + 0.474, + 0.689 + ], + "angle": 0, + "content": "Human pose estimation in videos has wide-ranging practical applications across various fields, many of which require fast inference on resource-scarce devices, necessitating the development of efficient and accurate algorithms. Previous works have demonstrated the feasibility of exploiting motion continuity to conduct pose estimation using sparsely sampled frames with transformer-based models. However, these methods only consider the temporal relation while neglecting spatial attention, and the complexity of dot product self-attention calculations in transformers are quadratically proportional to the embedding size. To address these limitations, we propose MixSynthFormer, a transformer encoder-like model with MLP-based mixed synthetic attention. By mixing synthesized spatial and temporal attentions, our model incorporates inter-joint and inter-frame importance and can accurately estimate human poses in an entire video sequence from sparsely sampled frames. Additionally, the flexible design of our model makes it versatile for other motion synthesis tasks. Our extensive experiments on 2D/3D pose estimation, body mesh recovery, and motion prediction validate the effectiveness and efficiency of MixSynthFormer. The code is available at https://github.com/irenesesun/MixSynthFormer.git" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.723, + 0.21, + 0.739 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Human pose estimation is a crucial task in computer vision which aims to estimate the keypoint locations of a human body from visual inputs. It has a wide range of applications in virtual/augmented reality, healthcare, and security surveillance [23, 5]. In recent years, there has been a growing demand for real-time pose estimation in many of these applications. However, the computational burden of deep learning models makes their real-time estimation on resource-constrained devices (e.g., CPU, mobile devices) challenging. How to estimate human poses in videos ef" + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.291, + 0.878, + 0.342 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.599, + 0.348, + 0.796, + 0.362 + ], + "angle": 0, + "content": "(a) Feature-based Keyframe Selector" + }, + { + "type": "image", + "bbox": [ + 0.538, + 0.369, + 0.857, + 0.413 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.593, + 0.416, + 0.8, + 0.429 + ], + "angle": 0, + "content": "(b) Sampling-based Keyframe Selector" + }, + { + "type": "image", + "bbox": [ + 0.558, + 0.436, + 0.838, + 0.48 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.674, + 0.483, + 0.72, + 0.495 + ], + "angle": 0, + "content": "(c) Ours" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.5, + 0.895, + 0.613 + ], + "angle": 0, + "content": "Figure 1: Pipelines of keyframe-based pose estimation frameworks. The recover process is similar to interpolation. (a) is the feature-based pipeline [40, 7], which selects \\(30\\%\\) to \\(40\\%\\) of frames based on input features and recovers the whole sequence. (b) is the existing sampling-based pipeline [38], which uses a sampler to select frames and conducts keyframe refinement, whole sequence recovery and whole sequence refinement. (c) is our proposed simplified sampling-based pipeline excluding keyframe refinement." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.629, + 0.791, + 0.644 + ], + "angle": 0, + "content": "frequently remains an open research problem." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.895, + 0.779 + ], + "angle": 0, + "content": "Conventional pose estimators [3, 22, 41, 29, 4, 37, 27] estimate poses frame-by-frame, and the efficiency depends on the model design. Recent methods [40, 7, 38] have proven the viability of estimating poses in sequences based solely on keyframes. By leveraging the temporal redundancy in videos, poses in the remaining frames can be reconstructed from keyframe poses, similar to motion completion, which can significantly reduce the cost of resource-intensive pose estimators." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.896, + 0.903 + ], + "angle": 0, + "content": "In current keyframe-based pose estimation frameworks, keyframes are selected using a feature-based selector or a sampler, as illustrated in Figures 1a and 1b. Feature-based keyframe selectors [40, 7] select \"good\" frames based on features extracted from inputs. The final poses in the whole sequence are recovered from the estimated poses in those frames without further refinements. A more effective approach is to sample a portion of frames directly from inputs" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14884" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.468, + 0.152 + ], + "angle": 0, + "content": "[38]. Without knowing the quality of selected frames in advance, poses detected from them may be noisy. To tackle this issue, the current design employs a refine-recover-refine pipeline to obtain the final pose sequence." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.154, + 0.468, + 0.304 + ], + "angle": 0, + "content": "Is there a way to simplify the pipeline and further reduce the computational cost? The two refinement modules for keyframe poses and recovered poses appear repetitive and unnecessary, as the poses in keyframes are refined twice. To address this, we propose a simplified recover-refine pipeline, as shown in Figure 1c. Within our framework, keyframes are selected using a sampler, and the pose sequence is recovered from detected poses in keyframes using an interpolator. The rough sequence is then refined using a single refinement module." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.307, + 0.468, + 0.547 + ], + "angle": 0, + "content": "We present a novel framework for sampling-based pose estimation utilizing a lightweight transformer encoder-like structure. The scaled dot product self-attention mechanism in the transformer network [34] is used to determine the relative importance of a token with respect to other tokens. However, the computational cost can be prohibitively high when using a large embedding size. To mitigate this problem, we replace the standard key-query attention with a synthetic self-attention module that generates attention weights using linear layers. To improve the quality of refinements, we synthesize both spatial and temporal attention matrices, which dynamically capture the inter-joint and inter-frame relationships. The features from both dimensions are combined and passed forward for further processing. We name our model MixSynthFormer. The main contributions of this work are summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.55, + 0.468, + 0.611 + ], + "angle": 0, + "content": "\\(\\triangleright\\) We propose a highly-efficient keyframe-based pose estimation model MixSynthFormer following the transformer encoder structure. It can effectively estimate poses from sampled keyframe poses in a recover-refine pipeline." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.612, + 0.468, + 0.747 + ], + "angle": 0, + "content": "\\(\\triangleright\\) We design an MLP-based mixed synthetic attention matrix generation module, MixSynth Attention, which generates attention matrices spatially and temporally from input representations. This design enables our model to dynamically fuse channel-wise and token-wise features and refine poses effectively. To speed up the computation, we introduce a reduction factor in the attention matrix generation, which further saves computation without compromising performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.468, + 0.9 + ], + "angle": 0, + "content": "\\(\\triangleright\\) We validate our model on 2D and 3D pose estimation and body recovery tasks with four datasets and five estimators. Experimental results demonstrate that our model outperforms all keyframe-based pose estimation frameworks in terms of accuracy and efficiency. Additionally, our model can adapt to other motion synthesis tasks by indicating different keyframes. We conduct experiments on short-term motion prediction as a sub-task, and results show that it is also competitive compared to state-of-the-art motion prediction models." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.09, + 0.642, + 0.105 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.115, + 0.722, + 0.131 + ], + "angle": 0, + "content": "2.1. Human Pose Estimation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.139, + 0.892, + 0.442 + ], + "angle": 0, + "content": "Pose estimation models can be categorized into two types based on how frames are fed into the model: frame-by-frame and keyframe-based estimators. Common pose estimation frameworks estimate poses in every frame and optimize efficiency through knowledge distillation [22, 27] or model structure design [3, 41, 29, 4, 37]. However, the computational costs are still high due to the frame-by-frame estimation. Besides, these methods are sensitive to occlusion cases in which partial joints are invisible in the camera view due to complex poses or interactions with environments, resulting in incoherent poses regardless of incorporating temporal information. In contrast, keyframe-based pose estimation frameworks exploit human motion continuity and can produce smoother sequences. Only keyframes are used for heavy single-frame estimation, while poses in the rest of the frames are recovered by a lightweight module. Thus, they can boost the efficiency of single-frame pose estimators in different tasks, such as SimplePose [36] for 2D poses, FCN [25] for 3D poses, and SPIN [20], PARE [19] and EFT [17] for body recovery." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.442, + 0.892, + 0.608 + ], + "angle": 0, + "content": "Keyframe-based methods can be further divided into two categories depending on how the keyframes are selected: feature-based and sampling-based. Feature-based methods [40, 7] select \"good\" keyframes relying on intermediate feature representations and recover the whole sequence without refinement. KFPN [40] selects frames that capture global context based on image features extracted from inputs. MAPN [7] uses the internal motion signals and residual errors to determine whether the heavy pose estimation needs to be conducted on a frame. Nevertheless, the cost of feature extraction cannot be ignored." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.609, + 0.892, + 0.82 + ], + "angle": 0, + "content": "Sampling-based methods [38] select keyframes using a uniform, random or customized sampling strategy. As selected frame may not be \"good\", these frameworks add a refinement module to clean noisy poses. Deciwatch [38] uses a standard transformer encoder to refine the uniformly sampled poses and a decoder to refine the recovered pose sequence based on denoised poses. The refinement on sampled keyframe poses is redundant and can be merged with the subsequent refinement module in the decoder. Moreover, Deciwatch [38] focuses on the temporal aspects and does not take spatial dependencies into consideration, which reflect interdependence among joints. Understanding the patterns of how joints are moving together can facilitate the refinement of incorrectly estimated joints." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.832, + 0.805, + 0.848 + ], + "angle": 0, + "content": "2.2. Motion Completion and Prediction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Motion completion aims to fill the motion of missing frames with specified keyframe constraints, presenting both past and future frames. Traditional methods utilize lin" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.956 + ], + "angle": 0, + "content": "14885" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.107, + 0.094, + 0.422, + 0.352 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.439, + 0.096, + 0.634, + 0.334 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.653, + 0.097, + 0.868, + 0.355 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.075, + 0.356, + 0.892, + 0.427 + ], + "angle": 0, + "content": "Figure 2: Overview of MixSynthFormer. MixSynthFormer recovers and refines poses from sparsely sampled keyframes. It consists of \\(L\\) blocks of MixSynthEncoder blocks and two linear projection layers. MixSynthEncoder follows a standard transformer encoder structure but replaces multi-head self-attention with MixSynth Attention. MixSynth Attention synthesizes spatial and temporal attention via SynthAttention operations (depicted in Figure 3). The output from the two branches are combined and forwarded to a linear layer for feature fusion. (Detected poses in keyframes are colored, and recovered poses by interpolators are in gray.)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.441, + 0.47, + 0.592 + ], + "angle": 0, + "content": "ear, cubic-spline, Lagrange, and low-rank matrix completion, producing smooth transitions but lacking details [13]. Early learning-based methods employ RNN [9, 10] and convolutional models [12, 18]. Transformer-based models [6, 28, 30] are also adopted due to their exceptional performance in sequence-to-sequence problems. The aforementioned motion completion models are prevalent in the animation field and utilize ground-truth joint rotations and positions. However, in our case, the inputs are detected poses that can be noisy and aperiodic." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.593, + 0.47, + 0.698 + ], + "angle": 0, + "content": "Motion prediction generates future motion given only historical frames. RNN [8, 24] and transformer-based [2, 1] methods are proposed to capture temporal dynamics. GCN-based methods, such as STSGCN [31] and STGAGCN [42], further model the spatial relationships among joints, obtaining high performance by closely combining spatio-temporal modeling." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.698, + 0.47, + 0.803 + ], + "angle": 0, + "content": "Despite a range of frameworks, none of them treat motion completion and prediction as two mutually dependent tasks. Rather, each approach is specialized for one particular motion synthesis task. Notably, the sole distinction between motion completion and motion prediction pertains to the keyframe constraints. In this work, our model can handle both tasks with a unified structure." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.815, + 0.169, + 0.83 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Problem Definition. Given an input video of \\( T \\) frames, a sampler samples one frame out of every \\( K \\) frames (\\( T \\) is a multiple of \\( K \\)). The sampled frames are regarded as keyframes where poses will be estimated by a pose esti" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.441, + 0.892, + 0.593 + ], + "angle": 0, + "content": "mator. The detected poses from sampled frames may be unreliable due to complex poses or occlusion. We denote poses detected from sampled frames as \\(\\hat{\\mathbf{X}}_{\\text{noisy}}^{\\text{sampled}} \\in \\mathbb{R}^{\\frac{T}{K} \\times P}\\) which serves as the input to our framework. \\(P\\) is the number of pose parameters, which can denote joint positions (2D/3D) or rotations (6D) and may vary depending on the dataset and body representation. The objective of sampling-based pose estimation is to recover all the poses \\(\\hat{\\mathbf{X}} \\in \\mathbb{R}^{T \\times P}\\) in the original sequence from detected poses \\(\\hat{\\mathbf{X}}_{\\text{noisy}}^{\\text{sampled}}\\) in the sampled frames (referred to as sampled detected poses)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.596, + 0.893, + 0.838 + ], + "angle": 0, + "content": "Model Overview. Figure 2 provides an overview of our proposed model. The goal of MixSynthFormer is to recover and refine the poses to obtain accurate estimations efficiently. Initially, the entire pose sequence is recovered through linear interpolation or a linear layer from the sampled detected poses. Those recovered poses are transformed into pose embeddings using linear projection and are fed into \\( L \\) blocks of MixSynthEncoder. Each MixSynthEncoder comprises an attention block and a feed-forward network with residual connection, followed by a layer normalization layer. The attention block MixSynth Attention synthesizes spatial and temporal attention matrices concurrently. By integrating the spatial and temporal information, our model can refine the entire pose sequence in a simultaneous manner. Finally, the recovered poses are output via another linear layer." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.894, + 0.901 + ], + "angle": 0, + "content": "We next present details of MixSynthFormer, starting with an overview of the structure and then proceeding to the design of MixSynth Attention and the detailed operations within it. Finally, we describe the settings of using our" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14886" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.122 + ], + "angle": 0, + "content": "model on motion prediction tasks, showcasing its adaptability to other motion synthesis tasks." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.131, + 0.325, + 0.147 + ], + "angle": 0, + "content": "3.1. Design of MixSynthFormer" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.154, + 0.468, + 0.235 + ], + "angle": 0, + "content": "We adopt a recover-refine pipeline in our framework. The whole pose sequence is preliminarily recovered along the temporal dimension by a traditional or a learned interpolator based on the detected poses \\(\\hat{\\mathbf{X}}_{\\text{noise}}^{\\text{sample}}\\) in keyframes, denoted as \\(\\hat{\\mathbf{X}}_{\\text{noise}}^{\\text{recover}} \\in \\mathbb{R}^{T \\times P}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.168, + 0.244, + 0.469, + 0.267 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {X}} _ {n o i s y} ^ {r e c o v e r} = I n t e r p (\\hat {\\mathbf {X}} _ {n o i s y} ^ {s a m p l e d}) \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.274, + 0.469, + 0.469 + ], + "angle": 0, + "content": "Recovering poses from sparse and noisy inputs results in inaccurate estimates, which necessitates additional processing to obtain a clean output. Moreover, traditional interpolation methods tend to produce overly smooth motion sequences that lack details. Hence, a refinement step is necessary to generate a more precise pose sequence, which can be formulated as a sequence-to-sequence problem. Transformers have shown remarkable success in solving such problems owing to their ability to capture global correlations among tokens. We design MixSynthFormer following the workflow of a standard transformer encoder, except for replacing the self-attention module with MixSynth Attention. Following are the high-level operations of MixSynthFormer." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.47, + 0.469, + 0.593 + ], + "angle": 0, + "content": "All poses in \\(\\hat{\\mathbf{X}}_{\\text {noisy }}^{\\text {recover }}\\) are transformed to the pose embeddings \\(\\mathbf{Z}_0 \\in \\mathbb{R}^{T \\times C}\\) through a linear layer with weights \\(\\mathbf{W}_0 \\in \\mathbb{R}^{P \\times C}\\), where \\(C\\) is the dimension of the embedding space. Attention layers in transformers need position embeddings to specify the locations of input tokens, whereas our MLP-based MixSynth Attention is sensitive to the order of tokens in temporal attention synthesis like [33] and does not require additional position embeddings." + }, + { + "type": "equation", + "bbox": [ + 0.207, + 0.606, + 0.469, + 0.626 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Z} _ {0} = \\hat {\\mathbf {X}} _ {\\text {n o i s y}} ^ {\\text {r e c o v e r}} \\mathbf {W} _ {0} \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.63, + 0.469, + 0.736 + ], + "angle": 0, + "content": "The pose embeddings are then passed to \\(L\\) blocks of MixSynthEncoder. The model conforms to the conventional transformer encoder design, consisting of stacked MixSynth Attention module and feed-forward network (FFN) which is a two-layer point-wise fully connected layer with GELU activation [11]. Residual connection and layer normalization \\((LN)\\) are applied sequentially after every block." + }, + { + "type": "equation", + "bbox": [ + 0.132, + 0.745, + 0.469, + 0.763 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {Z}} _ {l} = L N \\left(M i x S y n t h A t t \\left(\\mathbf {Z} _ {l - 1}\\right) + \\mathbf {Z} _ {l - 1}\\right) \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.179, + 0.786, + 0.469, + 0.805 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Z} _ {l} = L N \\left(F F N \\left(\\hat {\\mathbf {Z}} _ {l}\\right) + \\hat {\\mathbf {Z}} _ {l}\\right) \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.469, + 0.87 + ], + "angle": 0, + "content": "Here \\(l \\in [1, L]\\) denotes the \\(l\\)-th block. \\(\\mathbf{Z}_{l-1}\\) is the output from the previous encoder block, \\(\\hat{\\mathbf{Z}}_l\\) is the intermediate representation and \\(\\mathbf{Z}_l\\) is the output of the current encoder block. \\(\\mathbf{Z}_l\\) and \\(\\hat{\\mathbf{Z}}_l\\) have the same dimension in \\(\\mathbb{R}^{T \\times C}\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "After \\(L\\) blocks of operations, the features in the embedding space \\(\\mathbf{Z}_L\\) are transformed back to the pose dimension" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.091, + 0.892, + 0.185 + ], + "angle": 0, + "content": "via another linear layer with weights \\(\\mathbf{W}_p\\in \\mathbb{R}^{C\\times P}\\). The use of the residual connection can expedite model convergence and yield more stable results. The final recovered pose sequence \\(\\hat{\\mathbf{X}}\\) is thereby the summation of the output from MixSynthEncoder blocks and the preliminarily recovered noisy poses \\(\\hat{\\mathbf{X}}_{noisy}^{recover}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.585, + 0.195, + 0.892, + 0.216 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {X}} = \\left(L N (\\mathbf {Z} _ {L})\\right) \\mathbf {W} _ {p} + \\hat {\\mathbf {X}} _ {n o i s y} ^ {r e c o v e r} \\tag {5}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.224, + 0.691, + 0.24 + ], + "angle": 0, + "content": "3.2. MixSynth Attention" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.248, + 0.892, + 0.503 + ], + "angle": 0, + "content": "Transformers are effective in capturing global correlations among tokens, but they may not be sufficient for refining noisy sequences. Token-wise attention primarily focuses on the temporal aspect, while local attention that captures the correlation among joints is also essential, particularly for recovering complex motions. To learn both global and local features, we propose MixSynth Attention, which mixes spatial and temporal synthetic attention matrices. The weights in these matrices reflect the relative inter-joint and inter-frame importance. The spatial matrix reveals the correlation among joints. When performing some motion patterns, joints that move together are highly correlated. It is helpful in locating a wrongly-detected joint from its related joints with accurate detection. The temporal matrix determines the impact of a frame with respect to other frames in the sequence, signifying the extent to which a frame affects the remaining frames." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.504, + 0.892, + 0.595 + ], + "angle": 0, + "content": "We explain the MixSynth Attention operations in detail. For simplicity, we eliminate the block index \\(l\\) in the following explanation. The synthetic attention operation (SynthAttenOP) operates on \\(\\mathbf{Z} \\in \\mathbb{R}^{T \\times C}\\) and outputs feature \\(\\mathbf{Y}_i \\in \\mathbb{R}^{T \\times C}\\), which can be spatial or temporal, denoted as \\(\\mathbf{Y}_s\\) and \\(\\mathbf{Y}_t\\), respectively." + }, + { + "type": "equation", + "bbox": [ + 0.568, + 0.607, + 0.891, + 0.624 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Y} _ {i} = \\operatorname {S y n t h A t t e n O P} _ {i} (\\mathbf {Z}), i \\in \\{s, t \\} \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.634, + 0.892, + 0.742 + ], + "angle": 0, + "content": "The spatially and temporally attended features are generated simultaneously. Inspired by [39], we apply split attention to re-balance the contribution of the two branches. Different motions may have different emphases. Inter-joint relations are more important for certain motions, while others may be more influenced by inter-frame relations. The weights \\(\\mathbf{A}_y\\in \\mathbb{R}^{2\\times C}\\) of \\(\\mathbf{Y}_s\\) and \\(\\mathbf{Y}_t\\) are calculated as" + }, + { + "type": "equation", + "bbox": [ + 0.55, + 0.752, + 0.891, + 0.769 + ], + "angle": 0, + "content": "\\[\n\\mathbf {A} _ {y} = \\operatorname {S o f t m a x} (F F N (G A P (\\mathbf {Y} _ {s} + \\mathbf {Y} _ {t}))) \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.872 + ], + "angle": 0, + "content": "where \\( GAP \\) denotes the global average pooling function, \\( FFN \\) contains two fully connected layers with ReLU activation [26] and Softmax is for normalization. The weighted sum \\( \\mathbf{Y}_{out} \\in \\mathbb{R}^{T \\times C} \\) is the summation of the element-wise product of the concatenated representations from two branches with the re-balancing weights \\( \\mathbf{A}_y \\):" + }, + { + "type": "equation", + "bbox": [ + 0.595, + 0.885, + 0.891, + 0.903 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Y} _ {\\text {o u t}} = \\operatorname {S u m} \\left(\\mathbf {A} _ {y} \\circ \\left[ \\mathbf {Y} _ {s}; \\mathbf {Y} _ {t} \\right]\\right) \\tag {8}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14887" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.123 + ], + "angle": 0, + "content": "The output of the MixSynth Attention block is attained by linearly transforming \\(\\mathbf{Y}_{out}\\) with weights \\(\\mathbf{W}_o\\in \\mathbb{R}^{C\\times C}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.167, + 0.132, + 0.469, + 0.149 + ], + "angle": 0, + "content": "\\[\nM i x S y n t h A t t (\\mathbf {Z}) = \\mathbf {Y} _ {o u t} \\mathbf {W} _ {o} \\tag {9}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.157, + 0.317, + 0.175 + ], + "angle": 0, + "content": "3.3. SynthAttention Operation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.181, + 0.47, + 0.346 + ], + "angle": 0, + "content": "The self-attention module in transformers utilizes the pairwise dot product to calculate attention weights. The computation of the query-key matrix multiplication expands quadratically as the embedding size increases. To alleviate the impact of embedding size on computational cost, we propose synthetic attention operation (SynthAttenOp), whose computation grows linearly with the increase of embedding size, as a substitute for the standard attention. We discuss this part in detail in supplementary materials. SynthAttenOp generates attention matrices using linear layers. Details of its operation are described below." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.347, + 0.469, + 0.437 + ], + "angle": 0, + "content": "SynthAttenOp operates spatially and temporally. In spatial attention synthesis, input and output are transposed. Here we use \\(\\mathbf{Z} \\in \\mathbb{R}^{N \\times D}\\) to illustrate the general case, where \\(N\\) and \\(D\\) can be substituted with either \\(C\\) or \\(T\\). The coarse synthetic attention matrix \\(\\mathbf{A}_s \\in \\mathbb{R}^{N \\times N}\\) is generated by a linear layer with weights \\(\\mathbf{W}_z \\in \\mathbb{R}^{D \\times N}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.23, + 0.448, + 0.469, + 0.464 + ], + "angle": 0, + "content": "\\[\n\\mathbf {A} _ {s} = \\mathbf {Z W} _ {z} \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.474, + 0.469, + 0.551 + ], + "angle": 0, + "content": "As different frames or joints have different contributions, we apply the Squeeze-and-Excitation layer (SELayer) [14] to regulate the influence. It can amplify critical channels while mitigating the effect of less important ones. The fine-grained attention matrix \\(\\mathbf{A}_{\\text {synth }} \\in \\mathbb{R}^{N \\times N}\\) is obtained by" + }, + { + "type": "equation", + "bbox": [ + 0.094, + 0.571, + 0.469, + 0.588 + ], + "angle": 0, + "content": "\\[\n\\operatorname {S E L a y e r} \\left(\\mathbf {A} _ {s}\\right) = \\mathbf {A} _ {s} \\circ \\sigma \\left(\\mathbf {W} _ {e} \\delta \\left(\\mathbf {W} _ {s} G A P \\left(\\mathbf {A} _ {s}\\right)\\right)\\right) \\tag {11}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.145, + 0.612, + 0.469, + 0.629 + ], + "angle": 0, + "content": "\\[\n\\mathbf {A} _ {\\text {s y n t h}} = \\operatorname {S o f t m a x} (\\operatorname {S E L a y e r} (\\mathbf {A} _ {s})) \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.634, + 0.469, + 0.789 + ], + "angle": 0, + "content": "where GAP denotes global average pooling and \\(GAP(\\mathbf{A}) \\in \\mathbb{R}^N\\), \\(\\delta\\) and \\(\\sigma\\) are Sigmoid activation and ReLU functions [26]. The reduction ratio \\((r_{se})\\) is an empirically found hyperparameter that limits model complexity [14]. \\(\\mathbf{W}_s \\in \\mathbb{R}^{\\frac{N}{r_{se}} \\times N}\\) is for dimension reduction, and \\(\\mathbf{W}_e \\in \\mathbb{R}^{N \\times \\frac{N}{r_{se}}}\\) is for expanding to the original dimension. The output of SELayer is a re-scaled input after channelwise multiplication with calculated weights. Softmax is inherited from the standard transformer, which normalizes the attention weights." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.79, + 0.469, + 0.819 + ], + "angle": 0, + "content": "In alignment with the standard transformer encoder, the output is the product of the attention matrix and the value:" + }, + { + "type": "equation", + "bbox": [ + 0.22, + 0.83, + 0.469, + 0.846 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Y} = \\mathbf {A} _ {\\text {s y n t h}} \\mathbf {V} \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.854, + 0.36, + 0.87 + ], + "angle": 0, + "content": "where \\(\\mathbf{V} = \\mathbf{Z}\\in \\mathbb{R}^{N\\times D}\\) and \\(\\mathbf{Y}\\in \\mathbb{R}^{N\\times D}\\)." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "The method described above is applicable for cases when \\( N \\) is relatively small. When \\( N \\) is large, the computation" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.092, + 0.892, + 0.151 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.545, + 0.157, + 0.846, + 0.172 + ], + "angle": 0, + "content": "Figure 3: The procedure of reduced SynthAttenOp" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.189, + 0.892, + 0.31 + ], + "angle": 0, + "content": "cost grows quadratically owing to the matrix multiplication in Eqn. 13. We apply a reduction factor \\( r \\) to the last dimension \\( D \\), saving the computation in Eqn. 13 by \\( r^2 \\) times. We denote the reduced dimension as \\( d = \\lfloor N / r \\rfloor \\). Figure 3 shows the process of reduced attention matrix generation and feature fusion. The reduced coarse attention matrix \\( \\mathbf{A}_s^r \\in \\mathbb{R}^{N \\times d} \\) and reduced value \\( \\mathbf{V}^r \\in \\mathbb{R}^{d \\times D} \\) are obtained through" + }, + { + "type": "equation", + "bbox": [ + 0.608, + 0.325, + 0.891, + 0.342 + ], + "angle": 0, + "content": "\\[\n\\mathbf {A} _ {s} ^ {r} = \\mathbf {Z} \\mathbf {W} _ {z} ^ {r}, \\mathbf {V} ^ {r} = \\mathbf {W} _ {v} \\mathbf {Z} \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.347, + 0.892, + 0.392 + ], + "angle": 0, + "content": "where weights for reduced attention matrix generation and for reducing the value are \\(\\mathbf{W}_z^r\\in \\mathbb{R}^{D\\times d}\\) and \\(\\mathbf{W}_v\\in \\mathbb{R}^{d\\times N}\\), respectively." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.401, + 0.706, + 0.417 + ], + "angle": 0, + "content": "3.4. Efficiency Calculation" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.424, + 0.892, + 0.454 + ], + "angle": 0, + "content": "The overall cost of the model per frame combines the cost of a pose estimator and the cost of MixSynthFormer:" + }, + { + "type": "equation", + "bbox": [ + 0.568, + 0.462, + 0.891, + 0.492 + ], + "angle": 0, + "content": "\\[\nF L O P s = \\frac {1}{K} * f (E s t.) + f (M S F) \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.5, + 0.892, + 0.636 + ], + "angle": 0, + "content": "\\(f(\\cdot)\\) evaluates the FLOPs of a model per frame. As one frame out of \\(K\\) frames is sampled for estimation, the per-frame cost of the estimator is \\(\\frac{1}{K} * f(Ext.\\). MixSynthFormer operates on every frame, recovering and refining poses on the whole sequence, and its FLOPs per frame is \\(f(MSF)\\). In particular, \\(f(MSF)\\) is at least \\(10^{4}\\) times smaller than \\(f(Ext.\\) and is negligible compared to the heavy pose estimator. With \\(10\\%\\) sampling ratio (\\(K = 10\\)), our framework can speed up the computation by ten times." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.644, + 0.645, + 0.659 + ], + "angle": 0, + "content": "3.5. Loss Function" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.668, + 0.892, + 0.714 + ], + "angle": 0, + "content": "Following [38], we apply L1 loss to minimize the error between the finely recovered pose sequence \\(\\hat{\\mathbf{X}}\\) and the ground-truth pose sequence \\(\\mathbf{X}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.62, + 0.723, + 0.891, + 0.763 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\frac {1}{T} \\sum_ {t = 1} ^ {T} | \\hat {\\mathbf {X}} ^ {t} - \\mathbf {X} ^ {t} | \\tag {16}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.772, + 0.736, + 0.789 + ], + "angle": 0, + "content": "3.6. Motion Prediction Setting" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.87 + ], + "angle": 0, + "content": "Motion prediction and motion completion are two subfields in conditional motion generation with the only difference lying in the keyframe constraints. We include short-term motion prediction as a sub-task and demonstrate the versatility of our model on this task." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "The input of motion prediction to our model is a historical ground-truth motion sequence \\(\\mathbf{X}_{1:T_h} \\in \\mathbb{R}^{T_h \\times P}\\), where" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "14888" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.212 + ], + "angle": 0, + "content": "\\(T_{h}\\) is the number of consecutive historical frames and \\(P\\) is the size of pose parameters (i.e., 3D positions of human body joints). The goal is to predict the future sequence \\(\\mathbf{X}_{T_h + 1:T_h + T_f} \\in \\mathbb{R}^{T_f \\times P}\\) given \\(\\mathbf{X}_{1:T_h}\\), where \\(T_{f}\\) is the number of frames to be predicted. Similar to the pose estimation settings, the future poses are coarsely generated by interpolation, and then MixSynthFormer refines and outputs the future poses." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.213, + 0.47, + 0.273 + ], + "angle": 0, + "content": "We adopt the L2-norm between the predicted sequence and the ground-truth sequence calculated only on future frames as the loss function, which is equivalent to the Mean Per Joint Position Error (MPJPE) in [31, 42]:" + }, + { + "type": "equation", + "bbox": [ + 0.17, + 0.282, + 0.469, + 0.326 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {f} = \\frac {1}{T _ {f}} \\sum_ {t = T _ {h} + 1} ^ {T _ {h} + T _ {f}} | | \\hat {\\mathbf {X}} ^ {t} - \\mathbf {X} ^ {t} | | _ {2} \\tag {17}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.335, + 0.469, + 0.365 + ], + "angle": 0, + "content": "We will test the above model in experiments, which showcases our model's adaptability to other synthesis tasks." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.378, + 0.21, + 0.394 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.403, + 0.469, + 0.567 + ], + "angle": 0, + "content": "Datasets. We evaluate MixSynthFormer on four datasets for three tasks. For 2D pose estimation (to locate the 2D coordinates of joints from images), we use the Sub-JHMDB dataset [16] that contains daily and sports actions. For 3D pose estimation (to extend 2D pose data with depth information prediction), we use the widely-used Human3.6M indoor dataset [15]. For 3D body recovery (to estimate human shape and joint angles), we use the in-the-wild dataset 3DPW which includes videos taken by a moving phone camera [35] and AIST++ [21] with diverse dancing actions shot indoors." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.569, + 0.469, + 0.718 + ], + "angle": 0, + "content": "Evaluation Metrics. We adopt the same evaluation metrics as in [38]. For 2D pose estimation, Percentage of the Correct Keypoints (PCK) is used, and three thresholds \\((20\\%, 10\\%\\) and \\(5\\%\\) of the bounding box size under the pixel level) are set. For 3D tasks, Mean Per Joint Position Error (MPJPE) is utilized to report distance error and the mean Acceleration error (Accel) is adopted to reflect the smoothness of the estimated pose sequence. Mean Floating Point Operations (FLOPs (G)) per frame are also reported to show the computation costs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Implementation Details. We use the same single-frame pose estimators and sampling strategy as in [38]. The uniform sampling ratio is set to \\(10\\%\\) (\\(K = 10\\)) in all experiments. The presence of the first and last frames is vital in recovery. In practice, we sample \\(Q\\) frames with index \\(K \\times q\\), \\(q \\in [0, \\dots, Q - 1]\\) from the input of length \\(K \\times Q + 1\\) and additionally include the last frame of the input sequence as keyframes. The number of keyframes \\(Q\\), the embedding dimension \\(C\\) and the number of MixSynthEncoder blocks \\(L\\) vary among datasets and tasks. We train the model on a single A100 GPU with testing performed on an 8-core CPU Apple M1 Pro chip to obtain the inference time. Due to" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "page limit, other detailed training settings and qualitative results are provided in supplementary materials." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.133, + 0.808, + 0.149 + ], + "angle": 0, + "content": "4.1. Comparison on 2D Pose Estimation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.156, + 0.892, + 0.231 + ], + "angle": 0, + "content": "Existing keyframe-based pose estimation methods use SimplePose [36] as the pose estimator. We follow the same experiment settings as in [40, 7, 38]. Table 1 presents the detailed PCK@0.2 results of each joint, the average performance of all three metrics and computation costs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.232, + 0.892, + 0.351 + ], + "angle": 0, + "content": "Compared with feature-based methods, KFP [40] and MAPN [7], our method improves the accuracy by over \\(4.6\\%\\) in PCK@0.2. The improvements on fast-moving joints, such as elbows, wrists and ankles, are significant with a maximum increase of \\(14.8\\%\\). Those joints often cause image blur, leading to wrong detection results. Our sampling-based method incorporates a refinement module and can mitigate the effects of incorrect detection." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.353, + 0.892, + 0.549 + ], + "angle": 0, + "content": "Compared to the sampling-based model DeciWatch [38], our model features a lighter design with 0.4M FLOPs computation, yet achieving a superior accuracy of \\(99.3\\%\\) under PCK@0.2. Notably, our model achieves almost \\(100\\%\\) in predicting the head and torso positions, which can be attributed to the integration of spatial dependencies. While the attention mechanism in [38] only considers inter-frame relations, our method also leverages inter-joint relations, which is particularly useful for limb position estimation. The accuracy of ankle increases from \\(96.5\\%\\) to \\(97.8\\%\\). By fusing information from highly-correlated joints, our model also outperforms DeciWatch in strict metrics PCK@0.1 by \\(1\\%\\) and PCK@0.05 by \\(1.3\\%\\)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.56, + 0.808, + 0.575 + ], + "angle": 0, + "content": "4.2. Comparison on 3D Pose Estimation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.583, + 0.892, + 0.657 + ], + "angle": 0, + "content": "We next compare our method on 3D keypoint estimation and body recovery tasks against single-frame estimators [25, 20, 19, 17] and the sampling-based model DeciWatch [38]. Results on localization error and acceleration error are in Table 2." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.892, + 0.81 + ], + "angle": 0, + "content": "Compared with DeciWatch [38], our model is significantly smaller with no performance degradation, thanks to SynthAttention. Our model achieves a 1-2mm reduction in MPJPE on Human3.6M and 3DPW without compromising smoothness. Notably, the FLOPs of the model trained on 3DPW are 0.03M, which is more than ten times smaller than DeciWatch. The inference time is less than 0.1 ms per frame on CPU. There are two main reasons for this: first, we only do refinements once; second, the attention matrix in our model is generated by the cost-efficient SynthAttenOp." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.901 + ], + "angle": 0, + "content": "On AIST++, our model reduces the acceleration error by \\(33\\%\\) compared to DeciWatch and \\(86\\%\\) compared to the single-frame estimator SPIN. We attribute the acceleration reduction to the integration of spatial and temporal attention. AIST++ contains poses with fast movements and diverse dancing actions. Due to the complexity of these poses," + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.956 + ], + "angle": 0, + "content": "14889" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.892, + 0.119 + ], + "angle": 0, + "content": "Table 1: Comparison with keyframe-based pose estimation methods on Sub-JHMDB dataset [16] for 2D pose estimation. R means ResNet [39]. Ratio represents the sampling ratio. Sho., Elb., Wri., Ank., Avg. stand for shoulder, elbow, wrist, ankle and average PCK, respectively." + }, + { + "type": "table", + "bbox": [ + 0.087, + 0.122, + 0.88, + 0.242 + ], + "angle": 0, + "content": "
Sub-JHMDB dataset - 2D Pose Estimation PCK@0.2PCK@0.1PCK@0.05
MethodsHeadSho.Elb.Wri.HipKneeAnk.Avg.FLOPs(G)Ratio
KFP(R18) [40]94.796.395.290.296.495.593.294.57.1940.8%--
MAPN(R18) [7]98.297.491.785.299.296.792.294.72.7035.2%--
SimplePose [36]98.697.396.598.690.395.486.594.011.96100%81.657.3
DeciWatch [38]99.899.599.799.798.799.496.598.81.196+0.000510.0%94.179.4
Ours99.999.999.8100.099.299.997.899.31.196+0.000410.0%95.180.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.258, + 0.47, + 0.314 + ], + "angle": 0, + "content": "Table 2: Comparison for 3D pose estimation and body recovery on Human3.6M [15], 3DPW [35] and AIST++ [21]. The estimators in keyframe-based frameworks are the same as the corresponding single-frame pose models." + }, + { + "type": "table", + "bbox": [ + 0.1, + 0.318, + 0.445, + 0.63 + ], + "angle": 0, + "content": "
MethodsMPJPEAccelFLOPs(G)
Human3.6M - 3D Pose Estimation
FCN [25]54.619.26.21
DeciWatch [38]52.81.50.621+0.0007
Ours50.91.50.621+0.0001
3DPW - 3D Body Recovery
SPIN [20]96.634.74.13
DeciWatch [38]93.37.10.413+0.0004
Ours91.26.80.413+0.00003
EFT [17]90.332.84.13
DeciWatch [38]89.06.80.413+0.0004
Ours88.16.30.413+0.00003
PARE [19]78.925.715.51
DeciWatch [38]77.26.91.551+0.0004
Ours76.56.71.551+0.00003
AIST++ - 3D Body Recovery
SPIN [20]107.733.84.13
DeciWatch [38]71.37.10.413+0.0007
Ours71.24.70.413+0.0005
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.651, + 0.47, + 0.698 + ], + "angle": 0, + "content": "original detections may contain erroneous estimations. By mixing spatial and temporal attention, we can effectively refine incorrect joints while maintaining the smoothness." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.71, + 0.388, + 0.727 + ], + "angle": 0, + "content": "4.3. Comparison on Motion Completion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Our model recovers and refines poses in a completion-like manner. We compare our model with traditional interpolation methods and a transformer-encoder based Motion Completion Model (MCT) [6] from the animation field. MCT can handle different motion completion tasks, and uses the concatenation of positional and rotational data as input. To be consistent with the pose estimation task, we re-implement the MCT model and tune it on our datasets. Our recover-refine process is similar to the in-filling task in MCT. Both are to recover missing poses from uniformly sampled keyframes." + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.258, + 0.892, + 0.342 + ], + "angle": 0, + "content": "Table 3: Comparison with motion completion methods on Human3.6M [15], 3DPW [35] and AIST++ [21] with estimators stated inside brackets. Nearest, linear, quadratic, cubic-spline methods are used for traditional interpolation. MPJPE (Accel) of different recovery methods are reported. The results from traditional interpolators with the lowest MPJPE are underlined." + }, + { + "type": "table", + "bbox": [ + 0.507, + 0.346, + 0.882, + 0.46 + ], + "angle": 0, + "content": "
DataNea.Lin.Qua.Cub.MCTOurs
H36M (FCN)57.054.854.654.654.550.9
(10.2)(1.9)(1.6)(1.5)(2.1)(1.5)
3DPW (SPIN)100.597.297.597.791.991.2
(19.9)(6.7)(6.2)(6.3)(8.0)(6.8)
AIST (SPIN)114.7105.9107.1107.672.071.2
(28.5)(5.7)(4.6)(4.6)(6.9)(4.7)
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.482, + 0.892, + 0.694 + ], + "angle": 0, + "content": "The results are presented in Table 3. Traditional interpolators tend to smooth the sequence but lack the ability to correct noisy poses, resulting in low acceleration errors and high position errors. MCT can reduce position errors at the expense of reduced smoothness. Our model surpasses all other methods. It can produce smooth sequences like interpolation but with more detailed and accurate motions. Specifically, when applied to Human3.6M, our model achieves the same smoothness as cubic-spline interpolation and decrease MPJPE by \\(7\\%\\). When evaluated on AIST++, our model reduces MPJPE by over \\(30\\%\\). The significant improvement in position errors without tradeoffs in smoothness shows the superiority of MixSynthFormer in recovering noisy sequences." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.708, + 0.886, + 0.725 + ], + "angle": 0, + "content": "4.4. Comparison with Motion Prediction Methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.733, + 0.892, + 0.794 + ], + "angle": 0, + "content": "We evaluate our model on the sub-task short-term motion prediction (Sec. 3.6) under four testing intervals ranging from \\(80~\\mathrm{ms}\\) to \\(400~\\mathrm{ms}\\), using \\(400~\\mathrm{ms}\\) input sequences. Table 4 gives the results." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Our model outperforms STSGCN [31] and STGAGCN [42]. Taking advantage of motion continuity, our model can predict short-term poses that conform to the motion pattern of the historical input poses. It reduces error by \\(17\\%\\) in an 80 ms interval while the improvement is less than \\(3\\%\\) in a 400 ms interval. Limited by refinement on the overly-smoothed interpolation results, our model cannot learn spe" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "14890" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.09, + 0.47, + 0.118 + ], + "angle": 0, + "content": "Table 4: Comparison for short-term motion prediction. Average MPJPE across frames on Human3.6M [15] are reported." + }, + { + "type": "table", + "bbox": [ + 0.121, + 0.123, + 0.424, + 0.194 + ], + "angle": 0, + "content": "
Methods80160320400
STSGCN [31]10.117.133.138.3
STGAGCN [42]10.116.932.538.5
Ours8.415.830.537.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.201, + 0.468, + 0.228 + ], + "angle": 0, + "content": "Table 5: Comparison with different attention matrix generation methods on 3DPW [35]" + }, + { + "type": "table", + "bbox": [ + 0.113, + 0.233, + 0.432, + 0.319 + ], + "angle": 0, + "content": "
MethodsMPJPEAccel#ParamFLOPs
Vanilla92.66.80.14M0.12M
Random92.66.90.12M0.09M
Dense92.56.80.13M0.11M
Ours92.16.80.10M0.09M
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.338, + 0.468, + 0.444 + ], + "angle": 0, + "content": "cific periodic motion patterns and high-frequency motions. The uncertainty of human motions grows as the prediction interval increases, leading to a downgraded performance in longer intervals. Nevertheless, it yields improvements on complex actions or actions with occlusion like sitting and taking photos. Action-wise results are reported in supplementary materials." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.454, + 0.231, + 0.47 + ], + "angle": 0, + "content": "4.5. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.478, + 0.469, + 0.522 + ], + "angle": 0, + "content": "We conduct the ablation study on attention matrix generation, reduction factor \\( r \\) and model structure. The input sequences are linearly interpolated from keyframe poses." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.523, + 0.469, + 0.718 + ], + "angle": 0, + "content": "Attention Matrix Generation. The attention matrix in our model is generated by a linear layer followed by a SELayer. It can also be generated by a FFN or is a learnable matrix as proposed in [32], referred to as Dense and Random. We compare our generation method with these two methods, together with the vanilla self-attention in transformers. To ensure a fair evaluation, we exclusively focus on the temporal attention matrix. Table 5 presents a comparative analysis of various attention methods, among which our generation approach stands out with the lowest number of parameters (0.1M) and minimum FLOPs (0.09M), owing to the reduction factor. Importantly, our method achieves the lowest MPJPE of \\(92.1\\mathrm{mm}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Effect of Reduction Factor. We examine the impact of the reduction factor \\( r \\) which is introduced for computation saving in SynthAttention. Specifically, we investigate how \\( r \\) in spatial \\( (r_s) \\) and temporal \\( (r_t) \\) dimensions affects the model size and its performance. As shown in Table 6, overall, applying \\( r \\) on one dimension saves \\( 8\\% \\) of the computation and up to \\( 25\\% \\) of parameters. When \\( r \\) is applied in temporal attention synthesis, we observe a smoother motion sequence with a decrease in MPJPE by \\( 0.8 \\mathrm{~mm} \\). Applying reduction on both dimensions further reduces the model parameters by \\( 30\\% \\) compared to a non-reduced one at the expense of slightly increased MPJPE." + }, + { + "type": "table_caption", + "bbox": [ + 0.512, + 0.09, + 0.88, + 0.104 + ], + "angle": 0, + "content": "Table 6: Effects of the reduction factor \\( r \\) on Human3.6M [15]" + }, + { + "type": "table", + "bbox": [ + 0.539, + 0.109, + 0.852, + 0.194 + ], + "angle": 0, + "content": "
rtrsMPJPEAccel#ParamFLOPs
1152.21.70.26M0.13M
4151.41.60.21M0.12M
1451.81.70.23M0.12M
4451.81.60.18M0.11M
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.2, + 0.892, + 0.228 + ], + "angle": 0, + "content": "Table 7: Effects of components in MixSynth Attention block on Sub-JHMDB [16]. w/o means that the component is removed." + }, + { + "type": "table", + "bbox": [ + 0.536, + 0.232, + 0.855, + 0.332 + ], + "angle": 0, + "content": "
PCK@0.2PCK@0.1
Ours99.395.1
w/o SE Layer99.094.2
w/o weighted sum98.994.7
w/o temporal attention98.894.4
w/o spatial attention98.692.9
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.349, + 0.892, + 0.485 + ], + "angle": 0, + "content": "Components in MixSynth Attention Block. MixSynth Attention blocks mix synthesized spatial and temporal attention. SELayer is incorporated to augment feature efficacy by emphasizing salient features while suppressing uninformative ones during attention matrix generation. The final output is the weighted sum of spatial and temporal representations. To evaluate the contribution of each component, we conduct ablation experiments by removing one of the components." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.485, + 0.893, + 0.681 + ], + "angle": 0, + "content": "Results under different settings are summarized in Table 7. Removing any component in MixSynth Attention leads to worse performance. When SELayer is removed, PCK@0.1 decreases by \\(0.9\\%\\), indicating its crucial role in re-calibrating attention weights. The most significant performance decrease is observed when the spatial attention component is excluded: PCK@0.1 drops from \\(95.1\\%\\) to \\(92.9\\%\\). This finding highlights the usefulness of the inter-joint relation from spatial attention generation in refinement. Moreover, combining spatial and temporal attention through a weighted sum further improves the performance by \\(0.4\\%\\). These results demonstrate the effectiveness of all components in MixSynth Attention." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.695, + 0.619, + 0.71 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.9 + ], + "angle": 0, + "content": "In this paper, we propose MixSynthFormer, a transformer encoder-like structure with mixed synthetic attention for efficient human pose estimation in videos. The MLP-based synthetic attention module generates spatial and temporal matrices simultaneously, allowing fast and accurate recovery and refinement. The flexible model design also enables it to easily adapt to other motion synthesis tasks such as short-term motion prediction. Comprehensive experiments demonstrate the superior performance of our model in 2D/3D pose estimation, body mesh recovery, and motion prediction tasks, making it a promising solution for practical use cases." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "14891" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.138 + ], + "angle": 0, + "content": "Acknowledgement. This work was supported in part by Hong Kong Innovation and Technology Support Programme Platform Research Project fund (ITS/332/21FP)." + }, + { + "type": "title", + "bbox": [ + 0.08, + 0.151, + 0.175, + 0.167 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.177, + 0.47, + 0.233 + ], + "angle": 0, + "content": "[1] Emre Aksan, Manuel Kaufmann, Peng Cao, and Otmar Hilliges. A spatio-temporal transformer for 3d human motion prediction. In 2021 International Conference on 3D Vision (3DV), pages 565-574. IEEE, 2021. 3" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.234, + 0.472, + 0.317 + ], + "angle": 0, + "content": "[2] Yujun Cai, Lin Huang, Yiwei Wang, Tat-Jen Cham, Jianfei Cai, Junsong Yuan, Jun Liu, Xu Yang, Yiheng Zhu, Xiaohui Shen, et al. Learning progressive joint propagation for human motion prediction. In Proceedings of the European Conference on Computer Vision, pages 226-242. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 6447–6456, 2022. 3, 6, 7, 8" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.092, + 0.893, + 0.36 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.956 + ], + "angle": 0, + "content": "14893" + } + ] +] \ No newline at end of file diff --git a/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/846dbe02-0b5b-4bf4-a391-96d12e988697_origin.pdf b/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/846dbe02-0b5b-4bf4-a391-96d12e988697_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..15f0e69782a7bd718000fe64f62c11a82863340d --- /dev/null +++ b/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/846dbe02-0b5b-4bf4-a391-96d12e988697_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:2fe2a504fbeb314631f54eb56318276f922c07b15cb2783da9bd032192306469 +size 575477 diff --git a/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/full.md b/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/full.md new file mode 100644 index 0000000000000000000000000000000000000000..33603b87894f8f2f005d3b099a1d11fe4571a08f --- /dev/null +++ b/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/full.md @@ -0,0 +1,358 @@ +# MixSynthFormer: A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation + +Yuran Sun, Alan William Dougherty, Zhuoying Zhang, Yi King Choi, Chuan Wu The University of Hong Kong + +yuransun@connect.hku.hk,{alanwd,tinawork}@hku.hk,{ykchoi,cwu}@cs.hku.hk + +# Abstract + +Human pose estimation in videos has wide-ranging practical applications across various fields, many of which require fast inference on resource-scarce devices, necessitating the development of efficient and accurate algorithms. Previous works have demonstrated the feasibility of exploiting motion continuity to conduct pose estimation using sparsely sampled frames with transformer-based models. However, these methods only consider the temporal relation while neglecting spatial attention, and the complexity of dot product self-attention calculations in transformers are quadratically proportional to the embedding size. To address these limitations, we propose MixSynthFormer, a transformer encoder-like model with MLP-based mixed synthetic attention. By mixing synthesized spatial and temporal attentions, our model incorporates inter-joint and inter-frame importance and can accurately estimate human poses in an entire video sequence from sparsely sampled frames. Additionally, the flexible design of our model makes it versatile for other motion synthesis tasks. Our extensive experiments on 2D/3D pose estimation, body mesh recovery, and motion prediction validate the effectiveness and efficiency of MixSynthFormer. The code is available at https://github.com/irenesesun/MixSynthFormer.git + +# 1. Introduction + +Human pose estimation is a crucial task in computer vision which aims to estimate the keypoint locations of a human body from visual inputs. It has a wide range of applications in virtual/augmented reality, healthcare, and security surveillance [23, 5]. In recent years, there has been a growing demand for real-time pose estimation in many of these applications. However, the computational burden of deep learning models makes their real-time estimation on resource-constrained devices (e.g., CPU, mobile devices) challenging. How to estimate human poses in videos ef + +![](images/e8bd756ea35c49dc38310397c312f3996facd74f6e24c1b8465e944151b606af.jpg) +(a) Feature-based Keyframe Selector + +![](images/63913df22c7377e0faec804750e093645a5dc651c436b520cf7faf4b3659db39.jpg) +(b) Sampling-based Keyframe Selector + +![](images/7521788d817b6f1540170364e75a89536f202e321c2d7eb40ddba898157e6dd7.jpg) +(c) Ours +Figure 1: Pipelines of keyframe-based pose estimation frameworks. The recover process is similar to interpolation. (a) is the feature-based pipeline [40, 7], which selects $30\%$ to $40\%$ of frames based on input features and recovers the whole sequence. (b) is the existing sampling-based pipeline [38], which uses a sampler to select frames and conducts keyframe refinement, whole sequence recovery and whole sequence refinement. (c) is our proposed simplified sampling-based pipeline excluding keyframe refinement. + +frequently remains an open research problem. + +Conventional pose estimators [3, 22, 41, 29, 4, 37, 27] estimate poses frame-by-frame, and the efficiency depends on the model design. Recent methods [40, 7, 38] have proven the viability of estimating poses in sequences based solely on keyframes. By leveraging the temporal redundancy in videos, poses in the remaining frames can be reconstructed from keyframe poses, similar to motion completion, which can significantly reduce the cost of resource-intensive pose estimators. + +In current keyframe-based pose estimation frameworks, keyframes are selected using a feature-based selector or a sampler, as illustrated in Figures 1a and 1b. Feature-based keyframe selectors [40, 7] select "good" frames based on features extracted from inputs. The final poses in the whole sequence are recovered from the estimated poses in those frames without further refinements. A more effective approach is to sample a portion of frames directly from inputs + +[38]. Without knowing the quality of selected frames in advance, poses detected from them may be noisy. To tackle this issue, the current design employs a refine-recover-refine pipeline to obtain the final pose sequence. + +Is there a way to simplify the pipeline and further reduce the computational cost? The two refinement modules for keyframe poses and recovered poses appear repetitive and unnecessary, as the poses in keyframes are refined twice. To address this, we propose a simplified recover-refine pipeline, as shown in Figure 1c. Within our framework, keyframes are selected using a sampler, and the pose sequence is recovered from detected poses in keyframes using an interpolator. The rough sequence is then refined using a single refinement module. + +We present a novel framework for sampling-based pose estimation utilizing a lightweight transformer encoder-like structure. The scaled dot product self-attention mechanism in the transformer network [34] is used to determine the relative importance of a token with respect to other tokens. However, the computational cost can be prohibitively high when using a large embedding size. To mitigate this problem, we replace the standard key-query attention with a synthetic self-attention module that generates attention weights using linear layers. To improve the quality of refinements, we synthesize both spatial and temporal attention matrices, which dynamically capture the inter-joint and inter-frame relationships. The features from both dimensions are combined and passed forward for further processing. We name our model MixSynthFormer. The main contributions of this work are summarized as follows: + +$\triangleright$ We propose a highly-efficient keyframe-based pose estimation model MixSynthFormer following the transformer encoder structure. It can effectively estimate poses from sampled keyframe poses in a recover-refine pipeline. + +$\triangleright$ We design an MLP-based mixed synthetic attention matrix generation module, MixSynth Attention, which generates attention matrices spatially and temporally from input representations. This design enables our model to dynamically fuse channel-wise and token-wise features and refine poses effectively. To speed up the computation, we introduce a reduction factor in the attention matrix generation, which further saves computation without compromising performance. + +$\triangleright$ We validate our model on 2D and 3D pose estimation and body recovery tasks with four datasets and five estimators. Experimental results demonstrate that our model outperforms all keyframe-based pose estimation frameworks in terms of accuracy and efficiency. Additionally, our model can adapt to other motion synthesis tasks by indicating different keyframes. We conduct experiments on short-term motion prediction as a sub-task, and results show that it is also competitive compared to state-of-the-art motion prediction models. + +# 2. Related Work + +# 2.1. Human Pose Estimation + +Pose estimation models can be categorized into two types based on how frames are fed into the model: frame-by-frame and keyframe-based estimators. Common pose estimation frameworks estimate poses in every frame and optimize efficiency through knowledge distillation [22, 27] or model structure design [3, 41, 29, 4, 37]. However, the computational costs are still high due to the frame-by-frame estimation. Besides, these methods are sensitive to occlusion cases in which partial joints are invisible in the camera view due to complex poses or interactions with environments, resulting in incoherent poses regardless of incorporating temporal information. In contrast, keyframe-based pose estimation frameworks exploit human motion continuity and can produce smoother sequences. Only keyframes are used for heavy single-frame estimation, while poses in the rest of the frames are recovered by a lightweight module. Thus, they can boost the efficiency of single-frame pose estimators in different tasks, such as SimplePose [36] for 2D poses, FCN [25] for 3D poses, and SPIN [20], PARE [19] and EFT [17] for body recovery. + +Keyframe-based methods can be further divided into two categories depending on how the keyframes are selected: feature-based and sampling-based. Feature-based methods [40, 7] select "good" keyframes relying on intermediate feature representations and recover the whole sequence without refinement. KFPN [40] selects frames that capture global context based on image features extracted from inputs. MAPN [7] uses the internal motion signals and residual errors to determine whether the heavy pose estimation needs to be conducted on a frame. Nevertheless, the cost of feature extraction cannot be ignored. + +Sampling-based methods [38] select keyframes using a uniform, random or customized sampling strategy. As selected frame may not be "good", these frameworks add a refinement module to clean noisy poses. Deciwatch [38] uses a standard transformer encoder to refine the uniformly sampled poses and a decoder to refine the recovered pose sequence based on denoised poses. The refinement on sampled keyframe poses is redundant and can be merged with the subsequent refinement module in the decoder. Moreover, Deciwatch [38] focuses on the temporal aspects and does not take spatial dependencies into consideration, which reflect interdependence among joints. Understanding the patterns of how joints are moving together can facilitate the refinement of incorrectly estimated joints. + +# 2.2. Motion Completion and Prediction + +Motion completion aims to fill the motion of missing frames with specified keyframe constraints, presenting both past and future frames. Traditional methods utilize lin + +![](images/901c1b48819d0e6a06a8ed5090a62be210b9b844d091b6db34c3ba83b1857d9f.jpg) + +![](images/12957400a5b7ec853386d7cdcce8ef0746b514da3291f8c96551761a067b5473.jpg) + +![](images/3c12733e75330dca013e530acd8e31ab4bd719562922a430ec766c729fb258f9.jpg) +Figure 2: Overview of MixSynthFormer. MixSynthFormer recovers and refines poses from sparsely sampled keyframes. It consists of $L$ blocks of MixSynthEncoder blocks and two linear projection layers. MixSynthEncoder follows a standard transformer encoder structure but replaces multi-head self-attention with MixSynth Attention. MixSynth Attention synthesizes spatial and temporal attention via SynthAttention operations (depicted in Figure 3). The output from the two branches are combined and forwarded to a linear layer for feature fusion. (Detected poses in keyframes are colored, and recovered poses by interpolators are in gray.) + +ear, cubic-spline, Lagrange, and low-rank matrix completion, producing smooth transitions but lacking details [13]. Early learning-based methods employ RNN [9, 10] and convolutional models [12, 18]. Transformer-based models [6, 28, 30] are also adopted due to their exceptional performance in sequence-to-sequence problems. The aforementioned motion completion models are prevalent in the animation field and utilize ground-truth joint rotations and positions. However, in our case, the inputs are detected poses that can be noisy and aperiodic. + +Motion prediction generates future motion given only historical frames. RNN [8, 24] and transformer-based [2, 1] methods are proposed to capture temporal dynamics. GCN-based methods, such as STSGCN [31] and STGAGCN [42], further model the spatial relationships among joints, obtaining high performance by closely combining spatio-temporal modeling. + +Despite a range of frameworks, none of them treat motion completion and prediction as two mutually dependent tasks. Rather, each approach is specialized for one particular motion synthesis task. Notably, the sole distinction between motion completion and motion prediction pertains to the keyframe constraints. In this work, our model can handle both tasks with a unified structure. + +# 3. Method + +Problem Definition. Given an input video of $T$ frames, a sampler samples one frame out of every $K$ frames ( $T$ is a multiple of $K$ ). The sampled frames are regarded as keyframes where poses will be estimated by a pose esti + +mator. The detected poses from sampled frames may be unreliable due to complex poses or occlusion. We denote poses detected from sampled frames as $\hat{\mathbf{X}}_{\text{noisy}}^{\text{sampled}} \in \mathbb{R}^{\frac{T}{K} \times P}$ which serves as the input to our framework. $P$ is the number of pose parameters, which can denote joint positions (2D/3D) or rotations (6D) and may vary depending on the dataset and body representation. The objective of sampling-based pose estimation is to recover all the poses $\hat{\mathbf{X}} \in \mathbb{R}^{T \times P}$ in the original sequence from detected poses $\hat{\mathbf{X}}_{\text{noisy}}^{\text{sampled}}$ in the sampled frames (referred to as sampled detected poses). + +Model Overview. Figure 2 provides an overview of our proposed model. The goal of MixSynthFormer is to recover and refine the poses to obtain accurate estimations efficiently. Initially, the entire pose sequence is recovered through linear interpolation or a linear layer from the sampled detected poses. Those recovered poses are transformed into pose embeddings using linear projection and are fed into $L$ blocks of MixSynthEncoder. Each MixSynthEncoder comprises an attention block and a feed-forward network with residual connection, followed by a layer normalization layer. The attention block MixSynth Attention synthesizes spatial and temporal attention matrices concurrently. By integrating the spatial and temporal information, our model can refine the entire pose sequence in a simultaneous manner. Finally, the recovered poses are output via another linear layer. + +We next present details of MixSynthFormer, starting with an overview of the structure and then proceeding to the design of MixSynth Attention and the detailed operations within it. Finally, we describe the settings of using our + +model on motion prediction tasks, showcasing its adaptability to other motion synthesis tasks. + +# 3.1. Design of MixSynthFormer + +We adopt a recover-refine pipeline in our framework. The whole pose sequence is preliminarily recovered along the temporal dimension by a traditional or a learned interpolator based on the detected poses $\hat{\mathbf{X}}_{\text{noise}}^{\text{sample}}$ in keyframes, denoted as $\hat{\mathbf{X}}_{\text{noise}}^{\text{recover}} \in \mathbb{R}^{T \times P}$ : + +$$ +\hat {\mathbf {X}} _ {n o i s y} ^ {r e c o v e r} = I n t e r p (\hat {\mathbf {X}} _ {n o i s y} ^ {s a m p l e d}) \tag {1} +$$ + +Recovering poses from sparse and noisy inputs results in inaccurate estimates, which necessitates additional processing to obtain a clean output. Moreover, traditional interpolation methods tend to produce overly smooth motion sequences that lack details. Hence, a refinement step is necessary to generate a more precise pose sequence, which can be formulated as a sequence-to-sequence problem. Transformers have shown remarkable success in solving such problems owing to their ability to capture global correlations among tokens. We design MixSynthFormer following the workflow of a standard transformer encoder, except for replacing the self-attention module with MixSynth Attention. Following are the high-level operations of MixSynthFormer. + +All poses in $\hat{\mathbf{X}}_{\text {noisy }}^{\text {recover }}$ are transformed to the pose embeddings $\mathbf{Z}_0 \in \mathbb{R}^{T \times C}$ through a linear layer with weights $\mathbf{W}_0 \in \mathbb{R}^{P \times C}$ , where $C$ is the dimension of the embedding space. Attention layers in transformers need position embeddings to specify the locations of input tokens, whereas our MLP-based MixSynth Attention is sensitive to the order of tokens in temporal attention synthesis like [33] and does not require additional position embeddings. + +$$ +\mathbf {Z} _ {0} = \hat {\mathbf {X}} _ {\text {n o i s y}} ^ {\text {r e c o v e r}} \mathbf {W} _ {0} \tag {2} +$$ + +The pose embeddings are then passed to $L$ blocks of MixSynthEncoder. The model conforms to the conventional transformer encoder design, consisting of stacked MixSynth Attention module and feed-forward network (FFN) which is a two-layer point-wise fully connected layer with GELU activation [11]. Residual connection and layer normalization $(LN)$ are applied sequentially after every block. + +$$ +\hat {\mathbf {Z}} _ {l} = L N \left(M i x S y n t h A t t \left(\mathbf {Z} _ {l - 1}\right) + \mathbf {Z} _ {l - 1}\right) \tag {3} +$$ + +$$ +\mathbf {Z} _ {l} = L N \left(F F N \left(\hat {\mathbf {Z}} _ {l}\right) + \hat {\mathbf {Z}} _ {l}\right) \tag {4} +$$ + +Here $l \in [1, L]$ denotes the $l$ -th block. $\mathbf{Z}_{l-1}$ is the output from the previous encoder block, $\hat{\mathbf{Z}}_l$ is the intermediate representation and $\mathbf{Z}_l$ is the output of the current encoder block. $\mathbf{Z}_l$ and $\hat{\mathbf{Z}}_l$ have the same dimension in $\mathbb{R}^{T \times C}$ . + +After $L$ blocks of operations, the features in the embedding space $\mathbf{Z}_L$ are transformed back to the pose dimension + +via another linear layer with weights $\mathbf{W}_p\in \mathbb{R}^{C\times P}$ . The use of the residual connection can expedite model convergence and yield more stable results. The final recovered pose sequence $\hat{\mathbf{X}}$ is thereby the summation of the output from MixSynthEncoder blocks and the preliminarily recovered noisy poses $\hat{\mathbf{X}}_{noisy}^{recover}$ : + +$$ +\hat {\mathbf {X}} = \left(L N (\mathbf {Z} _ {L})\right) \mathbf {W} _ {p} + \hat {\mathbf {X}} _ {n o i s y} ^ {r e c o v e r} \tag {5} +$$ + +# 3.2. MixSynth Attention + +Transformers are effective in capturing global correlations among tokens, but they may not be sufficient for refining noisy sequences. Token-wise attention primarily focuses on the temporal aspect, while local attention that captures the correlation among joints is also essential, particularly for recovering complex motions. To learn both global and local features, we propose MixSynth Attention, which mixes spatial and temporal synthetic attention matrices. The weights in these matrices reflect the relative inter-joint and inter-frame importance. The spatial matrix reveals the correlation among joints. When performing some motion patterns, joints that move together are highly correlated. It is helpful in locating a wrongly-detected joint from its related joints with accurate detection. The temporal matrix determines the impact of a frame with respect to other frames in the sequence, signifying the extent to which a frame affects the remaining frames. + +We explain the MixSynth Attention operations in detail. For simplicity, we eliminate the block index $l$ in the following explanation. The synthetic attention operation (SynthAttenOP) operates on $\mathbf{Z} \in \mathbb{R}^{T \times C}$ and outputs feature $\mathbf{Y}_i \in \mathbb{R}^{T \times C}$ , which can be spatial or temporal, denoted as $\mathbf{Y}_s$ and $\mathbf{Y}_t$ , respectively. + +$$ +\mathbf {Y} _ {i} = \operatorname {S y n t h A t t e n O P} _ {i} (\mathbf {Z}), i \in \{s, t \} \tag {6} +$$ + +The spatially and temporally attended features are generated simultaneously. Inspired by [39], we apply split attention to re-balance the contribution of the two branches. Different motions may have different emphases. Inter-joint relations are more important for certain motions, while others may be more influenced by inter-frame relations. The weights $\mathbf{A}_y\in \mathbb{R}^{2\times C}$ of $\mathbf{Y}_s$ and $\mathbf{Y}_t$ are calculated as + +$$ +\mathbf {A} _ {y} = \operatorname {S o f t m a x} (F F N (G A P (\mathbf {Y} _ {s} + \mathbf {Y} _ {t}))) \tag {7} +$$ + +where $GAP$ denotes the global average pooling function, $FFN$ contains two fully connected layers with ReLU activation [26] and Softmax is for normalization. The weighted sum $\mathbf{Y}_{out} \in \mathbb{R}^{T \times C}$ is the summation of the element-wise product of the concatenated representations from two branches with the re-balancing weights $\mathbf{A}_y$ : + +$$ +\mathbf {Y} _ {\text {o u t}} = \operatorname {S u m} \left(\mathbf {A} _ {y} \circ \left[ \mathbf {Y} _ {s}; \mathbf {Y} _ {t} \right]\right) \tag {8} +$$ + +The output of the MixSynth Attention block is attained by linearly transforming $\mathbf{Y}_{out}$ with weights $\mathbf{W}_o\in \mathbb{R}^{C\times C}$ : + +$$ +M i x S y n t h A t t (\mathbf {Z}) = \mathbf {Y} _ {o u t} \mathbf {W} _ {o} \tag {9} +$$ + +# 3.3. SynthAttention Operation + +The self-attention module in transformers utilizes the pairwise dot product to calculate attention weights. The computation of the query-key matrix multiplication expands quadratically as the embedding size increases. To alleviate the impact of embedding size on computational cost, we propose synthetic attention operation (SynthAttenOp), whose computation grows linearly with the increase of embedding size, as a substitute for the standard attention. We discuss this part in detail in supplementary materials. SynthAttenOp generates attention matrices using linear layers. Details of its operation are described below. + +SynthAttenOp operates spatially and temporally. In spatial attention synthesis, input and output are transposed. Here we use $\mathbf{Z} \in \mathbb{R}^{N \times D}$ to illustrate the general case, where $N$ and $D$ can be substituted with either $C$ or $T$ . The coarse synthetic attention matrix $\mathbf{A}_s \in \mathbb{R}^{N \times N}$ is generated by a linear layer with weights $\mathbf{W}_z \in \mathbb{R}^{D \times N}$ : + +$$ +\mathbf {A} _ {s} = \mathbf {Z W} _ {z} \tag {10} +$$ + +As different frames or joints have different contributions, we apply the Squeeze-and-Excitation layer (SELayer) [14] to regulate the influence. It can amplify critical channels while mitigating the effect of less important ones. The fine-grained attention matrix $\mathbf{A}_{\text {synth }} \in \mathbb{R}^{N \times N}$ is obtained by + +$$ +\operatorname {S E L a y e r} \left(\mathbf {A} _ {s}\right) = \mathbf {A} _ {s} \circ \sigma \left(\mathbf {W} _ {e} \delta \left(\mathbf {W} _ {s} G A P \left(\mathbf {A} _ {s}\right)\right)\right) \tag {11} +$$ + +$$ +\mathbf {A} _ {\text {s y n t h}} = \operatorname {S o f t m a x} (\operatorname {S E L a y e r} (\mathbf {A} _ {s})) \tag {12} +$$ + +where GAP denotes global average pooling and $GAP(\mathbf{A}) \in \mathbb{R}^N$ , $\delta$ and $\sigma$ are Sigmoid activation and ReLU functions [26]. The reduction ratio $(r_{se})$ is an empirically found hyperparameter that limits model complexity [14]. $\mathbf{W}_s \in \mathbb{R}^{\frac{N}{r_{se}} \times N}$ is for dimension reduction, and $\mathbf{W}_e \in \mathbb{R}^{N \times \frac{N}{r_{se}}}$ is for expanding to the original dimension. The output of SELayer is a re-scaled input after channelwise multiplication with calculated weights. Softmax is inherited from the standard transformer, which normalizes the attention weights. + +In alignment with the standard transformer encoder, the output is the product of the attention matrix and the value: + +$$ +\mathbf {Y} = \mathbf {A} _ {\text {s y n t h}} \mathbf {V} \tag {13} +$$ + +where $\mathbf{V} = \mathbf{Z}\in \mathbb{R}^{N\times D}$ and $\mathbf{Y}\in \mathbb{R}^{N\times D}$ . + +The method described above is applicable for cases when $N$ is relatively small. When $N$ is large, the computation + +![](images/8a97663b6eccb8f6b299245b3ad8871f839592586046d9a46967aedc9c04cc0d.jpg) +Figure 3: The procedure of reduced SynthAttenOp + +cost grows quadratically owing to the matrix multiplication in Eqn. 13. We apply a reduction factor $r$ to the last dimension $D$ , saving the computation in Eqn. 13 by $r^2$ times. We denote the reduced dimension as $d = \lfloor N / r \rfloor$ . Figure 3 shows the process of reduced attention matrix generation and feature fusion. The reduced coarse attention matrix $\mathbf{A}_s^r \in \mathbb{R}^{N \times d}$ and reduced value $\mathbf{V}^r \in \mathbb{R}^{d \times D}$ are obtained through + +$$ +\mathbf {A} _ {s} ^ {r} = \mathbf {Z} \mathbf {W} _ {z} ^ {r}, \mathbf {V} ^ {r} = \mathbf {W} _ {v} \mathbf {Z} \tag {14} +$$ + +where weights for reduced attention matrix generation and for reducing the value are $\mathbf{W}_z^r\in \mathbb{R}^{D\times d}$ and $\mathbf{W}_v\in \mathbb{R}^{d\times N}$ , respectively. + +# 3.4. Efficiency Calculation + +The overall cost of the model per frame combines the cost of a pose estimator and the cost of MixSynthFormer: + +$$ +F L O P s = \frac {1}{K} * f (E s t.) + f (M S F) \tag {15} +$$ + +$f(\cdot)$ evaluates the FLOPs of a model per frame. As one frame out of $K$ frames is sampled for estimation, the per-frame cost of the estimator is $\frac{1}{K} * f(Ext.$ . MixSynthFormer operates on every frame, recovering and refining poses on the whole sequence, and its FLOPs per frame is $f(MSF)$ . In particular, $f(MSF)$ is at least $10^{4}$ times smaller than $f(Ext.$ and is negligible compared to the heavy pose estimator. With $10\%$ sampling ratio ( $K = 10$ ), our framework can speed up the computation by ten times. + +# 3.5. Loss Function + +Following [38], we apply L1 loss to minimize the error between the finely recovered pose sequence $\hat{\mathbf{X}}$ and the ground-truth pose sequence $\mathbf{X}$ : + +$$ +\mathcal {L} = \frac {1}{T} \sum_ {t = 1} ^ {T} | \hat {\mathbf {X}} ^ {t} - \mathbf {X} ^ {t} | \tag {16} +$$ + +# 3.6. Motion Prediction Setting + +Motion prediction and motion completion are two subfields in conditional motion generation with the only difference lying in the keyframe constraints. We include short-term motion prediction as a sub-task and demonstrate the versatility of our model on this task. + +The input of motion prediction to our model is a historical ground-truth motion sequence $\mathbf{X}_{1:T_h} \in \mathbb{R}^{T_h \times P}$ , where + +$T_{h}$ is the number of consecutive historical frames and $P$ is the size of pose parameters (i.e., 3D positions of human body joints). The goal is to predict the future sequence $\mathbf{X}_{T_h + 1:T_h + T_f} \in \mathbb{R}^{T_f \times P}$ given $\mathbf{X}_{1:T_h}$ , where $T_{f}$ is the number of frames to be predicted. Similar to the pose estimation settings, the future poses are coarsely generated by interpolation, and then MixSynthFormer refines and outputs the future poses. + +We adopt the L2-norm between the predicted sequence and the ground-truth sequence calculated only on future frames as the loss function, which is equivalent to the Mean Per Joint Position Error (MPJPE) in [31, 42]: + +$$ +\mathcal {L} _ {f} = \frac {1}{T _ {f}} \sum_ {t = T _ {h} + 1} ^ {T _ {h} + T _ {f}} | | \hat {\mathbf {X}} ^ {t} - \mathbf {X} ^ {t} | | _ {2} \tag {17} +$$ + +We will test the above model in experiments, which showcases our model's adaptability to other synthesis tasks. + +# 4. Experiments + +Datasets. We evaluate MixSynthFormer on four datasets for three tasks. For 2D pose estimation (to locate the 2D coordinates of joints from images), we use the Sub-JHMDB dataset [16] that contains daily and sports actions. For 3D pose estimation (to extend 2D pose data with depth information prediction), we use the widely-used Human3.6M indoor dataset [15]. For 3D body recovery (to estimate human shape and joint angles), we use the in-the-wild dataset 3DPW which includes videos taken by a moving phone camera [35] and AIST++ [21] with diverse dancing actions shot indoors. + +Evaluation Metrics. We adopt the same evaluation metrics as in [38]. For 2D pose estimation, Percentage of the Correct Keypoints (PCK) is used, and three thresholds $(20\%, 10\%$ and $5\%$ of the bounding box size under the pixel level) are set. For 3D tasks, Mean Per Joint Position Error (MPJPE) is utilized to report distance error and the mean Acceleration error (Accel) is adopted to reflect the smoothness of the estimated pose sequence. Mean Floating Point Operations (FLOPs (G)) per frame are also reported to show the computation costs. + +Implementation Details. We use the same single-frame pose estimators and sampling strategy as in [38]. The uniform sampling ratio is set to $10\%$ ( $K = 10$ ) in all experiments. The presence of the first and last frames is vital in recovery. In practice, we sample $Q$ frames with index $K \times q$ , $q \in [0, \dots, Q - 1]$ from the input of length $K \times Q + 1$ and additionally include the last frame of the input sequence as keyframes. The number of keyframes $Q$ , the embedding dimension $C$ and the number of MixSynthEncoder blocks $L$ vary among datasets and tasks. We train the model on a single A100 GPU with testing performed on an 8-core CPU Apple M1 Pro chip to obtain the inference time. Due to + +page limit, other detailed training settings and qualitative results are provided in supplementary materials. + +# 4.1. Comparison on 2D Pose Estimation + +Existing keyframe-based pose estimation methods use SimplePose [36] as the pose estimator. We follow the same experiment settings as in [40, 7, 38]. Table 1 presents the detailed PCK@0.2 results of each joint, the average performance of all three metrics and computation costs. + +Compared with feature-based methods, KFP [40] and MAPN [7], our method improves the accuracy by over $4.6\%$ in PCK@0.2. The improvements on fast-moving joints, such as elbows, wrists and ankles, are significant with a maximum increase of $14.8\%$ . Those joints often cause image blur, leading to wrong detection results. Our sampling-based method incorporates a refinement module and can mitigate the effects of incorrect detection. + +Compared to the sampling-based model DeciWatch [38], our model features a lighter design with 0.4M FLOPs computation, yet achieving a superior accuracy of $99.3\%$ under PCK@0.2. Notably, our model achieves almost $100\%$ in predicting the head and torso positions, which can be attributed to the integration of spatial dependencies. While the attention mechanism in [38] only considers inter-frame relations, our method also leverages inter-joint relations, which is particularly useful for limb position estimation. The accuracy of ankle increases from $96.5\%$ to $97.8\%$ . By fusing information from highly-correlated joints, our model also outperforms DeciWatch in strict metrics PCK@0.1 by $1\%$ and PCK@0.05 by $1.3\%$ . + +# 4.2. Comparison on 3D Pose Estimation + +We next compare our method on 3D keypoint estimation and body recovery tasks against single-frame estimators [25, 20, 19, 17] and the sampling-based model DeciWatch [38]. Results on localization error and acceleration error are in Table 2. + +Compared with DeciWatch [38], our model is significantly smaller with no performance degradation, thanks to SynthAttention. Our model achieves a 1-2mm reduction in MPJPE on Human3.6M and 3DPW without compromising smoothness. Notably, the FLOPs of the model trained on 3DPW are 0.03M, which is more than ten times smaller than DeciWatch. The inference time is less than 0.1 ms per frame on CPU. There are two main reasons for this: first, we only do refinements once; second, the attention matrix in our model is generated by the cost-efficient SynthAttenOp. + +On AIST++, our model reduces the acceleration error by $33\%$ compared to DeciWatch and $86\%$ compared to the single-frame estimator SPIN. We attribute the acceleration reduction to the integration of spatial and temporal attention. AIST++ contains poses with fast movements and diverse dancing actions. Due to the complexity of these poses, + +Table 1: Comparison with keyframe-based pose estimation methods on Sub-JHMDB dataset [16] for 2D pose estimation. R means ResNet [39]. Ratio represents the sampling ratio. Sho., Elb., Wri., Ank., Avg. stand for shoulder, elbow, wrist, ankle and average PCK, respectively. + +
Sub-JHMDB dataset - 2D Pose Estimation PCK@0.2PCK@0.1PCK@0.05
MethodsHeadSho.Elb.Wri.HipKneeAnk.Avg.FLOPs(G)Ratio
KFP(R18) [40]94.796.395.290.296.495.593.294.57.1940.8%--
MAPN(R18) [7]98.297.491.785.299.296.792.294.72.7035.2%--
SimplePose [36]98.697.396.598.690.395.486.594.011.96100%81.657.3
DeciWatch [38]99.899.599.799.798.799.496.598.81.196+0.000510.0%94.179.4
Ours99.999.999.8100.099.299.997.899.31.196+0.000410.0%95.180.7
+ +Table 2: Comparison for 3D pose estimation and body recovery on Human3.6M [15], 3DPW [35] and AIST++ [21]. The estimators in keyframe-based frameworks are the same as the corresponding single-frame pose models. + +
MethodsMPJPEAccelFLOPs(G)
Human3.6M - 3D Pose Estimation
FCN [25]54.619.26.21
DeciWatch [38]52.81.50.621+0.0007
Ours50.91.50.621+0.0001
3DPW - 3D Body Recovery
SPIN [20]96.634.74.13
DeciWatch [38]93.37.10.413+0.0004
Ours91.26.80.413+0.00003
EFT [17]90.332.84.13
DeciWatch [38]89.06.80.413+0.0004
Ours88.16.30.413+0.00003
PARE [19]78.925.715.51
DeciWatch [38]77.26.91.551+0.0004
Ours76.56.71.551+0.00003
AIST++ - 3D Body Recovery
SPIN [20]107.733.84.13
DeciWatch [38]71.37.10.413+0.0007
Ours71.24.70.413+0.0005
+ +original detections may contain erroneous estimations. By mixing spatial and temporal attention, we can effectively refine incorrect joints while maintaining the smoothness. + +# 4.3. Comparison on Motion Completion + +Our model recovers and refines poses in a completion-like manner. We compare our model with traditional interpolation methods and a transformer-encoder based Motion Completion Model (MCT) [6] from the animation field. MCT can handle different motion completion tasks, and uses the concatenation of positional and rotational data as input. To be consistent with the pose estimation task, we re-implement the MCT model and tune it on our datasets. Our recover-refine process is similar to the in-filling task in MCT. Both are to recover missing poses from uniformly sampled keyframes. + +Table 3: Comparison with motion completion methods on Human3.6M [15], 3DPW [35] and AIST++ [21] with estimators stated inside brackets. Nearest, linear, quadratic, cubic-spline methods are used for traditional interpolation. MPJPE (Accel) of different recovery methods are reported. The results from traditional interpolators with the lowest MPJPE are underlined. + +
DataNea.Lin.Qua.Cub.MCTOurs
H36M (FCN)57.054.854.654.654.550.9
(10.2)(1.9)(1.6)(1.5)(2.1)(1.5)
3DPW (SPIN)100.597.297.597.791.991.2
(19.9)(6.7)(6.2)(6.3)(8.0)(6.8)
AIST (SPIN)114.7105.9107.1107.672.071.2
(28.5)(5.7)(4.6)(4.6)(6.9)(4.7)
+ +The results are presented in Table 3. Traditional interpolators tend to smooth the sequence but lack the ability to correct noisy poses, resulting in low acceleration errors and high position errors. MCT can reduce position errors at the expense of reduced smoothness. Our model surpasses all other methods. It can produce smooth sequences like interpolation but with more detailed and accurate motions. Specifically, when applied to Human3.6M, our model achieves the same smoothness as cubic-spline interpolation and decrease MPJPE by $7\%$ . When evaluated on AIST++, our model reduces MPJPE by over $30\%$ . The significant improvement in position errors without tradeoffs in smoothness shows the superiority of MixSynthFormer in recovering noisy sequences. + +# 4.4. Comparison with Motion Prediction Methods + +We evaluate our model on the sub-task short-term motion prediction (Sec. 3.6) under four testing intervals ranging from $80~\mathrm{ms}$ to $400~\mathrm{ms}$ , using $400~\mathrm{ms}$ input sequences. Table 4 gives the results. + +Our model outperforms STSGCN [31] and STGAGCN [42]. Taking advantage of motion continuity, our model can predict short-term poses that conform to the motion pattern of the historical input poses. It reduces error by $17\%$ in an 80 ms interval while the improvement is less than $3\%$ in a 400 ms interval. Limited by refinement on the overly-smoothed interpolation results, our model cannot learn spe + +Table 4: Comparison for short-term motion prediction. Average MPJPE across frames on Human3.6M [15] are reported. + +
Methods80160320400
STSGCN [31]10.117.133.138.3
STGAGCN [42]10.116.932.538.5
Ours8.415.830.537.4
+ +Table 5: Comparison with different attention matrix generation methods on 3DPW [35] + +
MethodsMPJPEAccel#ParamFLOPs
Vanilla92.66.80.14M0.12M
Random92.66.90.12M0.09M
Dense92.56.80.13M0.11M
Ours92.16.80.10M0.09M
+ +cific periodic motion patterns and high-frequency motions. The uncertainty of human motions grows as the prediction interval increases, leading to a downgraded performance in longer intervals. Nevertheless, it yields improvements on complex actions or actions with occlusion like sitting and taking photos. Action-wise results are reported in supplementary materials. + +# 4.5. Ablation Study + +We conduct the ablation study on attention matrix generation, reduction factor $r$ and model structure. The input sequences are linearly interpolated from keyframe poses. + +Attention Matrix Generation. The attention matrix in our model is generated by a linear layer followed by a SELayer. It can also be generated by a FFN or is a learnable matrix as proposed in [32], referred to as Dense and Random. We compare our generation method with these two methods, together with the vanilla self-attention in transformers. To ensure a fair evaluation, we exclusively focus on the temporal attention matrix. Table 5 presents a comparative analysis of various attention methods, among which our generation approach stands out with the lowest number of parameters (0.1M) and minimum FLOPs (0.09M), owing to the reduction factor. Importantly, our method achieves the lowest MPJPE of $92.1\mathrm{mm}$ . + +Effect of Reduction Factor. We examine the impact of the reduction factor $r$ which is introduced for computation saving in SynthAttention. Specifically, we investigate how $r$ in spatial $(r_s)$ and temporal $(r_t)$ dimensions affects the model size and its performance. As shown in Table 6, overall, applying $r$ on one dimension saves $8\%$ of the computation and up to $25\%$ of parameters. When $r$ is applied in temporal attention synthesis, we observe a smoother motion sequence with a decrease in MPJPE by $0.8 \mathrm{~mm}$ . Applying reduction on both dimensions further reduces the model parameters by $30\%$ compared to a non-reduced one at the expense of slightly increased MPJPE. + +Table 6: Effects of the reduction factor $r$ on Human3.6M [15] + +
rtrsMPJPEAccel#ParamFLOPs
1152.21.70.26M0.13M
4151.41.60.21M0.12M
1451.81.70.23M0.12M
4451.81.60.18M0.11M
+ +Table 7: Effects of components in MixSynth Attention block on Sub-JHMDB [16]. w/o means that the component is removed. + +
PCK@0.2PCK@0.1
Ours99.395.1
w/o SE Layer99.094.2
w/o weighted sum98.994.7
w/o temporal attention98.894.4
w/o spatial attention98.692.9
+ +Components in MixSynth Attention Block. MixSynth Attention blocks mix synthesized spatial and temporal attention. SELayer is incorporated to augment feature efficacy by emphasizing salient features while suppressing uninformative ones during attention matrix generation. The final output is the weighted sum of spatial and temporal representations. To evaluate the contribution of each component, we conduct ablation experiments by removing one of the components. + +Results under different settings are summarized in Table 7. Removing any component in MixSynth Attention leads to worse performance. When SELayer is removed, PCK@0.1 decreases by $0.9\%$ , indicating its crucial role in re-calibrating attention weights. The most significant performance decrease is observed when the spatial attention component is excluded: PCK@0.1 drops from $95.1\%$ to $92.9\%$ . This finding highlights the usefulness of the inter-joint relation from spatial attention generation in refinement. Moreover, combining spatial and temporal attention through a weighted sum further improves the performance by $0.4\%$ . These results demonstrate the effectiveness of all components in MixSynth Attention. + +# 5. Conclusion + +In this paper, we propose MixSynthFormer, a transformer encoder-like structure with mixed synthetic attention for efficient human pose estimation in videos. The MLP-based synthetic attention module generates spatial and temporal matrices simultaneously, allowing fast and accurate recovery and refinement. The flexible model design also enables it to easily adapt to other motion synthesis tasks such as short-term motion prediction. Comprehensive experiments demonstrate the superior performance of our model in 2D/3D pose estimation, body mesh recovery, and motion prediction tasks, making it a promising solution for practical use cases. + +Acknowledgement. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 6447–6456, 2022. 3, 6, 7, 8 \ No newline at end of file diff --git a/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/images.zip b/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..d4bb83f4753072a90741ee90e5b572b11728113d --- /dev/null +++ b/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:a848b428e9f01162b33807ac835b95a06778ae52885f9b01e53d0710bd141c5f +size 400458 diff --git a/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/layout.json b/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..3aafb01800754c6c12e99c8635741a4ab8bdad06 --- /dev/null +++ b/2023/MixSynthFormer_ A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation/layout.json @@ -0,0 +1,9595 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 52, + 103, + 541, + 138 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 103, + 541, + 138 + ], + "spans": [ + { + "bbox": [ + 52, + 103, + 541, + 138 + ], + "type": "text", + "content": "MixSynthFormer: A Transformer Encoder-like Structure with Mixed Synthetic Self-attention for Efficient Human Pose Estimation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 101, + 161, + 493, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 101, + 161, + 493, + 190 + ], + "spans": [ + { + "bbox": [ + 101, + 161, + 493, + 190 + ], + "type": "text", + "content": "Yuran Sun, Alan William Dougherty, Zhuoying Zhang, Yi King Choi, Chuan Wu The University of Hong Kong" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 105, + 191, + 487, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 105, + 191, + 487, + 204 + ], + "spans": [ + { + "bbox": [ + 105, + 191, + 487, + 204 + ], + "type": "text", + "content": "yuransun@connect.hku.hk,{alanwd,tinawork}@hku.hk,{ykchoi,cwu}@cs.hku.hk" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "spans": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 258, + 290, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 258, + 290, + 545 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 290, + 545 + ], + "type": "text", + "content": "Human pose estimation in videos has wide-ranging practical applications across various fields, many of which require fast inference on resource-scarce devices, necessitating the development of efficient and accurate algorithms. Previous works have demonstrated the feasibility of exploiting motion continuity to conduct pose estimation using sparsely sampled frames with transformer-based models. However, these methods only consider the temporal relation while neglecting spatial attention, and the complexity of dot product self-attention calculations in transformers are quadratically proportional to the embedding size. To address these limitations, we propose MixSynthFormer, a transformer encoder-like model with MLP-based mixed synthetic attention. By mixing synthesized spatial and temporal attentions, our model incorporates inter-joint and inter-frame importance and can accurately estimate human poses in an entire video sequence from sparsely sampled frames. Additionally, the flexible design of our model makes it versatile for other motion synthesis tasks. Our extensive experiments on 2D/3D pose estimation, body mesh recovery, and motion prediction validate the effectiveness and efficiency of MixSynthFormer. 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How to estimate human poses in videos ef" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 317, + 230, + 537, + 270 + ], + "blocks": [ + { + "bbox": [ + 317, + 230, + 537, + 270 + ], + "lines": [ + { + "bbox": [ + 317, + 230, + 537, + 270 + ], + "spans": [ + { + "bbox": [ + 317, + 230, + 537, + 270 + ], + "type": "image", + "image_path": "e8bd756ea35c49dc38310397c312f3996facd74f6e24c1b8465e944151b606af.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 366, + 275, + 487, + 286 + ], + "lines": [ + { + "bbox": [ + 366, + 275, + 487, + 286 + ], + "spans": [ + { + "bbox": [ + 366, + 275, + 487, + 286 + ], + "type": "text", + "content": "(a) Feature-based Keyframe Selector" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 329, + 292, + 524, + 327 + ], + "blocks": [ + { + "bbox": [ + 329, + 292, + 524, + 327 + ], + "lines": [ + { + "bbox": [ + 329, + 292, + 524, + 327 + ], + "spans": [ + { + "bbox": [ + 329, + 292, + 524, + 327 + ], + "type": "image", + "image_path": "63913df22c7377e0faec804750e093645a5dc651c436b520cf7faf4b3659db39.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 362, + 329, + 489, + 339 + ], + "lines": [ + { + "bbox": [ + 362, + 329, + 489, + 339 + ], + "spans": [ + { + "bbox": [ + 362, + 329, + 489, + 339 + ], + "type": "text", + "content": "(b) Sampling-based Keyframe Selector" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 341, + 345, + 512, + 380 + ], + "blocks": [ + { + "bbox": [ + 341, + 345, + 512, + 380 + ], + "lines": [ + { + "bbox": [ + 341, + 345, + 512, + 380 + ], + "spans": [ + { + "bbox": [ + 341, + 345, + 512, + 380 + ], + "type": "image", + "image_path": "7521788d817b6f1540170364e75a89536f202e321c2d7eb40ddba898157e6dd7.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 412, + 382, + 440, + 392 + ], + "lines": [ + { + "bbox": [ + 412, + 382, + 440, + 392 + ], + "spans": [ + { + "bbox": [ + 412, + 382, + 440, + 392 + ], + "type": "text", + "content": "(c) Ours" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 396, + 547, + 485 + ], + "lines": [ + { + "bbox": [ + 304, + 396, + 547, + 485 + ], + "spans": [ + { + "bbox": [ + 304, + 396, + 547, + 485 + ], + "type": "text", + "content": "Figure 1: Pipelines of keyframe-based pose estimation frameworks. The recover process is similar to interpolation. (a) is the feature-based pipeline [40, 7], which selects " + }, + { + "bbox": [ + 304, + 396, + 547, + 485 + ], + "type": "inline_equation", + "content": "30\\%" + }, + { + "bbox": [ + 304, + 396, + 547, + 485 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 396, + 547, + 485 + ], + "type": "inline_equation", + "content": "40\\%" + }, + { + "bbox": [ + 304, + 396, + 547, + 485 + ], + "type": "text", + "content": " of frames based on input features and recovers the whole sequence. (b) is the existing sampling-based pipeline [38], which uses a sampler to select frames and conducts keyframe refinement, whole sequence recovery and whole sequence refinement. (c) is our proposed simplified sampling-based pipeline excluding keyframe refinement." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 498, + 484, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 498, + 484, + 510 + ], + "spans": [ + { + "bbox": [ + 306, + 498, + 484, + 510 + ], + "type": "text", + "content": "frequently remains an open research problem." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 510, + 547, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 547, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 547, + 616 + ], + "type": "text", + "content": "Conventional pose estimators [3, 22, 41, 29, 4, 37, 27] estimate poses frame-by-frame, and the efficiency depends on the model design. Recent methods [40, 7, 38] have proven the viability of estimating poses in sequences based solely on keyframes. By leveraging the temporal redundancy in videos, poses in the remaining frames can be reconstructed from keyframe poses, similar to motion completion, which can significantly reduce the cost of resource-intensive pose estimators." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 617, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 548, + 715 + ], + "type": "text", + "content": "In current keyframe-based pose estimation frameworks, keyframes are selected using a feature-based selector or a sampler, as illustrated in Figures 1a and 1b. Feature-based keyframe selectors [40, 7] select \"good\" frames based on features extracted from inputs. The final poses in the whole sequence are recovered from the estimated poses in those frames without further refinements. A more effective approach is to sample a portion of frames directly from inputs" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "14884" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 286, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 286, + 120 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 286, + 120 + ], + "type": "text", + "content": "[38]. Without knowing the quality of selected frames in advance, poses detected from them may be noisy. To tackle this issue, the current design employs a refine-recover-refine pipeline to obtain the final pose sequence." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 121, + 286, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 121, + 286, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 121, + 286, + 240 + ], + "type": "text", + "content": "Is there a way to simplify the pipeline and further reduce the computational cost? The two refinement modules for keyframe poses and recovered poses appear repetitive and unnecessary, as the poses in keyframes are refined twice. To address this, we propose a simplified recover-refine pipeline, as shown in Figure 1c. Within our framework, keyframes are selected using a sampler, and the pose sequence is recovered from detected poses in keyframes using an interpolator. The rough sequence is then refined using a single refinement module." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 243, + 286, + 433 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 243, + 286, + 433 + ], + "spans": [ + { + "bbox": [ + 46, + 243, + 286, + 433 + ], + "type": "text", + "content": "We present a novel framework for sampling-based pose estimation utilizing a lightweight transformer encoder-like structure. The scaled dot product self-attention mechanism in the transformer network [34] is used to determine the relative importance of a token with respect to other tokens. However, the computational cost can be prohibitively high when using a large embedding size. To mitigate this problem, we replace the standard key-query attention with a synthetic self-attention module that generates attention weights using linear layers. To improve the quality of refinements, we synthesize both spatial and temporal attention matrices, which dynamically capture the inter-joint and inter-frame relationships. The features from both dimensions are combined and passed forward for further processing. We name our model MixSynthFormer. The main contributions of this work are summarized as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 435, + 286, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 435, + 286, + 483 + ], + "spans": [ + { + "bbox": [ + 47, + 435, + 286, + 483 + ], + "type": "inline_equation", + "content": "\\triangleright" + }, + { + "bbox": [ + 47, + 435, + 286, + 483 + ], + "type": "text", + "content": " We propose a highly-efficient keyframe-based pose estimation model MixSynthFormer following the transformer encoder structure. It can effectively estimate poses from sampled keyframe poses in a recover-refine pipeline." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 484, + 286, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 484, + 286, + 591 + ], + "spans": [ + { + "bbox": [ + 46, + 484, + 286, + 591 + ], + "type": "inline_equation", + "content": "\\triangleright" + }, + { + "bbox": [ + 46, + 484, + 286, + 591 + ], + "type": "text", + "content": " We design an MLP-based mixed synthetic attention matrix generation module, MixSynth Attention, which generates attention matrices spatially and temporally from input representations. This design enables our model to dynamically fuse channel-wise and token-wise features and refine poses effectively. To speed up the computation, we introduce a reduction factor in the attention matrix generation, which further saves computation without compromising performance." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 594, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 286, + 712 + ], + "type": "inline_equation", + "content": "\\triangleright" + }, + { + "bbox": [ + 46, + 594, + 286, + 712 + ], + "type": "text", + "content": " We validate our model on 2D and 3D pose estimation and body recovery tasks with four datasets and five estimators. Experimental results demonstrate that our model outperforms all keyframe-based pose estimation frameworks in terms of accuracy and efficiency. Additionally, our model can adapt to other motion synthesis tasks by indicating different keyframes. We conduct experiments on short-term motion prediction as a sub-task, and results show that it is also competitive compared to state-of-the-art motion prediction models." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 71, + 392, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 71, + 392, + 83 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 392, + 83 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 91, + 441, + 103 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 91, + 441, + 103 + ], + "spans": [ + { + "bbox": [ + 306, + 91, + 441, + 103 + ], + "type": "text", + "content": "2.1. Human Pose Estimation" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 110, + 545, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 110, + 545, + 350 + ], + "spans": [ + { + "bbox": [ + 304, + 110, + 545, + 350 + ], + "type": "text", + "content": "Pose estimation models can be categorized into two types based on how frames are fed into the model: frame-by-frame and keyframe-based estimators. Common pose estimation frameworks estimate poses in every frame and optimize efficiency through knowledge distillation [22, 27] or model structure design [3, 41, 29, 4, 37]. However, the computational costs are still high due to the frame-by-frame estimation. Besides, these methods are sensitive to occlusion cases in which partial joints are invisible in the camera view due to complex poses or interactions with environments, resulting in incoherent poses regardless of incorporating temporal information. In contrast, keyframe-based pose estimation frameworks exploit human motion continuity and can produce smoother sequences. Only keyframes are used for heavy single-frame estimation, while poses in the rest of the frames are recovered by a lightweight module. Thus, they can boost the efficiency of single-frame pose estimators in different tasks, such as SimplePose [36] for 2D poses, FCN [25] for 3D poses, and SPIN [20], PARE [19] and EFT [17] for body recovery." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 350, + 545, + 481 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 350, + 545, + 481 + ], + "spans": [ + { + "bbox": [ + 304, + 350, + 545, + 481 + ], + "type": "text", + "content": "Keyframe-based methods can be further divided into two categories depending on how the keyframes are selected: feature-based and sampling-based. Feature-based methods [40, 7] select \"good\" keyframes relying on intermediate feature representations and recover the whole sequence without refinement. KFPN [40] selects frames that capture global context based on image features extracted from inputs. MAPN [7] uses the internal motion signals and residual errors to determine whether the heavy pose estimation needs to be conducted on a frame. Nevertheless, the cost of feature extraction cannot be ignored." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 482, + 545, + 649 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 482, + 545, + 649 + ], + "spans": [ + { + "bbox": [ + 304, + 482, + 545, + 649 + ], + "type": "text", + "content": "Sampling-based methods [38] select keyframes using a uniform, random or customized sampling strategy. As selected frame may not be \"good\", these frameworks add a refinement module to clean noisy poses. Deciwatch [38] uses a standard transformer encoder to refine the uniformly sampled poses and a decoder to refine the recovered pose sequence based on denoised poses. The refinement on sampled keyframe poses is redundant and can be merged with the subsequent refinement module in the decoder. Moreover, Deciwatch [38] focuses on the temporal aspects and does not take spatial dependencies into consideration, which reflect interdependence among joints. Understanding the patterns of how joints are moving together can facilitate the refinement of incorrectly estimated joints." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 658, + 492, + 671 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 658, + 492, + 671 + ], + "spans": [ + { + "bbox": [ + 306, + 658, + 492, + 671 + ], + "type": "text", + "content": "2.2. Motion Completion and Prediction" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "Motion completion aims to fill the motion of missing frames with specified keyframe constraints, presenting both past and future frames. Traditional methods utilize lin" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14885" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 65, + 74, + 258, + 278 + ], + "blocks": [ + { + "bbox": [ + 65, + 74, + 258, + 278 + ], + "lines": [ + { + "bbox": [ + 65, + 74, + 258, + 278 + ], + "spans": [ + { + "bbox": [ + 65, + 74, + 258, + 278 + ], + "type": "image", + "image_path": "901c1b48819d0e6a06a8ed5090a62be210b9b844d091b6db34c3ba83b1857d9f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 268, + 76, + 388, + 264 + ], + "blocks": [ + { + "bbox": [ + 268, + 76, + 388, + 264 + ], + "lines": [ + { + "bbox": [ + 268, + 76, + 388, + 264 + ], + "spans": [ + { + "bbox": [ + 268, + 76, + 388, + 264 + ], + "type": "image", + "image_path": "12957400a5b7ec853386d7cdcce8ef0746b514da3291f8c96551761a067b5473.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 399, + 76, + 531, + 281 + ], + "blocks": [ + { + "bbox": [ + 399, + 76, + 531, + 281 + ], + "lines": [ + { + "bbox": [ + 399, + 76, + 531, + 281 + ], + "spans": [ + { + "bbox": [ + 399, + 76, + 531, + 281 + ], + "type": "image", + "image_path": "3c12733e75330dca013e530acd8e31ab4bd719562922a430ec766c729fb258f9.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 281, + 545, + 338 + ], + "lines": [ + { + "bbox": [ + 45, + 281, + 545, + 338 + ], + "spans": [ + { + "bbox": [ + 45, + 281, + 545, + 338 + ], + "type": "text", + "content": "Figure 2: Overview of MixSynthFormer. MixSynthFormer recovers and refines poses from sparsely sampled keyframes. It consists of " + }, + { + "bbox": [ + 45, + 281, + 545, + 338 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 45, + 281, + 545, + 338 + ], + "type": "text", + "content": " blocks of MixSynthEncoder blocks and two linear projection layers. MixSynthEncoder follows a standard transformer encoder structure but replaces multi-head self-attention with MixSynth Attention. MixSynth Attention synthesizes spatial and temporal attention via SynthAttention operations (depicted in Figure 3). The output from the two branches are combined and forwarded to a linear layer for feature fusion. (Detected poses in keyframes are colored, and recovered poses by interpolators are in gray.)" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 349, + 287, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 349, + 287, + 468 + ], + "spans": [ + { + "bbox": [ + 46, + 349, + 287, + 468 + ], + "type": "text", + "content": "ear, cubic-spline, Lagrange, and low-rank matrix completion, producing smooth transitions but lacking details [13]. Early learning-based methods employ RNN [9, 10] and convolutional models [12, 18]. Transformer-based models [6, 28, 30] are also adopted due to their exceptional performance in sequence-to-sequence problems. The aforementioned motion completion models are prevalent in the animation field and utilize ground-truth joint rotations and positions. However, in our case, the inputs are detected poses that can be noisy and aperiodic." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 469, + 287, + 552 + ], + "type": "text", + "content": "Motion prediction generates future motion given only historical frames. RNN [8, 24] and transformer-based [2, 1] methods are proposed to capture temporal dynamics. GCN-based methods, such as STSGCN [31] and STGAGCN [42], further model the spatial relationships among joints, obtaining high performance by closely combining spatio-temporal modeling." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 552, + 287, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 552, + 287, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 552, + 287, + 635 + ], + "type": "text", + "content": "Despite a range of frameworks, none of them treat motion completion and prediction as two mutually dependent tasks. Rather, each approach is specialized for one particular motion synthesis task. Notably, the sole distinction between motion completion and motion prediction pertains to the keyframe constraints. In this work, our model can handle both tasks with a unified structure." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 645, + 103, + 657 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 645, + 103, + 657 + ], + "spans": [ + { + "bbox": [ + 47, + 645, + 103, + 657 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "content": "Problem Definition. Given an input video of " + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "content": " frames, a sampler samples one frame out of every " + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "content": " frames (" + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "content": " is a multiple of " + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "content": "). The sampled frames are regarded as keyframes where poses will be estimated by a pose esti" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 349, + 545, + 469 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 349, + 545, + 469 + ], + "spans": [ + { + "bbox": [ + 304, + 349, + 545, + 469 + ], + "type": "text", + "content": "mator. The detected poses from sampled frames may be unreliable due to complex poses or occlusion. We denote poses detected from sampled frames as " + }, + { + "bbox": [ + 304, + 349, + 545, + 469 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}_{\\text{noisy}}^{\\text{sampled}} \\in \\mathbb{R}^{\\frac{T}{K} \\times P}" + }, + { + "bbox": [ + 304, + 349, + 545, + 469 + ], + "type": "text", + "content": " which serves as the input to our framework. " + }, + { + "bbox": [ + 304, + 349, + 545, + 469 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 304, + 349, + 545, + 469 + ], + "type": "text", + "content": " is the number of pose parameters, which can denote joint positions (2D/3D) or rotations (6D) and may vary depending on the dataset and body representation. The objective of sampling-based pose estimation is to recover all the poses " + }, + { + "bbox": [ + 304, + 349, + 545, + 469 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}} \\in \\mathbb{R}^{T \\times P}" + }, + { + "bbox": [ + 304, + 349, + 545, + 469 + ], + "type": "text", + "content": " in the original sequence from detected poses " + }, + { + "bbox": [ + 304, + 349, + 545, + 469 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}_{\\text{noisy}}^{\\text{sampled}}" + }, + { + "bbox": [ + 304, + 349, + 545, + 469 + ], + "type": "text", + "content": " in the sampled frames (referred to as sampled detected poses)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 472, + 546, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 472, + 546, + 663 + ], + "spans": [ + { + "bbox": [ + 304, + 472, + 546, + 663 + ], + "type": "text", + "content": "Model Overview. Figure 2 provides an overview of our proposed model. The goal of MixSynthFormer is to recover and refine the poses to obtain accurate estimations efficiently. Initially, the entire pose sequence is recovered through linear interpolation or a linear layer from the sampled detected poses. Those recovered poses are transformed into pose embeddings using linear projection and are fed into " + }, + { + "bbox": [ + 304, + 472, + 546, + 663 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 472, + 546, + 663 + ], + "type": "text", + "content": " blocks of MixSynthEncoder. Each MixSynthEncoder comprises an attention block and a feed-forward network with residual connection, followed by a layer normalization layer. The attention block MixSynth Attention synthesizes spatial and temporal attention matrices concurrently. By integrating the spatial and temporal information, our model can refine the entire pose sequence in a simultaneous manner. Finally, the recovered poses are output via another linear layer." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": "We next present details of MixSynthFormer, starting with an overview of the structure and then proceeding to the design of MixSynth Attention and the detailed operations within it. Finally, we describe the settings of using our" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "14886" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 96 + ], + "type": "text", + "content": "model on motion prediction tasks, showcasing its adaptability to other motion synthesis tasks." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 103, + 198, + 116 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 103, + 198, + 116 + ], + "spans": [ + { + "bbox": [ + 47, + 103, + 198, + 116 + ], + "type": "text", + "content": "3.1. Design of MixSynthFormer" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 121, + 286, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 121, + 286, + 186 + ], + "spans": [ + { + "bbox": [ + 47, + 121, + 286, + 186 + ], + "type": "text", + "content": "We adopt a recover-refine pipeline in our framework. The whole pose sequence is preliminarily recovered along the temporal dimension by a traditional or a learned interpolator based on the detected poses " + }, + { + "bbox": [ + 47, + 121, + 286, + 186 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}_{\\text{noise}}^{\\text{sample}}" + }, + { + "bbox": [ + 47, + 121, + 286, + 186 + ], + "type": "text", + "content": " in keyframes, denoted as " + }, + { + "bbox": [ + 47, + 121, + 286, + 186 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}_{\\text{noise}}^{\\text{recover}} \\in \\mathbb{R}^{T \\times P}" + }, + { + "bbox": [ + 47, + 121, + 286, + 186 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 102, + 193, + 287, + 211 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 193, + 287, + 211 + ], + "spans": [ + { + "bbox": [ + 102, + 193, + 287, + 211 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {X}} _ {n o i s y} ^ {r e c o v e r} = I n t e r p (\\hat {\\mathbf {X}} _ {n o i s y} ^ {s a m p l e d}) \\tag {1}", + "image_path": "a01d2ec286892ca12a470c8abecff6979a98aa5f446d8500fbea6ac69b60b2d2.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 217, + 287, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 217, + 287, + 371 + ], + "spans": [ + { + "bbox": [ + 46, + 217, + 287, + 371 + ], + "type": "text", + "content": "Recovering poses from sparse and noisy inputs results in inaccurate estimates, which necessitates additional processing to obtain a clean output. Moreover, traditional interpolation methods tend to produce overly smooth motion sequences that lack details. Hence, a refinement step is necessary to generate a more precise pose sequence, which can be formulated as a sequence-to-sequence problem. Transformers have shown remarkable success in solving such problems owing to their ability to capture global correlations among tokens. We design MixSynthFormer following the workflow of a standard transformer encoder, except for replacing the self-attention module with MixSynth Attention. Following are the high-level operations of MixSynthFormer." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 372, + 287, + 469 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 372, + 287, + 469 + ], + "spans": [ + { + "bbox": [ + 46, + 372, + 287, + 469 + ], + "type": "text", + "content": "All poses in " + }, + { + "bbox": [ + 46, + 372, + 287, + 469 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}_{\\text {noisy }}^{\\text {recover }}" + }, + { + "bbox": [ + 46, + 372, + 287, + 469 + ], + "type": "text", + "content": " are transformed to the pose embeddings " + }, + { + "bbox": [ + 46, + 372, + 287, + 469 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}_0 \\in \\mathbb{R}^{T \\times C}" + }, + { + "bbox": [ + 46, + 372, + 287, + 469 + ], + "type": "text", + "content": " through a linear layer with weights " + }, + { + "bbox": [ + 46, + 372, + 287, + 469 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_0 \\in \\mathbb{R}^{P \\times C}" + }, + { + "bbox": [ + 46, + 372, + 287, + 469 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 372, + 287, + 469 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 372, + 287, + 469 + ], + "type": "text", + "content": " is the dimension of the embedding space. Attention layers in transformers need position embeddings to specify the locations of input tokens, whereas our MLP-based MixSynth Attention is sensitive to the order of tokens in temporal attention synthesis like [33] and does not require additional position embeddings." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 126, + 479, + 287, + 495 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 126, + 479, + 287, + 495 + ], + "spans": [ + { + "bbox": [ + 126, + 479, + 287, + 495 + ], + "type": "interline_equation", + "content": "\\mathbf {Z} _ {0} = \\hat {\\mathbf {X}} _ {\\text {n o i s y}} ^ {\\text {r e c o v e r}} \\mathbf {W} _ {0} \\tag {2}", + "image_path": "dd09c89b8b0173332ed54295584235193f546da1e2c26ad83de4208ac95c79dd.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 498, + 287, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 287, + 582 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 287, + 582 + ], + "type": "text", + "content": "The pose embeddings are then passed to " + }, + { + "bbox": [ + 46, + 498, + 287, + 582 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 498, + 287, + 582 + ], + "type": "text", + "content": " blocks of MixSynthEncoder. The model conforms to the conventional transformer encoder design, consisting of stacked MixSynth Attention module and feed-forward network (FFN) which is a two-layer point-wise fully connected layer with GELU activation [11]. Residual connection and layer normalization " + }, + { + "bbox": [ + 46, + 498, + 287, + 582 + ], + "type": "inline_equation", + "content": "(LN)" + }, + { + "bbox": [ + 46, + 498, + 287, + 582 + ], + "type": "text", + "content": " are applied sequentially after every block." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 80, + 590, + 287, + 604 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 590, + 287, + 604 + ], + "spans": [ + { + "bbox": [ + 80, + 590, + 287, + 604 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {Z}} _ {l} = L N \\left(M i x S y n t h A t t \\left(\\mathbf {Z} _ {l - 1}\\right) + \\mathbf {Z} _ {l - 1}\\right) \\tag {3}", + "image_path": "ad639a9e72065cf4f073e0470ca8dd93a2fd8586f83d7044720bdf457a03d88c.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 109, + 622, + 287, + 637 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 109, + 622, + 287, + 637 + ], + "spans": [ + { + "bbox": [ + 109, + 622, + 287, + 637 + ], + "type": "interline_equation", + "content": "\\mathbf {Z} _ {l} = L N \\left(F F N \\left(\\hat {\\mathbf {Z}} _ {l}\\right) + \\hat {\\mathbf {Z}} _ {l}\\right) \\tag {4}", + "image_path": "cda9d5f6795b9a949d1e42c2d49443f724c98da655b92b6992dbcd200aad29a2.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "text", + "content": "Here " + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "inline_equation", + "content": "l \\in [1, L]" + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "text", + "content": " denotes the " + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "text", + "content": "-th block. " + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}_{l-1}" + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "text", + "content": " is the output from the previous encoder block, " + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{Z}}_l" + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "text", + "content": " is the intermediate representation and " + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}_l" + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "text", + "content": " is the output of the current encoder block. " + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}_l" + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{Z}}_l" + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "text", + "content": " have the same dimension in " + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{T \\times C}" + }, + { + "bbox": [ + 46, + 641, + 287, + 689 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "After " + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": " blocks of operations, the features in the embedding space " + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}_L" + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": " are transformed back to the pose dimension" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 72, + 545, + 146 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 146 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 146 + ], + "type": "text", + "content": "via another linear layer with weights " + }, + { + "bbox": [ + 304, + 72, + 545, + 146 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_p\\in \\mathbb{R}^{C\\times P}" + }, + { + "bbox": [ + 304, + 72, + 545, + 146 + ], + "type": "text", + "content": ". The use of the residual connection can expedite model convergence and yield more stable results. The final recovered pose sequence " + }, + { + "bbox": [ + 304, + 72, + 545, + 146 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 146 + ], + "type": "text", + "content": " is thereby the summation of the output from MixSynthEncoder blocks and the preliminarily recovered noisy poses " + }, + { + "bbox": [ + 304, + 72, + 545, + 146 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}_{noisy}^{recover}" + }, + { + "bbox": [ + 304, + 72, + 545, + 146 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 358, + 154, + 545, + 171 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 358, + 154, + 545, + 171 + ], + "spans": [ + { + "bbox": [ + 358, + 154, + 545, + 171 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {X}} = \\left(L N (\\mathbf {Z} _ {L})\\right) \\mathbf {W} _ {p} + \\hat {\\mathbf {X}} _ {n o i s y} ^ {r e c o v e r} \\tag {5}", + "image_path": "3f7bc7eab5f28894bcc5a87bca2f4fe1eec2291b65b96b78d2acaafd13387ef1.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 177, + 422, + 190 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 177, + 422, + 190 + ], + "spans": [ + { + "bbox": [ + 306, + 177, + 422, + 190 + ], + "type": "text", + "content": "3.2. MixSynth Attention" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 196, + 545, + 398 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 196, + 545, + 398 + ], + "spans": [ + { + "bbox": [ + 304, + 196, + 545, + 398 + ], + "type": "text", + "content": "Transformers are effective in capturing global correlations among tokens, but they may not be sufficient for refining noisy sequences. Token-wise attention primarily focuses on the temporal aspect, while local attention that captures the correlation among joints is also essential, particularly for recovering complex motions. To learn both global and local features, we propose MixSynth Attention, which mixes spatial and temporal synthetic attention matrices. The weights in these matrices reflect the relative inter-joint and inter-frame importance. The spatial matrix reveals the correlation among joints. When performing some motion patterns, joints that move together are highly correlated. It is helpful in locating a wrongly-detected joint from its related joints with accurate detection. The temporal matrix determines the impact of a frame with respect to other frames in the sequence, signifying the extent to which a frame affects the remaining frames." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "spans": [ + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "type": "text", + "content": "We explain the MixSynth Attention operations in detail. For simplicity, we eliminate the block index " + }, + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "type": "text", + "content": " in the following explanation. The synthetic attention operation (SynthAttenOP) operates on " + }, + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "type": "inline_equation", + "content": "\\mathbf{Z} \\in \\mathbb{R}^{T \\times C}" + }, + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "type": "text", + "content": " and outputs feature " + }, + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}_i \\in \\mathbb{R}^{T \\times C}" + }, + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "type": "text", + "content": ", which can be spatial or temporal, denoted as " + }, + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}_s" + }, + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}_t" + }, + { + "bbox": [ + 304, + 399, + 545, + 471 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 347, + 480, + 545, + 494 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 480, + 545, + 494 + ], + "spans": [ + { + "bbox": [ + 347, + 480, + 545, + 494 + ], + "type": "interline_equation", + "content": "\\mathbf {Y} _ {i} = \\operatorname {S y n t h A t t e n O P} _ {i} (\\mathbf {Z}), i \\in \\{s, t \\} \\tag {6}", + "image_path": "9a95e875b75490e983e4ff9b319121e8e811e0310c673906bef6271613a74e85.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 502, + 545, + 587 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 502, + 545, + 587 + ], + "spans": [ + { + "bbox": [ + 304, + 502, + 545, + 587 + ], + "type": "text", + "content": "The spatially and temporally attended features are generated simultaneously. Inspired by [39], we apply split attention to re-balance the contribution of the two branches. Different motions may have different emphases. Inter-joint relations are more important for certain motions, while others may be more influenced by inter-frame relations. The weights " + }, + { + "bbox": [ + 304, + 502, + 545, + 587 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_y\\in \\mathbb{R}^{2\\times C}" + }, + { + "bbox": [ + 304, + 502, + 545, + 587 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 304, + 502, + 545, + 587 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}_s" + }, + { + "bbox": [ + 304, + 502, + 545, + 587 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 502, + 545, + 587 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}_t" + }, + { + "bbox": [ + 304, + 502, + 545, + 587 + ], + "type": "text", + "content": " are calculated as" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 336, + 595, + 545, + 609 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 336, + 595, + 545, + 609 + ], + "spans": [ + { + "bbox": [ + 336, + 595, + 545, + 609 + ], + "type": "interline_equation", + "content": "\\mathbf {A} _ {y} = \\operatorname {S o f t m a x} (F F N (G A P (\\mathbf {Y} _ {s} + \\mathbf {Y} _ {t}))) \\tag {7}", + "image_path": "545e301541c82e65dfd26e6fdc36a3a1f220d1bead48e0e5e5486f439eaf4704.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 617, + 545, + 690 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 690 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 690 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 617, + 545, + 690 + ], + "type": "inline_equation", + "content": "GAP" + }, + { + "bbox": [ + 304, + 617, + 545, + 690 + ], + "type": "text", + "content": " denotes the global average pooling function, " + }, + { + "bbox": [ + 304, + 617, + 545, + 690 + ], + "type": "inline_equation", + "content": "FFN" + }, + { + "bbox": [ + 304, + 617, + 545, + 690 + ], + "type": "text", + "content": " contains two fully connected layers with ReLU activation [26] and Softmax is for normalization. The weighted sum " + }, + { + "bbox": [ + 304, + 617, + 545, + 690 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}_{out} \\in \\mathbb{R}^{T \\times C}" + }, + { + "bbox": [ + 304, + 617, + 545, + 690 + ], + "type": "text", + "content": " is the summation of the element-wise product of the concatenated representations from two branches with the re-balancing weights " + }, + { + "bbox": [ + 304, + 617, + 545, + 690 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_y" + }, + { + "bbox": [ + 304, + 617, + 545, + 690 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 364, + 700, + 545, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 364, + 700, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 364, + 700, + 545, + 715 + ], + "type": "interline_equation", + "content": "\\mathbf {Y} _ {\\text {o u t}} = \\operatorname {S u m} \\left(\\mathbf {A} _ {y} \\circ \\left[ \\mathbf {Y} _ {s}; \\mathbf {Y} _ {t} \\right]\\right) \\tag {8}", + "image_path": "0f59da732a149d981fe61b41d920f8217aa3ba882ab56be6d648bf4b9d77dc9b.jpg" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14887" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 97 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 97 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 97 + ], + "type": "text", + "content": "The output of the MixSynth Attention block is attained by linearly transforming " + }, + { + "bbox": [ + 47, + 72, + 287, + 97 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}_{out}" + }, + { + "bbox": [ + 47, + 72, + 287, + 97 + ], + "type": "text", + "content": " with weights " + }, + { + "bbox": [ + 47, + 72, + 287, + 97 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_o\\in \\mathbb{R}^{C\\times C}" + }, + { + "bbox": [ + 47, + 72, + 287, + 97 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 102, + 104, + 287, + 118 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 104, + 287, + 118 + ], + "spans": [ + { + "bbox": [ + 102, + 104, + 287, + 118 + ], + "type": "interline_equation", + "content": "M i x S y n t h A t t (\\mathbf {Z}) = \\mathbf {Y} _ {o u t} \\mathbf {W} _ {o} \\tag {9}", + "image_path": "7ef6561b2dad4ab3e7a031c920190cec7be9342794df09b7be24c13aa68c5cb5.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 124, + 194, + 138 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 124, + 194, + 138 + ], + "spans": [ + { + "bbox": [ + 47, + 124, + 194, + 138 + ], + "type": "text", + "content": "3.3. SynthAttention Operation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 143, + 287, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 143, + 287, + 274 + ], + "spans": [ + { + "bbox": [ + 46, + 143, + 287, + 274 + ], + "type": "text", + "content": "The self-attention module in transformers utilizes the pairwise dot product to calculate attention weights. The computation of the query-key matrix multiplication expands quadratically as the embedding size increases. To alleviate the impact of embedding size on computational cost, we propose synthetic attention operation (SynthAttenOp), whose computation grows linearly with the increase of embedding size, as a substitute for the standard attention. We discuss this part in detail in supplementary materials. SynthAttenOp generates attention matrices using linear layers. Details of its operation are described below." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "spans": [ + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "text", + "content": "SynthAttenOp operates spatially and temporally. In spatial attention synthesis, input and output are transposed. Here we use " + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "inline_equation", + "content": "\\mathbf{Z} \\in \\mathbb{R}^{N \\times D}" + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "text", + "content": " to illustrate the general case, where " + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "text", + "content": " can be substituted with either " + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "text", + "content": ". The coarse synthetic attention matrix " + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_s \\in \\mathbb{R}^{N \\times N}" + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "text", + "content": " is generated by a linear layer with weights " + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_z \\in \\mathbb{R}^{D \\times N}" + }, + { + "bbox": [ + 46, + 274, + 287, + 346 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 140, + 354, + 287, + 367 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 140, + 354, + 287, + 367 + ], + "spans": [ + { + "bbox": [ + 140, + 354, + 287, + 367 + ], + "type": "interline_equation", + "content": "\\mathbf {A} _ {s} = \\mathbf {Z W} _ {z} \\tag {10}", + "image_path": "050460db6dd7ba1ecb027cfabaad17277c7110fd0b618cd6f635da42cf835687.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 375, + 287, + 436 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 375, + 287, + 436 + ], + "spans": [ + { + "bbox": [ + 47, + 375, + 287, + 436 + ], + "type": "text", + "content": "As different frames or joints have different contributions, we apply the Squeeze-and-Excitation layer (SELayer) [14] to regulate the influence. It can amplify critical channels while mitigating the effect of less important ones. The fine-grained attention matrix " + }, + { + "bbox": [ + 47, + 375, + 287, + 436 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_{\\text {synth }} \\in \\mathbb{R}^{N \\times N}" + }, + { + "bbox": [ + 47, + 375, + 287, + 436 + ], + "type": "text", + "content": " is obtained by" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 57, + 452, + 287, + 465 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 452, + 287, + 465 + ], + "spans": [ + { + "bbox": [ + 57, + 452, + 287, + 465 + ], + "type": "interline_equation", + "content": "\\operatorname {S E L a y e r} \\left(\\mathbf {A} _ {s}\\right) = \\mathbf {A} _ {s} \\circ \\sigma \\left(\\mathbf {W} _ {e} \\delta \\left(\\mathbf {W} _ {s} G A P \\left(\\mathbf {A} _ {s}\\right)\\right)\\right) \\tag {11}", + "image_path": "34dd9f048eca34d0862f34cfd85b9f956ad000f07f3c3bffe56d89bc2ea2a649.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 88, + 484, + 287, + 498 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 484, + 287, + 498 + ], + "spans": [ + { + "bbox": [ + 88, + 484, + 287, + 498 + ], + "type": "interline_equation", + "content": "\\mathbf {A} _ {\\text {s y n t h}} = \\operatorname {S o f t m a x} (\\operatorname {S E L a y e r} (\\mathbf {A} _ {s})) \\tag {12}", + "image_path": "73ba7d3866733b54e1207261520c4aaaa2008c614c645048377b0b789d3d994f.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "spans": [ + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "text", + "content": "where GAP denotes global average pooling and " + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "inline_equation", + "content": "GAP(\\mathbf{A}) \\in \\mathbb{R}^N" + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "text", + "content": " are Sigmoid activation and ReLU functions [26]. The reduction ratio " + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "inline_equation", + "content": "(r_{se})" + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "text", + "content": " is an empirically found hyperparameter that limits model complexity [14]. " + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_s \\in \\mathbb{R}^{\\frac{N}{r_{se}} \\times N}" + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "text", + "content": " is for dimension reduction, and " + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_e \\in \\mathbb{R}^{N \\times \\frac{N}{r_{se}}}" + }, + { + "bbox": [ + 47, + 502, + 287, + 624 + ], + "type": "text", + "content": " is for expanding to the original dimension. The output of SELayer is a re-scaled input after channelwise multiplication with calculated weights. Softmax is inherited from the standard transformer, which normalizes the attention weights." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 625, + 287, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 625, + 287, + 648 + ], + "spans": [ + { + "bbox": [ + 47, + 625, + 287, + 648 + ], + "type": "text", + "content": "In alignment with the standard transformer encoder, the output is the product of the attention matrix and the value:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 134, + 657, + 287, + 670 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 134, + 657, + 287, + 670 + ], + "spans": [ + { + "bbox": [ + 134, + 657, + 287, + 670 + ], + "type": "interline_equation", + "content": "\\mathbf {Y} = \\mathbf {A} _ {\\text {s y n t h}} \\mathbf {V} \\tag {13}", + "image_path": "d28eef838f714b2031475596cc4826fff18b331fdb4af1e797495380d0541261.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 676, + 220, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 676, + 220, + 689 + ], + "spans": [ + { + "bbox": [ + 47, + 676, + 220, + 689 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 676, + 220, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{V} = \\mathbf{Z}\\in \\mathbb{R}^{N\\times D}" + }, + { + "bbox": [ + 47, + 676, + 220, + 689 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 676, + 220, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}\\in \\mathbb{R}^{N\\times D}" + }, + { + "bbox": [ + 47, + 676, + 220, + 689 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "The method described above is applicable for cases when " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " is relatively small. When " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " is large, the computation" + } + ] + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 307, + 72, + 545, + 119 + ], + "blocks": [ + { + "bbox": [ + 307, + 72, + 545, + 119 + ], + "lines": [ + { + "bbox": [ + 307, + 72, + 545, + 119 + ], + "spans": [ + { + "bbox": [ + 307, + 72, + 545, + 119 + ], + "type": "image", + "image_path": "8a97663b6eccb8f6b299245b3ad8871f839592586046d9a46967aedc9c04cc0d.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 333, + 124, + 517, + 136 + ], + "lines": [ + { + "bbox": [ + 333, + 124, + 517, + 136 + ], + "spans": [ + { + "bbox": [ + 333, + 124, + 517, + 136 + ], + "type": "text", + "content": "Figure 3: The procedure of reduced SynthAttenOp" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "spans": [ + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "text", + "content": "cost grows quadratically owing to the matrix multiplication in Eqn. 13. We apply a reduction factor " + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "text", + "content": " to the last dimension " + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "text", + "content": ", saving the computation in Eqn. 13 by " + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "inline_equation", + "content": "r^2" + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "text", + "content": " times. We denote the reduced dimension as " + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "inline_equation", + "content": "d = \\lfloor N / r \\rfloor" + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "text", + "content": ". Figure 3 shows the process of reduced attention matrix generation and feature fusion. The reduced coarse attention matrix " + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_s^r \\in \\mathbb{R}^{N \\times d}" + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "text", + "content": " and reduced value " + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "inline_equation", + "content": "\\mathbf{V}^r \\in \\mathbb{R}^{d \\times D}" + }, + { + "bbox": [ + 304, + 149, + 545, + 245 + ], + "type": "text", + "content": " are obtained through" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 372, + 257, + 545, + 270 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 372, + 257, + 545, + 270 + ], + "spans": [ + { + "bbox": [ + 372, + 257, + 545, + 270 + ], + "type": "interline_equation", + "content": "\\mathbf {A} _ {s} ^ {r} = \\mathbf {Z} \\mathbf {W} _ {z} ^ {r}, \\mathbf {V} ^ {r} = \\mathbf {W} _ {v} \\mathbf {Z} \\tag {14}", + "image_path": "7e970cc4bbd9ac9874c560541951ff0f10fa7cf2af5555dd3c357da12b86068e.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 274, + 545, + 310 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 274, + 545, + 310 + ], + "spans": [ + { + "bbox": [ + 304, + 274, + 545, + 310 + ], + "type": "text", + "content": "where weights for reduced attention matrix generation and for reducing the value are " + }, + { + "bbox": [ + 304, + 274, + 545, + 310 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_z^r\\in \\mathbb{R}^{D\\times d}" + }, + { + "bbox": [ + 304, + 274, + 545, + 310 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 274, + 545, + 310 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_v\\in \\mathbb{R}^{d\\times N}" + }, + { + "bbox": [ + 304, + 274, + 545, + 310 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 317, + 432, + 330 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 317, + 432, + 330 + ], + "spans": [ + { + "bbox": [ + 306, + 317, + 432, + 330 + ], + "type": "text", + "content": "3.4. Efficiency Calculation" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 335, + 545, + 359 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 335, + 545, + 359 + ], + "spans": [ + { + "bbox": [ + 305, + 335, + 545, + 359 + ], + "type": "text", + "content": "The overall cost of the model per frame combines the cost of a pose estimator and the cost of MixSynthFormer:" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 347, + 365, + 545, + 389 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 365, + 545, + 389 + ], + "spans": [ + { + "bbox": [ + 347, + 365, + 545, + 389 + ], + "type": "interline_equation", + "content": "F L O P s = \\frac {1}{K} * f (E s t.) + f (M S F) \\tag {15}", + "image_path": "c624763f51452c48033f424027f8a4c03dd4b5a3e9c49a1a25d0e78c56f3584d.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "spans": [ + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "inline_equation", + "content": "f(\\cdot)" + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "text", + "content": " evaluates the FLOPs of a model per frame. As one frame out of " + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "text", + "content": " frames is sampled for estimation, the per-frame cost of the estimator is " + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "inline_equation", + "content": "\\frac{1}{K} * f(Ext." + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "text", + "content": ". MixSynthFormer operates on every frame, recovering and refining poses on the whole sequence, and its FLOPs per frame is " + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "inline_equation", + "content": "f(MSF)" + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "text", + "content": ". In particular, " + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "inline_equation", + "content": "f(MSF)" + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "text", + "content": " is at least " + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "inline_equation", + "content": "10^{4}" + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "text", + "content": " times smaller than " + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "inline_equation", + "content": "f(Ext." + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "text", + "content": " and is negligible compared to the heavy pose estimator. With " + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "text", + "content": " sampling ratio (" + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "inline_equation", + "content": "K = 10" + }, + { + "bbox": [ + 304, + 396, + 545, + 503 + ], + "type": "text", + "content": "), our framework can speed up the computation by ten times." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 306, + 510, + 394, + 521 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 510, + 394, + 521 + ], + "spans": [ + { + "bbox": [ + 306, + 510, + 394, + 521 + ], + "type": "text", + "content": "3.5. Loss Function" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 529, + 545, + 565 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 529, + 545, + 565 + ], + "spans": [ + { + "bbox": [ + 304, + 529, + 545, + 565 + ], + "type": "text", + "content": "Following [38], we apply L1 loss to minimize the error between the finely recovered pose sequence " + }, + { + "bbox": [ + 304, + 529, + 545, + 565 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}" + }, + { + "bbox": [ + 304, + 529, + 545, + 565 + ], + "type": "text", + "content": " and the ground-truth pose sequence " + }, + { + "bbox": [ + 304, + 529, + 545, + 565 + ], + "type": "inline_equation", + "content": "\\mathbf{X}" + }, + { + "bbox": [ + 304, + 529, + 545, + 565 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 379, + 572, + 545, + 604 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 379, + 572, + 545, + 604 + ], + "spans": [ + { + "bbox": [ + 379, + 572, + 545, + 604 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\frac {1}{T} \\sum_ {t = 1} ^ {T} | \\hat {\\mathbf {X}} ^ {t} - \\mathbf {X} ^ {t} | \\tag {16}", + "image_path": "5e35390947a2306f394d05794bb45b008c5537b774438021f84b30c09acc39a4.jpg" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 306, + 611, + 450, + 624 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 611, + 450, + 624 + ], + "spans": [ + { + "bbox": [ + 306, + 611, + 450, + 624 + ], + "type": "text", + "content": "3.6. Motion Prediction Setting" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 630, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 689 + ], + "type": "text", + "content": "Motion prediction and motion completion are two subfields in conditional motion generation with the only difference lying in the keyframe constraints. We include short-term motion prediction as a sub-task and demonstrate the versatility of our model on this task." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "content": "The input of motion prediction to our model is a historical ground-truth motion sequence " + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_{1:T_h} \\in \\mathbb{R}^{T_h \\times P}" + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "content": ", where" + } + ] + } + ], + "index": 28 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14888" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "inline_equation", + "content": "T_{h}" + }, + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "content": " is the number of consecutive historical frames and " + }, + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "content": " is the size of pose parameters (i.e., 3D positions of human body joints). The goal is to predict the future sequence " + }, + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_{T_h + 1:T_h + T_f} \\in \\mathbb{R}^{T_f \\times P}" + }, + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "content": " given " + }, + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_{1:T_h}" + }, + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "inline_equation", + "content": "T_{f}" + }, + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "content": " is the number of frames to be predicted. Similar to the pose estimation settings, the future poses are coarsely generated by interpolation, and then MixSynthFormer refines and outputs the future poses." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 168, + 287, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 168, + 287, + 216 + ], + "spans": [ + { + "bbox": [ + 46, + 168, + 287, + 216 + ], + "type": "text", + "content": "We adopt the L2-norm between the predicted sequence and the ground-truth sequence calculated only on future frames as the loss function, which is equivalent to the Mean Per Joint Position Error (MPJPE) in [31, 42]:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 104, + 223, + 287, + 258 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 223, + 287, + 258 + ], + "spans": [ + { + "bbox": [ + 104, + 223, + 287, + 258 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {f} = \\frac {1}{T _ {f}} \\sum_ {t = T _ {h} + 1} ^ {T _ {h} + T _ {f}} | | \\hat {\\mathbf {X}} ^ {t} - \\mathbf {X} ^ {t} | | _ {2} \\tag {17}", + "image_path": "7883804802f1a78b1e4528feb55f73305198d4df50f537924b6f3077fd17b1d1.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 265, + 287, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 265, + 287, + 289 + ], + "spans": [ + { + "bbox": [ + 47, + 265, + 287, + 289 + ], + "type": "text", + "content": "We will test the above model in experiments, which showcases our model's adaptability to other synthesis tasks." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 299, + 128, + 312 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 299, + 128, + 312 + ], + "spans": [ + { + "bbox": [ + 47, + 299, + 128, + 312 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 319, + 287, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 319, + 287, + 449 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 287, + 449 + ], + "type": "text", + "content": "Datasets. We evaluate MixSynthFormer on four datasets for three tasks. For 2D pose estimation (to locate the 2D coordinates of joints from images), we use the Sub-JHMDB dataset [16] that contains daily and sports actions. For 3D pose estimation (to extend 2D pose data with depth information prediction), we use the widely-used Human3.6M indoor dataset [15]. For 3D body recovery (to estimate human shape and joint angles), we use the in-the-wild dataset 3DPW which includes videos taken by a moving phone camera [35] and AIST++ [21] with diverse dancing actions shot indoors." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 450, + 287, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 450, + 287, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 287, + 568 + ], + "type": "text", + "content": "Evaluation Metrics. We adopt the same evaluation metrics as in [38]. For 2D pose estimation, Percentage of the Correct Keypoints (PCK) is used, and three thresholds " + }, + { + "bbox": [ + 46, + 450, + 287, + 568 + ], + "type": "inline_equation", + "content": "(20\\%, 10\\%" + }, + { + "bbox": [ + 46, + 450, + 287, + 568 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 450, + 287, + 568 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 46, + 450, + 287, + 568 + ], + "type": "text", + "content": " of the bounding box size under the pixel level) are set. For 3D tasks, Mean Per Joint Position Error (MPJPE) is utilized to report distance error and the mean Acceleration error (Accel) is adopted to reflect the smoothness of the estimated pose sequence. Mean Floating Point Operations (FLOPs (G)) per frame are also reported to show the computation costs." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": "Implementation Details. We use the same single-frame pose estimators and sampling strategy as in [38]. The uniform sampling ratio is set to " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "K = 10" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": ") in all experiments. The presence of the first and last frames is vital in recovery. In practice, we sample " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "Q" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " frames with index " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "K \\times q" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "q \\in [0, \\dots, Q - 1]" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " from the input of length " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "K \\times Q + 1" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " and additionally include the last frame of the input sequence as keyframes. The number of keyframes " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "Q" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": ", the embedding dimension " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " and the number of MixSynthEncoder blocks " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " vary among datasets and tasks. We train the model on a single A100 GPU with testing performed on an 8-core CPU Apple M1 Pro chip to obtain the inference time. Due to" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": "page limit, other detailed training settings and qualitative results are provided in supplementary materials." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 105, + 494, + 118 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 105, + 494, + 118 + ], + "spans": [ + { + "bbox": [ + 305, + 105, + 494, + 118 + ], + "type": "text", + "content": "4.1. Comparison on 2D Pose Estimation" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 123, + 545, + 182 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 123, + 545, + 182 + ], + "spans": [ + { + "bbox": [ + 304, + 123, + 545, + 182 + ], + "type": "text", + "content": "Existing keyframe-based pose estimation methods use SimplePose [36] as the pose estimator. We follow the same experiment settings as in [40, 7, 38]. Table 1 presents the detailed PCK@0.2 results of each joint, the average performance of all three metrics and computation costs." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 183, + 545, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 183, + 545, + 277 + ], + "spans": [ + { + "bbox": [ + 304, + 183, + 545, + 277 + ], + "type": "text", + "content": "Compared with feature-based methods, KFP [40] and MAPN [7], our method improves the accuracy by over " + }, + { + "bbox": [ + 304, + 183, + 545, + 277 + ], + "type": "inline_equation", + "content": "4.6\\%" + }, + { + "bbox": [ + 304, + 183, + 545, + 277 + ], + "type": "text", + "content": " in PCK@0.2. The improvements on fast-moving joints, such as elbows, wrists and ankles, are significant with a maximum increase of " + }, + { + "bbox": [ + 304, + 183, + 545, + 277 + ], + "type": "inline_equation", + "content": "14.8\\%" + }, + { + "bbox": [ + 304, + 183, + 545, + 277 + ], + "type": "text", + "content": ". Those joints often cause image blur, leading to wrong detection results. Our sampling-based method incorporates a refinement module and can mitigate the effects of incorrect detection." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "spans": [ + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "text", + "content": "Compared to the sampling-based model DeciWatch [38], our model features a lighter design with 0.4M FLOPs computation, yet achieving a superior accuracy of " + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "inline_equation", + "content": "99.3\\%" + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "text", + "content": " under PCK@0.2. Notably, our model achieves almost " + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "text", + "content": " in predicting the head and torso positions, which can be attributed to the integration of spatial dependencies. While the attention mechanism in [38] only considers inter-frame relations, our method also leverages inter-joint relations, which is particularly useful for limb position estimation. The accuracy of ankle increases from " + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "inline_equation", + "content": "96.5\\%" + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "inline_equation", + "content": "97.8\\%" + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "text", + "content": ". By fusing information from highly-correlated joints, our model also outperforms DeciWatch in strict metrics PCK@0.1 by " + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "text", + "content": " and PCK@0.05 by " + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "inline_equation", + "content": "1.3\\%" + }, + { + "bbox": [ + 304, + 279, + 545, + 434 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 443, + 494, + 455 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 443, + 494, + 455 + ], + "spans": [ + { + "bbox": [ + 305, + 443, + 494, + 455 + ], + "type": "text", + "content": "4.2. Comparison on 3D Pose Estimation" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 461, + 545, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 461, + 545, + 520 + ], + "spans": [ + { + "bbox": [ + 304, + 461, + 545, + 520 + ], + "type": "text", + "content": "We next compare our method on 3D keypoint estimation and body recovery tasks against single-frame estimators [25, 20, 19, 17] and the sampling-based model DeciWatch [38]. Results on localization error and acceleration error are in Table 2." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 521, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 641 + ], + "type": "text", + "content": "Compared with DeciWatch [38], our model is significantly smaller with no performance degradation, thanks to SynthAttention. Our model achieves a 1-2mm reduction in MPJPE on Human3.6M and 3DPW without compromising smoothness. Notably, the FLOPs of the model trained on 3DPW are 0.03M, which is more than ten times smaller than DeciWatch. The inference time is less than 0.1 ms per frame on CPU. There are two main reasons for this: first, we only do refinements once; second, the attention matrix in our model is generated by the cost-efficient SynthAttenOp." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": "On AIST++, our model reduces the acceleration error by " + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "inline_equation", + "content": "33\\%" + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": " compared to DeciWatch and " + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "inline_equation", + "content": "86\\%" + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": " compared to the single-frame estimator SPIN. We attribute the acceleration reduction to the integration of spatial and temporal attention. AIST++ contains poses with fast movements and diverse dancing actions. Due to the complexity of these poses," + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14889" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 96, + 538, + 191 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 545, + 94 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 545, + 94 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 545, + 94 + ], + "type": "text", + "content": "Table 1: Comparison with keyframe-based pose estimation methods on Sub-JHMDB dataset [16] for 2D pose estimation. R means ResNet [39]. Ratio represents the sampling ratio. Sho., Elb., Wri., Ank., Avg. stand for shoulder, elbow, wrist, ankle and average PCK, respectively." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 53, + 96, + 538, + 191 + ], + "lines": [ + { + "bbox": [ + 53, + 96, + 538, + 191 + ], + "spans": [ + { + "bbox": [ + 53, + 96, + 538, + 191 + ], + "type": "table", + "html": "
Sub-JHMDB dataset - 2D Pose Estimation PCK@0.2PCK@0.1PCK@0.05
MethodsHeadSho.Elb.Wri.HipKneeAnk.Avg.FLOPs(G)Ratio
KFP(R18) [40]94.796.395.290.296.495.593.294.57.1940.8%--
MAPN(R18) [7]98.297.491.785.299.296.792.294.72.7035.2%--
SimplePose [36]98.697.396.598.690.395.486.594.011.96100%81.657.3
DeciWatch [38]99.899.599.799.798.799.496.598.81.196+0.000510.0%94.179.4
Ours99.999.999.8100.099.299.997.899.31.196+0.000410.0%95.180.7
", + "image_path": "79dc8f94be3cd51022fdafa4648a2583e80b8a4370be98329578526036851c42.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 61, + 251, + 272, + 498 + ], + "blocks": [ + { + "bbox": [ + 46, + 204, + 287, + 248 + ], + "lines": [ + { + "bbox": [ + 46, + 204, + 287, + 248 + ], + "spans": [ + { + "bbox": [ + 46, + 204, + 287, + 248 + ], + "type": "text", + "content": "Table 2: Comparison for 3D pose estimation and body recovery on Human3.6M [15], 3DPW [35] and AIST++ [21]. The estimators in keyframe-based frameworks are the same as the corresponding single-frame pose models." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 61, + 251, + 272, + 498 + ], + "lines": [ + { + "bbox": [ + 61, + 251, + 272, + 498 + ], + "spans": [ + { + "bbox": [ + 61, + 251, + 272, + 498 + ], + "type": "table", + "html": "
MethodsMPJPEAccelFLOPs(G)
Human3.6M - 3D Pose Estimation
FCN [25]54.619.26.21
DeciWatch [38]52.81.50.621+0.0007
Ours50.91.50.621+0.0001
3DPW - 3D Body Recovery
SPIN [20]96.634.74.13
DeciWatch [38]93.37.10.413+0.0004
Ours91.26.80.413+0.00003
EFT [17]90.332.84.13
DeciWatch [38]89.06.80.413+0.0004
Ours88.16.30.413+0.00003
PARE [19]78.925.715.51
DeciWatch [38]77.26.91.551+0.0004
Ours76.56.71.551+0.00003
AIST++ - 3D Body Recovery
SPIN [20]107.733.84.13
DeciWatch [38]71.37.10.413+0.0007
Ours71.24.70.413+0.0005
", + "image_path": "0cbd315f82e9b9842749d6badd2903cc14db7572d95dd4a9cbc1e9f044d1ce42.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 515, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 515, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 515, + 287, + 552 + ], + "type": "text", + "content": "original detections may contain erroneous estimations. By mixing spatial and temporal attention, we can effectively refine incorrect joints while maintaining the smoothness." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 562, + 237, + 575 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 562, + 237, + 575 + ], + "spans": [ + { + "bbox": [ + 47, + 562, + 237, + 575 + ], + "type": "text", + "content": "4.3. Comparison on Motion Completion" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": "Our model recovers and refines poses in a completion-like manner. We compare our model with traditional interpolation methods and a transformer-encoder based Motion Completion Model (MCT) [6] from the animation field. MCT can handle different motion completion tasks, and uses the concatenation of positional and rotational data as input. To be consistent with the pose estimation task, we re-implement the MCT model and tune it on our datasets. Our recover-refine process is similar to the in-filling task in MCT. Both are to recover missing poses from uniformly sampled keyframes." + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 310, + 274, + 539, + 364 + ], + "blocks": [ + { + "bbox": [ + 304, + 204, + 545, + 270 + ], + "lines": [ + { + "bbox": [ + 304, + 204, + 545, + 270 + ], + "spans": [ + { + "bbox": [ + 304, + 204, + 545, + 270 + ], + "type": "text", + "content": "Table 3: Comparison with motion completion methods on Human3.6M [15], 3DPW [35] and AIST++ [21] with estimators stated inside brackets. Nearest, linear, quadratic, cubic-spline methods are used for traditional interpolation. MPJPE (Accel) of different recovery methods are reported. The results from traditional interpolators with the lowest MPJPE are underlined." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 310, + 274, + 539, + 364 + ], + "lines": [ + { + "bbox": [ + 310, + 274, + 539, + 364 + ], + "spans": [ + { + "bbox": [ + 310, + 274, + 539, + 364 + ], + "type": "table", + "html": "
DataNea.Lin.Qua.Cub.MCTOurs
H36M (FCN)57.054.854.654.654.550.9
(10.2)(1.9)(1.6)(1.5)(2.1)(1.5)
3DPW (SPIN)100.597.297.597.791.991.2
(19.9)(6.7)(6.2)(6.3)(8.0)(6.8)
AIST (SPIN)114.7105.9107.1107.672.071.2
(28.5)(5.7)(4.6)(4.6)(6.9)(4.7)
", + "image_path": "6feaf09ac45ddda717800559d315440d551b9536663fdf67cdc82d2fd3ea11fb.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 381, + 545, + 549 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 381, + 545, + 549 + ], + "spans": [ + { + "bbox": [ + 304, + 381, + 545, + 549 + ], + "type": "text", + "content": "The results are presented in Table 3. Traditional interpolators tend to smooth the sequence but lack the ability to correct noisy poses, resulting in low acceleration errors and high position errors. MCT can reduce position errors at the expense of reduced smoothness. Our model surpasses all other methods. It can produce smooth sequences like interpolation but with more detailed and accurate motions. Specifically, when applied to Human3.6M, our model achieves the same smoothness as cubic-spline interpolation and decrease MPJPE by " + }, + { + "bbox": [ + 304, + 381, + 545, + 549 + ], + "type": "inline_equation", + "content": "7\\%" + }, + { + "bbox": [ + 304, + 381, + 545, + 549 + ], + "type": "text", + "content": ". When evaluated on AIST++, our model reduces MPJPE by over " + }, + { + "bbox": [ + 304, + 381, + 545, + 549 + ], + "type": "inline_equation", + "content": "30\\%" + }, + { + "bbox": [ + 304, + 381, + 545, + 549 + ], + "type": "text", + "content": ". The significant improvement in position errors without tradeoffs in smoothness shows the superiority of MixSynthFormer in recovering noisy sequences." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 560, + 542, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 560, + 542, + 574 + ], + "spans": [ + { + "bbox": [ + 305, + 560, + 542, + 574 + ], + "type": "text", + "content": "4.4. Comparison with Motion Prediction Methods" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 580, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 580, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 580, + 545, + 628 + ], + "type": "text", + "content": "We evaluate our model on the sub-task short-term motion prediction (Sec. 3.6) under four testing intervals ranging from " + }, + { + "bbox": [ + 304, + 580, + 545, + 628 + ], + "type": "inline_equation", + "content": "80~\\mathrm{ms}" + }, + { + "bbox": [ + 304, + 580, + 545, + 628 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 580, + 545, + 628 + ], + "type": "inline_equation", + "content": "400~\\mathrm{ms}" + }, + { + "bbox": [ + 304, + 580, + 545, + 628 + ], + "type": "text", + "content": ", using " + }, + { + "bbox": [ + 304, + 580, + 545, + 628 + ], + "type": "inline_equation", + "content": "400~\\mathrm{ms}" + }, + { + "bbox": [ + 304, + 580, + 545, + 628 + ], + "type": "text", + "content": " input sequences. Table 4 gives the results." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 629, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 715 + ], + "type": "text", + "content": "Our model outperforms STSGCN [31] and STGAGCN [42]. Taking advantage of motion continuity, our model can predict short-term poses that conform to the motion pattern of the historical input poses. It reduces error by " + }, + { + "bbox": [ + 304, + 629, + 545, + 715 + ], + "type": "inline_equation", + "content": "17\\%" + }, + { + "bbox": [ + 304, + 629, + 545, + 715 + ], + "type": "text", + "content": " in an 80 ms interval while the improvement is less than " + }, + { + "bbox": [ + 304, + 629, + 545, + 715 + ], + "type": "inline_equation", + "content": "3\\%" + }, + { + "bbox": [ + 304, + 629, + 545, + 715 + ], + "type": "text", + "content": " in a 400 ms interval. Limited by refinement on the overly-smoothed interpolation results, our model cannot learn spe" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "14890" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 74, + 97, + 259, + 153 + ], + "blocks": [ + { + "bbox": [ + 47, + 71, + 287, + 93 + ], + "lines": [ + { + "bbox": [ + 47, + 71, + 287, + 93 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 287, + 93 + ], + "type": "text", + "content": "Table 4: Comparison for short-term motion prediction. Average MPJPE across frames on Human3.6M [15] are reported." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 74, + 97, + 259, + 153 + ], + "lines": [ + { + "bbox": [ + 74, + 97, + 259, + 153 + ], + "spans": [ + { + "bbox": [ + 74, + 97, + 259, + 153 + ], + "type": "table", + "html": "
Methods80160320400
STSGCN [31]10.117.133.138.3
STGAGCN [42]10.116.932.538.5
Ours8.415.830.537.4
", + "image_path": "f7014c8829f4f42f2b62f48493daa5858f6dd08e2f0e0a3c30cd5ed1a7b09333.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 69, + 184, + 264, + 252 + ], + "blocks": [ + { + "bbox": [ + 47, + 159, + 286, + 180 + ], + "lines": [ + { + "bbox": [ + 47, + 159, + 286, + 180 + ], + "spans": [ + { + "bbox": [ + 47, + 159, + 286, + 180 + ], + "type": "text", + "content": "Table 5: Comparison with different attention matrix generation methods on 3DPW [35]" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 69, + 184, + 264, + 252 + ], + "lines": [ + { + "bbox": [ + 69, + 184, + 264, + 252 + ], + "spans": [ + { + "bbox": [ + 69, + 184, + 264, + 252 + ], + "type": "table", + "html": "
MethodsMPJPEAccel#ParamFLOPs
Vanilla92.66.80.14M0.12M
Random92.66.90.12M0.09M
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Action-wise results are reported in supplementary materials." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 359, + 141, + 372 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 359, + 141, + 372 + ], + "spans": [ + { + "bbox": [ + 47, + 359, + 141, + 372 + ], + "type": "text", + "content": "4.5. Ablation Study" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 378, + 287, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 378, + 287, + 413 + ], + "spans": [ + { + "bbox": [ + 46, + 378, + 287, + 413 + ], + "type": "text", + "content": "We conduct the ablation study on attention matrix generation, reduction factor " + }, + { + "bbox": [ + 46, + 378, + 287, + 413 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 378, + 287, + 413 + ], + "type": "text", + "content": " and model structure. The input sequences are linearly interpolated from keyframe poses." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 414, + 287, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 414, + 287, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 414, + 287, + 568 + ], + "type": "text", + "content": "Attention Matrix Generation. The attention matrix in our model is generated by a linear layer followed by a SELayer. It can also be generated by a FFN or is a learnable matrix as proposed in [32], referred to as Dense and Random. We compare our generation method with these two methods, together with the vanilla self-attention in transformers. To ensure a fair evaluation, we exclusively focus on the temporal attention matrix. Table 5 presents a comparative analysis of various attention methods, among which our generation approach stands out with the lowest number of parameters (0.1M) and minimum FLOPs (0.09M), owing to the reduction factor. Importantly, our method achieves the lowest MPJPE of " + }, + { + "bbox": [ + 46, + 414, + 287, + 568 + ], + "type": "inline_equation", + "content": "92.1\\mathrm{mm}" + }, + { + "bbox": [ + 46, + 414, + 287, + 568 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": "Effect of Reduction Factor. We examine the impact of the reduction factor " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " which is introduced for computation saving in SynthAttention. Specifically, we investigate how " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " in spatial " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "(r_s)" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " and temporal " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "(r_t)" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " dimensions affects the model size and its performance. As shown in Table 6, overall, applying " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " on one dimension saves " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "8\\%" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " of the computation and up to " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "25\\%" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " of parameters. When " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " is applied in temporal attention synthesis, we observe a smoother motion sequence with a decrease in MPJPE by " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "0.8 \\mathrm{~mm}" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": ". Applying reduction on both dimensions further reduces the model parameters by " + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "inline_equation", + "content": "30\\%" + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": " compared to a non-reduced one at the expense of slightly increased MPJPE." + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 329, + 86, + 521, + 153 + ], + "blocks": [ + { + "bbox": [ + 313, + 71, + 538, + 82 + ], + "lines": [ + { + "bbox": [ + 313, + 71, + 538, + 82 + ], + "spans": [ + { + "bbox": [ + 313, + 71, + 538, + 82 + ], + "type": "text", + "content": "Table 6: Effects of the reduction factor " + }, + { + "bbox": [ + 313, + 71, + 538, + 82 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 313, + 71, + 538, + 82 + ], + "type": "text", + "content": " on Human3.6M [15]" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 329, + 86, + 521, + 153 + ], + "lines": [ + { + "bbox": [ + 329, + 86, + 521, + 153 + ], + "spans": [ + { + "bbox": [ + 329, + 86, + 521, + 153 + ], + "type": "table", + "html": "
rtrsMPJPEAccel#ParamFLOPs
1152.21.70.26M0.13M
4151.41.60.21M0.12M
1451.81.70.23M0.12M
4451.81.60.18M0.11M
", + "image_path": "f427103372013bed38b6fc5fd54455201c5b823ff88d40352a809e4b650d95d3.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 328, + 183, + 523, + 262 + ], + "blocks": [ + { + "bbox": [ + 305, + 158, + 545, + 180 + ], + "lines": [ + { + "bbox": [ + 305, + 158, + 545, + 180 + ], + "spans": [ + { + "bbox": [ + 305, + 158, + 545, + 180 + ], + "type": "text", + "content": "Table 7: Effects of components in MixSynth Attention block on Sub-JHMDB [16]. w/o means that the component is removed." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 328, + 183, + 523, + 262 + ], + "lines": [ + { + "bbox": [ + 328, + 183, + 523, + 262 + ], + "spans": [ + { + "bbox": [ + 328, + 183, + 523, + 262 + ], + "type": "table", + "html": "
PCK@0.2PCK@0.1
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w/o SE Layer99.094.2
w/o weighted sum98.994.7
w/o temporal attention98.894.4
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", + "image_path": "2483ca05eb7f61b0ca6bc284f25fd565f7e3c9413dd528228215de440f0066e9.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 276, + 545, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 276, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 304, + 276, + 545, + 384 + ], + "type": "text", + "content": "Components in MixSynth Attention Block. MixSynth Attention blocks mix synthesized spatial and temporal attention. SELayer is incorporated to augment feature efficacy by emphasizing salient features while suppressing uninformative ones during attention matrix generation. The final output is the weighted sum of spatial and temporal representations. To evaluate the contribution of each component, we conduct ablation experiments by removing one of the components." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 384, + 546, + 539 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 546, + 539 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 546, + 539 + ], + "type": "text", + "content": "Results under different settings are summarized in Table 7. Removing any component in MixSynth Attention leads to worse performance. When SELayer is removed, PCK@0.1 decreases by " + }, + { + "bbox": [ + 304, + 384, + 546, + 539 + ], + "type": "inline_equation", + "content": "0.9\\%" + }, + { + "bbox": [ + 304, + 384, + 546, + 539 + ], + "type": "text", + "content": ", indicating its crucial role in re-calibrating attention weights. The most significant performance decrease is observed when the spatial attention component is excluded: PCK@0.1 drops from " + }, + { + "bbox": [ + 304, + 384, + 546, + 539 + ], + "type": "inline_equation", + "content": "95.1\\%" + }, + { + "bbox": [ + 304, + 384, + 546, + 539 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 384, + 546, + 539 + ], + "type": "inline_equation", + "content": "92.9\\%" + }, + { + "bbox": [ + 304, + 384, + 546, + 539 + ], + "type": "text", + "content": ". This finding highlights the usefulness of the inter-joint relation from spatial attention generation in refinement. Moreover, combining spatial and temporal attention through a weighted sum further improves the performance by " + }, + { + "bbox": [ + 304, + 384, + 546, + 539 + ], + "type": "inline_equation", + "content": "0.4\\%" + }, + { + "bbox": [ + 304, + 384, + 546, + 539 + ], + "type": "text", + "content": ". These results demonstrate the effectiveness of all components in MixSynth Attention." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 550, + 378, + 562 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 550, + 378, + 562 + ], + "spans": [ + { + "bbox": [ + 306, + 550, + 378, + 562 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 570, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 712 + ], + "type": "text", + "content": "In this paper, we propose MixSynthFormer, a transformer encoder-like structure with mixed synthetic attention for efficient human pose estimation in videos. The MLP-based synthetic attention module generates spatial and temporal matrices simultaneously, allowing fast and accurate recovery and refinement. The flexible model design also enables it to easily adapt to other motion synthesis tasks such as short-term motion prediction. Comprehensive experiments demonstrate the superior performance of our model in 2D/3D pose estimation, body mesh recovery, and motion prediction tasks, making it a promising solution for practical use cases." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "14891" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 109 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 109 + ], + "type": "text", + "content": "Acknowledgement. This work was supported in part by Hong Kong Innovation and Technology Support Programme Platform Research Project fund (ITS/332/21FP)." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 119, + 107, + 132 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 119, + 107, + 132 + ], + "spans": [ + { + "bbox": [ + 48, + 119, + 107, + 132 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 48, + 140, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 140, + 287, + 184 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 140, + 287, + 184 + ], + "spans": [ + { + "bbox": [ + 53, + 140, + 287, + 184 + ], + "type": "text", + "content": "[1] Emre Aksan, Manuel Kaufmann, Peng Cao, and Otmar Hilliges. A spatio-temporal transformer for 3d human motion prediction. In 2021 International Conference on 3D Vision (3DV), pages 565-574. 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Previous works based on neural radiance fields have demonstrated high-quality reconstructions of dynamic scenes. However, training such models on real-world scenes is time-consuming, usually taking days or weeks. In this paper, we present a novel method named MixVoxels to efficiently represent dynamic scenes, enabling fast training and rendering speed. The proposed MixVoxels represents the 4D dynamic scenes as a mixture of static and dynamic voxels and processes them with different networks. In this way, the computation of the required modalities for static voxels can be processed by a lightweight model, which essentially reduces the amount of computation as many daily dynamic scenes are dominated by static backgrounds. To distinguish the two kinds of voxels, we propose a novel variation field to estimate the temporal variance of each voxel. For the dynamic representations, we design an inner product time query method to efficiently query multiple time steps, which is essential to recover the high-dynamic movements. As a result, with 15 minutes of training for dynamic scenes with inputs of 300-frame videos, MixVoxels achieves better PSNR than previous methods. For rendering, MixVoxels can render a novel view video with 1K resolution at 37 fps. Codes and trained models are available at https://github.com/fengres/mixvoxels.", + "bbox": [ + 76, + 361, + 473, + 770 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 801, + 209, + 816 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Dynamic scene reconstruction from multi-view videos is a critical and challenging problem, with many potential applications such as interactively free-viewpoint control", + "bbox": [ + 76, + 828, + 470, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/434e95b5beca54124bbd7146f0cb20487115e2209f822042ef43568486176c75.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 504, + 328, + 632, + 404 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e1deef51198de0d49c73ce050767bc32fb1fcc1d571d368dd25e838d17242edc.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 632, + 328, + 758, + 404 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/7af1183edd93e16a49f4c73c5fae842041970494a9c1c770d37c088e0b08bf3b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 759, + 328, + 888, + 404 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d4bb0fb6d4a72eb4a737256ce21820806fbcc8be846525bc6068f8f036fd8ce3.jpg", + "image_caption": [ + "1 min", + "15 min", + "Figure 1. Our method enables rapid reconstruction of 4D dynamic scenes. We visualize the rendering results with different training schedules. With only 15 minutes of training, our approach achieves comparable PSNRs to other methods. Increasing the training time further enhances the ability to recover fine details." + ], + "image_footnote": [], + "bbox": [ + 503, + 414, + 632, + 489 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/21938a87638836a3cad4e37c37d330a70261ff9506365e67162bc247758a7251.jpg", + "image_caption": [ + "5 min", + "40 min" + ], + "image_footnote": [], + "bbox": [ + 632, + 414, + 761, + 489 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/331234465f81d82a42d19cf1659a53e647c36c4e3a846c8884ecd3c97896dac3.jpg", + "image_caption": [ + "10 min", + "300 min" + ], + "image_footnote": [], + "bbox": [ + 761, + 414, + 888, + 489 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "for movies, cinematic effects like freeze-frame bullet time, novel view replays for sporting events, and various potential VR/AR applications. Recently, neural radiance fields [26] have demonstrated the possibility of rendering photorealistic novel views for static scenes, with physically motivated 3D density and radiance modelling. Many methods [19, 20, 49, 13, 10, 31, 28, 29, 44] extend the neural radiance fields to dynamic scenes with additional time queries or an explicit deformation field. Many of these methods focus on the monocular input video setting on relatively simple dynamic scenes. To model more complex real-world dynamic scenes, a more practical solution is to use multi-view synchronized videos to provide dense spatial-temporal supervi", + "bbox": [ + 496, + 580, + 892, + 792 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recently, Li et al. [19] propose a real-world dynamic scene dataset including many challenging situations such as objects of high specularity, topology changes, and volumetric effects. They address the problem by a hierarchical training scheme and the ray importance sampling strategies. Although significant improvements have been achieved, some challenges still exist: (1) The training and rendering take a", + "bbox": [ + 496, + 794, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author.", + "bbox": [ + 94, + 886, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "19706", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "lot of time and computation resources. (2) Highly dynamic scenes with complex motions are still difficult to track.", + "bbox": [ + 76, + 90, + 467, + 119 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we focus on the multi-view 3D video synthesis problem and present a novel method named MixVoxels to address the above two challenges. The proposed MixVoxels is based on the explicit voxel-grid representation, which is recently popular due to its fast training and rendering speed on static scenes [50, 40, 8, 27]. We extend the voxel-grid representations to support dynamic scenes and propose an efficient inner product time querying method that can query a large number of time steps simultaneously, which is essential to recover the sharp details for highly-dynamic objects. Additionally, we represent dynamic scenes as a mixed static-dynamic voxel-grid representation. Specifically, the 3D spaces are split into static and dynamic voxels by our proposed variation field. The two components are processed by different models to reduce the redundant computations for the static space. Theoretically, once a dynamic scene consists of some static spaces, the training speed will benefit from the proposed mixed voxels. For a variety of events that occur in the physical world, the static components of environments are dominated in most cases, and the mixed voxels will speed up the training significantly in these scenarios. Besides, the separation of voxels makes the time-variant model focus on the dynamic regions, avoiding the time-aware voxels being biased by the static spaces to produce blurred motions. Our empirical validation confirms that the separation enables the model to learn sharp and distinct boundaries in high-dynamic regions. This also frees our method from the complex importance sampling strategies. With these designs, our method is capable of reconstructing a dynamic scene consisting of 300 frames within 15 minutes. To summarize, the main contributions of this work are:", + "bbox": [ + 76, + 121, + 468, + 604 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a simple yet effective dynamic representation with inner product time querying method that can efficiently query multiple times simultaneously, improving the rendering quality for dynamic objects.", + "- We design an efficient variation field to separate static and dynamic spaces and present a mixed voxel-grid representation to accelerate training and rendering.", + "- We conduct qualitative and quantitative experiments to validate our method. As a result, the proposed MixVoxels achieves competitive or better rendering qualities with a $5000 \\times$ training speedup compared to implicit dynamic scene representations." + ], + "bbox": [ + 96, + 611, + 467, + 801 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works", + "text_level": 1, + "bbox": [ + 76, + 815, + 225, + 830 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Novel View Synthesis for Static Scenes. Synthesizing novel views for static scenes is a classical and well-studied problem. Different approaches represent the underlying geometric with different representations. Mesh-based meth", + "bbox": [ + 76, + 839, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ods [6, 9, 46, 48, 34, 43] represent the scenes with surfaces which is compact and easy to render, while optimizing a mesh to fit complex scenes is challenging. Volume-based methods such as voxel-grid [17, 35, 30, 23, 36] and multiplane images (MPIs) [54, 11, 25, 39, 38, 45] are more suitable to model the complex and translucent scenes such as smooth and fluid. Particularly, Neural radiance fields [26] represent the scenes with an implicit volumetric neural representation, which employs a coordinate-based neural network to query the density and color for each point. The achieved photo-realistic rendering quality of NeRF led to an explosion of developments in the field. Advances have been made including improving the rendering qualities [42, 4], adapting to more general scenarios [52, 24, 41, 5], accelerating rendering or training speed [22, 51, 50, 40, 8], etc.", + "bbox": [ + 496, + 90, + 890, + 318 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Novel View Synthesis for Dynamic Scenes. Synthesizing novel views for dynamic scenes is a more challenging and applicable problem. Recently, many extensions of NeRF for non-rigid dynamic scenes were proposed, which take a monocular video as input to learn the deformation and radiance fields. These methods can be categorized to modelling deformation implicitly [20, 49, 13, 10] (learn the non-decoupled deformation and appearance jointly) and explicitly [31, 28, 29, 44] (learn separated deformation and radiance fields and the deformation fields are usually in the form of relative motion with a canonical static space). Though improvements are achieved, reconstructing the complex general scenes is still difficult with only monocular videos. Most methods are constrained to fixed scenes like human-model or restricted motions. For real-world complex scenes, reconstructing from synchronized multi-view videos is more promising due to the dense supervision for every viewpoint and time instant. Earlier works [14, 55] explore the problem and show the possibility of rendering novel videos from a set of input views. Neural Volumes [23] proposes to use volumetric representations. They employ an encoder-decoder network to convert input images into a 3D volume, and decode the latent representations by the differentiable ray marching operation. [3] presents a data-driven approach for 4D space-time visualization of dynamic scenes by splitting static and dynamic components and using a U-Net structure in screen space to convert intermediate representation to image. Different with this method, our method split the static and dynamic components in the 3D voxel space instead of the pixel space. More recently, DyNerf [19] uses a temporal-aware neural radiance field to address the problem, and proposes some sampling strategies to train it efficiently. Compared with previous methods, they propose a more complicated real-world dataset and validate their method. For accelerating the reconstruction of dynamic scenes, FourierPlenoctree [47] proposes to model the dynamics in frequency domain, and generate a Plenoctree through multi", + "bbox": [ + 496, + 325, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "19707", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "view blending to accelerate rendering. They focus on the foreground moving objects extracted via chroma key segmentation, which requires the background should be a pure color (or rely on segmentation algorithms). Recently, the acceleration of training and rendering for dynamic scenes has attracted much attention. Cocurrent works include StreamRF [18] which proposes to accelerate the training of dynamic scenes by modeling the differences of adjacent frames, NeRFPlayer [37] which decomposes the dynamic scenes into static, new and deforming components, Hyperreel [2] which proposes an efficient sampling network and models keyframes. K-Planes [12] and HexPlanes [7] decompose the 4D dynamic scenes into different 2D representations.", + "bbox": [ + 75, + 90, + 472, + 301 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Acceleration of Neural Radiance Fields. While Neural radiance fields can render novel views with high fidelity, training and rendering require querying a deep MLP millions of times which is computationally intensive. Many recent methods propose to accelerate the training and rendering speed of NeRF. For rendering, Neural Sparse Voxel Fields [22] proposes a voxel-grid representation to skip over many empty regions. PlenOctree [51] accelerates the rendering process by pre-tabulating the NeRF into a PlenOctree and using the spherical harmonic representation of radiance. Derf [32] and Kilonerf [33] propose to accelerate the rendering speed by dividing the scenes into multiple areas, and employ multiple small network in each area. AutoInt [21] proposes to restructure the MLP network to accelerate the computations of ray integrals, which helps accelerate the rendering speed. For accelerating the training of NeRF, some methods use explicit voxel-grid representations [50, 40] to accelerate the training process and convergence speed. Instant-NGP [27] proposes a multi-resolution hash table structure to accelerate the training. The model sizes of most fast training methods are relatively large due to a large number of voxels. TensoRF [8] proposes to reduce the model size by factorizing the 4D scene tensor into multiple compact low-rank tensor components.", + "bbox": [ + 75, + 301, + 472, + 666 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 676, + 169, + 694 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we introduce the proposed MixVoxels, which represents the 4D dynamic scenes as mixtures of static and dynamic voxels. Fig. 2 illustrates the overview of our method. In the following subsections, we will first introduce the voxel-grid representations for static scenes and our extension to dynamic scenes. Then we introduce the variation field for identifying the dynamic voxels. At last, we introduce the training of MixVoxels.", + "bbox": [ + 75, + 702, + 468, + 824 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Static Voxel-grid Representation", + "text_level": 1, + "bbox": [ + 76, + 832, + 362, + 848 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Neural radiance fields [26] have demonstrated photorealistic novel viewpoint synthesis, while the training of NeRF requires extensive computation due to millions of", + "bbox": [ + 75, + 854, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "neural network queries. For accelerating NeRF, many recent works [22, 50, 40, 8] have explored the explicit volumetric representation, which avoids the huge amount of computation of querying neural network. Specifically, a 3D scene is split into $N_{x} \\times N_{y} \\times N_{z}$ voxels. The densities and color features are stored in these voxels and denoted as $\\mathcal{S}^{\\sigma} \\in \\mathbb{R}^{N_x \\times N_y \\times N_z}$ and $\\mathcal{S}^c \\in \\mathbb{R}^{N_x \\times N_y \\times N_z \\times C}$ . $\\mathcal{S}_{i,j,k}^{\\sigma}$ and $\\mathcal{S}_{i,j,k}^c$ represent the learnable density and color feature of the voxel corner at a discrete position $(i,j,k)$ . For a continuous position $(x,y,z)$ , the representation $\\mathcal{S}_{x,y,z}$ can be calculated by interpolating the nearest 8 discrete positions. A small MLP network $\\mathcal{C}_{\\theta}$ is used to parse the color features into RGB values, taking $S^c$ and view direction $d$ as input. Formally, the density $\\sigma$ and color $c$ is formulated as", + "bbox": [ + 496, + 90, + 893, + 303 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\sigma (x, y, z) = \\mathcal {S} _ {x, y, z} ^ {\\sigma}, \\quad c (x, y, z, \\boldsymbol {d}) = \\mathcal {C} _ {\\theta} \\left(\\mathcal {S} _ {x, y, z} ^ {c}, \\boldsymbol {d}\\right). \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 311, + 890, + 330 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Dynamic Voxel-grid Representation", + "text_level": 1, + "bbox": [ + 498, + 338, + 810, + 356 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For dynamic scenes, a direct extension is to add the time dimension to the static voxel-grid representation $S$ explicitly. However, this direct extension is almost memory-prohibitive due to the large and linearly increasing memory footprint. For a 300-frame video, the learned models will occupy 30 GB of memory and be difficult to train with GPUs due to the limitation of GPU memory. To address this problem, we propose a spatially explicit and temporally implicit representation to reduce the memory footprint. Specifically, we represent the dynamic scene as a 4D learnable voxel-grid $\\mathcal{G}^{\\sigma} \\in \\mathbb{R}^{N_x \\times N_y \\times N_z \\times C_1}$ and $\\mathcal{G}^c \\in \\mathbb{R}^{N_x \\times N_y \\times N_z \\times C_2}$ . Different from the static scene representations, the densities and colors for all time steps are implicitly encoded as compact features stored in each voxel corner. The compact features will be processed by a time-aware projection to acquire density and color for each time step. Concretely, for the compact density feature $\\mathcal{G}_{x,y,z}^{\\sigma}$ and color feature $\\mathcal{G}_{x,y,z}^c$ in any position(x,y,z), we employ two MLPs $T_{\\theta_1}^{\\sigma}$ and $T_{\\theta_2}^c$ to increase the feature dimensions for better parsing time-variant density and color. The MLPs here can be viewed as decompressors that decompress the compact low-dimensional voxel-grid features into more tractable ones. Compared with directly storing high-dimensional features in each voxel, the temporally implicit representation reduces the memory footprint significantly since the shared MLPs only increase memory slightly.", + "bbox": [ + 496, + 361, + 890, + 753 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Inner product time query. For a discrete time step $t$ , we use a learnable time-variant latent representation $\\omega_{t}$ to represent the time query. Instead of concatenating the time query with the intermediate features, we propose to calculate the inner product between the learned time query and the decompressed features as the required output $\\sigma$ and $c$ . Formally, the density and color of a space-time query $(x,y,z,t)$ are formulated as", + "bbox": [ + 496, + 753, + 890, + 875 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\sigma (x, y, z, t) = \\omega_ {t} ^ {\\sigma} \\cdot \\mathcal {T} _ {\\theta_ {1}} ^ {\\sigma} (\\mathcal {G} _ {x, y, z} ^ {\\sigma}), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 586, + 883, + 890, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "19708", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/c89e4ffa935ae9ddbb7365c32977e96baa21992548d3434e797cf798a990e952.jpg", + "image_caption": [ + "Figure 2. Overview of our method. Given a ray, we first sample points, and split them into static and dynamic ones using the variation field. After that, we feed these points to the corresponding branches and query the required properties. Then we merge the static output and dynamic output for rendering the ray color. An L2 loss is employed to calculate loss and back-propagate." + ], + "image_footnote": [], + "bbox": [ + 83, + 87, + 467, + 227 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nc (x, y, z, \\boldsymbol {d}, t) = \\omega_ {t} ^ {c} \\cdot \\mathcal {T} _ {\\theta_ {2}} ^ {c} (\\mathcal {G} _ {x, y, z} ^ {c}, \\boldsymbol {d}). \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 330, + 468, + 349 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In practice, simultaneously querying multiple time steps helps reconstruct the detail of high-dynamic motions and reduces the training iterations to traverse through all time steps. The inner product based query will facilitate the training speed when simultaneously querying many time steps in a training iteration. Specifically, we denote the FLOPs of the MLP $\\mathcal{T}_{\\theta_1}$ and the inner product operation as $\\mathrm{FLOP}_{mlp}$ and $\\mathrm{FLOP}_{inn}$ , respectively. For a $T$ -frame video, the FLOPs of the concatenation query [19] is larger than $T\\cdot \\mathrm{FLOP}_{mlp}$ (due to the extra temporal embedding dimension), while the FLOPs of our inner product query is only $\\mathrm{FLOP}_{mlp} + T\\cdot \\mathrm{FLOP}_{inn}$ ( $\\mathrm{FLOP}_{mlp} >> \\mathrm{FLOP}_{inn}$ ).", + "bbox": [ + 75, + 354, + 472, + 537 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Variation Field", + "text_level": 1, + "bbox": [ + 76, + 544, + 230, + 559 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this subsection, we introduce the variation field to identify which voxels in the 3D space are dynamic, i.e., the densities or colors are not constant over different time steps. By separating the static and dynamic voxels, the redundant computations caused by using a relatively heavy time-varying model to process the static components will be avoided, which accelerates the training and rendering.", + "bbox": [ + 75, + 568, + 468, + 674 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "A simpler solution for accelerate training is to separate the static and dynamic regions in pixel-level, i.e., using the temporal variance of pixels to produce static and dynamic ones. However this scheme is actually not feasible because we can only separate dynamic and static regions in training views using the ground truth. For rendering novel views, we can not get the pixel variance for rendering since we have no ground truth in novel views. Thus a feasible solution is to learn the voxel-level temporal variance which is shared for all possible views. In addition, separating in the voxel-level is more efficient compared to pixel-level, even if we have an oracle to make the pixel-level separation feasible in novel views. This is because not all voxels projected to a dynamic pixel are dynamic, there will be only a small fraction of voxels around the object surfaces are actually", + "bbox": [ + 75, + 674, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/79e725cf185f6588c324292fbd174a0631bc5e8c63203adf7ff36b2844498488.jpg", + "image_caption": [ + "Figure 3. Implicit interaction of multiple rays to decide which point is dynamic. For a static ray (blue line), all points are set to be low dynamic. For a dynamic ray (green line), at least one point is dynamic. The intersection of multiple dynamic ray is more likely to be a dynamic point, which is also physically intuitive." + ], + "image_footnote": [], + "bbox": [ + 526, + 93, + 870, + 271 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "dynamic. Therefore, the voxel level separation will produce much fewer dynamic queries.", + "bbox": [ + 496, + 347, + 890, + 378 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To perform the voxel-level separation, we utilize the pixel-level temporal variances from training videos as the supervision to estimate the voxel-level variances. The pixel-level (or ray-level) temporal variances of different videos are shown in Fig. 3. Formally, given a ray $r(s) = o + s \\cdot d$ with origin $o$ and direction $d$ , the corresponding pixel color at time step $t$ is defined as $C(r,t)$ . Then the pixel-level temporal variance $D^2(r)$ is formalized as", + "bbox": [ + 496, + 377, + 892, + 489 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nD ^ {2} (\\boldsymbol {r}) = \\frac {1}{T} \\sum_ {t = 1} ^ {T} (C (\\boldsymbol {r}, t) - \\bar {C} (\\boldsymbol {r})) ^ {2}, \\quad \\bar {C} (\\boldsymbol {r}) = \\frac {1}{T} \\sum_ {t = 1} ^ {T} C (\\boldsymbol {r}, t),\n$$\n", + "text_format": "latex", + "bbox": [ + 504, + 494, + 887, + 532 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\bar{C} (\\pmb {r})$ is the mean color of pixel corresponding to the ray $\\pmb{r}$ . For identifying the dynamic pixels, the standard deviation $D(\\pmb {r})$ is binarized to $M(r)$ with a threshold $\\gamma$ to provide pixel-level dynamic supervision, i.e. $M(r) = 1$ if $D(\\boldsymbol {r})\\geq \\gamma$ , else $M(\\boldsymbol {r}) = 0$ . In this way, we judge that a ray $\\pmb{r}$ is dynamic if $M(r) = 1$ . Next, we use the $M(r)$ as supervision to estimate the voxel-level variations $\\mathcal{V}$ .", + "bbox": [ + 496, + 537, + 893, + 643 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The relations between the pixel-level variance and voxel-level variance lie in the following aspects: (1) If a pixel is static, then all voxels passed through by the ray corresponding to the pixel should be static in most cases (We will discuss some special cases which violate this rule later in this subsection.). (2) If a pixel is dynamic, then at least one of the voxels passed through by the corresponding ray is dynamic. Fig. 3 shows the two situations. With the above two relations, we design the variation field, which is denoted as $\\mathcal{V} \\in \\mathbb{R}^{N_x \\times N_y \\times N_z}$ to represent the voxel-level temporal variance. Specifically, we uniformly sample $N_s$ points from the near plane to the far plane in $\\mathbf{r}$ , and build the following equation to satisfy the two relations mentioned above:", + "bbox": [ + 496, + 643, + 893, + 840 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {M} (\\boldsymbol {r}) = \\boldsymbol {s} (\\max (\\{\\mathcal {V} _ {\\boldsymbol {r} (s _ {i})} | i \\in \\{1, \\dots , N _ {s} \\} \\})), \\qquad (4)\n$$\n", + "text_format": "latex", + "bbox": [ + 558, + 845, + 890, + 864 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\hat{M}(\\boldsymbol{r})$ is an estimation of $M(\\boldsymbol{r})$ , and $\\boldsymbol{s}$ is the sigmoid function. Then we train the variation field by minimizing", + "bbox": [ + 496, + 869, + 893, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "19709", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "the following binary cross-entropy loss:", + "bbox": [ + 76, + 90, + 341, + 104 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {v} = \\mathbb {E} _ {\\boldsymbol {r}} \\left[ - M (\\boldsymbol {r}) \\log (\\hat {M} (\\boldsymbol {r})) - (1 - M (\\boldsymbol {r})) \\log (1 - \\hat {M} (\\boldsymbol {r})) \\right]. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 108, + 468, + 128 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "By optimizing the above loss function to all rays, we can get the learned variation field $\\mathcal{V}$ . The training of the variation field is very efficient, usually taking less than 30 seconds.", + "bbox": [ + 75, + 131, + 468, + 175 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The maximization operation well formulates the relations between a pixel and its corresponding voxels. If a pixel is static, then the equations of Eq. (4) and Eq. (5) will force all voxels passed through by the corresponding ray to be static $(\\mathcal{V}_{x,y,z} = 0)$ . If a pixel is dynamic, Eq. (4) requires at least one of the corresponding voxels (i.e., the max value of the voxel variances) to be dynamic $(\\mathcal{V}_{x,y,z} = +\\infty)$ . Although we provide no information about which specific voxels in a dynamic ray are dynamic, the implicit interaction of multiple different rays will force the solution to be physically reasonable. To explain this, we focus on the observable voxels which at least passed through by one ray. If a point $(x,y,z)$ is passed through by at least one static ray, then $\\mathcal{V}_{x,y,z}$ will tend to be optimized to be close to zero. If a point $(x,y,z)$ is only passed through by dynamic rays, and not occluded by other dynamic voxels, then $\\mathcal{V}_{x,y,z}$ will be optimized to $+\\infty$ . This is because without occlusion, the above point of $(x,y,z)$ along the dynamic rays will be passed by other static rays (the front space along these rays are observable from other views). We illustrate this situation in Fig. 3.", + "bbox": [ + 75, + 176, + 472, + 492 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Inference. After the training process, the temporal variation at a specific 3D position $(x,y,z)$ is $\\mathcal{V}_{x,y,z}$ , which is easily acquired by interpolating the discrete variation field. We then identify a voxel in the scene as dynamic if $\\mathcal{V}_{x,y,z}$ is larger than a hyper-parameter $\\beta$ , and as static if it is smaller than $\\beta$ . Formally, we will get a dynamic mask $\\dot{\\mathrm{M}} \\in \\{0,1\\}^{N_x \\times N_y \\times N_z}$ , which will be used to split sampling points in a ray into static points and dynamic points. We evaluate the effectiveness of this inference method in the test views and find that the recall and precision are reasonable for splitting the dynamic and static parts (recall: 0.97, precision: 0.94 when $\\beta = 0.9$ ). Although the recall seems sufficient to retrieve most dynamic parts, we empirically find some false negatives in the rendering images affect the rendering quality. To address this problem, we use a ray-wise max-pooling operation to identify the points near to a dynamic point as dynamic. The kernel size of max-pooling is set to $k_m = 21$ , and the stride is set to 1. In this way, the recall is very closed to 1. Although many hyperparameters are incorporated, we have empirically found that the thresholds $\\gamma$ and $\\beta$ are not sensitive over a wide range of reasonable values.", + "bbox": [ + 75, + 493, + 472, + 824 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Discussion. There may be some situations in which the rules (1) are broken due to occlusion. Specifically, when a dynamic voxel is occluded by some static voxels, the occluded parts should not be classified as static, which makes the 2D supervision noisy. However in practice, we found", + "bbox": [ + 75, + 824, + 472, + 902 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/fd018c329e90016f33eb3920dc52ee1785fe6173ec4a3f488380f422fe93f132.jpg", + "image_caption": [ + "Figure 4. Impact of occlusions to the variation field." + ], + "image_footnote": [], + "bbox": [ + 501, + 88, + 630, + 146 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/c6d3ac47cd7332f032240af5cac3493ba5b7079cbc2afec51855a8ad62fe23c7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 630, + 88, + 759, + 146 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/103d74a2bf401c86aa7b4477a2c0a2db74ecfacbbd10833e0f3784e48314e3fd.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 761, + 88, + 890, + 146 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "the learning-based separation has a certain degree of tolerance for this situation. We conducted experiments to verify this and present the results in Fig. 4. The occluded region is visualized in the leftmost view (the area behind the static roadblock). Although the dynamic region marked in yellow is occluded in the left view, it is actually classified as dynamic region. This can be inferred from another view where the occluded region has changed, as illustrated in the middle and right images in Fig. 4). The variation field is learning-based and will learn a solution that satisfies most constraints. If it forces some dynamic voxels occluded by static voxels to be 0, then the loss function from other visible views will be high. As a result, the learning-based process tends to assign a \"middle solution\" to voxels with inconsistent supervisions from different views. We also attempted to use the transmittance as a weight (in a way of volumetric rendering) to learn the variation field which can explicitly handle the occlusion problem. However, we found a large efficiency drop with similar performance. As a result, we use the proposed variation field and find this formulation works well for most scenes, including some challenging scenes with large areas of motions.", + "bbox": [ + 496, + 167, + 890, + 500 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Training of Mixed Neural Voxels", + "text_level": 1, + "bbox": [ + 500, + 508, + 785, + 525 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "With the help of the variation field, we can split a scene into dynamic voxels and static voxels. To reduce redundant computations, we use the lightweight static model described in Sec. 3.1 to compute the densities and colors for static voxels and the dynamic model described in Sec. 3.2 to compute the densities and colors for dynamic voxels. The overall architecture is illustrated in Fig. 2.", + "bbox": [ + 496, + 532, + 890, + 637 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Specifically for a given ray $r(s) = o + sd$ with origin $o$ and view direction $d$ , we apply stratified sampling from the near to the far planes and get $N_{s}$ points. Then the $N_{s}$ points are separated into static and dynamic ones by inferring these points with the proposed variation field. For the static points, we pass them into the static branch to retrieve the colors and densities. For the dynamic points, we pass them into the dynamic branch together with a deferred time query $\\omega_{t}$ to retrieve the corresponding properties. After that, we merge the static points and dynamic points according to their order. Then we apply volumetric rendering to the merged points to obtain the rendered color, which is formulated as", + "bbox": [ + 496, + 638, + 890, + 833 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nC (\\boldsymbol {r}, t) = \\sum_ {i = 1} ^ {N _ {s}} T _ {i, t} \\cdot \\left(1 - \\exp \\left(- \\sigma_ {i, t} \\delta_ {i}\\right)\\right) \\cdot c _ {i, t}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 544, + 837, + 890, + 878 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathrm{T}_{i,t}$ is the accumulated opacity (or transmittance):", + "bbox": [ + 500, + 885, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "19710", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$\\mathrm{T}_{i,t} = \\exp (-\\sum_{j = 1}^{i - 1}\\sigma_{j,t}\\delta_j)$ , and $\\delta_{i}$ is the distance between adjacent samples. Given the ground truth color $C_g(\\boldsymbol {r},t)$ , an l2-loss is employed to train the model:", + "bbox": [ + 75, + 89, + 468, + 137 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathbb {E} _ {\\left(\\boldsymbol {r}, t\\right)} \\left[ \\| C _ {g} (\\boldsymbol {r}, t) - C (\\boldsymbol {r}, t) \\| _ {2} ^ {2} \\right]. \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 148, + 147, + 468, + 167 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For both static and dynamic branches, we omit the computation of color for points whose densities are close to zero, which is a widely adopted pruning strategy [22, 50, 8].", + "bbox": [ + 75, + 170, + 468, + 215 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Efficiency analysis. We define the proportion of dynamic points in a scene as $\\lambda$ ( $\\approx 0.05$ for most scenes). Besides, the FLOPs of static and dynamic branches are denoted as $FLOP_{sta}$ and $FLOP_{dyn}$ , respectively. Then the total FLOPs of MixVoxels are $FLOP_{sta} + \\lambda \\cdot FLOP_{dyn}$ . Empirically, $FLOP_{dyn} / FLOP_{sta}$ ranges from 50 to 100 with different reasonable dimension settings. Then the acceleration ratio of splitting static and dynamic models is $FLOP_{dyn} / (FLOP_{sta} + \\lambda FLOP_{dyn}) \\approx 10$ . In practice, the actual speedup with a 3090 GPU is about 5, the inconsistency between analysis and experiment may come from the GPU features, which are friendly to a more consistent network.", + "bbox": [ + 75, + 215, + 468, + 397 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.5. Implementation Detail", + "text_level": 1, + "bbox": [ + 76, + 406, + 287, + 422 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The voxel-grid representations require large GPU memory to store the cubically growing voxel numbers. To implement the voxel-grid representations more memory efficient, we use the tensor factorization technique proposed in TensoRF [8] to reduce the memory footprint. In this way, a 3D tensor is factorized into the outer product of a vector and a 2D matrix. We factorize all the voxel-grid tensors, including static voxels, dynamic voxels and the variation field. With the help of tensor factorization, the learned model costs about 500MB for a 300-frame multi-view video scene. For the voxel resolutions, we follow [8] to start from an initial low resolution of $256^{3}$ , and upsample the resolution at steps 1500, 2000, 2500, and 2750 with a linear increase in the log space. The final resolution is set to $640^{3}$ . Once the resolution is changed, we re-train the variation field, which only takes about 15-30s. The voxel-grid feature dimension is set to 27, and the hidden state of MLP is set to 512. For training, we use Adam [15] optimizer with a learning rate of 0.02 for voxels and $3e - 3$ for MLPs. The total variation loss [50] is incorporated as a regularization to encourage the space smoothness.", + "bbox": [ + 75, + 430, + 470, + 748 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 761, + 209, + 779 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Experiment Setting", + "text_level": 1, + "bbox": [ + 76, + 786, + 264, + 803 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Dataset. We validate our method on two datasets: (1) The Plenoptic Video Dataset [19], which consists of 6 publicly accessible scenes: coffee-martini, flame-salmon, cook-spinach, cut-roasted-beef, flame-steam and sear-steam. We conduct experiments on all six scenes. Each scene contains 19 videos with different camera views. The dataset", + "bbox": [ + 75, + 809, + 468, + 898 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/f0ec872bd625902d7260c11cf1dc992750fb252b45ac69637e4cba8bf213eb05.jpg", + "table_caption": [ + "Table 1. Results on our collected dataset, including two scenes." + ], + "table_footnote": [], + "table_body": "
SceneModelPSNR↑DSSIM↓LPIPS↓
Moving-CarsMixVoxels-S18.720.2510.689
MixVoxels-M18.970.2280.552
MixVoxels-L18.890.2220.540
MixVoxels-X19.110.2100.516
Solving-RubikMixVoxels-S25.390.0650.339
MixVoxels-M26.050.0590.275
MixVoxels-L26.280.0550.241
MixVoxels-X26.800.0470.209
", + "bbox": [ + 521, + 104, + 870, + 226 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "contains many challenging scenes including objects with topology changes, objects with volumetric effects, various lighting conditions, etc. (2) Our proposed dataset including two more complex dynamic scenes: moving-cars and solving-rubik. The moving-cars scene features several vehicles passing across the screen, with significant motion and displacement. Meanwhile, in the solving-rubik scene, a man solves a Rubik's cube at a rapid pace, averaging 4 rotations per second, providing an opportunity to evaluate the model's ability to capture swift movements. The collection procedures used are similar to those of DyNeRF. More details are presented in the appendix.", + "bbox": [ + 496, + 232, + 890, + 412 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For training and evaluation, we follow the experiment setting in [19] that employs 18 views for training and 1 view for evaluation. To quantitatively evaluate the rendering quality on novel views, we measure PSNR, DSSIM and LPIPS[53] on the test views. We also provide more metrics in the appendix including FLIP [1] and JOD [16], which we find the comparisons are similar with PSNR and LPIPS. We follow the setting of [19] to evaluate our model frame by frame. For videos consisting of equal or more than 300 frames, we evaluate our model every 10 frames [19] to calculate the frame-by-frame metrics except for the JOD metrics, which requires a stack of continuous video.", + "bbox": [ + 496, + 412, + 892, + 594 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training Schedules. For evaluating the effect of training time, we train MixVoxels with different configurations shown in Tab. 2. The configurations vary in terms of training iterations and the number of sample points per ray. By default, the step size for sampling points is set to four times of the voxel width. The $8 \\times$ means that there will be eight times as many sampling points compared to the default.", + "bbox": [ + 496, + 595, + 890, + 700 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/858331641d42e66e300005c8768cbb4fc6964c8987cc488e4cbdd54885d97e95.jpg", + "table_caption": [ + "Table 2. Different training configurations of MixVoxels." + ], + "table_footnote": [], + "table_body": "
ModelIterationsSampling pointsTraining Time
MixVoxels-S50001 ×15 min
MixVoxels-M125001 ×40 min
MixVoxels-L250001 ×80 min
MixVoxels-X500008 ×300 min
", + "bbox": [ + 532, + 720, + 859, + 792 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Results", + "text_level": 1, + "bbox": [ + 500, + 801, + 591, + 816 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Quantitative results and comparisons. For quantitative results, we present the metrics and compare with other methods in Tab. 3. Compared with the previous state-of-the-art method DyNeRF, we reduce the training time from $1.3\\mathrm{K}$ GPU hours to 15 minutes, making the training of complex", + "bbox": [ + 496, + 825, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "19711", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/568836bbd6a296632e70842fd23b25efc3ab4705b2bc62e88094b776173fb85e.jpg", + "image_caption": [ + "Figure 5. Visual comparisons with state-of-the-art methods. K-Planes [12] and HexPlane [7] are concurrent works. We have selected four representative patches to better inspect the details. Our method performs well on reconstructing details and capturing movements." + ], + "image_footnote": [], + "bbox": [ + 80, + 89, + 282, + 253 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/4f2d0189c19bb3a69a78f0ee6976aff14f242fdaa5d28a39e92219b08e372f9c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 282, + 88, + 483, + 253 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/ccf7bcc8ba4c17aea0eaff80d748501f90b07f48c27c7313a4cc2461bedd8946.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 483, + 88, + 687, + 253 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/095c3814f0f631827a7185d40e050bfcbf8e052232f66cf316ec7633114ef842.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 689, + 89, + 890, + 253 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/9e9e095c439d97280855e703ec5d6d102c0d0af2d1837d471eb5c04cb9a2f589.jpg", + "table_caption": [ + "Table 3. Quantitative results comparisons. All metrics are measured on 300-frame scenes. We also report the training time, rendering speed (FPS) and model size. * Note DyNeRF is trained on 8 GPUs, while others are trained on one GPU." + ], + "table_footnote": [], + "table_body": "
MethodTrainRenderSizePSNR↑DSSIM↓LPIPS↓
DyNeRF[19]7 days*-28 MB29.580.01970.083
Concurrent work
StreamRF[18]75 min8.35310MB28.26--
NeRFPlayer[37]360 min0.05-30.690.0340.111
Hyperreel[2]540 min2.0360 MB31.100.0360.096
K-Planes[12]108 min--31.630.018-
HexPlanes[7]720 min-200MB31.710.0140.075
Mix Voxels-S15 min37.7500 MB31.030.0220.129
Mix Voxels-M40 min37.7500 MB31.220.0190.102
Mix Voxels-L80 min37.7500 MB31.340.0170.096
Mix Voxels-X300 min4.6500 MB31.730.0150.064
", + "bbox": [ + 78, + 348, + 470, + 507 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "dynamic scenes more practical. For rendering, the Mix Voxels has a 37.7 fps rendering speed for 1K resolution. Compared with concurrent works, Mix Voxels requires less training time and achieves faster rendering speed, while achieving competitive PSNR and LPIPS. For example, with only 15 minutes of training, Mix Voxels achieve 31.03 PSNR which is comparable to other methods trained for hours. With sufficient training, all metrics are further improved. For the quantitative results on our collected more complex scenes, we present them on Tab. 1.", + "bbox": [ + 75, + 518, + 468, + 669 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Qualitative results and comparisons. Fig. 6 demonstrates the novel view rendering results on different dynamic scenes. The first four rows are novel view videos from Plenoptic Video Dataset [19]. The last two rows present the novel view videos from our collected two more complex dynamic scenes. The results show that our method can achieve near photo-realistic rendering quality. We provide the video results at the supplementary material. For qualitative comparisons, we show them in Fig. 5. MixVoxels can better reconstruct the moving object (the firing gun) and textual details like the hat and the salmon stripes.", + "bbox": [ + 75, + 671, + 468, + 838 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We further investigate the relations between rendering efficiency and rendering quality. As shown in the lower part of Tab. 3, it was observed that an increase in training time leads to improvements in both PSNR and LPIPS. Longer", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/7463cb1b9c5b0a2eb6b561b61b95cba370c8e8c6cf425b8c5863db6436877f40.jpg", + "image_caption": [ + "Figure 6. Novel view synthesis of MixVoxels. We select some frames at different views. The last column demonstrates the normalized depth. We provide videos at the supplemental material." + ], + "image_footnote": [], + "bbox": [ + 501, + 291, + 890, + 606 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "training facilitates the reconstruction of sharp boundaries and fine details. Visual comparisons presented in Fig. 7 reveals that 15 minutes of training produces satisfactory recovery of most scene components but resulted in blurry motion details. With longer training, the moving objects become clearer with a distinct boundary.", + "bbox": [ + 496, + 656, + 890, + 748 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 756, + 653, + 773 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this subsection, we empirically justify the design of MixVoxels by ablating or modifying several key features. We also provide analysis that intuitively explains the ablations. We conduct all experiments in this subsection on the coffee-martini scene, which we find is typical for demonstrating the fast-moving complex objects.", + "bbox": [ + 496, + 779, + 890, + 869 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation on splitting voxels. To study the effect of splitting static and dynamic voxels, we compare MixVox-", + "bbox": [ + 498, + 869, + 890, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "19712", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/340d6c855123630c3abf9455f1da3f1c953bf85c7a2ae0bcfbb676afc73c01e0.jpg", + "image_caption": [ + "Figure 7. Qualitative demonstration of different training schedules. Longer training helps better reconstruct the high-dynamic parts." + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 468, + 244 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/348214fb9bf1f61771b03da913a9ce284021e56d9b8b6600c927a900e8b2c5f0.jpg", + "image_caption": [ + "Figure 8. Qualitative comparison of MixVoxels and the full-dynamic model. Training with full-dynamic models with the same iterations can not well reconstruct the motion details." + ], + "image_footnote": [], + "bbox": [ + 84, + 282, + 468, + 415 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/e7aa6470160850f0cc25595bda9c00f64c643410f48d711950f2f10dd88853aa.jpg", + "table_caption": [ + "Table 4. Ablation on the mixed voxels. Training with the fulldynamic voxel model hurts both efficiency and efficacy." + ], + "table_footnote": [], + "table_body": "
MethodTimePSNR↑DSSIM↓LPIPS↓FLIP↓JOD↑
Full-Dynamic2.5h28.360.0360.22360.11967.44
MixVoxels0.6h29.470.0260.11670.12237.99
", + "bbox": [ + 78, + 498, + 467, + 541 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/fc7fdf3d6a91fbc9725216ffc253051ee1bd5cadd31de20be96e04856da231c4.jpg", + "table_caption": [ + "Table 5. Ablation on three different methods for time query. We only substitute the time query with different method, and train them on the proposed MixVoxels framework." + ], + "table_footnote": [], + "table_body": "
MethodTimePSNR↑DSSIM↓LPIPS↓FLIP↓JOD↑
Concat58m28.950.0370.21460.12947.44
Fourier43m28.670.0290.18240.12867.60
Inner product40m29.470.0260.11670.12237.99
", + "bbox": [ + 81, + 594, + 465, + 648 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "els with a full-dynamic voxel-grid representation, where all points are processed by the dynamic model. Tab. 4 shows the comparisons. With the same training iterations, the fulldynamic model is more time-consuming, which is intuitive because it processes all voxels with the dynamic models. Fig. 8 shows the qualitative comparison. The full-dynamic model recovered blurred motions. We speculate the reason is because the large area of static regions affects the capturing of dynamic information. The network will be biased by most static voxels with no motions and tend to learn low-frequency information.", + "bbox": [ + 75, + 657, + 468, + 823 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Ablation on time query. We compare our inner product time query method with other variants: (1) Concatenation which concatenates the temporal embedding with the voxel features to be processed by an MLP. (2) Fourier head proposed by [47] which reconstructs the dynamics in", + "bbox": [ + 75, + 824, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c9241656e7ece3d370d83ef4455c607773efe5f7fcaf39f3b1962dc33fac968c.jpg", + "image_caption": [ + "Figure 9. Ablation on the number of time query denoted as Q. frequency-domain. Tab. 5 shows the performance comparison. The concatenation query method is both space- and time-consuming. Querying one time step requires forwarding the fused features through the whole MLP. Limited by the GPU memory, we can only query 50 time steps per iteration with the concatenation way, which harms the performance on high-dynamic regions. The Fourier head processes the features to predict the magnitudes of different frequency components and the performance is competitive, while it requires an additional inverse discrete Fourier transform to recover the information in the temporal domain. Overall, the inner product query is the simplest and most efficient way for querying." + ], + "image_footnote": [], + "bbox": [ + 501, + 88, + 890, + 165 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Number of time queries per-iteration. We empirically find that simultaneously querying multiple time steps in an iteration helps reconstruct the details of moving parts. Fig. 9 demonstrates the effect of different numbers of time queries denoted as Q. With more time queries, the boundaries of the moving hand and the flowing coffee become clearer. Querying more time steps can provide dense supervision and make the model acquire global temporal information in every iteration, which accelerates the convergence speed. The effective inner product time queries allow adding more time queries with negligible increase in computation.", + "bbox": [ + 496, + 381, + 892, + 547 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Limitations", + "text_level": 1, + "bbox": [ + 500, + 556, + 625, + 571 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Our method can synthesize novel view videos with a relative high quality. However, for some scenes with complex lighting conditions, some inconsistent property predictions may appear at the boundary between dynamic and static voxels, which is shown in Fig. 10. We suspect that the phenomenon is caused by the under-sampling of dynamic regions on scenes with some bad conditions. We will investigate ways to address the problem in future works.", + "bbox": [ + 496, + 580, + 890, + 700 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3fa2e51a701c78673a132eae85df356ac77ef87803a44d9a5783c28ecf2bda84.jpg", + "image_caption": [ + "Figure 10. Some inconsistent density and color predictions in the boundaries between dynamic and static regions." + ], + "image_footnote": [], + "bbox": [ + 501, + 707, + 888, + 777 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 814, + 617, + 830 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This paper demonstrates a new method named MixVoxels to efficiently reconstruct the 4D dynamic scenes and synthesize novel view videos. The core of our method is to split the 3D space into static and dynamic components", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "19713", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "with the proposed variation field, and process them with different branches. The separation speeds up the training and makes the dynamic branch focus on the dynamic parts to improve the performance. We also design an efficient dynamic voxel-grid representation with an inner product time query. The proposed method achieves competitive results with only 15 minutes of training, making the training and rendering of complex dynamic scenes more practical. We believe the fast training speed will enable potentially useful applications that are bottlenecked by training efficiency.", + "bbox": [ + 75, + 90, + 472, + 243 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Acknowledgement", + "text_level": 1, + "bbox": [ + 76, + 256, + 256, + 273 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was supported in part by the National Natural Science Fund for Distinguished Young Scholars under Grant 62025304.", + "bbox": [ + 75, + 280, + 468, + 321 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 337, + 174, + 353 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Pontus Andersson, Jim Nilsson, Tomas Akenine-Möller, Magnus Oskarsson, Kalle Åström, and Mark D Fairchild. Flip: A difference evaluator for alternating images. Proc. ACM Comput. Graph. Interact. Tech., 3(2):15-1, 2020. 6", + "[2] Benjamin Attal, Jia-Bin Huang, Christian Richardt, Michael Zollhoefer, Johannes Kopf, Matthew O'Toole, and Changil Kim. 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Let there be color! large-scale texturing of 3d reconstructions." + ], + "bbox": [ + 501, + 92, + 892, + 900 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "19715", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "In European conference on computer vision, pages 836-850. Springer, 2014. 2", + "[47] Liao Wang, Jiakai Zhang, Xinhang Liu, Fuqiang Zhao, Yanshun Zhang, Yingliang Zhang, Minye Wu, Jingyi Yu, and Lan Xu. Fourier plenoctrees for dynamic radiance field rendering in real-time. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 13524-13534, 2022. 2, 8", + "[48] Daniel N Wood, Daniel I Azuma, Ken Aldinger, Brian Curless, Tom Duchamp, David H Salesin, and Werner Stuetzle. Surface light fields for 3d photography. 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Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.197, + 0.131, + 0.775, + 0.154 + ], + "angle": 0, + "content": "Mixed Neural Voxels for Fast Multi-view Video Synthesis" + }, + { + "type": "text", + "bbox": [ + 0.098, + 0.18, + 0.873, + 0.201 + ], + "angle": 0, + "content": "Feng Wang\\(^{1}\\) Sinan Tan\\(^{1}\\) Xinghang Li\\(^{1}\\) Zeyue Tian\\(^{2}\\) Yafei Song\\(^{3}\\) Huaping Liu\\(^{1*}\\)" + }, + { + "type": "text", + "bbox": [ + 0.153, + 0.205, + 0.827, + 0.277 + ], + "angle": 0, + "content": "\\(^{1}\\)Beijing National Research Center for Information Science and Technology(BNRist), Department of Computer Science and Technology, Tsinghua University \\(^{2}\\)Hong Kong University of Science and Technology \\(^{3}\\)XR Lab, DAMO Academy, Alibaba Group" + }, + { + "type": "text", + "bbox": [ + 0.254, + 0.28, + 0.715, + 0.294 + ], + "angle": 0, + "content": "wang-f20@mails.tsinghua.edu.cn,hpliu@tsinghua.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.329, + 0.314, + 0.345 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.362, + 0.474, + 0.771 + ], + "angle": 0, + "content": "Synthesizing high-fidelity videos from real-world multiview input is challenging due to the complexities of real-world environments and high-dynamic movements. Previous works based on neural radiance fields have demonstrated high-quality reconstructions of dynamic scenes. However, training such models on real-world scenes is time-consuming, usually taking days or weeks. In this paper, we present a novel method named MixVoxels to efficiently represent dynamic scenes, enabling fast training and rendering speed. The proposed MixVoxels represents the 4D dynamic scenes as a mixture of static and dynamic voxels and processes them with different networks. In this way, the computation of the required modalities for static voxels can be processed by a lightweight model, which essentially reduces the amount of computation as many daily dynamic scenes are dominated by static backgrounds. To distinguish the two kinds of voxels, we propose a novel variation field to estimate the temporal variance of each voxel. For the dynamic representations, we design an inner product time query method to efficiently query multiple time steps, which is essential to recover the high-dynamic movements. As a result, with 15 minutes of training for dynamic scenes with inputs of 300-frame videos, MixVoxels achieves better PSNR than previous methods. For rendering, MixVoxels can render a novel view video with 1K resolution at 37 fps. Codes and trained models are available at https://github.com/fengres/mixvoxels." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.802, + 0.21, + 0.818 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.829, + 0.471, + 0.876 + ], + "angle": 0, + "content": "Dynamic scene reconstruction from multi-view videos is a critical and challenging problem, with many potential applications such as interactively free-viewpoint control" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.329, + 0.633, + 0.405 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.55, + 0.406, + 0.582, + 0.415 + ], + "angle": 0, + "content": "1 min" + }, + { + "type": "image", + "bbox": [ + 0.633, + 0.329, + 0.759, + 0.405 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.674, + 0.406, + 0.706, + 0.415 + ], + "angle": 0, + "content": "5 min" + }, + { + "type": "image", + "bbox": [ + 0.76, + 0.329, + 0.889, + 0.405 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.8, + 0.406, + 0.838, + 0.415 + ], + "angle": 0, + "content": "10 min" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.415, + 0.633, + 0.49 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.545, + 0.491, + 0.582, + 0.5 + ], + "angle": 0, + "content": "15 min" + }, + { + "type": "image", + "bbox": [ + 0.633, + 0.415, + 0.762, + 0.49 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.671, + 0.491, + 0.71, + 0.5 + ], + "angle": 0, + "content": "40 min" + }, + { + "type": "image", + "bbox": [ + 0.762, + 0.415, + 0.89, + 0.49 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.797, + 0.491, + 0.842, + 0.5 + ], + "angle": 0, + "content": "300 min" + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.505, + 0.893, + 0.576 + ], + "angle": 0, + "content": "Figure 1. Our method enables rapid reconstruction of 4D dynamic scenes. We visualize the rendering results with different training schedules. With only 15 minutes of training, our approach achieves comparable PSNRs to other methods. Increasing the training time further enhances the ability to recover fine details." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.893, + 0.793 + ], + "angle": 0, + "content": "for movies, cinematic effects like freeze-frame bullet time, novel view replays for sporting events, and various potential VR/AR applications. Recently, neural radiance fields [26] have demonstrated the possibility of rendering photorealistic novel views for static scenes, with physically motivated 3D density and radiance modelling. Many methods [19, 20, 49, 13, 10, 31, 28, 29, 44] extend the neural radiance fields to dynamic scenes with additional time queries or an explicit deformation field. Many of these methods focus on the monocular input video setting on relatively simple dynamic scenes. To model more complex real-world dynamic scenes, a more practical solution is to use multi-view synchronized videos to provide dense spatial-temporal supervi" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Recently, Li et al. [19] propose a real-world dynamic scene dataset including many challenging situations such as objects of high specularity, topology changes, and volumetric effects. They address the problem by a hierarchical training scheme and the ray importance sampling strategies. Although significant improvements have been achieved, some challenges still exist: (1) The training and rendering take a" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.222, + 0.9 + ], + "angle": 0, + "content": "*Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "19706" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.468, + 0.121 + ], + "angle": 0, + "content": "lot of time and computation resources. (2) Highly dynamic scenes with complex motions are still difficult to track." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.122, + 0.47, + 0.606 + ], + "angle": 0, + "content": "In this paper, we focus on the multi-view 3D video synthesis problem and present a novel method named MixVoxels to address the above two challenges. The proposed MixVoxels is based on the explicit voxel-grid representation, which is recently popular due to its fast training and rendering speed on static scenes [50, 40, 8, 27]. We extend the voxel-grid representations to support dynamic scenes and propose an efficient inner product time querying method that can query a large number of time steps simultaneously, which is essential to recover the sharp details for highly-dynamic objects. Additionally, we represent dynamic scenes as a mixed static-dynamic voxel-grid representation. Specifically, the 3D spaces are split into static and dynamic voxels by our proposed variation field. The two components are processed by different models to reduce the redundant computations for the static space. Theoretically, once a dynamic scene consists of some static spaces, the training speed will benefit from the proposed mixed voxels. For a variety of events that occur in the physical world, the static components of environments are dominated in most cases, and the mixed voxels will speed up the training significantly in these scenarios. Besides, the separation of voxels makes the time-variant model focus on the dynamic regions, avoiding the time-aware voxels being biased by the static spaces to produce blurred motions. Our empirical validation confirms that the separation enables the model to learn sharp and distinct boundaries in high-dynamic regions. This also frees our method from the complex importance sampling strategies. With these designs, our method is capable of reconstructing a dynamic scene consisting of 300 frames within 15 minutes. To summarize, the main contributions of this work are:" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.612, + 0.468, + 0.672 + ], + "angle": 0, + "content": "- We propose a simple yet effective dynamic representation with inner product time querying method that can efficiently query multiple times simultaneously, improving the rendering quality for dynamic objects." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.677, + 0.468, + 0.722 + ], + "angle": 0, + "content": "- We design an efficient variation field to separate static and dynamic spaces and present a mixed voxel-grid representation to accelerate training and rendering." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.728, + 0.468, + 0.803 + ], + "angle": 0, + "content": "- We conduct qualitative and quantitative experiments to validate our method. As a result, the proposed MixVoxels achieves competitive or better rendering qualities with a \\(5000 \\times\\) training speedup compared to implicit dynamic scene representations." + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.612, + 0.468, + 0.803 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.816, + 0.227, + 0.831 + ], + "angle": 0, + "content": "2. Related Works" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.84, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Novel View Synthesis for Static Scenes. Synthesizing novel views for static scenes is a classical and well-studied problem. Different approaches represent the underlying geometric with different representations. Mesh-based meth" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.319 + ], + "angle": 0, + "content": "ods [6, 9, 46, 48, 34, 43] represent the scenes with surfaces which is compact and easy to render, while optimizing a mesh to fit complex scenes is challenging. Volume-based methods such as voxel-grid [17, 35, 30, 23, 36] and multiplane images (MPIs) [54, 11, 25, 39, 38, 45] are more suitable to model the complex and translucent scenes such as smooth and fluid. Particularly, Neural radiance fields [26] represent the scenes with an implicit volumetric neural representation, which employs a coordinate-based neural network to query the density and color for each point. The achieved photo-realistic rendering quality of NeRF led to an explosion of developments in the field. Advances have been made including improving the rendering qualities [42, 4], adapting to more general scenarios [52, 24, 41, 5], accelerating rendering or training speed [22, 51, 50, 40, 8], etc." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.327, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Novel View Synthesis for Dynamic Scenes. Synthesizing novel views for dynamic scenes is a more challenging and applicable problem. Recently, many extensions of NeRF for non-rigid dynamic scenes were proposed, which take a monocular video as input to learn the deformation and radiance fields. These methods can be categorized to modelling deformation implicitly [20, 49, 13, 10] (learn the non-decoupled deformation and appearance jointly) and explicitly [31, 28, 29, 44] (learn separated deformation and radiance fields and the deformation fields are usually in the form of relative motion with a canonical static space). Though improvements are achieved, reconstructing the complex general scenes is still difficult with only monocular videos. Most methods are constrained to fixed scenes like human-model or restricted motions. For real-world complex scenes, reconstructing from synchronized multi-view videos is more promising due to the dense supervision for every viewpoint and time instant. Earlier works [14, 55] explore the problem and show the possibility of rendering novel videos from a set of input views. Neural Volumes [23] proposes to use volumetric representations. They employ an encoder-decoder network to convert input images into a 3D volume, and decode the latent representations by the differentiable ray marching operation. [3] presents a data-driven approach for 4D space-time visualization of dynamic scenes by splitting static and dynamic components and using a U-Net structure in screen space to convert intermediate representation to image. Different with this method, our method split the static and dynamic components in the 3D voxel space instead of the pixel space. More recently, DyNerf [19] uses a temporal-aware neural radiance field to address the problem, and proposes some sampling strategies to train it efficiently. Compared with previous methods, they propose a more complicated real-world dataset and validate their method. For accelerating the reconstruction of dynamic scenes, FourierPlenoctree [47] proposes to model the dynamics in frequency domain, and generate a Plenoctree through multi" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.956 + ], + "angle": 0, + "content": "19707" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.302 + ], + "angle": 0, + "content": "view blending to accelerate rendering. They focus on the foreground moving objects extracted via chroma key segmentation, which requires the background should be a pure color (or rely on segmentation algorithms). Recently, the acceleration of training and rendering for dynamic scenes has attracted much attention. Cocurrent works include StreamRF [18] which proposes to accelerate the training of dynamic scenes by modeling the differences of adjacent frames, NeRFPlayer [37] which decomposes the dynamic scenes into static, new and deforming components, Hyperreel [2] which proposes an efficient sampling network and models keyframes. K-Planes [12] and HexPlanes [7] decompose the 4D dynamic scenes into different 2D representations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.303, + 0.473, + 0.667 + ], + "angle": 0, + "content": "Acceleration of Neural Radiance Fields. While Neural radiance fields can render novel views with high fidelity, training and rendering require querying a deep MLP millions of times which is computationally intensive. Many recent methods propose to accelerate the training and rendering speed of NeRF. For rendering, Neural Sparse Voxel Fields [22] proposes a voxel-grid representation to skip over many empty regions. PlenOctree [51] accelerates the rendering process by pre-tabulating the NeRF into a PlenOctree and using the spherical harmonic representation of radiance. Derf [32] and Kilonerf [33] propose to accelerate the rendering speed by dividing the scenes into multiple areas, and employ multiple small network in each area. AutoInt [21] proposes to restructure the MLP network to accelerate the computations of ray integrals, which helps accelerate the rendering speed. For accelerating the training of NeRF, some methods use explicit voxel-grid representations [50, 40] to accelerate the training process and convergence speed. Instant-NGP [27] proposes a multi-resolution hash table structure to accelerate the training. The model sizes of most fast training methods are relatively large due to a large number of voxels. TensoRF [8] proposes to reduce the model size by factorizing the 4D scene tensor into multiple compact low-rank tensor components." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.678, + 0.17, + 0.695 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.703, + 0.47, + 0.825 + ], + "angle": 0, + "content": "In this section, we introduce the proposed MixVoxels, which represents the 4D dynamic scenes as mixtures of static and dynamic voxels. Fig. 2 illustrates the overview of our method. In the following subsections, we will first introduce the voxel-grid representations for static scenes and our extension to dynamic scenes. Then we introduce the variation field for identifying the dynamic voxels. At last, we introduce the training of MixVoxels." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.833, + 0.364, + 0.849 + ], + "angle": 0, + "content": "3.1. Static Voxel-grid Representation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.472, + 0.903 + ], + "angle": 0, + "content": "Neural radiance fields [26] have demonstrated photorealistic novel viewpoint synthesis, while the training of NeRF requires extensive computation due to millions of" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.304 + ], + "angle": 0, + "content": "neural network queries. For accelerating NeRF, many recent works [22, 50, 40, 8] have explored the explicit volumetric representation, which avoids the huge amount of computation of querying neural network. Specifically, a 3D scene is split into \\(N_{x} \\times N_{y} \\times N_{z}\\) voxels. The densities and color features are stored in these voxels and denoted as \\(\\mathcal{S}^{\\sigma} \\in \\mathbb{R}^{N_x \\times N_y \\times N_z}\\) and \\(\\mathcal{S}^c \\in \\mathbb{R}^{N_x \\times N_y \\times N_z \\times C}\\). \\(\\mathcal{S}_{i,j,k}^{\\sigma}\\) and \\(\\mathcal{S}_{i,j,k}^c\\) represent the learnable density and color feature of the voxel corner at a discrete position \\((i,j,k)\\). For a continuous position \\((x,y,z)\\), the representation \\(\\mathcal{S}_{x,y,z}\\) can be calculated by interpolating the nearest 8 discrete positions. A small MLP network \\(\\mathcal{C}_{\\theta}\\) is used to parse the color features into RGB values, taking \\(S^c\\) and view direction \\(d\\) as input. Formally, the density \\(\\sigma\\) and color \\(c\\) is formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.515, + 0.313, + 0.892, + 0.332 + ], + "angle": 0, + "content": "\\[\n\\sigma (x, y, z) = \\mathcal {S} _ {x, y, z} ^ {\\sigma}, \\quad c (x, y, z, \\boldsymbol {d}) = \\mathcal {C} _ {\\theta} \\left(\\mathcal {S} _ {x, y, z} ^ {c}, \\boldsymbol {d}\\right). \\tag {1}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.339, + 0.812, + 0.357 + ], + "angle": 0, + "content": "3.2. Dynamic Voxel-grid Representation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.362, + 0.892, + 0.755 + ], + "angle": 0, + "content": "For dynamic scenes, a direct extension is to add the time dimension to the static voxel-grid representation \\( S \\) explicitly. However, this direct extension is almost memory-prohibitive due to the large and linearly increasing memory footprint. For a 300-frame video, the learned models will occupy 30 GB of memory and be difficult to train with GPUs due to the limitation of GPU memory. To address this problem, we propose a spatially explicit and temporally implicit representation to reduce the memory footprint. Specifically, we represent the dynamic scene as a 4D learnable voxel-grid \\( \\mathcal{G}^{\\sigma} \\in \\mathbb{R}^{N_x \\times N_y \\times N_z \\times C_1} \\) and \\( \\mathcal{G}^c \\in \\mathbb{R}^{N_x \\times N_y \\times N_z \\times C_2} \\). Different from the static scene representations, the densities and colors for all time steps are implicitly encoded as compact features stored in each voxel corner. The compact features will be processed by a time-aware projection to acquire density and color for each time step. Concretely, for the compact density feature \\( \\mathcal{G}_{x,y,z}^{\\sigma} \\) and color feature \\( \\mathcal{G}_{x,y,z}^c \\) in any position(x,y,z), we employ two MLPs \\( T_{\\theta_1}^{\\sigma} \\) and \\( T_{\\theta_2}^c \\) to increase the feature dimensions for better parsing time-variant density and color. The MLPs here can be viewed as decompressors that decompress the compact low-dimensional voxel-grid features into more tractable ones. Compared with directly storing high-dimensional features in each voxel, the temporally implicit representation reduces the memory footprint significantly since the shared MLPs only increase memory slightly." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.755, + 0.892, + 0.876 + ], + "angle": 0, + "content": "Inner product time query. For a discrete time step \\( t \\), we use a learnable time-variant latent representation \\( \\omega_{t} \\) to represent the time query. Instead of concatenating the time query with the intermediate features, we propose to calculate the inner product between the learned time query and the decompressed features as the required output \\( \\sigma \\) and \\( c \\). Formally, the density and color of a space-time query \\( (x,y,z,t) \\) are formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.588, + 0.885, + 0.892, + 0.904 + ], + "angle": 0, + "content": "\\[\n\\sigma (x, y, z, t) = \\omega_ {t} ^ {\\sigma} \\cdot \\mathcal {T} _ {\\theta_ {1}} ^ {\\sigma} (\\mathcal {G} _ {x, y, z} ^ {\\sigma}), \\tag {2}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "19708" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.088, + 0.468, + 0.228 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.229, + 0.473, + 0.314 + ], + "angle": 0, + "content": "Figure 2. Overview of our method. Given a ray, we first sample points, and split them into static and dynamic ones using the variation field. After that, we feed these points to the corresponding branches and query the required properties. Then we merge the static output and dynamic output for rendering the ray color. An L2 loss is employed to calculate loss and back-propagate." + }, + { + "type": "equation", + "bbox": [ + 0.152, + 0.332, + 0.47, + 0.351 + ], + "angle": 0, + "content": "\\[\nc (x, y, z, \\boldsymbol {d}, t) = \\omega_ {t} ^ {c} \\cdot \\mathcal {T} _ {\\theta_ {2}} ^ {c} (\\mathcal {G} _ {x, y, z} ^ {c}, \\boldsymbol {d}). \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.355, + 0.473, + 0.538 + ], + "angle": 0, + "content": "In practice, simultaneously querying multiple time steps helps reconstruct the detail of high-dynamic motions and reduces the training iterations to traverse through all time steps. The inner product based query will facilitate the training speed when simultaneously querying many time steps in a training iteration. Specifically, we denote the FLOPs of the MLP \\(\\mathcal{T}_{\\theta_1}\\) and the inner product operation as \\(\\mathrm{FLOP}_{mlp}\\) and \\(\\mathrm{FLOP}_{inn}\\), respectively. For a \\(T\\)-frame video, the FLOPs of the concatenation query [19] is larger than \\(T\\cdot \\mathrm{FLOP}_{mlp}\\) (due to the extra temporal embedding dimension), while the FLOPs of our inner product query is only \\(\\mathrm{FLOP}_{mlp} + T\\cdot \\mathrm{FLOP}_{inn}\\) (\\(\\mathrm{FLOP}_{mlp} >> \\mathrm{FLOP}_{inn}\\))." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.545, + 0.232, + 0.56 + ], + "angle": 0, + "content": "3.3. Variation Field" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.569, + 0.47, + 0.675 + ], + "angle": 0, + "content": "In this subsection, we introduce the variation field to identify which voxels in the 3D space are dynamic, i.e., the densities or colors are not constant over different time steps. By separating the static and dynamic voxels, the redundant computations caused by using a relatively heavy time-varying model to process the static components will be avoided, which accelerates the training and rendering." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.675, + 0.471, + 0.902 + ], + "angle": 0, + "content": "A simpler solution for accelerate training is to separate the static and dynamic regions in pixel-level, i.e., using the temporal variance of pixels to produce static and dynamic ones. However this scheme is actually not feasible because we can only separate dynamic and static regions in training views using the ground truth. For rendering novel views, we can not get the pixel variance for rendering since we have no ground truth in novel views. Thus a feasible solution is to learn the voxel-level temporal variance which is shared for all possible views. In addition, separating in the voxel-level is more efficient compared to pixel-level, even if we have an oracle to make the pixel-level separation feasible in novel views. This is because not all voxels projected to a dynamic pixel are dynamic, there will be only a small fraction of voxels around the object surfaces are actually" + }, + { + "type": "image", + "bbox": [ + 0.527, + 0.094, + 0.872, + 0.272 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.273, + 0.895, + 0.343 + ], + "angle": 0, + "content": "Figure 3. Implicit interaction of multiple rays to decide which point is dynamic. For a static ray (blue line), all points are set to be low dynamic. For a dynamic ray (green line), at least one point is dynamic. The intersection of multiple dynamic ray is more likely to be a dynamic point, which is also physically intuitive." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.348, + 0.892, + 0.379 + ], + "angle": 0, + "content": "dynamic. Therefore, the voxel level separation will produce much fewer dynamic queries." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.378, + 0.893, + 0.49 + ], + "angle": 0, + "content": "To perform the voxel-level separation, we utilize the pixel-level temporal variances from training videos as the supervision to estimate the voxel-level variances. The pixel-level (or ray-level) temporal variances of different videos are shown in Fig. 3. Formally, given a ray \\( r(s) = o + s \\cdot d \\) with origin \\( o \\) and direction \\( d \\), the corresponding pixel color at time step \\( t \\) is defined as \\( C(r,t) \\). Then the pixel-level temporal variance \\( D^2(r) \\) is formalized as" + }, + { + "type": "equation", + "bbox": [ + 0.505, + 0.495, + 0.888, + 0.533 + ], + "angle": 0, + "content": "\\[\nD ^ {2} (\\boldsymbol {r}) = \\frac {1}{T} \\sum_ {t = 1} ^ {T} (C (\\boldsymbol {r}, t) - \\bar {C} (\\boldsymbol {r})) ^ {2}, \\quad \\bar {C} (\\boldsymbol {r}) = \\frac {1}{T} \\sum_ {t = 1} ^ {T} C (\\boldsymbol {r}, t),\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.539, + 0.895, + 0.645 + ], + "angle": 0, + "content": "where \\(\\bar{C} (\\pmb {r})\\) is the mean color of pixel corresponding to the ray \\(\\pmb{r}\\). For identifying the dynamic pixels, the standard deviation \\(D(\\pmb {r})\\) is binarized to \\(M(r)\\) with a threshold \\(\\gamma\\) to provide pixel-level dynamic supervision, i.e. \\(M(r) = 1\\) if \\(D(\\boldsymbol {r})\\geq \\gamma\\), else \\(M(\\boldsymbol {r}) = 0\\). In this way, we judge that a ray \\(\\pmb{r}\\) is dynamic if \\(M(r) = 1\\). Next, we use the \\(M(r)\\) as supervision to estimate the voxel-level variations \\(\\mathcal{V}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.645, + 0.895, + 0.841 + ], + "angle": 0, + "content": "The relations between the pixel-level variance and voxel-level variance lie in the following aspects: (1) If a pixel is static, then all voxels passed through by the ray corresponding to the pixel should be static in most cases (We will discuss some special cases which violate this rule later in this subsection.). (2) If a pixel is dynamic, then at least one of the voxels passed through by the corresponding ray is dynamic. Fig. 3 shows the two situations. With the above two relations, we design the variation field, which is denoted as \\(\\mathcal{V} \\in \\mathbb{R}^{N_x \\times N_y \\times N_z}\\) to represent the voxel-level temporal variance. Specifically, we uniformly sample \\(N_s\\) points from the near plane to the far plane in \\(\\mathbf{r}\\), and build the following equation to satisfy the two relations mentioned above:" + }, + { + "type": "equation", + "bbox": [ + 0.559, + 0.846, + 0.892, + 0.865 + ], + "angle": 0, + "content": "\\[\n\\hat {M} (\\boldsymbol {r}) = \\boldsymbol {s} (\\max (\\{\\mathcal {V} _ {\\boldsymbol {r} (s _ {i})} | i \\in \\{1, \\dots , N _ {s} \\} \\})), \\qquad (4)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.87, + 0.895, + 0.902 + ], + "angle": 0, + "content": "where \\(\\hat{M}(\\boldsymbol{r})\\) is an estimation of \\(M(\\boldsymbol{r})\\), and \\(\\boldsymbol{s}\\) is the sigmoid function. Then we train the variation field by minimizing" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "19709" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.342, + 0.106 + ], + "angle": 0, + "content": "the following binary cross-entropy loss:" + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.109, + 0.469, + 0.13 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {v} = \\mathbb {E} _ {\\boldsymbol {r}} \\left[ - M (\\boldsymbol {r}) \\log (\\hat {M} (\\boldsymbol {r})) - (1 - M (\\boldsymbol {r})) \\log (1 - \\hat {M} (\\boldsymbol {r})) \\right]. \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.132, + 0.47, + 0.176 + ], + "angle": 0, + "content": "By optimizing the above loss function to all rays, we can get the learned variation field \\(\\mathcal{V}\\). The training of the variation field is very efficient, usually taking less than 30 seconds." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.177, + 0.473, + 0.493 + ], + "angle": 0, + "content": "The maximization operation well formulates the relations between a pixel and its corresponding voxels. If a pixel is static, then the equations of Eq. (4) and Eq. (5) will force all voxels passed through by the corresponding ray to be static \\((\\mathcal{V}_{x,y,z} = 0)\\). If a pixel is dynamic, Eq. (4) requires at least one of the corresponding voxels (i.e., the max value of the voxel variances) to be dynamic \\((\\mathcal{V}_{x,y,z} = +\\infty)\\). Although we provide no information about which specific voxels in a dynamic ray are dynamic, the implicit interaction of multiple different rays will force the solution to be physically reasonable. To explain this, we focus on the observable voxels which at least passed through by one ray. If a point \\((x,y,z)\\) is passed through by at least one static ray, then \\(\\mathcal{V}_{x,y,z}\\) will tend to be optimized to be close to zero. If a point \\((x,y,z)\\) is only passed through by dynamic rays, and not occluded by other dynamic voxels, then \\(\\mathcal{V}_{x,y,z}\\) will be optimized to \\(+\\infty\\). This is because without occlusion, the above point of \\((x,y,z)\\) along the dynamic rays will be passed by other static rays (the front space along these rays are observable from other views). We illustrate this situation in Fig. 3." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.494, + 0.473, + 0.825 + ], + "angle": 0, + "content": "Inference. After the training process, the temporal variation at a specific 3D position \\((x,y,z)\\) is \\(\\mathcal{V}_{x,y,z}\\), which is easily acquired by interpolating the discrete variation field. We then identify a voxel in the scene as dynamic if \\(\\mathcal{V}_{x,y,z}\\) is larger than a hyper-parameter \\(\\beta\\), and as static if it is smaller than \\(\\beta\\). Formally, we will get a dynamic mask \\(\\dot{\\mathrm{M}} \\in \\{0,1\\}^{N_x \\times N_y \\times N_z}\\), which will be used to split sampling points in a ray into static points and dynamic points. We evaluate the effectiveness of this inference method in the test views and find that the recall and precision are reasonable for splitting the dynamic and static parts (recall: 0.97, precision: 0.94 when \\(\\beta = 0.9\\)). Although the recall seems sufficient to retrieve most dynamic parts, we empirically find some false negatives in the rendering images affect the rendering quality. To address this problem, we use a ray-wise max-pooling operation to identify the points near to a dynamic point as dynamic. The kernel size of max-pooling is set to \\(k_m = 21\\), and the stride is set to 1. In this way, the recall is very closed to 1. Although many hyperparameters are incorporated, we have empirically found that the thresholds \\(\\gamma\\) and \\(\\beta\\) are not sensitive over a wide range of reasonable values." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Discussion. There may be some situations in which the rules (1) are broken due to occlusion. Specifically, when a dynamic voxel is occluded by some static voxels, the occluded parts should not be classified as static, which makes the 2D supervision noisy. However in practice, we found" + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.089, + 0.631, + 0.147 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.632, + 0.089, + 0.761, + 0.147 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.762, + 0.089, + 0.892, + 0.147 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.54, + 0.153, + 0.851, + 0.167 + ], + "angle": 0, + "content": "Figure 4. Impact of occlusions to the variation field." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.169, + 0.892, + 0.501 + ], + "angle": 0, + "content": "the learning-based separation has a certain degree of tolerance for this situation. We conducted experiments to verify this and present the results in Fig. 4. The occluded region is visualized in the leftmost view (the area behind the static roadblock). Although the dynamic region marked in yellow is occluded in the left view, it is actually classified as dynamic region. This can be inferred from another view where the occluded region has changed, as illustrated in the middle and right images in Fig. 4). The variation field is learning-based and will learn a solution that satisfies most constraints. If it forces some dynamic voxels occluded by static voxels to be 0, then the loss function from other visible views will be high. As a result, the learning-based process tends to assign a \"middle solution\" to voxels with inconsistent supervisions from different views. We also attempted to use the transmittance as a weight (in a way of volumetric rendering) to learn the variation field which can explicitly handle the occlusion problem. However, we found a large efficiency drop with similar performance. As a result, we use the proposed variation field and find this formulation works well for most scenes, including some challenging scenes with large areas of motions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.51, + 0.787, + 0.526 + ], + "angle": 0, + "content": "3.4. Training of Mixed Neural Voxels" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.533, + 0.892, + 0.638 + ], + "angle": 0, + "content": "With the help of the variation field, we can split a scene into dynamic voxels and static voxels. To reduce redundant computations, we use the lightweight static model described in Sec. 3.1 to compute the densities and colors for static voxels and the dynamic model described in Sec. 3.2 to compute the densities and colors for dynamic voxels. The overall architecture is illustrated in Fig. 2." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.639, + 0.892, + 0.834 + ], + "angle": 0, + "content": "Specifically for a given ray \\(r(s) = o + sd\\) with origin \\(o\\) and view direction \\(d\\), we apply stratified sampling from the near to the far planes and get \\(N_{s}\\) points. Then the \\(N_{s}\\) points are separated into static and dynamic ones by inferring these points with the proposed variation field. For the static points, we pass them into the static branch to retrieve the colors and densities. For the dynamic points, we pass them into the dynamic branch together with a deferred time query \\(\\omega_{t}\\) to retrieve the corresponding properties. After that, we merge the static points and dynamic points according to their order. Then we apply volumetric rendering to the merged points to obtain the rendered color, which is formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.545, + 0.838, + 0.892, + 0.88 + ], + "angle": 0, + "content": "\\[\nC (\\boldsymbol {r}, t) = \\sum_ {i = 1} ^ {N _ {s}} T _ {i, t} \\cdot \\left(1 - \\exp \\left(- \\sigma_ {i, t} \\delta_ {i}\\right)\\right) \\cdot c _ {i, t}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "where \\(\\mathrm{T}_{i,t}\\) is the accumulated opacity (or transmittance):" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "19710" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.09, + 0.47, + 0.138 + ], + "angle": 0, + "content": "\\(\\mathrm{T}_{i,t} = \\exp (-\\sum_{j = 1}^{i - 1}\\sigma_{j,t}\\delta_j)\\), and \\(\\delta_{i}\\) is the distance between adjacent samples. Given the ground truth color \\(C_g(\\boldsymbol {r},t)\\), an l2-loss is employed to train the model:" + }, + { + "type": "equation", + "bbox": [ + 0.15, + 0.148, + 0.469, + 0.169 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathbb {E} _ {\\left(\\boldsymbol {r}, t\\right)} \\left[ \\| C _ {g} (\\boldsymbol {r}, t) - C (\\boldsymbol {r}, t) \\| _ {2} ^ {2} \\right]. \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.171, + 0.469, + 0.217 + ], + "angle": 0, + "content": "For both static and dynamic branches, we omit the computation of color for points whose densities are close to zero, which is a widely adopted pruning strategy [22, 50, 8]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.217, + 0.47, + 0.398 + ], + "angle": 0, + "content": "Efficiency analysis. We define the proportion of dynamic points in a scene as \\(\\lambda\\) (\\(\\approx 0.05\\) for most scenes). Besides, the FLOPs of static and dynamic branches are denoted as \\(FLOP_{sta}\\) and \\(FLOP_{dyn}\\), respectively. Then the total FLOPs of MixVoxels are \\(FLOP_{sta} + \\lambda \\cdot FLOP_{dyn}\\). Empirically, \\(FLOP_{dyn} / FLOP_{sta}\\) ranges from 50 to 100 with different reasonable dimension settings. Then the acceleration ratio of splitting static and dynamic models is \\(FLOP_{dyn} / (FLOP_{sta} + \\lambda FLOP_{dyn}) \\approx 10\\). In practice, the actual speedup with a 3090 GPU is about 5, the inconsistency between analysis and experiment may come from the GPU features, which are friendly to a more consistent network." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.407, + 0.288, + 0.423 + ], + "angle": 0, + "content": "3.5. Implementation Detail" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.431, + 0.471, + 0.749 + ], + "angle": 0, + "content": "The voxel-grid representations require large GPU memory to store the cubically growing voxel numbers. To implement the voxel-grid representations more memory efficient, we use the tensor factorization technique proposed in TensoRF [8] to reduce the memory footprint. In this way, a 3D tensor is factorized into the outer product of a vector and a 2D matrix. We factorize all the voxel-grid tensors, including static voxels, dynamic voxels and the variation field. With the help of tensor factorization, the learned model costs about 500MB for a 300-frame multi-view video scene. For the voxel resolutions, we follow [8] to start from an initial low resolution of \\(256^{3}\\), and upsample the resolution at steps 1500, 2000, 2500, and 2750 with a linear increase in the log space. The final resolution is set to \\(640^{3}\\). Once the resolution is changed, we re-train the variation field, which only takes about 15-30s. The voxel-grid feature dimension is set to 27, and the hidden state of MLP is set to 512. For training, we use Adam [15] optimizer with a learning rate of 0.02 for voxels and \\(3e - 3\\) for MLPs. The total variation loss [50] is incorporated as a regularization to encourage the space smoothness." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.762, + 0.21, + 0.78 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.265, + 0.804 + ], + "angle": 0, + "content": "4.1. Experiment Setting" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.47, + 0.9 + ], + "angle": 0, + "content": "Dataset. We validate our method on two datasets: (1) The Plenoptic Video Dataset [19], which consists of 6 publicly accessible scenes: coffee-martini, flame-salmon, cook-spinach, cut-roasted-beef, flame-steam and sear-steam. We conduct experiments on all six scenes. Each scene contains 19 videos with different camera views. The dataset" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.088, + 0.875, + 0.102 + ], + "angle": 0, + "content": "Table 1. Results on our collected dataset, including two scenes." + }, + { + "type": "table", + "bbox": [ + 0.522, + 0.106, + 0.872, + 0.227 + ], + "angle": 0, + "content": "
SceneModelPSNR↑DSSIM↓LPIPS↓
Moving-CarsMixVoxels-S18.720.2510.689
MixVoxels-M18.970.2280.552
MixVoxels-L18.890.2220.540
MixVoxels-X19.110.2100.516
Solving-RubikMixVoxels-S25.390.0650.339
MixVoxels-M26.050.0590.275
MixVoxels-L26.280.0550.241
MixVoxels-X26.800.0470.209
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.233, + 0.892, + 0.414 + ], + "angle": 0, + "content": "contains many challenging scenes including objects with topology changes, objects with volumetric effects, various lighting conditions, etc. (2) Our proposed dataset including two more complex dynamic scenes: moving-cars and solving-rubik. The moving-cars scene features several vehicles passing across the screen, with significant motion and displacement. Meanwhile, in the solving-rubik scene, a man solves a Rubik's cube at a rapid pace, averaging 4 rotations per second, providing an opportunity to evaluate the model's ability to capture swift movements. The collection procedures used are similar to those of DyNeRF. More details are presented in the appendix." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.414, + 0.893, + 0.595 + ], + "angle": 0, + "content": "For training and evaluation, we follow the experiment setting in [19] that employs 18 views for training and 1 view for evaluation. To quantitatively evaluate the rendering quality on novel views, we measure PSNR, DSSIM and LPIPS[53] on the test views. We also provide more metrics in the appendix including FLIP [1] and JOD [16], which we find the comparisons are similar with PSNR and LPIPS. We follow the setting of [19] to evaluate our model frame by frame. For videos consisting of equal or more than 300 frames, we evaluate our model every 10 frames [19] to calculate the frame-by-frame metrics except for the JOD metrics, which requires a stack of continuous video." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.596, + 0.892, + 0.702 + ], + "angle": 0, + "content": "Training Schedules. For evaluating the effect of training time, we train MixVoxels with different configurations shown in Tab. 2. The configurations vary in terms of training iterations and the number of sample points per ray. By default, the step size for sampling points is set to four times of the voxel width. The \\(8 \\times\\) means that there will be eight times as many sampling points compared to the default." + }, + { + "type": "table_caption", + "bbox": [ + 0.529, + 0.707, + 0.862, + 0.72 + ], + "angle": 0, + "content": "Table 2. Different training configurations of MixVoxels." + }, + { + "type": "table", + "bbox": [ + 0.533, + 0.722, + 0.86, + 0.793 + ], + "angle": 0, + "content": "
ModelIterationsSampling pointsTraining Time
MixVoxels-S50001 ×15 min
MixVoxels-M125001 ×40 min
MixVoxels-L250001 ×80 min
MixVoxels-X500008 ×300 min
" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.802, + 0.593, + 0.817 + ], + "angle": 0, + "content": "4.2. Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Quantitative results and comparisons. For quantitative results, we present the metrics and compare with other methods in Tab. 3. Compared with the previous state-of-the-art method DyNeRF, we reduce the training time from \\(1.3\\mathrm{K}\\) GPU hours to 15 minutes, making the training of complex" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "19711" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.09, + 0.283, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.089, + 0.484, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.485, + 0.089, + 0.688, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.69, + 0.09, + 0.892, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.256, + 0.894, + 0.285 + ], + "angle": 0, + "content": "Figure 5. Visual comparisons with state-of-the-art methods. K-Planes [12] and HexPlane [7] are concurrent works. We have selected four representative patches to better inspect the details. Our method performs well on reconstructing details and capturing movements." + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.29, + 0.471, + 0.346 + ], + "angle": 0, + "content": "Table 3. Quantitative results comparisons. All metrics are measured on 300-frame scenes. We also report the training time, rendering speed (FPS) and model size. * Note DyNeRF is trained on 8 GPUs, while others are trained on one GPU." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.349, + 0.472, + 0.508 + ], + "angle": 0, + "content": "
MethodTrainRenderSizePSNR↑DSSIM↓LPIPS↓
DyNeRF[19]7 days*-28 MB29.580.01970.083
Concurrent work
StreamRF[18]75 min8.35310MB28.26--
NeRFPlayer[37]360 min0.05-30.690.0340.111
Hyperreel[2]540 min2.0360 MB31.100.0360.096
K-Planes[12]108 min--31.630.018-
HexPlanes[7]720 min-200MB31.710.0140.075
Mix Voxels-S15 min37.7500 MB31.030.0220.129
Mix Voxels-M40 min37.7500 MB31.220.0190.102
Mix Voxels-L80 min37.7500 MB31.340.0170.096
Mix Voxels-X300 min4.6500 MB31.730.0150.064
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.519, + 0.47, + 0.67 + ], + "angle": 0, + "content": "dynamic scenes more practical. For rendering, the Mix Voxels has a 37.7 fps rendering speed for 1K resolution. Compared with concurrent works, Mix Voxels requires less training time and achieves faster rendering speed, while achieving competitive PSNR and LPIPS. For example, with only 15 minutes of training, Mix Voxels achieve 31.03 PSNR which is comparable to other methods trained for hours. With sufficient training, all metrics are further improved. For the quantitative results on our collected more complex scenes, we present them on Tab. 1." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.672, + 0.47, + 0.839 + ], + "angle": 0, + "content": "Qualitative results and comparisons. Fig. 6 demonstrates the novel view rendering results on different dynamic scenes. The first four rows are novel view videos from Plenoptic Video Dataset [19]. The last two rows present the novel view videos from our collected two more complex dynamic scenes. The results show that our method can achieve near photo-realistic rendering quality. We provide the video results at the supplementary material. For qualitative comparisons, we show them in Fig. 5. MixVoxels can better reconstruct the moving object (the firing gun) and textual details like the hat and the salmon stripes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.903 + ], + "angle": 0, + "content": "We further investigate the relations between rendering efficiency and rendering quality. As shown in the lower part of Tab. 3, it was observed that an increase in training time leads to improvements in both PSNR and LPIPS. Longer" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.292, + 0.892, + 0.607 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.61, + 0.892, + 0.652 + ], + "angle": 0, + "content": "Figure 6. Novel view synthesis of MixVoxels. We select some frames at different views. The last column demonstrates the normalized depth. We provide videos at the supplemental material." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.657, + 0.892, + 0.749 + ], + "angle": 0, + "content": "training facilitates the reconstruction of sharp boundaries and fine details. Visual comparisons presented in Fig. 7 reveals that 15 minutes of training produces satisfactory recovery of most scene components but resulted in blurry motion details. With longer training, the moving objects become clearer with a distinct boundary." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.757, + 0.655, + 0.774 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.871 + ], + "angle": 0, + "content": "In this subsection, we empirically justify the design of MixVoxels by ablating or modifying several key features. We also provide analysis that intuitively explains the ablations. We conduct all experiments in this subsection on the coffee-martini scene, which we find is typical for demonstrating the fast-moving complex objects." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Ablation on splitting voxels. To study the effect of splitting static and dynamic voxels, we compare MixVox-" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "19712" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.47, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.078, + 0.248, + 0.468, + 0.276 + ], + "angle": 0, + "content": "Figure 7. Qualitative demonstration of different training schedules. Longer training helps better reconstruct the high-dynamic parts." + }, + { + "type": "image", + "bbox": [ + 0.086, + 0.283, + 0.47, + 0.416 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.421, + 0.469, + 0.462 + ], + "angle": 0, + "content": "Figure 8. Qualitative comparison of MixVoxels and the full-dynamic model. Training with full-dynamic models with the same iterations can not well reconstruct the motion details." + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.467, + 0.469, + 0.496 + ], + "angle": 0, + "content": "Table 4. Ablation on the mixed voxels. Training with the fulldynamic voxel model hurts both efficiency and efficacy." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.499, + 0.468, + 0.542 + ], + "angle": 0, + "content": "
MethodTimePSNR↑DSSIM↓LPIPS↓FLIP↓JOD↑
Full-Dynamic2.5h28.360.0360.22360.11967.44
MixVoxels0.6h29.470.0260.11670.12237.99
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.549, + 0.469, + 0.592 + ], + "angle": 0, + "content": "Table 5. Ablation on three different methods for time query. We only substitute the time query with different method, and train them on the proposed MixVoxels framework." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.595, + 0.466, + 0.65 + ], + "angle": 0, + "content": "
MethodTimePSNR↑DSSIM↓LPIPS↓FLIP↓JOD↑
Concat58m28.950.0370.21460.12947.44
Fourier43m28.670.0290.18240.12867.60
Inner product40m29.470.0260.11670.12237.99
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.469, + 0.824 + ], + "angle": 0, + "content": "els with a full-dynamic voxel-grid representation, where all points are processed by the dynamic model. Tab. 4 shows the comparisons. With the same training iterations, the fulldynamic model is more time-consuming, which is intuitive because it processes all voxels with the dynamic models. Fig. 8 shows the qualitative comparison. The full-dynamic model recovered blurred motions. We speculate the reason is because the large area of static regions affects the capturing of dynamic information. The network will be biased by most static voxels with no motions and tend to learn low-frequency information." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Ablation on time query. We compare our inner product time query method with other variants: (1) Concatenation which concatenates the temporal embedding with the voxel features to be processed by an MLP. (2) Fourier head proposed by [47] which reconstructs the dynamics in" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.089, + 0.892, + 0.166 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.169, + 0.892, + 0.381 + ], + "angle": 0, + "content": "Figure 9. Ablation on the number of time query denoted as Q. frequency-domain. Tab. 5 shows the performance comparison. The concatenation query method is both space- and time-consuming. Querying one time step requires forwarding the fused features through the whole MLP. Limited by the GPU memory, we can only query 50 time steps per iteration with the concatenation way, which harms the performance on high-dynamic regions. The Fourier head processes the features to predict the magnitudes of different frequency components and the performance is competitive, while it requires an additional inverse discrete Fourier transform to recover the information in the temporal domain. Overall, the inner product query is the simplest and most efficient way for querying." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.382, + 0.893, + 0.548 + ], + "angle": 0, + "content": "Number of time queries per-iteration. We empirically find that simultaneously querying multiple time steps in an iteration helps reconstruct the details of moving parts. Fig. 9 demonstrates the effect of different numbers of time queries denoted as Q. With more time queries, the boundaries of the moving hand and the flowing coffee become clearer. Querying more time steps can provide dense supervision and make the model acquire global temporal information in every iteration, which accelerates the convergence speed. The effective inner product time queries allow adding more time queries with negligible increase in computation." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.558, + 0.627, + 0.572 + ], + "angle": 0, + "content": "4.4. Limitations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.892, + 0.701 + ], + "angle": 0, + "content": "Our method can synthesize novel view videos with a relative high quality. However, for some scenes with complex lighting conditions, some inconsistent property predictions may appear at the boundary between dynamic and static voxels, which is shown in Fig. 10. We suspect that the phenomenon is caused by the under-sampling of dynamic regions on scenes with some bad conditions. We will investigate ways to address the problem in future works." + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.708, + 0.89, + 0.779 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.781, + 0.891, + 0.809 + ], + "angle": 0, + "content": "Figure 10. Some inconsistent density and color predictions in the boundaries between dynamic and static regions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.815, + 0.619, + 0.831 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This paper demonstrates a new method named MixVoxels to efficiently reconstruct the 4D dynamic scenes and synthesize novel view videos. The core of our method is to split the 3D space into static and dynamic components" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19713" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.244 + ], + "angle": 0, + "content": "with the proposed variation field, and process them with different branches. The separation speeds up the training and makes the dynamic branch focus on the dynamic parts to improve the performance. We also design an efficient dynamic voxel-grid representation with an inner product time query. The proposed method achieves competitive results with only 15 minutes of training, making the training and rendering of complex dynamic scenes more practical. We believe the fast training speed will enable potentially useful applications that are bottlenecked by training efficiency." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.257, + 0.258, + 0.274 + ], + "angle": 0, + "content": "6. Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.281, + 0.47, + 0.323 + ], + "angle": 0, + "content": "This work was supported in part by the National Natural Science Fund for Distinguished Young Scholars under Grant 62025304." + }, + { + "type": "title", + "bbox": [ + 0.08, + 0.338, + 0.175, + 0.354 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.363, + 0.47, + 0.419 + ], + "angle": 0, + "content": "[1] Pontus Andersson, Jim Nilsson, Tomas Akenine-Möller, Magnus Oskarsson, Kalle Åström, and Mark D Fairchild. Flip: A difference evaluator for alternating images. Proc. ACM Comput. Graph. Interact. 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Previous works based on neural radiance fields have demonstrated high-quality reconstructions of dynamic scenes. However, training such models on real-world scenes is time-consuming, usually taking days or weeks. In this paper, we present a novel method named MixVoxels to efficiently represent dynamic scenes, enabling fast training and rendering speed. The proposed MixVoxels represents the 4D dynamic scenes as a mixture of static and dynamic voxels and processes them with different networks. In this way, the computation of the required modalities for static voxels can be processed by a lightweight model, which essentially reduces the amount of computation as many daily dynamic scenes are dominated by static backgrounds. To distinguish the two kinds of voxels, we propose a novel variation field to estimate the temporal variance of each voxel. For the dynamic representations, we design an inner product time query method to efficiently query multiple time steps, which is essential to recover the high-dynamic movements. As a result, with 15 minutes of training for dynamic scenes with inputs of 300-frame videos, MixVoxels achieves better PSNR than previous methods. For rendering, MixVoxels can render a novel view video with 1K resolution at 37 fps. Codes and trained models are available at https://github.com/fengres/mixvoxels. + +# 1. Introduction + +Dynamic scene reconstruction from multi-view videos is a critical and challenging problem, with many potential applications such as interactively free-viewpoint control + +![](images/434e95b5beca54124bbd7146f0cb20487115e2209f822042ef43568486176c75.jpg) + +![](images/e1deef51198de0d49c73ce050767bc32fb1fcc1d571d368dd25e838d17242edc.jpg) + +![](images/7af1183edd93e16a49f4c73c5fae842041970494a9c1c770d37c088e0b08bf3b.jpg) + +![](images/d4bb0fb6d4a72eb4a737256ce21820806fbcc8be846525bc6068f8f036fd8ce3.jpg) +1 min +15 min +Figure 1. Our method enables rapid reconstruction of 4D dynamic scenes. We visualize the rendering results with different training schedules. With only 15 minutes of training, our approach achieves comparable PSNRs to other methods. Increasing the training time further enhances the ability to recover fine details. + +![](images/21938a87638836a3cad4e37c37d330a70261ff9506365e67162bc247758a7251.jpg) +5 min +40 min + +![](images/331234465f81d82a42d19cf1659a53e647c36c4e3a846c8884ecd3c97896dac3.jpg) +10 min +300 min + +for movies, cinematic effects like freeze-frame bullet time, novel view replays for sporting events, and various potential VR/AR applications. Recently, neural radiance fields [26] have demonstrated the possibility of rendering photorealistic novel views for static scenes, with physically motivated 3D density and radiance modelling. Many methods [19, 20, 49, 13, 10, 31, 28, 29, 44] extend the neural radiance fields to dynamic scenes with additional time queries or an explicit deformation field. Many of these methods focus on the monocular input video setting on relatively simple dynamic scenes. To model more complex real-world dynamic scenes, a more practical solution is to use multi-view synchronized videos to provide dense spatial-temporal supervi + +Recently, Li et al. [19] propose a real-world dynamic scene dataset including many challenging situations such as objects of high specularity, topology changes, and volumetric effects. They address the problem by a hierarchical training scheme and the ray importance sampling strategies. Although significant improvements have been achieved, some challenges still exist: (1) The training and rendering take a + +lot of time and computation resources. (2) Highly dynamic scenes with complex motions are still difficult to track. + +In this paper, we focus on the multi-view 3D video synthesis problem and present a novel method named MixVoxels to address the above two challenges. The proposed MixVoxels is based on the explicit voxel-grid representation, which is recently popular due to its fast training and rendering speed on static scenes [50, 40, 8, 27]. We extend the voxel-grid representations to support dynamic scenes and propose an efficient inner product time querying method that can query a large number of time steps simultaneously, which is essential to recover the sharp details for highly-dynamic objects. Additionally, we represent dynamic scenes as a mixed static-dynamic voxel-grid representation. Specifically, the 3D spaces are split into static and dynamic voxels by our proposed variation field. The two components are processed by different models to reduce the redundant computations for the static space. Theoretically, once a dynamic scene consists of some static spaces, the training speed will benefit from the proposed mixed voxels. For a variety of events that occur in the physical world, the static components of environments are dominated in most cases, and the mixed voxels will speed up the training significantly in these scenarios. Besides, the separation of voxels makes the time-variant model focus on the dynamic regions, avoiding the time-aware voxels being biased by the static spaces to produce blurred motions. Our empirical validation confirms that the separation enables the model to learn sharp and distinct boundaries in high-dynamic regions. This also frees our method from the complex importance sampling strategies. With these designs, our method is capable of reconstructing a dynamic scene consisting of 300 frames within 15 minutes. To summarize, the main contributions of this work are: + +- We propose a simple yet effective dynamic representation with inner product time querying method that can efficiently query multiple times simultaneously, improving the rendering quality for dynamic objects. +- We design an efficient variation field to separate static and dynamic spaces and present a mixed voxel-grid representation to accelerate training and rendering. +- We conduct qualitative and quantitative experiments to validate our method. As a result, the proposed MixVoxels achieves competitive or better rendering qualities with a $5000 \times$ training speedup compared to implicit dynamic scene representations. + +# 2. Related Works + +Novel View Synthesis for Static Scenes. Synthesizing novel views for static scenes is a classical and well-studied problem. Different approaches represent the underlying geometric with different representations. Mesh-based meth + +ods [6, 9, 46, 48, 34, 43] represent the scenes with surfaces which is compact and easy to render, while optimizing a mesh to fit complex scenes is challenging. Volume-based methods such as voxel-grid [17, 35, 30, 23, 36] and multiplane images (MPIs) [54, 11, 25, 39, 38, 45] are more suitable to model the complex and translucent scenes such as smooth and fluid. Particularly, Neural radiance fields [26] represent the scenes with an implicit volumetric neural representation, which employs a coordinate-based neural network to query the density and color for each point. The achieved photo-realistic rendering quality of NeRF led to an explosion of developments in the field. Advances have been made including improving the rendering qualities [42, 4], adapting to more general scenarios [52, 24, 41, 5], accelerating rendering or training speed [22, 51, 50, 40, 8], etc. + +Novel View Synthesis for Dynamic Scenes. Synthesizing novel views for dynamic scenes is a more challenging and applicable problem. Recently, many extensions of NeRF for non-rigid dynamic scenes were proposed, which take a monocular video as input to learn the deformation and radiance fields. These methods can be categorized to modelling deformation implicitly [20, 49, 13, 10] (learn the non-decoupled deformation and appearance jointly) and explicitly [31, 28, 29, 44] (learn separated deformation and radiance fields and the deformation fields are usually in the form of relative motion with a canonical static space). Though improvements are achieved, reconstructing the complex general scenes is still difficult with only monocular videos. Most methods are constrained to fixed scenes like human-model or restricted motions. For real-world complex scenes, reconstructing from synchronized multi-view videos is more promising due to the dense supervision for every viewpoint and time instant. Earlier works [14, 55] explore the problem and show the possibility of rendering novel videos from a set of input views. Neural Volumes [23] proposes to use volumetric representations. They employ an encoder-decoder network to convert input images into a 3D volume, and decode the latent representations by the differentiable ray marching operation. [3] presents a data-driven approach for 4D space-time visualization of dynamic scenes by splitting static and dynamic components and using a U-Net structure in screen space to convert intermediate representation to image. Different with this method, our method split the static and dynamic components in the 3D voxel space instead of the pixel space. More recently, DyNerf [19] uses a temporal-aware neural radiance field to address the problem, and proposes some sampling strategies to train it efficiently. Compared with previous methods, they propose a more complicated real-world dataset and validate their method. For accelerating the reconstruction of dynamic scenes, FourierPlenoctree [47] proposes to model the dynamics in frequency domain, and generate a Plenoctree through multi + +view blending to accelerate rendering. They focus on the foreground moving objects extracted via chroma key segmentation, which requires the background should be a pure color (or rely on segmentation algorithms). Recently, the acceleration of training and rendering for dynamic scenes has attracted much attention. Cocurrent works include StreamRF [18] which proposes to accelerate the training of dynamic scenes by modeling the differences of adjacent frames, NeRFPlayer [37] which decomposes the dynamic scenes into static, new and deforming components, Hyperreel [2] which proposes an efficient sampling network and models keyframes. K-Planes [12] and HexPlanes [7] decompose the 4D dynamic scenes into different 2D representations. + +Acceleration of Neural Radiance Fields. While Neural radiance fields can render novel views with high fidelity, training and rendering require querying a deep MLP millions of times which is computationally intensive. Many recent methods propose to accelerate the training and rendering speed of NeRF. For rendering, Neural Sparse Voxel Fields [22] proposes a voxel-grid representation to skip over many empty regions. PlenOctree [51] accelerates the rendering process by pre-tabulating the NeRF into a PlenOctree and using the spherical harmonic representation of radiance. Derf [32] and Kilonerf [33] propose to accelerate the rendering speed by dividing the scenes into multiple areas, and employ multiple small network in each area. AutoInt [21] proposes to restructure the MLP network to accelerate the computations of ray integrals, which helps accelerate the rendering speed. For accelerating the training of NeRF, some methods use explicit voxel-grid representations [50, 40] to accelerate the training process and convergence speed. Instant-NGP [27] proposes a multi-resolution hash table structure to accelerate the training. The model sizes of most fast training methods are relatively large due to a large number of voxels. TensoRF [8] proposes to reduce the model size by factorizing the 4D scene tensor into multiple compact low-rank tensor components. + +# 3. Method + +In this section, we introduce the proposed MixVoxels, which represents the 4D dynamic scenes as mixtures of static and dynamic voxels. Fig. 2 illustrates the overview of our method. In the following subsections, we will first introduce the voxel-grid representations for static scenes and our extension to dynamic scenes. Then we introduce the variation field for identifying the dynamic voxels. At last, we introduce the training of MixVoxels. + +# 3.1. Static Voxel-grid Representation + +Neural radiance fields [26] have demonstrated photorealistic novel viewpoint synthesis, while the training of NeRF requires extensive computation due to millions of + +neural network queries. For accelerating NeRF, many recent works [22, 50, 40, 8] have explored the explicit volumetric representation, which avoids the huge amount of computation of querying neural network. Specifically, a 3D scene is split into $N_{x} \times N_{y} \times N_{z}$ voxels. The densities and color features are stored in these voxels and denoted as $\mathcal{S}^{\sigma} \in \mathbb{R}^{N_x \times N_y \times N_z}$ and $\mathcal{S}^c \in \mathbb{R}^{N_x \times N_y \times N_z \times C}$ . $\mathcal{S}_{i,j,k}^{\sigma}$ and $\mathcal{S}_{i,j,k}^c$ represent the learnable density and color feature of the voxel corner at a discrete position $(i,j,k)$ . For a continuous position $(x,y,z)$ , the representation $\mathcal{S}_{x,y,z}$ can be calculated by interpolating the nearest 8 discrete positions. A small MLP network $\mathcal{C}_{\theta}$ is used to parse the color features into RGB values, taking $S^c$ and view direction $d$ as input. Formally, the density $\sigma$ and color $c$ is formulated as + +$$ +\sigma (x, y, z) = \mathcal {S} _ {x, y, z} ^ {\sigma}, \quad c (x, y, z, \boldsymbol {d}) = \mathcal {C} _ {\theta} \left(\mathcal {S} _ {x, y, z} ^ {c}, \boldsymbol {d}\right). \tag {1} +$$ + +# 3.2. Dynamic Voxel-grid Representation + +For dynamic scenes, a direct extension is to add the time dimension to the static voxel-grid representation $S$ explicitly. However, this direct extension is almost memory-prohibitive due to the large and linearly increasing memory footprint. For a 300-frame video, the learned models will occupy 30 GB of memory and be difficult to train with GPUs due to the limitation of GPU memory. To address this problem, we propose a spatially explicit and temporally implicit representation to reduce the memory footprint. Specifically, we represent the dynamic scene as a 4D learnable voxel-grid $\mathcal{G}^{\sigma} \in \mathbb{R}^{N_x \times N_y \times N_z \times C_1}$ and $\mathcal{G}^c \in \mathbb{R}^{N_x \times N_y \times N_z \times C_2}$ . Different from the static scene representations, the densities and colors for all time steps are implicitly encoded as compact features stored in each voxel corner. The compact features will be processed by a time-aware projection to acquire density and color for each time step. Concretely, for the compact density feature $\mathcal{G}_{x,y,z}^{\sigma}$ and color feature $\mathcal{G}_{x,y,z}^c$ in any position(x,y,z), we employ two MLPs $T_{\theta_1}^{\sigma}$ and $T_{\theta_2}^c$ to increase the feature dimensions for better parsing time-variant density and color. The MLPs here can be viewed as decompressors that decompress the compact low-dimensional voxel-grid features into more tractable ones. Compared with directly storing high-dimensional features in each voxel, the temporally implicit representation reduces the memory footprint significantly since the shared MLPs only increase memory slightly. + +Inner product time query. For a discrete time step $t$ , we use a learnable time-variant latent representation $\omega_{t}$ to represent the time query. Instead of concatenating the time query with the intermediate features, we propose to calculate the inner product between the learned time query and the decompressed features as the required output $\sigma$ and $c$ . Formally, the density and color of a space-time query $(x,y,z,t)$ are formulated as + +$$ +\sigma (x, y, z, t) = \omega_ {t} ^ {\sigma} \cdot \mathcal {T} _ {\theta_ {1}} ^ {\sigma} (\mathcal {G} _ {x, y, z} ^ {\sigma}), \tag {2} +$$ + +![](images/c89e4ffa935ae9ddbb7365c32977e96baa21992548d3434e797cf798a990e952.jpg) +Figure 2. Overview of our method. Given a ray, we first sample points, and split them into static and dynamic ones using the variation field. After that, we feed these points to the corresponding branches and query the required properties. Then we merge the static output and dynamic output for rendering the ray color. An L2 loss is employed to calculate loss and back-propagate. + +$$ +c (x, y, z, \boldsymbol {d}, t) = \omega_ {t} ^ {c} \cdot \mathcal {T} _ {\theta_ {2}} ^ {c} (\mathcal {G} _ {x, y, z} ^ {c}, \boldsymbol {d}). \tag {3} +$$ + +In practice, simultaneously querying multiple time steps helps reconstruct the detail of high-dynamic motions and reduces the training iterations to traverse through all time steps. The inner product based query will facilitate the training speed when simultaneously querying many time steps in a training iteration. Specifically, we denote the FLOPs of the MLP $\mathcal{T}_{\theta_1}$ and the inner product operation as $\mathrm{FLOP}_{mlp}$ and $\mathrm{FLOP}_{inn}$ , respectively. For a $T$ -frame video, the FLOPs of the concatenation query [19] is larger than $T\cdot \mathrm{FLOP}_{mlp}$ (due to the extra temporal embedding dimension), while the FLOPs of our inner product query is only $\mathrm{FLOP}_{mlp} + T\cdot \mathrm{FLOP}_{inn}$ ( $\mathrm{FLOP}_{mlp} >> \mathrm{FLOP}_{inn}$ ). + +# 3.3. Variation Field + +In this subsection, we introduce the variation field to identify which voxels in the 3D space are dynamic, i.e., the densities or colors are not constant over different time steps. By separating the static and dynamic voxels, the redundant computations caused by using a relatively heavy time-varying model to process the static components will be avoided, which accelerates the training and rendering. + +A simpler solution for accelerate training is to separate the static and dynamic regions in pixel-level, i.e., using the temporal variance of pixels to produce static and dynamic ones. However this scheme is actually not feasible because we can only separate dynamic and static regions in training views using the ground truth. For rendering novel views, we can not get the pixel variance for rendering since we have no ground truth in novel views. Thus a feasible solution is to learn the voxel-level temporal variance which is shared for all possible views. In addition, separating in the voxel-level is more efficient compared to pixel-level, even if we have an oracle to make the pixel-level separation feasible in novel views. This is because not all voxels projected to a dynamic pixel are dynamic, there will be only a small fraction of voxels around the object surfaces are actually + +![](images/79e725cf185f6588c324292fbd174a0631bc5e8c63203adf7ff36b2844498488.jpg) +Figure 3. Implicit interaction of multiple rays to decide which point is dynamic. For a static ray (blue line), all points are set to be low dynamic. For a dynamic ray (green line), at least one point is dynamic. The intersection of multiple dynamic ray is more likely to be a dynamic point, which is also physically intuitive. + +dynamic. Therefore, the voxel level separation will produce much fewer dynamic queries. + +To perform the voxel-level separation, we utilize the pixel-level temporal variances from training videos as the supervision to estimate the voxel-level variances. The pixel-level (or ray-level) temporal variances of different videos are shown in Fig. 3. Formally, given a ray $r(s) = o + s \cdot d$ with origin $o$ and direction $d$ , the corresponding pixel color at time step $t$ is defined as $C(r,t)$ . Then the pixel-level temporal variance $D^2(r)$ is formalized as + +$$ +D ^ {2} (\boldsymbol {r}) = \frac {1}{T} \sum_ {t = 1} ^ {T} (C (\boldsymbol {r}, t) - \bar {C} (\boldsymbol {r})) ^ {2}, \quad \bar {C} (\boldsymbol {r}) = \frac {1}{T} \sum_ {t = 1} ^ {T} C (\boldsymbol {r}, t), +$$ + +where $\bar{C} (\pmb {r})$ is the mean color of pixel corresponding to the ray $\pmb{r}$ . For identifying the dynamic pixels, the standard deviation $D(\pmb {r})$ is binarized to $M(r)$ with a threshold $\gamma$ to provide pixel-level dynamic supervision, i.e. $M(r) = 1$ if $D(\boldsymbol {r})\geq \gamma$ , else $M(\boldsymbol {r}) = 0$ . In this way, we judge that a ray $\pmb{r}$ is dynamic if $M(r) = 1$ . Next, we use the $M(r)$ as supervision to estimate the voxel-level variations $\mathcal{V}$ . + +The relations between the pixel-level variance and voxel-level variance lie in the following aspects: (1) If a pixel is static, then all voxels passed through by the ray corresponding to the pixel should be static in most cases (We will discuss some special cases which violate this rule later in this subsection.). (2) If a pixel is dynamic, then at least one of the voxels passed through by the corresponding ray is dynamic. Fig. 3 shows the two situations. With the above two relations, we design the variation field, which is denoted as $\mathcal{V} \in \mathbb{R}^{N_x \times N_y \times N_z}$ to represent the voxel-level temporal variance. Specifically, we uniformly sample $N_s$ points from the near plane to the far plane in $\mathbf{r}$ , and build the following equation to satisfy the two relations mentioned above: + +$$ +\hat {M} (\boldsymbol {r}) = \boldsymbol {s} (\max (\{\mathcal {V} _ {\boldsymbol {r} (s _ {i})} | i \in \{1, \dots , N _ {s} \} \})), \qquad (4) +$$ + +where $\hat{M}(\boldsymbol{r})$ is an estimation of $M(\boldsymbol{r})$ , and $\boldsymbol{s}$ is the sigmoid function. Then we train the variation field by minimizing + +the following binary cross-entropy loss: + +$$ +\mathcal {L} _ {v} = \mathbb {E} _ {\boldsymbol {r}} \left[ - M (\boldsymbol {r}) \log (\hat {M} (\boldsymbol {r})) - (1 - M (\boldsymbol {r})) \log (1 - \hat {M} (\boldsymbol {r})) \right]. \tag {5} +$$ + +By optimizing the above loss function to all rays, we can get the learned variation field $\mathcal{V}$ . The training of the variation field is very efficient, usually taking less than 30 seconds. + +The maximization operation well formulates the relations between a pixel and its corresponding voxels. If a pixel is static, then the equations of Eq. (4) and Eq. (5) will force all voxels passed through by the corresponding ray to be static $(\mathcal{V}_{x,y,z} = 0)$ . If a pixel is dynamic, Eq. (4) requires at least one of the corresponding voxels (i.e., the max value of the voxel variances) to be dynamic $(\mathcal{V}_{x,y,z} = +\infty)$ . Although we provide no information about which specific voxels in a dynamic ray are dynamic, the implicit interaction of multiple different rays will force the solution to be physically reasonable. To explain this, we focus on the observable voxels which at least passed through by one ray. If a point $(x,y,z)$ is passed through by at least one static ray, then $\mathcal{V}_{x,y,z}$ will tend to be optimized to be close to zero. If a point $(x,y,z)$ is only passed through by dynamic rays, and not occluded by other dynamic voxels, then $\mathcal{V}_{x,y,z}$ will be optimized to $+\infty$ . This is because without occlusion, the above point of $(x,y,z)$ along the dynamic rays will be passed by other static rays (the front space along these rays are observable from other views). We illustrate this situation in Fig. 3. + +Inference. After the training process, the temporal variation at a specific 3D position $(x,y,z)$ is $\mathcal{V}_{x,y,z}$ , which is easily acquired by interpolating the discrete variation field. We then identify a voxel in the scene as dynamic if $\mathcal{V}_{x,y,z}$ is larger than a hyper-parameter $\beta$ , and as static if it is smaller than $\beta$ . Formally, we will get a dynamic mask $\dot{\mathrm{M}} \in \{0,1\}^{N_x \times N_y \times N_z}$ , which will be used to split sampling points in a ray into static points and dynamic points. We evaluate the effectiveness of this inference method in the test views and find that the recall and precision are reasonable for splitting the dynamic and static parts (recall: 0.97, precision: 0.94 when $\beta = 0.9$ ). Although the recall seems sufficient to retrieve most dynamic parts, we empirically find some false negatives in the rendering images affect the rendering quality. To address this problem, we use a ray-wise max-pooling operation to identify the points near to a dynamic point as dynamic. The kernel size of max-pooling is set to $k_m = 21$ , and the stride is set to 1. In this way, the recall is very closed to 1. Although many hyperparameters are incorporated, we have empirically found that the thresholds $\gamma$ and $\beta$ are not sensitive over a wide range of reasonable values. + +Discussion. There may be some situations in which the rules (1) are broken due to occlusion. Specifically, when a dynamic voxel is occluded by some static voxels, the occluded parts should not be classified as static, which makes the 2D supervision noisy. However in practice, we found + +![](images/fd018c329e90016f33eb3920dc52ee1785fe6173ec4a3f488380f422fe93f132.jpg) +Figure 4. Impact of occlusions to the variation field. + +![](images/c6d3ac47cd7332f032240af5cac3493ba5b7079cbc2afec51855a8ad62fe23c7.jpg) + +![](images/103d74a2bf401c86aa7b4477a2c0a2db74ecfacbbd10833e0f3784e48314e3fd.jpg) + +the learning-based separation has a certain degree of tolerance for this situation. We conducted experiments to verify this and present the results in Fig. 4. The occluded region is visualized in the leftmost view (the area behind the static roadblock). Although the dynamic region marked in yellow is occluded in the left view, it is actually classified as dynamic region. This can be inferred from another view where the occluded region has changed, as illustrated in the middle and right images in Fig. 4). The variation field is learning-based and will learn a solution that satisfies most constraints. If it forces some dynamic voxels occluded by static voxels to be 0, then the loss function from other visible views will be high. As a result, the learning-based process tends to assign a "middle solution" to voxels with inconsistent supervisions from different views. We also attempted to use the transmittance as a weight (in a way of volumetric rendering) to learn the variation field which can explicitly handle the occlusion problem. However, we found a large efficiency drop with similar performance. As a result, we use the proposed variation field and find this formulation works well for most scenes, including some challenging scenes with large areas of motions. + +# 3.4. Training of Mixed Neural Voxels + +With the help of the variation field, we can split a scene into dynamic voxels and static voxels. To reduce redundant computations, we use the lightweight static model described in Sec. 3.1 to compute the densities and colors for static voxels and the dynamic model described in Sec. 3.2 to compute the densities and colors for dynamic voxels. The overall architecture is illustrated in Fig. 2. + +Specifically for a given ray $r(s) = o + sd$ with origin $o$ and view direction $d$ , we apply stratified sampling from the near to the far planes and get $N_{s}$ points. Then the $N_{s}$ points are separated into static and dynamic ones by inferring these points with the proposed variation field. For the static points, we pass them into the static branch to retrieve the colors and densities. For the dynamic points, we pass them into the dynamic branch together with a deferred time query $\omega_{t}$ to retrieve the corresponding properties. After that, we merge the static points and dynamic points according to their order. Then we apply volumetric rendering to the merged points to obtain the rendered color, which is formulated as + +$$ +C (\boldsymbol {r}, t) = \sum_ {i = 1} ^ {N _ {s}} T _ {i, t} \cdot \left(1 - \exp \left(- \sigma_ {i, t} \delta_ {i}\right)\right) \cdot c _ {i, t}, \tag {6} +$$ + +where $\mathrm{T}_{i,t}$ is the accumulated opacity (or transmittance): + +$\mathrm{T}_{i,t} = \exp (-\sum_{j = 1}^{i - 1}\sigma_{j,t}\delta_j)$ , and $\delta_{i}$ is the distance between adjacent samples. Given the ground truth color $C_g(\boldsymbol {r},t)$ , an l2-loss is employed to train the model: + +$$ +\mathcal {L} = \mathbb {E} _ {\left(\boldsymbol {r}, t\right)} \left[ \| C _ {g} (\boldsymbol {r}, t) - C (\boldsymbol {r}, t) \| _ {2} ^ {2} \right]. \tag {7} +$$ + +For both static and dynamic branches, we omit the computation of color for points whose densities are close to zero, which is a widely adopted pruning strategy [22, 50, 8]. + +Efficiency analysis. We define the proportion of dynamic points in a scene as $\lambda$ ( $\approx 0.05$ for most scenes). Besides, the FLOPs of static and dynamic branches are denoted as $FLOP_{sta}$ and $FLOP_{dyn}$ , respectively. Then the total FLOPs of MixVoxels are $FLOP_{sta} + \lambda \cdot FLOP_{dyn}$ . Empirically, $FLOP_{dyn} / FLOP_{sta}$ ranges from 50 to 100 with different reasonable dimension settings. Then the acceleration ratio of splitting static and dynamic models is $FLOP_{dyn} / (FLOP_{sta} + \lambda FLOP_{dyn}) \approx 10$ . In practice, the actual speedup with a 3090 GPU is about 5, the inconsistency between analysis and experiment may come from the GPU features, which are friendly to a more consistent network. + +# 3.5. Implementation Detail + +The voxel-grid representations require large GPU memory to store the cubically growing voxel numbers. To implement the voxel-grid representations more memory efficient, we use the tensor factorization technique proposed in TensoRF [8] to reduce the memory footprint. In this way, a 3D tensor is factorized into the outer product of a vector and a 2D matrix. We factorize all the voxel-grid tensors, including static voxels, dynamic voxels and the variation field. With the help of tensor factorization, the learned model costs about 500MB for a 300-frame multi-view video scene. For the voxel resolutions, we follow [8] to start from an initial low resolution of $256^{3}$ , and upsample the resolution at steps 1500, 2000, 2500, and 2750 with a linear increase in the log space. The final resolution is set to $640^{3}$ . Once the resolution is changed, we re-train the variation field, which only takes about 15-30s. The voxel-grid feature dimension is set to 27, and the hidden state of MLP is set to 512. For training, we use Adam [15] optimizer with a learning rate of 0.02 for voxels and $3e - 3$ for MLPs. The total variation loss [50] is incorporated as a regularization to encourage the space smoothness. + +# 4. Experiments + +# 4.1. Experiment Setting + +Dataset. We validate our method on two datasets: (1) The Plenoptic Video Dataset [19], which consists of 6 publicly accessible scenes: coffee-martini, flame-salmon, cook-spinach, cut-roasted-beef, flame-steam and sear-steam. We conduct experiments on all six scenes. Each scene contains 19 videos with different camera views. The dataset + +Table 1. Results on our collected dataset, including two scenes. + +
SceneModelPSNR↑DSSIM↓LPIPS↓
Moving-CarsMixVoxels-S18.720.2510.689
MixVoxels-M18.970.2280.552
MixVoxels-L18.890.2220.540
MixVoxels-X19.110.2100.516
Solving-RubikMixVoxels-S25.390.0650.339
MixVoxels-M26.050.0590.275
MixVoxels-L26.280.0550.241
MixVoxels-X26.800.0470.209
+ +contains many challenging scenes including objects with topology changes, objects with volumetric effects, various lighting conditions, etc. (2) Our proposed dataset including two more complex dynamic scenes: moving-cars and solving-rubik. The moving-cars scene features several vehicles passing across the screen, with significant motion and displacement. Meanwhile, in the solving-rubik scene, a man solves a Rubik's cube at a rapid pace, averaging 4 rotations per second, providing an opportunity to evaluate the model's ability to capture swift movements. The collection procedures used are similar to those of DyNeRF. More details are presented in the appendix. + +For training and evaluation, we follow the experiment setting in [19] that employs 18 views for training and 1 view for evaluation. To quantitatively evaluate the rendering quality on novel views, we measure PSNR, DSSIM and LPIPS[53] on the test views. We also provide more metrics in the appendix including FLIP [1] and JOD [16], which we find the comparisons are similar with PSNR and LPIPS. We follow the setting of [19] to evaluate our model frame by frame. For videos consisting of equal or more than 300 frames, we evaluate our model every 10 frames [19] to calculate the frame-by-frame metrics except for the JOD metrics, which requires a stack of continuous video. + +Training Schedules. For evaluating the effect of training time, we train MixVoxels with different configurations shown in Tab. 2. The configurations vary in terms of training iterations and the number of sample points per ray. By default, the step size for sampling points is set to four times of the voxel width. The $8 \times$ means that there will be eight times as many sampling points compared to the default. + +Table 2. Different training configurations of MixVoxels. + +
ModelIterationsSampling pointsTraining Time
MixVoxels-S50001 ×15 min
MixVoxels-M125001 ×40 min
MixVoxels-L250001 ×80 min
MixVoxels-X500008 ×300 min
+ +# 4.2. Results + +Quantitative results and comparisons. For quantitative results, we present the metrics and compare with other methods in Tab. 3. Compared with the previous state-of-the-art method DyNeRF, we reduce the training time from $1.3\mathrm{K}$ GPU hours to 15 minutes, making the training of complex + +![](images/568836bbd6a296632e70842fd23b25efc3ab4705b2bc62e88094b776173fb85e.jpg) +Figure 5. Visual comparisons with state-of-the-art methods. K-Planes [12] and HexPlane [7] are concurrent works. We have selected four representative patches to better inspect the details. Our method performs well on reconstructing details and capturing movements. + +![](images/4f2d0189c19bb3a69a78f0ee6976aff14f242fdaa5d28a39e92219b08e372f9c.jpg) + +![](images/ccf7bcc8ba4c17aea0eaff80d748501f90b07f48c27c7313a4cc2461bedd8946.jpg) + +![](images/095c3814f0f631827a7185d40e050bfcbf8e052232f66cf316ec7633114ef842.jpg) + +Table 3. Quantitative results comparisons. All metrics are measured on 300-frame scenes. We also report the training time, rendering speed (FPS) and model size. * Note DyNeRF is trained on 8 GPUs, while others are trained on one GPU. + +
MethodTrainRenderSizePSNR↑DSSIM↓LPIPS↓
DyNeRF[19]7 days*-28 MB29.580.01970.083
Concurrent work
StreamRF[18]75 min8.35310MB28.26--
NeRFPlayer[37]360 min0.05-30.690.0340.111
Hyperreel[2]540 min2.0360 MB31.100.0360.096
K-Planes[12]108 min--31.630.018-
HexPlanes[7]720 min-200MB31.710.0140.075
Mix Voxels-S15 min37.7500 MB31.030.0220.129
Mix Voxels-M40 min37.7500 MB31.220.0190.102
Mix Voxels-L80 min37.7500 MB31.340.0170.096
Mix Voxels-X300 min4.6500 MB31.730.0150.064
+ +dynamic scenes more practical. For rendering, the Mix Voxels has a 37.7 fps rendering speed for 1K resolution. Compared with concurrent works, Mix Voxels requires less training time and achieves faster rendering speed, while achieving competitive PSNR and LPIPS. For example, with only 15 minutes of training, Mix Voxels achieve 31.03 PSNR which is comparable to other methods trained for hours. With sufficient training, all metrics are further improved. For the quantitative results on our collected more complex scenes, we present them on Tab. 1. + +Qualitative results and comparisons. Fig. 6 demonstrates the novel view rendering results on different dynamic scenes. The first four rows are novel view videos from Plenoptic Video Dataset [19]. The last two rows present the novel view videos from our collected two more complex dynamic scenes. The results show that our method can achieve near photo-realistic rendering quality. We provide the video results at the supplementary material. For qualitative comparisons, we show them in Fig. 5. MixVoxels can better reconstruct the moving object (the firing gun) and textual details like the hat and the salmon stripes. + +We further investigate the relations between rendering efficiency and rendering quality. As shown in the lower part of Tab. 3, it was observed that an increase in training time leads to improvements in both PSNR and LPIPS. Longer + +![](images/7463cb1b9c5b0a2eb6b561b61b95cba370c8e8c6cf425b8c5863db6436877f40.jpg) +Figure 6. Novel view synthesis of MixVoxels. We select some frames at different views. The last column demonstrates the normalized depth. We provide videos at the supplemental material. + +training facilitates the reconstruction of sharp boundaries and fine details. Visual comparisons presented in Fig. 7 reveals that 15 minutes of training produces satisfactory recovery of most scene components but resulted in blurry motion details. With longer training, the moving objects become clearer with a distinct boundary. + +# 4.3. Ablation Study + +In this subsection, we empirically justify the design of MixVoxels by ablating or modifying several key features. We also provide analysis that intuitively explains the ablations. We conduct all experiments in this subsection on the coffee-martini scene, which we find is typical for demonstrating the fast-moving complex objects. + +Ablation on splitting voxels. To study the effect of splitting static and dynamic voxels, we compare MixVox- + +![](images/340d6c855123630c3abf9455f1da3f1c953bf85c7a2ae0bcfbb676afc73c01e0.jpg) +Figure 7. Qualitative demonstration of different training schedules. Longer training helps better reconstruct the high-dynamic parts. + +![](images/348214fb9bf1f61771b03da913a9ce284021e56d9b8b6600c927a900e8b2c5f0.jpg) +Figure 8. Qualitative comparison of MixVoxels and the full-dynamic model. Training with full-dynamic models with the same iterations can not well reconstruct the motion details. + +Table 4. Ablation on the mixed voxels. Training with the fulldynamic voxel model hurts both efficiency and efficacy. + +
MethodTimePSNR↑DSSIM↓LPIPS↓FLIP↓JOD↑
Full-Dynamic2.5h28.360.0360.22360.11967.44
MixVoxels0.6h29.470.0260.11670.12237.99
+ +Table 5. Ablation on three different methods for time query. We only substitute the time query with different method, and train them on the proposed MixVoxels framework. + +
MethodTimePSNR↑DSSIM↓LPIPS↓FLIP↓JOD↑
Concat58m28.950.0370.21460.12947.44
Fourier43m28.670.0290.18240.12867.60
Inner product40m29.470.0260.11670.12237.99
+ +els with a full-dynamic voxel-grid representation, where all points are processed by the dynamic model. Tab. 4 shows the comparisons. With the same training iterations, the fulldynamic model is more time-consuming, which is intuitive because it processes all voxels with the dynamic models. Fig. 8 shows the qualitative comparison. The full-dynamic model recovered blurred motions. We speculate the reason is because the large area of static regions affects the capturing of dynamic information. The network will be biased by most static voxels with no motions and tend to learn low-frequency information. + +Ablation on time query. We compare our inner product time query method with other variants: (1) Concatenation which concatenates the temporal embedding with the voxel features to be processed by an MLP. (2) Fourier head proposed by [47] which reconstructs the dynamics in + +![](images/c9241656e7ece3d370d83ef4455c607773efe5f7fcaf39f3b1962dc33fac968c.jpg) +Figure 9. Ablation on the number of time query denoted as Q. frequency-domain. Tab. 5 shows the performance comparison. The concatenation query method is both space- and time-consuming. Querying one time step requires forwarding the fused features through the whole MLP. Limited by the GPU memory, we can only query 50 time steps per iteration with the concatenation way, which harms the performance on high-dynamic regions. The Fourier head processes the features to predict the magnitudes of different frequency components and the performance is competitive, while it requires an additional inverse discrete Fourier transform to recover the information in the temporal domain. Overall, the inner product query is the simplest and most efficient way for querying. + +Number of time queries per-iteration. We empirically find that simultaneously querying multiple time steps in an iteration helps reconstruct the details of moving parts. Fig. 9 demonstrates the effect of different numbers of time queries denoted as Q. With more time queries, the boundaries of the moving hand and the flowing coffee become clearer. Querying more time steps can provide dense supervision and make the model acquire global temporal information in every iteration, which accelerates the convergence speed. The effective inner product time queries allow adding more time queries with negligible increase in computation. + +# 4.4. Limitations + +Our method can synthesize novel view videos with a relative high quality. However, for some scenes with complex lighting conditions, some inconsistent property predictions may appear at the boundary between dynamic and static voxels, which is shown in Fig. 10. We suspect that the phenomenon is caused by the under-sampling of dynamic regions on scenes with some bad conditions. We will investigate ways to address the problem in future works. + +![](images/3fa2e51a701c78673a132eae85df356ac77ef87803a44d9a5783c28ecf2bda84.jpg) +Figure 10. Some inconsistent density and color predictions in the boundaries between dynamic and static regions. + +# 5. Conclusion + +This paper demonstrates a new method named MixVoxels to efficiently reconstruct the 4D dynamic scenes and synthesize novel view videos. The core of our method is to split the 3D space into static and dynamic components + +with the proposed variation field, and process them with different branches. The separation speeds up the training and makes the dynamic branch focus on the dynamic parts to improve the performance. We also design an efficient dynamic voxel-grid representation with an inner product time query. The proposed method achieves competitive results with only 15 minutes of training, making the training and rendering of complex dynamic scenes more practical. We believe the fast training speed will enable potentially useful applications that are bottlenecked by training efficiency. + +# 6. Acknowledgement + +This work was supported in part by the National Natural Science Fund for Distinguished Young Scholars under Grant 62025304. + +# References + +[1] Pontus Andersson, Jim Nilsson, Tomas Akenine-Möller, Magnus Oskarsson, Kalle Åström, and Mark D Fairchild. Flip: A difference evaluator for alternating images. Proc. ACM Comput. Graph. Interact. Tech., 3(2):15-1, 2020. 6 +[2] Benjamin Attal, Jia-Bin Huang, Christian Richardt, Michael Zollhoefer, Johannes Kopf, Matthew O'Toole, and Changil Kim. Hyperreel: High-fidelity 6-dof video with ray-conditioned sampling. arXiv preprint arXiv:2301.02238, 2023. 3, 7 +[3] Aayush Bansal, Minh Vo, Yaser Sheikh, Deva Ramanan, and Srinivasa Narasimhan. 4d visualization of dynamic events from unconstrained multi-view videos. 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Previous works based on neural radiance fields have demonstrated high-quality reconstructions of dynamic scenes. However, training such models on real-world scenes is time-consuming, usually taking days or weeks. In this paper, we present a novel method named MixVoxels to efficiently represent dynamic scenes, enabling fast training and rendering speed. The proposed MixVoxels represents the 4D dynamic scenes as a mixture of static and dynamic voxels and processes them with different networks. In this way, the computation of the required modalities for static voxels can be processed by a lightweight model, which essentially reduces the amount of computation as many daily dynamic scenes are dominated by static backgrounds. To distinguish the two kinds of voxels, we propose a novel variation field to estimate the temporal variance of each voxel. For the dynamic representations, we design an inner product time query method to efficiently query multiple time steps, which is essential to recover the high-dynamic movements. As a result, with 15 minutes of training for dynamic scenes with inputs of 300-frame videos, MixVoxels achieves better PSNR than previous methods. For rendering, MixVoxels can render a novel view video with 1K resolution at 37 fps. Codes and trained models are available at https://github.com/fengres/mixvoxels." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 635, + 128, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 635, + 128, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 635, + 128, + 647 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 656, + 288, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 656, + 288, + 693 + ], + "spans": [ + { + "bbox": [ + 47, + 656, + 288, + 693 + ], + "type": "text", + "content": "Dynamic scene reconstruction from multi-view videos is a critical and challenging problem, with many potential applications such as interactively free-viewpoint control" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 309, + 260, + 387, + 320 + ], + "blocks": [ + { + "bbox": [ + 309, + 260, + 387, + 320 + ], + "lines": [ + { + "bbox": [ + 309, + 260, + 387, + 320 + ], + "spans": [ + { + "bbox": [ + 309, + 260, + 387, + 320 + ], + "type": "image", + "image_path": "434e95b5beca54124bbd7146f0cb20487115e2209f822042ef43568486176c75.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 387, + 260, + 464, + 320 + ], + "blocks": [ + { + "bbox": [ + 387, + 260, + 464, + 320 + ], + "lines": [ + { + "bbox": [ + 387, + 260, + 464, + 320 + ], + "spans": [ + { + "bbox": [ + 387, + 260, + 464, + 320 + ], + "type": "image", + "image_path": "e1deef51198de0d49c73ce050767bc32fb1fcc1d571d368dd25e838d17242edc.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 465, + 260, + 544, + 320 + ], + "blocks": [ + { + "bbox": [ + 465, + 260, + 544, + 320 + ], + "lines": [ + { + "bbox": [ + 465, + 260, + 544, + 320 + ], + "spans": [ + { + "bbox": [ + 465, + 260, + 544, + 320 + ], + "type": "image", + "image_path": "7af1183edd93e16a49f4c73c5fae842041970494a9c1c770d37c088e0b08bf3b.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 308, + 328, + 387, + 388 + ], + "blocks": [ + { + "bbox": [ + 336, + 321, + 356, + 328 + ], + "lines": [ + { + "bbox": [ + 336, + 321, + 356, + 328 + ], + "spans": [ + { + "bbox": [ + 336, + 321, + 356, + 328 + ], + "type": "text", + "content": "1 min" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 308, + 328, + 387, + 388 + ], + "lines": [ + { + "bbox": [ + 308, + 328, + 387, + 388 + ], + "spans": [ + { + "bbox": [ + 308, + 328, + 387, + 388 + ], + "type": "image", + "image_path": "d4bb0fb6d4a72eb4a737256ce21820806fbcc8be846525bc6068f8f036fd8ce3.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 333, + 388, + 356, + 396 + ], + "lines": [ + { + "bbox": [ + 333, + 388, + 356, + 396 + ], + "spans": [ + { + "bbox": [ + 333, + 388, + 356, + 396 + ], + "type": "text", + "content": "15 min" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 306, + 399, + 546, + 456 + ], + "lines": [ + { + "bbox": [ + 306, + 399, + 546, + 456 + ], + "spans": [ + { + "bbox": [ + 306, + 399, + 546, + 456 + ], + "type": "text", + "content": "Figure 1. Our method enables rapid reconstruction of 4D dynamic scenes. We visualize the rendering results with different training schedules. With only 15 minutes of training, our approach achieves comparable PSNRs to other methods. Increasing the training time further enhances the ability to recover fine details." + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 387, + 328, + 466, + 388 + ], + "blocks": [ + { + "bbox": [ + 412, + 321, + 432, + 328 + ], + "lines": [ + { + "bbox": [ + 412, + 321, + 432, + 328 + ], + "spans": [ + { + "bbox": [ + 412, + 321, + 432, + 328 + ], + "type": "text", + "content": "5 min" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 387, + 328, + 466, + 388 + ], + "lines": [ + { + "bbox": [ + 387, + 328, + 466, + 388 + ], + "spans": [ + { + "bbox": [ + 387, + 328, + 466, + 388 + ], + "type": "image", + "image_path": "21938a87638836a3cad4e37c37d330a70261ff9506365e67162bc247758a7251.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 410, + 388, + 434, + 396 + ], + "lines": [ + { + "bbox": [ + 410, + 388, + 434, + 396 + ], + "spans": [ + { + "bbox": [ + 410, + 388, + 434, + 396 + ], + "type": "text", + "content": "40 min" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "type": "image", + "bbox": [ + 466, + 328, + 544, + 388 + ], + "blocks": [ + { + "bbox": [ + 489, + 321, + 512, + 328 + ], + "lines": [ + { + "bbox": [ + 489, + 321, + 512, + 328 + ], + "spans": [ + { + "bbox": [ + 489, + 321, + 512, + 328 + ], + "type": "text", + "content": "10 min" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 466, + 328, + 544, + 388 + ], + "lines": [ + { + "bbox": [ + 466, + 328, + 544, + 388 + ], + "spans": [ + { + "bbox": [ + 466, + 328, + 544, + 388 + ], + "type": "image", + "image_path": "331234465f81d82a42d19cf1659a53e647c36c4e3a846c8884ecd3c97896dac3.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 487, + 388, + 515, + 396 + ], + "lines": [ + { + "bbox": [ + 487, + 388, + 515, + 396 + ], + "spans": [ + { + "bbox": [ + 487, + 388, + 515, + 396 + ], + "type": "text", + "content": "300 min" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_caption" + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 460, + 546, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 546, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 546, + 628 + ], + "type": "text", + "content": "for movies, cinematic effects like freeze-frame bullet time, novel view replays for sporting events, and various potential VR/AR applications. Recently, neural radiance fields [26] have demonstrated the possibility of rendering photorealistic novel views for static scenes, with physically motivated 3D density and radiance modelling. Many methods [19, 20, 49, 13, 10, 31, 28, 29, 44] extend the neural radiance fields to dynamic scenes with additional time queries or an explicit deformation field. Many of these methods focus on the monocular input video setting on relatively simple dynamic scenes. To model more complex real-world dynamic scenes, a more practical solution is to use multi-view synchronized videos to provide dense spatial-temporal supervi" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "content": "Recently, Li et al. [19] propose a real-world dynamic scene dataset including many challenging situations such as objects of high specularity, topology changes, and volumetric effects. They address the problem by a hierarchical training scheme and the ray importance sampling strategies. Although significant improvements have been achieved, some challenges still exist: (1) The training and rendering take a" + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 135, + 712 + ], + "type": "text", + "content": "*Corresponding author." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "19706" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 286, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 286, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 286, + 95 + ], + "type": "text", + "content": "lot of time and computation resources. (2) Highly dynamic scenes with complex motions are still difficult to track." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 96, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 96, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 47, + 96, + 287, + 479 + ], + "type": "text", + "content": "In this paper, we focus on the multi-view 3D video synthesis problem and present a novel method named MixVoxels to address the above two challenges. The proposed MixVoxels is based on the explicit voxel-grid representation, which is recently popular due to its fast training and rendering speed on static scenes [50, 40, 8, 27]. We extend the voxel-grid representations to support dynamic scenes and propose an efficient inner product time querying method that can query a large number of time steps simultaneously, which is essential to recover the sharp details for highly-dynamic objects. Additionally, we represent dynamic scenes as a mixed static-dynamic voxel-grid representation. Specifically, the 3D spaces are split into static and dynamic voxels by our proposed variation field. The two components are processed by different models to reduce the redundant computations for the static space. Theoretically, once a dynamic scene consists of some static spaces, the training speed will benefit from the proposed mixed voxels. For a variety of events that occur in the physical world, the static components of environments are dominated in most cases, and the mixed voxels will speed up the training significantly in these scenarios. Besides, the separation of voxels makes the time-variant model focus on the dynamic regions, avoiding the time-aware voxels being biased by the static spaces to produce blurred motions. Our empirical validation confirms that the separation enables the model to learn sharp and distinct boundaries in high-dynamic regions. This also frees our method from the complex importance sampling strategies. With these designs, our method is capable of reconstructing a dynamic scene consisting of 300 frames within 15 minutes. To summarize, the main contributions of this work are:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 484, + 286, + 635 + ], + "type": "list", + "angle": 0, + "index": 5, + "blocks": [ + { + "bbox": [ + 59, + 484, + 286, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 484, + 286, + 532 + ], + "spans": [ + { + "bbox": [ + 59, + 484, + 286, + 532 + ], + "type": "text", + "content": "- We propose a simple yet effective dynamic representation with inner product time querying method that can efficiently query multiple times simultaneously, improving the rendering quality for dynamic objects." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 536, + 286, + 571 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 536, + 286, + 571 + ], + "spans": [ + { + "bbox": [ + 59, + 536, + 286, + 571 + ], + "type": "text", + "content": "- We design an efficient variation field to separate static and dynamic spaces and present a mixed voxel-grid representation to accelerate training and rendering." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 576, + 286, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 576, + 286, + 635 + ], + "spans": [ + { + "bbox": [ + 59, + 576, + 286, + 635 + ], + "type": "text", + "content": "- We conduct qualitative and quantitative experiments to validate our method. As a result, the proposed MixVoxels achieves competitive or better rendering qualities with a " + }, + { + "bbox": [ + 59, + 576, + 286, + 635 + ], + "type": "inline_equation", + "content": "5000 \\times" + }, + { + "bbox": [ + 59, + 576, + 286, + 635 + ], + "type": "text", + "content": " training speedup compared to implicit dynamic scene representations." + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 646, + 138, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 646, + 138, + 658 + ], + "spans": [ + { + "bbox": [ + 47, + 646, + 138, + 658 + ], + "type": "text", + "content": "2. Related Works" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 665, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 665, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 665, + 286, + 713 + ], + "type": "text", + "content": "Novel View Synthesis for Static Scenes. Synthesizing novel views for static scenes is a classical and well-studied problem. Different approaches represent the underlying geometric with different representations. Mesh-based meth" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 252 + ], + "type": "text", + "content": "ods [6, 9, 46, 48, 34, 43] represent the scenes with surfaces which is compact and easy to render, while optimizing a mesh to fit complex scenes is challenging. Volume-based methods such as voxel-grid [17, 35, 30, 23, 36] and multiplane images (MPIs) [54, 11, 25, 39, 38, 45] are more suitable to model the complex and translucent scenes such as smooth and fluid. Particularly, Neural radiance fields [26] represent the scenes with an implicit volumetric neural representation, which employs a coordinate-based neural network to query the density and color for each point. The achieved photo-realistic rendering quality of NeRF led to an explosion of developments in the field. Advances have been made including improving the rendering qualities [42, 4], adapting to more general scenarios [52, 24, 41, 5], accelerating rendering or training speed [22, 51, 50, 40, 8], etc." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 258, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 258, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 258, + 545, + 713 + ], + "type": "text", + "content": "Novel View Synthesis for Dynamic Scenes. Synthesizing novel views for dynamic scenes is a more challenging and applicable problem. Recently, many extensions of NeRF for non-rigid dynamic scenes were proposed, which take a monocular video as input to learn the deformation and radiance fields. These methods can be categorized to modelling deformation implicitly [20, 49, 13, 10] (learn the non-decoupled deformation and appearance jointly) and explicitly [31, 28, 29, 44] (learn separated deformation and radiance fields and the deformation fields are usually in the form of relative motion with a canonical static space). Though improvements are achieved, reconstructing the complex general scenes is still difficult with only monocular videos. Most methods are constrained to fixed scenes like human-model or restricted motions. For real-world complex scenes, reconstructing from synchronized multi-view videos is more promising due to the dense supervision for every viewpoint and time instant. Earlier works [14, 55] explore the problem and show the possibility of rendering novel videos from a set of input views. Neural Volumes [23] proposes to use volumetric representations. They employ an encoder-decoder network to convert input images into a 3D volume, and decode the latent representations by the differentiable ray marching operation. [3] presents a data-driven approach for 4D space-time visualization of dynamic scenes by splitting static and dynamic components and using a U-Net structure in screen space to convert intermediate representation to image. Different with this method, our method split the static and dynamic components in the 3D voxel space instead of the pixel space. More recently, DyNerf [19] uses a temporal-aware neural radiance field to address the problem, and proposes some sampling strategies to train it efficiently. Compared with previous methods, they propose a more complicated real-world dataset and validate their method. For accelerating the reconstruction of dynamic scenes, FourierPlenoctree [47] proposes to model the dynamics in frequency domain, and generate a Plenoctree through multi" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19707" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 239 + ], + "type": "text", + "content": "view blending to accelerate rendering. They focus on the foreground moving objects extracted via chroma key segmentation, which requires the background should be a pure color (or rely on segmentation algorithms). Recently, the acceleration of training and rendering for dynamic scenes has attracted much attention. Cocurrent works include StreamRF [18] which proposes to accelerate the training of dynamic scenes by modeling the differences of adjacent frames, NeRFPlayer [37] which decomposes the dynamic scenes into static, new and deforming components, Hyperreel [2] which proposes an efficient sampling network and models keyframes. K-Planes [12] and HexPlanes [7] decompose the 4D dynamic scenes into different 2D representations." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 239, + 289, + 528 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 289, + 528 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 289, + 528 + ], + "type": "text", + "content": "Acceleration of Neural Radiance Fields. While Neural radiance fields can render novel views with high fidelity, training and rendering require querying a deep MLP millions of times which is computationally intensive. Many recent methods propose to accelerate the training and rendering speed of NeRF. For rendering, Neural Sparse Voxel Fields [22] proposes a voxel-grid representation to skip over many empty regions. PlenOctree [51] accelerates the rendering process by pre-tabulating the NeRF into a PlenOctree and using the spherical harmonic representation of radiance. Derf [32] and Kilonerf [33] propose to accelerate the rendering speed by dividing the scenes into multiple areas, and employ multiple small network in each area. AutoInt [21] proposes to restructure the MLP network to accelerate the computations of ray integrals, which helps accelerate the rendering speed. For accelerating the training of NeRF, some methods use explicit voxel-grid representations [50, 40] to accelerate the training process and convergence speed. Instant-NGP [27] proposes a multi-resolution hash table structure to accelerate the training. The model sizes of most fast training methods are relatively large due to a large number of voxels. TensoRF [8] proposes to reduce the model size by factorizing the 4D scene tensor into multiple compact low-rank tensor components." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 536, + 104, + 550 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 536, + 104, + 550 + ], + "spans": [ + { + "bbox": [ + 47, + 536, + 104, + 550 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 556, + 287, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 556, + 287, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 556, + 287, + 653 + ], + "type": "text", + "content": "In this section, we introduce the proposed MixVoxels, which represents the 4D dynamic scenes as mixtures of static and dynamic voxels. Fig. 2 illustrates the overview of our method. In the following subsections, we will first introduce the voxel-grid representations for static scenes and our extension to dynamic scenes. Then we introduce the variation field for identifying the dynamic voxels. At last, we introduce the training of MixVoxels." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 659, + 222, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 659, + 222, + 672 + ], + "spans": [ + { + "bbox": [ + 47, + 659, + 222, + 672 + ], + "type": "text", + "content": "3.1. Static Voxel-grid Representation" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": "Neural radiance fields [26] have demonstrated photorealistic novel viewpoint synthesis, while the training of NeRF requires extensive computation due to millions of" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": "neural network queries. For accelerating NeRF, many recent works [22, 50, 40, 8] have explored the explicit volumetric representation, which avoids the huge amount of computation of querying neural network. Specifically, a 3D scene is split into " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "N_{x} \\times N_{y} \\times N_{z}" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": " voxels. The densities and color features are stored in these voxels and denoted as " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{S}^{\\sigma} \\in \\mathbb{R}^{N_x \\times N_y \\times N_z}" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{S}^c \\in \\mathbb{R}^{N_x \\times N_y \\times N_z \\times C}" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{S}_{i,j,k}^{\\sigma}" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{S}_{i,j,k}^c" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": " represent the learnable density and color feature of the voxel corner at a discrete position " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "(i,j,k)" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": ". For a continuous position " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "(x,y,z)" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": ", the representation " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{S}_{x,y,z}" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": " can be calculated by interpolating the nearest 8 discrete positions. A small MLP network " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_{\\theta}" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": " is used to parse the color features into RGB values, taking " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "S^c" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": " and view direction " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": " as input. Formally, the density " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": " and color " + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 72, + 547, + 240 + ], + "type": "text", + "content": " is formulated as" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 315, + 247, + 545, + 262 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 247, + 545, + 262 + ], + "spans": [ + { + "bbox": [ + 315, + 247, + 545, + 262 + ], + "type": "interline_equation", + "content": "\\sigma (x, y, z) = \\mathcal {S} _ {x, y, z} ^ {\\sigma}, \\quad c (x, y, z, \\boldsymbol {d}) = \\mathcal {C} _ {\\theta} \\left(\\mathcal {S} _ {x, y, z} ^ {c}, \\boldsymbol {d}\\right). \\tag {1}", + "image_path": "0b74f5f98aeb310a1e7cb53cb945105be8fdd5e2ec80a01d6d57b6ff4f308eca.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 268, + 496, + 282 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 268, + 496, + 282 + ], + "spans": [ + { + "bbox": [ + 305, + 268, + 496, + 282 + ], + "type": "text", + "content": "3.2. Dynamic Voxel-grid Representation" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "spans": [ + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "text", + "content": "For dynamic scenes, a direct extension is to add the time dimension to the static voxel-grid representation " + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "text", + "content": " explicitly. However, this direct extension is almost memory-prohibitive due to the large and linearly increasing memory footprint. For a 300-frame video, the learned models will occupy 30 GB of memory and be difficult to train with GPUs due to the limitation of GPU memory. To address this problem, we propose a spatially explicit and temporally implicit representation to reduce the memory footprint. Specifically, we represent the dynamic scene as a 4D learnable voxel-grid " + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "inline_equation", + "content": "\\mathcal{G}^{\\sigma} \\in \\mathbb{R}^{N_x \\times N_y \\times N_z \\times C_1}" + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "inline_equation", + "content": "\\mathcal{G}^c \\in \\mathbb{R}^{N_x \\times N_y \\times N_z \\times C_2}" + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "text", + "content": ". Different from the static scene representations, the densities and colors for all time steps are implicitly encoded as compact features stored in each voxel corner. The compact features will be processed by a time-aware projection to acquire density and color for each time step. Concretely, for the compact density feature " + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "inline_equation", + "content": "\\mathcal{G}_{x,y,z}^{\\sigma}" + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "text", + "content": " and color feature " + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "inline_equation", + "content": "\\mathcal{G}_{x,y,z}^c" + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "text", + "content": " in any position(x,y,z), we employ two MLPs " + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "inline_equation", + "content": "T_{\\theta_1}^{\\sigma}" + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "inline_equation", + "content": "T_{\\theta_2}^c" + }, + { + "bbox": [ + 304, + 286, + 545, + 597 + ], + "type": "text", + "content": " to increase the feature dimensions for better parsing time-variant density and color. The MLPs here can be viewed as decompressors that decompress the compact low-dimensional voxel-grid features into more tractable ones. Compared with directly storing high-dimensional features in each voxel, the temporally implicit representation reduces the memory footprint significantly since the shared MLPs only increase memory slightly." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "spans": [ + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "type": "text", + "content": "Inner product time query. For a discrete time step " + }, + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "type": "text", + "content": ", we use a learnable time-variant latent representation " + }, + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "type": "inline_equation", + "content": "\\omega_{t}" + }, + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "type": "text", + "content": " to represent the time query. Instead of concatenating the time query with the intermediate features, we propose to calculate the inner product between the learned time query and the decompressed features as the required output " + }, + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "type": "text", + "content": ". Formally, the density and color of a space-time query " + }, + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "type": "inline_equation", + "content": "(x,y,z,t)" + }, + { + "bbox": [ + 304, + 597, + 545, + 693 + ], + "type": "text", + "content": " are formulated as" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 359, + 700, + 545, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 359, + 700, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 359, + 700, + 545, + 715 + ], + "type": "interline_equation", + "content": "\\sigma (x, y, z, t) = \\omega_ {t} ^ {\\sigma} \\cdot \\mathcal {T} _ {\\theta_ {1}} ^ {\\sigma} (\\mathcal {G} _ {x, y, z} ^ {\\sigma}), \\tag {2}", + "image_path": "43b0214715931c56eec6fbeb3ad2ccace4ec8ea8f3ea4f71029198561816f2b0.jpg" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "19708" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 69, + 286, + 180 + ], + "blocks": [ + { + "bbox": [ + 51, + 69, + 286, + 180 + ], + "lines": [ + { + "bbox": [ + 51, + 69, + 286, + 180 + ], + "spans": [ + { + "bbox": [ + 51, + 69, + 286, + 180 + ], + "type": "image", + "image_path": "c89e4ffa935ae9ddbb7365c32977e96baa21992548d3434e797cf798a990e952.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 181, + 289, + 248 + ], + "lines": [ + { + "bbox": [ + 46, + 181, + 289, + 248 + ], + "spans": [ + { + "bbox": [ + 46, + 181, + 289, + 248 + ], + "type": "text", + "content": "Figure 2. Overview of our method. Given a ray, we first sample points, and split them into static and dynamic ones using the variation field. After that, we feed these points to the corresponding branches and query the required properties. Then we merge the static output and dynamic output for rendering the ray color. An L2 loss is employed to calculate loss and back-propagate." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 93, + 262, + 287, + 277 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 262, + 287, + 277 + ], + "spans": [ + { + "bbox": [ + 93, + 262, + 287, + 277 + ], + "type": "interline_equation", + "content": "c (x, y, z, \\boldsymbol {d}, t) = \\omega_ {t} ^ {c} \\cdot \\mathcal {T} _ {\\theta_ {2}} ^ {c} (\\mathcal {G} _ {x, y, z} ^ {c}, \\boldsymbol {d}). \\tag {3}", + "image_path": "c4fc59bb33d82b69ee823d23f327369cec77a09a8b11060333f28f26119655ce.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "spans": [ + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "text", + "content": "In practice, simultaneously querying multiple time steps helps reconstruct the detail of high-dynamic motions and reduces the training iterations to traverse through all time steps. The inner product based query will facilitate the training speed when simultaneously querying many time steps in a training iteration. Specifically, we denote the FLOPs of the MLP " + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{\\theta_1}" + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "text", + "content": " and the inner product operation as " + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "inline_equation", + "content": "\\mathrm{FLOP}_{mlp}" + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "inline_equation", + "content": "\\mathrm{FLOP}_{inn}" + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "text", + "content": ", respectively. For a " + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "text", + "content": "-frame video, the FLOPs of the concatenation query [19] is larger than " + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "inline_equation", + "content": "T\\cdot \\mathrm{FLOP}_{mlp}" + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "text", + "content": " (due to the extra temporal embedding dimension), while the FLOPs of our inner product query is only " + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "inline_equation", + "content": "\\mathrm{FLOP}_{mlp} + T\\cdot \\mathrm{FLOP}_{inn}" + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "inline_equation", + "content": "\\mathrm{FLOP}_{mlp} >> \\mathrm{FLOP}_{inn}" + }, + { + "bbox": [ + 46, + 281, + 289, + 426 + ], + "type": "text", + "content": ")." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 431, + 141, + 443 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 431, + 141, + 443 + ], + "spans": [ + { + "bbox": [ + 47, + 431, + 141, + 443 + ], + "type": "text", + "content": "3.3. Variation Field" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 450, + 287, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 450, + 287, + 534 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 287, + 534 + ], + "type": "text", + "content": "In this subsection, we introduce the variation field to identify which voxels in the 3D space are dynamic, i.e., the densities or colors are not constant over different time steps. By separating the static and dynamic voxels, the redundant computations caused by using a relatively heavy time-varying model to process the static components will be avoided, which accelerates the training and rendering." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 534, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 534, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 534, + 288, + 714 + ], + "type": "text", + "content": "A simpler solution for accelerate training is to separate the static and dynamic regions in pixel-level, i.e., using the temporal variance of pixels to produce static and dynamic ones. However this scheme is actually not feasible because we can only separate dynamic and static regions in training views using the ground truth. For rendering novel views, we can not get the pixel variance for rendering since we have no ground truth in novel views. Thus a feasible solution is to learn the voxel-level temporal variance which is shared for all possible views. In addition, separating in the voxel-level is more efficient compared to pixel-level, even if we have an oracle to make the pixel-level separation feasible in novel views. This is because not all voxels projected to a dynamic pixel are dynamic, there will be only a small fraction of voxels around the object surfaces are actually" + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 322, + 74, + 533, + 215 + ], + "blocks": [ + { + "bbox": [ + 322, + 74, + 533, + 215 + ], + "lines": [ + { + "bbox": [ + 322, + 74, + 533, + 215 + ], + "spans": [ + { + "bbox": [ + 322, + 74, + 533, + 215 + ], + "type": "image", + "image_path": "79e725cf185f6588c324292fbd174a0631bc5e8c63203adf7ff36b2844498488.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 216, + 547, + 271 + ], + "lines": [ + { + "bbox": [ + 304, + 216, + 547, + 271 + ], + "spans": [ + { + "bbox": [ + 304, + 216, + 547, + 271 + ], + "type": "text", + "content": "Figure 3. Implicit interaction of multiple rays to decide which point is dynamic. For a static ray (blue line), all points are set to be low dynamic. For a dynamic ray (green line), at least one point is dynamic. The intersection of multiple dynamic ray is more likely to be a dynamic point, which is also physically intuitive." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 275, + 545, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 275, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 304, + 275, + 545, + 300 + ], + "type": "text", + "content": "dynamic. Therefore, the voxel level separation will produce much fewer dynamic queries." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "spans": [ + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "text", + "content": "To perform the voxel-level separation, we utilize the pixel-level temporal variances from training videos as the supervision to estimate the voxel-level variances. The pixel-level (or ray-level) temporal variances of different videos are shown in Fig. 3. Formally, given a ray " + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "inline_equation", + "content": "r(s) = o + s \\cdot d" + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "text", + "content": " with origin " + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "inline_equation", + "content": "o" + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "text", + "content": " and direction " + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "text", + "content": ", the corresponding pixel color at time step " + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "text", + "content": " is defined as " + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "inline_equation", + "content": "C(r,t)" + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "text", + "content": ". Then the pixel-level temporal variance " + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "inline_equation", + "content": "D^2(r)" + }, + { + "bbox": [ + 304, + 299, + 546, + 388 + ], + "type": "text", + "content": " is formalized as" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 309, + 392, + 543, + 422 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 309, + 392, + 543, + 422 + ], + "spans": [ + { + "bbox": [ + 309, + 392, + 543, + 422 + ], + "type": "interline_equation", + "content": "D ^ {2} (\\boldsymbol {r}) = \\frac {1}{T} \\sum_ {t = 1} ^ {T} (C (\\boldsymbol {r}, t) - \\bar {C} (\\boldsymbol {r})) ^ {2}, \\quad \\bar {C} (\\boldsymbol {r}) = \\frac {1}{T} \\sum_ {t = 1} ^ {T} C (\\boldsymbol {r}, t),", + "image_path": "adc63daf6332b0e7c6edb3175ecc3110104ea07c3768347cda5e3a79484543aa.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "inline_equation", + "content": "\\bar{C} (\\pmb {r})" + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": " is the mean color of pixel corresponding to the ray " + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "inline_equation", + "content": "\\pmb{r}" + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": ". For identifying the dynamic pixels, the standard deviation " + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "inline_equation", + "content": "D(\\pmb {r})" + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": " is binarized to " + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "inline_equation", + "content": "M(r)" + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": " with a threshold " + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": " to provide pixel-level dynamic supervision, i.e. " + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "inline_equation", + "content": "M(r) = 1" + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": " if " + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "inline_equation", + "content": "D(\\boldsymbol {r})\\geq \\gamma" + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": ", else " + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "inline_equation", + "content": "M(\\boldsymbol {r}) = 0" + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": ". In this way, we judge that a ray " + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "inline_equation", + "content": "\\pmb{r}" + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": " is dynamic if " + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "inline_equation", + "content": "M(r) = 1" + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": ". Next, we use the " + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "inline_equation", + "content": "M(r)" + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": " as supervision to estimate the voxel-level variations " + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "inline_equation", + "content": "\\mathcal{V}" + }, + { + "bbox": [ + 304, + 426, + 547, + 510 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 510, + 547, + 666 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 547, + 666 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 547, + 666 + ], + "type": "text", + "content": "The relations between the pixel-level variance and voxel-level variance lie in the following aspects: (1) If a pixel is static, then all voxels passed through by the ray corresponding to the pixel should be static in most cases (We will discuss some special cases which violate this rule later in this subsection.). (2) If a pixel is dynamic, then at least one of the voxels passed through by the corresponding ray is dynamic. Fig. 3 shows the two situations. With the above two relations, we design the variation field, which is denoted as " + }, + { + "bbox": [ + 304, + 510, + 547, + 666 + ], + "type": "inline_equation", + "content": "\\mathcal{V} \\in \\mathbb{R}^{N_x \\times N_y \\times N_z}" + }, + { + "bbox": [ + 304, + 510, + 547, + 666 + ], + "type": "text", + "content": " to represent the voxel-level temporal variance. Specifically, we uniformly sample " + }, + { + "bbox": [ + 304, + 510, + 547, + 666 + ], + "type": "inline_equation", + "content": "N_s" + }, + { + "bbox": [ + 304, + 510, + 547, + 666 + ], + "type": "text", + "content": " points from the near plane to the far plane in " + }, + { + "bbox": [ + 304, + 510, + 547, + 666 + ], + "type": "inline_equation", + "content": "\\mathbf{r}" + }, + { + "bbox": [ + 304, + 510, + 547, + 666 + ], + "type": "text", + "content": ", and build the following equation to satisfy the two relations mentioned above:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 342, + 670, + 545, + 685 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 342, + 670, + 545, + 685 + ], + "spans": [ + { + "bbox": [ + 342, + 670, + 545, + 685 + ], + "type": "interline_equation", + "content": "\\hat {M} (\\boldsymbol {r}) = \\boldsymbol {s} (\\max (\\{\\mathcal {V} _ {\\boldsymbol {r} (s _ {i})} | i \\in \\{1, \\dots , N _ {s} \\} \\})), \\qquad (4)", + "image_path": "64882d223127900edc710461ecd96612257086ac7694f3dcf325877bdf2a33e6.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 689, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 547, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 689, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\hat{M}(\\boldsymbol{r})" + }, + { + "bbox": [ + 304, + 689, + 547, + 714 + ], + "type": "text", + "content": " is an estimation of " + }, + { + "bbox": [ + 304, + 689, + 547, + 714 + ], + "type": "inline_equation", + "content": "M(\\boldsymbol{r})" + }, + { + "bbox": [ + 304, + 689, + 547, + 714 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 689, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\boldsymbol{s}" + }, + { + "bbox": [ + 304, + 689, + 547, + 714 + ], + "type": "text", + "content": " is the sigmoid function. Then we train the variation field by minimizing" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "19709" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 209, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 209, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 209, + 83 + ], + "type": "text", + "content": "the following binary cross-entropy loss:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 53, + 86, + 287, + 102 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 86, + 287, + 102 + ], + "spans": [ + { + "bbox": [ + 53, + 86, + 287, + 102 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {v} = \\mathbb {E} _ {\\boldsymbol {r}} \\left[ - M (\\boldsymbol {r}) \\log (\\hat {M} (\\boldsymbol {r})) - (1 - M (\\boldsymbol {r})) \\log (1 - \\hat {M} (\\boldsymbol {r})) \\right]. \\tag {5}", + "image_path": "716a0ff4738affb1f99f3d095e3d64dbede9de23d33de39b8dcea01e37bc6c4b.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 104, + 287, + 139 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 104, + 287, + 139 + ], + "spans": [ + { + "bbox": [ + 46, + 104, + 287, + 139 + ], + "type": "text", + "content": "By optimizing the above loss function to all rays, we can get the learned variation field " + }, + { + "bbox": [ + 46, + 104, + 287, + 139 + ], + "type": "inline_equation", + "content": "\\mathcal{V}" + }, + { + "bbox": [ + 46, + 104, + 287, + 139 + ], + "type": "text", + "content": ". The training of the variation field is very efficient, usually taking less than 30 seconds." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "spans": [ + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "text", + "content": "The maximization operation well formulates the relations between a pixel and its corresponding voxels. If a pixel is static, then the equations of Eq. (4) and Eq. (5) will force all voxels passed through by the corresponding ray to be static " + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "inline_equation", + "content": "(\\mathcal{V}_{x,y,z} = 0)" + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "text", + "content": ". If a pixel is dynamic, Eq. (4) requires at least one of the corresponding voxels (i.e., the max value of the voxel variances) to be dynamic " + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "inline_equation", + "content": "(\\mathcal{V}_{x,y,z} = +\\infty)" + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "text", + "content": ". Although we provide no information about which specific voxels in a dynamic ray are dynamic, the implicit interaction of multiple different rays will force the solution to be physically reasonable. To explain this, we focus on the observable voxels which at least passed through by one ray. If a point " + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "inline_equation", + "content": "(x,y,z)" + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "text", + "content": " is passed through by at least one static ray, then " + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_{x,y,z}" + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "text", + "content": " will tend to be optimized to be close to zero. If a point " + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "inline_equation", + "content": "(x,y,z)" + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "text", + "content": " is only passed through by dynamic rays, and not occluded by other dynamic voxels, then " + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_{x,y,z}" + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "text", + "content": " will be optimized to " + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "inline_equation", + "content": "+\\infty" + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "text", + "content": ". This is because without occlusion, the above point of " + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "inline_equation", + "content": "(x,y,z)" + }, + { + "bbox": [ + 46, + 140, + 289, + 390 + ], + "type": "text", + "content": " along the dynamic rays will be passed by other static rays (the front space along these rays are observable from other views). We illustrate this situation in Fig. 3." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "text", + "content": "Inference. After the training process, the temporal variation at a specific 3D position " + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "inline_equation", + "content": "(x,y,z)" + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_{x,y,z}" + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "text", + "content": ", which is easily acquired by interpolating the discrete variation field. We then identify a voxel in the scene as dynamic if " + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_{x,y,z}" + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "text", + "content": " is larger than a hyper-parameter " + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "text", + "content": ", and as static if it is smaller than " + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "text", + "content": ". Formally, we will get a dynamic mask " + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "inline_equation", + "content": "\\dot{\\mathrm{M}} \\in \\{0,1\\}^{N_x \\times N_y \\times N_z}" + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "text", + "content": ", which will be used to split sampling points in a ray into static points and dynamic points. We evaluate the effectiveness of this inference method in the test views and find that the recall and precision are reasonable for splitting the dynamic and static parts (recall: 0.97, precision: 0.94 when " + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "inline_equation", + "content": "\\beta = 0.9" + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "text", + "content": "). Although the recall seems sufficient to retrieve most dynamic parts, we empirically find some false negatives in the rendering images affect the rendering quality. To address this problem, we use a ray-wise max-pooling operation to identify the points near to a dynamic point as dynamic. The kernel size of max-pooling is set to " + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "inline_equation", + "content": "k_m = 21" + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "text", + "content": ", and the stride is set to 1. In this way, the recall is very closed to 1. Although many hyperparameters are incorporated, we have empirically found that the thresholds " + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 46, + 391, + 289, + 653 + ], + "type": "text", + "content": " are not sensitive over a wide range of reasonable values." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 653, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 289, + 715 + ], + "type": "text", + "content": "Discussion. There may be some situations in which the rules (1) are broken due to occlusion. Specifically, when a dynamic voxel is occluded by some static voxels, the occluded parts should not be classified as static, which makes the 2D supervision noisy. However in practice, we found" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 307, + 70, + 386, + 116 + ], + "blocks": [ + { + "bbox": [ + 307, + 70, + 386, + 116 + ], + "lines": [ + { + "bbox": [ + 307, + 70, + 386, + 116 + ], + "spans": [ + { + "bbox": [ + 307, + 70, + 386, + 116 + ], + "type": "image", + "image_path": "fd018c329e90016f33eb3920dc52ee1785fe6173ec4a3f488380f422fe93f132.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 330, + 121, + 520, + 132 + ], + "lines": [ + { + "bbox": [ + 330, + 121, + 520, + 132 + ], + "spans": [ + { + "bbox": [ + 330, + 121, + 520, + 132 + ], + "type": "text", + "content": "Figure 4. Impact of occlusions to the variation field." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 386, + 70, + 465, + 116 + ], + "blocks": [ + { + "bbox": [ + 386, + 70, + 465, + 116 + ], + "lines": [ + { + "bbox": [ + 386, + 70, + 465, + 116 + ], + "spans": [ + { + "bbox": [ + 386, + 70, + 465, + 116 + ], + "type": "image", + "image_path": "c6d3ac47cd7332f032240af5cac3493ba5b7079cbc2afec51855a8ad62fe23c7.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 466, + 70, + 545, + 116 + ], + "blocks": [ + { + "bbox": [ + 466, + 70, + 545, + 116 + ], + "lines": [ + { + "bbox": [ + 466, + 70, + 545, + 116 + ], + "spans": [ + { + "bbox": [ + 466, + 70, + 545, + 116 + ], + "type": "image", + "image_path": "103d74a2bf401c86aa7b4477a2c0a2db74ecfacbbd10833e0f3784e48314e3fd.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 133, + 545, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 133, + 545, + 396 + ], + "spans": [ + { + "bbox": [ + 304, + 133, + 545, + 396 + ], + "type": "text", + "content": "the learning-based separation has a certain degree of tolerance for this situation. We conducted experiments to verify this and present the results in Fig. 4. The occluded region is visualized in the leftmost view (the area behind the static roadblock). Although the dynamic region marked in yellow is occluded in the left view, it is actually classified as dynamic region. This can be inferred from another view where the occluded region has changed, as illustrated in the middle and right images in Fig. 4). The variation field is learning-based and will learn a solution that satisfies most constraints. If it forces some dynamic voxels occluded by static voxels to be 0, then the loss function from other visible views will be high. As a result, the learning-based process tends to assign a \"middle solution\" to voxels with inconsistent supervisions from different views. We also attempted to use the transmittance as a weight (in a way of volumetric rendering) to learn the variation field which can explicitly handle the occlusion problem. However, we found a large efficiency drop with similar performance. As a result, we use the proposed variation field and find this formulation works well for most scenes, including some challenging scenes with large areas of motions." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 403, + 481, + 416 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 403, + 481, + 416 + ], + "spans": [ + { + "bbox": [ + 306, + 403, + 481, + 416 + ], + "type": "text", + "content": "3.4. Training of Mixed Neural Voxels" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 422, + 545, + 505 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 422, + 545, + 505 + ], + "spans": [ + { + "bbox": [ + 304, + 422, + 545, + 505 + ], + "type": "text", + "content": "With the help of the variation field, we can split a scene into dynamic voxels and static voxels. To reduce redundant computations, we use the lightweight static model described in Sec. 3.1 to compute the densities and colors for static voxels and the dynamic model described in Sec. 3.2 to compute the densities and colors for dynamic voxels. The overall architecture is illustrated in Fig. 2." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "spans": [ + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "text", + "content": "Specifically for a given ray " + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "inline_equation", + "content": "r(s) = o + sd" + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "text", + "content": " with origin " + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "inline_equation", + "content": "o" + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "text", + "content": " and view direction " + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "text", + "content": ", we apply stratified sampling from the near to the far planes and get " + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "inline_equation", + "content": "N_{s}" + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "text", + "content": " points. Then the " + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "inline_equation", + "content": "N_{s}" + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "text", + "content": " points are separated into static and dynamic ones by inferring these points with the proposed variation field. For the static points, we pass them into the static branch to retrieve the colors and densities. For the dynamic points, we pass them into the dynamic branch together with a deferred time query " + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "inline_equation", + "content": "\\omega_{t}" + }, + { + "bbox": [ + 304, + 506, + 545, + 660 + ], + "type": "text", + "content": " to retrieve the corresponding properties. After that, we merge the static points and dynamic points according to their order. Then we apply volumetric rendering to the merged points to obtain the rendered color, which is formulated as" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 333, + 663, + 545, + 696 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 333, + 663, + 545, + 696 + ], + "spans": [ + { + "bbox": [ + 333, + 663, + 545, + 696 + ], + "type": "interline_equation", + "content": "C (\\boldsymbol {r}, t) = \\sum_ {i = 1} ^ {N _ {s}} T _ {i, t} \\cdot \\left(1 - \\exp \\left(- \\sigma_ {i, t} \\delta_ {i}\\right)\\right) \\cdot c _ {i, t}, \\tag {6}", + "image_path": "5eae807edf5efdcdd82dc6881861f03b4bc9c95a0b06de02f6c593035f964fa8.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 306, + 701, + 545, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 701, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{T}_{i,t}" + }, + { + "bbox": [ + 306, + 701, + 545, + 714 + ], + "type": "text", + "content": " is the accumulated opacity (or transmittance):" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "19710" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 71, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 71, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 46, + 71, + 287, + 109 + ], + "type": "inline_equation", + "content": "\\mathrm{T}_{i,t} = \\exp (-\\sum_{j = 1}^{i - 1}\\sigma_{j,t}\\delta_j)" + }, + { + "bbox": [ + 46, + 71, + 287, + 109 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 71, + 287, + 109 + ], + "type": "inline_equation", + "content": "\\delta_{i}" + }, + { + "bbox": [ + 46, + 71, + 287, + 109 + ], + "type": "text", + "content": " is the distance between adjacent samples. Given the ground truth color " + }, + { + "bbox": [ + 46, + 71, + 287, + 109 + ], + "type": "inline_equation", + "content": "C_g(\\boldsymbol {r},t)" + }, + { + "bbox": [ + 46, + 71, + 287, + 109 + ], + "type": "text", + "content": ", an l2-loss is employed to train the model:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 91, + 117, + 287, + 133 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 91, + 117, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 91, + 117, + 287, + 133 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathbb {E} _ {\\left(\\boldsymbol {r}, t\\right)} \\left[ \\| C _ {g} (\\boldsymbol {r}, t) - C (\\boldsymbol {r}, t) \\| _ {2} ^ {2} \\right]. \\tag {7}", + "image_path": "aa19f8a68e2e90ff61a73c3488e274d3ec3bf843e9af25fd77864bc796a1b8fb.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 135, + 287, + 171 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 135, + 287, + 171 + ], + "spans": [ + { + "bbox": [ + 46, + 135, + 287, + 171 + ], + "type": "text", + "content": "For both static and dynamic branches, we omit the computation of color for points whose densities are close to zero, which is a widely adopted pruning strategy [22, 50, 8]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "spans": [ + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "text", + "content": "Efficiency analysis. We define the proportion of dynamic points in a scene as " + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "inline_equation", + "content": "\\approx 0.05" + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "text", + "content": " for most scenes). Besides, the FLOPs of static and dynamic branches are denoted as " + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "inline_equation", + "content": "FLOP_{sta}" + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "inline_equation", + "content": "FLOP_{dyn}" + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "text", + "content": ", respectively. Then the total FLOPs of MixVoxels are " + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "inline_equation", + "content": "FLOP_{sta} + \\lambda \\cdot FLOP_{dyn}" + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "text", + "content": ". Empirically, " + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "inline_equation", + "content": "FLOP_{dyn} / FLOP_{sta}" + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "text", + "content": " ranges from 50 to 100 with different reasonable dimension settings. Then the acceleration ratio of splitting static and dynamic models is " + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "inline_equation", + "content": "FLOP_{dyn} / (FLOP_{sta} + \\lambda FLOP_{dyn}) \\approx 10" + }, + { + "bbox": [ + 46, + 171, + 287, + 315 + ], + "type": "text", + "content": ". In practice, the actual speedup with a 3090 GPU is about 5, the inconsistency between analysis and experiment may come from the GPU features, which are friendly to a more consistent network." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 322, + 176, + 335 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 322, + 176, + 335 + ], + "spans": [ + { + "bbox": [ + 47, + 322, + 176, + 335 + ], + "type": "text", + "content": "3.5. Implementation Detail" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 341, + 288, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 341, + 288, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 341, + 288, + 593 + ], + "type": "text", + "content": "The voxel-grid representations require large GPU memory to store the cubically growing voxel numbers. To implement the voxel-grid representations more memory efficient, we use the tensor factorization technique proposed in TensoRF [8] to reduce the memory footprint. In this way, a 3D tensor is factorized into the outer product of a vector and a 2D matrix. We factorize all the voxel-grid tensors, including static voxels, dynamic voxels and the variation field. With the help of tensor factorization, the learned model costs about 500MB for a 300-frame multi-view video scene. For the voxel resolutions, we follow [8] to start from an initial low resolution of " + }, + { + "bbox": [ + 46, + 341, + 288, + 593 + ], + "type": "inline_equation", + "content": "256^{3}" + }, + { + "bbox": [ + 46, + 341, + 288, + 593 + ], + "type": "text", + "content": ", and upsample the resolution at steps 1500, 2000, 2500, and 2750 with a linear increase in the log space. The final resolution is set to " + }, + { + "bbox": [ + 46, + 341, + 288, + 593 + ], + "type": "inline_equation", + "content": "640^{3}" + }, + { + "bbox": [ + 46, + 341, + 288, + 593 + ], + "type": "text", + "content": ". Once the resolution is changed, we re-train the variation field, which only takes about 15-30s. The voxel-grid feature dimension is set to 27, and the hidden state of MLP is set to 512. For training, we use Adam [15] optimizer with a learning rate of 0.02 for voxels and " + }, + { + "bbox": [ + 46, + 341, + 288, + 593 + ], + "type": "inline_equation", + "content": "3e - 3" + }, + { + "bbox": [ + 46, + 341, + 288, + 593 + ], + "type": "text", + "content": " for MLPs. The total variation loss [50] is incorporated as a regularization to encourage the space smoothness." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 603, + 128, + 617 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 603, + 128, + 617 + ], + "spans": [ + { + "bbox": [ + 47, + 603, + 128, + 617 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 623, + 162, + 636 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 162, + 636 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 162, + 636 + ], + "type": "text", + "content": "4.1. Experiment Setting" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 641, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 712 + ], + "type": "text", + "content": "Dataset. We validate our method on two datasets: (1) The Plenoptic Video Dataset [19], which consists of 6 publicly accessible scenes: coffee-martini, flame-salmon, cook-spinach, cut-roasted-beef, flame-steam and sear-steam. We conduct experiments on all six scenes. Each scene contains 19 videos with different camera views. The dataset" + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 319, + 83, + 533, + 179 + ], + "blocks": [ + { + "bbox": [ + 306, + 69, + 535, + 80 + ], + "lines": [ + { + "bbox": [ + 306, + 69, + 535, + 80 + ], + "spans": [ + { + "bbox": [ + 306, + 69, + 535, + 80 + ], + "type": "text", + "content": "Table 1. Results on our collected dataset, including two scenes." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 319, + 83, + 533, + 179 + ], + "lines": [ + { + "bbox": [ + 319, + 83, + 533, + 179 + ], + "spans": [ + { + "bbox": [ + 319, + 83, + 533, + 179 + ], + "type": "table", + "html": "
SceneModelPSNR↑DSSIM↓LPIPS↓
Moving-CarsMixVoxels-S18.720.2510.689
MixVoxels-M18.970.2280.552
MixVoxels-L18.890.2220.540
MixVoxels-X19.110.2100.516
Solving-RubikMixVoxels-S25.390.0650.339
MixVoxels-M26.050.0590.275
MixVoxels-L26.280.0550.241
MixVoxels-X26.800.0470.209
", + "image_path": "f0ec872bd625902d7260c11cf1dc992750fb252b45ac69637e4cba8bf213eb05.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 184, + 545, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 184, + 545, + 327 + ], + "spans": [ + { + "bbox": [ + 304, + 184, + 545, + 327 + ], + "type": "text", + "content": "contains many challenging scenes including objects with topology changes, objects with volumetric effects, various lighting conditions, etc. (2) Our proposed dataset including two more complex dynamic scenes: moving-cars and solving-rubik. The moving-cars scene features several vehicles passing across the screen, with significant motion and displacement. Meanwhile, in the solving-rubik scene, a man solves a Rubik's cube at a rapid pace, averaging 4 rotations per second, providing an opportunity to evaluate the model's ability to capture swift movements. The collection procedures used are similar to those of DyNeRF. More details are presented in the appendix." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 327, + 546, + 471 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 327, + 546, + 471 + ], + "spans": [ + { + "bbox": [ + 304, + 327, + 546, + 471 + ], + "type": "text", + "content": "For training and evaluation, we follow the experiment setting in [19] that employs 18 views for training and 1 view for evaluation. To quantitatively evaluate the rendering quality on novel views, we measure PSNR, DSSIM and LPIPS[53] on the test views. We also provide more metrics in the appendix including FLIP [1] and JOD [16], which we find the comparisons are similar with PSNR and LPIPS. We follow the setting of [19] to evaluate our model frame by frame. For videos consisting of equal or more than 300 frames, we evaluate our model every 10 frames [19] to calculate the frame-by-frame metrics except for the JOD metrics, which requires a stack of continuous video." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 472, + 545, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 472, + 545, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 472, + 545, + 555 + ], + "type": "text", + "content": "Training Schedules. For evaluating the effect of training time, we train MixVoxels with different configurations shown in Tab. 2. The configurations vary in terms of training iterations and the number of sample points per ray. By default, the step size for sampling points is set to four times of the voxel width. The " + }, + { + "bbox": [ + 304, + 472, + 545, + 555 + ], + "type": "inline_equation", + "content": "8 \\times" + }, + { + "bbox": [ + 304, + 472, + 545, + 555 + ], + "type": "text", + "content": " means that there will be eight times as many sampling points compared to the default." + } + ] + } + ], + "index": 13 + }, + { + "type": "table", + "bbox": [ + 326, + 571, + 526, + 628 + ], + "blocks": [ + { + "bbox": [ + 323, + 559, + 527, + 570 + ], + "lines": [ + { + "bbox": [ + 323, + 559, + 527, + 570 + ], + "spans": [ + { + "bbox": [ + 323, + 559, + 527, + 570 + ], + "type": "text", + "content": "Table 2. Different training configurations of MixVoxels." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 326, + 571, + 526, + 628 + ], + "lines": [ + { + "bbox": [ + 326, + 571, + 526, + 628 + ], + "spans": [ + { + "bbox": [ + 326, + 571, + 526, + 628 + ], + "type": "table", + "html": "
ModelIterationsSampling pointsTraining Time
MixVoxels-S50001 ×15 min
MixVoxels-M125001 ×40 min
MixVoxels-L250001 ×80 min
MixVoxels-X500008 ×300 min
", + "image_path": "858331641d42e66e300005c8768cbb4fc6964c8987cc488e4cbdd54885d97e95.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "table_body" + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 635, + 362, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 635, + 362, + 647 + ], + "spans": [ + { + "bbox": [ + 306, + 635, + 362, + 647 + ], + "type": "text", + "content": "4.2. Results" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": "Quantitative results and comparisons. For quantitative results, we present the metrics and compare with other methods in Tab. 3. Compared with the previous state-of-the-art method DyNeRF, we reduce the training time from " + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "inline_equation", + "content": "1.3\\mathrm{K}" + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": " GPU hours to 15 minutes, making the training of complex" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19711" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 71, + 173, + 201 + ], + "blocks": [ + { + "bbox": [ + 49, + 71, + 173, + 201 + ], + "lines": [ + { + "bbox": [ + 49, + 71, + 173, + 201 + ], + "spans": [ + { + "bbox": [ + 49, + 71, + 173, + 201 + ], + "type": "image", + "image_path": "568836bbd6a296632e70842fd23b25efc3ab4705b2bc62e88094b776173fb85e.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 202, + 547, + 225 + ], + "lines": [ + { + "bbox": [ + 46, + 202, + 547, + 225 + ], + "spans": [ + { + "bbox": [ + 46, + 202, + 547, + 225 + ], + "type": "text", + "content": "Figure 5. Visual comparisons with state-of-the-art methods. K-Planes [12] and HexPlane [7] are concurrent works. We have selected four representative patches to better inspect the details. Our method performs well on reconstructing details and capturing movements." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 173, + 70, + 296, + 201 + ], + "blocks": [ + { + "bbox": [ + 173, + 70, + 296, + 201 + ], + "lines": [ + { + "bbox": [ + 173, + 70, + 296, + 201 + ], + "spans": [ + { + "bbox": [ + 173, + 70, + 296, + 201 + ], + "type": "image", + "image_path": "4f2d0189c19bb3a69a78f0ee6976aff14f242fdaa5d28a39e92219b08e372f9c.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 296, + 70, + 421, + 201 + ], + "blocks": [ + { + "bbox": [ + 296, + 70, + 421, + 201 + ], + "lines": [ + { + "bbox": [ + 296, + 70, + 421, + 201 + ], + "spans": [ + { + "bbox": [ + 296, + 70, + 421, + 201 + ], + "type": "image", + "image_path": "ccf7bcc8ba4c17aea0eaff80d748501f90b07f48c27c7313a4cc2461bedd8946.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 422, + 71, + 545, + 201 + ], + "blocks": [ + { + "bbox": [ + 422, + 71, + 545, + 201 + ], + "lines": [ + { + "bbox": [ + 422, + 71, + 545, + 201 + ], + "spans": [ + { + "bbox": [ + 422, + 71, + 545, + 201 + ], + "type": "image", + "image_path": "095c3814f0f631827a7185d40e050bfcbf8e052232f66cf316ec7633114ef842.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 48, + 276, + 288, + 402 + ], + "blocks": [ + { + "bbox": [ + 47, + 229, + 288, + 274 + ], + "lines": [ + { + "bbox": [ + 47, + 229, + 288, + 274 + ], + "spans": [ + { + "bbox": [ + 47, + 229, + 288, + 274 + ], + "type": "text", + "content": "Table 3. Quantitative results comparisons. All metrics are measured on 300-frame scenes. We also report the training time, rendering speed (FPS) and model size. * Note DyNeRF is trained on 8 GPUs, while others are trained on one GPU." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 276, + 288, + 402 + ], + "lines": [ + { + "bbox": [ + 48, + 276, + 288, + 402 + ], + "spans": [ + { + "bbox": [ + 48, + 276, + 288, + 402 + ], + "type": "table", + "html": "
MethodTrainRenderSizePSNR↑DSSIM↓LPIPS↓
DyNeRF[19]7 days*-28 MB29.580.01970.083
Concurrent work
StreamRF[18]75 min8.35310MB28.26--
NeRFPlayer[37]360 min0.05-30.690.0340.111
Hyperreel[2]540 min2.0360 MB31.100.0360.096
K-Planes[12]108 min--31.630.018-
HexPlanes[7]720 min-200MB31.710.0140.075
Mix Voxels-S15 min37.7500 MB31.030.0220.129
Mix Voxels-M40 min37.7500 MB31.220.0190.102
Mix Voxels-L80 min37.7500 MB31.340.0170.096
Mix Voxels-X300 min4.6500 MB31.730.0150.064
", + "image_path": "9e9e095c439d97280855e703ec5d6d102c0d0af2d1837d471eb5c04cb9a2f589.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 411, + 287, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 411, + 287, + 530 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 287, + 530 + ], + "type": "text", + "content": "dynamic scenes more practical. For rendering, the Mix Voxels has a 37.7 fps rendering speed for 1K resolution. Compared with concurrent works, Mix Voxels requires less training time and achieves faster rendering speed, while achieving competitive PSNR and LPIPS. For example, with only 15 minutes of training, Mix Voxels achieve 31.03 PSNR which is comparable to other methods trained for hours. With sufficient training, all metrics are further improved. For the quantitative results on our collected more complex scenes, we present them on Tab. 1." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 532, + 287, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 532, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 532, + 287, + 664 + ], + "type": "text", + "content": "Qualitative results and comparisons. Fig. 6 demonstrates the novel view rendering results on different dynamic scenes. The first four rows are novel view videos from Plenoptic Video Dataset [19]. The last two rows present the novel view videos from our collected two more complex dynamic scenes. The results show that our method can achieve near photo-realistic rendering quality. We provide the video results at the supplementary material. For qualitative comparisons, we show them in Fig. 5. MixVoxels can better reconstruct the moving object (the firing gun) and textual details like the hat and the salmon stripes." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": "We further investigate the relations between rendering efficiency and rendering quality. As shown in the lower part of Tab. 3, it was observed that an increase in training time leads to improvements in both PSNR and LPIPS. Longer" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 307, + 231, + 545, + 480 + ], + "blocks": [ + { + "bbox": [ + 307, + 231, + 545, + 480 + ], + "lines": [ + { + "bbox": [ + 307, + 231, + 545, + 480 + ], + "spans": [ + { + "bbox": [ + 307, + 231, + 545, + 480 + ], + "type": "image", + "image_path": "7463cb1b9c5b0a2eb6b561b61b95cba370c8e8c6cf425b8c5863db6436877f40.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 483, + 545, + 516 + ], + "lines": [ + { + "bbox": [ + 304, + 483, + 545, + 516 + ], + "spans": [ + { + "bbox": [ + 304, + 483, + 545, + 516 + ], + "type": "text", + "content": "Figure 6. Novel view synthesis of MixVoxels. We select some frames at different views. The last column demonstrates the normalized depth. We provide videos at the supplemental material." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 520, + 545, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 520, + 545, + 593 + ], + "spans": [ + { + "bbox": [ + 304, + 520, + 545, + 593 + ], + "type": "text", + "content": "training facilitates the reconstruction of sharp boundaries and fine details. Visual comparisons presented in Fig. 7 reveals that 15 minutes of training produces satisfactory recovery of most scene components but resulted in blurry motion details. With longer training, the moving objects become clearer with a distinct boundary." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 599, + 400, + 613 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 599, + 400, + 613 + ], + "spans": [ + { + "bbox": [ + 306, + 599, + 400, + 613 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 689 + ], + "type": "text", + "content": "In this subsection, we empirically justify the design of MixVoxels by ablating or modifying several key features. We also provide analysis that intuitively explains the ablations. We conduct all experiments in this subsection on the coffee-martini scene, which we find is typical for demonstrating the fast-moving complex objects." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "content": "Ablation on splitting voxels. To study the effect of splitting static and dynamic voxels, we compare MixVox-" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "19712" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 70, + 287, + 194 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 287, + 194 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 287, + 194 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 287, + 194 + ], + "type": "image", + "image_path": "340d6c855123630c3abf9455f1da3f1c953bf85c7a2ae0bcfbb676afc73c01e0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 196, + 286, + 218 + ], + "lines": [ + { + "bbox": [ + 47, + 196, + 286, + 218 + ], + "spans": [ + { + "bbox": [ + 47, + 196, + 286, + 218 + ], + "type": "text", + "content": "Figure 7. Qualitative demonstration of different training schedules. Longer training helps better reconstruct the high-dynamic parts." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 52, + 224, + 287, + 329 + ], + "blocks": [ + { + "bbox": [ + 52, + 224, + 287, + 329 + ], + "lines": [ + { + "bbox": [ + 52, + 224, + 287, + 329 + ], + "spans": [ + { + "bbox": [ + 52, + 224, + 287, + 329 + ], + "type": "image", + "image_path": "348214fb9bf1f61771b03da913a9ce284021e56d9b8b6600c927a900e8b2c5f0.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 333, + 287, + 365 + ], + "lines": [ + { + "bbox": [ + 47, + 333, + 287, + 365 + ], + "spans": [ + { + "bbox": [ + 47, + 333, + 287, + 365 + ], + "type": "text", + "content": "Figure 8. Qualitative comparison of MixVoxels and the full-dynamic model. Training with full-dynamic models with the same iterations can not well reconstruct the motion details." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 48, + 395, + 286, + 429 + ], + "blocks": [ + { + "bbox": [ + 47, + 369, + 287, + 392 + ], + "lines": [ + { + "bbox": [ + 47, + 369, + 287, + 392 + ], + "spans": [ + { + "bbox": [ + 47, + 369, + 287, + 392 + ], + "type": "text", + "content": "Table 4. Ablation on the mixed voxels. Training with the fulldynamic voxel model hurts both efficiency and efficacy." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 395, + 286, + 429 + ], + "lines": [ + { + "bbox": [ + 48, + 395, + 286, + 429 + ], + "spans": [ + { + "bbox": [ + 48, + 395, + 286, + 429 + ], + "type": "table", + "html": "
MethodTimePSNR↑DSSIM↓LPIPS↓FLIP↓JOD↑
Full-Dynamic2.5h28.360.0360.22360.11967.44
MixVoxels0.6h29.470.0260.11670.12237.99
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MethodTimePSNR↑DSSIM↓LPIPS↓FLIP↓JOD↑
Concat58m28.950.0370.21460.12947.44
Fourier43m28.670.0290.18240.12867.60
Inner product40m29.470.0260.11670.12237.99
", + "image_path": "fc7fdf3d6a91fbc9725216ffc253051ee1bd5cadd31de20be96e04856da231c4.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 521, + 287, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 652 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 652 + ], + "type": "text", + "content": "els with a full-dynamic voxel-grid representation, where all points are processed by the dynamic model. Tab. 4 shows the comparisons. With the same training iterations, the fulldynamic model is more time-consuming, which is intuitive because it processes all voxels with the dynamic models. Fig. 8 shows the qualitative comparison. The full-dynamic model recovered blurred motions. We speculate the reason is because the large area of static regions affects the capturing of dynamic information. The network will be biased by most static voxels with no motions and tend to learn low-frequency information." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "content": "Ablation on time query. We compare our inner product time query method with other variants: (1) Concatenation which concatenates the temporal embedding with the voxel features to be processed by an MLP. (2) Fourier head proposed by [47] which reconstructs the dynamics in" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 307, + 70, + 545, + 131 + ], + "blocks": [ + { + "bbox": [ + 307, + 70, + 545, + 131 + ], + "lines": [ + { + "bbox": [ + 307, + 70, + 545, + 131 + ], + "spans": [ + { + "bbox": [ + 307, + 70, + 545, + 131 + ], + "type": "image", + "image_path": "c9241656e7ece3d370d83ef4455c607773efe5f7fcaf39f3b1962dc33fac968c.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 133, + 545, + 301 + ], + "lines": [ + { + "bbox": [ + 305, + 133, + 545, + 301 + ], + "spans": [ + { + "bbox": [ + 305, + 133, + 545, + 301 + ], + "type": "text", + "content": "Figure 9. Ablation on the number of time query denoted as Q. frequency-domain. Tab. 5 shows the performance comparison. The concatenation query method is both space- and time-consuming. Querying one time step requires forwarding the fused features through the whole MLP. Limited by the GPU memory, we can only query 50 time steps per iteration with the concatenation way, which harms the performance on high-dynamic regions. The Fourier head processes the features to predict the magnitudes of different frequency components and the performance is competitive, while it requires an additional inverse discrete Fourier transform to recover the information in the temporal domain. Overall, the inner product query is the simplest and most efficient way for querying." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 302, + 546, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 302, + 546, + 434 + ], + "spans": [ + { + "bbox": [ + 304, + 302, + 546, + 434 + ], + "type": "text", + "content": "Number of time queries per-iteration. We empirically find that simultaneously querying multiple time steps in an iteration helps reconstruct the details of moving parts. Fig. 9 demonstrates the effect of different numbers of time queries denoted as Q. With more time queries, the boundaries of the moving hand and the flowing coffee become clearer. Querying more time steps can provide dense supervision and make the model acquire global temporal information in every iteration, which accelerates the convergence speed. The effective inner product time queries allow adding more time queries with negligible increase in computation." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 441, + 383, + 453 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 441, + 383, + 453 + ], + "spans": [ + { + "bbox": [ + 306, + 441, + 383, + 453 + ], + "type": "text", + "content": "4.4. Limitations" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 460, + 545, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 545, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 545, + 555 + ], + "type": "text", + "content": "Our method can synthesize novel view videos with a relative high quality. However, for some scenes with complex lighting conditions, some inconsistent property predictions may appear at the boundary between dynamic and static voxels, which is shown in Fig. 10. We suspect that the phenomenon is caused by the under-sampling of dynamic regions on scenes with some bad conditions. We will investigate ways to address the problem in future works." + } + ] + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 307, + 560, + 544, + 616 + ], + "blocks": [ + { + "bbox": [ + 307, + 560, + 544, + 616 + ], + "lines": [ + { + "bbox": [ + 307, + 560, + 544, + 616 + ], + "spans": [ + { + "bbox": [ + 307, + 560, + 544, + 616 + ], + "type": "image", + "image_path": "3fa2e51a701c78673a132eae85df356ac77ef87803a44d9a5783c28ecf2bda84.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 618, + 545, + 640 + ], + "lines": [ + { + "bbox": [ + 305, + 618, + 545, + 640 + ], + "spans": [ + { + "bbox": [ + 305, + 618, + 545, + 640 + ], + "type": "text", + "content": "Figure 10. Some inconsistent density and color predictions in the boundaries between dynamic and static regions." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 645, + 378, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 645, + 378, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 645, + 378, + 658 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "This paper demonstrates a new method named MixVoxels to efficiently reconstruct the 4D dynamic scenes and synthesize novel view videos. The core of our method is to split the 3D space into static and dynamic components" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19713" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": "with the proposed variation field, and process them with different branches. The separation speeds up the training and makes the dynamic branch focus on the dynamic parts to improve the performance. We also design an efficient dynamic voxel-grid representation with an inner product time query. The proposed method achieves competitive results with only 15 minutes of training, making the training and rendering of complex dynamic scenes more practical. We believe the fast training speed will enable potentially useful applications that are bottlenecked by training efficiency." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 203, + 157, + 217 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 203, + 157, + 217 + ], + "spans": [ + { + "bbox": [ + 47, + 203, + 157, + 217 + ], + "type": "text", + "content": "6. Acknowledgement" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 222, + 287, + 255 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 222, + 287, + 255 + ], + "spans": [ + { + "bbox": [ + 46, + 222, + 287, + 255 + ], + "type": "text", + "content": "This work was supported in part by the National Natural Science Fund for Distinguished Young Scholars under Grant 62025304." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 48, + 267, + 107, + 280 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 267, + 107, + 280 + ], + "spans": [ + { + "bbox": [ + 48, + 267, + 107, + 280 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 287, + 289, + 714 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 287, + 287, + 331 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 287, + 287, + 331 + ], + "spans": [ + { + "bbox": [ + 53, + 287, + 287, + 331 + ], + "type": "text", + "content": "[1] Pontus Andersson, Jim Nilsson, Tomas Akenine-Möller, Magnus Oskarsson, Kalle Åström, and Mark D Fairchild. 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High-quality video view interpolation using a layered representation. ACM transactions on graphics (TOG), 23(3):600-608, 2004. 1, 2" + } + ] + } + ], + "index": 9 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "19716" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/MoTIF_ Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution/b7d53caf-5b95-474a-8203-b3df729d9009_content_list.json b/2023/MoTIF_ Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution/b7d53caf-5b95-474a-8203-b3df729d9009_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..8b9066c6febccd8d9615e1bdcdc672b971c8ee0d --- /dev/null +++ b/2023/MoTIF_ Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution/b7d53caf-5b95-474a-8203-b3df729d9009_content_list.json @@ -0,0 +1,1515 @@ +[ + { + "type": "text", + "text": "MoTIF: Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution", + "text_level": 1, + "bbox": [ + 153, + 128, + 818, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yi-Hsin Chen*", + "bbox": [ + 120, + 203, + 240, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Si-Cun Chen*", + "bbox": [ + 272, + 203, + 385, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yi-Hsin Chen", + "bbox": [ + 426, + 203, + 537, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yen-Yu Lin", + "bbox": [ + 576, + 203, + 673, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Wen-Hsiao Peng", + "bbox": [ + 714, + 203, + 848, + 222 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "National Yang Ming Chiao Tung University, Taiwan", + "bbox": [ + 277, + 222, + 691, + 239 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{yhchen12101, sicun.map1, karta6120}.cs09@nycu.edu.tw", + "bbox": [ + 251, + 241, + 718, + 257 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "lin@cs.nycu.edu.tw wpeng@cs.nctu.edu.tw", + "bbox": [ + 310, + 258, + 660, + 273 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 308, + 313, + 325 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "This work addresses continuous space-time video superresolution (C-STVSR) that aims to up-scale an input video both spatially and temporally by any scaling factors. One key challenge of C-STVSR is to propagate information temporally among the input video frames. To this end, we introduce a space-time local implicit neural function. It has the striking feature of learning forward motion for a continuum of pixels. We motivate the use of forward motion from the perspective of learning individual motion trajectories, as opposed to learning a mixture of motion trajectories with backward motion. To ease motion interpolation, we encode sparsely sampled forward motion extracted from the input video as the contextual input. Along with a reliability-aware splatting and decoding scheme, our framework, termed MoTIF, achieves the state-of-the-art performance on C-STVSR. The source code of MoTIF is available at https://github.com/sichun233746/MoTIF.", + "bbox": [ + 75, + 340, + 473, + 598 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 626, + 209, + 642 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "This work addresses continuous space-time video super-resolution (C-STVSR). The task of C-STVSR is to increase simultaneously the spatial resolution and temporal frame-rate of an input video by any scaling factors with only one single model. It is to be distinguished from fixed-scale space-time video super-resolution (F-STVSR), for which a model is learned to perform space-time super-resolution for only one specific spatiotemporal scale. As compared to F-STVSR, C-STVSR is more flexible and practical in real-world scenarios, which often call for up-scaling low-resolution and low-frame-rate videos of varied spatiotemporal resolutions on heterogeneous video-enabled devices.", + "bbox": [ + 75, + 651, + 468, + 832 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "C-STVSR remains largely under-explored. One trivial solution to C-STVSR is to perform continuous video frame interpolation [2, 11, 21, 20, 33], followed by interpolat", + "bbox": [ + 75, + 832, + 468, + 878 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/39144613a19aede586c77afe17756adac61f39238450fd7b45959db2054907c9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 501, + 305, + 862, + 421 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/38d9a3fd6b64247fc764f542f771d8cacf18925c25928873bef48fcfe362ccc0.jpg", + "image_caption": [ + "(a) VideoINR [6]", + "(b) MoTIF", + "Figure 1: Illustrations of (a) VideoINR [6] and (b) MoTIF. The red dash lines highlight their major differences." + ], + "image_footnote": [], + "bbox": [ + 501, + 440, + 861, + 601 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "ing individual video frames with continuous image superresolution [5, 34, 14], or the other way around. However, their divide-and-conquer nature of treating C-STVSR as two independent sub-tasks-i.e. temporal interpolation and spatial super-resolution-misses the opportunity to attain the best achievable performance. By leveraging the spatiotemporal information in an end-to-end optimized fashion, some recent works [10, 31, 32, 9] for F-STVSR adopt a one-stage approach, combining the extraction of individual frame features and the temporal aggregation of these features as a unified task. Nonetheless, these F-STVSR methods can hardly be extended straightforwardly to C-STVSR.", + "bbox": [ + 496, + 672, + 890, + 853 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Inspired by continuous image super-resolution [5, 34, 14], VideoINR [6] presents an early attempt at C-STVSR. Given any query coordinates $(x,y,t)$ in the continuous spa", + "bbox": [ + 500, + 854, + 890, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Both authors contributed equally to this work.", + "bbox": [ + 94, + 886, + 346, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "23131", + "bbox": [ + 478, + 944, + 517, + 957 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3ef7e9f04a832905fd15a3c78be5c8e69f60141b875bc0bba2e5bdce5f2d80b9.jpg", + "image_caption": [ + "(a) Backward Motion" + ], + "image_footnote": [], + "bbox": [ + 84, + 93, + 271, + 227 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/b89b8a2e7190f9e02e7bb5002ac83e0a54ae9771693afc4867431f884f84a08c.jpg", + "image_caption": [ + "(b) Forward Motion", + "Figure 2: Illustration of backward and forward motion. The circles denote pixels accessible in the input video. The dashed lines display the motion trajectories of pixels in the reference frame at $t = 0$ . The blue arrows are backward/forward motion in the form of displacement vectors. The red arrows show the displacement vectors for an arbitrary time instance that are to be predicted from blue arrows." + ], + "image_footnote": [], + "bbox": [ + 277, + 93, + 464, + 228 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tiotemporal space, it takes the latent representation of the input video as the contextual information to decode the corresponding RGB value. The process involves learning a spatial implicit neural function (S-INF in Fig. 1 (a)) for super-resoluting the frame features, followed by learning another temporal implicit neural function (T-INF in Fig. 1 (a)) to generate motion estimates at time $t$ to backward warp the super-resoluted frame features. However, learning implicitly backward motion (indicating displacement vectors that identify matching pixels/features in the reference frame) as a function of time is challenging. Essentially, the backward motion at the same spatial coordinates $(x,y)$ yet at different time instances $t$ may capture the motion trajectories of different pixels/features in the reference frame. For example, in Fig. 2 (a), the backward motion vectors of $p_2$ at $t = 1$ and $t = 2$ are governed by the two distinct motion trajectories that originate from pixels $p_1$ and $p_2$ in the reference frame at $t = 0$ , respectively. In other words, the backward motion vectors at $p_2$ , when viewed as a function of time, are a mixture of multiple motion trajectories. This could potentially introduce undesirable randomness and discontinuities in the resulting time function, which must be learned by TINF in Fig. 1 (a). Furthermore, learning implicitly such a time function based solely on frame features complicates the task.", + "bbox": [ + 75, + 383, + 468, + 760 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To circumvent the aforementioned issues, we propose learning forward motion of pixels in the form of motion trajectories with a space-time implicit neural function (STINF in Fig. 1 (b)). Considering each reference frame in the input video as sitting at the origin in time, our ST-INF takes $(x,y,t)$ as input and outputs a displacement vector that specifies where the pixel at the coordinates $(x,y)$ of the reference frame will appear in a synthesized frame at time $t$ . That is, it encodes the motion trajectory of the", + "bbox": [ + 75, + 763, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/e37193d5139a9b5eea1dbbf3728ca91d8dc5edd3083bde821d0542fd64d96090.jpg", + "image_caption": [ + "Figure 3: Illustration of fixed-scale video frame interpolation (F-VFI), continuous video frame interpolation (C-VFI), fixed-scale video super-resolution (F-VSR), fixed-scale space-time video super-resolution (F-STVSR), TM-Net [32], and continuous space-time video super-resolution (C-STVSR) in terms of their supported space-time scales." + ], + "image_footnote": [], + "bbox": [ + 598, + 93, + 794, + 204 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "pixel at $(x,y)$ , e.g. the highlighted motion trajectory of $p_2$ in the reference frame at $t = 0$ in Fig. 2 (b). Moreover, to facilitate the learning of such a neural function in an explicit way, we supply forward optical flow maps estimated between reference frames as the contextual information (i.e. $M_{0\\rightarrow 1}^{L}, M_{1\\rightarrow 0}^{L}$ in Fig. 1 (b)). Our space-time neural function is also learned to predict the reliability of every motion trajectory (i.e. $\\hat{Z}_{0\\rightarrow t}^{H}, \\hat{Z}_{1\\rightarrow t}^{H}$ in Fig. 1 (b)), which is essential to ensure the quality of forward warping. Explicit motion modeling allows us to extract rough reliability estimates from the input video for better prediction.", + "bbox": [ + 496, + 316, + 890, + 484 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Fig. 1 (b) depicts our end-to-end trainable C-STVSR framework, MoTIF. The main contributions of our work include: (1) we propose a space-time local implicit neural function that predicts forward motion and its reliability in a continuous manner; (2) we propose a reliability-aware splatting and decoding scheme that fuses simultaneously information from multiple reference frames; and (3) our MoTIF achieves the state-of-the-art performance on C-STVSR and provides out-of-distribution generalization.", + "bbox": [ + 496, + 484, + 890, + 619 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 633, + 640, + 648 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "This section surveys methods for video frame interpolation, video super-resolution, and space-time video super-resolution. Fig. 3 presents a Venn diagram to illustrate how C-STVSR, the focus of our work, is related to these methods in terms of their supported space-time scales. As shown, the fixed-scale methods-e.g. fixed-scale video super-resolution [4], fixed-scale video frame interpolation [1, 13] and F-STVSR [9, 31, 10]-perform only one specific type of space-time interpolation. Their supported space-time scales are visualized as singletons in Fig. 3. In comparison, the continuous-scale methods-such as continuous video frame interpolation [2, 11, 21, 20, 33] and TMNet[32]-are able to cover a continuum of temporal scales. Of these approaches, C-STVSR [6] is the most flexible and challenging one, with its supported space-time scales covering the entire space-time space.", + "bbox": [ + 496, + 657, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "23132", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Video Frame Interpolation", + "text_level": 1, + "bbox": [ + 76, + 90, + 318, + 107 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Video frame interpolation [2, 11, 21, 33, 17, 13, 1] aims to increase the frame rate of a video by interpolating between existing reference frames. The key to successful frame interpolation is to predict how the pixels/features of the reference frames progress temporally to the interpolated frame. The flow-based methods [20, 2, 21, 19, 16, 11] rely on optical flow maps to propagate features/pixels from the neighboring reference frames, whereas the kernel-based methods [13, 7, 8] estimate motion implicitly as kernels for motion compensation with deformable convolution. Most flow-based approaches adopt backward warping [11, 16, 23, 22], but more recently, forward warping [2, 20, 21, 19] emerges as an attractive alternative. Forward warping, however, is faced with the challenge that multiple features/pixels in the reference frame may be mapped to the same location in the target frame. To tackle this issue, Niklaus et al. [21] introduce softmax splatting, weighting the conflicting features/pixels according to the reliability of their forward motion.", + "bbox": [ + 75, + 112, + 472, + 400 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Video Super-Resolution", + "text_level": 1, + "bbox": [ + 76, + 407, + 294, + 424 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Video super-resolution is to increase the spatial resolution of a video. Its central theme is to exploit temporal information from neighboring frames in order to complement a low-resolution video frame in recovering its missing high-frequency details. Early deep learning-based methods [27, 3, 24, 35, 4] rely on optical flows to align the features/pixels of the neighboring frames. However, optical flow estimation can be expensive. As such, Tian et al. [29] adopt deformable convolution for temporal alignment. Wang et al.[30] extend the idea to perform temporal alignment in a coarse-to-fine manner. These works target fixed-scale video super-resolution.", + "bbox": [ + 75, + 431, + 472, + 613 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Space-Time Video Super-Resolution", + "text_level": 1, + "bbox": [ + 76, + 619, + 390, + 637 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Recognizing that both video frame interpolation and video super-resolution involve aggregating temporal information from neighboring frames, Haris et al. [10] adopt a unified network to address space-time video superresolution (STVSR). STVSR is much more challenging than the previous two tasks, as the low-resolution neighboring frames are the only source of information to interpolate a high-resolution video frame. Along this line of research, Xiang et al. [31] propose using bidirectional deformable ConvLSTM to mine useful space-time information from the input video in an end-to-end fashion. Based on [31], Xu et al. [32] introduce a temporal modulation block, which allows STVSR to be continuous in the temporal scale. By contrast, both [10] and [31] support only F-STVSR.", + "bbox": [ + 75, + 643, + 468, + 854 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "More recently, Chen et al. [6] present the first work on end-to-end learned C-STVSR, allowing both the spatial and temporal scales to be continuous. Inspired by [5], which", + "bbox": [ + 75, + 854, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "learns local implicit neural functions for continuous image super-resolution, their C-STVSR scheme includes a spatial and a temporal implicit neural function. The former generates the pixel features at any given spatial coordinates $(x,y)$ for super-resolution, while the latter predicts the backward motion for any spatiotemporal coordinates $(x,y,t)$ to propagate temporally the resulting features to time $t$ . Both neural functions are local; they refer to neighboring latents extracted from the input video as additional contextual information.", + "bbox": [ + 496, + 90, + 893, + 242 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed Method", + "text_level": 1, + "bbox": [ + 498, + 261, + 671, + 279 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given two low-resolution RGB video frames $I_0^L, I_1^L \\in \\mathbb{R}^{3 \\times H \\times W}$ of size $H \\times W$ , our task is to interpolate a high-resolution video frame $I_t^H \\in \\mathbb{R}^{3 \\times H' \\times W'}$ with an arbitrary scale $s = W'/W = H'/H \\geq 1$ and at any time $t \\in [0,1]$ .", + "bbox": [ + 498, + 287, + 892, + 351 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. System Overview", + "text_level": 1, + "bbox": [ + 498, + 364, + 669, + 381 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Fig. 4 depicts our proposed MoTIF, which comprises four major components and operates as follows. First, given $I_0^L$ and $I_1^L$ , (1) the encoder $E_I$ converts them into their latent representations $F_0^L, F_1^L, F_{(0,1)}^L \\in \\mathbb{R}^{C \\times H \\times W}$ , where $F_{(0,1)}^L$ serves as a rough estimate of the feature of the target frame $I_t^H$ . Similar to recent STVSR works [32, 6], we adopt the off-the-shelf video-based encoder from [31], which fuses information from both $I_0^L$ and $I_1^L$ in generating $F_0^L, F_1^L$ and $F_{(0,1)}^L$ . Second, (2) the spatial local implicit neural function (S-INF) is queried to super-resolute $F_0^L, F_1^L$ as $F_0^H, F_1^H \\in \\mathbb{R}^{C \\times H' \\times W'}$ , respectively. Our S-INF follows the design of LIIF [5]. Third, considering $I_0^L$ as sitting at the origin in time, (3) the motion encoder $E_M$ encodes $M_{0\\to 1}^L \\in \\mathbb{R}^{2 \\times H \\times W}$ -namely, the forward optical flow map capturing the forward motion from $I_0^L$ to $I_1^L$ together with its reliability map $Z_{0\\to 1}^L \\in \\mathbb{R}^{3 \\times H \\times W}$ into $T_0^L \\in \\mathbb{R}^{C \\times H \\times W}$ . The optical flow estimation is not always perfect; $Z_{0\\to 1}^L$ indicates how reliable $M_{0\\to 1}^L$ is across spatial locations $(x,y)$ (Section 3.2). Forth, using $T_0^L$ as the motion latent, (4) our space-time local implicit neural function (ST-INF) renders a high-resolution, forward motion map $\\hat{M}_{0\\to t}^H \\in \\mathbb{R}^{2 \\times H' \\times W'}$ and its reliability map $\\hat{Z}_{0\\to t}^H \\in \\mathbb{R}^{H' \\times W'}$ according to the query space-time coordinates $(x,y,t)$ . $\\hat{M}_{0\\to t}^H$ specifies the forward motion of the features in $F_0^H$ and is utilized to forward warp $F_0^H$ to $F_t^H$ (Section 3.2). The same motion encoding, rendering and warping processes are repeated for $I_1^L$ , in aggregating temporally the information from all the reference frames. Lastly, we follow [21] to perform softmax splatting to create $F_t^H$ and $Z_t^H$ , which are further combined with $F_{(0,1)}^H$ to decode the high-resolution video frame $\\hat{I}_t^H$ at time $t$ (Section 3.3). $Z_t^H$ indicates how good $F_t^H$ is across spatial locations. It is used to condition the pixel-based decoding of the RGB values from $F_t^H$ and $F_{(0,1)}^H$ .", + "bbox": [ + 496, + 388, + 893, + 904 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "23133", + "bbox": [ + 478, + 944, + 517, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/fd021243518579d2117031cba3751aecaa938f5b71b2e57b52ad20d79abeaec2.jpg", + "image_caption": [ + "Figure 4: The proposed MoTIF for C-STVSR, where the dash double arrows represent the shared-weight networks." + ], + "image_footnote": [], + "bbox": [ + 89, + 90, + 888, + 402 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/4cecf0574073ec4985d16ce27bc0e2fce6393bf8c6db66dd3dee6b374c7a266b.jpg", + "image_caption": [ + "Figure 5: Illustration of low-resolution coordinates (blue dots) and high-resolution coordinates (green dots)." + ], + "image_footnote": [], + "bbox": [ + 151, + 443, + 225, + 520 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/d916f359c3b405c8710b64654dcdf7953ba10365986bc9ea84c9d5e9f5d2ad2d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 236, + 443, + 310, + 520 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/4587728de2dedea34155434d0040698721766c0edd1d588870d81513666f11eb.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 318, + 444, + 392, + 520 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Space-time Local Implicit Neural Functions", + "text_level": 1, + "bbox": [ + 76, + 579, + 449, + 595 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The very core of our C-STVSR scheme is the space-time local implicit neural function (ST-INF) in Fig. 4. Our STINF has the striking feature of predicting forward motion rather than backward motion. That is, it specifies how the feature at coordinates $p = (x,y)$ in $F_0^H$ or $F_1^H$ are propagated temporally to any designated time $t$ . The forward motion is represented in the form of displacement vectors along with their reliability values. For example, to get the forward motion $\\hat{M}_{0\\rightarrow t}^{H}(p)$ and its reliability value $\\hat{Z}_{0\\rightarrow t}^{H}(p)$ for propagating the feature $F_0^H (p)$ of $F_0^H$ at $p = (x,y)$ , it is queried as follows:", + "bbox": [ + 75, + 603, + 468, + 770 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\{\\hat {Z} _ {t _ {r} \\rightarrow t} ^ {H} (p), \\hat {M} _ {t _ {r} \\rightarrow t} ^ {H} (p) \\} = f _ {\\theta} (v _ {r}, p - p _ {r}, t - t _ {r}), \\quad (1)\n$$\n", + "text_format": "latex", + "bbox": [ + 101, + 779, + 468, + 800 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $v_{r} = T_{0}^{L}(p_{r})$ is the motion latent at $p_{r} = (x_{r},y_{r})$ that is nearest to the query coordinates $p = (x,y)$ , $t_r = 0$ is the temporal location where the reference frame $I_0^L$ sits, and $\\theta$ is the network parameters. Fig. 5 depicts an example of the geometrical relationship between $p$ and $p_{r}$ . The sum $p + \\hat{M}_{0\\to t}^{H}(p)$ gives the landing location of the query feature", + "bbox": [ + 75, + 809, + 470, + 905 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$F_0^H (p)$ at time $t$ . In much the same way, $\\hat{M}_{1\\rightarrow t}^{H}(p)$ and $\\hat{Z}_{1\\rightarrow t}^{H}(p)$ for propagating the feature $F_{1}^{H}(p)$ can be obtained by having in Eq. (1) $v_{r} = T_{1}^{L}(p_{r})$ and $t_r = 1$ , i.e. the temporal location of $I_1^L$ .", + "bbox": [ + 498, + 445, + 890, + 508 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In Eq. (1), both $p = (x, y)$ and $t$ can take any values. Together they can refer to any space-time coordinates. Therefore, $f_{\\theta}$ is able to generate forward motion in a continuous manner to warp $F_0^H, F_1^H$ of any spatial resolution to any time instance $t \\in [0, 1]$ . However, in essence, $f_{\\theta}$ is a local function that predicts forward motion in the vicinity of the reference space-time coordinates $p_r, t_r$ by referring to the local motion latent $v_r$ .", + "bbox": [ + 496, + 508, + 892, + 630 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Learning motion trajectories. Learning forward motion can be interpreted as learning motion trajectories along the temporal axis. To see this, in Eq. (1), we fix $p = (x,y)$ at some coordinates, e.g. $p_2$ in Fig. 2 (b), take $t_r = 0$ , and view $f_{\\theta}$ as a function of time $t$ . With this setting, the forward motion predicted by $f_{\\theta}$ specifies a displacement vector indicating where $p_2$ should appear at time $t$ . Collectively, the displacement vectors evaluated at different time instances $t$ 's define the motion trajectory of $p_2$ . Generally, this motion trajectory is a smooth function of time and is relatively easier to approximate. While it is completely feasible to change the output semantics of $f_{\\theta}$ to learn backward motion, the resulting time function can be discontinuous. The reason is illustrated in Fig. 2 (a), where fixing the query coordinates $p$ at $p_2$ , $f_{\\theta}$ returns at every time instance $t$ a backward displacement vector identifying the location of the matching pixel/feature in the reference frame", + "bbox": [ + 496, + 643, + 893, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "23134", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "at $t_r = 0$ . In this case, the displacement vectors evaluated for the same $p_2$ yet at different time instances $t$ 's may correspond to the distinct motion trajectories of different matching pixels. This suggests that $f_{\\theta}$ has to model a less smooth function of time. Section 5.1 presents an ablation study to justify the use of forward motion.", + "bbox": [ + 75, + 90, + 468, + 181 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Learning motion latents. Predicting the forward motion of a pixel (or a feature vector) at any given $p = (x, y)$ and for any $t$ is a non-trivial task. We formulate the problem as learning a $f_{\\theta}$ that interpolates between forward motion sampled sparsely in both the spatial and temporal dimensions. This is achieved by providing $f_{\\theta}$ with the motion latent that encodes the sparsely sampled forward motion as the contextual input. Take Eq. (1) as an example, where $f_{\\theta}$ is queried to predict the forward motion of $F_0^H(p)$ for time $t$ . The prediction is conditioned on the nearest motion latent $T_0^L(p_r)$ , which captures the forward motion $M_{0 \\to 1}^L$ estimated from $I_0^L$ to $I_1^L$ in the vicinity of $p_r$ . In this work, we adopt Raft-lite [28] to estimate the forward optical flow map $M_{0 \\to 1}^L$ . Recognizing that the flow estimation is often not perfect, we follow [19] to quantify the reliability of the resulting flow map $M_{0 \\to 1}^L$ based on three metrics, including (1) the intensity warping error, (2) the flow warping error, and (3) the local variances of the flow map. Further details of these metrics are provided in the supplementary document. The reliability evaluation with each of these metrics yields a real-valued map of size the same as $M_{0 \\to 1}^L$ , reflecting the reliability of $M_{0 \\to 1}^L$ across spatial locations. These maps are concatenated channel-wisely to form $Z_{0 \\to 1}^L$ , which is encoded jointly with $M_{0 \\to 1}^L$ by the motion encoder $E_M$ as $T_0^L$ . Section 5.1 shows that $Z_{0 \\to 1}^L$ benefits $f_{\\theta}$ considerably in interpolating forward motion.", + "bbox": [ + 75, + 200, + 472, + 593 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Multi-Frame Forward Warping", + "text_level": 1, + "bbox": [ + 76, + 609, + 357, + 626 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To come up with a prediction of $F_{t}^{H}$ for decoding a high-resolution video frame $\\hat{I}_{t}^{H}$ at time $t$ , we aggregate temporally $F_{0}^{H}, F_{1}^{H}$ , each of which represents the high-resolution feature of a reference frame (Fig. 4). Inspired by [21], we adopt softmax splatting to resolve the potential issue that multiple features from $F_{0}^{H}, F_{1}^{H}$ or both may be forward warped to the same location in $F_{t}^{H}$ . Considering that our task is to interpolate and super-resolute a new frame from the ground up, we perform softmax splatting after $F_{0}^{H}, F_{1}^{H}$ have both been forward warped to time $t$ . Our approach differs from [21], which targets video frame interpolation and applies softmax splatting separately to individual reference frames for late fusion. In symbols, we have", + "bbox": [ + 75, + 633, + 468, + 832 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nF _ {t} ^ {H} (p) = \\sum_ {i = 0} ^ {1} \\sum_ {q} \\frac {b (u) \\cdot \\exp (\\alpha \\cdot \\hat {Z} _ {i \\rightarrow t} ^ {H} (q)) \\cdot F _ {i} ^ {H} (q)}{\\sum_ {i = 0} ^ {1} \\sum_ {q} b (u) \\cdot \\exp (\\alpha \\cdot \\hat {Z} _ {i \\rightarrow t} ^ {H} (q))}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 848, + 468, + 904 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the feature $F_{t}^{H}(p)$ of $F_{t}^{H}$ at $p$ is formulated as a weighted sum of all the reference features $F_{0}^{H}(q), F_{1}^{H}(q)$ with the weighting determined by the distance $u = p - (q + \\hat{M}_{i\\rightarrow t}^{H}(q))$ , the bilinear kernel $b(u) = \\max(0, 1 - |u_x|)$ and $\\max(0, 1 - |u_y|)$ , as well as the reliability $\\hat{Z}_{i\\rightarrow t}^{H}(q)$ of the forward motion at $q$ . $\\alpha = -20$ is the temperature of the softmax operation. Since the bilinear kernel has a finite support, only those $F_{0}^{H}(q), F_{1}^{H}(q)$ warped to the neighborhood of $p$ will actually contribute to the evaluation of $F_{t}^{H}(p)$ .", + "bbox": [ + 496, + 90, + 890, + 227 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Additionally, we generate a map $Z_{t}^{H}$ to indicate how good $F_{t}^{H}$ is across spatial locations. Intuitively, if $F_{t}^{H}(p)$ is synthesized from those $F_{0}^{H}(q), F_{1}^{H}(q)$ whose forward motion is unreliable, the quality of $F_{t}^{H}(p)$ should be downgraded. $Z_{t}^{H}(p)$ serves as a conditioning factor for decoding the RGB values at $p$ , and is obtained by", + "bbox": [ + 496, + 228, + 890, + 319 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nZ _ {t} ^ {H} (p) = \\max _ {i = 0, 1} \\max _ {q} b (u) \\cdot \\exp \\left(\\alpha \\cdot \\hat {Z} _ {i \\rightarrow t} ^ {H} (q)\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 542, + 325, + 890, + 349 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "which takes the maximum value among the (unnormized) contributing weights from $F_0^H(q), F_1^H(q)$ . When none of these contributing $F_0^H(q), F_1^H(q)$ has reliable forward motion, the quality of $F_t^H(p)$ is regarded as poor.", + "bbox": [ + 496, + 357, + 890, + 417 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To synthesize a high-resolution video frame $\\hat{I}_t^H$ , we implement a pixel-wise decoder that incorporates a multi-layer perceptron. It decodes the RGB values at $p$ by taking as inputs $F_t^H(p)$ , $F_{(0,1)}^H(p)$ , $Z_t^H(p)$ , and $t$ (the rightmost part of Fig. 4).", + "bbox": [ + 496, + 417, + 890, + 492 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Training Objective", + "text_level": 1, + "bbox": [ + 500, + 500, + 681, + 517 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We train our MoTIF end-to-end with the following objective:", + "bbox": [ + 496, + 523, + 890, + 554 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathcal {L} _ {\\text {c h a r}} \\left(\\hat {I} _ {t} ^ {H}, I _ {t} ^ {H}\\right) + \\beta \\sum_ {i = 0} ^ {1} \\mathcal {L} _ {\\text {c h a r}} \\left(\\hat {M} _ {i \\rightarrow t} ^ {H}, M _ {i \\rightarrow t} ^ {H}\\right), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 561, + 890, + 602 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{char}(\\hat{x},x) = \\sqrt{\\|\\hat{x} - x\\|^2 + \\epsilon^2}$ is the Charbonnier loss [12] and $\\beta$ is a hyper-parameter. $\\epsilon, \\beta$ are set empirically to $10^{-3}$ and 0.01, respectively. Our objective requires both the decoded frame $\\hat{I}_t^H$ and the predicted forward motion $\\hat{M}_{i\\rightarrow t}^{H}$ to approximate their respective ground-truths.", + "bbox": [ + 496, + 611, + 890, + 688 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.5. Comparison with Prior Works", + "text_level": 1, + "bbox": [ + 500, + 696, + 769, + 712 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Both our MoTIF and VideoINR [6] use implicit neural functions to tackle space-time video super-resolution (STVSR). As illustrated in Fig. 1, our MoTIF differs from VideoINR [6] in three significant ways:", + "bbox": [ + 496, + 719, + 890, + 779 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "First, for the C-STVSR task, our MoTIF uses forward motion rather than backward motion. This aspect in its own right has a significant impact on the quality of the generated videos (Section 5.1 and Table 4).", + "bbox": [ + 496, + 779, + 890, + 839 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Second, our MoTIF models motion explicitly rather than implicitly. This allows our ST-INF to directly learn to interpolate between motion trajectories derived from a pretrained optical flow estimation model. The supplementary", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "23135", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "document provides additional results, showing that our MoTIF can work well with well-behaved, off-the-shelf optical flow estimation networks. Using explicit motion also allows us to evaluate the reliability information $Z_{0\\rightarrow 1}^{L}, Z_{1\\rightarrow 0}^{L}$ based on the input video for better predicting $\\hat{Z}_{0\\rightarrow t}^{H}, \\hat{Z}_{1\\rightarrow t}^{H}$ (see Fig. 4).", + "bbox": [ + 75, + 90, + 467, + 181 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Third, our MoTIF introduces the reliability-aware splatting and decoding schemes, which are not seen in VideoINR [6]. Their benefits are studied in Section 5.1 and Table 6.", + "bbox": [ + 75, + 181, + 467, + 241 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Different from [21], our reliability-aware splatting adopts early fusion of reference frames by forward warping all the reference features to the target frame according to Eq. (2). In contrast, [21] applies softmax splatting to each individual reference frame, followed by late fusing the results with a synthesis network. Our reliability-aware decoding scheme, which incorporates the reliability information for decoding (Eq. (3)) is not seen in [21].", + "bbox": [ + 75, + 243, + 467, + 363 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 378, + 207, + 395 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To our best knowledge, VideoINR [6] is the only prior work that addresses specifically C-STVSR. We thus follow its training and test protocols, unless otherwise specified. VideoINR [6] is also included as the major baseline method.", + "bbox": [ + 75, + 405, + 467, + 465 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training Datasets. We train our model on Adobe240 dataset[26], which contains 133 720P hand-held videos. Of these videos, 100 are used for training, 16 for validation, and 17 for test. In each video, we take 9 consecutive frames to form a training sample, where the $1^{\\text{st}}$ and $9^{\\text{th}}$ frames are bicubic down-sampled and used as the low-resolution, low-frame-rate input.", + "bbox": [ + 75, + 474, + 467, + 580 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation. We compare the competing methods on Vid4 [15], Adobe240 [26], and Gopro [18] datasets. Unless otherwise specified, the spatial scaling factor defaults to 4. On Vid4, the temporal scaling factor is fixed at 2 to test single-frame interpolation. On Adobe240-average and Gopro-average, the temporal scaling factor is set to 8 for multi-frame interpolation. Under the same setting, we also report results on Adobe240-center and Gopro-center for only the $1^{\\text{st}}$ , $4^{\\text{th}}$ and $9^{\\text{th}}$ frames (namely, single-frame interpolation).", + "bbox": [ + 75, + 589, + 467, + 739 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Baselines and Quality Metrics. The baseline methods include (1) two-stage F-STVSR methods, namely video frame interpolation (SuperSloMo [11], QVI [33], DAIN [2]) plus video super-resolution (Bicubic Interpolation, EDVR [30], BasicVSR [4]); (2) one-stage F-STVSR methods (Zooming SloMo [31]); (3) two-stage C-STVSR methods, namely continuous video frame interpolation (SuperSloMo [11], DAIN [2]) plus continuous image superresolution (LIIF [5]); (4) one-stage C-STVSR methods (VideoINR [6]); and (5) TMNet [32]. The quality metrics", + "bbox": [ + 75, + 750, + 467, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "are Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index (SSIM) on the Y channel.", + "bbox": [ + 498, + 90, + 888, + 119 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation and Training Details. We adopt the same two-stage training strategy as VideoINR [6]. The spatial scaling factor is set to 4 for the first 450,000 iterations, and is chosen uniformly from $[1,4]$ in the following 150,000 iterations. The training batch size is 24; within each batch, every input frame is down-sampled spatially by the same factor and cropped to $32\\times 32$ . For training stability, we use the ground-truth forward motion in place of the predicted forward motion with a certain probability, the value of which is attenuated from 1 to 0 in the first 150,000 iterations. We adopt Adam optimizer with $\\beta_{1} = 0.9,\\beta_{2} = 0.999$ and cosine annealing to decay the learning rate from $10^{-4}$ to $10^{-7}$ for every 150,000 iterations. For data augmentation, we perform random rotation and horizontal-flipping. Both our S-INF and ST-INF (Fig. 4) are implemented with 3-layer SIRENs [25], the hidden dimensions of which are 64, 64, and 256. More network details are in the supplementary document.", + "bbox": [ + 496, + 127, + 890, + 398 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Comparison with State-of-the-art Methods", + "text_level": 1, + "bbox": [ + 498, + 409, + 862, + 425 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1 presents qualitative results, comparing the competing methods on the F-STVSR task. Both VideoINR [6] and our MoTIF are trained for C-STVSR, whereas the other methods are trained for F-STVSR and their results are excerpted from [6]. Notably, VideoINR-fixed is trained specifically for single-frame interpolation. From Table 1, several observations can be made. (1) Our MoTIF outperforms VideoINR [6] in all the test cases. It also outperforms VideoINR-fixed, although not trained for F-STVSR. (2) While both VideoINR [6] and our MoTIF adopt the same $E_{I}$ encoder from Zooming SloMo [31], VideoINR [6] performs worse than Zooming SloMo [31] under the single-frame interpolation on Vid4, GoPro-Center, and AdobeCenter; on the contrary, our MoTIF is superior to Zooming SloMo [31]. (3) On Vid4, our MoTIF performs slightly worse than TMNet [32]. This may be because TMNet [32] is trained on Vimeo-90K dataset [35], which shares similar characteristics to Vid4. (4) All the one-stage methods (our MoTIF, [32, 6, 31]) perform better than the two-stage methods (video frame interpolation plus video superresolution) due to end-to-end optimization. (5) Our MoTIF (with Raft-lite [28] included) has a similar model size to VideoINR [6]. Section 5 further shows that MoTIF (including Raft) has comparable or even lower GMACs than VideoINR, and thus similar or higher FPS.", + "bbox": [ + 496, + 433, + 890, + 809 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 3 further presents results on the C-STVSR task, with most of the spatiotemporal scaling factors not seen during training. Except TMNet [32], which supports continuous temporal scaling but only $4\\mathrm{x}$ spatial scaling, all the methods are able to achieve C-STVSR. Again, our MoTIF achieves the best performance in all the test cases, con", + "bbox": [ + 496, + 810, + 890, + 898 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "23136", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/ad2bf5d42e5933f2e4baa550b97678e343ecbb1c05738ebf2b02635d160c4721.jpg", + "table_caption": [ + "Table 1: Performance comparison on the F-STVSR task. Red, blue, and green indicate the best, the second best, and the third best performance, respectively. Quality metrics: PSNR/SSIM." + ], + "table_footnote": [], + "table_body": "
VFI\nMethodVSR\nMethodVid4GoPro-CenterGoPro-AverageAdobe-CenterAdobe-AverageParameters\n(Millions)
SuperSloMo [11]Bicubic22.42 / 0.564527.04 / 0.793726.06 / 0.772026.09 / 0.743525.29 / 0.727919.8
SuperSloMo [11]EDVR[30]23.01 / 0.613628.24 / 0.832226.30 / 0.796027.25 / 0.797225.95 / 0.768219.8+20.7
SuperSloMo [11]BasicVSR [4]23.17 / 0.615928.23 / 0.830826.36 / 0.797727.28 / 0.796125.94 / 0.767919.8+6.3
QVI [33]Bicubic [30]22.11 / 0.549826.50 / 0.779125.41 / 0.755425.57 / 0.732424.72 / 0.711429.2
QVI [33]EDVR [30]23.60 / 0.647127.43 / 0.808125.55 / 0.773926.40 / 0.769225.09 / 0.740629.2+20.7
QVI [33]BasicVSR [4]23.15 / 0.642827.44 / 0.807026.27 / 0.795526.43 / 0.768225.20 / 0.742129.2+6.3
DAIN [2]Bicubic22.57 / 0.573226.92 / 0.791126.11 / 0.774026.01 / 0.746125.40 / 0.732124.0
DAIN [2]EDVR [30]23.48 / 0.654728.01 / 0.823926.37 / 0.796427.06 / 0.789526.01 / 0.770324.0+20.7
DAIN [2]BasicVSR [4]23.43 / 0.651428.00 / 0.822726.46 / 0.796627.07 / 0.789026.23 / 0.772524.0+6.3
Zooming SlowMo [31]25.72 / 0.771730.69 / 0.8847-/-30.26 / 0.8821-/-11.10
TMNet [32]25.96 / 0.780330.14 / 0.869228.83 / 0.851429.41 / 0.852428.30 / 0.835412.26
VideoINR-fixed [6]25.78 / 0.773030.73 / 0.8850-/-30.21 / 0.8805-/-11.31
VideoINR [6]25.61 / 0.770930.26 / 0.879229.41 / 0.866929.92 / 0.874629.27 / 0.865111.31
Ours25.79 / 0.774531.04 / 0.887730.04 / 0.877330.63 / 0.883929.82 / 0.875012.55
", + "bbox": [ + 102, + 130, + 864, + 340 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/2ab16a7dd98740953d62b205b70faca010565d8213d8edce77bd3a886b5dfb14.jpg", + "table_caption": [ + "Table 2: PSNR/SSIM performance comparison on the C-STVSR task (on Gopro). Bold indicates the best performance." + ], + "table_footnote": [], + "table_body": "
Temporal ScaleSpatial ScaleSuperSloMo [11] + LIIF [5]DAIN [2] + LIIF [5]TMNet [32]VideoINR [6]Ours
×6×426.70 / 0.798826.71 / 0.799830.49 / 0.886130.78 / 0.895431.56 / 0.9064
×6×623.47 / 0.693123.36 / 0.6902-25.56 / 0.767129.36 / 0.8505
×6×1221.92 / 0.649522.01 / 0.6499-24.02 / 0.690025.81 / 0.7330
×12×425.07 / 0.749125.14 / 0.749726.38 / 0.793127.32 / 0.814127.77 / 0.8230
×12×622.91 / 0.678322.92 / 0.6785-24.68 / 0.735826.78 / 0.7908
×12×1221.61 / 0.645721.78 / 0.6473-23.70 / 0.683024.72 / 0.7108
×16×424.42 / 0.729624.20 / 0.724424.72 / 0.752625.81 / 0.773925.98 / 0.7758
×16×623.28 / 0.688322.80 / 0.6722-23.86 / 0.712325.34 / 0.7527
×16×1221.80 / 0.648122.22 / 0.6420-22.88 / 0.665923.88 / 0.6923
×6×1---32.34 / 0.954534.77 / 0.9696
×1×4--33.02 / 0.920632.26 / 0.919833.84 / 0.9328
", + "bbox": [ + 107, + 380, + 859, + 550 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "firming its better generalization to unseen scaling factors. Notably, on the video frame interpolation task (i.e. temporal scale $= 6$ and spatial scale $= 1$ ), MoTIF outperforms VideoINR [6] by 2.5dB in terms of PSNR. This underlines the merit of using forward motion for better modeling.", + "bbox": [ + 75, + 574, + 468, + 648 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In Fig. 6, our MoTIF shows consistently better subjective quality than VideoINR [6]. More results are provided in the supplementary document.", + "bbox": [ + 75, + 650, + 468, + 696 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5. Complexity Comparison", + "text_level": 1, + "bbox": [ + 76, + 709, + 307, + 727 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3 characterizes the complexity of the competing methods [31, 32, 6]. We follow [31] to report frames per second (FPS) on Vid4 [15] dataset; that is, FPS is evaluated to be the ratio of the total number of output frames to the total runtime for processing the entire dataset. We also report the corresponding multiply-accumulate (MAC) operations per frame. These numbers are evaluated on one Tesla V100. From Table 3, our MoTIF has comparable FPS and GMACs to the other baseline methods on the lower-scale tasks (i.e. temporal scale = 2 and spatial scale = 4) while showing higher FPS and lower GMACs than the base", + "bbox": [ + 75, + 734, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "line methods on the tasks with higher temporal and spatial scales.", + "bbox": [ + 498, + 574, + 890, + 603 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Note that when we increase the temporal scale while fixing the spatial scale, the FPS increases and the MAC per frame decreases. The same observation holds true for all the competing methods. This is because higher temporal scales invoke less frequent feature extraction to generate $F_0^L, F_1^L, F_{(0,1)}^L$ . For example, a temporal scale of 16 (respectively, 2) implies that the feature extraction process is invoked only once every 16 frames (respectively, 2 frames). Given that the total number of frames to be processed is fixed, more frequent feature extraction leads to lower FPS and higher GMACs per frame. It is also seen that the complexity advantage of our MoTIF over VideoINR becomes more obvious when the temporal scale becomes higher and the spatial scale remains fixed. This is mainly because VideoINR backward warps the latent representations $F_0^H, F_1^H, F_{(0,1)}^H \\in \\mathbb{R}^{C \\times H' \\times W'}$ simultaneously and this operation is done twice. In comparison, our MoTIF forward warps the latent $F_0^H, F_1^H \\in \\mathbb{R}^{C \\times H' \\times W'}$ individually and this operation is done only once.", + "bbox": [ + 496, + 613, + 892, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "23137", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b7593228ef1d971b786f849532e0b8fffa6cf0459236ccc4766fbdf5951d1364.jpg", + "image_caption": [ + "Figure 6: Subjective quality comparison. The temporal scaling factor of the upper example is 8 (in-distribution), whereas that of the lower example is 6 (out-of-distribution). Zoom in for better visualization." + ], + "image_footnote": [], + "bbox": [ + 96, + 88, + 872, + 416 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/ff4a38a2106d341b03a63153094c50094c2b09edd1db55e45c1778bcc6dce321.jpg", + "table_caption": [ + "Table 3: Complexity comparison on the C-STVSR task. Red indicates the best performance. Complexity metrics: FPS (↑) / GMACs (↓) per frame. The FPS and GMACs are evaluated based on processing the entire Vid4 [15] dataset on one Tesla V100." + ], + "table_footnote": [], + "table_body": "
Temporal ScaleSpatial ScaleZSM [31]TMNet[32]VideoINR[6]Ours
×2×425.52 / 42.2724.75 / 45.3616.05 / 51.1815.15 / 52.11
×4×4-23.68 / 46.3021.69 / 36.5920.70 / 33.90
×8×4-22.84 / 46.5726.17 / 26.6527.71 / 21.49
×16×4-21.54 / 48.1529.06 / 21.5042.50 / 14.69
×2×6--11.76 / 69.5113.59 / 70.82
×4×6--15.13 / 54.9317.51 / 47.91
×8×6--17.63 / 44.8521.20 / 32.54
×16×6--18.14 / 40.1825.20 / 24.46
×2×8--9.24 / 95.1910.72 / 97.44
×4×8--10.40 / 80.6113.84 / 68.95
×8×8--11.93 / 70.3416.30 / 49.22
×16×8--14.09 / 66.3223.93 / 35.49
", + "bbox": [ + 205, + 527, + 761, + 691 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.1. Ablation Experiments", + "text_level": 1, + "bbox": [ + 76, + 715, + 284, + 732 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Backward vs. Forward Motion. Table 4 presents results for an ablation experiment that replaces forward motion with backward motion in our MoTIF. This replacement includes the following changes: (1) learning ST-INF to predicting backward motion $\\hat{M}_{t\\rightarrow 0}^{H},\\hat{M}_{t\\rightarrow 1}^{H}$ and their reliability maps $\\hat{Z}_{t\\rightarrow 0}^{H},\\hat{Z}_{t\\rightarrow 1}^{H}$ , (2) applying backward warping with $\\hat{M}_{t\\rightarrow 0}^{H},\\hat{M}_{t\\rightarrow 1}^{H}$ to each reference feature $F_{0}^{H},F_{1}^{H}$ , and (3) synthesizing a high-resolution video frame $\\hat{I}_t^H$ by taking as inputs the two backward warped reference features, their warped reliability maps, $F_{(0,1)}^{H}$ , and $t$ . From Table 4, using", + "bbox": [ + 75, + 750, + 472, + 905 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "backward motion instead of forward motion in MoTIF results in a considerable PSNR drop (0.4-1dB) across the test cases. Our supplementary document provides additional Fourier analyses to compare forward and backward motion.", + "bbox": [ + 496, + 715, + 890, + 777 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Implicit vs. Explicit Motion Modeling. Table 5 presents ablation results based on predicting the high-resolution forward motion without using a pre-trained optical flow estimation network, i.e. the implicit motion modeling. In this case, $F_0^L, F_1^L$ (see Fig. 4) are used as inputs to our ST-INF. Compared with the explicit method, the implicit method has 0.1-0.4dB PSNR loss. Notably, even with the implicit method, MoTIF outperforms VideoINR by 0.1-0.4dB in", + "bbox": [ + 496, + 779, + 892, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "23138", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/cd5adb101cfbce59a347d8d420f467f2c1559385ceb7a1afdedcf6b47c23e6d1.jpg", + "table_caption": [ + "Table 4: Backward vs. forward motion in MoTIF. Quality metrics: PSNR/SSIM. Bold indicates the best performance." + ], + "table_footnote": [], + "table_body": "
BackwardForward
Vid425.35 / 0.769625.79 / 0.7745
GoPro-Center29.98 / 0.876531.04 / 0.8877
GoPro-Average29.38 / 0.869330.04 / 0.8773
Adobe-Center29.73 / 0.872330.63 / 0.8839
Adobe-Average29.14 / 0.865829.82 / 0.8750
", + "bbox": [ + 133, + 130, + 408, + 208 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/8bc2a381033739aecf9ee2df8907a2dc4166ac59f5fac2fd2b7b19b8ca5fd1cd.jpg", + "table_caption": [ + "Table 5: Explicit vs. implicit motion modeling in MoTIF. Quality metrics: PSNR/SSIM. Bold indicates the best performance." + ], + "table_footnote": [], + "table_body": "
VideoINRMoTIF (Implicit)MoTIF (Explicit)
Vid425.61 / 0.770925.71 / 0.772125.79 / 0.7745
GoPro-Center30.26 / 0.879230.58 / 0.885631.04 / 0.8877
GoPro-Average29.41 / 0.866929.81 / 0.874430.04 / 0.8773
Adobe-Center29.92 / 0.874630.24 / 0.879630.63 / 0.8839
Adobe-Average29.27 / 0.865129.59 / 0.871929.82 / 0.8750
", + "bbox": [ + 78, + 273, + 460, + 351 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "PSNR, suggesting that the other components of MoTIF are essential.", + "bbox": [ + 76, + 359, + 467, + 388 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Feature Warping and Reliability Maps. Table 6 presents ablation results to understand the contributions of different components in MoTIF. Four variants of MoTIF are investigated, including (a) using only $F_{(0,1)}^{H}$ for decoding, (b) using both $F_{(0,1)}^{H}$ and $F_{t}^{H}$ for decoding, (c) using $F_{(0,1)}^{H}$ , $F_{t}^{H}$ for decoding while encoding the reliability maps $Z_{0\\to 1}^{L}, Z_{1\\to 0}^{L}$ of forward motion into the motion latents, and (d) the full model (i.e. variant (c) plus $Z_{t}^{H}$ ). From Table 6, the considerable PSNR gain of (b) over (a) indicates that our ST-INF is effective in interpolating forward motion for propagating the reference features. The incremental improvement from (b) to (c) suggests that the reliability maps $Z_{0\\to 1}^{L}, Z_{1\\to 0}^{L}$ help to improve the quality of the interpolated forward motion. Last but not least, the additional use of $Z_{t}^{H}$ in the decoding process ((d) vs. (c)) does allow the decoder to better combine $F_{(0,1)}^{H}$ and $F_{t}^{H}$ .", + "bbox": [ + 76, + 398, + 468, + 652 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Tri-linear Motion and More Reference Frames. Table 7 investigates the benefits of our space-time implicit neural function (ST-INF) by comparing its performance with tri-linear motion interpolation and by showing its applicability to more reference frames. From Table 7, we observe that when ST-INF is replaced with tri-linear motion interpolation-i.e., $\\hat{M}_{0\\rightarrow t}^{H},\\hat{M}_{1\\rightarrow t}^{H}$ are interpolated bilinearly from $M_{0\\rightarrow 1}^{L},M_{1\\rightarrow 0}^{L}$ , respectively-the performance drops by 0.1-0.2dB in PSNR. Although ST-INF provides seemingly moderate gain, its advantage becomes obvious when the number of reference frames goes beyond two. In this case, ST-INF can benefit from encoding more forward motion into the motion latents. Conceptually, this amounts to taking more forward motion samples, which help to construct accurate motion trajectories. In the ablation experiment, two more reference frames $I_{-1}^{L},I_{2}^{L}$", + "bbox": [ + 76, + 657, + 468, + 902 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/f43cdd32fd37ba0362d0a08abbc1b21e9714afbbcb32136889e8b1a639edb131.jpg", + "table_caption": [ + "Table 6: Ablation experiment on individual components. (d) is the proposed MoTIF. Quality metric: PSNR." + ], + "table_footnote": [], + "table_body": "
Settings(a)(b)(c)(d)
FH(0,1)VVVV
FTtVVV
Z0L, Z1LVV
ZHtV
Vid422.3825.2625.6125.79
Gopro-Center26.6830.5430.9731.04
Gopro-Average26.4429.7229.9730.08
Adobe-Center25.8230.0430.4930.63
Adobe-Average25.6129.4029.6829.82
", + "bbox": [ + 527, + 130, + 861, + 267 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/d313db9f56f8651f2845762398df91547678967746cbe90e16f5ef59f72b765b.jpg", + "table_caption": [ + "Table 7: Ablation experiment on tri-linear motion interpolation and multiple reference frames. Quality metrics: PSNR/SSIM." + ], + "table_footnote": [], + "table_body": "
Tri-linear MotionOurs (2 ref.)Ours (4 ref.)
Vid425.57 / 0.772825.79 / 0.774526.32 / 0.7864
GoPro-Center30.89 / 0.886030.96 / 0.886831.44 / 0.9003
GoPro-Average29.93 / 0.875930.08 / 0.878030.77 / 0.8948
Adobe-Center30.42 / 0.881830.63 / 0.883931.03 / 0.8919
Adobe-Average29.64 / 0.872729.82 / 0.875030.37 / 0.8849
", + "bbox": [ + 509, + 340, + 875, + 417 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "are made available; we thus encode jointly information from $\\{M_{0\\rightarrow i}^{L},Z_{0\\rightarrow i}^{L}\\}_{i = -1,1,2}$ as $T_0^L$ , and information from $\\{M_{1\\rightarrow i}^{L},Z_{1\\rightarrow i}^{L}\\}_{i = -1,0,2}$ as $T_{1}^{L}$ . As a consequence, the PSNR improves by 0.5-0.7dB. We expect the gain to be even higher if we generate more motion latents to propagate information from these extra reference frames (instead of only $I_0^L,I_1^L)$ . The simple tri-linear motion interpolation cannot benefit similarly from having more reference frames.", + "bbox": [ + 498, + 434, + 890, + 556 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 573, + 617, + 588 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This paper introduces a C-STVSR framework, known as MoTIF. It features a space-time implicit neural function for encoding forward motion, and a reliability-aware splatting and decoding scheme for fusing spatiotemporal information from multiple reference frames. We show that learning forward motion amounts to learning individual motion trajectories rather than a mixture of motion trajectories as with learning backward motion. In addition, for better aggregating temporal information via forward warping, performing splatting and decoding based on the reliability of forward motion is crucial. With all these techniques combined, MoTIF demonstrates superior quantitative and qualitative performance to the state-of-the-art methods for C-STVSR.", + "bbox": [ + 498, + 599, + 890, + 795 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 500, + 813, + 658, + 830 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work is supported by National Science and Technology Council, Taiwan under Grants NSTC 111-2634-F-A49-010- and MOST 110-2221-E-A49-065-MY3, and National Center for High-performance Computing.", + "bbox": [ + 498, + 839, + 890, + 901 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "23139", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Wenbo Bao, Wei Sheng Lai, Xiaoyun Zhang, Zhiyong Gao, and Ming Hsuan Yang. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), 2020.", + "[32] Gang Xu, Jun Xu, Zhen Li, Liang Wang, Xing Sun, and Ming-Ming Cheng. Temporal modulation network for controllable space-time video super-resolution. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), pages 6388-6397, 2021.", + "[33] Xiangyu Xu, Li Siyao, Wenxiu Sun, Qian Yin, and Ming-Hsuan Yang. *Quadratic Video Interpolation*. 2019.", + "[34] Xingqian Xu, Zhangyang Wang, and Humphrey Shi. Ultrasr: Spatial encoding is a missing key for implicit image function-based arbitrary-scale super-resolution. arXiv preprint arXiv:2103.12716, 2021.", + "[35] Tianfan Xue, Baian Chen, Jiajun Wu, Donglai Wei, and William T Freeman. Video enhancement with task-oriented flow. International Journal of Computer Vision (IJCV), 127(8):1106-1125, 2019." + ], + "bbox": [ + 78, + 92, + 468, + 698 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "23141", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/MoTIF_ Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution/b7d53caf-5b95-474a-8203-b3df729d9009_model.json b/2023/MoTIF_ Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution/b7d53caf-5b95-474a-8203-b3df729d9009_model.json new file mode 100644 index 0000000000000000000000000000000000000000..e98d3c495088c5a7d35397bf4b1ff8fd0f685da0 --- /dev/null +++ b/2023/MoTIF_ Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution/b7d53caf-5b95-474a-8203-b3df729d9009_model.json @@ -0,0 +1,1982 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.155, + 0.13, + 0.819, + 0.177 + ], + "angle": 0, + "content": "MoTIF: Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution" + }, + { + "type": "text", + "bbox": [ + 0.121, + 0.204, + 0.241, + 0.221 + ], + "angle": 0, + "content": "Yi-Hsin Chen*" + }, + { + "type": "text", + "bbox": [ + 0.274, + 0.204, + 0.387, + 0.221 + ], + "angle": 0, + "content": "Si-Cun Chen*" + }, + { + "type": "text", + "bbox": [ + 0.428, + 0.204, + 0.538, + 0.221 + ], + "angle": 0, + "content": "Yi-Hsin Chen" + }, + { + "type": "text", + "bbox": [ + 0.578, + 0.204, + 0.674, + 0.221 + ], + "angle": 0, + "content": "Yen-Yu Lin" + }, + { + "type": "text", + "bbox": [ + 0.715, + 0.204, + 0.849, + 0.223 + ], + "angle": 0, + "content": "Wen-Hsiao Peng" + }, + { + "type": "text", + "bbox": [ + 0.278, + 0.223, + 0.692, + 0.24 + ], + "angle": 0, + "content": "National Yang Ming Chiao Tung University, Taiwan" + }, + { + "type": "text", + "bbox": [ + 0.252, + 0.242, + 0.72, + 0.258 + ], + "angle": 0, + "content": "{yhchen12101, sicun.map1, karta6120}.cs09@nycu.edu.tw" + }, + { + "type": "text", + "bbox": [ + 0.312, + 0.26, + 0.661, + 0.275 + ], + "angle": 0, + "content": "lin@cs.nycu.edu.tw wpeng@cs.nctu.edu.tw" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.309, + 0.314, + 0.326 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.342, + 0.474, + 0.599 + ], + "angle": 0, + "content": "This work addresses continuous space-time video superresolution (C-STVSR) that aims to up-scale an input video both spatially and temporally by any scaling factors. One key challenge of C-STVSR is to propagate information temporally among the input video frames. To this end, we introduce a space-time local implicit neural function. It has the striking feature of learning forward motion for a continuum of pixels. We motivate the use of forward motion from the perspective of learning individual motion trajectories, as opposed to learning a mixture of motion trajectories with backward motion. To ease motion interpolation, we encode sparsely sampled forward motion extracted from the input video as the contextual input. Along with a reliability-aware splatting and decoding scheme, our framework, termed MoTIF, achieves the state-of-the-art performance on C-STVSR. The source code of MoTIF is available at https://github.com/sichun233746/MoTIF." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.627, + 0.21, + 0.643 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.652, + 0.47, + 0.833 + ], + "angle": 0, + "content": "This work addresses continuous space-time video super-resolution (C-STVSR). The task of C-STVSR is to increase simultaneously the spatial resolution and temporal frame-rate of an input video by any scaling factors with only one single model. It is to be distinguished from fixed-scale space-time video super-resolution (F-STVSR), for which a model is learned to perform space-time super-resolution for only one specific spatiotemporal scale. As compared to F-STVSR, C-STVSR is more flexible and practical in real-world scenarios, which often call for up-scaling low-resolution and low-frame-rate videos of varied spatiotemporal resolutions on heterogeneous video-enabled devices." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.833, + 0.47, + 0.879 + ], + "angle": 0, + "content": "C-STVSR remains largely under-explored. One trivial solution to C-STVSR is to perform continuous video frame interpolation [2, 11, 21, 20, 33], followed by interpolat" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.306, + 0.864, + 0.422 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.645, + 0.427, + 0.748, + 0.441 + ], + "angle": 0, + "content": "(a) VideoINR [6]" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.441, + 0.862, + 0.602 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.664, + 0.607, + 0.731, + 0.621 + ], + "angle": 0, + "content": "(b) MoTIF" + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.631, + 0.892, + 0.663 + ], + "angle": 0, + "content": "Figure 1: Illustrations of (a) VideoINR [6] and (b) MoTIF. The red dash lines highlight their major differences." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.673, + 0.892, + 0.854 + ], + "angle": 0, + "content": "ing individual video frames with continuous image superresolution [5, 34, 14], or the other way around. However, their divide-and-conquer nature of treating C-STVSR as two independent sub-tasks-i.e. temporal interpolation and spatial super-resolution-misses the opportunity to attain the best achievable performance. By leveraging the spatiotemporal information in an end-to-end optimized fashion, some recent works [10, 31, 32, 9] for F-STVSR adopt a one-stage approach, combining the extraction of individual frame features and the temporal aggregation of these features as a unified task. Nonetheless, these F-STVSR methods can hardly be extended straightforwardly to C-STVSR." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.856, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Inspired by continuous image super-resolution [5, 34, 14], VideoINR [6] presents an early attempt at C-STVSR. Given any query coordinates \\((x,y,t)\\) in the continuous spa" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.347, + 0.901 + ], + "angle": 0, + "content": "*Both authors contributed equally to this work." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.958 + ], + "angle": 0, + "content": "23131" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.094, + 0.272, + 0.228 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.113, + 0.235, + 0.241, + 0.248 + ], + "angle": 0, + "content": "(a) Backward Motion" + }, + { + "type": "image", + "bbox": [ + 0.278, + 0.094, + 0.465, + 0.229 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.311, + 0.235, + 0.43, + 0.248 + ], + "angle": 0, + "content": "(b) Forward Motion" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.26, + 0.47, + 0.366 + ], + "angle": 0, + "content": "Figure 2: Illustration of backward and forward motion. The circles denote pixels accessible in the input video. The dashed lines display the motion trajectories of pixels in the reference frame at \\( t = 0 \\). The blue arrows are backward/forward motion in the form of displacement vectors. The red arrows show the displacement vectors for an arbitrary time instance that are to be predicted from blue arrows." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.385, + 0.47, + 0.761 + ], + "angle": 0, + "content": "tiotemporal space, it takes the latent representation of the input video as the contextual information to decode the corresponding RGB value. The process involves learning a spatial implicit neural function (S-INF in Fig. 1 (a)) for super-resoluting the frame features, followed by learning another temporal implicit neural function (T-INF in Fig. 1 (a)) to generate motion estimates at time \\( t \\) to backward warp the super-resoluted frame features. However, learning implicitly backward motion (indicating displacement vectors that identify matching pixels/features in the reference frame) as a function of time is challenging. Essentially, the backward motion at the same spatial coordinates \\( (x,y) \\) yet at different time instances \\( t \\) may capture the motion trajectories of different pixels/features in the reference frame. For example, in Fig. 2 (a), the backward motion vectors of \\( p_2 \\) at \\( t = 1 \\) and \\( t = 2 \\) are governed by the two distinct motion trajectories that originate from pixels \\( p_1 \\) and \\( p_2 \\) in the reference frame at \\( t = 0 \\), respectively. In other words, the backward motion vectors at \\( p_2 \\), when viewed as a function of time, are a mixture of multiple motion trajectories. This could potentially introduce undesirable randomness and discontinuities in the resulting time function, which must be learned by TINF in Fig. 1 (a). Furthermore, learning implicitly such a time function based solely on frame features complicates the task." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.468, + 0.901 + ], + "angle": 0, + "content": "To circumvent the aforementioned issues, we propose learning forward motion of pixels in the form of motion trajectories with a space-time implicit neural function (STINF in Fig. 1 (b)). Considering each reference frame in the input video as sitting at the origin in time, our ST-INF takes \\((x,y,t)\\) as input and outputs a displacement vector that specifies where the pixel at the coordinates \\((x,y)\\) of the reference frame will appear in a synthesized frame at time \\(t\\). That is, it encodes the motion trajectory of the" + }, + { + "type": "image", + "bbox": [ + 0.599, + 0.094, + 0.795, + 0.205 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.215, + 0.892, + 0.307 + ], + "angle": 0, + "content": "Figure 3: Illustration of fixed-scale video frame interpolation (F-VFI), continuous video frame interpolation (C-VFI), fixed-scale video super-resolution (F-VSR), fixed-scale space-time video super-resolution (F-STVSR), TM-Net [32], and continuous space-time video super-resolution (C-STVSR) in terms of their supported space-time scales." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.318, + 0.892, + 0.485 + ], + "angle": 0, + "content": "pixel at \\((x,y)\\), e.g. the highlighted motion trajectory of \\(p_2\\) in the reference frame at \\(t = 0\\) in Fig. 2 (b). Moreover, to facilitate the learning of such a neural function in an explicit way, we supply forward optical flow maps estimated between reference frames as the contextual information (i.e. \\(M_{0\\rightarrow 1}^{L}, M_{1\\rightarrow 0}^{L}\\) in Fig. 1 (b)). Our space-time neural function is also learned to predict the reliability of every motion trajectory (i.e. \\(\\hat{Z}_{0\\rightarrow t}^{H}, \\hat{Z}_{1\\rightarrow t}^{H}\\) in Fig. 1 (b)), which is essential to ensure the quality of forward warping. Explicit motion modeling allows us to extract rough reliability estimates from the input video for better prediction." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.485, + 0.892, + 0.621 + ], + "angle": 0, + "content": "Fig. 1 (b) depicts our end-to-end trainable C-STVSR framework, MoTIF. The main contributions of our work include: (1) we propose a space-time local implicit neural function that predicts forward motion and its reliability in a continuous manner; (2) we propose a reliability-aware splatting and decoding scheme that fuses simultaneously information from multiple reference frames; and (3) our MoTIF achieves the state-of-the-art performance on C-STVSR and provides out-of-distribution generalization." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.634, + 0.641, + 0.649 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This section surveys methods for video frame interpolation, video super-resolution, and space-time video super-resolution. Fig. 3 presents a Venn diagram to illustrate how C-STVSR, the focus of our work, is related to these methods in terms of their supported space-time scales. As shown, the fixed-scale methods-e.g. fixed-scale video super-resolution [4], fixed-scale video frame interpolation [1, 13] and F-STVSR [9, 31, 10]-perform only one specific type of space-time interpolation. Their supported space-time scales are visualized as singletons in Fig. 3. In comparison, the continuous-scale methods-such as continuous video frame interpolation [2, 11, 21, 20, 33] and TMNet[32]-are able to cover a continuum of temporal scales. Of these approaches, C-STVSR [6] is the most flexible and challenging one, with its supported space-time scales covering the entire space-time space." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23132" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.091, + 0.32, + 0.108 + ], + "angle": 0, + "content": "2.1. Video Frame Interpolation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.113, + 0.473, + 0.401 + ], + "angle": 0, + "content": "Video frame interpolation [2, 11, 21, 33, 17, 13, 1] aims to increase the frame rate of a video by interpolating between existing reference frames. The key to successful frame interpolation is to predict how the pixels/features of the reference frames progress temporally to the interpolated frame. The flow-based methods [20, 2, 21, 19, 16, 11] rely on optical flow maps to propagate features/pixels from the neighboring reference frames, whereas the kernel-based methods [13, 7, 8] estimate motion implicitly as kernels for motion compensation with deformable convolution. Most flow-based approaches adopt backward warping [11, 16, 23, 22], but more recently, forward warping [2, 20, 21, 19] emerges as an attractive alternative. Forward warping, however, is faced with the challenge that multiple features/pixels in the reference frame may be mapped to the same location in the target frame. To tackle this issue, Niklaus et al. [21] introduce softmax splatting, weighting the conflicting features/pixels according to the reliability of their forward motion." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.409, + 0.295, + 0.425 + ], + "angle": 0, + "content": "2.2. Video Super-Resolution" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.432, + 0.473, + 0.614 + ], + "angle": 0, + "content": "Video super-resolution is to increase the spatial resolution of a video. Its central theme is to exploit temporal information from neighboring frames in order to complement a low-resolution video frame in recovering its missing high-frequency details. Early deep learning-based methods [27, 3, 24, 35, 4] rely on optical flows to align the features/pixels of the neighboring frames. However, optical flow estimation can be expensive. As such, Tian et al. [29] adopt deformable convolution for temporal alignment. Wang et al.[30] extend the idea to perform temporal alignment in a coarse-to-fine manner. These works target fixed-scale video super-resolution." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.621, + 0.391, + 0.638 + ], + "angle": 0, + "content": "2.3. Space-Time Video Super-Resolution" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.645, + 0.47, + 0.856 + ], + "angle": 0, + "content": "Recognizing that both video frame interpolation and video super-resolution involve aggregating temporal information from neighboring frames, Haris et al. [10] adopt a unified network to address space-time video superresolution (STVSR). STVSR is much more challenging than the previous two tasks, as the low-resolution neighboring frames are the only source of information to interpolate a high-resolution video frame. Along this line of research, Xiang et al. [31] propose using bidirectional deformable ConvLSTM to mine useful space-time information from the input video in an end-to-end fashion. Based on [31], Xu et al. [32] introduce a temporal modulation block, which allows STVSR to be continuous in the temporal scale. By contrast, both [10] and [31] support only F-STVSR." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.902 + ], + "angle": 0, + "content": "More recently, Chen et al. [6] present the first work on end-to-end learned C-STVSR, allowing both the spatial and temporal scales to be continuous. Inspired by [5], which" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.243 + ], + "angle": 0, + "content": "learns local implicit neural functions for continuous image super-resolution, their C-STVSR scheme includes a spatial and a temporal implicit neural function. The former generates the pixel features at any given spatial coordinates \\((x,y)\\) for super-resolution, while the latter predicts the backward motion for any spatiotemporal coordinates \\((x,y,t)\\) to propagate temporally the resulting features to time \\(t\\). Both neural functions are local; they refer to neighboring latents extracted from the input video as additional contextual information." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.262, + 0.673, + 0.28 + ], + "angle": 0, + "content": "3. Proposed Method" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.289, + 0.893, + 0.352 + ], + "angle": 0, + "content": "Given two low-resolution RGB video frames \\( I_0^L, I_1^L \\in \\mathbb{R}^{3 \\times H \\times W} \\) of size \\( H \\times W \\), our task is to interpolate a high-resolution video frame \\( I_t^H \\in \\mathbb{R}^{3 \\times H' \\times W'} \\) with an arbitrary scale \\( s = W'/W = H'/H \\geq 1 \\) and at any time \\( t \\in [0,1] \\)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.366, + 0.67, + 0.382 + ], + "angle": 0, + "content": "3.1. System Overview" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.39, + 0.895, + 0.905 + ], + "angle": 0, + "content": "Fig. 4 depicts our proposed MoTIF, which comprises four major components and operates as follows. First, given \\( I_0^L \\) and \\( I_1^L \\), (1) the encoder \\( E_I \\) converts them into their latent representations \\( F_0^L, F_1^L, F_{(0,1)}^L \\in \\mathbb{R}^{C \\times H \\times W} \\), where \\( F_{(0,1)}^L \\) serves as a rough estimate of the feature of the target frame \\( I_t^H \\). Similar to recent STVSR works [32, 6], we adopt the off-the-shelf video-based encoder from [31], which fuses information from both \\( I_0^L \\) and \\( I_1^L \\) in generating \\( F_0^L, F_1^L \\) and \\( F_{(0,1)}^L \\). Second, (2) the spatial local implicit neural function (S-INF) is queried to super-resolute \\( F_0^L, F_1^L \\) as \\( F_0^H, F_1^H \\in \\mathbb{R}^{C \\times H' \\times W'} \\), respectively. Our S-INF follows the design of LIIF [5]. Third, considering \\( I_0^L \\) as sitting at the origin in time, (3) the motion encoder \\( E_M \\) encodes \\( M_{0\\to 1}^L \\in \\mathbb{R}^{2 \\times H \\times W} \\) -namely, the forward optical flow map capturing the forward motion from \\( I_0^L \\) to \\( I_1^L \\) together with its reliability map \\( Z_{0\\to 1}^L \\in \\mathbb{R}^{3 \\times H \\times W} \\) into \\( T_0^L \\in \\mathbb{R}^{C \\times H \\times W} \\). The optical flow estimation is not always perfect; \\( Z_{0\\to 1}^L \\) indicates how reliable \\( M_{0\\to 1}^L \\) is across spatial locations \\( (x,y) \\) (Section 3.2). Forth, using \\( T_0^L \\) as the motion latent, (4) our space-time local implicit neural function (ST-INF) renders a high-resolution, forward motion map \\( \\hat{M}_{0\\to t}^H \\in \\mathbb{R}^{2 \\times H' \\times W'} \\) and its reliability map \\( \\hat{Z}_{0\\to t}^H \\in \\mathbb{R}^{H' \\times W'} \\) according to the query space-time coordinates \\( (x,y,t) \\). \\( \\hat{M}_{0\\to t}^H \\) specifies the forward motion of the features in \\( F_0^H \\) and is utilized to forward warp \\( F_0^H \\) to \\( F_t^H \\) (Section 3.2). The same motion encoding, rendering and warping processes are repeated for \\( I_1^L \\), in aggregating temporally the information from all the reference frames. Lastly, we follow [21] to perform softmax splatting to create \\( F_t^H \\) and \\( Z_t^H \\), which are further combined with \\( F_{(0,1)}^H \\) to decode the high-resolution video frame \\( \\hat{I}_t^H \\) at time \\( t \\) (Section 3.3). \\( Z_t^H \\) indicates how good \\( F_t^H \\) is across spatial locations. It is used to condition the pixel-based decoding of the RGB values from \\( F_t^H \\) and \\( F_{(0,1)}^H \\)." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.958 + ], + "angle": 0, + "content": "23133" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.091, + 0.092, + 0.889, + 0.403 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.104, + 0.413, + 0.863, + 0.43 + ], + "angle": 0, + "content": "Figure 4: The proposed MoTIF for C-STVSR, where the dash double arrows represent the shared-weight networks." + }, + { + "type": "image", + "bbox": [ + 0.153, + 0.444, + 0.226, + 0.521 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.238, + 0.444, + 0.311, + 0.521 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.319, + 0.445, + 0.393, + 0.521 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.531, + 0.47, + 0.562 + ], + "angle": 0, + "content": "Figure 5: Illustration of low-resolution coordinates (blue dots) and high-resolution coordinates (green dots)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.58, + 0.45, + 0.597 + ], + "angle": 0, + "content": "3.2. Space-time Local Implicit Neural Functions" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.604, + 0.47, + 0.771 + ], + "angle": 0, + "content": "The very core of our C-STVSR scheme is the space-time local implicit neural function (ST-INF) in Fig. 4. Our STINF has the striking feature of predicting forward motion rather than backward motion. That is, it specifies how the feature at coordinates \\( p = (x,y) \\) in \\( F_0^H \\) or \\( F_1^H \\) are propagated temporally to any designated time \\( t \\). The forward motion is represented in the form of displacement vectors along with their reliability values. For example, to get the forward motion \\( \\hat{M}_{0\\rightarrow t}^{H}(p) \\) and its reliability value \\( \\hat{Z}_{0\\rightarrow t}^{H}(p) \\) for propagating the feature \\( F_0^H (p) \\) of \\( F_0^H \\) at \\( p = (x,y) \\), it is queried as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.102, + 0.78, + 0.47, + 0.801 + ], + "angle": 0, + "content": "\\[\n\\{\\hat {Z} _ {t _ {r} \\rightarrow t} ^ {H} (p), \\hat {M} _ {t _ {r} \\rightarrow t} ^ {H} (p) \\} = f _ {\\theta} (v _ {r}, p - p _ {r}, t - t _ {r}), \\quad (1)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.906 + ], + "angle": 0, + "content": "where \\( v_{r} = T_{0}^{L}(p_{r}) \\) is the motion latent at \\( p_{r} = (x_{r},y_{r}) \\) that is nearest to the query coordinates \\( p = (x,y) \\), \\( t_r = 0 \\) is the temporal location where the reference frame \\( I_0^L \\) sits, and \\( \\theta \\) is the network parameters. Fig. 5 depicts an example of the geometrical relationship between \\( p \\) and \\( p_{r} \\). The sum \\( p + \\hat{M}_{0\\to t}^{H}(p) \\) gives the landing location of the query feature" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.446, + 0.892, + 0.509 + ], + "angle": 0, + "content": "\\(F_0^H (p)\\) at time \\(t\\). In much the same way, \\(\\hat{M}_{1\\rightarrow t}^{H}(p)\\) and \\(\\hat{Z}_{1\\rightarrow t}^{H}(p)\\) for propagating the feature \\(F_{1}^{H}(p)\\) can be obtained by having in Eq. (1) \\(v_{r} = T_{1}^{L}(p_{r})\\) and \\(t_r = 1\\), i.e. the temporal location of \\(I_1^L\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.51, + 0.893, + 0.631 + ], + "angle": 0, + "content": "In Eq. (1), both \\( p = (x, y) \\) and \\( t \\) can take any values. Together they can refer to any space-time coordinates. Therefore, \\( f_{\\theta} \\) is able to generate forward motion in a continuous manner to warp \\( F_0^H, F_1^H \\) of any spatial resolution to any time instance \\( t \\in [0, 1] \\). However, in essence, \\( f_{\\theta} \\) is a local function that predicts forward motion in the vicinity of the reference space-time coordinates \\( p_r, t_r \\) by referring to the local motion latent \\( v_r \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.895, + 0.902 + ], + "angle": 0, + "content": "Learning motion trajectories. Learning forward motion can be interpreted as learning motion trajectories along the temporal axis. To see this, in Eq. (1), we fix \\( p = (x,y) \\) at some coordinates, e.g. \\( p_2 \\) in Fig. 2 (b), take \\( t_r = 0 \\), and view \\( f_{\\theta} \\) as a function of time \\( t \\). With this setting, the forward motion predicted by \\( f_{\\theta} \\) specifies a displacement vector indicating where \\( p_2 \\) should appear at time \\( t \\). Collectively, the displacement vectors evaluated at different time instances \\( t \\)'s define the motion trajectory of \\( p_2 \\). Generally, this motion trajectory is a smooth function of time and is relatively easier to approximate. While it is completely feasible to change the output semantics of \\( f_{\\theta} \\) to learn backward motion, the resulting time function can be discontinuous. The reason is illustrated in Fig. 2 (a), where fixing the query coordinates \\( p \\) at \\( p_2 \\), \\( f_{\\theta} \\) returns at every time instance \\( t \\) a backward displacement vector identifying the location of the matching pixel/feature in the reference frame" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "23134" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.182 + ], + "angle": 0, + "content": "at \\( t_r = 0 \\). In this case, the displacement vectors evaluated for the same \\( p_2 \\) yet at different time instances \\( t \\)'s may correspond to the distinct motion trajectories of different matching pixels. This suggests that \\( f_{\\theta} \\) has to model a less smooth function of time. Section 5.1 presents an ablation study to justify the use of forward motion." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.201, + 0.473, + 0.594 + ], + "angle": 0, + "content": "Learning motion latents. Predicting the forward motion of a pixel (or a feature vector) at any given \\( p = (x, y) \\) and for any \\( t \\) is a non-trivial task. We formulate the problem as learning a \\( f_{\\theta} \\) that interpolates between forward motion sampled sparsely in both the spatial and temporal dimensions. This is achieved by providing \\( f_{\\theta} \\) with the motion latent that encodes the sparsely sampled forward motion as the contextual input. Take Eq. (1) as an example, where \\( f_{\\theta} \\) is queried to predict the forward motion of \\( F_0^H(p) \\) for time \\( t \\). The prediction is conditioned on the nearest motion latent \\( T_0^L(p_r) \\), which captures the forward motion \\( M_{0 \\to 1}^L \\) estimated from \\( I_0^L \\) to \\( I_1^L \\) in the vicinity of \\( p_r \\). In this work, we adopt Raft-lite [28] to estimate the forward optical flow map \\( M_{0 \\to 1}^L \\). Recognizing that the flow estimation is often not perfect, we follow [19] to quantify the reliability of the resulting flow map \\( M_{0 \\to 1}^L \\) based on three metrics, including (1) the intensity warping error, (2) the flow warping error, and (3) the local variances of the flow map. Further details of these metrics are provided in the supplementary document. The reliability evaluation with each of these metrics yields a real-valued map of size the same as \\( M_{0 \\to 1}^L \\), reflecting the reliability of \\( M_{0 \\to 1}^L \\) across spatial locations. These maps are concatenated channel-wisely to form \\( Z_{0 \\to 1}^L \\), which is encoded jointly with \\( M_{0 \\to 1}^L \\) by the motion encoder \\( E_M \\) as \\( T_0^L \\). Section 5.1 shows that \\( Z_{0 \\to 1}^L \\) benefits \\( f_{\\theta} \\) considerably in interpolating forward motion." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.61, + 0.358, + 0.627 + ], + "angle": 0, + "content": "3.3. Multi-Frame Forward Warping" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.635, + 0.47, + 0.833 + ], + "angle": 0, + "content": "To come up with a prediction of \\( F_{t}^{H} \\) for decoding a high-resolution video frame \\( \\hat{I}_{t}^{H} \\) at time \\( t \\), we aggregate temporally \\( F_{0}^{H}, F_{1}^{H} \\), each of which represents the high-resolution feature of a reference frame (Fig. 4). Inspired by [21], we adopt softmax splatting to resolve the potential issue that multiple features from \\( F_{0}^{H}, F_{1}^{H} \\) or both may be forward warped to the same location in \\( F_{t}^{H} \\). Considering that our task is to interpolate and super-resolute a new frame from the ground up, we perform softmax splatting after \\( F_{0}^{H}, F_{1}^{H} \\) have both been forward warped to time \\( t \\). Our approach differs from [21], which targets video frame interpolation and applies softmax splatting separately to individual reference frames for late fusion. In symbols, we have" + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.849, + 0.47, + 0.905 + ], + "angle": 0, + "content": "\\[\nF _ {t} ^ {H} (p) = \\sum_ {i = 0} ^ {1} \\sum_ {q} \\frac {b (u) \\cdot \\exp (\\alpha \\cdot \\hat {Z} _ {i \\rightarrow t} ^ {H} (q)) \\cdot F _ {i} ^ {H} (q)}{\\sum_ {i = 0} ^ {1} \\sum_ {q} b (u) \\cdot \\exp (\\alpha \\cdot \\hat {Z} _ {i \\rightarrow t} ^ {H} (q))}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.091, + 0.892, + 0.228 + ], + "angle": 0, + "content": "where the feature \\(F_{t}^{H}(p)\\) of \\(F_{t}^{H}\\) at \\(p\\) is formulated as a weighted sum of all the reference features \\(F_{0}^{H}(q), F_{1}^{H}(q)\\) with the weighting determined by the distance \\(u = p - (q + \\hat{M}_{i\\rightarrow t}^{H}(q))\\), the bilinear kernel \\(b(u) = \\max(0, 1 - |u_x|)\\) and \\(\\max(0, 1 - |u_y|)\\), as well as the reliability \\(\\hat{Z}_{i\\rightarrow t}^{H}(q)\\) of the forward motion at \\(q\\). \\(\\alpha = -20\\) is the temperature of the softmax operation. Since the bilinear kernel has a finite support, only those \\(F_{0}^{H}(q), F_{1}^{H}(q)\\) warped to the neighborhood of \\(p\\) will actually contribute to the evaluation of \\(F_{t}^{H}(p)\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.229, + 0.892, + 0.32 + ], + "angle": 0, + "content": "Additionally, we generate a map \\( Z_{t}^{H} \\) to indicate how good \\( F_{t}^{H} \\) is across spatial locations. Intuitively, if \\( F_{t}^{H}(p) \\) is synthesized from those \\( F_{0}^{H}(q), F_{1}^{H}(q) \\) whose forward motion is unreliable, the quality of \\( F_{t}^{H}(p) \\) should be downgraded. \\( Z_{t}^{H}(p) \\) serves as a conditioning factor for decoding the RGB values at \\( p \\), and is obtained by" + }, + { + "type": "equation", + "bbox": [ + 0.543, + 0.326, + 0.892, + 0.351 + ], + "angle": 0, + "content": "\\[\nZ _ {t} ^ {H} (p) = \\max _ {i = 0, 1} \\max _ {q} b (u) \\cdot \\exp \\left(\\alpha \\cdot \\hat {Z} _ {i \\rightarrow t} ^ {H} (q)\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.358, + 0.892, + 0.418 + ], + "angle": 0, + "content": "which takes the maximum value among the (unnormized) contributing weights from \\( F_0^H(q), F_1^H(q) \\). When none of these contributing \\( F_0^H(q), F_1^H(q) \\) has reliable forward motion, the quality of \\( F_t^H(p) \\) is regarded as poor." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.418, + 0.892, + 0.493 + ], + "angle": 0, + "content": "To synthesize a high-resolution video frame \\(\\hat{I}_t^H\\), we implement a pixel-wise decoder that incorporates a multi-layer perceptron. It decodes the RGB values at \\(p\\) by taking as inputs \\(F_t^H(p)\\), \\(F_{(0,1)}^H(p)\\), \\(Z_t^H(p)\\), and \\(t\\) (the rightmost part of Fig. 4)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.501, + 0.682, + 0.518 + ], + "angle": 0, + "content": "3.4. Training Objective" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.525, + 0.892, + 0.555 + ], + "angle": 0, + "content": "We train our MoTIF end-to-end with the following objective:" + }, + { + "type": "equation", + "bbox": [ + 0.516, + 0.563, + 0.892, + 0.603 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathcal {L} _ {\\text {c h a r}} \\left(\\hat {I} _ {t} ^ {H}, I _ {t} ^ {H}\\right) + \\beta \\sum_ {i = 0} ^ {1} \\mathcal {L} _ {\\text {c h a r}} \\left(\\hat {M} _ {i \\rightarrow t} ^ {H}, M _ {i \\rightarrow t} ^ {H}\\right), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.612, + 0.892, + 0.689 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{char}(\\hat{x},x) = \\sqrt{\\|\\hat{x} - x\\|^2 + \\epsilon^2}\\) is the Charbonnier loss [12] and \\(\\beta\\) is a hyper-parameter. \\(\\epsilon, \\beta\\) are set empirically to \\(10^{-3}\\) and 0.01, respectively. Our objective requires both the decoded frame \\(\\hat{I}_t^H\\) and the predicted forward motion \\(\\hat{M}_{i\\rightarrow t}^{H}\\) to approximate their respective ground-truths." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.697, + 0.771, + 0.713 + ], + "angle": 0, + "content": "3.5. Comparison with Prior Works" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.78 + ], + "angle": 0, + "content": "Both our MoTIF and VideoINR [6] use implicit neural functions to tackle space-time video super-resolution (STVSR). As illustrated in Fig. 1, our MoTIF differs from VideoINR [6] in three significant ways:" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.84 + ], + "angle": 0, + "content": "First, for the C-STVSR task, our MoTIF uses forward motion rather than backward motion. This aspect in its own right has a significant impact on the quality of the generated videos (Section 5.1 and Table 4)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Second, our MoTIF models motion explicitly rather than implicitly. This allows our ST-INF to directly learn to interpolate between motion trajectories derived from a pretrained optical flow estimation model. The supplementary" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23135" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.468, + 0.182 + ], + "angle": 0, + "content": "document provides additional results, showing that our MoTIF can work well with well-behaved, off-the-shelf optical flow estimation networks. Using explicit motion also allows us to evaluate the reliability information \\( Z_{0\\rightarrow 1}^{L}, Z_{1\\rightarrow 0}^{L} \\) based on the input video for better predicting \\( \\hat{Z}_{0\\rightarrow t}^{H}, \\hat{Z}_{1\\rightarrow t}^{H} \\) (see Fig. 4)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.183, + 0.468, + 0.242 + ], + "angle": 0, + "content": "Third, our MoTIF introduces the reliability-aware splatting and decoding schemes, which are not seen in VideoINR [6]. Their benefits are studied in Section 5.1 and Table 6." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.244, + 0.468, + 0.364 + ], + "angle": 0, + "content": "Different from [21], our reliability-aware splatting adopts early fusion of reference frames by forward warping all the reference features to the target frame according to Eq. (2). In contrast, [21] applies softmax splatting to each individual reference frame, followed by late fusing the results with a synthesis network. Our reliability-aware decoding scheme, which incorporates the reliability information for decoding (Eq. (3)) is not seen in [21]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.38, + 0.208, + 0.396 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.406, + 0.468, + 0.466 + ], + "angle": 0, + "content": "To our best knowledge, VideoINR [6] is the only prior work that addresses specifically C-STVSR. We thus follow its training and test protocols, unless otherwise specified. VideoINR [6] is also included as the major baseline method." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.476, + 0.468, + 0.581 + ], + "angle": 0, + "content": "Training Datasets. We train our model on Adobe240 dataset[26], which contains 133 720P hand-held videos. Of these videos, 100 are used for training, 16 for validation, and 17 for test. In each video, we take 9 consecutive frames to form a training sample, where the \\(1^{\\text{st}}\\) and \\(9^{\\text{th}}\\) frames are bicubic down-sampled and used as the low-resolution, low-frame-rate input." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.59, + 0.468, + 0.741 + ], + "angle": 0, + "content": "Evaluation. We compare the competing methods on Vid4 [15], Adobe240 [26], and Gopro [18] datasets. Unless otherwise specified, the spatial scaling factor defaults to 4. On Vid4, the temporal scaling factor is fixed at 2 to test single-frame interpolation. On Adobe240-average and Gopro-average, the temporal scaling factor is set to 8 for multi-frame interpolation. Under the same setting, we also report results on Adobe240-center and Gopro-center for only the \\(1^{\\text{st}}\\), \\(4^{\\text{th}}\\) and \\(9^{\\text{th}}\\) frames (namely, single-frame interpolation)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Baselines and Quality Metrics. The baseline methods include (1) two-stage F-STVSR methods, namely video frame interpolation (SuperSloMo [11], QVI [33], DAIN [2]) plus video super-resolution (Bicubic Interpolation, EDVR [30], BasicVSR [4]); (2) one-stage F-STVSR methods (Zooming SloMo [31]); (3) two-stage C-STVSR methods, namely continuous video frame interpolation (SuperSloMo [11], DAIN [2]) plus continuous image superresolution (LIIF [5]); (4) one-stage C-STVSR methods (VideoINR [6]); and (5) TMNet [32]. The quality metrics" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.89, + 0.121 + ], + "angle": 0, + "content": "are Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index (SSIM) on the Y channel." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.128, + 0.892, + 0.4 + ], + "angle": 0, + "content": "Implementation and Training Details. We adopt the same two-stage training strategy as VideoINR [6]. The spatial scaling factor is set to 4 for the first 450,000 iterations, and is chosen uniformly from \\([1,4]\\) in the following 150,000 iterations. The training batch size is 24; within each batch, every input frame is down-sampled spatially by the same factor and cropped to \\(32\\times 32\\). For training stability, we use the ground-truth forward motion in place of the predicted forward motion with a certain probability, the value of which is attenuated from 1 to 0 in the first 150,000 iterations. We adopt Adam optimizer with \\(\\beta_{1} = 0.9,\\beta_{2} = 0.999\\) and cosine annealing to decay the learning rate from \\(10^{-4}\\) to \\(10^{-7}\\) for every 150,000 iterations. For data augmentation, we perform random rotation and horizontal-flipping. Both our S-INF and ST-INF (Fig. 4) are implemented with 3-layer SIRENs [25], the hidden dimensions of which are 64, 64, and 256. More network details are in the supplementary document." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.41, + 0.864, + 0.426 + ], + "angle": 0, + "content": "4.1. Comparison with State-of-the-art Methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.434, + 0.892, + 0.81 + ], + "angle": 0, + "content": "Table 1 presents qualitative results, comparing the competing methods on the F-STVSR task. Both VideoINR [6] and our MoTIF are trained for C-STVSR, whereas the other methods are trained for F-STVSR and their results are excerpted from [6]. Notably, VideoINR-fixed is trained specifically for single-frame interpolation. From Table 1, several observations can be made. (1) Our MoTIF outperforms VideoINR [6] in all the test cases. It also outperforms VideoINR-fixed, although not trained for F-STVSR. (2) While both VideoINR [6] and our MoTIF adopt the same \\( E_{I} \\) encoder from Zooming SloMo [31], VideoINR [6] performs worse than Zooming SloMo [31] under the single-frame interpolation on Vid4, GoPro-Center, and AdobeCenter; on the contrary, our MoTIF is superior to Zooming SloMo [31]. (3) On Vid4, our MoTIF performs slightly worse than TMNet [32]. This may be because TMNet [32] is trained on Vimeo-90K dataset [35], which shares similar characteristics to Vid4. (4) All the one-stage methods (our MoTIF, [32, 6, 31]) perform better than the two-stage methods (video frame interpolation plus video superresolution) due to end-to-end optimization. (5) Our MoTIF (with Raft-lite [28] included) has a similar model size to VideoINR [6]. Section 5 further shows that MoTIF (including Raft) has comparable or even lower GMACs than VideoINR, and thus similar or higher FPS." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Table 3 further presents results on the C-STVSR task, with most of the spatiotemporal scaling factors not seen during training. Except TMNet [32], which supports continuous temporal scaling but only \\(4\\mathrm{x}\\) spatial scaling, all the methods are able to achieve C-STVSR. Again, our MoTIF achieves the best performance in all the test cases, con" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23136" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.089, + 0.895, + 0.121 + ], + "angle": 0, + "content": "Table 1: Performance comparison on the F-STVSR task. Red, blue, and green indicate the best, the second best, and the third best performance, respectively. Quality metrics: PSNR/SSIM." + }, + { + "type": "table", + "bbox": [ + 0.103, + 0.131, + 0.865, + 0.342 + ], + "angle": 0, + "content": "
VFI\nMethodVSR\nMethodVid4GoPro-CenterGoPro-AverageAdobe-CenterAdobe-AverageParameters\n(Millions)
SuperSloMo [11]Bicubic22.42 / 0.564527.04 / 0.793726.06 / 0.772026.09 / 0.743525.29 / 0.727919.8
SuperSloMo [11]EDVR[30]23.01 / 0.613628.24 / 0.832226.30 / 0.796027.25 / 0.797225.95 / 0.768219.8+20.7
SuperSloMo [11]BasicVSR [4]23.17 / 0.615928.23 / 0.830826.36 / 0.797727.28 / 0.796125.94 / 0.767919.8+6.3
QVI [33]Bicubic [30]22.11 / 0.549826.50 / 0.779125.41 / 0.755425.57 / 0.732424.72 / 0.711429.2
QVI [33]EDVR [30]23.60 / 0.647127.43 / 0.808125.55 / 0.773926.40 / 0.769225.09 / 0.740629.2+20.7
QVI [33]BasicVSR [4]23.15 / 0.642827.44 / 0.807026.27 / 0.795526.43 / 0.768225.20 / 0.742129.2+6.3
DAIN [2]Bicubic22.57 / 0.573226.92 / 0.791126.11 / 0.774026.01 / 0.746125.40 / 0.732124.0
DAIN [2]EDVR [30]23.48 / 0.654728.01 / 0.823926.37 / 0.796427.06 / 0.789526.01 / 0.770324.0+20.7
DAIN [2]BasicVSR [4]23.43 / 0.651428.00 / 0.822726.46 / 0.796627.07 / 0.789026.23 / 0.772524.0+6.3
Zooming SlowMo [31]25.72 / 0.771730.69 / 0.8847-/-30.26 / 0.8821-/-11.10
TMNet [32]25.96 / 0.780330.14 / 0.869228.83 / 0.851429.41 / 0.852428.30 / 0.835412.26
VideoINR-fixed [6]25.78 / 0.773030.73 / 0.8850-/-30.21 / 0.8805-/-11.31
VideoINR [6]25.61 / 0.770930.26 / 0.879229.41 / 0.866929.92 / 0.874629.27 / 0.865111.31
Ours25.79 / 0.774531.04 / 0.887730.04 / 0.877330.63 / 0.883929.82 / 0.875012.55
" + }, + { + "type": "table_caption", + "bbox": [ + 0.093, + 0.354, + 0.877, + 0.371 + ], + "angle": 0, + "content": "Table 2: PSNR/SSIM performance comparison on the C-STVSR task (on Gopro). Bold indicates the best performance." + }, + { + "type": "table", + "bbox": [ + 0.108, + 0.381, + 0.861, + 0.551 + ], + "angle": 0, + "content": "
Temporal ScaleSpatial ScaleSuperSloMo [11] + LIIF [5]DAIN [2] + LIIF [5]TMNet [32]VideoINR [6]Ours
×6×426.70 / 0.798826.71 / 0.799830.49 / 0.886130.78 / 0.895431.56 / 0.9064
×6×623.47 / 0.693123.36 / 0.6902-25.56 / 0.767129.36 / 0.8505
×6×1221.92 / 0.649522.01 / 0.6499-24.02 / 0.690025.81 / 0.7330
×12×425.07 / 0.749125.14 / 0.749726.38 / 0.793127.32 / 0.814127.77 / 0.8230
×12×622.91 / 0.678322.92 / 0.6785-24.68 / 0.735826.78 / 0.7908
×12×1221.61 / 0.645721.78 / 0.6473-23.70 / 0.683024.72 / 0.7108
×16×424.42 / 0.729624.20 / 0.724424.72 / 0.752625.81 / 0.773925.98 / 0.7758
×16×623.28 / 0.688322.80 / 0.6722-23.86 / 0.712325.34 / 0.7527
×16×1221.80 / 0.648122.22 / 0.6420-22.88 / 0.665923.88 / 0.6923
×6×1---32.34 / 0.954534.77 / 0.9696
×1×4--33.02 / 0.920632.26 / 0.919833.84 / 0.9328
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.575, + 0.47, + 0.65 + ], + "angle": 0, + "content": "firming its better generalization to unseen scaling factors. Notably, on the video frame interpolation task (i.e. temporal scale \\(= 6\\) and spatial scale \\(= 1\\)), MoTIF outperforms VideoINR [6] by 2.5dB in terms of PSNR. This underlines the merit of using forward motion for better modeling." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.651, + 0.47, + 0.697 + ], + "angle": 0, + "content": "In Fig. 6, our MoTIF shows consistently better subjective quality than VideoINR [6]. More results are provided in the supplementary document." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.71, + 0.308, + 0.728 + ], + "angle": 0, + "content": "5. Complexity Comparison" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Table 3 characterizes the complexity of the competing methods [31, 32, 6]. We follow [31] to report frames per second (FPS) on Vid4 [15] dataset; that is, FPS is evaluated to be the ratio of the total number of output frames to the total runtime for processing the entire dataset. We also report the corresponding multiply-accumulate (MAC) operations per frame. These numbers are evaluated on one Tesla V100. From Table 3, our MoTIF has comparable FPS and GMACs to the other baseline methods on the lower-scale tasks (i.e. temporal scale = 2 and spatial scale = 4) while showing higher FPS and lower GMACs than the base" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.575, + 0.892, + 0.604 + ], + "angle": 0, + "content": "line methods on the tasks with higher temporal and spatial scales." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.893, + 0.903 + ], + "angle": 0, + "content": "Note that when we increase the temporal scale while fixing the spatial scale, the FPS increases and the MAC per frame decreases. The same observation holds true for all the competing methods. This is because higher temporal scales invoke less frequent feature extraction to generate \\( F_0^L, F_1^L, F_{(0,1)}^L \\). For example, a temporal scale of 16 (respectively, 2) implies that the feature extraction process is invoked only once every 16 frames (respectively, 2 frames). Given that the total number of frames to be processed is fixed, more frequent feature extraction leads to lower FPS and higher GMACs per frame. It is also seen that the complexity advantage of our MoTIF over VideoINR becomes more obvious when the temporal scale becomes higher and the spatial scale remains fixed. This is mainly because VideoINR backward warps the latent representations \\( F_0^H, F_1^H, F_{(0,1)}^H \\in \\mathbb{R}^{C \\times H' \\times W'} \\) simultaneously and this operation is done twice. In comparison, our MoTIF forward warps the latent \\( F_0^H, F_1^H \\in \\mathbb{R}^{C \\times H' \\times W'} \\) individually and this operation is done only once." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "23137" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.097, + 0.089, + 0.874, + 0.417 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.426, + 0.895, + 0.457 + ], + "angle": 0, + "content": "Figure 6: Subjective quality comparison. The temporal scaling factor of the upper example is 8 (in-distribution), whereas that of the lower example is 6 (out-of-distribution). Zoom in for better visualization." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.471, + 0.893, + 0.515 + ], + "angle": 0, + "content": "Table 3: Complexity comparison on the C-STVSR task. Red indicates the best performance. Complexity metrics: FPS (↑) / GMACs (↓) per frame. The FPS and GMACs are evaluated based on processing the entire Vid4 [15] dataset on one Tesla V100." + }, + { + "type": "table", + "bbox": [ + 0.207, + 0.528, + 0.763, + 0.692 + ], + "angle": 0, + "content": "
Temporal ScaleSpatial ScaleZSM [31]TMNet[32]VideoINR[6]Ours
×2×425.52 / 42.2724.75 / 45.3616.05 / 51.1815.15 / 52.11
×4×4-23.68 / 46.3021.69 / 36.5920.70 / 33.90
×8×4-22.84 / 46.5726.17 / 26.6527.71 / 21.49
×16×4-21.54 / 48.1529.06 / 21.5042.50 / 14.69
×2×6--11.76 / 69.5113.59 / 70.82
×4×6--15.13 / 54.9317.51 / 47.91
×8×6--17.63 / 44.8521.20 / 32.54
×16×6--18.14 / 40.1825.20 / 24.46
×2×8--9.24 / 95.1910.72 / 97.44
×4×8--10.40 / 80.6113.84 / 68.95
×8×8--11.93 / 70.3416.30 / 49.22
×16×8--14.09 / 66.3223.93 / 35.49
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.716, + 0.285, + 0.733 + ], + "angle": 0, + "content": "5.1. Ablation Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.906 + ], + "angle": 0, + "content": "Backward vs. Forward Motion. Table 4 presents results for an ablation experiment that replaces forward motion with backward motion in our MoTIF. This replacement includes the following changes: (1) learning ST-INF to predicting backward motion \\(\\hat{M}_{t\\rightarrow 0}^{H},\\hat{M}_{t\\rightarrow 1}^{H}\\) and their reliability maps \\(\\hat{Z}_{t\\rightarrow 0}^{H},\\hat{Z}_{t\\rightarrow 1}^{H}\\), (2) applying backward warping with \\(\\hat{M}_{t\\rightarrow 0}^{H},\\hat{M}_{t\\rightarrow 1}^{H}\\) to each reference feature \\(F_{0}^{H},F_{1}^{H}\\), and (3) synthesizing a high-resolution video frame \\(\\hat{I}_t^H\\) by taking as inputs the two backward warped reference features, their warped reliability maps, \\(F_{(0,1)}^{H}\\), and \\(t\\). From Table 4, using" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.717, + 0.892, + 0.778 + ], + "angle": 0, + "content": "backward motion instead of forward motion in MoTIF results in a considerable PSNR drop (0.4-1dB) across the test cases. Our supplementary document provides additional Fourier analyses to compare forward and backward motion." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Implicit vs. Explicit Motion Modeling. Table 5 presents ablation results based on predicting the high-resolution forward motion without using a pre-trained optical flow estimation network, i.e. the implicit motion modeling. In this case, \\( F_0^L, F_1^L \\) (see Fig. 4) are used as inputs to our ST-INF. Compared with the explicit method, the implicit method has 0.1-0.4dB PSNR loss. Notably, even with the implicit method, MoTIF outperforms VideoINR by 0.1-0.4dB in" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "23138" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.47, + 0.12 + ], + "angle": 0, + "content": "Table 4: Backward vs. forward motion in MoTIF. Quality metrics: PSNR/SSIM. Bold indicates the best performance." + }, + { + "type": "table", + "bbox": [ + 0.134, + 0.131, + 0.409, + 0.209 + ], + "angle": 0, + "content": "
BackwardForward
Vid425.35 / 0.769625.79 / 0.7745
GoPro-Center29.98 / 0.876531.04 / 0.8877
GoPro-Average29.38 / 0.869330.04 / 0.8773
Adobe-Center29.73 / 0.872330.63 / 0.8839
Adobe-Average29.14 / 0.865829.82 / 0.8750
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.218, + 0.468, + 0.261 + ], + "angle": 0, + "content": "Table 5: Explicit vs. implicit motion modeling in MoTIF. Quality metrics: PSNR/SSIM. Bold indicates the best performance." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.275, + 0.462, + 0.352 + ], + "angle": 0, + "content": "
VideoINRMoTIF (Implicit)MoTIF (Explicit)
Vid425.61 / 0.770925.71 / 0.772125.79 / 0.7745
GoPro-Center30.26 / 0.879230.58 / 0.885631.04 / 0.8877
GoPro-Average29.41 / 0.866929.81 / 0.874430.04 / 0.8773
Adobe-Center29.92 / 0.874630.24 / 0.879630.63 / 0.8839
Adobe-Average29.27 / 0.865129.59 / 0.871929.82 / 0.8750
" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.36, + 0.468, + 0.39 + ], + "angle": 0, + "content": "PSNR, suggesting that the other components of MoTIF are essential." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.4, + 0.47, + 0.653 + ], + "angle": 0, + "content": "Feature Warping and Reliability Maps. Table 6 presents ablation results to understand the contributions of different components in MoTIF. Four variants of MoTIF are investigated, including (a) using only \\( F_{(0,1)}^{H} \\) for decoding, (b) using both \\( F_{(0,1)}^{H} \\) and \\( F_{t}^{H} \\) for decoding, (c) using \\( F_{(0,1)}^{H} \\), \\( F_{t}^{H} \\) for decoding while encoding the reliability maps \\( Z_{0\\to 1}^{L}, Z_{1\\to 0}^{L} \\) of forward motion into the motion latents, and (d) the full model (i.e. variant (c) plus \\( Z_{t}^{H} \\)). From Table 6, the considerable PSNR gain of (b) over (a) indicates that our ST-INF is effective in interpolating forward motion for propagating the reference features. The incremental improvement from (b) to (c) suggests that the reliability maps \\( Z_{0\\to 1}^{L}, Z_{1\\to 0}^{L} \\) help to improve the quality of the interpolated forward motion. Last but not least, the additional use of \\( Z_{t}^{H} \\) in the decoding process ((d) vs. (c)) does allow the decoder to better combine \\( F_{(0,1)}^{H} \\) and \\( F_{t}^{H} \\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.659, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Tri-linear Motion and More Reference Frames. Table 7 investigates the benefits of our space-time implicit neural function (ST-INF) by comparing its performance with tri-linear motion interpolation and by showing its applicability to more reference frames. From Table 7, we observe that when ST-INF is replaced with tri-linear motion interpolation-i.e., \\(\\hat{M}_{0\\rightarrow t}^{H},\\hat{M}_{1\\rightarrow t}^{H}\\) are interpolated bilinearly from \\(M_{0\\rightarrow 1}^{L},M_{1\\rightarrow 0}^{L}\\), respectively-the performance drops by 0.1-0.2dB in PSNR. Although ST-INF provides seemingly moderate gain, its advantage becomes obvious when the number of reference frames goes beyond two. In this case, ST-INF can benefit from encoding more forward motion into the motion latents. Conceptually, this amounts to taking more forward motion samples, which help to construct accurate motion trajectories. In the ablation experiment, two more reference frames \\(I_{-1}^{L},I_{2}^{L}\\)" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.089, + 0.89, + 0.12 + ], + "angle": 0, + "content": "Table 6: Ablation experiment on individual components. (d) is the proposed MoTIF. Quality metric: PSNR." + }, + { + "type": "table", + "bbox": [ + 0.528, + 0.131, + 0.862, + 0.268 + ], + "angle": 0, + "content": "
Settings(a)(b)(c)(d)
FH(0,1)VVVV
FTtVVV
Z0L, Z1LVV
ZHtV
Vid422.3825.2625.6125.79
Gopro-Center26.6830.5430.9731.04
Gopro-Average26.4429.7229.9730.08
Adobe-Center25.8230.0430.4930.63
Adobe-Average25.6129.4029.6829.82
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.283, + 0.892, + 0.328 + ], + "angle": 0, + "content": "Table 7: Ablation experiment on tri-linear motion interpolation and multiple reference frames. Quality metrics: PSNR/SSIM." + }, + { + "type": "table", + "bbox": [ + 0.511, + 0.341, + 0.876, + 0.418 + ], + "angle": 0, + "content": "
Tri-linear MotionOurs (2 ref.)Ours (4 ref.)
Vid425.57 / 0.772825.79 / 0.774526.32 / 0.7864
GoPro-Center30.89 / 0.886030.96 / 0.886831.44 / 0.9003
GoPro-Average29.93 / 0.875930.08 / 0.878030.77 / 0.8948
Adobe-Center30.42 / 0.881830.63 / 0.883931.03 / 0.8919
Adobe-Average29.64 / 0.872729.82 / 0.875030.37 / 0.8849
" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.435, + 0.892, + 0.557 + ], + "angle": 0, + "content": "are made available; we thus encode jointly information from \\(\\{M_{0\\rightarrow i}^{L},Z_{0\\rightarrow i}^{L}\\}_{i = -1,1,2}\\) as \\(T_0^L\\) , and information from \\(\\{M_{1\\rightarrow i}^{L},Z_{1\\rightarrow i}^{L}\\}_{i = -1,0,2}\\) as \\(T_{1}^{L}\\) . As a consequence, the PSNR improves by 0.5-0.7dB. We expect the gain to be even higher if we generate more motion latents to propagate information from these extra reference frames (instead of only \\(I_0^L,I_1^L)\\) . The simple tri-linear motion interpolation cannot benefit similarly from having more reference frames." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.574, + 0.619, + 0.589 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.6, + 0.892, + 0.796 + ], + "angle": 0, + "content": "This paper introduces a C-STVSR framework, known as MoTIF. It features a space-time implicit neural function for encoding forward motion, and a reliability-aware splatting and decoding scheme for fusing spatiotemporal information from multiple reference frames. We show that learning forward motion amounts to learning individual motion trajectories rather than a mixture of motion trajectories as with learning backward motion. In addition, for better aggregating temporal information via forward warping, performing splatting and decoding based on the reliability of forward motion is crucial. With all these techniques combined, MoTIF demonstrates superior quantitative and qualitative performance to the state-of-the-art methods for C-STVSR." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.814, + 0.66, + 0.831 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.892, + 0.902 + ], + "angle": 0, + "content": "This work is supported by National Science and Technology Council, Taiwan under Grants NSTC 111-2634-F-A49-010- and MOST 110-2221-E-A49-065-MY3, and National Center for High-performance Computing." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "23139" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.117, + 0.47, + 0.186 + ], + "angle": 0, + "content": "[1] Wenbo Bao, Wei Sheng Lai, Xiaoyun Zhang, Zhiyong Gao, and Ming Hsuan Yang. 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International Journal of Computer Vision (IJCV), 127(8):1106-1125, 2019." + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.093, + 0.469, + 0.699 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "23141" + } + ] +] \ No newline at end of file diff --git a/2023/MoTIF_ Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution/b7d53caf-5b95-474a-8203-b3df729d9009_origin.pdf b/2023/MoTIF_ Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution/b7d53caf-5b95-474a-8203-b3df729d9009_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..5bdd58a1372e756db979cef671b88f70125f79d7 --- /dev/null +++ b/2023/MoTIF_ Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution/b7d53caf-5b95-474a-8203-b3df729d9009_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:0a2731ebf6eaaa4f082bf48ee944d345ba827eb36c84ac613e48571d53a8de5e +size 10269189 diff --git a/2023/MoTIF_ Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution/full.md b/2023/MoTIF_ Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution/full.md new file mode 100644 index 0000000000000000000000000000000000000000..89a15ba425b52b3e8f7484ed41f97b16016a0946 --- /dev/null +++ b/2023/MoTIF_ Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution/full.md @@ -0,0 +1,289 @@ +# MoTIF: Learning Motion Trajectories with Local Implicit Neural Functions for Continuous Space-Time Video Super-Resolution + +Yi-Hsin Chen* + +Si-Cun Chen* + +Yi-Hsin Chen + +Yen-Yu Lin + +Wen-Hsiao Peng + +National Yang Ming Chiao Tung University, Taiwan + +{yhchen12101, sicun.map1, karta6120}.cs09@nycu.edu.tw + +lin@cs.nycu.edu.tw wpeng@cs.nctu.edu.tw + +# Abstract + +This work addresses continuous space-time video superresolution (C-STVSR) that aims to up-scale an input video both spatially and temporally by any scaling factors. One key challenge of C-STVSR is to propagate information temporally among the input video frames. To this end, we introduce a space-time local implicit neural function. It has the striking feature of learning forward motion for a continuum of pixels. We motivate the use of forward motion from the perspective of learning individual motion trajectories, as opposed to learning a mixture of motion trajectories with backward motion. To ease motion interpolation, we encode sparsely sampled forward motion extracted from the input video as the contextual input. Along with a reliability-aware splatting and decoding scheme, our framework, termed MoTIF, achieves the state-of-the-art performance on C-STVSR. The source code of MoTIF is available at https://github.com/sichun233746/MoTIF. + +# 1. Introduction + +This work addresses continuous space-time video super-resolution (C-STVSR). The task of C-STVSR is to increase simultaneously the spatial resolution and temporal frame-rate of an input video by any scaling factors with only one single model. It is to be distinguished from fixed-scale space-time video super-resolution (F-STVSR), for which a model is learned to perform space-time super-resolution for only one specific spatiotemporal scale. As compared to F-STVSR, C-STVSR is more flexible and practical in real-world scenarios, which often call for up-scaling low-resolution and low-frame-rate videos of varied spatiotemporal resolutions on heterogeneous video-enabled devices. + +C-STVSR remains largely under-explored. One trivial solution to C-STVSR is to perform continuous video frame interpolation [2, 11, 21, 20, 33], followed by interpolat + +![](images/39144613a19aede586c77afe17756adac61f39238450fd7b45959db2054907c9.jpg) + +![](images/38d9a3fd6b64247fc764f542f771d8cacf18925c25928873bef48fcfe362ccc0.jpg) +(a) VideoINR [6] +(b) MoTIF +Figure 1: Illustrations of (a) VideoINR [6] and (b) MoTIF. The red dash lines highlight their major differences. + +ing individual video frames with continuous image superresolution [5, 34, 14], or the other way around. However, their divide-and-conquer nature of treating C-STVSR as two independent sub-tasks-i.e. temporal interpolation and spatial super-resolution-misses the opportunity to attain the best achievable performance. By leveraging the spatiotemporal information in an end-to-end optimized fashion, some recent works [10, 31, 32, 9] for F-STVSR adopt a one-stage approach, combining the extraction of individual frame features and the temporal aggregation of these features as a unified task. Nonetheless, these F-STVSR methods can hardly be extended straightforwardly to C-STVSR. + +Inspired by continuous image super-resolution [5, 34, 14], VideoINR [6] presents an early attempt at C-STVSR. Given any query coordinates $(x,y,t)$ in the continuous spa + +![](images/3ef7e9f04a832905fd15a3c78be5c8e69f60141b875bc0bba2e5bdce5f2d80b9.jpg) +(a) Backward Motion + +![](images/b89b8a2e7190f9e02e7bb5002ac83e0a54ae9771693afc4867431f884f84a08c.jpg) +(b) Forward Motion +Figure 2: Illustration of backward and forward motion. The circles denote pixels accessible in the input video. The dashed lines display the motion trajectories of pixels in the reference frame at $t = 0$ . The blue arrows are backward/forward motion in the form of displacement vectors. The red arrows show the displacement vectors for an arbitrary time instance that are to be predicted from blue arrows. + +tiotemporal space, it takes the latent representation of the input video as the contextual information to decode the corresponding RGB value. The process involves learning a spatial implicit neural function (S-INF in Fig. 1 (a)) for super-resoluting the frame features, followed by learning another temporal implicit neural function (T-INF in Fig. 1 (a)) to generate motion estimates at time $t$ to backward warp the super-resoluted frame features. However, learning implicitly backward motion (indicating displacement vectors that identify matching pixels/features in the reference frame) as a function of time is challenging. Essentially, the backward motion at the same spatial coordinates $(x,y)$ yet at different time instances $t$ may capture the motion trajectories of different pixels/features in the reference frame. For example, in Fig. 2 (a), the backward motion vectors of $p_2$ at $t = 1$ and $t = 2$ are governed by the two distinct motion trajectories that originate from pixels $p_1$ and $p_2$ in the reference frame at $t = 0$ , respectively. In other words, the backward motion vectors at $p_2$ , when viewed as a function of time, are a mixture of multiple motion trajectories. This could potentially introduce undesirable randomness and discontinuities in the resulting time function, which must be learned by TINF in Fig. 1 (a). Furthermore, learning implicitly such a time function based solely on frame features complicates the task. + +To circumvent the aforementioned issues, we propose learning forward motion of pixels in the form of motion trajectories with a space-time implicit neural function (STINF in Fig. 1 (b)). Considering each reference frame in the input video as sitting at the origin in time, our ST-INF takes $(x,y,t)$ as input and outputs a displacement vector that specifies where the pixel at the coordinates $(x,y)$ of the reference frame will appear in a synthesized frame at time $t$ . That is, it encodes the motion trajectory of the + +![](images/e37193d5139a9b5eea1dbbf3728ca91d8dc5edd3083bde821d0542fd64d96090.jpg) +Figure 3: Illustration of fixed-scale video frame interpolation (F-VFI), continuous video frame interpolation (C-VFI), fixed-scale video super-resolution (F-VSR), fixed-scale space-time video super-resolution (F-STVSR), TM-Net [32], and continuous space-time video super-resolution (C-STVSR) in terms of their supported space-time scales. + +pixel at $(x,y)$ , e.g. the highlighted motion trajectory of $p_2$ in the reference frame at $t = 0$ in Fig. 2 (b). Moreover, to facilitate the learning of such a neural function in an explicit way, we supply forward optical flow maps estimated between reference frames as the contextual information (i.e. $M_{0\rightarrow 1}^{L}, M_{1\rightarrow 0}^{L}$ in Fig. 1 (b)). Our space-time neural function is also learned to predict the reliability of every motion trajectory (i.e. $\hat{Z}_{0\rightarrow t}^{H}, \hat{Z}_{1\rightarrow t}^{H}$ in Fig. 1 (b)), which is essential to ensure the quality of forward warping. Explicit motion modeling allows us to extract rough reliability estimates from the input video for better prediction. + +Fig. 1 (b) depicts our end-to-end trainable C-STVSR framework, MoTIF. The main contributions of our work include: (1) we propose a space-time local implicit neural function that predicts forward motion and its reliability in a continuous manner; (2) we propose a reliability-aware splatting and decoding scheme that fuses simultaneously information from multiple reference frames; and (3) our MoTIF achieves the state-of-the-art performance on C-STVSR and provides out-of-distribution generalization. + +# 2. Related Work + +This section surveys methods for video frame interpolation, video super-resolution, and space-time video super-resolution. Fig. 3 presents a Venn diagram to illustrate how C-STVSR, the focus of our work, is related to these methods in terms of their supported space-time scales. As shown, the fixed-scale methods-e.g. fixed-scale video super-resolution [4], fixed-scale video frame interpolation [1, 13] and F-STVSR [9, 31, 10]-perform only one specific type of space-time interpolation. Their supported space-time scales are visualized as singletons in Fig. 3. In comparison, the continuous-scale methods-such as continuous video frame interpolation [2, 11, 21, 20, 33] and TMNet[32]-are able to cover a continuum of temporal scales. Of these approaches, C-STVSR [6] is the most flexible and challenging one, with its supported space-time scales covering the entire space-time space. + +# 2.1. Video Frame Interpolation + +Video frame interpolation [2, 11, 21, 33, 17, 13, 1] aims to increase the frame rate of a video by interpolating between existing reference frames. The key to successful frame interpolation is to predict how the pixels/features of the reference frames progress temporally to the interpolated frame. The flow-based methods [20, 2, 21, 19, 16, 11] rely on optical flow maps to propagate features/pixels from the neighboring reference frames, whereas the kernel-based methods [13, 7, 8] estimate motion implicitly as kernels for motion compensation with deformable convolution. Most flow-based approaches adopt backward warping [11, 16, 23, 22], but more recently, forward warping [2, 20, 21, 19] emerges as an attractive alternative. Forward warping, however, is faced with the challenge that multiple features/pixels in the reference frame may be mapped to the same location in the target frame. To tackle this issue, Niklaus et al. [21] introduce softmax splatting, weighting the conflicting features/pixels according to the reliability of their forward motion. + +# 2.2. Video Super-Resolution + +Video super-resolution is to increase the spatial resolution of a video. Its central theme is to exploit temporal information from neighboring frames in order to complement a low-resolution video frame in recovering its missing high-frequency details. Early deep learning-based methods [27, 3, 24, 35, 4] rely on optical flows to align the features/pixels of the neighboring frames. However, optical flow estimation can be expensive. As such, Tian et al. [29] adopt deformable convolution for temporal alignment. Wang et al.[30] extend the idea to perform temporal alignment in a coarse-to-fine manner. These works target fixed-scale video super-resolution. + +# 2.3. Space-Time Video Super-Resolution + +Recognizing that both video frame interpolation and video super-resolution involve aggregating temporal information from neighboring frames, Haris et al. [10] adopt a unified network to address space-time video superresolution (STVSR). STVSR is much more challenging than the previous two tasks, as the low-resolution neighboring frames are the only source of information to interpolate a high-resolution video frame. Along this line of research, Xiang et al. [31] propose using bidirectional deformable ConvLSTM to mine useful space-time information from the input video in an end-to-end fashion. Based on [31], Xu et al. [32] introduce a temporal modulation block, which allows STVSR to be continuous in the temporal scale. By contrast, both [10] and [31] support only F-STVSR. + +More recently, Chen et al. [6] present the first work on end-to-end learned C-STVSR, allowing both the spatial and temporal scales to be continuous. Inspired by [5], which + +learns local implicit neural functions for continuous image super-resolution, their C-STVSR scheme includes a spatial and a temporal implicit neural function. The former generates the pixel features at any given spatial coordinates $(x,y)$ for super-resolution, while the latter predicts the backward motion for any spatiotemporal coordinates $(x,y,t)$ to propagate temporally the resulting features to time $t$ . Both neural functions are local; they refer to neighboring latents extracted from the input video as additional contextual information. + +# 3. Proposed Method + +Given two low-resolution RGB video frames $I_0^L, I_1^L \in \mathbb{R}^{3 \times H \times W}$ of size $H \times W$ , our task is to interpolate a high-resolution video frame $I_t^H \in \mathbb{R}^{3 \times H' \times W'}$ with an arbitrary scale $s = W'/W = H'/H \geq 1$ and at any time $t \in [0,1]$ . + +# 3.1. System Overview + +Fig. 4 depicts our proposed MoTIF, which comprises four major components and operates as follows. First, given $I_0^L$ and $I_1^L$ , (1) the encoder $E_I$ converts them into their latent representations $F_0^L, F_1^L, F_{(0,1)}^L \in \mathbb{R}^{C \times H \times W}$ , where $F_{(0,1)}^L$ serves as a rough estimate of the feature of the target frame $I_t^H$ . Similar to recent STVSR works [32, 6], we adopt the off-the-shelf video-based encoder from [31], which fuses information from both $I_0^L$ and $I_1^L$ in generating $F_0^L, F_1^L$ and $F_{(0,1)}^L$ . Second, (2) the spatial local implicit neural function (S-INF) is queried to super-resolute $F_0^L, F_1^L$ as $F_0^H, F_1^H \in \mathbb{R}^{C \times H' \times W'}$ , respectively. Our S-INF follows the design of LIIF [5]. Third, considering $I_0^L$ as sitting at the origin in time, (3) the motion encoder $E_M$ encodes $M_{0\to 1}^L \in \mathbb{R}^{2 \times H \times W}$ -namely, the forward optical flow map capturing the forward motion from $I_0^L$ to $I_1^L$ together with its reliability map $Z_{0\to 1}^L \in \mathbb{R}^{3 \times H \times W}$ into $T_0^L \in \mathbb{R}^{C \times H \times W}$ . The optical flow estimation is not always perfect; $Z_{0\to 1}^L$ indicates how reliable $M_{0\to 1}^L$ is across spatial locations $(x,y)$ (Section 3.2). Forth, using $T_0^L$ as the motion latent, (4) our space-time local implicit neural function (ST-INF) renders a high-resolution, forward motion map $\hat{M}_{0\to t}^H \in \mathbb{R}^{2 \times H' \times W'}$ and its reliability map $\hat{Z}_{0\to t}^H \in \mathbb{R}^{H' \times W'}$ according to the query space-time coordinates $(x,y,t)$ . $\hat{M}_{0\to t}^H$ specifies the forward motion of the features in $F_0^H$ and is utilized to forward warp $F_0^H$ to $F_t^H$ (Section 3.2). The same motion encoding, rendering and warping processes are repeated for $I_1^L$ , in aggregating temporally the information from all the reference frames. Lastly, we follow [21] to perform softmax splatting to create $F_t^H$ and $Z_t^H$ , which are further combined with $F_{(0,1)}^H$ to decode the high-resolution video frame $\hat{I}_t^H$ at time $t$ (Section 3.3). $Z_t^H$ indicates how good $F_t^H$ is across spatial locations. It is used to condition the pixel-based decoding of the RGB values from $F_t^H$ and $F_{(0,1)}^H$ . + +![](images/fd021243518579d2117031cba3751aecaa938f5b71b2e57b52ad20d79abeaec2.jpg) +Figure 4: The proposed MoTIF for C-STVSR, where the dash double arrows represent the shared-weight networks. + +![](images/4cecf0574073ec4985d16ce27bc0e2fce6393bf8c6db66dd3dee6b374c7a266b.jpg) +Figure 5: Illustration of low-resolution coordinates (blue dots) and high-resolution coordinates (green dots). + +![](images/d916f359c3b405c8710b64654dcdf7953ba10365986bc9ea84c9d5e9f5d2ad2d.jpg) + +![](images/4587728de2dedea34155434d0040698721766c0edd1d588870d81513666f11eb.jpg) + +# 3.2. Space-time Local Implicit Neural Functions + +The very core of our C-STVSR scheme is the space-time local implicit neural function (ST-INF) in Fig. 4. Our STINF has the striking feature of predicting forward motion rather than backward motion. That is, it specifies how the feature at coordinates $p = (x,y)$ in $F_0^H$ or $F_1^H$ are propagated temporally to any designated time $t$ . The forward motion is represented in the form of displacement vectors along with their reliability values. For example, to get the forward motion $\hat{M}_{0\rightarrow t}^{H}(p)$ and its reliability value $\hat{Z}_{0\rightarrow t}^{H}(p)$ for propagating the feature $F_0^H (p)$ of $F_0^H$ at $p = (x,y)$ , it is queried as follows: + +$$ +\{\hat {Z} _ {t _ {r} \rightarrow t} ^ {H} (p), \hat {M} _ {t _ {r} \rightarrow t} ^ {H} (p) \} = f _ {\theta} (v _ {r}, p - p _ {r}, t - t _ {r}), \quad (1) +$$ + +where $v_{r} = T_{0}^{L}(p_{r})$ is the motion latent at $p_{r} = (x_{r},y_{r})$ that is nearest to the query coordinates $p = (x,y)$ , $t_r = 0$ is the temporal location where the reference frame $I_0^L$ sits, and $\theta$ is the network parameters. Fig. 5 depicts an example of the geometrical relationship between $p$ and $p_{r}$ . The sum $p + \hat{M}_{0\to t}^{H}(p)$ gives the landing location of the query feature + +$F_0^H (p)$ at time $t$ . In much the same way, $\hat{M}_{1\rightarrow t}^{H}(p)$ and $\hat{Z}_{1\rightarrow t}^{H}(p)$ for propagating the feature $F_{1}^{H}(p)$ can be obtained by having in Eq. (1) $v_{r} = T_{1}^{L}(p_{r})$ and $t_r = 1$ , i.e. the temporal location of $I_1^L$ . + +In Eq. (1), both $p = (x, y)$ and $t$ can take any values. Together they can refer to any space-time coordinates. Therefore, $f_{\theta}$ is able to generate forward motion in a continuous manner to warp $F_0^H, F_1^H$ of any spatial resolution to any time instance $t \in [0, 1]$ . However, in essence, $f_{\theta}$ is a local function that predicts forward motion in the vicinity of the reference space-time coordinates $p_r, t_r$ by referring to the local motion latent $v_r$ . + +Learning motion trajectories. Learning forward motion can be interpreted as learning motion trajectories along the temporal axis. To see this, in Eq. (1), we fix $p = (x,y)$ at some coordinates, e.g. $p_2$ in Fig. 2 (b), take $t_r = 0$ , and view $f_{\theta}$ as a function of time $t$ . With this setting, the forward motion predicted by $f_{\theta}$ specifies a displacement vector indicating where $p_2$ should appear at time $t$ . Collectively, the displacement vectors evaluated at different time instances $t$ 's define the motion trajectory of $p_2$ . Generally, this motion trajectory is a smooth function of time and is relatively easier to approximate. While it is completely feasible to change the output semantics of $f_{\theta}$ to learn backward motion, the resulting time function can be discontinuous. The reason is illustrated in Fig. 2 (a), where fixing the query coordinates $p$ at $p_2$ , $f_{\theta}$ returns at every time instance $t$ a backward displacement vector identifying the location of the matching pixel/feature in the reference frame + +at $t_r = 0$ . In this case, the displacement vectors evaluated for the same $p_2$ yet at different time instances $t$ 's may correspond to the distinct motion trajectories of different matching pixels. This suggests that $f_{\theta}$ has to model a less smooth function of time. Section 5.1 presents an ablation study to justify the use of forward motion. + +Learning motion latents. Predicting the forward motion of a pixel (or a feature vector) at any given $p = (x, y)$ and for any $t$ is a non-trivial task. We formulate the problem as learning a $f_{\theta}$ that interpolates between forward motion sampled sparsely in both the spatial and temporal dimensions. This is achieved by providing $f_{\theta}$ with the motion latent that encodes the sparsely sampled forward motion as the contextual input. Take Eq. (1) as an example, where $f_{\theta}$ is queried to predict the forward motion of $F_0^H(p)$ for time $t$ . The prediction is conditioned on the nearest motion latent $T_0^L(p_r)$ , which captures the forward motion $M_{0 \to 1}^L$ estimated from $I_0^L$ to $I_1^L$ in the vicinity of $p_r$ . In this work, we adopt Raft-lite [28] to estimate the forward optical flow map $M_{0 \to 1}^L$ . Recognizing that the flow estimation is often not perfect, we follow [19] to quantify the reliability of the resulting flow map $M_{0 \to 1}^L$ based on three metrics, including (1) the intensity warping error, (2) the flow warping error, and (3) the local variances of the flow map. Further details of these metrics are provided in the supplementary document. The reliability evaluation with each of these metrics yields a real-valued map of size the same as $M_{0 \to 1}^L$ , reflecting the reliability of $M_{0 \to 1}^L$ across spatial locations. These maps are concatenated channel-wisely to form $Z_{0 \to 1}^L$ , which is encoded jointly with $M_{0 \to 1}^L$ by the motion encoder $E_M$ as $T_0^L$ . Section 5.1 shows that $Z_{0 \to 1}^L$ benefits $f_{\theta}$ considerably in interpolating forward motion. + +# 3.3. Multi-Frame Forward Warping + +To come up with a prediction of $F_{t}^{H}$ for decoding a high-resolution video frame $\hat{I}_{t}^{H}$ at time $t$ , we aggregate temporally $F_{0}^{H}, F_{1}^{H}$ , each of which represents the high-resolution feature of a reference frame (Fig. 4). Inspired by [21], we adopt softmax splatting to resolve the potential issue that multiple features from $F_{0}^{H}, F_{1}^{H}$ or both may be forward warped to the same location in $F_{t}^{H}$ . Considering that our task is to interpolate and super-resolute a new frame from the ground up, we perform softmax splatting after $F_{0}^{H}, F_{1}^{H}$ have both been forward warped to time $t$ . Our approach differs from [21], which targets video frame interpolation and applies softmax splatting separately to individual reference frames for late fusion. In symbols, we have + +$$ +F _ {t} ^ {H} (p) = \sum_ {i = 0} ^ {1} \sum_ {q} \frac {b (u) \cdot \exp (\alpha \cdot \hat {Z} _ {i \rightarrow t} ^ {H} (q)) \cdot F _ {i} ^ {H} (q)}{\sum_ {i = 0} ^ {1} \sum_ {q} b (u) \cdot \exp (\alpha \cdot \hat {Z} _ {i \rightarrow t} ^ {H} (q))}, \tag {2} +$$ + +where the feature $F_{t}^{H}(p)$ of $F_{t}^{H}$ at $p$ is formulated as a weighted sum of all the reference features $F_{0}^{H}(q), F_{1}^{H}(q)$ with the weighting determined by the distance $u = p - (q + \hat{M}_{i\rightarrow t}^{H}(q))$ , the bilinear kernel $b(u) = \max(0, 1 - |u_x|)$ and $\max(0, 1 - |u_y|)$ , as well as the reliability $\hat{Z}_{i\rightarrow t}^{H}(q)$ of the forward motion at $q$ . $\alpha = -20$ is the temperature of the softmax operation. Since the bilinear kernel has a finite support, only those $F_{0}^{H}(q), F_{1}^{H}(q)$ warped to the neighborhood of $p$ will actually contribute to the evaluation of $F_{t}^{H}(p)$ . + +Additionally, we generate a map $Z_{t}^{H}$ to indicate how good $F_{t}^{H}$ is across spatial locations. Intuitively, if $F_{t}^{H}(p)$ is synthesized from those $F_{0}^{H}(q), F_{1}^{H}(q)$ whose forward motion is unreliable, the quality of $F_{t}^{H}(p)$ should be downgraded. $Z_{t}^{H}(p)$ serves as a conditioning factor for decoding the RGB values at $p$ , and is obtained by + +$$ +Z _ {t} ^ {H} (p) = \max _ {i = 0, 1} \max _ {q} b (u) \cdot \exp \left(\alpha \cdot \hat {Z} _ {i \rightarrow t} ^ {H} (q)\right), \tag {3} +$$ + +which takes the maximum value among the (unnormized) contributing weights from $F_0^H(q), F_1^H(q)$ . When none of these contributing $F_0^H(q), F_1^H(q)$ has reliable forward motion, the quality of $F_t^H(p)$ is regarded as poor. + +To synthesize a high-resolution video frame $\hat{I}_t^H$ , we implement a pixel-wise decoder that incorporates a multi-layer perceptron. It decodes the RGB values at $p$ by taking as inputs $F_t^H(p)$ , $F_{(0,1)}^H(p)$ , $Z_t^H(p)$ , and $t$ (the rightmost part of Fig. 4). + +# 3.4. Training Objective + +We train our MoTIF end-to-end with the following objective: + +$$ +\mathcal {L} = \mathcal {L} _ {\text {c h a r}} \left(\hat {I} _ {t} ^ {H}, I _ {t} ^ {H}\right) + \beta \sum_ {i = 0} ^ {1} \mathcal {L} _ {\text {c h a r}} \left(\hat {M} _ {i \rightarrow t} ^ {H}, M _ {i \rightarrow t} ^ {H}\right), \tag {4} +$$ + +where $\mathcal{L}_{char}(\hat{x},x) = \sqrt{\|\hat{x} - x\|^2 + \epsilon^2}$ is the Charbonnier loss [12] and $\beta$ is a hyper-parameter. $\epsilon, \beta$ are set empirically to $10^{-3}$ and 0.01, respectively. Our objective requires both the decoded frame $\hat{I}_t^H$ and the predicted forward motion $\hat{M}_{i\rightarrow t}^{H}$ to approximate their respective ground-truths. + +# 3.5. Comparison with Prior Works + +Both our MoTIF and VideoINR [6] use implicit neural functions to tackle space-time video super-resolution (STVSR). As illustrated in Fig. 1, our MoTIF differs from VideoINR [6] in three significant ways: + +First, for the C-STVSR task, our MoTIF uses forward motion rather than backward motion. This aspect in its own right has a significant impact on the quality of the generated videos (Section 5.1 and Table 4). + +Second, our MoTIF models motion explicitly rather than implicitly. This allows our ST-INF to directly learn to interpolate between motion trajectories derived from a pretrained optical flow estimation model. The supplementary + +document provides additional results, showing that our MoTIF can work well with well-behaved, off-the-shelf optical flow estimation networks. Using explicit motion also allows us to evaluate the reliability information $Z_{0\rightarrow 1}^{L}, Z_{1\rightarrow 0}^{L}$ based on the input video for better predicting $\hat{Z}_{0\rightarrow t}^{H}, \hat{Z}_{1\rightarrow t}^{H}$ (see Fig. 4). + +Third, our MoTIF introduces the reliability-aware splatting and decoding schemes, which are not seen in VideoINR [6]. Their benefits are studied in Section 5.1 and Table 6. + +Different from [21], our reliability-aware splatting adopts early fusion of reference frames by forward warping all the reference features to the target frame according to Eq. (2). In contrast, [21] applies softmax splatting to each individual reference frame, followed by late fusing the results with a synthesis network. Our reliability-aware decoding scheme, which incorporates the reliability information for decoding (Eq. (3)) is not seen in [21]. + +# 4. Experiments + +To our best knowledge, VideoINR [6] is the only prior work that addresses specifically C-STVSR. We thus follow its training and test protocols, unless otherwise specified. VideoINR [6] is also included as the major baseline method. + +Training Datasets. We train our model on Adobe240 dataset[26], which contains 133 720P hand-held videos. Of these videos, 100 are used for training, 16 for validation, and 17 for test. In each video, we take 9 consecutive frames to form a training sample, where the $1^{\text{st}}$ and $9^{\text{th}}$ frames are bicubic down-sampled and used as the low-resolution, low-frame-rate input. + +Evaluation. We compare the competing methods on Vid4 [15], Adobe240 [26], and Gopro [18] datasets. Unless otherwise specified, the spatial scaling factor defaults to 4. On Vid4, the temporal scaling factor is fixed at 2 to test single-frame interpolation. On Adobe240-average and Gopro-average, the temporal scaling factor is set to 8 for multi-frame interpolation. Under the same setting, we also report results on Adobe240-center and Gopro-center for only the $1^{\text{st}}$ , $4^{\text{th}}$ and $9^{\text{th}}$ frames (namely, single-frame interpolation). + +Baselines and Quality Metrics. The baseline methods include (1) two-stage F-STVSR methods, namely video frame interpolation (SuperSloMo [11], QVI [33], DAIN [2]) plus video super-resolution (Bicubic Interpolation, EDVR [30], BasicVSR [4]); (2) one-stage F-STVSR methods (Zooming SloMo [31]); (3) two-stage C-STVSR methods, namely continuous video frame interpolation (SuperSloMo [11], DAIN [2]) plus continuous image superresolution (LIIF [5]); (4) one-stage C-STVSR methods (VideoINR [6]); and (5) TMNet [32]. The quality metrics + +are Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index (SSIM) on the Y channel. + +Implementation and Training Details. We adopt the same two-stage training strategy as VideoINR [6]. The spatial scaling factor is set to 4 for the first 450,000 iterations, and is chosen uniformly from $[1,4]$ in the following 150,000 iterations. The training batch size is 24; within each batch, every input frame is down-sampled spatially by the same factor and cropped to $32\times 32$ . For training stability, we use the ground-truth forward motion in place of the predicted forward motion with a certain probability, the value of which is attenuated from 1 to 0 in the first 150,000 iterations. We adopt Adam optimizer with $\beta_{1} = 0.9,\beta_{2} = 0.999$ and cosine annealing to decay the learning rate from $10^{-4}$ to $10^{-7}$ for every 150,000 iterations. For data augmentation, we perform random rotation and horizontal-flipping. Both our S-INF and ST-INF (Fig. 4) are implemented with 3-layer SIRENs [25], the hidden dimensions of which are 64, 64, and 256. More network details are in the supplementary document. + +# 4.1. Comparison with State-of-the-art Methods + +Table 1 presents qualitative results, comparing the competing methods on the F-STVSR task. Both VideoINR [6] and our MoTIF are trained for C-STVSR, whereas the other methods are trained for F-STVSR and their results are excerpted from [6]. Notably, VideoINR-fixed is trained specifically for single-frame interpolation. From Table 1, several observations can be made. (1) Our MoTIF outperforms VideoINR [6] in all the test cases. It also outperforms VideoINR-fixed, although not trained for F-STVSR. (2) While both VideoINR [6] and our MoTIF adopt the same $E_{I}$ encoder from Zooming SloMo [31], VideoINR [6] performs worse than Zooming SloMo [31] under the single-frame interpolation on Vid4, GoPro-Center, and AdobeCenter; on the contrary, our MoTIF is superior to Zooming SloMo [31]. (3) On Vid4, our MoTIF performs slightly worse than TMNet [32]. This may be because TMNet [32] is trained on Vimeo-90K dataset [35], which shares similar characteristics to Vid4. (4) All the one-stage methods (our MoTIF, [32, 6, 31]) perform better than the two-stage methods (video frame interpolation plus video superresolution) due to end-to-end optimization. (5) Our MoTIF (with Raft-lite [28] included) has a similar model size to VideoINR [6]. Section 5 further shows that MoTIF (including Raft) has comparable or even lower GMACs than VideoINR, and thus similar or higher FPS. + +Table 3 further presents results on the C-STVSR task, with most of the spatiotemporal scaling factors not seen during training. Except TMNet [32], which supports continuous temporal scaling but only $4\mathrm{x}$ spatial scaling, all the methods are able to achieve C-STVSR. Again, our MoTIF achieves the best performance in all the test cases, con + +Table 1: Performance comparison on the F-STVSR task. Red, blue, and green indicate the best, the second best, and the third best performance, respectively. Quality metrics: PSNR/SSIM. + +
VFI +MethodVSR +MethodVid4GoPro-CenterGoPro-AverageAdobe-CenterAdobe-AverageParameters +(Millions)
SuperSloMo [11]Bicubic22.42 / 0.564527.04 / 0.793726.06 / 0.772026.09 / 0.743525.29 / 0.727919.8
SuperSloMo [11]EDVR[30]23.01 / 0.613628.24 / 0.832226.30 / 0.796027.25 / 0.797225.95 / 0.768219.8+20.7
SuperSloMo [11]BasicVSR [4]23.17 / 0.615928.23 / 0.830826.36 / 0.797727.28 / 0.796125.94 / 0.767919.8+6.3
QVI [33]Bicubic [30]22.11 / 0.549826.50 / 0.779125.41 / 0.755425.57 / 0.732424.72 / 0.711429.2
QVI [33]EDVR [30]23.60 / 0.647127.43 / 0.808125.55 / 0.773926.40 / 0.769225.09 / 0.740629.2+20.7
QVI [33]BasicVSR [4]23.15 / 0.642827.44 / 0.807026.27 / 0.795526.43 / 0.768225.20 / 0.742129.2+6.3
DAIN [2]Bicubic22.57 / 0.573226.92 / 0.791126.11 / 0.774026.01 / 0.746125.40 / 0.732124.0
DAIN [2]EDVR [30]23.48 / 0.654728.01 / 0.823926.37 / 0.796427.06 / 0.789526.01 / 0.770324.0+20.7
DAIN [2]BasicVSR [4]23.43 / 0.651428.00 / 0.822726.46 / 0.796627.07 / 0.789026.23 / 0.772524.0+6.3
Zooming SlowMo [31]25.72 / 0.771730.69 / 0.8847-/-30.26 / 0.8821-/-11.10
TMNet [32]25.96 / 0.780330.14 / 0.869228.83 / 0.851429.41 / 0.852428.30 / 0.835412.26
VideoINR-fixed [6]25.78 / 0.773030.73 / 0.8850-/-30.21 / 0.8805-/-11.31
VideoINR [6]25.61 / 0.770930.26 / 0.879229.41 / 0.866929.92 / 0.874629.27 / 0.865111.31
Ours25.79 / 0.774531.04 / 0.887730.04 / 0.877330.63 / 0.883929.82 / 0.875012.55
+ +Table 2: PSNR/SSIM performance comparison on the C-STVSR task (on Gopro). Bold indicates the best performance. + +
Temporal ScaleSpatial ScaleSuperSloMo [11] + LIIF [5]DAIN [2] + LIIF [5]TMNet [32]VideoINR [6]Ours
×6×426.70 / 0.798826.71 / 0.799830.49 / 0.886130.78 / 0.895431.56 / 0.9064
×6×623.47 / 0.693123.36 / 0.6902-25.56 / 0.767129.36 / 0.8505
×6×1221.92 / 0.649522.01 / 0.6499-24.02 / 0.690025.81 / 0.7330
×12×425.07 / 0.749125.14 / 0.749726.38 / 0.793127.32 / 0.814127.77 / 0.8230
×12×622.91 / 0.678322.92 / 0.6785-24.68 / 0.735826.78 / 0.7908
×12×1221.61 / 0.645721.78 / 0.6473-23.70 / 0.683024.72 / 0.7108
×16×424.42 / 0.729624.20 / 0.724424.72 / 0.752625.81 / 0.773925.98 / 0.7758
×16×623.28 / 0.688322.80 / 0.6722-23.86 / 0.712325.34 / 0.7527
×16×1221.80 / 0.648122.22 / 0.6420-22.88 / 0.665923.88 / 0.6923
×6×1---32.34 / 0.954534.77 / 0.9696
×1×4--33.02 / 0.920632.26 / 0.919833.84 / 0.9328
+ +firming its better generalization to unseen scaling factors. Notably, on the video frame interpolation task (i.e. temporal scale $= 6$ and spatial scale $= 1$ ), MoTIF outperforms VideoINR [6] by 2.5dB in terms of PSNR. This underlines the merit of using forward motion for better modeling. + +In Fig. 6, our MoTIF shows consistently better subjective quality than VideoINR [6]. More results are provided in the supplementary document. + +# 5. Complexity Comparison + +Table 3 characterizes the complexity of the competing methods [31, 32, 6]. We follow [31] to report frames per second (FPS) on Vid4 [15] dataset; that is, FPS is evaluated to be the ratio of the total number of output frames to the total runtime for processing the entire dataset. We also report the corresponding multiply-accumulate (MAC) operations per frame. These numbers are evaluated on one Tesla V100. From Table 3, our MoTIF has comparable FPS and GMACs to the other baseline methods on the lower-scale tasks (i.e. temporal scale = 2 and spatial scale = 4) while showing higher FPS and lower GMACs than the base + +line methods on the tasks with higher temporal and spatial scales. + +Note that when we increase the temporal scale while fixing the spatial scale, the FPS increases and the MAC per frame decreases. The same observation holds true for all the competing methods. This is because higher temporal scales invoke less frequent feature extraction to generate $F_0^L, F_1^L, F_{(0,1)}^L$ . For example, a temporal scale of 16 (respectively, 2) implies that the feature extraction process is invoked only once every 16 frames (respectively, 2 frames). Given that the total number of frames to be processed is fixed, more frequent feature extraction leads to lower FPS and higher GMACs per frame. It is also seen that the complexity advantage of our MoTIF over VideoINR becomes more obvious when the temporal scale becomes higher and the spatial scale remains fixed. This is mainly because VideoINR backward warps the latent representations $F_0^H, F_1^H, F_{(0,1)}^H \in \mathbb{R}^{C \times H' \times W'}$ simultaneously and this operation is done twice. In comparison, our MoTIF forward warps the latent $F_0^H, F_1^H \in \mathbb{R}^{C \times H' \times W'}$ individually and this operation is done only once. + +![](images/b7593228ef1d971b786f849532e0b8fffa6cf0459236ccc4766fbdf5951d1364.jpg) +Figure 6: Subjective quality comparison. The temporal scaling factor of the upper example is 8 (in-distribution), whereas that of the lower example is 6 (out-of-distribution). Zoom in for better visualization. + +Table 3: Complexity comparison on the C-STVSR task. Red indicates the best performance. Complexity metrics: FPS (↑) / GMACs (↓) per frame. The FPS and GMACs are evaluated based on processing the entire Vid4 [15] dataset on one Tesla V100. + +
Temporal ScaleSpatial ScaleZSM [31]TMNet[32]VideoINR[6]Ours
×2×425.52 / 42.2724.75 / 45.3616.05 / 51.1815.15 / 52.11
×4×4-23.68 / 46.3021.69 / 36.5920.70 / 33.90
×8×4-22.84 / 46.5726.17 / 26.6527.71 / 21.49
×16×4-21.54 / 48.1529.06 / 21.5042.50 / 14.69
×2×6--11.76 / 69.5113.59 / 70.82
×4×6--15.13 / 54.9317.51 / 47.91
×8×6--17.63 / 44.8521.20 / 32.54
×16×6--18.14 / 40.1825.20 / 24.46
×2×8--9.24 / 95.1910.72 / 97.44
×4×8--10.40 / 80.6113.84 / 68.95
×8×8--11.93 / 70.3416.30 / 49.22
×16×8--14.09 / 66.3223.93 / 35.49
+ +# 5.1. Ablation Experiments + +Backward vs. Forward Motion. Table 4 presents results for an ablation experiment that replaces forward motion with backward motion in our MoTIF. This replacement includes the following changes: (1) learning ST-INF to predicting backward motion $\hat{M}_{t\rightarrow 0}^{H},\hat{M}_{t\rightarrow 1}^{H}$ and their reliability maps $\hat{Z}_{t\rightarrow 0}^{H},\hat{Z}_{t\rightarrow 1}^{H}$ , (2) applying backward warping with $\hat{M}_{t\rightarrow 0}^{H},\hat{M}_{t\rightarrow 1}^{H}$ to each reference feature $F_{0}^{H},F_{1}^{H}$ , and (3) synthesizing a high-resolution video frame $\hat{I}_t^H$ by taking as inputs the two backward warped reference features, their warped reliability maps, $F_{(0,1)}^{H}$ , and $t$ . From Table 4, using + +backward motion instead of forward motion in MoTIF results in a considerable PSNR drop (0.4-1dB) across the test cases. Our supplementary document provides additional Fourier analyses to compare forward and backward motion. + +Implicit vs. Explicit Motion Modeling. Table 5 presents ablation results based on predicting the high-resolution forward motion without using a pre-trained optical flow estimation network, i.e. the implicit motion modeling. In this case, $F_0^L, F_1^L$ (see Fig. 4) are used as inputs to our ST-INF. Compared with the explicit method, the implicit method has 0.1-0.4dB PSNR loss. Notably, even with the implicit method, MoTIF outperforms VideoINR by 0.1-0.4dB in + +Table 4: Backward vs. forward motion in MoTIF. Quality metrics: PSNR/SSIM. Bold indicates the best performance. + +
BackwardForward
Vid425.35 / 0.769625.79 / 0.7745
GoPro-Center29.98 / 0.876531.04 / 0.8877
GoPro-Average29.38 / 0.869330.04 / 0.8773
Adobe-Center29.73 / 0.872330.63 / 0.8839
Adobe-Average29.14 / 0.865829.82 / 0.8750
+ +Table 5: Explicit vs. implicit motion modeling in MoTIF. Quality metrics: PSNR/SSIM. Bold indicates the best performance. + +
VideoINRMoTIF (Implicit)MoTIF (Explicit)
Vid425.61 / 0.770925.71 / 0.772125.79 / 0.7745
GoPro-Center30.26 / 0.879230.58 / 0.885631.04 / 0.8877
GoPro-Average29.41 / 0.866929.81 / 0.874430.04 / 0.8773
Adobe-Center29.92 / 0.874630.24 / 0.879630.63 / 0.8839
Adobe-Average29.27 / 0.865129.59 / 0.871929.82 / 0.8750
+ +PSNR, suggesting that the other components of MoTIF are essential. + +Feature Warping and Reliability Maps. Table 6 presents ablation results to understand the contributions of different components in MoTIF. Four variants of MoTIF are investigated, including (a) using only $F_{(0,1)}^{H}$ for decoding, (b) using both $F_{(0,1)}^{H}$ and $F_{t}^{H}$ for decoding, (c) using $F_{(0,1)}^{H}$ , $F_{t}^{H}$ for decoding while encoding the reliability maps $Z_{0\to 1}^{L}, Z_{1\to 0}^{L}$ of forward motion into the motion latents, and (d) the full model (i.e. variant (c) plus $Z_{t}^{H}$ ). From Table 6, the considerable PSNR gain of (b) over (a) indicates that our ST-INF is effective in interpolating forward motion for propagating the reference features. The incremental improvement from (b) to (c) suggests that the reliability maps $Z_{0\to 1}^{L}, Z_{1\to 0}^{L}$ help to improve the quality of the interpolated forward motion. Last but not least, the additional use of $Z_{t}^{H}$ in the decoding process ((d) vs. (c)) does allow the decoder to better combine $F_{(0,1)}^{H}$ and $F_{t}^{H}$ . + +Tri-linear Motion and More Reference Frames. Table 7 investigates the benefits of our space-time implicit neural function (ST-INF) by comparing its performance with tri-linear motion interpolation and by showing its applicability to more reference frames. From Table 7, we observe that when ST-INF is replaced with tri-linear motion interpolation-i.e., $\hat{M}_{0\rightarrow t}^{H},\hat{M}_{1\rightarrow t}^{H}$ are interpolated bilinearly from $M_{0\rightarrow 1}^{L},M_{1\rightarrow 0}^{L}$ , respectively-the performance drops by 0.1-0.2dB in PSNR. Although ST-INF provides seemingly moderate gain, its advantage becomes obvious when the number of reference frames goes beyond two. In this case, ST-INF can benefit from encoding more forward motion into the motion latents. Conceptually, this amounts to taking more forward motion samples, which help to construct accurate motion trajectories. In the ablation experiment, two more reference frames $I_{-1}^{L},I_{2}^{L}$ + +Table 6: Ablation experiment on individual components. (d) is the proposed MoTIF. Quality metric: PSNR. + +
Settings(a)(b)(c)(d)
FH(0,1)VVVV
FTtVVV
Z0L, Z1LVV
ZHtV
Vid422.3825.2625.6125.79
Gopro-Center26.6830.5430.9731.04
Gopro-Average26.4429.7229.9730.08
Adobe-Center25.8230.0430.4930.63
Adobe-Average25.6129.4029.6829.82
+ +Table 7: Ablation experiment on tri-linear motion interpolation and multiple reference frames. Quality metrics: PSNR/SSIM. + +
Tri-linear MotionOurs (2 ref.)Ours (4 ref.)
Vid425.57 / 0.772825.79 / 0.774526.32 / 0.7864
GoPro-Center30.89 / 0.886030.96 / 0.886831.44 / 0.9003
GoPro-Average29.93 / 0.875930.08 / 0.878030.77 / 0.8948
Adobe-Center30.42 / 0.881830.63 / 0.883931.03 / 0.8919
Adobe-Average29.64 / 0.872729.82 / 0.875030.37 / 0.8849
+ +are made available; we thus encode jointly information from $\{M_{0\rightarrow i}^{L},Z_{0\rightarrow i}^{L}\}_{i = -1,1,2}$ as $T_0^L$ , and information from $\{M_{1\rightarrow i}^{L},Z_{1\rightarrow i}^{L}\}_{i = -1,0,2}$ as $T_{1}^{L}$ . As a consequence, the PSNR improves by 0.5-0.7dB. We expect the gain to be even higher if we generate more motion latents to propagate information from these extra reference frames (instead of only $I_0^L,I_1^L)$ . The simple tri-linear motion interpolation cannot benefit similarly from having more reference frames. + +# 6. Conclusion + +This paper introduces a C-STVSR framework, known as MoTIF. It features a space-time implicit neural function for encoding forward motion, and a reliability-aware splatting and decoding scheme for fusing spatiotemporal information from multiple reference frames. We show that learning forward motion amounts to learning individual motion trajectories rather than a mixture of motion trajectories as with learning backward motion. In addition, for better aggregating temporal information via forward warping, performing splatting and decoding based on the reliability of forward motion is crucial. With all these techniques combined, MoTIF demonstrates superior quantitative and qualitative performance to the state-of-the-art methods for C-STVSR. + +# Acknowledgement + +This work is supported by National Science and Technology Council, Taiwan under Grants NSTC 111-2634-F-A49-010- and MOST 110-2221-E-A49-065-MY3, and National Center for High-performance Computing. + +# References + +[1] Wenbo Bao, Wei Sheng Lai, Xiaoyun Zhang, Zhiyong Gao, and Ming Hsuan Yang. Memc-net: Motion estimation and motion compensation driven neural network for video interpolation and enhancement. 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Ultrasr: Spatial encoding is a missing key for implicit image function-based arbitrary-scale super-resolution. arXiv preprint arXiv:2103.12716, 2021. +[35] Tianfan Xue, Baian Chen, Jiajun Wu, Donglai Wei, and William T Freeman. Video enhancement with task-oriented flow. 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The red dash lines highlight their major differences." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 533, + 545, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 533, + 545, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 533, + 545, + 676 + ], + "type": "text", + "content": "ing individual video frames with continuous image superresolution [5, 34, 14], or the other way around. However, their divide-and-conquer nature of treating C-STVSR as two independent sub-tasks-i.e. temporal interpolation and spatial super-resolution-misses the opportunity to attain the best achievable performance. By leveraging the spatiotemporal information in an end-to-end optimized fashion, some recent works [10, 31, 32, 9] for F-STVSR adopt a one-stage approach, combining the extraction of individual frame features and the temporal aggregation of these features as a unified task. 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The circles denote pixels accessible in the input video. The dashed lines display the motion trajectories of pixels in the reference frame at " + }, + { + "bbox": [ + 46, + 205, + 287, + 289 + ], + "type": "inline_equation", + "content": "t = 0" + }, + { + "bbox": [ + 46, + 205, + 287, + 289 + ], + "type": "text", + "content": ". The blue arrows are backward/forward motion in the form of displacement vectors. The red arrows show the displacement vectors for an arbitrary time instance that are to be predicted from blue arrows." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "text", + "content": "tiotemporal space, it takes the latent representation of the input video as the contextual information to decode the corresponding RGB value. The process involves learning a spatial implicit neural function (S-INF in Fig. 1 (a)) for super-resoluting the frame features, followed by learning another temporal implicit neural function (T-INF in Fig. 1 (a)) to generate motion estimates at time " + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "text", + "content": " to backward warp the super-resoluted frame features. However, learning implicitly backward motion (indicating displacement vectors that identify matching pixels/features in the reference frame) as a function of time is challenging. Essentially, the backward motion at the same spatial coordinates " + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "text", + "content": " yet at different time instances " + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "text", + "content": " may capture the motion trajectories of different pixels/features in the reference frame. For example, in Fig. 2 (a), the backward motion vectors of " + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "inline_equation", + "content": "p_2" + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "inline_equation", + "content": "t = 1" + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "inline_equation", + "content": "t = 2" + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "text", + "content": " are governed by the two distinct motion trajectories that originate from pixels " + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "inline_equation", + "content": "p_1" + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "inline_equation", + "content": "p_2" + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "text", + "content": " in the reference frame at " + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "inline_equation", + "content": "t = 0" + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "text", + "content": ", respectively. In other words, the backward motion vectors at " + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "inline_equation", + "content": "p_2" + }, + { + "bbox": [ + 46, + 304, + 287, + 602 + ], + "type": "text", + "content": ", when viewed as a function of time, are a mixture of multiple motion trajectories. This could potentially introduce undesirable randomness and discontinuities in the resulting time function, which must be learned by TINF in Fig. 1 (a). Furthermore, learning implicitly such a time function based solely on frame features complicates the task." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 605, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 286, + 713 + ], + "type": "text", + "content": "To circumvent the aforementioned issues, we propose learning forward motion of pixels in the form of motion trajectories with a space-time implicit neural function (STINF in Fig. 1 (b)). Considering each reference frame in the input video as sitting at the origin in time, our ST-INF takes " + }, + { + "bbox": [ + 46, + 605, + 286, + 713 + ], + "type": "inline_equation", + "content": "(x,y,t)" + }, + { + "bbox": [ + 46, + 605, + 286, + 713 + ], + "type": "text", + "content": " as input and outputs a displacement vector that specifies where the pixel at the coordinates " + }, + { + "bbox": [ + 46, + 605, + 286, + 713 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 46, + 605, + 286, + 713 + ], + "type": "text", + "content": " of the reference frame will appear in a synthesized frame at time " + }, + { + "bbox": [ + 46, + 605, + 286, + 713 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 605, + 286, + 713 + ], + "type": "text", + "content": ". That is, it encodes the motion trajectory of the" + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 366, + 74, + 486, + 162 + ], + "blocks": [ + { + "bbox": [ + 366, + 74, + 486, + 162 + ], + "lines": [ + { + "bbox": [ + 366, + 74, + 486, + 162 + ], + "spans": [ + { + "bbox": [ + 366, + 74, + 486, + 162 + ], + "type": "image", + "image_path": "e37193d5139a9b5eea1dbbf3728ca91d8dc5edd3083bde821d0542fd64d96090.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 170, + 545, + 243 + ], + "lines": [ + { + "bbox": [ + 304, + 170, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 304, + 170, + 545, + 243 + ], + "type": "text", + "content": "Figure 3: Illustration of fixed-scale video frame interpolation (F-VFI), continuous video frame interpolation (C-VFI), fixed-scale video super-resolution (F-VSR), fixed-scale space-time video super-resolution (F-STVSR), TM-Net [32], and continuous space-time video super-resolution (C-STVSR) in terms of their supported space-time scales." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "type": "text", + "content": "pixel at " + }, + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "type": "text", + "content": ", e.g. the highlighted motion trajectory of " + }, + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "type": "inline_equation", + "content": "p_2" + }, + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "type": "text", + "content": " in the reference frame at " + }, + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "type": "inline_equation", + "content": "t = 0" + }, + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "type": "text", + "content": " in Fig. 2 (b). Moreover, to facilitate the learning of such a neural function in an explicit way, we supply forward optical flow maps estimated between reference frames as the contextual information (i.e. " + }, + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "type": "inline_equation", + "content": "M_{0\\rightarrow 1}^{L}, M_{1\\rightarrow 0}^{L}" + }, + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "type": "text", + "content": " in Fig. 1 (b)). Our space-time neural function is also learned to predict the reliability of every motion trajectory (i.e. " + }, + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "type": "inline_equation", + "content": "\\hat{Z}_{0\\rightarrow t}^{H}, \\hat{Z}_{1\\rightarrow t}^{H}" + }, + { + "bbox": [ + 304, + 251, + 545, + 384 + ], + "type": "text", + "content": " in Fig. 1 (b)), which is essential to ensure the quality of forward warping. Explicit motion modeling allows us to extract rough reliability estimates from the input video for better prediction." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 384, + 545, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 545, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 545, + 491 + ], + "type": "text", + "content": "Fig. 1 (b) depicts our end-to-end trainable C-STVSR framework, MoTIF. The main contributions of our work include: (1) we propose a space-time local implicit neural function that predicts forward motion and its reliability in a continuous manner; (2) we propose a reliability-aware splatting and decoding scheme that fuses simultaneously information from multiple reference frames; and (3) our MoTIF achieves the state-of-the-art performance on C-STVSR and provides out-of-distribution generalization." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 502, + 392, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 502, + 392, + 514 + ], + "spans": [ + { + "bbox": [ + 306, + 502, + 392, + 514 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 521, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 713 + ], + "type": "text", + "content": "This section surveys methods for video frame interpolation, video super-resolution, and space-time video super-resolution. Fig. 3 presents a Venn diagram to illustrate how C-STVSR, the focus of our work, is related to these methods in terms of their supported space-time scales. As shown, the fixed-scale methods-e.g. fixed-scale video super-resolution [4], fixed-scale video frame interpolation [1, 13] and F-STVSR [9, 31, 10]-perform only one specific type of space-time interpolation. Their supported space-time scales are visualized as singletons in Fig. 3. In comparison, the continuous-scale methods-such as continuous video frame interpolation [2, 11, 21, 20, 33] and TMNet[32]-are able to cover a continuum of temporal scales. Of these approaches, C-STVSR [6] is the most flexible and challenging one, with its supported space-time scales covering the entire space-time space." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23132" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 195, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 195, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 195, + 85 + ], + "type": "text", + "content": "2.1. Video Frame Interpolation" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 89, + 289, + 317 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 89, + 289, + 317 + ], + "spans": [ + { + "bbox": [ + 46, + 89, + 289, + 317 + ], + "type": "text", + "content": "Video frame interpolation [2, 11, 21, 33, 17, 13, 1] aims to increase the frame rate of a video by interpolating between existing reference frames. The key to successful frame interpolation is to predict how the pixels/features of the reference frames progress temporally to the interpolated frame. The flow-based methods [20, 2, 21, 19, 16, 11] rely on optical flow maps to propagate features/pixels from the neighboring reference frames, whereas the kernel-based methods [13, 7, 8] estimate motion implicitly as kernels for motion compensation with deformable convolution. Most flow-based approaches adopt backward warping [11, 16, 23, 22], but more recently, forward warping [2, 20, 21, 19] emerges as an attractive alternative. Forward warping, however, is faced with the challenge that multiple features/pixels in the reference frame may be mapped to the same location in the target frame. To tackle this issue, Niklaus et al. [21] introduce softmax splatting, weighting the conflicting features/pixels according to the reliability of their forward motion." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 323, + 180, + 336 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 323, + 180, + 336 + ], + "spans": [ + { + "bbox": [ + 47, + 323, + 180, + 336 + ], + "type": "text", + "content": "2.2. Video Super-Resolution" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "text", + "content": "Video super-resolution is to increase the spatial resolution of a video. Its central theme is to exploit temporal information from neighboring frames in order to complement a low-resolution video frame in recovering its missing high-frequency details. Early deep learning-based methods [27, 3, 24, 35, 4] rely on optical flows to align the features/pixels of the neighboring frames. However, optical flow estimation can be expensive. As such, Tian et al. [29] adopt deformable convolution for temporal alignment. Wang et al.[30] extend the idea to perform temporal alignment in a coarse-to-fine manner. These works target fixed-scale video super-resolution." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 491, + 239, + 505 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 491, + 239, + 505 + ], + "spans": [ + { + "bbox": [ + 47, + 491, + 239, + 505 + ], + "type": "text", + "content": "2.3. Space-Time Video Super-Resolution" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 510, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 287, + 677 + ], + "type": "text", + "content": "Recognizing that both video frame interpolation and video super-resolution involve aggregating temporal information from neighboring frames, Haris et al. [10] adopt a unified network to address space-time video superresolution (STVSR). STVSR is much more challenging than the previous two tasks, as the low-resolution neighboring frames are the only source of information to interpolate a high-resolution video frame. Along this line of research, Xiang et al. [31] propose using bidirectional deformable ConvLSTM to mine useful space-time information from the input video in an end-to-end fashion. Based on [31], Xu et al. [32] introduce a temporal modulation block, which allows STVSR to be continuous in the temporal scale. By contrast, both [10] and [31] support only F-STVSR." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": "More recently, Chen et al. [6] present the first work on end-to-end learned C-STVSR, allowing both the spatial and temporal scales to be continuous. Inspired by [5], which" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "text", + "content": "learns local implicit neural functions for continuous image super-resolution, their C-STVSR scheme includes a spatial and a temporal implicit neural function. The former generates the pixel features at any given spatial coordinates " + }, + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "text", + "content": " for super-resolution, while the latter predicts the backward motion for any spatiotemporal coordinates " + }, + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "inline_equation", + "content": "(x,y,t)" + }, + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "text", + "content": " to propagate temporally the resulting features to time " + }, + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "text", + "content": ". Both neural functions are local; they refer to neighboring latents extracted from the input video as additional contextual information." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 207, + 411, + 221 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 207, + 411, + 221 + ], + "spans": [ + { + "bbox": [ + 305, + 207, + 411, + 221 + ], + "type": "text", + "content": "3. Proposed Method" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "spans": [ + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "type": "text", + "content": "Given two low-resolution RGB video frames " + }, + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "type": "inline_equation", + "content": "I_0^L, I_1^L \\in \\mathbb{R}^{3 \\times H \\times W}" + }, + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "type": "text", + "content": " of size " + }, + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "type": "inline_equation", + "content": "H \\times W" + }, + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "type": "text", + "content": ", our task is to interpolate a high-resolution video frame " + }, + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "type": "inline_equation", + "content": "I_t^H \\in \\mathbb{R}^{3 \\times H' \\times W'}" + }, + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "type": "text", + "content": " with an arbitrary scale " + }, + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "type": "inline_equation", + "content": "s = W'/W = H'/H \\geq 1" + }, + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "type": "text", + "content": " and at any time " + }, + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "type": "inline_equation", + "content": "t \\in [0,1]" + }, + { + "bbox": [ + 305, + 228, + 546, + 278 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 289, + 410, + 302 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 289, + 410, + 302 + ], + "spans": [ + { + "bbox": [ + 305, + 289, + 410, + 302 + ], + "type": "text", + "content": "3.1. System Overview" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "spans": [ + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": "Fig. 4 depicts our proposed MoTIF, which comprises four major components and operates as follows. First, given " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "I_0^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "I_1^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": ", (1) the encoder " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "E_I" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " converts them into their latent representations " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_0^L, F_1^L, F_{(0,1)}^L \\in \\mathbb{R}^{C \\times H \\times W}" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_{(0,1)}^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " serves as a rough estimate of the feature of the target frame " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "I_t^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": ". Similar to recent STVSR works [32, 6], we adopt the off-the-shelf video-based encoder from [31], which fuses information from both " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "I_0^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "I_1^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " in generating " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_0^L, F_1^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_{(0,1)}^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": ". Second, (2) the spatial local implicit neural function (S-INF) is queried to super-resolute " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_0^L, F_1^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_0^H, F_1^H \\in \\mathbb{R}^{C \\times H' \\times W'}" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": ", respectively. Our S-INF follows the design of LIIF [5]. Third, considering " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "I_0^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " as sitting at the origin in time, (3) the motion encoder " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "E_M" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " encodes " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "M_{0\\to 1}^L \\in \\mathbb{R}^{2 \\times H \\times W}" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " -namely, the forward optical flow map capturing the forward motion from " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "I_0^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "I_1^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " together with its reliability map " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "Z_{0\\to 1}^L \\in \\mathbb{R}^{3 \\times H \\times W}" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " into " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "T_0^L \\in \\mathbb{R}^{C \\times H \\times W}" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": ". The optical flow estimation is not always perfect; " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "Z_{0\\to 1}^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " indicates how reliable " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "M_{0\\to 1}^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " is across spatial locations " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " (Section 3.2). Forth, using " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "T_0^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " as the motion latent, (4) our space-time local implicit neural function (ST-INF) renders a high-resolution, forward motion map " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "\\hat{M}_{0\\to t}^H \\in \\mathbb{R}^{2 \\times H' \\times W'}" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " and its reliability map " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "\\hat{Z}_{0\\to t}^H \\in \\mathbb{R}^{H' \\times W'}" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " according to the query space-time coordinates " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "(x,y,t)" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "\\hat{M}_{0\\to t}^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " specifies the forward motion of the features in " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_0^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " and is utilized to forward warp " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_0^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_t^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " (Section 3.2). The same motion encoding, rendering and warping processes are repeated for " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "I_1^L" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": ", in aggregating temporally the information from all the reference frames. Lastly, we follow [21] to perform softmax splatting to create " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_t^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "Z_t^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": ", which are further combined with " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_{(0,1)}^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " to decode the high-resolution video frame " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "\\hat{I}_t^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " at time " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " (Section 3.3). " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "Z_t^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " indicates how good " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_t^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " is across spatial locations. It is used to condition the pixel-based decoding of the RGB values from " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_t^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "inline_equation", + "content": "F_{(0,1)}^H" + }, + { + "bbox": [ + 304, + 308, + 547, + 716 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "text", + "content": "23133" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 72, + 544, + 319 + ], + "blocks": [ + { + "bbox": [ + 55, + 72, + 544, + 319 + ], + "lines": [ + { + "bbox": [ + 55, + 72, + 544, + 319 + ], + "spans": [ + { + "bbox": [ + 55, + 72, + 544, + 319 + ], + "type": "image", + "image_path": "fd021243518579d2117031cba3751aecaa938f5b71b2e57b52ad20d79abeaec2.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 63, + 327, + 528, + 340 + ], + "lines": [ + { + "bbox": [ + 63, + 327, + 528, + 340 + ], + "spans": [ + { + "bbox": [ + 63, + 327, + 528, + 340 + ], + "type": "text", + "content": "Figure 4: The proposed MoTIF for C-STVSR, where the dash double arrows represent the shared-weight networks." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 93, + 351, + 138, + 412 + ], + "blocks": [ + { + "bbox": [ + 93, + 351, + 138, + 412 + ], + "lines": [ + { + "bbox": [ + 93, + 351, + 138, + 412 + ], + "spans": [ + { + "bbox": [ + 93, + 351, + 138, + 412 + ], + "type": "image", + "image_path": "4cecf0574073ec4985d16ce27bc0e2fce6393bf8c6db66dd3dee6b374c7a266b.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 420, + 287, + 445 + ], + "lines": [ + { + "bbox": [ + 46, + 420, + 287, + 445 + ], + "spans": [ + { + "bbox": [ + 46, + 420, + 287, + 445 + ], + "type": "text", + "content": "Figure 5: Illustration of low-resolution coordinates (blue dots) and high-resolution coordinates (green dots)." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 145, + 351, + 190, + 412 + ], + "blocks": [ + { + "bbox": [ + 145, + 351, + 190, + 412 + ], + "lines": [ + { + "bbox": [ + 145, + 351, + 190, + 412 + ], + "spans": [ + { + "bbox": [ + 145, + 351, + 190, + 412 + ], + "type": "image", + "image_path": "d916f359c3b405c8710b64654dcdf7953ba10365986bc9ea84c9d5e9f5d2ad2d.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 195, + 352, + 240, + 412 + ], + "blocks": [ + { + "bbox": [ + 195, + 352, + 240, + 412 + ], + "lines": [ + { + "bbox": [ + 195, + 352, + 240, + 412 + ], + "spans": [ + { + "bbox": [ + 195, + 352, + 240, + 412 + ], + "type": "image", + "image_path": "4587728de2dedea34155434d0040698721766c0edd1d588870d81513666f11eb.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 459, + 275, + 472 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 459, + 275, + 472 + ], + "spans": [ + { + "bbox": [ + 47, + 459, + 275, + 472 + ], + "type": "text", + "content": "3.2. Space-time Local Implicit Neural Functions" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "spans": [ + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "text", + "content": "The very core of our C-STVSR scheme is the space-time local implicit neural function (ST-INF) in Fig. 4. Our STINF has the striking feature of predicting forward motion rather than backward motion. That is, it specifies how the feature at coordinates " + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "inline_equation", + "content": "p = (x,y)" + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "inline_equation", + "content": "F_0^H" + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "inline_equation", + "content": "F_1^H" + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "text", + "content": " are propagated temporally to any designated time " + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "text", + "content": ". The forward motion is represented in the form of displacement vectors along with their reliability values. For example, to get the forward motion " + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "inline_equation", + "content": "\\hat{M}_{0\\rightarrow t}^{H}(p)" + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "text", + "content": " and its reliability value " + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "inline_equation", + "content": "\\hat{Z}_{0\\rightarrow t}^{H}(p)" + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "text", + "content": " for propagating the feature " + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "inline_equation", + "content": "F_0^H (p)" + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "inline_equation", + "content": "F_0^H" + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "inline_equation", + "content": "p = (x,y)" + }, + { + "bbox": [ + 46, + 478, + 287, + 610 + ], + "type": "text", + "content": ", it is queried as follows:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 62, + 617, + 287, + 634 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 62, + 617, + 287, + 634 + ], + "spans": [ + { + "bbox": [ + 62, + 617, + 287, + 634 + ], + "type": "interline_equation", + "content": "\\{\\hat {Z} _ {t _ {r} \\rightarrow t} ^ {H} (p), \\hat {M} _ {t _ {r} \\rightarrow t} ^ {H} (p) \\} = f _ {\\theta} (v _ {r}, p - p _ {r}, t - t _ {r}), \\quad (1)", + "image_path": "80130808724fb074f5462bd683f50a7464b1bf687dea8e4619fdf6b3ffffddd5.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "inline_equation", + "content": "v_{r} = T_{0}^{L}(p_{r})" + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "text", + "content": " is the motion latent at " + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "inline_equation", + "content": "p_{r} = (x_{r},y_{r})" + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "text", + "content": " that is nearest to the query coordinates " + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "inline_equation", + "content": "p = (x,y)" + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "inline_equation", + "content": "t_r = 0" + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "text", + "content": " is the temporal location where the reference frame " + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "inline_equation", + "content": "I_0^L" + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "text", + "content": " sits, and " + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "text", + "content": " is the network parameters. Fig. 5 depicts an example of the geometrical relationship between " + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "inline_equation", + "content": "p_{r}" + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "text", + "content": ". The sum " + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "inline_equation", + "content": "p + \\hat{M}_{0\\to t}^{H}(p)" + }, + { + "bbox": [ + 46, + 641, + 288, + 717 + ], + "type": "text", + "content": " gives the landing location of the query feature" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "inline_equation", + "content": "F_0^H (p)" + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "text", + "content": " at time " + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "text", + "content": ". In much the same way, " + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\hat{M}_{1\\rightarrow t}^{H}(p)" + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\hat{Z}_{1\\rightarrow t}^{H}(p)" + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "text", + "content": " for propagating the feature " + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "inline_equation", + "content": "F_{1}^{H}(p)" + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "text", + "content": " can be obtained by having in Eq. (1) " + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "inline_equation", + "content": "v_{r} = T_{1}^{L}(p_{r})" + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "inline_equation", + "content": "t_r = 1" + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "text", + "content": ", i.e. the temporal location of " + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "inline_equation", + "content": "I_1^L" + }, + { + "bbox": [ + 305, + 353, + 545, + 403 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "text", + "content": "In Eq. (1), both " + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "inline_equation", + "content": "p = (x, y)" + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "text", + "content": " can take any values. Together they can refer to any space-time coordinates. Therefore, " + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "text", + "content": " is able to generate forward motion in a continuous manner to warp " + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "inline_equation", + "content": "F_0^H, F_1^H" + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "text", + "content": " of any spatial resolution to any time instance " + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "inline_equation", + "content": "t \\in [0, 1]" + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "text", + "content": ". However, in essence, " + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "text", + "content": " is a local function that predicts forward motion in the vicinity of the reference space-time coordinates " + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "inline_equation", + "content": "p_r, t_r" + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "text", + "content": " by referring to the local motion latent " + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "inline_equation", + "content": "v_r" + }, + { + "bbox": [ + 304, + 403, + 546, + 499 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": "Learning motion trajectories. Learning forward motion can be interpreted as learning motion trajectories along the temporal axis. To see this, in Eq. (1), we fix " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "p = (x,y)" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": " at some coordinates, e.g. " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "p_2" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": " in Fig. 2 (b), take " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "t_r = 0" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": ", and view " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": " as a function of time " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": ". With this setting, the forward motion predicted by " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": " specifies a displacement vector indicating where " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "p_2" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": " should appear at time " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": ". Collectively, the displacement vectors evaluated at different time instances " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": "'s define the motion trajectory of " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "p_2" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": ". Generally, this motion trajectory is a smooth function of time and is relatively easier to approximate. While it is completely feasible to change the output semantics of " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": " to learn backward motion, the resulting time function can be discontinuous. The reason is illustrated in Fig. 2 (a), where fixing the query coordinates " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "p_2" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": " returns at every time instance " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": " a backward displacement vector identifying the location of the matching pixel/feature in the reference frame" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "23134" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "at " + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "inline_equation", + "content": "t_r = 0" + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": ". In this case, the displacement vectors evaluated for the same " + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "inline_equation", + "content": "p_2" + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": " yet at different time instances " + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "'s may correspond to the distinct motion trajectories of different matching pixels. This suggests that " + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": " has to model a less smooth function of time. Section 5.1 presents an ablation study to justify the use of forward motion." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "spans": [ + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": "Learning motion latents. Predicting the forward motion of a pixel (or a feature vector) at any given " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "p = (x, y)" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " and for any " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " is a non-trivial task. We formulate the problem as learning a " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " that interpolates between forward motion sampled sparsely in both the spatial and temporal dimensions. This is achieved by providing " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " with the motion latent that encodes the sparsely sampled forward motion as the contextual input. Take Eq. (1) as an example, where " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " is queried to predict the forward motion of " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "F_0^H(p)" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " for time " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": ". The prediction is conditioned on the nearest motion latent " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "T_0^L(p_r)" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": ", which captures the forward motion " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "M_{0 \\to 1}^L" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " estimated from " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "I_0^L" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "I_1^L" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " in the vicinity of " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "p_r" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": ". In this work, we adopt Raft-lite [28] to estimate the forward optical flow map " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "M_{0 \\to 1}^L" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": ". Recognizing that the flow estimation is often not perfect, we follow [19] to quantify the reliability of the resulting flow map " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "M_{0 \\to 1}^L" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " based on three metrics, including (1) the intensity warping error, (2) the flow warping error, and (3) the local variances of the flow map. Further details of these metrics are provided in the supplementary document. The reliability evaluation with each of these metrics yields a real-valued map of size the same as " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "M_{0 \\to 1}^L" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": ", reflecting the reliability of " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "M_{0 \\to 1}^L" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " across spatial locations. These maps are concatenated channel-wisely to form " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "Z_{0 \\to 1}^L" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": ", which is encoded jointly with " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "M_{0 \\to 1}^L" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " by the motion encoder " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "E_M" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "T_0^L" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": ". Section 5.1 shows that " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "Z_{0 \\to 1}^L" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " benefits " + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "inline_equation", + "content": "f_{\\theta}" + }, + { + "bbox": [ + 46, + 159, + 289, + 470 + ], + "type": "text", + "content": " considerably in interpolating forward motion." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 483, + 219, + 496 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 483, + 219, + 496 + ], + "spans": [ + { + "bbox": [ + 47, + 483, + 219, + 496 + ], + "type": "text", + "content": "3.3. Multi-Frame Forward Warping" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "spans": [ + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "text", + "content": "To come up with a prediction of " + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "inline_equation", + "content": "F_{t}^{H}" + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "text", + "content": " for decoding a high-resolution video frame " + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "inline_equation", + "content": "\\hat{I}_{t}^{H}" + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "text", + "content": " at time " + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "text", + "content": ", we aggregate temporally " + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "inline_equation", + "content": "F_{0}^{H}, F_{1}^{H}" + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "text", + "content": ", each of which represents the high-resolution feature of a reference frame (Fig. 4). Inspired by [21], we adopt softmax splatting to resolve the potential issue that multiple features from " + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "inline_equation", + "content": "F_{0}^{H}, F_{1}^{H}" + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "text", + "content": " or both may be forward warped to the same location in " + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "inline_equation", + "content": "F_{t}^{H}" + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "text", + "content": ". Considering that our task is to interpolate and super-resolute a new frame from the ground up, we perform softmax splatting after " + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "inline_equation", + "content": "F_{0}^{H}, F_{1}^{H}" + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "text", + "content": " have both been forward warped to time " + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 502, + 287, + 659 + ], + "type": "text", + "content": ". Our approach differs from [21], which targets video frame interpolation and applies softmax splatting separately to individual reference frames for late fusion. In symbols, we have" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 672, + 287, + 716 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 672, + 287, + 716 + ], + "spans": [ + { + "bbox": [ + 53, + 672, + 287, + 716 + ], + "type": "interline_equation", + "content": "F _ {t} ^ {H} (p) = \\sum_ {i = 0} ^ {1} \\sum_ {q} \\frac {b (u) \\cdot \\exp (\\alpha \\cdot \\hat {Z} _ {i \\rightarrow t} ^ {H} (q)) \\cdot F _ {i} ^ {H} (q)}{\\sum_ {i = 0} ^ {1} \\sum_ {q} b (u) \\cdot \\exp (\\alpha \\cdot \\hat {Z} _ {i \\rightarrow t} ^ {H} (q))}, \\tag {2}", + "image_path": "5be35789ead04a9dbcd94617b8309997dc79c1174d59437dbc7d1dbbe051f9c4.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": "where the feature " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "F_{t}^{H}(p)" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "F_{t}^{H}" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": " is formulated as a weighted sum of all the reference features " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "F_{0}^{H}(q), F_{1}^{H}(q)" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": " with the weighting determined by the distance " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "u = p - (q + \\hat{M}_{i\\rightarrow t}^{H}(q))" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": ", the bilinear kernel " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "b(u) = \\max(0, 1 - |u_x|)" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "\\max(0, 1 - |u_y|)" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": ", as well as the reliability " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "\\hat{Z}_{i\\rightarrow t}^{H}(q)" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": " of the forward motion at " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "\\alpha = -20" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": " is the temperature of the softmax operation. Since the bilinear kernel has a finite support, only those " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "F_{0}^{H}(q), F_{1}^{H}(q)" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": " warped to the neighborhood of " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": " will actually contribute to the evaluation of " + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "inline_equation", + "content": "F_{t}^{H}(p)" + }, + { + "bbox": [ + 304, + 72, + 545, + 180 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "spans": [ + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "text", + "content": "Additionally, we generate a map " + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "inline_equation", + "content": "Z_{t}^{H}" + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "text", + "content": " to indicate how good " + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "inline_equation", + "content": "F_{t}^{H}" + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "text", + "content": " is across spatial locations. Intuitively, if " + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "inline_equation", + "content": "F_{t}^{H}(p)" + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "text", + "content": " is synthesized from those " + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "inline_equation", + "content": "F_{0}^{H}(q), F_{1}^{H}(q)" + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "text", + "content": " whose forward motion is unreliable, the quality of " + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "inline_equation", + "content": "F_{t}^{H}(p)" + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "text", + "content": " should be downgraded. " + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "inline_equation", + "content": "Z_{t}^{H}(p)" + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "text", + "content": " serves as a conditioning factor for decoding the RGB values at " + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 181, + 545, + 253 + ], + "type": "text", + "content": ", and is obtained by" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 332, + 258, + 545, + 277 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 332, + 258, + 545, + 277 + ], + "spans": [ + { + "bbox": [ + 332, + 258, + 545, + 277 + ], + "type": "interline_equation", + "content": "Z _ {t} ^ {H} (p) = \\max _ {i = 0, 1} \\max _ {q} b (u) \\cdot \\exp \\left(\\alpha \\cdot \\hat {Z} _ {i \\rightarrow t} ^ {H} (q)\\right), \\tag {3}", + "image_path": "16cb596dda922971bc43a3b506ea25670d111465f12f222450bc3b42dc3efdb5.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 283, + 545, + 331 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 283, + 545, + 331 + ], + "spans": [ + { + "bbox": [ + 304, + 283, + 545, + 331 + ], + "type": "text", + "content": "which takes the maximum value among the (unnormized) contributing weights from " + }, + { + "bbox": [ + 304, + 283, + 545, + 331 + ], + "type": "inline_equation", + "content": "F_0^H(q), F_1^H(q)" + }, + { + "bbox": [ + 304, + 283, + 545, + 331 + ], + "type": "text", + "content": ". When none of these contributing " + }, + { + "bbox": [ + 304, + 283, + 545, + 331 + ], + "type": "inline_equation", + "content": "F_0^H(q), F_1^H(q)" + }, + { + "bbox": [ + 304, + 283, + 545, + 331 + ], + "type": "text", + "content": " has reliable forward motion, the quality of " + }, + { + "bbox": [ + 304, + 283, + 545, + 331 + ], + "type": "inline_equation", + "content": "F_t^H(p)" + }, + { + "bbox": [ + 304, + 283, + 545, + 331 + ], + "type": "text", + "content": " is regarded as poor." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "spans": [ + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "text", + "content": "To synthesize a high-resolution video frame " + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "inline_equation", + "content": "\\hat{I}_t^H" + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "text", + "content": ", we implement a pixel-wise decoder that incorporates a multi-layer perceptron. It decodes the RGB values at " + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "text", + "content": " by taking as inputs " + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "inline_equation", + "content": "F_t^H(p)" + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "inline_equation", + "content": "F_{(0,1)}^H(p)" + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "inline_equation", + "content": "Z_t^H(p)" + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 331, + 545, + 390 + ], + "type": "text", + "content": " (the rightmost part of Fig. 4)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 396, + 417, + 410 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 396, + 417, + 410 + ], + "spans": [ + { + "bbox": [ + 306, + 396, + 417, + 410 + ], + "type": "text", + "content": "3.4. Training Objective" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 415, + 545, + 439 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 545, + 439 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 545, + 439 + ], + "type": "text", + "content": "We train our MoTIF end-to-end with the following objective:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 315, + 445, + 545, + 477 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 445, + 545, + 477 + ], + "spans": [ + { + "bbox": [ + 315, + 445, + 545, + 477 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathcal {L} _ {\\text {c h a r}} \\left(\\hat {I} _ {t} ^ {H}, I _ {t} ^ {H}\\right) + \\beta \\sum_ {i = 0} ^ {1} \\mathcal {L} _ {\\text {c h a r}} \\left(\\hat {M} _ {i \\rightarrow t} ^ {H}, M _ {i \\rightarrow t} ^ {H}\\right), \\tag {4}", + "image_path": "a6ab46db852aace772a10f0dcb3fb2257ffc57a3c91ce3dcc7634d2873dcd017.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{char}(\\hat{x},x) = \\sqrt{\\|\\hat{x} - x\\|^2 + \\epsilon^2}" + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "text", + "content": " is the Charbonnier loss [12] and " + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "text", + "content": " is a hyper-parameter. " + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\epsilon, \\beta" + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "text", + "content": " are set empirically to " + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "inline_equation", + "content": "10^{-3}" + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "text", + "content": " and 0.01, respectively. Our objective requires both the decoded frame " + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\hat{I}_t^H" + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "text", + "content": " and the predicted forward motion " + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\hat{M}_{i\\rightarrow t}^{H}" + }, + { + "bbox": [ + 304, + 484, + 545, + 545 + ], + "type": "text", + "content": " to approximate their respective ground-truths." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 552, + 471, + 564 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 552, + 471, + 564 + ], + "spans": [ + { + "bbox": [ + 306, + 552, + 471, + 564 + ], + "type": "text", + "content": "3.5. Comparison with Prior Works" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 570, + 545, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 617 + ], + "type": "text", + "content": "Both our MoTIF and VideoINR [6] use implicit neural functions to tackle space-time video super-resolution (STVSR). As illustrated in Fig. 1, our MoTIF differs from VideoINR [6] in three significant ways:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 617, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 665 + ], + "type": "text", + "content": "First, for the C-STVSR task, our MoTIF uses forward motion rather than backward motion. This aspect in its own right has a significant impact on the quality of the generated videos (Section 5.1 and Table 4)." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "Second, our MoTIF models motion explicitly rather than implicitly. This allows our ST-INF to directly learn to interpolate between motion trajectories derived from a pretrained optical flow estimation model. The supplementary" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23135" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 286, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 286, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 286, + 144 + ], + "type": "text", + "content": "document provides additional results, showing that our MoTIF can work well with well-behaved, off-the-shelf optical flow estimation networks. Using explicit motion also allows us to evaluate the reliability information " + }, + { + "bbox": [ + 46, + 72, + 286, + 144 + ], + "type": "inline_equation", + "content": "Z_{0\\rightarrow 1}^{L}, Z_{1\\rightarrow 0}^{L}" + }, + { + "bbox": [ + 46, + 72, + 286, + 144 + ], + "type": "text", + "content": " based on the input video for better predicting " + }, + { + "bbox": [ + 46, + 72, + 286, + 144 + ], + "type": "inline_equation", + "content": "\\hat{Z}_{0\\rightarrow t}^{H}, \\hat{Z}_{1\\rightarrow t}^{H}" + }, + { + "bbox": [ + 46, + 72, + 286, + 144 + ], + "type": "text", + "content": " (see Fig. 4)." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 144, + 286, + 191 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 144, + 286, + 191 + ], + "spans": [ + { + "bbox": [ + 46, + 144, + 286, + 191 + ], + "type": "text", + "content": "Third, our MoTIF introduces the reliability-aware splatting and decoding schemes, which are not seen in VideoINR [6]. Their benefits are studied in Section 5.1 and Table 6." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 193, + 286, + 288 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 193, + 286, + 288 + ], + "spans": [ + { + "bbox": [ + 46, + 193, + 286, + 288 + ], + "type": "text", + "content": "Different from [21], our reliability-aware splatting adopts early fusion of reference frames by forward warping all the reference features to the target frame according to Eq. (2). In contrast, [21] applies softmax splatting to each individual reference frame, followed by late fusing the results with a synthesis network. Our reliability-aware decoding scheme, which incorporates the reliability information for decoding (Eq. (3)) is not seen in [21]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 300, + 127, + 313 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 300, + 127, + 313 + ], + "spans": [ + { + "bbox": [ + 47, + 300, + 127, + 313 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 321, + 286, + 369 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 321, + 286, + 369 + ], + "spans": [ + { + "bbox": [ + 46, + 321, + 286, + 369 + ], + "type": "text", + "content": "To our best knowledge, VideoINR [6] is the only prior work that addresses specifically C-STVSR. We thus follow its training and test protocols, unless otherwise specified. VideoINR [6] is also included as the major baseline method." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 376, + 286, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 376, + 286, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 376, + 286, + 460 + ], + "type": "text", + "content": "Training Datasets. We train our model on Adobe240 dataset[26], which contains 133 720P hand-held videos. Of these videos, 100 are used for training, 16 for validation, and 17 for test. In each video, we take 9 consecutive frames to form a training sample, where the " + }, + { + "bbox": [ + 46, + 376, + 286, + 460 + ], + "type": "inline_equation", + "content": "1^{\\text{st}}" + }, + { + "bbox": [ + 46, + 376, + 286, + 460 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 376, + 286, + 460 + ], + "type": "inline_equation", + "content": "9^{\\text{th}}" + }, + { + "bbox": [ + 46, + 376, + 286, + 460 + ], + "type": "text", + "content": " frames are bicubic down-sampled and used as the low-resolution, low-frame-rate input." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 467, + 286, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 467, + 286, + 586 + ], + "spans": [ + { + "bbox": [ + 46, + 467, + 286, + 586 + ], + "type": "text", + "content": "Evaluation. We compare the competing methods on Vid4 [15], Adobe240 [26], and Gopro [18] datasets. Unless otherwise specified, the spatial scaling factor defaults to 4. On Vid4, the temporal scaling factor is fixed at 2 to test single-frame interpolation. On Adobe240-average and Gopro-average, the temporal scaling factor is set to 8 for multi-frame interpolation. Under the same setting, we also report results on Adobe240-center and Gopro-center for only the " + }, + { + "bbox": [ + 46, + 467, + 286, + 586 + ], + "type": "inline_equation", + "content": "1^{\\text{st}}" + }, + { + "bbox": [ + 46, + 467, + 286, + 586 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 467, + 286, + 586 + ], + "type": "inline_equation", + "content": "4^{\\text{th}}" + }, + { + "bbox": [ + 46, + 467, + 286, + 586 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 467, + 286, + 586 + ], + "type": "inline_equation", + "content": "9^{\\text{th}}" + }, + { + "bbox": [ + 46, + 467, + 286, + 586 + ], + "type": "text", + "content": " frames (namely, single-frame interpolation)." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "type": "text", + "content": "Baselines and Quality Metrics. The baseline methods include (1) two-stage F-STVSR methods, namely video frame interpolation (SuperSloMo [11], QVI [33], DAIN [2]) plus video super-resolution (Bicubic Interpolation, EDVR [30], BasicVSR [4]); (2) one-stage F-STVSR methods (Zooming SloMo [31]); (3) two-stage C-STVSR methods, namely continuous video frame interpolation (SuperSloMo [11], DAIN [2]) plus continuous image superresolution (LIIF [5]); (4) one-stage C-STVSR methods (VideoINR [6]); and (5) TMNet [32]. The quality metrics" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 72, + 544, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 544, + 95 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 544, + 95 + ], + "type": "text", + "content": "are Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index (SSIM) on the Y channel." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "spans": [ + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "type": "text", + "content": "Implementation and Training Details. We adopt the same two-stage training strategy as VideoINR [6]. The spatial scaling factor is set to 4 for the first 450,000 iterations, and is chosen uniformly from " + }, + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "type": "inline_equation", + "content": "[1,4]" + }, + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "type": "text", + "content": " in the following 150,000 iterations. The training batch size is 24; within each batch, every input frame is down-sampled spatially by the same factor and cropped to " + }, + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "type": "inline_equation", + "content": "32\\times 32" + }, + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "type": "text", + "content": ". For training stability, we use the ground-truth forward motion in place of the predicted forward motion with a certain probability, the value of which is attenuated from 1 to 0 in the first 150,000 iterations. We adopt Adam optimizer with " + }, + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "type": "inline_equation", + "content": "\\beta_{1} = 0.9,\\beta_{2} = 0.999" + }, + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "type": "text", + "content": " and cosine annealing to decay the learning rate from " + }, + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "type": "inline_equation", + "content": "10^{-7}" + }, + { + "bbox": [ + 304, + 101, + 545, + 316 + ], + "type": "text", + "content": " for every 150,000 iterations. For data augmentation, we perform random rotation and horizontal-flipping. Both our S-INF and ST-INF (Fig. 4) are implemented with 3-layer SIRENs [25], the hidden dimensions of which are 64, 64, and 256. More network details are in the supplementary document." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 324, + 528, + 337 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 324, + 528, + 337 + ], + "spans": [ + { + "bbox": [ + 305, + 324, + 528, + 337 + ], + "type": "text", + "content": "4.1. Comparison with State-of-the-art Methods" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 343, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 343, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 343, + 545, + 641 + ], + "type": "text", + "content": "Table 1 presents qualitative results, comparing the competing methods on the F-STVSR task. Both VideoINR [6] and our MoTIF are trained for C-STVSR, whereas the other methods are trained for F-STVSR and their results are excerpted from [6]. Notably, VideoINR-fixed is trained specifically for single-frame interpolation. From Table 1, several observations can be made. (1) Our MoTIF outperforms VideoINR [6] in all the test cases. It also outperforms VideoINR-fixed, although not trained for F-STVSR. (2) While both VideoINR [6] and our MoTIF adopt the same " + }, + { + "bbox": [ + 304, + 343, + 545, + 641 + ], + "type": "inline_equation", + "content": "E_{I}" + }, + { + "bbox": [ + 304, + 343, + 545, + 641 + ], + "type": "text", + "content": " encoder from Zooming SloMo [31], VideoINR [6] performs worse than Zooming SloMo [31] under the single-frame interpolation on Vid4, GoPro-Center, and AdobeCenter; on the contrary, our MoTIF is superior to Zooming SloMo [31]. (3) On Vid4, our MoTIF performs slightly worse than TMNet [32]. This may be because TMNet [32] is trained on Vimeo-90K dataset [35], which shares similar characteristics to Vid4. (4) All the one-stage methods (our MoTIF, [32, 6, 31]) perform better than the two-stage methods (video frame interpolation plus video superresolution) due to end-to-end optimization. (5) Our MoTIF (with Raft-lite [28] included) has a similar model size to VideoINR [6]. Section 5 further shows that MoTIF (including Raft) has comparable or even lower GMACs than VideoINR, and thus similar or higher FPS." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "type": "text", + "content": "Table 3 further presents results on the C-STVSR task, with most of the spatiotemporal scaling factors not seen during training. Except TMNet [32], which supports continuous temporal scaling but only " + }, + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "type": "inline_equation", + "content": "4\\mathrm{x}" + }, + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "type": "text", + "content": " spatial scaling, all the methods are able to achieve C-STVSR. Again, our MoTIF achieves the best performance in all the test cases, con" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "23136" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 63, + 103, + 529, + 270 + ], + "blocks": [ + { + "bbox": [ + 46, + 70, + 547, + 95 + ], + "lines": [ + { + "bbox": [ + 46, + 70, + 547, + 95 + ], + "spans": [ + { + "bbox": [ + 46, + 70, + 547, + 95 + ], + "type": "text", + "content": "Table 1: Performance comparison on the F-STVSR task. Red, blue, and green indicate the best, the second best, and the third best performance, respectively. Quality metrics: PSNR/SSIM." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 63, + 103, + 529, + 270 + ], + "lines": [ + { + "bbox": [ + 63, + 103, + 529, + 270 + ], + "spans": [ + { + "bbox": [ + 63, + 103, + 529, + 270 + ], + "type": "table", + "html": "
VFI\nMethodVSR\nMethodVid4GoPro-CenterGoPro-AverageAdobe-CenterAdobe-AverageParameters\n(Millions)
SuperSloMo [11]Bicubic22.42 / 0.564527.04 / 0.793726.06 / 0.772026.09 / 0.743525.29 / 0.727919.8
SuperSloMo [11]EDVR[30]23.01 / 0.613628.24 / 0.832226.30 / 0.796027.25 / 0.797225.95 / 0.768219.8+20.7
SuperSloMo [11]BasicVSR [4]23.17 / 0.615928.23 / 0.830826.36 / 0.797727.28 / 0.796125.94 / 0.767919.8+6.3
QVI [33]Bicubic [30]22.11 / 0.549826.50 / 0.779125.41 / 0.755425.57 / 0.732424.72 / 0.711429.2
QVI [33]EDVR [30]23.60 / 0.647127.43 / 0.808125.55 / 0.773926.40 / 0.769225.09 / 0.740629.2+20.7
QVI [33]BasicVSR [4]23.15 / 0.642827.44 / 0.807026.27 / 0.795526.43 / 0.768225.20 / 0.742129.2+6.3
DAIN [2]Bicubic22.57 / 0.573226.92 / 0.791126.11 / 0.774026.01 / 0.746125.40 / 0.732124.0
DAIN [2]EDVR [30]23.48 / 0.654728.01 / 0.823926.37 / 0.796427.06 / 0.789526.01 / 0.770324.0+20.7
DAIN [2]BasicVSR [4]23.43 / 0.651428.00 / 0.822726.46 / 0.796627.07 / 0.789026.23 / 0.772524.0+6.3
Zooming SlowMo [31]25.72 / 0.771730.69 / 0.8847-/-30.26 / 0.8821-/-11.10
TMNet [32]25.96 / 0.780330.14 / 0.869228.83 / 0.851429.41 / 0.852428.30 / 0.835412.26
VideoINR-fixed [6]25.78 / 0.773030.73 / 0.8850-/-30.21 / 0.8805-/-11.31
VideoINR [6]25.61 / 0.770930.26 / 0.879229.41 / 0.866929.92 / 0.874629.27 / 0.865111.31
Ours25.79 / 0.774531.04 / 0.887730.04 / 0.877330.63 / 0.883929.82 / 0.875012.55
", + "image_path": "ad2bf5d42e5933f2e4baa550b97678e343ecbb1c05738ebf2b02635d160c4721.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 66, + 301, + 526, + 436 + ], + "blocks": [ + { + "bbox": [ + 56, + 280, + 536, + 293 + ], + "lines": [ + { + "bbox": [ + 56, + 280, + 536, + 293 + ], + "spans": [ + { + "bbox": [ + 56, + 280, + 536, + 293 + ], + "type": "text", + "content": "Table 2: PSNR/SSIM performance comparison on the C-STVSR task (on Gopro). Bold indicates the best performance." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 66, + 301, + 526, + 436 + ], + "lines": [ + { + "bbox": [ + 66, + 301, + 526, + 436 + ], + "spans": [ + { + "bbox": [ + 66, + 301, + 526, + 436 + ], + "type": "table", + "html": "
Temporal ScaleSpatial ScaleSuperSloMo [11] + LIIF [5]DAIN [2] + LIIF [5]TMNet [32]VideoINR [6]Ours
×6×426.70 / 0.798826.71 / 0.799830.49 / 0.886130.78 / 0.895431.56 / 0.9064
×6×623.47 / 0.693123.36 / 0.6902-25.56 / 0.767129.36 / 0.8505
×6×1221.92 / 0.649522.01 / 0.6499-24.02 / 0.690025.81 / 0.7330
×12×425.07 / 0.749125.14 / 0.749726.38 / 0.793127.32 / 0.814127.77 / 0.8230
×12×622.91 / 0.678322.92 / 0.6785-24.68 / 0.735826.78 / 0.7908
×12×1221.61 / 0.645721.78 / 0.6473-23.70 / 0.683024.72 / 0.7108
×16×424.42 / 0.729624.20 / 0.724424.72 / 0.752625.81 / 0.773925.98 / 0.7758
×16×623.28 / 0.688322.80 / 0.6722-23.86 / 0.712325.34 / 0.7527
×16×1221.80 / 0.648122.22 / 0.6420-22.88 / 0.665923.88 / 0.6923
×6×1---32.34 / 0.954534.77 / 0.9696
×1×4--33.02 / 0.920632.26 / 0.919833.84 / 0.9328
", + "image_path": "2ab16a7dd98740953d62b205b70faca010565d8213d8edce77bd3a886b5dfb14.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 455, + 287, + 514 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 455, + 287, + 514 + ], + "spans": [ + { + "bbox": [ + 46, + 455, + 287, + 514 + ], + "type": "text", + "content": "firming its better generalization to unseen scaling factors. Notably, on the video frame interpolation task (i.e. temporal scale " + }, + { + "bbox": [ + 46, + 455, + 287, + 514 + ], + "type": "inline_equation", + "content": "= 6" + }, + { + "bbox": [ + 46, + 455, + 287, + 514 + ], + "type": "text", + "content": " and spatial scale " + }, + { + "bbox": [ + 46, + 455, + 287, + 514 + ], + "type": "inline_equation", + "content": "= 1" + }, + { + "bbox": [ + 46, + 455, + 287, + 514 + ], + "type": "text", + "content": "), MoTIF outperforms VideoINR [6] by 2.5dB in terms of PSNR. This underlines the merit of using forward motion for better modeling." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 515, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 515, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 515, + 287, + 552 + ], + "type": "text", + "content": "In Fig. 6, our MoTIF shows consistently better subjective quality than VideoINR [6]. More results are provided in the supplementary document." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 562, + 188, + 576 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 562, + 188, + 576 + ], + "spans": [ + { + "bbox": [ + 47, + 562, + 188, + 576 + ], + "type": "text", + "content": "5. Complexity Comparison" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": "Table 3 characterizes the complexity of the competing methods [31, 32, 6]. We follow [31] to report frames per second (FPS) on Vid4 [15] dataset; that is, FPS is evaluated to be the ratio of the total number of output frames to the total runtime for processing the entire dataset. We also report the corresponding multiply-accumulate (MAC) operations per frame. These numbers are evaluated on one Tesla V100. From Table 3, our MoTIF has comparable FPS and GMACs to the other baseline methods on the lower-scale tasks (i.e. temporal scale = 2 and spatial scale = 4) while showing higher FPS and lower GMACs than the base" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 455, + 545, + 478 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 455, + 545, + 478 + ], + "spans": [ + { + "bbox": [ + 305, + 455, + 545, + 478 + ], + "type": "text", + "content": "line methods on the tasks with higher temporal and spatial scales." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 486, + 546, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 546, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 546, + 715 + ], + "type": "text", + "content": "Note that when we increase the temporal scale while fixing the spatial scale, the FPS increases and the MAC per frame decreases. The same observation holds true for all the competing methods. This is because higher temporal scales invoke less frequent feature extraction to generate " + }, + { + "bbox": [ + 304, + 486, + 546, + 715 + ], + "type": "inline_equation", + "content": "F_0^L, F_1^L, F_{(0,1)}^L" + }, + { + "bbox": [ + 304, + 486, + 546, + 715 + ], + "type": "text", + "content": ". For example, a temporal scale of 16 (respectively, 2) implies that the feature extraction process is invoked only once every 16 frames (respectively, 2 frames). Given that the total number of frames to be processed is fixed, more frequent feature extraction leads to lower FPS and higher GMACs per frame. It is also seen that the complexity advantage of our MoTIF over VideoINR becomes more obvious when the temporal scale becomes higher and the spatial scale remains fixed. This is mainly because VideoINR backward warps the latent representations " + }, + { + "bbox": [ + 304, + 486, + 546, + 715 + ], + "type": "inline_equation", + "content": "F_0^H, F_1^H, F_{(0,1)}^H \\in \\mathbb{R}^{C \\times H' \\times W'}" + }, + { + "bbox": [ + 304, + 486, + 546, + 715 + ], + "type": "text", + "content": " simultaneously and this operation is done twice. In comparison, our MoTIF forward warps the latent " + }, + { + "bbox": [ + 304, + 486, + 546, + 715 + ], + "type": "inline_equation", + "content": "F_0^H, F_1^H \\in \\mathbb{R}^{C \\times H' \\times W'}" + }, + { + "bbox": [ + 304, + 486, + 546, + 715 + ], + "type": "text", + "content": " individually and this operation is done only once." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "23137" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 59, + 70, + 534, + 330 + ], + "blocks": [ + { + "bbox": [ + 59, + 70, + 534, + 330 + ], + "lines": [ + { + "bbox": [ + 59, + 70, + 534, + 330 + ], + "spans": [ + { + "bbox": [ + 59, + 70, + 534, + 330 + ], + "type": "image", + "image_path": "b7593228ef1d971b786f849532e0b8fffa6cf0459236ccc4766fbdf5951d1364.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 337, + 547, + 361 + ], + "lines": [ + { + "bbox": [ + 46, + 337, + 547, + 361 + ], + "spans": [ + { + "bbox": [ + 46, + 337, + 547, + 361 + ], + "type": "text", + "content": "Figure 6: Subjective quality comparison. The temporal scaling factor of the upper example is 8 (in-distribution), whereas that of the lower example is 6 (out-of-distribution). Zoom in for better visualization." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 126, + 418, + 466, + 548 + ], + "blocks": [ + { + "bbox": [ + 46, + 373, + 546, + 407 + ], + "lines": [ + { + "bbox": [ + 46, + 373, + 546, + 407 + ], + "spans": [ + { + "bbox": [ + 46, + 373, + 546, + 407 + ], + "type": "text", + "content": "Table 3: Complexity comparison on the C-STVSR task. Red indicates the best performance. Complexity metrics: FPS (↑) / GMACs (↓) per frame. The FPS and GMACs are evaluated based on processing the entire Vid4 [15] dataset on one Tesla V100." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 126, + 418, + 466, + 548 + ], + "lines": [ + { + "bbox": [ + 126, + 418, + 466, + 548 + ], + "spans": [ + { + "bbox": [ + 126, + 418, + 466, + 548 + ], + "type": "table", + "html": "
Temporal ScaleSpatial ScaleZSM [31]TMNet[32]VideoINR[6]Ours
×2×425.52 / 42.2724.75 / 45.3616.05 / 51.1815.15 / 52.11
×4×4-23.68 / 46.3021.69 / 36.5920.70 / 33.90
×8×4-22.84 / 46.5726.17 / 26.6527.71 / 21.49
×16×4-21.54 / 48.1529.06 / 21.5042.50 / 14.69
×2×6--11.76 / 69.5113.59 / 70.82
×4×6--15.13 / 54.9317.51 / 47.91
×8×6--17.63 / 44.8521.20 / 32.54
×16×6--18.14 / 40.1825.20 / 24.46
×2×8--9.24 / 95.1910.72 / 97.44
×4×8--10.40 / 80.6113.84 / 68.95
×8×8--11.93 / 70.3416.30 / 49.22
×16×8--14.09 / 66.3223.93 / 35.49
", + "image_path": "ff4a38a2106d341b03a63153094c50094c2b09edd1db55e45c1778bcc6dce321.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 567, + 174, + 580 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 567, + 174, + 580 + ], + "spans": [ + { + "bbox": [ + 47, + 567, + 174, + 580 + ], + "type": "text", + "content": "5.1. Ablation Experiments" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "text", + "content": "Backward vs. Forward Motion. Table 4 presents results for an ablation experiment that replaces forward motion with backward motion in our MoTIF. This replacement includes the following changes: (1) learning ST-INF to predicting backward motion " + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "inline_equation", + "content": "\\hat{M}_{t\\rightarrow 0}^{H},\\hat{M}_{t\\rightarrow 1}^{H}" + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "text", + "content": " and their reliability maps " + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "inline_equation", + "content": "\\hat{Z}_{t\\rightarrow 0}^{H},\\hat{Z}_{t\\rightarrow 1}^{H}" + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "text", + "content": ", (2) applying backward warping with " + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "inline_equation", + "content": "\\hat{M}_{t\\rightarrow 0}^{H},\\hat{M}_{t\\rightarrow 1}^{H}" + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "text", + "content": " to each reference feature " + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "inline_equation", + "content": "F_{0}^{H},F_{1}^{H}" + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "text", + "content": ", and (3) synthesizing a high-resolution video frame " + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "inline_equation", + "content": "\\hat{I}_t^H" + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "text", + "content": " by taking as inputs the two backward warped reference features, their warped reliability maps, " + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "inline_equation", + "content": "F_{(0,1)}^{H}" + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 594, + 289, + 717 + ], + "type": "text", + "content": ". From Table 4, using" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 567, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 567, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 567, + 545, + 616 + ], + "type": "text", + "content": "backward motion instead of forward motion in MoTIF results in a considerable PSNR drop (0.4-1dB) across the test cases. Our supplementary document provides additional Fourier analyses to compare forward and backward motion." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "content": "Implicit vs. Explicit Motion Modeling. Table 5 presents ablation results based on predicting the high-resolution forward motion without using a pre-trained optical flow estimation network, i.e. the implicit motion modeling. In this case, " + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "inline_equation", + "content": "F_0^L, F_1^L" + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "content": " (see Fig. 4) are used as inputs to our ST-INF. Compared with the explicit method, the implicit method has 0.1-0.4dB PSNR loss. Notably, even with the implicit method, MoTIF outperforms VideoINR by 0.1-0.4dB in" + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "23138" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 82, + 103, + 250, + 165 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 287, + 95 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 287, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 287, + 95 + ], + "type": "text", + "content": "Table 4: Backward vs. forward motion in MoTIF. Quality metrics: PSNR/SSIM. Bold indicates the best performance." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 82, + 103, + 250, + 165 + ], + "lines": [ + { + "bbox": [ + 82, + 103, + 250, + 165 + ], + "spans": [ + { + "bbox": [ + 82, + 103, + 250, + 165 + ], + "type": "table", + "html": "
BackwardForward
Vid425.35 / 0.769625.79 / 0.7745
GoPro-Center29.98 / 0.876531.04 / 0.8877
GoPro-Average29.38 / 0.869330.04 / 0.8773
Adobe-Center29.73 / 0.872330.63 / 0.8839
Adobe-Average29.14 / 0.865829.82 / 0.8750
", + "image_path": "cd5adb101cfbce59a347d8d420f467f2c1559385ceb7a1afdedcf6b47c23e6d1.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 48, + 217, + 282, + 278 + ], + "blocks": [ + { + "bbox": [ + 47, + 172, + 286, + 206 + ], + "lines": [ + { + "bbox": [ + 47, + 172, + 286, + 206 + ], + "spans": [ + { + "bbox": [ + 47, + 172, + 286, + 206 + ], + "type": "text", + "content": "Table 5: Explicit vs. implicit motion modeling in MoTIF. Quality metrics: PSNR/SSIM. Bold indicates the best performance." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 217, + 282, + 278 + ], + "lines": [ + { + "bbox": [ + 48, + 217, + 282, + 278 + ], + "spans": [ + { + "bbox": [ + 48, + 217, + 282, + 278 + ], + "type": "table", + "html": "
VideoINRMoTIF (Implicit)MoTIF (Explicit)
Vid425.61 / 0.770925.71 / 0.772125.79 / 0.7745
GoPro-Center30.26 / 0.879230.58 / 0.885631.04 / 0.8877
GoPro-Average29.41 / 0.866929.81 / 0.874430.04 / 0.8773
Adobe-Center29.92 / 0.874630.24 / 0.879630.63 / 0.8839
Adobe-Average29.27 / 0.865129.59 / 0.871929.82 / 0.8750
", + "image_path": "8bc2a381033739aecf9ee2df8907a2dc4166ac59f5fac2fd2b7b19b8ca5fd1cd.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 285, + 286, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 285, + 286, + 308 + ], + "spans": [ + { + "bbox": [ + 47, + 285, + 286, + 308 + ], + "type": "text", + "content": "PSNR, suggesting that the other components of MoTIF are essential." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "spans": [ + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "content": "Feature Warping and Reliability Maps. Table 6 presents ablation results to understand the contributions of different components in MoTIF. Four variants of MoTIF are investigated, including (a) using only " + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "inline_equation", + "content": "F_{(0,1)}^{H}" + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "content": " for decoding, (b) using both " + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "inline_equation", + "content": "F_{(0,1)}^{H}" + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "inline_equation", + "content": "F_{t}^{H}" + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "content": " for decoding, (c) using " + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "inline_equation", + "content": "F_{(0,1)}^{H}" + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "inline_equation", + "content": "F_{t}^{H}" + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "content": " for decoding while encoding the reliability maps " + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "inline_equation", + "content": "Z_{0\\to 1}^{L}, Z_{1\\to 0}^{L}" + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "content": " of forward motion into the motion latents, and (d) the full model (i.e. variant (c) plus " + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "inline_equation", + "content": "Z_{t}^{H}" + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "content": "). From Table 6, the considerable PSNR gain of (b) over (a) indicates that our ST-INF is effective in interpolating forward motion for propagating the reference features. The incremental improvement from (b) to (c) suggests that the reliability maps " + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "inline_equation", + "content": "Z_{0\\to 1}^{L}, Z_{1\\to 0}^{L}" + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "content": " help to improve the quality of the interpolated forward motion. Last but not least, the additional use of " + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "inline_equation", + "content": "Z_{t}^{H}" + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "content": " in the decoding process ((d) vs. (c)) does allow the decoder to better combine " + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "inline_equation", + "content": "F_{(0,1)}^{H}" + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "inline_equation", + "content": "F_{t}^{H}" + }, + { + "bbox": [ + 47, + 316, + 287, + 517 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 521, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 521, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 521, + 287, + 715 + ], + "type": "text", + "content": "Tri-linear Motion and More Reference Frames. Table 7 investigates the benefits of our space-time implicit neural function (ST-INF) by comparing its performance with tri-linear motion interpolation and by showing its applicability to more reference frames. From Table 7, we observe that when ST-INF is replaced with tri-linear motion interpolation-i.e., " + }, + { + "bbox": [ + 47, + 521, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\hat{M}_{0\\rightarrow t}^{H},\\hat{M}_{1\\rightarrow t}^{H}" + }, + { + "bbox": [ + 47, + 521, + 287, + 715 + ], + "type": "text", + "content": " are interpolated bilinearly from " + }, + { + "bbox": [ + 47, + 521, + 287, + 715 + ], + "type": "inline_equation", + "content": "M_{0\\rightarrow 1}^{L},M_{1\\rightarrow 0}^{L}" + }, + { + "bbox": [ + 47, + 521, + 287, + 715 + ], + "type": "text", + "content": ", respectively-the performance drops by 0.1-0.2dB in PSNR. Although ST-INF provides seemingly moderate gain, its advantage becomes obvious when the number of reference frames goes beyond two. In this case, ST-INF can benefit from encoding more forward motion into the motion latents. Conceptually, this amounts to taking more forward motion samples, which help to construct accurate motion trajectories. In the ablation experiment, two more reference frames " + }, + { + "bbox": [ + 47, + 521, + 287, + 715 + ], + "type": "inline_equation", + "content": "I_{-1}^{L},I_{2}^{L}" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 323, + 103, + 527, + 212 + ], + "blocks": [ + { + "bbox": [ + 306, + 70, + 544, + 95 + ], + "lines": [ + { + "bbox": [ + 306, + 70, + 544, + 95 + ], + "spans": [ + { + "bbox": [ + 306, + 70, + 544, + 95 + ], + "type": "text", + "content": "Table 6: Ablation experiment on individual components. (d) is the proposed MoTIF. Quality metric: PSNR." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 323, + 103, + 527, + 212 + ], + "lines": [ + { + "bbox": [ + 323, + 103, + 527, + 212 + ], + "spans": [ + { + "bbox": [ + 323, + 103, + 527, + 212 + ], + "type": "table", + "html": "
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As a consequence, the PSNR improves by 0.5-0.7dB. We expect the gain to be even higher if we generate more motion latents to propagate information from these extra reference frames (instead of only " + }, + { + "bbox": [ + 305, + 344, + 545, + 441 + ], + "type": "inline_equation", + "content": "I_0^L,I_1^L)" + }, + { + "bbox": [ + 305, + 344, + 545, + 441 + ], + "type": "text", + "content": " . The simple tri-linear motion interpolation cannot benefit similarly from having more reference frames." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 454, + 378, + 466 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 454, + 378, + 466 + ], + "spans": [ + { + "bbox": [ + 306, + 454, + 378, + 466 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 475, + 545, + 630 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 475, + 545, + 630 + ], + "spans": [ + { + "bbox": [ + 305, + 475, + 545, + 630 + ], + "type": "text", + "content": "This paper introduces a C-STVSR framework, known as MoTIF. It features a space-time implicit neural function for encoding forward motion, and a reliability-aware splatting and decoding scheme for fusing spatiotemporal information from multiple reference frames. We show that learning forward motion amounts to learning individual motion trajectories rather than a mixture of motion trajectories as with learning backward motion. In addition, for better aggregating temporal information via forward warping, performing splatting and decoding based on the reliability of forward motion is crucial. With all these techniques combined, MoTIF demonstrates superior quantitative and qualitative performance to the state-of-the-art methods for C-STVSR." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 644, + 403, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 644, + 403, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 644, + 403, + 658 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 665, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 545, + 714 + ], + "type": "text", + "content": "This work is supported by National Science and Technology Council, Taiwan under Grants NSTC 111-2634-F-A49-010- and MOST 110-2221-E-A49-065-MY3, and National Center for High-performance Computing." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "23139" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 92, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "spans": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "type": "text", + "content": "[1] Wenbo Bao, Wei Sheng Lai, Xiaoyun Zhang, Zhiyong Gao, and Ming Hsuan Yang. 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International Journal of Computer Vision (IJCV), 127(8):1106-1125, 2019." + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "23141" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Modality Unifying Network for Visible-Infrared Person Re-Identification/c25cccee-cf9c-444a-bfaa-52844fa6cb10_content_list.json b/2023/Modality Unifying Network for Visible-Infrared Person Re-Identification/c25cccee-cf9c-444a-bfaa-52844fa6cb10_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..8f44832dda46b517d08d8bccb467d242402b2dcb --- /dev/null +++ b/2023/Modality Unifying Network for Visible-Infrared Person Re-Identification/c25cccee-cf9c-444a-bfaa-52844fa6cb10_content_list.json @@ -0,0 +1,1908 @@ +[ + { + "type": "text", + "text": "Modality Unifying Network for Visible-Infrared Person Re-Identification", + "text_level": 1, + "bbox": [ + 117, + 130, + 852, + 151 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Hao Yu $^{1}$ , Xu Cheng $^{1*}$ , Wei Peng $^{2}$ , Weihao Liu $^{3}$ , Guoying Zhao $^{4}$", + "bbox": [ + 217, + 179, + 776, + 198 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1School of Computer Science, Nanjing University of Information Science and Technology, China", + "bbox": [ + 116, + 198, + 880, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{2}$ Department of Psychiatry and Behavioral Sciences, Stanford University, USA", + "bbox": [ + 187, + 215, + 807, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{3}$ School of Computer Science and Technology, Soochow University, China", + "bbox": [ + 205, + 233, + 792, + 251 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "4Center for Machine Vision and Signal Analysis, University of Oulu, Finland", + "bbox": [ + 192, + 251, + 800, + 268 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{yuhao,xcheng}@nuist.edu.cn, wepeng@stanford.edu, whliu@stu.suda.edu.cn, guoying.zhao@oulu.fi", + "bbox": [ + 86, + 272, + 906, + 287 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 321, + 313, + 338 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Visible-infrared person re-identification (VI-ReID) is a challenging task due to large cross-modality discrepancies and intra-class variations. Existing methods mainly focus on learning modality-shared representations by embedding different modalities into the same feature space. As a result, the learned feature emphasizes the common patterns across modalities while suppressing modality-specific and identity-aware information that is valuable for Re-ID. To address these issues, we propose a novel Modality Unifying Network (MUN) to explore a robust auxiliary modality for VI-ReID. First, the auxiliary modality is generated by combining the proposed cross-modality learner and intra-modality learner, which can dynamically model the modality-specific and modality-shared representations to alleviate both cross-modality and intra-modality variations. Second, by aligning identity centres across the three modalities, an identity alignment loss function is proposed to discover the discriminative feature representations. Third, a modality alignment loss is introduced to consistently reduce the distribution distance of visible and infrared images by modality prototype modeling. Extensive experiments on multiple public datasets demonstrate that the proposed method surpasses the current state-of-the-art methods by a significant margin.", + "bbox": [ + 76, + 353, + 472, + 703 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 744, + 209, + 760 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Person re-identification (Re-ID) [8,33] aims at matching pedestrian images captured from multiple non-overlapping cameras. Over the past few years, it has received increased attention due to its huge practical value in modern surveillance systems. Previous studies [10, 16, 19, 30, 40] mainly focus on matching pedestrian images captured from visible cameras and formulate the Re-ID task as a single-modality", + "bbox": [ + 75, + 771, + 468, + 878 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "matching issue. Nevertheless, visible cameras may not provide accurate appearance information about persons in scenarios with poor illumination. To address this limitation, modern surveillance systems also employ infrared cameras, which can capture clear images in low-light conditions at night. As a result, visible-infrared person re-identification (VI-ReID) [1, 28, 29] has become a topic of growing interest in recent times, which seeks to match infrared images of the same identity when given a visible query across multiple camera views and vice versa.", + "bbox": [ + 500, + 323, + 893, + 473 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "VI-ReID is challenging due to the huge cross-modality discrepancy between visible and infrared images, as well as the intra-modality variation in person bodies such as pose variation and dress change. Existing methods [1, 20, 29, 31, 36, 37] primarily focus on relieving the cross-modality discrepancy by extracting modality-shared features to perform the feature-level alignment. Some studies [1, 20, 28, 31, 34] employ two-stream networks for cross-modality feature embedding, while others [3, 24, 25, 36] utilize Generative Adversarial Networks (GANs) to generate shared representations from visible and infrared images. However, these methods discard modality-specific features (such as colour and texture) that contain useful identity-aware patterns against intra-modality variations. Consequently, the learned features may not fully capture the variation of human bodies and thus lack discriminability. To address this limitation, the modality-unifying methods, e.g., X-modality [9], DFM [7], SMCL [27], have been proposed to acquire the auxiliary modality by fusing visible and infrared modalities, encoding both modality-specific and modality-shared patterns to jointly relieve cross- and intramodality discrepancies. In the SMCL [27], the authors proposed a syncretic modality generated by fusing visible and infrared pixels, which can bridge the gap between visible and infrared modalities while maintaining discriminability as the modality-specific information is preserved.", + "bbox": [ + 496, + 474, + 893, + 868 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "However, the existing modality-unifying works still have three weaknesses. (1) Pixel fusion. Previous works gener-", + "bbox": [ + 500, + 869, + 893, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding Author (Email: xcheng@nuist.edu.cn)", + "bbox": [ + 94, + 886, + 387, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "11185", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/99eeae7753986a7c0b731b38bb3cce3f2652ebd86627c480950a271a0c41b221.jpg", + "image_caption": [ + "Figure 1. The main idea behind generating a strong auxiliary modality for the VI-ReID task. The IML and CML denote the intra-modality learner and cross-modality learner, respectively." + ], + "image_footnote": [], + "bbox": [ + 81, + 88, + 460, + 257 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ate the auxiliary modality by fusing pixels of the raw visible and infrared images, which makes the richness of semantic patterns either equal to the original two modalities or lower in the case of pixel misalignment. In fact, the auxiliary modality is utilized to guide the learning of visible and infrared modalities, but the insufficient semantic patterns lead to a lack of identity-related information and severely limit the capacity to relieve intra-modality variations in VI-ReID. (2) Discrepancy bias. During the VI training, the relative distances between visible and infrared images are constantly changing, which causes a dynamic bias toward the balance of intra- and cross-modality discrepancies. Thus, an ideal auxiliary modality should be able to dynamically control the ratio of modality-specific and modality-shared patterns it contains to model the evolving modality discrepancies. However, the existing studies simply use the global information of visible and infrared images to obtain the auxiliary representations, which are inflexible in adjusting the patterns they describe, leading to low robustness.", + "bbox": [ + 75, + 324, + 467, + 611 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "(3) Inconsistency constraints. Existing studies usually utilize features in the current batch to represent the overall distribution for distance optimization. However, this strategy suffers from randomness, as the training samples are different in each batch, which may cause a certain inconsistency in the learned feature relationships in different training stages, thus damaging the generalizability.", + "bbox": [ + 75, + 611, + 467, + 717 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Inspired by the above discussions, we propose a novel Modality Unifying Network (MUN) to explore an effective and robust auxiliary modality for VI-ReID. The main idea of our auxiliary modality is illustrated in Figure 1. Specifically, we introduce an auxiliary generator comprising two intra-modality learners (IML) and one cross-modality learner (CML) to distil the modality-related patterns from visible and infrared images. Two IMLs are presented to identify the modality-specific and identity-aware patterns from visible and infrared images, respectively. They exploit multiple depth-wise convolutions with various kernel sizes to capture fine-grained semantic patterns in the human", + "bbox": [ + 75, + 719, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "body across multiple receptive fields. Based on the outputs of two IMLs, the CML leverages spatial pyramid pooling to extract multi-scale feature representations and then fuse the modality-shared patterns learned in each feature scale. By combining IML and CML, the proposed auxiliary generator can generate a powerful auxiliary modality that is rich in modality-shared and discriminative patterns to alleviate both cross-modality and intra-modality discrepancies. In addition, the layer scale scheme is used to control the ratio of patterns learned from IML and CML, which can dynamically adjust the modality-specific and modality-shared patterns in the generated auxiliary representation.", + "bbox": [ + 496, + 90, + 890, + 271 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Furthermore, to reveal the identity-related patterns in each identity set, an effective identity alignment loss $(L_{ia})$ is designed to optimize the distances of tri-modality identity centres. In addition, to regulate the distribution level feature relationships while relieving the inconsistency issue caused by sample variations, a novel modality alignment loss $(L_{ma})$ is designed to minimize the distances of three modalities, which utilizes the modality prototype to represent the learned modality information in each iteration.", + "bbox": [ + 496, + 272, + 890, + 407 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In general, the major contributions of this paper can be summarized as follows.", + "bbox": [ + 500, + 407, + 890, + 436 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a novel modality unifying network for the VI-ReID task by constructing a robust auxiliary modality, which contains rich semantic information from visible and infrared images to address modality discrepancies and reveal discriminative knowledge.", + "- A novel auxiliary generator constructed by the intramodality and cross-modality learners is introduced to dynamically extract identity-aware and modality-shared patterns from heterogeneous images.", + "- The identity alignment loss and modality alignment loss are designed to jointly explore the generalized and discriminative feature relationships of the three modalities at both the identity and distribution levels.", + "- Extensive experiments on several public VI-ReID datasets verify the effectiveness of the proposed method and modality unifying scheme, which outperforms the current state of the arts by a large margin." + ], + "bbox": [ + 517, + 443, + 890, + 722 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 739, + 640, + 753 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Single-Modality Person Re-ID. Single-modality person re-identification [11, 17, 33] aims to match pedestrian images across different visible cameras. It presents challenges such as changes in viewpoint and human pose across camera views. Current approaches mainly focus on feature representation learning [15, 19, 39] and distance metric learning [10, 30, 35, 40]. Over the past few years, excellent performances have been achieved on several academic benchmarks. However, in practical scenarios, numerous crucial", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "11186", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/729e9611e84e0aa4722a76ed2bfc5b5169886ccd909bdf7b6fd258548c03a811.jpg", + "image_caption": [ + "Figure 2. The overall architecture of the proposed MUN for VI-ReID. GeMP denotes the Generalized Mean Pooling [21]. The pretrained ResNet-50 [4] is adopted as the baseline network. To meet the specific requirements of VI-ReID, we initialize the first stage of the ResNet-50 twice as two independent ResBlocks to extract the low-level visible and infrared features, respectively. The remaining stages are utilized as modality-shared ResBlocks. During the inference, only visible and infrared modalities are utilized to perform cross-modality retrieval." + ], + "image_footnote": [], + "bbox": [ + 112, + 102, + 844, + 354 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "surveillance photos and videos are captured at night using infrared cameras. When it comes to matching pedestrians across visible and infrared modalities, the capabilities of these single-modality methods are limited due to their inability to address the huge modality gap. In contrast, we present an effective modality unifying network to bridge the modality gap and achieve precise cross-modality pedestrian matching in 24-hour monitoring scenarios.", + "bbox": [ + 75, + 436, + 470, + 556 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Visible-Infrared Person Re-ID. Visible-Infrared person Re-ID [28] is a challenging task due to the cross-modality discrepancies between visible and infrared images, as well as the intra-modality variations such as pose and dress changes. Existing studies [20, 29, 31, 32, 34] mainly focus on learning the modality-shared representations to align the visible and infrared modalities. Some generation-based methods [24-26,36] have been developed to achieve modality alignment or translation by using Generative Adversarial Network (GAN). For instance, Wang et al. [24] proposed a dual-alignment network that used GAN to jointly learn pixel and feature level alignment. The D2RL [26] is proposed to perform image-level modality translation by adversarial training that relieves the cross-modality discrepancy. Other works [1, 20, 29, 31, 34] attempt to learn modality-shared features by designing two-stream networks to perform cross-modality feature embedding. Ye et al. [34] proposed a dual-constrained top-ranking method with a weight-shared two-stream network. Wu et al. [29] designed a cross-modality attention scheme to help the two-stream backbone discover cross-modality nuances. However, these methods usually discard modality-specific representations", + "bbox": [ + 75, + 568, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "that help to relieve intra-modality variations, leading to low robustness and discriminability in learned features.", + "bbox": [ + 498, + 436, + 890, + 467 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In order to capture both the modality-shared and identity-aware patterns from heterogeneous images, modality-unifying methods have been developed. These methods aim to obtain the auxiliary modality by combining modality-specific and modality-shared representations from both visible and infrared images. The syncretic modality [27] is proposed to guide the generation of discriminative and modality-invariant representations. The DFM [7] acquires the mixed modality by integrating visible and infrared pixels. However, these methods generate the auxiliary modality by directly fusing the raw pixels of visible and infrared images, making their auxiliary modality lack high-level semantic patterns and inflexible to adjust its representations.", + "bbox": [ + 496, + 468, + 892, + 678 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To tackle these challenges, this paper presents the intramodality learner and cross-modality learner to dynamically uncover substantial modality-shared and discriminative patterns from multiple receptive fields and feature scales. By integrating these learners, we introduce a powerful auxiliary modality that effectively bridges the modality discrepancy and enhances the discriminability of learned features.", + "bbox": [ + 496, + 679, + 890, + 787 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 500, + 799, + 635, + 816 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As shown in Figure 2, we introduce the details of the Modality Unifying Network. We first utilize two independent ResBlocks to extract low-level features from visible and infrared images, respectively. Then, the auxiliary generator is designed to generate the auxiliary features by com", + "bbox": [ + 496, + 825, + 890, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "11187", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "bining intra-modality and cross-modality learners. Afterwards, the visible, infrared, and auxiliary features are fed into weight-shared ResBlocks to learn high-level patterns. The auxiliary features can serve as a bridge to relieve both intra- and cross-modality discrepancies during the training. Based on the visible, infrared, and auxiliary features learned by weight-shared ResBlocks, four loss functions are developed to effectively improve cross-modality matching accuracy, including identity loss $L_{id}$ , identity consistency loss $L_{idc}$ , identity alignment loss $L_{ia}$ and modality alignment loss $L_{ma}$ .", + "bbox": [ + 75, + 90, + 472, + 257 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Auxiliary Generator", + "text_level": 1, + "bbox": [ + 76, + 265, + 271, + 280 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The auxiliary generator contains two intra-modality learners (IML) and one cross-modality learner (CML). The two IMLs are designed to mine identity-related patterns from visible and infrared images, respectively. The CML is designed to learn modality-shared patterns based on the outcomes of two IMLs. The detailed architectures of IML and CML are shown in Figure 3.", + "bbox": [ + 75, + 287, + 468, + 393 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Intra-Modality Learner. The intra-modality learner (IML) is designed to capture the discriminative and identity-aware patterns in human bodies. The visible or infrared low-level features $\\mathbf{F}^m\\in \\mathbb{R}^{C\\times H\\times W}$ , $m\\in \\{v,r\\}$ extracted from two independent ResBlocks are regarded as the input of IML, where $m$ denotes the visible or infrared modality.", + "bbox": [ + 75, + 393, + 468, + 484 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To enrich the receptive field while keeping low computational complexity, we equally divide $\\mathbf{F}^m$ into two parts along the channel dimension by matrix slice operation.", + "bbox": [ + 75, + 484, + 468, + 530 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {F} _ {c _ {1}} ^ {m} = \\mathbf {F} ^ {m} [ 0: C / 2,: :, ] \\quad , \\quad \\mathbf {F} _ {c _ {2}} ^ {m} = \\mathbf {F} ^ {m} [ C / 2: C,:,: ]. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 114, + 536, + 468, + 554 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Then, we employ $7 \\times 7$ and $5 \\times 5$ depth-wise convolutions $(D)$ to operate on $\\mathbf{F}_{c_1}^m$ and $\\mathbf{F}_{c_2}^m$ , respectively. This allows us to capture spatial patterns in different receptive fields.", + "bbox": [ + 76, + 560, + 468, + 604 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {R} ^ {m} = \\operatorname {C o n c a t} \\left\\{D _ {5 \\times 5} \\left(\\mathbf {F} _ {c _ {1}} ^ {m}\\right), D _ {7 \\times 7} \\left(\\mathbf {F} _ {c _ {2}} ^ {m}\\right) \\right\\}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 143, + 612, + 468, + 628 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\text{Concat}$ denotes the concatenation on channel dimension; $\\mathbf{R}^m$ indicates the visible or infrared features captured from multiple receptive fields. Then, a point-wise convolution $(P)$ is utilized to fuse patterns with diverse receptive fields by connecting pixels in each channel.", + "bbox": [ + 75, + 636, + 468, + 710 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {R} _ {1} ^ {m} = P _ {1 \\times 1} (B a t c h N o r m (\\mathbf {R} ^ {m})). \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 718, + 468, + 734 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To integrate and encode the structural information in human bodies, another depth-wise convolution with $3 \\times 3$ kernel size is introduced to remodel the learned spatial map. This layer also utilizes a residual branch to retain information from the previous layer.", + "bbox": [ + 75, + 741, + 468, + 816 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {R} _ {2} ^ {m} = D _ {3 \\times 3} \\left(R e L U \\left(\\mathbf {R} _ {1} ^ {m}\\right)\\right) + \\mathbf {R} _ {1} ^ {m}. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 165, + 824, + 468, + 840 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In addition, another point-wise convolution is utilized to fuse patterns with diverse receptive fields in $\\mathbf{R}_2^m$ .", + "bbox": [ + 76, + 847, + 468, + 878 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {F}} ^ {m} = I _ {\\text {s c a l e}} * P _ {1 \\times 1} \\left(\\operatorname {B a t c h N r o m} \\left(\\mathbf {R} _ {2} ^ {m}\\right)\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 142, + 883, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/11e61430bce8992a46b6512243bb67e6ed134a2ba566f83bfca42d438b382215.jpg", + "image_caption": [ + "Figure 3. The detailed architecture of the proposed intra-modality learner (IML) and cross-modality learner (CML). They are designed to decouple the modeling of modality-related knowledge." + ], + "image_footnote": [], + "bbox": [ + 514, + 89, + 687, + 301 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/a40481b955e23157285d07657fbce6c91c9830b3ec344e3a1d44649c7447657a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 702, + 89, + 880, + 301 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $I_{scale} \\in (0,1]$ is the learnable layer scale factor used to control the ratio of intra-modality patterns learned by IML; $\\hat{\\mathbf{F}}^m$ denotes the outcomes of the two IMLs.", + "bbox": [ + 498, + 372, + 890, + 419 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In the proposed intra-modality learner, three depth-wise convolutions with various kernel sizes are well combined to capture the identity-related patterns that existed in various receptive fields. Two point-wise convolutions are utilized for pattern integration and channel relation reasoning based on the inverted residual architecture [12]. The first point-wise convolution increases the channel dimension from $C$ to $C * 4$ and the last point-wise convolution reduces the channel dimension from $C * 4$ to $C$ .", + "bbox": [ + 496, + 419, + 892, + 554 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Cross-Modality Learner. The cross-modality learner is designed to mine the modality-shared patterns from multiple feature scales based on the outcomes of two IMLs. Specifically, the spatial pyramid features are mined by applying $n$ average pooling layers with various ratios.", + "bbox": [ + 496, + 555, + 890, + 631 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {S} _ {1} ^ {m} = \\operatorname {A v g p o o l} _ {1} (\\hat {\\mathbf {F}} ^ {m}) ,\n$$\n", + "text_format": "latex", + "bbox": [ + 616, + 636, + 774, + 654 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{c c} \\mathbf {S} _ {2} ^ {m} = A v g p o o l _ {2} (\\hat {\\mathbf {F}} ^ {m}) & , \\\\ \\dots & , \\end{array} \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 616, + 656, + 890, + 691 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {S} _ {n} ^ {m} = \\operatorname {A v g p o o l} _ {n} (\\hat {\\mathbf {F}} ^ {m}) ,\n$$\n", + "text_format": "latex", + "bbox": [ + 616, + 694, + 774, + 710 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\{\\mathbf{S}_1^m,\\mathbf{S}_2^m,\\dots,\\mathbf{S}_n^m\\}, m\\in \\{v,r\\}$ denote the spatial pyramid features with various feature scales. Afterwards, we obtain the modality-shared spatial patterns from each pair of cross-modality spatial pyramid features $\\{\\mathbf{S}_i^v,\\mathbf{S}_i^r\\}_{i = 1}^n$ with the same feature scale by using a group of learnable transposed convolutions $\\{TR_1,TR_2,\\dots,TR_n\\}$ .", + "bbox": [ + 496, + 717, + 890, + 809 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {S}} _ {i} ^ {v} = T R _ {i} \\left(\\mathbf {S} _ {i} ^ {v}\\right), \\quad \\hat {\\mathbf {S}} _ {i} ^ {r} = T R _ {i} \\left(\\mathbf {S} _ {i} ^ {r}\\right), \\quad i = 1, 2, \\dots , n. \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 519, + 814, + 890, + 834 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here, the spatial dimensions of each cross-modality feature pair $\\hat{\\mathbf{S}}_i^v$ and $\\hat{\\mathbf{S}}_i^r$ are rebuilt to $H\\times W$ by the corresponding transposed convolution $TR_{i}$ , respectively. In this manner, the significant patterns of visible and infrared features", + "bbox": [ + 496, + 840, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "11188", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "on each feature scale are embedded together, which helps to discover and amplify the abundant modality-shared information on multiple feature scales.", + "bbox": [ + 75, + 90, + 468, + 135 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Further, all the embedded features are concatenated on the channel dimension via Eq.(8).", + "bbox": [ + 76, + 136, + 468, + 167 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {S}} = \\operatorname {C o n c a t} \\left\\{\\hat {\\mathbf {S}} _ {i} ^ {v}, \\hat {\\mathbf {S}} _ {2} ^ {v}, \\dots , \\hat {\\mathbf {S}} _ {n} ^ {v}, \\hat {\\mathbf {S}} _ {1} ^ {r}, \\hat {\\mathbf {S}} _ {2} ^ {r}, \\dots , \\hat {\\mathbf {S}} _ {n} ^ {r} \\right\\}. \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 138, + 171, + 468, + 189 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Then, the auxiliary feature is obtained by fusing patterns captured from multiple feature scales.", + "bbox": [ + 76, + 195, + 468, + 224 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {F} ^ {a} = C _ {\\text {s c a l e}} * P _ {1 \\times 1} (\\operatorname {B a t c h N o m r} (\\hat {\\mathbf {S}})), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 148, + 232, + 468, + 248 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{F}^a$ denotes the auxiliary feature generated by our method. It contains substantial modality-shared and identity-aware information captured by three learners; $C_{scale} \\in (0,1]$ denotes the learnable layer scale factor used to control the ratio of modality-shared representations in the learned auxiliary feature $\\mathbf{F}^a$ ; $P_{1 \\times 1}$ is a point-wise convolution used to fuse patterns across different channels.", + "bbox": [ + 75, + 253, + 468, + 358 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The CML mines significant patterns from multiple feature scales and amplifies the modality-shared parts from them using transposed convolutions. It makes our auxiliary feature a powerful tool to handle cross-modality variations.", + "bbox": [ + 75, + 359, + 468, + 420 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2. Classification Constraint", + "text_level": 1, + "bbox": [ + 76, + 426, + 303, + 441 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To ensure the learned visible and infrared features are identity-related, the identity loss $(L_{id})$ implemented with the cross-entropy term is introduced as follows.", + "bbox": [ + 75, + 450, + 468, + 494 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {i d} ^ {m} = - \\frac {1}{k} \\sum_ {i = 1} ^ {k} \\log P \\left(y _ {i} \\mid C _ {m} \\left(\\mathbf {Z} _ {i} ^ {m}\\right)\\right), \\quad s. t. \\quad m \\in \\{v, r \\}, \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 501, + 468, + 549 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{Z}_i^v$ and $\\mathbf{Z}_i^r$ denote the generalized mean pooled visible and infrared features in the $i$ -th identity, respectively. $k$ is the number of visible or infrared images in each batch; $y_i$ is the $i$ -th identity label; $C_v(\\cdot)$ and $C_r(\\cdot)$ are the predictions of visible and infrared classifiers, respectively.", + "bbox": [ + 75, + 550, + 468, + 626 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The learned presentations are modality-shared if two classifiers can give consistent predictions for features from any modalities. However, if we directly apply features in one modality to the classifier in another modality (e.g., $C_r(\\mathbf{Z}^v)$ ), it may impose the classifier to learn modality-specific patterns rather than the modality-shared patterns, as the former is typically more discriminative. To solve this issue, we present an identity-consistency loss $L_{idc}$ to update the parameters of both visible and infrared classifiers with the aid of auxiliary features. It can be defined as follows.", + "bbox": [ + 75, + 626, + 468, + 777 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {i d c} = - \\frac {1}{k} \\sum_ {i = 1} ^ {k} \\left[ \\log P \\left(y _ {i} \\mid C _ {v} \\left(\\mathbf {Z} _ {i} ^ {a}\\right)\\right) + \\log P \\left(y _ {i} \\mid C _ {r} \\left(\\mathbf {Z} _ {i} ^ {a}\\right)\\right) \\right], \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 782, + 468, + 820 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{Z}_i^a$ denotes the pooled auxiliary feature in the $i$ -th identity. The auxiliary features effectively integrate visible and infrared patterns, facilitating the transfer of identity-related knowledge between modalities without compromising the original intra-modality learning.", + "bbox": [ + 75, + 824, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Identity Alignment Loss", + "text_level": 1, + "bbox": [ + 500, + 90, + 720, + 106 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To relieve the class-level modality discrepancies and learn discriminative feature relationships, the identity alignment loss $L_{ia}$ is designed to align the visible and infrared features of each identity with the aid of auxiliary features.", + "bbox": [ + 498, + 114, + 890, + 175 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} L _ {i a} = \\sum_ {i = 1} ^ {P} \\left[ \\alpha + \\max _ {m _ {1} \\in \\{v, r \\}} \\left| \\left| \\mathbf {C} _ {i} ^ {a} - \\mathbf {C} _ {i} ^ {m _ {1}} \\right| \\right| _ {2} \\right. \\tag {12} \\\\ -\\min_{\\substack{m_{2}\\in \\{v,r\\} \\\\ q\\neq i}}||\\mathbf{C}_{i}^{a} - \\mathbf{C}_{q}^{m_{2}}||_{2}\\Bigg], \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 563, + 186, + 890, + 258 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\alpha$ is the margin parameter; $P$ denotes the number of person identities; $N$ is the number of images in the $i$ -th identity; $\\mathbf{C}_i^a = \\frac{1}{N}\\sum_{j=1}^{N}\\mathbf{Z}_{i,j}^a$ , $\\mathbf{C}_i^v = \\frac{1}{N}\\sum_{j=1}^{N}\\mathbf{Z}_{i,j}^v$ , $\\mathbf{C}_i^r = \\frac{1}{N}\\sum_{j=1}^{N}\\mathbf{Z}_{i,j}^r$ are the auxiliary, visible, and infrared centres in the $i$ -th identity, respectively; $\\mathbf{Z}_{i,j}^v$ , $\\mathbf{Z}_{i,j}^r$ and $\\mathbf{Z}_{i,j}^a$ denote the $j$ -th visible, infrared, and auxiliary features in the $i$ -th identity set.", + "bbox": [ + 496, + 272, + 890, + 381 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this paper, identity alignment loss is proposed to optimize the hardest cross-modality positive and negative centre pairs in a triplet-metric manner. It regulates discriminative and robust feature relationships by forcing all identities to form a tight intra-class space and pushing centres of different identities away across the three modalities.", + "bbox": [ + 496, + 383, + 890, + 473 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Modality Alignment Loss", + "text_level": 1, + "bbox": [ + 500, + 484, + 730, + 500 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Previous works [7, 20, 29] typically align the two modalities by constraining visible and infrared features in each iteration. This scheme suffers from inconsistencies in the learned cross-modality feature relationships because the training samples are different in each iteration. To overcome this issue, we propose a modality alignment strategy that consistently aligns visible and infrared modalities by modeling the prototypes from features in each iteration.", + "bbox": [ + 496, + 508, + 890, + 628 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Specifically, we first introduce three modality prototypes to represent the global information of visible, infrared, and auxiliary modalities, respectively. They can be denoted as $\\mathbf{T}^v = \\{\\mathbf{t}_1^v,\\mathbf{t}_2^v,\\dots,\\mathbf{t}_B^v\\}$ , $\\mathbf{T}^r = \\{\\mathbf{t}_1^r,\\mathbf{t}_2^r,\\dots,\\mathbf{t}_B^r\\}$ and $\\mathbf{T}^a = \\{\\mathbf{t}_1^a,\\mathbf{t}_2^a,\\dots,\\mathbf{t}_B^a\\} \\in \\mathbb{R}^{B\\times C}$ , where $\\mathbf{t}_i^v,\\mathbf{t}_i^r$ and $\\mathbf{t}_i^a$ are the modality prototypes for the $i$ -th visible, infrared, and auxiliary features in each training batch $(B)$ , respectively.", + "bbox": [ + 496, + 630, + 890, + 734 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The initial prototypes of the three modalities are obtained based on the pooled features $[\\mathbf{Z}^v ]^0$ $[\\mathbf{Z}^r ]^0$ and $[\\mathbf{Z}^a ]^0\\in$ $R^{B\\times C}$ in the 0-th iteration.", + "bbox": [ + 500, + 736, + 890, + 781 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n[ \\mathbf {T} ^ {m} ] ^ {0} = \\mathbf {W} _ {p} ^ {m} [ \\mathbf {Z} ^ {m} ] ^ {0}, \\quad s. t. \\quad m \\in \\{v, r, a \\}, \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 794, + 890, + 811 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{W}_p^m$ are learnable matrices to distil modality-related patterns from the $m$ -th modality. $[\\mathbf{T}^m]^{0}$ denotes the prototype of the $m$ -th modality calculated in the 0-th iteration.", + "bbox": [ + 496, + 824, + 890, + 869 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Further, to dynamically model the modality information during the training, we develop a temporal accumulation", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "11189", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "strategy to update the modality prototype by the learned features in each iteration, which can be defined as follows.", + "bbox": [ + 76, + 90, + 468, + 119 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} [ \\mathbf {T} ^ {m} ] ^ {i} = [ \\beta ] ^ {i} * \\mathbf {W} _ {p} ^ {m} [ \\mathbf {Z} ^ {m} ] ^ {i} + (1 - [ \\beta ] ^ {i}) * [ \\mathbf {T} ^ {m} ] ^ {i - 1}, \\tag {14} \\\\ s. t. \\quad m \\in \\{v, r, a \\}, \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 104, + 132, + 467, + 166 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $[\\mathbf{T}^m ]^i$ is the $m$ -th modality prototype calculated in the $i$ -th iteration; $\\beta$ is the updating ratio, which gradually increases from $1e^{-8}$ to 1 with the training goes on. The temporal accumulation strategy ensures that the modality information in each iteration is considered, thereby synchronizing the cross-modality alignment during the training.", + "bbox": [ + 76, + 179, + 467, + 271 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Based on the modality prototypes, the modality alignment loss $(L_{ma})$ is designed as:", + "bbox": [ + 76, + 272, + 467, + 301 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {m a} = \\frac {1}{P} \\sum_ {p = 1} ^ {P} \\left[ m m d \\left(\\mathbf {T} _ {p} ^ {v}, \\mathbf {T} _ {p} ^ {a}\\right) + m m d \\left(\\mathbf {T} _ {p} ^ {a}, \\mathbf {T} _ {p} ^ {r}\\right) \\right], \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 109, + 314, + 468, + 352 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathbf{T}_p^v$ , $\\mathbf{T}_p^r$ and $\\mathbf{T}_p^a$ denote visible, infrared, and auxiliary prototypes of the $p$ -th identity, respectively. $mmd(\\cdot, \\cdot)$ is the MMD loss [5] implemented the modality level alignment by constraining the distance of modality prototypes in each iteration. In Equation 15, the $mmd(\\mathbf{T}_p^v, \\mathbf{T}_p^a)$ is defined as:", + "bbox": [ + 76, + 364, + 468, + 443 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nm m d \\left(\\mathbf {T} _ {p} ^ {v}, \\mathbf {T} _ {p} ^ {a}\\right) = | | \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\phi \\left(\\mathbf {T} _ {p, i} ^ {v}\\right) - \\frac {1}{M} \\sum_ {j = 1} ^ {M} \\phi \\left(\\mathbf {T} _ {p, j} ^ {a}\\right) | | _ {H} ^ {2}, \\tag {16}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 454, + 468, + 492 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathbf{T}_{p,i}^{v}$ and $\\mathbf{T}_{p,j}^{a}$ denote the $i$ -th visible prototype and the $j$ -th auxiliary prototype in the $p$ -th identity, respectively; $||\\cdot||_{H}$ denotes the distribution measured by Gaussian kernel function $\\phi(\\cdot)$ which projects prototypes into the reproducing kernel Hilbert space. The $mmd(\\mathbf{T}_p^a,\\mathbf{T}_p^r)$ term can also be obtained in a similar way.", + "bbox": [ + 76, + 505, + 468, + 595 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The modality alignment loss is used to constrain the identity-guided distribution distances of visible, infrared, and auxiliary modalities through the prototypes. It can effectively reduce the modality discrepancy and relieve the inconsistency issue in learned feature relationships. Meanwhile, the auxiliary modality can act as a bridge to decrease the relative distance between visible and infrared modalities in the common feature space, thereby significantly reducing the optimization difficulty of cross-modality alignment.", + "bbox": [ + 75, + 595, + 468, + 732 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.5. Overall Loss Function", + "text_level": 1, + "bbox": [ + 76, + 743, + 284, + 757 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Following the previous works, we employ the identity loss $(L_{id} = L_{id}^{v} + L_{id}^{r})$ and hard-mining triplet loss $(L_{tri})$ [26,32] as our baseline loss functions. The overall loss function of the proposed MUN can be summarized as:", + "bbox": [ + 76, + 767, + 468, + 827 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {t o t a l} = L _ {i d} + L _ {t r i} + \\gamma * L _ {i d c} + \\theta * L _ {i a} + \\sigma * L _ {m a}, \\tag {17}\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 840, + 468, + 856 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\gamma, \\theta$ , and $\\sigma$ are parameters to balance the contribution of each proposed loss term during the training.", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 90, + 633, + 107 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Datasets and Evaluation Settings", + "text_level": 1, + "bbox": [ + 500, + 114, + 787, + 131 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "SYSU-MM01 [28] is the largest dataset for VI-ReID, which comprises six cameras, including four visible and two infrared cameras. It encompasses a total of 491 individuals, with 287,628 visible images and 15,792 infrared images. The training set is composed of 395 individuals, with 22,258 visible images and 11,909 infrared images. The test set consists of 96 individuals, with 3,803 infrared images for queries and a gallery selected from 301 visible images. The dataset offers two testing settings: all-search mode and indoor-search mode. For both modes, we employ the hardest single-shot setting to perform the evaluation.", + "bbox": [ + 496, + 137, + 890, + 303 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "RegDB [18] comprises 412 identities and a total of 8,240 images, with 206 identities allocated for training and another 206 identities for testing. Each identity is represented by 10 visible and 10 infrared images. The testing phase in RegDB involves two modes: Visible to Infrared, where visible images are searched using an infrared image, and Infrared to Visible, which entails the reverse scenario. For both modes, we repeat the testing process 10 times and average the results to report the mean values.", + "bbox": [ + 496, + 304, + 890, + 439 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation Settings. We utilize the standard cumulative matching characteristics (CMC) and mean average precision(mAP) as the evaluation metrics.", + "bbox": [ + 496, + 440, + 890, + 484 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Implementation Details", + "text_level": 1, + "bbox": [ + 500, + 496, + 715, + 511 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We implement all the experiments on the PyTorch framework with an NVIDIA RTX-3090 GPU. To ensure repeatability and facilitate fair comparisons with existing methods, we adopt the pretrained ResNet-50 [4] as our backbone network, where the first stage is initialized twice as two modality-specific ResBlocks, and the rest stages are used as the modality-shared ResBlocks.", + "bbox": [ + 496, + 518, + 890, + 625 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "At the training stage, all images are resized to $288 \\times 144$ . Data augmentations, including random horizontal flipping, erasing, and channel augmentations [31], are utilized against overfitting. Our model is trained with the AdamW optimizer [13] for 90 epochs with a weight decay of 0.01. The learning rate is gradually increased from $10^{-8}$ to 0.002 in the first 15 epochs and then decays by 0.1 at the $30^{th}$ and $60^{th}$ epochs. We find the optimal settings of all the hyper-parameters by grid search and repeated ablation experiments. Specifically, the pooling ratios of the spatial pyramid pooling in CML are set to be $\\{2, 4, 6, 12\\}$ ; The margin parameter $\\alpha$ is set to 0.55; the loss balance parameters $\\gamma$ , $\\theta$ , and $\\sigma$ are set to 0.25, 0.5, and 0.008, respectively.", + "bbox": [ + 496, + 625, + 890, + 821 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 830, + 653, + 847 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We evaluate the effectiveness of each proposed component on SYSY-MM01 and RegDB datasets, as shown in Table 1. Compared with the baseline (B) which only learns", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "11190", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "from visible and infrared modalities, the leveraging of auxiliary modality (Aux.) can effectively relieve both cross-modality and intra-modality discrepancies, thus greatly improving all the metrics on two datasets. Further, when applying the identity consistency loss $(L_{idc})$ to refine the modality-shared discriminative patterns, the performance is further improved. Meanwhile, the proposed identity alignment loss $(L_{ia})$ or modality alignment loss $(L_{ma})$ can enhance the cross-modality matching accuracy by aligning the visible and infrared features at the identity level or distribution level. By combining them, we can regulate a more robust cross-modality feature relationship, achieving a rank-1 of $76.24\\%$ and mAP of $73.81\\%$ on the SYSU-MM01 dataset. The results demonstrate that all the proposed components contribute consistently to the accuracy gain.", + "bbox": [ + 75, + 90, + 472, + 316 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "It is worth noting that when adding only the auxiliary modality to the baseline in Table 1, we employed a simple identity loss (like $L_{id}^{a}$ ) to supervise the auxiliary modality. This loss is deprecated when employing the proposed $L_{idc}$ to jointly supervise the three modalities.", + "bbox": [ + 75, + 316, + 470, + 393 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/ef88ecbb4f6f183e794bb1aacd9685ec935f37adfd79defffe545004f99525f6.jpg", + "table_caption": [ + "Table 1. Evaluation of different components of the proposed method on SYSU-MM01 and RegDB datasets. CMC (\\%) at rank 1 and mAP (\\%). The Red bold font and blue bold front denote the best and second best performances, respectively." + ], + "table_footnote": [], + "table_body": "
BAux.LidcLiaLmaSYSU-MM01RegDB
r=1mAPr=1mAP
✓57.4955.8375.4271.93
✓✓62.5558.4279.2673.81
✓✓✓66.5861.2983.5179.79
✓✓✓✓71.3565.5489.4284.66
✓✓✓✓69.7766.9689.9384.02
✓✓✓✓✓76.2473.8195.1987.15
", + "bbox": [ + 80, + 460, + 468, + 577 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/6f48439e235d87f034ace8d2d67fdd84174d9096d25b6d651c2724ac304ed31c.jpg", + "table_caption": [ + "Table 2. Performance of using different intermediate modalities in our MUN on two datasets. CMC (%) at rank 1 and mAP (%)" + ], + "table_footnote": [], + "table_body": "
Intermediate ModalitySYSU-MM01RegDB
r=1mAPr=1mAP
X-modality [9]66.1763.0679.9574.28
Mixed modality [7]66.4262.8579.4373.09
Syncretic modality [27]72.9568.7484.5979.11
Auxiliary modality (Ours)76.2473.8195.1987.15
", + "bbox": [ + 81, + 632, + 468, + 733 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Effectiveness of auxiliary modality. We conduct the ablations in the MUN by replacing our auxiliary modality with intermediate modalities designed by previous works, namely X [9], mixed [7], and syncretic [27]. As shown in Table 2, the X-modality is generated from visible images only, ignoring the impact of infrared modality and achieving relatively low performances. Although syncretic and mixed modalities combine both visible and infrared patterns, they only utilize pixel-level information, lacking the ability to discover fine-grained and semantic patterns.", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "When switching back to our auxiliary modality, we observed a significant improvement in performance with a boost of $3.29\\% / 5.07\\%$ in terms of rank-1/mAP on the SYSU-MM01 dataset. These results further prove that our auxiliary modality is superior to other intermediate modalities. In summary, our auxiliary modality can effectively integrate modality-related information from both visible and infrared images, while preserving strong discriminability. This promotes robust representation learning in VI-ReID.", + "bbox": [ + 496, + 90, + 890, + 226 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Effectiveness of loss design schemes. In the modality alignment loss $(L_{ia})$ , we design the modality prototype scheme to relieve the inconsistency issue and the auxiliary bridge scheme to reduce the optimization difficulty. To validate the effectiveness of these two schemes, we compare the performance of our method with or without using these two proposed schemes. As shown in Table 3.", + "bbox": [ + 496, + 227, + 890, + 333 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/7e45598e3a5a5145cf0a64ef5545c268e08748c526ee703525a26467ad895b6b.jpg", + "table_caption": [ + "Table 3. Performance comparison of with or without using the modality prototype and auxiliary (Aux.) bridge schemes in the modality alignment loss. CMC (%) at rank 1 and mAP (\\%)." + ], + "table_footnote": [], + "table_body": "
Schemes in LmaSYSU-MM01RegDB
PrototypeAux. bridger=1mAPr=1mAP
69.0265.8380.0973.97
✓74.1572.1086.7377.24
✓71.6668.3583.9275.54
✓✓76.2473.8195.1987.15
", + "bbox": [ + 504, + 388, + 887, + 484 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In Table 3, it is evident that both the modality prototype scheme and the auxiliary bridge scheme contribute to the VI-ReID accuracy gain. The modality prototype consistently captures global modality information, enhancing the robustness of learned modality relationships by synchronizing the alignment in each iteration; The auxiliary bridge scheme reduces the relative distance between visible and infrared features, effectively alleviating the difficulty of cross-modality distance optimization.", + "bbox": [ + 496, + 501, + 890, + 637 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Comparison with State-of-the-art Methods", + "text_level": 1, + "bbox": [ + 498, + 648, + 864, + 666 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we compare our MUN with state-of-the-art works on two public datasets, as shown in Table 4.", + "bbox": [ + 496, + 672, + 890, + 702 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Comparison on SYSU-MM01 dataset. As illustrated in Table 4, the proposed MUN achieves impressive results with $76.24\\%$ rank-1 and $73.81\\%$ mAP on the all-search mode of the SYSU-MM01 dataset. Compared to traditional visible-infrared representation learning methods (AGW [33], DELN-ViT [38], SPOT [1], PMT [14], CMT [6], MPANet [29]), our MUN outperforms them by a margin of at least $4.36\\%$ rank-1 and $5.24\\%$ mAP on the all-search mode. The reason can be attributed that the proposed visible-auxiliary-infrared learning framework can capture more identity-related knowledge across modalities and regulate the discriminative feature relationships well. Additionally, the overall performance of our approach is also", + "bbox": [ + 496, + 704, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "11191", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/2a1325370d346c8b962b124fab15f50c4e8c172187c4f6f81391ddd44ebd5555.jpg", + "table_caption": [ + "Table 4. Comparison with state-of-the-art methods on SYSU-MM01 and RegDB datasets. CMC (%) at rank r and mAP (%)" + ], + "table_footnote": [], + "table_body": "
MethodsRef.SYSU-MM01RegDB
All-SearchIndoor-SearchVisible to InfraredInfrared to Visible
r=1r=10mAPr=1r=10mAPr=1r=10mAPr=1r=10mAP
Zero-padding [28]ICCV1714.8054.1215.9520.5868.3826.9217.7534.2118.9016.6334.6817.82
JSIA-ReID [25]AAAI2038.1080.7036.9043.8086.2052.9048.50-49.3048.10-48.90
AlignGAN [24]ICCV1942.4085.0040.7045.9087.6054.3057.90-53.6056.30-53.40
AGW [33]TPAMI2147.5084.3947.6554.1791.1462.9770.0586.2167.6470.4987.2165.90
X-Modality [9]AAAI2049.9289.7950.73---62.2183.1360.18---
DFLN-ViT [38]TMM2259.8492.4957.7062.1394.8369.0392.1097.9782.1191.2198.2081.62
SPOT [1]TIP2265.3492.7362.2569.4296.2274.6380.3593.4872.4679.3792.7972.26
FMCNet [36]CVPR2266.34-62.5168.15-63.8289.12-84.4388.23-83.86
SMCL [27]ICCV2167.3992.8761.7868.8496.5575.5683.93-79.8383.05-78.57
PMT [14]AAAI2367.5395.3664.9871.6696.7376.5284.83-76.5584.16-75.13
AGW+J [31]ICCV2169.8895.7166.8976.2697.8880.3785.0395.4979.1484.7595.3377.82
MPANet [29]CVPR2170.5896.1068.2476.7498.2180.9583.70-80.9082.80-80.70
CMT [6]ECCV2271.8896.4568.5776.9097.6879.9195.1798.8287.3091.9797.9284.46
MUN (Ours)ICCV2376.2497.8473.8179.4298.0982.0695.1998.9387.1591.8697.9985.01
", + "bbox": [ + 81, + 101, + 893, + 351 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "superior to GAN-based methods (JSIA-ReID [25], AlignGAN [24], FMCNet [36]) thanks to the powerful auxiliary modality which dynamically combines the information of visible and infrared images without introducing extra noise.", + "bbox": [ + 75, + 377, + 468, + 438 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Furthermore, the proposed method significantly outperforms existing modality-unifying methods (SMCL [27], X-Modality [9]) by at least $8.85\\%$ on the rank-1 metric. This can be attributed to the fact that we not only mine the fine-grained semantic representations to generate the auxiliary modality but also decouple the extraction of specific and shared patterns in two modalities, which contribute to the dynamic generation of the auxiliary modality for relieving the changeable modality discrepancies during the training.", + "bbox": [ + 75, + 439, + 468, + 575 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Comparison on RegDB dataset. The results on RegDB are also listed in Table 4. In this dataset, image samples are spatially aligned and present less intra-class variations. Thus, the accuracy of all methods is higher than that on SYSU-MM01. The proposed MUN achieves Rank-1 of $95.19\\%$ and mAP of $87.15\\%$ in visible to infrared mode. Similar improvement can also be observed in the infrared to visible mode, which shows that our method obtains Rank-1 of $91.86\\%$ and mAP of $85.01\\%$ . This improvement can be attributed to the capacity of our method to generate a robust auxiliary modality, effectively mitigating both cross-modality and intra-modality discrepancies.", + "bbox": [ + 75, + 575, + 468, + 758 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Evaluation on Generalizability", + "text_level": 1, + "bbox": [ + 76, + 768, + 346, + 787 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To verify the generalizability of MUN, we conduct experiments on two corrupted VI Re-ID datasets [2], namely SYSU-MM01-C and RegDB-C. We utilize the same corruption settings as [2], which only performs corruptions during the testing stage and randomly selects one corruption type (e.g., elastic, snow, frosted glass, etc.) and one severity level for each image in the visible gallery set. The results re", + "bbox": [ + 75, + 794, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/dda05574a3e0a09ca1dbedc6c0c4975dede81ee38e8e5629ca1c8ddf0133486b.jpg", + "table_caption": [ + "Table 5. Evaluations on corrupted datasets. Each evaluation is performed 10 times to obtain the mean value. $L_{id}^{a}$ denotes an individual identity loss used to supervise the auxiliary modality." + ], + "table_footnote": [], + "table_body": "
IndexMethodSYSU-MM01-CRegDB-C
r=1mAPr=1mAP
1X-Modality [9]31.9826.2037.2635.97
2CIL [2]36.9535.9252.2549.76
3SMCL [27]37.0836.1251.9349.22
4AGW+J [31]40.0937.8651.5349.04
5B25.9223.1332.0529.64
6+Aux.+Lda30.8526.5436.4031.21
7+Aux.+Lidc31.1227.4438.1332.29
8+Aux.+Lidc+Lia36.7832.3245.4442.89
9+Aux.+Lidc+Lia+Lma41.1738.6352.6950.18
", + "bbox": [ + 504, + 415, + 890, + 568 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "ported for all the compared methods are obtained using the official best settings as provided in their respective papers.", + "bbox": [ + 498, + 593, + 890, + 625 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5 shows that the performance of baseline (B) is relatively lower than that of existing SOTAs under data corruption scenarios. However, by introducing the auxiliary modality to bridge the gap between visible and infrared modalities (Index 6), the accuracy is significantly improved. Furthermore, by incorporating the proposed identity alignment loss $(L_{ia})$ and modality alignment loss $(L_{ma})$ to refine the learned cross-modality feature relationships, the rank-1 and mAP accuracies experience a substantial enhancement of $15.25\\%$ and $15.5\\%$ respectively on the SYSU-MM01-C dataset. This outperforms the current SOTAs by a remarkable margin. Specifically, our MUN method exceeds the highly robust AGW+J [31] by $1.08\\%$ in rank-1 and $0.77\\%$ in mAP. The experiments on two corrupted datasets verify the strong generalizability and robustness of the proposed MUN, which can consistently learn modality-shared patterns and regulate stable feature relationships under corrupted data scenarios.", + "bbox": [ + 496, + 628, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "11192", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/7a4ddfab3b384a2c8482dc1f7e49b6c319021159ad3e608ef7c8b516eb625002.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 80, + 89, + 256, + 212 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/a9140398046886bdefa01e26d26c20ef3f9e36add93fd5a06e9303eef5cf3fc0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 282, + 98, + 460, + 210 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/c016fdcb3a2334a6b9069318db3ac225952b88cda89c17e9628ab017fafd288e.jpg", + "image_caption": [ + "Figure 4. Distributions of learned visible, infrared and auxiliary features during the training. All the samples are randomly selected in the SYSU-MM01 dataset. The 3D visualization is made by T-SNE [23]. Please view in colour and zoom in." + ], + "image_footnote": [], + "bbox": [ + 78, + 219, + 254, + 335 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/4038246cdde7d41cece84cb88176cb49b6772da80699d004dbf0f8126ebc439c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 282, + 219, + 460, + 335 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "4.6. Visualization", + "text_level": 1, + "bbox": [ + 76, + 422, + 212, + 436 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Distribution Visualization. To visually demonstrate the effectiveness of MUN, we randomly select 10 identities from the SYSU-MM01 dataset and visualize their feature distributions during the training. The visualization results are presented in Figure 4.", + "bbox": [ + 75, + 446, + 468, + 521 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "At the onset of training (epoch 0 in Figure 4 (a)), significant modality disparities arise between visible (depicted by blue dots) and infrared images (depicted by red dots), rendering cross-modality matching unfeasible. As the training progresses, the proposed auxiliary modality (depicted by green dots) serves as a bridge to connect the visible and infrared modalities in the common feature space. We can observe that the learned visible and infrared features show a convergence trend, and the modality discrepancies are gradually eliminated at epoch 5 in Figure 4 (b). Afterwards, the network learns identity-aware patterns by regulating smaller intra-class distances and larger inter-class distances at epoch 45. Finally, in Figure 4 (d), all the learned features are well grouped into their respective identity centers, demonstrating powerful discriminability under cross-modality scenes, which proves the effectiveness of MUN in learning robustness and identity-aware features.", + "bbox": [ + 75, + 522, + 468, + 779 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Pattern Visualization. In order to further illustrate the effectiveness of our auxiliary modality, we select one visible and one infrared image with the same identity in the SYSUMM01 dataset to visualize the corresponding learned feature maps and attention maps via Grad-CAM [22].", + "bbox": [ + 75, + 779, + 468, + 854 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "The visualization results are shown in Figure 5. It is clear that the visible $(\\mathbf{F}^v)$ and infrared $(\\mathbf{F}^r)$ feature maps extracted from the backbone have different patterns and struc", + "bbox": [ + 75, + 854, + 468, + 900 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/f7931947a8fa9bbae67586007ecf957b98ad962bd75fecf2e715525adcdacf9f.jpg", + "image_caption": [ + "Figure 5. Visualization of learned feature maps and attention maps. Given the input visible image $\\mathbf{I}^v$ and infrared image $\\mathbf{I}^r$ , we visualize the corresponding learned visible feature $\\mathbf{F}^v$ , infrared feature $\\mathbf{F}^r$ , and the generated auxiliary feature $\\mathbf{F}^a$ . It is obvious that the auxiliary feature $\\mathbf{F}^a$ can preserve most of the modality-shared patterns, including body shape and structure. The attention visualizations on the input images are made by Grad-CAM [22]. Please view in colour and zoom in." + ], + "image_footnote": [], + "bbox": [ + 500, + 93, + 883, + 219 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "tures, which makes it difficult to perform cross-modality matching. Notably, the proposed auxiliary generator can dynamically reconstruct and align the modality-shared spatial patterns using multiple transposed convolutions. This makes our auxiliary feature $(\\mathbf{F}^a$ in Figure 5) preserves most of the shared patterns between $\\mathbf{F}^v$ and $\\mathbf{F}^r$ without corrupting the structure information of person bodies. In addition, the attention visualization in Figure 5 further indicates that the proposed auxiliary modality plays a critical role in helping the network learn modality-shared representations.", + "bbox": [ + 496, + 366, + 890, + 517 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 537, + 617, + 553 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This paper proposes a novel Modality Unifying Network to jointly explore the robust auxiliary modality and generalize cross-modality feature relationships for VI-ReID. The auxiliary modality is generated by combining the cross-modality learner and the intra-modality learner, enabling the dynamic extraction of modality-specific patterns from multiple receptive fields and feature scales. This approach empowers our auxiliary modality to effectively alleviate both cross-modality and intra-modality discrepancies. Moreover, we propose identity alignment loss and modality alignment loss to regulate discriminative feature relationships in multi-modality tasks. Extensive experiments on public datasets demonstrate the effectiveness and generalizability of our MUN as well as each proposed component.", + "bbox": [ + 496, + 565, + 890, + 777 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements. This work is supported by the Academy of Finland for Academy Professor project EmotionAI (Grants No. 336116, 345122), the University of Oulu & The Academy of Finland Profi 7 (Grant No. 352788), and the National Natural Science Foundation of China (Grant No. 61802058, 61911530397). We appreciate the professional and cost-effective GPU computing service provided by www.AutoDL.com.", + "bbox": [ + 496, + 779, + 890, + 900 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "11193", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Cuiqun Chen, Mang Ye, Meibin Qi, Jingjing Wu, Jianguo Jiang, and Chia-Wen Lin. Structure-aware positional transformer for visible-infrared person re-identification. IEEE Transactions on Image Processing, 31:2352-2364, 2022.", + "[2] Minghui Chen, Zhiqiang Wang, and Feng Zheng. Benchmarks for corruption invariant person re-identification. arXiv preprint arXiv:2111.00880, 2021.", + "[3] Pingyang Dai, Rongrong Ji, Haibin Wang, Qiong Wu, and Yuyu Huang. 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In Proceedings of the AAAI conference on artificial intelligence, volume 34, pages 13114–13121, 2020." + ], + "bbox": [ + 501, + 92, + 890, + 190 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "11195", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Modality Unifying Network for Visible-Infrared Person Re-Identification/c25cccee-cf9c-444a-bfaa-52844fa6cb10_model.json b/2023/Modality Unifying Network for Visible-Infrared Person Re-Identification/c25cccee-cf9c-444a-bfaa-52844fa6cb10_model.json new file mode 100644 index 0000000000000000000000000000000000000000..cb55dd7161786be683c86d1f218f2167aa57698f --- /dev/null +++ b/2023/Modality Unifying Network for Visible-Infrared Person Re-Identification/c25cccee-cf9c-444a-bfaa-52844fa6cb10_model.json @@ -0,0 +1,2389 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.118, + 0.131, + 0.853, + 0.152 + ], + "angle": 0, + "content": "Modality Unifying Network for Visible-Infrared Person Re-Identification" + }, + { + "type": "text", + "bbox": [ + 0.218, + 0.18, + 0.777, + 0.199 + ], + "angle": 0, + "content": "Hao Yu\\(^{1}\\), Xu Cheng\\(^{1*}\\), Wei Peng\\(^{2}\\), Weihao Liu\\(^{3}\\), Guoying Zhao\\(^{4}\\)" + }, + { + "type": "text", + "bbox": [ + 0.117, + 0.199, + 0.882, + 0.217 + ], + "angle": 0, + "content": "1School of Computer Science, Nanjing University of Information Science and Technology, China" + }, + { + "type": "text", + "bbox": [ + 0.188, + 0.217, + 0.808, + 0.234 + ], + "angle": 0, + "content": "\\(^{2}\\)Department of Psychiatry and Behavioral Sciences, Stanford University, USA" + }, + { + "type": "text", + "bbox": [ + 0.206, + 0.234, + 0.794, + 0.252 + ], + "angle": 0, + "content": "\\(^{3}\\)School of Computer Science and Technology, Soochow University, China" + }, + { + "type": "text", + "bbox": [ + 0.194, + 0.252, + 0.802, + 0.269 + ], + "angle": 0, + "content": "4Center for Machine Vision and Signal Analysis, University of Oulu, Finland" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.273, + 0.908, + 0.288 + ], + "angle": 0, + "content": "{yuhao,xcheng}@nuist.edu.cn, wepeng@stanford.edu, whliu@stu.suda.edu.cn, guoying.zhao@oulu.fi" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.322, + 0.314, + 0.339 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.354, + 0.473, + 0.704 + ], + "angle": 0, + "content": "Visible-infrared person re-identification (VI-ReID) is a challenging task due to large cross-modality discrepancies and intra-class variations. Existing methods mainly focus on learning modality-shared representations by embedding different modalities into the same feature space. As a result, the learned feature emphasizes the common patterns across modalities while suppressing modality-specific and identity-aware information that is valuable for Re-ID. To address these issues, we propose a novel Modality Unifying Network (MUN) to explore a robust auxiliary modality for VI-ReID. First, the auxiliary modality is generated by combining the proposed cross-modality learner and intra-modality learner, which can dynamically model the modality-specific and modality-shared representations to alleviate both cross-modality and intra-modality variations. Second, by aligning identity centres across the three modalities, an identity alignment loss function is proposed to discover the discriminative feature representations. Third, a modality alignment loss is introduced to consistently reduce the distribution distance of visible and infrared images by modality prototype modeling. Extensive experiments on multiple public datasets demonstrate that the proposed method surpasses the current state-of-the-art methods by a significant margin." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.746, + 0.21, + 0.761 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.772, + 0.47, + 0.879 + ], + "angle": 0, + "content": "Person re-identification (Re-ID) [8,33] aims at matching pedestrian images captured from multiple non-overlapping cameras. Over the past few years, it has received increased attention due to its huge practical value in modern surveillance systems. Previous studies [10, 16, 19, 30, 40] mainly focus on matching pedestrian images captured from visible cameras and formulate the Re-ID task as a single-modality" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.324, + 0.895, + 0.474 + ], + "angle": 0, + "content": "matching issue. Nevertheless, visible cameras may not provide accurate appearance information about persons in scenarios with poor illumination. To address this limitation, modern surveillance systems also employ infrared cameras, which can capture clear images in low-light conditions at night. As a result, visible-infrared person re-identification (VI-ReID) [1, 28, 29] has become a topic of growing interest in recent times, which seeks to match infrared images of the same identity when given a visible query across multiple camera views and vice versa." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.476, + 0.895, + 0.869 + ], + "angle": 0, + "content": "VI-ReID is challenging due to the huge cross-modality discrepancy between visible and infrared images, as well as the intra-modality variation in person bodies such as pose variation and dress change. Existing methods [1, 20, 29, 31, 36, 37] primarily focus on relieving the cross-modality discrepancy by extracting modality-shared features to perform the feature-level alignment. Some studies [1, 20, 28, 31, 34] employ two-stream networks for cross-modality feature embedding, while others [3, 24, 25, 36] utilize Generative Adversarial Networks (GANs) to generate shared representations from visible and infrared images. However, these methods discard modality-specific features (such as colour and texture) that contain useful identity-aware patterns against intra-modality variations. Consequently, the learned features may not fully capture the variation of human bodies and thus lack discriminability. To address this limitation, the modality-unifying methods, e.g., X-modality [9], DFM [7], SMCL [27], have been proposed to acquire the auxiliary modality by fusing visible and infrared modalities, encoding both modality-specific and modality-shared patterns to jointly relieve cross- and intramodality discrepancies. In the SMCL [27], the authors proposed a syncretic modality generated by fusing visible and infrared pixels, which can bridge the gap between visible and infrared modalities while maintaining discriminability as the modality-specific information is preserved." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.894, + 0.902 + ], + "angle": 0, + "content": "However, the existing modality-unifying works still have three weaknesses. (1) Pixel fusion. Previous works gener-" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.388, + 0.901 + ], + "angle": 0, + "content": "*Corresponding Author (Email: xcheng@nuist.edu.cn)" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11185" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.089, + 0.462, + 0.258 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.261, + 0.47, + 0.304 + ], + "angle": 0, + "content": "Figure 1. The main idea behind generating a strong auxiliary modality for the VI-ReID task. The IML and CML denote the intra-modality learner and cross-modality learner, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.325, + 0.468, + 0.612 + ], + "angle": 0, + "content": "ate the auxiliary modality by fusing pixels of the raw visible and infrared images, which makes the richness of semantic patterns either equal to the original two modalities or lower in the case of pixel misalignment. In fact, the auxiliary modality is utilized to guide the learning of visible and infrared modalities, but the insufficient semantic patterns lead to a lack of identity-related information and severely limit the capacity to relieve intra-modality variations in VI-ReID. (2) Discrepancy bias. During the VI training, the relative distances between visible and infrared images are constantly changing, which causes a dynamic bias toward the balance of intra- and cross-modality discrepancies. Thus, an ideal auxiliary modality should be able to dynamically control the ratio of modality-specific and modality-shared patterns it contains to model the evolving modality discrepancies. However, the existing studies simply use the global information of visible and infrared images to obtain the auxiliary representations, which are inflexible in adjusting the patterns they describe, leading to low robustness." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.612, + 0.468, + 0.718 + ], + "angle": 0, + "content": "(3) Inconsistency constraints. Existing studies usually utilize features in the current batch to represent the overall distribution for distance optimization. However, this strategy suffers from randomness, as the training samples are different in each batch, which may cause a certain inconsistency in the learned feature relationships in different training stages, thus damaging the generalizability." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Inspired by the above discussions, we propose a novel Modality Unifying Network (MUN) to explore an effective and robust auxiliary modality for VI-ReID. The main idea of our auxiliary modality is illustrated in Figure 1. Specifically, we introduce an auxiliary generator comprising two intra-modality learners (IML) and one cross-modality learner (CML) to distil the modality-related patterns from visible and infrared images. Two IMLs are presented to identify the modality-specific and identity-aware patterns from visible and infrared images, respectively. They exploit multiple depth-wise convolutions with various kernel sizes to capture fine-grained semantic patterns in the human" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.272 + ], + "angle": 0, + "content": "body across multiple receptive fields. Based on the outputs of two IMLs, the CML leverages spatial pyramid pooling to extract multi-scale feature representations and then fuse the modality-shared patterns learned in each feature scale. By combining IML and CML, the proposed auxiliary generator can generate a powerful auxiliary modality that is rich in modality-shared and discriminative patterns to alleviate both cross-modality and intra-modality discrepancies. In addition, the layer scale scheme is used to control the ratio of patterns learned from IML and CML, which can dynamically adjust the modality-specific and modality-shared patterns in the generated auxiliary representation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.273, + 0.892, + 0.408 + ], + "angle": 0, + "content": "Furthermore, to reveal the identity-related patterns in each identity set, an effective identity alignment loss \\((L_{ia})\\) is designed to optimize the distances of tri-modality identity centres. In addition, to regulate the distribution level feature relationships while relieving the inconsistency issue caused by sample variations, a novel modality alignment loss \\((L_{ma})\\) is designed to minimize the distances of three modalities, which utilizes the modality prototype to represent the learned modality information in each iteration." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.409, + 0.892, + 0.438 + ], + "angle": 0, + "content": "In general, the major contributions of this paper can be summarized as follows." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.444, + 0.892, + 0.52 + ], + "angle": 0, + "content": "- We propose a novel modality unifying network for the VI-ReID task by constructing a robust auxiliary modality, which contains rich semantic information from visible and infrared images to address modality discrepancies and reveal discriminative knowledge." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.527, + 0.892, + 0.587 + ], + "angle": 0, + "content": "- A novel auxiliary generator constructed by the intramodality and cross-modality learners is introduced to dynamically extract identity-aware and modality-shared patterns from heterogeneous images." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.595, + 0.892, + 0.655 + ], + "angle": 0, + "content": "- The identity alignment loss and modality alignment loss are designed to jointly explore the generalized and discriminative feature relationships of the three modalities at both the identity and distribution levels." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.663, + 0.892, + 0.723 + ], + "angle": 0, + "content": "- Extensive experiments on several public VI-ReID datasets verify the effectiveness of the proposed method and modality unifying scheme, which outperforms the current state of the arts by a large margin." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.444, + 0.892, + 0.723 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.74, + 0.642, + 0.755 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Single-Modality Person Re-ID. Single-modality person re-identification [11, 17, 33] aims to match pedestrian images across different visible cameras. It presents challenges such as changes in viewpoint and human pose across camera views. Current approaches mainly focus on feature representation learning [15, 19, 39] and distance metric learning [10, 30, 35, 40]. Over the past few years, excellent performances have been achieved on several academic benchmarks. However, in practical scenarios, numerous crucial" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "11186" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.113, + 0.103, + 0.845, + 0.356 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.357, + 0.895, + 0.414 + ], + "angle": 0, + "content": "Figure 2. The overall architecture of the proposed MUN for VI-ReID. GeMP denotes the Generalized Mean Pooling [21]. The pretrained ResNet-50 [4] is adopted as the baseline network. To meet the specific requirements of VI-ReID, we initialize the first stage of the ResNet-50 twice as two independent ResBlocks to extract the low-level visible and infrared features, respectively. The remaining stages are utilized as modality-shared ResBlocks. During the inference, only visible and infrared modalities are utilized to perform cross-modality retrieval." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.438, + 0.471, + 0.558 + ], + "angle": 0, + "content": "surveillance photos and videos are captured at night using infrared cameras. When it comes to matching pedestrians across visible and infrared modalities, the capabilities of these single-modality methods are limited due to their inability to address the huge modality gap. In contrast, we present an effective modality unifying network to bridge the modality gap and achieve precise cross-modality pedestrian matching in 24-hour monitoring scenarios." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.569, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Visible-Infrared Person Re-ID. Visible-Infrared person Re-ID [28] is a challenging task due to the cross-modality discrepancies between visible and infrared images, as well as the intra-modality variations such as pose and dress changes. Existing studies [20, 29, 31, 32, 34] mainly focus on learning the modality-shared representations to align the visible and infrared modalities. Some generation-based methods [24-26,36] have been developed to achieve modality alignment or translation by using Generative Adversarial Network (GAN). For instance, Wang et al. [24] proposed a dual-alignment network that used GAN to jointly learn pixel and feature level alignment. The D2RL [26] is proposed to perform image-level modality translation by adversarial training that relieves the cross-modality discrepancy. Other works [1, 20, 29, 31, 34] attempt to learn modality-shared features by designing two-stream networks to perform cross-modality feature embedding. Ye et al. [34] proposed a dual-constrained top-ranking method with a weight-shared two-stream network. Wu et al. [29] designed a cross-modality attention scheme to help the two-stream backbone discover cross-modality nuances. However, these methods usually discard modality-specific representations" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.438, + 0.892, + 0.468 + ], + "angle": 0, + "content": "that help to relieve intra-modality variations, leading to low robustness and discriminability in learned features." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.469, + 0.893, + 0.679 + ], + "angle": 0, + "content": "In order to capture both the modality-shared and identity-aware patterns from heterogeneous images, modality-unifying methods have been developed. These methods aim to obtain the auxiliary modality by combining modality-specific and modality-shared representations from both visible and infrared images. The syncretic modality [27] is proposed to guide the generation of discriminative and modality-invariant representations. The DFM [7] acquires the mixed modality by integrating visible and infrared pixels. However, these methods generate the auxiliary modality by directly fusing the raw pixels of visible and infrared images, making their auxiliary modality lack high-level semantic patterns and inflexible to adjust its representations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.68, + 0.892, + 0.788 + ], + "angle": 0, + "content": "To tackle these challenges, this paper presents the intramodality learner and cross-modality learner to dynamically uncover substantial modality-shared and discriminative patterns from multiple receptive fields and feature scales. By integrating these learners, we introduce a powerful auxiliary modality that effectively bridges the modality discrepancy and enhances the discriminability of learned features." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.8, + 0.636, + 0.818 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.903 + ], + "angle": 0, + "content": "As shown in Figure 2, we introduce the details of the Modality Unifying Network. We first utilize two independent ResBlocks to extract low-level features from visible and infrared images, respectively. Then, the auxiliary generator is designed to generate the auxiliary features by com" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11187" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.258 + ], + "angle": 0, + "content": "bining intra-modality and cross-modality learners. Afterwards, the visible, infrared, and auxiliary features are fed into weight-shared ResBlocks to learn high-level patterns. The auxiliary features can serve as a bridge to relieve both intra- and cross-modality discrepancies during the training. Based on the visible, infrared, and auxiliary features learned by weight-shared ResBlocks, four loss functions are developed to effectively improve cross-modality matching accuracy, including identity loss \\( L_{id} \\), identity consistency loss \\( L_{idc} \\), identity alignment loss \\( L_{ia} \\) and modality alignment loss \\( L_{ma} \\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.266, + 0.272, + 0.281 + ], + "angle": 0, + "content": "3.1. Auxiliary Generator" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.289, + 0.47, + 0.394 + ], + "angle": 0, + "content": "The auxiliary generator contains two intra-modality learners (IML) and one cross-modality learner (CML). The two IMLs are designed to mine identity-related patterns from visible and infrared images, respectively. The CML is designed to learn modality-shared patterns based on the outcomes of two IMLs. The detailed architectures of IML and CML are shown in Figure 3." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.395, + 0.47, + 0.485 + ], + "angle": 0, + "content": "Intra-Modality Learner. The intra-modality learner (IML) is designed to capture the discriminative and identity-aware patterns in human bodies. The visible or infrared low-level features \\(\\mathbf{F}^m\\in \\mathbb{R}^{C\\times H\\times W}\\), \\(m\\in \\{v,r\\}\\) extracted from two independent ResBlocks are regarded as the input of IML, where \\(m\\) denotes the visible or infrared modality." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.485, + 0.47, + 0.531 + ], + "angle": 0, + "content": "To enrich the receptive field while keeping low computational complexity, we equally divide \\(\\mathbf{F}^m\\) into two parts along the channel dimension by matrix slice operation." + }, + { + "type": "equation", + "bbox": [ + 0.116, + 0.537, + 0.47, + 0.555 + ], + "angle": 0, + "content": "\\[\n\\mathbf {F} _ {c _ {1}} ^ {m} = \\mathbf {F} ^ {m} [ 0: C / 2,: :, ] \\quad , \\quad \\mathbf {F} _ {c _ {2}} ^ {m} = \\mathbf {F} ^ {m} [ C / 2: C,:,: ]. \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.561, + 0.47, + 0.606 + ], + "angle": 0, + "content": "Then, we employ \\(7 \\times 7\\) and \\(5 \\times 5\\) depth-wise convolutions \\((D)\\) to operate on \\(\\mathbf{F}_{c_1}^m\\) and \\(\\mathbf{F}_{c_2}^m\\), respectively. This allows us to capture spatial patterns in different receptive fields." + }, + { + "type": "equation", + "bbox": [ + 0.144, + 0.613, + 0.47, + 0.63 + ], + "angle": 0, + "content": "\\[\n\\mathbf {R} ^ {m} = \\operatorname {C o n c a t} \\left\\{D _ {5 \\times 5} \\left(\\mathbf {F} _ {c _ {1}} ^ {m}\\right), D _ {7 \\times 7} \\left(\\mathbf {F} _ {c _ {2}} ^ {m}\\right) \\right\\}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.637, + 0.469, + 0.711 + ], + "angle": 0, + "content": "where \\( \\text{Concat} \\) denotes the concatenation on channel dimension; \\( \\mathbf{R}^m \\) indicates the visible or infrared features captured from multiple receptive fields. Then, a point-wise convolution \\( (P) \\) is utilized to fuse patterns with diverse receptive fields by connecting pixels in each channel." + }, + { + "type": "equation", + "bbox": [ + 0.167, + 0.719, + 0.469, + 0.735 + ], + "angle": 0, + "content": "\\[\n\\mathbf {R} _ {1} ^ {m} = P _ {1 \\times 1} (B a t c h N o r m (\\mathbf {R} ^ {m})). \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.742, + 0.469, + 0.817 + ], + "angle": 0, + "content": "To integrate and encode the structural information in human bodies, another depth-wise convolution with \\(3 \\times 3\\) kernel size is introduced to remodel the learned spatial map. This layer also utilizes a residual branch to retain information from the previous layer." + }, + { + "type": "equation", + "bbox": [ + 0.166, + 0.825, + 0.469, + 0.841 + ], + "angle": 0, + "content": "\\[\n\\mathbf {R} _ {2} ^ {m} = D _ {3 \\times 3} \\left(R e L U \\left(\\mathbf {R} _ {1} ^ {m}\\right)\\right) + \\mathbf {R} _ {1} ^ {m}. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.848, + 0.469, + 0.879 + ], + "angle": 0, + "content": "In addition, another point-wise convolution is utilized to fuse patterns with diverse receptive fields in \\(\\mathbf{R}_2^m\\)." + }, + { + "type": "equation", + "bbox": [ + 0.143, + 0.884, + 0.469, + 0.902 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {F}} ^ {m} = I _ {\\text {s c a l e}} * P _ {1 \\times 1} \\left(\\operatorname {B a t c h N r o m} \\left(\\mathbf {R} _ {2} ^ {m}\\right)\\right), \\tag {5}\n\\]" + }, + { + "type": "image", + "bbox": [ + 0.515, + 0.09, + 0.689, + 0.303 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.704, + 0.09, + 0.882, + 0.302 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.31, + 0.892, + 0.352 + ], + "angle": 0, + "content": "Figure 3. The detailed architecture of the proposed intra-modality learner (IML) and cross-modality learner (CML). They are designed to decouple the modeling of modality-related knowledge." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.373, + 0.892, + 0.42 + ], + "angle": 0, + "content": "where \\( I_{scale} \\in (0,1] \\) is the learnable layer scale factor used to control the ratio of intra-modality patterns learned by IML; \\( \\hat{\\mathbf{F}}^m \\) denotes the outcomes of the two IMLs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.42, + 0.893, + 0.555 + ], + "angle": 0, + "content": "In the proposed intra-modality learner, three depth-wise convolutions with various kernel sizes are well combined to capture the identity-related patterns that existed in various receptive fields. Two point-wise convolutions are utilized for pattern integration and channel relation reasoning based on the inverted residual architecture [12]. The first point-wise convolution increases the channel dimension from \\( C \\) to \\( C * 4 \\) and the last point-wise convolution reduces the channel dimension from \\( C * 4 \\) to \\( C \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.556, + 0.892, + 0.632 + ], + "angle": 0, + "content": "Cross-Modality Learner. The cross-modality learner is designed to mine the modality-shared patterns from multiple feature scales based on the outcomes of two IMLs. Specifically, the spatial pyramid features are mined by applying \\( n \\) average pooling layers with various ratios." + }, + { + "type": "equation", + "bbox": [ + 0.617, + 0.637, + 0.775, + 0.655 + ], + "angle": 0, + "content": "\\[\n\\mathbf {S} _ {1} ^ {m} = \\operatorname {A v g p o o l} _ {1} (\\hat {\\mathbf {F}} ^ {m}) ,\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.617, + 0.657, + 0.892, + 0.692 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{c c} \\mathbf {S} _ {2} ^ {m} = A v g p o o l _ {2} (\\hat {\\mathbf {F}} ^ {m}) & , \\\\ \\dots & , \\end{array} \\tag {6}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.617, + 0.695, + 0.775, + 0.712 + ], + "angle": 0, + "content": "\\[\n\\mathbf {S} _ {n} ^ {m} = \\operatorname {A v g p o o l} _ {n} (\\hat {\\mathbf {F}} ^ {m}) ,\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.718, + 0.892, + 0.81 + ], + "angle": 0, + "content": "where \\(\\{\\mathbf{S}_1^m,\\mathbf{S}_2^m,\\dots,\\mathbf{S}_n^m\\}, m\\in \\{v,r\\}\\) denote the spatial pyramid features with various feature scales. Afterwards, we obtain the modality-shared spatial patterns from each pair of cross-modality spatial pyramid features \\(\\{\\mathbf{S}_i^v,\\mathbf{S}_i^r\\}_{i = 1}^n\\) with the same feature scale by using a group of learnable transposed convolutions \\(\\{TR_1,TR_2,\\dots,TR_n\\}\\)." + }, + { + "type": "equation", + "bbox": [ + 0.52, + 0.815, + 0.892, + 0.835 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {S}} _ {i} ^ {v} = T R _ {i} \\left(\\mathbf {S} _ {i} ^ {v}\\right), \\quad \\hat {\\mathbf {S}} _ {i} ^ {r} = T R _ {i} \\left(\\mathbf {S} _ {i} ^ {r}\\right), \\quad i = 1, 2, \\dots , n. \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.841, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Here, the spatial dimensions of each cross-modality feature pair \\(\\hat{\\mathbf{S}}_i^v\\) and \\(\\hat{\\mathbf{S}}_i^r\\) are rebuilt to \\(H\\times W\\) by the corresponding transposed convolution \\(TR_{i}\\), respectively. In this manner, the significant patterns of visible and infrared features" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11188" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.136 + ], + "angle": 0, + "content": "on each feature scale are embedded together, which helps to discover and amplify the abundant modality-shared information on multiple feature scales." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.137, + 0.47, + 0.168 + ], + "angle": 0, + "content": "Further, all the embedded features are concatenated on the channel dimension via Eq.(8)." + }, + { + "type": "equation", + "bbox": [ + 0.139, + 0.172, + 0.469, + 0.19 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {S}} = \\operatorname {C o n c a t} \\left\\{\\hat {\\mathbf {S}} _ {i} ^ {v}, \\hat {\\mathbf {S}} _ {2} ^ {v}, \\dots , \\hat {\\mathbf {S}} _ {n} ^ {v}, \\hat {\\mathbf {S}} _ {1} ^ {r}, \\hat {\\mathbf {S}} _ {2} ^ {r}, \\dots , \\hat {\\mathbf {S}} _ {n} ^ {r} \\right\\}. \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.196, + 0.469, + 0.226 + ], + "angle": 0, + "content": "Then, the auxiliary feature is obtained by fusing patterns captured from multiple feature scales." + }, + { + "type": "equation", + "bbox": [ + 0.15, + 0.233, + 0.469, + 0.249 + ], + "angle": 0, + "content": "\\[\n\\mathbf {F} ^ {a} = C _ {\\text {s c a l e}} * P _ {1 \\times 1} (\\operatorname {B a t c h N o m r} (\\hat {\\mathbf {S}})), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.254, + 0.469, + 0.359 + ], + "angle": 0, + "content": "where \\(\\mathbf{F}^a\\) denotes the auxiliary feature generated by our method. It contains substantial modality-shared and identity-aware information captured by three learners; \\(C_{scale} \\in (0,1]\\) denotes the learnable layer scale factor used to control the ratio of modality-shared representations in the learned auxiliary feature \\(\\mathbf{F}^a\\); \\(P_{1 \\times 1}\\) is a point-wise convolution used to fuse patterns across different channels." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.361, + 0.469, + 0.421 + ], + "angle": 0, + "content": "The CML mines significant patterns from multiple feature scales and amplifies the modality-shared parts from them using transposed convolutions. It makes our auxiliary feature a powerful tool to handle cross-modality variations." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.428, + 0.305, + 0.442 + ], + "angle": 0, + "content": "3.2. Classification Constraint" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.451, + 0.469, + 0.496 + ], + "angle": 0, + "content": "To ensure the learned visible and infrared features are identity-related, the identity loss \\((L_{id})\\) implemented with the cross-entropy term is introduced as follows." + }, + { + "type": "equation", + "bbox": [ + 0.092, + 0.502, + 0.469, + 0.55 + ], + "angle": 0, + "content": "\\[\nL _ {i d} ^ {m} = - \\frac {1}{k} \\sum_ {i = 1} ^ {k} \\log P \\left(y _ {i} \\mid C _ {m} \\left(\\mathbf {Z} _ {i} ^ {m}\\right)\\right), \\quad s. t. \\quad m \\in \\{v, r \\}, \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.551, + 0.469, + 0.627 + ], + "angle": 0, + "content": "where \\(\\mathbf{Z}_i^v\\) and \\(\\mathbf{Z}_i^r\\) denote the generalized mean pooled visible and infrared features in the \\(i\\)-th identity, respectively. \\(k\\) is the number of visible or infrared images in each batch; \\(y_i\\) is the \\(i\\)-th identity label; \\(C_v(\\cdot)\\) and \\(C_r(\\cdot)\\) are the predictions of visible and infrared classifiers, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.627, + 0.469, + 0.778 + ], + "angle": 0, + "content": "The learned presentations are modality-shared if two classifiers can give consistent predictions for features from any modalities. However, if we directly apply features in one modality to the classifier in another modality (e.g., \\( C_r(\\mathbf{Z}^v) \\)), it may impose the classifier to learn modality-specific patterns rather than the modality-shared patterns, as the former is typically more discriminative. To solve this issue, we present an identity-consistency loss \\( L_{idc} \\) to update the parameters of both visible and infrared classifiers with the aid of auxiliary features. It can be defined as follows." + }, + { + "type": "equation", + "bbox": [ + 0.087, + 0.784, + 0.469, + 0.821 + ], + "angle": 0, + "content": "\\[\nL _ {i d c} = - \\frac {1}{k} \\sum_ {i = 1} ^ {k} \\left[ \\log P \\left(y _ {i} \\mid C _ {v} \\left(\\mathbf {Z} _ {i} ^ {a}\\right)\\right) + \\log P \\left(y _ {i} \\mid C _ {r} \\left(\\mathbf {Z} _ {i} ^ {a}\\right)\\right) \\right], \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.469, + 0.902 + ], + "angle": 0, + "content": "where \\(\\mathbf{Z}_i^a\\) denotes the pooled auxiliary feature in the \\(i\\)-th identity. The auxiliary features effectively integrate visible and infrared patterns, facilitating the transfer of identity-related knowledge between modalities without compromising the original intra-modality learning." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.722, + 0.107 + ], + "angle": 0, + "content": "3.3. Identity Alignment Loss" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.115, + 0.892, + 0.176 + ], + "angle": 0, + "content": "To relieve the class-level modality discrepancies and learn discriminative feature relationships, the identity alignment loss \\( L_{ia} \\) is designed to align the visible and infrared features of each identity with the aid of auxiliary features." + }, + { + "type": "equation", + "bbox": [ + 0.564, + 0.187, + 0.892, + 0.26 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} L _ {i a} = \\sum_ {i = 1} ^ {P} \\left[ \\alpha + \\max _ {m _ {1} \\in \\{v, r \\}} \\left| \\left| \\mathbf {C} _ {i} ^ {a} - \\mathbf {C} _ {i} ^ {m _ {1}} \\right| \\right| _ {2} \\right. \\tag {12} \\\\ -\\min_{\\substack{m_{2}\\in \\{v,r\\} \\\\ q\\neq i}}||\\mathbf{C}_{i}^{a} - \\mathbf{C}_{q}^{m_{2}}||_{2}\\Bigg], \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.273, + 0.892, + 0.382 + ], + "angle": 0, + "content": "where \\(\\alpha\\) is the margin parameter; \\(P\\) denotes the number of person identities; \\(N\\) is the number of images in the \\(i\\)-th identity; \\(\\mathbf{C}_i^a = \\frac{1}{N}\\sum_{j=1}^{N}\\mathbf{Z}_{i,j}^a\\), \\(\\mathbf{C}_i^v = \\frac{1}{N}\\sum_{j=1}^{N}\\mathbf{Z}_{i,j}^v\\), \\(\\mathbf{C}_i^r = \\frac{1}{N}\\sum_{j=1}^{N}\\mathbf{Z}_{i,j}^r\\) are the auxiliary, visible, and infrared centres in the \\(i\\)-th identity, respectively; \\(\\mathbf{Z}_{i,j}^v\\), \\(\\mathbf{Z}_{i,j}^r\\) and \\(\\mathbf{Z}_{i,j}^a\\) denote the \\(j\\)-th visible, infrared, and auxiliary features in the \\(i\\)-th identity set." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.384, + 0.892, + 0.474 + ], + "angle": 0, + "content": "In this paper, identity alignment loss is proposed to optimize the hardest cross-modality positive and negative centre pairs in a triplet-metric manner. It regulates discriminative and robust feature relationships by forcing all identities to form a tight intra-class space and pushing centres of different identities away across the three modalities." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.485, + 0.731, + 0.501 + ], + "angle": 0, + "content": "3.4. Modality Alignment Loss" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.509, + 0.892, + 0.63 + ], + "angle": 0, + "content": "Previous works [7, 20, 29] typically align the two modalities by constraining visible and infrared features in each iteration. This scheme suffers from inconsistencies in the learned cross-modality feature relationships because the training samples are different in each iteration. To overcome this issue, we propose a modality alignment strategy that consistently aligns visible and infrared modalities by modeling the prototypes from features in each iteration." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.631, + 0.892, + 0.736 + ], + "angle": 0, + "content": "Specifically, we first introduce three modality prototypes to represent the global information of visible, infrared, and auxiliary modalities, respectively. They can be denoted as \\(\\mathbf{T}^v = \\{\\mathbf{t}_1^v,\\mathbf{t}_2^v,\\dots,\\mathbf{t}_B^v\\}\\), \\(\\mathbf{T}^r = \\{\\mathbf{t}_1^r,\\mathbf{t}_2^r,\\dots,\\mathbf{t}_B^r\\}\\) and \\(\\mathbf{T}^a = \\{\\mathbf{t}_1^a,\\mathbf{t}_2^a,\\dots,\\mathbf{t}_B^a\\} \\in \\mathbb{R}^{B\\times C}\\), where \\(\\mathbf{t}_i^v,\\mathbf{t}_i^r\\) and \\(\\mathbf{t}_i^a\\) are the modality prototypes for the \\(i\\)-th visible, infrared, and auxiliary features in each training batch \\((B)\\), respectively." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.737, + 0.892, + 0.782 + ], + "angle": 0, + "content": "The initial prototypes of the three modalities are obtained based on the pooled features \\([\\mathbf{Z}^v ]^0\\) \\([\\mathbf{Z}^r ]^0\\) and \\([\\mathbf{Z}^a ]^0\\in\\) \\(R^{B\\times C}\\) in the 0-th iteration." + }, + { + "type": "equation", + "bbox": [ + 0.562, + 0.795, + 0.892, + 0.813 + ], + "angle": 0, + "content": "\\[\n[ \\mathbf {T} ^ {m} ] ^ {0} = \\mathbf {W} _ {p} ^ {m} [ \\mathbf {Z} ^ {m} ] ^ {0}, \\quad s. t. \\quad m \\in \\{v, r, a \\}, \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.892, + 0.87 + ], + "angle": 0, + "content": "where \\(\\mathbf{W}_p^m\\) are learnable matrices to distil modality-related patterns from the \\(m\\)-th modality. \\([\\mathbf{T}^m]^{0}\\) denotes the prototype of the \\(m\\)-th modality calculated in the 0-th iteration." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Further, to dynamically model the modality information during the training, we develop a temporal accumulation" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11189" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.121 + ], + "angle": 0, + "content": "strategy to update the modality prototype by the learned features in each iteration, which can be defined as follows." + }, + { + "type": "equation", + "bbox": [ + 0.106, + 0.133, + 0.468, + 0.167 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} [ \\mathbf {T} ^ {m} ] ^ {i} = [ \\beta ] ^ {i} * \\mathbf {W} _ {p} ^ {m} [ \\mathbf {Z} ^ {m} ] ^ {i} + (1 - [ \\beta ] ^ {i}) * [ \\mathbf {T} ^ {m} ] ^ {i - 1}, \\tag {14} \\\\ s. t. \\quad m \\in \\{v, r, a \\}, \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.18, + 0.468, + 0.272 + ], + "angle": 0, + "content": "where \\([\\mathbf{T}^m ]^i\\) is the \\(m\\)-th modality prototype calculated in the \\(i\\)-th iteration; \\(\\beta\\) is the updating ratio, which gradually increases from \\(1e^{-8}\\) to 1 with the training goes on. The temporal accumulation strategy ensures that the modality information in each iteration is considered, thereby synchronizing the cross-modality alignment during the training." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.273, + 0.468, + 0.303 + ], + "angle": 0, + "content": "Based on the modality prototypes, the modality alignment loss \\((L_{ma})\\) is designed as:" + }, + { + "type": "equation", + "bbox": [ + 0.11, + 0.315, + 0.469, + 0.353 + ], + "angle": 0, + "content": "\\[\nL _ {m a} = \\frac {1}{P} \\sum_ {p = 1} ^ {P} \\left[ m m d \\left(\\mathbf {T} _ {p} ^ {v}, \\mathbf {T} _ {p} ^ {a}\\right) + m m d \\left(\\mathbf {T} _ {p} ^ {a}, \\mathbf {T} _ {p} ^ {r}\\right) \\right], \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.365, + 0.469, + 0.444 + ], + "angle": 0, + "content": "where \\(\\mathbf{T}_p^v\\), \\(\\mathbf{T}_p^r\\) and \\(\\mathbf{T}_p^a\\) denote visible, infrared, and auxiliary prototypes of the \\(p\\)-th identity, respectively. \\(mmd(\\cdot, \\cdot)\\) is the MMD loss [5] implemented the modality level alignment by constraining the distance of modality prototypes in each iteration. In Equation 15, the \\(mmd(\\mathbf{T}_p^v, \\mathbf{T}_p^a)\\) is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.455, + 0.469, + 0.493 + ], + "angle": 0, + "content": "\\[\nm m d \\left(\\mathbf {T} _ {p} ^ {v}, \\mathbf {T} _ {p} ^ {a}\\right) = | | \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\phi \\left(\\mathbf {T} _ {p, i} ^ {v}\\right) - \\frac {1}{M} \\sum_ {j = 1} ^ {M} \\phi \\left(\\mathbf {T} _ {p, j} ^ {a}\\right) | | _ {H} ^ {2}, \\tag {16}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.506, + 0.469, + 0.596 + ], + "angle": 0, + "content": "where \\(\\mathbf{T}_{p,i}^{v}\\) and \\(\\mathbf{T}_{p,j}^{a}\\) denote the \\(i\\)-th visible prototype and the \\(j\\)-th auxiliary prototype in the \\(p\\)-th identity, respectively; \\(||\\cdot||_{H}\\) denotes the distribution measured by Gaussian kernel function \\(\\phi(\\cdot)\\) which projects prototypes into the reproducing kernel Hilbert space. The \\(mmd(\\mathbf{T}_p^a,\\mathbf{T}_p^r)\\) term can also be obtained in a similar way." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.597, + 0.469, + 0.733 + ], + "angle": 0, + "content": "The modality alignment loss is used to constrain the identity-guided distribution distances of visible, infrared, and auxiliary modalities through the prototypes. It can effectively reduce the modality discrepancy and relieve the inconsistency issue in learned feature relationships. Meanwhile, the auxiliary modality can act as a bridge to decrease the relative distance between visible and infrared modalities in the common feature space, thereby significantly reducing the optimization difficulty of cross-modality alignment." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.744, + 0.285, + 0.758 + ], + "angle": 0, + "content": "3.5. Overall Loss Function" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.768, + 0.469, + 0.828 + ], + "angle": 0, + "content": "Following the previous works, we employ the identity loss \\((L_{id} = L_{id}^{v} + L_{id}^{r})\\) and hard-mining triplet loss \\((L_{tri})\\) [26,32] as our baseline loss functions. The overall loss function of the proposed MUN can be summarized as:" + }, + { + "type": "equation", + "bbox": [ + 0.093, + 0.842, + 0.469, + 0.857 + ], + "angle": 0, + "content": "\\[\nL _ {t o t a l} = L _ {i d} + L _ {t r i} + \\gamma * L _ {i d c} + \\theta * L _ {i a} + \\sigma * L _ {m a}, \\tag {17}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "where \\(\\gamma, \\theta\\), and \\(\\sigma\\) are parameters to balance the contribution of each proposed loss term during the training." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.634, + 0.108 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.115, + 0.788, + 0.132 + ], + "angle": 0, + "content": "4.1. Datasets and Evaluation Settings" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.138, + 0.892, + 0.304 + ], + "angle": 0, + "content": "SYSU-MM01 [28] is the largest dataset for VI-ReID, which comprises six cameras, including four visible and two infrared cameras. It encompasses a total of 491 individuals, with 287,628 visible images and 15,792 infrared images. The training set is composed of 395 individuals, with 22,258 visible images and 11,909 infrared images. The test set consists of 96 individuals, with 3,803 infrared images for queries and a gallery selected from 301 visible images. The dataset offers two testing settings: all-search mode and indoor-search mode. For both modes, we employ the hardest single-shot setting to perform the evaluation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.305, + 0.892, + 0.44 + ], + "angle": 0, + "content": "RegDB [18] comprises 412 identities and a total of 8,240 images, with 206 identities allocated for training and another 206 identities for testing. Each identity is represented by 10 visible and 10 infrared images. The testing phase in RegDB involves two modes: Visible to Infrared, where visible images are searched using an infrared image, and Infrared to Visible, which entails the reverse scenario. For both modes, we repeat the testing process 10 times and average the results to report the mean values." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.441, + 0.892, + 0.486 + ], + "angle": 0, + "content": "Evaluation Settings. We utilize the standard cumulative matching characteristics (CMC) and mean average precision(mAP) as the evaluation metrics." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.497, + 0.717, + 0.512 + ], + "angle": 0, + "content": "4.2. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.52, + 0.892, + 0.625 + ], + "angle": 0, + "content": "We implement all the experiments on the PyTorch framework with an NVIDIA RTX-3090 GPU. To ensure repeatability and facilitate fair comparisons with existing methods, we adopt the pretrained ResNet-50 [4] as our backbone network, where the first stage is initialized twice as two modality-specific ResBlocks, and the rest stages are used as the modality-shared ResBlocks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.626, + 0.892, + 0.822 + ], + "angle": 0, + "content": "At the training stage, all images are resized to \\(288 \\times 144\\). Data augmentations, including random horizontal flipping, erasing, and channel augmentations [31], are utilized against overfitting. Our model is trained with the AdamW optimizer [13] for 90 epochs with a weight decay of 0.01. The learning rate is gradually increased from \\(10^{-8}\\) to 0.002 in the first 15 epochs and then decays by 0.1 at the \\(30^{th}\\) and \\(60^{th}\\) epochs. We find the optimal settings of all the hyper-parameters by grid search and repeated ablation experiments. Specifically, the pooling ratios of the spatial pyramid pooling in CML are set to be \\(\\{2, 4, 6, 12\\}\\); The margin parameter \\(\\alpha\\) is set to 0.55; the loss balance parameters \\(\\gamma\\), \\(\\theta\\), and \\(\\sigma\\) are set to 0.25, 0.5, and 0.008, respectively." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.832, + 0.654, + 0.848 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We evaluate the effectiveness of each proposed component on SYSY-MM01 and RegDB datasets, as shown in Table 1. Compared with the baseline (B) which only learns" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11190" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.318 + ], + "angle": 0, + "content": "from visible and infrared modalities, the leveraging of auxiliary modality (Aux.) can effectively relieve both cross-modality and intra-modality discrepancies, thus greatly improving all the metrics on two datasets. Further, when applying the identity consistency loss \\((L_{idc})\\) to refine the modality-shared discriminative patterns, the performance is further improved. Meanwhile, the proposed identity alignment loss \\((L_{ia})\\) or modality alignment loss \\((L_{ma})\\) can enhance the cross-modality matching accuracy by aligning the visible and infrared features at the identity level or distribution level. By combining them, we can regulate a more robust cross-modality feature relationship, achieving a rank-1 of \\(76.24\\%\\) and mAP of \\(73.81\\%\\) on the SYSU-MM01 dataset. The results demonstrate that all the proposed components contribute consistently to the accuracy gain." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.318, + 0.472, + 0.395 + ], + "angle": 0, + "content": "It is worth noting that when adding only the auxiliary modality to the baseline in Table 1, we employed a simple identity loss (like \\( L_{id}^{a} \\)) to supervise the auxiliary modality. This loss is deprecated when employing the proposed \\( L_{idc} \\) to jointly supervise the three modalities." + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.406, + 0.472, + 0.462 + ], + "angle": 0, + "content": "Table 1. Evaluation of different components of the proposed method on SYSU-MM01 and RegDB datasets. CMC (\\%) at rank 1 and mAP (\\%). The Red bold font and blue bold front denote the best and second best performances, respectively." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.462, + 0.47, + 0.578 + ], + "angle": 0, + "content": "
BAux.LidcLiaLmaSYSU-MM01RegDB
r=1mAPr=1mAP
✓57.4955.8375.4271.93
✓✓62.5558.4279.2673.81
✓✓✓66.5861.2983.5179.79
✓✓✓✓71.3565.5489.4284.66
✓✓✓✓69.7766.9689.9384.02
✓✓✓✓✓76.2473.8195.1987.15
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.606, + 0.47, + 0.633 + ], + "angle": 0, + "content": "Table 2. Performance of using different intermediate modalities in our MUN on two datasets. CMC (%) at rank 1 and mAP (%)" + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.633, + 0.47, + 0.734 + ], + "angle": 0, + "content": "
Intermediate ModalitySYSU-MM01RegDB
r=1mAPr=1mAP
X-modality [9]66.1763.0679.9574.28
Mixed modality [7]66.4262.8579.4373.09
Syncretic modality [27]72.9568.7484.5979.11
Auxiliary modality (Ours)76.2473.8195.1987.15
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Effectiveness of auxiliary modality. We conduct the ablations in the MUN by replacing our auxiliary modality with intermediate modalities designed by previous works, namely X [9], mixed [7], and syncretic [27]. As shown in Table 2, the X-modality is generated from visible images only, ignoring the impact of infrared modality and achieving relatively low performances. Although syncretic and mixed modalities combine both visible and infrared patterns, they only utilize pixel-level information, lacking the ability to discover fine-grained and semantic patterns." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.227 + ], + "angle": 0, + "content": "When switching back to our auxiliary modality, we observed a significant improvement in performance with a boost of \\(3.29\\% / 5.07\\%\\) in terms of rank-1/mAP on the SYSU-MM01 dataset. These results further prove that our auxiliary modality is superior to other intermediate modalities. In summary, our auxiliary modality can effectively integrate modality-related information from both visible and infrared images, while preserving strong discriminability. This promotes robust representation learning in VI-ReID." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.228, + 0.892, + 0.334 + ], + "angle": 0, + "content": "Effectiveness of loss design schemes. In the modality alignment loss \\((L_{ia})\\), we design the modality prototype scheme to relieve the inconsistency issue and the auxiliary bridge scheme to reduce the optimization difficulty. To validate the effectiveness of these two schemes, we compare the performance of our method with or without using these two proposed schemes. As shown in Table 3." + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.347, + 0.892, + 0.388 + ], + "angle": 0, + "content": "Table 3. Performance comparison of with or without using the modality prototype and auxiliary (Aux.) bridge schemes in the modality alignment loss. CMC (%) at rank 1 and mAP (\\%)." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.389, + 0.888, + 0.485 + ], + "angle": 0, + "content": "
Schemes in LmaSYSU-MM01RegDB
PrototypeAux. bridger=1mAPr=1mAP
69.0265.8380.0973.97
✓74.1572.1086.7377.24
✓71.6668.3583.9275.54
✓✓76.2473.8195.1987.15
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.502, + 0.892, + 0.638 + ], + "angle": 0, + "content": "In Table 3, it is evident that both the modality prototype scheme and the auxiliary bridge scheme contribute to the VI-ReID accuracy gain. The modality prototype consistently captures global modality information, enhancing the robustness of learned modality relationships by synchronizing the alignment in each iteration; The auxiliary bridge scheme reduces the relative distance between visible and infrared features, effectively alleviating the difficulty of cross-modality distance optimization." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.65, + 0.866, + 0.667 + ], + "angle": 0, + "content": "4.4. Comparison with State-of-the-art Methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.674, + 0.892, + 0.703 + ], + "angle": 0, + "content": "In this section, we compare our MUN with state-of-the-art works on two public datasets, as shown in Table 4." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Comparison on SYSU-MM01 dataset. As illustrated in Table 4, the proposed MUN achieves impressive results with \\(76.24\\%\\) rank-1 and \\(73.81\\%\\) mAP on the all-search mode of the SYSU-MM01 dataset. Compared to traditional visible-infrared representation learning methods (AGW [33], DELN-ViT [38], SPOT [1], PMT [14], CMT [6], MPANet [29]), our MUN outperforms them by a margin of at least \\(4.36\\%\\) rank-1 and \\(5.24\\%\\) mAP on the all-search mode. The reason can be attributed that the proposed visible-auxiliary-infrared learning framework can capture more identity-related knowledge across modalities and regulate the discriminative feature relationships well. Additionally, the overall performance of our approach is also" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "11191" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.116, + 0.088, + 0.851, + 0.101 + ], + "angle": 0, + "content": "Table 4. Comparison with state-of-the-art methods on SYSU-MM01 and RegDB datasets. CMC (%) at rank r and mAP (%)" + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.102, + 0.894, + 0.352 + ], + "angle": 0, + "content": "
MethodsRef.SYSU-MM01RegDB
All-SearchIndoor-SearchVisible to InfraredInfrared to Visible
r=1r=10mAPr=1r=10mAPr=1r=10mAPr=1r=10mAP
Zero-padding [28]ICCV1714.8054.1215.9520.5868.3826.9217.7534.2118.9016.6334.6817.82
JSIA-ReID [25]AAAI2038.1080.7036.9043.8086.2052.9048.50-49.3048.10-48.90
AlignGAN [24]ICCV1942.4085.0040.7045.9087.6054.3057.90-53.6056.30-53.40
AGW [33]TPAMI2147.5084.3947.6554.1791.1462.9770.0586.2167.6470.4987.2165.90
X-Modality [9]AAAI2049.9289.7950.73---62.2183.1360.18---
DFLN-ViT [38]TMM2259.8492.4957.7062.1394.8369.0392.1097.9782.1191.2198.2081.62
SPOT [1]TIP2265.3492.7362.2569.4296.2274.6380.3593.4872.4679.3792.7972.26
FMCNet [36]CVPR2266.34-62.5168.15-63.8289.12-84.4388.23-83.86
SMCL [27]ICCV2167.3992.8761.7868.8496.5575.5683.93-79.8383.05-78.57
PMT [14]AAAI2367.5395.3664.9871.6696.7376.5284.83-76.5584.16-75.13
AGW+J [31]ICCV2169.8895.7166.8976.2697.8880.3785.0395.4979.1484.7595.3377.82
MPANet [29]CVPR2170.5896.1068.2476.7498.2180.9583.70-80.9082.80-80.70
CMT [6]ECCV2271.8896.4568.5776.9097.6879.9195.1798.8287.3091.9797.9284.46
MUN (Ours)ICCV2376.2497.8473.8179.4298.0982.0695.1998.9387.1591.8697.9985.01
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.378, + 0.469, + 0.439 + ], + "angle": 0, + "content": "superior to GAN-based methods (JSIA-ReID [25], AlignGAN [24], FMCNet [36]) thanks to the powerful auxiliary modality which dynamically combines the information of visible and infrared images without introducing extra noise." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.44, + 0.469, + 0.576 + ], + "angle": 0, + "content": "Furthermore, the proposed method significantly outperforms existing modality-unifying methods (SMCL [27], X-Modality [9]) by at least \\(8.85\\%\\) on the rank-1 metric. This can be attributed to the fact that we not only mine the fine-grained semantic representations to generate the auxiliary modality but also decouple the extraction of specific and shared patterns in two modalities, which contribute to the dynamic generation of the auxiliary modality for relieving the changeable modality discrepancies during the training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.577, + 0.469, + 0.759 + ], + "angle": 0, + "content": "Comparison on RegDB dataset. The results on RegDB are also listed in Table 4. In this dataset, image samples are spatially aligned and present less intra-class variations. Thus, the accuracy of all methods is higher than that on SYSU-MM01. The proposed MUN achieves Rank-1 of \\(95.19\\%\\) and mAP of \\(87.15\\%\\) in visible to infrared mode. Similar improvement can also be observed in the infrared to visible mode, which shows that our method obtains Rank-1 of \\(91.86\\%\\) and mAP of \\(85.01\\%\\). This improvement can be attributed to the capacity of our method to generate a robust auxiliary modality, effectively mitigating both cross-modality and intra-modality discrepancies." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.77, + 0.348, + 0.788 + ], + "angle": 0, + "content": "4.5. Evaluation on Generalizability" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.469, + 0.901 + ], + "angle": 0, + "content": "To verify the generalizability of MUN, we conduct experiments on two corrupted VI Re-ID datasets [2], namely SYSU-MM01-C and RegDB-C. We utilize the same corruption settings as [2], which only performs corruptions during the testing stage and randomly selects one corruption type (e.g., elastic, snow, frosted glass, etc.) and one severity level for each image in the visible gallery set. The results re" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.375, + 0.892, + 0.415 + ], + "angle": 0, + "content": "Table 5. Evaluations on corrupted datasets. Each evaluation is performed 10 times to obtain the mean value. \\( L_{id}^{a} \\) denotes an individual identity loss used to supervise the auxiliary modality." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.416, + 0.892, + 0.569 + ], + "angle": 0, + "content": "
IndexMethodSYSU-MM01-CRegDB-C
r=1mAPr=1mAP
1X-Modality [9]31.9826.2037.2635.97
2CIL [2]36.9535.9252.2549.76
3SMCL [27]37.0836.1251.9349.22
4AGW+J [31]40.0937.8651.5349.04
5B25.9223.1332.0529.64
6+Aux.+Lda30.8526.5436.4031.21
7+Aux.+Lidc31.1227.4438.1332.29
8+Aux.+Lidc+Lia36.7832.3245.4442.89
9+Aux.+Lidc+Lia+Lma41.1738.6352.6950.18
" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.594, + 0.891, + 0.625 + ], + "angle": 0, + "content": "ported for all the compared methods are obtained using the official best settings as provided in their respective papers." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Table 5 shows that the performance of baseline (B) is relatively lower than that of existing SOTAs under data corruption scenarios. However, by introducing the auxiliary modality to bridge the gap between visible and infrared modalities (Index 6), the accuracy is significantly improved. Furthermore, by incorporating the proposed identity alignment loss \\((L_{ia})\\) and modality alignment loss \\((L_{ma})\\) to refine the learned cross-modality feature relationships, the rank-1 and mAP accuracies experience a substantial enhancement of \\(15.25\\%\\) and \\(15.5\\%\\) respectively on the SYSU-MM01-C dataset. This outperforms the current SOTAs by a remarkable margin. Specifically, our MUN method exceeds the highly robust AGW+J [31] by \\(1.08\\%\\) in rank-1 and \\(0.77\\%\\) in mAP. The experiments on two corrupted datasets verify the strong generalizability and robustness of the proposed MUN, which can consistently learn modality-shared patterns and regulate stable feature relationships under corrupted data scenarios." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11192" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.09, + 0.257, + 0.213 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.099, + 0.462, + 0.212 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.08, + 0.22, + 0.256, + 0.337 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.22, + 0.462, + 0.337 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.343, + 0.47, + 0.4 + ], + "angle": 0, + "content": "Figure 4. Distributions of learned visible, infrared and auxiliary features during the training. All the samples are randomly selected in the SYSU-MM01 dataset. The 3D visualization is made by T-SNE [23]. Please view in colour and zoom in." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.424, + 0.214, + 0.438 + ], + "angle": 0, + "content": "4.6. Visualization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.447, + 0.47, + 0.522 + ], + "angle": 0, + "content": "Distribution Visualization. To visually demonstrate the effectiveness of MUN, we randomly select 10 identities from the SYSU-MM01 dataset and visualize their feature distributions during the training. The visualization results are presented in Figure 4." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.523, + 0.47, + 0.78 + ], + "angle": 0, + "content": "At the onset of training (epoch 0 in Figure 4 (a)), significant modality disparities arise between visible (depicted by blue dots) and infrared images (depicted by red dots), rendering cross-modality matching unfeasible. As the training progresses, the proposed auxiliary modality (depicted by green dots) serves as a bridge to connect the visible and infrared modalities in the common feature space. We can observe that the learned visible and infrared features show a convergence trend, and the modality discrepancies are gradually eliminated at epoch 5 in Figure 4 (b). Afterwards, the network learns identity-aware patterns by regulating smaller intra-class distances and larger inter-class distances at epoch 45. Finally, in Figure 4 (d), all the learned features are well grouped into their respective identity centers, demonstrating powerful discriminability under cross-modality scenes, which proves the effectiveness of MUN in learning robustness and identity-aware features." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.469, + 0.856 + ], + "angle": 0, + "content": "Pattern Visualization. In order to further illustrate the effectiveness of our auxiliary modality, we select one visible and one infrared image with the same identity in the SYSUMM01 dataset to visualize the corresponding learned feature maps and attention maps via Grad-CAM [22]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.901 + ], + "angle": 0, + "content": "The visualization results are shown in Figure 5. It is clear that the visible \\((\\mathbf{F}^v)\\) and infrared \\((\\mathbf{F}^r)\\) feature maps extracted from the backbone have different patterns and struc" + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.094, + 0.885, + 0.22 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.228, + 0.892, + 0.338 + ], + "angle": 0, + "content": "Figure 5. Visualization of learned feature maps and attention maps. Given the input visible image \\(\\mathbf{I}^v\\) and infrared image \\(\\mathbf{I}^r\\), we visualize the corresponding learned visible feature \\(\\mathbf{F}^v\\), infrared feature \\(\\mathbf{F}^r\\), and the generated auxiliary feature \\(\\mathbf{F}^a\\). It is obvious that the auxiliary feature \\(\\mathbf{F}^a\\) can preserve most of the modality-shared patterns, including body shape and structure. The attention visualizations on the input images are made by Grad-CAM [22]. Please view in colour and zoom in." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.367, + 0.892, + 0.518 + ], + "angle": 0, + "content": "tures, which makes it difficult to perform cross-modality matching. Notably, the proposed auxiliary generator can dynamically reconstruct and align the modality-shared spatial patterns using multiple transposed convolutions. This makes our auxiliary feature \\((\\mathbf{F}^a\\) in Figure 5) preserves most of the shared patterns between \\(\\mathbf{F}^v\\) and \\(\\mathbf{F}^r\\) without corrupting the structure information of person bodies. In addition, the attention visualization in Figure 5 further indicates that the proposed auxiliary modality plays a critical role in helping the network learn modality-shared representations." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.538, + 0.619, + 0.554 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.566, + 0.892, + 0.779 + ], + "angle": 0, + "content": "This paper proposes a novel Modality Unifying Network to jointly explore the robust auxiliary modality and generalize cross-modality feature relationships for VI-ReID. The auxiliary modality is generated by combining the cross-modality learner and the intra-modality learner, enabling the dynamic extraction of modality-specific patterns from multiple receptive fields and feature scales. This approach empowers our auxiliary modality to effectively alleviate both cross-modality and intra-modality discrepancies. Moreover, we propose identity alignment loss and modality alignment loss to regulate discriminative feature relationships in multi-modality tasks. Extensive experiments on public datasets demonstrate the effectiveness and generalizability of our MUN as well as each proposed component." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgements. This work is supported by the Academy of Finland for Academy Professor project EmotionAI (Grants No. 336116, 345122), the University of Oulu & The Academy of Finland Profi 7 (Grant No. 352788), and the National Natural Science Foundation of China (Grant No. 61802058, 61911530397). We appreciate the professional and cost-effective GPU computing service provided by www.AutoDL.com." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11193" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Cuiqun Chen, Mang Ye, Meibin Qi, Jingjing Wu, Jianguo Jiang, and Chia-Wen Lin. Structure-aware positional transformer for visible-infrared person re-identification. IEEE Transactions on Image Processing, 31:2352-2364, 2022." + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.171, + 0.471, + 0.213 + ], + "angle": 0, + "content": "[2] Minghui Chen, Zhiqiang Wang, and Feng Zheng. 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In Proceedings of the AAAI conference on artificial intelligence, volume 34, pages 13114–13121, 2020." + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.191 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11195" + } + ] +] \ No newline at end of file diff --git a/2023/Modality Unifying Network for Visible-Infrared Person Re-Identification/c25cccee-cf9c-444a-bfaa-52844fa6cb10_origin.pdf b/2023/Modality Unifying Network for Visible-Infrared Person Re-Identification/c25cccee-cf9c-444a-bfaa-52844fa6cb10_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..2c1c97cb1d7c0873bca7483cfca6fea351815b23 --- /dev/null +++ b/2023/Modality Unifying Network for Visible-Infrared Person Re-Identification/c25cccee-cf9c-444a-bfaa-52844fa6cb10_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:62c549520f915c33a832bb1dd66d794103c2d527471310ddfbf4a5f73f26b0ad +size 1449836 diff --git a/2023/Modality Unifying Network for Visible-Infrared Person Re-Identification/full.md b/2023/Modality Unifying Network for Visible-Infrared Person Re-Identification/full.md new file mode 100644 index 0000000000000000000000000000000000000000..ffdd65f5cab03d91f2b9b56a6b52393e548bf3d8 --- /dev/null +++ b/2023/Modality Unifying Network for Visible-Infrared Person Re-Identification/full.md @@ -0,0 +1,384 @@ +# Modality Unifying Network for Visible-Infrared Person Re-Identification + +Hao Yu $^{1}$ , Xu Cheng $^{1*}$ , Wei Peng $^{2}$ , Weihao Liu $^{3}$ , Guoying Zhao $^{4}$ + +1School of Computer Science, Nanjing University of Information Science and Technology, China + +$^{2}$ Department of Psychiatry and Behavioral Sciences, Stanford University, USA + +$^{3}$ School of Computer Science and Technology, Soochow University, China + +4Center for Machine Vision and Signal Analysis, University of Oulu, Finland + +{yuhao,xcheng}@nuist.edu.cn, wepeng@stanford.edu, whliu@stu.suda.edu.cn, guoying.zhao@oulu.fi + +# Abstract + +Visible-infrared person re-identification (VI-ReID) is a challenging task due to large cross-modality discrepancies and intra-class variations. Existing methods mainly focus on learning modality-shared representations by embedding different modalities into the same feature space. As a result, the learned feature emphasizes the common patterns across modalities while suppressing modality-specific and identity-aware information that is valuable for Re-ID. To address these issues, we propose a novel Modality Unifying Network (MUN) to explore a robust auxiliary modality for VI-ReID. First, the auxiliary modality is generated by combining the proposed cross-modality learner and intra-modality learner, which can dynamically model the modality-specific and modality-shared representations to alleviate both cross-modality and intra-modality variations. Second, by aligning identity centres across the three modalities, an identity alignment loss function is proposed to discover the discriminative feature representations. Third, a modality alignment loss is introduced to consistently reduce the distribution distance of visible and infrared images by modality prototype modeling. Extensive experiments on multiple public datasets demonstrate that the proposed method surpasses the current state-of-the-art methods by a significant margin. + +# 1. Introduction + +Person re-identification (Re-ID) [8,33] aims at matching pedestrian images captured from multiple non-overlapping cameras. Over the past few years, it has received increased attention due to its huge practical value in modern surveillance systems. Previous studies [10, 16, 19, 30, 40] mainly focus on matching pedestrian images captured from visible cameras and formulate the Re-ID task as a single-modality + +matching issue. Nevertheless, visible cameras may not provide accurate appearance information about persons in scenarios with poor illumination. To address this limitation, modern surveillance systems also employ infrared cameras, which can capture clear images in low-light conditions at night. As a result, visible-infrared person re-identification (VI-ReID) [1, 28, 29] has become a topic of growing interest in recent times, which seeks to match infrared images of the same identity when given a visible query across multiple camera views and vice versa. + +VI-ReID is challenging due to the huge cross-modality discrepancy between visible and infrared images, as well as the intra-modality variation in person bodies such as pose variation and dress change. Existing methods [1, 20, 29, 31, 36, 37] primarily focus on relieving the cross-modality discrepancy by extracting modality-shared features to perform the feature-level alignment. Some studies [1, 20, 28, 31, 34] employ two-stream networks for cross-modality feature embedding, while others [3, 24, 25, 36] utilize Generative Adversarial Networks (GANs) to generate shared representations from visible and infrared images. However, these methods discard modality-specific features (such as colour and texture) that contain useful identity-aware patterns against intra-modality variations. Consequently, the learned features may not fully capture the variation of human bodies and thus lack discriminability. To address this limitation, the modality-unifying methods, e.g., X-modality [9], DFM [7], SMCL [27], have been proposed to acquire the auxiliary modality by fusing visible and infrared modalities, encoding both modality-specific and modality-shared patterns to jointly relieve cross- and intramodality discrepancies. In the SMCL [27], the authors proposed a syncretic modality generated by fusing visible and infrared pixels, which can bridge the gap between visible and infrared modalities while maintaining discriminability as the modality-specific information is preserved. + +However, the existing modality-unifying works still have three weaknesses. (1) Pixel fusion. Previous works gener- + +![](images/99eeae7753986a7c0b731b38bb3cce3f2652ebd86627c480950a271a0c41b221.jpg) +Figure 1. The main idea behind generating a strong auxiliary modality for the VI-ReID task. The IML and CML denote the intra-modality learner and cross-modality learner, respectively. + +ate the auxiliary modality by fusing pixels of the raw visible and infrared images, which makes the richness of semantic patterns either equal to the original two modalities or lower in the case of pixel misalignment. In fact, the auxiliary modality is utilized to guide the learning of visible and infrared modalities, but the insufficient semantic patterns lead to a lack of identity-related information and severely limit the capacity to relieve intra-modality variations in VI-ReID. (2) Discrepancy bias. During the VI training, the relative distances between visible and infrared images are constantly changing, which causes a dynamic bias toward the balance of intra- and cross-modality discrepancies. Thus, an ideal auxiliary modality should be able to dynamically control the ratio of modality-specific and modality-shared patterns it contains to model the evolving modality discrepancies. However, the existing studies simply use the global information of visible and infrared images to obtain the auxiliary representations, which are inflexible in adjusting the patterns they describe, leading to low robustness. + +(3) Inconsistency constraints. Existing studies usually utilize features in the current batch to represent the overall distribution for distance optimization. However, this strategy suffers from randomness, as the training samples are different in each batch, which may cause a certain inconsistency in the learned feature relationships in different training stages, thus damaging the generalizability. + +Inspired by the above discussions, we propose a novel Modality Unifying Network (MUN) to explore an effective and robust auxiliary modality for VI-ReID. The main idea of our auxiliary modality is illustrated in Figure 1. Specifically, we introduce an auxiliary generator comprising two intra-modality learners (IML) and one cross-modality learner (CML) to distil the modality-related patterns from visible and infrared images. Two IMLs are presented to identify the modality-specific and identity-aware patterns from visible and infrared images, respectively. They exploit multiple depth-wise convolutions with various kernel sizes to capture fine-grained semantic patterns in the human + +body across multiple receptive fields. Based on the outputs of two IMLs, the CML leverages spatial pyramid pooling to extract multi-scale feature representations and then fuse the modality-shared patterns learned in each feature scale. By combining IML and CML, the proposed auxiliary generator can generate a powerful auxiliary modality that is rich in modality-shared and discriminative patterns to alleviate both cross-modality and intra-modality discrepancies. In addition, the layer scale scheme is used to control the ratio of patterns learned from IML and CML, which can dynamically adjust the modality-specific and modality-shared patterns in the generated auxiliary representation. + +Furthermore, to reveal the identity-related patterns in each identity set, an effective identity alignment loss $(L_{ia})$ is designed to optimize the distances of tri-modality identity centres. In addition, to regulate the distribution level feature relationships while relieving the inconsistency issue caused by sample variations, a novel modality alignment loss $(L_{ma})$ is designed to minimize the distances of three modalities, which utilizes the modality prototype to represent the learned modality information in each iteration. + +In general, the major contributions of this paper can be summarized as follows. + +- We propose a novel modality unifying network for the VI-ReID task by constructing a robust auxiliary modality, which contains rich semantic information from visible and infrared images to address modality discrepancies and reveal discriminative knowledge. +- A novel auxiliary generator constructed by the intramodality and cross-modality learners is introduced to dynamically extract identity-aware and modality-shared patterns from heterogeneous images. +- The identity alignment loss and modality alignment loss are designed to jointly explore the generalized and discriminative feature relationships of the three modalities at both the identity and distribution levels. +- Extensive experiments on several public VI-ReID datasets verify the effectiveness of the proposed method and modality unifying scheme, which outperforms the current state of the arts by a large margin. + +# 2. Related Work + +Single-Modality Person Re-ID. Single-modality person re-identification [11, 17, 33] aims to match pedestrian images across different visible cameras. It presents challenges such as changes in viewpoint and human pose across camera views. Current approaches mainly focus on feature representation learning [15, 19, 39] and distance metric learning [10, 30, 35, 40]. Over the past few years, excellent performances have been achieved on several academic benchmarks. However, in practical scenarios, numerous crucial + +![](images/729e9611e84e0aa4722a76ed2bfc5b5169886ccd909bdf7b6fd258548c03a811.jpg) +Figure 2. The overall architecture of the proposed MUN for VI-ReID. GeMP denotes the Generalized Mean Pooling [21]. The pretrained ResNet-50 [4] is adopted as the baseline network. To meet the specific requirements of VI-ReID, we initialize the first stage of the ResNet-50 twice as two independent ResBlocks to extract the low-level visible and infrared features, respectively. The remaining stages are utilized as modality-shared ResBlocks. During the inference, only visible and infrared modalities are utilized to perform cross-modality retrieval. + +surveillance photos and videos are captured at night using infrared cameras. When it comes to matching pedestrians across visible and infrared modalities, the capabilities of these single-modality methods are limited due to their inability to address the huge modality gap. In contrast, we present an effective modality unifying network to bridge the modality gap and achieve precise cross-modality pedestrian matching in 24-hour monitoring scenarios. + +Visible-Infrared Person Re-ID. Visible-Infrared person Re-ID [28] is a challenging task due to the cross-modality discrepancies between visible and infrared images, as well as the intra-modality variations such as pose and dress changes. Existing studies [20, 29, 31, 32, 34] mainly focus on learning the modality-shared representations to align the visible and infrared modalities. Some generation-based methods [24-26,36] have been developed to achieve modality alignment or translation by using Generative Adversarial Network (GAN). For instance, Wang et al. [24] proposed a dual-alignment network that used GAN to jointly learn pixel and feature level alignment. The D2RL [26] is proposed to perform image-level modality translation by adversarial training that relieves the cross-modality discrepancy. Other works [1, 20, 29, 31, 34] attempt to learn modality-shared features by designing two-stream networks to perform cross-modality feature embedding. Ye et al. [34] proposed a dual-constrained top-ranking method with a weight-shared two-stream network. Wu et al. [29] designed a cross-modality attention scheme to help the two-stream backbone discover cross-modality nuances. However, these methods usually discard modality-specific representations + +that help to relieve intra-modality variations, leading to low robustness and discriminability in learned features. + +In order to capture both the modality-shared and identity-aware patterns from heterogeneous images, modality-unifying methods have been developed. These methods aim to obtain the auxiliary modality by combining modality-specific and modality-shared representations from both visible and infrared images. The syncretic modality [27] is proposed to guide the generation of discriminative and modality-invariant representations. The DFM [7] acquires the mixed modality by integrating visible and infrared pixels. However, these methods generate the auxiliary modality by directly fusing the raw pixels of visible and infrared images, making their auxiliary modality lack high-level semantic patterns and inflexible to adjust its representations. + +To tackle these challenges, this paper presents the intramodality learner and cross-modality learner to dynamically uncover substantial modality-shared and discriminative patterns from multiple receptive fields and feature scales. By integrating these learners, we introduce a powerful auxiliary modality that effectively bridges the modality discrepancy and enhances the discriminability of learned features. + +# 3. Methodology + +As shown in Figure 2, we introduce the details of the Modality Unifying Network. We first utilize two independent ResBlocks to extract low-level features from visible and infrared images, respectively. Then, the auxiliary generator is designed to generate the auxiliary features by com + +bining intra-modality and cross-modality learners. Afterwards, the visible, infrared, and auxiliary features are fed into weight-shared ResBlocks to learn high-level patterns. The auxiliary features can serve as a bridge to relieve both intra- and cross-modality discrepancies during the training. Based on the visible, infrared, and auxiliary features learned by weight-shared ResBlocks, four loss functions are developed to effectively improve cross-modality matching accuracy, including identity loss $L_{id}$ , identity consistency loss $L_{idc}$ , identity alignment loss $L_{ia}$ and modality alignment loss $L_{ma}$ . + +# 3.1. Auxiliary Generator + +The auxiliary generator contains two intra-modality learners (IML) and one cross-modality learner (CML). The two IMLs are designed to mine identity-related patterns from visible and infrared images, respectively. The CML is designed to learn modality-shared patterns based on the outcomes of two IMLs. The detailed architectures of IML and CML are shown in Figure 3. + +Intra-Modality Learner. The intra-modality learner (IML) is designed to capture the discriminative and identity-aware patterns in human bodies. The visible or infrared low-level features $\mathbf{F}^m\in \mathbb{R}^{C\times H\times W}$ , $m\in \{v,r\}$ extracted from two independent ResBlocks are regarded as the input of IML, where $m$ denotes the visible or infrared modality. + +To enrich the receptive field while keeping low computational complexity, we equally divide $\mathbf{F}^m$ into two parts along the channel dimension by matrix slice operation. + +$$ +\mathbf {F} _ {c _ {1}} ^ {m} = \mathbf {F} ^ {m} [ 0: C / 2,: :, ] \quad , \quad \mathbf {F} _ {c _ {2}} ^ {m} = \mathbf {F} ^ {m} [ C / 2: C,:,: ]. \tag {1} +$$ + +Then, we employ $7 \times 7$ and $5 \times 5$ depth-wise convolutions $(D)$ to operate on $\mathbf{F}_{c_1}^m$ and $\mathbf{F}_{c_2}^m$ , respectively. This allows us to capture spatial patterns in different receptive fields. + +$$ +\mathbf {R} ^ {m} = \operatorname {C o n c a t} \left\{D _ {5 \times 5} \left(\mathbf {F} _ {c _ {1}} ^ {m}\right), D _ {7 \times 7} \left(\mathbf {F} _ {c _ {2}} ^ {m}\right) \right\}, \tag {2} +$$ + +where $\text{Concat}$ denotes the concatenation on channel dimension; $\mathbf{R}^m$ indicates the visible or infrared features captured from multiple receptive fields. Then, a point-wise convolution $(P)$ is utilized to fuse patterns with diverse receptive fields by connecting pixels in each channel. + +$$ +\mathbf {R} _ {1} ^ {m} = P _ {1 \times 1} (B a t c h N o r m (\mathbf {R} ^ {m})). \tag {3} +$$ + +To integrate and encode the structural information in human bodies, another depth-wise convolution with $3 \times 3$ kernel size is introduced to remodel the learned spatial map. This layer also utilizes a residual branch to retain information from the previous layer. + +$$ +\mathbf {R} _ {2} ^ {m} = D _ {3 \times 3} \left(R e L U \left(\mathbf {R} _ {1} ^ {m}\right)\right) + \mathbf {R} _ {1} ^ {m}. \tag {4} +$$ + +In addition, another point-wise convolution is utilized to fuse patterns with diverse receptive fields in $\mathbf{R}_2^m$ . + +$$ +\hat {\mathbf {F}} ^ {m} = I _ {\text {s c a l e}} * P _ {1 \times 1} \left(\operatorname {B a t c h N r o m} \left(\mathbf {R} _ {2} ^ {m}\right)\right), \tag {5} +$$ + +![](images/11e61430bce8992a46b6512243bb67e6ed134a2ba566f83bfca42d438b382215.jpg) +Figure 3. The detailed architecture of the proposed intra-modality learner (IML) and cross-modality learner (CML). They are designed to decouple the modeling of modality-related knowledge. + +![](images/a40481b955e23157285d07657fbce6c91c9830b3ec344e3a1d44649c7447657a.jpg) + +where $I_{scale} \in (0,1]$ is the learnable layer scale factor used to control the ratio of intra-modality patterns learned by IML; $\hat{\mathbf{F}}^m$ denotes the outcomes of the two IMLs. + +In the proposed intra-modality learner, three depth-wise convolutions with various kernel sizes are well combined to capture the identity-related patterns that existed in various receptive fields. Two point-wise convolutions are utilized for pattern integration and channel relation reasoning based on the inverted residual architecture [12]. The first point-wise convolution increases the channel dimension from $C$ to $C * 4$ and the last point-wise convolution reduces the channel dimension from $C * 4$ to $C$ . + +Cross-Modality Learner. The cross-modality learner is designed to mine the modality-shared patterns from multiple feature scales based on the outcomes of two IMLs. Specifically, the spatial pyramid features are mined by applying $n$ average pooling layers with various ratios. + +$$ +\mathbf {S} _ {1} ^ {m} = \operatorname {A v g p o o l} _ {1} (\hat {\mathbf {F}} ^ {m}) , +$$ + +$$ +\begin{array}{c c} \mathbf {S} _ {2} ^ {m} = A v g p o o l _ {2} (\hat {\mathbf {F}} ^ {m}) & , \\ \dots & , \end{array} \tag {6} +$$ + +$$ +\mathbf {S} _ {n} ^ {m} = \operatorname {A v g p o o l} _ {n} (\hat {\mathbf {F}} ^ {m}) , +$$ + +where $\{\mathbf{S}_1^m,\mathbf{S}_2^m,\dots,\mathbf{S}_n^m\}, m\in \{v,r\}$ denote the spatial pyramid features with various feature scales. Afterwards, we obtain the modality-shared spatial patterns from each pair of cross-modality spatial pyramid features $\{\mathbf{S}_i^v,\mathbf{S}_i^r\}_{i = 1}^n$ with the same feature scale by using a group of learnable transposed convolutions $\{TR_1,TR_2,\dots,TR_n\}$ . + +$$ +\hat {\mathbf {S}} _ {i} ^ {v} = T R _ {i} \left(\mathbf {S} _ {i} ^ {v}\right), \quad \hat {\mathbf {S}} _ {i} ^ {r} = T R _ {i} \left(\mathbf {S} _ {i} ^ {r}\right), \quad i = 1, 2, \dots , n. \tag {7} +$$ + +Here, the spatial dimensions of each cross-modality feature pair $\hat{\mathbf{S}}_i^v$ and $\hat{\mathbf{S}}_i^r$ are rebuilt to $H\times W$ by the corresponding transposed convolution $TR_{i}$ , respectively. In this manner, the significant patterns of visible and infrared features + +on each feature scale are embedded together, which helps to discover and amplify the abundant modality-shared information on multiple feature scales. + +Further, all the embedded features are concatenated on the channel dimension via Eq.(8). + +$$ +\hat {\mathbf {S}} = \operatorname {C o n c a t} \left\{\hat {\mathbf {S}} _ {i} ^ {v}, \hat {\mathbf {S}} _ {2} ^ {v}, \dots , \hat {\mathbf {S}} _ {n} ^ {v}, \hat {\mathbf {S}} _ {1} ^ {r}, \hat {\mathbf {S}} _ {2} ^ {r}, \dots , \hat {\mathbf {S}} _ {n} ^ {r} \right\}. \tag {8} +$$ + +Then, the auxiliary feature is obtained by fusing patterns captured from multiple feature scales. + +$$ +\mathbf {F} ^ {a} = C _ {\text {s c a l e}} * P _ {1 \times 1} (\operatorname {B a t c h N o m r} (\hat {\mathbf {S}})), \tag {9} +$$ + +where $\mathbf{F}^a$ denotes the auxiliary feature generated by our method. It contains substantial modality-shared and identity-aware information captured by three learners; $C_{scale} \in (0,1]$ denotes the learnable layer scale factor used to control the ratio of modality-shared representations in the learned auxiliary feature $\mathbf{F}^a$ ; $P_{1 \times 1}$ is a point-wise convolution used to fuse patterns across different channels. + +The CML mines significant patterns from multiple feature scales and amplifies the modality-shared parts from them using transposed convolutions. It makes our auxiliary feature a powerful tool to handle cross-modality variations. + +# 3.2. Classification Constraint + +To ensure the learned visible and infrared features are identity-related, the identity loss $(L_{id})$ implemented with the cross-entropy term is introduced as follows. + +$$ +L _ {i d} ^ {m} = - \frac {1}{k} \sum_ {i = 1} ^ {k} \log P \left(y _ {i} \mid C _ {m} \left(\mathbf {Z} _ {i} ^ {m}\right)\right), \quad s. t. \quad m \in \{v, r \}, \tag {10} +$$ + +where $\mathbf{Z}_i^v$ and $\mathbf{Z}_i^r$ denote the generalized mean pooled visible and infrared features in the $i$ -th identity, respectively. $k$ is the number of visible or infrared images in each batch; $y_i$ is the $i$ -th identity label; $C_v(\cdot)$ and $C_r(\cdot)$ are the predictions of visible and infrared classifiers, respectively. + +The learned presentations are modality-shared if two classifiers can give consistent predictions for features from any modalities. However, if we directly apply features in one modality to the classifier in another modality (e.g., $C_r(\mathbf{Z}^v)$ ), it may impose the classifier to learn modality-specific patterns rather than the modality-shared patterns, as the former is typically more discriminative. To solve this issue, we present an identity-consistency loss $L_{idc}$ to update the parameters of both visible and infrared classifiers with the aid of auxiliary features. It can be defined as follows. + +$$ +L _ {i d c} = - \frac {1}{k} \sum_ {i = 1} ^ {k} \left[ \log P \left(y _ {i} \mid C _ {v} \left(\mathbf {Z} _ {i} ^ {a}\right)\right) + \log P \left(y _ {i} \mid C _ {r} \left(\mathbf {Z} _ {i} ^ {a}\right)\right) \right], \tag {11} +$$ + +where $\mathbf{Z}_i^a$ denotes the pooled auxiliary feature in the $i$ -th identity. The auxiliary features effectively integrate visible and infrared patterns, facilitating the transfer of identity-related knowledge between modalities without compromising the original intra-modality learning. + +# 3.3. Identity Alignment Loss + +To relieve the class-level modality discrepancies and learn discriminative feature relationships, the identity alignment loss $L_{ia}$ is designed to align the visible and infrared features of each identity with the aid of auxiliary features. + +$$ +\begin{array}{l} L _ {i a} = \sum_ {i = 1} ^ {P} \left[ \alpha + \max _ {m _ {1} \in \{v, r \}} \left| \left| \mathbf {C} _ {i} ^ {a} - \mathbf {C} _ {i} ^ {m _ {1}} \right| \right| _ {2} \right. \tag {12} \\ -\min_{\substack{m_{2}\in \{v,r\} \\ q\neq i}}||\mathbf{C}_{i}^{a} - \mathbf{C}_{q}^{m_{2}}||_{2}\Bigg], \\ \end{array} +$$ + +where $\alpha$ is the margin parameter; $P$ denotes the number of person identities; $N$ is the number of images in the $i$ -th identity; $\mathbf{C}_i^a = \frac{1}{N}\sum_{j=1}^{N}\mathbf{Z}_{i,j}^a$ , $\mathbf{C}_i^v = \frac{1}{N}\sum_{j=1}^{N}\mathbf{Z}_{i,j}^v$ , $\mathbf{C}_i^r = \frac{1}{N}\sum_{j=1}^{N}\mathbf{Z}_{i,j}^r$ are the auxiliary, visible, and infrared centres in the $i$ -th identity, respectively; $\mathbf{Z}_{i,j}^v$ , $\mathbf{Z}_{i,j}^r$ and $\mathbf{Z}_{i,j}^a$ denote the $j$ -th visible, infrared, and auxiliary features in the $i$ -th identity set. + +In this paper, identity alignment loss is proposed to optimize the hardest cross-modality positive and negative centre pairs in a triplet-metric manner. It regulates discriminative and robust feature relationships by forcing all identities to form a tight intra-class space and pushing centres of different identities away across the three modalities. + +# 3.4. Modality Alignment Loss + +Previous works [7, 20, 29] typically align the two modalities by constraining visible and infrared features in each iteration. This scheme suffers from inconsistencies in the learned cross-modality feature relationships because the training samples are different in each iteration. To overcome this issue, we propose a modality alignment strategy that consistently aligns visible and infrared modalities by modeling the prototypes from features in each iteration. + +Specifically, we first introduce three modality prototypes to represent the global information of visible, infrared, and auxiliary modalities, respectively. They can be denoted as $\mathbf{T}^v = \{\mathbf{t}_1^v,\mathbf{t}_2^v,\dots,\mathbf{t}_B^v\}$ , $\mathbf{T}^r = \{\mathbf{t}_1^r,\mathbf{t}_2^r,\dots,\mathbf{t}_B^r\}$ and $\mathbf{T}^a = \{\mathbf{t}_1^a,\mathbf{t}_2^a,\dots,\mathbf{t}_B^a\} \in \mathbb{R}^{B\times C}$ , where $\mathbf{t}_i^v,\mathbf{t}_i^r$ and $\mathbf{t}_i^a$ are the modality prototypes for the $i$ -th visible, infrared, and auxiliary features in each training batch $(B)$ , respectively. + +The initial prototypes of the three modalities are obtained based on the pooled features $[\mathbf{Z}^v ]^0$ $[\mathbf{Z}^r ]^0$ and $[\mathbf{Z}^a ]^0\in$ $R^{B\times C}$ in the 0-th iteration. + +$$ +[ \mathbf {T} ^ {m} ] ^ {0} = \mathbf {W} _ {p} ^ {m} [ \mathbf {Z} ^ {m} ] ^ {0}, \quad s. t. \quad m \in \{v, r, a \}, \tag {13} +$$ + +where $\mathbf{W}_p^m$ are learnable matrices to distil modality-related patterns from the $m$ -th modality. $[\mathbf{T}^m]^{0}$ denotes the prototype of the $m$ -th modality calculated in the 0-th iteration. + +Further, to dynamically model the modality information during the training, we develop a temporal accumulation + +strategy to update the modality prototype by the learned features in each iteration, which can be defined as follows. + +$$ +\begin{array}{l} [ \mathbf {T} ^ {m} ] ^ {i} = [ \beta ] ^ {i} * \mathbf {W} _ {p} ^ {m} [ \mathbf {Z} ^ {m} ] ^ {i} + (1 - [ \beta ] ^ {i}) * [ \mathbf {T} ^ {m} ] ^ {i - 1}, \tag {14} \\ s. t. \quad m \in \{v, r, a \}, \\ \end{array} +$$ + +where $[\mathbf{T}^m ]^i$ is the $m$ -th modality prototype calculated in the $i$ -th iteration; $\beta$ is the updating ratio, which gradually increases from $1e^{-8}$ to 1 with the training goes on. The temporal accumulation strategy ensures that the modality information in each iteration is considered, thereby synchronizing the cross-modality alignment during the training. + +Based on the modality prototypes, the modality alignment loss $(L_{ma})$ is designed as: + +$$ +L _ {m a} = \frac {1}{P} \sum_ {p = 1} ^ {P} \left[ m m d \left(\mathbf {T} _ {p} ^ {v}, \mathbf {T} _ {p} ^ {a}\right) + m m d \left(\mathbf {T} _ {p} ^ {a}, \mathbf {T} _ {p} ^ {r}\right) \right], \tag {15} +$$ + +where $\mathbf{T}_p^v$ , $\mathbf{T}_p^r$ and $\mathbf{T}_p^a$ denote visible, infrared, and auxiliary prototypes of the $p$ -th identity, respectively. $mmd(\cdot, \cdot)$ is the MMD loss [5] implemented the modality level alignment by constraining the distance of modality prototypes in each iteration. In Equation 15, the $mmd(\mathbf{T}_p^v, \mathbf{T}_p^a)$ is defined as: + +$$ +m m d \left(\mathbf {T} _ {p} ^ {v}, \mathbf {T} _ {p} ^ {a}\right) = | | \frac {1}{N} \sum_ {i = 1} ^ {N} \phi \left(\mathbf {T} _ {p, i} ^ {v}\right) - \frac {1}{M} \sum_ {j = 1} ^ {M} \phi \left(\mathbf {T} _ {p, j} ^ {a}\right) | | _ {H} ^ {2}, \tag {16} +$$ + +where $\mathbf{T}_{p,i}^{v}$ and $\mathbf{T}_{p,j}^{a}$ denote the $i$ -th visible prototype and the $j$ -th auxiliary prototype in the $p$ -th identity, respectively; $||\cdot||_{H}$ denotes the distribution measured by Gaussian kernel function $\phi(\cdot)$ which projects prototypes into the reproducing kernel Hilbert space. The $mmd(\mathbf{T}_p^a,\mathbf{T}_p^r)$ term can also be obtained in a similar way. + +The modality alignment loss is used to constrain the identity-guided distribution distances of visible, infrared, and auxiliary modalities through the prototypes. It can effectively reduce the modality discrepancy and relieve the inconsistency issue in learned feature relationships. Meanwhile, the auxiliary modality can act as a bridge to decrease the relative distance between visible and infrared modalities in the common feature space, thereby significantly reducing the optimization difficulty of cross-modality alignment. + +# 3.5. Overall Loss Function + +Following the previous works, we employ the identity loss $(L_{id} = L_{id}^{v} + L_{id}^{r})$ and hard-mining triplet loss $(L_{tri})$ [26,32] as our baseline loss functions. The overall loss function of the proposed MUN can be summarized as: + +$$ +L _ {t o t a l} = L _ {i d} + L _ {t r i} + \gamma * L _ {i d c} + \theta * L _ {i a} + \sigma * L _ {m a}, \tag {17} +$$ + +where $\gamma, \theta$ , and $\sigma$ are parameters to balance the contribution of each proposed loss term during the training. + +# 4. Experiments + +# 4.1. Datasets and Evaluation Settings + +SYSU-MM01 [28] is the largest dataset for VI-ReID, which comprises six cameras, including four visible and two infrared cameras. It encompasses a total of 491 individuals, with 287,628 visible images and 15,792 infrared images. The training set is composed of 395 individuals, with 22,258 visible images and 11,909 infrared images. The test set consists of 96 individuals, with 3,803 infrared images for queries and a gallery selected from 301 visible images. The dataset offers two testing settings: all-search mode and indoor-search mode. For both modes, we employ the hardest single-shot setting to perform the evaluation. + +RegDB [18] comprises 412 identities and a total of 8,240 images, with 206 identities allocated for training and another 206 identities for testing. Each identity is represented by 10 visible and 10 infrared images. The testing phase in RegDB involves two modes: Visible to Infrared, where visible images are searched using an infrared image, and Infrared to Visible, which entails the reverse scenario. For both modes, we repeat the testing process 10 times and average the results to report the mean values. + +Evaluation Settings. We utilize the standard cumulative matching characteristics (CMC) and mean average precision(mAP) as the evaluation metrics. + +# 4.2. Implementation Details + +We implement all the experiments on the PyTorch framework with an NVIDIA RTX-3090 GPU. To ensure repeatability and facilitate fair comparisons with existing methods, we adopt the pretrained ResNet-50 [4] as our backbone network, where the first stage is initialized twice as two modality-specific ResBlocks, and the rest stages are used as the modality-shared ResBlocks. + +At the training stage, all images are resized to $288 \times 144$ . Data augmentations, including random horizontal flipping, erasing, and channel augmentations [31], are utilized against overfitting. Our model is trained with the AdamW optimizer [13] for 90 epochs with a weight decay of 0.01. The learning rate is gradually increased from $10^{-8}$ to 0.002 in the first 15 epochs and then decays by 0.1 at the $30^{th}$ and $60^{th}$ epochs. We find the optimal settings of all the hyper-parameters by grid search and repeated ablation experiments. Specifically, the pooling ratios of the spatial pyramid pooling in CML are set to be $\{2, 4, 6, 12\}$ ; The margin parameter $\alpha$ is set to 0.55; the loss balance parameters $\gamma$ , $\theta$ , and $\sigma$ are set to 0.25, 0.5, and 0.008, respectively. + +# 4.3. Ablation Study + +We evaluate the effectiveness of each proposed component on SYSY-MM01 and RegDB datasets, as shown in Table 1. Compared with the baseline (B) which only learns + +from visible and infrared modalities, the leveraging of auxiliary modality (Aux.) can effectively relieve both cross-modality and intra-modality discrepancies, thus greatly improving all the metrics on two datasets. Further, when applying the identity consistency loss $(L_{idc})$ to refine the modality-shared discriminative patterns, the performance is further improved. Meanwhile, the proposed identity alignment loss $(L_{ia})$ or modality alignment loss $(L_{ma})$ can enhance the cross-modality matching accuracy by aligning the visible and infrared features at the identity level or distribution level. By combining them, we can regulate a more robust cross-modality feature relationship, achieving a rank-1 of $76.24\%$ and mAP of $73.81\%$ on the SYSU-MM01 dataset. The results demonstrate that all the proposed components contribute consistently to the accuracy gain. + +It is worth noting that when adding only the auxiliary modality to the baseline in Table 1, we employed a simple identity loss (like $L_{id}^{a}$ ) to supervise the auxiliary modality. This loss is deprecated when employing the proposed $L_{idc}$ to jointly supervise the three modalities. + +Table 1. Evaluation of different components of the proposed method on SYSU-MM01 and RegDB datasets. CMC (\%) at rank 1 and mAP (\%). The Red bold font and blue bold front denote the best and second best performances, respectively. + +
BAux.LidcLiaLmaSYSU-MM01RegDB
r=1mAPr=1mAP
✓57.4955.8375.4271.93
✓✓62.5558.4279.2673.81
✓✓✓66.5861.2983.5179.79
✓✓✓✓71.3565.5489.4284.66
✓✓✓✓69.7766.9689.9384.02
✓✓✓✓✓76.2473.8195.1987.15
+ +Table 2. Performance of using different intermediate modalities in our MUN on two datasets. CMC (%) at rank 1 and mAP (%) + +
Intermediate ModalitySYSU-MM01RegDB
r=1mAPr=1mAP
X-modality [9]66.1763.0679.9574.28
Mixed modality [7]66.4262.8579.4373.09
Syncretic modality [27]72.9568.7484.5979.11
Auxiliary modality (Ours)76.2473.8195.1987.15
+ +Effectiveness of auxiliary modality. We conduct the ablations in the MUN by replacing our auxiliary modality with intermediate modalities designed by previous works, namely X [9], mixed [7], and syncretic [27]. As shown in Table 2, the X-modality is generated from visible images only, ignoring the impact of infrared modality and achieving relatively low performances. Although syncretic and mixed modalities combine both visible and infrared patterns, they only utilize pixel-level information, lacking the ability to discover fine-grained and semantic patterns. + +When switching back to our auxiliary modality, we observed a significant improvement in performance with a boost of $3.29\% / 5.07\%$ in terms of rank-1/mAP on the SYSU-MM01 dataset. These results further prove that our auxiliary modality is superior to other intermediate modalities. In summary, our auxiliary modality can effectively integrate modality-related information from both visible and infrared images, while preserving strong discriminability. This promotes robust representation learning in VI-ReID. + +Effectiveness of loss design schemes. In the modality alignment loss $(L_{ia})$ , we design the modality prototype scheme to relieve the inconsistency issue and the auxiliary bridge scheme to reduce the optimization difficulty. To validate the effectiveness of these two schemes, we compare the performance of our method with or without using these two proposed schemes. As shown in Table 3. + +Table 3. Performance comparison of with or without using the modality prototype and auxiliary (Aux.) bridge schemes in the modality alignment loss. CMC (%) at rank 1 and mAP (\%). + +
Schemes in LmaSYSU-MM01RegDB
PrototypeAux. bridger=1mAPr=1mAP
69.0265.8380.0973.97
✓74.1572.1086.7377.24
✓71.6668.3583.9275.54
✓✓76.2473.8195.1987.15
+ +In Table 3, it is evident that both the modality prototype scheme and the auxiliary bridge scheme contribute to the VI-ReID accuracy gain. The modality prototype consistently captures global modality information, enhancing the robustness of learned modality relationships by synchronizing the alignment in each iteration; The auxiliary bridge scheme reduces the relative distance between visible and infrared features, effectively alleviating the difficulty of cross-modality distance optimization. + +# 4.4. Comparison with State-of-the-art Methods + +In this section, we compare our MUN with state-of-the-art works on two public datasets, as shown in Table 4. + +Comparison on SYSU-MM01 dataset. As illustrated in Table 4, the proposed MUN achieves impressive results with $76.24\%$ rank-1 and $73.81\%$ mAP on the all-search mode of the SYSU-MM01 dataset. Compared to traditional visible-infrared representation learning methods (AGW [33], DELN-ViT [38], SPOT [1], PMT [14], CMT [6], MPANet [29]), our MUN outperforms them by a margin of at least $4.36\%$ rank-1 and $5.24\%$ mAP on the all-search mode. The reason can be attributed that the proposed visible-auxiliary-infrared learning framework can capture more identity-related knowledge across modalities and regulate the discriminative feature relationships well. Additionally, the overall performance of our approach is also + +Table 4. Comparison with state-of-the-art methods on SYSU-MM01 and RegDB datasets. CMC (%) at rank r and mAP (%) + +
MethodsRef.SYSU-MM01RegDB
All-SearchIndoor-SearchVisible to InfraredInfrared to Visible
r=1r=10mAPr=1r=10mAPr=1r=10mAPr=1r=10mAP
Zero-padding [28]ICCV1714.8054.1215.9520.5868.3826.9217.7534.2118.9016.6334.6817.82
JSIA-ReID [25]AAAI2038.1080.7036.9043.8086.2052.9048.50-49.3048.10-48.90
AlignGAN [24]ICCV1942.4085.0040.7045.9087.6054.3057.90-53.6056.30-53.40
AGW [33]TPAMI2147.5084.3947.6554.1791.1462.9770.0586.2167.6470.4987.2165.90
X-Modality [9]AAAI2049.9289.7950.73---62.2183.1360.18---
DFLN-ViT [38]TMM2259.8492.4957.7062.1394.8369.0392.1097.9782.1191.2198.2081.62
SPOT [1]TIP2265.3492.7362.2569.4296.2274.6380.3593.4872.4679.3792.7972.26
FMCNet [36]CVPR2266.34-62.5168.15-63.8289.12-84.4388.23-83.86
SMCL [27]ICCV2167.3992.8761.7868.8496.5575.5683.93-79.8383.05-78.57
PMT [14]AAAI2367.5395.3664.9871.6696.7376.5284.83-76.5584.16-75.13
AGW+J [31]ICCV2169.8895.7166.8976.2697.8880.3785.0395.4979.1484.7595.3377.82
MPANet [29]CVPR2170.5896.1068.2476.7498.2180.9583.70-80.9082.80-80.70
CMT [6]ECCV2271.8896.4568.5776.9097.6879.9195.1798.8287.3091.9797.9284.46
MUN (Ours)ICCV2376.2497.8473.8179.4298.0982.0695.1998.9387.1591.8697.9985.01
+ +superior to GAN-based methods (JSIA-ReID [25], AlignGAN [24], FMCNet [36]) thanks to the powerful auxiliary modality which dynamically combines the information of visible and infrared images without introducing extra noise. + +Furthermore, the proposed method significantly outperforms existing modality-unifying methods (SMCL [27], X-Modality [9]) by at least $8.85\%$ on the rank-1 metric. This can be attributed to the fact that we not only mine the fine-grained semantic representations to generate the auxiliary modality but also decouple the extraction of specific and shared patterns in two modalities, which contribute to the dynamic generation of the auxiliary modality for relieving the changeable modality discrepancies during the training. + +Comparison on RegDB dataset. The results on RegDB are also listed in Table 4. In this dataset, image samples are spatially aligned and present less intra-class variations. Thus, the accuracy of all methods is higher than that on SYSU-MM01. The proposed MUN achieves Rank-1 of $95.19\%$ and mAP of $87.15\%$ in visible to infrared mode. Similar improvement can also be observed in the infrared to visible mode, which shows that our method obtains Rank-1 of $91.86\%$ and mAP of $85.01\%$ . This improvement can be attributed to the capacity of our method to generate a robust auxiliary modality, effectively mitigating both cross-modality and intra-modality discrepancies. + +# 4.5. Evaluation on Generalizability + +To verify the generalizability of MUN, we conduct experiments on two corrupted VI Re-ID datasets [2], namely SYSU-MM01-C and RegDB-C. We utilize the same corruption settings as [2], which only performs corruptions during the testing stage and randomly selects one corruption type (e.g., elastic, snow, frosted glass, etc.) and one severity level for each image in the visible gallery set. The results re + +Table 5. Evaluations on corrupted datasets. Each evaluation is performed 10 times to obtain the mean value. $L_{id}^{a}$ denotes an individual identity loss used to supervise the auxiliary modality. + +
IndexMethodSYSU-MM01-CRegDB-C
r=1mAPr=1mAP
1X-Modality [9]31.9826.2037.2635.97
2CIL [2]36.9535.9252.2549.76
3SMCL [27]37.0836.1251.9349.22
4AGW+J [31]40.0937.8651.5349.04
5B25.9223.1332.0529.64
6+Aux.+Lda30.8526.5436.4031.21
7+Aux.+Lidc31.1227.4438.1332.29
8+Aux.+Lidc+Lia36.7832.3245.4442.89
9+Aux.+Lidc+Lia+Lma41.1738.6352.6950.18
+ +ported for all the compared methods are obtained using the official best settings as provided in their respective papers. + +Table 5 shows that the performance of baseline (B) is relatively lower than that of existing SOTAs under data corruption scenarios. However, by introducing the auxiliary modality to bridge the gap between visible and infrared modalities (Index 6), the accuracy is significantly improved. Furthermore, by incorporating the proposed identity alignment loss $(L_{ia})$ and modality alignment loss $(L_{ma})$ to refine the learned cross-modality feature relationships, the rank-1 and mAP accuracies experience a substantial enhancement of $15.25\%$ and $15.5\%$ respectively on the SYSU-MM01-C dataset. This outperforms the current SOTAs by a remarkable margin. Specifically, our MUN method exceeds the highly robust AGW+J [31] by $1.08\%$ in rank-1 and $0.77\%$ in mAP. The experiments on two corrupted datasets verify the strong generalizability and robustness of the proposed MUN, which can consistently learn modality-shared patterns and regulate stable feature relationships under corrupted data scenarios. + +![](images/7a4ddfab3b384a2c8482dc1f7e49b6c319021159ad3e608ef7c8b516eb625002.jpg) + +![](images/a9140398046886bdefa01e26d26c20ef3f9e36add93fd5a06e9303eef5cf3fc0.jpg) + +![](images/c016fdcb3a2334a6b9069318db3ac225952b88cda89c17e9628ab017fafd288e.jpg) +Figure 4. Distributions of learned visible, infrared and auxiliary features during the training. All the samples are randomly selected in the SYSU-MM01 dataset. The 3D visualization is made by T-SNE [23]. Please view in colour and zoom in. + +![](images/4038246cdde7d41cece84cb88176cb49b6772da80699d004dbf0f8126ebc439c.jpg) + +# 4.6. Visualization + +Distribution Visualization. To visually demonstrate the effectiveness of MUN, we randomly select 10 identities from the SYSU-MM01 dataset and visualize their feature distributions during the training. The visualization results are presented in Figure 4. + +At the onset of training (epoch 0 in Figure 4 (a)), significant modality disparities arise between visible (depicted by blue dots) and infrared images (depicted by red dots), rendering cross-modality matching unfeasible. As the training progresses, the proposed auxiliary modality (depicted by green dots) serves as a bridge to connect the visible and infrared modalities in the common feature space. We can observe that the learned visible and infrared features show a convergence trend, and the modality discrepancies are gradually eliminated at epoch 5 in Figure 4 (b). Afterwards, the network learns identity-aware patterns by regulating smaller intra-class distances and larger inter-class distances at epoch 45. Finally, in Figure 4 (d), all the learned features are well grouped into their respective identity centers, demonstrating powerful discriminability under cross-modality scenes, which proves the effectiveness of MUN in learning robustness and identity-aware features. + +Pattern Visualization. In order to further illustrate the effectiveness of our auxiliary modality, we select one visible and one infrared image with the same identity in the SYSUMM01 dataset to visualize the corresponding learned feature maps and attention maps via Grad-CAM [22]. + +The visualization results are shown in Figure 5. It is clear that the visible $(\mathbf{F}^v)$ and infrared $(\mathbf{F}^r)$ feature maps extracted from the backbone have different patterns and struc + +![](images/f7931947a8fa9bbae67586007ecf957b98ad962bd75fecf2e715525adcdacf9f.jpg) +Figure 5. Visualization of learned feature maps and attention maps. Given the input visible image $\mathbf{I}^v$ and infrared image $\mathbf{I}^r$ , we visualize the corresponding learned visible feature $\mathbf{F}^v$ , infrared feature $\mathbf{F}^r$ , and the generated auxiliary feature $\mathbf{F}^a$ . It is obvious that the auxiliary feature $\mathbf{F}^a$ can preserve most of the modality-shared patterns, including body shape and structure. The attention visualizations on the input images are made by Grad-CAM [22]. Please view in colour and zoom in. + +tures, which makes it difficult to perform cross-modality matching. Notably, the proposed auxiliary generator can dynamically reconstruct and align the modality-shared spatial patterns using multiple transposed convolutions. This makes our auxiliary feature $(\mathbf{F}^a$ in Figure 5) preserves most of the shared patterns between $\mathbf{F}^v$ and $\mathbf{F}^r$ without corrupting the structure information of person bodies. In addition, the attention visualization in Figure 5 further indicates that the proposed auxiliary modality plays a critical role in helping the network learn modality-shared representations. + +# 5. Conclusion + +This paper proposes a novel Modality Unifying Network to jointly explore the robust auxiliary modality and generalize cross-modality feature relationships for VI-ReID. The auxiliary modality is generated by combining the cross-modality learner and the intra-modality learner, enabling the dynamic extraction of modality-specific patterns from multiple receptive fields and feature scales. This approach empowers our auxiliary modality to effectively alleviate both cross-modality and intra-modality discrepancies. Moreover, we propose identity alignment loss and modality alignment loss to regulate discriminative feature relationships in multi-modality tasks. Extensive experiments on public datasets demonstrate the effectiveness and generalizability of our MUN as well as each proposed component. + +Acknowledgements. This work is supported by the Academy of Finland for Academy Professor project EmotionAI (Grants No. 336116, 345122), the University of Oulu & The Academy of Finland Profi 7 (Grant No. 352788), and the National Natural Science Foundation of China (Grant No. 61802058, 61911530397). We appreciate the professional and cost-effective GPU computing service provided by www.AutoDL.com. + +# References + +[1] Cuiqun Chen, Mang Ye, Meibin Qi, Jingjing Wu, Jianguo Jiang, and Chia-Wen Lin. Structure-aware positional transformer for visible-infrared person re-identification. IEEE Transactions on Image Processing, 31:2352-2364, 2022. +[2] Minghui Chen, Zhiqiang Wang, and Feng Zheng. 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Existing methods mainly focus on learning modality-shared representations by embedding different modalities into the same feature space. As a result, the learned feature emphasizes the common patterns across modalities while suppressing modality-specific and identity-aware information that is valuable for Re-ID. To address these issues, we propose a novel Modality Unifying Network (MUN) to explore a robust auxiliary modality for VI-ReID. First, the auxiliary modality is generated by combining the proposed cross-modality learner and intra-modality learner, which can dynamically model the modality-specific and modality-shared representations to alleviate both cross-modality and intra-modality variations. Second, by aligning identity centres across the three modalities, an identity alignment loss function is proposed to discover the discriminative feature representations. Third, a modality alignment loss is introduced to consistently reduce the distribution distance of visible and infrared images by modality prototype modeling. Extensive experiments on multiple public datasets demonstrate that the proposed method surpasses the current state-of-the-art methods by a significant margin." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 590, + 128, + 602 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 590, + 128, + 602 + ], + "spans": [ + { + "bbox": [ + 47, + 590, + 128, + 602 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 611, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 611, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 611, + 287, + 696 + ], + "type": "text", + "content": "Person re-identification (Re-ID) [8,33] aims at matching pedestrian images captured from multiple non-overlapping cameras. Over the past few years, it has received increased attention due to its huge practical value in modern surveillance systems. Previous studies [10, 16, 19, 30, 40] mainly focus on matching pedestrian images captured from visible cameras and formulate the Re-ID task as a single-modality" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 256, + 547, + 375 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 256, + 547, + 375 + ], + "spans": [ + { + "bbox": [ + 306, + 256, + 547, + 375 + ], + "type": "text", + "content": "matching issue. Nevertheless, visible cameras may not provide accurate appearance information about persons in scenarios with poor illumination. To address this limitation, modern surveillance systems also employ infrared cameras, which can capture clear images in low-light conditions at night. As a result, visible-infrared person re-identification (VI-ReID) [1, 28, 29] has become a topic of growing interest in recent times, which seeks to match infrared images of the same identity when given a visible query across multiple camera views and vice versa." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 376, + 547, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 376, + 547, + 688 + ], + "spans": [ + { + "bbox": [ + 304, + 376, + 547, + 688 + ], + "type": "text", + "content": "VI-ReID is challenging due to the huge cross-modality discrepancy between visible and infrared images, as well as the intra-modality variation in person bodies such as pose variation and dress change. Existing methods [1, 20, 29, 31, 36, 37] primarily focus on relieving the cross-modality discrepancy by extracting modality-shared features to perform the feature-level alignment. Some studies [1, 20, 28, 31, 34] employ two-stream networks for cross-modality feature embedding, while others [3, 24, 25, 36] utilize Generative Adversarial Networks (GANs) to generate shared representations from visible and infrared images. However, these methods discard modality-specific features (such as colour and texture) that contain useful identity-aware patterns against intra-modality variations. Consequently, the learned features may not fully capture the variation of human bodies and thus lack discriminability. To address this limitation, the modality-unifying methods, e.g., X-modality [9], DFM [7], SMCL [27], have been proposed to acquire the auxiliary modality by fusing visible and infrared modalities, encoding both modality-specific and modality-shared patterns to jointly relieve cross- and intramodality discrepancies. In the SMCL [27], the authors proposed a syncretic modality generated by fusing visible and infrared pixels, which can bridge the gap between visible and infrared modalities while maintaining discriminability as the modality-specific information is preserved." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 689, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 547, + 714 + ], + "type": "text", + "content": "However, the existing modality-unifying works still have three weaknesses. (1) Pixel fusion. Previous works gener-" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 237, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 237, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 237, + 713 + ], + "type": "text", + "content": "*Corresponding Author (Email: xcheng@nuist.edu.cn)" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11185" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 70, + 282, + 204 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 282, + 204 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 282, + 204 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 282, + 204 + ], + "type": "image", + "image_path": "99eeae7753986a7c0b731b38bb3cce3f2652ebd86627c480950a271a0c41b221.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 206, + 287, + 240 + ], + "lines": [ + { + "bbox": [ + 46, + 206, + 287, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 206, + 287, + 240 + ], + "type": "text", + "content": "Figure 1. The main idea behind generating a strong auxiliary modality for the VI-ReID task. The IML and CML denote the intra-modality learner and cross-modality learner, respectively." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 257, + 286, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 257, + 286, + 484 + ], + "spans": [ + { + "bbox": [ + 46, + 257, + 286, + 484 + ], + "type": "text", + "content": "ate the auxiliary modality by fusing pixels of the raw visible and infrared images, which makes the richness of semantic patterns either equal to the original two modalities or lower in the case of pixel misalignment. In fact, the auxiliary modality is utilized to guide the learning of visible and infrared modalities, but the insufficient semantic patterns lead to a lack of identity-related information and severely limit the capacity to relieve intra-modality variations in VI-ReID. (2) Discrepancy bias. During the VI training, the relative distances between visible and infrared images are constantly changing, which causes a dynamic bias toward the balance of intra- and cross-modality discrepancies. Thus, an ideal auxiliary modality should be able to dynamically control the ratio of modality-specific and modality-shared patterns it contains to model the evolving modality discrepancies. However, the existing studies simply use the global information of visible and infrared images to obtain the auxiliary representations, which are inflexible in adjusting the patterns they describe, leading to low robustness." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 484, + 286, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 484, + 286, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 484, + 286, + 568 + ], + "type": "text", + "content": "(3) Inconsistency constraints. Existing studies usually utilize features in the current batch to represent the overall distribution for distance optimization. However, this strategy suffers from randomness, as the training samples are different in each batch, which may cause a certain inconsistency in the learned feature relationships in different training stages, thus damaging the generalizability." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 286, + 713 + ], + "type": "text", + "content": "Inspired by the above discussions, we propose a novel Modality Unifying Network (MUN) to explore an effective and robust auxiliary modality for VI-ReID. The main idea of our auxiliary modality is illustrated in Figure 1. Specifically, we introduce an auxiliary generator comprising two intra-modality learners (IML) and one cross-modality learner (CML) to distil the modality-related patterns from visible and infrared images. Two IMLs are presented to identify the modality-specific and identity-aware patterns from visible and infrared images, respectively. They exploit multiple depth-wise convolutions with various kernel sizes to capture fine-grained semantic patterns in the human" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 215 + ], + "type": "text", + "content": "body across multiple receptive fields. Based on the outputs of two IMLs, the CML leverages spatial pyramid pooling to extract multi-scale feature representations and then fuse the modality-shared patterns learned in each feature scale. By combining IML and CML, the proposed auxiliary generator can generate a powerful auxiliary modality that is rich in modality-shared and discriminative patterns to alleviate both cross-modality and intra-modality discrepancies. In addition, the layer scale scheme is used to control the ratio of patterns learned from IML and CML, which can dynamically adjust the modality-specific and modality-shared patterns in the generated auxiliary representation." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "text", + "content": "Furthermore, to reveal the identity-related patterns in each identity set, an effective identity alignment loss " + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "inline_equation", + "content": "(L_{ia})" + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "text", + "content": " is designed to optimize the distances of tri-modality identity centres. In addition, to regulate the distribution level feature relationships while relieving the inconsistency issue caused by sample variations, a novel modality alignment loss " + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "inline_equation", + "content": "(L_{ma})" + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "text", + "content": " is designed to minimize the distances of three modalities, which utilizes the modality prototype to represent the learned modality information in each iteration." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 323, + 545, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 323, + 545, + 346 + ], + "spans": [ + { + "bbox": [ + 306, + 323, + 545, + 346 + ], + "type": "text", + "content": "In general, the major contributions of this paper can be summarized as follows." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 351, + 545, + 572 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 317, + 351, + 545, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 351, + 545, + 411 + ], + "spans": [ + { + "bbox": [ + 317, + 351, + 545, + 411 + ], + "type": "text", + "content": "- We propose a novel modality unifying network for the VI-ReID task by constructing a robust auxiliary modality, which contains rich semantic information from visible and infrared images to address modality discrepancies and reveal discriminative knowledge." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 317, + 417, + 545, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 417, + 545, + 464 + ], + "spans": [ + { + "bbox": [ + 317, + 417, + 545, + 464 + ], + "type": "text", + "content": "- A novel auxiliary generator constructed by the intramodality and cross-modality learners is introduced to dynamically extract identity-aware and modality-shared patterns from heterogeneous images." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 471, + 545, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 471, + 545, + 518 + ], + "spans": [ + { + "bbox": [ + 317, + 471, + 545, + 518 + ], + "type": "text", + "content": "- The identity alignment loss and modality alignment loss are designed to jointly explore the generalized and discriminative feature relationships of the three modalities at both the identity and distribution levels." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 525, + 545, + 572 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 525, + 545, + 572 + ], + "spans": [ + { + "bbox": [ + 317, + 525, + 545, + 572 + ], + "type": "text", + "content": "- Extensive experiments on several public VI-ReID datasets verify the effectiveness of the proposed method and modality unifying scheme, which outperforms the current state of the arts by a large margin." + } + ] + } + ], + "index": 11 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 586, + 392, + 597 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 586, + 392, + 597 + ], + "spans": [ + { + "bbox": [ + 306, + 586, + 392, + 597 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Single-Modality Person Re-ID. Single-modality person re-identification [11, 17, 33] aims to match pedestrian images across different visible cameras. It presents challenges such as changes in viewpoint and human pose across camera views. Current approaches mainly focus on feature representation learning [15, 19, 39] and distance metric learning [10, 30, 35, 40]. Over the past few years, excellent performances have been achieved on several academic benchmarks. However, in practical scenarios, numerous crucial" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "11186" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 69, + 81, + 517, + 281 + ], + "blocks": [ + { + "bbox": [ + 69, + 81, + 517, + 281 + ], + "lines": [ + { + "bbox": [ + 69, + 81, + 517, + 281 + ], + "spans": [ + { + "bbox": [ + 69, + 81, + 517, + 281 + ], + "type": "image", + "image_path": "729e9611e84e0aa4722a76ed2bfc5b5169886ccd909bdf7b6fd258548c03a811.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 282, + 547, + 327 + ], + "lines": [ + { + "bbox": [ + 46, + 282, + 547, + 327 + ], + "spans": [ + { + "bbox": [ + 46, + 282, + 547, + 327 + ], + "type": "text", + "content": "Figure 2. The overall architecture of the proposed MUN for VI-ReID. GeMP denotes the Generalized Mean Pooling [21]. The pretrained ResNet-50 [4] is adopted as the baseline network. To meet the specific requirements of VI-ReID, we initialize the first stage of the ResNet-50 twice as two independent ResBlocks to extract the low-level visible and infrared features, respectively. The remaining stages are utilized as modality-shared ResBlocks. During the inference, only visible and infrared modalities are utilized to perform cross-modality retrieval." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 346, + 288, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 346, + 288, + 441 + ], + "spans": [ + { + "bbox": [ + 46, + 346, + 288, + 441 + ], + "type": "text", + "content": "surveillance photos and videos are captured at night using infrared cameras. When it comes to matching pedestrians across visible and infrared modalities, the capabilities of these single-modality methods are limited due to their inability to address the huge modality gap. In contrast, we present an effective modality unifying network to bridge the modality gap and achieve precise cross-modality pedestrian matching in 24-hour monitoring scenarios." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 450, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 450, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 288, + 715 + ], + "type": "text", + "content": "Visible-Infrared Person Re-ID. Visible-Infrared person Re-ID [28] is a challenging task due to the cross-modality discrepancies between visible and infrared images, as well as the intra-modality variations such as pose and dress changes. Existing studies [20, 29, 31, 32, 34] mainly focus on learning the modality-shared representations to align the visible and infrared modalities. Some generation-based methods [24-26,36] have been developed to achieve modality alignment or translation by using Generative Adversarial Network (GAN). For instance, Wang et al. [24] proposed a dual-alignment network that used GAN to jointly learn pixel and feature level alignment. The D2RL [26] is proposed to perform image-level modality translation by adversarial training that relieves the cross-modality discrepancy. Other works [1, 20, 29, 31, 34] attempt to learn modality-shared features by designing two-stream networks to perform cross-modality feature embedding. Ye et al. [34] proposed a dual-constrained top-ranking method with a weight-shared two-stream network. Wu et al. [29] designed a cross-modality attention scheme to help the two-stream backbone discover cross-modality nuances. However, these methods usually discard modality-specific representations" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 305, + 346, + 545, + 370 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 346, + 545, + 370 + ], + "spans": [ + { + "bbox": [ + 305, + 346, + 545, + 370 + ], + "type": "text", + "content": "that help to relieve intra-modality variations, leading to low robustness and discriminability in learned features." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 371, + 546, + 537 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 371, + 546, + 537 + ], + "spans": [ + { + "bbox": [ + 304, + 371, + 546, + 537 + ], + "type": "text", + "content": "In order to capture both the modality-shared and identity-aware patterns from heterogeneous images, modality-unifying methods have been developed. These methods aim to obtain the auxiliary modality by combining modality-specific and modality-shared representations from both visible and infrared images. The syncretic modality [27] is proposed to guide the generation of discriminative and modality-invariant representations. The DFM [7] acquires the mixed modality by integrating visible and infrared pixels. However, these methods generate the auxiliary modality by directly fusing the raw pixels of visible and infrared images, making their auxiliary modality lack high-level semantic patterns and inflexible to adjust its representations." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 538, + 545, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 538, + 545, + 624 + ], + "spans": [ + { + "bbox": [ + 304, + 538, + 545, + 624 + ], + "type": "text", + "content": "To tackle these challenges, this paper presents the intramodality learner and cross-modality learner to dynamically uncover substantial modality-shared and discriminative patterns from multiple receptive fields and feature scales. By integrating these learners, we introduce a powerful auxiliary modality that effectively bridges the modality discrepancy and enhances the discriminability of learned features." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 633, + 389, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 633, + 389, + 647 + ], + "spans": [ + { + "bbox": [ + 306, + 633, + 389, + 647 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 654, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 715 + ], + "type": "text", + "content": "As shown in Figure 2, we introduce the details of the Modality Unifying Network. We first utilize two independent ResBlocks to extract low-level features from visible and infrared images, respectively. Then, the auxiliary generator is designed to generate the auxiliary features by com" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11187" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": "bining intra-modality and cross-modality learners. Afterwards, the visible, infrared, and auxiliary features are fed into weight-shared ResBlocks to learn high-level patterns. The auxiliary features can serve as a bridge to relieve both intra- and cross-modality discrepancies during the training. Based on the visible, infrared, and auxiliary features learned by weight-shared ResBlocks, four loss functions are developed to effectively improve cross-modality matching accuracy, including identity loss " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "L_{id}" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": ", identity consistency loss " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "L_{idc}" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": ", identity alignment loss " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "L_{ia}" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": " and modality alignment loss " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "L_{ma}" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 210, + 166, + 222 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 210, + 166, + 222 + ], + "spans": [ + { + "bbox": [ + 47, + 210, + 166, + 222 + ], + "type": "text", + "content": "3.1. Auxiliary Generator" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 228, + 287, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 228, + 287, + 312 + ], + "spans": [ + { + "bbox": [ + 46, + 228, + 287, + 312 + ], + "type": "text", + "content": "The auxiliary generator contains two intra-modality learners (IML) and one cross-modality learner (CML). The two IMLs are designed to mine identity-related patterns from visible and infrared images, respectively. The CML is designed to learn modality-shared patterns based on the outcomes of two IMLs. The detailed architectures of IML and CML are shown in Figure 3." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "spans": [ + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "text", + "content": "Intra-Modality Learner. The intra-modality learner (IML) is designed to capture the discriminative and identity-aware patterns in human bodies. The visible or infrared low-level features " + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^m\\in \\mathbb{R}^{C\\times H\\times W}" + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "inline_equation", + "content": "m\\in \\{v,r\\}" + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "text", + "content": " extracted from two independent ResBlocks are regarded as the input of IML, where " + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 46, + 312, + 287, + 384 + ], + "type": "text", + "content": " denotes the visible or infrared modality." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 384, + 287, + 420 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 384, + 287, + 420 + ], + "spans": [ + { + "bbox": [ + 46, + 384, + 287, + 420 + ], + "type": "text", + "content": "To enrich the receptive field while keeping low computational complexity, we equally divide " + }, + { + "bbox": [ + 46, + 384, + 287, + 420 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^m" + }, + { + "bbox": [ + 46, + 384, + 287, + 420 + ], + "type": "text", + "content": " into two parts along the channel dimension by matrix slice operation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 70, + 425, + 287, + 439 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 70, + 425, + 287, + 439 + ], + "spans": [ + { + "bbox": [ + 70, + 425, + 287, + 439 + ], + "type": "interline_equation", + "content": "\\mathbf {F} _ {c _ {1}} ^ {m} = \\mathbf {F} ^ {m} [ 0: C / 2,: :, ] \\quad , \\quad \\mathbf {F} _ {c _ {2}} ^ {m} = \\mathbf {F} ^ {m} [ C / 2: C,:,: ]. \\tag {1}", + "image_path": "88e8fae9318a0701330e03bebe9e3caac8e47d5c5b4a321cf832d8bc7ea8e47b.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "text", + "content": "Then, we employ " + }, + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "inline_equation", + "content": "7 \\times 7" + }, + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "inline_equation", + "content": "5 \\times 5" + }, + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "text", + "content": " depth-wise convolutions " + }, + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "inline_equation", + "content": "(D)" + }, + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "text", + "content": " to operate on " + }, + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{c_1}^m" + }, + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{c_2}^m" + }, + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "text", + "content": ", respectively. This allows us to capture spatial patterns in different receptive fields." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 88, + 485, + 287, + 498 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 485, + 287, + 498 + ], + "spans": [ + { + "bbox": [ + 88, + 485, + 287, + 498 + ], + "type": "interline_equation", + "content": "\\mathbf {R} ^ {m} = \\operatorname {C o n c a t} \\left\\{D _ {5 \\times 5} \\left(\\mathbf {F} _ {c _ {1}} ^ {m}\\right), D _ {7 \\times 7} \\left(\\mathbf {F} _ {c _ {2}} ^ {m}\\right) \\right\\}, \\tag {2}", + "image_path": "dfd570cbe0f88c14b1725cda17a6e0cadfefd8e27fc378db48011713a7289e2f.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 504, + 287, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 504, + 287, + 563 + ], + "spans": [ + { + "bbox": [ + 46, + 504, + 287, + 563 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 504, + 287, + 563 + ], + "type": "inline_equation", + "content": "\\text{Concat}" + }, + { + "bbox": [ + 46, + 504, + 287, + 563 + ], + "type": "text", + "content": " denotes the concatenation on channel dimension; " + }, + { + "bbox": [ + 46, + 504, + 287, + 563 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^m" + }, + { + "bbox": [ + 46, + 504, + 287, + 563 + ], + "type": "text", + "content": " indicates the visible or infrared features captured from multiple receptive fields. Then, a point-wise convolution " + }, + { + "bbox": [ + 46, + 504, + 287, + 563 + ], + "type": "inline_equation", + "content": "(P)" + }, + { + "bbox": [ + 46, + 504, + 287, + 563 + ], + "type": "text", + "content": " is utilized to fuse patterns with diverse receptive fields by connecting pixels in each channel." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 102, + 569, + 287, + 582 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 569, + 287, + 582 + ], + "spans": [ + { + "bbox": [ + 102, + 569, + 287, + 582 + ], + "type": "interline_equation", + "content": "\\mathbf {R} _ {1} ^ {m} = P _ {1 \\times 1} (B a t c h N o r m (\\mathbf {R} ^ {m})). \\tag {3}", + "image_path": "4ea682282b761ac4c0d2553d9376136ca98f4ed384744196797621715876299c.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "spans": [ + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "type": "text", + "content": "To integrate and encode the structural information in human bodies, another depth-wise convolution with " + }, + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "type": "text", + "content": " kernel size is introduced to remodel the learned spatial map. This layer also utilizes a residual branch to retain information from the previous layer." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 101, + 653, + 287, + 666 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 101, + 653, + 287, + 666 + ], + "spans": [ + { + "bbox": [ + 101, + 653, + 287, + 666 + ], + "type": "interline_equation", + "content": "\\mathbf {R} _ {2} ^ {m} = D _ {3 \\times 3} \\left(R e L U \\left(\\mathbf {R} _ {1} ^ {m}\\right)\\right) + \\mathbf {R} _ {1} ^ {m}. \\tag {4}", + "image_path": "15cb3fb370132e225d24f6230dee941e587ce875d7a659f7ea318359504fc3ee.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 671, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 287, + 696 + ], + "type": "text", + "content": "In addition, another point-wise convolution is utilized to fuse patterns with diverse receptive fields in " + }, + { + "bbox": [ + 47, + 671, + 287, + 696 + ], + "type": "inline_equation", + "content": "\\mathbf{R}_2^m" + }, + { + "bbox": [ + 47, + 671, + 287, + 696 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 87, + 700, + 287, + 714 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 87, + 700, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 87, + 700, + 287, + 714 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {F}} ^ {m} = I _ {\\text {s c a l e}} * P _ {1 \\times 1} \\left(\\operatorname {B a t c h N r o m} \\left(\\mathbf {R} _ {2} ^ {m}\\right)\\right), \\tag {5}", + "image_path": "c312bf816c076126941cbf91acae47d650d59306a6687ca1bf1be6e319d37ab4.jpg" + } + ] + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 315, + 71, + 421, + 239 + ], + "blocks": [ + { + "bbox": [ + 315, + 71, + 421, + 239 + ], + "lines": [ + { + "bbox": [ + 315, + 71, + 421, + 239 + ], + "spans": [ + { + "bbox": [ + 315, + 71, + 421, + 239 + ], + "type": "image", + "image_path": "11e61430bce8992a46b6512243bb67e6ed134a2ba566f83bfca42d438b382215.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 245, + 545, + 278 + ], + "lines": [ + { + "bbox": [ + 305, + 245, + 545, + 278 + ], + "spans": [ + { + "bbox": [ + 305, + 245, + 545, + 278 + ], + "type": "text", + "content": "Figure 3. The detailed architecture of the proposed intra-modality learner (IML) and cross-modality learner (CML). They are designed to decouple the modeling of modality-related knowledge." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 430, + 71, + 539, + 239 + ], + "blocks": [ + { + "bbox": [ + 430, + 71, + 539, + 239 + ], + "lines": [ + { + "bbox": [ + 430, + 71, + 539, + 239 + ], + "spans": [ + { + "bbox": [ + 430, + 71, + 539, + 239 + ], + "type": "image", + "image_path": "a40481b955e23157285d07657fbce6c91c9830b3ec344e3a1d44649c7447657a.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 295, + 545, + 332 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 295, + 545, + 332 + ], + "spans": [ + { + "bbox": [ + 305, + 295, + 545, + 332 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 295, + 545, + 332 + ], + "type": "inline_equation", + "content": "I_{scale} \\in (0,1]" + }, + { + "bbox": [ + 305, + 295, + 545, + 332 + ], + "type": "text", + "content": " is the learnable layer scale factor used to control the ratio of intra-modality patterns learned by IML; " + }, + { + "bbox": [ + 305, + 295, + 545, + 332 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{F}}^m" + }, + { + "bbox": [ + 305, + 295, + 545, + 332 + ], + "type": "text", + "content": " denotes the outcomes of the two IMLs." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 332, + 546, + 439 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 332, + 546, + 439 + ], + "spans": [ + { + "bbox": [ + 304, + 332, + 546, + 439 + ], + "type": "text", + "content": "In the proposed intra-modality learner, three depth-wise convolutions with various kernel sizes are well combined to capture the identity-related patterns that existed in various receptive fields. Two point-wise convolutions are utilized for pattern integration and channel relation reasoning based on the inverted residual architecture [12]. The first point-wise convolution increases the channel dimension from " + }, + { + "bbox": [ + 304, + 332, + 546, + 439 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 332, + 546, + 439 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 332, + 546, + 439 + ], + "type": "inline_equation", + "content": "C * 4" + }, + { + "bbox": [ + 304, + 332, + 546, + 439 + ], + "type": "text", + "content": " and the last point-wise convolution reduces the channel dimension from " + }, + { + "bbox": [ + 304, + 332, + 546, + 439 + ], + "type": "inline_equation", + "content": "C * 4" + }, + { + "bbox": [ + 304, + 332, + 546, + 439 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 332, + 546, + 439 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 332, + 546, + 439 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 440, + 545, + 500 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 440, + 545, + 500 + ], + "spans": [ + { + "bbox": [ + 304, + 440, + 545, + 500 + ], + "type": "text", + "content": "Cross-Modality Learner. The cross-modality learner is designed to mine the modality-shared patterns from multiple feature scales based on the outcomes of two IMLs. Specifically, the spatial pyramid features are mined by applying " + }, + { + "bbox": [ + 304, + 440, + 545, + 500 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 440, + 545, + 500 + ], + "type": "text", + "content": " average pooling layers with various ratios." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 377, + 504, + 474, + 518 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 377, + 504, + 474, + 518 + ], + "spans": [ + { + "bbox": [ + 377, + 504, + 474, + 518 + ], + "type": "interline_equation", + "content": "\\mathbf {S} _ {1} ^ {m} = \\operatorname {A v g p o o l} _ {1} (\\hat {\\mathbf {F}} ^ {m}) ,", + "image_path": "7fc8af637df2a3668f6fbad69805d266254d9d00fe7165894314f1f84c50b38e.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 377, + 520, + 545, + 548 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 377, + 520, + 545, + 548 + ], + "spans": [ + { + "bbox": [ + 377, + 520, + 545, + 548 + ], + "type": "interline_equation", + "content": "\\begin{array}{c c} \\mathbf {S} _ {2} ^ {m} = A v g p o o l _ {2} (\\hat {\\mathbf {F}} ^ {m}) & , \\\\ \\dots & , \\end{array} \\tag {6}", + "image_path": "7bda35aac3685dcad7f9cf522934dd3ffdb5f749b147c086b377a64370c4128d.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 377, + 550, + 474, + 563 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 377, + 550, + 474, + 563 + ], + "spans": [ + { + "bbox": [ + 377, + 550, + 474, + 563 + ], + "type": "interline_equation", + "content": "\\mathbf {S} _ {n} ^ {m} = \\operatorname {A v g p o o l} _ {n} (\\hat {\\mathbf {F}} ^ {m}) ,", + "image_path": "1bffaab316ac6486b4de32b2c677e68a96b04e8c6477fe3ca1f5ee70ea99b771.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 568, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 568, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 568, + 545, + 641 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 568, + 545, + 641 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{S}_1^m,\\mathbf{S}_2^m,\\dots,\\mathbf{S}_n^m\\}, m\\in \\{v,r\\}" + }, + { + "bbox": [ + 304, + 568, + 545, + 641 + ], + "type": "text", + "content": " denote the spatial pyramid features with various feature scales. Afterwards, we obtain the modality-shared spatial patterns from each pair of cross-modality spatial pyramid features " + }, + { + "bbox": [ + 304, + 568, + 545, + 641 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{S}_i^v,\\mathbf{S}_i^r\\}_{i = 1}^n" + }, + { + "bbox": [ + 304, + 568, + 545, + 641 + ], + "type": "text", + "content": " with the same feature scale by using a group of learnable transposed convolutions " + }, + { + "bbox": [ + 304, + 568, + 545, + 641 + ], + "type": "inline_equation", + "content": "\\{TR_1,TR_2,\\dots,TR_n\\}" + }, + { + "bbox": [ + 304, + 568, + 545, + 641 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 318, + 645, + 545, + 661 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 645, + 545, + 661 + ], + "spans": [ + { + "bbox": [ + 318, + 645, + 545, + 661 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {S}} _ {i} ^ {v} = T R _ {i} \\left(\\mathbf {S} _ {i} ^ {v}\\right), \\quad \\hat {\\mathbf {S}} _ {i} ^ {r} = T R _ {i} \\left(\\mathbf {S} _ {i} ^ {r}\\right), \\quad i = 1, 2, \\dots , n. \\tag {7}", + "image_path": "121fa85f88bfbfa39a2b10171e2001ee0394622f23306c6768d8b4e83fa14272.jpg" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": "Here, the spatial dimensions of each cross-modality feature pair " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{S}}_i^v" + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{S}}_i^r" + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": " are rebuilt to " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "H\\times W" + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": " by the corresponding transposed convolution " + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "inline_equation", + "content": "TR_{i}" + }, + { + "bbox": [ + 304, + 666, + 545, + 713 + ], + "type": "text", + "content": ", respectively. In this manner, the significant patterns of visible and infrared features" + } + ] + } + ], + "index": 25 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11188" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "type": "text", + "content": "on each feature scale are embedded together, which helps to discover and amplify the abundant modality-shared information on multiple feature scales." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 108, + 287, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 108, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 47, + 108, + 287, + 133 + ], + "type": "text", + "content": "Further, all the embedded features are concatenated on the channel dimension via Eq.(8)." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 85, + 136, + 287, + 150 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 85, + 136, + 287, + 150 + ], + "spans": [ + { + "bbox": [ + 85, + 136, + 287, + 150 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {S}} = \\operatorname {C o n c a t} \\left\\{\\hat {\\mathbf {S}} _ {i} ^ {v}, \\hat {\\mathbf {S}} _ {2} ^ {v}, \\dots , \\hat {\\mathbf {S}} _ {n} ^ {v}, \\hat {\\mathbf {S}} _ {1} ^ {r}, \\hat {\\mathbf {S}} _ {2} ^ {r}, \\dots , \\hat {\\mathbf {S}} _ {n} ^ {r} \\right\\}. \\tag {8}", + "image_path": "b17f0362d90c2afe9a780213e6aecb6c9d2b34d274fc8ddb70ff7b5c47d88275.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 155, + 287, + 178 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 155, + 287, + 178 + ], + "spans": [ + { + "bbox": [ + 47, + 155, + 287, + 178 + ], + "type": "text", + "content": "Then, the auxiliary feature is obtained by fusing patterns captured from multiple feature scales." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 91, + 184, + 287, + 197 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 91, + 184, + 287, + 197 + ], + "spans": [ + { + "bbox": [ + 91, + 184, + 287, + 197 + ], + "type": "interline_equation", + "content": "\\mathbf {F} ^ {a} = C _ {\\text {s c a l e}} * P _ {1 \\times 1} (\\operatorname {B a t c h N o m r} (\\hat {\\mathbf {S}})), \\tag {9}", + "image_path": "4ce962846c9f99f480b5d581bf488e1c8b9db8f0108d6c3b296de8e49361c750.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 201, + 287, + 284 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 201, + 287, + 284 + ], + "spans": [ + { + "bbox": [ + 46, + 201, + 287, + 284 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 201, + 287, + 284 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^a" + }, + { + "bbox": [ + 46, + 201, + 287, + 284 + ], + "type": "text", + "content": " denotes the auxiliary feature generated by our method. It contains substantial modality-shared and identity-aware information captured by three learners; " + }, + { + "bbox": [ + 46, + 201, + 287, + 284 + ], + "type": "inline_equation", + "content": "C_{scale} \\in (0,1]" + }, + { + "bbox": [ + 46, + 201, + 287, + 284 + ], + "type": "text", + "content": " denotes the learnable layer scale factor used to control the ratio of modality-shared representations in the learned auxiliary feature " + }, + { + "bbox": [ + 46, + 201, + 287, + 284 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^a" + }, + { + "bbox": [ + 46, + 201, + 287, + 284 + ], + "type": "text", + "content": "; " + }, + { + "bbox": [ + 46, + 201, + 287, + 284 + ], + "type": "inline_equation", + "content": "P_{1 \\times 1}" + }, + { + "bbox": [ + 46, + 201, + 287, + 284 + ], + "type": "text", + "content": " is a point-wise convolution used to fuse patterns across different channels." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 285, + 287, + 333 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 285, + 287, + 333 + ], + "spans": [ + { + "bbox": [ + 46, + 285, + 287, + 333 + ], + "type": "text", + "content": "The CML mines significant patterns from multiple feature scales and amplifies the modality-shared parts from them using transposed convolutions. It makes our auxiliary feature a powerful tool to handle cross-modality variations." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 338, + 186, + 350 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 338, + 186, + 350 + ], + "spans": [ + { + "bbox": [ + 47, + 338, + 186, + 350 + ], + "type": "text", + "content": "3.2. Classification Constraint" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 357, + 287, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 357, + 287, + 392 + ], + "spans": [ + { + "bbox": [ + 46, + 357, + 287, + 392 + ], + "type": "text", + "content": "To ensure the learned visible and infrared features are identity-related, the identity loss " + }, + { + "bbox": [ + 46, + 357, + 287, + 392 + ], + "type": "inline_equation", + "content": "(L_{id})" + }, + { + "bbox": [ + 46, + 357, + 287, + 392 + ], + "type": "text", + "content": " implemented with the cross-entropy term is introduced as follows." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 56, + 397, + 287, + 435 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 397, + 287, + 435 + ], + "spans": [ + { + "bbox": [ + 56, + 397, + 287, + 435 + ], + "type": "interline_equation", + "content": "L _ {i d} ^ {m} = - \\frac {1}{k} \\sum_ {i = 1} ^ {k} \\log P \\left(y _ {i} \\mid C _ {m} \\left(\\mathbf {Z} _ {i} ^ {m}\\right)\\right), \\quad s. t. \\quad m \\in \\{v, r \\}, \\tag {10}", + "image_path": "c818aea33d7fab5e295b524ace6eba69226b93c1d1cacfa6622b25edb981fe88.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "spans": [ + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}_i^v" + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}_i^r" + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "text", + "content": " denote the generalized mean pooled visible and infrared features in the " + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "text", + "content": "-th identity, respectively. " + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "text", + "content": " is the number of visible or infrared images in each batch; " + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "inline_equation", + "content": "y_i" + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "text", + "content": "-th identity label; " + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "inline_equation", + "content": "C_v(\\cdot)" + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "inline_equation", + "content": "C_r(\\cdot)" + }, + { + "bbox": [ + 46, + 436, + 287, + 496 + ], + "type": "text", + "content": " are the predictions of visible and infrared classifiers, respectively." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 496, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 496, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 496, + 287, + 616 + ], + "type": "text", + "content": "The learned presentations are modality-shared if two classifiers can give consistent predictions for features from any modalities. However, if we directly apply features in one modality to the classifier in another modality (e.g., " + }, + { + "bbox": [ + 46, + 496, + 287, + 616 + ], + "type": "inline_equation", + "content": "C_r(\\mathbf{Z}^v)" + }, + { + "bbox": [ + 46, + 496, + 287, + 616 + ], + "type": "text", + "content": "), it may impose the classifier to learn modality-specific patterns rather than the modality-shared patterns, as the former is typically more discriminative. To solve this issue, we present an identity-consistency loss " + }, + { + "bbox": [ + 46, + 496, + 287, + 616 + ], + "type": "inline_equation", + "content": "L_{idc}" + }, + { + "bbox": [ + 46, + 496, + 287, + 616 + ], + "type": "text", + "content": " to update the parameters of both visible and infrared classifiers with the aid of auxiliary features. It can be defined as follows." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 53, + 620, + 287, + 650 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 620, + 287, + 650 + ], + "spans": [ + { + "bbox": [ + 53, + 620, + 287, + 650 + ], + "type": "interline_equation", + "content": "L _ {i d c} = - \\frac {1}{k} \\sum_ {i = 1} ^ {k} \\left[ \\log P \\left(y _ {i} \\mid C _ {v} \\left(\\mathbf {Z} _ {i} ^ {a}\\right)\\right) + \\log P \\left(y _ {i} \\mid C _ {r} \\left(\\mathbf {Z} _ {i} ^ {a}\\right)\\right) \\right], \\tag {11}", + "image_path": "e50d3ea50c9c58346605c8754b47a96162f8f7b1293399a1f9fc9d0e23360250.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 653, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 653, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}_i^a" + }, + { + "bbox": [ + 46, + 653, + 287, + 714 + ], + "type": "text", + "content": " denotes the pooled auxiliary feature in the " + }, + { + "bbox": [ + 46, + 653, + 287, + 714 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 653, + 287, + 714 + ], + "type": "text", + "content": "-th identity. The auxiliary features effectively integrate visible and infrared patterns, facilitating the transfer of identity-related knowledge between modalities without compromising the original intra-modality learning." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 72, + 441, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 441, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 441, + 84 + ], + "type": "text", + "content": "3.3. Identity Alignment Loss" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 91, + 545, + 139 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 91, + 545, + 139 + ], + "spans": [ + { + "bbox": [ + 305, + 91, + 545, + 139 + ], + "type": "text", + "content": "To relieve the class-level modality discrepancies and learn discriminative feature relationships, the identity alignment loss " + }, + { + "bbox": [ + 305, + 91, + 545, + 139 + ], + "type": "inline_equation", + "content": "L_{ia}" + }, + { + "bbox": [ + 305, + 91, + 545, + 139 + ], + "type": "text", + "content": " is designed to align the visible and infrared features of each identity with the aid of auxiliary features." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 345, + 148, + 545, + 205 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 345, + 148, + 545, + 205 + ], + "spans": [ + { + "bbox": [ + 345, + 148, + 545, + 205 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} L _ {i a} = \\sum_ {i = 1} ^ {P} \\left[ \\alpha + \\max _ {m _ {1} \\in \\{v, r \\}} \\left| \\left| \\mathbf {C} _ {i} ^ {a} - \\mathbf {C} _ {i} ^ {m _ {1}} \\right| \\right| _ {2} \\right. \\tag {12} \\\\ -\\min_{\\substack{m_{2}\\in \\{v,r\\} \\\\ q\\neq i}}||\\mathbf{C}_{i}^{a} - \\mathbf{C}_{q}^{m_{2}}||_{2}\\Bigg], \\\\ \\end{array}", + "image_path": "d6930c46620bc737ab19e25cc149c2ed11be7b57849926f37e13e014b31e2fe6.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "spans": [ + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": " is the margin parameter; " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": " denotes the number of person identities; " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": " is the number of images in the " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": "-th identity; " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "\\mathbf{C}_i^a = \\frac{1}{N}\\sum_{j=1}^{N}\\mathbf{Z}_{i,j}^a" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "\\mathbf{C}_i^v = \\frac{1}{N}\\sum_{j=1}^{N}\\mathbf{Z}_{i,j}^v" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "\\mathbf{C}_i^r = \\frac{1}{N}\\sum_{j=1}^{N}\\mathbf{Z}_{i,j}^r" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": " are the auxiliary, visible, and infrared centres in the " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": "-th identity, respectively; " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}_{i,j}^v" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}_{i,j}^r" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}_{i,j}^a" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": " denote the " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": "-th visible, infrared, and auxiliary features in the " + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 216, + 545, + 302 + ], + "type": "text", + "content": "-th identity set." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 304, + 545, + 375 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 304, + 545, + 375 + ], + "spans": [ + { + "bbox": [ + 304, + 304, + 545, + 375 + ], + "type": "text", + "content": "In this paper, identity alignment loss is proposed to optimize the hardest cross-modality positive and negative centre pairs in a triplet-metric manner. It regulates discriminative and robust feature relationships by forcing all identities to form a tight intra-class space and pushing centres of different identities away across the three modalities." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 384, + 447, + 396 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 384, + 447, + 396 + ], + "spans": [ + { + "bbox": [ + 306, + 384, + 447, + 396 + ], + "type": "text", + "content": "3.4. Modality Alignment Loss" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 403, + 545, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 545, + 498 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 545, + 498 + ], + "type": "text", + "content": "Previous works [7, 20, 29] typically align the two modalities by constraining visible and infrared features in each iteration. This scheme suffers from inconsistencies in the learned cross-modality feature relationships because the training samples are different in each iteration. To overcome this issue, we propose a modality alignment strategy that consistently aligns visible and infrared modalities by modeling the prototypes from features in each iteration." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "spans": [ + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "text", + "content": "Specifically, we first introduce three modality prototypes to represent the global information of visible, infrared, and auxiliary modalities, respectively. They can be denoted as " + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\mathbf{T}^v = \\{\\mathbf{t}_1^v,\\mathbf{t}_2^v,\\dots,\\mathbf{t}_B^v\\}" + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\mathbf{T}^r = \\{\\mathbf{t}_1^r,\\mathbf{t}_2^r,\\dots,\\mathbf{t}_B^r\\}" + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\mathbf{T}^a = \\{\\mathbf{t}_1^a,\\mathbf{t}_2^a,\\dots,\\mathbf{t}_B^a\\} \\in \\mathbb{R}^{B\\times C}" + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\mathbf{t}_i^v,\\mathbf{t}_i^r" + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\mathbf{t}_i^a" + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "text", + "content": " are the modality prototypes for the " + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "text", + "content": "-th visible, infrared, and auxiliary features in each training batch " + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "inline_equation", + "content": "(B)" + }, + { + "bbox": [ + 304, + 499, + 545, + 582 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 583, + 545, + 619 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 583, + 545, + 619 + ], + "spans": [ + { + "bbox": [ + 306, + 583, + 545, + 619 + ], + "type": "text", + "content": "The initial prototypes of the three modalities are obtained based on the pooled features " + }, + { + "bbox": [ + 306, + 583, + 545, + 619 + ], + "type": "inline_equation", + "content": "[\\mathbf{Z}^v ]^0" + }, + { + "bbox": [ + 306, + 583, + 545, + 619 + ], + "type": "inline_equation", + "content": "[\\mathbf{Z}^r ]^0" + }, + { + "bbox": [ + 306, + 583, + 545, + 619 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 583, + 545, + 619 + ], + "type": "inline_equation", + "content": "[\\mathbf{Z}^a ]^0\\in" + }, + { + "bbox": [ + 306, + 583, + 545, + 619 + ], + "type": "inline_equation", + "content": "R^{B\\times C}" + }, + { + "bbox": [ + 306, + 583, + 545, + 619 + ], + "type": "text", + "content": " in the 0-th iteration." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 343, + 629, + 545, + 643 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 629, + 545, + 643 + ], + "spans": [ + { + "bbox": [ + 343, + 629, + 545, + 643 + ], + "type": "interline_equation", + "content": "[ \\mathbf {T} ^ {m} ] ^ {0} = \\mathbf {W} _ {p} ^ {m} [ \\mathbf {Z} ^ {m} ] ^ {0}, \\quad s. t. \\quad m \\in \\{v, r, a \\}, \\tag {13}", + "image_path": "9d095daffaedb2be3e11d523ca26414a972079763b37be53fdb81e2c780bdc49.jpg" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 653, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 545, + 689 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 653, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_p^m" + }, + { + "bbox": [ + 304, + 653, + 545, + 689 + ], + "type": "text", + "content": " are learnable matrices to distil modality-related patterns from the " + }, + { + "bbox": [ + 304, + 653, + 545, + 689 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 653, + 545, + 689 + ], + "type": "text", + "content": "-th modality. " + }, + { + "bbox": [ + 304, + 653, + 545, + 689 + ], + "type": "inline_equation", + "content": "[\\mathbf{T}^m]^{0}" + }, + { + "bbox": [ + 304, + 653, + 545, + 689 + ], + "type": "text", + "content": " denotes the prototype of the " + }, + { + "bbox": [ + 304, + 653, + 545, + 689 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 653, + 545, + 689 + ], + "type": "text", + "content": "-th modality calculated in the 0-th iteration." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "Further, to dynamically model the modality information during the training, we develop a temporal accumulation" + } + ] + } + ], + "index": 25 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11189" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 95 + ], + "type": "text", + "content": "strategy to update the modality prototype by the learned features in each iteration, which can be defined as follows." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 64, + 105, + 286, + 132 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 64, + 105, + 286, + 132 + ], + "spans": [ + { + "bbox": [ + 64, + 105, + 286, + 132 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} [ \\mathbf {T} ^ {m} ] ^ {i} = [ \\beta ] ^ {i} * \\mathbf {W} _ {p} ^ {m} [ \\mathbf {Z} ^ {m} ] ^ {i} + (1 - [ \\beta ] ^ {i}) * [ \\mathbf {T} ^ {m} ] ^ {i - 1}, \\tag {14} \\\\ s. t. \\quad m \\in \\{v, r, a \\}, \\\\ \\end{array}", + "image_path": "e11b54c81ecb4400ddb92fcee1c4bf6672fa63abb29391b1c8e9761fc6238db0.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "spans": [ + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "type": "inline_equation", + "content": "[\\mathbf{T}^m ]^i" + }, + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "type": "text", + "content": "-th modality prototype calculated in the " + }, + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "type": "text", + "content": "-th iteration; " + }, + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "type": "text", + "content": " is the updating ratio, which gradually increases from " + }, + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "type": "inline_equation", + "content": "1e^{-8}" + }, + { + "bbox": [ + 47, + 142, + 286, + 215 + ], + "type": "text", + "content": " to 1 with the training goes on. The temporal accumulation strategy ensures that the modality information in each iteration is considered, thereby synchronizing the cross-modality alignment during the training." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 216, + 286, + 239 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 216, + 286, + 239 + ], + "spans": [ + { + "bbox": [ + 47, + 216, + 286, + 239 + ], + "type": "text", + "content": "Based on the modality prototypes, the modality alignment loss " + }, + { + "bbox": [ + 47, + 216, + 286, + 239 + ], + "type": "inline_equation", + "content": "(L_{ma})" + }, + { + "bbox": [ + 47, + 216, + 286, + 239 + ], + "type": "text", + "content": " is designed as:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 67, + 249, + 287, + 279 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 249, + 287, + 279 + ], + "spans": [ + { + "bbox": [ + 67, + 249, + 287, + 279 + ], + "type": "interline_equation", + "content": "L _ {m a} = \\frac {1}{P} \\sum_ {p = 1} ^ {P} \\left[ m m d \\left(\\mathbf {T} _ {p} ^ {v}, \\mathbf {T} _ {p} ^ {a}\\right) + m m d \\left(\\mathbf {T} _ {p} ^ {a}, \\mathbf {T} _ {p} ^ {r}\\right) \\right], \\tag {15}", + "image_path": "33a9b210310501c6136f5c08e0fe16bd3c8a9e5fa22123db2dffc1c4ca173b68.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "spans": [ + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_p^v" + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_p^r" + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_p^a" + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "text", + "content": " denote visible, infrared, and auxiliary prototypes of the " + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "text", + "content": "-th identity, respectively. " + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "inline_equation", + "content": "mmd(\\cdot, \\cdot)" + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "text", + "content": " is the MMD loss [5] implemented the modality level alignment by constraining the distance of modality prototypes in each iteration. In Equation 15, the " + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "inline_equation", + "content": "mmd(\\mathbf{T}_p^v, \\mathbf{T}_p^a)" + }, + { + "bbox": [ + 47, + 289, + 287, + 351 + ], + "type": "text", + "content": " is defined as:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 52, + 360, + 287, + 390 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 360, + 287, + 390 + ], + "spans": [ + { + "bbox": [ + 52, + 360, + 287, + 390 + ], + "type": "interline_equation", + "content": "m m d \\left(\\mathbf {T} _ {p} ^ {v}, \\mathbf {T} _ {p} ^ {a}\\right) = | | \\frac {1}{N} \\sum_ {i = 1} ^ {N} \\phi \\left(\\mathbf {T} _ {p, i} ^ {v}\\right) - \\frac {1}{M} \\sum_ {j = 1} ^ {M} \\phi \\left(\\mathbf {T} _ {p, j} ^ {a}\\right) | | _ {H} ^ {2}, \\tag {16}", + "image_path": "db40d2d14a97f33a7bd1571ee8e95b44b811067611f4324001cfde74233e9578.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "spans": [ + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_{p,i}^{v}" + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "inline_equation", + "content": "\\mathbf{T}_{p,j}^{a}" + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "text", + "content": " denote the " + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "text", + "content": "-th visible prototype and the " + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "text", + "content": "-th auxiliary prototype in the " + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "text", + "content": "-th identity, respectively; " + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "inline_equation", + "content": "||\\cdot||_{H}" + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "text", + "content": " denotes the distribution measured by Gaussian kernel function " + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "inline_equation", + "content": "\\phi(\\cdot)" + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "text", + "content": " which projects prototypes into the reproducing kernel Hilbert space. The " + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "inline_equation", + "content": "mmd(\\mathbf{T}_p^a,\\mathbf{T}_p^r)" + }, + { + "bbox": [ + 47, + 400, + 287, + 472 + ], + "type": "text", + "content": " term can also be obtained in a similar way." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 472, + 287, + 580 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 287, + 580 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 287, + 580 + ], + "type": "text", + "content": "The modality alignment loss is used to constrain the identity-guided distribution distances of visible, infrared, and auxiliary modalities through the prototypes. It can effectively reduce the modality discrepancy and relieve the inconsistency issue in learned feature relationships. Meanwhile, the auxiliary modality can act as a bridge to decrease the relative distance between visible and infrared modalities in the common feature space, thereby significantly reducing the optimization difficulty of cross-modality alignment." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 589, + 174, + 600 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 589, + 174, + 600 + ], + "spans": [ + { + "bbox": [ + 47, + 589, + 174, + 600 + ], + "type": "text", + "content": "3.5. Overall Loss Function" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 608, + 287, + 655 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 608, + 287, + 655 + ], + "spans": [ + { + "bbox": [ + 47, + 608, + 287, + 655 + ], + "type": "text", + "content": "Following the previous works, we employ the identity loss " + }, + { + "bbox": [ + 47, + 608, + 287, + 655 + ], + "type": "inline_equation", + "content": "(L_{id} = L_{id}^{v} + L_{id}^{r})" + }, + { + "bbox": [ + 47, + 608, + 287, + 655 + ], + "type": "text", + "content": " and hard-mining triplet loss " + }, + { + "bbox": [ + 47, + 608, + 287, + 655 + ], + "type": "inline_equation", + "content": "(L_{tri})" + }, + { + "bbox": [ + 47, + 608, + 287, + 655 + ], + "type": "text", + "content": " [26,32] as our baseline loss functions. The overall loss function of the proposed MUN can be summarized as:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 56, + 666, + 287, + 678 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 666, + 287, + 678 + ], + "spans": [ + { + "bbox": [ + 56, + 666, + 287, + 678 + ], + "type": "interline_equation", + "content": "L _ {t o t a l} = L _ {i d} + L _ {t r i} + \\gamma * L _ {i d c} + \\theta * L _ {i a} + \\sigma * L _ {m a}, \\tag {17}", + "image_path": "89fbc08f3b9dea5e5529c623776354409f27e1fa2b196396314df75595345fe3.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\gamma, \\theta" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " are parameters to balance the contribution of each proposed loss term during the training." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 72, + 388, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 388, + 85 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 388, + 85 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 91, + 482, + 104 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 91, + 482, + 104 + ], + "spans": [ + { + "bbox": [ + 306, + 91, + 482, + 104 + ], + "type": "text", + "content": "4.1. Datasets and Evaluation Settings" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "spans": [ + { + "bbox": [ + 304, + 109, + 545, + 240 + ], + "type": "text", + "content": "SYSU-MM01 [28] is the largest dataset for VI-ReID, which comprises six cameras, including four visible and two infrared cameras. It encompasses a total of 491 individuals, with 287,628 visible images and 15,792 infrared images. The training set is composed of 395 individuals, with 22,258 visible images and 11,909 infrared images. The test set consists of 96 individuals, with 3,803 infrared images for queries and a gallery selected from 301 visible images. The dataset offers two testing settings: all-search mode and indoor-search mode. For both modes, we employ the hardest single-shot setting to perform the evaluation." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 241, + 545, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 241, + 545, + 348 + ], + "spans": [ + { + "bbox": [ + 304, + 241, + 545, + 348 + ], + "type": "text", + "content": "RegDB [18] comprises 412 identities and a total of 8,240 images, with 206 identities allocated for training and another 206 identities for testing. Each identity is represented by 10 visible and 10 infrared images. The testing phase in RegDB involves two modes: Visible to Infrared, where visible images are searched using an infrared image, and Infrared to Visible, which entails the reverse scenario. For both modes, we repeat the testing process 10 times and average the results to report the mean values." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 349, + 545, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 349, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 304, + 349, + 545, + 384 + ], + "type": "text", + "content": "Evaluation Settings. We utilize the standard cumulative matching characteristics (CMC) and mean average precision(mAP) as the evaluation metrics." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 393, + 438, + 405 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 393, + 438, + 405 + ], + "spans": [ + { + "bbox": [ + 306, + 393, + 438, + 405 + ], + "type": "text", + "content": "4.2. Implementation Details" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 411, + 545, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 411, + 545, + 495 + ], + "spans": [ + { + "bbox": [ + 304, + 411, + 545, + 495 + ], + "type": "text", + "content": "We implement all the experiments on the PyTorch framework with an NVIDIA RTX-3090 GPU. To ensure repeatability and facilitate fair comparisons with existing methods, we adopt the pretrained ResNet-50 [4] as our backbone network, where the first stage is initialized twice as two modality-specific ResBlocks, and the rest stages are used as the modality-shared ResBlocks." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "text", + "content": "At the training stage, all images are resized to " + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "inline_equation", + "content": "288 \\times 144" + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "text", + "content": ". Data augmentations, including random horizontal flipping, erasing, and channel augmentations [31], are utilized against overfitting. Our model is trained with the AdamW optimizer [13] for 90 epochs with a weight decay of 0.01. The learning rate is gradually increased from " + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "inline_equation", + "content": "10^{-8}" + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "text", + "content": " to 0.002 in the first 15 epochs and then decays by 0.1 at the " + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "inline_equation", + "content": "30^{th}" + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "inline_equation", + "content": "60^{th}" + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "text", + "content": " epochs. We find the optimal settings of all the hyper-parameters by grid search and repeated ablation experiments. Specifically, the pooling ratios of the spatial pyramid pooling in CML are set to be " + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "inline_equation", + "content": "\\{2, 4, 6, 12\\}" + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "text", + "content": "; The margin parameter " + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "text", + "content": " is set to 0.55; the loss balance parameters " + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 495, + 545, + 651 + ], + "type": "text", + "content": " are set to 0.25, 0.5, and 0.008, respectively." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 658, + 400, + 671 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 658, + 400, + 671 + ], + "spans": [ + { + "bbox": [ + 306, + 658, + 400, + 671 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "We evaluate the effectiveness of each proposed component on SYSY-MM01 and RegDB datasets, as shown in Table 1. Compared with the baseline (B) which only learns" + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11190" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": "from visible and infrared modalities, the leveraging of auxiliary modality (Aux.) can effectively relieve both cross-modality and intra-modality discrepancies, thus greatly improving all the metrics on two datasets. Further, when applying the identity consistency loss " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "(L_{idc})" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " to refine the modality-shared discriminative patterns, the performance is further improved. Meanwhile, the proposed identity alignment loss " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "(L_{ia})" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " or modality alignment loss " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "(L_{ma})" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " can enhance the cross-modality matching accuracy by aligning the visible and infrared features at the identity level or distribution level. By combining them, we can regulate a more robust cross-modality feature relationship, achieving a rank-1 of " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "76.24\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " and mAP of " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "73.81\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " on the SYSU-MM01 dataset. The results demonstrate that all the proposed components contribute consistently to the accuracy gain." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 251, + 288, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 251, + 288, + 312 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 288, + 312 + ], + "type": "text", + "content": "It is worth noting that when adding only the auxiliary modality to the baseline in Table 1, we employed a simple identity loss (like " + }, + { + "bbox": [ + 46, + 251, + 288, + 312 + ], + "type": "inline_equation", + "content": "L_{id}^{a}" + }, + { + "bbox": [ + 46, + 251, + 288, + 312 + ], + "type": "text", + "content": ") to supervise the auxiliary modality. This loss is deprecated when employing the proposed " + }, + { + "bbox": [ + 46, + 251, + 288, + 312 + ], + "type": "inline_equation", + "content": "L_{idc}" + }, + { + "bbox": [ + 46, + 251, + 288, + 312 + ], + "type": "text", + "content": " to jointly supervise the three modalities." + } + ] + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 49, + 365, + 287, + 457 + ], + "blocks": [ + { + "bbox": [ + 47, + 321, + 288, + 365 + ], + "lines": [ + { + "bbox": [ + 47, + 321, + 288, + 365 + ], + "spans": [ + { + "bbox": [ + 47, + 321, + 288, + 365 + ], + "type": "text", + "content": "Table 1. Evaluation of different components of the proposed method on SYSU-MM01 and RegDB datasets. CMC (\\%) at rank 1 and mAP (\\%). The Red bold font and blue bold front denote the best and second best performances, respectively." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 365, + 287, + 457 + ], + "lines": [ + { + "bbox": [ + 49, + 365, + 287, + 457 + ], + "spans": [ + { + "bbox": [ + 49, + 365, + 287, + 457 + ], + "type": "table", + "html": "
BAux.LidcLiaLmaSYSU-MM01RegDB
r=1mAPr=1mAP
✓57.4955.8375.4271.93
✓✓62.5558.4279.2673.81
✓✓✓66.5861.2983.5179.79
✓✓✓✓71.3565.5489.4284.66
✓✓✓✓69.7766.9689.9384.02
✓✓✓✓✓76.2473.8195.1987.15
", + "image_path": "ef88ecbb4f6f183e794bb1aacd9685ec935f37adfd79defffe545004f99525f6.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 50, + 501, + 287, + 581 + ], + "blocks": [ + { + "bbox": [ + 47, + 479, + 287, + 501 + ], + "lines": [ + { + "bbox": [ + 47, + 479, + 287, + 501 + ], + "spans": [ + { + "bbox": [ + 47, + 479, + 287, + 501 + ], + "type": "text", + "content": "Table 2. Performance of using different intermediate modalities in our MUN on two datasets. CMC (%) at rank 1 and mAP (%)" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 501, + 287, + 581 + ], + "lines": [ + { + "bbox": [ + 50, + 501, + 287, + 581 + ], + "spans": [ + { + "bbox": [ + 50, + 501, + 287, + 581 + ], + "type": "table", + "html": "
Intermediate ModalitySYSU-MM01RegDB
r=1mAPr=1mAP
X-modality [9]66.1763.0679.9574.28
Mixed modality [7]66.4262.8579.4373.09
Syncretic modality [27]72.9568.7484.5979.11
Auxiliary modality (Ours)76.2473.8195.1987.15
", + "image_path": "6f48439e235d87f034ace8d2d67fdd84174d9096d25b6d651c2724ac304ed31c.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "Effectiveness of auxiliary modality. We conduct the ablations in the MUN by replacing our auxiliary modality with intermediate modalities designed by previous works, namely X [9], mixed [7], and syncretic [27]. As shown in Table 2, the X-modality is generated from visible images only, ignoring the impact of infrared modality and achieving relatively low performances. Although syncretic and mixed modalities combine both visible and infrared patterns, they only utilize pixel-level information, lacking the ability to discover fine-grained and semantic patterns." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 179 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 179 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 179 + ], + "type": "text", + "content": "When switching back to our auxiliary modality, we observed a significant improvement in performance with a boost of " + }, + { + "bbox": [ + 304, + 72, + 545, + 179 + ], + "type": "inline_equation", + "content": "3.29\\% / 5.07\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 179 + ], + "type": "text", + "content": " in terms of rank-1/mAP on the SYSU-MM01 dataset. These results further prove that our auxiliary modality is superior to other intermediate modalities. In summary, our auxiliary modality can effectively integrate modality-related information from both visible and infrared images, while preserving strong discriminability. This promotes robust representation learning in VI-ReID." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 180, + 545, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 180, + 545, + 264 + ], + "spans": [ + { + "bbox": [ + 304, + 180, + 545, + 264 + ], + "type": "text", + "content": "Effectiveness of loss design schemes. In the modality alignment loss " + }, + { + "bbox": [ + 304, + 180, + 545, + 264 + ], + "type": "inline_equation", + "content": "(L_{ia})" + }, + { + "bbox": [ + 304, + 180, + 545, + 264 + ], + "type": "text", + "content": ", we design the modality prototype scheme to relieve the inconsistency issue and the auxiliary bridge scheme to reduce the optimization difficulty. To validate the effectiveness of these two schemes, we compare the performance of our method with or without using these two proposed schemes. As shown in Table 3." + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 309, + 308, + 543, + 384 + ], + "blocks": [ + { + "bbox": [ + 304, + 274, + 545, + 307 + ], + "lines": [ + { + "bbox": [ + 304, + 274, + 545, + 307 + ], + "spans": [ + { + "bbox": [ + 304, + 274, + 545, + 307 + ], + "type": "text", + "content": "Table 3. Performance comparison of with or without using the modality prototype and auxiliary (Aux.) bridge schemes in the modality alignment loss. CMC (%) at rank 1 and mAP (\\%)." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 308, + 543, + 384 + ], + "lines": [ + { + "bbox": [ + 309, + 308, + 543, + 384 + ], + "spans": [ + { + "bbox": [ + 309, + 308, + 543, + 384 + ], + "type": "table", + "html": "
Schemes in LmaSYSU-MM01RegDB
PrototypeAux. bridger=1mAPr=1mAP
69.0265.8380.0973.97
✓74.1572.1086.7377.24
✓71.6668.3583.9275.54
✓✓76.2473.8195.1987.15
", + "image_path": "7e45598e3a5a5145cf0a64ef5545c268e08748c526ee703525a26467ad895b6b.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 397, + 545, + 505 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 397, + 545, + 505 + ], + "spans": [ + { + "bbox": [ + 304, + 397, + 545, + 505 + ], + "type": "text", + "content": "In Table 3, it is evident that both the modality prototype scheme and the auxiliary bridge scheme contribute to the VI-ReID accuracy gain. The modality prototype consistently captures global modality information, enhancing the robustness of learned modality relationships by synchronizing the alignment in each iteration; The auxiliary bridge scheme reduces the relative distance between visible and infrared features, effectively alleviating the difficulty of cross-modality distance optimization." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 514, + 529, + 528 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 514, + 529, + 528 + ], + "spans": [ + { + "bbox": [ + 305, + 514, + 529, + 528 + ], + "type": "text", + "content": "4.4. Comparison with State-of-the-art Methods" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 533, + 545, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 533, + 545, + 556 + ], + "spans": [ + { + "bbox": [ + 304, + 533, + 545, + 556 + ], + "type": "text", + "content": "In this section, we compare our MUN with state-of-the-art works on two public datasets, as shown in Table 4." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "text", + "content": "Comparison on SYSU-MM01 dataset. As illustrated in Table 4, the proposed MUN achieves impressive results with " + }, + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "inline_equation", + "content": "76.24\\%" + }, + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "text", + "content": " rank-1 and " + }, + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "inline_equation", + "content": "73.81\\%" + }, + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "text", + "content": " mAP on the all-search mode of the SYSU-MM01 dataset. Compared to traditional visible-infrared representation learning methods (AGW [33], DELN-ViT [38], SPOT [1], PMT [14], CMT [6], MPANet [29]), our MUN outperforms them by a margin of at least " + }, + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "inline_equation", + "content": "4.36\\%" + }, + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "text", + "content": " rank-1 and " + }, + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "inline_equation", + "content": "5.24\\%" + }, + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "text", + "content": " mAP on the all-search mode. The reason can be attributed that the proposed visible-auxiliary-infrared learning framework can capture more identity-related knowledge across modalities and regulate the discriminative feature relationships well. Additionally, the overall performance of our approach is also" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "11191" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 80, + 547, + 278 + ], + "blocks": [ + { + "bbox": [ + 70, + 69, + 520, + 79 + ], + "lines": [ + { + "bbox": [ + 70, + 69, + 520, + 79 + ], + "spans": [ + { + "bbox": [ + 70, + 69, + 520, + 79 + ], + "type": "text", + "content": "Table 4. Comparison with state-of-the-art methods on SYSU-MM01 and RegDB datasets. CMC (%) at rank r and mAP (%)" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 80, + 547, + 278 + ], + "lines": [ + { + "bbox": [ + 50, + 80, + 547, + 278 + ], + "spans": [ + { + "bbox": [ + 50, + 80, + 547, + 278 + ], + "type": "table", + "html": "
MethodsRef.SYSU-MM01RegDB
All-SearchIndoor-SearchVisible to InfraredInfrared to Visible
r=1r=10mAPr=1r=10mAPr=1r=10mAPr=1r=10mAP
Zero-padding [28]ICCV1714.8054.1215.9520.5868.3826.9217.7534.2118.9016.6334.6817.82
JSIA-ReID [25]AAAI2038.1080.7036.9043.8086.2052.9048.50-49.3048.10-48.90
AlignGAN [24]ICCV1942.4085.0040.7045.9087.6054.3057.90-53.6056.30-53.40
AGW [33]TPAMI2147.5084.3947.6554.1791.1462.9770.0586.2167.6470.4987.2165.90
X-Modality [9]AAAI2049.9289.7950.73---62.2183.1360.18---
DFLN-ViT [38]TMM2259.8492.4957.7062.1394.8369.0392.1097.9782.1191.2198.2081.62
SPOT [1]TIP2265.3492.7362.2569.4296.2274.6380.3593.4872.4679.3792.7972.26
FMCNet [36]CVPR2266.34-62.5168.15-63.8289.12-84.4388.23-83.86
SMCL [27]ICCV2167.3992.8761.7868.8496.5575.5683.93-79.8383.05-78.57
PMT [14]AAAI2367.5395.3664.9871.6696.7376.5284.83-76.5584.16-75.13
AGW+J [31]ICCV2169.8895.7166.8976.2697.8880.3785.0395.4979.1484.7595.3377.82
MPANet [29]CVPR2170.5896.1068.2476.7498.2180.9583.70-80.9082.80-80.70
CMT [6]ECCV2271.8896.4568.5776.9097.6879.9195.1798.8287.3091.9797.9284.46
MUN (Ours)ICCV2376.2497.8473.8179.4298.0982.0695.1998.9387.1591.8697.9985.01
", + "image_path": "2a1325370d346c8b962b124fab15f50c4e8c172187c4f6f81391ddd44ebd5555.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 299, + 287, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 299, + 287, + 347 + ], + "spans": [ + { + "bbox": [ + 46, + 299, + 287, + 347 + ], + "type": "text", + "content": "superior to GAN-based methods (JSIA-ReID [25], AlignGAN [24], FMCNet [36]) thanks to the powerful auxiliary modality which dynamically combines the information of visible and infrared images without introducing extra noise." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 348, + 287, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 348, + 287, + 456 + ], + "spans": [ + { + "bbox": [ + 46, + 348, + 287, + 456 + ], + "type": "text", + "content": "Furthermore, the proposed method significantly outperforms existing modality-unifying methods (SMCL [27], X-Modality [9]) by at least " + }, + { + "bbox": [ + 46, + 348, + 287, + 456 + ], + "type": "inline_equation", + "content": "8.85\\%" + }, + { + "bbox": [ + 46, + 348, + 287, + 456 + ], + "type": "text", + "content": " on the rank-1 metric. This can be attributed to the fact that we not only mine the fine-grained semantic representations to generate the auxiliary modality but also decouple the extraction of specific and shared patterns in two modalities, which contribute to the dynamic generation of the auxiliary modality for relieving the changeable modality discrepancies during the training." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 456, + 287, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 456, + 287, + 601 + ], + "spans": [ + { + "bbox": [ + 46, + 456, + 287, + 601 + ], + "type": "text", + "content": "Comparison on RegDB dataset. The results on RegDB are also listed in Table 4. In this dataset, image samples are spatially aligned and present less intra-class variations. Thus, the accuracy of all methods is higher than that on SYSU-MM01. The proposed MUN achieves Rank-1 of " + }, + { + "bbox": [ + 46, + 456, + 287, + 601 + ], + "type": "inline_equation", + "content": "95.19\\%" + }, + { + "bbox": [ + 46, + 456, + 287, + 601 + ], + "type": "text", + "content": " and mAP of " + }, + { + "bbox": [ + 46, + 456, + 287, + 601 + ], + "type": "inline_equation", + "content": "87.15\\%" + }, + { + "bbox": [ + 46, + 456, + 287, + 601 + ], + "type": "text", + "content": " in visible to infrared mode. Similar improvement can also be observed in the infrared to visible mode, which shows that our method obtains Rank-1 of " + }, + { + "bbox": [ + 46, + 456, + 287, + 601 + ], + "type": "inline_equation", + "content": "91.86\\%" + }, + { + "bbox": [ + 46, + 456, + 287, + 601 + ], + "type": "text", + "content": " and mAP of " + }, + { + "bbox": [ + 46, + 456, + 287, + 601 + ], + "type": "inline_equation", + "content": "85.01\\%" + }, + { + "bbox": [ + 46, + 456, + 287, + 601 + ], + "type": "text", + "content": ". This improvement can be attributed to the capacity of our method to generate a robust auxiliary modality, effectively mitigating both cross-modality and intra-modality discrepancies." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 609, + 212, + 624 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 609, + 212, + 624 + ], + "spans": [ + { + "bbox": [ + 47, + 609, + 212, + 624 + ], + "type": "text", + "content": "4.5. Evaluation on Generalizability" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "content": "To verify the generalizability of MUN, we conduct experiments on two corrupted VI Re-ID datasets [2], namely SYSU-MM01-C and RegDB-C. We utilize the same corruption settings as [2], which only performs corruptions during the testing stage and randomly selects one corruption type (e.g., elastic, snow, frosted glass, etc.) and one severity level for each image in the visible gallery set. The results re" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 309, + 329, + 545, + 450 + ], + "blocks": [ + { + "bbox": [ + 305, + 297, + 545, + 328 + ], + "lines": [ + { + "bbox": [ + 305, + 297, + 545, + 328 + ], + "spans": [ + { + "bbox": [ + 305, + 297, + 545, + 328 + ], + "type": "text", + "content": "Table 5. Evaluations on corrupted datasets. Each evaluation is performed 10 times to obtain the mean value. " + }, + { + "bbox": [ + 305, + 297, + 545, + 328 + ], + "type": "inline_equation", + "content": "L_{id}^{a}" + }, + { + "bbox": [ + 305, + 297, + 545, + 328 + ], + "type": "text", + "content": " denotes an individual identity loss used to supervise the auxiliary modality." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 329, + 545, + 450 + ], + "lines": [ + { + "bbox": [ + 309, + 329, + 545, + 450 + ], + "spans": [ + { + "bbox": [ + 309, + 329, + 545, + 450 + ], + "type": "table", + "html": "
IndexMethodSYSU-MM01-CRegDB-C
r=1mAPr=1mAP
1X-Modality [9]31.9826.2037.2635.97
2CIL [2]36.9535.9252.2549.76
3SMCL [27]37.0836.1251.9349.22
4AGW+J [31]40.0937.8651.5349.04
5B25.9223.1332.0529.64
6+Aux.+Lda30.8526.5436.4031.21
7+Aux.+Lidc31.1227.4438.1332.29
8+Aux.+Lidc+Lia36.7832.3245.4442.89
9+Aux.+Lidc+Lia+Lma41.1738.6352.6950.18
", + "image_path": "dda05574a3e0a09ca1dbedc6c0c4975dede81ee38e8e5629ca1c8ddf0133486b.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "spans": [ + { + "bbox": [ + 305, + 470, + 545, + 495 + ], + "type": "text", + "content": "ported for all the compared methods are obtained using the official best settings as provided in their respective papers." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "content": "Table 5 shows that the performance of baseline (B) is relatively lower than that of existing SOTAs under data corruption scenarios. However, by introducing the auxiliary modality to bridge the gap between visible and infrared modalities (Index 6), the accuracy is significantly improved. Furthermore, by incorporating the proposed identity alignment loss " + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "inline_equation", + "content": "(L_{ia})" + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "content": " and modality alignment loss " + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "inline_equation", + "content": "(L_{ma})" + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "content": " to refine the learned cross-modality feature relationships, the rank-1 and mAP accuracies experience a substantial enhancement of " + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "inline_equation", + "content": "15.25\\%" + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "inline_equation", + "content": "15.5\\%" + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "content": " respectively on the SYSU-MM01-C dataset. This outperforms the current SOTAs by a remarkable margin. Specifically, our MUN method exceeds the highly robust AGW+J [31] by " + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "inline_equation", + "content": "1.08\\%" + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "content": " in rank-1 and " + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "inline_equation", + "content": "0.77\\%" + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "content": " in mAP. The experiments on two corrupted datasets verify the strong generalizability and robustness of the proposed MUN, which can consistently learn modality-shared patterns and regulate stable feature relationships under corrupted data scenarios." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "11192" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 71, + 157, + 168 + ], + "blocks": [ + { + "bbox": [ + 49, + 71, + 157, + 168 + ], + "lines": [ + { + "bbox": [ + 49, + 71, + 157, + 168 + ], + "spans": [ + { + "bbox": [ + 49, + 71, + 157, + 168 + ], + "type": "image", + "image_path": "7a4ddfab3b384a2c8482dc1f7e49b6c319021159ad3e608ef7c8b516eb625002.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 173, + 78, + 282, + 167 + ], + "blocks": [ + { + "bbox": [ + 173, + 78, + 282, + 167 + ], + "lines": [ + { + "bbox": [ + 173, + 78, + 282, + 167 + ], + "spans": [ + { + "bbox": [ + 173, + 78, + 282, + 167 + ], + "type": "image", + "image_path": "a9140398046886bdefa01e26d26c20ef3f9e36add93fd5a06e9303eef5cf3fc0.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 48, + 174, + 156, + 266 + ], + "blocks": [ + { + "bbox": [ + 48, + 174, + 156, + 266 + ], + "lines": [ + { + "bbox": [ + 48, + 174, + 156, + 266 + ], + "spans": [ + { + "bbox": [ + 48, + 174, + 156, + 266 + ], + "type": "image", + "image_path": "c016fdcb3a2334a6b9069318db3ac225952b88cda89c17e9628ab017fafd288e.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 271, + 287, + 316 + ], + "lines": [ + { + "bbox": [ + 46, + 271, + 287, + 316 + ], + "spans": [ + { + "bbox": [ + 46, + 271, + 287, + 316 + ], + "type": "text", + "content": "Figure 4. Distributions of learned visible, infrared and auxiliary features during the training. All the samples are randomly selected in the SYSU-MM01 dataset. The 3D visualization is made by T-SNE [23]. Please view in colour and zoom in." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 173, + 174, + 282, + 266 + ], + "blocks": [ + { + "bbox": [ + 173, + 174, + 282, + 266 + ], + "lines": [ + { + "bbox": [ + 173, + 174, + 282, + 266 + ], + "spans": [ + { + "bbox": [ + 173, + 174, + 282, + 266 + ], + "type": "image", + "image_path": "4038246cdde7d41cece84cb88176cb49b6772da80699d004dbf0f8126ebc439c.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 335, + 130, + 346 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 335, + 130, + 346 + ], + "spans": [ + { + "bbox": [ + 47, + 335, + 130, + 346 + ], + "type": "text", + "content": "4.6. Visualization" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "spans": [ + { + "bbox": [ + 46, + 354, + 287, + 413 + ], + "type": "text", + "content": "Distribution Visualization. To visually demonstrate the effectiveness of MUN, we randomly select 10 identities from the SYSU-MM01 dataset and visualize their feature distributions during the training. The visualization results are presented in Figure 4." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 414, + 287, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 414, + 287, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 414, + 287, + 617 + ], + "type": "text", + "content": "At the onset of training (epoch 0 in Figure 4 (a)), significant modality disparities arise between visible (depicted by blue dots) and infrared images (depicted by red dots), rendering cross-modality matching unfeasible. As the training progresses, the proposed auxiliary modality (depicted by green dots) serves as a bridge to connect the visible and infrared modalities in the common feature space. We can observe that the learned visible and infrared features show a convergence trend, and the modality discrepancies are gradually eliminated at epoch 5 in Figure 4 (b). Afterwards, the network learns identity-aware patterns by regulating smaller intra-class distances and larger inter-class distances at epoch 45. Finally, in Figure 4 (d), all the learned features are well grouped into their respective identity centers, demonstrating powerful discriminability under cross-modality scenes, which proves the effectiveness of MUN in learning robustness and identity-aware features." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 617, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 677 + ], + "type": "text", + "content": "Pattern Visualization. In order to further illustrate the effectiveness of our auxiliary modality, we select one visible and one infrared image with the same identity in the SYSUMM01 dataset to visualize the corresponding learned feature maps and attention maps via Grad-CAM [22]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": "The visualization results are shown in Figure 5. It is clear that the visible " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "(\\mathbf{F}^v)" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": " and infrared " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "(\\mathbf{F}^r)" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": " feature maps extracted from the backbone have different patterns and struc" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 306, + 74, + 541, + 174 + ], + "blocks": [ + { + "bbox": [ + 306, + 74, + 541, + 174 + ], + "lines": [ + { + "bbox": [ + 306, + 74, + 541, + 174 + ], + "spans": [ + { + "bbox": [ + 306, + 74, + 541, + 174 + ], + "type": "image", + "image_path": "f7931947a8fa9bbae67586007ecf957b98ad962bd75fecf2e715525adcdacf9f.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "lines": [ + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "spans": [ + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "text", + "content": "Figure 5. Visualization of learned feature maps and attention maps. Given the input visible image " + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "inline_equation", + "content": "\\mathbf{I}^v" + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "text", + "content": " and infrared image " + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "inline_equation", + "content": "\\mathbf{I}^r" + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "text", + "content": ", we visualize the corresponding learned visible feature " + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^v" + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "text", + "content": ", infrared feature " + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^r" + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "text", + "content": ", and the generated auxiliary feature " + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^a" + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "text", + "content": ". It is obvious that the auxiliary feature " + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^a" + }, + { + "bbox": [ + 304, + 180, + 545, + 267 + ], + "type": "text", + "content": " can preserve most of the modality-shared patterns, including body shape and structure. The attention visualizations on the input images are made by Grad-CAM [22]. Please view in colour and zoom in." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 290, + 545, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 290, + 545, + 410 + ], + "spans": [ + { + "bbox": [ + 304, + 290, + 545, + 410 + ], + "type": "text", + "content": "tures, which makes it difficult to perform cross-modality matching. Notably, the proposed auxiliary generator can dynamically reconstruct and align the modality-shared spatial patterns using multiple transposed convolutions. This makes our auxiliary feature " + }, + { + "bbox": [ + 304, + 290, + 545, + 410 + ], + "type": "inline_equation", + "content": "(\\mathbf{F}^a" + }, + { + "bbox": [ + 304, + 290, + 545, + 410 + ], + "type": "text", + "content": " in Figure 5) preserves most of the shared patterns between " + }, + { + "bbox": [ + 304, + 290, + 545, + 410 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^v" + }, + { + "bbox": [ + 304, + 290, + 545, + 410 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 290, + 545, + 410 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^r" + }, + { + "bbox": [ + 304, + 290, + 545, + 410 + ], + "type": "text", + "content": " without corrupting the structure information of person bodies. In addition, the attention visualization in Figure 5 further indicates that the proposed auxiliary modality plays a critical role in helping the network learn modality-shared representations." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 426, + 378, + 438 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 426, + 378, + 438 + ], + "spans": [ + { + "bbox": [ + 306, + 426, + 378, + 438 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 448, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 448, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 545, + 616 + ], + "type": "text", + "content": "This paper proposes a novel Modality Unifying Network to jointly explore the robust auxiliary modality and generalize cross-modality feature relationships for VI-ReID. The auxiliary modality is generated by combining the cross-modality learner and the intra-modality learner, enabling the dynamic extraction of modality-specific patterns from multiple receptive fields and feature scales. This approach empowers our auxiliary modality to effectively alleviate both cross-modality and intra-modality discrepancies. Moreover, we propose identity alignment loss and modality alignment loss to regulate discriminative feature relationships in multi-modality tasks. Extensive experiments on public datasets demonstrate the effectiveness and generalizability of our MUN as well as each proposed component." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgements. This work is supported by the Academy of Finland for Academy Professor project EmotionAI (Grants No. 336116, 345122), the University of Oulu & The Academy of Finland Profi 7 (Grant No. 352788), and the National Natural Science Foundation of China (Grant No. 61802058, 61911530397). We appreciate the professional and cost-effective GPU computing service provided by www.AutoDL.com." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "11193" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Cuiqun Chen, Mang Ye, Meibin Qi, Jingjing Wu, Jianguo Jiang, and Chia-Wen Lin. 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In Proceedings of the AAAI conference on artificial intelligence, volume 34, pages 13114–13121, 2020." + } + ] + } + ], + "index": 15 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "11195" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/7e446bd7-c368-40d4-8d81-6aee3f5055e8_content_list.json b/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/7e446bd7-c368-40d4-8d81-6aee3f5055e8_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..58587e573657c499a54c37807ba6af9caac1fa28 --- /dev/null +++ b/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/7e446bd7-c368-40d4-8d81-6aee3f5055e8_content_list.json @@ -0,0 +1,1743 @@ +[ + { + "type": "text", + "text": "Model Calibration in Dense Classification with Adaptive Label Perturbation", + "text_level": 1, + "bbox": [ + 99, + 130, + 869, + 151 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Jiawei Liu Changkun Ye Shan Wang Ruikai Cui Jing Zhang Kaihao Zhang Nick Barnes The Australian National University", + "bbox": [ + 96, + 180, + 870, + 217 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 251, + 313, + 266 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "For safety-related applications, it is crucial to produce trustworthy deep neural networks whose prediction is associated with confidence that can represent the likelihood of correctness for subsequent decision-making. Existing dense binary classification models are prone to being over-confident. To improve model calibration, we propose Adaptive Stochastic Label Perturbation (ASLP) which learns a unique label perturbation level for each training image. ASLP employs our proposed Self-Calibrating Binary Cross Entropy (SC-BCE) loss, which unifies label perturbation processes including stochastic approaches (like DisturbLabel), and label smoothing, to correct calibration while maintaining classification rates. ASLP follows Maximum Entropy Inference of classic statistical mechanics to maximise prediction entropy with respect to missing information. It performs this while: (1) preserving classification accuracy on known data as a conservative solution, or (2) specifically improves model calibration degree by minimising the gap between the prediction accuracy and expected confidence of the target training label. Extensive results demonstrate that ASLP can significantly improve calibration degrees of dense binary classification models on both in-distribution and out-of-distribution data. The code is available on https://github.com/Carlisle-Liu/ASLP.", + "bbox": [ + 76, + 282, + 473, + 660 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 78, + 691, + 209, + 707 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Binary segmentation aims to differentiate foreground areas from the background in images. Its tasks include Salient Object Detection [86], Camouflaged Object Detection [13], Smoke Detection [79], etc. Performance in these tasks has been significantly advanced using the strong representation powers of Deep Neural Networks (DNNs). However, with complex structures and a tremendous number of parameters, DNNs are prone to over-fitting to training data and producing over-confident predictions in the real world [18]. Such issues can render the model predictions unreliable in decision making or utilisation in downstream tasks.", + "bbox": [ + 75, + 718, + 468, + 883 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recently, a growing body of literature has been pro", + "bbox": [ + 96, + 885, + 468, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/0b48a447877521fb5e19777c78e824597d2821e87a72290b0de4c5e0aac4997e.jpg", + "image_caption": [ + "Figure 1: Applying Adaptive Label Perturbation during training can effectively moderate predictions at incorrect areas, highlighting them with high entropy values (red). $Z_{t}(x,y)$ is a sample-wise Bernoulli variable, parameterized by $\\alpha$ , at the $t^{\\mathrm{th}}$ iteration. After $k$ iterations, update $\\alpha$ using Eq. (5) to adjust the likelihood (or level) of label perturbation to increase entropy for incorrect predictions and so correct model calibration. The Perturbed Label (shown inverted) replaces the Groundtruth Label with probability $\\alpha$ ." + ], + "image_footnote": [], + "bbox": [ + 506, + 250, + 880, + 377 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "posed to address model mis-calibration problems in DNNs. They can be roughly categorised as: (1) post-hoc operations, such as temperature scaling [18], Platt scaling [54], etc., (2) training objective approaches [27], like MMCE [30], soft calibration objective [27], focal loss [45, 17], and (3) data/label augmentation techniques, e.g. label smoothing [46] and mixup [85]. We propose an Adaptive Label Perturbation which learns a unique label perturbation level for each training image. As illustrated in Fig. 1, training with Adaptive Stochastic Label Perturbation, a form of ALP, can effectively moderate incorrect predictions and highlight them with high entropy values.", + "bbox": [ + 496, + 536, + 893, + 718 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Adaptive Label Perturbation employs our proposed Self-Calibrating Binary Cross Entropy (SC-BCE) loss, which unifies label perturbation processes including stochastic approaches (like DisturbLabel [75]), and label smoothing [60] to correct calibration while maintaining classification accuracy. SC-BCE loss is equivalent to a factored combination of (i) a BCE loss w.r.t. groundtruth label, and (ii) a BCE loss w.r.t. a uniform binary categorical distribution. The former enhances dense binary classification performance and the latter improves the model calibration degree. Our method can be connected to Maximum Entropy Inference [23] of classic statistical mechanics, to maximise prediction", + "bbox": [ + 496, + 719, + 895, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "1173", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "entropy with respect to missing information while preserving the classification accuracy on known data.", + "bbox": [ + 76, + 90, + 467, + 119 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The proposed Adaptive Label Perturbation (ALP) can approximate Maximum Entropy Inference [23] to maximise prediction entropy while preserving the ideal dense classification performance on known data. This represents a conservative solution that adopts classification accuracy as a proxy for known data and assumes maximum disorder on unknown data. We also present an alternative ALP solution that, instead, takes model calibration degree as a proxy for known data, using a calibration regulariser which constrains the expected confidence of individual supervision signal to not drop below the ideal accuracy on the validation set. This effectively minimises the gap between the distributions of prediction confidence and prediction accuracy, which is the source of model mis-calibration.", + "bbox": [ + 75, + 121, + 467, + 330 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our contributions can be summarised as: (i) We propose Adaptive Stochastic Label Perturbation that learns a sample-wise label perturbation level to improve model calibration; (ii) We present a Self-Calibrating Binary Cross Entropy loss that unifies label perturbation processes including stochastic approaches and label smoothing; (iii) Following Maximum Entropy Inference [23] we show that Adaptive Stochastic Label Perturbation $(\\mathrm{ASLP}_{\\mathrm{MEI}})$ , can maximise the prediction entropy while preserving the ideal dense classification accuracy, and (iv) We present an alternative Adaptive Stochastic Label Perturbation $(\\mathrm{ASLP}_{\\mathrm{MC}})$ solution to maximise model calibration degree, which achieves state-of-the-art performance in terms of model calibration degree on both in-distribution and out-of-distribution data. We thoroughly evaluate our method on Salient Object Detection and demonstrate its effectiveness for Camouflaged Object Detection, Smoke Detection and Semantic Segmentation.", + "bbox": [ + 75, + 332, + 467, + 589 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works", + "text_level": 1, + "bbox": [ + 76, + 603, + 225, + 619 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Model Calibration: Model calibration methods can be roughly divided into three categories of approach: (1) post hoc processing (2) training object, and (3) input/label augmentation. The first category utilises a validation set to align the prediction confidence distribution with prediction accuracy distribution. It includes histogram binning [82], isotropic regression [83], Platt scaling [54, 49], Bayesian binning into quantiles [47], Dirichlet scaling [28], mix-n-match [87] and temperature scaling [18, 81].", + "bbox": [ + 75, + 628, + 467, + 763 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The second category focuses on designing training objectives that (in)directly improve model calibration degree. Some methods address the in-continuity of expected calibration error, a widely adopted model calibration measure, and propose trainable calibration objectives like maximum mean calibration error [30], soft calibration objective [27]. Other works discover that certain existing training objects are beneficial to model calibration, e.g. Brier loss [4, 10], confidence penalty [52] and focal loss [45, 17].", + "bbox": [ + 75, + 765, + 467, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The third category employs data or label augmentation techniques to regularise the prediction confidence distribution. Mixup [85, 62] explores the neighbourhood of training data through random interpolation of input images and associated labels to improve model calibration degree. Label smoothing [46] augments the one-hot training labels with softer versions to prevent the model being over-confident.", + "bbox": [ + 496, + 90, + 890, + 196 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Salient Object Detection: Inspired by pioneering work [22], traditional Saliency Object Detection (SOD) methods rely on various heuristic priors with handcraft features to explore low-level cures [1, 25, 26, 38, 66]. However, these methods cannot cope with complex scenes because of the limited representation ability of handcrafted features [3]. Recently, deep learning based SOD methods broke the bottleneck of traditional methods due to the powerful capability of neural networks, achieving improved performance [6, 24, 55, 76, 37, 64, 68]. Early deep SOD methods use multi-layer perception to predict a map with a pixel-wise score for each image [71, 8]. These approaches rely on fixed fully connected layers and thus severely limit the ability of spatial information extraction. Later methods address this issue via using fully convolutional networks (FCNs) [40].", + "bbox": [ + 496, + 199, + 890, + 425 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Most contemporary SOD methods are designed based on FCNs with various schemes to improve performance. One of the most popular strategies is to fuse multi-scale information extracted from different layers and aggregate them in the network [91, 74, 16, 51, 96, 90]. Attention modules are also applied to capture powerful multi-scale features via exploring relationship between local and global information [37, 53, 95, 21]. Training SOD networks using auxiliary supervision is also a popular strategy [70, 70, 61]. For example, the body map and detail map are utilized by [70] to help the network focus on center areas and edges, respectively. Skeleton [35] and uncertainty [61] are applied to the training processing due to their important roles in taking photos.", + "bbox": [ + 496, + 428, + 890, + 625 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Noisy Label: Noisy labels refer to incorrect ground truth classes/values in classification/regression tasks. They arise from data collection or annotation processes, and exist commonly in real-world datasets [2]. Efforts are put to identify the noisy labels and exclude them from network training in various computer vision tasks, deeming their incorporation as harmful. [88] proposes a framework that learns from noisy labels, being a collection of predictions from classic SOD methods. The framework approximates the noise distribution in order to recover clean labels for model training.", + "bbox": [ + 496, + 626, + 890, + 777 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Differently from data augmentation techniques that are applied simultaneously to training samples and corresponding labels to generate more training data, one may artificially corrupt the label. We refer to this category of approaches as label perturbation, which includes label smoothing approaches [60], and DisturbLabel, Xie et al. [75]. In image classification, Xie et al. [75] shows that randomly replacing training labels with a prior distribution", + "bbox": [ + 496, + 779, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "1174", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "leads to a regularising effect, preventing overfitting. Our work is different from [75] by employing labels corrupted to different scales to enhance the model calibration degrees for both in-distribution and out-of-distribution data. Further, in performing this, we assume noise that varies with different samples, making our method more adaptable.", + "bbox": [ + 75, + 90, + 472, + 183 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed Method", + "text_level": 1, + "bbox": [ + 76, + 196, + 250, + 212 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We first lay out the task setting in Sec. 3.1. Then we introduce our proposed Self-Calibrating Binary Cross Entropy loss in Sec. 3.2 and prove its connection to Maximum Entropy Inference [23] in Sec. 3.3. Lastly, we detail our major contribution - Adaptive Label Perturbation in Sec. 3.4.", + "bbox": [ + 75, + 220, + 468, + 297 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Task Setting", + "text_level": 1, + "bbox": [ + 76, + 306, + 209, + 324 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Binary segmentation problems aim to differentiate between foreground object(s) and background. They can be formulated as a pixel-wise binary classification problem. Given an independent and identically distributed (i.i.d) training dataset $\\mathcal{D}_{\\mathrm{TR}} = \\{x_i,y_i\\}_{i = 1}^N$ drawn from an unknown joint distribution of training images and groundtruth labels $P(\\mathcal{X},\\mathcal{Y})$ , a neural network model parameterised by $\\theta$ is employed to predict labels for an input image $x\\in \\mathcal{X}$ : $f_{\\theta}(x)\\in (0,1)^{1\\times H\\times W}$ . We use $\\hat{y}$ and $P_{\\hat{y}}$ to denote the winning class and its associated probability respectively. The groundtruth label $y\\in \\{0,1\\}^{1\\times H\\times W}$ represents the foreground pixels with \"1\" and background with \"0\". In the following equations, we omit the spatial indexes $H$ and $W$ for simplicity. A perfectly calibrated model has $\\mathrm{P}(\\hat{y} = y|P_{\\hat{y}}) = P_{\\hat{y}},\\forall P_{\\hat{y}}\\in (0,1)$ . That is, in the entire range of prediction probabilities, prediction with probability $P_{\\hat{y}}$ has exactly $P_{\\hat{y}}$ chance to be correct. The calibration degree of a model $f_{\\theta}(\\cdot)$ over a distribution $\\mathcal{D}$ is quantified with Expected Calibration Error (ECE), defined as $\\mathbb{E}_{f_{\\theta}(x)}[|\\mathrm{P}(\\hat{y} = y|f_{\\theta}(x)) - f_{\\theta}(x)|]$ .", + "bbox": [ + 75, + 330, + 472, + 633 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Self-Calibrating Binary Cross Entropy Loss", + "text_level": 1, + "bbox": [ + 76, + 642, + 449, + 660 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We propose a Self-Calibrating Binary Cross Entropy (SC-BCE) loss that unifies Label Smoothing [60], DisturbLabel [75] and Stochastic Label Perturbation as:", + "bbox": [ + 75, + 666, + 468, + 712 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {L} _ {\\mathrm {S C - B C E}} (\\theta , X, Y, \\alpha , \\beta) \\\\ = \\mathbb {E} _ {x, y \\in X, Y} \\left[ \\left(1 - Z _ {t} (x, y)\\right) \\cdot \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x, y) \\right. \\\\ \\left. + Z _ {t} (x, y) \\cdot \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x, p (y, \\beta)) \\right] \\tag {1} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 125, + 724, + 468, + 796 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\beta \\in [ 0, 2 ], \\quad \\alpha \\in [ 0, \\frac {1}{\\beta}),\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 799, + 299, + 829 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $Z_{t}(x,y) \\sim B(1,\\alpha)$ follows a Bernoulli distribution with $\\alpha$ probability to be 1 and $1 - \\alpha$ chance to be 0, $t$ denotes the training epoch, $\\alpha \\in [0,\\frac{1}{\\beta})$ and $\\beta \\in [0,2]$ are Label Perturbation Probability (LPP) and Label Perturbation Strength", + "bbox": [ + 75, + 839, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "(LPS) respectively, $p(y,\\beta) = (1 - \\beta)\\cdot y + \\frac{\\beta}{2},\\beta \\in [0,2]$ is a perturbed label and $\\mathcal{L}_{\\mathrm{BCE}}(\\theta ,x,y)^1$ is a Binary Cross Entropy (BCE) loss computed for training pair $(x,y)$ . For $\\alpha = 1$ , the label perturbation equation follows the label smoothing equation for a binary label [60]. In the proposed SC-BCE loss, different label perturbations can be applied by setting (i) Label Smoothing [60]: $\\alpha = 1$ and $\\beta \\in [0,1)$ , (2) DisturbLabel: $\\beta = 1$ and $\\alpha \\in (0,1)$ , and (3) Stochastic Label Perturbation (SLP): $\\beta \\in (0,2]$ and $\\alpha \\in (0,\\frac{1}{\\beta})$ . For example, Hard Inversion (HI) that inverts the label category as shown in Fig. 2, can be stochastically applied by setting $\\beta = 2$ and $\\alpha \\in (0,\\frac{1}{2})$ .", + "bbox": [ + 496, + 89, + 890, + 273 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the implementation of SLP, the supervision for an individual training image in each epoch is sampled by drawing from a Bernoulli distribution. That is, the individual supervision can take the form of the groundtruth label or perturbed label in each training iteration. The overall function of SLP can be connected to that of a smoothed label by taking expectation of the Bernoulli variable: $\\mathbb{E}_{Z_t}[(1 - Z_t(y))\\cdot Y + Z_t(y)\\cdot p(y,\\beta)],\\forall y\\in Y.$ Taking the expectation over the Bernoulli variation in each iteration is too expensive to implement in model training. Instead, following [75], the expectation of stochastically perturbed label is approximated by taking expectation across training epochs: $\\mathbb{E}_{t\\in T}[(1 - Z_t(y))\\cdot Y + Z_t(y)\\cdot p(y,\\beta)],\\forall y\\in Y,$ where $T$ is the total number of training epochs and $Z_{t}(y)$ is a variable drawn from a Bernoulli distribution for the $\\mathrm{t^{th}}$ epoch.", + "bbox": [ + 496, + 275, + 890, + 503 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. Maximum Entropy Inference", + "text_level": 1, + "bbox": [ + 498, + 521, + 761, + 537 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Maximum Entropy Inference (MEI), assuming minimum distribution commitment in respect to missing information, was initially proposed by Jaynes [23]. That is, the probability distribution should have maximum Shannon entropy subject to the partially available information. Thus, in the complete absence of information, Shannon entropy for a binary prediction defined in Eq. (2) should be maximised:", + "bbox": [ + 496, + 547, + 890, + 655 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathbb {H} \\left(f _ {\\theta} (X)\\right) = \\mathbb {E} _ {x \\in X} \\left[ - f _ {\\theta} (x) \\cdot \\log f _ {\\theta} (x) - \\right. \\tag {2} \\\\ \\left. \\left(1 - f _ {\\theta} (x)\\right) \\cdot \\log \\left(1 - f _ {\\theta} (x)\\right) \\right\\rfloor \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 516, + 685, + 890, + 738 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For salient object detection and other binary segmentation problems, maximising Eq. (2) can be achieved with a binary uniform categorical distribution.", + "bbox": [ + 496, + 755, + 890, + 799 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The proposed SC-BCE loss can be transformed into a factored combination of a BCE loss w.r.t. groundtruth label (the constraints of the data) and a BCE loss w.r.t. a binary uniform categorical distribution (See Appendix A.2 for", + "bbox": [ + 496, + 803, + 890, + 864 + ], + "page_idx": 2 + }, + { + "type": "page_footnote", + "text": "$^{1}$ $\\mathcal{L}_{\\mathrm{BCE}}(\\theta, x, y) = -y \\cdot \\log(f_{\\theta}(x)) - (1 - y) \\cdot \\log(1 - f_{\\theta}(x))$", + "bbox": [ + 517, + 886, + 862, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "1175", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/f6c598fa19f5650a8473a987e821c23524573c8c0834c19b585b2123d047b08d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 114, + 88, + 504, + 188 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/a3ff5e673a93dee465d07f7cd59370dea9b324ad897e89909b6b70bd82b553e9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 509, + 88, + 651, + 188 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/be4472f6f51616a582d5b67e8dcb45701b4d1ec579f23d0c97358464d9183019.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 653, + 88, + 846, + 188 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/62d63950f255c962c00b28214888f62f86ebbb3323c18f95611ea024c47f0bd0.jpg", + "image_caption": [ + "Figure 2: The method overview is comprised of model implementation (top) and Adaptive Stochastic Label Perturbation (ASLP) learning rule (bottom). In each iteration, the model uses a Bernoulli variable to sample a supervision, which can be a groundtruth label $y_{i}$ or a perturbed label $p_i$ and computes a sample-specific $\\nabla_{\\alpha_i}$ based on the prediction. Regularisation is computed with Eq. 5 (ASLPMEI) or Eq. 6 (ASLPMC) on a validation set after each training epoch. The ASLP learning rule combines Grad- $\\alpha_{i}$ and a factored regularisation to update label perturbation probability $\\alpha_{i}$ for each individual sample." + ], + "image_footnote": [], + "bbox": [ + 117, + 190, + 295, + 299 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/249056d26564fe63e5438aa5d759d1c7713c2d80aa95010923d78fd3608c0bac.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
L BCE(θ, x_i, p(y_i, β)) - L BCE(θ, x_i, y_i)∇αi
>0>0
=0=0
<0<0
", + "bbox": [ + 297, + 191, + 475, + 297 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/82138053606d6826add6d2f0fa3d5fd15700a62b101851ceff63fa933f1b4e45.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Regularisation
A(θ, DVAL) - A(θlm, DVAL) or (1 - β · αi2) - A(θlm, DVAL)Regularisation
> 0= 0
= 0= 0
< 0< 0
", + "bbox": [ + 480, + 190, + 691, + 297 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/6cfadaf02f8dcde3a27850bbbe40657ddac5fed80deadd3880051764748297d9.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ASLP - Learning Rule
∇αi+λ·RegularisationΔαi
>0>0
=0=0
<0<0
", + "bbox": [ + 694, + 190, + 844, + 297 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "derivation) as:", + "bbox": [ + 76, + 393, + 174, + 407 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {L} _ {\\mathrm {S C - B C E}} (\\theta , X, Y, \\alpha , \\beta) \\\\ = \\mathbb {E} _ {x, y \\in X, Y} \\left[ (1 - \\beta Z _ {t} (x, y)) \\cdot \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x, y) \\right. \\tag {3} \\\\ \\left. + \\beta Z _ {t} (x, y) \\cdot \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x, u) \\right], \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 127, + 420, + 468, + 494 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $Z_{t}(x,y) \\sim B(1,\\alpha)$ , $u$ is a binary uniform categorical distribution, and minimising the second term pushes the prediction distribution towards a uniform binary categorical distribution, equivalently maximising the inference entropy. Therefore, our proposed SC-BCE loss, a combination of a regular BCE loss and a BCE loss with a perturbed label, effectively performs a type of MEI. That is, the regular BCE loss component improves the model's binary classification accuracy in the presence of information while the perturbed label maximizes prediction entropy with respect to missing information in order to close the gap between the available training data and the entire data distribution.", + "bbox": [ + 75, + 505, + 468, + 686 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Adaptive Label Perturbation", + "text_level": 1, + "bbox": [ + 76, + 696, + 334, + 713 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Stochastic Label Perturbation (SLP) uses a single label perturbation probability and perturbation strength for the entire training dataset. However, this approach cannot adapt to predictive error that varies for different input images. To address this, we propose an Adaptive Stochastic Label Augmentation (ASLP) method to adjust the label augmentation probability for individual training samples. That is we allow the variable in Eq. (1) to be drawn from a per training image Bernoulli distribution with sample-specific label perturbation probability as:", + "bbox": [ + 75, + 720, + 467, + 871 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nZ _ {t} (x, y) \\sim B (1, \\alpha_ {x, y}), \\forall x, y \\in X, Y \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 147, + 883, + 468, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\alpha_{x,y}$ is the label perturbation probability for sample (image-label) pair $(x,y)$ . Initially, we set all label perturbation probabilities to $\\{\\alpha_{i} = 0\\}_{i = 1}^{N}$ and train a model with a regular BCE loss without label augmentation techniques, which is equivalent to $\\mathcal{L}_{\\mathrm{SC - BCE}}(\\theta ,X,Y,\\alpha = 0,\\beta = 0)$ . The trained model has weight $\\theta_{\\mathrm{lm}}$ and its accuracy on the validation set, $\\mathbb{A}(\\theta_{lm},\\mathcal{D}_{\\mathrm{VAL}})$ , is held as an ideal performance. Subsequently, we select a label perturbation technique and continue to train the model with SC-BCE loss with a learning rule to update the label perturbation probability for individual training samples.", + "bbox": [ + 496, + 393, + 890, + 559 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We propose the learning rule for $\\alpha$ , $(\\mathrm{ASLP}_{\\mathrm{MEI}})$ to approximate maximum entropy inference. The rule has two components: (1) $\\nabla_{\\alpha_i} = (2 / \\beta)\\cdot$ $\\partial \\mathbb{E}_{Z_t}(x_i,y_i)\\big[\\mathcal{L}_{\\mathrm{SC - BCE}}(X,Y,\\theta ,\\{\\alpha_i\\}_{i = 1}^N,\\beta)\\big] / \\partial \\alpha_i$ is the derivative of the expectation of SC-BCE over the Bernoulli variable w.r.t. $\\alpha_{i}$ . We divide this by $\\beta /2$ to ensure that different perturbation techniques (varying $\\beta$ values) have the same convergence speed (See derivation in Appendix A.3), and (2) Accuracy Regularization to encourage maintenance of prediction accuracy. The rule is:", + "bbox": [ + 496, + 560, + 890, + 712 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\alpha_ {i} ^ {n + 1} = \\alpha_ {i} ^ {n} + \\eta \\cdot \\left(\\nabla_ {\\alpha_ {i}} + \\lambda \\cdot \\operatorname {R e g} _ {A}\\right), \\quad \\text {f o r} i = 1, \\dots , N, \\\\ \\nabla_ {\\alpha_ {i}} = \\frac {2 \\cdot \\left(\\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x _ {i} , p (y _ {i} , \\beta)) - \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x _ {i} , y _ {i})\\right)}{\\beta}, \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 504, + 722, + 883, + 776 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {R e g} _ {\\mathrm {A}} = \\min \\left(\\frac {\\mathbb {A} (\\theta , \\mathcal {D} _ {\\mathrm {V A L}}) - \\mathbb {A} (\\theta_ {l m} , \\mathcal {D} _ {\\mathrm {V A L}})}{\\mathbb {A} (\\theta_ {l m} , \\mathcal {D} _ {\\mathrm {V A L}})}, 0\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 779, + 890, + 824 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\eta$ and $\\lambda$ are hyperparameters controlling the updating pace of label perturbation probability and the regularisation strength respectively, $\\mathbb{A}(\\theta ,\\mathcal{D}_{\\mathrm{VAL}})$ and $\\mathbb{A}(\\theta_{lm},and\\mathcal{D}_{\\mathrm{VAL}})$ denote the current and ideal accuracy on the validation set separately. $\\nabla_{\\alpha_i}$ aims to increase label perturbation proba", + "bbox": [ + 496, + 825, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "1176", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "bility to confident and correct samples and otherwise for incorrectly classified samples. For example, it returns a large positive value for correct predictions with small BCE loss value w.r.t. to groundtruth label $y_{i}$ and large BCE loss value w.r.t. to perturbed label $p(y_{i},\\beta)$ . The \"Accuracy Regularisation\" (RegA) is designed to reduce the overall perturbation probability if the accuracy on the validation set reduces to be below the local minima. It returns 0 if there is no accuracy drop on the validation set and a large decrease will overwhelm the $\\nabla_{\\alpha_i}$ value and reduce the sample label perturbation probability. Intuitively, ASLPMEI aims to construct a model that preserves the ideal classification accuracy while otherwise maximising the entropy [23]. Note that which particular examples are classified correctly are able to change, but the accuracy is constrained to remain the same. Intuitively, having a model that better captures ignorance may lead to changes in the treatment of test examples that are distant from training distribution. Note, however that adopting classification accuracy as proxy for known data and otherwise maximizing entropy is a conservative strategy and we find that it results in the model being significantly under-confident.", + "bbox": [ + 76, + 90, + 472, + 421 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The model mis-calibration arises from the distribution mismatch between prediction confidence and prediction accuracy [45]. We offer an alternative model that uses the model calibration as proxy for known data and maximises the prediction entropy in respect to unknown data $\\mathrm{ASLP}_{\\mathrm{MC}}$ . The learning rule replaces the \"Accuracy Regularisation\" in Eq. (5) with a \"Calibration Regularisation\" $(\\mathrm{Reg}_{\\mathrm{C}})$ as:", + "bbox": [ + 76, + 422, + 472, + 532 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {R e g} _ {\\mathrm {C}} = \\min \\left(\\left(1 - \\frac {\\beta \\cdot \\alpha_ {i} ^ {n}}{2}\\right) - \\mathbb {A} \\left(\\theta_ {l m}, \\mathcal {D} _ {\\mathrm {V A L}}\\right), 0\\right), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 99, + 537, + 468, + 566 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $1 - (\\beta \\cdot \\alpha_{i}^{n} / 2)$ denotes the expected confidence of the perturbed label (Derivation in Appendix A.4). For example, a foreground label \"1\" with $5\\%$ chance of being inverted to \"0\" has an expected confidence of 0.95. \"Calibration Regularisation\" constrains the expected confidence of perturbed label of each sample to not drop below the ideal classification accuracy on validation set, preventing the model from becoming under-confident. Note that we can also have an updating rule $\\mathrm{ALS}_{\\mathrm{MC}}$ to learn per-image label perturbation strength (adaptive $\\beta$ and fixed $\\alpha = 1$ ) (See Appendix A.5).", + "bbox": [ + 76, + 574, + 472, + 727 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments and Results", + "text_level": 1, + "bbox": [ + 76, + 738, + 312, + 756 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We verify the proposed method primarily on Salient Object Detection and also implement it for Camouflaged Object Detection, Smoke Detection and Semantic Segmentation tasks and report their results in the Appendices.", + "bbox": [ + 75, + 762, + 468, + 825 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Implementation Details", + "text_level": 1, + "bbox": [ + 76, + 832, + 294, + 848 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluation Metrics: We use Equal-Width Expected Calibration Error $\\left(\\mathrm{ECE}_{\\mathrm{EW}}\\right)$ [18] and Equal-Width Overconfidence Error $\\left(\\mathrm{OE}_{\\mathrm{EW}}\\right)$ [62] with 10 bins ( $B = 10$ ) to", + "bbox": [ + 75, + 854, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "evaluate the model calibration degrees. Additionally, we adopt $\\mathrm{ECE}_{\\mathrm{EM}}$ [48], $\\mathrm{ECE}_{\\mathrm{DEBIAS}}$ [29] and $\\mathrm{ECE}_{\\mathrm{Sweep}}$ [56] to corroborate with the results of $\\mathrm{ECE}_{\\mathrm{EW}}$ (See Appendix C).", + "bbox": [ + 496, + 90, + 890, + 136 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Datasets: The proposed methods are trained with the DUTS-TR [63] training dataset. It is divided into a training set $|\\mathcal{D}_{\\mathrm{TR}}| = 9,553$ and validation set $|\\mathcal{D}_{\\mathrm{VAL}}| = 1,000$ . We use six testing datasets, including DUTS-TE [63], DUTOMRON [80], SOD [44], PASCAL-S [34], ECSSD [78], HKU-IS [33], to evaluate the model calibration degree.", + "bbox": [ + 496, + 137, + 890, + 227 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Compared Methods: We compare with both SOD models and model calibration methods in terms of model calibration degrees. The SOD models include: MSRNet [32], SRM [65], Amulet [92], BMPM [91], DGRL [67], PAGR [93], PiCANet [37], CPD [73], BASNet [55], EGNet [94], AFNet [15], PoolNet [36], GCPANet [7], MINet [51], $\\mathrm{F}^3\\mathrm{Met}$ [69], EBMGSOD [89], ICON [97], EDN [72]. We evaluate ECE on their published prediction results, or results produced with their released model weights. We also compare with model calibration methods include: Temperature Scaling (TS) [18], Brier Loss [4], MMCE [30], Label Smoothing [46], Mixup [62], Focal Loss [45] and AdaFocal [17] implemented on our baseline model.", + "bbox": [ + 496, + 228, + 892, + 422 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Baseline Model Structure: We implement our method in the Pytorch framework. Our model has a simple U-Net structure, comprising of a ResNet50 encoder [20] and a decoder, where the former is initialised with ImageNet-pretrained weights and the later by default. We also experiment with VGG16 [58] and Swin transformer [39] encoders and report their results in Appendix I.", + "bbox": [ + 496, + 425, + 893, + 530 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Label Perturbation Techniques: We experiment with four different label perturbation strategies: (1) Hard Inversion $T(Y, \\alpha, \\beta = 1.0)$ , (2) Soft Inversion (SI) $T(Y, \\alpha, \\beta = 0.75)$ , (3) Moderation (M) $T(Y, \\alpha, \\beta = 0.5)$ and Dynamic Moderation (DM) $T(Y, \\alpha, \\beta = 0.5)$ with additional Gaussian noise. See Appendix H.1 for implementation details.", + "bbox": [ + 496, + 532, + 893, + 621 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Training Details: Each model is trained with an Adam optimiser for 30 epochs. The learning rate is initialised to $2.5 \\times 10^{-5}$ , and decays by a factor of 0.9 for each epoch after the $10^{\\text{th}}$ epoch. All training images are scaled to $384 \\times 384$ . Basic data augmentation techniques, including random flipping, random translation and random cropping, are applied.", + "bbox": [ + 496, + 623, + 890, + 712 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Hyperparameters: The reported model calibration results associated with ASLP are obtained by setting $\\eta = 0.002$ and $\\lambda = 2,000$ . We set the number of bins to $B = 10$ for ECE and OE evaluation metrics.", + "bbox": [ + 496, + 714, + 890, + 773 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Model Calibration Degree Performance", + "text_level": 1, + "bbox": [ + 496, + 786, + 841, + 801 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Tab. 1 presents the calibration degree of existing SOD models, existing model calibration methods and our proposed technique on the six SOD testing datasets. Our proposed $\\mathrm{ASLP}_{\\mathrm{MC}}$ , designed to optimise the model calibration degree, achieves the best ECE performances on all testing datasets. In addition, $\\mathrm{ASLP}_{\\mathrm{MC}}$ also obtains the second-best", + "bbox": [ + 496, + 809, + 893, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "1177", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/70c8882efecddcd13d3a995447955b546d83528dcd53d398296af00ff4d310b4.jpg", + "table_caption": [ + "Table 1: Salient object detection model calibration degree benchmark. Results are evaluated in with $\\mathrm{ECE}_{\\mathrm{EW}}$ and $\\mathrm{OE}_{\\mathrm{EW}}$ with 10 bins (units in %). See Appendix C for evaluations with $\\mathrm{ECE}_{\\mathrm{EM}}$ [48], $\\mathrm{ECE}_{\\mathrm{DEBIAS}}$ [29] and $\\mathrm{ECE}_{\\mathrm{SWEEP}}$ [56]." + ], + "table_footnote": [], + "table_body": "
MethodsYearDUTS-TE [63]DUT-OMRON [80]PASCAL-S [34]SOD [44]ECSSD [78]HKU-IS [33]
ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓
SOD MethodsMSRNet [32]20172.572.343.323.163.443.236.426.140.970.940.920.87
SRM [65]20174.023.724.193.964.884.599.939.582.532.351.861.72
Amulet [92]20175.675.285.845.495.765.4310.039.592.562.421.981.87
BMPM [91]20183.743.524.524.374.884.688.167.931.951.891.581.53
DGRL [67]20184.123.864.414.215.014.778.448.202.132.021.631.53
PAGR [93]20184.043.795.144.965.645.3712.1711.872.842.701.621.54
PiCANet [37]20185.124.904.844.708.147.9210.5010.303.483.392.552.47
CPD [73]20193.973.784.204.065.375.179.659.392.292.191.991.90
BASNet [55]20195.004.864.934.836.506.3610.4010.272.742.702.302.26
EGNet [94]20193.333.143.663.505.425.198.047.791.981.881.471.40
AFNet [15]20193.953.744.254.095.064.848.158.022.382.271.871.78
PoolNet [36]20193.333.123.863.705.325.078.147.872.001.901.821.75
GCPANet [7]20203.182.993.993.844.163.977.056.881.611.541.271.21
MINet [51]20203.653.484.454.294.944.758.017.892.132.031.741.65
F3Met [69]20203.673.504.254.104.854.677.957.782.262.161.921.83
EBMGSD [89]20213.453.294.113.954.794.617.487.302.142.051.791.70
ICON [97]20212.892.763.843.714.083.956.706.551.561.491.381.32
PFSNet [43]20212.942.723.953.814.454.277.597.392.412.252.061.96
EDN [72]20223.623.474.023.904.894.748.818.662.202.131.651.58
Model Calibration MethodsBrier Loss [4]19502.772.583.553.383.903.706.406.161.371.301.040.99
Temperature Scaling [18]20172.532.343.183.033.563.366.326.050.960.930.830.70
MMCE [30]20182.862.673.563.414.003.816.856.631.411.351.181.13
Label Smoothing [46]20192.001.792.892.713.042.835.975.690.830.680.820.47
Mixup [62]20192.452.253.413.233.132.995.825.701.410.183.830.05
Focal Loss [45]20202.252.083.102.823.403.136.215.981.411.031.240.77
AdaFocal [17]20221.611.412.311.842.532.275.885.471.630.791.350.52
Our MethodsASLPMC20231.401.221.991.832.312.105.505.170.480.200.790.17
ASLPMEI202327.90.0126.00.0026.10.0022.40.0029.90.0030.50.00
", + "bbox": [ + 98, + 128, + 870, + 508 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/9410c42d2da13b67128c4cb35468d0046b63752676d7fc85d22c22a7f53302a4.jpg", + "image_caption": [ + "Figure 3: Joint distribution of prediction confidence (horizontal axis) and prediction accuracy (vertical axis) on the DUTS-TE dataset. A perfectly calibrated model has an identical confidence distribution and accuracy distribution, denoted as the oracle (diagonal red dotted line). The joint distribution of a better calibrated model is more aligned with the oracle line, especially its high density area. See Appendix D for results of other methods and on other testing datasets." + ], + "image_footnote": [], + "bbox": [ + 117, + 526, + 233, + 713 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/50bf657d44382ec78932238038a5ae4db914d1223b88c52b5645234bd00bdf9b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 235, + 526, + 349, + 713 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/e64b3e51f8c95ac670f1ec4e1fe8177bf78f43667f12c450f01ce5d30b3c7d8a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 351, + 526, + 468, + 713 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/80add01356da9634d48a866bbce202fdf8df1142f7e85663727ee5f7d071f0ab.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 468, + 526, + 584, + 713 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/d7c6f5307d77f3b0fff7ec337a0b060588890d7aa1b0bc5a134350f06df8054b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 586, + 526, + 702, + 713 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/68bd1b189f642883122fd09858994ec2bf688b7e48b2074ff68fc3b398f342db.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 704, + 526, + 841, + 713 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "OE performances on all six testing datasets, outperformed only by our $\\mathrm{ASLP}_{\\mathrm{MEI}}$ . On the other hand, $\\mathrm{ASLP}_{\\mathrm{MEI}}$ , though almost eliminates the over-confidence issue completely, is significantly mis-calibrated on the six testing datasets. This can be attributed to it being significantly under-confident rather than over-confident. The observed performances of", + "bbox": [ + 75, + 808, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "$\\mathrm{ASLP}_{\\mathrm{MEI}}$ are in accordance with its design - assuming minimum distribution commitment with respect to missing information. That is, in the presence of limited training data, to maximise the prediction entropy while maintaining the prediction accuracy for in-distribution data.", + "bbox": [ + 496, + 809, + 890, + 883 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Fig. 3 presents the joint distribution of prediction con", + "bbox": [ + 517, + 885, + 890, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "1178", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "fidence and prediction accuracy of some of the best calibrated methods and our proposed technique on DUTS-TE dataset (See Appendix D for other testing datasets and other methods). Existing SOD methods produce extremely confident predictions whose confidence scores are nearly $100\\%$ for the majority of samples. On the contrary, the prediction accuracy is on average lower than prediction confidence, resulting in the model being over-confident. On the other hand, existing model calibration methods are generally more calibrated than the SOD methods which in general do not strive to improve model calibration degree.", + "bbox": [ + 75, + 90, + 472, + 257 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Our proposed $\\mathrm{ASLP}_{\\mathrm{MC}}$ produces the most calibrated model whose joint distribution is closer to the oracle than those of the compared calibration methods and SOD methods. AdaFocal [17] produces the second most calibrated model on DUTS-TE. However, the majority of their joint distribution (blue high density area) is slightly to the right bottom of the oracle line, making their model slightly less calibrated. Whereas the high density area of our joint distribution is well aligned with the oracle line, showing $\\mathrm{ASLP}_{\\mathrm{MC}}$ is more calibrated. Despite the small difference on the plot, $\\mathrm{ASLP}_{\\mathrm{MC}}$ improves over AdaFocal by more than $10\\%$ in terms of ECE scores on DUTS-TE dataset. We can also observe that $\\mathrm{ASLP}_{\\mathrm{MEI}}$ is significantly under-confident for in-distribution data with its joint distribution being at the top-left side of the oracle line. Its prediction accuracies are limited to between $70\\%$ and $80\\%$ while the prediction accuracies are generally above $90\\%$ .", + "bbox": [ + 75, + 258, + 472, + 517 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Model Calibration Degrees on Out-of-Distribution Dataset", + "text_level": 1, + "bbox": [ + 76, + 527, + 468, + 559 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We compare our proposed method with existing model calibration methods in terms of model calibration degrees on Out-of-Distribution data. We consider texture images, where salient objects are completely absent, as OoD samples for the SOD task. We use Describable Texture Dataset [9] to evaluate the model calibration degrees on OoD samples. Fig. 4 shows the joint distribution of prediction confidence and prediction accuracy of various model calibration methods and our proposed techniques. It can be seen that the baseline model produces extremely confident predictions for OoD data. However, its accuracy is only $41.88\\%$ , worse than a uniform prior in a binary classification task. We also observe that Temperature Scaling does not calibrate the model under data distribution shift in accordance with literature [50, 45]. Our $\\mathrm{ASLP}_{\\mathrm{MC}}$ , being the most calibrated for in-distribution data, is also more calibrated on the OoD samples than the existing model calibration methods by a large margin as shown in Tab. 2. On the other hand, our $\\mathrm{ASLP}_{\\mathrm{MEI}}$ is more successful in handling OoD data. It is the most calibrated on OoD data, with a larger proportion of the distribution aligned with the oracle line. As shown in Tab. 2, it outperforms existing model calibration methods in", + "bbox": [ + 75, + 568, + 472, + 902 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/94957d75b27cc1fe73e8a7e7b75f7d212ec8b1fbbf41ac0a16f900762c93a3bc.jpg", + "image_caption": [ + "Baseline" + ], + "image_footnote": [], + "bbox": [ + 501, + 93, + 625, + 183 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/04bffeb601ce457d981081628183ffe10a8740a52752c4dc01049605f0fd237c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 625, + 94, + 738, + 183 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/8d7f2f156db864f82a879ebecd61cd0ad2fc05a4b6cbc8efaa1745336e9d9045.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 740, + 94, + 852, + 185 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/5d389e1fa03afaec967c38fce82c3e7369a6bb3472be3f83cbaea3b362a2c9ef.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 501, + 196, + 624, + 282 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9336ff3df9dcae127395ab9299e047bd9e3f28e24b6eba42f38e39d5d1979cda.jpg", + "image_caption": [ + "Temperature Scaling" + ], + "image_footnote": [], + "bbox": [ + 624, + 196, + 738, + 282 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/dee80f765e09f345ed26eef071d41df902182ebae8cc4a7a9fc555b3e8db5f0a.jpg", + "image_caption": [ + "Label Smoothing" + ], + "image_footnote": [], + "bbox": [ + 740, + 196, + 852, + 282 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e1dce49e24d7a192a85d363eda14030745b9586649aa9f5c7cde5c8fa44938d7.jpg", + "image_caption": [ + "Mixup", + "AdaFocal", + "Figure 4: Joint distribution of prediction confidence (horizontal axis) and prediction accuracy (vertical axis) on the Describable Texture Dataset [9], of compared model calibration methods and our proposed $\\mathrm{ASLP}_{\\mathrm{MC}}$ and $\\mathrm{ASLP}_{\\mathrm{MEI}}$ ." + ], + "image_footnote": [], + "bbox": [ + 501, + 296, + 624, + 383 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/ade4a26ca3956a305430ec102b0f4a04037f1222991fef0ffb21875a862c2354.jpg", + "image_caption": [ + "MMCE", + "ASLPMEMI" + ], + "image_footnote": [], + "bbox": [ + 624, + 296, + 738, + 383 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/28a0889fb08ca638fc57d5ee3b235b98532fd279c7a088972f9de3a9f4e612fe.jpg", + "image_caption": [ + "Focal Loss", + "ASLPMC" + ], + "image_footnote": [], + "bbox": [ + 740, + 296, + 852, + 383 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "terms of both ECE and OE by significant margins. This can be attributed to its minimum distribution assumption in the presence of limited training data.", + "bbox": [ + 496, + 482, + 890, + 527 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/9da15646b0fa041ddd2db4605841bbfa798aaec1ae0e956a66f9e7e6c1aeaf8d.jpg", + "table_caption": [ + "Table 2: Model calibration methods and our $\\mathrm{ASLP}_{\\mathrm{MC}}$ and $\\mathrm{ASLP}_{\\mathrm{MEI}}$ are evaluated on the Out-of-Distribution dataset, Describable Texture Dataset [9], in terms of $\\mathrm{ECE}_{\\mathrm{EW}}$ and $\\mathrm{OE}_{\\mathrm{EW}}$ with 10 bins, and Accuracy (ACC)." + ], + "table_footnote": [], + "table_body": "
MethodEvaluation (%)
ECE ↓OE ↓ACC ↑
Baseline52.3651.0541.88
Brier Loss [4]38.8537.1853.62
Temperature Scaling [18]51.9550.4641.59
Label Smoothing [46]37.2235.4855.41
MMCE [30]40.6439.6754.39
Mixup [62]31.0729.1058.71
Focal Loss [45]40.0138.4349.71
AdaFocal [17]27.5525.0755.39
ASLPMC18.3116.3761.93
ASLPMEI13.438.4062.47
", + "bbox": [ + 524, + 606, + 866, + 768 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Discussion", + "text_level": 1, + "bbox": [ + 500, + 785, + 617, + 799 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Adaptive Stochastic Label Perturbation: We study the effect of ASLP on ECE and OE and present the experimental results in Tab. 3. It shows that ASLPs significantly outperforms the baseline model, \"B\", which does not adopt any model calibration measures. In addition, ASLPs also outperforms their static counterparts (SLPs) which use a single", + "bbox": [ + 496, + 809, + 890, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "1179", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/8116d9571cebfab9471ca002b5de9edc149d130917748ef64d216557b64c6c7b.jpg", + "table_caption": [ + "Table 3: Ablation: Effect of Stochastic Label Perturbation (SLP) and Adaptive Stochastic Label Perturbation (ASLP) with different label perturbation techniques on the model calibration degrees evaluated on Expected Calibration Error (ECE) and Over-confidence Error (OE). The proposed ASLP is generalised to an Adaptive Label Smoothing (ALS) technique that adaptively tunes the label softening scale $(\\beta_{\\mathrm{ada}})$ ." + ], + "table_footnote": [], + "table_body": "
MethodsPerturbation ParamsDUTS-TE [63]DUT-OMRON [80]PASCAL-S [34]SOD [44]ECSSD [78]HKU-IS [33]
αβeECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓
Baseline (“B”)0003.483.294.174.024.604.417.427.171.931.861.641.59
SLPα=0.01HI0.011.0X2.211.842.962.783.112.826.095.801.030.681.010.53
SLPα=0.02SI0.020.75X2.252.053.002.823.052.836.406.090.930.840.870.60
SLPα=0.03M0.030.5X2.242.033.172.973.413.206.265.970.830.770.960.81
SLPα=0.03DM0.030.5✓2.292.093.002.833.473.246.726.431.131.040.960.80
LSβ=0.031.00.03X2.201.993.092.913.243.036.275.991.030.780.920.67
ASLPHIαada1.0X1.401.221.991.832.312.105.505.170.480.200.790.17
ASLPSIαada0.75X1.511.292.141.952.292.075.124.800.610.340.840.22
ASLPMαada0.5X1.471.271.871.802.372.135.635.290.510.230.800.20
ASLPMCMαada0.5✓1.641.201.941.752.031.814.143.840.800.420.870.42
ALS1.0βadaX1.461.252.071.872.302.105.445.180.610.250.810.32
", + "bbox": [ + 117, + 152, + 849, + 314 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "$\\alpha$ for the entire dataset. This can be attributed to the approach modelling variance of noise with input image.", + "bbox": [ + 75, + 327, + 468, + 357 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Generalisation of Adaptive Label Smoothing: We generalise the proposed ASLP to label smoothing, developing an Adaptive Label Smoothing (ALS) that fixes the label perturbation probability to $100\\%$ , akin to the label smoothing technique [46], and tunes a smoothing factor for each training sample. As shown in Tab. 3, ALS effectively reduces the ECE and OE scores over its static version $\\mathrm{LS}^{\\beta = 0.03}$ , and achieves similar performances with $\\mathrm{ASLP}_{\\mathrm{MC}}$ approaches on the six testing datasets. It manifests that our proposed ASLP can be generalised onto other label perturbation techniques as a measure to calibrate the SOD models.", + "bbox": [ + 75, + 359, + 468, + 523 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Compatibility with SOTA SOD Models We retrain EBMGSOD [89], ICON [97] and EDN [72] with the proposed $\\mathrm{ASLP}_{\\mathrm{MC}}$ and find significant improvements in terms of model calibration degrees without compromising their classification abilities (See Appendix E).", + "bbox": [ + 75, + 525, + 468, + 602 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Compatibility with Different Backbones: We demonstrate that our proposed method is also compatible with VGG16 [58] and Swin transformer [39] backbones. See Appendix I for details.", + "bbox": [ + 75, + 603, + 468, + 662 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effectiveness in Other Dense Binary Classification Tasks: Experiments on Smoke Detection [79] and Camouflaged Object Detection [14] demonstrate that our method can be generalised to dense binary classification tasks to improve model calibration degrees. See Appendix F.", + "bbox": [ + 75, + 664, + 468, + 739 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Generalisation to Multi-Class Segmentation task: Experiments on Semantic Segmentation [11] demonstrate that our method can also be generalised to dense multi-class classification tasks. See Appendix G.", + "bbox": [ + 75, + 741, + 468, + 801 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Hyperparameters", + "text_level": 1, + "bbox": [ + 76, + 815, + 250, + 832 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Static Stochastic Label Perturbation: Tab. 3 shows that, under a small label perturbation probability, the four label perturbation techniques can alleviate the model overconfidence issues of the baseline model, \"B\", on the six", + "bbox": [ + 75, + 839, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "testing datasets. They also achieve similar results to Label Smoothing [46], setting $\\beta = 0.03$ and $\\alpha = 1$ . Each SLP has a wide range of effective label perturbation probabilities that improves model calibrations (See Appendix H.2 Tab. 13), and these improvements do not sacrifice the model's classification performance (see Appendix H.3). Larger values of the label perturbation probability eventually lead to increasing ECE scores as the model transitions to being under-confident (see Appendix H.2).", + "bbox": [ + 496, + 327, + 890, + 463 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Updating Rate $\\eta$ : $\\mathrm{ASLP}_{\\mathrm{MC}}$ models trained with $\\eta \\in [0.0002, 0.005]$ are generally stable, producing similar calibration degrees and classification performances. Values smaller than 0.001 require longer training and high values lead to sub-optimal results (See Appendix J).", + "bbox": [ + 496, + 463, + 890, + 537 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Regularisation Strength $\\lambda$ : $\\lambda$ spanning between 500 and 10,000 are optimal. Very high values for $\\lambda$ can lead to oscillation resulting in poor performance (See Appendix J).", + "bbox": [ + 496, + 537, + 890, + 584 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 595, + 617, + 612 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work first introduces a Self-Calibrating Binary Cross Entropy loss that unifies label perturbation processes including stochastic approaches and label smoothing to improve model calibration while preserving classification accuracy. We further propose an Adaptive Stochastic Label Perturbation that learns a unique label perturbation level for individual training image. Following Maximum Entropy Inference, ASLP adopts classification / calibration as proxy for known data and maximises the prediction entropy with respect to missing data. The proposed $\\mathrm{ASLP}_{\\mathrm{MC}}$ improves model calibration degrees on both in-distribution samples and out-of-distribution samples, without negatively impacting classification performance. The approach can be easily applied to different models, which we demonstrate with several SOTA models. It is also demonstrated to be effective on a semantic segmentation task and other binary tasks.", + "bbox": [ + 496, + 622, + 890, + 864 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments. This research was in-part supported by the ANU-Optus Bushfire Research Center of Excellence.", + "bbox": [ + 500, + 872, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "1180", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Radhakrishna Achanta, Sheila Hemami, Francisco Estrada, and Sabine Susstrunk. Frequency-tuned salient region detection. In CVPR, pages 1597-1604. IEEE, 2009. 2", + "[2] Gorkem Algan and Ilkay Ulusoy. Image classification with deep learning in the presence of noisy labels: A survey. 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IEEE TPAMI, 2022. 5, 6, 8, 20, 21, 22, 27" + ], + "bbox": [ + 78, + 90, + 468, + 246 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "1184", + "bbox": [ + 483, + 945, + 514, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/7e446bd7-c368-40d4-8d81-6aee3f5055e8_model.json b/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/7e446bd7-c368-40d4-8d81-6aee3f5055e8_model.json new file mode 100644 index 0000000000000000000000000000000000000000..c9c1e020a78e46a9a7308fcdc6f19c8624ca5ef9 --- /dev/null +++ b/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/7e446bd7-c368-40d4-8d81-6aee3f5055e8_model.json @@ -0,0 +1,2798 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.101, + 0.131, + 0.87, + 0.152 + ], + "angle": 0, + "content": "Model Calibration in Dense Classification with Adaptive Label Perturbation" + }, + { + "type": "text", + "bbox": [ + 0.098, + 0.181, + 0.872, + 0.218 + ], + "angle": 0, + "content": "Jiawei Liu Changkun Ye Shan Wang Ruikai Cui Jing Zhang Kaihao Zhang Nick Barnes The Australian National University" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.252, + 0.314, + 0.267 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.284, + 0.474, + 0.661 + ], + "angle": 0, + "content": "For safety-related applications, it is crucial to produce trustworthy deep neural networks whose prediction is associated with confidence that can represent the likelihood of correctness for subsequent decision-making. Existing dense binary classification models are prone to being over-confident. To improve model calibration, we propose Adaptive Stochastic Label Perturbation (ASLP) which learns a unique label perturbation level for each training image. ASLP employs our proposed Self-Calibrating Binary Cross Entropy (SC-BCE) loss, which unifies label perturbation processes including stochastic approaches (like DisturbLabel), and label smoothing, to correct calibration while maintaining classification rates. ASLP follows Maximum Entropy Inference of classic statistical mechanics to maximise prediction entropy with respect to missing information. It performs this while: (1) preserving classification accuracy on known data as a conservative solution, or (2) specifically improves model calibration degree by minimising the gap between the prediction accuracy and expected confidence of the target training label. Extensive results demonstrate that ASLP can significantly improve calibration degrees of dense binary classification models on both in-distribution and out-of-distribution data. The code is available on https://github.com/Carlisle-Liu/ASLP." + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.693, + 0.21, + 0.708 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.719, + 0.47, + 0.884 + ], + "angle": 0, + "content": "Binary segmentation aims to differentiate foreground areas from the background in images. Its tasks include Salient Object Detection [86], Camouflaged Object Detection [13], Smoke Detection [79], etc. Performance in these tasks has been significantly advanced using the strong representation powers of Deep Neural Networks (DNNs). However, with complex structures and a tremendous number of parameters, DNNs are prone to over-fitting to training data and producing over-confident predictions in the real world [18]. Such issues can render the model predictions unreliable in decision making or utilisation in downstream tasks." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Recently, a growing body of literature has been pro" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.25, + 0.882, + 0.378 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.383, + 0.895, + 0.52 + ], + "angle": 0, + "content": "Figure 1: Applying Adaptive Label Perturbation during training can effectively moderate predictions at incorrect areas, highlighting them with high entropy values (red). \\( Z_{t}(x,y) \\) is a sample-wise Bernoulli variable, parameterized by \\( \\alpha \\), at the \\( t^{\\mathrm{th}} \\) iteration. After \\( k \\) iterations, update \\( \\alpha \\) using Eq. (5) to adjust the likelihood (or level) of label perturbation to increase entropy for incorrect predictions and so correct model calibration. The Perturbed Label (shown inverted) replaces the Groundtruth Label with probability \\( \\alpha \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.537, + 0.895, + 0.719 + ], + "angle": 0, + "content": "posed to address model mis-calibration problems in DNNs. They can be roughly categorised as: (1) post-hoc operations, such as temperature scaling [18], Platt scaling [54], etc., (2) training objective approaches [27], like MMCE [30], soft calibration objective [27], focal loss [45, 17], and (3) data/label augmentation techniques, e.g. label smoothing [46] and mixup [85]. We propose an Adaptive Label Perturbation which learns a unique label perturbation level for each training image. As illustrated in Fig. 1, training with Adaptive Stochastic Label Perturbation, a form of ALP, can effectively moderate incorrect predictions and highlight them with high entropy values." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.896, + 0.902 + ], + "angle": 0, + "content": "Adaptive Label Perturbation employs our proposed Self-Calibrating Binary Cross Entropy (SC-BCE) loss, which unifies label perturbation processes including stochastic approaches (like DisturbLabel [75]), and label smoothing [60] to correct calibration while maintaining classification accuracy. SC-BCE loss is equivalent to a factored combination of (i) a BCE loss w.r.t. groundtruth label, and (ii) a BCE loss w.r.t. a uniform binary categorical distribution. The former enhances dense binary classification performance and the latter improves the model calibration degree. Our method can be connected to Maximum Entropy Inference [23] of classic statistical mechanics, to maximise prediction" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1173" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.468, + 0.121 + ], + "angle": 0, + "content": "entropy with respect to missing information while preserving the classification accuracy on known data." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.122, + 0.468, + 0.332 + ], + "angle": 0, + "content": "The proposed Adaptive Label Perturbation (ALP) can approximate Maximum Entropy Inference [23] to maximise prediction entropy while preserving the ideal dense classification performance on known data. This represents a conservative solution that adopts classification accuracy as a proxy for known data and assumes maximum disorder on unknown data. We also present an alternative ALP solution that, instead, takes model calibration degree as a proxy for known data, using a calibration regulariser which constrains the expected confidence of individual supervision signal to not drop below the ideal accuracy on the validation set. This effectively minimises the gap between the distributions of prediction confidence and prediction accuracy, which is the source of model mis-calibration." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.333, + 0.468, + 0.59 + ], + "angle": 0, + "content": "Our contributions can be summarised as: (i) We propose Adaptive Stochastic Label Perturbation that learns a sample-wise label perturbation level to improve model calibration; (ii) We present a Self-Calibrating Binary Cross Entropy loss that unifies label perturbation processes including stochastic approaches and label smoothing; (iii) Following Maximum Entropy Inference [23] we show that Adaptive Stochastic Label Perturbation \\((\\mathrm{ASLP}_{\\mathrm{MEI}})\\), can maximise the prediction entropy while preserving the ideal dense classification accuracy, and (iv) We present an alternative Adaptive Stochastic Label Perturbation \\((\\mathrm{ASLP}_{\\mathrm{MC}})\\) solution to maximise model calibration degree, which achieves state-of-the-art performance in terms of model calibration degree on both in-distribution and out-of-distribution data. We thoroughly evaluate our method on Salient Object Detection and demonstrate its effectiveness for Camouflaged Object Detection, Smoke Detection and Semantic Segmentation." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.604, + 0.227, + 0.62 + ], + "angle": 0, + "content": "2. Related Works" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.468, + 0.765 + ], + "angle": 0, + "content": "Model Calibration: Model calibration methods can be roughly divided into three categories of approach: (1) post hoc processing (2) training object, and (3) input/label augmentation. The first category utilises a validation set to align the prediction confidence distribution with prediction accuracy distribution. It includes histogram binning [82], isotropic regression [83], Platt scaling [54, 49], Bayesian binning into quantiles [47], Dirichlet scaling [28], mix-n-match [87] and temperature scaling [18, 81]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.766, + 0.468, + 0.902 + ], + "angle": 0, + "content": "The second category focuses on designing training objectives that (in)directly improve model calibration degree. Some methods address the in-continuity of expected calibration error, a widely adopted model calibration measure, and propose trainable calibration objectives like maximum mean calibration error [30], soft calibration objective [27]. Other works discover that certain existing training objects are beneficial to model calibration, e.g. Brier loss [4, 10], confidence penalty [52] and focal loss [45, 17]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.198 + ], + "angle": 0, + "content": "The third category employs data or label augmentation techniques to regularise the prediction confidence distribution. Mixup [85, 62] explores the neighbourhood of training data through random interpolation of input images and associated labels to improve model calibration degree. Label smoothing [46] augments the one-hot training labels with softer versions to prevent the model being over-confident." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.2, + 0.892, + 0.426 + ], + "angle": 0, + "content": "Salient Object Detection: Inspired by pioneering work [22], traditional Saliency Object Detection (SOD) methods rely on various heuristic priors with handcraft features to explore low-level cures [1, 25, 26, 38, 66]. However, these methods cannot cope with complex scenes because of the limited representation ability of handcrafted features [3]. Recently, deep learning based SOD methods broke the bottleneck of traditional methods due to the powerful capability of neural networks, achieving improved performance [6, 24, 55, 76, 37, 64, 68]. Early deep SOD methods use multi-layer perception to predict a map with a pixel-wise score for each image [71, 8]. These approaches rely on fixed fully connected layers and thus severely limit the ability of spatial information extraction. Later methods address this issue via using fully convolutional networks (FCNs) [40]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.429, + 0.892, + 0.625 + ], + "angle": 0, + "content": "Most contemporary SOD methods are designed based on FCNs with various schemes to improve performance. One of the most popular strategies is to fuse multi-scale information extracted from different layers and aggregate them in the network [91, 74, 16, 51, 96, 90]. Attention modules are also applied to capture powerful multi-scale features via exploring relationship between local and global information [37, 53, 95, 21]. Training SOD networks using auxiliary supervision is also a popular strategy [70, 70, 61]. For example, the body map and detail map are utilized by [70] to help the network focus on center areas and edges, respectively. Skeleton [35] and uncertainty [61] are applied to the training processing due to their important roles in taking photos." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.627, + 0.892, + 0.778 + ], + "angle": 0, + "content": "Noisy Label: Noisy labels refer to incorrect ground truth classes/values in classification/regression tasks. They arise from data collection or annotation processes, and exist commonly in real-world datasets [2]. Efforts are put to identify the noisy labels and exclude them from network training in various computer vision tasks, deeming their incorporation as harmful. [88] proposes a framework that learns from noisy labels, being a collection of predictions from classic SOD methods. The framework approximates the noise distribution in order to recover clean labels for model training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Differently from data augmentation techniques that are applied simultaneously to training samples and corresponding labels to generate more training data, one may artificially corrupt the label. We refer to this category of approaches as label perturbation, which includes label smoothing approaches [60], and DisturbLabel, Xie et al. [75]. In image classification, Xie et al. [75] shows that randomly replacing training labels with a prior distribution" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "1174" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.184 + ], + "angle": 0, + "content": "leads to a regularising effect, preventing overfitting. Our work is different from [75] by employing labels corrupted to different scales to enhance the model calibration degrees for both in-distribution and out-of-distribution data. Further, in performing this, we assume noise that varies with different samples, making our method more adaptable." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.197, + 0.251, + 0.213 + ], + "angle": 0, + "content": "3. Proposed Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.222, + 0.47, + 0.299 + ], + "angle": 0, + "content": "We first lay out the task setting in Sec. 3.1. Then we introduce our proposed Self-Calibrating Binary Cross Entropy loss in Sec. 3.2 and prove its connection to Maximum Entropy Inference [23] in Sec. 3.3. Lastly, we detail our major contribution - Adaptive Label Perturbation in Sec. 3.4." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.308, + 0.21, + 0.325 + ], + "angle": 0, + "content": "3.1. Task Setting" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.331, + 0.473, + 0.635 + ], + "angle": 0, + "content": "Binary segmentation problems aim to differentiate between foreground object(s) and background. They can be formulated as a pixel-wise binary classification problem. Given an independent and identically distributed (i.i.d) training dataset \\(\\mathcal{D}_{\\mathrm{TR}} = \\{x_i,y_i\\}_{i = 1}^N\\) drawn from an unknown joint distribution of training images and groundtruth labels \\(P(\\mathcal{X},\\mathcal{Y})\\), a neural network model parameterised by \\(\\theta\\) is employed to predict labels for an input image \\(x\\in \\mathcal{X}\\): \\(f_{\\theta}(x)\\in (0,1)^{1\\times H\\times W}\\). We use \\(\\hat{y}\\) and \\(P_{\\hat{y}}\\) to denote the winning class and its associated probability respectively. The groundtruth label \\(y\\in \\{0,1\\}^{1\\times H\\times W}\\) represents the foreground pixels with \"1\" and background with \"0\". In the following equations, we omit the spatial indexes \\(H\\) and \\(W\\) for simplicity. A perfectly calibrated model has \\(\\mathrm{P}(\\hat{y} = y|P_{\\hat{y}}) = P_{\\hat{y}},\\forall P_{\\hat{y}}\\in (0,1)\\). That is, in the entire range of prediction probabilities, prediction with probability \\(P_{\\hat{y}}\\) has exactly \\(P_{\\hat{y}}\\) chance to be correct. The calibration degree of a model \\(f_{\\theta}(\\cdot)\\) over a distribution \\(\\mathcal{D}\\) is quantified with Expected Calibration Error (ECE), defined as \\(\\mathbb{E}_{f_{\\theta}(x)}[|\\mathrm{P}(\\hat{y} = y|f_{\\theta}(x)) - f_{\\theta}(x)|]\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.643, + 0.45, + 0.661 + ], + "angle": 0, + "content": "3.2. Self-Calibrating Binary Cross Entropy Loss" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.667, + 0.47, + 0.713 + ], + "angle": 0, + "content": "We propose a Self-Calibrating Binary Cross Entropy (SC-BCE) loss that unifies Label Smoothing [60], DisturbLabel [75] and Stochastic Label Perturbation as:" + }, + { + "type": "equation", + "bbox": [ + 0.126, + 0.725, + 0.469, + 0.797 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {L} _ {\\mathrm {S C - B C E}} (\\theta , X, Y, \\alpha , \\beta) \\\\ = \\mathbb {E} _ {x, y \\in X, Y} \\left[ \\left(1 - Z _ {t} (x, y)\\right) \\cdot \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x, y) \\right. \\\\ \\left. + Z _ {t} (x, y) \\cdot \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x, p (y, \\beta)) \\right] \\tag {1} \\\\ \\end{array}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.137, + 0.8, + 0.3, + 0.83 + ], + "angle": 0, + "content": "\\[\n\\beta \\in [ 0, 2 ], \\quad \\alpha \\in [ 0, \\frac {1}{\\beta}),\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.902 + ], + "angle": 0, + "content": "where \\( Z_{t}(x,y) \\sim B(1,\\alpha) \\) follows a Bernoulli distribution with \\( \\alpha \\) probability to be 1 and \\( 1 - \\alpha \\) chance to be 0, \\( t \\) denotes the training epoch, \\( \\alpha \\in [0,\\frac{1}{\\beta}) \\) and \\( \\beta \\in [0,2] \\) are Label Perturbation Probability (LPP) and Label Perturbation Strength" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.09, + 0.892, + 0.274 + ], + "angle": 0, + "content": "(LPS) respectively, \\(p(y,\\beta) = (1 - \\beta)\\cdot y + \\frac{\\beta}{2},\\beta \\in [0,2]\\) is a perturbed label and \\(\\mathcal{L}_{\\mathrm{BCE}}(\\theta ,x,y)^1\\) is a Binary Cross Entropy (BCE) loss computed for training pair \\((x,y)\\). For \\(\\alpha = 1\\), the label perturbation equation follows the label smoothing equation for a binary label [60]. In the proposed SC-BCE loss, different label perturbations can be applied by setting (i) Label Smoothing [60]: \\(\\alpha = 1\\) and \\(\\beta \\in [0,1)\\), (2) DisturbLabel: \\(\\beta = 1\\) and \\(\\alpha \\in (0,1)\\), and (3) Stochastic Label Perturbation (SLP): \\(\\beta \\in (0,2]\\) and \\(\\alpha \\in (0,\\frac{1}{\\beta})\\). For example, Hard Inversion (HI) that inverts the label category as shown in Fig. 2, can be stochastically applied by setting \\(\\beta = 2\\) and \\(\\alpha \\in (0,\\frac{1}{2})\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.276, + 0.892, + 0.504 + ], + "angle": 0, + "content": "In the implementation of SLP, the supervision for an individual training image in each epoch is sampled by drawing from a Bernoulli distribution. That is, the individual supervision can take the form of the groundtruth label or perturbed label in each training iteration. The overall function of SLP can be connected to that of a smoothed label by taking expectation of the Bernoulli variable: \\(\\mathbb{E}_{Z_t}[(1 - Z_t(y))\\cdot Y + Z_t(y)\\cdot p(y,\\beta)],\\forall y\\in Y.\\) Taking the expectation over the Bernoulli variation in each iteration is too expensive to implement in model training. Instead, following [75], the expectation of stochastically perturbed label is approximated by taking expectation across training epochs: \\(\\mathbb{E}_{t\\in T}[(1 - Z_t(y))\\cdot Y + Z_t(y)\\cdot p(y,\\beta)],\\forall y\\in Y,\\) where \\(T\\) is the total number of training epochs and \\(Z_{t}(y)\\) is a variable drawn from a Bernoulli distribution for the \\(\\mathrm{t^{th}}\\) epoch." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.522, + 0.763, + 0.539 + ], + "angle": 0, + "content": "3.3. Maximum Entropy Inference" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.549, + 0.892, + 0.656 + ], + "angle": 0, + "content": "Maximum Entropy Inference (MEI), assuming minimum distribution commitment in respect to missing information, was initially proposed by Jaynes [23]. That is, the probability distribution should have maximum Shannon entropy subject to the partially available information. Thus, in the complete absence of information, Shannon entropy for a binary prediction defined in Eq. (2) should be maximised:" + }, + { + "type": "equation", + "bbox": [ + 0.517, + 0.686, + 0.892, + 0.739 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathbb {H} \\left(f _ {\\theta} (X)\\right) = \\mathbb {E} _ {x \\in X} \\left[ - f _ {\\theta} (x) \\cdot \\log f _ {\\theta} (x) - \\right. \\tag {2} \\\\ \\left. \\left(1 - f _ {\\theta} (x)\\right) \\cdot \\log \\left(1 - f _ {\\theta} (x)\\right) \\right\\rfloor \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.756, + 0.892, + 0.8 + ], + "angle": 0, + "content": "For salient object detection and other binary segmentation problems, maximising Eq. (2) can be achieved with a binary uniform categorical distribution." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.804, + 0.892, + 0.866 + ], + "angle": 0, + "content": "The proposed SC-BCE loss can be transformed into a factored combination of a BCE loss w.r.t. groundtruth label (the constraints of the data) and a BCE loss w.r.t. a binary uniform categorical distribution (See Appendix A.2 for" + }, + { + "type": "page_footnote", + "bbox": [ + 0.518, + 0.887, + 0.864, + 0.902 + ], + "angle": 0, + "content": "\\(^{1}\\) \\(\\mathcal{L}_{\\mathrm{BCE}}(\\theta, x, y) = -y \\cdot \\log(f_{\\theta}(x)) - (1 - y) \\cdot \\log(1 - f_{\\theta}(x))\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1175" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.116, + 0.089, + 0.505, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.51, + 0.089, + 0.653, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.654, + 0.089, + 0.848, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.119, + 0.191, + 0.297, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "table", + "bbox": [ + 0.298, + 0.192, + 0.477, + 0.299 + ], + "angle": 0, + "content": "
L BCE(θ, x_i, p(y_i, β)) - L BCE(θ, x_i, y_i)∇αi
>0>0
=0=0
<0<0
" + }, + { + "type": "table", + "bbox": [ + 0.482, + 0.191, + 0.692, + 0.299 + ], + "angle": 0, + "content": "
Regularisation
A(θ, DVAL) - A(θlm, DVAL) or (1 - β · αi2) - A(θlm, DVAL)Regularisation
> 0= 0
= 0= 0
< 0< 0
" + }, + { + "type": "table", + "bbox": [ + 0.696, + 0.191, + 0.845, + 0.299 + ], + "angle": 0, + "content": "
ASLP - Learning Rule
∇αi+λ·RegularisationΔαi
>0>0
=0=0
<0<0
" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.304, + 0.892, + 0.381 + ], + "angle": 0, + "content": "Figure 2: The method overview is comprised of model implementation (top) and Adaptive Stochastic Label Perturbation (ASLP) learning rule (bottom). In each iteration, the model uses a Bernoulli variable to sample a supervision, which can be a groundtruth label \\( y_{i} \\) or a perturbed label \\( p_i \\) and computes a sample-specific \\( \\nabla_{\\alpha_i} \\) based on the prediction. Regularisation is computed with Eq. 5 (ASLPMEI) or Eq. 6 (ASLPMC) on a validation set after each training epoch. The ASLP learning rule combines Grad- \\( \\alpha_{i} \\) and a factored regularisation to update label perturbation probability \\( \\alpha_{i} \\) for each individual sample." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.395, + 0.175, + 0.409 + ], + "angle": 0, + "content": "derivation) as:" + }, + { + "type": "equation", + "bbox": [ + 0.128, + 0.421, + 0.469, + 0.495 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {L} _ {\\mathrm {S C - B C E}} (\\theta , X, Y, \\alpha , \\beta) \\\\ = \\mathbb {E} _ {x, y \\in X, Y} \\left[ (1 - \\beta Z _ {t} (x, y)) \\cdot \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x, y) \\right. \\tag {3} \\\\ \\left. + \\beta Z _ {t} (x, y) \\cdot \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x, u) \\right], \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.506, + 0.47, + 0.687 + ], + "angle": 0, + "content": "where \\( Z_{t}(x,y) \\sim B(1,\\alpha) \\), \\( u \\) is a binary uniform categorical distribution, and minimising the second term pushes the prediction distribution towards a uniform binary categorical distribution, equivalently maximising the inference entropy. Therefore, our proposed SC-BCE loss, a combination of a regular BCE loss and a BCE loss with a perturbed label, effectively performs a type of MEI. That is, the regular BCE loss component improves the model's binary classification accuracy in the presence of information while the perturbed label maximizes prediction entropy with respect to missing information in order to close the gap between the available training data and the entire data distribution." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.698, + 0.336, + 0.714 + ], + "angle": 0, + "content": "3.4. Adaptive Label Perturbation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.721, + 0.468, + 0.872 + ], + "angle": 0, + "content": "Stochastic Label Perturbation (SLP) uses a single label perturbation probability and perturbation strength for the entire training dataset. However, this approach cannot adapt to predictive error that varies for different input images. To address this, we propose an Adaptive Stochastic Label Augmentation (ASLP) method to adjust the label augmentation probability for individual training samples. That is we allow the variable in Eq. (1) to be drawn from a per training image Bernoulli distribution with sample-specific label perturbation probability as:" + }, + { + "type": "equation", + "bbox": [ + 0.148, + 0.885, + 0.469, + 0.903 + ], + "angle": 0, + "content": "\\[\nZ _ {t} (x, y) \\sim B (1, \\alpha_ {x, y}), \\forall x, y \\in X, Y \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.394, + 0.892, + 0.56 + ], + "angle": 0, + "content": "where \\(\\alpha_{x,y}\\) is the label perturbation probability for sample (image-label) pair \\((x,y)\\). Initially, we set all label perturbation probabilities to \\(\\{\\alpha_{i} = 0\\}_{i = 1}^{N}\\) and train a model with a regular BCE loss without label augmentation techniques, which is equivalent to \\(\\mathcal{L}_{\\mathrm{SC - BCE}}(\\theta ,X,Y,\\alpha = 0,\\beta = 0)\\). The trained model has weight \\(\\theta_{\\mathrm{lm}}\\) and its accuracy on the validation set, \\(\\mathbb{A}(\\theta_{lm},\\mathcal{D}_{\\mathrm{VAL}})\\), is held as an ideal performance. Subsequently, we select a label perturbation technique and continue to train the model with SC-BCE loss with a learning rule to update the label perturbation probability for individual training samples." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.561, + 0.892, + 0.713 + ], + "angle": 0, + "content": "We propose the learning rule for \\(\\alpha\\), \\((\\mathrm{ASLP}_{\\mathrm{MEI}})\\) to approximate maximum entropy inference. The rule has two components: (1) \\(\\nabla_{\\alpha_i} = (2 / \\beta)\\cdot\\) \\(\\partial \\mathbb{E}_{Z_t}(x_i,y_i)\\big[\\mathcal{L}_{\\mathrm{SC - BCE}}(X,Y,\\theta ,\\{\\alpha_i\\}_{i = 1}^N,\\beta)\\big] / \\partial \\alpha_i\\) is the derivative of the expectation of SC-BCE over the Bernoulli variable w.r.t. \\(\\alpha_{i}\\). We divide this by \\(\\beta /2\\) to ensure that different perturbation techniques (varying \\(\\beta\\) values) have the same convergence speed (See derivation in Appendix A.3), and (2) Accuracy Regularization to encourage maintenance of prediction accuracy. The rule is:" + }, + { + "type": "equation", + "bbox": [ + 0.506, + 0.723, + 0.885, + 0.777 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\alpha_ {i} ^ {n + 1} = \\alpha_ {i} ^ {n} + \\eta \\cdot \\left(\\nabla_ {\\alpha_ {i}} + \\lambda \\cdot \\operatorname {R e g} _ {A}\\right), \\quad \\text {f o r} i = 1, \\dots , N, \\\\ \\nabla_ {\\alpha_ {i}} = \\frac {2 \\cdot \\left(\\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x _ {i} , p (y _ {i} , \\beta)) - \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x _ {i} , y _ {i})\\right)}{\\beta}, \\\\ \\end{array}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.507, + 0.78, + 0.891, + 0.825 + ], + "angle": 0, + "content": "\\[\n\\operatorname {R e g} _ {\\mathrm {A}} = \\min \\left(\\frac {\\mathbb {A} (\\theta , \\mathcal {D} _ {\\mathrm {V A L}}) - \\mathbb {A} (\\theta_ {l m} , \\mathcal {D} _ {\\mathrm {V A L}})}{\\mathbb {A} (\\theta_ {l m} , \\mathcal {D} _ {\\mathrm {V A L}})}, 0\\right), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.902 + ], + "angle": 0, + "content": "where \\(\\eta\\) and \\(\\lambda\\) are hyperparameters controlling the updating pace of label perturbation probability and the regularisation strength respectively, \\(\\mathbb{A}(\\theta ,\\mathcal{D}_{\\mathrm{VAL}})\\) and \\(\\mathbb{A}(\\theta_{lm},and\\mathcal{D}_{\\mathrm{VAL}})\\) denote the current and ideal accuracy on the validation set separately. \\(\\nabla_{\\alpha_i}\\) aims to increase label perturbation proba" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1176" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.422 + ], + "angle": 0, + "content": "bility to confident and correct samples and otherwise for incorrectly classified samples. For example, it returns a large positive value for correct predictions with small BCE loss value w.r.t. to groundtruth label \\( y_{i} \\) and large BCE loss value w.r.t. to perturbed label \\( p(y_{i},\\beta) \\). The \"Accuracy Regularisation\" (RegA) is designed to reduce the overall perturbation probability if the accuracy on the validation set reduces to be below the local minima. It returns 0 if there is no accuracy drop on the validation set and a large decrease will overwhelm the \\( \\nabla_{\\alpha_i} \\) value and reduce the sample label perturbation probability. Intuitively, ASLPMEI aims to construct a model that preserves the ideal classification accuracy while otherwise maximising the entropy [23]. Note that which particular examples are classified correctly are able to change, but the accuracy is constrained to remain the same. Intuitively, having a model that better captures ignorance may lead to changes in the treatment of test examples that are distant from training distribution. Note, however that adopting classification accuracy as proxy for known data and otherwise maximizing entropy is a conservative strategy and we find that it results in the model being significantly under-confident." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.424, + 0.473, + 0.533 + ], + "angle": 0, + "content": "The model mis-calibration arises from the distribution mismatch between prediction confidence and prediction accuracy [45]. We offer an alternative model that uses the model calibration as proxy for known data and maximises the prediction entropy in respect to unknown data \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\). The learning rule replaces the \"Accuracy Regularisation\" in Eq. (5) with a \"Calibration Regularisation\" \\((\\mathrm{Reg}_{\\mathrm{C}})\\) as:" + }, + { + "type": "equation", + "bbox": [ + 0.1, + 0.538, + 0.47, + 0.568 + ], + "angle": 0, + "content": "\\[\n\\operatorname {R e g} _ {\\mathrm {C}} = \\min \\left(\\left(1 - \\frac {\\beta \\cdot \\alpha_ {i} ^ {n}}{2}\\right) - \\mathbb {A} \\left(\\theta_ {l m}, \\mathcal {D} _ {\\mathrm {V A L}}\\right), 0\\right), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.575, + 0.473, + 0.728 + ], + "angle": 0, + "content": "where \\(1 - (\\beta \\cdot \\alpha_{i}^{n} / 2)\\) denotes the expected confidence of the perturbed label (Derivation in Appendix A.4). For example, a foreground label \"1\" with \\(5\\%\\) chance of being inverted to \"0\" has an expected confidence of 0.95. \"Calibration Regularisation\" constrains the expected confidence of perturbed label of each sample to not drop below the ideal classification accuracy on validation set, preventing the model from becoming under-confident. Note that we can also have an updating rule \\(\\mathrm{ALS}_{\\mathrm{MC}}\\) to learn per-image label perturbation strength (adaptive \\(\\beta\\) and fixed \\(\\alpha = 1\\)) (See Appendix A.5)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.739, + 0.313, + 0.757 + ], + "angle": 0, + "content": "4. Experiments and Results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.763, + 0.47, + 0.826 + ], + "angle": 0, + "content": "We verify the proposed method primarily on Salient Object Detection and also implement it for Camouflaged Object Detection, Smoke Detection and Semantic Segmentation tasks and report their results in the Appendices." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.833, + 0.295, + 0.849 + ], + "angle": 0, + "content": "4.1. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Evaluation Metrics: We use Equal-Width Expected Calibration Error \\(\\left(\\mathrm{ECE}_{\\mathrm{EW}}\\right)\\) [18] and Equal-Width Overconfidence Error \\(\\left(\\mathrm{OE}_{\\mathrm{EW}}\\right)\\) [62] with 10 bins (\\(B = 10\\)) to" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.137 + ], + "angle": 0, + "content": "evaluate the model calibration degrees. Additionally, we adopt \\(\\mathrm{ECE}_{\\mathrm{EM}}\\) [48], \\(\\mathrm{ECE}_{\\mathrm{DEBIAS}}\\) [29] and \\(\\mathrm{ECE}_{\\mathrm{Sweep}}\\) [56] to corroborate with the results of \\(\\mathrm{ECE}_{\\mathrm{EW}}\\) (See Appendix C)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.138, + 0.892, + 0.228 + ], + "angle": 0, + "content": "Datasets: The proposed methods are trained with the DUTS-TR [63] training dataset. It is divided into a training set \\( |\\mathcal{D}_{\\mathrm{TR}}| = 9,553 \\) and validation set \\( |\\mathcal{D}_{\\mathrm{VAL}}| = 1,000 \\). We use six testing datasets, including DUTS-TE [63], DUTOMRON [80], SOD [44], PASCAL-S [34], ECSSD [78], HKU-IS [33], to evaluate the model calibration degree." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.229, + 0.893, + 0.424 + ], + "angle": 0, + "content": "Compared Methods: We compare with both SOD models and model calibration methods in terms of model calibration degrees. The SOD models include: MSRNet [32], SRM [65], Amulet [92], BMPM [91], DGRL [67], PAGR [93], PiCANet [37], CPD [73], BASNet [55], EGNet [94], AFNet [15], PoolNet [36], GCPANet [7], MINet [51], \\(\\mathrm{F}^3\\mathrm{Met}\\) [69], EBMGSOD [89], ICON [97], EDN [72]. We evaluate ECE on their published prediction results, or results produced with their released model weights. We also compare with model calibration methods include: Temperature Scaling (TS) [18], Brier Loss [4], MMCE [30], Label Smoothing [46], Mixup [62], Focal Loss [45] and AdaFocal [17] implemented on our baseline model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.426, + 0.894, + 0.531 + ], + "angle": 0, + "content": "Baseline Model Structure: We implement our method in the Pytorch framework. Our model has a simple U-Net structure, comprising of a ResNet50 encoder [20] and a decoder, where the former is initialised with ImageNet-pretrained weights and the later by default. We also experiment with VGG16 [58] and Swin transformer [39] encoders and report their results in Appendix I." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.533, + 0.894, + 0.622 + ], + "angle": 0, + "content": "Label Perturbation Techniques: We experiment with four different label perturbation strategies: (1) Hard Inversion \\( T(Y, \\alpha, \\beta = 1.0) \\), (2) Soft Inversion (SI) \\( T(Y, \\alpha, \\beta = 0.75) \\), (3) Moderation (M) \\( T(Y, \\alpha, \\beta = 0.5) \\) and Dynamic Moderation (DM) \\( T(Y, \\alpha, \\beta = 0.5) \\) with additional Gaussian noise. See Appendix H.1 for implementation details." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.624, + 0.892, + 0.713 + ], + "angle": 0, + "content": "Training Details: Each model is trained with an Adam optimiser for 30 epochs. The learning rate is initialised to \\(2.5 \\times 10^{-5}\\), and decays by a factor of 0.9 for each epoch after the \\(10^{\\text{th}}\\) epoch. All training images are scaled to \\(384 \\times 384\\). Basic data augmentation techniques, including random flipping, random translation and random cropping, are applied." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.715, + 0.892, + 0.774 + ], + "angle": 0, + "content": "Hyperparameters: The reported model calibration results associated with ASLP are obtained by setting \\(\\eta = 0.002\\) and \\(\\lambda = 2,000\\). We set the number of bins to \\(B = 10\\) for ECE and OE evaluation metrics." + }, + { + "type": "title", + "bbox": [ + 0.498, + 0.787, + 0.842, + 0.803 + ], + "angle": 0, + "content": "4.2. Model Calibration Degree Performance" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Tab. 1 presents the calibration degree of existing SOD models, existing model calibration methods and our proposed technique on the six SOD testing datasets. Our proposed \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\), designed to optimise the model calibration degree, achieves the best ECE performances on all testing datasets. In addition, \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\) also obtains the second-best" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1177" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.089, + 0.892, + 0.121 + ], + "angle": 0, + "content": "Table 1: Salient object detection model calibration degree benchmark. Results are evaluated in with \\(\\mathrm{ECE}_{\\mathrm{EW}}\\) and \\(\\mathrm{OE}_{\\mathrm{EW}}\\) with 10 bins (units in %). See Appendix C for evaluations with \\(\\mathrm{ECE}_{\\mathrm{EM}}\\) [48], \\(\\mathrm{ECE}_{\\mathrm{DEBIAS}}\\) [29] and \\(\\mathrm{ECE}_{\\mathrm{SWEEP}}\\) [56]." + }, + { + "type": "table", + "bbox": [ + 0.099, + 0.13, + 0.872, + 0.51 + ], + "angle": 0, + "content": "
MethodsYearDUTS-TE [63]DUT-OMRON [80]PASCAL-S [34]SOD [44]ECSSD [78]HKU-IS [33]
ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓
SOD MethodsMSRNet [32]20172.572.343.323.163.443.236.426.140.970.940.920.87
SRM [65]20174.023.724.193.964.884.599.939.582.532.351.861.72
Amulet [92]20175.675.285.845.495.765.4310.039.592.562.421.981.87
BMPM [91]20183.743.524.524.374.884.688.167.931.951.891.581.53
DGRL [67]20184.123.864.414.215.014.778.448.202.132.021.631.53
PAGR [93]20184.043.795.144.965.645.3712.1711.872.842.701.621.54
PiCANet [37]20185.124.904.844.708.147.9210.5010.303.483.392.552.47
CPD [73]20193.973.784.204.065.375.179.659.392.292.191.991.90
BASNet [55]20195.004.864.934.836.506.3610.4010.272.742.702.302.26
EGNet [94]20193.333.143.663.505.425.198.047.791.981.881.471.40
AFNet [15]20193.953.744.254.095.064.848.158.022.382.271.871.78
PoolNet [36]20193.333.123.863.705.325.078.147.872.001.901.821.75
GCPANet [7]20203.182.993.993.844.163.977.056.881.611.541.271.21
MINet [51]20203.653.484.454.294.944.758.017.892.132.031.741.65
F3Met [69]20203.673.504.254.104.854.677.957.782.262.161.921.83
EBMGSD [89]20213.453.294.113.954.794.617.487.302.142.051.791.70
ICON [97]20212.892.763.843.714.083.956.706.551.561.491.381.32
PFSNet [43]20212.942.723.953.814.454.277.597.392.412.252.061.96
EDN [72]20223.623.474.023.904.894.748.818.662.202.131.651.58
Model Calibration MethodsBrier Loss [4]19502.772.583.553.383.903.706.406.161.371.301.040.99
Temperature Scaling [18]20172.532.343.183.033.563.366.326.050.960.930.830.70
MMCE [30]20182.862.673.563.414.003.816.856.631.411.351.181.13
Label Smoothing [46]20192.001.792.892.713.042.835.975.690.830.680.820.47
Mixup [62]20192.452.253.413.233.132.995.825.701.410.183.830.05
Focal Loss [45]20202.252.083.102.823.403.136.215.981.411.031.240.77
AdaFocal [17]20221.611.412.311.842.532.275.885.471.630.791.350.52
Our MethodsASLPMC20231.401.221.991.832.312.105.505.170.480.200.790.17
ASLPMEI202327.90.0126.00.0026.10.0022.40.0029.90.0030.50.00
" + }, + { + "type": "image", + "bbox": [ + 0.118, + 0.527, + 0.235, + 0.714 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.236, + 0.527, + 0.351, + 0.714 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.352, + 0.527, + 0.469, + 0.714 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.47, + 0.527, + 0.586, + 0.714 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.587, + 0.527, + 0.703, + 0.714 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.705, + 0.527, + 0.842, + 0.714 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.722, + 0.895, + 0.786 + ], + "angle": 0, + "content": "Figure 3: Joint distribution of prediction confidence (horizontal axis) and prediction accuracy (vertical axis) on the DUTS-TE dataset. A perfectly calibrated model has an identical confidence distribution and accuracy distribution, denoted as the oracle (diagonal red dotted line). The joint distribution of a better calibrated model is more aligned with the oracle line, especially its high density area. See Appendix D for results of other methods and on other testing datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.809, + 0.471, + 0.901 + ], + "angle": 0, + "content": "OE performances on all six testing datasets, outperformed only by our \\(\\mathrm{ASLP}_{\\mathrm{MEI}}\\). On the other hand, \\(\\mathrm{ASLP}_{\\mathrm{MEI}}\\), though almost eliminates the over-confidence issue completely, is significantly mis-calibrated on the six testing datasets. This can be attributed to it being significantly under-confident rather than over-confident. The observed performances of" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.884 + ], + "angle": 0, + "content": "\\(\\mathrm{ASLP}_{\\mathrm{MEI}}\\) are in accordance with its design - assuming minimum distribution commitment with respect to missing information. That is, in the presence of limited training data, to maximise the prediction entropy while maintaining the prediction accuracy for in-distribution data." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Fig. 3 presents the joint distribution of prediction con" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1178" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.258 + ], + "angle": 0, + "content": "fidence and prediction accuracy of some of the best calibrated methods and our proposed technique on DUTS-TE dataset (See Appendix D for other testing datasets and other methods). Existing SOD methods produce extremely confident predictions whose confidence scores are nearly \\(100\\%\\) for the majority of samples. On the contrary, the prediction accuracy is on average lower than prediction confidence, resulting in the model being over-confident. On the other hand, existing model calibration methods are generally more calibrated than the SOD methods which in general do not strive to improve model calibration degree." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.259, + 0.473, + 0.518 + ], + "angle": 0, + "content": "Our proposed \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\) produces the most calibrated model whose joint distribution is closer to the oracle than those of the compared calibration methods and SOD methods. AdaFocal [17] produces the second most calibrated model on DUTS-TE. However, the majority of their joint distribution (blue high density area) is slightly to the right bottom of the oracle line, making their model slightly less calibrated. Whereas the high density area of our joint distribution is well aligned with the oracle line, showing \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\) is more calibrated. Despite the small difference on the plot, \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\) improves over AdaFocal by more than \\(10\\%\\) in terms of ECE scores on DUTS-TE dataset. We can also observe that \\(\\mathrm{ASLP}_{\\mathrm{MEI}}\\) is significantly under-confident for in-distribution data with its joint distribution being at the top-left side of the oracle line. Its prediction accuracies are limited to between \\(70\\%\\) and \\(80\\%\\) while the prediction accuracies are generally above \\(90\\%\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.529, + 0.47, + 0.56 + ], + "angle": 0, + "content": "4.3. Model Calibration Degrees on Out-of-Distribution Dataset" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.569, + 0.473, + 0.903 + ], + "angle": 0, + "content": "We compare our proposed method with existing model calibration methods in terms of model calibration degrees on Out-of-Distribution data. We consider texture images, where salient objects are completely absent, as OoD samples for the SOD task. We use Describable Texture Dataset [9] to evaluate the model calibration degrees on OoD samples. Fig. 4 shows the joint distribution of prediction confidence and prediction accuracy of various model calibration methods and our proposed techniques. It can be seen that the baseline model produces extremely confident predictions for OoD data. However, its accuracy is only \\(41.88\\%\\), worse than a uniform prior in a binary classification task. We also observe that Temperature Scaling does not calibrate the model under data distribution shift in accordance with literature [50, 45]. Our \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\), being the most calibrated for in-distribution data, is also more calibrated on the OoD samples than the existing model calibration methods by a large margin as shown in Tab. 2. On the other hand, our \\(\\mathrm{ASLP}_{\\mathrm{MEI}}\\) is more successful in handling OoD data. It is the most calibrated on OoD data, with a larger proportion of the distribution aligned with the oracle line. As shown in Tab. 2, it outperforms existing model calibration methods in" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.094, + 0.626, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.542, + 0.186, + 0.585, + 0.196 + ], + "angle": 0, + "content": "Baseline" + }, + { + "type": "image", + "bbox": [ + 0.626, + 0.095, + 0.74, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.636, + 0.186, + 0.736, + 0.197 + ], + "angle": 0, + "content": "Temperature Scaling" + }, + { + "type": "image", + "bbox": [ + 0.741, + 0.095, + 0.854, + 0.186 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.761, + 0.187, + 0.842, + 0.197 + ], + "angle": 0, + "content": "Label Smoothing" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.197, + 0.625, + 0.284 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.548, + 0.287, + 0.58, + 0.297 + ], + "angle": 0, + "content": "Mixup" + }, + { + "type": "image", + "bbox": [ + 0.625, + 0.197, + 0.74, + 0.284 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.665, + 0.287, + 0.7, + 0.297 + ], + "angle": 0, + "content": "MMCE" + }, + { + "type": "image", + "bbox": [ + 0.741, + 0.197, + 0.854, + 0.284 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.775, + 0.287, + 0.828, + 0.297 + ], + "angle": 0, + "content": "Focal Loss" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.297, + 0.625, + 0.385 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.54, + 0.386, + 0.588, + 0.397 + ], + "angle": 0, + "content": "AdaFocal" + }, + { + "type": "image", + "bbox": [ + 0.625, + 0.297, + 0.74, + 0.385 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.659, + 0.386, + 0.705, + 0.398 + ], + "angle": 0, + "content": "ASLPMEMI" + }, + { + "type": "image", + "bbox": [ + 0.741, + 0.297, + 0.854, + 0.385 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.779, + 0.386, + 0.823, + 0.398 + ], + "angle": 0, + "content": "ASLPMC" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.406, + 0.892, + 0.468 + ], + "angle": 0, + "content": "Figure 4: Joint distribution of prediction confidence (horizontal axis) and prediction accuracy (vertical axis) on the Describable Texture Dataset [9], of compared model calibration methods and our proposed \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\) and \\(\\mathrm{ASLP}_{\\mathrm{MEI}}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.483, + 0.892, + 0.529 + ], + "angle": 0, + "content": "terms of both ECE and OE by significant margins. This can be attributed to its minimum distribution assumption in the presence of limited training data." + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.544, + 0.894, + 0.605 + ], + "angle": 0, + "content": "Table 2: Model calibration methods and our \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\) and \\(\\mathrm{ASLP}_{\\mathrm{MEI}}\\) are evaluated on the Out-of-Distribution dataset, Describable Texture Dataset [9], in terms of \\(\\mathrm{ECE}_{\\mathrm{EW}}\\) and \\(\\mathrm{OE}_{\\mathrm{EW}}\\) with 10 bins, and Accuracy (ACC)." + }, + { + "type": "table", + "bbox": [ + 0.525, + 0.607, + 0.867, + 0.77 + ], + "angle": 0, + "content": "
MethodEvaluation (%)
ECE ↓OE ↓ACC ↑
Baseline52.3651.0541.88
Brier Loss [4]38.8537.1853.62
Temperature Scaling [18]51.9550.4641.59
Label Smoothing [46]37.2235.4855.41
MMCE [30]40.6439.6754.39
Mixup [62]31.0729.1058.71
Focal Loss [45]40.0138.4349.71
AdaFocal [17]27.5525.0755.39
ASLPMC18.3116.3761.93
ASLPMEI13.438.4062.47
" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.786, + 0.618, + 0.8 + ], + "angle": 0, + "content": "4.4. Discussion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Adaptive Stochastic Label Perturbation: We study the effect of ASLP on ECE and OE and present the experimental results in Tab. 3. It shows that ASLPs significantly outperforms the baseline model, \"B\", which does not adopt any model calibration measures. In addition, ASLPs also outperforms their static counterparts (SLPs) which use a single" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1179" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.089, + 0.895, + 0.151 + ], + "angle": 0, + "content": "Table 3: Ablation: Effect of Stochastic Label Perturbation (SLP) and Adaptive Stochastic Label Perturbation (ASLP) with different label perturbation techniques on the model calibration degrees evaluated on Expected Calibration Error (ECE) and Over-confidence Error (OE). The proposed ASLP is generalised to an Adaptive Label Smoothing (ALS) technique that adaptively tunes the label softening scale \\((\\beta_{\\mathrm{ada}})\\)." + }, + { + "type": "table", + "bbox": [ + 0.119, + 0.153, + 0.85, + 0.315 + ], + "angle": 0, + "content": "
MethodsPerturbation ParamsDUTS-TE [63]DUT-OMRON [80]PASCAL-S [34]SOD [44]ECSSD [78]HKU-IS [33]
αβeECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓
Baseline (“B”)0003.483.294.174.024.604.417.427.171.931.861.641.59
SLPα=0.01HI0.011.0X2.211.842.962.783.112.826.095.801.030.681.010.53
SLPα=0.02SI0.020.75X2.252.053.002.823.052.836.406.090.930.840.870.60
SLPα=0.03M0.030.5X2.242.033.172.973.413.206.265.970.830.770.960.81
SLPα=0.03DM0.030.5✓2.292.093.002.833.473.246.726.431.131.040.960.80
LSβ=0.031.00.03X2.201.993.092.913.243.036.275.991.030.780.920.67
ASLPHIαada1.0X1.401.221.991.832.312.105.505.170.480.200.790.17
ASLPSIαada0.75X1.511.292.141.952.292.075.124.800.610.340.840.22
ASLPMαada0.5X1.471.271.871.802.372.135.635.290.510.230.800.20
ASLPMCMαada0.5✓1.641.201.941.752.031.814.143.840.800.420.870.42
ALS1.0βadaX1.461.252.071.872.302.105.445.180.610.250.810.32
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.328, + 0.47, + 0.358 + ], + "angle": 0, + "content": "\\(\\alpha\\) for the entire dataset. This can be attributed to the approach modelling variance of noise with input image." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.36, + 0.47, + 0.525 + ], + "angle": 0, + "content": "Generalisation of Adaptive Label Smoothing: We generalise the proposed ASLP to label smoothing, developing an Adaptive Label Smoothing (ALS) that fixes the label perturbation probability to \\(100\\%\\), akin to the label smoothing technique [46], and tunes a smoothing factor for each training sample. As shown in Tab. 3, ALS effectively reduces the ECE and OE scores over its static version \\(\\mathrm{LS}^{\\beta = 0.03}\\), and achieves similar performances with \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\) approaches on the six testing datasets. It manifests that our proposed ASLP can be generalised onto other label perturbation techniques as a measure to calibrate the SOD models." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.526, + 0.47, + 0.603 + ], + "angle": 0, + "content": "Compatibility with SOTA SOD Models We retrain EBMGSOD [89], ICON [97] and EDN [72] with the proposed \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\) and find significant improvements in terms of model calibration degrees without compromising their classification abilities (See Appendix E)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.604, + 0.47, + 0.664 + ], + "angle": 0, + "content": "Compatibility with Different Backbones: We demonstrate that our proposed method is also compatible with VGG16 [58] and Swin transformer [39] backbones. See Appendix I for details." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.665, + 0.47, + 0.741 + ], + "angle": 0, + "content": "Effectiveness in Other Dense Binary Classification Tasks: Experiments on Smoke Detection [79] and Camouflaged Object Detection [14] demonstrate that our method can be generalised to dense binary classification tasks to improve model calibration degrees. See Appendix F." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.742, + 0.47, + 0.803 + ], + "angle": 0, + "content": "Generalisation to Multi-Class Segmentation task: Experiments on Semantic Segmentation [11] demonstrate that our method can also be generalised to dense multi-class classification tasks. See Appendix G." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.816, + 0.251, + 0.833 + ], + "angle": 0, + "content": "4.5. Hyperparameters" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Static Stochastic Label Perturbation: Tab. 3 shows that, under a small label perturbation probability, the four label perturbation techniques can alleviate the model overconfidence issues of the baseline model, \"B\", on the six" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.328, + 0.892, + 0.464 + ], + "angle": 0, + "content": "testing datasets. They also achieve similar results to Label Smoothing [46], setting \\(\\beta = 0.03\\) and \\(\\alpha = 1\\). Each SLP has a wide range of effective label perturbation probabilities that improves model calibrations (See Appendix H.2 Tab. 13), and these improvements do not sacrifice the model's classification performance (see Appendix H.3). Larger values of the label perturbation probability eventually lead to increasing ECE scores as the model transitions to being under-confident (see Appendix H.2)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.464, + 0.892, + 0.539 + ], + "angle": 0, + "content": "Updating Rate \\(\\eta\\): \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\) models trained with \\(\\eta \\in [0.0002, 0.005]\\) are generally stable, producing similar calibration degrees and classification performances. Values smaller than 0.001 require longer training and high values lead to sub-optimal results (See Appendix J)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.539, + 0.892, + 0.585 + ], + "angle": 0, + "content": "Regularisation Strength \\(\\lambda\\): \\(\\lambda\\) spanning between 500 and 10,000 are optimal. Very high values for \\(\\lambda\\) can lead to oscillation resulting in poor performance (See Appendix J)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.597, + 0.619, + 0.613 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.623, + 0.892, + 0.865 + ], + "angle": 0, + "content": "This work first introduces a Self-Calibrating Binary Cross Entropy loss that unifies label perturbation processes including stochastic approaches and label smoothing to improve model calibration while preserving classification accuracy. We further propose an Adaptive Stochastic Label Perturbation that learns a unique label perturbation level for individual training image. Following Maximum Entropy Inference, ASLP adopts classification / calibration as proxy for known data and maximises the prediction entropy with respect to missing data. The proposed \\(\\mathrm{ASLP}_{\\mathrm{MC}}\\) improves model calibration degrees on both in-distribution samples and out-of-distribution samples, without negatively impacting classification performance. The approach can be easily applied to different models, which we demonstrate with several SOTA models. It is also demonstrated to be effective on a semantic segmentation task and other binary tasks." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.873, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgments. This research was in-part supported by the ANU-Optus Bushfire Research Center of Excellence." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "1180" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.468, + 0.157 + ], + "angle": 0, + "content": "[1] Radhakrishna Achanta, Sheila Hemami, Francisco Estrada, and Sabine Susstrunk. Frequency-tuned salient region detection. In CVPR, pages 1597-1604. IEEE, 2009. 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.159, + 0.468, + 0.2 + ], + "angle": 0, + "content": "[2] Gorkem Algan and Ilkay Ulusoy. Image classification with deep learning in the presence of noisy labels: A survey. 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IEEE TPAMI, 2022. 5, 6, 8, 20, 21, 22, 27" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.247 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.946, + 0.516, + 0.956 + ], + "angle": 0, + "content": "1184" + } + ] +] \ No newline at end of file diff --git a/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/7e446bd7-c368-40d4-8d81-6aee3f5055e8_origin.pdf b/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/7e446bd7-c368-40d4-8d81-6aee3f5055e8_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..d497133f3c1f6e2e742402b81ca9c208f63426ba --- /dev/null +++ b/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/7e446bd7-c368-40d4-8d81-6aee3f5055e8_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:ee82b2c3e75b81113a70ddd7706b583300adaf9494134031ab1676031b275785 +size 1310970 diff --git a/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/full.md b/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/full.md new file mode 100644 index 0000000000000000000000000000000000000000..5a716add77762a2de983472d34efdf9c996e90c2 --- /dev/null +++ b/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/full.md @@ -0,0 +1,371 @@ +# Model Calibration in Dense Classification with Adaptive Label Perturbation + +Jiawei Liu Changkun Ye Shan Wang Ruikai Cui Jing Zhang Kaihao Zhang Nick Barnes The Australian National University + +# Abstract + +For safety-related applications, it is crucial to produce trustworthy deep neural networks whose prediction is associated with confidence that can represent the likelihood of correctness for subsequent decision-making. Existing dense binary classification models are prone to being over-confident. To improve model calibration, we propose Adaptive Stochastic Label Perturbation (ASLP) which learns a unique label perturbation level for each training image. ASLP employs our proposed Self-Calibrating Binary Cross Entropy (SC-BCE) loss, which unifies label perturbation processes including stochastic approaches (like DisturbLabel), and label smoothing, to correct calibration while maintaining classification rates. ASLP follows Maximum Entropy Inference of classic statistical mechanics to maximise prediction entropy with respect to missing information. It performs this while: (1) preserving classification accuracy on known data as a conservative solution, or (2) specifically improves model calibration degree by minimising the gap between the prediction accuracy and expected confidence of the target training label. Extensive results demonstrate that ASLP can significantly improve calibration degrees of dense binary classification models on both in-distribution and out-of-distribution data. The code is available on https://github.com/Carlisle-Liu/ASLP. + +# 1. Introduction + +Binary segmentation aims to differentiate foreground areas from the background in images. Its tasks include Salient Object Detection [86], Camouflaged Object Detection [13], Smoke Detection [79], etc. Performance in these tasks has been significantly advanced using the strong representation powers of Deep Neural Networks (DNNs). However, with complex structures and a tremendous number of parameters, DNNs are prone to over-fitting to training data and producing over-confident predictions in the real world [18]. Such issues can render the model predictions unreliable in decision making or utilisation in downstream tasks. + +Recently, a growing body of literature has been pro + +![](images/0b48a447877521fb5e19777c78e824597d2821e87a72290b0de4c5e0aac4997e.jpg) +Figure 1: Applying Adaptive Label Perturbation during training can effectively moderate predictions at incorrect areas, highlighting them with high entropy values (red). $Z_{t}(x,y)$ is a sample-wise Bernoulli variable, parameterized by $\alpha$ , at the $t^{\mathrm{th}}$ iteration. After $k$ iterations, update $\alpha$ using Eq. (5) to adjust the likelihood (or level) of label perturbation to increase entropy for incorrect predictions and so correct model calibration. The Perturbed Label (shown inverted) replaces the Groundtruth Label with probability $\alpha$ . + +posed to address model mis-calibration problems in DNNs. They can be roughly categorised as: (1) post-hoc operations, such as temperature scaling [18], Platt scaling [54], etc., (2) training objective approaches [27], like MMCE [30], soft calibration objective [27], focal loss [45, 17], and (3) data/label augmentation techniques, e.g. label smoothing [46] and mixup [85]. We propose an Adaptive Label Perturbation which learns a unique label perturbation level for each training image. As illustrated in Fig. 1, training with Adaptive Stochastic Label Perturbation, a form of ALP, can effectively moderate incorrect predictions and highlight them with high entropy values. + +Adaptive Label Perturbation employs our proposed Self-Calibrating Binary Cross Entropy (SC-BCE) loss, which unifies label perturbation processes including stochastic approaches (like DisturbLabel [75]), and label smoothing [60] to correct calibration while maintaining classification accuracy. SC-BCE loss is equivalent to a factored combination of (i) a BCE loss w.r.t. groundtruth label, and (ii) a BCE loss w.r.t. a uniform binary categorical distribution. The former enhances dense binary classification performance and the latter improves the model calibration degree. Our method can be connected to Maximum Entropy Inference [23] of classic statistical mechanics, to maximise prediction + +entropy with respect to missing information while preserving the classification accuracy on known data. + +The proposed Adaptive Label Perturbation (ALP) can approximate Maximum Entropy Inference [23] to maximise prediction entropy while preserving the ideal dense classification performance on known data. This represents a conservative solution that adopts classification accuracy as a proxy for known data and assumes maximum disorder on unknown data. We also present an alternative ALP solution that, instead, takes model calibration degree as a proxy for known data, using a calibration regulariser which constrains the expected confidence of individual supervision signal to not drop below the ideal accuracy on the validation set. This effectively minimises the gap between the distributions of prediction confidence and prediction accuracy, which is the source of model mis-calibration. + +Our contributions can be summarised as: (i) We propose Adaptive Stochastic Label Perturbation that learns a sample-wise label perturbation level to improve model calibration; (ii) We present a Self-Calibrating Binary Cross Entropy loss that unifies label perturbation processes including stochastic approaches and label smoothing; (iii) Following Maximum Entropy Inference [23] we show that Adaptive Stochastic Label Perturbation $(\mathrm{ASLP}_{\mathrm{MEI}})$ , can maximise the prediction entropy while preserving the ideal dense classification accuracy, and (iv) We present an alternative Adaptive Stochastic Label Perturbation $(\mathrm{ASLP}_{\mathrm{MC}})$ solution to maximise model calibration degree, which achieves state-of-the-art performance in terms of model calibration degree on both in-distribution and out-of-distribution data. We thoroughly evaluate our method on Salient Object Detection and demonstrate its effectiveness for Camouflaged Object Detection, Smoke Detection and Semantic Segmentation. + +# 2. Related Works + +Model Calibration: Model calibration methods can be roughly divided into three categories of approach: (1) post hoc processing (2) training object, and (3) input/label augmentation. The first category utilises a validation set to align the prediction confidence distribution with prediction accuracy distribution. It includes histogram binning [82], isotropic regression [83], Platt scaling [54, 49], Bayesian binning into quantiles [47], Dirichlet scaling [28], mix-n-match [87] and temperature scaling [18, 81]. + +The second category focuses on designing training objectives that (in)directly improve model calibration degree. Some methods address the in-continuity of expected calibration error, a widely adopted model calibration measure, and propose trainable calibration objectives like maximum mean calibration error [30], soft calibration objective [27]. Other works discover that certain existing training objects are beneficial to model calibration, e.g. Brier loss [4, 10], confidence penalty [52] and focal loss [45, 17]. + +The third category employs data or label augmentation techniques to regularise the prediction confidence distribution. Mixup [85, 62] explores the neighbourhood of training data through random interpolation of input images and associated labels to improve model calibration degree. Label smoothing [46] augments the one-hot training labels with softer versions to prevent the model being over-confident. + +Salient Object Detection: Inspired by pioneering work [22], traditional Saliency Object Detection (SOD) methods rely on various heuristic priors with handcraft features to explore low-level cures [1, 25, 26, 38, 66]. However, these methods cannot cope with complex scenes because of the limited representation ability of handcrafted features [3]. Recently, deep learning based SOD methods broke the bottleneck of traditional methods due to the powerful capability of neural networks, achieving improved performance [6, 24, 55, 76, 37, 64, 68]. Early deep SOD methods use multi-layer perception to predict a map with a pixel-wise score for each image [71, 8]. These approaches rely on fixed fully connected layers and thus severely limit the ability of spatial information extraction. Later methods address this issue via using fully convolutional networks (FCNs) [40]. + +Most contemporary SOD methods are designed based on FCNs with various schemes to improve performance. One of the most popular strategies is to fuse multi-scale information extracted from different layers and aggregate them in the network [91, 74, 16, 51, 96, 90]. Attention modules are also applied to capture powerful multi-scale features via exploring relationship between local and global information [37, 53, 95, 21]. Training SOD networks using auxiliary supervision is also a popular strategy [70, 70, 61]. For example, the body map and detail map are utilized by [70] to help the network focus on center areas and edges, respectively. Skeleton [35] and uncertainty [61] are applied to the training processing due to their important roles in taking photos. + +Noisy Label: Noisy labels refer to incorrect ground truth classes/values in classification/regression tasks. They arise from data collection or annotation processes, and exist commonly in real-world datasets [2]. Efforts are put to identify the noisy labels and exclude them from network training in various computer vision tasks, deeming their incorporation as harmful. [88] proposes a framework that learns from noisy labels, being a collection of predictions from classic SOD methods. The framework approximates the noise distribution in order to recover clean labels for model training. + +Differently from data augmentation techniques that are applied simultaneously to training samples and corresponding labels to generate more training data, one may artificially corrupt the label. We refer to this category of approaches as label perturbation, which includes label smoothing approaches [60], and DisturbLabel, Xie et al. [75]. In image classification, Xie et al. [75] shows that randomly replacing training labels with a prior distribution + +leads to a regularising effect, preventing overfitting. Our work is different from [75] by employing labels corrupted to different scales to enhance the model calibration degrees for both in-distribution and out-of-distribution data. Further, in performing this, we assume noise that varies with different samples, making our method more adaptable. + +# 3. Proposed Method + +We first lay out the task setting in Sec. 3.1. Then we introduce our proposed Self-Calibrating Binary Cross Entropy loss in Sec. 3.2 and prove its connection to Maximum Entropy Inference [23] in Sec. 3.3. Lastly, we detail our major contribution - Adaptive Label Perturbation in Sec. 3.4. + +# 3.1. Task Setting + +Binary segmentation problems aim to differentiate between foreground object(s) and background. They can be formulated as a pixel-wise binary classification problem. Given an independent and identically distributed (i.i.d) training dataset $\mathcal{D}_{\mathrm{TR}} = \{x_i,y_i\}_{i = 1}^N$ drawn from an unknown joint distribution of training images and groundtruth labels $P(\mathcal{X},\mathcal{Y})$ , a neural network model parameterised by $\theta$ is employed to predict labels for an input image $x\in \mathcal{X}$ : $f_{\theta}(x)\in (0,1)^{1\times H\times W}$ . We use $\hat{y}$ and $P_{\hat{y}}$ to denote the winning class and its associated probability respectively. The groundtruth label $y\in \{0,1\}^{1\times H\times W}$ represents the foreground pixels with "1" and background with "0". In the following equations, we omit the spatial indexes $H$ and $W$ for simplicity. A perfectly calibrated model has $\mathrm{P}(\hat{y} = y|P_{\hat{y}}) = P_{\hat{y}},\forall P_{\hat{y}}\in (0,1)$ . That is, in the entire range of prediction probabilities, prediction with probability $P_{\hat{y}}$ has exactly $P_{\hat{y}}$ chance to be correct. The calibration degree of a model $f_{\theta}(\cdot)$ over a distribution $\mathcal{D}$ is quantified with Expected Calibration Error (ECE), defined as $\mathbb{E}_{f_{\theta}(x)}[|\mathrm{P}(\hat{y} = y|f_{\theta}(x)) - f_{\theta}(x)|]$ . + +# 3.2. Self-Calibrating Binary Cross Entropy Loss + +We propose a Self-Calibrating Binary Cross Entropy (SC-BCE) loss that unifies Label Smoothing [60], DisturbLabel [75] and Stochastic Label Perturbation as: + +$$ +\begin{array}{l} \mathcal {L} _ {\mathrm {S C - B C E}} (\theta , X, Y, \alpha , \beta) \\ = \mathbb {E} _ {x, y \in X, Y} \left[ \left(1 - Z _ {t} (x, y)\right) \cdot \mathcal {L} _ {\mathrm {B C E}} (\theta , x, y) \right. \\ \left. + Z _ {t} (x, y) \cdot \mathcal {L} _ {\mathrm {B C E}} (\theta , x, p (y, \beta)) \right] \tag {1} \\ \end{array} +$$ + +$$ +\beta \in [ 0, 2 ], \quad \alpha \in [ 0, \frac {1}{\beta}), +$$ + +where $Z_{t}(x,y) \sim B(1,\alpha)$ follows a Bernoulli distribution with $\alpha$ probability to be 1 and $1 - \alpha$ chance to be 0, $t$ denotes the training epoch, $\alpha \in [0,\frac{1}{\beta})$ and $\beta \in [0,2]$ are Label Perturbation Probability (LPP) and Label Perturbation Strength + +(LPS) respectively, $p(y,\beta) = (1 - \beta)\cdot y + \frac{\beta}{2},\beta \in [0,2]$ is a perturbed label and $\mathcal{L}_{\mathrm{BCE}}(\theta ,x,y)^1$ is a Binary Cross Entropy (BCE) loss computed for training pair $(x,y)$ . For $\alpha = 1$ , the label perturbation equation follows the label smoothing equation for a binary label [60]. In the proposed SC-BCE loss, different label perturbations can be applied by setting (i) Label Smoothing [60]: $\alpha = 1$ and $\beta \in [0,1)$ , (2) DisturbLabel: $\beta = 1$ and $\alpha \in (0,1)$ , and (3) Stochastic Label Perturbation (SLP): $\beta \in (0,2]$ and $\alpha \in (0,\frac{1}{\beta})$ . For example, Hard Inversion (HI) that inverts the label category as shown in Fig. 2, can be stochastically applied by setting $\beta = 2$ and $\alpha \in (0,\frac{1}{2})$ . + +In the implementation of SLP, the supervision for an individual training image in each epoch is sampled by drawing from a Bernoulli distribution. That is, the individual supervision can take the form of the groundtruth label or perturbed label in each training iteration. The overall function of SLP can be connected to that of a smoothed label by taking expectation of the Bernoulli variable: $\mathbb{E}_{Z_t}[(1 - Z_t(y))\cdot Y + Z_t(y)\cdot p(y,\beta)],\forall y\in Y.$ Taking the expectation over the Bernoulli variation in each iteration is too expensive to implement in model training. Instead, following [75], the expectation of stochastically perturbed label is approximated by taking expectation across training epochs: $\mathbb{E}_{t\in T}[(1 - Z_t(y))\cdot Y + Z_t(y)\cdot p(y,\beta)],\forall y\in Y,$ where $T$ is the total number of training epochs and $Z_{t}(y)$ is a variable drawn from a Bernoulli distribution for the $\mathrm{t^{th}}$ epoch. + +# 3.3. Maximum Entropy Inference + +Maximum Entropy Inference (MEI), assuming minimum distribution commitment in respect to missing information, was initially proposed by Jaynes [23]. That is, the probability distribution should have maximum Shannon entropy subject to the partially available information. Thus, in the complete absence of information, Shannon entropy for a binary prediction defined in Eq. (2) should be maximised: + +$$ +\begin{array}{l} \mathbb {H} \left(f _ {\theta} (X)\right) = \mathbb {E} _ {x \in X} \left[ - f _ {\theta} (x) \cdot \log f _ {\theta} (x) - \right. \tag {2} \\ \left. \left(1 - f _ {\theta} (x)\right) \cdot \log \left(1 - f _ {\theta} (x)\right) \right\rfloor \\ \end{array} +$$ + +For salient object detection and other binary segmentation problems, maximising Eq. (2) can be achieved with a binary uniform categorical distribution. + +The proposed SC-BCE loss can be transformed into a factored combination of a BCE loss w.r.t. groundtruth label (the constraints of the data) and a BCE loss w.r.t. a binary uniform categorical distribution (See Appendix A.2 for + +![](images/f6c598fa19f5650a8473a987e821c23524573c8c0834c19b585b2123d047b08d.jpg) + +![](images/a3ff5e673a93dee465d07f7cd59370dea9b324ad897e89909b6b70bd82b553e9.jpg) + +![](images/be4472f6f51616a582d5b67e8dcb45701b4d1ec579f23d0c97358464d9183019.jpg) + +![](images/62d63950f255c962c00b28214888f62f86ebbb3323c18f95611ea024c47f0bd0.jpg) +Figure 2: The method overview is comprised of model implementation (top) and Adaptive Stochastic Label Perturbation (ASLP) learning rule (bottom). In each iteration, the model uses a Bernoulli variable to sample a supervision, which can be a groundtruth label $y_{i}$ or a perturbed label $p_i$ and computes a sample-specific $\nabla_{\alpha_i}$ based on the prediction. Regularisation is computed with Eq. 5 (ASLPMEI) or Eq. 6 (ASLPMC) on a validation set after each training epoch. The ASLP learning rule combines Grad- $\alpha_{i}$ and a factored regularisation to update label perturbation probability $\alpha_{i}$ for each individual sample. + +
L BCE(θ, x_i, p(y_i, β)) - L BCE(θ, x_i, y_i)∇αi
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=0=0
<0<0
+ +derivation) as: + +$$ +\begin{array}{l} \mathcal {L} _ {\mathrm {S C - B C E}} (\theta , X, Y, \alpha , \beta) \\ = \mathbb {E} _ {x, y \in X, Y} \left[ (1 - \beta Z _ {t} (x, y)) \cdot \mathcal {L} _ {\mathrm {B C E}} (\theta , x, y) \right. \tag {3} \\ \left. + \beta Z _ {t} (x, y) \cdot \mathcal {L} _ {\mathrm {B C E}} (\theta , x, u) \right], \\ \end{array} +$$ + +where $Z_{t}(x,y) \sim B(1,\alpha)$ , $u$ is a binary uniform categorical distribution, and minimising the second term pushes the prediction distribution towards a uniform binary categorical distribution, equivalently maximising the inference entropy. Therefore, our proposed SC-BCE loss, a combination of a regular BCE loss and a BCE loss with a perturbed label, effectively performs a type of MEI. That is, the regular BCE loss component improves the model's binary classification accuracy in the presence of information while the perturbed label maximizes prediction entropy with respect to missing information in order to close the gap between the available training data and the entire data distribution. + +# 3.4. Adaptive Label Perturbation + +Stochastic Label Perturbation (SLP) uses a single label perturbation probability and perturbation strength for the entire training dataset. However, this approach cannot adapt to predictive error that varies for different input images. To address this, we propose an Adaptive Stochastic Label Augmentation (ASLP) method to adjust the label augmentation probability for individual training samples. That is we allow the variable in Eq. (1) to be drawn from a per training image Bernoulli distribution with sample-specific label perturbation probability as: + +$$ +Z _ {t} (x, y) \sim B (1, \alpha_ {x, y}), \forall x, y \in X, Y \tag {4} +$$ + +where $\alpha_{x,y}$ is the label perturbation probability for sample (image-label) pair $(x,y)$ . Initially, we set all label perturbation probabilities to $\{\alpha_{i} = 0\}_{i = 1}^{N}$ and train a model with a regular BCE loss without label augmentation techniques, which is equivalent to $\mathcal{L}_{\mathrm{SC - BCE}}(\theta ,X,Y,\alpha = 0,\beta = 0)$ . The trained model has weight $\theta_{\mathrm{lm}}$ and its accuracy on the validation set, $\mathbb{A}(\theta_{lm},\mathcal{D}_{\mathrm{VAL}})$ , is held as an ideal performance. Subsequently, we select a label perturbation technique and continue to train the model with SC-BCE loss with a learning rule to update the label perturbation probability for individual training samples. + +We propose the learning rule for $\alpha$ , $(\mathrm{ASLP}_{\mathrm{MEI}})$ to approximate maximum entropy inference. The rule has two components: (1) $\nabla_{\alpha_i} = (2 / \beta)\cdot$ $\partial \mathbb{E}_{Z_t}(x_i,y_i)\big[\mathcal{L}_{\mathrm{SC - BCE}}(X,Y,\theta ,\{\alpha_i\}_{i = 1}^N,\beta)\big] / \partial \alpha_i$ is the derivative of the expectation of SC-BCE over the Bernoulli variable w.r.t. $\alpha_{i}$ . We divide this by $\beta /2$ to ensure that different perturbation techniques (varying $\beta$ values) have the same convergence speed (See derivation in Appendix A.3), and (2) Accuracy Regularization to encourage maintenance of prediction accuracy. The rule is: + +$$ +\begin{array}{l} \alpha_ {i} ^ {n + 1} = \alpha_ {i} ^ {n} + \eta \cdot \left(\nabla_ {\alpha_ {i}} + \lambda \cdot \operatorname {R e g} _ {A}\right), \quad \text {f o r} i = 1, \dots , N, \\ \nabla_ {\alpha_ {i}} = \frac {2 \cdot \left(\mathcal {L} _ {\mathrm {B C E}} (\theta , x _ {i} , p (y _ {i} , \beta)) - \mathcal {L} _ {\mathrm {B C E}} (\theta , x _ {i} , y _ {i})\right)}{\beta}, \\ \end{array} +$$ + +$$ +\operatorname {R e g} _ {\mathrm {A}} = \min \left(\frac {\mathbb {A} (\theta , \mathcal {D} _ {\mathrm {V A L}}) - \mathbb {A} (\theta_ {l m} , \mathcal {D} _ {\mathrm {V A L}})}{\mathbb {A} (\theta_ {l m} , \mathcal {D} _ {\mathrm {V A L}})}, 0\right), \tag {5} +$$ + +where $\eta$ and $\lambda$ are hyperparameters controlling the updating pace of label perturbation probability and the regularisation strength respectively, $\mathbb{A}(\theta ,\mathcal{D}_{\mathrm{VAL}})$ and $\mathbb{A}(\theta_{lm},and\mathcal{D}_{\mathrm{VAL}})$ denote the current and ideal accuracy on the validation set separately. $\nabla_{\alpha_i}$ aims to increase label perturbation proba + +bility to confident and correct samples and otherwise for incorrectly classified samples. For example, it returns a large positive value for correct predictions with small BCE loss value w.r.t. to groundtruth label $y_{i}$ and large BCE loss value w.r.t. to perturbed label $p(y_{i},\beta)$ . The "Accuracy Regularisation" (RegA) is designed to reduce the overall perturbation probability if the accuracy on the validation set reduces to be below the local minima. It returns 0 if there is no accuracy drop on the validation set and a large decrease will overwhelm the $\nabla_{\alpha_i}$ value and reduce the sample label perturbation probability. Intuitively, ASLPMEI aims to construct a model that preserves the ideal classification accuracy while otherwise maximising the entropy [23]. Note that which particular examples are classified correctly are able to change, but the accuracy is constrained to remain the same. Intuitively, having a model that better captures ignorance may lead to changes in the treatment of test examples that are distant from training distribution. Note, however that adopting classification accuracy as proxy for known data and otherwise maximizing entropy is a conservative strategy and we find that it results in the model being significantly under-confident. + +The model mis-calibration arises from the distribution mismatch between prediction confidence and prediction accuracy [45]. We offer an alternative model that uses the model calibration as proxy for known data and maximises the prediction entropy in respect to unknown data $\mathrm{ASLP}_{\mathrm{MC}}$ . The learning rule replaces the "Accuracy Regularisation" in Eq. (5) with a "Calibration Regularisation" $(\mathrm{Reg}_{\mathrm{C}})$ as: + +$$ +\operatorname {R e g} _ {\mathrm {C}} = \min \left(\left(1 - \frac {\beta \cdot \alpha_ {i} ^ {n}}{2}\right) - \mathbb {A} \left(\theta_ {l m}, \mathcal {D} _ {\mathrm {V A L}}\right), 0\right), \tag {6} +$$ + +where $1 - (\beta \cdot \alpha_{i}^{n} / 2)$ denotes the expected confidence of the perturbed label (Derivation in Appendix A.4). For example, a foreground label "1" with $5\%$ chance of being inverted to "0" has an expected confidence of 0.95. "Calibration Regularisation" constrains the expected confidence of perturbed label of each sample to not drop below the ideal classification accuracy on validation set, preventing the model from becoming under-confident. Note that we can also have an updating rule $\mathrm{ALS}_{\mathrm{MC}}$ to learn per-image label perturbation strength (adaptive $\beta$ and fixed $\alpha = 1$ ) (See Appendix A.5). + +# 4. Experiments and Results + +We verify the proposed method primarily on Salient Object Detection and also implement it for Camouflaged Object Detection, Smoke Detection and Semantic Segmentation tasks and report their results in the Appendices. + +# 4.1. Implementation Details + +Evaluation Metrics: We use Equal-Width Expected Calibration Error $\left(\mathrm{ECE}_{\mathrm{EW}}\right)$ [18] and Equal-Width Overconfidence Error $\left(\mathrm{OE}_{\mathrm{EW}}\right)$ [62] with 10 bins ( $B = 10$ ) to + +evaluate the model calibration degrees. Additionally, we adopt $\mathrm{ECE}_{\mathrm{EM}}$ [48], $\mathrm{ECE}_{\mathrm{DEBIAS}}$ [29] and $\mathrm{ECE}_{\mathrm{Sweep}}$ [56] to corroborate with the results of $\mathrm{ECE}_{\mathrm{EW}}$ (See Appendix C). + +Datasets: The proposed methods are trained with the DUTS-TR [63] training dataset. It is divided into a training set $|\mathcal{D}_{\mathrm{TR}}| = 9,553$ and validation set $|\mathcal{D}_{\mathrm{VAL}}| = 1,000$ . We use six testing datasets, including DUTS-TE [63], DUTOMRON [80], SOD [44], PASCAL-S [34], ECSSD [78], HKU-IS [33], to evaluate the model calibration degree. + +Compared Methods: We compare with both SOD models and model calibration methods in terms of model calibration degrees. The SOD models include: MSRNet [32], SRM [65], Amulet [92], BMPM [91], DGRL [67], PAGR [93], PiCANet [37], CPD [73], BASNet [55], EGNet [94], AFNet [15], PoolNet [36], GCPANet [7], MINet [51], $\mathrm{F}^3\mathrm{Met}$ [69], EBMGSOD [89], ICON [97], EDN [72]. We evaluate ECE on their published prediction results, or results produced with their released model weights. We also compare with model calibration methods include: Temperature Scaling (TS) [18], Brier Loss [4], MMCE [30], Label Smoothing [46], Mixup [62], Focal Loss [45] and AdaFocal [17] implemented on our baseline model. + +Baseline Model Structure: We implement our method in the Pytorch framework. Our model has a simple U-Net structure, comprising of a ResNet50 encoder [20] and a decoder, where the former is initialised with ImageNet-pretrained weights and the later by default. We also experiment with VGG16 [58] and Swin transformer [39] encoders and report their results in Appendix I. + +Label Perturbation Techniques: We experiment with four different label perturbation strategies: (1) Hard Inversion $T(Y, \alpha, \beta = 1.0)$ , (2) Soft Inversion (SI) $T(Y, \alpha, \beta = 0.75)$ , (3) Moderation (M) $T(Y, \alpha, \beta = 0.5)$ and Dynamic Moderation (DM) $T(Y, \alpha, \beta = 0.5)$ with additional Gaussian noise. See Appendix H.1 for implementation details. + +Training Details: Each model is trained with an Adam optimiser for 30 epochs. The learning rate is initialised to $2.5 \times 10^{-5}$ , and decays by a factor of 0.9 for each epoch after the $10^{\text{th}}$ epoch. All training images are scaled to $384 \times 384$ . Basic data augmentation techniques, including random flipping, random translation and random cropping, are applied. + +Hyperparameters: The reported model calibration results associated with ASLP are obtained by setting $\eta = 0.002$ and $\lambda = 2,000$ . We set the number of bins to $B = 10$ for ECE and OE evaluation metrics. + +# 4.2. Model Calibration Degree Performance + +Tab. 1 presents the calibration degree of existing SOD models, existing model calibration methods and our proposed technique on the six SOD testing datasets. Our proposed $\mathrm{ASLP}_{\mathrm{MC}}$ , designed to optimise the model calibration degree, achieves the best ECE performances on all testing datasets. In addition, $\mathrm{ASLP}_{\mathrm{MC}}$ also obtains the second-best + +Table 1: Salient object detection model calibration degree benchmark. Results are evaluated in with $\mathrm{ECE}_{\mathrm{EW}}$ and $\mathrm{OE}_{\mathrm{EW}}$ with 10 bins (units in %). See Appendix C for evaluations with $\mathrm{ECE}_{\mathrm{EM}}$ [48], $\mathrm{ECE}_{\mathrm{DEBIAS}}$ [29] and $\mathrm{ECE}_{\mathrm{SWEEP}}$ [56]. + +
MethodsYearDUTS-TE [63]DUT-OMRON [80]PASCAL-S [34]SOD [44]ECSSD [78]HKU-IS [33]
ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓
SOD MethodsMSRNet [32]20172.572.343.323.163.443.236.426.140.970.940.920.87
SRM [65]20174.023.724.193.964.884.599.939.582.532.351.861.72
Amulet [92]20175.675.285.845.495.765.4310.039.592.562.421.981.87
BMPM [91]20183.743.524.524.374.884.688.167.931.951.891.581.53
DGRL [67]20184.123.864.414.215.014.778.448.202.132.021.631.53
PAGR [93]20184.043.795.144.965.645.3712.1711.872.842.701.621.54
PiCANet [37]20185.124.904.844.708.147.9210.5010.303.483.392.552.47
CPD [73]20193.973.784.204.065.375.179.659.392.292.191.991.90
BASNet [55]20195.004.864.934.836.506.3610.4010.272.742.702.302.26
EGNet [94]20193.333.143.663.505.425.198.047.791.981.881.471.40
AFNet [15]20193.953.744.254.095.064.848.158.022.382.271.871.78
PoolNet [36]20193.333.123.863.705.325.078.147.872.001.901.821.75
GCPANet [7]20203.182.993.993.844.163.977.056.881.611.541.271.21
MINet [51]20203.653.484.454.294.944.758.017.892.132.031.741.65
F3Met [69]20203.673.504.254.104.854.677.957.782.262.161.921.83
EBMGSD [89]20213.453.294.113.954.794.617.487.302.142.051.791.70
ICON [97]20212.892.763.843.714.083.956.706.551.561.491.381.32
PFSNet [43]20212.942.723.953.814.454.277.597.392.412.252.061.96
EDN [72]20223.623.474.023.904.894.748.818.662.202.131.651.58
Model Calibration MethodsBrier Loss [4]19502.772.583.553.383.903.706.406.161.371.301.040.99
Temperature Scaling [18]20172.532.343.183.033.563.366.326.050.960.930.830.70
MMCE [30]20182.862.673.563.414.003.816.856.631.411.351.181.13
Label Smoothing [46]20192.001.792.892.713.042.835.975.690.830.680.820.47
Mixup [62]20192.452.253.413.233.132.995.825.701.410.183.830.05
Focal Loss [45]20202.252.083.102.823.403.136.215.981.411.031.240.77
AdaFocal [17]20221.611.412.311.842.532.275.885.471.630.791.350.52
Our MethodsASLPMC20231.401.221.991.832.312.105.505.170.480.200.790.17
ASLPMEI202327.90.0126.00.0026.10.0022.40.0029.90.0030.50.00
+ +![](images/9410c42d2da13b67128c4cb35468d0046b63752676d7fc85d22c22a7f53302a4.jpg) +Figure 3: Joint distribution of prediction confidence (horizontal axis) and prediction accuracy (vertical axis) on the DUTS-TE dataset. A perfectly calibrated model has an identical confidence distribution and accuracy distribution, denoted as the oracle (diagonal red dotted line). The joint distribution of a better calibrated model is more aligned with the oracle line, especially its high density area. See Appendix D for results of other methods and on other testing datasets. + +![](images/50bf657d44382ec78932238038a5ae4db914d1223b88c52b5645234bd00bdf9b.jpg) + +![](images/e64b3e51f8c95ac670f1ec4e1fe8177bf78f43667f12c450f01ce5d30b3c7d8a.jpg) + +![](images/80add01356da9634d48a866bbce202fdf8df1142f7e85663727ee5f7d071f0ab.jpg) + +![](images/d7c6f5307d77f3b0fff7ec337a0b060588890d7aa1b0bc5a134350f06df8054b.jpg) + +![](images/68bd1b189f642883122fd09858994ec2bf688b7e48b2074ff68fc3b398f342db.jpg) + +OE performances on all six testing datasets, outperformed only by our $\mathrm{ASLP}_{\mathrm{MEI}}$ . On the other hand, $\mathrm{ASLP}_{\mathrm{MEI}}$ , though almost eliminates the over-confidence issue completely, is significantly mis-calibrated on the six testing datasets. This can be attributed to it being significantly under-confident rather than over-confident. The observed performances of + +$\mathrm{ASLP}_{\mathrm{MEI}}$ are in accordance with its design - assuming minimum distribution commitment with respect to missing information. That is, in the presence of limited training data, to maximise the prediction entropy while maintaining the prediction accuracy for in-distribution data. + +Fig. 3 presents the joint distribution of prediction con + +fidence and prediction accuracy of some of the best calibrated methods and our proposed technique on DUTS-TE dataset (See Appendix D for other testing datasets and other methods). Existing SOD methods produce extremely confident predictions whose confidence scores are nearly $100\%$ for the majority of samples. On the contrary, the prediction accuracy is on average lower than prediction confidence, resulting in the model being over-confident. On the other hand, existing model calibration methods are generally more calibrated than the SOD methods which in general do not strive to improve model calibration degree. + +Our proposed $\mathrm{ASLP}_{\mathrm{MC}}$ produces the most calibrated model whose joint distribution is closer to the oracle than those of the compared calibration methods and SOD methods. AdaFocal [17] produces the second most calibrated model on DUTS-TE. However, the majority of their joint distribution (blue high density area) is slightly to the right bottom of the oracle line, making their model slightly less calibrated. Whereas the high density area of our joint distribution is well aligned with the oracle line, showing $\mathrm{ASLP}_{\mathrm{MC}}$ is more calibrated. Despite the small difference on the plot, $\mathrm{ASLP}_{\mathrm{MC}}$ improves over AdaFocal by more than $10\%$ in terms of ECE scores on DUTS-TE dataset. We can also observe that $\mathrm{ASLP}_{\mathrm{MEI}}$ is significantly under-confident for in-distribution data with its joint distribution being at the top-left side of the oracle line. Its prediction accuracies are limited to between $70\%$ and $80\%$ while the prediction accuracies are generally above $90\%$ . + +# 4.3. Model Calibration Degrees on Out-of-Distribution Dataset + +We compare our proposed method with existing model calibration methods in terms of model calibration degrees on Out-of-Distribution data. We consider texture images, where salient objects are completely absent, as OoD samples for the SOD task. We use Describable Texture Dataset [9] to evaluate the model calibration degrees on OoD samples. Fig. 4 shows the joint distribution of prediction confidence and prediction accuracy of various model calibration methods and our proposed techniques. It can be seen that the baseline model produces extremely confident predictions for OoD data. However, its accuracy is only $41.88\%$ , worse than a uniform prior in a binary classification task. We also observe that Temperature Scaling does not calibrate the model under data distribution shift in accordance with literature [50, 45]. Our $\mathrm{ASLP}_{\mathrm{MC}}$ , being the most calibrated for in-distribution data, is also more calibrated on the OoD samples than the existing model calibration methods by a large margin as shown in Tab. 2. On the other hand, our $\mathrm{ASLP}_{\mathrm{MEI}}$ is more successful in handling OoD data. It is the most calibrated on OoD data, with a larger proportion of the distribution aligned with the oracle line. As shown in Tab. 2, it outperforms existing model calibration methods in + +![](images/94957d75b27cc1fe73e8a7e7b75f7d212ec8b1fbbf41ac0a16f900762c93a3bc.jpg) +Baseline + +![](images/04bffeb601ce457d981081628183ffe10a8740a52752c4dc01049605f0fd237c.jpg) + +![](images/8d7f2f156db864f82a879ebecd61cd0ad2fc05a4b6cbc8efaa1745336e9d9045.jpg) + +![](images/5d389e1fa03afaec967c38fce82c3e7369a6bb3472be3f83cbaea3b362a2c9ef.jpg) + +![](images/9336ff3df9dcae127395ab9299e047bd9e3f28e24b6eba42f38e39d5d1979cda.jpg) +Temperature Scaling + +![](images/dee80f765e09f345ed26eef071d41df902182ebae8cc4a7a9fc555b3e8db5f0a.jpg) +Label Smoothing + +![](images/e1dce49e24d7a192a85d363eda14030745b9586649aa9f5c7cde5c8fa44938d7.jpg) +Mixup +AdaFocal +Figure 4: Joint distribution of prediction confidence (horizontal axis) and prediction accuracy (vertical axis) on the Describable Texture Dataset [9], of compared model calibration methods and our proposed $\mathrm{ASLP}_{\mathrm{MC}}$ and $\mathrm{ASLP}_{\mathrm{MEI}}$ . + +![](images/ade4a26ca3956a305430ec102b0f4a04037f1222991fef0ffb21875a862c2354.jpg) +MMCE +ASLPMEMI + +![](images/28a0889fb08ca638fc57d5ee3b235b98532fd279c7a088972f9de3a9f4e612fe.jpg) +Focal Loss +ASLPMC + +terms of both ECE and OE by significant margins. This can be attributed to its minimum distribution assumption in the presence of limited training data. + +Table 2: Model calibration methods and our $\mathrm{ASLP}_{\mathrm{MC}}$ and $\mathrm{ASLP}_{\mathrm{MEI}}$ are evaluated on the Out-of-Distribution dataset, Describable Texture Dataset [9], in terms of $\mathrm{ECE}_{\mathrm{EW}}$ and $\mathrm{OE}_{\mathrm{EW}}$ with 10 bins, and Accuracy (ACC). + +
MethodEvaluation (%)
ECE ↓OE ↓ACC ↑
Baseline52.3651.0541.88
Brier Loss [4]38.8537.1853.62
Temperature Scaling [18]51.9550.4641.59
Label Smoothing [46]37.2235.4855.41
MMCE [30]40.6439.6754.39
Mixup [62]31.0729.1058.71
Focal Loss [45]40.0138.4349.71
AdaFocal [17]27.5525.0755.39
ASLPMC18.3116.3761.93
ASLPMEI13.438.4062.47
+ +# 4.4. Discussion + +Adaptive Stochastic Label Perturbation: We study the effect of ASLP on ECE and OE and present the experimental results in Tab. 3. It shows that ASLPs significantly outperforms the baseline model, "B", which does not adopt any model calibration measures. In addition, ASLPs also outperforms their static counterparts (SLPs) which use a single + +Table 3: Ablation: Effect of Stochastic Label Perturbation (SLP) and Adaptive Stochastic Label Perturbation (ASLP) with different label perturbation techniques on the model calibration degrees evaluated on Expected Calibration Error (ECE) and Over-confidence Error (OE). The proposed ASLP is generalised to an Adaptive Label Smoothing (ALS) technique that adaptively tunes the label softening scale $(\beta_{\mathrm{ada}})$ . + +
MethodsPerturbation ParamsDUTS-TE [63]DUT-OMRON [80]PASCAL-S [34]SOD [44]ECSSD [78]HKU-IS [33]
αβeECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓
Baseline (“B”)0003.483.294.174.024.604.417.427.171.931.861.641.59
SLPα=0.01HI0.011.0X2.211.842.962.783.112.826.095.801.030.681.010.53
SLPα=0.02SI0.020.75X2.252.053.002.823.052.836.406.090.930.840.870.60
SLPα=0.03M0.030.5X2.242.033.172.973.413.206.265.970.830.770.960.81
SLPα=0.03DM0.030.5✓2.292.093.002.833.473.246.726.431.131.040.960.80
LSβ=0.031.00.03X2.201.993.092.913.243.036.275.991.030.780.920.67
ASLPHIαada1.0X1.401.221.991.832.312.105.505.170.480.200.790.17
ASLPSIαada0.75X1.511.292.141.952.292.075.124.800.610.340.840.22
ASLPMαada0.5X1.471.271.871.802.372.135.635.290.510.230.800.20
ASLPMCMαada0.5✓1.641.201.941.752.031.814.143.840.800.420.870.42
ALS1.0βadaX1.461.252.071.872.302.105.445.180.610.250.810.32
+ +$\alpha$ for the entire dataset. This can be attributed to the approach modelling variance of noise with input image. + +Generalisation of Adaptive Label Smoothing: We generalise the proposed ASLP to label smoothing, developing an Adaptive Label Smoothing (ALS) that fixes the label perturbation probability to $100\%$ , akin to the label smoothing technique [46], and tunes a smoothing factor for each training sample. As shown in Tab. 3, ALS effectively reduces the ECE and OE scores over its static version $\mathrm{LS}^{\beta = 0.03}$ , and achieves similar performances with $\mathrm{ASLP}_{\mathrm{MC}}$ approaches on the six testing datasets. It manifests that our proposed ASLP can be generalised onto other label perturbation techniques as a measure to calibrate the SOD models. + +Compatibility with SOTA SOD Models We retrain EBMGSOD [89], ICON [97] and EDN [72] with the proposed $\mathrm{ASLP}_{\mathrm{MC}}$ and find significant improvements in terms of model calibration degrees without compromising their classification abilities (See Appendix E). + +Compatibility with Different Backbones: We demonstrate that our proposed method is also compatible with VGG16 [58] and Swin transformer [39] backbones. See Appendix I for details. + +Effectiveness in Other Dense Binary Classification Tasks: Experiments on Smoke Detection [79] and Camouflaged Object Detection [14] demonstrate that our method can be generalised to dense binary classification tasks to improve model calibration degrees. See Appendix F. + +Generalisation to Multi-Class Segmentation task: Experiments on Semantic Segmentation [11] demonstrate that our method can also be generalised to dense multi-class classification tasks. See Appendix G. + +# 4.5. Hyperparameters + +Static Stochastic Label Perturbation: Tab. 3 shows that, under a small label perturbation probability, the four label perturbation techniques can alleviate the model overconfidence issues of the baseline model, "B", on the six + +testing datasets. They also achieve similar results to Label Smoothing [46], setting $\beta = 0.03$ and $\alpha = 1$ . Each SLP has a wide range of effective label perturbation probabilities that improves model calibrations (See Appendix H.2 Tab. 13), and these improvements do not sacrifice the model's classification performance (see Appendix H.3). Larger values of the label perturbation probability eventually lead to increasing ECE scores as the model transitions to being under-confident (see Appendix H.2). + +Updating Rate $\eta$ : $\mathrm{ASLP}_{\mathrm{MC}}$ models trained with $\eta \in [0.0002, 0.005]$ are generally stable, producing similar calibration degrees and classification performances. Values smaller than 0.001 require longer training and high values lead to sub-optimal results (See Appendix J). + +Regularisation Strength $\lambda$ : $\lambda$ spanning between 500 and 10,000 are optimal. Very high values for $\lambda$ can lead to oscillation resulting in poor performance (See Appendix J). + +# 5. Conclusion + +This work first introduces a Self-Calibrating Binary Cross Entropy loss that unifies label perturbation processes including stochastic approaches and label smoothing to improve model calibration while preserving classification accuracy. We further propose an Adaptive Stochastic Label Perturbation that learns a unique label perturbation level for individual training image. Following Maximum Entropy Inference, ASLP adopts classification / calibration as proxy for known data and maximises the prediction entropy with respect to missing data. The proposed $\mathrm{ASLP}_{\mathrm{MC}}$ improves model calibration degrees on both in-distribution samples and out-of-distribution samples, without negatively impacting classification performance. The approach can be easily applied to different models, which we demonstrate with several SOTA models. It is also demonstrated to be effective on a semantic segmentation task and other binary tasks. + +Acknowledgments. This research was in-part supported by the ANU-Optus Bushfire Research Center of Excellence. + +# References + +[1] Radhakrishna Achanta, Sheila Hemami, Francisco Estrada, and Sabine Susstrunk. Frequency-tuned salient region detection. In CVPR, pages 1597-1604. 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IEEE TPAMI, 2022. 5, 6, 8, 20, 21, 22, 27 \ No newline at end of file diff --git a/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/images.zip b/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..fd21d3894ad8eeaa2555a1343a0a0ec44705e347 --- /dev/null +++ b/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:ddd3fd6f7535cbb6649a70b5ae751dfe70109e97f603b1840ae517f28344b058 +size 541647 diff --git a/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/layout.json b/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..a5baadded4177bd990e904eebac0fb62236676fa --- /dev/null +++ b/2023/Model Calibration in Dense Classification with Adaptive Label Perturbation/layout.json @@ -0,0 +1,11527 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 61, + 103, + 532, + 120 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 103, + 532, + 120 + ], + "spans": [ + { + "bbox": [ + 61, + 103, + 532, + 120 + ], + "type": "text", + "content": "Model Calibration in Dense Classification with Adaptive Label Perturbation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 143, + 533, + 172 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 143, + 533, + 172 + ], + "spans": [ + { + "bbox": [ + 59, + 143, + 533, + 172 + ], + "type": "text", + "content": "Jiawei Liu Changkun Ye Shan Wang Ruikai Cui Jing Zhang Kaihao Zhang Nick Barnes The Australian National University" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 199, + 192, + 211 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 199, + 192, + 211 + ], + "spans": [ + { + "bbox": [ + 143, + 199, + 192, + 211 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 224, + 290, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 224, + 290, + 523 + ], + "spans": [ + { + "bbox": [ + 47, + 224, + 290, + 523 + ], + "type": "text", + "content": "For safety-related applications, it is crucial to produce trustworthy deep neural networks whose prediction is associated with confidence that can represent the likelihood of correctness for subsequent decision-making. Existing dense binary classification models are prone to being over-confident. To improve model calibration, we propose Adaptive Stochastic Label Perturbation (ASLP) which learns a unique label perturbation level for each training image. ASLP employs our proposed Self-Calibrating Binary Cross Entropy (SC-BCE) loss, which unifies label perturbation processes including stochastic approaches (like DisturbLabel), and label smoothing, to correct calibration while maintaining classification rates. ASLP follows Maximum Entropy Inference of classic statistical mechanics to maximise prediction entropy with respect to missing information. It performs this while: (1) preserving classification accuracy on known data as a conservative solution, or (2) specifically improves model calibration degree by minimising the gap between the prediction accuracy and expected confidence of the target training label. 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Its tasks include Salient Object Detection [86], Camouflaged Object Detection [13], Smoke Detection [79], etc. Performance in these tasks has been significantly advanced using the strong representation powers of Deep Neural Networks (DNNs). However, with complex structures and a tremendous number of parameters, DNNs are prone to over-fitting to training data and producing over-confident predictions in the real world [18]. Such issues can render the model predictions unreliable in decision making or utilisation in downstream tasks." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 59, + 701, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 714 + ], + "type": "text", + "content": "Recently, a growing body of literature has been pro" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 310, + 198, + 539, + 299 + ], + "blocks": [ + { + "bbox": [ + 310, + 198, + 539, + 299 + ], + "lines": [ + { + "bbox": [ + 310, + 198, + 539, + 299 + ], + "spans": [ + { + "bbox": [ + 310, + 198, + 539, + 299 + ], + "type": "image", + "image_path": "0b48a447877521fb5e19777c78e824597d2821e87a72290b0de4c5e0aac4997e.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "lines": [ + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "spans": [ + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "text", + "content": "Figure 1: Applying Adaptive Label Perturbation during training can effectively moderate predictions at incorrect areas, highlighting them with high entropy values (red). " + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "inline_equation", + "content": "Z_{t}(x,y)" + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "text", + "content": " is a sample-wise Bernoulli variable, parameterized by " + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "text", + "content": ", at the " + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "inline_equation", + "content": "t^{\\mathrm{th}}" + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "text", + "content": " iteration. After " + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "text", + "content": " iterations, update " + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "text", + "content": " using Eq. (5) to adjust the likelihood (or level) of label perturbation to increase entropy for incorrect predictions and so correct model calibration. The Perturbed Label (shown inverted) replaces the Groundtruth Label with probability " + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 303, + 547, + 411 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 425, + 547, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 425, + 547, + 569 + ], + "spans": [ + { + "bbox": [ + 304, + 425, + 547, + 569 + ], + "type": "text", + "content": "posed to address model mis-calibration problems in DNNs. They can be roughly categorised as: (1) post-hoc operations, such as temperature scaling [18], Platt scaling [54], etc., (2) training objective approaches [27], like MMCE [30], soft calibration objective [27], focal loss [45, 17], and (3) data/label augmentation techniques, e.g. label smoothing [46] and mixup [85]. We propose an Adaptive Label Perturbation which learns a unique label perturbation level for each training image. As illustrated in Fig. 1, training with Adaptive Stochastic Label Perturbation, a form of ALP, can effectively moderate incorrect predictions and highlight them with high entropy values." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "text", + "content": "Adaptive Label Perturbation employs our proposed Self-Calibrating Binary Cross Entropy (SC-BCE) loss, which unifies label perturbation processes including stochastic approaches (like DisturbLabel [75]), and label smoothing [60] to correct calibration while maintaining classification accuracy. SC-BCE loss is equivalent to a factored combination of (i) a BCE loss w.r.t. groundtruth label, and (ii) a BCE loss w.r.t. a uniform binary categorical distribution. The former enhances dense binary classification performance and the latter improves the model calibration degree. Our method can be connected to Maximum Entropy Inference [23] of classic statistical mechanics, to maximise prediction" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "1173" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 286, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 286, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 286, + 95 + ], + "type": "text", + "content": "entropy with respect to missing information while preserving the classification accuracy on known data." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 96, + 286, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 96, + 286, + 262 + ], + "spans": [ + { + "bbox": [ + 46, + 96, + 286, + 262 + ], + "type": "text", + "content": "The proposed Adaptive Label Perturbation (ALP) can approximate Maximum Entropy Inference [23] to maximise prediction entropy while preserving the ideal dense classification performance on known data. This represents a conservative solution that adopts classification accuracy as a proxy for known data and assumes maximum disorder on unknown data. We also present an alternative ALP solution that, instead, takes model calibration degree as a proxy for known data, using a calibration regulariser which constrains the expected confidence of individual supervision signal to not drop below the ideal accuracy on the validation set. This effectively minimises the gap between the distributions of prediction confidence and prediction accuracy, which is the source of model mis-calibration." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 263, + 286, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 263, + 286, + 467 + ], + "spans": [ + { + "bbox": [ + 46, + 263, + 286, + 467 + ], + "type": "text", + "content": "Our contributions can be summarised as: (i) We propose Adaptive Stochastic Label Perturbation that learns a sample-wise label perturbation level to improve model calibration; (ii) We present a Self-Calibrating Binary Cross Entropy loss that unifies label perturbation processes including stochastic approaches and label smoothing; (iii) Following Maximum Entropy Inference [23] we show that Adaptive Stochastic Label Perturbation " + }, + { + "bbox": [ + 46, + 263, + 286, + 467 + ], + "type": "inline_equation", + "content": "(\\mathrm{ASLP}_{\\mathrm{MEI}})" + }, + { + "bbox": [ + 46, + 263, + 286, + 467 + ], + "type": "text", + "content": ", can maximise the prediction entropy while preserving the ideal dense classification accuracy, and (iv) We present an alternative Adaptive Stochastic Label Perturbation " + }, + { + "bbox": [ + 46, + 263, + 286, + 467 + ], + "type": "inline_equation", + "content": "(\\mathrm{ASLP}_{\\mathrm{MC}})" + }, + { + "bbox": [ + 46, + 263, + 286, + 467 + ], + "type": "text", + "content": " solution to maximise model calibration degree, which achieves state-of-the-art performance in terms of model calibration degree on both in-distribution and out-of-distribution data. We thoroughly evaluate our method on Salient Object Detection and demonstrate its effectiveness for Camouflaged Object Detection, Smoke Detection and Semantic Segmentation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 478, + 138, + 491 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 478, + 138, + 491 + ], + "spans": [ + { + "bbox": [ + 47, + 478, + 138, + 491 + ], + "type": "text", + "content": "2. Related Works" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 498, + 286, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 286, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 286, + 605 + ], + "type": "text", + "content": "Model Calibration: Model calibration methods can be roughly divided into three categories of approach: (1) post hoc processing (2) training object, and (3) input/label augmentation. The first category utilises a validation set to align the prediction confidence distribution with prediction accuracy distribution. It includes histogram binning [82], isotropic regression [83], Platt scaling [54, 49], Bayesian binning into quantiles [47], Dirichlet scaling [28], mix-n-match [87] and temperature scaling [18, 81]." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 606, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 606, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 606, + 286, + 714 + ], + "type": "text", + "content": "The second category focuses on designing training objectives that (in)directly improve model calibration degree. Some methods address the in-continuity of expected calibration error, a widely adopted model calibration measure, and propose trainable calibration objectives like maximum mean calibration error [30], soft calibration objective [27]. Other works discover that certain existing training objects are beneficial to model calibration, e.g. Brier loss [4, 10], confidence penalty [52] and focal loss [45, 17]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": "The third category employs data or label augmentation techniques to regularise the prediction confidence distribution. Mixup [85, 62] explores the neighbourhood of training data through random interpolation of input images and associated labels to improve model calibration degree. Label smoothing [46] augments the one-hot training labels with softer versions to prevent the model being over-confident." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 158, + 545, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 158, + 545, + 337 + ], + "spans": [ + { + "bbox": [ + 304, + 158, + 545, + 337 + ], + "type": "text", + "content": "Salient Object Detection: Inspired by pioneering work [22], traditional Saliency Object Detection (SOD) methods rely on various heuristic priors with handcraft features to explore low-level cures [1, 25, 26, 38, 66]. However, these methods cannot cope with complex scenes because of the limited representation ability of handcrafted features [3]. Recently, deep learning based SOD methods broke the bottleneck of traditional methods due to the powerful capability of neural networks, achieving improved performance [6, 24, 55, 76, 37, 64, 68]. Early deep SOD methods use multi-layer perception to predict a map with a pixel-wise score for each image [71, 8]. These approaches rely on fixed fully connected layers and thus severely limit the ability of spatial information extraction. Later methods address this issue via using fully convolutional networks (FCNs) [40]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 339, + 545, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 339, + 545, + 495 + ], + "spans": [ + { + "bbox": [ + 304, + 339, + 545, + 495 + ], + "type": "text", + "content": "Most contemporary SOD methods are designed based on FCNs with various schemes to improve performance. One of the most popular strategies is to fuse multi-scale information extracted from different layers and aggregate them in the network [91, 74, 16, 51, 96, 90]. Attention modules are also applied to capture powerful multi-scale features via exploring relationship between local and global information [37, 53, 95, 21]. Training SOD networks using auxiliary supervision is also a popular strategy [70, 70, 61]. For example, the body map and detail map are utilized by [70] to help the network focus on center areas and edges, respectively. Skeleton [35] and uncertainty [61] are applied to the training processing due to their important roles in taking photos." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 496, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 496, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 496, + 545, + 616 + ], + "type": "text", + "content": "Noisy Label: Noisy labels refer to incorrect ground truth classes/values in classification/regression tasks. They arise from data collection or annotation processes, and exist commonly in real-world datasets [2]. Efforts are put to identify the noisy labels and exclude them from network training in various computer vision tasks, deeming their incorporation as harmful. [88] proposes a framework that learns from noisy labels, being a collection of predictions from classic SOD methods. The framework approximates the noise distribution in order to recover clean labels for model training." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": "Differently from data augmentation techniques that are applied simultaneously to training samples and corresponding labels to generate more training data, one may artificially corrupt the label. We refer to this category of approaches as label perturbation, which includes label smoothing approaches [60], and DisturbLabel, Xie et al. [75]. In image classification, Xie et al. [75] shows that randomly replacing training labels with a prior distribution" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "1174" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": "leads to a regularising effect, preventing overfitting. Our work is different from [75] by employing labels corrupted to different scales to enhance the model calibration degrees for both in-distribution and out-of-distribution data. Further, in performing this, we assume noise that varies with different samples, making our method more adaptable." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 156, + 153, + 168 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 156, + 153, + 168 + ], + "spans": [ + { + "bbox": [ + 47, + 156, + 153, + 168 + ], + "type": "text", + "content": "3. Proposed Method" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 175, + 287, + 236 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 175, + 287, + 236 + ], + "spans": [ + { + "bbox": [ + 46, + 175, + 287, + 236 + ], + "type": "text", + "content": "We first lay out the task setting in Sec. 3.1. Then we introduce our proposed Self-Calibrating Binary Cross Entropy loss in Sec. 3.2 and prove its connection to Maximum Entropy Inference [23] in Sec. 3.3. Lastly, we detail our major contribution - Adaptive Label Perturbation in Sec. 3.4." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 243, + 128, + 257 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 243, + 128, + 257 + ], + "spans": [ + { + "bbox": [ + 47, + 243, + 128, + 257 + ], + "type": "text", + "content": "3.1. Task Setting" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "spans": [ + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": "Binary segmentation problems aim to differentiate between foreground object(s) and background. They can be formulated as a pixel-wise binary classification problem. Given an independent and identically distributed (i.i.d) training dataset " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_{\\mathrm{TR}} = \\{x_i,y_i\\}_{i = 1}^N" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": " drawn from an unknown joint distribution of training images and groundtruth labels " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "P(\\mathcal{X},\\mathcal{Y})" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": ", a neural network model parameterised by " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": " is employed to predict labels for an input image " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "x\\in \\mathcal{X}" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": ": " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "f_{\\theta}(x)\\in (0,1)^{1\\times H\\times W}" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": ". We use " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "\\hat{y}" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "P_{\\hat{y}}" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": " to denote the winning class and its associated probability respectively. The groundtruth label " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "y\\in \\{0,1\\}^{1\\times H\\times W}" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": " represents the foreground pixels with \"1\" and background with \"0\". In the following equations, we omit the spatial indexes " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": " for simplicity. A perfectly calibrated model has " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "\\mathrm{P}(\\hat{y} = y|P_{\\hat{y}}) = P_{\\hat{y}},\\forall P_{\\hat{y}}\\in (0,1)" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": ". That is, in the entire range of prediction probabilities, prediction with probability " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "P_{\\hat{y}}" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": " has exactly " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "P_{\\hat{y}}" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": " chance to be correct. The calibration degree of a model " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "f_{\\theta}(\\cdot)" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": " over a distribution " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": " is quantified with Expected Calibration Error (ECE), defined as " + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "inline_equation", + "content": "\\mathbb{E}_{f_{\\theta}(x)}[|\\mathrm{P}(\\hat{y} = y|f_{\\theta}(x)) - f_{\\theta}(x)|]" + }, + { + "bbox": [ + 46, + 262, + 289, + 502 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 509, + 275, + 523 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 509, + 275, + 523 + ], + "spans": [ + { + "bbox": [ + 47, + 509, + 275, + 523 + ], + "type": "text", + "content": "3.2. Self-Calibrating Binary Cross Entropy Loss" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 528, + 287, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 528, + 287, + 564 + ], + "spans": [ + { + "bbox": [ + 46, + 528, + 287, + 564 + ], + "type": "text", + "content": "We propose a Self-Calibrating Binary Cross Entropy (SC-BCE) loss that unifies Label Smoothing [60], DisturbLabel [75] and Stochastic Label Perturbation as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 77, + 574, + 287, + 631 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 574, + 287, + 631 + ], + "spans": [ + { + "bbox": [ + 77, + 574, + 287, + 631 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {L} _ {\\mathrm {S C - B C E}} (\\theta , X, Y, \\alpha , \\beta) \\\\ = \\mathbb {E} _ {x, y \\in X, Y} \\left[ \\left(1 - Z _ {t} (x, y)\\right) \\cdot \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x, y) \\right. \\\\ \\left. + Z _ {t} (x, y) \\cdot \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x, p (y, \\beta)) \\right] \\tag {1} \\\\ \\end{array}", + "image_path": "8d68cf4628bbd041ca8bbcd021c7e6e530ce97eb0b1b195d33044bd2f6a3de3d.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 83, + 633, + 183, + 657 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 633, + 183, + 657 + ], + "spans": [ + { + "bbox": [ + 83, + 633, + 183, + 657 + ], + "type": "interline_equation", + "content": "\\beta \\in [ 0, 2 ], \\quad \\alpha \\in [ 0, \\frac {1}{\\beta}),", + "image_path": "d7cd9b1b7811dda9cb04de3f714e97f51543e07929ef1b911113b1a3024b6c2d.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "Z_{t}(x,y) \\sim B(1,\\alpha)" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " follows a Bernoulli distribution with " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " probability to be 1 and " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "1 - \\alpha" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " chance to be 0, " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " denotes the training epoch, " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\alpha \\in [0,\\frac{1}{\\beta})" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\beta \\in [0,2]" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " are Label Perturbation Probability (LPP) and Label Perturbation Strength" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "spans": [ + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": "(LPS) respectively, " + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "inline_equation", + "content": "p(y,\\beta) = (1 - \\beta)\\cdot y + \\frac{\\beta}{2},\\beta \\in [0,2]" + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": " is a perturbed label and " + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{BCE}}(\\theta ,x,y)^1" + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": " is a Binary Cross Entropy (BCE) loss computed for training pair " + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": ". For " + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\alpha = 1" + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": ", the label perturbation equation follows the label smoothing equation for a binary label [60]. In the proposed SC-BCE loss, different label perturbations can be applied by setting (i) Label Smoothing [60]: " + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\alpha = 1" + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\beta \\in [0,1)" + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": ", (2) DisturbLabel: " + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\beta = 1" + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\alpha \\in (0,1)" + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": ", and (3) Stochastic Label Perturbation (SLP): " + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\beta \\in (0,2]" + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\alpha \\in (0,\\frac{1}{\\beta})" + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": ". For example, Hard Inversion (HI) that inverts the label category as shown in Fig. 2, can be stochastically applied by setting " + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\beta = 2" + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\alpha \\in (0,\\frac{1}{2})" + }, + { + "bbox": [ + 304, + 71, + 545, + 217 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "spans": [ + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "type": "text", + "content": "In the implementation of SLP, the supervision for an individual training image in each epoch is sampled by drawing from a Bernoulli distribution. That is, the individual supervision can take the form of the groundtruth label or perturbed label in each training iteration. The overall function of SLP can be connected to that of a smoothed label by taking expectation of the Bernoulli variable: " + }, + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "type": "inline_equation", + "content": "\\mathbb{E}_{Z_t}[(1 - Z_t(y))\\cdot Y + Z_t(y)\\cdot p(y,\\beta)],\\forall y\\in Y." + }, + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "type": "text", + "content": " Taking the expectation over the Bernoulli variation in each iteration is too expensive to implement in model training. Instead, following [75], the expectation of stochastically perturbed label is approximated by taking expectation across training epochs: " + }, + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "type": "inline_equation", + "content": "\\mathbb{E}_{t\\in T}[(1 - Z_t(y))\\cdot Y + Z_t(y)\\cdot p(y,\\beta)],\\forall y\\in Y," + }, + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "type": "text", + "content": " is the total number of training epochs and " + }, + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "type": "inline_equation", + "content": "Z_{t}(y)" + }, + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "type": "text", + "content": " is a variable drawn from a Bernoulli distribution for the " + }, + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "type": "inline_equation", + "content": "\\mathrm{t^{th}}" + }, + { + "bbox": [ + 304, + 218, + 545, + 399 + ], + "type": "text", + "content": " epoch." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 413, + 466, + 426 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 413, + 466, + 426 + ], + "spans": [ + { + "bbox": [ + 305, + 413, + 466, + 426 + ], + "type": "text", + "content": "3.3. Maximum Entropy Inference" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 434, + 545, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 434, + 545, + 519 + ], + "spans": [ + { + "bbox": [ + 304, + 434, + 545, + 519 + ], + "type": "text", + "content": "Maximum Entropy Inference (MEI), assuming minimum distribution commitment in respect to missing information, was initially proposed by Jaynes [23]. That is, the probability distribution should have maximum Shannon entropy subject to the partially available information. Thus, in the complete absence of information, Shannon entropy for a binary prediction defined in Eq. (2) should be maximised:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 316, + 543, + 545, + 585 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 543, + 545, + 585 + ], + "spans": [ + { + "bbox": [ + 316, + 543, + 545, + 585 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathbb {H} \\left(f _ {\\theta} (X)\\right) = \\mathbb {E} _ {x \\in X} \\left[ - f _ {\\theta} (x) \\cdot \\log f _ {\\theta} (x) - \\right. \\tag {2} \\\\ \\left. \\left(1 - f _ {\\theta} (x)\\right) \\cdot \\log \\left(1 - f _ {\\theta} (x)\\right) \\right\\rfloor \\\\ \\end{array}", + "image_path": "b4a7b1d27c3881c2d59cf5814331e8074cd67b009e49bf7cf9d6ab5928fbb455.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 598, + 545, + 633 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 598, + 545, + 633 + ], + "spans": [ + { + "bbox": [ + 304, + 598, + 545, + 633 + ], + "type": "text", + "content": "For salient object detection and other binary segmentation problems, maximising Eq. 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In each iteration, the model uses a Bernoulli variable to sample a supervision, which can be a groundtruth label " + }, + { + "bbox": [ + 46, + 240, + 545, + 301 + ], + "type": "inline_equation", + "content": "y_{i}" + }, + { + "bbox": [ + 46, + 240, + 545, + 301 + ], + "type": "text", + "content": " or a perturbed label " + }, + { + "bbox": [ + 46, + 240, + 545, + 301 + ], + "type": "inline_equation", + "content": "p_i" + }, + { + "bbox": [ + 46, + 240, + 545, + 301 + ], + "type": "text", + "content": " and computes a sample-specific " + }, + { + "bbox": [ + 46, + 240, + 545, + 301 + ], + "type": "inline_equation", + "content": "\\nabla_{\\alpha_i}" + }, + { + "bbox": [ + 46, + 240, + 545, + 301 + ], + "type": "text", + "content": " based on the prediction. Regularisation is computed with Eq. 5 (ASLPMEI) or Eq. 6 (ASLPMC) on a validation set after each training epoch. The ASLP learning rule combines Grad- " + }, + { + "bbox": [ + 46, + 240, + 545, + 301 + ], + "type": "inline_equation", + "content": "\\alpha_{i}" + }, + { + "bbox": [ + 46, + 240, + 545, + 301 + ], + "type": "text", + "content": " and a factored regularisation to update label perturbation probability " + }, + { + "bbox": [ + 46, + 240, + 545, + 301 + ], + "type": "inline_equation", + "content": "\\alpha_{i}" + }, + { + "bbox": [ + 46, + 240, + 545, + 301 + ], + "type": "text", + "content": " for each individual sample." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 182, + 152, + 291, + 236 + ], + "blocks": [ + { + "bbox": [ + 182, + 152, + 291, + 236 + ], + "lines": [ + { + "bbox": [ + 182, + 152, + 291, + 236 + ], + "spans": [ + { + "bbox": [ + 182, + 152, + 291, + 236 + ], + "type": "table", + "html": "
L BCE(θ, x_i, p(y_i, β)) - L BCE(θ, x_i, y_i)∇αi
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Regularisation
A(θ, DVAL) - A(θlm, DVAL) or (1 - β · αi2) - A(θlm, DVAL)Regularisation
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ASLP - Learning Rule
∇αi+λ·RegularisationΔαi
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", + "image_path": "6cfadaf02f8dcde3a27850bbbe40657ddac5fed80deadd3880051764748297d9.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 312, + 107, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 312, + 107, + 323 + ], + "spans": [ + { + "bbox": [ + 47, + 312, + 107, + 323 + ], + "type": "text", + "content": "derivation) as:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 78, + 333, + 287, + 392 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 78, + 333, + 287, + 392 + ], + "spans": [ + { + "bbox": [ + 78, + 333, + 287, + 392 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {L} _ {\\mathrm {S C - B C E}} (\\theta , X, Y, \\alpha , \\beta) \\\\ = \\mathbb {E} _ {x, y \\in X, Y} \\left[ (1 - \\beta Z _ {t} (x, y)) \\cdot \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x, y) \\right. \\tag {3} \\\\ \\left. + \\beta Z _ {t} (x, y) \\cdot \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x, u) \\right], \\\\ \\end{array}", + "image_path": "8f228d93730115274345e70b2b10086e3d2dc0baa3cd53979b88d04650ff1491.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "type": "inline_equation", + "content": "Z_{t}(x,y) \\sim B(1,\\alpha)" + }, + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "type": "inline_equation", + "content": "u" + }, + { + "bbox": [ + 46, + 400, + 287, + 544 + ], + "type": "text", + "content": " is a binary uniform categorical distribution, and minimising the second term pushes the prediction distribution towards a uniform binary categorical distribution, equivalently maximising the inference entropy. Therefore, our proposed SC-BCE loss, a combination of a regular BCE loss and a BCE loss with a perturbed label, effectively performs a type of MEI. That is, the regular BCE loss component improves the model's binary classification accuracy in the presence of information while the perturbed label maximizes prediction entropy with respect to missing information in order to close the gap between the available training data and the entire data distribution." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 552, + 205, + 565 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 552, + 205, + 565 + ], + "spans": [ + { + "bbox": [ + 47, + 552, + 205, + 565 + ], + "type": "text", + "content": "3.4. Adaptive Label Perturbation" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 571, + 286, + 690 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 571, + 286, + 690 + ], + "spans": [ + { + "bbox": [ + 46, + 571, + 286, + 690 + ], + "type": "text", + "content": "Stochastic Label Perturbation (SLP) uses a single label perturbation probability and perturbation strength for the entire training dataset. However, this approach cannot adapt to predictive error that varies for different input images. To address this, we propose an Adaptive Stochastic Label Augmentation (ASLP) method to adjust the label augmentation probability for individual training samples. That is we allow the variable in Eq. (1) to be drawn from a per training image Bernoulli distribution with sample-specific label perturbation probability as:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 90, + 700, + 287, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 90, + 700, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 90, + 700, + 287, + 715 + ], + "type": "interline_equation", + "content": "Z _ {t} (x, y) \\sim B (1, \\alpha_ {x, y}), \\forall x, y \\in X, Y \\tag {4}", + "image_path": "4a0f4abac6591990c87d74aa9d38aa645f648aae1c2bf47d78743ca3b2ca0905.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\alpha_{x,y}" + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "text", + "content": " is the label perturbation probability for sample (image-label) pair " + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "text", + "content": ". Initially, we set all label perturbation probabilities to " + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\{\\alpha_{i} = 0\\}_{i = 1}^{N}" + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "text", + "content": " and train a model with a regular BCE loss without label augmentation techniques, which is equivalent to " + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{SC - BCE}}(\\theta ,X,Y,\\alpha = 0,\\beta = 0)" + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "text", + "content": ". The trained model has weight " + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\theta_{\\mathrm{lm}}" + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "text", + "content": " and its accuracy on the validation set, " + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\mathbb{A}(\\theta_{lm},\\mathcal{D}_{\\mathrm{VAL}})" + }, + { + "bbox": [ + 304, + 312, + 545, + 443 + ], + "type": "text", + "content": ", is held as an ideal performance. Subsequently, we select a label perturbation technique and continue to train the model with SC-BCE loss with a learning rule to update the label perturbation probability for individual training samples." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "spans": [ + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "text", + "content": "We propose the learning rule for " + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "inline_equation", + "content": "(\\mathrm{ASLP}_{\\mathrm{MEI}})" + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "text", + "content": " to approximate maximum entropy inference. The rule has two components: (1) " + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "inline_equation", + "content": "\\nabla_{\\alpha_i} = (2 / \\beta)\\cdot" + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "inline_equation", + "content": "\\partial \\mathbb{E}_{Z_t}(x_i,y_i)\\big[\\mathcal{L}_{\\mathrm{SC - BCE}}(X,Y,\\theta ,\\{\\alpha_i\\}_{i = 1}^N,\\beta)\\big] / \\partial \\alpha_i" + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "text", + "content": " is the derivative of the expectation of SC-BCE over the Bernoulli variable w.r.t. " + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "inline_equation", + "content": "\\alpha_{i}" + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "text", + "content": ". We divide this by " + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "inline_equation", + "content": "\\beta /2" + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "text", + "content": " to ensure that different perturbation techniques (varying " + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 304, + 444, + 545, + 564 + ], + "type": "text", + "content": " values) have the same convergence speed (See derivation in Appendix A.3), and (2) Accuracy Regularization to encourage maintenance of prediction accuracy. The rule is:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 309, + 572, + 541, + 615 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 309, + 572, + 541, + 615 + ], + "spans": [ + { + "bbox": [ + 309, + 572, + 541, + 615 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\alpha_ {i} ^ {n + 1} = \\alpha_ {i} ^ {n} + \\eta \\cdot \\left(\\nabla_ {\\alpha_ {i}} + \\lambda \\cdot \\operatorname {R e g} _ {A}\\right), \\quad \\text {f o r} i = 1, \\dots , N, \\\\ \\nabla_ {\\alpha_ {i}} = \\frac {2 \\cdot \\left(\\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x _ {i} , p (y _ {i} , \\beta)) - \\mathcal {L} _ {\\mathrm {B C E}} (\\theta , x _ {i} , y _ {i})\\right)}{\\beta}, \\\\ \\end{array}", + "image_path": "099258f48b4429cf20a7e8f8a4adb53d760a2c3676126fb0c128f6bddb44d16d.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 310, + 617, + 545, + 653 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 617, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 310, + 617, + 545, + 653 + ], + "type": "interline_equation", + "content": "\\operatorname {R e g} _ {\\mathrm {A}} = \\min \\left(\\frac {\\mathbb {A} (\\theta , \\mathcal {D} _ {\\mathrm {V A L}}) - \\mathbb {A} (\\theta_ {l m} , \\mathcal {D} _ {\\mathrm {V A L}})}{\\mathbb {A} (\\theta_ {l m} , \\mathcal {D} _ {\\mathrm {V A L}})}, 0\\right), \\tag {5}", + "image_path": "58a71a93619f372790dc267c5e4664f2652b955fd670740b96a1ec6003c942bd.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "text", + "content": " are hyperparameters controlling the updating pace of label perturbation probability and the regularisation strength respectively, " + }, + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathbb{A}(\\theta ,\\mathcal{D}_{\\mathrm{VAL}})" + }, + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathbb{A}(\\theta_{lm},and\\mathcal{D}_{\\mathrm{VAL}})" + }, + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "text", + "content": " denote the current and ideal accuracy on the validation set separately. " + }, + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\nabla_{\\alpha_i}" + }, + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "text", + "content": " aims to increase label perturbation proba" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "1176" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 334 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 334 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 334 + ], + "type": "text", + "content": "bility to confident and correct samples and otherwise for incorrectly classified samples. For example, it returns a large positive value for correct predictions with small BCE loss value w.r.t. to groundtruth label " + }, + { + "bbox": [ + 47, + 72, + 289, + 334 + ], + "type": "inline_equation", + "content": "y_{i}" + }, + { + "bbox": [ + 47, + 72, + 289, + 334 + ], + "type": "text", + "content": " and large BCE loss value w.r.t. to perturbed label " + }, + { + "bbox": [ + 47, + 72, + 289, + 334 + ], + "type": "inline_equation", + "content": "p(y_{i},\\beta)" + }, + { + "bbox": [ + 47, + 72, + 289, + 334 + ], + "type": "text", + "content": ". The \"Accuracy Regularisation\" (RegA) is designed to reduce the overall perturbation probability if the accuracy on the validation set reduces to be below the local minima. It returns 0 if there is no accuracy drop on the validation set and a large decrease will overwhelm the " + }, + { + "bbox": [ + 47, + 72, + 289, + 334 + ], + "type": "inline_equation", + "content": "\\nabla_{\\alpha_i}" + }, + { + "bbox": [ + 47, + 72, + 289, + 334 + ], + "type": "text", + "content": " value and reduce the sample label perturbation probability. Intuitively, ASLPMEI aims to construct a model that preserves the ideal classification accuracy while otherwise maximising the entropy [23]. Note that which particular examples are classified correctly are able to change, but the accuracy is constrained to remain the same. Intuitively, having a model that better captures ignorance may lead to changes in the treatment of test examples that are distant from training distribution. Note, however that adopting classification accuracy as proxy for known data and otherwise maximizing entropy is a conservative strategy and we find that it results in the model being significantly under-confident." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 335, + 289, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 335, + 289, + 422 + ], + "spans": [ + { + "bbox": [ + 47, + 335, + 289, + 422 + ], + "type": "text", + "content": "The model mis-calibration arises from the distribution mismatch between prediction confidence and prediction accuracy [45]. We offer an alternative model that uses the model calibration as proxy for known data and maximises the prediction entropy in respect to unknown data " + }, + { + "bbox": [ + 47, + 335, + 289, + 422 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 47, + 335, + 289, + 422 + ], + "type": "text", + "content": ". The learning rule replaces the \"Accuracy Regularisation\" in Eq. (5) with a \"Calibration Regularisation\" " + }, + { + "bbox": [ + 47, + 335, + 289, + 422 + ], + "type": "inline_equation", + "content": "(\\mathrm{Reg}_{\\mathrm{C}})" + }, + { + "bbox": [ + 47, + 335, + 289, + 422 + ], + "type": "text", + "content": " as:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 61, + 426, + 287, + 449 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 426, + 287, + 449 + ], + "spans": [ + { + "bbox": [ + 61, + 426, + 287, + 449 + ], + "type": "interline_equation", + "content": "\\operatorname {R e g} _ {\\mathrm {C}} = \\min \\left(\\left(1 - \\frac {\\beta \\cdot \\alpha_ {i} ^ {n}}{2}\\right) - \\mathbb {A} \\left(\\theta_ {l m}, \\mathcal {D} _ {\\mathrm {V A L}}\\right), 0\\right), \\tag {6}", + "image_path": "71a28619440467ffb6922b7414b369112a33b1bbaf9bd5f21ed664898426ce96.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "spans": [ + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "type": "inline_equation", + "content": "1 - (\\beta \\cdot \\alpha_{i}^{n} / 2)" + }, + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "type": "text", + "content": " denotes the expected confidence of the perturbed label (Derivation in Appendix A.4). For example, a foreground label \"1\" with " + }, + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "type": "text", + "content": " chance of being inverted to \"0\" has an expected confidence of 0.95. \"Calibration Regularisation\" constrains the expected confidence of perturbed label of each sample to not drop below the ideal classification accuracy on validation set, preventing the model from becoming under-confident. Note that we can also have an updating rule " + }, + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "type": "inline_equation", + "content": "\\mathrm{ALS}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "type": "text", + "content": " to learn per-image label perturbation strength (adaptive " + }, + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "type": "text", + "content": " and fixed " + }, + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "type": "inline_equation", + "content": "\\alpha = 1" + }, + { + "bbox": [ + 47, + 455, + 289, + 576 + ], + "type": "text", + "content": ") (See Appendix A.5)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 585, + 191, + 599 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 585, + 191, + 599 + ], + "spans": [ + { + "bbox": [ + 47, + 585, + 191, + 599 + ], + "type": "text", + "content": "4. Experiments and Results" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 604, + 287, + 654 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 604, + 287, + 654 + ], + "spans": [ + { + "bbox": [ + 46, + 604, + 287, + 654 + ], + "type": "text", + "content": "We verify the proposed method primarily on Salient Object Detection and also implement it for Camouflaged Object Detection, Smoke Detection and Semantic Segmentation tasks and report their results in the Appendices." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 659, + 180, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 659, + 180, + 672 + ], + "spans": [ + { + "bbox": [ + 47, + 659, + 180, + 672 + ], + "type": "text", + "content": "4.1. Implementation Details" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "type": "text", + "content": "Evaluation Metrics: We use Equal-Width Expected Calibration Error " + }, + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\left(\\mathrm{ECE}_{\\mathrm{EW}}\\right)" + }, + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "type": "text", + "content": " [18] and Equal-Width Overconfidence Error " + }, + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\left(\\mathrm{OE}_{\\mathrm{EW}}\\right)" + }, + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "type": "text", + "content": " [62] with 10 bins (" + }, + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "type": "inline_equation", + "content": "B = 10" + }, + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "type": "text", + "content": ") to" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": "evaluate the model calibration degrees. Additionally, we adopt " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "\\mathrm{ECE}_{\\mathrm{EM}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": " [48], " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "\\mathrm{ECE}_{\\mathrm{DEBIAS}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": " [29] and " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "\\mathrm{ECE}_{\\mathrm{Sweep}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": " [56] to corroborate with the results of " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "\\mathrm{ECE}_{\\mathrm{EW}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": " (See Appendix C)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 109, + 545, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 109, + 545, + 180 + ], + "spans": [ + { + "bbox": [ + 304, + 109, + 545, + 180 + ], + "type": "text", + "content": "Datasets: The proposed methods are trained with the DUTS-TR [63] training dataset. It is divided into a training set " + }, + { + "bbox": [ + 304, + 109, + 545, + 180 + ], + "type": "inline_equation", + "content": "|\\mathcal{D}_{\\mathrm{TR}}| = 9,553" + }, + { + "bbox": [ + 304, + 109, + 545, + 180 + ], + "type": "text", + "content": " and validation set " + }, + { + "bbox": [ + 304, + 109, + 545, + 180 + ], + "type": "inline_equation", + "content": "|\\mathcal{D}_{\\mathrm{VAL}}| = 1,000" + }, + { + "bbox": [ + 304, + 109, + 545, + 180 + ], + "type": "text", + "content": ". We use six testing datasets, including DUTS-TE [63], DUTOMRON [80], SOD [44], PASCAL-S [34], ECSSD [78], HKU-IS [33], to evaluate the model calibration degree." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 181, + 546, + 335 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 181, + 546, + 335 + ], + "spans": [ + { + "bbox": [ + 304, + 181, + 546, + 335 + ], + "type": "text", + "content": "Compared Methods: We compare with both SOD models and model calibration methods in terms of model calibration degrees. The SOD models include: MSRNet [32], SRM [65], Amulet [92], BMPM [91], DGRL [67], PAGR [93], PiCANet [37], CPD [73], BASNet [55], EGNet [94], AFNet [15], PoolNet [36], GCPANet [7], MINet [51], " + }, + { + "bbox": [ + 304, + 181, + 546, + 335 + ], + "type": "inline_equation", + "content": "\\mathrm{F}^3\\mathrm{Met}" + }, + { + "bbox": [ + 304, + 181, + 546, + 335 + ], + "type": "text", + "content": " [69], EBMGSOD [89], ICON [97], EDN [72]. We evaluate ECE on their published prediction results, or results produced with their released model weights. We also compare with model calibration methods include: Temperature Scaling (TS) [18], Brier Loss [4], MMCE [30], Label Smoothing [46], Mixup [62], Focal Loss [45] and AdaFocal [17] implemented on our baseline model." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 337, + 547, + 420 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 337, + 547, + 420 + ], + "spans": [ + { + "bbox": [ + 304, + 337, + 547, + 420 + ], + "type": "text", + "content": "Baseline Model Structure: We implement our method in the Pytorch framework. Our model has a simple U-Net structure, comprising of a ResNet50 encoder [20] and a decoder, where the former is initialised with ImageNet-pretrained weights and the later by default. We also experiment with VGG16 [58] and Swin transformer [39] encoders and report their results in Appendix I." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 422, + 547, + 492 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 422, + 547, + 492 + ], + "spans": [ + { + "bbox": [ + 304, + 422, + 547, + 492 + ], + "type": "text", + "content": "Label Perturbation Techniques: We experiment with four different label perturbation strategies: (1) Hard Inversion " + }, + { + "bbox": [ + 304, + 422, + 547, + 492 + ], + "type": "inline_equation", + "content": "T(Y, \\alpha, \\beta = 1.0)" + }, + { + "bbox": [ + 304, + 422, + 547, + 492 + ], + "type": "text", + "content": ", (2) Soft Inversion (SI) " + }, + { + "bbox": [ + 304, + 422, + 547, + 492 + ], + "type": "inline_equation", + "content": "T(Y, \\alpha, \\beta = 0.75)" + }, + { + "bbox": [ + 304, + 422, + 547, + 492 + ], + "type": "text", + "content": ", (3) Moderation (M) " + }, + { + "bbox": [ + 304, + 422, + 547, + 492 + ], + "type": "inline_equation", + "content": "T(Y, \\alpha, \\beta = 0.5)" + }, + { + "bbox": [ + 304, + 422, + 547, + 492 + ], + "type": "text", + "content": " and Dynamic Moderation (DM) " + }, + { + "bbox": [ + 304, + 422, + 547, + 492 + ], + "type": "inline_equation", + "content": "T(Y, \\alpha, \\beta = 0.5)" + }, + { + "bbox": [ + 304, + 422, + 547, + 492 + ], + "type": "text", + "content": " with additional Gaussian noise. See Appendix H.1 for implementation details." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 494, + 545, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 494, + 545, + 564 + ], + "spans": [ + { + "bbox": [ + 304, + 494, + 545, + 564 + ], + "type": "text", + "content": "Training Details: Each model is trained with an Adam optimiser for 30 epochs. The learning rate is initialised to " + }, + { + "bbox": [ + 304, + 494, + 545, + 564 + ], + "type": "inline_equation", + "content": "2.5 \\times 10^{-5}" + }, + { + "bbox": [ + 304, + 494, + 545, + 564 + ], + "type": "text", + "content": ", and decays by a factor of 0.9 for each epoch after the " + }, + { + "bbox": [ + 304, + 494, + 545, + 564 + ], + "type": "inline_equation", + "content": "10^{\\text{th}}" + }, + { + "bbox": [ + 304, + 494, + 545, + 564 + ], + "type": "text", + "content": " epoch. All training images are scaled to " + }, + { + "bbox": [ + 304, + 494, + 545, + 564 + ], + "type": "inline_equation", + "content": "384 \\times 384" + }, + { + "bbox": [ + 304, + 494, + 545, + 564 + ], + "type": "text", + "content": ". Basic data augmentation techniques, including random flipping, random translation and random cropping, are applied." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 566, + 545, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 566, + 545, + 613 + ], + "spans": [ + { + "bbox": [ + 304, + 566, + 545, + 613 + ], + "type": "text", + "content": "Hyperparameters: The reported model calibration results associated with ASLP are obtained by setting " + }, + { + "bbox": [ + 304, + 566, + 545, + 613 + ], + "type": "inline_equation", + "content": "\\eta = 0.002" + }, + { + "bbox": [ + 304, + 566, + 545, + 613 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 566, + 545, + 613 + ], + "type": "inline_equation", + "content": "\\lambda = 2,000" + }, + { + "bbox": [ + 304, + 566, + 545, + 613 + ], + "type": "text", + "content": ". We set the number of bins to " + }, + { + "bbox": [ + 304, + 566, + 545, + 613 + ], + "type": "inline_equation", + "content": "B = 10" + }, + { + "bbox": [ + 304, + 566, + 545, + 613 + ], + "type": "text", + "content": " for ECE and OE evaluation metrics." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 623, + 515, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 623, + 515, + 635 + ], + "spans": [ + { + "bbox": [ + 304, + 623, + 515, + 635 + ], + "type": "text", + "content": "4.2. Model Calibration Degree Performance" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 641, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 547, + 713 + ], + "type": "text", + "content": "Tab. 1 presents the calibration degree of existing SOD models, existing model calibration methods and our proposed technique on the six SOD testing datasets. Our proposed " + }, + { + "bbox": [ + 304, + 641, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 304, + 641, + 547, + 713 + ], + "type": "text", + "content": ", designed to optimise the model calibration degree, achieves the best ECE performances on all testing datasets. In addition, " + }, + { + "bbox": [ + 304, + 641, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 304, + 641, + 547, + 713 + ], + "type": "text", + "content": " also obtains the second-best" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "1177" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 60, + 102, + 533, + 403 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "text", + "content": "Table 1: Salient object detection model calibration degree benchmark. Results are evaluated in with " + }, + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "inline_equation", + "content": "\\mathrm{ECE}_{\\mathrm{EW}}" + }, + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "inline_equation", + "content": "\\mathrm{OE}_{\\mathrm{EW}}" + }, + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "text", + "content": " with 10 bins (units in %). See Appendix C for evaluations with " + }, + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "inline_equation", + "content": "\\mathrm{ECE}_{\\mathrm{EM}}" + }, + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "text", + "content": " [48], " + }, + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "inline_equation", + "content": "\\mathrm{ECE}_{\\mathrm{DEBIAS}}" + }, + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "text", + "content": " [29] and " + }, + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "inline_equation", + "content": "\\mathrm{ECE}_{\\mathrm{SWEEP}}" + }, + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "text", + "content": " [56]." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 60, + 102, + 533, + 403 + ], + "lines": [ + { + "bbox": [ + 60, + 102, + 533, + 403 + ], + "spans": [ + { + "bbox": [ + 60, + 102, + 533, + 403 + ], + "type": "table", + "html": "
MethodsYearDUTS-TE [63]DUT-OMRON [80]PASCAL-S [34]SOD [44]ECSSD [78]HKU-IS [33]
ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓
SOD MethodsMSRNet [32]20172.572.343.323.163.443.236.426.140.970.940.920.87
SRM [65]20174.023.724.193.964.884.599.939.582.532.351.861.72
Amulet [92]20175.675.285.845.495.765.4310.039.592.562.421.981.87
BMPM [91]20183.743.524.524.374.884.688.167.931.951.891.581.53
DGRL [67]20184.123.864.414.215.014.778.448.202.132.021.631.53
PAGR [93]20184.043.795.144.965.645.3712.1711.872.842.701.621.54
PiCANet [37]20185.124.904.844.708.147.9210.5010.303.483.392.552.47
CPD [73]20193.973.784.204.065.375.179.659.392.292.191.991.90
BASNet [55]20195.004.864.934.836.506.3610.4010.272.742.702.302.26
EGNet [94]20193.333.143.663.505.425.198.047.791.981.881.471.40
AFNet [15]20193.953.744.254.095.064.848.158.022.382.271.871.78
PoolNet [36]20193.333.123.863.705.325.078.147.872.001.901.821.75
GCPANet [7]20203.182.993.993.844.163.977.056.881.611.541.271.21
MINet [51]20203.653.484.454.294.944.758.017.892.132.031.741.65
F3Met [69]20203.673.504.254.104.854.677.957.782.262.161.921.83
EBMGSD [89]20213.453.294.113.954.794.617.487.302.142.051.791.70
ICON [97]20212.892.763.843.714.083.956.706.551.561.491.381.32
PFSNet [43]20212.942.723.953.814.454.277.597.392.412.252.061.96
EDN [72]20223.623.474.023.904.894.748.818.662.202.131.651.58
Model Calibration MethodsBrier Loss [4]19502.772.583.553.383.903.706.406.161.371.301.040.99
Temperature Scaling [18]20172.532.343.183.033.563.366.326.050.960.930.830.70
MMCE [30]20182.862.673.563.414.003.816.856.631.411.351.181.13
Label Smoothing [46]20192.001.792.892.713.042.835.975.690.830.680.820.47
Mixup [62]20192.452.253.413.233.132.995.825.701.410.183.830.05
Focal Loss [45]20202.252.083.102.823.403.136.215.981.411.031.240.77
AdaFocal [17]20221.611.412.311.842.532.275.885.471.630.791.350.52
Our MethodsASLPMC20231.401.221.991.832.312.105.505.170.480.200.790.17
ASLPMEI202327.90.0126.00.0026.10.0022.40.0029.90.0030.50.00
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A perfectly calibrated model has an identical confidence distribution and accuracy distribution, denoted as the oracle (diagonal red dotted line). The joint distribution of a better calibrated model is more aligned with the oracle line, especially its high density area. See Appendix D for results of other methods and on other testing datasets." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 144, + 417, + 214, + 565 + ], + "blocks": [ + { + "bbox": [ + 144, + 417, + 214, + 565 + ], + "lines": [ + { + "bbox": [ + 144, + 417, + 214, + 565 + ], + "spans": [ + { + "bbox": [ + 144, + 417, + 214, + 565 + ], + "type": "image", + "image_path": "50bf657d44382ec78932238038a5ae4db914d1223b88c52b5645234bd00bdf9b.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 215, + 417, + 287, + 565 + ], + "blocks": [ + { + "bbox": [ + 215, + 417, + 287, + 565 + ], + "lines": [ + { + "bbox": [ + 215, + 417, + 287, + 565 + ], + "spans": [ + { + "bbox": [ + 215, + 417, + 287, + 565 + ], + "type": "image", + "image_path": "e64b3e51f8c95ac670f1ec4e1fe8177bf78f43667f12c450f01ce5d30b3c7d8a.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 287, + 417, + 358, + 565 + ], + "blocks": [ + { + "bbox": [ + 287, + 417, + 358, + 565 + ], + "lines": [ + { + "bbox": [ + 287, + 417, + 358, + 565 + ], + "spans": [ + { + "bbox": [ + 287, + 417, + 358, + 565 + ], + "type": "image", + "image_path": "80add01356da9634d48a866bbce202fdf8df1142f7e85663727ee5f7d071f0ab.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 359, + 417, + 430, + 565 + ], + "blocks": [ + { + "bbox": [ + 359, + 417, + 430, + 565 + ], + "lines": [ + { + "bbox": [ + 359, + 417, + 430, + 565 + ], + "spans": [ + { + "bbox": [ + 359, + 417, + 430, + 565 + ], + "type": "image", + "image_path": "d7c6f5307d77f3b0fff7ec337a0b060588890d7aa1b0bc5a134350f06df8054b.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 431, + 417, + 515, + 565 + ], + "blocks": [ + { + "bbox": [ + 431, + 417, + 515, + 565 + ], + "lines": [ + { + "bbox": [ + 431, + 417, + 515, + 565 + ], + "spans": [ + { + "bbox": [ + 431, + 417, + 515, + 565 + ], + "type": "image", + "image_path": "68bd1b189f642883122fd09858994ec2bf688b7e48b2074ff68fc3b398f342db.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 640, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 640, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 640, + 288, + 713 + ], + "type": "text", + "content": "OE performances on all six testing datasets, outperformed only by our " + }, + { + "bbox": [ + 46, + 640, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MEI}}" + }, + { + "bbox": [ + 46, + 640, + 288, + 713 + ], + "type": "text", + "content": ". On the other hand, " + }, + { + "bbox": [ + 46, + 640, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MEI}}" + }, + { + "bbox": [ + 46, + 640, + 288, + 713 + ], + "type": "text", + "content": ", though almost eliminates the over-confidence issue completely, is significantly mis-calibrated on the six testing datasets. This can be attributed to it being significantly under-confident rather than over-confident. The observed performances of" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 641, + 545, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 700 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MEI}}" + }, + { + "bbox": [ + 304, + 641, + 545, + 700 + ], + "type": "text", + "content": " are in accordance with its design - assuming minimum distribution commitment with respect to missing information. That is, in the presence of limited training data, to maximise the prediction entropy while maintaining the prediction accuracy for in-distribution data." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "content": "Fig. 3 presents the joint distribution of prediction con" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "1178" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": "fidence and prediction accuracy of some of the best calibrated methods and our proposed technique on DUTS-TE dataset (See Appendix D for other testing datasets and other methods). Existing SOD methods produce extremely confident predictions whose confidence scores are nearly " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": " for the majority of samples. On the contrary, the prediction accuracy is on average lower than prediction confidence, resulting in the model being over-confident. On the other hand, existing model calibration methods are generally more calibrated than the SOD methods which in general do not strive to improve model calibration degree." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "spans": [ + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "text", + "content": "Our proposed " + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "text", + "content": " produces the most calibrated model whose joint distribution is closer to the oracle than those of the compared calibration methods and SOD methods. AdaFocal [17] produces the second most calibrated model on DUTS-TE. However, the majority of their joint distribution (blue high density area) is slightly to the right bottom of the oracle line, making their model slightly less calibrated. Whereas the high density area of our joint distribution is well aligned with the oracle line, showing " + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "text", + "content": " is more calibrated. Despite the small difference on the plot, " + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "text", + "content": " improves over AdaFocal by more than " + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "text", + "content": " in terms of ECE scores on DUTS-TE dataset. We can also observe that " + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MEI}}" + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "text", + "content": " is significantly under-confident for in-distribution data with its joint distribution being at the top-left side of the oracle line. Its prediction accuracies are limited to between " + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "inline_equation", + "content": "70\\%" + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "inline_equation", + "content": "80\\%" + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "text", + "content": " while the prediction accuracies are generally above " + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 46, + 205, + 289, + 410 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 418, + 287, + 443 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 418, + 287, + 443 + ], + "spans": [ + { + "bbox": [ + 47, + 418, + 287, + 443 + ], + "type": "text", + "content": "4.3. Model Calibration Degrees on Out-of-Distribution Dataset" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "type": "text", + "content": "We compare our proposed method with existing model calibration methods in terms of model calibration degrees on Out-of-Distribution data. We consider texture images, where salient objects are completely absent, as OoD samples for the SOD task. We use Describable Texture Dataset [9] to evaluate the model calibration degrees on OoD samples. Fig. 4 shows the joint distribution of prediction confidence and prediction accuracy of various model calibration methods and our proposed techniques. It can be seen that the baseline model produces extremely confident predictions for OoD data. However, its accuracy is only " + }, + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "type": "inline_equation", + "content": "41.88\\%" + }, + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "type": "text", + "content": ", worse than a uniform prior in a binary classification task. We also observe that Temperature Scaling does not calibrate the model under data distribution shift in accordance with literature [50, 45]. Our " + }, + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "type": "text", + "content": ", being the most calibrated for in-distribution data, is also more calibrated on the OoD samples than the existing model calibration methods by a large margin as shown in Tab. 2. On the other hand, our " + }, + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MEI}}" + }, + { + "bbox": [ + 46, + 450, + 289, + 715 + ], + "type": "text", + "content": " is more successful in handling OoD data. It is the most calibrated on OoD data, with a larger proportion of the distribution aligned with the oracle line. As shown in Tab. 2, it outperforms existing model calibration methods in" + } + ] + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 307, + 74, + 383, + 145 + ], + "blocks": [ + { + "bbox": [ + 307, + 74, + 383, + 145 + ], + "lines": [ + { + "bbox": [ + 307, + 74, + 383, + 145 + ], + "spans": [ + { + "bbox": [ + 307, + 74, + 383, + 145 + ], + "type": "image", + "image_path": "94957d75b27cc1fe73e8a7e7b75f7d212ec8b1fbbf41ac0a16f900762c93a3bc.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 331, + 147, + 358, + 155 + ], + "lines": [ + { + "bbox": [ + 331, + 147, + 358, + 155 + ], + "spans": [ + { + "bbox": [ + 331, + 147, + 358, + 155 + ], + "type": "text", + "content": "Baseline" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 383, + 75, + 452, + 145 + ], + "blocks": [ + { + "bbox": [ + 383, + 75, + 452, + 145 + ], + "lines": [ + { + "bbox": [ 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This can be attributed to its minimum distribution assumption in the presence of limited training data." + } + ] + } + ], + "index": 23 + }, + { + "type": "table", + "bbox": [ + 321, + 480, + 530, + 609 + ], + "blocks": [ + { + "bbox": [ + 304, + 430, + 547, + 479 + ], + "lines": [ + { + "bbox": [ + 304, + 430, + 547, + 479 + ], + "spans": [ + { + "bbox": [ + 304, + 430, + 547, + 479 + ], + "type": "text", + "content": "Table 2: Model calibration methods and our " + }, + { + "bbox": [ + 304, + 430, + 547, + 479 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 304, + 430, + 547, + 479 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 430, + 547, + 479 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MEI}}" + }, + { + "bbox": [ + 304, + 430, + 547, + 479 + ], + "type": "text", + "content": " are evaluated on the Out-of-Distribution dataset, Describable Texture Dataset [9], in terms of " + }, + { + "bbox": [ + 304, + 430, + 547, + 479 + ], + "type": "inline_equation", + "content": "\\mathrm{ECE}_{\\mathrm{EW}}" + }, + { + "bbox": [ + 304, + 430, + 547, + 479 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 430, + 547, + 479 + ], + "type": "inline_equation", + "content": "\\mathrm{OE}_{\\mathrm{EW}}" + }, + { + "bbox": [ + 304, + 430, + 547, + 479 + ], + "type": "text", + "content": " with 10 bins, and Accuracy (ACC)." + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 321, + 480, + 530, + 609 + ], + "lines": [ + { + "bbox": [ + 321, + 480, + 530, + 609 + ], + "spans": [ + { + "bbox": [ + 321, + 480, + 530, + 609 + ], + "type": "table", + "html": "
MethodEvaluation (%)
ECE ↓OE ↓ACC ↑
Baseline52.3651.0541.88
Brier Loss [4]38.8537.1853.62
Temperature Scaling [18]51.9550.4641.59
Label Smoothing [46]37.2235.4855.41
MMCE [30]40.6439.6754.39
Mixup [62]31.0729.1058.71
Focal Loss [45]40.0138.4349.71
AdaFocal [17]27.5525.0755.39
ASLPMC18.3116.3761.93
ASLPMEI13.438.4062.47
", + "image_path": "9da15646b0fa041ddd2db4605841bbfa798aaec1ae0e956a66f9e7e6c1aeaf8d.jpg" + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "table_body" + } + ], + "index": 25 + }, + { + "bbox": [ + 306, + 622, + 378, + 633 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 622, + 378, + 633 + ], + "spans": [ + { + "bbox": [ + 306, + 622, + 378, + 633 + ], + "type": "text", + "content": "4.4. Discussion" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 641, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 715 + ], + "type": "text", + "content": "Adaptive Stochastic Label Perturbation: We study the effect of ASLP on ECE and OE and present the experimental results in Tab. 3. It shows that ASLPs significantly outperforms the baseline model, \"B\", which does not adopt any model calibration measures. In addition, ASLPs also outperforms their static counterparts (SLPs) which use a single" + } + ] + } + ], + "index": 27 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "1179" + } + ] + } + ], + "index": 28 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 72, + 121, + 520, + 249 + ], + "blocks": [ + { + "bbox": [ + 46, + 70, + 547, + 119 + ], + "lines": [ + { + "bbox": [ + 46, + 70, + 547, + 119 + ], + "spans": [ + { + "bbox": [ + 46, + 70, + 547, + 119 + ], + "type": "text", + "content": "Table 3: Ablation: Effect of Stochastic Label Perturbation (SLP) and Adaptive Stochastic Label Perturbation (ASLP) with different label perturbation techniques on the model calibration degrees evaluated on Expected Calibration Error (ECE) and Over-confidence Error (OE). The proposed ASLP is generalised to an Adaptive Label Smoothing (ALS) technique that adaptively tunes the label softening scale " + }, + { + "bbox": [ + 46, + 70, + 547, + 119 + ], + "type": "inline_equation", + "content": "(\\beta_{\\mathrm{ada}})" + }, + { + "bbox": [ + 46, + 70, + 547, + 119 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 72, + 121, + 520, + 249 + ], + "lines": [ + { + "bbox": [ + 72, + 121, + 520, + 249 + ], + "spans": [ + { + "bbox": [ + 72, + 121, + 520, + 249 + ], + "type": "table", + "html": "
MethodsPerturbation ParamsDUTS-TE [63]DUT-OMRON [80]PASCAL-S [34]SOD [44]ECSSD [78]HKU-IS [33]
αβeECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓ECE ↓OE ↓
Baseline (“B”)0003.483.294.174.024.604.417.427.171.931.861.641.59
SLPα=0.01HI0.011.0X2.211.842.962.783.112.826.095.801.030.681.010.53
SLPα=0.02SI0.020.75X2.252.053.002.823.052.836.406.090.930.840.870.60
SLPα=0.03M0.030.5X2.242.033.172.973.413.206.265.970.830.770.960.81
SLPα=0.03DM0.030.5✓2.292.093.002.833.473.246.726.431.131.040.960.80
LSβ=0.031.00.03X2.201.993.092.913.243.036.275.991.030.780.920.67
ASLPHIαada1.0X1.401.221.991.832.312.105.505.170.480.200.790.17
ASLPSIαada0.75X1.511.292.141.952.292.075.124.800.610.340.840.22
ASLPMαada0.5X1.471.271.871.802.372.135.635.290.510.230.800.20
ASLPMCMαada0.5✓1.641.201.941.752.031.814.143.840.800.420.870.42
ALS1.0βadaX1.461.252.071.872.302.105.445.180.610.250.810.32
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This can be attributed to the approach modelling variance of noise with input image." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 285, + 287, + 415 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 285, + 287, + 415 + ], + "spans": [ + { + "bbox": [ + 46, + 285, + 287, + 415 + ], + "type": "text", + "content": "Generalisation of Adaptive Label Smoothing: We generalise the proposed ASLP to label smoothing, developing an Adaptive Label Smoothing (ALS) that fixes the label perturbation probability to " + }, + { + "bbox": [ + 46, + 285, + 287, + 415 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 46, + 285, + 287, + 415 + ], + "type": "text", + "content": ", akin to the label smoothing technique [46], and tunes a smoothing factor for each training sample. As shown in Tab. 3, ALS effectively reduces the ECE and OE scores over its static version " + }, + { + "bbox": [ + 46, + 285, + 287, + 415 + ], + "type": "inline_equation", + "content": "\\mathrm{LS}^{\\beta = 0.03}" + }, + { + "bbox": [ + 46, + 285, + 287, + 415 + ], + "type": "text", + "content": ", and achieves similar performances with " + }, + { + "bbox": [ + 46, + 285, + 287, + 415 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 46, + 285, + 287, + 415 + ], + "type": "text", + "content": " approaches on the six testing datasets. It manifests that our proposed ASLP can be generalised onto other label perturbation techniques as a measure to calibrate the SOD models." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 416, + 287, + 477 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 416, + 287, + 477 + ], + "spans": [ + { + "bbox": [ + 46, + 416, + 287, + 477 + ], + "type": "text", + "content": "Compatibility with SOTA SOD Models We retrain EBMGSOD [89], ICON [97] and EDN [72] with the proposed " + }, + { + "bbox": [ + 46, + 416, + 287, + 477 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 46, + 416, + 287, + 477 + ], + "type": "text", + "content": " and find significant improvements in terms of model calibration degrees without compromising their classification abilities (See Appendix E)." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 478, + 287, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 478, + 287, + 525 + ], + "spans": [ + { + "bbox": [ + 46, + 478, + 287, + 525 + ], + "type": "text", + "content": "Compatibility with Different Backbones: We demonstrate that our proposed method is also compatible with VGG16 [58] and Swin transformer [39] backbones. See Appendix I for details." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 526, + 287, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 526, + 287, + 586 + ], + "spans": [ + { + "bbox": [ + 46, + 526, + 287, + 586 + ], + "type": "text", + "content": "Effectiveness in Other Dense Binary Classification Tasks: Experiments on Smoke Detection [79] and Camouflaged Object Detection [14] demonstrate that our method can be generalised to dense binary classification tasks to improve model calibration degrees. See Appendix F." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 587, + 287, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 587, + 287, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 587, + 287, + 635 + ], + "type": "text", + "content": "Generalisation to Multi-Class Segmentation task: Experiments on Semantic Segmentation [11] demonstrate that our method can also be generalised to dense multi-class classification tasks. See Appendix G." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 646, + 153, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 646, + 153, + 659 + ], + "spans": [ + { + "bbox": [ + 47, + 646, + 153, + 659 + ], + "type": "text", + "content": "4.5. Hyperparameters" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": "Static Stochastic Label Perturbation: Tab. 3 shows that, under a small label perturbation probability, the four label perturbation techniques can alleviate the model overconfidence issues of the baseline model, \"B\", on the six" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 259, + 545, + 367 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 259, + 545, + 367 + ], + "spans": [ + { + "bbox": [ + 304, + 259, + 545, + 367 + ], + "type": "text", + "content": "testing datasets. They also achieve similar results to Label Smoothing [46], setting " + }, + { + "bbox": [ + 304, + 259, + 545, + 367 + ], + "type": "inline_equation", + "content": "\\beta = 0.03" + }, + { + "bbox": [ + 304, + 259, + 545, + 367 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 259, + 545, + 367 + ], + "type": "inline_equation", + "content": "\\alpha = 1" + }, + { + "bbox": [ + 304, + 259, + 545, + 367 + ], + "type": "text", + "content": ". Each SLP has a wide range of effective label perturbation probabilities that improves model calibrations (See Appendix H.2 Tab. 13), and these improvements do not sacrifice the model's classification performance (see Appendix H.3). Larger values of the label perturbation probability eventually lead to increasing ECE scores as the model transitions to being under-confident (see Appendix H.2)." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 367, + 545, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 367, + 545, + 426 + ], + "spans": [ + { + "bbox": [ + 304, + 367, + 545, + 426 + ], + "type": "text", + "content": "Updating Rate " + }, + { + "bbox": [ + 304, + 367, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 304, + 367, + 545, + 426 + ], + "type": "text", + "content": ": " + }, + { + "bbox": [ + 304, + 367, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 304, + 367, + 545, + 426 + ], + "type": "text", + "content": " models trained with " + }, + { + "bbox": [ + 304, + 367, + 545, + 426 + ], + "type": "inline_equation", + "content": "\\eta \\in [0.0002, 0.005]" + }, + { + "bbox": [ + 304, + 367, + 545, + 426 + ], + "type": "text", + "content": " are generally stable, producing similar calibration degrees and classification performances. Values smaller than 0.001 require longer training and high values lead to sub-optimal results (See Appendix J)." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 426, + 545, + 463 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 545, + 463 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 545, + 463 + ], + "type": "text", + "content": "Regularisation Strength " + }, + { + "bbox": [ + 304, + 426, + 545, + 463 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 426, + 545, + 463 + ], + "type": "text", + "content": ": " + }, + { + "bbox": [ + 304, + 426, + 545, + 463 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 426, + 545, + 463 + ], + "type": "text", + "content": " spanning between 500 and 10,000 are optimal. Very high values for " + }, + { + "bbox": [ + 304, + 426, + 545, + 463 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 426, + 545, + 463 + ], + "type": "text", + "content": " can lead to oscillation resulting in poor performance (See Appendix J)." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 472, + 378, + 485 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 472, + 378, + 485 + ], + "spans": [ + { + "bbox": [ + 306, + 472, + 378, + 485 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 493, + 545, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 493, + 545, + 685 + ], + "spans": [ + { + "bbox": [ + 304, + 493, + 545, + 685 + ], + "type": "text", + "content": "This work first introduces a Self-Calibrating Binary Cross Entropy loss that unifies label perturbation processes including stochastic approaches and label smoothing to improve model calibration while preserving classification accuracy. We further propose an Adaptive Stochastic Label Perturbation that learns a unique label perturbation level for individual training image. Following Maximum Entropy Inference, ASLP adopts classification / calibration as proxy for known data and maximises the prediction entropy with respect to missing data. The proposed " + }, + { + "bbox": [ + 304, + 493, + 545, + 685 + ], + "type": "inline_equation", + "content": "\\mathrm{ASLP}_{\\mathrm{MC}}" + }, + { + "bbox": [ + 304, + 493, + 545, + 685 + ], + "type": "text", + "content": " improves model calibration degrees on both in-distribution samples and out-of-distribution samples, without negatively impacting classification performance. The approach can be easily applied to different models, which we demonstrate with several SOTA models. It is also demonstrated to be effective on a semantic segmentation task and other binary tasks." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 691, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 691, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 691, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgments. This research was in-part supported by the ANU-Optus Bushfire Research Center of Excellence." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1180" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 286, + 713 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 53, + 91, + 286, + 124 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 286, + 124 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 286, + 124 + ], + "type": "text", + "content": "[1] Radhakrishna Achanta, Sheila Hemami, Francisco Estrada, and Sabine Susstrunk. 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IEEE TPAMI, 2022. 5, 6, 8, 20, 21, 22, 27" + } + ] + } + ], + "index": 2 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 749, + 315, + 757 + ], + "type": "text", + "content": "1184" + } + ] + } + ], + "index": 4 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 11 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/ModelGiF_ Gradient Fields for Model Functional Distance/5efa34c8-5ce4-47e6-bc15-889009199a89_content_list.json b/2023/ModelGiF_ Gradient Fields for Model Functional Distance/5efa34c8-5ce4-47e6-bc15-889009199a89_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..34046087442768b8482b49f09bb19cdd7f815cb2 --- /dev/null +++ b/2023/ModelGiF_ Gradient Fields for Model Functional Distance/5efa34c8-5ce4-47e6-bc15-889009199a89_content_list.json @@ -0,0 +1,1483 @@ +[ + { + "type": "text", + "text": "ModelGiF: Gradient Fields for Model Functional Distance", + "text_level": 1, + "bbox": [ + 189, + 130, + 779, + 150 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Jie Song, Zhengqi Xu, Sai Wu, Gang Chen, and Mingli Song* Zhejiang University", + "bbox": [ + 241, + 180, + 733, + 217 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{sjie,xuzhengqi,wusai,cg,brooksong}@zju.edu.cn", + "bbox": [ + 281, + 219, + 687, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The last decade has witnessed the success of deep learning and the surge of publicly released trained models, which necessitates the quantification of the model functional distance for various purposes. However, quantifying the model functional distance is always challenging due to the opacity in inner workings and the heterogeneity in architectures or tasks. Inspired by the concept of \"field\" in physics, in this work we introduce Model Gradient Field (abbr. ModelGiF) to extract homogeneous representations from the heterogeneous pre-trained models. Our main assumption underlying ModelGiF is that each pre-trained deep model uniquely determines a ModelGiF over the input space. The distance between models can thus be measured by the similarity between their ModelGiFs. We validate the effectiveness of the proposed ModelGiF with a suite of testbeds, including task relatedness estimation, intellectual property protection, and model unlearning verification. Experimental results demonstrate the versatility of the proposed ModelGiF on these tasks, with significantly superiority performance to state-of-the-art competitors. Codes are available at https://github.com/zju-vipa/modelgif.", + "bbox": [ + 75, + 301, + 473, + 619 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 652, + 209, + 669 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The last decade has witnessed the great progress of deep learning in various fields, and a plethora of deep neural networks are developed and released publicly, with either their architectures and trained parameters (e.g., Tensorflow Hub1, Pytorch Hub2) for research, or the prediction API (e.g., BigML, Amazon Machine Learning) as ML-as-a-Service (MLaaS) for commercial purposes. These off-the-shelf pre-trained models become extremely important resources for not only practitioners to solve their own problems, but also researchers to explore and exploit the huge potential underlying these pre-trained models.", + "bbox": [ + 75, + 680, + 468, + 847 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/de2835115b675baaacba88effd7b19407700459d0c55f2ef66d9608d45f82f15.jpg", + "image_caption": [ + "Magnetic Field" + ], + "image_footnote": [], + "bbox": [ + 702, + 273, + 879, + 362 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/c49224e73d7b377c1f3e92c31cd4ed2262951df2ce973acfa0ceb6c0e52b07c5.jpg", + "image_caption": [ + "Model Gradient Field" + ], + "image_footnote": [], + "bbox": [ + 516, + 372, + 759, + 444 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/7f071db1062f8a00a9eb58650d781e6b06caa8e29f32a6bd533ba63dd7defb32.jpg", + "image_caption": [ + "Figure 1. An illustrative diagram of the magnetic field and the proposed model gradient field (ModelGiF) defined on the input space." + ], + "image_footnote": [], + "bbox": [ + 767, + 373, + 883, + 460 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "With the surge of pre-trained models released, quantifying the model relationship emerges as an important question. The large-scale open-sourced deep models, heterogeneous in architectures and tasks and trained isolatedly or dependently, are related to each other in various manners. For example, a student model trained by knowledge distillation [19] should behave more similarly with the teacher than an independently trained identical model. Likewise, a fine-tuned model should be more closely related to its pretrained model than the one trained from scratch. More generally, models trained in isolation on heterogeneous tasks should inherit the intrinsic task relatedness [53] as task-specific features are extracted by these models. Broadly speaking, there exists a model metric space where models with similar functional behaviors are clustered together and dissimilar ones are far apart. The model functional distance between models, if left unresolved, leaves existing model repositories still simple unstructured collections of many isolated open-sourced models, hindering the exploitation of their great value as a whole.", + "bbox": [ + 496, + 506, + 892, + 808 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Despite the ever-increasing number of publicly available pre-trained models, the study on the model functional distance, i.e., structure of the model metric space, lags far behind. This phenomenon can be largely attributed to the great challenge of computing the functional distance between any deep models, where the barriers are three-folds: (1) Hetero-", + "bbox": [ + 496, + 810, + 893, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "\\*Corresponding author \n1https://www.tensorflow.org/hub \n2https://pytorch.org/hub/", + "bbox": [ + 93, + 862, + 339, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "6125", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "geneity: deep models usually differ significantly in architectures. Even with the same architecture, models trained on different datasets or tasks can also behave quite differently; (2) Opacity: the opaque inner workings of deep models render computing the model similarity extremely difficult; (3) Efficiency: as the cost of computing pairwise distance grows quadratically with the number of models, the computation of the functional distance should be efficient.", + "bbox": [ + 75, + 90, + 470, + 210 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "A few prior works have been devoted to computing model distance, in either weight space [1, 24] or representation space [28, 12]. For example, Task2Vec [1] computes task or model representations based on estimates of the Fisher information matrix associated with the probe network parameters, which provides a fixed-dimensional embedding of the model agnostic to the task variations. However, Task2Vec assumes all probe models share the same architecture, which is highly restrictive in practice. ModelDiff [28] and representation similarity analysis (RSA) [12], on the other hand, adopt the similarity of representations on a small set of reference inputs as the model representations, and the model distance is thus calculated resorting to these model representations, which is shown effective for model reuse detection and transferability estimation. However, these methods only capture the point-wise behavior of the models at a small number of chosen reference points, which is limited in representation capacity and fails at harder tasks such as detecting model extraction [28]. Recently, DEPARA [43, 44] and ZEST [22] are proposed as pilot studies by applying explanation methods for computing model distance. However, they are validated on disjoint downstream tasks, and the performance on comprehensive tasks remains unclear. Moreover, these methods also use a small number of chosen reference points to extract the model representations, which makes them suffer from low representation capacity.", + "bbox": [ + 75, + 217, + 470, + 625 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, inspired by the concept of \"field\" in physics, we propose Model Gradient Field (as shown in Figure 1), abbreviated as ModelGiF, as the proxy to extract homogeneous representations from pre-trained heterogeneous models to derive their functionality distance. Specifically, the proposed ModelGiF is defined on the input space, i.e., every point in the ModelGiF denotes the gradient vector of the model output w.r.t. the input on the same point. The main assumption underlying ModelGiF is that each pretrained deep model uniquely determines a ModelGiF over the input space. The functional distance between any two models can thus be measured by the similarity between their ModelGiFs. Unlike prior methods where the point-wise features are adopted for representing the model, ModelGiFs represents these models by their gradient on the whole input space, which makes it more capable of differentiating highly related models (i.e., model extraction detection). Moreover, we provide theoretical insights into the proposed", + "bbox": [ + 75, + 628, + 468, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ModelGiFs for model functional distance, and make extensive discussions on different implementation details. We validate the effectiveness of the proposed ModelGiF with a suite of testbeds, including transferability estimation, intellectual property protection, and model unlearning verification. Experimental results demonstrate the versatility of the proposed ModelGiF on these tasks, with significantly superiority to state-of-the-art (SOTA) methods.", + "bbox": [ + 496, + 90, + 890, + 210 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To sum up, we make the following contributions: (1) we propose the concept of \"model gradient field\", a novel method for quantifying the functionality similarity between pre-trained deep models; (2) we provide theoretical insights into the proposed ModelGiFs for model functional distance, and make extensive discussions on different implementation details; (3) extensive experiments demonstrate the effectiveness and the superiority of ModelGiF on various tasks, including transferability estimation, intellectual property protection, and model unlearning verification.", + "bbox": [ + 496, + 212, + 890, + 364 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 377, + 640, + 393 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "This section briefly reviews some related topics to model functional distance, including task relatedness estimation, intellectual property protection, and model unlearning.", + "bbox": [ + 496, + 404, + 890, + 450 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Task Relatedness Estimation. Recent studies [53, 43, 44, 5, 51, 3, 6, 26] reveals the existence of task relatedness or task structure among visual tasks. It is the concept underlying transfer learning and provides a principled way to seamlessly reuse supervision among related tasks or solve many tasks in one system [53]. Existing works to obtain task relatedness can be roughly divided into empirical and analytical approaches. Taskonomy [53] is the most representative work of empirical methods. It proposes a fully computational approach to obtain task relatedness by exhaustively computing the actual transfer learning performance, which is thus usually taken as the ground truth for evaluating other estimators. Despite the indisputable results, the computational cost of empirical methods is extremely high. On the other hand, analytical methods, e.g., DEPARA [44, 43], Task2Vec [1] and RSA [12], try to estimate the task relatedness without conducting the actual transfer learning. Analytical methods generally significantly reduce the computation overhead, but can be highly restrictive in model architectures or estimation performance. The proposed Model-GiF relaxes these restrictions and achieves task relatedness more consistent to taskonomy than existing approaches.", + "bbox": [ + 496, + 455, + 890, + 787 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Intellectual Property Protection. Since training deep models usually consumes expensive data collection and large computation resources, the trained models constitute valuable intellectual property (IP) that should be protected in cases where reusing is not allowed without authorization. However, model IP can be infringed in a variety of forms, such as fine-tuning [2, 48], pruning [29, 33], transfer learn-", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "6126", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ing [39, 49, 50] and model extraction [34, 47, 25, 21], which poses great challenge to IP protection. Existing IP protection approaches can be roughly categorized into watermarking [23, 48, 13, 54, 2] and fingerprinting [30, 8, 28, 17]. Watermarking methods usually leverage weight regularization [48, 13] to put secret watermark in the model parameters or train models on a triggered set to leave backdoor [2, 54] in them. While being able to provide exact ownership verification, these techniques are invasive, i.e., they need to tamper with the training process, which may affect the model utility or introduce new security risks into the model. Fingerprinting, on the contrary, extracts a unique identifier, i.e., fingerprint, from the owner model to differentiate it from other models. Latest fingerprinting (e.g., ModelDiff [28], IPGuard [8], SAC [17]) on deep learning models, though being non-invasive, also fall short when facing the diverse and ever-growing attack scenarios [10]. In this work, we propose ModelGiF as the homogeneous representations for heterogeneous pre-trained models, which can be naturally adopted as the fingerprint for IP protection and yields superior IP protection performance to existing approaches.", + "bbox": [ + 76, + 90, + 472, + 424 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Model Unlearning Verification. Model unlearning aims to remove the effects of data points from the trained model, which has been attracting increasing attentions in recent years due to legislation and privacy ethics. Cao et al. [9] are dedicated to making learning systems forget and present an unlearning approach capable of forgetting specific data. Graves et al. [16] propose an effective method to eliminate the influence of personal data from the model while maintaining the validity. Bourtoule et al. [7] particularly propose a model unlearning method to decrease the time it takes to retrain exactly. However, how to identify whether the impact of data has been eliminated is an essential but rarely studied problem. Recently ZEST [22] verifies the unlearning of data by comparing the Local Interpretable Model-Agnostic Explanations (LIME) [37]. In this work, we adopt the proposed ModelGiF for unlearning verification, which yields competitive performance in our experiments.", + "bbox": [ + 76, + 429, + 472, + 686 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 76, + 699, + 212, + 717 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Problem Setup", + "text_level": 1, + "bbox": [ + 76, + 723, + 228, + 739 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Assume there is a model repository consisting of $N$ pre-trained models $\\mathcal{M} = \\{M_1, M_2, \\dots, M_N\\}$ . With mild assumptions, these models are defined on the same input space $\\mathbb{R}^D$ ( $D = WHC$ , where $W, H$ and $C$ denotes the width, height and channel of the input space), yet trained with data sampled from different data distributions $\\mathcal{P} = \\{p_1, p_2, \\dots, p_N\\}$ . Note that here we made no assumptions on the model architectures and the tasks, which means", + "bbox": [ + 76, + 746, + 468, + 867 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "that these models can be different in architectures (e.g., ResNet [18] and VGG [42]), and tasks (e.g., visual classification [27], detection [36] or segmentation [11]). The goal in this work is to construct a model metric space where models with similar functional behaviors are clustered together and dissimilar ones are far apart, where the vital step is quantifying the functional distance between these models.", + "bbox": [ + 500, + 90, + 890, + 196 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. The Proposed ModelGiF", + "text_level": 1, + "bbox": [ + 500, + 205, + 725, + 220 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As aforementioned, quantifying the functional distance between pre-trained models is challenging due to the heterogeneity, opacity and efficiency issues. Our main idea is extracting homogeneous descriptors from these heterogeneous models to make them comparable. To this end, we proposed the concept ModelGiF, as shown in Figure 1, to derive the comparable identifier of the pre-trained models for quantifying model distance.", + "bbox": [ + 496, + 229, + 890, + 348 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ModelGiF is inspired by the concept \"field\" in physics where a field is a mapping from space to some physical quantity, represented by a scalar, vector, or tensor, that has a value for each point in the space [32]. For example, the magnetic field describes the magnetic influence on moving electric charges, electric currents, and magnetic materials [14]. Likewise, we define ModelGiF as a mapping from the input space to the gradient space such that each point in the input space is assigned to a gradient vector. The formal definition is provided as follows.", + "bbox": [ + 496, + 349, + 892, + 500 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Definition 3.1 (Model Gradient Field) Let $M$ be a deep model trained on the data which is sampled according to some distribution $p$ from the data space $\\mathcal{X}$ , outputting a scalar4 prediction in the label space $\\mathcal{Y}$ . A point $\\mathbf{x}$ can be described as $\\mathbf{x} = (x_1, x_2, \\dots, x_D)$ . We define the model gradient field of $M$ as the gradient of every possible input point in $\\mathcal{X}$ w.r.t. the model output:", + "bbox": [ + 496, + 508, + 890, + 616 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {M O D E L G I F} (M) \\triangleq \\nabla_ {\\mathbf {x}} M, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 604, + 626, + 890, + 642 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "which is a mapping from the input space $\\mathbb{R}^D$ to the gradient space $\\mathbb{G}^D$ , MODELGiF: $\\mathbb{R}^D \\to \\mathbb{G}^D$ . Note that the ModelGiF is defined on the whole input space (which is shared by all the models) rather than some discretely points sampled from the data distribution $p$ specific to the model $M$ . As the architecture of $M$ and the tasks (i.e., the label space $\\mathcal{V}$ ) can be heterogeneous, the ModelGiF of a model can be seen as a projection of the model to the common input space.", + "bbox": [ + 496, + 652, + 890, + 773 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. Field Curves for ModelGiF", + "text_level": 1, + "bbox": [ + 500, + 782, + 743, + 797 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "With the proposed ModelGiF, the model functional distance can be quantified by the ModelGiF similarity. However, as ModelGiF is defined on the whole input space that is usually extremely huge, how to extract its representation", + "bbox": [ + 496, + 805, + 890, + 867 + ], + "page_idx": 2 + }, + { + "type": "page_footnote", + "text": "3Without losing generality, we use vector instead of tensor for notation simplicity.", + "bbox": [ + 76, + 875, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_footnote", + "text": "4For vector or tensor predictions, we simply take their $l_{2}$ norm as the scalar output.", + "bbox": [ + 500, + 875, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "6127", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/86b1123d4c5082e4e95c8a3e779772a8723680717d27c5e90bad91574839eb33.jpg", + "image_caption": [ + "Figure 2. An illustrative diagram of the overall pipeline of obtaining ModelGiF curves. The more similar the ModelGiFs, the more similar the corresponding trained models. Note that ModelGiF Curves are in high-dimensional space in reality." + ], + "image_footnote": [], + "bbox": [ + 81, + 90, + 890, + 404 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "or signature becomes the vital step for quantifying model distance. In physics, a field is usually depicted by the field curves (as shown in Figure 1), i.e., the integral curves for the field, and can be constructed by starting at a point and tracing a curve through space that follows the direction of the vector field, by making the field curve tangent to the field vector at each point [46]. Inspired by this, we propose ModelGiF Curves as the descriptors of ModelGiF to measure the model functional distance.", + "bbox": [ + 75, + 460, + 472, + 597 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Definition 3.2 (Field Curves) For a field $F$ : $\\mathbb{R}^D \\to \\mathbb{G}^D$ , a curve $\\mathbf{x}(t) = (x_1(t), x_2(t), \\ldots, x_D(t))$ is called a field curve of the field $F$ if the following condition is satisfied: For all points $P \\in \\mathbf{x}(t)$ , the tangent vector of the curve in the point $P$ has the same direction as the vector $F(P)$ :", + "bbox": [ + 75, + 603, + 470, + 681 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {d x _ {1} (t)}{d t} = F \\left(\\mathbf {x} (t)\\right) _ {1}, \\frac {d x _ {2} (t)}{d t} = F \\left(\\mathbf {x} (t)\\right) _ {2}, \\dots \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 124, + 688, + 468, + 720 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The field curve can be described as the solution of the system of differential equations in Eqn. 2, and it plays an important role for both analysis and visualization of vector fields [46]. Unfortunately, as the ModelGiF is usually complicated for a pre-trained deep model, there is no closed solution. The field curves are in general not describable as parameterized curves, which hinders the comparisons between different ModelGiFs. To resolve this issue, we introduce the definition of ModelGiF curves as follows.", + "bbox": [ + 75, + 726, + 468, + 862 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Definition 3.3 (ModelGiF Curves) For a ModelGiF $F$ : $\\mathbb{R}^D \\to \\mathbb{G}^D$ , a curve $\\mathbf{g}(t) = (g_1(t), g_2(t), \\dots, g_D(t))$ is", + "bbox": [ + 76, + 869, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "called the ModelGiF curve of $F$ if the following condition is satisfied:", + "bbox": [ + 498, + 460, + 892, + 491 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {d g _ {1} (t)}{d t} = F (\\mathbf {x} (t)) _ {1}, \\frac {d g _ {2} (t)}{d t} = F (\\mathbf {x} (t)) _ {2}, \\dots \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 549, + 501, + 890, + 532 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Note that different from the definition of field curves, the ModelGiF curves are defined on the gradient space $\\mathbb{G}^D$ instead of the input space $\\mathbb{R}^D$ .", + "bbox": [ + 498, + 540, + 892, + 587 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Proposition 1 For a ModelGiF $F \\colon \\mathbb{R}^D \\to \\mathbb{G}^D$ , and two points $\\mathbf{x}_0, \\mathbf{x}_1$ in $\\mathbb{R}^D$ , the gradient integral along the straight line from $\\mathbf{x}_0$ to $\\mathbf{x}_1$ is a ModelGiF curve of $F$ :", + "bbox": [ + 498, + 595, + 893, + 642 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {g} (t) = \\int_ {\\alpha = 0} ^ {t} F \\left(\\mathbf {x} _ {0} + \\alpha \\left(\\mathbf {x} _ {1} - \\mathbf {x} _ {0}\\right)\\right) d \\alpha , \\quad t \\in [ 0, 1 ] \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 519, + 652, + 890, + 686 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "With the proposition, we can make comparisons between ModelGiFs by simply comparing their ModelGiF curves between some predefined pairs of points. Now we provide the detailed pipeline of quantifying the Model functional distance with the proposed ModelGiF.", + "bbox": [ + 498, + 695, + 890, + 771 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. ModelGiF for Model Distance", + "text_level": 1, + "bbox": [ + 500, + 779, + 766, + 794 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Provided with the trained deep models as described in Section 3.1, we compute the model distance with the proposed ModelGiF in two steps (in Figure 2): 1) Sampling reference points, and 2) Computing the model distance.", + "bbox": [ + 498, + 803, + 890, + 864 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Sampling Reference Points. As described in Proposition 1, the first step before obtaining ModelGiF curves is", + "bbox": [ + 498, + 869, + 892, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "6128", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "determining the reference points (i.e., $\\mathbf{x}_1^5$ in Eqn. 4.), which determines the domain of these curves. Let $K$ be the number of reference points to be sampled. Intuitively, these reference points should representative. However, as the models in $\\mathcal{M}$ can be heterogeneous in architectures and tasks and trained on data sampled from different distributions, it is hard to determine a common set of reference points which are representative for all these models. In this work, we investigate three types of reference points as follows.", + "bbox": [ + 75, + 90, + 472, + 227 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1) Random samples drawn from $\\mathcal{P}$ . Each data point is sampled in two stages: first randomly sampling the distribution $p$ from $\\mathcal{P}$ and then randomly sampling the reference point from $p$ .", + "2) Augmented samples using CutMix [52]. Let $\\mathbf{x}$ and $\\mathbf{x}^*$ be two randomly sampled points in $\\mathcal{P}$ . CutMix generates a new sample $\\tilde{\\mathbf{x}}$ using the two samples by cutting off and pasting patches among them: $\\tilde{\\mathbf{x}} = \\mathbf{m} \\odot \\mathbf{x} + (1 - \\mathbf{m}) \\odot \\mathbf{x}^*$ , where $\\mathbf{m}$ represents the binary mask to combine images with different parts, and $\\odot$ the element-wise multiplication.", + "3) Adversarial samples generated with PGD [31]. PGD attack is a multi-step variant of Fast Gradient Sign Method (FGSM) [15]: $\\mathbf{x}_{t + 1} = \\prod \\left(\\mathbf{x}_t + \\alpha \\mathrm{SGN}\\bigl (\\nabla \\mathcal{J}(\\mathbf{x}_t)\\bigr)\\right)$ , where $\\prod$ denotes the projection to the allowed space." + ], + "bbox": [ + 75, + 229, + 468, + 449 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The performance of these types of reference points are discussed in Section 4.1. We also provide the sensitivity analysis of the number of reference points $K$ , which demonstrates that the performance of ModelGiF quickly becomes superior to existing methods as $K$ increases.", + "bbox": [ + 75, + 450, + 468, + 527 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Computing the model distance. Let $S = \\{\\mathbf{x}_1, \\mathbf{x}_2, \\dots, \\mathbf{x}_K\\}$ be the reference points obtained from the last step. For the $i$ -th model $M_i$ , we can get $K$ ModelGiF curves by substituting each point in $S$ for the $\\mathbf{x}_1$ in Eqn. 4. These curves are used as the identifier of the ModelGiF, and thus serve as the representations of the trained deep model. There are several distance metrics to measure the similarity between curves, e.g., Hausdorff distance and Fréchet distance. As the method for curve distance is not our contribution in this work, we simply adopt the integrated point-wise cosine distance to validate the performance of the proposed method:", + "bbox": [ + 75, + 535, + 472, + 704 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nd \\left(M _ {i}, M _ {j}\\right) = \\sum_ {k = 1} ^ {K} \\int_ {t = 0} ^ {1} \\left(1 - \\cos \\left(\\mathbf {g} ^ {i, k} (t), \\mathbf {g} ^ {j, k} (t)\\right)\\right) d t, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 731, + 468, + 773 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{g}^{i,k}$ denotes the $k$ -th curve of the $i$ -th model in $\\mathcal{M}$ , and $\\cdot$ denotes the inner product between $\\mathbf{g}^{i,k}(t)$ and $\\mathbf{g}^{i,k}(t)$ . In practice, we approximate the integral with summation by sampling with some fixed intervals.", + "bbox": [ + 75, + 791, + 468, + 854 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.5. Theoretical Analysis of ModelGiF", + "text_level": 1, + "bbox": [ + 500, + 90, + 795, + 107 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "From the definition of model distance in Eqn. 5, we can see that the defined distance can be seen as the summation of point-wise similarities over all the curves. Here we provide some theoretical insights into ModelGiF by dissecting the model-level distance into point-level distance.", + "bbox": [ + 496, + 114, + 890, + 190 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Proposition 2 For the point $\\mathbf{g}(t_1)$ along the ModelGiF curves $\\mathbf{g}(t)$ defined from $\\mathbf{x}^*$ to $\\mathbf{x}$ , then", + "bbox": [ + 496, + 204, + 893, + 236 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\sum_ {i} t _ {1} \\left(x _ {i} - x _ {i} ^ {*}\\right) g _ {i} \\left(t _ {1}\\right) = M (\\mathbf {x}) - M \\left(\\mathbf {x} ^ {*}\\right), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 550, + 247, + 890, + 271 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the left side is actually the summation over Integrated Gradients [45]. Eqn. 6 tells us that the every point in proposed ModelGiF curve is strongly related to the model prediction differences from this point and the baseline point, thus the proposed model distance is a powerful distance metric to quantifying the model function distance.", + "bbox": [ + 496, + 282, + 890, + 375 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 388, + 633, + 406 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we verify the effectiveness of ModelGiF with a suite of testbeds, including task relatedness estimation, intellectual property protection and model unlearning verification. Details are provided as follows.", + "bbox": [ + 496, + 414, + 890, + 474 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Application: Task Relatedness Estimation", + "text_level": 1, + "bbox": [ + 498, + 484, + 857, + 502 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Experimental Setup. We adopt 17 pre-trained heterogeneous models from Taskonomy [53] to compare their functionality similarity. These models are trained on various tasks (including Autoencoder, Curvature, Denoise, Edge 2D, Edge 3D, Keypoint 2D, Keypoint 3D, Reshade, RGB2depth, RGB2mist, RGB2sfnorm, Room Layout, Segment25D, Segment2D, Vanishing Point, Segmentation, and Classification) and are different in architectures. Generally speaking, the architectures of these models follow an encoder-decoder scheme, in which the encoder is implemented by fully convolutional layers and the decoder varies according to the tasks. Please refer to [53] for more detailed information. In our experiments, only the encoders of these models are adopted for generating their ModelGiFs.", + "bbox": [ + 496, + 516, + 890, + 729 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Competitors and Evaluation Metric. The proposed ModelGiF is compared with several prior approaches to task relatedness estimation, including RSA [12], Attribution-Maps [43], and ZEST [22]. Note that AttributionMaps adopts saliency [41], DeepLIFT [40] and $\\epsilon$ -LRP [4] to generate attributions for task relatedness estimation. We compare ModelGiF with all these variants to demonstrate its superiority in task relatedness prediction. As the affinity matrix from Taskonomy is obtained based on the actual transfer learning performance, it is used as the ground truth of the affinity among these tasks. In this experiment, we will", + "bbox": [ + 496, + 734, + 893, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "Here we simply set $\\mathbf{x}_0$ to the zero vector. Other settings do not yield significantly superior performance in our experiments.", + "bbox": [ + 76, + 875, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "6129", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/6834f8232963b5ad2260e6ffb9bc4e0f177d9f49df02dcf33625945c86f8703c.jpg", + "image_caption": [ + "(a) Affinity Matrix from Taskonomy" + ], + "image_footnote": [], + "bbox": [ + 89, + 94, + 354, + 227 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/b457a29dba003eee0d19c03e3729d852b6274d83ecc9686c476a61adb9820620.jpg", + "image_caption": [ + "(b) Affinity Matrix from RSA" + ], + "image_footnote": [], + "bbox": [ + 357, + 95, + 620, + 228 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/f24bec5d274bea9fe5fec1c47b27e09ad34e2b7a4c573401c1f664c847d33498.jpg", + "image_caption": [ + "(c) Affinity Matrix from ModelGiF" + ], + "image_footnote": [], + "bbox": [ + 624, + 95, + 885, + 227 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/aa30cad153c71255768d86218b26285a4bf02a88cda5614d4ea6c70a197f35a6.jpg", + "image_caption": [ + "(d) Similarity Tree from ModelGiF", + "Figure 3. Results of task related estimation: (a) affinity matrix from Taskonomy; (b) affinity matrix from RSA; (c) affinity matrix from ModelGiF; (d) the similarity tree derived from ModelGiF; (e) performance with varying $K$ of different reference points; (e) performance with varying $K$ of different implementations." + ], + "image_footnote": [], + "bbox": [ + 89, + 253, + 362, + 378 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/97191c17e4cce016b4388176c3137f0df030cdebcdad303d4e9032da346d3d15.jpg", + "image_caption": [ + "(e) Different reference points" + ], + "image_footnote": [], + "bbox": [ + 361, + 253, + 612, + 378 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/23a47142c51ca8a7001737fbfae2d0c839ca01ef5d52741ac9e54ab14a8f9f7b.jpg", + "image_caption": [ + "(f) Different implementations" + ], + "image_footnote": [], + "bbox": [ + 625, + 253, + 880, + 378 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/b0405607c89e692499a0bbbb2ac275f5457ce2e4ae13abac05fc654138bc4646.jpg", + "table_caption": [], + "table_footnote": [ + "Table 1. Comparison between the proposed ModelGiF and existing methods. Here 1, 000 reference points are sampled in ModelGiF." + ], + "table_body": "
MethodSpearman's Correlation
Zest [22]0.359
AttributionMapsSALIENCY [43]0.619
AttributionMapsDEEPLIFT [43]0.685
AttributionMapsε-LRP [43]0.682
RSA [12]0.777
ModelGiFRANDOM0.834
ModelGiFAUGMENT0.835
ModelGiFADVERSARIAL0.830
", + "bbox": [ + 78, + 459, + 480, + 609 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "verify that the functionality similarity obtained by ModelGiF positively correlates with that from taskonomy. In order to quantify the similarity between the affinity matrix representing functionality similarity obtained by ModelGiF and the affinity matrix obtained by Taskonomy, we use Spearman's correlation as the metric for evaluation.", + "bbox": [ + 75, + 665, + 468, + 755 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Results. We first test the proposed ModelGiF with by randomly sampling 1,000 reference points. The visualization of the affinity matrix (as well as that from Taskonomy [53] and RSA [12]) and the similarity tree are provided in Figure 3. This similarity tree is constructed by agglomerative hierarchical clustering based on the affinity matrix. It can be seen that the affinity matrix from the proposed ModelGiF is visually highly similar to that from Taskonomy in most regions. The similarity tree derived from ModelGiF", + "bbox": [ + 75, + 763, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "perfectly matches the results from taskonomy where 3D (in green font) tasks, 2D (in blue font), geometric (in red font) tasks, and semantic (in purple font) tasks cluster into corresponding groups as expected.", + "bbox": [ + 496, + 460, + 890, + 521 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1 provide a quantitative comparison between the proposed ModelGiF with existing works in Spearman's correlation. It can be easily seen that the proposed ModelGiF yields significantly superior performance to existing methods, improving the SOTA Spearman's correlation from 0.777 to 0.835. Furthermore, all the three types of reference points produce Spearman's correlation more than 0.83, which implies that the proposed method is quite robust to the choice of the reference points. To make a more comprehensive study, we test ModelGiF with varying number of reference points. The correlation curves are depicted in Figure 3e, where different types of reference points are compared. It can be seen that as the number of reference points increases, the correlation steadily grows. Surprisingly, with only 16 points, ModelGiF already achieves comparable performance to RSA [12] in Spearman's correlation. It is attractive as the computation overhead of the proposed method grows linearly with the number of reference points. The results indicate that we can safely reduce the computation cost by decreasing the number of reference points, and we can also strive for higher performance by adding more reference points, which makes ModelGiF flexible and applicable in a variety of scenarios. Another conclusion we can draw from Figure 3e is that the adversarial samples generally yields superior performance to other ref", + "bbox": [ + 496, + 523, + 892, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "6130", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/641a116be54f58c130b66442a143163fbf3fae6e46d3a1f3b94850b5554a6204.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
CIFARtiny-ImageNet
AttackIPGuard [8]CAE [30]EWE [23]SAC [17]ModelGiF (Ours)IPGuard [8]CAE [30]EWE [23]SAC [17]ModelGiF (Ours)
Finetune-A1.001.001.001.001.001.001.000.481.001.00
Finetune-L1.001.001.001.001.001.001.001.001.001.00
Pruning1.000.950.871.001.001.001.000.581.001.00
Extract-L0.810.830.971.001.000.971.001.001.001.00
Extract-P0.810.900.971.001.000.971.001.001.001.00
Extract-Adv0.540.520.910.921.000.650.781.000.911.00
Transfer-10C1.001.001.001.001.00N/AN/AN/AN/AN/A
Transfer-A---1.001.00---1.001.00
Transfer-L---1.001.00---1.001.00
", + "bbox": [ + 109, + 88, + 859, + 290 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2. Comparison between the proposed ModelGiF and existing methods for IP protection. The performance is measured in AUC value under the AUC-ROC curve. “–” represent the IP protection method can not detect this kind of attack. “N/A” denotes not applicable.", + "bbox": [ + 75, + 290, + 890, + 319 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "erence points, which gives implications of future work to strive for higher performance of task relatedness estimation.", + "bbox": [ + 75, + 343, + 468, + 372 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In Figure 3f, we make comparisons between some different implementations of ModelGiF. \"ModelGiF with random baselines\" denotes $\\mathbf{x}_0$ in Eqn. 4 is fixed to be zero, and \"ModelGiF with random baselines\" denotes $\\mathbf{x}_0$ is randomly sampled. We also include Integrated Gradient (IG, with zero as the baseline) and IG with random baselines for comparisons. Albeit bearing some similarity with IG, it can be seen that ModelGiF with zero baselines significantly outperforms these baselines in most cases. ModelGiF with random baselines, however, is more promising when the number of reference points becomes sufficiently larger.", + "bbox": [ + 75, + 373, + 470, + 541 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Application: Intellectual Property Protection", + "text_level": 1, + "bbox": [ + 76, + 551, + 459, + 569 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We evaluate the performance of ModelGiF for IP protection against different model stealing attacks. To make fair comparisons with SOTA methods, we follow the experimental settings of [17] to conduct our experiments.", + "bbox": [ + 75, + 575, + 468, + 638 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Experimental Setup. Five categories of stealing attacks are considered here to test the protection performance. including finetuning, pruning, transfer learning, model extraction and adversarial model extraction. For finetuning, FinetuneL denotes fine-tuning only the last layer and leaves the other layers unchanged. Finetune-A fine-tunes all the layers in the model. For transfer learning, the CIFAR10 model is transferred to CIFAR10-C and CIFAR100. The tiny-ImageNet model (trained with the front 100 labels in Tiny-ImageNet) is transferred to the 100 labels left behind in tiny-ImageNet dataset. In model extraction, the victim model can be extracted in two manners: probability-based model extraction (Extract-P), and label-based model extraction (Extract-L). However, the attacker can evade the detection by applying adversarial training after the label-based model extraction [30]. In our experiment, adversarial model extraction (Extract-adv) adopts the predicted label to evade the", + "bbox": [ + 75, + 643, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "detection by adversarial training.", + "bbox": [ + 500, + 343, + 718, + 359 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Models and Competitors. Different IP protection methods are evaluated on most of the common model architectures, including VGG [42], ResNet [18], DenseNet [20] and MobileNet [38]. To demonstrate the superiority of the proposed ModelGiF, we make comparisons with SOTA IP protection methods, including IPGuard [8], CAE [30], EWE [23] and SAC [17]. IPGuard and CAE utilizes the transferability of adversarial examples and test the attack success rate of these adversarial examples on the suspect models. A model will be recognized as a stolen model if its attack success rate is larger than a threshold. SAC propose to leverage the pairwise relationship between samples as the model fingerprint. EWE, on the contrary, trains the source model on backdoor data and leaves the watermark in the model. Please refer to [17] for more detailed experimental settings.", + "bbox": [ + 496, + 372, + 893, + 599 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results. To validate the effectiveness and the superiority of the proposed ModelGiF, we conduct experiments on different datasets for the defender and the attacker. We we leverage AUC-ROC curve and use AUC value between the fingerprinting scores of the irrelevant models and the stolen models to measure the fingerprinting effectiveness. Results are listed in Table 2. It can be seen that the proposed ModelGiF, although not tailored for IP protection, achieve superior performance in all the attack scenarios. The AUC value is 1.0 across all attacks (including the challenging \"Extract-adv\" attack), which means it perfectly recognize all the attacks to protect the IP, outperforming existing SOTA approaches like SAC [17]. We acknowledge the existing benchmark for IP protection methods is not sufficient large and challenging to provide thorough comparisons between IP methods. However, the superiority of ModelGiF to SOTA methods on this benchmark still provides us a strong confidence of the proposed method for quantifying model functional distance.", + "bbox": [ + 496, + 613, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "6131", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c76314d8e8b95a658a1945c52edc48a5221a38bac59a9ce07cb5049568704c4d.jpg", + "image_caption": [ + "Figure 4. Cosine distances between the reference classifier $C_{ref}$ and unrelated classifier $C_{unrelated}$ , the directly unlearned classifier $C_{direct}$ and the approximately unlearned classifier $C_{approx}$ ." + ], + "image_footnote": [], + "bbox": [ + 98, + 90, + 480, + 237 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/80a67a38d27d540c935c49717a975ded9e53093c7ba9388a25b8975f2642d26a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 486, + 90, + 875, + 239 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.3. Application: Model Unlearning Verification", + "text_level": 1, + "bbox": [ + 76, + 295, + 449, + 313 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Machine unlearning studies how we can efficiently delete data points used to train models without retraining from scratch [7]. In this section, we demonstrate the effectiveness of the proposed ModelGiF for model unlearning verification, i.e., ModelGiF can distinguish the models trained with and without the data points that is requested to be unlearned.", + "bbox": [ + 75, + 321, + 470, + 428 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Experimental Setup. Following the experimental settings of [22], we training four classifiers to evaluate ModelGiF for model unlearning verification. The first classifier is called the reference classifier $C_{ref}^{(t)}$ , where $t$ denotes that the classifier is obtained after $t$ epochs training. The reference classifier serves as the original classifier trained on all the training data, including the data points which are requested to be deleted later. The second classifier is called the unrelated classifier, which is another classifier trained on all the training data, but from different initialization. The third classifier is called the exactly unlearned classifier, which is trained on the remaining data after removing the data points requested to be deleted. Note that the exactly unlearned classifier is trained from scratch and has never seen those data points which are requested to be removed, and it thus can be seen as the exactly unlearned classifier [7]. The last classifier is called approximately unlearned classifier, which is obtained by directly optimizing the original reference classifier to remove the knowledge learned from those data points requested to be unlearned [16]. We compare the ModelGiFs of the unrelated classifier, the exactly unlearned classifier and the approximately unlearned classifier to that of the reference classifier. The goal is to test whether the proposed ModelGiF can recognize the exactly unlearned classifier from the unrelated classifier.", + "bbox": [ + 75, + 436, + 468, + 816 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Experimental Details and Results. Experiments are conducted on CIFAR10 and CIFAR100. On CIFAR10, all classifiers are implemented by ResNet20. On CIFAR100, all classifiers are implemented by ResNet50. We randomly sample 128 data points from the training data to be un-", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "learned, and use these data as the reference points to compute the distance between ModelGIFs of these classifiers. Experimental results are provided in Figure 4. It can be seen that with the proposed ModelGiF, exactly unlearned classifier gets significantly higher distance with the reference classifier than the unrelated classifier. It implies that ModelGiF can also be used as a tool to verify the unlearning performance of existing unlearning methods. Another observation from Figure 4 is that the distance between the approximately unlearned classifier and the reference classifier is much lower than unrelated classifier, which implies that existing approximately unlearning methods can not delete the data from the model thoroughly. However, as the training for unlearning continues, the information can be gradually forgotten, as implied by the increasing distance shown in Figure 4. These results also accord with prior finding that continual learning easily lead to catastrophic forgetting problem [35], which validate the rationality of the results from the proposed ModelGiF.", + "bbox": [ + 496, + 296, + 893, + 583 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion and Future Work", + "text_level": 1, + "bbox": [ + 498, + 601, + 769, + 617 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this work, we propose ModelGiF to quantify model functional distance. The main assumption underlying ModelGiF is that each pre-trained deep model uniquely determines a ModelGiF over the input space. The distance between models can thus be measured by the similarity between their ModelGiFs. We apply the proposed ModelGiF to task relatedness estimation, intellectual property protection, and model unlearning verification. Experimental results demonstrate the versatility of the proposed ModelGiF on these tasks, with significantly superiority performance to state-of-the-art competitors. There are several directions for future work with the proposed ModelGiF. For example, exploring more scenarios where ModelGiF can be applied. Another interesting research direction is proposing more informative reference points to extract stronger representations of ModelGiF. Finally, how to further speed up the computation of the proposed method is also important to make it easier to use.", + "bbox": [ + 496, + 628, + 893, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "6132", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement. This work is funded by the National Key Research and Development Project (Grant No: 2022YFB2703100), National Natural Science Foundation of China (62106220, 61976186, U20B2066), and Ningbo Natural Science Foundation (2021J189).", + "bbox": [ + 76, + 90, + 472, + 167 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 180, + 174, + 196 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Alessandro Achille, Michael Lam, Rahul Tewari, Avinash Ravichandran, Subhransu Maji, Charless C Fowlkes, Stefano Soatto, and Pietro Perona. Task2vec: Task embedding for meta-learning. In Proceedings of the IEEE/CVF international conference on computer vision, pages 6430-6439, 2019. 2", + "[2] Yossi Adi, Carsten Baum, Moustapha Cisse, Benny Pinkas, and Joseph Keshet. Turning your weakness into a strength: Watermarking deep neural networks by backdooring. 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In Proceedings of the 2018 on Asia Conference on Computer and Communications Security, pages 159-172, 2018. 3" + ], + "bbox": [ + 501, + 90, + 890, + 275 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "6135", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/ModelGiF_ Gradient Fields for Model Functional Distance/5efa34c8-5ce4-47e6-bc15-889009199a89_model.json b/2023/ModelGiF_ Gradient Fields for Model Functional Distance/5efa34c8-5ce4-47e6-bc15-889009199a89_model.json new file mode 100644 index 0000000000000000000000000000000000000000..cabe2f3dc4f2dd35a7df8dfd4456e68fbacd208c --- /dev/null +++ b/2023/ModelGiF_ Gradient Fields for Model Functional Distance/5efa34c8-5ce4-47e6-bc15-889009199a89_model.json @@ -0,0 +1,2147 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.191, + 0.131, + 0.78, + 0.151 + ], + "angle": 0, + "content": "ModelGiF: Gradient Fields for Model Functional Distance" + }, + { + "type": "text", + "bbox": [ + 0.243, + 0.181, + 0.734, + 0.218 + ], + "angle": 0, + "content": "Jie Song, Zhengqi Xu, Sai Wu, Gang Chen, and Mingli Song* Zhejiang University" + }, + { + "type": "text", + "bbox": [ + 0.282, + 0.22, + 0.688, + 0.234 + ], + "angle": 0, + "content": "{sjie,xuzhengqi,wusai,cg,brooksong}@zju.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.303, + 0.474, + 0.621 + ], + "angle": 0, + "content": "The last decade has witnessed the success of deep learning and the surge of publicly released trained models, which necessitates the quantification of the model functional distance for various purposes. However, quantifying the model functional distance is always challenging due to the opacity in inner workings and the heterogeneity in architectures or tasks. Inspired by the concept of \"field\" in physics, in this work we introduce Model Gradient Field (abbr. ModelGiF) to extract homogeneous representations from the heterogeneous pre-trained models. Our main assumption underlying ModelGiF is that each pre-trained deep model uniquely determines a ModelGiF over the input space. The distance between models can thus be measured by the similarity between their ModelGiFs. We validate the effectiveness of the proposed ModelGiF with a suite of testbeds, including task relatedness estimation, intellectual property protection, and model unlearning verification. Experimental results demonstrate the versatility of the proposed ModelGiF on these tasks, with significantly superiority performance to state-of-the-art competitors. Codes are available at https://github.com/zju-vipa/modelgif." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.654, + 0.21, + 0.67 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.681, + 0.47, + 0.848 + ], + "angle": 0, + "content": "The last decade has witnessed the great progress of deep learning in various fields, and a plethora of deep neural networks are developed and released publicly, with either their architectures and trained parameters (e.g., Tensorflow Hub1, Pytorch Hub2) for research, or the prediction API (e.g., BigML, Amazon Machine Learning) as ML-as-a-Service (MLaaS) for commercial purposes. These off-the-shelf pre-trained models become extremely important resources for not only practitioners to solve their own problems, but also researchers to explore and exploit the huge potential underlying these pre-trained models." + }, + { + "type": "image_caption", + "bbox": [ + 0.556, + 0.315, + 0.669, + 0.332 + ], + "angle": 0, + "content": "Magnetic Field" + }, + { + "type": "image", + "bbox": [ + 0.704, + 0.274, + 0.88, + 0.363 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.517, + 0.373, + 0.76, + 0.445 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.572, + 0.447, + 0.73, + 0.461 + ], + "angle": 0, + "content": "Model Gradient Field" + }, + { + "type": "image", + "bbox": [ + 0.769, + 0.374, + 0.884, + 0.461 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.47, + 0.892, + 0.499 + ], + "angle": 0, + "content": "Figure 1. An illustrative diagram of the magnetic field and the proposed model gradient field (ModelGiF) defined on the input space." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.507, + 0.893, + 0.809 + ], + "angle": 0, + "content": "With the surge of pre-trained models released, quantifying the model relationship emerges as an important question. The large-scale open-sourced deep models, heterogeneous in architectures and tasks and trained isolatedly or dependently, are related to each other in various manners. For example, a student model trained by knowledge distillation [19] should behave more similarly with the teacher than an independently trained identical model. Likewise, a fine-tuned model should be more closely related to its pretrained model than the one trained from scratch. More generally, models trained in isolation on heterogeneous tasks should inherit the intrinsic task relatedness [53] as task-specific features are extracted by these models. Broadly speaking, there exists a model metric space where models with similar functional behaviors are clustered together and dissimilar ones are far apart. The model functional distance between models, if left unresolved, leaves existing model repositories still simple unstructured collections of many isolated open-sourced models, hindering the exploitation of their great value as a whole." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.894, + 0.902 + ], + "angle": 0, + "content": "Despite the ever-increasing number of publicly available pre-trained models, the study on the model functional distance, i.e., structure of the model metric space, lags far behind. This phenomenon can be largely attributed to the great challenge of computing the functional distance between any deep models, where the barriers are three-folds: (1) Hetero-" + }, + { + "type": "page_footnote", + "bbox": [ + 0.094, + 0.863, + 0.341, + 0.901 + ], + "angle": 0, + "content": "\\*Corresponding author \n1https://www.tensorflow.org/hub \n2https://pytorch.org/hub/" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6125" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.212 + ], + "angle": 0, + "content": "geneity: deep models usually differ significantly in architectures. Even with the same architecture, models trained on different datasets or tasks can also behave quite differently; (2) Opacity: the opaque inner workings of deep models render computing the model similarity extremely difficult; (3) Efficiency: as the cost of computing pairwise distance grows quadratically with the number of models, the computation of the functional distance should be efficient." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.218, + 0.471, + 0.626 + ], + "angle": 0, + "content": "A few prior works have been devoted to computing model distance, in either weight space [1, 24] or representation space [28, 12]. For example, Task2Vec [1] computes task or model representations based on estimates of the Fisher information matrix associated with the probe network parameters, which provides a fixed-dimensional embedding of the model agnostic to the task variations. However, Task2Vec assumes all probe models share the same architecture, which is highly restrictive in practice. ModelDiff [28] and representation similarity analysis (RSA) [12], on the other hand, adopt the similarity of representations on a small set of reference inputs as the model representations, and the model distance is thus calculated resorting to these model representations, which is shown effective for model reuse detection and transferability estimation. However, these methods only capture the point-wise behavior of the models at a small number of chosen reference points, which is limited in representation capacity and fails at harder tasks such as detecting model extraction [28]. Recently, DEPARA [43, 44] and ZEST [22] are proposed as pilot studies by applying explanation methods for computing model distance. However, they are validated on disjoint downstream tasks, and the performance on comprehensive tasks remains unclear. Moreover, these methods also use a small number of chosen reference points to extract the model representations, which makes them suffer from low representation capacity." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.47, + 0.902 + ], + "angle": 0, + "content": "In this work, inspired by the concept of \"field\" in physics, we propose Model Gradient Field (as shown in Figure 1), abbreviated as ModelGiF, as the proxy to extract homogeneous representations from pre-trained heterogeneous models to derive their functionality distance. Specifically, the proposed ModelGiF is defined on the input space, i.e., every point in the ModelGiF denotes the gradient vector of the model output w.r.t. the input on the same point. The main assumption underlying ModelGiF is that each pretrained deep model uniquely determines a ModelGiF over the input space. The functional distance between any two models can thus be measured by the similarity between their ModelGiFs. Unlike prior methods where the point-wise features are adopted for representing the model, ModelGiFs represents these models by their gradient on the whole input space, which makes it more capable of differentiating highly related models (i.e., model extraction detection). Moreover, we provide theoretical insights into the proposed" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.212 + ], + "angle": 0, + "content": "ModelGiFs for model functional distance, and make extensive discussions on different implementation details. We validate the effectiveness of the proposed ModelGiF with a suite of testbeds, including transferability estimation, intellectual property protection, and model unlearning verification. Experimental results demonstrate the versatility of the proposed ModelGiF on these tasks, with significantly superiority to state-of-the-art (SOTA) methods." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.213, + 0.892, + 0.365 + ], + "angle": 0, + "content": "To sum up, we make the following contributions: (1) we propose the concept of \"model gradient field\", a novel method for quantifying the functionality similarity between pre-trained deep models; (2) we provide theoretical insights into the proposed ModelGiFs for model functional distance, and make extensive discussions on different implementation details; (3) extensive experiments demonstrate the effectiveness and the superiority of ModelGiF on various tasks, including transferability estimation, intellectual property protection, and model unlearning verification." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.378, + 0.642, + 0.394 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.405, + 0.892, + 0.451 + ], + "angle": 0, + "content": "This section briefly reviews some related topics to model functional distance, including task relatedness estimation, intellectual property protection, and model unlearning." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.456, + 0.892, + 0.789 + ], + "angle": 0, + "content": "Task Relatedness Estimation. Recent studies [53, 43, 44, 5, 51, 3, 6, 26] reveals the existence of task relatedness or task structure among visual tasks. It is the concept underlying transfer learning and provides a principled way to seamlessly reuse supervision among related tasks or solve many tasks in one system [53]. Existing works to obtain task relatedness can be roughly divided into empirical and analytical approaches. Taskonomy [53] is the most representative work of empirical methods. It proposes a fully computational approach to obtain task relatedness by exhaustively computing the actual transfer learning performance, which is thus usually taken as the ground truth for evaluating other estimators. Despite the indisputable results, the computational cost of empirical methods is extremely high. On the other hand, analytical methods, e.g., DEPARA [44, 43], Task2Vec [1] and RSA [12], try to estimate the task relatedness without conducting the actual transfer learning. Analytical methods generally significantly reduce the computation overhead, but can be highly restrictive in model architectures or estimation performance. The proposed Model-GiF relaxes these restrictions and achieves task relatedness more consistent to taskonomy than existing approaches." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Intellectual Property Protection. Since training deep models usually consumes expensive data collection and large computation resources, the trained models constitute valuable intellectual property (IP) that should be protected in cases where reusing is not allowed without authorization. However, model IP can be infringed in a variety of forms, such as fine-tuning [2, 48], pruning [29, 33], transfer learn-" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6126" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.091, + 0.473, + 0.425 + ], + "angle": 0, + "content": "ing [39, 49, 50] and model extraction [34, 47, 25, 21], which poses great challenge to IP protection. Existing IP protection approaches can be roughly categorized into watermarking [23, 48, 13, 54, 2] and fingerprinting [30, 8, 28, 17]. Watermarking methods usually leverage weight regularization [48, 13] to put secret watermark in the model parameters or train models on a triggered set to leave backdoor [2, 54] in them. While being able to provide exact ownership verification, these techniques are invasive, i.e., they need to tamper with the training process, which may affect the model utility or introduce new security risks into the model. Fingerprinting, on the contrary, extracts a unique identifier, i.e., fingerprint, from the owner model to differentiate it from other models. Latest fingerprinting (e.g., ModelDiff [28], IPGuard [8], SAC [17]) on deep learning models, though being non-invasive, also fall short when facing the diverse and ever-growing attack scenarios [10]. In this work, we propose ModelGiF as the homogeneous representations for heterogeneous pre-trained models, which can be naturally adopted as the fingerprint for IP protection and yields superior IP protection performance to existing approaches." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.43, + 0.473, + 0.688 + ], + "angle": 0, + "content": "Model Unlearning Verification. Model unlearning aims to remove the effects of data points from the trained model, which has been attracting increasing attentions in recent years due to legislation and privacy ethics. Cao et al. [9] are dedicated to making learning systems forget and present an unlearning approach capable of forgetting specific data. Graves et al. [16] propose an effective method to eliminate the influence of personal data from the model while maintaining the validity. Bourtoule et al. [7] particularly propose a model unlearning method to decrease the time it takes to retrain exactly. However, how to identify whether the impact of data has been eliminated is an essential but rarely studied problem. Recently ZEST [22] verifies the unlearning of data by comparing the Local Interpretable Model-Agnostic Explanations (LIME) [37]. In this work, we adopt the proposed ModelGiF for unlearning verification, which yields competitive performance in our experiments." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.7, + 0.214, + 0.718 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.724, + 0.229, + 0.74 + ], + "angle": 0, + "content": "3.1. Problem Setup" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.747, + 0.47, + 0.868 + ], + "angle": 0, + "content": "Assume there is a model repository consisting of \\(N\\) pre-trained models \\(\\mathcal{M} = \\{M_1, M_2, \\dots, M_N\\}\\). With mild assumptions, these models are defined on the same input space \\(\\mathbb{R}^D\\) (\\(D = WHC\\), where \\(W, H\\) and \\(C\\) denotes the width, height and channel of the input space), yet trained with data sampled from different data distributions \\(\\mathcal{P} = \\{p_1, p_2, \\dots, p_N\\}\\). Note that here we made no assumptions on the model architectures and the tasks, which means" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.892, + 0.198 + ], + "angle": 0, + "content": "that these models can be different in architectures (e.g., ResNet [18] and VGG [42]), and tasks (e.g., visual classification [27], detection [36] or segmentation [11]). The goal in this work is to construct a model metric space where models with similar functional behaviors are clustered together and dissimilar ones are far apart, where the vital step is quantifying the functional distance between these models." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.206, + 0.727, + 0.222 + ], + "angle": 0, + "content": "3.2. The Proposed ModelGiF" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.23, + 0.892, + 0.349 + ], + "angle": 0, + "content": "As aforementioned, quantifying the functional distance between pre-trained models is challenging due to the heterogeneity, opacity and efficiency issues. Our main idea is extracting homogeneous descriptors from these heterogeneous models to make them comparable. To this end, we proposed the concept ModelGiF, as shown in Figure 1, to derive the comparable identifier of the pre-trained models for quantifying model distance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.35, + 0.893, + 0.501 + ], + "angle": 0, + "content": "ModelGiF is inspired by the concept \"field\" in physics where a field is a mapping from space to some physical quantity, represented by a scalar, vector, or tensor, that has a value for each point in the space [32]. For example, the magnetic field describes the magnetic influence on moving electric charges, electric currents, and magnetic materials [14]. Likewise, we define ModelGiF as a mapping from the input space to the gradient space such that each point in the input space is assigned to a gradient vector. The formal definition is provided as follows." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.51, + 0.892, + 0.617 + ], + "angle": 0, + "content": "Definition 3.1 (Model Gradient Field) Let \\( M \\) be a deep model trained on the data which is sampled according to some distribution \\( p \\) from the data space \\( \\mathcal{X} \\), outputting a scalar4 prediction in the label space \\( \\mathcal{Y} \\). A point \\( \\mathbf{x} \\) can be described as \\( \\mathbf{x} = (x_1, x_2, \\dots, x_D) \\). We define the model gradient field of \\( M \\) as the gradient of every possible input point in \\( \\mathcal{X} \\) w.r.t. the model output:" + }, + { + "type": "equation", + "bbox": [ + 0.605, + 0.627, + 0.892, + 0.643 + ], + "angle": 0, + "content": "\\[\n\\operatorname {M O D E L G I F} (M) \\triangleq \\nabla_ {\\mathbf {x}} M, \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.653, + 0.892, + 0.775 + ], + "angle": 0, + "content": "which is a mapping from the input space \\(\\mathbb{R}^D\\) to the gradient space \\(\\mathbb{G}^D\\), MODELGiF: \\(\\mathbb{R}^D \\to \\mathbb{G}^D\\). Note that the ModelGiF is defined on the whole input space (which is shared by all the models) rather than some discretely points sampled from the data distribution \\(p\\) specific to the model \\(M\\). As the architecture of \\(M\\) and the tasks (i.e., the label space \\(\\mathcal{V}\\)) can be heterogeneous, the ModelGiF of a model can be seen as a projection of the model to the common input space." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.783, + 0.745, + 0.798 + ], + "angle": 0, + "content": "3.3. Field Curves for ModelGiF" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.806, + 0.892, + 0.868 + ], + "angle": 0, + "content": "With the proposed ModelGiF, the model functional distance can be quantified by the ModelGiF similarity. However, as ModelGiF is defined on the whole input space that is usually extremely huge, how to extract its representation" + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.875, + 0.47, + 0.901 + ], + "angle": 0, + "content": "3Without losing generality, we use vector instead of tensor for notation simplicity." + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.892, + 0.901 + ], + "angle": 0, + "content": "4For vector or tensor predictions, we simply take their \\(l_{2}\\) norm as the scalar output." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6127" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.083, + 0.092, + 0.891, + 0.405 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.408, + 0.893, + 0.438 + ], + "angle": 0, + "content": "Figure 2. An illustrative diagram of the overall pipeline of obtaining ModelGiF curves. The more similar the ModelGiFs, the more similar the corresponding trained models. Note that ModelGiF Curves are in high-dimensional space in reality." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.462, + 0.473, + 0.598 + ], + "angle": 0, + "content": "or signature becomes the vital step for quantifying model distance. In physics, a field is usually depicted by the field curves (as shown in Figure 1), i.e., the integral curves for the field, and can be constructed by starting at a point and tracing a curve through space that follows the direction of the vector field, by making the field curve tangent to the field vector at each point [46]. Inspired by this, we propose ModelGiF Curves as the descriptors of ModelGiF to measure the model functional distance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.604, + 0.471, + 0.682 + ], + "angle": 0, + "content": "Definition 3.2 (Field Curves) For a field \\(F\\): \\(\\mathbb{R}^D \\to \\mathbb{G}^D\\), a curve \\(\\mathbf{x}(t) = (x_1(t), x_2(t), \\ldots, x_D(t))\\) is called a field curve of the field \\(F\\) if the following condition is satisfied: For all points \\(P \\in \\mathbf{x}(t)\\), the tangent vector of the curve in the point \\(P\\) has the same direction as the vector \\(F(P)\\):" + }, + { + "type": "equation", + "bbox": [ + 0.125, + 0.689, + 0.47, + 0.721 + ], + "angle": 0, + "content": "\\[\n\\frac {d x _ {1} (t)}{d t} = F \\left(\\mathbf {x} (t)\\right) _ {1}, \\frac {d x _ {2} (t)}{d t} = F \\left(\\mathbf {x} (t)\\right) _ {2}, \\dots \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.727, + 0.47, + 0.863 + ], + "angle": 0, + "content": "The field curve can be described as the solution of the system of differential equations in Eqn. 2, and it plays an important role for both analysis and visualization of vector fields [46]. Unfortunately, as the ModelGiF is usually complicated for a pre-trained deep model, there is no closed solution. The field curves are in general not describable as parameterized curves, which hinders the comparisons between different ModelGiFs. To resolve this issue, we introduce the definition of ModelGiF curves as follows." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Definition 3.3 (ModelGiF Curves) For a ModelGiF \\( F \\): \\( \\mathbb{R}^D \\to \\mathbb{G}^D \\), a curve \\( \\mathbf{g}(t) = (g_1(t), g_2(t), \\dots, g_D(t)) \\) is" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.462, + 0.893, + 0.492 + ], + "angle": 0, + "content": "called the ModelGiF curve of \\( F \\) if the following condition is satisfied:" + }, + { + "type": "equation", + "bbox": [ + 0.55, + 0.502, + 0.892, + 0.533 + ], + "angle": 0, + "content": "\\[\n\\frac {d g _ {1} (t)}{d t} = F (\\mathbf {x} (t)) _ {1}, \\frac {d g _ {2} (t)}{d t} = F (\\mathbf {x} (t)) _ {2}, \\dots \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.541, + 0.893, + 0.588 + ], + "angle": 0, + "content": "Note that different from the definition of field curves, the ModelGiF curves are defined on the gradient space \\(\\mathbb{G}^D\\) instead of the input space \\(\\mathbb{R}^D\\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.596, + 0.894, + 0.643 + ], + "angle": 0, + "content": "Proposition 1 For a ModelGiF \\( F \\colon \\mathbb{R}^D \\to \\mathbb{G}^D \\), and two points \\( \\mathbf{x}_0, \\mathbf{x}_1 \\) in \\( \\mathbb{R}^D \\), the gradient integral along the straight line from \\( \\mathbf{x}_0 \\) to \\( \\mathbf{x}_1 \\) is a ModelGiF curve of \\( F \\):" + }, + { + "type": "equation", + "bbox": [ + 0.52, + 0.653, + 0.892, + 0.687 + ], + "angle": 0, + "content": "\\[\n\\mathbf {g} (t) = \\int_ {\\alpha = 0} ^ {t} F \\left(\\mathbf {x} _ {0} + \\alpha \\left(\\mathbf {x} _ {1} - \\mathbf {x} _ {0}\\right)\\right) d \\alpha , \\quad t \\in [ 0, 1 ] \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.696, + 0.892, + 0.772 + ], + "angle": 0, + "content": "With the proposition, we can make comparisons between ModelGiFs by simply comparing their ModelGiF curves between some predefined pairs of points. Now we provide the detailed pipeline of quantifying the Model functional distance with the proposed ModelGiF." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.78, + 0.767, + 0.795 + ], + "angle": 0, + "content": "3.4. ModelGiF for Model Distance" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.804, + 0.892, + 0.866 + ], + "angle": 0, + "content": "Provided with the trained deep models as described in Section 3.1, we compute the model distance with the proposed ModelGiF in two steps (in Figure 2): 1) Sampling reference points, and 2) Computing the model distance." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.893, + 0.902 + ], + "angle": 0, + "content": "Sampling Reference Points. As described in Proposition 1, the first step before obtaining ModelGiF curves is" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6128" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.228 + ], + "angle": 0, + "content": "determining the reference points (i.e., \\(\\mathbf{x}_1^5\\) in Eqn. 4.), which determines the domain of these curves. Let \\(K\\) be the number of reference points to be sampled. Intuitively, these reference points should representative. However, as the models in \\(\\mathcal{M}\\) can be heterogeneous in architectures and tasks and trained on data sampled from different distributions, it is hard to determine a common set of reference points which are representative for all these models. In this work, we investigate three types of reference points as follows." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.23, + 0.47, + 0.292 + ], + "angle": 0, + "content": "1) Random samples drawn from \\(\\mathcal{P}\\). Each data point is sampled in two stages: first randomly sampling the distribution \\(p\\) from \\(\\mathcal{P}\\) and then randomly sampling the reference point from \\(p\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.293, + 0.47, + 0.386 + ], + "angle": 0, + "content": "2) Augmented samples using CutMix [52]. Let \\(\\mathbf{x}\\) and \\(\\mathbf{x}^*\\) be two randomly sampled points in \\(\\mathcal{P}\\). CutMix generates a new sample \\(\\tilde{\\mathbf{x}}\\) using the two samples by cutting off and pasting patches among them: \\(\\tilde{\\mathbf{x}} = \\mathbf{m} \\odot \\mathbf{x} + (1 - \\mathbf{m}) \\odot \\mathbf{x}^*\\), where \\(\\mathbf{m}\\) represents the binary mask to combine images with different parts, and \\(\\odot\\) the element-wise multiplication." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.388, + 0.469, + 0.45 + ], + "angle": 0, + "content": "3) Adversarial samples generated with PGD [31]. PGD attack is a multi-step variant of Fast Gradient Sign Method (FGSM) [15]: \\(\\mathbf{x}_{t + 1} = \\prod \\left(\\mathbf{x}_t + \\alpha \\mathrm{SGN}\\bigl (\\nabla \\mathcal{J}(\\mathbf{x}_t)\\bigr)\\right)\\), where \\(\\prod\\) denotes the projection to the allowed space." + }, + { + "type": "list", + "bbox": [ + 0.076, + 0.23, + 0.47, + 0.45 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.452, + 0.47, + 0.528 + ], + "angle": 0, + "content": "The performance of these types of reference points are discussed in Section 4.1. We also provide the sensitivity analysis of the number of reference points \\( K \\), which demonstrates that the performance of ModelGiF quickly becomes superior to existing methods as \\( K \\) increases." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.536, + 0.473, + 0.705 + ], + "angle": 0, + "content": "Computing the model distance. Let \\(S = \\{\\mathbf{x}_1, \\mathbf{x}_2, \\dots, \\mathbf{x}_K\\}\\) be the reference points obtained from the last step. For the \\(i\\)-th model \\(M_i\\), we can get \\(K\\) ModelGiF curves by substituting each point in \\(S\\) for the \\(\\mathbf{x}_1\\) in Eqn. 4. These curves are used as the identifier of the ModelGiF, and thus serve as the representations of the trained deep model. There are several distance metrics to measure the similarity between curves, e.g., Hausdorff distance and Fréchet distance. As the method for curve distance is not our contribution in this work, we simply adopt the integrated point-wise cosine distance to validate the performance of the proposed method:" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.732, + 0.47, + 0.775 + ], + "angle": 0, + "content": "\\[\nd \\left(M _ {i}, M _ {j}\\right) = \\sum_ {k = 1} ^ {K} \\int_ {t = 0} ^ {1} \\left(1 - \\cos \\left(\\mathbf {g} ^ {i, k} (t), \\mathbf {g} ^ {j, k} (t)\\right)\\right) d t, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.792, + 0.469, + 0.855 + ], + "angle": 0, + "content": "where \\(\\mathbf{g}^{i,k}\\) denotes the \\(k\\)-th curve of the \\(i\\)-th model in \\(\\mathcal{M}\\), and \\(\\cdot\\) denotes the inner product between \\(\\mathbf{g}^{i,k}(t)\\) and \\(\\mathbf{g}^{i,k}(t)\\). In practice, we approximate the integral with summation by sampling with some fixed intervals." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.797, + 0.108 + ], + "angle": 0, + "content": "3.5. Theoretical Analysis of ModelGiF" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.115, + 0.892, + 0.191 + ], + "angle": 0, + "content": "From the definition of model distance in Eqn. 5, we can see that the defined distance can be seen as the summation of point-wise similarities over all the curves. Here we provide some theoretical insights into ModelGiF by dissecting the model-level distance into point-level distance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.205, + 0.894, + 0.237 + ], + "angle": 0, + "content": "Proposition 2 For the point \\(\\mathbf{g}(t_1)\\) along the ModelGiF curves \\(\\mathbf{g}(t)\\) defined from \\(\\mathbf{x}^*\\) to \\(\\mathbf{x}\\), then" + }, + { + "type": "equation", + "bbox": [ + 0.551, + 0.248, + 0.892, + 0.272 + ], + "angle": 0, + "content": "\\[\n\\sum_ {i} t _ {1} \\left(x _ {i} - x _ {i} ^ {*}\\right) g _ {i} \\left(t _ {1}\\right) = M (\\mathbf {x}) - M \\left(\\mathbf {x} ^ {*}\\right), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.283, + 0.892, + 0.376 + ], + "angle": 0, + "content": "where the left side is actually the summation over Integrated Gradients [45]. Eqn. 6 tells us that the every point in proposed ModelGiF curve is strongly related to the model prediction differences from this point and the baseline point, thus the proposed model distance is a powerful distance metric to quantifying the model function distance." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.389, + 0.634, + 0.407 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.415, + 0.892, + 0.476 + ], + "angle": 0, + "content": "In this section, we verify the effectiveness of ModelGiF with a suite of testbeds, including task relatedness estimation, intellectual property protection and model unlearning verification. Details are provided as follows." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.486, + 0.859, + 0.503 + ], + "angle": 0, + "content": "4.1. Application: Task Relatedness Estimation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.517, + 0.892, + 0.73 + ], + "angle": 0, + "content": "Experimental Setup. We adopt 17 pre-trained heterogeneous models from Taskonomy [53] to compare their functionality similarity. These models are trained on various tasks (including Autoencoder, Curvature, Denoise, Edge 2D, Edge 3D, Keypoint 2D, Keypoint 3D, Reshade, RGB2depth, RGB2mist, RGB2sfnorm, Room Layout, Segment25D, Segment2D, Vanishing Point, Segmentation, and Classification) and are different in architectures. Generally speaking, the architectures of these models follow an encoder-decoder scheme, in which the encoder is implemented by fully convolutional layers and the decoder varies according to the tasks. Please refer to [53] for more detailed information. In our experiments, only the encoders of these models are adopted for generating their ModelGiFs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Competitors and Evaluation Metric. The proposed ModelGiF is compared with several prior approaches to task relatedness estimation, including RSA [12], Attribution-Maps [43], and ZEST [22]. Note that AttributionMaps adopts saliency [41], DeepLIFT [40] and \\(\\epsilon\\)-LRP [4] to generate attributions for task relatedness estimation. We compare ModelGiF with all these variants to demonstrate its superiority in task relatedness prediction. As the affinity matrix from Taskonomy is obtained based on the actual transfer learning performance, it is used as the ground truth of the affinity among these tasks. In this experiment, we will" + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.875, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Here we simply set \\(\\mathbf{x}_0\\) to the zero vector. Other settings do not yield significantly superior performance in our experiments." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6129" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.09, + 0.095, + 0.355, + 0.228 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.121, + 0.23, + 0.317, + 0.242 + ], + "angle": 0, + "content": "(a) Affinity Matrix from Taskonomy" + }, + { + "type": "image", + "bbox": [ + 0.358, + 0.096, + 0.621, + 0.229 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.406, + 0.23, + 0.565, + 0.242 + ], + "angle": 0, + "content": "(b) Affinity Matrix from RSA" + }, + { + "type": "image", + "bbox": [ + 0.625, + 0.096, + 0.887, + 0.228 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.659, + 0.23, + 0.846, + 0.241 + ], + "angle": 0, + "content": "(c) Affinity Matrix from ModelGiF" + }, + { + "type": "image", + "bbox": [ + 0.091, + 0.254, + 0.364, + 0.379 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.126, + 0.38, + 0.312, + 0.391 + ], + "angle": 0, + "content": "(d) Similarity Tree from ModelGiF" + }, + { + "type": "image", + "bbox": [ + 0.362, + 0.254, + 0.614, + 0.379 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.407, + 0.38, + 0.563, + 0.392 + ], + "angle": 0, + "content": "(e) Different reference points" + }, + { + "type": "image", + "bbox": [ + 0.627, + 0.254, + 0.882, + 0.379 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.673, + 0.38, + 0.832, + 0.391 + ], + "angle": 0, + "content": "(f) Different implementations" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.395, + 0.894, + 0.438 + ], + "angle": 0, + "content": "Figure 3. Results of task related estimation: (a) affinity matrix from Taskonomy; (b) affinity matrix from RSA; (c) affinity matrix from ModelGiF; (d) the similarity tree derived from ModelGiF; (e) performance with varying \\( K \\) of different reference points; (e) performance with varying \\( K \\) of different implementations." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.46, + 0.482, + 0.61 + ], + "angle": 0, + "content": "
MethodSpearman's Correlation
Zest [22]0.359
AttributionMapsSALIENCY [43]0.619
AttributionMapsDEEPLIFT [43]0.685
AttributionMapsε-LRP [43]0.682
RSA [12]0.777
ModelGiFRANDOM0.834
ModelGiFAUGMENT0.835
ModelGiFADVERSARIAL0.830
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.077, + 0.611, + 0.468, + 0.639 + ], + "angle": 0, + "content": "Table 1. Comparison between the proposed ModelGiF and existing methods. Here 1, 000 reference points are sampled in ModelGiF." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.666, + 0.47, + 0.756 + ], + "angle": 0, + "content": "verify that the functionality similarity obtained by ModelGiF positively correlates with that from taskonomy. In order to quantify the similarity between the affinity matrix representing functionality similarity obtained by ModelGiF and the affinity matrix obtained by Taskonomy, we use Spearman's correlation as the metric for evaluation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Results. We first test the proposed ModelGiF with by randomly sampling 1,000 reference points. The visualization of the affinity matrix (as well as that from Taskonomy [53] and RSA [12]) and the similarity tree are provided in Figure 3. This similarity tree is constructed by agglomerative hierarchical clustering based on the affinity matrix. It can be seen that the affinity matrix from the proposed ModelGiF is visually highly similar to that from Taskonomy in most regions. The similarity tree derived from ModelGiF" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.462, + 0.892, + 0.522 + ], + "angle": 0, + "content": "perfectly matches the results from taskonomy where 3D (in green font) tasks, 2D (in blue font), geometric (in red font) tasks, and semantic (in purple font) tasks cluster into corresponding groups as expected." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.524, + 0.893, + 0.902 + ], + "angle": 0, + "content": "Table 1 provide a quantitative comparison between the proposed ModelGiF with existing works in Spearman's correlation. It can be easily seen that the proposed ModelGiF yields significantly superior performance to existing methods, improving the SOTA Spearman's correlation from 0.777 to 0.835. Furthermore, all the three types of reference points produce Spearman's correlation more than 0.83, which implies that the proposed method is quite robust to the choice of the reference points. To make a more comprehensive study, we test ModelGiF with varying number of reference points. The correlation curves are depicted in Figure 3e, where different types of reference points are compared. It can be seen that as the number of reference points increases, the correlation steadily grows. Surprisingly, with only 16 points, ModelGiF already achieves comparable performance to RSA [12] in Spearman's correlation. It is attractive as the computation overhead of the proposed method grows linearly with the number of reference points. The results indicate that we can safely reduce the computation cost by decreasing the number of reference points, and we can also strive for higher performance by adding more reference points, which makes ModelGiF flexible and applicable in a variety of scenarios. Another conclusion we can draw from Figure 3e is that the adversarial samples generally yields superior performance to other ref" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "6130" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.11, + 0.089, + 0.86, + 0.291 + ], + "angle": 0, + "content": "
CIFARtiny-ImageNet
AttackIPGuard [8]CAE [30]EWE [23]SAC [17]ModelGiF (Ours)IPGuard [8]CAE [30]EWE [23]SAC [17]ModelGiF (Ours)
Finetune-A1.001.001.001.001.001.001.000.481.001.00
Finetune-L1.001.001.001.001.001.001.001.001.001.00
Pruning1.000.950.871.001.001.001.000.581.001.00
Extract-L0.810.830.971.001.000.971.001.001.001.00
Extract-P0.810.900.971.001.000.971.001.001.001.00
Extract-Adv0.540.520.910.921.000.650.781.000.911.00
Transfer-10C1.001.001.001.001.00N/AN/AN/AN/AN/A
Transfer-A---1.001.00---1.001.00
Transfer-L---1.001.00---1.001.00
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.291, + 0.892, + 0.32 + ], + "angle": 0, + "content": "Table 2. Comparison between the proposed ModelGiF and existing methods for IP protection. The performance is measured in AUC value under the AUC-ROC curve. “–” represent the IP protection method can not detect this kind of attack. “N/A” denotes not applicable." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.344, + 0.47, + 0.373 + ], + "angle": 0, + "content": "erence points, which gives implications of future work to strive for higher performance of task relatedness estimation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.374, + 0.471, + 0.542 + ], + "angle": 0, + "content": "In Figure 3f, we make comparisons between some different implementations of ModelGiF. \"ModelGiF with random baselines\" denotes \\(\\mathbf{x}_0\\) in Eqn. 4 is fixed to be zero, and \"ModelGiF with random baselines\" denotes \\(\\mathbf{x}_0\\) is randomly sampled. We also include Integrated Gradient (IG, with zero as the baseline) and IG with random baselines for comparisons. Albeit bearing some similarity with IG, it can be seen that ModelGiF with zero baselines significantly outperforms these baselines in most cases. ModelGiF with random baselines, however, is more promising when the number of reference points becomes sufficiently larger." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.552, + 0.46, + 0.57 + ], + "angle": 0, + "content": "4.2. Application: Intellectual Property Protection" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.577, + 0.47, + 0.639 + ], + "angle": 0, + "content": "We evaluate the performance of ModelGiF for IP protection against different model stealing attacks. To make fair comparisons with SOTA methods, we follow the experimental settings of [17] to conduct our experiments." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Experimental Setup. Five categories of stealing attacks are considered here to test the protection performance. including finetuning, pruning, transfer learning, model extraction and adversarial model extraction. For finetuning, FinetuneL denotes fine-tuning only the last layer and leaves the other layers unchanged. Finetune-A fine-tunes all the layers in the model. For transfer learning, the CIFAR10 model is transferred to CIFAR10-C and CIFAR100. The tiny-ImageNet model (trained with the front 100 labels in Tiny-ImageNet) is transferred to the 100 labels left behind in tiny-ImageNet dataset. In model extraction, the victim model can be extracted in two manners: probability-based model extraction (Extract-P), and label-based model extraction (Extract-L). However, the attacker can evade the detection by applying adversarial training after the label-based model extraction [30]. In our experiment, adversarial model extraction (Extract-adv) adopts the predicted label to evade the" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.344, + 0.72, + 0.36 + ], + "angle": 0, + "content": "detection by adversarial training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.373, + 0.895, + 0.6 + ], + "angle": 0, + "content": "Models and Competitors. Different IP protection methods are evaluated on most of the common model architectures, including VGG [42], ResNet [18], DenseNet [20] and MobileNet [38]. To demonstrate the superiority of the proposed ModelGiF, we make comparisons with SOTA IP protection methods, including IPGuard [8], CAE [30], EWE [23] and SAC [17]. IPGuard and CAE utilizes the transferability of adversarial examples and test the attack success rate of these adversarial examples on the suspect models. A model will be recognized as a stolen model if its attack success rate is larger than a threshold. SAC propose to leverage the pairwise relationship between samples as the model fingerprint. EWE, on the contrary, trains the source model on backdoor data and leaves the watermark in the model. Please refer to [17] for more detailed experimental settings." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Results. To validate the effectiveness and the superiority of the proposed ModelGiF, we conduct experiments on different datasets for the defender and the attacker. We we leverage AUC-ROC curve and use AUC value between the fingerprinting scores of the irrelevant models and the stolen models to measure the fingerprinting effectiveness. Results are listed in Table 2. It can be seen that the proposed ModelGiF, although not tailored for IP protection, achieve superior performance in all the attack scenarios. The AUC value is 1.0 across all attacks (including the challenging \"Extract-adv\" attack), which means it perfectly recognize all the attacks to protect the IP, outperforming existing SOTA approaches like SAC [17]. We acknowledge the existing benchmark for IP protection methods is not sufficient large and challenging to provide thorough comparisons between IP methods. However, the superiority of ModelGiF to SOTA methods on this benchmark still provides us a strong confidence of the proposed method for quantifying model functional distance." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "6131" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.099, + 0.091, + 0.482, + 0.238 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.487, + 0.091, + 0.877, + 0.24 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.243, + 0.892, + 0.273 + ], + "angle": 0, + "content": "Figure 4. Cosine distances between the reference classifier \\( C_{ref} \\) and unrelated classifier \\( C_{unrelated} \\), the directly unlearned classifier \\( C_{direct} \\) and the approximately unlearned classifier \\( C_{approx} \\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.296, + 0.45, + 0.314 + ], + "angle": 0, + "content": "4.3. Application: Model Unlearning Verification" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.322, + 0.471, + 0.429 + ], + "angle": 0, + "content": "Machine unlearning studies how we can efficiently delete data points used to train models without retraining from scratch [7]. In this section, we demonstrate the effectiveness of the proposed ModelGiF for model unlearning verification, i.e., ModelGiF can distinguish the models trained with and without the data points that is requested to be unlearned." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.438, + 0.47, + 0.817 + ], + "angle": 0, + "content": "Experimental Setup. Following the experimental settings of [22], we training four classifiers to evaluate ModelGiF for model unlearning verification. The first classifier is called the reference classifier \\( C_{ref}^{(t)} \\), where \\( t \\) denotes that the classifier is obtained after \\( t \\) epochs training. The reference classifier serves as the original classifier trained on all the training data, including the data points which are requested to be deleted later. The second classifier is called the unrelated classifier, which is another classifier trained on all the training data, but from different initialization. The third classifier is called the exactly unlearned classifier, which is trained on the remaining data after removing the data points requested to be deleted. Note that the exactly unlearned classifier is trained from scratch and has never seen those data points which are requested to be removed, and it thus can be seen as the exactly unlearned classifier [7]. The last classifier is called approximately unlearned classifier, which is obtained by directly optimizing the original reference classifier to remove the knowledge learned from those data points requested to be unlearned [16]. We compare the ModelGiFs of the unrelated classifier, the exactly unlearned classifier and the approximately unlearned classifier to that of the reference classifier. The goal is to test whether the proposed ModelGiF can recognize the exactly unlearned classifier from the unrelated classifier." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Experimental Details and Results. Experiments are conducted on CIFAR10 and CIFAR100. On CIFAR10, all classifiers are implemented by ResNet20. On CIFAR100, all classifiers are implemented by ResNet50. We randomly sample 128 data points from the training data to be un-" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.297, + 0.895, + 0.584 + ], + "angle": 0, + "content": "learned, and use these data as the reference points to compute the distance between ModelGIFs of these classifiers. Experimental results are provided in Figure 4. It can be seen that with the proposed ModelGiF, exactly unlearned classifier gets significantly higher distance with the reference classifier than the unrelated classifier. It implies that ModelGiF can also be used as a tool to verify the unlearning performance of existing unlearning methods. Another observation from Figure 4 is that the distance between the approximately unlearned classifier and the reference classifier is much lower than unrelated classifier, which implies that existing approximately unlearning methods can not delete the data from the model thoroughly. However, as the training for unlearning continues, the information can be gradually forgotten, as implied by the increasing distance shown in Figure 4. These results also accord with prior finding that continual learning easily lead to catastrophic forgetting problem [35], which validate the rationality of the results from the proposed ModelGiF." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.602, + 0.771, + 0.618 + ], + "angle": 0, + "content": "5. Conclusion and Future Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.895, + 0.901 + ], + "angle": 0, + "content": "In this work, we propose ModelGiF to quantify model functional distance. The main assumption underlying ModelGiF is that each pre-trained deep model uniquely determines a ModelGiF over the input space. The distance between models can thus be measured by the similarity between their ModelGiFs. We apply the proposed ModelGiF to task relatedness estimation, intellectual property protection, and model unlearning verification. Experimental results demonstrate the versatility of the proposed ModelGiF on these tasks, with significantly superiority performance to state-of-the-art competitors. There are several directions for future work with the proposed ModelGiF. For example, exploring more scenarios where ModelGiF can be applied. Another interesting research direction is proposing more informative reference points to extract stronger representations of ModelGiF. Finally, how to further speed up the computation of the proposed method is also important to make it easier to use." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6132" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.168 + ], + "angle": 0, + "content": "Acknowledgement. This work is funded by the National Key Research and Development Project (Grant No: 2022YFB2703100), National Natural Science Foundation of China (62106220, 61976186, U20B2066), and Ningbo Natural Science Foundation (2021J189)." + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.181, + 0.175, + 0.198 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.207, + 0.473, + 0.298 + ], + "angle": 0, + "content": "[1] Alessandro Achille, Michael Lam, Rahul Tewari, Avinash Ravichandran, Subhransu Maji, Charless C Fowlkes, Stefano Soatto, and Pietro Perona. Task2vec: Task embedding for meta-learning. In Proceedings of the IEEE/CVF international conference on computer vision, pages 6430-6439, 2019. 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.301, + 0.472, + 0.393 + ], + "angle": 0, + "content": "[2] Yossi Adi, Carsten Baum, Moustapha Cisse, Benny Pinkas, and Joseph Keshet. 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However, quantifying the model functional distance is always challenging due to the opacity in inner workings and the heterogeneity in architectures or tasks. Inspired by the concept of "field" in physics, in this work we introduce Model Gradient Field (abbr. ModelGiF) to extract homogeneous representations from the heterogeneous pre-trained models. Our main assumption underlying ModelGiF is that each pre-trained deep model uniquely determines a ModelGiF over the input space. The distance between models can thus be measured by the similarity between their ModelGiFs. We validate the effectiveness of the proposed ModelGiF with a suite of testbeds, including task relatedness estimation, intellectual property protection, and model unlearning verification. Experimental results demonstrate the versatility of the proposed ModelGiF on these tasks, with significantly superiority performance to state-of-the-art competitors. Codes are available at https://github.com/zju-vipa/modelgif. + +# 1. Introduction + +The last decade has witnessed the great progress of deep learning in various fields, and a plethora of deep neural networks are developed and released publicly, with either their architectures and trained parameters (e.g., Tensorflow Hub1, Pytorch Hub2) for research, or the prediction API (e.g., BigML, Amazon Machine Learning) as ML-as-a-Service (MLaaS) for commercial purposes. These off-the-shelf pre-trained models become extremely important resources for not only practitioners to solve their own problems, but also researchers to explore and exploit the huge potential underlying these pre-trained models. + +![](images/de2835115b675baaacba88effd7b19407700459d0c55f2ef66d9608d45f82f15.jpg) +Magnetic Field + +![](images/c49224e73d7b377c1f3e92c31cd4ed2262951df2ce973acfa0ceb6c0e52b07c5.jpg) +Model Gradient Field + +![](images/7f071db1062f8a00a9eb58650d781e6b06caa8e29f32a6bd533ba63dd7defb32.jpg) +Figure 1. An illustrative diagram of the magnetic field and the proposed model gradient field (ModelGiF) defined on the input space. + +With the surge of pre-trained models released, quantifying the model relationship emerges as an important question. The large-scale open-sourced deep models, heterogeneous in architectures and tasks and trained isolatedly or dependently, are related to each other in various manners. For example, a student model trained by knowledge distillation [19] should behave more similarly with the teacher than an independently trained identical model. Likewise, a fine-tuned model should be more closely related to its pretrained model than the one trained from scratch. More generally, models trained in isolation on heterogeneous tasks should inherit the intrinsic task relatedness [53] as task-specific features are extracted by these models. Broadly speaking, there exists a model metric space where models with similar functional behaviors are clustered together and dissimilar ones are far apart. The model functional distance between models, if left unresolved, leaves existing model repositories still simple unstructured collections of many isolated open-sourced models, hindering the exploitation of their great value as a whole. + +Despite the ever-increasing number of publicly available pre-trained models, the study on the model functional distance, i.e., structure of the model metric space, lags far behind. This phenomenon can be largely attributed to the great challenge of computing the functional distance between any deep models, where the barriers are three-folds: (1) Hetero- + +geneity: deep models usually differ significantly in architectures. Even with the same architecture, models trained on different datasets or tasks can also behave quite differently; (2) Opacity: the opaque inner workings of deep models render computing the model similarity extremely difficult; (3) Efficiency: as the cost of computing pairwise distance grows quadratically with the number of models, the computation of the functional distance should be efficient. + +A few prior works have been devoted to computing model distance, in either weight space [1, 24] or representation space [28, 12]. For example, Task2Vec [1] computes task or model representations based on estimates of the Fisher information matrix associated with the probe network parameters, which provides a fixed-dimensional embedding of the model agnostic to the task variations. However, Task2Vec assumes all probe models share the same architecture, which is highly restrictive in practice. ModelDiff [28] and representation similarity analysis (RSA) [12], on the other hand, adopt the similarity of representations on a small set of reference inputs as the model representations, and the model distance is thus calculated resorting to these model representations, which is shown effective for model reuse detection and transferability estimation. However, these methods only capture the point-wise behavior of the models at a small number of chosen reference points, which is limited in representation capacity and fails at harder tasks such as detecting model extraction [28]. Recently, DEPARA [43, 44] and ZEST [22] are proposed as pilot studies by applying explanation methods for computing model distance. However, they are validated on disjoint downstream tasks, and the performance on comprehensive tasks remains unclear. Moreover, these methods also use a small number of chosen reference points to extract the model representations, which makes them suffer from low representation capacity. + +In this work, inspired by the concept of "field" in physics, we propose Model Gradient Field (as shown in Figure 1), abbreviated as ModelGiF, as the proxy to extract homogeneous representations from pre-trained heterogeneous models to derive their functionality distance. Specifically, the proposed ModelGiF is defined on the input space, i.e., every point in the ModelGiF denotes the gradient vector of the model output w.r.t. the input on the same point. The main assumption underlying ModelGiF is that each pretrained deep model uniquely determines a ModelGiF over the input space. The functional distance between any two models can thus be measured by the similarity between their ModelGiFs. Unlike prior methods where the point-wise features are adopted for representing the model, ModelGiFs represents these models by their gradient on the whole input space, which makes it more capable of differentiating highly related models (i.e., model extraction detection). Moreover, we provide theoretical insights into the proposed + +ModelGiFs for model functional distance, and make extensive discussions on different implementation details. We validate the effectiveness of the proposed ModelGiF with a suite of testbeds, including transferability estimation, intellectual property protection, and model unlearning verification. Experimental results demonstrate the versatility of the proposed ModelGiF on these tasks, with significantly superiority to state-of-the-art (SOTA) methods. + +To sum up, we make the following contributions: (1) we propose the concept of "model gradient field", a novel method for quantifying the functionality similarity between pre-trained deep models; (2) we provide theoretical insights into the proposed ModelGiFs for model functional distance, and make extensive discussions on different implementation details; (3) extensive experiments demonstrate the effectiveness and the superiority of ModelGiF on various tasks, including transferability estimation, intellectual property protection, and model unlearning verification. + +# 2. Related Work + +This section briefly reviews some related topics to model functional distance, including task relatedness estimation, intellectual property protection, and model unlearning. + +Task Relatedness Estimation. Recent studies [53, 43, 44, 5, 51, 3, 6, 26] reveals the existence of task relatedness or task structure among visual tasks. It is the concept underlying transfer learning and provides a principled way to seamlessly reuse supervision among related tasks or solve many tasks in one system [53]. Existing works to obtain task relatedness can be roughly divided into empirical and analytical approaches. Taskonomy [53] is the most representative work of empirical methods. It proposes a fully computational approach to obtain task relatedness by exhaustively computing the actual transfer learning performance, which is thus usually taken as the ground truth for evaluating other estimators. Despite the indisputable results, the computational cost of empirical methods is extremely high. On the other hand, analytical methods, e.g., DEPARA [44, 43], Task2Vec [1] and RSA [12], try to estimate the task relatedness without conducting the actual transfer learning. Analytical methods generally significantly reduce the computation overhead, but can be highly restrictive in model architectures or estimation performance. The proposed Model-GiF relaxes these restrictions and achieves task relatedness more consistent to taskonomy than existing approaches. + +Intellectual Property Protection. Since training deep models usually consumes expensive data collection and large computation resources, the trained models constitute valuable intellectual property (IP) that should be protected in cases where reusing is not allowed without authorization. However, model IP can be infringed in a variety of forms, such as fine-tuning [2, 48], pruning [29, 33], transfer learn- + +ing [39, 49, 50] and model extraction [34, 47, 25, 21], which poses great challenge to IP protection. Existing IP protection approaches can be roughly categorized into watermarking [23, 48, 13, 54, 2] and fingerprinting [30, 8, 28, 17]. Watermarking methods usually leverage weight regularization [48, 13] to put secret watermark in the model parameters or train models on a triggered set to leave backdoor [2, 54] in them. While being able to provide exact ownership verification, these techniques are invasive, i.e., they need to tamper with the training process, which may affect the model utility or introduce new security risks into the model. Fingerprinting, on the contrary, extracts a unique identifier, i.e., fingerprint, from the owner model to differentiate it from other models. Latest fingerprinting (e.g., ModelDiff [28], IPGuard [8], SAC [17]) on deep learning models, though being non-invasive, also fall short when facing the diverse and ever-growing attack scenarios [10]. In this work, we propose ModelGiF as the homogeneous representations for heterogeneous pre-trained models, which can be naturally adopted as the fingerprint for IP protection and yields superior IP protection performance to existing approaches. + +Model Unlearning Verification. Model unlearning aims to remove the effects of data points from the trained model, which has been attracting increasing attentions in recent years due to legislation and privacy ethics. Cao et al. [9] are dedicated to making learning systems forget and present an unlearning approach capable of forgetting specific data. Graves et al. [16] propose an effective method to eliminate the influence of personal data from the model while maintaining the validity. Bourtoule et al. [7] particularly propose a model unlearning method to decrease the time it takes to retrain exactly. However, how to identify whether the impact of data has been eliminated is an essential but rarely studied problem. Recently ZEST [22] verifies the unlearning of data by comparing the Local Interpretable Model-Agnostic Explanations (LIME) [37]. In this work, we adopt the proposed ModelGiF for unlearning verification, which yields competitive performance in our experiments. + +# 3. Methodology + +# 3.1. Problem Setup + +Assume there is a model repository consisting of $N$ pre-trained models $\mathcal{M} = \{M_1, M_2, \dots, M_N\}$ . With mild assumptions, these models are defined on the same input space $\mathbb{R}^D$ ( $D = WHC$ , where $W, H$ and $C$ denotes the width, height and channel of the input space), yet trained with data sampled from different data distributions $\mathcal{P} = \{p_1, p_2, \dots, p_N\}$ . Note that here we made no assumptions on the model architectures and the tasks, which means + +that these models can be different in architectures (e.g., ResNet [18] and VGG [42]), and tasks (e.g., visual classification [27], detection [36] or segmentation [11]). The goal in this work is to construct a model metric space where models with similar functional behaviors are clustered together and dissimilar ones are far apart, where the vital step is quantifying the functional distance between these models. + +# 3.2. The Proposed ModelGiF + +As aforementioned, quantifying the functional distance between pre-trained models is challenging due to the heterogeneity, opacity and efficiency issues. Our main idea is extracting homogeneous descriptors from these heterogeneous models to make them comparable. To this end, we proposed the concept ModelGiF, as shown in Figure 1, to derive the comparable identifier of the pre-trained models for quantifying model distance. + +ModelGiF is inspired by the concept "field" in physics where a field is a mapping from space to some physical quantity, represented by a scalar, vector, or tensor, that has a value for each point in the space [32]. For example, the magnetic field describes the magnetic influence on moving electric charges, electric currents, and magnetic materials [14]. Likewise, we define ModelGiF as a mapping from the input space to the gradient space such that each point in the input space is assigned to a gradient vector. The formal definition is provided as follows. + +Definition 3.1 (Model Gradient Field) Let $M$ be a deep model trained on the data which is sampled according to some distribution $p$ from the data space $\mathcal{X}$ , outputting a scalar4 prediction in the label space $\mathcal{Y}$ . A point $\mathbf{x}$ can be described as $\mathbf{x} = (x_1, x_2, \dots, x_D)$ . We define the model gradient field of $M$ as the gradient of every possible input point in $\mathcal{X}$ w.r.t. the model output: + +$$ +\operatorname {M O D E L G I F} (M) \triangleq \nabla_ {\mathbf {x}} M, \tag {1} +$$ + +which is a mapping from the input space $\mathbb{R}^D$ to the gradient space $\mathbb{G}^D$ , MODELGiF: $\mathbb{R}^D \to \mathbb{G}^D$ . Note that the ModelGiF is defined on the whole input space (which is shared by all the models) rather than some discretely points sampled from the data distribution $p$ specific to the model $M$ . As the architecture of $M$ and the tasks (i.e., the label space $\mathcal{V}$ ) can be heterogeneous, the ModelGiF of a model can be seen as a projection of the model to the common input space. + +# 3.3. Field Curves for ModelGiF + +With the proposed ModelGiF, the model functional distance can be quantified by the ModelGiF similarity. However, as ModelGiF is defined on the whole input space that is usually extremely huge, how to extract its representation + +![](images/86b1123d4c5082e4e95c8a3e779772a8723680717d27c5e90bad91574839eb33.jpg) +Figure 2. An illustrative diagram of the overall pipeline of obtaining ModelGiF curves. The more similar the ModelGiFs, the more similar the corresponding trained models. Note that ModelGiF Curves are in high-dimensional space in reality. + +or signature becomes the vital step for quantifying model distance. In physics, a field is usually depicted by the field curves (as shown in Figure 1), i.e., the integral curves for the field, and can be constructed by starting at a point and tracing a curve through space that follows the direction of the vector field, by making the field curve tangent to the field vector at each point [46]. Inspired by this, we propose ModelGiF Curves as the descriptors of ModelGiF to measure the model functional distance. + +Definition 3.2 (Field Curves) For a field $F$ : $\mathbb{R}^D \to \mathbb{G}^D$ , a curve $\mathbf{x}(t) = (x_1(t), x_2(t), \ldots, x_D(t))$ is called a field curve of the field $F$ if the following condition is satisfied: For all points $P \in \mathbf{x}(t)$ , the tangent vector of the curve in the point $P$ has the same direction as the vector $F(P)$ : + +$$ +\frac {d x _ {1} (t)}{d t} = F \left(\mathbf {x} (t)\right) _ {1}, \frac {d x _ {2} (t)}{d t} = F \left(\mathbf {x} (t)\right) _ {2}, \dots \tag {2} +$$ + +The field curve can be described as the solution of the system of differential equations in Eqn. 2, and it plays an important role for both analysis and visualization of vector fields [46]. Unfortunately, as the ModelGiF is usually complicated for a pre-trained deep model, there is no closed solution. The field curves are in general not describable as parameterized curves, which hinders the comparisons between different ModelGiFs. To resolve this issue, we introduce the definition of ModelGiF curves as follows. + +Definition 3.3 (ModelGiF Curves) For a ModelGiF $F$ : $\mathbb{R}^D \to \mathbb{G}^D$ , a curve $\mathbf{g}(t) = (g_1(t), g_2(t), \dots, g_D(t))$ is + +called the ModelGiF curve of $F$ if the following condition is satisfied: + +$$ +\frac {d g _ {1} (t)}{d t} = F (\mathbf {x} (t)) _ {1}, \frac {d g _ {2} (t)}{d t} = F (\mathbf {x} (t)) _ {2}, \dots \tag {3} +$$ + +Note that different from the definition of field curves, the ModelGiF curves are defined on the gradient space $\mathbb{G}^D$ instead of the input space $\mathbb{R}^D$ . + +Proposition 1 For a ModelGiF $F \colon \mathbb{R}^D \to \mathbb{G}^D$ , and two points $\mathbf{x}_0, \mathbf{x}_1$ in $\mathbb{R}^D$ , the gradient integral along the straight line from $\mathbf{x}_0$ to $\mathbf{x}_1$ is a ModelGiF curve of $F$ : + +$$ +\mathbf {g} (t) = \int_ {\alpha = 0} ^ {t} F \left(\mathbf {x} _ {0} + \alpha \left(\mathbf {x} _ {1} - \mathbf {x} _ {0}\right)\right) d \alpha , \quad t \in [ 0, 1 ] \tag {4} +$$ + +With the proposition, we can make comparisons between ModelGiFs by simply comparing their ModelGiF curves between some predefined pairs of points. Now we provide the detailed pipeline of quantifying the Model functional distance with the proposed ModelGiF. + +# 3.4. ModelGiF for Model Distance + +Provided with the trained deep models as described in Section 3.1, we compute the model distance with the proposed ModelGiF in two steps (in Figure 2): 1) Sampling reference points, and 2) Computing the model distance. + +Sampling Reference Points. As described in Proposition 1, the first step before obtaining ModelGiF curves is + +determining the reference points (i.e., $\mathbf{x}_1^5$ in Eqn. 4.), which determines the domain of these curves. Let $K$ be the number of reference points to be sampled. Intuitively, these reference points should representative. However, as the models in $\mathcal{M}$ can be heterogeneous in architectures and tasks and trained on data sampled from different distributions, it is hard to determine a common set of reference points which are representative for all these models. In this work, we investigate three types of reference points as follows. + +1) Random samples drawn from $\mathcal{P}$ . Each data point is sampled in two stages: first randomly sampling the distribution $p$ from $\mathcal{P}$ and then randomly sampling the reference point from $p$ . +2) Augmented samples using CutMix [52]. Let $\mathbf{x}$ and $\mathbf{x}^*$ be two randomly sampled points in $\mathcal{P}$ . CutMix generates a new sample $\tilde{\mathbf{x}}$ using the two samples by cutting off and pasting patches among them: $\tilde{\mathbf{x}} = \mathbf{m} \odot \mathbf{x} + (1 - \mathbf{m}) \odot \mathbf{x}^*$ , where $\mathbf{m}$ represents the binary mask to combine images with different parts, and $\odot$ the element-wise multiplication. +3) Adversarial samples generated with PGD [31]. PGD attack is a multi-step variant of Fast Gradient Sign Method (FGSM) [15]: $\mathbf{x}_{t + 1} = \prod \left(\mathbf{x}_t + \alpha \mathrm{SGN}\bigl (\nabla \mathcal{J}(\mathbf{x}_t)\bigr)\right)$ , where $\prod$ denotes the projection to the allowed space. + +The performance of these types of reference points are discussed in Section 4.1. We also provide the sensitivity analysis of the number of reference points $K$ , which demonstrates that the performance of ModelGiF quickly becomes superior to existing methods as $K$ increases. + +Computing the model distance. Let $S = \{\mathbf{x}_1, \mathbf{x}_2, \dots, \mathbf{x}_K\}$ be the reference points obtained from the last step. For the $i$ -th model $M_i$ , we can get $K$ ModelGiF curves by substituting each point in $S$ for the $\mathbf{x}_1$ in Eqn. 4. These curves are used as the identifier of the ModelGiF, and thus serve as the representations of the trained deep model. There are several distance metrics to measure the similarity between curves, e.g., Hausdorff distance and Fréchet distance. As the method for curve distance is not our contribution in this work, we simply adopt the integrated point-wise cosine distance to validate the performance of the proposed method: + +$$ +d \left(M _ {i}, M _ {j}\right) = \sum_ {k = 1} ^ {K} \int_ {t = 0} ^ {1} \left(1 - \cos \left(\mathbf {g} ^ {i, k} (t), \mathbf {g} ^ {j, k} (t)\right)\right) d t, \tag {5} +$$ + +where $\mathbf{g}^{i,k}$ denotes the $k$ -th curve of the $i$ -th model in $\mathcal{M}$ , and $\cdot$ denotes the inner product between $\mathbf{g}^{i,k}(t)$ and $\mathbf{g}^{i,k}(t)$ . In practice, we approximate the integral with summation by sampling with some fixed intervals. + +# 3.5. Theoretical Analysis of ModelGiF + +From the definition of model distance in Eqn. 5, we can see that the defined distance can be seen as the summation of point-wise similarities over all the curves. Here we provide some theoretical insights into ModelGiF by dissecting the model-level distance into point-level distance. + +Proposition 2 For the point $\mathbf{g}(t_1)$ along the ModelGiF curves $\mathbf{g}(t)$ defined from $\mathbf{x}^*$ to $\mathbf{x}$ , then + +$$ +\sum_ {i} t _ {1} \left(x _ {i} - x _ {i} ^ {*}\right) g _ {i} \left(t _ {1}\right) = M (\mathbf {x}) - M \left(\mathbf {x} ^ {*}\right), \tag {6} +$$ + +where the left side is actually the summation over Integrated Gradients [45]. Eqn. 6 tells us that the every point in proposed ModelGiF curve is strongly related to the model prediction differences from this point and the baseline point, thus the proposed model distance is a powerful distance metric to quantifying the model function distance. + +# 4. Experiments + +In this section, we verify the effectiveness of ModelGiF with a suite of testbeds, including task relatedness estimation, intellectual property protection and model unlearning verification. Details are provided as follows. + +# 4.1. Application: Task Relatedness Estimation + +Experimental Setup. We adopt 17 pre-trained heterogeneous models from Taskonomy [53] to compare their functionality similarity. These models are trained on various tasks (including Autoencoder, Curvature, Denoise, Edge 2D, Edge 3D, Keypoint 2D, Keypoint 3D, Reshade, RGB2depth, RGB2mist, RGB2sfnorm, Room Layout, Segment25D, Segment2D, Vanishing Point, Segmentation, and Classification) and are different in architectures. Generally speaking, the architectures of these models follow an encoder-decoder scheme, in which the encoder is implemented by fully convolutional layers and the decoder varies according to the tasks. Please refer to [53] for more detailed information. In our experiments, only the encoders of these models are adopted for generating their ModelGiFs. + +Competitors and Evaluation Metric. The proposed ModelGiF is compared with several prior approaches to task relatedness estimation, including RSA [12], Attribution-Maps [43], and ZEST [22]. Note that AttributionMaps adopts saliency [41], DeepLIFT [40] and $\epsilon$ -LRP [4] to generate attributions for task relatedness estimation. We compare ModelGiF with all these variants to demonstrate its superiority in task relatedness prediction. As the affinity matrix from Taskonomy is obtained based on the actual transfer learning performance, it is used as the ground truth of the affinity among these tasks. In this experiment, we will + +![](images/6834f8232963b5ad2260e6ffb9bc4e0f177d9f49df02dcf33625945c86f8703c.jpg) +(a) Affinity Matrix from Taskonomy + +![](images/b457a29dba003eee0d19c03e3729d852b6274d83ecc9686c476a61adb9820620.jpg) +(b) Affinity Matrix from RSA + +![](images/f24bec5d274bea9fe5fec1c47b27e09ad34e2b7a4c573401c1f664c847d33498.jpg) +(c) Affinity Matrix from ModelGiF + +![](images/aa30cad153c71255768d86218b26285a4bf02a88cda5614d4ea6c70a197f35a6.jpg) +(d) Similarity Tree from ModelGiF +Figure 3. Results of task related estimation: (a) affinity matrix from Taskonomy; (b) affinity matrix from RSA; (c) affinity matrix from ModelGiF; (d) the similarity tree derived from ModelGiF; (e) performance with varying $K$ of different reference points; (e) performance with varying $K$ of different implementations. + +![](images/97191c17e4cce016b4388176c3137f0df030cdebcdad303d4e9032da346d3d15.jpg) +(e) Different reference points + +![](images/23a47142c51ca8a7001737fbfae2d0c839ca01ef5d52741ac9e54ab14a8f9f7b.jpg) +(f) Different implementations + +
MethodSpearman's Correlation
Zest [22]0.359
AttributionMapsSALIENCY [43]0.619
AttributionMapsDEEPLIFT [43]0.685
AttributionMapsε-LRP [43]0.682
RSA [12]0.777
ModelGiFRANDOM0.834
ModelGiFAUGMENT0.835
ModelGiFADVERSARIAL0.830
+ +Table 1. Comparison between the proposed ModelGiF and existing methods. Here 1, 000 reference points are sampled in ModelGiF. + +verify that the functionality similarity obtained by ModelGiF positively correlates with that from taskonomy. In order to quantify the similarity between the affinity matrix representing functionality similarity obtained by ModelGiF and the affinity matrix obtained by Taskonomy, we use Spearman's correlation as the metric for evaluation. + +Results. We first test the proposed ModelGiF with by randomly sampling 1,000 reference points. The visualization of the affinity matrix (as well as that from Taskonomy [53] and RSA [12]) and the similarity tree are provided in Figure 3. This similarity tree is constructed by agglomerative hierarchical clustering based on the affinity matrix. It can be seen that the affinity matrix from the proposed ModelGiF is visually highly similar to that from Taskonomy in most regions. The similarity tree derived from ModelGiF + +perfectly matches the results from taskonomy where 3D (in green font) tasks, 2D (in blue font), geometric (in red font) tasks, and semantic (in purple font) tasks cluster into corresponding groups as expected. + +Table 1 provide a quantitative comparison between the proposed ModelGiF with existing works in Spearman's correlation. It can be easily seen that the proposed ModelGiF yields significantly superior performance to existing methods, improving the SOTA Spearman's correlation from 0.777 to 0.835. Furthermore, all the three types of reference points produce Spearman's correlation more than 0.83, which implies that the proposed method is quite robust to the choice of the reference points. To make a more comprehensive study, we test ModelGiF with varying number of reference points. The correlation curves are depicted in Figure 3e, where different types of reference points are compared. It can be seen that as the number of reference points increases, the correlation steadily grows. Surprisingly, with only 16 points, ModelGiF already achieves comparable performance to RSA [12] in Spearman's correlation. It is attractive as the computation overhead of the proposed method grows linearly with the number of reference points. The results indicate that we can safely reduce the computation cost by decreasing the number of reference points, and we can also strive for higher performance by adding more reference points, which makes ModelGiF flexible and applicable in a variety of scenarios. Another conclusion we can draw from Figure 3e is that the adversarial samples generally yields superior performance to other ref + +
CIFARtiny-ImageNet
AttackIPGuard [8]CAE [30]EWE [23]SAC [17]ModelGiF (Ours)IPGuard [8]CAE [30]EWE [23]SAC [17]ModelGiF (Ours)
Finetune-A1.001.001.001.001.001.001.000.481.001.00
Finetune-L1.001.001.001.001.001.001.001.001.001.00
Pruning1.000.950.871.001.001.001.000.581.001.00
Extract-L0.810.830.971.001.000.971.001.001.001.00
Extract-P0.810.900.971.001.000.971.001.001.001.00
Extract-Adv0.540.520.910.921.000.650.781.000.911.00
Transfer-10C1.001.001.001.001.00N/AN/AN/AN/AN/A
Transfer-A---1.001.00---1.001.00
Transfer-L---1.001.00---1.001.00
+ +Table 2. Comparison between the proposed ModelGiF and existing methods for IP protection. The performance is measured in AUC value under the AUC-ROC curve. “–” represent the IP protection method can not detect this kind of attack. “N/A” denotes not applicable. + +erence points, which gives implications of future work to strive for higher performance of task relatedness estimation. + +In Figure 3f, we make comparisons between some different implementations of ModelGiF. "ModelGiF with random baselines" denotes $\mathbf{x}_0$ in Eqn. 4 is fixed to be zero, and "ModelGiF with random baselines" denotes $\mathbf{x}_0$ is randomly sampled. We also include Integrated Gradient (IG, with zero as the baseline) and IG with random baselines for comparisons. Albeit bearing some similarity with IG, it can be seen that ModelGiF with zero baselines significantly outperforms these baselines in most cases. ModelGiF with random baselines, however, is more promising when the number of reference points becomes sufficiently larger. + +# 4.2. Application: Intellectual Property Protection + +We evaluate the performance of ModelGiF for IP protection against different model stealing attacks. To make fair comparisons with SOTA methods, we follow the experimental settings of [17] to conduct our experiments. + +Experimental Setup. Five categories of stealing attacks are considered here to test the protection performance. including finetuning, pruning, transfer learning, model extraction and adversarial model extraction. For finetuning, FinetuneL denotes fine-tuning only the last layer and leaves the other layers unchanged. Finetune-A fine-tunes all the layers in the model. For transfer learning, the CIFAR10 model is transferred to CIFAR10-C and CIFAR100. The tiny-ImageNet model (trained with the front 100 labels in Tiny-ImageNet) is transferred to the 100 labels left behind in tiny-ImageNet dataset. In model extraction, the victim model can be extracted in two manners: probability-based model extraction (Extract-P), and label-based model extraction (Extract-L). However, the attacker can evade the detection by applying adversarial training after the label-based model extraction [30]. In our experiment, adversarial model extraction (Extract-adv) adopts the predicted label to evade the + +detection by adversarial training. + +Models and Competitors. Different IP protection methods are evaluated on most of the common model architectures, including VGG [42], ResNet [18], DenseNet [20] and MobileNet [38]. To demonstrate the superiority of the proposed ModelGiF, we make comparisons with SOTA IP protection methods, including IPGuard [8], CAE [30], EWE [23] and SAC [17]. IPGuard and CAE utilizes the transferability of adversarial examples and test the attack success rate of these adversarial examples on the suspect models. A model will be recognized as a stolen model if its attack success rate is larger than a threshold. SAC propose to leverage the pairwise relationship between samples as the model fingerprint. EWE, on the contrary, trains the source model on backdoor data and leaves the watermark in the model. Please refer to [17] for more detailed experimental settings. + +Results. To validate the effectiveness and the superiority of the proposed ModelGiF, we conduct experiments on different datasets for the defender and the attacker. We we leverage AUC-ROC curve and use AUC value between the fingerprinting scores of the irrelevant models and the stolen models to measure the fingerprinting effectiveness. Results are listed in Table 2. It can be seen that the proposed ModelGiF, although not tailored for IP protection, achieve superior performance in all the attack scenarios. The AUC value is 1.0 across all attacks (including the challenging "Extract-adv" attack), which means it perfectly recognize all the attacks to protect the IP, outperforming existing SOTA approaches like SAC [17]. We acknowledge the existing benchmark for IP protection methods is not sufficient large and challenging to provide thorough comparisons between IP methods. However, the superiority of ModelGiF to SOTA methods on this benchmark still provides us a strong confidence of the proposed method for quantifying model functional distance. + +![](images/c76314d8e8b95a658a1945c52edc48a5221a38bac59a9ce07cb5049568704c4d.jpg) +Figure 4. Cosine distances between the reference classifier $C_{ref}$ and unrelated classifier $C_{unrelated}$ , the directly unlearned classifier $C_{direct}$ and the approximately unlearned classifier $C_{approx}$ . + +![](images/80a67a38d27d540c935c49717a975ded9e53093c7ba9388a25b8975f2642d26a.jpg) + +# 4.3. Application: Model Unlearning Verification + +Machine unlearning studies how we can efficiently delete data points used to train models without retraining from scratch [7]. In this section, we demonstrate the effectiveness of the proposed ModelGiF for model unlearning verification, i.e., ModelGiF can distinguish the models trained with and without the data points that is requested to be unlearned. + +Experimental Setup. Following the experimental settings of [22], we training four classifiers to evaluate ModelGiF for model unlearning verification. The first classifier is called the reference classifier $C_{ref}^{(t)}$ , where $t$ denotes that the classifier is obtained after $t$ epochs training. The reference classifier serves as the original classifier trained on all the training data, including the data points which are requested to be deleted later. The second classifier is called the unrelated classifier, which is another classifier trained on all the training data, but from different initialization. The third classifier is called the exactly unlearned classifier, which is trained on the remaining data after removing the data points requested to be deleted. Note that the exactly unlearned classifier is trained from scratch and has never seen those data points which are requested to be removed, and it thus can be seen as the exactly unlearned classifier [7]. The last classifier is called approximately unlearned classifier, which is obtained by directly optimizing the original reference classifier to remove the knowledge learned from those data points requested to be unlearned [16]. We compare the ModelGiFs of the unrelated classifier, the exactly unlearned classifier and the approximately unlearned classifier to that of the reference classifier. The goal is to test whether the proposed ModelGiF can recognize the exactly unlearned classifier from the unrelated classifier. + +Experimental Details and Results. Experiments are conducted on CIFAR10 and CIFAR100. On CIFAR10, all classifiers are implemented by ResNet20. On CIFAR100, all classifiers are implemented by ResNet50. We randomly sample 128 data points from the training data to be un- + +learned, and use these data as the reference points to compute the distance between ModelGIFs of these classifiers. Experimental results are provided in Figure 4. It can be seen that with the proposed ModelGiF, exactly unlearned classifier gets significantly higher distance with the reference classifier than the unrelated classifier. It implies that ModelGiF can also be used as a tool to verify the unlearning performance of existing unlearning methods. Another observation from Figure 4 is that the distance between the approximately unlearned classifier and the reference classifier is much lower than unrelated classifier, which implies that existing approximately unlearning methods can not delete the data from the model thoroughly. However, as the training for unlearning continues, the information can be gradually forgotten, as implied by the increasing distance shown in Figure 4. These results also accord with prior finding that continual learning easily lead to catastrophic forgetting problem [35], which validate the rationality of the results from the proposed ModelGiF. + +# 5. Conclusion and Future Work + +In this work, we propose ModelGiF to quantify model functional distance. The main assumption underlying ModelGiF is that each pre-trained deep model uniquely determines a ModelGiF over the input space. The distance between models can thus be measured by the similarity between their ModelGiFs. We apply the proposed ModelGiF to task relatedness estimation, intellectual property protection, and model unlearning verification. Experimental results demonstrate the versatility of the proposed ModelGiF on these tasks, with significantly superiority performance to state-of-the-art competitors. There are several directions for future work with the proposed ModelGiF. For example, exploring more scenarios where ModelGiF can be applied. Another interesting research direction is proposing more informative reference points to extract stronger representations of ModelGiF. 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In Proceedings of the 2018 on Asia Conference on Computer and Communications Security, pages 159-172, 2018. 3 \ No newline at end of file diff --git a/2023/ModelGiF_ Gradient Fields for Model Functional Distance/images.zip b/2023/ModelGiF_ Gradient Fields for Model Functional Distance/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..62cc8fac3c7e58ef5af9c4a7adb8a48b48aaaf5d --- /dev/null +++ b/2023/ModelGiF_ Gradient Fields for Model Functional Distance/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:24978da824ac1a11d5d86d8ef282c93811d68a19a030c930c0c22146d44074c9 +size 504784 diff --git a/2023/ModelGiF_ Gradient Fields for Model Functional Distance/layout.json b/2023/ModelGiF_ Gradient Fields for Model Functional Distance/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..ba013591289656bb7aa6c0a72c5bead9218ad0dd --- /dev/null +++ b/2023/ModelGiF_ Gradient Fields for Model Functional Distance/layout.json @@ -0,0 +1,8339 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 116, + 103, + 477, + 119 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 103, + 477, + 119 + ], + "spans": [ + { + "bbox": [ + 116, + 103, + 477, + 119 + ], + "type": "text", + "content": "ModelGiF: Gradient Fields for Model Functional Distance" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 148, + 143, + 449, + 172 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 148, + 143, + 449, + 172 + ], + "spans": [ + { + "bbox": [ + 148, + 143, + 449, + 172 + ], + "type": "text", + "content": "Jie Song, Zhengqi Xu, Sai Wu, Gang Chen, and Mingli Song* Zhejiang University" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 172, + 174, + 421, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 172, + 174, + 421, + 185 + ], + "spans": [ + { + "bbox": [ + 172, + 174, + 421, + 185 + ], + "type": "text", + "content": "{sjie,xuzhengqi,wusai,cg,brooksong}@zju.edu.cn" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "spans": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 239, + 290, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 290, + 491 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 290, + 491 + ], + "type": "text", + "content": "The last decade has witnessed the success of deep learning and the surge of publicly released trained models, which necessitates the quantification of the model functional distance for various purposes. However, quantifying the model functional distance is always challenging due to the opacity in inner workings and the heterogeneity in architectures or tasks. Inspired by the concept of \"field\" in physics, in this work we introduce Model Gradient Field (abbr. ModelGiF) to extract homogeneous representations from the heterogeneous pre-trained models. Our main assumption underlying ModelGiF is that each pre-trained deep model uniquely determines a ModelGiF over the input space. The distance between models can thus be measured by the similarity between their ModelGiFs. We validate the effectiveness of the proposed ModelGiF with a suite of testbeds, including task relatedness estimation, intellectual property protection, and model unlearning verification. Experimental results demonstrate the versatility of the proposed ModelGiF on these tasks, with significantly superiority performance to state-of-the-art competitors. Codes are available at https://github.com/zju-vipa/modelgif." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 517, + 128, + 530 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 517, + 128, + 530 + ], + "spans": [ + { + "bbox": [ + 47, + 517, + 128, + 530 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 539, + 287, + 671 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 539, + 287, + 671 + ], + "spans": [ + { + "bbox": [ + 46, + 539, + 287, + 671 + ], + "type": "text", + "content": "The last decade has witnessed the great progress of deep learning in various fields, and a plethora of deep neural networks are developed and released publicly, with either their architectures and trained parameters (e.g., Tensorflow Hub1, Pytorch Hub2) for research, or the prediction API (e.g., BigML, Amazon Machine Learning) as ML-as-a-Service (MLaaS) for commercial purposes. These off-the-shelf pre-trained models become extremely important resources for not only practitioners to solve their own problems, but also researchers to explore and exploit the huge potential underlying these pre-trained models." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 430, + 217, + 538, + 287 + ], + "blocks": [ + { + "bbox": [ + 340, + 249, + 409, + 262 + ], + "lines": [ + { + "bbox": [ + 340, + 249, + 409, + 262 + ], + "spans": [ + { + "bbox": [ + 340, + 249, + 409, + 262 + ], + "type": "text", + "content": "Magnetic Field" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 430, + 217, + 538, + 287 + ], + "lines": [ + { + "bbox": [ + 430, + 217, + 538, + 287 + ], + "spans": [ + { + "bbox": [ + 430, + 217, + 538, + 287 + ], + "type": "image", + "image_path": "de2835115b675baaacba88effd7b19407700459d0c55f2ef66d9608d45f82f15.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 316, + 295, + 465, + 352 + ], + "blocks": [ + { + "bbox": [ + 316, + 295, + 465, + 352 + ], + "lines": [ + { + "bbox": [ + 316, + 295, + 465, + 352 + ], + "spans": [ + { + "bbox": [ + 316, + 295, + 465, + 352 + ], + "type": "image", + "image_path": "c49224e73d7b377c1f3e92c31cd4ed2262951df2ce973acfa0ceb6c0e52b07c5.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 350, + 354, + 446, + 365 + ], + "lines": [ + { + "bbox": [ + 350, + 354, + 446, + 365 + ], + "spans": [ + { + "bbox": [ + 350, + 354, + 446, + 365 + ], + "type": "text", + "content": "Model Gradient Field" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 470, + 296, + 541, + 365 + ], + "blocks": [ + { + "bbox": [ + 470, + 296, + 541, + 365 + ], + "lines": [ + { + "bbox": [ + 470, + 296, + 541, + 365 + ], + "spans": [ + { + "bbox": [ + 470, + 296, + 541, + 365 + ], + "type": "image", + "image_path": "7f071db1062f8a00a9eb58650d781e6b06caa8e29f32a6bd533ba63dd7defb32.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 372, + 545, + 395 + ], + "lines": [ + { + "bbox": [ + 306, + 372, + 545, + 395 + ], + "spans": [ + { + "bbox": [ + 306, + 372, + 545, + 395 + ], + "type": "text", + "content": "Figure 1. An illustrative diagram of the magnetic field and the proposed model gradient field (ModelGiF) defined on the input space." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 401, + 546, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 401, + 546, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 401, + 546, + 640 + ], + "type": "text", + "content": "With the surge of pre-trained models released, quantifying the model relationship emerges as an important question. The large-scale open-sourced deep models, heterogeneous in architectures and tasks and trained isolatedly or dependently, are related to each other in various manners. For example, a student model trained by knowledge distillation [19] should behave more similarly with the teacher than an independently trained identical model. Likewise, a fine-tuned model should be more closely related to its pretrained model than the one trained from scratch. More generally, models trained in isolation on heterogeneous tasks should inherit the intrinsic task relatedness [53] as task-specific features are extracted by these models. Broadly speaking, there exists a model metric space where models with similar functional behaviors are clustered together and dissimilar ones are far apart. The model functional distance between models, if left unresolved, leaves existing model repositories still simple unstructured collections of many isolated open-sourced models, hindering the exploitation of their great value as a whole." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 642, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 547, + 714 + ], + "type": "text", + "content": "Despite the ever-increasing number of publicly available pre-trained models, the study on the model functional distance, i.e., structure of the model metric space, lags far behind. This phenomenon can be largely attributed to the great challenge of computing the functional distance between any deep models, where the barriers are three-folds: (1) Hetero-" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 57, + 683, + 208, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 683, + 208, + 713 + ], + "spans": [ + { + "bbox": [ + 57, + 683, + 208, + 713 + ], + "type": "text", + "content": "\\*Corresponding author \n1https://www.tensorflow.org/hub \n2https://pytorch.org/hub/" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6125" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 167 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 167 + ], + "type": "text", + "content": "geneity: deep models usually differ significantly in architectures. Even with the same architecture, models trained on different datasets or tasks can also behave quite differently; (2) Opacity: the opaque inner workings of deep models render computing the model similarity extremely difficult; (3) Efficiency: as the cost of computing pairwise distance grows quadratically with the number of models, the computation of the functional distance should be efficient." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 172, + 288, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 172, + 288, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 172, + 288, + 495 + ], + "type": "text", + "content": "A few prior works have been devoted to computing model distance, in either weight space [1, 24] or representation space [28, 12]. For example, Task2Vec [1] computes task or model representations based on estimates of the Fisher information matrix associated with the probe network parameters, which provides a fixed-dimensional embedding of the model agnostic to the task variations. However, Task2Vec assumes all probe models share the same architecture, which is highly restrictive in practice. ModelDiff [28] and representation similarity analysis (RSA) [12], on the other hand, adopt the similarity of representations on a small set of reference inputs as the model representations, and the model distance is thus calculated resorting to these model representations, which is shown effective for model reuse detection and transferability estimation. However, these methods only capture the point-wise behavior of the models at a small number of chosen reference points, which is limited in representation capacity and fails at harder tasks such as detecting model extraction [28]. Recently, DEPARA [43, 44] and ZEST [22] are proposed as pilot studies by applying explanation methods for computing model distance. However, they are validated on disjoint downstream tasks, and the performance on comprehensive tasks remains unclear. Moreover, these methods also use a small number of chosen reference points to extract the model representations, which makes them suffer from low representation capacity." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 498, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 287, + 714 + ], + "type": "text", + "content": "In this work, inspired by the concept of \"field\" in physics, we propose Model Gradient Field (as shown in Figure 1), abbreviated as ModelGiF, as the proxy to extract homogeneous representations from pre-trained heterogeneous models to derive their functionality distance. Specifically, the proposed ModelGiF is defined on the input space, i.e., every point in the ModelGiF denotes the gradient vector of the model output w.r.t. the input on the same point. The main assumption underlying ModelGiF is that each pretrained deep model uniquely determines a ModelGiF over the input space. The functional distance between any two models can thus be measured by the similarity between their ModelGiFs. Unlike prior methods where the point-wise features are adopted for representing the model, ModelGiFs represents these models by their gradient on the whole input space, which makes it more capable of differentiating highly related models (i.e., model extraction detection). Moreover, we provide theoretical insights into the proposed" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": "ModelGiFs for model functional distance, and make extensive discussions on different implementation details. We validate the effectiveness of the proposed ModelGiF with a suite of testbeds, including transferability estimation, intellectual property protection, and model unlearning verification. Experimental results demonstrate the versatility of the proposed ModelGiF on these tasks, with significantly superiority to state-of-the-art (SOTA) methods." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 168, + 545, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 168, + 545, + 289 + ], + "spans": [ + { + "bbox": [ + 304, + 168, + 545, + 289 + ], + "type": "text", + "content": "To sum up, we make the following contributions: (1) we propose the concept of \"model gradient field\", a novel method for quantifying the functionality similarity between pre-trained deep models; (2) we provide theoretical insights into the proposed ModelGiFs for model functional distance, and make extensive discussions on different implementation details; (3) extensive experiments demonstrate the effectiveness and the superiority of ModelGiF on various tasks, including transferability estimation, intellectual property protection, and model unlearning verification." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 299, + 392, + 312 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 299, + 392, + 312 + ], + "spans": [ + { + "bbox": [ + 306, + 299, + 392, + 312 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 320, + 545, + 357 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 320, + 545, + 357 + ], + "spans": [ + { + "bbox": [ + 304, + 320, + 545, + 357 + ], + "type": "text", + "content": "This section briefly reviews some related topics to model functional distance, including task relatedness estimation, intellectual property protection, and model unlearning." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 361, + 545, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 361, + 545, + 624 + ], + "spans": [ + { + "bbox": [ + 304, + 361, + 545, + 624 + ], + "type": "text", + "content": "Task Relatedness Estimation. Recent studies [53, 43, 44, 5, 51, 3, 6, 26] reveals the existence of task relatedness or task structure among visual tasks. It is the concept underlying transfer learning and provides a principled way to seamlessly reuse supervision among related tasks or solve many tasks in one system [53]. Existing works to obtain task relatedness can be roughly divided into empirical and analytical approaches. Taskonomy [53] is the most representative work of empirical methods. It proposes a fully computational approach to obtain task relatedness by exhaustively computing the actual transfer learning performance, which is thus usually taken as the ground truth for evaluating other estimators. Despite the indisputable results, the computational cost of empirical methods is extremely high. On the other hand, analytical methods, e.g., DEPARA [44, 43], Task2Vec [1] and RSA [12], try to estimate the task relatedness without conducting the actual transfer learning. Analytical methods generally significantly reduce the computation overhead, but can be highly restrictive in model architectures or estimation performance. The proposed Model-GiF relaxes these restrictions and achieves task relatedness more consistent to taskonomy than existing approaches." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "Intellectual Property Protection. Since training deep models usually consumes expensive data collection and large computation resources, the trained models constitute valuable intellectual property (IP) that should be protected in cases where reusing is not allowed without authorization. However, model IP can be infringed in a variety of forms, such as fine-tuning [2, 48], pruning [29, 33], transfer learn-" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "6126" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 336 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 336 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 336 + ], + "type": "text", + "content": "ing [39, 49, 50] and model extraction [34, 47, 25, 21], which poses great challenge to IP protection. Existing IP protection approaches can be roughly categorized into watermarking [23, 48, 13, 54, 2] and fingerprinting [30, 8, 28, 17]. Watermarking methods usually leverage weight regularization [48, 13] to put secret watermark in the model parameters or train models on a triggered set to leave backdoor [2, 54] in them. While being able to provide exact ownership verification, these techniques are invasive, i.e., they need to tamper with the training process, which may affect the model utility or introduce new security risks into the model. Fingerprinting, on the contrary, extracts a unique identifier, i.e., fingerprint, from the owner model to differentiate it from other models. Latest fingerprinting (e.g., ModelDiff [28], IPGuard [8], SAC [17]) on deep learning models, though being non-invasive, also fall short when facing the diverse and ever-growing attack scenarios [10]. In this work, we propose ModelGiF as the homogeneous representations for heterogeneous pre-trained models, which can be naturally adopted as the fingerprint for IP protection and yields superior IP protection performance to existing approaches." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 340, + 289, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 340, + 289, + 544 + ], + "spans": [ + { + "bbox": [ + 47, + 340, + 289, + 544 + ], + "type": "text", + "content": "Model Unlearning Verification. Model unlearning aims to remove the effects of data points from the trained model, which has been attracting increasing attentions in recent years due to legislation and privacy ethics. Cao et al. [9] are dedicated to making learning systems forget and present an unlearning approach capable of forgetting specific data. Graves et al. [16] propose an effective method to eliminate the influence of personal data from the model while maintaining the validity. Bourtoule et al. [7] particularly propose a model unlearning method to decrease the time it takes to retrain exactly. However, how to identify whether the impact of data has been eliminated is an essential but rarely studied problem. Recently ZEST [22] verifies the unlearning of data by comparing the Local Interpretable Model-Agnostic Explanations (LIME) [37]. In this work, we adopt the proposed ModelGiF for unlearning verification, which yields competitive performance in our experiments." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 554, + 130, + 568 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 554, + 130, + 568 + ], + "spans": [ + { + "bbox": [ + 47, + 554, + 130, + 568 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 573, + 140, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 573, + 140, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 573, + 140, + 586 + ], + "type": "text", + "content": "3.1. Problem Setup" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "spans": [ + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "text", + "content": "Assume there is a model repository consisting of " + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "text", + "content": " pre-trained models " + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "inline_equation", + "content": "\\mathcal{M} = \\{M_1, M_2, \\dots, M_N\\}" + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "text", + "content": ". With mild assumptions, these models are defined on the same input space " + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^D" + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "inline_equation", + "content": "D = WHC" + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "inline_equation", + "content": "W, H" + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "text", + "content": " denotes the width, height and channel of the input space), yet trained with data sampled from different data distributions " + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "inline_equation", + "content": "\\mathcal{P} = \\{p_1, p_2, \\dots, p_N\\}" + }, + { + "bbox": [ + 47, + 591, + 287, + 687 + ], + "type": "text", + "content": ". Note that here we made no assumptions on the model architectures and the tasks, which means" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 72, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 545, + 156 + ], + "type": "text", + "content": "that these models can be different in architectures (e.g., ResNet [18] and VGG [42]), and tasks (e.g., visual classification [27], detection [36] or segmentation [11]). The goal in this work is to construct a model metric space where models with similar functional behaviors are clustered together and dissimilar ones are far apart, where the vital step is quantifying the functional distance between these models." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 163, + 444, + 175 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 163, + 444, + 175 + ], + "spans": [ + { + "bbox": [ + 306, + 163, + 444, + 175 + ], + "type": "text", + "content": "3.2. The Proposed ModelGiF" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 182, + 545, + 276 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 182, + 545, + 276 + ], + "spans": [ + { + "bbox": [ + 304, + 182, + 545, + 276 + ], + "type": "text", + "content": "As aforementioned, quantifying the functional distance between pre-trained models is challenging due to the heterogeneity, opacity and efficiency issues. Our main idea is extracting homogeneous descriptors from these heterogeneous models to make them comparable. To this end, we proposed the concept ModelGiF, as shown in Figure 1, to derive the comparable identifier of the pre-trained models for quantifying model distance." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 277, + 546, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 277, + 546, + 396 + ], + "spans": [ + { + "bbox": [ + 304, + 277, + 546, + 396 + ], + "type": "text", + "content": "ModelGiF is inspired by the concept \"field\" in physics where a field is a mapping from space to some physical quantity, represented by a scalar, vector, or tensor, that has a value for each point in the space [32]. For example, the magnetic field describes the magnetic influence on moving electric charges, electric currents, and magnetic materials [14]. Likewise, we define ModelGiF as a mapping from the input space to the gradient space such that each point in the input space is assigned to a gradient vector. The formal definition is provided as follows." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "text", + "content": "Definition 3.1 (Model Gradient Field) Let " + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "text", + "content": " be a deep model trained on the data which is sampled according to some distribution " + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "text", + "content": " from the data space " + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\mathcal{X}" + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "text", + "content": ", outputting a scalar4 prediction in the label space " + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\mathcal{Y}" + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "text", + "content": ". A point " + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "text", + "content": " can be described as " + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\mathbf{x} = (x_1, x_2, \\dots, x_D)" + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "text", + "content": ". We define the model gradient field of " + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "text", + "content": " as the gradient of every possible input point in " + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "inline_equation", + "content": "\\mathcal{X}" + }, + { + "bbox": [ + 304, + 403, + 545, + 488 + ], + "type": "text", + "content": " w.r.t. the model output:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 370, + 496, + 545, + 509 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 370, + 496, + 545, + 509 + ], + "spans": [ + { + "bbox": [ + 370, + 496, + 545, + 509 + ], + "type": "interline_equation", + "content": "\\operatorname {M O D E L G I F} (M) \\triangleq \\nabla_ {\\mathbf {x}} M, \\tag {1}", + "image_path": "5d80af802ae0c1635b86e2ac3dd38bfa1b88f1a6c9ff7d2c0ae3ae6b1238d1fa.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "spans": [ + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "text", + "content": "which is a mapping from the input space " + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^D" + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "text", + "content": " to the gradient space " + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "inline_equation", + "content": "\\mathbb{G}^D" + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "text", + "content": ", MODELGiF: " + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^D \\to \\mathbb{G}^D" + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "text", + "content": ". Note that the ModelGiF is defined on the whole input space (which is shared by all the models) rather than some discretely points sampled from the data distribution " + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "text", + "content": " specific to the model " + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "text", + "content": ". As the architecture of " + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "text", + "content": " and the tasks (i.e., the label space " + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "inline_equation", + "content": "\\mathcal{V}" + }, + { + "bbox": [ + 304, + 517, + 545, + 613 + ], + "type": "text", + "content": ") can be heterogeneous, the ModelGiF of a model can be seen as a projection of the model to the common input space." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 620, + 455, + 632 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 620, + 455, + 632 + ], + "spans": [ + { + "bbox": [ + 306, + 620, + 455, + 632 + ], + "type": "text", + "content": "3.3. Field Curves for ModelGiF" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 638, + 545, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 638, + 545, + 687 + ], + "spans": [ + { + "bbox": [ + 304, + 638, + 545, + 687 + ], + "type": "text", + "content": "With the proposed ModelGiF, the model functional distance can be quantified by the ModelGiF similarity. However, as ModelGiF is defined on the whole input space that is usually extremely huge, how to extract its representation" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "text", + "content": "3Without losing generality, we use vector instead of tensor for notation simplicity." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": "4For vector or tensor predictions, we simply take their " + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "inline_equation", + "content": "l_{2}" + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": " norm as the scalar output." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "6127" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 72, + 545, + 320 + ], + "blocks": [ + { + "bbox": [ + 50, + 72, + 545, + 320 + ], + "lines": [ + { + "bbox": [ + 50, + 72, + 545, + 320 + ], + "spans": [ + { + "bbox": [ + 50, + 72, + 545, + 320 + ], + "type": "image", + "image_path": "86b1123d4c5082e4e95c8a3e779772a8723680717d27c5e90bad91574839eb33.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 323, + 546, + 346 + ], + "lines": [ + { + "bbox": [ + 46, + 323, + 546, + 346 + ], + "spans": [ + { + "bbox": [ + 46, + 323, + 546, + 346 + ], + "type": "text", + "content": "Figure 2. An illustrative diagram of the overall pipeline of obtaining ModelGiF curves. The more similar the ModelGiFs, the more similar the corresponding trained models. Note that ModelGiF Curves are in high-dimensional space in reality." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 365, + 289, + 473 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 289, + 473 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 289, + 473 + ], + "type": "text", + "content": "or signature becomes the vital step for quantifying model distance. In physics, a field is usually depicted by the field curves (as shown in Figure 1), i.e., the integral curves for the field, and can be constructed by starting at a point and tracing a curve through space that follows the direction of the vector field, by making the field curve tangent to the field vector at each point [46]. Inspired by this, we propose ModelGiF Curves as the descriptors of ModelGiF to measure the model functional distance." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "spans": [ + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "text", + "content": "Definition 3.2 (Field Curves) For a field " + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "text", + "content": ": " + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^D \\to \\mathbb{G}^D" + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "text", + "content": ", a curve " + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "inline_equation", + "content": "\\mathbf{x}(t) = (x_1(t), x_2(t), \\ldots, x_D(t))" + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "text", + "content": " is called a field curve of the field " + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "text", + "content": " if the following condition is satisfied: For all points " + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "inline_equation", + "content": "P \\in \\mathbf{x}(t)" + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "text", + "content": ", the tangent vector of the curve in the point " + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "text", + "content": " has the same direction as the vector " + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "inline_equation", + "content": "F(P)" + }, + { + "bbox": [ + 46, + 478, + 288, + 540 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 76, + 545, + 287, + 571 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 76, + 545, + 287, + 571 + ], + "spans": [ + { + "bbox": [ + 76, + 545, + 287, + 571 + ], + "type": "interline_equation", + "content": "\\frac {d x _ {1} (t)}{d t} = F \\left(\\mathbf {x} (t)\\right) _ {1}, \\frac {d x _ {2} (t)}{d t} = F \\left(\\mathbf {x} (t)\\right) _ {2}, \\dots \\tag {2}", + "image_path": "9a605b98225a3d9444a51a793e315a001e64d0e8980414798f8d1c4711e36359.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 575, + 287, + 683 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 575, + 287, + 683 + ], + "spans": [ + { + "bbox": [ + 46, + 575, + 287, + 683 + ], + "type": "text", + "content": "The field curve can be described as the solution of the system of differential equations in Eqn. 2, and it plays an important role for both analysis and visualization of vector fields [46]. Unfortunately, as the ModelGiF is usually complicated for a pre-trained deep model, there is no closed solution. The field curves are in general not describable as parameterized curves, which hinders the comparisons between different ModelGiFs. To resolve this issue, we introduce the definition of ModelGiF curves as follows." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": "Definition 3.3 (ModelGiF Curves) For a ModelGiF " + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": ": " + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^D \\to \\mathbb{G}^D" + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": ", a curve " + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{g}(t) = (g_1(t), g_2(t), \\dots, g_D(t))" + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": " is" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 365, + 546, + 389 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 365, + 546, + 389 + ], + "spans": [ + { + "bbox": [ + 305, + 365, + 546, + 389 + ], + "type": "text", + "content": "called the ModelGiF curve of " + }, + { + "bbox": [ + 305, + 365, + 546, + 389 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 305, + 365, + 546, + 389 + ], + "type": "text", + "content": " if the following condition is satisfied:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 336, + 397, + 545, + 422 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 336, + 397, + 545, + 422 + ], + "spans": [ + { + "bbox": [ + 336, + 397, + 545, + 422 + ], + "type": "interline_equation", + "content": "\\frac {d g _ {1} (t)}{d t} = F (\\mathbf {x} (t)) _ {1}, \\frac {d g _ {2} (t)}{d t} = F (\\mathbf {x} (t)) _ {2}, \\dots \\tag {3}", + "image_path": "9727ad21e6a96cfc080f29ab34aea33811374005df95dc3cfd32a1d1b0b1c4fc.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 428, + 546, + 465 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 428, + 546, + 465 + ], + "spans": [ + { + "bbox": [ + 305, + 428, + 546, + 465 + ], + "type": "text", + "content": "Note that different from the definition of field curves, the ModelGiF curves are defined on the gradient space " + }, + { + "bbox": [ + 305, + 428, + 546, + 465 + ], + "type": "inline_equation", + "content": "\\mathbb{G}^D" + }, + { + "bbox": [ + 305, + 428, + 546, + 465 + ], + "type": "text", + "content": " instead of the input space " + }, + { + "bbox": [ + 305, + 428, + 546, + 465 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^D" + }, + { + "bbox": [ + 305, + 428, + 546, + 465 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "spans": [ + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "text", + "content": "Proposition 1 For a ModelGiF " + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "inline_equation", + "content": "F \\colon \\mathbb{R}^D \\to \\mathbb{G}^D" + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "text", + "content": ", and two points " + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_0, \\mathbf{x}_1" + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^D" + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "text", + "content": ", the gradient integral along the straight line from " + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_0" + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_1" + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "text", + "content": " is a ModelGiF curve of " + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 305, + 472, + 547, + 509 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 318, + 517, + 545, + 544 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 517, + 545, + 544 + ], + "spans": [ + { + "bbox": [ + 318, + 517, + 545, + 544 + ], + "type": "interline_equation", + "content": "\\mathbf {g} (t) = \\int_ {\\alpha = 0} ^ {t} F \\left(\\mathbf {x} _ {0} + \\alpha \\left(\\mathbf {x} _ {1} - \\mathbf {x} _ {0}\\right)\\right) d \\alpha , \\quad t \\in [ 0, 1 ] \\tag {4}", + "image_path": "63da39237a4ff7315915aea7148d8f76f1eeb110c1e71730271a32432bc3ecd1.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 551, + 545, + 611 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 551, + 545, + 611 + ], + "spans": [ + { + "bbox": [ + 305, + 551, + 545, + 611 + ], + "type": "text", + "content": "With the proposition, we can make comparisons between ModelGiFs by simply comparing their ModelGiF curves between some predefined pairs of points. Now we provide the detailed pipeline of quantifying the Model functional distance with the proposed ModelGiF." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 617, + 469, + 629 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 617, + 469, + 629 + ], + "spans": [ + { + "bbox": [ + 306, + 617, + 469, + 629 + ], + "type": "text", + "content": "3.4. ModelGiF for Model Distance" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 636, + 545, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 636, + 545, + 685 + ], + "spans": [ + { + "bbox": [ + 305, + 636, + 545, + 685 + ], + "type": "text", + "content": "Provided with the trained deep models as described in Section 3.1, we compute the model distance with the proposed ModelGiF in two steps (in Figure 2): 1) Sampling reference points, and 2) Computing the model distance." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 689, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 546, + 714 + ], + "type": "text", + "content": "Sampling Reference Points. As described in Proposition 1, the first step before obtaining ModelGiF curves is" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6128" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "text", + "content": "determining the reference points (i.e., " + }, + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_1^5" + }, + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "text", + "content": " in Eqn. 4.), which determines the domain of these curves. Let " + }, + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "text", + "content": " be the number of reference points to be sampled. Intuitively, these reference points should representative. However, as the models in " + }, + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "inline_equation", + "content": "\\mathcal{M}" + }, + { + "bbox": [ + 46, + 72, + 289, + 180 + ], + "type": "text", + "content": " can be heterogeneous in architectures and tasks and trained on data sampled from different distributions, it is hard to determine a common set of reference points which are representative for all these models. In this work, we investigate three types of reference points as follows." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 182, + 287, + 356 + ], + "type": "list", + "angle": 0, + "index": 4, + "blocks": [ + { + "bbox": [ + 46, + 182, + 287, + 231 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 182, + 287, + 231 + ], + "spans": [ + { + "bbox": [ + 46, + 182, + 287, + 231 + ], + "type": "text", + "content": "1) Random samples drawn from " + }, + { + "bbox": [ + 46, + 182, + 287, + 231 + ], + "type": "inline_equation", + "content": "\\mathcal{P}" + }, + { + "bbox": [ + 46, + 182, + 287, + 231 + ], + "type": "text", + "content": ". Each data point is sampled in two stages: first randomly sampling the distribution " + }, + { + "bbox": [ + 46, + 182, + 287, + 231 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 182, + 287, + 231 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 46, + 182, + 287, + 231 + ], + "type": "inline_equation", + "content": "\\mathcal{P}" + }, + { + "bbox": [ + 46, + 182, + 287, + 231 + ], + "type": "text", + "content": " and then randomly sampling the reference point from " + }, + { + "bbox": [ + 46, + 182, + 287, + 231 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 182, + 287, + 231 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "spans": [ + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "text", + "content": "2) Augmented samples using CutMix [52]. Let " + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^*" + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "text", + "content": " be two randomly sampled points in " + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "inline_equation", + "content": "\\mathcal{P}" + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "text", + "content": ". CutMix generates a new sample " + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{x}}" + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "text", + "content": " using the two samples by cutting off and pasting patches among them: " + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{x}} = \\mathbf{m} \\odot \\mathbf{x} + (1 - \\mathbf{m}) \\odot \\mathbf{x}^*" + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "inline_equation", + "content": "\\mathbf{m}" + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "text", + "content": " represents the binary mask to combine images with different parts, and " + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 46, + 232, + 287, + 305 + ], + "type": "text", + "content": " the element-wise multiplication." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 307, + 287, + 356 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 307, + 287, + 356 + ], + "spans": [ + { + "bbox": [ + 46, + 307, + 287, + 356 + ], + "type": "text", + "content": "3) Adversarial samples generated with PGD [31]. PGD attack is a multi-step variant of Fast Gradient Sign Method (FGSM) [15]: " + }, + { + "bbox": [ + 46, + 307, + 287, + 356 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{t + 1} = \\prod \\left(\\mathbf{x}_t + \\alpha \\mathrm{SGN}\\bigl (\\nabla \\mathcal{J}(\\mathbf{x}_t)\\bigr)\\right)" + }, + { + "bbox": [ + 46, + 307, + 287, + 356 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 307, + 287, + 356 + ], + "type": "inline_equation", + "content": "\\prod" + }, + { + "bbox": [ + 46, + 307, + 287, + 356 + ], + "type": "text", + "content": " denotes the projection to the allowed space." + } + ] + } + ], + "index": 3 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 357, + 287, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 357, + 287, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 357, + 287, + 418 + ], + "type": "text", + "content": "The performance of these types of reference points are discussed in Section 4.1. We also provide the sensitivity analysis of the number of reference points " + }, + { + "bbox": [ + 46, + 357, + 287, + 418 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 357, + 287, + 418 + ], + "type": "text", + "content": ", which demonstrates that the performance of ModelGiF quickly becomes superior to existing methods as " + }, + { + "bbox": [ + 46, + 357, + 287, + 418 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 357, + 287, + 418 + ], + "type": "text", + "content": " increases." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "spans": [ + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "text", + "content": "Computing the model distance. Let " + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "inline_equation", + "content": "S = \\{\\mathbf{x}_1, \\mathbf{x}_2, \\dots, \\mathbf{x}_K\\}" + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "text", + "content": " be the reference points obtained from the last step. For the " + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "text", + "content": "-th model " + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "inline_equation", + "content": "M_i" + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "text", + "content": ", we can get " + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "text", + "content": " ModelGiF curves by substituting each point in " + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "text", + "content": " for the " + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_1" + }, + { + "bbox": [ + 46, + 424, + 289, + 558 + ], + "type": "text", + "content": " in Eqn. 4. These curves are used as the identifier of the ModelGiF, and thus serve as the representations of the trained deep model. There are several distance metrics to measure the similarity between curves, e.g., Hausdorff distance and Fréchet distance. As the method for curve distance is not our contribution in this work, we simply adopt the integrated point-wise cosine distance to validate the performance of the proposed method:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 52, + 579, + 287, + 613 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 579, + 287, + 613 + ], + "spans": [ + { + "bbox": [ + 52, + 579, + 287, + 613 + ], + "type": "interline_equation", + "content": "d \\left(M _ {i}, M _ {j}\\right) = \\sum_ {k = 1} ^ {K} \\int_ {t = 0} ^ {1} \\left(1 - \\cos \\left(\\mathbf {g} ^ {i, k} (t), \\mathbf {g} ^ {j, k} (t)\\right)\\right) d t, \\tag {5}", + "image_path": "f9e99dbd89769da1588bb02440b3a21a8549a3b8d3f9873b32a34e83a5a39388.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{g}^{i,k}" + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "text", + "content": " denotes the " + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "text", + "content": "-th curve of the " + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "text", + "content": "-th model in " + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "inline_equation", + "content": "\\mathcal{M}" + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "inline_equation", + "content": "\\cdot" + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "text", + "content": " denotes the inner product between " + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{g}^{i,k}(t)" + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{g}^{i,k}(t)" + }, + { + "bbox": [ + 46, + 627, + 287, + 677 + ], + "type": "text", + "content": ". In practice, we approximate the integral with summation by sampling with some fixed intervals." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 72, + 487, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 487, + 85 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 487, + 85 + ], + "type": "text", + "content": "3.5. Theoretical Analysis of ModelGiF" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 91, + 545, + 151 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 91, + 545, + 151 + ], + "spans": [ + { + "bbox": [ + 304, + 91, + 545, + 151 + ], + "type": "text", + "content": "From the definition of model distance in Eqn. 5, we can see that the defined distance can be seen as the summation of point-wise similarities over all the curves. Here we provide some theoretical insights into ModelGiF by dissecting the model-level distance into point-level distance." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 162, + 547, + 187 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 162, + 547, + 187 + ], + "spans": [ + { + "bbox": [ + 304, + 162, + 547, + 187 + ], + "type": "text", + "content": "Proposition 2 For the point " + }, + { + "bbox": [ + 304, + 162, + 547, + 187 + ], + "type": "inline_equation", + "content": "\\mathbf{g}(t_1)" + }, + { + "bbox": [ + 304, + 162, + 547, + 187 + ], + "type": "text", + "content": " along the ModelGiF curves " + }, + { + "bbox": [ + 304, + 162, + 547, + 187 + ], + "type": "inline_equation", + "content": "\\mathbf{g}(t)" + }, + { + "bbox": [ + 304, + 162, + 547, + 187 + ], + "type": "text", + "content": " defined from " + }, + { + "bbox": [ + 304, + 162, + 547, + 187 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^*" + }, + { + "bbox": [ + 304, + 162, + 547, + 187 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 162, + 547, + 187 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 162, + 547, + 187 + ], + "type": "text", + "content": ", then" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 337, + 196, + 545, + 215 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 337, + 196, + 545, + 215 + ], + "spans": [ + { + "bbox": [ + 337, + 196, + 545, + 215 + ], + "type": "interline_equation", + "content": "\\sum_ {i} t _ {1} \\left(x _ {i} - x _ {i} ^ {*}\\right) g _ {i} \\left(t _ {1}\\right) = M (\\mathbf {x}) - M \\left(\\mathbf {x} ^ {*}\\right), \\tag {6}", + "image_path": "8bf5ae9fd84c4b3bde8d1318b724d825b55bb965cf4156bd27212c78f48e513a.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 224, + 545, + 297 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 224, + 545, + 297 + ], + "spans": [ + { + "bbox": [ + 304, + 224, + 545, + 297 + ], + "type": "text", + "content": "where the left side is actually the summation over Integrated Gradients [45]. Eqn. 6 tells us that the every point in proposed ModelGiF curve is strongly related to the model prediction differences from this point and the baseline point, thus the proposed model distance is a powerful distance metric to quantifying the model function distance." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 308, + 388, + 322 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 308, + 388, + 322 + ], + "spans": [ + { + "bbox": [ + 306, + 308, + 388, + 322 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 328, + 545, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 328, + 545, + 376 + ], + "spans": [ + { + "bbox": [ + 304, + 328, + 545, + 376 + ], + "type": "text", + "content": "In this section, we verify the effectiveness of ModelGiF with a suite of testbeds, including task relatedness estimation, intellectual property protection and model unlearning verification. Details are provided as follows." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 384, + 525, + 398 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 384, + 525, + 398 + ], + "spans": [ + { + "bbox": [ + 305, + 384, + 525, + 398 + ], + "type": "text", + "content": "4.1. Application: Task Relatedness Estimation" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 409, + 545, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 409, + 545, + 578 + ], + "spans": [ + { + "bbox": [ + 304, + 409, + 545, + 578 + ], + "type": "text", + "content": "Experimental Setup. We adopt 17 pre-trained heterogeneous models from Taskonomy [53] to compare their functionality similarity. These models are trained on various tasks (including Autoencoder, Curvature, Denoise, Edge 2D, Edge 3D, Keypoint 2D, Keypoint 3D, Reshade, RGB2depth, RGB2mist, RGB2sfnorm, Room Layout, Segment25D, Segment2D, Vanishing Point, Segmentation, and Classification) and are different in architectures. Generally speaking, the architectures of these models follow an encoder-decoder scheme, in which the encoder is implemented by fully convolutional layers and the decoder varies according to the tasks. Please refer to [53] for more detailed information. In our experiments, only the encoders of these models are adopted for generating their ModelGiFs." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "type": "text", + "content": "Competitors and Evaluation Metric. The proposed ModelGiF is compared with several prior approaches to task relatedness estimation, including RSA [12], Attribution-Maps [43], and ZEST [22]. Note that AttributionMaps adopts saliency [41], DeepLIFT [40] and " + }, + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "type": "text", + "content": "-LRP [4] to generate attributions for task relatedness estimation. We compare ModelGiF with all these variants to demonstrate its superiority in task relatedness prediction. As the affinity matrix from Taskonomy is obtained based on the actual transfer learning performance, it is used as the ground truth of the affinity among these tasks. In this experiment, we will" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 693, + 287, + 714 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 287, + 714 + ], + "type": "text", + "content": "Here we simply set " + }, + { + "bbox": [ + 47, + 693, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_0" + }, + { + "bbox": [ + 47, + 693, + 287, + 714 + ], + "type": "text", + "content": " to the zero vector. Other settings do not yield significantly superior performance in our experiments." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6129" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 75, + 217, + 180 + ], + "blocks": [ + { + "bbox": [ + 55, + 75, + 217, + 180 + ], + "lines": [ + { + "bbox": [ + 55, + 75, + 217, + 180 + ], + "spans": [ + { + "bbox": [ + 55, + 75, + 217, + 180 + ], + "type": "image", + "image_path": "6834f8232963b5ad2260e6ffb9bc4e0f177d9f49df02dcf33625945c86f8703c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 74, + 182, + 194, + 191 + ], + "lines": [ + { + "bbox": [ + 74, + 182, + 194, + 191 + ], + "spans": [ + { + "bbox": [ + 74, + 182, + 194, + 191 + ], + "type": "text", + "content": "(a) Affinity Matrix from Taskonomy" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 219, + 76, + 380, + 181 + ], + "blocks": [ + { + "bbox": [ + 219, + 76, + 380, + 181 + ], + "lines": [ + { + "bbox": [ + 219, + 76, + 380, + 181 + ], + "spans": [ + { + "bbox": [ + 219, + 76, + 380, + 181 + ], + "type": "image", + "image_path": "b457a29dba003eee0d19c03e3729d852b6274d83ecc9686c476a61adb9820620.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 248, + 182, + 345, + 191 + ], + "lines": [ + { + "bbox": [ + 248, + 182, + 345, + 191 + ], + "spans": [ + { + "bbox": [ + 248, + 182, + 345, + 191 + ], + "type": "text", + "content": "(b) Affinity Matrix from RSA" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 382, + 76, + 542, + 180 + ], + "blocks": [ + { + "bbox": [ + 382, + 76, + 542, + 180 + ], + "lines": [ + { + "bbox": [ + 382, + 76, + 542, + 180 + ], + "spans": [ + { + "bbox": [ + 382, + 76, + 542, + 180 + ], + "type": "image", + "image_path": "f24bec5d274bea9fe5fec1c47b27e09ad34e2b7a4c573401c1f664c847d33498.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 403, + 182, + 517, + 190 + ], + "lines": [ + { + "bbox": [ + 403, + 182, + 517, + 190 + ], + "spans": [ + { + "bbox": [ + 403, + 182, + 517, + 190 + ], + "type": "text", + "content": "(c) Affinity Matrix from ModelGiF" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 55, + 201, + 222, + 300 + ], + "blocks": [ + { + "bbox": [ + 55, + 201, + 222, + 300 + ], + "lines": [ + { + "bbox": [ + 55, + 201, + 222, + 300 + ], + "spans": [ + { + "bbox": [ + 55, + 201, + 222, + 300 + ], + "type": "image", + "image_path": "aa30cad153c71255768d86218b26285a4bf02a88cda5614d4ea6c70a197f35a6.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 77, + 300, + 190, + 309 + ], + "lines": [ + { + "bbox": [ + 77, + 300, + 190, + 309 + ], + "spans": [ + { + "bbox": [ + 77, + 300, + 190, + 309 + ], + "type": "text", + "content": "(d) Similarity Tree from ModelGiF" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 312, + 547, + 346 + ], + "lines": [ + { + "bbox": [ + 46, + 312, + 547, + 346 + ], + "spans": [ + { + "bbox": [ + 46, + 312, + 547, + 346 + ], + "type": "text", + "content": "Figure 3. Results of task related estimation: (a) affinity matrix from Taskonomy; (b) affinity matrix from RSA; (c) affinity matrix from ModelGiF; (d) the similarity tree derived from ModelGiF; (e) performance with varying " + }, + { + "bbox": [ + 46, + 312, + 547, + 346 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 312, + 547, + 346 + ], + "type": "text", + "content": " of different reference points; (e) performance with varying " + }, + { + "bbox": [ + 46, + 312, + 547, + 346 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 312, + 547, + 346 + ], + "type": "text", + "content": " of different implementations." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 221, + 201, + 375, + 300 + ], + "blocks": [ + { + "bbox": [ + 221, + 201, + 375, + 300 + ], + "lines": [ + { + "bbox": [ + 221, + 201, + 375, + 300 + ], + "spans": [ + { + "bbox": [ + 221, + 201, + 375, + 300 + ], + "type": "image", + "image_path": "97191c17e4cce016b4388176c3137f0df030cdebcdad303d4e9032da346d3d15.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 249, + 300, + 344, + 310 + ], + "lines": [ + { + "bbox": [ + 249, + 300, + 344, + 310 + ], + "spans": [ + { + "bbox": [ + 249, + 300, + 344, + 310 + ], + "type": "text", + "content": "(e) Different reference points" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 383, + 201, + 539, + 300 + ], + "blocks": [ + { + "bbox": [ + 383, + 201, + 539, + 300 + ], + "lines": [ + { + "bbox": [ + 383, + 201, + 539, + 300 + ], + "spans": [ + { + "bbox": [ + 383, + 201, + 539, + 300 + ], + "type": "image", + "image_path": "23a47142c51ca8a7001737fbfae2d0c839ca01ef5d52741ac9e54ab14a8f9f7b.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 411, + 300, + 509, + 309 + ], + "lines": [ + { + "bbox": [ + 411, + 300, + 509, + 309 + ], + "spans": [ + { + "bbox": [ + 411, + 300, + 509, + 309 + ], + "type": "text", + "content": "(f) Different implementations" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 48, + 364, + 294, + 483 + ], + "blocks": [ + { + "bbox": [ + 48, + 364, + 294, + 483 + ], + "lines": [ + { + "bbox": [ + 48, + 364, + 294, + 483 + ], + "spans": [ + { + "bbox": [ + 48, + 364, + 294, + 483 + ], + "type": "table", + "html": "
MethodSpearman's Correlation
Zest [22]0.359
AttributionMapsSALIENCY [43]0.619
AttributionMapsDEEPLIFT [43]0.685
AttributionMapsε-LRP [43]0.682
RSA [12]0.777
ModelGiFRANDOM0.834
ModelGiFAUGMENT0.835
ModelGiFADVERSARIAL0.830
", + "image_path": "b0405607c89e692499a0bbbb2ac275f5457ce2e4ae13abac05fc654138bc4646.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 47, + 483, + 286, + 506 + ], + "lines": [ + { + "bbox": [ + 47, + 483, + 286, + 506 + ], + "spans": [ + { + "bbox": [ + 47, + 483, + 286, + 506 + ], + "type": "text", + "content": "Table 1. Comparison between the proposed ModelGiF and existing methods. Here 1, 000 reference points are sampled in ModelGiF." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 527, + 287, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 527, + 287, + 598 + ], + "spans": [ + { + "bbox": [ + 46, + 527, + 287, + 598 + ], + "type": "text", + "content": "verify that the functionality similarity obtained by ModelGiF positively correlates with that from taskonomy. In order to quantify the similarity between the affinity matrix representing functionality similarity obtained by ModelGiF and the affinity matrix obtained by Taskonomy, we use Spearman's correlation as the metric for evaluation." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 713 + ], + "type": "text", + "content": "Results. We first test the proposed ModelGiF with by randomly sampling 1,000 reference points. The visualization of the affinity matrix (as well as that from Taskonomy [53] and RSA [12]) and the similarity tree are provided in Figure 3. This similarity tree is constructed by agglomerative hierarchical clustering based on the affinity matrix. It can be seen that the affinity matrix from the proposed ModelGiF is visually highly similar to that from Taskonomy in most regions. The similarity tree derived from ModelGiF" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 365, + 545, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 365, + 545, + 413 + ], + "spans": [ + { + "bbox": [ + 304, + 365, + 545, + 413 + ], + "type": "text", + "content": "perfectly matches the results from taskonomy where 3D (in green font) tasks, 2D (in blue font), geometric (in red font) tasks, and semantic (in purple font) tasks cluster into corresponding groups as expected." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 415, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 546, + 714 + ], + "type": "text", + "content": "Table 1 provide a quantitative comparison between the proposed ModelGiF with existing works in Spearman's correlation. It can be easily seen that the proposed ModelGiF yields significantly superior performance to existing methods, improving the SOTA Spearman's correlation from 0.777 to 0.835. Furthermore, all the three types of reference points produce Spearman's correlation more than 0.83, which implies that the proposed method is quite robust to the choice of the reference points. To make a more comprehensive study, we test ModelGiF with varying number of reference points. The correlation curves are depicted in Figure 3e, where different types of reference points are compared. It can be seen that as the number of reference points increases, the correlation steadily grows. Surprisingly, with only 16 points, ModelGiF already achieves comparable performance to RSA [12] in Spearman's correlation. It is attractive as the computation overhead of the proposed method grows linearly with the number of reference points. The results indicate that we can safely reduce the computation cost by decreasing the number of reference points, and we can also strive for higher performance by adding more reference points, which makes ModelGiF flexible and applicable in a variety of scenarios. Another conclusion we can draw from Figure 3e is that the adversarial samples generally yields superior performance to other ref" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6130" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 67, + 70, + 526, + 230 + ], + "blocks": [ + { + "bbox": [ + 67, + 70, + 526, + 230 + ], + "lines": [ + { + "bbox": [ + 67, + 70, + 526, + 230 + ], + "spans": [ + { + "bbox": [ + 67, + 70, + 526, + 230 + ], + "type": "table", + "html": "
CIFARtiny-ImageNet
AttackIPGuard [8]CAE [30]EWE [23]SAC [17]ModelGiF (Ours)IPGuard [8]CAE [30]EWE [23]SAC [17]ModelGiF (Ours)
Finetune-A1.001.001.001.001.001.001.000.481.001.00
Finetune-L1.001.001.001.001.001.001.001.001.001.00
Pruning1.000.950.871.001.001.001.000.581.001.00
Extract-L0.810.830.971.001.000.971.001.001.001.00
Extract-P0.810.900.971.001.000.971.001.001.001.00
Extract-Adv0.540.520.910.921.000.650.781.000.911.00
Transfer-10C1.001.001.001.001.00N/AN/AN/AN/AN/A
Transfer-A---1.001.00---1.001.00
Transfer-L---1.001.00---1.001.00
", + "image_path": "641a116be54f58c130b66442a143163fbf3fae6e46d3a1f3b94850b5554a6204.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 230, + 545, + 253 + ], + "lines": [ + { + "bbox": [ + 46, + 230, + 545, + 253 + ], + "spans": [ + { + "bbox": [ + 46, + 230, + 545, + 253 + ], + "type": "text", + "content": "Table 2. Comparison between the proposed ModelGiF and existing methods for IP protection. The performance is measured in AUC value under the AUC-ROC curve. “–” represent the IP protection method can not detect this kind of attack. “N/A” denotes not applicable." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 272, + 287, + 295 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 272, + 287, + 295 + ], + "spans": [ + { + "bbox": [ + 46, + 272, + 287, + 295 + ], + "type": "text", + "content": "erence points, which gives implications of future work to strive for higher performance of task relatedness estimation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 296, + 288, + 429 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 296, + 288, + 429 + ], + "spans": [ + { + "bbox": [ + 46, + 296, + 288, + 429 + ], + "type": "text", + "content": "In Figure 3f, we make comparisons between some different implementations of ModelGiF. \"ModelGiF with random baselines\" denotes " + }, + { + "bbox": [ + 46, + 296, + 288, + 429 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_0" + }, + { + "bbox": [ + 46, + 296, + 288, + 429 + ], + "type": "text", + "content": " in Eqn. 4 is fixed to be zero, and \"ModelGiF with random baselines\" denotes " + }, + { + "bbox": [ + 46, + 296, + 288, + 429 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_0" + }, + { + "bbox": [ + 46, + 296, + 288, + 429 + ], + "type": "text", + "content": " is randomly sampled. We also include Integrated Gradient (IG, with zero as the baseline) and IG with random baselines for comparisons. Albeit bearing some similarity with IG, it can be seen that ModelGiF with zero baselines significantly outperforms these baselines in most cases. ModelGiF with random baselines, however, is more promising when the number of reference points becomes sufficiently larger." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 437, + 281, + 451 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 437, + 281, + 451 + ], + "spans": [ + { + "bbox": [ + 47, + 437, + 281, + 451 + ], + "type": "text", + "content": "4.2. Application: Intellectual Property Protection" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 456, + 287, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 456, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 456, + 287, + 506 + ], + "type": "text", + "content": "We evaluate the performance of ModelGiF for IP protection against different model stealing attacks. To make fair comparisons with SOTA methods, we follow the experimental settings of [17] to conduct our experiments." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "content": "Experimental Setup. Five categories of stealing attacks are considered here to test the protection performance. including finetuning, pruning, transfer learning, model extraction and adversarial model extraction. For finetuning, FinetuneL denotes fine-tuning only the last layer and leaves the other layers unchanged. Finetune-A fine-tunes all the layers in the model. For transfer learning, the CIFAR10 model is transferred to CIFAR10-C and CIFAR100. The tiny-ImageNet model (trained with the front 100 labels in Tiny-ImageNet) is transferred to the 100 labels left behind in tiny-ImageNet dataset. In model extraction, the victim model can be extracted in two manners: probability-based model extraction (Extract-P), and label-based model extraction (Extract-L). However, the attacker can evade the detection by applying adversarial training after the label-based model extraction [30]. In our experiment, adversarial model extraction (Extract-adv) adopts the predicted label to evade the" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 272, + 440, + 285 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 272, + 440, + 285 + ], + "spans": [ + { + "bbox": [ + 306, + 272, + 440, + 285 + ], + "type": "text", + "content": "detection by adversarial training." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 295, + 547, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 295, + 547, + 475 + ], + "spans": [ + { + "bbox": [ + 304, + 295, + 547, + 475 + ], + "type": "text", + "content": "Models and Competitors. Different IP protection methods are evaluated on most of the common model architectures, including VGG [42], ResNet [18], DenseNet [20] and MobileNet [38]. To demonstrate the superiority of the proposed ModelGiF, we make comparisons with SOTA IP protection methods, including IPGuard [8], CAE [30], EWE [23] and SAC [17]. IPGuard and CAE utilizes the transferability of adversarial examples and test the attack success rate of these adversarial examples on the suspect models. A model will be recognized as a stolen model if its attack success rate is larger than a threshold. SAC propose to leverage the pairwise relationship between samples as the model fingerprint. EWE, on the contrary, trains the source model on backdoor data and leaves the watermark in the model. Please refer to [17] for more detailed experimental settings." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 486, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 547, + 715 + ], + "type": "text", + "content": "Results. To validate the effectiveness and the superiority of the proposed ModelGiF, we conduct experiments on different datasets for the defender and the attacker. We we leverage AUC-ROC curve and use AUC value between the fingerprinting scores of the irrelevant models and the stolen models to measure the fingerprinting effectiveness. Results are listed in Table 2. It can be seen that the proposed ModelGiF, although not tailored for IP protection, achieve superior performance in all the attack scenarios. The AUC value is 1.0 across all attacks (including the challenging \"Extract-adv\" attack), which means it perfectly recognize all the attacks to protect the IP, outperforming existing SOTA approaches like SAC [17]. We acknowledge the existing benchmark for IP protection methods is not sufficient large and challenging to provide thorough comparisons between IP methods. However, the superiority of ModelGiF to SOTA methods on this benchmark still provides us a strong confidence of the proposed method for quantifying model functional distance." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "6131" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 60, + 72, + 294, + 188 + ], + "blocks": [ + { + "bbox": [ + 60, + 72, + 294, + 188 + ], + "lines": [ + { + "bbox": [ + 60, + 72, + 294, + 188 + ], + "spans": [ + { + "bbox": [ + 60, + 72, + 294, + 188 + ], + "type": "image", + "image_path": "c76314d8e8b95a658a1945c52edc48a5221a38bac59a9ce07cb5049568704c4d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 192, + 545, + 216 + ], + "lines": [ + { + "bbox": [ + 46, + 192, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 46, + 192, + 545, + 216 + ], + "type": "text", + "content": "Figure 4. Cosine distances between the reference classifier " + }, + { + "bbox": [ + 46, + 192, + 545, + 216 + ], + "type": "inline_equation", + "content": "C_{ref}" + }, + { + "bbox": [ + 46, + 192, + 545, + 216 + ], + "type": "text", + "content": " and unrelated classifier " + }, + { + "bbox": [ + 46, + 192, + 545, + 216 + ], + "type": "inline_equation", + "content": "C_{unrelated}" + }, + { + "bbox": [ + 46, + 192, + 545, + 216 + ], + "type": "text", + "content": ", the directly unlearned classifier " + }, + { + "bbox": [ + 46, + 192, + 545, + 216 + ], + "type": "inline_equation", + "content": "C_{direct}" + }, + { + "bbox": [ + 46, + 192, + 545, + 216 + ], + "type": "text", + "content": " and the approximately unlearned classifier " + }, + { + "bbox": [ + 46, + 192, + 545, + 216 + ], + "type": "inline_equation", + "content": "C_{approx}" + }, + { + "bbox": [ + 46, + 192, + 545, + 216 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 298, + 72, + 536, + 190 + ], + "blocks": [ + { + "bbox": [ + 298, + 72, + 536, + 190 + ], + "lines": [ + { + "bbox": [ + 298, + 72, + 536, + 190 + ], + "spans": [ + { + "bbox": [ + 298, + 72, + 536, + 190 + ], + "type": "image", + "image_path": "80a67a38d27d540c935c49717a975ded9e53093c7ba9388a25b8975f2642d26a.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 234, + 275, + 248 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 234, + 275, + 248 + ], + "spans": [ + { + "bbox": [ + 47, + 234, + 275, + 248 + ], + "type": "text", + "content": "4.3. Application: Model Unlearning Verification" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 255, + 288, + 339 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 255, + 288, + 339 + ], + "spans": [ + { + "bbox": [ + 46, + 255, + 288, + 339 + ], + "type": "text", + "content": "Machine unlearning studies how we can efficiently delete data points used to train models without retraining from scratch [7]. In this section, we demonstrate the effectiveness of the proposed ModelGiF for model unlearning verification, i.e., ModelGiF can distinguish the models trained with and without the data points that is requested to be unlearned." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 346, + 287, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 346, + 287, + 647 + ], + "spans": [ + { + "bbox": [ + 46, + 346, + 287, + 647 + ], + "type": "text", + "content": "Experimental Setup. Following the experimental settings of [22], we training four classifiers to evaluate ModelGiF for model unlearning verification. The first classifier is called the reference classifier " + }, + { + "bbox": [ + 46, + 346, + 287, + 647 + ], + "type": "inline_equation", + "content": "C_{ref}^{(t)}" + }, + { + "bbox": [ + 46, + 346, + 287, + 647 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 346, + 287, + 647 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 346, + 287, + 647 + ], + "type": "text", + "content": " denotes that the classifier is obtained after " + }, + { + "bbox": [ + 46, + 346, + 287, + 647 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 346, + 287, + 647 + ], + "type": "text", + "content": " epochs training. The reference classifier serves as the original classifier trained on all the training data, including the data points which are requested to be deleted later. The second classifier is called the unrelated classifier, which is another classifier trained on all the training data, but from different initialization. The third classifier is called the exactly unlearned classifier, which is trained on the remaining data after removing the data points requested to be deleted. Note that the exactly unlearned classifier is trained from scratch and has never seen those data points which are requested to be removed, and it thus can be seen as the exactly unlearned classifier [7]. The last classifier is called approximately unlearned classifier, which is obtained by directly optimizing the original reference classifier to remove the knowledge learned from those data points requested to be unlearned [16]. We compare the ModelGiFs of the unrelated classifier, the exactly unlearned classifier and the approximately unlearned classifier to that of the reference classifier. The goal is to test whether the proposed ModelGiF can recognize the exactly unlearned classifier from the unrelated classifier." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "Experimental Details and Results. Experiments are conducted on CIFAR10 and CIFAR100. On CIFAR10, all classifiers are implemented by ResNet20. On CIFAR100, all classifiers are implemented by ResNet50. We randomly sample 128 data points from the training data to be un-" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 235, + 547, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 235, + 547, + 462 + ], + "spans": [ + { + "bbox": [ + 304, + 235, + 547, + 462 + ], + "type": "text", + "content": "learned, and use these data as the reference points to compute the distance between ModelGIFs of these classifiers. Experimental results are provided in Figure 4. It can be seen that with the proposed ModelGiF, exactly unlearned classifier gets significantly higher distance with the reference classifier than the unrelated classifier. It implies that ModelGiF can also be used as a tool to verify the unlearning performance of existing unlearning methods. Another observation from Figure 4 is that the distance between the approximately unlearned classifier and the reference classifier is much lower than unrelated classifier, which implies that existing approximately unlearning methods can not delete the data from the model thoroughly. However, as the training for unlearning continues, the information can be gradually forgotten, as implied by the increasing distance shown in Figure 4. These results also accord with prior finding that continual learning easily lead to catastrophic forgetting problem [35], which validate the rationality of the results from the proposed ModelGiF." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 476, + 471, + 489 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 476, + 471, + 489 + ], + "spans": [ + { + "bbox": [ + 305, + 476, + 471, + 489 + ], + "type": "text", + "content": "5. Conclusion and Future Work" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 498, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 547, + 713 + ], + "type": "text", + "content": "In this work, we propose ModelGiF to quantify model functional distance. The main assumption underlying ModelGiF is that each pre-trained deep model uniquely determines a ModelGiF over the input space. The distance between models can thus be measured by the similarity between their ModelGiFs. We apply the proposed ModelGiF to task relatedness estimation, intellectual property protection, and model unlearning verification. Experimental results demonstrate the versatility of the proposed ModelGiF on these tasks, with significantly superiority performance to state-of-the-art competitors. There are several directions for future work with the proposed ModelGiF. For example, exploring more scenarios where ModelGiF can be applied. Another interesting research direction is proposing more informative reference points to extract stronger representations of ModelGiF. Finally, how to further speed up the computation of the proposed method is also important to make it easier to use." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6132" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 133 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 133 + ], + "type": "text", + "content": "Acknowledgement. This work is funded by the National Key Research and Development Project (Grant No: 2022YFB2703100), National Natural Science Foundation of China (62106220, 61976186, U20B2066), and Ningbo Natural Science Foundation (2021J189)." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 143, + 107, + 156 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 143, + 107, + 156 + ], + "spans": [ + { + "bbox": [ + 48, + 143, + 107, + 156 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 53, + 163, + 289, + 714 + ], + "type": "list", + "angle": 0, + "index": 10, + "blocks": [ + { + "bbox": [ + 53, + 163, + 289, + 236 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 163, + 289, + 236 + ], + "spans": [ + { + "bbox": [ + 53, + 163, + 289, + 236 + ], + "type": "text", + "content": "[1] Alessandro Achille, Michael Lam, Rahul Tewari, Avinash Ravichandran, Subhransu Maji, Charless C Fowlkes, Stefano Soatto, and Pietro Perona. 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In Proceedings of the 2018 on Asia Conference on Computer and Communications Security, pages 159-172, 2018. 3" + } + ] + } + ], + "index": 14 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "6135" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition/dbdfe6ed-ba3c-4daf-ac10-86c2b2f20cde_content_list.json b/2023/Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition/dbdfe6ed-ba3c-4daf-ac10-86c2b2f20cde_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..3c49fc169bf3159fbd396707dbda08b4bdd33272 --- /dev/null +++ b/2023/Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition/dbdfe6ed-ba3c-4daf-ac10-86c2b2f20cde_content_list.json @@ -0,0 +1,1718 @@ +[ + { + "type": "text", + "text": "Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition", + "text_level": 1, + "bbox": [ + 89, + 128, + 880, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yisheng Zhu $^{1}$ , Hu Han $^{2,3}$ , Zhengtao Yu $^{4}$ , Guangcan Liu $^{5*}$", + "bbox": [ + 267, + 202, + 720, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ Nanjing University of Posts and Telecommunications", + "bbox": [ + 276, + 220, + 705, + 238 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{2}$ Key Laboratory of Intelligent Information Processing, Institute of Computing Technology (ICT), Chinese Academy of Sciences (CAS)", + "bbox": [ + 106, + 238, + 875, + 273 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "3University of the Chinese Academy of Sciences", + "bbox": [ + 297, + 273, + 684, + 291 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{4}$ Faculty of Information Engineering and Automation, Kunming University of Science and Technology $^{5}$ School of Automation, Southeast University", + "bbox": [ + 86, + 292, + 895, + 327 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "yszhu1995@163.com, huhan@ict.ac.cn, ztyu@hotmail.com, guangcanliu@seu.edu.cn", + "bbox": [ + 153, + 330, + 828, + 344 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 378, + 313, + 395 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Visual tempo characterizes the dynamics and the temporal evolution, which helps describe actions. Recent approaches directly perform visual tempo prediction on skeleton sequences, which may suffer from insufficient feature representation issue. In this paper, we observe that relative visual tempo is more in line with human intuition, and thus providing more effective supervision signals. Based on this, we propose a novel Relative Visual Tempo Contrastive Learning framework for skeleton action Representation (RVTCLR). Specifically, we design a Relative Visual Tempo Learning (RVTL) task to explore the motion information in intra-video clips, and an Appearance-Consistency (AC) task to learn appearance information simultaneously, resulting in more representative spatiotemporal features. Furthermore, skeleton sequence data is much s-parser than RGB data, making the network learn shortcuts, and overfit to low-level information such as skeleton scales. To learn high-order semantics, we further design a new Distribution-Consistency (DC) branch, containing three components: Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. We term our entire method (RVTCLR with DC) as RVTCLR+. Extensive experiments on NTU RGB+D 60 and NTU RGB+D 120 datasets demonstrate that our RVTCLR+ can achieve competitive results over the state-of-the-art methods. Code is available at https://github.com/Zhuysheng/RVTCLR.", + "bbox": [ + 76, + 412, + 473, + 820 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Basic idea of visual tempo prediction", + "bbox": [ + 506, + 378, + 696, + 391 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3f1f7042a456af3ba0cc80ddda05313d77ca71a14d4cf60d5c348328b9956727.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 506, + 390, + 576, + 470 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/0e24985cd7d38418ceabefc9e3354ccd3d408c67c9bff3dfa1a281b6286f3db7.jpg", + "image_caption": [ + "(a) Top-1 Accuracy on NTU-60 Xsub: 52.7%" + ], + "image_footnote": [], + "bbox": [ + 581, + 390, + 640, + 469 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/c646e7a6a972f68a623ffab8ac0b393eb466da2178188f2e06198156f10725ca.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 640, + 390, + 710, + 469 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/1cd5faa73718ce48ebc5706b482b46e207dd5b479abaa93db4f43c367dfc25b1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 710, + 390, + 841, + 448 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Relative visual tempo learning and appearance-consistency", + "bbox": [ + 506, + 483, + 805, + 494 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/c814ecd2553d52430c42e974aacc1d85b8d1964e7a58e2e64aff2bbd2e72a920.jpg", + "image_caption": [ + "Figure 1. The basic visual tempo prediction is considered a classification task, where the learned model is used to assign tempo labels to individual video clips. We introduce relative visual tempo learning and appearance-consistency based on contrastive learning. It's more human-intuitive for modeling actions. The top-1 accuracy on NTU-60 Xsub benchmark supports our claim." + ], + "image_footnote": [], + "bbox": [ + 506, + 494, + 576, + 613 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/fc6830ffbba93c8d5348d88d85befd97c5bcc101bda8b003908ff93bfb720594.jpg", + "image_caption": [ + "(b) Top-1 Accuracy on NTU-60 Xsub: $73.3\\%$" + ], + "image_footnote": [], + "bbox": [ + 581, + 494, + 640, + 612 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/39a689b6f4003dd70cacd189a3289977ffe464f1dca5178b1f616b1b4acb94cc.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 640, + 494, + 756, + 612 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/57a790439ae4dab23b7504323de97de0e39a93f6ed1a1f4284548357d1a716ff.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 763, + 494, + 864, + 551 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 500, + 738, + 630, + 753 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "As one of the most fundamental topics in video understanding, human action recognition has been widely explored in many real-world scenarios, such as human-computer interaction [22], autonomous driving [30], and so on [34, 17]. Skeleton data provides more abstract and well-structured information with less computation and storage than raw RGB video. It is less susceptible to camera viewpoint changes and background distractions. Thus, skeleton-based action recognition has attracted extensive at", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author. This work was supported in part by the New Generation AI Major Project of Ministry of Science and Technology of China under Grant 2018AAA0102501 and in part by the National Natural Science Foundation of China (NSFC) under Grant U21B2027.", + "bbox": [ + 75, + 849, + 470, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "13913", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "tention [39, 21, 28, 7, 35]. However, most of these methods rely heavily on full supervision. The collection of massive annotations is labor-intensive and time-consuming. Under this circumstance, learning action representations directly from the data in a self-supervised manner has attracted increasing attentions.", + "bbox": [ + 75, + 90, + 470, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Several existing works [11, 38, 41] draw inspiration from video self-supervised learning and directly apply video pretext tasks on skeleton sequences, such as jigsaw puzzle recognition [1, 9] and temporal order prediction [15, 37]. For sequence data, a commonly used technique to model spatiotemporal information is visual tempo prediction [42, 29]. Action visual tempo describes the speed at which actions are performed, which is crucial for distinguishing actions that exhibit similar temporal evolutions (e.g., walking and jogging). The basic idea is shown in the upper part of Figure 1. For each video, clips are sampled at different sampling frequencies to mimic different visual tempos (e.g., $1 \\times$ and $2 \\times$ ), and predictions are made using the backbone network. However, there are limitations in directly applying it to skeleton sequences. People perform actions at their own tempo due to the influence of gender, age, etc. Even at the same tempo, the athlete's walking speed is visibly faster than that of a child in a third-person perspective. Therefore, it's obviously inappropriate to treat tempo prediction as a classification task. Furthermore, this basic strategy mainly focuses on motion information and cannot explicitly encourage the model to explore appearance information that is equally important for recognizing actions. Recently, contrastive learning has shown its great potential in extracting informative features [10, 6] in skeleton-based action recognition. Contrastive learning typically converts the naive classification task to a matching problem and learns an embedding space in which augmentations of same skeleton sequence are kept closer together, while different augmentations are far apart. In this way, the above issues can be alleviated in an elegant way. However, skeleton sequence data is much sparser than RGB data, and applying contrastive learning naively without explicit guidance may lead to model overfitting low-level information such as skeleton scales and angles, while failing to learn high-order semantics, resulting in insufficient feature representation capabilities.", + "bbox": [ + 75, + 185, + 472, + 744 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To this end, we propose RVTCLR: a Relative Visual Tempo Contrastive Learning framework for skeleton action Representation. The basic idea is shown at the bottom of Figure 1. First, we observe that it's intuitively plausible to compare relative visual tempos within videos rather than to predict a specific visual tempo for each video. Specifically, for each video, we sample 3 clips with different visual tempos (e.g., $1 \\times$ , $1 \\times$ , and $2 \\times$ ) to construct the contrastive pairs and train a network to pull the anchor-positive pairs closer while repelling the anchor-negative pairs. Furthermore,", + "bbox": [ + 75, + 750, + 470, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "to make the representations explicitly focus on appearance information, we design another Appearance-Consistency (AC) task. In this task, pairs from the same video are attracted no matter their visual tempos, while pairs from different videos are pushed away. In this way, the learned representations are expected to focus on both skeleton motion and appearance information simultaneously.", + "bbox": [ + 496, + 90, + 890, + 196 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In addition, in order to encourage the models to learn high-order semantics, we introduce a new Distribution-Consistency (DC) branch based on RVTCLR, which contains three components: Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. We refer to this as RVTCLR+. First, we leverage SDA to generate more difficult contrastive pairs by applying more skeleton-specific transformations (e.g., gaussian noise) at the input level, since augmentation plays a key role in learning better representations, as demonstrated by SimCLR [3] and MoCo [8]. However, too much strong augmentations may blur the joint connections compared to the normal augmented sequence (i.e., crop and shear), resulting in performance degradation. Benefiting from recent attention mechanisms [5, 13, 44], we try to emphasize these connections by designing a novel module, FSEM, which contains an Intra-Inter-Part block (IIPB) for local spatial modeling and a Non-local block (NLB) [32] for global spatiotemporal modeling. Finally, inspired by [33, 6], we introduce a DD loss to minimize the distributional divergence between the normal augmented view and our DC branch. By combining these components, we hope that the DC branch can better learn local and global spatiotemporal features, which help to extract discriminative high-order semantics.", + "bbox": [ + 496, + 198, + 892, + 573 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To sum up, the contributions of this work include: (1) We propose a novel contrastive representation learning framework named RVTCLR. The proposed RVTCLR leverages Relative Visual Tempo Learning (RVTL) task to learn better skeleton motion information. By combining another Appearance-Consistency (AC) task, our model explicitly learns to concentrate on skeleton appearance information simultaneously. (2) To encourage models to focus on high-order semantics, we propose RVTCLR+ by introducing a new Distribution-Consistency (DC) branch. This DC branch contains three components: Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. (3) These contrastive tasks are jointly trained using a two-branch structure such that the models can learn both spatiotemporal and high-order semantics simultaneously.", + "bbox": [ + 496, + 575, + 893, + 818 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 830, + 640, + 845 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Self-supervised skeleton-based action recognition. To meet the requirements of real-time recognition, it's necessary for the models to be able to directly extract dis", + "bbox": [ + 498, + 854, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "13914", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "criminative action representations from the label-free online videos. Recent progress in self-supervised skeleton-based action recognition can be summarized into two categories: pretext-task based learning [11, 38, 41, 43, 23] and contrastive learning [18, 10, 6, 25, 31, 24]. For example, Zheng et al. [43] design a skeleton inpainting architecture to learn the long-term dynamics. Lin et al. [11] integrate multiple tasks such as jigsaw puzzle recognition to learn more general skeleton features. Xu et al. [38] propose reverse sequential predictions based on encoder-decoder structure to extract motion pattern. However, the representations learned by these methods may not be good enough, in the sense that they could be exclusively particular to the pre-designed tasks. Inspired by the success of contrastive learning in image classification (e.g., instance discrimination [36], SimCLR [3], and MoCo [8]), Rao et al. [18] first propose to perform contrastive learning among different augmentations of unlabeled skeleton data, to learn inherent action patterns. Thoker et al. [25] propose to generate contrastive pairs based on different input-representations of the skeleton sequences, i.e., graph, sequence, and image representation. By leveraging multiple views of the skeleton data, i.e., joint, bone, and motion, Li et al. [10] introduce SkeletonCLR and CrosSCLR to perform the single-view and cross-view contrastive learning. Guo et al. [6] further propose AimCLR to learn from extremely augmented skeleton sequences.", + "bbox": [ + 76, + 90, + 472, + 484 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Nevertheless, none of the aforementioned methods concentrate on visual tempo, which is crucial for characterizing human action dynamics. To our best knowledge, Su et al. [24] propose motion consistency and continuity learning, which has overlap with our framework. However, the differences are obvious, which mainly lie in three aspects: (1) contrastive pairs are generated differently. In [24], speed-changed clips are considered as positive pairs, while we focus on relative visual tempo and regard these clips as negative pairs. (2) appearance information is modeled differently. In [24], appearance information is implicitly modeled in the contrastive learning process, while we design another Appearance-Consistency (AC) task specifically for spatial modeling. (3) learned features are enhanced differently. In [24], learned features are enhanced by designing a self-reconstruction based motion continuity module, while we introduce a novel Distribution-Consistency (DC) branch to guide the models focus on high-order semantics.", + "bbox": [ + 76, + 488, + 472, + 760 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Visual tempo modeling. Visual tempo describes the speed of human movements, which has already been applied into various action recognition methods [4, 40, 14]. For example, Feichtenhofer et al. [4] first propose SlowFast network to explore the potential of different visual tempos. It consists of two pathways, operating at different frame rates, to capture both spatial semantics and motion dynamics. When it comes to video self-supervised learning [42, 29, 2], the potential of visual tempo in motion mod", + "bbox": [ + 76, + 763, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "eling is further verified. Yao et al. [42] utilize video playback rates as self-supervision signals and propose playback rate perception to learn spatiotemporal features in a collaborative discrimination-generation manner. The above methods usually require assigning visual tempos to each video clip according to different sampling rates, and then elaborate learning paradigms through reconstruction or prediction, but this is suboptimal in learning discriminative representations. Chen et al. [2] argue that relative speed is more in line with motion pattern. They propose a new video self-supervised learning framework (called RSPNet) to leverage the relative speed between two video clips to supervise the representation learning. Inspired by RSPNet, the proposed RVTCLR focuses on relative visual tempo learning with skeleton-specific modifications.", + "bbox": [ + 496, + 90, + 893, + 318 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methods", + "text_level": 1, + "bbox": [ + 500, + 329, + 599, + 345 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Preliminaries", + "text_level": 1, + "bbox": [ + 500, + 354, + 640, + 369 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "SkeletonCLR. SkeletonCLR [10] utilizes ST-GCN [39] as its backbone and follows the practice in MoCo [8] to learn skeleton action representations. Suppose that a skeleton sequence $s = (s^1, s^2, \\ldots, s^T)$ contains $T$ consecutive skeleton frames, where $s^i \\in \\mathbb{R}^{3 \\times V \\times M}$ means 3D coordinates of $V$ joints for $M$ actors. A data augmentation module $\\mathcal{T}$ is first utilized to randomly transform the given $s$ into different augmentations $x_q$ and $x_k$ . Then, a query encoder $f(\\cdot; \\theta_q)$ and a momentum updated key encoder $f(\\cdot; \\theta_k)$ are leveraged to encode $x_q$ and $x_k$ into hidden space $h_q$ and $h_k$ . These embeddings are further passed through a projector $g(\\cdot; \\theta_q)$ and its momentum updated version $g(\\cdot; \\theta_k)$ to get the final query features $q$ and key features $k$ . In each training step, samples in the queue $\\mathbf{Q} = \\{m_o\\}_{o=1}^K$ are progressively replaced by the key features $k$ following a first-in-first-out scheme. Following MoCo, $q$ and $k$ serve as positive pairs while $q$ and embeddings in $\\mathbf{Q}$ serve as negative pairs. The InfoNCE loss [36] is used to guide the network learning, which can be formulated as:", + "bbox": [ + 496, + 377, + 893, + 665 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {I n f o} = - \\log \\frac {\\exp (q \\cdot k / \\tau)}{\\exp (q \\cdot k / \\tau) + \\sum_ {o = 1} ^ {K} \\exp (q \\cdot m _ {o} / \\tau)} (1)\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 672, + 890, + 710 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\tau$ is the temperature hyper-parameter, and $\\cdot$ represents the similarity measured by dot product.", + "bbox": [ + 496, + 715, + 890, + 744 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "After computing the InfoNCE loss, the parameters of $\\theta_{q}$ are updated by gradient back-propagation while the parameters of $\\theta_{k}$ are updated as their moving-average:", + "bbox": [ + 496, + 746, + 890, + 792 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\theta_ {k} \\leftarrow \\alpha \\theta_ {k} + (1 - \\alpha) \\theta_ {q} \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 614, + 800, + 890, + 816 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\alpha$ is a momentum coefficient (set to 0.999 by default).", + "bbox": [ + 496, + 825, + 890, + 840 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Nearest Neighbors Mining. Traditional InfoNCE regards all samples in the memory bank as negative. This overly hard approach may lead to non-generic feature embeddings. To address the above issue, [10, 6] propose", + "bbox": [ + 496, + 840, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "13915", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/4c30ef37b7ae45b07a21750cf0b57165bfa3883a7813b02c47a250bf2dca3517.jpg", + "image_caption": [ + "Figure 2. The pipeline of our method. For each skeleton sequence, we sample clips with varying visual tempos. Then, we use a two-branch structure to extract discriminative feature from each sequence. Specifically, in RVTCLR, the Relative Visual Tempo Learning (RVTL) is responsible for modeling motion dynamics. The Appearance-Consistency (AC) is responsible for modeling appearance characteristics. These two tasks are combined into one branch to achieve a more comprehensive spatial-temporal representation. In another Distribution-Consistency (DC) branch, we introduce Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss to guide the network to concentrate on extracting high-order semantics." + ], + "image_footnote": [], + "bbox": [ + 161, + 88, + 810, + 354 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "to leverage Nearest Neighbors Mining (NNM) to generate more positive pairs:", + "bbox": [ + 75, + 465, + 468, + 497 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {N N M} = - \\log \\frac {\\exp (q \\cdot k / \\tau) + \\sum_ {o \\in N _ {+}} \\exp (q \\cdot m _ {o} / \\tau)}{\\exp (q \\cdot k / \\tau) + \\sum_ {o = 1} ^ {K} \\exp (q \\cdot m _ {o} / \\tau)} \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 83, + 508, + 468, + 558 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $N_{+}$ represents the top- $N$ nearest neighbors that are most similar to the query features $q$ in the memory queue.", + "bbox": [ + 76, + 560, + 468, + 590 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Since the model learned in the early training stages may not be strong enough to provide confident nearest neighbors, [10, 6] propose to perform a two-stage training, i.e., first train the model using Equation 1, and then train the model to mine the nearest neighbors using Equation 3.", + "bbox": [ + 75, + 590, + 468, + 666 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this paper, we mainly implement our method based on SkeletonCLR and two-stage training strategy.", + "bbox": [ + 76, + 667, + 468, + 699 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2.RVTCLR", + "text_level": 1, + "bbox": [ + 76, + 709, + 191, + 724 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Relative Visual Tempo Learning (RVTL). Observing that each person performs actions at his/her own visual tempo, we introduce a RVTL task, which aims to learn better skeleton motion information. Specifically, given a skeleton sequence $s$ with $T$ frames, we first sample 3 clips $c_{i}$ , $c_{j}$ and $c_{k}$ with visual tempos $v_{i}$ , $v_{j}$ and $v_{k}$ , respectively, where $v_{i} = v_{j} \\neq v_{k}$ . Note that visual tempos can be set arbitrarily, i.e., $\\{1 \\times, 2 \\times, 3 \\times,..\\}$ . However, to avoid the temporal ambiguity in skeleton sequences, we only consider $1 \\times$ and $2 \\times$ , which represent that the sampling interval is set to 1 and 2 frames. We sample from the first frame and keep", + "bbox": [ + 75, + 734, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "a duration of $T / 2$ for each clip. Then, we apply normal skeleton augmentations $\\mathcal{T}$ on these three clips respectively to construct a triplet, i.e., anchor $a = \\mathcal{T}(c_i)$ , positive $p = \\mathcal{T}(c_j)$ and negative $n = \\mathcal{T}(c_k)$ . This triplet is further fed into SkeletonCLR with a projection head $g_{r}(\\cdot ;\\theta_{q_{r}})$ and its momentum updated $g_{r}(\\cdot ;\\theta_{k_{r}})$ to generate the encoded features $(q_{a},k_{p},k_{n})$ . Finally, these features are normalized and combined as anchor-positive pairs $(q_{a},k_{p})$ and anchor-negative pairs $(q_{a},k_{n})$ , and our goal is to pull $(q_{a},k_{p})$ closer while pushing $(q_{a},k_{n})$ away. The assumption here is that the network can only succeed in such a RVTL task if it understands the intrinsic visual tempo of each clip and learns discriminative motion information. This task is realized by a triplet loss [19]:", + "bbox": [ + 496, + 465, + 893, + 679 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {R V T L} = \\max \\left\\{- \\left(q _ {a} \\cdot k _ {p} - q _ {a} \\cdot k _ {n}\\right) + \\operatorname {m a r g i n}, 0 \\right\\} \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 511, + 690, + 890, + 708 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where the margin (set to 1 by default) is a hyper-parameter to control the distance between two components.", + "bbox": [ + 496, + 719, + 890, + 748 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Appearance-Consistency (AC). Appearance information is also essential for recognizing actions. To this end, we introduce another AC task to explicitly learn such information. Specifically, given a skeleton sequence, we first sample two clips $c_{i}$ , $c_{j}$ with visual tempos randomly selected in $\\{1\\times ,2\\times \\}$ . Then, they are normally augmented and sent to SkeletonCLR with another projection head $g_{a}(\\cdot ;\\theta_{q_{a}})$ and its momentum updated $g_{a}(\\cdot ;\\theta_{k_{a}})$ to generate the encoded features $(q_{i},k_{j})$ . Note that the query and key encoders in AC share weights with the encoders in RVTL while the", + "bbox": [ + 496, + 750, + 893, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "13916", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "projection heads $g_{a}(\\cdot;\\theta_{q_{a}})$ and $g_{a}(\\cdot;\\theta_{k_{a}})$ have weights independent of $g_{r}(\\cdot;\\theta_{q_{r}})$ and $g_{r}(\\cdot;\\theta_{k_{r}})$ . Here, the goal is to pull $q_{i}$ and $k_{j}$ closer while pushing away $q_{i}$ and negative samples in queue $\\mathbf{Q}$ . Although from the same sample, clips with various visual tempos show different temporal motion dynamics, by pulling such a pair closer while pushing away different samples, we want the model to explicitly focus on appearance information. This task is realized by the InfoNCE loss:", + "bbox": [ + 75, + 90, + 472, + 224 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {A C} = - \\log \\frac {\\exp \\left(q _ {i} \\cdot k _ {j} / \\tau\\right)}{\\exp \\left(q _ {i} \\cdot k _ {j} / \\tau\\right) + \\sum_ {o = 1} ^ {K} \\exp \\left(q _ {i} \\cdot m _ {o} / \\tau\\right)} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 236, + 468, + 284 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Based on SkeletonCLR, we jointly train these tasks. In the first training stage, we train the model with the loss function: $\\mathcal{L}_1 = \\lambda_1\\mathcal{L}_{RVTL} + \\lambda_2\\mathcal{L}_{AC}$ , and then in the second training stage, we try to obtain more positive samples by using $\\mathcal{L}_2 = \\lambda_1\\mathcal{L}_{RVTL} + \\lambda_2\\mathcal{L}_{AC'}$ , where $\\lambda$ (set to 1 by default) is the coefficient to balance the loss and $\\mathcal{L}_{AC'}$ is defined in Equation 3.", + "bbox": [ + 75, + 285, + 472, + 391 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/dfbf49ac5609bbeff85a355dfa5ceb80cf82cf47aeff78ac9a6a348926400428.jpg", + "image_caption": [ + "Figure 3. Illustration of FSEM. (a) The workflow of FSEM. (b) IIPB is responsible for local spatial modeling, containing intra-part and inter-part relational reasoning submodules. (c) NLB is responsible for global spatial-temporal modeling." + ], + "image_footnote": [], + "bbox": [ + 81, + 407, + 486, + 579 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3.RVTCLR+", + "text_level": 1, + "bbox": [ + 76, + 664, + 199, + 679 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The success of contrastive learning depends on the construction of contrastive pairs and the difficulty of learning paradigm. Given that the skeleton sequences are much s-sparser, naive contrastive learning may risk overfitting low-level information such as skeleton scales. It would be even better if we could design a new branch to explicitly learn skeleton high-order semantics. We thus propose RVTCLR+ by designing our Distribution-Consistency (DC).", + "bbox": [ + 75, + 688, + 468, + 808 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "SDA. We leverage SDA to generate more difficult contrastive pairs. The SDA contains normal augmentations $\\mathcal{T}$ : crop and shear, and additional strong augmentations $\\mathcal{T}'$ : gaussian noise, gaussian blur, and channel mask. Given a skeleton sequence $s$ , we apply $\\mathcal{T}$ and $\\mathcal{T}'$ to get the transformed version: $e = \\mathcal{T}'(\\mathcal{T}(s))$ . Afterwards, we send it", + "bbox": [ + 75, + 810, + 470, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "to the weight-sharing query encoder to encode $e$ into hidden space $h_e$ , which is further passed through a projector $g_e(\\cdot; \\theta_{q_e})$ to obtain the final embeddings $q_e$ .", + "bbox": [ + 496, + 90, + 890, + 136 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "FSEM. Such a direct modeling method may be suboptimal, since the additional augmentations may cause blurred joint connections. Considering that skeleton sequences are spatiotemporal cubes, we design FSEM to highlight these connections. As shown in Figure 3, our FSEM contains an Intra-Inter-Part block (IIPB), which is responsible for local spatial modeling, and a Non-local block (NLB), which is responsible for global spatial-temporal modeling. Given the encoded $h_e \\in \\mathbb{R}^{C \\times T \\times V}$ , in IIPB, we first divide each human skeleton into 5 parts according to the physical topology of the body. Then, average pooling is applied on each part to generate the intra-part representations $h_{e'} \\in \\mathbb{R}^{C \\times T \\times 5}$ . Two $1 \\times 1$ convolution layers are further utilized to establish the inter-part relations:", + "bbox": [ + 496, + 137, + 892, + 347 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nh _ {\\hat {e}} = \\operatorname {C o n v 2} \\left(\\operatorname {R e L U} \\left(\\operatorname {C o n v 1} \\left(h _ {e ^ {\\prime}}, W _ {1}\\right)\\right), W _ {2}\\right) \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 544, + 359, + 890, + 377 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $W_{1} \\in \\mathbb{R}^{\\frac{C}{2} \\times C}$ and $W_{2} \\in \\mathbb{R}^{C \\times \\frac{C}{2}}$ are learnable parameters. $ReLU$ is the activation function. The intuition here is that connections between body parts can sometimes better describe actions (e.g., the coordination of arm and leg in 'running'). By using IIPB, we establish the part-based connections that seek to mitigate the effects of blurred joints.", + "bbox": [ + 496, + 388, + 890, + 479 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "IIPB can capture the local dependencies of intra-frame parts. However, global inter-frame connections are ignored, which are also essential for describing actions. We introduce NLB to associate all possible frames of a skeleton sequence in a self-attention mechanism [27]. The non-local operation computes frame dependencies by enumerating all possible frames:", + "bbox": [ + 496, + 481, + 890, + 585 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\ny ^ {t} = \\frac {1}{\\mathcal {C} \\left(h _ {\\hat {e}}\\right)} \\sum_ {\\forall t ^ {\\prime}} f \\left(h _ {\\hat {e}} ^ {t}, h _ {\\hat {e}} ^ {t ^ {\\prime}}\\right) g \\left(h _ {\\hat {e}} ^ {t ^ {\\prime}}\\right) \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 573, + 597, + 890, + 633 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $h_{\\hat{e}}^{t}$ and $h_{\\hat{e}}^{t'}$ denote the input at frame $t$ and $t'$ , respectively. $g(\\cdot)$ is a linear function. $\\mathcal{C}(\\cdot)$ is a normalization term. An embedded gaussian function $f(\\cdot, \\cdot)$ [32] computes the relationships between $t$ and all $t'$ . We wrap the non-local operation in Equation 7 into NLB with a residual layer as:", + "bbox": [ + 496, + 646, + 890, + 723 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nh _ {\\tilde {e}} = W _ {3} y + h _ {\\hat {e}} \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 638, + 736, + 890, + 752 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $W_{3}$ is a learnable embedding for $y$ . Finally, we send it to the projector to generate the new embeddings $q_{\\widetilde{e}}$ . Note that FSEM can be plugged into different GCN layers, we only insert the FSEM before the projector for the reduction of experiment cost.", + "bbox": [ + 496, + 763, + 890, + 839 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "DD Loss. The distributional divergence between weakly augmented counterparts and strongly augmented views enables the framework to explore novel patterns, which may help extract representative high-level features. Formally,", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "13917", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "given the encoded query features $q_{a}$ , the encoded key features $k_{p}$ , and the memory queue $\\mathbf{Q} = \\{m_{o}\\}_{o=1}^{K}$ , we can obtain a conditional distribution:", + "bbox": [ + 75, + 90, + 468, + 135 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\np \\left(k _ {p} \\mid q _ {a}\\right) = \\frac {\\exp \\left(q _ {a} \\cdot k _ {p} / \\tau\\right)}{\\exp \\left(q _ {a} \\cdot k _ {p} / \\tau\\right) + \\sum_ {o = 1} ^ {K} \\exp \\left(q _ {a} \\cdot m _ {o} / \\tau\\right)} (9)\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 142, + 468, + 179 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "which encodes the likelihood of the query $q_{a}$ being assigned to the key $k_{p}$ . By replacing $k_{p}$ with $m_{o}$ , we can also obtain the likelihood that the query $q_{a}$ is assigned to the negative embeddings in $\\mathbf{Q}$ . Then, the InfoNCE loss in Equation 1 can be rewritten as:", + "bbox": [ + 75, + 186, + 468, + 261 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {I n f o}} = - q \\left(k _ {p} \\mid q _ {a}\\right) \\log p \\left(k _ {p} \\mid q _ {a}\\right) - \\sum_ {o = 1} ^ {K} q \\left(m _ {o} \\mid q _ {a}\\right) \\log p \\left(m _ {o} \\mid q _ {a}\\right) \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 268, + 495, + 321 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $q(\\cdot|\\cdot)$ is the ideal distribution of the likelihood, $p(k_p|q_a)$ is the distribution learned by network. In InfoNCE, $q(k_p|q_a)$ and $q(m_o|q_a)$ are simply set to 1 and 0 based on one-hot distribution, respectively. When applied to $q_{\\widetilde{e}}$ , a straightforward approach is to directly replace $q_a$ in Equation 10 with $q_{\\widetilde{e}}$ . However, as demonstrated in [33, 6], the one-hot distribution cannot mimic the ideal distribution and thus cannot help representations learning any more. Conversely, the similarity distribution of weakly-augmented queries for the same instance in a queue can provide useful clues for strong-augmentation based learning. This inspires us to leverage $p(k_p|q_a)$ and $p(m_o|q_a)$ as the ideal distribution to supervise $q_{\\widetilde{e}}$ :", + "bbox": [ + 75, + 321, + 468, + 518 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {L} _ {D C} = - p \\left(k _ {p} \\mid q _ {a}\\right) \\log p \\left(k _ {p} \\mid q _ {\\bar {e}}\\right) \\\\ - \\sum_ {o = 1} ^ {K} p \\left(m _ {o} \\mid q _ {a}\\right) \\log p \\left(m _ {o} \\mid q _ {\\tilde {e}}\\right) \\tag {11} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 101, + 527, + 468, + 589 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "By combining DC, the final loss our RVTCLR+ can be formulated as $\\mathcal{L}_1 = \\lambda_1\\mathcal{L}_{RVTL} + \\lambda_2\\mathcal{L}_{AC} + \\lambda_3\\mathcal{L}_{DC}$ and $\\mathcal{L}_2 = \\lambda_1\\mathcal{L}_{RVTL} + \\lambda_2\\mathcal{L}_{AC'} + \\lambda_3\\mathcal{L}_{DC}$ .", + "bbox": [ + 76, + 598, + 468, + 643 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 656, + 209, + 672 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Datasets", + "text_level": 1, + "bbox": [ + 76, + 681, + 179, + 695 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "NTU RGB+D 60 Dataset [20]: It contains 56880 skeleton video clips over 60 action classes capture from 40 subjects and 3 different camera view angles. Each clip provides 25 body joints with 3D coordinates for at most 2 subjects. There are two evaluation benchmarks: cross-subject (Xsub) and cross-view (Xview). In Xsub, clips of 20 subjects are used for training, and the rest are used for testing. In Xview, clips of camera 2 and 3 are used for training, and clips of camera 1 are used for testing.", + "bbox": [ + 75, + 703, + 468, + 839 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "NTU RGB+D 120 Dataset [12]: It is an extension of N-TU RGB+D 60 with 113945 samples over 120 classes capture from 106 subjects and 32 different camera setups. Two evaluation benchmarks are recommended: cross-subject", + "bbox": [ + 75, + 839, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "(Xsub) and cross-setup (Xset). In Xsub, clips of 53 subjects are used for training, and the rest are used for testing. In Xset, clips of even camera IDs are used for training, and clips of odd IDs are used for testing.", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Implementation Details", + "text_level": 1, + "bbox": [ + 498, + 162, + 718, + 178 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For data pre-processing, we follow CrosCLR [10] and AimCLR [6] except for that we resize the length of skeleton sequences to 100 frames, rather than 50 frames (Actually, by $2\\times$ temporal sampling, we also maintain 50 frames for each clip). The mini-batch size is set to 128.", + "bbox": [ + 496, + 185, + 890, + 260 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Data Augmentation. For skeleton sequences, shear and crop are used as the normal augmentations $\\mathcal{T}$ . For strong augmentations $\\mathcal{T}'$ , we mainly use gaussian noise, gaussian blur, and channel mask. Since [18, 6] use more augmentations, we test if these augmentations (spatial flip, temporal flip, rotate) work in our approach.", + "bbox": [ + 496, + 261, + 890, + 351 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Self-supervised Pre-training. The baseline is Skeleton-CLR which follows the MoCo [8] framework. The queue size $\\mathbf{Q}$ and temperature $\\tau$ are set to 32768 and 0.07, respectively. For the backbone, we adopt ST-GCN [39], but the number of channels in each layer is reduced to $1/4$ of the original settings. For the optimizer, we use SGD with momentum 0.9 and weight decay 0.0001. The pre-training runs 300 epochs with the initial learning rate 0.1 and multiplied by 0.1 at 250 epochs. For the two-stage training strategy, we train 150 epochs with the loss function $\\mathcal{L}_1$ , and another 150 epochs with $\\mathcal{L}_2$ . In the second training stage, nearest neighbors $N$ is set to 1.", + "bbox": [ + 496, + 352, + 890, + 532 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Linear Evaluation Protocol. We add a linear classifier after the pre-trained encoder. During the linear evaluation, we freeze the parameters in encoder and only train the parameters in linear classifier. We use SGD with momentum 0.9. The model runs 100 epochs with the initial learning rate 3.0 and decayed by 10 at 80 epochs.", + "bbox": [ + 496, + 532, + 890, + 623 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Finetune Protocol. We add a linear classifier after the pre-trained encoder. During the finetune, we train the whole model with SGD optimizer, the momentum is set to 0.9 and the weight decay is set to 0.0001. The model runs 100 epochs with the initial learning rate 0.01 and decayed by 10 at 80 epochs.", + "bbox": [ + 496, + 625, + 890, + 714 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Semi-supervised Evaluation Protocol. We add a linear classifier after the pre-trained encoder. During the semi-supervised evaluation, we train the whole model with only $1\\%$ or $10\\%$ randomly selected labeled data. We choose SGD optimizer with momentum 0.9 and weight decay 0.0001. The model runs 100 epochs with the initial learning rate 0.01 and decayed by 10 at 80 epochs.", + "bbox": [ + 496, + 715, + 890, + 821 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 830, + 653, + 847 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Tempo Prediction or RVTCLR. We first compare RVTCLR with the tempo prediction. Table 1 shows the comparison results of the joint stream on the NTU RGB+D 60", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "13918", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "dataset using the linear evaluation protocol. It is obviously found that tempo prediction cannot bring good performance compared to RVTL, which verifies our claim that predicting each video's specific visual tempo results in unreasonable action features. The outcome of AC demonstrates that explicit consideration of apparent information also plays an important role in modeling actions. AC+RVTL's performance proves that relative visual tempo and appearance modeling can work collaboratively to better concentrate on both skeleton motion and appearance clues. By further combining NNM, the performance of RVTCLR boosts to $74.4\\%$ (79.4%) on Xsub (Xview) benchmark, surpassing the tempo prediction by a large margin.", + "bbox": [ + 75, + 90, + 472, + 287 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d59f1d1364388ab5cb8dc9b64fcf697b08917452966e22540c852acd5691cde3.jpg", + "table_caption": [ + "Table 1. Comparisons between Tempo Prediction and RVTCLR. We report linear evaluation results of the joint stream on the NTU-60 dataset." + ], + "table_footnote": [], + "table_body": "
MethodsNTU-60
XsubXview
Tempo prediction52.758.0
RVTL63.173.4
AC65.168.4
AC+RVTL73.377.8
AC+RVTL+NNM74.479.4
", + "bbox": [ + 163, + 340, + 383, + 428 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Effectiveness of RVTCLR+. We then verify the effectiveness of RVTCLR+. Table 2 shows the comparison results of three streams. From the table, we have several observations: (1) RVTCLR performs much better than SkeletonCLR in most cases. For example, we can obtain $+4.2\\%$ $(+9.2\\%)$ performance gain on Xsub (Xview) in the motion stream. By further combining DC branch, our RVTCLR+ can still significantly improve the accuracy by $+13.3\\%$ and $+12\\%$ , respectively, which shows the efficacy of our method. (2) DC plays a more important role in the motion and bone streams. The primary reason we believe is due to the inherent presence of higher-order semantics in these two streams. The sparsity of skeleton data, however, may hinder the ability of naive contrastive learning to fully release their potential. As a result, recognition success may be limited to relying solely on low-level information. Our DC, however, force the model to focus on high-level semantics, thereby enabling the learning of more discriminative representations. (3) our 2-stream and 3-stream fusion results are always better than the comparative counterparts.", + "bbox": [ + 75, + 445, + 472, + 748 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We also conduct experiments in the motion stream to validate the effect of DC. As shown in Table 3 (a), we first determine whether all augmentations mentioned in [18, 6] applicable to SDA. Compared to the normal augmentation, we can find that gaussian noise, gaussian blur, and channel mask work well on both benchmarks. Although the others may perform better on Xsub, their results on Xview are relatively poor. Through empirical experimentation, we determine the former three augmentations as our best choice, yielding $+12.7\\%$ and $+11.4\\%$ accuracy increases over using", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/807eec3a5544d85bb9f88bb3fd4e365d282245d559997152974fb2707ee1a3f3.jpg", + "table_caption": [ + "Table 2. Linear evaluation compared with SkeletonCLR. '2s' and '3s' means two-stream and three-stream fusion, respectively." + ], + "table_footnote": [], + "table_body": "
MethodsDCStreamNTU-60
XsubXview
SkeletonCLRjoint68.376.4
RVTCLRjoint74.479.4
RVTCLR+✓joint74.779.1
SkeletonCLRmotion53.350.8
RVTCLRmotion57.560.0
RVTCLR+✓motion70.872.0
SkeletonCLRbone69.467.4
RVTCLRbone68.171.7
RVTCLR+✓bone72.278.4
2s-SkeletonCLRjoint+motion70.577.9
2s-RVTCLRjoint+motion75.781.6
2s-RVTCLR+✓joint+motion77.882.2
3s-SkeletonCLRjoint+motion+bone75.079.8
3s-RVTCLRjoint+motion+bone77.282.0
3s-RVTCLR+✓joint+motion+bone79.784.6
", + "bbox": [ + 509, + 114, + 883, + 323 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "the normal augmentation.", + "bbox": [ + 498, + 349, + 671, + 364 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "FSEM is designed to emphasize the blurred joint connections. As shown in Table 3 (b), IIPB brings $+3.3\\%$ performance improvement on Xview, proving its ability to adeptly capture the local spatial features. The accuracies of NLB are $70.0\\%$ and $70.7\\%$ , respectively, which demonstrate that constructing global dependencies among frames can achieve a more representative feature extraction. By combining these two blocks, the performance of our final FSEM further boots to $70.8\\%$ and $72.0\\%$ .", + "bbox": [ + 496, + 364, + 890, + 500 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "DD loss is introduced to help learn more representative high-level features. From the Table 3 (b), we can see a large performance drop when we replace the DD loss with the original one. This suggests that compared to the one-hot distribution, the weakly augmented view provides more suitable supervision signals.", + "bbox": [ + 496, + 502, + 890, + 594 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/a4c9701478d451764c7a9b309c8118e4a17474f525f21308763cecadbdc30c1c.jpg", + "table_caption": [ + "Table 3. Comparisons of DC's each component. We report linear evaluation results of the motion stream on the NTU-60 dataset." + ], + "table_footnote": [], + "table_body": "
SDANTU-60
XsubXview
Normal55.258.2
Gaussian noise66.872.6
Gaussian blur56.259.4
Channel mask57.358.6
Rotate55.557.1
Spatial flip57.656.1
Temporal flip59.455.9
Best Combination67.969.6
", + "bbox": [ + 521, + 642, + 710, + 767 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/5d4a7fee1e3e10b9071fc9cf452cdae31708cd9c4250ab9c4eccea7ae885e0ad.jpg", + "table_caption": [ + "(a) SDA" + ], + "table_footnote": [], + "table_body": "
FSEMNTU-60
XsubXview
-67.969.6
IIPB68.072.9
NLB70.070.7
IIPB+NLB70.872.0
DD lossNTU-60
XsubXview
✓70.872.0
-64.663.6
", + "bbox": [ + 714, + 642, + 867, + 770 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "(b) FSEM and DD loss", + "bbox": [ + 727, + 773, + 854, + 786 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Performance Comparison", + "text_level": 1, + "bbox": [ + 500, + 816, + 735, + 832 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Linear Evaluation. Table 4 and Table 5 show the comparisons on NTU-60 and NTU-120 under linear evaluation protocol. From the Table 4, we observe that our joint-stream RVTCLR+ achieves competitive results compared to the", + "bbox": [ + 496, + 839, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "13919", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "most recent SkeletonCLR [10] and AimCLR [6]. For example, $74.7\\%$ vs $74.3\\%$ on Xsub when compared to AimCLR. When multiple streams are fused, the performance of our method can be further improved. From the Table 5, we find that the performance of our 3s-RVTCLR+ remains at the forefront.", + "bbox": [ + 75, + 90, + 470, + 180 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Finetune Evaluation. Table 6 shows the comparisons on NTU-60 and NTU-120 under fineture evaluation protocol. The table reveals that our single-stream RVTCLR+ achieves $0.8\\% \\sim 2.1\\%$ improvement over AimCLR on both datasets. Notably, 3s-ST-GCN [39] is pretrained under full supervision, and its performance is the ensemble of multi-streams, compared to it, our single-stream RVTCLR+ can still get comparable performance. When combining different streams, the accuracy of our 3s-RVTCLR+ can be further increased by $2.6\\% \\sim 5\\%$ , greatly outperforming AimCLR.", + "bbox": [ + 75, + 181, + 473, + 347 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/163b3f2e7a19b3cdc73fd9d4528a1d9676150f445b9b13d2d8ebb6766601865f.jpg", + "table_caption": [ + "Table 4. Linear evaluation results on NTU-60 dataset." + ], + "table_footnote": [], + "table_body": "
MethodsNTU-60
XsubXview
Single-stream
LongT GAN [43]39.148.1
P&C [23]50.776.3
MS2L [11]52.6-
PCRP [38]54.963.4
AS-CAL [18]58.564.8
CRRL [31]67.673.8
SeBiReNet [16]-79.7
SkeletonCLR [10]68.376.4
AimCLR [6]74.379.7
RVTCLR+ (ours)74.779.1
Three-stream
3s-SkeletonCLR [10]75.079.8
3s-Colorization [41]75.283.1
3s-CrosSCLR [10]77.883.4
3s-AimCLR [6]78.983.8
3s-RVTCLR+ (Ours)79.784.6
", + "bbox": [ + 151, + 369, + 395, + 598 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/b70ef8c521b899036dcbd67e83d7c8c27ea67d6e943f0e5fda42cf6282c550f8.jpg", + "table_caption": [ + "Table 5. Linear evaluation results on NTU-120 dataset." + ], + "table_footnote": [], + "table_body": "
MethodsNTU-120
XsubXset
P&C [23]42.741.7
PCRP [38]43.044.6
AS-CAL [18]48.649.2
CRRL [31]56.257.0
ISC [25]67.967.1
3s-CrosSCLR [10]67.966.7
3s-AimCLR [6]68.268.8
3s-RVTCLR+ (Ours)68.068.9
", + "bbox": [ + 156, + 625, + 388, + 747 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Semi-supervised Evaluation. As shown in Table 7, with only $1\\%$ and $10\\%$ labeled data, the results of our 3s-RVTCLR+ far exceed MCC [24], 3s-CrosCLR [10], and 3s-AimCLR. For example, 3s-RVTCLR+ increases the accuracies by $2.5\\%$ and $4.6\\%$ compared with 3s-AimCLR on NTU-120 dataset. These results suggest that the representational capacity of our learned features is considerable.", + "bbox": [ + 75, + 763, + 468, + 869 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Qualitative Results. We apply t-SNE [26] with fixed settings to show the embedding distribution of Skeleton-", + "bbox": [ + 76, + 869, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/75db2dcdc5259ba80f3f318031b8697ba6d561e6f8175dfe8b19159e61476690.jpg", + "table_caption": [ + "Table 6. Finetune evaluation results on NTU-60 and NTU-120 dastatets. †means using the same bone stream. ‡means the model is pretrained under full supervision." + ], + "table_footnote": [], + "table_body": "
MethodsNTU-60NTU-120
XsubXviewXsubXset
SkeletonCLR† [10]82.288.973.675.3
MCC [24]83.089.777.077.8
AimCLR† [6]83.089.276.476.7
RVTCLR+†(Ours)84.491.377.278.4
3s-ST-GCN‡ [39]85.291.477.277.1
3s-CrosSCLR [10]86.292.580.580.4
3s-AimCLR [6]86.992.980.180.9
3s-RVTCLR+ (Ours)87.593.982.083.4
", + "bbox": [ + 529, + 128, + 862, + 251 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/620aea2f1ed1a6b6da150da892257b293ffbb249813978efd1919b1dbde7d7c6.jpg", + "table_caption": [ + "Table 7. Seim-supervised evaluation on NTU-60 and NTU-120 datasets. * means the results are obtained by their released codes." + ], + "table_footnote": [], + "table_body": "
MethodsNTU-60NTU-120
XsubXviewXsubXset
1% labeled data
ISC [25]35.738.1--
3s-Colorization [41]48.352.5--
3s-CrosCLR [10]51.150.028.6*28.0*
3s-AimCLR [6]54.854.334.8*32.6*
3s-RVTCLR+ (Ours)54.953.633.332.8
10% labeled data
ISC [25]65.972.5--
3s-Colorization [41]71.778.9--
MCC-ST-GCN [24]55.659.940.743.4
MCC-2s-AGCN [24]60.865.847.051.8
MCC-AS-GCN [24]59.263.144.947.8
3s-CrosCLR [10]74.477.861.3*61.1*
3s-AimCLR [6]78.281.664.8*63.7*
3s-RVTCLR+ (Ours)79.583.767.368.3
", + "bbox": [ + 524, + 289, + 864, + 494 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/36b09c9ba3115e47019c4508255322bc30958839f386345d8c51ac53e1581166.jpg", + "image_caption": [ + "(a) SkeletonCLR, j" + ], + "image_footnote": [], + "bbox": [ + 501, + 510, + 633, + 590 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b970d31757a69e055560cbcb6f5eb87cff79159089ed801858097dd103392db5.jpg", + "image_caption": [ + "(b) SkeletonCLR, m" + ], + "image_footnote": [], + "bbox": [ + 637, + 511, + 763, + 590 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/70206c4834515c0cb4825a55c0a4083ec4261968ed835e30793094f10481698d.jpg", + "image_caption": [ + "(c) SkeletonCLR, b" + ], + "image_footnote": [], + "bbox": [ + 764, + 511, + 893, + 590 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c639a7fee82614f8e5e694b2ab65cd236e615d46a45b4a1c15b519f271eaffec.jpg", + "image_caption": [ + "(d) RVTCLR+, j" + ], + "image_footnote": [], + "bbox": [ + 501, + 619, + 633, + 699 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/ffd05d60081e5e99fcacbdfa2b3e1ee8eddf2bd1d325d4638bba0419c53203d8.jpg", + "image_caption": [ + "(e) RVTCLR+, m" + ], + "image_footnote": [], + "bbox": [ + 637, + 621, + 763, + 700 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/7faa679dbd1be46a4281f84eef9f975f8d4a7c06bb195b1b926ce2f9e361a6d5.jpg", + "image_caption": [ + "(f) RVTCLR+, b", + "Figure 4. The t-SNE visualization of embeddings on NTU-60 X-sub. These models are trained for 300 epochs. j, b, and m represent joint-stream, bone-stream, and motion-stream, respectively." + ], + "image_footnote": [], + "bbox": [ + 764, + 621, + 893, + 700 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "CLR and our RVTCLR+ on NTU-60 Xsub benchmark. For a fair comparison, we select the same 11 classes for visualization, where each class is represented by a dot of the same color. From the Figure 4, we can obviously see that the embeddings extracted from our method have better inter-class separability and intra-class compactness, indicating that our learned features are more discriminative.", + "bbox": [ + 496, + 794, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "13920", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 89, + 194, + 104 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this paper, we propose a Relative Visual Tempo Contrastive Learning framework for skeleton action representation (RVTCLR). The proposed RVTCLR combines Relative Visual Tempo Learning (RVTL) and Appearance-Consistency (AC) into a single-branch to obtain a more comprehensive spatial-temporal representation. Given the inherent sparsity of skeleton sequence data compared to RGB data, we design a new Distribution-Consistency (DC) branch aimed at emphasizing high-order semantics and preventing the network from learning shortcuts. The DC branch consists of Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. We refer to this new two-branch structure as RVTCLR+. Experimental results and visualization analysis verify that RVTCLR+ can obtain a more discriminative skeleton action representation.", + "bbox": [ + 76, + 114, + 472, + 357 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 369, + 174, + 386 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Unaiza Ahsan, Rishi Madhok, and Irfan Essa. Video jigsaw: Unsupervised learning of spatiotemporal context for video action recognition. In 2019 IEEE Winter Conference on Applications of Computer Vision (WACV), pages 179-189, 2019.", + "[2] Peihao Chen, Deng Huang, Dongliang He, Xiang Long, Runhao Zeng, Shilei Wen, Mingkui Tan, and Chuang Gan. Rspnet: Relative speed perception for unsupervised video representation learning. 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The Visual Computer, 36(9):1771-1781, 2020." + ], + "bbox": [ + 501, + 92, + 890, + 613 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "13922", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition/dbdfe6ed-ba3c-4daf-ac10-86c2b2f20cde_model.json b/2023/Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition/dbdfe6ed-ba3c-4daf-ac10-86c2b2f20cde_model.json new file mode 100644 index 0000000000000000000000000000000000000000..4e7f5c336373176423dada4af8778dd9e698d5a6 --- /dev/null +++ b/2023/Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition/dbdfe6ed-ba3c-4daf-ac10-86c2b2f20cde_model.json @@ -0,0 +1,2299 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.091, + 0.13, + 0.882, + 0.178 + ], + "angle": 0, + "content": "Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition" + }, + { + "type": "text", + "bbox": [ + 0.268, + 0.203, + 0.721, + 0.222 + ], + "angle": 0, + "content": "Yisheng Zhu\\(^{1}\\), Hu Han\\(^{2,3}\\), Zhengtao Yu\\(^{4}\\), Guangcan Liu\\(^{5*}\\)" + }, + { + "type": "text", + "bbox": [ + 0.277, + 0.222, + 0.707, + 0.239 + ], + "angle": 0, + "content": "\\(^{1}\\)Nanjing University of Posts and Telecommunications" + }, + { + "type": "text", + "bbox": [ + 0.107, + 0.239, + 0.877, + 0.274 + ], + "angle": 0, + "content": "\\(^{2}\\)Key Laboratory of Intelligent Information Processing, Institute of Computing Technology (ICT), Chinese Academy of Sciences (CAS)" + }, + { + "type": "text", + "bbox": [ + 0.299, + 0.274, + 0.686, + 0.292 + ], + "angle": 0, + "content": "3University of the Chinese Academy of Sciences" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.293, + 0.897, + 0.328 + ], + "angle": 0, + "content": "\\(^{4}\\)Faculty of Information Engineering and Automation, Kunming University of Science and Technology \\(^{5}\\)School of Automation, Southeast University" + }, + { + "type": "text", + "bbox": [ + 0.154, + 0.331, + 0.829, + 0.345 + ], + "angle": 0, + "content": "yszhu1995@163.com, huhan@ict.ac.cn, ztyu@hotmail.com, guangcanliu@seu.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.38, + 0.314, + 0.396 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.414, + 0.474, + 0.821 + ], + "angle": 0, + "content": "Visual tempo characterizes the dynamics and the temporal evolution, which helps describe actions. Recent approaches directly perform visual tempo prediction on skeleton sequences, which may suffer from insufficient feature representation issue. In this paper, we observe that relative visual tempo is more in line with human intuition, and thus providing more effective supervision signals. Based on this, we propose a novel Relative Visual Tempo Contrastive Learning framework for skeleton action Representation (RVTCLR). Specifically, we design a Relative Visual Tempo Learning (RVTL) task to explore the motion information in intra-video clips, and an Appearance-Consistency (AC) task to learn appearance information simultaneously, resulting in more representative spatiotemporal features. Furthermore, skeleton sequence data is much s-parser than RGB data, making the network learn shortcuts, and overfit to low-level information such as skeleton scales. To learn high-order semantics, we further design a new Distribution-Consistency (DC) branch, containing three components: Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. We term our entire method (RVTCLR with DC) as RVTCLR+. Extensive experiments on NTU RGB+D 60 and NTU RGB+D 120 datasets demonstrate that our RVTCLR+ can achieve competitive results over the state-of-the-art methods. Code is available at https://github.com/Zhuysheng/RVTCLR." + }, + { + "type": "text", + "bbox": [ + 0.507, + 0.38, + 0.697, + 0.392 + ], + "angle": 0, + "content": "Basic idea of visual tempo prediction" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.391, + 0.577, + 0.471 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.582, + 0.391, + 0.642, + 0.47 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.642, + 0.391, + 0.712, + 0.47 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.712, + 0.391, + 0.843, + 0.449 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.585, + 0.47, + 0.815, + 0.482 + ], + "angle": 0, + "content": "(a) Top-1 Accuracy on NTU-60 Xsub: 52.7%" + }, + { + "type": "text", + "bbox": [ + 0.507, + 0.484, + 0.807, + 0.496 + ], + "angle": 0, + "content": "Relative visual tempo learning and appearance-consistency" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.495, + 0.577, + 0.614 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.582, + 0.495, + 0.642, + 0.613 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.642, + 0.495, + 0.757, + 0.613 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.764, + 0.495, + 0.865, + 0.553 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.584, + 0.615, + 0.816, + 0.627 + ], + "angle": 0, + "content": "(b) Top-1 Accuracy on NTU-60 Xsub: \\(73.3\\%\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.629, + 0.892, + 0.714 + ], + "angle": 0, + "content": "Figure 1. The basic visual tempo prediction is considered a classification task, where the learned model is used to assign tempo labels to individual video clips. We introduce relative visual tempo learning and appearance-consistency based on contrastive learning. It's more human-intuitive for modeling actions. The top-1 accuracy on NTU-60 Xsub benchmark supports our claim." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.739, + 0.632, + 0.755 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "As one of the most fundamental topics in video understanding, human action recognition has been widely explored in many real-world scenarios, such as human-computer interaction [22], autonomous driving [30], and so on [34, 17]. Skeleton data provides more abstract and well-structured information with less computation and storage than raw RGB video. It is less susceptible to camera viewpoint changes and background distractions. Thus, skeleton-based action recognition has attracted extensive at" + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.851, + 0.471, + 0.9 + ], + "angle": 0, + "content": "*Corresponding author. This work was supported in part by the New Generation AI Major Project of Ministry of Science and Technology of China under Grant 2018AAA0102501 and in part by the National Natural Science Foundation of China (NSFC) under Grant U21B2027." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13913" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.182 + ], + "angle": 0, + "content": "tention [39, 21, 28, 7, 35]. However, most of these methods rely heavily on full supervision. The collection of massive annotations is labor-intensive and time-consuming. Under this circumstance, learning action representations directly from the data in a self-supervised manner has attracted increasing attentions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.186, + 0.473, + 0.746 + ], + "angle": 0, + "content": "Several existing works [11, 38, 41] draw inspiration from video self-supervised learning and directly apply video pretext tasks on skeleton sequences, such as jigsaw puzzle recognition [1, 9] and temporal order prediction [15, 37]. For sequence data, a commonly used technique to model spatiotemporal information is visual tempo prediction [42, 29]. Action visual tempo describes the speed at which actions are performed, which is crucial for distinguishing actions that exhibit similar temporal evolutions (e.g., walking and jogging). The basic idea is shown in the upper part of Figure 1. For each video, clips are sampled at different sampling frequencies to mimic different visual tempos (e.g., \\(1 \\times\\) and \\(2 \\times\\)), and predictions are made using the backbone network. However, there are limitations in directly applying it to skeleton sequences. People perform actions at their own tempo due to the influence of gender, age, etc. Even at the same tempo, the athlete's walking speed is visibly faster than that of a child in a third-person perspective. Therefore, it's obviously inappropriate to treat tempo prediction as a classification task. Furthermore, this basic strategy mainly focuses on motion information and cannot explicitly encourage the model to explore appearance information that is equally important for recognizing actions. Recently, contrastive learning has shown its great potential in extracting informative features [10, 6] in skeleton-based action recognition. Contrastive learning typically converts the naive classification task to a matching problem and learns an embedding space in which augmentations of same skeleton sequence are kept closer together, while different augmentations are far apart. In this way, the above issues can be alleviated in an elegant way. However, skeleton sequence data is much sparser than RGB data, and applying contrastive learning naively without explicit guidance may lead to model overfitting low-level information such as skeleton scales and angles, while failing to learn high-order semantics, resulting in insufficient feature representation capabilities." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.472, + 0.903 + ], + "angle": 0, + "content": "To this end, we propose RVTCLR: a Relative Visual Tempo Contrastive Learning framework for skeleton action Representation. The basic idea is shown at the bottom of Figure 1. First, we observe that it's intuitively plausible to compare relative visual tempos within videos rather than to predict a specific visual tempo for each video. Specifically, for each video, we sample 3 clips with different visual tempos (e.g., \\(1 \\times\\), \\(1 \\times\\), and \\(2 \\times\\)) to construct the contrastive pairs and train a network to pull the anchor-positive pairs closer while repelling the anchor-negative pairs. Furthermore," + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.092, + 0.892, + 0.198 + ], + "angle": 0, + "content": "to make the representations explicitly focus on appearance information, we design another Appearance-Consistency (AC) task. In this task, pairs from the same video are attracted no matter their visual tempos, while pairs from different videos are pushed away. In this way, the learned representations are expected to focus on both skeleton motion and appearance information simultaneously." + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.199, + 0.893, + 0.574 + ], + "angle": 0, + "content": "In addition, in order to encourage the models to learn high-order semantics, we introduce a new Distribution-Consistency (DC) branch based on RVTCLR, which contains three components: Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. We refer to this as RVTCLR+. First, we leverage SDA to generate more difficult contrastive pairs by applying more skeleton-specific transformations (e.g., gaussian noise) at the input level, since augmentation plays a key role in learning better representations, as demonstrated by SimCLR [3] and MoCo [8]. However, too much strong augmentations may blur the joint connections compared to the normal augmented sequence (i.e., crop and shear), resulting in performance degradation. Benefiting from recent attention mechanisms [5, 13, 44], we try to emphasize these connections by designing a novel module, FSEM, which contains an Intra-Inter-Part block (IIPB) for local spatial modeling and a Non-local block (NLB) [32] for global spatiotemporal modeling. Finally, inspired by [33, 6], we introduce a DD loss to minimize the distributional divergence between the normal augmented view and our DC branch. By combining these components, we hope that the DC branch can better learn local and global spatiotemporal features, which help to extract discriminative high-order semantics." + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.576, + 0.895, + 0.819 + ], + "angle": 0, + "content": "To sum up, the contributions of this work include: (1) We propose a novel contrastive representation learning framework named RVTCLR. The proposed RVTCLR leverages Relative Visual Tempo Learning (RVTL) task to learn better skeleton motion information. By combining another Appearance-Consistency (AC) task, our model explicitly learns to concentrate on skeleton appearance information simultaneously. (2) To encourage models to focus on high-order semantics, we propose RVTCLR+ by introducing a new Distribution-Consistency (DC) branch. This DC branch contains three components: Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. (3) These contrastive tasks are jointly trained using a two-branch structure such that the models can learn both spatiotemporal and high-order semantics simultaneously." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.831, + 0.642, + 0.847 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Self-supervised skeleton-based action recognition. To meet the requirements of real-time recognition, it's necessary for the models to be able to directly extract dis" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.52, + 0.957 + ], + "angle": 0, + "content": "13914" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.485 + ], + "angle": 0, + "content": "criminative action representations from the label-free online videos. Recent progress in self-supervised skeleton-based action recognition can be summarized into two categories: pretext-task based learning [11, 38, 41, 43, 23] and contrastive learning [18, 10, 6, 25, 31, 24]. For example, Zheng et al. [43] design a skeleton inpainting architecture to learn the long-term dynamics. Lin et al. [11] integrate multiple tasks such as jigsaw puzzle recognition to learn more general skeleton features. Xu et al. [38] propose reverse sequential predictions based on encoder-decoder structure to extract motion pattern. However, the representations learned by these methods may not be good enough, in the sense that they could be exclusively particular to the pre-designed tasks. Inspired by the success of contrastive learning in image classification (e.g., instance discrimination [36], SimCLR [3], and MoCo [8]), Rao et al. [18] first propose to perform contrastive learning among different augmentations of unlabeled skeleton data, to learn inherent action patterns. Thoker et al. [25] propose to generate contrastive pairs based on different input-representations of the skeleton sequences, i.e., graph, sequence, and image representation. By leveraging multiple views of the skeleton data, i.e., joint, bone, and motion, Li et al. [10] introduce SkeletonCLR and CrosSCLR to perform the single-view and cross-view contrastive learning. Guo et al. [6] further propose AimCLR to learn from extremely augmented skeleton sequences." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.489, + 0.473, + 0.761 + ], + "angle": 0, + "content": "Nevertheless, none of the aforementioned methods concentrate on visual tempo, which is crucial for characterizing human action dynamics. To our best knowledge, Su et al. [24] propose motion consistency and continuity learning, which has overlap with our framework. However, the differences are obvious, which mainly lie in three aspects: (1) contrastive pairs are generated differently. In [24], speed-changed clips are considered as positive pairs, while we focus on relative visual tempo and regard these clips as negative pairs. (2) appearance information is modeled differently. In [24], appearance information is implicitly modeled in the contrastive learning process, while we design another Appearance-Consistency (AC) task specifically for spatial modeling. (3) learned features are enhanced differently. In [24], learned features are enhanced by designing a self-reconstruction based motion continuity module, while we introduce a novel Distribution-Consistency (DC) branch to guide the models focus on high-order semantics." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.765, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Visual tempo modeling. Visual tempo describes the speed of human movements, which has already been applied into various action recognition methods [4, 40, 14]. For example, Feichtenhofer et al. [4] first propose SlowFast network to explore the potential of different visual tempos. It consists of two pathways, operating at different frame rates, to capture both spatial semantics and motion dynamics. When it comes to video self-supervised learning [42, 29, 2], the potential of visual tempo in motion mod" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.319 + ], + "angle": 0, + "content": "eling is further verified. Yao et al. [42] utilize video playback rates as self-supervision signals and propose playback rate perception to learn spatiotemporal features in a collaborative discrimination-generation manner. The above methods usually require assigning visual tempos to each video clip according to different sampling rates, and then elaborate learning paradigms through reconstruction or prediction, but this is suboptimal in learning discriminative representations. Chen et al. [2] argue that relative speed is more in line with motion pattern. They propose a new video self-supervised learning framework (called RSPNet) to leverage the relative speed between two video clips to supervise the representation learning. Inspired by RSPNet, the proposed RVTCLR focuses on relative visual tempo learning with skeleton-specific modifications." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.33, + 0.6, + 0.347 + ], + "angle": 0, + "content": "3. Methods" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.355, + 0.642, + 0.37 + ], + "angle": 0, + "content": "3.1. Preliminaries" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.378, + 0.895, + 0.666 + ], + "angle": 0, + "content": "SkeletonCLR. SkeletonCLR [10] utilizes ST-GCN [39] as its backbone and follows the practice in MoCo [8] to learn skeleton action representations. Suppose that a skeleton sequence \\( s = (s^1, s^2, \\ldots, s^T) \\) contains \\( T \\) consecutive skeleton frames, where \\( s^i \\in \\mathbb{R}^{3 \\times V \\times M} \\) means 3D coordinates of \\( V \\) joints for \\( M \\) actors. A data augmentation module \\( \\mathcal{T} \\) is first utilized to randomly transform the given \\( s \\) into different augmentations \\( x_q \\) and \\( x_k \\). Then, a query encoder \\( f(\\cdot; \\theta_q) \\) and a momentum updated key encoder \\( f(\\cdot; \\theta_k) \\) are leveraged to encode \\( x_q \\) and \\( x_k \\) into hidden space \\( h_q \\) and \\( h_k \\). These embeddings are further passed through a projector \\( g(\\cdot; \\theta_q) \\) and its momentum updated version \\( g(\\cdot; \\theta_k) \\) to get the final query features \\( q \\) and key features \\( k \\). In each training step, samples in the queue \\( \\mathbf{Q} = \\{m_o\\}_{o=1}^K \\) are progressively replaced by the key features \\( k \\) following a first-in-first-out scheme. Following MoCo, \\( q \\) and \\( k \\) serve as positive pairs while \\( q \\) and embeddings in \\( \\mathbf{Q} \\) serve as negative pairs. The InfoNCE loss [36] is used to guide the network learning, which can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.508, + 0.673, + 0.892, + 0.711 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {I n f o} = - \\log \\frac {\\exp (q \\cdot k / \\tau)}{\\exp (q \\cdot k / \\tau) + \\sum_ {o = 1} ^ {K} \\exp (q \\cdot m _ {o} / \\tau)} (1)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.716, + 0.892, + 0.746 + ], + "angle": 0, + "content": "where \\(\\tau\\) is the temperature hyper-parameter, and \\(\\cdot\\) represents the similarity measured by dot product." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.747, + 0.892, + 0.793 + ], + "angle": 0, + "content": "After computing the InfoNCE loss, the parameters of \\(\\theta_{q}\\) are updated by gradient back-propagation while the parameters of \\(\\theta_{k}\\) are updated as their moving-average:" + }, + { + "type": "equation", + "bbox": [ + 0.616, + 0.801, + 0.891, + 0.817 + ], + "angle": 0, + "content": "\\[\n\\theta_ {k} \\leftarrow \\alpha \\theta_ {k} + (1 - \\alpha) \\theta_ {q} \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.841 + ], + "angle": 0, + "content": "where \\(\\alpha\\) is a momentum coefficient (set to 0.999 by default)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.841, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Nearest Neighbors Mining. Traditional InfoNCE regards all samples in the memory bank as negative. This overly hard approach may lead to non-generic feature embeddings. To address the above issue, [10, 6] propose" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "13915" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.162, + 0.089, + 0.812, + 0.356 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.359, + 0.895, + 0.442 + ], + "angle": 0, + "content": "Figure 2. The pipeline of our method. For each skeleton sequence, we sample clips with varying visual tempos. Then, we use a two-branch structure to extract discriminative feature from each sequence. Specifically, in RVTCLR, the Relative Visual Tempo Learning (RVTL) is responsible for modeling motion dynamics. The Appearance-Consistency (AC) is responsible for modeling appearance characteristics. These two tasks are combined into one branch to achieve a more comprehensive spatial-temporal representation. In another Distribution-Consistency (DC) branch, we introduce Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss to guide the network to concentrate on extracting high-order semantics." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.467, + 0.47, + 0.498 + ], + "angle": 0, + "content": "to leverage Nearest Neighbors Mining (NNM) to generate more positive pairs:" + }, + { + "type": "equation", + "bbox": [ + 0.084, + 0.509, + 0.469, + 0.559 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {N N M} = - \\log \\frac {\\exp (q \\cdot k / \\tau) + \\sum_ {o \\in N _ {+}} \\exp (q \\cdot m _ {o} / \\tau)}{\\exp (q \\cdot k / \\tau) + \\sum_ {o = 1} ^ {K} \\exp (q \\cdot m _ {o} / \\tau)} \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.561, + 0.47, + 0.592 + ], + "angle": 0, + "content": "where \\(N_{+}\\) represents the top- \\(N\\) nearest neighbors that are most similar to the query features \\(q\\) in the memory queue." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.592, + 0.47, + 0.667 + ], + "angle": 0, + "content": "Since the model learned in the early training stages may not be strong enough to provide confident nearest neighbors, [10, 6] propose to perform a two-stage training, i.e., first train the model using Equation 1, and then train the model to mine the nearest neighbors using Equation 3." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.668, + 0.47, + 0.7 + ], + "angle": 0, + "content": "In this paper, we mainly implement our method based on SkeletonCLR and two-stage training strategy." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.71, + 0.192, + 0.725 + ], + "angle": 0, + "content": "3.2.RVTCLR" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Relative Visual Tempo Learning (RVTL). Observing that each person performs actions at his/her own visual tempo, we introduce a RVTL task, which aims to learn better skeleton motion information. Specifically, given a skeleton sequence \\( s \\) with \\( T \\) frames, we first sample 3 clips \\( c_{i} \\), \\( c_{j} \\) and \\( c_{k} \\) with visual tempos \\( v_{i} \\), \\( v_{j} \\) and \\( v_{k} \\), respectively, where \\( v_{i} = v_{j} \\neq v_{k} \\). Note that visual tempos can be set arbitrarily, i.e., \\( \\{1 \\times, 2 \\times, 3 \\times,..\\} \\). However, to avoid the temporal ambiguity in skeleton sequences, we only consider \\( 1 \\times \\) and \\( 2 \\times \\), which represent that the sampling interval is set to 1 and 2 frames. We sample from the first frame and keep" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.467, + 0.895, + 0.68 + ], + "angle": 0, + "content": "a duration of \\( T / 2 \\) for each clip. Then, we apply normal skeleton augmentations \\( \\mathcal{T} \\) on these three clips respectively to construct a triplet, i.e., anchor \\( a = \\mathcal{T}(c_i) \\), positive \\( p = \\mathcal{T}(c_j) \\) and negative \\( n = \\mathcal{T}(c_k) \\). This triplet is further fed into SkeletonCLR with a projection head \\( g_{r}(\\cdot ;\\theta_{q_{r}}) \\) and its momentum updated \\( g_{r}(\\cdot ;\\theta_{k_{r}}) \\) to generate the encoded features \\( (q_{a},k_{p},k_{n}) \\). Finally, these features are normalized and combined as anchor-positive pairs \\( (q_{a},k_{p}) \\) and anchor-negative pairs \\( (q_{a},k_{n}) \\), and our goal is to pull \\( (q_{a},k_{p}) \\) closer while pushing \\( (q_{a},k_{n}) \\) away. The assumption here is that the network can only succeed in such a RVTL task if it understands the intrinsic visual tempo of each clip and learns discriminative motion information. This task is realized by a triplet loss [19]:" + }, + { + "type": "equation", + "bbox": [ + 0.513, + 0.691, + 0.892, + 0.709 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {R V T L} = \\max \\left\\{- \\left(q _ {a} \\cdot k _ {p} - q _ {a} \\cdot k _ {n}\\right) + \\operatorname {m a r g i n}, 0 \\right\\} \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.749 + ], + "angle": 0, + "content": "where the margin (set to 1 by default) is a hyper-parameter to control the distance between two components." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Appearance-Consistency (AC). Appearance information is also essential for recognizing actions. To this end, we introduce another AC task to explicitly learn such information. Specifically, given a skeleton sequence, we first sample two clips \\( c_{i} \\), \\( c_{j} \\) with visual tempos randomly selected in \\( \\{1\\times ,2\\times \\} \\). Then, they are normally augmented and sent to SkeletonCLR with another projection head \\( g_{a}(\\cdot ;\\theta_{q_{a}}) \\) and its momentum updated \\( g_{a}(\\cdot ;\\theta_{k_{a}}) \\) to generate the encoded features \\( (q_{i},k_{j}) \\). Note that the query and key encoders in AC share weights with the encoders in RVTL while the" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "13916" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.226 + ], + "angle": 0, + "content": "projection heads \\( g_{a}(\\cdot;\\theta_{q_{a}}) \\) and \\( g_{a}(\\cdot;\\theta_{k_{a}}) \\) have weights independent of \\( g_{r}(\\cdot;\\theta_{q_{r}}) \\) and \\( g_{r}(\\cdot;\\theta_{k_{r}}) \\). Here, the goal is to pull \\( q_{i} \\) and \\( k_{j} \\) closer while pushing away \\( q_{i} \\) and negative samples in queue \\( \\mathbf{Q} \\). Although from the same sample, clips with various visual tempos show different temporal motion dynamics, by pulling such a pair closer while pushing away different samples, we want the model to explicitly focus on appearance information. This task is realized by the InfoNCE loss:" + }, + { + "type": "equation", + "bbox": [ + 0.091, + 0.237, + 0.47, + 0.285 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {A C} = - \\log \\frac {\\exp \\left(q _ {i} \\cdot k _ {j} / \\tau\\right)}{\\exp \\left(q _ {i} \\cdot k _ {j} / \\tau\\right) + \\sum_ {o = 1} ^ {K} \\exp \\left(q _ {i} \\cdot m _ {o} / \\tau\\right)} \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.286, + 0.473, + 0.392 + ], + "angle": 0, + "content": "Based on SkeletonCLR, we jointly train these tasks. In the first training stage, we train the model with the loss function: \\(\\mathcal{L}_1 = \\lambda_1\\mathcal{L}_{RVTL} + \\lambda_2\\mathcal{L}_{AC}\\), and then in the second training stage, we try to obtain more positive samples by using \\(\\mathcal{L}_2 = \\lambda_1\\mathcal{L}_{RVTL} + \\lambda_2\\mathcal{L}_{AC'}\\), where \\(\\lambda\\) (set to 1 by default) is the coefficient to balance the loss and \\(\\mathcal{L}_{AC'}\\) is defined in Equation 3." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.409, + 0.487, + 0.58 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.583, + 0.47, + 0.64 + ], + "angle": 0, + "content": "Figure 3. Illustration of FSEM. (a) The workflow of FSEM. (b) IIPB is responsible for local spatial modeling, containing intra-part and inter-part relational reasoning submodules. (c) NLB is responsible for global spatial-temporal modeling." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.665, + 0.2, + 0.68 + ], + "angle": 0, + "content": "3.3.RVTCLR+" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.47, + 0.809 + ], + "angle": 0, + "content": "The success of contrastive learning depends on the construction of contrastive pairs and the difficulty of learning paradigm. Given that the skeleton sequences are much s-sparser, naive contrastive learning may risk overfitting low-level information such as skeleton scales. It would be even better if we could design a new branch to explicitly learn skeleton high-order semantics. We thus propose RVTCLR+ by designing our Distribution-Consistency (DC)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.471, + 0.902 + ], + "angle": 0, + "content": "SDA. We leverage SDA to generate more difficult contrastive pairs. The SDA contains normal augmentations \\(\\mathcal{T}\\): crop and shear, and additional strong augmentations \\(\\mathcal{T}'\\): gaussian noise, gaussian blur, and channel mask. Given a skeleton sequence \\(s\\), we apply \\(\\mathcal{T}\\) and \\(\\mathcal{T}'\\) to get the transformed version: \\(e = \\mathcal{T}'(\\mathcal{T}(s))\\). Afterwards, we send it" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.137 + ], + "angle": 0, + "content": "to the weight-sharing query encoder to encode \\( e \\) into hidden space \\( h_e \\), which is further passed through a projector \\( g_e(\\cdot; \\theta_{q_e}) \\) to obtain the final embeddings \\( q_e \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.138, + 0.893, + 0.348 + ], + "angle": 0, + "content": "FSEM. Such a direct modeling method may be suboptimal, since the additional augmentations may cause blurred joint connections. Considering that skeleton sequences are spatiotemporal cubes, we design FSEM to highlight these connections. As shown in Figure 3, our FSEM contains an Intra-Inter-Part block (IIPB), which is responsible for local spatial modeling, and a Non-local block (NLB), which is responsible for global spatial-temporal modeling. Given the encoded \\( h_e \\in \\mathbb{R}^{C \\times T \\times V} \\), in IIPB, we first divide each human skeleton into 5 parts according to the physical topology of the body. Then, average pooling is applied on each part to generate the intra-part representations \\( h_{e'} \\in \\mathbb{R}^{C \\times T \\times 5} \\). Two \\( 1 \\times 1 \\) convolution layers are further utilized to establish the inter-part relations:" + }, + { + "type": "equation", + "bbox": [ + 0.545, + 0.361, + 0.892, + 0.378 + ], + "angle": 0, + "content": "\\[\nh _ {\\hat {e}} = \\operatorname {C o n v 2} \\left(\\operatorname {R e L U} \\left(\\operatorname {C o n v 1} \\left(h _ {e ^ {\\prime}}, W _ {1}\\right)\\right), W _ {2}\\right) \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.389, + 0.892, + 0.481 + ], + "angle": 0, + "content": "where \\( W_{1} \\in \\mathbb{R}^{\\frac{C}{2} \\times C} \\) and \\( W_{2} \\in \\mathbb{R}^{C \\times \\frac{C}{2}} \\) are learnable parameters. \\( ReLU \\) is the activation function. The intuition here is that connections between body parts can sometimes better describe actions (e.g., the coordination of arm and leg in 'running'). By using IIPB, we establish the part-based connections that seek to mitigate the effects of blurred joints." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.482, + 0.892, + 0.587 + ], + "angle": 0, + "content": "IIPB can capture the local dependencies of intra-frame parts. However, global inter-frame connections are ignored, which are also essential for describing actions. We introduce NLB to associate all possible frames of a skeleton sequence in a self-attention mechanism [27]. The non-local operation computes frame dependencies by enumerating all possible frames:" + }, + { + "type": "equation", + "bbox": [ + 0.575, + 0.598, + 0.892, + 0.634 + ], + "angle": 0, + "content": "\\[\ny ^ {t} = \\frac {1}{\\mathcal {C} \\left(h _ {\\hat {e}}\\right)} \\sum_ {\\forall t ^ {\\prime}} f \\left(h _ {\\hat {e}} ^ {t}, h _ {\\hat {e}} ^ {t ^ {\\prime}}\\right) g \\left(h _ {\\hat {e}} ^ {t ^ {\\prime}}\\right) \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.647, + 0.892, + 0.724 + ], + "angle": 0, + "content": "where \\( h_{\\hat{e}}^{t} \\) and \\( h_{\\hat{e}}^{t'} \\) denote the input at frame \\( t \\) and \\( t' \\), respectively. \\( g(\\cdot) \\) is a linear function. \\( \\mathcal{C}(\\cdot) \\) is a normalization term. An embedded gaussian function \\( f(\\cdot, \\cdot) \\) [32] computes the relationships between \\( t \\) and all \\( t' \\). We wrap the non-local operation in Equation 7 into NLB with a residual layer as:" + }, + { + "type": "equation", + "bbox": [ + 0.64, + 0.737, + 0.892, + 0.753 + ], + "angle": 0, + "content": "\\[\nh _ {\\tilde {e}} = W _ {3} y + h _ {\\hat {e}} \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.84 + ], + "angle": 0, + "content": "where \\( W_{3} \\) is a learnable embedding for \\( y \\). Finally, we send it to the projector to generate the new embeddings \\( q_{\\widetilde{e}} \\). Note that FSEM can be plugged into different GCN layers, we only insert the FSEM before the projector for the reduction of experiment cost." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "DD Loss. The distributional divergence between weakly augmented counterparts and strongly augmented views enables the framework to explore novel patterns, which may help extract representative high-level features. Formally," + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13917" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.136 + ], + "angle": 0, + "content": "given the encoded query features \\( q_{a} \\), the encoded key features \\( k_{p} \\), and the memory queue \\( \\mathbf{Q} = \\{m_{o}\\}_{o=1}^{K} \\), we can obtain a conditional distribution:" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.143, + 0.47, + 0.18 + ], + "angle": 0, + "content": "\\[\np \\left(k _ {p} \\mid q _ {a}\\right) = \\frac {\\exp \\left(q _ {a} \\cdot k _ {p} / \\tau\\right)}{\\exp \\left(q _ {a} \\cdot k _ {p} / \\tau\\right) + \\sum_ {o = 1} ^ {K} \\exp \\left(q _ {a} \\cdot m _ {o} / \\tau\\right)} (9)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.187, + 0.469, + 0.262 + ], + "angle": 0, + "content": "which encodes the likelihood of the query \\( q_{a} \\) being assigned to the key \\( k_{p} \\). By replacing \\( k_{p} \\) with \\( m_{o} \\), we can also obtain the likelihood that the query \\( q_{a} \\) is assigned to the negative embeddings in \\( \\mathbf{Q} \\). Then, the InfoNCE loss in Equation 1 can be rewritten as:" + }, + { + "type": "equation", + "bbox": [ + 0.077, + 0.27, + 0.496, + 0.322 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {I n f o}} = - q \\left(k _ {p} \\mid q _ {a}\\right) \\log p \\left(k _ {p} \\mid q _ {a}\\right) - \\sum_ {o = 1} ^ {K} q \\left(m _ {o} \\mid q _ {a}\\right) \\log p \\left(m _ {o} \\mid q _ {a}\\right) \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.323, + 0.47, + 0.52 + ], + "angle": 0, + "content": "where \\( q(\\cdot|\\cdot) \\) is the ideal distribution of the likelihood, \\( p(k_p|q_a) \\) is the distribution learned by network. In InfoNCE, \\( q(k_p|q_a) \\) and \\( q(m_o|q_a) \\) are simply set to 1 and 0 based on one-hot distribution, respectively. When applied to \\( q_{\\widetilde{e}} \\), a straightforward approach is to directly replace \\( q_a \\) in Equation 10 with \\( q_{\\widetilde{e}} \\). However, as demonstrated in [33, 6], the one-hot distribution cannot mimic the ideal distribution and thus cannot help representations learning any more. Conversely, the similarity distribution of weakly-augmented queries for the same instance in a queue can provide useful clues for strong-augmentation based learning. This inspires us to leverage \\( p(k_p|q_a) \\) and \\( p(m_o|q_a) \\) as the ideal distribution to supervise \\( q_{\\widetilde{e}} \\):" + }, + { + "type": "equation", + "bbox": [ + 0.102, + 0.529, + 0.469, + 0.59 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {L} _ {D C} = - p \\left(k _ {p} \\mid q _ {a}\\right) \\log p \\left(k _ {p} \\mid q _ {\\bar {e}}\\right) \\\\ - \\sum_ {o = 1} ^ {K} p \\left(m _ {o} \\mid q _ {a}\\right) \\log p \\left(m _ {o} \\mid q _ {\\tilde {e}}\\right) \\tag {11} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.599, + 0.47, + 0.645 + ], + "angle": 0, + "content": "By combining DC, the final loss our RVTCLR+ can be formulated as \\(\\mathcal{L}_1 = \\lambda_1\\mathcal{L}_{RVTL} + \\lambda_2\\mathcal{L}_{AC} + \\lambda_3\\mathcal{L}_{DC}\\) and \\(\\mathcal{L}_2 = \\lambda_1\\mathcal{L}_{RVTL} + \\lambda_2\\mathcal{L}_{AC'} + \\lambda_3\\mathcal{L}_{DC}\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.657, + 0.21, + 0.673 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.682, + 0.18, + 0.696 + ], + "angle": 0, + "content": "4.1. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.469, + 0.84 + ], + "angle": 0, + "content": "NTU RGB+D 60 Dataset [20]: It contains 56880 skeleton video clips over 60 action classes capture from 40 subjects and 3 different camera view angles. Each clip provides 25 body joints with 3D coordinates for at most 2 subjects. There are two evaluation benchmarks: cross-subject (Xsub) and cross-view (Xview). In Xsub, clips of 20 subjects are used for training, and the rest are used for testing. In Xview, clips of camera 2 and 3 are used for training, and clips of camera 1 are used for testing." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.901 + ], + "angle": 0, + "content": "NTU RGB+D 120 Dataset [12]: It is an extension of N-TU RGB+D 60 with 113945 samples over 120 classes capture from 106 subjects and 32 different camera setups. Two evaluation benchmarks are recommended: cross-subject" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "(Xsub) and cross-setup (Xset). In Xsub, clips of 53 subjects are used for training, and the rest are used for testing. In Xset, clips of even camera IDs are used for training, and clips of odd IDs are used for testing." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.163, + 0.719, + 0.179 + ], + "angle": 0, + "content": "4.2. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.186, + 0.892, + 0.261 + ], + "angle": 0, + "content": "For data pre-processing, we follow CrosCLR [10] and AimCLR [6] except for that we resize the length of skeleton sequences to 100 frames, rather than 50 frames (Actually, by \\(2\\times\\) temporal sampling, we also maintain 50 frames for each clip). The mini-batch size is set to 128." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.262, + 0.892, + 0.352 + ], + "angle": 0, + "content": "Data Augmentation. For skeleton sequences, shear and crop are used as the normal augmentations \\(\\mathcal{T}\\). For strong augmentations \\(\\mathcal{T}'\\), we mainly use gaussian noise, gaussian blur, and channel mask. Since [18, 6] use more augmentations, we test if these augmentations (spatial flip, temporal flip, rotate) work in our approach." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.353, + 0.892, + 0.533 + ], + "angle": 0, + "content": "Self-supervised Pre-training. The baseline is Skeleton-CLR which follows the MoCo [8] framework. The queue size \\(\\mathbf{Q}\\) and temperature \\(\\tau\\) are set to 32768 and 0.07, respectively. For the backbone, we adopt ST-GCN [39], but the number of channels in each layer is reduced to \\(1/4\\) of the original settings. For the optimizer, we use SGD with momentum 0.9 and weight decay 0.0001. The pre-training runs 300 epochs with the initial learning rate 0.1 and multiplied by 0.1 at 250 epochs. For the two-stage training strategy, we train 150 epochs with the loss function \\(\\mathcal{L}_1\\), and another 150 epochs with \\(\\mathcal{L}_2\\). In the second training stage, nearest neighbors \\(N\\) is set to 1." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.534, + 0.892, + 0.624 + ], + "angle": 0, + "content": "Linear Evaluation Protocol. We add a linear classifier after the pre-trained encoder. During the linear evaluation, we freeze the parameters in encoder and only train the parameters in linear classifier. We use SGD with momentum 0.9. The model runs 100 epochs with the initial learning rate 3.0 and decayed by 10 at 80 epochs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.625, + 0.892, + 0.715 + ], + "angle": 0, + "content": "Finetune Protocol. We add a linear classifier after the pre-trained encoder. During the finetune, we train the whole model with SGD optimizer, the momentum is set to 0.9 and the weight decay is set to 0.0001. The model runs 100 epochs with the initial learning rate 0.01 and decayed by 10 at 80 epochs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.716, + 0.892, + 0.822 + ], + "angle": 0, + "content": "Semi-supervised Evaluation Protocol. We add a linear classifier after the pre-trained encoder. During the semi-supervised evaluation, we train the whole model with only \\(1\\%\\) or \\(10\\%\\) randomly selected labeled data. We choose SGD optimizer with momentum 0.9 and weight decay 0.0001. The model runs 100 epochs with the initial learning rate 0.01 and decayed by 10 at 80 epochs." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.832, + 0.654, + 0.848 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Tempo Prediction or RVTCLR. We first compare RVTCLR with the tempo prediction. Table 1 shows the comparison results of the joint stream on the NTU RGB+D 60" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13918" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.289 + ], + "angle": 0, + "content": "dataset using the linear evaluation protocol. It is obviously found that tempo prediction cannot bring good performance compared to RVTL, which verifies our claim that predicting each video's specific visual tempo results in unreasonable action features. The outcome of AC demonstrates that explicit consideration of apparent information also plays an important role in modeling actions. AC+RVTL's performance proves that relative visual tempo and appearance modeling can work collaboratively to better concentrate on both skeleton motion and appearance clues. By further combining NNM, the performance of RVTCLR boosts to \\(74.4\\%\\) (79.4%) on Xsub (Xview) benchmark, surpassing the tempo prediction by a large margin." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.302, + 0.472, + 0.342 + ], + "angle": 0, + "content": "Table 1. Comparisons between Tempo Prediction and RVTCLR. We report linear evaluation results of the joint stream on the NTU-60 dataset." + }, + { + "type": "table", + "bbox": [ + 0.164, + 0.342, + 0.385, + 0.429 + ], + "angle": 0, + "content": "
MethodsNTU-60
XsubXview
Tempo prediction52.758.0
RVTL63.173.4
AC65.168.4
AC+RVTL73.377.8
AC+RVTL+NNM74.479.4
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.446, + 0.473, + 0.749 + ], + "angle": 0, + "content": "Effectiveness of RVTCLR+. We then verify the effectiveness of RVTCLR+. Table 2 shows the comparison results of three streams. From the table, we have several observations: (1) RVTCLR performs much better than SkeletonCLR in most cases. For example, we can obtain \\(+4.2\\%\\) \\((+9.2\\%)\\) performance gain on Xsub (Xview) in the motion stream. By further combining DC branch, our RVTCLR+ can still significantly improve the accuracy by \\(+13.3\\%\\) and \\(+12\\%\\), respectively, which shows the efficacy of our method. (2) DC plays a more important role in the motion and bone streams. The primary reason we believe is due to the inherent presence of higher-order semantics in these two streams. The sparsity of skeleton data, however, may hinder the ability of naive contrastive learning to fully release their potential. As a result, recognition success may be limited to relying solely on low-level information. Our DC, however, force the model to focus on high-level semantics, thereby enabling the learning of more discriminative representations. (3) our 2-stream and 3-stream fusion results are always better than the comparative counterparts." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.904 + ], + "angle": 0, + "content": "We also conduct experiments in the motion stream to validate the effect of DC. As shown in Table 3 (a), we first determine whether all augmentations mentioned in [18, 6] applicable to SDA. Compared to the normal augmentation, we can find that gaussian noise, gaussian blur, and channel mask work well on both benchmarks. Although the others may perform better on Xsub, their results on Xview are relatively poor. Through empirical experimentation, we determine the former three augmentations as our best choice, yielding \\(+12.7\\%\\) and \\(+11.4\\%\\) accuracy increases over using" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.088, + 0.894, + 0.113 + ], + "angle": 0, + "content": "Table 2. Linear evaluation compared with SkeletonCLR. '2s' and '3s' means two-stream and three-stream fusion, respectively." + }, + { + "type": "table", + "bbox": [ + 0.511, + 0.115, + 0.885, + 0.324 + ], + "angle": 0, + "content": "
MethodsDCStreamNTU-60
XsubXview
SkeletonCLRjoint68.376.4
RVTCLRjoint74.479.4
RVTCLR+✓joint74.779.1
SkeletonCLRmotion53.350.8
RVTCLRmotion57.560.0
RVTCLR+✓motion70.872.0
SkeletonCLRbone69.467.4
RVTCLRbone68.171.7
RVTCLR+✓bone72.278.4
2s-SkeletonCLRjoint+motion70.577.9
2s-RVTCLRjoint+motion75.781.6
2s-RVTCLR+✓joint+motion77.882.2
3s-SkeletonCLRjoint+motion+bone75.079.8
3s-RVTCLRjoint+motion+bone77.282.0
3s-RVTCLR+✓joint+motion+bone79.784.6
" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.351, + 0.673, + 0.366 + ], + "angle": 0, + "content": "the normal augmentation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.366, + 0.892, + 0.501 + ], + "angle": 0, + "content": "FSEM is designed to emphasize the blurred joint connections. As shown in Table 3 (b), IIPB brings \\(+3.3\\%\\) performance improvement on Xview, proving its ability to adeptly capture the local spatial features. The accuracies of NLB are \\(70.0\\%\\) and \\(70.7\\%\\), respectively, which demonstrate that constructing global dependencies among frames can achieve a more representative feature extraction. By combining these two blocks, the performance of our final FSEM further boots to \\(70.8\\%\\) and \\(72.0\\%\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.503, + 0.892, + 0.595 + ], + "angle": 0, + "content": "DD loss is introduced to help learn more representative high-level features. From the Table 3 (b), we can see a large performance drop when we replace the DD loss with the original one. This suggests that compared to the one-hot distribution, the weakly augmented view provides more suitable supervision signals." + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.606, + 0.894, + 0.634 + ], + "angle": 0, + "content": "Table 3. Comparisons of DC's each component. We report linear evaluation results of the motion stream on the NTU-60 dataset." + }, + { + "type": "table", + "bbox": [ + 0.522, + 0.643, + 0.712, + 0.768 + ], + "angle": 0, + "content": "
SDANTU-60
XsubXview
Normal55.258.2
Gaussian noise66.872.6
Gaussian blur56.259.4
Channel mask57.358.6
Rotate55.557.1
Spatial flip57.656.1
Temporal flip59.455.9
Best Combination67.969.6
" + }, + { + "type": "table_caption", + "bbox": [ + 0.593, + 0.771, + 0.642, + 0.783 + ], + "angle": 0, + "content": "(a) SDA" + }, + { + "type": "table", + "bbox": [ + 0.715, + 0.643, + 0.868, + 0.771 + ], + "angle": 0, + "content": "
FSEMNTU-60
XsubXview
-67.969.6
IIPB68.072.9
NLB70.070.7
IIPB+NLB70.872.0
DD lossNTU-60
XsubXview
✓70.872.0
-64.663.6
" + }, + { + "type": "table_caption", + "bbox": [ + 0.728, + 0.774, + 0.855, + 0.787 + ], + "angle": 0, + "content": "(b) FSEM and DD loss" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.817, + 0.736, + 0.833 + ], + "angle": 0, + "content": "4.4. Performance Comparison" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Linear Evaluation. Table 4 and Table 5 show the comparisons on NTU-60 and NTU-120 under linear evaluation protocol. From the Table 4, we observe that our joint-stream RVTCLR+ achieves competitive results compared to the" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "13919" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.471, + 0.181 + ], + "angle": 0, + "content": "most recent SkeletonCLR [10] and AimCLR [6]. For example, \\(74.7\\%\\) vs \\(74.3\\%\\) on Xsub when compared to AimCLR. When multiple streams are fused, the performance of our method can be further improved. From the Table 5, we find that the performance of our 3s-RVTCLR+ remains at the forefront." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.182, + 0.474, + 0.348 + ], + "angle": 0, + "content": "Finetune Evaluation. Table 6 shows the comparisons on NTU-60 and NTU-120 under fineture evaluation protocol. The table reveals that our single-stream RVTCLR+ achieves \\(0.8\\% \\sim 2.1\\%\\) improvement over AimCLR on both datasets. Notably, 3s-ST-GCN [39] is pretrained under full supervision, and its performance is the ensemble of multi-streams, compared to it, our single-stream RVTCLR+ can still get comparable performance. When combining different streams, the accuracy of our 3s-RVTCLR+ can be further increased by \\(2.6\\% \\sim 5\\%\\), greatly outperforming AimCLR." + }, + { + "type": "table_caption", + "bbox": [ + 0.114, + 0.357, + 0.432, + 0.37 + ], + "angle": 0, + "content": "Table 4. Linear evaluation results on NTU-60 dataset." + }, + { + "type": "table", + "bbox": [ + 0.153, + 0.371, + 0.396, + 0.599 + ], + "angle": 0, + "content": "
MethodsNTU-60
XsubXview
Single-stream
LongT GAN [43]39.148.1
P&C [23]50.776.3
MS2L [11]52.6-
PCRP [38]54.963.4
AS-CAL [18]58.564.8
CRRL [31]67.673.8
SeBiReNet [16]-79.7
SkeletonCLR [10]68.376.4
AimCLR [6]74.379.7
RVTCLR+ (ours)74.779.1
Three-stream
3s-SkeletonCLR [10]75.079.8
3s-Colorization [41]75.283.1
3s-CrosSCLR [10]77.883.4
3s-AimCLR [6]78.983.8
3s-RVTCLR+ (Ours)79.784.6
" + }, + { + "type": "table_caption", + "bbox": [ + 0.11, + 0.614, + 0.436, + 0.626 + ], + "angle": 0, + "content": "Table 5. Linear evaluation results on NTU-120 dataset." + }, + { + "type": "table", + "bbox": [ + 0.158, + 0.626, + 0.39, + 0.748 + ], + "angle": 0, + "content": "
MethodsNTU-120
XsubXset
P&C [23]42.741.7
PCRP [38]43.044.6
AS-CAL [18]48.649.2
CRRL [31]56.257.0
ISC [25]67.967.1
3s-CrosSCLR [10]67.966.7
3s-AimCLR [6]68.268.8
3s-RVTCLR+ (Ours)68.068.9
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.87 + ], + "angle": 0, + "content": "Semi-supervised Evaluation. As shown in Table 7, with only \\(1\\%\\) and \\(10\\%\\) labeled data, the results of our 3s-RVTCLR+ far exceed MCC [24], 3s-CrosCLR [10], and 3s-AimCLR. For example, 3s-RVTCLR+ increases the accuracies by \\(2.5\\%\\) and \\(4.6\\%\\) compared with 3s-AimCLR on NTU-120 dataset. These results suggest that the representational capacity of our learned features is considerable." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Qualitative Results. We apply t-SNE [26] with fixed settings to show the embedding distribution of Skeleton-" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.087, + 0.892, + 0.129 + ], + "angle": 0, + "content": "Table 6. Finetune evaluation results on NTU-60 and NTU-120 dastatets. †means using the same bone stream. ‡means the model is pretrained under full supervision." + }, + { + "type": "table", + "bbox": [ + 0.53, + 0.129, + 0.864, + 0.252 + ], + "angle": 0, + "content": "
MethodsNTU-60NTU-120
XsubXviewXsubXset
SkeletonCLR† [10]82.288.973.675.3
MCC [24]83.089.777.077.8
AimCLR† [6]83.089.276.476.7
RVTCLR+†(Ours)84.491.377.278.4
3s-ST-GCN‡ [39]85.291.477.277.1
3s-CrosSCLR [10]86.292.580.580.4
3s-AimCLR [6]86.992.980.180.9
3s-RVTCLR+ (Ours)87.593.982.083.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.262, + 0.892, + 0.29 + ], + "angle": 0, + "content": "Table 7. Seim-supervised evaluation on NTU-60 and NTU-120 datasets. * means the results are obtained by their released codes." + }, + { + "type": "table", + "bbox": [ + 0.525, + 0.29, + 0.866, + 0.496 + ], + "angle": 0, + "content": "
MethodsNTU-60NTU-120
XsubXviewXsubXset
1% labeled data
ISC [25]35.738.1--
3s-Colorization [41]48.352.5--
3s-CrosCLR [10]51.150.028.6*28.0*
3s-AimCLR [6]54.854.334.8*32.6*
3s-RVTCLR+ (Ours)54.953.633.332.8
10% labeled data
ISC [25]65.972.5--
3s-Colorization [41]71.778.9--
MCC-ST-GCN [24]55.659.940.743.4
MCC-2s-AGCN [24]60.865.847.051.8
MCC-AS-GCN [24]59.263.144.947.8
3s-CrosCLR [10]74.477.861.3*61.1*
3s-AimCLR [6]78.281.664.8*63.7*
3s-RVTCLR+ (Ours)79.583.767.368.3
" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.511, + 0.634, + 0.591 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.518, + 0.596, + 0.62, + 0.608 + ], + "angle": 0, + "content": "(a) SkeletonCLR, j" + }, + { + "type": "image", + "bbox": [ + 0.638, + 0.512, + 0.764, + 0.591 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.645, + 0.596, + 0.752, + 0.607 + ], + "angle": 0, + "content": "(b) SkeletonCLR, m" + }, + { + "type": "image", + "bbox": [ + 0.766, + 0.512, + 0.894, + 0.591 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.776, + 0.596, + 0.88, + 0.607 + ], + "angle": 0, + "content": "(c) SkeletonCLR, b" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.621, + 0.634, + 0.7 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.525, + 0.706, + 0.614, + 0.718 + ], + "angle": 0, + "content": "(d) RVTCLR+, j" + }, + { + "type": "image", + "bbox": [ + 0.638, + 0.622, + 0.764, + 0.701 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.651, + 0.706, + 0.745, + 0.717 + ], + "angle": 0, + "content": "(e) RVTCLR+, m" + }, + { + "type": "image", + "bbox": [ + 0.766, + 0.622, + 0.894, + 0.701 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.783, + 0.706, + 0.873, + 0.717 + ], + "angle": 0, + "content": "(f) RVTCLR+, b" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.718, + 0.892, + 0.759 + ], + "angle": 0, + "content": "Figure 4. The t-SNE visualization of embeddings on NTU-60 X-sub. These models are trained for 300 epochs. j, b, and m represent joint-stream, bone-stream, and motion-stream, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.9 + ], + "angle": 0, + "content": "CLR and our RVTCLR+ on NTU-60 Xsub benchmark. For a fair comparison, we select the same 11 classes for visualization, where each class is represented by a dot of the same color. From the Figure 4, we can obviously see that the embeddings extracted from our method have better inter-class separability and intra-class compactness, indicating that our learned features are more discriminative." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13920" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.09, + 0.196, + 0.106 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.115, + 0.473, + 0.358 + ], + "angle": 0, + "content": "In this paper, we propose a Relative Visual Tempo Contrastive Learning framework for skeleton action representation (RVTCLR). The proposed RVTCLR combines Relative Visual Tempo Learning (RVTL) and Appearance-Consistency (AC) into a single-branch to obtain a more comprehensive spatial-temporal representation. Given the inherent sparsity of skeleton sequence data compared to RGB data, we design a new Distribution-Consistency (DC) branch aimed at emphasizing high-order semantics and preventing the network from learning shortcuts. The DC branch consists of Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. We refer to this new two-branch structure as RVTCLR+. Experimental results and visualization analysis verify that RVTCLR+ can obtain a more discriminative skeleton action representation." + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.371, + 0.175, + 0.387 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.395, + 0.47, + 0.464 + ], + "angle": 0, + "content": "[1] Unaiza Ahsan, Rishi Madhok, and Irfan Essa. Video jigsaw: Unsupervised learning of spatiotemporal context for video action recognition. In 2019 IEEE Winter Conference on Applications of Computer Vision (WACV), pages 179-189, 2019." + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.466, + 0.472, + 0.548 + ], + "angle": 0, + "content": "[2] Peihao Chen, Deng Huang, Dongliang He, Xiang Long, Runhao Zeng, Shilei Wen, Mingkui Tan, and Chuang Gan. Rspnet: Relative speed perception for unsupervised video representation learning. 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The Visual Computer, 36(9):1771-1781, 2020." + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.614 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "13922" + } + ] +] \ No newline at end of file diff --git a/2023/Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition/dbdfe6ed-ba3c-4daf-ac10-86c2b2f20cde_origin.pdf b/2023/Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition/dbdfe6ed-ba3c-4daf-ac10-86c2b2f20cde_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..38d371967d5092dbd429b9f7d0b938469e5df0ec --- /dev/null +++ b/2023/Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition/dbdfe6ed-ba3c-4daf-ac10-86c2b2f20cde_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:03f32ffe88a8bd72f487c1bbec72f2e60fc883be5bc968f80cc84278d0240abf +size 3467510 diff --git a/2023/Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition/full.md b/2023/Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition/full.md new file mode 100644 index 0000000000000000000000000000000000000000..aba513f573512bd7674d192a51da621d9a0d0cad --- /dev/null +++ b/2023/Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition/full.md @@ -0,0 +1,346 @@ +# Modeling the Relative Visual Tempo for Self-supervised Skeleton-based Action Recognition + +Yisheng Zhu $^{1}$ , Hu Han $^{2,3}$ , Zhengtao Yu $^{4}$ , Guangcan Liu $^{5*}$ + +$^{1}$ Nanjing University of Posts and Telecommunications + +$^{2}$ Key Laboratory of Intelligent Information Processing, Institute of Computing Technology (ICT), Chinese Academy of Sciences (CAS) + +3University of the Chinese Academy of Sciences + +$^{4}$ Faculty of Information Engineering and Automation, Kunming University of Science and Technology $^{5}$ School of Automation, Southeast University + +yszhu1995@163.com, huhan@ict.ac.cn, ztyu@hotmail.com, guangcanliu@seu.edu.cn + +# Abstract + +Visual tempo characterizes the dynamics and the temporal evolution, which helps describe actions. Recent approaches directly perform visual tempo prediction on skeleton sequences, which may suffer from insufficient feature representation issue. In this paper, we observe that relative visual tempo is more in line with human intuition, and thus providing more effective supervision signals. Based on this, we propose a novel Relative Visual Tempo Contrastive Learning framework for skeleton action Representation (RVTCLR). Specifically, we design a Relative Visual Tempo Learning (RVTL) task to explore the motion information in intra-video clips, and an Appearance-Consistency (AC) task to learn appearance information simultaneously, resulting in more representative spatiotemporal features. Furthermore, skeleton sequence data is much s-parser than RGB data, making the network learn shortcuts, and overfit to low-level information such as skeleton scales. To learn high-order semantics, we further design a new Distribution-Consistency (DC) branch, containing three components: Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. We term our entire method (RVTCLR with DC) as RVTCLR+. Extensive experiments on NTU RGB+D 60 and NTU RGB+D 120 datasets demonstrate that our RVTCLR+ can achieve competitive results over the state-of-the-art methods. Code is available at https://github.com/Zhuysheng/RVTCLR. + +Basic idea of visual tempo prediction + +![](images/3f1f7042a456af3ba0cc80ddda05313d77ca71a14d4cf60d5c348328b9956727.jpg) + +![](images/0e24985cd7d38418ceabefc9e3354ccd3d408c67c9bff3dfa1a281b6286f3db7.jpg) +(a) Top-1 Accuracy on NTU-60 Xsub: 52.7% + +![](images/c646e7a6a972f68a623ffab8ac0b393eb466da2178188f2e06198156f10725ca.jpg) + +![](images/1cd5faa73718ce48ebc5706b482b46e207dd5b479abaa93db4f43c367dfc25b1.jpg) + +Relative visual tempo learning and appearance-consistency + +![](images/c814ecd2553d52430c42e974aacc1d85b8d1964e7a58e2e64aff2bbd2e72a920.jpg) +Figure 1. The basic visual tempo prediction is considered a classification task, where the learned model is used to assign tempo labels to individual video clips. We introduce relative visual tempo learning and appearance-consistency based on contrastive learning. It's more human-intuitive for modeling actions. The top-1 accuracy on NTU-60 Xsub benchmark supports our claim. + +![](images/fc6830ffbba93c8d5348d88d85befd97c5bcc101bda8b003908ff93bfb720594.jpg) +(b) Top-1 Accuracy on NTU-60 Xsub: $73.3\%$ + +![](images/39a689b6f4003dd70cacd189a3289977ffe464f1dca5178b1f616b1b4acb94cc.jpg) + +![](images/57a790439ae4dab23b7504323de97de0e39a93f6ed1a1f4284548357d1a716ff.jpg) + +# 1. Introduction + +As one of the most fundamental topics in video understanding, human action recognition has been widely explored in many real-world scenarios, such as human-computer interaction [22], autonomous driving [30], and so on [34, 17]. Skeleton data provides more abstract and well-structured information with less computation and storage than raw RGB video. It is less susceptible to camera viewpoint changes and background distractions. Thus, skeleton-based action recognition has attracted extensive at + +tention [39, 21, 28, 7, 35]. However, most of these methods rely heavily on full supervision. The collection of massive annotations is labor-intensive and time-consuming. Under this circumstance, learning action representations directly from the data in a self-supervised manner has attracted increasing attentions. + +Several existing works [11, 38, 41] draw inspiration from video self-supervised learning and directly apply video pretext tasks on skeleton sequences, such as jigsaw puzzle recognition [1, 9] and temporal order prediction [15, 37]. For sequence data, a commonly used technique to model spatiotemporal information is visual tempo prediction [42, 29]. Action visual tempo describes the speed at which actions are performed, which is crucial for distinguishing actions that exhibit similar temporal evolutions (e.g., walking and jogging). The basic idea is shown in the upper part of Figure 1. For each video, clips are sampled at different sampling frequencies to mimic different visual tempos (e.g., $1 \times$ and $2 \times$ ), and predictions are made using the backbone network. However, there are limitations in directly applying it to skeleton sequences. People perform actions at their own tempo due to the influence of gender, age, etc. Even at the same tempo, the athlete's walking speed is visibly faster than that of a child in a third-person perspective. Therefore, it's obviously inappropriate to treat tempo prediction as a classification task. Furthermore, this basic strategy mainly focuses on motion information and cannot explicitly encourage the model to explore appearance information that is equally important for recognizing actions. Recently, contrastive learning has shown its great potential in extracting informative features [10, 6] in skeleton-based action recognition. Contrastive learning typically converts the naive classification task to a matching problem and learns an embedding space in which augmentations of same skeleton sequence are kept closer together, while different augmentations are far apart. In this way, the above issues can be alleviated in an elegant way. However, skeleton sequence data is much sparser than RGB data, and applying contrastive learning naively without explicit guidance may lead to model overfitting low-level information such as skeleton scales and angles, while failing to learn high-order semantics, resulting in insufficient feature representation capabilities. + +To this end, we propose RVTCLR: a Relative Visual Tempo Contrastive Learning framework for skeleton action Representation. The basic idea is shown at the bottom of Figure 1. First, we observe that it's intuitively plausible to compare relative visual tempos within videos rather than to predict a specific visual tempo for each video. Specifically, for each video, we sample 3 clips with different visual tempos (e.g., $1 \times$ , $1 \times$ , and $2 \times$ ) to construct the contrastive pairs and train a network to pull the anchor-positive pairs closer while repelling the anchor-negative pairs. Furthermore, + +to make the representations explicitly focus on appearance information, we design another Appearance-Consistency (AC) task. In this task, pairs from the same video are attracted no matter their visual tempos, while pairs from different videos are pushed away. In this way, the learned representations are expected to focus on both skeleton motion and appearance information simultaneously. + +In addition, in order to encourage the models to learn high-order semantics, we introduce a new Distribution-Consistency (DC) branch based on RVTCLR, which contains three components: Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. We refer to this as RVTCLR+. First, we leverage SDA to generate more difficult contrastive pairs by applying more skeleton-specific transformations (e.g., gaussian noise) at the input level, since augmentation plays a key role in learning better representations, as demonstrated by SimCLR [3] and MoCo [8]. However, too much strong augmentations may blur the joint connections compared to the normal augmented sequence (i.e., crop and shear), resulting in performance degradation. Benefiting from recent attention mechanisms [5, 13, 44], we try to emphasize these connections by designing a novel module, FSEM, which contains an Intra-Inter-Part block (IIPB) for local spatial modeling and a Non-local block (NLB) [32] for global spatiotemporal modeling. Finally, inspired by [33, 6], we introduce a DD loss to minimize the distributional divergence between the normal augmented view and our DC branch. By combining these components, we hope that the DC branch can better learn local and global spatiotemporal features, which help to extract discriminative high-order semantics. + +To sum up, the contributions of this work include: (1) We propose a novel contrastive representation learning framework named RVTCLR. The proposed RVTCLR leverages Relative Visual Tempo Learning (RVTL) task to learn better skeleton motion information. By combining another Appearance-Consistency (AC) task, our model explicitly learns to concentrate on skeleton appearance information simultaneously. (2) To encourage models to focus on high-order semantics, we propose RVTCLR+ by introducing a new Distribution-Consistency (DC) branch. This DC branch contains three components: Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. (3) These contrastive tasks are jointly trained using a two-branch structure such that the models can learn both spatiotemporal and high-order semantics simultaneously. + +# 2. Related Work + +Self-supervised skeleton-based action recognition. To meet the requirements of real-time recognition, it's necessary for the models to be able to directly extract dis + +criminative action representations from the label-free online videos. Recent progress in self-supervised skeleton-based action recognition can be summarized into two categories: pretext-task based learning [11, 38, 41, 43, 23] and contrastive learning [18, 10, 6, 25, 31, 24]. For example, Zheng et al. [43] design a skeleton inpainting architecture to learn the long-term dynamics. Lin et al. [11] integrate multiple tasks such as jigsaw puzzle recognition to learn more general skeleton features. Xu et al. [38] propose reverse sequential predictions based on encoder-decoder structure to extract motion pattern. However, the representations learned by these methods may not be good enough, in the sense that they could be exclusively particular to the pre-designed tasks. Inspired by the success of contrastive learning in image classification (e.g., instance discrimination [36], SimCLR [3], and MoCo [8]), Rao et al. [18] first propose to perform contrastive learning among different augmentations of unlabeled skeleton data, to learn inherent action patterns. Thoker et al. [25] propose to generate contrastive pairs based on different input-representations of the skeleton sequences, i.e., graph, sequence, and image representation. By leveraging multiple views of the skeleton data, i.e., joint, bone, and motion, Li et al. [10] introduce SkeletonCLR and CrosSCLR to perform the single-view and cross-view contrastive learning. Guo et al. [6] further propose AimCLR to learn from extremely augmented skeleton sequences. + +Nevertheless, none of the aforementioned methods concentrate on visual tempo, which is crucial for characterizing human action dynamics. To our best knowledge, Su et al. [24] propose motion consistency and continuity learning, which has overlap with our framework. However, the differences are obvious, which mainly lie in three aspects: (1) contrastive pairs are generated differently. In [24], speed-changed clips are considered as positive pairs, while we focus on relative visual tempo and regard these clips as negative pairs. (2) appearance information is modeled differently. In [24], appearance information is implicitly modeled in the contrastive learning process, while we design another Appearance-Consistency (AC) task specifically for spatial modeling. (3) learned features are enhanced differently. In [24], learned features are enhanced by designing a self-reconstruction based motion continuity module, while we introduce a novel Distribution-Consistency (DC) branch to guide the models focus on high-order semantics. + +Visual tempo modeling. Visual tempo describes the speed of human movements, which has already been applied into various action recognition methods [4, 40, 14]. For example, Feichtenhofer et al. [4] first propose SlowFast network to explore the potential of different visual tempos. It consists of two pathways, operating at different frame rates, to capture both spatial semantics and motion dynamics. When it comes to video self-supervised learning [42, 29, 2], the potential of visual tempo in motion mod + +eling is further verified. Yao et al. [42] utilize video playback rates as self-supervision signals and propose playback rate perception to learn spatiotemporal features in a collaborative discrimination-generation manner. The above methods usually require assigning visual tempos to each video clip according to different sampling rates, and then elaborate learning paradigms through reconstruction or prediction, but this is suboptimal in learning discriminative representations. Chen et al. [2] argue that relative speed is more in line with motion pattern. They propose a new video self-supervised learning framework (called RSPNet) to leverage the relative speed between two video clips to supervise the representation learning. Inspired by RSPNet, the proposed RVTCLR focuses on relative visual tempo learning with skeleton-specific modifications. + +# 3. Methods + +# 3.1. Preliminaries + +SkeletonCLR. SkeletonCLR [10] utilizes ST-GCN [39] as its backbone and follows the practice in MoCo [8] to learn skeleton action representations. Suppose that a skeleton sequence $s = (s^1, s^2, \ldots, s^T)$ contains $T$ consecutive skeleton frames, where $s^i \in \mathbb{R}^{3 \times V \times M}$ means 3D coordinates of $V$ joints for $M$ actors. A data augmentation module $\mathcal{T}$ is first utilized to randomly transform the given $s$ into different augmentations $x_q$ and $x_k$ . Then, a query encoder $f(\cdot; \theta_q)$ and a momentum updated key encoder $f(\cdot; \theta_k)$ are leveraged to encode $x_q$ and $x_k$ into hidden space $h_q$ and $h_k$ . These embeddings are further passed through a projector $g(\cdot; \theta_q)$ and its momentum updated version $g(\cdot; \theta_k)$ to get the final query features $q$ and key features $k$ . In each training step, samples in the queue $\mathbf{Q} = \{m_o\}_{o=1}^K$ are progressively replaced by the key features $k$ following a first-in-first-out scheme. Following MoCo, $q$ and $k$ serve as positive pairs while $q$ and embeddings in $\mathbf{Q}$ serve as negative pairs. The InfoNCE loss [36] is used to guide the network learning, which can be formulated as: + +$$ +\mathcal {L} _ {I n f o} = - \log \frac {\exp (q \cdot k / \tau)}{\exp (q \cdot k / \tau) + \sum_ {o = 1} ^ {K} \exp (q \cdot m _ {o} / \tau)} (1) +$$ + +where $\tau$ is the temperature hyper-parameter, and $\cdot$ represents the similarity measured by dot product. + +After computing the InfoNCE loss, the parameters of $\theta_{q}$ are updated by gradient back-propagation while the parameters of $\theta_{k}$ are updated as their moving-average: + +$$ +\theta_ {k} \leftarrow \alpha \theta_ {k} + (1 - \alpha) \theta_ {q} \tag {2} +$$ + +where $\alpha$ is a momentum coefficient (set to 0.999 by default). + +Nearest Neighbors Mining. Traditional InfoNCE regards all samples in the memory bank as negative. This overly hard approach may lead to non-generic feature embeddings. To address the above issue, [10, 6] propose + +![](images/4c30ef37b7ae45b07a21750cf0b57165bfa3883a7813b02c47a250bf2dca3517.jpg) +Figure 2. The pipeline of our method. For each skeleton sequence, we sample clips with varying visual tempos. Then, we use a two-branch structure to extract discriminative feature from each sequence. Specifically, in RVTCLR, the Relative Visual Tempo Learning (RVTL) is responsible for modeling motion dynamics. The Appearance-Consistency (AC) is responsible for modeling appearance characteristics. These two tasks are combined into one branch to achieve a more comprehensive spatial-temporal representation. In another Distribution-Consistency (DC) branch, we introduce Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss to guide the network to concentrate on extracting high-order semantics. + +to leverage Nearest Neighbors Mining (NNM) to generate more positive pairs: + +$$ +\mathcal {L} _ {N N M} = - \log \frac {\exp (q \cdot k / \tau) + \sum_ {o \in N _ {+}} \exp (q \cdot m _ {o} / \tau)}{\exp (q \cdot k / \tau) + \sum_ {o = 1} ^ {K} \exp (q \cdot m _ {o} / \tau)} \tag {3} +$$ + +where $N_{+}$ represents the top- $N$ nearest neighbors that are most similar to the query features $q$ in the memory queue. + +Since the model learned in the early training stages may not be strong enough to provide confident nearest neighbors, [10, 6] propose to perform a two-stage training, i.e., first train the model using Equation 1, and then train the model to mine the nearest neighbors using Equation 3. + +In this paper, we mainly implement our method based on SkeletonCLR and two-stage training strategy. + +# 3.2.RVTCLR + +Relative Visual Tempo Learning (RVTL). Observing that each person performs actions at his/her own visual tempo, we introduce a RVTL task, which aims to learn better skeleton motion information. Specifically, given a skeleton sequence $s$ with $T$ frames, we first sample 3 clips $c_{i}$ , $c_{j}$ and $c_{k}$ with visual tempos $v_{i}$ , $v_{j}$ and $v_{k}$ , respectively, where $v_{i} = v_{j} \neq v_{k}$ . Note that visual tempos can be set arbitrarily, i.e., $\{1 \times, 2 \times, 3 \times,..\}$ . However, to avoid the temporal ambiguity in skeleton sequences, we only consider $1 \times$ and $2 \times$ , which represent that the sampling interval is set to 1 and 2 frames. We sample from the first frame and keep + +a duration of $T / 2$ for each clip. Then, we apply normal skeleton augmentations $\mathcal{T}$ on these three clips respectively to construct a triplet, i.e., anchor $a = \mathcal{T}(c_i)$ , positive $p = \mathcal{T}(c_j)$ and negative $n = \mathcal{T}(c_k)$ . This triplet is further fed into SkeletonCLR with a projection head $g_{r}(\cdot ;\theta_{q_{r}})$ and its momentum updated $g_{r}(\cdot ;\theta_{k_{r}})$ to generate the encoded features $(q_{a},k_{p},k_{n})$ . Finally, these features are normalized and combined as anchor-positive pairs $(q_{a},k_{p})$ and anchor-negative pairs $(q_{a},k_{n})$ , and our goal is to pull $(q_{a},k_{p})$ closer while pushing $(q_{a},k_{n})$ away. The assumption here is that the network can only succeed in such a RVTL task if it understands the intrinsic visual tempo of each clip and learns discriminative motion information. This task is realized by a triplet loss [19]: + +$$ +\mathcal {L} _ {R V T L} = \max \left\{- \left(q _ {a} \cdot k _ {p} - q _ {a} \cdot k _ {n}\right) + \operatorname {m a r g i n}, 0 \right\} \tag {4} +$$ + +where the margin (set to 1 by default) is a hyper-parameter to control the distance between two components. + +Appearance-Consistency (AC). Appearance information is also essential for recognizing actions. To this end, we introduce another AC task to explicitly learn such information. Specifically, given a skeleton sequence, we first sample two clips $c_{i}$ , $c_{j}$ with visual tempos randomly selected in $\{1\times ,2\times \}$ . Then, they are normally augmented and sent to SkeletonCLR with another projection head $g_{a}(\cdot ;\theta_{q_{a}})$ and its momentum updated $g_{a}(\cdot ;\theta_{k_{a}})$ to generate the encoded features $(q_{i},k_{j})$ . Note that the query and key encoders in AC share weights with the encoders in RVTL while the + +projection heads $g_{a}(\cdot;\theta_{q_{a}})$ and $g_{a}(\cdot;\theta_{k_{a}})$ have weights independent of $g_{r}(\cdot;\theta_{q_{r}})$ and $g_{r}(\cdot;\theta_{k_{r}})$ . Here, the goal is to pull $q_{i}$ and $k_{j}$ closer while pushing away $q_{i}$ and negative samples in queue $\mathbf{Q}$ . Although from the same sample, clips with various visual tempos show different temporal motion dynamics, by pulling such a pair closer while pushing away different samples, we want the model to explicitly focus on appearance information. This task is realized by the InfoNCE loss: + +$$ +\mathcal {L} _ {A C} = - \log \frac {\exp \left(q _ {i} \cdot k _ {j} / \tau\right)}{\exp \left(q _ {i} \cdot k _ {j} / \tau\right) + \sum_ {o = 1} ^ {K} \exp \left(q _ {i} \cdot m _ {o} / \tau\right)} \tag {5} +$$ + +Based on SkeletonCLR, we jointly train these tasks. In the first training stage, we train the model with the loss function: $\mathcal{L}_1 = \lambda_1\mathcal{L}_{RVTL} + \lambda_2\mathcal{L}_{AC}$ , and then in the second training stage, we try to obtain more positive samples by using $\mathcal{L}_2 = \lambda_1\mathcal{L}_{RVTL} + \lambda_2\mathcal{L}_{AC'}$ , where $\lambda$ (set to 1 by default) is the coefficient to balance the loss and $\mathcal{L}_{AC'}$ is defined in Equation 3. + +![](images/dfbf49ac5609bbeff85a355dfa5ceb80cf82cf47aeff78ac9a6a348926400428.jpg) +Figure 3. Illustration of FSEM. (a) The workflow of FSEM. (b) IIPB is responsible for local spatial modeling, containing intra-part and inter-part relational reasoning submodules. (c) NLB is responsible for global spatial-temporal modeling. + +# 3.3.RVTCLR+ + +The success of contrastive learning depends on the construction of contrastive pairs and the difficulty of learning paradigm. Given that the skeleton sequences are much s-sparser, naive contrastive learning may risk overfitting low-level information such as skeleton scales. It would be even better if we could design a new branch to explicitly learn skeleton high-order semantics. We thus propose RVTCLR+ by designing our Distribution-Consistency (DC). + +SDA. We leverage SDA to generate more difficult contrastive pairs. The SDA contains normal augmentations $\mathcal{T}$ : crop and shear, and additional strong augmentations $\mathcal{T}'$ : gaussian noise, gaussian blur, and channel mask. Given a skeleton sequence $s$ , we apply $\mathcal{T}$ and $\mathcal{T}'$ to get the transformed version: $e = \mathcal{T}'(\mathcal{T}(s))$ . Afterwards, we send it + +to the weight-sharing query encoder to encode $e$ into hidden space $h_e$ , which is further passed through a projector $g_e(\cdot; \theta_{q_e})$ to obtain the final embeddings $q_e$ . + +FSEM. Such a direct modeling method may be suboptimal, since the additional augmentations may cause blurred joint connections. Considering that skeleton sequences are spatiotemporal cubes, we design FSEM to highlight these connections. As shown in Figure 3, our FSEM contains an Intra-Inter-Part block (IIPB), which is responsible for local spatial modeling, and a Non-local block (NLB), which is responsible for global spatial-temporal modeling. Given the encoded $h_e \in \mathbb{R}^{C \times T \times V}$ , in IIPB, we first divide each human skeleton into 5 parts according to the physical topology of the body. Then, average pooling is applied on each part to generate the intra-part representations $h_{e'} \in \mathbb{R}^{C \times T \times 5}$ . Two $1 \times 1$ convolution layers are further utilized to establish the inter-part relations: + +$$ +h _ {\hat {e}} = \operatorname {C o n v 2} \left(\operatorname {R e L U} \left(\operatorname {C o n v 1} \left(h _ {e ^ {\prime}}, W _ {1}\right)\right), W _ {2}\right) \tag {6} +$$ + +where $W_{1} \in \mathbb{R}^{\frac{C}{2} \times C}$ and $W_{2} \in \mathbb{R}^{C \times \frac{C}{2}}$ are learnable parameters. $ReLU$ is the activation function. The intuition here is that connections between body parts can sometimes better describe actions (e.g., the coordination of arm and leg in 'running'). By using IIPB, we establish the part-based connections that seek to mitigate the effects of blurred joints. + +IIPB can capture the local dependencies of intra-frame parts. However, global inter-frame connections are ignored, which are also essential for describing actions. We introduce NLB to associate all possible frames of a skeleton sequence in a self-attention mechanism [27]. The non-local operation computes frame dependencies by enumerating all possible frames: + +$$ +y ^ {t} = \frac {1}{\mathcal {C} \left(h _ {\hat {e}}\right)} \sum_ {\forall t ^ {\prime}} f \left(h _ {\hat {e}} ^ {t}, h _ {\hat {e}} ^ {t ^ {\prime}}\right) g \left(h _ {\hat {e}} ^ {t ^ {\prime}}\right) \tag {7} +$$ + +where $h_{\hat{e}}^{t}$ and $h_{\hat{e}}^{t'}$ denote the input at frame $t$ and $t'$ , respectively. $g(\cdot)$ is a linear function. $\mathcal{C}(\cdot)$ is a normalization term. An embedded gaussian function $f(\cdot, \cdot)$ [32] computes the relationships between $t$ and all $t'$ . We wrap the non-local operation in Equation 7 into NLB with a residual layer as: + +$$ +h _ {\tilde {e}} = W _ {3} y + h _ {\hat {e}} \tag {8} +$$ + +where $W_{3}$ is a learnable embedding for $y$ . Finally, we send it to the projector to generate the new embeddings $q_{\widetilde{e}}$ . Note that FSEM can be plugged into different GCN layers, we only insert the FSEM before the projector for the reduction of experiment cost. + +DD Loss. The distributional divergence between weakly augmented counterparts and strongly augmented views enables the framework to explore novel patterns, which may help extract representative high-level features. Formally, + +given the encoded query features $q_{a}$ , the encoded key features $k_{p}$ , and the memory queue $\mathbf{Q} = \{m_{o}\}_{o=1}^{K}$ , we can obtain a conditional distribution: + +$$ +p \left(k _ {p} \mid q _ {a}\right) = \frac {\exp \left(q _ {a} \cdot k _ {p} / \tau\right)}{\exp \left(q _ {a} \cdot k _ {p} / \tau\right) + \sum_ {o = 1} ^ {K} \exp \left(q _ {a} \cdot m _ {o} / \tau\right)} (9) +$$ + +which encodes the likelihood of the query $q_{a}$ being assigned to the key $k_{p}$ . By replacing $k_{p}$ with $m_{o}$ , we can also obtain the likelihood that the query $q_{a}$ is assigned to the negative embeddings in $\mathbf{Q}$ . Then, the InfoNCE loss in Equation 1 can be rewritten as: + +$$ +\mathcal {L} _ {\text {I n f o}} = - q \left(k _ {p} \mid q _ {a}\right) \log p \left(k _ {p} \mid q _ {a}\right) - \sum_ {o = 1} ^ {K} q \left(m _ {o} \mid q _ {a}\right) \log p \left(m _ {o} \mid q _ {a}\right) \tag {10} +$$ + +where $q(\cdot|\cdot)$ is the ideal distribution of the likelihood, $p(k_p|q_a)$ is the distribution learned by network. In InfoNCE, $q(k_p|q_a)$ and $q(m_o|q_a)$ are simply set to 1 and 0 based on one-hot distribution, respectively. When applied to $q_{\widetilde{e}}$ , a straightforward approach is to directly replace $q_a$ in Equation 10 with $q_{\widetilde{e}}$ . However, as demonstrated in [33, 6], the one-hot distribution cannot mimic the ideal distribution and thus cannot help representations learning any more. Conversely, the similarity distribution of weakly-augmented queries for the same instance in a queue can provide useful clues for strong-augmentation based learning. This inspires us to leverage $p(k_p|q_a)$ and $p(m_o|q_a)$ as the ideal distribution to supervise $q_{\widetilde{e}}$ : + +$$ +\begin{array}{l} \mathcal {L} _ {D C} = - p \left(k _ {p} \mid q _ {a}\right) \log p \left(k _ {p} \mid q _ {\bar {e}}\right) \\ - \sum_ {o = 1} ^ {K} p \left(m _ {o} \mid q _ {a}\right) \log p \left(m _ {o} \mid q _ {\tilde {e}}\right) \tag {11} \\ \end{array} +$$ + +By combining DC, the final loss our RVTCLR+ can be formulated as $\mathcal{L}_1 = \lambda_1\mathcal{L}_{RVTL} + \lambda_2\mathcal{L}_{AC} + \lambda_3\mathcal{L}_{DC}$ and $\mathcal{L}_2 = \lambda_1\mathcal{L}_{RVTL} + \lambda_2\mathcal{L}_{AC'} + \lambda_3\mathcal{L}_{DC}$ . + +# 4. Experiments + +# 4.1. Datasets + +NTU RGB+D 60 Dataset [20]: It contains 56880 skeleton video clips over 60 action classes capture from 40 subjects and 3 different camera view angles. Each clip provides 25 body joints with 3D coordinates for at most 2 subjects. There are two evaluation benchmarks: cross-subject (Xsub) and cross-view (Xview). In Xsub, clips of 20 subjects are used for training, and the rest are used for testing. In Xview, clips of camera 2 and 3 are used for training, and clips of camera 1 are used for testing. + +NTU RGB+D 120 Dataset [12]: It is an extension of N-TU RGB+D 60 with 113945 samples over 120 classes capture from 106 subjects and 32 different camera setups. Two evaluation benchmarks are recommended: cross-subject + +(Xsub) and cross-setup (Xset). In Xsub, clips of 53 subjects are used for training, and the rest are used for testing. In Xset, clips of even camera IDs are used for training, and clips of odd IDs are used for testing. + +# 4.2. Implementation Details + +For data pre-processing, we follow CrosCLR [10] and AimCLR [6] except for that we resize the length of skeleton sequences to 100 frames, rather than 50 frames (Actually, by $2\times$ temporal sampling, we also maintain 50 frames for each clip). The mini-batch size is set to 128. + +Data Augmentation. For skeleton sequences, shear and crop are used as the normal augmentations $\mathcal{T}$ . For strong augmentations $\mathcal{T}'$ , we mainly use gaussian noise, gaussian blur, and channel mask. Since [18, 6] use more augmentations, we test if these augmentations (spatial flip, temporal flip, rotate) work in our approach. + +Self-supervised Pre-training. The baseline is Skeleton-CLR which follows the MoCo [8] framework. The queue size $\mathbf{Q}$ and temperature $\tau$ are set to 32768 and 0.07, respectively. For the backbone, we adopt ST-GCN [39], but the number of channels in each layer is reduced to $1/4$ of the original settings. For the optimizer, we use SGD with momentum 0.9 and weight decay 0.0001. The pre-training runs 300 epochs with the initial learning rate 0.1 and multiplied by 0.1 at 250 epochs. For the two-stage training strategy, we train 150 epochs with the loss function $\mathcal{L}_1$ , and another 150 epochs with $\mathcal{L}_2$ . In the second training stage, nearest neighbors $N$ is set to 1. + +Linear Evaluation Protocol. We add a linear classifier after the pre-trained encoder. During the linear evaluation, we freeze the parameters in encoder and only train the parameters in linear classifier. We use SGD with momentum 0.9. The model runs 100 epochs with the initial learning rate 3.0 and decayed by 10 at 80 epochs. + +Finetune Protocol. We add a linear classifier after the pre-trained encoder. During the finetune, we train the whole model with SGD optimizer, the momentum is set to 0.9 and the weight decay is set to 0.0001. The model runs 100 epochs with the initial learning rate 0.01 and decayed by 10 at 80 epochs. + +Semi-supervised Evaluation Protocol. We add a linear classifier after the pre-trained encoder. During the semi-supervised evaluation, we train the whole model with only $1\%$ or $10\%$ randomly selected labeled data. We choose SGD optimizer with momentum 0.9 and weight decay 0.0001. The model runs 100 epochs with the initial learning rate 0.01 and decayed by 10 at 80 epochs. + +# 4.3. Ablation Study + +Tempo Prediction or RVTCLR. We first compare RVTCLR with the tempo prediction. Table 1 shows the comparison results of the joint stream on the NTU RGB+D 60 + +dataset using the linear evaluation protocol. It is obviously found that tempo prediction cannot bring good performance compared to RVTL, which verifies our claim that predicting each video's specific visual tempo results in unreasonable action features. The outcome of AC demonstrates that explicit consideration of apparent information also plays an important role in modeling actions. AC+RVTL's performance proves that relative visual tempo and appearance modeling can work collaboratively to better concentrate on both skeleton motion and appearance clues. By further combining NNM, the performance of RVTCLR boosts to $74.4\%$ (79.4%) on Xsub (Xview) benchmark, surpassing the tempo prediction by a large margin. + +Table 1. Comparisons between Tempo Prediction and RVTCLR. We report linear evaluation results of the joint stream on the NTU-60 dataset. + +
MethodsNTU-60
XsubXview
Tempo prediction52.758.0
RVTL63.173.4
AC65.168.4
AC+RVTL73.377.8
AC+RVTL+NNM74.479.4
+ +Effectiveness of RVTCLR+. We then verify the effectiveness of RVTCLR+. Table 2 shows the comparison results of three streams. From the table, we have several observations: (1) RVTCLR performs much better than SkeletonCLR in most cases. For example, we can obtain $+4.2\%$ $(+9.2\%)$ performance gain on Xsub (Xview) in the motion stream. By further combining DC branch, our RVTCLR+ can still significantly improve the accuracy by $+13.3\%$ and $+12\%$ , respectively, which shows the efficacy of our method. (2) DC plays a more important role in the motion and bone streams. The primary reason we believe is due to the inherent presence of higher-order semantics in these two streams. The sparsity of skeleton data, however, may hinder the ability of naive contrastive learning to fully release their potential. As a result, recognition success may be limited to relying solely on low-level information. Our DC, however, force the model to focus on high-level semantics, thereby enabling the learning of more discriminative representations. (3) our 2-stream and 3-stream fusion results are always better than the comparative counterparts. + +We also conduct experiments in the motion stream to validate the effect of DC. As shown in Table 3 (a), we first determine whether all augmentations mentioned in [18, 6] applicable to SDA. Compared to the normal augmentation, we can find that gaussian noise, gaussian blur, and channel mask work well on both benchmarks. Although the others may perform better on Xsub, their results on Xview are relatively poor. Through empirical experimentation, we determine the former three augmentations as our best choice, yielding $+12.7\%$ and $+11.4\%$ accuracy increases over using + +Table 2. Linear evaluation compared with SkeletonCLR. '2s' and '3s' means two-stream and three-stream fusion, respectively. + +
MethodsDCStreamNTU-60
XsubXview
SkeletonCLRjoint68.376.4
RVTCLRjoint74.479.4
RVTCLR+✓joint74.779.1
SkeletonCLRmotion53.350.8
RVTCLRmotion57.560.0
RVTCLR+✓motion70.872.0
SkeletonCLRbone69.467.4
RVTCLRbone68.171.7
RVTCLR+✓bone72.278.4
2s-SkeletonCLRjoint+motion70.577.9
2s-RVTCLRjoint+motion75.781.6
2s-RVTCLR+✓joint+motion77.882.2
3s-SkeletonCLRjoint+motion+bone75.079.8
3s-RVTCLRjoint+motion+bone77.282.0
3s-RVTCLR+✓joint+motion+bone79.784.6
+ +the normal augmentation. + +FSEM is designed to emphasize the blurred joint connections. As shown in Table 3 (b), IIPB brings $+3.3\%$ performance improvement on Xview, proving its ability to adeptly capture the local spatial features. The accuracies of NLB are $70.0\%$ and $70.7\%$ , respectively, which demonstrate that constructing global dependencies among frames can achieve a more representative feature extraction. By combining these two blocks, the performance of our final FSEM further boots to $70.8\%$ and $72.0\%$ . + +DD loss is introduced to help learn more representative high-level features. From the Table 3 (b), we can see a large performance drop when we replace the DD loss with the original one. This suggests that compared to the one-hot distribution, the weakly augmented view provides more suitable supervision signals. + +Table 3. Comparisons of DC's each component. We report linear evaluation results of the motion stream on the NTU-60 dataset. + +
SDANTU-60
XsubXview
Normal55.258.2
Gaussian noise66.872.6
Gaussian blur56.259.4
Channel mask57.358.6
Rotate55.557.1
Spatial flip57.656.1
Temporal flip59.455.9
Best Combination67.969.6
+ +(a) SDA + +
FSEMNTU-60
XsubXview
-67.969.6
IIPB68.072.9
NLB70.070.7
IIPB+NLB70.872.0
DD lossNTU-60
XsubXview
✓70.872.0
-64.663.6
+ +(b) FSEM and DD loss + +# 4.4. Performance Comparison + +Linear Evaluation. Table 4 and Table 5 show the comparisons on NTU-60 and NTU-120 under linear evaluation protocol. From the Table 4, we observe that our joint-stream RVTCLR+ achieves competitive results compared to the + +most recent SkeletonCLR [10] and AimCLR [6]. For example, $74.7\%$ vs $74.3\%$ on Xsub when compared to AimCLR. When multiple streams are fused, the performance of our method can be further improved. From the Table 5, we find that the performance of our 3s-RVTCLR+ remains at the forefront. + +Finetune Evaluation. Table 6 shows the comparisons on NTU-60 and NTU-120 under fineture evaluation protocol. The table reveals that our single-stream RVTCLR+ achieves $0.8\% \sim 2.1\%$ improvement over AimCLR on both datasets. Notably, 3s-ST-GCN [39] is pretrained under full supervision, and its performance is the ensemble of multi-streams, compared to it, our single-stream RVTCLR+ can still get comparable performance. When combining different streams, the accuracy of our 3s-RVTCLR+ can be further increased by $2.6\% \sim 5\%$ , greatly outperforming AimCLR. + +Table 4. Linear evaluation results on NTU-60 dataset. + +
MethodsNTU-60
XsubXview
Single-stream
LongT GAN [43]39.148.1
P&C [23]50.776.3
MS2L [11]52.6-
PCRP [38]54.963.4
AS-CAL [18]58.564.8
CRRL [31]67.673.8
SeBiReNet [16]-79.7
SkeletonCLR [10]68.376.4
AimCLR [6]74.379.7
RVTCLR+ (ours)74.779.1
Three-stream
3s-SkeletonCLR [10]75.079.8
3s-Colorization [41]75.283.1
3s-CrosSCLR [10]77.883.4
3s-AimCLR [6]78.983.8
3s-RVTCLR+ (Ours)79.784.6
+ +Table 5. Linear evaluation results on NTU-120 dataset. + +
MethodsNTU-120
XsubXset
P&C [23]42.741.7
PCRP [38]43.044.6
AS-CAL [18]48.649.2
CRRL [31]56.257.0
ISC [25]67.967.1
3s-CrosSCLR [10]67.966.7
3s-AimCLR [6]68.268.8
3s-RVTCLR+ (Ours)68.068.9
+ +Semi-supervised Evaluation. As shown in Table 7, with only $1\%$ and $10\%$ labeled data, the results of our 3s-RVTCLR+ far exceed MCC [24], 3s-CrosCLR [10], and 3s-AimCLR. For example, 3s-RVTCLR+ increases the accuracies by $2.5\%$ and $4.6\%$ compared with 3s-AimCLR on NTU-120 dataset. These results suggest that the representational capacity of our learned features is considerable. + +Qualitative Results. We apply t-SNE [26] with fixed settings to show the embedding distribution of Skeleton- + +Table 6. Finetune evaluation results on NTU-60 and NTU-120 dastatets. †means using the same bone stream. ‡means the model is pretrained under full supervision. + +
MethodsNTU-60NTU-120
XsubXviewXsubXset
SkeletonCLR† [10]82.288.973.675.3
MCC [24]83.089.777.077.8
AimCLR† [6]83.089.276.476.7
RVTCLR+†(Ours)84.491.377.278.4
3s-ST-GCN‡ [39]85.291.477.277.1
3s-CrosSCLR [10]86.292.580.580.4
3s-AimCLR [6]86.992.980.180.9
3s-RVTCLR+ (Ours)87.593.982.083.4
+ +Table 7. Seim-supervised evaluation on NTU-60 and NTU-120 datasets. * means the results are obtained by their released codes. + +
MethodsNTU-60NTU-120
XsubXviewXsubXset
1% labeled data
ISC [25]35.738.1--
3s-Colorization [41]48.352.5--
3s-CrosCLR [10]51.150.028.6*28.0*
3s-AimCLR [6]54.854.334.8*32.6*
3s-RVTCLR+ (Ours)54.953.633.332.8
10% labeled data
ISC [25]65.972.5--
3s-Colorization [41]71.778.9--
MCC-ST-GCN [24]55.659.940.743.4
MCC-2s-AGCN [24]60.865.847.051.8
MCC-AS-GCN [24]59.263.144.947.8
3s-CrosCLR [10]74.477.861.3*61.1*
3s-AimCLR [6]78.281.664.8*63.7*
3s-RVTCLR+ (Ours)79.583.767.368.3
+ +![](images/36b09c9ba3115e47019c4508255322bc30958839f386345d8c51ac53e1581166.jpg) +(a) SkeletonCLR, j + +![](images/b970d31757a69e055560cbcb6f5eb87cff79159089ed801858097dd103392db5.jpg) +(b) SkeletonCLR, m + +![](images/70206c4834515c0cb4825a55c0a4083ec4261968ed835e30793094f10481698d.jpg) +(c) SkeletonCLR, b + +![](images/c639a7fee82614f8e5e694b2ab65cd236e615d46a45b4a1c15b519f271eaffec.jpg) +(d) RVTCLR+, j + +![](images/ffd05d60081e5e99fcacbdfa2b3e1ee8eddf2bd1d325d4638bba0419c53203d8.jpg) +(e) RVTCLR+, m + +![](images/7faa679dbd1be46a4281f84eef9f975f8d4a7c06bb195b1b926ce2f9e361a6d5.jpg) +(f) RVTCLR+, b +Figure 4. The t-SNE visualization of embeddings on NTU-60 X-sub. These models are trained for 300 epochs. j, b, and m represent joint-stream, bone-stream, and motion-stream, respectively. + +CLR and our RVTCLR+ on NTU-60 Xsub benchmark. For a fair comparison, we select the same 11 classes for visualization, where each class is represented by a dot of the same color. From the Figure 4, we can obviously see that the embeddings extracted from our method have better inter-class separability and intra-class compactness, indicating that our learned features are more discriminative. + +# 5. Conclusion + +In this paper, we propose a Relative Visual Tempo Contrastive Learning framework for skeleton action representation (RVTCLR). The proposed RVTCLR combines Relative Visual Tempo Learning (RVTL) and Appearance-Consistency (AC) into a single-branch to obtain a more comprehensive spatial-temporal representation. Given the inherent sparsity of skeleton sequence data compared to RGB data, we design a new Distribution-Consistency (DC) branch aimed at emphasizing high-order semantics and preventing the network from learning shortcuts. The DC branch consists of Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. We refer to this new two-branch structure as RVTCLR+. 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[ + { + "bbox": [ + 143, + 300, + 192, + 313 + ], + "spans": [ + { + "bbox": [ + 143, + 300, + 192, + 313 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 327, + 290, + 650 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 327, + 290, + 650 + ], + "spans": [ + { + "bbox": [ + 47, + 327, + 290, + 650 + ], + "type": "text", + "content": "Visual tempo characterizes the dynamics and the temporal evolution, which helps describe actions. Recent approaches directly perform visual tempo prediction on skeleton sequences, which may suffer from insufficient feature representation issue. In this paper, we observe that relative visual tempo is more in line with human intuition, and thus providing more effective supervision signals. Based on this, we propose a novel Relative Visual Tempo Contrastive Learning framework for skeleton action Representation (RVTCLR). Specifically, we design a Relative Visual Tempo Learning (RVTL) task to explore the motion information in intra-video clips, and an Appearance-Consistency (AC) task to learn appearance information simultaneously, resulting in more representative spatiotemporal features. Furthermore, skeleton sequence data is much s-parser than RGB data, making the network learn shortcuts, and overfit to low-level information such as skeleton scales. To learn high-order semantics, we further design a new Distribution-Consistency (DC) branch, containing three components: Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. We term our entire method (RVTCLR with DC) as RVTCLR+. Extensive experiments on NTU RGB+D 60 and NTU RGB+D 120 datasets demonstrate that our RVTCLR+ can achieve competitive results over the state-of-the-art methods. 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The basic visual tempo prediction is considered a classification task, where the learned model is used to assign tempo labels to individual video clips. We introduce relative visual tempo learning and appearance-consistency based on contrastive learning. It's more human-intuitive for modeling actions. 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Introduction" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "As one of the most fundamental topics in video understanding, human action recognition has been widely explored in many real-world scenarios, such as human-computer interaction [22], autonomous driving [30], and so on [34, 17]. Skeleton data provides more abstract and well-structured information with less computation and storage than raw RGB video. It is less susceptible to camera viewpoint changes and background distractions. Thus, skeleton-based action recognition has attracted extensive at" + } + ] + } + ], + "index": 25 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 673, + 288, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 673, + 288, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 673, + 288, + 712 + ], + "type": "text", + "content": "*Corresponding author. This work was supported in part by the New Generation AI Major Project of Ministry of Science and Technology of China under Grant 2018AAA0102501 and in part by the National Natural Science Foundation of China (NSFC) under Grant U21B2027." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13913" + } + ] + } + ], + "index": 27 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "content": "tention [39, 21, 28, 7, 35]. However, most of these methods rely heavily on full supervision. The collection of massive annotations is labor-intensive and time-consuming. Under this circumstance, learning action representations directly from the data in a self-supervised manner has attracted increasing attentions." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 147, + 289, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 147, + 289, + 590 + ], + "spans": [ + { + "bbox": [ + 46, + 147, + 289, + 590 + ], + "type": "text", + "content": "Several existing works [11, 38, 41] draw inspiration from video self-supervised learning and directly apply video pretext tasks on skeleton sequences, such as jigsaw puzzle recognition [1, 9] and temporal order prediction [15, 37]. For sequence data, a commonly used technique to model spatiotemporal information is visual tempo prediction [42, 29]. Action visual tempo describes the speed at which actions are performed, which is crucial for distinguishing actions that exhibit similar temporal evolutions (e.g., walking and jogging). The basic idea is shown in the upper part of Figure 1. For each video, clips are sampled at different sampling frequencies to mimic different visual tempos (e.g., " + }, + { + "bbox": [ + 46, + 147, + 289, + 590 + ], + "type": "inline_equation", + "content": "1 \\times" + }, + { + "bbox": [ + 46, + 147, + 289, + 590 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 147, + 289, + 590 + ], + "type": "inline_equation", + "content": "2 \\times" + }, + { + "bbox": [ + 46, + 147, + 289, + 590 + ], + "type": "text", + "content": "), and predictions are made using the backbone network. However, there are limitations in directly applying it to skeleton sequences. People perform actions at their own tempo due to the influence of gender, age, etc. Even at the same tempo, the athlete's walking speed is visibly faster than that of a child in a third-person perspective. Therefore, it's obviously inappropriate to treat tempo prediction as a classification task. Furthermore, this basic strategy mainly focuses on motion information and cannot explicitly encourage the model to explore appearance information that is equally important for recognizing actions. Recently, contrastive learning has shown its great potential in extracting informative features [10, 6] in skeleton-based action recognition. Contrastive learning typically converts the naive classification task to a matching problem and learns an embedding space in which augmentations of same skeleton sequence are kept closer together, while different augmentations are far apart. In this way, the above issues can be alleviated in an elegant way. However, skeleton sequence data is much sparser than RGB data, and applying contrastive learning naively without explicit guidance may lead to model overfitting low-level information such as skeleton scales and angles, while failing to learn high-order semantics, resulting in insufficient feature representation capabilities." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "content": "To this end, we propose RVTCLR: a Relative Visual Tempo Contrastive Learning framework for skeleton action Representation. The basic idea is shown at the bottom of Figure 1. First, we observe that it's intuitively plausible to compare relative visual tempos within videos rather than to predict a specific visual tempo for each video. Specifically, for each video, we sample 3 clips with different visual tempos (e.g., " + }, + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "inline_equation", + "content": "1 \\times" + }, + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "inline_equation", + "content": "1 \\times" + }, + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "inline_equation", + "content": "2 \\times" + }, + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "content": ") to construct the contrastive pairs and train a network to pull the anchor-positive pairs closer while repelling the anchor-negative pairs. Furthermore," + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": "to make the representations explicitly focus on appearance information, we design another Appearance-Consistency (AC) task. In this task, pairs from the same video are attracted no matter their visual tempos, while pairs from different videos are pushed away. In this way, the learned representations are expected to focus on both skeleton motion and appearance information simultaneously." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 157, + 546, + 454 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 157, + 546, + 454 + ], + "spans": [ + { + "bbox": [ + 304, + 157, + 546, + 454 + ], + "type": "text", + "content": "In addition, in order to encourage the models to learn high-order semantics, we introduce a new Distribution-Consistency (DC) branch based on RVTCLR, which contains three components: Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. We refer to this as RVTCLR+. First, we leverage SDA to generate more difficult contrastive pairs by applying more skeleton-specific transformations (e.g., gaussian noise) at the input level, since augmentation plays a key role in learning better representations, as demonstrated by SimCLR [3] and MoCo [8]. However, too much strong augmentations may blur the joint connections compared to the normal augmented sequence (i.e., crop and shear), resulting in performance degradation. Benefiting from recent attention mechanisms [5, 13, 44], we try to emphasize these connections by designing a novel module, FSEM, which contains an Intra-Inter-Part block (IIPB) for local spatial modeling and a Non-local block (NLB) [32] for global spatiotemporal modeling. Finally, inspired by [33, 6], we introduce a DD loss to minimize the distributional divergence between the normal augmented view and our DC branch. By combining these components, we hope that the DC branch can better learn local and global spatiotemporal features, which help to extract discriminative high-order semantics." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 456, + 547, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 456, + 547, + 648 + ], + "spans": [ + { + "bbox": [ + 304, + 456, + 547, + 648 + ], + "type": "text", + "content": "To sum up, the contributions of this work include: (1) We propose a novel contrastive representation learning framework named RVTCLR. The proposed RVTCLR leverages Relative Visual Tempo Learning (RVTL) task to learn better skeleton motion information. By combining another Appearance-Consistency (AC) task, our model explicitly learns to concentrate on skeleton appearance information simultaneously. (2) To encourage models to focus on high-order semantics, we propose RVTCLR+ by introducing a new Distribution-Consistency (DC) branch. This DC branch contains three components: Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. (3) These contrastive tasks are jointly trained using a two-branch structure such that the models can learn both spatiotemporal and high-order semantics simultaneously." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 658, + 392, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 658, + 392, + 670 + ], + "spans": [ + { + "bbox": [ + 306, + 658, + 392, + 670 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 677, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 547, + 715 + ], + "type": "text", + "content": "Self-supervised skeleton-based action recognition. To meet the requirements of real-time recognition, it's necessary for the models to be able to directly extract dis" + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "text", + "content": "13914" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 384 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 384 + ], + "type": "text", + "content": "criminative action representations from the label-free online videos. Recent progress in self-supervised skeleton-based action recognition can be summarized into two categories: pretext-task based learning [11, 38, 41, 43, 23] and contrastive learning [18, 10, 6, 25, 31, 24]. For example, Zheng et al. [43] design a skeleton inpainting architecture to learn the long-term dynamics. Lin et al. [11] integrate multiple tasks such as jigsaw puzzle recognition to learn more general skeleton features. Xu et al. [38] propose reverse sequential predictions based on encoder-decoder structure to extract motion pattern. However, the representations learned by these methods may not be good enough, in the sense that they could be exclusively particular to the pre-designed tasks. Inspired by the success of contrastive learning in image classification (e.g., instance discrimination [36], SimCLR [3], and MoCo [8]), Rao et al. [18] first propose to perform contrastive learning among different augmentations of unlabeled skeleton data, to learn inherent action patterns. Thoker et al. [25] propose to generate contrastive pairs based on different input-representations of the skeleton sequences, i.e., graph, sequence, and image representation. By leveraging multiple views of the skeleton data, i.e., joint, bone, and motion, Li et al. [10] introduce SkeletonCLR and CrosSCLR to perform the single-view and cross-view contrastive learning. Guo et al. [6] further propose AimCLR to learn from extremely augmented skeleton sequences." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 387, + 289, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 387, + 289, + 602 + ], + "spans": [ + { + "bbox": [ + 47, + 387, + 289, + 602 + ], + "type": "text", + "content": "Nevertheless, none of the aforementioned methods concentrate on visual tempo, which is crucial for characterizing human action dynamics. To our best knowledge, Su et al. [24] propose motion consistency and continuity learning, which has overlap with our framework. However, the differences are obvious, which mainly lie in three aspects: (1) contrastive pairs are generated differently. In [24], speed-changed clips are considered as positive pairs, while we focus on relative visual tempo and regard these clips as negative pairs. (2) appearance information is modeled differently. In [24], appearance information is implicitly modeled in the contrastive learning process, while we design another Appearance-Consistency (AC) task specifically for spatial modeling. (3) learned features are enhanced differently. In [24], learned features are enhanced by designing a self-reconstruction based motion continuity module, while we introduce a novel Distribution-Consistency (DC) branch to guide the models focus on high-order semantics." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 605, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 605, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 605, + 289, + 715 + ], + "type": "text", + "content": "Visual tempo modeling. Visual tempo describes the speed of human movements, which has already been applied into various action recognition methods [4, 40, 14]. For example, Feichtenhofer et al. [4] first propose SlowFast network to explore the potential of different visual tempos. It consists of two pathways, operating at different frame rates, to capture both spatial semantics and motion dynamics. When it comes to video self-supervised learning [42, 29, 2], the potential of visual tempo in motion mod" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 252 + ], + "type": "text", + "content": "eling is further verified. Yao et al. [42] utilize video playback rates as self-supervision signals and propose playback rate perception to learn spatiotemporal features in a collaborative discrimination-generation manner. The above methods usually require assigning visual tempos to each video clip according to different sampling rates, and then elaborate learning paradigms through reconstruction or prediction, but this is suboptimal in learning discriminative representations. Chen et al. [2] argue that relative speed is more in line with motion pattern. They propose a new video self-supervised learning framework (called RSPNet) to leverage the relative speed between two video clips to supervise the representation learning. Inspired by RSPNet, the proposed RVTCLR focuses on relative visual tempo learning with skeleton-specific modifications." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 306, + 261, + 367, + 274 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 261, + 367, + 274 + ], + "spans": [ + { + "bbox": [ + 306, + 261, + 367, + 274 + ], + "type": "text", + "content": "3. Methods" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 281, + 392, + 293 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 281, + 392, + 293 + ], + "spans": [ + { + "bbox": [ + 306, + 281, + 392, + 293 + ], + "type": "text", + "content": "3.1. Preliminaries" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "spans": [ + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": "SkeletonCLR. SkeletonCLR [10] utilizes ST-GCN [39] as its backbone and follows the practice in MoCo [8] to learn skeleton action representations. Suppose that a skeleton sequence " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "s = (s^1, s^2, \\ldots, s^T)" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " contains " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " consecutive skeleton frames, where " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "s^i \\in \\mathbb{R}^{3 \\times V \\times M}" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " means 3D coordinates of " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " joints for " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " actors. A data augmentation module " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " is first utilized to randomly transform the given " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " into different augmentations " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "x_q" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "x_k" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": ". Then, a query encoder " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "f(\\cdot; \\theta_q)" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " and a momentum updated key encoder " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "f(\\cdot; \\theta_k)" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " are leveraged to encode " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "x_q" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "x_k" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " into hidden space " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "h_q" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "h_k" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": ". These embeddings are further passed through a projector " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "g(\\cdot; \\theta_q)" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " and its momentum updated version " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "g(\\cdot; \\theta_k)" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " to get the final query features " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " and key features " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": ". In each training step, samples in the queue " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "\\mathbf{Q} = \\{m_o\\}_{o=1}^K" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " are progressively replaced by the key features " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " following a first-in-first-out scheme. Following MoCo, " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " serve as positive pairs while " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " and embeddings in " + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}" + }, + { + "bbox": [ + 304, + 299, + 547, + 527 + ], + "type": "text", + "content": " serve as negative pairs. The InfoNCE loss [36] is used to guide the network learning, which can be formulated as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 310, + 533, + 545, + 563 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 533, + 545, + 563 + ], + "spans": [ + { + "bbox": [ + 310, + 533, + 545, + 563 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {I n f o} = - \\log \\frac {\\exp (q \\cdot k / \\tau)}{\\exp (q \\cdot k / \\tau) + \\sum_ {o = 1} ^ {K} \\exp (q \\cdot m _ {o} / \\tau)} (1)", + "image_path": "1d9adaf83b8d1cf906f6d5a50f58b4a9793d7be1e3d5494fe09e67cdfd9f0f40.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 567, + 545, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 567, + 545, + 590 + ], + "spans": [ + { + "bbox": [ + 304, + 567, + 545, + 590 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 567, + 545, + 590 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 304, + 567, + 545, + 590 + ], + "type": "text", + "content": " is the temperature hyper-parameter, and " + }, + { + "bbox": [ + 304, + 567, + 545, + 590 + ], + "type": "inline_equation", + "content": "\\cdot" + }, + { + "bbox": [ + 304, + 567, + 545, + 590 + ], + "type": "text", + "content": " represents the similarity measured by dot product." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 591, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 591, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 591, + 545, + 628 + ], + "type": "text", + "content": "After computing the InfoNCE loss, the parameters of " + }, + { + "bbox": [ + 304, + 591, + 545, + 628 + ], + "type": "inline_equation", + "content": "\\theta_{q}" + }, + { + "bbox": [ + 304, + 591, + 545, + 628 + ], + "type": "text", + "content": " are updated by gradient back-propagation while the parameters of " + }, + { + "bbox": [ + 304, + 591, + 545, + 628 + ], + "type": "inline_equation", + "content": "\\theta_{k}" + }, + { + "bbox": [ + 304, + 591, + 545, + 628 + ], + "type": "text", + "content": " are updated as their moving-average:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 376, + 634, + 545, + 647 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 376, + 634, + 545, + 647 + ], + "spans": [ + { + "bbox": [ + 376, + 634, + 545, + 647 + ], + "type": "interline_equation", + "content": "\\theta_ {k} \\leftarrow \\alpha \\theta_ {k} + (1 - \\alpha) \\theta_ {q} \\tag {2}", + "image_path": "67c59d4ef8d34c305777b82a101f430d9aff27f1c9280bebe8d41eddf4e3df0c.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 654, + 545, + 666 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 666 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 666 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 654, + 545, + 666 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 654, + 545, + 666 + ], + "type": "text", + "content": " is a momentum coefficient (set to 0.999 by default)." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "text", + "content": "Nearest Neighbors Mining. Traditional InfoNCE regards all samples in the memory bank as negative. This overly hard approach may lead to non-generic feature embeddings. To address the above issue, [10, 6] propose" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "13915" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 99, + 70, + 496, + 281 + ], + "blocks": [ + { + "bbox": [ + 99, + 70, + 496, + 281 + ], + "lines": [ + { + "bbox": [ + 99, + 70, + 496, + 281 + ], + "spans": [ + { + "bbox": [ + 99, + 70, + 496, + 281 + ], + "type": "image", + "image_path": "4c30ef37b7ae45b07a21750cf0b57165bfa3883a7813b02c47a250bf2dca3517.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 284, + 547, + 350 + ], + "lines": [ + { + "bbox": [ + 46, + 284, + 547, + 350 + ], + "spans": [ + { + "bbox": [ + 46, + 284, + 547, + 350 + ], + "type": "text", + "content": "Figure 2. The pipeline of our method. For each skeleton sequence, we sample clips with varying visual tempos. Then, we use a two-branch structure to extract discriminative feature from each sequence. Specifically, in RVTCLR, the Relative Visual Tempo Learning (RVTL) is responsible for modeling motion dynamics. The Appearance-Consistency (AC) is responsible for modeling appearance characteristics. These two tasks are combined into one branch to achieve a more comprehensive spatial-temporal representation. In another Distribution-Consistency (DC) branch, we introduce Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss to guide the network to concentrate on extracting high-order semantics." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 369, + 287, + 394 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 369, + 287, + 394 + ], + "spans": [ + { + "bbox": [ + 46, + 369, + 287, + 394 + ], + "type": "text", + "content": "to leverage Nearest Neighbors Mining (NNM) to generate more positive pairs:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 51, + 403, + 287, + 442 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 51, + 403, + 287, + 442 + ], + "spans": [ + { + "bbox": [ + 51, + 403, + 287, + 442 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {N N M} = - \\log \\frac {\\exp (q \\cdot k / \\tau) + \\sum_ {o \\in N _ {+}} \\exp (q \\cdot m _ {o} / \\tau)}{\\exp (q \\cdot k / \\tau) + \\sum_ {o = 1} ^ {K} \\exp (q \\cdot m _ {o} / \\tau)} \\tag {3}", + "image_path": "ea9c6abb17190fb6a7c2f5d76c0c5d31c4e84ff3d8448e83e02c175c5b279dcd.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 444, + 287, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 444, + 287, + 468 + ], + "spans": [ + { + "bbox": [ + 47, + 444, + 287, + 468 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 444, + 287, + 468 + ], + "type": "inline_equation", + "content": "N_{+}" + }, + { + "bbox": [ + 47, + 444, + 287, + 468 + ], + "type": "text", + "content": " represents the top- " + }, + { + "bbox": [ + 47, + 444, + 287, + 468 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 47, + 444, + 287, + 468 + ], + "type": "text", + "content": " nearest neighbors that are most similar to the query features " + }, + { + "bbox": [ + 47, + 444, + 287, + 468 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 47, + 444, + 287, + 468 + ], + "type": "text", + "content": " in the memory queue." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 468, + 287, + 528 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 468, + 287, + 528 + ], + "spans": [ + { + "bbox": [ + 46, + 468, + 287, + 528 + ], + "type": "text", + "content": "Since the model learned in the early training stages may not be strong enough to provide confident nearest neighbors, [10, 6] propose to perform a two-stage training, i.e., first train the model using Equation 1, and then train the model to mine the nearest neighbors using Equation 3." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 529, + 287, + 554 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 529, + 287, + 554 + ], + "spans": [ + { + "bbox": [ + 47, + 529, + 287, + 554 + ], + "type": "text", + "content": "In this paper, we mainly implement our method based on SkeletonCLR and two-stage training strategy." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 562, + 117, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 562, + 117, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 562, + 117, + 574 + ], + "type": "text", + "content": "3.2.RVTCLR" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": "Relative Visual Tempo Learning (RVTL). Observing that each person performs actions at his/her own visual tempo, we introduce a RVTL task, which aims to learn better skeleton motion information. Specifically, given a skeleton sequence " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " frames, we first sample 3 clips " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "c_{i}" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "c_{j}" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "c_{k}" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " with visual tempos " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "v_{i}" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "v_{j}" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "v_{k}" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": ", respectively, where " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "v_{i} = v_{j} \\neq v_{k}" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": ". Note that visual tempos can be set arbitrarily, i.e., " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\{1 \\times, 2 \\times, 3 \\times,..\\}" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": ". However, to avoid the temporal ambiguity in skeleton sequences, we only consider " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "1 \\times" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "2 \\times" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": ", which represent that the sampling interval is set to 1 and 2 frames. We sample from the first frame and keep" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "spans": [ + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": "a duration of " + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "inline_equation", + "content": "T / 2" + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": " for each clip. Then, we apply normal skeleton augmentations " + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": " on these three clips respectively to construct a triplet, i.e., anchor " + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "inline_equation", + "content": "a = \\mathcal{T}(c_i)" + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": ", positive " + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "inline_equation", + "content": "p = \\mathcal{T}(c_j)" + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": " and negative " + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "inline_equation", + "content": "n = \\mathcal{T}(c_k)" + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": ". This triplet is further fed into SkeletonCLR with a projection head " + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "inline_equation", + "content": "g_{r}(\\cdot ;\\theta_{q_{r}})" + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": " and its momentum updated " + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "inline_equation", + "content": "g_{r}(\\cdot ;\\theta_{k_{r}})" + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": " to generate the encoded features " + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "inline_equation", + "content": "(q_{a},k_{p},k_{n})" + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": ". Finally, these features are normalized and combined as anchor-positive pairs " + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "inline_equation", + "content": "(q_{a},k_{p})" + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": " and anchor-negative pairs " + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "inline_equation", + "content": "(q_{a},k_{n})" + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": ", and our goal is to pull " + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "inline_equation", + "content": "(q_{a},k_{p})" + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": " closer while pushing " + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "inline_equation", + "content": "(q_{a},k_{n})" + }, + { + "bbox": [ + 304, + 369, + 547, + 538 + ], + "type": "text", + "content": " away. The assumption here is that the network can only succeed in such a RVTL task if it understands the intrinsic visual tempo of each clip and learns discriminative motion information. This task is realized by a triplet loss [19]:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 313, + 547, + 545, + 561 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 547, + 545, + 561 + ], + "spans": [ + { + "bbox": [ + 313, + 547, + 545, + 561 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {R V T L} = \\max \\left\\{- \\left(q _ {a} \\cdot k _ {p} - q _ {a} \\cdot k _ {n}\\right) + \\operatorname {m a r g i n}, 0 \\right\\} \\tag {4}", + "image_path": "d76501168770a9e9cf37e7747806106c3c314c0d3e7ceced9d99d7be88bd5de3.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 570, + 545, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 593 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 593 + ], + "type": "text", + "content": "where the margin (set to 1 by default) is a hyper-parameter to control the distance between two components." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": "Appearance-Consistency (AC). Appearance information is also essential for recognizing actions. To this end, we introduce another AC task to explicitly learn such information. Specifically, given a skeleton sequence, we first sample two clips " + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "inline_equation", + "content": "c_{i}" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "inline_equation", + "content": "c_{j}" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": " with visual tempos randomly selected in " + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\{1\\times ,2\\times \\}" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": ". Then, they are normally augmented and sent to SkeletonCLR with another projection head " + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "inline_equation", + "content": "g_{a}(\\cdot ;\\theta_{q_{a}})" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": " and its momentum updated " + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "inline_equation", + "content": "g_{a}(\\cdot ;\\theta_{k_{a}})" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": " to generate the encoded features " + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "inline_equation", + "content": "(q_{i},k_{j})" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": ". Note that the query and key encoders in AC share weights with the encoders in RVTL while the" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "13916" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "text", + "content": "projection heads " + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "inline_equation", + "content": "g_{a}(\\cdot;\\theta_{q_{a}})" + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "inline_equation", + "content": "g_{a}(\\cdot;\\theta_{k_{a}})" + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "text", + "content": " have weights independent of " + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "inline_equation", + "content": "g_{r}(\\cdot;\\theta_{q_{r}})" + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "inline_equation", + "content": "g_{r}(\\cdot;\\theta_{k_{r}})" + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "text", + "content": ". Here, the goal is to pull " + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "inline_equation", + "content": "q_{i}" + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "inline_equation", + "content": "k_{j}" + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "text", + "content": " closer while pushing away " + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "inline_equation", + "content": "q_{i}" + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "text", + "content": " and negative samples in queue " + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}" + }, + { + "bbox": [ + 46, + 72, + 289, + 178 + ], + "type": "text", + "content": ". Although from the same sample, clips with various visual tempos show different temporal motion dynamics, by pulling such a pair closer while pushing away different samples, we want the model to explicitly focus on appearance information. This task is realized by the InfoNCE loss:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 55, + 187, + 287, + 225 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 187, + 287, + 225 + ], + "spans": [ + { + "bbox": [ + 55, + 187, + 287, + 225 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {A C} = - \\log \\frac {\\exp \\left(q _ {i} \\cdot k _ {j} / \\tau\\right)}{\\exp \\left(q _ {i} \\cdot k _ {j} / \\tau\\right) + \\sum_ {o = 1} ^ {K} \\exp \\left(q _ {i} \\cdot m _ {o} / \\tau\\right)} \\tag {5}", + "image_path": "2ee6b9f19c16e3d0e08fd302a6d3733b5e9d1bc79448909feabfc97b0f4c2b3d.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 226, + 289, + 310 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 226, + 289, + 310 + ], + "spans": [ + { + "bbox": [ + 46, + 226, + 289, + 310 + ], + "type": "text", + "content": "Based on SkeletonCLR, we jointly train these tasks. In the first training stage, we train the model with the loss function: " + }, + { + "bbox": [ + 46, + 226, + 289, + 310 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_1 = \\lambda_1\\mathcal{L}_{RVTL} + \\lambda_2\\mathcal{L}_{AC}" + }, + { + "bbox": [ + 46, + 226, + 289, + 310 + ], + "type": "text", + "content": ", and then in the second training stage, we try to obtain more positive samples by using " + }, + { + "bbox": [ + 46, + 226, + 289, + 310 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_2 = \\lambda_1\\mathcal{L}_{RVTL} + \\lambda_2\\mathcal{L}_{AC'}" + }, + { + "bbox": [ + 46, + 226, + 289, + 310 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 226, + 289, + 310 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 226, + 289, + 310 + ], + "type": "text", + "content": " (set to 1 by default) is the coefficient to balance the loss and " + }, + { + "bbox": [ + 46, + 226, + 289, + 310 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{AC'}" + }, + { + "bbox": [ + 46, + 226, + 289, + 310 + ], + "type": "text", + "content": " is defined in Equation 3." + } + ] + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 50, + 323, + 298, + 459 + ], + "blocks": [ + { + "bbox": [ + 50, + 323, + 298, + 459 + ], + "lines": [ + { + "bbox": [ + 50, + 323, + 298, + 459 + ], + "spans": [ + { + "bbox": [ + 50, + 323, + 298, + 459 + ], + "type": "image", + "image_path": "dfbf49ac5609bbeff85a355dfa5ceb80cf82cf47aeff78ac9a6a348926400428.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 461, + 287, + 506 + ], + "lines": [ + { + "bbox": [ + 46, + 461, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 461, + 287, + 506 + ], + "type": "text", + "content": "Figure 3. Illustration of FSEM. (a) The workflow of FSEM. (b) IIPB is responsible for local spatial modeling, containing intra-part and inter-part relational reasoning submodules. (c) NLB is responsible for global spatial-temporal modeling." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 526, + 122, + 538 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 526, + 122, + 538 + ], + "spans": [ + { + "bbox": [ + 47, + 526, + 122, + 538 + ], + "type": "text", + "content": "3.3.RVTCLR+" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 545, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 640 + ], + "type": "text", + "content": "The success of contrastive learning depends on the construction of contrastive pairs and the difficulty of learning paradigm. Given that the skeleton sequences are much s-sparser, naive contrastive learning may risk overfitting low-level information such as skeleton scales. It would be even better if we could design a new branch to explicitly learn skeleton high-order semantics. We thus propose RVTCLR+ by designing our Distribution-Consistency (DC)." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": "SDA. We leverage SDA to generate more difficult contrastive pairs. The SDA contains normal augmentations " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": ": crop and shear, and additional strong augmentations " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{T}'" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": ": gaussian noise, gaussian blur, and channel mask. Given a skeleton sequence " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": ", we apply " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{T}'" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": " to get the transformed version: " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "e = \\mathcal{T}'(\\mathcal{T}(s))" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": ". Afterwards, we send it" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": "to the weight-sharing query encoder to encode " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": " into hidden space " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "h_e" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": ", which is further passed through a projector " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "g_e(\\cdot; \\theta_{q_e})" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": " to obtain the final embeddings " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "q_e" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 109, + 546, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 109, + 546, + 275 + ], + "spans": [ + { + "bbox": [ + 304, + 109, + 546, + 275 + ], + "type": "text", + "content": "FSEM. Such a direct modeling method may be suboptimal, since the additional augmentations may cause blurred joint connections. Considering that skeleton sequences are spatiotemporal cubes, we design FSEM to highlight these connections. As shown in Figure 3, our FSEM contains an Intra-Inter-Part block (IIPB), which is responsible for local spatial modeling, and a Non-local block (NLB), which is responsible for global spatial-temporal modeling. Given the encoded " + }, + { + "bbox": [ + 304, + 109, + 546, + 275 + ], + "type": "inline_equation", + "content": "h_e \\in \\mathbb{R}^{C \\times T \\times V}" + }, + { + "bbox": [ + 304, + 109, + 546, + 275 + ], + "type": "text", + "content": ", in IIPB, we first divide each human skeleton into 5 parts according to the physical topology of the body. Then, average pooling is applied on each part to generate the intra-part representations " + }, + { + "bbox": [ + 304, + 109, + 546, + 275 + ], + "type": "inline_equation", + "content": "h_{e'} \\in \\mathbb{R}^{C \\times T \\times 5}" + }, + { + "bbox": [ + 304, + 109, + 546, + 275 + ], + "type": "text", + "content": ". Two " + }, + { + "bbox": [ + 304, + 109, + 546, + 275 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 304, + 109, + 546, + 275 + ], + "type": "text", + "content": " convolution layers are further utilized to establish the inter-part relations:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 333, + 285, + 545, + 299 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 333, + 285, + 545, + 299 + ], + "spans": [ + { + "bbox": [ + 333, + 285, + 545, + 299 + ], + "type": "interline_equation", + "content": "h _ {\\hat {e}} = \\operatorname {C o n v 2} \\left(\\operatorname {R e L U} \\left(\\operatorname {C o n v 1} \\left(h _ {e ^ {\\prime}}, W _ {1}\\right)\\right), W _ {2}\\right) \\tag {6}", + "image_path": "0963e2330a8205e8c831af67f4b00ac80d7f24b85cfaf97ab0121602cc1060e8.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 308, + 545, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 308, + 545, + 380 + ], + "spans": [ + { + "bbox": [ + 304, + 308, + 545, + 380 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 308, + 545, + 380 + ], + "type": "inline_equation", + "content": "W_{1} \\in \\mathbb{R}^{\\frac{C}{2} \\times C}" + }, + { + "bbox": [ + 304, + 308, + 545, + 380 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 308, + 545, + 380 + ], + "type": "inline_equation", + "content": "W_{2} \\in \\mathbb{R}^{C \\times \\frac{C}{2}}" + }, + { + "bbox": [ + 304, + 308, + 545, + 380 + ], + "type": "text", + "content": " are learnable parameters. " + }, + { + "bbox": [ + 304, + 308, + 545, + 380 + ], + "type": "inline_equation", + "content": "ReLU" + }, + { + "bbox": [ + 304, + 308, + 545, + 380 + ], + "type": "text", + "content": " is the activation function. The intuition here is that connections between body parts can sometimes better describe actions (e.g., the coordination of arm and leg in 'running'). By using IIPB, we establish the part-based connections that seek to mitigate the effects of blurred joints." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 381, + 545, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 381, + 545, + 464 + ], + "spans": [ + { + "bbox": [ + 304, + 381, + 545, + 464 + ], + "type": "text", + "content": "IIPB can capture the local dependencies of intra-frame parts. However, global inter-frame connections are ignored, which are also essential for describing actions. We introduce NLB to associate all possible frames of a skeleton sequence in a self-attention mechanism [27]. The non-local operation computes frame dependencies by enumerating all possible frames:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 351, + 473, + 545, + 502 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 351, + 473, + 545, + 502 + ], + "spans": [ + { + "bbox": [ + 351, + 473, + 545, + 502 + ], + "type": "interline_equation", + "content": "y ^ {t} = \\frac {1}{\\mathcal {C} \\left(h _ {\\hat {e}}\\right)} \\sum_ {\\forall t ^ {\\prime}} f \\left(h _ {\\hat {e}} ^ {t}, h _ {\\hat {e}} ^ {t ^ {\\prime}}\\right) g \\left(h _ {\\hat {e}} ^ {t ^ {\\prime}}\\right) \\tag {7}", + "image_path": "ecc7456aaa6942fa8d343116b01116951df3a0eeb8c0ac84b3d3870f9487aba6.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "spans": [ + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "inline_equation", + "content": "h_{\\hat{e}}^{t}" + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "inline_equation", + "content": "h_{\\hat{e}}^{t'}" + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "text", + "content": " denote the input at frame " + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "inline_equation", + "content": "t'" + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "text", + "content": ", respectively. " + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "inline_equation", + "content": "g(\\cdot)" + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "text", + "content": " is a linear function. " + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "inline_equation", + "content": "\\mathcal{C}(\\cdot)" + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "text", + "content": " is a normalization term. An embedded gaussian function " + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "inline_equation", + "content": "f(\\cdot, \\cdot)" + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "text", + "content": " [32] computes the relationships between " + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "text", + "content": " and all " + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "inline_equation", + "content": "t'" + }, + { + "bbox": [ + 304, + 512, + 545, + 573 + ], + "type": "text", + "content": ". We wrap the non-local operation in Equation 7 into NLB with a residual layer as:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 391, + 583, + 545, + 596 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 391, + 583, + 545, + 596 + ], + "spans": [ + { + "bbox": [ + 391, + 583, + 545, + 596 + ], + "type": "interline_equation", + "content": "h _ {\\tilde {e}} = W _ {3} y + h _ {\\hat {e}} \\tag {8}", + "image_path": "4dee24169b652a76ce2479162fc540326e9f8e7e7c31b24c37c4a9536faba290.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "type": "inline_equation", + "content": "W_{3}" + }, + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "type": "text", + "content": " is a learnable embedding for " + }, + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "type": "text", + "content": ". Finally, we send it to the projector to generate the new embeddings " + }, + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "type": "inline_equation", + "content": "q_{\\widetilde{e}}" + }, + { + "bbox": [ + 304, + 605, + 545, + 665 + ], + "type": "text", + "content": ". Note that FSEM can be plugged into different GCN layers, we only insert the FSEM before the projector for the reduction of experiment cost." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "DD Loss. The distributional divergence between weakly augmented counterparts and strongly augmented views enables the framework to explore novel patterns, which may help extract representative high-level features. Formally," + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "13917" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "type": "text", + "content": "given the encoded query features " + }, + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "type": "inline_equation", + "content": "q_{a}" + }, + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "type": "text", + "content": ", the encoded key features " + }, + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "type": "inline_equation", + "content": "k_{p}" + }, + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "type": "text", + "content": ", and the memory queue " + }, + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "type": "inline_equation", + "content": "\\mathbf{Q} = \\{m_{o}\\}_{o=1}^{K}" + }, + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "type": "text", + "content": ", we can obtain a conditional distribution:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 52, + 113, + 287, + 142 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 113, + 287, + 142 + ], + "spans": [ + { + "bbox": [ + 52, + 113, + 287, + 142 + ], + "type": "interline_equation", + "content": "p \\left(k _ {p} \\mid q _ {a}\\right) = \\frac {\\exp \\left(q _ {a} \\cdot k _ {p} / \\tau\\right)}{\\exp \\left(q _ {a} \\cdot k _ {p} / \\tau\\right) + \\sum_ {o = 1} ^ {K} \\exp \\left(q _ {a} \\cdot m _ {o} / \\tau\\right)} (9)", + "image_path": "12d72b5eb4ede70f523e246ab787c69ca09b4a49f9f2efcce4a4a30382ba13fa.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "spans": [ + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "text", + "content": "which encodes the likelihood of the query " + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "inline_equation", + "content": "q_{a}" + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "text", + "content": " being assigned to the key " + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "inline_equation", + "content": "k_{p}" + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "text", + "content": ". By replacing " + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "inline_equation", + "content": "k_{p}" + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "inline_equation", + "content": "m_{o}" + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "text", + "content": ", we can also obtain the likelihood that the query " + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "inline_equation", + "content": "q_{a}" + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "text", + "content": " is assigned to the negative embeddings in " + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}" + }, + { + "bbox": [ + 46, + 148, + 287, + 207 + ], + "type": "text", + "content": ". Then, the InfoNCE loss in Equation 1 can be rewritten as:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 213, + 303, + 255 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 213, + 303, + 255 + ], + "spans": [ + { + "bbox": [ + 47, + 213, + 303, + 255 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {I n f o}} = - q \\left(k _ {p} \\mid q _ {a}\\right) \\log p \\left(k _ {p} \\mid q _ {a}\\right) - \\sum_ {o = 1} ^ {K} q \\left(m _ {o} \\mid q _ {a}\\right) \\log p \\left(m _ {o} \\mid q _ {a}\\right) \\tag {10}", + "image_path": "479c911eb4a3c4458988684e7ac7c29adfa891e38ca7bc56279d8e0a793126dd.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "spans": [ + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "inline_equation", + "content": "q(\\cdot|\\cdot)" + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "text", + "content": " is the ideal distribution of the likelihood, " + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "inline_equation", + "content": "p(k_p|q_a)" + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "text", + "content": " is the distribution learned by network. In InfoNCE, " + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "inline_equation", + "content": "q(k_p|q_a)" + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "inline_equation", + "content": "q(m_o|q_a)" + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "text", + "content": " are simply set to 1 and 0 based on one-hot distribution, respectively. When applied to " + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "inline_equation", + "content": "q_{\\widetilde{e}}" + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "text", + "content": ", a straightforward approach is to directly replace " + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "inline_equation", + "content": "q_a" + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "text", + "content": " in Equation 10 with " + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "inline_equation", + "content": "q_{\\widetilde{e}}" + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "text", + "content": ". However, as demonstrated in [33, 6], the one-hot distribution cannot mimic the ideal distribution and thus cannot help representations learning any more. Conversely, the similarity distribution of weakly-augmented queries for the same instance in a queue can provide useful clues for strong-augmentation based learning. This inspires us to leverage " + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "inline_equation", + "content": "p(k_p|q_a)" + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "inline_equation", + "content": "p(m_o|q_a)" + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "text", + "content": " as the ideal distribution to supervise " + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "inline_equation", + "content": "q_{\\widetilde{e}}" + }, + { + "bbox": [ + 46, + 255, + 287, + 411 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 62, + 418, + 287, + 467 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 62, + 418, + 287, + 467 + ], + "spans": [ + { + "bbox": [ + 62, + 418, + 287, + 467 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {L} _ {D C} = - p \\left(k _ {p} \\mid q _ {a}\\right) \\log p \\left(k _ {p} \\mid q _ {\\bar {e}}\\right) \\\\ - \\sum_ {o = 1} ^ {K} p \\left(m _ {o} \\mid q _ {a}\\right) \\log p \\left(m _ {o} \\mid q _ {\\tilde {e}}\\right) \\tag {11} \\\\ \\end{array}", + "image_path": "a948dc5c731ca63c1e9cc9ca38c9ccf28c27ed801326f2ea5b8a6ae7b0d6ca72.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 474, + 287, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 474, + 287, + 510 + ], + "spans": [ + { + "bbox": [ + 47, + 474, + 287, + 510 + ], + "type": "text", + "content": "By combining DC, the final loss our RVTCLR+ can be formulated as " + }, + { + "bbox": [ + 47, + 474, + 287, + 510 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_1 = \\lambda_1\\mathcal{L}_{RVTL} + \\lambda_2\\mathcal{L}_{AC} + \\lambda_3\\mathcal{L}_{DC}" + }, + { + "bbox": [ + 47, + 474, + 287, + 510 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 474, + 287, + 510 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_2 = \\lambda_1\\mathcal{L}_{RVTL} + \\lambda_2\\mathcal{L}_{AC'} + \\lambda_3\\mathcal{L}_{DC}" + }, + { + "bbox": [ + 47, + 474, + 287, + 510 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 520, + 128, + 533 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 520, + 128, + 533 + ], + "spans": [ + { + "bbox": [ + 47, + 520, + 128, + 533 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 540, + 110, + 551 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 540, + 110, + 551 + ], + "spans": [ + { + "bbox": [ + 47, + 540, + 110, + 551 + ], + "type": "text", + "content": "4.1. Datasets" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "text", + "content": "NTU RGB+D 60 Dataset [20]: It contains 56880 skeleton video clips over 60 action classes capture from 40 subjects and 3 different camera view angles. Each clip provides 25 body joints with 3D coordinates for at most 2 subjects. There are two evaluation benchmarks: cross-subject (Xsub) and cross-view (Xview). In Xsub, clips of 20 subjects are used for training, and the rest are used for testing. In Xview, clips of camera 2 and 3 are used for training, and clips of camera 1 are used for testing." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": "NTU RGB+D 120 Dataset [12]: It is an extension of N-TU RGB+D 60 with 113945 samples over 120 classes capture from 106 subjects and 32 different camera setups. Two evaluation benchmarks are recommended: cross-subject" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "(Xsub) and cross-setup (Xset). In Xsub, clips of 53 subjects are used for training, and the rest are used for testing. In Xset, clips of even camera IDs are used for training, and clips of odd IDs are used for testing." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 129, + 440, + 141 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 129, + 440, + 141 + ], + "spans": [ + { + "bbox": [ + 305, + 129, + 440, + 141 + ], + "type": "text", + "content": "4.2. Implementation Details" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 147, + 545, + 206 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 147, + 545, + 206 + ], + "spans": [ + { + "bbox": [ + 304, + 147, + 545, + 206 + ], + "type": "text", + "content": "For data pre-processing, we follow CrosCLR [10] and AimCLR [6] except for that we resize the length of skeleton sequences to 100 frames, rather than 50 frames (Actually, by " + }, + { + "bbox": [ + 304, + 147, + 545, + 206 + ], + "type": "inline_equation", + "content": "2\\times" + }, + { + "bbox": [ + 304, + 147, + 545, + 206 + ], + "type": "text", + "content": " temporal sampling, we also maintain 50 frames for each clip). The mini-batch size is set to 128." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 207, + 545, + 278 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 207, + 545, + 278 + ], + "spans": [ + { + "bbox": [ + 304, + 207, + 545, + 278 + ], + "type": "text", + "content": "Data Augmentation. For skeleton sequences, shear and crop are used as the normal augmentations " + }, + { + "bbox": [ + 304, + 207, + 545, + 278 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 304, + 207, + 545, + 278 + ], + "type": "text", + "content": ". For strong augmentations " + }, + { + "bbox": [ + 304, + 207, + 545, + 278 + ], + "type": "inline_equation", + "content": "\\mathcal{T}'" + }, + { + "bbox": [ + 304, + 207, + 545, + 278 + ], + "type": "text", + "content": ", we mainly use gaussian noise, gaussian blur, and channel mask. Since [18, 6] use more augmentations, we test if these augmentations (spatial flip, temporal flip, rotate) work in our approach." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "spans": [ + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "text", + "content": "Self-supervised Pre-training. The baseline is Skeleton-CLR which follows the MoCo [8] framework. The queue size " + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}" + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "text", + "content": " and temperature " + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "text", + "content": " are set to 32768 and 0.07, respectively. For the backbone, we adopt ST-GCN [39], but the number of channels in each layer is reduced to " + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "inline_equation", + "content": "1/4" + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "text", + "content": " of the original settings. For the optimizer, we use SGD with momentum 0.9 and weight decay 0.0001. The pre-training runs 300 epochs with the initial learning rate 0.1 and multiplied by 0.1 at 250 epochs. For the two-stage training strategy, we train 150 epochs with the loss function " + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_1" + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "text", + "content": ", and another 150 epochs with " + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_2" + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "text", + "content": ". In the second training stage, nearest neighbors " + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 279, + 545, + 422 + ], + "type": "text", + "content": " is set to 1." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 422, + 545, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 422, + 545, + 494 + ], + "spans": [ + { + "bbox": [ + 304, + 422, + 545, + 494 + ], + "type": "text", + "content": "Linear Evaluation Protocol. We add a linear classifier after the pre-trained encoder. During the linear evaluation, we freeze the parameters in encoder and only train the parameters in linear classifier. We use SGD with momentum 0.9. The model runs 100 epochs with the initial learning rate 3.0 and decayed by 10 at 80 epochs." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 495, + 545, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 545, + 566 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 545, + 566 + ], + "type": "text", + "content": "Finetune Protocol. We add a linear classifier after the pre-trained encoder. During the finetune, we train the whole model with SGD optimizer, the momentum is set to 0.9 and the weight decay is set to 0.0001. The model runs 100 epochs with the initial learning rate 0.01 and decayed by 10 at 80 epochs." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "spans": [ + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "type": "text", + "content": "Semi-supervised Evaluation Protocol. We add a linear classifier after the pre-trained encoder. During the semi-supervised evaluation, we train the whole model with only " + }, + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 304, + 567, + 545, + 651 + ], + "type": "text", + "content": " randomly selected labeled data. We choose SGD optimizer with momentum 0.9 and weight decay 0.0001. The model runs 100 epochs with the initial learning rate 0.01 and decayed by 10 at 80 epochs." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 658, + 400, + 671 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 658, + 400, + 671 + ], + "spans": [ + { + "bbox": [ + 306, + 658, + 400, + 671 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "Tempo Prediction or RVTCLR. We first compare RVTCLR with the tempo prediction. Table 1 shows the comparison results of the joint stream on the NTU RGB+D 60" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13918" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": "dataset using the linear evaluation protocol. It is obviously found that tempo prediction cannot bring good performance compared to RVTL, which verifies our claim that predicting each video's specific visual tempo results in unreasonable action features. The outcome of AC demonstrates that explicit consideration of apparent information also plays an important role in modeling actions. AC+RVTL's performance proves that relative visual tempo and appearance modeling can work collaboratively to better concentrate on both skeleton motion and appearance clues. By further combining NNM, the performance of RVTCLR boosts to " + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "inline_equation", + "content": "74.4\\%" + }, + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": " (79.4%) on Xsub (Xview) benchmark, surpassing the tempo prediction by a large margin." + } + ] + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 100, + 270, + 235, + 339 + ], + "blocks": [ + { + "bbox": [ + 46, + 239, + 288, + 270 + ], + "lines": [ + { + "bbox": [ + 46, + 239, + 288, + 270 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 288, + 270 + ], + "type": "text", + "content": "Table 1. Comparisons between Tempo Prediction and RVTCLR. We report linear evaluation results of the joint stream on the NTU-60 dataset." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 100, + 270, + 235, + 339 + ], + "lines": [ + { + "bbox": [ + 100, + 270, + 235, + 339 + ], + "spans": [ + { + "bbox": [ + 100, + 270, + 235, + 339 + ], + "type": "table", + "html": "
MethodsNTU-60
XsubXview
Tempo prediction52.758.0
RVTL63.173.4
AC65.168.4
AC+RVTL73.377.8
AC+RVTL+NNM74.479.4
", + "image_path": "d59f1d1364388ab5cb8dc9b64fcf697b08917452966e22540c852acd5691cde3.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 353, + 289, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 353, + 289, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 353, + 289, + 593 + ], + "type": "text", + "content": "Effectiveness of RVTCLR+. We then verify the effectiveness of RVTCLR+. Table 2 shows the comparison results of three streams. From the table, we have several observations: (1) RVTCLR performs much better than SkeletonCLR in most cases. For example, we can obtain " + }, + { + "bbox": [ + 46, + 353, + 289, + 593 + ], + "type": "inline_equation", + "content": "+4.2\\%" + }, + { + "bbox": [ + 46, + 353, + 289, + 593 + ], + "type": "inline_equation", + "content": "(+9.2\\%)" + }, + { + "bbox": [ + 46, + 353, + 289, + 593 + ], + "type": "text", + "content": " performance gain on Xsub (Xview) in the motion stream. By further combining DC branch, our RVTCLR+ can still significantly improve the accuracy by " + }, + { + "bbox": [ + 46, + 353, + 289, + 593 + ], + "type": "inline_equation", + "content": "+13.3\\%" + }, + { + "bbox": [ + 46, + 353, + 289, + 593 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 353, + 289, + 593 + ], + "type": "inline_equation", + "content": "+12\\%" + }, + { + "bbox": [ + 46, + 353, + 289, + 593 + ], + "type": "text", + "content": ", respectively, which shows the efficacy of our method. (2) DC plays a more important role in the motion and bone streams. The primary reason we believe is due to the inherent presence of higher-order semantics in these two streams. The sparsity of skeleton data, however, may hinder the ability of naive contrastive learning to fully release their potential. As a result, recognition success may be limited to relying solely on low-level information. Our DC, however, force the model to focus on high-level semantics, thereby enabling the learning of more discriminative representations. (3) our 2-stream and 3-stream fusion results are always better than the comparative counterparts." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "We also conduct experiments in the motion stream to validate the effect of DC. As shown in Table 3 (a), we first determine whether all augmentations mentioned in [18, 6] applicable to SDA. Compared to the normal augmentation, we can find that gaussian noise, gaussian blur, and channel mask work well on both benchmarks. Although the others may perform better on Xsub, their results on Xview are relatively poor. Through empirical experimentation, we determine the former three augmentations as our best choice, yielding " + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "inline_equation", + "content": "+12.7\\%" + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "inline_equation", + "content": "+11.4\\%" + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": " accuracy increases over using" + } + ] + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 312, + 91, + 541, + 256 + ], + "blocks": [ + { + "bbox": [ + 305, + 69, + 547, + 89 + ], + "lines": [ + { + "bbox": [ + 305, + 69, + 547, + 89 + ], + "spans": [ + { + "bbox": [ + 305, + 69, + 547, + 89 + ], + "type": "text", + "content": "Table 2. Linear evaluation compared with SkeletonCLR. '2s' and '3s' means two-stream and three-stream fusion, respectively." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 312, + 91, + 541, + 256 + ], + "lines": [ + { + "bbox": [ + 312, + 91, + 541, + 256 + ], + "spans": [ + { + "bbox": [ + 312, + 91, + 541, + 256 + ], + "type": "table", + "html": "
MethodsDCStreamNTU-60
XsubXview
SkeletonCLRjoint68.376.4
RVTCLRjoint74.479.4
RVTCLR+✓joint74.779.1
SkeletonCLRmotion53.350.8
RVTCLRmotion57.560.0
RVTCLR+✓motion70.872.0
SkeletonCLRbone69.467.4
RVTCLRbone68.171.7
RVTCLR+✓bone72.278.4
2s-SkeletonCLRjoint+motion70.577.9
2s-RVTCLRjoint+motion75.781.6
2s-RVTCLR+✓joint+motion77.882.2
3s-SkeletonCLRjoint+motion+bone75.079.8
3s-RVTCLRjoint+motion+bone77.282.0
3s-RVTCLR+✓joint+motion+bone79.784.6
", + "image_path": "807eec3a5544d85bb9f88bb3fd4e365d282245d559997152974fb2707ee1a3f3.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 277, + 411, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 277, + 411, + 289 + ], + "spans": [ + { + "bbox": [ + 305, + 277, + 411, + 289 + ], + "type": "text", + "content": "the normal augmentation." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "spans": [ + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "type": "text", + "content": "FSEM is designed to emphasize the blurred joint connections. As shown in Table 3 (b), IIPB brings " + }, + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "type": "inline_equation", + "content": "+3.3\\%" + }, + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "type": "text", + "content": " performance improvement on Xview, proving its ability to adeptly capture the local spatial features. The accuracies of NLB are " + }, + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "type": "inline_equation", + "content": "70.0\\%" + }, + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "type": "inline_equation", + "content": "70.7\\%" + }, + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "type": "text", + "content": ", respectively, which demonstrate that constructing global dependencies among frames can achieve a more representative feature extraction. By combining these two blocks, the performance of our final FSEM further boots to " + }, + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "type": "inline_equation", + "content": "70.8\\%" + }, + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "type": "inline_equation", + "content": "72.0\\%" + }, + { + "bbox": [ + 304, + 289, + 545, + 396 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 398, + 545, + 471 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 398, + 545, + 471 + ], + "spans": [ + { + "bbox": [ + 304, + 398, + 545, + 471 + ], + "type": "text", + "content": "DD loss is introduced to help learn more representative high-level features. From the Table 3 (b), we can see a large performance drop when we replace the DD loss with the original one. This suggests that compared to the one-hot distribution, the weakly augmented view provides more suitable supervision signals." + } + ] + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 319, + 509, + 435, + 608 + ], + "blocks": [ + { + "bbox": [ + 305, + 479, + 547, + 502 + ], + "lines": [ + { + "bbox": [ + 305, + 479, + 547, + 502 + ], + "spans": [ + { + "bbox": [ + 305, + 479, + 547, + 502 + ], + "type": "text", + "content": "Table 3. Comparisons of DC's each component. We report linear evaluation results of the motion stream on the NTU-60 dataset." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 319, + 509, + 435, + 608 + ], + "lines": [ + { + "bbox": [ + 319, + 509, + 435, + 608 + ], + "spans": [ + { + "bbox": [ + 319, + 509, + 435, + 608 + ], + "type": "table", + "html": "
SDANTU-60
XsubXview
Normal55.258.2
Gaussian noise66.872.6
Gaussian blur56.259.4
Channel mask57.358.6
Rotate55.557.1
Spatial flip57.656.1
Temporal flip59.455.9
Best Combination67.969.6
", + "image_path": "a4c9701478d451764c7a9b309c8118e4a17474f525f21308763cecadbdc30c1c.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "type": "table", + "bbox": [ + 437, + 509, + 531, + 610 + ], + "blocks": [ + { + "bbox": [ + 362, + 610, + 392, + 620 + ], + "lines": [ + { + "bbox": [ + 362, + 610, + 392, + 620 + ], + "spans": [ + { + "bbox": [ + 362, + 610, + 392, + 620 + ], + "type": "text", + "content": "(a) SDA" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 437, + 509, + 531, + 610 + ], + "lines": [ + { + "bbox": [ + 437, + 509, + 531, + 610 + ], + "spans": [ + { + "bbox": [ + 437, + 509, + 531, + 610 + ], + "type": "table", + "html": "
FSEMNTU-60
XsubXview
-67.969.6
IIPB68.072.9
NLB70.070.7
IIPB+NLB70.872.0
DD lossNTU-60
XsubXview
✓70.872.0
-64.663.6
", + "image_path": "5d4a7fee1e3e10b9071fc9cf452cdae31708cd9c4250ab9c4eccea7ae885e0ad.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_body" + } + ], + "index": 13 + }, + { + "bbox": [ + 445, + 613, + 523, + 623 + ], + "lines": [ + { + "bbox": [ + 445, + 613, + 523, + 623 + ], + "spans": [ + { + "bbox": [ + 445, + 613, + 523, + 623 + ], + "type": "text", + "content": "(b) FSEM and DD loss" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 647, + 450, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 647, + 450, + 659 + ], + "spans": [ + { + "bbox": [ + 306, + 647, + 450, + 659 + ], + "type": "text", + "content": "4.4. Performance Comparison" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "content": "Linear Evaluation. Table 4 and Table 5 show the comparisons on NTU-60 and NTU-120 under linear evaluation protocol. From the Table 4, we observe that our joint-stream RVTCLR+ achieves competitive results compared to the" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "13919" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 143 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 143 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 143 + ], + "type": "text", + "content": "most recent SkeletonCLR [10] and AimCLR [6]. For example, " + }, + { + "bbox": [ + 46, + 72, + 288, + 143 + ], + "type": "inline_equation", + "content": "74.7\\%" + }, + { + "bbox": [ + 46, + 72, + 288, + 143 + ], + "type": "text", + "content": " vs " + }, + { + "bbox": [ + 46, + 72, + 288, + 143 + ], + "type": "inline_equation", + "content": "74.3\\%" + }, + { + "bbox": [ + 46, + 72, + 288, + 143 + ], + "type": "text", + "content": " on Xsub when compared to AimCLR. When multiple streams are fused, the performance of our method can be further improved. From the Table 5, we find that the performance of our 3s-RVTCLR+ remains at the forefront." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 144, + 290, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 144, + 290, + 275 + ], + "spans": [ + { + "bbox": [ + 46, + 144, + 290, + 275 + ], + "type": "text", + "content": "Finetune Evaluation. Table 6 shows the comparisons on NTU-60 and NTU-120 under fineture evaluation protocol. The table reveals that our single-stream RVTCLR+ achieves " + }, + { + "bbox": [ + 46, + 144, + 290, + 275 + ], + "type": "inline_equation", + "content": "0.8\\% \\sim 2.1\\%" + }, + { + "bbox": [ + 46, + 144, + 290, + 275 + ], + "type": "text", + "content": " improvement over AimCLR on both datasets. Notably, 3s-ST-GCN [39] is pretrained under full supervision, and its performance is the ensemble of multi-streams, compared to it, our single-stream RVTCLR+ can still get comparable performance. When combining different streams, the accuracy of our 3s-RVTCLR+ can be further increased by " + }, + { + "bbox": [ + 46, + 144, + 290, + 275 + ], + "type": "inline_equation", + "content": "2.6\\% \\sim 5\\%" + }, + { + "bbox": [ + 46, + 144, + 290, + 275 + ], + "type": "text", + "content": ", greatly outperforming AimCLR." + } + ] + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 93, + 293, + 242, + 474 + ], + "blocks": [ + { + "bbox": [ + 69, + 282, + 264, + 293 + ], + "lines": [ + { + "bbox": [ + 69, + 282, + 264, + 293 + ], + "spans": [ + { + "bbox": [ + 69, + 282, + 264, + 293 + ], + "type": "text", + "content": "Table 4. Linear evaluation results on NTU-60 dataset." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 93, + 293, + 242, + 474 + ], + "lines": [ + { + "bbox": [ + 93, + 293, + 242, + 474 + ], + "spans": [ + { + "bbox": [ + 93, + 293, + 242, + 474 + ], + "type": "table", + "html": "
MethodsNTU-60
XsubXview
Single-stream
LongT GAN [43]39.148.1
P&C [23]50.776.3
MS2L [11]52.6-
PCRP [38]54.963.4
AS-CAL [18]58.564.8
CRRL [31]67.673.8
SeBiReNet [16]-79.7
SkeletonCLR [10]68.376.4
AimCLR [6]74.379.7
RVTCLR+ (ours)74.779.1
Three-stream
3s-SkeletonCLR [10]75.079.8
3s-Colorization [41]75.283.1
3s-CrosSCLR [10]77.883.4
3s-AimCLR [6]78.983.8
3s-RVTCLR+ (Ours)79.784.6
", + "image_path": "163b3f2e7a19b3cdc73fd9d4528a1d9676150f445b9b13d2d8ebb6766601865f.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 96, + 495, + 238, + 592 + ], + "blocks": [ + { + "bbox": [ + 67, + 486, + 266, + 495 + ], + "lines": [ + { + "bbox": [ + 67, + 486, + 266, + 495 + ], + "spans": [ + { + "bbox": [ + 67, + 486, + 266, + 495 + ], + "type": "text", + "content": "Table 5. Linear evaluation results on NTU-120 dataset." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 96, + 495, + 238, + 592 + ], + "lines": [ + { + "bbox": [ + 96, + 495, + 238, + 592 + ], + "spans": [ + { + "bbox": [ + 96, + 495, + 238, + 592 + ], + "type": "table", + "html": "
MethodsNTU-120
XsubXset
P&C [23]42.741.7
PCRP [38]43.044.6
AS-CAL [18]48.649.2
CRRL [31]56.257.0
ISC [25]67.967.1
3s-CrosSCLR [10]67.966.7
3s-AimCLR [6]68.268.8
3s-RVTCLR+ (Ours)68.068.9
", + "image_path": "b70ef8c521b899036dcbd67e83d7c8c27ea67d6e943f0e5fda42cf6282c550f8.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 605, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 689 + ], + "type": "text", + "content": "Semi-supervised Evaluation. As shown in Table 7, with only " + }, + { + "bbox": [ + 46, + 605, + 287, + 689 + ], + "type": "inline_equation", + "content": "1\\%" + }, + { + "bbox": [ + 46, + 605, + 287, + 689 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 605, + 287, + 689 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 605, + 287, + 689 + ], + "type": "text", + "content": " labeled data, the results of our 3s-RVTCLR+ far exceed MCC [24], 3s-CrosCLR [10], and 3s-AimCLR. For example, 3s-RVTCLR+ increases the accuracies by " + }, + { + "bbox": [ + 46, + 605, + 287, + 689 + ], + "type": "inline_equation", + "content": "2.5\\%" + }, + { + "bbox": [ + 46, + 605, + 287, + 689 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 605, + 287, + 689 + ], + "type": "inline_equation", + "content": "4.6\\%" + }, + { + "bbox": [ + 46, + 605, + 287, + 689 + ], + "type": "text", + "content": " compared with 3s-AimCLR on NTU-120 dataset. These results suggest that the representational capacity of our learned features is considerable." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "content": "Qualitative Results. We apply t-SNE [26] with fixed settings to show the embedding distribution of Skeleton-" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 324, + 102, + 528, + 199 + ], + "blocks": [ + { + "bbox": [ + 305, + 68, + 545, + 102 + ], + "lines": [ + { + "bbox": [ + 305, + 68, + 545, + 102 + ], + "spans": [ + { + "bbox": [ + 305, + 68, + 545, + 102 + ], + "type": "text", + "content": "Table 6. Finetune evaluation results on NTU-60 and NTU-120 dastatets. †means using the same bone stream. ‡means the model is pretrained under full supervision." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 324, + 102, + 528, + 199 + ], + "lines": [ + { + "bbox": [ + 324, + 102, + 528, + 199 + ], + "spans": [ + { + "bbox": [ + 324, + 102, + 528, + 199 + ], + "type": "table", + "html": "
MethodsNTU-60NTU-120
XsubXviewXsubXset
SkeletonCLR† [10]82.288.973.675.3
MCC [24]83.089.777.077.8
AimCLR† [6]83.089.276.476.7
RVTCLR+†(Ours)84.491.377.278.4
3s-ST-GCN‡ [39]85.291.477.277.1
3s-CrosSCLR [10]86.292.580.580.4
3s-AimCLR [6]86.992.980.180.9
3s-RVTCLR+ (Ours)87.593.982.083.4
", + "image_path": "75db2dcdc5259ba80f3f318031b8697ba6d561e6f8175dfe8b19159e61476690.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 321, + 229, + 529, + 392 + ], + "blocks": [ + { + "bbox": [ + 305, + 207, + 545, + 229 + ], + "lines": [ + { + "bbox": [ + 305, + 207, + 545, + 229 + ], + "spans": [ + { + "bbox": [ + 305, + 207, + 545, + 229 + ], + "type": "text", + "content": "Table 7. Seim-supervised evaluation on NTU-60 and NTU-120 datasets. * means the results are obtained by their released codes." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 321, + 229, + 529, + 392 + ], + "lines": [ + { + "bbox": [ + 321, + 229, + 529, + 392 + ], + "spans": [ + { + "bbox": [ + 321, + 229, + 529, + 392 + ], + "type": "table", + "html": "
MethodsNTU-60NTU-120
XsubXviewXsubXset
1% labeled data
ISC [25]35.738.1--
3s-Colorization [41]48.352.5--
3s-CrosCLR [10]51.150.028.6*28.0*
3s-AimCLR [6]54.854.334.8*32.6*
3s-RVTCLR+ (Ours)54.953.633.332.8
10% labeled data
ISC [25]65.972.5--
3s-Colorization [41]71.778.9--
MCC-ST-GCN [24]55.659.940.743.4
MCC-2s-AGCN [24]60.865.847.051.8
MCC-AS-GCN [24]59.263.144.947.8
3s-CrosCLR [10]74.477.861.3*61.1*
3s-AimCLR [6]78.281.664.8*63.7*
3s-RVTCLR+ (Ours)79.583.767.368.3
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The t-SNE visualization of embeddings on NTU-60 X-sub. These models are trained for 300 epochs. j, b, and m represent joint-stream, bone-stream, and motion-stream, respectively." + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_caption" + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 629, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 712 + ], + "type": "text", + "content": "CLR and our RVTCLR+ on NTU-60 Xsub benchmark. For a fair comparison, we select the same 11 classes for visualization, where each class is represented by a dot of the same color. From the Figure 4, we can obviously see that the embeddings extracted from our method have better inter-class separability and intra-class compactness, indicating that our learned features are more discriminative." + } + ] + } + ], + "index": 25 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13920" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 119, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 119, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 119, + 83 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 91, + 289, + 283 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 91, + 289, + 283 + ], + "spans": [ + { + "bbox": [ + 47, + 91, + 289, + 283 + ], + "type": "text", + "content": "In this paper, we propose a Relative Visual Tempo Contrastive Learning framework for skeleton action representation (RVTCLR). The proposed RVTCLR combines Relative Visual Tempo Learning (RVTL) and Appearance-Consistency (AC) into a single-branch to obtain a more comprehensive spatial-temporal representation. Given the inherent sparsity of skeleton sequence data compared to RGB data, we design a new Distribution-Consistency (DC) branch aimed at emphasizing high-order semantics and preventing the network from learning shortcuts. The DC branch consists of Skeleton-specific Data Augmentation (SDA), Fine-grained Skeleton Encoding Module (FSEM), and Distribution-aware Diversity (DD) Loss. We refer to this new two-branch structure as RVTCLR+. Experimental results and visualization analysis verify that RVTCLR+ can obtain a more discriminative skeleton action representation." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 48, + 293, + 107, + 306 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 293, + 107, + 306 + ], + "spans": [ + { + "bbox": [ + 48, + 293, + 107, + 306 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 53, + 312, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 53, + 312, + 287, + 367 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 312, + 287, + 367 + ], + "spans": [ + { + "bbox": [ + 53, + 312, + 287, + 367 + ], + "type": "text", + "content": "[1] Unaiza Ahsan, Rishi Madhok, and Irfan Essa. Video jigsaw: Unsupervised learning of spatiotemporal context for video action recognition. 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Much of the critical information in patent documents and scientific articles is contained in figures, depicting the molecule structures. However, automatically parsing the exact chemical structure is a formidable challenge, due to the amount of detailed information, the diversity of drawing styles, and the need for training data. In this work, we introduce MolGrapher to recognize chemical structures visually. First, a deep keypoint detector detects the atoms. Second, we treat all candidate atoms and bonds as nodes and put them in a graph. This construct allows a natural graph representation of the molecule. Last, we classify atom and bond nodes in the graph with a Graph Neural Network. To address the lack of real training data, we propose a synthetic data generation pipeline producing diverse and realistic results. In addition, we introduce a large-scale benchmark of annotated real molecule images, USPTO-30K, to spur research on this critical topic. Extensive experiments on five datasets show that our approach significantly outperforms classical and learning-based methods in most settings. Code, models, and datasets are available1.", + "bbox": [ + 75, + 318, + 473, + 652 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 681, + 209, + 698 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The creation of an open-source database offering a unified view of our current knowledge of all studied molecules, would greatly accelerate research and development in numerous fields, ranging from the pharmaceutical industry to semiconductor manufacturing. Currently, information about a molecule's properties is distributed across various databases, research articles, and chemical patents, each measuring different subsets of properties. In such documents, molecules are most often described using images, by drawing their molecular structures. Automatic parsing of molecules from document images, known as Optical Chem-", + "bbox": [ + 75, + 708, + 468, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/46b9c0fea3bd844716a1aaddb891bffd018838c53ce420519ad5a4bbce23ddc8.jpg", + "image_caption": [ + "Figure 1. MolGrapher extracts the chemical structure, including all atoms and bonds, from a molecule image in a document. Our approach constructs a supergraph of the molecule (bottom right), containing all detected atom and bond candidates. These nodes are then classified by a Graph Neural Network in order to retrieve the chemical structure." + ], + "image_footnote": [], + "bbox": [ + 535, + 292, + 888, + 515 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "ical Structure Recognition (OCSR), is thus a critical task in the quest towards establishing a large-scale digital molecule database.", + "bbox": [ + 498, + 625, + 892, + 670 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "OCSR, however, poses multiple key challenges, which limit the accuracy of current solutions. First, a molecule can be drawn with a variety of styles and conventions. Even the projection of the molecular structure from 3-D onto a 2-D drawing is not unique, leading to the development of various projection algorithms with diverse results. Secondly, OCSR requires the extraction of detailed information from the image. Molecules often contain even hundreds of atoms and bonds, which all need to be correctly classified and linked. Thirdly, molecules have a virtually endless diversity stemming from the combinatorical explosion of possibilities, presenting particular challenges to data-driven deep learning methods. Lastly, available real training datasets are extremely limited, further complicating the application of deep learning.", + "bbox": [ + 496, + 674, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "$^{1}$ https://github.com/DS4SD/MolGrapher", + "bbox": [ + 94, + 886, + 312, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "19552", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Initial OCR approaches followed the graph reconstruction paradigm. These methods start by extracting the fundamental components of molecules, such as atoms, bonds, and charges, often using hand-crafted image processing algorithms [8, 29, 21]. Then, rules are applied to connect these elements to reconstruct a graph representation of the molecule. Some recent works [19, 33, 38] introduce deep learning elements into the atom and bond detection steps. However, these approaches still rely on hand-crafted rules to link the recognized constituents, and thus not fully benefit from the advantages brought by deep learning.", + "bbox": [ + 80, + 90, + 467, + 271 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Most recently, approaches instead follow the image captioning [4, 24, 34] paradigm by applying a deep network to directly output a character string identifying the molecule, e.g. in the form of SMILES [32]. However, these methods do not explicitly exploit the rich priors and invariances provided by the graph structure. The SMILES representation does not encode the geometrical and neighborhood structure of the molecule graph in a natural manner. While a recent work [36] predicts a graph in an autoregressive manner, adding one atom at a time prevents from fully exploiting the graph structure. Partially due to the lack of such a strong inductive bias, image captioning based methods still lag behind from the performance of state-of-the-art rule-based methods [8, 29, 21] on standard benchmarks [8, 9, 28, 22]. Moreover, the performance of captioning based methods severely degrade when increasing the size and complexity of the molecule, as they struggle to recover the detailed information in the image.", + "bbox": [ + 80, + 275, + 467, + 546 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We introduce MolGrapher for Optical Chemical Structure Recognition, illustrated in Fig. 1. Our approach explicitly utilizes the graph structure as a strong inductive bias, while also allowing for the final molecule structure itself to be predicted by a deep learning model. MolGrapher operates in three steps. First, we locate atoms and abbreviations in the image with a keypoint detector network. Given the estimated locations of the atoms, we form a supergraph of the molecular structure, where two types of nodes represent candidate atoms and bonds respectively (see Fig. 1). Unlike previous approaches, we do not commit to a final molecule structure at this point, instead extracting a larger set of candidate bonds, forming a superset of the final molecular graph. Candidates that do not correspond to any bond are removed in the final prediction step by including a 'no bond' class.", + "bbox": [ + 80, + 550, + 467, + 790 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In the final step, we input the constructed supergraph into a Graph Neural Network (GNN). We first extract deep node embeddings through a backbone network. The GNN then operates on the neighborhood structure provided by the supergraph in order to integrate visual information with learned chemistry priors. We then read-out the results with MLPs, classifying each node into a set of atom and bond", + "bbox": [ + 80, + 795, + 467, + 898 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "classes. We also identify abbreviations through a separate class, which are parsed by an OCR component. Since training data is scarce, we develop, and release, a synthetic training data generation pipeline, capable of generating diverse and challenging examples to ensure robust generalization to a wide variety of drawing styles.", + "bbox": [ + 503, + 90, + 888, + 180 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To further aid the research in the community, we introduce USPTO-30K, a large-scale benchmark dataset of annotated real molecule images. It contains separate subsets, in order to independently study the recognition of simple molecules, abbreviated molecules and extremely large molecules. We perform comprehensive experiments on five benchmarks: our USPTO-30K, USPTO [8], Maybridge UoB [28], CLEF-2012 [22] and JPO [9]. We outperform all deep learning based methods that only utilizes synthetic training. Our approach even surpass previous methods that rely on finetuning on real data on most benchmarks, and outperform the longstanding state-of-the-art by rule-based methods [8, 29, 21] in most settings.", + "bbox": [ + 503, + 181, + 888, + 377 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 503, + 391, + 635, + 407 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "OCSR approaches can be divided in two main categories. Image captioning based OCSR. Most of the recent end-to-end deep learning approaches are based on image captioning. These models use an encoder to extract visual features from the image and a decoder to translate them to a SMILES [32] or InChI [10] sequence. More precisely, DECIMER [26], MICER [35], MSE-DUDL [30] and Img2Mol [4] are using a convolutional encoder and a recurrent decoder which is respectively, a GRU decoder, a LSTM decoder, a GridLSTM decoder, and a RNN decoder. Later works proposed replacing the recurrent decoder with a transformer encoder-decoder, including DECIMER 1.0 [27], SwinOCSR [34], IMG2SMI [3] and Image2SMILES [13]. Other image captioning methods are solely based on transformers, using a vision transformer in [31], a Swin transformer in [23] or a Deep TNT transformer encoder with a transformer decoder in ICMDT [17].", + "bbox": [ + 503, + 417, + 888, + 672 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "One drawback of image captioning methods is the need of large training sets. The SMILES representation has numerous downsides for a learning task [15], one of them which is ambiguity due to the association of very different string identifiers to similar molecules. By predicting SMILES, instead of a more faithful representation of the image, the model needs to learn jointly to recognize the image and understand the SMILES language. Multiple string identifiers, possibly suited for a learning task have been proposed, including SELFIES, DeepSMILES [25] or abstract mathematical identifiers [4]. Nevertheless, representing a molecule image as a string adds extra complexity for a learning task. Additionally, these models to not properly handle uncertainty by predicting incorrect, but still valid, molecules for challenging inputs such as large molecules.", + "bbox": [ + 503, + 674, + 888, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "19553", + "bbox": [ + 482, + 946, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/5d3ef430de4467b99100b8764aa556dd3e89a6779c8ed5ef35106f1107110a27.jpg", + "image_caption": [ + "Figure 2. Molecular graph recognition architecture. We illustrate the architecture of MolGrapher, a graph-based network for Optical Chemical Structure Recognition. The keypoint detector (red) locates atoms nodes in the molecule. A supergraph containing atom and bond candidates is constructed (green). Atoms and bonds are classified using a Graph Neural Network (blue)." + ], + "image_footnote": [], + "bbox": [ + 96, + 89, + 870, + 258 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Yet, to parse scientific literature at large scale, avoiding these false positives is critical. This behaviour is explained by the fact that the model is trained to always output valid SMILES, while using global image features. Contrary to these approaches, our model extracts precise visual features for each elementary component of a molecule and operate on a graph, allowing substantially better recognition performance for large molecules, possibly larger than the ones used for training.", + "bbox": [ + 75, + 325, + 472, + 464 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Graph reconstruction based OCSR. Traditional approaches for Optical Chemical Structure Recognition rely on hand-crafted image processing algorithms to detect elementary components of the molecules and connect them to reconstruct the molecular graph [2, 8, 12, 20, 28, 29, 21]. More recent works detect elementary components using machine learning models. For instance, ChemGrapher [19] or ABC-Net [38] use convolutional segmentation networks while MolMiner [33] employs aYOLO object detector. As studied in [11], detection based methods can be trained with fewer training samples. By doing multiple low-level detections, it is possible to supervise precisely the training. It also offers a natural way to inject prior knowledge, or impose chemistry rules to the model. Our method benefits from these advantages but differentiates itself by learning both the detection and the association of the fundamental components of molecules.", + "bbox": [ + 75, + 469, + 472, + 727 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Image2Graph [36] uses a transformer to build the graph in an auto-regressive way, by adding one atom at the time. [23] predicts a SMILES sequence, but enriched with atoms positions, and connectivity information, drifting away from the string identifier and getting closer to a graphical representation. Our new graph reconstruction approach do not build a graph auto-repressively. We first detects all possible components and associations, and then classify them. It allows to use localized visual features, as well as a complete neighborhood contextual information for each atom and bond prediction.", + "bbox": [ + 75, + 734, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. MolGrapher", + "text_level": 1, + "bbox": [ + 498, + 323, + 632, + 340 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We introduce MolGrapher, a graph-based network for Optical Chemical Structure Recognition. Our model architecture is illustrated in Figure 2. Our pipeline consists of three steps. Firstly, the keypoint detector locates atoms nodes in the molecule. Secondly, we construct a graph containing atom and bond candidates. Finally, atoms and bonds are classified using a Graph Neural Network.", + "bbox": [ + 496, + 349, + 893, + 455 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Keypoint Detection", + "text_level": 1, + "bbox": [ + 498, + 465, + 684, + 482 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In order to construct the molecular graph, we first need to localize keypoints in the image. Keypoints refer to the position of atoms and 'superatoms', i.e. abbreviated groups of atoms. In the later stages, this enables the extraction of relevant visual features for atoms and bonds, as well as the construction of our molecule supergraph.", + "bbox": [ + 496, + 488, + 893, + 580 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our keypoint detector predicts a heatmap, where each peak corresponds to an atom location. The output of a feature extractor is passed through convolutional layers to predict the final single-channel heatmap of the atom locations. To extract the peak locations, we first threshold the heatmap by removing any value in the bottom $10^{\\mathrm{th}}$ percentile. We then collect regional maxima, using a window size of $5 \\times 5$ , as the final atom locations.", + "bbox": [ + 496, + 580, + 893, + 699 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Atoms are labeled with Gaussian functions, allowing smoother supervision as well as capturing a degree of uncertainty regarding the predicted positions. Since the groundtruth heatmaps predominantly contains background values, we use the weight-adaptive heatmap regression loss [18] to overcome the class imbalance. It reduces the impact of well-classified samples, which mostly constitute background, allowing the training to focus on harder samples.", + "bbox": [ + 496, + 700, + 893, + 823 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Supergraph Construction", + "text_level": 1, + "bbox": [ + 498, + 830, + 735, + 848 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we describe the construction of the supergraph, which contains all atom and bond candidates to be classified. The supergraph is composed of two types of", + "bbox": [ + 496, + 854, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "19554", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/42990e13da558e4fc561693313483516f20350b6a45ae2db0923b0e133dddb73.jpg", + "image_caption": [ + "Figure 3. Supergraph construction. The figure presents the construction of bonds proposals for an atom denoted $A$ . Considered bonds are depicted with dashed lines. Green bonds are accepted in the supergraph, while red bonds are discarded because: (1) there are no filled pixels around their centerpoints or (2) they are obstructed by other keypoints." + ], + "image_footnote": [], + "bbox": [ + 81, + 102, + 486, + 210 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "nodes: atoms and bonds. Further, each edge in the graph only connects an atom node to a bond node. Representing both of these entities as nodes allows us to process them uniformly through standard message passing layers.", + "bbox": [ + 75, + 321, + 468, + 382 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The input to our supergraph construction is a set of approximate atom locations. Since the connectivity between the detected atoms is unknown, our graph has to represent a superset of the final molecule prediction, thus termed 'supergraph'. That is, it contains all possible bonds. By including a prediction class corresponding to 'no bond', bond candidates which are not actually in the molecule can be removed in the later stage. Including an analogous class for 'no atom', our approach can even correct false positives predicted by the keypoint detection network.", + "bbox": [ + 75, + 383, + 468, + 532 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Our supergraph construction is illustrated in Figure 3. We first consider each keypoint individually, adding connections to all other keypoints within a radius of three times the estimated bond length [8]. Subsequently, we remove connections which have no filled pixels around their centerpoints or if there is a third keypoint located between its two extremities. Finally, we keep at most six bond candidates for each atom, by eliminating the longest connections. Chemistry prior knowledge ensures that it is extremely unlikely for an atom to have more than five neighboring bonds. Our settings are highly conservative to avoid deleting any actual bond. On the other hand, pruning superfluous bonds avoids any unnecessary false positives in the later stage and a more effective connectivity for the GNN.", + "bbox": [ + 75, + 534, + 470, + 746 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Node Classification", + "text_level": 1, + "bbox": [ + 76, + 756, + 261, + 771 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In order to classify atom and bond nodes, we integrate a Graph Neural Network (GNN) that operates on the constructed supergraph. The embeddings for all nodes are initialized using visual features as well as their types. This approach leverages the local context of atoms and bonds to predict their class. Intuitively, it enables the learning of chemistry rules, i.e. atoms have a fixed valence, as well as chemistry prior knowledge, i.e. some typical substructures", + "bbox": [ + 75, + 780, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "are more common than others.", + "bbox": [ + 498, + 92, + 702, + 104 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Let $e_i^1 \\in R^D$ denotes the initial embedding of the node $i$ of type $t_i \\in \\{\\text{atom}, \\text{bond}\\}$ located at position $(x_i, y_i)$ . It is computed by combining a visual feature vector $v_i$ and a learnable type encoding $w_{t_i}$ ,", + "bbox": [ + 496, + 104, + 893, + 167 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ne _ {i} ^ {0} = v _ {i} + w _ {t _ {i}} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 645, + 175, + 890, + 193 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The visual features $v_{i}$ are extracted from a deep feature map $F$ , extracted by a backbone network. For an atom node $i$ we evaluate the feature map in the corresponding location $(x_{i},y_{i})$ with bilinear interpolation,", + "bbox": [ + 498, + 200, + 893, + 262 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nv _ {i} = F \\left(x _ {i}, y _ {i}\\right). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 640, + 272, + 890, + 287 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For a bond node $i$ , we aggregate features at locations along the bond as", + "bbox": [ + 496, + 297, + 890, + 325 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nv _ {i} = \\frac {1}{J} \\sum_ {j = 1} ^ {J} F \\left(x _ {i} ^ {j}, y _ {i} ^ {j}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 617, + 324, + 890, + 366 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $(x_i^j, y_i^j)$ are the locations of $J$ uniformly spaced points along the bond itself.", + "bbox": [ + 496, + 372, + 890, + 402 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Given initial node embeddings, information is propagated through the graph to learn local dependencies between atoms and bonds. Indeed, directly neighboring atoms and bonds respect strict chemistry rules, and larger neighborhoods form patterns called functional groups, which are typically abundant in nature. We employ GNN layers, denoted $\\{g^k\\}_{k\\in [1,N]}$ , to iteratively update the node embeddings,", + "bbox": [ + 496, + 404, + 890, + 525 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ne ^ {k + 1} = g ^ {k} \\left(e ^ {k}\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 640, + 525, + 890, + 542 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The final predictions $\\{p_i\\}$ are then obtained using two Multi-Layer Perceptrons, one for each node type $t$", + "bbox": [ + 496, + 547, + 890, + 579 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\np _ {i} = M L P _ {t} \\left(e _ {i} ^ {N}\\right). \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 632, + 587, + 890, + 604 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The vector $p_i \\in \\mathbb{R}^{C_t}$ contains the logits for the final atom or bond classes.", + "bbox": [ + 496, + 613, + 890, + 642 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The most represented bond types include 'no bond', 'single', 'double' and 'triple'. Atom classes include the common (e.g. O) and exotic atoms as well as charged atoms (e.g. $\\mathrm{O}^{-}$ ). Since molecule images often include whole groups in the nodes, e.g. COOH, we further include a class 'superatom' to recognize these cases. Such nodes are then parsed as described in Section 3.4.", + "bbox": [ + 496, + 643, + 890, + 748 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Our node classification model is trained using the cross-entropy loss for both the atom and bond prediction heads. During training, the supergraph structure used as input is obtained by applying the graph construction algorithm on augmented ground truth keypoints. To simulate possible errors from the keypoint detector, we add noise to the atom positions and randomly include false-positive keypoints. Decoupling the keypoint detection and the node classification allow to train faster and to use optimized training sets for each task.", + "bbox": [ + 496, + 750, + 890, + 898 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "19555", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Superatom Groups Recognition", + "text_level": 1, + "bbox": [ + 80, + 90, + 354, + 107 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To recognize abbreviated substructures, named superatoms, we use an external Optical Character Recognition (OCR) system. Relying on an external OCR system provides strong robustness, since the model is trained on a diversity of text representations that cannot necessarily be generated in a molecule image. At the location of an abbreviated group, the node classifier predicts a 'superatom' class. Then, the OCR engine PP-OCR [6] is used to recognize the text written at this location, which is finally replaced by its corresponding sub-molecule, stored in a precomputed mapping.", + "bbox": [ + 80, + 114, + 467, + 279 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Datasets", + "text_level": 1, + "bbox": [ + 80, + 292, + 169, + 309 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Synthetic Training Data Generation", + "text_level": 1, + "bbox": [ + 80, + 316, + 385, + 334 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Training datasets of annotated molecule images extracted from scientific publications are extremely limited. Therefore, we develop a synthetic training pipeline to generate a broad diversity of molecular representations. It further allows us to extract atom-level annotations.", + "bbox": [ + 80, + 340, + 467, + 415 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Our dataset is created using molecule SMILES retrieved from the database PubChem [14]. To increase the probability that the dataset covers the largest variety of molecular structures, we sample SMILES using a strategy based on functional groups. A functional group is molecule substructure typically abundant in nature. Thus, we retrieve molecules from PubChem containing each functional group in a defined collection of 1540 functional groups. To further increase diversity, these molecules are queried with different ranges of number of atoms. Finally the dataset is filtered by removing salts, molecules containing complex polycycles, isotopes or radical electrons. Training images are then generated from SMILES using the molecule drawing library RDKit [16].", + "bbox": [ + 80, + 417, + 467, + 627 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To capture the large diversity of drawing styles and conventions from different scientific documents, the synthetic set is highly augmented, at multiple levels. Firstly, molecules are randomly transformed, notably by setting the selection of a molecular conformation, adding artificial superatom groups with single or multiple attachment points or displaying solid, dashed or wavy bonds. Secondly, the rendering parameters used in RDKit are randomly set, including the font, the bond width, the display of aromatic cycles using circles. This leads to substantial variations in the drawn molecule, to aid generalization to real datasets.", + "bbox": [ + 80, + 628, + 467, + 792 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The generated molecule images are saved together with their corresponding MolFiles. A MolFile [5] stores information about the atoms and their positions in a molecule, as well as bonds and their connectivity. It provides the necessary information for supervising the training. This generation pipeline covers a large diversity of molecules including stereo-chemistry and molecules with superatom groups.", + "bbox": [ + 80, + 795, + 467, + 898 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Finally, the images undergo several image augmentations on the fly such as gaussian blurring, the adding of pepper patches, random lines, and random captions.", + "bbox": [ + 503, + 90, + 890, + 135 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The exhaustive lists of molecule, rendering and image augmentations, as well as details regarding the generation of atom-level annotations are available in the supplementary materials.", + "bbox": [ + 503, + 136, + 890, + 195 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. The USPTO-30K Dataset", + "text_level": 1, + "bbox": [ + 503, + 204, + 728, + 219 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Existing benchmarks have some limitations. Being created using only a few documents, they contain batches of very similar molecules. For example in a patent, a molecule could typically be displayed together with all the substituent of one particular substructure, resulting in large batches of almost identical molecules. Additionally, the existing sets contain molecules of different kinds, including superatom groups and various markush [7] features, which should be evaluated independently. In practice, it is important to delimit on which types of molecules models can be applied.", + "bbox": [ + 503, + 227, + 890, + 378 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We introduce USPTO-30K, a large-scale benchmark dataset of annotated molecule images, which overcomes these limitations. It is created using the pairs of images and MolFiles [5] by the United States Patent and Trademark Office (USPTO) [1]. Each molecule was independently selected among all the available images from 2001 to 2020. The set consists of three subsets to decouple the study of clean molecules, molecules with abbreviations and large molecules. USPTO-10K contains 10,000 clean molecules, i.e. without any abbreviated groups. USPTO-10K-abb contains 10,000 molecules with superatom groups. USPTO-10K-L contains 10,000 clean molecules with more than 70 atoms. We provide visualizations and analysis in the supplementary materials.", + "bbox": [ + 503, + 378, + 890, + 589 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 503, + 602, + 627, + 619 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we perform comprehensive experiments on multiple OCSR benchmarks. Moreover, we propose an analysis of the different components of our method.", + "bbox": [ + 503, + 627, + 890, + 672 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.1. Implementation details", + "text_level": 1, + "bbox": [ + 503, + 680, + 710, + 696 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The implementation is done with PyTorch 1.12 with CUDA 11.3. For the keypoint detector features extractor, we use a ResNet-18 backbone with $8 \\times$ dilatation factor [37] to preserve a high spatial resolution. For the node classifier features extractor, we resort to a ResNet-50 with a $2 \\times$ dilation factor. The model is trained on 300,000 synthetic images, presented in subsection 4.1. We train for 20 epochs on 3 NVIDIA A100 GPUs using ADAM with a learning rate of 0.0001 that we decay after 5000 iterations by a factor of 0.8. The losses for atoms and bonds classifiers are weighted by factors 1 and 3, respectively. During inference, we pre-process images by removing captions using PP-OCR [6]. Additionally, in case an initial prediction is an", + "bbox": [ + 503, + 703, + 890, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "19556", + "bbox": [ + 482, + 946, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/dc06013906e99b635b8e186f7cd4aa944420c5b651ed8665f8ae675d1f74a54c.jpg", + "table_caption": [ + "Table 1. Comparison of our method with existing OCR models. We report the accuracy, i.e. the percentage of perfectly recognized molecule images, on datasets coming from real scientific documents. $\\ast$ : re-implemented results. †: results from original publications. $\\ddagger$ : results from [11]." + ], + "table_footnote": [], + "table_body": "
MethodUSPTO (5719)Maybridge UoB (5740)CLEF-2012 (992)JPO (450)USPTO-10K (10 000)USPTO-10K-Abb (10 000)USPTO-10K-L (10 000)
Rule-based methods
OSRA 2.1 [8]*89.386.393.456.389.763.943.1
MolVec 0.9.7 [21]*89.188.381.266.892.470.364.0
Imago 2.0 [29]*89.463.968.241.089.963.047.3
Only synthetic training
DECIMER 2.0 [24]†61.088.072.064.0---
Image2Graph [36]†44.972.037.824.0---
Graph Generation [23]†67.083.174.6----
CEDe [11]‡79.074.168.049.4---
Chemographer [19]‡80.983.275.553.3---
Img2Mol [4]*25.268.017.916.135.413.80.0
MolGrapher (Ours)91.594.990.567.593.382.831.4
", + "bbox": [ + 117, + 128, + 851, + 309 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "invalid molecule, we use PP-OCR to merge keypoints located in a same detected text cell. See the supplementary material for more details.", + "bbox": [ + 75, + 330, + 468, + 377 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. Evaluation datasets and metrics", + "text_level": 1, + "bbox": [ + 76, + 388, + 357, + 402 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To compare our method with state-of-the-art, the model is evaluated on the standard benchmarks USPTO [8], Maybridge UoB [28], CLEF-2012 [22] and JPO [9]. USPTO and CLEF are collections of 5,719 and 992 molecule images. Besides, JPO contains 450 images published by the Japanese Patent Office (JPO). JPO is particularly challenging because of its non-standard drawing conventions and poor images qualities. Lastly, Maybridge UoB is a dataset of 5,740 scanned molecule images taken from a catalogue of drug compounds by Maybridge. To compare methods, we compute accuracy, defined as the percentage of perfectly recognized molecules. In practice, this is done by verifying that the predicted and ground-truth molecules have identical InChI [10] keys. For evaluation, stereo-chemistry is removed and markush structures are not considered.", + "bbox": [ + 75, + 412, + 470, + 638 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.3. State-of-the-art Comparison", + "text_level": 1, + "bbox": [ + 76, + 650, + 333, + 666 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1 compares the OCSR methods on different benchmarks. Our method achieves superior results compared to rule-based models on most datasets, including USPTO, Maybridge UoB and JPO. Solely using synthetic training, our method reduces the error rate by more than half compared to other deep learning methods on USPTO, Maybridge UoB, and CLEF-2012. The design of our model confers a strong generalization ability. In practice, this is very important as our model will be applied to a wide variety of documents, which are not necessarily evaluated by the current benchmark datasets. MolGrapher also maintains good performance for extremely large molecules in USPTO-10K-L, which only contains examples with more than 70 atoms. On the contrary, recognizing large molecules is a significant challenge for image captioning based methods. For", + "bbox": [ + 75, + 672, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/4d84b60a79c04ca6682b525ee15b98ad3c5812ec06f4db17ecaae2a6c3505223.jpg", + "table_caption": [ + "Table 2. Comparison of our method with deep OCSR models finetuned on real data. We report the accuracy, i.e. the percentage of perfectly recognized molecule images, on datasets coming from real scientific documents. †: results from original publications. ‡: results (in grey) from unavailable sub-splits of the original benchmarks, only reported for reference." + ], + "table_footnote": [], + "table_body": "
MethodUSPTO (5719)Maybridge UoB (5740)CLEF-2012 (992)JPO (450)
Real data finetuning
Image2Graph [36]†55.183.051.750.0
Graph Generation [23]†92.986.687.5-
CEDe [11]†‡91.091.586.674.0
Only synthetic training
MolGrapher (Ours)91.594.990.567.5
", + "bbox": [ + 501, + 409, + 890, + 503 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "instance, Clevert et al. point out that the performance of Img2Mol [4] drop sharply for molecules larger than 40 atoms. This is confirmed in our evaluation, where it fails to correctly recognize virtually any molecule in USPTO-10K-L. Table 2 also provides comparison with models finetuned using real data. Our model surpasses these methods on Maybridge UoB, CLEF-2012 and JPO and is second best on USPTO, while not relying on any real data for training.", + "bbox": [ + 496, + 520, + 890, + 640 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Our model outperforms existing methods on our USPTO-10K and USPTO-10K-Abb. The performance is particularly improved for molecules containing abbreviated groups. The performance gap between USPTO and USPTO-10K-Abb for rule-based approaches suggests that these methods are specifically parameterized for abbreviations in the existing benchmark datasets. Our model is the only deep learning method to provide a competitive performance for extremely large molecules. This is allowed by our architecture, which extracts localized visual features.", + "bbox": [ + 496, + 641, + 890, + 790 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.4. Model Robustness", + "text_level": 1, + "bbox": [ + 500, + 801, + 676, + 816 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Clevert et al. [4] introduced modified version of the standard benchmarks by applying slight perturbations, such as rotation and shearing, to the input images. Table 3 presents a comparison to previous methods on the same perturbed sets. The augmented images can be seen as a simulation", + "bbox": [ + 496, + 824, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "19557", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/2f7167d5c8e3437b80960bd0e3dc18a845fb7d92b38dfe6fead0654031630eed.jpg", + "table_caption": [ + "Table 3. Evaluation of model robustness. We report the accuracy, i.e. the percentage of perfectly recognized molecule images, on perturbed datasets coming from real scientific documents. $\\dagger$ : results from [4]." + ], + "table_footnote": [], + "table_body": "
MethodUSPTOP(4852)Maybridge UoBP(5716)CLEF-2012P(711)JPOP(365)
OSRA 2.1 [8]†6.470.917.033.0
MolVec 0.9.7 [21]†30.775.044.549.5
Imago 2.0 [29]†5.15.126.723.2
Img2Mol [4]†42.378.248.845.1
MolGrapher (Ours)86.794.187.855.4
", + "bbox": [ + 80, + 141, + 468, + 231 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "of scanned images, which are typically found in chemical patents. We observe that the performance of rule based approaches, OSRA, MolVec and Imago, decreases sharply. However, our model maintains a good result, outperforming other methods by a significant margin. This robustness is essential for large-scale analysis of chemical literature, as input molecule image quality cannot be controlled.", + "bbox": [ + 75, + 247, + 468, + 353 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.5. Qualitative evaluation", + "text_level": 1, + "bbox": [ + 76, + 361, + 282, + 376 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we conduct a qualitative evaluation of MolGrapher, in comparison to state-of-the-art methods. First, Figure 4 illustrates the intermediate outputs of MolGrapher. Note that MolGrapher accurately recognizes molecules in challenging cases with overlapping bonds, without the use of any post-processing rules. Figure 5 showcases examples of predicted molecules for images from various benchmark datasets. MolGrapher demonstrates robustness to images containing captions (Figure 5 row 1). It can correctly recognize extremely large molecules (Figure 5 row 4), and is robust to solid, dashed or wavy bonds (Figure 5 row 5). Unlike image captioning based methods such as $\\mathrm{Img2Mol}$ , our predictions preserve the projection and atom placement used in the input image (Figure 5 row 2). This can convey critical information for human interpretation.", + "bbox": [ + 75, + 383, + 468, + 625 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.6. Ablation study", + "text_level": 1, + "bbox": [ + 76, + 633, + 225, + 648 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We conduct an ablation study to demonstrate the impact of each component in the proposed method.", + "bbox": [ + 75, + 657, + 468, + 686 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Synthetic training set. We evaluate the impact of the three levels of augmentation of the training set, illustrated in Ta", + "bbox": [ + 75, + 686, + 468, + 718 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/884fa1672620c34628b0205583ea52b131e11f183f3d175780992a475e2a651f.jpg", + "table_caption": [ + "Table 4. Training set analysis. Impact of training set augmentations on performance. Molecule, rendering and image level augmentation are independently removed." + ], + "table_footnote": [], + "table_body": "
USPTOJPOJPOp
All augmentations91.567.555.4
No molecule augmentation52.452.743.4
No rendering augmentation78.455.744.1
No image augmentation69.829.322.5
", + "bbox": [ + 524, + 128, + 874, + 208 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ble 4. The image augmentations have a major impact on the performance of the model. In practice, we noticed that the keypoint detector benefits greatly from using heavy image transformations. Additionally, the molecule augmentations, which allow training molecules to contain abbreviated groups, proved crucial to handle images containing abbreviated groups, such as in USPTO.", + "bbox": [ + 496, + 224, + 890, + 330 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Keypoint detector. In Table 5, we experiment with different standard deviations for the Gaussian keypoint labels, and keypoint regression losses. Using a large standard deviation of $b / 5$ , where $b$ denotes the bond length, creates overlaps between keypoints and significantly decreases performance. While the model is not sensitive to the choice of training loss, the WAHR loss offers a slight advantage.", + "bbox": [ + 496, + 330, + 890, + 436 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Supergraph construction. In Table 7, we evaluate the impact of the maximum number of bond candidates and the search radius in the supergraph construction. We observe that our approach is not sensitive to these settings, but only experiences a small drop when increasing the number of bond candidates. This drop is explained by false positives predicted during the node classification stage.", + "bbox": [ + 496, + 438, + 890, + 542 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Node classifier. As demonstrated in Table 7, initializing nodes embeddings with both visual and type encoding increases performance. We also experimented with positional", + "bbox": [ + 496, + 544, + 890, + 590 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/3dca10a92e91517c54ac43cdc6d3e1a0eaaf3043aaa66b28daced7eddf4806fc.jpg", + "table_caption": [ + "Table 5. Keypoint detector analysis. We analyse the standard deviation of the Gaussian functions (top), as well as the training loss function (bottom). $b$ denotes the molecule bond length." + ], + "table_footnote": [], + "table_body": "
USPTOJPOJPOp
Heatmap standard deviationb/581.354.746.8
b/1091.567.555.4
b/1591.464.751.6
Training lossL291.166.255.1
WAHR [18]91.567.555.4
", + "bbox": [ + 522, + 641, + 874, + 719 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/5dacef82858d2cfcd4183469519d103a6eb6de66bdbb40a23f2bb58fd7a4a8cd.jpg", + "image_caption": [ + "Figure 4. Prediction steps. Keypoints are detected and then used to build a supergraph. After classifying the nodes of the graph and recognizing abbreviated groups, the output molecule is created. In this example, the polycyclic molecule contains overlapping bonds, a challenging feature for OCSR models, and is still correctly recognized." + ], + "image_footnote": [], + "bbox": [ + 106, + 738, + 869, + 847 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "19558", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/77527c0a258a629f927f0398f4f3ca3dcc00a03ae935097d21edff08cee4070f.jpg", + "image_caption": [ + "Figure 5. Qualitative comparison. The figure shows examples of predictions for characteristic images from different benchmarks. Compared to previous rule-based and learning based methods, our approach robustly recognizes the exact molecular structure in challenging cases, such as with distracting captions, stereo-chemistry, and very large molecules." + ], + "image_footnote": [], + "bbox": [ + 127, + 87, + 841, + 433 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/cba94af9d3795111e662ede0be6b23cb6675e3107fac8a93fcbecd5946c399b1.jpg", + "table_caption": [ + "Table 6. Supergraph construction analysis. We analyse the maximum number of bond candidates (top), and the maximum search radius (bottom). $b$ denotes the molecule bond length." + ], + "table_footnote": [], + "table_body": "
USPTOJPOJPOp
Number bond candidates691.567.555.4
1091.065.754.1
Search radius3b91.567.555.4
5b91.365.053.1
", + "bbox": [ + 101, + 536, + 450, + 614 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/54949e9415cc745fec2df7245721e9dcd576b1bffb8a437b849eb4a2c9943082.jpg", + "table_caption": [ + "Table 7. Node classifier analysis. We analyse the features representing graph nodes (top), and the usage of GCN layers (bottom). $\\dagger$ : without abbreviated molecules and charges." + ], + "table_footnote": [], + "table_body": "
USPTOJPOJPOp
Node embeddingVisual90.064.754.9
+ Type91.567.555.4
+ Position91.362.854.8
USPTO†JPO†JPOp†
Number of GCN Layers090.158.053.6
490.466.661.6
", + "bbox": [ + 99, + 667, + 450, + 758 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "embedding but found it to reduce the overall performance. The model demonstrating, in average, best performances does not include GCN layers. However, as demonstrated in Table 7, for a limited evaluation setup, GCN layers have positive impact on performance, leading to significant gains of $8.6\\%$ and $8.0\\%$ on JPO and $\\mathrm{JPO^p}$ when using 4 instead of 0 GCN layers. Note that even the version using 0 GNN layers, still employs our supergraph for feature aggregation", + "bbox": [ + 75, + 780, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e21ec738d6e38ef25682ea0cb246ad80e8ab0b548603c14d4fc4d7171f64b03a.jpg", + "image_caption": [ + "Figure 6. Ablation experiment. The figure shows MolGrapher predictions with and without using GCN layers, illustrating that GCN layers allow the model to learn chemistry rules. Indeed, the model correctly connect the oxygen atom highlighted in red to a double bond only." + ], + "image_footnote": [], + "bbox": [ + 514, + 494, + 897, + 580 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "and classification. The propagation of information through the graph is beneficial for challenging cases, such as the one illustrated in Figure 6. In this example, interpreting only the visual information would be misleading, even for humans. Understanding chemistry rules is mandatory to resolve the ambiguities in the drawing, which is correctly done by our model.", + "bbox": [ + 496, + 675, + 893, + 780 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 799, + 619, + 814 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We propose a novel architecture for recognizing 2-D molecule depictions in documents by exploiting the natural graph representation of molecules and graph symmetries. Our model accurately detects atoms and bonds based on their visual features and local context, outperforming exist-", + "bbox": [ + 496, + 825, + 893, + 902 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "19559", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "ing methods on standard benchmarks and our new USPTO-30K dataset. The model is trained on synthetic images and demonstrates strong generalization capabilities, making it useful at scale without requiring annotations for each journal or patent office.", + "bbox": [ + 76, + 90, + 472, + 167 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 181, + 174, + 196 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] United states patent and trademark office. http://uspto.gov. Accessed: 1 January 2023.", + "[2] Syed Saqib Bukhari, Zaryab Iftikhar, and Andreas Dengel. 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Bioinform., 23(2), March 2022." + ], + "bbox": [ + 501, + 92, + 893, + 260 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "19561", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/0cbbbec6-ac8d-47e3-9896-a438f1a62616_model.json b/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/0cbbbec6-ac8d-47e3-9896-a438f1a62616_model.json new file mode 100644 index 0000000000000000000000000000000000000000..ffba4f98cb2c11bdd2e80cb471034c600797c85f --- /dev/null +++ b/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/0cbbbec6-ac8d-47e3-9896-a438f1a62616_model.json @@ -0,0 +1,1936 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.129, + 0.131, + 0.842, + 0.154 + ], + "angle": 0, + "content": "MolGrapher: Graph-based Visual Recognition of Chemical Structures" + }, + { + "type": "text", + "bbox": [ + 0.177, + 0.18, + 0.791, + 0.233 + ], + "angle": 0, + "content": "Lucas Morin\\(^{1,2}\\) Martin Danelljan\\(^{2}\\) Maria Isabel Agea\\(^{1}\\) Ahmed Nassar\\(^{1}\\) Valery Weber\\(^{1}\\) Ingmar Meijer\\(^{1}\\) Peter Staar\\(^{1}\\) Fisher Yu\\(^{2}\\) IBM Research ETH Zurich" + }, + { + "type": "text", + "bbox": [ + 0.103, + 0.237, + 0.868, + 0.253 + ], + "angle": 0, + "content": "{lum, ahn, vwe, inm, taa}@zurich.ibm.com martin.danelljan@vision.ee.ethz.ch i@yf.io" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.319, + 0.474, + 0.653 + ], + "angle": 0, + "content": "The automatic analysis of chemical literature has immense potential to accelerate the discovery of new materials and drugs. Much of the critical information in patent documents and scientific articles is contained in figures, depicting the molecule structures. However, automatically parsing the exact chemical structure is a formidable challenge, due to the amount of detailed information, the diversity of drawing styles, and the need for training data. In this work, we introduce MolGrapher to recognize chemical structures visually. First, a deep keypoint detector detects the atoms. Second, we treat all candidate atoms and bonds as nodes and put them in a graph. This construct allows a natural graph representation of the molecule. Last, we classify atom and bond nodes in the graph with a Graph Neural Network. To address the lack of real training data, we propose a synthetic data generation pipeline producing diverse and realistic results. In addition, we introduce a large-scale benchmark of annotated real molecule images, USPTO-30K, to spur research on this critical topic. Extensive experiments on five datasets show that our approach significantly outperforms classical and learning-based methods in most settings. Code, models, and datasets are available1." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.683, + 0.21, + 0.699 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.709, + 0.47, + 0.875 + ], + "angle": 0, + "content": "The creation of an open-source database offering a unified view of our current knowledge of all studied molecules, would greatly accelerate research and development in numerous fields, ranging from the pharmaceutical industry to semiconductor manufacturing. Currently, information about a molecule's properties is distributed across various databases, research articles, and chemical patents, each measuring different subsets of properties. In such documents, molecules are most often described using images, by drawing their molecular structures. Automatic parsing of molecules from document images, known as Optical Chem-" + }, + { + "type": "image", + "bbox": [ + 0.537, + 0.293, + 0.889, + 0.516 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.519, + 0.895, + 0.603 + ], + "angle": 0, + "content": "Figure 1. MolGrapher extracts the chemical structure, including all atoms and bonds, from a molecule image in a document. Our approach constructs a supergraph of the molecule (bottom right), containing all detected atom and bond candidates. These nodes are then classified by a Graph Neural Network in order to retrieve the chemical structure." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.625, + 0.893, + 0.671 + ], + "angle": 0, + "content": "ical Structure Recognition (OCSR), is thus a critical task in the quest towards establishing a large-scale digital molecule database." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.895, + 0.903 + ], + "angle": 0, + "content": "OCSR, however, poses multiple key challenges, which limit the accuracy of current solutions. First, a molecule can be drawn with a variety of styles and conventions. Even the projection of the molecular structure from 3-D onto a 2-D drawing is not unique, leading to the development of various projection algorithms with diverse results. Secondly, OCSR requires the extraction of detailed information from the image. Molecules often contain even hundreds of atoms and bonds, which all need to be correctly classified and linked. Thirdly, molecules have a virtually endless diversity stemming from the combinatorical explosion of possibilities, presenting particular challenges to data-driven deep learning methods. Lastly, available real training datasets are extremely limited, further complicating the application of deep learning." + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.313, + 0.901 + ], + "angle": 0, + "content": "\\(^{1}\\)https://github.com/DS4SD/MolGrapher" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "19552" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.081, + 0.092, + 0.468, + 0.272 + ], + "angle": 0, + "content": "Initial OCR approaches followed the graph reconstruction paradigm. These methods start by extracting the fundamental components of molecules, such as atoms, bonds, and charges, often using hand-crafted image processing algorithms [8, 29, 21]. Then, rules are applied to connect these elements to reconstruct a graph representation of the molecule. Some recent works [19, 33, 38] introduce deep learning elements into the atom and bond detection steps. However, these approaches still rely on hand-crafted rules to link the recognized constituents, and thus not fully benefit from the advantages brought by deep learning." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.276, + 0.468, + 0.547 + ], + "angle": 0, + "content": "Most recently, approaches instead follow the image captioning [4, 24, 34] paradigm by applying a deep network to directly output a character string identifying the molecule, e.g. in the form of SMILES [32]. However, these methods do not explicitly exploit the rich priors and invariances provided by the graph structure. The SMILES representation does not encode the geometrical and neighborhood structure of the molecule graph in a natural manner. While a recent work [36] predicts a graph in an autoregressive manner, adding one atom at a time prevents from fully exploiting the graph structure. Partially due to the lack of such a strong inductive bias, image captioning based methods still lag behind from the performance of state-of-the-art rule-based methods [8, 29, 21] on standard benchmarks [8, 9, 28, 22]. Moreover, the performance of captioning based methods severely degrade when increasing the size and complexity of the molecule, as they struggle to recover the detailed information in the image." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.551, + 0.468, + 0.791 + ], + "angle": 0, + "content": "We introduce MolGrapher for Optical Chemical Structure Recognition, illustrated in Fig. 1. Our approach explicitly utilizes the graph structure as a strong inductive bias, while also allowing for the final molecule structure itself to be predicted by a deep learning model. MolGrapher operates in three steps. First, we locate atoms and abbreviations in the image with a keypoint detector network. Given the estimated locations of the atoms, we form a supergraph of the molecular structure, where two types of nodes represent candidate atoms and bonds respectively (see Fig. 1). Unlike previous approaches, we do not commit to a final molecule structure at this point, instead extracting a larger set of candidate bonds, forming a superset of the final molecular graph. Candidates that do not correspond to any bond are removed in the final prediction step by including a 'no bond' class." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.796, + 0.468, + 0.9 + ], + "angle": 0, + "content": "In the final step, we input the constructed supergraph into a Graph Neural Network (GNN). We first extract deep node embeddings through a backbone network. The GNN then operates on the neighborhood structure provided by the supergraph in order to integrate visual information with learned chemistry priors. We then read-out the results with MLPs, classifying each node into a set of atom and bond" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.092, + 0.89, + 0.181 + ], + "angle": 0, + "content": "classes. We also identify abbreviations through a separate class, which are parsed by an OCR component. Since training data is scarce, we develop, and release, a synthetic training data generation pipeline, capable of generating diverse and challenging examples to ensure robust generalization to a wide variety of drawing styles." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.183, + 0.89, + 0.378 + ], + "angle": 0, + "content": "To further aid the research in the community, we introduce USPTO-30K, a large-scale benchmark dataset of annotated real molecule images. It contains separate subsets, in order to independently study the recognition of simple molecules, abbreviated molecules and extremely large molecules. We perform comprehensive experiments on five benchmarks: our USPTO-30K, USPTO [8], Maybridge UoB [28], CLEF-2012 [22] and JPO [9]. We outperform all deep learning based methods that only utilizes synthetic training. Our approach even surpass previous methods that rely on finetuning on real data on most benchmarks, and outperform the longstanding state-of-the-art by rule-based methods [8, 29, 21] in most settings." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.392, + 0.636, + 0.408 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.418, + 0.89, + 0.674 + ], + "angle": 0, + "content": "OCSR approaches can be divided in two main categories. Image captioning based OCSR. Most of the recent end-to-end deep learning approaches are based on image captioning. These models use an encoder to extract visual features from the image and a decoder to translate them to a SMILES [32] or InChI [10] sequence. More precisely, DECIMER [26], MICER [35], MSE-DUDL [30] and Img2Mol [4] are using a convolutional encoder and a recurrent decoder which is respectively, a GRU decoder, a LSTM decoder, a GridLSTM decoder, and a RNN decoder. Later works proposed replacing the recurrent decoder with a transformer encoder-decoder, including DECIMER 1.0 [27], SwinOCSR [34], IMG2SMI [3] and Image2SMILES [13]. Other image captioning methods are solely based on transformers, using a vision transformer in [31], a Swin transformer in [23] or a Deep TNT transformer encoder with a transformer decoder in ICMDT [17]." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.675, + 0.89, + 0.9 + ], + "angle": 0, + "content": "One drawback of image captioning methods is the need of large training sets. The SMILES representation has numerous downsides for a learning task [15], one of them which is ambiguity due to the association of very different string identifiers to similar molecules. By predicting SMILES, instead of a more faithful representation of the image, the model needs to learn jointly to recognize the image and understand the SMILES language. Multiple string identifiers, possibly suited for a learning task have been proposed, including SELFIES, DeepSMILES [25] or abstract mathematical identifiers [4]. Nevertheless, representing a molecule image as a string adds extra complexity for a learning task. Additionally, these models to not properly handle uncertainty by predicting incorrect, but still valid, molecules for challenging inputs such as large molecules." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.947, + 0.518, + 0.957 + ], + "angle": 0, + "content": "19553" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.098, + 0.09, + 0.872, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.266, + 0.895, + 0.31 + ], + "angle": 0, + "content": "Figure 2. Molecular graph recognition architecture. We illustrate the architecture of MolGrapher, a graph-based network for Optical Chemical Structure Recognition. The keypoint detector (red) locates atoms nodes in the molecule. A supergraph containing atom and bond candidates is constructed (green). Atoms and bonds are classified using a Graph Neural Network (blue)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.326, + 0.473, + 0.465 + ], + "angle": 0, + "content": "Yet, to parse scientific literature at large scale, avoiding these false positives is critical. This behaviour is explained by the fact that the model is trained to always output valid SMILES, while using global image features. Contrary to these approaches, our model extracts precise visual features for each elementary component of a molecule and operate on a graph, allowing substantially better recognition performance for large molecules, possibly larger than the ones used for training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.47, + 0.473, + 0.728 + ], + "angle": 0, + "content": "Graph reconstruction based OCSR. Traditional approaches for Optical Chemical Structure Recognition rely on hand-crafted image processing algorithms to detect elementary components of the molecules and connect them to reconstruct the molecular graph [2, 8, 12, 20, 28, 29, 21]. More recent works detect elementary components using machine learning models. For instance, ChemGrapher [19] or ABC-Net [38] use convolutional segmentation networks while MolMiner [33] employs aYOLO object detector. As studied in [11], detection based methods can be trained with fewer training samples. By doing multiple low-level detections, it is possible to supervise precisely the training. It also offers a natural way to inject prior knowledge, or impose chemistry rules to the model. Our method benefits from these advantages but differentiates itself by learning both the detection and the association of the fundamental components of molecules." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Image2Graph [36] uses a transformer to build the graph in an auto-regressive way, by adding one atom at the time. [23] predicts a SMILES sequence, but enriched with atoms positions, and connectivity information, drifting away from the string identifier and getting closer to a graphical representation. Our new graph reconstruction approach do not build a graph auto-repressively. We first detects all possible components and associations, and then classify them. It allows to use localized visual features, as well as a complete neighborhood contextual information for each atom and bond prediction." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.324, + 0.633, + 0.341 + ], + "angle": 0, + "content": "3. MolGrapher" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.35, + 0.895, + 0.457 + ], + "angle": 0, + "content": "We introduce MolGrapher, a graph-based network for Optical Chemical Structure Recognition. Our model architecture is illustrated in Figure 2. Our pipeline consists of three steps. Firstly, the keypoint detector locates atoms nodes in the molecule. Secondly, we construct a graph containing atom and bond candidates. Finally, atoms and bonds are classified using a Graph Neural Network." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.466, + 0.686, + 0.483 + ], + "angle": 0, + "content": "3.1. Keypoint Detection" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.489, + 0.895, + 0.581 + ], + "angle": 0, + "content": "In order to construct the molecular graph, we first need to localize keypoints in the image. Keypoints refer to the position of atoms and 'superatoms', i.e. abbreviated groups of atoms. In the later stages, this enables the extraction of relevant visual features for atoms and bonds, as well as the construction of our molecule supergraph." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.895, + 0.7 + ], + "angle": 0, + "content": "Our keypoint detector predicts a heatmap, where each peak corresponds to an atom location. The output of a feature extractor is passed through convolutional layers to predict the final single-channel heatmap of the atom locations. To extract the peak locations, we first threshold the heatmap by removing any value in the bottom \\(10^{\\mathrm{th}}\\) percentile. We then collect regional maxima, using a window size of \\(5 \\times 5\\), as the final atom locations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.701, + 0.895, + 0.824 + ], + "angle": 0, + "content": "Atoms are labeled with Gaussian functions, allowing smoother supervision as well as capturing a degree of uncertainty regarding the predicted positions. Since the groundtruth heatmaps predominantly contains background values, we use the weight-adaptive heatmap regression loss [18] to overcome the class imbalance. It reduces the impact of well-classified samples, which mostly constitute background, allowing the training to focus on harder samples." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.832, + 0.736, + 0.849 + ], + "angle": 0, + "content": "3.2. Supergraph Construction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.895, + 0.903 + ], + "angle": 0, + "content": "In this section, we describe the construction of the supergraph, which contains all atom and bond candidates to be classified. The supergraph is composed of two types of" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "19554" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.103, + 0.487, + 0.212 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.22, + 0.471, + 0.304 + ], + "angle": 0, + "content": "Figure 3. Supergraph construction. The figure presents the construction of bonds proposals for an atom denoted \\( A \\). Considered bonds are depicted with dashed lines. Green bonds are accepted in the supergraph, while red bonds are discarded because: (1) there are no filled pixels around their centerpoints or (2) they are obstructed by other keypoints." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.323, + 0.47, + 0.383 + ], + "angle": 0, + "content": "nodes: atoms and bonds. Further, each edge in the graph only connects an atom node to a bond node. Representing both of these entities as nodes allows us to process them uniformly through standard message passing layers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.384, + 0.47, + 0.534 + ], + "angle": 0, + "content": "The input to our supergraph construction is a set of approximate atom locations. Since the connectivity between the detected atoms is unknown, our graph has to represent a superset of the final molecule prediction, thus termed 'supergraph'. That is, it contains all possible bonds. By including a prediction class corresponding to 'no bond', bond candidates which are not actually in the molecule can be removed in the later stage. Including an analogous class for 'no atom', our approach can even correct false positives predicted by the keypoint detection network." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.535, + 0.471, + 0.747 + ], + "angle": 0, + "content": "Our supergraph construction is illustrated in Figure 3. We first consider each keypoint individually, adding connections to all other keypoints within a radius of three times the estimated bond length [8]. Subsequently, we remove connections which have no filled pixels around their centerpoints or if there is a third keypoint located between its two extremities. Finally, we keep at most six bond candidates for each atom, by eliminating the longest connections. Chemistry prior knowledge ensures that it is extremely unlikely for an atom to have more than five neighboring bonds. Our settings are highly conservative to avoid deleting any actual bond. On the other hand, pruning superfluous bonds avoids any unnecessary false positives in the later stage and a more effective connectivity for the GNN." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.757, + 0.262, + 0.772 + ], + "angle": 0, + "content": "3.3. Node Classification" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.471, + 0.903 + ], + "angle": 0, + "content": "In order to classify atom and bond nodes, we integrate a Graph Neural Network (GNN) that operates on the constructed supergraph. The embeddings for all nodes are initialized using visual features as well as their types. This approach leverages the local context of atoms and bonds to predict their class. Intuitively, it enables the learning of chemistry rules, i.e. atoms have a fixed valence, as well as chemistry prior knowledge, i.e. some typical substructures" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.093, + 0.704, + 0.105 + ], + "angle": 0, + "content": "are more common than others." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.106, + 0.894, + 0.168 + ], + "angle": 0, + "content": "Let \\( e_i^1 \\in R^D \\) denotes the initial embedding of the node \\( i \\) of type \\( t_i \\in \\{\\text{atom}, \\text{bond}\\} \\) located at position \\( (x_i, y_i) \\). It is computed by combining a visual feature vector \\( v_i \\) and a learnable type encoding \\( w_{t_i} \\)," + }, + { + "type": "equation", + "bbox": [ + 0.647, + 0.176, + 0.892, + 0.194 + ], + "angle": 0, + "content": "\\[\ne _ {i} ^ {0} = v _ {i} + w _ {t _ {i}} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.202, + 0.894, + 0.263 + ], + "angle": 0, + "content": "The visual features \\( v_{i} \\) are extracted from a deep feature map \\( F \\), extracted by a backbone network. For an atom node \\( i \\) we evaluate the feature map in the corresponding location \\( (x_{i},y_{i}) \\) with bilinear interpolation," + }, + { + "type": "equation", + "bbox": [ + 0.642, + 0.273, + 0.892, + 0.289 + ], + "angle": 0, + "content": "\\[\nv _ {i} = F \\left(x _ {i}, y _ {i}\\right). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.298, + 0.892, + 0.326 + ], + "angle": 0, + "content": "For a bond node \\(i\\), we aggregate features at locations along the bond as" + }, + { + "type": "equation", + "bbox": [ + 0.618, + 0.325, + 0.892, + 0.367 + ], + "angle": 0, + "content": "\\[\nv _ {i} = \\frac {1}{J} \\sum_ {j = 1} ^ {J} F \\left(x _ {i} ^ {j}, y _ {i} ^ {j}\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.373, + 0.892, + 0.404 + ], + "angle": 0, + "content": "where \\((x_i^j, y_i^j)\\) are the locations of \\(J\\) uniformly spaced points along the bond itself." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.405, + 0.892, + 0.526 + ], + "angle": 0, + "content": "Given initial node embeddings, information is propagated through the graph to learn local dependencies between atoms and bonds. Indeed, directly neighboring atoms and bonds respect strict chemistry rules, and larger neighborhoods form patterns called functional groups, which are typically abundant in nature. We employ GNN layers, denoted \\(\\{g^k\\}_{k\\in [1,N]}\\), to iteratively update the node embeddings," + }, + { + "type": "equation", + "bbox": [ + 0.641, + 0.526, + 0.892, + 0.544 + ], + "angle": 0, + "content": "\\[\ne ^ {k + 1} = g ^ {k} \\left(e ^ {k}\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.548, + 0.892, + 0.58 + ], + "angle": 0, + "content": "The final predictions \\(\\{p_i\\}\\) are then obtained using two Multi-Layer Perceptrons, one for each node type \\(t\\)" + }, + { + "type": "equation", + "bbox": [ + 0.633, + 0.588, + 0.892, + 0.606 + ], + "angle": 0, + "content": "\\[\np _ {i} = M L P _ {t} \\left(e _ {i} ^ {N}\\right). \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.892, + 0.643 + ], + "angle": 0, + "content": "The vector \\(p_i \\in \\mathbb{R}^{C_t}\\) contains the logits for the final atom or bond classes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.645, + 0.892, + 0.749 + ], + "angle": 0, + "content": "The most represented bond types include 'no bond', 'single', 'double' and 'triple'. Atom classes include the common (e.g. O) and exotic atoms as well as charged atoms (e.g. \\(\\mathrm{O}^{-}\\)). Since molecule images often include whole groups in the nodes, e.g. COOH, we further include a class 'superatom' to recognize these cases. Such nodes are then parsed as described in Section 3.4." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Our node classification model is trained using the cross-entropy loss for both the atom and bond prediction heads. During training, the supergraph structure used as input is obtained by applying the graph construction algorithm on augmented ground truth keypoints. To simulate possible errors from the keypoint detector, we add noise to the atom positions and randomly include false-positive keypoints. Decoupling the keypoint detection and the node classification allow to train faster and to use optimized training sets for each task." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19555" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.081, + 0.091, + 0.355, + 0.108 + ], + "angle": 0, + "content": "3.4. Superatom Groups Recognition" + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.115, + 0.468, + 0.28 + ], + "angle": 0, + "content": "To recognize abbreviated substructures, named superatoms, we use an external Optical Character Recognition (OCR) system. Relying on an external OCR system provides strong robustness, since the model is trained on a diversity of text representations that cannot necessarily be generated in a molecule image. At the location of an abbreviated group, the node classifier predicts a 'superatom' class. Then, the OCR engine PP-OCR [6] is used to recognize the text written at this location, which is finally replaced by its corresponding sub-molecule, stored in a precomputed mapping." + }, + { + "type": "title", + "bbox": [ + 0.081, + 0.293, + 0.17, + 0.31 + ], + "angle": 0, + "content": "4. Datasets" + }, + { + "type": "title", + "bbox": [ + 0.081, + 0.318, + 0.387, + 0.335 + ], + "angle": 0, + "content": "4.1. Synthetic Training Data Generation" + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.342, + 0.468, + 0.416 + ], + "angle": 0, + "content": "Training datasets of annotated molecule images extracted from scientific publications are extremely limited. Therefore, we develop a synthetic training pipeline to generate a broad diversity of molecular representations. It further allows us to extract atom-level annotations." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.418, + 0.468, + 0.628 + ], + "angle": 0, + "content": "Our dataset is created using molecule SMILES retrieved from the database PubChem [14]. To increase the probability that the dataset covers the largest variety of molecular structures, we sample SMILES using a strategy based on functional groups. A functional group is molecule substructure typically abundant in nature. Thus, we retrieve molecules from PubChem containing each functional group in a defined collection of 1540 functional groups. To further increase diversity, these molecules are queried with different ranges of number of atoms. Finally the dataset is filtered by removing salts, molecules containing complex polycycles, isotopes or radical electrons. Training images are then generated from SMILES using the molecule drawing library RDKit [16]." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.63, + 0.468, + 0.794 + ], + "angle": 0, + "content": "To capture the large diversity of drawing styles and conventions from different scientific documents, the synthetic set is highly augmented, at multiple levels. Firstly, molecules are randomly transformed, notably by setting the selection of a molecular conformation, adding artificial superatom groups with single or multiple attachment points or displaying solid, dashed or wavy bonds. Secondly, the rendering parameters used in RDKit are randomly set, including the font, the bond width, the display of aromatic cycles using circles. This leads to substantial variations in the drawn molecule, to aid generalization to real datasets." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.796, + 0.468, + 0.9 + ], + "angle": 0, + "content": "The generated molecule images are saved together with their corresponding MolFiles. A MolFile [5] stores information about the atoms and their positions in a molecule, as well as bonds and their connectivity. It provides the necessary information for supervising the training. This generation pipeline covers a large diversity of molecules including stereo-chemistry and molecules with superatom groups." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.091, + 0.891, + 0.136 + ], + "angle": 0, + "content": "Finally, the images undergo several image augmentations on the fly such as gaussian blurring, the adding of pepper patches, random lines, and random captions." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.137, + 0.891, + 0.196 + ], + "angle": 0, + "content": "The exhaustive lists of molecule, rendering and image augmentations, as well as details regarding the generation of atom-level annotations are available in the supplementary materials." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.205, + 0.729, + 0.22 + ], + "angle": 0, + "content": "4.2. The USPTO-30K Dataset" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.228, + 0.891, + 0.379 + ], + "angle": 0, + "content": "Existing benchmarks have some limitations. Being created using only a few documents, they contain batches of very similar molecules. For example in a patent, a molecule could typically be displayed together with all the substituent of one particular substructure, resulting in large batches of almost identical molecules. Additionally, the existing sets contain molecules of different kinds, including superatom groups and various markush [7] features, which should be evaluated independently. In practice, it is important to delimit on which types of molecules models can be applied." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.38, + 0.891, + 0.59 + ], + "angle": 0, + "content": "We introduce USPTO-30K, a large-scale benchmark dataset of annotated molecule images, which overcomes these limitations. It is created using the pairs of images and MolFiles [5] by the United States Patent and Trademark Office (USPTO) [1]. Each molecule was independently selected among all the available images from 2001 to 2020. The set consists of three subsets to decouple the study of clean molecules, molecules with abbreviations and large molecules. USPTO-10K contains 10,000 clean molecules, i.e. without any abbreviated groups. USPTO-10K-abb contains 10,000 molecules with superatom groups. USPTO-10K-L contains 10,000 clean molecules with more than 70 atoms. We provide visualizations and analysis in the supplementary materials." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.603, + 0.629, + 0.62 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.628, + 0.891, + 0.673 + ], + "angle": 0, + "content": "In this section, we perform comprehensive experiments on multiple OCSR benchmarks. Moreover, we propose an analysis of the different components of our method." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.681, + 0.712, + 0.697 + ], + "angle": 0, + "content": "5.1. Implementation details" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.704, + 0.891, + 0.9 + ], + "angle": 0, + "content": "The implementation is done with PyTorch 1.12 with CUDA 11.3. For the keypoint detector features extractor, we use a ResNet-18 backbone with \\(8 \\times\\) dilatation factor [37] to preserve a high spatial resolution. For the node classifier features extractor, we resort to a ResNet-50 with a \\(2 \\times\\) dilation factor. The model is trained on 300,000 synthetic images, presented in subsection 4.1. We train for 20 epochs on 3 NVIDIA A100 GPUs using ADAM with a learning rate of 0.0001 that we decay after 5000 iterations by a factor of 0.8. The losses for atoms and bonds classifiers are weighted by factors 1 and 3, respectively. During inference, we pre-process images by removing captions using PP-OCR [6]. Additionally, in case an initial prediction is an" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.947, + 0.518, + 0.957 + ], + "angle": 0, + "content": "19556" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.087, + 0.895, + 0.129 + ], + "angle": 0, + "content": "Table 1. Comparison of our method with existing OCR models. We report the accuracy, i.e. the percentage of perfectly recognized molecule images, on datasets coming from real scientific documents. \\(\\ast\\): re-implemented results. †: results from original publications. \\(\\ddagger\\): results from [11]." + }, + { + "type": "table", + "bbox": [ + 0.119, + 0.13, + 0.852, + 0.31 + ], + "angle": 0, + "content": "
MethodUSPTO (5719)Maybridge UoB (5740)CLEF-2012 (992)JPO (450)USPTO-10K (10 000)USPTO-10K-Abb (10 000)USPTO-10K-L (10 000)
Rule-based methods
OSRA 2.1 [8]*89.386.393.456.389.763.943.1
MolVec 0.9.7 [21]*89.188.381.266.892.470.364.0
Imago 2.0 [29]*89.463.968.241.089.963.047.3
Only synthetic training
DECIMER 2.0 [24]†61.088.072.064.0---
Image2Graph [36]†44.972.037.824.0---
Graph Generation [23]†67.083.174.6----
CEDe [11]‡79.074.168.049.4---
Chemographer [19]‡80.983.275.553.3---
Img2Mol [4]*25.268.017.916.135.413.80.0
MolGrapher (Ours)91.594.990.567.593.382.831.4
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.332, + 0.47, + 0.378 + ], + "angle": 0, + "content": "invalid molecule, we use PP-OCR to merge keypoints located in a same detected text cell. See the supplementary material for more details." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.389, + 0.358, + 0.403 + ], + "angle": 0, + "content": "5.2. Evaluation datasets and metrics" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.413, + 0.471, + 0.639 + ], + "angle": 0, + "content": "To compare our method with state-of-the-art, the model is evaluated on the standard benchmarks USPTO [8], Maybridge UoB [28], CLEF-2012 [22] and JPO [9]. USPTO and CLEF are collections of 5,719 and 992 molecule images. Besides, JPO contains 450 images published by the Japanese Patent Office (JPO). JPO is particularly challenging because of its non-standard drawing conventions and poor images qualities. Lastly, Maybridge UoB is a dataset of 5,740 scanned molecule images taken from a catalogue of drug compounds by Maybridge. To compare methods, we compute accuracy, defined as the percentage of perfectly recognized molecules. In practice, this is done by verifying that the predicted and ground-truth molecules have identical InChI [10] keys. For evaluation, stereo-chemistry is removed and markush structures are not considered." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.651, + 0.334, + 0.667 + ], + "angle": 0, + "content": "5.3. State-of-the-art Comparison" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.674, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Table 1 compares the OCSR methods on different benchmarks. Our method achieves superior results compared to rule-based models on most datasets, including USPTO, Maybridge UoB and JPO. Solely using synthetic training, our method reduces the error rate by more than half compared to other deep learning methods on USPTO, Maybridge UoB, and CLEF-2012. The design of our model confers a strong generalization ability. In practice, this is very important as our model will be applied to a wide variety of documents, which are not necessarily evaluated by the current benchmark datasets. MolGrapher also maintains good performance for extremely large molecules in USPTO-10K-L, which only contains examples with more than 70 atoms. On the contrary, recognizing large molecules is a significant challenge for image captioning based methods. For" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.328, + 0.892, + 0.41 + ], + "angle": 0, + "content": "Table 2. Comparison of our method with deep OCSR models finetuned on real data. We report the accuracy, i.e. the percentage of perfectly recognized molecule images, on datasets coming from real scientific documents. †: results from original publications. ‡: results (in grey) from unavailable sub-splits of the original benchmarks, only reported for reference." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.41, + 0.892, + 0.505 + ], + "angle": 0, + "content": "
MethodUSPTO (5719)Maybridge UoB (5740)CLEF-2012 (992)JPO (450)
Real data finetuning
Image2Graph [36]†55.183.051.750.0
Graph Generation [23]†92.986.687.5-
CEDe [11]†‡91.091.586.674.0
Only synthetic training
MolGrapher (Ours)91.594.990.567.5
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.521, + 0.892, + 0.641 + ], + "angle": 0, + "content": "instance, Clevert et al. point out that the performance of Img2Mol [4] drop sharply for molecules larger than 40 atoms. This is confirmed in our evaluation, where it fails to correctly recognize virtually any molecule in USPTO-10K-L. Table 2 also provides comparison with models finetuned using real data. Our model surpasses these methods on Maybridge UoB, CLEF-2012 and JPO and is second best on USPTO, while not relying on any real data for training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.642, + 0.892, + 0.791 + ], + "angle": 0, + "content": "Our model outperforms existing methods on our USPTO-10K and USPTO-10K-Abb. The performance is particularly improved for molecules containing abbreviated groups. The performance gap between USPTO and USPTO-10K-Abb for rule-based approaches suggests that these methods are specifically parameterized for abbreviations in the existing benchmark datasets. Our model is the only deep learning method to provide a competitive performance for extremely large molecules. This is allowed by our architecture, which extracts localized visual features." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.802, + 0.677, + 0.817 + ], + "angle": 0, + "content": "5.4. Model Robustness" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Clevert et al. [4] introduced modified version of the standard benchmarks by applying slight perturbations, such as rotation and shearing, to the input images. Table 3 presents a comparison to previous methods on the same perturbed sets. The augmented images can be seen as a simulation" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19557" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.088, + 0.47, + 0.142 + ], + "angle": 0, + "content": "Table 3. Evaluation of model robustness. We report the accuracy, i.e. the percentage of perfectly recognized molecule images, on perturbed datasets coming from real scientific documents. \\(\\dagger\\): results from [4]." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.142, + 0.47, + 0.232 + ], + "angle": 0, + "content": "
MethodUSPTOP(4852)Maybridge UoBP(5716)CLEF-2012P(711)JPOP(365)
OSRA 2.1 [8]†6.470.917.033.0
MolVec 0.9.7 [21]†30.775.044.549.5
Imago 2.0 [29]†5.15.126.723.2
Img2Mol [4]†42.378.248.845.1
MolGrapher (Ours)86.794.187.855.4
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.248, + 0.469, + 0.354 + ], + "angle": 0, + "content": "of scanned images, which are typically found in chemical patents. We observe that the performance of rule based approaches, OSRA, MolVec and Imago, decreases sharply. However, our model maintains a good result, outperforming other methods by a significant margin. This robustness is essential for large-scale analysis of chemical literature, as input molecule image quality cannot be controlled." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.362, + 0.283, + 0.377 + ], + "angle": 0, + "content": "5.5. Qualitative evaluation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.385, + 0.47, + 0.626 + ], + "angle": 0, + "content": "In this section, we conduct a qualitative evaluation of MolGrapher, in comparison to state-of-the-art methods. First, Figure 4 illustrates the intermediate outputs of MolGrapher. Note that MolGrapher accurately recognizes molecules in challenging cases with overlapping bonds, without the use of any post-processing rules. Figure 5 showcases examples of predicted molecules for images from various benchmark datasets. MolGrapher demonstrates robustness to images containing captions (Figure 5 row 1). It can correctly recognize extremely large molecules (Figure 5 row 4), and is robust to solid, dashed or wavy bonds (Figure 5 row 5). Unlike image captioning based methods such as \\(\\mathrm{Img2Mol}\\), our predictions preserve the projection and atom placement used in the input image (Figure 5 row 2). This can convey critical information for human interpretation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.635, + 0.227, + 0.65 + ], + "angle": 0, + "content": "5.6. Ablation study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.469, + 0.688 + ], + "angle": 0, + "content": "We conduct an ablation study to demonstrate the impact of each component in the proposed method." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.688, + 0.469, + 0.719 + ], + "angle": 0, + "content": "Synthetic training set. We evaluate the impact of the three levels of augmentation of the training set, illustrated in Ta" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.088, + 0.892, + 0.129 + ], + "angle": 0, + "content": "Table 4. Training set analysis. Impact of training set augmentations on performance. Molecule, rendering and image level augmentation are independently removed." + }, + { + "type": "table", + "bbox": [ + 0.525, + 0.13, + 0.875, + 0.209 + ], + "angle": 0, + "content": "
USPTOJPOJPOp
All augmentations91.567.555.4
No molecule augmentation52.452.743.4
No rendering augmentation78.455.744.1
No image augmentation69.829.322.5
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.225, + 0.892, + 0.331 + ], + "angle": 0, + "content": "ble 4. The image augmentations have a major impact on the performance of the model. In practice, we noticed that the keypoint detector benefits greatly from using heavy image transformations. Additionally, the molecule augmentations, which allow training molecules to contain abbreviated groups, proved crucial to handle images containing abbreviated groups, such as in USPTO." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.332, + 0.892, + 0.437 + ], + "angle": 0, + "content": "Keypoint detector. In Table 5, we experiment with different standard deviations for the Gaussian keypoint labels, and keypoint regression losses. Using a large standard deviation of \\( b / 5 \\), where \\( b \\) denotes the bond length, creates overlaps between keypoints and significantly decreases performance. While the model is not sensitive to the choice of training loss, the WAHR loss offers a slight advantage." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.439, + 0.892, + 0.544 + ], + "angle": 0, + "content": "Supergraph construction. In Table 7, we evaluate the impact of the maximum number of bond candidates and the search radius in the supergraph construction. We observe that our approach is not sensitive to these settings, but only experiences a small drop when increasing the number of bond candidates. This drop is explained by false positives predicted during the node classification stage." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.545, + 0.892, + 0.591 + ], + "angle": 0, + "content": "Node classifier. As demonstrated in Table 7, initializing nodes embeddings with both visual and type encoding increases performance. We also experimented with positional" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.6, + 0.892, + 0.641 + ], + "angle": 0, + "content": "Table 5. Keypoint detector analysis. We analyse the standard deviation of the Gaussian functions (top), as well as the training loss function (bottom). \\( b \\) denotes the molecule bond length." + }, + { + "type": "table", + "bbox": [ + 0.524, + 0.642, + 0.875, + 0.72 + ], + "angle": 0, + "content": "
USPTOJPOJPOp
Heatmap standard deviationb/581.354.746.8
b/1091.567.555.4
b/1591.464.751.6
Training lossL291.166.255.1
WAHR [18]91.567.555.4
" + }, + { + "type": "image", + "bbox": [ + 0.107, + 0.739, + 0.87, + 0.848 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.857, + 0.892, + 0.899 + ], + "angle": 0, + "content": "Figure 4. Prediction steps. Keypoints are detected and then used to build a supergraph. After classifying the nodes of the graph and recognizing abbreviated groups, the output molecule is created. In this example, the polycyclic molecule contains overlapping bonds, a challenging feature for OCSR models, and is still correctly recognized." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "19558" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.129, + 0.088, + 0.842, + 0.434 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.438, + 0.895, + 0.482 + ], + "angle": 0, + "content": "Figure 5. Qualitative comparison. The figure shows examples of predictions for characteristic images from different benchmarks. Compared to previous rule-based and learning based methods, our approach robustly recognizes the exact molecular structure in challenging cases, such as with distracting captions, stereo-chemistry, and very large molecules." + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.494, + 0.471, + 0.536 + ], + "angle": 0, + "content": "Table 6. Supergraph construction analysis. We analyse the maximum number of bond candidates (top), and the maximum search radius (bottom). \\( b \\) denotes the molecule bond length." + }, + { + "type": "table", + "bbox": [ + 0.102, + 0.537, + 0.451, + 0.616 + ], + "angle": 0, + "content": "
USPTOJPOJPOp
Number bond candidates691.567.555.4
1091.065.754.1
Search radius3b91.567.555.4
5b91.365.053.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.627, + 0.47, + 0.668 + ], + "angle": 0, + "content": "Table 7. Node classifier analysis. We analyse the features representing graph nodes (top), and the usage of GCN layers (bottom). \\(\\dagger\\): without abbreviated molecules and charges." + }, + { + "type": "table", + "bbox": [ + 0.101, + 0.669, + 0.451, + 0.759 + ], + "angle": 0, + "content": "
USPTOJPOJPOp
Node embeddingVisual90.064.754.9
+ Type91.567.555.4
+ Position91.362.854.8
USPTO†JPO†JPOp†
Number of GCN Layers090.158.053.6
490.466.661.6
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.471, + 0.903 + ], + "angle": 0, + "content": "embedding but found it to reduce the overall performance. The model demonstrating, in average, best performances does not include GCN layers. However, as demonstrated in Table 7, for a limited evaluation setup, GCN layers have positive impact on performance, leading to significant gains of \\(8.6\\%\\) and \\(8.0\\%\\) on JPO and \\(\\mathrm{JPO^p}\\) when using 4 instead of 0 GCN layers. Note that even the version using 0 GNN layers, still employs our supergraph for feature aggregation" + }, + { + "type": "image", + "bbox": [ + 0.515, + 0.495, + 0.898, + 0.582 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.59, + 0.895, + 0.66 + ], + "angle": 0, + "content": "Figure 6. Ablation experiment. The figure shows MolGrapher predictions with and without using GCN layers, illustrating that GCN layers allow the model to learn chemistry rules. Indeed, the model correctly connect the oxygen atom highlighted in red to a double bond only." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.676, + 0.894, + 0.781 + ], + "angle": 0, + "content": "and classification. The propagation of information through the graph is beneficial for challenging cases, such as the one illustrated in Figure 6. In this example, interpreting only the visual information would be misleading, even for humans. Understanding chemistry rules is mandatory to resolve the ambiguities in the drawing, which is correctly done by our model." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.8, + 0.62, + 0.815 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.894, + 0.903 + ], + "angle": 0, + "content": "We propose a novel architecture for recognizing 2-D molecule depictions in documents by exploiting the natural graph representation of molecules and graph symmetries. Our model accurately detects atoms and bonds based on their visual features and local context, outperforming exist-" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "19559" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.168 + ], + "angle": 0, + "content": "ing methods on standard benchmarks and our new USPTO-30K dataset. The model is trained on synthetic images and demonstrates strong generalization capabilities, making it useful at scale without requiring annotations for each journal or patent office." + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.182, + 0.175, + 0.198 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.207, + 0.468, + 0.235 + ], + "angle": 0, + "content": "[1] United states patent and trademark office. http://uspto.gov. Accessed: 1 January 2023." + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.236, + 0.469, + 0.307 + ], + "angle": 0, + "content": "[2] Syed Saqib Bukhari, Zaryab Iftikhar, and Andreas Dengel. Chemical structure recognition (csr) system: Automatic analysis of 2d chemical structures in document images. In 2019 International Conference on Document Analysis and Recognition (ICDAR), pages 1262-1267. 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Bioinform., 23(2), March 2022." + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.894, + 0.261 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "19561" + } + ] +] \ No newline at end of file diff --git a/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/0cbbbec6-ac8d-47e3-9896-a438f1a62616_origin.pdf b/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/0cbbbec6-ac8d-47e3-9896-a438f1a62616_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..4c4ae56cc12b07e6d6726764cf9005601edc03b7 --- /dev/null +++ b/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/0cbbbec6-ac8d-47e3-9896-a438f1a62616_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:bb1ada24f21eb9928e4f4a11d66f840efbdbafe5e2f00dc7b73ca9a8dd2c9499 +size 896723 diff --git a/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/full.md b/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/full.md new file mode 100644 index 0000000000000000000000000000000000000000..74dc00353c69ab75465378e3e87c3b15d716eaab --- /dev/null +++ b/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/full.md @@ -0,0 +1,281 @@ +# MolGrapher: Graph-based Visual Recognition of Chemical Structures + +Lucas Morin $^{1,2}$ Martin Danelljan $^{2}$ Maria Isabel Agea $^{1}$ Ahmed Nassar $^{1}$ Valery Weber $^{1}$ Ingmar Meijer $^{1}$ Peter Staar $^{1}$ Fisher Yu $^{2}$ IBM Research ETH Zurich + +{lum, ahn, vwe, inm, taa}@zurich.ibm.com martin.danelljan@vision.ee.ethz.ch i@yf.io + +# Abstract + +The automatic analysis of chemical literature has immense potential to accelerate the discovery of new materials and drugs. Much of the critical information in patent documents and scientific articles is contained in figures, depicting the molecule structures. However, automatically parsing the exact chemical structure is a formidable challenge, due to the amount of detailed information, the diversity of drawing styles, and the need for training data. In this work, we introduce MolGrapher to recognize chemical structures visually. First, a deep keypoint detector detects the atoms. Second, we treat all candidate atoms and bonds as nodes and put them in a graph. This construct allows a natural graph representation of the molecule. Last, we classify atom and bond nodes in the graph with a Graph Neural Network. To address the lack of real training data, we propose a synthetic data generation pipeline producing diverse and realistic results. In addition, we introduce a large-scale benchmark of annotated real molecule images, USPTO-30K, to spur research on this critical topic. Extensive experiments on five datasets show that our approach significantly outperforms classical and learning-based methods in most settings. Code, models, and datasets are available1. + +# 1. Introduction + +The creation of an open-source database offering a unified view of our current knowledge of all studied molecules, would greatly accelerate research and development in numerous fields, ranging from the pharmaceutical industry to semiconductor manufacturing. Currently, information about a molecule's properties is distributed across various databases, research articles, and chemical patents, each measuring different subsets of properties. In such documents, molecules are most often described using images, by drawing their molecular structures. Automatic parsing of molecules from document images, known as Optical Chem- + +![](images/46b9c0fea3bd844716a1aaddb891bffd018838c53ce420519ad5a4bbce23ddc8.jpg) +Figure 1. MolGrapher extracts the chemical structure, including all atoms and bonds, from a molecule image in a document. Our approach constructs a supergraph of the molecule (bottom right), containing all detected atom and bond candidates. These nodes are then classified by a Graph Neural Network in order to retrieve the chemical structure. + +ical Structure Recognition (OCSR), is thus a critical task in the quest towards establishing a large-scale digital molecule database. + +OCSR, however, poses multiple key challenges, which limit the accuracy of current solutions. First, a molecule can be drawn with a variety of styles and conventions. Even the projection of the molecular structure from 3-D onto a 2-D drawing is not unique, leading to the development of various projection algorithms with diverse results. Secondly, OCSR requires the extraction of detailed information from the image. Molecules often contain even hundreds of atoms and bonds, which all need to be correctly classified and linked. Thirdly, molecules have a virtually endless diversity stemming from the combinatorical explosion of possibilities, presenting particular challenges to data-driven deep learning methods. Lastly, available real training datasets are extremely limited, further complicating the application of deep learning. + +Initial OCR approaches followed the graph reconstruction paradigm. These methods start by extracting the fundamental components of molecules, such as atoms, bonds, and charges, often using hand-crafted image processing algorithms [8, 29, 21]. Then, rules are applied to connect these elements to reconstruct a graph representation of the molecule. Some recent works [19, 33, 38] introduce deep learning elements into the atom and bond detection steps. However, these approaches still rely on hand-crafted rules to link the recognized constituents, and thus not fully benefit from the advantages brought by deep learning. + +Most recently, approaches instead follow the image captioning [4, 24, 34] paradigm by applying a deep network to directly output a character string identifying the molecule, e.g. in the form of SMILES [32]. However, these methods do not explicitly exploit the rich priors and invariances provided by the graph structure. The SMILES representation does not encode the geometrical and neighborhood structure of the molecule graph in a natural manner. While a recent work [36] predicts a graph in an autoregressive manner, adding one atom at a time prevents from fully exploiting the graph structure. Partially due to the lack of such a strong inductive bias, image captioning based methods still lag behind from the performance of state-of-the-art rule-based methods [8, 29, 21] on standard benchmarks [8, 9, 28, 22]. Moreover, the performance of captioning based methods severely degrade when increasing the size and complexity of the molecule, as they struggle to recover the detailed information in the image. + +We introduce MolGrapher for Optical Chemical Structure Recognition, illustrated in Fig. 1. Our approach explicitly utilizes the graph structure as a strong inductive bias, while also allowing for the final molecule structure itself to be predicted by a deep learning model. MolGrapher operates in three steps. First, we locate atoms and abbreviations in the image with a keypoint detector network. Given the estimated locations of the atoms, we form a supergraph of the molecular structure, where two types of nodes represent candidate atoms and bonds respectively (see Fig. 1). Unlike previous approaches, we do not commit to a final molecule structure at this point, instead extracting a larger set of candidate bonds, forming a superset of the final molecular graph. Candidates that do not correspond to any bond are removed in the final prediction step by including a 'no bond' class. + +In the final step, we input the constructed supergraph into a Graph Neural Network (GNN). We first extract deep node embeddings through a backbone network. The GNN then operates on the neighborhood structure provided by the supergraph in order to integrate visual information with learned chemistry priors. We then read-out the results with MLPs, classifying each node into a set of atom and bond + +classes. We also identify abbreviations through a separate class, which are parsed by an OCR component. Since training data is scarce, we develop, and release, a synthetic training data generation pipeline, capable of generating diverse and challenging examples to ensure robust generalization to a wide variety of drawing styles. + +To further aid the research in the community, we introduce USPTO-30K, a large-scale benchmark dataset of annotated real molecule images. It contains separate subsets, in order to independently study the recognition of simple molecules, abbreviated molecules and extremely large molecules. We perform comprehensive experiments on five benchmarks: our USPTO-30K, USPTO [8], Maybridge UoB [28], CLEF-2012 [22] and JPO [9]. We outperform all deep learning based methods that only utilizes synthetic training. Our approach even surpass previous methods that rely on finetuning on real data on most benchmarks, and outperform the longstanding state-of-the-art by rule-based methods [8, 29, 21] in most settings. + +# 2. Related work + +OCSR approaches can be divided in two main categories. Image captioning based OCSR. Most of the recent end-to-end deep learning approaches are based on image captioning. These models use an encoder to extract visual features from the image and a decoder to translate them to a SMILES [32] or InChI [10] sequence. More precisely, DECIMER [26], MICER [35], MSE-DUDL [30] and Img2Mol [4] are using a convolutional encoder and a recurrent decoder which is respectively, a GRU decoder, a LSTM decoder, a GridLSTM decoder, and a RNN decoder. Later works proposed replacing the recurrent decoder with a transformer encoder-decoder, including DECIMER 1.0 [27], SwinOCSR [34], IMG2SMI [3] and Image2SMILES [13]. Other image captioning methods are solely based on transformers, using a vision transformer in [31], a Swin transformer in [23] or a Deep TNT transformer encoder with a transformer decoder in ICMDT [17]. + +One drawback of image captioning methods is the need of large training sets. The SMILES representation has numerous downsides for a learning task [15], one of them which is ambiguity due to the association of very different string identifiers to similar molecules. By predicting SMILES, instead of a more faithful representation of the image, the model needs to learn jointly to recognize the image and understand the SMILES language. Multiple string identifiers, possibly suited for a learning task have been proposed, including SELFIES, DeepSMILES [25] or abstract mathematical identifiers [4]. Nevertheless, representing a molecule image as a string adds extra complexity for a learning task. Additionally, these models to not properly handle uncertainty by predicting incorrect, but still valid, molecules for challenging inputs such as large molecules. + +![](images/5d3ef430de4467b99100b8764aa556dd3e89a6779c8ed5ef35106f1107110a27.jpg) +Figure 2. Molecular graph recognition architecture. We illustrate the architecture of MolGrapher, a graph-based network for Optical Chemical Structure Recognition. The keypoint detector (red) locates atoms nodes in the molecule. A supergraph containing atom and bond candidates is constructed (green). Atoms and bonds are classified using a Graph Neural Network (blue). + +Yet, to parse scientific literature at large scale, avoiding these false positives is critical. This behaviour is explained by the fact that the model is trained to always output valid SMILES, while using global image features. Contrary to these approaches, our model extracts precise visual features for each elementary component of a molecule and operate on a graph, allowing substantially better recognition performance for large molecules, possibly larger than the ones used for training. + +Graph reconstruction based OCSR. Traditional approaches for Optical Chemical Structure Recognition rely on hand-crafted image processing algorithms to detect elementary components of the molecules and connect them to reconstruct the molecular graph [2, 8, 12, 20, 28, 29, 21]. More recent works detect elementary components using machine learning models. For instance, ChemGrapher [19] or ABC-Net [38] use convolutional segmentation networks while MolMiner [33] employs aYOLO object detector. As studied in [11], detection based methods can be trained with fewer training samples. By doing multiple low-level detections, it is possible to supervise precisely the training. It also offers a natural way to inject prior knowledge, or impose chemistry rules to the model. Our method benefits from these advantages but differentiates itself by learning both the detection and the association of the fundamental components of molecules. + +Image2Graph [36] uses a transformer to build the graph in an auto-regressive way, by adding one atom at the time. [23] predicts a SMILES sequence, but enriched with atoms positions, and connectivity information, drifting away from the string identifier and getting closer to a graphical representation. Our new graph reconstruction approach do not build a graph auto-repressively. We first detects all possible components and associations, and then classify them. It allows to use localized visual features, as well as a complete neighborhood contextual information for each atom and bond prediction. + +# 3. MolGrapher + +We introduce MolGrapher, a graph-based network for Optical Chemical Structure Recognition. Our model architecture is illustrated in Figure 2. Our pipeline consists of three steps. Firstly, the keypoint detector locates atoms nodes in the molecule. Secondly, we construct a graph containing atom and bond candidates. Finally, atoms and bonds are classified using a Graph Neural Network. + +# 3.1. Keypoint Detection + +In order to construct the molecular graph, we first need to localize keypoints in the image. Keypoints refer to the position of atoms and 'superatoms', i.e. abbreviated groups of atoms. In the later stages, this enables the extraction of relevant visual features for atoms and bonds, as well as the construction of our molecule supergraph. + +Our keypoint detector predicts a heatmap, where each peak corresponds to an atom location. The output of a feature extractor is passed through convolutional layers to predict the final single-channel heatmap of the atom locations. To extract the peak locations, we first threshold the heatmap by removing any value in the bottom $10^{\mathrm{th}}$ percentile. We then collect regional maxima, using a window size of $5 \times 5$ , as the final atom locations. + +Atoms are labeled with Gaussian functions, allowing smoother supervision as well as capturing a degree of uncertainty regarding the predicted positions. Since the groundtruth heatmaps predominantly contains background values, we use the weight-adaptive heatmap regression loss [18] to overcome the class imbalance. It reduces the impact of well-classified samples, which mostly constitute background, allowing the training to focus on harder samples. + +# 3.2. Supergraph Construction + +In this section, we describe the construction of the supergraph, which contains all atom and bond candidates to be classified. The supergraph is composed of two types of + +![](images/42990e13da558e4fc561693313483516f20350b6a45ae2db0923b0e133dddb73.jpg) +Figure 3. Supergraph construction. The figure presents the construction of bonds proposals for an atom denoted $A$ . Considered bonds are depicted with dashed lines. Green bonds are accepted in the supergraph, while red bonds are discarded because: (1) there are no filled pixels around their centerpoints or (2) they are obstructed by other keypoints. + +nodes: atoms and bonds. Further, each edge in the graph only connects an atom node to a bond node. Representing both of these entities as nodes allows us to process them uniformly through standard message passing layers. + +The input to our supergraph construction is a set of approximate atom locations. Since the connectivity between the detected atoms is unknown, our graph has to represent a superset of the final molecule prediction, thus termed 'supergraph'. That is, it contains all possible bonds. By including a prediction class corresponding to 'no bond', bond candidates which are not actually in the molecule can be removed in the later stage. Including an analogous class for 'no atom', our approach can even correct false positives predicted by the keypoint detection network. + +Our supergraph construction is illustrated in Figure 3. We first consider each keypoint individually, adding connections to all other keypoints within a radius of three times the estimated bond length [8]. Subsequently, we remove connections which have no filled pixels around their centerpoints or if there is a third keypoint located between its two extremities. Finally, we keep at most six bond candidates for each atom, by eliminating the longest connections. Chemistry prior knowledge ensures that it is extremely unlikely for an atom to have more than five neighboring bonds. Our settings are highly conservative to avoid deleting any actual bond. On the other hand, pruning superfluous bonds avoids any unnecessary false positives in the later stage and a more effective connectivity for the GNN. + +# 3.3. Node Classification + +In order to classify atom and bond nodes, we integrate a Graph Neural Network (GNN) that operates on the constructed supergraph. The embeddings for all nodes are initialized using visual features as well as their types. This approach leverages the local context of atoms and bonds to predict their class. Intuitively, it enables the learning of chemistry rules, i.e. atoms have a fixed valence, as well as chemistry prior knowledge, i.e. some typical substructures + +are more common than others. + +Let $e_i^1 \in R^D$ denotes the initial embedding of the node $i$ of type $t_i \in \{\text{atom}, \text{bond}\}$ located at position $(x_i, y_i)$ . It is computed by combining a visual feature vector $v_i$ and a learnable type encoding $w_{t_i}$ , + +$$ +e _ {i} ^ {0} = v _ {i} + w _ {t _ {i}} \tag {1} +$$ + +The visual features $v_{i}$ are extracted from a deep feature map $F$ , extracted by a backbone network. For an atom node $i$ we evaluate the feature map in the corresponding location $(x_{i},y_{i})$ with bilinear interpolation, + +$$ +v _ {i} = F \left(x _ {i}, y _ {i}\right). \tag {2} +$$ + +For a bond node $i$ , we aggregate features at locations along the bond as + +$$ +v _ {i} = \frac {1}{J} \sum_ {j = 1} ^ {J} F \left(x _ {i} ^ {j}, y _ {i} ^ {j}\right), \tag {3} +$$ + +where $(x_i^j, y_i^j)$ are the locations of $J$ uniformly spaced points along the bond itself. + +Given initial node embeddings, information is propagated through the graph to learn local dependencies between atoms and bonds. Indeed, directly neighboring atoms and bonds respect strict chemistry rules, and larger neighborhoods form patterns called functional groups, which are typically abundant in nature. We employ GNN layers, denoted $\{g^k\}_{k\in [1,N]}$ , to iteratively update the node embeddings, + +$$ +e ^ {k + 1} = g ^ {k} \left(e ^ {k}\right). \tag {4} +$$ + +The final predictions $\{p_i\}$ are then obtained using two Multi-Layer Perceptrons, one for each node type $t$ + +$$ +p _ {i} = M L P _ {t} \left(e _ {i} ^ {N}\right). \tag {5} +$$ + +The vector $p_i \in \mathbb{R}^{C_t}$ contains the logits for the final atom or bond classes. + +The most represented bond types include 'no bond', 'single', 'double' and 'triple'. Atom classes include the common (e.g. O) and exotic atoms as well as charged atoms (e.g. $\mathrm{O}^{-}$ ). Since molecule images often include whole groups in the nodes, e.g. COOH, we further include a class 'superatom' to recognize these cases. Such nodes are then parsed as described in Section 3.4. + +Our node classification model is trained using the cross-entropy loss for both the atom and bond prediction heads. During training, the supergraph structure used as input is obtained by applying the graph construction algorithm on augmented ground truth keypoints. To simulate possible errors from the keypoint detector, we add noise to the atom positions and randomly include false-positive keypoints. Decoupling the keypoint detection and the node classification allow to train faster and to use optimized training sets for each task. + +# 3.4. Superatom Groups Recognition + +To recognize abbreviated substructures, named superatoms, we use an external Optical Character Recognition (OCR) system. Relying on an external OCR system provides strong robustness, since the model is trained on a diversity of text representations that cannot necessarily be generated in a molecule image. At the location of an abbreviated group, the node classifier predicts a 'superatom' class. Then, the OCR engine PP-OCR [6] is used to recognize the text written at this location, which is finally replaced by its corresponding sub-molecule, stored in a precomputed mapping. + +# 4. Datasets + +# 4.1. Synthetic Training Data Generation + +Training datasets of annotated molecule images extracted from scientific publications are extremely limited. Therefore, we develop a synthetic training pipeline to generate a broad diversity of molecular representations. It further allows us to extract atom-level annotations. + +Our dataset is created using molecule SMILES retrieved from the database PubChem [14]. To increase the probability that the dataset covers the largest variety of molecular structures, we sample SMILES using a strategy based on functional groups. A functional group is molecule substructure typically abundant in nature. Thus, we retrieve molecules from PubChem containing each functional group in a defined collection of 1540 functional groups. To further increase diversity, these molecules are queried with different ranges of number of atoms. Finally the dataset is filtered by removing salts, molecules containing complex polycycles, isotopes or radical electrons. Training images are then generated from SMILES using the molecule drawing library RDKit [16]. + +To capture the large diversity of drawing styles and conventions from different scientific documents, the synthetic set is highly augmented, at multiple levels. Firstly, molecules are randomly transformed, notably by setting the selection of a molecular conformation, adding artificial superatom groups with single or multiple attachment points or displaying solid, dashed or wavy bonds. Secondly, the rendering parameters used in RDKit are randomly set, including the font, the bond width, the display of aromatic cycles using circles. This leads to substantial variations in the drawn molecule, to aid generalization to real datasets. + +The generated molecule images are saved together with their corresponding MolFiles. A MolFile [5] stores information about the atoms and their positions in a molecule, as well as bonds and their connectivity. It provides the necessary information for supervising the training. This generation pipeline covers a large diversity of molecules including stereo-chemistry and molecules with superatom groups. + +Finally, the images undergo several image augmentations on the fly such as gaussian blurring, the adding of pepper patches, random lines, and random captions. + +The exhaustive lists of molecule, rendering and image augmentations, as well as details regarding the generation of atom-level annotations are available in the supplementary materials. + +# 4.2. The USPTO-30K Dataset + +Existing benchmarks have some limitations. Being created using only a few documents, they contain batches of very similar molecules. For example in a patent, a molecule could typically be displayed together with all the substituent of one particular substructure, resulting in large batches of almost identical molecules. Additionally, the existing sets contain molecules of different kinds, including superatom groups and various markush [7] features, which should be evaluated independently. In practice, it is important to delimit on which types of molecules models can be applied. + +We introduce USPTO-30K, a large-scale benchmark dataset of annotated molecule images, which overcomes these limitations. It is created using the pairs of images and MolFiles [5] by the United States Patent and Trademark Office (USPTO) [1]. Each molecule was independently selected among all the available images from 2001 to 2020. The set consists of three subsets to decouple the study of clean molecules, molecules with abbreviations and large molecules. USPTO-10K contains 10,000 clean molecules, i.e. without any abbreviated groups. USPTO-10K-abb contains 10,000 molecules with superatom groups. USPTO-10K-L contains 10,000 clean molecules with more than 70 atoms. We provide visualizations and analysis in the supplementary materials. + +# 5. Experiments + +In this section, we perform comprehensive experiments on multiple OCSR benchmarks. Moreover, we propose an analysis of the different components of our method. + +# 5.1. Implementation details + +The implementation is done with PyTorch 1.12 with CUDA 11.3. For the keypoint detector features extractor, we use a ResNet-18 backbone with $8 \times$ dilatation factor [37] to preserve a high spatial resolution. For the node classifier features extractor, we resort to a ResNet-50 with a $2 \times$ dilation factor. The model is trained on 300,000 synthetic images, presented in subsection 4.1. We train for 20 epochs on 3 NVIDIA A100 GPUs using ADAM with a learning rate of 0.0001 that we decay after 5000 iterations by a factor of 0.8. The losses for atoms and bonds classifiers are weighted by factors 1 and 3, respectively. During inference, we pre-process images by removing captions using PP-OCR [6]. Additionally, in case an initial prediction is an + +Table 1. Comparison of our method with existing OCR models. We report the accuracy, i.e. the percentage of perfectly recognized molecule images, on datasets coming from real scientific documents. $\ast$ : re-implemented results. †: results from original publications. $\ddagger$ : results from [11]. + +
MethodUSPTO (5719)Maybridge UoB (5740)CLEF-2012 (992)JPO (450)USPTO-10K (10 000)USPTO-10K-Abb (10 000)USPTO-10K-L (10 000)
Rule-based methods
OSRA 2.1 [8]*89.386.393.456.389.763.943.1
MolVec 0.9.7 [21]*89.188.381.266.892.470.364.0
Imago 2.0 [29]*89.463.968.241.089.963.047.3
Only synthetic training
DECIMER 2.0 [24]†61.088.072.064.0---
Image2Graph [36]†44.972.037.824.0---
Graph Generation [23]†67.083.174.6----
CEDe [11]‡79.074.168.049.4---
Chemographer [19]‡80.983.275.553.3---
Img2Mol [4]*25.268.017.916.135.413.80.0
MolGrapher (Ours)91.594.990.567.593.382.831.4
+ +invalid molecule, we use PP-OCR to merge keypoints located in a same detected text cell. See the supplementary material for more details. + +# 5.2. Evaluation datasets and metrics + +To compare our method with state-of-the-art, the model is evaluated on the standard benchmarks USPTO [8], Maybridge UoB [28], CLEF-2012 [22] and JPO [9]. USPTO and CLEF are collections of 5,719 and 992 molecule images. Besides, JPO contains 450 images published by the Japanese Patent Office (JPO). JPO is particularly challenging because of its non-standard drawing conventions and poor images qualities. Lastly, Maybridge UoB is a dataset of 5,740 scanned molecule images taken from a catalogue of drug compounds by Maybridge. To compare methods, we compute accuracy, defined as the percentage of perfectly recognized molecules. In practice, this is done by verifying that the predicted and ground-truth molecules have identical InChI [10] keys. For evaluation, stereo-chemistry is removed and markush structures are not considered. + +# 5.3. State-of-the-art Comparison + +Table 1 compares the OCSR methods on different benchmarks. Our method achieves superior results compared to rule-based models on most datasets, including USPTO, Maybridge UoB and JPO. Solely using synthetic training, our method reduces the error rate by more than half compared to other deep learning methods on USPTO, Maybridge UoB, and CLEF-2012. The design of our model confers a strong generalization ability. In practice, this is very important as our model will be applied to a wide variety of documents, which are not necessarily evaluated by the current benchmark datasets. MolGrapher also maintains good performance for extremely large molecules in USPTO-10K-L, which only contains examples with more than 70 atoms. On the contrary, recognizing large molecules is a significant challenge for image captioning based methods. For + +Table 2. Comparison of our method with deep OCSR models finetuned on real data. We report the accuracy, i.e. the percentage of perfectly recognized molecule images, on datasets coming from real scientific documents. †: results from original publications. ‡: results (in grey) from unavailable sub-splits of the original benchmarks, only reported for reference. + +
MethodUSPTO (5719)Maybridge UoB (5740)CLEF-2012 (992)JPO (450)
Real data finetuning
Image2Graph [36]†55.183.051.750.0
Graph Generation [23]†92.986.687.5-
CEDe [11]†‡91.091.586.674.0
Only synthetic training
MolGrapher (Ours)91.594.990.567.5
+ +instance, Clevert et al. point out that the performance of Img2Mol [4] drop sharply for molecules larger than 40 atoms. This is confirmed in our evaluation, where it fails to correctly recognize virtually any molecule in USPTO-10K-L. Table 2 also provides comparison with models finetuned using real data. Our model surpasses these methods on Maybridge UoB, CLEF-2012 and JPO and is second best on USPTO, while not relying on any real data for training. + +Our model outperforms existing methods on our USPTO-10K and USPTO-10K-Abb. The performance is particularly improved for molecules containing abbreviated groups. The performance gap between USPTO and USPTO-10K-Abb for rule-based approaches suggests that these methods are specifically parameterized for abbreviations in the existing benchmark datasets. Our model is the only deep learning method to provide a competitive performance for extremely large molecules. This is allowed by our architecture, which extracts localized visual features. + +# 5.4. Model Robustness + +Clevert et al. [4] introduced modified version of the standard benchmarks by applying slight perturbations, such as rotation and shearing, to the input images. Table 3 presents a comparison to previous methods on the same perturbed sets. The augmented images can be seen as a simulation + +Table 3. Evaluation of model robustness. We report the accuracy, i.e. the percentage of perfectly recognized molecule images, on perturbed datasets coming from real scientific documents. $\dagger$ : results from [4]. + +
MethodUSPTOP(4852)Maybridge UoBP(5716)CLEF-2012P(711)JPOP(365)
OSRA 2.1 [8]†6.470.917.033.0
MolVec 0.9.7 [21]†30.775.044.549.5
Imago 2.0 [29]†5.15.126.723.2
Img2Mol [4]†42.378.248.845.1
MolGrapher (Ours)86.794.187.855.4
+ +of scanned images, which are typically found in chemical patents. We observe that the performance of rule based approaches, OSRA, MolVec and Imago, decreases sharply. However, our model maintains a good result, outperforming other methods by a significant margin. This robustness is essential for large-scale analysis of chemical literature, as input molecule image quality cannot be controlled. + +# 5.5. Qualitative evaluation + +In this section, we conduct a qualitative evaluation of MolGrapher, in comparison to state-of-the-art methods. First, Figure 4 illustrates the intermediate outputs of MolGrapher. Note that MolGrapher accurately recognizes molecules in challenging cases with overlapping bonds, without the use of any post-processing rules. Figure 5 showcases examples of predicted molecules for images from various benchmark datasets. MolGrapher demonstrates robustness to images containing captions (Figure 5 row 1). It can correctly recognize extremely large molecules (Figure 5 row 4), and is robust to solid, dashed or wavy bonds (Figure 5 row 5). Unlike image captioning based methods such as $\mathrm{Img2Mol}$ , our predictions preserve the projection and atom placement used in the input image (Figure 5 row 2). This can convey critical information for human interpretation. + +# 5.6. Ablation study + +We conduct an ablation study to demonstrate the impact of each component in the proposed method. + +Synthetic training set. We evaluate the impact of the three levels of augmentation of the training set, illustrated in Ta + +Table 4. Training set analysis. Impact of training set augmentations on performance. Molecule, rendering and image level augmentation are independently removed. + +
USPTOJPOJPOp
All augmentations91.567.555.4
No molecule augmentation52.452.743.4
No rendering augmentation78.455.744.1
No image augmentation69.829.322.5
+ +ble 4. The image augmentations have a major impact on the performance of the model. In practice, we noticed that the keypoint detector benefits greatly from using heavy image transformations. Additionally, the molecule augmentations, which allow training molecules to contain abbreviated groups, proved crucial to handle images containing abbreviated groups, such as in USPTO. + +Keypoint detector. In Table 5, we experiment with different standard deviations for the Gaussian keypoint labels, and keypoint regression losses. Using a large standard deviation of $b / 5$ , where $b$ denotes the bond length, creates overlaps between keypoints and significantly decreases performance. While the model is not sensitive to the choice of training loss, the WAHR loss offers a slight advantage. + +Supergraph construction. In Table 7, we evaluate the impact of the maximum number of bond candidates and the search radius in the supergraph construction. We observe that our approach is not sensitive to these settings, but only experiences a small drop when increasing the number of bond candidates. This drop is explained by false positives predicted during the node classification stage. + +Node classifier. As demonstrated in Table 7, initializing nodes embeddings with both visual and type encoding increases performance. We also experimented with positional + +Table 5. Keypoint detector analysis. We analyse the standard deviation of the Gaussian functions (top), as well as the training loss function (bottom). $b$ denotes the molecule bond length. + +
USPTOJPOJPOp
Heatmap standard deviationb/581.354.746.8
b/1091.567.555.4
b/1591.464.751.6
Training lossL291.166.255.1
WAHR [18]91.567.555.4
+ +![](images/5dacef82858d2cfcd4183469519d103a6eb6de66bdbb40a23f2bb58fd7a4a8cd.jpg) +Figure 4. Prediction steps. Keypoints are detected and then used to build a supergraph. After classifying the nodes of the graph and recognizing abbreviated groups, the output molecule is created. In this example, the polycyclic molecule contains overlapping bonds, a challenging feature for OCSR models, and is still correctly recognized. + +![](images/77527c0a258a629f927f0398f4f3ca3dcc00a03ae935097d21edff08cee4070f.jpg) +Figure 5. Qualitative comparison. The figure shows examples of predictions for characteristic images from different benchmarks. Compared to previous rule-based and learning based methods, our approach robustly recognizes the exact molecular structure in challenging cases, such as with distracting captions, stereo-chemistry, and very large molecules. + +Table 6. Supergraph construction analysis. We analyse the maximum number of bond candidates (top), and the maximum search radius (bottom). $b$ denotes the molecule bond length. + +
USPTOJPOJPOp
Number bond candidates691.567.555.4
1091.065.754.1
Search radius3b91.567.555.4
5b91.365.053.1
+ +Table 7. Node classifier analysis. We analyse the features representing graph nodes (top), and the usage of GCN layers (bottom). $\dagger$ : without abbreviated molecules and charges. + +
USPTOJPOJPOp
Node embeddingVisual90.064.754.9
+ Type91.567.555.4
+ Position91.362.854.8
USPTO†JPO†JPOp†
Number of GCN Layers090.158.053.6
490.466.661.6
+ +embedding but found it to reduce the overall performance. The model demonstrating, in average, best performances does not include GCN layers. However, as demonstrated in Table 7, for a limited evaluation setup, GCN layers have positive impact on performance, leading to significant gains of $8.6\%$ and $8.0\%$ on JPO and $\mathrm{JPO^p}$ when using 4 instead of 0 GCN layers. Note that even the version using 0 GNN layers, still employs our supergraph for feature aggregation + +![](images/e21ec738d6e38ef25682ea0cb246ad80e8ab0b548603c14d4fc4d7171f64b03a.jpg) +Figure 6. Ablation experiment. The figure shows MolGrapher predictions with and without using GCN layers, illustrating that GCN layers allow the model to learn chemistry rules. Indeed, the model correctly connect the oxygen atom highlighted in red to a double bond only. + +and classification. The propagation of information through the graph is beneficial for challenging cases, such as the one illustrated in Figure 6. In this example, interpreting only the visual information would be misleading, even for humans. Understanding chemistry rules is mandatory to resolve the ambiguities in the drawing, which is correctly done by our model. + +# 6. Conclusion + +We propose a novel architecture for recognizing 2-D molecule depictions in documents by exploiting the natural graph representation of molecules and graph symmetries. Our model accurately detects atoms and bonds based on their visual features and local context, outperforming exist- + +ing methods on standard benchmarks and our new USPTO-30K dataset. The model is trained on synthetic images and demonstrates strong generalization capabilities, making it useful at scale without requiring annotations for each journal or patent office. + +# References + +[1] United states patent and trademark office. http://uspto.gov. Accessed: 1 January 2023. +[2] Syed Saqib Bukhari, Zaryab Iftikhar, and Andreas Dengel. 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Bioinform., 23(2), March 2022. \ No newline at end of file diff --git a/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/images.zip b/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..9c2deed033144e6f3de20d89e727e4682616d953 --- /dev/null +++ b/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:89ced8c10bb3ac53d6e159e85530a597678cf752e317542ec9c9417062fc26b6 +size 392933 diff --git a/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/layout.json b/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..c3338a9608d1120bb321c07ca0ef3f40a3328718 --- /dev/null +++ b/2023/MolGrapher_ Graph-based Visual Recognition of Chemical Structures/layout.json @@ -0,0 +1,6810 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 78, + 103, + 515, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 78, + 103, + 515, + 121 + ], + "spans": [ + { + "bbox": [ + 78, + 103, + 515, + 121 + ], + "type": "text", + "content": "MolGrapher: Graph-based Visual Recognition of Chemical Structures" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "spans": [ + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "text", + "content": "Lucas Morin" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "inline_equation", + "content": "^{1,2}" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "text", + "content": " Martin Danelljan" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "text", + "content": " Maria Isabel Agea" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "text", + "content": " Ahmed Nassar" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "text", + "content": " Valery Weber" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "text", + "content": " Ingmar Meijer" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "text", + "content": " Peter Staar" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "text", + "content": " Fisher Yu" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 108, + 142, + 484, + 184 + ], + "type": "text", + "content": " IBM Research ETH Zurich" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 63, + 187, + 531, + 200 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 187, + 531, + 200 + ], + "spans": [ + { + "bbox": [ + 63, + 187, + 531, + 200 + ], + "type": "text", + "content": "{lum, ahn, vwe, inm, taa}@zurich.ibm.com martin.danelljan@vision.ee.ethz.ch i@yf.io" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "spans": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 252, + 290, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 252, + 290, + 517 + ], + "spans": [ + { + "bbox": [ + 46, + 252, + 290, + 517 + ], + "type": "text", + "content": "The automatic analysis of chemical literature has immense potential to accelerate the discovery of new materials and drugs. Much of the critical information in patent documents and scientific articles is contained in figures, depicting the molecule structures. However, automatically parsing the exact chemical structure is a formidable challenge, due to the amount of detailed information, the diversity of drawing styles, and the need for training data. In this work, we introduce MolGrapher to recognize chemical structures visually. First, a deep keypoint detector detects the atoms. Second, we treat all candidate atoms and bonds as nodes and put them in a graph. This construct allows a natural graph representation of the molecule. Last, we classify atom and bond nodes in the graph with a Graph Neural Network. To address the lack of real training data, we propose a synthetic data generation pipeline producing diverse and realistic results. In addition, we introduce a large-scale benchmark of annotated real molecule images, USPTO-30K, to spur research on this critical topic. Extensive experiments on five datasets show that our approach significantly outperforms classical and learning-based methods in most settings. Code, models, and datasets are available1." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 540, + 128, + 553 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 540, + 128, + 553 + ], + "spans": [ + { + "bbox": [ + 47, + 540, + 128, + 553 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 561, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 561, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 561, + 287, + 693 + ], + "type": "text", + "content": "The creation of an open-source database offering a unified view of our current knowledge of all studied molecules, would greatly accelerate research and development in numerous fields, ranging from the pharmaceutical industry to semiconductor manufacturing. Currently, information about a molecule's properties is distributed across various databases, research articles, and chemical patents, each measuring different subsets of properties. In such documents, molecules are most often described using images, by drawing their molecular structures. Automatic parsing of molecules from document images, known as Optical Chem-" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 328, + 232, + 544, + 408 + ], + "blocks": [ + { + "bbox": [ + 328, + 232, + 544, + 408 + ], + "lines": [ + { + "bbox": [ + 328, + 232, + 544, + 408 + ], + "spans": [ + { + "bbox": [ + 328, + 232, + 544, + 408 + ], + "type": "image", + "image_path": "46b9c0fea3bd844716a1aaddb891bffd018838c53ce420519ad5a4bbce23ddc8.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 411, + 547, + 477 + ], + "lines": [ + { + "bbox": [ + 305, + 411, + 547, + 477 + ], + "spans": [ + { + "bbox": [ + 305, + 411, + 547, + 477 + ], + "type": "text", + "content": "Figure 1. MolGrapher extracts the chemical structure, including all atoms and bonds, from a molecule image in a document. Our approach constructs a supergraph of the molecule (bottom right), containing all detected atom and bond candidates. These nodes are then classified by a Graph Neural Network in order to retrieve the chemical structure." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 495, + 546, + 531 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 495, + 546, + 531 + ], + "spans": [ + { + "bbox": [ + 305, + 495, + 546, + 531 + ], + "type": "text", + "content": "ical Structure Recognition (OCSR), is thus a critical task in the quest towards establishing a large-scale digital molecule database." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 534, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 547, + 715 + ], + "type": "text", + "content": "OCSR, however, poses multiple key challenges, which limit the accuracy of current solutions. First, a molecule can be drawn with a variety of styles and conventions. Even the projection of the molecular structure from 3-D onto a 2-D drawing is not unique, leading to the development of various projection algorithms with diverse results. Secondly, OCSR requires the extraction of detailed information from the image. Molecules often contain even hundreds of atoms and bonds, which all need to be correctly classified and linked. Thirdly, molecules have a virtually endless diversity stemming from the combinatorical explosion of possibilities, presenting particular challenges to data-driven deep learning methods. Lastly, available real training datasets are extremely limited, further complicating the application of deep learning." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 191, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 191, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 191, + 713 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 58, + 702, + 191, + 713 + ], + "type": "text", + "content": "https://github.com/DS4SD/MolGrapher" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "19552" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 49, + 72, + 286, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 72, + 286, + 215 + ], + "spans": [ + { + "bbox": [ + 49, + 72, + 286, + 215 + ], + "type": "text", + "content": "Initial OCR approaches followed the graph reconstruction paradigm. These methods start by extracting the fundamental components of molecules, such as atoms, bonds, and charges, often using hand-crafted image processing algorithms [8, 29, 21]. Then, rules are applied to connect these elements to reconstruct a graph representation of the molecule. Some recent works [19, 33, 38] introduce deep learning elements into the atom and bond detection steps. However, these approaches still rely on hand-crafted rules to link the recognized constituents, and thus not fully benefit from the advantages brought by deep learning." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 49, + 218, + 286, + 433 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 218, + 286, + 433 + ], + "spans": [ + { + "bbox": [ + 49, + 218, + 286, + 433 + ], + "type": "text", + "content": "Most recently, approaches instead follow the image captioning [4, 24, 34] paradigm by applying a deep network to directly output a character string identifying the molecule, e.g. in the form of SMILES [32]. However, these methods do not explicitly exploit the rich priors and invariances provided by the graph structure. The SMILES representation does not encode the geometrical and neighborhood structure of the molecule graph in a natural manner. While a recent work [36] predicts a graph in an autoregressive manner, adding one atom at a time prevents from fully exploiting the graph structure. Partially due to the lack of such a strong inductive bias, image captioning based methods still lag behind from the performance of state-of-the-art rule-based methods [8, 29, 21] on standard benchmarks [8, 9, 28, 22]. Moreover, the performance of captioning based methods severely degrade when increasing the size and complexity of the molecule, as they struggle to recover the detailed information in the image." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 49, + 436, + 286, + 626 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 436, + 286, + 626 + ], + "spans": [ + { + "bbox": [ + 49, + 436, + 286, + 626 + ], + "type": "text", + "content": "We introduce MolGrapher for Optical Chemical Structure Recognition, illustrated in Fig. 1. Our approach explicitly utilizes the graph structure as a strong inductive bias, while also allowing for the final molecule structure itself to be predicted by a deep learning model. MolGrapher operates in three steps. First, we locate atoms and abbreviations in the image with a keypoint detector network. Given the estimated locations of the atoms, we form a supergraph of the molecular structure, where two types of nodes represent candidate atoms and bonds respectively (see Fig. 1). Unlike previous approaches, we do not commit to a final molecule structure at this point, instead extracting a larger set of candidate bonds, forming a superset of the final molecular graph. Candidates that do not correspond to any bond are removed in the final prediction step by including a 'no bond' class." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 49, + 630, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 630, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 49, + 630, + 286, + 712 + ], + "type": "text", + "content": "In the final step, we input the constructed supergraph into a Graph Neural Network (GNN). We first extract deep node embeddings through a backbone network. The GNN then operates on the neighborhood structure provided by the supergraph in order to integrate visual information with learned chemistry priors. We then read-out the results with MLPs, classifying each node into a set of atom and bond" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 308, + 72, + 544, + 143 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 72, + 544, + 143 + ], + "spans": [ + { + "bbox": [ + 308, + 72, + 544, + 143 + ], + "type": "text", + "content": "classes. We also identify abbreviations through a separate class, which are parsed by an OCR component. Since training data is scarce, we develop, and release, a synthetic training data generation pipeline, capable of generating diverse and challenging examples to ensure robust generalization to a wide variety of drawing styles." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 308, + 144, + 544, + 299 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 144, + 544, + 299 + ], + "spans": [ + { + "bbox": [ + 308, + 144, + 544, + 299 + ], + "type": "text", + "content": "To further aid the research in the community, we introduce USPTO-30K, a large-scale benchmark dataset of annotated real molecule images. It contains separate subsets, in order to independently study the recognition of simple molecules, abbreviated molecules and extremely large molecules. We perform comprehensive experiments on five benchmarks: our USPTO-30K, USPTO [8], Maybridge UoB [28], CLEF-2012 [22] and JPO [9]. We outperform all deep learning based methods that only utilizes synthetic training. Our approach even surpass previous methods that rely on finetuning on real data on most benchmarks, and outperform the longstanding state-of-the-art by rule-based methods [8, 29, 21] in most settings." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 308, + 310, + 389, + 323 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 310, + 389, + 323 + ], + "spans": [ + { + "bbox": [ + 308, + 310, + 389, + 323 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 308, + 331, + 544, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 331, + 544, + 533 + ], + "spans": [ + { + "bbox": [ + 308, + 331, + 544, + 533 + ], + "type": "text", + "content": "OCSR approaches can be divided in two main categories. Image captioning based OCSR. Most of the recent end-to-end deep learning approaches are based on image captioning. These models use an encoder to extract visual features from the image and a decoder to translate them to a SMILES [32] or InChI [10] sequence. More precisely, DECIMER [26], MICER [35], MSE-DUDL [30] and Img2Mol [4] are using a convolutional encoder and a recurrent decoder which is respectively, a GRU decoder, a LSTM decoder, a GridLSTM decoder, and a RNN decoder. Later works proposed replacing the recurrent decoder with a transformer encoder-decoder, including DECIMER 1.0 [27], SwinOCSR [34], IMG2SMI [3] and Image2SMILES [13]. Other image captioning methods are solely based on transformers, using a vision transformer in [31], a Swin transformer in [23] or a Deep TNT transformer encoder with a transformer decoder in ICMDT [17]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 308, + 534, + 544, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 534, + 544, + 712 + ], + "spans": [ + { + "bbox": [ + 308, + 534, + 544, + 712 + ], + "type": "text", + "content": "One drawback of image captioning methods is the need of large training sets. The SMILES representation has numerous downsides for a learning task [15], one of them which is ambiguity due to the association of very different string identifiers to similar molecules. By predicting SMILES, instead of a more faithful representation of the image, the model needs to learn jointly to recognize the image and understand the SMILES language. Multiple string identifiers, possibly suited for a learning task have been proposed, including SELFIES, DeepSMILES [25] or abstract mathematical identifiers [4]. Nevertheless, representing a molecule image as a string adds extra complexity for a learning task. Additionally, these models to not properly handle uncertainty by predicting incorrect, but still valid, molecules for challenging inputs such as large molecules." + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 750, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 750, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 750, + 317, + 757 + ], + "type": "text", + "content": "19553" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 59, + 71, + 533, + 205 + ], + "blocks": [ + { + "bbox": [ + 59, + 71, + 533, + 205 + ], + "lines": [ + { + "bbox": [ + 59, + 71, + 533, + 205 + ], + "spans": [ + { + "bbox": [ + 59, + 71, + 533, + 205 + ], + "type": "image", + "image_path": "5d3ef430de4467b99100b8764aa556dd3e89a6779c8ed5ef35106f1107110a27.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 210, + 547, + 245 + ], + "lines": [ + { + "bbox": [ + 46, + 210, + 547, + 245 + ], + "spans": [ + { + "bbox": [ + 46, + 210, + 547, + 245 + ], + "type": "text", + "content": "Figure 2. Molecular graph recognition architecture. We illustrate the architecture of MolGrapher, a graph-based network for Optical Chemical Structure Recognition. The keypoint detector (red) locates atoms nodes in the molecule. A supergraph containing atom and bond candidates is constructed (green). Atoms and bonds are classified using a Graph Neural Network (blue)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 258, + 289, + 368 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 258, + 289, + 368 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 289, + 368 + ], + "type": "text", + "content": "Yet, to parse scientific literature at large scale, avoiding these false positives is critical. This behaviour is explained by the fact that the model is trained to always output valid SMILES, while using global image features. Contrary to these approaches, our model extracts precise visual features for each elementary component of a molecule and operate on a graph, allowing substantially better recognition performance for large molecules, possibly larger than the ones used for training." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 372, + 289, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 372, + 289, + 576 + ], + "spans": [ + { + "bbox": [ + 46, + 372, + 289, + 576 + ], + "type": "text", + "content": "Graph reconstruction based OCSR. Traditional approaches for Optical Chemical Structure Recognition rely on hand-crafted image processing algorithms to detect elementary components of the molecules and connect them to reconstruct the molecular graph [2, 8, 12, 20, 28, 29, 21]. More recent works detect elementary components using machine learning models. For instance, ChemGrapher [19] or ABC-Net [38] use convolutional segmentation networks while MolMiner [33] employs aYOLO object detector. As studied in [11], detection based methods can be trained with fewer training samples. By doing multiple low-level detections, it is possible to supervise precisely the training. It also offers a natural way to inject prior knowledge, or impose chemistry rules to the model. Our method benefits from these advantages but differentiates itself by learning both the detection and the association of the fundamental components of molecules." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": "Image2Graph [36] uses a transformer to build the graph in an auto-regressive way, by adding one atom at the time. [23] predicts a SMILES sequence, but enriched with atoms positions, and connectivity information, drifting away from the string identifier and getting closer to a graphical representation. Our new graph reconstruction approach do not build a graph auto-repressively. We first detects all possible components and associations, and then classify them. It allows to use localized visual features, as well as a complete neighborhood contextual information for each atom and bond prediction." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 256, + 387, + 270 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 256, + 387, + 270 + ], + "spans": [ + { + "bbox": [ + 305, + 256, + 387, + 270 + ], + "type": "text", + "content": "3. MolGrapher" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 277, + 547, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 277, + 547, + 361 + ], + "spans": [ + { + "bbox": [ + 304, + 277, + 547, + 361 + ], + "type": "text", + "content": "We introduce MolGrapher, a graph-based network for Optical Chemical Structure Recognition. Our model architecture is illustrated in Figure 2. Our pipeline consists of three steps. Firstly, the keypoint detector locates atoms nodes in the molecule. Secondly, we construct a graph containing atom and bond candidates. Finally, atoms and bonds are classified using a Graph Neural Network." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 369, + 419, + 382 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 369, + 419, + 382 + ], + "spans": [ + { + "bbox": [ + 305, + 369, + 419, + 382 + ], + "type": "text", + "content": "3.1. Keypoint Detection" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 387, + 547, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 387, + 547, + 460 + ], + "spans": [ + { + "bbox": [ + 304, + 387, + 547, + 460 + ], + "type": "text", + "content": "In order to construct the molecular graph, we first need to localize keypoints in the image. Keypoints refer to the position of atoms and 'superatoms', i.e. abbreviated groups of atoms. In the later stages, this enables the extraction of relevant visual features for atoms and bonds, as well as the construction of our molecule supergraph." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 460, + 547, + 554 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 547, + 554 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 547, + 554 + ], + "type": "text", + "content": "Our keypoint detector predicts a heatmap, where each peak corresponds to an atom location. The output of a feature extractor is passed through convolutional layers to predict the final single-channel heatmap of the atom locations. To extract the peak locations, we first threshold the heatmap by removing any value in the bottom " + }, + { + "bbox": [ + 304, + 460, + 547, + 554 + ], + "type": "inline_equation", + "content": "10^{\\mathrm{th}}" + }, + { + "bbox": [ + 304, + 460, + 547, + 554 + ], + "type": "text", + "content": " percentile. We then collect regional maxima, using a window size of " + }, + { + "bbox": [ + 304, + 460, + 547, + 554 + ], + "type": "inline_equation", + "content": "5 \\times 5" + }, + { + "bbox": [ + 304, + 460, + 547, + 554 + ], + "type": "text", + "content": ", as the final atom locations." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 555, + 547, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 555, + 547, + 652 + ], + "spans": [ + { + "bbox": [ + 304, + 555, + 547, + 652 + ], + "type": "text", + "content": "Atoms are labeled with Gaussian functions, allowing smoother supervision as well as capturing a degree of uncertainty regarding the predicted positions. Since the groundtruth heatmaps predominantly contains background values, we use the weight-adaptive heatmap regression loss [18] to overcome the class imbalance. It reduces the impact of well-classified samples, which mostly constitute background, allowing the training to focus on harder samples." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 658, + 450, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 658, + 450, + 672 + ], + "spans": [ + { + "bbox": [ + 305, + 658, + 450, + 672 + ], + "type": "text", + "content": "3.2. Supergraph Construction" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "content": "In this section, we describe the construction of the supergraph, which contains all atom and bond candidates to be classified. The supergraph is composed of two types of" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "19554" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 81, + 298, + 167 + ], + "blocks": [ + { + "bbox": [ + 50, + 81, + 298, + 167 + ], + "lines": [ + { + "bbox": [ + 50, + 81, + 298, + 167 + ], + "spans": [ + { + "bbox": [ + 50, + 81, + 298, + 167 + ], + "type": "image", + "image_path": "42990e13da558e4fc561693313483516f20350b6a45ae2db0923b0e133dddb73.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 174, + 288, + 240 + ], + "lines": [ + { + "bbox": [ + 46, + 174, + 288, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 174, + 288, + 240 + ], + "type": "text", + "content": "Figure 3. Supergraph construction. The figure presents the construction of bonds proposals for an atom denoted " + }, + { + "bbox": [ + 46, + 174, + 288, + 240 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 46, + 174, + 288, + 240 + ], + "type": "text", + "content": ". Considered bonds are depicted with dashed lines. Green bonds are accepted in the supergraph, while red bonds are discarded because: (1) there are no filled pixels around their centerpoints or (2) they are obstructed by other keypoints." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 255, + 287, + 303 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 255, + 287, + 303 + ], + "spans": [ + { + "bbox": [ + 46, + 255, + 287, + 303 + ], + "type": "text", + "content": "nodes: atoms and bonds. Further, each edge in the graph only connects an atom node to a bond node. Representing both of these entities as nodes allows us to process them uniformly through standard message passing layers." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 304, + 287, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 287, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 287, + 422 + ], + "type": "text", + "content": "The input to our supergraph construction is a set of approximate atom locations. Since the connectivity between the detected atoms is unknown, our graph has to represent a superset of the final molecule prediction, thus termed 'supergraph'. That is, it contains all possible bonds. By including a prediction class corresponding to 'no bond', bond candidates which are not actually in the molecule can be removed in the later stage. Including an analogous class for 'no atom', our approach can even correct false positives predicted by the keypoint detection network." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 423, + 288, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 423, + 288, + 591 + ], + "spans": [ + { + "bbox": [ + 46, + 423, + 288, + 591 + ], + "type": "text", + "content": "Our supergraph construction is illustrated in Figure 3. We first consider each keypoint individually, adding connections to all other keypoints within a radius of three times the estimated bond length [8]. Subsequently, we remove connections which have no filled pixels around their centerpoints or if there is a third keypoint located between its two extremities. Finally, we keep at most six bond candidates for each atom, by eliminating the longest connections. Chemistry prior knowledge ensures that it is extremely unlikely for an atom to have more than five neighboring bonds. Our settings are highly conservative to avoid deleting any actual bond. On the other hand, pruning superfluous bonds avoids any unnecessary false positives in the later stage and a more effective connectivity for the GNN." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 599, + 160, + 611 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 599, + 160, + 611 + ], + "spans": [ + { + "bbox": [ + 47, + 599, + 160, + 611 + ], + "type": "text", + "content": "3.3. Node Classification" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "content": "In order to classify atom and bond nodes, we integrate a Graph Neural Network (GNN) that operates on the constructed supergraph. The embeddings for all nodes are initialized using visual features as well as their types. This approach leverages the local context of atoms and bonds to predict their class. Intuitively, it enables the learning of chemistry rules, i.e. atoms have a fixed valence, as well as chemistry prior knowledge, i.e. some typical substructures" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 73, + 430, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 73, + 430, + 83 + ], + "spans": [ + { + "bbox": [ + 305, + 73, + 430, + 83 + ], + "type": "text", + "content": "are more common than others." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "spans": [ + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "inline_equation", + "content": "e_i^1 \\in R^D" + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "text", + "content": " denotes the initial embedding of the node " + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "text", + "content": " of type " + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "inline_equation", + "content": "t_i \\in \\{\\text{atom}, \\text{bond}\\}" + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "text", + "content": " located at position " + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "inline_equation", + "content": "(x_i, y_i)" + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "text", + "content": ". It is computed by combining a visual feature vector " + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "inline_equation", + "content": "v_i" + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "text", + "content": " and a learnable type encoding " + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "inline_equation", + "content": "w_{t_i}" + }, + { + "bbox": [ + 304, + 83, + 547, + 133 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 395, + 139, + 545, + 153 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 395, + 139, + 545, + 153 + ], + "spans": [ + { + "bbox": [ + 395, + 139, + 545, + 153 + ], + "type": "interline_equation", + "content": "e _ {i} ^ {0} = v _ {i} + w _ {t _ {i}} \\tag {1}", + "image_path": "73a36744e9ebf9dcb68a60e4842fa7f23008c67d1a80ff375529d26874491b8b.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "spans": [ + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "type": "text", + "content": "The visual features " + }, + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "type": "inline_equation", + "content": "v_{i}" + }, + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "type": "text", + "content": " are extracted from a deep feature map " + }, + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "type": "text", + "content": ", extracted by a backbone network. For an atom node " + }, + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "type": "text", + "content": " we evaluate the feature map in the corresponding location " + }, + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "type": "inline_equation", + "content": "(x_{i},y_{i})" + }, + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "type": "text", + "content": " with bilinear interpolation," + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 392, + 216, + 545, + 228 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 392, + 216, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 392, + 216, + 545, + 228 + ], + "type": "interline_equation", + "content": "v _ {i} = F \\left(x _ {i}, y _ {i}\\right). \\tag {2}", + "image_path": "12d19f4869807bb57834ea9a0422c634e50ceb0b31f0b19b937684e8cc177b45.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 236, + 545, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 236, + 545, + 258 + ], + "spans": [ + { + "bbox": [ + 304, + 236, + 545, + 258 + ], + "type": "text", + "content": "For a bond node " + }, + { + "bbox": [ + 304, + 236, + 545, + 258 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 236, + 545, + 258 + ], + "type": "text", + "content": ", we aggregate features at locations along the bond as" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 378, + 257, + 545, + 290 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 378, + 257, + 545, + 290 + ], + "spans": [ + { + "bbox": [ + 378, + 257, + 545, + 290 + ], + "type": "interline_equation", + "content": "v _ {i} = \\frac {1}{J} \\sum_ {j = 1} ^ {J} F \\left(x _ {i} ^ {j}, y _ {i} ^ {j}\\right), \\tag {3}", + "image_path": "09923d9f61e594afb26bd0f63f56347824a370beae78044ae3cac9bc981f35c4.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 295, + 545, + 319 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 295, + 545, + 319 + ], + "spans": [ + { + "bbox": [ + 304, + 295, + 545, + 319 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 295, + 545, + 319 + ], + "type": "inline_equation", + "content": "(x_i^j, y_i^j)" + }, + { + "bbox": [ + 304, + 295, + 545, + 319 + ], + "type": "text", + "content": " are the locations of " + }, + { + "bbox": [ + 304, + 295, + 545, + 319 + ], + "type": "inline_equation", + "content": "J" + }, + { + "bbox": [ + 304, + 295, + 545, + 319 + ], + "type": "text", + "content": " uniformly spaced points along the bond itself." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 320, + 545, + 416 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 320, + 545, + 416 + ], + "spans": [ + { + "bbox": [ + 304, + 320, + 545, + 416 + ], + "type": "text", + "content": "Given initial node embeddings, information is propagated through the graph to learn local dependencies between atoms and bonds. Indeed, directly neighboring atoms and bonds respect strict chemistry rules, and larger neighborhoods form patterns called functional groups, which are typically abundant in nature. We employ GNN layers, denoted " + }, + { + "bbox": [ + 304, + 320, + 545, + 416 + ], + "type": "inline_equation", + "content": "\\{g^k\\}_{k\\in [1,N]}" + }, + { + "bbox": [ + 304, + 320, + 545, + 416 + ], + "type": "text", + "content": ", to iteratively update the node embeddings," + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 392, + 416, + 545, + 430 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 392, + 416, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 392, + 416, + 545, + 430 + ], + "type": "interline_equation", + "content": "e ^ {k + 1} = g ^ {k} \\left(e ^ {k}\\right). \\tag {4}", + "image_path": "c24aa76694667af9b4424676d1c0957285eeb3d7e5fa4c2e62f759c2498568ba.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 434, + 545, + 459 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 434, + 545, + 459 + ], + "spans": [ + { + "bbox": [ + 304, + 434, + 545, + 459 + ], + "type": "text", + "content": "The final predictions " + }, + { + "bbox": [ + 304, + 434, + 545, + 459 + ], + "type": "inline_equation", + "content": "\\{p_i\\}" + }, + { + "bbox": [ + 304, + 434, + 545, + 459 + ], + "type": "text", + "content": " are then obtained using two Multi-Layer Perceptrons, one for each node type " + }, + { + "bbox": [ + 304, + 434, + 545, + 459 + ], + "type": "inline_equation", + "content": "t" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 387, + 465, + 545, + 479 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 387, + 465, + 545, + 479 + ], + "spans": [ + { + "bbox": [ + 387, + 465, + 545, + 479 + ], + "type": "interline_equation", + "content": "p _ {i} = M L P _ {t} \\left(e _ {i} ^ {N}\\right). \\tag {5}", + "image_path": "6e3782d5d8d60f1ffc81670223bb7a77e0f118292aa0b8a257d72cd05ebc9bb4.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 486, + 545, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 545, + 509 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 545, + 509 + ], + "type": "text", + "content": "The vector " + }, + { + "bbox": [ + 304, + 486, + 545, + 509 + ], + "type": "inline_equation", + "content": "p_i \\in \\mathbb{R}^{C_t}" + }, + { + "bbox": [ + 304, + 486, + 545, + 509 + ], + "type": "text", + "content": " contains the logits for the final atom or bond classes." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 510, + 545, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 593 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 593 + ], + "type": "text", + "content": "The most represented bond types include 'no bond', 'single', 'double' and 'triple'. Atom classes include the common (e.g. O) and exotic atoms as well as charged atoms (e.g. " + }, + { + "bbox": [ + 304, + 510, + 545, + 593 + ], + "type": "inline_equation", + "content": "\\mathrm{O}^{-}" + }, + { + "bbox": [ + 304, + 510, + 545, + 593 + ], + "type": "text", + "content": "). Since molecule images often include whole groups in the nodes, e.g. COOH, we further include a class 'superatom' to recognize these cases. Such nodes are then parsed as described in Section 3.4." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 594, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 712 + ], + "type": "text", + "content": "Our node classification model is trained using the cross-entropy loss for both the atom and bond prediction heads. During training, the supergraph structure used as input is obtained by applying the graph construction algorithm on augmented ground truth keypoints. To simulate possible errors from the keypoint detector, we add noise to the atom positions and randomly include false-positive keypoints. Decoupling the keypoint detection and the node classification allow to train faster and to use optimized training sets for each task." + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19555" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 49, + 72, + 217, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 72, + 217, + 85 + ], + "spans": [ + { + "bbox": [ + 49, + 72, + 217, + 85 + ], + "type": "text", + "content": "3.4. Superatom Groups Recognition" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 49, + 91, + 286, + 221 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 91, + 286, + 221 + ], + "spans": [ + { + "bbox": [ + 49, + 91, + 286, + 221 + ], + "type": "text", + "content": "To recognize abbreviated substructures, named superatoms, we use an external Optical Character Recognition (OCR) system. Relying on an external OCR system provides strong robustness, since the model is trained on a diversity of text representations that cannot necessarily be generated in a molecule image. At the location of an abbreviated group, the node classifier predicts a 'superatom' class. Then, the OCR engine PP-OCR [6] is used to recognize the text written at this location, which is finally replaced by its corresponding sub-molecule, stored in a precomputed mapping." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 49, + 232, + 104, + 245 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 232, + 104, + 245 + ], + "spans": [ + { + "bbox": [ + 49, + 232, + 104, + 245 + ], + "type": "text", + "content": "4. Datasets" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 49, + 251, + 236, + 265 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 251, + 236, + 265 + ], + "spans": [ + { + "bbox": [ + 49, + 251, + 236, + 265 + ], + "type": "text", + "content": "4.1. Synthetic Training Data Generation" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 49, + 270, + 286, + 329 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 270, + 286, + 329 + ], + "spans": [ + { + "bbox": [ + 49, + 270, + 286, + 329 + ], + "type": "text", + "content": "Training datasets of annotated molecule images extracted from scientific publications are extremely limited. Therefore, we develop a synthetic training pipeline to generate a broad diversity of molecular representations. It further allows us to extract atom-level annotations." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 49, + 331, + 286, + 497 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 331, + 286, + 497 + ], + "spans": [ + { + "bbox": [ + 49, + 331, + 286, + 497 + ], + "type": "text", + "content": "Our dataset is created using molecule SMILES retrieved from the database PubChem [14]. To increase the probability that the dataset covers the largest variety of molecular structures, we sample SMILES using a strategy based on functional groups. A functional group is molecule substructure typically abundant in nature. Thus, we retrieve molecules from PubChem containing each functional group in a defined collection of 1540 functional groups. To further increase diversity, these molecules are queried with different ranges of number of atoms. Finally the dataset is filtered by removing salts, molecules containing complex polycycles, isotopes or radical electrons. Training images are then generated from SMILES using the molecule drawing library RDKit [16]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 49, + 498, + 286, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 498, + 286, + 628 + ], + "spans": [ + { + "bbox": [ + 49, + 498, + 286, + 628 + ], + "type": "text", + "content": "To capture the large diversity of drawing styles and conventions from different scientific documents, the synthetic set is highly augmented, at multiple levels. Firstly, molecules are randomly transformed, notably by setting the selection of a molecular conformation, adding artificial superatom groups with single or multiple attachment points or displaying solid, dashed or wavy bonds. Secondly, the rendering parameters used in RDKit are randomly set, including the font, the bond width, the display of aromatic cycles using circles. This leads to substantial variations in the drawn molecule, to aid generalization to real datasets." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 49, + 630, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 630, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 49, + 630, + 286, + 712 + ], + "type": "text", + "content": "The generated molecule images are saved together with their corresponding MolFiles. A MolFile [5] stores information about the atoms and their positions in a molecule, as well as bonds and their connectivity. It provides the necessary information for supervising the training. This generation pipeline covers a large diversity of molecules including stereo-chemistry and molecules with superatom groups." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 308, + 72, + 545, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 72, + 545, + 107 + ], + "spans": [ + { + "bbox": [ + 308, + 72, + 545, + 107 + ], + "type": "text", + "content": "Finally, the images undergo several image augmentations on the fly such as gaussian blurring, the adding of pepper patches, random lines, and random captions." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 308, + 108, + 545, + 155 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 108, + 545, + 155 + ], + "spans": [ + { + "bbox": [ + 308, + 108, + 545, + 155 + ], + "type": "text", + "content": "The exhaustive lists of molecule, rendering and image augmentations, as well as details regarding the generation of atom-level annotations are available in the supplementary materials." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 308, + 162, + 446, + 174 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 162, + 446, + 174 + ], + "spans": [ + { + "bbox": [ + 308, + 162, + 446, + 174 + ], + "type": "text", + "content": "4.2. The USPTO-30K Dataset" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 308, + 180, + 545, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 180, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 308, + 180, + 545, + 300 + ], + "type": "text", + "content": "Existing benchmarks have some limitations. Being created using only a few documents, they contain batches of very similar molecules. For example in a patent, a molecule could typically be displayed together with all the substituent of one particular substructure, resulting in large batches of almost identical molecules. Additionally, the existing sets contain molecules of different kinds, including superatom groups and various markush [7] features, which should be evaluated independently. In practice, it is important to delimit on which types of molecules models can be applied." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 308, + 300, + 545, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 300, + 545, + 467 + ], + "spans": [ + { + "bbox": [ + 308, + 300, + 545, + 467 + ], + "type": "text", + "content": "We introduce USPTO-30K, a large-scale benchmark dataset of annotated molecule images, which overcomes these limitations. It is created using the pairs of images and MolFiles [5] by the United States Patent and Trademark Office (USPTO) [1]. Each molecule was independently selected among all the available images from 2001 to 2020. The set consists of three subsets to decouple the study of clean molecules, molecules with abbreviations and large molecules. USPTO-10K contains 10,000 clean molecules, i.e. without any abbreviated groups. USPTO-10K-abb contains 10,000 molecules with superatom groups. USPTO-10K-L contains 10,000 clean molecules with more than 70 atoms. We provide visualizations and analysis in the supplementary materials." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 308, + 477, + 384, + 491 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 477, + 384, + 491 + ], + "spans": [ + { + "bbox": [ + 308, + 477, + 384, + 491 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 308, + 497, + 545, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 497, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 308, + 497, + 545, + 533 + ], + "type": "text", + "content": "In this section, we perform comprehensive experiments on multiple OCSR benchmarks. Moreover, we propose an analysis of the different components of our method." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 308, + 539, + 435, + 552 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 539, + 435, + 552 + ], + "spans": [ + { + "bbox": [ + 308, + 539, + 435, + 552 + ], + "type": "text", + "content": "5.1. Implementation details" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 308, + 557, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 557, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 308, + 557, + 545, + 712 + ], + "type": "text", + "content": "The implementation is done with PyTorch 1.12 with CUDA 11.3. For the keypoint detector features extractor, we use a ResNet-18 backbone with " + }, + { + "bbox": [ + 308, + 557, + 545, + 712 + ], + "type": "inline_equation", + "content": "8 \\times" + }, + { + "bbox": [ + 308, + 557, + 545, + 712 + ], + "type": "text", + "content": " dilatation factor [37] to preserve a high spatial resolution. For the node classifier features extractor, we resort to a ResNet-50 with a " + }, + { + "bbox": [ + 308, + 557, + 545, + 712 + ], + "type": "inline_equation", + "content": "2 \\times" + }, + { + "bbox": [ + 308, + 557, + 545, + 712 + ], + "type": "text", + "content": " dilation factor. The model is trained on 300,000 synthetic images, presented in subsection 4.1. We train for 20 epochs on 3 NVIDIA A100 GPUs using ADAM with a learning rate of 0.0001 that we decay after 5000 iterations by a factor of 0.8. The losses for atoms and bonds classifiers are weighted by factors 1 and 3, respectively. During inference, we pre-process images by removing captions using PP-OCR [6]. Additionally, in case an initial prediction is an" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 750, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 750, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 750, + 317, + 757 + ], + "type": "text", + "content": "19556" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 72, + 102, + 521, + 245 + ], + "blocks": [ + { + "bbox": [ + 46, + 68, + 547, + 102 + ], + "lines": [ + { + "bbox": [ + 46, + 68, + 547, + 102 + ], + "spans": [ + { + "bbox": [ + 46, + 68, + 547, + 102 + ], + "type": "text", + "content": "Table 1. Comparison of our method with existing OCR models. We report the accuracy, i.e. the percentage of perfectly recognized molecule images, on datasets coming from real scientific documents. " + }, + { + "bbox": [ + 46, + 68, + 547, + 102 + ], + "type": "inline_equation", + "content": "\\ast" + }, + { + "bbox": [ + 46, + 68, + 547, + 102 + ], + "type": "text", + "content": ": re-implemented results. †: results from original publications. " + }, + { + "bbox": [ + 46, + 68, + 547, + 102 + ], + "type": "inline_equation", + "content": "\\ddagger" + }, + { + "bbox": [ + 46, + 68, + 547, + 102 + ], + "type": "text", + "content": ": results from [11]." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 72, + 102, + 521, + 245 + ], + "lines": [ + { + "bbox": [ + 72, + 102, + 521, + 245 + ], + "spans": [ + { + "bbox": [ + 72, + 102, + 521, + 245 + ], + "type": "table", + "html": "
MethodUSPTO (5719)Maybridge UoB (5740)CLEF-2012 (992)JPO (450)USPTO-10K (10 000)USPTO-10K-Abb (10 000)USPTO-10K-L (10 000)
Rule-based methods
OSRA 2.1 [8]*89.386.393.456.389.763.943.1
MolVec 0.9.7 [21]*89.188.381.266.892.470.364.0
Imago 2.0 [29]*89.463.968.241.089.963.047.3
Only synthetic training
DECIMER 2.0 [24]†61.088.072.064.0---
Image2Graph [36]†44.972.037.824.0---
Graph Generation [23]†67.083.174.6----
CEDe [11]‡79.074.168.049.4---
Chemographer [19]‡80.983.275.553.3---
Img2Mol [4]*25.268.017.916.135.413.80.0
MolGrapher (Ours)91.594.990.567.593.382.831.4
", + "image_path": "dc06013906e99b635b8e186f7cd4aa944420c5b651ed8665f8ae675d1f74a54c.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 262, + 287, + 299 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 262, + 287, + 299 + ], + "spans": [ + { + "bbox": [ + 46, + 262, + 287, + 299 + ], + "type": "text", + "content": "invalid molecule, we use PP-OCR to merge keypoints located in a same detected text cell. See the supplementary material for more details." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 308, + 219, + 319 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 308, + 219, + 319 + ], + "spans": [ + { + "bbox": [ + 47, + 308, + 219, + 319 + ], + "type": "text", + "content": "5.2. Evaluation datasets and metrics" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 327, + 288, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 327, + 288, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 327, + 288, + 506 + ], + "type": "text", + "content": "To compare our method with state-of-the-art, the model is evaluated on the standard benchmarks USPTO [8], Maybridge UoB [28], CLEF-2012 [22] and JPO [9]. USPTO and CLEF are collections of 5,719 and 992 molecule images. Besides, JPO contains 450 images published by the Japanese Patent Office (JPO). JPO is particularly challenging because of its non-standard drawing conventions and poor images qualities. Lastly, Maybridge UoB is a dataset of 5,740 scanned molecule images taken from a catalogue of drug compounds by Maybridge. To compare methods, we compute accuracy, defined as the percentage of perfectly recognized molecules. In practice, this is done by verifying that the predicted and ground-truth molecules have identical InChI [10] keys. For evaluation, stereo-chemistry is removed and markush structures are not considered." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 515, + 204, + 528 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 515, + 204, + 528 + ], + "spans": [ + { + "bbox": [ + 47, + 515, + 204, + 528 + ], + "type": "text", + "content": "5.3. State-of-the-art Comparison" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 533, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 287, + 713 + ], + "type": "text", + "content": "Table 1 compares the OCSR methods on different benchmarks. Our method achieves superior results compared to rule-based models on most datasets, including USPTO, Maybridge UoB and JPO. Solely using synthetic training, our method reduces the error rate by more than half compared to other deep learning methods on USPTO, Maybridge UoB, and CLEF-2012. The design of our model confers a strong generalization ability. In practice, this is very important as our model will be applied to a wide variety of documents, which are not necessarily evaluated by the current benchmark datasets. MolGrapher also maintains good performance for extremely large molecules in USPTO-10K-L, which only contains examples with more than 70 atoms. On the contrary, recognizing large molecules is a significant challenge for image captioning based methods. For" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 307, + 324, + 545, + 399 + ], + "blocks": [ + { + "bbox": [ + 304, + 259, + 545, + 324 + ], + "lines": [ + { + "bbox": [ + 304, + 259, + 545, + 324 + ], + "spans": [ + { + "bbox": [ + 304, + 259, + 545, + 324 + ], + "type": "text", + "content": "Table 2. Comparison of our method with deep OCSR models finetuned on real data. We report the accuracy, i.e. the percentage of perfectly recognized molecule images, on datasets coming from real scientific documents. †: results from original publications. ‡: results (in grey) from unavailable sub-splits of the original benchmarks, only reported for reference." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 324, + 545, + 399 + ], + "lines": [ + { + "bbox": [ + 307, + 324, + 545, + 399 + ], + "spans": [ + { + "bbox": [ + 307, + 324, + 545, + 399 + ], + "type": "table", + "html": "
MethodUSPTO (5719)Maybridge UoB (5740)CLEF-2012 (992)JPO (450)
Real data finetuning
Image2Graph [36]†55.183.051.750.0
Graph Generation [23]†92.986.687.5-
CEDe [11]†‡91.091.586.674.0
Only synthetic training
MolGrapher (Ours)91.594.990.567.5
", + "image_path": "4d84b60a79c04ca6682b525ee15b98ad3c5812ec06f4db17ecaae2a6c3505223.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 412, + 545, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 412, + 545, + 507 + ], + "spans": [ + { + "bbox": [ + 304, + 412, + 545, + 507 + ], + "type": "text", + "content": "instance, Clevert et al. point out that the performance of Img2Mol [4] drop sharply for molecules larger than 40 atoms. This is confirmed in our evaluation, where it fails to correctly recognize virtually any molecule in USPTO-10K-L. Table 2 also provides comparison with models finetuned using real data. Our model surpasses these methods on Maybridge UoB, CLEF-2012 and JPO and is second best on USPTO, while not relying on any real data for training." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 508, + 545, + 626 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 508, + 545, + 626 + ], + "spans": [ + { + "bbox": [ + 304, + 508, + 545, + 626 + ], + "type": "text", + "content": "Our model outperforms existing methods on our USPTO-10K and USPTO-10K-Abb. The performance is particularly improved for molecules containing abbreviated groups. The performance gap between USPTO and USPTO-10K-Abb for rule-based approaches suggests that these methods are specifically parameterized for abbreviations in the existing benchmark datasets. Our model is the only deep learning method to provide a competitive performance for extremely large molecules. This is allowed by our architecture, which extracts localized visual features." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 635, + 414, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 635, + 414, + 647 + ], + "spans": [ + { + "bbox": [ + 306, + 635, + 414, + 647 + ], + "type": "text", + "content": "5.4. Model Robustness" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "type": "text", + "content": "Clevert et al. [4] introduced modified version of the standard benchmarks by applying slight perturbations, such as rotation and shearing, to the input images. Table 3 presents a comparison to previous methods on the same perturbed sets. The augmented images can be seen as a simulation" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19557" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 112, + 287, + 183 + ], + "blocks": [ + { + "bbox": [ + 47, + 69, + 287, + 112 + ], + "lines": [ + { + "bbox": [ + 47, + 69, + 287, + 112 + ], + "spans": [ + { + "bbox": [ + 47, + 69, + 287, + 112 + ], + "type": "text", + "content": "Table 3. Evaluation of model robustness. We report the accuracy, i.e. the percentage of perfectly recognized molecule images, on perturbed datasets coming from real scientific documents. " + }, + { + "bbox": [ + 47, + 69, + 287, + 112 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 47, + 69, + 287, + 112 + ], + "type": "text", + "content": ": results from [4]." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 112, + 287, + 183 + ], + "lines": [ + { + "bbox": [ + 49, + 112, + 287, + 183 + ], + "spans": [ + { + "bbox": [ + 49, + 112, + 287, + 183 + ], + "type": "table", + "html": "
MethodUSPTOP(4852)Maybridge UoBP(5716)CLEF-2012P(711)JPOP(365)
OSRA 2.1 [8]†6.470.917.033.0
MolVec 0.9.7 [21]†30.775.044.549.5
Imago 2.0 [29]†5.15.126.723.2
Img2Mol [4]†42.378.248.845.1
MolGrapher (Ours)86.794.187.855.4
", + "image_path": "2f7167d5c8e3437b80960bd0e3dc18a845fb7d92b38dfe6fead0654031630eed.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 196, + 287, + 280 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 196, + 287, + 280 + ], + "spans": [ + { + "bbox": [ + 46, + 196, + 287, + 280 + ], + "type": "text", + "content": "of scanned images, which are typically found in chemical patents. We observe that the performance of rule based approaches, OSRA, MolVec and Imago, decreases sharply. However, our model maintains a good result, outperforming other methods by a significant margin. This robustness is essential for large-scale analysis of chemical literature, as input molecule image quality cannot be controlled." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 286, + 173, + 298 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 286, + 173, + 298 + ], + "spans": [ + { + "bbox": [ + 47, + 286, + 173, + 298 + ], + "type": "text", + "content": "5.5. Qualitative evaluation" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 304, + 287, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 287, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 287, + 495 + ], + "type": "text", + "content": "In this section, we conduct a qualitative evaluation of MolGrapher, in comparison to state-of-the-art methods. First, Figure 4 illustrates the intermediate outputs of MolGrapher. Note that MolGrapher accurately recognizes molecules in challenging cases with overlapping bonds, without the use of any post-processing rules. Figure 5 showcases examples of predicted molecules for images from various benchmark datasets. MolGrapher demonstrates robustness to images containing captions (Figure 5 row 1). It can correctly recognize extremely large molecules (Figure 5 row 4), and is robust to solid, dashed or wavy bonds (Figure 5 row 5). Unlike image captioning based methods such as " + }, + { + "bbox": [ + 46, + 304, + 287, + 495 + ], + "type": "inline_equation", + "content": "\\mathrm{Img2Mol}" + }, + { + "bbox": [ + 46, + 304, + 287, + 495 + ], + "type": "text", + "content": ", our predictions preserve the projection and atom placement used in the input image (Figure 5 row 2). This can convey critical information for human interpretation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 502, + 138, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 502, + 138, + 514 + ], + "spans": [ + { + "bbox": [ + 47, + 502, + 138, + 514 + ], + "type": "text", + "content": "5.6. Ablation study" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 521, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 544 + ], + "type": "text", + "content": "We conduct an ablation study to demonstrate the impact of each component in the proposed method." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 544, + 287, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 544, + 287, + 569 + ], + "spans": [ + { + "bbox": [ + 46, + 544, + 287, + 569 + ], + "type": "text", + "content": "Synthetic training set. We evaluate the impact of the three levels of augmentation of the training set, illustrated in Ta" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 321, + 102, + 535, + 165 + ], + "blocks": [ + { + "bbox": [ + 305, + 69, + 545, + 102 + ], + "lines": [ + { + "bbox": [ + 305, + 69, + 545, + 102 + ], + "spans": [ + { + "bbox": [ + 305, + 69, + 545, + 102 + ], + "type": "text", + "content": "Table 4. Training set analysis. Impact of training set augmentations on performance. Molecule, rendering and image level augmentation are independently removed." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 321, + 102, + 535, + 165 + ], + "lines": [ + { + "bbox": [ + 321, + 102, + 535, + 165 + ], + "spans": [ + { + "bbox": [ + 321, + 102, + 535, + 165 + ], + "type": "table", + "html": "
USPTOJPOJPOp
All augmentations91.567.555.4
No molecule augmentation52.452.743.4
No rendering augmentation78.455.744.1
No image augmentation69.829.322.5
", + "image_path": "884fa1672620c34628b0205583ea52b131e11f183f3d175780992a475e2a651f.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 178, + 545, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 178, + 545, + 262 + ], + "spans": [ + { + "bbox": [ + 304, + 178, + 545, + 262 + ], + "type": "text", + "content": "ble 4. The image augmentations have a major impact on the performance of the model. In practice, we noticed that the keypoint detector benefits greatly from using heavy image transformations. Additionally, the molecule augmentations, which allow training molecules to contain abbreviated groups, proved crucial to handle images containing abbreviated groups, such as in USPTO." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "spans": [ + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "type": "text", + "content": "Keypoint detector. In Table 5, we experiment with different standard deviations for the Gaussian keypoint labels, and keypoint regression losses. Using a large standard deviation of " + }, + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "type": "inline_equation", + "content": "b / 5" + }, + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 304, + 262, + 545, + 346 + ], + "type": "text", + "content": " denotes the bond length, creates overlaps between keypoints and significantly decreases performance. While the model is not sensitive to the choice of training loss, the WAHR loss offers a slight advantage." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 347, + 545, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 347, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 304, + 347, + 545, + 430 + ], + "type": "text", + "content": "Supergraph construction. In Table 7, we evaluate the impact of the maximum number of bond candidates and the search radius in the supergraph construction. We observe that our approach is not sensitive to these settings, but only experiences a small drop when increasing the number of bond candidates. This drop is explained by false positives predicted during the node classification stage." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 431, + 545, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 431, + 545, + 468 + ], + "spans": [ + { + "bbox": [ + 304, + 431, + 545, + 468 + ], + "type": "text", + "content": "Node classifier. As demonstrated in Table 7, initializing nodes embeddings with both visual and type encoding increases performance. We also experimented with positional" + } + ] + } + ], + "index": 13 + }, + { + "type": "table", + "bbox": [ + 320, + 508, + 535, + 570 + ], + "blocks": [ + { + "bbox": [ + 305, + 475, + 545, + 507 + ], + "lines": [ + { + "bbox": [ + 305, + 475, + 545, + 507 + ], + "spans": [ + { + "bbox": [ + 305, + 475, + 545, + 507 + ], + "type": "text", + "content": "Table 5. Keypoint detector analysis. We analyse the standard deviation of the Gaussian functions (top), as well as the training loss function (bottom). " + }, + { + "bbox": [ + 305, + 475, + 545, + 507 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 305, + 475, + 545, + 507 + ], + "type": "text", + "content": " denotes the molecule bond length." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 320, + 508, + 535, + 570 + ], + "lines": [ + { + "bbox": [ + 320, + 508, + 535, + 570 + ], + "spans": [ + { + "bbox": [ + 320, + 508, + 535, + 570 + ], + "type": "table", + "html": "
USPTOJPOJPOp
Heatmap standard deviationb/581.354.746.8
b/1091.567.555.4
b/1591.464.751.6
Training lossL291.166.255.1
WAHR [18]91.567.555.4
", + "image_path": "3dca10a92e91517c54ac43cdc6d3e1a0eaaf3043aaa66b28daced7eddf4806fc.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "table_body" + } + ], + "index": 15 + }, + { + "type": "image", + "bbox": [ + 65, + 585, + 532, + 671 + ], + "blocks": [ + { + "bbox": [ + 65, + 585, + 532, + 671 + ], + "lines": [ + { + "bbox": [ + 65, + 585, + 532, + 671 + ], + "spans": [ + { + "bbox": [ + 65, + 585, + 532, + 671 + ], + "type": "image", + "image_path": "5dacef82858d2cfcd4183469519d103a6eb6de66bdbb40a23f2bb58fd7a4a8cd.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 678, + 545, + 712 + ], + "lines": [ + { + "bbox": [ + 46, + 678, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 678, + 545, + 712 + ], + "type": "text", + "content": "Figure 4. Prediction steps. Keypoints are detected and then used to build a supergraph. After classifying the nodes of the graph and recognizing abbreviated groups, the output molecule is created. In this example, the polycyclic molecule contains overlapping bonds, a challenging feature for OCSR models, and is still correctly recognized." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "19558" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 78, + 69, + 515, + 343 + ], + "blocks": [ + { + "bbox": [ + 78, + 69, + 515, + 343 + ], + "lines": [ + { + "bbox": [ + 78, + 69, + 515, + 343 + ], + "spans": [ + { + "bbox": [ + 78, + 69, + 515, + 343 + ], + "type": "image", + "image_path": "77527c0a258a629f927f0398f4f3ca3dcc00a03ae935097d21edff08cee4070f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 346, + 547, + 381 + ], + "lines": [ + { + "bbox": [ + 46, + 346, + 547, + 381 + ], + "spans": [ + { + "bbox": [ + 46, + 346, + 547, + 381 + ], + "type": "text", + "content": "Figure 5. Qualitative comparison. The figure shows examples of predictions for characteristic images from different benchmarks. Compared to previous rule-based and learning based methods, our approach robustly recognizes the exact molecular structure in challenging cases, such as with distracting captions, stereo-chemistry, and very large molecules." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 62, + 425, + 276, + 487 + ], + "blocks": [ + { + "bbox": [ + 47, + 391, + 288, + 424 + ], + "lines": [ + { + "bbox": [ + 47, + 391, + 288, + 424 + ], + "spans": [ + { + "bbox": [ + 47, + 391, + 288, + 424 + ], + "type": "text", + "content": "Table 6. Supergraph construction analysis. We analyse the maximum number of bond candidates (top), and the maximum search radius (bottom). " + }, + { + "bbox": [ + 47, + 391, + 288, + 424 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 47, + 391, + 288, + 424 + ], + "type": "text", + "content": " denotes the molecule bond length." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 62, + 425, + 276, + 487 + ], + "lines": [ + { + "bbox": [ + 62, + 425, + 276, + 487 + ], + "spans": [ + { + "bbox": [ + 62, + 425, + 276, + 487 + ], + "type": "table", + "html": "
USPTOJPOJPOp
Number bond candidates691.567.555.4
1091.065.754.1
Search radius3b91.567.555.4
5b91.365.053.1
", + "image_path": "cba94af9d3795111e662ede0be6b23cb6675e3107fac8a93fcbecd5946c399b1.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 61, + 529, + 276, + 601 + ], + "blocks": [ + { + "bbox": [ + 47, + 496, + 287, + 529 + ], + "lines": [ + { + "bbox": [ + 47, + 496, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 47, + 496, + 287, + 529 + ], + "type": "text", + "content": "Table 7. Node classifier analysis. We analyse the features representing graph nodes (top), and the usage of GCN layers (bottom). " + }, + { + "bbox": [ + 47, + 496, + 287, + 529 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 47, + 496, + 287, + 529 + ], + "type": "text", + "content": ": without abbreviated molecules and charges." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 61, + 529, + 276, + 601 + ], + "lines": [ + { + "bbox": [ + 61, + 529, + 276, + 601 + ], + "spans": [ + { + "bbox": [ + 61, + 529, + 276, + 601 + ], + "type": "table", + "html": "
USPTOJPOJPOp
Node embeddingVisual90.064.754.9
+ Type91.567.555.4
+ Position91.362.854.8
USPTO†JPO†JPOp†
Number of GCN Layers090.158.053.6
490.466.661.6
", + "image_path": "54949e9415cc745fec2df7245721e9dcd576b1bffb8a437b849eb4a2c9943082.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "content": "embedding but found it to reduce the overall performance. The model demonstrating, in average, best performances does not include GCN layers. However, as demonstrated in Table 7, for a limited evaluation setup, GCN layers have positive impact on performance, leading to significant gains of " + }, + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "inline_equation", + "content": "8.6\\%" + }, + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "inline_equation", + "content": "8.0\\%" + }, + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "content": " on JPO and " + }, + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathrm{JPO^p}" + }, + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "content": " when using 4 instead of 0 GCN layers. Note that even the version using 0 GNN layers, still employs our supergraph for feature aggregation" + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 315, + 392, + 549, + 460 + ], + "blocks": [ + { + "bbox": [ + 315, + 392, + 549, + 460 + ], + "lines": [ + { + "bbox": [ + 315, + 392, + 549, + 460 + ], + "spans": [ + { + "bbox": [ + 315, + 392, + 549, + 460 + ], + "type": "image", + "image_path": "e21ec738d6e38ef25682ea0cb246ad80e8ab0b548603c14d4fc4d7171f64b03a.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 467, + 547, + 522 + ], + "lines": [ + { + "bbox": [ + 304, + 467, + 547, + 522 + ], + "spans": [ + { + "bbox": [ + 304, + 467, + 547, + 522 + ], + "type": "text", + "content": "Figure 6. Ablation experiment. The figure shows MolGrapher predictions with and without using GCN layers, illustrating that GCN layers allow the model to learn chemistry rules. Indeed, the model correctly connect the oxygen atom highlighted in red to a double bond only." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 535, + 547, + 618 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 535, + 547, + 618 + ], + "spans": [ + { + "bbox": [ + 304, + 535, + 547, + 618 + ], + "type": "text", + "content": "and classification. The propagation of information through the graph is beneficial for challenging cases, such as the one illustrated in Figure 6. In this example, interpreting only the visual information would be misleading, even for humans. Understanding chemistry rules is mandatory to resolve the ambiguities in the drawing, which is correctly done by our model." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 633, + 379, + 645 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 633, + 379, + 645 + ], + "spans": [ + { + "bbox": [ + 306, + 633, + 379, + 645 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": "We propose a novel architecture for recognizing 2-D molecule depictions in documents by exploiting the natural graph representation of molecules and graph symmetries. Our model accurately detects atoms and bonds based on their visual features and local context, outperforming exist-" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "19559" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 133 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 133 + ], + "type": "text", + "content": "ing methods on standard benchmarks and our new USPTO-30K dataset. The model is trained on synthetic images and demonstrates strong generalization capabilities, making it useful at scale without requiring annotations for each journal or patent office." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 144, + 107, + 156 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 144, + 107, + 156 + ], + "spans": [ + { + "bbox": [ + 48, + 144, + 107, + 156 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 48, + 163, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 163, + 286, + 186 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 163, + 286, + 186 + ], + "spans": [ + { + "bbox": [ + 53, + 163, + 286, + 186 + ], + "type": "text", + "content": "[1] United states patent and trademark office. http://uspto.gov. Accessed: 1 January 2023." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 53, + 186, + 287, + 243 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 186, + 287, + 243 + ], + "spans": [ + { + "bbox": [ + 53, + 186, + 287, + 243 + ], + "type": "text", + "content": "[2] Syed Saqib Bukhari, Zaryab Iftikhar, and Andreas Dengel. Chemical structure recognition (csr) system: Automatic analysis of 2d chemical structures in document images. In 2019 International Conference on Document Analysis and Recognition (ICDAR), pages 1262-1267. IEEE, 9 2019." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 243, + 286, + 275 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 243, + 286, + 275 + ], + "spans": [ + { + "bbox": [ + 53, + 243, + 286, + 275 + ], + "type": "text", + "content": "[3] Daniel Campos and Heng Ji. IMG2SMI: translating molecular structure images to simplified molecular-input line-entry system. 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Bioinform., 23(2), March 2022." + } + ] + } + ], + "index": 16 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "19561" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Moment Detection in Long Tutorial Videos/d0d347cf-3a4a-4154-afe6-e8c1e6e24d00_content_list.json b/2023/Moment Detection in Long Tutorial Videos/d0d347cf-3a4a-4154-afe6-e8c1e6e24d00_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..9a2400396e801a8cb520d509d2d0dfbaee34bcb5 --- /dev/null +++ b/2023/Moment Detection in Long Tutorial Videos/d0d347cf-3a4a-4154-afe6-e8c1e6e24d00_content_list.json @@ -0,0 +1,1542 @@ +[ + { + "type": "text", + "text": "Moment Detection in Long Tutorial Videos", + "text_level": 1, + "bbox": [ + 267, + 130, + 702, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Ioana Croitoru\\* Simion-Vlad Bogolin3 Samuel Albanie2 Yang Liu4 Zhaowen Wang1 Seunghyun Yoon1 Franck Dernoncourt1 Hailin Jin1 Trung Bui1 1Adobe Research Department of Engineering, University of Cambridge 3 Filtir 4 Wangxuan Inst. of Computer Technology, Peking University", + "bbox": [ + 89, + 178, + 875, + 252 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 313, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Tutorial videos play an increasingly important role in professional development and self-directed education. For users to realise the full benefits of this medium, tutorial videos must be efficiently searchable. In this work, we focus on the task of moment detection, in which the goal is to localise the temporal window where a given event occurs within a given tutorial video. Prior work on moment detection has focused primarily on short videos (typically on videos shorter than three minutes). However, many tutorial videos are substantially longer (stretching to hours in duration), presenting significant challenges for existing moment detection approaches.", + "bbox": [ + 75, + 318, + 473, + 500 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To study this problem, we propose the first dataset of untrimmed, long-form tutorial videos for the task of Moment Detection called the Behance Moment Detection (BMD) dataset. BMD videos have an average duration of over one hour and are characterised by slowly evolving visual content and wide-ranging dialogue. To meet the unique challenges of this dataset, we propose a new framework, LONGMOMENT-DETR, and demonstrate that it outperforms strong baselines. Additionally, we introduce a variation of the dataset that contains YouTube Chapter annotations and show that the features obtained by our framework can be successfully used to boost the performance on the task of chapter detection. Code and data can be found at https://github.com/ioanacroi/longmoment-detr.", + "bbox": [ + 73, + 500, + 473, + 727 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 758, + 209, + 773 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Enabled by cheaper disk storage and networking technology, long-form videos of tutorial content are proliferating. As such, there is a pressing need to develop effective tools for searching within videos. In this work, we consider this problem through the lens of moment detection—given a video and a natural language query, our task is to find the", + "bbox": [ + 75, + 782, + 470, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d3bbdb4abdc8e2794bcf3cd34edd8b0025c741975c91beb7c56d864f07379873.jpg", + "image_caption": [ + "Figure 1. LONGMOMENT-DETR. Our framework performs moment detection and unlike previous state of the art methods, it works on long tutorial videos." + ], + "image_footnote": [], + "bbox": [ + 511, + 290, + 888, + 545 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "temporal span of the video that best matches the query (as shown in Fig. 1). Beyond tutorial content, this task also has applications in domains such as security and entertainment.", + "bbox": [ + 496, + 604, + 890, + 650 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To study moment detection in the long-form setting, we introduce, the first database of long tutorial videos with manual annotations for validation and testing, called Behance Moment Detection (BMD). The videos, which are collected from the Behance platform, consist of tutorial videos that teach skills with various creative tools such as drawing, movie editing, animation and photo editing.", + "bbox": [ + 496, + 650, + 892, + 755 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Existing moment detection datasets predominantly feature short videos centered on human activities, such as cooking or swimming. In contrast, our BMD dataset emphasizes long tutorial videos that explore the use of software tools for digital artistry. Typically, these tutorials involve screen-sharing sessions detailing creative processes, often spanning several hours. Efficiently localizing specific segments in such long videos can greatly enhance user nav", + "bbox": [ + 496, + 756, + 893, + 878 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Work done during an internship at Adobe. Now at V7 Labs.", + "bbox": [ + 99, + 886, + 423, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "1https://behance.net", + "bbox": [ + 517, + 886, + 676, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "2594", + "bbox": [ + 482, + 944, + 514, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "igation experience. This makes the BMD dataset unique for the task of moment detection. Moreover, to scale up training beyond costly manual annotation, we propose a framework for moment detection that leverages weak supervision derived from ASR (Automatic Speech Recognition) and video segmentation. In this new long video setup, using the timings from ASR, similar to previous works [24, 17], produces poor results, as we will show experimentally. So, in order to adjust for long videos setup, we rely on a mix of using video segmentation methods [36, 37] and summarization [50, 27, 5, 3] in order to generate good timings and textual descriptions to use for training.", + "bbox": [ + 75, + 90, + 468, + 271 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Lastly, in order to further validate our approach, we propose a second dataset, called YouTube Chapters (YTC) that contains full chapter annotation for all splits. In this way, we are able to assess the quality of the learnt features on BMD on the downstream task of chapter detection.", + "bbox": [ + 76, + 272, + 468, + 347 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We summarise our contributions as: (1) we introduce the first two long tutorial video datasets: Behance Moment Detection (BMD) a multi-modal dataset, suitable for weak supervision with manual annotations for validation and testing and YouTube Chapters (YTC) with chapters annotations for all splits (2) we propose an effective way to automatically generate moments for the training split of BMD that leverages Automatic Speech Recognition (ASR) and employs large language models (LLMs) to eliminate the inherent noise that appears in ASR. (3) we show the effectiveness of using BMD to improve the performance on the downstream task of YouTube chapter detection.", + "bbox": [ + 75, + 348, + 468, + 527 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Leveraging the multi-modal features of our new dataset and utilizing automatic annotations, we present LONGMOMENT-DETR, the first framework for moment detection in long tutorial videos consisting of the segment timing generator and query generator.", + "bbox": [ + 76, + 529, + 468, + 604 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 76, + 618, + 215, + 633 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Moment detection from video. Many works have been proposed for the task of moment localization [17, 24, 14, 12, 19]. There are two popular families of approaches for moment detection on short videos: two-stage approaches and one-stage approaches. In the two-stage approaches [28, 39, 51, 14, 9, 49, 47, 46], firstly a list of potential candidates is generated and then the candidates are ranked according to various scores. In the one-stage approaches [17, 24, 18, 19, 48], the methods directly process the entire video and output the moment localization. The most recent methods are based on the transformer encoder-decoder architecture. Additionally, the methods [24, 17] are designed to jointly predict moment detection and highlight detection, while [28] tackles zero-shot moment detection. [28] is tailored for short videos and it consists of various modules (temporal event proposal, object detector, pseudoquery generation module). For our use case, running an", + "bbox": [ + 75, + 643, + 470, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "object detector is highly expensive, since the videos are very long. Moreover, the produced results are usually of poor quality for tutorial videos since general object detectors are not tailored for this type of content where the host shares their screen and presents how to use specific software applications. Very recently, [29, 30] propose architectural changes to accommodate for long-formed videos, specifically within the movie domain. However, given the scarcity of datasets dedicated to long videos, particularly those with lengthy segments, this area remains underexplored. To address this issue, we are the first to propose the task of moment detection in long tutorial videos, along with two datasets containing very long untrimmed tutorial videos: one having manual segments annotations for evaluation (Behance Moment Detection) and the other having YouTube Chapters annotations for all splits.", + "bbox": [ + 496, + 90, + 890, + 330 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Large Language Models (LLMs). These models are trained on vastly large corpora of text consisting of tens of TB of data and have shown surprising zero-shot capabilities on a variety of NLP tasks [50, 3, 27, 40, 34, 6]. Notable among these are OPT175B [50], Bloom175B [38], and GPT3 [3], each boasting roughly 175B parameters. While GPT3 is available only through a paid API, OPT and Bloom models are open-source and are freely accessible to the research community. Even without task-specific finetuning, they exhibit strong zero-shot performance on multiple NLP benchmarks [20, 35, 10]. A distinguishing trait of LLMs is their prompt-driven adaptability to varied tasks. In our case, for tutorial videos, the available transcripts, although informative, can be noisy. These transcripts, generated using efficient automatic speech recognition tools [32, 2], are refined by LLMs, which we employ to extract relevant information and eliminate noise.", + "bbox": [ + 496, + 332, + 890, + 588 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Video segmentation. The task of temporal video segmentation aims to split the whole video into smaller sub-videos based on the semantic content. This is an important task in computer vision, being an essential pre-processing step for various other video understanding downstream tasks, such as video retrieval, moment detection or video summarization. In our case, we aim to use such models for segment timing generation. Various methods have been proposed for this task [44, 37, 36, 45], however they are designed and trained on short videos databases [42, 13]. Because of this, we have chosen to use unsupervised temporal video segmentation methods [36, 37, 15], that do not require retraining for our particular case.", + "bbox": [ + 496, + 589, + 890, + 785 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Dataset", + "text_level": 1, + "bbox": [ + 500, + 800, + 589, + 814 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Both datasets, Behance Moment Detection (BMD) and YouTube Chapters (YTC), consist of long tutorial videos and are collected from the Behance platform. These are the first two datasets containing untrimmed, long-form tutorial videos for the tasks of moment detection and chapters detec", + "bbox": [ + 496, + 825, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "2595", + "bbox": [ + 482, + 944, + 514, + 957 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/8451a0959d6ae1aeb125809c2a27d786a801c0bf0efd7e16860023746595eb80.jpg", + "image_caption": [ + "Figure 2. Behavior Moment Detection example. We propose a moment retrieval dataset containing long tutorial videos. Each video is split into multiple segments and each segment has an associated query. We highlight with green the moment associated to the given query." + ], + "image_footnote": [], + "bbox": [ + 91, + 125, + 877, + 215 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "tion, respectively. While these tasks are important in videos of any duration, moment localization in long-form tutorial videos can add extra value since it improves the user experience and eases video navigation by saving significant searching time (for example a user can only be interested where a specific character is drawn, but it is time-consuming to find that part in a long video).", + "bbox": [ + 75, + 258, + 470, + 364 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The validation and testing splits of BMD are manually annotated, while the training split is automatically curated. For YTC, we sourced human-annotated chapters from YouTube. All data is publicly accessible online.", + "bbox": [ + 75, + 364, + 468, + 425 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Behance Moment Detection", + "text_level": 1, + "bbox": [ + 76, + 436, + 326, + 452 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We collected videos from Behance Livestream, a platform for creative users who share their work, having over 30 million users. The videos from our dataset were livestreamed and then made publicly available on the platform. We choose Behance since the videos are of high quality with relatively little noise and the type of the videos are aligned with our target videos, namely long tutorial videos. The usual flow for these videos is: 1) the host greets the viewers and talks about what they will showcase in the video (usually they show how to use different creative apps such as Adobe Fresco or Photoshop), 2) the host shares their screen and 3) they start using the chosen app while talking and giving useful tips and details about the creative process. For example, the host can use drawing tools for creating cartoon characters or can showcase how to use video editing tools for creating a movie, how to add shadows, etc. One such example can be seen in Fig. 2. These tutorial livestreams are usually very long, the majority being over one hour long, as presented in Fig. 3. The videos represent source materials that teach skills for educational purposes. There are thousands of long tutorial videos available on Behance and there are thousands more on other video platforms such as YouTube, which can directly benefit from our method of moment detection in long videos.", + "bbox": [ + 75, + 460, + 470, + 824 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In Tab. 1 we present a comparison with other moment detection datasets. There is a striking difference when comparing the average length of the videos and of the segments with other existing datasets. There is only one other dataset which contains long videos, namely the MAD [41] dataset.", + "bbox": [ + 75, + 825, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/05cb36704a5d80366d280902842df5c08c83756476418550394c603d1f53f3a1.jpg", + "image_caption": [ + "Figure 3. Histogram of video duration. The majority of the videos in the BMD dataset are longer than one hour." + ], + "image_footnote": [], + "bbox": [ + 516, + 261, + 870, + 391 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "MAD contains videos extracted from movies and leverages the audio descriptions of movies for visually impaired audiences, having the average length of the segment of around 4.1s, while ours has a much longer segment duration of over 17 minutes. This makes our dataset more suitable for downstream tasks, such as chapter detection. Another major difference is that the videos from our datasets are untrimmed, while for some other datasets such as QVHighlights [17], the videos are automatically split into 3-minute segments. This can result in loss of context or some actions being trimmed in an unnatural way, which can lead to annotations issues. The BMD dataset contains over 13,000 hours of videos (with over 630 hours of human-annotated videos). There are 7.9k videos used for training, 117 for validation and 171 for testing. While other moment retrieval datasets suffer from temporal biases [14, 9, 19] where the segments tend to occur in the beginning of the video, our dataset contains segments that span the entire video. All the videos in the dataset have transcripts, extracted with Azure speech-to-text. On average each transcript contains 1500 sentences.", + "bbox": [ + 496, + 430, + 892, + 733 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Validation and testing split. For the validation and testing splits we outsourced the annotation task to a specialised company having a team of qualified and experienced annotators. The annotators were asked to watch the tutorial video, segment it into high-level chapters and write a natural language description for each segment. The description is a brief summary of what happens in the segment and should contain no more than a few sentences. The cost for annotating the validation and testing split was approximately $10,000 and took around 3 months for the 288 videos.", + "bbox": [ + 496, + 734, + 890, + 883 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Training split. Due to the high cost of collecting the an-", + "bbox": [ + 500, + 885, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "header", + "text": "Query: \"The host starts sketching a teddy and also adds details to the sketch.\"", + "bbox": [ + 153, + 102, + 746, + 118 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "2596", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "table", + "img_path": "images/ac17011797878684a54bcab7f9b04fb7f7e41e18a22aab7c1b12feca19547693.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DatasetDomain#videos#queriesAvg len videos(sec)Avg len segmentTotal number of hours
DiDeMo [14]Flickr10.6k41.2K29.36.588
ActivityNet [16]Activity15K72K117.636.2490
CharadesSTA [12]Activity6.7k16.1K30.68.157
TVR [19]TV show21.8K109K76.29.1461
QVHighlights [17]Vlog/News10.2K10.3K15024.6425
MAD [41]Movies650384.6K6646(1.8 hours)4.11207.3
BMD-Train†Livestream7.9K35.9K5768 (1.6 hours)1022 (17 mins)12.7k
BMD-EvalLivestream28814997957 (2.2 hours)1537 (25.6 mins)638
YouTube ChaptersLivestream46743916472 (1.8 hours)687 (11.5 mins)840
", + "bbox": [ + 81, + 90, + 893, + 242 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Table 1. Comparison between BMD and YTC to existing moment retrieval datasets. The segments from our datasets are significantly longer than the ones from any other existing datasets. Moreover, in our datasets the segments span the entire duration of the video eliminating potential biases. ${}^{ \\dagger }$ BMD-Train contains automatically curated annotation.", + "bbox": [ + 75, + 246, + 892, + 289 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "notations, the training set was annotated automatically by leveraging the transcript together with pretrained large language models. Since the videos are livestreamed, the host interacts with the viewers and verbally explains the steps involved in the creative process for making digital art, including a detailed description of what they create or how to efficiently use the tools to obtain the desired outcome. While parts of the transcripts are extremely informative regarding what is happening in the video, there is also a lot of noise, which includes redundant information or information that is irrelevant to the tutorial (for example chit-chat about events that happened lately). Because the average length of the transcript is around 1500 sentences, we need an efficient way of condensing and extracting the relevant information. We achieve this by using GPT3 through the API provided by OpenAI. This incurs an additional cost of approximately $1,000 for all training videos. More details about the summarization procedure and a detailed comparison between different LLMs can be found in Sec. 4.3.", + "bbox": [ + 75, + 303, + 472, + 589 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "While this gives us the ability to generate high-quality queries for the segments, another challenge is how to generate timings and split the video into meaningful parts. This step is equally important and affects the final performance of the model as we will show later. In order to address this challenge, we considered various state-of-the-art methods for video segmentation [36, 37] in order to generate segment timings. As the final model, we use the OSG [36] method. More details can be found in Sec. 4.3.", + "bbox": [ + 75, + 590, + 468, + 726 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. YouTube Chapters", + "text_level": 1, + "bbox": [ + 76, + 739, + 256, + 757 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Recently, YouTube introduced the functionality to add video chapters as a way to improve the user experience, especially for long videos. The creator of the video has the possibility to segment the video into several sections and to add a short description to each section. This facilitates easy rewatching or skipping to the desired content in the video. Some of the videos from our Behance Moment Detection dataset are also published on the YouTube platform and contain manual chapter labels. In order to further", + "bbox": [ + 75, + 763, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "test the quality of our method, we collected chapter annotations from almost 500 videos (379 in training, 17 in validation and 71 in the testing split). Most of the visual content of the videos from YouTube Chapters already exists in the Behance Moment Detection dataset, which assures the fact that the videos are from the domain we are interested in (namely tutorial videos). However, there are clear differences between the two annotations. Firstly, the queries from YouTube Chapters are very brief and consist of just a few words (such as How to remove chromatic aberration or Creating GIFs in Photoshop) while the annotations from BMD dataset are fully formed sentences describing the actions happening in that segment of the video, as presented in Fig. 4. Secondly, the temporal segmentation of the video is different (the average segment length in BMD is approx. 20 minutes long, while in YTC is approx. 11 minutes long, as illustrated in Tab. 1), thus being a domain gap between the BMD and YTC annotations.", + "bbox": [ + 496, + 303, + 893, + 575 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Method", + "text_level": 1, + "bbox": [ + 500, + 602, + 589, + 618 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We first define the task of moment retrieval in long tutorial videos (Sec. 4.1). Then, we introduce our full framework (Sec. 4.2), providing additional insights about our automatic moment generation pipeline (Sec. 4.3). Finally, we present architecture details (Sec. 4.4) and elaborate about our design choices.", + "bbox": [ + 496, + 632, + 893, + 724 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Task definition", + "text_level": 1, + "bbox": [ + 500, + 747, + 650, + 762 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Given a video $v = \\{f_1, f_2, \\dots, f_V\\}$ (where $f_i$ represents the $i$ -th frame of the video) and a query $q$ in natural language, the objective of moment detection is to find the pair $(i,j), i < j$ so that the video segment starting at $f_i$ and finishing at $f_j$ is best described by the query $q$ . Our goal is to train a model that receives as input the whole video $v$ and query $q$ and outputs the start and end time $(i,j)$ .", + "bbox": [ + 496, + 773, + 893, + 881 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Let $D = \\{v_l | l = 1..N\\}$ be a dataset of $N$ videos with", + "bbox": [ + 517, + 883, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "2597", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "segment annotations $A = \\bigcup_{l = 1}^{N}A_{l}$ where", + "bbox": [ + 76, + 88, + 339, + 121 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nA _ {l} = \\left\\{\\left(q _ {k}, \\left(i _ {k}, j _ {k}\\right)\\right) | f _ {i _ {k}}, f _ {j _ {k}} \\in v _ {l}, i _ {k} < j _ {k}, k = 1.. Q _ {l} \\right\\}\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 137, + 452, + 156 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "denotes the segment annotations for video $v_{l}$ . $Q_{l}$ represents the number of segments in $v_{l}$ while $q_{k}$ represents the query written in natural language for the segment starting at $i_{k}$ and finishing at $j_{k}$ . In order to train the model $M$ for the task of moment detection we use a similar setup as Moment-DETR [17], which is described in more detail in Sec. 4.4.", + "bbox": [ + 75, + 169, + 468, + 258 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. The LONGMOMENT-DETR framework", + "text_level": 1, + "bbox": [ + 76, + 273, + 397, + 287 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In Algorithm 1 we present the process for our LONGMOMENT-DETR framework. Since the cost (both time and financial resources) of collecting manual annotations for thousands of videos is high, an effective way of decreasing this cost is to curate automatic annotations for the training split $D$ . After gathering the videos from the Behance platform, the first step is to automatically generate the transcripts from the audio modality using the Azure speech recognition tool. Next, the videos are split into several segments representing different key parts of the video. After having the timings for the segments, we use the corresponding transcript for that timespan and we summarize it in order to extract the essential information. We then proceed to train our final model $M$ using a standard approach for this task, similarly to [17].", + "bbox": [ + 75, + 299, + 472, + 526 + ], + "page_idx": 4 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [ + "Algorithm 1 LONGMOMENT-DETR framework" + ], + "code_body": "1: Phase 1: generate Moment Annotations $(D) \\to A$ \n2: $A = \\emptyset$ \n3: for video $v_{l}$ in $D$ do \n4: Generate transcript $s_l$ for $v_{l}$ \n5: $T_{l} = \\text{segmentsGeneration}(v_{l})$ \n6: $A_{l} = \\emptyset$ \n7: for timing $(i_k, j_k) \\in T_l$ do \n8: $q_{k} = \\text{queryGeneration}((i_k, j_k), s_l)$ \n9: Add $(q_k, (i_k, j_k))$ to $A_{l}$ \n10: end for \n11: $A = A \\cup A_l$ \n12: end for \n13: Phase 2: Train the final model, $M$ \n14: for minibatch of paired samples $(v, a)$ , $a = (q_k, (i_k, j_k)) \\in A, v \\in D$ do \n15: Extract video features $x$ from $v$ \n16: Extract text features $p_k$ from $q_k$ \n17: Feed $x$ and $q_k$ to $M$ and get output $o$ . \n18: Compute the loss between $o$ and $(i_k, j_k)$ . \n19: Update $M$ base on loss \n20: end for", + "bbox": [ + 81, + 561, + 472, + 878 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Moment generation", + "text_level": 1, + "bbox": [ + 500, + 90, + 687, + 106 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Our approach has two steps: segments timing generation and query generation which will be discussed next.", + "bbox": [ + 498, + 114, + 890, + 143 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Segment timing generation. Temporally segmenting the video according to topics is an important step in our pipeline which affects the final performance of the system. We considered and compared various potential solutions: starting directly from using the timings given by the speech recognition tool or splitting the video into random segments to using state of the art unsupervised methods such as OSG [36] and ONG [37]. The last two video segmentation methods receive as input the video features (in our case, SlowFast [11] features) and a parameter $s$ , representing the number of segments to split the video in. For choosing the parameter $s$ , we tested two approaches: estimate the number of segments based on SVD (as described in [36]) or using a constant. Based on the results of these experiments (for full results, see Sec. 5.2) for the final method we use OSG [36] with five scenes per video. This step acts as the segmentsGeneration function in Algorithm 1.", + "bbox": [ + 496, + 143, + 890, + 400 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Query generation. For this task, the simplest approach is to use directly the transcript. However, while parts of the transcript are quite informative, it also contains noise and information that is not relevant to the visual content or to the tutorial (for example the host may converse about the weather). It would therefore be useful to have an automatic method to extract a condensed version of the relevant information from the transcript associated with a video segment. For this, we considered various techniques such as extractive summarization [5] or using large language models (LLMs). Models such as Bloom175B [27], OPT175B [50] and GPT3 [3] are able to perform a large variety of tasks, including summarization and information extraction from large chunks of text. We begin by concatenating all the sentences from the transcript that span during the start and end time of a segment proposal and feed it to the language model along with the instructions to summarize the text. We used the following prompt: \"Summarize this tutorial transcript:\" In Sec. 5.2 we present detailed ablations studies between different summarization methods. For the final model, we used GPT3 (Curie model) to obtain the query for each generated segment. In cases where the segment transcript is too long to be processed by GPT3, the final query is the concatenation of several splits of the transcript, each processed by GPT3 independently. This step acts as the queryGeneration function in Algorithm 1.", + "bbox": [ + 496, + 401, + 892, + 792 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.4. Architecture details", + "text_level": 1, + "bbox": [ + 500, + 801, + 687, + 816 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We start from the Moment-DETR [17] architecture which uses an encoder-decoder transformer [43] and is based on the DETR architecture [4]. The model receives as input the concatenation between the video and text features and outputs the center and width of the predicted moment.", + "bbox": [ + 496, + 824, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "2598", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/13a45c82dc2cdb7c4f26dbc30b15c4897145532b2600022fe0ac39d998a7657c.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Method#scenesPrecisionRecallF1
Transcript timing20097.88.715.0
Random split554.571.653.5
ONG [37]SVD48.1986.7043.42
OSG [36]SVD67.0876.4557.18
ONG [37]545.9589.2142.69
OSG [36]562.1783.3759.51
", + "bbox": [ + 101, + 88, + 450, + 183 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/de3ac7779c9ed5b49daa8cc276e1f18ff779d4e975b6dc4cf0ae91b5ba8751c1.jpg", + "table_caption": [ + "Table 2. Comparison of different video segmentation methods. Using directly the timings from the transcript has very poor results, while OSG performs the best in terms of F1 score." + ], + "table_footnote": [], + "table_body": "
Segmentation MethodR1@0.5 ↑R1@0.7 ↑
Transcript timing3.1±0.40.5±0.2
Random9.4±1.62.6±0.8
ONG7.1±0.61.7±1.4
OSG13.4±0.56.3±0.3
", + "bbox": [ + 120, + 232, + 431, + 306 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "One limitation of [17] is that it assumes the video has a length of 3 minutes. In order to make it suitable for running on longer videos, we adjust the meta-parameters and make low-level changes to the model implementation such as removing hard-coded constraints. Please see Suppl.Mat. for more details. This modified version becomes the architecture used in our whole LONGMOMENT-DETR framework. For features, we employ SlowFast [11] video understanding features extracted every 8 seconds and GPT2-x1 [33] features for the text.", + "bbox": [ + 75, + 380, + 467, + 530 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation details. Our model is trained in PyTorch, using the AdamW optimizer [25] with a learning rate of 1e-4 and weight decay of 1e-4. All the models were trained on an NVIDIA A100 GPU. Due to memory limitations, we trained the model with a batch size of 16.", + "bbox": [ + 75, + 532, + 467, + 607 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 76, + 622, + 207, + 638 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Metrics", + "text_level": 1, + "bbox": [ + 76, + 647, + 171, + 662 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We report the standard metrics used in moment detection: $R1@0.5$ and $R1@0.7$ , where a prediction is considered correct if it has an intersection over union (IoU) with the ground truth $\\geq 0.5$ , respectively $\\geq 0.7$ . When it comes to assessing the performance of video segmentation methods we report the standard metrics for this task: precision, recall and F1-score, while for comparing query generations we report the ROUGE metrics [22] which are commonly used for the task of summarization [26, 8, 1] and are proven to have a good correlation with the human judgment [23].", + "bbox": [ + 75, + 670, + 467, + 821 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. Ablations", + "text_level": 1, + "bbox": [ + 76, + 830, + 187, + 845 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For all the ablation experiments, we report results on the validation split, unless otherwise stated.", + "bbox": [ + 76, + 854, + 467, + 883 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Segment timing generation. We begin by testing several", + "bbox": [ + 76, + 885, + 467, + 900 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/acca61d69d69963c374c1107cd87d18fbc74c204b02c600cc2e78441d95e3b13.jpg", + "table_caption": [ + "Table 3. Comparison between different video segmentation methods combined with LONGMOMENT-DETR. The timings generation has a direct impact on performance. The number of scenes considered as input parameter for OSG and ONG is 5." + ], + "table_footnote": [], + "table_body": "
MethodR-1R-2R-L
Transcript2.310.341.85
Captioning BLIP [21]7.560.56.8
Extractive [5]8.540.596.17
Bloom175B [38]9.090.527.36
OPT175B [50]10.990.748.23
GPT3 [3]15.491.3611.85
", + "bbox": [ + 544, + 89, + 852, + 194 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 4. Evaluation of query generation using ROUGE metrics. We assess the performance of different query generation methods. The transcript, being significantly longer than the human annotation, has a low score, while the LLMs perform the best.", + "bbox": [ + 498, + 199, + 890, + 255 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "methods and assess their video segmentation performance in Tab. 2. This performance correlates with the moment detection results shown in Tab. 3. Moreover, we observe that following prior works [17, 24] and using only the timings from the transcripts gives poor results. This is expected, since for BMD the average segment length is considerably longer than the segment obtained from transcript timing. In fact, just by randomly splitting the video into 5 segments, the performance improves significantly. We obtain the best results using the OSG [36] video segmentation method using five scenes.", + "bbox": [ + 496, + 273, + 890, + 439 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Query generation. Another important step in our method is automatic query generation. Since the image and video captioning systems are trained on visual data that is out of domain as compared to our tutorial videos, we expect those systems to perform worse than the systems based on textual information. In Tab. 4 we present summarization results as compared to the human annotation for the validation split and observe that GPT3 obtains the best results. Also, in Fig. 4 we present a qualitative example for the query generation task using LLMs.", + "bbox": [ + 496, + 441, + 890, + 593 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In Tab. 5 we present results for LONGMOMENT-DETR using various query generation techniques. The best score is obtained using the GPT3 model which correlates with the results from Tab. 4. However, while there is a correlation between the results, we notice that there is a significantly smaller gap between the performance of using LLMs such as Bloom175B or OPT175B and using the raw transcript for the task of moment detection. An explanation for this, is that even though the transcript is very long, which directly affects the ROUGE score, for the task of moment detection it contains enough relevant information in order to make up for the differences in performance. For the final model, we use the GPT3 model as the query generation method.", + "bbox": [ + 496, + 595, + 890, + 792 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Influence of pre-trained features. Our model receives at input pre-trained features for both the visual and textual component. For this ablation study, we assess the influence of such features on the final performance as seen in Tab. 6. For the visual side, we consider the SlowFast [11] and CLIP [31] features while for the textual side, we consider GPT2-x1 [33], DiffCSE [7] and CLIP [31]. The best", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "2599", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/a74e8ae578983d21427a52b02dfe3d6e7dc0e8f9b9b39a5e4b0ffdf34d37ed55.jpg", + "image_caption": [ + "Figure 4. Comparison of summaries generated by GPT3, OPT175B and Bloom175B. During the summarization process no human annotation was used. In this figure, the human description and video frames are shown only for reference. While the AI generated summaries are obtained only from the transcript, the human had access to the whole video and audio when making the annotation." + ], + "image_footnote": [], + "bbox": [ + 86, + 95, + 284, + 181 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/4233b2dc8e1bf5ee1609e3f912227287c045e687327e350b02c93ca3fddbb601.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 285, + 95, + 483, + 181 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/34fe41ba686d07da24165b0a6bb195446f67b9c34086b5a542ba7e64f3462e9d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 486, + 95, + 683, + 181 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/59ffd2cf74231eeb0693444782a95ff474f1bdc29b55a0b3751fabcb93d31d1b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 684, + 95, + 883, + 181 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Human: \"The host starts working on the video on After effect. The host sync the video with music and sync the movement of the arm to the music. The host adjust the animation movement of the flag according to the action of the arm.\"", + "bbox": [ + 102, + 194, + 856, + 220 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "GPT3: \"In this tutorial, the speaker demonstrates how to animate a character's hand using the software After Effects. This tutorial is about creating an animation in which a character's arms move up and down in time with a beat.\"", + "bbox": [ + 102, + 222, + 856, + 250 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "OPT: \"I wanted to take you through the process Learn how to improve the animation and timing in your 3D walk cycle by using the graph editor. First learn the basics of changing a keyframe. Finally, learn the In this tutorial, you learned how to add a simple effect to your hand movements.\"", + "bbox": [ + 102, + 250, + 856, + 291 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Bloom: \"How to make a simple animation in After Effects. We learned how to create a simple animation using the Pen Tool, how to add a simple text animation. how to make a cartoon character walk in After Effects. We learned how to create a simple walk cycle, how to animate the walk cycle.\"", + "bbox": [ + 102, + 292, + 856, + 333 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/71aad53ed804878ecb4ce6812a9e6aa1003ee7b19dc284c2e05431bdc88987d8.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Summ MethodR1@0.5↑R1@0.7↑
Transcript13.6±0.56.3±0.3
Bloom175B13.4±0.67.0±0.2
OPT175B14.0±0.66.7±0.8
GPT316.8±0.59.2±1.0
", + "bbox": [ + 148, + 397, + 401, + 468 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/806306f5875e38f84efef5c8031a70808285d34442e77f55598676fbebdfd446.jpg", + "table_caption": [ + "Table 5. Comparison between different LLM query generation methods in conjunction with LONGMOMENT-DETR. As it can be seen, GPT3 performs the best. What is interesting is that by using the raw transcript, the performance is only slightly worse than using other power full summarization methods such as Bloom175B and OPT175B." + ], + "table_footnote": [], + "table_body": "
Video featsText featsR1@0.5 ↑R1@0.7 ↑
SlowFastGPT2-x116.8±0.59.2±1.0
SlowFastDiffCSE13.1±1.56.5±1.2
SlowFastCLIP11.2±0.74.9±0.9
CLIPCLIP12.7±0.66.2±0.3
CLIPGPT2-x113.8±1.27.1±1.8
CLIPDiffCSE13.8±1.97.5±0.7
", + "bbox": [ + 120, + 558, + 429, + 656 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "results are obtained using SlowFast for the visual side and GPT2-x1 for the textual side.", + "bbox": [ + 75, + 718, + 468, + 746 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Influence of different components. In Tab. 7 we present an overview of the influence of different components on the testing split (the results on validation split are presented previously in each corresponding section). We start with a Moment-DETR [17] model as Baseline. We observe that both the segment timing generation and the query generation have a strong impact on performance. We obtain the best results by combining the timing generation from OSG with the GPT3 query generation which represents our final LONGMOMENT-DETR framework.", + "bbox": [ + 75, + 750, + 468, + 898 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/fb36dde4cebfc1aa8836ae851f8972e2b6ea399d29ba91c1db5ac20a992e5f8a.jpg", + "table_caption": [ + "Table 6. Influence of pre-trained features on performance. The best performance is obtained using SlowFast features for the visual side and GPT2-xl features for the textual side." + ], + "table_footnote": [], + "table_body": "
ComponentSegmentsQueriesR1@0.5↑R1@0.7↑
Baseline [17]NoNo2.7±0.60.3±0.1
Random segRandomNo9.2±1.82.6±0.4
SummarizeRandomGPT313.2±0.35.6±0.6
ShotDetectOSGNo12.6±0.45.5±0.4
LONGMOMENT-DETROSGGPT316.3±0.38.3±0.5
", + "bbox": [ + 504, + 398, + 890, + 474 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 7. Effect of different components on performance. Both the segment timing generation and query generation have a strong impact on performance. Hence, in the final model, we use OSG and GPT3, thus obtaining our final model LONGMOMENT-DETR. The results are presented on the testing split.", + "bbox": [ + 498, + 478, + 890, + 549 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Comparison with others", + "text_level": 1, + "bbox": [ + 500, + 564, + 720, + 580 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we compare our method against two recent methods: Moment-DETR [17] and UMT [24] adjusted for ingesting long videos. For UMT we use the video only version as introduced in the paper [24]. This comparison can be seen in Tab. 8. By training using the raw transcripts, which is similar to the pre-training stage of [17], the results in our case for long tutorial videos are poor. However, by adjusting the base architecture and use the automatic generated segments tailored for long videos, the results improve significantly for Moment-DETR as observed in the table. Moreover, if we use our full LONGMOMENT-DETR framework, as described in Sec. 4.2, the results are significantly better than previously published methods.", + "bbox": [ + 496, + 589, + 890, + 785 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.4. YouTube Chapters", + "text_level": 1, + "bbox": [ + 500, + 799, + 679, + 815 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To further evaluate the quality of our features obtained using the automatic annotations, we have collected new data from YouTube Chapters as described in Sec. 3.2.", + "bbox": [ + 496, + 823, + 890, + 868 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Experimental setup. We initially train the network using BMD. Once trained, these weights serve as the founda", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "2600", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "BMD Query: \"The host colors the cow with lime yellow color and a part of the body of the cow is colored with brown color. The nose of the cow is colored with skin color. A few skin color strokes are added to the coat of the cow. The background of the cow is added with green color to the grass and sky blue color to the sky.\"", + "bbox": [ + 106, + 95, + 872, + 132 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9513679795b762d5223ccf57999c82b327e787c620a1a144dc936c6850cc66d5.jpg", + "image_caption": [ + "(A)" + ], + "image_footnote": [], + "bbox": [ + 109, + 137, + 883, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2d129fe2a1df8ef345a9fa4f7fc5d02d98723d1c9963cb2eaaaa063d2f4f310a.jpg", + "image_caption": [ + "(B)", + "Figure 5. Qualitative examples for BMD (A) and YTC (B). Along with the query, we show several video frames, the prediction results in orange and the ground truth in green. We also specify the overlap between the prediction and ground truth segments. Please note how different the queries between BMD and YTC are. Also, while the prediction results have an offset from the ground truth, we want to highlight how subtle is the change in scenery for our proposed datasets." + ], + "image_footnote": [], + "bbox": [ + 109, + 223, + 883, + 320 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/888a7b24c2e2aa2dcf44d1cb0dc4f40db626063eef2f1f557b89f8d827ad5b00.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelR1@0.5↑R1@0.7↑
Moment-DETR [17]2.7±0.60.3±0.1
UMT [24]†11.5±1.04.6±1.3
Moment-DETR [17]†12.6±0.45.5±0.4
LONGMOMENT-DETR16.3±0.38.3±0.5
", + "bbox": [ + 120, + 406, + 431, + 479 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "tion for fine-tuning on the subsequent task of chapter detection. While the BMD training data is automatically curated, when we transition to training on the manually annotated data from the YTC dataset, we distinguish this model by referring to it as CHAPTER-DETR. This model uses the same architecture as LONGMOMENT-DETR.", + "bbox": [ + 75, + 575, + 468, + 666 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Results. The results for chapter detection are presented in Tab. 9. We observe that when only pre-training on BMD and directly assessing performance, the performance is low, the main reason being the distribution shift between the queries and segments in BMD and the ones in YTC. The queries from BMD are often composed of several sentences while the chapter annotation only contains a few words (as showcased in Fig. 5). However, if we first pre-train on BMD and then finetune with chapter annotations, there is a major boost in performance. These results prove that not only LONGMOMENT-DETR can be used on its own for moment detection, but it can be used to significantly improve the performance for the task of chapter detection.", + "bbox": [ + 75, + 670, + 470, + 866 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitations. Since our method relies on automatic annotation generation, various problems such as text hallucination", + "bbox": [ + 75, + 869, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/a9a5a213c05d7a92e596c2af87ae6f6918f5a6c2b249fff3baa2fad5ac467434.jpg", + "table_caption": [ + "Table 8. Comparison with other methods. As it can be seen, LONGMOMENT-DETR achieves better results than other moment detection methods. $\\dagger$ denotes training the models with the timings obtained by our proposed method using OSG. The results are presented on the testing split." + ], + "table_footnote": [], + "table_body": "
ModelPre-trainingTrainingR1@0.5 ↑R1@0.7 ↑
LONGMOMENT-DETRBMD-5.0±2.42.2±1.5
CHAPTER-DETR-YTC12.6±0.35.8±0.6
CHAPTER-DETRBMDYTC16.1±0.56.6±0.3
", + "bbox": [ + 503, + 407, + 890, + 459 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 9. Results on YouTube-Chapters. If we evaluate LONGMOMENT-DETR trained with BMD directly on the task of chapter detection on the YTC dataset, the performance is low. However, if we use BMD as pre-training data and then train fully supervised for the task of chapter detection, there is a significant boost in performance as opposed to randomly initializing the model (4th line vs 3rd line).", + "bbox": [ + 498, + 463, + 892, + 559 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "or incorrect segment timing generation directly affect the results of our system. Other limitations regarding particular components are discussed throughout the paper.", + "bbox": [ + 496, + 574, + 890, + 619 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Societal impact. Moment retrieval systems enable efficient content discovery for learning. However, these systems can exhibit biases towards particular groups or they can be used for spreading misinformation. Another aspect is the notable cost and carbon footprint required to train modern models.", + "bbox": [ + 496, + 619, + 890, + 695 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusions", + "text_level": 1, + "bbox": [ + 500, + 709, + 627, + 724 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper we presented the LONGMOMENT-DETR framework which tackles the task of moment detection in long tutorial videos. We introduced, the first two long tutorial video datasets, Behance Moment Detection (BMD) and YouTube Chapters (YTC). BMD has human annotations for testing and validation splits and we propose a novel system to automatically curate the annotations for the training split by leveraging the information from the transcript. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 15555-15564, 2022. 2" + ], + "bbox": [ + 78, + 90, + 468, + 763 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "2604", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Moment Detection in Long Tutorial Videos/d0d347cf-3a4a-4154-afe6-e8c1e6e24d00_model.json b/2023/Moment Detection in Long Tutorial Videos/d0d347cf-3a4a-4154-afe6-e8c1e6e24d00_model.json new file mode 100644 index 0000000000000000000000000000000000000000..86919111701bba663eca8383d7d1370cd6192edd --- /dev/null +++ b/2023/Moment Detection in Long Tutorial Videos/d0d347cf-3a4a-4154-afe6-e8c1e6e24d00_model.json @@ -0,0 +1,2125 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.268, + 0.131, + 0.703, + 0.154 + ], + "angle": 0, + "content": "Moment Detection in Long Tutorial Videos" + }, + { + "type": "text", + "bbox": [ + 0.09, + 0.179, + 0.877, + 0.253 + ], + "angle": 0, + "content": "Ioana Croitoru\\* Simion-Vlad Bogolin3 Samuel Albanie2 Yang Liu4 Zhaowen Wang1 Seunghyun Yoon1 Franck Dernoncourt1 Hailin Jin1 Trung Bui1 1Adobe Research Department of Engineering, University of Cambridge 3 Filtir 4 Wangxuan Inst. of Computer Technology, Peking University" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.319, + 0.474, + 0.501 + ], + "angle": 0, + "content": "Tutorial videos play an increasingly important role in professional development and self-directed education. For users to realise the full benefits of this medium, tutorial videos must be efficiently searchable. In this work, we focus on the task of moment detection, in which the goal is to localise the temporal window where a given event occurs within a given tutorial video. Prior work on moment detection has focused primarily on short videos (typically on videos shorter than three minutes). However, many tutorial videos are substantially longer (stretching to hours in duration), presenting significant challenges for existing moment detection approaches." + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.501, + 0.474, + 0.728 + ], + "angle": 0, + "content": "To study this problem, we propose the first dataset of untrimmed, long-form tutorial videos for the task of Moment Detection called the Behance Moment Detection (BMD) dataset. BMD videos have an average duration of over one hour and are characterised by slowly evolving visual content and wide-ranging dialogue. To meet the unique challenges of this dataset, we propose a new framework, LONGMOMENT-DETR, and demonstrate that it outperforms strong baselines. Additionally, we introduce a variation of the dataset that contains YouTube Chapter annotations and show that the features obtained by our framework can be successfully used to boost the performance on the task of chapter detection. Code and data can be found at https://github.com/ioanacroi/longmoment-detr." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.759, + 0.21, + 0.774 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.784, + 0.471, + 0.876 + ], + "angle": 0, + "content": "Enabled by cheaper disk storage and networking technology, long-form videos of tutorial content are proliferating. As such, there is a pressing need to develop effective tools for searching within videos. In this work, we consider this problem through the lens of moment detection—given a video and a natural language query, our task is to find the" + }, + { + "type": "image", + "bbox": [ + 0.513, + 0.291, + 0.889, + 0.546 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.553, + 0.895, + 0.595 + ], + "angle": 0, + "content": "Figure 1. LONGMOMENT-DETR. Our framework performs moment detection and unlike previous state of the art methods, it works on long tutorial videos." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.606, + 0.892, + 0.651 + ], + "angle": 0, + "content": "temporal span of the video that best matches the query (as shown in Fig. 1). Beyond tutorial content, this task also has applications in domains such as security and entertainment." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.651, + 0.893, + 0.756 + ], + "angle": 0, + "content": "To study moment detection in the long-form setting, we introduce, the first database of long tutorial videos with manual annotations for validation and testing, called Behance Moment Detection (BMD). The videos, which are collected from the Behance platform, consist of tutorial videos that teach skills with various creative tools such as drawing, movie editing, animation and photo editing." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.757, + 0.895, + 0.879 + ], + "angle": 0, + "content": "Existing moment detection datasets predominantly feature short videos centered on human activities, such as cooking or swimming. In contrast, our BMD dataset emphasizes long tutorial videos that explore the use of software tools for digital artistry. Typically, these tutorials involve screen-sharing sessions detailing creative processes, often spanning several hours. Efficiently localizing specific segments in such long videos can greatly enhance user nav" + }, + { + "type": "page_footnote", + "bbox": [ + 0.101, + 0.887, + 0.424, + 0.9 + ], + "angle": 0, + "content": "*Work done during an internship at Adobe. Now at V7 Labs." + }, + { + "type": "page_footnote", + "bbox": [ + 0.518, + 0.887, + 0.678, + 0.9 + ], + "angle": 0, + "content": "1https://behance.net" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.958 + ], + "angle": 0, + "content": "2594" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.272 + ], + "angle": 0, + "content": "igation experience. This makes the BMD dataset unique for the task of moment detection. Moreover, to scale up training beyond costly manual annotation, we propose a framework for moment detection that leverages weak supervision derived from ASR (Automatic Speech Recognition) and video segmentation. In this new long video setup, using the timings from ASR, similar to previous works [24, 17], produces poor results, as we will show experimentally. So, in order to adjust for long videos setup, we rely on a mix of using video segmentation methods [36, 37] and summarization [50, 27, 5, 3] in order to generate good timings and textual descriptions to use for training." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.273, + 0.47, + 0.348 + ], + "angle": 0, + "content": "Lastly, in order to further validate our approach, we propose a second dataset, called YouTube Chapters (YTC) that contains full chapter annotation for all splits. In this way, we are able to assess the quality of the learnt features on BMD on the downstream task of chapter detection." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.349, + 0.47, + 0.529 + ], + "angle": 0, + "content": "We summarise our contributions as: (1) we introduce the first two long tutorial video datasets: Behance Moment Detection (BMD) a multi-modal dataset, suitable for weak supervision with manual annotations for validation and testing and YouTube Chapters (YTC) with chapters annotations for all splits (2) we propose an effective way to automatically generate moments for the training split of BMD that leverages Automatic Speech Recognition (ASR) and employs large language models (LLMs) to eliminate the inherent noise that appears in ASR. (3) we show the effectiveness of using BMD to improve the performance on the downstream task of YouTube chapter detection." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.53, + 0.47, + 0.606 + ], + "angle": 0, + "content": "Leveraging the multi-modal features of our new dataset and utilizing automatic annotations, we present LONGMOMENT-DETR, the first framework for moment detection in long tutorial videos consisting of the segment timing generator and query generator." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.619, + 0.216, + 0.635 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Moment detection from video. Many works have been proposed for the task of moment localization [17, 24, 14, 12, 19]. There are two popular families of approaches for moment detection on short videos: two-stage approaches and one-stage approaches. In the two-stage approaches [28, 39, 51, 14, 9, 49, 47, 46], firstly a list of potential candidates is generated and then the candidates are ranked according to various scores. In the one-stage approaches [17, 24, 18, 19, 48], the methods directly process the entire video and output the moment localization. The most recent methods are based on the transformer encoder-decoder architecture. Additionally, the methods [24, 17] are designed to jointly predict moment detection and highlight detection, while [28] tackles zero-shot moment detection. [28] is tailored for short videos and it consists of various modules (temporal event proposal, object detector, pseudoquery generation module). For our use case, running an" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.332 + ], + "angle": 0, + "content": "object detector is highly expensive, since the videos are very long. Moreover, the produced results are usually of poor quality for tutorial videos since general object detectors are not tailored for this type of content where the host shares their screen and presents how to use specific software applications. Very recently, [29, 30] propose architectural changes to accommodate for long-formed videos, specifically within the movie domain. However, given the scarcity of datasets dedicated to long videos, particularly those with lengthy segments, this area remains underexplored. To address this issue, we are the first to propose the task of moment detection in long tutorial videos, along with two datasets containing very long untrimmed tutorial videos: one having manual segments annotations for evaluation (Behance Moment Detection) and the other having YouTube Chapters annotations for all splits." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.333, + 0.892, + 0.589 + ], + "angle": 0, + "content": "Large Language Models (LLMs). These models are trained on vastly large corpora of text consisting of tens of TB of data and have shown surprising zero-shot capabilities on a variety of NLP tasks [50, 3, 27, 40, 34, 6]. Notable among these are OPT175B [50], Bloom175B [38], and GPT3 [3], each boasting roughly 175B parameters. While GPT3 is available only through a paid API, OPT and Bloom models are open-source and are freely accessible to the research community. Even without task-specific finetuning, they exhibit strong zero-shot performance on multiple NLP benchmarks [20, 35, 10]. A distinguishing trait of LLMs is their prompt-driven adaptability to varied tasks. In our case, for tutorial videos, the available transcripts, although informative, can be noisy. These transcripts, generated using efficient automatic speech recognition tools [32, 2], are refined by LLMs, which we employ to extract relevant information and eliminate noise." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.59, + 0.892, + 0.786 + ], + "angle": 0, + "content": "Video segmentation. The task of temporal video segmentation aims to split the whole video into smaller sub-videos based on the semantic content. This is an important task in computer vision, being an essential pre-processing step for various other video understanding downstream tasks, such as video retrieval, moment detection or video summarization. In our case, we aim to use such models for segment timing generation. Various methods have been proposed for this task [44, 37, 36, 45], however they are designed and trained on short videos databases [42, 13]. Because of this, we have chosen to use unsupervised temporal video segmentation methods [36, 37, 15], that do not require retraining for our particular case." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.801, + 0.59, + 0.815 + ], + "angle": 0, + "content": "3. Dataset" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Both datasets, Behance Moment Detection (BMD) and YouTube Chapters (YTC), consist of long tutorial videos and are collected from the Behance platform. These are the first two datasets containing untrimmed, long-form tutorial videos for the tasks of moment detection and chapters detec" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.958 + ], + "angle": 0, + "content": "2595" + } + ], + [ + { + "type": "header", + "bbox": [ + 0.155, + 0.103, + 0.747, + 0.119 + ], + "angle": 0, + "content": "Query: \"The host starts sketching a teddy and also adds details to the sketch.\"" + }, + { + "type": "image", + "bbox": [ + 0.093, + 0.126, + 0.878, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.217, + 0.895, + 0.247 + ], + "angle": 0, + "content": "Figure 2. Behavior Moment Detection example. We propose a moment retrieval dataset containing long tutorial videos. Each video is split into multiple segments and each segment has an associated query. We highlight with green the moment associated to the given query." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.259, + 0.471, + 0.365 + ], + "angle": 0, + "content": "tion, respectively. While these tasks are important in videos of any duration, moment localization in long-form tutorial videos can add extra value since it improves the user experience and eases video navigation by saving significant searching time (for example a user can only be interested where a specific character is drawn, but it is time-consuming to find that part in a long video)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.365, + 0.47, + 0.426 + ], + "angle": 0, + "content": "The validation and testing splits of BMD are manually annotated, while the training split is automatically curated. For YTC, we sourced human-annotated chapters from YouTube. All data is publicly accessible online." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.438, + 0.327, + 0.453 + ], + "angle": 0, + "content": "3.1. Behance Moment Detection" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.462, + 0.471, + 0.825 + ], + "angle": 0, + "content": "We collected videos from Behance Livestream, a platform for creative users who share their work, having over 30 million users. The videos from our dataset were livestreamed and then made publicly available on the platform. We choose Behance since the videos are of high quality with relatively little noise and the type of the videos are aligned with our target videos, namely long tutorial videos. The usual flow for these videos is: 1) the host greets the viewers and talks about what they will showcase in the video (usually they show how to use different creative apps such as Adobe Fresco or Photoshop), 2) the host shares their screen and 3) they start using the chosen app while talking and giving useful tips and details about the creative process. For example, the host can use drawing tools for creating cartoon characters or can showcase how to use video editing tools for creating a movie, how to add shadows, etc. One such example can be seen in Fig. 2. These tutorial livestreams are usually very long, the majority being over one hour long, as presented in Fig. 3. The videos represent source materials that teach skills for educational purposes. There are thousands of long tutorial videos available on Behance and there are thousands more on other video platforms such as YouTube, which can directly benefit from our method of moment detection in long videos." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.47, + 0.902 + ], + "angle": 0, + "content": "In Tab. 1 we present a comparison with other moment detection datasets. There is a striking difference when comparing the average length of the videos and of the segments with other existing datasets. There is only one other dataset which contains long videos, namely the MAD [41] dataset." + }, + { + "type": "image", + "bbox": [ + 0.517, + 0.262, + 0.872, + 0.392 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.393, + 0.892, + 0.421 + ], + "angle": 0, + "content": "Figure 3. Histogram of video duration. The majority of the videos in the BMD dataset are longer than one hour." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.431, + 0.893, + 0.734 + ], + "angle": 0, + "content": "MAD contains videos extracted from movies and leverages the audio descriptions of movies for visually impaired audiences, having the average length of the segment of around 4.1s, while ours has a much longer segment duration of over 17 minutes. This makes our dataset more suitable for downstream tasks, such as chapter detection. Another major difference is that the videos from our datasets are untrimmed, while for some other datasets such as QVHighlights [17], the videos are automatically split into 3-minute segments. This can result in loss of context or some actions being trimmed in an unnatural way, which can lead to annotations issues. The BMD dataset contains over 13,000 hours of videos (with over 630 hours of human-annotated videos). There are 7.9k videos used for training, 117 for validation and 171 for testing. While other moment retrieval datasets suffer from temporal biases [14, 9, 19] where the segments tend to occur in the beginning of the video, our dataset contains segments that span the entire video. All the videos in the dataset have transcripts, extracted with Azure speech-to-text. On average each transcript contains 1500 sentences." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.884 + ], + "angle": 0, + "content": "Validation and testing split. For the validation and testing splits we outsourced the annotation task to a specialised company having a team of qualified and experienced annotators. The annotators were asked to watch the tutorial video, segment it into high-level chapters and write a natural language description for each segment. The description is a brief summary of what happens in the segment and should contain no more than a few sentences. The cost for annotating the validation and testing split was approximately $10,000 and took around 3 months for the 288 videos." + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.886, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Training split. Due to the high cost of collecting the an-" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2596" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.091, + 0.894, + 0.243 + ], + "angle": 0, + "content": "
DatasetDomain#videos#queriesAvg len videos(sec)Avg len segmentTotal number of hours
DiDeMo [14]Flickr10.6k41.2K29.36.588
ActivityNet [16]Activity15K72K117.636.2490
CharadesSTA [12]Activity6.7k16.1K30.68.157
TVR [19]TV show21.8K109K76.29.1461
QVHighlights [17]Vlog/News10.2K10.3K15024.6425
MAD [41]Movies650384.6K6646(1.8 hours)4.11207.3
BMD-Train†Livestream7.9K35.9K5768 (1.6 hours)1022 (17 mins)12.7k
BMD-EvalLivestream28814997957 (2.2 hours)1537 (25.6 mins)638
YouTube ChaptersLivestream46743916472 (1.8 hours)687 (11.5 mins)840
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.247, + 0.893, + 0.29 + ], + "angle": 0, + "content": "Table 1. Comparison between BMD and YTC to existing moment retrieval datasets. The segments from our datasets are significantly longer than the ones from any other existing datasets. Moreover, in our datasets the segments span the entire duration of the video eliminating potential biases. \\( {}^{ \\dagger } \\) BMD-Train contains automatically curated annotation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.304, + 0.473, + 0.59 + ], + "angle": 0, + "content": "notations, the training set was annotated automatically by leveraging the transcript together with pretrained large language models. Since the videos are livestreamed, the host interacts with the viewers and verbally explains the steps involved in the creative process for making digital art, including a detailed description of what they create or how to efficiently use the tools to obtain the desired outcome. While parts of the transcripts are extremely informative regarding what is happening in the video, there is also a lot of noise, which includes redundant information or information that is irrelevant to the tutorial (for example chit-chat about events that happened lately). Because the average length of the transcript is around 1500 sentences, we need an efficient way of condensing and extracting the relevant information. We achieve this by using GPT3 through the API provided by OpenAI. This incurs an additional cost of approximately $1,000 for all training videos. More details about the summarization procedure and a detailed comparison between different LLMs can be found in Sec. 4.3." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.592, + 0.47, + 0.727 + ], + "angle": 0, + "content": "While this gives us the ability to generate high-quality queries for the segments, another challenge is how to generate timings and split the video into meaningful parts. This step is equally important and affects the final performance of the model as we will show later. In order to address this challenge, we considered various state-of-the-art methods for video segmentation [36, 37] in order to generate segment timings. As the final model, we use the OSG [36] method. More details can be found in Sec. 4.3." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.741, + 0.258, + 0.758 + ], + "angle": 0, + "content": "3.2. YouTube Chapters" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Recently, YouTube introduced the functionality to add video chapters as a way to improve the user experience, especially for long videos. The creator of the video has the possibility to segment the video into several sections and to add a short description to each section. This facilitates easy rewatching or skipping to the desired content in the video. Some of the videos from our Behance Moment Detection dataset are also published on the YouTube platform and contain manual chapter labels. In order to further" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.304, + 0.895, + 0.576 + ], + "angle": 0, + "content": "test the quality of our method, we collected chapter annotations from almost 500 videos (379 in training, 17 in validation and 71 in the testing split). Most of the visual content of the videos from YouTube Chapters already exists in the Behance Moment Detection dataset, which assures the fact that the videos are from the domain we are interested in (namely tutorial videos). However, there are clear differences between the two annotations. Firstly, the queries from YouTube Chapters are very brief and consist of just a few words (such as How to remove chromatic aberration or Creating GIFs in Photoshop) while the annotations from BMD dataset are fully formed sentences describing the actions happening in that segment of the video, as presented in Fig. 4. Secondly, the temporal segmentation of the video is different (the average segment length in BMD is approx. 20 minutes long, while in YTC is approx. 11 minutes long, as illustrated in Tab. 1), thus being a domain gap between the BMD and YTC annotations." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.603, + 0.591, + 0.619 + ], + "angle": 0, + "content": "4. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.633, + 0.894, + 0.725 + ], + "angle": 0, + "content": "We first define the task of moment retrieval in long tutorial videos (Sec. 4.1). Then, we introduce our full framework (Sec. 4.2), providing additional insights about our automatic moment generation pipeline (Sec. 4.3). Finally, we present architecture details (Sec. 4.4) and elaborate about our design choices." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.748, + 0.651, + 0.763 + ], + "angle": 0, + "content": "4.1. Task definition" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.775, + 0.894, + 0.882 + ], + "angle": 0, + "content": "Given a video \\( v = \\{f_1, f_2, \\dots, f_V\\} \\) (where \\( f_i \\) represents the \\( i \\)-th frame of the video) and a query \\( q \\) in natural language, the objective of moment detection is to find the pair \\( (i,j), i < j \\) so that the video segment starting at \\( f_i \\) and finishing at \\( f_j \\) is best described by the query \\( q \\). Our goal is to train a model that receives as input the whole video \\( v \\) and query \\( q \\) and outputs the start and end time \\( (i,j) \\)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.885, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Let \\( D = \\{v_l | l = 1..N\\} \\) be a dataset of \\( N \\) videos with" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2597" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.089, + 0.341, + 0.122 + ], + "angle": 0, + "content": "segment annotations \\(A = \\bigcup_{l = 1}^{N}A_{l}\\) where" + }, + { + "type": "equation", + "bbox": [ + 0.093, + 0.138, + 0.454, + 0.157 + ], + "angle": 0, + "content": "\\[\nA _ {l} = \\left\\{\\left(q _ {k}, \\left(i _ {k}, j _ {k}\\right)\\right) | f _ {i _ {k}}, f _ {j _ {k}} \\in v _ {l}, i _ {k} < j _ {k}, k = 1.. Q _ {l} \\right\\}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.17, + 0.47, + 0.26 + ], + "angle": 0, + "content": "denotes the segment annotations for video \\( v_{l} \\). \\( Q_{l} \\) represents the number of segments in \\( v_{l} \\) while \\( q_{k} \\) represents the query written in natural language for the segment starting at \\( i_{k} \\) and finishing at \\( j_{k} \\). In order to train the model \\( M \\) for the task of moment detection we use a similar setup as Moment-DETR [17], which is described in more detail in Sec. 4.4." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.275, + 0.398, + 0.289 + ], + "angle": 0, + "content": "4.2. The LONGMOMENT-DETR framework" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.3, + 0.473, + 0.527 + ], + "angle": 0, + "content": "In Algorithm 1 we present the process for our LONGMOMENT-DETR framework. Since the cost (both time and financial resources) of collecting manual annotations for thousands of videos is high, an effective way of decreasing this cost is to curate automatic annotations for the training split \\( D \\). After gathering the videos from the Behance platform, the first step is to automatically generate the transcripts from the audio modality using the Azure speech recognition tool. Next, the videos are split into several segments representing different key parts of the video. After having the timings for the segments, we use the corresponding transcript for that timespan and we summarize it in order to extract the essential information. We then proceed to train our final model \\( M \\) using a standard approach for this task, similarly to [17]." + }, + { + "type": "code_caption", + "bbox": [ + 0.08, + 0.544, + 0.4, + 0.559 + ], + "angle": 0, + "content": "Algorithm 1 LONGMOMENT-DETR framework" + }, + { + "type": "algorithm", + "bbox": [ + 0.083, + 0.562, + 0.473, + 0.88 + ], + "angle": 0, + "content": "1: Phase 1: generate Moment Annotations \\((D) \\to A\\) \n2: \\(A = \\emptyset\\) \n3: for video \\(v_{l}\\) in \\(D\\) do \n4: Generate transcript \\(s_l\\) for \\(v_{l}\\) \n5: \\(T_{l} = \\text{segmentsGeneration}(v_{l})\\) \n6: \\(A_{l} = \\emptyset\\) \n7: for timing \\((i_k, j_k) \\in T_l\\) do \n8: \\(q_{k} = \\text{queryGeneration}((i_k, j_k), s_l)\\) \n9: Add \\((q_k, (i_k, j_k))\\) to \\(A_{l}\\) \n10: end for \n11: \\(A = A \\cup A_l\\) \n12: end for \n13: Phase 2: Train the final model, \\(M\\) \n14: for minibatch of paired samples \\((v, a)\\), \\(a = (q_k, (i_k, j_k)) \\in A, v \\in D\\) do \n15: Extract video features \\(x\\) from \\(v\\) \n16: Extract text features \\(p_k\\) from \\(q_k\\) \n17: Feed \\(x\\) and \\(q_k\\) to \\(M\\) and get output \\(o\\). \n18: Compute the loss between \\(o\\) and \\((i_k, j_k)\\). \n19: Update \\(M\\) base on loss \n20: end for" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.689, + 0.107 + ], + "angle": 0, + "content": "4.3. Moment generation" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.115, + 0.892, + 0.144 + ], + "angle": 0, + "content": "Our approach has two steps: segments timing generation and query generation which will be discussed next." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.145, + 0.892, + 0.401 + ], + "angle": 0, + "content": "Segment timing generation. Temporally segmenting the video according to topics is an important step in our pipeline which affects the final performance of the system. We considered and compared various potential solutions: starting directly from using the timings given by the speech recognition tool or splitting the video into random segments to using state of the art unsupervised methods such as OSG [36] and ONG [37]. The last two video segmentation methods receive as input the video features (in our case, SlowFast [11] features) and a parameter \\( s \\), representing the number of segments to split the video in. For choosing the parameter \\( s \\), we tested two approaches: estimate the number of segments based on SVD (as described in [36]) or using a constant. Based on the results of these experiments (for full results, see Sec. 5.2) for the final method we use OSG [36] with five scenes per video. This step acts as the segmentsGeneration function in Algorithm 1." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.402, + 0.893, + 0.794 + ], + "angle": 0, + "content": "Query generation. For this task, the simplest approach is to use directly the transcript. However, while parts of the transcript are quite informative, it also contains noise and information that is not relevant to the visual content or to the tutorial (for example the host may converse about the weather). It would therefore be useful to have an automatic method to extract a condensed version of the relevant information from the transcript associated with a video segment. For this, we considered various techniques such as extractive summarization [5] or using large language models (LLMs). Models such as Bloom175B [27], OPT175B [50] and GPT3 [3] are able to perform a large variety of tasks, including summarization and information extraction from large chunks of text. We begin by concatenating all the sentences from the transcript that span during the start and end time of a segment proposal and feed it to the language model along with the instructions to summarize the text. We used the following prompt: \"Summarize this tutorial transcript:\" In Sec. 5.2 we present detailed ablations studies between different summarization methods. For the final model, we used GPT3 (Curie model) to obtain the query for each generated segment. In cases where the segment transcript is too long to be processed by GPT3, the final query is the concatenation of several splits of the transcript, each processed by GPT3 independently. This step acts as the queryGeneration function in Algorithm 1." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.802, + 0.689, + 0.817 + ], + "angle": 0, + "content": "4.4. Architecture details" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We start from the Moment-DETR [17] architecture which uses an encoder-decoder transformer [43] and is based on the DETR architecture [4]. The model receives as input the concatenation between the video and text features and outputs the center and width of the predicted moment." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2598" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.102, + 0.089, + 0.451, + 0.184 + ], + "angle": 0, + "content": "
Method#scenesPrecisionRecallF1
Transcript timing20097.88.715.0
Random split554.571.653.5
ONG [37]SVD48.1986.7043.42
OSG [36]SVD67.0876.4557.18
ONG [37]545.9589.2142.69
OSG [36]562.1783.3759.51
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.188, + 0.468, + 0.229 + ], + "angle": 0, + "content": "Table 2. Comparison of different video segmentation methods. Using directly the timings from the transcript has very poor results, while OSG performs the best in terms of F1 score." + }, + { + "type": "table", + "bbox": [ + 0.121, + 0.233, + 0.432, + 0.307 + ], + "angle": 0, + "content": "
Segmentation MethodR1@0.5 ↑R1@0.7 ↑
Transcript timing3.1±0.40.5±0.2
Random9.4±1.62.6±0.8
ONG7.1±0.61.7±1.4
OSG13.4±0.56.3±0.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.311, + 0.47, + 0.368 + ], + "angle": 0, + "content": "Table 3. Comparison between different video segmentation methods combined with LONGMOMENT-DETR. The timings generation has a direct impact on performance. The number of scenes considered as input parameter for OSG and ONG is 5." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.381, + 0.468, + 0.531 + ], + "angle": 0, + "content": "One limitation of [17] is that it assumes the video has a length of 3 minutes. In order to make it suitable for running on longer videos, we adjust the meta-parameters and make low-level changes to the model implementation such as removing hard-coded constraints. Please see Suppl.Mat. for more details. This modified version becomes the architecture used in our whole LONGMOMENT-DETR framework. For features, we employ SlowFast [11] video understanding features extracted every 8 seconds and GPT2-x1 [33] features for the text." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.533, + 0.468, + 0.608 + ], + "angle": 0, + "content": "Implementation details. Our model is trained in PyTorch, using the AdamW optimizer [25] with a learning rate of 1e-4 and weight decay of 1e-4. All the models were trained on an NVIDIA A100 GPU. Due to memory limitations, we trained the model with a batch size of 16." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.623, + 0.208, + 0.64 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.648, + 0.173, + 0.663 + ], + "angle": 0, + "content": "5.1. Metrics" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.671, + 0.468, + 0.822 + ], + "angle": 0, + "content": "We report the standard metrics used in moment detection: \\( R1@0.5 \\) and \\( R1@0.7 \\), where a prediction is considered correct if it has an intersection over union (IoU) with the ground truth \\( \\geq 0.5 \\), respectively \\( \\geq 0.7 \\). When it comes to assessing the performance of video segmentation methods we report the standard metrics for this task: precision, recall and F1-score, while for comparing query generations we report the ROUGE metrics [22] which are commonly used for the task of summarization [26, 8, 1] and are proven to have a good correlation with the human judgment [23]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.832, + 0.188, + 0.847 + ], + "angle": 0, + "content": "5.2. Ablations" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.468, + 0.884 + ], + "angle": 0, + "content": "For all the ablation experiments, we report results on the validation split, unless otherwise stated." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.886, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Segment timing generation. We begin by testing several" + }, + { + "type": "table", + "bbox": [ + 0.545, + 0.09, + 0.853, + 0.195 + ], + "angle": 0, + "content": "
MethodR-1R-2R-L
Transcript2.310.341.85
Captioning BLIP [21]7.560.56.8
Extractive [5]8.540.596.17
Bloom175B [38]9.090.527.36
OPT175B [50]10.990.748.23
GPT3 [3]15.491.3611.85
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.2, + 0.892, + 0.256 + ], + "angle": 0, + "content": "Table 4. Evaluation of query generation using ROUGE metrics. We assess the performance of different query generation methods. The transcript, being significantly longer than the human annotation, has a low score, while the LLMs perform the best." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.275, + 0.892, + 0.44 + ], + "angle": 0, + "content": "methods and assess their video segmentation performance in Tab. 2. This performance correlates with the moment detection results shown in Tab. 3. Moreover, we observe that following prior works [17, 24] and using only the timings from the transcripts gives poor results. This is expected, since for BMD the average segment length is considerably longer than the segment obtained from transcript timing. In fact, just by randomly splitting the video into 5 segments, the performance improves significantly. We obtain the best results using the OSG [36] video segmentation method using five scenes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.443, + 0.892, + 0.594 + ], + "angle": 0, + "content": "Query generation. Another important step in our method is automatic query generation. Since the image and video captioning systems are trained on visual data that is out of domain as compared to our tutorial videos, we expect those systems to perform worse than the systems based on textual information. In Tab. 4 we present summarization results as compared to the human annotation for the validation split and observe that GPT3 obtains the best results. Also, in Fig. 4 we present a qualitative example for the query generation task using LLMs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.597, + 0.892, + 0.793 + ], + "angle": 0, + "content": "In Tab. 5 we present results for LONGMOMENT-DETR using various query generation techniques. The best score is obtained using the GPT3 model which correlates with the results from Tab. 4. However, while there is a correlation between the results, we notice that there is a significantly smaller gap between the performance of using LLMs such as Bloom175B or OPT175B and using the raw transcript for the task of moment detection. An explanation for this, is that even though the transcript is very long, which directly affects the ROUGE score, for the task of moment detection it contains enough relevant information in order to make up for the differences in performance. For the final model, we use the GPT3 model as the query generation method." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Influence of pre-trained features. Our model receives at input pre-trained features for both the visual and textual component. For this ablation study, we assess the influence of such features on the final performance as seen in Tab. 6. For the visual side, we consider the SlowFast [11] and CLIP [31] features while for the textual side, we consider GPT2-x1 [33], DiffCSE [7] and CLIP [31]. The best" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2599" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.097, + 0.285, + 0.183 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.287, + 0.097, + 0.484, + 0.183 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.487, + 0.097, + 0.684, + 0.183 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.686, + 0.097, + 0.885, + 0.183 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.104, + 0.195, + 0.857, + 0.222 + ], + "angle": 0, + "content": "Human: \"The host starts working on the video on After effect. The host sync the video with music and sync the movement of the arm to the music. The host adjust the animation movement of the flag according to the action of the arm.\"" + }, + { + "type": "text", + "bbox": [ + 0.104, + 0.223, + 0.857, + 0.251 + ], + "angle": 0, + "content": "GPT3: \"In this tutorial, the speaker demonstrates how to animate a character's hand using the software After Effects. This tutorial is about creating an animation in which a character's arms move up and down in time with a beat.\"" + }, + { + "type": "text", + "bbox": [ + 0.104, + 0.251, + 0.857, + 0.292 + ], + "angle": 0, + "content": "OPT: \"I wanted to take you through the process Learn how to improve the animation and timing in your 3D walk cycle by using the graph editor. First learn the basics of changing a keyframe. Finally, learn the In this tutorial, you learned how to add a simple effect to your hand movements.\"" + }, + { + "type": "text", + "bbox": [ + 0.104, + 0.293, + 0.857, + 0.334 + ], + "angle": 0, + "content": "Bloom: \"How to make a simple animation in After Effects. We learned how to create a simple animation using the Pen Tool, how to add a simple text animation. how to make a cartoon character walk in After Effects. We learned how to create a simple walk cycle, how to animate the walk cycle.\"" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.345, + 0.892, + 0.387 + ], + "angle": 0, + "content": "Figure 4. Comparison of summaries generated by GPT3, OPT175B and Bloom175B. During the summarization process no human annotation was used. In this figure, the human description and video frames are shown only for reference. While the AI generated summaries are obtained only from the transcript, the human had access to the whole video and audio when making the annotation." + }, + { + "type": "table", + "bbox": [ + 0.149, + 0.398, + 0.402, + 0.469 + ], + "angle": 0, + "content": "
Summ MethodR1@0.5↑R1@0.7↑
Transcript13.6±0.56.3±0.3
Bloom175B13.4±0.67.0±0.2
OPT175B14.0±0.66.7±0.8
GPT316.8±0.59.2±1.0
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.473, + 0.47, + 0.555 + ], + "angle": 0, + "content": "Table 5. Comparison between different LLM query generation methods in conjunction with LONGMOMENT-DETR. As it can be seen, GPT3 performs the best. What is interesting is that by using the raw transcript, the performance is only slightly worse than using other power full summarization methods such as Bloom175B and OPT175B." + }, + { + "type": "table", + "bbox": [ + 0.122, + 0.559, + 0.43, + 0.657 + ], + "angle": 0, + "content": "
Video featsText featsR1@0.5 ↑R1@0.7 ↑
SlowFastGPT2-x116.8±0.59.2±1.0
SlowFastDiffCSE13.1±1.56.5±1.2
SlowFastCLIP11.2±0.74.9±0.9
CLIPCLIP12.7±0.66.2±0.3
CLIPGPT2-x113.8±1.27.1±1.8
CLIPDiffCSE13.8±1.97.5±0.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.662, + 0.47, + 0.703 + ], + "angle": 0, + "content": "Table 6. Influence of pre-trained features on performance. The best performance is obtained using SlowFast features for the visual side and GPT2-xl features for the textual side." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.719, + 0.469, + 0.747 + ], + "angle": 0, + "content": "results are obtained using SlowFast for the visual side and GPT2-x1 for the textual side." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.47, + 0.9 + ], + "angle": 0, + "content": "Influence of different components. In Tab. 7 we present an overview of the influence of different components on the testing split (the results on validation split are presented previously in each corresponding section). We start with a Moment-DETR [17] model as Baseline. We observe that both the segment timing generation and the query generation have a strong impact on performance. We obtain the best results by combining the timing generation from OSG with the GPT3 query generation which represents our final LONGMOMENT-DETR framework." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.4, + 0.892, + 0.475 + ], + "angle": 0, + "content": "
ComponentSegmentsQueriesR1@0.5↑R1@0.7↑
Baseline [17]NoNo2.7±0.60.3±0.1
Random segRandomNo9.2±1.82.6±0.4
SummarizeRandomGPT313.2±0.35.6±0.6
ShotDetectOSGNo12.6±0.45.5±0.4
LONGMOMENT-DETROSGGPT316.3±0.38.3±0.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.479, + 0.892, + 0.55 + ], + "angle": 0, + "content": "Table 7. Effect of different components on performance. Both the segment timing generation and query generation have a strong impact on performance. Hence, in the final model, we use OSG and GPT3, thus obtaining our final model LONGMOMENT-DETR. The results are presented on the testing split." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.565, + 0.722, + 0.581 + ], + "angle": 0, + "content": "5.3. Comparison with others" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.59, + 0.892, + 0.786 + ], + "angle": 0, + "content": "In this section, we compare our method against two recent methods: Moment-DETR [17] and UMT [24] adjusted for ingesting long videos. For UMT we use the video only version as introduced in the paper [24]. This comparison can be seen in Tab. 8. By training using the raw transcripts, which is similar to the pre-training stage of [17], the results in our case for long tutorial videos are poor. However, by adjusting the base architecture and use the automatic generated segments tailored for long videos, the results improve significantly for Moment-DETR as observed in the table. Moreover, if we use our full LONGMOMENT-DETR framework, as described in Sec. 4.2, the results are significantly better than previously published methods." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.8, + 0.681, + 0.816 + ], + "angle": 0, + "content": "5.4. YouTube Chapters" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.824, + 0.892, + 0.869 + ], + "angle": 0, + "content": "To further evaluate the quality of our features obtained using the automatic annotations, we have collected new data from YouTube Chapters as described in Sec. 3.2." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Experimental setup. We initially train the network using BMD. Once trained, these weights serve as the founda" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2600" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.107, + 0.096, + 0.873, + 0.133 + ], + "angle": 0, + "content": "BMD Query: \"The host colors the cow with lime yellow color and a part of the body of the cow is colored with brown color. The nose of the cow is colored with skin color. A few skin color strokes are added to the coat of the cow. The background of the cow is added with green color to the grass and sky blue color to the sky.\"" + }, + { + "type": "image_caption", + "bbox": [ + 0.085, + 0.167, + 0.108, + 0.185 + ], + "angle": 0, + "content": "(A)" + }, + { + "type": "image", + "bbox": [ + 0.111, + 0.138, + 0.885, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.086, + 0.269, + 0.108, + 0.284 + ], + "angle": 0, + "content": "(B)" + }, + { + "type": "image", + "bbox": [ + 0.111, + 0.224, + 0.884, + 0.321 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.075, + 0.327, + 0.893, + 0.385 + ], + "angle": 0, + "content": "Figure 5. Qualitative examples for BMD (A) and YTC (B). Along with the query, we show several video frames, the prediction results in orange and the ground truth in green. We also specify the overlap between the prediction and ground truth segments. Please note how different the queries between BMD and YTC are. Also, while the prediction results have an offset from the ground truth, we want to highlight how subtle is the change in scenery for our proposed datasets." + }, + { + "type": "table", + "bbox": [ + 0.121, + 0.407, + 0.432, + 0.48 + ], + "angle": 0, + "content": "
ModelR1@0.5↑R1@0.7↑
Moment-DETR [17]2.7±0.60.3±0.1
UMT [24]†11.5±1.04.6±1.3
Moment-DETR [17]†12.6±0.45.5±0.4
LONGMOMENT-DETR16.3±0.38.3±0.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.486, + 0.471, + 0.556 + ], + "angle": 0, + "content": "Table 8. Comparison with other methods. As it can be seen, LONGMOMENT-DETR achieves better results than other moment detection methods. \\(\\dagger\\) denotes training the models with the timings obtained by our proposed method using OSG. The results are presented on the testing split." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.577, + 0.47, + 0.667 + ], + "angle": 0, + "content": "tion for fine-tuning on the subsequent task of chapter detection. While the BMD training data is automatically curated, when we transition to training on the manually annotated data from the YTC dataset, we distinguish this model by referring to it as CHAPTER-DETR. This model uses the same architecture as LONGMOMENT-DETR." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.671, + 0.471, + 0.867 + ], + "angle": 0, + "content": "Results. The results for chapter detection are presented in Tab. 9. We observe that when only pre-training on BMD and directly assessing performance, the performance is low, the main reason being the distribution shift between the queries and segments in BMD and the ones in YTC. The queries from BMD are often composed of several sentences while the chapter annotation only contains a few words (as showcased in Fig. 5). However, if we first pre-train on BMD and then finetune with chapter annotations, there is a major boost in performance. These results prove that not only LONGMOMENT-DETR can be used on its own for moment detection, but it can be used to significantly improve the performance for the task of chapter detection." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Limitations. Since our method relies on automatic annotation generation, various problems such as text hallucination" + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.409, + 0.892, + 0.46 + ], + "angle": 0, + "content": "
ModelPre-trainingTrainingR1@0.5 ↑R1@0.7 ↑
LONGMOMENT-DETRBMD-5.0±2.42.2±1.5
CHAPTER-DETR-YTC12.6±0.35.8±0.6
CHAPTER-DETRBMDYTC16.1±0.56.6±0.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.464, + 0.893, + 0.56 + ], + "angle": 0, + "content": "Table 9. Results on YouTube-Chapters. If we evaluate LONGMOMENT-DETR trained with BMD directly on the task of chapter detection on the YTC dataset, the performance is low. However, if we use BMD as pre-training data and then train fully supervised for the task of chapter detection, there is a significant boost in performance as opposed to randomly initializing the model (4th line vs 3rd line)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.575, + 0.892, + 0.621 + ], + "angle": 0, + "content": "or incorrect segment timing generation directly affect the results of our system. Other limitations regarding particular components are discussed throughout the paper." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.62, + 0.892, + 0.696 + ], + "angle": 0, + "content": "Societal impact. Moment retrieval systems enable efficient content discovery for learning. However, these systems can exhibit biases towards particular groups or they can be used for spreading misinformation. Another aspect is the notable cost and carbon footprint required to train modern models." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.71, + 0.628, + 0.725 + ], + "angle": 0, + "content": "6. Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.895, + 0.901 + ], + "angle": 0, + "content": "In this paper we presented the LONGMOMENT-DETR framework which tackles the task of moment detection in long tutorial videos. We introduced, the first two long tutorial video datasets, Behance Moment Detection (BMD) and YouTube Chapters (YTC). BMD has human annotations for testing and validation splits and we propose a novel system to automatically curate the annotations for the training split by leveraging the information from the transcript. Lastly, we introduced YTC, a dataset containing human annotated chapters, and we further test and prove the effectiveness of the features obtained from BMD for chapter detection." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "2601" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.117, + 0.47, + 0.186 + ], + "angle": 0, + "content": "[1] Stefanos Angelidis, Reinald Kim Amplayo, Yoshihiko Suhara, Xiaolan Wang, and Mirella Lapata. Extractive opinion summarization in quantized transformer spaces. Transactions of the Association for Computational Linguistics, 9:277-293, 2021. 6" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.188, + 0.472, + 0.245 + ], + "angle": 0, + "content": "[2] Alexei Baevski, Wei-Ning Hsu, Alexis Conneau, and Michael Auli. Unsupervised speech recognition. 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For users to realise the full benefits of this medium, tutorial videos must be efficiently searchable. In this work, we focus on the task of moment detection, in which the goal is to localise the temporal window where a given event occurs within a given tutorial video. Prior work on moment detection has focused primarily on short videos (typically on videos shorter than three minutes). However, many tutorial videos are substantially longer (stretching to hours in duration), presenting significant challenges for existing moment detection approaches. + +To study this problem, we propose the first dataset of untrimmed, long-form tutorial videos for the task of Moment Detection called the Behance Moment Detection (BMD) dataset. BMD videos have an average duration of over one hour and are characterised by slowly evolving visual content and wide-ranging dialogue. To meet the unique challenges of this dataset, we propose a new framework, LONGMOMENT-DETR, and demonstrate that it outperforms strong baselines. Additionally, we introduce a variation of the dataset that contains YouTube Chapter annotations and show that the features obtained by our framework can be successfully used to boost the performance on the task of chapter detection. Code and data can be found at https://github.com/ioanacroi/longmoment-detr. + +# 1. Introduction + +Enabled by cheaper disk storage and networking technology, long-form videos of tutorial content are proliferating. As such, there is a pressing need to develop effective tools for searching within videos. In this work, we consider this problem through the lens of moment detection—given a video and a natural language query, our task is to find the + +![](images/d3bbdb4abdc8e2794bcf3cd34edd8b0025c741975c91beb7c56d864f07379873.jpg) +Figure 1. LONGMOMENT-DETR. Our framework performs moment detection and unlike previous state of the art methods, it works on long tutorial videos. + +temporal span of the video that best matches the query (as shown in Fig. 1). Beyond tutorial content, this task also has applications in domains such as security and entertainment. + +To study moment detection in the long-form setting, we introduce, the first database of long tutorial videos with manual annotations for validation and testing, called Behance Moment Detection (BMD). The videos, which are collected from the Behance platform, consist of tutorial videos that teach skills with various creative tools such as drawing, movie editing, animation and photo editing. + +Existing moment detection datasets predominantly feature short videos centered on human activities, such as cooking or swimming. In contrast, our BMD dataset emphasizes long tutorial videos that explore the use of software tools for digital artistry. Typically, these tutorials involve screen-sharing sessions detailing creative processes, often spanning several hours. Efficiently localizing specific segments in such long videos can greatly enhance user nav + +igation experience. This makes the BMD dataset unique for the task of moment detection. Moreover, to scale up training beyond costly manual annotation, we propose a framework for moment detection that leverages weak supervision derived from ASR (Automatic Speech Recognition) and video segmentation. In this new long video setup, using the timings from ASR, similar to previous works [24, 17], produces poor results, as we will show experimentally. So, in order to adjust for long videos setup, we rely on a mix of using video segmentation methods [36, 37] and summarization [50, 27, 5, 3] in order to generate good timings and textual descriptions to use for training. + +Lastly, in order to further validate our approach, we propose a second dataset, called YouTube Chapters (YTC) that contains full chapter annotation for all splits. In this way, we are able to assess the quality of the learnt features on BMD on the downstream task of chapter detection. + +We summarise our contributions as: (1) we introduce the first two long tutorial video datasets: Behance Moment Detection (BMD) a multi-modal dataset, suitable for weak supervision with manual annotations for validation and testing and YouTube Chapters (YTC) with chapters annotations for all splits (2) we propose an effective way to automatically generate moments for the training split of BMD that leverages Automatic Speech Recognition (ASR) and employs large language models (LLMs) to eliminate the inherent noise that appears in ASR. (3) we show the effectiveness of using BMD to improve the performance on the downstream task of YouTube chapter detection. + +Leveraging the multi-modal features of our new dataset and utilizing automatic annotations, we present LONGMOMENT-DETR, the first framework for moment detection in long tutorial videos consisting of the segment timing generator and query generator. + +# 2. Related work + +Moment detection from video. Many works have been proposed for the task of moment localization [17, 24, 14, 12, 19]. There are two popular families of approaches for moment detection on short videos: two-stage approaches and one-stage approaches. In the two-stage approaches [28, 39, 51, 14, 9, 49, 47, 46], firstly a list of potential candidates is generated and then the candidates are ranked according to various scores. In the one-stage approaches [17, 24, 18, 19, 48], the methods directly process the entire video and output the moment localization. The most recent methods are based on the transformer encoder-decoder architecture. Additionally, the methods [24, 17] are designed to jointly predict moment detection and highlight detection, while [28] tackles zero-shot moment detection. [28] is tailored for short videos and it consists of various modules (temporal event proposal, object detector, pseudoquery generation module). For our use case, running an + +object detector is highly expensive, since the videos are very long. Moreover, the produced results are usually of poor quality for tutorial videos since general object detectors are not tailored for this type of content where the host shares their screen and presents how to use specific software applications. Very recently, [29, 30] propose architectural changes to accommodate for long-formed videos, specifically within the movie domain. However, given the scarcity of datasets dedicated to long videos, particularly those with lengthy segments, this area remains underexplored. To address this issue, we are the first to propose the task of moment detection in long tutorial videos, along with two datasets containing very long untrimmed tutorial videos: one having manual segments annotations for evaluation (Behance Moment Detection) and the other having YouTube Chapters annotations for all splits. + +Large Language Models (LLMs). These models are trained on vastly large corpora of text consisting of tens of TB of data and have shown surprising zero-shot capabilities on a variety of NLP tasks [50, 3, 27, 40, 34, 6]. Notable among these are OPT175B [50], Bloom175B [38], and GPT3 [3], each boasting roughly 175B parameters. While GPT3 is available only through a paid API, OPT and Bloom models are open-source and are freely accessible to the research community. Even without task-specific finetuning, they exhibit strong zero-shot performance on multiple NLP benchmarks [20, 35, 10]. A distinguishing trait of LLMs is their prompt-driven adaptability to varied tasks. In our case, for tutorial videos, the available transcripts, although informative, can be noisy. These transcripts, generated using efficient automatic speech recognition tools [32, 2], are refined by LLMs, which we employ to extract relevant information and eliminate noise. + +Video segmentation. The task of temporal video segmentation aims to split the whole video into smaller sub-videos based on the semantic content. This is an important task in computer vision, being an essential pre-processing step for various other video understanding downstream tasks, such as video retrieval, moment detection or video summarization. In our case, we aim to use such models for segment timing generation. Various methods have been proposed for this task [44, 37, 36, 45], however they are designed and trained on short videos databases [42, 13]. Because of this, we have chosen to use unsupervised temporal video segmentation methods [36, 37, 15], that do not require retraining for our particular case. + +# 3. Dataset + +Both datasets, Behance Moment Detection (BMD) and YouTube Chapters (YTC), consist of long tutorial videos and are collected from the Behance platform. These are the first two datasets containing untrimmed, long-form tutorial videos for the tasks of moment detection and chapters detec + +![](images/8451a0959d6ae1aeb125809c2a27d786a801c0bf0efd7e16860023746595eb80.jpg) +Figure 2. Behavior Moment Detection example. We propose a moment retrieval dataset containing long tutorial videos. Each video is split into multiple segments and each segment has an associated query. We highlight with green the moment associated to the given query. + +tion, respectively. While these tasks are important in videos of any duration, moment localization in long-form tutorial videos can add extra value since it improves the user experience and eases video navigation by saving significant searching time (for example a user can only be interested where a specific character is drawn, but it is time-consuming to find that part in a long video). + +The validation and testing splits of BMD are manually annotated, while the training split is automatically curated. For YTC, we sourced human-annotated chapters from YouTube. All data is publicly accessible online. + +# 3.1. Behance Moment Detection + +We collected videos from Behance Livestream, a platform for creative users who share their work, having over 30 million users. The videos from our dataset were livestreamed and then made publicly available on the platform. We choose Behance since the videos are of high quality with relatively little noise and the type of the videos are aligned with our target videos, namely long tutorial videos. The usual flow for these videos is: 1) the host greets the viewers and talks about what they will showcase in the video (usually they show how to use different creative apps such as Adobe Fresco or Photoshop), 2) the host shares their screen and 3) they start using the chosen app while talking and giving useful tips and details about the creative process. For example, the host can use drawing tools for creating cartoon characters or can showcase how to use video editing tools for creating a movie, how to add shadows, etc. One such example can be seen in Fig. 2. These tutorial livestreams are usually very long, the majority being over one hour long, as presented in Fig. 3. The videos represent source materials that teach skills for educational purposes. There are thousands of long tutorial videos available on Behance and there are thousands more on other video platforms such as YouTube, which can directly benefit from our method of moment detection in long videos. + +In Tab. 1 we present a comparison with other moment detection datasets. There is a striking difference when comparing the average length of the videos and of the segments with other existing datasets. There is only one other dataset which contains long videos, namely the MAD [41] dataset. + +![](images/05cb36704a5d80366d280902842df5c08c83756476418550394c603d1f53f3a1.jpg) +Figure 3. Histogram of video duration. The majority of the videos in the BMD dataset are longer than one hour. + +MAD contains videos extracted from movies and leverages the audio descriptions of movies for visually impaired audiences, having the average length of the segment of around 4.1s, while ours has a much longer segment duration of over 17 minutes. This makes our dataset more suitable for downstream tasks, such as chapter detection. Another major difference is that the videos from our datasets are untrimmed, while for some other datasets such as QVHighlights [17], the videos are automatically split into 3-minute segments. This can result in loss of context or some actions being trimmed in an unnatural way, which can lead to annotations issues. The BMD dataset contains over 13,000 hours of videos (with over 630 hours of human-annotated videos). There are 7.9k videos used for training, 117 for validation and 171 for testing. While other moment retrieval datasets suffer from temporal biases [14, 9, 19] where the segments tend to occur in the beginning of the video, our dataset contains segments that span the entire video. All the videos in the dataset have transcripts, extracted with Azure speech-to-text. On average each transcript contains 1500 sentences. + +Validation and testing split. For the validation and testing splits we outsourced the annotation task to a specialised company having a team of qualified and experienced annotators. The annotators were asked to watch the tutorial video, segment it into high-level chapters and write a natural language description for each segment. The description is a brief summary of what happens in the segment and should contain no more than a few sentences. The cost for annotating the validation and testing split was approximately $10,000 and took around 3 months for the 288 videos. + +Training split. Due to the high cost of collecting the an- + +
DatasetDomain#videos#queriesAvg len videos(sec)Avg len segmentTotal number of hours
DiDeMo [14]Flickr10.6k41.2K29.36.588
ActivityNet [16]Activity15K72K117.636.2490
CharadesSTA [12]Activity6.7k16.1K30.68.157
TVR [19]TV show21.8K109K76.29.1461
QVHighlights [17]Vlog/News10.2K10.3K15024.6425
MAD [41]Movies650384.6K6646(1.8 hours)4.11207.3
BMD-Train†Livestream7.9K35.9K5768 (1.6 hours)1022 (17 mins)12.7k
BMD-EvalLivestream28814997957 (2.2 hours)1537 (25.6 mins)638
YouTube ChaptersLivestream46743916472 (1.8 hours)687 (11.5 mins)840
+ +Table 1. Comparison between BMD and YTC to existing moment retrieval datasets. The segments from our datasets are significantly longer than the ones from any other existing datasets. Moreover, in our datasets the segments span the entire duration of the video eliminating potential biases. ${}^{ \dagger }$ BMD-Train contains automatically curated annotation. + +notations, the training set was annotated automatically by leveraging the transcript together with pretrained large language models. Since the videos are livestreamed, the host interacts with the viewers and verbally explains the steps involved in the creative process for making digital art, including a detailed description of what they create or how to efficiently use the tools to obtain the desired outcome. While parts of the transcripts are extremely informative regarding what is happening in the video, there is also a lot of noise, which includes redundant information or information that is irrelevant to the tutorial (for example chit-chat about events that happened lately). Because the average length of the transcript is around 1500 sentences, we need an efficient way of condensing and extracting the relevant information. We achieve this by using GPT3 through the API provided by OpenAI. This incurs an additional cost of approximately $1,000 for all training videos. More details about the summarization procedure and a detailed comparison between different LLMs can be found in Sec. 4.3. + +While this gives us the ability to generate high-quality queries for the segments, another challenge is how to generate timings and split the video into meaningful parts. This step is equally important and affects the final performance of the model as we will show later. In order to address this challenge, we considered various state-of-the-art methods for video segmentation [36, 37] in order to generate segment timings. As the final model, we use the OSG [36] method. More details can be found in Sec. 4.3. + +# 3.2. YouTube Chapters + +Recently, YouTube introduced the functionality to add video chapters as a way to improve the user experience, especially for long videos. The creator of the video has the possibility to segment the video into several sections and to add a short description to each section. This facilitates easy rewatching or skipping to the desired content in the video. Some of the videos from our Behance Moment Detection dataset are also published on the YouTube platform and contain manual chapter labels. In order to further + +test the quality of our method, we collected chapter annotations from almost 500 videos (379 in training, 17 in validation and 71 in the testing split). Most of the visual content of the videos from YouTube Chapters already exists in the Behance Moment Detection dataset, which assures the fact that the videos are from the domain we are interested in (namely tutorial videos). However, there are clear differences between the two annotations. Firstly, the queries from YouTube Chapters are very brief and consist of just a few words (such as How to remove chromatic aberration or Creating GIFs in Photoshop) while the annotations from BMD dataset are fully formed sentences describing the actions happening in that segment of the video, as presented in Fig. 4. Secondly, the temporal segmentation of the video is different (the average segment length in BMD is approx. 20 minutes long, while in YTC is approx. 11 minutes long, as illustrated in Tab. 1), thus being a domain gap between the BMD and YTC annotations. + +# 4. Method + +We first define the task of moment retrieval in long tutorial videos (Sec. 4.1). Then, we introduce our full framework (Sec. 4.2), providing additional insights about our automatic moment generation pipeline (Sec. 4.3). Finally, we present architecture details (Sec. 4.4) and elaborate about our design choices. + +# 4.1. Task definition + +Given a video $v = \{f_1, f_2, \dots, f_V\}$ (where $f_i$ represents the $i$ -th frame of the video) and a query $q$ in natural language, the objective of moment detection is to find the pair $(i,j), i < j$ so that the video segment starting at $f_i$ and finishing at $f_j$ is best described by the query $q$ . Our goal is to train a model that receives as input the whole video $v$ and query $q$ and outputs the start and end time $(i,j)$ . + +Let $D = \{v_l | l = 1..N\}$ be a dataset of $N$ videos with + +segment annotations $A = \bigcup_{l = 1}^{N}A_{l}$ where + +$$ +A _ {l} = \left\{\left(q _ {k}, \left(i _ {k}, j _ {k}\right)\right) | f _ {i _ {k}}, f _ {j _ {k}} \in v _ {l}, i _ {k} < j _ {k}, k = 1.. Q _ {l} \right\} +$$ + +denotes the segment annotations for video $v_{l}$ . $Q_{l}$ represents the number of segments in $v_{l}$ while $q_{k}$ represents the query written in natural language for the segment starting at $i_{k}$ and finishing at $j_{k}$ . In order to train the model $M$ for the task of moment detection we use a similar setup as Moment-DETR [17], which is described in more detail in Sec. 4.4. + +# 4.2. The LONGMOMENT-DETR framework + +In Algorithm 1 we present the process for our LONGMOMENT-DETR framework. Since the cost (both time and financial resources) of collecting manual annotations for thousands of videos is high, an effective way of decreasing this cost is to curate automatic annotations for the training split $D$ . After gathering the videos from the Behance platform, the first step is to automatically generate the transcripts from the audio modality using the Azure speech recognition tool. Next, the videos are split into several segments representing different key parts of the video. After having the timings for the segments, we use the corresponding transcript for that timespan and we summarize it in order to extract the essential information. We then proceed to train our final model $M$ using a standard approach for this task, similarly to [17]. + +Algorithm 1 LONGMOMENT-DETR framework +1: Phase 1: generate Moment Annotations $(D) \to A$ +2: $A = \emptyset$ +3: for video $v_{l}$ in $D$ do +4: Generate transcript $s_l$ for $v_{l}$ +5: $T_{l} = \text{segmentsGeneration}(v_{l})$ +6: $A_{l} = \emptyset$ +7: for timing $(i_k, j_k) \in T_l$ do +8: $q_{k} = \text{queryGeneration}((i_k, j_k), s_l)$ +9: Add $(q_k, (i_k, j_k))$ to $A_{l}$ +10: end for +11: $A = A \cup A_l$ +12: end for +13: Phase 2: Train the final model, $M$ +14: for minibatch of paired samples $(v, a)$ , $a = (q_k, (i_k, j_k)) \in A, v \in D$ do +15: Extract video features $x$ from $v$ +16: Extract text features $p_k$ from $q_k$ +17: Feed $x$ and $q_k$ to $M$ and get output $o$ . +18: Compute the loss between $o$ and $(i_k, j_k)$ . +19: Update $M$ base on loss +20: end for + +# 4.3. Moment generation + +Our approach has two steps: segments timing generation and query generation which will be discussed next. + +Segment timing generation. Temporally segmenting the video according to topics is an important step in our pipeline which affects the final performance of the system. We considered and compared various potential solutions: starting directly from using the timings given by the speech recognition tool or splitting the video into random segments to using state of the art unsupervised methods such as OSG [36] and ONG [37]. The last two video segmentation methods receive as input the video features (in our case, SlowFast [11] features) and a parameter $s$ , representing the number of segments to split the video in. For choosing the parameter $s$ , we tested two approaches: estimate the number of segments based on SVD (as described in [36]) or using a constant. Based on the results of these experiments (for full results, see Sec. 5.2) for the final method we use OSG [36] with five scenes per video. This step acts as the segmentsGeneration function in Algorithm 1. + +Query generation. For this task, the simplest approach is to use directly the transcript. However, while parts of the transcript are quite informative, it also contains noise and information that is not relevant to the visual content or to the tutorial (for example the host may converse about the weather). It would therefore be useful to have an automatic method to extract a condensed version of the relevant information from the transcript associated with a video segment. For this, we considered various techniques such as extractive summarization [5] or using large language models (LLMs). Models such as Bloom175B [27], OPT175B [50] and GPT3 [3] are able to perform a large variety of tasks, including summarization and information extraction from large chunks of text. We begin by concatenating all the sentences from the transcript that span during the start and end time of a segment proposal and feed it to the language model along with the instructions to summarize the text. We used the following prompt: "Summarize this tutorial transcript:" In Sec. 5.2 we present detailed ablations studies between different summarization methods. For the final model, we used GPT3 (Curie model) to obtain the query for each generated segment. In cases where the segment transcript is too long to be processed by GPT3, the final query is the concatenation of several splits of the transcript, each processed by GPT3 independently. This step acts as the queryGeneration function in Algorithm 1. + +# 4.4. Architecture details + +We start from the Moment-DETR [17] architecture which uses an encoder-decoder transformer [43] and is based on the DETR architecture [4]. The model receives as input the concatenation between the video and text features and outputs the center and width of the predicted moment. + +
Method#scenesPrecisionRecallF1
Transcript timing20097.88.715.0
Random split554.571.653.5
ONG [37]SVD48.1986.7043.42
OSG [36]SVD67.0876.4557.18
ONG [37]545.9589.2142.69
OSG [36]562.1783.3759.51
+ +Table 2. Comparison of different video segmentation methods. Using directly the timings from the transcript has very poor results, while OSG performs the best in terms of F1 score. + +
Segmentation MethodR1@0.5 ↑R1@0.7 ↑
Transcript timing3.1±0.40.5±0.2
Random9.4±1.62.6±0.8
ONG7.1±0.61.7±1.4
OSG13.4±0.56.3±0.3
+ +One limitation of [17] is that it assumes the video has a length of 3 minutes. In order to make it suitable for running on longer videos, we adjust the meta-parameters and make low-level changes to the model implementation such as removing hard-coded constraints. Please see Suppl.Mat. for more details. This modified version becomes the architecture used in our whole LONGMOMENT-DETR framework. For features, we employ SlowFast [11] video understanding features extracted every 8 seconds and GPT2-x1 [33] features for the text. + +Implementation details. Our model is trained in PyTorch, using the AdamW optimizer [25] with a learning rate of 1e-4 and weight decay of 1e-4. All the models were trained on an NVIDIA A100 GPU. Due to memory limitations, we trained the model with a batch size of 16. + +# 5. Experiments + +# 5.1. Metrics + +We report the standard metrics used in moment detection: $R1@0.5$ and $R1@0.7$ , where a prediction is considered correct if it has an intersection over union (IoU) with the ground truth $\geq 0.5$ , respectively $\geq 0.7$ . When it comes to assessing the performance of video segmentation methods we report the standard metrics for this task: precision, recall and F1-score, while for comparing query generations we report the ROUGE metrics [22] which are commonly used for the task of summarization [26, 8, 1] and are proven to have a good correlation with the human judgment [23]. + +# 5.2. Ablations + +For all the ablation experiments, we report results on the validation split, unless otherwise stated. + +Segment timing generation. We begin by testing several + +Table 3. Comparison between different video segmentation methods combined with LONGMOMENT-DETR. The timings generation has a direct impact on performance. The number of scenes considered as input parameter for OSG and ONG is 5. + +
MethodR-1R-2R-L
Transcript2.310.341.85
Captioning BLIP [21]7.560.56.8
Extractive [5]8.540.596.17
Bloom175B [38]9.090.527.36
OPT175B [50]10.990.748.23
GPT3 [3]15.491.3611.85
+ +Table 4. Evaluation of query generation using ROUGE metrics. We assess the performance of different query generation methods. The transcript, being significantly longer than the human annotation, has a low score, while the LLMs perform the best. + +methods and assess their video segmentation performance in Tab. 2. This performance correlates with the moment detection results shown in Tab. 3. Moreover, we observe that following prior works [17, 24] and using only the timings from the transcripts gives poor results. This is expected, since for BMD the average segment length is considerably longer than the segment obtained from transcript timing. In fact, just by randomly splitting the video into 5 segments, the performance improves significantly. We obtain the best results using the OSG [36] video segmentation method using five scenes. + +Query generation. Another important step in our method is automatic query generation. Since the image and video captioning systems are trained on visual data that is out of domain as compared to our tutorial videos, we expect those systems to perform worse than the systems based on textual information. In Tab. 4 we present summarization results as compared to the human annotation for the validation split and observe that GPT3 obtains the best results. Also, in Fig. 4 we present a qualitative example for the query generation task using LLMs. + +In Tab. 5 we present results for LONGMOMENT-DETR using various query generation techniques. The best score is obtained using the GPT3 model which correlates with the results from Tab. 4. However, while there is a correlation between the results, we notice that there is a significantly smaller gap between the performance of using LLMs such as Bloom175B or OPT175B and using the raw transcript for the task of moment detection. An explanation for this, is that even though the transcript is very long, which directly affects the ROUGE score, for the task of moment detection it contains enough relevant information in order to make up for the differences in performance. For the final model, we use the GPT3 model as the query generation method. + +Influence of pre-trained features. Our model receives at input pre-trained features for both the visual and textual component. For this ablation study, we assess the influence of such features on the final performance as seen in Tab. 6. For the visual side, we consider the SlowFast [11] and CLIP [31] features while for the textual side, we consider GPT2-x1 [33], DiffCSE [7] and CLIP [31]. The best + +![](images/a74e8ae578983d21427a52b02dfe3d6e7dc0e8f9b9b39a5e4b0ffdf34d37ed55.jpg) +Figure 4. Comparison of summaries generated by GPT3, OPT175B and Bloom175B. During the summarization process no human annotation was used. In this figure, the human description and video frames are shown only for reference. While the AI generated summaries are obtained only from the transcript, the human had access to the whole video and audio when making the annotation. + +![](images/4233b2dc8e1bf5ee1609e3f912227287c045e687327e350b02c93ca3fddbb601.jpg) + +![](images/34fe41ba686d07da24165b0a6bb195446f67b9c34086b5a542ba7e64f3462e9d.jpg) + +![](images/59ffd2cf74231eeb0693444782a95ff474f1bdc29b55a0b3751fabcb93d31d1b.jpg) + +Human: "The host starts working on the video on After effect. The host sync the video with music and sync the movement of the arm to the music. The host adjust the animation movement of the flag according to the action of the arm." + +GPT3: "In this tutorial, the speaker demonstrates how to animate a character's hand using the software After Effects. This tutorial is about creating an animation in which a character's arms move up and down in time with a beat." + +OPT: "I wanted to take you through the process Learn how to improve the animation and timing in your 3D walk cycle by using the graph editor. First learn the basics of changing a keyframe. Finally, learn the In this tutorial, you learned how to add a simple effect to your hand movements." + +Bloom: "How to make a simple animation in After Effects. We learned how to create a simple animation using the Pen Tool, how to add a simple text animation. how to make a cartoon character walk in After Effects. We learned how to create a simple walk cycle, how to animate the walk cycle." + +
Summ MethodR1@0.5↑R1@0.7↑
Transcript13.6±0.56.3±0.3
Bloom175B13.4±0.67.0±0.2
OPT175B14.0±0.66.7±0.8
GPT316.8±0.59.2±1.0
+ +Table 5. Comparison between different LLM query generation methods in conjunction with LONGMOMENT-DETR. As it can be seen, GPT3 performs the best. What is interesting is that by using the raw transcript, the performance is only slightly worse than using other power full summarization methods such as Bloom175B and OPT175B. + +
Video featsText featsR1@0.5 ↑R1@0.7 ↑
SlowFastGPT2-x116.8±0.59.2±1.0
SlowFastDiffCSE13.1±1.56.5±1.2
SlowFastCLIP11.2±0.74.9±0.9
CLIPCLIP12.7±0.66.2±0.3
CLIPGPT2-x113.8±1.27.1±1.8
CLIPDiffCSE13.8±1.97.5±0.7
+ +results are obtained using SlowFast for the visual side and GPT2-x1 for the textual side. + +Influence of different components. In Tab. 7 we present an overview of the influence of different components on the testing split (the results on validation split are presented previously in each corresponding section). We start with a Moment-DETR [17] model as Baseline. We observe that both the segment timing generation and the query generation have a strong impact on performance. We obtain the best results by combining the timing generation from OSG with the GPT3 query generation which represents our final LONGMOMENT-DETR framework. + +Table 6. Influence of pre-trained features on performance. The best performance is obtained using SlowFast features for the visual side and GPT2-xl features for the textual side. + +
ComponentSegmentsQueriesR1@0.5↑R1@0.7↑
Baseline [17]NoNo2.7±0.60.3±0.1
Random segRandomNo9.2±1.82.6±0.4
SummarizeRandomGPT313.2±0.35.6±0.6
ShotDetectOSGNo12.6±0.45.5±0.4
LONGMOMENT-DETROSGGPT316.3±0.38.3±0.5
+ +Table 7. Effect of different components on performance. Both the segment timing generation and query generation have a strong impact on performance. Hence, in the final model, we use OSG and GPT3, thus obtaining our final model LONGMOMENT-DETR. The results are presented on the testing split. + +# 5.3. Comparison with others + +In this section, we compare our method against two recent methods: Moment-DETR [17] and UMT [24] adjusted for ingesting long videos. For UMT we use the video only version as introduced in the paper [24]. This comparison can be seen in Tab. 8. By training using the raw transcripts, which is similar to the pre-training stage of [17], the results in our case for long tutorial videos are poor. However, by adjusting the base architecture and use the automatic generated segments tailored for long videos, the results improve significantly for Moment-DETR as observed in the table. Moreover, if we use our full LONGMOMENT-DETR framework, as described in Sec. 4.2, the results are significantly better than previously published methods. + +# 5.4. YouTube Chapters + +To further evaluate the quality of our features obtained using the automatic annotations, we have collected new data from YouTube Chapters as described in Sec. 3.2. + +Experimental setup. We initially train the network using BMD. Once trained, these weights serve as the founda + +BMD Query: "The host colors the cow with lime yellow color and a part of the body of the cow is colored with brown color. The nose of the cow is colored with skin color. A few skin color strokes are added to the coat of the cow. The background of the cow is added with green color to the grass and sky blue color to the sky." + +![](images/9513679795b762d5223ccf57999c82b327e787c620a1a144dc936c6850cc66d5.jpg) +(A) + +![](images/2d129fe2a1df8ef345a9fa4f7fc5d02d98723d1c9963cb2eaaaa063d2f4f310a.jpg) +(B) +Figure 5. Qualitative examples for BMD (A) and YTC (B). Along with the query, we show several video frames, the prediction results in orange and the ground truth in green. We also specify the overlap between the prediction and ground truth segments. Please note how different the queries between BMD and YTC are. Also, while the prediction results have an offset from the ground truth, we want to highlight how subtle is the change in scenery for our proposed datasets. + +
ModelR1@0.5↑R1@0.7↑
Moment-DETR [17]2.7±0.60.3±0.1
UMT [24]†11.5±1.04.6±1.3
Moment-DETR [17]†12.6±0.45.5±0.4
LONGMOMENT-DETR16.3±0.38.3±0.5
+ +tion for fine-tuning on the subsequent task of chapter detection. While the BMD training data is automatically curated, when we transition to training on the manually annotated data from the YTC dataset, we distinguish this model by referring to it as CHAPTER-DETR. This model uses the same architecture as LONGMOMENT-DETR. + +Results. The results for chapter detection are presented in Tab. 9. We observe that when only pre-training on BMD and directly assessing performance, the performance is low, the main reason being the distribution shift between the queries and segments in BMD and the ones in YTC. The queries from BMD are often composed of several sentences while the chapter annotation only contains a few words (as showcased in Fig. 5). However, if we first pre-train on BMD and then finetune with chapter annotations, there is a major boost in performance. These results prove that not only LONGMOMENT-DETR can be used on its own for moment detection, but it can be used to significantly improve the performance for the task of chapter detection. + +Limitations. Since our method relies on automatic annotation generation, various problems such as text hallucination + +Table 8. Comparison with other methods. As it can be seen, LONGMOMENT-DETR achieves better results than other moment detection methods. $\dagger$ denotes training the models with the timings obtained by our proposed method using OSG. The results are presented on the testing split. + +
ModelPre-trainingTrainingR1@0.5 ↑R1@0.7 ↑
LONGMOMENT-DETRBMD-5.0±2.42.2±1.5
CHAPTER-DETR-YTC12.6±0.35.8±0.6
CHAPTER-DETRBMDYTC16.1±0.56.6±0.3
+ +Table 9. Results on YouTube-Chapters. If we evaluate LONGMOMENT-DETR trained with BMD directly on the task of chapter detection on the YTC dataset, the performance is low. However, if we use BMD as pre-training data and then train fully supervised for the task of chapter detection, there is a significant boost in performance as opposed to randomly initializing the model (4th line vs 3rd line). + +or incorrect segment timing generation directly affect the results of our system. Other limitations regarding particular components are discussed throughout the paper. + +Societal impact. Moment retrieval systems enable efficient content discovery for learning. However, these systems can exhibit biases towards particular groups or they can be used for spreading misinformation. Another aspect is the notable cost and carbon footprint required to train modern models. + +# 6. Conclusions + +In this paper we presented the LONGMOMENT-DETR framework which tackles the task of moment detection in long tutorial videos. We introduced, the first two long tutorial video datasets, Behance Moment Detection (BMD) and YouTube Chapters (YTC). BMD has human annotations for testing and validation splits and we propose a novel system to automatically curate the annotations for the training split by leveraging the information from the transcript. Lastly, we introduced YTC, a dataset containing human annotated chapters, and we further test and prove the effectiveness of the features obtained from BMD for chapter detection. + +# References + +[1] Stefanos Angelidis, Reinald Kim Amplayo, Yoshihiko Suhara, Xiaolan Wang, and Mirella Lapata. Extractive opinion summarization in quantized transformer spaces. Transactions of the Association for Computational Linguistics, 9:277-293, 2021. 6 +[2] Alexei Baevski, Wei-Ning Hsu, Alexis Conneau, and Michael Auli. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 15555-15564, 2022. 2 \ No newline at end of file diff --git a/2023/Moment Detection in Long Tutorial Videos/images.zip b/2023/Moment Detection in Long Tutorial Videos/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..d807043601ce02c9c6d17d453e036c5582b5ff7f --- /dev/null +++ b/2023/Moment Detection in Long Tutorial Videos/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:c4661198fdb95ad9c13b2da27dd32d0926df2dc9259815ce4095b8ef5491f231 +size 461483 diff --git a/2023/Moment Detection in Long Tutorial Videos/layout.json b/2023/Moment Detection in Long Tutorial Videos/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..124a2f04b7563b7f5b4ac89013145050c32ece00 --- /dev/null +++ b/2023/Moment Detection in Long Tutorial Videos/layout.json @@ -0,0 +1,7734 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 164, + 103, + 430, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 164, + 103, + 430, + 121 + ], + "spans": [ + { + "bbox": [ + 164, + 103, + 430, + 121 + ], + "type": "text", + "content": "Moment Detection in Long Tutorial Videos" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 55, + 141, + 536, + 200 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 141, + 536, + 200 + ], + "spans": [ + { + "bbox": [ + 55, + 141, + 536, + 200 + ], + "type": "text", + "content": "Ioana Croitoru\\* Simion-Vlad Bogolin3 Samuel Albanie2 Yang Liu4 Zhaowen Wang1 Seunghyun Yoon1 Franck Dernoncourt1 Hailin Jin1 Trung Bui1 1Adobe Research Department of Engineering, University of Cambridge 3 Filtir 4 Wangxuan Inst. of Computer Technology, Peking University" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "spans": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 252, + 290, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 252, + 290, + 396 + ], + "spans": [ + { + "bbox": [ + 46, + 252, + 290, + 396 + ], + "type": "text", + "content": "Tutorial videos play an increasingly important role in professional development and self-directed education. For users to realise the full benefits of this medium, tutorial videos must be efficiently searchable. In this work, we focus on the task of moment detection, in which the goal is to localise the temporal window where a given event occurs within a given tutorial video. Prior work on moment detection has focused primarily on short videos (typically on videos shorter than three minutes). However, many tutorial videos are substantially longer (stretching to hours in duration), presenting significant challenges for existing moment detection approaches." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 396, + 290, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 396, + 290, + 576 + ], + "spans": [ + { + "bbox": [ + 45, + 396, + 290, + 576 + ], + "type": "text", + "content": "To study this problem, we propose the first dataset of untrimmed, long-form tutorial videos for the task of Moment Detection called the Behance Moment Detection (BMD) dataset. BMD videos have an average duration of over one hour and are characterised by slowly evolving visual content and wide-ranging dialogue. To meet the unique challenges of this dataset, we propose a new framework, LONGMOMENT-DETR, and demonstrate that it outperforms strong baselines. Additionally, we introduce a variation of the dataset that contains YouTube Chapter annotations and show that the features obtained by our framework can be successfully used to boost the performance on the task of chapter detection. Code and data can be found at https://github.com/ioanacroi/longmoment-detr." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 601, + 128, + 613 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 601, + 128, + 613 + ], + "spans": [ + { + "bbox": [ + 47, + 601, + 128, + 613 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 620, + 288, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 620, + 288, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 620, + 288, + 693 + ], + "type": "text", + "content": "Enabled by cheaper disk storage and networking technology, long-form videos of tutorial content are proliferating. As such, there is a pressing need to develop effective tools for searching within videos. In this work, we consider this problem through the lens of moment detection—given a video and a natural language query, our task is to find the" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 313, + 230, + 544, + 432 + ], + "blocks": [ + { + "bbox": [ + 313, + 230, + 544, + 432 + ], + "lines": [ + { + "bbox": [ + 313, + 230, + 544, + 432 + ], + "spans": [ + { + "bbox": [ + 313, + 230, + 544, + 432 + ], + "type": "image", + "image_path": "d3bbdb4abdc8e2794bcf3cd34edd8b0025c741975c91beb7c56d864f07379873.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 437, + 547, + 471 + ], + "lines": [ + { + "bbox": [ + 305, + 437, + 547, + 471 + ], + "spans": [ + { + "bbox": [ + 305, + 437, + 547, + 471 + ], + "type": "text", + "content": "Figure 1. LONGMOMENT-DETR. Our framework performs moment detection and unlike previous state of the art methods, it works on long tutorial videos." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 479, + 545, + 515 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 479, + 545, + 515 + ], + "spans": [ + { + "bbox": [ + 304, + 479, + 545, + 515 + ], + "type": "text", + "content": "temporal span of the video that best matches the query (as shown in Fig. 1). Beyond tutorial content, this task also has applications in domains such as security and entertainment." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 515, + 546, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 515, + 546, + 598 + ], + "spans": [ + { + "bbox": [ + 304, + 515, + 546, + 598 + ], + "type": "text", + "content": "To study moment detection in the long-form setting, we introduce, the first database of long tutorial videos with manual annotations for validation and testing, called Behance Moment Detection (BMD). The videos, which are collected from the Behance platform, consist of tutorial videos that teach skills with various creative tools such as drawing, movie editing, animation and photo editing." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 599, + 547, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 599, + 547, + 696 + ], + "spans": [ + { + "bbox": [ + 304, + 599, + 547, + 696 + ], + "type": "text", + "content": "Existing moment detection datasets predominantly feature short videos centered on human activities, such as cooking or swimming. In contrast, our BMD dataset emphasizes long tutorial videos that explore the use of software tools for digital artistry. Typically, these tutorials involve screen-sharing sessions detailing creative processes, often spanning several hours. Efficiently localizing specific segments in such long videos can greatly enhance user nav" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 61, + 702, + 259, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 702, + 259, + 712 + ], + "spans": [ + { + "bbox": [ + 61, + 702, + 259, + 712 + ], + "type": "text", + "content": "*Work done during an internship at Adobe. Now at V7 Labs." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 317, + 702, + 414, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 702, + 414, + 712 + ], + "spans": [ + { + "bbox": [ + 317, + 702, + 414, + 712 + ], + "type": "text", + "content": "1https://behance.net" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "type": "text", + "content": "2594" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 215 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 215 + ], + "type": "text", + "content": "igation experience. This makes the BMD dataset unique for the task of moment detection. Moreover, to scale up training beyond costly manual annotation, we propose a framework for moment detection that leverages weak supervision derived from ASR (Automatic Speech Recognition) and video segmentation. In this new long video setup, using the timings from ASR, similar to previous works [24, 17], produces poor results, as we will show experimentally. So, in order to adjust for long videos setup, we rely on a mix of using video segmentation methods [36, 37] and summarization [50, 27, 5, 3] in order to generate good timings and textual descriptions to use for training." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 216, + 287, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 216, + 287, + 275 + ], + "spans": [ + { + "bbox": [ + 47, + 216, + 287, + 275 + ], + "type": "text", + "content": "Lastly, in order to further validate our approach, we propose a second dataset, called YouTube Chapters (YTC) that contains full chapter annotation for all splits. In this way, we are able to assess the quality of the learnt features on BMD on the downstream task of chapter detection." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 276, + 287, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 276, + 287, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 276, + 287, + 418 + ], + "type": "text", + "content": "We summarise our contributions as: (1) we introduce the first two long tutorial video datasets: Behance Moment Detection (BMD) a multi-modal dataset, suitable for weak supervision with manual annotations for validation and testing and YouTube Chapters (YTC) with chapters annotations for all splits (2) we propose an effective way to automatically generate moments for the training split of BMD that leverages Automatic Speech Recognition (ASR) and employs large language models (LLMs) to eliminate the inherent noise that appears in ASR. (3) we show the effectiveness of using BMD to improve the performance on the downstream task of YouTube chapter detection." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 419, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 419, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 47, + 419, + 287, + 479 + ], + "type": "text", + "content": "Leveraging the multi-modal features of our new dataset and utilizing automatic annotations, we present LONGMOMENT-DETR, the first framework for moment detection in long tutorial videos consisting of the segment timing generator and query generator." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 490, + 132, + 502 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 490, + 132, + 502 + ], + "spans": [ + { + "bbox": [ + 47, + 490, + 132, + 502 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 288, + 715 + ], + "type": "text", + "content": "Moment detection from video. Many works have been proposed for the task of moment localization [17, 24, 14, 12, 19]. There are two popular families of approaches for moment detection on short videos: two-stage approaches and one-stage approaches. In the two-stage approaches [28, 39, 51, 14, 9, 49, 47, 46], firstly a list of potential candidates is generated and then the candidates are ranked according to various scores. In the one-stage approaches [17, 24, 18, 19, 48], the methods directly process the entire video and output the moment localization. The most recent methods are based on the transformer encoder-decoder architecture. Additionally, the methods [24, 17] are designed to jointly predict moment detection and highlight detection, while [28] tackles zero-shot moment detection. [28] is tailored for short videos and it consists of various modules (temporal event proposal, object detector, pseudoquery generation module). For our use case, running an" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 262 + ], + "type": "text", + "content": "object detector is highly expensive, since the videos are very long. Moreover, the produced results are usually of poor quality for tutorial videos since general object detectors are not tailored for this type of content where the host shares their screen and presents how to use specific software applications. Very recently, [29, 30] propose architectural changes to accommodate for long-formed videos, specifically within the movie domain. However, given the scarcity of datasets dedicated to long videos, particularly those with lengthy segments, this area remains underexplored. To address this issue, we are the first to propose the task of moment detection in long tutorial videos, along with two datasets containing very long untrimmed tutorial videos: one having manual segments annotations for evaluation (Behance Moment Detection) and the other having YouTube Chapters annotations for all splits." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 263, + 545, + 466 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 263, + 545, + 466 + ], + "spans": [ + { + "bbox": [ + 304, + 263, + 545, + 466 + ], + "type": "text", + "content": "Large Language Models (LLMs). These models are trained on vastly large corpora of text consisting of tens of TB of data and have shown surprising zero-shot capabilities on a variety of NLP tasks [50, 3, 27, 40, 34, 6]. Notable among these are OPT175B [50], Bloom175B [38], and GPT3 [3], each boasting roughly 175B parameters. While GPT3 is available only through a paid API, OPT and Bloom models are open-source and are freely accessible to the research community. Even without task-specific finetuning, they exhibit strong zero-shot performance on multiple NLP benchmarks [20, 35, 10]. A distinguishing trait of LLMs is their prompt-driven adaptability to varied tasks. In our case, for tutorial videos, the available transcripts, although informative, can be noisy. These transcripts, generated using efficient automatic speech recognition tools [32, 2], are refined by LLMs, which we employ to extract relevant information and eliminate noise." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 467, + 545, + 622 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 467, + 545, + 622 + ], + "spans": [ + { + "bbox": [ + 304, + 467, + 545, + 622 + ], + "type": "text", + "content": "Video segmentation. The task of temporal video segmentation aims to split the whole video into smaller sub-videos based on the semantic content. This is an important task in computer vision, being an essential pre-processing step for various other video understanding downstream tasks, such as video retrieval, moment detection or video summarization. In our case, we aim to use such models for segment timing generation. Various methods have been proposed for this task [44, 37, 36, 45], however they are designed and trained on short videos databases [42, 13]. Because of this, we have chosen to use unsupervised temporal video segmentation methods [36, 37, 15], that do not require retraining for our particular case." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 634, + 361, + 645 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 634, + 361, + 645 + ], + "spans": [ + { + "bbox": [ + 306, + 634, + 361, + 645 + ], + "type": "text", + "content": "3. Dataset" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": "Both datasets, Behance Moment Detection (BMD) and YouTube Chapters (YTC), consist of long tutorial videos and are collected from the Behance platform. These are the first two datasets containing untrimmed, long-form tutorial videos for the tasks of moment detection and chapters detec" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "type": "text", + "content": "2595" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 56, + 99, + 537, + 171 + ], + "blocks": [ + { + "bbox": [ + 56, + 99, + 537, + 171 + ], + "lines": [ + { + "bbox": [ + 56, + 99, + 537, + 171 + ], + "spans": [ + { + "bbox": [ + 56, + 99, + 537, + 171 + ], + "type": "image", + "image_path": "8451a0959d6ae1aeb125809c2a27d786a801c0bf0efd7e16860023746595eb80.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 171, + 547, + 195 + ], + "lines": [ + { + "bbox": [ + 46, + 171, + 547, + 195 + ], + "spans": [ + { + "bbox": [ + 46, + 171, + 547, + 195 + ], + "type": "text", + "content": "Figure 2. Behavior Moment Detection example. We propose a moment retrieval dataset containing long tutorial videos. Each video is split into multiple segments and each segment has an associated query. We highlight with green the moment associated to the given query." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 205, + 288, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 205, + 288, + 289 + ], + "spans": [ + { + "bbox": [ + 46, + 205, + 288, + 289 + ], + "type": "text", + "content": "tion, respectively. While these tasks are important in videos of any duration, moment localization in long-form tutorial videos can add extra value since it improves the user experience and eases video navigation by saving significant searching time (for example a user can only be interested where a specific character is drawn, but it is time-consuming to find that part in a long video)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 289, + 287, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 289, + 287, + 337 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 287, + 337 + ], + "type": "text", + "content": "The validation and testing splits of BMD are manually annotated, while the training split is automatically curated. For YTC, we sourced human-annotated chapters from YouTube. All data is publicly accessible online." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 346, + 200, + 358 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 346, + 200, + 358 + ], + "spans": [ + { + "bbox": [ + 47, + 346, + 200, + 358 + ], + "type": "text", + "content": "3.1. Behance Moment Detection" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 365, + 288, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 288, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 288, + 653 + ], + "type": "text", + "content": "We collected videos from Behance Livestream, a platform for creative users who share their work, having over 30 million users. The videos from our dataset were livestreamed and then made publicly available on the platform. We choose Behance since the videos are of high quality with relatively little noise and the type of the videos are aligned with our target videos, namely long tutorial videos. The usual flow for these videos is: 1) the host greets the viewers and talks about what they will showcase in the video (usually they show how to use different creative apps such as Adobe Fresco or Photoshop), 2) the host shares their screen and 3) they start using the chosen app while talking and giving useful tips and details about the creative process. For example, the host can use drawing tools for creating cartoon characters or can showcase how to use video editing tools for creating a movie, how to add shadows, etc. One such example can be seen in Fig. 2. These tutorial livestreams are usually very long, the majority being over one hour long, as presented in Fig. 3. The videos represent source materials that teach skills for educational purposes. There are thousands of long tutorial videos available on Behance and there are thousands more on other video platforms such as YouTube, which can directly benefit from our method of moment detection in long videos." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 654, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 287, + 714 + ], + "type": "text", + "content": "In Tab. 1 we present a comparison with other moment detection datasets. There is a striking difference when comparing the average length of the videos and of the segments with other existing datasets. There is only one other dataset which contains long videos, namely the MAD [41] dataset." + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 316, + 207, + 533, + 310 + ], + "blocks": [ + { + "bbox": [ + 316, + 207, + 533, + 310 + ], + "lines": [ + { + "bbox": [ + 316, + 207, + 533, + 310 + ], + "spans": [ + { + "bbox": [ + 316, + 207, + 533, + 310 + ], + "type": "image", + "image_path": "05cb36704a5d80366d280902842df5c08c83756476418550394c603d1f53f3a1.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 311, + 545, + 333 + ], + "lines": [ + { + "bbox": [ + 305, + 311, + 545, + 333 + ], + "spans": [ + { + "bbox": [ + 305, + 311, + 545, + 333 + ], + "type": "text", + "content": "Figure 3. Histogram of video duration. The majority of the videos in the BMD dataset are longer than one hour." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 341, + 546, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 341, + 546, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 341, + 546, + 581 + ], + "type": "text", + "content": "MAD contains videos extracted from movies and leverages the audio descriptions of movies for visually impaired audiences, having the average length of the segment of around 4.1s, while ours has a much longer segment duration of over 17 minutes. This makes our dataset more suitable for downstream tasks, such as chapter detection. Another major difference is that the videos from our datasets are untrimmed, while for some other datasets such as QVHighlights [17], the videos are automatically split into 3-minute segments. This can result in loss of context or some actions being trimmed in an unnatural way, which can lead to annotations issues. The BMD dataset contains over 13,000 hours of videos (with over 630 hours of human-annotated videos). There are 7.9k videos used for training, 117 for validation and 171 for testing. While other moment retrieval datasets suffer from temporal biases [14, 9, 19] where the segments tend to occur in the beginning of the video, our dataset contains segments that span the entire video. All the videos in the dataset have transcripts, extracted with Azure speech-to-text. On average each transcript contains 1500 sentences." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 700 + ], + "type": "text", + "content": "Validation and testing split. For the validation and testing splits we outsourced the annotation task to a specialised company having a team of qualified and experienced annotators. The annotators were asked to watch the tutorial video, segment it into high-level chapters and write a natural language description for each segment. The description is a brief summary of what happens in the segment and should contain no more than a few sentences. The cost for annotating the validation and testing split was approximately $10,000 and took around 3 months for the 288 videos." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 701, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 701, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 701, + 545, + 713 + ], + "type": "text", + "content": "Training split. Due to the high cost of collecting the an-" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 94, + 81, + 457, + 94 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 94, + 81, + 457, + 94 + ], + "spans": [ + { + "bbox": [ + 94, + 81, + 457, + 94 + ], + "type": "text", + "content": "Query: \"The host starts sketching a teddy and also adds details to the sketch.\"" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2596" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 72, + 547, + 192 + ], + "blocks": [ + { + "bbox": [ + 50, + 72, + 547, + 192 + ], + "lines": [ + { + "bbox": [ + 50, + 72, + 547, + 192 + ], + "spans": [ + { + "bbox": [ + 50, + 72, + 547, + 192 + ], + "type": "table", + "html": "
DatasetDomain#videos#queriesAvg len videos(sec)Avg len segmentTotal number of hours
DiDeMo [14]Flickr10.6k41.2K29.36.588
ActivityNet [16]Activity15K72K117.636.2490
CharadesSTA [12]Activity6.7k16.1K30.68.157
TVR [19]TV show21.8K109K76.29.1461
QVHighlights [17]Vlog/News10.2K10.3K15024.6425
MAD [41]Movies650384.6K6646(1.8 hours)4.11207.3
BMD-Train†Livestream7.9K35.9K5768 (1.6 hours)1022 (17 mins)12.7k
BMD-EvalLivestream28814997957 (2.2 hours)1537 (25.6 mins)638
YouTube ChaptersLivestream46743916472 (1.8 hours)687 (11.5 mins)840
", + "image_path": "ac17011797878684a54bcab7f9b04fb7f7e41e18a22aab7c1b12feca19547693.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 195, + 546, + 229 + ], + "lines": [ + { + "bbox": [ + 46, + 195, + 546, + 229 + ], + "spans": [ + { + "bbox": [ + 46, + 195, + 546, + 229 + ], + "type": "text", + "content": "Table 1. Comparison between BMD and YTC to existing moment retrieval datasets. The segments from our datasets are significantly longer than the ones from any other existing datasets. Moreover, in our datasets the segments span the entire duration of the video eliminating potential biases. " + }, + { + "bbox": [ + 46, + 195, + 546, + 229 + ], + "type": "inline_equation", + "content": "{}^{ \\dagger }" + }, + { + "bbox": [ + 46, + 195, + 546, + 229 + ], + "type": "text", + "content": " BMD-Train contains automatically curated annotation." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 240, + 289, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 240, + 289, + 467 + ], + "spans": [ + { + "bbox": [ + 46, + 240, + 289, + 467 + ], + "type": "text", + "content": "notations, the training set was annotated automatically by leveraging the transcript together with pretrained large language models. Since the videos are livestreamed, the host interacts with the viewers and verbally explains the steps involved in the creative process for making digital art, including a detailed description of what they create or how to efficiently use the tools to obtain the desired outcome. While parts of the transcripts are extremely informative regarding what is happening in the video, there is also a lot of noise, which includes redundant information or information that is irrelevant to the tutorial (for example chit-chat about events that happened lately). Because the average length of the transcript is around 1500 sentences, we need an efficient way of condensing and extracting the relevant information. We achieve this by using GPT3 through the API provided by OpenAI. This incurs an additional cost of approximately $1,000 for all training videos. More details about the summarization procedure and a detailed comparison between different LLMs can be found in Sec. 4.3." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 468, + 287, + 575 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 468, + 287, + 575 + ], + "spans": [ + { + "bbox": [ + 46, + 468, + 287, + 575 + ], + "type": "text", + "content": "While this gives us the ability to generate high-quality queries for the segments, another challenge is how to generate timings and split the video into meaningful parts. This step is equally important and affects the final performance of the model as we will show later. In order to address this challenge, we considered various state-of-the-art methods for video segmentation [36, 37] in order to generate segment timings. As the final model, we use the OSG [36] method. More details can be found in Sec. 4.3." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 586, + 157, + 600 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 157, + 600 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 157, + 600 + ], + "type": "text", + "content": "3.2. YouTube Chapters" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 713 + ], + "type": "text", + "content": "Recently, YouTube introduced the functionality to add video chapters as a way to improve the user experience, especially for long videos. The creator of the video has the possibility to segment the video into several sections and to add a short description to each section. This facilitates easy rewatching or skipping to the desired content in the video. Some of the videos from our Behance Moment Detection dataset are also published on the YouTube platform and contain manual chapter labels. In order to further" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 240, + 547, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 240, + 547, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 240, + 547, + 456 + ], + "type": "text", + "content": "test the quality of our method, we collected chapter annotations from almost 500 videos (379 in training, 17 in validation and 71 in the testing split). Most of the visual content of the videos from YouTube Chapters already exists in the Behance Moment Detection dataset, which assures the fact that the videos are from the domain we are interested in (namely tutorial videos). However, there are clear differences between the two annotations. Firstly, the queries from YouTube Chapters are very brief and consist of just a few words (such as How to remove chromatic aberration or Creating GIFs in Photoshop) while the annotations from BMD dataset are fully formed sentences describing the actions happening in that segment of the video, as presented in Fig. 4. Secondly, the temporal segmentation of the video is different (the average segment length in BMD is approx. 20 minutes long, while in YTC is approx. 11 minutes long, as illustrated in Tab. 1), thus being a domain gap between the BMD and YTC annotations." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 477, + 361, + 490 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 477, + 361, + 490 + ], + "spans": [ + { + "bbox": [ + 306, + 477, + 361, + 490 + ], + "type": "text", + "content": "4. Method" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 501, + 547, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 501, + 547, + 574 + ], + "spans": [ + { + "bbox": [ + 304, + 501, + 547, + 574 + ], + "type": "text", + "content": "We first define the task of moment retrieval in long tutorial videos (Sec. 4.1). Then, we introduce our full framework (Sec. 4.2), providing additional insights about our automatic moment generation pipeline (Sec. 4.3). Finally, we present architecture details (Sec. 4.4) and elaborate about our design choices." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 592, + 398, + 604 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 592, + 398, + 604 + ], + "spans": [ + { + "bbox": [ + 306, + 592, + 398, + 604 + ], + "type": "text", + "content": "4.1. Task definition" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "spans": [ + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "content": "Given a video " + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "inline_equation", + "content": "v = \\{f_1, f_2, \\dots, f_V\\}" + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "content": " (where " + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "inline_equation", + "content": "f_i" + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "content": " represents the " + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "content": "-th frame of the video) and a query " + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "content": " in natural language, the objective of moment detection is to find the pair " + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "inline_equation", + "content": "(i,j), i < j" + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "content": " so that the video segment starting at " + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "inline_equation", + "content": "f_i" + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "content": " and finishing at " + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "inline_equation", + "content": "f_j" + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "content": " is best described by the query " + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "content": ". Our goal is to train a model that receives as input the whole video " + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "content": " and query " + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "content": " and outputs the start and end time " + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "inline_equation", + "content": "(i,j)" + }, + { + "bbox": [ + 304, + 613, + 547, + 698 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 700, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 700, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 700, + 545, + 714 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 317, + 700, + 545, + 714 + ], + "type": "inline_equation", + "content": "D = \\{v_l | l = 1..N\\}" + }, + { + "bbox": [ + 317, + 700, + 545, + 714 + ], + "type": "text", + "content": " be a dataset of " + }, + { + "bbox": [ + 317, + 700, + 545, + 714 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 317, + 700, + 545, + 714 + ], + "type": "text", + "content": " videos with" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2597" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 70, + 208, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 70, + 208, + 96 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 208, + 96 + ], + "type": "text", + "content": "segment annotations " + }, + { + "bbox": [ + 47, + 70, + 208, + 96 + ], + "type": "inline_equation", + "content": "A = \\bigcup_{l = 1}^{N}A_{l}" + }, + { + "bbox": [ + 47, + 70, + 208, + 96 + ], + "type": "text", + "content": " where" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 56, + 109, + 277, + 124 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 109, + 277, + 124 + ], + "spans": [ + { + "bbox": [ + 56, + 109, + 277, + 124 + ], + "type": "interline_equation", + "content": "A _ {l} = \\left\\{\\left(q _ {k}, \\left(i _ {k}, j _ {k}\\right)\\right) | f _ {i _ {k}}, f _ {j _ {k}} \\in v _ {l}, i _ {k} < j _ {k}, k = 1.. Q _ {l} \\right\\}", + "image_path": "0a49c6eecaa641af9dbcd26667a84616180eb7b5fbd2fcf9cd3e19c82a06466e.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "spans": [ + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "text", + "content": "denotes the segment annotations for video " + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "inline_equation", + "content": "v_{l}" + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "inline_equation", + "content": "Q_{l}" + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "text", + "content": " represents the number of segments in " + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "inline_equation", + "content": "v_{l}" + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "text", + "content": " while " + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "inline_equation", + "content": "q_{k}" + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "text", + "content": " represents the query written in natural language for the segment starting at " + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "inline_equation", + "content": "i_{k}" + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "text", + "content": " and finishing at " + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "inline_equation", + "content": "j_{k}" + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "text", + "content": ". In order to train the model " + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 134, + 287, + 205 + ], + "type": "text", + "content": " for the task of moment detection we use a similar setup as Moment-DETR [17], which is described in more detail in Sec. 4.4." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 217, + 243, + 228 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 217, + 243, + 228 + ], + "spans": [ + { + "bbox": [ + 47, + 217, + 243, + 228 + ], + "type": "text", + "content": "4.2. The LONGMOMENT-DETR framework" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 237, + 289, + 417 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 237, + 289, + 417 + ], + "spans": [ + { + "bbox": [ + 46, + 237, + 289, + 417 + ], + "type": "text", + "content": "In Algorithm 1 we present the process for our LONGMOMENT-DETR framework. Since the cost (both time and financial resources) of collecting manual annotations for thousands of videos is high, an effective way of decreasing this cost is to curate automatic annotations for the training split " + }, + { + "bbox": [ + 46, + 237, + 289, + 417 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 46, + 237, + 289, + 417 + ], + "type": "text", + "content": ". After gathering the videos from the Behance platform, the first step is to automatically generate the transcripts from the audio modality using the Azure speech recognition tool. Next, the videos are split into several segments representing different key parts of the video. After having the timings for the segments, we use the corresponding transcript for that timespan and we summarize it in order to extract the essential information. We then proceed to train our final model " + }, + { + "bbox": [ + 46, + 237, + 289, + 417 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 237, + 289, + 417 + ], + "type": "text", + "content": " using a standard approach for this task, similarly to [17]." + } + ] + } + ], + "index": 4 + }, + { + "type": "code", + "bbox": [ + 50, + 445, + 289, + 696 + ], + "blocks": [ + { + "bbox": [ + 48, + 430, + 244, + 442 + ], + "lines": [ + { + "bbox": [ + 48, + 430, + 244, + 442 + ], + "spans": [ + { + "bbox": [ + 48, + 430, + 244, + 442 + ], + "type": "text", + "content": "Algorithm 1 LONGMOMENT-DETR framework" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "lines": [ + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "spans": [ + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": "1: Phase 1: generate Moment Annotations " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "(D) \\to A" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " \n2: " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "A = \\emptyset" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " \n3: for video " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "v_{l}" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " do \n4: Generate transcript " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "s_l" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "v_{l}" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " \n5: " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "T_{l} = \\text{segmentsGeneration}(v_{l})" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " \n6: " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "A_{l} = \\emptyset" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " \n7: for timing " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "(i_k, j_k) \\in T_l" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " do \n8: " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "q_{k} = \\text{queryGeneration}((i_k, j_k), s_l)" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " \n9: Add " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "(q_k, (i_k, j_k))" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "A_{l}" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " \n10: end for \n11: " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "A = A \\cup A_l" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " \n12: end for \n13: Phase 2: Train the final model, " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " \n14: for minibatch of paired samples " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "(v, a)" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "a = (q_k, (i_k, j_k)) \\in A, v \\in D" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " do \n15: Extract video features " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " \n16: Extract text features " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "p_k" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "q_k" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " \n17: Feed " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "q_k" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " and get output " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "o" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": ". \n18: Compute the loss between " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "o" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "(i_k, j_k)" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": ". \n19: Update " + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 50, + 445, + 289, + 696 + ], + "type": "text", + "content": " base on loss \n20: end for" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "code_body" + } + ], + "index": 6, + "sub_type": "algorithm" + }, + { + "bbox": [ + 306, + 72, + 421, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 421, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 421, + 84 + ], + "type": "text", + "content": "4.3. Moment generation" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 91, + 545, + 114 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 91, + 545, + 114 + ], + "spans": [ + { + "bbox": [ + 305, + 91, + 545, + 114 + ], + "type": "text", + "content": "Our approach has two steps: segments timing generation and query generation which will be discussed next." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 114, + 545, + 317 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 114, + 545, + 317 + ], + "spans": [ + { + "bbox": [ + 304, + 114, + 545, + 317 + ], + "type": "text", + "content": "Segment timing generation. Temporally segmenting the video according to topics is an important step in our pipeline which affects the final performance of the system. We considered and compared various potential solutions: starting directly from using the timings given by the speech recognition tool or splitting the video into random segments to using state of the art unsupervised methods such as OSG [36] and ONG [37]. The last two video segmentation methods receive as input the video features (in our case, SlowFast [11] features) and a parameter " + }, + { + "bbox": [ + 304, + 114, + 545, + 317 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 114, + 545, + 317 + ], + "type": "text", + "content": ", representing the number of segments to split the video in. For choosing the parameter " + }, + { + "bbox": [ + 304, + 114, + 545, + 317 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 304, + 114, + 545, + 317 + ], + "type": "text", + "content": ", we tested two approaches: estimate the number of segments based on SVD (as described in [36]) or using a constant. Based on the results of these experiments (for full results, see Sec. 5.2) for the final method we use OSG [36] with five scenes per video. This step acts as the segmentsGeneration function in Algorithm 1." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 318, + 546, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 318, + 546, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 318, + 546, + 628 + ], + "type": "text", + "content": "Query generation. For this task, the simplest approach is to use directly the transcript. However, while parts of the transcript are quite informative, it also contains noise and information that is not relevant to the visual content or to the tutorial (for example the host may converse about the weather). It would therefore be useful to have an automatic method to extract a condensed version of the relevant information from the transcript associated with a video segment. For this, we considered various techniques such as extractive summarization [5] or using large language models (LLMs). Models such as Bloom175B [27], OPT175B [50] and GPT3 [3] are able to perform a large variety of tasks, including summarization and information extraction from large chunks of text. We begin by concatenating all the sentences from the transcript that span during the start and end time of a segment proposal and feed it to the language model along with the instructions to summarize the text. We used the following prompt: \"Summarize this tutorial transcript:\" In Sec. 5.2 we present detailed ablations studies between different summarization methods. For the final model, we used GPT3 (Curie model) to obtain the query for each generated segment. In cases where the segment transcript is too long to be processed by GPT3, the final query is the concatenation of several splits of the transcript, each processed by GPT3 independently. This step acts as the queryGeneration function in Algorithm 1." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 635, + 421, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 635, + 421, + 647 + ], + "spans": [ + { + "bbox": [ + 306, + 635, + 421, + 647 + ], + "type": "text", + "content": "4.4. Architecture details" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "type": "text", + "content": "We start from the Moment-DETR [17] architecture which uses an encoder-decoder transformer [43] and is based on the DETR architecture [4]. The model receives as input the concatenation between the video and text features and outputs the center and width of the predicted moment." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2598" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 62, + 70, + 276, + 145 + ], + "blocks": [ + { + "bbox": [ + 62, + 70, + 276, + 145 + ], + "lines": [ + { + "bbox": [ + 62, + 70, + 276, + 145 + ], + "spans": [ + { + "bbox": [ + 62, + 70, + 276, + 145 + ], + "type": "table", + "html": "
Method#scenesPrecisionRecallF1
Transcript timing20097.88.715.0
Random split554.571.653.5
ONG [37]SVD48.1986.7043.42
OSG [36]SVD67.0876.4557.18
ONG [37]545.9589.2142.69
OSG [36]562.1783.3759.51
", + "image_path": "13a45c82dc2cdb7c4f26dbc30b15c4897145532b2600022fe0ac39d998a7657c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 74, + 184, + 264, + 243 + ], + "blocks": [ + { + "bbox": [ + 47, + 148, + 286, + 181 + ], + "lines": [ + { + "bbox": [ + 47, + 148, + 286, + 181 + ], + "spans": [ + { + "bbox": [ + 47, + 148, + 286, + 181 + ], + "type": "text", + "content": "Table 2. Comparison of different video segmentation methods. Using directly the timings from the transcript has very poor results, while OSG performs the best in terms of F1 score." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 74, + 184, + 264, + 243 + ], + "lines": [ + { + "bbox": [ + 74, + 184, + 264, + 243 + ], + "spans": [ + { + "bbox": [ + 74, + 184, + 264, + 243 + ], + "type": "table", + "html": "
Segmentation MethodR1@0.5 ↑R1@0.7 ↑
Transcript timing3.1±0.40.5±0.2
Random9.4±1.62.6±0.8
ONG7.1±0.61.7±1.4
OSG13.4±0.56.3±0.3
", + "image_path": "de3ac7779c9ed5b49daa8cc276e1f18ff779d4e975b6dc4cf0ae91b5ba8751c1.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 301, + 286, + 420 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 301, + 286, + 420 + ], + "spans": [ + { + "bbox": [ + 46, + 301, + 286, + 420 + ], + "type": "text", + "content": "One limitation of [17] is that it assumes the video has a length of 3 minutes. In order to make it suitable for running on longer videos, we adjust the meta-parameters and make low-level changes to the model implementation such as removing hard-coded constraints. Please see Suppl.Mat. for more details. This modified version becomes the architecture used in our whole LONGMOMENT-DETR framework. For features, we employ SlowFast [11] video understanding features extracted every 8 seconds and GPT2-x1 [33] features for the text." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 422, + 286, + 481 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 422, + 286, + 481 + ], + "spans": [ + { + "bbox": [ + 46, + 422, + 286, + 481 + ], + "type": "text", + "content": "Implementation details. Our model is trained in PyTorch, using the AdamW optimizer [25] with a learning rate of 1e-4 and weight decay of 1e-4. All the models were trained on an NVIDIA A100 GPU. Due to memory limitations, we trained the model with a batch size of 16." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 493, + 127, + 506 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 493, + 127, + 506 + ], + "spans": [ + { + "bbox": [ + 47, + 493, + 127, + 506 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 513, + 105, + 525 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 513, + 105, + 525 + ], + "spans": [ + { + "bbox": [ + 47, + 513, + 105, + 525 + ], + "type": "text", + "content": "5.1. Metrics" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 531, + 286, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 531, + 286, + 651 + ], + "spans": [ + { + "bbox": [ + 46, + 531, + 286, + 651 + ], + "type": "text", + "content": "We report the standard metrics used in moment detection: " + }, + { + "bbox": [ + 46, + 531, + 286, + 651 + ], + "type": "inline_equation", + "content": "R1@0.5" + }, + { + "bbox": [ + 46, + 531, + 286, + 651 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 531, + 286, + 651 + ], + "type": "inline_equation", + "content": "R1@0.7" + }, + { + "bbox": [ + 46, + 531, + 286, + 651 + ], + "type": "text", + "content": ", where a prediction is considered correct if it has an intersection over union (IoU) with the ground truth " + }, + { + "bbox": [ + 46, + 531, + 286, + 651 + ], + "type": "inline_equation", + "content": "\\geq 0.5" + }, + { + "bbox": [ + 46, + 531, + 286, + 651 + ], + "type": "text", + "content": ", respectively " + }, + { + "bbox": [ + 46, + 531, + 286, + 651 + ], + "type": "inline_equation", + "content": "\\geq 0.7" + }, + { + "bbox": [ + 46, + 531, + 286, + 651 + ], + "type": "text", + "content": ". When it comes to assessing the performance of video segmentation methods we report the standard metrics for this task: precision, recall and F1-score, while for comparing query generations we report the ROUGE metrics [22] which are commonly used for the task of summarization [26, 8, 1] and are proven to have a good correlation with the human judgment [23]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 658, + 115, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 658, + 115, + 670 + ], + "spans": [ + { + "bbox": [ + 47, + 658, + 115, + 670 + ], + "type": "text", + "content": "5.2. Ablations" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 677, + 286, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 286, + 700 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 286, + 700 + ], + "type": "text", + "content": "For all the ablation experiments, we report results on the validation split, unless otherwise stated." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 701, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 701, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 701, + 286, + 713 + ], + "type": "text", + "content": "Segment timing generation. We begin by testing several" + } + ] + } + ], + "index": 11 + }, + { + "type": "table", + "bbox": [ + 333, + 71, + 522, + 154 + ], + "blocks": [ + { + "bbox": [ + 47, + 246, + 287, + 291 + ], + "lines": [ + { + "bbox": [ + 47, + 246, + 287, + 291 + ], + "spans": [ + { + "bbox": [ + 47, + 246, + 287, + 291 + ], + "type": "text", + "content": "Table 3. Comparison between different video segmentation methods combined with LONGMOMENT-DETR. The timings generation has a direct impact on performance. The number of scenes considered as input parameter for OSG and ONG is 5." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 333, + 71, + 522, + 154 + ], + "lines": [ + { + "bbox": [ + 333, + 71, + 522, + 154 + ], + "spans": [ + { + "bbox": [ + 333, + 71, + 522, + 154 + ], + "type": "table", + "html": "
MethodR-1R-2R-L
Transcript2.310.341.85
Captioning BLIP [21]7.560.56.8
Extractive [5]8.540.596.17
Bloom175B [38]9.090.527.36
OPT175B [50]10.990.748.23
GPT3 [3]15.491.3611.85
", + "image_path": "acca61d69d69963c374c1107cd87d18fbc74c204b02c600cc2e78441d95e3b13.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 158, + 545, + 202 + ], + "lines": [ + { + "bbox": [ + 305, + 158, + 545, + 202 + ], + "spans": [ + { + "bbox": [ + 305, + 158, + 545, + 202 + ], + "type": "text", + "content": "Table 4. Evaluation of query generation using ROUGE metrics. We assess the performance of different query generation methods. The transcript, being significantly longer than the human annotation, has a low score, while the LLMs perform the best." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 217, + 545, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 217, + 545, + 348 + ], + "spans": [ + { + "bbox": [ + 304, + 217, + 545, + 348 + ], + "type": "text", + "content": "methods and assess their video segmentation performance in Tab. 2. This performance correlates with the moment detection results shown in Tab. 3. Moreover, we observe that following prior works [17, 24] and using only the timings from the transcripts gives poor results. This is expected, since for BMD the average segment length is considerably longer than the segment obtained from transcript timing. In fact, just by randomly splitting the video into 5 segments, the performance improves significantly. We obtain the best results using the OSG [36] video segmentation method using five scenes." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 350, + 545, + 470 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 350, + 545, + 470 + ], + "spans": [ + { + "bbox": [ + 304, + 350, + 545, + 470 + ], + "type": "text", + "content": "Query generation. Another important step in our method is automatic query generation. Since the image and video captioning systems are trained on visual data that is out of domain as compared to our tutorial videos, we expect those systems to perform worse than the systems based on textual information. In Tab. 4 we present summarization results as compared to the human annotation for the validation split and observe that GPT3 obtains the best results. Also, in Fig. 4 we present a qualitative example for the query generation task using LLMs." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 472, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 472, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 472, + 545, + 628 + ], + "type": "text", + "content": "In Tab. 5 we present results for LONGMOMENT-DETR using various query generation techniques. The best score is obtained using the GPT3 model which correlates with the results from Tab. 4. However, while there is a correlation between the results, we notice that there is a significantly smaller gap between the performance of using LLMs such as Bloom175B or OPT175B and using the raw transcript for the task of moment detection. An explanation for this, is that even though the transcript is very long, which directly affects the ROUGE score, for the task of moment detection it contains enough relevant information in order to make up for the differences in performance. For the final model, we use the GPT3 model as the query generation method." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "Influence of pre-trained features. Our model receives at input pre-trained features for both the visual and textual component. For this ablation study, we assess the influence of such features on the final performance as seen in Tab. 6. For the visual side, we consider the SlowFast [11] and CLIP [31] features while for the textual side, we consider GPT2-x1 [33], DiffCSE [7] and CLIP [31]. The best" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2599" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 76, + 174, + 144 + ], + "blocks": [ + { + "bbox": [ + 53, + 76, + 174, + 144 + ], + "lines": [ + { + "bbox": [ + 53, + 76, + 174, + 144 + ], + "spans": [ + { + "bbox": [ + 53, + 76, + 174, + 144 + ], + "type": "image", + "image_path": "a74e8ae578983d21427a52b02dfe3d6e7dc0e8f9b9b39a5e4b0ffdf34d37ed55.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 273, + 545, + 306 + ], + "lines": [ + { + "bbox": [ + 46, + 273, + 545, + 306 + ], + "spans": [ + { + "bbox": [ + 46, + 273, + 545, + 306 + ], + "type": "text", + "content": "Figure 4. Comparison of summaries generated by GPT3, OPT175B and Bloom175B. During the summarization process no human annotation was used. In this figure, the human description and video frames are shown only for reference. While the AI generated summaries are obtained only from the transcript, the human had access to the whole video and audio when making the annotation." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 175, + 76, + 296, + 144 + ], + "blocks": [ + { + "bbox": [ + 175, + 76, + 296, + 144 + ], + "lines": [ + { + "bbox": [ + 175, + 76, + 296, + 144 + ], + "spans": [ + { + "bbox": [ + 175, + 76, + 296, + 144 + ], + "type": "image", + "image_path": "4233b2dc8e1bf5ee1609e3f912227287c045e687327e350b02c93ca3fddbb601.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 298, + 76, + 418, + 144 + ], + "blocks": [ + { + "bbox": [ + 298, + 76, + 418, + 144 + ], + "lines": [ + { + "bbox": [ + 298, + 76, + 418, + 144 + ], + "spans": [ + { + "bbox": [ + 298, + 76, + 418, + 144 + ], + "type": "image", + "image_path": "34fe41ba686d07da24165b0a6bb195446f67b9c34086b5a542ba7e64f3462e9d.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 419, + 76, + 541, + 144 + ], + "blocks": [ + { + "bbox": [ + 419, + 76, + 541, + 144 + ], + "lines": [ + { + "bbox": [ + 419, + 76, + 541, + 144 + ], + "spans": [ + { + "bbox": [ + 419, + 76, + 541, + 144 + ], + "type": "image", + "image_path": "59ffd2cf74231eeb0693444782a95ff474f1bdc29b55a0b3751fabcb93d31d1b.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 63, + 154, + 524, + 175 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 154, + 524, + 175 + ], + "spans": [ + { + "bbox": [ + 63, + 154, + 524, + 175 + ], + "type": "text", + "content": "Human: \"The host starts working on the video on After effect. The host sync the video with music and sync the movement of the arm to the music. The host adjust the animation movement of the flag according to the action of the arm.\"" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 63, + 176, + 524, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 176, + 524, + 198 + ], + "spans": [ + { + "bbox": [ + 63, + 176, + 524, + 198 + ], + "type": "text", + "content": "GPT3: \"In this tutorial, the speaker demonstrates how to animate a character's hand using the software After Effects. This tutorial is about creating an animation in which a character's arms move up and down in time with a beat.\"" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 63, + 198, + 524, + 231 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 198, + 524, + 231 + ], + "spans": [ + { + "bbox": [ + 63, + 198, + 524, + 231 + ], + "type": "text", + "content": "OPT: \"I wanted to take you through the process Learn how to improve the animation and timing in your 3D walk cycle by using the graph editor. First learn the basics of changing a keyframe. Finally, learn the In this tutorial, you learned how to add a simple effect to your hand movements.\"" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 63, + 232, + 524, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 232, + 524, + 264 + ], + "spans": [ + { + "bbox": [ + 63, + 232, + 524, + 264 + ], + "type": "text", + "content": "Bloom: \"How to make a simple animation in After Effects. We learned how to create a simple animation using the Pen Tool, how to add a simple text animation. how to make a cartoon character walk in After Effects. We learned how to create a simple walk cycle, how to animate the walk cycle.\"" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 91, + 315, + 246, + 371 + ], + "blocks": [ + { + "bbox": [ + 91, + 315, + 246, + 371 + ], + "lines": [ + { + "bbox": [ + 91, + 315, + 246, + 371 + ], + "spans": [ + { + "bbox": [ + 91, + 315, + 246, + 371 + ], + "type": "table", + "html": "
Summ MethodR1@0.5↑R1@0.7↑
Transcript13.6±0.56.3±0.3
Bloom175B13.4±0.67.0±0.2
OPT175B14.0±0.66.7±0.8
GPT316.8±0.59.2±1.0
", + "image_path": "71aad53ed804878ecb4ce6812a9e6aa1003ee7b19dc284c2e05431bdc88987d8.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 74, + 442, + 263, + 520 + ], + "blocks": [ + { + "bbox": [ + 46, + 374, + 287, + 439 + ], + "lines": [ + { + "bbox": [ + 46, + 374, + 287, + 439 + ], + "spans": [ + { + "bbox": [ + 46, + 374, + 287, + 439 + ], + "type": "text", + "content": "Table 5. Comparison between different LLM query generation methods in conjunction with LONGMOMENT-DETR. As it can be seen, GPT3 performs the best. What is interesting is that by using the raw transcript, the performance is only slightly worse than using other power full summarization methods such as Bloom175B and OPT175B." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 74, + 442, + 263, + 520 + ], + "lines": [ + { + "bbox": [ + 74, + 442, + 263, + 520 + ], + "spans": [ + { + "bbox": [ + 74, + 442, + 263, + 520 + ], + "type": "table", + "html": "
Video featsText featsR1@0.5 ↑R1@0.7 ↑
SlowFastGPT2-x116.8±0.59.2±1.0
SlowFastDiffCSE13.1±1.56.5±1.2
SlowFastCLIP11.2±0.74.9±0.9
CLIPCLIP12.7±0.66.2±0.3
CLIPGPT2-x113.8±1.27.1±1.8
CLIPDiffCSE13.8±1.97.5±0.7
", + "image_path": "806306f5875e38f84efef5c8031a70808285d34442e77f55598676fbebdfd446.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 569, + 287, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 569, + 287, + 591 + ], + "spans": [ + { + "bbox": [ + 46, + 569, + 287, + 591 + ], + "type": "text", + "content": "results are obtained using SlowFast for the visual side and GPT2-x1 for the textual side." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 594, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 287, + 712 + ], + "type": "text", + "content": "Influence of different components. In Tab. 7 we present an overview of the influence of different components on the testing split (the results on validation split are presented previously in each corresponding section). We start with a Moment-DETR [17] model as Baseline. We observe that both the segment timing generation and the query generation have a strong impact on performance. We obtain the best results by combining the timing generation from OSG with the GPT3 query generation which represents our final LONGMOMENT-DETR framework." + } + ] + } + ], + "index": 14 + }, + { + "type": "table", + "bbox": [ + 309, + 316, + 545, + 376 + ], + "blocks": [ + { + "bbox": [ + 46, + 524, + 287, + 556 + ], + "lines": [ + { + "bbox": [ + 46, + 524, + 287, + 556 + ], + "spans": [ + { + "bbox": [ + 46, + 524, + 287, + 556 + ], + "type": "text", + "content": "Table 6. Influence of pre-trained features on performance. The best performance is obtained using SlowFast features for the visual side and GPT2-xl features for the textual side." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 316, + 545, + 376 + ], + "lines": [ + { + "bbox": [ + 309, + 316, + 545, + 376 + ], + "spans": [ + { + "bbox": [ + 309, + 316, + 545, + 376 + ], + "type": "table", + "html": "
ComponentSegmentsQueriesR1@0.5↑R1@0.7↑
Baseline [17]NoNo2.7±0.60.3±0.1
Random segRandomNo9.2±1.82.6±0.4
SummarizeRandomGPT313.2±0.35.6±0.6
ShotDetectOSGNo12.6±0.45.5±0.4
LONGMOMENT-DETROSGGPT316.3±0.38.3±0.5
", + "image_path": "fb36dde4cebfc1aa8836ae851f8972e2b6ea399d29ba91c1db5ac20a992e5f8a.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "table_body" + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 379, + 545, + 435 + ], + "lines": [ + { + "bbox": [ + 305, + 379, + 545, + 435 + ], + "spans": [ + { + "bbox": [ + 305, + 379, + 545, + 435 + ], + "type": "text", + "content": "Table 7. Effect of different components on performance. Both the segment timing generation and query generation have a strong impact on performance. Hence, in the final model, we use OSG and GPT3, thus obtaining our final model LONGMOMENT-DETR. The results are presented on the testing split." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 447, + 441, + 460 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 447, + 441, + 460 + ], + "spans": [ + { + "bbox": [ + 306, + 447, + 441, + 460 + ], + "type": "text", + "content": "5.3. Comparison with others" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 467, + 545, + 622 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 467, + 545, + 622 + ], + "spans": [ + { + "bbox": [ + 304, + 467, + 545, + 622 + ], + "type": "text", + "content": "In this section, we compare our method against two recent methods: Moment-DETR [17] and UMT [24] adjusted for ingesting long videos. For UMT we use the video only version as introduced in the paper [24]. This comparison can be seen in Tab. 8. By training using the raw transcripts, which is similar to the pre-training stage of [17], the results in our case for long tutorial videos are poor. However, by adjusting the base architecture and use the automatic generated segments tailored for long videos, the results improve significantly for Moment-DETR as observed in the table. Moreover, if we use our full LONGMOMENT-DETR framework, as described in Sec. 4.2, the results are significantly better than previously published methods." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 633, + 416, + 646 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 633, + 416, + 646 + ], + "spans": [ + { + "bbox": [ + 306, + 633, + 416, + 646 + ], + "type": "text", + "content": "5.4. YouTube Chapters" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 652, + 545, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 652, + 545, + 688 + ], + "spans": [ + { + "bbox": [ + 304, + 652, + 545, + 688 + ], + "type": "text", + "content": "To further evaluate the quality of our features obtained using the automatic annotations, we have collected new data from YouTube Chapters as described in Sec. 3.2." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "Experimental setup. We initially train the network using BMD. Once trained, these weights serve as the founda" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2600" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "bbox": [ + 65, + 76, + 534, + 105 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 76, + 534, + 105 + ], + "spans": [ + { + "bbox": [ + 65, + 76, + 534, + 105 + ], + "type": "text", + "content": "BMD Query: \"The host colors the cow with lime yellow color and a part of the body of the cow is colored with brown color. The nose of the cow is colored with skin color. A few skin color strokes are added to the coat of the cow. The background of the cow is added with green color to the grass and sky blue color to the sky.\"" + } + ] + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 67, + 109, + 541, + 177 + ], + "blocks": [ + { + "bbox": [ + 52, + 132, + 66, + 146 + ], + "lines": [ + { + "bbox": [ + 52, + 132, + 66, + 146 + ], + "spans": [ + { + "bbox": [ + 52, + 132, + 66, + 146 + ], + "type": "text", + "content": "(A)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 67, + 109, + 541, + 177 + ], + "lines": [ + { + "bbox": [ + 67, + 109, + 541, + 177 + ], + "spans": [ + { + "bbox": [ + 67, + 109, + 541, + 177 + ], + "type": "image", + "image_path": "9513679795b762d5223ccf57999c82b327e787c620a1a144dc936c6850cc66d5.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 67, + 177, + 541, + 254 + ], + "blocks": [ + { + "bbox": [ + 52, + 213, + 66, + 224 + ], + "lines": [ + { + "bbox": [ + 52, + 213, + 66, + 224 + ], + "spans": [ + { + "bbox": [ + 52, + 213, + 66, + 224 + ], + "type": "text", + "content": "(B)" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 67, + 177, + 541, + 254 + ], + "lines": [ + { + "bbox": [ + 67, + 177, + 541, + 254 + ], + "spans": [ + { + "bbox": [ + 67, + 177, + 541, + 254 + ], + "type": "image", + "image_path": "2d129fe2a1df8ef345a9fa4f7fc5d02d98723d1c9963cb2eaaaa063d2f4f310a.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 258, + 546, + 304 + ], + "lines": [ + { + "bbox": [ + 45, + 258, + 546, + 304 + ], + "spans": [ + { + "bbox": [ + 45, + 258, + 546, + 304 + ], + "type": "text", + "content": "Figure 5. Qualitative examples for BMD (A) and YTC (B). Along with the query, we show several video frames, the prediction results in orange and the ground truth in green. We also specify the overlap between the prediction and ground truth segments. Please note how different the queries between BMD and YTC are. Also, while the prediction results have an offset from the ground truth, we want to highlight how subtle is the change in scenery for our proposed datasets." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 74, + 322, + 264, + 380 + ], + "blocks": [ + { + "bbox": [ + 74, + 322, + 264, + 380 + ], + "lines": [ + { + "bbox": [ + 74, + 322, + 264, + 380 + ], + "spans": [ + { + "bbox": [ + 74, + 322, + 264, + 380 + ], + "type": "table", + "html": "
ModelR1@0.5↑R1@0.7↑
Moment-DETR [17]2.7±0.60.3±0.1
UMT [24]†11.5±1.04.6±1.3
Moment-DETR [17]†12.6±0.45.5±0.4
LONGMOMENT-DETR16.3±0.38.3±0.5
", + "image_path": "888a7b24c2e2aa2dcf44d1cb0dc4f40db626063eef2f1f557b89f8d827ad5b00.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 456, + 287, + 528 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 456, + 287, + 528 + ], + "spans": [ + { + "bbox": [ + 46, + 456, + 287, + 528 + ], + "type": "text", + "content": "tion for fine-tuning on the subsequent task of chapter detection. While the BMD training data is automatically curated, when we transition to training on the manually annotated data from the YTC dataset, we distinguish this model by referring to it as CHAPTER-DETR. This model uses the same architecture as LONGMOMENT-DETR." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 531, + 288, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 531, + 288, + 686 + ], + "spans": [ + { + "bbox": [ + 46, + 531, + 288, + 686 + ], + "type": "text", + "content": "Results. The results for chapter detection are presented in Tab. 9. We observe that when only pre-training on BMD and directly assessing performance, the performance is low, the main reason being the distribution shift between the queries and segments in BMD and the ones in YTC. The queries from BMD are often composed of several sentences while the chapter annotation only contains a few words (as showcased in Fig. 5). However, if we first pre-train on BMD and then finetune with chapter annotations, there is a major boost in performance. These results prove that not only LONGMOMENT-DETR can be used on its own for moment detection, but it can be used to significantly improve the performance for the task of chapter detection." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "content": "Limitations. Since our method relies on automatic annotation generation, various problems such as text hallucination" + } + ] + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 308, + 323, + 545, + 364 + ], + "blocks": [ + { + "bbox": [ + 46, + 384, + 288, + 440 + ], + "lines": [ + { + "bbox": [ + 46, + 384, + 288, + 440 + ], + "spans": [ + { + "bbox": [ + 46, + 384, + 288, + 440 + ], + "type": "text", + "content": "Table 8. Comparison with other methods. As it can be seen, LONGMOMENT-DETR achieves better results than other moment detection methods. " + }, + { + "bbox": [ + 46, + 384, + 288, + 440 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 46, + 384, + 288, + 440 + ], + "type": "text", + "content": " denotes training the models with the timings obtained by our proposed method using OSG. The results are presented on the testing split." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 323, + 545, + 364 + ], + "lines": [ + { + "bbox": [ + 308, + 323, + 545, + 364 + ], + "spans": [ + { + "bbox": [ + 308, + 323, + 545, + 364 + ], + "type": "table", + "html": "
ModelPre-trainingTrainingR1@0.5 ↑R1@0.7 ↑
LONGMOMENT-DETRBMD-5.0±2.42.2±1.5
CHAPTER-DETR-YTC12.6±0.35.8±0.6
CHAPTER-DETRBMDYTC16.1±0.56.6±0.3
", + "image_path": "a9a5a213c05d7a92e596c2af87ae6f6918f5a6c2b249fff3baa2fad5ac467434.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 367, + 546, + 443 + ], + "lines": [ + { + "bbox": [ + 305, + 367, + 546, + 443 + ], + "spans": [ + { + "bbox": [ + 305, + 367, + 546, + 443 + ], + "type": "text", + "content": "Table 9. Results on YouTube-Chapters. If we evaluate LONGMOMENT-DETR trained with BMD directly on the task of chapter detection on the YTC dataset, the performance is low. However, if we use BMD as pre-training data and then train fully supervised for the task of chapter detection, there is a significant boost in performance as opposed to randomly initializing the model (4th line vs 3rd line)." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 455, + 545, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 455, + 545, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 455, + 545, + 491 + ], + "type": "text", + "content": "or incorrect segment timing generation directly affect the results of our system. Other limitations regarding particular components are discussed throughout the paper." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 491, + 545, + 551 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 491, + 545, + 551 + ], + "spans": [ + { + "bbox": [ + 304, + 491, + 545, + 551 + ], + "type": "text", + "content": "Societal impact. Moment retrieval systems enable efficient content discovery for learning. However, these systems can exhibit biases towards particular groups or they can be used for spreading misinformation. Another aspect is the notable cost and carbon footprint required to train modern models." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 562, + 384, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 562, + 384, + 574 + ], + "spans": [ + { + "bbox": [ + 306, + 562, + 384, + 574 + ], + "type": "text", + "content": "6. Conclusions" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 582, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 547, + 713 + ], + "type": "text", + "content": "In this paper we presented the LONGMOMENT-DETR framework which tackles the task of moment detection in long tutorial videos. We introduced, the first two long tutorial video datasets, Behance Moment Detection (BMD) and YouTube Chapters (YTC). BMD has human annotations for testing and validation splits and we propose a novel system to automatically curate the annotations for the training split by leveraging the information from the transcript. Lastly, we introduced YTC, a dataset containing human annotated chapters, and we further test and prove the effectiveness of the features obtained from BMD for chapter detection." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "2601" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 53, + 92, + 289, + 714 + ], + "type": "list", + "angle": 0, + "index": 10, + "blocks": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "spans": [ + { + "bbox": [ + 53, + 92, + 287, + 147 + ], + "type": "text", + "content": "[1] Stefanos Angelidis, Reinald Kim Amplayo, Yoshihiko Suhara, Xiaolan Wang, and Mirella Lapata. 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AAAI Press, 2020. 2" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 48, + 485, + 287, + 538 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 485, + 287, + 538 + ], + "spans": [ + { + "bbox": [ + 48, + 485, + 287, + 538 + ], + "type": "text", + "content": "[50] Susan Zhang, Stephen Roller, Naman Goyal, Mikel Artetxe, Moya Chen, Shuohui Chen, Christopher Dewan, Mona Diab, Xian Li, Xi Victoria Lin, et al. Opt: Open pre-trained transformer language models. ArXiv preprint, abs/2205.01068, 2022. 2, 5, 6" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 48, + 540, + 287, + 605 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 540, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 48, + 540, + 287, + 605 + ], + "type": "text", + "content": "[51] Minghang Zheng, Yanjie Huang, Qingchao Chen, Yuxin Peng, and Yang Liu. Weakly supervised temporal sentence grounding with gaussian-based contrastive proposal learning. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 15555-15564, 2022. 2" + } + ] + } + ], + "index": 7 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2604" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/MonoDETR_ Depth-guided Transformer for Monocular 3D Object Detection/3836a1be-d313-4152-8663-e644f7bd2a45_content_list.json b/2023/MonoDETR_ Depth-guided Transformer for Monocular 3D Object Detection/3836a1be-d313-4152-8663-e644f7bd2a45_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..b20177aa769c51dee285c788d4e5be8714fd4ea2 --- /dev/null +++ b/2023/MonoDETR_ Depth-guided Transformer for Monocular 3D Object Detection/3836a1be-d313-4152-8663-e644f7bd2a45_content_list.json @@ -0,0 +1,1627 @@ +[ + { + "type": "text", + "text": "MonoDETR: Depth-guided Transformer for Monocular 3D Object Detection", + "text_level": 1, + "bbox": [ + 98, + 130, + 870, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Renrui Zhang $^{1,2}$ , Han Qiu $^{2}$ , Tai Wang $^{1,2}$ , Ziyu Guo $^{2}$ , Ziteng Cui $^{2}$ Yu Qiao $^{2}$ , Hongsheng Li $^{\\dagger 1,2,3}$ , Peng Gao $^{\\dagger 2}$", + "bbox": [ + 227, + 179, + 743, + 217 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ CUHK MMLab $^{2}$ Shanghai Artificial Intelligence Laboratory $^{3}$ Centre for Perceptual and Interactive Intelligence (CPII)", + "bbox": [ + 233, + 224, + 736, + 262 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{zhangrenrui, wangtai, gaopeng}@pjlab.org.cn, hsli@ee.cuhk.edu.hk", + "bbox": [ + 102, + 268, + 867, + 287 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 258, + 321, + 336, + 338 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Monocular 3D object detection has long been a challenging task in autonomous driving. Most existing methods follow conventional 2D detectors to first localize object centers, and then predict 3D attributes by neighboring features. However, only using local visual features is insufficient to understand the scene-level 3D spatial structures and ignores the long-range inter-object depth relations. In this paper, we introduce the first DETR framework for Monocular DTection with a depth-guided TRansformer, named MonoDETR. We modify the vanilla transformer to be depth-aware and guide the whole detection process by contextual depth cues. Specifically, concurrent to the visual encoder that captures object appearances, we introduce to predict a foreground depth map, and specialize a depth encoder to extract non-local depth embeddings. Then, we formulate 3D object candidates as learnable queries and propose a depth-guided decoder to conduct object-scene depth interactions. In this way, each object query estimates its 3D attributes adaptively from the depth-guided regions on the image and is no longer constrained to local visual features. On KITTI benchmark with monocular images as input, MonoDETR achieves state-of-the-art performance and requires no extra dense depth annotations. Besides, our depth-guided modules can also be plug-and-play to enhance multi-view 3D object detectors on nuScenes dataset, demonstrating our superior generalization capacity. Code is available at https://github.com/ZrrSkywalker/MonoDETR.", + "bbox": [ + 76, + 353, + 473, + 777 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 78, + 805, + 209, + 821 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "With a wide range of applications in autonomous driving, 3D object detection is more challenging than its 2D counterparts, due to the complex spatial circumstances.", + "bbox": [ + 76, + 830, + 468, + 878 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/02e855ce7534f2ed2b7b1787e8560924b0e6ee9e3bc68bf1046fdd8de9a296e1.jpg", + "image_caption": [ + "Figure 1. Center-guided (Top) and Depth-guided Paradigms (Bottom) for monocular 3D object detection. Existing center-guided methods predict 3D attributes from local visual features around the centers, while our MonoDETR guides the detection by a predicted foreground depth map and adaptively aggregates features in global context. The lower right figure visualizes the attention map of the target query in the depth cross-attention layer." + ], + "image_footnote": [], + "bbox": [ + 509, + 320, + 879, + 476 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Compared to methods based on LiDAR [57, 20, 41, 50] and multi-view images [49, 22, 26, 17], 3D object detection from monocular (single-view) images [9, 1, 46] is of most difficulty, which generally does not rely on depth measurements or multi-view geometry. The detection accuracy thus severely suffers from the ill-posed depth estimation, leading to inferior performance.", + "bbox": [ + 496, + 609, + 892, + 715 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Except for leveraging pseudo 3D representations [48, 51, 32, 38], standard monocular 3D detection methods [33, 52, 53, 31] follow the pipeline of traditional 2D object detection [40, 24, 43, 56]. They first localize objects by detecting the projected centers on the image, and then aggregate the neighboring visual features for 3D property prediction, as illustrated in Figure 1 (Top). Although it is conceptually straightforward, such center-guided methods are limited by the local appearances without long-range context, and fail to capture implicit geometric cues from 2D images, e.g., depth guidance, which are critical to detect objects in 3D space.", + "bbox": [ + 496, + 718, + 893, + 883 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To tackle this issue, we propose MonoDETR, which", + "bbox": [ + 519, + 885, + 892, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Corresponding author", + "bbox": [ + 101, + 887, + 230, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "9155", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/5ec4506b34b33f6ecb376831da7b887324f4c0846dbfa219caf705de935e6f1c.jpg", + "image_caption": [ + "Figure 2. Comparison of DETR-based methods for camera-based 3D object detection. We utilize yellow, blue, green, and red to respectively denote the feature or prediction space related with 2D, depth, 3D, and BEV. Different from other methods, our MonoDETR leverages depth cues to guide 3D object detection from monocular images." + ], + "image_footnote": [], + "bbox": [ + 86, + 85, + 236, + 289 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/de4705794926c829fedab5a79b1b0eaa8e75686214253ce6145c2b625f50d285.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 258, + 85, + 472, + 292 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/e1d237b7818079d52bedeafc8e70a765bbb205a8c1bad3d67020727f55ca5fba.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 504, + 85, + 697, + 287 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/9b050e0e68757f5bcdfac6e095600c750fede0f5da9594822198cf18610aa1e6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 720, + 85, + 877, + 286 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "presents a novel depth-guided 3D detection scheme in Figure 1 (Bottom). Compared to DETR [4] in 2D detection, the transformer in MonoDETR is equipped with depth-guided modules to better capture contextual depth cues, serving as the first DETR model for monocular 3D object detection, as shown in Figure 2 (a) and (b). It consists of: two parallel encoders for visual and depth representation learning, and a decoder for adaptive depth-guided detection.", + "bbox": [ + 75, + 364, + 468, + 487 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Specifically, after the feature backbone, we first utilize a lightweight depth predictor to acquire the depth features of the input image. To inject effective depth cues, a foreground depth map is predicted on top, and supervised only by discrete depth labels of objects, which requires no dense depth annotations during training. Then, we apply the parallel encoders to respectively generate non-local depth and visual embeddings, which represent the input image from two aspects: depth geometry and visual appearance. On top of that, a set of object queries is fed into the depth-guided decoder, and conducts adaptive feature aggregation from the two embeddings. Via a proposed depth cross-attention layer, the queries can capture geometric cues from the depth-guided regions on the image, and explore interobject depth relations. In this way, the 3D attribute prediction can be guided by informative depth hints, no longer constrained by the limited visual features around centers.", + "bbox": [ + 75, + 488, + 468, + 744 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "As an end-to-end transformer-based network, MonoDETR is free from non-maximum suppression (NMS) or rule-based label assignment. We only utilize the object-wise labels for supervision without using auxiliary data, such as dense depth maps or LiDAR. Taking monocular images as input, MonoDETR achieves state-of-the-art performance among existing center-guided methods, and surpasses the second-best by $+2.53\\%$ , $+1.08\\%$ , and $+0.85\\%$ for three-level difficulties on KITTI [14] test set.", + "bbox": [ + 75, + 748, + 468, + 883 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Besides single-view images, the depth-guided mod", + "bbox": [ + 96, + 885, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ules in MonoDETR can also be extended as a plug-and-play module for multi-view 3D detection on nuScenes [3] dataset. By providing multi-view depth cues, our method can not only improve the end-to-end detection performance of PETRv2 [27] by $+1.2\\%$ NDS, but also benefit the BEV representation learning in BEVFormer [22] by $+0.9\\%$ NDS. This further demonstrates the effectiveness and generalizability of our proposed depth guidance.", + "bbox": [ + 496, + 364, + 890, + 487 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We summarize the contributions of our paper as follows:", + "bbox": [ + 517, + 488, + 890, + 503 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose MonoDETR, a depth-guided framework to capture scene-level geometries and inter-object depth relations for monocular 3D object detection.", + "- We introduce a foreground depth map for object-wise depth supervision, and a depth cross-attention layer for adaptive depth features interaction.", + "- MonoDETR achieves leading results on monocular KITTI benchmark, and can also be generalized to enhance multi-view detection on nuScenes benchmark." + ], + "bbox": [ + 517, + 516, + 890, + 675 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 691, + 640, + 709 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Existing methods for camera-based 3D object detection can be categorized as two groups according to the input number of views: monocular (single-view) and multi-view methods. Monocular detectors only take as input the front-view images and solve a more challenging task from insufficient 2D signals. Multi-view detectors simultaneously encode images of surrounding scenes and can leverage cross-view dependence to understand the 3D space.", + "bbox": [ + 496, + 719, + 890, + 840 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Monocular (Single-view) 3D Object Detection. Most previous monocular detectors adopt center-guided pipelines following conventional 2D detectors [40, 43, 56]. As early", + "bbox": [ + 496, + 854, + 892, + 901 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "9156", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "table", + "img_path": "images/22fc58a43495161499026d4fd49ae354d8f851cf0037c192fe598138a1d71fc8.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodDETR-basedExtra DataGuided byObject QueryFeat. Aggre.
Mutli-view Methods
DETR3D [49]✓-Visual3DLocal
PETR (v2) [26]✓TemporalVisual3DGlobal
BEVFormer [22]✓TemporalVisualBEV, 3DGlobal
Monocular Methods
MonoDTR [18]×LiDARCenter×Local
MonoDETR✓-DepthDepthGlobal
", + "bbox": [ + 78, + 90, + 472, + 215 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Table 1. Comparison of DETR-based methods for camera-based 3D object detection. Our MonoDETR is uniquely guided by depth cues with depth-aware object queries.", + "bbox": [ + 75, + 220, + 470, + 263 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "works, Deep3Box [35] introduces discretized representation with perspective constraints, and M3D-RPN [1] designs a depth-aware convolution for better 3D region proposals. With very few handcrafted modules, SMOKE [28] and FCOS3D [46] propose concise architectures for efficient one-stage detection, while MonoDLE [33] and PGD [47] analyze depth errors on top with improved performance. To supplement the limited 3D cues, additional data are utilized for assistance: dense depth annotations [32, 12, 45, 36], CAD models [29], and LiDAR [7, 38, 18]. Some recent methods introduce complicated geometric priors into the networks: adjacent object pairs [10], 2D-3D keypoints [21], and uncertainty-related depth [52, 31]. Despite this, the center-guided methods are still limited by local visual features without scene-level spatial cues. In contrast, MonoDETR discards the center localization step and conducts adaptive feature aggregation via a depth-guided transformer. MonoDETR requires no additional annotations and contains minimal 2D-3D geometric priors.", + "bbox": [ + 75, + 294, + 472, + 583 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Multi-view 3D Object Detection. For jointly extracting features from surrounding views, DETR3D [49] firstly utilizes a set of 3D object queries and back-projects them onto multi-view images for feature aggregation. PETR series [26, 27] further proposes to generate 3D position features without unstable projection and explores the advantage of temporal information from previous frames. From another point of view, BEVDet [17, 16] follows [37] to lift 2D images into a unified Bird's-Eye-View (BEV) representation and appends BEV-based heads [50] for detection. BEVFormer [22] instead generates BEV features via a set of learnable BEV queries, and introduces a spatiotemporal BEV transformer for visual features aggregation. Follow-up works also introduce cross-modal distillation [19, 11] and masked image modeling [25, 6] for improved performance. Different from the above methods for multi-view input, MonoDETR targets monocular images and extracts depth guidance to capture more geometric cues. Our depth-guided modules can also be generalized to surrounding views as a plug-and-play module to enhance multi-view detectors.", + "bbox": [ + 75, + 598, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/ad84401c4e25971a9f646f5380235658817b5552b93b4f8d93ebecfe9575de9b.jpg", + "image_caption": [ + "Figure 3. The lightweight depth predictor. We utilize the depth predictor to predict the depth features and foreground depth map, which only contains discrete object-wise depth values." + ], + "image_footnote": [], + "bbox": [ + 501, + 89, + 895, + 200 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Comparison of DETR-based Methods. DETR [5] and its follow-up works [13, 59, 54, 34] have attained great success on 2D object detection without NMS or anchors. Inspired by this, some efforts have transferred DETR into camera-based 3D object detection. We specifically compare our MonoDETR with existing DETR-based 3D object detectors in Figure 2 and Table 1. (1) MonoDTR [18]. Also as a single-view detector, MonoDTR utilizes transformers [44] to incorporate depth features with visual representations. However, MonoDTR is not a DETR-based method, and still adopts the traditional center-guided paradigm, which localizes objects by their centers and only aggregate local features. MonoDTR contains no object queries for global feature aggregation, and follows YOLOv3 [39] to adopt complicated NMS post-processing with pre-defined anchors. (2) DETR3D [49] and PETR (v2) [26, 27] (Figure 2 (c)) are multi-view methods and follow the DETR detection pipeline. In contrast, they contain no transformer-based encoders (visual or depth), and detect objects by 3D object queries without the perspective transformation. Importantly, they are only guided by visual features and explores no depth cues from the input images. (3) BEVFormer [22] (Figure 2 (d)) firstly utilizes a BEV transformer to lift multiview images into BEV representations, and then conducts DETR-based detection within the BEV space. Different from all aforementioned methods, MonoDETR introduces a unique depth-guided transformer that guides the 3D detection by geometric depth cues, which can generalize well to both monocular and multi-view inputs.", + "bbox": [ + 496, + 295, + 893, + 734 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 752, + 591, + 768 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The overall framework of MonoDETR is shown in Figure 4. We first illustrate the concurrent visual and depth feature extraction in Section 3.1, and detail our depth-guided transformer for aggregating appearance and geometric cues in Section 3.2. Then, we introduce the attribute prediction and loss functions of MonoDETR in Section 3.3. Finally, we illustrate how to plug our depth-guided transformer into existing multi-view object detectors in Section 3.4.", + "bbox": [ + 496, + 779, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "9157", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/b4b5956ff1d1c64f05de6f13102cbe3680fdacfa10715d931de094aa23a8d9bd.jpg", + "image_caption": [ + "Figure 4. Overall pipeline of MonoDETR. We first acquire the visual and depth features of the input image and utilize two parallel encoders for non-local encoding. Then, we propose a depth-guided decoder to adaptively aggregate scene-level features in global context." + ], + "image_footnote": [], + "bbox": [ + 158, + 85, + 810, + 364 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Feature Extraction", + "text_level": 1, + "bbox": [ + 76, + 428, + 261, + 441 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Taking as input a monocular (single-view) image, our framework utilizes a feature backbone, e.g., ResNet-50 [15], and a lightweight depth predictor to generate its visual and depth features, respectively.", + "bbox": [ + 75, + 450, + 470, + 513 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Visual Features. Given the image $I \\in \\mathbb{R}^{H \\times W \\times 3}$ , where $H$ and $W$ denote its height and width, we obtain its multiscale feature maps, $f_{\\frac{1}{8}}$ , $f_{\\frac{1}{16}}$ , and $f_{\\frac{1}{32}}$ , from the last three stages of ResNet-50. Their downsample ratios to the original size are $\\frac{1}{8}$ , $\\frac{1}{16}$ and $\\frac{1}{32}$ . We regard the highest-level $f_{\\frac{1}{32}} \\in \\mathbb{R}^{\\frac{H}{32} \\times \\frac{W}{32} \\times C}$ with sufficient semantics as the visual features $f_V$ of the input image.", + "bbox": [ + 76, + 517, + 468, + 628 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Depth Features. We obtain the depth features from the image by a lightweight depth predictor, as shown in Figure 3. We first unify the sizes of three-level features to the same $\\frac{1}{16}$ downsample ratio via bilinear pooling, and fuse them by element-wise addition. In this way, we can integrate multi-scale visual appearances and also preserve fine-grained patterns for objects of small sizes. Then, we apply two $3\\times 3$ convolutional layers to obtain the depth features $f_{D}\\in \\mathbb{R}^{\\frac{H}{16}\\times \\frac{W}{16}\\times C}$ for the input image.", + "bbox": [ + 75, + 635, + 468, + 772 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Foreground Depth Map. To incorporate effective depth information into the depth features, we predict a foreground depth map $D_{fg} \\in \\mathbb{R}_{16}^{\\frac{H}{16} \\times \\frac{W}{16} \\times (k + 1)}$ on top of $f_{D}$ via a $1 \\times 1$ convolutional layer. We supervise the depth map only by discrete object-wise depth labels, without extra dense depth annotations. The pixels within the same 2D bounding box are assigned with the same depth label of the corresponding object. For pixels within multiple boxes, we select the", + "bbox": [ + 75, + 779, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "depth label of the object that is nearest to the camera, which accords with the visual appearance of the image. Here, We discretize the depth into $k + 1$ bins [38], where the first ordinal $k$ bins denote foreground depth and the last one denotes the background. We adopt linear-increasing discretization (LID), since the larger depth estimation errors of farther objects can be suppressed with a wider categorization interval. We limit the foreground depth values within $[d_{min}, d_{max}]$ , and set both the first interval length and LID's common difference as $\\delta$ . We then categorize a ground-truth depth label $d$ into the $k$ -th bin as:", + "bbox": [ + 496, + 429, + 893, + 594 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nk = \\left\\lfloor - 0. 5 + 0. 5 \\sqrt {1 + \\frac {8 (d - d _ {\\min })}{\\delta}} \\right\\rfloor , \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 563, + 598, + 890, + 631 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\delta = \\frac{2(d_{max} - d_{min})}{k(k + 1)}$ . By focusing on the object-wise depth values, the network can better capture foreground spatial structures and inter-object depth relations, which produces informative depth features for the subsequent depth-guided transformer.", + "bbox": [ + 496, + 636, + 893, + 717 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Depth-guided Transformer", + "text_level": 1, + "bbox": [ + 500, + 729, + 743, + 744 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The depth-guided transformer of MonoDETR is composed of a visual encoder, a depth encoder, and a depth-guided decoder. The two encoders produce non-local visual and depth embeddings, and the decoder enables object queries to adaptively capture scene-level information.", + "bbox": [ + 496, + 752, + 893, + 829 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Visual and Depth Encoders. Given depth and visual features $f_{D}, f_{V}$ , we specialize two transformer encoders to generate their scene-level embeddings with global receptive fields, denoted as $f_{D}^{e} \\in \\mathbb{R}_{16^{2}}^{\\frac{HW}{2} \\times C}$ and $f_{V}^{e} \\in \\mathbb{R}_{32^{2}}^{\\frac{HW}{2} \\times C}$ .", + "bbox": [ + 496, + 837, + 893, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "9158", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We set three blocks for the visual encoder and only one block for the depth encoder, since the discrete foreground depth information is easier to be encoded than the rich visual appearances. Each encoder block consists of a self-attention layer and a feed-forward neural network (FFN). By the global self-attention mechanism, the depth encoder explores long-range dependencies of depth values from different foreground areas, which provides non-local geometric cues of the stereo space. In addition, the decoupling of depth and visual encoders allows them to better learn features for themselves, encoding the input image from two perspectives, i.e., depth geometry and visual appearance.", + "bbox": [ + 75, + 90, + 472, + 273 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Depth-guided Decoder. Based on the non-local $f_{D}^{e}, f_{V}^{e}$ , we utilize a set of learnable object queries $q \\in \\mathbb{R}^{N \\times C}$ to detect 3D objects via the depth-guided decoder, where $N$ denotes the pre-defined maximum number of objects in the input image. Each decoder block sequentially contains a depth cross-attention layer, an inter-query self-attention layer, a visual cross-attention layer, and an FFN. Specifically, the queries first capture informative depth features from $f_{D}^{e}$ via the depth cross-attention layer, in which we linearly transform the object queries and depth embeddings into queries, keys, and values,", + "bbox": [ + 75, + 289, + 472, + 457 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nQ _ {q} = \\operatorname {L i n e a r} (q), \\quad K _ {D}, V _ {D} = \\operatorname {L i n e a r} \\left(f _ {D} ^ {e}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 124, + 465, + 468, + 483 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $Q_{q}\\in \\mathbb{R}^{N\\times C}$ and $K_{D},V_{D}\\in \\mathbb{R}^{\\frac{HW}{16^{2}}\\times C}$ . Then, we calculate the query-depth attention map $A_{D}\\in \\mathbb{R}^{N\\times \\frac{HW}{16^{2}}}$ , and aggregate informative depth features weighted by $A_{D}$ to produce the depth-aware queries $q^{\\prime}$ , formulated as,", + "bbox": [ + 75, + 491, + 468, + 558 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nA _ {D} = \\operatorname {S o f t m a x} \\left(Q _ {q} K _ {D} ^ {T} / \\sqrt {C}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 565, + 468, + 583 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nq ^ {\\prime} = \\operatorname {L i n e a r} \\left(A _ {D} V _ {D}\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 181, + 585, + 468, + 602 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Such a mechanism enables each object query to adaptively capture spatial cues from depth-guided regions on the image, leading to better scene-level spatial understanding. Then, the depth-aware queries are fed into the inter-query self-attention layer for feature interaction between objects, and the visual cross-attention layer for collecting visual semantics from $f_V^e$ . We stack three decoder blocks to fully fuse the scene-level depth cues into object queries.", + "bbox": [ + 75, + 611, + 468, + 732 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Depth Positional Encodings. In the depth cross-attention layer, we propose learnable depth positional encodings for $f_{D}^{e}$ instead of conventional sinusoidal functions. In detail, we maintain a set of learnable embeddings, $p_{D} \\in \\mathbb{R}^{(d_{max} - d_{min} + 1) \\times C}$ , where each row encodes the depth positional information for a meter, ranging from $d_{min}$ to $d_{max}$ . For each pixel $(x,y)$ in $D_{fg}$ , we first obtain its $(k + 1)$ -categorical depth prediction confidence, $D_{fg}(x,y) \\in \\mathbb{R}^{k + 1}$ , each channel of which denotes the predicted confidence for the corresponding depth bin. The estimated depth", + "bbox": [ + 75, + 750, + 472, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "of pixel $(x,y)$ can then be obtained by the weighted summation of the depth-bin confidences and their corresponding depth values, which is formulated as", + "bbox": [ + 496, + 90, + 890, + 136 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nd _ {m a p} (x, y) = \\sum_ {i = 1} ^ {k + 1} D _ {f g} (x, y) [ i ] \\cdot d _ {b i n} ^ {i}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 568, + 148, + 890, + 191 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $d_{bin}^{i}$ denotes the starting value of the $i$ -th depth bin and $\\sum_{i=1}^{k+1} D_{fg}(x,y)[i] = 1$ . Then, we linearly interpolate $p_{D}$ according to the depth $d_{map}(x,y)$ to obtain the depth positional encoding for the pixel $(x,y)$ . By pixel-wisely adding $f_{D}^{e}$ with such encodings, object queries can better capture scene-level depth cues and understand 3D geometry in the depth cross-attention layer.", + "bbox": [ + 496, + 204, + 890, + 313 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Detection Heads and Loss", + "text_level": 1, + "bbox": [ + 498, + 325, + 735, + 339 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "After the decoder, the depth-aware queries are fed into a series of MLP-based heads for 3D attribute predictions, including object category, 2D size, projected 3D center, depth, 3D size, and orientation. For inference, we convert these perspective attributes into 3D-space bounding boxes using camera parameters without NMS post-processing or pre-defined anchors. For training, we match the orderless queries with ground-truth labels and compute losses for the paired ones. We refer to Supplementary Material for details.", + "bbox": [ + 496, + 349, + 890, + 486 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Bipartite Matching. To correctly match each query with ground-truth objects, we calculate the loss for each query-label pair and utilize Hungarian algorithm [4] to find the globally optimal matching. For each pair, we integrate the losses of six attributes into two groups. The first contains object category, 2D size and the projected 3D center, since these attributes mainly concern 2D visual appearances of the image. The second group consists of depth, 3D size and orientation, which are 3D spatial properties of the object. We respectively sum the losses of two groups and denote them as $\\mathcal{L}_{2D}$ and $\\mathcal{L}_{3D}$ . As the network generally predicts less accurate 3D attributes than 2D attributes, especially at the beginning of training, the value of $\\mathcal{L}_{3D}$ is unstable and would disturb the matching process. We only utilize $\\mathcal{L}_{2D}$ as the matching cost for matching each query-label pair.", + "bbox": [ + 496, + 502, + 890, + 729 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Overall Loss. After the matching, we obtain $N_{gt}$ valid pairs out of $N$ queries, where $N_{gt}$ denotes the number of ground-truth objects. Then, the overall loss of a training image is formulated as", + "bbox": [ + 496, + 741, + 890, + 801 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {o v e r a l l}} = \\frac {1}{N _ {g t}} \\cdot \\sum_ {n = 1} ^ {N _ {g t}} \\left(\\mathcal {L} _ {2 D} + \\mathcal {L} _ {3 D}\\right) + \\mathcal {L} _ {\\text {d m a p}}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 540, + 816, + 890, + 858 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{dmap}$ represents the Focal loss [23] of the predicted categorical foreground depth map $D_{fg}$ in Section 3.1.", + "bbox": [ + 496, + 869, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "9159", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/d8fd9e60a21cc964658874fdbe868cef4ecc8012a12d88a1d6bdf9ceeecf6430.jpg", + "image_caption": [ + "Figure 5. Plug-and-play for multi-view 3D object detection. We utilize yellow, blue, green, and red to respectively denote the feature space related to 2D, depth, 3D, and BEV. The depth-guided transformer of MonoDETR is adopted to enhance PETR (v2) [26, 27] and BEVFormer [22] in a plug-and-play manner, which provides depth guidance from surrounding scenes." + ], + "image_footnote": [], + "bbox": [ + 98, + 85, + 869, + 310 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.4. Plug-and-play for Multi-view Detectors", + "text_level": 1, + "bbox": [ + 76, + 383, + 415, + 400 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Besides monocular images, our depth-guided transformer can also serve as a plug-and-play module upon multi-view methods for depth-guided detection. Specifically, we append our depth predictors and depth encoders after the backbones of multi-view methods, which are shared across views and extract surrounding depth embeddings. Then, we inject our depth cross-attention layer into their transformer blocks to guide the 3D or BEV object queries by scene-level depth cues.", + "bbox": [ + 75, + 407, + 470, + 544 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For PETR (v2) [26, 27] in Figure 5 (a), we modify its previous visual decoder as a depth-guided decoder. In each decoder block, the 3D object queries are first fed into our depth cross-attention layer for depth cues aggregation, and then into the original 3D self-attention and visual cross-attention for 3D position features interaction. This enables PETR's 3D queries to be depth-aware and better capture spatial characteristics of surrounding scenes.", + "bbox": [ + 75, + 554, + 468, + 676 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For BEVFormer [22] in Figure 5 (b), as its decoder is conducted in BEV space, we incorporate the depth guidance into its BEV encoder, which lifts image features into BEV space by transformers. In each encoder block, the BEV queries also sequentially pass through our depth cross-attention layer and the original spatial cross-attention layer. This contributes to better BEV representation learning guided by the multi-view depth information.", + "bbox": [ + 75, + 685, + 468, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 821, + 209, + 838 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Settings", + "text_level": 1, + "bbox": [ + 76, + 845, + 176, + 863 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Dataset. We evaluate MonoDETR on the widely-adopted KITTI [14] benchmark, including 7,481 training and 7,518", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "test images. We follow [8, 9] to split 3,769 val images from the training set. We report the detection results with three-level difficulties, easy, moderate, and hard, and evaluate by the average precision $(AP)$ of bounding boxes in 3D space and the bird-eye view, denoted as $AP_{3D}$ and $AP_{BEV}$ , respectively, which are both at 40 recall positions.", + "bbox": [ + 496, + 383, + 892, + 476 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation details. We adopt ResNet-50 [15] as our feature backbone. To save GPU memory, we apply deformable attention [59] for the visual encoder and visual cross-attention layers, and utilize the vanilla global attention [4] to better capture non-local geometries for the depth encoder and depth cross-attention layers. We utilize 8 heads for all attention modules and set the number of queries $N$ as 50, which are learnable embeddings with predicted 2D reference points. We set the channel $C$ and all MLP's latent dimensions as 256. For the foreground depth map, we set $[d_{min}, d_{max}]$ as $[0m, 60m]$ and the number of bins $k$ as 80. On a single RTX 3090 GPU, we train MonoDETR for 195 epochs with batch size 16 and a learning rate $2 \\times 10^{-4}$ . We adopt AdamW [30] optimizer with weight decay $10^{-4}$ , and decrease the learning rate at 125 and 165 epochs by 0.1. For training stability, we discard the training samples with depth labels larger than 65 meters or smaller than 2 meters. During inference, we simply filter out the object queries with the category confidence lower than 0.2 without NMS post-processing, and recover the 3D bounding box using the predicted six attributes following previous works [33, 31].", + "bbox": [ + 496, + 484, + 892, + 801 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison", + "text_level": 1, + "bbox": [ + 500, + 813, + 632, + 829 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Performance. In Table 2, MonoDETR achieves state-of-the-art performance on KITTI test and val sets. On test set, MonoDETR exceeds all existing methods including those with different additional data input and surpasses", + "bbox": [ + 496, + 839, + 892, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "9160", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/4ede43b2b38110803f6839c4cccf644e837a6cd6a6d9431eb49a044b96a350da.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodExtra dataTest, AP3DTest, APBEVVal, AP3D
EasyMod.HardEasyMod.HardEasyMod.Hard
PatchNet [32]Depth15.6811.1210.1722.9716.8614.97---
D4LCN [12]16.6511.729.5122.5116.0212.55---
DDMP-3D [45]19.7112.789.8028.0817.8913.44---
Kinematic3D [2]Video19.0712.729.1726.6917.5213.1019.7614.1010.47
MonoRUn [7]LiDAR19.6512.3010.5827.9417.3415.2420.0214.6512.61
CaDDN [38]19.1713.4111.4627.9418.9117.1923.5716.3113.84
MonoDTR [18]21.9915.3912.7328.5920.3817.1424.5218.5715.51
AutoShape [29]CAD22.4714.1711.3630.6620.0815.5920.0914.6512.07
SMOKE [28]None14.039.767.8420.8314.4912.7514.7612.8511.50
MonoPair [10]13.049.998.6519.2814.8312.8916.2812.3010.42
RTM3D [21]13.6110.098.18---19.4716.2915.57
PGD [47]19.0511.769.3926.8916.5113.4919.2713.2310.65
IAFA [55]17.8112.0110.6125.8817.8815.3518.9514.9614.84
MonoDLE [33]17.2312.2610.2924.7918.8916.0017.4513.6611.68
MonoRCNN [42]18.3612.6510.0325.4818.1114.1016.6113.1910.65
MonoGeo [53]18.8513.8111.5225.8618.9916.1918.4514.4812.87
MonoFlex [52]19.9413.8912.0728.2319.7516.8923.6417.5114.83
GUPNet [31]20.1114.2011.77---22.7616.4613.72
MonoDETR (Ours)None25.0016.4713.5833.6022.1118.6028.8420.6116.38
Improvementv.s. second-best+2.53+1.08+0.85+2.94+1.73+1.41+4.32+2.04+0.81
", + "bbox": [ + 109, + 88, + 857, + 444 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "the second-best under three-level difficulties by $+2.53\\%$ , $+1.08\\%$ and $+0.85\\%$ in $AP_{3D}$ , and by $+2.94\\%$ , $+1.73\\%$ and $+1.41\\%$ in $AP_{BEV}$ . The competitive MonoDTR [18] also applies transformers to fuse depth features, but it is still a center-guided method and highly relies on additional dense depth supervision, anchors and NMS. In contrast, MonoDETR performs better without extra input or handcrafted designs, illustrating its simplicity and effectiveness.", + "bbox": [ + 75, + 502, + 468, + 623 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Efficiency. Compared to existing methods in Table 3, MonoDETR can achieve the best detection performance without consuming too much computational budget. As illustrated in Section 3, we only process the feature maps with $\\frac{1}{16}$ and $\\frac{1}{32}$ downsample ratios, which reduces our Runtime and GFlops, while others adopt $\\frac{1}{4}$ and $\\frac{1}{8}$ ratios.", + "bbox": [ + 75, + 635, + 468, + 728 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Studies", + "text_level": 1, + "bbox": [ + 76, + 739, + 241, + 753 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We verify the effectiveness of each our component and report $AP_{3D}$ for the car category on the KITTI val set.", + "bbox": [ + 75, + 763, + 468, + 792 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Depth-guided Transformer. In Table 5, we first remove the entire depth-guided transformer along with the depth predictor, which constructs a pure center-guided baseline. This variant, denoted as 'w/o Depth-guided Trans.' can be regarded as a re-implementation of MonoDLE [33] with our detection heads and loss functions. As shown, the absence", + "bbox": [ + 75, + 809, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/f11783ca7891b84c6a2b6def5a5e6393cd1626d15c15e45e046d84e0557705e4.jpg", + "table_caption": [ + "Table 2. Monocular performance of the car category on KITTI test and val sets. We utilize bold numbers to highlight the best results, and color the second-best ones and our gain over them in blue." + ], + "table_footnote": [], + "table_body": "
MethodMonoDLEGUPNetMonoDTRMonoDETR
Runtime↓40343738
GFlops↓79.1262.32120.4862.12
AP3D Mod.12.2615.0215.3916.47
", + "bbox": [ + 501, + 500, + 890, + 565 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. Efficiency comparison. We test the Runtime (ms) on one RTX 3090 GPU with batch size 1, and compare $AP_{3D}$ on test set.", + "bbox": [ + 500, + 570, + 890, + 598 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "of the depth-guided transformer greatly hurts the performance, for the lack of non-local geometric cues. Then, we investigate two key designs within the depth-guided transformer: the transformer architecture and depth guidance. For 'w/o Transformer', we only append the depth predictor upon the center-guided baseline to provide implicit depth guidance without transformers. For 'w/o Depth Guidance', we equip the center-guided baseline with a visual encoder and decoder, but include no depth predictor, depth encoder, and the depth cross-attention layer in the decoder. This builds a transformer network guided by visual appearances, without any depth guidance for object queries. The performance degradation of both variants indicates their significance for our depth-guided feature aggregation paradigm.", + "bbox": [ + 496, + 625, + 890, + 839 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Depth Encoder. The depth encoder produces non-local depth embeddings $f_{D}^{e}$ , which are essential for queries to", + "bbox": [ + 498, + 869, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "9161", + "bbox": [ + 480, + 944, + 513, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/c3dba3d0ab52e2b003c24c0baaa6b837663292ff0eeb9ab47997f7d2d094e3a7.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodImage SizeNDS↑mAP↑mATE↓mASE↓mAOE↓mAVE↓mAAE↓
CenterNet [56]-0.3280.3060.7160.2640.6091.4260.658
FCOS3D* [46]1600×9000.4150.3430.7250.2630.4221.2920.153
PGD* [47]1600×9000.4280.3690.6830.2600.4391.2680.185
DETR3D† [49]1600×9000.4340.3490.7160.2680.3790.8420.200
BEVDet† [17]1408×5120.4170.3490.6370.2690.4900.9140.268
PETR† [26]1600×9000.4420.3700.7110.2670.3830.8650.201
PETRv2 [27] + Depth-gudied800×3200.4960.4010.7450.2680.4480.3940.184
0.5080.4100.7270.2650.3890.4190.187
BEVFormer [22] + Depth-gudied1600×9000.5170.4160.6730.2740.3720.3940.198
0.5260.4230.6610.2720.3490.3710.192
", + "bbox": [ + 153, + 88, + 812, + 268 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/5c22d1a016f8c5382755b7b84dd212d5d2cf9ed7ba10da9c93d79e31d7907bd6.jpg", + "table_caption": [ + "Table 4. Multi-view performance on nuScenes val set. * denotes the two-step fine-tuning with test-time augmentation, and † denotes CBGS [58] training. We compare with the best-performing variants of other methods and utilize bold numbers to highlight the best results." + ], + "table_footnote": [], + "table_body": "
ArchitectureEasyMod.Hard
MonoDETR28.8420.6116.38
w/o Depth-guided Trans.19.6915.1513.93
w/o Transformer20.1916.0514.18
w/o Depth Guidance24.1417.8115.60
", + "bbox": [ + 107, + 324, + 434, + 414 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "explore scene-level depth cues in the depth cross-attention layer. We experiment with different encoder designs in Table 6. 'Deform. SA' and $3 \\times 3$ Conv. $\\times 2'$ represent one-block of deformable attention and two $3 \\times 3$ convolutional layers, respectively. As reported, 'Global SA' with only one block generates the best $f_{D}^{e}$ for global geoentry encoding.", + "bbox": [ + 75, + 486, + 468, + 580 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Depth-guided Decoder. As the core depth-guided component, we explore how to better guide object queries to interact with depth embeddings $f_{D}^{e}$ in Table 7. With the sequential inter-query self-attention ( $I'$ ) and visual cross-attention ( $V'$ ) layers, we insert the depth cross-attention layer ( $D'$ ) into each decoder block with four positions. For $I \\rightarrow D + V'$ , we fuse the depth and visual embeddings $f_{D}^{e}, f_{V}^{e}$ by element-wise addition, and apply only one unified cross-attention layer. As shown, the $D \\rightarrow I \\rightarrow V'$ order performs the best. By placing $D'$ in the front, object queries can first aggregate depth cues to guide the remaining operations in each decoder block.", + "bbox": [ + 75, + 587, + 468, + 770 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Foreground Depth Map. We explore different representations for our depth map in Table 8. Compared to dense depth supervision ('Dense'), adopting object-wise depth labels ('Fore.') can focus the network on more important foreground geometric cues, and better capture depth relations between objects. 'LID' outperforms other discretization methods, since the linear-increasing intervals can suppress the larger estimation errors of farther objects.", + "bbox": [ + 75, + 779, + 468, + 902 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/466fd3f821bf54ccf9678926e5cb666680541eb58f7ec3443f1faa8b9f40f051.jpg", + "table_caption": [ + "Table 5. Effectiveness of depth-guided transformer. 'Depth-guided Trans.' and 'Depth Guidance' denote the depth-guided transformer and the depth cross-attention layer, respectively" + ], + "table_footnote": [], + "table_body": "
MechanismEasyMod.Hard
Global SA28.8420.6116.38
Deform. SA26.4318.9115.55
3×3 Conv.×2 w/o25.5518.3615.28
24.2518.3815.41
", + "bbox": [ + 563, + 324, + 826, + 414 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 6. The design of depth encoder. 'Deform. SA' denotes a one-block deformable self-attention layer. 'w/o' denotes directly feeding depth features into the decoder without the depth encoder.", + "bbox": [ + 498, + 417, + 892, + 462 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Depth Positional Encodings $p_D$ . In Table 9, we experiment with different depth positional encodings for $f_D^e$ in the depth cross-attention layer. By default, we apply the meterwise encodings $p_D \\in \\mathbb{R}^{(d_{max} - d_{min} + 1) \\times C}$ that assign one learnable embedding per meter with depth value interpolation for output. We then assign one learnable embedding for each depth bin, denoted as 'k-bin $p_D \\in \\mathbb{R}^{k \\times C}$ , and also experiment sinusoidal functions to encode either the depth values or 2D coordinates of the feature map, denoted as 'Depth sin/cos' and '2D sin/cos', respectively. As shown, 'meter-wise $p_D$ ' performs the best for encoding more fine-grained depth cues ranging from $d_{min}$ to $d_{max}$ , which provides the queries with more scene-level spatial structures.", + "bbox": [ + 496, + 487, + 890, + 684 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Multi-view Experiments", + "text_level": 1, + "bbox": [ + 500, + 695, + 723, + 710 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "As a plug-and-play module for multi-view 3D object detection, we append our depth-guided transformer upon two DETR-based multi-view networks, PETR v2 [27] and BEVFormer [22]. The detailed network architectures are shown in Figure 5. For a fair comparison, we adopt the same training configurations as the two baseline models, and utilize the same $[d_{min}, d_{max}]$ with $k$ as monocular experiments. We report the performance on nuScenes [3] val set in Table 4, where we apply no test-time augmentation or CGBS [58] training. For end-to-end detection in PETRv2, the depth guidance contributes to $+1.2\\%$ NDS and $+0.9\\%$ mAP by providing sufficient multi-view geometric cues.", + "bbox": [ + 496, + 719, + 892, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "9162", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0cc48f129910ed97c69db42eb1361e13c1d88acac4747ce23f137ec15dc4311b.jpg", + "image_caption": [ + "Figure 6. Visualizations of attention maps $A_{D}$ in the depth cross-attention layer. The top column denotes the input image, and the last three columns denote the attention maps of the target queries (denoted as white dots). Hotter colors indicate higher attention weights." + ], + "image_footnote": [], + "bbox": [ + 81, + 89, + 281, + 237 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/5ab5c61c38bb24ea37716344d6a75087d94f215de3b6ed38fc1d89e0f71a8989.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 282, + 90, + 483, + 237 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/67e90c1fccbbdbf4a5740d40650cf2108806ab22428744b5ec9e5bbf17651fcd.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 483, + 90, + 684, + 237 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/6f26fadc0ed7a03d14f7d1545144b28f3e7c0e4fdd9bb02fcfabb58837989ca1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 686, + 90, + 887, + 237 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/16fc32a2b1d6384aec03c8342fbd15bac15520a248cbf37534ac852c551fc652.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ArchitectureEasyMod.Hard
D → I → V28.8420.6116.38
I → D → V26.2419.2816.03
I → V → D25.8418.8515.72
I → D + V24.9418.4115.39
", + "bbox": [ + 122, + 290, + 421, + 378 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "For the BEV feature generation, our modules benefit BEV-Former by $+0.9\\%$ NDS and $+0.7\\%$ mAP, indicating the importance of auxiliary depth information for BEV-space feature encoding. The additional experiments on multi-view 3D object detection well demonstrate the effectiveness and generalizability of our approach.", + "bbox": [ + 75, + 453, + 468, + 544 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Visualization", + "text_level": 1, + "bbox": [ + 76, + 560, + 210, + 575 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We visualize the attention maps $A_{D}$ in Equation 3 of the depth cross-attention layer at the last decoder block. As shown in Figure 6, the areas with high attention scores for the target object query spread over the entire image, concentrating on other objects with long distances. This indicates, via our depth guidance, object queries are able to adaptively capture non-local depth cues from the image and are no longer limited by neighboring visual features.", + "bbox": [ + 75, + 585, + 468, + 708 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 724, + 194, + 739 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We propose MonoDETR, an end-to-end transformer-based framework for monocular 3D object detection, which is free from any additional input, anchors, or NMS. Different from existing center-guided methods, we enable object queries to explore geometric cues adaptively from the depth-guided regions, and conduct inter-object and object-scene depth interactions via attention mechanisms. Extensive experiments have demonstrated the effectiveness of our approach for both single-view (KITTI) and multi-view (nuScenes) input. We hope MonoDETR can serve as a", + "bbox": [ + 75, + 750, + 470, + 901 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/139da808a42bca946cb902e5f8f11b33ee6307910d5b328438a1e6d4a42deefa.jpg", + "table_caption": [ + "Table 7. The design of depth-guided decoder. 'D', 'I', and 'V' denote the depth cross-attention, inter-query self-attention, and visual cross-attention layers, respectively." + ], + "table_footnote": [], + "table_body": "
Depth MapEasyMod.Hard
Fore. LID28.8420.6116.38
Dense LID27.6919.8515.98
Fore. UD25.6118.9015.49
Fore. SID26.0518.9515.59
", + "bbox": [ + 547, + 290, + 841, + 381 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/13d3e40fe3cfff8ff2696f252b69cdab2b07692a806707636b837e1a4d7e059d.jpg", + "table_caption": [ + "Table 8. Different representations of the predicted depth map. 'UD', 'SID', and 'LID' denote uniform, spacing-increasing, and linear-increasing discretizations." + ], + "table_footnote": [], + "table_body": "
SettingsEasyMod.Hard
Meter-wise pD28.8420.6116.38
k-bin pD28.0619.6816.04
Depth sin/cos27.4219.5715.82
2D sin/cos26.4818.6315.52
w/o26.7618.9415.85
", + "bbox": [ + 558, + 453, + 828, + 556 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Table 9. The design of depth positional encodings. 'Meter-wise' and $k$ -bin' assign learnable embeddings by meters and depth bins, respectively. 'sin/cos' denotes sinusoidal functions for encodings.", + "bbox": [ + 498, + 561, + 890, + 604 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "strong DETR baseline for future research in monocular 3D object detection. Limitations. How to effectively incorporate multi-modal input into our transformer framework is not discussed in the paper. Our future direction will focus on this to further improve the performance of depth-guided transformers, e.g., distilling more sufficient geometric knowledge from LiDAR and RADAR modalities.", + "bbox": [ + 496, + 630, + 890, + 736 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 500, + 753, + 660, + 770 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This project is funded in part by the National Natural Science Foundation of China (No.62206272), by the National Key R&D Program of China Project (No.2022ZD0161100), by the Centre for Perceptual and Interactive Intelligence (CPII) Ltd under the Innovation and Technology Commission (ITC)'s InnoHK, and by the General Research Fund of Hong Kong RGC Project 14204021. Hongsheng Li is a PI of CPII under the InnoHK.", + "bbox": [ + 496, + 779, + 890, + 898 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "9163", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Garrick Brazil and Xiaoming Liu. M3d-rpn: Monocular 3d region proposal network for object detection. In IEEE International Conference on Computer Vision, 2019. 1, 3", + "[2] Garrick Brazil, Gerard Pons-Moll, Xiaoming Liu, and Bernt Schiele. Kinematic 3d object detection in monocular video. In Proceedings of the European Conference on Computer Vision, 2020. 7", + "[3] Holger Caesar, Varun Bankiti, Alex H. Lang, Sourabh Vora, Venice Erin Liong, Qiang Xu, Anush Krishnan, Yu Pan, Giancarlo Baldan, and Oscar Beijbom. nuscenes: A multimodal dataset for autonomous driving. 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Deformable detr: Deformable transformers for end-to-end object detection. arXiv preprint arXiv:2010.04159, 2020. 3, 6" + ], + "bbox": [ + 78, + 90, + 467, + 289 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "9166", + "bbox": [ + 482, + 945, + 516, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/MonoDETR_ Depth-guided Transformer for Monocular 3D Object Detection/3836a1be-d313-4152-8663-e644f7bd2a45_model.json b/2023/MonoDETR_ Depth-guided Transformer for Monocular 3D Object Detection/3836a1be-d313-4152-8663-e644f7bd2a45_model.json new file mode 100644 index 0000000000000000000000000000000000000000..9ae175c4a99b9a59eebb3633a301b8e302cb92aa --- /dev/null +++ b/2023/MonoDETR_ Depth-guided Transformer for Monocular 3D Object Detection/3836a1be-d313-4152-8663-e644f7bd2a45_model.json @@ -0,0 +1,2303 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.099, + 0.131, + 0.872, + 0.153 + ], + "angle": 0, + "content": "MonoDETR: Depth-guided Transformer for Monocular 3D Object Detection" + }, + { + "type": "text", + "bbox": [ + 0.228, + 0.18, + 0.744, + 0.218 + ], + "angle": 0, + "content": "Renrui Zhang\\(^{1,2}\\), Han Qiu\\(^{2}\\), Tai Wang\\(^{1,2}\\), Ziyu Guo\\(^{2}\\), Ziteng Cui\\(^{2}\\) Yu Qiao\\(^{2}\\), Hongsheng Li\\(^{\\dagger 1,2,3}\\), Peng Gao\\(^{\\dagger 2}\\)" + }, + { + "type": "text", + "bbox": [ + 0.235, + 0.226, + 0.737, + 0.263 + ], + "angle": 0, + "content": "\\(^{1}\\)CUHK MMLab \\(^{2}\\)Shanghai Artificial Intelligence Laboratory \\(^{3}\\)Centre for Perceptual and Interactive Intelligence (CPII)" + }, + { + "type": "text", + "bbox": [ + 0.104, + 0.27, + 0.868, + 0.289 + ], + "angle": 0, + "content": "{zhangrenrui, wangtai, gaopeng}@pjlab.org.cn, hsli@ee.cuhk.edu.hk" + }, + { + "type": "title", + "bbox": [ + 0.259, + 0.323, + 0.337, + 0.339 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.354, + 0.474, + 0.778 + ], + "angle": 0, + "content": "Monocular 3D object detection has long been a challenging task in autonomous driving. Most existing methods follow conventional 2D detectors to first localize object centers, and then predict 3D attributes by neighboring features. However, only using local visual features is insufficient to understand the scene-level 3D spatial structures and ignores the long-range inter-object depth relations. In this paper, we introduce the first DETR framework for Monocular DTection with a depth-guided TRansformer, named MonoDETR. We modify the vanilla transformer to be depth-aware and guide the whole detection process by contextual depth cues. Specifically, concurrent to the visual encoder that captures object appearances, we introduce to predict a foreground depth map, and specialize a depth encoder to extract non-local depth embeddings. Then, we formulate 3D object candidates as learnable queries and propose a depth-guided decoder to conduct object-scene depth interactions. In this way, each object query estimates its 3D attributes adaptively from the depth-guided regions on the image and is no longer constrained to local visual features. On KITTI benchmark with monocular images as input, MonoDETR achieves state-of-the-art performance and requires no extra dense depth annotations. Besides, our depth-guided modules can also be plug-and-play to enhance multi-view 3D object detectors on nuScenes dataset, demonstrating our superior generalization capacity. Code is available at https://github.com/ZrrSkywalker/MonoDETR." + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.806, + 0.21, + 0.822 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.832, + 0.47, + 0.879 + ], + "angle": 0, + "content": "With a wide range of applications in autonomous driving, 3D object detection is more challenging than its 2D counterparts, due to the complex spatial circumstances." + }, + { + "type": "image", + "bbox": [ + 0.511, + 0.321, + 0.88, + 0.477 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.486, + 0.893, + 0.584 + ], + "angle": 0, + "content": "Figure 1. Center-guided (Top) and Depth-guided Paradigms (Bottom) for monocular 3D object detection. Existing center-guided methods predict 3D attributes from local visual features around the centers, while our MonoDETR guides the detection by a predicted foreground depth map and adaptively aggregates features in global context. The lower right figure visualizes the attention map of the target query in the depth cross-attention layer." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.611, + 0.893, + 0.717 + ], + "angle": 0, + "content": "Compared to methods based on LiDAR [57, 20, 41, 50] and multi-view images [49, 22, 26, 17], 3D object detection from monocular (single-view) images [9, 1, 46] is of most difficulty, which generally does not rely on depth measurements or multi-view geometry. The detection accuracy thus severely suffers from the ill-posed depth estimation, leading to inferior performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.719, + 0.895, + 0.885 + ], + "angle": 0, + "content": "Except for leveraging pseudo 3D representations [48, 51, 32, 38], standard monocular 3D detection methods [33, 52, 53, 31] follow the pipeline of traditional 2D object detection [40, 24, 43, 56]. They first localize objects by detecting the projected centers on the image, and then aggregate the neighboring visual features for 3D property prediction, as illustrated in Figure 1 (Top). Although it is conceptually straightforward, such center-guided methods are limited by the local appearances without long-range context, and fail to capture implicit geometric cues from 2D images, e.g., depth guidance, which are critical to detect objects in 3D space." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.886, + 0.893, + 0.901 + ], + "angle": 0, + "content": "To tackle this issue, we propose MonoDETR, which" + }, + { + "type": "page_footnote", + "bbox": [ + 0.102, + 0.888, + 0.231, + 0.901 + ], + "angle": 0, + "content": "† Corresponding author" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "9155" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.086, + 0.238, + 0.29 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.259, + 0.087, + 0.473, + 0.294 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.506, + 0.087, + 0.699, + 0.288 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.721, + 0.087, + 0.878, + 0.287 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.299, + 0.893, + 0.342 + ], + "angle": 0, + "content": "Figure 2. Comparison of DETR-based methods for camera-based 3D object detection. We utilize yellow, blue, green, and red to respectively denote the feature or prediction space related with 2D, depth, 3D, and BEV. Different from other methods, our MonoDETR leverages depth cues to guide 3D object detection from monocular images." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.366, + 0.47, + 0.488 + ], + "angle": 0, + "content": "presents a novel depth-guided 3D detection scheme in Figure 1 (Bottom). Compared to DETR [4] in 2D detection, the transformer in MonoDETR is equipped with depth-guided modules to better capture contextual depth cues, serving as the first DETR model for monocular 3D object detection, as shown in Figure 2 (a) and (b). It consists of: two parallel encoders for visual and depth representation learning, and a decoder for adaptive depth-guided detection." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.489, + 0.47, + 0.746 + ], + "angle": 0, + "content": "Specifically, after the feature backbone, we first utilize a lightweight depth predictor to acquire the depth features of the input image. To inject effective depth cues, a foreground depth map is predicted on top, and supervised only by discrete depth labels of objects, which requires no dense depth annotations during training. Then, we apply the parallel encoders to respectively generate non-local depth and visual embeddings, which represent the input image from two aspects: depth geometry and visual appearance. On top of that, a set of object queries is fed into the depth-guided decoder, and conducts adaptive feature aggregation from the two embeddings. Via a proposed depth cross-attention layer, the queries can capture geometric cues from the depth-guided regions on the image, and explore interobject depth relations. In this way, the 3D attribute prediction can be guided by informative depth hints, no longer constrained by the limited visual features around centers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.749, + 0.47, + 0.884 + ], + "angle": 0, + "content": "As an end-to-end transformer-based network, MonoDETR is free from non-maximum suppression (NMS) or rule-based label assignment. We only utilize the object-wise labels for supervision without using auxiliary data, such as dense depth maps or LiDAR. Taking monocular images as input, MonoDETR achieves state-of-the-art performance among existing center-guided methods, and surpasses the second-best by \\(+2.53\\%\\), \\(+1.08\\%\\), and \\(+0.85\\%\\) for three-level difficulties on KITTI [14] test set." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Besides single-view images, the depth-guided mod" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.366, + 0.892, + 0.488 + ], + "angle": 0, + "content": "ules in MonoDETR can also be extended as a plug-and-play module for multi-view 3D detection on nuScenes [3] dataset. By providing multi-view depth cues, our method can not only improve the end-to-end detection performance of PETRv2 [27] by \\(+1.2\\%\\) NDS, but also benefit the BEV representation learning in BEVFormer [22] by \\(+0.9\\%\\) NDS. This further demonstrates the effectiveness and generalizability of our proposed depth guidance." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.489, + 0.891, + 0.504 + ], + "angle": 0, + "content": "We summarize the contributions of our paper as follows:" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.517, + 0.892, + 0.563 + ], + "angle": 0, + "content": "- We propose MonoDETR, a depth-guided framework to capture scene-level geometries and inter-object depth relations for monocular 3D object detection." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.574, + 0.892, + 0.62 + ], + "angle": 0, + "content": "- We introduce a foreground depth map for object-wise depth supervision, and a depth cross-attention layer for adaptive depth features interaction." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.631, + 0.892, + 0.676 + ], + "angle": 0, + "content": "- MonoDETR achieves leading results on monocular KITTI benchmark, and can also be generalized to enhance multi-view detection on nuScenes benchmark." + }, + { + "type": "list", + "bbox": [ + 0.519, + 0.517, + 0.892, + 0.676 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.693, + 0.641, + 0.71 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.842 + ], + "angle": 0, + "content": "Existing methods for camera-based 3D object detection can be categorized as two groups according to the input number of views: monocular (single-view) and multi-view methods. Monocular detectors only take as input the front-view images and solve a more challenging task from insufficient 2D signals. Multi-view detectors simultaneously encode images of surrounding scenes and can leverage cross-view dependence to understand the 3D space." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.893, + 0.902 + ], + "angle": 0, + "content": "Monocular (Single-view) 3D Object Detection. Most previous monocular detectors adopt center-guided pipelines following conventional 2D detectors [40, 43, 56]. As early" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "9156" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.08, + 0.092, + 0.473, + 0.216 + ], + "angle": 0, + "content": "
MethodDETR-basedExtra DataGuided byObject QueryFeat. Aggre.
Mutli-view Methods
DETR3D [49]✓-Visual3DLocal
PETR (v2) [26]✓TemporalVisual3DGlobal
BEVFormer [22]✓TemporalVisualBEV, 3DGlobal
Monocular Methods
MonoDTR [18]×LiDARCenter×Local
MonoDETR✓-DepthDepthGlobal
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.222, + 0.471, + 0.264 + ], + "angle": 0, + "content": "Table 1. Comparison of DETR-based methods for camera-based 3D object detection. Our MonoDETR is uniquely guided by depth cues with depth-aware object queries." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.295, + 0.473, + 0.584 + ], + "angle": 0, + "content": "works, Deep3Box [35] introduces discretized representation with perspective constraints, and M3D-RPN [1] designs a depth-aware convolution for better 3D region proposals. With very few handcrafted modules, SMOKE [28] and FCOS3D [46] propose concise architectures for efficient one-stage detection, while MonoDLE [33] and PGD [47] analyze depth errors on top with improved performance. To supplement the limited 3D cues, additional data are utilized for assistance: dense depth annotations [32, 12, 45, 36], CAD models [29], and LiDAR [7, 38, 18]. Some recent methods introduce complicated geometric priors into the networks: adjacent object pairs [10], 2D-3D keypoints [21], and uncertainty-related depth [52, 31]. Despite this, the center-guided methods are still limited by local visual features without scene-level spatial cues. In contrast, MonoDETR discards the center localization step and conducts adaptive feature aggregation via a depth-guided transformer. MonoDETR requires no additional annotations and contains minimal 2D-3D geometric priors." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.599, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Multi-view 3D Object Detection. For jointly extracting features from surrounding views, DETR3D [49] firstly utilizes a set of 3D object queries and back-projects them onto multi-view images for feature aggregation. PETR series [26, 27] further proposes to generate 3D position features without unstable projection and explores the advantage of temporal information from previous frames. From another point of view, BEVDet [17, 16] follows [37] to lift 2D images into a unified Bird's-Eye-View (BEV) representation and appends BEV-based heads [50] for detection. BEVFormer [22] instead generates BEV features via a set of learnable BEV queries, and introduces a spatiotemporal BEV transformer for visual features aggregation. Follow-up works also introduce cross-modal distillation [19, 11] and masked image modeling [25, 6] for improved performance. Different from the above methods for multi-view input, MonoDETR targets monocular images and extracts depth guidance to capture more geometric cues. Our depth-guided modules can also be generalized to surrounding views as a plug-and-play module to enhance multi-view detectors." + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.09, + 0.897, + 0.202 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.222, + 0.895, + 0.264 + ], + "angle": 0, + "content": "Figure 3. The lightweight depth predictor. We utilize the depth predictor to predict the depth features and foreground depth map, which only contains discrete object-wise depth values." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.296, + 0.895, + 0.735 + ], + "angle": 0, + "content": "Comparison of DETR-based Methods. DETR [5] and its follow-up works [13, 59, 54, 34] have attained great success on 2D object detection without NMS or anchors. Inspired by this, some efforts have transferred DETR into camera-based 3D object detection. We specifically compare our MonoDETR with existing DETR-based 3D object detectors in Figure 2 and Table 1. (1) MonoDTR [18]. Also as a single-view detector, MonoDTR utilizes transformers [44] to incorporate depth features with visual representations. However, MonoDTR is not a DETR-based method, and still adopts the traditional center-guided paradigm, which localizes objects by their centers and only aggregate local features. MonoDTR contains no object queries for global feature aggregation, and follows YOLOv3 [39] to adopt complicated NMS post-processing with pre-defined anchors. (2) DETR3D [49] and PETR (v2) [26, 27] (Figure 2 (c)) are multi-view methods and follow the DETR detection pipeline. In contrast, they contain no transformer-based encoders (visual or depth), and detect objects by 3D object queries without the perspective transformation. Importantly, they are only guided by visual features and explores no depth cues from the input images. (3) BEVFormer [22] (Figure 2 (d)) firstly utilizes a BEV transformer to lift multiview images into BEV representations, and then conducts DETR-based detection within the BEV space. Different from all aforementioned methods, MonoDETR introduces a unique depth-guided transformer that guides the 3D detection by geometric depth cues, which can generalize well to both monocular and multi-view inputs." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.753, + 0.593, + 0.769 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.903 + ], + "angle": 0, + "content": "The overall framework of MonoDETR is shown in Figure 4. We first illustrate the concurrent visual and depth feature extraction in Section 3.1, and detail our depth-guided transformer for aggregating appearance and geometric cues in Section 3.2. Then, we introduce the attribute prediction and loss functions of MonoDETR in Section 3.3. Finally, we illustrate how to plug our depth-guided transformer into existing multi-view object detectors in Section 3.4." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "9157" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.159, + 0.087, + 0.812, + 0.366 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.373, + 0.895, + 0.403 + ], + "angle": 0, + "content": "Figure 4. Overall pipeline of MonoDETR. We first acquire the visual and depth features of the input image and utilize two parallel encoders for non-local encoding. Then, we propose a depth-guided decoder to adaptively aggregate scene-level features in global context." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.429, + 0.262, + 0.443 + ], + "angle": 0, + "content": "3.1. Feature Extraction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.452, + 0.471, + 0.514 + ], + "angle": 0, + "content": "Taking as input a monocular (single-view) image, our framework utilizes a feature backbone, e.g., ResNet-50 [15], and a lightweight depth predictor to generate its visual and depth features, respectively." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.518, + 0.47, + 0.629 + ], + "angle": 0, + "content": "Visual Features. Given the image \\( I \\in \\mathbb{R}^{H \\times W \\times 3} \\), where \\( H \\) and \\( W \\) denote its height and width, we obtain its multiscale feature maps, \\( f_{\\frac{1}{8}} \\), \\( f_{\\frac{1}{16}} \\), and \\( f_{\\frac{1}{32}} \\), from the last three stages of ResNet-50. Their downsample ratios to the original size are \\( \\frac{1}{8} \\), \\( \\frac{1}{16} \\) and \\( \\frac{1}{32} \\). We regard the highest-level \\( f_{\\frac{1}{32}} \\in \\mathbb{R}^{\\frac{H}{32} \\times \\frac{W}{32} \\times C} \\) with sufficient semantics as the visual features \\( f_V \\) of the input image." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.636, + 0.47, + 0.773 + ], + "angle": 0, + "content": "Depth Features. We obtain the depth features from the image by a lightweight depth predictor, as shown in Figure 3. We first unify the sizes of three-level features to the same \\(\\frac{1}{16}\\) downsample ratio via bilinear pooling, and fuse them by element-wise addition. In this way, we can integrate multi-scale visual appearances and also preserve fine-grained patterns for objects of small sizes. Then, we apply two \\(3\\times 3\\) convolutional layers to obtain the depth features \\(f_{D}\\in \\mathbb{R}^{\\frac{H}{16}\\times \\frac{W}{16}\\times C}\\) for the input image." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Foreground Depth Map. To incorporate effective depth information into the depth features, we predict a foreground depth map \\( D_{fg} \\in \\mathbb{R}_{16}^{\\frac{H}{16} \\times \\frac{W}{16} \\times (k + 1)} \\) on top of \\( f_{D} \\) via a \\( 1 \\times 1 \\) convolutional layer. We supervise the depth map only by discrete object-wise depth labels, without extra dense depth annotations. The pixels within the same 2D bounding box are assigned with the same depth label of the corresponding object. For pixels within multiple boxes, we select the" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.43, + 0.895, + 0.595 + ], + "angle": 0, + "content": "depth label of the object that is nearest to the camera, which accords with the visual appearance of the image. Here, We discretize the depth into \\( k + 1 \\) bins [38], where the first ordinal \\( k \\) bins denote foreground depth and the last one denotes the background. We adopt linear-increasing discretization (LID), since the larger depth estimation errors of farther objects can be suppressed with a wider categorization interval. We limit the foreground depth values within \\( [d_{min}, d_{max}] \\), and set both the first interval length and LID's common difference as \\( \\delta \\). We then categorize a ground-truth depth label \\( d \\) into the \\( k \\)-th bin as:" + }, + { + "type": "equation", + "bbox": [ + 0.565, + 0.599, + 0.892, + 0.632 + ], + "angle": 0, + "content": "\\[\nk = \\left\\lfloor - 0. 5 + 0. 5 \\sqrt {1 + \\frac {8 (d - d _ {\\min })}{\\delta}} \\right\\rfloor , \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.637, + 0.894, + 0.718 + ], + "angle": 0, + "content": "where \\(\\delta = \\frac{2(d_{max} - d_{min})}{k(k + 1)}\\). By focusing on the object-wise depth values, the network can better capture foreground spatial structures and inter-object depth relations, which produces informative depth features for the subsequent depth-guided transformer." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.73, + 0.745, + 0.746 + ], + "angle": 0, + "content": "3.2. Depth-guided Transformer" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.753, + 0.894, + 0.83 + ], + "angle": 0, + "content": "The depth-guided transformer of MonoDETR is composed of a visual encoder, a depth encoder, and a depth-guided decoder. The two encoders produce non-local visual and depth embeddings, and the decoder enables object queries to adaptively capture scene-level information." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.838, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Visual and Depth Encoders. Given depth and visual features \\( f_{D}, f_{V} \\), we specialize two transformer encoders to generate their scene-level embeddings with global receptive fields, denoted as \\( f_{D}^{e} \\in \\mathbb{R}_{16^{2}}^{\\frac{HW}{2} \\times C} \\) and \\( f_{V}^{e} \\in \\mathbb{R}_{32^{2}}^{\\frac{HW}{2} \\times C} \\)." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "9158" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.274 + ], + "angle": 0, + "content": "We set three blocks for the visual encoder and only one block for the depth encoder, since the discrete foreground depth information is easier to be encoded than the rich visual appearances. Each encoder block consists of a self-attention layer and a feed-forward neural network (FFN). By the global self-attention mechanism, the depth encoder explores long-range dependencies of depth values from different foreground areas, which provides non-local geometric cues of the stereo space. In addition, the decoupling of depth and visual encoders allows them to better learn features for themselves, encoding the input image from two perspectives, i.e., depth geometry and visual appearance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.29, + 0.473, + 0.458 + ], + "angle": 0, + "content": "Depth-guided Decoder. Based on the non-local \\( f_{D}^{e}, f_{V}^{e} \\), we utilize a set of learnable object queries \\( q \\in \\mathbb{R}^{N \\times C} \\) to detect 3D objects via the depth-guided decoder, where \\( N \\) denotes the pre-defined maximum number of objects in the input image. Each decoder block sequentially contains a depth cross-attention layer, an inter-query self-attention layer, a visual cross-attention layer, and an FFN. Specifically, the queries first capture informative depth features from \\( f_{D}^{e} \\) via the depth cross-attention layer, in which we linearly transform the object queries and depth embeddings into queries, keys, and values," + }, + { + "type": "equation", + "bbox": [ + 0.125, + 0.466, + 0.47, + 0.484 + ], + "angle": 0, + "content": "\\[\nQ _ {q} = \\operatorname {L i n e a r} (q), \\quad K _ {D}, V _ {D} = \\operatorname {L i n e a r} \\left(f _ {D} ^ {e}\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.492, + 0.47, + 0.559 + ], + "angle": 0, + "content": "where \\(Q_{q}\\in \\mathbb{R}^{N\\times C}\\) and \\(K_{D},V_{D}\\in \\mathbb{R}^{\\frac{HW}{16^{2}}\\times C}\\). Then, we calculate the query-depth attention map \\(A_{D}\\in \\mathbb{R}^{N\\times \\frac{HW}{16^{2}}}\\), and aggregate informative depth features weighted by \\(A_{D}\\) to produce the depth-aware queries \\(q^{\\prime}\\), formulated as," + }, + { + "type": "equation", + "bbox": [ + 0.17, + 0.566, + 0.469, + 0.584 + ], + "angle": 0, + "content": "\\[\nA _ {D} = \\operatorname {S o f t m a x} \\left(Q _ {q} K _ {D} ^ {T} / \\sqrt {C}\\right), \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.182, + 0.586, + 0.469, + 0.603 + ], + "angle": 0, + "content": "\\[\nq ^ {\\prime} = \\operatorname {L i n e a r} \\left(A _ {D} V _ {D}\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.612, + 0.47, + 0.733 + ], + "angle": 0, + "content": "Such a mechanism enables each object query to adaptively capture spatial cues from depth-guided regions on the image, leading to better scene-level spatial understanding. Then, the depth-aware queries are fed into the inter-query self-attention layer for feature interaction between objects, and the visual cross-attention layer for collecting visual semantics from \\( f_V^e \\). We stack three decoder blocks to fully fuse the scene-level depth cues into object queries." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.902 + ], + "angle": 0, + "content": "Depth Positional Encodings. In the depth cross-attention layer, we propose learnable depth positional encodings for \\( f_{D}^{e} \\) instead of conventional sinusoidal functions. In detail, we maintain a set of learnable embeddings, \\( p_{D} \\in \\mathbb{R}^{(d_{max} - d_{min} + 1) \\times C} \\), where each row encodes the depth positional information for a meter, ranging from \\( d_{min} \\) to \\( d_{max} \\). For each pixel \\( (x,y) \\) in \\( D_{fg} \\), we first obtain its \\( (k + 1) \\)-categorical depth prediction confidence, \\( D_{fg}(x,y) \\in \\mathbb{R}^{k + 1} \\), each channel of which denotes the predicted confidence for the corresponding depth bin. The estimated depth" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.137 + ], + "angle": 0, + "content": "of pixel \\((x,y)\\) can then be obtained by the weighted summation of the depth-bin confidences and their corresponding depth values, which is formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.57, + 0.15, + 0.892, + 0.192 + ], + "angle": 0, + "content": "\\[\nd _ {m a p} (x, y) = \\sum_ {i = 1} ^ {k + 1} D _ {f g} (x, y) [ i ] \\cdot d _ {b i n} ^ {i}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.205, + 0.892, + 0.314 + ], + "angle": 0, + "content": "where \\(d_{bin}^{i}\\) denotes the starting value of the \\(i\\)-th depth bin and \\(\\sum_{i=1}^{k+1} D_{fg}(x,y)[i] = 1\\). Then, we linearly interpolate \\(p_{D}\\) according to the depth \\(d_{map}(x,y)\\) to obtain the depth positional encoding for the pixel \\((x,y)\\). By pixel-wisely adding \\(f_{D}^{e}\\) with such encodings, object queries can better capture scene-level depth cues and understand 3D geometry in the depth cross-attention layer." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.326, + 0.736, + 0.34 + ], + "angle": 0, + "content": "3.3. Detection Heads and Loss" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.35, + 0.892, + 0.487 + ], + "angle": 0, + "content": "After the decoder, the depth-aware queries are fed into a series of MLP-based heads for 3D attribute predictions, including object category, 2D size, projected 3D center, depth, 3D size, and orientation. For inference, we convert these perspective attributes into 3D-space bounding boxes using camera parameters without NMS post-processing or pre-defined anchors. For training, we match the orderless queries with ground-truth labels and compute losses for the paired ones. We refer to Supplementary Material for details." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.503, + 0.892, + 0.731 + ], + "angle": 0, + "content": "Bipartite Matching. To correctly match each query with ground-truth objects, we calculate the loss for each query-label pair and utilize Hungarian algorithm [4] to find the globally optimal matching. For each pair, we integrate the losses of six attributes into two groups. The first contains object category, 2D size and the projected 3D center, since these attributes mainly concern 2D visual appearances of the image. The second group consists of depth, 3D size and orientation, which are 3D spatial properties of the object. We respectively sum the losses of two groups and denote them as \\(\\mathcal{L}_{2D}\\) and \\(\\mathcal{L}_{3D}\\). As the network generally predicts less accurate 3D attributes than 2D attributes, especially at the beginning of training, the value of \\(\\mathcal{L}_{3D}\\) is unstable and would disturb the matching process. We only utilize \\(\\mathcal{L}_{2D}\\) as the matching cost for matching each query-label pair." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.742, + 0.892, + 0.803 + ], + "angle": 0, + "content": "Overall Loss. After the matching, we obtain \\( N_{gt} \\) valid pairs out of \\( N \\) queries, where \\( N_{gt} \\) denotes the number of ground-truth objects. Then, the overall loss of a training image is formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.542, + 0.817, + 0.892, + 0.859 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {o v e r a l l}} = \\frac {1}{N _ {g t}} \\cdot \\sum_ {n = 1} ^ {N _ {g t}} \\left(\\mathcal {L} _ {2 D} + \\mathcal {L} _ {3 D}\\right) + \\mathcal {L} _ {\\text {d m a p}}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{dmap}\\) represents the Focal loss [23] of the predicted categorical foreground depth map \\(D_{fg}\\) in Section 3.1." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "9159" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.099, + 0.087, + 0.87, + 0.311 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.318, + 0.895, + 0.364 + ], + "angle": 0, + "content": "Figure 5. Plug-and-play for multi-view 3D object detection. We utilize yellow, blue, green, and red to respectively denote the feature space related to 2D, depth, 3D, and BEV. The depth-guided transformer of MonoDETR is adopted to enhance PETR (v2) [26, 27] and BEVFormer [22] in a plug-and-play manner, which provides depth guidance from surrounding scenes." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.385, + 0.416, + 0.401 + ], + "angle": 0, + "content": "3.4. Plug-and-play for Multi-view Detectors" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.409, + 0.471, + 0.545 + ], + "angle": 0, + "content": "Besides monocular images, our depth-guided transformer can also serve as a plug-and-play module upon multi-view methods for depth-guided detection. Specifically, we append our depth predictors and depth encoders after the backbones of multi-view methods, which are shared across views and extract surrounding depth embeddings. Then, we inject our depth cross-attention layer into their transformer blocks to guide the 3D or BEV object queries by scene-level depth cues." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.555, + 0.47, + 0.678 + ], + "angle": 0, + "content": "For PETR (v2) [26, 27] in Figure 5 (a), we modify its previous visual decoder as a depth-guided decoder. In each decoder block, the 3D object queries are first fed into our depth cross-attention layer for depth cues aggregation, and then into the original 3D self-attention and visual cross-attention for 3D position features interaction. This enables PETR's 3D queries to be depth-aware and better capture spatial characteristics of surrounding scenes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.686, + 0.47, + 0.809 + ], + "angle": 0, + "content": "For BEVFormer [22] in Figure 5 (b), as its decoder is conducted in BEV space, we incorporate the depth guidance into its BEV encoder, which lifts image features into BEV space by transformers. In each encoder block, the BEV queries also sequentially pass through our depth cross-attention layer and the original spatial cross-attention layer. This contributes to better BEV representation learning guided by the multi-view depth information." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.822, + 0.21, + 0.839 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.847, + 0.177, + 0.864 + ], + "angle": 0, + "content": "4.1. Settings" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Dataset. We evaluate MonoDETR on the widely-adopted KITTI [14] benchmark, including 7,481 training and 7,518" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.385, + 0.893, + 0.477 + ], + "angle": 0, + "content": "test images. We follow [8, 9] to split 3,769 val images from the training set. We report the detection results with three-level difficulties, easy, moderate, and hard, and evaluate by the average precision \\((AP)\\) of bounding boxes in 3D space and the bird-eye view, denoted as \\(AP_{3D}\\) and \\(AP_{BEV}\\), respectively, which are both at 40 recall positions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.485, + 0.893, + 0.803 + ], + "angle": 0, + "content": "Implementation details. We adopt ResNet-50 [15] as our feature backbone. To save GPU memory, we apply deformable attention [59] for the visual encoder and visual cross-attention layers, and utilize the vanilla global attention [4] to better capture non-local geometries for the depth encoder and depth cross-attention layers. We utilize 8 heads for all attention modules and set the number of queries \\(N\\) as 50, which are learnable embeddings with predicted 2D reference points. We set the channel \\(C\\) and all MLP's latent dimensions as 256. For the foreground depth map, we set \\([d_{min}, d_{max}]\\) as \\([0m, 60m]\\) and the number of bins \\(k\\) as 80. On a single RTX 3090 GPU, we train MonoDETR for 195 epochs with batch size 16 and a learning rate \\(2 \\times 10^{-4}\\). We adopt AdamW [30] optimizer with weight decay \\(10^{-4}\\), and decrease the learning rate at 125 and 165 epochs by 0.1. For training stability, we discard the training samples with depth labels larger than 65 meters or smaller than 2 meters. During inference, we simply filter out the object queries with the category confidence lower than 0.2 without NMS post-processing, and recover the 3D bounding box using the predicted six attributes following previous works [33, 31]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.814, + 0.633, + 0.83 + ], + "angle": 0, + "content": "4.2. Comparison" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.893, + 0.902 + ], + "angle": 0, + "content": "Performance. In Table 2, MonoDETR achieves state-of-the-art performance on KITTI test and val sets. On test set, MonoDETR exceeds all existing methods including those with different additional data input and surpasses" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "9160" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.11, + 0.089, + 0.859, + 0.445 + ], + "angle": 0, + "content": "
MethodExtra dataTest, AP3DTest, APBEVVal, AP3D
EasyMod.HardEasyMod.HardEasyMod.Hard
PatchNet [32]Depth15.6811.1210.1722.9716.8614.97---
D4LCN [12]16.6511.729.5122.5116.0212.55---
DDMP-3D [45]19.7112.789.8028.0817.8913.44---
Kinematic3D [2]Video19.0712.729.1726.6917.5213.1019.7614.1010.47
MonoRUn [7]LiDAR19.6512.3010.5827.9417.3415.2420.0214.6512.61
CaDDN [38]19.1713.4111.4627.9418.9117.1923.5716.3113.84
MonoDTR [18]21.9915.3912.7328.5920.3817.1424.5218.5715.51
AutoShape [29]CAD22.4714.1711.3630.6620.0815.5920.0914.6512.07
SMOKE [28]None14.039.767.8420.8314.4912.7514.7612.8511.50
MonoPair [10]13.049.998.6519.2814.8312.8916.2812.3010.42
RTM3D [21]13.6110.098.18---19.4716.2915.57
PGD [47]19.0511.769.3926.8916.5113.4919.2713.2310.65
IAFA [55]17.8112.0110.6125.8817.8815.3518.9514.9614.84
MonoDLE [33]17.2312.2610.2924.7918.8916.0017.4513.6611.68
MonoRCNN [42]18.3612.6510.0325.4818.1114.1016.6113.1910.65
MonoGeo [53]18.8513.8111.5225.8618.9916.1918.4514.4812.87
MonoFlex [52]19.9413.8912.0728.2319.7516.8923.6417.5114.83
GUPNet [31]20.1114.2011.77---22.7616.4613.72
MonoDETR (Ours)None25.0016.4713.5833.6022.1118.6028.8420.6116.38
Improvementv.s. second-best+2.53+1.08+0.85+2.94+1.73+1.41+4.32+2.04+0.81
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.45, + 0.892, + 0.478 + ], + "angle": 0, + "content": "Table 2. Monocular performance of the car category on KITTI test and val sets. We utilize bold numbers to highlight the best results, and color the second-best ones and our gain over them in blue." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.503, + 0.47, + 0.624 + ], + "angle": 0, + "content": "the second-best under three-level difficulties by \\(+2.53\\%\\), \\(+1.08\\%\\) and \\(+0.85\\%\\) in \\(AP_{3D}\\), and by \\(+2.94\\%\\), \\(+1.73\\%\\) and \\(+1.41\\%\\) in \\(AP_{BEV}\\). The competitive MonoDTR [18] also applies transformers to fuse depth features, but it is still a center-guided method and highly relies on additional dense depth supervision, anchors and NMS. In contrast, MonoDETR performs better without extra input or handcrafted designs, illustrating its simplicity and effectiveness." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.636, + 0.47, + 0.729 + ], + "angle": 0, + "content": "Efficiency. Compared to existing methods in Table 3, MonoDETR can achieve the best detection performance without consuming too much computational budget. As illustrated in Section 3, we only process the feature maps with \\(\\frac{1}{16}\\) and \\(\\frac{1}{32}\\) downsample ratios, which reduces our Runtime and GFlops, while others adopt \\(\\frac{1}{4}\\) and \\(\\frac{1}{8}\\) ratios." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.741, + 0.242, + 0.755 + ], + "angle": 0, + "content": "4.3. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.764, + 0.47, + 0.794 + ], + "angle": 0, + "content": "We verify the effectiveness of each our component and report \\(AP_{3D}\\) for the car category on the KITTI val set." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Depth-guided Transformer. In Table 5, we first remove the entire depth-guided transformer along with the depth predictor, which constructs a pure center-guided baseline. This variant, denoted as 'w/o Depth-guided Trans.' can be regarded as a re-implementation of MonoDLE [33] with our detection heads and loss functions. As shown, the absence" + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.5, + 0.892, + 0.566 + ], + "angle": 0, + "content": "
MethodMonoDLEGUPNetMonoDTRMonoDETR
Runtime↓40343738
GFlops↓79.1262.32120.4862.12
AP3D Mod.12.2615.0215.3916.47
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.571, + 0.892, + 0.599 + ], + "angle": 0, + "content": "Table 3. Efficiency comparison. We test the Runtime (ms) on one RTX 3090 GPU with batch size 1, and compare \\( AP_{3D} \\) on test set." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.626, + 0.892, + 0.84 + ], + "angle": 0, + "content": "of the depth-guided transformer greatly hurts the performance, for the lack of non-local geometric cues. Then, we investigate two key designs within the depth-guided transformer: the transformer architecture and depth guidance. For 'w/o Transformer', we only append the depth predictor upon the center-guided baseline to provide implicit depth guidance without transformers. For 'w/o Depth Guidance', we equip the center-guided baseline with a visual encoder and decoder, but include no depth predictor, depth encoder, and the depth cross-attention layer in the decoder. This builds a transformer network guided by visual appearances, without any depth guidance for object queries. The performance degradation of both variants indicates their significance for our depth-guided feature aggregation paradigm." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Depth Encoder. The depth encoder produces non-local depth embeddings \\( f_{D}^{e} \\), which are essential for queries to" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "9161" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.154, + 0.089, + 0.813, + 0.27 + ], + "angle": 0, + "content": "
MethodImage SizeNDS↑mAP↑mATE↓mASE↓mAOE↓mAVE↓mAAE↓
CenterNet [56]-0.3280.3060.7160.2640.6091.4260.658
FCOS3D* [46]1600×9000.4150.3430.7250.2630.4221.2920.153
PGD* [47]1600×9000.4280.3690.6830.2600.4391.2680.185
DETR3D† [49]1600×9000.4340.3490.7160.2680.3790.8420.200
BEVDet† [17]1408×5120.4170.3490.6370.2690.4900.9140.268
PETR† [26]1600×9000.4420.3700.7110.2670.3830.8650.201
PETRv2 [27] + Depth-gudied800×3200.4960.4010.7450.2680.4480.3940.184
0.5080.4100.7270.2650.3890.4190.187
BEVFormer [22] + Depth-gudied1600×9000.5170.4160.6730.2740.3720.3940.198
0.5260.4230.6610.2720.3490.3710.192
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.275, + 0.893, + 0.305 + ], + "angle": 0, + "content": "Table 4. Multi-view performance on nuScenes val set. * denotes the two-step fine-tuning with test-time augmentation, and † denotes CBGS [58] training. We compare with the best-performing variants of other methods and utilize bold numbers to highlight the best results." + }, + { + "type": "table", + "bbox": [ + 0.108, + 0.325, + 0.436, + 0.415 + ], + "angle": 0, + "content": "
ArchitectureEasyMod.Hard
MonoDETR28.8420.6116.38
w/o Depth-guided Trans.19.6915.1513.93
w/o Transformer20.1916.0514.18
w/o Depth Guidance24.1417.8115.60
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.419, + 0.47, + 0.463 + ], + "angle": 0, + "content": "Table 5. Effectiveness of depth-guided transformer. 'Depth-guided Trans.' and 'Depth Guidance' denote the depth-guided transformer and the depth cross-attention layer, respectively" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.487, + 0.469, + 0.581 + ], + "angle": 0, + "content": "explore scene-level depth cues in the depth cross-attention layer. We experiment with different encoder designs in Table 6. 'Deform. SA' and \\(3 \\times 3\\) Conv.\\(\\times 2'\\) represent one-block of deformable attention and two \\(3 \\times 3\\) convolutional layers, respectively. As reported, 'Global SA' with only one block generates the best \\(f_{D}^{e}\\) for global geoentry encoding." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.588, + 0.47, + 0.771 + ], + "angle": 0, + "content": "Depth-guided Decoder. As the core depth-guided component, we explore how to better guide object queries to interact with depth embeddings \\( f_{D}^{e} \\) in Table 7. With the sequential inter-query self-attention (\\( I' \\)) and visual cross-attention (\\( V' \\)) layers, we insert the depth cross-attention layer (\\( D' \\)) into each decoder block with four positions. For \\( I \\rightarrow D + V' \\), we fuse the depth and visual embeddings \\( f_{D}^{e}, f_{V}^{e} \\) by element-wise addition, and apply only one unified cross-attention layer. As shown, the \\( D \\rightarrow I \\rightarrow V' \\) order performs the best. By placing \\( D' \\) in the front, object queries can first aggregate depth cues to guide the remaining operations in each decoder block." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Foreground Depth Map. We explore different representations for our depth map in Table 8. Compared to dense depth supervision ('Dense'), adopting object-wise depth labels ('Fore.') can focus the network on more important foreground geometric cues, and better capture depth relations between objects. 'LID' outperforms other discretization methods, since the linear-increasing intervals can suppress the larger estimation errors of farther objects." + }, + { + "type": "table", + "bbox": [ + 0.564, + 0.325, + 0.828, + 0.415 + ], + "angle": 0, + "content": "
MechanismEasyMod.Hard
Global SA28.8420.6116.38
Deform. SA26.4318.9115.55
3×3 Conv.×2 w/o25.5518.3615.28
24.2518.3815.41
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.419, + 0.893, + 0.463 + ], + "angle": 0, + "content": "Table 6. The design of depth encoder. 'Deform. SA' denotes a one-block deformable self-attention layer. 'w/o' denotes directly feeding depth features into the decoder without the depth encoder." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.488, + 0.892, + 0.685 + ], + "angle": 0, + "content": "Depth Positional Encodings \\( p_D \\). In Table 9, we experiment with different depth positional encodings for \\( f_D^e \\) in the depth cross-attention layer. By default, we apply the meterwise encodings \\( p_D \\in \\mathbb{R}^{(d_{max} - d_{min} + 1) \\times C} \\) that assign one learnable embedding per meter with depth value interpolation for output. We then assign one learnable embedding for each depth bin, denoted as 'k-bin \\( p_D \\in \\mathbb{R}^{k \\times C} \\), and also experiment sinusoidal functions to encode either the depth values or 2D coordinates of the feature map, denoted as 'Depth sin/cos' and '2D sin/cos', respectively. As shown, 'meter-wise \\( p_D \\)' performs the best for encoding more fine-grained depth cues ranging from \\( d_{min} \\) to \\( d_{max} \\), which provides the queries with more scene-level spatial structures." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.696, + 0.724, + 0.712 + ], + "angle": 0, + "content": "4.4. Multi-view Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.893, + 0.901 + ], + "angle": 0, + "content": "As a plug-and-play module for multi-view 3D object detection, we append our depth-guided transformer upon two DETR-based multi-view networks, PETR v2 [27] and BEVFormer [22]. The detailed network architectures are shown in Figure 5. For a fair comparison, we adopt the same training configurations as the two baseline models, and utilize the same \\([d_{min}, d_{max}]\\) with \\(k\\) as monocular experiments. We report the performance on nuScenes [3] val set in Table 4, where we apply no test-time augmentation or CGBS [58] training. For end-to-end detection in PETRv2, the depth guidance contributes to \\(+1.2\\%\\) NDS and \\(+0.9\\%\\) mAP by providing sufficient multi-view geometric cues." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "9162" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.09, + 0.282, + 0.238 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.091, + 0.484, + 0.238 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.485, + 0.091, + 0.686, + 0.238 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.687, + 0.091, + 0.888, + 0.238 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.241, + 0.892, + 0.27 + ], + "angle": 0, + "content": "Figure 6. Visualizations of attention maps \\( A_{D} \\) in the depth cross-attention layer. The top column denotes the input image, and the last three columns denote the attention maps of the target queries (denoted as white dots). Hotter colors indicate higher attention weights." + }, + { + "type": "table", + "bbox": [ + 0.123, + 0.291, + 0.422, + 0.38 + ], + "angle": 0, + "content": "
ArchitectureEasyMod.Hard
D → I → V28.8420.6116.38
I → D → V26.2419.2816.03
I → V → D25.8418.8515.72
I → D + V24.9418.4115.39
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.387, + 0.47, + 0.43 + ], + "angle": 0, + "content": "Table 7. The design of depth-guided decoder. 'D', 'I', and 'V' denote the depth cross-attention, inter-query self-attention, and visual cross-attention layers, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.454, + 0.47, + 0.545 + ], + "angle": 0, + "content": "For the BEV feature generation, our modules benefit BEV-Former by \\(+0.9\\%\\) NDS and \\(+0.7\\%\\) mAP, indicating the importance of auxiliary depth information for BEV-space feature encoding. The additional experiments on multi-view 3D object detection well demonstrate the effectiveness and generalizability of our approach." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.561, + 0.212, + 0.577 + ], + "angle": 0, + "content": "5. Visualization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.587, + 0.47, + 0.709 + ], + "angle": 0, + "content": "We visualize the attention maps \\( A_{D} \\) in Equation 3 of the depth cross-attention layer at the last decoder block. As shown in Figure 6, the areas with high attention scores for the target object query spread over the entire image, concentrating on other objects with long distances. This indicates, via our depth guidance, object queries are able to adaptively capture non-local depth cues from the image and are no longer limited by neighboring visual features." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.725, + 0.196, + 0.74 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.471, + 0.902 + ], + "angle": 0, + "content": "We propose MonoDETR, an end-to-end transformer-based framework for monocular 3D object detection, which is free from any additional input, anchors, or NMS. Different from existing center-guided methods, we enable object queries to explore geometric cues adaptively from the depth-guided regions, and conduct inter-object and object-scene depth interactions via attention mechanisms. Extensive experiments have demonstrated the effectiveness of our approach for both single-view (KITTI) and multi-view (nuScenes) input. We hope MonoDETR can serve as a" + }, + { + "type": "table", + "bbox": [ + 0.549, + 0.291, + 0.842, + 0.382 + ], + "angle": 0, + "content": "
Depth MapEasyMod.Hard
Fore. LID28.8420.6116.38
Dense LID27.6919.8515.98
Fore. UD25.6118.9015.49
Fore. SID26.0518.9515.59
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.387, + 0.892, + 0.43 + ], + "angle": 0, + "content": "Table 8. Different representations of the predicted depth map. 'UD', 'SID', and 'LID' denote uniform, spacing-increasing, and linear-increasing discretizations." + }, + { + "type": "table", + "bbox": [ + 0.56, + 0.454, + 0.83, + 0.557 + ], + "angle": 0, + "content": "
SettingsEasyMod.Hard
Meter-wise pD28.8420.6116.38
k-bin pD28.0619.6816.04
Depth sin/cos27.4219.5715.82
2D sin/cos26.4818.6315.52
w/o26.7618.9415.85
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.562, + 0.892, + 0.605 + ], + "angle": 0, + "content": "Table 9. The design of depth positional encodings. 'Meter-wise' and \\( k \\) -bin' assign learnable embeddings by meters and depth bins, respectively. 'sin/cos' denotes sinusoidal functions for encodings." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.631, + 0.892, + 0.737 + ], + "angle": 0, + "content": "strong DETR baseline for future research in monocular 3D object detection. Limitations. How to effectively incorporate multi-modal input into our transformer framework is not discussed in the paper. Our future direction will focus on this to further improve the performance of depth-guided transformers, e.g., distilling more sufficient geometric knowledge from LiDAR and RADAR modalities." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.754, + 0.661, + 0.771 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.9 + ], + "angle": 0, + "content": "This project is funded in part by the National Natural Science Foundation of China (No.62206272), by the National Key R&D Program of China Project (No.2022ZD0161100), by the Centre for Perceptual and Interactive Intelligence (CPII) Ltd under the Innovation and Technology Commission (ITC)'s InnoHK, and by the General Research Fund of Hong Kong RGC Project 14204021. Hongsheng Li is a PI of CPII under the InnoHK." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "9163" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.469, + 0.156 + ], + "angle": 0, + "content": "[1] Garrick Brazil and Xiaoming Liu. M3d-rpn: Monocular 3d region proposal network for object detection. In IEEE International Conference on Computer Vision, 2019. 1, 3" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.157, + 0.469, + 0.212 + ], + "angle": 0, + "content": "[2] Garrick Brazil, Gerard Pons-Moll, Xiaoming Liu, and Bernt Schiele. Kinematic 3d object detection in monocular video. 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Deformable detr: Deformable transformers for end-to-end object detection. arXiv preprint arXiv:2010.04159, 2020. 3, 6" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.468, + 0.29 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.517, + 0.956 + ], + "angle": 0, + "content": "9166" + } + ] +] \ No newline at end of file diff --git a/2023/MonoDETR_ Depth-guided Transformer for Monocular 3D Object Detection/3836a1be-d313-4152-8663-e644f7bd2a45_origin.pdf b/2023/MonoDETR_ Depth-guided Transformer for Monocular 3D Object Detection/3836a1be-d313-4152-8663-e644f7bd2a45_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..ccaf1d3d03eb0614d90886c9c9820af4531f1009 --- /dev/null +++ b/2023/MonoDETR_ Depth-guided Transformer for Monocular 3D Object Detection/3836a1be-d313-4152-8663-e644f7bd2a45_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:8e63eacba5e584c40b3cfccd0249878c24aa78211a1a0883b127caa8e6eae6ee +size 1582694 diff --git a/2023/MonoDETR_ Depth-guided Transformer for Monocular 3D Object Detection/full.md b/2023/MonoDETR_ Depth-guided Transformer for Monocular 3D Object Detection/full.md new file mode 100644 index 0000000000000000000000000000000000000000..077491f330d028e2a3b48c44bf2bf6c65cfa31c1 --- /dev/null +++ b/2023/MonoDETR_ Depth-guided Transformer for Monocular 3D Object Detection/full.md @@ -0,0 +1,319 @@ +# MonoDETR: Depth-guided Transformer for Monocular 3D Object Detection + +Renrui Zhang $^{1,2}$ , Han Qiu $^{2}$ , Tai Wang $^{1,2}$ , Ziyu Guo $^{2}$ , Ziteng Cui $^{2}$ Yu Qiao $^{2}$ , Hongsheng Li $^{\dagger 1,2,3}$ , Peng Gao $^{\dagger 2}$ + +$^{1}$ CUHK MMLab $^{2}$ Shanghai Artificial Intelligence Laboratory $^{3}$ Centre for Perceptual and Interactive Intelligence (CPII) + +{zhangrenrui, wangtai, gaopeng}@pjlab.org.cn, hsli@ee.cuhk.edu.hk + +# Abstract + +Monocular 3D object detection has long been a challenging task in autonomous driving. Most existing methods follow conventional 2D detectors to first localize object centers, and then predict 3D attributes by neighboring features. However, only using local visual features is insufficient to understand the scene-level 3D spatial structures and ignores the long-range inter-object depth relations. In this paper, we introduce the first DETR framework for Monocular DTection with a depth-guided TRansformer, named MonoDETR. We modify the vanilla transformer to be depth-aware and guide the whole detection process by contextual depth cues. Specifically, concurrent to the visual encoder that captures object appearances, we introduce to predict a foreground depth map, and specialize a depth encoder to extract non-local depth embeddings. Then, we formulate 3D object candidates as learnable queries and propose a depth-guided decoder to conduct object-scene depth interactions. In this way, each object query estimates its 3D attributes adaptively from the depth-guided regions on the image and is no longer constrained to local visual features. On KITTI benchmark with monocular images as input, MonoDETR achieves state-of-the-art performance and requires no extra dense depth annotations. Besides, our depth-guided modules can also be plug-and-play to enhance multi-view 3D object detectors on nuScenes dataset, demonstrating our superior generalization capacity. Code is available at https://github.com/ZrrSkywalker/MonoDETR. + +# 1. Introduction + +With a wide range of applications in autonomous driving, 3D object detection is more challenging than its 2D counterparts, due to the complex spatial circumstances. + +![](images/02e855ce7534f2ed2b7b1787e8560924b0e6ee9e3bc68bf1046fdd8de9a296e1.jpg) +Figure 1. Center-guided (Top) and Depth-guided Paradigms (Bottom) for monocular 3D object detection. Existing center-guided methods predict 3D attributes from local visual features around the centers, while our MonoDETR guides the detection by a predicted foreground depth map and adaptively aggregates features in global context. The lower right figure visualizes the attention map of the target query in the depth cross-attention layer. + +Compared to methods based on LiDAR [57, 20, 41, 50] and multi-view images [49, 22, 26, 17], 3D object detection from monocular (single-view) images [9, 1, 46] is of most difficulty, which generally does not rely on depth measurements or multi-view geometry. The detection accuracy thus severely suffers from the ill-posed depth estimation, leading to inferior performance. + +Except for leveraging pseudo 3D representations [48, 51, 32, 38], standard monocular 3D detection methods [33, 52, 53, 31] follow the pipeline of traditional 2D object detection [40, 24, 43, 56]. They first localize objects by detecting the projected centers on the image, and then aggregate the neighboring visual features for 3D property prediction, as illustrated in Figure 1 (Top). Although it is conceptually straightforward, such center-guided methods are limited by the local appearances without long-range context, and fail to capture implicit geometric cues from 2D images, e.g., depth guidance, which are critical to detect objects in 3D space. + +To tackle this issue, we propose MonoDETR, which + +![](images/5ec4506b34b33f6ecb376831da7b887324f4c0846dbfa219caf705de935e6f1c.jpg) +Figure 2. Comparison of DETR-based methods for camera-based 3D object detection. We utilize yellow, blue, green, and red to respectively denote the feature or prediction space related with 2D, depth, 3D, and BEV. Different from other methods, our MonoDETR leverages depth cues to guide 3D object detection from monocular images. + +![](images/de4705794926c829fedab5a79b1b0eaa8e75686214253ce6145c2b625f50d285.jpg) + +![](images/e1d237b7818079d52bedeafc8e70a765bbb205a8c1bad3d67020727f55ca5fba.jpg) + +![](images/9b050e0e68757f5bcdfac6e095600c750fede0f5da9594822198cf18610aa1e6.jpg) + +presents a novel depth-guided 3D detection scheme in Figure 1 (Bottom). Compared to DETR [4] in 2D detection, the transformer in MonoDETR is equipped with depth-guided modules to better capture contextual depth cues, serving as the first DETR model for monocular 3D object detection, as shown in Figure 2 (a) and (b). It consists of: two parallel encoders for visual and depth representation learning, and a decoder for adaptive depth-guided detection. + +Specifically, after the feature backbone, we first utilize a lightweight depth predictor to acquire the depth features of the input image. To inject effective depth cues, a foreground depth map is predicted on top, and supervised only by discrete depth labels of objects, which requires no dense depth annotations during training. Then, we apply the parallel encoders to respectively generate non-local depth and visual embeddings, which represent the input image from two aspects: depth geometry and visual appearance. On top of that, a set of object queries is fed into the depth-guided decoder, and conducts adaptive feature aggregation from the two embeddings. Via a proposed depth cross-attention layer, the queries can capture geometric cues from the depth-guided regions on the image, and explore interobject depth relations. In this way, the 3D attribute prediction can be guided by informative depth hints, no longer constrained by the limited visual features around centers. + +As an end-to-end transformer-based network, MonoDETR is free from non-maximum suppression (NMS) or rule-based label assignment. We only utilize the object-wise labels for supervision without using auxiliary data, such as dense depth maps or LiDAR. Taking monocular images as input, MonoDETR achieves state-of-the-art performance among existing center-guided methods, and surpasses the second-best by $+2.53\%$ , $+1.08\%$ , and $+0.85\%$ for three-level difficulties on KITTI [14] test set. + +Besides single-view images, the depth-guided mod + +ules in MonoDETR can also be extended as a plug-and-play module for multi-view 3D detection on nuScenes [3] dataset. By providing multi-view depth cues, our method can not only improve the end-to-end detection performance of PETRv2 [27] by $+1.2\%$ NDS, but also benefit the BEV representation learning in BEVFormer [22] by $+0.9\%$ NDS. This further demonstrates the effectiveness and generalizability of our proposed depth guidance. + +We summarize the contributions of our paper as follows: + +- We propose MonoDETR, a depth-guided framework to capture scene-level geometries and inter-object depth relations for monocular 3D object detection. +- We introduce a foreground depth map for object-wise depth supervision, and a depth cross-attention layer for adaptive depth features interaction. +- MonoDETR achieves leading results on monocular KITTI benchmark, and can also be generalized to enhance multi-view detection on nuScenes benchmark. + +# 2. Related Work + +Existing methods for camera-based 3D object detection can be categorized as two groups according to the input number of views: monocular (single-view) and multi-view methods. Monocular detectors only take as input the front-view images and solve a more challenging task from insufficient 2D signals. Multi-view detectors simultaneously encode images of surrounding scenes and can leverage cross-view dependence to understand the 3D space. + +Monocular (Single-view) 3D Object Detection. Most previous monocular detectors adopt center-guided pipelines following conventional 2D detectors [40, 43, 56]. As early + +
MethodDETR-basedExtra DataGuided byObject QueryFeat. Aggre.
Mutli-view Methods
DETR3D [49]✓-Visual3DLocal
PETR (v2) [26]✓TemporalVisual3DGlobal
BEVFormer [22]✓TemporalVisualBEV, 3DGlobal
Monocular Methods
MonoDTR [18]×LiDARCenter×Local
MonoDETR✓-DepthDepthGlobal
+ +Table 1. Comparison of DETR-based methods for camera-based 3D object detection. Our MonoDETR is uniquely guided by depth cues with depth-aware object queries. + +works, Deep3Box [35] introduces discretized representation with perspective constraints, and M3D-RPN [1] designs a depth-aware convolution for better 3D region proposals. With very few handcrafted modules, SMOKE [28] and FCOS3D [46] propose concise architectures for efficient one-stage detection, while MonoDLE [33] and PGD [47] analyze depth errors on top with improved performance. To supplement the limited 3D cues, additional data are utilized for assistance: dense depth annotations [32, 12, 45, 36], CAD models [29], and LiDAR [7, 38, 18]. Some recent methods introduce complicated geometric priors into the networks: adjacent object pairs [10], 2D-3D keypoints [21], and uncertainty-related depth [52, 31]. Despite this, the center-guided methods are still limited by local visual features without scene-level spatial cues. In contrast, MonoDETR discards the center localization step and conducts adaptive feature aggregation via a depth-guided transformer. MonoDETR requires no additional annotations and contains minimal 2D-3D geometric priors. + +Multi-view 3D Object Detection. For jointly extracting features from surrounding views, DETR3D [49] firstly utilizes a set of 3D object queries and back-projects them onto multi-view images for feature aggregation. PETR series [26, 27] further proposes to generate 3D position features without unstable projection and explores the advantage of temporal information from previous frames. From another point of view, BEVDet [17, 16] follows [37] to lift 2D images into a unified Bird's-Eye-View (BEV) representation and appends BEV-based heads [50] for detection. BEVFormer [22] instead generates BEV features via a set of learnable BEV queries, and introduces a spatiotemporal BEV transformer for visual features aggregation. Follow-up works also introduce cross-modal distillation [19, 11] and masked image modeling [25, 6] for improved performance. Different from the above methods for multi-view input, MonoDETR targets monocular images and extracts depth guidance to capture more geometric cues. Our depth-guided modules can also be generalized to surrounding views as a plug-and-play module to enhance multi-view detectors. + +![](images/ad84401c4e25971a9f646f5380235658817b5552b93b4f8d93ebecfe9575de9b.jpg) +Figure 3. The lightweight depth predictor. We utilize the depth predictor to predict the depth features and foreground depth map, which only contains discrete object-wise depth values. + +Comparison of DETR-based Methods. DETR [5] and its follow-up works [13, 59, 54, 34] have attained great success on 2D object detection without NMS or anchors. Inspired by this, some efforts have transferred DETR into camera-based 3D object detection. We specifically compare our MonoDETR with existing DETR-based 3D object detectors in Figure 2 and Table 1. (1) MonoDTR [18]. Also as a single-view detector, MonoDTR utilizes transformers [44] to incorporate depth features with visual representations. However, MonoDTR is not a DETR-based method, and still adopts the traditional center-guided paradigm, which localizes objects by their centers and only aggregate local features. MonoDTR contains no object queries for global feature aggregation, and follows YOLOv3 [39] to adopt complicated NMS post-processing with pre-defined anchors. (2) DETR3D [49] and PETR (v2) [26, 27] (Figure 2 (c)) are multi-view methods and follow the DETR detection pipeline. In contrast, they contain no transformer-based encoders (visual or depth), and detect objects by 3D object queries without the perspective transformation. Importantly, they are only guided by visual features and explores no depth cues from the input images. (3) BEVFormer [22] (Figure 2 (d)) firstly utilizes a BEV transformer to lift multiview images into BEV representations, and then conducts DETR-based detection within the BEV space. Different from all aforementioned methods, MonoDETR introduces a unique depth-guided transformer that guides the 3D detection by geometric depth cues, which can generalize well to both monocular and multi-view inputs. + +# 3. Method + +The overall framework of MonoDETR is shown in Figure 4. We first illustrate the concurrent visual and depth feature extraction in Section 3.1, and detail our depth-guided transformer for aggregating appearance and geometric cues in Section 3.2. Then, we introduce the attribute prediction and loss functions of MonoDETR in Section 3.3. Finally, we illustrate how to plug our depth-guided transformer into existing multi-view object detectors in Section 3.4. + +![](images/b4b5956ff1d1c64f05de6f13102cbe3680fdacfa10715d931de094aa23a8d9bd.jpg) +Figure 4. Overall pipeline of MonoDETR. We first acquire the visual and depth features of the input image and utilize two parallel encoders for non-local encoding. Then, we propose a depth-guided decoder to adaptively aggregate scene-level features in global context. + +# 3.1. Feature Extraction + +Taking as input a monocular (single-view) image, our framework utilizes a feature backbone, e.g., ResNet-50 [15], and a lightweight depth predictor to generate its visual and depth features, respectively. + +Visual Features. Given the image $I \in \mathbb{R}^{H \times W \times 3}$ , where $H$ and $W$ denote its height and width, we obtain its multiscale feature maps, $f_{\frac{1}{8}}$ , $f_{\frac{1}{16}}$ , and $f_{\frac{1}{32}}$ , from the last three stages of ResNet-50. Their downsample ratios to the original size are $\frac{1}{8}$ , $\frac{1}{16}$ and $\frac{1}{32}$ . We regard the highest-level $f_{\frac{1}{32}} \in \mathbb{R}^{\frac{H}{32} \times \frac{W}{32} \times C}$ with sufficient semantics as the visual features $f_V$ of the input image. + +Depth Features. We obtain the depth features from the image by a lightweight depth predictor, as shown in Figure 3. We first unify the sizes of three-level features to the same $\frac{1}{16}$ downsample ratio via bilinear pooling, and fuse them by element-wise addition. In this way, we can integrate multi-scale visual appearances and also preserve fine-grained patterns for objects of small sizes. Then, we apply two $3\times 3$ convolutional layers to obtain the depth features $f_{D}\in \mathbb{R}^{\frac{H}{16}\times \frac{W}{16}\times C}$ for the input image. + +Foreground Depth Map. To incorporate effective depth information into the depth features, we predict a foreground depth map $D_{fg} \in \mathbb{R}_{16}^{\frac{H}{16} \times \frac{W}{16} \times (k + 1)}$ on top of $f_{D}$ via a $1 \times 1$ convolutional layer. We supervise the depth map only by discrete object-wise depth labels, without extra dense depth annotations. The pixels within the same 2D bounding box are assigned with the same depth label of the corresponding object. For pixels within multiple boxes, we select the + +depth label of the object that is nearest to the camera, which accords with the visual appearance of the image. Here, We discretize the depth into $k + 1$ bins [38], where the first ordinal $k$ bins denote foreground depth and the last one denotes the background. We adopt linear-increasing discretization (LID), since the larger depth estimation errors of farther objects can be suppressed with a wider categorization interval. We limit the foreground depth values within $[d_{min}, d_{max}]$ , and set both the first interval length and LID's common difference as $\delta$ . We then categorize a ground-truth depth label $d$ into the $k$ -th bin as: + +$$ +k = \left\lfloor - 0. 5 + 0. 5 \sqrt {1 + \frac {8 (d - d _ {\min })}{\delta}} \right\rfloor , \tag {1} +$$ + +where $\delta = \frac{2(d_{max} - d_{min})}{k(k + 1)}$ . By focusing on the object-wise depth values, the network can better capture foreground spatial structures and inter-object depth relations, which produces informative depth features for the subsequent depth-guided transformer. + +# 3.2. Depth-guided Transformer + +The depth-guided transformer of MonoDETR is composed of a visual encoder, a depth encoder, and a depth-guided decoder. The two encoders produce non-local visual and depth embeddings, and the decoder enables object queries to adaptively capture scene-level information. + +Visual and Depth Encoders. Given depth and visual features $f_{D}, f_{V}$ , we specialize two transformer encoders to generate their scene-level embeddings with global receptive fields, denoted as $f_{D}^{e} \in \mathbb{R}_{16^{2}}^{\frac{HW}{2} \times C}$ and $f_{V}^{e} \in \mathbb{R}_{32^{2}}^{\frac{HW}{2} \times C}$ . + +We set three blocks for the visual encoder and only one block for the depth encoder, since the discrete foreground depth information is easier to be encoded than the rich visual appearances. Each encoder block consists of a self-attention layer and a feed-forward neural network (FFN). By the global self-attention mechanism, the depth encoder explores long-range dependencies of depth values from different foreground areas, which provides non-local geometric cues of the stereo space. In addition, the decoupling of depth and visual encoders allows them to better learn features for themselves, encoding the input image from two perspectives, i.e., depth geometry and visual appearance. + +Depth-guided Decoder. Based on the non-local $f_{D}^{e}, f_{V}^{e}$ , we utilize a set of learnable object queries $q \in \mathbb{R}^{N \times C}$ to detect 3D objects via the depth-guided decoder, where $N$ denotes the pre-defined maximum number of objects in the input image. Each decoder block sequentially contains a depth cross-attention layer, an inter-query self-attention layer, a visual cross-attention layer, and an FFN. Specifically, the queries first capture informative depth features from $f_{D}^{e}$ via the depth cross-attention layer, in which we linearly transform the object queries and depth embeddings into queries, keys, and values, + +$$ +Q _ {q} = \operatorname {L i n e a r} (q), \quad K _ {D}, V _ {D} = \operatorname {L i n e a r} \left(f _ {D} ^ {e}\right), \tag {2} +$$ + +where $Q_{q}\in \mathbb{R}^{N\times C}$ and $K_{D},V_{D}\in \mathbb{R}^{\frac{HW}{16^{2}}\times C}$ . Then, we calculate the query-depth attention map $A_{D}\in \mathbb{R}^{N\times \frac{HW}{16^{2}}}$ , and aggregate informative depth features weighted by $A_{D}$ to produce the depth-aware queries $q^{\prime}$ , formulated as, + +$$ +A _ {D} = \operatorname {S o f t m a x} \left(Q _ {q} K _ {D} ^ {T} / \sqrt {C}\right), \tag {3} +$$ + +$$ +q ^ {\prime} = \operatorname {L i n e a r} \left(A _ {D} V _ {D}\right). \tag {4} +$$ + +Such a mechanism enables each object query to adaptively capture spatial cues from depth-guided regions on the image, leading to better scene-level spatial understanding. Then, the depth-aware queries are fed into the inter-query self-attention layer for feature interaction between objects, and the visual cross-attention layer for collecting visual semantics from $f_V^e$ . We stack three decoder blocks to fully fuse the scene-level depth cues into object queries. + +Depth Positional Encodings. In the depth cross-attention layer, we propose learnable depth positional encodings for $f_{D}^{e}$ instead of conventional sinusoidal functions. In detail, we maintain a set of learnable embeddings, $p_{D} \in \mathbb{R}^{(d_{max} - d_{min} + 1) \times C}$ , where each row encodes the depth positional information for a meter, ranging from $d_{min}$ to $d_{max}$ . For each pixel $(x,y)$ in $D_{fg}$ , we first obtain its $(k + 1)$ -categorical depth prediction confidence, $D_{fg}(x,y) \in \mathbb{R}^{k + 1}$ , each channel of which denotes the predicted confidence for the corresponding depth bin. The estimated depth + +of pixel $(x,y)$ can then be obtained by the weighted summation of the depth-bin confidences and their corresponding depth values, which is formulated as + +$$ +d _ {m a p} (x, y) = \sum_ {i = 1} ^ {k + 1} D _ {f g} (x, y) [ i ] \cdot d _ {b i n} ^ {i}, \tag {5} +$$ + +where $d_{bin}^{i}$ denotes the starting value of the $i$ -th depth bin and $\sum_{i=1}^{k+1} D_{fg}(x,y)[i] = 1$ . Then, we linearly interpolate $p_{D}$ according to the depth $d_{map}(x,y)$ to obtain the depth positional encoding for the pixel $(x,y)$ . By pixel-wisely adding $f_{D}^{e}$ with such encodings, object queries can better capture scene-level depth cues and understand 3D geometry in the depth cross-attention layer. + +# 3.3. Detection Heads and Loss + +After the decoder, the depth-aware queries are fed into a series of MLP-based heads for 3D attribute predictions, including object category, 2D size, projected 3D center, depth, 3D size, and orientation. For inference, we convert these perspective attributes into 3D-space bounding boxes using camera parameters without NMS post-processing or pre-defined anchors. For training, we match the orderless queries with ground-truth labels and compute losses for the paired ones. We refer to Supplementary Material for details. + +Bipartite Matching. To correctly match each query with ground-truth objects, we calculate the loss for each query-label pair and utilize Hungarian algorithm [4] to find the globally optimal matching. For each pair, we integrate the losses of six attributes into two groups. The first contains object category, 2D size and the projected 3D center, since these attributes mainly concern 2D visual appearances of the image. The second group consists of depth, 3D size and orientation, which are 3D spatial properties of the object. We respectively sum the losses of two groups and denote them as $\mathcal{L}_{2D}$ and $\mathcal{L}_{3D}$ . As the network generally predicts less accurate 3D attributes than 2D attributes, especially at the beginning of training, the value of $\mathcal{L}_{3D}$ is unstable and would disturb the matching process. We only utilize $\mathcal{L}_{2D}$ as the matching cost for matching each query-label pair. + +Overall Loss. After the matching, we obtain $N_{gt}$ valid pairs out of $N$ queries, where $N_{gt}$ denotes the number of ground-truth objects. Then, the overall loss of a training image is formulated as + +$$ +\mathcal {L} _ {\text {o v e r a l l}} = \frac {1}{N _ {g t}} \cdot \sum_ {n = 1} ^ {N _ {g t}} \left(\mathcal {L} _ {2 D} + \mathcal {L} _ {3 D}\right) + \mathcal {L} _ {\text {d m a p}}, \tag {6} +$$ + +where $\mathcal{L}_{dmap}$ represents the Focal loss [23] of the predicted categorical foreground depth map $D_{fg}$ in Section 3.1. + +![](images/d8fd9e60a21cc964658874fdbe868cef4ecc8012a12d88a1d6bdf9ceeecf6430.jpg) +Figure 5. Plug-and-play for multi-view 3D object detection. We utilize yellow, blue, green, and red to respectively denote the feature space related to 2D, depth, 3D, and BEV. The depth-guided transformer of MonoDETR is adopted to enhance PETR (v2) [26, 27] and BEVFormer [22] in a plug-and-play manner, which provides depth guidance from surrounding scenes. + +# 3.4. Plug-and-play for Multi-view Detectors + +Besides monocular images, our depth-guided transformer can also serve as a plug-and-play module upon multi-view methods for depth-guided detection. Specifically, we append our depth predictors and depth encoders after the backbones of multi-view methods, which are shared across views and extract surrounding depth embeddings. Then, we inject our depth cross-attention layer into their transformer blocks to guide the 3D or BEV object queries by scene-level depth cues. + +For PETR (v2) [26, 27] in Figure 5 (a), we modify its previous visual decoder as a depth-guided decoder. In each decoder block, the 3D object queries are first fed into our depth cross-attention layer for depth cues aggregation, and then into the original 3D self-attention and visual cross-attention for 3D position features interaction. This enables PETR's 3D queries to be depth-aware and better capture spatial characteristics of surrounding scenes. + +For BEVFormer [22] in Figure 5 (b), as its decoder is conducted in BEV space, we incorporate the depth guidance into its BEV encoder, which lifts image features into BEV space by transformers. In each encoder block, the BEV queries also sequentially pass through our depth cross-attention layer and the original spatial cross-attention layer. This contributes to better BEV representation learning guided by the multi-view depth information. + +# 4. Experiments + +# 4.1. Settings + +Dataset. We evaluate MonoDETR on the widely-adopted KITTI [14] benchmark, including 7,481 training and 7,518 + +test images. We follow [8, 9] to split 3,769 val images from the training set. We report the detection results with three-level difficulties, easy, moderate, and hard, and evaluate by the average precision $(AP)$ of bounding boxes in 3D space and the bird-eye view, denoted as $AP_{3D}$ and $AP_{BEV}$ , respectively, which are both at 40 recall positions. + +Implementation details. We adopt ResNet-50 [15] as our feature backbone. To save GPU memory, we apply deformable attention [59] for the visual encoder and visual cross-attention layers, and utilize the vanilla global attention [4] to better capture non-local geometries for the depth encoder and depth cross-attention layers. We utilize 8 heads for all attention modules and set the number of queries $N$ as 50, which are learnable embeddings with predicted 2D reference points. We set the channel $C$ and all MLP's latent dimensions as 256. For the foreground depth map, we set $[d_{min}, d_{max}]$ as $[0m, 60m]$ and the number of bins $k$ as 80. On a single RTX 3090 GPU, we train MonoDETR for 195 epochs with batch size 16 and a learning rate $2 \times 10^{-4}$ . We adopt AdamW [30] optimizer with weight decay $10^{-4}$ , and decrease the learning rate at 125 and 165 epochs by 0.1. For training stability, we discard the training samples with depth labels larger than 65 meters or smaller than 2 meters. During inference, we simply filter out the object queries with the category confidence lower than 0.2 without NMS post-processing, and recover the 3D bounding box using the predicted six attributes following previous works [33, 31]. + +# 4.2. Comparison + +Performance. In Table 2, MonoDETR achieves state-of-the-art performance on KITTI test and val sets. On test set, MonoDETR exceeds all existing methods including those with different additional data input and surpasses + +
MethodExtra dataTest, AP3DTest, APBEVVal, AP3D
EasyMod.HardEasyMod.HardEasyMod.Hard
PatchNet [32]Depth15.6811.1210.1722.9716.8614.97---
D4LCN [12]16.6511.729.5122.5116.0212.55---
DDMP-3D [45]19.7112.789.8028.0817.8913.44---
Kinematic3D [2]Video19.0712.729.1726.6917.5213.1019.7614.1010.47
MonoRUn [7]LiDAR19.6512.3010.5827.9417.3415.2420.0214.6512.61
CaDDN [38]19.1713.4111.4627.9418.9117.1923.5716.3113.84
MonoDTR [18]21.9915.3912.7328.5920.3817.1424.5218.5715.51
AutoShape [29]CAD22.4714.1711.3630.6620.0815.5920.0914.6512.07
SMOKE [28]None14.039.767.8420.8314.4912.7514.7612.8511.50
MonoPair [10]13.049.998.6519.2814.8312.8916.2812.3010.42
RTM3D [21]13.6110.098.18---19.4716.2915.57
PGD [47]19.0511.769.3926.8916.5113.4919.2713.2310.65
IAFA [55]17.8112.0110.6125.8817.8815.3518.9514.9614.84
MonoDLE [33]17.2312.2610.2924.7918.8916.0017.4513.6611.68
MonoRCNN [42]18.3612.6510.0325.4818.1114.1016.6113.1910.65
MonoGeo [53]18.8513.8111.5225.8618.9916.1918.4514.4812.87
MonoFlex [52]19.9413.8912.0728.2319.7516.8923.6417.5114.83
GUPNet [31]20.1114.2011.77---22.7616.4613.72
MonoDETR (Ours)None25.0016.4713.5833.6022.1118.6028.8420.6116.38
Improvementv.s. second-best+2.53+1.08+0.85+2.94+1.73+1.41+4.32+2.04+0.81
+ +the second-best under three-level difficulties by $+2.53\%$ , $+1.08\%$ and $+0.85\%$ in $AP_{3D}$ , and by $+2.94\%$ , $+1.73\%$ and $+1.41\%$ in $AP_{BEV}$ . The competitive MonoDTR [18] also applies transformers to fuse depth features, but it is still a center-guided method and highly relies on additional dense depth supervision, anchors and NMS. In contrast, MonoDETR performs better without extra input or handcrafted designs, illustrating its simplicity and effectiveness. + +Efficiency. Compared to existing methods in Table 3, MonoDETR can achieve the best detection performance without consuming too much computational budget. As illustrated in Section 3, we only process the feature maps with $\frac{1}{16}$ and $\frac{1}{32}$ downsample ratios, which reduces our Runtime and GFlops, while others adopt $\frac{1}{4}$ and $\frac{1}{8}$ ratios. + +# 4.3. Ablation Studies + +We verify the effectiveness of each our component and report $AP_{3D}$ for the car category on the KITTI val set. + +Depth-guided Transformer. In Table 5, we first remove the entire depth-guided transformer along with the depth predictor, which constructs a pure center-guided baseline. This variant, denoted as 'w/o Depth-guided Trans.' can be regarded as a re-implementation of MonoDLE [33] with our detection heads and loss functions. As shown, the absence + +Table 2. Monocular performance of the car category on KITTI test and val sets. We utilize bold numbers to highlight the best results, and color the second-best ones and our gain over them in blue. + +
MethodMonoDLEGUPNetMonoDTRMonoDETR
Runtime↓40343738
GFlops↓79.1262.32120.4862.12
AP3D Mod.12.2615.0215.3916.47
+ +Table 3. Efficiency comparison. We test the Runtime (ms) on one RTX 3090 GPU with batch size 1, and compare $AP_{3D}$ on test set. + +of the depth-guided transformer greatly hurts the performance, for the lack of non-local geometric cues. Then, we investigate two key designs within the depth-guided transformer: the transformer architecture and depth guidance. For 'w/o Transformer', we only append the depth predictor upon the center-guided baseline to provide implicit depth guidance without transformers. For 'w/o Depth Guidance', we equip the center-guided baseline with a visual encoder and decoder, but include no depth predictor, depth encoder, and the depth cross-attention layer in the decoder. This builds a transformer network guided by visual appearances, without any depth guidance for object queries. The performance degradation of both variants indicates their significance for our depth-guided feature aggregation paradigm. + +Depth Encoder. The depth encoder produces non-local depth embeddings $f_{D}^{e}$ , which are essential for queries to + +
MethodImage SizeNDS↑mAP↑mATE↓mASE↓mAOE↓mAVE↓mAAE↓
CenterNet [56]-0.3280.3060.7160.2640.6091.4260.658
FCOS3D* [46]1600×9000.4150.3430.7250.2630.4221.2920.153
PGD* [47]1600×9000.4280.3690.6830.2600.4391.2680.185
DETR3D† [49]1600×9000.4340.3490.7160.2680.3790.8420.200
BEVDet† [17]1408×5120.4170.3490.6370.2690.4900.9140.268
PETR† [26]1600×9000.4420.3700.7110.2670.3830.8650.201
PETRv2 [27] + Depth-gudied800×3200.4960.4010.7450.2680.4480.3940.184
0.5080.4100.7270.2650.3890.4190.187
BEVFormer [22] + Depth-gudied1600×9000.5170.4160.6730.2740.3720.3940.198
0.5260.4230.6610.2720.3490.3710.192
+ +Table 4. Multi-view performance on nuScenes val set. * denotes the two-step fine-tuning with test-time augmentation, and † denotes CBGS [58] training. We compare with the best-performing variants of other methods and utilize bold numbers to highlight the best results. + +
ArchitectureEasyMod.Hard
MonoDETR28.8420.6116.38
w/o Depth-guided Trans.19.6915.1513.93
w/o Transformer20.1916.0514.18
w/o Depth Guidance24.1417.8115.60
+ +explore scene-level depth cues in the depth cross-attention layer. We experiment with different encoder designs in Table 6. 'Deform. SA' and $3 \times 3$ Conv. $\times 2'$ represent one-block of deformable attention and two $3 \times 3$ convolutional layers, respectively. As reported, 'Global SA' with only one block generates the best $f_{D}^{e}$ for global geoentry encoding. + +Depth-guided Decoder. As the core depth-guided component, we explore how to better guide object queries to interact with depth embeddings $f_{D}^{e}$ in Table 7. With the sequential inter-query self-attention ( $I'$ ) and visual cross-attention ( $V'$ ) layers, we insert the depth cross-attention layer ( $D'$ ) into each decoder block with four positions. For $I \rightarrow D + V'$ , we fuse the depth and visual embeddings $f_{D}^{e}, f_{V}^{e}$ by element-wise addition, and apply only one unified cross-attention layer. As shown, the $D \rightarrow I \rightarrow V'$ order performs the best. By placing $D'$ in the front, object queries can first aggregate depth cues to guide the remaining operations in each decoder block. + +Foreground Depth Map. We explore different representations for our depth map in Table 8. Compared to dense depth supervision ('Dense'), adopting object-wise depth labels ('Fore.') can focus the network on more important foreground geometric cues, and better capture depth relations between objects. 'LID' outperforms other discretization methods, since the linear-increasing intervals can suppress the larger estimation errors of farther objects. + +Table 5. Effectiveness of depth-guided transformer. 'Depth-guided Trans.' and 'Depth Guidance' denote the depth-guided transformer and the depth cross-attention layer, respectively + +
MechanismEasyMod.Hard
Global SA28.8420.6116.38
Deform. SA26.4318.9115.55
3×3 Conv.×2 w/o25.5518.3615.28
24.2518.3815.41
+ +Table 6. The design of depth encoder. 'Deform. SA' denotes a one-block deformable self-attention layer. 'w/o' denotes directly feeding depth features into the decoder without the depth encoder. + +Depth Positional Encodings $p_D$ . In Table 9, we experiment with different depth positional encodings for $f_D^e$ in the depth cross-attention layer. By default, we apply the meterwise encodings $p_D \in \mathbb{R}^{(d_{max} - d_{min} + 1) \times C}$ that assign one learnable embedding per meter with depth value interpolation for output. We then assign one learnable embedding for each depth bin, denoted as 'k-bin $p_D \in \mathbb{R}^{k \times C}$ , and also experiment sinusoidal functions to encode either the depth values or 2D coordinates of the feature map, denoted as 'Depth sin/cos' and '2D sin/cos', respectively. As shown, 'meter-wise $p_D$ ' performs the best for encoding more fine-grained depth cues ranging from $d_{min}$ to $d_{max}$ , which provides the queries with more scene-level spatial structures. + +# 4.4. Multi-view Experiments + +As a plug-and-play module for multi-view 3D object detection, we append our depth-guided transformer upon two DETR-based multi-view networks, PETR v2 [27] and BEVFormer [22]. The detailed network architectures are shown in Figure 5. For a fair comparison, we adopt the same training configurations as the two baseline models, and utilize the same $[d_{min}, d_{max}]$ with $k$ as monocular experiments. We report the performance on nuScenes [3] val set in Table 4, where we apply no test-time augmentation or CGBS [58] training. For end-to-end detection in PETRv2, the depth guidance contributes to $+1.2\%$ NDS and $+0.9\%$ mAP by providing sufficient multi-view geometric cues. + +![](images/0cc48f129910ed97c69db42eb1361e13c1d88acac4747ce23f137ec15dc4311b.jpg) +Figure 6. Visualizations of attention maps $A_{D}$ in the depth cross-attention layer. The top column denotes the input image, and the last three columns denote the attention maps of the target queries (denoted as white dots). Hotter colors indicate higher attention weights. + +![](images/5ab5c61c38bb24ea37716344d6a75087d94f215de3b6ed38fc1d89e0f71a8989.jpg) + +![](images/67e90c1fccbbdbf4a5740d40650cf2108806ab22428744b5ec9e5bbf17651fcd.jpg) + +![](images/6f26fadc0ed7a03d14f7d1545144b28f3e7c0e4fdd9bb02fcfabb58837989ca1.jpg) + +
ArchitectureEasyMod.Hard
D → I → V28.8420.6116.38
I → D → V26.2419.2816.03
I → V → D25.8418.8515.72
I → D + V24.9418.4115.39
+ +For the BEV feature generation, our modules benefit BEV-Former by $+0.9\%$ NDS and $+0.7\%$ mAP, indicating the importance of auxiliary depth information for BEV-space feature encoding. The additional experiments on multi-view 3D object detection well demonstrate the effectiveness and generalizability of our approach. + +# 5. Visualization + +We visualize the attention maps $A_{D}$ in Equation 3 of the depth cross-attention layer at the last decoder block. As shown in Figure 6, the areas with high attention scores for the target object query spread over the entire image, concentrating on other objects with long distances. This indicates, via our depth guidance, object queries are able to adaptively capture non-local depth cues from the image and are no longer limited by neighboring visual features. + +# 6. Conclusion + +We propose MonoDETR, an end-to-end transformer-based framework for monocular 3D object detection, which is free from any additional input, anchors, or NMS. Different from existing center-guided methods, we enable object queries to explore geometric cues adaptively from the depth-guided regions, and conduct inter-object and object-scene depth interactions via attention mechanisms. Extensive experiments have demonstrated the effectiveness of our approach for both single-view (KITTI) and multi-view (nuScenes) input. We hope MonoDETR can serve as a + +Table 7. The design of depth-guided decoder. 'D', 'I', and 'V' denote the depth cross-attention, inter-query self-attention, and visual cross-attention layers, respectively. + +
Depth MapEasyMod.Hard
Fore. LID28.8420.6116.38
Dense LID27.6919.8515.98
Fore. UD25.6118.9015.49
Fore. SID26.0518.9515.59
+ +Table 8. Different representations of the predicted depth map. 'UD', 'SID', and 'LID' denote uniform, spacing-increasing, and linear-increasing discretizations. + +
SettingsEasyMod.Hard
Meter-wise pD28.8420.6116.38
k-bin pD28.0619.6816.04
Depth sin/cos27.4219.5715.82
2D sin/cos26.4818.6315.52
w/o26.7618.9415.85
+ +Table 9. The design of depth positional encodings. 'Meter-wise' and $k$ -bin' assign learnable embeddings by meters and depth bins, respectively. 'sin/cos' denotes sinusoidal functions for encodings. + +strong DETR baseline for future research in monocular 3D object detection. Limitations. How to effectively incorporate multi-modal input into our transformer framework is not discussed in the paper. Our future direction will focus on this to further improve the performance of depth-guided transformers, e.g., distilling more sufficient geometric knowledge from LiDAR and RADAR modalities. + +# Acknowledgement + +This project is funded in part by the National Natural Science Foundation of China (No.62206272), by the National Key R&D Program of China Project (No.2022ZD0161100), by the Centre for Perceptual and Interactive Intelligence (CPII) Ltd under the Innovation and Technology Commission (ITC)'s InnoHK, and by the General Research Fund of Hong Kong RGC Project 14204021. 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"content": "Monocular 3D object detection has long been a challenging task in autonomous driving. Most existing methods follow conventional 2D detectors to first localize object centers, and then predict 3D attributes by neighboring features. However, only using local visual features is insufficient to understand the scene-level 3D spatial structures and ignores the long-range inter-object depth relations. In this paper, we introduce the first DETR framework for Monocular DTection with a depth-guided TRansformer, named MonoDETR. We modify the vanilla transformer to be depth-aware and guide the whole detection process by contextual depth cues. Specifically, concurrent to the visual encoder that captures object appearances, we introduce to predict a foreground depth map, and specialize a depth encoder to extract non-local depth embeddings. Then, we formulate 3D object candidates as learnable queries and propose a depth-guided decoder to conduct object-scene depth interactions. In this way, each object query estimates its 3D attributes adaptively from the depth-guided regions on the image and is no longer constrained to local visual features. On KITTI benchmark with monocular images as input, MonoDETR achieves state-of-the-art performance and requires no extra dense depth annotations. Besides, our depth-guided modules can also be plug-and-play to enhance multi-view 3D object detectors on nuScenes dataset, demonstrating our superior generalization capacity. Code is available at https://github.com/ZrrSkywalker/MonoDETR." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 48, + 638, + 128, + 651 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 638, + 128, + 651 + ], + "spans": [ + { + "bbox": [ + 48, + 638, + 128, + 651 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 658, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 658, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 47, + 658, + 287, + 696 + ], + "type": "text", + "content": "With a wide range of applications in autonomous driving, 3D object detection is more challenging than its 2D counterparts, due to the complex spatial circumstances." + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 312, + 254, + 538, + 377 + ], + "blocks": [ + { + "bbox": [ + 312, + 254, + 538, + 377 + ], + "lines": [ + { + "bbox": [ + 312, + 254, + 538, + 377 + ], + "spans": [ + { + "bbox": [ + 312, + 254, + 538, + 377 + ], + "type": "image", + "image_path": "02e855ce7534f2ed2b7b1787e8560924b0e6ee9e3bc68bf1046fdd8de9a296e1.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 384, + 546, + 462 + ], + "lines": [ + { + "bbox": [ + 305, + 384, + 546, + 462 + ], + "spans": [ + { + "bbox": [ + 305, + 384, + 546, + 462 + ], + "type": "text", + "content": "Figure 1. Center-guided (Top) and Depth-guided Paradigms (Bottom) for monocular 3D object detection. Existing center-guided methods predict 3D attributes from local visual features around the centers, while our MonoDETR guides the detection by a predicted foreground depth map and adaptively aggregates features in global context. The lower right figure visualizes the attention map of the target query in the depth cross-attention layer." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 483, + 546, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 483, + 546, + 567 + ], + "spans": [ + { + "bbox": [ + 304, + 483, + 546, + 567 + ], + "type": "text", + "content": "Compared to methods based on LiDAR [57, 20, 41, 50] and multi-view images [49, 22, 26, 17], 3D object detection from monocular (single-view) images [9, 1, 46] is of most difficulty, which generally does not rely on depth measurements or multi-view geometry. The detection accuracy thus severely suffers from the ill-posed depth estimation, leading to inferior performance." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "text", + "content": "Except for leveraging pseudo 3D representations [48, 51, 32, 38], standard monocular 3D detection methods [33, 52, 53, 31] follow the pipeline of traditional 2D object detection [40, 24, 43, 56]. They first localize objects by detecting the projected centers on the image, and then aggregate the neighboring visual features for 3D property prediction, as illustrated in Figure 1 (Top). Although it is conceptually straightforward, such center-guided methods are limited by the local appearances without long-range context, and fail to capture implicit geometric cues from 2D images, e.g., depth guidance, which are critical to detect objects in 3D space." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 318, + 701, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 701, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 318, + 701, + 546, + 713 + ], + "type": "text", + "content": "To tackle this issue, we propose MonoDETR, which" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 62, + 703, + 141, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 62, + 703, + 141, + 713 + ], + "spans": [ + { + "bbox": [ + 62, + 703, + 141, + 713 + ], + "type": "text", + "content": "† Corresponding author" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "9155" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 68, + 145, + 229 + ], + "blocks": [ + { + "bbox": [ + 53, + 68, + 145, + 229 + ], + "lines": [ + { + "bbox": [ + 53, + 68, + 145, + 229 + ], + "spans": [ + { + "bbox": [ + 53, + 68, + 145, + 229 + ], + "type": "image", + "image_path": "5ec4506b34b33f6ecb376831da7b887324f4c0846dbfa219caf705de935e6f1c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 236, + 546, + 270 + ], + "lines": [ + { + "bbox": [ + 46, + 236, + 546, + 270 + ], + "spans": [ + { + "bbox": [ + 46, + 236, + 546, + 270 + ], + "type": "text", + "content": "Figure 2. Comparison of DETR-based methods for camera-based 3D object detection. We utilize yellow, blue, green, and red to respectively denote the feature or prediction space related with 2D, depth, 3D, and BEV. Different from other methods, our MonoDETR leverages depth cues to guide 3D object detection from monocular images." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 158, + 68, + 289, + 232 + ], + "blocks": [ + { + "bbox": [ + 158, + 68, + 289, + 232 + ], + "lines": [ + { + "bbox": [ + 158, + 68, + 289, + 232 + ], + "spans": [ + { + "bbox": [ + 158, + 68, + 289, + 232 + ], + "type": "image", + "image_path": "de4705794926c829fedab5a79b1b0eaa8e75686214253ce6145c2b625f50d285.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 309, + 68, + 427, + 228 + ], + "blocks": [ + { + "bbox": [ + 309, + 68, + 427, + 228 + ], + "lines": [ + { + "bbox": [ + 309, + 68, + 427, + 228 + ], + "spans": [ + { + "bbox": [ + 309, + 68, + 427, + 228 + ], + "type": "image", + "image_path": "e1d237b7818079d52bedeafc8e70a765bbb205a8c1bad3d67020727f55ca5fba.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 441, + 68, + 537, + 227 + ], + "blocks": [ + { + "bbox": [ + 441, + 68, + 537, + 227 + ], + "lines": [ + { + "bbox": [ + 441, + 68, + 537, + 227 + ], + "spans": [ + { + "bbox": [ + 441, + 68, + 537, + 227 + ], + "type": "image", + "image_path": "9b050e0e68757f5bcdfac6e095600c750fede0f5da9594822198cf18610aa1e6.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 289, + 287, + 386 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 289, + 287, + 386 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 287, + 386 + ], + "type": "text", + "content": "presents a novel depth-guided 3D detection scheme in Figure 1 (Bottom). Compared to DETR [4] in 2D detection, the transformer in MonoDETR is equipped with depth-guided modules to better capture contextual depth cues, serving as the first DETR model for monocular 3D object detection, as shown in Figure 2 (a) and (b). It consists of: two parallel encoders for visual and depth representation learning, and a decoder for adaptive depth-guided detection." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 387, + 287, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 387, + 287, + 590 + ], + "spans": [ + { + "bbox": [ + 46, + 387, + 287, + 590 + ], + "type": "text", + "content": "Specifically, after the feature backbone, we first utilize a lightweight depth predictor to acquire the depth features of the input image. To inject effective depth cues, a foreground depth map is predicted on top, and supervised only by discrete depth labels of objects, which requires no dense depth annotations during training. Then, we apply the parallel encoders to respectively generate non-local depth and visual embeddings, which represent the input image from two aspects: depth geometry and visual appearance. On top of that, a set of object queries is fed into the depth-guided decoder, and conducts adaptive feature aggregation from the two embeddings. Via a proposed depth cross-attention layer, the queries can capture geometric cues from the depth-guided regions on the image, and explore interobject depth relations. In this way, the 3D attribute prediction can be guided by informative depth hints, no longer constrained by the limited visual features around centers." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 593, + 287, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 593, + 287, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 593, + 287, + 700 + ], + "type": "text", + "content": "As an end-to-end transformer-based network, MonoDETR is free from non-maximum suppression (NMS) or rule-based label assignment. We only utilize the object-wise labels for supervision without using auxiliary data, such as dense depth maps or LiDAR. Taking monocular images as input, MonoDETR achieves state-of-the-art performance among existing center-guided methods, and surpasses the second-best by " + }, + { + "bbox": [ + 46, + 593, + 287, + 700 + ], + "type": "inline_equation", + "content": "+2.53\\%" + }, + { + "bbox": [ + 46, + 593, + 287, + 700 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 593, + 287, + 700 + ], + "type": "inline_equation", + "content": "+1.08\\%" + }, + { + "bbox": [ + 46, + 593, + 287, + 700 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 593, + 287, + 700 + ], + "type": "inline_equation", + "content": "+0.85\\%" + }, + { + "bbox": [ + 46, + 593, + 287, + 700 + ], + "type": "text", + "content": " for three-level difficulties on KITTI [14] test set." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "content": "Besides single-view images, the depth-guided mod" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 289, + 545, + 386 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 289, + 545, + 386 + ], + "spans": [ + { + "bbox": [ + 304, + 289, + 545, + 386 + ], + "type": "text", + "content": "ules in MonoDETR can also be extended as a plug-and-play module for multi-view 3D detection on nuScenes [3] dataset. By providing multi-view depth cues, our method can not only improve the end-to-end detection performance of PETRv2 [27] by " + }, + { + "bbox": [ + 304, + 289, + 545, + 386 + ], + "type": "inline_equation", + "content": "+1.2\\%" + }, + { + "bbox": [ + 304, + 289, + 545, + 386 + ], + "type": "text", + "content": " NDS, but also benefit the BEV representation learning in BEVFormer [22] by " + }, + { + "bbox": [ + 304, + 289, + 545, + 386 + ], + "type": "inline_equation", + "content": "+0.9\\%" + }, + { + "bbox": [ + 304, + 289, + 545, + 386 + ], + "type": "text", + "content": " NDS. This further demonstrates the effectiveness and generalizability of our proposed depth guidance." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 387, + 545, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 387, + 545, + 399 + ], + "spans": [ + { + "bbox": [ + 317, + 387, + 545, + 399 + ], + "type": "text", + "content": "We summarize the contributions of our paper as follows:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 409, + 545, + 535 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 317, + 409, + 545, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 409, + 545, + 445 + ], + "spans": [ + { + "bbox": [ + 317, + 409, + 545, + 445 + ], + "type": "text", + "content": "- We propose MonoDETR, a depth-guided framework to capture scene-level geometries and inter-object depth relations for monocular 3D object detection." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 317, + 454, + 545, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 454, + 545, + 491 + ], + "spans": [ + { + "bbox": [ + 317, + 454, + 545, + 491 + ], + "type": "text", + "content": "- We introduce a foreground depth map for object-wise depth supervision, and a depth cross-attention layer for adaptive depth features interaction." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 317, + 499, + 545, + 535 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 499, + 545, + 535 + ], + "spans": [ + { + "bbox": [ + 317, + 499, + 545, + 535 + ], + "type": "text", + "content": "- MonoDETR achieves leading results on monocular KITTI benchmark, and can also be generalized to enhance multi-view detection on nuScenes benchmark." + } + ] + } + ], + "index": 13 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 548, + 392, + 562 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 548, + 392, + 562 + ], + "spans": [ + { + "bbox": [ + 306, + 548, + 392, + 562 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 570, + 545, + 666 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 666 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 666 + ], + "type": "text", + "content": "Existing methods for camera-based 3D object detection can be categorized as two groups according to the input number of views: monocular (single-view) and multi-view methods. Monocular detectors only take as input the front-view images and solve a more challenging task from insufficient 2D signals. Multi-view detectors simultaneously encode images of surrounding scenes and can leverage cross-view dependence to understand the 3D space." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 677, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 546, + 714 + ], + "type": "text", + "content": "Monocular (Single-view) 3D Object Detection. Most previous monocular detectors adopt center-guided pipelines following conventional 2D detectors [40, 43, 56]. As early" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "9156" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 72, + 289, + 171 + ], + "blocks": [ + { + "bbox": [ + 48, + 72, + 289, + 171 + ], + "lines": [ + { + "bbox": [ + 48, + 72, + 289, + 171 + ], + "spans": [ + { + "bbox": [ + 48, + 72, + 289, + 171 + ], + "type": "table", + "html": "
MethodDETR-basedExtra DataGuided byObject QueryFeat. Aggre.
Mutli-view Methods
DETR3D [49]✓-Visual3DLocal
PETR (v2) [26]✓TemporalVisual3DGlobal
BEVFormer [22]✓TemporalVisualBEV, 3DGlobal
Monocular Methods
MonoDTR [18]×LiDARCenter×Local
MonoDETR✓-DepthDepthGlobal
", + "image_path": "22fc58a43495161499026d4fd49ae354d8f851cf0037c192fe598138a1d71fc8.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 175, + 288, + 209 + ], + "lines": [ + { + "bbox": [ + 46, + 175, + 288, + 209 + ], + "spans": [ + { + "bbox": [ + 46, + 175, + 288, + 209 + ], + "type": "text", + "content": "Table 1. Comparison of DETR-based methods for camera-based 3D object detection. Our MonoDETR is uniquely guided by depth cues with depth-aware object queries." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 233, + 289, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 233, + 289, + 462 + ], + "spans": [ + { + "bbox": [ + 46, + 233, + 289, + 462 + ], + "type": "text", + "content": "works, Deep3Box [35] introduces discretized representation with perspective constraints, and M3D-RPN [1] designs a depth-aware convolution for better 3D region proposals. With very few handcrafted modules, SMOKE [28] and FCOS3D [46] propose concise architectures for efficient one-stage detection, while MonoDLE [33] and PGD [47] analyze depth errors on top with improved performance. To supplement the limited 3D cues, additional data are utilized for assistance: dense depth annotations [32, 12, 45, 36], CAD models [29], and LiDAR [7, 38, 18]. Some recent methods introduce complicated geometric priors into the networks: adjacent object pairs [10], 2D-3D keypoints [21], and uncertainty-related depth [52, 31]. Despite this, the center-guided methods are still limited by local visual features without scene-level spatial cues. In contrast, MonoDETR discards the center localization step and conducts adaptive feature aggregation via a depth-guided transformer. MonoDETR requires no additional annotations and contains minimal 2D-3D geometric priors." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 474, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 474, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 474, + 289, + 715 + ], + "type": "text", + "content": "Multi-view 3D Object Detection. For jointly extracting features from surrounding views, DETR3D [49] firstly utilizes a set of 3D object queries and back-projects them onto multi-view images for feature aggregation. PETR series [26, 27] further proposes to generate 3D position features without unstable projection and explores the advantage of temporal information from previous frames. From another point of view, BEVDet [17, 16] follows [37] to lift 2D images into a unified Bird's-Eye-View (BEV) representation and appends BEV-based heads [50] for detection. BEVFormer [22] instead generates BEV features via a set of learnable BEV queries, and introduces a spatiotemporal BEV transformer for visual features aggregation. Follow-up works also introduce cross-modal distillation [19, 11] and masked image modeling [25, 6] for improved performance. Different from the above methods for multi-view input, MonoDETR targets monocular images and extracts depth guidance to capture more geometric cues. Our depth-guided modules can also be generalized to surrounding views as a plug-and-play module to enhance multi-view detectors." + } + ] + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 307, + 71, + 548, + 159 + ], + "blocks": [ + { + "bbox": [ + 307, + 71, + 548, + 159 + ], + "lines": [ + { + "bbox": [ + 307, + 71, + 548, + 159 + ], + "spans": [ + { + "bbox": [ + 307, + 71, + 548, + 159 + ], + "type": "image", + "image_path": "ad84401c4e25971a9f646f5380235658817b5552b93b4f8d93ebecfe9575de9b.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 175, + 547, + 209 + ], + "lines": [ + { + "bbox": [ + 304, + 175, + 547, + 209 + ], + "spans": [ + { + "bbox": [ + 304, + 175, + 547, + 209 + ], + "type": "text", + "content": "Figure 3. The lightweight depth predictor. We utilize the depth predictor to predict the depth features and foreground depth map, which only contains discrete object-wise depth values." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 234, + 547, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 234, + 547, + 582 + ], + "spans": [ + { + "bbox": [ + 304, + 234, + 547, + 582 + ], + "type": "text", + "content": "Comparison of DETR-based Methods. DETR [5] and its follow-up works [13, 59, 54, 34] have attained great success on 2D object detection without NMS or anchors. Inspired by this, some efforts have transferred DETR into camera-based 3D object detection. We specifically compare our MonoDETR with existing DETR-based 3D object detectors in Figure 2 and Table 1. (1) MonoDTR [18]. Also as a single-view detector, MonoDTR utilizes transformers [44] to incorporate depth features with visual representations. However, MonoDTR is not a DETR-based method, and still adopts the traditional center-guided paradigm, which localizes objects by their centers and only aggregate local features. MonoDTR contains no object queries for global feature aggregation, and follows YOLOv3 [39] to adopt complicated NMS post-processing with pre-defined anchors. (2) DETR3D [49] and PETR (v2) [26, 27] (Figure 2 (c)) are multi-view methods and follow the DETR detection pipeline. In contrast, they contain no transformer-based encoders (visual or depth), and detect objects by 3D object queries without the perspective transformation. Importantly, they are only guided by visual features and explores no depth cues from the input images. (3) BEVFormer [22] (Figure 2 (d)) firstly utilizes a BEV transformer to lift multiview images into BEV representations, and then conducts DETR-based detection within the BEV space. Different from all aforementioned methods, MonoDETR introduces a unique depth-guided transformer that guides the 3D detection by geometric depth cues, which can generalize well to both monocular and multi-view inputs." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 596, + 362, + 609 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 596, + 362, + 609 + ], + "spans": [ + { + "bbox": [ + 306, + 596, + 362, + 609 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": "The overall framework of MonoDETR is shown in Figure 4. We first illustrate the concurrent visual and depth feature extraction in Section 3.1, and detail our depth-guided transformer for aggregating appearance and geometric cues in Section 3.2. Then, we introduce the attribute prediction and loss functions of MonoDETR in Section 3.3. Finally, we illustrate how to plug our depth-guided transformer into existing multi-view object detectors in Section 3.4." + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "9157" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 97, + 68, + 496, + 289 + ], + "blocks": [ + { + "bbox": [ + 97, + 68, + 496, + 289 + ], + "lines": [ + { + "bbox": [ + 97, + 68, + 496, + 289 + ], + "spans": [ + { + "bbox": [ + 97, + 68, + 496, + 289 + ], + "type": "image", + "image_path": "b4b5956ff1d1c64f05de6f13102cbe3680fdacfa10715d931de094aa23a8d9bd.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 295, + 547, + 319 + ], + "lines": [ + { + "bbox": [ + 46, + 295, + 547, + 319 + ], + "spans": [ + { + "bbox": [ + 46, + 295, + 547, + 319 + ], + "type": "text", + "content": "Figure 4. Overall pipeline of MonoDETR. We first acquire the visual and depth features of the input image and utilize two parallel encoders for non-local encoding. Then, we propose a depth-guided decoder to adaptively aggregate scene-level features in global context." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 339, + 160, + 350 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 339, + 160, + 350 + ], + "spans": [ + { + "bbox": [ + 47, + 339, + 160, + 350 + ], + "type": "text", + "content": "3.1. Feature Extraction" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 357, + 288, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 357, + 288, + 407 + ], + "spans": [ + { + "bbox": [ + 46, + 357, + 288, + 407 + ], + "type": "text", + "content": "Taking as input a monocular (single-view) image, our framework utilizes a feature backbone, e.g., ResNet-50 [15], and a lightweight depth predictor to generate its visual and depth features, respectively." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "spans": [ + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "content": "Visual Features. Given the image " + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "inline_equation", + "content": "I \\in \\mathbb{R}^{H \\times W \\times 3}" + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "content": " denote its height and width, we obtain its multiscale feature maps, " + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "inline_equation", + "content": "f_{\\frac{1}{8}}" + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "inline_equation", + "content": "f_{\\frac{1}{16}}" + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "inline_equation", + "content": "f_{\\frac{1}{32}}" + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "content": ", from the last three stages of ResNet-50. Their downsample ratios to the original size are " + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "inline_equation", + "content": "\\frac{1}{8}" + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "inline_equation", + "content": "\\frac{1}{16}" + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "inline_equation", + "content": "\\frac{1}{32}" + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "content": ". We regard the highest-level " + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "inline_equation", + "content": "f_{\\frac{1}{32}} \\in \\mathbb{R}^{\\frac{H}{32} \\times \\frac{W}{32} \\times C}" + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "content": " with sufficient semantics as the visual features " + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "inline_equation", + "content": "f_V" + }, + { + "bbox": [ + 47, + 410, + 287, + 498 + ], + "type": "text", + "content": " of the input image." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 503, + 287, + 612 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 503, + 287, + 612 + ], + "spans": [ + { + "bbox": [ + 46, + 503, + 287, + 612 + ], + "type": "text", + "content": "Depth Features. We obtain the depth features from the image by a lightweight depth predictor, as shown in Figure 3. We first unify the sizes of three-level features to the same " + }, + { + "bbox": [ + 46, + 503, + 287, + 612 + ], + "type": "inline_equation", + "content": "\\frac{1}{16}" + }, + { + "bbox": [ + 46, + 503, + 287, + 612 + ], + "type": "text", + "content": " downsample ratio via bilinear pooling, and fuse them by element-wise addition. In this way, we can integrate multi-scale visual appearances and also preserve fine-grained patterns for objects of small sizes. Then, we apply two " + }, + { + "bbox": [ + 46, + 503, + 287, + 612 + ], + "type": "inline_equation", + "content": "3\\times 3" + }, + { + "bbox": [ + 46, + 503, + 287, + 612 + ], + "type": "text", + "content": " convolutional layers to obtain the depth features " + }, + { + "bbox": [ + 46, + 503, + 287, + 612 + ], + "type": "inline_equation", + "content": "f_{D}\\in \\mathbb{R}^{\\frac{H}{16}\\times \\frac{W}{16}\\times C}" + }, + { + "bbox": [ + 46, + 503, + 287, + 612 + ], + "type": "text", + "content": " for the input image." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": "Foreground Depth Map. To incorporate effective depth information into the depth features, we predict a foreground depth map " + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "inline_equation", + "content": "D_{fg} \\in \\mathbb{R}_{16}^{\\frac{H}{16} \\times \\frac{W}{16} \\times (k + 1)}" + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": " on top of " + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{D}" + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": " via a " + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": " convolutional layer. We supervise the depth map only by discrete object-wise depth labels, without extra dense depth annotations. The pixels within the same 2D bounding box are assigned with the same depth label of the corresponding object. For pixels within multiple boxes, we select the" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "spans": [ + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "text", + "content": "depth label of the object that is nearest to the camera, which accords with the visual appearance of the image. Here, We discretize the depth into " + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "inline_equation", + "content": "k + 1" + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "text", + "content": " bins [38], where the first ordinal " + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "text", + "content": " bins denote foreground depth and the last one denotes the background. We adopt linear-increasing discretization (LID), since the larger depth estimation errors of farther objects can be suppressed with a wider categorization interval. We limit the foreground depth values within " + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "inline_equation", + "content": "[d_{min}, d_{max}]" + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "text", + "content": ", and set both the first interval length and LID's common difference as " + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "text", + "content": ". We then categorize a ground-truth depth label " + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "text", + "content": " into the " + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 340, + 547, + 471 + ], + "type": "text", + "content": "-th bin as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 345, + 474, + 545, + 500 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 345, + 474, + 545, + 500 + ], + "spans": [ + { + "bbox": [ + 345, + 474, + 545, + 500 + ], + "type": "interline_equation", + "content": "k = \\left\\lfloor - 0. 5 + 0. 5 \\sqrt {1 + \\frac {8 (d - d _ {\\min })}{\\delta}} \\right\\rfloor , \\tag {1}", + "image_path": "fcea01b26f609468634869895eea9e55f4e7c3c155ceebcc5f4e49b3fc6a7c4e.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 504, + 547, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 504, + 547, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 504, + 547, + 568 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 504, + 547, + 568 + ], + "type": "inline_equation", + "content": "\\delta = \\frac{2(d_{max} - d_{min})}{k(k + 1)}" + }, + { + "bbox": [ + 304, + 504, + 547, + 568 + ], + "type": "text", + "content": ". By focusing on the object-wise depth values, the network can better capture foreground spatial structures and inter-object depth relations, which produces informative depth features for the subsequent depth-guided transformer." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 578, + 455, + 590 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 578, + 455, + 590 + ], + "spans": [ + { + "bbox": [ + 306, + 578, + 455, + 590 + ], + "type": "text", + "content": "3.2. Depth-guided Transformer" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 596, + 547, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 596, + 547, + 657 + ], + "spans": [ + { + "bbox": [ + 304, + 596, + 547, + 657 + ], + "type": "text", + "content": "The depth-guided transformer of MonoDETR is composed of a visual encoder, a depth encoder, and a depth-guided decoder. The two encoders produce non-local visual and depth embeddings, and the decoder enables object queries to adaptively capture scene-level information." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 663, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 663, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 663, + 547, + 715 + ], + "type": "text", + "content": "Visual and Depth Encoders. Given depth and visual features " + }, + { + "bbox": [ + 304, + 663, + 547, + 715 + ], + "type": "inline_equation", + "content": "f_{D}, f_{V}" + }, + { + "bbox": [ + 304, + 663, + 547, + 715 + ], + "type": "text", + "content": ", we specialize two transformer encoders to generate their scene-level embeddings with global receptive fields, denoted as " + }, + { + "bbox": [ + 304, + 663, + 547, + 715 + ], + "type": "inline_equation", + "content": "f_{D}^{e} \\in \\mathbb{R}_{16^{2}}^{\\frac{HW}{2} \\times C}" + }, + { + "bbox": [ + 304, + 663, + 547, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 663, + 547, + 715 + ], + "type": "inline_equation", + "content": "f_{V}^{e} \\in \\mathbb{R}_{32^{2}}^{\\frac{HW}{2} \\times C}" + }, + { + "bbox": [ + 304, + 663, + 547, + 715 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "9158" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 217 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 217 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 217 + ], + "type": "text", + "content": "We set three blocks for the visual encoder and only one block for the depth encoder, since the discrete foreground depth information is easier to be encoded than the rich visual appearances. Each encoder block consists of a self-attention layer and a feed-forward neural network (FFN). By the global self-attention mechanism, the depth encoder explores long-range dependencies of depth values from different foreground areas, which provides non-local geometric cues of the stereo space. In addition, the decoupling of depth and visual encoders allows them to better learn features for themselves, encoding the input image from two perspectives, i.e., depth geometry and visual appearance." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 229, + 289, + 362 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 229, + 289, + 362 + ], + "spans": [ + { + "bbox": [ + 46, + 229, + 289, + 362 + ], + "type": "text", + "content": "Depth-guided Decoder. Based on the non-local " + }, + { + "bbox": [ + 46, + 229, + 289, + 362 + ], + "type": "inline_equation", + "content": "f_{D}^{e}, f_{V}^{e}" + }, + { + "bbox": [ + 46, + 229, + 289, + 362 + ], + "type": "text", + "content": ", we utilize a set of learnable object queries " + }, + { + "bbox": [ + 46, + 229, + 289, + 362 + ], + "type": "inline_equation", + "content": "q \\in \\mathbb{R}^{N \\times C}" + }, + { + "bbox": [ + 46, + 229, + 289, + 362 + ], + "type": "text", + "content": " to detect 3D objects via the depth-guided decoder, where " + }, + { + "bbox": [ + 46, + 229, + 289, + 362 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 229, + 289, + 362 + ], + "type": "text", + "content": " denotes the pre-defined maximum number of objects in the input image. Each decoder block sequentially contains a depth cross-attention layer, an inter-query self-attention layer, a visual cross-attention layer, and an FFN. Specifically, the queries first capture informative depth features from " + }, + { + "bbox": [ + 46, + 229, + 289, + 362 + ], + "type": "inline_equation", + "content": "f_{D}^{e}" + }, + { + "bbox": [ + 46, + 229, + 289, + 362 + ], + "type": "text", + "content": " via the depth cross-attention layer, in which we linearly transform the object queries and depth embeddings into queries, keys, and values," + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 76, + 369, + 287, + 383 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 76, + 369, + 287, + 383 + ], + "spans": [ + { + "bbox": [ + 76, + 369, + 287, + 383 + ], + "type": "interline_equation", + "content": "Q _ {q} = \\operatorname {L i n e a r} (q), \\quad K _ {D}, V _ {D} = \\operatorname {L i n e a r} \\left(f _ {D} ^ {e}\\right), \\tag {2}", + "image_path": "ddbd9492f38740977b923af5951b6e16696f3362e310c130e65a6d9dabdcf59c.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "spans": [ + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "type": "inline_equation", + "content": "Q_{q}\\in \\mathbb{R}^{N\\times C}" + }, + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "type": "inline_equation", + "content": "K_{D},V_{D}\\in \\mathbb{R}^{\\frac{HW}{16^{2}}\\times C}" + }, + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "type": "text", + "content": ". Then, we calculate the query-depth attention map " + }, + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "type": "inline_equation", + "content": "A_{D}\\in \\mathbb{R}^{N\\times \\frac{HW}{16^{2}}}" + }, + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "type": "text", + "content": ", and aggregate informative depth features weighted by " + }, + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "type": "inline_equation", + "content": "A_{D}" + }, + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "type": "text", + "content": " to produce the depth-aware queries " + }, + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "type": "inline_equation", + "content": "q^{\\prime}" + }, + { + "bbox": [ + 46, + 389, + 287, + 442 + ], + "type": "text", + "content": ", formulated as," + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 104, + 448, + 287, + 462 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 104, + 448, + 287, + 462 + ], + "spans": [ + { + "bbox": [ + 104, + 448, + 287, + 462 + ], + "type": "interline_equation", + "content": "A _ {D} = \\operatorname {S o f t m a x} \\left(Q _ {q} K _ {D} ^ {T} / \\sqrt {C}\\right), \\tag {3}", + "image_path": "012d237fc7f0cf4e1a4109215d9b0336c4a0cb90a5798c734e045111001661fc.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 111, + 464, + 287, + 477 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 464, + 287, + 477 + ], + "spans": [ + { + "bbox": [ + 111, + 464, + 287, + 477 + ], + "type": "interline_equation", + "content": "q ^ {\\prime} = \\operatorname {L i n e a r} \\left(A _ {D} V _ {D}\\right). \\tag {4}", + "image_path": "a0ec84fbfe5260bdbe40edfc5746bb542f7bd4fc10d4b42d9509028660add5b9.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 484, + 287, + 580 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 484, + 287, + 580 + ], + "spans": [ + { + "bbox": [ + 46, + 484, + 287, + 580 + ], + "type": "text", + "content": "Such a mechanism enables each object query to adaptively capture spatial cues from depth-guided regions on the image, leading to better scene-level spatial understanding. Then, the depth-aware queries are fed into the inter-query self-attention layer for feature interaction between objects, and the visual cross-attention layer for collecting visual semantics from " + }, + { + "bbox": [ + 46, + 484, + 287, + 580 + ], + "type": "inline_equation", + "content": "f_V^e" + }, + { + "bbox": [ + 46, + 484, + 287, + 580 + ], + "type": "text", + "content": ". We stack three decoder blocks to fully fuse the scene-level depth cues into object queries." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": "Depth Positional Encodings. In the depth cross-attention layer, we propose learnable depth positional encodings for " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "f_{D}^{e}" + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": " instead of conventional sinusoidal functions. In detail, we maintain a set of learnable embeddings, " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "p_{D} \\in \\mathbb{R}^{(d_{max} - d_{min} + 1) \\times C}" + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": ", where each row encodes the depth positional information for a meter, ranging from " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "d_{min}" + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "d_{max}" + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": ". For each pixel " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "D_{fg}" + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": ", we first obtain its " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "(k + 1)" + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": "-categorical depth prediction confidence, " + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "inline_equation", + "content": "D_{fg}(x,y) \\in \\mathbb{R}^{k + 1}" + }, + { + "bbox": [ + 46, + 594, + 289, + 714 + ], + "type": "text", + "content": ", each channel of which denotes the predicted confidence for the corresponding depth bin. The estimated depth" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": "of pixel " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": " can then be obtained by the weighted summation of the depth-bin confidences and their corresponding depth values, which is formulated as" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 348, + 118, + 545, + 152 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 348, + 118, + 545, + 152 + ], + "spans": [ + { + "bbox": [ + 348, + 118, + 545, + 152 + ], + "type": "interline_equation", + "content": "d _ {m a p} (x, y) = \\sum_ {i = 1} ^ {k + 1} D _ {f g} (x, y) [ i ] \\cdot d _ {b i n} ^ {i}, \\tag {5}", + "image_path": "63301d0365b156ada3025c466cc90669ba36d947a7273eb7d65f5b0b497d62c5.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "spans": [ + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "inline_equation", + "content": "d_{bin}^{i}" + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "text", + "content": " denotes the starting value of the " + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "text", + "content": "-th depth bin and " + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "inline_equation", + "content": "\\sum_{i=1}^{k+1} D_{fg}(x,y)[i] = 1" + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "text", + "content": ". Then, we linearly interpolate " + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "inline_equation", + "content": "p_{D}" + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "text", + "content": " according to the depth " + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "inline_equation", + "content": "d_{map}(x,y)" + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "text", + "content": " to obtain the depth positional encoding for the pixel " + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "inline_equation", + "content": "(x,y)" + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "text", + "content": ". By pixel-wisely adding " + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "inline_equation", + "content": "f_{D}^{e}" + }, + { + "bbox": [ + 304, + 162, + 545, + 248 + ], + "type": "text", + "content": " with such encodings, object queries can better capture scene-level depth cues and understand 3D geometry in the depth cross-attention layer." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 258, + 450, + 269 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 258, + 450, + 269 + ], + "spans": [ + { + "bbox": [ + 305, + 258, + 450, + 269 + ], + "type": "text", + "content": "3.3. Detection Heads and Loss" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 277, + 545, + 385 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 277, + 545, + 385 + ], + "spans": [ + { + "bbox": [ + 304, + 277, + 545, + 385 + ], + "type": "text", + "content": "After the decoder, the depth-aware queries are fed into a series of MLP-based heads for 3D attribute predictions, including object category, 2D size, projected 3D center, depth, 3D size, and orientation. For inference, we convert these perspective attributes into 3D-space bounding boxes using camera parameters without NMS post-processing or pre-defined anchors. For training, we match the orderless queries with ground-truth labels and compute losses for the paired ones. We refer to Supplementary Material for details." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 398, + 545, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 398, + 545, + 578 + ], + "spans": [ + { + "bbox": [ + 304, + 398, + 545, + 578 + ], + "type": "text", + "content": "Bipartite Matching. To correctly match each query with ground-truth objects, we calculate the loss for each query-label pair and utilize Hungarian algorithm [4] to find the globally optimal matching. For each pair, we integrate the losses of six attributes into two groups. The first contains object category, 2D size and the projected 3D center, since these attributes mainly concern 2D visual appearances of the image. The second group consists of depth, 3D size and orientation, which are 3D spatial properties of the object. We respectively sum the losses of two groups and denote them as " + }, + { + "bbox": [ + 304, + 398, + 545, + 578 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{2D}" + }, + { + "bbox": [ + 304, + 398, + 545, + 578 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 398, + 545, + 578 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{3D}" + }, + { + "bbox": [ + 304, + 398, + 545, + 578 + ], + "type": "text", + "content": ". As the network generally predicts less accurate 3D attributes than 2D attributes, especially at the beginning of training, the value of " + }, + { + "bbox": [ + 304, + 398, + 545, + 578 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{3D}" + }, + { + "bbox": [ + 304, + 398, + 545, + 578 + ], + "type": "text", + "content": " is unstable and would disturb the matching process. We only utilize " + }, + { + "bbox": [ + 304, + 398, + 545, + 578 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{2D}" + }, + { + "bbox": [ + 304, + 398, + 545, + 578 + ], + "type": "text", + "content": " as the matching cost for matching each query-label pair." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 587, + 545, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 587, + 545, + 635 + ], + "spans": [ + { + "bbox": [ + 304, + 587, + 545, + 635 + ], + "type": "text", + "content": "Overall Loss. After the matching, we obtain " + }, + { + "bbox": [ + 304, + 587, + 545, + 635 + ], + "type": "inline_equation", + "content": "N_{gt}" + }, + { + "bbox": [ + 304, + 587, + 545, + 635 + ], + "type": "text", + "content": " valid pairs out of " + }, + { + "bbox": [ + 304, + 587, + 545, + 635 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 587, + 545, + 635 + ], + "type": "text", + "content": " queries, where " + }, + { + "bbox": [ + 304, + 587, + 545, + 635 + ], + "type": "inline_equation", + "content": "N_{gt}" + }, + { + "bbox": [ + 304, + 587, + 545, + 635 + ], + "type": "text", + "content": " denotes the number of ground-truth objects. Then, the overall loss of a training image is formulated as" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 331, + 647, + 545, + 680 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 331, + 647, + 545, + 680 + ], + "spans": [ + { + "bbox": [ + 331, + 647, + 545, + 680 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {o v e r a l l}} = \\frac {1}{N _ {g t}} \\cdot \\sum_ {n = 1} ^ {N _ {g t}} \\left(\\mathcal {L} _ {2 D} + \\mathcal {L} _ {3 D}\\right) + \\mathcal {L} _ {\\text {d m a p}}, \\tag {6}", + "image_path": "ef6919cbffc81a5ce3a0c12841125961f9dfc54b6fa09846a757d2b68be8b8aa.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{dmap}" + }, + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "type": "text", + "content": " represents the Focal loss [23] of the predicted categorical foreground depth map " + }, + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "type": "inline_equation", + "content": "D_{fg}" + }, + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "type": "text", + "content": " in Section 3.1." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "9159" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 60, + 68, + 532, + 246 + ], + "blocks": [ + { + "bbox": [ + 60, + 68, + 532, + 246 + ], + "lines": [ + { + "bbox": [ + 60, + 68, + 532, + 246 + ], + "spans": [ + { + "bbox": [ + 60, + 68, + 532, + 246 + ], + "type": "image", + "image_path": "d8fd9e60a21cc964658874fdbe868cef4ecc8012a12d88a1d6bdf9ceeecf6430.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 251, + 547, + 288 + ], + "lines": [ + { + "bbox": [ + 46, + 251, + 547, + 288 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 547, + 288 + ], + "type": "text", + "content": "Figure 5. Plug-and-play for multi-view 3D object detection. We utilize yellow, blue, green, and red to respectively denote the feature space related to 2D, depth, 3D, and BEV. The depth-guided transformer of MonoDETR is adopted to enhance PETR (v2) [26, 27] and BEVFormer [22] in a plug-and-play manner, which provides depth guidance from surrounding scenes." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 304, + 254, + 317 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 304, + 254, + 317 + ], + "spans": [ + { + "bbox": [ + 47, + 304, + 254, + 317 + ], + "type": "text", + "content": "3.4. Plug-and-play for Multi-view Detectors" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 323, + 288, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 323, + 288, + 431 + ], + "spans": [ + { + "bbox": [ + 46, + 323, + 288, + 431 + ], + "type": "text", + "content": "Besides monocular images, our depth-guided transformer can also serve as a plug-and-play module upon multi-view methods for depth-guided detection. Specifically, we append our depth predictors and depth encoders after the backbones of multi-view methods, which are shared across views and extract surrounding depth embeddings. Then, we inject our depth cross-attention layer into their transformer blocks to guide the 3D or BEV object queries by scene-level depth cues." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 439, + 287, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 439, + 287, + 536 + ], + "spans": [ + { + "bbox": [ + 46, + 439, + 287, + 536 + ], + "type": "text", + "content": "For PETR (v2) [26, 27] in Figure 5 (a), we modify its previous visual decoder as a depth-guided decoder. In each decoder block, the 3D object queries are first fed into our depth cross-attention layer for depth cues aggregation, and then into the original 3D self-attention and visual cross-attention for 3D position features interaction. This enables PETR's 3D queries to be depth-aware and better capture spatial characteristics of surrounding scenes." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 543, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 543, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 543, + 287, + 640 + ], + "type": "text", + "content": "For BEVFormer [22] in Figure 5 (b), as its decoder is conducted in BEV space, we incorporate the depth guidance into its BEV encoder, which lifts image features into BEV space by transformers. In each encoder block, the BEV queries also sequentially pass through our depth cross-attention layer and the original spatial cross-attention layer. This contributes to better BEV representation learning guided by the multi-view depth information." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 651, + 128, + 664 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 651, + 128, + 664 + ], + "spans": [ + { + "bbox": [ + 47, + 651, + 128, + 664 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 670, + 108, + 684 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 670, + 108, + 684 + ], + "spans": [ + { + "bbox": [ + 47, + 670, + 108, + 684 + ], + "type": "text", + "content": "4.1. Settings" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "Dataset. We evaluate MonoDETR on the widely-adopted KITTI [14] benchmark, including 7,481 training and 7,518" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 304, + 546, + 377 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 304, + 546, + 377 + ], + "spans": [ + { + "bbox": [ + 304, + 304, + 546, + 377 + ], + "type": "text", + "content": "test images. We follow [8, 9] to split 3,769 val images from the training set. We report the detection results with three-level difficulties, easy, moderate, and hard, and evaluate by the average precision " + }, + { + "bbox": [ + 304, + 304, + 546, + 377 + ], + "type": "inline_equation", + "content": "(AP)" + }, + { + "bbox": [ + 304, + 304, + 546, + 377 + ], + "type": "text", + "content": " of bounding boxes in 3D space and the bird-eye view, denoted as " + }, + { + "bbox": [ + 304, + 304, + 546, + 377 + ], + "type": "inline_equation", + "content": "AP_{3D}" + }, + { + "bbox": [ + 304, + 304, + 546, + 377 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 304, + 546, + 377 + ], + "type": "inline_equation", + "content": "AP_{BEV}" + }, + { + "bbox": [ + 304, + 304, + 546, + 377 + ], + "type": "text", + "content": ", respectively, which are both at 40 recall positions." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "text", + "content": "Implementation details. We adopt ResNet-50 [15] as our feature backbone. To save GPU memory, we apply deformable attention [59] for the visual encoder and visual cross-attention layers, and utilize the vanilla global attention [4] to better capture non-local geometries for the depth encoder and depth cross-attention layers. We utilize 8 heads for all attention modules and set the number of queries " + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "text", + "content": " as 50, which are learnable embeddings with predicted 2D reference points. We set the channel " + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "text", + "content": " and all MLP's latent dimensions as 256. For the foreground depth map, we set " + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "inline_equation", + "content": "[d_{min}, d_{max}]" + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "inline_equation", + "content": "[0m, 60m]" + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "text", + "content": " and the number of bins " + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "text", + "content": " as 80. On a single RTX 3090 GPU, we train MonoDETR for 195 epochs with batch size 16 and a learning rate " + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "inline_equation", + "content": "2 \\times 10^{-4}" + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "text", + "content": ". We adopt AdamW [30] optimizer with weight decay " + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 304, + 384, + 546, + 635 + ], + "type": "text", + "content": ", and decrease the learning rate at 125 and 165 epochs by 0.1. For training stability, we discard the training samples with depth labels larger than 65 meters or smaller than 2 meters. During inference, we simply filter out the object queries with the category confidence lower than 0.2 without NMS post-processing, and recover the 3D bounding box using the predicted six attributes following previous works [33, 31]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 644, + 387, + 657 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 644, + 387, + 657 + ], + "spans": [ + { + "bbox": [ + 306, + 644, + 387, + 657 + ], + "type": "text", + "content": "4.2. Comparison" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 665, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 546, + 714 + ], + "type": "text", + "content": "Performance. In Table 2, MonoDETR achieves state-of-the-art performance on KITTI test and val sets. On test set, MonoDETR exceeds all existing methods including those with different additional data input and surpasses" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "9160" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 67, + 70, + 525, + 352 + ], + "blocks": [ + { + "bbox": [ + 67, + 70, + 525, + 352 + ], + "lines": [ + { + "bbox": [ + 67, + 70, + 525, + 352 + ], + "spans": [ + { + "bbox": [ + 67, + 70, + 525, + 352 + ], + "type": "table", + "html": "
MethodExtra dataTest, AP3DTest, APBEVVal, AP3D
EasyMod.HardEasyMod.HardEasyMod.Hard
PatchNet [32]Depth15.6811.1210.1722.9716.8614.97---
D4LCN [12]16.6511.729.5122.5116.0212.55---
DDMP-3D [45]19.7112.789.8028.0817.8913.44---
Kinematic3D [2]Video19.0712.729.1726.6917.5213.1019.7614.1010.47
MonoRUn [7]LiDAR19.6512.3010.5827.9417.3415.2420.0214.6512.61
CaDDN [38]19.1713.4111.4627.9418.9117.1923.5716.3113.84
MonoDTR [18]21.9915.3912.7328.5920.3817.1424.5218.5715.51
AutoShape [29]CAD22.4714.1711.3630.6620.0815.5920.0914.6512.07
SMOKE [28]None14.039.767.8420.8314.4912.7514.7612.8511.50
MonoPair [10]13.049.998.6519.2814.8312.8916.2812.3010.42
RTM3D [21]13.6110.098.18---19.4716.2915.57
PGD [47]19.0511.769.3926.8916.5113.4919.2713.2310.65
IAFA [55]17.8112.0110.6125.8817.8815.3518.9514.9614.84
MonoDLE [33]17.2312.2610.2924.7918.8916.0017.4513.6611.68
MonoRCNN [42]18.3612.6510.0325.4818.1114.1016.6113.1910.65
MonoGeo [53]18.8513.8111.5225.8618.9916.1918.4514.4812.87
MonoFlex [52]19.9413.8912.0728.2319.7516.8923.6417.5114.83
GUPNet [31]20.1114.2011.77---22.7616.4613.72
MonoDETR (Ours)None25.0016.4713.5833.6022.1118.6028.8420.6116.38
Improvementv.s. second-best+2.53+1.08+0.85+2.94+1.73+1.41+4.32+2.04+0.81
", + "image_path": "4ede43b2b38110803f6839c4cccf644e837a6cd6a6d9431eb49a044b96a350da.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "spans": [ + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "text", + "content": "the second-best under three-level difficulties by " + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "inline_equation", + "content": "+2.53\\%" + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "inline_equation", + "content": "+1.08\\%" + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "inline_equation", + "content": "+0.85\\%" + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "inline_equation", + "content": "AP_{3D}" + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "text", + "content": ", and by " + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "inline_equation", + "content": "+2.94\\%" + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "inline_equation", + "content": "+1.73\\%" + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "inline_equation", + "content": "+1.41\\%" + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "inline_equation", + "content": "AP_{BEV}" + }, + { + "bbox": [ + 46, + 398, + 287, + 494 + ], + "type": "text", + "content": ". The competitive MonoDTR [18] also applies transformers to fuse depth features, but it is still a center-guided method and highly relies on additional dense depth supervision, anchors and NMS. In contrast, MonoDETR performs better without extra input or handcrafted designs, illustrating its simplicity and effectiveness." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 503, + 287, + 577 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 503, + 287, + 577 + ], + "spans": [ + { + "bbox": [ + 46, + 503, + 287, + 577 + ], + "type": "text", + "content": "Efficiency. Compared to existing methods in Table 3, MonoDETR can achieve the best detection performance without consuming too much computational budget. As illustrated in Section 3, we only process the feature maps with " + }, + { + "bbox": [ + 46, + 503, + 287, + 577 + ], + "type": "inline_equation", + "content": "\\frac{1}{16}" + }, + { + "bbox": [ + 46, + 503, + 287, + 577 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 503, + 287, + 577 + ], + "type": "inline_equation", + "content": "\\frac{1}{32}" + }, + { + "bbox": [ + 46, + 503, + 287, + 577 + ], + "type": "text", + "content": " downsample ratios, which reduces our Runtime and GFlops, while others adopt " + }, + { + "bbox": [ + 46, + 503, + 287, + 577 + ], + "type": "inline_equation", + "content": "\\frac{1}{4}" + }, + { + "bbox": [ + 46, + 503, + 287, + 577 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 503, + 287, + 577 + ], + "type": "inline_equation", + "content": "\\frac{1}{8}" + }, + { + "bbox": [ + 46, + 503, + 287, + 577 + ], + "type": "text", + "content": " ratios." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 586, + 148, + 597 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 148, + 597 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 148, + 597 + ], + "type": "text", + "content": "4.3. Ablation Studies" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 605, + 287, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 628 + ], + "type": "text", + "content": "We verify the effectiveness of each our component and report " + }, + { + "bbox": [ + 46, + 605, + 287, + 628 + ], + "type": "inline_equation", + "content": "AP_{3D}" + }, + { + "bbox": [ + 46, + 605, + 287, + 628 + ], + "type": "text", + "content": " for the car category on the KITTI val set." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 713 + ], + "type": "text", + "content": "Depth-guided Transformer. In Table 5, we first remove the entire depth-guided transformer along with the depth predictor, which constructs a pure center-guided baseline. This variant, denoted as 'w/o Depth-guided Trans.' can be regarded as a re-implementation of MonoDLE [33] with our detection heads and loss functions. As shown, the absence" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 307, + 396, + 545, + 448 + ], + "blocks": [ + { + "bbox": [ + 46, + 356, + 545, + 378 + ], + "lines": [ + { + "bbox": [ + 46, + 356, + 545, + 378 + ], + "spans": [ + { + "bbox": [ + 46, + 356, + 545, + 378 + ], + "type": "text", + "content": "Table 2. Monocular performance of the car category on KITTI test and val sets. We utilize bold numbers to highlight the best results, and color the second-best ones and our gain over them in blue." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 396, + 545, + 448 + ], + "lines": [ + { + "bbox": [ + 307, + 396, + 545, + 448 + ], + "spans": [ + { + "bbox": [ + 307, + 396, + 545, + 448 + ], + "type": "table", + "html": "
MethodMonoDLEGUPNetMonoDTRMonoDETR
Runtime↓40343738
GFlops↓79.1262.32120.4862.12
AP3D Mod.12.2615.0215.3916.47
", + "image_path": "f11783ca7891b84c6a2b6def5a5e6393cd1626d15c15e45e046d84e0557705e4.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 452, + 545, + 474 + ], + "lines": [ + { + "bbox": [ + 306, + 452, + 545, + 474 + ], + "spans": [ + { + "bbox": [ + 306, + 452, + 545, + 474 + ], + "type": "text", + "content": "Table 3. Efficiency comparison. We test the Runtime (ms) on one RTX 3090 GPU with batch size 1, and compare " + }, + { + "bbox": [ + 306, + 452, + 545, + 474 + ], + "type": "inline_equation", + "content": "AP_{3D}" + }, + { + "bbox": [ + 306, + 452, + 545, + 474 + ], + "type": "text", + "content": " on test set." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 495, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 545, + 665 + ], + "type": "text", + "content": "of the depth-guided transformer greatly hurts the performance, for the lack of non-local geometric cues. Then, we investigate two key designs within the depth-guided transformer: the transformer architecture and depth guidance. For 'w/o Transformer', we only append the depth predictor upon the center-guided baseline to provide implicit depth guidance without transformers. For 'w/o Depth Guidance', we equip the center-guided baseline with a visual encoder and decoder, but include no depth predictor, depth encoder, and the depth cross-attention layer in the decoder. This builds a transformer network guided by visual appearances, without any depth guidance for object queries. The performance degradation of both variants indicates their significance for our depth-guided feature aggregation paradigm." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "type": "text", + "content": "Depth Encoder. The depth encoder produces non-local depth embeddings " + }, + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "type": "inline_equation", + "content": "f_{D}^{e}" + }, + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "type": "text", + "content": ", which are essential for queries to" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 314, + 757 + ], + "type": "text", + "content": "9161" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 94, + 70, + 497, + 213 + ], + "blocks": [ + { + "bbox": [ + 94, + 70, + 497, + 213 + ], + "lines": [ + { + "bbox": [ + 94, + 70, + 497, + 213 + ], + "spans": [ + { + "bbox": [ + 94, + 70, + 497, + 213 + ], + "type": "table", + "html": "
MethodImage SizeNDS↑mAP↑mATE↓mASE↓mAOE↓mAVE↓mAAE↓
CenterNet [56]-0.3280.3060.7160.2640.6091.4260.658
FCOS3D* [46]1600×9000.4150.3430.7250.2630.4221.2920.153
PGD* [47]1600×9000.4280.3690.6830.2600.4391.2680.185
DETR3D† [49]1600×9000.4340.3490.7160.2680.3790.8420.200
BEVDet† [17]1408×5120.4170.3490.6370.2690.4900.9140.268
PETR† [26]1600×9000.4420.3700.7110.2670.3830.8650.201
PETRv2 [27] + Depth-gudied800×3200.4960.4010.7450.2680.4480.3940.184
0.5080.4100.7270.2650.3890.4190.187
BEVFormer [22] + Depth-gudied1600×9000.5170.4160.6730.2740.3720.3940.198
0.5260.4230.6610.2720.3490.3710.192
", + "image_path": "c3dba3d0ab52e2b003c24c0baaa6b837663292ff0eeb9ab47997f7d2d094e3a7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 66, + 257, + 266, + 328 + ], + "blocks": [ + { + "bbox": [ + 46, + 217, + 546, + 241 + ], + "lines": [ + { + "bbox": [ + 46, + 217, + 546, + 241 + ], + "spans": [ + { + "bbox": [ + 46, + 217, + 546, + 241 + ], + "type": "text", + "content": "Table 4. Multi-view performance on nuScenes val set. * denotes the two-step fine-tuning with test-time augmentation, and † denotes CBGS [58] training. We compare with the best-performing variants of other methods and utilize bold numbers to highlight the best results." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 66, + 257, + 266, + 328 + ], + "lines": [ + { + "bbox": [ + 66, + 257, + 266, + 328 + ], + "spans": [ + { + "bbox": [ + 66, + 257, + 266, + 328 + ], + "type": "table", + "html": "
ArchitectureEasyMod.Hard
MonoDETR28.8420.6116.38
w/o Depth-guided Trans.19.6915.1513.93
w/o Transformer20.1916.0514.18
w/o Depth Guidance24.1417.8115.60
", + "image_path": "5c22d1a016f8c5382755b7b84dd212d5d2cf9ed7ba10da9c93d79e31d7907bd6.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 385, + 287, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 385, + 287, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 385, + 287, + 460 + ], + "type": "text", + "content": "explore scene-level depth cues in the depth cross-attention layer. We experiment with different encoder designs in Table 6. 'Deform. SA' and " + }, + { + "bbox": [ + 46, + 385, + 287, + 460 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 46, + 385, + 287, + 460 + ], + "type": "text", + "content": " Conv." + }, + { + "bbox": [ + 46, + 385, + 287, + 460 + ], + "type": "inline_equation", + "content": "\\times 2'" + }, + { + "bbox": [ + 46, + 385, + 287, + 460 + ], + "type": "text", + "content": " represent one-block of deformable attention and two " + }, + { + "bbox": [ + 46, + 385, + 287, + 460 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 46, + 385, + 287, + 460 + ], + "type": "text", + "content": " convolutional layers, respectively. As reported, 'Global SA' with only one block generates the best " + }, + { + "bbox": [ + 46, + 385, + 287, + 460 + ], + "type": "inline_equation", + "content": "f_{D}^{e}" + }, + { + "bbox": [ + 46, + 385, + 287, + 460 + ], + "type": "text", + "content": " for global geoentry encoding." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "spans": [ + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "text", + "content": "Depth-guided Decoder. As the core depth-guided component, we explore how to better guide object queries to interact with depth embeddings " + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "inline_equation", + "content": "f_{D}^{e}" + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "text", + "content": " in Table 7. With the sequential inter-query self-attention (" + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "inline_equation", + "content": "I'" + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "text", + "content": ") and visual cross-attention (" + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "inline_equation", + "content": "V'" + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "text", + "content": ") layers, we insert the depth cross-attention layer (" + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "inline_equation", + "content": "D'" + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "text", + "content": ") into each decoder block with four positions. For " + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "inline_equation", + "content": "I \\rightarrow D + V'" + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "text", + "content": ", we fuse the depth and visual embeddings " + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "inline_equation", + "content": "f_{D}^{e}, f_{V}^{e}" + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "text", + "content": " by element-wise addition, and apply only one unified cross-attention layer. As shown, the " + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "inline_equation", + "content": "D \\rightarrow I \\rightarrow V'" + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "text", + "content": " order performs the best. By placing " + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "inline_equation", + "content": "D'" + }, + { + "bbox": [ + 46, + 465, + 287, + 610 + ], + "type": "text", + "content": " in the front, object queries can first aggregate depth cues to guide the remaining operations in each decoder block." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "content": "Foreground Depth Map. We explore different representations for our depth map in Table 8. Compared to dense depth supervision ('Dense'), adopting object-wise depth labels ('Fore.') can focus the network on more important foreground geometric cues, and better capture depth relations between objects. 'LID' outperforms other discretization methods, since the linear-increasing intervals can suppress the larger estimation errors of farther objects." + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 345, + 257, + 506, + 328 + ], + "blocks": [ + { + "bbox": [ + 46, + 331, + 287, + 366 + ], + "lines": [ + { + "bbox": [ + 46, + 331, + 287, + 366 + ], + "spans": [ + { + "bbox": [ + 46, + 331, + 287, + 366 + ], + "type": "text", + "content": "Table 5. Effectiveness of depth-guided transformer. 'Depth-guided Trans.' and 'Depth Guidance' denote the depth-guided transformer and the depth cross-attention layer, respectively" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 345, + 257, + 506, + 328 + ], + "lines": [ + { + "bbox": [ + 345, + 257, + 506, + 328 + ], + "spans": [ + { + "bbox": [ + 345, + 257, + 506, + 328 + ], + "type": "table", + "html": "
MechanismEasyMod.Hard
Global SA28.8420.6116.38
Deform. SA26.4318.9115.55
3×3 Conv.×2 w/o25.5518.3615.28
24.2518.3815.41
", + "image_path": "466fd3f821bf54ccf9678926e5cb666680541eb58f7ec3443f1faa8b9f40f051.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 331, + 546, + 366 + ], + "lines": [ + { + "bbox": [ + 305, + 331, + 546, + 366 + ], + "spans": [ + { + "bbox": [ + 305, + 331, + 546, + 366 + ], + "type": "text", + "content": "Table 6. The design of depth encoder. 'Deform. SA' denotes a one-block deformable self-attention layer. 'w/o' denotes directly feeding depth features into the decoder without the depth encoder." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "spans": [ + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "text", + "content": "Depth Positional Encodings " + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "inline_equation", + "content": "p_D" + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "text", + "content": ". In Table 9, we experiment with different depth positional encodings for " + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "inline_equation", + "content": "f_D^e" + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "text", + "content": " in the depth cross-attention layer. By default, we apply the meterwise encodings " + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "inline_equation", + "content": "p_D \\in \\mathbb{R}^{(d_{max} - d_{min} + 1) \\times C}" + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "text", + "content": " that assign one learnable embedding per meter with depth value interpolation for output. We then assign one learnable embedding for each depth bin, denoted as 'k-bin " + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "inline_equation", + "content": "p_D \\in \\mathbb{R}^{k \\times C}" + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "text", + "content": ", and also experiment sinusoidal functions to encode either the depth values or 2D coordinates of the feature map, denoted as 'Depth sin/cos' and '2D sin/cos', respectively. As shown, 'meter-wise " + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "inline_equation", + "content": "p_D" + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "text", + "content": "' performs the best for encoding more fine-grained depth cues ranging from " + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "inline_equation", + "content": "d_{min}" + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "inline_equation", + "content": "d_{max}" + }, + { + "bbox": [ + 304, + 386, + 545, + 542 + ], + "type": "text", + "content": ", which provides the queries with more scene-level spatial structures." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 551, + 443, + 563 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 551, + 443, + 563 + ], + "spans": [ + { + "bbox": [ + 306, + 551, + 443, + 563 + ], + "type": "text", + "content": "4.4. Multi-view Experiments" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": "As a plug-and-play module for multi-view 3D object detection, we append our depth-guided transformer upon two DETR-based multi-view networks, PETR v2 [27] and BEVFormer [22]. The detailed network architectures are shown in Figure 5. For a fair comparison, we adopt the same training configurations as the two baseline models, and utilize the same " + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "inline_equation", + "content": "[d_{min}, d_{max}]" + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": " as monocular experiments. We report the performance on nuScenes [3] val set in Table 4, where we apply no test-time augmentation or CGBS [58] training. For end-to-end detection in PETRv2, the depth guidance contributes to " + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "inline_equation", + "content": "+1.2\\%" + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": " NDS and " + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "inline_equation", + "content": "+0.9\\%" + }, + { + "bbox": [ + 304, + 570, + 546, + 713 + ], + "type": "text", + "content": " mAP by providing sufficient multi-view geometric cues." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "9162" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 71, + 172, + 188 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 172, + 188 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 172, + 188 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 172, + 188 + ], + "type": "image", + "image_path": "0cc48f129910ed97c69db42eb1361e13c1d88acac4747ce23f137ec15dc4311b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 190, + 545, + 213 + ], + "lines": [ + { + "bbox": [ + 46, + 190, + 545, + 213 + ], + "spans": [ + { + "bbox": [ + 46, + 190, + 545, + 213 + ], + "type": "text", + "content": "Figure 6. Visualizations of attention maps " + }, + { + "bbox": [ + 46, + 190, + 545, + 213 + ], + "type": "inline_equation", + "content": "A_{D}" + }, + { + "bbox": [ + 46, + 190, + 545, + 213 + ], + "type": "text", + "content": " in the depth cross-attention layer. The top column denotes the input image, and the last three columns denote the attention maps of the target queries (denoted as white dots). Hotter colors indicate higher attention weights." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 173, + 72, + 296, + 188 + ], + "blocks": [ + { + "bbox": [ + 173, + 72, + 296, + 188 + ], + "lines": [ + { + "bbox": [ + 173, + 72, + 296, + 188 + ], + "spans": [ + { + "bbox": [ + 173, + 72, + 296, + 188 + ], + "type": "image", + "image_path": "5ab5c61c38bb24ea37716344d6a75087d94f215de3b6ed38fc1d89e0f71a8989.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 296, + 72, + 419, + 188 + ], + "blocks": [ + { + "bbox": [ + 296, + 72, + 419, + 188 + ], + "lines": [ + { + "bbox": [ + 296, + 72, + 419, + 188 + ], + "spans": [ + { + "bbox": [ + 296, + 72, + 419, + 188 + ], + "type": "image", + "image_path": "67e90c1fccbbdbf4a5740d40650cf2108806ab22428744b5ec9e5bbf17651fcd.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 420, + 72, + 543, + 188 + ], + "blocks": [ + { + "bbox": [ + 420, + 72, + 543, + 188 + ], + "lines": [ + { + "bbox": [ + 420, + 72, + 543, + 188 + ], + "spans": [ + { + "bbox": [ + 420, + 72, + 543, + 188 + ], + "type": "image", + "image_path": "6f26fadc0ed7a03d14f7d1545144b28f3e7c0e4fdd9bb02fcfabb58837989ca1.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 75, + 230, + 258, + 300 + ], + "blocks": [ + { + "bbox": [ + 75, + 230, + 258, + 300 + ], + "lines": [ + { + "bbox": [ + 75, + 230, + 258, + 300 + ], + "spans": [ + { + "bbox": [ + 75, + 230, + 258, + 300 + ], + "type": "table", + "html": "
ArchitectureEasyMod.Hard
D → I → V28.8420.6116.38
I → D → V26.2419.2816.03
I → V → D25.8418.8515.72
I → D + V24.9418.4115.39
", + "image_path": "16fc32a2b1d6384aec03c8342fbd15bac15520a248cbf37534ac852c551fc652.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 359, + 287, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 359, + 287, + 431 + ], + "spans": [ + { + "bbox": [ + 46, + 359, + 287, + 431 + ], + "type": "text", + "content": "For the BEV feature generation, our modules benefit BEV-Former by " + }, + { + "bbox": [ + 46, + 359, + 287, + 431 + ], + "type": "inline_equation", + "content": "+0.9\\%" + }, + { + "bbox": [ + 46, + 359, + 287, + 431 + ], + "type": "text", + "content": " NDS and " + }, + { + "bbox": [ + 46, + 359, + 287, + 431 + ], + "type": "inline_equation", + "content": "+0.7\\%" + }, + { + "bbox": [ + 46, + 359, + 287, + 431 + ], + "type": "text", + "content": " mAP, indicating the importance of auxiliary depth information for BEV-space feature encoding. The additional experiments on multi-view 3D object detection well demonstrate the effectiveness and generalizability of our approach." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 444, + 129, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 444, + 129, + 456 + ], + "spans": [ + { + "bbox": [ + 47, + 444, + 129, + 456 + ], + "type": "text", + "content": "5. Visualization" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 464, + 287, + 561 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 464, + 287, + 561 + ], + "spans": [ + { + "bbox": [ + 46, + 464, + 287, + 561 + ], + "type": "text", + "content": "We visualize the attention maps " + }, + { + "bbox": [ + 46, + 464, + 287, + 561 + ], + "type": "inline_equation", + "content": "A_{D}" + }, + { + "bbox": [ + 46, + 464, + 287, + 561 + ], + "type": "text", + "content": " in Equation 3 of the depth cross-attention layer at the last decoder block. As shown in Figure 6, the areas with high attention scores for the target object query spread over the entire image, concentrating on other objects with long distances. This indicates, via our depth guidance, object queries are able to adaptively capture non-local depth cues from the image and are no longer limited by neighboring visual features." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 574, + 119, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 574, + 119, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 574, + 119, + 586 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "content": "We propose MonoDETR, an end-to-end transformer-based framework for monocular 3D object detection, which is free from any additional input, anchors, or NMS. Different from existing center-guided methods, we enable object queries to explore geometric cues adaptively from the depth-guided regions, and conduct inter-object and object-scene depth interactions via attention mechanisms. Extensive experiments have demonstrated the effectiveness of our approach for both single-view (KITTI) and multi-view (nuScenes) input. We hope MonoDETR can serve as a" + } + ] + } + ], + "index": 11 + }, + { + "type": "table", + "bbox": [ + 335, + 230, + 515, + 302 + ], + "blocks": [ + { + "bbox": [ + 46, + 306, + 287, + 340 + ], + "lines": [ + { + "bbox": [ + 46, + 306, + 287, + 340 + ], + "spans": [ + { + "bbox": [ + 46, + 306, + 287, + 340 + ], + "type": "text", + "content": "Table 7. The design of depth-guided decoder. 'D', 'I', and 'V' denote the depth cross-attention, inter-query self-attention, and visual cross-attention layers, respectively." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 335, + 230, + 515, + 302 + ], + "lines": [ + { + "bbox": [ + 335, + 230, + 515, + 302 + ], + "spans": [ + { + "bbox": [ + 335, + 230, + 515, + 302 + ], + "type": "table", + "html": "
Depth MapEasyMod.Hard
Fore. LID28.8420.6116.38
Dense LID27.6919.8515.98
Fore. UD25.6118.9015.49
Fore. SID26.0518.9515.59
", + "image_path": "139da808a42bca946cb902e5f8f11b33ee6307910d5b328438a1e6d4a42deefa.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "type": "table", + "bbox": [ + 342, + 359, + 507, + 441 + ], + "blocks": [ + { + "bbox": [ + 306, + 306, + 545, + 340 + ], + "lines": [ + { + "bbox": [ + 306, + 306, + 545, + 340 + ], + "spans": [ + { + "bbox": [ + 306, + 306, + 545, + 340 + ], + "type": "text", + "content": "Table 8. Different representations of the predicted depth map. 'UD', 'SID', and 'LID' denote uniform, spacing-increasing, and linear-increasing discretizations." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 342, + 359, + 507, + 441 + ], + "lines": [ + { + "bbox": [ + 342, + 359, + 507, + 441 + ], + "spans": [ + { + "bbox": [ + 342, + 359, + 507, + 441 + ], + "type": "table", + "html": "
SettingsEasyMod.Hard
Meter-wise pD28.8420.6116.38
k-bin pD28.0619.6816.04
Depth sin/cos27.4219.5715.82
2D sin/cos26.4818.6315.52
w/o26.7618.9415.85
", + "image_path": "13d3e40fe3cfff8ff2696f252b69cdab2b07692a806707636b837e1a4d7e059d.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 445, + 545, + 479 + ], + "lines": [ + { + "bbox": [ + 305, + 445, + 545, + 479 + ], + "spans": [ + { + "bbox": [ + 305, + 445, + 545, + 479 + ], + "type": "text", + "content": "Table 9. The design of depth positional encodings. 'Meter-wise' and " + }, + { + "bbox": [ + 305, + 445, + 545, + 479 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 445, + 545, + 479 + ], + "type": "text", + "content": " -bin' assign learnable embeddings by meters and depth bins, respectively. 'sin/cos' denotes sinusoidal functions for encodings." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 499, + 545, + 583 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 499, + 545, + 583 + ], + "spans": [ + { + "bbox": [ + 304, + 499, + 545, + 583 + ], + "type": "text", + "content": "strong DETR baseline for future research in monocular 3D object detection. Limitations. How to effectively incorporate multi-modal input into our transformer framework is not discussed in the paper. Our future direction will focus on this to further improve the performance of depth-guided transformers, e.g., distilling more sufficient geometric knowledge from LiDAR and RADAR modalities." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 597, + 404, + 610 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 597, + 404, + 610 + ], + "spans": [ + { + "bbox": [ + 306, + 597, + 404, + 610 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 617, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 712 + ], + "type": "text", + "content": "This project is funded in part by the National Natural Science Foundation of China (No.62206272), by the National Key R&D Program of China Project (No.2022ZD0161100), by the Centre for Perceptual and Interactive Intelligence (CPII) Ltd under the Innovation and Technology Commission (ITC)'s InnoHK, and by the General Research Fund of Hong Kong RGC Project 14204021. 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Deformable detr: Deformable transformers for end-to-end object detection. arXiv preprint arXiv:2010.04159, 2020. 3, 6" + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 316, + 757 + ], + "type": "text", + "content": "9166" + } + ] + } + ], + "index": 6 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 11 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/MonoNeRD_ NeRF-like Representations for Monocular 3D Object Detection/63ab896a-8106-40c7-82f9-2e2b03ab3262_content_list.json b/2023/MonoNeRD_ NeRF-like Representations for Monocular 3D Object Detection/63ab896a-8106-40c7-82f9-2e2b03ab3262_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..0d635486dc21d68e3b976d1ad62ede11c6848b3f --- /dev/null +++ b/2023/MonoNeRD_ NeRF-like Representations for Monocular 3D Object Detection/63ab896a-8106-40c7-82f9-2e2b03ab3262_content_list.json @@ -0,0 +1,1869 @@ +[ + { + "type": "text", + "text": "MonoNeRD: NeRF-like Representations for Monocular 3D Object Detection", + "text_level": 1, + "bbox": [ + 99, + 130, + 870, + 151 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Junkai Xu $^{1,2*}$ Liang Peng $^{1,2,*}$ Haoran Chen $^{1,2,*}$ Hao Li $^{2}$ Wei Qian $^{2}$ Ke Li $^{4}$ Wenxiao Wang $^{3\\dagger}$ Deng Cai $^{1,2}$ $^{1}$ State Key Lab of CAD & CG, Zhejiang University $^{2}$ FABU Inc. $^{3}$ School of Software Technology, Zhejiang University $^{4}$ Fullong Inc. {xujunkai, pengliang, haorancheng}@zju.edu.cn", + "bbox": [ + 212, + 178, + 759, + 272 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 305, + 313, + 321 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In the field of monocular 3D detection, it is common practice to utilize scene geometric clues to enhance the detector's performance. However, many existing works adopt these clues explicitly such as estimating a depth map and back-projecting it into 3D space. This explicit methodology induces sparsity in 3D representations due to the increased dimensionality from 2D to 3D, and leads to substantial information loss, especially for distant and occluded objects. To alleviate this issue, we propose MonoNeRD, a novel detection framework that can infer dense 3D geometry and occupancy. Specifically, we model scenes with Signed Distance Functions (SDF), facilitating the production of dense 3D representations. We treat these representations as Neural Radiance Fields (NeRF) and then employ volume rendering to recover RGB images and depth maps. To the best of our knowledge, this work is the first to introduce volume rendering for M3D, and demonstrates the potential of implicit reconstruction for image-based 3D perception. Extensive experiments conducted on the KITTI-3D benchmark and Waymo Open Dataset demonstrate the effectiveness of MonoNeRD. Codes are available at https://github.com/cskkxjk/MonoNeRD.", + "bbox": [ + 75, + 338, + 473, + 670 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 700, + 209, + 715 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Monocular 3D detection (M3D) is an active research topic in the computer vision community due to its convenience, low cost and wide range of applications, including autonomous driving, robotic navigation and more. The key point of the task is to establish reasonable correspondences between 2D images and 3D space. Some works leverage geometrical priors to extract 3D information, such as object poses via 2D-3D constraints. These constraints usually require additional keypoint annotations [10, 21] or", + "bbox": [ + 75, + 726, + 468, + 863 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d54e9d1bda41287b5bc7206772dd6c3738e45cf114ae68ab79f6e2864daff70d.jpg", + "image_caption": [ + "Figure 1. Different intermediate 3D representations. Previous depth-based methods generate 3D representations by backprojecting estimated depth maps to 3D space, whereas our method predicts implicit 3D representations, and obtains depth estimates through volume rendering." + ], + "image_footnote": [], + "bbox": [ + 549, + 306, + 849, + 534 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "CAD models [5, 34]. Other works convert estimated depth maps into 3D point cloud representations (Pseudo-LiDAR) [32, 55, 60]. Depth estimates are also used to combine with image features [58, 33] or generate meaningful bird's-eye-view (BEV) representations [45, 47, 48, 51], then produce 3D object detection results. These methods have made remarkable progress in M3D.", + "bbox": [ + 496, + 654, + 893, + 760 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Unfortunately, current 3D representations transformed by explicit depths have some limitations. First, the lifted features obtained from depth estimates or pseudo-LiDAR exhibit an uneven distribution throughout the 3D space. Specifically, they have high density in close range, but the density decreases as the distance increases. (See top part of Figure 1). Second, the final detection performance heavily depends on the accuracy of the depth estimation, which remains challenging to improve. Thus such representations", + "bbox": [ + 496, + 763, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Work performed during an internship at FABU Inc.", + "bbox": [ + 94, + 875, + 372, + 887 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Corresponding author", + "bbox": [ + 96, + 887, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "6814", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "cannot produce dense reasonable 3D features for M3D.", + "bbox": [ + 76, + 90, + 442, + 104 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Recent researches in Neural Radiance Fields (NeRF) [3, 38, 64] have shown the capability to reconstruct detailed and dense 3D scene geometry and occupancy information from posed images (images with known camera poses). Inspired by NeRF and its follow-ups [20, 25, 59], we reformulate the intermediate 3D representations in M3D to NeRF-like 3D representations, which can produce dense reasonable 3D geometry and occupancy. To achieve this goal, we combine extracted 2D backbone features and corresponding normalized frustum 3D coordinates to construct 3D Position-aware Frustum features (Section 4.1.1). These 3D features are used to create signed distance fields and radiance fields (RGB color). The signed distance fields encode the distance to the closest surface at every location as a scalar value. This allows us to model scenes implicitly by the zero-level set of the signed distance fields. (Section 3.1). We then adopt volume rendering [35] technique to generate RGB images and depth maps from the signed distance fields and radiance fields (Section 4.1.2), supervising them by original RGB images and LiDAR points (Section 4.2). While the previous depth-based methods generate 3D representations based on predicted depth maps, our method generates depth maps based on 3D representations (Figure 1). It is worth noting that our approach is capable of generating dense 3D occupancy (i.e., volume density) without requiring explicit binary occupancy annotations for individual voxels. Experiments on KITTI [17] 3D benchmark and Waymo Open Dataset [52] show the superiority of our NeRF-like representations in monocular 3D detection.", + "bbox": [ + 75, + 106, + 472, + 542 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our main contributions are threefold:", + "bbox": [ + 96, + 544, + 344, + 556 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We present a novel detection framework, named MonoNeRD, that connects Neural Radiance Fields and monocular 3D detection. It leverages NeRF-like continuous 3D representations to enable accurate 3D perception and understanding from a single image.", + "- We propose to use volume rendering to directly optimize 3D representations in detection tasks. To the best of our knowledge, our work is the first to introduce volume rendering for 3D detection tasks.", + "- Extensive experiments on KITTI [17] 3D detection benchmark and Waymo Open Dataset [52] demonstrate the effectiveness of our method, which is competitive with previous state-of-the-art works. This research presents the potential of 3D implicit reconstruction for image-based 3D perception." + ], + "bbox": [ + 94, + 566, + 468, + 810 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 821, + 218, + 835 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Monocular 3D Object Detection", + "text_level": 1, + "bbox": [ + 76, + 847, + 357, + 862 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Many impressive researches [47, 9, 43] been done in monocular 3D object detection. As the essential informa", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tion of depth dimension is collapsed in the 2D image, it is an ill-posed but necessary problem of finding an approach to lift the 2D information to 3D space.", + "bbox": [ + 496, + 90, + 890, + 136 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Some Monocular 3D Object Detection methods lift 2D to 3D directly by incorporating the geometric relationship between the 2D image plane and 3D space. For example, many methods assume rigidity of objects, aligning 2D keypoints with their 3D counterparts [1, 2, 21, 46]. Some researchers try to build the bridge between 2D and 3D structures by template matching [5, 34]. These methods usually require additional data (e.g., 3D CAD models, object keypoint annotations).", + "bbox": [ + 496, + 137, + 890, + 272 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Other methods generate intermediate 3D representations to solve the lifting problem. Many approaches [60, 33, 32] convert the estimated depth map (always predicted by an off-the-shelf model) to pseudo-LiDAR point cloud representations, and then feed them to sophisticated LiDAR-based detectors. CaDDN [47] learns categorical depth distributions over pixels to lift camera images into 3D space, constructing BEV representations. Pseudo-Stereo [12] uses some sophisticated modules (e.g., stereo cost volume) to achieve better depth estimation. These methods typically involve estimating depth maps beforehand and subsequently extracting corresponding 3D representations from them. Instead, our method recovers depth maps from the 3D representations and supervises them to improve the detection performance.", + "bbox": [ + 496, + 273, + 892, + 501 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Neural Implicit Representations", + "text_level": 1, + "bbox": [ + 500, + 513, + 782, + 529 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Representing 3D geometry with implicit functions has gained popularity in the past few years. Learning-based 3D reconstruction methods [13, 18, 36, 37, 41, 49] and their scene-level counterparts [6, 15, 23, 44] demonstrate compelling results but require 3D input and supervision. Neural Radiance Fields (NeRFs) [38] introduce a new perspective to learn continuous geometry representations from posed multi-view images only by volume rendering [35]. Due to the low efficiency of original MLP-based NeRF, their grid-based variants [22, 28, 61, 7] have been explored to accelerate the rendering process or save GPU memory. To circumvent the requirement of dense inputs, some works [62, 8, 14, 39] explicitly consider sparse input scenarios and show astonishing results for novel view synthesis, but these representations still need to be optimized per scene. Li et al. [25] propose MINE in which they combine Multiplane Images (MPI) and NeRF for single-image-based novel view synthesis. SceneRF [4] uses posed image sequences for training, alleviating the reliance on datasets. Wimbauer et al. [57] construct a density field to preform both depth prediction and novel view synthesis. Unlike our approach, the works mentioned primarily focus on the Novel View Synthesis task, requiring multi-view or sequenced images with camera poses as supervision, which cannot generalize to un", + "bbox": [ + 496, + 537, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "6815", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "seen scenes (except [25, 57]). Instead, we take advantage of volume rendering to optimize 3D feature representations and improve the performance in M3D task.", + "bbox": [ + 75, + 90, + 468, + 137 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Preliminaries", + "text_level": 1, + "bbox": [ + 76, + 148, + 217, + 165 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Here we introduce some essential preliminaries for our idea. We use the same notation as [59] for the concepts of SDF and Volume density. Concerning the space limitation, here we provide a brief overview. Please refer to [38, 59, 35] for more details.", + "bbox": [ + 75, + 174, + 470, + 248 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Signed Distance Function (SDF)", + "text_level": 1, + "bbox": [ + 76, + 257, + 359, + 273 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For a given spatial point, Signed Distance Function (SDF) is a continuous function that outputs the point's distance to the closest surface, whose sign indicates whether the point is inside (negative) or outside (positive) of the surface.", + "bbox": [ + 75, + 281, + 468, + 354 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Let $\\mathbb{R}^3$ represent a 3D space containing some objects, $\\Omega \\subset \\mathbb{R}^3$ refers to the occupied part, and $\\mathcal{M} = \\partial \\Omega$ be the boundary surface. Denote the $\\Omega$ indicator function by $\\mathbf{1}_{\\Omega}$ and the Signed Distance Function (SDF) by $d_{\\Omega}$ ,", + "bbox": [ + 75, + 356, + 468, + 417 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {1} _ {\\Omega} (\\boldsymbol {x}) = \\left\\{ \\begin{array}{l l} 1 & \\text {i f} \\boldsymbol {x} \\in \\Omega \\\\ 0 & \\text {i f} \\boldsymbol {x} \\notin \\Omega \\end{array} \\right. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 189, + 425, + 468, + 467 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nd _ {\\Omega} (\\boldsymbol {x}) = (- 1) ^ {\\mathbf {1} _ {\\Omega} (\\boldsymbol {x})} \\min _ {\\boldsymbol {y} \\in \\mathcal {M}} \\| \\boldsymbol {x} - \\boldsymbol {y} \\| \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 156, + 477, + 468, + 502 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\| \\cdot \\|$ is the standard Euclidean 2-norm. The underlying surface $\\mathcal{M}$ can be implicitly represented by the zero-level set of $d_{\\Omega}(\\cdot) = 0$ .", + "bbox": [ + 75, + 506, + 468, + 551 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Transform SDF to Density", + "text_level": 1, + "bbox": [ + 76, + 560, + 316, + 575 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The volume density $\\sigma : \\mathbb{R}^3 \\to \\mathbb{R}_+$ is a scalar volumetric function, where $\\sigma(x)$ can be interpreted as the probability that light is occluded at point $x$ . Previous works et al. [59, 63] suggest modeling the density $\\sigma$ using a certain transformation of a learnable Signed Distance Function (SDF), as follows:", + "bbox": [ + 75, + 583, + 468, + 672 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\sigma (\\boldsymbol {x}) = \\alpha \\Psi_ {\\beta} (- d _ {\\Omega} (\\boldsymbol {x})) \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 192, + 683, + 468, + 700 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\alpha, \\beta > 0$ are learnable parameters and $\\Psi_{\\beta}$ is the cumulative distribution function of the Laplace distribution with zero mean and $\\beta$ scale,", + "bbox": [ + 75, + 709, + 468, + 753 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\Psi_ {\\beta} (s) = \\left\\{ \\begin{array}{l l} \\frac {1}{2} \\exp (\\frac {s}{\\beta}) & \\text {i f} s \\leq 0 \\\\ 1 - \\frac {1}{2} \\exp (- \\frac {s}{\\beta}) & \\text {i f} s > 0 \\end{array} \\right. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 143, + 762, + 468, + 801 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As $\\beta$ approaches zero, the density $\\sigma$ converges to scaled indicator function of $\\Omega$ , means $\\sigma \\rightarrow \\alpha \\mathbf{1}_{\\Omega}$ for all points $\\pmb{x} \\in \\Omega \\setminus \\mathcal{M}$ . The benefits of modeling density in this way have been discussed in [59]. We simply set $\\alpha = \\beta^{-1}$ in our implementations. Figure 2 depicts an example of how density varies along SDF when a ray passes through an object.", + "bbox": [ + 75, + 809, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/001a5110f01da076e14074d84991ba4ea353b229d26c28679b9dcfd6afa68a82.jpg", + "image_caption": [ + "Figure 2. Example of transformation from SDF to Density. The black arrow line represents a ray passing through a spherical object; the gradient color line describes how density varies along with SDF values by Equation 3, where we set $\\beta = 0.01$ , $\\alpha = \\beta^{-1} = 100$ ." + ], + "image_footnote": [], + "bbox": [ + 511, + 99, + 846, + 372 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. Volume Rendering", + "text_level": 1, + "bbox": [ + 500, + 489, + 679, + 506 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Volume intensity (RGB color) $\\pmb{c} : \\mathbb{R}^3 \\to \\mathbb{R}^3$ is a vector volumetric function of spatial position $\\pmb{x}$ , where $\\pmb{c}(x)$ represents the intensity or color at a certain point $\\pmb{x}$ . Given color $c$ and density $\\sigma$ , the expected color $C(\\pmb{r})$ of ray $\\pmb{r}(t) = \\pmb{o} + t\\pmb{d}$ (where $\\pmb{o}$ and $\\pmb{d}$ are the origin and direction of the ray respectively) with near and far bounds $t_n$ and $t_f$ is:", + "bbox": [ + 496, + 512, + 890, + 604 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {C} (\\boldsymbol {r}) = \\int_ {t _ {n}} ^ {t _ {f}} \\boldsymbol {T} (t) \\sigma (\\boldsymbol {r} (t)) \\boldsymbol {c} (\\boldsymbol {r} (t)) d t, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 562, + 614, + 890, + 656 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\text {w h e r e} \\boldsymbol {T} (t) = \\exp \\left(- \\int_ {t _ {n}} ^ {t} \\sigma (\\boldsymbol {r} (s)) d s\\right)\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 651, + 823, + 686 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\sigma$ refers to the volume density. The function $T(t)$ denotes the accumulated transmittance along the ray from $t_n$ to $t$ , namely, the probability that the ray (or light) travels from $t_n$ to $t$ without being occluded by any particle. In Section 4.1.2, we describe the details to calculate volume rendering numerical integration in our setup.", + "bbox": [ + 496, + 695, + 890, + 786 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. Method", + "text_level": 1, + "bbox": [ + 500, + 800, + 589, + 814 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Overview. The overall framework is illustrated in Figure 3. We follow the network design in LIGA-Stereo [19]. Note that the stereo part of LIGA-Stereo [19] is not applicable for monocular 3D detection (M3D) task. We replace the intermediate 3D feature representations with the proposed", + "bbox": [ + 496, + 824, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "6816", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/405ddffd09d22220912d25578b45b2bdcca3a90b2cb307beae5fa7503eb6a5f9.jpg", + "image_caption": [ + "Figure 3. Overview of MonoNeRD. \"F. Voxel\" and \"D. Voxel\" in the figure refer to Feature Voxel and Density Voxel, respectively. Position-Aware Frustum Features $F_{P}$ are generated from an image $I$ and Positional Frustum Features $F_{pos}$ in a query-based manner (Section 4.1.1), which are then transformed to 3D features $F''$ and signed distance fields $F_{sdf}$ . After that, the radiance fields $F_{rgb}$ are produced by $F''$ (Section 4.1.2). $F_{sdf}$ can be transformed to frustum volume density $F_{density}$ (Equation 3) by a scaled cumulative distribution function of Laplace distribution (Equation 4). Volume rendering from $F_{rgb}$ and $F_{density}$ provides supervision for such NeRF-like representations which generate voxel features $V_{3d}$ for M3D (Section 4.1.3)." + ], + "image_footnote": [], + "bbox": [ + 83, + 85, + 861, + 284 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "NeRF-like representations while keeping the 2D image backbone and downstream detection module unchanged.", + "bbox": [ + 75, + 405, + 468, + 434 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Given an input RGB image $I \\in \\mathbb{R}^{H \\times W \\times 3}$ , it is passed to a 2D image backbone for extracting image features. Then we use the 2D image features to generate the proposed NeRF-like 3D representations. Specifically, we first build the Position-aware Frustum (See Section 4.1.1), which is transformed to 3D frustum features and SDF frustum features. Such features can be used for obtaining RGB and density features to achieve rendered RGB images and depth maps via Volume Rendering (See Section 4.1.2). They are supervised by RGB loss and depth loss to guide previous features, serving as auxiliary tasks in training. Furthermore, we use grid-sampling on 3D frustum features and density frustum features to build regular 3D voxel features and corresponding density. They are used for forming 3D Voxel Features (See Section 4.1.3), which are fed into the detection modules. We elaborate on each part of our method in the following.", + "bbox": [ + 75, + 435, + 473, + 691 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. NeRF-like Representation", + "text_level": 1, + "bbox": [ + 76, + 700, + 313, + 715 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We need to clarify the difference between NeRF and the proposed NeRF-like representation. NeRF encodes a scene with a MLP and has to be trained per scene. The proposed method predicts continuous 3D geometry information from the single input RGB image. Similar ideas have been explored in researches about single-image-based novel view synthesis. Please refer to [20, 25] for details.", + "bbox": [ + 75, + 723, + 468, + 829 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1.1 Position-aware Frustum Construction", + "text_level": 1, + "bbox": [ + 76, + 847, + 397, + 861 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To lift 2D backbone features to 3D space without depth, a naive manner is to simply repeat 2D features on different", + "bbox": [ + 75, + 869, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "depth planes. However, this way does not contain any position information, causing ambiguous spatial features. To resolve this problem, we propose to generate position-aware frustum features.", + "bbox": [ + 496, + 405, + 892, + 463 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Taking an RGB image as input, the 2D image backbone produces image features $F_{image} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times C}$ , where $H_{2d}$ and $W_{2d}$ are the height and width of the 2D image feature map, and $C$ is the number of feature channels. Such 2D image features are mapped to a camera frustum along with corresponding normalized frustum 3D coordinates in a query-based manner. More specifically, given pre-defined near depth $z_{n}$ and far depth $z_{f}$ , we sample $D$ planes from this depth range under equal depth intervals with random perturbation as described in [38, 25]. Each depth plane consists of frustum 3D position coordinates $p: [u, v, z]^{T}$ of every pixel point $[u, v]^{T} \\in \\mathbb{R}^{2}$ . These coordinates are normalized later. Thus we have 3D positional frustum features $F_{pos} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times D \\times 3}$ , where $D$ refers to the number of depth planes and 3 denotes the normalized coordinates. To combine 3D position and original 2D image features, we use three linear layers $f_{q}, f_{k}, f_{v}$ to do the Query-Key-Value mapping and attention calculation (in Figure 4).", + "bbox": [ + 496, + 465, + 893, + 739 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nf _ {q}: F _ {p o s} \\rightarrow Q \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times D \\times C}\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 750, + 812, + 768 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nf _ {k}: F _ {\\text {i m a g e}} \\rightarrow K \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times C} \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 578, + 770, + 890, + 787 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nf _ {v}: F _ {i m a g e} \\to V \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times C}\n$$\n", + "text_format": "latex", + "bbox": [ + 578, + 791, + 808, + 809 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Therefore, the Position-Aware Frustum features can be calculated by a softmax function along the depth dimension.", + "bbox": [ + 500, + 821, + 892, + 851 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nF _ {P} = \\operatorname {S o f t m a x} (Q K, \\dim = D) V \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 599, + 864, + 892, + 878 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "6817", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/91b6426e8e0a39b277fbce259f8a68f1565e0e5e4621b2d246b023c19d88a0f4.jpg", + "image_caption": [ + "Figure 4. The Query-Key-Value mapping procedure for constructing Position-Aware Frustum features." + ], + "image_footnote": [], + "bbox": [ + 86, + 90, + 452, + 224 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1.2 Volume Rendering within Frustum", + "text_level": 1, + "bbox": [ + 76, + 299, + 374, + 314 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "After constructing position-aware frustum features, we try to encode such features in 3D space to obtain more informative 3D features for volume rendering. Towards this goal, we employ two 3D convolution blocks $f_{1}$ and $f_{2}$ . $f_{1}$ consists of a three-layer 3D-convolution with kernel size 3 and softplus activation. It takes position-aware frustum features $F_{P} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times D \\times C}$ as input, outputting a same shape feature $F'$ except the channel number, as follows:", + "bbox": [ + 75, + 323, + 468, + 444 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nf _ {1}: F _ {P} \\rightarrow F ^ {\\prime} \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times D \\times (1 + C)} \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 143, + 454, + 468, + 472 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "i) SDF and density features. The first channel feature in $F'$ is regarded as SDF feature $F_{sdf} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times D \\times 1}$ . The signed distance fields $F_{sdf}$ represent the scene geometry of the input image. For any 3D point $[x, y, z]^T$ in frustum space, we can get its signed distance $s(x, y, z) \\in \\mathbb{R}^1$ by trilinear sampling in $F_{sdf}$ . Furthermore, scene volume density $\\sigma$ (or density frustum $F_{density} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times D \\times 1}$ ) can be transformed by Equation 3:", + "bbox": [ + 75, + 484, + 468, + 606 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\sigma (x, y, z) = \\alpha \\Psi_ {\\beta} (s (x, y, z)) \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 173, + 618, + 468, + 641 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nF _ {d e n s i t y} = \\alpha \\Psi_ {\\beta} (F _ {s d f})\n$$\n", + "text_format": "latex", + "bbox": [ + 176, + 638, + 331, + 654 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The density will be used for rendering depth maps and weighing the voxel features.", + "bbox": [ + 75, + 664, + 468, + 694 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "ii) RGB features. The remaining $C$ channel feature in $F'$ , called $F''$ , is then passed to $f_{2}$ , which consists of a one-layer 3D-convolution with kernel size 3 and sigmoid activation.", + "bbox": [ + 75, + 695, + 468, + 753 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nf _ {2}: F ^ {\\prime \\prime} \\rightarrow F _ {r g b} \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times D \\times 3} \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 153, + 753, + 468, + 772 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The resulting feature is used for approximating the scene radiance field $F_{rgb}$ . We can also get color intensity $c(x,y,z) \\in \\mathbb{R}^3$ by trilinear sampling in $F_{rgb}$ .", + "bbox": [ + 75, + 779, + 468, + 825 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Rendering from original view. To save GPU memory, we render downsampled RGB image $\\hat{I}_{low}$ and depth map $\\hat{Z}_{low}$ . According to known camera calibration and multiple depth value $\\{z_i | i = 1, \\dots, D\\}$ , a pixel point $[u, v]^T$ in $\\hat{I}$ can be back-projected to several 3D point coordinates", + "bbox": [ + 75, + 825, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$\\{[x_i,y_i,z_i]^T |i = 1,\\dots ,D\\}$ . We can calculate the distance between two successive 3D points as follows:", + "bbox": [ + 498, + 90, + 890, + 121 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\delta_ {x _ {i}, y _ {i}, z _ {i}} = \\left\\| \\left[ x _ {i + 1}, y _ {i + 1}, z _ {i + 1} \\right] ^ {T} - \\left[ x _ {i}, y _ {i}, z _ {i} \\right] ^ {T} \\right\\| _ {2} \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 519, + 131, + 890, + 152 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Denote the distance map at depth $z_{i}$ as $\\delta_{z_i} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times 1}$ , we can easily get the density map $\\sigma_{z_i} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times 1}$ from $F_{density}$ and color map $c_{z_i} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times 3}$ from $F_{rgb}$ . Then we can render $\\hat{I}$ by:", + "bbox": [ + 498, + 162, + 890, + 224 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {I} _ {\\text {l o w}} = \\sum_ {i = 1} ^ {D} T _ {i} \\left(1 - \\exp \\left(- \\sigma_ {z _ {i}} \\delta_ {z _ {i}}\\right)\\right) c _ {z _ {i}}, \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 568, + 236, + 890, + 277 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $T_{i} = \\exp \\left(-\\sum_{j = 1}^{i - 1}\\sigma_{z_{j}}\\delta_{z_{j}}\\right)$ denotes the accumulated transmittance map from plane 1 to plane $i$ . Similarly, the low resolution depth map $\\hat{Z}_{low}\\in \\mathbb{R}^{H_{2d}\\times W_{2d}\\times 1}$ can be rendered by:", + "bbox": [ + 498, + 290, + 890, + 358 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {Z} _ {\\text {l o w}} (u, v) = \\sum_ {i = 1} ^ {D} T _ {i} \\left(1 - \\exp \\left(- \\sigma_ {z _ {i}} \\delta_ {z _ {i}}\\right)\\right) z _ {i} \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 553, + 368, + 890, + 411 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We simply upsample $\\hat{I}_{low}$ and $\\hat{Z}_{low}$ to original image resolution to get target image $\\hat{I} \\in \\mathbb{R}^{H \\times W \\times 3}$ and depth map $\\hat{Z} \\in \\mathbb{R}^{H \\times W \\times 1}$ . Such recovered RGB images and depth maps will be supervised by RGB loss and depth loss (See", + "bbox": [ + 498, + 426, + 890, + 488 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/76ce98bc5c58cc0a12eff87d09ca4ac77c59e15327cb05f10d720039eac95a75.jpg", + "image_caption": [ + "Figure 5. Supervision from two RGB images by using volume rendering. We can obtain associated rendered RGB images from frustum density features $F_{\\text{density}}$ and frustum radiance fields $F_{\\text{rgb}}$ via Equation 12. Under this setting, we do not require explicit depth labels (i.e., LiDAR depths). Instead, the depth can be implicitly learned by calculating RGB reconstruction loss between original and rendered images." + ], + "image_footnote": [], + "bbox": [ + 513, + 518, + 875, + 776 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "6818", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Section 4.2). They are used in training as auxiliary tasks to facilitate the learning process and can be discarded at the inference stage.", + "bbox": [ + 75, + 90, + 468, + 135 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Rendering from other views. Moreover, we can render from other views as long as such views' frustum overlaps with the original view's frustum and their camera calibrations are available. The rendered images can be produced in the same way described above. By calculating the image reconstruction loss from other views' rendered images, our NeRF-like representations can get extra supervisions. In Figure 5, we give an example of taking the stereo images (left and right images) in KITTI [17] as volume rendering targets. In this way, we can even eliminate the reliance on explicit depth supervisions. Considering the space limitation of the main text, we provided ablation of depth supervision in this supplementary material.", + "bbox": [ + 75, + 137, + 470, + 333 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1.3 Voxel Features Generation", + "text_level": 1, + "bbox": [ + 76, + 354, + 316, + 369 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Aforementioned frustum features cannot be directly used for downstream detection modules as they are irregular in 3D space. Therefore, we must transform 3D frustum features to regular 3D voxel features. We perform this process of converting frustum to voxel just like CaDDN [47] by leveraging camera calibration and differentiable sampling. First, we define a voxel grid $V \\in \\mathbb{R}^{H_{3d} \\times W_{3d} \\times D_{3d} \\times 3}$ , the sampling points $s_k^v = [x,y,z]_k^T$ are the center of each voxel. We can transform $s_k^v$ to get corresponding frustum sampling points $s_k^f = [u,v,d]_k^T$ according to the camera calibration matrix. Frustum features $(F'', F_{density})$ are sampled using sampling points $s_k^f$ with trilinear interpolation to inhabit voxel features $(V'', V_{density})$ . Different from [47], the spatial resolutions of the frustum grid and voxel grid are not required to be similar because $F_{sdf}$ and $F_{rgb}$ are not limited by spatial resolution.", + "bbox": [ + 75, + 380, + 468, + 625 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Considering that the density indicates 3D occupancy in the 3D space, we use it to enhance sampled 3D voxel features $V''$ . Specifically, we obtain the final 3D voxel features by:", + "bbox": [ + 75, + 626, + 468, + 686 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nV _ {3 d} = V ^ {\\prime \\prime} \\cdot \\tanh \\left(V _ {\\text {d e n s i t y}}\\right) \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 181, + 688, + 468, + 705 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\tanh (\\cdot)$ is used to scale $V_{\\text{density}}$ to the range of $[0,1]$ . $V_{3d}$ is a NeRF-like representation since it is optimized in the same way as NeRF to learn the implicit scene geometry and occupancy.", + "bbox": [ + 75, + 713, + 468, + 773 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Loss Function", + "text_level": 1, + "bbox": [ + 76, + 786, + 220, + 800 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Equation 12 and 13 build connections between 3D scene representation and 2D observations (i.e., texture and depth). We can therefore optimize the 3D representations with raw 2D RGB images and depth maps. Based on this, there are four terms in the loss function: RGB loss $L_{rgb}$ , depth loss $L_{depth}$ , SDF loss $L_{sdf}$ , and the original loss in the baseline", + "bbox": [ + 75, + 809, + 468, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "framework LIGA [19] $L_{\\mathrm{LIGA}}$ . The overall loss is formulated as:", + "bbox": [ + 498, + 90, + 890, + 119 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL = \\lambda_ {r g b} L _ {r g b} + \\lambda_ {\\text {d e p t h}} L _ {\\text {d e p t h}} + \\lambda_ {s d f} L _ {s d f} + \\lambda_ {\\mathrm {L I G A}} L _ {\\mathrm {L I G A}}, \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 501, + 133, + 890, + 162 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\lambda_{rgb},\\lambda_{depth},\\lambda_{sdf},\\lambda_{LIGA}$ are fixed loss weights. We empirically set all weights to 1 by default.", + "bbox": [ + 496, + 164, + 890, + 191 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "RGB loss. The RGB loss consists of two items: Smooth L1 loss $L_{\\mathrm{smoothL1}}$ and SSIM [56] loss $L_{\\mathrm{SSIM}}$ which are usually used in image reconstruction:", + "bbox": [ + 498, + 193, + 890, + 239 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {r g b} = \\lambda_ {\\text {s m o o t h L 1}} L _ {\\text {s m o o t h L 1}} + \\lambda_ {\\text {S S I M}} L _ {\\text {S S I M}} \\tag {16}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 253, + 890, + 268 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Depth loss. Depth map labels are obtained by projecting associated LiDAR points onto the image plane. The depth loss is L1 loss between ground truth sparse depth map $Z$ and predicted depth map $\\hat{Z}$ ,", + "bbox": [ + 496, + 281, + 890, + 342 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {d e p t h} = \\frac {1}{N _ {d e p t h}} \\sum_ {u, v} \\left\\| \\hat {Z} - Z \\right\\| _ {1} \\tag {17}\n$$\n", + "text_format": "latex", + "bbox": [ + 583, + 352, + 890, + 388 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $N_{depth}$ denotes the number of valid pixels $(u,v)$ with LiDAR depth.", + "bbox": [ + 496, + 398, + 890, + 429 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "SDF loss. The SDF loss encourages $F_{sdf}$ to vanish on geometry surface $\\mathcal{M}$ ,", + "bbox": [ + 496, + 430, + 890, + 460 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {s d f} = \\frac {1}{N _ {g t}} \\sum_ {x, y, z} \\left(\\left\\| F _ {s d f} (x, y, z) \\right\\| _ {2}\\right) \\tag {18}\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 470, + 890, + 507 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $N_{gt}$ denotes the number of LiDAR points in the current camera view.", + "bbox": [ + 496, + 517, + 890, + 545 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "LIGA loss We denote the original loss in LIGA [19] as $L_{\\mathrm{LIGA}}$ . We keep the detection, imitation and auxiliary 2D supervision loss items but remove the stereo depth estimation item to fit the monocular setting. The imitation item is removed in all Waymo [52] experiments for convenience.", + "bbox": [ + 498, + 547, + 890, + 622 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {\\text {L I G A - K I T T I}} = L _ {\\text {d e t}} + \\lambda_ {i m} L _ {i m} + \\lambda_ {2 d} L _ {2 d} \\tag {19}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 633, + 890, + 657 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {\\text {L I G A - W a y m o}} = L _ {\\det} + \\lambda_ {2 d} L _ {2 d}\n$$\n", + "text_format": "latex", + "bbox": [ + 563, + 652, + 761, + 669 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 500, + 700, + 632, + 718 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Dataset and Metrics", + "text_level": 1, + "bbox": [ + 500, + 726, + 691, + 739 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "KITTI. The KITTI dataset [17] comprises of 7,481 images in the training (trainval set) and 7,518 images in the testing (test set) with synchronized LiDAR point clouds. In previous works [11], the training images were split into a train set (3,712 samples) and a val set (3,769 samples). We also follow this setting. Results on the KITTI dataset [17] are measured using IoU-based criteria with a threshold of 0.7 to compute averaged precision over 40 recall values $(AP|_{R40})$ for the car class in both bird's-eye-view (BEV) and 3D tasks.", + "bbox": [ + 496, + 750, + 890, + 898 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "6819", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/df7d4484ee83eadc945a82ba4913ca2248a86a7493e9bf986454239cf0fcafd4.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodsReferenceCategoryAPBEVAP3D
EasyModerateHardEasyModerateHard
D4LCN[16]CVPR20Pretained Depth22.5116.0212.5516.6511.729.51
DDMP-3D[53]CVPR2128.0817.8913.4419.7112.789.80
Ground-Aware[29]RAL21Directly Regress29.8117.9813.0821.6513.259.91
MonoRCNN[50]ICCV2125.4818.1114.1018.3612.6510.03
MonoEF[66]CVPR2129.0319.7017.2621.2913.8711.71
MonoRUn[9]CVPR21Geometric-based27.9417.3415.2419.6512.3010.58
GUPNet[31]ICCV2130.2921.1918.2022.2615.0213.12
MonoFlex[65]CVPR2128.2319.7516.8919.9413.8912.07
DCD[26]ECCV2232.5521.5018.2523.8115.9013.21
CaDDN[47]CVPR21LiDAR Auxiliary27.9418.9117.1919.1713.4111.46
DD3D[40]ICCV2130.9822.5620.0323.2216.3414.20
DID-M3D[43]ECCV2232.9522.7619.8324.4016.2913.75
MonoNeRD (ours)-31.1323.4620.9722.7517.1315.63
", + "bbox": [ + 135, + 88, + 831, + 300 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 1. Comparisons for Car category on KITTI test at IOU threshold 0.7. We obtain the values of other methods from respective papers. We use red to indicate the highest result and blue for the second-highest result. We can see that our method sets a new state of the art.", + "bbox": [ + 75, + 311, + 888, + 339 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Waymo. The Waymo Open Dataset [52] consists of 798 training sequences and 202 validation sequences. We follow the setting in CaDDN [47] which only considers the front camera and uses the sampled training set (51,564 samples). Results on Waymo val are measured by officially evaluation of the mean average precision (mAP) and the mean average precision weighted by heading (mAPH) with IoU criteria of 0.7 and 0.5. The evaluation is performed on two difficulty levels (Level_1 and Level_2) and three distance ranges (0 - 30m, 30m - 50m, 50m - $\\infty$ ).", + "bbox": [ + 75, + 364, + 468, + 513 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Implementation Details", + "text_level": 1, + "bbox": [ + 76, + 554, + 294, + 571 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Training details. Our method is implemented with Pytorch [42] framework. We have done all experiments with four NVIDIA 3080Ti (12G) GPUs. The detector is trained using AdamW [30] optimizer with $\\beta_{1} = 0.9, \\beta_{2} = 0.999$ . The batch size is fixed to 4, with 1 sample on each GPU. On KITTI [17], the input size is fixed to $320 \\times 1248$ , we train 50 epochs using an initial learning rate of 0.001, and 10 epochs with a reduced learning rate of 0.0001, weight decay is 0.0001. On Waymo [52], the input size is fixed to $640 \\times 960$ , we train 16 epochs using an initial learning rate of 0.001, and 4 epochs with a reduced learning rate of 0.0001, weight decay is 0.0001.", + "bbox": [ + 75, + 588, + 468, + 770 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Hyperparameters. On KITTI [17], we sample $D = 72$ planes within depth range $[z_{n}, z_{f}] = [2, 59.6]$ (meter) in the frustum space. The voxel grid range is $[2, 59.6] \\times [-30.4, 30.4] \\times [-3, 1]$ (meter) and voxel size is $[0.2, 0.2, 0.2]$ (meter) for the depth, width, and height axis in 3D space, respectively. On Waymo [52] the voxel grid range is $[2, 59.6] \\times [-25.6, 25.6] \\times [-3, 1]$ (meter) while all other hyperparameters are the same as KITTI experiments.", + "bbox": [ + 75, + 779, + 468, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Main Results", + "text_level": 1, + "bbox": [ + 500, + 364, + 638, + 378 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "KITTI. Table 1 shows the main results of MonoNeRD on the KITTI test set. Our method is competitive with previous methods without any extra data. MonoNeRD achieves the best results under the Moderate and Hard settings in both $AP_{BEV}$ and $AP_{3D}$ . Compared to DD3D [40], which uses a vast private dataset for depth pre-training, we boost the performance from 22.56/16.34 to 23.46/17.13 under moderate setting, and from 20.03/14.20 to 20.97/15.63 under hard setting for $AP_{BEV} / AP_{3D}$ , respectively. As for DID-M3D [43], we exceed it on both moderate and hard settings with 0.7/1.14 $AP_{BEV}$ and 0.84/1.88 $AP_{3D}$ .", + "bbox": [ + 496, + 388, + 890, + 555 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Waymo. Table 2 shows the main results of on the Waymo val set. MonoNeRD achieves competitive results without using data augmentation techniques. It has a lightweight backbone (ResNet34) compared to other depth-based methods like CaDDN (ResNet101) and DID-M3D (DLA34).", + "bbox": [ + 496, + 556, + 890, + 631 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The Results on both KITTI [17] hard and Waymo [52] distance ranges (30m - 50m, 50m - $\\infty$ ) demonstrate the superiority of our method in handling distant and occluded objects.", + "bbox": [ + 496, + 633, + 890, + 694 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.4. Ablation Studies", + "text_level": 1, + "bbox": [ + 500, + 709, + 663, + 724 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Architectural components. We conduct an ablation study on the car category in KITTI val to analyze the effectiveness of the proposed NeRF-like representations. In Table 3, Exp. (a) is the baseline which directly takes features sampled from $F_{P}$ as voxel representations $V_{3d}$ for M3D. In Exp. (b), we use more 3D convolution layers to prevent enhancements from complex model structures. Exp. (c) shows that supervision only from a single RGB image is useless and even harmful for detection since a purely single image cannot provide depth information. We can see that sparse depth map labels from LiDAR can significantly improve the per", + "bbox": [ + 496, + 734, + 890, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "6820", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/5fd4743f7abea39fc71aea041dac932a527722f62e7f963d3d2a0c2461cdfd1a.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Methods3D mAP / mAPH (IoU = 0.7)3D mAP / mAPH (IoU = 0.5)
Overall0 - 30m30 - 50m50m - ∞Overall0 - 30m30 - 50m50m - ∞
LEVEL 1
PatchNet [32]0.39 / 0.371.67 / 1.630.13 / 0.120.03 / 0.032.92 / 2.7410.03 / 9.751.09 / 0.960.23 / 0.18
CaDDN [47]5.03 / 4.9914.54 / 14.431.47 / 1.450.10 / 0.1017.54 / 17.3145.00 / 44.469.24 / 9.110.64 / 0.62
PCT [54]0.89 / 0.883.18 / 3.150.27 / 0.270.07 / 0.074.20 / 4.1514.70 / 14.541.78 / 1.750.39 / 0.39
MonoJSG [27]0.97 / 0.954.65 / 4.590.55 / 0.530.10 / 0.095.65 / 5.4720.86 / 20.263.91 / 3.790.97 / 0.92
DEVIANT [24]2.69 / 2.676.95 / 6.900.99 / 0.980.02 / 0.0210.98 / 10.8926.85 / 26.645.13 / 5.080.18 / 0.18
DID-M3D [43]- / -- / -- / -- / -20.66 / 20.4740.92 / 40.6015.63 / 15.485.35 / 5.24
MonoNeRD (ours)10.66 / 10.5627.84 / 27.575.40 / 5.360.72 / 0.7131.18 / 30.7061.11 / 60.2826.08 / 25.716.60 / 6.47
LEVEL 2
PatchNet [32]0.38 / 0.361.67 / 1.630.13 / 0.110.03 / 0.032.42 / 2.2810.01 / 9.731.07 / 0.940.22 / 0.16
CaDDN [47]4.49 / 4.4514.50 / 14.381.42 / 1.410.09 / 0.0916.51 / 16.2844.87 / 44.338.99 / 8.860.58 / 0.55
PCT [54]0.66 / 0.663.18 / 3.150.27 / 0.260.07 / 0.074.03 / 3.9914.67 / 14.511.74 / 1.710.36 / 0.35
MonoJSG [27]0.91 / 0.894.64 / 4.650.55 / 0.530.09 / 0.095.34 / 5.1720.79 / 20.193.79 / 3.670.85 / 0.82
DEVIANT [24]2.52 / 2.506.93 / 6.870.95 / 0.940.02 / 0.0210.29 / 10.2026.75 / 26.544.95 / 4.900.16 / 0.16
DID-M3D [43]- / -- / -- / -- / -19.37 / 19.1940.77 / 40.4615.18 / 15.044.69 / 4.59
MonoNeRD (ours)10.03 / 9.9327.75 / 27.485.25 / 5.210.60 / 0.5929.29 / 28.8460.91 / 60.0825.36 / 25.005.77 / 5.66
", + "bbox": [ + 89, + 87, + 883, + 310 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "formance of the detector from Exp. (d). The effectiveness of $L_{rgb}$ can be revealed by comparing Exp. (d, e) or Exp. (f, g). Finally, SDF loss brings noticeable performance gains, especially on $AP_{BEV}$ .", + "bbox": [ + 75, + 359, + 468, + 421 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/a9342338aae69e3085dca22925876bf9f66c1194523d7c4e1e27bf552615a248.jpg", + "table_caption": [ + "Table 2. Results on Waymo val set. We obtain the values of other methods from their respective papers. Our method performs the best." + ], + "table_footnote": [], + "table_body": "
Exp.Setting\\(AP_{BEV}/AP_{3D}\\)
3D Conv.\\(L_{rgb}\\)\\(L_{depth}\\)\\(L_{sdf}\\)EasyModerateHard
(a)24.96 / 17.0119.27 / 13.3816.89 / 11.73
(b)✓25.64 / 17.2219.75 / 13.6518.01 / 11.99
(c)✓✓24.83 / 16.9219.10 / 13.1116.74 / 11.73
(d)✓✓26.91 / 18.7220.87 / 14.5418.57 / 12.60
(e)✓✓✓26.46 / 19.4420.16 / 15.0317.59 / 12.83
(f)✓✓✓27.94 / 20.2821.44 / 15.3218.82 / 13.48
(g)✓✓✓✓29.03 / 20.6422.03 / 15.4419.41 / 13.99
", + "bbox": [ + 80, + 434, + 468, + 522 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Positional aware module. based on experiment (g) in Table 3, we replace the query-key-value (QKV) based positional aware module with the concatenation of positional features and back-projected image features. The results show a performance degradation in $AP_{BEV}$ from 29.03/22.03/19.41 to 28.39/21.60/18.94, and in $AP_{3D}$ from 20.64/15.44/13.99 to 19.73/15.16/12.94. This experiment demonstrates the effectiveness of the proposed design.", + "bbox": [ + 75, + 590, + 468, + 712 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/63a5c5626ecffb6478c548936b4522463bd29d5da68187c40839e07e696c22e8.jpg", + "table_caption": [ + "Table 3. Ablation of network structure and volume rendering loss. \"3D Conv\": 3D convolution blocks as mentioned in Section 4.1.2; $L_{(\\cdot)}$ : use the loss for supervision; \"Exp\": Experiment." + ], + "table_footnote": [], + "table_body": "
Exp.Pos.APBEV/AP3D
EasyModerateHard
1QKV29.03 / 20.6422.03 / 15.4419.41 / 13.99
2Cat.28.39 / 19.7321.60 / 15.1618.94 / 12.94
", + "bbox": [ + 109, + 724, + 437, + 770 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 4. Ablation of the position aware frustum. \"Pos:\": the injection method of positional information. \"Cat:\": positional feature concatenation.", + "bbox": [ + 75, + 780, + 468, + 821 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.5. Visualization", + "text_level": 1, + "bbox": [ + 76, + 845, + 212, + 859 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In Figure 6, we replace the proposed representation with depth-transformed one used in previous works [12, 47] and", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "visualize them for comparison. For depth-transformed category, we first predict the depth map from the input RGB image and apply the same transformation as CaDDN [47] to get its 3D representation. We visualize such representation by back-projecting the estimated depth map to the 3D space. For the NeRF-like representation, we directly visualize the predicted 3D volume density. Our method produces dense and continuous geometry in the distance (as indicated", + "bbox": [ + 496, + 359, + 893, + 481 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/543387f9c840c173bcb878b09a56d1974a312344817d6d6293b8a7467057c404.jpg", + "image_caption": [ + "Figure 6. Visualization for depth-map-based representation and the proposed NeRF-like representation. From top to bottom: input image, NeRF-like representation, depth-map-based representation. Our method generates denser features for distant objects." + ], + "image_footnote": [], + "bbox": [ + 519, + 512, + 874, + 825 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "6821", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "by the red box area). Due to space constraints, we provide additional quantitative and qualitative results in the Supplementary materials. Occupancy results are best viewed as videos, so we urge readers to view our supplementary video.", + "bbox": [ + 75, + 90, + 472, + 152 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 167, + 196, + 184 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this paper, we explore how to optimize the intermediate 3D feature representations implicitly for monocular 3D object detection (M3D) without explicit binary occupancy annotations. We build a bridge between Neural Radiance Fields (NeRF) and 3D object detection, and propose a novel monocular 3D object detection framework, i.e. MonoNeRD, which produces continuous NeRF-like Representations for M3D. MonoNeRD treats intermediate 3D representations as SDF-based neural radiance fields and optimizes them using volume rendering techniques. Extensive experiments show that our method sets a new baseline for monocular 3D detection and has the potential to be extended to other 3D perception tasks.", + "bbox": [ + 75, + 194, + 472, + 391 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Limitations and future work. The performance of our method is highly dependent on the modeling approaches. We are currently limited by the working with bounds modeling (see Section 3.3), which could fail to predict 3D occupancy when its 2D projected pixel represents sky or other things not within the specified bounds. We believe this is an interesting direction for future research.", + "bbox": [ + 75, + 391, + 472, + 500 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 76, + 513, + 238, + 532 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was supported in part by The National Nature Science Foundation of China (Grant Nos: 62273301, 62273302, 62273303, 62036009, 61936006), in part by the Key R&D Program of Zhejiang Province, China (2023C01135), and in part by Yongjiang Talent Introduction Programme (Grant No: 2022A-240-G).", + "bbox": [ + 75, + 540, + 472, + 632 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 76, + 647, + 174, + 664 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Junaid Ahmed Ansari, Sarthak Sharma, Anshuman Majumdar, J Krishna Murthy, and K Madhava Krishna. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 7556-7566, 2021. 7" + ], + "bbox": [ + 501, + 92, + 893, + 868 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "6824", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/MonoNeRD_ NeRF-like Representations for Monocular 3D Object Detection/63ab896a-8106-40c7-82f9-2e2b03ab3262_model.json b/2023/MonoNeRD_ NeRF-like Representations for Monocular 3D Object Detection/63ab896a-8106-40c7-82f9-2e2b03ab3262_model.json new file mode 100644 index 0000000000000000000000000000000000000000..0d8f1970e3e5c550cdaaa5717fb48c425a07641f --- /dev/null +++ b/2023/MonoNeRD_ NeRF-like Representations for Monocular 3D Object Detection/63ab896a-8106-40c7-82f9-2e2b03ab3262_model.json @@ -0,0 +1,2587 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.101, + 0.131, + 0.871, + 0.152 + ], + "angle": 0, + "content": "MonoNeRD: NeRF-like Representations for Monocular 3D Object Detection" + }, + { + "type": "text", + "bbox": [ + 0.213, + 0.179, + 0.761, + 0.273 + ], + "angle": 0, + "content": "Junkai Xu\\(^{1,2*}\\) Liang Peng\\(^{1,2,*}\\) Haoran Chen\\(^{1,2,*}\\) Hao Li\\(^{2}\\) Wei Qian\\(^{2}\\) Ke Li\\(^{4}\\) Wenxiao Wang\\(^{3\\dagger}\\) Deng Cai\\(^{1,2}\\) \\(^{1}\\)State Key Lab of CAD & CG, Zhejiang University \\(^{2}\\)FABU Inc. \\(^{3}\\)School of Software Technology, Zhejiang University \\(^{4}\\)Fullong Inc. {xujunkai, pengliang, haorancheng}@zju.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.306, + 0.314, + 0.322 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.339, + 0.474, + 0.671 + ], + "angle": 0, + "content": "In the field of monocular 3D detection, it is common practice to utilize scene geometric clues to enhance the detector's performance. However, many existing works adopt these clues explicitly such as estimating a depth map and back-projecting it into 3D space. This explicit methodology induces sparsity in 3D representations due to the increased dimensionality from 2D to 3D, and leads to substantial information loss, especially for distant and occluded objects. To alleviate this issue, we propose MonoNeRD, a novel detection framework that can infer dense 3D geometry and occupancy. Specifically, we model scenes with Signed Distance Functions (SDF), facilitating the production of dense 3D representations. We treat these representations as Neural Radiance Fields (NeRF) and then employ volume rendering to recover RGB images and depth maps. To the best of our knowledge, this work is the first to introduce volume rendering for M3D, and demonstrates the potential of implicit reconstruction for image-based 3D perception. Extensive experiments conducted on the KITTI-3D benchmark and Waymo Open Dataset demonstrate the effectiveness of MonoNeRD. Codes are available at https://github.com/cskkxjk/MonoNeRD." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.702, + 0.21, + 0.717 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.727, + 0.47, + 0.864 + ], + "angle": 0, + "content": "Monocular 3D detection (M3D) is an active research topic in the computer vision community due to its convenience, low cost and wide range of applications, including autonomous driving, robotic navigation and more. The key point of the task is to establish reasonable correspondences between 2D images and 3D space. Some works leverage geometrical priors to extract 3D information, such as object poses via 2D-3D constraints. These constraints usually require additional keypoint annotations [10, 21] or" + }, + { + "type": "image", + "bbox": [ + 0.55, + 0.308, + 0.851, + 0.535 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.551, + 0.895, + 0.621 + ], + "angle": 0, + "content": "Figure 1. Different intermediate 3D representations. Previous depth-based methods generate 3D representations by backprojecting estimated depth maps to 3D space, whereas our method predicts implicit 3D representations, and obtains depth estimates through volume rendering." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.655, + 0.894, + 0.761 + ], + "angle": 0, + "content": "CAD models [5, 34]. Other works convert estimated depth maps into 3D point cloud representations (Pseudo-LiDAR) [32, 55, 60]. Depth estimates are also used to combine with image features [58, 33] or generate meaningful bird's-eye-view (BEV) representations [45, 47, 48, 51], then produce 3D object detection results. These methods have made remarkable progress in M3D." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Unfortunately, current 3D representations transformed by explicit depths have some limitations. First, the lifted features obtained from depth estimates or pseudo-LiDAR exhibit an uneven distribution throughout the 3D space. Specifically, they have high density in close range, but the density decreases as the distance increases. (See top part of Figure 1). Second, the final detection performance heavily depends on the accuracy of the depth estimation, which remains challenging to improve. Thus such representations" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.875, + 0.374, + 0.888 + ], + "angle": 0, + "content": "*Work performed during an internship at FABU Inc." + }, + { + "type": "page_footnote", + "bbox": [ + 0.098, + 0.888, + 0.221, + 0.9 + ], + "angle": 0, + "content": "† Corresponding author" + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.875, + 0.374, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6814" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.443, + 0.106 + ], + "angle": 0, + "content": "cannot produce dense reasonable 3D features for M3D." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.107, + 0.473, + 0.544 + ], + "angle": 0, + "content": "Recent researches in Neural Radiance Fields (NeRF) [3, 38, 64] have shown the capability to reconstruct detailed and dense 3D scene geometry and occupancy information from posed images (images with known camera poses). Inspired by NeRF and its follow-ups [20, 25, 59], we reformulate the intermediate 3D representations in M3D to NeRF-like 3D representations, which can produce dense reasonable 3D geometry and occupancy. To achieve this goal, we combine extracted 2D backbone features and corresponding normalized frustum 3D coordinates to construct 3D Position-aware Frustum features (Section 4.1.1). These 3D features are used to create signed distance fields and radiance fields (RGB color). The signed distance fields encode the distance to the closest surface at every location as a scalar value. This allows us to model scenes implicitly by the zero-level set of the signed distance fields. (Section 3.1). We then adopt volume rendering [35] technique to generate RGB images and depth maps from the signed distance fields and radiance fields (Section 4.1.2), supervising them by original RGB images and LiDAR points (Section 4.2). While the previous depth-based methods generate 3D representations based on predicted depth maps, our method generates depth maps based on 3D representations (Figure 1). It is worth noting that our approach is capable of generating dense 3D occupancy (i.e., volume density) without requiring explicit binary occupancy annotations for individual voxels. Experiments on KITTI [17] 3D benchmark and Waymo Open Dataset [52] show the superiority of our NeRF-like representations in monocular 3D detection." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.545, + 0.345, + 0.558 + ], + "angle": 0, + "content": "Our main contributions are threefold:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.567, + 0.47, + 0.643 + ], + "angle": 0, + "content": "- We present a novel detection framework, named MonoNeRD, that connects Neural Radiance Fields and monocular 3D detection. It leverages NeRF-like continuous 3D representations to enable accurate 3D perception and understanding from a single image." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.651, + 0.47, + 0.711 + ], + "angle": 0, + "content": "- We propose to use volume rendering to directly optimize 3D representations in detection tasks. To the best of our knowledge, our work is the first to introduce volume rendering for 3D detection tasks." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.72, + 0.47, + 0.811 + ], + "angle": 0, + "content": "- Extensive experiments on KITTI [17] 3D detection benchmark and Waymo Open Dataset [52] demonstrate the effectiveness of our method, which is competitive with previous state-of-the-art works. This research presents the potential of 3D implicit reconstruction for image-based 3D perception." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.567, + 0.47, + 0.811 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.822, + 0.219, + 0.837 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.848, + 0.358, + 0.863 + ], + "angle": 0, + "content": "2.1. Monocular 3D Object Detection" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.871, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Many impressive researches [47, 9, 43] been done in monocular 3D object detection. As the essential informa" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.137 + ], + "angle": 0, + "content": "tion of depth dimension is collapsed in the 2D image, it is an ill-posed but necessary problem of finding an approach to lift the 2D information to 3D space." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.138, + 0.892, + 0.273 + ], + "angle": 0, + "content": "Some Monocular 3D Object Detection methods lift 2D to 3D directly by incorporating the geometric relationship between the 2D image plane and 3D space. For example, many methods assume rigidity of objects, aligning 2D keypoints with their 3D counterparts [1, 2, 21, 46]. Some researchers try to build the bridge between 2D and 3D structures by template matching [5, 34]. These methods usually require additional data (e.g., 3D CAD models, object keypoint annotations)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.275, + 0.893, + 0.502 + ], + "angle": 0, + "content": "Other methods generate intermediate 3D representations to solve the lifting problem. Many approaches [60, 33, 32] convert the estimated depth map (always predicted by an off-the-shelf model) to pseudo-LiDAR point cloud representations, and then feed them to sophisticated LiDAR-based detectors. CaDDN [47] learns categorical depth distributions over pixels to lift camera images into 3D space, constructing BEV representations. Pseudo-Stereo [12] uses some sophisticated modules (e.g., stereo cost volume) to achieve better depth estimation. These methods typically involve estimating depth maps beforehand and subsequently extracting corresponding 3D representations from them. Instead, our method recovers depth maps from the 3D representations and supervises them to improve the detection performance." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.515, + 0.783, + 0.53 + ], + "angle": 0, + "content": "2.2. Neural Implicit Representations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.539, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Representing 3D geometry with implicit functions has gained popularity in the past few years. Learning-based 3D reconstruction methods [13, 18, 36, 37, 41, 49] and their scene-level counterparts [6, 15, 23, 44] demonstrate compelling results but require 3D input and supervision. Neural Radiance Fields (NeRFs) [38] introduce a new perspective to learn continuous geometry representations from posed multi-view images only by volume rendering [35]. Due to the low efficiency of original MLP-based NeRF, their grid-based variants [22, 28, 61, 7] have been explored to accelerate the rendering process or save GPU memory. To circumvent the requirement of dense inputs, some works [62, 8, 14, 39] explicitly consider sparse input scenarios and show astonishing results for novel view synthesis, but these representations still need to be optimized per scene. Li et al. [25] propose MINE in which they combine Multiplane Images (MPI) and NeRF for single-image-based novel view synthesis. SceneRF [4] uses posed image sequences for training, alleviating the reliance on datasets. Wimbauer et al. [57] construct a density field to preform both depth prediction and novel view synthesis. Unlike our approach, the works mentioned primarily focus on the Novel View Synthesis task, requiring multi-view or sequenced images with camera poses as supervision, which cannot generalize to un" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6815" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.138 + ], + "angle": 0, + "content": "seen scenes (except [25, 57]). Instead, we take advantage of volume rendering to optimize 3D feature representations and improve the performance in M3D task." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.15, + 0.218, + 0.166 + ], + "angle": 0, + "content": "3. Preliminaries" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.175, + 0.471, + 0.249 + ], + "angle": 0, + "content": "Here we introduce some essential preliminaries for our idea. We use the same notation as [59] for the concepts of SDF and Volume density. Concerning the space limitation, here we provide a brief overview. Please refer to [38, 59, 35] for more details." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.258, + 0.36, + 0.274 + ], + "angle": 0, + "content": "3.1. Signed Distance Function (SDF)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.282, + 0.469, + 0.356 + ], + "angle": 0, + "content": "For a given spatial point, Signed Distance Function (SDF) is a continuous function that outputs the point's distance to the closest surface, whose sign indicates whether the point is inside (negative) or outside (positive) of the surface." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.357, + 0.469, + 0.418 + ], + "angle": 0, + "content": "Let \\(\\mathbb{R}^3\\) represent a 3D space containing some objects, \\(\\Omega \\subset \\mathbb{R}^3\\) refers to the occupied part, and \\(\\mathcal{M} = \\partial \\Omega\\) be the boundary surface. Denote the \\(\\Omega\\) indicator function by \\(\\mathbf{1}_{\\Omega}\\) and the Signed Distance Function (SDF) by \\(d_{\\Omega}\\)," + }, + { + "type": "equation", + "bbox": [ + 0.19, + 0.426, + 0.469, + 0.468 + ], + "angle": 0, + "content": "\\[\n\\mathbf {1} _ {\\Omega} (\\boldsymbol {x}) = \\left\\{ \\begin{array}{l l} 1 & \\text {i f} \\boldsymbol {x} \\in \\Omega \\\\ 0 & \\text {i f} \\boldsymbol {x} \\notin \\Omega \\end{array} \\right. \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.157, + 0.478, + 0.469, + 0.503 + ], + "angle": 0, + "content": "\\[\nd _ {\\Omega} (\\boldsymbol {x}) = (- 1) ^ {\\mathbf {1} _ {\\Omega} (\\boldsymbol {x})} \\min _ {\\boldsymbol {y} \\in \\mathcal {M}} \\| \\boldsymbol {x} - \\boldsymbol {y} \\| \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.507, + 0.47, + 0.553 + ], + "angle": 0, + "content": "where \\( \\| \\cdot \\| \\) is the standard Euclidean 2-norm. The underlying surface \\( \\mathcal{M} \\) can be implicitly represented by the zero-level set of \\( d_{\\Omega}(\\cdot) = 0 \\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.561, + 0.317, + 0.577 + ], + "angle": 0, + "content": "3.2. Transform SDF to Density" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.469, + 0.674 + ], + "angle": 0, + "content": "The volume density \\(\\sigma : \\mathbb{R}^3 \\to \\mathbb{R}_+\\) is a scalar volumetric function, where \\(\\sigma(x)\\) can be interpreted as the probability that light is occluded at point \\(x\\). Previous works et al. [59, 63] suggest modeling the density \\(\\sigma\\) using a certain transformation of a learnable Signed Distance Function (SDF), as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.193, + 0.684, + 0.469, + 0.701 + ], + "angle": 0, + "content": "\\[\n\\sigma (\\boldsymbol {x}) = \\alpha \\Psi_ {\\beta} (- d _ {\\Omega} (\\boldsymbol {x})) \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.71, + 0.469, + 0.754 + ], + "angle": 0, + "content": "where \\(\\alpha, \\beta > 0\\) are learnable parameters and \\(\\Psi_{\\beta}\\) is the cumulative distribution function of the Laplace distribution with zero mean and \\(\\beta\\) scale," + }, + { + "type": "equation", + "bbox": [ + 0.145, + 0.763, + 0.469, + 0.803 + ], + "angle": 0, + "content": "\\[\n\\Psi_ {\\beta} (s) = \\left\\{ \\begin{array}{l l} \\frac {1}{2} \\exp (\\frac {s}{\\beta}) & \\text {i f} s \\leq 0 \\\\ 1 - \\frac {1}{2} \\exp (- \\frac {s}{\\beta}) & \\text {i f} s > 0 \\end{array} \\right. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.469, + 0.901 + ], + "angle": 0, + "content": "As \\(\\beta\\) approaches zero, the density \\(\\sigma\\) converges to scaled indicator function of \\(\\Omega\\), means \\(\\sigma \\rightarrow \\alpha \\mathbf{1}_{\\Omega}\\) for all points \\(\\pmb{x} \\in \\Omega \\setminus \\mathcal{M}\\). The benefits of modeling density in this way have been discussed in [59]. We simply set \\(\\alpha = \\beta^{-1}\\) in our implementations. Figure 2 depicts an example of how density varies along SDF when a ray passes through an object." + }, + { + "type": "image", + "bbox": [ + 0.513, + 0.1, + 0.847, + 0.373 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.397, + 0.892, + 0.467 + ], + "angle": 0, + "content": "Figure 2. Example of transformation from SDF to Density. The black arrow line represents a ray passing through a spherical object; the gradient color line describes how density varies along with SDF values by Equation 3, where we set \\(\\beta = 0.01\\), \\(\\alpha = \\beta^{-1} = 100\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.49, + 0.681, + 0.507 + ], + "angle": 0, + "content": "3.3. Volume Rendering" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.513, + 0.892, + 0.605 + ], + "angle": 0, + "content": "Volume intensity (RGB color) \\( \\pmb{c} : \\mathbb{R}^3 \\to \\mathbb{R}^3 \\) is a vector volumetric function of spatial position \\( \\pmb{x} \\), where \\( \\pmb{c}(x) \\) represents the intensity or color at a certain point \\( \\pmb{x} \\). Given color \\( c \\) and density \\( \\sigma \\), the expected color \\( C(\\pmb{r}) \\) of ray \\( \\pmb{r}(t) = \\pmb{o} + t\\pmb{d} \\) (where \\( \\pmb{o} \\) and \\( \\pmb{d} \\) are the origin and direction of the ray respectively) with near and far bounds \\( t_n \\) and \\( t_f \\) is:" + }, + { + "type": "equation", + "bbox": [ + 0.563, + 0.615, + 0.892, + 0.657 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {C} (\\boldsymbol {r}) = \\int_ {t _ {n}} ^ {t _ {f}} \\boldsymbol {T} (t) \\sigma (\\boldsymbol {r} (t)) \\boldsymbol {c} (\\boldsymbol {r} (t)) d t, \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.567, + 0.652, + 0.825, + 0.687 + ], + "angle": 0, + "content": "\\[\n\\text {w h e r e} \\boldsymbol {T} (t) = \\exp \\left(- \\int_ {t _ {n}} ^ {t} \\sigma (\\boldsymbol {r} (s)) d s\\right)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.696, + 0.892, + 0.787 + ], + "angle": 0, + "content": "where \\(\\sigma\\) refers to the volume density. The function \\(T(t)\\) denotes the accumulated transmittance along the ray from \\(t_n\\) to \\(t\\), namely, the probability that the ray (or light) travels from \\(t_n\\) to \\(t\\) without being occluded by any particle. In Section 4.1.2, we describe the details to calculate volume rendering numerical integration in our setup." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.801, + 0.591, + 0.815 + ], + "angle": 0, + "content": "4. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Overview. The overall framework is illustrated in Figure 3. We follow the network design in LIGA-Stereo [19]. Note that the stereo part of LIGA-Stereo [19] is not applicable for monocular 3D detection (M3D) task. We replace the intermediate 3D feature representations with the proposed" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "6816" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.087, + 0.862, + 0.285 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.298, + 0.895, + 0.385 + ], + "angle": 0, + "content": "Figure 3. Overview of MonoNeRD. \"F. Voxel\" and \"D. Voxel\" in the figure refer to Feature Voxel and Density Voxel, respectively. Position-Aware Frustum Features \\( F_{P} \\) are generated from an image \\( I \\) and Positional Frustum Features \\( F_{pos} \\) in a query-based manner (Section 4.1.1), which are then transformed to 3D features \\( F'' \\) and signed distance fields \\( F_{sdf} \\). After that, the radiance fields \\( F_{rgb} \\) are produced by \\( F'' \\) (Section 4.1.2). \\( F_{sdf} \\) can be transformed to frustum volume density \\( F_{density} \\) (Equation 3) by a scaled cumulative distribution function of Laplace distribution (Equation 4). Volume rendering from \\( F_{rgb} \\) and \\( F_{density} \\) provides supervision for such NeRF-like representations which generate voxel features \\( V_{3d} \\) for M3D (Section 4.1.3)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.406, + 0.47, + 0.435 + ], + "angle": 0, + "content": "NeRF-like representations while keeping the 2D image backbone and downstream detection module unchanged." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.436, + 0.474, + 0.693 + ], + "angle": 0, + "content": "Given an input RGB image \\( I \\in \\mathbb{R}^{H \\times W \\times 3} \\), it is passed to a 2D image backbone for extracting image features. Then we use the 2D image features to generate the proposed NeRF-like 3D representations. Specifically, we first build the Position-aware Frustum (See Section 4.1.1), which is transformed to 3D frustum features and SDF frustum features. Such features can be used for obtaining RGB and density features to achieve rendered RGB images and depth maps via Volume Rendering (See Section 4.1.2). They are supervised by RGB loss and depth loss to guide previous features, serving as auxiliary tasks in training. Furthermore, we use grid-sampling on 3D frustum features and density frustum features to build regular 3D voxel features and corresponding density. They are used for forming 3D Voxel Features (See Section 4.1.3), which are fed into the detection modules. We elaborate on each part of our method in the following." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.701, + 0.315, + 0.717 + ], + "angle": 0, + "content": "4.1. NeRF-like Representation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.724, + 0.47, + 0.83 + ], + "angle": 0, + "content": "We need to clarify the difference between NeRF and the proposed NeRF-like representation. NeRF encodes a scene with a MLP and has to be trained per scene. The proposed method predicts continuous 3D geometry information from the single input RGB image. Similar ideas have been explored in researches about single-image-based novel view synthesis. Please refer to [20, 25] for details." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.848, + 0.398, + 0.862 + ], + "angle": 0, + "content": "4.1.1 Position-aware Frustum Construction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.471, + 0.903 + ], + "angle": 0, + "content": "To lift 2D backbone features to 3D space without depth, a naive manner is to simply repeat 2D features on different" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.406, + 0.893, + 0.464 + ], + "angle": 0, + "content": "depth planes. However, this way does not contain any position information, causing ambiguous spatial features. To resolve this problem, we propose to generate position-aware frustum features." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.467, + 0.895, + 0.74 + ], + "angle": 0, + "content": "Taking an RGB image as input, the 2D image backbone produces image features \\( F_{image} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times C} \\), where \\( H_{2d} \\) and \\( W_{2d} \\) are the height and width of the 2D image feature map, and \\( C \\) is the number of feature channels. Such 2D image features are mapped to a camera frustum along with corresponding normalized frustum 3D coordinates in a query-based manner. More specifically, given pre-defined near depth \\( z_{n} \\) and far depth \\( z_{f} \\), we sample \\( D \\) planes from this depth range under equal depth intervals with random perturbation as described in [38, 25]. Each depth plane consists of frustum 3D position coordinates \\( p: [u, v, z]^{T} \\) of every pixel point \\( [u, v]^{T} \\in \\mathbb{R}^{2} \\). These coordinates are normalized later. Thus we have 3D positional frustum features \\( F_{pos} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times D \\times 3} \\), where \\( D \\) refers to the number of depth planes and 3 denotes the normalized coordinates. To combine 3D position and original 2D image features, we use three linear layers \\( f_{q}, f_{k}, f_{v} \\) to do the Query-Key-Value mapping and attention calculation (in Figure 4)." + }, + { + "type": "equation", + "bbox": [ + 0.577, + 0.75, + 0.813, + 0.769 + ], + "angle": 0, + "content": "\\[\nf _ {q}: F _ {p o s} \\rightarrow Q \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times D \\times C}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.579, + 0.771, + 0.891, + 0.789 + ], + "angle": 0, + "content": "\\[\nf _ {k}: F _ {\\text {i m a g e}} \\rightarrow K \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times C} \\tag {6}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.58, + 0.792, + 0.81, + 0.81 + ], + "angle": 0, + "content": "\\[\nf _ {v}: F _ {i m a g e} \\to V \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times C}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.822, + 0.893, + 0.852 + ], + "angle": 0, + "content": "Therefore, the Position-Aware Frustum features can be calculated by a softmax function along the depth dimension." + }, + { + "type": "equation", + "bbox": [ + 0.6, + 0.865, + 0.893, + 0.88 + ], + "angle": 0, + "content": "\\[\nF _ {P} = \\operatorname {S o f t m a x} (Q K, \\dim = D) V \\tag {7}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6817" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.091, + 0.454, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.246, + 0.47, + 0.274 + ], + "angle": 0, + "content": "Figure 4. The Query-Key-Value mapping procedure for constructing Position-Aware Frustum features." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.3, + 0.375, + 0.315 + ], + "angle": 0, + "content": "4.1.2 Volume Rendering within Frustum" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.324, + 0.47, + 0.445 + ], + "angle": 0, + "content": "After constructing position-aware frustum features, we try to encode such features in 3D space to obtain more informative 3D features for volume rendering. Towards this goal, we employ two 3D convolution blocks \\( f_{1} \\) and \\( f_{2} \\). \\( f_{1} \\) consists of a three-layer 3D-convolution with kernel size 3 and softplus activation. It takes position-aware frustum features \\( F_{P} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times D \\times C} \\) as input, outputting a same shape feature \\( F' \\) except the channel number, as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.144, + 0.455, + 0.469, + 0.473 + ], + "angle": 0, + "content": "\\[\nf _ {1}: F _ {P} \\rightarrow F ^ {\\prime} \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times D \\times (1 + C)} \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.485, + 0.47, + 0.607 + ], + "angle": 0, + "content": "i) SDF and density features. The first channel feature in \\( F' \\) is regarded as SDF feature \\( F_{sdf} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times D \\times 1} \\). The signed distance fields \\( F_{sdf} \\) represent the scene geometry of the input image. For any 3D point \\( [x, y, z]^T \\) in frustum space, we can get its signed distance \\( s(x, y, z) \\in \\mathbb{R}^1 \\) by trilinear sampling in \\( F_{sdf} \\). Furthermore, scene volume density \\( \\sigma \\) (or density frustum \\( F_{density} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times D \\times 1} \\)) can be transformed by Equation 3:" + }, + { + "type": "equation", + "bbox": [ + 0.174, + 0.619, + 0.47, + 0.642 + ], + "angle": 0, + "content": "\\[\n\\sigma (x, y, z) = \\alpha \\Psi_ {\\beta} (s (x, y, z)) \\tag {9}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.178, + 0.639, + 0.332, + 0.655 + ], + "angle": 0, + "content": "\\[\nF _ {d e n s i t y} = \\alpha \\Psi_ {\\beta} (F _ {s d f})\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.665, + 0.469, + 0.695 + ], + "angle": 0, + "content": "The density will be used for rendering depth maps and weighing the voxel features." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.696, + 0.469, + 0.754 + ], + "angle": 0, + "content": "ii) RGB features. The remaining \\(C\\) channel feature in \\(F'\\), called \\(F''\\), is then passed to \\(f_{2}\\), which consists of a one-layer 3D-convolution with kernel size 3 and sigmoid activation." + }, + { + "type": "equation", + "bbox": [ + 0.154, + 0.755, + 0.469, + 0.773 + ], + "angle": 0, + "content": "\\[\nf _ {2}: F ^ {\\prime \\prime} \\rightarrow F _ {r g b} \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times D \\times 3} \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.469, + 0.826 + ], + "angle": 0, + "content": "The resulting feature is used for approximating the scene radiance field \\(F_{rgb}\\). We can also get color intensity \\(c(x,y,z) \\in \\mathbb{R}^3\\) by trilinear sampling in \\(F_{rgb}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Rendering from original view. To save GPU memory, we render downsampled RGB image \\(\\hat{I}_{low}\\) and depth map \\(\\hat{Z}_{low}\\). According to known camera calibration and multiple depth value \\(\\{z_i | i = 1, \\dots, D\\}\\), a pixel point \\([u, v]^T\\) in \\(\\hat{I}\\) can be back-projected to several 3D point coordinates" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.091, + 0.892, + 0.122 + ], + "angle": 0, + "content": "\\(\\{[x_i,y_i,z_i]^T |i = 1,\\dots ,D\\}\\) . We can calculate the distance between two successive 3D points as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.52, + 0.132, + 0.892, + 0.153 + ], + "angle": 0, + "content": "\\[\n\\delta_ {x _ {i}, y _ {i}, z _ {i}} = \\left\\| \\left[ x _ {i + 1}, y _ {i + 1}, z _ {i + 1} \\right] ^ {T} - \\left[ x _ {i}, y _ {i}, z _ {i} \\right] ^ {T} \\right\\| _ {2} \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.163, + 0.892, + 0.226 + ], + "angle": 0, + "content": "Denote the distance map at depth \\(z_{i}\\) as \\(\\delta_{z_i} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times 1}\\), we can easily get the density map \\(\\sigma_{z_i} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times 1}\\) from \\(F_{density}\\) and color map \\(c_{z_i} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times 3}\\) from \\(F_{rgb}\\). Then we can render \\(\\hat{I}\\) by:" + }, + { + "type": "equation", + "bbox": [ + 0.57, + 0.237, + 0.892, + 0.279 + ], + "angle": 0, + "content": "\\[\n\\hat {I} _ {\\text {l o w}} = \\sum_ {i = 1} ^ {D} T _ {i} \\left(1 - \\exp \\left(- \\sigma_ {z _ {i}} \\delta_ {z _ {i}}\\right)\\right) c _ {z _ {i}}, \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.291, + 0.892, + 0.359 + ], + "angle": 0, + "content": "where \\(T_{i} = \\exp \\left(-\\sum_{j = 1}^{i - 1}\\sigma_{z_{j}}\\delta_{z_{j}}\\right)\\) denotes the accumulated transmittance map from plane 1 to plane \\(i\\) . Similarly, the low resolution depth map \\(\\hat{Z}_{low}\\in \\mathbb{R}^{H_{2d}\\times W_{2d}\\times 1}\\) can be rendered by:" + }, + { + "type": "equation", + "bbox": [ + 0.555, + 0.369, + 0.892, + 0.412 + ], + "angle": 0, + "content": "\\[\n\\hat {Z} _ {\\text {l o w}} (u, v) = \\sum_ {i = 1} ^ {D} T _ {i} \\left(1 - \\exp \\left(- \\sigma_ {z _ {i}} \\delta_ {z _ {i}}\\right)\\right) z _ {i} \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.427, + 0.892, + 0.489 + ], + "angle": 0, + "content": "We simply upsample \\(\\hat{I}_{low}\\) and \\(\\hat{Z}_{low}\\) to original image resolution to get target image \\(\\hat{I} \\in \\mathbb{R}^{H \\times W \\times 3}\\) and depth map \\(\\hat{Z} \\in \\mathbb{R}^{H \\times W \\times 1}\\). Such recovered RGB images and depth maps will be supervised by RGB loss and depth loss (See" + }, + { + "type": "image", + "bbox": [ + 0.514, + 0.52, + 0.877, + 0.777 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.801, + 0.892, + 0.899 + ], + "angle": 0, + "content": "Figure 5. Supervision from two RGB images by using volume rendering. We can obtain associated rendered RGB images from frustum density features \\( F_{\\text{density}} \\) and frustum radiance fields \\( F_{\\text{rgb}} \\) via Equation 12. Under this setting, we do not require explicit depth labels (i.e., LiDAR depths). Instead, the depth can be implicitly learned by calculating RGB reconstruction loss between original and rendered images." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6818" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.136 + ], + "angle": 0, + "content": "Section 4.2). They are used in training as auxiliary tasks to facilitate the learning process and can be discarded at the inference stage." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.138, + 0.471, + 0.334 + ], + "angle": 0, + "content": "Rendering from other views. Moreover, we can render from other views as long as such views' frustum overlaps with the original view's frustum and their camera calibrations are available. The rendered images can be produced in the same way described above. By calculating the image reconstruction loss from other views' rendered images, our NeRF-like representations can get extra supervisions. In Figure 5, we give an example of taking the stereo images (left and right images) in KITTI [17] as volume rendering targets. In this way, we can even eliminate the reliance on explicit depth supervisions. Considering the space limitation of the main text, we provided ablation of depth supervision in this supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.356, + 0.317, + 0.37 + ], + "angle": 0, + "content": "4.1.3 Voxel Features Generation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.381, + 0.47, + 0.626 + ], + "angle": 0, + "content": "Aforementioned frustum features cannot be directly used for downstream detection modules as they are irregular in 3D space. Therefore, we must transform 3D frustum features to regular 3D voxel features. We perform this process of converting frustum to voxel just like CaDDN [47] by leveraging camera calibration and differentiable sampling. First, we define a voxel grid \\( V \\in \\mathbb{R}^{H_{3d} \\times W_{3d} \\times D_{3d} \\times 3} \\), the sampling points \\( s_k^v = [x,y,z]_k^T \\) are the center of each voxel. We can transform \\( s_k^v \\) to get corresponding frustum sampling points \\( s_k^f = [u,v,d]_k^T \\) according to the camera calibration matrix. Frustum features \\( (F'', F_{density}) \\) are sampled using sampling points \\( s_k^f \\) with trilinear interpolation to inhabit voxel features \\( (V'', V_{density}) \\). Different from [47], the spatial resolutions of the frustum grid and voxel grid are not required to be similar because \\( F_{sdf} \\) and \\( F_{rgb} \\) are not limited by spatial resolution." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.627, + 0.47, + 0.687 + ], + "angle": 0, + "content": "Considering that the density indicates 3D occupancy in the 3D space, we use it to enhance sampled 3D voxel features \\( V'' \\). Specifically, we obtain the final 3D voxel features by:" + }, + { + "type": "equation", + "bbox": [ + 0.182, + 0.689, + 0.469, + 0.707 + ], + "angle": 0, + "content": "\\[\nV _ {3 d} = V ^ {\\prime \\prime} \\cdot \\tanh \\left(V _ {\\text {d e n s i t y}}\\right) \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.714, + 0.469, + 0.775 + ], + "angle": 0, + "content": "where \\(\\tanh (\\cdot)\\) is used to scale \\(V_{\\text{density}}\\) to the range of \\([0,1]\\). \\(V_{3d}\\) is a NeRF-like representation since it is optimized in the same way as NeRF to learn the implicit scene geometry and occupancy." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.222, + 0.801 + ], + "angle": 0, + "content": "4.2. Loss Function" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.469, + 0.902 + ], + "angle": 0, + "content": "Equation 12 and 13 build connections between 3D scene representation and 2D observations (i.e., texture and depth). We can therefore optimize the 3D representations with raw 2D RGB images and depth maps. Based on this, there are four terms in the loss function: RGB loss \\( L_{rgb} \\), depth loss \\( L_{depth} \\), SDF loss \\( L_{sdf} \\), and the original loss in the baseline" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.12 + ], + "angle": 0, + "content": "framework LIGA [19] \\(L_{\\mathrm{LIGA}}\\). The overall loss is formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.503, + 0.134, + 0.892, + 0.164 + ], + "angle": 0, + "content": "\\[\nL = \\lambda_ {r g b} L _ {r g b} + \\lambda_ {\\text {d e p t h}} L _ {\\text {d e p t h}} + \\lambda_ {s d f} L _ {s d f} + \\lambda_ {\\mathrm {L I G A}} L _ {\\mathrm {L I G A}}, \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.165, + 0.891, + 0.193 + ], + "angle": 0, + "content": "where \\(\\lambda_{rgb},\\lambda_{depth},\\lambda_{sdf},\\lambda_{LIGA}\\) are fixed loss weights. We empirically set all weights to 1 by default." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.194, + 0.892, + 0.24 + ], + "angle": 0, + "content": "RGB loss. The RGB loss consists of two items: Smooth L1 loss \\(L_{\\mathrm{smoothL1}}\\) and SSIM [56] loss \\(L_{\\mathrm{SSIM}}\\) which are usually used in image reconstruction:" + }, + { + "type": "equation", + "bbox": [ + 0.562, + 0.254, + 0.892, + 0.27 + ], + "angle": 0, + "content": "\\[\nL _ {r g b} = \\lambda_ {\\text {s m o o t h L 1}} L _ {\\text {s m o o t h L 1}} + \\lambda_ {\\text {S S I M}} L _ {\\text {S S I M}} \\tag {16}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.282, + 0.892, + 0.343 + ], + "angle": 0, + "content": "Depth loss. Depth map labels are obtained by projecting associated LiDAR points onto the image plane. The depth loss is L1 loss between ground truth sparse depth map \\( Z \\) and predicted depth map \\( \\hat{Z} \\)," + }, + { + "type": "equation", + "bbox": [ + 0.584, + 0.353, + 0.892, + 0.389 + ], + "angle": 0, + "content": "\\[\nL _ {d e p t h} = \\frac {1}{N _ {d e p t h}} \\sum_ {u, v} \\left\\| \\hat {Z} - Z \\right\\| _ {1} \\tag {17}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.4, + 0.891, + 0.43 + ], + "angle": 0, + "content": "where \\(N_{depth}\\) denotes the number of valid pixels \\((u,v)\\) with LiDAR depth." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.431, + 0.892, + 0.461 + ], + "angle": 0, + "content": "SDF loss. The SDF loss encourages \\( F_{sdf} \\) to vanish on geometry surface \\( \\mathcal{M} \\)," + }, + { + "type": "equation", + "bbox": [ + 0.577, + 0.471, + 0.891, + 0.508 + ], + "angle": 0, + "content": "\\[\nL _ {s d f} = \\frac {1}{N _ {g t}} \\sum_ {x, y, z} \\left(\\left\\| F _ {s d f} (x, y, z) \\right\\| _ {2}\\right) \\tag {18}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.518, + 0.891, + 0.546 + ], + "angle": 0, + "content": "where \\(N_{gt}\\) denotes the number of LiDAR points in the current camera view." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.548, + 0.892, + 0.623 + ], + "angle": 0, + "content": "LIGA loss We denote the original loss in LIGA [19] as \\( L_{\\mathrm{LIGA}} \\). We keep the detection, imitation and auxiliary 2D supervision loss items but remove the stereo depth estimation item to fit the monocular setting. The imitation item is removed in all Waymo [52] experiments for convenience." + }, + { + "type": "equation", + "bbox": [ + 0.561, + 0.635, + 0.892, + 0.658 + ], + "angle": 0, + "content": "\\[\nL _ {\\text {L I G A - K I T T I}} = L _ {\\text {d e t}} + \\lambda_ {i m} L _ {i m} + \\lambda_ {2 d} L _ {2 d} \\tag {19}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.564, + 0.654, + 0.762, + 0.67 + ], + "angle": 0, + "content": "\\[\nL _ {\\text {L I G A - W a y m o}} = L _ {\\det} + \\lambda_ {2 d} L _ {2 d}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.702, + 0.633, + 0.719 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.727, + 0.692, + 0.741 + ], + "angle": 0, + "content": "5.1. Dataset and Metrics" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.9 + ], + "angle": 0, + "content": "KITTI. The KITTI dataset [17] comprises of 7,481 images in the training (trainval set) and 7,518 images in the testing (test set) with synchronized LiDAR point clouds. In previous works [11], the training images were split into a train set (3,712 samples) and a val set (3,769 samples). We also follow this setting. Results on the KITTI dataset [17] are measured using IoU-based criteria with a threshold of 0.7 to compute averaged precision over 40 recall values \\((AP|_{R40})\\) for the car class in both bird's-eye-view (BEV) and 3D tasks." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6819" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.137, + 0.089, + 0.833, + 0.301 + ], + "angle": 0, + "content": "
MethodsReferenceCategoryAPBEVAP3D
EasyModerateHardEasyModerateHard
D4LCN[16]CVPR20Pretained Depth22.5116.0212.5516.6511.729.51
DDMP-3D[53]CVPR2128.0817.8913.4419.7112.789.80
Ground-Aware[29]RAL21Directly Regress29.8117.9813.0821.6513.259.91
MonoRCNN[50]ICCV2125.4818.1114.1018.3612.6510.03
MonoEF[66]CVPR2129.0319.7017.2621.2913.8711.71
MonoRUn[9]CVPR21Geometric-based27.9417.3415.2419.6512.3010.58
GUPNet[31]ICCV2130.2921.1918.2022.2615.0213.12
MonoFlex[65]CVPR2128.2319.7516.8919.9413.8912.07
DCD[26]ECCV2232.5521.5018.2523.8115.9013.21
CaDDN[47]CVPR21LiDAR Auxiliary27.9418.9117.1919.1713.4111.46
DD3D[40]ICCV2130.9822.5620.0323.2216.3414.20
DID-M3D[43]ECCV2232.9522.7619.8324.4016.2913.75
MonoNeRD (ours)-31.1323.4620.9722.7517.1315.63
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.312, + 0.89, + 0.34 + ], + "angle": 0, + "content": "Table 1. Comparisons for Car category on KITTI test at IOU threshold 0.7. We obtain the values of other methods from respective papers. We use red to indicate the highest result and blue for the second-highest result. We can see that our method sets a new state of the art." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.365, + 0.47, + 0.515 + ], + "angle": 0, + "content": "Waymo. The Waymo Open Dataset [52] consists of 798 training sequences and 202 validation sequences. We follow the setting in CaDDN [47] which only considers the front camera and uses the sampled training set (51,564 samples). Results on Waymo val are measured by officially evaluation of the mean average precision (mAP) and the mean average precision weighted by heading (mAPH) with IoU criteria of 0.7 and 0.5. The evaluation is performed on two difficulty levels (Level_1 and Level_2) and three distance ranges (0 - 30m, 30m - 50m, 50m - \\(\\infty\\))." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.555, + 0.295, + 0.572 + ], + "angle": 0, + "content": "5.2. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.589, + 0.47, + 0.771 + ], + "angle": 0, + "content": "Training details. Our method is implemented with Pytorch [42] framework. We have done all experiments with four NVIDIA 3080Ti (12G) GPUs. The detector is trained using AdamW [30] optimizer with \\(\\beta_{1} = 0.9, \\beta_{2} = 0.999\\). The batch size is fixed to 4, with 1 sample on each GPU. On KITTI [17], the input size is fixed to \\(320 \\times 1248\\), we train 50 epochs using an initial learning rate of 0.001, and 10 epochs with a reduced learning rate of 0.0001, weight decay is 0.0001. On Waymo [52], the input size is fixed to \\(640 \\times 960\\), we train 16 epochs using an initial learning rate of 0.001, and 4 epochs with a reduced learning rate of 0.0001, weight decay is 0.0001." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Hyperparameters. On KITTI [17], we sample \\( D = 72 \\) planes within depth range \\( [z_{n}, z_{f}] = [2, 59.6] \\) (meter) in the frustum space. The voxel grid range is \\( [2, 59.6] \\times [-30.4, 30.4] \\times [-3, 1] \\) (meter) and voxel size is \\( [0.2, 0.2, 0.2] \\) (meter) for the depth, width, and height axis in 3D space, respectively. On Waymo [52] the voxel grid range is \\( [2, 59.6] \\times [-25.6, 25.6] \\times [-3, 1] \\) (meter) while all other hyperparameters are the same as KITTI experiments." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.365, + 0.64, + 0.38 + ], + "angle": 0, + "content": "5.3. Main Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.389, + 0.892, + 0.556 + ], + "angle": 0, + "content": "KITTI. Table 1 shows the main results of MonoNeRD on the KITTI test set. Our method is competitive with previous methods without any extra data. MonoNeRD achieves the best results under the Moderate and Hard settings in both \\(AP_{BEV}\\) and \\(AP_{3D}\\). Compared to DD3D [40], which uses a vast private dataset for depth pre-training, we boost the performance from 22.56/16.34 to 23.46/17.13 under moderate setting, and from 20.03/14.20 to 20.97/15.63 under hard setting for \\(AP_{BEV} / AP_{3D}\\), respectively. As for DID-M3D [43], we exceed it on both moderate and hard settings with 0.7/1.14 \\(AP_{BEV}\\) and 0.84/1.88 \\(AP_{3D}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.557, + 0.892, + 0.632 + ], + "angle": 0, + "content": "Waymo. Table 2 shows the main results of on the Waymo val set. MonoNeRD achieves competitive results without using data augmentation techniques. It has a lightweight backbone (ResNet34) compared to other depth-based methods like CaDDN (ResNet101) and DID-M3D (DLA34)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.634, + 0.892, + 0.695 + ], + "angle": 0, + "content": "The Results on both KITTI [17] hard and Waymo [52] distance ranges (30m - 50m, 50m - \\(\\infty\\)) demonstrate the superiority of our method in handling distant and occluded objects." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.71, + 0.665, + 0.725 + ], + "angle": 0, + "content": "5.4. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Architectural components. We conduct an ablation study on the car category in KITTI val to analyze the effectiveness of the proposed NeRF-like representations. In Table 3, Exp. (a) is the baseline which directly takes features sampled from \\( F_{P} \\) as voxel representations \\( V_{3d} \\) for M3D. In Exp. (b), we use more 3D convolution layers to prevent enhancements from complex model structures. Exp. (c) shows that supervision only from a single RGB image is useless and even harmful for detection since a purely single image cannot provide depth information. We can see that sparse depth map labels from LiDAR can significantly improve the per" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6820" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.09, + 0.088, + 0.885, + 0.311 + ], + "angle": 0, + "content": "
Methods3D mAP / mAPH (IoU = 0.7)3D mAP / mAPH (IoU = 0.5)
Overall0 - 30m30 - 50m50m - ∞Overall0 - 30m30 - 50m50m - ∞
LEVEL 1
PatchNet [32]0.39 / 0.371.67 / 1.630.13 / 0.120.03 / 0.032.92 / 2.7410.03 / 9.751.09 / 0.960.23 / 0.18
CaDDN [47]5.03 / 4.9914.54 / 14.431.47 / 1.450.10 / 0.1017.54 / 17.3145.00 / 44.469.24 / 9.110.64 / 0.62
PCT [54]0.89 / 0.883.18 / 3.150.27 / 0.270.07 / 0.074.20 / 4.1514.70 / 14.541.78 / 1.750.39 / 0.39
MonoJSG [27]0.97 / 0.954.65 / 4.590.55 / 0.530.10 / 0.095.65 / 5.4720.86 / 20.263.91 / 3.790.97 / 0.92
DEVIANT [24]2.69 / 2.676.95 / 6.900.99 / 0.980.02 / 0.0210.98 / 10.8926.85 / 26.645.13 / 5.080.18 / 0.18
DID-M3D [43]- / -- / -- / -- / -20.66 / 20.4740.92 / 40.6015.63 / 15.485.35 / 5.24
MonoNeRD (ours)10.66 / 10.5627.84 / 27.575.40 / 5.360.72 / 0.7131.18 / 30.7061.11 / 60.2826.08 / 25.716.60 / 6.47
LEVEL 2
PatchNet [32]0.38 / 0.361.67 / 1.630.13 / 0.110.03 / 0.032.42 / 2.2810.01 / 9.731.07 / 0.940.22 / 0.16
CaDDN [47]4.49 / 4.4514.50 / 14.381.42 / 1.410.09 / 0.0916.51 / 16.2844.87 / 44.338.99 / 8.860.58 / 0.55
PCT [54]0.66 / 0.663.18 / 3.150.27 / 0.260.07 / 0.074.03 / 3.9914.67 / 14.511.74 / 1.710.36 / 0.35
MonoJSG [27]0.91 / 0.894.64 / 4.650.55 / 0.530.09 / 0.095.34 / 5.1720.79 / 20.193.79 / 3.670.85 / 0.82
DEVIANT [24]2.52 / 2.506.93 / 6.870.95 / 0.940.02 / 0.0210.29 / 10.2026.75 / 26.544.95 / 4.900.16 / 0.16
DID-M3D [43]- / -- / -- / -- / -19.37 / 19.1940.77 / 40.4615.18 / 15.044.69 / 4.59
MonoNeRD (ours)10.03 / 9.9327.75 / 27.485.25 / 5.210.60 / 0.5929.29 / 28.8460.91 / 60.0825.36 / 25.005.77 / 5.66
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.321, + 0.872, + 0.335 + ], + "angle": 0, + "content": "Table 2. Results on Waymo val set. We obtain the values of other methods from their respective papers. Our method performs the best." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.36, + 0.47, + 0.422 + ], + "angle": 0, + "content": "formance of the detector from Exp. (d). The effectiveness of \\( L_{rgb} \\) can be revealed by comparing Exp. (d, e) or Exp. (f, g). Finally, SDF loss brings noticeable performance gains, especially on \\( AP_{BEV} \\)." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.435, + 0.47, + 0.523 + ], + "angle": 0, + "content": "
Exp.Setting\\(AP_{BEV}/AP_{3D}\\)
3D Conv.\\(L_{rgb}\\)\\(L_{depth}\\)\\(L_{sdf}\\)EasyModerateHard
(a)24.96 / 17.0119.27 / 13.3816.89 / 11.73
(b)✓25.64 / 17.2219.75 / 13.6518.01 / 11.99
(c)✓✓24.83 / 16.9219.10 / 13.1116.74 / 11.73
(d)✓✓26.91 / 18.7220.87 / 14.5418.57 / 12.60
(e)✓✓✓26.46 / 19.4420.16 / 15.0317.59 / 12.83
(f)✓✓✓27.94 / 20.2821.44 / 15.3218.82 / 13.48
(g)✓✓✓✓29.03 / 20.6422.03 / 15.4419.41 / 13.99
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.533, + 0.469, + 0.576 + ], + "angle": 0, + "content": "Table 3. Ablation of network structure and volume rendering loss. \"3D Conv\": 3D convolution blocks as mentioned in Section 4.1.2; \\(L_{(\\cdot)}\\): use the loss for supervision; \"Exp\": Experiment." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.592, + 0.47, + 0.713 + ], + "angle": 0, + "content": "Positional aware module. based on experiment (g) in Table 3, we replace the query-key-value (QKV) based positional aware module with the concatenation of positional features and back-projected image features. The results show a performance degradation in \\( AP_{BEV} \\) from 29.03/22.03/19.41 to 28.39/21.60/18.94, and in \\( AP_{3D} \\) from 20.64/15.44/13.99 to 19.73/15.16/12.94. This experiment demonstrates the effectiveness of the proposed design." + }, + { + "type": "table", + "bbox": [ + 0.11, + 0.726, + 0.438, + 0.771 + ], + "angle": 0, + "content": "
Exp.Pos.APBEV/AP3D
EasyModerateHard
1QKV29.03 / 20.6422.03 / 15.4419.41 / 13.99
2Cat.28.39 / 19.7321.60 / 15.1618.94 / 12.94
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.781, + 0.47, + 0.822 + ], + "angle": 0, + "content": "Table 4. Ablation of the position aware frustum. \"Pos:\": the injection method of positional information. \"Cat:\": positional feature concatenation." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.847, + 0.214, + 0.861 + ], + "angle": 0, + "content": "5.5. Visualization" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.901 + ], + "angle": 0, + "content": "In Figure 6, we replace the proposed representation with depth-transformed one used in previous works [12, 47] and" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.36, + 0.895, + 0.482 + ], + "angle": 0, + "content": "visualize them for comparison. For depth-transformed category, we first predict the depth map from the input RGB image and apply the same transformation as CaDDN [47] to get its 3D representation. We visualize such representation by back-projecting the estimated depth map to the 3D space. For the NeRF-like representation, we directly visualize the predicted 3D volume density. Our method produces dense and continuous geometry in the distance (as indicated" + }, + { + "type": "image", + "bbox": [ + 0.52, + 0.513, + 0.875, + 0.827 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.843, + 0.895, + 0.899 + ], + "angle": 0, + "content": "Figure 6. Visualization for depth-map-based representation and the proposed NeRF-like representation. From top to bottom: input image, NeRF-like representation, depth-map-based representation. Our method generates denser features for distant objects." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "6821" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.154 + ], + "angle": 0, + "content": "by the red box area). Due to space constraints, we provide additional quantitative and qualitative results in the Supplementary materials. Occupancy results are best viewed as videos, so we urge readers to view our supplementary video." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.169, + 0.197, + 0.185 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.195, + 0.473, + 0.392 + ], + "angle": 0, + "content": "In this paper, we explore how to optimize the intermediate 3D feature representations implicitly for monocular 3D object detection (M3D) without explicit binary occupancy annotations. We build a bridge between Neural Radiance Fields (NeRF) and 3D object detection, and propose a novel monocular 3D object detection framework, i.e. MonoNeRD, which produces continuous NeRF-like Representations for M3D. MonoNeRD treats intermediate 3D representations as SDF-based neural radiance fields and optimizes them using volume rendering techniques. Extensive experiments show that our method sets a new baseline for monocular 3D detection and has the potential to be extended to other 3D perception tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.392, + 0.473, + 0.5 + ], + "angle": 0, + "content": "Limitations and future work. The performance of our method is highly dependent on the modeling approaches. We are currently limited by the working with bounds modeling (see Section 3.3), which could fail to predict 3D occupancy when its 2D projected pixel represents sky or other things not within the specified bounds. We believe this is an interesting direction for future research." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.515, + 0.24, + 0.533 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.541, + 0.473, + 0.633 + ], + "angle": 0, + "content": "This work was supported in part by The National Nature Science Foundation of China (Grant Nos: 62273301, 62273302, 62273303, 62036009, 61936006), in part by the Key R&D Program of Zhejiang Province, China (2023C01135), and in part by Yongjiang Talent Introduction Programme (Grant No: 2022A-240-G)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.648, + 0.175, + 0.665 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.085, + 0.674, + 0.47, + 0.758 + ], + "angle": 0, + "content": "[1] Junaid Ahmed Ansari, Sarthak Sharma, Anshuman Majumdar, J Krishna Murthy, and K Madhava Krishna. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 7556-7566, 2021. 7" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.894, + 0.869 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6824" + } + ] +] \ No newline at end of file diff --git a/2023/MonoNeRD_ NeRF-like Representations for Monocular 3D Object Detection/63ab896a-8106-40c7-82f9-2e2b03ab3262_origin.pdf b/2023/MonoNeRD_ NeRF-like Representations for Monocular 3D Object Detection/63ab896a-8106-40c7-82f9-2e2b03ab3262_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..3db6f1d6692dd913f3720b66ab1b7472c328e979 --- /dev/null +++ b/2023/MonoNeRD_ NeRF-like Representations for Monocular 3D Object Detection/63ab896a-8106-40c7-82f9-2e2b03ab3262_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:bb11b1052cbfee6140926766e6dc0558cb5ea97a2b81d484e9304f00130d089b +size 2673119 diff --git a/2023/MonoNeRD_ NeRF-like Representations for Monocular 3D Object Detection/full.md b/2023/MonoNeRD_ NeRF-like Representations for Monocular 3D Object Detection/full.md new file mode 100644 index 0000000000000000000000000000000000000000..2e301f685a6acdcfcc4820702cb695dfb33a0c3e --- /dev/null +++ b/2023/MonoNeRD_ NeRF-like Representations for Monocular 3D Object Detection/full.md @@ -0,0 +1,398 @@ +# MonoNeRD: NeRF-like Representations for Monocular 3D Object Detection + +Junkai Xu $^{1,2*}$ Liang Peng $^{1,2,*}$ Haoran Chen $^{1,2,*}$ Hao Li $^{2}$ Wei Qian $^{2}$ Ke Li $^{4}$ Wenxiao Wang $^{3\dagger}$ Deng Cai $^{1,2}$ $^{1}$ State Key Lab of CAD & CG, Zhejiang University $^{2}$ FABU Inc. $^{3}$ School of Software Technology, Zhejiang University $^{4}$ Fullong Inc. {xujunkai, pengliang, haorancheng}@zju.edu.cn + +# Abstract + +In the field of monocular 3D detection, it is common practice to utilize scene geometric clues to enhance the detector's performance. However, many existing works adopt these clues explicitly such as estimating a depth map and back-projecting it into 3D space. This explicit methodology induces sparsity in 3D representations due to the increased dimensionality from 2D to 3D, and leads to substantial information loss, especially for distant and occluded objects. To alleviate this issue, we propose MonoNeRD, a novel detection framework that can infer dense 3D geometry and occupancy. Specifically, we model scenes with Signed Distance Functions (SDF), facilitating the production of dense 3D representations. We treat these representations as Neural Radiance Fields (NeRF) and then employ volume rendering to recover RGB images and depth maps. To the best of our knowledge, this work is the first to introduce volume rendering for M3D, and demonstrates the potential of implicit reconstruction for image-based 3D perception. Extensive experiments conducted on the KITTI-3D benchmark and Waymo Open Dataset demonstrate the effectiveness of MonoNeRD. Codes are available at https://github.com/cskkxjk/MonoNeRD. + +# 1. Introduction + +Monocular 3D detection (M3D) is an active research topic in the computer vision community due to its convenience, low cost and wide range of applications, including autonomous driving, robotic navigation and more. The key point of the task is to establish reasonable correspondences between 2D images and 3D space. Some works leverage geometrical priors to extract 3D information, such as object poses via 2D-3D constraints. These constraints usually require additional keypoint annotations [10, 21] or + +![](images/d54e9d1bda41287b5bc7206772dd6c3738e45cf114ae68ab79f6e2864daff70d.jpg) +Figure 1. Different intermediate 3D representations. Previous depth-based methods generate 3D representations by backprojecting estimated depth maps to 3D space, whereas our method predicts implicit 3D representations, and obtains depth estimates through volume rendering. + +CAD models [5, 34]. Other works convert estimated depth maps into 3D point cloud representations (Pseudo-LiDAR) [32, 55, 60]. Depth estimates are also used to combine with image features [58, 33] or generate meaningful bird's-eye-view (BEV) representations [45, 47, 48, 51], then produce 3D object detection results. These methods have made remarkable progress in M3D. + +Unfortunately, current 3D representations transformed by explicit depths have some limitations. First, the lifted features obtained from depth estimates or pseudo-LiDAR exhibit an uneven distribution throughout the 3D space. Specifically, they have high density in close range, but the density decreases as the distance increases. (See top part of Figure 1). Second, the final detection performance heavily depends on the accuracy of the depth estimation, which remains challenging to improve. Thus such representations + +cannot produce dense reasonable 3D features for M3D. + +Recent researches in Neural Radiance Fields (NeRF) [3, 38, 64] have shown the capability to reconstruct detailed and dense 3D scene geometry and occupancy information from posed images (images with known camera poses). Inspired by NeRF and its follow-ups [20, 25, 59], we reformulate the intermediate 3D representations in M3D to NeRF-like 3D representations, which can produce dense reasonable 3D geometry and occupancy. To achieve this goal, we combine extracted 2D backbone features and corresponding normalized frustum 3D coordinates to construct 3D Position-aware Frustum features (Section 4.1.1). These 3D features are used to create signed distance fields and radiance fields (RGB color). The signed distance fields encode the distance to the closest surface at every location as a scalar value. This allows us to model scenes implicitly by the zero-level set of the signed distance fields. (Section 3.1). We then adopt volume rendering [35] technique to generate RGB images and depth maps from the signed distance fields and radiance fields (Section 4.1.2), supervising them by original RGB images and LiDAR points (Section 4.2). While the previous depth-based methods generate 3D representations based on predicted depth maps, our method generates depth maps based on 3D representations (Figure 1). It is worth noting that our approach is capable of generating dense 3D occupancy (i.e., volume density) without requiring explicit binary occupancy annotations for individual voxels. Experiments on KITTI [17] 3D benchmark and Waymo Open Dataset [52] show the superiority of our NeRF-like representations in monocular 3D detection. + +Our main contributions are threefold: + +- We present a novel detection framework, named MonoNeRD, that connects Neural Radiance Fields and monocular 3D detection. It leverages NeRF-like continuous 3D representations to enable accurate 3D perception and understanding from a single image. +- We propose to use volume rendering to directly optimize 3D representations in detection tasks. To the best of our knowledge, our work is the first to introduce volume rendering for 3D detection tasks. +- Extensive experiments on KITTI [17] 3D detection benchmark and Waymo Open Dataset [52] demonstrate the effectiveness of our method, which is competitive with previous state-of-the-art works. This research presents the potential of 3D implicit reconstruction for image-based 3D perception. + +# 2. Related Work + +# 2.1. Monocular 3D Object Detection + +Many impressive researches [47, 9, 43] been done in monocular 3D object detection. As the essential informa + +tion of depth dimension is collapsed in the 2D image, it is an ill-posed but necessary problem of finding an approach to lift the 2D information to 3D space. + +Some Monocular 3D Object Detection methods lift 2D to 3D directly by incorporating the geometric relationship between the 2D image plane and 3D space. For example, many methods assume rigidity of objects, aligning 2D keypoints with their 3D counterparts [1, 2, 21, 46]. Some researchers try to build the bridge between 2D and 3D structures by template matching [5, 34]. These methods usually require additional data (e.g., 3D CAD models, object keypoint annotations). + +Other methods generate intermediate 3D representations to solve the lifting problem. Many approaches [60, 33, 32] convert the estimated depth map (always predicted by an off-the-shelf model) to pseudo-LiDAR point cloud representations, and then feed them to sophisticated LiDAR-based detectors. CaDDN [47] learns categorical depth distributions over pixels to lift camera images into 3D space, constructing BEV representations. Pseudo-Stereo [12] uses some sophisticated modules (e.g., stereo cost volume) to achieve better depth estimation. These methods typically involve estimating depth maps beforehand and subsequently extracting corresponding 3D representations from them. Instead, our method recovers depth maps from the 3D representations and supervises them to improve the detection performance. + +# 2.2. Neural Implicit Representations + +Representing 3D geometry with implicit functions has gained popularity in the past few years. Learning-based 3D reconstruction methods [13, 18, 36, 37, 41, 49] and their scene-level counterparts [6, 15, 23, 44] demonstrate compelling results but require 3D input and supervision. Neural Radiance Fields (NeRFs) [38] introduce a new perspective to learn continuous geometry representations from posed multi-view images only by volume rendering [35]. Due to the low efficiency of original MLP-based NeRF, their grid-based variants [22, 28, 61, 7] have been explored to accelerate the rendering process or save GPU memory. To circumvent the requirement of dense inputs, some works [62, 8, 14, 39] explicitly consider sparse input scenarios and show astonishing results for novel view synthesis, but these representations still need to be optimized per scene. Li et al. [25] propose MINE in which they combine Multiplane Images (MPI) and NeRF for single-image-based novel view synthesis. SceneRF [4] uses posed image sequences for training, alleviating the reliance on datasets. Wimbauer et al. [57] construct a density field to preform both depth prediction and novel view synthesis. Unlike our approach, the works mentioned primarily focus on the Novel View Synthesis task, requiring multi-view or sequenced images with camera poses as supervision, which cannot generalize to un + +seen scenes (except [25, 57]). Instead, we take advantage of volume rendering to optimize 3D feature representations and improve the performance in M3D task. + +# 3. Preliminaries + +Here we introduce some essential preliminaries for our idea. We use the same notation as [59] for the concepts of SDF and Volume density. Concerning the space limitation, here we provide a brief overview. Please refer to [38, 59, 35] for more details. + +# 3.1. Signed Distance Function (SDF) + +For a given spatial point, Signed Distance Function (SDF) is a continuous function that outputs the point's distance to the closest surface, whose sign indicates whether the point is inside (negative) or outside (positive) of the surface. + +Let $\mathbb{R}^3$ represent a 3D space containing some objects, $\Omega \subset \mathbb{R}^3$ refers to the occupied part, and $\mathcal{M} = \partial \Omega$ be the boundary surface. Denote the $\Omega$ indicator function by $\mathbf{1}_{\Omega}$ and the Signed Distance Function (SDF) by $d_{\Omega}$ , + +$$ +\mathbf {1} _ {\Omega} (\boldsymbol {x}) = \left\{ \begin{array}{l l} 1 & \text {i f} \boldsymbol {x} \in \Omega \\ 0 & \text {i f} \boldsymbol {x} \notin \Omega \end{array} \right. \tag {1} +$$ + +$$ +d _ {\Omega} (\boldsymbol {x}) = (- 1) ^ {\mathbf {1} _ {\Omega} (\boldsymbol {x})} \min _ {\boldsymbol {y} \in \mathcal {M}} \| \boldsymbol {x} - \boldsymbol {y} \| \tag {2} +$$ + +where $\| \cdot \|$ is the standard Euclidean 2-norm. The underlying surface $\mathcal{M}$ can be implicitly represented by the zero-level set of $d_{\Omega}(\cdot) = 0$ . + +# 3.2. Transform SDF to Density + +The volume density $\sigma : \mathbb{R}^3 \to \mathbb{R}_+$ is a scalar volumetric function, where $\sigma(x)$ can be interpreted as the probability that light is occluded at point $x$ . Previous works et al. [59, 63] suggest modeling the density $\sigma$ using a certain transformation of a learnable Signed Distance Function (SDF), as follows: + +$$ +\sigma (\boldsymbol {x}) = \alpha \Psi_ {\beta} (- d _ {\Omega} (\boldsymbol {x})) \tag {3} +$$ + +where $\alpha, \beta > 0$ are learnable parameters and $\Psi_{\beta}$ is the cumulative distribution function of the Laplace distribution with zero mean and $\beta$ scale, + +$$ +\Psi_ {\beta} (s) = \left\{ \begin{array}{l l} \frac {1}{2} \exp (\frac {s}{\beta}) & \text {i f} s \leq 0 \\ 1 - \frac {1}{2} \exp (- \frac {s}{\beta}) & \text {i f} s > 0 \end{array} \right. \tag {4} +$$ + +As $\beta$ approaches zero, the density $\sigma$ converges to scaled indicator function of $\Omega$ , means $\sigma \rightarrow \alpha \mathbf{1}_{\Omega}$ for all points $\pmb{x} \in \Omega \setminus \mathcal{M}$ . The benefits of modeling density in this way have been discussed in [59]. We simply set $\alpha = \beta^{-1}$ in our implementations. Figure 2 depicts an example of how density varies along SDF when a ray passes through an object. + +![](images/001a5110f01da076e14074d84991ba4ea353b229d26c28679b9dcfd6afa68a82.jpg) +Figure 2. Example of transformation from SDF to Density. The black arrow line represents a ray passing through a spherical object; the gradient color line describes how density varies along with SDF values by Equation 3, where we set $\beta = 0.01$ , $\alpha = \beta^{-1} = 100$ . + +# 3.3. Volume Rendering + +Volume intensity (RGB color) $\pmb{c} : \mathbb{R}^3 \to \mathbb{R}^3$ is a vector volumetric function of spatial position $\pmb{x}$ , where $\pmb{c}(x)$ represents the intensity or color at a certain point $\pmb{x}$ . Given color $c$ and density $\sigma$ , the expected color $C(\pmb{r})$ of ray $\pmb{r}(t) = \pmb{o} + t\pmb{d}$ (where $\pmb{o}$ and $\pmb{d}$ are the origin and direction of the ray respectively) with near and far bounds $t_n$ and $t_f$ is: + +$$ +\boldsymbol {C} (\boldsymbol {r}) = \int_ {t _ {n}} ^ {t _ {f}} \boldsymbol {T} (t) \sigma (\boldsymbol {r} (t)) \boldsymbol {c} (\boldsymbol {r} (t)) d t, \tag {5} +$$ + +$$ +\text {w h e r e} \boldsymbol {T} (t) = \exp \left(- \int_ {t _ {n}} ^ {t} \sigma (\boldsymbol {r} (s)) d s\right) +$$ + +where $\sigma$ refers to the volume density. The function $T(t)$ denotes the accumulated transmittance along the ray from $t_n$ to $t$ , namely, the probability that the ray (or light) travels from $t_n$ to $t$ without being occluded by any particle. In Section 4.1.2, we describe the details to calculate volume rendering numerical integration in our setup. + +# 4. Method + +Overview. The overall framework is illustrated in Figure 3. We follow the network design in LIGA-Stereo [19]. Note that the stereo part of LIGA-Stereo [19] is not applicable for monocular 3D detection (M3D) task. We replace the intermediate 3D feature representations with the proposed + +![](images/405ddffd09d22220912d25578b45b2bdcca3a90b2cb307beae5fa7503eb6a5f9.jpg) +Figure 3. Overview of MonoNeRD. "F. Voxel" and "D. Voxel" in the figure refer to Feature Voxel and Density Voxel, respectively. Position-Aware Frustum Features $F_{P}$ are generated from an image $I$ and Positional Frustum Features $F_{pos}$ in a query-based manner (Section 4.1.1), which are then transformed to 3D features $F''$ and signed distance fields $F_{sdf}$ . After that, the radiance fields $F_{rgb}$ are produced by $F''$ (Section 4.1.2). $F_{sdf}$ can be transformed to frustum volume density $F_{density}$ (Equation 3) by a scaled cumulative distribution function of Laplace distribution (Equation 4). Volume rendering from $F_{rgb}$ and $F_{density}$ provides supervision for such NeRF-like representations which generate voxel features $V_{3d}$ for M3D (Section 4.1.3). + +NeRF-like representations while keeping the 2D image backbone and downstream detection module unchanged. + +Given an input RGB image $I \in \mathbb{R}^{H \times W \times 3}$ , it is passed to a 2D image backbone for extracting image features. Then we use the 2D image features to generate the proposed NeRF-like 3D representations. Specifically, we first build the Position-aware Frustum (See Section 4.1.1), which is transformed to 3D frustum features and SDF frustum features. Such features can be used for obtaining RGB and density features to achieve rendered RGB images and depth maps via Volume Rendering (See Section 4.1.2). They are supervised by RGB loss and depth loss to guide previous features, serving as auxiliary tasks in training. Furthermore, we use grid-sampling on 3D frustum features and density frustum features to build regular 3D voxel features and corresponding density. They are used for forming 3D Voxel Features (See Section 4.1.3), which are fed into the detection modules. We elaborate on each part of our method in the following. + +# 4.1. NeRF-like Representation + +We need to clarify the difference between NeRF and the proposed NeRF-like representation. NeRF encodes a scene with a MLP and has to be trained per scene. The proposed method predicts continuous 3D geometry information from the single input RGB image. Similar ideas have been explored in researches about single-image-based novel view synthesis. Please refer to [20, 25] for details. + +# 4.1.1 Position-aware Frustum Construction + +To lift 2D backbone features to 3D space without depth, a naive manner is to simply repeat 2D features on different + +depth planes. However, this way does not contain any position information, causing ambiguous spatial features. To resolve this problem, we propose to generate position-aware frustum features. + +Taking an RGB image as input, the 2D image backbone produces image features $F_{image} \in \mathbb{R}^{H_{2d} \times W_{2d} \times C}$ , where $H_{2d}$ and $W_{2d}$ are the height and width of the 2D image feature map, and $C$ is the number of feature channels. Such 2D image features are mapped to a camera frustum along with corresponding normalized frustum 3D coordinates in a query-based manner. More specifically, given pre-defined near depth $z_{n}$ and far depth $z_{f}$ , we sample $D$ planes from this depth range under equal depth intervals with random perturbation as described in [38, 25]. Each depth plane consists of frustum 3D position coordinates $p: [u, v, z]^{T}$ of every pixel point $[u, v]^{T} \in \mathbb{R}^{2}$ . These coordinates are normalized later. Thus we have 3D positional frustum features $F_{pos} \in \mathbb{R}^{H_{2d} \times W_{2d} \times D \times 3}$ , where $D$ refers to the number of depth planes and 3 denotes the normalized coordinates. To combine 3D position and original 2D image features, we use three linear layers $f_{q}, f_{k}, f_{v}$ to do the Query-Key-Value mapping and attention calculation (in Figure 4). + +$$ +f _ {q}: F _ {p o s} \rightarrow Q \in \mathbb {R} ^ {H _ {2 d} \times W _ {2 d} \times D \times C} +$$ + +$$ +f _ {k}: F _ {\text {i m a g e}} \rightarrow K \in \mathbb {R} ^ {H _ {2 d} \times W _ {2 d} \times C} \tag {6} +$$ + +$$ +f _ {v}: F _ {i m a g e} \to V \in \mathbb {R} ^ {H _ {2 d} \times W _ {2 d} \times C} +$$ + +Therefore, the Position-Aware Frustum features can be calculated by a softmax function along the depth dimension. + +$$ +F _ {P} = \operatorname {S o f t m a x} (Q K, \dim = D) V \tag {7} +$$ + +![](images/91b6426e8e0a39b277fbce259f8a68f1565e0e5e4621b2d246b023c19d88a0f4.jpg) +Figure 4. The Query-Key-Value mapping procedure for constructing Position-Aware Frustum features. + +# 4.1.2 Volume Rendering within Frustum + +After constructing position-aware frustum features, we try to encode such features in 3D space to obtain more informative 3D features for volume rendering. Towards this goal, we employ two 3D convolution blocks $f_{1}$ and $f_{2}$ . $f_{1}$ consists of a three-layer 3D-convolution with kernel size 3 and softplus activation. It takes position-aware frustum features $F_{P} \in \mathbb{R}^{H_{2d} \times W_{2d} \times D \times C}$ as input, outputting a same shape feature $F'$ except the channel number, as follows: + +$$ +f _ {1}: F _ {P} \rightarrow F ^ {\prime} \in \mathbb {R} ^ {H _ {2 d} \times W _ {2 d} \times D \times (1 + C)} \tag {8} +$$ + +i) SDF and density features. The first channel feature in $F'$ is regarded as SDF feature $F_{sdf} \in \mathbb{R}^{H_{2d} \times W_{2d} \times D \times 1}$ . The signed distance fields $F_{sdf}$ represent the scene geometry of the input image. For any 3D point $[x, y, z]^T$ in frustum space, we can get its signed distance $s(x, y, z) \in \mathbb{R}^1$ by trilinear sampling in $F_{sdf}$ . Furthermore, scene volume density $\sigma$ (or density frustum $F_{density} \in \mathbb{R}^{H_{2d} \times W_{2d} \times D \times 1}$ ) can be transformed by Equation 3: + +$$ +\sigma (x, y, z) = \alpha \Psi_ {\beta} (s (x, y, z)) \tag {9} +$$ + +$$ +F _ {d e n s i t y} = \alpha \Psi_ {\beta} (F _ {s d f}) +$$ + +The density will be used for rendering depth maps and weighing the voxel features. + +ii) RGB features. The remaining $C$ channel feature in $F'$ , called $F''$ , is then passed to $f_{2}$ , which consists of a one-layer 3D-convolution with kernel size 3 and sigmoid activation. + +$$ +f _ {2}: F ^ {\prime \prime} \rightarrow F _ {r g b} \in \mathbb {R} ^ {H _ {2 d} \times W _ {2 d} \times D \times 3} \tag {10} +$$ + +The resulting feature is used for approximating the scene radiance field $F_{rgb}$ . We can also get color intensity $c(x,y,z) \in \mathbb{R}^3$ by trilinear sampling in $F_{rgb}$ . + +Rendering from original view. To save GPU memory, we render downsampled RGB image $\hat{I}_{low}$ and depth map $\hat{Z}_{low}$ . According to known camera calibration and multiple depth value $\{z_i | i = 1, \dots, D\}$ , a pixel point $[u, v]^T$ in $\hat{I}$ can be back-projected to several 3D point coordinates + +$\{[x_i,y_i,z_i]^T |i = 1,\dots ,D\}$ . We can calculate the distance between two successive 3D points as follows: + +$$ +\delta_ {x _ {i}, y _ {i}, z _ {i}} = \left\| \left[ x _ {i + 1}, y _ {i + 1}, z _ {i + 1} \right] ^ {T} - \left[ x _ {i}, y _ {i}, z _ {i} \right] ^ {T} \right\| _ {2} \tag {11} +$$ + +Denote the distance map at depth $z_{i}$ as $\delta_{z_i} \in \mathbb{R}^{H_{2d} \times W_{2d} \times 1}$ , we can easily get the density map $\sigma_{z_i} \in \mathbb{R}^{H_{2d} \times W_{2d} \times 1}$ from $F_{density}$ and color map $c_{z_i} \in \mathbb{R}^{H_{2d} \times W_{2d} \times 3}$ from $F_{rgb}$ . Then we can render $\hat{I}$ by: + +$$ +\hat {I} _ {\text {l o w}} = \sum_ {i = 1} ^ {D} T _ {i} \left(1 - \exp \left(- \sigma_ {z _ {i}} \delta_ {z _ {i}}\right)\right) c _ {z _ {i}}, \tag {12} +$$ + +where $T_{i} = \exp \left(-\sum_{j = 1}^{i - 1}\sigma_{z_{j}}\delta_{z_{j}}\right)$ denotes the accumulated transmittance map from plane 1 to plane $i$ . Similarly, the low resolution depth map $\hat{Z}_{low}\in \mathbb{R}^{H_{2d}\times W_{2d}\times 1}$ can be rendered by: + +$$ +\hat {Z} _ {\text {l o w}} (u, v) = \sum_ {i = 1} ^ {D} T _ {i} \left(1 - \exp \left(- \sigma_ {z _ {i}} \delta_ {z _ {i}}\right)\right) z _ {i} \tag {13} +$$ + +We simply upsample $\hat{I}_{low}$ and $\hat{Z}_{low}$ to original image resolution to get target image $\hat{I} \in \mathbb{R}^{H \times W \times 3}$ and depth map $\hat{Z} \in \mathbb{R}^{H \times W \times 1}$ . Such recovered RGB images and depth maps will be supervised by RGB loss and depth loss (See + +![](images/76ce98bc5c58cc0a12eff87d09ca4ac77c59e15327cb05f10d720039eac95a75.jpg) +Figure 5. Supervision from two RGB images by using volume rendering. We can obtain associated rendered RGB images from frustum density features $F_{\text{density}}$ and frustum radiance fields $F_{\text{rgb}}$ via Equation 12. Under this setting, we do not require explicit depth labels (i.e., LiDAR depths). Instead, the depth can be implicitly learned by calculating RGB reconstruction loss between original and rendered images. + +Section 4.2). They are used in training as auxiliary tasks to facilitate the learning process and can be discarded at the inference stage. + +Rendering from other views. Moreover, we can render from other views as long as such views' frustum overlaps with the original view's frustum and their camera calibrations are available. The rendered images can be produced in the same way described above. By calculating the image reconstruction loss from other views' rendered images, our NeRF-like representations can get extra supervisions. In Figure 5, we give an example of taking the stereo images (left and right images) in KITTI [17] as volume rendering targets. In this way, we can even eliminate the reliance on explicit depth supervisions. Considering the space limitation of the main text, we provided ablation of depth supervision in this supplementary material. + +# 4.1.3 Voxel Features Generation + +Aforementioned frustum features cannot be directly used for downstream detection modules as they are irregular in 3D space. Therefore, we must transform 3D frustum features to regular 3D voxel features. We perform this process of converting frustum to voxel just like CaDDN [47] by leveraging camera calibration and differentiable sampling. First, we define a voxel grid $V \in \mathbb{R}^{H_{3d} \times W_{3d} \times D_{3d} \times 3}$ , the sampling points $s_k^v = [x,y,z]_k^T$ are the center of each voxel. We can transform $s_k^v$ to get corresponding frustum sampling points $s_k^f = [u,v,d]_k^T$ according to the camera calibration matrix. Frustum features $(F'', F_{density})$ are sampled using sampling points $s_k^f$ with trilinear interpolation to inhabit voxel features $(V'', V_{density})$ . Different from [47], the spatial resolutions of the frustum grid and voxel grid are not required to be similar because $F_{sdf}$ and $F_{rgb}$ are not limited by spatial resolution. + +Considering that the density indicates 3D occupancy in the 3D space, we use it to enhance sampled 3D voxel features $V''$ . Specifically, we obtain the final 3D voxel features by: + +$$ +V _ {3 d} = V ^ {\prime \prime} \cdot \tanh \left(V _ {\text {d e n s i t y}}\right) \tag {14} +$$ + +where $\tanh (\cdot)$ is used to scale $V_{\text{density}}$ to the range of $[0,1]$ . $V_{3d}$ is a NeRF-like representation since it is optimized in the same way as NeRF to learn the implicit scene geometry and occupancy. + +# 4.2. Loss Function + +Equation 12 and 13 build connections between 3D scene representation and 2D observations (i.e., texture and depth). We can therefore optimize the 3D representations with raw 2D RGB images and depth maps. Based on this, there are four terms in the loss function: RGB loss $L_{rgb}$ , depth loss $L_{depth}$ , SDF loss $L_{sdf}$ , and the original loss in the baseline + +framework LIGA [19] $L_{\mathrm{LIGA}}$ . The overall loss is formulated as: + +$$ +L = \lambda_ {r g b} L _ {r g b} + \lambda_ {\text {d e p t h}} L _ {\text {d e p t h}} + \lambda_ {s d f} L _ {s d f} + \lambda_ {\mathrm {L I G A}} L _ {\mathrm {L I G A}}, \tag {15} +$$ + +where $\lambda_{rgb},\lambda_{depth},\lambda_{sdf},\lambda_{LIGA}$ are fixed loss weights. We empirically set all weights to 1 by default. + +RGB loss. The RGB loss consists of two items: Smooth L1 loss $L_{\mathrm{smoothL1}}$ and SSIM [56] loss $L_{\mathrm{SSIM}}$ which are usually used in image reconstruction: + +$$ +L _ {r g b} = \lambda_ {\text {s m o o t h L 1}} L _ {\text {s m o o t h L 1}} + \lambda_ {\text {S S I M}} L _ {\text {S S I M}} \tag {16} +$$ + +Depth loss. Depth map labels are obtained by projecting associated LiDAR points onto the image plane. The depth loss is L1 loss between ground truth sparse depth map $Z$ and predicted depth map $\hat{Z}$ , + +$$ +L _ {d e p t h} = \frac {1}{N _ {d e p t h}} \sum_ {u, v} \left\| \hat {Z} - Z \right\| _ {1} \tag {17} +$$ + +where $N_{depth}$ denotes the number of valid pixels $(u,v)$ with LiDAR depth. + +SDF loss. The SDF loss encourages $F_{sdf}$ to vanish on geometry surface $\mathcal{M}$ , + +$$ +L _ {s d f} = \frac {1}{N _ {g t}} \sum_ {x, y, z} \left(\left\| F _ {s d f} (x, y, z) \right\| _ {2}\right) \tag {18} +$$ + +where $N_{gt}$ denotes the number of LiDAR points in the current camera view. + +LIGA loss We denote the original loss in LIGA [19] as $L_{\mathrm{LIGA}}$ . We keep the detection, imitation and auxiliary 2D supervision loss items but remove the stereo depth estimation item to fit the monocular setting. The imitation item is removed in all Waymo [52] experiments for convenience. + +$$ +L _ {\text {L I G A - K I T T I}} = L _ {\text {d e t}} + \lambda_ {i m} L _ {i m} + \lambda_ {2 d} L _ {2 d} \tag {19} +$$ + +$$ +L _ {\text {L I G A - W a y m o}} = L _ {\det} + \lambda_ {2 d} L _ {2 d} +$$ + +# 5. Experiments + +# 5.1. Dataset and Metrics + +KITTI. The KITTI dataset [17] comprises of 7,481 images in the training (trainval set) and 7,518 images in the testing (test set) with synchronized LiDAR point clouds. In previous works [11], the training images were split into a train set (3,712 samples) and a val set (3,769 samples). We also follow this setting. Results on the KITTI dataset [17] are measured using IoU-based criteria with a threshold of 0.7 to compute averaged precision over 40 recall values $(AP|_{R40})$ for the car class in both bird's-eye-view (BEV) and 3D tasks. + +
MethodsReferenceCategoryAPBEVAP3D
EasyModerateHardEasyModerateHard
D4LCN[16]CVPR20Pretained Depth22.5116.0212.5516.6511.729.51
DDMP-3D[53]CVPR2128.0817.8913.4419.7112.789.80
Ground-Aware[29]RAL21Directly Regress29.8117.9813.0821.6513.259.91
MonoRCNN[50]ICCV2125.4818.1114.1018.3612.6510.03
MonoEF[66]CVPR2129.0319.7017.2621.2913.8711.71
MonoRUn[9]CVPR21Geometric-based27.9417.3415.2419.6512.3010.58
GUPNet[31]ICCV2130.2921.1918.2022.2615.0213.12
MonoFlex[65]CVPR2128.2319.7516.8919.9413.8912.07
DCD[26]ECCV2232.5521.5018.2523.8115.9013.21
CaDDN[47]CVPR21LiDAR Auxiliary27.9418.9117.1919.1713.4111.46
DD3D[40]ICCV2130.9822.5620.0323.2216.3414.20
DID-M3D[43]ECCV2232.9522.7619.8324.4016.2913.75
MonoNeRD (ours)-31.1323.4620.9722.7517.1315.63
+ +Table 1. Comparisons for Car category on KITTI test at IOU threshold 0.7. We obtain the values of other methods from respective papers. We use red to indicate the highest result and blue for the second-highest result. We can see that our method sets a new state of the art. + +Waymo. The Waymo Open Dataset [52] consists of 798 training sequences and 202 validation sequences. We follow the setting in CaDDN [47] which only considers the front camera and uses the sampled training set (51,564 samples). Results on Waymo val are measured by officially evaluation of the mean average precision (mAP) and the mean average precision weighted by heading (mAPH) with IoU criteria of 0.7 and 0.5. The evaluation is performed on two difficulty levels (Level_1 and Level_2) and three distance ranges (0 - 30m, 30m - 50m, 50m - $\infty$ ). + +# 5.2. Implementation Details + +Training details. Our method is implemented with Pytorch [42] framework. We have done all experiments with four NVIDIA 3080Ti (12G) GPUs. The detector is trained using AdamW [30] optimizer with $\beta_{1} = 0.9, \beta_{2} = 0.999$ . The batch size is fixed to 4, with 1 sample on each GPU. On KITTI [17], the input size is fixed to $320 \times 1248$ , we train 50 epochs using an initial learning rate of 0.001, and 10 epochs with a reduced learning rate of 0.0001, weight decay is 0.0001. On Waymo [52], the input size is fixed to $640 \times 960$ , we train 16 epochs using an initial learning rate of 0.001, and 4 epochs with a reduced learning rate of 0.0001, weight decay is 0.0001. + +Hyperparameters. On KITTI [17], we sample $D = 72$ planes within depth range $[z_{n}, z_{f}] = [2, 59.6]$ (meter) in the frustum space. The voxel grid range is $[2, 59.6] \times [-30.4, 30.4] \times [-3, 1]$ (meter) and voxel size is $[0.2, 0.2, 0.2]$ (meter) for the depth, width, and height axis in 3D space, respectively. On Waymo [52] the voxel grid range is $[2, 59.6] \times [-25.6, 25.6] \times [-3, 1]$ (meter) while all other hyperparameters are the same as KITTI experiments. + +# 5.3. Main Results + +KITTI. Table 1 shows the main results of MonoNeRD on the KITTI test set. Our method is competitive with previous methods without any extra data. MonoNeRD achieves the best results under the Moderate and Hard settings in both $AP_{BEV}$ and $AP_{3D}$ . Compared to DD3D [40], which uses a vast private dataset for depth pre-training, we boost the performance from 22.56/16.34 to 23.46/17.13 under moderate setting, and from 20.03/14.20 to 20.97/15.63 under hard setting for $AP_{BEV} / AP_{3D}$ , respectively. As for DID-M3D [43], we exceed it on both moderate and hard settings with 0.7/1.14 $AP_{BEV}$ and 0.84/1.88 $AP_{3D}$ . + +Waymo. Table 2 shows the main results of on the Waymo val set. MonoNeRD achieves competitive results without using data augmentation techniques. It has a lightweight backbone (ResNet34) compared to other depth-based methods like CaDDN (ResNet101) and DID-M3D (DLA34). + +The Results on both KITTI [17] hard and Waymo [52] distance ranges (30m - 50m, 50m - $\infty$ ) demonstrate the superiority of our method in handling distant and occluded objects. + +# 5.4. Ablation Studies + +Architectural components. We conduct an ablation study on the car category in KITTI val to analyze the effectiveness of the proposed NeRF-like representations. In Table 3, Exp. (a) is the baseline which directly takes features sampled from $F_{P}$ as voxel representations $V_{3d}$ for M3D. In Exp. (b), we use more 3D convolution layers to prevent enhancements from complex model structures. Exp. (c) shows that supervision only from a single RGB image is useless and even harmful for detection since a purely single image cannot provide depth information. We can see that sparse depth map labels from LiDAR can significantly improve the per + +
Methods3D mAP / mAPH (IoU = 0.7)3D mAP / mAPH (IoU = 0.5)
Overall0 - 30m30 - 50m50m - ∞Overall0 - 30m30 - 50m50m - ∞
LEVEL 1
PatchNet [32]0.39 / 0.371.67 / 1.630.13 / 0.120.03 / 0.032.92 / 2.7410.03 / 9.751.09 / 0.960.23 / 0.18
CaDDN [47]5.03 / 4.9914.54 / 14.431.47 / 1.450.10 / 0.1017.54 / 17.3145.00 / 44.469.24 / 9.110.64 / 0.62
PCT [54]0.89 / 0.883.18 / 3.150.27 / 0.270.07 / 0.074.20 / 4.1514.70 / 14.541.78 / 1.750.39 / 0.39
MonoJSG [27]0.97 / 0.954.65 / 4.590.55 / 0.530.10 / 0.095.65 / 5.4720.86 / 20.263.91 / 3.790.97 / 0.92
DEVIANT [24]2.69 / 2.676.95 / 6.900.99 / 0.980.02 / 0.0210.98 / 10.8926.85 / 26.645.13 / 5.080.18 / 0.18
DID-M3D [43]- / -- / -- / -- / -20.66 / 20.4740.92 / 40.6015.63 / 15.485.35 / 5.24
MonoNeRD (ours)10.66 / 10.5627.84 / 27.575.40 / 5.360.72 / 0.7131.18 / 30.7061.11 / 60.2826.08 / 25.716.60 / 6.47
LEVEL 2
PatchNet [32]0.38 / 0.361.67 / 1.630.13 / 0.110.03 / 0.032.42 / 2.2810.01 / 9.731.07 / 0.940.22 / 0.16
CaDDN [47]4.49 / 4.4514.50 / 14.381.42 / 1.410.09 / 0.0916.51 / 16.2844.87 / 44.338.99 / 8.860.58 / 0.55
PCT [54]0.66 / 0.663.18 / 3.150.27 / 0.260.07 / 0.074.03 / 3.9914.67 / 14.511.74 / 1.710.36 / 0.35
MonoJSG [27]0.91 / 0.894.64 / 4.650.55 / 0.530.09 / 0.095.34 / 5.1720.79 / 20.193.79 / 3.670.85 / 0.82
DEVIANT [24]2.52 / 2.506.93 / 6.870.95 / 0.940.02 / 0.0210.29 / 10.2026.75 / 26.544.95 / 4.900.16 / 0.16
DID-M3D [43]- / -- / -- / -- / -19.37 / 19.1940.77 / 40.4615.18 / 15.044.69 / 4.59
MonoNeRD (ours)10.03 / 9.9327.75 / 27.485.25 / 5.210.60 / 0.5929.29 / 28.8460.91 / 60.0825.36 / 25.005.77 / 5.66
+ +formance of the detector from Exp. (d). The effectiveness of $L_{rgb}$ can be revealed by comparing Exp. (d, e) or Exp. (f, g). Finally, SDF loss brings noticeable performance gains, especially on $AP_{BEV}$ . + +Table 2. Results on Waymo val set. We obtain the values of other methods from their respective papers. Our method performs the best. + +
Exp.Setting\(AP_{BEV}/AP_{3D}\)
3D Conv.\(L_{rgb}\)\(L_{depth}\)\(L_{sdf}\)EasyModerateHard
(a)24.96 / 17.0119.27 / 13.3816.89 / 11.73
(b)✓25.64 / 17.2219.75 / 13.6518.01 / 11.99
(c)✓✓24.83 / 16.9219.10 / 13.1116.74 / 11.73
(d)✓✓26.91 / 18.7220.87 / 14.5418.57 / 12.60
(e)✓✓✓26.46 / 19.4420.16 / 15.0317.59 / 12.83
(f)✓✓✓27.94 / 20.2821.44 / 15.3218.82 / 13.48
(g)✓✓✓✓29.03 / 20.6422.03 / 15.4419.41 / 13.99
+ +Positional aware module. based on experiment (g) in Table 3, we replace the query-key-value (QKV) based positional aware module with the concatenation of positional features and back-projected image features. The results show a performance degradation in $AP_{BEV}$ from 29.03/22.03/19.41 to 28.39/21.60/18.94, and in $AP_{3D}$ from 20.64/15.44/13.99 to 19.73/15.16/12.94. This experiment demonstrates the effectiveness of the proposed design. + +Table 3. Ablation of network structure and volume rendering loss. "3D Conv": 3D convolution blocks as mentioned in Section 4.1.2; $L_{(\cdot)}$ : use the loss for supervision; "Exp": Experiment. + +
Exp.Pos.APBEV/AP3D
EasyModerateHard
1QKV29.03 / 20.6422.03 / 15.4419.41 / 13.99
2Cat.28.39 / 19.7321.60 / 15.1618.94 / 12.94
+ +Table 4. Ablation of the position aware frustum. "Pos:": the injection method of positional information. "Cat:": positional feature concatenation. + +# 5.5. Visualization + +In Figure 6, we replace the proposed representation with depth-transformed one used in previous works [12, 47] and + +visualize them for comparison. For depth-transformed category, we first predict the depth map from the input RGB image and apply the same transformation as CaDDN [47] to get its 3D representation. We visualize such representation by back-projecting the estimated depth map to the 3D space. For the NeRF-like representation, we directly visualize the predicted 3D volume density. Our method produces dense and continuous geometry in the distance (as indicated + +![](images/543387f9c840c173bcb878b09a56d1974a312344817d6d6293b8a7467057c404.jpg) +Figure 6. Visualization for depth-map-based representation and the proposed NeRF-like representation. From top to bottom: input image, NeRF-like representation, depth-map-based representation. Our method generates denser features for distant objects. + +by the red box area). Due to space constraints, we provide additional quantitative and qualitative results in the Supplementary materials. Occupancy results are best viewed as videos, so we urge readers to view our supplementary video. + +# 6. Conclusion + +In this paper, we explore how to optimize the intermediate 3D feature representations implicitly for monocular 3D object detection (M3D) without explicit binary occupancy annotations. We build a bridge between Neural Radiance Fields (NeRF) and 3D object detection, and propose a novel monocular 3D object detection framework, i.e. MonoNeRD, which produces continuous NeRF-like Representations for M3D. MonoNeRD treats intermediate 3D representations as SDF-based neural radiance fields and optimizes them using volume rendering techniques. Extensive experiments show that our method sets a new baseline for monocular 3D detection and has the potential to be extended to other 3D perception tasks. + +Limitations and future work. The performance of our method is highly dependent on the modeling approaches. We are currently limited by the working with bounds modeling (see Section 3.3), which could fail to predict 3D occupancy when its 2D projected pixel represents sky or other things not within the specified bounds. We believe this is an interesting direction for future research. + +# Acknowledgement + +This work was supported in part by The National Nature Science Foundation of China (Grant Nos: 62273301, 62273302, 62273303, 62036009, 61936006), in part by the Key R&D Program of Zhejiang Province, China (2023C01135), and in part by Yongjiang Talent Introduction Programme (Grant No: 2022A-240-G). + +# References + +[1] Junaid Ahmed Ansari, Sarthak Sharma, Anshuman Majumdar, J Krishna Murthy, and K Madhava Krishna. 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In Proceedings of the IEEE/CVF conference on computer vision and pattern recognition, pages 2446-2454, 2020. 2, 6, 7 +[53] Li Wang, Liang Du, Xiaqing Ye, Yanwei Fu, Guodong Guo, Xiangyang Xue, Jianfeng Feng, and Li Zhang. Depth-conditioned dynamic message propagation for monocular 3d object detection. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 454-463, 2021. 7 + +[54] Li Wang, Li Zhang, Yi Zhu, Zhi Zhang, Tong He, Mu Li, and Xiangyang Xue. Progressive coordinate transforms for monocular 3d object detection. Advances in Neural Information Processing Systems, 34:13364-13377, 2021. 8 +[55] Yan Wang, Wei-Lun Chao, Divyansh Garg, Bharath Hariharan, Mark Campbell, and Kilian Q Weinberger. Pseudolidar from visual depth estimation: Bridging the gap in 3d object detection for autonomous driving. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 8445-8453, 2019. 1 +[56] Zhou Wang, Alan C Bovik, Hamid R Sheikh, and Eero P Simoncelli. Image quality assessment: from error visibility to structural similarity. IEEE transactions on image processing, 13(4):600-612, 2004. 6 +[57] Felix Wimbauer, Nan Yang, Christian Rupprecht, and Daniel Cremers. Behind the scenes: Density fields for single view reconstruction. arXiv preprint arXiv:2301.07668, 2023. 2, 3 +[58] Bin Xu and Zhenzhong Chen. Multi-level fusion based 3d object detection from monocular images. In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 2345-2353, 2018. 1 +[59] Lior Yariv, Jiatao Gu, Yoni Kasten, and Yaron Lipman. Volume rendering of neural implicit surfaces. Advances in Neural Information Processing Systems, 34:4805-4815, 2021. 2, 3 +[60] Yurong You, Yan Wang, Wei-Lun Chao, Divyansh Garg, Geoff Pleiss, Bharath Hariharan, Mark Campbell, and Kilian Q Weinberger. Pseudo-lidar++: Accurate depth for 3d object detection in autonomous driving. arXiv preprint arXiv:1906.06310, 2019. 1, 2 +[61] Alex Yu, Ruilong Li, Matthew Tancik, Hao Li, Ren Ng, and Angjoo Kanazawa. Plenoctrees for real-time rendering of neural radiance fields. In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 5752-5761, 2021. 2 +[62] Alex Yu, Vickie Ye, Matthew Tancik, and Angjoo Kanazawa. pixelnerf: Neural radiance fields from one or few images. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 4578-4587, 2021. 2 +[63] Zehao Yu, Songyou Peng, Michael Niemeyer, Torsten Sattler, and Andreas Geiger. Monosdf: Exploring monocular geometric cues for neural implicit surface reconstruction. arXiv preprint arXiv:2206.00665, 2022. 3 +[64] Kai Zhang, Gernot Riegler, Noah Snavely, and Vladlen Koltun. Nerf++: Analyzing and improving neural radiance fields. arXiv preprint arXiv:2010.07492, 2020. 2 +[65] Yunpeng Zhang, Jiwen Lu, and Jie Zhou. Objects are different: Flexible monocular 3d object detection. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 3289-3298, 2021. 7 +[66] Yunsong Zhou, Yuan He, Hongzi Zhu, Cheng Wang, Hongyang Li, and Qinhong Jiang. Monocular 3d object detection: An extrinsic parameter free approach. 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However, many existing works adopt these clues explicitly such as estimating a depth map and back-projecting it into 3D space. This explicit methodology induces sparsity in 3D representations due to the increased dimensionality from 2D to 3D, and leads to substantial information loss, especially for distant and occluded objects. To alleviate this issue, we propose MonoNeRD, a novel detection framework that can infer dense 3D geometry and occupancy. Specifically, we model scenes with Signed Distance Functions (SDF), facilitating the production of dense 3D representations. We treat these representations as Neural Radiance Fields (NeRF) and then employ volume rendering to recover RGB images and depth maps. To the best of our knowledge, this work is the first to introduce volume rendering for M3D, and demonstrates the potential of implicit reconstruction for image-based 3D perception. Extensive experiments conducted on the KITTI-3D benchmark and Waymo Open Dataset demonstrate the effectiveness of MonoNeRD. Codes are available at https://github.com/cskkxjk/MonoNeRD." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 555, + 128, + 567 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 555, + 128, + 567 + ], + "spans": [ + { + "bbox": [ + 47, + 555, + 128, + 567 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 575, + 287, + 684 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 575, + 287, + 684 + ], + "spans": [ + { + "bbox": [ + 46, + 575, + 287, + 684 + ], + "type": "text", + "content": "Monocular 3D detection (M3D) is an active research topic in the computer vision community due to its convenience, low cost and wide range of applications, including autonomous driving, robotic navigation and more. The key point of the task is to establish reasonable correspondences between 2D images and 3D space. Some works leverage geometrical priors to extract 3D information, such as object poses via 2D-3D constraints. These constraints usually require additional keypoint annotations [10, 21] or" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 336, + 243, + 520, + 423 + ], + "blocks": [ + { + "bbox": [ + 336, + 243, + 520, + 423 + ], + "lines": [ + { + "bbox": [ + 336, + 243, + 520, + 423 + ], + "spans": [ + { + "bbox": [ + 336, + 243, + 520, + 423 + ], + "type": "image", + "image_path": "d54e9d1bda41287b5bc7206772dd6c3738e45cf114ae68ab79f6e2864daff70d.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 436, + 547, + 491 + ], + "lines": [ + { + "bbox": [ + 304, + 436, + 547, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 436, + 547, + 491 + ], + "type": "text", + "content": "Figure 1. Different intermediate 3D representations. Previous depth-based methods generate 3D representations by backprojecting estimated depth maps to 3D space, whereas our method predicts implicit 3D representations, and obtains depth estimates through volume rendering." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 518, + 547, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 518, + 547, + 602 + ], + "spans": [ + { + "bbox": [ + 304, + 518, + 547, + 602 + ], + "type": "text", + "content": "CAD models [5, 34]. Other works convert estimated depth maps into 3D point cloud representations (Pseudo-LiDAR) [32, 55, 60]. Depth estimates are also used to combine with image features [58, 33] or generate meaningful bird's-eye-view (BEV) representations [45, 47, 48, 51], then produce 3D object detection results. These methods have made remarkable progress in M3D." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "content": "Unfortunately, current 3D representations transformed by explicit depths have some limitations. First, the lifted features obtained from depth estimates or pseudo-LiDAR exhibit an uneven distribution throughout the 3D space. Specifically, they have high density in close range, but the density decreases as the distance increases. (See top part of Figure 1). Second, the final detection performance heavily depends on the accuracy of the depth estimation, which remains challenging to improve. Thus such representations" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 693, + 228, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 693, + 228, + 703 + ], + "spans": [ + { + "bbox": [ + 58, + 693, + 228, + 703 + ], + "type": "text", + "content": "*Work performed during an internship at FABU Inc." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 59, + 703, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 703, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 59, + 703, + 135, + 712 + ], + "type": "text", + "content": "† Corresponding author" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6814" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 271, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 271, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 271, + 83 + ], + "type": "text", + "content": "cannot produce dense reasonable 3D features for M3D." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 84, + 289, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 84, + 289, + 430 + ], + "spans": [ + { + "bbox": [ + 46, + 84, + 289, + 430 + ], + "type": "text", + "content": "Recent researches in Neural Radiance Fields (NeRF) [3, 38, 64] have shown the capability to reconstruct detailed and dense 3D scene geometry and occupancy information from posed images (images with known camera poses). Inspired by NeRF and its follow-ups [20, 25, 59], we reformulate the intermediate 3D representations in M3D to NeRF-like 3D representations, which can produce dense reasonable 3D geometry and occupancy. To achieve this goal, we combine extracted 2D backbone features and corresponding normalized frustum 3D coordinates to construct 3D Position-aware Frustum features (Section 4.1.1). These 3D features are used to create signed distance fields and radiance fields (RGB color). The signed distance fields encode the distance to the closest surface at every location as a scalar value. This allows us to model scenes implicitly by the zero-level set of the signed distance fields. (Section 3.1). We then adopt volume rendering [35] technique to generate RGB images and depth maps from the signed distance fields and radiance fields (Section 4.1.2), supervising them by original RGB images and LiDAR points (Section 4.2). While the previous depth-based methods generate 3D representations based on predicted depth maps, our method generates depth maps based on 3D representations (Figure 1). It is worth noting that our approach is capable of generating dense 3D occupancy (i.e., volume density) without requiring explicit binary occupancy annotations for individual voxels. Experiments on KITTI [17] 3D benchmark and Waymo Open Dataset [52] show the superiority of our NeRF-like representations in monocular 3D detection." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 431, + 211, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 431, + 211, + 441 + ], + "spans": [ + { + "bbox": [ + 59, + 431, + 211, + 441 + ], + "type": "text", + "content": "Our main contributions are threefold:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 449, + 287, + 642 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 58, + 449, + 287, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 449, + 287, + 509 + ], + "spans": [ + { + "bbox": [ + 58, + 449, + 287, + 509 + ], + "type": "text", + "content": "- We present a novel detection framework, named MonoNeRD, that connects Neural Radiance Fields and monocular 3D detection. It leverages NeRF-like continuous 3D representations to enable accurate 3D perception and understanding from a single image." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 515, + 287, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 515, + 287, + 563 + ], + "spans": [ + { + "bbox": [ + 58, + 515, + 287, + 563 + ], + "type": "text", + "content": "- We propose to use volume rendering to directly optimize 3D representations in detection tasks. To the best of our knowledge, our work is the first to introduce volume rendering for 3D detection tasks." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 570, + 287, + 642 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 570, + 287, + 642 + ], + "spans": [ + { + "bbox": [ + 58, + 570, + 287, + 642 + ], + "type": "text", + "content": "- Extensive experiments on KITTI [17] 3D detection benchmark and Waymo Open Dataset [52] demonstrate the effectiveness of our method, which is competitive with previous state-of-the-art works. This research presents the potential of 3D implicit reconstruction for image-based 3D perception." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 651, + 134, + 662 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 651, + 134, + 662 + ], + "spans": [ + { + "bbox": [ + 47, + 651, + 134, + 662 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 671, + 219, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 219, + 683 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 219, + 683 + ], + "type": "text", + "content": "2.1. Monocular 3D Object Detection" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "Many impressive researches [47, 9, 43] been done in monocular 3D object detection. As the essential informa" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": "tion of depth dimension is collapsed in the 2D image, it is an ill-posed but necessary problem of finding an approach to lift the 2D information to 3D space." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 109, + 545, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 109, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 304, + 109, + 545, + 216 + ], + "type": "text", + "content": "Some Monocular 3D Object Detection methods lift 2D to 3D directly by incorporating the geometric relationship between the 2D image plane and 3D space. For example, many methods assume rigidity of objects, aligning 2D keypoints with their 3D counterparts [1, 2, 21, 46]. Some researchers try to build the bridge between 2D and 3D structures by template matching [5, 34]. These methods usually require additional data (e.g., 3D CAD models, object keypoint annotations)." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 217, + 546, + 397 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 217, + 546, + 397 + ], + "spans": [ + { + "bbox": [ + 304, + 217, + 546, + 397 + ], + "type": "text", + "content": "Other methods generate intermediate 3D representations to solve the lifting problem. Many approaches [60, 33, 32] convert the estimated depth map (always predicted by an off-the-shelf model) to pseudo-LiDAR point cloud representations, and then feed them to sophisticated LiDAR-based detectors. CaDDN [47] learns categorical depth distributions over pixels to lift camera images into 3D space, constructing BEV representations. Pseudo-Stereo [12] uses some sophisticated modules (e.g., stereo cost volume) to achieve better depth estimation. These methods typically involve estimating depth maps beforehand and subsequently extracting corresponding 3D representations from them. Instead, our method recovers depth maps from the 3D representations and supervises them to improve the detection performance." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 407, + 479, + 419 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 407, + 479, + 419 + ], + "spans": [ + { + "bbox": [ + 306, + 407, + 479, + 419 + ], + "type": "text", + "content": "2.2. Neural Implicit Representations" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 426, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 547, + 715 + ], + "type": "text", + "content": "Representing 3D geometry with implicit functions has gained popularity in the past few years. Learning-based 3D reconstruction methods [13, 18, 36, 37, 41, 49] and their scene-level counterparts [6, 15, 23, 44] demonstrate compelling results but require 3D input and supervision. Neural Radiance Fields (NeRFs) [38] introduce a new perspective to learn continuous geometry representations from posed multi-view images only by volume rendering [35]. Due to the low efficiency of original MLP-based NeRF, their grid-based variants [22, 28, 61, 7] have been explored to accelerate the rendering process or save GPU memory. To circumvent the requirement of dense inputs, some works [62, 8, 14, 39] explicitly consider sparse input scenarios and show astonishing results for novel view synthesis, but these representations still need to be optimized per scene. Li et al. [25] propose MINE in which they combine Multiplane Images (MPI) and NeRF for single-image-based novel view synthesis. SceneRF [4] uses posed image sequences for training, alleviating the reliance on datasets. Wimbauer et al. [57] construct a density field to preform both depth prediction and novel view synthesis. Unlike our approach, the works mentioned primarily focus on the Novel View Synthesis task, requiring multi-view or sequenced images with camera poses as supervision, which cannot generalize to un" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6815" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "content": "seen scenes (except [25, 57]). Instead, we take advantage of volume rendering to optimize 3D feature representations and improve the performance in M3D task." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 118, + 133, + 131 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 118, + 133, + 131 + ], + "spans": [ + { + "bbox": [ + 47, + 118, + 133, + 131 + ], + "type": "text", + "content": "3. Preliminaries" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 138, + 288, + 197 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 138, + 288, + 197 + ], + "spans": [ + { + "bbox": [ + 46, + 138, + 288, + 197 + ], + "type": "text", + "content": "Here we introduce some essential preliminaries for our idea. We use the same notation as [59] for the concepts of SDF and Volume density. Concerning the space limitation, here we provide a brief overview. Please refer to [38, 59, 35] for more details." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 204, + 220, + 217 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 204, + 220, + 217 + ], + "spans": [ + { + "bbox": [ + 47, + 204, + 220, + 217 + ], + "type": "text", + "content": "3.1. Signed Distance Function (SDF)" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 223, + 287, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 223, + 287, + 281 + ], + "spans": [ + { + "bbox": [ + 46, + 223, + 287, + 281 + ], + "type": "text", + "content": "For a given spatial point, Signed Distance Function (SDF) is a continuous function that outputs the point's distance to the closest surface, whose sign indicates whether the point is inside (negative) or outside (positive) of the surface." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "spans": [ + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "text", + "content": " represent a 3D space containing some objects, " + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "inline_equation", + "content": "\\Omega \\subset \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "text", + "content": " refers to the occupied part, and " + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "inline_equation", + "content": "\\mathcal{M} = \\partial \\Omega" + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "text", + "content": " be the boundary surface. Denote the " + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "inline_equation", + "content": "\\Omega" + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "text", + "content": " indicator function by " + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "inline_equation", + "content": "\\mathbf{1}_{\\Omega}" + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "text", + "content": " and the Signed Distance Function (SDF) by " + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "inline_equation", + "content": "d_{\\Omega}" + }, + { + "bbox": [ + 46, + 282, + 287, + 331 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 116, + 337, + 287, + 370 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 116, + 337, + 287, + 370 + ], + "spans": [ + { + "bbox": [ + 116, + 337, + 287, + 370 + ], + "type": "interline_equation", + "content": "\\mathbf {1} _ {\\Omega} (\\boldsymbol {x}) = \\left\\{ \\begin{array}{l l} 1 & \\text {i f} \\boldsymbol {x} \\in \\Omega \\\\ 0 & \\text {i f} \\boldsymbol {x} \\notin \\Omega \\end{array} \\right. \\tag {1}", + "image_path": "22fb97d66f996439fa3fbcab87f0a0c6e09c1e8488cb63a321b0e56236b0f907.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 96, + 378, + 287, + 398 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 96, + 378, + 287, + 398 + ], + "spans": [ + { + "bbox": [ + 96, + 378, + 287, + 398 + ], + "type": "interline_equation", + "content": "d _ {\\Omega} (\\boldsymbol {x}) = (- 1) ^ {\\mathbf {1} _ {\\Omega} (\\boldsymbol {x})} \\min _ {\\boldsymbol {y} \\in \\mathcal {M}} \\| \\boldsymbol {x} - \\boldsymbol {y} \\| \\tag {2}", + "image_path": "c7065f83fcc4d071e73c08e4be6b09b3e6dc7e69eda2768a15904a6473d79881.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 401, + 287, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 401, + 287, + 437 + ], + "spans": [ + { + "bbox": [ + 46, + 401, + 287, + 437 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 401, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\|" + }, + { + "bbox": [ + 46, + 401, + 287, + 437 + ], + "type": "text", + "content": " is the standard Euclidean 2-norm. The underlying surface " + }, + { + "bbox": [ + 46, + 401, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\mathcal{M}" + }, + { + "bbox": [ + 46, + 401, + 287, + 437 + ], + "type": "text", + "content": " can be implicitly represented by the zero-level set of " + }, + { + "bbox": [ + 46, + 401, + 287, + 437 + ], + "type": "inline_equation", + "content": "d_{\\Omega}(\\cdot) = 0" + }, + { + "bbox": [ + 46, + 401, + 287, + 437 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 444, + 194, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 444, + 194, + 456 + ], + "spans": [ + { + "bbox": [ + 47, + 444, + 194, + 456 + ], + "type": "text", + "content": "3.2. Transform SDF to Density" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 462, + 287, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 462, + 287, + 533 + ], + "spans": [ + { + "bbox": [ + 46, + 462, + 287, + 533 + ], + "type": "text", + "content": "The volume density " + }, + { + "bbox": [ + 46, + 462, + 287, + 533 + ], + "type": "inline_equation", + "content": "\\sigma : \\mathbb{R}^3 \\to \\mathbb{R}_+" + }, + { + "bbox": [ + 46, + 462, + 287, + 533 + ], + "type": "text", + "content": " is a scalar volumetric function, where " + }, + { + "bbox": [ + 46, + 462, + 287, + 533 + ], + "type": "inline_equation", + "content": "\\sigma(x)" + }, + { + "bbox": [ + 46, + 462, + 287, + 533 + ], + "type": "text", + "content": " can be interpreted as the probability that light is occluded at point " + }, + { + "bbox": [ + 46, + 462, + 287, + 533 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 462, + 287, + 533 + ], + "type": "text", + "content": ". Previous works et al. [59, 63] suggest modeling the density " + }, + { + "bbox": [ + 46, + 462, + 287, + 533 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 46, + 462, + 287, + 533 + ], + "type": "text", + "content": " using a certain transformation of a learnable Signed Distance Function (SDF), as follows:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 118, + 541, + 287, + 555 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 118, + 541, + 287, + 555 + ], + "spans": [ + { + "bbox": [ + 118, + 541, + 287, + 555 + ], + "type": "interline_equation", + "content": "\\sigma (\\boldsymbol {x}) = \\alpha \\Psi_ {\\beta} (- d _ {\\Omega} (\\boldsymbol {x})) \\tag {3}", + "image_path": "3a4deec04d48dee692287cfb4ebaf53946d063cbec61c48f9b214368919750a5.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 562, + 287, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 562, + 287, + 597 + ], + "spans": [ + { + "bbox": [ + 46, + 562, + 287, + 597 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 562, + 287, + 597 + ], + "type": "inline_equation", + "content": "\\alpha, \\beta > 0" + }, + { + "bbox": [ + 46, + 562, + 287, + 597 + ], + "type": "text", + "content": " are learnable parameters and " + }, + { + "bbox": [ + 46, + 562, + 287, + 597 + ], + "type": "inline_equation", + "content": "\\Psi_{\\beta}" + }, + { + "bbox": [ + 46, + 562, + 287, + 597 + ], + "type": "text", + "content": " is the cumulative distribution function of the Laplace distribution with zero mean and " + }, + { + "bbox": [ + 46, + 562, + 287, + 597 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 46, + 562, + 287, + 597 + ], + "type": "text", + "content": " scale," + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 88, + 604, + 287, + 635 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 604, + 287, + 635 + ], + "spans": [ + { + "bbox": [ + 88, + 604, + 287, + 635 + ], + "type": "interline_equation", + "content": "\\Psi_ {\\beta} (s) = \\left\\{ \\begin{array}{l l} \\frac {1}{2} \\exp (\\frac {s}{\\beta}) & \\text {i f} s \\leq 0 \\\\ 1 - \\frac {1}{2} \\exp (- \\frac {s}{\\beta}) & \\text {i f} s > 0 \\end{array} \\right. \\tag {4}", + "image_path": "3620c3842f11a8b0387cabc0ba6dfdd2a55eeffdd7b9bcf4802d4d2c3566012e.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": "As " + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": " approaches zero, the density " + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": " converges to scaled indicator function of " + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\Omega" + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": ", means " + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\sigma \\rightarrow \\alpha \\mathbf{1}_{\\Omega}" + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": " for all points " + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\pmb{x} \\in \\Omega \\setminus \\mathcal{M}" + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": ". The benefits of modeling density in this way have been discussed in [59]. We simply set " + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\alpha = \\beta^{-1}" + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": " in our implementations. Figure 2 depicts an example of how density varies along SDF when a ray passes through an object." + } + ] + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 313, + 79, + 518, + 295 + ], + "blocks": [ + { + "bbox": [ + 313, + 79, + 518, + 295 + ], + "lines": [ + { + "bbox": [ + 313, + 79, + 518, + 295 + ], + "spans": [ + { + "bbox": [ + 313, + 79, + 518, + 295 + ], + "type": "image", + "image_path": "001a5110f01da076e14074d84991ba4ea353b229d26c28679b9dcfd6afa68a82.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 314, + 545, + 369 + ], + "lines": [ + { + "bbox": [ + 304, + 314, + 545, + 369 + ], + "spans": [ + { + "bbox": [ + 304, + 314, + 545, + 369 + ], + "type": "text", + "content": "Figure 2. Example of transformation from SDF to Density. The black arrow line represents a ray passing through a spherical object; the gradient color line describes how density varies along with SDF values by Equation 3, where we set " + }, + { + "bbox": [ + 304, + 314, + 545, + 369 + ], + "type": "inline_equation", + "content": "\\beta = 0.01" + }, + { + "bbox": [ + 304, + 314, + 545, + 369 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 314, + 545, + 369 + ], + "type": "inline_equation", + "content": "\\alpha = \\beta^{-1} = 100" + }, + { + "bbox": [ + 304, + 314, + 545, + 369 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 388, + 416, + 401 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 388, + 416, + 401 + ], + "spans": [ + { + "bbox": [ + 306, + 388, + 416, + 401 + ], + "type": "text", + "content": "3.3. Volume Rendering" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "spans": [ + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": "Volume intensity (RGB color) " + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "inline_equation", + "content": "\\pmb{c} : \\mathbb{R}^3 \\to \\mathbb{R}^3" + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": " is a vector volumetric function of spatial position " + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "inline_equation", + "content": "\\pmb{x}" + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "inline_equation", + "content": "\\pmb{c}(x)" + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": " represents the intensity or color at a certain point " + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "inline_equation", + "content": "\\pmb{x}" + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": ". Given color " + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": " and density " + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": ", the expected color " + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "inline_equation", + "content": "C(\\pmb{r})" + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": " of ray " + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "inline_equation", + "content": "\\pmb{r}(t) = \\pmb{o} + t\\pmb{d}" + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": " (where " + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "inline_equation", + "content": "\\pmb{o}" + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "inline_equation", + "content": "\\pmb{d}" + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": " are the origin and direction of the ray respectively) with near and far bounds " + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "inline_equation", + "content": "t_n" + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "inline_equation", + "content": "t_f" + }, + { + "bbox": [ + 304, + 406, + 545, + 479 + ], + "type": "text", + "content": " is:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 344, + 487, + 545, + 520 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 344, + 487, + 545, + 520 + ], + "spans": [ + { + "bbox": [ + 344, + 487, + 545, + 520 + ], + "type": "interline_equation", + "content": "\\boldsymbol {C} (\\boldsymbol {r}) = \\int_ {t _ {n}} ^ {t _ {f}} \\boldsymbol {T} (t) \\sigma (\\boldsymbol {r} (t)) \\boldsymbol {c} (\\boldsymbol {r} (t)) d t, \\tag {5}", + "image_path": "a07a284e304b3461825e93a90a4402557809308eb0d86485fe00d25c860a7554.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 347, + 516, + 504, + 544 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 516, + 504, + 544 + ], + "spans": [ + { + "bbox": [ + 347, + 516, + 504, + 544 + ], + "type": "interline_equation", + "content": "\\text {w h e r e} \\boldsymbol {T} (t) = \\exp \\left(- \\int_ {t _ {n}} ^ {t} \\sigma (\\boldsymbol {r} (s)) d s\\right)", + "image_path": "ae67414038477249439b9d4c9a4910c00eae1d489816a16e6034024bdfb5ebe6.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "spans": [ + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "text", + "content": " refers to the volume density. The function " + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "inline_equation", + "content": "T(t)" + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "text", + "content": " denotes the accumulated transmittance along the ray from " + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "inline_equation", + "content": "t_n" + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "text", + "content": ", namely, the probability that the ray (or light) travels from " + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "inline_equation", + "content": "t_n" + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 551, + 545, + 623 + ], + "type": "text", + "content": " without being occluded by any particle. In Section 4.1.2, we describe the details to calculate volume rendering numerical integration in our setup." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 634, + 361, + 645 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 634, + 361, + 645 + ], + "spans": [ + { + "bbox": [ + 306, + 634, + 361, + 645 + ], + "type": "text", + "content": "4. Method" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "type": "text", + "content": "Overview. The overall framework is illustrated in Figure 3. We follow the network design in LIGA-Stereo [19]. Note that the stereo part of LIGA-Stereo [19] is not applicable for monocular 3D detection (M3D) task. We replace the intermediate 3D feature representations with the proposed" + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6816" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 68, + 527, + 225 + ], + "blocks": [ + { + "bbox": [ + 51, + 68, + 527, + 225 + ], + "lines": [ + { + "bbox": [ + 51, + 68, + 527, + 225 + ], + "spans": [ + { + "bbox": [ + 51, + 68, + 527, + 225 + ], + "type": "image", + "image_path": "405ddffd09d22220912d25578b45b2bdcca3a90b2cb307beae5fa7503eb6a5f9.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "lines": [ + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "spans": [ + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": "Figure 3. Overview of MonoNeRD. \"F. Voxel\" and \"D. Voxel\" in the figure refer to Feature Voxel and Density Voxel, respectively. Position-Aware Frustum Features " + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "inline_equation", + "content": "F_{P}" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": " are generated from an image " + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": " and Positional Frustum Features " + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "inline_equation", + "content": "F_{pos}" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": " in a query-based manner (Section 4.1.1), which are then transformed to 3D features " + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "inline_equation", + "content": "F''" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": " and signed distance fields " + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "inline_equation", + "content": "F_{sdf}" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": ". After that, the radiance fields " + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "inline_equation", + "content": "F_{rgb}" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": " are produced by " + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "inline_equation", + "content": "F''" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": " (Section 4.1.2). " + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "inline_equation", + "content": "F_{sdf}" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": " can be transformed to frustum volume density " + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "inline_equation", + "content": "F_{density}" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": " (Equation 3) by a scaled cumulative distribution function of Laplace distribution (Equation 4). Volume rendering from " + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "inline_equation", + "content": "F_{rgb}" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "inline_equation", + "content": "F_{density}" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": " provides supervision for such NeRF-like representations which generate voxel features " + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "inline_equation", + "content": "V_{3d}" + }, + { + "bbox": [ + 46, + 236, + 547, + 304 + ], + "type": "text", + "content": " for M3D (Section 4.1.3)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 321, + 287, + 344 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 321, + 287, + 344 + ], + "spans": [ + { + "bbox": [ + 46, + 321, + 287, + 344 + ], + "type": "text", + "content": "NeRF-like representations while keeping the 2D image backbone and downstream detection module unchanged." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 345, + 290, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 345, + 290, + 548 + ], + "spans": [ + { + "bbox": [ + 46, + 345, + 290, + 548 + ], + "type": "text", + "content": "Given an input RGB image " + }, + { + "bbox": [ + 46, + 345, + 290, + 548 + ], + "type": "inline_equation", + "content": "I \\in \\mathbb{R}^{H \\times W \\times 3}" + }, + { + "bbox": [ + 46, + 345, + 290, + 548 + ], + "type": "text", + "content": ", it is passed to a 2D image backbone for extracting image features. Then we use the 2D image features to generate the proposed NeRF-like 3D representations. Specifically, we first build the Position-aware Frustum (See Section 4.1.1), which is transformed to 3D frustum features and SDF frustum features. Such features can be used for obtaining RGB and density features to achieve rendered RGB images and depth maps via Volume Rendering (See Section 4.1.2). They are supervised by RGB loss and depth loss to guide previous features, serving as auxiliary tasks in training. Furthermore, we use grid-sampling on 3D frustum features and density frustum features to build regular 3D voxel features and corresponding density. They are used for forming 3D Voxel Features (See Section 4.1.3), which are fed into the detection modules. We elaborate on each part of our method in the following." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 555, + 192, + 567 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 555, + 192, + 567 + ], + "spans": [ + { + "bbox": [ + 47, + 555, + 192, + 567 + ], + "type": "text", + "content": "4.1. NeRF-like Representation" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 573, + 287, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 573, + 287, + 657 + ], + "spans": [ + { + "bbox": [ + 46, + 573, + 287, + 657 + ], + "type": "text", + "content": "We need to clarify the difference between NeRF and the proposed NeRF-like representation. NeRF encodes a scene with a MLP and has to be trained per scene. The proposed method predicts continuous 3D geometry information from the single input RGB image. Similar ideas have been explored in researches about single-image-based novel view synthesis. Please refer to [20, 25] for details." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 671, + 243, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 243, + 682 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 243, + 682 + ], + "type": "text", + "content": "4.1.1 Position-aware Frustum Construction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 288, + 715 + ], + "type": "text", + "content": "To lift 2D backbone features to 3D space without depth, a naive manner is to simply repeat 2D features on different" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 321, + 546, + 367 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 321, + 546, + 367 + ], + "spans": [ + { + "bbox": [ + 304, + 321, + 546, + 367 + ], + "type": "text", + "content": "depth planes. However, this way does not contain any position information, causing ambiguous spatial features. To resolve this problem, we propose to generate position-aware frustum features." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "spans": [ + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": "Taking an RGB image as input, the 2D image backbone produces image features " + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "inline_equation", + "content": "F_{image} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times C}" + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "inline_equation", + "content": "H_{2d}" + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "inline_equation", + "content": "W_{2d}" + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": " are the height and width of the 2D image feature map, and " + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": " is the number of feature channels. Such 2D image features are mapped to a camera frustum along with corresponding normalized frustum 3D coordinates in a query-based manner. More specifically, given pre-defined near depth " + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "inline_equation", + "content": "z_{n}" + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": " and far depth " + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "inline_equation", + "content": "z_{f}" + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": ", we sample " + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": " planes from this depth range under equal depth intervals with random perturbation as described in [38, 25]. Each depth plane consists of frustum 3D position coordinates " + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "inline_equation", + "content": "p: [u, v, z]^{T}" + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": " of every pixel point " + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "inline_equation", + "content": "[u, v]^{T} \\in \\mathbb{R}^{2}" + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": ". These coordinates are normalized later. Thus we have 3D positional frustum features " + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "inline_equation", + "content": "F_{pos} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times D \\times 3}" + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": " refers to the number of depth planes and 3 denotes the normalized coordinates. To combine 3D position and original 2D image features, we use three linear layers " + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "inline_equation", + "content": "f_{q}, f_{k}, f_{v}" + }, + { + "bbox": [ + 304, + 369, + 547, + 586 + ], + "type": "text", + "content": " to do the Query-Key-Value mapping and attention calculation (in Figure 4)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 353, + 594, + 497, + 609 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 353, + 594, + 497, + 609 + ], + "spans": [ + { + "bbox": [ + 353, + 594, + 497, + 609 + ], + "type": "interline_equation", + "content": "f _ {q}: F _ {p o s} \\rightarrow Q \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times D \\times C}", + "image_path": "797855518cc8170c1413a5c377d6779773b2e1c25e0585a609add3e106d42df8.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 354, + 610, + 545, + 624 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 354, + 610, + 545, + 624 + ], + "spans": [ + { + "bbox": [ + 354, + 610, + 545, + 624 + ], + "type": "interline_equation", + "content": "f _ {k}: F _ {\\text {i m a g e}} \\rightarrow K \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times C} \\tag {6}", + "image_path": "80d51093db60fae136d5b108b70eabec6554e9f23440ebd5980a6d91aa33b1a3.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 354, + 627, + 495, + 641 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 354, + 627, + 495, + 641 + ], + "spans": [ + { + "bbox": [ + 354, + 627, + 495, + 641 + ], + "type": "interline_equation", + "content": "f _ {v}: F _ {i m a g e} \\to V \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times C}", + "image_path": "ad8a7218f05bcc496bbe54e2aa45dc59cb0bcd9a91dc5a5234c61e4c06a0305a.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 651, + 546, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 651, + 546, + 674 + ], + "spans": [ + { + "bbox": [ + 306, + 651, + 546, + 674 + ], + "type": "text", + "content": "Therefore, the Position-Aware Frustum features can be calculated by a softmax function along the depth dimension." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 367, + 685, + 546, + 696 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 367, + 685, + 546, + 696 + ], + "spans": [ + { + "bbox": [ + 367, + 685, + 546, + 696 + ], + "type": "interline_equation", + "content": "F _ {P} = \\operatorname {S o f t m a x} (Q K, \\dim = D) V \\tag {7}", + "image_path": "13d5e807369804c23b2a04f62cca8579ba329b8ea7ad8f3d3957d25fbbf2d4a9.jpg" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6817" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 72, + 277, + 178 + ], + "blocks": [ + { + "bbox": [ + 53, + 72, + 277, + 178 + ], + "lines": [ + { + "bbox": [ + 53, + 72, + 277, + 178 + ], + "spans": [ + { + "bbox": [ + 53, + 72, + 277, + 178 + ], + "type": "image", + "image_path": "91b6426e8e0a39b277fbce259f8a68f1565e0e5e4621b2d246b023c19d88a0f4.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 194, + 287, + 217 + ], + "lines": [ + { + "bbox": [ + 46, + 194, + 287, + 217 + ], + "spans": [ + { + "bbox": [ + 46, + 194, + 287, + 217 + ], + "type": "text", + "content": "Figure 4. The Query-Key-Value mapping procedure for constructing Position-Aware Frustum features." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 237, + 229, + 249 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 237, + 229, + 249 + ], + "spans": [ + { + "bbox": [ + 47, + 237, + 229, + 249 + ], + "type": "text", + "content": "4.1.2 Volume Rendering within Frustum" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "spans": [ + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "type": "text", + "content": "After constructing position-aware frustum features, we try to encode such features in 3D space to obtain more informative 3D features for volume rendering. Towards this goal, we employ two 3D convolution blocks " + }, + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "type": "inline_equation", + "content": "f_{1}" + }, + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "type": "inline_equation", + "content": "f_{2}" + }, + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "type": "inline_equation", + "content": "f_{1}" + }, + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "type": "text", + "content": " consists of a three-layer 3D-convolution with kernel size 3 and softplus activation. It takes position-aware frustum features " + }, + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "type": "inline_equation", + "content": "F_{P} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times D \\times C}" + }, + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "type": "text", + "content": " as input, outputting a same shape feature " + }, + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "type": "inline_equation", + "content": "F'" + }, + { + "bbox": [ + 46, + 256, + 287, + 352 + ], + "type": "text", + "content": " except the channel number, as follows:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 88, + 360, + 287, + 374 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 360, + 287, + 374 + ], + "spans": [ + { + "bbox": [ + 88, + 360, + 287, + 374 + ], + "type": "interline_equation", + "content": "f _ {1}: F _ {P} \\rightarrow F ^ {\\prime} \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times D \\times (1 + C)} \\tag {8}", + "image_path": "68010864f6a3ffbd5da961dab0bd5eb58d5d3f934cbd5a6df5fad76c07f2abe6.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "spans": [ + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "text", + "content": "i) SDF and density features. The first channel feature in " + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "inline_equation", + "content": "F'" + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "text", + "content": " is regarded as SDF feature " + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "inline_equation", + "content": "F_{sdf} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times D \\times 1}" + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "text", + "content": ". The signed distance fields " + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "inline_equation", + "content": "F_{sdf}" + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "text", + "content": " represent the scene geometry of the input image. For any 3D point " + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "inline_equation", + "content": "[x, y, z]^T" + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "text", + "content": " in frustum space, we can get its signed distance " + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "inline_equation", + "content": "s(x, y, z) \\in \\mathbb{R}^1" + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "text", + "content": " by trilinear sampling in " + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "inline_equation", + "content": "F_{sdf}" + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "text", + "content": ". Furthermore, scene volume density " + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "text", + "content": " (or density frustum " + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "inline_equation", + "content": "F_{density} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times D \\times 1}" + }, + { + "bbox": [ + 46, + 384, + 287, + 480 + ], + "type": "text", + "content": ") can be transformed by Equation 3:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 106, + 490, + 287, + 508 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 106, + 490, + 287, + 508 + ], + "spans": [ + { + "bbox": [ + 106, + 490, + 287, + 508 + ], + "type": "interline_equation", + "content": "\\sigma (x, y, z) = \\alpha \\Psi_ {\\beta} (s (x, y, z)) \\tag {9}", + "image_path": "109d537aabdb53efd88b01274c7f22152e727ec41598ae2762c05dfb1023f26c.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 108, + 506, + 203, + 518 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 108, + 506, + 203, + 518 + ], + "spans": [ + { + "bbox": [ + 108, + 506, + 203, + 518 + ], + "type": "interline_equation", + "content": "F _ {d e n s i t y} = \\alpha \\Psi_ {\\beta} (F _ {s d f})", + "image_path": "778857d63b8c4abe298597eb4e386709b5724b25074846662a2a199a3f8c733e.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 526, + 287, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 526, + 287, + 550 + ], + "spans": [ + { + "bbox": [ + 46, + 526, + 287, + 550 + ], + "type": "text", + "content": "The density will be used for rendering depth maps and weighing the voxel features." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 551, + 287, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 551, + 287, + 597 + ], + "spans": [ + { + "bbox": [ + 46, + 551, + 287, + 597 + ], + "type": "text", + "content": "ii) RGB features. The remaining " + }, + { + "bbox": [ + 46, + 551, + 287, + 597 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 551, + 287, + 597 + ], + "type": "text", + "content": " channel feature in " + }, + { + "bbox": [ + 46, + 551, + 287, + 597 + ], + "type": "inline_equation", + "content": "F'" + }, + { + "bbox": [ + 46, + 551, + 287, + 597 + ], + "type": "text", + "content": ", called " + }, + { + "bbox": [ + 46, + 551, + 287, + 597 + ], + "type": "inline_equation", + "content": "F''" + }, + { + "bbox": [ + 46, + 551, + 287, + 597 + ], + "type": "text", + "content": ", is then passed to " + }, + { + "bbox": [ + 46, + 551, + 287, + 597 + ], + "type": "inline_equation", + "content": "f_{2}" + }, + { + "bbox": [ + 46, + 551, + 287, + 597 + ], + "type": "text", + "content": ", which consists of a one-layer 3D-convolution with kernel size 3 and sigmoid activation." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 94, + 597, + 287, + 612 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 94, + 597, + 287, + 612 + ], + "spans": [ + { + "bbox": [ + 94, + 597, + 287, + 612 + ], + "type": "interline_equation", + "content": "f _ {2}: F ^ {\\prime \\prime} \\rightarrow F _ {r g b} \\in \\mathbb {R} ^ {H _ {2 d} \\times W _ {2 d} \\times D \\times 3} \\tag {10}", + "image_path": "ffa32185bb50b70346d26a0958dc13f7cc1166047f4a2451e5036dbb48420707.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 617, + 287, + 654 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 654 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 654 + ], + "type": "text", + "content": "The resulting feature is used for approximating the scene radiance field " + }, + { + "bbox": [ + 46, + 617, + 287, + 654 + ], + "type": "inline_equation", + "content": "F_{rgb}" + }, + { + "bbox": [ + 46, + 617, + 287, + 654 + ], + "type": "text", + "content": ". We can also get color intensity " + }, + { + "bbox": [ + 46, + 617, + 287, + 654 + ], + "type": "inline_equation", + "content": "c(x,y,z) \\in \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 617, + 287, + 654 + ], + "type": "text", + "content": " by trilinear sampling in " + }, + { + "bbox": [ + 46, + 617, + 287, + 654 + ], + "type": "inline_equation", + "content": "F_{rgb}" + }, + { + "bbox": [ + 46, + 617, + 287, + 654 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "type": "text", + "content": "Rendering from original view. To save GPU memory, we render downsampled RGB image " + }, + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\hat{I}_{low}" + }, + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "type": "text", + "content": " and depth map " + }, + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\hat{Z}_{low}" + }, + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "type": "text", + "content": ". According to known camera calibration and multiple depth value " + }, + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\{z_i | i = 1, \\dots, D\\}" + }, + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "type": "text", + "content": ", a pixel point " + }, + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "type": "inline_equation", + "content": "[u, v]^T" + }, + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\hat{I}" + }, + { + "bbox": [ + 46, + 654, + 287, + 713 + ], + "type": "text", + "content": " can be back-projected to several 3D point coordinates" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "\\{[x_i,y_i,z_i]^T |i = 1,\\dots ,D\\}" + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": " . We can calculate the distance between two successive 3D points as follows:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 318, + 104, + 545, + 121 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 104, + 545, + 121 + ], + "spans": [ + { + "bbox": [ + 318, + 104, + 545, + 121 + ], + "type": "interline_equation", + "content": "\\delta_ {x _ {i}, y _ {i}, z _ {i}} = \\left\\| \\left[ x _ {i + 1}, y _ {i + 1}, z _ {i + 1} \\right] ^ {T} - \\left[ x _ {i}, y _ {i}, z _ {i} \\right] ^ {T} \\right\\| _ {2} \\tag {11}", + "image_path": "91e4471190f005457a4dbd45f191f419940be961479160e9be2c2c7d48142042.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "spans": [ + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "text", + "content": "Denote the distance map at depth " + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "inline_equation", + "content": "z_{i}" + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "inline_equation", + "content": "\\delta_{z_i} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times 1}" + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "text", + "content": ", we can easily get the density map " + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "inline_equation", + "content": "\\sigma_{z_i} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times 1}" + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "inline_equation", + "content": "F_{density}" + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "text", + "content": " and color map " + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "inline_equation", + "content": "c_{z_i} \\in \\mathbb{R}^{H_{2d} \\times W_{2d} \\times 3}" + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "inline_equation", + "content": "F_{rgb}" + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "text", + "content": ". Then we can render " + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "inline_equation", + "content": "\\hat{I}" + }, + { + "bbox": [ + 305, + 129, + 545, + 178 + ], + "type": "text", + "content": " by:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 348, + 187, + 545, + 220 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 348, + 187, + 545, + 220 + ], + "spans": [ + { + "bbox": [ + 348, + 187, + 545, + 220 + ], + "type": "interline_equation", + "content": "\\hat {I} _ {\\text {l o w}} = \\sum_ {i = 1} ^ {D} T _ {i} \\left(1 - \\exp \\left(- \\sigma_ {z _ {i}} \\delta_ {z _ {i}}\\right)\\right) c _ {z _ {i}}, \\tag {12}", + "image_path": "8d18cd242f204d520bfe15d46f8e8f948a72ebe3d18bd78cc388d3d6e8fcead5.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 230, + 545, + 284 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 230, + 545, + 284 + ], + "spans": [ + { + "bbox": [ + 305, + 230, + 545, + 284 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 230, + 545, + 284 + ], + "type": "inline_equation", + "content": "T_{i} = \\exp \\left(-\\sum_{j = 1}^{i - 1}\\sigma_{z_{j}}\\delta_{z_{j}}\\right)" + }, + { + "bbox": [ + 305, + 230, + 545, + 284 + ], + "type": "text", + "content": " denotes the accumulated transmittance map from plane 1 to plane " + }, + { + "bbox": [ + 305, + 230, + 545, + 284 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 230, + 545, + 284 + ], + "type": "text", + "content": " . Similarly, the low resolution depth map " + }, + { + "bbox": [ + 305, + 230, + 545, + 284 + ], + "type": "inline_equation", + "content": "\\hat{Z}_{low}\\in \\mathbb{R}^{H_{2d}\\times W_{2d}\\times 1}" + }, + { + "bbox": [ + 305, + 230, + 545, + 284 + ], + "type": "text", + "content": " can be rendered by:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 339, + 292, + 545, + 326 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 339, + 292, + 545, + 326 + ], + "spans": [ + { + "bbox": [ + 339, + 292, + 545, + 326 + ], + "type": "interline_equation", + "content": "\\hat {Z} _ {\\text {l o w}} (u, v) = \\sum_ {i = 1} ^ {D} T _ {i} \\left(1 - \\exp \\left(- \\sigma_ {z _ {i}} \\delta_ {z _ {i}}\\right)\\right) z _ {i} \\tag {13}", + "image_path": "ed2f9fa0afc3c3393947e9e247c2f2dd7f7e8e86436d2bf7c9533753b8debc81.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 338, + 545, + 387 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 338, + 545, + 387 + ], + "spans": [ + { + "bbox": [ + 305, + 338, + 545, + 387 + ], + "type": "text", + "content": "We simply upsample " + }, + { + "bbox": [ + 305, + 338, + 545, + 387 + ], + "type": "inline_equation", + "content": "\\hat{I}_{low}" + }, + { + "bbox": [ + 305, + 338, + 545, + 387 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 338, + 545, + 387 + ], + "type": "inline_equation", + "content": "\\hat{Z}_{low}" + }, + { + "bbox": [ + 305, + 338, + 545, + 387 + ], + "type": "text", + "content": " to original image resolution to get target image " + }, + { + "bbox": [ + 305, + 338, + 545, + 387 + ], + "type": "inline_equation", + "content": "\\hat{I} \\in \\mathbb{R}^{H \\times W \\times 3}" + }, + { + "bbox": [ + 305, + 338, + 545, + 387 + ], + "type": "text", + "content": " and depth map " + }, + { + "bbox": [ + 305, + 338, + 545, + 387 + ], + "type": "inline_equation", + "content": "\\hat{Z} \\in \\mathbb{R}^{H \\times W \\times 1}" + }, + { + "bbox": [ + 305, + 338, + 545, + 387 + ], + "type": "text", + "content": ". Such recovered RGB images and depth maps will be supervised by RGB loss and depth loss (See" + } + ] + } + ], + "index": 19 + }, + { + "type": "image", + "bbox": [ + 314, + 411, + 536, + 615 + ], + "blocks": [ + { + "bbox": [ + 314, + 411, + 536, + 615 + ], + "lines": [ + { + "bbox": [ + 314, + 411, + 536, + 615 + ], + "spans": [ + { + "bbox": [ + 314, + 411, + 536, + 615 + ], + "type": "image", + "image_path": "76ce98bc5c58cc0a12eff87d09ca4ac77c59e15327cb05f10d720039eac95a75.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 634, + 545, + 712 + ], + "lines": [ + { + "bbox": [ + 304, + 634, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 634, + 545, + 712 + ], + "type": "text", + "content": "Figure 5. Supervision from two RGB images by using volume rendering. We can obtain associated rendered RGB images from frustum density features " + }, + { + "bbox": [ + 304, + 634, + 545, + 712 + ], + "type": "inline_equation", + "content": "F_{\\text{density}}" + }, + { + "bbox": [ + 304, + 634, + 545, + 712 + ], + "type": "text", + "content": " and frustum radiance fields " + }, + { + "bbox": [ + 304, + 634, + 545, + 712 + ], + "type": "inline_equation", + "content": "F_{\\text{rgb}}" + }, + { + "bbox": [ + 304, + 634, + 545, + 712 + ], + "type": "text", + "content": " via Equation 12. Under this setting, we do not require explicit depth labels (i.e., LiDAR depths). Instead, the depth can be implicitly learned by calculating RGB reconstruction loss between original and rendered images." + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_caption" + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6818" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 107 + ], + "type": "text", + "content": "Section 4.2). They are used in training as auxiliary tasks to facilitate the learning process and can be discarded at the inference stage." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 109, + 288, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 109, + 288, + 264 + ], + "spans": [ + { + "bbox": [ + 46, + 109, + 288, + 264 + ], + "type": "text", + "content": "Rendering from other views. Moreover, we can render from other views as long as such views' frustum overlaps with the original view's frustum and their camera calibrations are available. The rendered images can be produced in the same way described above. By calculating the image reconstruction loss from other views' rendered images, our NeRF-like representations can get extra supervisions. In Figure 5, we give an example of taking the stereo images (left and right images) in KITTI [17] as volume rendering targets. In this way, we can even eliminate the reliance on explicit depth supervisions. Considering the space limitation of the main text, we provided ablation of depth supervision in this supplementary material." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 281, + 194, + 293 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 281, + 194, + 293 + ], + "spans": [ + { + "bbox": [ + 47, + 281, + 194, + 293 + ], + "type": "text", + "content": "4.1.3 Voxel Features Generation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "text", + "content": "Aforementioned frustum features cannot be directly used for downstream detection modules as they are irregular in 3D space. Therefore, we must transform 3D frustum features to regular 3D voxel features. We perform this process of converting frustum to voxel just like CaDDN [47] by leveraging camera calibration and differentiable sampling. First, we define a voxel grid " + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "inline_equation", + "content": "V \\in \\mathbb{R}^{H_{3d} \\times W_{3d} \\times D_{3d} \\times 3}" + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "text", + "content": ", the sampling points " + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "inline_equation", + "content": "s_k^v = [x,y,z]_k^T" + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "text", + "content": " are the center of each voxel. We can transform " + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "inline_equation", + "content": "s_k^v" + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "text", + "content": " to get corresponding frustum sampling points " + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "inline_equation", + "content": "s_k^f = [u,v,d]_k^T" + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "text", + "content": " according to the camera calibration matrix. Frustum features " + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "inline_equation", + "content": "(F'', F_{density})" + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "text", + "content": " are sampled using sampling points " + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "inline_equation", + "content": "s_k^f" + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "text", + "content": " with trilinear interpolation to inhabit voxel features " + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "inline_equation", + "content": "(V'', V_{density})" + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "text", + "content": ". Different from [47], the spatial resolutions of the frustum grid and voxel grid are not required to be similar because " + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "inline_equation", + "content": "F_{sdf}" + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "inline_equation", + "content": "F_{rgb}" + }, + { + "bbox": [ + 46, + 301, + 287, + 495 + ], + "type": "text", + "content": " are not limited by spatial resolution." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 496, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 496, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 496, + 287, + 544 + ], + "type": "text", + "content": "Considering that the density indicates 3D occupancy in the 3D space, we use it to enhance sampled 3D voxel features " + }, + { + "bbox": [ + 46, + 496, + 287, + 544 + ], + "type": "inline_equation", + "content": "V''" + }, + { + "bbox": [ + 46, + 496, + 287, + 544 + ], + "type": "text", + "content": ". Specifically, we obtain the final 3D voxel features by:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 111, + 545, + 287, + 559 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 545, + 287, + 559 + ], + "spans": [ + { + "bbox": [ + 111, + 545, + 287, + 559 + ], + "type": "interline_equation", + "content": "V _ {3 d} = V ^ {\\prime \\prime} \\cdot \\tanh \\left(V _ {\\text {d e n s i t y}}\\right) \\tag {14}", + "image_path": "c99a1139ec4949a58ec9953a5219754eb29dac160f3beae2653748c59a31426c.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 565, + 287, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 565, + 287, + 613 + ], + "spans": [ + { + "bbox": [ + 46, + 565, + 287, + 613 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 565, + 287, + 613 + ], + "type": "inline_equation", + "content": "\\tanh (\\cdot)" + }, + { + "bbox": [ + 46, + 565, + 287, + 613 + ], + "type": "text", + "content": " is used to scale " + }, + { + "bbox": [ + 46, + 565, + 287, + 613 + ], + "type": "inline_equation", + "content": "V_{\\text{density}}" + }, + { + "bbox": [ + 46, + 565, + 287, + 613 + ], + "type": "text", + "content": " to the range of " + }, + { + "bbox": [ + 46, + 565, + 287, + 613 + ], + "type": "inline_equation", + "content": "[0,1]" + }, + { + "bbox": [ + 46, + 565, + 287, + 613 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 565, + 287, + 613 + ], + "type": "inline_equation", + "content": "V_{3d}" + }, + { + "bbox": [ + 46, + 565, + 287, + 613 + ], + "type": "text", + "content": " is a NeRF-like representation since it is optimized in the same way as NeRF to learn the implicit scene geometry and occupancy." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 623, + 135, + 634 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 135, + 634 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 135, + 634 + ], + "type": "text", + "content": "4.2. Loss Function" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "type": "text", + "content": "Equation 12 and 13 build connections between 3D scene representation and 2D observations (i.e., texture and depth). We can therefore optimize the 3D representations with raw 2D RGB images and depth maps. Based on this, there are four terms in the loss function: RGB loss " + }, + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "type": "inline_equation", + "content": "L_{rgb}" + }, + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "type": "text", + "content": ", depth loss " + }, + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "type": "inline_equation", + "content": "L_{depth}" + }, + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "type": "text", + "content": ", SDF loss " + }, + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "type": "inline_equation", + "content": "L_{sdf}" + }, + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "type": "text", + "content": ", and the original loss in the baseline" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 72, + 545, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 95 + ], + "type": "text", + "content": "framework LIGA [19] " + }, + { + "bbox": [ + 305, + 72, + 545, + 95 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{LIGA}}" + }, + { + "bbox": [ + 305, + 72, + 545, + 95 + ], + "type": "text", + "content": ". The overall loss is formulated as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 307, + 106, + 545, + 129 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 106, + 545, + 129 + ], + "spans": [ + { + "bbox": [ + 307, + 106, + 545, + 129 + ], + "type": "interline_equation", + "content": "L = \\lambda_ {r g b} L _ {r g b} + \\lambda_ {\\text {d e p t h}} L _ {\\text {d e p t h}} + \\lambda_ {s d f} L _ {s d f} + \\lambda_ {\\mathrm {L I G A}} L _ {\\mathrm {L I G A}}, \\tag {15}", + "image_path": "a46e088d5570eb58c57273a40e27064f366afa5d01847e3340a8c22c7e06f852.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 130, + 545, + 152 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 130, + 545, + 152 + ], + "spans": [ + { + "bbox": [ + 304, + 130, + 545, + 152 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 130, + 545, + 152 + ], + "type": "inline_equation", + "content": "\\lambda_{rgb},\\lambda_{depth},\\lambda_{sdf},\\lambda_{LIGA}" + }, + { + "bbox": [ + 304, + 130, + 545, + 152 + ], + "type": "text", + "content": " are fixed loss weights. We empirically set all weights to 1 by default." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 153, + 545, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 153, + 545, + 190 + ], + "spans": [ + { + "bbox": [ + 305, + 153, + 545, + 190 + ], + "type": "text", + "content": "RGB loss. The RGB loss consists of two items: Smooth L1 loss " + }, + { + "bbox": [ + 305, + 153, + 545, + 190 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{smoothL1}}" + }, + { + "bbox": [ + 305, + 153, + 545, + 190 + ], + "type": "text", + "content": " and SSIM [56] loss " + }, + { + "bbox": [ + 305, + 153, + 545, + 190 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{SSIM}}" + }, + { + "bbox": [ + 305, + 153, + 545, + 190 + ], + "type": "text", + "content": " which are usually used in image reconstruction:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 343, + 201, + 545, + 213 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 201, + 545, + 213 + ], + "spans": [ + { + "bbox": [ + 343, + 201, + 545, + 213 + ], + "type": "interline_equation", + "content": "L _ {r g b} = \\lambda_ {\\text {s m o o t h L 1}} L _ {\\text {s m o o t h L 1}} + \\lambda_ {\\text {S S I M}} L _ {\\text {S S I M}} \\tag {16}", + "image_path": "a7fe9513bd4dd66b01d233032ea520775406a59bb92bdc3799f9ce10cf9fdc15.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 223, + 545, + 271 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 223, + 545, + 271 + ], + "spans": [ + { + "bbox": [ + 304, + 223, + 545, + 271 + ], + "type": "text", + "content": "Depth loss. Depth map labels are obtained by projecting associated LiDAR points onto the image plane. The depth loss is L1 loss between ground truth sparse depth map " + }, + { + "bbox": [ + 304, + 223, + 545, + 271 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 304, + 223, + 545, + 271 + ], + "type": "text", + "content": " and predicted depth map " + }, + { + "bbox": [ + 304, + 223, + 545, + 271 + ], + "type": "inline_equation", + "content": "\\hat{Z}" + }, + { + "bbox": [ + 304, + 223, + 545, + 271 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 357, + 279, + 545, + 308 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 357, + 279, + 545, + 308 + ], + "spans": [ + { + "bbox": [ + 357, + 279, + 545, + 308 + ], + "type": "interline_equation", + "content": "L _ {d e p t h} = \\frac {1}{N _ {d e p t h}} \\sum_ {u, v} \\left\\| \\hat {Z} - Z \\right\\| _ {1} \\tag {17}", + "image_path": "d58b75adcb34511e79154b400a22a6e2b6a0171e84746db60131185c2af5e9c1.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 316, + 545, + 340 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 316, + 545, + 340 + ], + "spans": [ + { + "bbox": [ + 304, + 316, + 545, + 340 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 316, + 545, + 340 + ], + "type": "inline_equation", + "content": "N_{depth}" + }, + { + "bbox": [ + 304, + 316, + 545, + 340 + ], + "type": "text", + "content": " denotes the number of valid pixels " + }, + { + "bbox": [ + 304, + 316, + 545, + 340 + ], + "type": "inline_equation", + "content": "(u,v)" + }, + { + "bbox": [ + 304, + 316, + 545, + 340 + ], + "type": "text", + "content": " with LiDAR depth." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 341, + 545, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 341, + 545, + 365 + ], + "spans": [ + { + "bbox": [ + 304, + 341, + 545, + 365 + ], + "type": "text", + "content": "SDF loss. The SDF loss encourages " + }, + { + "bbox": [ + 304, + 341, + 545, + 365 + ], + "type": "inline_equation", + "content": "F_{sdf}" + }, + { + "bbox": [ + 304, + 341, + 545, + 365 + ], + "type": "text", + "content": " to vanish on geometry surface " + }, + { + "bbox": [ + 304, + 341, + 545, + 365 + ], + "type": "inline_equation", + "content": "\\mathcal{M}" + }, + { + "bbox": [ + 304, + 341, + 545, + 365 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 353, + 373, + 545, + 402 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 353, + 373, + 545, + 402 + ], + "spans": [ + { + "bbox": [ + 353, + 373, + 545, + 402 + ], + "type": "interline_equation", + "content": "L _ {s d f} = \\frac {1}{N _ {g t}} \\sum_ {x, y, z} \\left(\\left\\| F _ {s d f} (x, y, z) \\right\\| _ {2}\\right) \\tag {18}", + "image_path": "2cba8e47c1e4ab4bb2de55bc0cd5ba4f0051bc084071032ef6bdaa9ea184bf33.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 410, + 545, + 432 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 410, + 545, + 432 + ], + "spans": [ + { + "bbox": [ + 304, + 410, + 545, + 432 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 410, + 545, + 432 + ], + "type": "inline_equation", + "content": "N_{gt}" + }, + { + "bbox": [ + 304, + 410, + 545, + 432 + ], + "type": "text", + "content": " denotes the number of LiDAR points in the current camera view." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 434, + 545, + 493 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 434, + 545, + 493 + ], + "spans": [ + { + "bbox": [ + 305, + 434, + 545, + 493 + ], + "type": "text", + "content": "LIGA loss We denote the original loss in LIGA [19] as " + }, + { + "bbox": [ + 305, + 434, + 545, + 493 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{LIGA}}" + }, + { + "bbox": [ + 305, + 434, + 545, + 493 + ], + "type": "text", + "content": ". We keep the detection, imitation and auxiliary 2D supervision loss items but remove the stereo depth estimation item to fit the monocular setting. The imitation item is removed in all Waymo [52] experiments for convenience." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 343, + 502, + 545, + 521 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 502, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 343, + 502, + 545, + 521 + ], + "type": "interline_equation", + "content": "L _ {\\text {L I G A - K I T T I}} = L _ {\\text {d e t}} + \\lambda_ {i m} L _ {i m} + \\lambda_ {2 d} L _ {2 d} \\tag {19}", + "image_path": "92db7807c6f21e1236267c71c9174a6c68ad4edffdfa567f51c42e3d50ea0cb1.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 345, + 517, + 466, + 530 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 345, + 517, + 466, + 530 + ], + "spans": [ + { + "bbox": [ + 345, + 517, + 466, + 530 + ], + "type": "interline_equation", + "content": "L _ {\\text {L I G A - W a y m o}} = L _ {\\det} + \\lambda_ {2 d} L _ {2 d}", + "image_path": "3f3d5ec29250b1ed6828a2b0cee0c705290db103433c22241b1d311795445a4c.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 306, + 555, + 387, + 569 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 555, + 387, + 569 + ], + "spans": [ + { + "bbox": [ + 306, + 555, + 387, + 569 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 575, + 423, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 575, + 423, + 586 + ], + "spans": [ + { + "bbox": [ + 306, + 575, + 423, + 586 + ], + "type": "text", + "content": "5.1. Dataset and Metrics" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 594, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 712 + ], + "type": "text", + "content": "KITTI. The KITTI dataset [17] comprises of 7,481 images in the training (trainval set) and 7,518 images in the testing (test set) with synchronized LiDAR point clouds. In previous works [11], the training images were split into a train set (3,712 samples) and a val set (3,769 samples). We also follow this setting. Results on the KITTI dataset [17] are measured using IoU-based criteria with a threshold of 0.7 to compute averaged precision over 40 recall values " + }, + { + "bbox": [ + 304, + 594, + 545, + 712 + ], + "type": "inline_equation", + "content": "(AP|_{R40})" + }, + { + "bbox": [ + 304, + 594, + 545, + 712 + ], + "type": "text", + "content": " for the car class in both bird's-eye-view (BEV) and 3D tasks." + } + ] + } + ], + "index": 25 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6819" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 83, + 70, + 509, + 238 + ], + "blocks": [ + { + "bbox": [ + 83, + 70, + 509, + 238 + ], + "lines": [ + { + "bbox": [ + 83, + 70, + 509, + 238 + ], + "spans": [ + { + "bbox": [ + 83, + 70, + 509, + 238 + ], + "type": "table", + "html": "
MethodsReferenceCategoryAPBEVAP3D
EasyModerateHardEasyModerateHard
D4LCN[16]CVPR20Pretained Depth22.5116.0212.5516.6511.729.51
DDMP-3D[53]CVPR2128.0817.8913.4419.7112.789.80
Ground-Aware[29]RAL21Directly Regress29.8117.9813.0821.6513.259.91
MonoRCNN[50]ICCV2125.4818.1114.1018.3612.6510.03
MonoEF[66]CVPR2129.0319.7017.2621.2913.8711.71
MonoRUn[9]CVPR21Geometric-based27.9417.3415.2419.6512.3010.58
GUPNet[31]ICCV2130.2921.1918.2022.2615.0213.12
MonoFlex[65]CVPR2128.2319.7516.8919.9413.8912.07
DCD[26]ECCV2232.5521.5018.2523.8115.9013.21
CaDDN[47]CVPR21LiDAR Auxiliary27.9418.9117.1919.1713.4111.46
DD3D[40]ICCV2130.9822.5620.0323.2216.3414.20
DID-M3D[43]ECCV2232.9522.7619.8324.4016.2913.75
MonoNeRD (ours)-31.1323.4620.9722.7517.1315.63
", + "image_path": "df7d4484ee83eadc945a82ba4913ca2248a86a7493e9bf986454239cf0fcafd4.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 247, + 544, + 269 + ], + "lines": [ + { + "bbox": [ + 46, + 247, + 544, + 269 + ], + "spans": [ + { + "bbox": [ + 46, + 247, + 544, + 269 + ], + "type": "text", + "content": "Table 1. Comparisons for Car category on KITTI test at IOU threshold 0.7. We obtain the values of other methods from respective papers. We use red to indicate the highest result and blue for the second-highest result. We can see that our method sets a new state of the art." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 289, + 287, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 289, + 287, + 407 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 287, + 407 + ], + "type": "text", + "content": "Waymo. The Waymo Open Dataset [52] consists of 798 training sequences and 202 validation sequences. We follow the setting in CaDDN [47] which only considers the front camera and uses the sampled training set (51,564 samples). Results on Waymo val are measured by officially evaluation of the mean average precision (mAP) and the mean average precision weighted by heading (mAPH) with IoU criteria of 0.7 and 0.5. The evaluation is performed on two difficulty levels (Level_1 and Level_2) and three distance ranges (0 - 30m, 30m - 50m, 50m - " + }, + { + "bbox": [ + 46, + 289, + 287, + 407 + ], + "type": "inline_equation", + "content": "\\infty" + }, + { + "bbox": [ + 46, + 289, + 287, + 407 + ], + "type": "text", + "content": ")." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 439, + 180, + 453 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 439, + 180, + 453 + ], + "spans": [ + { + "bbox": [ + 47, + 439, + 180, + 453 + ], + "type": "text", + "content": "5.2. Implementation Details" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 466, + 287, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 466, + 287, + 610 + ], + "spans": [ + { + "bbox": [ + 46, + 466, + 287, + 610 + ], + "type": "text", + "content": "Training details. Our method is implemented with Pytorch [42] framework. We have done all experiments with four NVIDIA 3080Ti (12G) GPUs. The detector is trained using AdamW [30] optimizer with " + }, + { + "bbox": [ + 46, + 466, + 287, + 610 + ], + "type": "inline_equation", + "content": "\\beta_{1} = 0.9, \\beta_{2} = 0.999" + }, + { + "bbox": [ + 46, + 466, + 287, + 610 + ], + "type": "text", + "content": ". The batch size is fixed to 4, with 1 sample on each GPU. On KITTI [17], the input size is fixed to " + }, + { + "bbox": [ + 46, + 466, + 287, + 610 + ], + "type": "inline_equation", + "content": "320 \\times 1248" + }, + { + "bbox": [ + 46, + 466, + 287, + 610 + ], + "type": "text", + "content": ", we train 50 epochs using an initial learning rate of 0.001, and 10 epochs with a reduced learning rate of 0.0001, weight decay is 0.0001. On Waymo [52], the input size is fixed to " + }, + { + "bbox": [ + 46, + 466, + 287, + 610 + ], + "type": "inline_equation", + "content": "640 \\times 960" + }, + { + "bbox": [ + 46, + 466, + 287, + 610 + ], + "type": "text", + "content": ", we train 16 epochs using an initial learning rate of 0.001, and 4 epochs with a reduced learning rate of 0.0001, weight decay is 0.0001." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "content": "Hyperparameters. On KITTI [17], we sample " + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "inline_equation", + "content": "D = 72" + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "content": " planes within depth range " + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "inline_equation", + "content": "[z_{n}, z_{f}] = [2, 59.6]" + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "content": " (meter) in the frustum space. The voxel grid range is " + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "inline_equation", + "content": "[2, 59.6] \\times [-30.4, 30.4] \\times [-3, 1]" + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "content": " (meter) and voxel size is " + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "inline_equation", + "content": "[0.2, 0.2, 0.2]" + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "content": " (meter) for the depth, width, and height axis in 3D space, respectively. On Waymo [52] the voxel grid range is " + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "inline_equation", + "content": "[2, 59.6] \\times [-25.6, 25.6] \\times [-3, 1]" + }, + { + "bbox": [ + 46, + 617, + 287, + 715 + ], + "type": "text", + "content": " (meter) while all other hyperparameters are the same as KITTI experiments." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 289, + 391, + 300 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 289, + 391, + 300 + ], + "spans": [ + { + "bbox": [ + 306, + 289, + 391, + 300 + ], + "type": "text", + "content": "5.3. Main Results" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "spans": [ + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "type": "text", + "content": "KITTI. Table 1 shows the main results of MonoNeRD on the KITTI test set. Our method is competitive with previous methods without any extra data. MonoNeRD achieves the best results under the Moderate and Hard settings in both " + }, + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "type": "inline_equation", + "content": "AP_{BEV}" + }, + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "type": "inline_equation", + "content": "AP_{3D}" + }, + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "type": "text", + "content": ". Compared to DD3D [40], which uses a vast private dataset for depth pre-training, we boost the performance from 22.56/16.34 to 23.46/17.13 under moderate setting, and from 20.03/14.20 to 20.97/15.63 under hard setting for " + }, + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "type": "inline_equation", + "content": "AP_{BEV} / AP_{3D}" + }, + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "type": "text", + "content": ", respectively. As for DID-M3D [43], we exceed it on both moderate and hard settings with 0.7/1.14 " + }, + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "type": "inline_equation", + "content": "AP_{BEV}" + }, + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "type": "text", + "content": " and 0.84/1.88 " + }, + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "type": "inline_equation", + "content": "AP_{3D}" + }, + { + "bbox": [ + 304, + 308, + 545, + 440 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 441, + 545, + 500 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 441, + 545, + 500 + ], + "spans": [ + { + "bbox": [ + 304, + 441, + 545, + 500 + ], + "type": "text", + "content": "Waymo. Table 2 shows the main results of on the Waymo val set. MonoNeRD achieves competitive results without using data augmentation techniques. It has a lightweight backbone (ResNet34) compared to other depth-based methods like CaDDN (ResNet101) and DID-M3D (DLA34)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 502, + 545, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 502, + 545, + 550 + ], + "spans": [ + { + "bbox": [ + 304, + 502, + 545, + 550 + ], + "type": "text", + "content": "The Results on both KITTI [17] hard and Waymo [52] distance ranges (30m - 50m, 50m - " + }, + { + "bbox": [ + 304, + 502, + 545, + 550 + ], + "type": "inline_equation", + "content": "\\infty" + }, + { + "bbox": [ + 304, + 502, + 545, + 550 + ], + "type": "text", + "content": ") demonstrate the superiority of our method in handling distant and occluded objects." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 562, + 406, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 562, + 406, + 574 + ], + "spans": [ + { + "bbox": [ + 306, + 562, + 406, + 574 + ], + "type": "text", + "content": "5.4. Ablation Studies" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "text", + "content": "Architectural components. We conduct an ablation study on the car category in KITTI val to analyze the effectiveness of the proposed NeRF-like representations. In Table 3, Exp. (a) is the baseline which directly takes features sampled from " + }, + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "inline_equation", + "content": "F_{P}" + }, + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "text", + "content": " as voxel representations " + }, + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "inline_equation", + "content": "V_{3d}" + }, + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "text", + "content": " for M3D. In Exp. (b), we use more 3D convolution layers to prevent enhancements from complex model structures. Exp. (c) shows that supervision only from a single RGB image is useless and even harmful for detection since a purely single image cannot provide depth information. We can see that sparse depth map labels from LiDAR can significantly improve the per" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6820" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 55, + 69, + 541, + 246 + ], + "blocks": [ + { + "bbox": [ + 55, + 69, + 541, + 246 + ], + "lines": [ + { + "bbox": [ + 55, + 69, + 541, + 246 + ], + "spans": [ + { + "bbox": [ + 55, + 69, + 541, + 246 + ], + "type": "table", + "html": "
Methods3D mAP / mAPH (IoU = 0.7)3D mAP / mAPH (IoU = 0.5)
Overall0 - 30m30 - 50m50m - ∞Overall0 - 30m30 - 50m50m - ∞
LEVEL 1
PatchNet [32]0.39 / 0.371.67 / 1.630.13 / 0.120.03 / 0.032.92 / 2.7410.03 / 9.751.09 / 0.960.23 / 0.18
CaDDN [47]5.03 / 4.9914.54 / 14.431.47 / 1.450.10 / 0.1017.54 / 17.3145.00 / 44.469.24 / 9.110.64 / 0.62
PCT [54]0.89 / 0.883.18 / 3.150.27 / 0.270.07 / 0.074.20 / 4.1514.70 / 14.541.78 / 1.750.39 / 0.39
MonoJSG [27]0.97 / 0.954.65 / 4.590.55 / 0.530.10 / 0.095.65 / 5.4720.86 / 20.263.91 / 3.790.97 / 0.92
DEVIANT [24]2.69 / 2.676.95 / 6.900.99 / 0.980.02 / 0.0210.98 / 10.8926.85 / 26.645.13 / 5.080.18 / 0.18
DID-M3D [43]- / -- / -- / -- / -20.66 / 20.4740.92 / 40.6015.63 / 15.485.35 / 5.24
MonoNeRD (ours)10.66 / 10.5627.84 / 27.575.40 / 5.360.72 / 0.7131.18 / 30.7061.11 / 60.2826.08 / 25.716.60 / 6.47
LEVEL 2
PatchNet [32]0.38 / 0.361.67 / 1.630.13 / 0.110.03 / 0.032.42 / 2.2810.01 / 9.731.07 / 0.940.22 / 0.16
CaDDN [47]4.49 / 4.4514.50 / 14.381.42 / 1.410.09 / 0.0916.51 / 16.2844.87 / 44.338.99 / 8.860.58 / 0.55
PCT [54]0.66 / 0.663.18 / 3.150.27 / 0.260.07 / 0.074.03 / 3.9914.67 / 14.511.74 / 1.710.36 / 0.35
MonoJSG [27]0.91 / 0.894.64 / 4.650.55 / 0.530.09 / 0.095.34 / 5.1720.79 / 20.193.79 / 3.670.85 / 0.82
DEVIANT [24]2.52 / 2.506.93 / 6.870.95 / 0.940.02 / 0.0210.29 / 10.2026.75 / 26.544.95 / 4.900.16 / 0.16
DID-M3D [43]- / -- / -- / -- / -19.37 / 19.1940.77 / 40.4615.18 / 15.044.69 / 4.59
MonoNeRD (ours)10.03 / 9.9327.75 / 27.485.25 / 5.210.60 / 0.5929.29 / 28.8460.91 / 60.0825.36 / 25.005.77 / 5.66
", + "image_path": "5fd4743f7abea39fc71aea041dac932a527722f62e7f963d3d2a0c2461cdfd1a.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 285, + 287, + 334 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 285, + 287, + 334 + ], + "spans": [ + { + "bbox": [ + 46, + 285, + 287, + 334 + ], + "type": "text", + "content": "formance of the detector from Exp. (d). The effectiveness of " + }, + { + "bbox": [ + 46, + 285, + 287, + 334 + ], + "type": "inline_equation", + "content": "L_{rgb}" + }, + { + "bbox": [ + 46, + 285, + 287, + 334 + ], + "type": "text", + "content": " can be revealed by comparing Exp. (d, e) or Exp. (f, g). Finally, SDF loss brings noticeable performance gains, especially on " + }, + { + "bbox": [ + 46, + 285, + 287, + 334 + ], + "type": "inline_equation", + "content": "AP_{BEV}" + }, + { + "bbox": [ + 46, + 285, + 287, + 334 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 49, + 344, + 287, + 414 + ], + "blocks": [ + { + "bbox": [ + 47, + 254, + 533, + 265 + ], + "lines": [ + { + "bbox": [ + 47, + 254, + 533, + 265 + ], + "spans": [ + { + "bbox": [ + 47, + 254, + 533, + 265 + ], + "type": "text", + "content": "Table 2. Results on Waymo val set. We obtain the values of other methods from their respective papers. Our method performs the best." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 344, + 287, + 414 + ], + "lines": [ + { + "bbox": [ + 49, + 344, + 287, + 414 + ], + "spans": [ + { + "bbox": [ + 49, + 344, + 287, + 414 + ], + "type": "table", + "html": "
Exp.Setting\\(AP_{BEV}/AP_{3D}\\)
3D Conv.\\(L_{rgb}\\)\\(L_{depth}\\)\\(L_{sdf}\\)EasyModerateHard
(a)24.96 / 17.0119.27 / 13.3816.89 / 11.73
(b)✓25.64 / 17.2219.75 / 13.6518.01 / 11.99
(c)✓✓24.83 / 16.9219.10 / 13.1116.74 / 11.73
(d)✓✓26.91 / 18.7220.87 / 14.5418.57 / 12.60
(e)✓✓✓26.46 / 19.4420.16 / 15.0317.59 / 12.83
(f)✓✓✓27.94 / 20.2821.44 / 15.3218.82 / 13.48
(g)✓✓✓✓29.03 / 20.6422.03 / 15.4419.41 / 13.99
", + "image_path": "a9342338aae69e3085dca22925876bf9f66c1194523d7c4e1e27bf552615a248.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 468, + 287, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 468, + 287, + 564 + ], + "spans": [ + { + "bbox": [ + 46, + 468, + 287, + 564 + ], + "type": "text", + "content": "Positional aware module. based on experiment (g) in Table 3, we replace the query-key-value (QKV) based positional aware module with the concatenation of positional features and back-projected image features. The results show a performance degradation in " + }, + { + "bbox": [ + 46, + 468, + 287, + 564 + ], + "type": "inline_equation", + "content": "AP_{BEV}" + }, + { + "bbox": [ + 46, + 468, + 287, + 564 + ], + "type": "text", + "content": " from 29.03/22.03/19.41 to 28.39/21.60/18.94, and in " + }, + { + "bbox": [ + 46, + 468, + 287, + 564 + ], + "type": "inline_equation", + "content": "AP_{3D}" + }, + { + "bbox": [ + 46, + 468, + 287, + 564 + ], + "type": "text", + "content": " from 20.64/15.44/13.99 to 19.73/15.16/12.94. This experiment demonstrates the effectiveness of the proposed design." + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 67, + 574, + 268, + 610 + ], + "blocks": [ + { + "bbox": [ + 47, + 422, + 287, + 456 + ], + "lines": [ + { + "bbox": [ + 47, + 422, + 287, + 456 + ], + "spans": [ + { + "bbox": [ + 47, + 422, + 287, + 456 + ], + "type": "text", + "content": "Table 3. Ablation of network structure and volume rendering loss. \"3D Conv\": 3D convolution blocks as mentioned in Section 4.1.2; " + }, + { + "bbox": [ + 47, + 422, + 287, + 456 + ], + "type": "inline_equation", + "content": "L_{(\\cdot)}" + }, + { + "bbox": [ + 47, + 422, + 287, + 456 + ], + "type": "text", + "content": ": use the loss for supervision; \"Exp\": Experiment." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 67, + 574, + 268, + 610 + ], + "lines": [ + { + "bbox": [ + 67, + 574, + 268, + 610 + ], + "spans": [ + { + "bbox": [ + 67, + 574, + 268, + 610 + ], + "type": "table", + "html": "
Exp.Pos.APBEV/AP3D
EasyModerateHard
1QKV29.03 / 20.6422.03 / 15.4419.41 / 13.99
2Cat.28.39 / 19.7321.60 / 15.1618.94 / 12.94
", + "image_path": "63a5c5626ecffb6478c548936b4522463bd29d5da68187c40839e07e696c22e8.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 618, + 287, + 651 + ], + "lines": [ + { + "bbox": [ + 46, + 618, + 287, + 651 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 287, + 651 + ], + "type": "text", + "content": "Table 4. Ablation of the position aware frustum. \"Pos:\": the injection method of positional information. \"Cat:\": positional feature concatenation." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 670, + 130, + 681 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 670, + 130, + 681 + ], + "spans": [ + { + "bbox": [ + 47, + 670, + 130, + 681 + ], + "type": "text", + "content": "5.5. Visualization" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "In Figure 6, we replace the proposed representation with depth-transformed one used in previous works [12, 47] and" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 285, + 547, + 381 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 285, + 547, + 381 + ], + "spans": [ + { + "bbox": [ + 304, + 285, + 547, + 381 + ], + "type": "text", + "content": "visualize them for comparison. For depth-transformed category, we first predict the depth map from the input RGB image and apply the same transformation as CaDDN [47] to get its 3D representation. We visualize such representation by back-projecting the estimated depth map to the 3D space. For the NeRF-like representation, we directly visualize the predicted 3D volume density. Our method produces dense and continuous geometry in the distance (as indicated" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 318, + 406, + 535, + 654 + ], + "blocks": [ + { + "bbox": [ + 318, + 406, + 535, + 654 + ], + "lines": [ + { + "bbox": [ + 318, + 406, + 535, + 654 + ], + "spans": [ + { + "bbox": [ + 318, + 406, + 535, + 654 + ], + "type": "image", + "image_path": "543387f9c840c173bcb878b09a56d1974a312344817d6d6293b8a7467057c404.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 667, + 547, + 712 + ], + "lines": [ + { + "bbox": [ + 304, + 667, + 547, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 667, + 547, + 712 + ], + "type": "text", + "content": "Figure 6. Visualization for depth-map-based representation and the proposed NeRF-like representation. From top to bottom: input image, NeRF-like representation, depth-map-based representation. Our method generates denser features for distant objects." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "6821" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 121 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 121 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 121 + ], + "type": "text", + "content": "by the red box area). Due to space constraints, we provide additional quantitative and qualitative results in the Supplementary materials. Occupancy results are best viewed as videos, so we urge readers to view our supplementary video." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 133, + 120, + 146 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 133, + 120, + 146 + ], + "spans": [ + { + "bbox": [ + 47, + 133, + 120, + 146 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 154, + 289, + 310 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 154, + 289, + 310 + ], + "spans": [ + { + "bbox": [ + 46, + 154, + 289, + 310 + ], + "type": "text", + "content": "In this paper, we explore how to optimize the intermediate 3D feature representations implicitly for monocular 3D object detection (M3D) without explicit binary occupancy annotations. We build a bridge between Neural Radiance Fields (NeRF) and 3D object detection, and propose a novel monocular 3D object detection framework, i.e. MonoNeRD, which produces continuous NeRF-like Representations for M3D. MonoNeRD treats intermediate 3D representations as SDF-based neural radiance fields and optimizes them using volume rendering techniques. Extensive experiments show that our method sets a new baseline for monocular 3D detection and has the potential to be extended to other 3D perception tasks." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 310, + 289, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 310, + 289, + 396 + ], + "spans": [ + { + "bbox": [ + 46, + 310, + 289, + 396 + ], + "type": "text", + "content": "Limitations and future work. The performance of our method is highly dependent on the modeling approaches. We are currently limited by the working with bounds modeling (see Section 3.3), which could fail to predict 3D occupancy when its 2D projected pixel represents sky or other things not within the specified bounds. We believe this is an interesting direction for future research." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 407, + 146, + 422 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 407, + 146, + 422 + ], + "spans": [ + { + "bbox": [ + 47, + 407, + 146, + 422 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 428, + 289, + 501 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 428, + 289, + 501 + ], + "spans": [ + { + "bbox": [ + 46, + 428, + 289, + 501 + ], + "type": "text", + "content": "This work was supported in part by The National Nature Science Foundation of China (Grant Nos: 62273301, 62273302, 62273303, 62036009, 61936006), in part by the Key R&D Program of Zhejiang Province, China (2023C01135), and in part by Yongjiang Talent Introduction Programme (Grant No: 2022A-240-G)." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 513, + 107, + 526 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 513, + 107, + 526 + ], + "spans": [ + { + "bbox": [ + 47, + 513, + 107, + 526 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 52, + 533, + 289, + 712 + ], + "type": "list", + "angle": 0, + "index": 10, + "blocks": [ + { + "bbox": [ + 52, + 533, + 287, + 600 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 533, + 287, + 600 + ], + "spans": [ + { + "bbox": [ + 52, + 533, + 287, + 600 + ], + "type": "text", + "content": "[1] Junaid Ahmed Ansari, Sarthak Sharma, Anshuman Majumdar, J Krishna Murthy, and K Madhava Krishna. 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While video-based NeRF learns the field from positional encoding, we propose to learn from the extracted video features, which are generalizable to scenes. In this way, MonoNeRF supports scene editing applications (Top) and unseen frame synthesis (Middle). Compared with DynNeRF [13], MonoNeRF could adapt to novel scenes (Bottom) with hundreds of fine-tuning steps (about 10 minutes)." + ], + "image_footnote": [], + "bbox": [ + 100, + 357, + 868, + 605 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 685, + 310, + 699 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we target at the problem of learning a generalizable dynamic radiance field from monocular videos. Different from most existing NeRF methods that are based on multiple views, monocular videos only contain one view at each timestamp, thereby suffering from ambiguity along the view direction in estimating point features and scene flows. Previous studies such as DynNeRF disambiguate point features by positional encoding, which is not transferable and severely limits the generalization abl", + "bbox": [ + 75, + 714, + 470, + 840 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "ity. As a result, these methods have to train one independent model for each scene and suffer from heavy computational costs when applying to increasing monocular videos in real-world applications. To address this, We propose MonoNeRF to simultaneously learn point features and scene flows with point trajectory and feature correspondence constraints across frames. More specifically, we learn an implicit velocity field to estimate point trajectory from temporal features with Neural ODE, which is followed by a flow-based feature aggregation module to obtain spatial features along the point trajectory. We jointly optimize temporal and spatial features in an end", + "bbox": [ + 495, + 686, + 890, + 851 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "17903 ... and manner. Experiments show that our MonoNeRF is", + "bbox": [ + 465, + 850, + 890, + 866 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 129, + 49, + 200, + 84 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 253, + 48, + 789, + 86 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "†: Corresponding author.", + "bbox": [ + 100, + 853, + 236, + 866 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "1", + "bbox": [ + 480, + 887, + 489, + 897 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "able to learn from multiple scenes and support new applications such as scene editing, unseen frame synthesis, and fast novel scene adaptation. Codes are available at https://github.com/tianfr/MonoNeRF.", + "bbox": [ + 75, + 125, + 470, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 77, + 207, + 208, + 220 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Novel view synthesis [6] is a highly challenging problem. It facilitates many important applications in movie production, sports event, and virtual reality. The long standing problem recently has witnessed impressive progress due to the neural rendering technology [28, 26, 9]. Neural Radiance Field (NeRF) [28, 54, 22, 27, 46, 51, 52] shows that photo-realistic scenes can be represented by an implicit neural network. Concretely, taken as a query the position and viewing direction of the posed image, the network outputs the color of each pixel by volume rendering method. Among these approaches, it is supposed that the scene is static and can be observed from multiple views at the same time. Such assumptions are violated by numerous videos uploaded to the Internet, which usually contain dynamic foregrounds, recorded by the monocular camera.", + "bbox": [ + 75, + 230, + 468, + 437 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "More recently, some studies aim to explore how to learn dynamic radiance field from monocular videos [10, 13, 21, 49, 50, 40]. Novel view synthesis from monocular videos is a challenging task. As foreground usually dynamically changes in a video, there is ambiguity in the view direction to estimate precise point features and dense object motions (i.e., scene flow [44]) from single views. In other words, we can only extract the projected 2D intra-frame local features and inter-frame optical flows, but fail to obtain precise 3D estimations. Previous works address this challenge by representing points as 4D position features (coordinate and time), so that the learned positional encoding provides specific information for each 3D point in the space [10, 13, 21, 49, 50, 40]. Based on positional encoding, these methods make efforts on exploiting scene priors [12, 48, 49] or adding spatio-temporal regularization [10, 13, 21, 50] to learn a more accurate dynamic radiance field.", + "bbox": [ + 75, + 438, + 468, + 672 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "However, while positional encoding successfully disambiguates 3D points from monocular 2D projections, it severely overfits to the training video clip and is not transferable. Therefore, existing positional encoding based methods have to optimize one independent model for each dynamic scene. With the fast increase of monocular videos in reality, they suffer from heavy computational costs and lengthy training time to learn from multiple dynamic scenes. Also, the lack of generalization ability limits further applications of scene editing which requires interaction among different scenes. A natural question is raised: can we learn a generalizable dynamic radiance field from monocular videos?", + "bbox": [ + 75, + 672, + 468, + 850 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tion. The key challenge of this task is to learn to extract generalizable point features in the 3D space from monocular videos. While independently using 2D local features and optical flows suffers from ambiguity along the ray direction, they provide complementary constraints to jointly learn 3D point features and scene flows. On the one hand, for the sampled points on each ray, optical flow provides generalizable constraints that limit the relations of their point trajectories. On the other hand, for the flowing points on each estimated point trajectory, we consider that they should share the same point features. We estimate each point feature by aggregating their projected 2D local features, and design feature correspondence constraints to correct unreasonable trajectories.", + "bbox": [ + 499, + 125, + 890, + 318 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To achieve this, we propose MonoNeRF to build a generalizable dynamic radiance field for multiple dynamic scenes. We hypothesize that a point moving along its trajectory over time keeps the consistent point feature. Our method concurrently predicts 3D point features and scene flows with point trajectory and feature correspondence constraints in monocular video frames. More specifically, we first propose to learn an implicit velocity field that encodes the speed from the temporal feature of each point. We supervise the velocity field with optical flow and integrate continuous point trajectories on the field with Neural ODE [5]. Then, we propose a flow-based feature aggregation module to sample spatial features of each point along the point trajectory. We incorporate the spatial and temporal features as the point feature to query the color and density for image rendering and jointly optimize point features and trajectories in an end-to-end manner. As shown in Figure 1, experiments demonstrate that our MonoNeRF is able to render novel views from multiple dynamic videos and support new applications such as scene editing, unseen frame synthesis, and fast novel scene adaption. Also, in the widely-used setting of novel view synthesis on training frames from single videos, our MonoNeRF still achieves better performance than existing methods despite that cross-scene generalization ability is not required in this setting.", + "bbox": [ + 497, + 319, + 892, + 663 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 676, + 640, + 691 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Novel view synthesis for static scenes. The long standing problem of novel view synthesis aims to construct new views of a scene from multiple posed images. Early works needed dense views captured from the scene [19, 14]. Recent studies have shown great progress by explicitly representing 3D scenes as neural representations [26, 28, 9, 7, 51, 25, 18, 38]. However, these methods train a separate model for each scene and need various training time for optimization. PixelNeRF [54] and MVSNeRF [4] proposed feature-based methods that directly render new scenes from the encoded features. Additionally, many researchers stud", + "bbox": [ + 497, + 700, + 890, + 851 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we provide a positive answer to this 17904 generalization and decomposition abilities of novel", + "bbox": [ + 95, + 851, + 892, + 866 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/fcdc241bbfde4ce152d46242b774531537de1dfc486bf357b7352312f3c4f2f3.jpg", + "image_caption": [ + "Figure 2: The overview of our generalizable dynamic field. We first exploit an implicit velocity field from the extracted temporal feature $\\pmb{F}_{temp}$ . Then, we calculate point trajectory on the velocity field, and exploit the spatial feature $\\pmb{F}_{sp}$ with the proposed flow-based spatial feature aggregation module. We incorporate $\\pmb{F}_{temp}$ and $\\pmb{F}_{sp}$ as the point feature $\\pmb{F}_{dy}$ for rendering dynamic scene and design $L_{opt}$ and $L_{corr}$ to jointly optimize point features and trajectories." + ], + "image_footnote": [], + "bbox": [ + 80, + 124, + 892, + 456 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "view synthesis model [3, 37, 29, 15, 1, 18, 41]. Compared with these methods, our method studies the synthesis and generalization ability of dynamic scenes.", + "bbox": [ + 75, + 543, + 470, + 586 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Space-time view synthesis from monocular videos. With the development of neural radiance field in static scenes, recent studies started to address the dynamic scene reconstruction problem [21, 50, 10, 20, 31, 32]. In monocular videos, a key challenge is that there exist multiple scene constructions implying the same observed image sequences. Previous approaches addressed this challenge by using 3D coordinates with time as point features and adding scene priors or spatio-temporal regularization. Scene priors such as shadow modeling [49], human shape prior [48, 23], and facial appearance [12] are object-specific and closer to special contents. Spatio-temporal regularization such as depth and flow regularization [10, 13, 21, 50] and object deformations [40] are more object-agnostic, but weaker in applying consistency restriction to dynamic foregrounds. In this paper, we study the challenge by constraining point features.", + "bbox": [ + 75, + 587, + 468, + 809 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Scene flow for reconstruction. Scene flow firstly proposed by [44] depicts the motion of each point in the dynamic scene. Its 2D projection i.e., optical flow contributes to many downstream applications such as", + "bbox": [ + 75, + 811, + 468, + 866 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "super-resolution [45], video tracking [42], video segmentation [43], and video recognition [2]. Several methods studied the scene flow estimation problem based on point cloud sequences [30, 24]. However, estimating scene flow from an observed video is an ill-posed problem. In dynamic scene reconstruction, previous works [21, 13] established discrete scene flow for pixel consistency in observation time. In this way, the flow consistency in observed frames can only be constrained, leading to ambiguity in non-observed time. Du et al. [10] proposed to build the continuous flow field in a dynamic scene. Compared to these methods, we study the generalization ability of the flow field in different scenes.", + "bbox": [ + 497, + 543, + 890, + 712 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Approach", + "text_level": 1, + "bbox": [ + 499, + 725, + 606, + 739 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we introduce the proposed model that we term as MonoNeRF. We first present the overview of our model and then detail the approach of each part. Lastly, we introduce several strategies for optimizing the model.", + "bbox": [ + 497, + 749, + 890, + 806 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. MonoNeRF", + "text_level": 1, + "bbox": [ + 499, + 815, + 626, + 828 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "MonoNeRF aims to model generalizable radiance field 17905 amic scenes. Our method takes multiple monocu", + "bbox": [ + 465, + 838, + 890, + 866 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "lar videos as input and uses optical flows, depth maps, and binary masks of foreground objects as supervision signals. Those signals could be generated by pretrained models automatically. We build the generalizable static and dynamic fields for backgrounds and foregrounds separately. For generalizable dynamic field, we suppose that spatio-temporal points flow along their trajectories and hold consistent features over time. We first extract video features by a CNN encoder and generate the temporal feature vectors based on the extracted features. Then, we build an implicit velocity field from the temporal feature vectors to estimate point trajectories. Next, we exploit the estimated point trajectories as indexes to find the local image patches on each frame and extract the spatial features from the patches with the proposed flow-based feature aggregation module. Different from NeRF [28] that uses scene-agnostic point positions to render image color, we aggregate the scene-dependent spatial and temporal features as the final point features to render foreground scenes with volume rendering. Finally, we design the optical flow and feature correspondence constraints for jointly learning point features and trajectories. For generalizable static field, we suppose backgrounds are static and each video frame is considered as a different view of the background. Since some background parts may be occluded by the foreground, we design an effective strategy to sample background point features. In the end, we combine the generalizable static and dynamic fields for rendering free-point videos.", + "bbox": [ + 75, + 125, + 472, + 513 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Generalizable Dynamic Field", + "text_level": 1, + "bbox": [ + 77, + 521, + 337, + 536 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this section, we introduce our generalizable dynamic field that renders novel views of dynamic foregrounds. We denote a monocular video as $\\mathbf{V} = \\{V^i, i = 1,2\\ldots ,K\\}$ consisting of $K$ frames. For each frame $V^i$ , $t_i$ is the observed timestamp and $\\Pi^i$ is the projection transform from the world coordinate to the 2D frame pixel coordinate. As Figure 2 shows, given a video $\\mathbf{V}$ , we exploit a video encoder $E_{dy}$ to extract the video feature vector represented as $E_{dy}(\\mathbf{V})$ and generate the temporal feature vector $\\mathbf{F}_{temp}$ with a multiple layer perceptron (MLP) $W_{temp}: E_{dy}(\\mathbf{V}) \\rightarrow \\mathbf{F}_{temp}$ . We build the implicit velocity field based on $\\mathbf{F}_{temp}$ .", + "bbox": [ + 75, + 542, + 468, + 695 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Implicit velocity field. We suppose points are moving in the scene and represent a spatio-temporal point as $\\pmb{p} = (x_p, t_p)$ including the 3D point position $\\pmb{x}_p$ and time $t_p$ . We define $\\Phi$ as the continuous point trajectory and $\\Phi(\\pmb{p}, t)$ denotes the position of point $\\pmb{p}$ at timestamp $t$ . We further define the velocity field $\\pmb{v}$ which includes the 3D velocity of each point. The relationship between point velocity and trajectory is specified as follows,", + "bbox": [ + 75, + 695, + 468, + 806 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {\\partial \\Phi (\\boldsymbol {p} , t)}{\\partial t} = \\boldsymbol {v} \\left(\\Phi (\\boldsymbol {p}, t), t\\right), \\quad \\text {s . t .} \\quad \\Phi (\\boldsymbol {p}, t _ {p}) = \\boldsymbol {x} _ {p}. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 100, + 815, + 468, + 843 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$\\pmb{v}$ is conditioned on $F_{temp}$ and implemented by an", + "bbox": [ + 75, + 851, + 463, + 866 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "$W_{vel}\\colon (F_{temp}(\\boldsymbol {V}),\\Phi ,t)\\to \\boldsymbol{v}.$ We calculate the point trajectory at an observed timestamp $t_i$ with Neural ODE [5],", + "bbox": [ + 497, + 125, + 890, + 154 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {i}) = \\boldsymbol {x} _ {p} + \\int_ {t _ {p}} ^ {t _ {i}} \\boldsymbol {v} \\left(\\boldsymbol {\\Phi} (\\boldsymbol {p}, t), t\\right) d t. \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 163, + 890, + 197 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We take $\\Phi (\\pmb {p},t_i)$ as an index to query the spatial feature.", + "bbox": [ + 499, + 203, + 873, + 217 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Flow-based spatial feature aggregation. We employ $\\Pi^i$ to project $\\Phi (\\pmb {p},t_i)$ on $V^{i}$ and find the local image patch indexed by the projected position $\\Pi^i (\\Phi (\\pmb {p},t_i))$ . We extract the feature vector $F_{sp}^{i}$ from the patch with the encoder $E_{dy}$ and a fully connected layer $fc_{1}$ ,", + "bbox": [ + 497, + 218, + 890, + 287 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {F} _ {s p} ^ {i} (\\boldsymbol {V}; \\boldsymbol {p}) = f c _ {1} \\left(E _ {d y} \\left(\\boldsymbol {V} ^ {i}; \\Pi^ {i} (\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {i}))\\right)\\right). \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 544, + 296, + 890, + 320 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In practice, $E_{dy}\\big(\\mathbf{V}^i;\\Pi^i (\\Phi (\\mathbf{p},t_i))\\big)$ is implemented by using $E_{dy}$ to extract the frame-wise feature map of $V^{i}$ and sampling the feature vector at $\\Pi^i (\\Phi (\\pmb {p},t_i))$ with bilinear interpolation. The spatial feature vector $\\pmb{F}_{sp}$ is then calculated by incorporating $\\{\\pmb{F}_{sp}^{1},\\pmb{F}_{sp}^{2},\\dots,\\pmb{F}_{sp}^{K}\\}$ with a fully connected layer $fc_{2}$ ,", + "bbox": [ + 497, + 332, + 890, + 419 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {F} _ {s p} (\\boldsymbol {V}; \\boldsymbol {p}) = f c _ {2} \\left(\\boldsymbol {F} _ {s p} ^ {1} (\\boldsymbol {V}; \\boldsymbol {p}), \\boldsymbol {F} _ {s p} ^ {2} (\\boldsymbol {V}; \\boldsymbol {p}), \\dots , \\boldsymbol {F} _ {s p} ^ {K} (\\boldsymbol {V}; \\boldsymbol {p})\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 499, + 428, + 892, + 457 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Finally, we incorporate $\\mathbf{F}_{temp}$ and $\\mathbf{F}_{sp}$ as the point feature vector $\\mathbf{F}_{dy}$ ,", + "bbox": [ + 497, + 458, + 890, + 486 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {F} _ {d y} (\\boldsymbol {V}; \\boldsymbol {p}) = \\operatorname {c o n c a t} \\left\\{\\boldsymbol {F} _ {\\text {t e m p}} (\\boldsymbol {V}), \\boldsymbol {F} _ {\\text {s p}} (\\boldsymbol {V}; \\boldsymbol {p}) \\right\\}. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 526, + 496, + 890, + 513 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We build the generalizable dynamic field based on $\\mathbf{F}_{dy}$ .", + "bbox": [ + 499, + 523, + 870, + 536 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Dynamic foreground rendering. Taking a point $\\pmb{p}$ and its feature vector $\\pmb{F}_{dy}(\\pmb{V};\\pmb{p})$ as input, our generalizable dynamic radiance field $W_{dy} \\colon (\\pmb{p}, \\pmb{F}_{dy}(\\pmb{V};\\pmb{p})) \\to (\\pmb{c}_{dy}, \\sigma_{dy}, b)$ predicts the volume density $\\sigma_{dy}$ , color $c_{dy}$ and blending weight $b$ of the point. We follow DynNeRF [13] and utilize $b$ to judge whether a point belongs to static background or dynamic foreground. We exploit volume rendering to approximate each pixel color of an image. Concretely, given a ray $r(u) = o + ud$ starting from the camera center $o$ along the direction $d$ through a pixel, its color is integrated by", + "bbox": [ + 497, + 538, + 890, + 676 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {C} _ {d y} (\\boldsymbol {r}) = \\int_ {u _ {n}} ^ {u _ {f}} T _ {d y} (u) \\sigma_ {d y} (u) \\boldsymbol {c} _ {d y} (u) d u, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 557, + 685, + 890, + 718 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $u_{n}, u_{f}$ are the bounds of the volume rendering depth range and $T_{dy}(u) = \\exp(-\\int_{u_{n}}^{u} \\sigma_{dy}(\\boldsymbol{r}(s)) ds$ is the accumulated transparency. We simplify $c(u) = c(\\boldsymbol{r}(u), \\boldsymbol{d})$ and $\\sigma(u) = \\sigma(\\boldsymbol{r}(u))$ here and in the following sections. Next we present the optical flow and feature correspondence constraints that jointly supervise our model.", + "bbox": [ + 497, + 726, + 890, + 809 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Optical flow constraint. We supervise $\\pmb{v}$ with the optical flow $f^{gt}$ . In practice, it can only approximate the backward flow $f_{bw}^{gt}$ and forward flow $f_{fw}^{gt}$ between two consecutive video frames [39]. We hence estimate the point", + "bbox": [ + 497, + 811, + 890, + 866 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "backward and forward trajectory variations during the period that the point passes between two frames and calculate optical flows by integrating the trajectory variations of each point along camera rays. Formally, given a ray $\\pmb{r}(u)$ through a pixel on the frame $\\pmb{V}^i$ at time $t_i$ , for each point on the ray i.e., $\\pmb{p}(u) = (\\pmb{r}(u), t_i)$ the trajectory variations $\\Delta \\Phi_{bw}$ back to $t_{i-1}$ and $\\Delta \\Phi_{fw}$ forward to $t_{i+1}$ are obtained by the following equation,", + "bbox": [ + 75, + 125, + 472, + 238 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\Delta \\Phi_ {\\{b w, f w \\}} (\\boldsymbol {p} (u)) = \\int_ {t _ {i}} ^ {t _ {\\{i - 1, i + 1 \\}}} \\boldsymbol {v} (\\boldsymbol {\\Phi} (\\boldsymbol {p} (u), t), t) d t. \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 92, + 245, + 468, + 289 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We follow previous works [21, 13] and exploit the volume rendering to integrate pseudo optical flows $\\pmb{f}_{bw}$ and $\\pmb{f}_{fw}$ by utilizing the estimated volume density $\\sigma_{dy}$ of each point,", + "bbox": [ + 75, + 289, + 468, + 333 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {f} _ {\\{b w, f w \\}} (\\boldsymbol {r}) = \\int_ {u _ {n}} ^ {u _ {f}} T _ {d y} (u) \\sigma_ {d y} (u) \\Delta \\Phi_ {\\{b w, f w \\}} ^ {i} (\\boldsymbol {p} (u)) d u, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 78, + 340, + 468, + 382 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\Delta \\Phi_{\\{bw,fw\\}}^i = \\Pi^i (\\Delta \\Phi_{\\{bw,fw\\}})$ denotes we use $\\Pi^i$ to project 3D trajectory variations on the image plane of $V^i$ . We supervise the pseudo flows by the ground truth flows,", + "bbox": [ + 75, + 382, + 468, + 428 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {o p t} = \\sum_ {\\boldsymbol {r}} \\left(\\boldsymbol {f} _ {\\{b w, f w \\}} (\\boldsymbol {r}) - \\boldsymbol {f} _ {\\{b w, f w \\}} ^ {g t} (\\boldsymbol {r})\\right). \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 124, + 437, + 468, + 467 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this way, the relation of point trajectories along a ray is limited by the optical flow supervision.", + "bbox": [ + 75, + 476, + 468, + 504 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Feature correspondence constraint. According to Section 3.1, a point moving along the trajectory holds the same feature and represents the consistent color and density. For each ray $\\boldsymbol{r}_{curr}$ at the current time $t_i$ through a pixel of $V^i$ , we warp the ray from the neighboring observed timestamps $t_{i-1}$ and $t_{i+1}$ as $\\boldsymbol{r}_{bw}$ and $\\boldsymbol{r}_{fw}$ separately by using (7),", + "bbox": [ + 75, + 504, + 468, + 587 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {r} _ {\\{b w, f w \\}} (u) = \\boldsymbol {r} _ {\\text {c u r r}} (u) + \\Delta \\Phi_ {\\{b w, f w \\}} \\left(\\boldsymbol {p} _ {\\text {c u r r}} (u)\\right), \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 87, + 597, + 468, + 614 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\pmb{p}_{\\text{curr}}(u) = (\\pmb{r}_{\\text{curr}}(u), t_i)$ . We render the pixel color from the point features not only along the ray $\\pmb{r}_{\\text{curr}}$ at the time $t_i$ , but also along the wrapped rays $\\pmb{r}_{bw}$ at $t_{i-1}$ and $\\pmb{r}_{fw}$ at $t_{i+1}$ . The predicted pixel color $\\pmb{C}_{dy}$ is rendered by using (6) and supervised by the ground truth colors $\\pmb{C}_{dy}^{gt}$ ,", + "bbox": [ + 75, + 622, + 468, + 695 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {\\{b w, c u r r, f w \\}} = \\sum_ {\\boldsymbol {r}} | | \\boldsymbol {C} _ {d y} (\\boldsymbol {r} _ {\\{b w, c u r r, f w \\}}) - \\boldsymbol {C} _ {d y} ^ {g t} (\\boldsymbol {r}) | | _ {2}. \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 82, + 704, + 468, + 744 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The feature correspondence constraint $L_{corr}$ is defined as", + "bbox": [ + 77, + 745, + 457, + 758 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {c o r r} = L _ {b w} + L _ {c u r r} + L _ {f w}. \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 171, + 769, + 468, + 785 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$L_{corr}$ supervises the predicted color and point features $\\pmb{F}_{dy}$ .", + "bbox": [ + 77, + 795, + 468, + 809 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Generalizable Static Field", + "text_level": 1, + "bbox": [ + 77, + 815, + 312, + 830 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As mentioned in Section 3.1, for some background node occluded by the changing foreground in the current ..... 17907", + "bbox": [ + 75, + 838, + 505, + 866 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "their features implying the foreground cannot infer the correct background information. However, the occluded parts could be seen in non-occluded views with correct background features. To this end, given a point position $\\pmb{x}$ , the background point feature vector $\\pmb{F}_{st}$ is produced by", + "bbox": [ + 497, + 125, + 890, + 195 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {F} _ {s t} (\\boldsymbol {V}; \\boldsymbol {x}) = f c _ {3} \\left(E _ {s t} \\left(\\boldsymbol {V} ^ {*}; \\Pi^ {*} (\\boldsymbol {x})\\right)\\right), \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 205, + 890, + 229 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $f c_{3}$ is a fully connected layer and $E_{st}$ denotes the image encoder. $V^{*}$ and $\\Pi^{*}$ are the non-occluded frame and corresponding projection transform respectively. $E_{st}(V^{*};\\Pi^{*}(\\pmb {x}))$ denotes that we find the local image patch at $\\Pi^{*}(\\pmb {x})$ and extract the feature vectors with an image encoder $E_{st}$ similar to $E_{dy}\\big(V^i;\\Pi^i (\\Phi (\\pmb {p},t_i))\\big)$ . Since there is no prior in which frames they can be exposed, we apply a straightforward yet effective strategy by randomly sampling one frame from the other frames in the video. We represent the static scene as a radiance field to infer the color $c_{st}$ and density $\\sigma_{st}$ by using an MLP $W_{st}$ : $(\\pmb {x},\\pmb {d},\\pmb{F}_{st}(\\pmb {V};\\pmb {x}))\\rightarrow (c_{st},\\sigma_{st})$ . The expected background color $C_{st}$ is given by", + "bbox": [ + 497, + 237, + 892, + 404 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {C} _ {s t} (\\boldsymbol {r}) = \\int_ {u _ {n}} ^ {u _ {f}} T _ {s t} (u) \\sigma_ {s t} (u) \\boldsymbol {c} _ {s t} (u) d u, \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 564, + 413, + 890, + 444 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $T_{st}(t) = \\exp (-\\int_{u_n}^u\\sigma_{st}(\\boldsymbol {r}(s))ds$ . We employ foreground masks $M$ to optimize the static field by supervising the pixel color in each video frame in the background regions (where $M(\\boldsymbol {r}) = 0$ ),", + "bbox": [ + 497, + 454, + 890, + 511 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {s t} = \\sum_ {\\boldsymbol {r}} | | \\left(\\boldsymbol {C} _ {s t} (\\boldsymbol {r}) - \\boldsymbol {C} _ {s t} ^ {q t} (\\boldsymbol {r})\\right) (1 - M (\\boldsymbol {r})) \\| _ {2}, \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 522, + 521, + 890, + 549 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $C_{st}^{gt}$ represents the ground truth color.", + "bbox": [ + 499, + 560, + 794, + 576 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Optimization", + "text_level": 1, + "bbox": [ + 499, + 584, + 638, + 598 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The final dynamic scene color combines the colors from the generalizable dynamic and static fields,", + "bbox": [ + 499, + 605, + 890, + 633 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {C} _ {f u l l} (\\boldsymbol {r}) = \\int_ {u _ {n}} ^ {u _ {f}} T _ {f u l l} (u) \\sigma_ {f u l l} (u) \\boldsymbol {c} _ {f u l l} (u) d u, \\tag {16}\n$$\n", + "text_format": "latex", + "bbox": [ + 524, + 642, + 890, + 674 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where", + "bbox": [ + 500, + 682, + 546, + 695 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\sigma_ {f u l l} (u) \\boldsymbol {c} _ {f u l l} (u) = (1 - b) \\sigma_ {s t} (u) \\boldsymbol {c} _ {s t} (u) + b \\sigma_ {d y} (u) \\boldsymbol {c} _ {d y} (u), \\tag {17}\n$$\n", + "text_format": "latex", + "bbox": [ + 499, + 707, + 890, + 735 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "and applies the reconstruction loss,", + "bbox": [ + 499, + 735, + 732, + 749 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {f u l l} = \\sum_ {\\boldsymbol {r}} | | \\boldsymbol {C} _ {f u l l} (\\boldsymbol {r}) - \\boldsymbol {C} _ {f u l l} ^ {g t} (\\boldsymbol {r}) | | _ {2}. \\tag {18}\n$$\n", + "text_format": "latex", + "bbox": [ + 564, + 758, + 890, + 787 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Next we design several strategies to optimize our model.", + "bbox": [ + 499, + 796, + 873, + 809 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Point trajectory discretization. While point trajectory can be numerically estimated by the continuous integral (2) with Neural ODE solvers [5], it needs plenty of time for 7 ng each point trajectory. To accelerate the process,", + "bbox": [ + 497, + 811, + 890, + 866 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/2b6502bc8089f76b3b4e9ac3d31b75d37d92f53810847c2e359c316bbaed3177.jpg", + "table_caption": [ + "Table 1: Novel view synthesis on training frames from single videos. While this setting does not require cross-scene generalization ability, our MonoNeRF still achieves better performance." + ], + "table_footnote": [], + "table_body": "
PSNR ↑ / LPIPS ↓JumpingSkatingTruckUmbrellaBalloon1Balloon2PlaygroundAverage
NeRF [28]20.58 / 0.30523.05 / 0.31622.61 / 0.22521.08 / 0.44119.07 / 0.21424.08 / 0.09820.86 / 0.16421.62 / 0.252
NeRF [28] + time16.72 / 0.48919.23 / 0.54217.17 / 0.40317.17 / 0.75217.33 / 0.30419.67 / 0.23613.80 / 0.44417.30 / 0.453
Yoon et al. [53]20.16 / 0.14821.75 / 0.13523.93 / 0.10920.35 / 0.17918.76 / 0.17819.89 / 0.13815.09 / 0.18319.99 / 0.153
Tretschk et al. [40]19.38 / 0.29523.29 / 0.23419.02 / 0.45319.26 / 0.42716.98 / 0.35322.23 / 0.21214.24 / 0.33619.20 / 0.330
Li et al. [21]24.12 / 0.15628.91 / 0.13525.94 / 0.17122.58 / 0.30221.40 / 0.22524.09 / 0.22820.91 / 0.22023.99 / 0.205
NeuPhysics [33]20.16 / 0.20525.13 / 0.16622.62 / 0.21221.02 / 0.42616.68 / 0.23822.54 / 0.26515.10 / 0.36720.48 / 0.282
DynNeRF [13]24.23 / 0.14428.90 / 0.12425.78 / 0.13423.15 / 0.14621.47 / 0.12525.97 / 0.05923.65 / 0.09324.74 / 0.118
MonoNeRF24.26 / 0.09132.06 / 0.04427.56 / 0.11523.62 / 0.18021.89 / 0.12927.36 / 0.05222.61 / 0.13025.62 / 0.106
", + "bbox": [ + 77, + 161, + 894, + 269 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/22a40a3efafa65c4a4ca812a1db98cd5cf21f63a7d36ce2d3dde568692bc872f.jpg", + "image_caption": [ + "Figure 3: Qualitative results of jointly optimizing Balloon2 and Umbrella scenes. The foregrounds of two scenes are mixed without $F_{dy}$ . Our method renders more accurate novel views and predicts plausible scene flows (listed beside the RGB images) by incorporating $F_{temp}$ and $F_{sp}$ ." + ], + "image_footnote": [], + "bbox": [ + 94, + 277, + 875, + 426 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/730bb6621c0372d5a1c1f23ac55826b60df0f871fa44a727d282b6d228294b79.jpg", + "image_caption": [ + "Figure 4: Novel view synthesis on unseen frames. Compared to the ground truths, our model could transfer to new motions, whereas DynNeRF [13] only interpolates in the training frames." + ], + "image_footnote": [], + "bbox": [ + 87, + 498, + 457, + 612 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "we propose to partition $[t_p, t_i]$ into $N$ evenly-spaced bins and suppose the point velocity in each bin is a constant. The point trajectory can be estimated by the following equation,", + "bbox": [ + 75, + 700, + 468, + 743 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {i}) = \\boldsymbol {x} _ {p} + \\sum_ {n = 1} ^ {N} \\boldsymbol {v} \\left(\\boldsymbol {\\Phi} (\\boldsymbol {p}, t + \\Delta t), t + \\Delta t\\right) \\Delta t, \\tag {19}\n$$\n", + "text_format": "latex", + "bbox": [ + 90, + 763, + 468, + 801 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\Delta t = \\frac{n}{N} (t_{i} - t_{p})$", + "bbox": [ + 75, + 809, + 243, + 825 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Depth-blending restriction. To calculate the blending weights within a foreground ray in the generalizable dynamic field, only the points in close proximity to the", + "bbox": [ + 75, + 824, + 468, + 866 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/eba6feba723e2ddde9d60956424b3137bf1fdb5922e83879a33aa3dc9457b961.jpg", + "table_caption": [ + "Table 2: Quantitative results of novel view synthesis on unseen frames. We used the first four frames for training and tested the performance on the rest eight frames." + ], + "table_footnote": [], + "table_body": "
Balloon2 / TruckPSNR ↑SSIM ↑LPIPS ↓
NeRF [28]20.33 / 20.260.662 / 0.6690.224 / 0.256
NeRF [28] + time20.22 / 20.260.661 / 0.6390.218 / 0.256
NeuPhysics [33]19.45 / 20.240.478 / 0.5170.343 / 0.285
DynNeRF [13]19.99 / 20.330.641 / 0.6210.291 / 0.273
MonoNeRF21.30 / 23.740.669 / 0.7020.204 / 0.174
", + "bbox": [ + 500, + 549, + 890, + 625 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "mated ray depth are regarded as foreground points, whereas points beyond this range are excluded. We penalize the blending weights of non-foreground points in foreground rays. Specifically, given a ray $r(u)$ through a pixel and the pixel depth $u_{d}$ , We penalize the blending weights of the points on the ray out of the interval $(u_{d} - \\epsilon, u_{d} + \\epsilon)$ ,", + "bbox": [ + 497, + 656, + 890, + 739 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {d b} = \\sum_ {u \\in \\left(u _ {n}, u _ {d} - \\epsilon\\right) \\cup \\left(u _ {d} + \\epsilon , u _ {f}\\right)} \\| b (\\boldsymbol {r} (u)) \\| _ {2}, \\tag {20}\n$$\n", + "text_format": "latex", + "bbox": [ + 554, + 757, + 890, + 789 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $b(\\boldsymbol{r}(u))$ is the blending weight at the position $\\boldsymbol{r}(u)$ . $\\epsilon$ controls the surface thickness of the dynamic foreground.", + "bbox": [ + 497, + 806, + 889, + 834 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Musk flow loss. We further constrain the consistency 17908 point features by minimizing blending weight variations", + "bbox": [ + 465, + 838, + 890, + 866 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/a59d13ad5bbe83d9f6ac09ae7b80dd46cc15f70be89f923325a69ef3527d1b0f.jpg", + "image_caption": [ + "Figure 5: Fast novel scene adaption. We used the pretrained model on Balloon2 scene to fine-tune the novel views of unseen dynamic scenes. We employed LPIPS [55] (the lower is better) to evaluate the image similarity, which provides more correlation with human judgment than other indexes." + ], + "image_footnote": [], + "bbox": [ + 90, + 124, + 877, + 391 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "along trajectories,", + "bbox": [ + 75, + 470, + 200, + 483 + ], + "page_idx": 6 + }, + { + "type": "equation", + "text": "\n$$\nL _ {m f} = \\sum_ {i, j \\in \\{1, 2,.., K \\}} | | b (\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {i})) - b (\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {j})) | | _ {2}, \\tag {21}\n$$\n", + "text_format": "latex", + "bbox": [ + 87, + 494, + 468, + 526 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "where $b(\\Phi (\\pmb {p},t))$ denotes the blending weight at $\\Phi (p,t)$", + "bbox": [ + 75, + 536, + 453, + 549 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Other regularization. We follow previous works [21, 13, 10] to use the depth constraint, sparsity constraint, and motion regularization and smoothness to train the model.", + "bbox": [ + 75, + 549, + 468, + 591 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 75, + 605, + 208, + 619 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we conducted experiments on the Dynamic Scene dataset [53]. We first tested the performance of synthesizing novel views from single videos, and then we tested the generalization ability from multiple videos. In the end, we carried out ablation studies on our model.", + "bbox": [ + 75, + 628, + 468, + 698 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.1. Experimental Setup", + "text_level": 1, + "bbox": [ + 75, + 706, + 265, + 720 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Dataset. We used the Dynamic Scene dataset [53] to evaluate the proposed method. Concretely, it contains 9 video sequences that are captured with 12 cameras by using a camera rig. We followed previous works [21, 13] and derived each frame of the video from different cameras to simulate the camera motion. All the cameras capture images at 12 different timestamps $\\{t_i, i = 1, 2\\ldots, 12\\}$ . Each training video contains twelve frames sampled from the $i^{th}$ camera at time $t_i$ followed DynNeRF [13]. We used COI MAP [35, 36] to approximate the camera poses. It is assumed", + "bbox": [ + 75, + 726, + 468, + 866 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/44407472d7d7b9c2a7175b7acad1436211cebc04d1bd494bccd77d1df2ee0f11.jpg", + "table_caption": [ + "Table 3: Ablation studies on $\\mathbf{F}_{dy}$ , $\\mathbf{F}_{temp}$ , and $\\mathbf{F}_{sp}$ by jointly optimizing Balloon2 and Umbrella scenes." + ], + "table_footnote": [], + "table_body": "
PSNR ↑ / LPIPS ↓UmbrellaBalloon2Average
w/o. Fdy20.59 / 0.25622.79 / 0.15921.57 / 0.230
w/o. Ftemp22.75 / 0.17524.85 / 0.09823.80 / 0.137
w/o. Fsp22.81 / 0.18125.09 / 0.14323.95 / 0.162
Ours23.44 / 0.16925.44 / 0.09324.44 / 0.131
", + "bbox": [ + 500, + 505, + 890, + 568 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "trinsic parameters of all the cameras are the same. DynamicFace sequences were excluded because COLMAP fails to estimate camera poses. All video frames were resized to $480 \\times 270$ resolution. We generated the depth, mask, and optical flow signals from the depth estimation model [34], Mask R-CNN [16], and RAFT [39].", + "bbox": [ + 497, + 600, + 890, + 682 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Implementation details. We followed pixelNeRF [54] and used ResNet-based MLPs as our implicit velocity field $W_{vel}$ and rendering networks $W_{dy}$ and $W_{st}$ . For generalizable dynamic field, we utilized Slowonly50 [11] pretrained on Kinetics400 [2] dataset as the encoder $E_{dy}$ with the frozen weights. We removed the final fully connected layer in the backbone and incorporated the first, second, and third feature layers for querying $F_{sp}$ . We simplified (4) that $F_{sp}$ at time $t_i$ is sampled from $\\{V^{i-1}, V^i, V^{i+1}\\}$ . For generalizable static field, we used ResNet18 [17] pretrained on ImageNet [8] as the encoder $E_{st}$ . We extracted a feature pyramid from video frames for querying $F_{st}$ . The sizes of $F_{temp}, F_{sp}, F_{dy}$ , and $F_{st}$ are 256. Please", + "bbox": [ + 497, + 686, + 892, + 866 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e787085e5ab6629c2624730cb13c78db736050b2b08641018b97087cd86693cc.jpg", + "image_caption": [ + "Change BG" + ], + "image_footnote": [], + "bbox": [ + 89, + 136, + 211, + 186 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e1bd8dd725ae1e859c36925bde88936a8c19c165cbceec5208b0079fa0322bd6.jpg", + "image_caption": [ + "Move FG" + ], + "image_footnote": [], + "bbox": [ + 213, + 136, + 332, + 186 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c7328ce71aadfa7cd1059b18a982c422dfd5f0c5dbe3211fa235eda9f017d670.jpg", + "image_caption": [ + "Scale FG" + ], + "image_footnote": [], + "bbox": [ + 334, + 136, + 455, + 186 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/98a1aa70bce7a9e9d2e46cfb590dfd60d3894c053c6df9c5e32296a574e022ff.jpg", + "image_caption": [ + "Duplicate FG" + ], + "image_footnote": [], + "bbox": [ + 89, + 204, + 211, + 254 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/01ba4c928dc700d05e807551371736dfba2c9ae604166bfc81e0a9addbc76a7c.jpg", + "image_caption": [ + "Flip FG" + ], + "image_footnote": [], + "bbox": [ + 213, + 204, + 332, + 254 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c89b9a6067bc89224629a776338b8eb64e07e9c610692a1d9059ae030a6145e8.jpg", + "image_caption": [ + "Combinations", + "Figure 6: Our model supports many scene editing applications such as background changing, foreground moving, scaling, duplicating, flipping, and arbitrary combinations." + ], + "image_footnote": [], + "bbox": [ + 334, + 204, + 455, + 254 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/94a30a5a9afed09894dbd315b3d484728b3a0c1fdd78b06950a787ebc372fd94.jpg", + "table_caption": [ + "Table 4: Numeric comparisons on $L_{db}, L_{mf}, F_{st}$ , and random sampling strategy." + ], + "table_footnote": [], + "table_body": "
PSNR ↑ / LPIPS ↓Training framesUnseen framesUnseen videos
w/o. Ldb22.76 / 0.14820.69 / 0.34821.68 / 0.345
w/o. Lmf22.95 / 0.13520.95 / 0.35421.67 / 0.342
w/o. Fst21.75 / 0.23019.79 / 0.37121.81 / 0.337
w/o. random17.30 / 0.43516.93 / 0.51220.28 / 0.353
Ours23.02 / 0.13021.30 / 0.30422.63 / 0.277
", + "bbox": [ + 78, + 359, + 468, + 429 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/f79b27224f8fc1940d2ddb626a6a65f45c5e11aabbad551240e209430ca3bdbb.jpg", + "table_caption": [ + "Table 5: Comparisons of solving the continuous trajectory by using ODE solver [5] and our discretization method." + ], + "table_footnote": [], + "table_body": "
MethodN=1N=2ODE solver [5]
PSNR ↑ / LPIPS ↓22.90 / 0.13622.97 / 0.13423.75 / 0.129
", + "bbox": [ + 78, + 480, + 468, + 507 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "refer to the supplementary material for more details.", + "bbox": [ + 75, + 530, + 421, + 543 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.2. Novel View Synthesis from Single Video", + "text_level": 1, + "bbox": [ + 75, + 554, + 418, + 568 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this section, we trained the models from single monocular videos, where existing methods are applicable to this setting. Specifically, we first tested the performance on training frames, which is the widely-used setting to evaluate video-based NeRFs. Then, we tested the generalization ability on unseen frames in the video, where other existing methods are not able to transfer well to the unseen motions.", + "bbox": [ + 75, + 576, + 468, + 671 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Novel view synthesis on training frames. To evaluate the synthesized novel views, we followed DynNeRF [13] and tested the performance by fixing the view to the first camera and changing time. We reported the PSNR and LPIPS [55] in Table 1. We evaluated the performance of Li et al. [21], Tretschk et al. [40], NeuPhysics [33], and Chen et al. [13] from the official implementations. Even without the need of generalization ability, our method achieves better results.", + "bbox": [ + 75, + 672, + 468, + 795 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Novel view synthesis on unseen frames. We split the video frames into two groups: four front frames were used for training and the rest of eight unseen frames were utilized to render novel views. Figure 4 shows that our model", + "bbox": [ + 75, + 796, + 468, + 851 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "cessfully renders new motions in the unseen frames,", + "bbox": [ + 75, + 851, + 467, + 865 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/951ccb7a23a26ba741dc39843c21dea87e08576c2a08bef4aaa928ef4c6328a4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 514, + 124, + 626, + 188 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3d89f22fff8313c1c5510efea8514b67359ec59f8fd18e1c565dba007d3edf45.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 630, + 125, + 749, + 188 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/071d95c6b5a5ea560d731988e08cad9ec11f16c981666803acd6bbb13ee927f0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 752, + 125, + 878, + 190 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/dee79195ec2c50b8e47499c29a0217483388905ed193272eac66e5c10ff54dff.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 515, + 190, + 630, + 255 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/43ef605cdc2c1a1e142f90d55e153efe4649f6f3b5f2bc4d41e961b69daabff3.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 631, + 190, + 749, + 255 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3d020947aede9d0ebe4216d4edc8b1c2a2f05e386721311b98cf411d9dc87937.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 752, + 190, + 878, + 255 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/91d5471e5eb681f6e22e67d186f967b621b4f0712dc02272b3ed513d6869b82d.jpg", + "image_caption": [ + "Figure 7: Ablation studies on $L_{db}$ , $L_{mf}$ , random sampling, and $F_{st}$ ." + ], + "image_footnote": [], + "bbox": [ + 515, + 255, + 697, + 327 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/d48b4e5cdf109440435cdbfb90eebb4343f42092f73d37cceaa3128e87a531b3.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 697, + 255, + 878, + 327 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "DynNeRF [13] only interpolates novel views in the training frames. The reported PSNR, SSIM [47], and LPIPS scores in Table 2 quantitatively verify the superiority of our model.", + "bbox": [ + 497, + 391, + 890, + 433 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.3. Novel View Synthesis from Multiple Videos", + "text_level": 1, + "bbox": [ + 499, + 442, + 865, + 457 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In the section, we tested the novel view synthesis performance on multiple dynamic scenes. It is worth noting that as existing methods can only learn from single monocular videos, they are not applicable to the settings that need to train on multiple videos. Then, we evaluated the novel scene adaption ability on several novel monocular videos. Lastly, we conducted a series of scene editing experiments.", + "bbox": [ + 497, + 464, + 890, + 560 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Novel view synthesis on training videos. We selected Balloon2 and Umbrella scenes to train our model. As shown in Figure 3 and Table 3, our model could distinguish foregrounds from two scenes and perform well with $\\mathbf{F}_{dy}$ . Specifically, it predicts generalizable scene flows with $\\mathbf{F}_{temp}$ and renders more accurate details with $\\mathbf{F}_{sp}$ .", + "bbox": [ + 497, + 561, + 890, + 644 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Novel view synthesis on unseen videos. We explored the generalization ability of our model by pretraining on the Balloon2 scene and fine-tuning the pretrained model on other scenes. Figure 5 presents the results of four unseen videos: Playground, Skating, Truck, and Balloon1. We also pretrained DynNeRF [13] on the Balloon2 scene for a fair comparison. While DynNeRF only learns to render new scenes from scratch, our model transfers to scenes with correct dynamic motions. By further training with 500 steps, our model achieves better image rendering quality and higher LPIPS scores, which takes about 10 minutes.", + "bbox": [ + 497, + 644, + 890, + 796 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Scene editing. As Figure 6 shows, our model further supports many scene editing applications by directly processing point features without extra training. Changing background was implemented by exchanging the static", + "bbox": [ + 497, + 796, + 890, + 851 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "0 features between two scenes. Moving, scaling, dupi", + "bbox": [ + 497, + 851, + 890, + 866 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "cating and flipping foreground were directly applied by operating video features in dynamic radiance field. The above applications could be combined arbitrarily.", + "bbox": [ + 75, + 125, + 468, + 167 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "4.4. Ablation Study", + "text_level": 1, + "bbox": [ + 77, + 176, + 230, + 193 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We conducted a series of experiments to examine the proposed $L_{db}$ , $L_{mf}$ , $F_{st}$ , random sampling strategy, and trajectory discretization method. We show in Figure 7 that $L_{db}$ deblurs the margin of the synthesized foreground in novel views, $L_{mf}$ keeps the blending consistency in different views for delineating the foreground more accurately. The random sampling strategy successfully renders static scene without dynamic foreground, and backgrounds of two scenes are mixed without $F_{st}$ . We also show the numeric comparisons of $L_{db}$ , $L_{mf}$ , $F_{st}$ , and random sampling strategy in Table 4. In Table 5, our discretization method reaches comparable results with ODE solvers [5] and achieves higher performance with the increase of $N$ .", + "bbox": [ + 75, + 199, + 472, + 378 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 77, + 393, + 194, + 408 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this paper, we study the generalization ability of novel view synthesis from monocular videos. The challenge is the ambiguity of 3D point features and scene flows in the viewing directions. We find that video frame features and optical flows are a pair of complementary constraints for learning 3D point features and scene flows. To achieve this, we propose a generalizable dynamic radiance field called MonoNeRF. We estimate point features and trajectories from the video features extracted by a video encoder and render dynamic scenes from points features. Experiments show that our model could learn a generalizable radiance field for dynamic scenes, and support many scene editing applications.", + "bbox": [ + 75, + 416, + 468, + 583 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements. This work was supported by the National Key Research and Development Program of China under Grant No. 2020AAA0108100, the National Natural Science Foundation of China under Grant No. 62206147 and 61971343. The authors would like to thank the Shanghai Artificial Intelligence Laboratory for its generous support of computational resources.", + "bbox": [ + 75, + 583, + 468, + 684 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 699, + 173, + 713 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Shengqu Cai, Anton Obukhov, Dengxin Dai, and Luc Van Gool. 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In CVPR, June 2018. 7, 8" + ], + "bbox": [ + 78, + 125, + 468, + 214 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "17913", + "bbox": [ + 465, + 847, + 504, + 859 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/3b096572-4cf3-4c62-bc09-35a9369cf899_model.json b/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/3b096572-4cf3-4c62-bc09-35a9369cf899_model.json new file mode 100644 index 0000000000000000000000000000000000000000..4b5ae37e5b436ccb0a3236aa3f967aa80fae2257 --- /dev/null +++ b/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/3b096572-4cf3-4c62-bc09-35a9369cf899_model.json @@ -0,0 +1,2510 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.13, + 0.051, + 0.201, + 0.085 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.254, + 0.049, + 0.79, + 0.087 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.164, + 0.162, + 0.806, + 0.201 + ], + "angle": 0, + "content": "MonoNeRF: Learning a Generalizable Dynamic Radiance Field from Monocular Videos" + }, + { + "type": "text", + "bbox": [ + 0.306, + 0.229, + 0.663, + 0.246 + ], + "angle": 0, + "content": "Fengrui Tian\\(^{1}\\) Shaoyi Du\\(^{1}\\) Yueqi Duan\\(^{2\\dagger}\\)" + }, + { + "type": "text", + "bbox": [ + 0.171, + 0.246, + 0.798, + 0.311 + ], + "angle": 0, + "content": "\\(^{1}\\)National Key Laboratory of Human-Machine Hybrid Augmented Intelligence, National Engineering Research Center for Visual Information and Applications, and Institute of Artificial Intelligence and Robotics, Xi'an Jiaotong University \\(^{2}\\)Department of Electronic Engineering, Tsinghua University" + }, + { + "type": "text", + "bbox": [ + 0.179, + 0.313, + 0.79, + 0.326 + ], + "angle": 0, + "content": "tianfr@stu.xjtu.edu.cn, dushaoyi@gmail.com, duanyueqi@tsinghua.edu.cn" + }, + { + "type": "image", + "bbox": [ + 0.102, + 0.358, + 0.87, + 0.606 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.618, + 0.893, + 0.675 + ], + "angle": 0, + "content": "Figure 1: MonoNeRF learns a generalizable dynamic radiance field from multiple monocular videos. While video-based NeRF learns the field from positional encoding, we propose to learn from the extracted video features, which are generalizable to scenes. In this way, MonoNeRF supports scene editing applications (Top) and unseen frame synthesis (Middle). Compared with DynNeRF [13], MonoNeRF could adapt to novel scenes (Bottom) with hundreds of fine-tuning steps (about 10 minutes)." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.686, + 0.312, + 0.7 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.716, + 0.471, + 0.841 + ], + "angle": 0, + "content": "In this paper, we target at the problem of learning a generalizable dynamic radiance field from monocular videos. Different from most existing NeRF methods that are based on multiple views, monocular videos only contain one view at each timestamp, thereby suffering from ambiguity along the view direction in estimating point features and scene flows. Previous studies such as DynNeRF disambiguate point features by positional encoding, which is not transferable and severely limits the generalization abl" + }, + { + "type": "text", + "bbox": [ + 0.497, + 0.687, + 0.892, + 0.852 + ], + "angle": 0, + "content": "ity. As a result, these methods have to train one independent model for each scene and suffer from heavy computational costs when applying to increasing monocular videos in real-world applications. To address this, We propose MonoNeRF to simultaneously learn point features and scene flows with point trajectory and feature correspondence constraints across frames. More specifically, we learn an implicit velocity field to estimate point trajectory from temporal features with Neural ODE, which is followed by a flow-based feature aggregation module to obtain spatial features along the point trajectory. We jointly optimize temporal and spatial features in an end" + }, + { + "type": "text", + "bbox": [ + 0.466, + 0.851, + 0.892, + 0.867 + ], + "angle": 0, + "content": "17903 ... and manner. Experiments show that our MonoNeRF is" + }, + { + "type": "page_footnote", + "bbox": [ + 0.102, + 0.854, + 0.237, + 0.867 + ], + "angle": 0, + "content": "†: Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.888, + 0.49, + 0.899 + ], + "angle": 0, + "content": "1" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.127, + 0.472, + 0.182 + ], + "angle": 0, + "content": "able to learn from multiple scenes and support new applications such as scene editing, unseen frame synthesis, and fast novel scene adaptation. Codes are available at https://github.com/tianfr/MonoNeRF." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.208, + 0.21, + 0.222 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.231, + 0.47, + 0.438 + ], + "angle": 0, + "content": "Novel view synthesis [6] is a highly challenging problem. It facilitates many important applications in movie production, sports event, and virtual reality. The long standing problem recently has witnessed impressive progress due to the neural rendering technology [28, 26, 9]. Neural Radiance Field (NeRF) [28, 54, 22, 27, 46, 51, 52] shows that photo-realistic scenes can be represented by an implicit neural network. Concretely, taken as a query the position and viewing direction of the posed image, the network outputs the color of each pixel by volume rendering method. Among these approaches, it is supposed that the scene is static and can be observed from multiple views at the same time. Such assumptions are violated by numerous videos uploaded to the Internet, which usually contain dynamic foregrounds, recorded by the monocular camera." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.439, + 0.47, + 0.673 + ], + "angle": 0, + "content": "More recently, some studies aim to explore how to learn dynamic radiance field from monocular videos [10, 13, 21, 49, 50, 40]. Novel view synthesis from monocular videos is a challenging task. As foreground usually dynamically changes in a video, there is ambiguity in the view direction to estimate precise point features and dense object motions (i.e., scene flow [44]) from single views. In other words, we can only extract the projected 2D intra-frame local features and inter-frame optical flows, but fail to obtain precise 3D estimations. Previous works address this challenge by representing points as 4D position features (coordinate and time), so that the learned positional encoding provides specific information for each 3D point in the space [10, 13, 21, 49, 50, 40]. Based on positional encoding, these methods make efforts on exploiting scene priors [12, 48, 49] or adding spatio-temporal regularization [10, 13, 21, 50] to learn a more accurate dynamic radiance field." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.673, + 0.47, + 0.851 + ], + "angle": 0, + "content": "However, while positional encoding successfully disambiguates 3D points from monocular 2D projections, it severely overfits to the training video clip and is not transferable. Therefore, existing positional encoding based methods have to optimize one independent model for each dynamic scene. With the fast increase of monocular videos in reality, they suffer from heavy computational costs and lengthy training time to learn from multiple dynamic scenes. Also, the lack of generalization ability limits further applications of scene editing which requires interaction among different scenes. A natural question is raised: can we learn a generalizable dynamic radiance field from monocular videos?" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.127, + 0.892, + 0.319 + ], + "angle": 0, + "content": "tion. The key challenge of this task is to learn to extract generalizable point features in the 3D space from monocular videos. While independently using 2D local features and optical flows suffers from ambiguity along the ray direction, they provide complementary constraints to jointly learn 3D point features and scene flows. On the one hand, for the sampled points on each ray, optical flow provides generalizable constraints that limit the relations of their point trajectories. On the other hand, for the flowing points on each estimated point trajectory, we consider that they should share the same point features. We estimate each point feature by aggregating their projected 2D local features, and design feature correspondence constraints to correct unreasonable trajectories." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.32, + 0.893, + 0.665 + ], + "angle": 0, + "content": "To achieve this, we propose MonoNeRF to build a generalizable dynamic radiance field for multiple dynamic scenes. We hypothesize that a point moving along its trajectory over time keeps the consistent point feature. Our method concurrently predicts 3D point features and scene flows with point trajectory and feature correspondence constraints in monocular video frames. More specifically, we first propose to learn an implicit velocity field that encodes the speed from the temporal feature of each point. We supervise the velocity field with optical flow and integrate continuous point trajectories on the field with Neural ODE [5]. Then, we propose a flow-based feature aggregation module to sample spatial features of each point along the point trajectory. We incorporate the spatial and temporal features as the point feature to query the color and density for image rendering and jointly optimize point features and trajectories in an end-to-end manner. As shown in Figure 1, experiments demonstrate that our MonoNeRF is able to render novel views from multiple dynamic videos and support new applications such as scene editing, unseen frame synthesis, and fast novel scene adaption. Also, in the widely-used setting of novel view synthesis on training frames from single videos, our MonoNeRF still achieves better performance than existing methods despite that cross-scene generalization ability is not required in this setting." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.678, + 0.642, + 0.692 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.701, + 0.892, + 0.852 + ], + "angle": 0, + "content": "Novel view synthesis for static scenes. The long standing problem of novel view synthesis aims to construct new views of a scene from multiple posed images. Early works needed dense views captured from the scene [19, 14]. Recent studies have shown great progress by explicitly representing 3D scenes as neural representations [26, 28, 9, 7, 51, 25, 18, 38]. However, these methods train a separate model for each scene and need various training time for optimization. PixelNeRF [54] and MVSNeRF [4] proposed feature-based methods that directly render new scenes from the encoded features. Additionally, many researchers stud" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.852, + 0.893, + 0.867 + ], + "angle": 0, + "content": "In this paper, we provide a positive answer to this 17904 generalization and decomposition abilities of novel" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.125, + 0.894, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.465, + 0.893, + 0.522 + ], + "angle": 0, + "content": "Figure 2: The overview of our generalizable dynamic field. We first exploit an implicit velocity field from the extracted temporal feature \\( \\pmb{F}_{temp} \\). Then, we calculate point trajectory on the velocity field, and exploit the spatial feature \\( \\pmb{F}_{sp} \\) with the proposed flow-based spatial feature aggregation module. We incorporate \\( \\pmb{F}_{temp} \\) and \\( \\pmb{F}_{sp} \\) as the point feature \\( \\pmb{F}_{dy} \\) for rendering dynamic scene and design \\( L_{opt} \\) and \\( L_{corr} \\) to jointly optimize point features and trajectories." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.545, + 0.471, + 0.587 + ], + "angle": 0, + "content": "view synthesis model [3, 37, 29, 15, 1, 18, 41]. Compared with these methods, our method studies the synthesis and generalization ability of dynamic scenes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.589, + 0.47, + 0.811 + ], + "angle": 0, + "content": "Space-time view synthesis from monocular videos. With the development of neural radiance field in static scenes, recent studies started to address the dynamic scene reconstruction problem [21, 50, 10, 20, 31, 32]. In monocular videos, a key challenge is that there exist multiple scene constructions implying the same observed image sequences. Previous approaches addressed this challenge by using 3D coordinates with time as point features and adding scene priors or spatio-temporal regularization. Scene priors such as shadow modeling [49], human shape prior [48, 23], and facial appearance [12] are object-specific and closer to special contents. Spatio-temporal regularization such as depth and flow regularization [10, 13, 21, 50] and object deformations [40] are more object-agnostic, but weaker in applying consistency restriction to dynamic foregrounds. In this paper, we study the challenge by constraining point features." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.812, + 0.47, + 0.867 + ], + "angle": 0, + "content": "Scene flow for reconstruction. Scene flow firstly proposed by [44] depicts the motion of each point in the dynamic scene. Its 2D projection i.e., optical flow contributes to many downstream applications such as" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.545, + 0.892, + 0.713 + ], + "angle": 0, + "content": "super-resolution [45], video tracking [42], video segmentation [43], and video recognition [2]. Several methods studied the scene flow estimation problem based on point cloud sequences [30, 24]. However, estimating scene flow from an observed video is an ill-posed problem. In dynamic scene reconstruction, previous works [21, 13] established discrete scene flow for pixel consistency in observation time. In this way, the flow consistency in observed frames can only be constrained, leading to ambiguity in non-observed time. Du et al. [10] proposed to build the continuous flow field in a dynamic scene. Compared to these methods, we study the generalization ability of the flow field in different scenes." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.726, + 0.608, + 0.741 + ], + "angle": 0, + "content": "3. Approach" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.807 + ], + "angle": 0, + "content": "In this section, we introduce the proposed model that we term as MonoNeRF. We first present the overview of our model and then detail the approach of each part. Lastly, we introduce several strategies for optimizing the model." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.817, + 0.627, + 0.83 + ], + "angle": 0, + "content": "3.1. MonoNeRF" + }, + { + "type": "text", + "bbox": [ + 0.466, + 0.839, + 0.892, + 0.867 + ], + "angle": 0, + "content": "MonoNeRF aims to model generalizable radiance field 17905 amic scenes. Our method takes multiple monocu" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.126, + 0.473, + 0.514 + ], + "angle": 0, + "content": "lar videos as input and uses optical flows, depth maps, and binary masks of foreground objects as supervision signals. Those signals could be generated by pretrained models automatically. We build the generalizable static and dynamic fields for backgrounds and foregrounds separately. For generalizable dynamic field, we suppose that spatio-temporal points flow along their trajectories and hold consistent features over time. We first extract video features by a CNN encoder and generate the temporal feature vectors based on the extracted features. Then, we build an implicit velocity field from the temporal feature vectors to estimate point trajectories. Next, we exploit the estimated point trajectories as indexes to find the local image patches on each frame and extract the spatial features from the patches with the proposed flow-based feature aggregation module. Different from NeRF [28] that uses scene-agnostic point positions to render image color, we aggregate the scene-dependent spatial and temporal features as the final point features to render foreground scenes with volume rendering. Finally, we design the optical flow and feature correspondence constraints for jointly learning point features and trajectories. For generalizable static field, we suppose backgrounds are static and each video frame is considered as a different view of the background. Since some background parts may be occluded by the foreground, we design an effective strategy to sample background point features. In the end, we combine the generalizable static and dynamic fields for rendering free-point videos." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.522, + 0.338, + 0.537 + ], + "angle": 0, + "content": "3.2. Generalizable Dynamic Field" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.543, + 0.47, + 0.696 + ], + "angle": 0, + "content": "In this section, we introduce our generalizable dynamic field that renders novel views of dynamic foregrounds. We denote a monocular video as \\( \\mathbf{V} = \\{V^i, i = 1,2\\ldots ,K\\} \\) consisting of \\( K \\) frames. For each frame \\( V^i \\), \\( t_i \\) is the observed timestamp and \\( \\Pi^i \\) is the projection transform from the world coordinate to the 2D frame pixel coordinate. As Figure 2 shows, given a video \\( \\mathbf{V} \\), we exploit a video encoder \\( E_{dy} \\) to extract the video feature vector represented as \\( E_{dy}(\\mathbf{V}) \\) and generate the temporal feature vector \\( \\mathbf{F}_{temp} \\) with a multiple layer perceptron (MLP) \\( W_{temp}: E_{dy}(\\mathbf{V}) \\rightarrow \\mathbf{F}_{temp} \\). We build the implicit velocity field based on \\( \\mathbf{F}_{temp} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.696, + 0.47, + 0.807 + ], + "angle": 0, + "content": "Implicit velocity field. We suppose points are moving in the scene and represent a spatio-temporal point as \\(\\pmb{p} = (x_p, t_p)\\) including the 3D point position \\(\\pmb{x}_p\\) and time \\(t_p\\). We define \\(\\Phi\\) as the continuous point trajectory and \\(\\Phi(\\pmb{p}, t)\\) denotes the position of point \\(\\pmb{p}\\) at timestamp \\(t\\). We further define the velocity field \\(\\pmb{v}\\) which includes the 3D velocity of each point. The relationship between point velocity and trajectory is specified as follows," + }, + { + "type": "equation", + "bbox": [ + 0.102, + 0.816, + 0.469, + 0.844 + ], + "angle": 0, + "content": "\\[\n\\frac {\\partial \\Phi (\\boldsymbol {p} , t)}{\\partial t} = \\boldsymbol {v} \\left(\\Phi (\\boldsymbol {p}, t), t\\right), \\quad \\text {s . t .} \\quad \\Phi (\\boldsymbol {p}, t _ {p}) = \\boldsymbol {x} _ {p}. \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.852, + 0.465, + 0.868 + ], + "angle": 0, + "content": "\\(\\pmb{v}\\) is conditioned on \\(F_{temp}\\) and implemented by an" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.126, + 0.892, + 0.155 + ], + "angle": 0, + "content": "\\(W_{vel}\\colon (F_{temp}(\\boldsymbol {V}),\\Phi ,t)\\to \\boldsymbol{v}.\\) We calculate the point trajectory at an observed timestamp \\(t_i\\) with Neural ODE [5]," + }, + { + "type": "equation", + "bbox": [ + 0.568, + 0.164, + 0.892, + 0.198 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {i}) = \\boldsymbol {x} _ {p} + \\int_ {t _ {p}} ^ {t _ {i}} \\boldsymbol {v} \\left(\\boldsymbol {\\Phi} (\\boldsymbol {p}, t), t\\right) d t. \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.204, + 0.875, + 0.218 + ], + "angle": 0, + "content": "We take \\(\\Phi (\\pmb {p},t_i)\\) as an index to query the spatial feature." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.219, + 0.892, + 0.288 + ], + "angle": 0, + "content": "Flow-based spatial feature aggregation. We employ \\(\\Pi^i\\) to project \\(\\Phi (\\pmb {p},t_i)\\) on \\(V^{i}\\) and find the local image patch indexed by the projected position \\(\\Pi^i (\\Phi (\\pmb {p},t_i))\\). We extract the feature vector \\(F_{sp}^{i}\\) from the patch with the encoder \\(E_{dy}\\) and a fully connected layer \\(fc_{1}\\)," + }, + { + "type": "equation", + "bbox": [ + 0.545, + 0.297, + 0.892, + 0.321 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {F} _ {s p} ^ {i} (\\boldsymbol {V}; \\boldsymbol {p}) = f c _ {1} \\left(E _ {d y} \\left(\\boldsymbol {V} ^ {i}; \\Pi^ {i} (\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {i}))\\right)\\right). \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.333, + 0.892, + 0.42 + ], + "angle": 0, + "content": "In practice, \\( E_{dy}\\big(\\mathbf{V}^i;\\Pi^i (\\Phi (\\mathbf{p},t_i))\\big) \\) is implemented by using \\( E_{dy} \\) to extract the frame-wise feature map of \\( V^{i} \\) and sampling the feature vector at \\( \\Pi^i (\\Phi (\\pmb {p},t_i)) \\) with bilinear interpolation. The spatial feature vector \\( \\pmb{F}_{sp} \\) is then calculated by incorporating \\( \\{\\pmb{F}_{sp}^{1},\\pmb{F}_{sp}^{2},\\dots,\\pmb{F}_{sp}^{K}\\} \\) with a fully connected layer \\( fc_{2} \\)," + }, + { + "type": "equation", + "bbox": [ + 0.5, + 0.429, + 0.894, + 0.458 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {F} _ {s p} (\\boldsymbol {V}; \\boldsymbol {p}) = f c _ {2} \\left(\\boldsymbol {F} _ {s p} ^ {1} (\\boldsymbol {V}; \\boldsymbol {p}), \\boldsymbol {F} _ {s p} ^ {2} (\\boldsymbol {V}; \\boldsymbol {p}), \\dots , \\boldsymbol {F} _ {s p} ^ {K} (\\boldsymbol {V}; \\boldsymbol {p})\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.459, + 0.892, + 0.487 + ], + "angle": 0, + "content": "Finally, we incorporate \\( \\mathbf{F}_{temp} \\) and \\( \\mathbf{F}_{sp} \\) as the point feature vector \\( \\mathbf{F}_{dy} \\)," + }, + { + "type": "equation", + "bbox": [ + 0.527, + 0.497, + 0.892, + 0.514 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {F} _ {d y} (\\boldsymbol {V}; \\boldsymbol {p}) = \\operatorname {c o n c a t} \\left\\{\\boldsymbol {F} _ {\\text {t e m p}} (\\boldsymbol {V}), \\boldsymbol {F} _ {\\text {s p}} (\\boldsymbol {V}; \\boldsymbol {p}) \\right\\}. \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.524, + 0.871, + 0.538 + ], + "angle": 0, + "content": "We build the generalizable dynamic field based on \\( \\mathbf{F}_{dy} \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.539, + 0.892, + 0.678 + ], + "angle": 0, + "content": "Dynamic foreground rendering. Taking a point \\( \\pmb{p} \\) and its feature vector \\( \\pmb{F}_{dy}(\\pmb{V};\\pmb{p}) \\) as input, our generalizable dynamic radiance field \\( W_{dy} \\colon (\\pmb{p}, \\pmb{F}_{dy}(\\pmb{V};\\pmb{p})) \\to (\\pmb{c}_{dy}, \\sigma_{dy}, b) \\) predicts the volume density \\( \\sigma_{dy} \\), color \\( c_{dy} \\) and blending weight \\( b \\) of the point. We follow DynNeRF [13] and utilize \\( b \\) to judge whether a point belongs to static background or dynamic foreground. We exploit volume rendering to approximate each pixel color of an image. Concretely, given a ray \\( r(u) = o + ud \\) starting from the camera center \\( o \\) along the direction \\( d \\) through a pixel, its color is integrated by" + }, + { + "type": "equation", + "bbox": [ + 0.559, + 0.686, + 0.892, + 0.719 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {C} _ {d y} (\\boldsymbol {r}) = \\int_ {u _ {n}} ^ {u _ {f}} T _ {d y} (u) \\sigma_ {d y} (u) \\boldsymbol {c} _ {d y} (u) d u, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.727, + 0.892, + 0.811 + ], + "angle": 0, + "content": "where \\( u_{n}, u_{f} \\) are the bounds of the volume rendering depth range and \\( T_{dy}(u) = \\exp(-\\int_{u_{n}}^{u} \\sigma_{dy}(\\boldsymbol{r}(s)) ds \\) is the accumulated transparency. We simplify \\( c(u) = c(\\boldsymbol{r}(u), \\boldsymbol{d}) \\) and \\( \\sigma(u) = \\sigma(\\boldsymbol{r}(u)) \\) here and in the following sections. Next we present the optical flow and feature correspondence constraints that jointly supervise our model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.812, + 0.892, + 0.868 + ], + "angle": 0, + "content": "Optical flow constraint. We supervise \\(\\pmb{v}\\) with the optical flow \\(f^{gt}\\). In practice, it can only approximate the backward flow \\(f_{bw}^{gt}\\) and forward flow \\(f_{fw}^{gt}\\) between two consecutive video frames [39]. We hence estimate the point" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.126, + 0.473, + 0.239 + ], + "angle": 0, + "content": "backward and forward trajectory variations during the period that the point passes between two frames and calculate optical flows by integrating the trajectory variations of each point along camera rays. Formally, given a ray \\( \\pmb{r}(u) \\) through a pixel on the frame \\( \\pmb{V}^i \\) at time \\( t_i \\), for each point on the ray i.e., \\( \\pmb{p}(u) = (\\pmb{r}(u), t_i) \\) the trajectory variations \\( \\Delta \\Phi_{bw} \\) back to \\( t_{i-1} \\) and \\( \\Delta \\Phi_{fw} \\) forward to \\( t_{i+1} \\) are obtained by the following equation," + }, + { + "type": "equation", + "bbox": [ + 0.093, + 0.246, + 0.47, + 0.29 + ], + "angle": 0, + "content": "\\[\n\\Delta \\Phi_ {\\{b w, f w \\}} (\\boldsymbol {p} (u)) = \\int_ {t _ {i}} ^ {t _ {\\{i - 1, i + 1 \\}}} \\boldsymbol {v} (\\boldsymbol {\\Phi} (\\boldsymbol {p} (u), t), t) d t. \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.29, + 0.47, + 0.334 + ], + "angle": 0, + "content": "We follow previous works [21, 13] and exploit the volume rendering to integrate pseudo optical flows \\( \\pmb{f}_{bw} \\) and \\( \\pmb{f}_{fw} \\) by utilizing the estimated volume density \\( \\sigma_{dy} \\) of each point," + }, + { + "type": "equation", + "bbox": [ + 0.08, + 0.341, + 0.469, + 0.383 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {f} _ {\\{b w, f w \\}} (\\boldsymbol {r}) = \\int_ {u _ {n}} ^ {u _ {f}} T _ {d y} (u) \\sigma_ {d y} (u) \\Delta \\Phi_ {\\{b w, f w \\}} ^ {i} (\\boldsymbol {p} (u)) d u, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.383, + 0.469, + 0.429 + ], + "angle": 0, + "content": "where \\(\\Delta \\Phi_{\\{bw,fw\\}}^i = \\Pi^i (\\Delta \\Phi_{\\{bw,fw\\}})\\) denotes we use \\(\\Pi^i\\) to project 3D trajectory variations on the image plane of \\(V^i\\). We supervise the pseudo flows by the ground truth flows," + }, + { + "type": "equation", + "bbox": [ + 0.126, + 0.438, + 0.47, + 0.468 + ], + "angle": 0, + "content": "\\[\nL _ {o p t} = \\sum_ {\\boldsymbol {r}} \\left(\\boldsymbol {f} _ {\\{b w, f w \\}} (\\boldsymbol {r}) - \\boldsymbol {f} _ {\\{b w, f w \\}} ^ {g t} (\\boldsymbol {r})\\right). \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.477, + 0.47, + 0.505 + ], + "angle": 0, + "content": "In this way, the relation of point trajectories along a ray is limited by the optical flow supervision." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.505, + 0.47, + 0.589 + ], + "angle": 0, + "content": "Feature correspondence constraint. According to Section 3.1, a point moving along the trajectory holds the same feature and represents the consistent color and density. For each ray \\( \\boldsymbol{r}_{curr} \\) at the current time \\( t_i \\) through a pixel of \\( V^i \\), we warp the ray from the neighboring observed timestamps \\( t_{i-1} \\) and \\( t_{i+1} \\) as \\( \\boldsymbol{r}_{bw} \\) and \\( \\boldsymbol{r}_{fw} \\) separately by using (7)," + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.598, + 0.47, + 0.615 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {r} _ {\\{b w, f w \\}} (u) = \\boldsymbol {r} _ {\\text {c u r r}} (u) + \\Delta \\Phi_ {\\{b w, f w \\}} \\left(\\boldsymbol {p} _ {\\text {c u r r}} (u)\\right), \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.623, + 0.469, + 0.696 + ], + "angle": 0, + "content": "where \\(\\pmb{p}_{\\text{curr}}(u) = (\\pmb{r}_{\\text{curr}}(u), t_i)\\). We render the pixel color from the point features not only along the ray \\(\\pmb{r}_{\\text{curr}}\\) at the time \\(t_i\\), but also along the wrapped rays \\(\\pmb{r}_{bw}\\) at \\(t_{i-1}\\) and \\(\\pmb{r}_{fw}\\) at \\(t_{i+1}\\). The predicted pixel color \\(\\pmb{C}_{dy}\\) is rendered by using (6) and supervised by the ground truth colors \\(\\pmb{C}_{dy}^{gt}\\)," + }, + { + "type": "equation", + "bbox": [ + 0.084, + 0.705, + 0.469, + 0.745 + ], + "angle": 0, + "content": "\\[\nL _ {\\{b w, c u r r, f w \\}} = \\sum_ {\\boldsymbol {r}} | | \\boldsymbol {C} _ {d y} (\\boldsymbol {r} _ {\\{b w, c u r r, f w \\}}) - \\boldsymbol {C} _ {d y} ^ {g t} (\\boldsymbol {r}) | | _ {2}. \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.746, + 0.458, + 0.76 + ], + "angle": 0, + "content": "The feature correspondence constraint \\(L_{corr}\\) is defined as" + }, + { + "type": "equation", + "bbox": [ + 0.172, + 0.77, + 0.469, + 0.786 + ], + "angle": 0, + "content": "\\[\nL _ {c o r r} = L _ {b w} + L _ {c u r r} + L _ {f w}. \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.796, + 0.469, + 0.811 + ], + "angle": 0, + "content": "\\(L_{corr}\\) supervises the predicted color and point features \\(\\pmb{F}_{dy}\\)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.817, + 0.314, + 0.831 + ], + "angle": 0, + "content": "3.3. Generalizable Static Field" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.839, + 0.506, + 0.868 + ], + "angle": 0, + "content": "As mentioned in Section 3.1, for some background node occluded by the changing foreground in the current ..... 17907" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.126, + 0.892, + 0.197 + ], + "angle": 0, + "content": "their features implying the foreground cannot infer the correct background information. However, the occluded parts could be seen in non-occluded views with correct background features. To this end, given a point position \\( \\pmb{x} \\), the background point feature vector \\( \\pmb{F}_{st} \\) is produced by" + }, + { + "type": "equation", + "bbox": [ + 0.568, + 0.206, + 0.892, + 0.23 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {F} _ {s t} (\\boldsymbol {V}; \\boldsymbol {x}) = f c _ {3} \\left(E _ {s t} \\left(\\boldsymbol {V} ^ {*}; \\Pi^ {*} (\\boldsymbol {x})\\right)\\right), \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.238, + 0.893, + 0.405 + ], + "angle": 0, + "content": "where \\( f c_{3} \\) is a fully connected layer and \\( E_{st} \\) denotes the image encoder. \\( V^{*} \\) and \\( \\Pi^{*} \\) are the non-occluded frame and corresponding projection transform respectively. \\( E_{st}(V^{*};\\Pi^{*}(\\pmb {x})) \\) denotes that we find the local image patch at \\( \\Pi^{*}(\\pmb {x}) \\) and extract the feature vectors with an image encoder \\( E_{st} \\) similar to \\( E_{dy}\\big(V^i;\\Pi^i (\\Phi (\\pmb {p},t_i))\\big) \\). Since there is no prior in which frames they can be exposed, we apply a straightforward yet effective strategy by randomly sampling one frame from the other frames in the video. We represent the static scene as a radiance field to infer the color \\( c_{st} \\) and density \\( \\sigma_{st} \\) by using an MLP \\( W_{st} \\): \\( (\\pmb {x},\\pmb {d},\\pmb{F}_{st}(\\pmb {V};\\pmb {x}))\\rightarrow (c_{st},\\sigma_{st}) \\). The expected background color \\( C_{st} \\) is given by" + }, + { + "type": "equation", + "bbox": [ + 0.565, + 0.414, + 0.892, + 0.445 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {C} _ {s t} (\\boldsymbol {r}) = \\int_ {u _ {n}} ^ {u _ {f}} T _ {s t} (u) \\sigma_ {s t} (u) \\boldsymbol {c} _ {s t} (u) d u, \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.455, + 0.892, + 0.512 + ], + "angle": 0, + "content": "where \\( T_{st}(t) = \\exp (-\\int_{u_n}^u\\sigma_{st}(\\boldsymbol {r}(s))ds \\). We employ foreground masks \\( M \\) to optimize the static field by supervising the pixel color in each video frame in the background regions (where \\( M(\\boldsymbol {r}) = 0 \\))," + }, + { + "type": "equation", + "bbox": [ + 0.524, + 0.522, + 0.892, + 0.55 + ], + "angle": 0, + "content": "\\[\nL _ {s t} = \\sum_ {\\boldsymbol {r}} | | \\left(\\boldsymbol {C} _ {s t} (\\boldsymbol {r}) - \\boldsymbol {C} _ {s t} ^ {q t} (\\boldsymbol {r})\\right) (1 - M (\\boldsymbol {r})) \\| _ {2}, \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.561, + 0.796, + 0.577 + ], + "angle": 0, + "content": "where \\( C_{st}^{gt} \\) represents the ground truth color." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.585, + 0.64, + 0.599 + ], + "angle": 0, + "content": "3.4. Optimization" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.606, + 0.891, + 0.634 + ], + "angle": 0, + "content": "The final dynamic scene color combines the colors from the generalizable dynamic and static fields," + }, + { + "type": "equation", + "bbox": [ + 0.526, + 0.643, + 0.892, + 0.675 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {C} _ {f u l l} (\\boldsymbol {r}) = \\int_ {u _ {n}} ^ {u _ {f}} T _ {f u l l} (u) \\sigma_ {f u l l} (u) \\boldsymbol {c} _ {f u l l} (u) d u, \\tag {16}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.684, + 0.547, + 0.696 + ], + "angle": 0, + "content": "where" + }, + { + "type": "equation", + "bbox": [ + 0.5, + 0.708, + 0.892, + 0.736 + ], + "angle": 0, + "content": "\\[\n\\sigma_ {f u l l} (u) \\boldsymbol {c} _ {f u l l} (u) = (1 - b) \\sigma_ {s t} (u) \\boldsymbol {c} _ {s t} (u) + b \\sigma_ {d y} (u) \\boldsymbol {c} _ {d y} (u), \\tag {17}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.736, + 0.734, + 0.75 + ], + "angle": 0, + "content": "and applies the reconstruction loss," + }, + { + "type": "equation", + "bbox": [ + 0.565, + 0.759, + 0.892, + 0.788 + ], + "angle": 0, + "content": "\\[\nL _ {f u l l} = \\sum_ {\\boldsymbol {r}} | | \\boldsymbol {C} _ {f u l l} (\\boldsymbol {r}) - \\boldsymbol {C} _ {f u l l} ^ {g t} (\\boldsymbol {r}) | | _ {2}. \\tag {18}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.798, + 0.874, + 0.811 + ], + "angle": 0, + "content": "Next we design several strategies to optimize our model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.812, + 0.892, + 0.868 + ], + "angle": 0, + "content": "Point trajectory discretization. While point trajectory can be numerically estimated by the continuous integral (2) with Neural ODE solvers [5], it needs plenty of time for 7 ng each point trajectory. To accelerate the process," + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.124, + 0.892, + 0.154 + ], + "angle": 0, + "content": "Table 1: Novel view synthesis on training frames from single videos. While this setting does not require cross-scene generalization ability, our MonoNeRF still achieves better performance." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.162, + 0.895, + 0.27 + ], + "angle": 0, + "content": "
PSNR ↑ / LPIPS ↓JumpingSkatingTruckUmbrellaBalloon1Balloon2PlaygroundAverage
NeRF [28]20.58 / 0.30523.05 / 0.31622.61 / 0.22521.08 / 0.44119.07 / 0.21424.08 / 0.09820.86 / 0.16421.62 / 0.252
NeRF [28] + time16.72 / 0.48919.23 / 0.54217.17 / 0.40317.17 / 0.75217.33 / 0.30419.67 / 0.23613.80 / 0.44417.30 / 0.453
Yoon et al. [53]20.16 / 0.14821.75 / 0.13523.93 / 0.10920.35 / 0.17918.76 / 0.17819.89 / 0.13815.09 / 0.18319.99 / 0.153
Tretschk et al. [40]19.38 / 0.29523.29 / 0.23419.02 / 0.45319.26 / 0.42716.98 / 0.35322.23 / 0.21214.24 / 0.33619.20 / 0.330
Li et al. [21]24.12 / 0.15628.91 / 0.13525.94 / 0.17122.58 / 0.30221.40 / 0.22524.09 / 0.22820.91 / 0.22023.99 / 0.205
NeuPhysics [33]20.16 / 0.20525.13 / 0.16622.62 / 0.21221.02 / 0.42616.68 / 0.23822.54 / 0.26515.10 / 0.36720.48 / 0.282
DynNeRF [13]24.23 / 0.14428.90 / 0.12425.78 / 0.13423.15 / 0.14621.47 / 0.12525.97 / 0.05923.65 / 0.09324.74 / 0.118
MonoNeRF24.26 / 0.09132.06 / 0.04427.56 / 0.11523.62 / 0.18021.89 / 0.12927.36 / 0.05222.61 / 0.13025.62 / 0.106
" + }, + { + "type": "image", + "bbox": [ + 0.095, + 0.279, + 0.877, + 0.427 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.435, + 0.893, + 0.479 + ], + "angle": 0, + "content": "Figure 3: Qualitative results of jointly optimizing Balloon2 and Umbrella scenes. The foregrounds of two scenes are mixed without \\( F_{dy} \\). Our method renders more accurate novel views and predicts plausible scene flows (listed beside the RGB images) by incorporating \\( F_{temp} \\) and \\( F_{sp} \\)." + }, + { + "type": "image", + "bbox": [ + 0.088, + 0.499, + 0.458, + 0.613 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.621, + 0.471, + 0.678 + ], + "angle": 0, + "content": "Figure 4: Novel view synthesis on unseen frames. Compared to the ground truths, our model could transfer to new motions, whereas DynNeRF [13] only interpolates in the training frames." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.701, + 0.47, + 0.744 + ], + "angle": 0, + "content": "we propose to partition \\([t_p, t_i]\\) into \\(N\\) evenly-spaced bins and suppose the point velocity in each bin is a constant. The point trajectory can be estimated by the following equation," + }, + { + "type": "equation", + "bbox": [ + 0.091, + 0.764, + 0.47, + 0.802 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {i}) = \\boldsymbol {x} _ {p} + \\sum_ {n = 1} ^ {N} \\boldsymbol {v} \\left(\\boldsymbol {\\Phi} (\\boldsymbol {p}, t + \\Delta t), t + \\Delta t\\right) \\Delta t, \\tag {19}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.811, + 0.245, + 0.826 + ], + "angle": 0, + "content": "where \\(\\Delta t = \\frac{n}{N} (t_{i} - t_{p})\\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.469, + 0.867 + ], + "angle": 0, + "content": "Depth-blending restriction. To calculate the blending weights within a foreground ray in the generalizable dynamic field, only the points in close proximity to the" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.499, + 0.892, + 0.542 + ], + "angle": 0, + "content": "Table 2: Quantitative results of novel view synthesis on unseen frames. We used the first four frames for training and tested the performance on the rest eight frames." + }, + { + "type": "table", + "bbox": [ + 0.501, + 0.551, + 0.892, + 0.627 + ], + "angle": 0, + "content": "
Balloon2 / TruckPSNR ↑SSIM ↑LPIPS ↓
NeRF [28]20.33 / 20.260.662 / 0.6690.224 / 0.256
NeRF [28] + time20.22 / 20.260.661 / 0.6390.218 / 0.256
NeuPhysics [33]19.45 / 20.240.478 / 0.5170.343 / 0.285
DynNeRF [13]19.99 / 20.330.641 / 0.6210.291 / 0.273
MonoNeRF21.30 / 23.740.669 / 0.7020.204 / 0.174
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.657, + 0.892, + 0.741 + ], + "angle": 0, + "content": "mated ray depth are regarded as foreground points, whereas points beyond this range are excluded. We penalize the blending weights of non-foreground points in foreground rays. Specifically, given a ray \\( r(u) \\) through a pixel and the pixel depth \\( u_{d} \\), We penalize the blending weights of the points on the ray out of the interval \\( (u_{d} - \\epsilon, u_{d} + \\epsilon) \\)," + }, + { + "type": "equation", + "bbox": [ + 0.556, + 0.758, + 0.892, + 0.79 + ], + "angle": 0, + "content": "\\[\nL _ {d b} = \\sum_ {u \\in \\left(u _ {n}, u _ {d} - \\epsilon\\right) \\cup \\left(u _ {d} + \\epsilon , u _ {f}\\right)} \\| b (\\boldsymbol {r} (u)) \\| _ {2}, \\tag {20}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.807, + 0.89, + 0.836 + ], + "angle": 0, + "content": "where \\(b(\\boldsymbol{r}(u))\\) is the blending weight at the position \\(\\boldsymbol{r}(u)\\). \\(\\epsilon\\) controls the surface thickness of the dynamic foreground." + }, + { + "type": "text", + "bbox": [ + 0.466, + 0.839, + 0.892, + 0.868 + ], + "angle": 0, + "content": "Musk flow loss. We further constrain the consistency 17908 point features by minimizing blending weight variations" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.092, + 0.125, + 0.878, + 0.393 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.404, + 0.893, + 0.446 + ], + "angle": 0, + "content": "Figure 5: Fast novel scene adaption. We used the pretrained model on Balloon2 scene to fine-tune the novel views of unseen dynamic scenes. We employed LPIPS [55] (the lower is better) to evaluate the image similarity, which provides more correlation with human judgment than other indexes." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.471, + 0.2, + 0.484 + ], + "angle": 0, + "content": "along trajectories," + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.495, + 0.469, + 0.527 + ], + "angle": 0, + "content": "\\[\nL _ {m f} = \\sum_ {i, j \\in \\{1, 2,.., K \\}} | | b (\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {i})) - b (\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {j})) | | _ {2}, \\tag {21}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.537, + 0.455, + 0.551 + ], + "angle": 0, + "content": "where \\(b(\\Phi (\\pmb {p},t))\\) denotes the blending weight at \\(\\Phi (p,t)\\)" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.551, + 0.469, + 0.592 + ], + "angle": 0, + "content": "Other regularization. We follow previous works [21, 13, 10] to use the depth constraint, sparsity constraint, and motion regularization and smoothness to train the model." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.606, + 0.21, + 0.621 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.47, + 0.699 + ], + "angle": 0, + "content": "In this section, we conducted experiments on the Dynamic Scene dataset [53]. We first tested the performance of synthesizing novel views from single videos, and then we tested the generalization ability from multiple videos. In the end, we carried out ablation studies on our model." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.707, + 0.267, + 0.722 + ], + "angle": 0, + "content": "4.1. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.728, + 0.469, + 0.867 + ], + "angle": 0, + "content": "Dataset. We used the Dynamic Scene dataset [53] to evaluate the proposed method. Concretely, it contains 9 video sequences that are captured with 12 cameras by using a camera rig. We followed previous works [21, 13] and derived each frame of the video from different cameras to simulate the camera motion. All the cameras capture images at 12 different timestamps \\(\\{t_i, i = 1, 2\\ldots, 12\\}\\). Each training video contains twelve frames sampled from the \\(i^{th}\\) camera at time \\(t_i\\) followed DynNeRF [13]. We used COI MAP [35, 36] to approximate the camera poses. It is assumed" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.468, + 0.892, + 0.497 + ], + "angle": 0, + "content": "Table 3: Ablation studies on \\( \\mathbf{F}_{dy} \\), \\( \\mathbf{F}_{temp} \\), and \\( \\mathbf{F}_{sp} \\) by jointly optimizing Balloon2 and Umbrella scenes." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.506, + 0.892, + 0.57 + ], + "angle": 0, + "content": "
PSNR ↑ / LPIPS ↓UmbrellaBalloon2Average
w/o. Fdy20.59 / 0.25622.79 / 0.15921.57 / 0.230
w/o. Ftemp22.75 / 0.17524.85 / 0.09823.80 / 0.137
w/o. Fsp22.81 / 0.18125.09 / 0.14323.95 / 0.162
Ours23.44 / 0.16925.44 / 0.09324.44 / 0.131
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.601, + 0.892, + 0.683 + ], + "angle": 0, + "content": "trinsic parameters of all the cameras are the same. DynamicFace sequences were excluded because COLMAP fails to estimate camera poses. All video frames were resized to \\(480 \\times 270\\) resolution. We generated the depth, mask, and optical flow signals from the depth estimation model [34], Mask R-CNN [16], and RAFT [39]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.687, + 0.893, + 0.868 + ], + "angle": 0, + "content": "Implementation details. We followed pixelNeRF [54] and used ResNet-based MLPs as our implicit velocity field \\( W_{vel} \\) and rendering networks \\( W_{dy} \\) and \\( W_{st} \\). For generalizable dynamic field, we utilized Slowonly50 [11] pretrained on Kinetics400 [2] dataset as the encoder \\( E_{dy} \\) with the frozen weights. We removed the final fully connected layer in the backbone and incorporated the first, second, and third feature layers for querying \\( F_{sp} \\). We simplified (4) that \\( F_{sp} \\) at time \\( t_i \\) is sampled from \\( \\{V^{i-1}, V^i, V^{i+1}\\} \\). For generalizable static field, we used ResNet18 [17] pretrained on ImageNet [8] as the encoder \\( E_{st} \\). We extracted a feature pyramid from video frames for querying \\( F_{st} \\). The sizes of \\( F_{temp}, F_{sp}, F_{dy} \\), and \\( F_{st} \\) are 256. Please" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.115, + 0.125, + 0.187, + 0.136 + ], + "angle": 0, + "content": "Change BG" + }, + { + "type": "image", + "bbox": [ + 0.09, + 0.137, + 0.212, + 0.187 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.246, + 0.125, + 0.302, + 0.135 + ], + "angle": 0, + "content": "Move FG" + }, + { + "type": "image", + "bbox": [ + 0.214, + 0.137, + 0.334, + 0.187 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.368, + 0.125, + 0.425, + 0.135 + ], + "angle": 0, + "content": "Scale FG" + }, + { + "type": "image", + "bbox": [ + 0.336, + 0.137, + 0.457, + 0.187 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.111, + 0.193, + 0.191, + 0.204 + ], + "angle": 0, + "content": "Duplicate FG" + }, + { + "type": "image_caption", + "bbox": [ + 0.251, + 0.193, + 0.296, + 0.204 + ], + "angle": 0, + "content": "Flip FG" + }, + { + "type": "image", + "bbox": [ + 0.09, + 0.205, + 0.212, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.214, + 0.205, + 0.334, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.355, + 0.193, + 0.437, + 0.204 + ], + "angle": 0, + "content": "Combinations" + }, + { + "type": "image", + "bbox": [ + 0.336, + 0.205, + 0.457, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.267, + 0.468, + 0.308 + ], + "angle": 0, + "content": "Figure 6: Our model supports many scene editing applications such as background changing, foreground moving, scaling, duplicating, flipping, and arbitrary combinations." + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.323, + 0.468, + 0.351 + ], + "angle": 0, + "content": "Table 4: Numeric comparisons on \\(L_{db}, L_{mf}, F_{st}\\), and random sampling strategy." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.36, + 0.469, + 0.43 + ], + "angle": 0, + "content": "
PSNR ↑ / LPIPS ↓Training framesUnseen framesUnseen videos
w/o. Ldb22.76 / 0.14820.69 / 0.34821.68 / 0.345
w/o. Lmf22.95 / 0.13520.95 / 0.35421.67 / 0.342
w/o. Fst21.75 / 0.23019.79 / 0.37121.81 / 0.337
w/o. random17.30 / 0.43516.93 / 0.51220.28 / 0.353
Ours23.02 / 0.13021.30 / 0.30422.63 / 0.277
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.443, + 0.468, + 0.47 + ], + "angle": 0, + "content": "Table 5: Comparisons of solving the continuous trajectory by using ODE solver [5] and our discretization method." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.481, + 0.469, + 0.508 + ], + "angle": 0, + "content": "
MethodN=1N=2ODE solver [5]
PSNR ↑ / LPIPS ↓22.90 / 0.13622.97 / 0.13423.75 / 0.129
" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.532, + 0.423, + 0.545 + ], + "angle": 0, + "content": "refer to the supplementary material for more details." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.555, + 0.419, + 0.569 + ], + "angle": 0, + "content": "4.2. Novel View Synthesis from Single Video" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.577, + 0.469, + 0.672 + ], + "angle": 0, + "content": "In this section, we trained the models from single monocular videos, where existing methods are applicable to this setting. Specifically, we first tested the performance on training frames, which is the widely-used setting to evaluate video-based NeRFs. Then, we tested the generalization ability on unseen frames in the video, where other existing methods are not able to transfer well to the unseen motions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.673, + 0.469, + 0.796 + ], + "angle": 0, + "content": "Novel view synthesis on training frames. To evaluate the synthesized novel views, we followed DynNeRF [13] and tested the performance by fixing the view to the first camera and changing time. We reported the PSNR and LPIPS [55] in Table 1. We evaluated the performance of Li et al. [21], Tretschk et al. [40], NeuPhysics [33], and Chen et al. [13] from the official implementations. Even without the need of generalization ability, our method achieves better results." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.798, + 0.469, + 0.852 + ], + "angle": 0, + "content": "Novel view synthesis on unseen frames. We split the video frames into two groups: four front frames were used for training and the rest of eight unseen frames were utilized to render novel views. Figure 4 shows that our model" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.852, + 0.468, + 0.866 + ], + "angle": 0, + "content": "cessfully renders new motions in the unseen frames," + }, + { + "type": "image", + "bbox": [ + 0.515, + 0.125, + 0.627, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.631, + 0.126, + 0.751, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.753, + 0.126, + 0.88, + 0.191 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.516, + 0.191, + 0.631, + 0.256 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.633, + 0.191, + 0.751, + 0.256 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.753, + 0.191, + 0.88, + 0.256 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.516, + 0.256, + 0.698, + 0.328 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.698, + 0.256, + 0.88, + 0.328 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.339, + 0.892, + 0.366 + ], + "angle": 0, + "content": "Figure 7: Ablation studies on \\( L_{db} \\), \\( L_{mf} \\), random sampling, and \\( F_{st} \\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.392, + 0.892, + 0.434 + ], + "angle": 0, + "content": "DynNeRF [13] only interpolates novel views in the training frames. The reported PSNR, SSIM [47], and LPIPS scores in Table 2 quantitatively verify the superiority of our model." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.443, + 0.867, + 0.458 + ], + "angle": 0, + "content": "4.3. Novel View Synthesis from Multiple Videos" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.465, + 0.891, + 0.561 + ], + "angle": 0, + "content": "In the section, we tested the novel view synthesis performance on multiple dynamic scenes. It is worth noting that as existing methods can only learn from single monocular videos, they are not applicable to the settings that need to train on multiple videos. Then, we evaluated the novel scene adaption ability on several novel monocular videos. Lastly, we conducted a series of scene editing experiments." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.562, + 0.892, + 0.646 + ], + "angle": 0, + "content": "Novel view synthesis on training videos. We selected Balloon2 and Umbrella scenes to train our model. As shown in Figure 3 and Table 3, our model could distinguish foregrounds from two scenes and perform well with \\( \\mathbf{F}_{dy} \\). Specifically, it predicts generalizable scene flows with \\( \\mathbf{F}_{temp} \\) and renders more accurate details with \\( \\mathbf{F}_{sp} \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.646, + 0.892, + 0.797 + ], + "angle": 0, + "content": "Novel view synthesis on unseen videos. We explored the generalization ability of our model by pretraining on the Balloon2 scene and fine-tuning the pretrained model on other scenes. Figure 5 presents the results of four unseen videos: Playground, Skating, Truck, and Balloon1. We also pretrained DynNeRF [13] on the Balloon2 scene for a fair comparison. While DynNeRF only learns to render new scenes from scratch, our model transfers to scenes with correct dynamic motions. By further training with 500 steps, our model achieves better image rendering quality and higher LPIPS scores, which takes about 10 minutes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.798, + 0.892, + 0.852 + ], + "angle": 0, + "content": "Scene editing. As Figure 6 shows, our model further supports many scene editing applications by directly processing point features without extra training. Changing background was implemented by exchanging the static" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.852, + 0.892, + 0.867 + ], + "angle": 0, + "content": "0 features between two scenes. Moving, scaling, dupi" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.126, + 0.47, + 0.168 + ], + "angle": 0, + "content": "cating and flipping foreground were directly applied by operating video features in dynamic radiance field. The above applications could be combined arbitrarily." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.178, + 0.231, + 0.194 + ], + "angle": 0, + "content": "4.4. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.2, + 0.473, + 0.38 + ], + "angle": 0, + "content": "We conducted a series of experiments to examine the proposed \\( L_{db} \\), \\( L_{mf} \\), \\( F_{st} \\), random sampling strategy, and trajectory discretization method. We show in Figure 7 that \\( L_{db} \\) deblurs the margin of the synthesized foreground in novel views, \\( L_{mf} \\) keeps the blending consistency in different views for delineating the foreground more accurately. The random sampling strategy successfully renders static scene without dynamic foreground, and backgrounds of two scenes are mixed without \\( F_{st} \\). We also show the numeric comparisons of \\( L_{db} \\), \\( L_{mf} \\), \\( F_{st} \\), and random sampling strategy in Table 4. In Table 5, our discretization method reaches comparable results with ODE solvers [5] and achieves higher performance with the increase of \\( N \\)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.394, + 0.196, + 0.409 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.418, + 0.47, + 0.584 + ], + "angle": 0, + "content": "In this paper, we study the generalization ability of novel view synthesis from monocular videos. The challenge is the ambiguity of 3D point features and scene flows in the viewing directions. We find that video frame features and optical flows are a pair of complementary constraints for learning 3D point features and scene flows. To achieve this, we propose a generalizable dynamic radiance field called MonoNeRF. We estimate point features and trajectories from the video features extracted by a video encoder and render dynamic scenes from points features. Experiments show that our model could learn a generalizable radiance field for dynamic scenes, and support many scene editing applications." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.47, + 0.685 + ], + "angle": 0, + "content": "Acknowledgements. This work was supported by the National Key Research and Development Program of China under Grant No. 2020AAA0108100, the National Natural Science Foundation of China under Grant No. 62206147 and 61971343. The authors would like to thank the Shanghai Artificial Intelligence Laboratory for its generous support of computational resources." + }, + { + "type": "title", + "bbox": [ + 0.08, + 0.7, + 0.174, + 0.714 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.085, + 0.723, + 0.47, + 0.775 + ], + "angle": 0, + "content": "[1] Shengqu Cai, Anton Obukhov, Dengxin Dai, and Luc Van Gool. 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In CVPR, June 2018. 7, 8" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.127, + 0.47, + 0.215 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.467, + 0.849, + 0.505, + 0.86 + ], + "angle": 0, + "content": "17913" + } + ] +] \ No newline at end of file diff --git a/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/3b096572-4cf3-4c62-bc09-35a9369cf899_origin.pdf b/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/3b096572-4cf3-4c62-bc09-35a9369cf899_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..84f4a948d1eddf19131b2f5c10e561175596d9cf --- /dev/null +++ b/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/3b096572-4cf3-4c62-bc09-35a9369cf899_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:76b1525996512d16a812b178002788bc35d7bcc816347844a75b0b23d68776fc +size 891650 diff --git a/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/full.md b/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/full.md new file mode 100644 index 0000000000000000000000000000000000000000..0e833cbd28efd57042c91262ae0b57ec04c567cf --- /dev/null +++ b/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/full.md @@ -0,0 +1,408 @@ +# MonoNeRF: Learning a Generalizable Dynamic Radiance Field from Monocular Videos + +Fengrui Tian $^{1}$ Shaoyi Du $^{1}$ Yueqi Duan $^{2\dagger}$ + +$^{1}$ National Key Laboratory of Human-Machine Hybrid Augmented Intelligence, National Engineering Research Center for Visual Information and Applications, and Institute of Artificial Intelligence and Robotics, Xi'an Jiaotong University $^{2}$ Department of Electronic Engineering, Tsinghua University + +tianfr@stu.xjtu.edu.cn, dushaoyi@gmail.com, duanyueqi@tsinghua.edu.cn + +![](images/243509c992d2ddaa23575aeeeab07ec272f2ef91781ddc8225f2ba49491c3afe.jpg) +Figure 1: MonoNeRF learns a generalizable dynamic radiance field from multiple monocular videos. While video-based NeRF learns the field from positional encoding, we propose to learn from the extracted video features, which are generalizable to scenes. In this way, MonoNeRF supports scene editing applications (Top) and unseen frame synthesis (Middle). Compared with DynNeRF [13], MonoNeRF could adapt to novel scenes (Bottom) with hundreds of fine-tuning steps (about 10 minutes). + +# Abstract + +In this paper, we target at the problem of learning a generalizable dynamic radiance field from monocular videos. Different from most existing NeRF methods that are based on multiple views, monocular videos only contain one view at each timestamp, thereby suffering from ambiguity along the view direction in estimating point features and scene flows. Previous studies such as DynNeRF disambiguate point features by positional encoding, which is not transferable and severely limits the generalization abl + +ity. As a result, these methods have to train one independent model for each scene and suffer from heavy computational costs when applying to increasing monocular videos in real-world applications. To address this, We propose MonoNeRF to simultaneously learn point features and scene flows with point trajectory and feature correspondence constraints across frames. More specifically, we learn an implicit velocity field to estimate point trajectory from temporal features with Neural ODE, which is followed by a flow-based feature aggregation module to obtain spatial features along the point trajectory. We jointly optimize temporal and spatial features in an end + +17903 ... and manner. Experiments show that our MonoNeRF is + +able to learn from multiple scenes and support new applications such as scene editing, unseen frame synthesis, and fast novel scene adaptation. Codes are available at https://github.com/tianfr/MonoNeRF. + +# 1. Introduction + +Novel view synthesis [6] is a highly challenging problem. It facilitates many important applications in movie production, sports event, and virtual reality. The long standing problem recently has witnessed impressive progress due to the neural rendering technology [28, 26, 9]. Neural Radiance Field (NeRF) [28, 54, 22, 27, 46, 51, 52] shows that photo-realistic scenes can be represented by an implicit neural network. Concretely, taken as a query the position and viewing direction of the posed image, the network outputs the color of each pixel by volume rendering method. Among these approaches, it is supposed that the scene is static and can be observed from multiple views at the same time. Such assumptions are violated by numerous videos uploaded to the Internet, which usually contain dynamic foregrounds, recorded by the monocular camera. + +More recently, some studies aim to explore how to learn dynamic radiance field from monocular videos [10, 13, 21, 49, 50, 40]. Novel view synthesis from monocular videos is a challenging task. As foreground usually dynamically changes in a video, there is ambiguity in the view direction to estimate precise point features and dense object motions (i.e., scene flow [44]) from single views. In other words, we can only extract the projected 2D intra-frame local features and inter-frame optical flows, but fail to obtain precise 3D estimations. Previous works address this challenge by representing points as 4D position features (coordinate and time), so that the learned positional encoding provides specific information for each 3D point in the space [10, 13, 21, 49, 50, 40]. Based on positional encoding, these methods make efforts on exploiting scene priors [12, 48, 49] or adding spatio-temporal regularization [10, 13, 21, 50] to learn a more accurate dynamic radiance field. + +However, while positional encoding successfully disambiguates 3D points from monocular 2D projections, it severely overfits to the training video clip and is not transferable. Therefore, existing positional encoding based methods have to optimize one independent model for each dynamic scene. With the fast increase of monocular videos in reality, they suffer from heavy computational costs and lengthy training time to learn from multiple dynamic scenes. Also, the lack of generalization ability limits further applications of scene editing which requires interaction among different scenes. A natural question is raised: can we learn a generalizable dynamic radiance field from monocular videos? + +tion. The key challenge of this task is to learn to extract generalizable point features in the 3D space from monocular videos. While independently using 2D local features and optical flows suffers from ambiguity along the ray direction, they provide complementary constraints to jointly learn 3D point features and scene flows. On the one hand, for the sampled points on each ray, optical flow provides generalizable constraints that limit the relations of their point trajectories. On the other hand, for the flowing points on each estimated point trajectory, we consider that they should share the same point features. We estimate each point feature by aggregating their projected 2D local features, and design feature correspondence constraints to correct unreasonable trajectories. + +To achieve this, we propose MonoNeRF to build a generalizable dynamic radiance field for multiple dynamic scenes. We hypothesize that a point moving along its trajectory over time keeps the consistent point feature. Our method concurrently predicts 3D point features and scene flows with point trajectory and feature correspondence constraints in monocular video frames. More specifically, we first propose to learn an implicit velocity field that encodes the speed from the temporal feature of each point. We supervise the velocity field with optical flow and integrate continuous point trajectories on the field with Neural ODE [5]. Then, we propose a flow-based feature aggregation module to sample spatial features of each point along the point trajectory. We incorporate the spatial and temporal features as the point feature to query the color and density for image rendering and jointly optimize point features and trajectories in an end-to-end manner. As shown in Figure 1, experiments demonstrate that our MonoNeRF is able to render novel views from multiple dynamic videos and support new applications such as scene editing, unseen frame synthesis, and fast novel scene adaption. Also, in the widely-used setting of novel view synthesis on training frames from single videos, our MonoNeRF still achieves better performance than existing methods despite that cross-scene generalization ability is not required in this setting. + +# 2. Related Work + +Novel view synthesis for static scenes. The long standing problem of novel view synthesis aims to construct new views of a scene from multiple posed images. Early works needed dense views captured from the scene [19, 14]. Recent studies have shown great progress by explicitly representing 3D scenes as neural representations [26, 28, 9, 7, 51, 25, 18, 38]. However, these methods train a separate model for each scene and need various training time for optimization. PixelNeRF [54] and MVSNeRF [4] proposed feature-based methods that directly render new scenes from the encoded features. Additionally, many researchers stud + +In this paper, we provide a positive answer to this 17904 generalization and decomposition abilities of novel + +![](images/fcdc241bbfde4ce152d46242b774531537de1dfc486bf357b7352312f3c4f2f3.jpg) +Figure 2: The overview of our generalizable dynamic field. We first exploit an implicit velocity field from the extracted temporal feature $\pmb{F}_{temp}$ . Then, we calculate point trajectory on the velocity field, and exploit the spatial feature $\pmb{F}_{sp}$ with the proposed flow-based spatial feature aggregation module. We incorporate $\pmb{F}_{temp}$ and $\pmb{F}_{sp}$ as the point feature $\pmb{F}_{dy}$ for rendering dynamic scene and design $L_{opt}$ and $L_{corr}$ to jointly optimize point features and trajectories. + +view synthesis model [3, 37, 29, 15, 1, 18, 41]. Compared with these methods, our method studies the synthesis and generalization ability of dynamic scenes. + +Space-time view synthesis from monocular videos. With the development of neural radiance field in static scenes, recent studies started to address the dynamic scene reconstruction problem [21, 50, 10, 20, 31, 32]. In monocular videos, a key challenge is that there exist multiple scene constructions implying the same observed image sequences. Previous approaches addressed this challenge by using 3D coordinates with time as point features and adding scene priors or spatio-temporal regularization. Scene priors such as shadow modeling [49], human shape prior [48, 23], and facial appearance [12] are object-specific and closer to special contents. Spatio-temporal regularization such as depth and flow regularization [10, 13, 21, 50] and object deformations [40] are more object-agnostic, but weaker in applying consistency restriction to dynamic foregrounds. In this paper, we study the challenge by constraining point features. + +Scene flow for reconstruction. Scene flow firstly proposed by [44] depicts the motion of each point in the dynamic scene. Its 2D projection i.e., optical flow contributes to many downstream applications such as + +super-resolution [45], video tracking [42], video segmentation [43], and video recognition [2]. Several methods studied the scene flow estimation problem based on point cloud sequences [30, 24]. However, estimating scene flow from an observed video is an ill-posed problem. In dynamic scene reconstruction, previous works [21, 13] established discrete scene flow for pixel consistency in observation time. In this way, the flow consistency in observed frames can only be constrained, leading to ambiguity in non-observed time. Du et al. [10] proposed to build the continuous flow field in a dynamic scene. Compared to these methods, we study the generalization ability of the flow field in different scenes. + +# 3. Approach + +In this section, we introduce the proposed model that we term as MonoNeRF. We first present the overview of our model and then detail the approach of each part. Lastly, we introduce several strategies for optimizing the model. + +# 3.1. MonoNeRF + +MonoNeRF aims to model generalizable radiance field 17905 amic scenes. Our method takes multiple monocu + +lar videos as input and uses optical flows, depth maps, and binary masks of foreground objects as supervision signals. Those signals could be generated by pretrained models automatically. We build the generalizable static and dynamic fields for backgrounds and foregrounds separately. For generalizable dynamic field, we suppose that spatio-temporal points flow along their trajectories and hold consistent features over time. We first extract video features by a CNN encoder and generate the temporal feature vectors based on the extracted features. Then, we build an implicit velocity field from the temporal feature vectors to estimate point trajectories. Next, we exploit the estimated point trajectories as indexes to find the local image patches on each frame and extract the spatial features from the patches with the proposed flow-based feature aggregation module. Different from NeRF [28] that uses scene-agnostic point positions to render image color, we aggregate the scene-dependent spatial and temporal features as the final point features to render foreground scenes with volume rendering. Finally, we design the optical flow and feature correspondence constraints for jointly learning point features and trajectories. For generalizable static field, we suppose backgrounds are static and each video frame is considered as a different view of the background. Since some background parts may be occluded by the foreground, we design an effective strategy to sample background point features. In the end, we combine the generalizable static and dynamic fields for rendering free-point videos. + +# 3.2. Generalizable Dynamic Field + +In this section, we introduce our generalizable dynamic field that renders novel views of dynamic foregrounds. We denote a monocular video as $\mathbf{V} = \{V^i, i = 1,2\ldots ,K\}$ consisting of $K$ frames. For each frame $V^i$ , $t_i$ is the observed timestamp and $\Pi^i$ is the projection transform from the world coordinate to the 2D frame pixel coordinate. As Figure 2 shows, given a video $\mathbf{V}$ , we exploit a video encoder $E_{dy}$ to extract the video feature vector represented as $E_{dy}(\mathbf{V})$ and generate the temporal feature vector $\mathbf{F}_{temp}$ with a multiple layer perceptron (MLP) $W_{temp}: E_{dy}(\mathbf{V}) \rightarrow \mathbf{F}_{temp}$ . We build the implicit velocity field based on $\mathbf{F}_{temp}$ . + +Implicit velocity field. We suppose points are moving in the scene and represent a spatio-temporal point as $\pmb{p} = (x_p, t_p)$ including the 3D point position $\pmb{x}_p$ and time $t_p$ . We define $\Phi$ as the continuous point trajectory and $\Phi(\pmb{p}, t)$ denotes the position of point $\pmb{p}$ at timestamp $t$ . We further define the velocity field $\pmb{v}$ which includes the 3D velocity of each point. The relationship between point velocity and trajectory is specified as follows, + +$$ +\frac {\partial \Phi (\boldsymbol {p} , t)}{\partial t} = \boldsymbol {v} \left(\Phi (\boldsymbol {p}, t), t\right), \quad \text {s . t .} \quad \Phi (\boldsymbol {p}, t _ {p}) = \boldsymbol {x} _ {p}. \tag {1} +$$ + +$\pmb{v}$ is conditioned on $F_{temp}$ and implemented by an + +$W_{vel}\colon (F_{temp}(\boldsymbol {V}),\Phi ,t)\to \boldsymbol{v}.$ We calculate the point trajectory at an observed timestamp $t_i$ with Neural ODE [5], + +$$ +\boldsymbol {\Phi} (\boldsymbol {p}, t _ {i}) = \boldsymbol {x} _ {p} + \int_ {t _ {p}} ^ {t _ {i}} \boldsymbol {v} \left(\boldsymbol {\Phi} (\boldsymbol {p}, t), t\right) d t. \tag {2} +$$ + +We take $\Phi (\pmb {p},t_i)$ as an index to query the spatial feature. + +Flow-based spatial feature aggregation. We employ $\Pi^i$ to project $\Phi (\pmb {p},t_i)$ on $V^{i}$ and find the local image patch indexed by the projected position $\Pi^i (\Phi (\pmb {p},t_i))$ . We extract the feature vector $F_{sp}^{i}$ from the patch with the encoder $E_{dy}$ and a fully connected layer $fc_{1}$ , + +$$ +\boldsymbol {F} _ {s p} ^ {i} (\boldsymbol {V}; \boldsymbol {p}) = f c _ {1} \left(E _ {d y} \left(\boldsymbol {V} ^ {i}; \Pi^ {i} (\boldsymbol {\Phi} (\boldsymbol {p}, t _ {i}))\right)\right). \tag {3} +$$ + +In practice, $E_{dy}\big(\mathbf{V}^i;\Pi^i (\Phi (\mathbf{p},t_i))\big)$ is implemented by using $E_{dy}$ to extract the frame-wise feature map of $V^{i}$ and sampling the feature vector at $\Pi^i (\Phi (\pmb {p},t_i))$ with bilinear interpolation. The spatial feature vector $\pmb{F}_{sp}$ is then calculated by incorporating $\{\pmb{F}_{sp}^{1},\pmb{F}_{sp}^{2},\dots,\pmb{F}_{sp}^{K}\}$ with a fully connected layer $fc_{2}$ , + +$$ +\boldsymbol {F} _ {s p} (\boldsymbol {V}; \boldsymbol {p}) = f c _ {2} \left(\boldsymbol {F} _ {s p} ^ {1} (\boldsymbol {V}; \boldsymbol {p}), \boldsymbol {F} _ {s p} ^ {2} (\boldsymbol {V}; \boldsymbol {p}), \dots , \boldsymbol {F} _ {s p} ^ {K} (\boldsymbol {V}; \boldsymbol {p})\right). \tag {4} +$$ + +Finally, we incorporate $\mathbf{F}_{temp}$ and $\mathbf{F}_{sp}$ as the point feature vector $\mathbf{F}_{dy}$ , + +$$ +\boldsymbol {F} _ {d y} (\boldsymbol {V}; \boldsymbol {p}) = \operatorname {c o n c a t} \left\{\boldsymbol {F} _ {\text {t e m p}} (\boldsymbol {V}), \boldsymbol {F} _ {\text {s p}} (\boldsymbol {V}; \boldsymbol {p}) \right\}. \tag {5} +$$ + +We build the generalizable dynamic field based on $\mathbf{F}_{dy}$ . + +Dynamic foreground rendering. Taking a point $\pmb{p}$ and its feature vector $\pmb{F}_{dy}(\pmb{V};\pmb{p})$ as input, our generalizable dynamic radiance field $W_{dy} \colon (\pmb{p}, \pmb{F}_{dy}(\pmb{V};\pmb{p})) \to (\pmb{c}_{dy}, \sigma_{dy}, b)$ predicts the volume density $\sigma_{dy}$ , color $c_{dy}$ and blending weight $b$ of the point. We follow DynNeRF [13] and utilize $b$ to judge whether a point belongs to static background or dynamic foreground. We exploit volume rendering to approximate each pixel color of an image. Concretely, given a ray $r(u) = o + ud$ starting from the camera center $o$ along the direction $d$ through a pixel, its color is integrated by + +$$ +\boldsymbol {C} _ {d y} (\boldsymbol {r}) = \int_ {u _ {n}} ^ {u _ {f}} T _ {d y} (u) \sigma_ {d y} (u) \boldsymbol {c} _ {d y} (u) d u, \tag {6} +$$ + +where $u_{n}, u_{f}$ are the bounds of the volume rendering depth range and $T_{dy}(u) = \exp(-\int_{u_{n}}^{u} \sigma_{dy}(\boldsymbol{r}(s)) ds$ is the accumulated transparency. We simplify $c(u) = c(\boldsymbol{r}(u), \boldsymbol{d})$ and $\sigma(u) = \sigma(\boldsymbol{r}(u))$ here and in the following sections. Next we present the optical flow and feature correspondence constraints that jointly supervise our model. + +Optical flow constraint. We supervise $\pmb{v}$ with the optical flow $f^{gt}$ . In practice, it can only approximate the backward flow $f_{bw}^{gt}$ and forward flow $f_{fw}^{gt}$ between two consecutive video frames [39]. We hence estimate the point + +backward and forward trajectory variations during the period that the point passes between two frames and calculate optical flows by integrating the trajectory variations of each point along camera rays. Formally, given a ray $\pmb{r}(u)$ through a pixel on the frame $\pmb{V}^i$ at time $t_i$ , for each point on the ray i.e., $\pmb{p}(u) = (\pmb{r}(u), t_i)$ the trajectory variations $\Delta \Phi_{bw}$ back to $t_{i-1}$ and $\Delta \Phi_{fw}$ forward to $t_{i+1}$ are obtained by the following equation, + +$$ +\Delta \Phi_ {\{b w, f w \}} (\boldsymbol {p} (u)) = \int_ {t _ {i}} ^ {t _ {\{i - 1, i + 1 \}}} \boldsymbol {v} (\boldsymbol {\Phi} (\boldsymbol {p} (u), t), t) d t. \tag {7} +$$ + +We follow previous works [21, 13] and exploit the volume rendering to integrate pseudo optical flows $\pmb{f}_{bw}$ and $\pmb{f}_{fw}$ by utilizing the estimated volume density $\sigma_{dy}$ of each point, + +$$ +\boldsymbol {f} _ {\{b w, f w \}} (\boldsymbol {r}) = \int_ {u _ {n}} ^ {u _ {f}} T _ {d y} (u) \sigma_ {d y} (u) \Delta \Phi_ {\{b w, f w \}} ^ {i} (\boldsymbol {p} (u)) d u, \tag {8} +$$ + +where $\Delta \Phi_{\{bw,fw\}}^i = \Pi^i (\Delta \Phi_{\{bw,fw\}})$ denotes we use $\Pi^i$ to project 3D trajectory variations on the image plane of $V^i$ . We supervise the pseudo flows by the ground truth flows, + +$$ +L _ {o p t} = \sum_ {\boldsymbol {r}} \left(\boldsymbol {f} _ {\{b w, f w \}} (\boldsymbol {r}) - \boldsymbol {f} _ {\{b w, f w \}} ^ {g t} (\boldsymbol {r})\right). \tag {9} +$$ + +In this way, the relation of point trajectories along a ray is limited by the optical flow supervision. + +Feature correspondence constraint. According to Section 3.1, a point moving along the trajectory holds the same feature and represents the consistent color and density. For each ray $\boldsymbol{r}_{curr}$ at the current time $t_i$ through a pixel of $V^i$ , we warp the ray from the neighboring observed timestamps $t_{i-1}$ and $t_{i+1}$ as $\boldsymbol{r}_{bw}$ and $\boldsymbol{r}_{fw}$ separately by using (7), + +$$ +\boldsymbol {r} _ {\{b w, f w \}} (u) = \boldsymbol {r} _ {\text {c u r r}} (u) + \Delta \Phi_ {\{b w, f w \}} \left(\boldsymbol {p} _ {\text {c u r r}} (u)\right), \tag {10} +$$ + +where $\pmb{p}_{\text{curr}}(u) = (\pmb{r}_{\text{curr}}(u), t_i)$ . We render the pixel color from the point features not only along the ray $\pmb{r}_{\text{curr}}$ at the time $t_i$ , but also along the wrapped rays $\pmb{r}_{bw}$ at $t_{i-1}$ and $\pmb{r}_{fw}$ at $t_{i+1}$ . The predicted pixel color $\pmb{C}_{dy}$ is rendered by using (6) and supervised by the ground truth colors $\pmb{C}_{dy}^{gt}$ , + +$$ +L _ {\{b w, c u r r, f w \}} = \sum_ {\boldsymbol {r}} | | \boldsymbol {C} _ {d y} (\boldsymbol {r} _ {\{b w, c u r r, f w \}}) - \boldsymbol {C} _ {d y} ^ {g t} (\boldsymbol {r}) | | _ {2}. \tag {11} +$$ + +The feature correspondence constraint $L_{corr}$ is defined as + +$$ +L _ {c o r r} = L _ {b w} + L _ {c u r r} + L _ {f w}. \tag {12} +$$ + +$L_{corr}$ supervises the predicted color and point features $\pmb{F}_{dy}$ . + +# 3.3. Generalizable Static Field + +As mentioned in Section 3.1, for some background node occluded by the changing foreground in the current ..... 17907 + +their features implying the foreground cannot infer the correct background information. However, the occluded parts could be seen in non-occluded views with correct background features. To this end, given a point position $\pmb{x}$ , the background point feature vector $\pmb{F}_{st}$ is produced by + +$$ +\boldsymbol {F} _ {s t} (\boldsymbol {V}; \boldsymbol {x}) = f c _ {3} \left(E _ {s t} \left(\boldsymbol {V} ^ {*}; \Pi^ {*} (\boldsymbol {x})\right)\right), \tag {13} +$$ + +where $f c_{3}$ is a fully connected layer and $E_{st}$ denotes the image encoder. $V^{*}$ and $\Pi^{*}$ are the non-occluded frame and corresponding projection transform respectively. $E_{st}(V^{*};\Pi^{*}(\pmb {x}))$ denotes that we find the local image patch at $\Pi^{*}(\pmb {x})$ and extract the feature vectors with an image encoder $E_{st}$ similar to $E_{dy}\big(V^i;\Pi^i (\Phi (\pmb {p},t_i))\big)$ . Since there is no prior in which frames they can be exposed, we apply a straightforward yet effective strategy by randomly sampling one frame from the other frames in the video. We represent the static scene as a radiance field to infer the color $c_{st}$ and density $\sigma_{st}$ by using an MLP $W_{st}$ : $(\pmb {x},\pmb {d},\pmb{F}_{st}(\pmb {V};\pmb {x}))\rightarrow (c_{st},\sigma_{st})$ . The expected background color $C_{st}$ is given by + +$$ +\boldsymbol {C} _ {s t} (\boldsymbol {r}) = \int_ {u _ {n}} ^ {u _ {f}} T _ {s t} (u) \sigma_ {s t} (u) \boldsymbol {c} _ {s t} (u) d u, \tag {14} +$$ + +where $T_{st}(t) = \exp (-\int_{u_n}^u\sigma_{st}(\boldsymbol {r}(s))ds$ . We employ foreground masks $M$ to optimize the static field by supervising the pixel color in each video frame in the background regions (where $M(\boldsymbol {r}) = 0$ ), + +$$ +L _ {s t} = \sum_ {\boldsymbol {r}} | | \left(\boldsymbol {C} _ {s t} (\boldsymbol {r}) - \boldsymbol {C} _ {s t} ^ {q t} (\boldsymbol {r})\right) (1 - M (\boldsymbol {r})) \| _ {2}, \tag {15} +$$ + +where $C_{st}^{gt}$ represents the ground truth color. + +# 3.4. Optimization + +The final dynamic scene color combines the colors from the generalizable dynamic and static fields, + +$$ +\boldsymbol {C} _ {f u l l} (\boldsymbol {r}) = \int_ {u _ {n}} ^ {u _ {f}} T _ {f u l l} (u) \sigma_ {f u l l} (u) \boldsymbol {c} _ {f u l l} (u) d u, \tag {16} +$$ + +where + +$$ +\sigma_ {f u l l} (u) \boldsymbol {c} _ {f u l l} (u) = (1 - b) \sigma_ {s t} (u) \boldsymbol {c} _ {s t} (u) + b \sigma_ {d y} (u) \boldsymbol {c} _ {d y} (u), \tag {17} +$$ + +and applies the reconstruction loss, + +$$ +L _ {f u l l} = \sum_ {\boldsymbol {r}} | | \boldsymbol {C} _ {f u l l} (\boldsymbol {r}) - \boldsymbol {C} _ {f u l l} ^ {g t} (\boldsymbol {r}) | | _ {2}. \tag {18} +$$ + +Next we design several strategies to optimize our model. + +Point trajectory discretization. While point trajectory can be numerically estimated by the continuous integral (2) with Neural ODE solvers [5], it needs plenty of time for 7 ng each point trajectory. To accelerate the process, + +Table 1: Novel view synthesis on training frames from single videos. While this setting does not require cross-scene generalization ability, our MonoNeRF still achieves better performance. + +
PSNR ↑ / LPIPS ↓JumpingSkatingTruckUmbrellaBalloon1Balloon2PlaygroundAverage
NeRF [28]20.58 / 0.30523.05 / 0.31622.61 / 0.22521.08 / 0.44119.07 / 0.21424.08 / 0.09820.86 / 0.16421.62 / 0.252
NeRF [28] + time16.72 / 0.48919.23 / 0.54217.17 / 0.40317.17 / 0.75217.33 / 0.30419.67 / 0.23613.80 / 0.44417.30 / 0.453
Yoon et al. [53]20.16 / 0.14821.75 / 0.13523.93 / 0.10920.35 / 0.17918.76 / 0.17819.89 / 0.13815.09 / 0.18319.99 / 0.153
Tretschk et al. [40]19.38 / 0.29523.29 / 0.23419.02 / 0.45319.26 / 0.42716.98 / 0.35322.23 / 0.21214.24 / 0.33619.20 / 0.330
Li et al. [21]24.12 / 0.15628.91 / 0.13525.94 / 0.17122.58 / 0.30221.40 / 0.22524.09 / 0.22820.91 / 0.22023.99 / 0.205
NeuPhysics [33]20.16 / 0.20525.13 / 0.16622.62 / 0.21221.02 / 0.42616.68 / 0.23822.54 / 0.26515.10 / 0.36720.48 / 0.282
DynNeRF [13]24.23 / 0.14428.90 / 0.12425.78 / 0.13423.15 / 0.14621.47 / 0.12525.97 / 0.05923.65 / 0.09324.74 / 0.118
MonoNeRF24.26 / 0.09132.06 / 0.04427.56 / 0.11523.62 / 0.18021.89 / 0.12927.36 / 0.05222.61 / 0.13025.62 / 0.106
+ +![](images/22a40a3efafa65c4a4ca812a1db98cd5cf21f63a7d36ce2d3dde568692bc872f.jpg) +Figure 3: Qualitative results of jointly optimizing Balloon2 and Umbrella scenes. The foregrounds of two scenes are mixed without $F_{dy}$ . Our method renders more accurate novel views and predicts plausible scene flows (listed beside the RGB images) by incorporating $F_{temp}$ and $F_{sp}$ . + +![](images/730bb6621c0372d5a1c1f23ac55826b60df0f871fa44a727d282b6d228294b79.jpg) +Figure 4: Novel view synthesis on unseen frames. Compared to the ground truths, our model could transfer to new motions, whereas DynNeRF [13] only interpolates in the training frames. + +we propose to partition $[t_p, t_i]$ into $N$ evenly-spaced bins and suppose the point velocity in each bin is a constant. The point trajectory can be estimated by the following equation, + +$$ +\boldsymbol {\Phi} (\boldsymbol {p}, t _ {i}) = \boldsymbol {x} _ {p} + \sum_ {n = 1} ^ {N} \boldsymbol {v} \left(\boldsymbol {\Phi} (\boldsymbol {p}, t + \Delta t), t + \Delta t\right) \Delta t, \tag {19} +$$ + +where $\Delta t = \frac{n}{N} (t_{i} - t_{p})$ + +Depth-blending restriction. To calculate the blending weights within a foreground ray in the generalizable dynamic field, only the points in close proximity to the + +Table 2: Quantitative results of novel view synthesis on unseen frames. We used the first four frames for training and tested the performance on the rest eight frames. + +
Balloon2 / TruckPSNR ↑SSIM ↑LPIPS ↓
NeRF [28]20.33 / 20.260.662 / 0.6690.224 / 0.256
NeRF [28] + time20.22 / 20.260.661 / 0.6390.218 / 0.256
NeuPhysics [33]19.45 / 20.240.478 / 0.5170.343 / 0.285
DynNeRF [13]19.99 / 20.330.641 / 0.6210.291 / 0.273
MonoNeRF21.30 / 23.740.669 / 0.7020.204 / 0.174
+ +mated ray depth are regarded as foreground points, whereas points beyond this range are excluded. We penalize the blending weights of non-foreground points in foreground rays. Specifically, given a ray $r(u)$ through a pixel and the pixel depth $u_{d}$ , We penalize the blending weights of the points on the ray out of the interval $(u_{d} - \epsilon, u_{d} + \epsilon)$ , + +$$ +L _ {d b} = \sum_ {u \in \left(u _ {n}, u _ {d} - \epsilon\right) \cup \left(u _ {d} + \epsilon , u _ {f}\right)} \| b (\boldsymbol {r} (u)) \| _ {2}, \tag {20} +$$ + +where $b(\boldsymbol{r}(u))$ is the blending weight at the position $\boldsymbol{r}(u)$ . $\epsilon$ controls the surface thickness of the dynamic foreground. + +Musk flow loss. We further constrain the consistency 17908 point features by minimizing blending weight variations + +![](images/a59d13ad5bbe83d9f6ac09ae7b80dd46cc15f70be89f923325a69ef3527d1b0f.jpg) +Figure 5: Fast novel scene adaption. We used the pretrained model on Balloon2 scene to fine-tune the novel views of unseen dynamic scenes. We employed LPIPS [55] (the lower is better) to evaluate the image similarity, which provides more correlation with human judgment than other indexes. + +along trajectories, + +$$ +L _ {m f} = \sum_ {i, j \in \{1, 2,.., K \}} | | b (\boldsymbol {\Phi} (\boldsymbol {p}, t _ {i})) - b (\boldsymbol {\Phi} (\boldsymbol {p}, t _ {j})) | | _ {2}, \tag {21} +$$ + +where $b(\Phi (\pmb {p},t))$ denotes the blending weight at $\Phi (p,t)$ + +Other regularization. We follow previous works [21, 13, 10] to use the depth constraint, sparsity constraint, and motion regularization and smoothness to train the model. + +# 4. Experiments + +In this section, we conducted experiments on the Dynamic Scene dataset [53]. We first tested the performance of synthesizing novel views from single videos, and then we tested the generalization ability from multiple videos. In the end, we carried out ablation studies on our model. + +# 4.1. Experimental Setup + +Dataset. We used the Dynamic Scene dataset [53] to evaluate the proposed method. Concretely, it contains 9 video sequences that are captured with 12 cameras by using a camera rig. We followed previous works [21, 13] and derived each frame of the video from different cameras to simulate the camera motion. All the cameras capture images at 12 different timestamps $\{t_i, i = 1, 2\ldots, 12\}$ . Each training video contains twelve frames sampled from the $i^{th}$ camera at time $t_i$ followed DynNeRF [13]. We used COI MAP [35, 36] to approximate the camera poses. It is assumed + +Table 3: Ablation studies on $\mathbf{F}_{dy}$ , $\mathbf{F}_{temp}$ , and $\mathbf{F}_{sp}$ by jointly optimizing Balloon2 and Umbrella scenes. + +
PSNR ↑ / LPIPS ↓UmbrellaBalloon2Average
w/o. Fdy20.59 / 0.25622.79 / 0.15921.57 / 0.230
w/o. Ftemp22.75 / 0.17524.85 / 0.09823.80 / 0.137
w/o. Fsp22.81 / 0.18125.09 / 0.14323.95 / 0.162
Ours23.44 / 0.16925.44 / 0.09324.44 / 0.131
+ +trinsic parameters of all the cameras are the same. DynamicFace sequences were excluded because COLMAP fails to estimate camera poses. All video frames were resized to $480 \times 270$ resolution. We generated the depth, mask, and optical flow signals from the depth estimation model [34], Mask R-CNN [16], and RAFT [39]. + +Implementation details. We followed pixelNeRF [54] and used ResNet-based MLPs as our implicit velocity field $W_{vel}$ and rendering networks $W_{dy}$ and $W_{st}$ . For generalizable dynamic field, we utilized Slowonly50 [11] pretrained on Kinetics400 [2] dataset as the encoder $E_{dy}$ with the frozen weights. We removed the final fully connected layer in the backbone and incorporated the first, second, and third feature layers for querying $F_{sp}$ . We simplified (4) that $F_{sp}$ at time $t_i$ is sampled from $\{V^{i-1}, V^i, V^{i+1}\}$ . For generalizable static field, we used ResNet18 [17] pretrained on ImageNet [8] as the encoder $E_{st}$ . We extracted a feature pyramid from video frames for querying $F_{st}$ . The sizes of $F_{temp}, F_{sp}, F_{dy}$ , and $F_{st}$ are 256. Please + +![](images/e787085e5ab6629c2624730cb13c78db736050b2b08641018b97087cd86693cc.jpg) +Change BG + +![](images/e1bd8dd725ae1e859c36925bde88936a8c19c165cbceec5208b0079fa0322bd6.jpg) +Move FG + +![](images/c7328ce71aadfa7cd1059b18a982c422dfd5f0c5dbe3211fa235eda9f017d670.jpg) +Scale FG + +![](images/98a1aa70bce7a9e9d2e46cfb590dfd60d3894c053c6df9c5e32296a574e022ff.jpg) +Duplicate FG + +![](images/01ba4c928dc700d05e807551371736dfba2c9ae604166bfc81e0a9addbc76a7c.jpg) +Flip FG + +![](images/c89b9a6067bc89224629a776338b8eb64e07e9c610692a1d9059ae030a6145e8.jpg) +Combinations +Figure 6: Our model supports many scene editing applications such as background changing, foreground moving, scaling, duplicating, flipping, and arbitrary combinations. + +Table 4: Numeric comparisons on $L_{db}, L_{mf}, F_{st}$ , and random sampling strategy. + +
PSNR ↑ / LPIPS ↓Training framesUnseen framesUnseen videos
w/o. Ldb22.76 / 0.14820.69 / 0.34821.68 / 0.345
w/o. Lmf22.95 / 0.13520.95 / 0.35421.67 / 0.342
w/o. Fst21.75 / 0.23019.79 / 0.37121.81 / 0.337
w/o. random17.30 / 0.43516.93 / 0.51220.28 / 0.353
Ours23.02 / 0.13021.30 / 0.30422.63 / 0.277
+ +Table 5: Comparisons of solving the continuous trajectory by using ODE solver [5] and our discretization method. + +
MethodN=1N=2ODE solver [5]
PSNR ↑ / LPIPS ↓22.90 / 0.13622.97 / 0.13423.75 / 0.129
+ +refer to the supplementary material for more details. + +# 4.2. Novel View Synthesis from Single Video + +In this section, we trained the models from single monocular videos, where existing methods are applicable to this setting. Specifically, we first tested the performance on training frames, which is the widely-used setting to evaluate video-based NeRFs. Then, we tested the generalization ability on unseen frames in the video, where other existing methods are not able to transfer well to the unseen motions. + +Novel view synthesis on training frames. To evaluate the synthesized novel views, we followed DynNeRF [13] and tested the performance by fixing the view to the first camera and changing time. We reported the PSNR and LPIPS [55] in Table 1. We evaluated the performance of Li et al. [21], Tretschk et al. [40], NeuPhysics [33], and Chen et al. [13] from the official implementations. Even without the need of generalization ability, our method achieves better results. + +Novel view synthesis on unseen frames. We split the video frames into two groups: four front frames were used for training and the rest of eight unseen frames were utilized to render novel views. Figure 4 shows that our model + +cessfully renders new motions in the unseen frames, + +![](images/951ccb7a23a26ba741dc39843c21dea87e08576c2a08bef4aaa928ef4c6328a4.jpg) + +![](images/3d89f22fff8313c1c5510efea8514b67359ec59f8fd18e1c565dba007d3edf45.jpg) + +![](images/071d95c6b5a5ea560d731988e08cad9ec11f16c981666803acd6bbb13ee927f0.jpg) + +![](images/dee79195ec2c50b8e47499c29a0217483388905ed193272eac66e5c10ff54dff.jpg) + +![](images/43ef605cdc2c1a1e142f90d55e153efe4649f6f3b5f2bc4d41e961b69daabff3.jpg) + +![](images/3d020947aede9d0ebe4216d4edc8b1c2a2f05e386721311b98cf411d9dc87937.jpg) + +![](images/91d5471e5eb681f6e22e67d186f967b621b4f0712dc02272b3ed513d6869b82d.jpg) +Figure 7: Ablation studies on $L_{db}$ , $L_{mf}$ , random sampling, and $F_{st}$ . + +![](images/d48b4e5cdf109440435cdbfb90eebb4343f42092f73d37cceaa3128e87a531b3.jpg) + +DynNeRF [13] only interpolates novel views in the training frames. The reported PSNR, SSIM [47], and LPIPS scores in Table 2 quantitatively verify the superiority of our model. + +# 4.3. Novel View Synthesis from Multiple Videos + +In the section, we tested the novel view synthesis performance on multiple dynamic scenes. It is worth noting that as existing methods can only learn from single monocular videos, they are not applicable to the settings that need to train on multiple videos. Then, we evaluated the novel scene adaption ability on several novel monocular videos. Lastly, we conducted a series of scene editing experiments. + +Novel view synthesis on training videos. We selected Balloon2 and Umbrella scenes to train our model. As shown in Figure 3 and Table 3, our model could distinguish foregrounds from two scenes and perform well with $\mathbf{F}_{dy}$ . Specifically, it predicts generalizable scene flows with $\mathbf{F}_{temp}$ and renders more accurate details with $\mathbf{F}_{sp}$ . + +Novel view synthesis on unseen videos. We explored the generalization ability of our model by pretraining on the Balloon2 scene and fine-tuning the pretrained model on other scenes. Figure 5 presents the results of four unseen videos: Playground, Skating, Truck, and Balloon1. We also pretrained DynNeRF [13] on the Balloon2 scene for a fair comparison. While DynNeRF only learns to render new scenes from scratch, our model transfers to scenes with correct dynamic motions. By further training with 500 steps, our model achieves better image rendering quality and higher LPIPS scores, which takes about 10 minutes. + +Scene editing. As Figure 6 shows, our model further supports many scene editing applications by directly processing point features without extra training. Changing background was implemented by exchanging the static + +0 features between two scenes. Moving, scaling, dupi + +cating and flipping foreground were directly applied by operating video features in dynamic radiance field. The above applications could be combined arbitrarily. + +# 4.4. Ablation Study + +We conducted a series of experiments to examine the proposed $L_{db}$ , $L_{mf}$ , $F_{st}$ , random sampling strategy, and trajectory discretization method. We show in Figure 7 that $L_{db}$ deblurs the margin of the synthesized foreground in novel views, $L_{mf}$ keeps the blending consistency in different views for delineating the foreground more accurately. The random sampling strategy successfully renders static scene without dynamic foreground, and backgrounds of two scenes are mixed without $F_{st}$ . We also show the numeric comparisons of $L_{db}$ , $L_{mf}$ , $F_{st}$ , and random sampling strategy in Table 4. In Table 5, our discretization method reaches comparable results with ODE solvers [5] and achieves higher performance with the increase of $N$ . + +# 5. Conclusion + +In this paper, we study the generalization ability of novel view synthesis from monocular videos. The challenge is the ambiguity of 3D point features and scene flows in the viewing directions. We find that video frame features and optical flows are a pair of complementary constraints for learning 3D point features and scene flows. To achieve this, we propose a generalizable dynamic radiance field called MonoNeRF. We estimate point features and trajectories from the video features extracted by a video encoder and render dynamic scenes from points features. Experiments show that our model could learn a generalizable radiance field for dynamic scenes, and support many scene editing applications. + +Acknowledgements. This work was supported by the National Key Research and Development Program of China under Grant No. 2020AAA0108100, the National Natural Science Foundation of China under Grant No. 62206147 and 61971343. 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In CVPR, June 2018. 7, 8 \ No newline at end of file diff --git a/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/images.zip b/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..156e79750b3e04ea5797283fb7ede5e65be6dd7c --- /dev/null +++ b/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:e37c1884838e42678318962d48a420d1d1748a42e09647d8909a9366f70379d0 +size 915233 diff --git a/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/layout.json b/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..889bbc96b570eb43ad61b87da6760f7f74135715 --- /dev/null +++ b/2023/MonoNeRF_ Learning a Generalizable Dynamic Radiance Field from Monocular Videos/layout.json @@ -0,0 +1,11225 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 97, + 136, + 479, + 169 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 136, + 479, + 169 + ], + "spans": [ + { + "bbox": [ + 97, + 136, + 479, + 169 + ], + "type": "text", + "content": "MonoNeRF: Learning a Generalizable Dynamic Radiance Field from Monocular Videos" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 182, + 192, + 394, + 207 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 182, + 192, + 394, + 207 + ], + "spans": [ + { + "bbox": [ + 182, + 192, + 394, + 207 + ], + "type": "text", + "content": "Fengrui Tian" + }, + { + "bbox": [ + 182, + 192, + 394, + 207 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 182, + 192, + 394, + 207 + ], + "type": "text", + "content": " Shaoyi Du" + }, + { + "bbox": [ + 182, + 192, + 394, + 207 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 182, + 192, + 394, + 207 + ], + "type": "text", + "content": " Yueqi Duan" + }, + { + "bbox": [ + 182, + 192, + 394, + 207 + ], + "type": "inline_equation", + "content": "^{2\\dagger}" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 101, + 207, + 474, + 261 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 101, + 207, + 474, + 261 + ], + "spans": [ + { + "bbox": [ + 101, + 207, + 474, + 261 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 101, + 207, + 474, + 261 + ], + "type": "text", + "content": "National Key Laboratory of Human-Machine Hybrid Augmented Intelligence, National Engineering Research Center for Visual Information and Applications, and Institute of Artificial Intelligence and Robotics, Xi'an Jiaotong University " + }, + { + "bbox": [ + 101, + 207, + 474, + 261 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 101, + 207, + 474, + 261 + ], + "type": "text", + "content": "Department of Electronic Engineering, Tsinghua University" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 106, + 263, + 470, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 106, + 263, + 470, + 274 + ], + "spans": [ + { + "bbox": [ + 106, + 263, + 470, + 274 + ], + "type": "text", + "content": "tianfr@stu.xjtu.edu.cn, dushaoyi@gmail.com, duanyueqi@tsinghua.edu.cn" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 60, + 301, + 517, + 510 + ], + "blocks": [ + { + "bbox": [ + 60, + 301, + 517, + 510 + ], + "lines": [ + { + "bbox": [ + 60, + 301, + 517, + 510 + ], + "spans": [ + { + "bbox": [ + 60, + 301, + 517, + 510 + ], + "type": "image", + "image_path": "243509c992d2ddaa23575aeeeab07ec272f2ef91781ddc8225f2ba49491c3afe.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 520, + 531, + 568 + ], + "lines": [ + { + "bbox": [ + 45, + 520, + 531, + 568 + ], + "spans": [ + { + "bbox": [ + 45, + 520, + 531, + 568 + ], + "type": "text", + "content": "Figure 1: MonoNeRF learns a generalizable dynamic radiance field from multiple monocular videos. While video-based NeRF learns the field from positional encoding, we propose to learn from the extracted video features, which are generalizable to scenes. In this way, MonoNeRF supports scene editing applications (Top) and unseen frame synthesis (Middle). Compared with DynNeRF [13], MonoNeRF could adapt to novel scenes (Bottom) with hundreds of fine-tuning steps (about 10 minutes)." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "bbox": [ + 139, + 577, + 185, + 589 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 139, + 577, + 185, + 589 + ], + "spans": [ + { + "bbox": [ + 139, + 577, + 185, + 589 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 45, + 602, + 280, + 708 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 602, + 280, + 708 + ], + "spans": [ + { + "bbox": [ + 45, + 602, + 280, + 708 + ], + "type": "text", + "content": "In this paper, we target at the problem of learning a generalizable dynamic radiance field from monocular videos. Different from most existing NeRF methods that are based on multiple views, monocular videos only contain one view at each timestamp, thereby suffering from ambiguity along the view direction in estimating point features and scene flows. Previous studies such as DynNeRF disambiguate point features by positional encoding, which is not transferable and severely limits the generalization abl" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 295, + 578, + 530, + 717 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 578, + 530, + 717 + ], + "spans": [ + { + "bbox": [ + 295, + 578, + 530, + 717 + ], + "type": "text", + "content": "ity. As a result, these methods have to train one independent model for each scene and suffer from heavy computational costs when applying to increasing monocular videos in real-world applications. To address this, We propose MonoNeRF to simultaneously learn point features and scene flows with point trajectory and feature correspondence constraints across frames. More specifically, we learn an implicit velocity field to estimate point trajectory from temporal features with Neural ODE, which is followed by a flow-based feature aggregation module to obtain spatial features along the point trajectory. We jointly optimize temporal and spatial features in an end" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 277, + 716, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 716, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 277, + 716, + 530, + 730 + ], + "type": "text", + "content": "17903 ... and manner. Experiments show that our MonoNeRF is" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "spans": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 151, + 41, + 470, + 73 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 151, + 41, + 470, + 73 + ], + "spans": [ + { + "bbox": [ + 151, + 41, + 470, + 73 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 60, + 719, + 141, + 730 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 60, + 719, + 141, + 730 + ], + "spans": [ + { + "bbox": [ + 60, + 719, + 141, + 730 + ], + "type": "text", + "content": "†: Corresponding author." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 286, + 747, + 291, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 286, + 747, + 291, + 756 + ], + "spans": [ + { + "bbox": [ + 286, + 747, + 291, + 756 + ], + "type": "text", + "content": "1" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 280, + 153 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 280, + 153 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 280, + 153 + ], + "type": "text", + "content": "able to learn from multiple scenes and support new applications such as scene editing, unseen frame synthesis, and fast novel scene adaptation. Codes are available at https://github.com/tianfr/MonoNeRF." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 175, + 124, + 186 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 175, + 124, + 186 + ], + "spans": [ + { + "bbox": [ + 46, + 175, + 124, + 186 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 194, + 279, + 368 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 194, + 279, + 368 + ], + "spans": [ + { + "bbox": [ + 45, + 194, + 279, + 368 + ], + "type": "text", + "content": "Novel view synthesis [6] is a highly challenging problem. It facilitates many important applications in movie production, sports event, and virtual reality. The long standing problem recently has witnessed impressive progress due to the neural rendering technology [28, 26, 9]. Neural Radiance Field (NeRF) [28, 54, 22, 27, 46, 51, 52] shows that photo-realistic scenes can be represented by an implicit neural network. Concretely, taken as a query the position and viewing direction of the posed image, the network outputs the color of each pixel by volume rendering method. Among these approaches, it is supposed that the scene is static and can be observed from multiple views at the same time. Such assumptions are violated by numerous videos uploaded to the Internet, which usually contain dynamic foregrounds, recorded by the monocular camera." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 369, + 279, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 369, + 279, + 566 + ], + "spans": [ + { + "bbox": [ + 45, + 369, + 279, + 566 + ], + "type": "text", + "content": "More recently, some studies aim to explore how to learn dynamic radiance field from monocular videos [10, 13, 21, 49, 50, 40]. Novel view synthesis from monocular videos is a challenging task. As foreground usually dynamically changes in a video, there is ambiguity in the view direction to estimate precise point features and dense object motions (i.e., scene flow [44]) from single views. In other words, we can only extract the projected 2D intra-frame local features and inter-frame optical flows, but fail to obtain precise 3D estimations. Previous works address this challenge by representing points as 4D position features (coordinate and time), so that the learned positional encoding provides specific information for each 3D point in the space [10, 13, 21, 49, 50, 40]. Based on positional encoding, these methods make efforts on exploiting scene priors [12, 48, 49] or adding spatio-temporal regularization [10, 13, 21, 50] to learn a more accurate dynamic radiance field." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 566, + 279, + 716 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 566, + 279, + 716 + ], + "spans": [ + { + "bbox": [ + 45, + 566, + 279, + 716 + ], + "type": "text", + "content": "However, while positional encoding successfully disambiguates 3D points from monocular 2D projections, it severely overfits to the training video clip and is not transferable. Therefore, existing positional encoding based methods have to optimize one independent model for each dynamic scene. With the fast increase of monocular videos in reality, they suffer from heavy computational costs and lengthy training time to learn from multiple dynamic scenes. Also, the lack of generalization ability limits further applications of scene editing which requires interaction among different scenes. A natural question is raised: can we learn a generalizable dynamic radiance field from monocular videos?" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 297, + 106, + 530, + 268 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 106, + 530, + 268 + ], + "spans": [ + { + "bbox": [ + 297, + 106, + 530, + 268 + ], + "type": "text", + "content": "tion. The key challenge of this task is to learn to extract generalizable point features in the 3D space from monocular videos. While independently using 2D local features and optical flows suffers from ambiguity along the ray direction, they provide complementary constraints to jointly learn 3D point features and scene flows. On the one hand, for the sampled points on each ray, optical flow provides generalizable constraints that limit the relations of their point trajectories. On the other hand, for the flowing points on each estimated point trajectory, we consider that they should share the same point features. We estimate each point feature by aggregating their projected 2D local features, and design feature correspondence constraints to correct unreasonable trajectories." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 296, + 269, + 531, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 269, + 531, + 559 + ], + "spans": [ + { + "bbox": [ + 296, + 269, + 531, + 559 + ], + "type": "text", + "content": "To achieve this, we propose MonoNeRF to build a generalizable dynamic radiance field for multiple dynamic scenes. We hypothesize that a point moving along its trajectory over time keeps the consistent point feature. Our method concurrently predicts 3D point features and scene flows with point trajectory and feature correspondence constraints in monocular video frames. More specifically, we first propose to learn an implicit velocity field that encodes the speed from the temporal feature of each point. We supervise the velocity field with optical flow and integrate continuous point trajectories on the field with Neural ODE [5]. Then, we propose a flow-based feature aggregation module to sample spatial features of each point along the point trajectory. We incorporate the spatial and temporal features as the point feature to query the color and density for image rendering and jointly optimize point features and trajectories in an end-to-end manner. As shown in Figure 1, experiments demonstrate that our MonoNeRF is able to render novel views from multiple dynamic videos and support new applications such as scene editing, unseen frame synthesis, and fast novel scene adaption. Also, in the widely-used setting of novel view synthesis on training frames from single videos, our MonoNeRF still achieves better performance than existing methods despite that cross-scene generalization ability is not required in this setting." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 298, + 570, + 381, + 582 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 570, + 381, + 582 + ], + "spans": [ + { + "bbox": [ + 298, + 570, + 381, + 582 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 296, + 590, + 530, + 717 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 590, + 530, + 717 + ], + "spans": [ + { + "bbox": [ + 296, + 590, + 530, + 717 + ], + "type": "text", + "content": "Novel view synthesis for static scenes. The long standing problem of novel view synthesis aims to construct new views of a scene from multiple posed images. Early works needed dense views captured from the scene [19, 14]. Recent studies have shown great progress by explicitly representing 3D scenes as neural representations [26, 28, 9, 7, 51, 25, 18, 38]. However, these methods train a separate model for each scene and need various training time for optimization. PixelNeRF [54] and MVSNeRF [4] proposed feature-based methods that directly render new scenes from the encoded features. Additionally, many researchers stud" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 57, + 717, + 531, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 717, + 531, + 730 + ], + "spans": [ + { + "bbox": [ + 57, + 717, + 531, + 730 + ], + "type": "text", + "content": "In this paper, we provide a positive answer to this 17904 generalization and decomposition abilities of novel" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [], + "page_size": [ + 595, + 842 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 105, + 531, + 384 + ], + "blocks": [ + { + "bbox": [ + 48, + 105, + 531, + 384 + ], + "lines": [ + { + "bbox": [ + 48, + 105, + 531, + 384 + ], + "spans": [ + { + "bbox": [ + 48, + 105, + 531, + 384 + ], + "type": "image", + "image_path": "fcdc241bbfde4ce152d46242b774531537de1dfc486bf357b7352312f3c4f2f3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "lines": [ + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "spans": [ + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "text", + "content": "Figure 2: The overview of our generalizable dynamic field. We first exploit an implicit velocity field from the extracted temporal feature " + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "inline_equation", + "content": "\\pmb{F}_{temp}" + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "text", + "content": ". Then, we calculate point trajectory on the velocity field, and exploit the spatial feature " + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "inline_equation", + "content": "\\pmb{F}_{sp}" + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "text", + "content": " with the proposed flow-based spatial feature aggregation module. We incorporate " + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "inline_equation", + "content": "\\pmb{F}_{temp}" + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "inline_equation", + "content": "\\pmb{F}_{sp}" + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "text", + "content": " as the point feature " + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "inline_equation", + "content": "\\pmb{F}_{dy}" + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "text", + "content": " for rendering dynamic scene and design " + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "inline_equation", + "content": "L_{opt}" + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "inline_equation", + "content": "L_{corr}" + }, + { + "bbox": [ + 45, + 391, + 531, + 439 + ], + "type": "text", + "content": " to jointly optimize point features and trajectories." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 458, + 280, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 458, + 280, + 494 + ], + "spans": [ + { + "bbox": [ + 45, + 458, + 280, + 494 + ], + "type": "text", + "content": "view synthesis model [3, 37, 29, 15, 1, 18, 41]. Compared with these methods, our method studies the synthesis and generalization ability of dynamic scenes." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 495, + 279, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 495, + 279, + 682 + ], + "spans": [ + { + "bbox": [ + 45, + 495, + 279, + 682 + ], + "type": "text", + "content": "Space-time view synthesis from monocular videos. With the development of neural radiance field in static scenes, recent studies started to address the dynamic scene reconstruction problem [21, 50, 10, 20, 31, 32]. In monocular videos, a key challenge is that there exist multiple scene constructions implying the same observed image sequences. Previous approaches addressed this challenge by using 3D coordinates with time as point features and adding scene priors or spatio-temporal regularization. Scene priors such as shadow modeling [49], human shape prior [48, 23], and facial appearance [12] are object-specific and closer to special contents. Spatio-temporal regularization such as depth and flow regularization [10, 13, 21, 50] and object deformations [40] are more object-agnostic, but weaker in applying consistency restriction to dynamic foregrounds. In this paper, we study the challenge by constraining point features." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 683, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 683, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 683, + 279, + 730 + ], + "type": "text", + "content": "Scene flow for reconstruction. Scene flow firstly proposed by [44] depicts the motion of each point in the dynamic scene. Its 2D projection i.e., optical flow contributes to many downstream applications such as" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 296, + 458, + 530, + 600 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 458, + 530, + 600 + ], + "spans": [ + { + "bbox": [ + 296, + 458, + 530, + 600 + ], + "type": "text", + "content": "super-resolution [45], video tracking [42], video segmentation [43], and video recognition [2]. Several methods studied the scene flow estimation problem based on point cloud sequences [30, 24]. However, estimating scene flow from an observed video is an ill-posed problem. In dynamic scene reconstruction, previous works [21, 13] established discrete scene flow for pixel consistency in observation time. In this way, the flow consistency in observed frames can only be constrained, leading to ambiguity in non-observed time. Du et al. [10] proposed to build the continuous flow field in a dynamic scene. Compared to these methods, we study the generalization ability of the flow field in different scenes." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 297, + 611, + 361, + 623 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 611, + 361, + 623 + ], + "spans": [ + { + "bbox": [ + 297, + 611, + 361, + 623 + ], + "type": "text", + "content": "3. Approach" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 296, + 631, + 530, + 679 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 631, + 530, + 679 + ], + "spans": [ + { + "bbox": [ + 296, + 631, + 530, + 679 + ], + "type": "text", + "content": "In this section, we introduce the proposed model that we term as MonoNeRF. We first present the overview of our model and then detail the approach of each part. Lastly, we introduce several strategies for optimizing the model." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 297, + 687, + 373, + 698 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 687, + 373, + 698 + ], + "spans": [ + { + "bbox": [ + 297, + 687, + 373, + 698 + ], + "type": "text", + "content": "3.1. MonoNeRF" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 277, + 706, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 706, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 277, + 706, + 530, + 730 + ], + "type": "text", + "content": "MonoNeRF aims to model generalizable radiance field 17905 amic scenes. Our method takes multiple monocu" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [], + "page_size": [ + 595, + 842 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 281, + 432 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 281, + 432 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 281, + 432 + ], + "type": "text", + "content": "lar videos as input and uses optical flows, depth maps, and binary masks of foreground objects as supervision signals. Those signals could be generated by pretrained models automatically. We build the generalizable static and dynamic fields for backgrounds and foregrounds separately. For generalizable dynamic field, we suppose that spatio-temporal points flow along their trajectories and hold consistent features over time. We first extract video features by a CNN encoder and generate the temporal feature vectors based on the extracted features. Then, we build an implicit velocity field from the temporal feature vectors to estimate point trajectories. Next, we exploit the estimated point trajectories as indexes to find the local image patches on each frame and extract the spatial features from the patches with the proposed flow-based feature aggregation module. Different from NeRF [28] that uses scene-agnostic point positions to render image color, we aggregate the scene-dependent spatial and temporal features as the final point features to render foreground scenes with volume rendering. Finally, we design the optical flow and feature correspondence constraints for jointly learning point features and trajectories. For generalizable static field, we suppose backgrounds are static and each video frame is considered as a different view of the background. Since some background parts may be occluded by the foreground, we design an effective strategy to sample background point features. In the end, we combine the generalizable static and dynamic fields for rendering free-point videos." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 439, + 201, + 452 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 439, + 201, + 452 + ], + "spans": [ + { + "bbox": [ + 46, + 439, + 201, + 452 + ], + "type": "text", + "content": "3.2. Generalizable Dynamic Field" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "spans": [ + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "content": "In this section, we introduce our generalizable dynamic field that renders novel views of dynamic foregrounds. We denote a monocular video as " + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\mathbf{V} = \\{V^i, i = 1,2\\ldots ,K\\}" + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "content": " consisting of " + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "content": " frames. For each frame " + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "inline_equation", + "content": "V^i" + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "inline_equation", + "content": "t_i" + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "content": " is the observed timestamp and " + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\Pi^i" + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "content": " is the projection transform from the world coordinate to the 2D frame pixel coordinate. As Figure 2 shows, given a video " + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\mathbf{V}" + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "content": ", we exploit a video encoder " + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "inline_equation", + "content": "E_{dy}" + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "content": " to extract the video feature vector represented as " + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "inline_equation", + "content": "E_{dy}(\\mathbf{V})" + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "content": " and generate the temporal feature vector " + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{temp}" + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "content": " with a multiple layer perceptron (MLP) " + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "inline_equation", + "content": "W_{temp}: E_{dy}(\\mathbf{V}) \\rightarrow \\mathbf{F}_{temp}" + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "content": ". We build the implicit velocity field based on " + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{temp}" + }, + { + "bbox": [ + 45, + 457, + 279, + 586 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "spans": [ + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "text", + "content": "Implicit velocity field. We suppose points are moving in the scene and represent a spatio-temporal point as " + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "inline_equation", + "content": "\\pmb{p} = (x_p, t_p)" + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "text", + "content": " including the 3D point position " + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "inline_equation", + "content": "\\pmb{x}_p" + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "text", + "content": " and time " + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "inline_equation", + "content": "t_p" + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "text", + "content": ". We define " + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "inline_equation", + "content": "\\Phi" + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "text", + "content": " as the continuous point trajectory and " + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "inline_equation", + "content": "\\Phi(\\pmb{p}, t)" + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "text", + "content": " denotes the position of point " + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "inline_equation", + "content": "\\pmb{p}" + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "text", + "content": " at timestamp " + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "text", + "content": ". We further define the velocity field " + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "inline_equation", + "content": "\\pmb{v}" + }, + { + "bbox": [ + 45, + 586, + 279, + 679 + ], + "type": "text", + "content": " which includes the 3D velocity of each point. The relationship between point velocity and trajectory is specified as follows," + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 60, + 687, + 279, + 710 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 60, + 687, + 279, + 710 + ], + "spans": [ + { + "bbox": [ + 60, + 687, + 279, + 710 + ], + "type": "interline_equation", + "content": "\\frac {\\partial \\Phi (\\boldsymbol {p} , t)}{\\partial t} = \\boldsymbol {v} \\left(\\Phi (\\boldsymbol {p}, t), t\\right), \\quad \\text {s . t .} \\quad \\Phi (\\boldsymbol {p}, t _ {p}) = \\boldsymbol {x} _ {p}. \\tag {1}", + "image_path": "0b7480aeb47b3dede5dfce93916f07fff9825f7a1c395438b3b00a6a3895fd47.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 717, + 276, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 717, + 276, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 717, + 276, + 730 + ], + "type": "inline_equation", + "content": "\\pmb{v}" + }, + { + "bbox": [ + 45, + 717, + 276, + 730 + ], + "type": "text", + "content": " is conditioned on " + }, + { + "bbox": [ + 45, + 717, + 276, + 730 + ], + "type": "inline_equation", + "content": "F_{temp}" + }, + { + "bbox": [ + 45, + 717, + 276, + 730 + ], + "type": "text", + "content": " and implemented by an" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 296, + 106, + 530, + 130 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 106, + 530, + 130 + ], + "spans": [ + { + "bbox": [ + 296, + 106, + 530, + 130 + ], + "type": "inline_equation", + "content": "W_{vel}\\colon (F_{temp}(\\boldsymbol {V}),\\Phi ,t)\\to \\boldsymbol{v}." + }, + { + "bbox": [ + 296, + 106, + 530, + 130 + ], + "type": "text", + "content": " We calculate the point trajectory at an observed timestamp " + }, + { + "bbox": [ + 296, + 106, + 530, + 130 + ], + "type": "inline_equation", + "content": "t_i" + }, + { + "bbox": [ + 296, + 106, + 530, + 130 + ], + "type": "text", + "content": " with Neural ODE [5]," + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 337, + 138, + 530, + 166 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 337, + 138, + 530, + 166 + ], + "spans": [ + { + "bbox": [ + 337, + 138, + 530, + 166 + ], + "type": "interline_equation", + "content": "\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {i}) = \\boldsymbol {x} _ {p} + \\int_ {t _ {p}} ^ {t _ {i}} \\boldsymbol {v} \\left(\\boldsymbol {\\Phi} (\\boldsymbol {p}, t), t\\right) d t. \\tag {2}", + "image_path": "33f84656bf0e78119266ebedc44ce2b6a5c3e2430230c5b284e3a53bd2ccbbca.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 297, + 171, + 520, + 183 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 171, + 520, + 183 + ], + "spans": [ + { + "bbox": [ + 297, + 171, + 520, + 183 + ], + "type": "text", + "content": "We take " + }, + { + "bbox": [ + 297, + 171, + 520, + 183 + ], + "type": "inline_equation", + "content": "\\Phi (\\pmb {p},t_i)" + }, + { + "bbox": [ + 297, + 171, + 520, + 183 + ], + "type": "text", + "content": " as an index to query the spatial feature." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "spans": [ + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "text", + "content": "Flow-based spatial feature aggregation. We employ " + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "inline_equation", + "content": "\\Pi^i" + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "text", + "content": " to project " + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "inline_equation", + "content": "\\Phi (\\pmb {p},t_i)" + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "text", + "content": " on " + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "inline_equation", + "content": "V^{i}" + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "text", + "content": " and find the local image patch indexed by the projected position " + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "inline_equation", + "content": "\\Pi^i (\\Phi (\\pmb {p},t_i))" + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "text", + "content": ". We extract the feature vector " + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "inline_equation", + "content": "F_{sp}^{i}" + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "text", + "content": " from the patch with the encoder " + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "inline_equation", + "content": "E_{dy}" + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "text", + "content": " and a fully connected layer " + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "inline_equation", + "content": "fc_{1}" + }, + { + "bbox": [ + 296, + 184, + 530, + 242 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 324, + 250, + 530, + 270 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 324, + 250, + 530, + 270 + ], + "spans": [ + { + "bbox": [ + 324, + 250, + 530, + 270 + ], + "type": "interline_equation", + "content": "\\boldsymbol {F} _ {s p} ^ {i} (\\boldsymbol {V}; \\boldsymbol {p}) = f c _ {1} \\left(E _ {d y} \\left(\\boldsymbol {V} ^ {i}; \\Pi^ {i} (\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {i}))\\right)\\right). \\tag {3}", + "image_path": "a68a39c95c575ae20d21b8b36fa319b68ef59e4e0d25c6a94ccea361680403c5.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "spans": [ + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "text", + "content": "In practice, " + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "inline_equation", + "content": "E_{dy}\\big(\\mathbf{V}^i;\\Pi^i (\\Phi (\\mathbf{p},t_i))\\big)" + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "text", + "content": " is implemented by using " + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "inline_equation", + "content": "E_{dy}" + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "text", + "content": " to extract the frame-wise feature map of " + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "inline_equation", + "content": "V^{i}" + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "text", + "content": " and sampling the feature vector at " + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "inline_equation", + "content": "\\Pi^i (\\Phi (\\pmb {p},t_i))" + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "text", + "content": " with bilinear interpolation. The spatial feature vector " + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "inline_equation", + "content": "\\pmb{F}_{sp}" + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "text", + "content": " is then calculated by incorporating " + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "inline_equation", + "content": "\\{\\pmb{F}_{sp}^{1},\\pmb{F}_{sp}^{2},\\dots,\\pmb{F}_{sp}^{K}\\}" + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "text", + "content": " with a fully connected layer " + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "inline_equation", + "content": "fc_{2}" + }, + { + "bbox": [ + 296, + 280, + 530, + 353 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 297, + 361, + 531, + 385 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 361, + 531, + 385 + ], + "spans": [ + { + "bbox": [ + 297, + 361, + 531, + 385 + ], + "type": "interline_equation", + "content": "\\boldsymbol {F} _ {s p} (\\boldsymbol {V}; \\boldsymbol {p}) = f c _ {2} \\left(\\boldsymbol {F} _ {s p} ^ {1} (\\boldsymbol {V}; \\boldsymbol {p}), \\boldsymbol {F} _ {s p} ^ {2} (\\boldsymbol {V}; \\boldsymbol {p}), \\dots , \\boldsymbol {F} _ {s p} ^ {K} (\\boldsymbol {V}; \\boldsymbol {p})\\right). \\tag {4}", + "image_path": "13a2a811d60568190d040b35c2327974932a1fd312a080059b310fe7705cf1a8.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 296, + 386, + 530, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 386, + 530, + 410 + ], + "spans": [ + { + "bbox": [ + 296, + 386, + 530, + 410 + ], + "type": "text", + "content": "Finally, we incorporate " + }, + { + "bbox": [ + 296, + 386, + 530, + 410 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{temp}" + }, + { + "bbox": [ + 296, + 386, + 530, + 410 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 386, + 530, + 410 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{sp}" + }, + { + "bbox": [ + 296, + 386, + 530, + 410 + ], + "type": "text", + "content": " as the point feature vector " + }, + { + "bbox": [ + 296, + 386, + 530, + 410 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{dy}" + }, + { + "bbox": [ + 296, + 386, + 530, + 410 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 313, + 418, + 530, + 432 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 418, + 530, + 432 + ], + "spans": [ + { + "bbox": [ + 313, + 418, + 530, + 432 + ], + "type": "interline_equation", + "content": "\\boldsymbol {F} _ {d y} (\\boldsymbol {V}; \\boldsymbol {p}) = \\operatorname {c o n c a t} \\left\\{\\boldsymbol {F} _ {\\text {t e m p}} (\\boldsymbol {V}), \\boldsymbol {F} _ {\\text {s p}} (\\boldsymbol {V}; \\boldsymbol {p}) \\right\\}. \\tag {5}", + "image_path": "5d1fb617e32a9bef4edc45cb160a38b0b145b3797eb785957d5df22ef7b6b7e0.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 297, + 441, + 518, + 452 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 441, + 518, + 452 + ], + "spans": [ + { + "bbox": [ + 297, + 441, + 518, + 452 + ], + "type": "text", + "content": "We build the generalizable dynamic field based on " + }, + { + "bbox": [ + 297, + 441, + 518, + 452 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{dy}" + }, + { + "bbox": [ + 297, + 441, + 518, + 452 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "spans": [ + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "text", + "content": "Dynamic foreground rendering. Taking a point " + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "inline_equation", + "content": "\\pmb{p}" + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "text", + "content": " and its feature vector " + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "inline_equation", + "content": "\\pmb{F}_{dy}(\\pmb{V};\\pmb{p})" + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "text", + "content": " as input, our generalizable dynamic radiance field " + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "inline_equation", + "content": "W_{dy} \\colon (\\pmb{p}, \\pmb{F}_{dy}(\\pmb{V};\\pmb{p})) \\to (\\pmb{c}_{dy}, \\sigma_{dy}, b)" + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "text", + "content": " predicts the volume density " + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "inline_equation", + "content": "\\sigma_{dy}" + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "text", + "content": ", color " + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "inline_equation", + "content": "c_{dy}" + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "text", + "content": " and blending weight " + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "text", + "content": " of the point. We follow DynNeRF [13] and utilize " + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "text", + "content": " to judge whether a point belongs to static background or dynamic foreground. We exploit volume rendering to approximate each pixel color of an image. Concretely, given a ray " + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "inline_equation", + "content": "r(u) = o + ud" + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "text", + "content": " starting from the camera center " + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "inline_equation", + "content": "o" + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "text", + "content": " along the direction " + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 296, + 453, + 530, + 570 + ], + "type": "text", + "content": " through a pixel, its color is integrated by" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 332, + 577, + 530, + 605 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 332, + 577, + 530, + 605 + ], + "spans": [ + { + "bbox": [ + 332, + 577, + 530, + 605 + ], + "type": "interline_equation", + "content": "\\boldsymbol {C} _ {d y} (\\boldsymbol {r}) = \\int_ {u _ {n}} ^ {u _ {f}} T _ {d y} (u) \\sigma_ {d y} (u) \\boldsymbol {c} _ {d y} (u) d u, \\tag {6}", + "image_path": "cc04138a1dc8c3a1e3d1435dd5adff06b47e828e4bd07a832f48cfa9e34c334d.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 296, + 612, + 530, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 612, + 530, + 682 + ], + "spans": [ + { + "bbox": [ + 296, + 612, + 530, + 682 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 296, + 612, + 530, + 682 + ], + "type": "inline_equation", + "content": "u_{n}, u_{f}" + }, + { + "bbox": [ + 296, + 612, + 530, + 682 + ], + "type": "text", + "content": " are the bounds of the volume rendering depth range and " + }, + { + "bbox": [ + 296, + 612, + 530, + 682 + ], + "type": "inline_equation", + "content": "T_{dy}(u) = \\exp(-\\int_{u_{n}}^{u} \\sigma_{dy}(\\boldsymbol{r}(s)) ds" + }, + { + "bbox": [ + 296, + 612, + 530, + 682 + ], + "type": "text", + "content": " is the accumulated transparency. We simplify " + }, + { + "bbox": [ + 296, + 612, + 530, + 682 + ], + "type": "inline_equation", + "content": "c(u) = c(\\boldsymbol{r}(u), \\boldsymbol{d})" + }, + { + "bbox": [ + 296, + 612, + 530, + 682 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 612, + 530, + 682 + ], + "type": "inline_equation", + "content": "\\sigma(u) = \\sigma(\\boldsymbol{r}(u))" + }, + { + "bbox": [ + 296, + 612, + 530, + 682 + ], + "type": "text", + "content": " here and in the following sections. Next we present the optical flow and feature correspondence constraints that jointly supervise our model." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "type": "text", + "content": "Optical flow constraint. We supervise " + }, + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "type": "inline_equation", + "content": "\\pmb{v}" + }, + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "type": "text", + "content": " with the optical flow " + }, + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "type": "inline_equation", + "content": "f^{gt}" + }, + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "type": "text", + "content": ". In practice, it can only approximate the backward flow " + }, + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "type": "inline_equation", + "content": "f_{bw}^{gt}" + }, + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "type": "text", + "content": " and forward flow " + }, + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "type": "inline_equation", + "content": "f_{fw}^{gt}" + }, + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "type": "text", + "content": " between two consecutive video frames [39]. We hence estimate the point" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [], + "page_size": [ + 595, + 842 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "text", + "content": "backward and forward trajectory variations during the period that the point passes between two frames and calculate optical flows by integrating the trajectory variations of each point along camera rays. Formally, given a ray " + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "inline_equation", + "content": "\\pmb{r}(u)" + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "text", + "content": " through a pixel on the frame " + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "inline_equation", + "content": "\\pmb{V}^i" + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "text", + "content": " at time " + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "inline_equation", + "content": "t_i" + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "text", + "content": ", for each point on the ray i.e., " + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "inline_equation", + "content": "\\pmb{p}(u) = (\\pmb{r}(u), t_i)" + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "text", + "content": " the trajectory variations " + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "inline_equation", + "content": "\\Delta \\Phi_{bw}" + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "text", + "content": " back to " + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "inline_equation", + "content": "t_{i-1}" + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "inline_equation", + "content": "\\Delta \\Phi_{fw}" + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "text", + "content": " forward to " + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "inline_equation", + "content": "t_{i+1}" + }, + { + "bbox": [ + 45, + 106, + 281, + 201 + ], + "type": "text", + "content": " are obtained by the following equation," + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 55, + 207, + 279, + 244 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 207, + 279, + 244 + ], + "spans": [ + { + "bbox": [ + 55, + 207, + 279, + 244 + ], + "type": "interline_equation", + "content": "\\Delta \\Phi_ {\\{b w, f w \\}} (\\boldsymbol {p} (u)) = \\int_ {t _ {i}} ^ {t _ {\\{i - 1, i + 1 \\}}} \\boldsymbol {v} (\\boldsymbol {\\Phi} (\\boldsymbol {p} (u), t), t) d t. \\tag {7}", + "image_path": "72bebe97b9ceaaedc6179efdb944a0f96904cdfd2b17d3aee2208ede8da9c55d.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 244, + 279, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 244, + 279, + 281 + ], + "spans": [ + { + "bbox": [ + 45, + 244, + 279, + 281 + ], + "type": "text", + "content": "We follow previous works [21, 13] and exploit the volume rendering to integrate pseudo optical flows " + }, + { + "bbox": [ + 45, + 244, + 279, + 281 + ], + "type": "inline_equation", + "content": "\\pmb{f}_{bw}" + }, + { + "bbox": [ + 45, + 244, + 279, + 281 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 244, + 279, + 281 + ], + "type": "inline_equation", + "content": "\\pmb{f}_{fw}" + }, + { + "bbox": [ + 45, + 244, + 279, + 281 + ], + "type": "text", + "content": " by utilizing the estimated volume density " + }, + { + "bbox": [ + 45, + 244, + 279, + 281 + ], + "type": "inline_equation", + "content": "\\sigma_{dy}" + }, + { + "bbox": [ + 45, + 244, + 279, + 281 + ], + "type": "text", + "content": " of each point," + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 287, + 279, + 322 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 287, + 279, + 322 + ], + "spans": [ + { + "bbox": [ + 47, + 287, + 279, + 322 + ], + "type": "interline_equation", + "content": "\\boldsymbol {f} _ {\\{b w, f w \\}} (\\boldsymbol {r}) = \\int_ {u _ {n}} ^ {u _ {f}} T _ {d y} (u) \\sigma_ {d y} (u) \\Delta \\Phi_ {\\{b w, f w \\}} ^ {i} (\\boldsymbol {p} (u)) d u, \\tag {8}", + "image_path": "d03bf97e080c58e50b24f625d4eafacb2b32728bd3dd286f73b403db9216eb6e.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 322, + 279, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 322, + 279, + 361 + ], + "spans": [ + { + "bbox": [ + 45, + 322, + 279, + 361 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 322, + 279, + 361 + ], + "type": "inline_equation", + "content": "\\Delta \\Phi_{\\{bw,fw\\}}^i = \\Pi^i (\\Delta \\Phi_{\\{bw,fw\\}})" + }, + { + "bbox": [ + 45, + 322, + 279, + 361 + ], + "type": "text", + "content": " denotes we use " + }, + { + "bbox": [ + 45, + 322, + 279, + 361 + ], + "type": "inline_equation", + "content": "\\Pi^i" + }, + { + "bbox": [ + 45, + 322, + 279, + 361 + ], + "type": "text", + "content": " to project 3D trajectory variations on the image plane of " + }, + { + "bbox": [ + 45, + 322, + 279, + 361 + ], + "type": "inline_equation", + "content": "V^i" + }, + { + "bbox": [ + 45, + 322, + 279, + 361 + ], + "type": "text", + "content": ". We supervise the pseudo flows by the ground truth flows," + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 74, + 368, + 279, + 394 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 74, + 368, + 279, + 394 + ], + "spans": [ + { + "bbox": [ + 74, + 368, + 279, + 394 + ], + "type": "interline_equation", + "content": "L _ {o p t} = \\sum_ {\\boldsymbol {r}} \\left(\\boldsymbol {f} _ {\\{b w, f w \\}} (\\boldsymbol {r}) - \\boldsymbol {f} _ {\\{b w, f w \\}} ^ {g t} (\\boldsymbol {r})\\right). \\tag {9}", + "image_path": "1a3120e3ec210cff6137d85f613965af91a086c5ea2578fb8672d729991976d2.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 401, + 279, + 425 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 401, + 279, + 425 + ], + "spans": [ + { + "bbox": [ + 45, + 401, + 279, + 425 + ], + "type": "text", + "content": "In this way, the relation of point trajectories along a ray is limited by the optical flow supervision." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "spans": [ + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "text", + "content": "Feature correspondence constraint. According to Section 3.1, a point moving along the trajectory holds the same feature and represents the consistent color and density. For each ray " + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "inline_equation", + "content": "\\boldsymbol{r}_{curr}" + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "text", + "content": " at the current time " + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "inline_equation", + "content": "t_i" + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "text", + "content": " through a pixel of " + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "inline_equation", + "content": "V^i" + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "text", + "content": ", we warp the ray from the neighboring observed timestamps " + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "inline_equation", + "content": "t_{i-1}" + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "inline_equation", + "content": "t_{i+1}" + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "inline_equation", + "content": "\\boldsymbol{r}_{bw}" + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "inline_equation", + "content": "\\boldsymbol{r}_{fw}" + }, + { + "bbox": [ + 45, + 425, + 279, + 495 + ], + "type": "text", + "content": " separately by using (7)," + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 52, + 503, + 279, + 517 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 503, + 279, + 517 + ], + "spans": [ + { + "bbox": [ + 52, + 503, + 279, + 517 + ], + "type": "interline_equation", + "content": "\\boldsymbol {r} _ {\\{b w, f w \\}} (u) = \\boldsymbol {r} _ {\\text {c u r r}} (u) + \\Delta \\Phi_ {\\{b w, f w \\}} \\left(\\boldsymbol {p} _ {\\text {c u r r}} (u)\\right), \\tag {10}", + "image_path": "e958e3729c31345a52e408c0fed4f3113ff6fd9981611474b39961359f10778d.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "spans": [ + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\pmb{p}_{\\text{curr}}(u) = (\\pmb{r}_{\\text{curr}}(u), t_i)" + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "text", + "content": ". We render the pixel color from the point features not only along the ray " + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\pmb{r}_{\\text{curr}}" + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "text", + "content": " at the time " + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "inline_equation", + "content": "t_i" + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "text", + "content": ", but also along the wrapped rays " + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\pmb{r}_{bw}" + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "inline_equation", + "content": "t_{i-1}" + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\pmb{r}_{fw}" + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "inline_equation", + "content": "t_{i+1}" + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "text", + "content": ". The predicted pixel color " + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\pmb{C}_{dy}" + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "text", + "content": " is rendered by using (6) and supervised by the ground truth colors " + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\pmb{C}_{dy}^{gt}" + }, + { + "bbox": [ + 45, + 524, + 279, + 586 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 49, + 593, + 279, + 627 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 593, + 279, + 627 + ], + "spans": [ + { + "bbox": [ + 49, + 593, + 279, + 627 + ], + "type": "interline_equation", + "content": "L _ {\\{b w, c u r r, f w \\}} = \\sum_ {\\boldsymbol {r}} | | \\boldsymbol {C} _ {d y} (\\boldsymbol {r} _ {\\{b w, c u r r, f w \\}}) - \\boldsymbol {C} _ {d y} ^ {g t} (\\boldsymbol {r}) | | _ {2}. \\tag {11}", + "image_path": "ccac7b54f5b9455355a1f99f8a6eac6561b5f2174f95482f404d19f1724b931c.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 628, + 272, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 628, + 272, + 639 + ], + "spans": [ + { + "bbox": [ + 46, + 628, + 272, + 639 + ], + "type": "text", + "content": "The feature correspondence constraint " + }, + { + "bbox": [ + 46, + 628, + 272, + 639 + ], + "type": "inline_equation", + "content": "L_{corr}" + }, + { + "bbox": [ + 46, + 628, + 272, + 639 + ], + "type": "text", + "content": " is defined as" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 102, + 648, + 279, + 661 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 648, + 279, + 661 + ], + "spans": [ + { + "bbox": [ + 102, + 648, + 279, + 661 + ], + "type": "interline_equation", + "content": "L _ {c o r r} = L _ {b w} + L _ {c u r r} + L _ {f w}. \\tag {12}", + "image_path": "82c78703bf40157d7be91c53c73dd687ee308fb604310f4393d7940073e88aae.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 670, + 279, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 670, + 279, + 682 + ], + "spans": [ + { + "bbox": [ + 46, + 670, + 279, + 682 + ], + "type": "inline_equation", + "content": "L_{corr}" + }, + { + "bbox": [ + 46, + 670, + 279, + 682 + ], + "type": "text", + "content": " supervises the predicted color and point features " + }, + { + "bbox": [ + 46, + 670, + 279, + 682 + ], + "type": "inline_equation", + "content": "\\pmb{F}_{dy}" + }, + { + "bbox": [ + 46, + 670, + 279, + 682 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 687, + 186, + 699 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 687, + 186, + 699 + ], + "spans": [ + { + "bbox": [ + 46, + 687, + 186, + 699 + ], + "type": "text", + "content": "3.3. Generalizable Static Field" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 45, + 706, + 301, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 706, + 301, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 706, + 301, + 730 + ], + "type": "text", + "content": "As mentioned in Section 3.1, for some background node occluded by the changing foreground in the current ..... 17907" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 296, + 106, + 530, + 165 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 106, + 530, + 165 + ], + "spans": [ + { + "bbox": [ + 296, + 106, + 530, + 165 + ], + "type": "text", + "content": "their features implying the foreground cannot infer the correct background information. However, the occluded parts could be seen in non-occluded views with correct background features. To this end, given a point position " + }, + { + "bbox": [ + 296, + 106, + 530, + 165 + ], + "type": "inline_equation", + "content": "\\pmb{x}" + }, + { + "bbox": [ + 296, + 106, + 530, + 165 + ], + "type": "text", + "content": ", the background point feature vector " + }, + { + "bbox": [ + 296, + 106, + 530, + 165 + ], + "type": "inline_equation", + "content": "\\pmb{F}_{st}" + }, + { + "bbox": [ + 296, + 106, + 530, + 165 + ], + "type": "text", + "content": " is produced by" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 337, + 173, + 530, + 193 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 337, + 173, + 530, + 193 + ], + "spans": [ + { + "bbox": [ + 337, + 173, + 530, + 193 + ], + "type": "interline_equation", + "content": "\\boldsymbol {F} _ {s t} (\\boldsymbol {V}; \\boldsymbol {x}) = f c _ {3} \\left(E _ {s t} \\left(\\boldsymbol {V} ^ {*}; \\Pi^ {*} (\\boldsymbol {x})\\right)\\right), \\tag {13}", + "image_path": "16f66c98c6f2c8f32dea25d6db94c923630622c9f09c708babf449d72c5d236a.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "spans": [ + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "f c_{3}" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": " is a fully connected layer and " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "E_{st}" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": " denotes the image encoder. " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "V^{*}" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "\\Pi^{*}" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": " are the non-occluded frame and corresponding projection transform respectively. " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "E_{st}(V^{*};\\Pi^{*}(\\pmb {x}))" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": " denotes that we find the local image patch at " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "\\Pi^{*}(\\pmb {x})" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": " and extract the feature vectors with an image encoder " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "E_{st}" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": " similar to " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "E_{dy}\\big(V^i;\\Pi^i (\\Phi (\\pmb {p},t_i))\\big)" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": ". Since there is no prior in which frames they can be exposed, we apply a straightforward yet effective strategy by randomly sampling one frame from the other frames in the video. We represent the static scene as a radiance field to infer the color " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "c_{st}" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": " and density " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "\\sigma_{st}" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": " by using an MLP " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "W_{st}" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": ": " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "(\\pmb {x},\\pmb {d},\\pmb{F}_{st}(\\pmb {V};\\pmb {x}))\\rightarrow (c_{st},\\sigma_{st})" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": ". The expected background color " + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "inline_equation", + "content": "C_{st}" + }, + { + "bbox": [ + 296, + 200, + 531, + 341 + ], + "type": "text", + "content": " is given by" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 336, + 348, + 530, + 374 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 336, + 348, + 530, + 374 + ], + "spans": [ + { + "bbox": [ + 336, + 348, + 530, + 374 + ], + "type": "interline_equation", + "content": "\\boldsymbol {C} _ {s t} (\\boldsymbol {r}) = \\int_ {u _ {n}} ^ {u _ {f}} T _ {s t} (u) \\sigma_ {s t} (u) \\boldsymbol {c} _ {s t} (u) d u, \\tag {14}", + "image_path": "0b1f39f8ebe3da35b6558b23da4ebb9600adbd9894f8d6da2e0ad57f650d1b95.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 296, + 383, + 530, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 383, + 530, + 431 + ], + "spans": [ + { + "bbox": [ + 296, + 383, + 530, + 431 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 296, + 383, + 530, + 431 + ], + "type": "inline_equation", + "content": "T_{st}(t) = \\exp (-\\int_{u_n}^u\\sigma_{st}(\\boldsymbol {r}(s))ds" + }, + { + "bbox": [ + 296, + 383, + 530, + 431 + ], + "type": "text", + "content": ". We employ foreground masks " + }, + { + "bbox": [ + 296, + 383, + 530, + 431 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 296, + 383, + 530, + 431 + ], + "type": "text", + "content": " to optimize the static field by supervising the pixel color in each video frame in the background regions (where " + }, + { + "bbox": [ + 296, + 383, + 530, + 431 + ], + "type": "inline_equation", + "content": "M(\\boldsymbol {r}) = 0" + }, + { + "bbox": [ + 296, + 383, + 530, + 431 + ], + "type": "text", + "content": ")," + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 311, + 439, + 530, + 463 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 439, + 530, + 463 + ], + "spans": [ + { + "bbox": [ + 311, + 439, + 530, + 463 + ], + "type": "interline_equation", + "content": "L _ {s t} = \\sum_ {\\boldsymbol {r}} | | \\left(\\boldsymbol {C} _ {s t} (\\boldsymbol {r}) - \\boldsymbol {C} _ {s t} ^ {q t} (\\boldsymbol {r})\\right) (1 - M (\\boldsymbol {r})) \\| _ {2}, \\tag {15}", + "image_path": "d08da414f68c3be04db7e5c4557f01b5d04701613f6f017f5293dd123d0cc0d7.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 297, + 472, + 473, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 472, + 473, + 485 + ], + "spans": [ + { + "bbox": [ + 297, + 472, + 473, + 485 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 297, + 472, + 473, + 485 + ], + "type": "inline_equation", + "content": "C_{st}^{gt}" + }, + { + "bbox": [ + 297, + 472, + 473, + 485 + ], + "type": "text", + "content": " represents the ground truth color." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 297, + 492, + 380, + 504 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 492, + 380, + 504 + ], + "spans": [ + { + "bbox": [ + 297, + 492, + 380, + 504 + ], + "type": "text", + "content": "3.4. Optimization" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 297, + 510, + 530, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 510, + 530, + 533 + ], + "spans": [ + { + "bbox": [ + 297, + 510, + 530, + 533 + ], + "type": "text", + "content": "The final dynamic scene color combines the colors from the generalizable dynamic and static fields," + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 312, + 541, + 530, + 568 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 541, + 530, + 568 + ], + "spans": [ + { + "bbox": [ + 312, + 541, + 530, + 568 + ], + "type": "interline_equation", + "content": "\\boldsymbol {C} _ {f u l l} (\\boldsymbol {r}) = \\int_ {u _ {n}} ^ {u _ {f}} T _ {f u l l} (u) \\sigma_ {f u l l} (u) \\boldsymbol {c} _ {f u l l} (u) d u, \\tag {16}", + "image_path": "d15ea6055f60fc64831472ddd6cbcbd7664e739f342242a57e0a19d564b05518.jpg" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 298, + 575, + 325, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 575, + 325, + 586 + ], + "spans": [ + { + "bbox": [ + 298, + 575, + 325, + 586 + ], + "type": "text", + "content": "where" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 297, + 596, + 530, + 619 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 596, + 530, + 619 + ], + "spans": [ + { + "bbox": [ + 297, + 596, + 530, + 619 + ], + "type": "interline_equation", + "content": "\\sigma_ {f u l l} (u) \\boldsymbol {c} _ {f u l l} (u) = (1 - b) \\sigma_ {s t} (u) \\boldsymbol {c} _ {s t} (u) + b \\sigma_ {d y} (u) \\boldsymbol {c} _ {d y} (u), \\tag {17}", + "image_path": "901f91b206ebfc20fe0dcb84358e4e1f383a3326bfce2df3117c70bc570e250e.jpg" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 297, + 619, + 436, + 631 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 619, + 436, + 631 + ], + "spans": [ + { + "bbox": [ + 297, + 619, + 436, + 631 + ], + "type": "text", + "content": "and applies the reconstruction loss," + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 336, + 639, + 530, + 663 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 336, + 639, + 530, + 663 + ], + "spans": [ + { + "bbox": [ + 336, + 639, + 530, + 663 + ], + "type": "interline_equation", + "content": "L _ {f u l l} = \\sum_ {\\boldsymbol {r}} | | \\boldsymbol {C} _ {f u l l} (\\boldsymbol {r}) - \\boldsymbol {C} _ {f u l l} ^ {g t} (\\boldsymbol {r}) | | _ {2}. \\tag {18}", + "image_path": "11e57098eff71947f9d07a5ddb0d82f6130d0a4f38ebb417fbde39b11aa52e95.jpg" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 297, + 671, + 520, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 671, + 520, + 682 + ], + "spans": [ + { + "bbox": [ + 297, + 671, + 520, + 682 + ], + "type": "text", + "content": "Next we design several strategies to optimize our model." + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 683, + 530, + 730 + ], + "type": "text", + "content": "Point trajectory discretization. While point trajectory can be numerically estimated by the continuous integral (2) with Neural ODE solvers [5], it needs plenty of time for 7 ng each point trajectory. To accelerate the process," + } + ] + } + ], + "index": 31 + } + ], + "discarded_blocks": [], + "page_size": [ + 595, + 842 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 46, + 136, + 532, + 227 + ], + "blocks": [ + { + "bbox": [ + 45, + 104, + 530, + 129 + ], + "lines": [ + { + "bbox": [ + 45, + 104, + 530, + 129 + ], + "spans": [ + { + "bbox": [ + 45, + 104, + 530, + 129 + ], + "type": "text", + "content": "Table 1: Novel view synthesis on training frames from single videos. While this setting does not require cross-scene generalization ability, our MonoNeRF still achieves better performance." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 46, + 136, + 532, + 227 + ], + "lines": [ + { + "bbox": [ + 46, + 136, + 532, + 227 + ], + "spans": [ + { + "bbox": [ + 46, + 136, + 532, + 227 + ], + "type": "table", + "html": "
PSNR ↑ / LPIPS ↓JumpingSkatingTruckUmbrellaBalloon1Balloon2PlaygroundAverage
NeRF [28]20.58 / 0.30523.05 / 0.31622.61 / 0.22521.08 / 0.44119.07 / 0.21424.08 / 0.09820.86 / 0.16421.62 / 0.252
NeRF [28] + time16.72 / 0.48919.23 / 0.54217.17 / 0.40317.17 / 0.75217.33 / 0.30419.67 / 0.23613.80 / 0.44417.30 / 0.453
Yoon et al. [53]20.16 / 0.14821.75 / 0.13523.93 / 0.10920.35 / 0.17918.76 / 0.17819.89 / 0.13815.09 / 0.18319.99 / 0.153
Tretschk et al. [40]19.38 / 0.29523.29 / 0.23419.02 / 0.45319.26 / 0.42716.98 / 0.35322.23 / 0.21214.24 / 0.33619.20 / 0.330
Li et al. [21]24.12 / 0.15628.91 / 0.13525.94 / 0.17122.58 / 0.30221.40 / 0.22524.09 / 0.22820.91 / 0.22023.99 / 0.205
NeuPhysics [33]20.16 / 0.20525.13 / 0.16622.62 / 0.21221.02 / 0.42616.68 / 0.23822.54 / 0.26515.10 / 0.36720.48 / 0.282
DynNeRF [13]24.23 / 0.14428.90 / 0.12425.78 / 0.13423.15 / 0.14621.47 / 0.12525.97 / 0.05923.65 / 0.09324.74 / 0.118
MonoNeRF24.26 / 0.09132.06 / 0.04427.56 / 0.11523.62 / 0.18021.89 / 0.12927.36 / 0.05222.61 / 0.13025.62 / 0.106
", + "image_path": "2b6502bc8089f76b3b4e9ac3d31b75d37d92f53810847c2e359c316bbaed3177.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 56, + 234, + 521, + 359 + ], + "blocks": [ + { + "bbox": [ + 56, + 234, + 521, + 359 + ], + "lines": [ + { + "bbox": [ + 56, + 234, + 521, + 359 + ], + "spans": [ + { + "bbox": [ + 56, + 234, + 521, + 359 + ], + "type": "image", + "image_path": "22a40a3efafa65c4a4ca812a1db98cd5cf21f63a7d36ce2d3dde568692bc872f.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 366, + 531, + 403 + ], + "lines": [ + { + "bbox": [ + 45, + 366, + 531, + 403 + ], + "spans": [ + { + "bbox": [ + 45, + 366, + 531, + 403 + ], + "type": "text", + "content": "Figure 3: Qualitative results of jointly optimizing Balloon2 and Umbrella scenes. The foregrounds of two scenes are mixed without " + }, + { + "bbox": [ + 45, + 366, + 531, + 403 + ], + "type": "inline_equation", + "content": "F_{dy}" + }, + { + "bbox": [ + 45, + 366, + 531, + 403 + ], + "type": "text", + "content": ". Our method renders more accurate novel views and predicts plausible scene flows (listed beside the RGB images) by incorporating " + }, + { + "bbox": [ + 45, + 366, + 531, + 403 + ], + "type": "inline_equation", + "content": "F_{temp}" + }, + { + "bbox": [ + 45, + 366, + 531, + 403 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 366, + 531, + 403 + ], + "type": "inline_equation", + "content": "F_{sp}" + }, + { + "bbox": [ + 45, + 366, + 531, + 403 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 52, + 420, + 272, + 516 + ], + "blocks": [ + { + "bbox": [ + 52, + 420, + 272, + 516 + ], + "lines": [ + { + "bbox": [ + 52, + 420, + 272, + 516 + ], + "spans": [ + { + "bbox": [ + 52, + 420, + 272, + 516 + ], + "type": "image", + "image_path": "730bb6621c0372d5a1c1f23ac55826b60df0f871fa44a727d282b6d228294b79.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 522, + 280, + 570 + ], + "lines": [ + { + "bbox": [ + 45, + 522, + 280, + 570 + ], + "spans": [ + { + "bbox": [ + 45, + 522, + 280, + 570 + ], + "type": "text", + "content": "Figure 4: Novel view synthesis on unseen frames. Compared to the ground truths, our model could transfer to new motions, whereas DynNeRF [13] only interpolates in the training frames." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 590, + 279, + 626 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 590, + 279, + 626 + ], + "spans": [ + { + "bbox": [ + 45, + 590, + 279, + 626 + ], + "type": "text", + "content": "we propose to partition " + }, + { + "bbox": [ + 45, + 590, + 279, + 626 + ], + "type": "inline_equation", + "content": "[t_p, t_i]" + }, + { + "bbox": [ + 45, + 590, + 279, + 626 + ], + "type": "text", + "content": " into " + }, + { + "bbox": [ + 45, + 590, + 279, + 626 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 45, + 590, + 279, + 626 + ], + "type": "text", + "content": " evenly-spaced bins and suppose the point velocity in each bin is a constant. The point trajectory can be estimated by the following equation," + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 54, + 643, + 279, + 675 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 643, + 279, + 675 + ], + "spans": [ + { + "bbox": [ + 54, + 643, + 279, + 675 + ], + "type": "interline_equation", + "content": "\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {i}) = \\boldsymbol {x} _ {p} + \\sum_ {n = 1} ^ {N} \\boldsymbol {v} \\left(\\boldsymbol {\\Phi} (\\boldsymbol {p}, t + \\Delta t), t + \\Delta t\\right) \\Delta t, \\tag {19}", + "image_path": "ff936ec90a249204fbeaa9595a349e8e96b68cdfaf46865643f31a9ebec6b0da.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 45, + 682, + 145, + 695 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 682, + 145, + 695 + ], + "spans": [ + { + "bbox": [ + 45, + 682, + 145, + 695 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 682, + 145, + 695 + ], + "type": "inline_equation", + "content": "\\Delta t = \\frac{n}{N} (t_{i} - t_{p})" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 45, + 694, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 694, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 694, + 279, + 730 + ], + "type": "text", + "content": "Depth-blending restriction. To calculate the blending weights within a foreground ray in the generalizable dynamic field, only the points in close proximity to the" + } + ] + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 298, + 463, + 530, + 527 + ], + "blocks": [ + { + "bbox": [ + 296, + 420, + 530, + 456 + ], + "lines": [ + { + "bbox": [ + 296, + 420, + 530, + 456 + ], + "spans": [ + { + "bbox": [ + 296, + 420, + 530, + 456 + ], + "type": "text", + "content": "Table 2: Quantitative results of novel view synthesis on unseen frames. We used the first four frames for training and tested the performance on the rest eight frames." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 298, + 463, + 530, + 527 + ], + "lines": [ + { + "bbox": [ + 298, + 463, + 530, + 527 + ], + "spans": [ + { + "bbox": [ + 298, + 463, + 530, + 527 + ], + "type": "table", + "html": "
Balloon2 / TruckPSNR ↑SSIM ↑LPIPS ↓
NeRF [28]20.33 / 20.260.662 / 0.6690.224 / 0.256
NeRF [28] + time20.22 / 20.260.661 / 0.6390.218 / 0.256
NeuPhysics [33]19.45 / 20.240.478 / 0.5170.343 / 0.285
DynNeRF [13]19.99 / 20.330.641 / 0.6210.291 / 0.273
MonoNeRF21.30 / 23.740.669 / 0.7020.204 / 0.174
", + "image_path": "eba6feba723e2ddde9d60956424b3137bf1fdb5922e83879a33aa3dc9457b961.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 553, + 530, + 623 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 553, + 530, + 623 + ], + "spans": [ + { + "bbox": [ + 296, + 553, + 530, + 623 + ], + "type": "text", + "content": "mated ray depth are regarded as foreground points, whereas points beyond this range are excluded. We penalize the blending weights of non-foreground points in foreground rays. Specifically, given a ray " + }, + { + "bbox": [ + 296, + 553, + 530, + 623 + ], + "type": "inline_equation", + "content": "r(u)" + }, + { + "bbox": [ + 296, + 553, + 530, + 623 + ], + "type": "text", + "content": " through a pixel and the pixel depth " + }, + { + "bbox": [ + 296, + 553, + 530, + 623 + ], + "type": "inline_equation", + "content": "u_{d}" + }, + { + "bbox": [ + 296, + 553, + 530, + 623 + ], + "type": "text", + "content": ", We penalize the blending weights of the points on the ray out of the interval " + }, + { + "bbox": [ + 296, + 553, + 530, + 623 + ], + "type": "inline_equation", + "content": "(u_{d} - \\epsilon, u_{d} + \\epsilon)" + }, + { + "bbox": [ + 296, + 553, + 530, + 623 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 330, + 638, + 530, + 665 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 330, + 638, + 530, + 665 + ], + "spans": [ + { + "bbox": [ + 330, + 638, + 530, + 665 + ], + "type": "interline_equation", + "content": "L _ {d b} = \\sum_ {u \\in \\left(u _ {n}, u _ {d} - \\epsilon\\right) \\cup \\left(u _ {d} + \\epsilon , u _ {f}\\right)} \\| b (\\boldsymbol {r} (u)) \\| _ {2}, \\tag {20}", + "image_path": "e5f78f069281a9dd7e95b344a77d2d843679ae0abf05dd6ed3b48b502048cbf6.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 296, + 679, + 529, + 703 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 679, + 529, + 703 + ], + "spans": [ + { + "bbox": [ + 296, + 679, + 529, + 703 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 296, + 679, + 529, + 703 + ], + "type": "inline_equation", + "content": "b(\\boldsymbol{r}(u))" + }, + { + "bbox": [ + 296, + 679, + 529, + 703 + ], + "type": "text", + "content": " is the blending weight at the position " + }, + { + "bbox": [ + 296, + 679, + 529, + 703 + ], + "type": "inline_equation", + "content": "\\boldsymbol{r}(u)" + }, + { + "bbox": [ + 296, + 679, + 529, + 703 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 296, + 679, + 529, + 703 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 296, + 679, + 529, + 703 + ], + "type": "text", + "content": " controls the surface thickness of the dynamic foreground." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 277, + 706, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 706, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 277, + 706, + 530, + 730 + ], + "type": "text", + "content": "Musk flow loss. We further constrain the consistency 17908 point features by minimizing blending weight variations" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [], + "page_size": [ + 595, + 842 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 54, + 105, + 522, + 330 + ], + "blocks": [ + { + "bbox": [ + 54, + 105, + 522, + 330 + ], + "lines": [ + { + "bbox": [ + 54, + 105, + 522, + 330 + ], + "spans": [ + { + "bbox": [ + 54, + 105, + 522, + 330 + ], + "type": "image", + "image_path": "a59d13ad5bbe83d9f6ac09ae7b80dd46cc15f70be89f923325a69ef3527d1b0f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 340, + 531, + 375 + ], + "lines": [ + { + "bbox": [ + 45, + 340, + 531, + 375 + ], + "spans": [ + { + "bbox": [ + 45, + 340, + 531, + 375 + ], + "type": "text", + "content": "Figure 5: Fast novel scene adaption. We used the pretrained model on Balloon2 scene to fine-tune the novel views of unseen dynamic scenes. We employed LPIPS [55] (the lower is better) to evaluate the image similarity, which provides more correlation with human judgment than other indexes." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 396, + 119, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 396, + 119, + 407 + ], + "spans": [ + { + "bbox": [ + 45, + 396, + 119, + 407 + ], + "type": "text", + "content": "along trajectories," + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 52, + 416, + 279, + 443 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 416, + 279, + 443 + ], + "spans": [ + { + "bbox": [ + 52, + 416, + 279, + 443 + ], + "type": "interline_equation", + "content": "L _ {m f} = \\sum_ {i, j \\in \\{1, 2,.., K \\}} | | b (\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {i})) - b (\\boldsymbol {\\Phi} (\\boldsymbol {p}, t _ {j})) | | _ {2}, \\tag {21}", + "image_path": "83cd9398a5dd6030626ef056f4547f73d5e0d0a025cf64122dee7065028b6939.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 452, + 270, + 463 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 452, + 270, + 463 + ], + "spans": [ + { + "bbox": [ + 45, + 452, + 270, + 463 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 452, + 270, + 463 + ], + "type": "inline_equation", + "content": "b(\\Phi (\\pmb {p},t))" + }, + { + "bbox": [ + 45, + 452, + 270, + 463 + ], + "type": "text", + "content": " denotes the blending weight at " + }, + { + "bbox": [ + 45, + 452, + 270, + 463 + ], + "type": "inline_equation", + "content": "\\Phi (p,t)" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 463, + 279, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 463, + 279, + 498 + ], + "spans": [ + { + "bbox": [ + 45, + 463, + 279, + 498 + ], + "type": "text", + "content": "Other regularization. We follow previous works [21, 13, 10] to use the depth constraint, sparsity constraint, and motion regularization and smoothness to train the model." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 510, + 124, + 522 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 510, + 124, + 522 + ], + "spans": [ + { + "bbox": [ + 45, + 510, + 124, + 522 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 529, + 279, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 529, + 279, + 588 + ], + "spans": [ + { + "bbox": [ + 45, + 529, + 279, + 588 + ], + "type": "text", + "content": "In this section, we conducted experiments on the Dynamic Scene dataset [53]. We first tested the performance of synthesizing novel views from single videos, and then we tested the generalization ability from multiple videos. In the end, we carried out ablation studies on our model." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 45, + 595, + 158, + 607 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 595, + 158, + 607 + ], + "spans": [ + { + "bbox": [ + 45, + 595, + 158, + 607 + ], + "type": "text", + "content": "4.1. Experimental Setup" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 45, + 612, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 612, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 612, + 279, + 730 + ], + "type": "text", + "content": "Dataset. We used the Dynamic Scene dataset [53] to evaluate the proposed method. Concretely, it contains 9 video sequences that are captured with 12 cameras by using a camera rig. We followed previous works [21, 13] and derived each frame of the video from different cameras to simulate the camera motion. All the cameras capture images at 12 different timestamps " + }, + { + "bbox": [ + 45, + 612, + 279, + 730 + ], + "type": "inline_equation", + "content": "\\{t_i, i = 1, 2\\ldots, 12\\}" + }, + { + "bbox": [ + 45, + 612, + 279, + 730 + ], + "type": "text", + "content": ". Each training video contains twelve frames sampled from the " + }, + { + "bbox": [ + 45, + 612, + 279, + 730 + ], + "type": "inline_equation", + "content": "i^{th}" + }, + { + "bbox": [ + 45, + 612, + 279, + 730 + ], + "type": "text", + "content": " camera at time " + }, + { + "bbox": [ + 45, + 612, + 279, + 730 + ], + "type": "inline_equation", + "content": "t_i" + }, + { + "bbox": [ + 45, + 612, + 279, + 730 + ], + "type": "text", + "content": " followed DynNeRF [13]. We used COI MAP [35, 36] to approximate the camera poses. It is assumed" + } + ] + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 298, + 426, + 530, + 479 + ], + "blocks": [ + { + "bbox": [ + 296, + 394, + 530, + 418 + ], + "lines": [ + { + "bbox": [ + 296, + 394, + 530, + 418 + ], + "spans": [ + { + "bbox": [ + 296, + 394, + 530, + 418 + ], + "type": "text", + "content": "Table 3: Ablation studies on " + }, + { + "bbox": [ + 296, + 394, + 530, + 418 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{dy}" + }, + { + "bbox": [ + 296, + 394, + 530, + 418 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 394, + 530, + 418 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{temp}" + }, + { + "bbox": [ + 296, + 394, + 530, + 418 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 296, + 394, + 530, + 418 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{sp}" + }, + { + "bbox": [ + 296, + 394, + 530, + 418 + ], + "type": "text", + "content": " by jointly optimizing Balloon2 and Umbrella scenes." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 298, + 426, + 530, + 479 + ], + "lines": [ + { + "bbox": [ + 298, + 426, + 530, + 479 + ], + "spans": [ + { + "bbox": [ + 298, + 426, + 530, + 479 + ], + "type": "table", + "html": "
PSNR ↑ / LPIPS ↓UmbrellaBalloon2Average
w/o. Fdy20.59 / 0.25622.79 / 0.15921.57 / 0.230
w/o. Ftemp22.75 / 0.17524.85 / 0.09823.80 / 0.137
w/o. Fsp22.81 / 0.18125.09 / 0.14323.95 / 0.162
Ours23.44 / 0.16925.44 / 0.09324.44 / 0.131
", + "image_path": "44407472d7d7b9c2a7175b7acad1436211cebc04d1bd494bccd77d1df2ee0f11.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 506, + 530, + 575 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 506, + 530, + 575 + ], + "spans": [ + { + "bbox": [ + 296, + 506, + 530, + 575 + ], + "type": "text", + "content": "trinsic parameters of all the cameras are the same. DynamicFace sequences were excluded because COLMAP fails to estimate camera poses. All video frames were resized to " + }, + { + "bbox": [ + 296, + 506, + 530, + 575 + ], + "type": "inline_equation", + "content": "480 \\times 270" + }, + { + "bbox": [ + 296, + 506, + 530, + 575 + ], + "type": "text", + "content": " resolution. We generated the depth, mask, and optical flow signals from the depth estimation model [34], Mask R-CNN [16], and RAFT [39]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "text", + "content": "Implementation details. We followed pixelNeRF [54] and used ResNet-based MLPs as our implicit velocity field " + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "inline_equation", + "content": "W_{vel}" + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "text", + "content": " and rendering networks " + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "inline_equation", + "content": "W_{dy}" + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "inline_equation", + "content": "W_{st}" + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "text", + "content": ". For generalizable dynamic field, we utilized Slowonly50 [11] pretrained on Kinetics400 [2] dataset as the encoder " + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "inline_equation", + "content": "E_{dy}" + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "text", + "content": " with the frozen weights. We removed the final fully connected layer in the backbone and incorporated the first, second, and third feature layers for querying " + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "inline_equation", + "content": "F_{sp}" + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "text", + "content": ". We simplified (4) that " + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "inline_equation", + "content": "F_{sp}" + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "text", + "content": " at time " + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "inline_equation", + "content": "t_i" + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "text", + "content": " is sampled from " + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "inline_equation", + "content": "\\{V^{i-1}, V^i, V^{i+1}\\}" + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "text", + "content": ". For generalizable static field, we used ResNet18 [17] pretrained on ImageNet [8] as the encoder " + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "inline_equation", + "content": "E_{st}" + }, + { + "bbox": [ + 296, + 578, + 531, + 730 + ], + "type": "text", + "content": ". 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PSNR ↑ / LPIPS ↓Training framesUnseen framesUnseen videos
w/o. Ldb22.76 / 0.14820.69 / 0.34821.68 / 0.345
w/o. Lmf22.95 / 0.13520.95 / 0.35421.67 / 0.342
w/o. Fst21.75 / 0.23019.79 / 0.37121.81 / 0.337
w/o. random17.30 / 0.43516.93 / 0.51220.28 / 0.353
Ours23.02 / 0.13021.30 / 0.30422.63 / 0.277
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MethodN=1N=2ODE solver [5]
PSNR ↑ / LPIPS ↓22.90 / 0.13622.97 / 0.13423.75 / 0.129
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Novel View Synthesis from Single Video" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 45, + 485, + 279, + 565 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 485, + 279, + 565 + ], + "spans": [ + { + "bbox": [ + 45, + 485, + 279, + 565 + ], + "type": "text", + "content": "In this section, we trained the models from single monocular videos, where existing methods are applicable to this setting. Specifically, we first tested the performance on training frames, which is the widely-used setting to evaluate video-based NeRFs. Then, we tested the generalization ability on unseen frames in the video, where other existing methods are not able to transfer well to the unseen motions." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 45, + 566, + 279, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 566, + 279, + 670 + ], + "spans": [ + { + "bbox": [ + 45, + 566, + 279, + 670 + ], + "type": "text", + "content": "Novel view synthesis on training frames. To evaluate the synthesized novel views, we followed DynNeRF [13] and tested the performance by fixing the view to the first camera and changing time. We reported the PSNR and LPIPS [55] in Table 1. We evaluated the performance of Li et al. [21], Tretschk et al. [40], NeuPhysics [33], and Chen et al. [13] from the official implementations. Even without the need of generalization ability, our method achieves better results." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 45, + 671, + 279, + 717 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 671, + 279, + 717 + ], + "spans": [ + { + "bbox": [ + 45, + 671, + 279, + 717 + ], + "type": "text", + "content": "Novel view synthesis on unseen frames. We split the video frames into two groups: four front frames were used for training and the rest of eight unseen frames were utilized to render novel views. 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[ + 296, + 330, + 530, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 330, + 530, + 365 + ], + "spans": [ + { + "bbox": [ + 296, + 330, + 530, + 365 + ], + "type": "text", + "content": "DynNeRF [13] only interpolates novel views in the training frames. The reported PSNR, SSIM [47], and LPIPS scores in Table 2 quantitatively verify the superiority of our model." + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 297, + 373, + 515, + 385 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 373, + 515, + 385 + ], + "spans": [ + { + "bbox": [ + 297, + 373, + 515, + 385 + ], + "type": "text", + "content": "4.3. Novel View Synthesis from Multiple Videos" + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 296, + 391, + 530, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 391, + 530, + 472 + ], + "spans": [ + { + "bbox": [ + 296, + 391, + 530, + 472 + ], + "type": "text", + "content": "In the section, we tested the novel view synthesis performance on multiple dynamic scenes. It is worth noting that as existing methods can only learn from single monocular videos, they are not applicable to the settings that need to train on multiple videos. Then, we evaluated the novel scene adaption ability on several novel monocular videos. Lastly, we conducted a series of scene editing experiments." + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 296, + 473, + 530, + 543 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 473, + 530, + 543 + ], + "spans": [ + { + "bbox": [ + 296, + 473, + 530, + 543 + ], + "type": "text", + "content": "Novel view synthesis on training videos. We selected Balloon2 and Umbrella scenes to train our model. As shown in Figure 3 and Table 3, our model could distinguish foregrounds from two scenes and perform well with " + }, + { + "bbox": [ + 296, + 473, + 530, + 543 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{dy}" + }, + { + "bbox": [ + 296, + 473, + 530, + 543 + ], + "type": "text", + "content": ". Specifically, it predicts generalizable scene flows with " + }, + { + "bbox": [ + 296, + 473, + 530, + 543 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{temp}" + }, + { + "bbox": [ + 296, + 473, + 530, + 543 + ], + "type": "text", + "content": " and renders more accurate details with " + }, + { + "bbox": [ + 296, + 473, + 530, + 543 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{sp}" + }, + { + "bbox": [ + 296, + 473, + 530, + 543 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 296, + 543, + 530, + 671 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 543, + 530, + 671 + ], + "spans": [ + { + "bbox": [ + 296, + 543, + 530, + 671 + ], + "type": "text", + "content": "Novel view synthesis on unseen videos. We explored the generalization ability of our model by pretraining on the Balloon2 scene and fine-tuning the pretrained model on other scenes. Figure 5 presents the results of four unseen videos: Playground, Skating, Truck, and Balloon1. We also pretrained DynNeRF [13] on the Balloon2 scene for a fair comparison. While DynNeRF only learns to render new scenes from scratch, our model transfers to scenes with correct dynamic motions. By further training with 500 steps, our model achieves better image rendering quality and higher LPIPS scores, which takes about 10 minutes." + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 296, + 671, + 530, + 717 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 671, + 530, + 717 + ], + "spans": [ + { + "bbox": [ + 296, + 671, + 530, + 717 + ], + "type": "text", + "content": "Scene editing. As Figure 6 shows, our model further supports many scene editing applications by directly processing point features without extra training. Changing background was implemented by exchanging the static" + } + ] + } + ], + "index": 37 + }, + { + "bbox": [ + 296, + 717, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 717, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 717, + 530, + 730 + ], + "type": "text", + "content": "0 features between two scenes. Moving, scaling, dupi" + } + ] + } + ], + "index": 38 + } + ], + "discarded_blocks": [], + "page_size": [ + 595, + 842 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 279, + 141 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 279, + 141 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 279, + 141 + ], + "type": "text", + "content": "cating and flipping foreground were directly applied by operating video features in dynamic radiance field. The above applications could be combined arbitrarily." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 149, + 137, + 163 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 149, + 137, + 163 + ], + "spans": [ + { + "bbox": [ + 46, + 149, + 137, + 163 + ], + "type": "text", + "content": "4.4. Ablation Study" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "spans": [ + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "text", + "content": "We conducted a series of experiments to examine the proposed " + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "inline_equation", + "content": "L_{db}" + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "inline_equation", + "content": "L_{mf}" + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "inline_equation", + "content": "F_{st}" + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "text", + "content": ", random sampling strategy, and trajectory discretization method. We show in Figure 7 that " + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "inline_equation", + "content": "L_{db}" + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "text", + "content": " deblurs the margin of the synthesized foreground in novel views, " + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "inline_equation", + "content": "L_{mf}" + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "text", + "content": " keeps the blending consistency in different views for delineating the foreground more accurately. The random sampling strategy successfully renders static scene without dynamic foreground, and backgrounds of two scenes are mixed without " + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "inline_equation", + "content": "F_{st}" + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "text", + "content": ". We also show the numeric comparisons of " + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "inline_equation", + "content": "L_{db}" + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "inline_equation", + "content": "L_{mf}" + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "inline_equation", + "content": "F_{st}" + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "text", + "content": ", and random sampling strategy in Table 4. In Table 5, our discretization method reaches comparable results with ODE solvers [5] and achieves higher performance with the increase of " + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 45, + 168, + 281, + 319 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 331, + 116, + 344 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 331, + 116, + 344 + ], + "spans": [ + { + "bbox": [ + 46, + 331, + 116, + 344 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 351, + 279, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 351, + 279, + 491 + ], + "spans": [ + { + "bbox": [ + 45, + 351, + 279, + 491 + ], + "type": "text", + "content": "In this paper, we study the generalization ability of novel view synthesis from monocular videos. The challenge is the ambiguity of 3D point features and scene flows in the viewing directions. We find that video frame features and optical flows are a pair of complementary constraints for learning 3D point features and scene flows. To achieve this, we propose a generalizable dynamic radiance field called MonoNeRF. We estimate point features and trajectories from the video features extracted by a video encoder and render dynamic scenes from points features. Experiments show that our model could learn a generalizable radiance field for dynamic scenes, and support many scene editing applications." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 491, + 279, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 491, + 279, + 576 + ], + "spans": [ + { + "bbox": [ + 45, + 491, + 279, + 576 + ], + "type": "text", + "content": "Acknowledgements. This work was supported by the National Key Research and Development Program of China under Grant No. 2020AAA0108100, the National Natural Science Foundation of China under Grant No. 62206147 and 61971343. The authors would like to thank the Shanghai Artificial Intelligence Laboratory for its generous support of computational resources." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 589, + 103, + 601 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 589, + 103, + 601 + ], + "spans": [ + { + "bbox": [ + 47, + 589, + 103, + 601 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 50, + 608, + 279, + 727 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 50, + 608, + 279, + 652 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 50, + 608, + 279, + 652 + ], + "spans": [ + { + "bbox": [ + 50, + 608, + 279, + 652 + ], + "type": "text", + "content": "[1] Shengqu Cai, Anton Obukhov, Dengxin Dai, and Luc Van Gool. 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Motivated by a new and strong observation that this challenge can be remedied by a 3D-space local-grid search scheme in an ideal case, we propose a stage-wise approach, which combines the information flow from 2D-to-3D (3D bounding box proposal generation with a single 2D image) and 3D-to-2D (proposal verification by denoising with 3D-to-2D contexts) in a top-down manner. Specifically, we first obtain initial proposals from off-the-shelf backbone monocular 3D detectors. Then, we generate a 3D anchor space by local-grid sampling from the initial proposals. Finally, we perform 3D bounding box denoising at the 3D-to-2D proposal verification stage. To effectively learn discriminative features for denoising highly overlapped proposals, this paper presents a method of using the Perceiver I/O model [20] to fuse the 3D-to-2D geometric information and the 2D appearance information. With the encoded latent representation of a proposal, the verification head is implemented with a self-attention module. Our method, named as MonoXiver, is generic and can be easily adapted to any backbone monocular 3D detectors. Experimental results on the well-established KITTI dataset and the challenging large-scale Waymo dataset show that MonoXiver consistently achieves improvement with limited computation overhead.", + "bbox": [ + 75, + 354, + 473, + 734 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 762, + 209, + 777 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Detecting and locating objects in 3D using a single image, known as monocular 3D object detection, is a highly challenging task due to its ill-posed nature. However, the practical applications of low-cost system setups in fields such as self-driving cars and robotic manipulation have led", + "bbox": [ + 75, + 787, + 470, + 864 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "to the development of robust monocular 3D object detection systems, making it a prominent research topic in the computer vision community.", + "bbox": [ + 496, + 323, + 890, + 367 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Although significant progress has been achieved in this field [37], accurate 3D center localization remains a major challenge for state-of-the-art (SOTA) methods as indicated in [39]. Most of these methods follow a bottom-up paradigm, where a single 2D image is used to directly predict 3D bounding boxes (2D-to-3D) with or without extra information (e.g. LiDAR). However, due to the inherent depth ambiguity of this task, relying solely on bottom-up 2D-to-3D paradigms may not be enough to completely address this challenge.", + "bbox": [ + 496, + 368, + 892, + 520 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we observe that bottom-up 2D-to-3D predicted 3D bounding boxes are able to provide informative priors for monocular 3D object detection. We propose to leverage these contexts to improve detection performance in a top-down manner. Our proposed approach is motivated by a strong empirical upper-bound analysis with SOTA bottom-up monocular 3D object detectors.", + "bbox": [ + 496, + 521, + 893, + 626 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The empirical upper-bound experiment. We analyze vehicle detection performance on the well-established KITTI validation set [5-7]. We start with the recently proposed MonoCon [30] because it achieves SOTA performance with a very simple design. By using MonoCon's prediction results as bottom-up 3D anchors, we sample 3D bounding box proposals along both the $x$ and $z$ axes (i.e., in the bird-eye's view) with a simple strategy. First, we define a 2D local grid with a range (e.g., 2 meter) and a stride (e.g., 0.1 meter). For each bottom-up anchor, with its center located at the local-grid origin, we replicate the anchor at each grid vertex without changing its size, orientation and prediction score. We use all the generated 3D bounding boxes as top-down proposals and compute the empirical upper-bound of 3D detection performance by searching for the best match within top-down proposals for each ground-truth 3D object bounding box based on 3D Intersection-over-Union (3D IoU).", + "bbox": [ + 496, + 627, + 893, + 883 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "A strong observation from the experiment. As shown", + "bbox": [ + 517, + 885, + 890, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Work partially conducted during an internship of X. Liu at OPPO Seattle Research Center, USA in 2022.", + "bbox": [ + 75, + 875, + 470, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "6436", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "table", + "img_path": "images/a6dc8998a4aedee5ad7623eb9d3d01696a8e552af8c7559026c6fb2e298a03c5.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
RangeStrideEasyModerateHard#Bboxesmean IoUavg
MonoCon [30]26.3319.0115.98n-
± 20.176.98↑50.6564.93↑45.9256.91↑40.931600·n0.931
± 1.50.176.45↑50.1262.27↑43.2654.34↑38.36900·n0.931
± 1.50.274.00↑47.6761.78↑42.7753.64↑37.66225·n0.868
± 1.50.364.80↑38.4756.20↑37.1950.66↑34.68121·n0.812
± 1.50.554.00↑27.6745.93↑26.9240.99↑25.0149·n0.714
± 1.50.7541.58↑15.2534.44↑15.4330.12↑14.1425·n0.612
", + "bbox": [ + 81, + 88, + 464, + 176 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Table 1: A strong empirical upper-bound analysis. Our MonoXiver is motivated by the observation that bottom-up monocular 3D object detectors can be significantly improved by leveraging a simple 3D-space local-grid search scheme in an ideal case. This highlights the potential of exploring the 3D proposal space. However, this improvement comes at a cost: 1) the proposal verification stage experiences significant increases in number of bounding box proposals, and 2) a more powerful refinement module is required to handle highly overlapped boxes.", + "bbox": [ + 75, + 200, + 468, + 351 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "in Table 1, despite the evaluation result of initial bottom-up proposals is relatively low in 3D average precision $(AP_{3D})$ (e.g., 19.01 in Moderate settings), most of predicted 3D centers are already in the close proximity of the GT ones. An empirical upper-bound of 34.4 $AP_{3D}$ can be achieved even with a coarse sampling scheme (e.g., the last row), which is significantly higher than SOTA methods. We also obtained similar observations from other backbone 3D object detectors such as the MonoDLE [39] and the SMOKE [33]. These strong empirical observations demonstrate the potential of integrating the bottom-up initial proposals with top-down sampling and verification.", + "bbox": [ + 75, + 382, + 468, + 564 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The challenge in the 3D-to-2D proposal verification. The 3D-to-2D proposal verification phase can be treated as a 3D bounding box denoising process, as we want to search for the \"best\" bounding boxes from the top-down proposal set. This process is extremely challenging, as the proposals generated from the same bottom-up anchor are highly overlapped in both 3D and 2D (after projection), which leads to the long-standing problem of handling the \"crowd\" in detection. To quantitatively analyze the overlap extent after projection for top-down proposals, we consider one proposal and its top- $k$ overlapping neighbors in terms of Intersection-over-Union (IoU), which is denoted by $\\mathrm{IoU}_{avg}^k$ as the average IoU over the top- $k$ neighbors. The last column in Table 1 shows the statistics.", + "bbox": [ + 75, + 566, + 468, + 775 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The statistics clearly demonstrates the difficulty of denoising densely generated top-down proposal set (e.g., stride=0.1, IoU5 = 0.931). Even for a relative sparse generated top-down proposal set (e.g., stride=0.75, IoU5 = 0.612), the challenge still exists because proposals sampled in front and behind of the same anchor will almost collapse to the same 2D bounding box, especially when they are far away from the camera. So, how can we", + "bbox": [ + 75, + 779, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "encode the 3D bounding box proposal for verification under the monocular setting? From this perspective, we note that many methods that work well in multi-view 3D object detection are often not applicable for monocular 3D objection because they mainly rely on features that are obtained by fusing projection features from multi-view feature maps.", + "bbox": [ + 496, + 90, + 890, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Based on the intuition that even though highly overlapped proposals have similar appearance features, their inherent 3D-to-2D geometric features (e.g. 3D location, projected geometry, etc.) are extremely different, we propose to fuse these 3D-to-2D geometric feature with their correspondent appearance features to learn discriminative features for bounding box denoising. We present a method of using the Perceiver I/O model [20] to effectively fuse these contexts, as Perceiver has shown strong capabilities to fuse multi-modal inputs. With the encoded latent representation of a proposal, the verification head is implemented by a self-attention module (see the top in Fig. 1). The proposed method is named as MonoXiver, indicating its general applicability to any backbone monocular 3D detectors and the integration of the Perceiver model.", + "bbox": [ + 496, + 181, + 890, + 407 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In experiments, we evaluate our proposed MonoXiver on the well-established KITTI benchmark [14] and the challenging large-scale Waymo [51] dataset with various backbone monocular 3D detectors. It achieves consistent and significant performance improvement on both datasets with limited computation overhead. Moreover, it achieves the 1st place among monocular methods on the KITTI vehicle detection benchmark, outperforming the previous works by a large margin.", + "bbox": [ + 496, + 407, + 890, + 544 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works and Our Contributions", + "text_level": 1, + "bbox": [ + 500, + 558, + 846, + 573 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Monocular 3D Object Detection. The problem of monocular 3D object detection is considered ill-posed, prompting recent research efforts to leverage additional information sources, including LiDAR point clouds [4, 10, 19, 28, 45], depth estimation [12, 36, 42, 48, 53, 54, 62], CAD models [25, 34], temporal frames [2], etc. These approaches have shown improved detection performance when compared to purely image-based methods [1, 33, 41, 57]. However, they often come with increased computation load and inference time, making them less practical for real-time applications such as autonomous vehicles. In contrast, purely image-based methods have seen significant performance improvements in the literature by exploiting geometric constraints [26, 35, 41, 47, 59, 60], perspective projections [24, 38], auxiliary training [30], novel loss designs [8, 39, 49] and second-stage processing techniques [23]. These works focus on developing better bottom-up paradigms. Our proposed method, MonoXiver, takes a top-down paradigm, which explores 3D space differently than the aforementioned methods. It provides a generic and highly efficient second-stage refinement module for any pretrained state-of", + "bbox": [ + 496, + 583, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "6437", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/e63afead46451d0cdfd33b3caeb7df300e76ca24ba393f232443b157b3b1af42.jpg", + "image_caption": [ + "Figure 1: Illustration of the proposed MonoXiver method. MonoXiver is built for any off-the-shelf backbone monocular 3D object detectors. It consists of a 2D-to-3D proposal generation phase using a bottom-up anchoring and top-down sampling strategy, and a 3D-to-2D proposal verification (or denoising) phase using the Perceiver I/O [20] with a carefully designed 3D/2D input space to address the unique challenges. See text for details." + ], + "image_footnote": [], + "bbox": [ + 86, + 87, + 883, + 340 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "the-art monocular 3D object detection method, making it a complementary approach.", + "bbox": [ + 75, + 438, + 468, + 468 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Bird's-Eye-View 3D Object Detection. Bird's-Eye-View (BEV) 3D object detection [40] has recently gained significant attention as it provides a physical-interpretable feature space for integrating data from diverse sensors [27, 31, 44, 56] and modalities [13, 18]. To enable the learning of a physical-interpretable feature space, accurate physical measurements from depth perception systems such as multi-view cameras and LiDAR are crucial [16]. However, detecting 3D objects in BEV is challenging for monocular systems due to the intrinsic depth ambiguity. Directly accumulating image features based on projection reference points similar to recent query-based multi-view 3D detectors [31, 56] might fail because of lacking stereo-matching mechanism to resolve the depth ambiguity. To overcome this issue, recent BEV-based monocular methods [9, 45, 55] lift the image feature space to voxel-represented world-space using monocular depth estimation models. Our proposed method, MonoXiver, samples top-down proposals based on bottom-up initial proposals in BEV space. Unlike prior arts [9, 45, 55] that extract features represented in world-space, MonoXiver's top-down proposals extract features from both projected appearance features and inherent geometric features. We explore to address the challenging intrinsic feature ambiguity problem by applying a Perceiver-like attention mechanism to query informative features for 3D bounding box verification and refinement without the need for dense depth supervision.", + "bbox": [ + 75, + 468, + 470, + 875 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Transformers for Multi-modal Data. Transformers [52],", + "bbox": [ + 76, + 876, + 467, + 891 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "known for their powerful attention mechanism, have been successfully applied in multiple research areas and applications [3,11,32,50]. With the powerful attention mechanism, transformers can conveniently align multi-modal structured data, enabling the generation of universal multi-modal representation. The recent proposed Perceiver [20, 21] extends the transformers' querying mechanism and makes it capable of efficiently handling data from arbitrary settings. In our work, we adapt Perceiver to fuse appearance features and geometric features from the same bounding box to generate appearance-geometric aligned representation, which is then used as queries for the down-stream 3D bounding box refinement task.", + "bbox": [ + 496, + 438, + 890, + 633 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our Contributions. MonoXiver makes three main contributions to the field of monocular 3D object detection:", + "bbox": [ + 496, + 633, + 890, + 665 + ], + "page_idx": 2 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We conduct a new and strong empirical upper-bound analysis for state-of-the-art monocular 3D object detectors. We demonstrate that a simple, universally applicable sampling strategy can lead to consistent and significant performance improvement in an ideal situation. Based on these observations, we propose to explore the top-down, stage-wise detection paradigm with 2D-to-3D proposal generation and 3D-to-2D proposal verification for monocular 3D object detection.", + "- To address the challenge at the bounding box denoising stage, we propose to learn discriminative features by enhancing appearance features with 3D-to-2D inherent geometric features. We therefore propose a carefully-designed module with the integration of the powerful Perceiver and self-attention mechanism. The resulting mod" + ], + "bbox": [ + 500, + 670, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "6438", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ule can be applied generically to any off-the-shelf monocular 3D object detectors.", + "bbox": [ + 89, + 90, + 467, + 121 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "- Extensive experiments demonstrate the effectiveness and efficiency of our proposed method, MonoXiver, under a separate two-stage training setting. It achieves consistent improvement with limited overhead on both KITTI and Waymo dataset. It achieves the 1st place among monocular methods on the KITTI vehicle detection benchmark, outperforming the previous works by a large margin.", + "bbox": [ + 76, + 125, + 467, + 231 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3. Approach", + "text_level": 1, + "bbox": [ + 76, + 242, + 184, + 258 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this section, we first present the straightforward 2D-to-3D proposal generation on top of a backbone monocular 3D object detector. Then, we present the details of the proposed MonoXiver method (Fig. 1).", + "bbox": [ + 76, + 267, + 467, + 328 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. The 2D-to-3D Proposal Generation", + "text_level": 1, + "bbox": [ + 76, + 335, + 380, + 349 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Let $I$ be an RGB input image defined on the domain $\\Lambda$ . The goal of monocular 3D object detection is to detect 3D bounding boxes, along with their class labels denoted by $\\ell$ for each object instance in $I$ . The 3D bounding box is parameterized by the 3D center position $\\mathbf{P} = (X,Y,Z)$ in meters, the shape dimensions $\\mathbf{D} = (h,w,l)$ in meters, and the observation angle $\\alpha \\in [-\\pi ,\\pi ]$ , all measured in the camera coordinate system.", + "bbox": [ + 76, + 358, + 467, + 478 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For simplicity, consider the pure image-based settings, a monocular 3D object detector often consists of two main components in inference: the feature backbone (e.g., the DLA34 network [58]), denoted by $\\mathbf{F}_I$ for computing deep features from the raw image $I$ , and the regression heads for inferring the 3D bounding box parameters using the computed feature map. We generate bottom-up proposals using one off-the-shelf backbone monocular 3D object detector which is first trained following its own training receipts. Without loss of generality, we consider one of its detected 3D bounding boxes indexed by $i$ in an image $I$ ,", + "bbox": [ + 75, + 479, + 467, + 645 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {B} _ {i} = \\left(\\ell_ {i}, \\mathbf {P} _ {i}, \\mathbf {D} _ {i}, \\alpha_ {i}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 197, + 652, + 467, + 667 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As shown in Table 1, the top-down sampling with a bottom-up anchor proposal is a straightforward process. We start by generating a 2D local grid in the $X - Z$ plane (i.e. in the bird's-eye-view, BEV), centered at the position $(X,Z)$ of the anchor box $\\mathbb{B}$ . To accomplish this, we specify a search range and a stride. Based on the trade-off between the empirical upper bound and the computing overhead and the mean IoU among the proposals, we adopt a conservative strategy using the search range $\\pm 1.5$ meters and the stride 0.75, which will generate 25 proposals per bottom-up anchor (inclusive). We then place the anchor box $\\mathbb{B}$ at the 25 grid points, with only the position $\\mathbf{P}$ updated. To simplify the notation, we do not differentiate between the bottom-up anchor and the top-down sampled proposal, and we generally index them using $i$ , unless otherwise stated.", + "bbox": [ + 75, + 674, + 467, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. The 3D-to-2D Proposal Verification", + "text_level": 1, + "bbox": [ + 500, + 90, + 805, + 106 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The proposal verification will rely essentially on the information from the input 2D images in purely monocular 3D object detection. Due to the aforementioned unique challenges in the 3D proposal space, we utilize Perceiver I/O [20] to design an expressive proposal representation learning scheme.", + "bbox": [ + 498, + 114, + 890, + 204 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2.1 Proposal Representation", + "text_level": 1, + "bbox": [ + 500, + 224, + 723, + 239 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As illustrated in Fig. 1, we utilize three types of features in encoding a 3D bounding box proposal $\\mathbb{B}$ ,", + "bbox": [ + 498, + 250, + 890, + 279 + ], + "page_idx": 3 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- The 3D Shape Features represented by $(\\mathbf{P}, \\mathbf{D}, \\alpha)$ . It is a 7-dim vector. It encodes where the proposal is in the 3D space (the camera coordinate system), as well as its 3D occupancy. The position $\\mathbf{P}$ is empirically normalized by the typical detection range (e.g., $X, Y, Z$ are normalized by 50, 2 and 80 meters respectively).", + "- The 2D Projection Points from the 8 corners and the center of the 3D bounding box (with known camera intrinsic matrix). It is an 18-dim vector in the image coordinate system, and normalized by the image size. This 9-point projection provides the finegrained placement of a proposal in the 2D space, that is the geometric bond between a proposal in the 3D space and its 2D placement.", + "- The 2D Bounding Box projected from the proposal and truncated by the image boundary. We use the left-top and right-bottom two points to encode a 2D bounding box. It gives a 4-dim vector normalized by the image size. For a proposal whose 2D projection is entirely inside the image plane, the two points of the 2D bounding box will be just redundant with respect to the 9 project points. Otherwise, the truncation points on the image boundary will facilitate the learning to be truncation aware.", + "- The Appearance Features of the 9 projection points. We directly extract features from the final layer of the feature backbone $\\mathbf{F}_I$ . If a projection point is out of the image plane, we encode it using an all-zero vector.", + "- The RoI Appearance Features of the 2D bounding box. We use the RoIAign features [17] extracted from the final layer of the feature backbone $\\mathbf{F}_I$ . Since the 2D IoU overlapping between proposals is high on average (e.g., 0.612 in Table 1), we use a finer grid, $14 \\times 14$ , in computing the RoIAign features, such that the extracted appearance features contain \"sufficient\" details." + ], + "bbox": [ + 500, + 289, + 890, + 810 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2.2 Proposal Embedding", + "text_level": 1, + "bbox": [ + 500, + 830, + 700, + 845 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Let $N$ be the total number of proposals in an image $I$ . With the above representation scheme, denote by $f_{N\\times 29}^{geo}$ the geometric parameter matrix from the first three items above,", + "bbox": [ + 498, + 854, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "6439", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "and by $f_{N \\times 9 \\times C}^{pt}$ the projection point appearance feature matrix (where $C$ is the number of channels of the final layer of the feature backbone, e.g., $C = 64$ ), and by $f_{N \\times (14 \\times 14) \\times C}^{roi}$ the RoI feature matrix. Before applying the Perceiver I/O model, we embed the three to form \"tokens\" using multi-layer perceptron (MLP).", + "bbox": [ + 75, + 90, + 468, + 181 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For the geometric parameters $f_{N \\times 29}^{geo}$ , we have,", + "bbox": [ + 96, + 181, + 406, + 199 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nf _ {N \\times 2 9} ^ {\\text {g e o}} \\xrightarrow {\\mathrm {M L P}} z _ {N \\times (g \\times d)} \\xrightarrow {\\text {R e a r r a n g e}} \\mathbf {f} _ {g \\times N \\times d} ^ {\\text {g e o}}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 133, + 210, + 468, + 234 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $d$ is the hidden dimension (e.g., $d = 256$ ). $g$ is the group number, similar in spirit to the multi-head setup in the self-attention. We want to encode the geometric parameters in different latent spaces to account for the large variations in the proposal space (e.g., $g = 4$ ).", + "bbox": [ + 75, + 244, + 468, + 319 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For the project point features $f_{N \\times 9 \\times C}^{pt}$ , we have,", + "bbox": [ + 96, + 319, + 416, + 337 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nf _ {N \\times 9 \\times C} ^ {p t} \\xrightarrow {\\mathrm {M L P}} z _ {N \\times 9 \\times d} \\xrightarrow {\\text {R e a r r a n g e}} \\mathbf {f} _ {9 \\times N \\times d} ^ {p t}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 132, + 349, + 468, + 372 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where we reuse $z$ to denote the latent features for simplicity and without confusion.", + "bbox": [ + 76, + 383, + 468, + 411 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For the RoI features $f_{N\\times (14\\times 14)\\times C}^{roi}$ , we have,", + "bbox": [ + 96, + 412, + 398, + 431 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nf _ {N \\times (1 4 \\times 1 4) \\times C} ^ {r o i} \\xrightarrow {\\mathrm {M L P}} z _ {N \\times d} \\xrightarrow {\\text {R e a r r a g e}} \\mathbf {f} _ {1 \\times N \\times d} ^ {r o i}. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 120, + 444, + 468, + 465 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2.3 Intra-Proposal Attention via Perceiver", + "text_level": 1, + "bbox": [ + 76, + 484, + 398, + 500 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "With the above proposal embedding, before the proposal verification, our goal is to compute a final latent feature representation in the $d$ -dim space for each proposal by fusing information from the geometric encoding, projection-point-based appearance encoding and RoI-based appearance encoding (i.e., the intra-proposal attention), such that we can address the aforementioned unique challenges in the proposal space. We leverage the Perceiver I/O model for this intra-proposal attention.", + "bbox": [ + 75, + 508, + 468, + 643 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The Perceiver first fuses the projection-point appearance encoding $\\mathbf{f}_{9\\times N\\times d}^{pt}$ and the geometric encoding $\\mathbf{f}_{g\\times N\\times d}^{geo}$ . As shown in Fig. 1, it consists of a cross-attention by treating the former as Query (consisting of 9 projection-point tokens) and computing Key and Value from the latter (consisting of $g$ geometric tokens), followed by a self-attention module. We have,", + "bbox": [ + 75, + 645, + 468, + 750 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\mathbf {f} _ {9 \\times N \\times d} ^ {p t}, \\mathbf {f} _ {g \\times N \\times d} ^ {g e o}\\right) \\xrightarrow {\\text {C r o s s - A t t n}} \\cdot \\xrightarrow {\\text {S e l f - A t t n}} \\mathbf {F} _ {9 \\times N \\times d} ^ {g e o - p t}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 99, + 761, + 468, + 782 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "which results in geometry-aware projection-point encoding.", + "bbox": [ + 76, + 794, + 467, + 809 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Next, the Perceiver fuses the RoI appearance encoding $\\mathbf{f}_{1\\times N\\times d}^{roi}$ as the 1-token Query with the 9-token geometry-aware projection-point encoding using a cross attention module,", + "bbox": [ + 76, + 809, + 468, + 869 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left(\\mathbf {f} _ {1 \\times N \\times d} ^ {r o i}, \\mathbf {F} _ {9 \\times N \\times d} ^ {g e o - p t}\\right) \\xrightarrow {\\text {C r o s s - A t t n}} \\mathbf {F} _ {1 \\times N \\times d} ^ {g e o - p t - r o i}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 133, + 881, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "which results in the $d$ -dim latent features for each proposal, which fuse the three types of information sources: geometry, point-level appearance and region-level appearance.", + "bbox": [ + 498, + 90, + 890, + 136 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In the above, the cross-attention and self-attention modules are based on the standard formulation [52].", + "bbox": [ + 498, + 136, + 890, + 166 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2.4 Inter-Proposal Attention", + "text_level": 1, + "bbox": [ + 500, + 185, + 725, + 199 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "With all the above process, each proposal is still encoded individually with the hope of fusing geometry, point-level appearance and region-level appearance information in a semantically meaningful way via the Perceiver I/O model. With the compact latent vector computed for each proposal in $\\mathbf{F}_{1\\times N\\times d}^{geo-pt-rot}$ , their interactions need to be taken into account in order to resolve their \"crowding\" issue at the underlying scene level.", + "bbox": [ + 496, + 208, + 890, + 328 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To that end, we treat each proposal as a \"token\" and apply a standard self-attention module to capture the interproposal attention,", + "bbox": [ + 498, + 329, + 890, + 375 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {F} _ {1 \\times N \\times d} ^ {\\text {g e o - p t - r o i}} \\xrightarrow {\\text {R e a r r a n g e}} \\mathbf {F} _ {N \\times d} ^ {\\text {g e o - p t - r o i}} \\xrightarrow {\\text {S e l f - A t t n}} \\mathbb {F} _ {N \\times d}. \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 537, + 386, + 890, + 407 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2.5 Proposal Verification", + "text_level": 1, + "bbox": [ + 500, + 424, + 700, + 438 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "This verification is posed as a regression problem,", + "bbox": [ + 500, + 446, + 834, + 463 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {F} _ {N \\times d} \\xrightarrow {\\mathrm {M L P s}} \\left(\\mathbf {y} _ {N \\times L}, \\Delta \\mathbf {P} _ {N}, \\Delta \\mathbf {D} _ {N}\\right), \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 473, + 890, + 494 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $L$ is the total number of categories (e.g., $L = 3$ in the KITTI dataset), and $\\mathbf{y}_{N\\times L}$ is the classification scores (logits). $\\Delta \\mathbf{P}_N$ and $\\Delta \\mathbf{D}_N$ are the position and dimension residuals.", + "bbox": [ + 496, + 503, + 890, + 563 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Consider a proposal $\\mathbb{B}_i$ (Eqn. 1), it is verified via,", + "bbox": [ + 517, + 565, + 846, + 580 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\ell} _ {i} = \\arg \\max _ {l = 1, \\dots , L} \\mathbf {y} _ {i, l}, \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 624, + 589, + 890, + 614 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {P}} _ {i} = \\mathbf {P} _ {i} + \\Delta \\mathbf {P} _ {i}, \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 619, + 618, + 890, + 636 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {D}} _ {i} = \\mathbf {D} _ {i} + \\Delta \\mathbf {D} _ {i}, \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 617, + 641, + 890, + 657 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where a proper unnormalization step will be done for $\\hat{\\mathbf{P}}_i$ to counter the normalization step used in the proposal representation (Sec. 3.2.1). Based on the score $\\mathbf{y}_{i,\\hat{\\ell}_i}$ , we can keep top- $k$ proposals for each anchor position.", + "bbox": [ + 496, + 671, + 890, + 733 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Details of Training and Testing", + "text_level": 1, + "bbox": [ + 500, + 741, + 772, + 758 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For simplicity, we evaluate the proposed MonoXiver in a two-stage setting where the backbone monocular 3D object detector is first trained and kept frozen. Then, the MonoXiver component is trained end-to-end. One of the reasons for this choice is that off-the-shelf backbone monocular 3D object detectors often involve multiple loss functions, and joint training with MonoXiver would require sophisticated tuning of the trade-off parameters for different loss terms. We leave the joint end-to-end training or iterative training,", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "6440", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "as done in the early version of Faster RCNN [46] between the region proposal network and the region classification head network, for future work. Additionally, the separate two-stage training may also have advantages in leveraging the set of bottom-up anchor proposals merged from multiple backbone monocular 3D detectors, which we also leave for future work.", + "bbox": [ + 75, + 90, + 472, + 196 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.3.1 The Set Prediction Formulation in Training", + "text_level": 1, + "bbox": [ + 76, + 219, + 434, + 236 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Based on the separate two-stage setting, the proposed MonoXiver is trained with a fixed set of 3D bounding box proposals and a fixed set of ground-truth 3D bounding boxes. The ground-truth assignment for proposals is needed in training. Two straightforward methods are: using the maximum 3D IoU based assignment, or using the maximum 2D IoU assignment (after projected to the image plane). Due to the \"crowding\" issue in the proposal space, we observe that both of them do not work during our development of the MonoXiver since they will create difficult \"decision boundaries\" for the MonoXiver to learn or fit.", + "bbox": [ + 75, + 244, + 468, + 411 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Since we have the two fixed set as input, we resort to the set prediction formulation used in the DETR framework [3]. Denote by $\\Omega_{\\mathbb{B}} = \\{\\mathbb{B}_i\\}_{i=1}^N$ the set of generated proposals, by $\\Omega_{\\mathbb{B}^*} = \\{\\mathbb{B}_j^*\\}_{j=1}^M \\cup \\{\\emptyset_j\\}_{j=M+1}^N$ the set of ground-truth 3D bounding boxes padded with $N - M$ dummy $\\emptyset$ elements. Given a permutation of $N$ elements, denoted by $\\sigma$ which assigns the $i$ -th element in the ground-truth set to the $\\sigma(i)$ -the element in the proposal set, the loss for the one-to-one bipartite matching between $\\mathbb{B}_i^*$ and $\\mathbb{B}_{\\sigma(i)}$ is defined by,", + "bbox": [ + 75, + 412, + 472, + 550 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {m a t c h}} \\left(\\mathbb {B} _ {i} ^ {*}, \\mathbb {B} _ {\\sigma (i)}\\right) = \\mathbf {1} _ {\\ell_ {i} ^ {*} \\neq \\emptyset} \\cdot \\left(- \\lambda_ {1} \\cdot \\hat {p} _ {\\sigma (i)} \\left(\\ell_ {i} ^ {*}\\right) + \\right. \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 561, + 468, + 579 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\lambda_ {2} \\cdot \\mathcal {L} _ {b b o x} ^ {2 D} + \\lambda_ {3} \\cdot \\mathcal {L} _ {i o u} ^ {2 D} + \\lambda_ {4} \\cdot \\mathcal {L} _ {i o u} ^ {3 D}),\n$$\n", + "text_format": "latex", + "bbox": [ + 215, + 580, + 452, + 599 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\hat{p}_{\\sigma(i)}(\\ell_i^*)$ is computed using $\\mathbf{y}_{\\sigma(i)}$ (Eqn. 8) via Softmax. $\\mathcal{L}_{bbox}^{2D}$ represents the normalized L1 2D bounding box, and $\\mathcal{L}_{iou}^{2D}$ and $\\mathcal{L}_{iou}^{3D}$ the IoU loss in 2D and 3D respectively. $\\lambda_1$ to $\\lambda_4$ are the trade-off parameters.", + "bbox": [ + 76, + 613, + 468, + 674 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.3.2 Loss Functions for Proposal Verification", + "text_level": 1, + "bbox": [ + 76, + 696, + 411, + 710 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For the three outputs in Eqn. 8, we have three loss terms as follows,", + "bbox": [ + 75, + 720, + 468, + 750 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathcal {L} _ {\\text {c l s}} + \\mathcal {L} _ {\\text {s i z e}} + \\lambda \\cdot \\mathcal {L} _ {\\text {l o c}} \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 176, + 753, + 468, + 770 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{cls}$ is the Focal Loss [29] with the $\\alpha$ value of 0.5 to balance the number of positive and negative samples. The Focal loss is used due to the imbalance introduced by the explicit top-down proposal generation. $\\mathcal{L}_{size}$ are $\\mathcal{L}_{loc}$ are the loss functions for the 3D size and the 3D center respectively. $\\lambda$ is an trade-off hyper-parameter. We use $\\ell_1$ loss for $\\mathcal{L}_{size}$ and $\\mathcal{L}_{loc}$ . We set $\\lambda = 5$ to induce the model to focus more on the 3D localization refinement task.", + "bbox": [ + 75, + 779, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.3.3 Training", + "text_level": 1, + "bbox": [ + 500, + 90, + 616, + 106 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "MonoXiver is trained using a total of 8 GPUs, with a batch size of 64 for 24 epochs on KITTI (12 epochs on Waymo) using the AdamW optimizer. The optimizer is set with $(\\beta_{1},\\beta_{2}) = (0.95,0.99)$ and weight decay of 0.0001, excluding feature normalization layers and bias parameters. The initial learning rate is set to $2.25e - 5$ , and it is reduced by a factor of 10 at the 16th and 22nd epoch. Notably, the entire second-stage training process takes merely 1.5 hours on KITTI [14] using a single Nvidia RTX5000 GPU, indicating the low computational overhead of our proposed MonoXiver method. The training time on Waymo [51] varies depending on the training data and training recipes of off-the-shelf monocular 3D detectors. Overall, the second-stage training on Waymo is much faster compared to training the backbone monocular 3D object detector, leading to about a 3/4 reduction in training time.", + "bbox": [ + 496, + 114, + 893, + 357 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.3.4 Testing", + "text_level": 1, + "bbox": [ + 500, + 377, + 604, + 393 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "During testing, we keep at most top-3 predictions per initial anchor proposal with a score threshold of 0.03 (the score is predicted from the proposed MonoXiver module). The final prediction score is the product of the classification probability predicted from the backbone monocular 3D object detector and the score computed by the MonoXiver module.", + "bbox": [ + 496, + 402, + 892, + 494 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 507, + 633, + 523 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We evaluate our MonoXiver on the well-established KITTI [14] dataset and the large-scale Waymo [51] dataset. We first show that our improved baseline detector outperforms previous SOTA methods on the KITTI benchmark by a large margin. Then we show that we consistently improved pretrained monocular 3D object detectors with limited computation overhead on both datasets. We further analyze the contribution of each part of our MonoXiver in the ablation studies.", + "bbox": [ + 496, + 532, + 893, + 669 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Setup", + "text_level": 1, + "bbox": [ + 500, + 680, + 581, + 696 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Dataset. The KITTI dataset [14] consists of 7,481 training images and 7,518 testing images. In KITTI's experiments, we split the training data into a training subset with 3,712 images and a validation subset with 3,769 images following [5-7]. We conduct ablation studies on the defined split and report the test set results evaluated by the official KITTI benchmark. The Waymo dataset [51] contains 52,386 training and 39,848 validation images from the front camera. In Waymo experiments, we use a subset of its training set by sampling every third frame from the training sequences following [22,45].", + "bbox": [ + 496, + 703, + 893, + 869 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation Metrics. The KITTI vehicle benchmark evaluates detection results by the 40-point interpolated av-", + "bbox": [ + 498, + 869, + 893, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "6441", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/56493e2592445b838e27123b045331d1a9f2987cd3d001847da5b6c13ff86295.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodsVenuesExtra Info.APBEV|R40↑AP3D|R40↑
EasyMod.HardEasyMod.Hard
Kinematic3D [2]ECCV20Temporal26.6917.5213.1019.0712.729.17
AutoShape [34]ICCV21CAD30.6620.0815.9522.4714.1711.36
DCD [25]ECCV22CAD32.5521.5018.2523.8115.9013.21
MonoDistill [10]ICLR22LiDAR31.8722.5919.7222.9716.0313.60
DID-M3D [43]ECCV22LiDAR32.9522.7619.8324.4016.2913.75
DD3D [42]ICCV21Depth30.9822.5620.0323.2216.3414.20
DFM [55]ECCV22Temporal + LiDAR31.7122.8919.9722.9416.8214.65
Pseudo-Stereo [9]CVPR22Depth + LiDAR32.8423.6720.6423.7417.7415.14
MonoFlex [59]CVPR2128.2319.7516.8919.9413.8912.07
GUPNet [35]ICCV2130.2921.1918.2020.1114.2011.77
DEVIANT [22]ECCV22None29.6520.4417.4321.8814.4611.89
Homography [15]CVPR2229.6020.6817.8121.7514.9413.07
DimEmbedding [61]CVPR2232.8221.9818.7023.6216.1013.41
MonoCon [30]AAAI22None31.1222.1019.0022.5016.4613.95
Our MonoXiver + MonoCon-34.1425.3722.2025.2419.0416.39
", + "bbox": [ + 181, + 88, + 792, + 311 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/22e9c30a2bd9b17370f64f75f8de1f1fbc63bd464afd06ab8bb3a6f35f7940da.jpg", + "table_caption": [ + "Table 2: Comparisons with state-of-the-art methods on the Car category on the KITTI test set. According to the KITTI protocol, methods are ranked based on their performance under the moderate difficulty setting. We highlight the best results in bold and the second-best results in underline." + ], + "table_footnote": [], + "table_body": "
MethodsAP3D|R40↑Relative Improvement
EasyModerateHard
SMOKE [33]10.437.095.5711%-33%
SMOKE + Ours11.589.407.75
Improvement+1.15+2.31+2.18
MonoDLE [39]17.9413.7212.1018%-22%
MonoDLE + Ours21.1516.1914.75
Improvement+3.21+2.47+2.65
MonoCon [30]26.3319.0115.9816%-20%
MonoCon + Ours30.4822.4019.13
Improvement+4.15+3.39+3.15
", + "bbox": [ + 99, + 402, + 447, + 554 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "erage precision $(AP_{R40})$ of 3D bounding boxes in 3D space $(AP_{3D|R40})$ and bird eye's view $(AP_{BEV|R40})$ at $IoU_{3D} \\geq 0.7$ . The prediction results are evaluated based on three difficulty settings, easy, moderate and hard, according to the 2D box height, occlusion and truncation levels of objects. The vehicle detection results on Waymo are evaluated on two levels of difficulty including Level_1 and Level_2 at $IoU_{3D} \\geq 0.5$ . The level is assigned based on the number of LiDAR points included in each 3D box. Besides the $AP_{3D}$ metric, Waymo uses the $APH_{3D}$ metric to incorporate heading information in $AP_{3D}$ .", + "bbox": [ + 75, + 734, + 472, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/0749a4d79d87b60f8ff6490225f06b148e660f4a69191d2c858d42c7562aa82c.jpg", + "table_caption": [ + "Table 3: The effectiveness of MonoXiver based on different methods on the KITTI validation dataset. In order to demonstrate the ability of the proposed MonoXiver to generalize across different detectors, we utilized three distinct base detectors with varying levels of detection accuracy. We observe that MonoXiver consistently yields significant improvements across all three base detectors." + ], + "table_footnote": [], + "table_body": "
MethodsLevel_1Level_2
AP3D↑APH3D↑AP3D↑APH3D↑
PatchNet [36]2.922.742.422.28
PCT [54]4.204.154.034.15
GUPNet [35]10.029.949.399.31
GUPNet + ours11.4711.3510.6710.56
Improvement+1.45+1.41+1.28+1.25
DEVIANT [22]10.9810.8910.2910.20
DEVIANT + ours11.8811.7511.0610.93
Improvement+0.90+0.86+0.77+0.73
", + "bbox": [ + 522, + 402, + 870, + 547 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/4f49ece3ff4f8c0f0dae1bc12b0510ab41b4282dc101d4c68e65cc6c837698db.jpg", + "table_caption": [ + "Table 4: The effectiveness of MonoXiver based on different methods on Waymo validation dataset. In order to showcase the generalization capabilities of the proposed MonoXiver on large-scale datasets, we conducted testing on the challenging Waymo [51] validation set, utilizing two SOTA methods. We observed consistent improvements in performance." + ], + "table_footnote": [], + "table_body": "
MethodsFLOPsLatency (ms)FPS
SMOKE [33]/ + ours42.82/48.1923/3143/32
MonoDLE [39]/ + ours77.44/82.8022/3145/32
MonoCon [30]/ + ours56.22/61.5018/2555/40
", + "bbox": [ + 522, + 710, + 874, + 785 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 5: Computation overhead analysis. The GFLOPs is computed based on an input size of (384, 1248), while the latency and FPS are evaluated on a NVIDIA RTX5000 GPU.", + "bbox": [ + 496, + 806, + 893, + 849 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "6442", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Experimental Results", + "text_level": 1, + "bbox": [ + 76, + 90, + 279, + 106 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Comparison with SOTA methods on the KITTI dataset. We present the results of our proposed MonoXiver method on the challenging KITTI vehicle benchmark in Table 2. Notably, our method achieves the best performance across different evaluation metrics while only using image-level information, surpassing previous state-of-the-art methods by a large margin. Specifically, we observe a significant and consistent improvement from 2.44 AP (hard settings) to 2.74 AP (easy settings) absolute increase in $\\mathrm{AP}_{3D}$ for the boosted MonoCon approach compared to the vanilla MonoCon approach. These consistent improvements demonstrate the effectiveness of our method. More qualitative and quantitative results are provided in the Supplementary Materials. Generalization abilities across backbone monocular 3D object detectors and datasets. We evaluate our method with various state-of-the-art backbone monocular 3D object detection methods on the KITTI and the Waymo validation set, reported in Table 3 and Tabel 4 respectively. Monoxiver consistently demonstrates significant improvements across different methods and different difficult levels. Specifically, on the well-established KITTI dataset, our MonoXiver is able to enhance various backbone detectors with varying levels of detection accuracy by up to $33\\%$ relative improvement. On the challenging large-scale Waymo dataset, our MonoXiver consistently improves the performance of strong baseline methods GUPNet and DEVIANT by up to $1.45\\mathrm{AP}_{3D}$ on Level_1 and $1.28\\mathrm{AP}_{3D}$ on Level_2. These results validate the effectiveness and robustness of our approach.", + "bbox": [ + 75, + 113, + 468, + 551 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Computation overhead. As shown in Table 5, although our MonoXiver causes about an average of $8\\mathrm{ms}$ overhead compared with baseline detectors, it still achieves real-time detection. We note that its inference speed could be improved by optimizing the detailed implementation (e.g., we still have for-loops in our current code, which can be easily paralleled for better efficiency).", + "bbox": [ + 75, + 551, + 468, + 657 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Qualitative Comparison. We show the visualization comparisons with MonoCon in Fig. 2. It shows that MonoXiver achieves better 3D box center localization.", + "bbox": [ + 75, + 657, + 468, + 702 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.3. Ablation Studies", + "text_level": 1, + "bbox": [ + 76, + 710, + 241, + 724 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this section, we report ablation studies of MonoXiver structure and different bounding box branches on the KITTI validation set. More ablation studies are provided in the Supplementary Materials.", + "bbox": [ + 75, + 734, + 468, + 795 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effectiveness of MonoXiver structures. In this study, we explore the importance of RoI feature (Table 6 a.), the context information provided by geometric embeddings (Table 6 b.), and our complete MonoXiver model (Table 6 c.). In experiments a. and b., we replace the Perciver with a MLP layer to fuse the appearance feature and geometry feature to keep similar parameter size.", + "bbox": [ + 75, + 795, + 468, + 901 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/21c316b3b117a8c4540b63c2d9bf16a5bef9811ece88f7920dc03a594c939f20.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
AppearanceGeometryPerciverEasy/Mod./Hard
MonoCon [30]---26.33/19.01/15.98
a.✓--29.30/21.04/18.22
b.✓✓-29.33/21.67/18.46
c.✓✓✓30.48/22.40/19.13
", + "bbox": [ + 522, + 88, + 870, + 150 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/96fc0384648b278a9aa1ae707d21e55e96fe97b036d0723c2482eeaa1e1b604a.jpg", + "table_caption": [ + "Table 6: Ablation studies of MonoXiver structure on KITTI validation set." + ], + "table_footnote": [], + "table_body": "
RescoreResLocResDimEasyMod.Hard
MonoCon [30]---26.3319.0115.98
a.✓--29.6621.4118.38
b.✓✓-30.3222.3019.04
c.✓✓✓30.4822.4019.13
", + "bbox": [ + 522, + 218, + 870, + 282 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 7: Ablation studies of the effect of different branches on KITTI validation set", + "bbox": [ + 498, + 305, + 890, + 335 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Results show that the appearance feature plays the most important role in performance improvement. When using the appearance feature only, the Moderate AP is improved by 2.39. The performance is further improved by 0.6 AP and 0.7 AP after fusing with geometric embeddings and Perciver. It shows that Perceiver effectively fuses information between appearance and geometric embeddings.", + "bbox": [ + 496, + 363, + 890, + 468 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effectiveness of Different Head Branches. In Table 7, we present the impact of different branches on the detection performance of our MonoXiver. Since our method generates 25 proposals per each initial proposal, the rescoring head branch plays a crucial role in filtering out false detections, leading to significant improvements by up to 3.3 AP. The localization residual branch and the dimension residual branch further enhance the performance by about 1 AP, and we employ all branches to achieve a new state-of-the-art result.", + "bbox": [ + 496, + 469, + 890, + 619 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 633, + 619, + 648 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This paper explores the task of monocular 3D object detection. It begins with the strong observation that significant improvements in detection performance can be achieved by a local grid search based on initially detected 3D bounding boxes. This leads to a novel denoising-based approach called MonoXiver. The approach utilizes the Perceiver I/O model to produce a unified feature embedding, leverages the self-attention mechanism for proposal verification, and ultimately delivers high-quality 3D box predictions. MonoXiver can serve as a lightweight second-stage processing module to significantly improve the accuracy of detection results while only requiring 1.5 hours of training on a single GPU card for the KITTI dataset. Comprehensive evaluation experiments on the well-established KITTI benchmark and the large-scale challenging Waymo dataset demonstrate the effectiveness of our design, with a new state-of-the-art", + "bbox": [ + 496, + 657, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "6443", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a47f99d0275564abcf421b83af8efe4631616c14e12c4f791e37dfb47aa855c6.jpg", + "image_caption": [ + "Figure 2: Qualitative comparison of our MonoXiver with MonoCon on KITTI validation set [5]. The left column is MonoCon's prediction result; the right column is our MonoXiver's prediction result. The ground truth is shown in green and blue. The prediction result is shown in red." + ], + "image_footnote": [], + "bbox": [ + 99, + 89, + 870, + 450 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "achieved. Furthermore, our strong observation should encourage the community to further study refinement modules for 3D object detection.", + "bbox": [ + 75, + 532, + 470, + 578 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Limitations. Our work keeps at most top-3 predictions per bottom-up proposal for evaluation. Future work might be reducing the number of top-3 prediction by incorporating stronger priors for helping denoising proposals in 3D, i.e. temporal modeling, 3D geometric priors, large foundation models, etc. Our work has only been comprehensively tested on monocular settings with significant improvement, and it has not been tested on multiview settings.", + "bbox": [ + 75, + 580, + 468, + 702 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements", + "text_level": 1, + "bbox": [ + 76, + 722, + 243, + 739 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "X. Liu and T. Wu were partly supported by ARO Grant W911NF1810295, NSF IIS-1909644, ARO Grant W911NF2210010, NSF IIS-1822477, NSF CMMI-2024688 and NSF IUSE-2013451. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the ARO, NSF, DHHS or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any", + "bbox": [ + 75, + 750, + 470, + 902 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "copyright annotation thereon. The authors are grateful for the constructive comments by anonymous reviewers and area chairs.", + "bbox": [ + 498, + 532, + 892, + 578 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 500, + 590, + 596, + 607 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Garrick Brazil and Xiaoming Liu. M3d-rpn: Monocular 3d region proposal network for object detection. In ICCV, pages 9287-9296, 2019. 2", + "[2] Garrick Brazil, Gerard Pons-Moll, Xiaoming Liu, and Bernt Schiele. Kinematic 3d object detection in monocular video. In ECCV, pages 135-152. Springer, 2020. 2, 7", + "[3] Nicolas Carion, Francisco Massa, Gabriel Synnaeve, Nicolas Usunier, Alexander Kirillov, and Sergey Zagoruyko. End-to-end object detection with transformers. In ECCV, pages 213-229. Springer, 2020. 3, 6", + "[4] Hansheng Chen, Yuyao Huang, Wei Tian, Zhong Gao, and Lu Xiong. 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In ICCV, pages 2713-2722, 2021. 2" + ], + "bbox": [ + 503, + 92, + 890, + 714 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "6446", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Monocular 3D Object Detection with Bounding Box Denoising in 3D by Perceiver/3f374e4f-acb1-4e95-8005-f14f6138f707_model.json b/2023/Monocular 3D Object Detection with Bounding Box Denoising in 3D by Perceiver/3f374e4f-acb1-4e95-8005-f14f6138f707_model.json new file mode 100644 index 0000000000000000000000000000000000000000..d4eaeeb1f3fed8eedc193b320ce2e6f02f425455 --- /dev/null +++ b/2023/Monocular 3D Object Detection with Bounding Box Denoising in 3D by Perceiver/3f374e4f-acb1-4e95-8005-f14f6138f707_model.json @@ -0,0 +1,2455 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.131, + 0.895, + 0.155 + ], + "angle": 0, + "content": "Monocular 3D Object Detection with Bounding Box Denoising in 3D by Perceiver" + }, + { + "type": "text", + "bbox": [ + 0.157, + 0.179, + 0.812, + 0.234 + ], + "angle": 0, + "content": "Xianpeng Liu\\(^{1*}\\), Ce Zheng\\(^{2}\\), Kelvin Cheng\\(^{1}\\), Nan Xue\\(^{3}\\), Guo-Jun Qi\\(^{4,5}\\), Tianfu Wu\\(^{1}\\) \n\\(^{1}\\)North Carolina State University \\(^{2}\\)University of Central Florida \\(^{3}\\)Ant Group \\(^{4}\\)OPPO Seattle Research Center, USA \\(^{5}\\)Westlake University" + }, + { + "type": "text", + "bbox": [ + 0.209, + 0.236, + 0.761, + 0.288 + ], + "angle": 0, + "content": "{xliu59, kbcheng, tianfu_wu}@ncsu.edu; cezheng@knights.ucf.edu; xuanan@ieee.org; guojunq@gmail.com https://xianpeng919.github.io/monoxiver" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.322, + 0.314, + 0.339 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.355, + 0.474, + 0.735 + ], + "angle": 0, + "content": "The main challenge of monocular 3D object detection is the accurate localization of 3D center. Motivated by a new and strong observation that this challenge can be remedied by a 3D-space local-grid search scheme in an ideal case, we propose a stage-wise approach, which combines the information flow from 2D-to-3D (3D bounding box proposal generation with a single 2D image) and 3D-to-2D (proposal verification by denoising with 3D-to-2D contexts) in a top-down manner. Specifically, we first obtain initial proposals from off-the-shelf backbone monocular 3D detectors. Then, we generate a 3D anchor space by local-grid sampling from the initial proposals. Finally, we perform 3D bounding box denoising at the 3D-to-2D proposal verification stage. To effectively learn discriminative features for denoising highly overlapped proposals, this paper presents a method of using the Perceiver I/O model [20] to fuse the 3D-to-2D geometric information and the 2D appearance information. With the encoded latent representation of a proposal, the verification head is implemented with a self-attention module. Our method, named as MonoXiver, is generic and can be easily adapted to any backbone monocular 3D detectors. Experimental results on the well-established KITTI dataset and the challenging large-scale Waymo dataset show that MonoXiver consistently achieves improvement with limited computation overhead." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.763, + 0.21, + 0.779 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.788, + 0.471, + 0.866 + ], + "angle": 0, + "content": "Detecting and locating objects in 3D using a single image, known as monocular 3D object detection, is a highly challenging task due to its ill-posed nature. However, the practical applications of low-cost system setups in fields such as self-driving cars and robotic manipulation have led" + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.875, + 0.471, + 0.9 + ], + "angle": 0, + "content": "*Work partially conducted during an internship of X. Liu at OPPO Seattle Research Center, USA in 2022." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.324, + 0.892, + 0.368 + ], + "angle": 0, + "content": "to the development of robust monocular 3D object detection systems, making it a prominent research topic in the computer vision community." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.369, + 0.893, + 0.521 + ], + "angle": 0, + "content": "Although significant progress has been achieved in this field [37], accurate 3D center localization remains a major challenge for state-of-the-art (SOTA) methods as indicated in [39]. Most of these methods follow a bottom-up paradigm, where a single 2D image is used to directly predict 3D bounding boxes (2D-to-3D) with or without extra information (e.g. LiDAR). However, due to the inherent depth ambiguity of this task, relying solely on bottom-up 2D-to-3D paradigms may not be enough to completely address this challenge." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.522, + 0.894, + 0.627 + ], + "angle": 0, + "content": "In this paper, we observe that bottom-up 2D-to-3D predicted 3D bounding boxes are able to provide informative priors for monocular 3D object detection. We propose to leverage these contexts to improve detection performance in a top-down manner. Our proposed approach is motivated by a strong empirical upper-bound analysis with SOTA bottom-up monocular 3D object detectors." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.628, + 0.895, + 0.884 + ], + "angle": 0, + "content": "The empirical upper-bound experiment. We analyze vehicle detection performance on the well-established KITTI validation set [5-7]. We start with the recently proposed MonoCon [30] because it achieves SOTA performance with a very simple design. By using MonoCon's prediction results as bottom-up 3D anchors, we sample 3D bounding box proposals along both the \\( x \\) and \\( z \\) axes (i.e., in the bird-eye's view) with a simple strategy. First, we define a 2D local grid with a range (e.g., 2 meter) and a stride (e.g., 0.1 meter). For each bottom-up anchor, with its center located at the local-grid origin, we replicate the anchor at each grid vertex without changing its size, orientation and prediction score. We use all the generated 3D bounding boxes as top-down proposals and compute the empirical upper-bound of 3D detection performance by searching for the best match within top-down proposals for each ground-truth 3D object bounding box based on 3D Intersection-over-Union (3D IoU)." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "A strong observation from the experiment. As shown" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6436" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.465, + 0.178 + ], + "angle": 0, + "content": "
RangeStrideEasyModerateHard#Bboxesmean IoUavg
MonoCon [30]26.3319.0115.98n-
± 20.176.98↑50.6564.93↑45.9256.91↑40.931600·n0.931
± 1.50.176.45↑50.1262.27↑43.2654.34↑38.36900·n0.931
± 1.50.274.00↑47.6761.78↑42.7753.64↑37.66225·n0.868
± 1.50.364.80↑38.4756.20↑37.1950.66↑34.68121·n0.812
± 1.50.554.00↑27.6745.93↑26.9240.99↑25.0149·n0.714
± 1.50.7541.58↑15.2534.44↑15.4330.12↑14.1425·n0.612
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.201, + 0.47, + 0.352 + ], + "angle": 0, + "content": "Table 1: A strong empirical upper-bound analysis. Our MonoXiver is motivated by the observation that bottom-up monocular 3D object detectors can be significantly improved by leveraging a simple 3D-space local-grid search scheme in an ideal case. This highlights the potential of exploring the 3D proposal space. However, this improvement comes at a cost: 1) the proposal verification stage experiences significant increases in number of bounding box proposals, and 2) a more powerful refinement module is required to handle highly overlapped boxes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.383, + 0.47, + 0.565 + ], + "angle": 0, + "content": "in Table 1, despite the evaluation result of initial bottom-up proposals is relatively low in 3D average precision \\((AP_{3D})\\) (e.g., 19.01 in Moderate settings), most of predicted 3D centers are already in the close proximity of the GT ones. An empirical upper-bound of 34.4 \\(AP_{3D}\\) can be achieved even with a coarse sampling scheme (e.g., the last row), which is significantly higher than SOTA methods. We also obtained similar observations from other backbone 3D object detectors such as the MonoDLE [39] and the SMOKE [33]. These strong empirical observations demonstrate the potential of integrating the bottom-up initial proposals with top-down sampling and verification." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.567, + 0.469, + 0.776 + ], + "angle": 0, + "content": "The challenge in the 3D-to-2D proposal verification. The 3D-to-2D proposal verification phase can be treated as a 3D bounding box denoising process, as we want to search for the \"best\" bounding boxes from the top-down proposal set. This process is extremely challenging, as the proposals generated from the same bottom-up anchor are highly overlapped in both 3D and 2D (after projection), which leads to the long-standing problem of handling the \"crowd\" in detection. To quantitatively analyze the overlap extent after projection for top-down proposals, we consider one proposal and its top-\\(k\\) overlapping neighbors in terms of Intersection-over-Union (IoU), which is denoted by \\(\\mathrm{IoU}_{avg}^k\\) as the average IoU over the top-\\(k\\) neighbors. The last column in Table 1 shows the statistics." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.469, + 0.901 + ], + "angle": 0, + "content": "The statistics clearly demonstrates the difficulty of denoising densely generated top-down proposal set (e.g., stride=0.1, IoU5 = 0.931). Even for a relative sparse generated top-down proposal set (e.g., stride=0.75, IoU5 = 0.612), the challenge still exists because proposals sampled in front and behind of the same anchor will almost collapse to the same 2D bounding box, especially when they are far away from the camera. So, how can we" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.182 + ], + "angle": 0, + "content": "encode the 3D bounding box proposal for verification under the monocular setting? From this perspective, we note that many methods that work well in multi-view 3D object detection are often not applicable for monocular 3D objection because they mainly rely on features that are obtained by fusing projection features from multi-view feature maps." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.183, + 0.892, + 0.408 + ], + "angle": 0, + "content": "Based on the intuition that even though highly overlapped proposals have similar appearance features, their inherent 3D-to-2D geometric features (e.g. 3D location, projected geometry, etc.) are extremely different, we propose to fuse these 3D-to-2D geometric feature with their correspondent appearance features to learn discriminative features for bounding box denoising. We present a method of using the Perceiver I/O model [20] to effectively fuse these contexts, as Perceiver has shown strong capabilities to fuse multi-modal inputs. With the encoded latent representation of a proposal, the verification head is implemented by a self-attention module (see the top in Fig. 1). The proposed method is named as MonoXiver, indicating its general applicability to any backbone monocular 3D detectors and the integration of the Perceiver model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.409, + 0.892, + 0.545 + ], + "angle": 0, + "content": "In experiments, we evaluate our proposed MonoXiver on the well-established KITTI benchmark [14] and the challenging large-scale Waymo [51] dataset with various backbone monocular 3D detectors. It achieves consistent and significant performance improvement on both datasets with limited computation overhead. Moreover, it achieves the 1st place among monocular methods on the KITTI vehicle detection benchmark, outperforming the previous works by a large margin." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.559, + 0.847, + 0.574 + ], + "angle": 0, + "content": "2. Related Works and Our Contributions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.584, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Monocular 3D Object Detection. The problem of monocular 3D object detection is considered ill-posed, prompting recent research efforts to leverage additional information sources, including LiDAR point clouds [4, 10, 19, 28, 45], depth estimation [12, 36, 42, 48, 53, 54, 62], CAD models [25, 34], temporal frames [2], etc. These approaches have shown improved detection performance when compared to purely image-based methods [1, 33, 41, 57]. However, they often come with increased computation load and inference time, making them less practical for real-time applications such as autonomous vehicles. In contrast, purely image-based methods have seen significant performance improvements in the literature by exploiting geometric constraints [26, 35, 41, 47, 59, 60], perspective projections [24, 38], auxiliary training [30], novel loss designs [8, 39, 49] and second-stage processing techniques [23]. These works focus on developing better bottom-up paradigms. Our proposed method, MonoXiver, takes a top-down paradigm, which explores 3D space differently than the aforementioned methods. It provides a generic and highly efficient second-stage refinement module for any pretrained state-of" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "6437" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.087, + 0.088, + 0.885, + 0.341 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.351, + 0.895, + 0.414 + ], + "angle": 0, + "content": "Figure 1: Illustration of the proposed MonoXiver method. MonoXiver is built for any off-the-shelf backbone monocular 3D object detectors. It consists of a 2D-to-3D proposal generation phase using a bottom-up anchoring and top-down sampling strategy, and a 3D-to-2D proposal verification (or denoising) phase using the Perceiver I/O [20] with a carefully designed 3D/2D input space to address the unique challenges. See text for details." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.439, + 0.47, + 0.469 + ], + "angle": 0, + "content": "the-art monocular 3D object detection method, making it a complementary approach." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.469, + 0.471, + 0.875 + ], + "angle": 0, + "content": "Bird's-Eye-View 3D Object Detection. Bird's-Eye-View (BEV) 3D object detection [40] has recently gained significant attention as it provides a physical-interpretable feature space for integrating data from diverse sensors [27, 31, 44, 56] and modalities [13, 18]. To enable the learning of a physical-interpretable feature space, accurate physical measurements from depth perception systems such as multi-view cameras and LiDAR are crucial [16]. However, detecting 3D objects in BEV is challenging for monocular systems due to the intrinsic depth ambiguity. Directly accumulating image features based on projection reference points similar to recent query-based multi-view 3D detectors [31, 56] might fail because of lacking stereo-matching mechanism to resolve the depth ambiguity. To overcome this issue, recent BEV-based monocular methods [9, 45, 55] lift the image feature space to voxel-represented world-space using monocular depth estimation models. Our proposed method, MonoXiver, samples top-down proposals based on bottom-up initial proposals in BEV space. Unlike prior arts [9, 45, 55] that extract features represented in world-space, MonoXiver's top-down proposals extract features from both projected appearance features and inherent geometric features. We explore to address the challenging intrinsic feature ambiguity problem by applying a Perceiver-like attention mechanism to query informative features for 3D bounding box verification and refinement without the need for dense depth supervision." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.877, + 0.468, + 0.892 + ], + "angle": 0, + "content": "Transformers for Multi-modal Data. Transformers [52]," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.439, + 0.892, + 0.634 + ], + "angle": 0, + "content": "known for their powerful attention mechanism, have been successfully applied in multiple research areas and applications [3,11,32,50]. With the powerful attention mechanism, transformers can conveniently align multi-modal structured data, enabling the generation of universal multi-modal representation. The recent proposed Perceiver [20, 21] extends the transformers' querying mechanism and makes it capable of efficiently handling data from arbitrary settings. In our work, we adapt Perceiver to fuse appearance features and geometric features from the same bounding box to generate appearance-geometric aligned representation, which is then used as queries for the down-stream 3D bounding box refinement task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.635, + 0.892, + 0.666 + ], + "angle": 0, + "content": "Our Contributions. MonoXiver makes three main contributions to the field of monocular 3D object detection:" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.671, + 0.892, + 0.806 + ], + "angle": 0, + "content": "- We conduct a new and strong empirical upper-bound analysis for state-of-the-art monocular 3D object detectors. We demonstrate that a simple, universally applicable sampling strategy can lead to consistent and significant performance improvement in an ideal situation. Based on these observations, we propose to explore the top-down, stage-wise detection paradigm with 2D-to-3D proposal generation and 3D-to-2D proposal verification for monocular 3D object detection." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.811, + 0.892, + 0.901 + ], + "angle": 0, + "content": "- To address the challenge at the bounding box denoising stage, we propose to learn discriminative features by enhancing appearance features with 3D-to-2D inherent geometric features. We therefore propose a carefully-designed module with the integration of the powerful Perceiver and self-attention mechanism. The resulting mod" + }, + { + "type": "list", + "bbox": [ + 0.5, + 0.671, + 0.892, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "6438" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.09, + 0.092, + 0.468, + 0.122 + ], + "angle": 0, + "content": "ule can be applied generically to any off-the-shelf monocular 3D object detectors." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.126, + 0.468, + 0.232 + ], + "angle": 0, + "content": "- Extensive experiments demonstrate the effectiveness and efficiency of our proposed method, MonoXiver, under a separate two-stage training setting. It achieves consistent improvement with limited overhead on both KITTI and Waymo dataset. It achieves the 1st place among monocular methods on the KITTI vehicle detection benchmark, outperforming the previous works by a large margin." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.243, + 0.185, + 0.259 + ], + "angle": 0, + "content": "3. Approach" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.268, + 0.468, + 0.329 + ], + "angle": 0, + "content": "In this section, we first present the straightforward 2D-to-3D proposal generation on top of a backbone monocular 3D object detector. Then, we present the details of the proposed MonoXiver method (Fig. 1)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.336, + 0.382, + 0.351 + ], + "angle": 0, + "content": "3.1. The 2D-to-3D Proposal Generation" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.359, + 0.468, + 0.479 + ], + "angle": 0, + "content": "Let \\(I\\) be an RGB input image defined on the domain \\(\\Lambda\\). The goal of monocular 3D object detection is to detect 3D bounding boxes, along with their class labels denoted by \\(\\ell\\) for each object instance in \\(I\\). The 3D bounding box is parameterized by the 3D center position \\(\\mathbf{P} = (X,Y,Z)\\) in meters, the shape dimensions \\(\\mathbf{D} = (h,w,l)\\) in meters, and the observation angle \\(\\alpha \\in [-\\pi ,\\pi ]\\), all measured in the camera coordinate system." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.48, + 0.468, + 0.646 + ], + "angle": 0, + "content": "For simplicity, consider the pure image-based settings, a monocular 3D object detector often consists of two main components in inference: the feature backbone (e.g., the DLA34 network [58]), denoted by \\(\\mathbf{F}_I\\) for computing deep features from the raw image \\(I\\), and the regression heads for inferring the 3D bounding box parameters using the computed feature map. We generate bottom-up proposals using one off-the-shelf backbone monocular 3D object detector which is first trained following its own training receipts. Without loss of generality, we consider one of its detected 3D bounding boxes indexed by \\(i\\) in an image \\(I\\)," + }, + { + "type": "equation", + "bbox": [ + 0.198, + 0.653, + 0.468, + 0.668 + ], + "angle": 0, + "content": "\\[\n\\mathbb {B} _ {i} = \\left(\\ell_ {i}, \\mathbf {P} _ {i}, \\mathbf {D} _ {i}, \\alpha_ {i}\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.675, + 0.468, + 0.901 + ], + "angle": 0, + "content": "As shown in Table 1, the top-down sampling with a bottom-up anchor proposal is a straightforward process. We start by generating a 2D local grid in the \\(X - Z\\) plane (i.e. in the bird's-eye-view, BEV), centered at the position \\((X,Z)\\) of the anchor box \\(\\mathbb{B}\\). To accomplish this, we specify a search range and a stride. Based on the trade-off between the empirical upper bound and the computing overhead and the mean IoU among the proposals, we adopt a conservative strategy using the search range \\(\\pm 1.5\\) meters and the stride 0.75, which will generate 25 proposals per bottom-up anchor (inclusive). We then place the anchor box \\(\\mathbb{B}\\) at the 25 grid points, with only the position \\(\\mathbf{P}\\) updated. To simplify the notation, we do not differentiate between the bottom-up anchor and the top-down sampled proposal, and we generally index them using \\(i\\), unless otherwise stated." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.807, + 0.107 + ], + "angle": 0, + "content": "3.2. The 3D-to-2D Proposal Verification" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.115, + 0.892, + 0.205 + ], + "angle": 0, + "content": "The proposal verification will rely essentially on the information from the input 2D images in purely monocular 3D object detection. Due to the aforementioned unique challenges in the 3D proposal space, we utilize Perceiver I/O [20] to design an expressive proposal representation learning scheme." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.226, + 0.725, + 0.24 + ], + "angle": 0, + "content": "3.2.1 Proposal Representation" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.25, + 0.892, + 0.28 + ], + "angle": 0, + "content": "As illustrated in Fig. 1, we utilize three types of features in encoding a 3D bounding box proposal \\(\\mathbb{B}\\)," + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.29, + 0.892, + 0.382 + ], + "angle": 0, + "content": "- The 3D Shape Features represented by \\((\\mathbf{P}, \\mathbf{D}, \\alpha)\\). It is a 7-dim vector. It encodes where the proposal is in the 3D space (the camera coordinate system), as well as its 3D occupancy. The position \\(\\mathbf{P}\\) is empirically normalized by the typical detection range (e.g., \\(X, Y, Z\\) are normalized by 50, 2 and 80 meters respectively)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.387, + 0.892, + 0.492 + ], + "angle": 0, + "content": "- The 2D Projection Points from the 8 corners and the center of the 3D bounding box (with known camera intrinsic matrix). It is an 18-dim vector in the image coordinate system, and normalized by the image size. This 9-point projection provides the finegrained placement of a proposal in the 2D space, that is the geometric bond between a proposal in the 3D space and its 2D placement." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.498, + 0.892, + 0.634 + ], + "angle": 0, + "content": "- The 2D Bounding Box projected from the proposal and truncated by the image boundary. We use the left-top and right-bottom two points to encode a 2D bounding box. It gives a 4-dim vector normalized by the image size. For a proposal whose 2D projection is entirely inside the image plane, the two points of the 2D bounding box will be just redundant with respect to the 9 project points. Otherwise, the truncation points on the image boundary will facilitate the learning to be truncation aware." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.64, + 0.892, + 0.701 + ], + "angle": 0, + "content": "- The Appearance Features of the 9 projection points. We directly extract features from the final layer of the feature backbone \\(\\mathbf{F}_I\\). If a projection point is out of the image plane, we encode it using an all-zero vector." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.706, + 0.892, + 0.811 + ], + "angle": 0, + "content": "- The RoI Appearance Features of the 2D bounding box. We use the RoIAign features [17] extracted from the final layer of the feature backbone \\(\\mathbf{F}_I\\). Since the 2D IoU overlapping between proposals is high on average (e.g., 0.612 in Table 1), we use a finer grid, \\(14 \\times 14\\), in computing the RoIAign features, such that the extracted appearance features contain \"sufficient\" details." + }, + { + "type": "list", + "bbox": [ + 0.5, + 0.29, + 0.892, + 0.811 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.832, + 0.701, + 0.846 + ], + "angle": 0, + "content": "3.2.2 Proposal Embedding" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Let \\(N\\) be the total number of proposals in an image \\(I\\). With the above representation scheme, denote by \\(f_{N\\times 29}^{geo}\\) the geometric parameter matrix from the first three items above," + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6439" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.47, + 0.182 + ], + "angle": 0, + "content": "and by \\( f_{N \\times 9 \\times C}^{pt} \\) the projection point appearance feature matrix (where \\( C \\) is the number of channels of the final layer of the feature backbone, e.g., \\( C = 64 \\)), and by \\( f_{N \\times (14 \\times 14) \\times C}^{roi} \\) the RoI feature matrix. Before applying the Perceiver I/O model, we embed the three to form \"tokens\" using multi-layer perceptron (MLP)." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.183, + 0.407, + 0.2 + ], + "angle": 0, + "content": "For the geometric parameters \\( f_{N \\times 29}^{geo} \\), we have," + }, + { + "type": "equation", + "bbox": [ + 0.134, + 0.212, + 0.469, + 0.235 + ], + "angle": 0, + "content": "\\[\nf _ {N \\times 2 9} ^ {\\text {g e o}} \\xrightarrow {\\mathrm {M L P}} z _ {N \\times (g \\times d)} \\xrightarrow {\\text {R e a r r a n g e}} \\mathbf {f} _ {g \\times N \\times d} ^ {\\text {g e o}}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.245, + 0.469, + 0.32 + ], + "angle": 0, + "content": "where \\( d \\) is the hidden dimension (e.g., \\( d = 256 \\)). \\( g \\) is the group number, similar in spirit to the multi-head setup in the self-attention. We want to encode the geometric parameters in different latent spaces to account for the large variations in the proposal space (e.g., \\( g = 4 \\))." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.32, + 0.418, + 0.338 + ], + "angle": 0, + "content": "For the project point features \\( f_{N \\times 9 \\times C}^{pt} \\), we have," + }, + { + "type": "equation", + "bbox": [ + 0.133, + 0.351, + 0.469, + 0.373 + ], + "angle": 0, + "content": "\\[\nf _ {N \\times 9 \\times C} ^ {p t} \\xrightarrow {\\mathrm {M L P}} z _ {N \\times 9 \\times d} \\xrightarrow {\\text {R e a r r a n g e}} \\mathbf {f} _ {9 \\times N \\times d} ^ {p t}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.384, + 0.469, + 0.412 + ], + "angle": 0, + "content": "where we reuse \\( z \\) to denote the latent features for simplicity and without confusion." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.414, + 0.399, + 0.432 + ], + "angle": 0, + "content": "For the RoI features \\(f_{N\\times (14\\times 14)\\times C}^{roi}\\) , we have," + }, + { + "type": "equation", + "bbox": [ + 0.121, + 0.445, + 0.469, + 0.467 + ], + "angle": 0, + "content": "\\[\nf _ {N \\times (1 4 \\times 1 4) \\times C} ^ {r o i} \\xrightarrow {\\mathrm {M L P}} z _ {N \\times d} \\xrightarrow {\\text {R e a r r a g e}} \\mathbf {f} _ {1 \\times N \\times d} ^ {r o i}. \\tag {4}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.485, + 0.399, + 0.5 + ], + "angle": 0, + "content": "3.2.3 Intra-Proposal Attention via Perceiver" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.509, + 0.469, + 0.644 + ], + "angle": 0, + "content": "With the above proposal embedding, before the proposal verification, our goal is to compute a final latent feature representation in the \\(d\\)-dim space for each proposal by fusing information from the geometric encoding, projection-point-based appearance encoding and RoI-based appearance encoding (i.e., the intra-proposal attention), such that we can address the aforementioned unique challenges in the proposal space. We leverage the Perceiver I/O model for this intra-proposal attention." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.646, + 0.469, + 0.75 + ], + "angle": 0, + "content": "The Perceiver first fuses the projection-point appearance encoding \\(\\mathbf{f}_{9\\times N\\times d}^{pt}\\) and the geometric encoding \\(\\mathbf{f}_{g\\times N\\times d}^{geo}\\). As shown in Fig. 1, it consists of a cross-attention by treating the former as Query (consisting of 9 projection-point tokens) and computing Key and Value from the latter (consisting of \\(g\\) geometric tokens), followed by a self-attention module. We have," + }, + { + "type": "equation", + "bbox": [ + 0.101, + 0.762, + 0.469, + 0.784 + ], + "angle": 0, + "content": "\\[\n\\left(\\mathbf {f} _ {9 \\times N \\times d} ^ {p t}, \\mathbf {f} _ {g \\times N \\times d} ^ {g e o}\\right) \\xrightarrow {\\text {C r o s s - A t t n}} \\cdot \\xrightarrow {\\text {S e l f - A t t n}} \\mathbf {F} _ {9 \\times N \\times d} ^ {g e o - p t}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.795, + 0.468, + 0.81 + ], + "angle": 0, + "content": "which results in geometry-aware projection-point encoding." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.81, + 0.469, + 0.87 + ], + "angle": 0, + "content": "Next, the Perceiver fuses the RoI appearance encoding \\(\\mathbf{f}_{1\\times N\\times d}^{roi}\\) as the 1-token Query with the 9-token geometry-aware projection-point encoding using a cross attention module," + }, + { + "type": "equation", + "bbox": [ + 0.135, + 0.882, + 0.469, + 0.904 + ], + "angle": 0, + "content": "\\[\n\\left(\\mathbf {f} _ {1 \\times N \\times d} ^ {r o i}, \\mathbf {F} _ {9 \\times N \\times d} ^ {g e o - p t}\\right) \\xrightarrow {\\text {C r o s s - A t t n}} \\mathbf {F} _ {1 \\times N \\times d} ^ {g e o - p t - r o i}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.891, + 0.137 + ], + "angle": 0, + "content": "which results in the \\(d\\)-dim latent features for each proposal, which fuse the three types of information sources: geometry, point-level appearance and region-level appearance." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.137, + 0.891, + 0.167 + ], + "angle": 0, + "content": "In the above, the cross-attention and self-attention modules are based on the standard formulation [52]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.186, + 0.726, + 0.2 + ], + "angle": 0, + "content": "3.2.4 Inter-Proposal Attention" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.209, + 0.892, + 0.329 + ], + "angle": 0, + "content": "With all the above process, each proposal is still encoded individually with the hope of fusing geometry, point-level appearance and region-level appearance information in a semantically meaningful way via the Perceiver I/O model. With the compact latent vector computed for each proposal in \\(\\mathbf{F}_{1\\times N\\times d}^{geo-pt-rot}\\), their interactions need to be taken into account in order to resolve their \"crowding\" issue at the underlying scene level." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.33, + 0.892, + 0.375 + ], + "angle": 0, + "content": "To that end, we treat each proposal as a \"token\" and apply a standard self-attention module to capture the interproposal attention," + }, + { + "type": "equation", + "bbox": [ + 0.538, + 0.387, + 0.891, + 0.408 + ], + "angle": 0, + "content": "\\[\n\\mathbf {F} _ {1 \\times N \\times d} ^ {\\text {g e o - p t - r o i}} \\xrightarrow {\\text {R e a r r a n g e}} \\mathbf {F} _ {N \\times d} ^ {\\text {g e o - p t - r o i}} \\xrightarrow {\\text {S e l f - A t t n}} \\mathbb {F} _ {N \\times d}. \\tag {7}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.425, + 0.701, + 0.439 + ], + "angle": 0, + "content": "3.2.5 Proposal Verification" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.448, + 0.836, + 0.464 + ], + "angle": 0, + "content": "This verification is posed as a regression problem," + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.474, + 0.891, + 0.495 + ], + "angle": 0, + "content": "\\[\n\\mathbb {F} _ {N \\times d} \\xrightarrow {\\mathrm {M L P s}} \\left(\\mathbf {y} _ {N \\times L}, \\Delta \\mathbf {P} _ {N}, \\Delta \\mathbf {D} _ {N}\\right), \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.505, + 0.891, + 0.564 + ], + "angle": 0, + "content": "where \\(L\\) is the total number of categories (e.g., \\(L = 3\\) in the KITTI dataset), and \\(\\mathbf{y}_{N\\times L}\\) is the classification scores (logits). \\(\\Delta \\mathbf{P}_N\\) and \\(\\Delta \\mathbf{D}_N\\) are the position and dimension residuals." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.566, + 0.847, + 0.581 + ], + "angle": 0, + "content": "Consider a proposal \\(\\mathbb{B}_i\\) (Eqn. 1), it is verified via," + }, + { + "type": "equation", + "bbox": [ + 0.625, + 0.59, + 0.891, + 0.615 + ], + "angle": 0, + "content": "\\[\n\\hat {\\ell} _ {i} = \\arg \\max _ {l = 1, \\dots , L} \\mathbf {y} _ {i, l}, \\tag {9}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.62, + 0.619, + 0.891, + 0.637 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {P}} _ {i} = \\mathbf {P} _ {i} + \\Delta \\mathbf {P} _ {i}, \\tag {10}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.619, + 0.642, + 0.891, + 0.658 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {D}} _ {i} = \\mathbf {D} _ {i} + \\Delta \\mathbf {D} _ {i}, \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.672, + 0.891, + 0.734 + ], + "angle": 0, + "content": "where a proper unnormalization step will be done for \\(\\hat{\\mathbf{P}}_i\\) to counter the normalization step used in the proposal representation (Sec. 3.2.1). Based on the score \\(\\mathbf{y}_{i,\\hat{\\ell}_i}\\), we can keep top-\\(k\\) proposals for each anchor position." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.742, + 0.774, + 0.759 + ], + "angle": 0, + "content": "3.3. Details of Training and Testing" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "For simplicity, we evaluate the proposed MonoXiver in a two-stage setting where the backbone monocular 3D object detector is first trained and kept frozen. Then, the MonoXiver component is trained end-to-end. One of the reasons for this choice is that off-the-shelf backbone monocular 3D object detectors often involve multiple loss functions, and joint training with MonoXiver would require sophisticated tuning of the trade-off parameters for different loss terms. We leave the joint end-to-end training or iterative training," + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6440" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.198 + ], + "angle": 0, + "content": "as done in the early version of Faster RCNN [46] between the region proposal network and the region classification head network, for future work. Additionally, the separate two-stage training may also have advantages in leveraging the set of bottom-up anchor proposals merged from multiple backbone monocular 3D detectors, which we also leave for future work." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.22, + 0.436, + 0.237 + ], + "angle": 0, + "content": "3.3.1 The Set Prediction Formulation in Training" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.246, + 0.47, + 0.412 + ], + "angle": 0, + "content": "Based on the separate two-stage setting, the proposed MonoXiver is trained with a fixed set of 3D bounding box proposals and a fixed set of ground-truth 3D bounding boxes. The ground-truth assignment for proposals is needed in training. Two straightforward methods are: using the maximum 3D IoU based assignment, or using the maximum 2D IoU assignment (after projected to the image plane). Due to the \"crowding\" issue in the proposal space, we observe that both of them do not work during our development of the MonoXiver since they will create difficult \"decision boundaries\" for the MonoXiver to learn or fit." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.413, + 0.473, + 0.551 + ], + "angle": 0, + "content": "Since we have the two fixed set as input, we resort to the set prediction formulation used in the DETR framework [3]. Denote by \\(\\Omega_{\\mathbb{B}} = \\{\\mathbb{B}_i\\}_{i=1}^N\\) the set of generated proposals, by \\(\\Omega_{\\mathbb{B}^*} = \\{\\mathbb{B}_j^*\\}_{j=1}^M \\cup \\{\\emptyset_j\\}_{j=M+1}^N\\) the set of ground-truth 3D bounding boxes padded with \\(N - M\\) dummy \\(\\emptyset\\) elements. Given a permutation of \\(N\\) elements, denoted by \\(\\sigma\\) which assigns the \\(i\\)-th element in the ground-truth set to the \\(\\sigma(i)\\)-the element in the proposal set, the loss for the one-to-one bipartite matching between \\(\\mathbb{B}_i^*\\) and \\(\\mathbb{B}_{\\sigma(i)}\\) is defined by," + }, + { + "type": "equation", + "bbox": [ + 0.092, + 0.562, + 0.469, + 0.58 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {m a t c h}} \\left(\\mathbb {B} _ {i} ^ {*}, \\mathbb {B} _ {\\sigma (i)}\\right) = \\mathbf {1} _ {\\ell_ {i} ^ {*} \\neq \\emptyset} \\cdot \\left(- \\lambda_ {1} \\cdot \\hat {p} _ {\\sigma (i)} \\left(\\ell_ {i} ^ {*}\\right) + \\right. \\tag {12}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.216, + 0.582, + 0.454, + 0.601 + ], + "angle": 0, + "content": "\\[\n\\lambda_ {2} \\cdot \\mathcal {L} _ {b b o x} ^ {2 D} + \\lambda_ {3} \\cdot \\mathcal {L} _ {i o u} ^ {2 D} + \\lambda_ {4} \\cdot \\mathcal {L} _ {i o u} ^ {3 D}),\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.614, + 0.47, + 0.675 + ], + "angle": 0, + "content": "where \\(\\hat{p}_{\\sigma(i)}(\\ell_i^*)\\) is computed using \\(\\mathbf{y}_{\\sigma(i)}\\) (Eqn. 8) via Softmax. \\(\\mathcal{L}_{bbox}^{2D}\\) represents the normalized L1 2D bounding box, and \\(\\mathcal{L}_{iou}^{2D}\\) and \\(\\mathcal{L}_{iou}^{3D}\\) the IoU loss in 2D and 3D respectively. \\(\\lambda_1\\) to \\(\\lambda_4\\) are the trade-off parameters." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.697, + 0.412, + 0.712 + ], + "angle": 0, + "content": "3.3.2 Loss Functions for Proposal Verification" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.722, + 0.47, + 0.751 + ], + "angle": 0, + "content": "For the three outputs in Eqn. 8, we have three loss terms as follows," + }, + { + "type": "equation", + "bbox": [ + 0.177, + 0.755, + 0.469, + 0.771 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathcal {L} _ {\\text {c l s}} + \\mathcal {L} _ {\\text {s i z e}} + \\lambda \\cdot \\mathcal {L} _ {\\text {l o c}} \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.471, + 0.901 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{cls}\\) is the Focal Loss [29] with the \\(\\alpha\\) value of 0.5 to balance the number of positive and negative samples. The Focal loss is used due to the imbalance introduced by the explicit top-down proposal generation. \\(\\mathcal{L}_{size}\\) are \\(\\mathcal{L}_{loc}\\) are the loss functions for the 3D size and the 3D center respectively. \\(\\lambda\\) is an trade-off hyper-parameter. We use \\(\\ell_1\\) loss for \\(\\mathcal{L}_{size}\\) and \\(\\mathcal{L}_{loc}\\). We set \\(\\lambda = 5\\) to induce the model to focus more on the 3D localization refinement task." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.092, + 0.617, + 0.107 + ], + "angle": 0, + "content": "3.3.3 Training" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.115, + 0.895, + 0.358 + ], + "angle": 0, + "content": "MonoXiver is trained using a total of 8 GPUs, with a batch size of 64 for 24 epochs on KITTI (12 epochs on Waymo) using the AdamW optimizer. The optimizer is set with \\((\\beta_{1},\\beta_{2}) = (0.95,0.99)\\) and weight decay of 0.0001, excluding feature normalization layers and bias parameters. The initial learning rate is set to \\(2.25e - 5\\), and it is reduced by a factor of 10 at the 16th and 22nd epoch. Notably, the entire second-stage training process takes merely 1.5 hours on KITTI [14] using a single Nvidia RTX5000 GPU, indicating the low computational overhead of our proposed MonoXiver method. The training time on Waymo [51] varies depending on the training data and training recipes of off-the-shelf monocular 3D detectors. Overall, the second-stage training on Waymo is much faster compared to training the backbone monocular 3D object detector, leading to about a 3/4 reduction in training time." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.378, + 0.606, + 0.394 + ], + "angle": 0, + "content": "3.3.4 Testing" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.403, + 0.893, + 0.495 + ], + "angle": 0, + "content": "During testing, we keep at most top-3 predictions per initial anchor proposal with a score threshold of 0.03 (the score is predicted from the proposed MonoXiver module). The final prediction score is the product of the classification probability predicted from the backbone monocular 3D object detector and the score computed by the MonoXiver module." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.508, + 0.634, + 0.525 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.534, + 0.894, + 0.67 + ], + "angle": 0, + "content": "We evaluate our MonoXiver on the well-established KITTI [14] dataset and the large-scale Waymo [51] dataset. We first show that our improved baseline detector outperforms previous SOTA methods on the KITTI benchmark by a large margin. Then we show that we consistently improved pretrained monocular 3D object detectors with limited computation overhead on both datasets. We further analyze the contribution of each part of our MonoXiver in the ablation studies." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.681, + 0.582, + 0.697 + ], + "angle": 0, + "content": "4.1. Setup" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.895, + 0.87 + ], + "angle": 0, + "content": "Dataset. The KITTI dataset [14] consists of 7,481 training images and 7,518 testing images. In KITTI's experiments, we split the training data into a training subset with 3,712 images and a validation subset with 3,769 images following [5-7]. We conduct ablation studies on the defined split and report the test set results evaluated by the official KITTI benchmark. The Waymo dataset [51] contains 52,386 training and 39,848 validation images from the front camera. In Waymo experiments, we use a subset of its training set by sampling every third frame from the training sequences following [22,45]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.894, + 0.902 + ], + "angle": 0, + "content": "Evaluation Metrics. The KITTI vehicle benchmark evaluates detection results by the 40-point interpolated av-" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "6441" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.182, + 0.089, + 0.794, + 0.313 + ], + "angle": 0, + "content": "
MethodsVenuesExtra Info.APBEV|R40↑AP3D|R40↑
EasyMod.HardEasyMod.Hard
Kinematic3D [2]ECCV20Temporal26.6917.5213.1019.0712.729.17
AutoShape [34]ICCV21CAD30.6620.0815.9522.4714.1711.36
DCD [25]ECCV22CAD32.5521.5018.2523.8115.9013.21
MonoDistill [10]ICLR22LiDAR31.8722.5919.7222.9716.0313.60
DID-M3D [43]ECCV22LiDAR32.9522.7619.8324.4016.2913.75
DD3D [42]ICCV21Depth30.9822.5620.0323.2216.3414.20
DFM [55]ECCV22Temporal + LiDAR31.7122.8919.9722.9416.8214.65
Pseudo-Stereo [9]CVPR22Depth + LiDAR32.8423.6720.6423.7417.7415.14
MonoFlex [59]CVPR2128.2319.7516.8919.9413.8912.07
GUPNet [35]ICCV2130.2921.1918.2020.1114.2011.77
DEVIANT [22]ECCV22None29.6520.4417.4321.8814.4611.89
Homography [15]CVPR2229.6020.6817.8121.7514.9413.07
DimEmbedding [61]CVPR2232.8221.9818.7023.6216.1013.41
MonoCon [30]AAAI22None31.1222.1019.0022.5016.4613.95
Our MonoXiver + MonoCon-34.1425.3722.2025.2419.0416.39
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.334, + 0.895, + 0.381 + ], + "angle": 0, + "content": "Table 2: Comparisons with state-of-the-art methods on the Car category on the KITTI test set. According to the KITTI protocol, methods are ranked based on their performance under the moderate difficulty setting. We highlight the best results in bold and the second-best results in underline." + }, + { + "type": "table", + "bbox": [ + 0.101, + 0.404, + 0.449, + 0.555 + ], + "angle": 0, + "content": "
MethodsAP3D|R40↑Relative Improvement
EasyModerateHard
SMOKE [33]10.437.095.5711%-33%
SMOKE + Ours11.589.407.75
Improvement+1.15+2.31+2.18
MonoDLE [39]17.9413.7212.1018%-22%
MonoDLE + Ours21.1516.1914.75
Improvement+3.21+2.47+2.65
MonoCon [30]26.3319.0115.9816%-20%
MonoCon + Ours30.4822.4019.13
Improvement+4.15+3.39+3.15
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.578, + 0.472, + 0.684 + ], + "angle": 0, + "content": "Table 3: The effectiveness of MonoXiver based on different methods on the KITTI validation dataset. In order to demonstrate the ability of the proposed MonoXiver to generalize across different detectors, we utilized three distinct base detectors with varying levels of detection accuracy. We observe that MonoXiver consistently yields significant improvements across all three base detectors." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.473, + 0.903 + ], + "angle": 0, + "content": "erage precision \\((AP_{R40})\\) of 3D bounding boxes in 3D space \\((AP_{3D|R40})\\) and bird eye's view \\((AP_{BEV|R40})\\) at \\(IoU_{3D} \\geq 0.7\\). The prediction results are evaluated based on three difficulty settings, easy, moderate and hard, according to the 2D box height, occlusion and truncation levels of objects. The vehicle detection results on Waymo are evaluated on two levels of difficulty including Level_1 and Level_2 at \\(IoU_{3D} \\geq 0.5\\). The level is assigned based on the number of LiDAR points included in each 3D box. Besides the \\(AP_{3D}\\) metric, Waymo uses the \\(APH_{3D}\\) metric to incorporate heading information in \\(AP_{3D}\\)." + }, + { + "type": "table", + "bbox": [ + 0.524, + 0.404, + 0.871, + 0.548 + ], + "angle": 0, + "content": "
MethodsLevel_1Level_2
AP3D↑APH3D↑AP3D↑APH3D↑
PatchNet [36]2.922.742.422.28
PCT [54]4.204.154.034.15
GUPNet [35]10.029.949.399.31
GUPNet + ours11.4711.3510.6710.56
Improvement+1.45+1.41+1.28+1.25
DEVIANT [22]10.9810.8910.2910.20
DEVIANT + ours11.8811.7511.0610.93
Improvement+0.90+0.86+0.77+0.73
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.571, + 0.895, + 0.678 + ], + "angle": 0, + "content": "Table 4: The effectiveness of MonoXiver based on different methods on Waymo validation dataset. In order to showcase the generalization capabilities of the proposed MonoXiver on large-scale datasets, we conducted testing on the challenging Waymo [51] validation set, utilizing two SOTA methods. We observed consistent improvements in performance." + }, + { + "type": "table", + "bbox": [ + 0.524, + 0.712, + 0.875, + 0.786 + ], + "angle": 0, + "content": "
MethodsFLOPsLatency (ms)FPS
SMOKE [33]/ + ours42.82/48.1923/3143/32
MonoDLE [39]/ + ours77.44/82.8022/3145/32
MonoCon [30]/ + ours56.22/61.5018/2555/40
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.808, + 0.895, + 0.851 + ], + "angle": 0, + "content": "Table 5: Computation overhead analysis. The GFLOPs is computed based on an input size of (384, 1248), while the latency and FPS are evaluated on a NVIDIA RTX5000 GPU." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6442" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.091, + 0.281, + 0.107 + ], + "angle": 0, + "content": "4.2. Experimental Results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.114, + 0.47, + 0.552 + ], + "angle": 0, + "content": "Comparison with SOTA methods on the KITTI dataset. We present the results of our proposed MonoXiver method on the challenging KITTI vehicle benchmark in Table 2. Notably, our method achieves the best performance across different evaluation metrics while only using image-level information, surpassing previous state-of-the-art methods by a large margin. Specifically, we observe a significant and consistent improvement from 2.44 AP (hard settings) to 2.74 AP (easy settings) absolute increase in \\(\\mathrm{AP}_{3D}\\) for the boosted MonoCon approach compared to the vanilla MonoCon approach. These consistent improvements demonstrate the effectiveness of our method. More qualitative and quantitative results are provided in the Supplementary Materials. Generalization abilities across backbone monocular 3D object detectors and datasets. We evaluate our method with various state-of-the-art backbone monocular 3D object detection methods on the KITTI and the Waymo validation set, reported in Table 3 and Tabel 4 respectively. Monoxiver consistently demonstrates significant improvements across different methods and different difficult levels. Specifically, on the well-established KITTI dataset, our MonoXiver is able to enhance various backbone detectors with varying levels of detection accuracy by up to \\(33\\%\\) relative improvement. On the challenging large-scale Waymo dataset, our MonoXiver consistently improves the performance of strong baseline methods GUPNet and DEVIANT by up to \\(1.45\\mathrm{AP}_{3D}\\) on Level_1 and \\(1.28\\mathrm{AP}_{3D}\\) on Level_2. These results validate the effectiveness and robustness of our approach." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.552, + 0.47, + 0.658 + ], + "angle": 0, + "content": "Computation overhead. As shown in Table 5, although our MonoXiver causes about an average of \\(8\\mathrm{ms}\\) overhead compared with baseline detectors, it still achieves real-time detection. We note that its inference speed could be improved by optimizing the detailed implementation (e.g., we still have for-loops in our current code, which can be easily paralleled for better efficiency)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.658, + 0.47, + 0.703 + ], + "angle": 0, + "content": "Qualitative Comparison. We show the visualization comparisons with MonoCon in Fig. 2. It shows that MonoXiver achieves better 3D box center localization." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.712, + 0.242, + 0.726 + ], + "angle": 0, + "content": "4.3. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.47, + 0.796 + ], + "angle": 0, + "content": "In this section, we report ablation studies of MonoXiver structure and different bounding box branches on the KITTI validation set. More ablation studies are provided in the Supplementary Materials." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Effectiveness of MonoXiver structures. In this study, we explore the importance of RoI feature (Table 6 a.), the context information provided by geometric embeddings (Table 6 b.), and our complete MonoXiver model (Table 6 c.). In experiments a. and b., we replace the Perciver with a MLP layer to fuse the appearance feature and geometry feature to keep similar parameter size." + }, + { + "type": "table", + "bbox": [ + 0.524, + 0.089, + 0.872, + 0.151 + ], + "angle": 0, + "content": "
AppearanceGeometryPerciverEasy/Mod./Hard
MonoCon [30]---26.33/19.01/15.98
a.✓--29.30/21.04/18.22
b.✓✓-29.33/21.67/18.46
c.✓✓✓30.48/22.40/19.13
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.174, + 0.892, + 0.204 + ], + "angle": 0, + "content": "Table 6: Ablation studies of MonoXiver structure on KITTI validation set." + }, + { + "type": "table", + "bbox": [ + 0.524, + 0.219, + 0.872, + 0.283 + ], + "angle": 0, + "content": "
RescoreResLocResDimEasyMod.Hard
MonoCon [30]---26.3319.0115.98
a.✓--29.6621.4118.38
b.✓✓-30.3222.3019.04
c.✓✓✓30.4822.4019.13
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.306, + 0.892, + 0.336 + ], + "angle": 0, + "content": "Table 7: Ablation studies of the effect of different branches on KITTI validation set" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.364, + 0.892, + 0.469 + ], + "angle": 0, + "content": "Results show that the appearance feature plays the most important role in performance improvement. When using the appearance feature only, the Moderate AP is improved by 2.39. The performance is further improved by 0.6 AP and 0.7 AP after fusing with geometric embeddings and Perciver. It shows that Perceiver effectively fuses information between appearance and geometric embeddings." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.47, + 0.892, + 0.62 + ], + "angle": 0, + "content": "Effectiveness of Different Head Branches. In Table 7, we present the impact of different branches on the detection performance of our MonoXiver. Since our method generates 25 proposals per each initial proposal, the rescoring head branch plays a crucial role in filtering out false detections, leading to significant improvements by up to 3.3 AP. The localization residual branch and the dimension residual branch further enhance the performance by about 1 AP, and we employ all branches to achieve a new state-of-the-art result." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.634, + 0.62, + 0.65 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This paper explores the task of monocular 3D object detection. It begins with the strong observation that significant improvements in detection performance can be achieved by a local grid search based on initially detected 3D bounding boxes. This leads to a novel denoising-based approach called MonoXiver. The approach utilizes the Perceiver I/O model to produce a unified feature embedding, leverages the self-attention mechanism for proposal verification, and ultimately delivers high-quality 3D box predictions. MonoXiver can serve as a lightweight second-stage processing module to significantly improve the accuracy of detection results while only requiring 1.5 hours of training on a single GPU card for the KITTI dataset. Comprehensive evaluation experiments on the well-established KITTI benchmark and the large-scale challenging Waymo dataset demonstrate the effectiveness of our design, with a new state-of-the-art" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6443" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.1, + 0.09, + 0.871, + 0.452 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.461, + 0.895, + 0.507 + ], + "angle": 0, + "content": "Figure 2: Qualitative comparison of our MonoXiver with MonoCon on KITTI validation set [5]. The left column is MonoCon's prediction result; the right column is our MonoXiver's prediction result. The ground truth is shown in green and blue. The prediction result is shown in red." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.534, + 0.471, + 0.579 + ], + "angle": 0, + "content": "achieved. Furthermore, our strong observation should encourage the community to further study refinement modules for 3D object detection." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.47, + 0.703 + ], + "angle": 0, + "content": "Limitations. Our work keeps at most top-3 predictions per bottom-up proposal for evaluation. Future work might be reducing the number of top-3 prediction by incorporating stronger priors for helping denoising proposals in 3D, i.e. temporal modeling, 3D geometric priors, large foundation models, etc. Our work has only been comprehensively tested on monocular settings with significant improvement, and it has not been tested on multiview settings." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.723, + 0.245, + 0.74 + ], + "angle": 0, + "content": "Acknowledgements" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.471, + 0.903 + ], + "angle": 0, + "content": "X. Liu and T. Wu were partly supported by ARO Grant W911NF1810295, NSF IIS-1909644, ARO Grant W911NF2210010, NSF IIS-1822477, NSF CMMI-2024688 and NSF IUSE-2013451. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the ARO, NSF, DHHS or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.534, + 0.893, + 0.579 + ], + "angle": 0, + "content": "copyright annotation thereon. The authors are grateful for the constructive comments by anonymous reviewers and area chairs." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.592, + 0.597, + 0.608 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.508, + 0.617, + 0.892, + 0.658 + ], + "angle": 0, + "content": "[1] Garrick Brazil and Xiaoming Liu. M3d-rpn: Monocular 3d region proposal network for object detection. In ICCV, pages 9287-9296, 2019. 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.509, + 0.661, + 0.894, + 0.702 + ], + "angle": 0, + "content": "[2] Garrick Brazil, Gerard Pons-Moll, Xiaoming Liu, and Bernt Schiele. Kinematic 3d object detection in monocular video. In ECCV, pages 135-152. Springer, 2020. 2, 7" + }, + { + "type": "ref_text", + "bbox": [ + 0.509, + 0.704, + 0.895, + 0.758 + ], + "angle": 0, + "content": "[3] Nicolas Carion, Francisco Massa, Gabriel Synnaeve, Nicolas Usunier, Alexander Kirillov, and Sergey Zagoruyko. 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In ICCV, pages 2713-2722, 2021. 2" + }, + { + "type": "list", + "bbox": [ + 0.504, + 0.093, + 0.892, + 0.715 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.956 + ], + "angle": 0, + "content": "6446" + } + ] +] \ No newline at end of file diff --git a/2023/Monocular 3D Object Detection with Bounding Box Denoising in 3D by Perceiver/3f374e4f-acb1-4e95-8005-f14f6138f707_origin.pdf b/2023/Monocular 3D Object Detection with Bounding Box Denoising in 3D by Perceiver/3f374e4f-acb1-4e95-8005-f14f6138f707_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..ea954486453354ba4e336d2f3a5fdb7d42dcd37d --- /dev/null +++ b/2023/Monocular 3D Object Detection with Bounding Box Denoising in 3D by Perceiver/3f374e4f-acb1-4e95-8005-f14f6138f707_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:0a11853c05f16143700480e198acff253565c7a665da855b2c46afe413ed8ffd +size 5774412 diff --git a/2023/Monocular 3D Object Detection with Bounding Box Denoising in 3D by Perceiver/full.md b/2023/Monocular 3D Object Detection with Bounding Box Denoising in 3D by Perceiver/full.md new file mode 100644 index 0000000000000000000000000000000000000000..158d3cc2c6bc14f9103accc40878838024d604c4 --- /dev/null +++ b/2023/Monocular 3D Object Detection with Bounding Box Denoising in 3D by Perceiver/full.md @@ -0,0 +1,361 @@ +# Monocular 3D Object Detection with Bounding Box Denoising in 3D by Perceiver + +Xianpeng Liu $^{1*}$ , Ce Zheng $^{2}$ , Kelvin Cheng $^{1}$ , Nan Xue $^{3}$ , Guo-Jun Qi $^{4,5}$ , Tianfu Wu $^{1}$ $^{1}$ North Carolina State University $^{2}$ University of Central Florida $^{3}$ Ant Group $^{4}$ OPPO Seattle Research Center, USA $^{5}$ Westlake University + +{xliu59, kbcheng, tianfu_wu}@ncsu.edu; cezheng@knights.ucf.edu; xuanan@ieee.org; guojunq@gmail.com https://xianpeng919.github.io/monoxiver + +# Abstract + +The main challenge of monocular 3D object detection is the accurate localization of 3D center. Motivated by a new and strong observation that this challenge can be remedied by a 3D-space local-grid search scheme in an ideal case, we propose a stage-wise approach, which combines the information flow from 2D-to-3D (3D bounding box proposal generation with a single 2D image) and 3D-to-2D (proposal verification by denoising with 3D-to-2D contexts) in a top-down manner. Specifically, we first obtain initial proposals from off-the-shelf backbone monocular 3D detectors. Then, we generate a 3D anchor space by local-grid sampling from the initial proposals. Finally, we perform 3D bounding box denoising at the 3D-to-2D proposal verification stage. To effectively learn discriminative features for denoising highly overlapped proposals, this paper presents a method of using the Perceiver I/O model [20] to fuse the 3D-to-2D geometric information and the 2D appearance information. With the encoded latent representation of a proposal, the verification head is implemented with a self-attention module. Our method, named as MonoXiver, is generic and can be easily adapted to any backbone monocular 3D detectors. Experimental results on the well-established KITTI dataset and the challenging large-scale Waymo dataset show that MonoXiver consistently achieves improvement with limited computation overhead. + +# 1. Introduction + +Detecting and locating objects in 3D using a single image, known as monocular 3D object detection, is a highly challenging task due to its ill-posed nature. However, the practical applications of low-cost system setups in fields such as self-driving cars and robotic manipulation have led + +to the development of robust monocular 3D object detection systems, making it a prominent research topic in the computer vision community. + +Although significant progress has been achieved in this field [37], accurate 3D center localization remains a major challenge for state-of-the-art (SOTA) methods as indicated in [39]. Most of these methods follow a bottom-up paradigm, where a single 2D image is used to directly predict 3D bounding boxes (2D-to-3D) with or without extra information (e.g. LiDAR). However, due to the inherent depth ambiguity of this task, relying solely on bottom-up 2D-to-3D paradigms may not be enough to completely address this challenge. + +In this paper, we observe that bottom-up 2D-to-3D predicted 3D bounding boxes are able to provide informative priors for monocular 3D object detection. We propose to leverage these contexts to improve detection performance in a top-down manner. Our proposed approach is motivated by a strong empirical upper-bound analysis with SOTA bottom-up monocular 3D object detectors. + +The empirical upper-bound experiment. We analyze vehicle detection performance on the well-established KITTI validation set [5-7]. We start with the recently proposed MonoCon [30] because it achieves SOTA performance with a very simple design. By using MonoCon's prediction results as bottom-up 3D anchors, we sample 3D bounding box proposals along both the $x$ and $z$ axes (i.e., in the bird-eye's view) with a simple strategy. First, we define a 2D local grid with a range (e.g., 2 meter) and a stride (e.g., 0.1 meter). For each bottom-up anchor, with its center located at the local-grid origin, we replicate the anchor at each grid vertex without changing its size, orientation and prediction score. We use all the generated 3D bounding boxes as top-down proposals and compute the empirical upper-bound of 3D detection performance by searching for the best match within top-down proposals for each ground-truth 3D object bounding box based on 3D Intersection-over-Union (3D IoU). + +A strong observation from the experiment. As shown + +
RangeStrideEasyModerateHard#Bboxesmean IoUavg
MonoCon [30]26.3319.0115.98n-
± 20.176.98↑50.6564.93↑45.9256.91↑40.931600·n0.931
± 1.50.176.45↑50.1262.27↑43.2654.34↑38.36900·n0.931
± 1.50.274.00↑47.6761.78↑42.7753.64↑37.66225·n0.868
± 1.50.364.80↑38.4756.20↑37.1950.66↑34.68121·n0.812
± 1.50.554.00↑27.6745.93↑26.9240.99↑25.0149·n0.714
± 1.50.7541.58↑15.2534.44↑15.4330.12↑14.1425·n0.612
+ +Table 1: A strong empirical upper-bound analysis. Our MonoXiver is motivated by the observation that bottom-up monocular 3D object detectors can be significantly improved by leveraging a simple 3D-space local-grid search scheme in an ideal case. This highlights the potential of exploring the 3D proposal space. However, this improvement comes at a cost: 1) the proposal verification stage experiences significant increases in number of bounding box proposals, and 2) a more powerful refinement module is required to handle highly overlapped boxes. + +in Table 1, despite the evaluation result of initial bottom-up proposals is relatively low in 3D average precision $(AP_{3D})$ (e.g., 19.01 in Moderate settings), most of predicted 3D centers are already in the close proximity of the GT ones. An empirical upper-bound of 34.4 $AP_{3D}$ can be achieved even with a coarse sampling scheme (e.g., the last row), which is significantly higher than SOTA methods. We also obtained similar observations from other backbone 3D object detectors such as the MonoDLE [39] and the SMOKE [33]. These strong empirical observations demonstrate the potential of integrating the bottom-up initial proposals with top-down sampling and verification. + +The challenge in the 3D-to-2D proposal verification. The 3D-to-2D proposal verification phase can be treated as a 3D bounding box denoising process, as we want to search for the "best" bounding boxes from the top-down proposal set. This process is extremely challenging, as the proposals generated from the same bottom-up anchor are highly overlapped in both 3D and 2D (after projection), which leads to the long-standing problem of handling the "crowd" in detection. To quantitatively analyze the overlap extent after projection for top-down proposals, we consider one proposal and its top- $k$ overlapping neighbors in terms of Intersection-over-Union (IoU), which is denoted by $\mathrm{IoU}_{avg}^k$ as the average IoU over the top- $k$ neighbors. The last column in Table 1 shows the statistics. + +The statistics clearly demonstrates the difficulty of denoising densely generated top-down proposal set (e.g., stride=0.1, IoU5 = 0.931). Even for a relative sparse generated top-down proposal set (e.g., stride=0.75, IoU5 = 0.612), the challenge still exists because proposals sampled in front and behind of the same anchor will almost collapse to the same 2D bounding box, especially when they are far away from the camera. So, how can we + +encode the 3D bounding box proposal for verification under the monocular setting? From this perspective, we note that many methods that work well in multi-view 3D object detection are often not applicable for monocular 3D objection because they mainly rely on features that are obtained by fusing projection features from multi-view feature maps. + +Based on the intuition that even though highly overlapped proposals have similar appearance features, their inherent 3D-to-2D geometric features (e.g. 3D location, projected geometry, etc.) are extremely different, we propose to fuse these 3D-to-2D geometric feature with their correspondent appearance features to learn discriminative features for bounding box denoising. We present a method of using the Perceiver I/O model [20] to effectively fuse these contexts, as Perceiver has shown strong capabilities to fuse multi-modal inputs. With the encoded latent representation of a proposal, the verification head is implemented by a self-attention module (see the top in Fig. 1). The proposed method is named as MonoXiver, indicating its general applicability to any backbone monocular 3D detectors and the integration of the Perceiver model. + +In experiments, we evaluate our proposed MonoXiver on the well-established KITTI benchmark [14] and the challenging large-scale Waymo [51] dataset with various backbone monocular 3D detectors. It achieves consistent and significant performance improvement on both datasets with limited computation overhead. Moreover, it achieves the 1st place among monocular methods on the KITTI vehicle detection benchmark, outperforming the previous works by a large margin. + +# 2. Related Works and Our Contributions + +Monocular 3D Object Detection. The problem of monocular 3D object detection is considered ill-posed, prompting recent research efforts to leverage additional information sources, including LiDAR point clouds [4, 10, 19, 28, 45], depth estimation [12, 36, 42, 48, 53, 54, 62], CAD models [25, 34], temporal frames [2], etc. These approaches have shown improved detection performance when compared to purely image-based methods [1, 33, 41, 57]. However, they often come with increased computation load and inference time, making them less practical for real-time applications such as autonomous vehicles. In contrast, purely image-based methods have seen significant performance improvements in the literature by exploiting geometric constraints [26, 35, 41, 47, 59, 60], perspective projections [24, 38], auxiliary training [30], novel loss designs [8, 39, 49] and second-stage processing techniques [23]. These works focus on developing better bottom-up paradigms. Our proposed method, MonoXiver, takes a top-down paradigm, which explores 3D space differently than the aforementioned methods. It provides a generic and highly efficient second-stage refinement module for any pretrained state-of + +![](images/e63afead46451d0cdfd33b3caeb7df300e76ca24ba393f232443b157b3b1af42.jpg) +Figure 1: Illustration of the proposed MonoXiver method. MonoXiver is built for any off-the-shelf backbone monocular 3D object detectors. It consists of a 2D-to-3D proposal generation phase using a bottom-up anchoring and top-down sampling strategy, and a 3D-to-2D proposal verification (or denoising) phase using the Perceiver I/O [20] with a carefully designed 3D/2D input space to address the unique challenges. See text for details. + +the-art monocular 3D object detection method, making it a complementary approach. + +Bird's-Eye-View 3D Object Detection. Bird's-Eye-View (BEV) 3D object detection [40] has recently gained significant attention as it provides a physical-interpretable feature space for integrating data from diverse sensors [27, 31, 44, 56] and modalities [13, 18]. To enable the learning of a physical-interpretable feature space, accurate physical measurements from depth perception systems such as multi-view cameras and LiDAR are crucial [16]. However, detecting 3D objects in BEV is challenging for monocular systems due to the intrinsic depth ambiguity. Directly accumulating image features based on projection reference points similar to recent query-based multi-view 3D detectors [31, 56] might fail because of lacking stereo-matching mechanism to resolve the depth ambiguity. To overcome this issue, recent BEV-based monocular methods [9, 45, 55] lift the image feature space to voxel-represented world-space using monocular depth estimation models. Our proposed method, MonoXiver, samples top-down proposals based on bottom-up initial proposals in BEV space. Unlike prior arts [9, 45, 55] that extract features represented in world-space, MonoXiver's top-down proposals extract features from both projected appearance features and inherent geometric features. We explore to address the challenging intrinsic feature ambiguity problem by applying a Perceiver-like attention mechanism to query informative features for 3D bounding box verification and refinement without the need for dense depth supervision. + +Transformers for Multi-modal Data. Transformers [52], + +known for their powerful attention mechanism, have been successfully applied in multiple research areas and applications [3,11,32,50]. With the powerful attention mechanism, transformers can conveniently align multi-modal structured data, enabling the generation of universal multi-modal representation. The recent proposed Perceiver [20, 21] extends the transformers' querying mechanism and makes it capable of efficiently handling data from arbitrary settings. In our work, we adapt Perceiver to fuse appearance features and geometric features from the same bounding box to generate appearance-geometric aligned representation, which is then used as queries for the down-stream 3D bounding box refinement task. + +Our Contributions. MonoXiver makes three main contributions to the field of monocular 3D object detection: + +- We conduct a new and strong empirical upper-bound analysis for state-of-the-art monocular 3D object detectors. We demonstrate that a simple, universally applicable sampling strategy can lead to consistent and significant performance improvement in an ideal situation. Based on these observations, we propose to explore the top-down, stage-wise detection paradigm with 2D-to-3D proposal generation and 3D-to-2D proposal verification for monocular 3D object detection. +- To address the challenge at the bounding box denoising stage, we propose to learn discriminative features by enhancing appearance features with 3D-to-2D inherent geometric features. We therefore propose a carefully-designed module with the integration of the powerful Perceiver and self-attention mechanism. The resulting mod + +ule can be applied generically to any off-the-shelf monocular 3D object detectors. + +- Extensive experiments demonstrate the effectiveness and efficiency of our proposed method, MonoXiver, under a separate two-stage training setting. It achieves consistent improvement with limited overhead on both KITTI and Waymo dataset. It achieves the 1st place among monocular methods on the KITTI vehicle detection benchmark, outperforming the previous works by a large margin. + +# 3. Approach + +In this section, we first present the straightforward 2D-to-3D proposal generation on top of a backbone monocular 3D object detector. Then, we present the details of the proposed MonoXiver method (Fig. 1). + +# 3.1. The 2D-to-3D Proposal Generation + +Let $I$ be an RGB input image defined on the domain $\Lambda$ . The goal of monocular 3D object detection is to detect 3D bounding boxes, along with their class labels denoted by $\ell$ for each object instance in $I$ . The 3D bounding box is parameterized by the 3D center position $\mathbf{P} = (X,Y,Z)$ in meters, the shape dimensions $\mathbf{D} = (h,w,l)$ in meters, and the observation angle $\alpha \in [-\pi ,\pi ]$ , all measured in the camera coordinate system. + +For simplicity, consider the pure image-based settings, a monocular 3D object detector often consists of two main components in inference: the feature backbone (e.g., the DLA34 network [58]), denoted by $\mathbf{F}_I$ for computing deep features from the raw image $I$ , and the regression heads for inferring the 3D bounding box parameters using the computed feature map. We generate bottom-up proposals using one off-the-shelf backbone monocular 3D object detector which is first trained following its own training receipts. Without loss of generality, we consider one of its detected 3D bounding boxes indexed by $i$ in an image $I$ , + +$$ +\mathbb {B} _ {i} = \left(\ell_ {i}, \mathbf {P} _ {i}, \mathbf {D} _ {i}, \alpha_ {i}\right), \tag {1} +$$ + +As shown in Table 1, the top-down sampling with a bottom-up anchor proposal is a straightforward process. We start by generating a 2D local grid in the $X - Z$ plane (i.e. in the bird's-eye-view, BEV), centered at the position $(X,Z)$ of the anchor box $\mathbb{B}$ . To accomplish this, we specify a search range and a stride. Based on the trade-off between the empirical upper bound and the computing overhead and the mean IoU among the proposals, we adopt a conservative strategy using the search range $\pm 1.5$ meters and the stride 0.75, which will generate 25 proposals per bottom-up anchor (inclusive). We then place the anchor box $\mathbb{B}$ at the 25 grid points, with only the position $\mathbf{P}$ updated. To simplify the notation, we do not differentiate between the bottom-up anchor and the top-down sampled proposal, and we generally index them using $i$ , unless otherwise stated. + +# 3.2. The 3D-to-2D Proposal Verification + +The proposal verification will rely essentially on the information from the input 2D images in purely monocular 3D object detection. Due to the aforementioned unique challenges in the 3D proposal space, we utilize Perceiver I/O [20] to design an expressive proposal representation learning scheme. + +# 3.2.1 Proposal Representation + +As illustrated in Fig. 1, we utilize three types of features in encoding a 3D bounding box proposal $\mathbb{B}$ , + +- The 3D Shape Features represented by $(\mathbf{P}, \mathbf{D}, \alpha)$ . It is a 7-dim vector. It encodes where the proposal is in the 3D space (the camera coordinate system), as well as its 3D occupancy. The position $\mathbf{P}$ is empirically normalized by the typical detection range (e.g., $X, Y, Z$ are normalized by 50, 2 and 80 meters respectively). +- The 2D Projection Points from the 8 corners and the center of the 3D bounding box (with known camera intrinsic matrix). It is an 18-dim vector in the image coordinate system, and normalized by the image size. This 9-point projection provides the finegrained placement of a proposal in the 2D space, that is the geometric bond between a proposal in the 3D space and its 2D placement. +- The 2D Bounding Box projected from the proposal and truncated by the image boundary. We use the left-top and right-bottom two points to encode a 2D bounding box. It gives a 4-dim vector normalized by the image size. For a proposal whose 2D projection is entirely inside the image plane, the two points of the 2D bounding box will be just redundant with respect to the 9 project points. Otherwise, the truncation points on the image boundary will facilitate the learning to be truncation aware. +- The Appearance Features of the 9 projection points. We directly extract features from the final layer of the feature backbone $\mathbf{F}_I$ . If a projection point is out of the image plane, we encode it using an all-zero vector. +- The RoI Appearance Features of the 2D bounding box. We use the RoIAign features [17] extracted from the final layer of the feature backbone $\mathbf{F}_I$ . Since the 2D IoU overlapping between proposals is high on average (e.g., 0.612 in Table 1), we use a finer grid, $14 \times 14$ , in computing the RoIAign features, such that the extracted appearance features contain "sufficient" details. + +# 3.2.2 Proposal Embedding + +Let $N$ be the total number of proposals in an image $I$ . With the above representation scheme, denote by $f_{N\times 29}^{geo}$ the geometric parameter matrix from the first three items above, + +and by $f_{N \times 9 \times C}^{pt}$ the projection point appearance feature matrix (where $C$ is the number of channels of the final layer of the feature backbone, e.g., $C = 64$ ), and by $f_{N \times (14 \times 14) \times C}^{roi}$ the RoI feature matrix. Before applying the Perceiver I/O model, we embed the three to form "tokens" using multi-layer perceptron (MLP). + +For the geometric parameters $f_{N \times 29}^{geo}$ , we have, + +$$ +f _ {N \times 2 9} ^ {\text {g e o}} \xrightarrow {\mathrm {M L P}} z _ {N \times (g \times d)} \xrightarrow {\text {R e a r r a n g e}} \mathbf {f} _ {g \times N \times d} ^ {\text {g e o}}, \tag {2} +$$ + +where $d$ is the hidden dimension (e.g., $d = 256$ ). $g$ is the group number, similar in spirit to the multi-head setup in the self-attention. We want to encode the geometric parameters in different latent spaces to account for the large variations in the proposal space (e.g., $g = 4$ ). + +For the project point features $f_{N \times 9 \times C}^{pt}$ , we have, + +$$ +f _ {N \times 9 \times C} ^ {p t} \xrightarrow {\mathrm {M L P}} z _ {N \times 9 \times d} \xrightarrow {\text {R e a r r a n g e}} \mathbf {f} _ {9 \times N \times d} ^ {p t}, \tag {3} +$$ + +where we reuse $z$ to denote the latent features for simplicity and without confusion. + +For the RoI features $f_{N\times (14\times 14)\times C}^{roi}$ , we have, + +$$ +f _ {N \times (1 4 \times 1 4) \times C} ^ {r o i} \xrightarrow {\mathrm {M L P}} z _ {N \times d} \xrightarrow {\text {R e a r r a g e}} \mathbf {f} _ {1 \times N \times d} ^ {r o i}. \tag {4} +$$ + +# 3.2.3 Intra-Proposal Attention via Perceiver + +With the above proposal embedding, before the proposal verification, our goal is to compute a final latent feature representation in the $d$ -dim space for each proposal by fusing information from the geometric encoding, projection-point-based appearance encoding and RoI-based appearance encoding (i.e., the intra-proposal attention), such that we can address the aforementioned unique challenges in the proposal space. We leverage the Perceiver I/O model for this intra-proposal attention. + +The Perceiver first fuses the projection-point appearance encoding $\mathbf{f}_{9\times N\times d}^{pt}$ and the geometric encoding $\mathbf{f}_{g\times N\times d}^{geo}$ . As shown in Fig. 1, it consists of a cross-attention by treating the former as Query (consisting of 9 projection-point tokens) and computing Key and Value from the latter (consisting of $g$ geometric tokens), followed by a self-attention module. We have, + +$$ +\left(\mathbf {f} _ {9 \times N \times d} ^ {p t}, \mathbf {f} _ {g \times N \times d} ^ {g e o}\right) \xrightarrow {\text {C r o s s - A t t n}} \cdot \xrightarrow {\text {S e l f - A t t n}} \mathbf {F} _ {9 \times N \times d} ^ {g e o - p t}, \tag {5} +$$ + +which results in geometry-aware projection-point encoding. + +Next, the Perceiver fuses the RoI appearance encoding $\mathbf{f}_{1\times N\times d}^{roi}$ as the 1-token Query with the 9-token geometry-aware projection-point encoding using a cross attention module, + +$$ +\left(\mathbf {f} _ {1 \times N \times d} ^ {r o i}, \mathbf {F} _ {9 \times N \times d} ^ {g e o - p t}\right) \xrightarrow {\text {C r o s s - A t t n}} \mathbf {F} _ {1 \times N \times d} ^ {g e o - p t - r o i}, \tag {6} +$$ + +which results in the $d$ -dim latent features for each proposal, which fuse the three types of information sources: geometry, point-level appearance and region-level appearance. + +In the above, the cross-attention and self-attention modules are based on the standard formulation [52]. + +# 3.2.4 Inter-Proposal Attention + +With all the above process, each proposal is still encoded individually with the hope of fusing geometry, point-level appearance and region-level appearance information in a semantically meaningful way via the Perceiver I/O model. With the compact latent vector computed for each proposal in $\mathbf{F}_{1\times N\times d}^{geo-pt-rot}$ , their interactions need to be taken into account in order to resolve their "crowding" issue at the underlying scene level. + +To that end, we treat each proposal as a "token" and apply a standard self-attention module to capture the interproposal attention, + +$$ +\mathbf {F} _ {1 \times N \times d} ^ {\text {g e o - p t - r o i}} \xrightarrow {\text {R e a r r a n g e}} \mathbf {F} _ {N \times d} ^ {\text {g e o - p t - r o i}} \xrightarrow {\text {S e l f - A t t n}} \mathbb {F} _ {N \times d}. \tag {7} +$$ + +# 3.2.5 Proposal Verification + +This verification is posed as a regression problem, + +$$ +\mathbb {F} _ {N \times d} \xrightarrow {\mathrm {M L P s}} \left(\mathbf {y} _ {N \times L}, \Delta \mathbf {P} _ {N}, \Delta \mathbf {D} _ {N}\right), \tag {8} +$$ + +where $L$ is the total number of categories (e.g., $L = 3$ in the KITTI dataset), and $\mathbf{y}_{N\times L}$ is the classification scores (logits). $\Delta \mathbf{P}_N$ and $\Delta \mathbf{D}_N$ are the position and dimension residuals. + +Consider a proposal $\mathbb{B}_i$ (Eqn. 1), it is verified via, + +$$ +\hat {\ell} _ {i} = \arg \max _ {l = 1, \dots , L} \mathbf {y} _ {i, l}, \tag {9} +$$ + +$$ +\hat {\mathbf {P}} _ {i} = \mathbf {P} _ {i} + \Delta \mathbf {P} _ {i}, \tag {10} +$$ + +$$ +\hat {\mathbf {D}} _ {i} = \mathbf {D} _ {i} + \Delta \mathbf {D} _ {i}, \tag {11} +$$ + +where a proper unnormalization step will be done for $\hat{\mathbf{P}}_i$ to counter the normalization step used in the proposal representation (Sec. 3.2.1). Based on the score $\mathbf{y}_{i,\hat{\ell}_i}$ , we can keep top- $k$ proposals for each anchor position. + +# 3.3. Details of Training and Testing + +For simplicity, we evaluate the proposed MonoXiver in a two-stage setting where the backbone monocular 3D object detector is first trained and kept frozen. Then, the MonoXiver component is trained end-to-end. One of the reasons for this choice is that off-the-shelf backbone monocular 3D object detectors often involve multiple loss functions, and joint training with MonoXiver would require sophisticated tuning of the trade-off parameters for different loss terms. We leave the joint end-to-end training or iterative training, + +as done in the early version of Faster RCNN [46] between the region proposal network and the region classification head network, for future work. Additionally, the separate two-stage training may also have advantages in leveraging the set of bottom-up anchor proposals merged from multiple backbone monocular 3D detectors, which we also leave for future work. + +# 3.3.1 The Set Prediction Formulation in Training + +Based on the separate two-stage setting, the proposed MonoXiver is trained with a fixed set of 3D bounding box proposals and a fixed set of ground-truth 3D bounding boxes. The ground-truth assignment for proposals is needed in training. Two straightforward methods are: using the maximum 3D IoU based assignment, or using the maximum 2D IoU assignment (after projected to the image plane). Due to the "crowding" issue in the proposal space, we observe that both of them do not work during our development of the MonoXiver since they will create difficult "decision boundaries" for the MonoXiver to learn or fit. + +Since we have the two fixed set as input, we resort to the set prediction formulation used in the DETR framework [3]. Denote by $\Omega_{\mathbb{B}} = \{\mathbb{B}_i\}_{i=1}^N$ the set of generated proposals, by $\Omega_{\mathbb{B}^*} = \{\mathbb{B}_j^*\}_{j=1}^M \cup \{\emptyset_j\}_{j=M+1}^N$ the set of ground-truth 3D bounding boxes padded with $N - M$ dummy $\emptyset$ elements. Given a permutation of $N$ elements, denoted by $\sigma$ which assigns the $i$ -th element in the ground-truth set to the $\sigma(i)$ -the element in the proposal set, the loss for the one-to-one bipartite matching between $\mathbb{B}_i^*$ and $\mathbb{B}_{\sigma(i)}$ is defined by, + +$$ +\mathcal {L} _ {\text {m a t c h}} \left(\mathbb {B} _ {i} ^ {*}, \mathbb {B} _ {\sigma (i)}\right) = \mathbf {1} _ {\ell_ {i} ^ {*} \neq \emptyset} \cdot \left(- \lambda_ {1} \cdot \hat {p} _ {\sigma (i)} \left(\ell_ {i} ^ {*}\right) + \right. \tag {12} +$$ + +$$ +\lambda_ {2} \cdot \mathcal {L} _ {b b o x} ^ {2 D} + \lambda_ {3} \cdot \mathcal {L} _ {i o u} ^ {2 D} + \lambda_ {4} \cdot \mathcal {L} _ {i o u} ^ {3 D}), +$$ + +where $\hat{p}_{\sigma(i)}(\ell_i^*)$ is computed using $\mathbf{y}_{\sigma(i)}$ (Eqn. 8) via Softmax. $\mathcal{L}_{bbox}^{2D}$ represents the normalized L1 2D bounding box, and $\mathcal{L}_{iou}^{2D}$ and $\mathcal{L}_{iou}^{3D}$ the IoU loss in 2D and 3D respectively. $\lambda_1$ to $\lambda_4$ are the trade-off parameters. + +# 3.3.2 Loss Functions for Proposal Verification + +For the three outputs in Eqn. 8, we have three loss terms as follows, + +$$ +\mathcal {L} = \mathcal {L} _ {\text {c l s}} + \mathcal {L} _ {\text {s i z e}} + \lambda \cdot \mathcal {L} _ {\text {l o c}} \tag {13} +$$ + +where $\mathcal{L}_{cls}$ is the Focal Loss [29] with the $\alpha$ value of 0.5 to balance the number of positive and negative samples. The Focal loss is used due to the imbalance introduced by the explicit top-down proposal generation. $\mathcal{L}_{size}$ are $\mathcal{L}_{loc}$ are the loss functions for the 3D size and the 3D center respectively. $\lambda$ is an trade-off hyper-parameter. We use $\ell_1$ loss for $\mathcal{L}_{size}$ and $\mathcal{L}_{loc}$ . We set $\lambda = 5$ to induce the model to focus more on the 3D localization refinement task. + +# 3.3.3 Training + +MonoXiver is trained using a total of 8 GPUs, with a batch size of 64 for 24 epochs on KITTI (12 epochs on Waymo) using the AdamW optimizer. The optimizer is set with $(\beta_{1},\beta_{2}) = (0.95,0.99)$ and weight decay of 0.0001, excluding feature normalization layers and bias parameters. The initial learning rate is set to $2.25e - 5$ , and it is reduced by a factor of 10 at the 16th and 22nd epoch. Notably, the entire second-stage training process takes merely 1.5 hours on KITTI [14] using a single Nvidia RTX5000 GPU, indicating the low computational overhead of our proposed MonoXiver method. The training time on Waymo [51] varies depending on the training data and training recipes of off-the-shelf monocular 3D detectors. Overall, the second-stage training on Waymo is much faster compared to training the backbone monocular 3D object detector, leading to about a 3/4 reduction in training time. + +# 3.3.4 Testing + +During testing, we keep at most top-3 predictions per initial anchor proposal with a score threshold of 0.03 (the score is predicted from the proposed MonoXiver module). The final prediction score is the product of the classification probability predicted from the backbone monocular 3D object detector and the score computed by the MonoXiver module. + +# 4. Experiments + +We evaluate our MonoXiver on the well-established KITTI [14] dataset and the large-scale Waymo [51] dataset. We first show that our improved baseline detector outperforms previous SOTA methods on the KITTI benchmark by a large margin. Then we show that we consistently improved pretrained monocular 3D object detectors with limited computation overhead on both datasets. We further analyze the contribution of each part of our MonoXiver in the ablation studies. + +# 4.1. Setup + +Dataset. The KITTI dataset [14] consists of 7,481 training images and 7,518 testing images. In KITTI's experiments, we split the training data into a training subset with 3,712 images and a validation subset with 3,769 images following [5-7]. We conduct ablation studies on the defined split and report the test set results evaluated by the official KITTI benchmark. The Waymo dataset [51] contains 52,386 training and 39,848 validation images from the front camera. In Waymo experiments, we use a subset of its training set by sampling every third frame from the training sequences following [22,45]. + +Evaluation Metrics. The KITTI vehicle benchmark evaluates detection results by the 40-point interpolated av- + +
MethodsVenuesExtra Info.APBEV|R40↑AP3D|R40↑
EasyMod.HardEasyMod.Hard
Kinematic3D [2]ECCV20Temporal26.6917.5213.1019.0712.729.17
AutoShape [34]ICCV21CAD30.6620.0815.9522.4714.1711.36
DCD [25]ECCV22CAD32.5521.5018.2523.8115.9013.21
MonoDistill [10]ICLR22LiDAR31.8722.5919.7222.9716.0313.60
DID-M3D [43]ECCV22LiDAR32.9522.7619.8324.4016.2913.75
DD3D [42]ICCV21Depth30.9822.5620.0323.2216.3414.20
DFM [55]ECCV22Temporal + LiDAR31.7122.8919.9722.9416.8214.65
Pseudo-Stereo [9]CVPR22Depth + LiDAR32.8423.6720.6423.7417.7415.14
MonoFlex [59]CVPR2128.2319.7516.8919.9413.8912.07
GUPNet [35]ICCV2130.2921.1918.2020.1114.2011.77
DEVIANT [22]ECCV22None29.6520.4417.4321.8814.4611.89
Homography [15]CVPR2229.6020.6817.8121.7514.9413.07
DimEmbedding [61]CVPR2232.8221.9818.7023.6216.1013.41
MonoCon [30]AAAI22None31.1222.1019.0022.5016.4613.95
Our MonoXiver + MonoCon-34.1425.3722.2025.2419.0416.39
+ +Table 2: Comparisons with state-of-the-art methods on the Car category on the KITTI test set. According to the KITTI protocol, methods are ranked based on their performance under the moderate difficulty setting. We highlight the best results in bold and the second-best results in underline. + +
MethodsAP3D|R40↑Relative Improvement
EasyModerateHard
SMOKE [33]10.437.095.5711%-33%
SMOKE + Ours11.589.407.75
Improvement+1.15+2.31+2.18
MonoDLE [39]17.9413.7212.1018%-22%
MonoDLE + Ours21.1516.1914.75
Improvement+3.21+2.47+2.65
MonoCon [30]26.3319.0115.9816%-20%
MonoCon + Ours30.4822.4019.13
Improvement+4.15+3.39+3.15
+ +erage precision $(AP_{R40})$ of 3D bounding boxes in 3D space $(AP_{3D|R40})$ and bird eye's view $(AP_{BEV|R40})$ at $IoU_{3D} \geq 0.7$ . The prediction results are evaluated based on three difficulty settings, easy, moderate and hard, according to the 2D box height, occlusion and truncation levels of objects. The vehicle detection results on Waymo are evaluated on two levels of difficulty including Level_1 and Level_2 at $IoU_{3D} \geq 0.5$ . The level is assigned based on the number of LiDAR points included in each 3D box. Besides the $AP_{3D}$ metric, Waymo uses the $APH_{3D}$ metric to incorporate heading information in $AP_{3D}$ . + +Table 3: The effectiveness of MonoXiver based on different methods on the KITTI validation dataset. In order to demonstrate the ability of the proposed MonoXiver to generalize across different detectors, we utilized three distinct base detectors with varying levels of detection accuracy. We observe that MonoXiver consistently yields significant improvements across all three base detectors. + +
MethodsLevel_1Level_2
AP3D↑APH3D↑AP3D↑APH3D↑
PatchNet [36]2.922.742.422.28
PCT [54]4.204.154.034.15
GUPNet [35]10.029.949.399.31
GUPNet + ours11.4711.3510.6710.56
Improvement+1.45+1.41+1.28+1.25
DEVIANT [22]10.9810.8910.2910.20
DEVIANT + ours11.8811.7511.0610.93
Improvement+0.90+0.86+0.77+0.73
+ +Table 4: The effectiveness of MonoXiver based on different methods on Waymo validation dataset. In order to showcase the generalization capabilities of the proposed MonoXiver on large-scale datasets, we conducted testing on the challenging Waymo [51] validation set, utilizing two SOTA methods. We observed consistent improvements in performance. + +
MethodsFLOPsLatency (ms)FPS
SMOKE [33]/ + ours42.82/48.1923/3143/32
MonoDLE [39]/ + ours77.44/82.8022/3145/32
MonoCon [30]/ + ours56.22/61.5018/2555/40
+ +Table 5: Computation overhead analysis. The GFLOPs is computed based on an input size of (384, 1248), while the latency and FPS are evaluated on a NVIDIA RTX5000 GPU. + +# 4.2. Experimental Results + +Comparison with SOTA methods on the KITTI dataset. We present the results of our proposed MonoXiver method on the challenging KITTI vehicle benchmark in Table 2. Notably, our method achieves the best performance across different evaluation metrics while only using image-level information, surpassing previous state-of-the-art methods by a large margin. Specifically, we observe a significant and consistent improvement from 2.44 AP (hard settings) to 2.74 AP (easy settings) absolute increase in $\mathrm{AP}_{3D}$ for the boosted MonoCon approach compared to the vanilla MonoCon approach. These consistent improvements demonstrate the effectiveness of our method. More qualitative and quantitative results are provided in the Supplementary Materials. Generalization abilities across backbone monocular 3D object detectors and datasets. We evaluate our method with various state-of-the-art backbone monocular 3D object detection methods on the KITTI and the Waymo validation set, reported in Table 3 and Tabel 4 respectively. Monoxiver consistently demonstrates significant improvements across different methods and different difficult levels. Specifically, on the well-established KITTI dataset, our MonoXiver is able to enhance various backbone detectors with varying levels of detection accuracy by up to $33\%$ relative improvement. On the challenging large-scale Waymo dataset, our MonoXiver consistently improves the performance of strong baseline methods GUPNet and DEVIANT by up to $1.45\mathrm{AP}_{3D}$ on Level_1 and $1.28\mathrm{AP}_{3D}$ on Level_2. These results validate the effectiveness and robustness of our approach. + +Computation overhead. As shown in Table 5, although our MonoXiver causes about an average of $8\mathrm{ms}$ overhead compared with baseline detectors, it still achieves real-time detection. We note that its inference speed could be improved by optimizing the detailed implementation (e.g., we still have for-loops in our current code, which can be easily paralleled for better efficiency). + +Qualitative Comparison. We show the visualization comparisons with MonoCon in Fig. 2. It shows that MonoXiver achieves better 3D box center localization. + +# 4.3. Ablation Studies + +In this section, we report ablation studies of MonoXiver structure and different bounding box branches on the KITTI validation set. More ablation studies are provided in the Supplementary Materials. + +Effectiveness of MonoXiver structures. In this study, we explore the importance of RoI feature (Table 6 a.), the context information provided by geometric embeddings (Table 6 b.), and our complete MonoXiver model (Table 6 c.). In experiments a. and b., we replace the Perciver with a MLP layer to fuse the appearance feature and geometry feature to keep similar parameter size. + +
AppearanceGeometryPerciverEasy/Mod./Hard
MonoCon [30]---26.33/19.01/15.98
a.✓--29.30/21.04/18.22
b.✓✓-29.33/21.67/18.46
c.✓✓✓30.48/22.40/19.13
+ +Table 6: Ablation studies of MonoXiver structure on KITTI validation set. + +
RescoreResLocResDimEasyMod.Hard
MonoCon [30]---26.3319.0115.98
a.✓--29.6621.4118.38
b.✓✓-30.3222.3019.04
c.✓✓✓30.4822.4019.13
+ +Table 7: Ablation studies of the effect of different branches on KITTI validation set + +Results show that the appearance feature plays the most important role in performance improvement. When using the appearance feature only, the Moderate AP is improved by 2.39. The performance is further improved by 0.6 AP and 0.7 AP after fusing with geometric embeddings and Perciver. It shows that Perceiver effectively fuses information between appearance and geometric embeddings. + +Effectiveness of Different Head Branches. In Table 7, we present the impact of different branches on the detection performance of our MonoXiver. Since our method generates 25 proposals per each initial proposal, the rescoring head branch plays a crucial role in filtering out false detections, leading to significant improvements by up to 3.3 AP. The localization residual branch and the dimension residual branch further enhance the performance by about 1 AP, and we employ all branches to achieve a new state-of-the-art result. + +# 5. Conclusion + +This paper explores the task of monocular 3D object detection. It begins with the strong observation that significant improvements in detection performance can be achieved by a local grid search based on initially detected 3D bounding boxes. This leads to a novel denoising-based approach called MonoXiver. The approach utilizes the Perceiver I/O model to produce a unified feature embedding, leverages the self-attention mechanism for proposal verification, and ultimately delivers high-quality 3D box predictions. MonoXiver can serve as a lightweight second-stage processing module to significantly improve the accuracy of detection results while only requiring 1.5 hours of training on a single GPU card for the KITTI dataset. Comprehensive evaluation experiments on the well-established KITTI benchmark and the large-scale challenging Waymo dataset demonstrate the effectiveness of our design, with a new state-of-the-art + +![](images/a47f99d0275564abcf421b83af8efe4631616c14e12c4f791e37dfb47aa855c6.jpg) +Figure 2: Qualitative comparison of our MonoXiver with MonoCon on KITTI validation set [5]. The left column is MonoCon's prediction result; the right column is our MonoXiver's prediction result. The ground truth is shown in green and blue. The prediction result is shown in red. + +achieved. Furthermore, our strong observation should encourage the community to further study refinement modules for 3D object detection. + +Limitations. Our work keeps at most top-3 predictions per bottom-up proposal for evaluation. Future work might be reducing the number of top-3 prediction by incorporating stronger priors for helping denoising proposals in 3D, i.e. temporal modeling, 3D geometric priors, large foundation models, etc. Our work has only been comprehensively tested on monocular settings with significant improvement, and it has not been tested on multiview settings. + +# Acknowledgements + +X. Liu and T. Wu were partly supported by ARO Grant W911NF1810295, NSF IIS-1909644, ARO Grant W911NF2210010, NSF IIS-1822477, NSF CMMI-2024688 and NSF IUSE-2013451. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the ARO, NSF, DHHS or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any + +copyright annotation thereon. 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Learning geometry-guided depth via projective modeling for monocular 3d object detection. arXiv:2107.13931, 2021. 2 +[61] Yunpeng Zhang, Wenzhao Zheng, Zheng Zhu, Guan Huang, Dalong Du, Jie Zhou, and Jiwen Lu. Dimension embeddings for monocular 3d object detection. In CVPR, 2022. 7 +[62] Zhikang Zou, Xiaqing Ye, Liang Du, Xianhui Cheng, Xiao Tan, Li Zhang, Jianfeng Feng, Xiangyang Xue, and Errui Ding. The devil is in the task: Exploiting reciprocal appearance-localization features for monocular 3d object detection. 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Motivated by a new and strong observation that this challenge can be remedied by a 3D-space local-grid search scheme in an ideal case, we propose a stage-wise approach, which combines the information flow from 2D-to-3D (3D bounding box proposal generation with a single 2D image) and 3D-to-2D (proposal verification by denoising with 3D-to-2D contexts) in a top-down manner. Specifically, we first obtain initial proposals from off-the-shelf backbone monocular 3D detectors. Then, we generate a 3D anchor space by local-grid sampling from the initial proposals. Finally, we perform 3D bounding box denoising at the 3D-to-2D proposal verification stage. To effectively learn discriminative features for denoising highly overlapped proposals, this paper presents a method of using the Perceiver I/O model [20] to fuse the 3D-to-2D geometric information and the 2D appearance information. 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Most of these methods follow a bottom-up paradigm, where a single 2D image is used to directly predict 3D bounding boxes (2D-to-3D) with or without extra information (e.g. LiDAR). However, due to the inherent depth ambiguity of this task, relying solely on bottom-up 2D-to-3D paradigms may not be enough to completely address this challenge." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 413, + 547, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 413, + 547, + 496 + ], + "spans": [ + { + "bbox": [ + 304, + 413, + 547, + 496 + ], + "type": "text", + "content": "In this paper, we observe that bottom-up 2D-to-3D predicted 3D bounding boxes are able to provide informative priors for monocular 3D object detection. We propose to leverage these contexts to improve detection performance in a top-down manner. Our proposed approach is motivated by a strong empirical upper-bound analysis with SOTA bottom-up monocular 3D object detectors." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 497, + 547, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 497, + 547, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 497, + 547, + 700 + ], + "type": "text", + "content": "The empirical upper-bound experiment. We analyze vehicle detection performance on the well-established KITTI validation set [5-7]. We start with the recently proposed MonoCon [30] because it achieves SOTA performance with a very simple design. By using MonoCon's prediction results as bottom-up 3D anchors, we sample 3D bounding box proposals along both the " + }, + { + "bbox": [ + 304, + 497, + 547, + 700 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 497, + 547, + 700 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 497, + 547, + 700 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 304, + 497, + 547, + 700 + ], + "type": "text", + "content": " axes (i.e., in the bird-eye's view) with a simple strategy. First, we define a 2D local grid with a range (e.g., 2 meter) and a stride (e.g., 0.1 meter). For each bottom-up anchor, with its center located at the local-grid origin, we replicate the anchor at each grid vertex without changing its size, orientation and prediction score. We use all the generated 3D bounding boxes as top-down proposals and compute the empirical upper-bound of 3D detection performance by searching for the best match within top-down proposals for each ground-truth 3D object bounding box based on 3D Intersection-over-Union (3D IoU)." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "content": "A strong observation from the experiment. As shown" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 693, + 288, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 693, + 288, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 693, + 288, + 712 + ], + "type": "text", + "content": "*Work partially conducted during an internship of X. 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RangeStrideEasyModerateHard#Bboxesmean IoUavg
MonoCon [30]26.3319.0115.98n-
± 20.176.98↑50.6564.93↑45.9256.91↑40.931600·n0.931
± 1.50.176.45↑50.1262.27↑43.2654.34↑38.36900·n0.931
± 1.50.274.00↑47.6761.78↑42.7753.64↑37.66225·n0.868
± 1.50.364.80↑38.4756.20↑37.1950.66↑34.68121·n0.812
± 1.50.554.00↑27.6745.93↑26.9240.99↑25.0149·n0.714
± 1.50.7541.58↑15.2534.44↑15.4330.12↑14.1425·n0.612
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However, this improvement comes at a cost: 1) the proposal verification stage experiences significant increases in number of bounding box proposals, and 2) a more powerful refinement module is required to handle highly overlapped boxes." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 303, + 287, + 447 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 303, + 287, + 447 + ], + "spans": [ + { + "bbox": [ + 46, + 303, + 287, + 447 + ], + "type": "text", + "content": "in Table 1, despite the evaluation result of initial bottom-up proposals is relatively low in 3D average precision " + }, + { + "bbox": [ + 46, + 303, + 287, + 447 + ], + "type": "inline_equation", + "content": "(AP_{3D})" + }, + { + "bbox": [ + 46, + 303, + 287, + 447 + ], + "type": "text", + "content": " (e.g., 19.01 in Moderate settings), most of predicted 3D centers are already in the close proximity of the GT ones. An empirical upper-bound of 34.4 " + }, + { + "bbox": [ + 46, + 303, + 287, + 447 + ], + "type": "inline_equation", + "content": "AP_{3D}" + }, + { + "bbox": [ + 46, + 303, + 287, + 447 + ], + "type": "text", + "content": " can be achieved even with a coarse sampling scheme (e.g., the last row), which is significantly higher than SOTA methods. We also obtained similar observations from other backbone 3D object detectors such as the MonoDLE [39] and the SMOKE [33]. These strong empirical observations demonstrate the potential of integrating the bottom-up initial proposals with top-down sampling and verification." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 449, + 287, + 614 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 449, + 287, + 614 + ], + "spans": [ + { + "bbox": [ + 46, + 449, + 287, + 614 + ], + "type": "text", + "content": "The challenge in the 3D-to-2D proposal verification. The 3D-to-2D proposal verification phase can be treated as a 3D bounding box denoising process, as we want to search for the \"best\" bounding boxes from the top-down proposal set. This process is extremely challenging, as the proposals generated from the same bottom-up anchor are highly overlapped in both 3D and 2D (after projection), which leads to the long-standing problem of handling the \"crowd\" in detection. To quantitatively analyze the overlap extent after projection for top-down proposals, we consider one proposal and its top-" + }, + { + "bbox": [ + 46, + 449, + 287, + 614 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 449, + 287, + 614 + ], + "type": "text", + "content": " overlapping neighbors in terms of Intersection-over-Union (IoU), which is denoted by " + }, + { + "bbox": [ + 46, + 449, + 287, + 614 + ], + "type": "inline_equation", + "content": "\\mathrm{IoU}_{avg}^k" + }, + { + "bbox": [ + 46, + 449, + 287, + 614 + ], + "type": "text", + "content": " as the average IoU over the top-" + }, + { + "bbox": [ + 46, + 449, + 287, + 614 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 449, + 287, + 614 + ], + "type": "text", + "content": " neighbors. The last column in Table 1 shows the statistics." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 617, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 713 + ], + "type": "text", + "content": "The statistics clearly demonstrates the difficulty of denoising densely generated top-down proposal set (e.g., stride=0.1, IoU5 = 0.931). Even for a relative sparse generated top-down proposal set (e.g., stride=0.75, IoU5 = 0.612), the challenge still exists because proposals sampled in front and behind of the same anchor will almost collapse to the same 2D bounding box, especially when they are far away from the camera. So, how can we" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": "encode the 3D bounding box proposal for verification under the monocular setting? From this perspective, we note that many methods that work well in multi-view 3D object detection are often not applicable for monocular 3D objection because they mainly rely on features that are obtained by fusing projection features from multi-view feature maps." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 144, + 545, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 144, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 304, + 144, + 545, + 323 + ], + "type": "text", + "content": "Based on the intuition that even though highly overlapped proposals have similar appearance features, their inherent 3D-to-2D geometric features (e.g. 3D location, projected geometry, etc.) are extremely different, we propose to fuse these 3D-to-2D geometric feature with their correspondent appearance features to learn discriminative features for bounding box denoising. We present a method of using the Perceiver I/O model [20] to effectively fuse these contexts, as Perceiver has shown strong capabilities to fuse multi-modal inputs. With the encoded latent representation of a proposal, the verification head is implemented by a self-attention module (see the top in Fig. 1). The proposed method is named as MonoXiver, indicating its general applicability to any backbone monocular 3D detectors and the integration of the Perceiver model." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 323, + 545, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 323, + 545, + 431 + ], + "spans": [ + { + "bbox": [ + 304, + 323, + 545, + 431 + ], + "type": "text", + "content": "In experiments, we evaluate our proposed MonoXiver on the well-established KITTI benchmark [14] and the challenging large-scale Waymo [51] dataset with various backbone monocular 3D detectors. It achieves consistent and significant performance improvement on both datasets with limited computation overhead. Moreover, it achieves the 1st place among monocular methods on the KITTI vehicle detection benchmark, outperforming the previous works by a large margin." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 442, + 518, + 454 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 442, + 518, + 454 + ], + "spans": [ + { + "bbox": [ + 306, + 442, + 518, + 454 + ], + "type": "text", + "content": "2. Related Works and Our Contributions" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "content": "Monocular 3D Object Detection. The problem of monocular 3D object detection is considered ill-posed, prompting recent research efforts to leverage additional information sources, including LiDAR point clouds [4, 10, 19, 28, 45], depth estimation [12, 36, 42, 48, 53, 54, 62], CAD models [25, 34], temporal frames [2], etc. These approaches have shown improved detection performance when compared to purely image-based methods [1, 33, 41, 57]. However, they often come with increased computation load and inference time, making them less practical for real-time applications such as autonomous vehicles. In contrast, purely image-based methods have seen significant performance improvements in the literature by exploiting geometric constraints [26, 35, 41, 47, 59, 60], perspective projections [24, 38], auxiliary training [30], novel loss designs [8, 39, 49] and second-stage processing techniques [23]. These works focus on developing better bottom-up paradigms. Our proposed method, MonoXiver, takes a top-down paradigm, which explores 3D space differently than the aforementioned methods. It provides a generic and highly efficient second-stage refinement module for any pretrained state-of" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6437" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 69, + 541, + 270 + ], + "blocks": [ + { + "bbox": [ + 53, + 69, + 541, + 270 + ], + "lines": [ + { + "bbox": [ + 53, + 69, + 541, + 270 + ], + "spans": [ + { + "bbox": [ + 53, + 69, + 541, + 270 + ], + "type": "image", + "image_path": "e63afead46451d0cdfd33b3caeb7df300e76ca24ba393f232443b157b3b1af42.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 277, + 547, + 327 + ], + "lines": [ + { + "bbox": [ + 46, + 277, + 547, + 327 + ], + "spans": [ + { + "bbox": [ + 46, + 277, + 547, + 327 + ], + "type": "text", + "content": "Figure 1: Illustration of the proposed MonoXiver method. MonoXiver is built for any off-the-shelf backbone monocular 3D object detectors. It consists of a 2D-to-3D proposal generation phase using a bottom-up anchoring and top-down sampling strategy, and a 3D-to-2D proposal verification (or denoising) phase using the Perceiver I/O [20] with a carefully designed 3D/2D input space to address the unique challenges. See text for details." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 347, + 287, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 347, + 287, + 371 + ], + "spans": [ + { + "bbox": [ + 46, + 347, + 287, + 371 + ], + "type": "text", + "content": "the-art monocular 3D object detection method, making it a complementary approach." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 371, + 288, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 371, + 288, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 371, + 288, + 693 + ], + "type": "text", + "content": "Bird's-Eye-View 3D Object Detection. Bird's-Eye-View (BEV) 3D object detection [40] has recently gained significant attention as it provides a physical-interpretable feature space for integrating data from diverse sensors [27, 31, 44, 56] and modalities [13, 18]. To enable the learning of a physical-interpretable feature space, accurate physical measurements from depth perception systems such as multi-view cameras and LiDAR are crucial [16]. However, detecting 3D objects in BEV is challenging for monocular systems due to the intrinsic depth ambiguity. Directly accumulating image features based on projection reference points similar to recent query-based multi-view 3D detectors [31, 56] might fail because of lacking stereo-matching mechanism to resolve the depth ambiguity. To overcome this issue, recent BEV-based monocular methods [9, 45, 55] lift the image feature space to voxel-represented world-space using monocular depth estimation models. Our proposed method, MonoXiver, samples top-down proposals based on bottom-up initial proposals in BEV space. Unlike prior arts [9, 45, 55] that extract features represented in world-space, MonoXiver's top-down proposals extract features from both projected appearance features and inherent geometric features. We explore to address the challenging intrinsic feature ambiguity problem by applying a Perceiver-like attention mechanism to query informative features for 3D bounding box verification and refinement without the need for dense depth supervision." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 694, + 286, + 706 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 694, + 286, + 706 + ], + "spans": [ + { + "bbox": [ + 47, + 694, + 286, + 706 + ], + "type": "text", + "content": "Transformers for Multi-modal Data. Transformers [52]," + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 347, + 545, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 347, + 545, + 502 + ], + "spans": [ + { + "bbox": [ + 304, + 347, + 545, + 502 + ], + "type": "text", + "content": "known for their powerful attention mechanism, have been successfully applied in multiple research areas and applications [3,11,32,50]. With the powerful attention mechanism, transformers can conveniently align multi-modal structured data, enabling the generation of universal multi-modal representation. The recent proposed Perceiver [20, 21] extends the transformers' querying mechanism and makes it capable of efficiently handling data from arbitrary settings. In our work, we adapt Perceiver to fuse appearance features and geometric features from the same bounding box to generate appearance-geometric aligned representation, which is then used as queries for the down-stream 3D bounding box refinement task." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 502, + 545, + 527 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 502, + 545, + 527 + ], + "spans": [ + { + "bbox": [ + 304, + 502, + 545, + 527 + ], + "type": "text", + "content": "Our Contributions. MonoXiver makes three main contributions to the field of monocular 3D object detection:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 531, + 545, + 713 + ], + "type": "list", + "angle": 0, + "index": 9, + "blocks": [ + { + "bbox": [ + 306, + 531, + 545, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 531, + 545, + 638 + ], + "spans": [ + { + "bbox": [ + 306, + 531, + 545, + 638 + ], + "type": "text", + "content": "- We conduct a new and strong empirical upper-bound analysis for state-of-the-art monocular 3D object detectors. We demonstrate that a simple, universally applicable sampling strategy can lead to consistent and significant performance improvement in an ideal situation. Based on these observations, we propose to explore the top-down, stage-wise detection paradigm with 2D-to-3D proposal generation and 3D-to-2D proposal verification for monocular 3D object detection." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 642, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 642, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 642, + 545, + 713 + ], + "type": "text", + "content": "- To address the challenge at the bounding box denoising stage, we propose to learn discriminative features by enhancing appearance features with 3D-to-2D inherent geometric features. We therefore propose a carefully-designed module with the integration of the powerful Perceiver and self-attention mechanism. The resulting mod" + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6438" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 55, + 72, + 286, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 72, + 286, + 96 + ], + "spans": [ + { + "bbox": [ + 55, + 72, + 286, + 96 + ], + "type": "text", + "content": "ule can be applied generically to any off-the-shelf monocular 3D object detectors." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 99, + 286, + 183 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 99, + 286, + 183 + ], + "spans": [ + { + "bbox": [ + 47, + 99, + 286, + 183 + ], + "type": "text", + "content": "- Extensive experiments demonstrate the effectiveness and efficiency of our proposed method, MonoXiver, under a separate two-stage training setting. It achieves consistent improvement with limited overhead on both KITTI and Waymo dataset. It achieves the 1st place among monocular methods on the KITTI vehicle detection benchmark, outperforming the previous works by a large margin." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 192, + 113, + 205 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 192, + 113, + 205 + ], + "spans": [ + { + "bbox": [ + 47, + 192, + 113, + 205 + ], + "type": "text", + "content": "3. Approach" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 212, + 286, + 260 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 212, + 286, + 260 + ], + "spans": [ + { + "bbox": [ + 47, + 212, + 286, + 260 + ], + "type": "text", + "content": "In this section, we first present the straightforward 2D-to-3D proposal generation on top of a backbone monocular 3D object detector. Then, we present the details of the proposed MonoXiver method (Fig. 1)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 266, + 233, + 277 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 266, + 233, + 277 + ], + "spans": [ + { + "bbox": [ + 47, + 266, + 233, + 277 + ], + "type": "text", + "content": "3.1. The 2D-to-3D Proposal Generation" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "spans": [ + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "text", + "content": " be an RGB input image defined on the domain " + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "inline_equation", + "content": "\\Lambda" + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "text", + "content": ". The goal of monocular 3D object detection is to detect 3D bounding boxes, along with their class labels denoted by " + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "inline_equation", + "content": "\\ell" + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "text", + "content": " for each object instance in " + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "text", + "content": ". The 3D bounding box is parameterized by the 3D center position " + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "inline_equation", + "content": "\\mathbf{P} = (X,Y,Z)" + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "text", + "content": " in meters, the shape dimensions " + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "inline_equation", + "content": "\\mathbf{D} = (h,w,l)" + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "text", + "content": " in meters, and the observation angle " + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "inline_equation", + "content": "\\alpha \\in [-\\pi ,\\pi ]" + }, + { + "bbox": [ + 47, + 284, + 286, + 379 + ], + "type": "text", + "content": ", all measured in the camera coordinate system." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 380, + 286, + 511 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 380, + 286, + 511 + ], + "spans": [ + { + "bbox": [ + 46, + 380, + 286, + 511 + ], + "type": "text", + "content": "For simplicity, consider the pure image-based settings, a monocular 3D object detector often consists of two main components in inference: the feature backbone (e.g., the DLA34 network [58]), denoted by " + }, + { + "bbox": [ + 46, + 380, + 286, + 511 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_I" + }, + { + "bbox": [ + 46, + 380, + 286, + 511 + ], + "type": "text", + "content": " for computing deep features from the raw image " + }, + { + "bbox": [ + 46, + 380, + 286, + 511 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 46, + 380, + 286, + 511 + ], + "type": "text", + "content": ", and the regression heads for inferring the 3D bounding box parameters using the computed feature map. We generate bottom-up proposals using one off-the-shelf backbone monocular 3D object detector which is first trained following its own training receipts. Without loss of generality, we consider one of its detected 3D bounding boxes indexed by " + }, + { + "bbox": [ + 46, + 380, + 286, + 511 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 380, + 286, + 511 + ], + "type": "text", + "content": " in an image " + }, + { + "bbox": [ + 46, + 380, + 286, + 511 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 46, + 380, + 286, + 511 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 121, + 517, + 286, + 529 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 121, + 517, + 286, + 529 + ], + "spans": [ + { + "bbox": [ + 121, + 517, + 286, + 529 + ], + "type": "interline_equation", + "content": "\\mathbb {B} _ {i} = \\left(\\ell_ {i}, \\mathbf {P} _ {i}, \\mathbf {D} _ {i}, \\alpha_ {i}\\right), \\tag {1}", + "image_path": "c7f367fda0d7a67329623ced8bee1c9035e0ca994cc182cc2270dc654570ddb7.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "text", + "content": "As shown in Table 1, the top-down sampling with a bottom-up anchor proposal is a straightforward process. We start by generating a 2D local grid in the " + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "inline_equation", + "content": "X - Z" + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "text", + "content": " plane (i.e. in the bird's-eye-view, BEV), centered at the position " + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "inline_equation", + "content": "(X,Z)" + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "text", + "content": " of the anchor box " + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbb{B}" + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "text", + "content": ". To accomplish this, we specify a search range and a stride. Based on the trade-off between the empirical upper bound and the computing overhead and the mean IoU among the proposals, we adopt a conservative strategy using the search range " + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\pm 1.5" + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "text", + "content": " meters and the stride 0.75, which will generate 25 proposals per bottom-up anchor (inclusive). We then place the anchor box " + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbb{B}" + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "text", + "content": " at the 25 grid points, with only the position " + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{P}" + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "text", + "content": " updated. To simplify the notation, we do not differentiate between the bottom-up anchor and the top-down sampled proposal, and we generally index them using " + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 534, + 286, + 713 + ], + "type": "text", + "content": ", unless otherwise stated." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 72, + 493, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 493, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 493, + 84 + ], + "type": "text", + "content": "3.2. The 3D-to-2D Proposal Verification" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 91, + 545, + 162 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 91, + 545, + 162 + ], + "spans": [ + { + "bbox": [ + 305, + 91, + 545, + 162 + ], + "type": "text", + "content": "The proposal verification will rely essentially on the information from the input 2D images in purely monocular 3D object detection. Due to the aforementioned unique challenges in the 3D proposal space, we utilize Perceiver I/O [20] to design an expressive proposal representation learning scheme." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 178, + 443, + 190 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 178, + 443, + 190 + ], + "spans": [ + { + "bbox": [ + 306, + 178, + 443, + 190 + ], + "type": "text", + "content": "3.2.1 Proposal Representation" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 198, + 545, + 221 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 198, + 545, + 221 + ], + "spans": [ + { + "bbox": [ + 305, + 198, + 545, + 221 + ], + "type": "text", + "content": "As illustrated in Fig. 1, we utilize three types of features in encoding a 3D bounding box proposal " + }, + { + "bbox": [ + 305, + 198, + 545, + 221 + ], + "type": "inline_equation", + "content": "\\mathbb{B}" + }, + { + "bbox": [ + 305, + 198, + 545, + 221 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 229, + 545, + 642 + ], + "type": "list", + "angle": 0, + "index": 18, + "blocks": [ + { + "bbox": [ + 306, + 229, + 545, + 302 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 229, + 545, + 302 + ], + "spans": [ + { + "bbox": [ + 306, + 229, + 545, + 302 + ], + "type": "text", + "content": "- The 3D Shape Features represented by " + }, + { + "bbox": [ + 306, + 229, + 545, + 302 + ], + "type": "inline_equation", + "content": "(\\mathbf{P}, \\mathbf{D}, \\alpha)" + }, + { + "bbox": [ + 306, + 229, + 545, + 302 + ], + "type": "text", + "content": ". It is a 7-dim vector. It encodes where the proposal is in the 3D space (the camera coordinate system), as well as its 3D occupancy. The position " + }, + { + "bbox": [ + 306, + 229, + 545, + 302 + ], + "type": "inline_equation", + "content": "\\mathbf{P}" + }, + { + "bbox": [ + 306, + 229, + 545, + 302 + ], + "type": "text", + "content": " is empirically normalized by the typical detection range (e.g., " + }, + { + "bbox": [ + 306, + 229, + 545, + 302 + ], + "type": "inline_equation", + "content": "X, Y, Z" + }, + { + "bbox": [ + 306, + 229, + 545, + 302 + ], + "type": "text", + "content": " are normalized by 50, 2 and 80 meters respectively)." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 306, + 545, + 389 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 306, + 545, + 389 + ], + "spans": [ + { + "bbox": [ + 306, + 306, + 545, + 389 + ], + "type": "text", + "content": "- The 2D Projection Points from the 8 corners and the center of the 3D bounding box (with known camera intrinsic matrix). It is an 18-dim vector in the image coordinate system, and normalized by the image size. This 9-point projection provides the finegrained placement of a proposal in the 2D space, that is the geometric bond between a proposal in the 3D space and its 2D placement." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 394, + 545, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 394, + 545, + 502 + ], + "spans": [ + { + "bbox": [ + 306, + 394, + 545, + 502 + ], + "type": "text", + "content": "- The 2D Bounding Box projected from the proposal and truncated by the image boundary. We use the left-top and right-bottom two points to encode a 2D bounding box. It gives a 4-dim vector normalized by the image size. For a proposal whose 2D projection is entirely inside the image plane, the two points of the 2D bounding box will be just redundant with respect to the 9 project points. Otherwise, the truncation points on the image boundary will facilitate the learning to be truncation aware." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 506, + 545, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 506, + 545, + 555 + ], + "spans": [ + { + "bbox": [ + 306, + 506, + 545, + 555 + ], + "type": "text", + "content": "- The Appearance Features of the 9 projection points. We directly extract features from the final layer of the feature backbone " + }, + { + "bbox": [ + 306, + 506, + 545, + 555 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_I" + }, + { + "bbox": [ + 306, + 506, + 545, + 555 + ], + "type": "text", + "content": ". If a projection point is out of the image plane, we encode it using an all-zero vector." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 559, + 545, + 642 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 559, + 545, + 642 + ], + "spans": [ + { + "bbox": [ + 306, + 559, + 545, + 642 + ], + "type": "text", + "content": "- The RoI Appearance Features of the 2D bounding box. We use the RoIAign features [17] extracted from the final layer of the feature backbone " + }, + { + "bbox": [ + 306, + 559, + 545, + 642 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_I" + }, + { + "bbox": [ + 306, + 559, + 545, + 642 + ], + "type": "text", + "content": ". Since the 2D IoU overlapping between proposals is high on average (e.g., 0.612 in Table 1), we use a finer grid, " + }, + { + "bbox": [ + 306, + 559, + 545, + 642 + ], + "type": "inline_equation", + "content": "14 \\times 14" + }, + { + "bbox": [ + 306, + 559, + 545, + 642 + ], + "type": "text", + "content": ", in computing the RoIAign features, such that the extracted appearance features contain \"sufficient\" details." + } + ] + } + ], + "index": 17 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 658, + 429, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 658, + 429, + 670 + ], + "spans": [ + { + "bbox": [ + 306, + 658, + 429, + 670 + ], + "type": "text", + "content": "3.2.2 Proposal Embedding" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "content": " be the total number of proposals in an image " + }, + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "content": ". With the above representation scheme, denote by " + }, + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "inline_equation", + "content": "f_{N\\times 29}^{geo}" + }, + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "content": " the geometric parameter matrix from the first three items above," + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6439" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "and by " + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "inline_equation", + "content": "f_{N \\times 9 \\times C}^{pt}" + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": " the projection point appearance feature matrix (where " + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": " is the number of channels of the final layer of the feature backbone, e.g., " + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "inline_equation", + "content": "C = 64" + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "), and by " + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "inline_equation", + "content": "f_{N \\times (14 \\times 14) \\times C}^{roi}" + }, + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": " the RoI feature matrix. Before applying the Perceiver I/O model, we embed the three to form \"tokens\" using multi-layer perceptron (MLP)." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 59, + 144, + 249, + 158 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 144, + 249, + 158 + ], + "spans": [ + { + "bbox": [ + 59, + 144, + 249, + 158 + ], + "type": "text", + "content": "For the geometric parameters " + }, + { + "bbox": [ + 59, + 144, + 249, + 158 + ], + "type": "inline_equation", + "content": "f_{N \\times 29}^{geo}" + }, + { + "bbox": [ + 59, + 144, + 249, + 158 + ], + "type": "text", + "content": ", we have," + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 82, + 167, + 287, + 186 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 82, + 167, + 287, + 186 + ], + "spans": [ + { + "bbox": [ + 82, + 167, + 287, + 186 + ], + "type": "interline_equation", + "content": "f _ {N \\times 2 9} ^ {\\text {g e o}} \\xrightarrow {\\mathrm {M L P}} z _ {N \\times (g \\times d)} \\xrightarrow {\\text {R e a r r a n g e}} \\mathbf {f} _ {g \\times N \\times d} ^ {\\text {g e o}}, \\tag {2}", + "image_path": "dc817eba30bc6e46f961e29b344db5a2c766631f72b4aa507d713dcc17b9db5b.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 194, + 287, + 253 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 194, + 287, + 253 + ], + "spans": [ + { + "bbox": [ + 46, + 194, + 287, + 253 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 194, + 287, + 253 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 194, + 287, + 253 + ], + "type": "text", + "content": " is the hidden dimension (e.g., " + }, + { + "bbox": [ + 46, + 194, + 287, + 253 + ], + "type": "inline_equation", + "content": "d = 256" + }, + { + "bbox": [ + 46, + 194, + 287, + 253 + ], + "type": "text", + "content": "). " + }, + { + "bbox": [ + 46, + 194, + 287, + 253 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 46, + 194, + 287, + 253 + ], + "type": "text", + "content": " is the group number, similar in spirit to the multi-head setup in the self-attention. We want to encode the geometric parameters in different latent spaces to account for the large variations in the proposal space (e.g., " + }, + { + "bbox": [ + 46, + 194, + 287, + 253 + ], + "type": "inline_equation", + "content": "g = 4" + }, + { + "bbox": [ + 46, + 194, + 287, + 253 + ], + "type": "text", + "content": ")." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 253, + 255, + 267 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 253, + 255, + 267 + ], + "spans": [ + { + "bbox": [ + 59, + 253, + 255, + 267 + ], + "type": "text", + "content": "For the project point features " + }, + { + "bbox": [ + 59, + 253, + 255, + 267 + ], + "type": "inline_equation", + "content": "f_{N \\times 9 \\times C}^{pt}" + }, + { + "bbox": [ + 59, + 253, + 255, + 267 + ], + "type": "text", + "content": ", we have," + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 81, + 277, + 287, + 295 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 81, + 277, + 287, + 295 + ], + "spans": [ + { + "bbox": [ + 81, + 277, + 287, + 295 + ], + "type": "interline_equation", + "content": "f _ {N \\times 9 \\times C} ^ {p t} \\xrightarrow {\\mathrm {M L P}} z _ {N \\times 9 \\times d} \\xrightarrow {\\text {R e a r r a n g e}} \\mathbf {f} _ {9 \\times N \\times d} ^ {p t}, \\tag {3}", + "image_path": "0ff79ce672cd09bf01747a7079bdc5ecef6d3fb67840888bfc930b6379f7c918.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 304, + 287, + 326 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 304, + 287, + 326 + ], + "spans": [ + { + "bbox": [ + 47, + 304, + 287, + 326 + ], + "type": "text", + "content": "where we reuse " + }, + { + "bbox": [ + 47, + 304, + 287, + 326 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 47, + 304, + 287, + 326 + ], + "type": "text", + "content": " to denote the latent features for simplicity and without confusion." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 59, + 327, + 244, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 327, + 244, + 342 + ], + "spans": [ + { + "bbox": [ + 59, + 327, + 244, + 342 + ], + "type": "text", + "content": "For the RoI features " + }, + { + "bbox": [ + 59, + 327, + 244, + 342 + ], + "type": "inline_equation", + "content": "f_{N\\times (14\\times 14)\\times C}^{roi}" + }, + { + "bbox": [ + 59, + 327, + 244, + 342 + ], + "type": "text", + "content": " , we have," + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 74, + 352, + 287, + 369 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 74, + 352, + 287, + 369 + ], + "spans": [ + { + "bbox": [ + 74, + 352, + 287, + 369 + ], + "type": "interline_equation", + "content": "f _ {N \\times (1 4 \\times 1 4) \\times C} ^ {r o i} \\xrightarrow {\\mathrm {M L P}} z _ {N \\times d} \\xrightarrow {\\text {R e a r r a g e}} \\mathbf {f} _ {1 \\times N \\times d} ^ {r o i}. \\tag {4}", + "image_path": "2ab125eef43e0ab1f8e67d4e87b248f1938ee542ee86333bc9458bd3f33d6b61.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 384, + 244, + 396 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 384, + 244, + 396 + ], + "spans": [ + { + "bbox": [ + 47, + 384, + 244, + 396 + ], + "type": "text", + "content": "3.2.3 Intra-Proposal Attention via Perceiver" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 403, + 287, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 403, + 287, + 510 + ], + "spans": [ + { + "bbox": [ + 46, + 403, + 287, + 510 + ], + "type": "text", + "content": "With the above proposal embedding, before the proposal verification, our goal is to compute a final latent feature representation in the " + }, + { + "bbox": [ + 46, + 403, + 287, + 510 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 403, + 287, + 510 + ], + "type": "text", + "content": "-dim space for each proposal by fusing information from the geometric encoding, projection-point-based appearance encoding and RoI-based appearance encoding (i.e., the intra-proposal attention), such that we can address the aforementioned unique challenges in the proposal space. We leverage the Perceiver I/O model for this intra-proposal attention." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 511, + 287, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 511, + 287, + 594 + ], + "spans": [ + { + "bbox": [ + 46, + 511, + 287, + 594 + ], + "type": "text", + "content": "The Perceiver first fuses the projection-point appearance encoding " + }, + { + "bbox": [ + 46, + 511, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\mathbf{f}_{9\\times N\\times d}^{pt}" + }, + { + "bbox": [ + 46, + 511, + 287, + 594 + ], + "type": "text", + "content": " and the geometric encoding " + }, + { + "bbox": [ + 46, + 511, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\mathbf{f}_{g\\times N\\times d}^{geo}" + }, + { + "bbox": [ + 46, + 511, + 287, + 594 + ], + "type": "text", + "content": ". As shown in Fig. 1, it consists of a cross-attention by treating the former as Query (consisting of 9 projection-point tokens) and computing Key and Value from the latter (consisting of " + }, + { + "bbox": [ + 46, + 511, + 287, + 594 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 46, + 511, + 287, + 594 + ], + "type": "text", + "content": " geometric tokens), followed by a self-attention module. We have," + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 61, + 603, + 287, + 620 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 603, + 287, + 620 + ], + "spans": [ + { + "bbox": [ + 61, + 603, + 287, + 620 + ], + "type": "interline_equation", + "content": "\\left(\\mathbf {f} _ {9 \\times N \\times d} ^ {p t}, \\mathbf {f} _ {g \\times N \\times d} ^ {g e o}\\right) \\xrightarrow {\\text {C r o s s - A t t n}} \\cdot \\xrightarrow {\\text {S e l f - A t t n}} \\mathbf {F} _ {9 \\times N \\times d} ^ {g e o - p t}, \\tag {5}", + "image_path": "a365d6a6fc977f4bfcb0605d928d3df844b9d680658e7e40d164e8484882b424.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 629, + 286, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 629, + 286, + 641 + ], + "spans": [ + { + "bbox": [ + 47, + 629, + 286, + 641 + ], + "type": "text", + "content": "which results in geometry-aware projection-point encoding." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 641, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 641, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 47, + 641, + 287, + 689 + ], + "type": "text", + "content": "Next, the Perceiver fuses the RoI appearance encoding " + }, + { + "bbox": [ + 47, + 641, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{f}_{1\\times N\\times d}^{roi}" + }, + { + "bbox": [ + 47, + 641, + 287, + 689 + ], + "type": "text", + "content": " as the 1-token Query with the 9-token geometry-aware projection-point encoding using a cross attention module," + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 82, + 698, + 287, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 82, + 698, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 82, + 698, + 287, + 715 + ], + "type": "interline_equation", + "content": "\\left(\\mathbf {f} _ {1 \\times N \\times d} ^ {r o i}, \\mathbf {F} _ {9 \\times N \\times d} ^ {g e o - p t}\\right) \\xrightarrow {\\text {C r o s s - A t t n}} \\mathbf {F} _ {1 \\times N \\times d} ^ {g e o - p t - r o i}, \\tag {6}", + "image_path": "aef4cf631cf054b9a2a8d0a4dc53b4ad4aa984fcc0ccbcaf965a0a97ca948beb.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 72, + 545, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 108 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 108 + ], + "type": "text", + "content": "which results in the " + }, + { + "bbox": [ + 305, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 305, + 72, + 545, + 108 + ], + "type": "text", + "content": "-dim latent features for each proposal, which fuse the three types of information sources: geometry, point-level appearance and region-level appearance." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 108, + 545, + 132 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 108, + 545, + 132 + ], + "spans": [ + { + "bbox": [ + 305, + 108, + 545, + 132 + ], + "type": "text", + "content": "In the above, the cross-attention and self-attention modules are based on the standard formulation [52]." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 147, + 444, + 158 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 147, + 444, + 158 + ], + "spans": [ + { + "bbox": [ + 306, + 147, + 444, + 158 + ], + "type": "text", + "content": "3.2.4 Inter-Proposal Attention" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 165, + 545, + 260 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 165, + 545, + 260 + ], + "spans": [ + { + "bbox": [ + 304, + 165, + 545, + 260 + ], + "type": "text", + "content": "With all the above process, each proposal is still encoded individually with the hope of fusing geometry, point-level appearance and region-level appearance information in a semantically meaningful way via the Perceiver I/O model. With the compact latent vector computed for each proposal in " + }, + { + "bbox": [ + 304, + 165, + 545, + 260 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{1\\times N\\times d}^{geo-pt-rot}" + }, + { + "bbox": [ + 304, + 165, + 545, + 260 + ], + "type": "text", + "content": ", their interactions need to be taken into account in order to resolve their \"crowding\" issue at the underlying scene level." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 261, + 545, + 297 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 261, + 545, + 297 + ], + "spans": [ + { + "bbox": [ + 305, + 261, + 545, + 297 + ], + "type": "text", + "content": "To that end, we treat each proposal as a \"token\" and apply a standard self-attention module to capture the interproposal attention," + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 329, + 306, + 545, + 323 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 329, + 306, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 329, + 306, + 545, + 323 + ], + "type": "interline_equation", + "content": "\\mathbf {F} _ {1 \\times N \\times d} ^ {\\text {g e o - p t - r o i}} \\xrightarrow {\\text {R e a r r a n g e}} \\mathbf {F} _ {N \\times d} ^ {\\text {g e o - p t - r o i}} \\xrightarrow {\\text {S e l f - A t t n}} \\mathbb {F} _ {N \\times d}. \\tag {7}", + "image_path": "82dec0a87c69959eb87a858572639105a47923490485de17433d6c4614e1cbf8.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 336, + 429, + 347 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 336, + 429, + 347 + ], + "spans": [ + { + "bbox": [ + 306, + 336, + 429, + 347 + ], + "type": "text", + "content": "3.2.5 Proposal Verification" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 306, + 354, + 511, + 367 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 354, + 511, + 367 + ], + "spans": [ + { + "bbox": [ + 306, + 354, + 511, + 367 + ], + "type": "text", + "content": "This verification is posed as a regression problem," + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 350, + 375, + 545, + 392 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 375, + 545, + 392 + ], + "spans": [ + { + "bbox": [ + 350, + 375, + 545, + 392 + ], + "type": "interline_equation", + "content": "\\mathbb {F} _ {N \\times d} \\xrightarrow {\\mathrm {M L P s}} \\left(\\mathbf {y} _ {N \\times L}, \\Delta \\mathbf {P} _ {N}, \\Delta \\mathbf {D} _ {N}\\right), \\tag {8}", + "image_path": "83e68015ea097885d19bd6af0fc3c8a9a73ad00e4234ada945fc8672038b2c28.jpg" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "spans": [ + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "type": "text", + "content": " is the total number of categories (e.g., " + }, + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "type": "inline_equation", + "content": "L = 3" + }, + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "type": "text", + "content": " in the KITTI dataset), and " + }, + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "type": "inline_equation", + "content": "\\mathbf{y}_{N\\times L}" + }, + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "type": "text", + "content": " is the classification scores (logits). " + }, + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "type": "inline_equation", + "content": "\\Delta \\mathbf{P}_N" + }, + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "type": "inline_equation", + "content": "\\Delta \\mathbf{D}_N" + }, + { + "bbox": [ + 304, + 399, + 545, + 446 + ], + "type": "text", + "content": " are the position and dimension residuals." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 317, + 448, + 518, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 448, + 518, + 460 + ], + "spans": [ + { + "bbox": [ + 317, + 448, + 518, + 460 + ], + "type": "text", + "content": "Consider a proposal " + }, + { + "bbox": [ + 317, + 448, + 518, + 460 + ], + "type": "inline_equation", + "content": "\\mathbb{B}_i" + }, + { + "bbox": [ + 317, + 448, + 518, + 460 + ], + "type": "text", + "content": " (Eqn. 1), it is verified via," + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 382, + 467, + 545, + 487 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 382, + 467, + 545, + 487 + ], + "spans": [ + { + "bbox": [ + 382, + 467, + 545, + 487 + ], + "type": "interline_equation", + "content": "\\hat {\\ell} _ {i} = \\arg \\max _ {l = 1, \\dots , L} \\mathbf {y} _ {i, l}, \\tag {9}", + "image_path": "268fe2f71c538d126c7e94375a592177b8accac73697001f6680f2330a8309f2.jpg" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 379, + 490, + 545, + 504 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 379, + 490, + 545, + 504 + ], + "spans": [ + { + "bbox": [ + 379, + 490, + 545, + 504 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {P}} _ {i} = \\mathbf {P} _ {i} + \\Delta \\mathbf {P} _ {i}, \\tag {10}", + "image_path": "f30b64ae1ceda113e2301ad117d16a05cbe0eb29beefb8c21fb57f3eb04a71ce.jpg" + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 378, + 508, + 545, + 521 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 378, + 508, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 378, + 508, + 545, + 521 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {D}} _ {i} = \\mathbf {D} _ {i} + \\Delta \\mathbf {D} _ {i}, \\tag {11}", + "image_path": "f5ae220179a164d9277d90c5c3660068bb6235e09c3ac591759d6aa370034019.jpg" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 304, + 532, + 545, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 532, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 532, + 545, + 581 + ], + "type": "text", + "content": "where a proper unnormalization step will be done for " + }, + { + "bbox": [ + 304, + 532, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{P}}_i" + }, + { + "bbox": [ + 304, + 532, + 545, + 581 + ], + "type": "text", + "content": " to counter the normalization step used in the proposal representation (Sec. 3.2.1). Based on the score " + }, + { + "bbox": [ + 304, + 532, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathbf{y}_{i,\\hat{\\ell}_i}" + }, + { + "bbox": [ + 304, + 532, + 545, + 581 + ], + "type": "text", + "content": ", we can keep top-" + }, + { + "bbox": [ + 304, + 532, + 545, + 581 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 532, + 545, + 581 + ], + "type": "text", + "content": " proposals for each anchor position." + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 306, + 587, + 473, + 601 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 587, + 473, + 601 + ], + "spans": [ + { + "bbox": [ + 306, + 587, + 473, + 601 + ], + "type": "text", + "content": "3.3. Details of Training and Testing" + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "For simplicity, we evaluate the proposed MonoXiver in a two-stage setting where the backbone monocular 3D object detector is first trained and kept frozen. Then, the MonoXiver component is trained end-to-end. One of the reasons for this choice is that off-the-shelf backbone monocular 3D object detectors often involve multiple loss functions, and joint training with MonoXiver would require sophisticated tuning of the trade-off parameters for different loss terms. We leave the joint end-to-end training or iterative training," + } + ] + } + ], + "index": 32 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6440" + } + ] + } + ], + "index": 33 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "content": "as done in the early version of Faster RCNN [46] between the region proposal network and the region classification head network, for future work. Additionally, the separate two-stage training may also have advantages in leveraging the set of bottom-up anchor proposals merged from multiple backbone monocular 3D detectors, which we also leave for future work." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 174, + 266, + 187 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 174, + 266, + 187 + ], + "spans": [ + { + "bbox": [ + 47, + 174, + 266, + 187 + ], + "type": "text", + "content": "3.3.1 The Set Prediction Formulation in Training" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 194, + 287, + 326 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 194, + 287, + 326 + ], + "spans": [ + { + "bbox": [ + 46, + 194, + 287, + 326 + ], + "type": "text", + "content": "Based on the separate two-stage setting, the proposed MonoXiver is trained with a fixed set of 3D bounding box proposals and a fixed set of ground-truth 3D bounding boxes. The ground-truth assignment for proposals is needed in training. Two straightforward methods are: using the maximum 3D IoU based assignment, or using the maximum 2D IoU assignment (after projected to the image plane). Due to the \"crowding\" issue in the proposal space, we observe that both of them do not work during our development of the MonoXiver since they will create difficult \"decision boundaries\" for the MonoXiver to learn or fit." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "spans": [ + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "text", + "content": "Since we have the two fixed set as input, we resort to the set prediction formulation used in the DETR framework [3]. Denote by " + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "inline_equation", + "content": "\\Omega_{\\mathbb{B}} = \\{\\mathbb{B}_i\\}_{i=1}^N" + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "text", + "content": " the set of generated proposals, by " + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "inline_equation", + "content": "\\Omega_{\\mathbb{B}^*} = \\{\\mathbb{B}_j^*\\}_{j=1}^M \\cup \\{\\emptyset_j\\}_{j=M+1}^N" + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "text", + "content": " the set of ground-truth 3D bounding boxes padded with " + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "inline_equation", + "content": "N - M" + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "text", + "content": " dummy " + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "inline_equation", + "content": "\\emptyset" + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "text", + "content": " elements. Given a permutation of " + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "text", + "content": " elements, denoted by " + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "text", + "content": " which assigns the " + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "text", + "content": "-th element in the ground-truth set to the " + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "inline_equation", + "content": "\\sigma(i)" + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "text", + "content": "-the element in the proposal set, the loss for the one-to-one bipartite matching between " + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "inline_equation", + "content": "\\mathbb{B}_i^*" + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "inline_equation", + "content": "\\mathbb{B}_{\\sigma(i)}" + }, + { + "bbox": [ + 46, + 327, + 289, + 436 + ], + "type": "text", + "content": " is defined by," + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 56, + 445, + 287, + 459 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 445, + 287, + 459 + ], + "spans": [ + { + "bbox": [ + 56, + 445, + 287, + 459 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {m a t c h}} \\left(\\mathbb {B} _ {i} ^ {*}, \\mathbb {B} _ {\\sigma (i)}\\right) = \\mathbf {1} _ {\\ell_ {i} ^ {*} \\neq \\emptyset} \\cdot \\left(- \\lambda_ {1} \\cdot \\hat {p} _ {\\sigma (i)} \\left(\\ell_ {i} ^ {*}\\right) + \\right. \\tag {12}", + "image_path": "966c291d61a938e40871390c777684bb22efb1586e41c527303942fd05b20917.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 132, + 460, + 277, + 475 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 132, + 460, + 277, + 475 + ], + "spans": [ + { + "bbox": [ + 132, + 460, + 277, + 475 + ], + "type": "interline_equation", + "content": "\\lambda_ {2} \\cdot \\mathcal {L} _ {b b o x} ^ {2 D} + \\lambda_ {3} \\cdot \\mathcal {L} _ {i o u} ^ {2 D} + \\lambda_ {4} \\cdot \\mathcal {L} _ {i o u} ^ {3 D}),", + "image_path": "696a369769145d5c3b061f7852326a3d51c3c0b79c165c5ecf4e19f84d8322c9.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "spans": [ + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\hat{p}_{\\sigma(i)}(\\ell_i^*)" + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "text", + "content": " is computed using " + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathbf{y}_{\\sigma(i)}" + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "text", + "content": " (Eqn. 8) via Softmax. " + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{bbox}^{2D}" + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "text", + "content": " represents the normalized L1 2D bounding box, and " + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{iou}^{2D}" + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{iou}^{3D}" + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "text", + "content": " the IoU loss in 2D and 3D respectively. " + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\lambda_1" + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "inline_equation", + "content": "\\lambda_4" + }, + { + "bbox": [ + 47, + 486, + 287, + 534 + ], + "type": "text", + "content": " are the trade-off parameters." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 552, + 252, + 563 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 552, + 252, + 563 + ], + "spans": [ + { + "bbox": [ + 47, + 552, + 252, + 563 + ], + "type": "text", + "content": "3.3.2 Loss Functions for Proposal Verification" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 571, + 287, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 571, + 287, + 594 + ], + "spans": [ + { + "bbox": [ + 46, + 571, + 287, + 594 + ], + "type": "text", + "content": "For the three outputs in Eqn. 8, we have three loss terms as follows," + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 108, + 597, + 287, + 610 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 108, + 597, + 287, + 610 + ], + "spans": [ + { + "bbox": [ + 108, + 597, + 287, + 610 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathcal {L} _ {\\text {c l s}} + \\mathcal {L} _ {\\text {s i z e}} + \\lambda \\cdot \\mathcal {L} _ {\\text {l o c}} \\tag {13}", + "image_path": "de93c9803d5dcf232ef543f73e6f70d7bedac6dfa210375255bfc58e41371e2d.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{cls}" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " is the Focal Loss [29] with the " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " value of 0.5 to balance the number of positive and negative samples. The Focal loss is used due to the imbalance introduced by the explicit top-down proposal generation. " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{size}" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " are " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{loc}" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " are the loss functions for the 3D size and the 3D center respectively. " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " is an trade-off hyper-parameter. We use " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\ell_1" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " loss for " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{size}" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{loc}" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": ". We set " + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\lambda = 5" + }, + { + "bbox": [ + 46, + 617, + 288, + 713 + ], + "type": "text", + "content": " to induce the model to focus more on the 3D localization refinement task." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 72, + 377, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 377, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 377, + 84 + ], + "type": "text", + "content": "3.3.3 Training" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 91, + 547, + 283 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 91, + 547, + 283 + ], + "spans": [ + { + "bbox": [ + 304, + 91, + 547, + 283 + ], + "type": "text", + "content": "MonoXiver is trained using a total of 8 GPUs, with a batch size of 64 for 24 epochs on KITTI (12 epochs on Waymo) using the AdamW optimizer. The optimizer is set with " + }, + { + "bbox": [ + 304, + 91, + 547, + 283 + ], + "type": "inline_equation", + "content": "(\\beta_{1},\\beta_{2}) = (0.95,0.99)" + }, + { + "bbox": [ + 304, + 91, + 547, + 283 + ], + "type": "text", + "content": " and weight decay of 0.0001, excluding feature normalization layers and bias parameters. The initial learning rate is set to " + }, + { + "bbox": [ + 304, + 91, + 547, + 283 + ], + "type": "inline_equation", + "content": "2.25e - 5" + }, + { + "bbox": [ + 304, + 91, + 547, + 283 + ], + "type": "text", + "content": ", and it is reduced by a factor of 10 at the 16th and 22nd epoch. Notably, the entire second-stage training process takes merely 1.5 hours on KITTI [14] using a single Nvidia RTX5000 GPU, indicating the low computational overhead of our proposed MonoXiver method. The training time on Waymo [51] varies depending on the training data and training recipes of off-the-shelf monocular 3D detectors. Overall, the second-stage training on Waymo is much faster compared to training the backbone monocular 3D object detector, leading to about a 3/4 reduction in training time." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 299, + 370, + 312 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 299, + 370, + 312 + ], + "spans": [ + { + "bbox": [ + 306, + 299, + 370, + 312 + ], + "type": "text", + "content": "3.3.4 Testing" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 319, + 546, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 319, + 546, + 392 + ], + "spans": [ + { + "bbox": [ + 304, + 319, + 546, + 392 + ], + "type": "text", + "content": "During testing, we keep at most top-3 predictions per initial anchor proposal with a score threshold of 0.03 (the score is predicted from the proposed MonoXiver module). The final prediction score is the product of the classification probability predicted from the backbone monocular 3D object detector and the score computed by the MonoXiver module." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 402, + 388, + 415 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 402, + 388, + 415 + ], + "spans": [ + { + "bbox": [ + 306, + 402, + 388, + 415 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 422, + 547, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 422, + 547, + 530 + ], + "spans": [ + { + "bbox": [ + 304, + 422, + 547, + 530 + ], + "type": "text", + "content": "We evaluate our MonoXiver on the well-established KITTI [14] dataset and the large-scale Waymo [51] dataset. We first show that our improved baseline detector outperforms previous SOTA methods on the KITTI benchmark by a large margin. Then we show that we consistently improved pretrained monocular 3D object detectors with limited computation overhead on both datasets. We further analyze the contribution of each part of our MonoXiver in the ablation studies." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 539, + 356, + 552 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 539, + 356, + 552 + ], + "spans": [ + { + "bbox": [ + 306, + 539, + 356, + 552 + ], + "type": "text", + "content": "4.1. Setup" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 557, + 547, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 547, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 547, + 689 + ], + "type": "text", + "content": "Dataset. The KITTI dataset [14] consists of 7,481 training images and 7,518 testing images. In KITTI's experiments, we split the training data into a training subset with 3,712 images and a validation subset with 3,769 images following [5-7]. We conduct ablation studies on the defined split and report the test set results evaluated by the official KITTI benchmark. The Waymo dataset [51] contains 52,386 training and 39,848 validation images from the front camera. In Waymo experiments, we use a subset of its training set by sampling every third frame from the training sequences following [22,45]." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 689, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 547, + 714 + ], + "type": "text", + "content": "Evaluation Metrics. The KITTI vehicle benchmark evaluates detection results by the 40-point interpolated av-" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "6441" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 111, + 70, + 485, + 247 + ], + "blocks": [ + { + "bbox": [ + 111, + 70, + 485, + 247 + ], + "lines": [ + { + "bbox": [ + 111, + 70, + 485, + 247 + ], + "spans": [ + { + "bbox": [ + 111, + 70, + 485, + 247 + ], + "type": "table", + "html": "
MethodsVenuesExtra Info.APBEV|R40↑AP3D|R40↑
EasyMod.HardEasyMod.Hard
Kinematic3D [2]ECCV20Temporal26.6917.5213.1019.0712.729.17
AutoShape [34]ICCV21CAD30.6620.0815.9522.4714.1711.36
DCD [25]ECCV22CAD32.5521.5018.2523.8115.9013.21
MonoDistill [10]ICLR22LiDAR31.8722.5919.7222.9716.0313.60
DID-M3D [43]ECCV22LiDAR32.9522.7619.8324.4016.2913.75
DD3D [42]ICCV21Depth30.9822.5620.0323.2216.3414.20
DFM [55]ECCV22Temporal + LiDAR31.7122.8919.9722.9416.8214.65
Pseudo-Stereo [9]CVPR22Depth + LiDAR32.8423.6720.6423.7417.7415.14
MonoFlex [59]CVPR2128.2319.7516.8919.9413.8912.07
GUPNet [35]ICCV2130.2921.1918.2020.1114.2011.77
DEVIANT [22]ECCV22None29.6520.4417.4321.8814.4611.89
Homography [15]CVPR2229.6020.6817.8121.7514.9413.07
DimEmbedding [61]CVPR2232.8221.9818.7023.6216.1013.41
MonoCon [30]AAAI22None31.1222.1019.0022.5016.4613.95
Our MonoXiver + MonoCon-34.1425.3722.2025.2419.0416.39
", + "image_path": "56493e2592445b838e27123b045331d1a9f2987cd3d001847da5b6c13ff86295.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 61, + 319, + 274, + 439 + ], + "blocks": [ + { + "bbox": [ + 46, + 264, + 547, + 301 + ], + "lines": [ + { + "bbox": [ + 46, + 264, + 547, + 301 + ], + "spans": [ + { + "bbox": [ + 46, + 264, + 547, + 301 + ], + "type": "text", + "content": "Table 2: Comparisons with state-of-the-art methods on the Car category on the KITTI test set. According to the KITTI protocol, methods are ranked based on their performance under the moderate difficulty setting. We highlight the best results in bold and the second-best results in underline." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 61, + 319, + 274, + 439 + ], + "lines": [ + { + "bbox": [ + 61, + 319, + 274, + 439 + ], + "spans": [ + { + "bbox": [ + 61, + 319, + 274, + 439 + ], + "type": "table", + "html": "
MethodsAP3D|R40↑Relative Improvement
EasyModerateHard
SMOKE [33]10.437.095.5711%-33%
SMOKE + Ours11.589.407.75
Improvement+1.15+2.31+2.18
MonoDLE [39]17.9413.7212.1018%-22%
MonoDLE + Ours21.1516.1914.75
Improvement+3.21+2.47+2.65
MonoCon [30]26.3319.0115.9816%-20%
MonoCon + Ours30.4822.4019.13
Improvement+4.15+3.39+3.15
", + "image_path": "22e9c30a2bd9b17370f64f75f8de1f1fbc63bd464afd06ab8bb3a6f35f7940da.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": "erage precision " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "(AP_{R40})" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " of 3D bounding boxes in 3D space " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "(AP_{3D|R40})" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " and bird eye's view " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "(AP_{BEV|R40})" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "IoU_{3D} \\geq 0.7" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": ". The prediction results are evaluated based on three difficulty settings, easy, moderate and hard, according to the 2D box height, occlusion and truncation levels of objects. The vehicle detection results on Waymo are evaluated on two levels of difficulty including Level_1 and Level_2 at " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "IoU_{3D} \\geq 0.5" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": ". The level is assigned based on the number of LiDAR points included in each 3D box. Besides the " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "AP_{3D}" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " metric, Waymo uses the " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "APH_{3D}" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " metric to incorporate heading information in " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "AP_{3D}" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 320, + 319, + 533, + 434 + ], + "blocks": [ + { + "bbox": [ + 46, + 457, + 288, + 541 + ], + "lines": [ + { + "bbox": [ + 46, + 457, + 288, + 541 + ], + "spans": [ + { + "bbox": [ + 46, + 457, + 288, + 541 + ], + "type": "text", + "content": "Table 3: The effectiveness of MonoXiver based on different methods on the KITTI validation dataset. In order to demonstrate the ability of the proposed MonoXiver to generalize across different detectors, we utilized three distinct base detectors with varying levels of detection accuracy. We observe that MonoXiver consistently yields significant improvements across all three base detectors." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 320, + 319, + 533, + 434 + ], + "lines": [ + { + "bbox": [ + 320, + 319, + 533, + 434 + ], + "spans": [ + { + "bbox": [ + 320, + 319, + 533, + 434 + ], + "type": "table", + "html": "
MethodsLevel_1Level_2
AP3D↑APH3D↑AP3D↑APH3D↑
PatchNet [36]2.922.742.422.28
PCT [54]4.204.154.034.15
GUPNet [35]10.029.949.399.31
GUPNet + ours11.4711.3510.6710.56
Improvement+1.45+1.41+1.28+1.25
DEVIANT [22]10.9810.8910.2910.20
DEVIANT + ours11.8811.7511.0610.93
Improvement+0.90+0.86+0.77+0.73
", + "image_path": "0749a4d79d87b60f8ff6490225f06b148e660f4a69191d2c858d42c7562aa82c.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 320, + 563, + 535, + 622 + ], + "blocks": [ + { + "bbox": [ + 304, + 452, + 547, + 536 + ], + "lines": [ + { + "bbox": [ + 304, + 452, + 547, + 536 + ], + "spans": [ + { + "bbox": [ + 304, + 452, + 547, + 536 + ], + "type": "text", + "content": "Table 4: The effectiveness of MonoXiver based on different methods on Waymo validation dataset. In order to showcase the generalization capabilities of the proposed MonoXiver on large-scale datasets, we conducted testing on the challenging Waymo [51] validation set, utilizing two SOTA methods. We observed consistent improvements in performance." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 320, + 563, + 535, + 622 + ], + "lines": [ + { + "bbox": [ + 320, + 563, + 535, + 622 + ], + "spans": [ + { + "bbox": [ + 320, + 563, + 535, + 622 + ], + "type": "table", + "html": "
MethodsFLOPsLatency (ms)FPS
SMOKE [33]/ + ours42.82/48.1923/3143/32
MonoDLE [39]/ + ours77.44/82.8022/3145/32
MonoCon [30]/ + ours56.22/61.5018/2555/40
", + "image_path": "4f49ece3ff4f8c0f0dae1bc12b0510ab41b4282dc101d4c68e65cc6c837698db.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 639, + 547, + 673 + ], + "lines": [ + { + "bbox": [ + 304, + 639, + 547, + 673 + ], + "spans": [ + { + "bbox": [ + 304, + 639, + 547, + 673 + ], + "type": "text", + "content": "Table 5: Computation overhead analysis. The GFLOPs is computed based on an input size of (384, 1248), while the latency and FPS are evaluated on a NVIDIA RTX5000 GPU." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6442" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 171, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 171, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 171, + 84 + ], + "type": "text", + "content": "4.2. Experimental Results" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 90, + 287, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 90, + 287, + 437 + ], + "spans": [ + { + "bbox": [ + 46, + 90, + 287, + 437 + ], + "type": "text", + "content": "Comparison with SOTA methods on the KITTI dataset. We present the results of our proposed MonoXiver method on the challenging KITTI vehicle benchmark in Table 2. Notably, our method achieves the best performance across different evaluation metrics while only using image-level information, surpassing previous state-of-the-art methods by a large margin. Specifically, we observe a significant and consistent improvement from 2.44 AP (hard settings) to 2.74 AP (easy settings) absolute increase in " + }, + { + "bbox": [ + 46, + 90, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\mathrm{AP}_{3D}" + }, + { + "bbox": [ + 46, + 90, + 287, + 437 + ], + "type": "text", + "content": " for the boosted MonoCon approach compared to the vanilla MonoCon approach. These consistent improvements demonstrate the effectiveness of our method. More qualitative and quantitative results are provided in the Supplementary Materials. Generalization abilities across backbone monocular 3D object detectors and datasets. We evaluate our method with various state-of-the-art backbone monocular 3D object detection methods on the KITTI and the Waymo validation set, reported in Table 3 and Tabel 4 respectively. Monoxiver consistently demonstrates significant improvements across different methods and different difficult levels. Specifically, on the well-established KITTI dataset, our MonoXiver is able to enhance various backbone detectors with varying levels of detection accuracy by up to " + }, + { + "bbox": [ + 46, + 90, + 287, + 437 + ], + "type": "inline_equation", + "content": "33\\%" + }, + { + "bbox": [ + 46, + 90, + 287, + 437 + ], + "type": "text", + "content": " relative improvement. On the challenging large-scale Waymo dataset, our MonoXiver consistently improves the performance of strong baseline methods GUPNet and DEVIANT by up to " + }, + { + "bbox": [ + 46, + 90, + 287, + 437 + ], + "type": "inline_equation", + "content": "1.45\\mathrm{AP}_{3D}" + }, + { + "bbox": [ + 46, + 90, + 287, + 437 + ], + "type": "text", + "content": " on Level_1 and " + }, + { + "bbox": [ + 46, + 90, + 287, + 437 + ], + "type": "inline_equation", + "content": "1.28\\mathrm{AP}_{3D}" + }, + { + "bbox": [ + 46, + 90, + 287, + 437 + ], + "type": "text", + "content": " on Level_2. These results validate the effectiveness and robustness of our approach." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 437, + 287, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 521 + ], + "type": "text", + "content": "Computation overhead. As shown in Table 5, although our MonoXiver causes about an average of " + }, + { + "bbox": [ + 46, + 437, + 287, + 521 + ], + "type": "inline_equation", + "content": "8\\mathrm{ms}" + }, + { + "bbox": [ + 46, + 437, + 287, + 521 + ], + "type": "text", + "content": " overhead compared with baseline detectors, it still achieves real-time detection. We note that its inference speed could be improved by optimizing the detailed implementation (e.g., we still have for-loops in our current code, which can be easily paralleled for better efficiency)." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 521, + 287, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 556 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 556 + ], + "type": "text", + "content": "Qualitative Comparison. We show the visualization comparisons with MonoCon in Fig. 2. It shows that MonoXiver achieves better 3D box center localization." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 563, + 148, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 563, + 148, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 563, + 148, + 574 + ], + "type": "text", + "content": "4.3. Ablation Studies" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 582, + 287, + 630 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 287, + 630 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 287, + 630 + ], + "type": "text", + "content": "In this section, we report ablation studies of MonoXiver structure and different bounding box branches on the KITTI validation set. More ablation studies are provided in the Supplementary Materials." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 630, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 287, + 714 + ], + "type": "text", + "content": "Effectiveness of MonoXiver structures. In this study, we explore the importance of RoI feature (Table 6 a.), the context information provided by geometric embeddings (Table 6 b.), and our complete MonoXiver model (Table 6 c.). In experiments a. and b., we replace the Perciver with a MLP layer to fuse the appearance feature and geometry feature to keep similar parameter size." + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 320, + 70, + 533, + 119 + ], + "blocks": [ + { + "bbox": [ + 320, + 70, + 533, + 119 + ], + "lines": [ + { + "bbox": [ + 320, + 70, + 533, + 119 + ], + "spans": [ + { + "bbox": [ + 320, + 70, + 533, + 119 + ], + "type": "table", + "html": "
AppearanceGeometryPerciverEasy/Mod./Hard
MonoCon [30]---26.33/19.01/15.98
a.✓--29.30/21.04/18.22
b.✓✓-29.33/21.67/18.46
c.✓✓✓30.48/22.40/19.13
", + "image_path": "21c316b3b117a8c4540b63c2d9bf16a5bef9811ece88f7920dc03a594c939f20.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 320, + 173, + 533, + 224 + ], + "blocks": [ + { + "bbox": [ + 306, + 137, + 545, + 161 + ], + "lines": [ + { + "bbox": [ + 306, + 137, + 545, + 161 + ], + "spans": [ + { + "bbox": [ + 306, + 137, + 545, + 161 + ], + "type": "text", + "content": "Table 6: Ablation studies of MonoXiver structure on KITTI validation set." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 320, + 173, + 533, + 224 + ], + "lines": [ + { + "bbox": [ + 320, + 173, + 533, + 224 + ], + "spans": [ + { + "bbox": [ + 320, + 173, + 533, + 224 + ], + "type": "table", + "html": "
RescoreResLocResDimEasyMod.Hard
MonoCon [30]---26.3319.0115.98
a.✓--29.6621.4118.38
b.✓✓-30.3222.3019.04
c.✓✓✓30.4822.4019.13
", + "image_path": "96fc0384648b278a9aa1ae707d21e55e96fe97b036d0723c2482eeaa1e1b604a.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 242, + 545, + 266 + ], + "lines": [ + { + "bbox": [ + 305, + 242, + 545, + 266 + ], + "spans": [ + { + "bbox": [ + 305, + 242, + 545, + 266 + ], + "type": "text", + "content": "Table 7: Ablation studies of the effect of different branches on KITTI validation set" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 288, + 545, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 288, + 545, + 371 + ], + "spans": [ + { + "bbox": [ + 304, + 288, + 545, + 371 + ], + "type": "text", + "content": "Results show that the appearance feature plays the most important role in performance improvement. When using the appearance feature only, the Moderate AP is improved by 2.39. The performance is further improved by 0.6 AP and 0.7 AP after fusing with geometric embeddings and Perciver. It shows that Perceiver effectively fuses information between appearance and geometric embeddings." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 372, + 545, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 372, + 545, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 372, + 545, + 491 + ], + "type": "text", + "content": "Effectiveness of Different Head Branches. In Table 7, we present the impact of different branches on the detection performance of our MonoXiver. Since our method generates 25 proposals per each initial proposal, the rescoring head branch plays a crucial role in filtering out false detections, leading to significant improvements by up to 3.3 AP. The localization residual branch and the dimension residual branch further enhance the performance by about 1 AP, and we employ all branches to achieve a new state-of-the-art result." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 502, + 379, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 502, + 379, + 514 + ], + "spans": [ + { + "bbox": [ + 306, + 502, + 379, + 514 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 521, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 713 + ], + "type": "text", + "content": "This paper explores the task of monocular 3D object detection. It begins with the strong observation that significant improvements in detection performance can be achieved by a local grid search based on initially detected 3D bounding boxes. This leads to a novel denoising-based approach called MonoXiver. The approach utilizes the Perceiver I/O model to produce a unified feature embedding, leverages the self-attention mechanism for proposal verification, and ultimately delivers high-quality 3D box predictions. MonoXiver can serve as a lightweight second-stage processing module to significantly improve the accuracy of detection results while only requiring 1.5 hours of training on a single GPU card for the KITTI dataset. Comprehensive evaluation experiments on the well-established KITTI benchmark and the large-scale challenging Waymo dataset demonstrate the effectiveness of our design, with a new state-of-the-art" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6443" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 61, + 71, + 533, + 357 + ], + "blocks": [ + { + "bbox": [ + 61, + 71, + 533, + 357 + ], + "lines": [ + { + "bbox": [ + 61, + 71, + 533, + 357 + ], + "spans": [ + { + "bbox": [ + 61, + 71, + 533, + 357 + ], + "type": "image", + "image_path": "a47f99d0275564abcf421b83af8efe4631616c14e12c4f791e37dfb47aa855c6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 365, + 547, + 401 + ], + "lines": [ + { + "bbox": [ + 46, + 365, + 547, + 401 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 547, + 401 + ], + "type": "text", + "content": "Figure 2: Qualitative comparison of our MonoXiver with MonoCon on KITTI validation set [5]. The left column is MonoCon's prediction result; the right column is our MonoXiver's prediction result. The ground truth is shown in green and blue. The prediction result is shown in red." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 422, + 288, + 458 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 422, + 288, + 458 + ], + "spans": [ + { + "bbox": [ + 46, + 422, + 288, + 458 + ], + "type": "text", + "content": "achieved. Furthermore, our strong observation should encourage the community to further study refinement modules for 3D object detection." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 287, + 556 + ], + "type": "text", + "content": "Limitations. Our work keeps at most top-3 predictions per bottom-up proposal for evaluation. Future work might be reducing the number of top-3 prediction by incorporating stronger priors for helping denoising proposals in 3D, i.e. temporal modeling, 3D geometric priors, large foundation models, etc. Our work has only been comprehensively tested on monocular settings with significant improvement, and it has not been tested on multiview settings." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 572, + 149, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 572, + 149, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 572, + 149, + 586 + ], + "type": "text", + "content": "Acknowledgements" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 715 + ], + "type": "text", + "content": "X. Liu and T. Wu were partly supported by ARO Grant W911NF1810295, NSF IIS-1909644, ARO Grant W911NF2210010, NSF IIS-1822477, NSF CMMI-2024688 and NSF IUSE-2013451. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the ARO, NSF, DHHS or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 422, + 546, + 458 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 422, + 546, + 458 + ], + "spans": [ + { + "bbox": [ + 305, + 422, + 546, + 458 + ], + "type": "text", + "content": "copyright annotation thereon. The authors are grateful for the constructive comments by anonymous reviewers and area chairs." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 468, + 365, + 481 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 468, + 365, + 481 + ], + "spans": [ + { + "bbox": [ + 306, + 468, + 365, + 481 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 310, + 488, + 547, + 714 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 310, + 488, + 545, + 521 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 488, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 310, + 488, + 545, + 521 + ], + "type": "text", + "content": "[1] Garrick Brazil and Xiaoming Liu. M3d-rpn: Monocular 3d region proposal network for object detection. 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In ICCV, pages 2713-2722, 2021. 2" + } + ] + } + ], + "index": 28 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "6446" + } + ] + } + ], + "index": 30 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Monte Carlo Linear Clustering with Single-Point Supervision is Enough for Infrared Small Target Detection/ff32047e-26fb-4725-b960-eee153eb3232_content_list.json b/2023/Monte Carlo Linear Clustering with Single-Point Supervision is Enough for Infrared Small Target Detection/ff32047e-26fb-4725-b960-eee153eb3232_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..69fc2d1877372570b0476e36261bfb9fd0d95e1e --- /dev/null +++ b/2023/Monte Carlo Linear Clustering with Single-Point Supervision is Enough for Infrared Small Target Detection/ff32047e-26fb-4725-b960-eee153eb3232_content_list.json @@ -0,0 +1,1627 @@ +[ + { + "type": "text", + "text": "Monte Carlo Linear Clustering with Single-Point Supervision is Enough for Infrared Small Target Detection", + "text_level": 1, + "bbox": [ + 99, + 135, + 870, + 189 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Boyang Li $^{1}$ , Yingqian Wang $^{1}$ , Longguang Wang $^{2}$ , Fei Zhang $^{3}$ ,", + "bbox": [ + 236, + 210, + 730, + 229 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Ting Liu $^{1}$ , Zaiping Lin $^{1\\boxtimes}$ , Wei An $^{1}$ , Yulan Guo $^{1}$", + "bbox": [ + 294, + 229, + 673, + 247 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ National University of Defense Technology, $^{2}$ Aviation University of Air Force,", + "bbox": [ + 173, + 247, + 797, + 265 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{3}$ Shanghai Jiao Tong University", + "bbox": [ + 357, + 265, + 609, + 282 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{liboyang20, linzaiping}@nudt.edu.cn", + "bbox": [ + 326, + 285, + 643, + 300 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 345, + 313, + 361 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Single-frame infrared small target (SIRST) detection aims at separating small targets from clutter backgrounds on infrared images. Recently, deep learning based methods have achieved promising performance on SIRST detection, but at the cost of a large amount of training data with expensive pixel-level annotations. To reduce the annotation burden, we propose the first method to achieve SIRST detection with single-point supervision. The core idea of this work is to recover the per-pixel mask of each target from the given single point label by using clustering approaches, which looks simple but is indeed challenging since targets are always insalient and accompanied with background clutters. To handle this issue, we introduce randomness to the clustering process by adding noise to the input images, and then obtain much more reliable pseudo masks by averaging the clustered results. Thanks to this \"Monte Carlo\" clustering approach, our method can accurately recover pseudo masks and thus turn arbitrary fully supervised SIRST detection networks into weakly supervised ones with only single point annotation. Experiments on four datasets demonstrate that our method can be applied to existing SIRST detection networks to achieve comparable performance with their fully-supervised counterparts, which reveals that single-point supervision is strong enough for SIRST detection. Our code will be available at: https://github.com/YeRen123455/SIRST-Single-Point-Supervision.", + "bbox": [ + 76, + 378, + 473, + 785 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 814, + 209, + 830 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Single-frame infrared small target (SIRST) detection has been widely used in many applications such as marine resource utilization [23, 45], high-precision navigation [34, 13], and ecological environment monitoring [35].", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b8f139acdcc91b46ce997ced7e9adedf3978e929fad55a489e31d5fb53f52bec.jpg", + "image_caption": [ + "Figure 1. Pipeline of our method. The proposed Monte Carlo linear clustering along with single-point annotation can produce high-quality pseudo mask (i.e., target probability map (TPM))." + ], + "image_footnote": [], + "bbox": [ + 511, + 345, + 883, + 491 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "However, existing SIRST detection methods mainly rely on segmentation pipeline with pixel-level supervision. Pixel-level annotating is time-consuming and thus hinders the quick deployment of those large scale data-dependent scenarios. Therefore, it is in urgent need to alleviate the annotation burden while maintaining state-of-the-art performance in SIRST detection.", + "bbox": [ + 496, + 565, + 890, + 671 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Point-level supervision, as an annotation-friendly form of supervision, can provide both category and localization information for each target. Previous works in general object segmentation utilized rich semantic information to design various training loss [4] and network modules [29, 27], and continuously expand the single-point annotation to a pixel-level pseudo mask. Although having achieved promising performance, these methods heavily rely on prior semantic information (e.g., objectness prior in [4, 50], shape prior in [29, 27, 49]), and generally need more than one point as supervision. However, infrared small targets generally occupy no more than $0.15\\%$ area of the whole image [47] and lack texture, shape and color information. Consequently, previous semantic information-dependent methods cannot well adopt to this task.", + "bbox": [ + 496, + 674, + 892, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "1009", + "bbox": [ + 483, + 924, + 514, + 936 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b81573059ca7eeec6c99cf4c6c0d437235eef0de841a212f74a24b90e6f95986.jpg", + "image_caption": [ + "(a) Local Saliency", + "Figure 2. Some inherent characteristics of SIRST observed from the small local regions (i.e., salient in local region, similar shape, texture, and energy distribution)." + ], + "image_footnote": [], + "bbox": [ + 99, + 88, + 181, + 200 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/9634e87a22cdd4be3cf7288923343a5a420a74f7501b1f11e07c194c667e0eb0.jpg", + "image_caption": [ + "(b) Similar Shape" + ], + "image_footnote": [], + "bbox": [ + 186, + 88, + 267, + 200 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/87c7b9c23df3165eb0c8623c16a2d6342e97bf9c5035975073e88ea234a50a75.jpg", + "image_caption": [ + "(c) Similar Texture" + ], + "image_footnote": [], + "bbox": [ + 274, + 88, + 357, + 200 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/404d90aa754aae3a8b506637ca1259e9988bfb9538e8f588f931a5cc70a3ff2a.jpg", + "image_caption": [ + "(d) Similar Energy Distribution" + ], + "image_footnote": [], + "bbox": [ + 364, + 88, + 446, + 200 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We notice that although infrared small targets lack semantic information from the perspective of whole image, they are quite salient in the local small region. Specifically, as shown in Fig. 2, small targets in infrared images generally have high energy concentricity and exhibit significant gradient difference in their local regions. Moreover, limited semantic information (e.g., weak texture, shape, and color distribution) makes most point-like and spot-like targets exhibit similar energy distribution (e.g., Gaussian distribution). Consequently, it is straightforward to use a simple linear clustering approach (LCA) to separate the salient regions by measuring their color and spatial distances with adjacent backgrounds.", + "bbox": [ + 75, + 292, + 468, + 489 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "However, LCA easily falls into local optimum and produces inaccurate segmentation results due to their fixed hyper-parameters. To handle this problem, we propose a Monte Carlo linear clustering (MCLC) method to regularize the clustering process and recover the reliable clustering result by repetitive random experiments. Specifically, we introduce randomness to the clustering process by adding noise to the input images. With the help of random noise, the distance between unexpected background region and target region can be significantly enlarged. The misclustered target regions can be pushed away from the false clustering center and thus return back the true clustering center. In this way, the single-point annotation can be gradually recovered as a much more reliable pixel-level target probability map (TPM) by averaging the clustered results. Pixels with larger values in TPM represent a higher probability of belonging to the target. Finally, we use the refined TPM to turn arbitrary fully supervised SIRST detection networks into weakly supervised ones with only single point annotation. Fig. 1 shows the overall pipeline of our method, and the main contributions are summarized as follows:", + "bbox": [ + 75, + 489, + 468, + 808 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "- To the best of our knowledge, this is the first single-point supervised method to achieve SIRST detection. A Monte Carlo linear clustering-based pipeline is proposed to achieve comparable performance with the fully supervised counterpart by using single-point anno", + "bbox": [ + 93, + 824, + 468, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "taion.", + "bbox": [ + 532, + 92, + 575, + 104 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Inspired by the inherent characteristic of SIRST, a simple yet effective linear clustering approach with random noise-guided Monte Carlo regularization is proposed to coarsely extract and further refine the candidate target region.", + "- Experiments on four public SIRST datasets demonstrate the effectiveness of our method. Ablation study reveals that pixel-level labels are not necessary for SIRST detection while single-point supervision is strong enough." + ], + "bbox": [ + 516, + 119, + 890, + 287 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 304, + 640, + 320 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Infrared Small Target Detection", + "text_level": 1, + "bbox": [ + 500, + 330, + 782, + 345 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "SIRST detection has been extensively investigated for decades. Early traditional paradigm achieves SIRST detection by measuring the discontinuity between targets and backgrounds. Typical methods include filtering-based methods [31, 14], local contrast measure-based methods [6, 18, 19, 20, 22, 36], and low rank-based methods [16, 43, 9, 44, 51, 10]. Since real scenes are much more complex with dramatic changes in target size, shape, and clutter background, it is difficult to use handcrafted features and fixed hyper-parameters to handle such variations. To address this problem, recent deep learning-based methods learn trainable features in a data-driven manner and thus achieve better performance than traditional ones.", + "bbox": [ + 496, + 354, + 890, + 550 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Existing deep learning-based methods can be divided into detection based methods and segmentation based methods. Since the pixel-level classification result is essential for the subsequent recognition task in SIRST, segmentation-based methods have attracted increasing attention recently. Dai et al. [11] proposed the first segmentation-based network (i.e., ACM). They designed an asymmetric contextual module to aggregate features from shallow layers and deep layers. Then, Dai et al. [12] improved ACM by introducing a dilated local contrast measure. Specifically, a feature cyclic shift scheme was designed to achieve a trainable local contrast measure. After that, Zhang et al. [45] modeled SIRST detection as a shape detection task. A taylor finite difference (TFD)-inspired edge block and a two-orientation attention aggregation (TOAA) block were proposed to capture precise shape of infrared targets. Recently, Li et al. [23] proposed a dense nested attention network (DNANet). A specifically-designed dense nested interactive module (DNIM) was proposed to both extract high-level information and maintain the response of small targets in deep layers.", + "bbox": [ + 496, + 551, + 892, + 853 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Although the performance has been continuously improved by recent networks, existing deep learning-based methods rely on the fully-supervised training scheme with", + "bbox": [ + 496, + 854, + 893, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "1010", + "bbox": [ + 483, + 924, + 514, + 936 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/cc64a29001c91873ca0e7519078ba1ca8d4595d403768de2ef08c26b1fe0ed5e.jpg", + "image_caption": [ + "Figure 3. Sample of input images, four common weakly supervised annotations (i.e., single-point, multi-point, scribble, bounding box), and one fully supervised pixel-level annotation." + ], + "image_footnote": [], + "bbox": [ + 101, + 90, + 450, + 231 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "pixel-level annotations. Expensive labor cost makes existing methods hard to be deployed to large scale data-dependent tasks.", + "bbox": [ + 75, + 300, + 468, + 345 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Point-based Segmentation", + "text_level": 1, + "bbox": [ + 76, + 351, + 313, + 366 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Point-level supervision has been widely used in many high-level tasks (e.g., object detection [7, 46], object localization [41], and semantic segmentation [4, 29, 27, 24, 49]) and yield promising performance. For semantic segmentation task, Bearman et al. [4] proposed the first single-point supervised semantic segmentation method. They incorporated the single-point supervision along with an objectness prior as the loss function to infer the extent of the object. Then, Papadopoulos et al. [29] and Maninis et al. [27] utilized four extreme points (i.e., left-most, right-most, top, and bottom pixels) as supervision to further improve the quality of the pseudo mask. After that, Austin et al. [28] followed the class activation maps (CAM) [50] pipeline and used the point annotation to refine the quality of pseudo labels. More recently, Li et al. [24] utilized the semantical consistency property of general objects with 20 randomly annotated points to achieve comparable segmentation results with fully-supervised counterpart. Moreover, in the field of cell segmentation, Zhao et al. [49] proposed the first single-point supervised segmentation method, in which two semantic prior-based training losses (i.e., divergence loss and consistency loss) were proposed to achieve high-quality cell segmentation.", + "bbox": [ + 75, + 369, + 468, + 717 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Although promising performance has been achieved, existing works rely on rich semantic information (e.g., objectness prior in [4, 50], shape prior in [29, 27, 49]) and most of them need multi-point annotation. Infrared small targets generally occupy no more than $0.15\\%$ area of the whole image [47] and lack texture, shape and color information. Previous semantic information-dependent methods cannot be directly used for SIRST detection.", + "bbox": [ + 75, + 718, + 468, + 838 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 76, + 848, + 210, + 864 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we first introduce the motivation. Then, a detailed illustration of the proposed linear clustering ap", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "proach with Monte Carlo regularization is provided. Overall architecture of proposed method is shown in Fig. 4.", + "bbox": [ + 498, + 90, + 890, + 121 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Motivation", + "text_level": 1, + "bbox": [ + 500, + 131, + 620, + 145 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We investigate the annotation cost of four common weakly-supervised annotations (i.e., single point [5], multiple points[5, 29, 27], scribbles [25], bounding boxes[21]) by re-labelling the NUDT-SIRST [23] and NUAA-SIRST [11] datasets. Fig. 3 shows the average annotation time of four weakly-supervised and one fully-supervised approaches. Note that, single-point supervision can reduce about $87\\%$ annotation time as compared to the pixel-level annotation approach, which motivates us to apply single-point annotation to SIRST detection. Please refer to the supplementary material for more detailed analysis.", + "bbox": [ + 496, + 154, + 890, + 320 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "However, existing point-level supervised methods [5, 29, 27] are designed for general objects with rich semantic information (e.g., shape, texture, and color). As shown in Fig. 2, the characteristics of infrared small targets make the aforementioned semantic-based pipeline unsuitable for SIRST detection. Considering that infrared small targets are quite salient in their local regions and share similar shape, texture, and energy distribution. Intuitively, we can use simple linear clustering approaches (e.g., Super-pixel [1], K-Means [26]) to separate the salient regions by comparing their color and spatial distances among these clusters.", + "bbox": [ + 496, + 321, + 890, + 487 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Linear Clustering Approach", + "text_level": 1, + "bbox": [ + 500, + 497, + 754, + 513 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Without loss of generality, we take the quick linear clustering method SuperPixel [1] as an example to introduce how to use LCA to coarsely separate the target region. It should be noted that other linear clustering approaches such as KMeans [26] can be also used in our method, as demonstrated in Fig. 5. The pipeline of our LCA is shown in Fig. 4 (Step I $\\sim$ Step III), in which the clustering center of the image is first initialized, and then adjusted according to a color and spatial distance based measurement. Finally, the clustering center is continuously updated until the pre-defined convergence requirements are met.", + "bbox": [ + 496, + 520, + 890, + 686 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "1) Clustering Center Initialization: We initialize the clustering center based on the pre-defined number of clusters $N$ . Given an input image $I \\in \\mathbb{R}^{H \\times W}$ , we first divide it into $N$ regions with equal areas and fixed grid interval $S = \\sqrt{\\frac{H \\times W}{N}}$ (as shown in Fig. 4-Step 1). After that, the clustering center is first initialized as the centroid of each region, and then moved to the lowest gradient position of its $3 \\times 3$ neighborhood. The clustering center of the $n^{th}$ clustering region $\\mathcal{C}_n$ can be represented as a vector as:", + "bbox": [ + 496, + 686, + 890, + 830 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {C} _ {n} = \\left[ c _ {n}, s _ {n} \\right] ^ {T}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 638, + 842, + 890, + 862 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $[c_n]^T$ represents the CIELAB color [32] of $\\mathcal{C}_n$ , $[s_n]^T$ denotes the spatial position in image coordinate of $\\mathcal{C}_n$ .", + "bbox": [ + 496, + 867, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "1011", + "bbox": [ + 483, + 926, + 513, + 936 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/a7dd4ccc1d01683daee3003eeda05a5ba5719e0b056105548e3f7e7d2ce71ce5.jpg", + "image_caption": [ + "Figure 4. Illustration of our method. StepI $\\sim$ StepIII: LCA can coarsely separate target from clutter background, but easily falls into local optimum and produce incomplete pseudo mask. StepIV $\\sim$ StepV: Monte Carlo regularization can increase the color distance between background and target region and thus enforce the misclustered target region away from the false clustering center. After repetitive random experiments, the accumulated clustering results are finally shown as a target probability map (TPM), where pixels with larger values represent a higher probability of belonging to the target." + ], + "image_footnote": [], + "bbox": [ + 83, + 85, + 883, + 385 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "2) Distance Measurement: After clustering center initialization, we adopt a color and spatial distance based measurement to determine the clustering center of each pixel. As shown in Fig. 4-Step II, for each clustering center $\\mathcal{C}_n$ , we use $L_2$ distance to measure its distance with each pixel $p_i = [c_i, s_i]^T$ in its adjacent $2S \\times 2S$ regions. Considering that the ranges of color value and spatial position value are inconsistent, we normalize the both distance values with normalization coefficient $\\mu_s$ and $\\mu_c$ . $\\mathcal{D}(\\mathcal{C}_n, p_i)$ is written as:", + "bbox": [ + 75, + 486, + 468, + 623 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {D} (\\mathcal {C} _ {n}, p _ {i}) = \\sqrt {(\\mathcal {D} _ {c}) ^ {2} + (\\mathcal {D} _ {s}) ^ {2}} \\\\ = \\sqrt {\\frac {\\left(c _ {p _ {i}} - c _ {\\mathcal {C} _ {n}}\\right) ^ {2}}{\\mu_ {c} ^ {2}} + \\frac {\\left(s _ {p _ {i}} - s _ {\\mathcal {C} _ {n}}\\right) ^ {2}}{\\mu_ {s} ^ {2}}}. \\tag {2} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 119, + 643, + 468, + 705 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Then, the clustering label $l$ for each pixel $p_i$ can be determined as:", + "bbox": [ + 76, + 713, + 468, + 742 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nl \\left(p _ {i}\\right) = \\operatorname {a r g m i n} _ {\\mathrm {n} \\in \\{1, 2, 3, \\dots , \\mathrm {N} \\}} \\left[ \\mathcal {D} \\left(\\mathcal {C} _ {\\mathrm {n}}, \\mathrm {p} _ {\\mathrm {i}}\\right) \\right]. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 133, + 757, + 468, + 776 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3) Updating and Convergence: After determining the clustering center of each pixel at the current iteration, we repetitively update the position of each clustering center until convergence, as shown in Fig. 4-Step III. Specifically, we first calculate the clustering centers to be the mean vector $[c_m, s_m]^T$ of all the pixels $P = \\{p_1, p_2, \\dots, p_m\\}$ with the same clustering label $l(\\mathcal{C}_n')$ . The new clustering center $\\mathcal{C}_n'$ can be formulated as:", + "bbox": [ + 76, + 780, + 468, + 898 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/0f0086a783ebf8d88e111a66a8f249377c1f5b43679c38f5ec9db6839840c9fc.jpg", + "image_caption": [ + "Figure 5. Visualization results achieved by (a) Kmeans, (b) K-means with Monte Carlo Regularization, (c) Super pixel, (d) Super pixel with Monte Carlo Regularization. Our proposed Monte Carlo regularization helps to expand informative target region." + ], + "image_footnote": [], + "bbox": [ + 504, + 484, + 888, + 625 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {C} _ {n} ^ {\\prime} \\left(c _ {n}, x _ {n}, y _ {n}\\right) = \\frac {1}{| P |} \\sum_ {p _ {m} \\in P} \\left(c _ {p _ {m}}, s _ {p _ {m}}\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 562, + 728, + 890, + 766 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "After that, we adopt $L_{2}$ norm to compute a distance $\\mathcal{E}$ between new clustering center locations $\\mathcal{C}_n'$ and previous clustering center locations $\\mathcal{C}_n$ . The updating steps can be repeated iteratively until the error is smaller than the predefined threshold $T$ . That is $\\| \\mathcal{C}_n' - \\mathcal{C}_n \\|_2 < T$ , where $\\| \\cdot \\|_2$ denote the L2 norm. Finally, we assign the single-point annotation $p_{Aanno}$ located at the $n^{th}$ clustering region as the clustering result $M_{pred}$ .", + "bbox": [ + 496, + 779, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "1012", + "bbox": [ + 483, + 924, + 514, + 936 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/fd77ab1afd41e932334e815fc0b86e197c726a79719d97b816b80ce7119f284a.jpg", + "image_caption": [ + "Figure 6. Quantitative analysis on (a) Sensitivity of target and non-target regions to additional noise, and (b) Color distance of target edge region with true foreground region centroid $\\Delta (\\mathcal{D}_c(\\mathcal{C}^T,M_{pred}))$ and false background region centroid $\\Delta (\\mathcal{D}_c(\\mathcal{C}^F,M_{pred}))$ . Average results from 10 trails are reported. Readers can refer to the supplementary material for more detailed illustration." + ], + "image_footnote": [], + "bbox": [ + 81, + 88, + 276, + 210 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/56a037a578972acbb06e57e9a46a77ce70e983dfbf31f35c4aba78904651686a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 276, + 88, + 467, + 210 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Monte Carlo Regularization", + "text_level": 1, + "bbox": [ + 76, + 332, + 330, + 348 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Although LCA can coarsely separate local salient regions from the backgrounds, as shown in Fig. 5 (a) and (c), a linear clustering method easily falls into local optimum and generates incomplete or oversized results. In this subsection, we first analyze the reason of this issue, and then propose a Monte Carlo regularization to alleviate this issue, as shown in Fig. 4 (StepIV $\\sim$ StepV).", + "bbox": [ + 75, + 354, + 468, + 460 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "1) Inaccurate Result within a Single Clustering: Due to the varied size of small targets, LCA with fixed number of clustering centers cannot produce ideal results for all kinds of targets. That is because, both color $\\mathcal{D}_c$ and spatial distance $\\mathcal{D}_s$ determine the output of linear clustering model in Equation 2. Since edge areas $M_{pred}^{Edge} = \\{m_{pred}^{Edge(1)}, m_{pred}^{Edge(2)}, \\dots, m_{pred}^{Edge(Z)}\\}$ of the spot and extended target (i.e., big target) are generally far from the true clustering center $\\mathcal{C}^T$ (shown as the left-most green point in Fig. 4-Step III). The spatial distance $\\mathcal{D}_c(\\mathcal{C}^T, M_{pred}^{Edge})$ between the true clustering center $\\mathcal{C}^T$ and edge areas $M_{pred}^{Edge}$ is usually farther than that of the false clustering center $\\mathcal{C}^F$ . That is:", + "bbox": [ + 75, + 460, + 468, + 667 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {D} _ {s} \\left(\\mathcal {C} ^ {T}, m _ {\\text {p r e d}} ^ {\\text {E d g e} (z)}\\right) > \\mathcal {D} _ {s} \\left(\\mathcal {C} ^ {F}, m _ {\\text {p r e d}} ^ {\\text {E d g e} (z)}\\right). \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 137, + 679, + 468, + 702 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Moreover, the color value of big target generally exhibits Gaussian distribution. Those edge areas often exhibit relatively high color difference with the true clustering center, and are close to the adjacent false clustering center (shown as the right-most green point in Fig. 4 Step III). That is:", + "bbox": [ + 75, + 705, + 468, + 782 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {D} _ {c} \\left(\\mathcal {C} ^ {T}, m _ {\\text {p r e d}} ^ {\\text {E d g e} (z)}\\right) > \\mathcal {D} _ {c} \\left(\\mathcal {C} ^ {F}, m _ {\\text {p r e d}} ^ {\\text {E d g e} (z)}\\right). \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 137, + 792, + 468, + 814 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As a result, the label of edge areas $l_{pred}^{Edge}$ may be falsely included into the adjacent false clustering center $\\mathcal{C}^F$ , resulting in incomplete clustering result.", + "bbox": [ + 75, + 821, + 468, + 869 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "2) Random Noise Guided Regularization: Spatial distance $\\mathcal{D}_s$ is generally fixed and hard to change in the im", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "age. As shown in Fig. 6 (a), when adding random noise, target and non-target regions exhibit different sensitivity to the noise. Target regions with higher color vaule are more robust to the additional noise than the non-target regions. Based on this finding, we are motivated to introduce random noise to enlarge the color distance $\\mathcal{D}_c(\\mathcal{C}^F,M_{pred}^{Edge})$ between edge areas and false clustering center (as shown in Fig. 4-Step III), and thus make the edge areas be clustered to the true clustering center. Random noise-regularized clustering result can be formulated as follows:", + "bbox": [ + 496, + 90, + 890, + 241 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nM _ {p r e d} ^ {N o i s e} = L C A (c l i p (I + \\mathcal {N})), \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 589, + 255, + 890, + 273 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\text{clip}(\\cdot)$ operation represents that color values larger than 255 will be fixed at 255. $\\mathcal{N}$ is the additional random noise. The color value change caused by random noise can be formulated as:", + "bbox": [ + 496, + 277, + 890, + 337 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\Delta \\left(\\mathcal {D} _ {c} \\left(\\mathcal {C}, M _ {p r e d}\\right)\\right) = \\mathcal {D} _ {c} ^ {\\text {N o i s e}} - \\mathcal {D} _ {c} ^ {\\text {C l e a n}}. \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 562, + 351, + 890, + 369 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Since background region has relatively low color value than foreground region. Additional noise will greatly increase the color value of adjacent false clustering centers, and thus enlarges their color distance with the edge area of target region. On the contrary, when comparing Fig. 4-Step IV with Fig. 4-Step V, we observe that foreground regions have high energy concentricity and are usually close to saturation. Additional noise cannot bring so much color change to target regions as the background regions. Benefited by the additional noise, as shown in Fig. 6 (b), the change of color distance between edge areas and false clustering center (i.e., $\\Delta (\\mathcal{D}_c(\\mathcal{C}^F,M_{pred}))$ ) will be significantly larger than that between edge areas and true clustering center (i.e., $\\Delta (\\mathcal{D}_c(\\mathcal{C}^T,M_{pred}))$ ), making the misclustered target region be more closed to the true clustering center.", + "bbox": [ + 496, + 375, + 890, + 599 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3) Monte Carlo Process: As aforementioned, random noise can enforce the misclustered region to be gradually close to the true clustering center. Considering the randomness of noise, additional noise does not always bring such positive effect. We are motivated to adopt the Monte Carlo method to accumulate the clustering result from repetitive random experiments and gradually recover the reliable clustering result. To this end, we perform $K$ independent clustering and formulate this process as follows:", + "bbox": [ + 496, + 601, + 890, + 736 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nM _ {P r e d} ^ {F u l l} = \\frac {1}{K} \\sum_ {k = 1} ^ {K} \\left(L C A \\left(\\operatorname {c l i p} \\left(I + \\mathcal {N} ^ {(k)}\\right)\\right)\\right), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 547, + 758, + 890, + 799 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $M_{Pred}^{Full}$ is the accumulated clustering results after $K$ independent clustering by LCA, and finally shown as a target probability map (TPM), where pixels with larger values represent a higher probability of belonging to the target.", + "bbox": [ + 496, + 808, + 890, + 869 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The optimization process finally stops when the distance between the new clustering center locations $\\mathcal{C}'$ and previous", + "bbox": [ + 496, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "1013", + "bbox": [ + 483, + 925, + 514, + 936 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/15a0bff01a352de1de822896093f067d307b60fa0d12ef65185c8b9e314f02d7.jpg", + "image_caption": [ + "Figure 7. IoU scores achieved by our method with (a) different types and intensity of additional noise and (b) different number of clustering center on the NUAA-SIRST dataset. Average results from 5 trails are reported. Readers can refer to the supplementary material for additional experiments on the other datasets." + ], + "image_footnote": [], + "bbox": [ + 81, + 89, + 269, + 210 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c59546526f87359f1a1bdc0e673b1fb1c5cf05bb771e70c7202f68caf5a99a8f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 272, + 89, + 464, + 209 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/867059735c69b3b96f3776553829d97d2443f9792a6b21a3c2500187a5ec6f40.jpg", + "table_caption": [ + "Table 1. $IoU(10^{-2})$ value achieved by the different variants of our method on the training set of four representative datasets (i.e., NUAA, IRSTD, NUDT, NUDT-sea). MC Regu. refers to Monte Carlo regularization." + ], + "table_footnote": [], + "table_body": "
Point LabelLCAMC Regu.dCRFIoU(%)
✓✓2.53 / 1.62 / 2.28 / 1.82
✓✓51.8 / 55.5 / 51.2 / 38.1
✓✓✓70.4 / 66.2 / 52.5 / 43.9
✓✓✓✓76.3 / 68.8 / 60.2 / 47.1
", + "bbox": [ + 86, + 354, + 460, + 412 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "clustering center locations $\\mathcal{C}$ is smaller than the pre-defined threshold $T^F$ , i.e., $\\| \\mathcal{C}_n' - \\mathcal{C}_n\\|_2 < T^F$ .", + "bbox": [ + 75, + 441, + 468, + 472 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 488, + 209, + 506 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this section, we first introduce our evaluation metrics and implementation details. Then, we compare our MCLC to several state-of-the-art unsupervised, point-level supervised, and fully-supervised SIRST detection methods. Finally, we present ablation studies to investigate the effectiveness of our method. Note that, we search for optimal parameters of MCLC in the training set of NUAA-SIRST [11] and directly adopt them as default parameters to generate pseudo masks on the other three datasets[45, 23, 39].", + "bbox": [ + 75, + 515, + 468, + 651 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Evaluation Metrics", + "text_level": 1, + "bbox": [ + 76, + 664, + 261, + 679 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Considering that both the quality of pseudo labels and the final detection results are crucial to SIRST detection, we followed previous works [37, 42, 3, 2] and propose a two-stage pipeline (i.e., pseudo mask and final detection result evaluation) to comprehensively evaluate the effectiveness of the proposed method. Firstly, we followed the same metrics in weakly-supervised general object segmentation [3, 2] and adopted intersection of union $(IoU)$ to evaluate the quality of generated pseudo labels on the training set. For the final detection results evaluation, we followed previous works [11, 12, 23] and adopted probability of detection $(P_d)$ , and false-alarm rate $F_{a}$ to evaluate the localization precision, and used $IoU$ to evaluate the shape description ability on the test set.", + "bbox": [ + 75, + 688, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/61a49b4338e44973b4bb4ba283d96a9b9fa21a48c5966dc3cfc2d1cbb41f23e8.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 506, + 89, + 602, + 142 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/062e17142eb5258a4f283d81fdcf9b2831298ab40fe24939da0581ba92d1104a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 602, + 90, + 679, + 142 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/8d901cdf6133f5e08ac8eb36b52518d01de92f55d2ab93214b08ebfaf842142c.jpg", + "image_caption": [ + "Figure 8. (a) Labelling deviation examples of small target from four datasets. (b) Label deviation distribution map generated from 105 manually re-labelled targets. Real world labelling deviation of small target is generally less than 3 pixels." + ], + "image_footnote": [], + "bbox": [ + 506, + 143, + 602, + 215 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/7fd40b7ac9ee5db49e43a9d4d0d86c0633b681a6b70446466c1fb7971c867037.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 602, + 143, + 679, + 215 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/560d13ca74453ecedb01295fdc0e8e9588e806e0eff52b404fb2869055692cfb.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 681, + 90, + 887, + 215 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Implementation Details", + "text_level": 1, + "bbox": [ + 500, + 292, + 718, + 306 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "1) Datasets: We evaluated our method on the NUAA-SIRST [11], IRSTD-1k [45], NUDT-SIRST [23], and NUDT-SIRST-sea [39] datasets. Without specification, for the NUAA-SIRST and NUDT-SIRST datasets, we used the same division as in [23] and set the ratio of train-val set to test set as 1. For the IRSTD-1k dataset, we followed [45] and used $80\\%$ data for training and validation, and the remaining $20\\%$ data for test. The division setting in [39] was adopted for the NUDT-SIRST-sea dataset, i.e., 41 images were used for training and validation, and the remaining 7 images were used for test. Note that, only single point-level annotation with category information (i.e., point, spot, and extend categories) are available during network training.", + "bbox": [ + 496, + 309, + 890, + 503 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "2) Training Details: In our experiments, all input images were first normalized before training. Then, these normalized images were sequentially processed by random flip, and random crop for data augmentation. Next, these images were resized to a fixed resolution. Specifically, $1024 \\times 1024$ and $256 \\times 256$ spatial resolutions were used for the NUDT-SIRST-sea and the remaining three datasets, respectively. Finally, we fed these resized datasets into network for both training and evaluation. Without specification, we adopted the centroid of ground truth mask as the single-point label. The influence of label position deviation is discussed in the following ablation. Moreover, all networks were trained with the Soft-IoU loss function and optimized by the Ada-grad method [15] with the CosineAnnealingLR scheduler. The Xavier method [17] was used for all weights and bias parameters initialization. We set the learning rate and epoch number to 0.05 and 1500, respectively. The batch size was set to 16 for the NUAA-SIRST, IRSTD-1k, NUDT-SIRST datasets but set to 4 for the NUDT-SIRST-sea dataset due to its large image size. All models were implemented in PyTorch [30] on a computer with an AMD Ryzen 9 3950X @ 2.20 GHz CPU and an Nvidia GeForce 3090 GPU.", + "bbox": [ + 496, + 506, + 892, + 835 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 847, + 653, + 863 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "1) Effectiveness of Proposed Components: Table 1 shows the contribution of our proposed components on four", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "1014", + "bbox": [ + 483, + 926, + 514, + 936 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/24785da51d72cf222e91803d4ef6d38145a39d49d4cf27bb6b71b232d6bbe563.jpg", + "table_caption": [ + "Table 2. $IoU(10^{-2})$ values and corresponding labelling cost with stronger supervision on the train set of four datasets." + ], + "table_footnote": [], + "table_body": "
AnnotationDataset
NUAAIRSTDNUDTNUDT-sea
Single-Point76.368.860.247.1
Multi-Point76.669.162.653.7
Scribble78.570.563.255.2
Bounding-Box78.971.864.854.5
", + "bbox": [ + 114, + 116, + 433, + 186 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "datasets. Compared to the initial single-point label, linear clustering approach (LCA) introduces $49.3\\%$ , $53.9\\%$ , $48.9\\%$ , $36.3\\%$ improvements for the NUAA, IRSTD-1k, NUDT, NUDT-sea datasets, respectively. That is because, LCA utilizes the inherent characteristics of infrared small targets and thus coarsely separates the targets from clustering background. By introducing random salt noise to regularize the linear clustering process, we obtain much more reliable results and achieve additional $18.6\\%$ , $10.7\\%$ , $1.3\\%$ , $5.8\\%$ improvements on the above four datasets. After that, denseCRF [8] was used as a post-processing module to refine the target probability map (TPM) generated by MCLC. It further introduces $5.9\\%$ , $2.6\\%$ , $7.7\\%$ , $3.2\\%$ improvements for the above four datasets, respectively. We visualize the Monte Carlo linear clustering process in Fig. 9. Although easily producing inaccurate results at the beginning of clustering (e.g., iteration number less than 20), MCLC can gradually recover a reliable clustering result. More visualization samples are shown in supplementary material.", + "bbox": [ + 75, + 213, + 468, + 500 + ], + "page_idx": 6 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "2) Type and Intensity of Noise: Fig. 7 (a) shows the change trend of $IoU$ with respect to different noise intensity under three types of common noise (i.e., salt, pepper, and Gaussian). With the increase of noise intensity, the $IoU$ of MCLC with denseCRF under salt noise and pepper noise increases rapidly at the beginning, and reaches their peak scores of $76\\%$ and $71\\%$ at $0.05$ intensity1. After that, excessive intensity value reduces the saliency of target region and thus results in the decrease of $IoU$ . Moreover, Gaussian noise causes huge performance decrease under any intensity. That is because, Gaussian noise randomly changes the values of all pixels in the image, which is similar to the salt and pepper with high intensity. Since all pixels in the image are influenced by the random noise, the saliency of target is greatly decreased, resulting in dramatic performance drop.", + "3) Number of Clustering Center: The number of clustering center determines the initial area of each clustering region. Fig. 7 (b) reports the $IoU$ of the results generated by MCLC with denseCRF, MCLC with fixed threshold, and LCA under different number of clustering center. It shows that the $IoU$ firstly shows a rapid increasing trend with the increase number of clustering center, and then reaches the peak score of $76\\%$ with 9 clustering centers. Afterward-" + ], + "bbox": [ + 75, + 501, + 468, + 849 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/928b07312d119816202bb3b75d3d9289246b4a9bde892e01cf4ef89b5bad71bc.jpg", + "table_caption": [ + "Table 3. $IoU(10^{-2})$ values achieved with single point supervision under ideal and real scene." + ], + "table_footnote": [], + "table_body": "
Pseudo Mask (Ideal / Real)Final Results (Ideal / Real)Pseudo Mask (Ideal / Real)Final Results (Ideal / Real)
ResUnet(76.3 / 73.7)(71.6 / 71.2)(60.2 / 58.8)(68.0 / 66.5)
DNANet(72.9 / 72.0)NUDT(70.5 / 69.1)
ResUnet(68.8 / 66.7)(64.6 / 63.8)(47.1 / 45.7)(39.1 / 38.2)
DNANetIRSTD(62.2 / 60.9)NUDT-Sea(40.2 / 38.8)
", + "bbox": [ + 501, + 114, + 890, + 186 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/a8acecc4742c0f1429dd09e4d3bcac8822cbf9f193a8bab338494d6404c6e7f2.jpg", + "table_caption": [ + "Table 4. $IoU(10^{-2})$ values under fixed labelling time. $5.2 \\times$ (with search) and $8.0 \\times$ (w/o search) more point-level (P.) labels help to generate better results under fixed labelling time." + ], + "table_footnote": [], + "table_body": "
Sup.NUAA-SIRSTIRSTD-1k
Time Budget: 920s (427×P.) vs (82×F.) (5.2 × P. labels)Time Budget: 1400s (1000×P.) vs (125×F.) (8.0 × P. labels)
ResUnetFull56.843.8
ResUnet+MCLCP.71.6 ↑ 14.864.6 ↑ 20.8
DNANetFull58.746.1
DNANet+MCLCP.72.1 ↑ 13.462.2 ↑ 16.1
", + "bbox": [ + 501, + 242, + 890, + 328 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "s, the quality of TPM gradually decreases when the number of clustering center further increases. The above results demonstrate that inappropriate number of clustering center will result in over-small or over-large area of initial search region, and thus introduce negative effect on MCLC.", + "bbox": [ + 496, + 354, + 890, + 430 + ], + "page_idx": 6 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "4) Performance with Stronger Supervision: As shown in Table 2, stronger supervision can introduce additional $0.3\\% \\sim 2.6\\%$ improvements in term of IoU on the NUAA-SIRST dataset, but at a cost of $121\\% \\sim 700\\%$ increase of annotation time (i.e., 1.4s, 3.1s, and 11.2s for single-point, multi-point, and pixel-level annotation in Fig. 3). Similar results can be also found on the other three datasets. Therefore, we argue that single-point annotation is the most economical supervision and is strong enough for SIRST detection.", + "5) Labelling Position Deviation: Real-world SIRST application may suffer from labelling position deviation shown in Fig. 8 (a). To simulate the labelling position deviation in real world, we manually re-labelled 105 targets in NUAA-SIRST and IRSTD-1k dataset, and generated a distribution map of labelling position in Fig. 8 (b). Based on this distribution map, we re-produced the pseudo masks of whole dataset and generated the final detection results in Table 3. Average results from three trails demonstrate that our method can produce competitive results under practical labelling settings.", + "6) Time Efficiency: As aforementioned, once the optimal parameters (e.g., type and intensity of noise, number of clustering centers) are searched in one real-world dataset (e.g., NUAA-SIRST), we directly adopt these parameters to new scenes without secondary search (e.g., IRSTD in Table 4). As shown in Table 4, single-point labelling can produce about $5.2 \\times$ (with parameter search) $\\sim 8.0 \\times$ (w/o parameter search) annotation than the pixel-level labelling with the same annotation budget, and thus achieves much better performance. Note that, our MCLC can efficiently" + ], + "bbox": [ + 496, + 431, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_footnote", + "text": "1The intensity value for salt and pepper noise is defined as the area ratio of noise region and image region. Higher values denote that more pixels are replaced by salt or pepper pixels.", + "bbox": [ + 75, + 862, + 468, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "1015", + "bbox": [ + 483, + 926, + 514, + 936 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/b31b6cde55500ad99f23bebf95ae251ebb219213f5fef6b08eb7464a328e5717.jpg", + "table_caption": [ + "Table 5. $IoU(10^{-2})$ , $P_d(10^{-2})$ , and $F_a(10^{-6})$ values achieved by different state-of-the-art methods on four benchmark datasets. For $IoU$ and $P_d$ , larger values indicate better performance. For $F_a$ , smaller values indicate better performance. Unsup. refers to unsupervised methods. The best single-point supervised results are in red and the second best results are in blue." + ], + "table_footnote": [], + "table_body": "
MethodSup.Dataset
NUAA-SIRST [11]IRSTD-1k [45]NUDT-SIRST [23]NUDT-SIRST-sea [39]
Top-Hat [31]Unsup.7.14379.8410126.22255.48595.620.7278.41166.71.172.68095.37
WSLCM [20]Unsup.1.15877.9554460.01955.79315472.28356.8213090.6010.527.330
MSLSTIPT [16]Unsup.10.3082.13113110.3757.0537078.34247.40888.10.330.3506283
NRAM [43]Unsup.12.1674.5213.854.22149.2127.866.92756.4019.270.3517.313.585
PSTNN [44]Unsup.22.4077.9529.119.87151.7299.7514.8566.1344.171.5013.5115.44
ACM [11]Full70.3393.913.72860.9790.5821.7867.0895.9710.1847.5770.4621.31
ACM + KMeans[26]Point46.1688.5927.4533.4154.4241.8241.1877.8834.8638.1542.4523.25
ACM + SuperPixel[1]Point53.8490.4956.1849.6984.6942.3651.7692.3334.6040.4236.7016.92
ACM + GrabCut[33]Point57.6390.8760.4654.0381.9723.9955.2491.656.45738.7652.3715.54
ACM + OursPoint67.0892.0119.8056.5382.3125.0557.7492.3816.7743.6955.699.820
ResUnet[39]Full75.9397.7115.6866.3492.838.19883.7498.094.82046.0560.187.920
ResUnet + KMeans[26]Point22.3439.92156.533.8680.9510.3242.6589.2042.5131.1151.7444.63
ResUnet + SuperPixel[1]Point60.0293.1523.4559.2888.4324.3662.6593.4026.9536.4356.5030.61
ResUnet + GrabCut[33]Point61.3895.4325.1661.6790.1313.9663.0194.0313.4437.0456.1917.32
ResUnet + OursPoint71.5894.6715.2164.5990.816.22368.0493.8625.3539.0659.446.979
DNANet [23]Full76.2497.7112.8068.4494.778.80686.3697.396.89742.1761.6017.19
DNANet + KMeans[26]Point45.6990.4958.1132.9881.6325.1842.8488.0456.9920.5932.6721.59
DNANet + SuperPixel[1]Point62.5993.5314.5458.4489.4527.7064.6895.4433.3938.4236.706.921
DNANet + GrabCut[33]Point61.1497.7120.5361.0091.1520.8764.0097.0340.6528.0849.794.816
DNANet + OursPoint72.8696.9514.4362.2392.1324.1470.5295.5533.2040.2358.3211.29
ISNet [40]Full80.0199.234.9668.7295.6815.4382.5796.4944.1141.2758.8913.26
ISNet + KMeans[26]Point38.2774.88112.729.6769.5238.4344.5789.8766.2032.5744.2035.26
ISNet + SuperPixel[1]Point65.8293.7328.2657.9390.7541.7461.5995.6129.5935.2148.5615.32
ISNet + GrabCut[33]Point63.7296.2726.3262.2991.3719.3465.5394.8945.3133.6848.2423.56
ISNet + OursPoint75.9395.4411.0463.1992.5822.2366.8796.2248.5938.2952.2719.97
UIUNet [45]Full76.8397.6412.3165.2792.7612.4075.3593.3327.6941.8855.6911.56
UIUNet + KMeans[26]Point35.1790.9046.5321.2682.5219.4338.2788.2778.0929.3333.1714.22
UIUNet + SuperPixel[1]Point64.2392.1149.3454.4287.3029.8251.6891.3239.4037.8347.2220.09
UIUNet + GrabCut[33]Point63.2993.8633.2760.3789.2714.2464.3392.5733.5937.0351.5526.12
UIUNet + OursPoint74.2296.2016.1964.1390.7414.9369.3591.1138.2139.2753.2323.14
", + "bbox": [ + 112, + 130, + 857, + 445 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/24808d0399f25673366be30fb23361aea9f930837f47f16ac8cf236db3185fb7.jpg", + "image_caption": [ + "Figure 9. Examples of target probability map (TPM) and the corresponding refined pseudo masks during the MCLC process." + ], + "image_footnote": [], + "bbox": [ + 91, + 468, + 455, + 664 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "recover a single point annotation to a pixel-level one with only 0.075s (average result from 533 targets) on a PC-level CPU.", + "bbox": [ + 75, + 724, + 468, + 770 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Comparison to the State-of-the-art Methods", + "text_level": 1, + "bbox": [ + 76, + 784, + 450, + 800 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We compare our method to several state-of-the-art methods on four benchmark datasets in this subsection. For fair comparison, we used the same hyper-parameters and experimental settings (e.g., special dataset division method in UIUNet[40]) as reported in their original papers when re-implementing comparing methods and retrained all the", + "bbox": [ + 75, + 810, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/f78ab6c85fb761efe00ddf1bc385f11babeae41c0e7e406f57e5de5371321ca9.jpg", + "table_caption": [ + "Table 6. $IoU(10^{-2})$ , $Pd(10^{-2})$ , and $Fa(10^{-6})$ values achieved by existing salient object detection (SOD) methods." + ], + "table_footnote": [], + "table_body": "
Sup.NUAA-SIRSTIRSTD-1k
ResUnetFull75.997.715.766.392.88.19
Res.+PFAN [48]Point27.683.949.622.876.566.2
Res.+F3Net [38]Point33.281.6106.226.371.382.3
ResUnet+MCLCPoint71.694.715.264.690.86.22
DNANetFull76.297.712.868.494.78.8
DNA.+PFAN [48]Point29.385.266.837.678.657.7
DNA.+F3Net [38]Point33.684.978.031.277.161.2
DNANet+MCLCPoint72.996.914.462.292.124.1
", + "bbox": [ + 501, + 494, + 898, + 593 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "models from scratch on these four datasets.", + "bbox": [ + 500, + 626, + 787, + 640 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "1) Quantitative and Qualitative Results: Quantitative results are shown in Table 5. Our Monte Carlo linear clustering method (i.e., MCLC) achieves much better performance over those unsupervised methods. Compared to MCLC with other single-point supervised methods, MCLC can produce better pseudo masks and thus achieve better performance in terms of $P_{d}$ , $F_{a}$ , and $IoU$ . Compared to the fully-supervised counterparts, MCLC enables the respective networks to generate comparable results with $87\\%$ annotation time reduction. Qualitative results on four datasets are shown in Fig. 10. Compared to fully supervised methods, our MCLC can help existing detection methods to produce comparable results in a more time-efficient manner, especially for those point targets (e.g., img-1, img-4) and spot targets (e.g., img-2, img-3, img-5, img-6). Moreover, Fig. 10 (img-7, img-8) demonstrates the robustness of our method on the dense target scenarios. Readers can refer to", + "bbox": [ + 496, + 643, + 893, + 901 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "1016", + "bbox": [ + 483, + 926, + 514, + 936 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8b120c225e4e7b4578eda64dcf250ffb19444bff1b86c1c7c261c6d898ec7566.jpg", + "image_caption": [ + "Figure 10. Qualitative results achieved by DNANet[23] under (b) point-level and (c) pixel-level supervision. The correctly detected target, false alarm, and miss detection areas are highlighted by red, yellow, and green dotted circles. More visualization results are shown in supplementary material." + ], + "image_footnote": [], + "bbox": [ + 101, + 88, + 872, + 391 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "the supplementary material for more visualization results.", + "bbox": [ + 75, + 463, + 455, + 478 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "2) Compared with SOD Methods: Quantitative results in Table 6 show that our MCLC performs much better than those salient object detection (SOD) methods. That is because, although the small targets are salient in local region, a single point label can not provide sufficient supervision to train high-performance SOD methods (e.g., PFAN [48], F3Net [38]). In contrast, our MCLC can make full use of single point labels to obtain higher accuracy.", + "bbox": [ + 75, + 479, + 468, + 599 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 616, + 194, + 632 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this paper, we propose a simple yet effective pipeline for single-frame infrared small target detection with single-point annotation. First, we found that SIRST is generally salient in the local small region and exhibits high energy concentricity. Then, based on this observation, we proposed a linear clustering approach (LCA) to coarsely separate the targets from clustering background by measuring the color and spatial distance with clutter background. To further refine the results, we design a Monte Carlo regularization approach to constrain the clustering process and continuously expand the point-level annotation to a high-quality pixel-level one. Extensive experiments on four benchmark datasets demonstrate that our method achieves comparable performance with fully-supervised methods. We hope our study can draw attention to the research on weakly supervised SIRST detection.", + "bbox": [ + 75, + 642, + 470, + 883 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement: This work was supported in part", + "bbox": [ + 96, + 885, + 468, + 901 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China under Grant 61921001 and National Natural Science Foundation of China 62001478.", + "bbox": [ + 496, + 463, + 890, + 522 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 500, + 536, + 596, + 551 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Radhakrishna Achanta, Appu Shaji, Kevin Smith, Aurelien Lucchi, Pascal Fua, and Sabine Süsstrunk. Slic superpixels compared to state-of-the-art superpixel methods. 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IEEE TGRS, 58(2):1004-1016, 2019. 2" + ], + "bbox": [ + 78, + 90, + 467, + 672 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "1019", + "bbox": [ + 483, + 926, + 514, + 936 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Monte Carlo Linear Clustering with Single-Point Supervision is Enough for Infrared Small Target Detection/ff32047e-26fb-4725-b960-eee153eb3232_model.json b/2023/Monte Carlo Linear Clustering with Single-Point Supervision is Enough for Infrared Small Target Detection/ff32047e-26fb-4725-b960-eee153eb3232_model.json new file mode 100644 index 0000000000000000000000000000000000000000..0a04da97057586c78a94eb16293a1aa91961474c --- /dev/null +++ b/2023/Monte Carlo Linear Clustering with Single-Point Supervision is Enough for Infrared Small Target Detection/ff32047e-26fb-4725-b960-eee153eb3232_model.json @@ -0,0 +1,2334 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.101, + 0.136, + 0.872, + 0.19 + ], + "angle": 0, + "content": "Monte Carlo Linear Clustering with Single-Point Supervision is Enough for Infrared Small Target Detection" + }, + { + "type": "text", + "bbox": [ + 0.238, + 0.212, + 0.732, + 0.231 + ], + "angle": 0, + "content": "Boyang Li\\(^{1}\\), Yingqian Wang\\(^{1}\\), Longguang Wang\\(^{2}\\), Fei Zhang\\(^{3}\\)," + }, + { + "type": "text", + "bbox": [ + 0.295, + 0.231, + 0.674, + 0.248 + ], + "angle": 0, + "content": "Ting Liu\\(^{1}\\), Zaiping Lin\\(^{1\\boxtimes}\\), Wei An\\(^{1}\\), Yulan Guo\\(^{1}\\)" + }, + { + "type": "text", + "bbox": [ + 0.174, + 0.248, + 0.798, + 0.266 + ], + "angle": 0, + "content": "\\(^{1}\\)National University of Defense Technology, \\(^{2}\\)Aviation University of Air Force," + }, + { + "type": "text", + "bbox": [ + 0.359, + 0.266, + 0.611, + 0.284 + ], + "angle": 0, + "content": "\\(^{3}\\)Shanghai Jiao Tong University" + }, + { + "type": "text", + "bbox": [ + 0.327, + 0.286, + 0.644, + 0.301 + ], + "angle": 0, + "content": "{liboyang20, linzaiping}@nudt.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.347, + 0.314, + 0.362 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.379, + 0.474, + 0.786 + ], + "angle": 0, + "content": "Single-frame infrared small target (SIRST) detection aims at separating small targets from clutter backgrounds on infrared images. Recently, deep learning based methods have achieved promising performance on SIRST detection, but at the cost of a large amount of training data with expensive pixel-level annotations. To reduce the annotation burden, we propose the first method to achieve SIRST detection with single-point supervision. The core idea of this work is to recover the per-pixel mask of each target from the given single point label by using clustering approaches, which looks simple but is indeed challenging since targets are always insalient and accompanied with background clutters. To handle this issue, we introduce randomness to the clustering process by adding noise to the input images, and then obtain much more reliable pseudo masks by averaging the clustered results. Thanks to this \"Monte Carlo\" clustering approach, our method can accurately recover pseudo masks and thus turn arbitrary fully supervised SIRST detection networks into weakly supervised ones with only single point annotation. Experiments on four datasets demonstrate that our method can be applied to existing SIRST detection networks to achieve comparable performance with their fully-supervised counterparts, which reveals that single-point supervision is strong enough for SIRST detection. Our code will be available at: https://github.com/YeRen123455/SIRST-Single-Point-Supervision." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.815, + 0.21, + 0.831 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Single-frame infrared small target (SIRST) detection has been widely used in many applications such as marine resource utilization [23, 45], high-precision navigation [34, 13], and ecological environment monitoring [35]." + }, + { + "type": "image", + "bbox": [ + 0.513, + 0.347, + 0.885, + 0.492 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.494, + 0.895, + 0.537 + ], + "angle": 0, + "content": "Figure 1. Pipeline of our method. The proposed Monte Carlo linear clustering along with single-point annotation can produce high-quality pseudo mask (i.e., target probability map (TPM))." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.566, + 0.892, + 0.672 + ], + "angle": 0, + "content": "However, existing SIRST detection methods mainly rely on segmentation pipeline with pixel-level supervision. Pixel-level annotating is time-consuming and thus hinders the quick deployment of those large scale data-dependent scenarios. Therefore, it is in urgent need to alleviate the annotation burden while maintaining state-of-the-art performance in SIRST detection." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Point-level supervision, as an annotation-friendly form of supervision, can provide both category and localization information for each target. Previous works in general object segmentation utilized rich semantic information to design various training loss [4] and network modules [29, 27], and continuously expand the single-point annotation to a pixel-level pseudo mask. Although having achieved promising performance, these methods heavily rely on prior semantic information (e.g., objectness prior in [4, 50], shape prior in [29, 27, 49]), and generally need more than one point as supervision. However, infrared small targets generally occupy no more than \\(0.15\\%\\) area of the whole image [47] and lack texture, shape and color information. Consequently, previous semantic information-dependent methods cannot well adopt to this task." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.925, + 0.516, + 0.937 + ], + "angle": 0, + "content": "1009" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.1, + 0.089, + 0.182, + 0.201 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.121, + 0.202, + 0.16, + 0.219 + ], + "angle": 0, + "content": "(a) Local Saliency" + }, + { + "type": "image", + "bbox": [ + 0.187, + 0.089, + 0.269, + 0.201 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.206, + 0.202, + 0.252, + 0.219 + ], + "angle": 0, + "content": "(b) Similar Shape" + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.089, + 0.358, + 0.201 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.295, + 0.202, + 0.339, + 0.218 + ], + "angle": 0, + "content": "(c) Similar Texture" + }, + { + "type": "image", + "bbox": [ + 0.365, + 0.089, + 0.447, + 0.201 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.365, + 0.202, + 0.442, + 0.218 + ], + "angle": 0, + "content": "(d) Similar Energy Distribution" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.225, + 0.47, + 0.267 + ], + "angle": 0, + "content": "Figure 2. Some inherent characteristics of SIRST observed from the small local regions (i.e., salient in local region, similar shape, texture, and energy distribution)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.294, + 0.469, + 0.49 + ], + "angle": 0, + "content": "We notice that although infrared small targets lack semantic information from the perspective of whole image, they are quite salient in the local small region. Specifically, as shown in Fig. 2, small targets in infrared images generally have high energy concentricity and exhibit significant gradient difference in their local regions. Moreover, limited semantic information (e.g., weak texture, shape, and color distribution) makes most point-like and spot-like targets exhibit similar energy distribution (e.g., Gaussian distribution). Consequently, it is straightforward to use a simple linear clustering approach (LCA) to separate the salient regions by measuring their color and spatial distances with adjacent backgrounds." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.491, + 0.47, + 0.809 + ], + "angle": 0, + "content": "However, LCA easily falls into local optimum and produces inaccurate segmentation results due to their fixed hyper-parameters. To handle this problem, we propose a Monte Carlo linear clustering (MCLC) method to regularize the clustering process and recover the reliable clustering result by repetitive random experiments. Specifically, we introduce randomness to the clustering process by adding noise to the input images. With the help of random noise, the distance between unexpected background region and target region can be significantly enlarged. The misclustered target regions can be pushed away from the false clustering center and thus return back the true clustering center. In this way, the single-point annotation can be gradually recovered as a much more reliable pixel-level target probability map (TPM) by averaging the clustered results. Pixels with larger values in TPM represent a higher probability of belonging to the target. Finally, we use the refined TPM to turn arbitrary fully supervised SIRST detection networks into weakly supervised ones with only single point annotation. Fig. 1 shows the overall pipeline of our method, and the main contributions are summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.094, + 0.825, + 0.47, + 0.902 + ], + "angle": 0, + "content": "- To the best of our knowledge, this is the first single-point supervised method to achieve SIRST detection. A Monte Carlo linear clustering-based pipeline is proposed to achieve comparable performance with the fully supervised counterpart by using single-point anno" + }, + { + "type": "text", + "bbox": [ + 0.533, + 0.093, + 0.576, + 0.106 + ], + "angle": 0, + "content": "taion." + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.121, + 0.892, + 0.198 + ], + "angle": 0, + "content": "- Inspired by the inherent characteristic of SIRST, a simple yet effective linear clustering approach with random noise-guided Monte Carlo regularization is proposed to coarsely extract and further refine the candidate target region." + }, + { + "type": "text", + "bbox": [ + 0.517, + 0.211, + 0.892, + 0.288 + ], + "angle": 0, + "content": "- Experiments on four public SIRST datasets demonstrate the effectiveness of our method. Ablation study reveals that pixel-level labels are not necessary for SIRST detection while single-point supervision is strong enough." + }, + { + "type": "list", + "bbox": [ + 0.517, + 0.121, + 0.892, + 0.288 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.305, + 0.642, + 0.321 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.331, + 0.783, + 0.347 + ], + "angle": 0, + "content": "2.1. Infrared Small Target Detection" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.355, + 0.892, + 0.551 + ], + "angle": 0, + "content": "SIRST detection has been extensively investigated for decades. Early traditional paradigm achieves SIRST detection by measuring the discontinuity between targets and backgrounds. Typical methods include filtering-based methods [31, 14], local contrast measure-based methods [6, 18, 19, 20, 22, 36], and low rank-based methods [16, 43, 9, 44, 51, 10]. Since real scenes are much more complex with dramatic changes in target size, shape, and clutter background, it is difficult to use handcrafted features and fixed hyper-parameters to handle such variations. To address this problem, recent deep learning-based methods learn trainable features in a data-driven manner and thus achieve better performance than traditional ones." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.893, + 0.854 + ], + "angle": 0, + "content": "Existing deep learning-based methods can be divided into detection based methods and segmentation based methods. Since the pixel-level classification result is essential for the subsequent recognition task in SIRST, segmentation-based methods have attracted increasing attention recently. Dai et al. [11] proposed the first segmentation-based network (i.e., ACM). They designed an asymmetric contextual module to aggregate features from shallow layers and deep layers. Then, Dai et al. [12] improved ACM by introducing a dilated local contrast measure. Specifically, a feature cyclic shift scheme was designed to achieve a trainable local contrast measure. After that, Zhang et al. [45] modeled SIRST detection as a shape detection task. A taylor finite difference (TFD)-inspired edge block and a two-orientation attention aggregation (TOAA) block were proposed to capture precise shape of infrared targets. Recently, Li et al. [23] proposed a dense nested attention network (DNANet). A specifically-designed dense nested interactive module (DNIM) was proposed to both extract high-level information and maintain the response of small targets in deep layers." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Although the performance has been continuously improved by recent networks, existing deep learning-based methods rely on the fully-supervised training scheme with" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.925, + 0.516, + 0.937 + ], + "angle": 0, + "content": "1010" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.102, + 0.092, + 0.451, + 0.232 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.235, + 0.47, + 0.276 + ], + "angle": 0, + "content": "Figure 3. Sample of input images, four common weakly supervised annotations (i.e., single-point, multi-point, scribble, bounding box), and one fully supervised pixel-level annotation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.301, + 0.47, + 0.346 + ], + "angle": 0, + "content": "pixel-level annotations. Expensive labor cost makes existing methods hard to be deployed to large scale data-dependent tasks." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.352, + 0.315, + 0.367 + ], + "angle": 0, + "content": "2.2. Point-based Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.371, + 0.47, + 0.718 + ], + "angle": 0, + "content": "Point-level supervision has been widely used in many high-level tasks (e.g., object detection [7, 46], object localization [41], and semantic segmentation [4, 29, 27, 24, 49]) and yield promising performance. For semantic segmentation task, Bearman et al. [4] proposed the first single-point supervised semantic segmentation method. They incorporated the single-point supervision along with an objectness prior as the loss function to infer the extent of the object. Then, Papadopoulos et al. [29] and Maninis et al. [27] utilized four extreme points (i.e., left-most, right-most, top, and bottom pixels) as supervision to further improve the quality of the pseudo mask. After that, Austin et al. [28] followed the class activation maps (CAM) [50] pipeline and used the point annotation to refine the quality of pseudo labels. More recently, Li et al. [24] utilized the semantical consistency property of general objects with 20 randomly annotated points to achieve comparable segmentation results with fully-supervised counterpart. Moreover, in the field of cell segmentation, Zhao et al. [49] proposed the first single-point supervised segmentation method, in which two semantic prior-based training losses (i.e., divergence loss and consistency loss) were proposed to achieve high-quality cell segmentation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.719, + 0.47, + 0.839 + ], + "angle": 0, + "content": "Although promising performance has been achieved, existing works rely on rich semantic information (e.g., objectness prior in [4, 50], shape prior in [29, 27, 49]) and most of them need multi-point annotation. Infrared small targets generally occupy no more than \\(0.15\\%\\) area of the whole image [47] and lack texture, shape and color information. Previous semantic information-dependent methods cannot be directly used for SIRST detection." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.849, + 0.212, + 0.866 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "In this section, we first introduce the motivation. Then, a detailed illustration of the proposed linear clustering ap" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "proach with Monte Carlo regularization is provided. Overall architecture of proposed method is shown in Fig. 4." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.132, + 0.622, + 0.146 + ], + "angle": 0, + "content": "3.1. Motivation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.155, + 0.892, + 0.321 + ], + "angle": 0, + "content": "We investigate the annotation cost of four common weakly-supervised annotations (i.e., single point [5], multiple points[5, 29, 27], scribbles [25], bounding boxes[21]) by re-labelling the NUDT-SIRST [23] and NUAA-SIRST [11] datasets. Fig. 3 shows the average annotation time of four weakly-supervised and one fully-supervised approaches. Note that, single-point supervision can reduce about \\(87\\%\\) annotation time as compared to the pixel-level annotation approach, which motivates us to apply single-point annotation to SIRST detection. Please refer to the supplementary material for more detailed analysis." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.322, + 0.892, + 0.488 + ], + "angle": 0, + "content": "However, existing point-level supervised methods [5, 29, 27] are designed for general objects with rich semantic information (e.g., shape, texture, and color). As shown in Fig. 2, the characteristics of infrared small targets make the aforementioned semantic-based pipeline unsuitable for SIRST detection. Considering that infrared small targets are quite salient in their local regions and share similar shape, texture, and energy distribution. Intuitively, we can use simple linear clustering approaches (e.g., Super-pixel [1], K-Means [26]) to separate the salient regions by comparing their color and spatial distances among these clusters." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.498, + 0.755, + 0.514 + ], + "angle": 0, + "content": "3.2. Linear Clustering Approach" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.521, + 0.892, + 0.687 + ], + "angle": 0, + "content": "Without loss of generality, we take the quick linear clustering method SuperPixel [1] as an example to introduce how to use LCA to coarsely separate the target region. It should be noted that other linear clustering approaches such as KMeans [26] can be also used in our method, as demonstrated in Fig. 5. The pipeline of our LCA is shown in Fig. 4 (Step I \\(\\sim\\) Step III), in which the clustering center of the image is first initialized, and then adjusted according to a color and spatial distance based measurement. Finally, the clustering center is continuously updated until the pre-defined convergence requirements are met." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.687, + 0.892, + 0.831 + ], + "angle": 0, + "content": "1) Clustering Center Initialization: We initialize the clustering center based on the pre-defined number of clusters \\( N \\). Given an input image \\( I \\in \\mathbb{R}^{H \\times W} \\), we first divide it into \\( N \\) regions with equal areas and fixed grid interval \\( S = \\sqrt{\\frac{H \\times W}{N}} \\) (as shown in Fig. 4-Step 1). After that, the clustering center is first initialized as the centroid of each region, and then moved to the lowest gradient position of its \\( 3 \\times 3 \\) neighborhood. The clustering center of the \\( n^{th} \\) clustering region \\( \\mathcal{C}_n \\) can be represented as a vector as:" + }, + { + "type": "equation", + "bbox": [ + 0.64, + 0.843, + 0.892, + 0.863 + ], + "angle": 0, + "content": "\\[\n\\mathcal {C} _ {n} = \\left[ c _ {n}, s _ {n} \\right] ^ {T}, \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.868, + 0.891, + 0.902 + ], + "angle": 0, + "content": "where \\([c_n]^T\\) represents the CIELAB color [32] of \\(\\mathcal{C}_n\\), \\([s_n]^T\\) denotes the spatial position in image coordinate of \\(\\mathcal{C}_n\\)." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.927, + 0.514, + 0.938 + ], + "angle": 0, + "content": "1011" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.087, + 0.885, + 0.386 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.393, + 0.893, + 0.463 + ], + "angle": 0, + "content": "Figure 4. Illustration of our method. StepI \\(\\sim\\) StepIII: LCA can coarsely separate target from clutter background, but easily falls into local optimum and produce incomplete pseudo mask. StepIV \\(\\sim\\) StepV: Monte Carlo regularization can increase the color distance between background and target region and thus enforce the misclustered target region away from the false clustering center. After repetitive random experiments, the accumulated clustering results are finally shown as a target probability map (TPM), where pixels with larger values represent a higher probability of belonging to the target." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.487, + 0.47, + 0.624 + ], + "angle": 0, + "content": "2) Distance Measurement: After clustering center initialization, we adopt a color and spatial distance based measurement to determine the clustering center of each pixel. As shown in Fig. 4-Step II, for each clustering center \\( \\mathcal{C}_n \\), we use \\( L_2 \\) distance to measure its distance with each pixel \\( p_i = [c_i, s_i]^T \\) in its adjacent \\( 2S \\times 2S \\) regions. Considering that the ranges of color value and spatial position value are inconsistent, we normalize the both distance values with normalization coefficient \\( \\mu_s \\) and \\( \\mu_c \\). \\( \\mathcal{D}(\\mathcal{C}_n, p_i) \\) is written as:" + }, + { + "type": "equation", + "bbox": [ + 0.12, + 0.644, + 0.47, + 0.707 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {D} (\\mathcal {C} _ {n}, p _ {i}) = \\sqrt {(\\mathcal {D} _ {c}) ^ {2} + (\\mathcal {D} _ {s}) ^ {2}} \\\\ = \\sqrt {\\frac {\\left(c _ {p _ {i}} - c _ {\\mathcal {C} _ {n}}\\right) ^ {2}}{\\mu_ {c} ^ {2}} + \\frac {\\left(s _ {p _ {i}} - s _ {\\mathcal {C} _ {n}}\\right) ^ {2}}{\\mu_ {s} ^ {2}}}. \\tag {2} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.714, + 0.469, + 0.743 + ], + "angle": 0, + "content": "Then, the clustering label \\( l \\) for each pixel \\( p_i \\) can be determined as:" + }, + { + "type": "equation", + "bbox": [ + 0.135, + 0.758, + 0.469, + 0.777 + ], + "angle": 0, + "content": "\\[\nl \\left(p _ {i}\\right) = \\operatorname {a r g m i n} _ {\\mathrm {n} \\in \\{1, 2, 3, \\dots , \\mathrm {N} \\}} \\left[ \\mathcal {D} \\left(\\mathcal {C} _ {\\mathrm {n}}, \\mathrm {p} _ {\\mathrm {i}}\\right) \\right]. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.781, + 0.47, + 0.9 + ], + "angle": 0, + "content": "3) Updating and Convergence: After determining the clustering center of each pixel at the current iteration, we repetitively update the position of each clustering center until convergence, as shown in Fig. 4-Step III. Specifically, we first calculate the clustering centers to be the mean vector \\([c_m, s_m]^T\\) of all the pixels \\(P = \\{p_1, p_2, \\dots, p_m\\}\\) with the same clustering label \\(l(\\mathcal{C}_n')\\). The new clustering center \\(\\mathcal{C}_n'\\) can be formulated as:" + }, + { + "type": "image", + "bbox": [ + 0.506, + 0.485, + 0.889, + 0.625 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.629, + 0.892, + 0.685 + ], + "angle": 0, + "content": "Figure 5. Visualization results achieved by (a) Kmeans, (b) K-means with Monte Carlo Regularization, (c) Super pixel, (d) Super pixel with Monte Carlo Regularization. Our proposed Monte Carlo regularization helps to expand informative target region." + }, + { + "type": "equation", + "bbox": [ + 0.563, + 0.729, + 0.892, + 0.767 + ], + "angle": 0, + "content": "\\[\n\\mathcal {C} _ {n} ^ {\\prime} \\left(c _ {n}, x _ {n}, y _ {n}\\right) = \\frac {1}{| P |} \\sum_ {p _ {m} \\in P} \\left(c _ {p _ {m}}, s _ {p _ {m}}\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.902 + ], + "angle": 0, + "content": "After that, we adopt \\( L_{2} \\) norm to compute a distance \\( \\mathcal{E} \\) between new clustering center locations \\( \\mathcal{C}_n' \\) and previous clustering center locations \\( \\mathcal{C}_n \\). The updating steps can be repeated iteratively until the error is smaller than the predefined threshold \\( T \\). That is \\( \\| \\mathcal{C}_n' - \\mathcal{C}_n \\|_2 < T \\), where \\( \\| \\cdot \\|_2 \\) denote the L2 norm. Finally, we assign the single-point annotation \\( p_{Aanno} \\) located at the \\( n^{th} \\) clustering region as the clustering result \\( M_{pred} \\)." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.925, + 0.516, + 0.937 + ], + "angle": 0, + "content": "1012" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.089, + 0.277, + 0.212 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.277, + 0.089, + 0.468, + 0.212 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.214, + 0.47, + 0.31 + ], + "angle": 0, + "content": "Figure 6. Quantitative analysis on (a) Sensitivity of target and non-target regions to additional noise, and (b) Color distance of target edge region with true foreground region centroid \\(\\Delta (\\mathcal{D}_c(\\mathcal{C}^T,M_{pred}))\\) and false background region centroid \\(\\Delta (\\mathcal{D}_c(\\mathcal{C}^F,M_{pred}))\\). Average results from 10 trails are reported. Readers can refer to the supplementary material for more detailed illustration." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.333, + 0.331, + 0.349 + ], + "angle": 0, + "content": "3.3. Monte Carlo Regularization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.356, + 0.469, + 0.462 + ], + "angle": 0, + "content": "Although LCA can coarsely separate local salient regions from the backgrounds, as shown in Fig. 5 (a) and (c), a linear clustering method easily falls into local optimum and generates incomplete or oversized results. In this subsection, we first analyze the reason of this issue, and then propose a Monte Carlo regularization to alleviate this issue, as shown in Fig. 4 (StepIV \\(\\sim\\) StepV)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.462, + 0.47, + 0.668 + ], + "angle": 0, + "content": "1) Inaccurate Result within a Single Clustering: Due to the varied size of small targets, LCA with fixed number of clustering centers cannot produce ideal results for all kinds of targets. That is because, both color \\( \\mathcal{D}_c \\) and spatial distance \\( \\mathcal{D}_s \\) determine the output of linear clustering model in Equation 2. Since edge areas \\( M_{pred}^{Edge} = \\{m_{pred}^{Edge(1)}, m_{pred}^{Edge(2)}, \\dots, m_{pred}^{Edge(Z)}\\} \\) of the spot and extended target (i.e., big target) are generally far from the true clustering center \\( \\mathcal{C}^T \\) (shown as the left-most green point in Fig. 4-Step III). The spatial distance \\( \\mathcal{D}_c(\\mathcal{C}^T, M_{pred}^{Edge}) \\) between the true clustering center \\( \\mathcal{C}^T \\) and edge areas \\( M_{pred}^{Edge} \\) is usually farther than that of the false clustering center \\( \\mathcal{C}^F \\). That is:" + }, + { + "type": "equation", + "bbox": [ + 0.138, + 0.68, + 0.469, + 0.703 + ], + "angle": 0, + "content": "\\[\n\\mathcal {D} _ {s} \\left(\\mathcal {C} ^ {T}, m _ {\\text {p r e d}} ^ {\\text {E d g e} (z)}\\right) > \\mathcal {D} _ {s} \\left(\\mathcal {C} ^ {F}, m _ {\\text {p r e d}} ^ {\\text {E d g e} (z)}\\right). \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.707, + 0.469, + 0.783 + ], + "angle": 0, + "content": "Moreover, the color value of big target generally exhibits Gaussian distribution. Those edge areas often exhibit relatively high color difference with the true clustering center, and are close to the adjacent false clustering center (shown as the right-most green point in Fig. 4 Step III). That is:" + }, + { + "type": "equation", + "bbox": [ + 0.138, + 0.793, + 0.469, + 0.815 + ], + "angle": 0, + "content": "\\[\n\\mathcal {D} _ {c} \\left(\\mathcal {C} ^ {T}, m _ {\\text {p r e d}} ^ {\\text {E d g e} (z)}\\right) > \\mathcal {D} _ {c} \\left(\\mathcal {C} ^ {F}, m _ {\\text {p r e d}} ^ {\\text {E d g e} (z)}\\right). \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.822, + 0.469, + 0.87 + ], + "angle": 0, + "content": "As a result, the label of edge areas \\( l_{pred}^{Edge} \\) may be falsely included into the adjacent false clustering center \\( \\mathcal{C}^F \\), resulting in incomplete clustering result." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "2) Random Noise Guided Regularization: Spatial distance \\(\\mathcal{D}_s\\) is generally fixed and hard to change in the im" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.242 + ], + "angle": 0, + "content": "age. As shown in Fig. 6 (a), when adding random noise, target and non-target regions exhibit different sensitivity to the noise. Target regions with higher color vaule are more robust to the additional noise than the non-target regions. Based on this finding, we are motivated to introduce random noise to enlarge the color distance \\(\\mathcal{D}_c(\\mathcal{C}^F,M_{pred}^{Edge})\\) between edge areas and false clustering center (as shown in Fig. 4-Step III), and thus make the edge areas be clustered to the true clustering center. Random noise-regularized clustering result can be formulated as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.59, + 0.256, + 0.892, + 0.275 + ], + "angle": 0, + "content": "\\[\nM _ {p r e d} ^ {N o i s e} = L C A (c l i p (I + \\mathcal {N})), \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.279, + 0.892, + 0.338 + ], + "angle": 0, + "content": "where \\( \\text{clip}(\\cdot) \\) operation represents that color values larger than 255 will be fixed at 255. \\( \\mathcal{N} \\) is the additional random noise. The color value change caused by random noise can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.563, + 0.352, + 0.892, + 0.371 + ], + "angle": 0, + "content": "\\[\n\\Delta \\left(\\mathcal {D} _ {c} \\left(\\mathcal {C}, M _ {p r e d}\\right)\\right) = \\mathcal {D} _ {c} ^ {\\text {N o i s e}} - \\mathcal {D} _ {c} ^ {\\text {C l e a n}}. \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.375, + 0.892, + 0.601 + ], + "angle": 0, + "content": "Since background region has relatively low color value than foreground region. Additional noise will greatly increase the color value of adjacent false clustering centers, and thus enlarges their color distance with the edge area of target region. On the contrary, when comparing Fig. 4-Step IV with Fig. 4-Step V, we observe that foreground regions have high energy concentricity and are usually close to saturation. Additional noise cannot bring so much color change to target regions as the background regions. Benefited by the additional noise, as shown in Fig. 6 (b), the change of color distance between edge areas and false clustering center (i.e., \\(\\Delta (\\mathcal{D}_c(\\mathcal{C}^F,M_{pred}))\\)) will be significantly larger than that between edge areas and true clustering center (i.e., \\(\\Delta (\\mathcal{D}_c(\\mathcal{C}^T,M_{pred}))\\)), making the misclustered target region be more closed to the true clustering center." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.602, + 0.892, + 0.737 + ], + "angle": 0, + "content": "3) Monte Carlo Process: As aforementioned, random noise can enforce the misclustered region to be gradually close to the true clustering center. Considering the randomness of noise, additional noise does not always bring such positive effect. We are motivated to adopt the Monte Carlo method to accumulate the clustering result from repetitive random experiments and gradually recover the reliable clustering result. To this end, we perform \\( K \\) independent clustering and formulate this process as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.549, + 0.759, + 0.892, + 0.8 + ], + "angle": 0, + "content": "\\[\nM _ {P r e d} ^ {F u l l} = \\frac {1}{K} \\sum_ {k = 1} ^ {K} \\left(L C A \\left(\\operatorname {c l i p} \\left(I + \\mathcal {N} ^ {(k)}\\right)\\right)\\right), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.809, + 0.892, + 0.871 + ], + "angle": 0, + "content": "where \\( M_{Pred}^{Full} \\) is the accumulated clustering results after \\( K \\) independent clustering by LCA, and finally shown as a target probability map (TPM), where pixels with larger values represent a higher probability of belonging to the target." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The optimization process finally stops when the distance between the new clustering center locations \\(\\mathcal{C}'\\) and previous" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.926, + 0.516, + 0.938 + ], + "angle": 0, + "content": "1013" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.09, + 0.27, + 0.211 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.274, + 0.09, + 0.465, + 0.21 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.215, + 0.47, + 0.286 + ], + "angle": 0, + "content": "Figure 7. IoU scores achieved by our method with (a) different types and intensity of additional noise and (b) different number of clustering center on the NUAA-SIRST dataset. Average results from 5 trails are reported. Readers can refer to the supplementary material for additional experiments on the other datasets." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.299, + 0.47, + 0.355 + ], + "angle": 0, + "content": "Table 1. \\( IoU(10^{-2}) \\) value achieved by the different variants of our method on the training set of four representative datasets (i.e., NUAA, IRSTD, NUDT, NUDT-sea). MC Regu. refers to Monte Carlo regularization." + }, + { + "type": "table", + "bbox": [ + 0.088, + 0.355, + 0.462, + 0.414 + ], + "angle": 0, + "content": "
Point LabelLCAMC Regu.dCRFIoU(%)
✓✓2.53 / 1.62 / 2.28 / 1.82
✓✓51.8 / 55.5 / 51.2 / 38.1
✓✓✓70.4 / 66.2 / 52.5 / 43.9
✓✓✓✓76.3 / 68.8 / 60.2 / 47.1
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.442, + 0.47, + 0.473 + ], + "angle": 0, + "content": "clustering center locations \\(\\mathcal{C}\\) is smaller than the pre-defined threshold \\(T^F\\), i.e., \\(\\| \\mathcal{C}_n' - \\mathcal{C}_n\\|_2 < T^F\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.489, + 0.21, + 0.507 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.516, + 0.47, + 0.652 + ], + "angle": 0, + "content": "In this section, we first introduce our evaluation metrics and implementation details. Then, we compare our MCLC to several state-of-the-art unsupervised, point-level supervised, and fully-supervised SIRST detection methods. Finally, we present ablation studies to investigate the effectiveness of our method. Note that, we search for optimal parameters of MCLC in the training set of NUAA-SIRST [11] and directly adopt them as default parameters to generate pseudo masks on the other three datasets[45, 23, 39]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.665, + 0.262, + 0.68 + ], + "angle": 0, + "content": "4.1. Evaluation Metrics" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Considering that both the quality of pseudo labels and the final detection results are crucial to SIRST detection, we followed previous works [37, 42, 3, 2] and propose a two-stage pipeline (i.e., pseudo mask and final detection result evaluation) to comprehensively evaluate the effectiveness of the proposed method. Firstly, we followed the same metrics in weakly-supervised general object segmentation [3, 2] and adopted intersection of union \\((IoU)\\) to evaluate the quality of generated pseudo labels on the training set. For the final detection results evaluation, we followed previous works [11, 12, 23] and adopted probability of detection \\((P_d)\\), and false-alarm rate \\(F_{a}\\) to evaluate the localization precision, and used \\(IoU\\) to evaluate the shape description ability on the test set." + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.09, + 0.603, + 0.143 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.603, + 0.091, + 0.681, + 0.143 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.144, + 0.603, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.603, + 0.144, + 0.681, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.682, + 0.091, + 0.888, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.22, + 0.892, + 0.276 + ], + "angle": 0, + "content": "Figure 8. (a) Labelling deviation examples of small target from four datasets. (b) Label deviation distribution map generated from 105 manually re-labelled targets. Real world labelling deviation of small target is generally less than 3 pixels." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.293, + 0.719, + 0.308 + ], + "angle": 0, + "content": "4.2. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.31, + 0.892, + 0.505 + ], + "angle": 0, + "content": "1) Datasets: We evaluated our method on the NUAA-SIRST [11], IRSTD-1k [45], NUDT-SIRST [23], and NUDT-SIRST-sea [39] datasets. Without specification, for the NUAA-SIRST and NUDT-SIRST datasets, we used the same division as in [23] and set the ratio of train-val set to test set as 1. For the IRSTD-1k dataset, we followed [45] and used \\(80\\%\\) data for training and validation, and the remaining \\(20\\%\\) data for test. The division setting in [39] was adopted for the NUDT-SIRST-sea dataset, i.e., 41 images were used for training and validation, and the remaining 7 images were used for test. Note that, only single point-level annotation with category information (i.e., point, spot, and extend categories) are available during network training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.507, + 0.893, + 0.837 + ], + "angle": 0, + "content": "2) Training Details: In our experiments, all input images were first normalized before training. Then, these normalized images were sequentially processed by random flip, and random crop for data augmentation. Next, these images were resized to a fixed resolution. Specifically, \\(1024 \\times 1024\\) and \\(256 \\times 256\\) spatial resolutions were used for the NUDT-SIRST-sea and the remaining three datasets, respectively. Finally, we fed these resized datasets into network for both training and evaluation. Without specification, we adopted the centroid of ground truth mask as the single-point label. The influence of label position deviation is discussed in the following ablation. Moreover, all networks were trained with the Soft-IoU loss function and optimized by the Ada-grad method [15] with the CosineAnnealingLR scheduler. The Xavier method [17] was used for all weights and bias parameters initialization. We set the learning rate and epoch number to 0.05 and 1500, respectively. The batch size was set to 16 for the NUAA-SIRST, IRSTD-1k, NUDT-SIRST datasets but set to 4 for the NUDT-SIRST-sea dataset due to its large image size. All models were implemented in PyTorch [30] on a computer with an AMD Ryzen 9 3950X @ 2.20 GHz CPU and an Nvidia GeForce 3090 GPU." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.848, + 0.654, + 0.864 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "1) Effectiveness of Proposed Components: Table 1 shows the contribution of our proposed components on four" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.927, + 0.516, + 0.938 + ], + "angle": 0, + "content": "1014" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.47, + 0.117 + ], + "angle": 0, + "content": "Table 2. \\( IoU(10^{-2}) \\) values and corresponding labelling cost with stronger supervision on the train set of four datasets." + }, + { + "type": "table", + "bbox": [ + 0.115, + 0.117, + 0.434, + 0.187 + ], + "angle": 0, + "content": "
AnnotationDataset
NUAAIRSTDNUDTNUDT-sea
Single-Point76.368.860.247.1
Multi-Point76.669.162.653.7
Scribble78.570.563.255.2
Bounding-Box78.971.864.854.5
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.214, + 0.47, + 0.501 + ], + "angle": 0, + "content": "datasets. Compared to the initial single-point label, linear clustering approach (LCA) introduces \\(49.3\\%\\), \\(53.9\\%\\), \\(48.9\\%\\), \\(36.3\\%\\) improvements for the NUAA, IRSTD-1k, NUDT, NUDT-sea datasets, respectively. That is because, LCA utilizes the inherent characteristics of infrared small targets and thus coarsely separates the targets from clustering background. By introducing random salt noise to regularize the linear clustering process, we obtain much more reliable results and achieve additional \\(18.6\\%\\), \\(10.7\\%\\), \\(1.3\\%\\), \\(5.8\\%\\) improvements on the above four datasets. After that, denseCRF [8] was used as a post-processing module to refine the target probability map (TPM) generated by MCLC. It further introduces \\(5.9\\%\\), \\(2.6\\%\\), \\(7.7\\%\\), \\(3.2\\%\\) improvements for the above four datasets, respectively. We visualize the Monte Carlo linear clustering process in Fig. 9. Although easily producing inaccurate results at the beginning of clustering (e.g., iteration number less than 20), MCLC can gradually recover a reliable clustering result. More visualization samples are shown in supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.502, + 0.47, + 0.729 + ], + "angle": 0, + "content": "2) Type and Intensity of Noise: Fig. 7 (a) shows the change trend of \\( IoU \\) with respect to different noise intensity under three types of common noise (i.e., salt, pepper, and Gaussian). With the increase of noise intensity, the \\( IoU \\) of MCLC with denseCRF under salt noise and pepper noise increases rapidly at the beginning, and reaches their peak scores of \\( 76\\% \\) and \\( 71\\% \\) at \\( 0.05 \\) intensity1. After that, excessive intensity value reduces the saliency of target region and thus results in the decrease of \\( IoU \\). Moreover, Gaussian noise causes huge performance decrease under any intensity. That is because, Gaussian noise randomly changes the values of all pixels in the image, which is similar to the salt and pepper with high intensity. Since all pixels in the image are influenced by the random noise, the saliency of target is greatly decreased, resulting in dramatic performance drop." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.73, + 0.47, + 0.851 + ], + "angle": 0, + "content": "3) Number of Clustering Center: The number of clustering center determines the initial area of each clustering region. Fig. 7 (b) reports the \\( IoU \\) of the results generated by MCLC with denseCRF, MCLC with fixed threshold, and LCA under different number of clustering center. It shows that the \\( IoU \\) firstly shows a rapid increasing trend with the increase number of clustering center, and then reaches the peak score of \\( 76\\% \\) with 9 clustering centers. Afterward-" + }, + { + "type": "list", + "bbox": [ + 0.076, + 0.502, + 0.47, + 0.851 + ], + "angle": 0, + "content": null + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.863, + 0.47, + 0.902 + ], + "angle": 0, + "content": "1The intensity value for salt and pepper noise is defined as the area ratio of noise region and image region. Higher values denote that more pixels are replaced by salt or pepper pixels." + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.089, + 0.892, + 0.115 + ], + "angle": 0, + "content": "Table 3. \\( IoU(10^{-2}) \\) values achieved with single point supervision under ideal and real scene." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.115, + 0.892, + 0.188 + ], + "angle": 0, + "content": "
Pseudo Mask (Ideal / Real)Final Results (Ideal / Real)Pseudo Mask (Ideal / Real)Final Results (Ideal / Real)
ResUnet(76.3 / 73.7)(71.6 / 71.2)(60.2 / 58.8)(68.0 / 66.5)
DNANet(72.9 / 72.0)NUDT(70.5 / 69.1)
ResUnet(68.8 / 66.7)(64.6 / 63.8)(47.1 / 45.7)(39.1 / 38.2)
DNANetIRSTD(62.2 / 60.9)NUDT-Sea(40.2 / 38.8)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.202, + 0.892, + 0.243 + ], + "angle": 0, + "content": "Table 4. \\( IoU(10^{-2}) \\) values under fixed labelling time. \\( 5.2 \\times \\) (with search) and \\( 8.0 \\times \\) (w/o search) more point-level (P.) labels help to generate better results under fixed labelling time." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.243, + 0.892, + 0.329 + ], + "angle": 0, + "content": "
Sup.NUAA-SIRSTIRSTD-1k
Time Budget: 920s (427×P.) vs (82×F.) (5.2 × P. labels)Time Budget: 1400s (1000×P.) vs (125×F.) (8.0 × P. labels)
ResUnetFull56.843.8
ResUnet+MCLCP.71.6 ↑ 14.864.6 ↑ 20.8
DNANetFull58.746.1
DNANet+MCLCP.72.1 ↑ 13.462.2 ↑ 16.1
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.355, + 0.892, + 0.431 + ], + "angle": 0, + "content": "s, the quality of TPM gradually decreases when the number of clustering center further increases. The above results demonstrate that inappropriate number of clustering center will result in over-small or over-large area of initial search region, and thus introduce negative effect on MCLC." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.432, + 0.892, + 0.581 + ], + "angle": 0, + "content": "4) Performance with Stronger Supervision: As shown in Table 2, stronger supervision can introduce additional \\(0.3\\% \\sim 2.6\\%\\) improvements in term of IoU on the NUAA-SIRST dataset, but at a cost of \\(121\\% \\sim 700\\%\\) increase of annotation time (i.e., 1.4s, 3.1s, and 11.2s for single-point, multi-point, and pixel-level annotation in Fig. 3). Similar results can be also found on the other three datasets. Therefore, we argue that single-point annotation is the most economical supervision and is strong enough for SIRST detection." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.583, + 0.892, + 0.749 + ], + "angle": 0, + "content": "5) Labelling Position Deviation: Real-world SIRST application may suffer from labelling position deviation shown in Fig. 8 (a). To simulate the labelling position deviation in real world, we manually re-labelled 105 targets in NUAA-SIRST and IRSTD-1k dataset, and generated a distribution map of labelling position in Fig. 8 (b). Based on this distribution map, we re-produced the pseudo masks of whole dataset and generated the final detection results in Table 3. Average results from three trails demonstrate that our method can produce competitive results under practical labelling settings." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.901 + ], + "angle": 0, + "content": "6) Time Efficiency: As aforementioned, once the optimal parameters (e.g., type and intensity of noise, number of clustering centers) are searched in one real-world dataset (e.g., NUAA-SIRST), we directly adopt these parameters to new scenes without secondary search (e.g., IRSTD in Table 4). As shown in Table 4, single-point labelling can produce about \\(5.2 \\times\\) (with parameter search) \\(\\sim 8.0 \\times\\) (w/o parameter search) annotation than the pixel-level labelling with the same annotation budget, and thus achieves much better performance. Note that, our MCLC can efficiently" + }, + { + "type": "list", + "bbox": [ + 0.498, + 0.432, + 0.892, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.927, + 0.516, + 0.938 + ], + "angle": 0, + "content": "1015" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.892, + 0.131 + ], + "angle": 0, + "content": "Table 5. \\( IoU(10^{-2}) \\), \\( P_d(10^{-2}) \\), and \\( F_a(10^{-6}) \\) values achieved by different state-of-the-art methods on four benchmark datasets. For \\( IoU \\) and \\( P_d \\), larger values indicate better performance. For \\( F_a \\), smaller values indicate better performance. Unsup. refers to unsupervised methods. The best single-point supervised results are in red and the second best results are in blue." + }, + { + "type": "table", + "bbox": [ + 0.113, + 0.131, + 0.859, + 0.446 + ], + "angle": 0, + "content": "
MethodSup.Dataset
NUAA-SIRST [11]IRSTD-1k [45]NUDT-SIRST [23]NUDT-SIRST-sea [39]
Top-Hat [31]Unsup.7.14379.8410126.22255.48595.620.7278.41166.71.172.68095.37
WSLCM [20]Unsup.1.15877.9554460.01955.79315472.28356.8213090.6010.527.330
MSLSTIPT [16]Unsup.10.3082.13113110.3757.0537078.34247.40888.10.330.3506283
NRAM [43]Unsup.12.1674.5213.854.22149.2127.866.92756.4019.270.3517.313.585
PSTNN [44]Unsup.22.4077.9529.119.87151.7299.7514.8566.1344.171.5013.5115.44
ACM [11]Full70.3393.913.72860.9790.5821.7867.0895.9710.1847.5770.4621.31
ACM + KMeans[26]Point46.1688.5927.4533.4154.4241.8241.1877.8834.8638.1542.4523.25
ACM + SuperPixel[1]Point53.8490.4956.1849.6984.6942.3651.7692.3334.6040.4236.7016.92
ACM + GrabCut[33]Point57.6390.8760.4654.0381.9723.9955.2491.656.45738.7652.3715.54
ACM + OursPoint67.0892.0119.8056.5382.3125.0557.7492.3816.7743.6955.699.820
ResUnet[39]Full75.9397.7115.6866.3492.838.19883.7498.094.82046.0560.187.920
ResUnet + KMeans[26]Point22.3439.92156.533.8680.9510.3242.6589.2042.5131.1151.7444.63
ResUnet + SuperPixel[1]Point60.0293.1523.4559.2888.4324.3662.6593.4026.9536.4356.5030.61
ResUnet + GrabCut[33]Point61.3895.4325.1661.6790.1313.9663.0194.0313.4437.0456.1917.32
ResUnet + OursPoint71.5894.6715.2164.5990.816.22368.0493.8625.3539.0659.446.979
DNANet [23]Full76.2497.7112.8068.4494.778.80686.3697.396.89742.1761.6017.19
DNANet + KMeans[26]Point45.6990.4958.1132.9881.6325.1842.8488.0456.9920.5932.6721.59
DNANet + SuperPixel[1]Point62.5993.5314.5458.4489.4527.7064.6895.4433.3938.4236.706.921
DNANet + GrabCut[33]Point61.1497.7120.5361.0091.1520.8764.0097.0340.6528.0849.794.816
DNANet + OursPoint72.8696.9514.4362.2392.1324.1470.5295.5533.2040.2358.3211.29
ISNet [40]Full80.0199.234.9668.7295.6815.4382.5796.4944.1141.2758.8913.26
ISNet + KMeans[26]Point38.2774.88112.729.6769.5238.4344.5789.8766.2032.5744.2035.26
ISNet + SuperPixel[1]Point65.8293.7328.2657.9390.7541.7461.5995.6129.5935.2148.5615.32
ISNet + GrabCut[33]Point63.7296.2726.3262.2991.3719.3465.5394.8945.3133.6848.2423.56
ISNet + OursPoint75.9395.4411.0463.1992.5822.2366.8796.2248.5938.2952.2719.97
UIUNet [45]Full76.8397.6412.3165.2792.7612.4075.3593.3327.6941.8855.6911.56
UIUNet + KMeans[26]Point35.1790.9046.5321.2682.5219.4338.2788.2778.0929.3333.1714.22
UIUNet + SuperPixel[1]Point64.2392.1149.3454.4287.3029.8251.6891.3239.4037.8347.2220.09
UIUNet + GrabCut[33]Point63.2993.8633.2760.3789.2714.2464.3392.5733.5937.0351.5526.12
UIUNet + OursPoint74.2296.2016.1964.1390.7414.9369.3591.1138.2139.2753.2323.14
" + }, + { + "type": "image", + "bbox": [ + 0.093, + 0.469, + 0.456, + 0.665 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.669, + 0.47, + 0.699 + ], + "angle": 0, + "content": "Figure 9. Examples of target probability map (TPM) and the corresponding refined pseudo masks during the MCLC process." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.726, + 0.47, + 0.771 + ], + "angle": 0, + "content": "recover a single point annotation to a pixel-level one with only 0.075s (average result from 533 targets) on a PC-level CPU." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.785, + 0.452, + 0.801 + ], + "angle": 0, + "content": "4.4. Comparison to the State-of-the-art Methods" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.471, + 0.903 + ], + "angle": 0, + "content": "We compare our method to several state-of-the-art methods on four benchmark datasets in this subsection. For fair comparison, we used the same hyper-parameters and experimental settings (e.g., special dataset division method in UIUNet[40]) as reported in their original papers when re-implementing comparing methods and retrained all the" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.468, + 0.892, + 0.496 + ], + "angle": 0, + "content": "Table 6. \\( IoU(10^{-2}) \\), \\( Pd(10^{-2}) \\), and \\( Fa(10^{-6}) \\) values achieved by existing salient object detection (SOD) methods." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.496, + 0.9, + 0.594 + ], + "angle": 0, + "content": "
Sup.NUAA-SIRSTIRSTD-1k
ResUnetFull75.997.715.766.392.88.19
Res.+PFAN [48]Point27.683.949.622.876.566.2
Res.+F3Net [38]Point33.281.6106.226.371.382.3
ResUnet+MCLCPoint71.694.715.264.690.86.22
DNANetFull76.297.712.868.494.78.8
DNA.+PFAN [48]Point29.385.266.837.678.657.7
DNA.+F3Net [38]Point33.684.978.031.277.161.2
DNANet+MCLCPoint72.996.914.462.292.124.1
" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.627, + 0.788, + 0.641 + ], + "angle": 0, + "content": "models from scratch on these four datasets." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.645, + 0.895, + 0.902 + ], + "angle": 0, + "content": "1) Quantitative and Qualitative Results: Quantitative results are shown in Table 5. Our Monte Carlo linear clustering method (i.e., MCLC) achieves much better performance over those unsupervised methods. Compared to MCLC with other single-point supervised methods, MCLC can produce better pseudo masks and thus achieve better performance in terms of \\( P_{d} \\), \\( F_{a} \\), and \\( IoU \\). Compared to the fully-supervised counterparts, MCLC enables the respective networks to generate comparable results with \\( 87\\% \\) annotation time reduction. Qualitative results on four datasets are shown in Fig. 10. Compared to fully supervised methods, our MCLC can help existing detection methods to produce comparable results in a more time-efficient manner, especially for those point targets (e.g., img-1, img-4) and spot targets (e.g., img-2, img-3, img-5, img-6). Moreover, Fig. 10 (img-7, img-8) demonstrates the robustness of our method on the dense target scenarios. Readers can refer to" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.927, + 0.516, + 0.938 + ], + "angle": 0, + "content": "1016" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.102, + 0.089, + 0.873, + 0.392 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.396, + 0.893, + 0.44 + ], + "angle": 0, + "content": "Figure 10. Qualitative results achieved by DNANet[23] under (b) point-level and (c) pixel-level supervision. The correctly detected target, false alarm, and miss detection areas are highlighted by red, yellow, and green dotted circles. More visualization results are shown in supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.464, + 0.457, + 0.479 + ], + "angle": 0, + "content": "the supplementary material for more visualization results." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.48, + 0.47, + 0.601 + ], + "angle": 0, + "content": "2) Compared with SOD Methods: Quantitative results in Table 6 show that our MCLC performs much better than those salient object detection (SOD) methods. That is because, although the small targets are salient in local region, a single point label can not provide sufficient supervision to train high-performance SOD methods (e.g., PFAN [48], F3Net [38]). In contrast, our MCLC can make full use of single point labels to obtain higher accuracy." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.617, + 0.196, + 0.633 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.643, + 0.471, + 0.884 + ], + "angle": 0, + "content": "In this paper, we propose a simple yet effective pipeline for single-frame infrared small target detection with single-point annotation. First, we found that SIRST is generally salient in the local small region and exhibits high energy concentricity. Then, based on this observation, we proposed a linear clustering approach (LCA) to coarsely separate the targets from clustering background by measuring the color and spatial distance with clutter background. To further refine the results, we design a Monte Carlo regularization approach to constrain the clustering process and continuously expand the point-level annotation to a high-quality pixel-level one. Extensive experiments on four benchmark datasets demonstrate that our method achieves comparable performance with fully-supervised methods. We hope our study can draw attention to the research on weakly supervised SIRST detection." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Acknowledgement: This work was supported in part" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.464, + 0.892, + 0.523 + ], + "angle": 0, + "content": "by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China under Grant 61921001 and National Natural Science Foundation of China 62001478." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.537, + 0.597, + 0.552 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.508, + 0.562, + 0.893, + 0.617 + ], + "angle": 0, + "content": "[1] Radhakrishna Achanta, Appu Shaji, Kevin Smith, Aurelien Lucchi, Pascal Fua, and Sabine Süsstrunk. Slic superpixels compared to state-of-the-art superpixel methods. 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Recently, deep learning based methods have achieved promising performance on SIRST detection, but at the cost of a large amount of training data with expensive pixel-level annotations. To reduce the annotation burden, we propose the first method to achieve SIRST detection with single-point supervision. The core idea of this work is to recover the per-pixel mask of each target from the given single point label by using clustering approaches, which looks simple but is indeed challenging since targets are always insalient and accompanied with background clutters. To handle this issue, we introduce randomness to the clustering process by adding noise to the input images, and then obtain much more reliable pseudo masks by averaging the clustered results. Thanks to this "Monte Carlo" clustering approach, our method can accurately recover pseudo masks and thus turn arbitrary fully supervised SIRST detection networks into weakly supervised ones with only single point annotation. Experiments on four datasets demonstrate that our method can be applied to existing SIRST detection networks to achieve comparable performance with their fully-supervised counterparts, which reveals that single-point supervision is strong enough for SIRST detection. Our code will be available at: https://github.com/YeRen123455/SIRST-Single-Point-Supervision. + +# 1. Introduction + +Single-frame infrared small target (SIRST) detection has been widely used in many applications such as marine resource utilization [23, 45], high-precision navigation [34, 13], and ecological environment monitoring [35]. + +![](images/b8f139acdcc91b46ce997ced7e9adedf3978e929fad55a489e31d5fb53f52bec.jpg) +Figure 1. Pipeline of our method. The proposed Monte Carlo linear clustering along with single-point annotation can produce high-quality pseudo mask (i.e., target probability map (TPM)). + +However, existing SIRST detection methods mainly rely on segmentation pipeline with pixel-level supervision. Pixel-level annotating is time-consuming and thus hinders the quick deployment of those large scale data-dependent scenarios. Therefore, it is in urgent need to alleviate the annotation burden while maintaining state-of-the-art performance in SIRST detection. + +Point-level supervision, as an annotation-friendly form of supervision, can provide both category and localization information for each target. Previous works in general object segmentation utilized rich semantic information to design various training loss [4] and network modules [29, 27], and continuously expand the single-point annotation to a pixel-level pseudo mask. Although having achieved promising performance, these methods heavily rely on prior semantic information (e.g., objectness prior in [4, 50], shape prior in [29, 27, 49]), and generally need more than one point as supervision. However, infrared small targets generally occupy no more than $0.15\%$ area of the whole image [47] and lack texture, shape and color information. Consequently, previous semantic information-dependent methods cannot well adopt to this task. + +![](images/b81573059ca7eeec6c99cf4c6c0d437235eef0de841a212f74a24b90e6f95986.jpg) +(a) Local Saliency +Figure 2. Some inherent characteristics of SIRST observed from the small local regions (i.e., salient in local region, similar shape, texture, and energy distribution). + +![](images/9634e87a22cdd4be3cf7288923343a5a420a74f7501b1f11e07c194c667e0eb0.jpg) +(b) Similar Shape + +![](images/87c7b9c23df3165eb0c8623c16a2d6342e97bf9c5035975073e88ea234a50a75.jpg) +(c) Similar Texture + +![](images/404d90aa754aae3a8b506637ca1259e9988bfb9538e8f588f931a5cc70a3ff2a.jpg) +(d) Similar Energy Distribution + +We notice that although infrared small targets lack semantic information from the perspective of whole image, they are quite salient in the local small region. Specifically, as shown in Fig. 2, small targets in infrared images generally have high energy concentricity and exhibit significant gradient difference in their local regions. Moreover, limited semantic information (e.g., weak texture, shape, and color distribution) makes most point-like and spot-like targets exhibit similar energy distribution (e.g., Gaussian distribution). Consequently, it is straightforward to use a simple linear clustering approach (LCA) to separate the salient regions by measuring their color and spatial distances with adjacent backgrounds. + +However, LCA easily falls into local optimum and produces inaccurate segmentation results due to their fixed hyper-parameters. To handle this problem, we propose a Monte Carlo linear clustering (MCLC) method to regularize the clustering process and recover the reliable clustering result by repetitive random experiments. Specifically, we introduce randomness to the clustering process by adding noise to the input images. With the help of random noise, the distance between unexpected background region and target region can be significantly enlarged. The misclustered target regions can be pushed away from the false clustering center and thus return back the true clustering center. In this way, the single-point annotation can be gradually recovered as a much more reliable pixel-level target probability map (TPM) by averaging the clustered results. Pixels with larger values in TPM represent a higher probability of belonging to the target. Finally, we use the refined TPM to turn arbitrary fully supervised SIRST detection networks into weakly supervised ones with only single point annotation. Fig. 1 shows the overall pipeline of our method, and the main contributions are summarized as follows: + +- To the best of our knowledge, this is the first single-point supervised method to achieve SIRST detection. A Monte Carlo linear clustering-based pipeline is proposed to achieve comparable performance with the fully supervised counterpart by using single-point anno + +taion. + +- Inspired by the inherent characteristic of SIRST, a simple yet effective linear clustering approach with random noise-guided Monte Carlo regularization is proposed to coarsely extract and further refine the candidate target region. +- Experiments on four public SIRST datasets demonstrate the effectiveness of our method. Ablation study reveals that pixel-level labels are not necessary for SIRST detection while single-point supervision is strong enough. + +# 2. Related Work + +# 2.1. Infrared Small Target Detection + +SIRST detection has been extensively investigated for decades. Early traditional paradigm achieves SIRST detection by measuring the discontinuity between targets and backgrounds. Typical methods include filtering-based methods [31, 14], local contrast measure-based methods [6, 18, 19, 20, 22, 36], and low rank-based methods [16, 43, 9, 44, 51, 10]. Since real scenes are much more complex with dramatic changes in target size, shape, and clutter background, it is difficult to use handcrafted features and fixed hyper-parameters to handle such variations. To address this problem, recent deep learning-based methods learn trainable features in a data-driven manner and thus achieve better performance than traditional ones. + +Existing deep learning-based methods can be divided into detection based methods and segmentation based methods. Since the pixel-level classification result is essential for the subsequent recognition task in SIRST, segmentation-based methods have attracted increasing attention recently. Dai et al. [11] proposed the first segmentation-based network (i.e., ACM). They designed an asymmetric contextual module to aggregate features from shallow layers and deep layers. Then, Dai et al. [12] improved ACM by introducing a dilated local contrast measure. Specifically, a feature cyclic shift scheme was designed to achieve a trainable local contrast measure. After that, Zhang et al. [45] modeled SIRST detection as a shape detection task. A taylor finite difference (TFD)-inspired edge block and a two-orientation attention aggregation (TOAA) block were proposed to capture precise shape of infrared targets. Recently, Li et al. [23] proposed a dense nested attention network (DNANet). A specifically-designed dense nested interactive module (DNIM) was proposed to both extract high-level information and maintain the response of small targets in deep layers. + +Although the performance has been continuously improved by recent networks, existing deep learning-based methods rely on the fully-supervised training scheme with + +![](images/cc64a29001c91873ca0e7519078ba1ca8d4595d403768de2ef08c26b1fe0ed5e.jpg) +Figure 3. Sample of input images, four common weakly supervised annotations (i.e., single-point, multi-point, scribble, bounding box), and one fully supervised pixel-level annotation. + +pixel-level annotations. Expensive labor cost makes existing methods hard to be deployed to large scale data-dependent tasks. + +# 2.2. Point-based Segmentation + +Point-level supervision has been widely used in many high-level tasks (e.g., object detection [7, 46], object localization [41], and semantic segmentation [4, 29, 27, 24, 49]) and yield promising performance. For semantic segmentation task, Bearman et al. [4] proposed the first single-point supervised semantic segmentation method. They incorporated the single-point supervision along with an objectness prior as the loss function to infer the extent of the object. Then, Papadopoulos et al. [29] and Maninis et al. [27] utilized four extreme points (i.e., left-most, right-most, top, and bottom pixels) as supervision to further improve the quality of the pseudo mask. After that, Austin et al. [28] followed the class activation maps (CAM) [50] pipeline and used the point annotation to refine the quality of pseudo labels. More recently, Li et al. [24] utilized the semantical consistency property of general objects with 20 randomly annotated points to achieve comparable segmentation results with fully-supervised counterpart. Moreover, in the field of cell segmentation, Zhao et al. [49] proposed the first single-point supervised segmentation method, in which two semantic prior-based training losses (i.e., divergence loss and consistency loss) were proposed to achieve high-quality cell segmentation. + +Although promising performance has been achieved, existing works rely on rich semantic information (e.g., objectness prior in [4, 50], shape prior in [29, 27, 49]) and most of them need multi-point annotation. Infrared small targets generally occupy no more than $0.15\%$ area of the whole image [47] and lack texture, shape and color information. Previous semantic information-dependent methods cannot be directly used for SIRST detection. + +# 3. Methodology + +In this section, we first introduce the motivation. Then, a detailed illustration of the proposed linear clustering ap + +proach with Monte Carlo regularization is provided. Overall architecture of proposed method is shown in Fig. 4. + +# 3.1. Motivation + +We investigate the annotation cost of four common weakly-supervised annotations (i.e., single point [5], multiple points[5, 29, 27], scribbles [25], bounding boxes[21]) by re-labelling the NUDT-SIRST [23] and NUAA-SIRST [11] datasets. Fig. 3 shows the average annotation time of four weakly-supervised and one fully-supervised approaches. Note that, single-point supervision can reduce about $87\%$ annotation time as compared to the pixel-level annotation approach, which motivates us to apply single-point annotation to SIRST detection. Please refer to the supplementary material for more detailed analysis. + +However, existing point-level supervised methods [5, 29, 27] are designed for general objects with rich semantic information (e.g., shape, texture, and color). As shown in Fig. 2, the characteristics of infrared small targets make the aforementioned semantic-based pipeline unsuitable for SIRST detection. Considering that infrared small targets are quite salient in their local regions and share similar shape, texture, and energy distribution. Intuitively, we can use simple linear clustering approaches (e.g., Super-pixel [1], K-Means [26]) to separate the salient regions by comparing their color and spatial distances among these clusters. + +# 3.2. Linear Clustering Approach + +Without loss of generality, we take the quick linear clustering method SuperPixel [1] as an example to introduce how to use LCA to coarsely separate the target region. It should be noted that other linear clustering approaches such as KMeans [26] can be also used in our method, as demonstrated in Fig. 5. The pipeline of our LCA is shown in Fig. 4 (Step I $\sim$ Step III), in which the clustering center of the image is first initialized, and then adjusted according to a color and spatial distance based measurement. Finally, the clustering center is continuously updated until the pre-defined convergence requirements are met. + +1) Clustering Center Initialization: We initialize the clustering center based on the pre-defined number of clusters $N$ . Given an input image $I \in \mathbb{R}^{H \times W}$ , we first divide it into $N$ regions with equal areas and fixed grid interval $S = \sqrt{\frac{H \times W}{N}}$ (as shown in Fig. 4-Step 1). After that, the clustering center is first initialized as the centroid of each region, and then moved to the lowest gradient position of its $3 \times 3$ neighborhood. The clustering center of the $n^{th}$ clustering region $\mathcal{C}_n$ can be represented as a vector as: + +$$ +\mathcal {C} _ {n} = \left[ c _ {n}, s _ {n} \right] ^ {T}, \tag {1} +$$ + +where $[c_n]^T$ represents the CIELAB color [32] of $\mathcal{C}_n$ , $[s_n]^T$ denotes the spatial position in image coordinate of $\mathcal{C}_n$ . + +![](images/a7dd4ccc1d01683daee3003eeda05a5ba5719e0b056105548e3f7e7d2ce71ce5.jpg) +Figure 4. Illustration of our method. StepI $\sim$ StepIII: LCA can coarsely separate target from clutter background, but easily falls into local optimum and produce incomplete pseudo mask. StepIV $\sim$ StepV: Monte Carlo regularization can increase the color distance between background and target region and thus enforce the misclustered target region away from the false clustering center. After repetitive random experiments, the accumulated clustering results are finally shown as a target probability map (TPM), where pixels with larger values represent a higher probability of belonging to the target. + +2) Distance Measurement: After clustering center initialization, we adopt a color and spatial distance based measurement to determine the clustering center of each pixel. As shown in Fig. 4-Step II, for each clustering center $\mathcal{C}_n$ , we use $L_2$ distance to measure its distance with each pixel $p_i = [c_i, s_i]^T$ in its adjacent $2S \times 2S$ regions. Considering that the ranges of color value and spatial position value are inconsistent, we normalize the both distance values with normalization coefficient $\mu_s$ and $\mu_c$ . $\mathcal{D}(\mathcal{C}_n, p_i)$ is written as: + +$$ +\begin{array}{l} \mathcal {D} (\mathcal {C} _ {n}, p _ {i}) = \sqrt {(\mathcal {D} _ {c}) ^ {2} + (\mathcal {D} _ {s}) ^ {2}} \\ = \sqrt {\frac {\left(c _ {p _ {i}} - c _ {\mathcal {C} _ {n}}\right) ^ {2}}{\mu_ {c} ^ {2}} + \frac {\left(s _ {p _ {i}} - s _ {\mathcal {C} _ {n}}\right) ^ {2}}{\mu_ {s} ^ {2}}}. \tag {2} \\ \end{array} +$$ + +Then, the clustering label $l$ for each pixel $p_i$ can be determined as: + +$$ +l \left(p _ {i}\right) = \operatorname {a r g m i n} _ {\mathrm {n} \in \{1, 2, 3, \dots , \mathrm {N} \}} \left[ \mathcal {D} \left(\mathcal {C} _ {\mathrm {n}}, \mathrm {p} _ {\mathrm {i}}\right) \right]. \tag {3} +$$ + +3) Updating and Convergence: After determining the clustering center of each pixel at the current iteration, we repetitively update the position of each clustering center until convergence, as shown in Fig. 4-Step III. Specifically, we first calculate the clustering centers to be the mean vector $[c_m, s_m]^T$ of all the pixels $P = \{p_1, p_2, \dots, p_m\}$ with the same clustering label $l(\mathcal{C}_n')$ . The new clustering center $\mathcal{C}_n'$ can be formulated as: + +![](images/0f0086a783ebf8d88e111a66a8f249377c1f5b43679c38f5ec9db6839840c9fc.jpg) +Figure 5. Visualization results achieved by (a) Kmeans, (b) K-means with Monte Carlo Regularization, (c) Super pixel, (d) Super pixel with Monte Carlo Regularization. Our proposed Monte Carlo regularization helps to expand informative target region. + +$$ +\mathcal {C} _ {n} ^ {\prime} \left(c _ {n}, x _ {n}, y _ {n}\right) = \frac {1}{| P |} \sum_ {p _ {m} \in P} \left(c _ {p _ {m}}, s _ {p _ {m}}\right). \tag {4} +$$ + +After that, we adopt $L_{2}$ norm to compute a distance $\mathcal{E}$ between new clustering center locations $\mathcal{C}_n'$ and previous clustering center locations $\mathcal{C}_n$ . The updating steps can be repeated iteratively until the error is smaller than the predefined threshold $T$ . That is $\| \mathcal{C}_n' - \mathcal{C}_n \|_2 < T$ , where $\| \cdot \|_2$ denote the L2 norm. Finally, we assign the single-point annotation $p_{Aanno}$ located at the $n^{th}$ clustering region as the clustering result $M_{pred}$ . + +![](images/fd77ab1afd41e932334e815fc0b86e197c726a79719d97b816b80ce7119f284a.jpg) +Figure 6. Quantitative analysis on (a) Sensitivity of target and non-target regions to additional noise, and (b) Color distance of target edge region with true foreground region centroid $\Delta (\mathcal{D}_c(\mathcal{C}^T,M_{pred}))$ and false background region centroid $\Delta (\mathcal{D}_c(\mathcal{C}^F,M_{pred}))$ . Average results from 10 trails are reported. Readers can refer to the supplementary material for more detailed illustration. + +![](images/56a037a578972acbb06e57e9a46a77ce70e983dfbf31f35c4aba78904651686a.jpg) + +# 3.3. Monte Carlo Regularization + +Although LCA can coarsely separate local salient regions from the backgrounds, as shown in Fig. 5 (a) and (c), a linear clustering method easily falls into local optimum and generates incomplete or oversized results. In this subsection, we first analyze the reason of this issue, and then propose a Monte Carlo regularization to alleviate this issue, as shown in Fig. 4 (StepIV $\sim$ StepV). + +1) Inaccurate Result within a Single Clustering: Due to the varied size of small targets, LCA with fixed number of clustering centers cannot produce ideal results for all kinds of targets. That is because, both color $\mathcal{D}_c$ and spatial distance $\mathcal{D}_s$ determine the output of linear clustering model in Equation 2. Since edge areas $M_{pred}^{Edge} = \{m_{pred}^{Edge(1)}, m_{pred}^{Edge(2)}, \dots, m_{pred}^{Edge(Z)}\}$ of the spot and extended target (i.e., big target) are generally far from the true clustering center $\mathcal{C}^T$ (shown as the left-most green point in Fig. 4-Step III). The spatial distance $\mathcal{D}_c(\mathcal{C}^T, M_{pred}^{Edge})$ between the true clustering center $\mathcal{C}^T$ and edge areas $M_{pred}^{Edge}$ is usually farther than that of the false clustering center $\mathcal{C}^F$ . That is: + +$$ +\mathcal {D} _ {s} \left(\mathcal {C} ^ {T}, m _ {\text {p r e d}} ^ {\text {E d g e} (z)}\right) > \mathcal {D} _ {s} \left(\mathcal {C} ^ {F}, m _ {\text {p r e d}} ^ {\text {E d g e} (z)}\right). \tag {5} +$$ + +Moreover, the color value of big target generally exhibits Gaussian distribution. Those edge areas often exhibit relatively high color difference with the true clustering center, and are close to the adjacent false clustering center (shown as the right-most green point in Fig. 4 Step III). That is: + +$$ +\mathcal {D} _ {c} \left(\mathcal {C} ^ {T}, m _ {\text {p r e d}} ^ {\text {E d g e} (z)}\right) > \mathcal {D} _ {c} \left(\mathcal {C} ^ {F}, m _ {\text {p r e d}} ^ {\text {E d g e} (z)}\right). \tag {6} +$$ + +As a result, the label of edge areas $l_{pred}^{Edge}$ may be falsely included into the adjacent false clustering center $\mathcal{C}^F$ , resulting in incomplete clustering result. + +2) Random Noise Guided Regularization: Spatial distance $\mathcal{D}_s$ is generally fixed and hard to change in the im + +age. As shown in Fig. 6 (a), when adding random noise, target and non-target regions exhibit different sensitivity to the noise. Target regions with higher color vaule are more robust to the additional noise than the non-target regions. Based on this finding, we are motivated to introduce random noise to enlarge the color distance $\mathcal{D}_c(\mathcal{C}^F,M_{pred}^{Edge})$ between edge areas and false clustering center (as shown in Fig. 4-Step III), and thus make the edge areas be clustered to the true clustering center. Random noise-regularized clustering result can be formulated as follows: + +$$ +M _ {p r e d} ^ {N o i s e} = L C A (c l i p (I + \mathcal {N})), \tag {7} +$$ + +where $\text{clip}(\cdot)$ operation represents that color values larger than 255 will be fixed at 255. $\mathcal{N}$ is the additional random noise. The color value change caused by random noise can be formulated as: + +$$ +\Delta \left(\mathcal {D} _ {c} \left(\mathcal {C}, M _ {p r e d}\right)\right) = \mathcal {D} _ {c} ^ {\text {N o i s e}} - \mathcal {D} _ {c} ^ {\text {C l e a n}}. \tag {8} +$$ + +Since background region has relatively low color value than foreground region. Additional noise will greatly increase the color value of adjacent false clustering centers, and thus enlarges their color distance with the edge area of target region. On the contrary, when comparing Fig. 4-Step IV with Fig. 4-Step V, we observe that foreground regions have high energy concentricity and are usually close to saturation. Additional noise cannot bring so much color change to target regions as the background regions. Benefited by the additional noise, as shown in Fig. 6 (b), the change of color distance between edge areas and false clustering center (i.e., $\Delta (\mathcal{D}_c(\mathcal{C}^F,M_{pred}))$ ) will be significantly larger than that between edge areas and true clustering center (i.e., $\Delta (\mathcal{D}_c(\mathcal{C}^T,M_{pred}))$ ), making the misclustered target region be more closed to the true clustering center. + +3) Monte Carlo Process: As aforementioned, random noise can enforce the misclustered region to be gradually close to the true clustering center. Considering the randomness of noise, additional noise does not always bring such positive effect. We are motivated to adopt the Monte Carlo method to accumulate the clustering result from repetitive random experiments and gradually recover the reliable clustering result. To this end, we perform $K$ independent clustering and formulate this process as follows: + +$$ +M _ {P r e d} ^ {F u l l} = \frac {1}{K} \sum_ {k = 1} ^ {K} \left(L C A \left(\operatorname {c l i p} \left(I + \mathcal {N} ^ {(k)}\right)\right)\right), \tag {9} +$$ + +where $M_{Pred}^{Full}$ is the accumulated clustering results after $K$ independent clustering by LCA, and finally shown as a target probability map (TPM), where pixels with larger values represent a higher probability of belonging to the target. + +The optimization process finally stops when the distance between the new clustering center locations $\mathcal{C}'$ and previous + +![](images/15a0bff01a352de1de822896093f067d307b60fa0d12ef65185c8b9e314f02d7.jpg) +Figure 7. IoU scores achieved by our method with (a) different types and intensity of additional noise and (b) different number of clustering center on the NUAA-SIRST dataset. Average results from 5 trails are reported. Readers can refer to the supplementary material for additional experiments on the other datasets. + +![](images/c59546526f87359f1a1bdc0e673b1fb1c5cf05bb771e70c7202f68caf5a99a8f.jpg) + +Table 1. $IoU(10^{-2})$ value achieved by the different variants of our method on the training set of four representative datasets (i.e., NUAA, IRSTD, NUDT, NUDT-sea). MC Regu. refers to Monte Carlo regularization. + +
Point LabelLCAMC Regu.dCRFIoU(%)
✓✓2.53 / 1.62 / 2.28 / 1.82
✓✓51.8 / 55.5 / 51.2 / 38.1
✓✓✓70.4 / 66.2 / 52.5 / 43.9
✓✓✓✓76.3 / 68.8 / 60.2 / 47.1
+ +clustering center locations $\mathcal{C}$ is smaller than the pre-defined threshold $T^F$ , i.e., $\| \mathcal{C}_n' - \mathcal{C}_n\|_2 < T^F$ . + +# 4. Experiments + +In this section, we first introduce our evaluation metrics and implementation details. Then, we compare our MCLC to several state-of-the-art unsupervised, point-level supervised, and fully-supervised SIRST detection methods. Finally, we present ablation studies to investigate the effectiveness of our method. Note that, we search for optimal parameters of MCLC in the training set of NUAA-SIRST [11] and directly adopt them as default parameters to generate pseudo masks on the other three datasets[45, 23, 39]. + +# 4.1. Evaluation Metrics + +Considering that both the quality of pseudo labels and the final detection results are crucial to SIRST detection, we followed previous works [37, 42, 3, 2] and propose a two-stage pipeline (i.e., pseudo mask and final detection result evaluation) to comprehensively evaluate the effectiveness of the proposed method. Firstly, we followed the same metrics in weakly-supervised general object segmentation [3, 2] and adopted intersection of union $(IoU)$ to evaluate the quality of generated pseudo labels on the training set. For the final detection results evaluation, we followed previous works [11, 12, 23] and adopted probability of detection $(P_d)$ , and false-alarm rate $F_{a}$ to evaluate the localization precision, and used $IoU$ to evaluate the shape description ability on the test set. + +![](images/61a49b4338e44973b4bb4ba283d96a9b9fa21a48c5966dc3cfc2d1cbb41f23e8.jpg) + +![](images/062e17142eb5258a4f283d81fdcf9b2831298ab40fe24939da0581ba92d1104a.jpg) + +![](images/8d901cdf6133f5e08ac8eb36b52518d01de92f55d2ab93214b08ebfaf842142c.jpg) +Figure 8. (a) Labelling deviation examples of small target from four datasets. (b) Label deviation distribution map generated from 105 manually re-labelled targets. Real world labelling deviation of small target is generally less than 3 pixels. + +![](images/7fd40b7ac9ee5db49e43a9d4d0d86c0633b681a6b70446466c1fb7971c867037.jpg) + +![](images/560d13ca74453ecedb01295fdc0e8e9588e806e0eff52b404fb2869055692cfb.jpg) + +# 4.2. Implementation Details + +1) Datasets: We evaluated our method on the NUAA-SIRST [11], IRSTD-1k [45], NUDT-SIRST [23], and NUDT-SIRST-sea [39] datasets. Without specification, for the NUAA-SIRST and NUDT-SIRST datasets, we used the same division as in [23] and set the ratio of train-val set to test set as 1. For the IRSTD-1k dataset, we followed [45] and used $80\%$ data for training and validation, and the remaining $20\%$ data for test. The division setting in [39] was adopted for the NUDT-SIRST-sea dataset, i.e., 41 images were used for training and validation, and the remaining 7 images were used for test. Note that, only single point-level annotation with category information (i.e., point, spot, and extend categories) are available during network training. + +2) Training Details: In our experiments, all input images were first normalized before training. Then, these normalized images were sequentially processed by random flip, and random crop for data augmentation. Next, these images were resized to a fixed resolution. Specifically, $1024 \times 1024$ and $256 \times 256$ spatial resolutions were used for the NUDT-SIRST-sea and the remaining three datasets, respectively. Finally, we fed these resized datasets into network for both training and evaluation. Without specification, we adopted the centroid of ground truth mask as the single-point label. The influence of label position deviation is discussed in the following ablation. Moreover, all networks were trained with the Soft-IoU loss function and optimized by the Ada-grad method [15] with the CosineAnnealingLR scheduler. The Xavier method [17] was used for all weights and bias parameters initialization. We set the learning rate and epoch number to 0.05 and 1500, respectively. The batch size was set to 16 for the NUAA-SIRST, IRSTD-1k, NUDT-SIRST datasets but set to 4 for the NUDT-SIRST-sea dataset due to its large image size. All models were implemented in PyTorch [30] on a computer with an AMD Ryzen 9 3950X @ 2.20 GHz CPU and an Nvidia GeForce 3090 GPU. + +# 4.3. Ablation Study + +1) Effectiveness of Proposed Components: Table 1 shows the contribution of our proposed components on four + +Table 2. $IoU(10^{-2})$ values and corresponding labelling cost with stronger supervision on the train set of four datasets. + +
AnnotationDataset
NUAAIRSTDNUDTNUDT-sea
Single-Point76.368.860.247.1
Multi-Point76.669.162.653.7
Scribble78.570.563.255.2
Bounding-Box78.971.864.854.5
+ +datasets. Compared to the initial single-point label, linear clustering approach (LCA) introduces $49.3\%$ , $53.9\%$ , $48.9\%$ , $36.3\%$ improvements for the NUAA, IRSTD-1k, NUDT, NUDT-sea datasets, respectively. That is because, LCA utilizes the inherent characteristics of infrared small targets and thus coarsely separates the targets from clustering background. By introducing random salt noise to regularize the linear clustering process, we obtain much more reliable results and achieve additional $18.6\%$ , $10.7\%$ , $1.3\%$ , $5.8\%$ improvements on the above four datasets. After that, denseCRF [8] was used as a post-processing module to refine the target probability map (TPM) generated by MCLC. It further introduces $5.9\%$ , $2.6\%$ , $7.7\%$ , $3.2\%$ improvements for the above four datasets, respectively. We visualize the Monte Carlo linear clustering process in Fig. 9. Although easily producing inaccurate results at the beginning of clustering (e.g., iteration number less than 20), MCLC can gradually recover a reliable clustering result. More visualization samples are shown in supplementary material. + +2) Type and Intensity of Noise: Fig. 7 (a) shows the change trend of $IoU$ with respect to different noise intensity under three types of common noise (i.e., salt, pepper, and Gaussian). With the increase of noise intensity, the $IoU$ of MCLC with denseCRF under salt noise and pepper noise increases rapidly at the beginning, and reaches their peak scores of $76\%$ and $71\%$ at $0.05$ intensity1. After that, excessive intensity value reduces the saliency of target region and thus results in the decrease of $IoU$ . Moreover, Gaussian noise causes huge performance decrease under any intensity. That is because, Gaussian noise randomly changes the values of all pixels in the image, which is similar to the salt and pepper with high intensity. Since all pixels in the image are influenced by the random noise, the saliency of target is greatly decreased, resulting in dramatic performance drop. +3) Number of Clustering Center: The number of clustering center determines the initial area of each clustering region. Fig. 7 (b) reports the $IoU$ of the results generated by MCLC with denseCRF, MCLC with fixed threshold, and LCA under different number of clustering center. It shows that the $IoU$ firstly shows a rapid increasing trend with the increase number of clustering center, and then reaches the peak score of $76\%$ with 9 clustering centers. Afterward- + +Table 3. $IoU(10^{-2})$ values achieved with single point supervision under ideal and real scene. + +
Pseudo Mask (Ideal / Real)Final Results (Ideal / Real)Pseudo Mask (Ideal / Real)Final Results (Ideal / Real)
ResUnet(76.3 / 73.7)(71.6 / 71.2)(60.2 / 58.8)(68.0 / 66.5)
DNANet(72.9 / 72.0)NUDT(70.5 / 69.1)
ResUnet(68.8 / 66.7)(64.6 / 63.8)(47.1 / 45.7)(39.1 / 38.2)
DNANetIRSTD(62.2 / 60.9)NUDT-Sea(40.2 / 38.8)
+ +Table 4. $IoU(10^{-2})$ values under fixed labelling time. $5.2 \times$ (with search) and $8.0 \times$ (w/o search) more point-level (P.) labels help to generate better results under fixed labelling time. + +
Sup.NUAA-SIRSTIRSTD-1k
Time Budget: 920s (427×P.) vs (82×F.) (5.2 × P. labels)Time Budget: 1400s (1000×P.) vs (125×F.) (8.0 × P. labels)
ResUnetFull56.843.8
ResUnet+MCLCP.71.6 ↑ 14.864.6 ↑ 20.8
DNANetFull58.746.1
DNANet+MCLCP.72.1 ↑ 13.462.2 ↑ 16.1
+ +s, the quality of TPM gradually decreases when the number of clustering center further increases. The above results demonstrate that inappropriate number of clustering center will result in over-small or over-large area of initial search region, and thus introduce negative effect on MCLC. + +4) Performance with Stronger Supervision: As shown in Table 2, stronger supervision can introduce additional $0.3\% \sim 2.6\%$ improvements in term of IoU on the NUAA-SIRST dataset, but at a cost of $121\% \sim 700\%$ increase of annotation time (i.e., 1.4s, 3.1s, and 11.2s for single-point, multi-point, and pixel-level annotation in Fig. 3). Similar results can be also found on the other three datasets. Therefore, we argue that single-point annotation is the most economical supervision and is strong enough for SIRST detection. +5) Labelling Position Deviation: Real-world SIRST application may suffer from labelling position deviation shown in Fig. 8 (a). To simulate the labelling position deviation in real world, we manually re-labelled 105 targets in NUAA-SIRST and IRSTD-1k dataset, and generated a distribution map of labelling position in Fig. 8 (b). Based on this distribution map, we re-produced the pseudo masks of whole dataset and generated the final detection results in Table 3. Average results from three trails demonstrate that our method can produce competitive results under practical labelling settings. +6) Time Efficiency: As aforementioned, once the optimal parameters (e.g., type and intensity of noise, number of clustering centers) are searched in one real-world dataset (e.g., NUAA-SIRST), we directly adopt these parameters to new scenes without secondary search (e.g., IRSTD in Table 4). As shown in Table 4, single-point labelling can produce about $5.2 \times$ (with parameter search) $\sim 8.0 \times$ (w/o parameter search) annotation than the pixel-level labelling with the same annotation budget, and thus achieves much better performance. Note that, our MCLC can efficiently + +Table 5. $IoU(10^{-2})$ , $P_d(10^{-2})$ , and $F_a(10^{-6})$ values achieved by different state-of-the-art methods on four benchmark datasets. For $IoU$ and $P_d$ , larger values indicate better performance. For $F_a$ , smaller values indicate better performance. Unsup. refers to unsupervised methods. The best single-point supervised results are in red and the second best results are in blue. + +
MethodSup.Dataset
NUAA-SIRST [11]IRSTD-1k [45]NUDT-SIRST [23]NUDT-SIRST-sea [39]
Top-Hat [31]Unsup.7.14379.8410126.22255.48595.620.7278.41166.71.172.68095.37
WSLCM [20]Unsup.1.15877.9554460.01955.79315472.28356.8213090.6010.527.330
MSLSTIPT [16]Unsup.10.3082.13113110.3757.0537078.34247.40888.10.330.3506283
NRAM [43]Unsup.12.1674.5213.854.22149.2127.866.92756.4019.270.3517.313.585
PSTNN [44]Unsup.22.4077.9529.119.87151.7299.7514.8566.1344.171.5013.5115.44
ACM [11]Full70.3393.913.72860.9790.5821.7867.0895.9710.1847.5770.4621.31
ACM + KMeans[26]Point46.1688.5927.4533.4154.4241.8241.1877.8834.8638.1542.4523.25
ACM + SuperPixel[1]Point53.8490.4956.1849.6984.6942.3651.7692.3334.6040.4236.7016.92
ACM + GrabCut[33]Point57.6390.8760.4654.0381.9723.9955.2491.656.45738.7652.3715.54
ACM + OursPoint67.0892.0119.8056.5382.3125.0557.7492.3816.7743.6955.699.820
ResUnet[39]Full75.9397.7115.6866.3492.838.19883.7498.094.82046.0560.187.920
ResUnet + KMeans[26]Point22.3439.92156.533.8680.9510.3242.6589.2042.5131.1151.7444.63
ResUnet + SuperPixel[1]Point60.0293.1523.4559.2888.4324.3662.6593.4026.9536.4356.5030.61
ResUnet + GrabCut[33]Point61.3895.4325.1661.6790.1313.9663.0194.0313.4437.0456.1917.32
ResUnet + OursPoint71.5894.6715.2164.5990.816.22368.0493.8625.3539.0659.446.979
DNANet [23]Full76.2497.7112.8068.4494.778.80686.3697.396.89742.1761.6017.19
DNANet + KMeans[26]Point45.6990.4958.1132.9881.6325.1842.8488.0456.9920.5932.6721.59
DNANet + SuperPixel[1]Point62.5993.5314.5458.4489.4527.7064.6895.4433.3938.4236.706.921
DNANet + GrabCut[33]Point61.1497.7120.5361.0091.1520.8764.0097.0340.6528.0849.794.816
DNANet + OursPoint72.8696.9514.4362.2392.1324.1470.5295.5533.2040.2358.3211.29
ISNet [40]Full80.0199.234.9668.7295.6815.4382.5796.4944.1141.2758.8913.26
ISNet + KMeans[26]Point38.2774.88112.729.6769.5238.4344.5789.8766.2032.5744.2035.26
ISNet + SuperPixel[1]Point65.8293.7328.2657.9390.7541.7461.5995.6129.5935.2148.5615.32
ISNet + GrabCut[33]Point63.7296.2726.3262.2991.3719.3465.5394.8945.3133.6848.2423.56
ISNet + OursPoint75.9395.4411.0463.1992.5822.2366.8796.2248.5938.2952.2719.97
UIUNet [45]Full76.8397.6412.3165.2792.7612.4075.3593.3327.6941.8855.6911.56
UIUNet + KMeans[26]Point35.1790.9046.5321.2682.5219.4338.2788.2778.0929.3333.1714.22
UIUNet + SuperPixel[1]Point64.2392.1149.3454.4287.3029.8251.6891.3239.4037.8347.2220.09
UIUNet + GrabCut[33]Point63.2993.8633.2760.3789.2714.2464.3392.5733.5937.0351.5526.12
UIUNet + OursPoint74.2296.2016.1964.1390.7414.9369.3591.1138.2139.2753.2323.14
+ +![](images/24808d0399f25673366be30fb23361aea9f930837f47f16ac8cf236db3185fb7.jpg) +Figure 9. Examples of target probability map (TPM) and the corresponding refined pseudo masks during the MCLC process. + +recover a single point annotation to a pixel-level one with only 0.075s (average result from 533 targets) on a PC-level CPU. + +# 4.4. Comparison to the State-of-the-art Methods + +We compare our method to several state-of-the-art methods on four benchmark datasets in this subsection. For fair comparison, we used the same hyper-parameters and experimental settings (e.g., special dataset division method in UIUNet[40]) as reported in their original papers when re-implementing comparing methods and retrained all the + +Table 6. $IoU(10^{-2})$ , $Pd(10^{-2})$ , and $Fa(10^{-6})$ values achieved by existing salient object detection (SOD) methods. + +
Sup.NUAA-SIRSTIRSTD-1k
ResUnetFull75.997.715.766.392.88.19
Res.+PFAN [48]Point27.683.949.622.876.566.2
Res.+F3Net [38]Point33.281.6106.226.371.382.3
ResUnet+MCLCPoint71.694.715.264.690.86.22
DNANetFull76.297.712.868.494.78.8
DNA.+PFAN [48]Point29.385.266.837.678.657.7
DNA.+F3Net [38]Point33.684.978.031.277.161.2
DNANet+MCLCPoint72.996.914.462.292.124.1
+ +models from scratch on these four datasets. + +1) Quantitative and Qualitative Results: Quantitative results are shown in Table 5. Our Monte Carlo linear clustering method (i.e., MCLC) achieves much better performance over those unsupervised methods. Compared to MCLC with other single-point supervised methods, MCLC can produce better pseudo masks and thus achieve better performance in terms of $P_{d}$ , $F_{a}$ , and $IoU$ . Compared to the fully-supervised counterparts, MCLC enables the respective networks to generate comparable results with $87\%$ annotation time reduction. Qualitative results on four datasets are shown in Fig. 10. Compared to fully supervised methods, our MCLC can help existing detection methods to produce comparable results in a more time-efficient manner, especially for those point targets (e.g., img-1, img-4) and spot targets (e.g., img-2, img-3, img-5, img-6). Moreover, Fig. 10 (img-7, img-8) demonstrates the robustness of our method on the dense target scenarios. Readers can refer to + +![](images/8b120c225e4e7b4578eda64dcf250ffb19444bff1b86c1c7c261c6d898ec7566.jpg) +Figure 10. Qualitative results achieved by DNANet[23] under (b) point-level and (c) pixel-level supervision. The correctly detected target, false alarm, and miss detection areas are highlighted by red, yellow, and green dotted circles. More visualization results are shown in supplementary material. + +the supplementary material for more visualization results. + +2) Compared with SOD Methods: Quantitative results in Table 6 show that our MCLC performs much better than those salient object detection (SOD) methods. That is because, although the small targets are salient in local region, a single point label can not provide sufficient supervision to train high-performance SOD methods (e.g., PFAN [48], F3Net [38]). In contrast, our MCLC can make full use of single point labels to obtain higher accuracy. + +# 5. Conclusion + +In this paper, we propose a simple yet effective pipeline for single-frame infrared small target detection with single-point annotation. First, we found that SIRST is generally salient in the local small region and exhibits high energy concentricity. Then, based on this observation, we proposed a linear clustering approach (LCA) to coarsely separate the targets from clustering background by measuring the color and spatial distance with clutter background. To further refine the results, we design a Monte Carlo regularization approach to constrain the clustering process and continuously expand the point-level annotation to a high-quality pixel-level one. Extensive experiments on four benchmark datasets demonstrate that our method achieves comparable performance with fully-supervised methods. We hope our study can draw attention to the research on weakly supervised SIRST detection. + +Acknowledgement: This work was supported in part + +by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China under Grant 61921001 and National Natural Science Foundation of China 62001478. + +# References + +[1] Radhakrishna Achanta, Appu Shaji, Kevin Smith, Aurelien Lucchi, Pascal Fua, and Sabine Süsstrunk. Slic superpixels compared to state-of-the-art superpixel methods. IEEE TPA-MI, 34(11):2274-2282, 2012. 3, 8 +[2] Jiwoon Ahn, Sunghyun Cho, and Suha Kwak. Weakly supervised learning of instance segmentation with inter-pixel relations. In CVPR, 2019. 6 +[3] Jiwoon Ahn and Suha Kwak. Learning pixel-level semantic affinity with image-level supervision for weakly supervised semantic segmentation. In CVPR, 2018. 6 +[4] Amy Bearman, Olga Russakovsky, Vittorio Ferrari, and Li Fei-Fei. What's the point: Semantic segmentation with point supervision. 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Recently, deep learning based methods have achieved promising performance on SIRST detection, but at the cost of a large amount of training data with expensive pixel-level annotations. To reduce the annotation burden, we propose the first method to achieve SIRST detection with single-point supervision. The core idea of this work is to recover the per-pixel mask of each target from the given single point label by using clustering approaches, which looks simple but is indeed challenging since targets are always insalient and accompanied with background clutters. To handle this issue, we introduce randomness to the clustering process by adding noise to the input images, and then obtain much more reliable pseudo masks by averaging the clustered results. Thanks to this \"Monte Carlo\" clustering approach, our method can accurately recover pseudo masks and thus turn arbitrary fully supervised SIRST detection networks into weakly supervised ones with only single point annotation. Experiments on four datasets demonstrate that our method can be applied to existing SIRST detection networks to achieve comparable performance with their fully-supervised counterparts, which reveals that single-point supervision is strong enough for SIRST detection. Our code will be available at: https://github.com/YeRen123455/SIRST-Single-Point-Supervision." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 645, + 128, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 645, + 128, + 658 + ], + "spans": [ + { + "bbox": [ + 47, + 645, + 128, + 658 + ], + "type": "text", + "content": "1. 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Pipeline of our method. The proposed Monte Carlo linear clustering along with single-point annotation can produce high-quality pseudo mask (i.e., target probability map (TPM))." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 448, + 545, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 448, + 545, + 532 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 545, + 532 + ], + "type": "text", + "content": "However, existing SIRST detection methods mainly rely on segmentation pipeline with pixel-level supervision. Pixel-level annotating is time-consuming and thus hinders the quick deployment of those large scale data-dependent scenarios. Therefore, it is in urgent need to alleviate the annotation burden while maintaining state-of-the-art performance in SIRST detection." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "content": "Point-level supervision, as an annotation-friendly form of supervision, can provide both category and localization information for each target. Previous works in general object segmentation utilized rich semantic information to design various training loss [4] and network modules [29, 27], and continuously expand the single-point annotation to a pixel-level pseudo mask. Although having achieved promising performance, these methods heavily rely on prior semantic information (e.g., objectness prior in [4, 50], shape prior in [29, 27, 49]), and generally need more than one point as supervision. However, infrared small targets generally occupy no more than " + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "inline_equation", + "content": "0.15\\%" + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "content": " area of the whole image [47] and lack texture, shape and color information. Consequently, previous semantic information-dependent methods cannot well adopt to this task." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "type": "text", + "content": "1009" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 61, + 70, + 111, + 159 + ], + "blocks": [ + { + "bbox": [ + 61, + 70, + 111, + 159 + ], + "lines": [ + { + "bbox": [ + 61, + 70, + 111, + 159 + ], + "spans": [ + { + "bbox": [ + 61, + 70, + 111, + 159 + ], + "type": "image", + "image_path": "b81573059ca7eeec6c99cf4c6c0d437235eef0de841a212f74a24b90e6f95986.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 74, + 159, + 97, + 173 + ], + "lines": [ + { + "bbox": [ + 74, + 159, + 97, + 173 + ], + "spans": [ + { + "bbox": [ + 74, + 159, + 97, + 173 + ], + "type": "text", + "content": "(a) Local Saliency" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 178, + 287, + 211 + ], + "lines": [ + { + "bbox": [ + 46, + 178, + 287, + 211 + ], + "spans": [ + { + "bbox": [ + 46, + 178, + 287, + 211 + ], + "type": "text", + "content": "Figure 2. Some inherent characteristics of SIRST observed from the small local regions (i.e., salient in local region, similar shape, texture, and energy distribution)." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 114, + 70, + 164, + 159 + ], + "blocks": [ + { + "bbox": [ + 114, + 70, + 164, + 159 + ], + "lines": [ + { + "bbox": [ + 114, + 70, + 164, + 159 + ], + "spans": [ + { + "bbox": [ + 114, + 70, + 164, + 159 + ], + "type": "image", + "image_path": "9634e87a22cdd4be3cf7288923343a5a420a74f7501b1f11e07c194c667e0eb0.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 126, + 159, + 154, + 173 + ], + "lines": [ + { + "bbox": [ + 126, + 159, + 154, + 173 + ], + "spans": [ + { + "bbox": [ + 126, + 159, + 154, + 173 + ], + "type": "text", + "content": "(b) Similar Shape" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 168, + 70, + 219, + 159 + ], + "blocks": [ + { + "bbox": [ + 168, + 70, + 219, + 159 + ], + "lines": [ + { + "bbox": [ + 168, + 70, + 219, + 159 + ], + "spans": [ + { + "bbox": [ + 168, + 70, + 219, + 159 + ], + "type": "image", + "image_path": "87c7b9c23df3165eb0c8623c16a2d6342e97bf9c5035975073e88ea234a50a75.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 180, + 159, + 207, + 172 + ], + "lines": [ + { + "bbox": [ + 180, + 159, + 207, + 172 + ], + "spans": [ + { + "bbox": [ + 180, + 159, + 207, + 172 + ], + "type": "text", + "content": "(c) Similar Texture" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 223, + 70, + 273, + 159 + ], + "blocks": [ + { + "bbox": [ + 223, + 70, + 273, + 159 + ], + "lines": [ + { + "bbox": [ + 223, + 70, + 273, + 159 + ], + "spans": [ + { + "bbox": [ + 223, + 70, + 273, + 159 + ], + "type": "image", + "image_path": "404d90aa754aae3a8b506637ca1259e9988bfb9538e8f588f931a5cc70a3ff2a.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 223, + 159, + 270, + 172 + ], + "lines": [ + { + "bbox": [ + 223, + 159, + 270, + 172 + ], + "spans": [ + { + "bbox": [ + 223, + 159, + 270, + 172 + ], + "type": "text", + "content": "(d) Similar Energy Distribution" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 232, + 287, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 232, + 287, + 388 + ], + "spans": [ + { + "bbox": [ + 46, + 232, + 287, + 388 + ], + "type": "text", + "content": "We notice that although infrared small targets lack semantic information from the perspective of whole image, they are quite salient in the local small region. Specifically, as shown in Fig. 2, small targets in infrared images generally have high energy concentricity and exhibit significant gradient difference in their local regions. Moreover, limited semantic information (e.g., weak texture, shape, and color distribution) makes most point-like and spot-like targets exhibit similar energy distribution (e.g., Gaussian distribution). Consequently, it is straightforward to use a simple linear clustering approach (LCA) to separate the salient regions by measuring their color and spatial distances with adjacent backgrounds." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 388, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 388, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 388, + 287, + 640 + ], + "type": "text", + "content": "However, LCA easily falls into local optimum and produces inaccurate segmentation results due to their fixed hyper-parameters. To handle this problem, we propose a Monte Carlo linear clustering (MCLC) method to regularize the clustering process and recover the reliable clustering result by repetitive random experiments. Specifically, we introduce randomness to the clustering process by adding noise to the input images. With the help of random noise, the distance between unexpected background region and target region can be significantly enlarged. The misclustered target regions can be pushed away from the false clustering center and thus return back the true clustering center. In this way, the single-point annotation can be gradually recovered as a much more reliable pixel-level target probability map (TPM) by averaging the clustered results. Pixels with larger values in TPM represent a higher probability of belonging to the target. Finally, we use the refined TPM to turn arbitrary fully supervised SIRST detection networks into weakly supervised ones with only single point annotation. Fig. 1 shows the overall pipeline of our method, and the main contributions are summarized as follows:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 57, + 653, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 653, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 57, + 653, + 287, + 714 + ], + "type": "text", + "content": "- To the best of our knowledge, this is the first single-point supervised method to achieve SIRST detection. A Monte Carlo linear clustering-based pipeline is proposed to achieve comparable performance with the fully supervised counterpart by using single-point anno" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 326, + 73, + 352, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 326, + 73, + 352, + 83 + ], + "spans": [ + { + "bbox": [ + 326, + 73, + 352, + 83 + ], + "type": "text", + "content": "taion." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 316, + 95, + 545, + 228 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 316, + 95, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 95, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 316, + 95, + 545, + 156 + ], + "type": "text", + "content": "- Inspired by the inherent characteristic of SIRST, a simple yet effective linear clustering approach with random noise-guided Monte Carlo regularization is proposed to coarsely extract and further refine the candidate target region." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 316, + 167, + 545, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 167, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 316, + 167, + 545, + 228 + ], + "type": "text", + "content": "- Experiments on four public SIRST datasets demonstrate the effectiveness of our method. Ablation study reveals that pixel-level labels are not necessary for SIRST detection while single-point supervision is strong enough." + } + ] + } + ], + "index": 14 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 241, + 392, + 254 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 241, + 392, + 254 + ], + "spans": [ + { + "bbox": [ + 306, + 241, + 392, + 254 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 262, + 479, + 274 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 262, + 479, + 274 + ], + "spans": [ + { + "bbox": [ + 306, + 262, + 479, + 274 + ], + "type": "text", + "content": "2.1. Infrared Small Target Detection" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "spans": [ + { + "bbox": [ + 304, + 281, + 545, + 436 + ], + "type": "text", + "content": "SIRST detection has been extensively investigated for decades. Early traditional paradigm achieves SIRST detection by measuring the discontinuity between targets and backgrounds. Typical methods include filtering-based methods [31, 14], local contrast measure-based methods [6, 18, 19, 20, 22, 36], and low rank-based methods [16, 43, 9, 44, 51, 10]. Since real scenes are much more complex with dramatic changes in target size, shape, and clutter background, it is difficult to use handcrafted features and fixed hyper-parameters to handle such variations. To address this problem, recent deep learning-based methods learn trainable features in a data-driven manner and thus achieve better performance than traditional ones." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 437, + 546, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 546, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 546, + 676 + ], + "type": "text", + "content": "Existing deep learning-based methods can be divided into detection based methods and segmentation based methods. Since the pixel-level classification result is essential for the subsequent recognition task in SIRST, segmentation-based methods have attracted increasing attention recently. Dai et al. [11] proposed the first segmentation-based network (i.e., ACM). They designed an asymmetric contextual module to aggregate features from shallow layers and deep layers. Then, Dai et al. [12] improved ACM by introducing a dilated local contrast measure. Specifically, a feature cyclic shift scheme was designed to achieve a trainable local contrast measure. After that, Zhang et al. [45] modeled SIRST detection as a shape detection task. A taylor finite difference (TFD)-inspired edge block and a two-orientation attention aggregation (TOAA) block were proposed to capture precise shape of infrared targets. Recently, Li et al. [23] proposed a dense nested attention network (DNANet). A specifically-designed dense nested interactive module (DNIM) was proposed to both extract high-level information and maintain the response of small targets in deep layers." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 713 + ], + "type": "text", + "content": "Although the performance has been continuously improved by recent networks, existing deep learning-based methods rely on the fully-supervised training scheme with" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "type": "text", + "content": "1010" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 62, + 72, + 276, + 183 + ], + "blocks": [ + { + "bbox": [ + 62, + 72, + 276, + 183 + ], + "lines": [ + { + "bbox": [ + 62, + 72, + 276, + 183 + ], + "spans": [ + { + "bbox": [ + 62, + 72, + 276, + 183 + ], + "type": "image", + "image_path": "cc64a29001c91873ca0e7519078ba1ca8d4595d403768de2ef08c26b1fe0ed5e.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 186, + 287, + 218 + ], + "lines": [ + { + "bbox": [ + 46, + 186, + 287, + 218 + ], + "spans": [ + { + "bbox": [ + 46, + 186, + 287, + 218 + ], + "type": "text", + "content": "Figure 3. Sample of input images, four common weakly supervised annotations (i.e., single-point, multi-point, scribble, bounding box), and one fully supervised pixel-level annotation." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 238, + 287, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 238, + 287, + 274 + ], + "spans": [ + { + "bbox": [ + 46, + 238, + 287, + 274 + ], + "type": "text", + "content": "pixel-level annotations. Expensive labor cost makes existing methods hard to be deployed to large scale data-dependent tasks." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 278, + 192, + 290 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 278, + 192, + 290 + ], + "spans": [ + { + "bbox": [ + 47, + 278, + 192, + 290 + ], + "type": "text", + "content": "2.2. Point-based Segmentation" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 293, + 287, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 293, + 287, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 293, + 287, + 568 + ], + "type": "text", + "content": "Point-level supervision has been widely used in many high-level tasks (e.g., object detection [7, 46], object localization [41], and semantic segmentation [4, 29, 27, 24, 49]) and yield promising performance. For semantic segmentation task, Bearman et al. [4] proposed the first single-point supervised semantic segmentation method. They incorporated the single-point supervision along with an objectness prior as the loss function to infer the extent of the object. Then, Papadopoulos et al. [29] and Maninis et al. [27] utilized four extreme points (i.e., left-most, right-most, top, and bottom pixels) as supervision to further improve the quality of the pseudo mask. After that, Austin et al. [28] followed the class activation maps (CAM) [50] pipeline and used the point annotation to refine the quality of pseudo labels. More recently, Li et al. [24] utilized the semantical consistency property of general objects with 20 randomly annotated points to achieve comparable segmentation results with fully-supervised counterpart. Moreover, in the field of cell segmentation, Zhao et al. [49] proposed the first single-point supervised segmentation method, in which two semantic prior-based training losses (i.e., divergence loss and consistency loss) were proposed to achieve high-quality cell segmentation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 569, + 287, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 569, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 569, + 287, + 664 + ], + "type": "text", + "content": "Although promising performance has been achieved, existing works rely on rich semantic information (e.g., objectness prior in [4, 50], shape prior in [29, 27, 49]) and most of them need multi-point annotation. Infrared small targets generally occupy no more than " + }, + { + "bbox": [ + 46, + 569, + 287, + 664 + ], + "type": "inline_equation", + "content": "0.15\\%" + }, + { + "bbox": [ + 46, + 569, + 287, + 664 + ], + "type": "text", + "content": " area of the whole image [47] and lack texture, shape and color information. Previous semantic information-dependent methods cannot be directly used for SIRST detection." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 672, + 129, + 685 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 672, + 129, + 685 + ], + "spans": [ + { + "bbox": [ + 47, + 672, + 129, + 685 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "In this section, we first introduce the motivation. Then, a detailed illustration of the proposed linear clustering ap" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": "proach with Monte Carlo regularization is provided. Overall architecture of proposed method is shown in Fig. 4." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 104, + 380, + 115 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 104, + 380, + 115 + ], + "spans": [ + { + "bbox": [ + 306, + 104, + 380, + 115 + ], + "type": "text", + "content": "3.1. Motivation" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 122, + 545, + 254 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 122, + 545, + 254 + ], + "spans": [ + { + "bbox": [ + 304, + 122, + 545, + 254 + ], + "type": "text", + "content": "We investigate the annotation cost of four common weakly-supervised annotations (i.e., single point [5], multiple points[5, 29, 27], scribbles [25], bounding boxes[21]) by re-labelling the NUDT-SIRST [23] and NUAA-SIRST [11] datasets. Fig. 3 shows the average annotation time of four weakly-supervised and one fully-supervised approaches. Note that, single-point supervision can reduce about " + }, + { + "bbox": [ + 304, + 122, + 545, + 254 + ], + "type": "inline_equation", + "content": "87\\%" + }, + { + "bbox": [ + 304, + 122, + 545, + 254 + ], + "type": "text", + "content": " annotation time as compared to the pixel-level annotation approach, which motivates us to apply single-point annotation to SIRST detection. Please refer to the supplementary material for more detailed analysis." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 255, + 545, + 386 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 255, + 545, + 386 + ], + "spans": [ + { + "bbox": [ + 304, + 255, + 545, + 386 + ], + "type": "text", + "content": "However, existing point-level supervised methods [5, 29, 27] are designed for general objects with rich semantic information (e.g., shape, texture, and color). As shown in Fig. 2, the characteristics of infrared small targets make the aforementioned semantic-based pipeline unsuitable for SIRST detection. Considering that infrared small targets are quite salient in their local regions and share similar shape, texture, and energy distribution. Intuitively, we can use simple linear clustering approaches (e.g., Super-pixel [1], K-Means [26]) to separate the salient regions by comparing their color and spatial distances among these clusters." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 394, + 462, + 407 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 394, + 462, + 407 + ], + "spans": [ + { + "bbox": [ + 306, + 394, + 462, + 407 + ], + "type": "text", + "content": "3.2. Linear Clustering Approach" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 412, + 545, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 412, + 545, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 412, + 545, + 544 + ], + "type": "text", + "content": "Without loss of generality, we take the quick linear clustering method SuperPixel [1] as an example to introduce how to use LCA to coarsely separate the target region. It should be noted that other linear clustering approaches such as KMeans [26] can be also used in our method, as demonstrated in Fig. 5. The pipeline of our LCA is shown in Fig. 4 (Step I " + }, + { + "bbox": [ + 304, + 412, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\sim" + }, + { + "bbox": [ + 304, + 412, + 545, + 544 + ], + "type": "text", + "content": " Step III), in which the clustering center of the image is first initialized, and then adjusted according to a color and spatial distance based measurement. Finally, the clustering center is continuously updated until the pre-defined convergence requirements are met." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "spans": [ + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "text", + "content": "1) Clustering Center Initialization: We initialize the clustering center based on the pre-defined number of clusters " + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "text", + "content": ". Given an input image " + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "inline_equation", + "content": "I \\in \\mathbb{R}^{H \\times W}" + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "text", + "content": ", we first divide it into " + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "text", + "content": " regions with equal areas and fixed grid interval " + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "inline_equation", + "content": "S = \\sqrt{\\frac{H \\times W}{N}}" + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "text", + "content": " (as shown in Fig. 4-Step 1). After that, the clustering center is first initialized as the centroid of each region, and then moved to the lowest gradient position of its " + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "text", + "content": " neighborhood. The clustering center of the " + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "inline_equation", + "content": "n^{th}" + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "text", + "content": " clustering region " + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_n" + }, + { + "bbox": [ + 304, + 544, + 545, + 658 + ], + "type": "text", + "content": " can be represented as a vector as:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 391, + 667, + 545, + 683 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 391, + 667, + 545, + 683 + ], + "spans": [ + { + "bbox": [ + 391, + 667, + 545, + 683 + ], + "type": "interline_equation", + "content": "\\mathcal {C} _ {n} = \\left[ c _ {n}, s _ {n} \\right] ^ {T}, \\tag {1}", + "image_path": "263bfa76bbf4ec9f687e8871bec70e07724ec1f1921def7e558ea52007e9dfaf.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 687, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 687, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 687, + 545, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 687, + 545, + 714 + ], + "type": "inline_equation", + "content": "[c_n]^T" + }, + { + "bbox": [ + 304, + 687, + 545, + 714 + ], + "type": "text", + "content": " represents the CIELAB color [32] of " + }, + { + "bbox": [ + 304, + 687, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_n" + }, + { + "bbox": [ + 304, + 687, + 545, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 687, + 545, + 714 + ], + "type": "inline_equation", + "content": "[s_n]^T" + }, + { + "bbox": [ + 304, + 687, + 545, + 714 + ], + "type": "text", + "content": " denotes the spatial position in image coordinate of " + }, + { + "bbox": [ + 304, + 687, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_n" + }, + { + "bbox": [ + 304, + 687, + 545, + 714 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 734, + 314, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 734, + 314, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 734, + 314, + 742 + ], + "type": "text", + "content": "1011" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 68, + 541, + 305 + ], + "blocks": [ + { + "bbox": [ + 51, + 68, + 541, + 305 + ], + "lines": [ + { + "bbox": [ + 51, + 68, + 541, + 305 + ], + "spans": [ + { + "bbox": [ + 51, + 68, + 541, + 305 + ], + "type": "image", + "image_path": "a7dd4ccc1d01683daee3003eeda05a5ba5719e0b056105548e3f7e7d2ce71ce5.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 311, + 546, + 366 + ], + "lines": [ + { + "bbox": [ + 46, + 311, + 546, + 366 + ], + "spans": [ + { + "bbox": [ + 46, + 311, + 546, + 366 + ], + "type": "text", + "content": "Figure 4. Illustration of our method. StepI " + }, + { + "bbox": [ + 46, + 311, + 546, + 366 + ], + "type": "inline_equation", + "content": "\\sim" + }, + { + "bbox": [ + 46, + 311, + 546, + 366 + ], + "type": "text", + "content": " StepIII: LCA can coarsely separate target from clutter background, but easily falls into local optimum and produce incomplete pseudo mask. StepIV " + }, + { + "bbox": [ + 46, + 311, + 546, + 366 + ], + "type": "inline_equation", + "content": "\\sim" + }, + { + "bbox": [ + 46, + 311, + 546, + 366 + ], + "type": "text", + "content": " StepV: Monte Carlo regularization can increase the color distance between background and target region and thus enforce the misclustered target region away from the false clustering center. After repetitive random experiments, the accumulated clustering results are finally shown as a target probability map (TPM), where pixels with larger values represent a higher probability of belonging to the target." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "spans": [ + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "text", + "content": "2) Distance Measurement: After clustering center initialization, we adopt a color and spatial distance based measurement to determine the clustering center of each pixel. As shown in Fig. 4-Step II, for each clustering center " + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_n" + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "text", + "content": ", we use " + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "inline_equation", + "content": "L_2" + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "text", + "content": " distance to measure its distance with each pixel " + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "inline_equation", + "content": "p_i = [c_i, s_i]^T" + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "text", + "content": " in its adjacent " + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "inline_equation", + "content": "2S \\times 2S" + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "text", + "content": " regions. Considering that the ranges of color value and spatial position value are inconsistent, we normalize the both distance values with normalization coefficient " + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "inline_equation", + "content": "\\mu_s" + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "inline_equation", + "content": "\\mu_c" + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "inline_equation", + "content": "\\mathcal{D}(\\mathcal{C}_n, p_i)" + }, + { + "bbox": [ + 46, + 385, + 287, + 494 + ], + "type": "text", + "content": " is written as:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 73, + 510, + 287, + 559 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 73, + 510, + 287, + 559 + ], + "spans": [ + { + "bbox": [ + 73, + 510, + 287, + 559 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {D} (\\mathcal {C} _ {n}, p _ {i}) = \\sqrt {(\\mathcal {D} _ {c}) ^ {2} + (\\mathcal {D} _ {s}) ^ {2}} \\\\ = \\sqrt {\\frac {\\left(c _ {p _ {i}} - c _ {\\mathcal {C} _ {n}}\\right) ^ {2}}{\\mu_ {c} ^ {2}} + \\frac {\\left(s _ {p _ {i}} - s _ {\\mathcal {C} _ {n}}\\right) ^ {2}}{\\mu_ {s} ^ {2}}}. \\tag {2} \\\\ \\end{array}", + "image_path": "89230a6f7a12d28f9bd543f0816f55d15b53f2b19279b615b85c695084b14fce.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 565, + 287, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 565, + 287, + 588 + ], + "spans": [ + { + "bbox": [ + 47, + 565, + 287, + 588 + ], + "type": "text", + "content": "Then, the clustering label " + }, + { + "bbox": [ + 47, + 565, + 287, + 588 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 47, + 565, + 287, + 588 + ], + "type": "text", + "content": " for each pixel " + }, + { + "bbox": [ + 47, + 565, + 287, + 588 + ], + "type": "inline_equation", + "content": "p_i" + }, + { + "bbox": [ + 47, + 565, + 287, + 588 + ], + "type": "text", + "content": " can be determined as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 82, + 600, + 287, + 615 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 82, + 600, + 287, + 615 + ], + "spans": [ + { + "bbox": [ + 82, + 600, + 287, + 615 + ], + "type": "interline_equation", + "content": "l \\left(p _ {i}\\right) = \\operatorname {a r g m i n} _ {\\mathrm {n} \\in \\{1, 2, 3, \\dots , \\mathrm {N} \\}} \\left[ \\mathcal {D} \\left(\\mathcal {C} _ {\\mathrm {n}}, \\mathrm {p} _ {\\mathrm {i}}\\right) \\right]. \\tag {3}", + "image_path": "2f7743416a86dfed0576d3bc304e52d791c75fb617a033d78190bd85ff967451.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 618, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 618, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 618, + 287, + 712 + ], + "type": "text", + "content": "3) Updating and Convergence: After determining the clustering center of each pixel at the current iteration, we repetitively update the position of each clustering center until convergence, as shown in Fig. 4-Step III. Specifically, we first calculate the clustering centers to be the mean vector " + }, + { + "bbox": [ + 47, + 618, + 287, + 712 + ], + "type": "inline_equation", + "content": "[c_m, s_m]^T" + }, + { + "bbox": [ + 47, + 618, + 287, + 712 + ], + "type": "text", + "content": " of all the pixels " + }, + { + "bbox": [ + 47, + 618, + 287, + 712 + ], + "type": "inline_equation", + "content": "P = \\{p_1, p_2, \\dots, p_m\\}" + }, + { + "bbox": [ + 47, + 618, + 287, + 712 + ], + "type": "text", + "content": " with the same clustering label " + }, + { + "bbox": [ + 47, + 618, + 287, + 712 + ], + "type": "inline_equation", + "content": "l(\\mathcal{C}_n')" + }, + { + "bbox": [ + 47, + 618, + 287, + 712 + ], + "type": "text", + "content": ". The new clustering center " + }, + { + "bbox": [ + 47, + 618, + 287, + 712 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_n'" + }, + { + "bbox": [ + 47, + 618, + 287, + 712 + ], + "type": "text", + "content": " can be formulated as:" + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 309, + 384, + 544, + 495 + ], + "blocks": [ + { + "bbox": [ + 309, + 384, + 544, + 495 + ], + "lines": [ + { + "bbox": [ + 309, + 384, + 544, + 495 + ], + "spans": [ + { + "bbox": [ + 309, + 384, + 544, + 495 + ], + "type": "image", + "image_path": "0f0086a783ebf8d88e111a66a8f249377c1f5b43679c38f5ec9db6839840c9fc.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 498, + 545, + 542 + ], + "lines": [ + { + "bbox": [ + 305, + 498, + 545, + 542 + ], + "spans": [ + { + "bbox": [ + 305, + 498, + 545, + 542 + ], + "type": "text", + "content": "Figure 5. Visualization results achieved by (a) Kmeans, (b) K-means with Monte Carlo Regularization, (c) Super pixel, (d) Super pixel with Monte Carlo Regularization. Our proposed Monte Carlo regularization helps to expand informative target region." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 344, + 577, + 545, + 607 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 344, + 577, + 545, + 607 + ], + "spans": [ + { + "bbox": [ + 344, + 577, + 545, + 607 + ], + "type": "interline_equation", + "content": "\\mathcal {C} _ {n} ^ {\\prime} \\left(c _ {n}, x _ {n}, y _ {n}\\right) = \\frac {1}{| P |} \\sum_ {p _ {m} \\in P} \\left(c _ {p _ {m}}, s _ {p _ {m}}\\right). \\tag {4}", + "image_path": "dd0013b4281855d2493c7916223a99d5ceef4e76b6474bde6e64d4e8f88a22e0.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "content": "After that, we adopt " + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "content": " norm to compute a distance " + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{E}" + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "content": " between new clustering center locations " + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_n'" + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "content": " and previous clustering center locations " + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_n" + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "content": ". The updating steps can be repeated iteratively until the error is smaller than the predefined threshold " + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "content": ". That is " + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\| \\mathcal{C}_n' - \\mathcal{C}_n \\|_2 < T" + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\|_2" + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "content": " denote the L2 norm. Finally, we assign the single-point annotation " + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "inline_equation", + "content": "p_{Aanno}" + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "content": " located at the " + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "inline_equation", + "content": "n^{th}" + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "content": " clustering region as the clustering result " + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "inline_equation", + "content": "M_{pred}" + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 732, + 315, + 742 + ], + "type": "text", + "content": "1012" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 70, + 169, + 167 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 169, + 167 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 169, + 167 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 169, + 167 + ], + "type": "image", + "image_path": "fd77ab1afd41e932334e815fc0b86e197c726a79719d97b816b80ce7119f284a.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 169, + 287, + 245 + ], + "lines": [ + { + "bbox": [ + 46, + 169, + 287, + 245 + ], + "spans": [ + { + "bbox": [ + 46, + 169, + 287, + 245 + ], + "type": "text", + "content": "Figure 6. Quantitative analysis on (a) Sensitivity of target and non-target regions to additional noise, and (b) Color distance of target edge region with true foreground region centroid " + }, + { + "bbox": [ + 46, + 169, + 287, + 245 + ], + "type": "inline_equation", + "content": "\\Delta (\\mathcal{D}_c(\\mathcal{C}^T,M_{pred}))" + }, + { + "bbox": [ + 46, + 169, + 287, + 245 + ], + "type": "text", + "content": " and false background region centroid " + }, + { + "bbox": [ + 46, + 169, + 287, + 245 + ], + "type": "inline_equation", + "content": "\\Delta (\\mathcal{D}_c(\\mathcal{C}^F,M_{pred}))" + }, + { + "bbox": [ + 46, + 169, + 287, + 245 + ], + "type": "text", + "content": ". Average results from 10 trails are reported. Readers can refer to the supplementary material for more detailed illustration." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 169, + 70, + 286, + 167 + ], + "blocks": [ + { + "bbox": [ + 169, + 70, + 286, + 167 + ], + "lines": [ + { + "bbox": [ + 169, + 70, + 286, + 167 + ], + "spans": [ + { + "bbox": [ + 169, + 70, + 286, + 167 + ], + "type": "image", + "image_path": "56a037a578972acbb06e57e9a46a77ce70e983dfbf31f35c4aba78904651686a.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 263, + 202, + 276 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 263, + 202, + 276 + ], + "spans": [ + { + "bbox": [ + 47, + 263, + 202, + 276 + ], + "type": "text", + "content": "3.3. Monte Carlo Regularization" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 281, + 287, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 281, + 287, + 365 + ], + "spans": [ + { + "bbox": [ + 46, + 281, + 287, + 365 + ], + "type": "text", + "content": "Although LCA can coarsely separate local salient regions from the backgrounds, as shown in Fig. 5 (a) and (c), a linear clustering method easily falls into local optimum and generates incomplete or oversized results. In this subsection, we first analyze the reason of this issue, and then propose a Monte Carlo regularization to alleviate this issue, as shown in Fig. 4 (StepIV " + }, + { + "bbox": [ + 46, + 281, + 287, + 365 + ], + "type": "inline_equation", + "content": "\\sim" + }, + { + "bbox": [ + 46, + 281, + 287, + 365 + ], + "type": "text", + "content": " StepV)." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "text", + "content": "1) Inaccurate Result within a Single Clustering: Due to the varied size of small targets, LCA with fixed number of clustering centers cannot produce ideal results for all kinds of targets. That is because, both color " + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_c" + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "text", + "content": " and spatial distance " + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_s" + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "text", + "content": " determine the output of linear clustering model in Equation 2. Since edge areas " + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "inline_equation", + "content": "M_{pred}^{Edge} = \\{m_{pred}^{Edge(1)}, m_{pred}^{Edge(2)}, \\dots, m_{pred}^{Edge(Z)}\\}" + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "text", + "content": " of the spot and extended target (i.e., big target) are generally far from the true clustering center " + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "inline_equation", + "content": "\\mathcal{C}^T" + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "text", + "content": " (shown as the left-most green point in Fig. 4-Step III). The spatial distance " + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_c(\\mathcal{C}^T, M_{pred}^{Edge})" + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "text", + "content": " between the true clustering center " + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "inline_equation", + "content": "\\mathcal{C}^T" + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "text", + "content": " and edge areas " + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "inline_equation", + "content": "M_{pred}^{Edge}" + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "text", + "content": " is usually farther than that of the false clustering center " + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "inline_equation", + "content": "\\mathcal{C}^F" + }, + { + "bbox": [ + 46, + 365, + 287, + 529 + ], + "type": "text", + "content": ". That is:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 84, + 538, + 287, + 556 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 84, + 538, + 287, + 556 + ], + "spans": [ + { + "bbox": [ + 84, + 538, + 287, + 556 + ], + "type": "interline_equation", + "content": "\\mathcal {D} _ {s} \\left(\\mathcal {C} ^ {T}, m _ {\\text {p r e d}} ^ {\\text {E d g e} (z)}\\right) > \\mathcal {D} _ {s} \\left(\\mathcal {C} ^ {F}, m _ {\\text {p r e d}} ^ {\\text {E d g e} (z)}\\right). \\tag {5}", + "image_path": "4dc1556126020b8b9466b8dcc58572bb299dd935aadaaa2d06de4ed87c7ddb48.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 559, + 287, + 620 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 559, + 287, + 620 + ], + "spans": [ + { + "bbox": [ + 46, + 559, + 287, + 620 + ], + "type": "text", + "content": "Moreover, the color value of big target generally exhibits Gaussian distribution. Those edge areas often exhibit relatively high color difference with the true clustering center, and are close to the adjacent false clustering center (shown as the right-most green point in Fig. 4 Step III). That is:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 84, + 628, + 287, + 645 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 84, + 628, + 287, + 645 + ], + "spans": [ + { + "bbox": [ + 84, + 628, + 287, + 645 + ], + "type": "interline_equation", + "content": "\\mathcal {D} _ {c} \\left(\\mathcal {C} ^ {T}, m _ {\\text {p r e d}} ^ {\\text {E d g e} (z)}\\right) > \\mathcal {D} _ {c} \\left(\\mathcal {C} ^ {F}, m _ {\\text {p r e d}} ^ {\\text {E d g e} (z)}\\right). \\tag {6}", + "image_path": "7ef0fb7574f9bb92e5aa8b1310dde967f237df097c35e3a2bd6e1f925a736c7c.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 651, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 651, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 651, + 287, + 689 + ], + "type": "text", + "content": "As a result, the label of edge areas " + }, + { + "bbox": [ + 46, + 651, + 287, + 689 + ], + "type": "inline_equation", + "content": "l_{pred}^{Edge}" + }, + { + "bbox": [ + 46, + 651, + 287, + 689 + ], + "type": "text", + "content": " may be falsely included into the adjacent false clustering center " + }, + { + "bbox": [ + 46, + 651, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathcal{C}^F" + }, + { + "bbox": [ + 46, + 651, + 287, + 689 + ], + "type": "text", + "content": ", resulting in incomplete clustering result." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "2) Random Noise Guided Regularization: Spatial distance " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_s" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " is generally fixed and hard to change in the im" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "content": "age. As shown in Fig. 6 (a), when adding random noise, target and non-target regions exhibit different sensitivity to the noise. Target regions with higher color vaule are more robust to the additional noise than the non-target regions. Based on this finding, we are motivated to introduce random noise to enlarge the color distance " + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_c(\\mathcal{C}^F,M_{pred}^{Edge})" + }, + { + "bbox": [ + 304, + 72, + 545, + 191 + ], + "type": "text", + "content": " between edge areas and false clustering center (as shown in Fig. 4-Step III), and thus make the edge areas be clustered to the true clustering center. Random noise-regularized clustering result can be formulated as follows:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 361, + 202, + 545, + 217 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 361, + 202, + 545, + 217 + ], + "spans": [ + { + "bbox": [ + 361, + 202, + 545, + 217 + ], + "type": "interline_equation", + "content": "M _ {p r e d} ^ {N o i s e} = L C A (c l i p (I + \\mathcal {N})), \\tag {7}", + "image_path": "7510d91cc2f7ddc74679aafdc796d198103d3c1823f44adeb425615529705834.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 220, + 545, + 267 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 220, + 545, + 267 + ], + "spans": [ + { + "bbox": [ + 304, + 220, + 545, + 267 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 220, + 545, + 267 + ], + "type": "inline_equation", + "content": "\\text{clip}(\\cdot)" + }, + { + "bbox": [ + 304, + 220, + 545, + 267 + ], + "type": "text", + "content": " operation represents that color values larger than 255 will be fixed at 255. " + }, + { + "bbox": [ + 304, + 220, + 545, + 267 + ], + "type": "inline_equation", + "content": "\\mathcal{N}" + }, + { + "bbox": [ + 304, + 220, + 545, + 267 + ], + "type": "text", + "content": " is the additional random noise. The color value change caused by random noise can be formulated as:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 344, + 278, + 545, + 293 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 344, + 278, + 545, + 293 + ], + "spans": [ + { + "bbox": [ + 344, + 278, + 545, + 293 + ], + "type": "interline_equation", + "content": "\\Delta \\left(\\mathcal {D} _ {c} \\left(\\mathcal {C}, M _ {p r e d}\\right)\\right) = \\mathcal {D} _ {c} ^ {\\text {N o i s e}} - \\mathcal {D} _ {c} ^ {\\text {C l e a n}}. \\tag {8}", + "image_path": "ec21c8aace65d617ccf30431b5aa0e5f3585c1bb6f32b8a3629d42e5fe56eef2.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 297, + 545, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 297, + 545, + 475 + ], + "spans": [ + { + "bbox": [ + 304, + 297, + 545, + 475 + ], + "type": "text", + "content": "Since background region has relatively low color value than foreground region. Additional noise will greatly increase the color value of adjacent false clustering centers, and thus enlarges their color distance with the edge area of target region. On the contrary, when comparing Fig. 4-Step IV with Fig. 4-Step V, we observe that foreground regions have high energy concentricity and are usually close to saturation. Additional noise cannot bring so much color change to target regions as the background regions. Benefited by the additional noise, as shown in Fig. 6 (b), the change of color distance between edge areas and false clustering center (i.e., " + }, + { + "bbox": [ + 304, + 297, + 545, + 475 + ], + "type": "inline_equation", + "content": "\\Delta (\\mathcal{D}_c(\\mathcal{C}^F,M_{pred}))" + }, + { + "bbox": [ + 304, + 297, + 545, + 475 + ], + "type": "text", + "content": ") will be significantly larger than that between edge areas and true clustering center (i.e., " + }, + { + "bbox": [ + 304, + 297, + 545, + 475 + ], + "type": "inline_equation", + "content": "\\Delta (\\mathcal{D}_c(\\mathcal{C}^T,M_{pred}))" + }, + { + "bbox": [ + 304, + 297, + 545, + 475 + ], + "type": "text", + "content": "), making the misclustered target region be more closed to the true clustering center." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 476, + 545, + 583 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 476, + 545, + 583 + ], + "spans": [ + { + "bbox": [ + 304, + 476, + 545, + 583 + ], + "type": "text", + "content": "3) Monte Carlo Process: As aforementioned, random noise can enforce the misclustered region to be gradually close to the true clustering center. Considering the randomness of noise, additional noise does not always bring such positive effect. We are motivated to adopt the Monte Carlo method to accumulate the clustering result from repetitive random experiments and gradually recover the reliable clustering result. To this end, we perform " + }, + { + "bbox": [ + 304, + 476, + 545, + 583 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 476, + 545, + 583 + ], + "type": "text", + "content": " independent clustering and formulate this process as follows:" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 335, + 601, + 545, + 633 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 335, + 601, + 545, + 633 + ], + "spans": [ + { + "bbox": [ + 335, + 601, + 545, + 633 + ], + "type": "interline_equation", + "content": "M _ {P r e d} ^ {F u l l} = \\frac {1}{K} \\sum_ {k = 1} ^ {K} \\left(L C A \\left(\\operatorname {c l i p} \\left(I + \\mathcal {N} ^ {(k)}\\right)\\right)\\right), \\tag {9}", + "image_path": "1a3208ef8ae4833013a2b8a33a54ef6a55b32cc8913a3cb03fc901a5ee6bffeb.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 640, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 640, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 640, + 545, + 689 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 640, + 545, + 689 + ], + "type": "inline_equation", + "content": "M_{Pred}^{Full}" + }, + { + "bbox": [ + 304, + 640, + 545, + 689 + ], + "type": "text", + "content": " is the accumulated clustering results after " + }, + { + "bbox": [ + 304, + 640, + 545, + 689 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 640, + 545, + 689 + ], + "type": "text", + "content": " independent clustering by LCA, and finally shown as a target probability map (TPM), where pixels with larger values represent a higher probability of belonging to the target." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "content": "The optimization process finally stops when the distance between the new clustering center locations " + }, + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{C}'" + }, + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "content": " and previous" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 733, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 733, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 733, + 315, + 742 + ], + "type": "text", + "content": "1013" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 71, + 165, + 167 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 165, + 167 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 165, + 167 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 165, + 167 + ], + "type": "image", + "image_path": "15a0bff01a352de1de822896093f067d307b60fa0d12ef65185c8b9e314f02d7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 170, + 287, + 226 + ], + "lines": [ + { + "bbox": [ + 46, + 170, + 287, + 226 + ], + "spans": [ + { + "bbox": [ + 46, + 170, + 287, + 226 + ], + "type": "text", + "content": "Figure 7. IoU scores achieved by our method with (a) different types and intensity of additional noise and (b) different number of clustering center on the NUAA-SIRST dataset. Average results from 5 trails are reported. Readers can refer to the supplementary material for additional experiments on the other datasets." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 167, + 71, + 284, + 166 + ], + "blocks": [ + { + "bbox": [ + 167, + 71, + 284, + 166 + ], + "lines": [ + { + "bbox": [ + 167, + 71, + 284, + 166 + ], + "spans": [ + { + "bbox": [ + 167, + 71, + 284, + 166 + ], + "type": "image", + "image_path": "c59546526f87359f1a1bdc0e673b1fb1c5cf05bb771e70c7202f68caf5a99a8f.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 53, + 281, + 282, + 327 + ], + "blocks": [ + { + "bbox": [ + 46, + 236, + 287, + 281 + ], + "lines": [ + { + "bbox": [ + 46, + 236, + 287, + 281 + ], + "spans": [ + { + "bbox": [ + 46, + 236, + 287, + 281 + ], + "type": "text", + "content": "Table 1. " + }, + { + "bbox": [ + 46, + 236, + 287, + 281 + ], + "type": "inline_equation", + "content": "IoU(10^{-2})" + }, + { + "bbox": [ + 46, + 236, + 287, + 281 + ], + "type": "text", + "content": " value achieved by the different variants of our method on the training set of four representative datasets (i.e., NUAA, IRSTD, NUDT, NUDT-sea). MC Regu. refers to Monte Carlo regularization." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 53, + 281, + 282, + 327 + ], + "lines": [ + { + "bbox": [ + 53, + 281, + 282, + 327 + ], + "spans": [ + { + "bbox": [ + 53, + 281, + 282, + 327 + ], + "type": "table", + "html": "
Point LabelLCAMC Regu.dCRFIoU(%)
✓✓2.53 / 1.62 / 2.28 / 1.82
✓✓51.8 / 55.5 / 51.2 / 38.1
✓✓✓70.4 / 66.2 / 52.5 / 43.9
✓✓✓✓76.3 / 68.8 / 60.2 / 47.1
", + "image_path": "867059735c69b3b96f3776553829d97d2443f9792a6b21a3c2500187a5ec6f40.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 350, + 287, + 374 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 350, + 287, + 374 + ], + "spans": [ + { + "bbox": [ + 46, + 350, + 287, + 374 + ], + "type": "text", + "content": "clustering center locations " + }, + { + "bbox": [ + 46, + 350, + 287, + 374 + ], + "type": "inline_equation", + "content": "\\mathcal{C}" + }, + { + "bbox": [ + 46, + 350, + 287, + 374 + ], + "type": "text", + "content": " is smaller than the pre-defined threshold " + }, + { + "bbox": [ + 46, + 350, + 287, + 374 + ], + "type": "inline_equation", + "content": "T^F" + }, + { + "bbox": [ + 46, + 350, + 287, + 374 + ], + "type": "text", + "content": ", i.e., " + }, + { + "bbox": [ + 46, + 350, + 287, + 374 + ], + "type": "inline_equation", + "content": "\\| \\mathcal{C}_n' - \\mathcal{C}_n\\|_2 < T^F" + }, + { + "bbox": [ + 46, + 350, + 287, + 374 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 387, + 128, + 401 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 387, + 128, + 401 + ], + "spans": [ + { + "bbox": [ + 47, + 387, + 128, + 401 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 408, + 287, + 516 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 408, + 287, + 516 + ], + "spans": [ + { + "bbox": [ + 46, + 408, + 287, + 516 + ], + "type": "text", + "content": "In this section, we first introduce our evaluation metrics and implementation details. Then, we compare our MCLC to several state-of-the-art unsupervised, point-level supervised, and fully-supervised SIRST detection methods. Finally, we present ablation studies to investigate the effectiveness of our method. Note that, we search for optimal parameters of MCLC in the training set of NUAA-SIRST [11] and directly adopt them as default parameters to generate pseudo masks on the other three datasets[45, 23, 39]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 526, + 160, + 538 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 526, + 160, + 538 + ], + "spans": [ + { + "bbox": [ + 47, + 526, + 160, + 538 + ], + "type": "text", + "content": "4.1. Evaluation Metrics" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "Considering that both the quality of pseudo labels and the final detection results are crucial to SIRST detection, we followed previous works [37, 42, 3, 2] and propose a two-stage pipeline (i.e., pseudo mask and final detection result evaluation) to comprehensively evaluate the effectiveness of the proposed method. Firstly, we followed the same metrics in weakly-supervised general object segmentation [3, 2] and adopted intersection of union " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "(IoU)" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " to evaluate the quality of generated pseudo labels on the training set. For the final detection results evaluation, we followed previous works [11, 12, 23] and adopted probability of detection " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "(P_d)" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": ", and false-alarm rate " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "F_{a}" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " to evaluate the localization precision, and used " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "IoU" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " to evaluate the shape description ability on the test set." + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 310, + 71, + 369, + 113 + ], + "blocks": [ + { + "bbox": [ + 310, + 71, + 369, + 113 + ], + "lines": [ + { + "bbox": [ + 310, + 71, + 369, + 113 + ], + "spans": [ + { + "bbox": [ + 310, + 71, + 369, + 113 + ], + "type": "image", + "image_path": "61a49b4338e44973b4bb4ba283d96a9b9fa21a48c5966dc3cfc2d1cbb41f23e8.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 369, + 72, + 416, + 113 + ], + "blocks": [ + { + "bbox": [ + 369, + 72, + 416, + 113 + ], + "lines": [ + { + "bbox": [ + 369, + 72, + 416, + 113 + ], + "spans": [ + { + "bbox": [ + 369, + 72, + 416, + 113 + ], + "type": "image", + "image_path": "062e17142eb5258a4f283d81fdcf9b2831298ab40fe24939da0581ba92d1104a.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 310, + 114, + 369, + 171 + ], + "blocks": [ + { + "bbox": [ + 310, + 114, + 369, + 171 + ], + "lines": [ + { + "bbox": [ + 310, + 114, + 369, + 171 + ], + "spans": [ + { + "bbox": [ + 310, + 114, + 369, + 171 + ], + "type": "image", + "image_path": "8d901cdf6133f5e08ac8eb36b52518d01de92f55d2ab93214b08ebfaf842142c.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 174, + 545, + 218 + ], + "lines": [ + { + "bbox": [ + 305, + 174, + 545, + 218 + ], + "spans": [ + { + "bbox": [ + 305, + 174, + 545, + 218 + ], + "type": "text", + "content": "Figure 8. (a) Labelling deviation examples of small target from four datasets. (b) Label deviation distribution map generated from 105 manually re-labelled targets. Real world labelling deviation of small target is generally less than 3 pixels." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 369, + 114, + 416, + 171 + ], + "blocks": [ + { + "bbox": [ + 369, + 114, + 416, + 171 + ], + "lines": [ + { + "bbox": [ + 369, + 114, + 416, + 171 + ], + "spans": [ + { + "bbox": [ + 369, + 114, + 416, + 171 + ], + "type": "image", + "image_path": "7fd40b7ac9ee5db49e43a9d4d0d86c0633b681a6b70446466c1fb7971c867037.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 417, + 72, + 543, + 171 + ], + "blocks": [ + { + "bbox": [ + 417, + 72, + 543, + 171 + ], + "lines": [ + { + "bbox": [ + 417, + 72, + 543, + 171 + ], + "spans": [ + { + "bbox": [ + 417, + 72, + 543, + 171 + ], + "type": "image", + "image_path": "560d13ca74453ecedb01295fdc0e8e9588e806e0eff52b404fb2869055692cfb.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 232, + 440, + 243 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 232, + 440, + 243 + ], + "spans": [ + { + "bbox": [ + 306, + 232, + 440, + 243 + ], + "type": "text", + "content": "4.2. Implementation Details" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 245, + 545, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 245, + 545, + 399 + ], + "spans": [ + { + "bbox": [ + 304, + 245, + 545, + 399 + ], + "type": "text", + "content": "1) Datasets: We evaluated our method on the NUAA-SIRST [11], IRSTD-1k [45], NUDT-SIRST [23], and NUDT-SIRST-sea [39] datasets. Without specification, for the NUAA-SIRST and NUDT-SIRST datasets, we used the same division as in [23] and set the ratio of train-val set to test set as 1. For the IRSTD-1k dataset, we followed [45] and used " + }, + { + "bbox": [ + 304, + 245, + 545, + 399 + ], + "type": "inline_equation", + "content": "80\\%" + }, + { + "bbox": [ + 304, + 245, + 545, + 399 + ], + "type": "text", + "content": " data for training and validation, and the remaining " + }, + { + "bbox": [ + 304, + 245, + 545, + 399 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 304, + 245, + 545, + 399 + ], + "type": "text", + "content": " data for test. The division setting in [39] was adopted for the NUDT-SIRST-sea dataset, i.e., 41 images were used for training and validation, and the remaining 7 images were used for test. Note that, only single point-level annotation with category information (i.e., point, spot, and extend categories) are available during network training." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 401, + 546, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 401, + 546, + 662 + ], + "spans": [ + { + "bbox": [ + 304, + 401, + 546, + 662 + ], + "type": "text", + "content": "2) Training Details: In our experiments, all input images were first normalized before training. Then, these normalized images were sequentially processed by random flip, and random crop for data augmentation. Next, these images were resized to a fixed resolution. Specifically, " + }, + { + "bbox": [ + 304, + 401, + 546, + 662 + ], + "type": "inline_equation", + "content": "1024 \\times 1024" + }, + { + "bbox": [ + 304, + 401, + 546, + 662 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 401, + 546, + 662 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 304, + 401, + 546, + 662 + ], + "type": "text", + "content": " spatial resolutions were used for the NUDT-SIRST-sea and the remaining three datasets, respectively. Finally, we fed these resized datasets into network for both training and evaluation. Without specification, we adopted the centroid of ground truth mask as the single-point label. The influence of label position deviation is discussed in the following ablation. Moreover, all networks were trained with the Soft-IoU loss function and optimized by the Ada-grad method [15] with the CosineAnnealingLR scheduler. The Xavier method [17] was used for all weights and bias parameters initialization. We set the learning rate and epoch number to 0.05 and 1500, respectively. The batch size was set to 16 for the NUAA-SIRST, IRSTD-1k, NUDT-SIRST datasets but set to 4 for the NUDT-SIRST-sea dataset due to its large image size. All models were implemented in PyTorch [30] on a computer with an AMD Ryzen 9 3950X @ 2.20 GHz CPU and an Nvidia GeForce 3090 GPU." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 671, + 400, + 684 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 671, + 400, + 684 + ], + "spans": [ + { + "bbox": [ + 306, + 671, + 400, + 684 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "1) Effectiveness of Proposed Components: Table 1 shows the contribution of our proposed components on four" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "type": "text", + "content": "1014" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 70, + 92, + 265, + 148 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 287, + 92 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 287, + 92 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 287, + 92 + ], + "type": "text", + "content": "Table 2. " + }, + { + "bbox": [ + 47, + 70, + 287, + 92 + ], + "type": "inline_equation", + "content": "IoU(10^{-2})" + }, + { + "bbox": [ + 47, + 70, + 287, + 92 + ], + "type": "text", + "content": " values and corresponding labelling cost with stronger supervision on the train set of four datasets." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 70, + 92, + 265, + 148 + ], + "lines": [ + { + "bbox": [ + 70, + 92, + 265, + 148 + ], + "spans": [ + { + "bbox": [ + 70, + 92, + 265, + 148 + ], + "type": "table", + "html": "
AnnotationDataset
NUAAIRSTDNUDTNUDT-sea
Single-Point76.368.860.247.1
Multi-Point76.669.162.653.7
Scribble78.570.563.255.2
Bounding-Box78.971.864.854.5
", + "image_path": "24785da51d72cf222e91803d4ef6d38145a39d49d4cf27bb6b71b232d6bbe563.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "spans": [ + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": "datasets. Compared to the initial single-point label, linear clustering approach (LCA) introduces " + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "inline_equation", + "content": "49.3\\%" + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "inline_equation", + "content": "53.9\\%" + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "inline_equation", + "content": "48.9\\%" + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "inline_equation", + "content": "36.3\\%" + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": " improvements for the NUAA, IRSTD-1k, NUDT, NUDT-sea datasets, respectively. That is because, LCA utilizes the inherent characteristics of infrared small targets and thus coarsely separates the targets from clustering background. By introducing random salt noise to regularize the linear clustering process, we obtain much more reliable results and achieve additional " + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "inline_equation", + "content": "18.6\\%" + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "inline_equation", + "content": "10.7\\%" + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "inline_equation", + "content": "1.3\\%" + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "inline_equation", + "content": "5.8\\%" + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": " improvements on the above four datasets. After that, denseCRF [8] was used as a post-processing module to refine the target probability map (TPM) generated by MCLC. It further introduces " + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "inline_equation", + "content": "5.9\\%" + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "inline_equation", + "content": "2.6\\%" + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "inline_equation", + "content": "7.7\\%" + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "inline_equation", + "content": "3.2\\%" + }, + { + "bbox": [ + 46, + 169, + 287, + 396 + ], + "type": "text", + "content": " improvements for the above four datasets, respectively. We visualize the Monte Carlo linear clustering process in Fig. 9. Although easily producing inaccurate results at the beginning of clustering (e.g., iteration number less than 20), MCLC can gradually recover a reliable clustering result. More visualization samples are shown in supplementary material." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 397, + 287, + 673 + ], + "type": "list", + "angle": 0, + "index": 5, + "blocks": [ + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "spans": [ + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "text", + "content": "2) Type and Intensity of Noise: Fig. 7 (a) shows the change trend of " + }, + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "inline_equation", + "content": "IoU" + }, + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "text", + "content": " with respect to different noise intensity under three types of common noise (i.e., salt, pepper, and Gaussian). With the increase of noise intensity, the " + }, + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "inline_equation", + "content": "IoU" + }, + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "text", + "content": " of MCLC with denseCRF under salt noise and pepper noise increases rapidly at the beginning, and reaches their peak scores of " + }, + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "inline_equation", + "content": "76\\%" + }, + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "inline_equation", + "content": "71\\%" + }, + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "text", + "content": " at " + }, + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "inline_equation", + "content": "0.05" + }, + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "text", + "content": " intensity1. After that, excessive intensity value reduces the saliency of target region and thus results in the decrease of " + }, + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "inline_equation", + "content": "IoU" + }, + { + "bbox": [ + 46, + 397, + 287, + 577 + ], + "type": "text", + "content": ". Moreover, Gaussian noise causes huge performance decrease under any intensity. That is because, Gaussian noise randomly changes the values of all pixels in the image, which is similar to the salt and pepper with high intensity. Since all pixels in the image are influenced by the random noise, the saliency of target is greatly decreased, resulting in dramatic performance drop." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 578, + 287, + 673 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 578, + 287, + 673 + ], + "spans": [ + { + "bbox": [ + 46, + 578, + 287, + 673 + ], + "type": "text", + "content": "3) Number of Clustering Center: The number of clustering center determines the initial area of each clustering region. Fig. 7 (b) reports the " + }, + { + "bbox": [ + 46, + 578, + 287, + 673 + ], + "type": "inline_equation", + "content": "IoU" + }, + { + "bbox": [ + 46, + 578, + 287, + 673 + ], + "type": "text", + "content": " of the results generated by MCLC with denseCRF, MCLC with fixed threshold, and LCA under different number of clustering center. It shows that the " + }, + { + "bbox": [ + 46, + 578, + 287, + 673 + ], + "type": "inline_equation", + "content": "IoU" + }, + { + "bbox": [ + 46, + 578, + 287, + 673 + ], + "type": "text", + "content": " firstly shows a rapid increasing trend with the increase number of clustering center, and then reaches the peak score of " + }, + { + "bbox": [ + 46, + 578, + 287, + 673 + ], + "type": "inline_equation", + "content": "76\\%" + }, + { + "bbox": [ + 46, + 578, + 287, + 673 + ], + "type": "text", + "content": " with 9 clustering centers. Afterward-" + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "text" + }, + { + "type": "table", + "bbox": [ + 307, + 91, + 545, + 148 + ], + "blocks": [ + { + "bbox": [ + 305, + 70, + 545, + 91 + ], + "lines": [ + { + "bbox": [ + 305, + 70, + 545, + 91 + ], + "spans": [ + { + "bbox": [ + 305, + 70, + 545, + 91 + ], + "type": "text", + "content": "Table 3. " + }, + { + "bbox": [ + 305, + 70, + 545, + 91 + ], + "type": "inline_equation", + "content": "IoU(10^{-2})" + }, + { + "bbox": [ + 305, + 70, + 545, + 91 + ], + "type": "text", + "content": " values achieved with single point supervision under ideal and real scene." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 91, + 545, + 148 + ], + "lines": [ + { + "bbox": [ + 307, + 91, + 545, + 148 + ], + "spans": [ + { + "bbox": [ + 307, + 91, + 545, + 148 + ], + "type": "table", + "html": "
Pseudo Mask (Ideal / Real)Final Results (Ideal / Real)Pseudo Mask (Ideal / Real)Final Results (Ideal / Real)
ResUnet(76.3 / 73.7)(71.6 / 71.2)(60.2 / 58.8)(68.0 / 66.5)
DNANet(72.9 / 72.0)NUDT(70.5 / 69.1)
ResUnet(68.8 / 66.7)(64.6 / 63.8)(47.1 / 45.7)(39.1 / 38.2)
DNANetIRSTD(62.2 / 60.9)NUDT-Sea(40.2 / 38.8)
", + "image_path": "928b07312d119816202bb3b75d3d9289246b4a9bde892e01cf4ef89b5bad71bc.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 307, + 192, + 545, + 260 + ], + "blocks": [ + { + "bbox": [ + 305, + 159, + 545, + 192 + ], + "lines": [ + { + "bbox": [ + 305, + 159, + 545, + 192 + ], + "spans": [ + { + "bbox": [ + 305, + 159, + 545, + 192 + ], + "type": "text", + "content": "Table 4. " + }, + { + "bbox": [ + 305, + 159, + 545, + 192 + ], + "type": "inline_equation", + "content": "IoU(10^{-2})" + }, + { + "bbox": [ + 305, + 159, + 545, + 192 + ], + "type": "text", + "content": " values under fixed labelling time. " + }, + { + "bbox": [ + 305, + 159, + 545, + 192 + ], + "type": "inline_equation", + "content": "5.2 \\times" + }, + { + "bbox": [ + 305, + 159, + 545, + 192 + ], + "type": "text", + "content": " (with search) and " + }, + { + "bbox": [ + 305, + 159, + 545, + 192 + ], + "type": "inline_equation", + "content": "8.0 \\times" + }, + { + "bbox": [ + 305, + 159, + 545, + 192 + ], + "type": "text", + "content": " (w/o search) more point-level (P.) labels help to generate better results under fixed labelling time." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 192, + 545, + 260 + ], + "lines": [ + { + "bbox": [ + 307, + 192, + 545, + 260 + ], + "spans": [ + { + "bbox": [ + 307, + 192, + 545, + 260 + ], + "type": "table", + "html": "
Sup.NUAA-SIRSTIRSTD-1k
Time Budget: 920s (427×P.) vs (82×F.) (5.2 × P. labels)Time Budget: 1400s (1000×P.) vs (125×F.) (8.0 × P. labels)
ResUnetFull56.843.8
ResUnet+MCLCP.71.6 ↑ 14.864.6 ↑ 20.8
DNANetFull58.746.1
DNANet+MCLCP.72.1 ↑ 13.462.2 ↑ 16.1
", + "image_path": "a8acecc4742c0f1429dd09e4d3bcac8822cbf9f193a8bab338494d6404c6e7f2.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 281, + 545, + 341 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 281, + 545, + 341 + ], + "spans": [ + { + "bbox": [ + 304, + 281, + 545, + 341 + ], + "type": "text", + "content": "s, the quality of TPM gradually decreases when the number of clustering center further increases. The above results demonstrate that inappropriate number of clustering center will result in over-small or over-large area of initial search region, and thus introduce negative effect on MCLC." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 342, + 545, + 713 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 304, + 342, + 545, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 342, + 545, + 460 + ], + "spans": [ + { + "bbox": [ + 304, + 342, + 545, + 460 + ], + "type": "text", + "content": "4) Performance with Stronger Supervision: As shown in Table 2, stronger supervision can introduce additional " + }, + { + "bbox": [ + 304, + 342, + 545, + 460 + ], + "type": "inline_equation", + "content": "0.3\\% \\sim 2.6\\%" + }, + { + "bbox": [ + 304, + 342, + 545, + 460 + ], + "type": "text", + "content": " improvements in term of IoU on the NUAA-SIRST dataset, but at a cost of " + }, + { + "bbox": [ + 304, + 342, + 545, + 460 + ], + "type": "inline_equation", + "content": "121\\% \\sim 700\\%" + }, + { + "bbox": [ + 304, + 342, + 545, + 460 + ], + "type": "text", + "content": " increase of annotation time (i.e., 1.4s, 3.1s, and 11.2s for single-point, multi-point, and pixel-level annotation in Fig. 3). Similar results can be also found on the other three datasets. Therefore, we argue that single-point annotation is the most economical supervision and is strong enough for SIRST detection." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 461, + 545, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 461, + 545, + 593 + ], + "spans": [ + { + "bbox": [ + 304, + 461, + 545, + 593 + ], + "type": "text", + "content": "5) Labelling Position Deviation: Real-world SIRST application may suffer from labelling position deviation shown in Fig. 8 (a). To simulate the labelling position deviation in real world, we manually re-labelled 105 targets in NUAA-SIRST and IRSTD-1k dataset, and generated a distribution map of labelling position in Fig. 8 (b). Based on this distribution map, we re-produced the pseudo masks of whole dataset and generated the final detection results in Table 3. Average results from three trails demonstrate that our method can produce competitive results under practical labelling settings." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": "6) Time Efficiency: As aforementioned, once the optimal parameters (e.g., type and intensity of noise, number of clustering centers) are searched in one real-world dataset (e.g., NUAA-SIRST), we directly adopt these parameters to new scenes without secondary search (e.g., IRSTD in Table 4). As shown in Table 4, single-point labelling can produce about " + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "inline_equation", + "content": "5.2 \\times" + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": " (with parameter search) " + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\sim 8.0 \\times" + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": " (w/o parameter search) annotation than the pixel-level labelling with the same annotation budget, and thus achieves much better performance. Note that, our MCLC can efficiently" + } + ] + } + ], + "index": 14 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 46, + 683, + 287, + 714 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 683, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 683, + 287, + 714 + ], + "type": "text", + "content": "1The intensity value for salt and pepper noise is defined as the area ratio of noise region and image region. Higher values denote that more pixels are replaced by salt or pepper pixels." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "type": "text", + "content": "1015" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 69, + 103, + 525, + 353 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "text", + "content": "Table 5. " + }, + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "inline_equation", + "content": "IoU(10^{-2})" + }, + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "inline_equation", + "content": "P_d(10^{-2})" + }, + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "inline_equation", + "content": "F_a(10^{-6})" + }, + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "text", + "content": " values achieved by different state-of-the-art methods on four benchmark datasets. For " + }, + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "inline_equation", + "content": "IoU" + }, + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "inline_equation", + "content": "P_d" + }, + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "text", + "content": ", larger values indicate better performance. For " + }, + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "inline_equation", + "content": "F_a" + }, + { + "bbox": [ + 47, + 70, + 545, + 103 + ], + "type": "text", + "content": ", smaller values indicate better performance. Unsup. refers to unsupervised methods. The best single-point supervised results are in red and the second best results are in blue." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 69, + 103, + 525, + 353 + ], + "lines": [ + { + "bbox": [ + 69, + 103, + 525, + 353 + ], + "spans": [ + { + "bbox": [ + 69, + 103, + 525, + 353 + ], + "type": "table", + "html": "
MethodSup.Dataset
NUAA-SIRST [11]IRSTD-1k [45]NUDT-SIRST [23]NUDT-SIRST-sea [39]
Top-Hat [31]Unsup.7.14379.8410126.22255.48595.620.7278.41166.71.172.68095.37
WSLCM [20]Unsup.1.15877.9554460.01955.79315472.28356.8213090.6010.527.330
MSLSTIPT [16]Unsup.10.3082.13113110.3757.0537078.34247.40888.10.330.3506283
NRAM [43]Unsup.12.1674.5213.854.22149.2127.866.92756.4019.270.3517.313.585
PSTNN [44]Unsup.22.4077.9529.119.87151.7299.7514.8566.1344.171.5013.5115.44
ACM [11]Full70.3393.913.72860.9790.5821.7867.0895.9710.1847.5770.4621.31
ACM + KMeans[26]Point46.1688.5927.4533.4154.4241.8241.1877.8834.8638.1542.4523.25
ACM + SuperPixel[1]Point53.8490.4956.1849.6984.6942.3651.7692.3334.6040.4236.7016.92
ACM + GrabCut[33]Point57.6390.8760.4654.0381.9723.9955.2491.656.45738.7652.3715.54
ACM + OursPoint67.0892.0119.8056.5382.3125.0557.7492.3816.7743.6955.699.820
ResUnet[39]Full75.9397.7115.6866.3492.838.19883.7498.094.82046.0560.187.920
ResUnet + KMeans[26]Point22.3439.92156.533.8680.9510.3242.6589.2042.5131.1151.7444.63
ResUnet + SuperPixel[1]Point60.0293.1523.4559.2888.4324.3662.6593.4026.9536.4356.5030.61
ResUnet + GrabCut[33]Point61.3895.4325.1661.6790.1313.9663.0194.0313.4437.0456.1917.32
ResUnet + OursPoint71.5894.6715.2164.5990.816.22368.0493.8625.3539.0659.446.979
DNANet [23]Full76.2497.7112.8068.4494.778.80686.3697.396.89742.1761.6017.19
DNANet + KMeans[26]Point45.6990.4958.1132.9881.6325.1842.8488.0456.9920.5932.6721.59
DNANet + SuperPixel[1]Point62.5993.5314.5458.4489.4527.7064.6895.4433.3938.4236.706.921
DNANet + GrabCut[33]Point61.1497.7120.5361.0091.1520.8764.0097.0340.6528.0849.794.816
DNANet + OursPoint72.8696.9514.4362.2392.1324.1470.5295.5533.2040.2358.3211.29
ISNet [40]Full80.0199.234.9668.7295.6815.4382.5796.4944.1141.2758.8913.26
ISNet + KMeans[26]Point38.2774.88112.729.6769.5238.4344.5789.8766.2032.5744.2035.26
ISNet + SuperPixel[1]Point65.8293.7328.2657.9390.7541.7461.5995.6129.5935.2148.5615.32
ISNet + GrabCut[33]Point63.7296.2726.3262.2991.3719.3465.5394.8945.3133.6848.2423.56
ISNet + OursPoint75.9395.4411.0463.1992.5822.2366.8796.2248.5938.2952.2719.97
UIUNet [45]Full76.8397.6412.3165.2792.7612.4075.3593.3327.6941.8855.6911.56
UIUNet + KMeans[26]Point35.1790.9046.5321.2682.5219.4338.2788.2778.0929.3333.1714.22
UIUNet + SuperPixel[1]Point64.2392.1149.3454.4287.3029.8251.6891.3239.4037.8347.2220.09
UIUNet + GrabCut[33]Point63.2993.8633.2760.3789.2714.2464.3392.5733.5937.0351.5526.12
UIUNet + OursPoint74.2296.2016.1964.1390.7414.9369.3591.1138.2139.2753.2323.14
", + "image_path": "b31b6cde55500ad99f23bebf95ae251ebb219213f5fef6b08eb7464a328e5717.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 56, + 371, + 279, + 526 + ], + "blocks": [ + { + "bbox": [ + 56, + 371, + 279, + 526 + ], + "lines": [ + { + "bbox": [ + 56, + 371, + 279, + 526 + ], + "spans": [ + { + "bbox": [ + 56, + 371, + 279, + 526 + ], + "type": "image", + "image_path": "24808d0399f25673366be30fb23361aea9f930837f47f16ac8cf236db3185fb7.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 529, + 287, + 553 + ], + "lines": [ + { + "bbox": [ + 47, + 529, + 287, + 553 + ], + "spans": [ + { + "bbox": [ + 47, + 529, + 287, + 553 + ], + "type": "text", + "content": "Figure 9. Examples of target probability map (TPM) and the corresponding refined pseudo masks during the MCLC process." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 574, + 287, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 574, + 287, + 610 + ], + "spans": [ + { + "bbox": [ + 46, + 574, + 287, + 610 + ], + "type": "text", + "content": "recover a single point annotation to a pixel-level one with only 0.075s (average result from 533 targets) on a PC-level CPU." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 621, + 276, + 634 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 621, + 276, + 634 + ], + "spans": [ + { + "bbox": [ + 47, + 621, + 276, + 634 + ], + "type": "text", + "content": "4.4. Comparison to the State-of-the-art Methods" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "type": "text", + "content": "We compare our method to several state-of-the-art methods on four benchmark datasets in this subsection. For fair comparison, we used the same hyper-parameters and experimental settings (e.g., special dataset division method in UIUNet[40]) as reported in their original papers when re-implementing comparing methods and retrained all the" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 307, + 392, + 550, + 470 + ], + "blocks": [ + { + "bbox": [ + 305, + 370, + 545, + 392 + ], + "lines": [ + { + "bbox": [ + 305, + 370, + 545, + 392 + ], + "spans": [ + { + "bbox": [ + 305, + 370, + 545, + 392 + ], + "type": "text", + "content": "Table 6. " + }, + { + "bbox": [ + 305, + 370, + 545, + 392 + ], + "type": "inline_equation", + "content": "IoU(10^{-2})" + }, + { + "bbox": [ + 305, + 370, + 545, + 392 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 370, + 545, + 392 + ], + "type": "inline_equation", + "content": "Pd(10^{-2})" + }, + { + "bbox": [ + 305, + 370, + 545, + 392 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 370, + 545, + 392 + ], + "type": "inline_equation", + "content": "Fa(10^{-6})" + }, + { + "bbox": [ + 305, + 370, + 545, + 392 + ], + "type": "text", + "content": " values achieved by existing salient object detection (SOD) methods." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 392, + 550, + 470 + ], + "lines": [ + { + "bbox": [ + 307, + 392, + 550, + 470 + ], + "spans": [ + { + "bbox": [ + 307, + 392, + 550, + 470 + ], + "type": "table", + "html": "
Sup.NUAA-SIRSTIRSTD-1k
ResUnetFull75.997.715.766.392.88.19
Res.+PFAN [48]Point27.683.949.622.876.566.2
Res.+F3Net [38]Point33.281.6106.226.371.382.3
ResUnet+MCLCPoint71.694.715.264.690.86.22
DNANetFull76.297.712.868.494.78.8
DNA.+PFAN [48]Point29.385.266.837.678.657.7
DNA.+F3Net [38]Point33.684.978.031.277.161.2
DNANet+MCLCPoint72.996.914.462.292.124.1
", + "image_path": "f78ab6c85fb761efe00ddf1bc385f11babeae41c0e7e406f57e5de5371321ca9.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 496, + 482, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 496, + 482, + 507 + ], + "spans": [ + { + "bbox": [ + 306, + 496, + 482, + 507 + ], + "type": "text", + "content": "models from scratch on these four datasets." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": "1) Quantitative and Qualitative Results: Quantitative results are shown in Table 5. Our Monte Carlo linear clustering method (i.e., MCLC) achieves much better performance over those unsupervised methods. Compared to MCLC with other single-point supervised methods, MCLC can produce better pseudo masks and thus achieve better performance in terms of " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "P_{d}" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "F_{a}" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "IoU" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": ". Compared to the fully-supervised counterparts, MCLC enables the respective networks to generate comparable results with " + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "inline_equation", + "content": "87\\%" + }, + { + "bbox": [ + 304, + 510, + 547, + 714 + ], + "type": "text", + "content": " annotation time reduction. Qualitative results on four datasets are shown in Fig. 10. Compared to fully supervised methods, our MCLC can help existing detection methods to produce comparable results in a more time-efficient manner, especially for those point targets (e.g., img-1, img-4) and spot targets (e.g., img-2, img-3, img-5, img-6). Moreover, Fig. 10 (img-7, img-8) demonstrates the robustness of our method on the dense target scenarios. Readers can refer to" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "type": "text", + "content": "1016" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 62, + 70, + 534, + 310 + ], + "blocks": [ + { + "bbox": [ + 62, + 70, + 534, + 310 + ], + "lines": [ + { + "bbox": [ + 62, + 70, + 534, + 310 + ], + "spans": [ + { + "bbox": [ + 62, + 70, + 534, + 310 + ], + "type": "image", + "image_path": "8b120c225e4e7b4578eda64dcf250ffb19444bff1b86c1c7c261c6d898ec7566.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 313, + 546, + 348 + ], + "lines": [ + { + "bbox": [ + 46, + 313, + 546, + 348 + ], + "spans": [ + { + "bbox": [ + 46, + 313, + 546, + 348 + ], + "type": "text", + "content": "Figure 10. Qualitative results achieved by DNANet[23] under (b) point-level and (c) pixel-level supervision. The correctly detected target, false alarm, and miss detection areas are highlighted by red, yellow, and green dotted circles. More visualization results are shown in supplementary material." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 367, + 279, + 379 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 367, + 279, + 379 + ], + "spans": [ + { + "bbox": [ + 46, + 367, + 279, + 379 + ], + "type": "text", + "content": "the supplementary material for more visualization results." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 380, + 287, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 380, + 287, + 475 + ], + "spans": [ + { + "bbox": [ + 46, + 380, + 287, + 475 + ], + "type": "text", + "content": "2) Compared with SOD Methods: Quantitative results in Table 6 show that our MCLC performs much better than those salient object detection (SOD) methods. That is because, although the small targets are salient in local region, a single point label can not provide sufficient supervision to train high-performance SOD methods (e.g., PFAN [48], F3Net [38]). In contrast, our MCLC can make full use of single point labels to obtain higher accuracy." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 488, + 119, + 501 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 488, + 119, + 501 + ], + "spans": [ + { + "bbox": [ + 47, + 488, + 119, + 501 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 509, + 288, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 509, + 288, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 509, + 288, + 700 + ], + "type": "text", + "content": "In this paper, we propose a simple yet effective pipeline for single-frame infrared small target detection with single-point annotation. First, we found that SIRST is generally salient in the local small region and exhibits high energy concentricity. Then, based on this observation, we proposed a linear clustering approach (LCA) to coarsely separate the targets from clustering background by measuring the color and spatial distance with clutter background. To further refine the results, we design a Monte Carlo regularization approach to constrain the clustering process and continuously expand the point-level annotation to a high-quality pixel-level one. Extensive experiments on four benchmark datasets demonstrate that our method achieves comparable performance with fully-supervised methods. We hope our study can draw attention to the research on weakly supervised SIRST detection." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 59, + 701, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 714 + ], + "type": "text", + "content": "Acknowledgement: This work was supported in part" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 367, + 545, + 414 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 367, + 545, + 414 + ], + "spans": [ + { + "bbox": [ + 304, + 367, + 545, + 414 + ], + "type": "text", + "content": "by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China under Grant 61921001 and National Natural Science Foundation of China 62001478." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 425, + 365, + 437 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 425, + 365, + 437 + ], + "spans": [ + { + "bbox": [ + 306, + 425, + 365, + 437 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 310, + 445, + 546, + 714 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 310, + 445, + 546, + 488 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 445, + 546, + 488 + ], + "spans": [ + { + "bbox": [ + 310, + 445, + 546, + 488 + ], + "type": "text", + "content": "[1] Radhakrishna Achanta, Appu Shaji, Kevin Smith, Aurelien Lucchi, Pascal Fua, and Sabine Süsstrunk. 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IEEE TGRS, 58(2):1004-1016, 2019. 2" + } + ] + } + ], + "index": 11 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 296, + 734, + 315, + 742 + ], + "type": "text", + "content": "1019" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/MoreauGrad_ Sparse and Robust Interpretation of Neural Networks via Moreau Envelope/99846963-8ced-4bc2-923b-b6a5c1cca433_content_list.json b/2023/MoreauGrad_ Sparse and Robust Interpretation of Neural Networks via Moreau Envelope/99846963-8ced-4bc2-923b-b6a5c1cca433_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..4bb1810e0b3355e31073b40553a88f61ba305e9d --- /dev/null +++ b/2023/MoreauGrad_ Sparse and Robust Interpretation of Neural Networks via Moreau Envelope/99846963-8ced-4bc2-923b-b6a5c1cca433_content_list.json @@ -0,0 +1,2496 @@ +[ + { + "type": "text", + "text": "MoreauGrad: Sparse and Robust Interpretation of Neural Networks via Moreau Envelope", + "text_level": 1, + "bbox": [ + 78, + 128, + 890, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Jingwei Zhang \nThe Chinese University of Hong Kong \njwzhang22@cse.cuhk.edu.hk", + "bbox": [ + 155, + 204, + 460, + 256 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 291, + 313, + 306 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Explaining the predictions of deep neural nets has been a topic of great interest in the computer vision literature. While several gradient-based interpretation schemes have been proposed to reveal the influential variables in a neural net's prediction, standard gradient-based interpretation frameworks have been commonly observed to lack robustness to input perturbations and flexibility for incorporating prior knowledge of sparsity and group-sparsity structures. In this work, we propose MoreauGrad as an interpretation scheme based on the classifier neural net's Moreau envelope. We demonstrate that MoreauGrad results in a smooth and robust interpretation of a multi-layer neural network and can be efficiently computed through first-order optimization methods. Furthermore, we show that MoreauGrad can be naturally combined with $L_{1}$ -norm regularization techniques to output a sparse or group-sparse explanation which are prior conditions applicable to a wide range of deep learning applications. We empirically evaluate the proposed MoreauGrad scheme on standard computer vision datasets, showing the qualitative and quantitative success of the MoreauGrad approach in comparison to standard gradient-based interpretation methods1.", + "bbox": [ + 75, + 323, + 473, + 656 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 686, + 209, + 700 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Deep neural networks (DNNs) have achieved state-of-the-art performance in many computer vision problems including image classification [11], object detection [29], and medical image analysis [19]. While they manage to attain super-human scores on standard image and speech recognition tasks, a reliable application of deep learning models to real-world problems requires an interpretation of their predictions to help domain experts understand and investigate the basis of their predictions. Over the past few years, developing and analyzing interpretation schemes that reveal", + "bbox": [ + 75, + 712, + 468, + 863 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Farzan Farnia \nThe Chinese University of Hong Kong \nfarnia@cse.cuhk.edu.hk", + "bbox": [ + 506, + 204, + 815, + 256 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/fd2a911c589e2c0e855568f2937d08a457cc426946e088004289a3bfa0df39ff.jpg", + "image_caption": [ + "Figure 1. Interpretation of Sparse MoreauGrad (ours) vs. standard gradient-based baselines on an ImageNet sample before and after adding a norm-bounded interpretation adversarial attack." + ], + "image_footnote": [], + "bbox": [ + 506, + 290, + 888, + 681 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "the influential features in a neural network's prediction have attracted great interest in the computer vision community.", + "bbox": [ + 498, + 747, + 890, + 777 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "A standard approach for interpreting neural nets' predictions is to analyze the gradient of their prediction score function at or around an input data point. Such gradient-based interpretation mechanisms result in a feature saliency map revealing the influential variables that locally affect the neural net's assigned prediction score. Three well-known examples of gradient-based interpretation schemes are the simple gradient [21], integrated gradients [24], and", + "bbox": [ + 496, + 779, + 892, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "1The paper's code is available at https://github.com/buyeh1109/MoreauGrad.", + "bbox": [ + 76, + 875, + 467, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "2021", + "bbox": [ + 482, + 944, + 513, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "DeepLIFT [20] methods. While the mentioned methods have found many applications in explaining neural nets' predictions, they have been observed to lack robustness to input perturbations and to output a dense noisy saliency map in their application to computer vision datasets [6, 8]. Consequently, these gradient-based explanations can be considerably altered by minor random or adversarial input noise.", + "bbox": [ + 75, + 90, + 468, + 196 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "A widely-used approach to improve the robustness and sharpness of gradient-based interpretations is SmoothGrad [22] which applies Gaussian smoothing to the mentioned gradient-based interpretation methods. As shown by [22], SmoothGrad can significantly boost the visual quality of a neural net's gradient-based saliency map. On the other hand, SmoothGrad typically leads to a dense interpretation vector and remains inflexible to incorporate prior knowledge of sparsity and group-sparsity structures. Since a sparse saliency map is an applicable assumption to several image classification problems where a relatively small group of input variables can completely determine the image label, a counterpart of SmoothGrad which can simultaneously achieve sparse and robust interpretation will be of significant use in computer vision problems.", + "bbox": [ + 75, + 199, + 470, + 425 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we propose a novel approach, which we call MoreauGrad, to achieve a provably smooth gradient-based interpretation with potential sparsity or group-sparsity properties. The proposed MoreauGrad outputs the gradient of a classifier's Moreau envelope which is a useful optimization tool for enforcing smoothness in a target function. We leverage convex analysis to show that MoreauGrad behaves smoothly around an input sample and therefore provides an alternative optimization-based approach to SmoothGrad for achieving a smoothly-changing saliency map. As a result, we demonstrate that similar to SmoothGrad, MoreauGrad offers robustness to input perturbations, since a norm-bounded perturbation will only lead to a bounded change to the MoreauGrad interpretation.", + "bbox": [ + 75, + 428, + 468, + 638 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Next, we show that MoreauGrad can be flexibly combined with $L_{1}$ -norm-based regularization penalties to output sparse and group-sparse interpretations. Our proposed combinations, Sparse MoreauGrad and Group-Sparse MoreauGrad, take advantage of elastic-net [31] and group-norm [16] penalty terms to enforce sparse and group-sparse saliency maps, respectively. We show that these extensions of MoreauGrad preserve the smoothness and robustness properties of the original MoreauGrad scheme. Therefore, our discussion demonstrates the adaptable nature of MoreauGrad for incorporating prior knowledge of sparsity structures in the output interpretation.", + "bbox": [ + 75, + 641, + 468, + 823 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Finally, we present the empirical results of our numerical experiments applying MoreauGrad to standard image recognition datasets and neural net architectures. We compare the numerical performance of MoreauGrad with standard gradient-based interpretation baselines. Our numeri", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "cal results indicate the satisfactory performance of vanilla and $L_{1}$ -norm-based MoreauGrad in terms of visual quality and robustness. Figure 1 shows the robustness and sparsity of the Sparse MoreauGrad interpretation applied to an ImageNet sample in comparison to standard gradient-based saliency maps. As this and our other empirical findings suggest, MoreauGrad can outperform standard baselines in terms of the sparsity and robustness properties of the output interpretation. In the following, we summarize the main contributions of this paper:", + "bbox": [ + 496, + 90, + 890, + 243 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Proposing MoreauGrad as an interpretation scheme based on a classifier function's Moreau envelope", + "- Analyzing the smoothness and robustness properties of MoreauGrad by leveraging convex analysis", + "- Introducing $L_{1}$ -regularized Sparse MoreauGrad to obtain an interpretation satisfying prior sparsity conditions", + "- Providing numerical results supporting MoreauGrad over standard image recognition datasets" + ], + "bbox": [ + 500, + 255, + 890, + 407 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 421, + 640, + 436 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Gradient-based Interpretation. A large body of related works develop gradient-based interpretation methods. Simonyan et al. [21] propose to calculate the gradient of a classifier's output with respect to an input image. The simple gradient approach in [21] has been improved by several related works. Notably, the method of Integrated Gradients [24] is capable of keeping highly relevant pixels in the saliency map by aggregating gradients of image samples. SmoothGrad [22] removes noise in saliency maps by adding Gaussian-random noise to the input image. The CAM method [30] analyzes the information from global average pooling layer for localization, and Grad-CAM++ [1] improves over Grad-CAM [18] and generates coarse heatmaps with improved multi-object localization. The NormGrad [17] focuses on the weight-based gradient to analyze the contribution of each image region. DeepLIFT [20] uses difference from reference to propagate an attribution signal. However, the mentioned gradient-based methods do not obtain a sparse interpretation, and their proper combination with $L_{1}$ -regularization to promote sparsity remains highly non-trivial and challenging. On the other hand, our proposed MoreauGrad can be smoothly equipped with $L_{1}$ -regularization to output sparse interpretations and can further capture group-sparsity structures.", + "bbox": [ + 496, + 446, + 890, + 809 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Mask-based Interpretation. Mask-based interpretation methods rely on adversarial perturbations to interpret neural nets. Applying a mask which perturbs the neural net input, the importance of input pixels is measured by a masked-based method. This approach to explaining neural nets has been successfully applied in References [26, 5, 14, 2] and", + "bbox": [ + 496, + 810, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "2022", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "has been shown to benefit from dynamic perturbations [9]. More specifically, Dabkowski and Gal [2] introduce a real-time mask-based detection method; Fong and Vedaldi [5] develop a model-agnostic approach with interpretable perturbations; Wagner et al. [26] propose a method that could generate fine-grained visual interpretations. Moreover, Lim et al. [14] leverage local smoothness to enhance their robustness towards samples attacked by PGD [15]. However, [5] and [2] show that perturbation-based interpretation methods are still vulnerable to adversarial perturbations.", + "bbox": [ + 75, + 90, + 468, + 241 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We note that the discussed methods depend on optimizing perturbation masks for interpretations, and due to the non-convex nature of neural net loss functions, their interpretation remains sensitive to input perturbations. In contrast, our proposed MoreauGrad can provably smooth the neural net score function, and can adapt to non-convex functions using norm regularization. Hence, MoreauGrad can improve both the sparsity and robustness of the interpretation.", + "bbox": [ + 75, + 242, + 470, + 375 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Robust Interpretation. The robustness of interpretation methods has been a subject of great interest in the literature. Ghorbani et al. [6] introduce a gradient-based adversarial attack method to alter the neural nets' interpretation. Dombrowski et al. [4] demonstrate that interpretations could be manipulated, and they suggest improving the robustness via smoothing the neural net classifier. Heo et al. [8] propose a manipulation method that is capable of generalizing across datasets. Subramanya et al. [23] create adversarial patches fooling both the classifier and the interpretation.", + "bbox": [ + 75, + 378, + 468, + 527 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To improve the robustness, Sparsified-SmoothGrad [13] combines a sparsification technique with Gaussian smoothing to achieve certifiable robustness. The related works [26, 28, 5, 14, 2] discuss the application of adversarial defense methods against classification-based attacks to interpret the prediction of neural net classifiers. We note that these papers' main focus is not on defense schemes against interpretation-based attacks. Specifically, [26] filter gradients internally during backpropagation, and [14] leverage local smoothness to integrate more samples. Unlike the mentioned papers, our work proposes a model-agnostic optimization-based method which is capable of generating simultaneously sparse and robust interpretations.", + "bbox": [ + 75, + 529, + 470, + 724 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Preliminaries", + "text_level": 1, + "bbox": [ + 76, + 737, + 215, + 752 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we review three standard interpretation methods as well as the notation and definitions in the paper.", + "bbox": [ + 76, + 763, + 468, + 792 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Notation and Definitions", + "text_level": 1, + "bbox": [ + 76, + 801, + 302, + 816 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the paper, we use notation $\\mathbf{X} \\in \\mathbb{R}^d$ to denote the feature vector and $Y \\in \\{1, \\dots, k\\}$ to denote the label of a sample. In addition, $f_{\\mathbf{w}}: \\mathbb{R}^d \\to \\mathbb{R}^k$ denotes a neural net classifier with its weights contained in vector $\\mathbf{w} \\in \\mathcal{W}$ where $\\mathcal{W}$ is the feasible set of the neural net's weights. Here $f_{\\mathbf{w}}$ maps", + "bbox": [ + 76, + 824, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "the $d$ -dimensional input $\\mathbf{x}$ to a $k$ -dimensional prediction vector containing the likelihood of each of the $k$ classes in the classification problem. For every class $c \\in \\{1, \\dots, k\\}$ , we use the notation $f_{\\mathbf{w}, c}: \\mathbb{R}^d \\to \\mathbb{R}$ to denote the $c$ -th entry of $f_{\\mathbf{w}}$ 's output which corresponds to class $c$ .", + "bbox": [ + 496, + 90, + 890, + 166 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We use $\\| \\mathbf{x}\\| _p$ to denote the $\\ell_{p}$ -norm of input vector $\\mathbf{x}$ . Furthermore, we use notation $\\| \\mathbf{x}\\|_{p,q}$ to denote the $\\ell_{p,q}$ group-norm of $\\mathbf{x}$ defined in the following equation for given variable subsets $S_{1},\\ldots ,S_{t}\\subseteq \\{1,\\dots ,d\\}$ :", + "bbox": [ + 496, + 167, + 890, + 227 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\| \\mathbf {x} \\right\\| _ {p, q} = \\left\\| \\left[ \\| \\mathbf {x} _ {S _ {1}} \\| _ {p}, \\dots , \\| \\mathbf {x} _ {S _ {t}} \\| _ {p} \\right] \\right\\| _ {q} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 234, + 890, + 256 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In other words, $\\| \\mathbf{x}\\|_{p,q}$ is the $\\ell_p$ -norm of a vector containing the $\\ell_p$ -norms of the subvectors of $\\mathbf{x}$ characterized by index subsets $S_{1},\\ldots ,S_{t}$ .", + "bbox": [ + 496, + 263, + 890, + 308 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Gradient-based Saliency Maps", + "text_level": 1, + "bbox": [ + 500, + 316, + 772, + 333 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In our theoretical and numerical analysis, we consider the following widely-used gradient-based interpretation baselines which apply to a classifier neural net $f_{\\mathbf{w}}$ and predicted class $c$ for input $\\mathbf{x}$ :", + "bbox": [ + 496, + 340, + 890, + 401 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "1. Simple Gradient: The simple gradient interpretation returns the saliency map of a neural net score function's gradient with respect to input $\\mathbf{x}$ :", + "bbox": [ + 500, + 407, + 890, + 454 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {S G} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\nabla_ {\\mathbf {x}} f _ {\\mathbf {w}, c} (\\mathbf {x}). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 606, + 462, + 890, + 479 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the applications of the simple gradient approach, $c$ is commonly chosen as the neural net's predicted label with the maximum prediction score.", + "bbox": [ + 517, + 488, + 890, + 532 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2. Integrated Gradients: The integrated gradients approach approximates the integral of the neural net's gradient function between a reference point $\\mathbf{x}^0$ and the input $\\mathbf{x}$ . Using $m$ intermediate points on the line segment connecting $\\mathbf{x}^0$ and $\\mathbf{x}$ , the integrated gradient output will be", + "bbox": [ + 500, + 541, + 890, + 617 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {I G} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\frac {\\Delta \\mathbf {x}}{m} \\sum_ {i = 1} ^ {m} \\nabla_ {\\mathbf {x}} f _ {\\mathbf {w}, c} \\left(\\mathbf {x} ^ {0} + \\frac {i}{m} \\Delta \\mathbf {x}\\right). \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 534, + 638, + 890, + 676 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the above $\\Delta \\mathbf{x} \\coloneqq \\mathbf{x} - \\mathbf{x}^0$ denotes the difference between the target and reference points $\\mathbf{x}, \\mathbf{x}^0$ .", + "bbox": [ + 517, + 686, + 890, + 717 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. SmoothGrad: SmoothGrad considers the averaged simple gradient score over an additive random perturbation $Z$ drawn according to an isotropic Gaussian distribution $Z \\sim \\mathcal{N}(\\mathbf{0}, \\sigma^2 I_d)$ . In practice, the SmoothGrad interpretation is estimated over a number $t$ of independently drawn noise vectors $\\mathbf{z}_1, \\ldots, \\mathbf{z}_t \\stackrel{\\mathrm{i.i.d.}}{\\sim} \\mathcal{N}(\\mathbf{0}, \\sigma^2 I_d)$ according to the zero-mean Gaussian distribution:", + "bbox": [ + 500, + 724, + 890, + 834 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\operatorname {S m o o t h G r a d} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\mathbb {E} \\left[ \\nabla_ {\\mathbf {x}} f _ {\\mathbf {w}, c} (\\mathbf {x} + Z) \\right] \\tag {4} \\\\ \\approx \\frac {1}{t} \\sum_ {i = 1} ^ {t} \\nabla_ {\\mathbf {x}} f _ {\\mathbf {w}, c} (\\mathbf {x} + \\mathbf {z} _ {i}). \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 539, + 842, + 890, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "2023", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. MoreauGrad: An Optimization-based Interpretation Framework", + "text_level": 1, + "bbox": [ + 76, + 89, + 468, + 125 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As discussed earlier, smooth classifier functions with a Lipschitz gradient help to obtain a robust explanation of neural nets. Here, we propose an optimization-based smoothing approach based on Moreau-Yosida regularization. To introduce this optimization-based approach, we first define a function's Moreau envelope.", + "bbox": [ + 75, + 132, + 467, + 223 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Definition 1. Given regularization parameter $\\rho >0$ , we define the Moreau envelope of a function $g:\\mathbb{R}^d\\to \\mathbb{R}$ as:", + "bbox": [ + 76, + 229, + 467, + 261 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ng ^ {\\rho} (\\mathbf {x}) := \\min _ {\\widetilde {\\mathbf {x}} \\in \\mathbb {R} ^ {d}} g (\\widetilde {\\mathbf {x}}) + \\frac {1}{2 \\rho} \\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\| _ {2} ^ {2}. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 142, + 268, + 468, + 299 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In the above definition, $\\rho > 0$ represents the Moreau-Yosida regularization coefficient. Applying the Moreau envelope, we propose the MoreauGrad interpretation as the gradient of the classifier's Moreau envelope at an input $\\mathbf{x}$ .", + "bbox": [ + 76, + 306, + 467, + 368 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Definition 2. Given regularization parameter $\\rho >0$ , we define the MoreauGrad interpretation $MG_{\\rho}:\\mathbb{R}^{d}\\to \\mathbb{R}^{d}$ of a neural net $f_{\\mathbf{w}}$ predicting class $c$ for input $\\mathbf{x}$ as", + "bbox": [ + 76, + 375, + 472, + 421 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nM G _ {\\rho} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\nabla f _ {\\mathbf {w}, c} ^ {\\rho} (\\mathbf {x}).\n$$\n", + "text_format": "latex", + "bbox": [ + 171, + 429, + 372, + 446 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To compute and analyze the MoreauGrad explanation, we first discuss the optimization-based smoothing enforced by the Moreau envelope. Note that the Moreau envelope is known as an optimization tool to turn non-smooth convex functions (e.g. $\\ell_1$ -norm) into smooth functions. Here, we discuss an extension of this result to weakly-convex functions which also apply to non-convex functions.", + "bbox": [ + 75, + 454, + 467, + 560 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Definition 3. A function $g: \\mathbb{R}^d \\to \\mathbb{R}$ is called $\\lambda$ -weakly convex if $\\Phi(\\mathbf{x}) := g(\\mathbf{x}) + \\frac{\\lambda}{2} \\| \\mathbf{x} \\|_2^2$ is a convex function, i.e. for every $\\mathbf{x}_1, \\mathbf{x}_2 \\in \\mathbb{R}^d$ and $0 \\leq \\alpha \\leq 1$ we have:", + "bbox": [ + 73, + 566, + 467, + 613 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} g \\left(\\alpha \\mathbf {x} _ {1} + (1 - \\alpha) \\mathbf {x} _ {2}\\right) \\leq \\alpha g (\\mathbf {x} _ {1}) + (1 - \\alpha) g (\\mathbf {x} _ {2}) \\\\ + \\frac {\\lambda \\alpha (1 - \\alpha)}{2} \\| \\mathbf {x} _ {1} - \\mathbf {x} _ {2} \\| _ {2} ^ {2}. \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 96, + 621, + 444, + 671 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Theorem 1. Suppose that $g: \\mathbb{R}^d \\to \\mathbb{R}$ is a $\\lambda$ -weakly convex function. Assuming that $0 < \\rho < \\frac{1}{\\lambda}$ , the followings hold for the optimization problem of the Moreau envelope $g^\\rho$ and the optimal solution $\\widetilde{x}_\\rho^*(\\mathbf{x})$ solving the optimization problem:", + "bbox": [ + 75, + 680, + 467, + 742 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "1. For every $\\mathbf{x}$ , the gradient of $g^{\\rho}$ and Clarke subdifferential of $g$ (denoted by $\\partial_0 g$ ) are related as:", + "bbox": [ + 76, + 750, + 467, + 779 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\nabla g ^ {\\rho} (\\mathbf {x}) \\in \\partial_ {0} g \\big (\\widetilde {x} _ {\\rho} ^ {*} (\\mathbf {x}) \\big),\n$$\n", + "text_format": "latex", + "bbox": [ + 200, + 787, + 362, + 806 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "which implies that if $g$ is differentiable at $\\widetilde{x}_{\\rho}^{*}(\\mathbf{x})$ we have $\\nabla g^{\\rho}(\\mathbf{x}) = \\nabla g(\\widetilde{x}_{\\rho}^{*}(\\mathbf{x}))$", + "bbox": [ + 96, + 813, + 467, + 844 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "2. The difference $\\widetilde{x}_{\\rho}^{*}(\\mathbf{x}) - \\mathbf{x}$ is aligned with $g^{\\rho}$ 's gradient:", + "bbox": [ + 76, + 848, + 462, + 864 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\nabla g ^ {\\rho} (\\mathbf {x}) = \\frac {- 1}{\\rho} \\left(\\widetilde {x} _ {\\rho} ^ {*} (\\mathbf {x}) - \\mathbf {x}\\right).\n$$\n", + "text_format": "latex", + "bbox": [ + 183, + 872, + 380, + 904 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3. $g^{\\rho}$ will be $\\max \\left\\{\\frac{1}{\\rho},\\frac{\\lambda}{1 - \\rho\\lambda}\\right\\}$ smooth, i.e. for every $\\mathbf{x}_1,\\mathbf{x}_2$", + "bbox": [ + 500, + 89, + 885, + 109 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\| \\nabla g ^ {\\rho} (\\mathbf {x} _ {1}) - \\nabla g ^ {\\rho} (\\mathbf {x} _ {2}) \\right\\| _ {2} \\leq \\frac {1}{\\min \\left\\{\\rho , \\frac {1}{\\lambda} - \\rho \\right\\}} \\left\\| \\mathbf {x} _ {1} - \\mathbf {x} _ {2} \\right\\| _ {2}.\n$$\n", + "text_format": "latex", + "bbox": [ + 519, + 117, + 888, + 150 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Proof. This result is well-known for convex functions. In the Appendix, we provide a new proof for the result. $\\square$", + "bbox": [ + 498, + 162, + 890, + 193 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Corollary 1. Assume that the prediction score function $f_{\\mathbf{w},c}:\\mathbb{R}^d\\to \\mathbb{R}$ is $\\lambda$ -weakly convex. Then, the MoreauGrad interpretation $MG_{\\rho}$ will remain robust under an $\\epsilon -\\ell_2$ -norm bounded perturbation $\\| \\delta \\| _2\\leq \\epsilon$ as", + "bbox": [ + 498, + 202, + 890, + 263 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\| M G _ {\\rho} (\\mathbf {x} + \\boldsymbol {\\delta}) - M G _ {\\rho} (\\mathbf {x}) \\right\\| _ {2} \\leq \\frac {\\epsilon}{\\min \\left\\{\\rho , \\frac {1}{\\lambda} - \\rho \\right\\}}.\n$$\n", + "text_format": "latex", + "bbox": [ + 534, + 271, + 854, + 301 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The above results imply that by choosing a small enough coefficient $\\rho$ the Moreau envelope will be a differentiable smooth function. Moreover, the computation of the Moreau envelope will reduce to a convex optimization task that can be solved by standard or accelerated gradient descent with global convergence guarantees. Therefore, one can efficiently compute the MoreauGrad interpretation by solving the optimization problem via the gradient descent algorithm. Algorithm 1 applies gradient descent to compute the solution to the Moreau envelope optimization which according to Theorem 1 yields the MoreauGrad explanation.", + "bbox": [ + 496, + 309, + 890, + 474 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As discussed above, MoreauGrad will be provably robust as long as the regularization coefficient will dominate the weakly-convexity degree of the prediction score. In the following proposition, we show this condition can be enforced by applying either Gaussian smoothing.", + "bbox": [ + 496, + 474, + 890, + 551 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Proposition 1. Suppose that $f_{\\mathbf{w},c}$ is $L$ -Lipschitz, that is for every $\\mathbf{x}_1,\\mathbf{x}_2$ $|f_{\\mathbf{w},c}(\\mathbf{x}_1) - f_{\\mathbf{w},c}(\\mathbf{x}_2)| \\leq L\\| \\mathbf{x}_2 - \\mathbf{x}_1\\|_2$ , but could be potentially non-differentiable and nonsmooth. Then, $h_{\\mathbf{w},c}(\\mathbf{x}) := \\mathbb{E}[f_{\\mathbf{w},c}(\\mathbf{x} + \\mathbf{Z})]$ where $\\mathbf{Z} \\sim \\mathcal{N}(0,\\sigma^2 I_{d\\times d})$ will be $\\frac{L}{\\sigma}$ -weakly convex.", + "bbox": [ + 498, + 558, + 890, + 635 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Proof. We postpone the proof to the Appendix.", + "bbox": [ + 500, + 641, + 890, + 656 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The above proposition suggests the regularized Moreau-Grad which regularizes the neural net function to satisfy the weakly-convex condition through Gaussian smoothing.", + "bbox": [ + 496, + 666, + 890, + 712 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "5. Sparse and Group-Sparse MoreauGrad", + "text_level": 1, + "bbox": [ + 500, + 724, + 854, + 742 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To further extend the MoreauGrad approach to output sparsely-structured feature saliency maps, we further include an $L_{1}$ -norm-based penalty term in the Moreau-Yosida regularization and define the following $L_{1}$ -norm-based sparse and group-sparse Moreau envelope.", + "bbox": [ + 496, + 750, + 890, + 825 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Definition 4. For a function $g: \\mathbb{R}^d \\to \\mathbb{R}$ and regularization coefficients $\\rho, \\eta > 0$ , we define $L_1$ -Moreau envelope $g_{L_1}^{\\rho, \\eta}$ :", + "bbox": [ + 498, + 832, + 890, + 864 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ng _ {L _ {1}} ^ {\\rho , \\eta} (\\mathbf {x}) := \\min _ {\\widetilde {\\mathbf {x}} \\in \\mathbb {R} ^ {d}} g (\\widetilde {\\mathbf {x}}) + \\frac {1}{2 \\rho} \\left\\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\right\\| _ {2} ^ {2} + \\eta \\left\\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\right\\| _ {1}.\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 873, + 872, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "2024", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We also define $L_{2,1}$ -Moreau envelope $g_{L_{2,1}}^{\\rho,\\eta}$ as", + "bbox": [ + 76, + 90, + 383, + 109 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\ng _ {L _ {2, 1}} ^ {\\rho , \\eta} (\\mathbf {x}) := \\min _ {\\widetilde {\\mathbf {x}} \\in \\mathbb {R} ^ {d}} g (\\widetilde {\\mathbf {x}}) + \\frac {1}{2 \\rho} \\left\\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\right\\| _ {2} ^ {2} + \\eta \\left\\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\right\\| _ {2, 1}.\n$$\n", + "text_format": "latex", + "bbox": [ + 83, + 117, + 460, + 148 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In the above, the group norm $\\| \\cdot \\|_{2,1}$ is defined as $\\| \\mathbf{x} \\|_{2,1} := \\sum_{i=1}^{t} \\| \\mathbf{x}_{S_i} \\|_2$ for given subsets $S_1, \\ldots, S_t \\subseteq \\{1, \\ldots, d\\}$ .", + "bbox": [ + 76, + 156, + 468, + 190 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Definition 5. Given regularization coefficients $\\rho, \\eta > 0$ , we define the Sparse MoreauGrad ( $S-MG_{\\rho,\\eta}$ ) and Group-Sparse MoreauGrad ( $GS-MG_{\\rho,\\eta}$ ) interpretations as", + "bbox": [ + 76, + 196, + 468, + 244 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nS - M G _ {\\rho , \\eta} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\frac {1}{\\rho} \\left(\\widetilde {\\mathbf {x}} _ {L _ {1}} ^ {*} (\\mathbf {x}) - \\mathbf {x}\\right),\n$$\n", + "text_format": "latex", + "bbox": [ + 145, + 250, + 411, + 281 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nG S - M G _ {\\rho , \\eta} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\frac {1}{\\rho} \\left(\\widetilde {\\mathbf {x}} _ {L _ {2, 1}} ^ {*} (\\mathbf {x}) - \\mathbf {x}\\right),\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 282, + 419, + 314 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\widetilde{\\mathbf{x}}_{L_1}^* (\\mathbf{x})$ , $\\widetilde{\\mathbf{x}}_{L_{2,1}}^{*}(\\mathbf{x})$ denote the optimal solutions to the optimization tasks of $f_{\\mathbf{w},c,L_1}^{\\rho ,\\eta}(\\mathbf{x})$ , $f_{\\mathbf{w},c,L_{2,1}}^{\\rho ,\\eta}(\\mathbf{x})$ , respectively.", + "bbox": [ + 76, + 321, + 468, + 358 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In the following theorem, we extend the shown results for the smoothness and robustness of vanilla Moreau envelope to our proposed $L_{1}$ -norm-based extensions of the Moreau envelope. In this theorem, we use the following definitions for the soft-thresholding operators $\\mathrm{ST}_{\\alpha}$ and $\\mathrm{GST}_{\\alpha}$ for the sparse and group-sparse cases which are defined entrywise and group-entrywise as follows", + "bbox": [ + 75, + 361, + 468, + 468 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathrm {S T} _ {\\alpha} (\\mathbf {x}) _ {i} := \\left\\{ \\begin{array}{l l} 0 & \\text {i f} | x _ {i} | \\leq \\alpha \\\\ x _ {i} - \\operatorname {s i g n} (x _ {i}) \\alpha & \\text {i f} | x _ {i} | > \\alpha , \\end{array} \\right.\n$$\n", + "text_format": "latex", + "bbox": [ + 112, + 474, + 413, + 516 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathrm {G S T} _ {\\alpha} (\\mathbf {x}) _ {S _ {i}} := \\left\\{ \\begin{array}{l l} \\mathbf {0} & \\text {i f} \\| \\mathbf {x} _ {S _ {i}} \\| _ {2} \\leq \\alpha \\\\ \\big (1 - \\frac {\\alpha}{\\| \\mathbf {x} _ {S _ {i}} \\| _ {2}} \\big) \\mathbf {x} _ {S _ {i}} & \\text {i f} \\| \\mathbf {x} _ {S _ {i}} \\| _ {2} > \\alpha . \\end{array} \\right.\n$$\n", + "text_format": "latex", + "bbox": [ + 94, + 518, + 449, + 561 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Theorem 2. Suppose that $g:\\mathbb{R}^d\\to \\mathbb{R}$ is a $\\lambda$ -weakly convex function. Then, assuming that $0 < \\rho < \\frac{1}{\\lambda}$ , Theorem 1's parts 1 and 3 will further hold for the sparse Moreau envelope $g_{L_1}^{\\rho ,\\eta}$ and group-sparse Moreau envelope $g_{L_{2,1}}^{\\rho ,\\eta}$ and their optimization problems' optimal solutions $\\widetilde{\\mathbf{x}}_{\\rho ,\\eta ,L_1}^* (\\mathbf{x})$ and $\\widetilde{\\mathbf{x}}_{\\rho ,\\eta ,L_{2,1}}^{*}(\\mathbf{x})$ . To parallel Theorem 1's part 2 for $L_{1}$ -Moreau envelope, the followings hold", + "bbox": [ + 76, + 569, + 468, + 676 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathrm {S T} _ {\\rho \\eta} \\left(- \\rho \\nabla g _ {L _ {1}} ^ {\\rho , \\eta} (\\mathbf {x})\\right) = \\widetilde {\\mathbf {x}} _ {\\rho , \\eta , L _ {1}} ^ {*} (\\mathbf {x}) - \\mathbf {x},\n$$\n", + "text_format": "latex", + "bbox": [ + 140, + 685, + 411, + 704 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathrm {G S T} _ {\\rho \\eta} \\big (- \\rho \\nabla g _ {L _ {2, 1}} ^ {\\rho , \\eta} (\\mathbf {x}) \\big) = \\widetilde {\\mathbf {x}} _ {\\rho , \\eta , L _ {2, 1}} ^ {*} (\\mathbf {x}) - \\mathbf {x}.\n$$\n", + "text_format": "latex", + "bbox": [ + 125, + 705, + 421, + 726 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Proof. We defer the proof to the Appendix.", + "bbox": [ + 76, + 732, + 366, + 748 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Corollary 2. Suppose that the prediction score function $f_{\\mathbf{w},c}$ is $\\lambda$ -weakly convex. Assuming that $0 < \\rho < \\frac{1}{\\lambda}$ , the Sparse MoreauGrad $S - MG_{\\rho, \\eta}$ and Group-Sparse MoreauGrad $GS - MG_{\\rho, \\eta}$ interpretations will be robust to every norm-bounded perturbation $\\| \\delta \\|_2 \\leq \\epsilon$ as:", + "bbox": [ + 76, + 756, + 468, + 833 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\| S - M G _ {\\rho , \\eta} (\\mathbf {x} + \\boldsymbol {\\delta}) - S - M G _ {\\rho , \\eta} (\\mathbf {x}) \\right\\| _ {2} \\leq \\frac {\\epsilon}{\\min \\left\\{\\rho , \\frac {1}{\\lambda} - \\rho \\right\\}},\n$$\n", + "text_format": "latex", + "bbox": [ + 99, + 840, + 477, + 872 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\| G S - M G _ {\\rho , \\eta} (\\mathbf {x} + \\boldsymbol {\\delta}) - G S - M G _ {\\rho , \\eta} (\\mathbf {x}) \\right\\| _ {2} \\leq \\frac {\\epsilon}{\\min \\left\\{\\rho , \\frac {1}{\\lambda} - \\rho \\right\\}}.\n$$\n", + "text_format": "latex", + "bbox": [ + 78, + 873, + 477, + 905 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Algorithm 1 MoreauGrad Interpretation", + "bbox": [ + 500, + 104, + 769, + 121 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Input: data x, label c, classifier $f_{\\mathbf{w}}$ , regularization coeff. $\\rho$ , stepsize $\\gamma$ , noise std. parameter $\\sigma$ , number of updates $T$", + "bbox": [ + 500, + 122, + 890, + 152 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Initialize $\\mathbf{x}^{(0)} = \\mathbf{x}$", + "bbox": [ + 500, + 152, + 633, + 166 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "for $t = 0,\\dots ,T$ do", + "bbox": [ + 500, + 167, + 635, + 181 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "if Regularized Mode then", + "bbox": [ + 524, + 183, + 697, + 196 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\textbf {D r a w n o i s e v e c t o r s z _ {1} , \\ldots , z _ {m}} \\sim \\mathcal {N} (\\mathbf {0}, \\sigma^ {2} I _ {d \\times d}) \\\\ \\textbf {C o m p u t e g} _ {t} = \\frac {1}{m} \\sum_ {i = 1} ^ {m} \\nabla f _ {\\mathbf {w}, c} (\\mathbf {x} ^ {(t)} + \\mathbf {z} _ {i}) \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 550, + 198, + 874, + 234 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "else", + "bbox": [ + 526, + 236, + 555, + 247 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {C o m p u t e} \\mathbf {g} _ {t} = \\nabla f _ {\\mathbf {w}, c} (\\mathbf {x} ^ {(t)})\n$$\n", + "text_format": "latex", + "bbox": [ + 550, + 250, + 740, + 266 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "end", + "bbox": [ + 526, + 267, + 555, + 277 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {d a t e} \\mathbf {x} ^ {(t + 1)} \\leftarrow (1 - \\frac {\\gamma}{\\rho}) \\mathbf {x} ^ {(t)} - \\gamma (\\mathbf {g} _ {t} - \\frac {1}{\\rho} \\mathbf {x})\n$$\n", + "text_format": "latex", + "bbox": [ + 550, + 285, + 826, + 306 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "if Sparse Mode then", + "bbox": [ + 526, + 311, + 663, + 325 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {U p d a t e} \\mathbf {x} ^ {(t + 1)} \\leftarrow \\text {S o f t T h r e s h o l d} _ {\\gamma \\eta} \\left(\\mathbf {x} ^ {(t + 1)} - \\mathbf {x}\\right) + \\mathbf {x}\n$$\n", + "text_format": "latex", + "bbox": [ + 550, + 325, + 890, + 343 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "end", + "bbox": [ + 501, + 345, + 529, + 354 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {O u t p u t} \\mathrm {M G} (\\mathbf {x}) = \\frac {1}{\\rho} \\left(\\mathbf {x} ^ {(T)} - \\mathbf {x}\\right)\n$$\n", + "text_format": "latex", + "bbox": [ + 501, + 357, + 714, + 378 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Based on the above results, we propose applying the proximal gradient descent algorithm as described in Algorithm 1 to compute the Sparse and Group-Sparse Moreau-Grad. We defer discussing Algorithm 1's details to the Appendix.", + "bbox": [ + 496, + 421, + 890, + 497 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "6. Numerical Results", + "text_level": 1, + "bbox": [ + 500, + 510, + 679, + 526 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We conduct several numerical experiments to evaluate the performance of the proposed MoreauGrad. Our designed experiments focus on the smoothness, sparsity, and robustness properties of MoreauGrad interpretation maps as well as the feature maps of several standard baselines. In the following, we first describe the numerical setup in our experiments and then present the obtained numerical results on the qualitative and quantitative performance of interpretation methods.", + "bbox": [ + 496, + 536, + 890, + 671 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "6.1. Experiment Setup", + "text_level": 1, + "bbox": [ + 500, + 681, + 674, + 698 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In our numerical evaluation, we use the following benchmark image datasets: CIFAR-10 [10] consisting of 60,000 labeled samples with 10 different labels, tiny-[ImageNet [12] containing 100,000 labels samples with 200 labels, and ImageNet-1K [3] including 1.4 million labeled samples with 1,000 labels. For CIFAR-10 and tiny-[ImageNet experiments, we trained a standard ResNet-18 [7] neural network with the softmax activation on the training set. For ImageNet experiments, we used an EfficientNet-b0 network [25] pre-trained on the ImageNet training data. In our experiments, we compared the MoreauGrad schemes with the following baselines: 1) the simple gradient [21], 2) Integrated Gradients [18], 3) DeepLIFT [20], 4) SmoothGrad", + "bbox": [ + 496, + 704, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "2025", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/671c1d43917eaff991d7ed86bd7415cd1dff33c9797fea167da76d91dcc0436d.jpg", + "image_caption": [ + "Input" + ], + "image_footnote": [], + "bbox": [ + 81, + 89, + 228, + 189 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c3e61302d4b5f31c9a26bba9a3e97d257fb78cedcf0b4a9b6bcd9b1c198f6049.jpg", + "image_caption": [ + "$\\rho = 0$" + ], + "image_footnote": [], + "bbox": [ + 230, + 90, + 359, + 189 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/975545aa5a22e2414b9762064fa3ef0205d7fdb4eb16b1fd641d28c829777cba.jpg", + "image_caption": [ + "$\\rho = 0.3$" + ], + "image_footnote": [], + "bbox": [ + 362, + 90, + 491, + 189 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/9378d08c7124d38f6bbf39e0ea78c981dc3491693bc0953b5ddcae35857e91bd.jpg", + "image_caption": [ + "$\\rho = 1$" + ], + "image_footnote": [], + "bbox": [ + 493, + 90, + 622, + 189 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/cd93fd6ef31ca1f01b8d56fe609c8bf2df1506214d47a63ae77272fa80d0a033.jpg", + "image_caption": [ + "$\\rho = 3$" + ], + "image_footnote": [], + "bbox": [ + 625, + 90, + 751, + 189 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/7cb196ba7cfdef7682fca46154e6d04755116050343fa0a37992a1a619e8b159.jpg", + "image_caption": [ + "$\\rho = 10$" + ], + "image_footnote": [], + "bbox": [ + 756, + 90, + 883, + 189 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/9d05aa541811591164a6d68f3d25fe01679869414f7cc667e431a40e2a204c27.jpg", + "image_caption": [ + "Input" + ], + "image_footnote": [], + "bbox": [ + 80, + 203, + 227, + 301 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/960ec559f4a8afd48a170a6107c58d5dcc7fea210ce3dccae6c4f1ea363900ab.jpg", + "image_caption": [ + "$\\eta = 0$" + ], + "image_footnote": [], + "bbox": [ + 232, + 203, + 359, + 301 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/df89d1dbcee3669e000f3a075a416a3688a14fad3eeb8d51b447e8fd74a64c76.jpg", + "image_caption": [ + "$\\eta = 0.001$" + ], + "image_footnote": [], + "bbox": [ + 364, + 203, + 490, + 301 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/decaeffb9009eeb64fe54b952a8125beaeaf0e0ecc4db3a3ae428f2aaeba9c2f.jpg", + "image_caption": [ + "$\\eta = 0.005$" + ], + "image_footnote": [], + "bbox": [ + 495, + 203, + 620, + 301 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/926ef20588d7daf749d7d9725530534ab390a7f3a3420e4af9dfc96fed1a811b.jpg", + "image_caption": [ + "$\\eta = 0.01$" + ], + "image_footnote": [], + "bbox": [ + 625, + 203, + 751, + 301 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c5921d16ee8edc49580fb580be95bd2a7d42bb7fcad77cbb88e99aad280ed07f.jpg", + "image_caption": [ + "$\\eta = 0.015$" + ], + "image_footnote": [], + "bbox": [ + 756, + 203, + 883, + 301 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/a4fa8a36c0346426f936d6463665c79efec6f33941b58e247cd0095509e94339.jpg", + "image_caption": [ + "Figure 2. Top: Visualization of MoreauGrad maps with different coefficient $\\rho$ 's. $\\rho = 0$ reduces to the simple gradient method. Bottom: Visualization of Sparse MoreauGrad maps with different coefficient $\\eta$ 's. $\\eta = 0$ reduces to the Vanilla MoreauGrad." + ], + "image_footnote": [], + "bbox": [ + 81, + 362, + 290, + 518 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/db61ca39a9d22e252d0a4b8bc7a6bd23005fc8123d0a523bb6833dd153e58b04.jpg", + "image_caption": [ + "Figure 3. MoreauGrad vs. SmoothGrad gradient discrepancy, measured via the $l_{2}$ -norm distance from the simple gradient map." + ], + "image_footnote": [], + "bbox": [ + 295, + 362, + 488, + 518 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1dafd875b6a4d2a8b3d6e9034ff92f193d9eec9d19e80d9c63b7d858baaf7bd5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 493, + 362, + 687, + 518 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/5f644c271f3838aa3269e52ae1d3e3cc524cca29feb7e83f75e202993a02ef7c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 694, + 362, + 887, + 518 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "[22], 5) Sparsified SmoothGrad [13], 6) RelEx [14]. We note that for baseline experiments we adopted the official implementations and conducted the experiments with hyperparameters suggested in their work. We present the full implementation details in the Appendix, and our code is available in the supplementary material.", + "bbox": [ + 75, + 564, + 468, + 655 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "6.2. Effects of Smoothness and Sparsity Parameters", + "text_level": 1, + "bbox": [ + 76, + 665, + 468, + 681 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We ran the numerical experiments for unregularized Vanilla MoreauGrad with multiple smoothness coefficient $\\rho$ values to show the effect of the Moreau envelope's regularization. Figure 2 visualizes the effect of different $\\rho$ on the Vanilla MoreauGrad saliency map. As can be seen in this figure, the saliency map qualitatively improves by increasing the value of $\\rho$ from 0 to 1. Please note that for $\\rho = 0$ , the MoreauGrad simplifies to the simple gradient interpretation. However, as shown in Theorem 1 the proper performance of Vanilla MoreauGrad requires choosing a properly bounded $\\rho$ value, which is consistent with our observation that when $\\rho$ becomes too large, the Moreau envelope will be computationally difficult to optimize and the quality of interpretation maps could deteriorate to some", + "bbox": [ + 75, + 688, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "extent. As numerically verified in both CIFAR-10, tinyImageNet, and ImageNet experiments, we used the rule of thumb $\\rho = \\frac{1}{\\sqrt{\\mathbb{E}[\\|\\mathbf{X}\\|_2]}}$ measured over the empirical training data to set the value of $\\rho$ , which is equal to 1 for the normalized samples in our experiments.", + "bbox": [ + 496, + 564, + 890, + 647 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Regarding the sparsity hyperparameter $\\eta$ in Sparse and Group-Sparse MoreauGrad experiments, we ran several experimental tests to properly tune the hyperparameter. Note that a greater coefficient $\\eta$ enforces more strict sparsity or group-sparsity in the MoreauGrad interpretation, and the degree of sparsity could be simply adjusted by changing this coefficient $\\eta$ . As shown in Figure 2, in our experiments with different $\\eta$ coefficients the interpretation map becomes sparser as we increase the $L_{1}$ -norm penalty coefficient $\\eta$ . Similarly, to achieve a group-sparse interpretation, we used $L_{2,1}$ -regularization on groups of adjacent pixels as discussed in Definition 4. The effect of the group-sparsity coefficient was similar to the sparse case in our experiments, as fewer pixel groups took non-zero values and the output interpretations showed more structured interpretation maps when choosing a larger coefficient $\\eta$ . We defer the results on", + "bbox": [ + 496, + 659, + 892, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "2026", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/b2cbe87c06affa0be268735d40a1b75f3619a42318c270756a38b702bb739d52.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 94, + 95, + 189, + 167 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/7412015ca58d2301c785bd473e46fa705e224d18d6f16e8eeed3d367381fa239.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 94, + 169, + 187, + 244 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/8053e475ee353c8559f148b7948f40a7f7559606af7575c6e9139a4e8feec0a5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 96, + 246, + 189, + 318 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/df169f8da00a64b6e4f712804309cfd9ffdeddd7df0e7d7a04e5e58930e96a69.jpg", + "image_caption": [ + "Input" + ], + "image_footnote": [], + "bbox": [ + 94, + 321, + 189, + 395 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/0611a7a983bbcc9c2ca583191626dfef36da19eebcdd95aaf84f4c5eb50b0a31.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 192, + 95, + 287, + 167 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6941651e523c9774a57e27e61a8b072d987b908b4dd578c349e87cd81c4c5e30.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 192, + 169, + 287, + 244 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/910f3e3a70cf70ba50e80f07fc985924838d08df95218bbc9e947f56edbd250d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 192, + 246, + 287, + 318 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/8c037620033396c42806ac44989bb2b1e4f91c101a393e1c9e34dbb31e40cfc4.jpg", + "image_caption": [ + "SmoothGrad" + ], + "image_footnote": [], + "bbox": [ + 192, + 321, + 287, + 393 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6831a3ddd1ae9643dcb070b7d0ebef80f665f122381c9a3346bb3b58d98efa6a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 290, + 95, + 385, + 167 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/76e66f3dabed9ddeb7479b61a76b38e8c0d71b4719a22268bcc7cf811a9cdcc3.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 290, + 169, + 383, + 244 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/86b94df34c13fd344b9ab575588cfcde180020d686e6f34ff8a19369e1c23f91.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 290, + 246, + 383, + 318 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/7a89027d4d6aa87097412dd86aaf7d39d73b2908a8d159d27a2375c1898c8653.jpg", + "image_caption": [ + "Integrated Gradients" + ], + "image_footnote": [], + "bbox": [ + 290, + 321, + 383, + 393 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/5f3028e08f999b90382c5c57edc6b97f92671ffd3b1cfc1eab7e2ed97a83f1bc.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 388, + 95, + 482, + 167 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/284764dfdd65e7824517935c995f20c0335114286f3296997c48406aa1716060.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 388, + 169, + 483, + 244 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b2fdace16e61e1417c8988e299c4f08d2c1d404d2d9dc6f60356b96c346fbdf4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 388, + 246, + 483, + 318 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c7674bb26b93caa12b5a76d851093e0f84c1708283a8b651e38152195a857027.jpg", + "image_caption": [ + "Vanilla MoreauGrad" + ], + "image_footnote": [], + "bbox": [ + 388, + 321, + 483, + 393 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/3f9dc9090a32f1ca99102b0d574efd4ec7c70a7fa4171081c040f93e9c7c67b9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 488, + 95, + 581, + 167 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1e1f9e0677176717ad9f824406a1761b5e095408f2d79d5b39752f49b96ad677.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 488, + 169, + 581, + 244 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/a033f78c0f6b60eda958cbf97696197419fce3d6d3dd6824e04989248a983e38.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 488, + 246, + 581, + 318 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/669ba20dd2faf01f6431c045693acaec8a44130d90bec105c44595e7dcd25329.jpg", + "image_caption": [ + "Sparsified SmoothGrad", + "Figure 4. Qualitative comparison between Vanilla, Sparse, Group-Sparse MoreauGrad and the baseline methods." + ], + "image_footnote": [], + "bbox": [ + 488, + 321, + 581, + 393 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/3f04fe0ac36f5f5db24fd8c13045d21692b07dc7b740eb1c3fa2697b1ea49c7f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 584, + 95, + 679, + 167 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9889e6da74a1eb0aae661f660ca70f3793b9449a91f6660c2cfeafef5fc5082c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 584, + 169, + 679, + 244 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2ae76aaa603108d86e8b885213742b76757cb6dee46c8fc72e6a27176beeab11.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 584, + 246, + 679, + 318 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/5975b09c1ab7abe166861b159b0bd70117b45b011ec5ee9c612f47d2ad61abe5.jpg", + "image_caption": [ + "RelEx" + ], + "image_footnote": [], + "bbox": [ + 584, + 321, + 679, + 393 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/a6c146c47a6c2ce3b2f1fcd6b339093ba052c946d138b89e9b9f0ea7fbe01bef.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 683, + 95, + 777, + 167 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e4f0d510832c4431bd5c4f6736263a4cfb424fcf4e731a72fbd45ac47035c469.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 683, + 169, + 777, + 244 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/8ffd5a0262fd023f81f8c46b3a9de329f0dfb513138a9841ce3ad01e6a1f9933.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 683, + 246, + 777, + 318 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2e1abda7db2b3fb1533a2bc26c6283f23f6ff0534338054751208007cfbf92d9.jpg", + "image_caption": [ + "Group-Sparse MoreauGrad" + ], + "image_footnote": [], + "bbox": [ + 683, + 321, + 777, + 393 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/95c1b90e13a23e21e3e95fbe97c03d99414afe42af3d303d6ba7d382109a8b45.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 781, + 95, + 875, + 167 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b3ab53a0ef4d76dca8a200c7bd5de26a6addb6f6c7f3ad8a31a17cb560a788bb.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 781, + 169, + 875, + 244 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/d81d52e943bc696a15af0e0646c42299d6c151170377803d80157e82fa328cf8.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 781, + 246, + 875, + 318 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c1f5127db324f779d7be44af5e347f325d2438ed8c31d6d3ec2acffcb2428f04.jpg", + "image_caption": [ + "Sparse MoreauGrad" + ], + "image_footnote": [], + "bbox": [ + 781, + 321, + 875, + 393 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "the group-sparsity hyperparameter effect to the Appendix.", + "bbox": [ + 76, + 470, + 460, + 486 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Moreover, to investigate the MoreauGrad's regularization effect, we measured the averaged $\\ell_2$ -norm discrepancy between the MoreauGard and simple gradient maps for different smoothness parameter $\\rho$ 's. As shown in Figure 3, the $\\ell_2$ -norm discrepancy score grows smoothly with coefficient $\\rho$ . We also measured the averaged gradient discrepancy for SmoothGrad methods with different smoothness parameter $\\sigma$ 's. We adjusted $\\eta$ in Sparse MoreauGrad to standardize the sparsity level for fair comparisons with Sparsified SmoothGrad. As Figure 3 shows, SmoothGrad led to similar discrepancy values as in MoreauGrad. Also, Integrated Gradients [24] had a similar averaged gradient discrepancy of 0.34 for CIFAR-10 and 0.40 for ImageNet. As the results suggest, the baselines similarly deviate from the simple gradient maps, which could be linked to improved visual quality and robustness, as also observed by [22, 13].", + "bbox": [ + 75, + 487, + 468, + 728 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.3. Qualitative Comparison of MoreauGrad vs. Standard Gradient-based Baselines", + "text_level": 1, + "bbox": [ + 76, + 739, + 468, + 770 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In Figure 4, we illustrate the Vanilla, Sparse, and Group-Sparse MoreauGrad interpretation outputs as well as the saliency maps generated by the gradient-based baselines. The results demonstrate that MoreauGrad generates qualitatively sharp and, in the case of Sparse and Group-Sparse MoreauGrad, sparse interpretation maps. As shown in Figure 4, promoting sparsity in the MoreauGrad interpretation maps has improved the visual quality, and managed to erase", + "bbox": [ + 75, + 779, + 468, + 901 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "the less relevant pixels like the background ones. Also, the Group-Sparse MoreauGrad maps successfully exhibit both sparsity and connectivity of selected pixels.", + "bbox": [ + 496, + 470, + 890, + 516 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.4. Robustness of Interpretation Maps", + "text_level": 1, + "bbox": [ + 500, + 523, + 803, + 539 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We qualitatively and quantitatively evaluated the robustness of MoreauGrad interpretation. To assess the empirical robustness of interpretation methods, we adopt a $L_{2}$ -bounded interpretation attack method defined by [13]. Also, for quantifying the empirical robustness, we adopt three robustness metrics. The first metric is the Euclidean distance of the normalized interpretations before and after the attack:", + "bbox": [ + 496, + 546, + 890, + 652 + ], + "page_idx": 6 + }, + { + "type": "equation", + "text": "\n$$\nD \\left(I (\\mathbf {x}), I \\left(\\mathbf {x} ^ {\\prime}\\right)\\right) = \\left\\| \\frac {I (\\mathbf {x})}{\\| I (\\mathbf {x}) \\| _ {2}} - \\frac {I \\left(\\mathbf {x} ^ {\\prime}\\right)}{\\| I \\left(\\mathbf {x} ^ {\\prime}\\right) \\| _ {2}} \\right\\| _ {2} \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 547, + 664, + 890, + 698 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Note that a larger distance between the normalized maps indicates a smaller similarity and a higher vulnerability of the interpretation method to adversarial attacks.", + "bbox": [ + 496, + 703, + 890, + 748 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The second metric is the top-k intersection ratio. This metric is another standard robustness measure used in [6, 13]. This metric measures the ratio of pixels that remain salient after the interpretation attack. A robust interpretation is expected to preserve most of the salient pixels under an attack. The third metric is the structural similarity index measure (SSIM) [27]. A larger SSIM value indicates that the two input maps are more perceptively similar.", + "bbox": [ + 496, + 750, + 890, + 869 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Using the above metrics, we compared the MoreauGrad schemes with the baseline methods. As qualitatively shown", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "2027", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/81a2ea00f5fe6bd1a3d1777ee65c6bf92a87c399442ab2be2feba864633e5c99.jpg", + "image_caption": [ + "Figure 5. Visualization of robustness against interpretation attacks. The top and bottom rows show original and attacked maps." + ], + "image_footnote": [], + "bbox": [ + 96, + 90, + 877, + 318 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0a9f83b32d63679ba184421719bec217eaade9423b408ff9a30d1d764ccf4f5e.jpg", + "image_caption": [ + "Figure 6. Quantitative robustness comparison between MoreauGrad and the baselines." + ], + "image_footnote": [], + "bbox": [ + 91, + 362, + 877, + 830 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "2028", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3a6111a1b1708e90d0be507fbafaad5c58e0529357db0bdc80d54d2c11917958.jpg", + "image_caption": [ + "Input" + ], + "image_footnote": [], + "bbox": [ + 83, + 90, + 176, + 234 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/c4e5fd4260d72c33c6b687501c09fd96e3f3cc6c2398d9e6651bd40eb57abbcd.jpg", + "image_caption": [ + "$\\eta = 0$", + "MoreauGrad" + ], + "image_footnote": [], + "bbox": [ + 179, + 90, + 272, + 234 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/2cbda9385ef5f5b3b650fc4ac36f2205979208681b741d3615f2580b14c3d3e4.jpg", + "image_caption": [ + "$\\eta = 1\\times 10^{-3}$", + "Sparse MoreauGrad" + ], + "image_footnote": [], + "bbox": [ + 274, + 90, + 367, + 234 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/d152693cbc4cda9cada3c37ec6a011402f5a81e04e6e8a56b30980dd831b918e.jpg", + "image_caption": [ + "$\\eta = 5\\times 10^{-3}$", + "Figure 7. Applications of vanilla and sparse MoreauGrad to explain two misclassifications on the ImageNet test set." + ], + "image_footnote": [], + "bbox": [ + 370, + 90, + 462, + 234 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "in Figure 5, using the same attack magnitude, the MoreauGrad interpretations are mostly similar before and after the norm-bounded attack. The qualitative robustness of MoreauGrad seems satisfactory compared to the baseline methods. Finally, Figure 6 presents a quantitative comparison of the robustness measures for the baselines and proposed MoreauGrad on CIFAR-10, tiny ImageNet, and ImageNet datasets. As shown by these measures, MoreauGrad outperforms the baselines in terms of the discussed robustness metrics.", + "bbox": [ + 75, + 304, + 467, + 455 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6.5. Applications of MoreauGrad Interpretation", + "text_level": 1, + "bbox": [ + 76, + 464, + 447, + 481 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "As shown in Figure 2, MoreauGrad interpretation maps may be further refined to promote sparsity and retain only the salient pixels. The sparsity level could be flexibly adjusted via parameter $\\eta$ in accordance with the target dataset. Moreover, both vanilla and sparse MoreauGrad can be employed for explaining DNN's misclassifications in image recognition tasks. Figure 7 presents two examples of such misclassifications, where \"gas pump\" and \"church\" are erroneously classified as \"tricycle\" and \"restaurant\", respectively. Sparse MoreauGrad identifies the source of these errors and relates them to the presence of \"a person in the middle of two wheels\" and \"people sitting on benches\", respectively. In the Appendix, we present other examples of using MoreauGrad for explaining DNNs' misclassification.", + "bbox": [ + 75, + 484, + 467, + 696 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "7. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 709, + 194, + 724 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this work, we introduced MoreauGrad as an optimization-based interpretation method for deep neural networks. We demonstrated that MoreauGrad can be flexibly combined with $L_{1}$ -regularization methods to output sparse and group-sparse interpretations. We further showed that the MoreauGrad output will enjoy robustness against input perturbations. While our analysis focuses on the sparsity and robustness of the MoreauGrad explanation, studying the consistency and transferability of MoreauGrad interpretations is an interesting future direction. Moreover, the application of MoreauGrad to convex and norm-regularized", + "bbox": [ + 75, + 734, + 467, + 900 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "neural nets could be another topic for future study. Finally, our analysis of $\\ell_1$ -norm-based Moreau envelope could find independent applications in other deep learning contexts.", + "bbox": [ + 498, + 90, + 890, + 137 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgments", + "text_level": 1, + "bbox": [ + 500, + 148, + 658, + 165 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was partially supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China, Project 14209920, and was partially supported by a CUHK Direct Research Grant. 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Structured adversarial attack: Towards general implementation and better interpretability. arXiv preprint arXiv:1808.01664, 2018.3", + "[29] Zhong-Qiu Zhao, Peng Zheng, Shou-tao Xu, and Xindong Wu. Object detection with deep learning: A review. IEEE transactions on neural networks and learning systems, 30(11):3212-3232, 2019. 1", + "[30] Bolei Zhou, Aditya Khosla, Agata Lapedriza, Aude Oliva, and Antonio Torralba. Learning deep features for discriminative localization. In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 2921-2929, 2016. 2", + "[31] Hui Zou and Trevor Hastie. Regularization and variable selection via the elastic net. Journal of the royal statistical society: series B (statistical methodology), 67(2):301-320, 2005. 2" + ], + "bbox": [ + 501, + 90, + 890, + 818 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "2030", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/MoreauGrad_ Sparse and Robust Interpretation of Neural Networks via Moreau Envelope/99846963-8ced-4bc2-923b-b6a5c1cca433_model.json b/2023/MoreauGrad_ Sparse and Robust Interpretation of Neural Networks via Moreau Envelope/99846963-8ced-4bc2-923b-b6a5c1cca433_model.json new file mode 100644 index 0000000000000000000000000000000000000000..8fdf443dc4b7d89a31b12cade760bb735b6a88a9 --- /dev/null +++ b/2023/MoreauGrad_ Sparse and Robust Interpretation of Neural Networks via Moreau Envelope/99846963-8ced-4bc2-923b-b6a5c1cca433_model.json @@ -0,0 +1,3014 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.08, + 0.13, + 0.892, + 0.178 + ], + "angle": 0, + "content": "MoreauGrad: Sparse and Robust Interpretation of Neural Networks via Moreau Envelope" + }, + { + "type": "text", + "bbox": [ + 0.156, + 0.205, + 0.462, + 0.257 + ], + "angle": 0, + "content": "Jingwei Zhang \nThe Chinese University of Hong Kong \njwzhang22@cse.cuhk.edu.hk" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.314, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.324, + 0.474, + 0.657 + ], + "angle": 0, + "content": "Explaining the predictions of deep neural nets has been a topic of great interest in the computer vision literature. While several gradient-based interpretation schemes have been proposed to reveal the influential variables in a neural net's prediction, standard gradient-based interpretation frameworks have been commonly observed to lack robustness to input perturbations and flexibility for incorporating prior knowledge of sparsity and group-sparsity structures. In this work, we propose MoreauGrad as an interpretation scheme based on the classifier neural net's Moreau envelope. We demonstrate that MoreauGrad results in a smooth and robust interpretation of a multi-layer neural network and can be efficiently computed through first-order optimization methods. Furthermore, we show that MoreauGrad can be naturally combined with \\( L_{1} \\)-norm regularization techniques to output a sparse or group-sparse explanation which are prior conditions applicable to a wide range of deep learning applications. We empirically evaluate the proposed MoreauGrad scheme on standard computer vision datasets, showing the qualitative and quantitative success of the MoreauGrad approach in comparison to standard gradient-based interpretation methods1." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.687, + 0.21, + 0.702 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.713, + 0.47, + 0.864 + ], + "angle": 0, + "content": "Deep neural networks (DNNs) have achieved state-of-the-art performance in many computer vision problems including image classification [11], object detection [29], and medical image analysis [19]. While they manage to attain super-human scores on standard image and speech recognition tasks, a reliable application of deep learning models to real-world problems requires an interpretation of their predictions to help domain experts understand and investigate the basis of their predictions. Over the past few years, developing and analyzing interpretation schemes that reveal" + }, + { + "type": "text", + "bbox": [ + 0.508, + 0.205, + 0.816, + 0.257 + ], + "angle": 0, + "content": "Farzan Farnia \nThe Chinese University of Hong Kong \nfarnia@cse.cuhk.edu.hk" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.291, + 0.889, + 0.682 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.69, + 0.894, + 0.734 + ], + "angle": 0, + "content": "Figure 1. Interpretation of Sparse MoreauGrad (ours) vs. standard gradient-based baselines on an ImageNet sample before and after adding a norm-bounded interpretation adversarial attack." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.748, + 0.892, + 0.779 + ], + "angle": 0, + "content": "the influential features in a neural network's prediction have attracted great interest in the computer vision community." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.893, + 0.902 + ], + "angle": 0, + "content": "A standard approach for interpreting neural nets' predictions is to analyze the gradient of their prediction score function at or around an input data point. Such gradient-based interpretation mechanisms result in a feature saliency map revealing the influential variables that locally affect the neural net's assigned prediction score. Three well-known examples of gradient-based interpretation schemes are the simple gradient [21], integrated gradients [24], and" + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.875, + 0.468, + 0.901 + ], + "angle": 0, + "content": "1The paper's code is available at https://github.com/buyeh1109/MoreauGrad." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.958 + ], + "angle": 0, + "content": "2021" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.198 + ], + "angle": 0, + "content": "DeepLIFT [20] methods. While the mentioned methods have found many applications in explaining neural nets' predictions, they have been observed to lack robustness to input perturbations and to output a dense noisy saliency map in their application to computer vision datasets [6, 8]. Consequently, these gradient-based explanations can be considerably altered by minor random or adversarial input noise." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.2, + 0.471, + 0.426 + ], + "angle": 0, + "content": "A widely-used approach to improve the robustness and sharpness of gradient-based interpretations is SmoothGrad [22] which applies Gaussian smoothing to the mentioned gradient-based interpretation methods. As shown by [22], SmoothGrad can significantly boost the visual quality of a neural net's gradient-based saliency map. On the other hand, SmoothGrad typically leads to a dense interpretation vector and remains inflexible to incorporate prior knowledge of sparsity and group-sparsity structures. Since a sparse saliency map is an applicable assumption to several image classification problems where a relatively small group of input variables can completely determine the image label, a counterpart of SmoothGrad which can simultaneously achieve sparse and robust interpretation will be of significant use in computer vision problems." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.429, + 0.47, + 0.64 + ], + "angle": 0, + "content": "In this paper, we propose a novel approach, which we call MoreauGrad, to achieve a provably smooth gradient-based interpretation with potential sparsity or group-sparsity properties. The proposed MoreauGrad outputs the gradient of a classifier's Moreau envelope which is a useful optimization tool for enforcing smoothness in a target function. We leverage convex analysis to show that MoreauGrad behaves smoothly around an input sample and therefore provides an alternative optimization-based approach to SmoothGrad for achieving a smoothly-changing saliency map. As a result, we demonstrate that similar to SmoothGrad, MoreauGrad offers robustness to input perturbations, since a norm-bounded perturbation will only lead to a bounded change to the MoreauGrad interpretation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.642, + 0.47, + 0.824 + ], + "angle": 0, + "content": "Next, we show that MoreauGrad can be flexibly combined with \\( L_{1} \\)-norm-based regularization penalties to output sparse and group-sparse interpretations. Our proposed combinations, Sparse MoreauGrad and Group-Sparse MoreauGrad, take advantage of elastic-net [31] and group-norm [16] penalty terms to enforce sparse and group-sparse saliency maps, respectively. We show that these extensions of MoreauGrad preserve the smoothness and robustness properties of the original MoreauGrad scheme. Therefore, our discussion demonstrates the adaptable nature of MoreauGrad for incorporating prior knowledge of sparsity structures in the output interpretation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Finally, we present the empirical results of our numerical experiments applying MoreauGrad to standard image recognition datasets and neural net architectures. We compare the numerical performance of MoreauGrad with standard gradient-based interpretation baselines. Our numeri" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.244 + ], + "angle": 0, + "content": "cal results indicate the satisfactory performance of vanilla and \\( L_{1} \\)-norm-based MoreauGrad in terms of visual quality and robustness. Figure 1 shows the robustness and sparsity of the Sparse MoreauGrad interpretation applied to an ImageNet sample in comparison to standard gradient-based saliency maps. As this and our other empirical findings suggest, MoreauGrad can outperform standard baselines in terms of the sparsity and robustness properties of the output interpretation. In the following, we summarize the main contributions of this paper:" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.256, + 0.892, + 0.287 + ], + "angle": 0, + "content": "- Proposing MoreauGrad as an interpretation scheme based on a classifier function's Moreau envelope" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.296, + 0.892, + 0.327 + ], + "angle": 0, + "content": "- Analyzing the smoothness and robustness properties of MoreauGrad by leveraging convex analysis" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.337, + 0.892, + 0.368 + ], + "angle": 0, + "content": "- Introducing \\( L_{1} \\)-regularized Sparse MoreauGrad to obtain an interpretation satisfying prior sparsity conditions" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.378, + 0.892, + 0.409 + ], + "angle": 0, + "content": "- Providing numerical results supporting MoreauGrad over standard image recognition datasets" + }, + { + "type": "list", + "bbox": [ + 0.5, + 0.256, + 0.892, + 0.409 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.422, + 0.642, + 0.438 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.448, + 0.892, + 0.81 + ], + "angle": 0, + "content": "Gradient-based Interpretation. A large body of related works develop gradient-based interpretation methods. Simonyan et al. [21] propose to calculate the gradient of a classifier's output with respect to an input image. The simple gradient approach in [21] has been improved by several related works. Notably, the method of Integrated Gradients [24] is capable of keeping highly relevant pixels in the saliency map by aggregating gradients of image samples. SmoothGrad [22] removes noise in saliency maps by adding Gaussian-random noise to the input image. The CAM method [30] analyzes the information from global average pooling layer for localization, and Grad-CAM++ [1] improves over Grad-CAM [18] and generates coarse heatmaps with improved multi-object localization. The NormGrad [17] focuses on the weight-based gradient to analyze the contribution of each image region. DeepLIFT [20] uses difference from reference to propagate an attribution signal. However, the mentioned gradient-based methods do not obtain a sparse interpretation, and their proper combination with \\( L_{1} \\)-regularization to promote sparsity remains highly non-trivial and challenging. On the other hand, our proposed MoreauGrad can be smoothly equipped with \\( L_{1} \\)-regularization to output sparse interpretations and can further capture group-sparsity structures." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Mask-based Interpretation. Mask-based interpretation methods rely on adversarial perturbations to interpret neural nets. Applying a mask which perturbs the neural net input, the importance of input pixels is measured by a masked-based method. This approach to explaining neural nets has been successfully applied in References [26, 5, 14, 2] and" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2022" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.242 + ], + "angle": 0, + "content": "has been shown to benefit from dynamic perturbations [9]. More specifically, Dabkowski and Gal [2] introduce a real-time mask-based detection method; Fong and Vedaldi [5] develop a model-agnostic approach with interpretable perturbations; Wagner et al. [26] propose a method that could generate fine-grained visual interpretations. Moreover, Lim et al. [14] leverage local smoothness to enhance their robustness towards samples attacked by PGD [15]. However, [5] and [2] show that perturbation-based interpretation methods are still vulnerable to adversarial perturbations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.243, + 0.471, + 0.376 + ], + "angle": 0, + "content": "We note that the discussed methods depend on optimizing perturbation masks for interpretations, and due to the non-convex nature of neural net loss functions, their interpretation remains sensitive to input perturbations. In contrast, our proposed MoreauGrad can provably smooth the neural net score function, and can adapt to non-convex functions using norm regularization. Hence, MoreauGrad can improve both the sparsity and robustness of the interpretation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.379, + 0.47, + 0.529 + ], + "angle": 0, + "content": "Robust Interpretation. The robustness of interpretation methods has been a subject of great interest in the literature. Ghorbani et al. [6] introduce a gradient-based adversarial attack method to alter the neural nets' interpretation. Dombrowski et al. [4] demonstrate that interpretations could be manipulated, and they suggest improving the robustness via smoothing the neural net classifier. Heo et al. [8] propose a manipulation method that is capable of generalizing across datasets. Subramanya et al. [23] create adversarial patches fooling both the classifier and the interpretation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.53, + 0.471, + 0.726 + ], + "angle": 0, + "content": "To improve the robustness, Sparsified-SmoothGrad [13] combines a sparsification technique with Gaussian smoothing to achieve certifiable robustness. The related works [26, 28, 5, 14, 2] discuss the application of adversarial defense methods against classification-based attacks to interpret the prediction of neural net classifiers. We note that these papers' main focus is not on defense schemes against interpretation-based attacks. Specifically, [26] filter gradients internally during backpropagation, and [14] leverage local smoothness to integrate more samples. Unlike the mentioned papers, our work proposes a model-agnostic optimization-based method which is capable of generating simultaneously sparse and robust interpretations." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.738, + 0.216, + 0.753 + ], + "angle": 0, + "content": "3. Preliminaries" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.764, + 0.47, + 0.794 + ], + "angle": 0, + "content": "In this section, we review three standard interpretation methods as well as the notation and definitions in the paper." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.802, + 0.303, + 0.817 + ], + "angle": 0, + "content": "3.1. Notation and Definitions" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.825, + 0.47, + 0.902 + ], + "angle": 0, + "content": "In the paper, we use notation \\(\\mathbf{X} \\in \\mathbb{R}^d\\) to denote the feature vector and \\(Y \\in \\{1, \\dots, k\\}\\) to denote the label of a sample. In addition, \\(f_{\\mathbf{w}}: \\mathbb{R}^d \\to \\mathbb{R}^k\\) denotes a neural net classifier with its weights contained in vector \\(\\mathbf{w} \\in \\mathcal{W}\\) where \\(\\mathcal{W}\\) is the feasible set of the neural net's weights. Here \\(f_{\\mathbf{w}}\\) maps" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.167 + ], + "angle": 0, + "content": "the \\(d\\)-dimensional input \\(\\mathbf{x}\\) to a \\(k\\)-dimensional prediction vector containing the likelihood of each of the \\(k\\) classes in the classification problem. For every class \\(c \\in \\{1, \\dots, k\\}\\), we use the notation \\(f_{\\mathbf{w}, c}: \\mathbb{R}^d \\to \\mathbb{R}\\) to denote the \\(c\\)-th entry of \\(f_{\\mathbf{w}}\\)'s output which corresponds to class \\(c\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.168, + 0.892, + 0.228 + ], + "angle": 0, + "content": "We use \\(\\| \\mathbf{x}\\| _p\\) to denote the \\(\\ell_{p}\\) -norm of input vector \\(\\mathbf{x}\\). Furthermore, we use notation \\(\\| \\mathbf{x}\\|_{p,q}\\) to denote the \\(\\ell_{p,q}\\) group-norm of \\(\\mathbf{x}\\) defined in the following equation for given variable subsets \\(S_{1},\\ldots ,S_{t}\\subseteq \\{1,\\dots ,d\\}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.235, + 0.892, + 0.257 + ], + "angle": 0, + "content": "\\[\n\\left\\| \\mathbf {x} \\right\\| _ {p, q} = \\left\\| \\left[ \\| \\mathbf {x} _ {S _ {1}} \\| _ {p}, \\dots , \\| \\mathbf {x} _ {S _ {t}} \\| _ {p} \\right] \\right\\| _ {q} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.264, + 0.892, + 0.309 + ], + "angle": 0, + "content": "In other words, \\(\\| \\mathbf{x}\\|_{p,q}\\) is the \\(\\ell_p\\)-norm of a vector containing the \\(\\ell_p\\)-norms of the subvectors of \\(\\mathbf{x}\\) characterized by index subsets \\(S_{1},\\ldots ,S_{t}\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.318, + 0.773, + 0.334 + ], + "angle": 0, + "content": "3.2. Gradient-based Saliency Maps" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.341, + 0.892, + 0.402 + ], + "angle": 0, + "content": "In our theoretical and numerical analysis, we consider the following widely-used gradient-based interpretation baselines which apply to a classifier neural net \\( f_{\\mathbf{w}} \\) and predicted class \\( c \\) for input \\( \\mathbf{x} \\):" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.409, + 0.892, + 0.455 + ], + "angle": 0, + "content": "1. Simple Gradient: The simple gradient interpretation returns the saliency map of a neural net score function's gradient with respect to input \\(\\mathbf{x}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.607, + 0.463, + 0.892, + 0.481 + ], + "angle": 0, + "content": "\\[\n\\operatorname {S G} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\nabla_ {\\mathbf {x}} f _ {\\mathbf {w}, c} (\\mathbf {x}). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.489, + 0.892, + 0.534 + ], + "angle": 0, + "content": "In the applications of the simple gradient approach, \\( c \\) is commonly chosen as the neural net's predicted label with the maximum prediction score." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.542, + 0.892, + 0.618 + ], + "angle": 0, + "content": "2. Integrated Gradients: The integrated gradients approach approximates the integral of the neural net's gradient function between a reference point \\(\\mathbf{x}^0\\) and the input \\(\\mathbf{x}\\). Using \\(m\\) intermediate points on the line segment connecting \\(\\mathbf{x}^0\\) and \\(\\mathbf{x}\\), the integrated gradient output will be" + }, + { + "type": "equation", + "bbox": [ + 0.535, + 0.639, + 0.892, + 0.678 + ], + "angle": 0, + "content": "\\[\n\\operatorname {I G} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\frac {\\Delta \\mathbf {x}}{m} \\sum_ {i = 1} ^ {m} \\nabla_ {\\mathbf {x}} f _ {\\mathbf {w}, c} \\left(\\mathbf {x} ^ {0} + \\frac {i}{m} \\Delta \\mathbf {x}\\right). \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.687, + 0.892, + 0.718 + ], + "angle": 0, + "content": "In the above \\(\\Delta \\mathbf{x} \\coloneqq \\mathbf{x} - \\mathbf{x}^0\\) denotes the difference between the target and reference points \\(\\mathbf{x}, \\mathbf{x}^0\\)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.726, + 0.892, + 0.835 + ], + "angle": 0, + "content": "3. SmoothGrad: SmoothGrad considers the averaged simple gradient score over an additive random perturbation \\( Z \\) drawn according to an isotropic Gaussian distribution \\( Z \\sim \\mathcal{N}(\\mathbf{0}, \\sigma^2 I_d) \\). In practice, the SmoothGrad interpretation is estimated over a number \\( t \\) of independently drawn noise vectors \\( \\mathbf{z}_1, \\ldots, \\mathbf{z}_t \\stackrel{\\mathrm{i.i.d.}}{\\sim} \\mathcal{N}(\\mathbf{0}, \\sigma^2 I_d) \\) according to the zero-mean Gaussian distribution:" + }, + { + "type": "equation", + "bbox": [ + 0.54, + 0.843, + 0.892, + 0.904 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\operatorname {S m o o t h G r a d} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\mathbb {E} \\left[ \\nabla_ {\\mathbf {x}} f _ {\\mathbf {w}, c} (\\mathbf {x} + Z) \\right] \\tag {4} \\\\ \\approx \\frac {1}{t} \\sum_ {i = 1} ^ {t} \\nabla_ {\\mathbf {x}} f _ {\\mathbf {w}, c} (\\mathbf {x} + \\mathbf {z} _ {i}). \\\\ \\end{array}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2023" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.09, + 0.47, + 0.125 + ], + "angle": 0, + "content": "4. MoreauGrad: An Optimization-based Interpretation Framework" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.133, + 0.468, + 0.224 + ], + "angle": 0, + "content": "As discussed earlier, smooth classifier functions with a Lipschitz gradient help to obtain a robust explanation of neural nets. Here, we propose an optimization-based smoothing approach based on Moreau-Yosida regularization. To introduce this optimization-based approach, we first define a function's Moreau envelope." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.231, + 0.468, + 0.262 + ], + "angle": 0, + "content": "Definition 1. Given regularization parameter \\(\\rho >0\\), we define the Moreau envelope of a function \\(g:\\mathbb{R}^d\\to \\mathbb{R}\\) as:" + }, + { + "type": "equation", + "bbox": [ + 0.143, + 0.269, + 0.469, + 0.3 + ], + "angle": 0, + "content": "\\[\ng ^ {\\rho} (\\mathbf {x}) := \\min _ {\\widetilde {\\mathbf {x}} \\in \\mathbb {R} ^ {d}} g (\\widetilde {\\mathbf {x}}) + \\frac {1}{2 \\rho} \\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\| _ {2} ^ {2}. \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.307, + 0.468, + 0.369 + ], + "angle": 0, + "content": "In the above definition, \\(\\rho > 0\\) represents the Moreau-Yosida regularization coefficient. Applying the Moreau envelope, we propose the MoreauGrad interpretation as the gradient of the classifier's Moreau envelope at an input \\(\\mathbf{x}\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.376, + 0.473, + 0.422 + ], + "angle": 0, + "content": "Definition 2. Given regularization parameter \\(\\rho >0\\), we define the MoreauGrad interpretation \\(MG_{\\rho}:\\mathbb{R}^{d}\\to \\mathbb{R}^{d}\\) of a neural net \\(f_{\\mathbf{w}}\\) predicting class \\(c\\) for input \\(\\mathbf{x}\\) as" + }, + { + "type": "equation", + "bbox": [ + 0.172, + 0.43, + 0.373, + 0.448 + ], + "angle": 0, + "content": "\\[\nM G _ {\\rho} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\nabla f _ {\\mathbf {w}, c} ^ {\\rho} (\\mathbf {x}).\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.455, + 0.468, + 0.561 + ], + "angle": 0, + "content": "To compute and analyze the MoreauGrad explanation, we first discuss the optimization-based smoothing enforced by the Moreau envelope. Note that the Moreau envelope is known as an optimization tool to turn non-smooth convex functions (e.g. \\(\\ell_1\\)-norm) into smooth functions. Here, we discuss an extension of this result to weakly-convex functions which also apply to non-convex functions." + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.568, + 0.468, + 0.614 + ], + "angle": 0, + "content": "Definition 3. A function \\( g: \\mathbb{R}^d \\to \\mathbb{R} \\) is called \\( \\lambda \\)-weakly convex if \\( \\Phi(\\mathbf{x}) := g(\\mathbf{x}) + \\frac{\\lambda}{2} \\| \\mathbf{x} \\|_2^2 \\) is a convex function, i.e. for every \\( \\mathbf{x}_1, \\mathbf{x}_2 \\in \\mathbb{R}^d \\) and \\( 0 \\leq \\alpha \\leq 1 \\) we have:" + }, + { + "type": "equation", + "bbox": [ + 0.097, + 0.622, + 0.446, + 0.672 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} g \\left(\\alpha \\mathbf {x} _ {1} + (1 - \\alpha) \\mathbf {x} _ {2}\\right) \\leq \\alpha g (\\mathbf {x} _ {1}) + (1 - \\alpha) g (\\mathbf {x} _ {2}) \\\\ + \\frac {\\lambda \\alpha (1 - \\alpha)}{2} \\| \\mathbf {x} _ {1} - \\mathbf {x} _ {2} \\| _ {2} ^ {2}. \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.681, + 0.468, + 0.743 + ], + "angle": 0, + "content": "Theorem 1. Suppose that \\( g: \\mathbb{R}^d \\to \\mathbb{R} \\) is a \\( \\lambda \\)-weakly convex function. Assuming that \\( 0 < \\rho < \\frac{1}{\\lambda} \\), the followings hold for the optimization problem of the Moreau envelope \\( g^\\rho \\) and the optimal solution \\( \\widetilde{x}_\\rho^*(\\mathbf{x}) \\) solving the optimization problem:" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.75, + 0.468, + 0.78 + ], + "angle": 0, + "content": "1. For every \\(\\mathbf{x}\\), the gradient of \\(g^{\\rho}\\) and Clarke subdifferential of \\(g\\) (denoted by \\(\\partial_0 g\\)) are related as:" + }, + { + "type": "equation", + "bbox": [ + 0.202, + 0.788, + 0.363, + 0.807 + ], + "angle": 0, + "content": "\\[\n\\nabla g ^ {\\rho} (\\mathbf {x}) \\in \\partial_ {0} g \\big (\\widetilde {x} _ {\\rho} ^ {*} (\\mathbf {x}) \\big),\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.814, + 0.468, + 0.845 + ], + "angle": 0, + "content": "which implies that if \\(g\\) is differentiable at \\(\\widetilde{x}_{\\rho}^{*}(\\mathbf{x})\\) we have \\(\\nabla g^{\\rho}(\\mathbf{x}) = \\nabla g(\\widetilde{x}_{\\rho}^{*}(\\mathbf{x}))\\)" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.849, + 0.464, + 0.866 + ], + "angle": 0, + "content": "2. The difference \\(\\widetilde{x}_{\\rho}^{*}(\\mathbf{x}) - \\mathbf{x}\\) is aligned with \\(g^{\\rho}\\)'s gradient:" + }, + { + "type": "equation", + "bbox": [ + 0.184, + 0.873, + 0.382, + 0.905 + ], + "angle": 0, + "content": "\\[\n\\nabla g ^ {\\rho} (\\mathbf {x}) = \\frac {- 1}{\\rho} \\left(\\widetilde {x} _ {\\rho} ^ {*} (\\mathbf {x}) - \\mathbf {x}\\right).\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.09, + 0.886, + 0.11 + ], + "angle": 0, + "content": "3. \\(g^{\\rho}\\) will be \\(\\max \\left\\{\\frac{1}{\\rho},\\frac{\\lambda}{1 - \\rho\\lambda}\\right\\}\\) smooth, i.e. for every \\(\\mathbf{x}_1,\\mathbf{x}_2\\)" + }, + { + "type": "equation", + "bbox": [ + 0.521, + 0.118, + 0.89, + 0.151 + ], + "angle": 0, + "content": "\\[\n\\left\\| \\nabla g ^ {\\rho} (\\mathbf {x} _ {1}) - \\nabla g ^ {\\rho} (\\mathbf {x} _ {2}) \\right\\| _ {2} \\leq \\frac {1}{\\min \\left\\{\\rho , \\frac {1}{\\lambda} - \\rho \\right\\}} \\left\\| \\mathbf {x} _ {1} - \\mathbf {x} _ {2} \\right\\| _ {2}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.163, + 0.892, + 0.194 + ], + "angle": 0, + "content": "Proof. This result is well-known for convex functions. In the Appendix, we provide a new proof for the result. \\(\\square\\)" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.203, + 0.892, + 0.264 + ], + "angle": 0, + "content": "Corollary 1. Assume that the prediction score function \\( f_{\\mathbf{w},c}:\\mathbb{R}^d\\to \\mathbb{R} \\) is \\( \\lambda \\)-weakly convex. Then, the MoreauGrad interpretation \\( MG_{\\rho} \\) will remain robust under an \\( \\epsilon -\\ell_2 \\)-norm bounded perturbation \\( \\| \\delta \\| _2\\leq \\epsilon \\) as" + }, + { + "type": "equation", + "bbox": [ + 0.535, + 0.272, + 0.856, + 0.303 + ], + "angle": 0, + "content": "\\[\n\\left\\| M G _ {\\rho} (\\mathbf {x} + \\boldsymbol {\\delta}) - M G _ {\\rho} (\\mathbf {x}) \\right\\| _ {2} \\leq \\frac {\\epsilon}{\\min \\left\\{\\rho , \\frac {1}{\\lambda} - \\rho \\right\\}}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.31, + 0.892, + 0.476 + ], + "angle": 0, + "content": "The above results imply that by choosing a small enough coefficient \\(\\rho\\) the Moreau envelope will be a differentiable smooth function. Moreover, the computation of the Moreau envelope will reduce to a convex optimization task that can be solved by standard or accelerated gradient descent with global convergence guarantees. Therefore, one can efficiently compute the MoreauGrad interpretation by solving the optimization problem via the gradient descent algorithm. Algorithm 1 applies gradient descent to compute the solution to the Moreau envelope optimization which according to Theorem 1 yields the MoreauGrad explanation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.476, + 0.891, + 0.552 + ], + "angle": 0, + "content": "As discussed above, MoreauGrad will be provably robust as long as the regularization coefficient will dominate the weakly-convexity degree of the prediction score. In the following proposition, we show this condition can be enforced by applying either Gaussian smoothing." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.559, + 0.892, + 0.636 + ], + "angle": 0, + "content": "Proposition 1. Suppose that \\( f_{\\mathbf{w},c} \\) is \\( L \\)-Lipschitz, that is for every \\( \\mathbf{x}_1,\\mathbf{x}_2 \\) \\( |f_{\\mathbf{w},c}(\\mathbf{x}_1) - f_{\\mathbf{w},c}(\\mathbf{x}_2)| \\leq L\\| \\mathbf{x}_2 - \\mathbf{x}_1\\|_2 \\), but could be potentially non-differentiable and nonsmooth. Then, \\( h_{\\mathbf{w},c}(\\mathbf{x}) := \\mathbb{E}[f_{\\mathbf{w},c}(\\mathbf{x} + \\mathbf{Z})] \\) where \\( \\mathbf{Z} \\sim \\mathcal{N}(0,\\sigma^2 I_{d\\times d}) \\) will be \\( \\frac{L}{\\sigma} \\)-weakly convex." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.642, + 0.892, + 0.657 + ], + "angle": 0, + "content": "Proof. We postpone the proof to the Appendix." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.667, + 0.891, + 0.713 + ], + "angle": 0, + "content": "The above proposition suggests the regularized Moreau-Grad which regularizes the neural net function to satisfy the weakly-convex condition through Gaussian smoothing." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.725, + 0.856, + 0.743 + ], + "angle": 0, + "content": "5. Sparse and Group-Sparse MoreauGrad" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.891, + 0.826 + ], + "angle": 0, + "content": "To further extend the MoreauGrad approach to output sparsely-structured feature saliency maps, we further include an \\( L_{1} \\)-norm-based penalty term in the Moreau-Yosida regularization and define the following \\( L_{1} \\)-norm-based sparse and group-sparse Moreau envelope." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.833, + 0.891, + 0.866 + ], + "angle": 0, + "content": "Definition 4. For a function \\( g: \\mathbb{R}^d \\to \\mathbb{R} \\) and regularization coefficients \\( \\rho, \\eta > 0 \\), we define \\( L_1 \\)-Moreau envelope \\( g_{L_1}^{\\rho, \\eta} \\):" + }, + { + "type": "equation", + "bbox": [ + 0.515, + 0.874, + 0.874, + 0.904 + ], + "angle": 0, + "content": "\\[\ng _ {L _ {1}} ^ {\\rho , \\eta} (\\mathbf {x}) := \\min _ {\\widetilde {\\mathbf {x}} \\in \\mathbb {R} ^ {d}} g (\\widetilde {\\mathbf {x}}) + \\frac {1}{2 \\rho} \\left\\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\right\\| _ {2} ^ {2} + \\eta \\left\\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\right\\| _ {1}.\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2024" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.091, + 0.385, + 0.11 + ], + "angle": 0, + "content": "We also define \\(L_{2,1}\\)-Moreau envelope \\(g_{L_{2,1}}^{\\rho,\\eta}\\) as" + }, + { + "type": "equation", + "bbox": [ + 0.084, + 0.118, + 0.462, + 0.149 + ], + "angle": 0, + "content": "\\[\ng _ {L _ {2, 1}} ^ {\\rho , \\eta} (\\mathbf {x}) := \\min _ {\\widetilde {\\mathbf {x}} \\in \\mathbb {R} ^ {d}} g (\\widetilde {\\mathbf {x}}) + \\frac {1}{2 \\rho} \\left\\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\right\\| _ {2} ^ {2} + \\eta \\left\\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\right\\| _ {2, 1}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.157, + 0.47, + 0.191 + ], + "angle": 0, + "content": "In the above, the group norm \\(\\| \\cdot \\|_{2,1}\\) is defined as \\(\\| \\mathbf{x} \\|_{2,1} := \\sum_{i=1}^{t} \\| \\mathbf{x}_{S_i} \\|_2\\) for given subsets \\(S_1, \\ldots, S_t \\subseteq \\{1, \\ldots, d\\}\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.197, + 0.47, + 0.245 + ], + "angle": 0, + "content": "Definition 5. Given regularization coefficients \\(\\rho, \\eta > 0\\), we define the Sparse MoreauGrad (\\(S-MG_{\\rho,\\eta}\\)) and Group-Sparse MoreauGrad (\\(GS-MG_{\\rho,\\eta}\\)) interpretations as" + }, + { + "type": "equation", + "bbox": [ + 0.146, + 0.25, + 0.412, + 0.282 + ], + "angle": 0, + "content": "\\[\nS - M G _ {\\rho , \\eta} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\frac {1}{\\rho} \\left(\\widetilde {\\mathbf {x}} _ {L _ {1}} ^ {*} (\\mathbf {x}) - \\mathbf {x}\\right),\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.137, + 0.284, + 0.42, + 0.315 + ], + "angle": 0, + "content": "\\[\nG S - M G _ {\\rho , \\eta} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\frac {1}{\\rho} \\left(\\widetilde {\\mathbf {x}} _ {L _ {2, 1}} ^ {*} (\\mathbf {x}) - \\mathbf {x}\\right),\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.322, + 0.47, + 0.359 + ], + "angle": 0, + "content": "where \\(\\widetilde{\\mathbf{x}}_{L_1}^* (\\mathbf{x})\\), \\(\\widetilde{\\mathbf{x}}_{L_{2,1}}^{*}(\\mathbf{x})\\) denote the optimal solutions to the optimization tasks of \\(f_{\\mathbf{w},c,L_1}^{\\rho ,\\eta}(\\mathbf{x})\\), \\(f_{\\mathbf{w},c,L_{2,1}}^{\\rho ,\\eta}(\\mathbf{x})\\), respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.362, + 0.47, + 0.469 + ], + "angle": 0, + "content": "In the following theorem, we extend the shown results for the smoothness and robustness of vanilla Moreau envelope to our proposed \\(L_{1}\\)-norm-based extensions of the Moreau envelope. In this theorem, we use the following definitions for the soft-thresholding operators \\(\\mathrm{ST}_{\\alpha}\\) and \\(\\mathrm{GST}_{\\alpha}\\) for the sparse and group-sparse cases which are defined entrywise and group-entrywise as follows" + }, + { + "type": "equation", + "bbox": [ + 0.113, + 0.476, + 0.414, + 0.517 + ], + "angle": 0, + "content": "\\[\n\\mathrm {S T} _ {\\alpha} (\\mathbf {x}) _ {i} := \\left\\{ \\begin{array}{l l} 0 & \\text {i f} | x _ {i} | \\leq \\alpha \\\\ x _ {i} - \\operatorname {s i g n} (x _ {i}) \\alpha & \\text {i f} | x _ {i} | > \\alpha , \\end{array} \\right.\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.096, + 0.52, + 0.45, + 0.562 + ], + "angle": 0, + "content": "\\[\n\\mathrm {G S T} _ {\\alpha} (\\mathbf {x}) _ {S _ {i}} := \\left\\{ \\begin{array}{l l} \\mathbf {0} & \\text {i f} \\| \\mathbf {x} _ {S _ {i}} \\| _ {2} \\leq \\alpha \\\\ \\big (1 - \\frac {\\alpha}{\\| \\mathbf {x} _ {S _ {i}} \\| _ {2}} \\big) \\mathbf {x} _ {S _ {i}} & \\text {i f} \\| \\mathbf {x} _ {S _ {i}} \\| _ {2} > \\alpha . \\end{array} \\right.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.57, + 0.47, + 0.678 + ], + "angle": 0, + "content": "Theorem 2. Suppose that \\(g:\\mathbb{R}^d\\to \\mathbb{R}\\) is a \\(\\lambda\\) -weakly convex function. Then, assuming that \\(0 < \\rho < \\frac{1}{\\lambda}\\), Theorem 1's parts 1 and 3 will further hold for the sparse Moreau envelope \\(g_{L_1}^{\\rho ,\\eta}\\) and group-sparse Moreau envelope \\(g_{L_{2,1}}^{\\rho ,\\eta}\\) and their optimization problems' optimal solutions \\(\\widetilde{\\mathbf{x}}_{\\rho ,\\eta ,L_1}^* (\\mathbf{x})\\) and \\(\\widetilde{\\mathbf{x}}_{\\rho ,\\eta ,L_{2,1}}^{*}(\\mathbf{x})\\). To parallel Theorem 1's part 2 for \\(L_{1}\\)-Moreau envelope, the followings hold" + }, + { + "type": "equation", + "bbox": [ + 0.141, + 0.686, + 0.412, + 0.705 + ], + "angle": 0, + "content": "\\[\n\\mathrm {S T} _ {\\rho \\eta} \\left(- \\rho \\nabla g _ {L _ {1}} ^ {\\rho , \\eta} (\\mathbf {x})\\right) = \\widetilde {\\mathbf {x}} _ {\\rho , \\eta , L _ {1}} ^ {*} (\\mathbf {x}) - \\mathbf {x},\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.126, + 0.706, + 0.422, + 0.727 + ], + "angle": 0, + "content": "\\[\n\\mathrm {G S T} _ {\\rho \\eta} \\big (- \\rho \\nabla g _ {L _ {2, 1}} ^ {\\rho , \\eta} (\\mathbf {x}) \\big) = \\widetilde {\\mathbf {x}} _ {\\rho , \\eta , L _ {2, 1}} ^ {*} (\\mathbf {x}) - \\mathbf {x}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.733, + 0.367, + 0.749 + ], + "angle": 0, + "content": "Proof. We defer the proof to the Appendix." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.757, + 0.47, + 0.834 + ], + "angle": 0, + "content": "Corollary 2. Suppose that the prediction score function \\( f_{\\mathbf{w},c} \\) is \\( \\lambda \\)-weakly convex. Assuming that \\( 0 < \\rho < \\frac{1}{\\lambda} \\), the Sparse MoreauGrad \\( S - MG_{\\rho, \\eta} \\) and Group-Sparse MoreauGrad \\( GS - MG_{\\rho, \\eta} \\) interpretations will be robust to every norm-bounded perturbation \\( \\| \\delta \\|_2 \\leq \\epsilon \\) as:" + }, + { + "type": "equation", + "bbox": [ + 0.101, + 0.841, + 0.478, + 0.873 + ], + "angle": 0, + "content": "\\[\n\\left\\| S - M G _ {\\rho , \\eta} (\\mathbf {x} + \\boldsymbol {\\delta}) - S - M G _ {\\rho , \\eta} (\\mathbf {x}) \\right\\| _ {2} \\leq \\frac {\\epsilon}{\\min \\left\\{\\rho , \\frac {1}{\\lambda} - \\rho \\right\\}},\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.08, + 0.874, + 0.478, + 0.906 + ], + "angle": 0, + "content": "\\[\n\\left\\| G S - M G _ {\\rho , \\eta} (\\mathbf {x} + \\boldsymbol {\\delta}) - G S - M G _ {\\rho , \\eta} (\\mathbf {x}) \\right\\| _ {2} \\leq \\frac {\\epsilon}{\\min \\left\\{\\rho , \\frac {1}{\\lambda} - \\rho \\right\\}}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.106, + 0.771, + 0.122 + ], + "angle": 0, + "content": "Algorithm 1 MoreauGrad Interpretation" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.123, + 0.892, + 0.154 + ], + "angle": 0, + "content": "Input: data x, label c, classifier \\(f_{\\mathbf{w}}\\), regularization coeff. \\(\\rho\\), stepsize \\(\\gamma\\), noise std. parameter \\(\\sigma\\), number of updates \\(T\\)" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.154, + 0.635, + 0.167 + ], + "angle": 0, + "content": "Initialize \\(\\mathbf{x}^{(0)} = \\mathbf{x}\\)" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.169, + 0.636, + 0.183 + ], + "angle": 0, + "content": "for \\(t = 0,\\dots ,T\\) do" + }, + { + "type": "text", + "bbox": [ + 0.526, + 0.184, + 0.699, + 0.198 + ], + "angle": 0, + "content": "if Regularized Mode then" + }, + { + "type": "equation", + "bbox": [ + 0.551, + 0.199, + 0.875, + 0.236 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\textbf {D r a w n o i s e v e c t o r s z _ {1} , \\ldots , z _ {m}} \\sim \\mathcal {N} (\\mathbf {0}, \\sigma^ {2} I _ {d \\times d}) \\\\ \\textbf {C o m p u t e g} _ {t} = \\frac {1}{m} \\sum_ {i = 1} ^ {m} \\nabla f _ {\\mathbf {w}, c} (\\mathbf {x} ^ {(t)} + \\mathbf {z} _ {i}) \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.527, + 0.237, + 0.557, + 0.248 + ], + "angle": 0, + "content": "else" + }, + { + "type": "equation", + "bbox": [ + 0.552, + 0.25, + 0.741, + 0.267 + ], + "angle": 0, + "content": "\\[\n\\mathbf {C o m p u t e} \\mathbf {g} _ {t} = \\nabla f _ {\\mathbf {w}, c} (\\mathbf {x} ^ {(t)})\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.527, + 0.268, + 0.556, + 0.279 + ], + "angle": 0, + "content": "end" + }, + { + "type": "equation", + "bbox": [ + 0.552, + 0.286, + 0.828, + 0.308 + ], + "angle": 0, + "content": "\\[\n\\mathbf {d a t e} \\mathbf {x} ^ {(t + 1)} \\leftarrow (1 - \\frac {\\gamma}{\\rho}) \\mathbf {x} ^ {(t)} - \\gamma (\\mathbf {g} _ {t} - \\frac {1}{\\rho} \\mathbf {x})\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.527, + 0.312, + 0.664, + 0.326 + ], + "angle": 0, + "content": "if Sparse Mode then" + }, + { + "type": "equation", + "bbox": [ + 0.551, + 0.326, + 0.892, + 0.344 + ], + "angle": 0, + "content": "\\[\n\\mathbf {U p d a t e} \\mathbf {x} ^ {(t + 1)} \\leftarrow \\text {S o f t T h r e s h o l d} _ {\\gamma \\eta} \\left(\\mathbf {x} ^ {(t + 1)} - \\mathbf {x}\\right) + \\mathbf {x}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.502, + 0.346, + 0.531, + 0.356 + ], + "angle": 0, + "content": "end" + }, + { + "type": "equation", + "bbox": [ + 0.502, + 0.358, + 0.715, + 0.379 + ], + "angle": 0, + "content": "\\[\n\\operatorname {O u t p u t} \\mathrm {M G} (\\mathbf {x}) = \\frac {1}{\\rho} \\left(\\mathbf {x} ^ {(T)} - \\mathbf {x}\\right)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.422, + 0.892, + 0.498 + ], + "angle": 0, + "content": "Based on the above results, we propose applying the proximal gradient descent algorithm as described in Algorithm 1 to compute the Sparse and Group-Sparse Moreau-Grad. We defer discussing Algorithm 1's details to the Appendix." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.511, + 0.68, + 0.527 + ], + "angle": 0, + "content": "6. Numerical Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.537, + 0.892, + 0.672 + ], + "angle": 0, + "content": "We conduct several numerical experiments to evaluate the performance of the proposed MoreauGrad. Our designed experiments focus on the smoothness, sparsity, and robustness properties of MoreauGrad interpretation maps as well as the feature maps of several standard baselines. In the following, we first describe the numerical setup in our experiments and then present the obtained numerical results on the qualitative and quantitative performance of interpretation methods." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.682, + 0.676, + 0.699 + ], + "angle": 0, + "content": "6.1. Experiment Setup" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.892, + 0.902 + ], + "angle": 0, + "content": "In our numerical evaluation, we use the following benchmark image datasets: CIFAR-10 [10] consisting of 60,000 labeled samples with 10 different labels, tiny-[ImageNet [12] containing 100,000 labels samples with 200 labels, and ImageNet-1K [3] including 1.4 million labeled samples with 1,000 labels. For CIFAR-10 and tiny-[ImageNet experiments, we trained a standard ResNet-18 [7] neural network with the softmax activation on the training set. For ImageNet experiments, we used an EfficientNet-b0 network [25] pre-trained on the ImageNet training data. In our experiments, we compared the MoreauGrad schemes with the following baselines: 1) the simple gradient [21], 2) Integrated Gradients [18], 3) DeepLIFT [20], 4) SmoothGrad" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2025" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.09, + 0.229, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.149, + 0.191, + 0.18, + 0.202 + ], + "angle": 0, + "content": "Input" + }, + { + "type": "image", + "bbox": [ + 0.232, + 0.091, + 0.36, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.277, + 0.191, + 0.312, + 0.202 + ], + "angle": 0, + "content": "\\(\\rho = 0\\)" + }, + { + "type": "image", + "bbox": [ + 0.364, + 0.092, + 0.492, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.402, + 0.191, + 0.448, + 0.202 + ], + "angle": 0, + "content": "\\(\\rho = 0.3\\)" + }, + { + "type": "image", + "bbox": [ + 0.495, + 0.092, + 0.623, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.54, + 0.191, + 0.575, + 0.202 + ], + "angle": 0, + "content": "\\(\\rho = 1\\)" + }, + { + "type": "image", + "bbox": [ + 0.626, + 0.092, + 0.753, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.668, + 0.191, + 0.704, + 0.202 + ], + "angle": 0, + "content": "\\(\\rho = 3\\)" + }, + { + "type": "image", + "bbox": [ + 0.757, + 0.092, + 0.885, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.799, + 0.191, + 0.842, + 0.202 + ], + "angle": 0, + "content": "\\(\\rho = 10\\)" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.204, + 0.228, + 0.302 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.149, + 0.304, + 0.18, + 0.316 + ], + "angle": 0, + "content": "Input" + }, + { + "type": "image", + "bbox": [ + 0.233, + 0.204, + 0.36, + 0.302 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.277, + 0.304, + 0.312, + 0.316 + ], + "angle": 0, + "content": "\\(\\eta = 0\\)" + }, + { + "type": "image", + "bbox": [ + 0.365, + 0.204, + 0.491, + 0.302 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.396, + 0.304, + 0.455, + 0.316 + ], + "angle": 0, + "content": "\\(\\eta = 0.001\\)" + }, + { + "type": "image", + "bbox": [ + 0.496, + 0.204, + 0.622, + 0.302 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.527, + 0.304, + 0.588, + 0.316 + ], + "angle": 0, + "content": "\\(\\eta = 0.005\\)" + }, + { + "type": "image", + "bbox": [ + 0.627, + 0.204, + 0.753, + 0.302 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.66, + 0.304, + 0.712, + 0.316 + ], + "angle": 0, + "content": "\\(\\eta = 0.01\\)" + }, + { + "type": "image", + "bbox": [ + 0.758, + 0.204, + 0.885, + 0.302 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.79, + 0.304, + 0.85, + 0.316 + ], + "angle": 0, + "content": "\\(\\eta = 0.015\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.321, + 0.892, + 0.35 + ], + "angle": 0, + "content": "Figure 2. Top: Visualization of MoreauGrad maps with different coefficient \\(\\rho\\)'s. \\(\\rho = 0\\) reduces to the simple gradient method. Bottom: Visualization of Sparse MoreauGrad maps with different coefficient \\(\\eta\\)'s. \\(\\eta = 0\\) reduces to the Vanilla MoreauGrad." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.363, + 0.291, + 0.519 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.296, + 0.363, + 0.489, + 0.519 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.495, + 0.363, + 0.688, + 0.519 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.695, + 0.363, + 0.888, + 0.519 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.106, + 0.526, + 0.856, + 0.541 + ], + "angle": 0, + "content": "Figure 3. MoreauGrad vs. SmoothGrad gradient discrepancy, measured via the \\(l_{2}\\)-norm distance from the simple gradient map." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.565, + 0.47, + 0.656 + ], + "angle": 0, + "content": "[22], 5) Sparsified SmoothGrad [13], 6) RelEx [14]. We note that for baseline experiments we adopted the official implementations and conducted the experiments with hyperparameters suggested in their work. We present the full implementation details in the Appendix, and our code is available in the supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.666, + 0.47, + 0.683 + ], + "angle": 0, + "content": "6.2. Effects of Smoothness and Sparsity Parameters" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.901 + ], + "angle": 0, + "content": "We ran the numerical experiments for unregularized Vanilla MoreauGrad with multiple smoothness coefficient \\(\\rho\\) values to show the effect of the Moreau envelope's regularization. Figure 2 visualizes the effect of different \\(\\rho\\) on the Vanilla MoreauGrad saliency map. As can be seen in this figure, the saliency map qualitatively improves by increasing the value of \\(\\rho\\) from 0 to 1. Please note that for \\(\\rho = 0\\), the MoreauGrad simplifies to the simple gradient interpretation. However, as shown in Theorem 1 the proper performance of Vanilla MoreauGrad requires choosing a properly bounded \\(\\rho\\) value, which is consistent with our observation that when \\(\\rho\\) becomes too large, the Moreau envelope will be computationally difficult to optimize and the quality of interpretation maps could deteriorate to some" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.565, + 0.892, + 0.648 + ], + "angle": 0, + "content": "extent. As numerically verified in both CIFAR-10, tinyImageNet, and ImageNet experiments, we used the rule of thumb \\(\\rho = \\frac{1}{\\sqrt{\\mathbb{E}[\\|\\mathbf{X}\\|_2]}}\\) measured over the empirical training data to set the value of \\(\\rho\\), which is equal to 1 for the normalized samples in our experiments." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.66, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Regarding the sparsity hyperparameter \\(\\eta\\) in Sparse and Group-Sparse MoreauGrad experiments, we ran several experimental tests to properly tune the hyperparameter. Note that a greater coefficient \\(\\eta\\) enforces more strict sparsity or group-sparsity in the MoreauGrad interpretation, and the degree of sparsity could be simply adjusted by changing this coefficient \\(\\eta\\). As shown in Figure 2, in our experiments with different \\(\\eta\\) coefficients the interpretation map becomes sparser as we increase the \\(L_{1}\\)-norm penalty coefficient \\(\\eta\\). Similarly, to achieve a group-sparse interpretation, we used \\(L_{2,1}\\)-regularization on groups of adjacent pixels as discussed in Definition 4. The effect of the group-sparsity coefficient was similar to the sparse case in our experiments, as fewer pixel groups took non-zero values and the output interpretations showed more structured interpretation maps when choosing a larger coefficient \\(\\eta\\). We defer the results on" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2026" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.096, + 0.096, + 0.19, + 0.169 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.096, + 0.17, + 0.189, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.097, + 0.247, + 0.19, + 0.319 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.096, + 0.322, + 0.19, + 0.396 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.128, + 0.405, + 0.159, + 0.417 + ], + "angle": 0, + "content": "Input" + }, + { + "type": "image", + "bbox": [ + 0.194, + 0.096, + 0.288, + 0.169 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.194, + 0.17, + 0.288, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.194, + 0.247, + 0.288, + 0.319 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.194, + 0.323, + 0.288, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.204, + 0.405, + 0.278, + 0.416 + ], + "angle": 0, + "content": "SmoothGrad" + }, + { + "type": "image", + "bbox": [ + 0.292, + 0.096, + 0.386, + 0.169 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.292, + 0.17, + 0.385, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.292, + 0.247, + 0.385, + 0.319 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.292, + 0.323, + 0.385, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.309, + 0.398, + 0.367, + 0.423 + ], + "angle": 0, + "content": "Integrated Gradients" + }, + { + "type": "image", + "bbox": [ + 0.389, + 0.096, + 0.483, + 0.169 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.39, + 0.17, + 0.484, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.39, + 0.247, + 0.484, + 0.319 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.389, + 0.323, + 0.484, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.402, + 0.398, + 0.475, + 0.422 + ], + "angle": 0, + "content": "Vanilla MoreauGrad" + }, + { + "type": "image", + "bbox": [ + 0.489, + 0.096, + 0.582, + 0.169 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.489, + 0.17, + 0.582, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.489, + 0.247, + 0.582, + 0.319 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.489, + 0.323, + 0.582, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.399, + 0.572, + 0.422 + ], + "angle": 0, + "content": "Sparsified SmoothGrad" + }, + { + "type": "image", + "bbox": [ + 0.586, + 0.096, + 0.68, + 0.169 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.586, + 0.17, + 0.68, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.586, + 0.247, + 0.68, + 0.319 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.586, + 0.323, + 0.68, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.615, + 0.405, + 0.651, + 0.417 + ], + "angle": 0, + "content": "RelEx" + }, + { + "type": "image", + "bbox": [ + 0.684, + 0.096, + 0.778, + 0.169 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.684, + 0.17, + 0.778, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.684, + 0.247, + 0.778, + 0.319 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.684, + 0.323, + 0.778, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.694, + 0.399, + 0.769, + 0.422 + ], + "angle": 0, + "content": "Group-Sparse MoreauGrad" + }, + { + "type": "image", + "bbox": [ + 0.782, + 0.096, + 0.877, + 0.169 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.782, + 0.17, + 0.877, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.782, + 0.247, + 0.877, + 0.319 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.782, + 0.323, + 0.877, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.792, + 0.399, + 0.866, + 0.422 + ], + "angle": 0, + "content": "Sparse MoreauGrad" + }, + { + "type": "image_caption", + "bbox": [ + 0.15, + 0.432, + 0.815, + 0.446 + ], + "angle": 0, + "content": "Figure 4. Qualitative comparison between Vanilla, Sparse, Group-Sparse MoreauGrad and the baseline methods." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.472, + 0.461, + 0.487 + ], + "angle": 0, + "content": "the group-sparsity hyperparameter effect to the Appendix." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.488, + 0.47, + 0.729 + ], + "angle": 0, + "content": "Moreover, to investigate the MoreauGrad's regularization effect, we measured the averaged \\(\\ell_2\\)-norm discrepancy between the MoreauGard and simple gradient maps for different smoothness parameter \\(\\rho\\)'s. As shown in Figure 3, the \\(\\ell_2\\)-norm discrepancy score grows smoothly with coefficient \\(\\rho\\). We also measured the averaged gradient discrepancy for SmoothGrad methods with different smoothness parameter \\(\\sigma\\)'s. We adjusted \\(\\eta\\) in Sparse MoreauGrad to standardize the sparsity level for fair comparisons with Sparsified SmoothGrad. As Figure 3 shows, SmoothGrad led to similar discrepancy values as in MoreauGrad. Also, Integrated Gradients [24] had a similar averaged gradient discrepancy of 0.34 for CIFAR-10 and 0.40 for ImageNet. As the results suggest, the baselines similarly deviate from the simple gradient maps, which could be linked to improved visual quality and robustness, as also observed by [22, 13]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.741, + 0.469, + 0.771 + ], + "angle": 0, + "content": "6.3. Qualitative Comparison of MoreauGrad vs. Standard Gradient-based Baselines" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.47, + 0.902 + ], + "angle": 0, + "content": "In Figure 4, we illustrate the Vanilla, Sparse, and Group-Sparse MoreauGrad interpretation outputs as well as the saliency maps generated by the gradient-based baselines. The results demonstrate that MoreauGrad generates qualitatively sharp and, in the case of Sparse and Group-Sparse MoreauGrad, sparse interpretation maps. As shown in Figure 4, promoting sparsity in the MoreauGrad interpretation maps has improved the visual quality, and managed to erase" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.471, + 0.892, + 0.517 + ], + "angle": 0, + "content": "the less relevant pixels like the background ones. Also, the Group-Sparse MoreauGrad maps successfully exhibit both sparsity and connectivity of selected pixels." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.524, + 0.805, + 0.54 + ], + "angle": 0, + "content": "6.4. Robustness of Interpretation Maps" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.547, + 0.892, + 0.653 + ], + "angle": 0, + "content": "We qualitatively and quantitatively evaluated the robustness of MoreauGrad interpretation. To assess the empirical robustness of interpretation methods, we adopt a \\(L_{2}\\)-bounded interpretation attack method defined by [13]. Also, for quantifying the empirical robustness, we adopt three robustness metrics. The first metric is the Euclidean distance of the normalized interpretations before and after the attack:" + }, + { + "type": "equation", + "bbox": [ + 0.549, + 0.665, + 0.892, + 0.699 + ], + "angle": 0, + "content": "\\[\nD \\left(I (\\mathbf {x}), I \\left(\\mathbf {x} ^ {\\prime}\\right)\\right) = \\left\\| \\frac {I (\\mathbf {x})}{\\| I (\\mathbf {x}) \\| _ {2}} - \\frac {I \\left(\\mathbf {x} ^ {\\prime}\\right)}{\\| I \\left(\\mathbf {x} ^ {\\prime}\\right) \\| _ {2}} \\right\\| _ {2} \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.892, + 0.749 + ], + "angle": 0, + "content": "Note that a larger distance between the normalized maps indicates a smaller similarity and a higher vulnerability of the interpretation method to adversarial attacks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.87 + ], + "angle": 0, + "content": "The second metric is the top-k intersection ratio. This metric is another standard robustness measure used in [6, 13]. This metric measures the ratio of pixels that remain salient after the interpretation attack. A robust interpretation is expected to preserve most of the salient pixels under an attack. The third metric is the structural similarity index measure (SSIM) [27]. A larger SSIM value indicates that the two input maps are more perceptively similar." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Using the above metrics, we compared the MoreauGrad schemes with the baseline methods. As qualitatively shown" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2027" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.097, + 0.092, + 0.878, + 0.319 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.108, + 0.332, + 0.856, + 0.347 + ], + "angle": 0, + "content": "Figure 5. Visualization of robustness against interpretation attacks. The top and bottom rows show original and attacked maps." + }, + { + "type": "image", + "bbox": [ + 0.092, + 0.363, + 0.878, + 0.832 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.226, + 0.844, + 0.739, + 0.858 + ], + "angle": 0, + "content": "Figure 6. Quantitative robustness comparison between MoreauGrad and the baselines." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.957 + ], + "angle": 0, + "content": "2028" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.091, + 0.177, + 0.236 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.116, + 0.241, + 0.147, + 0.253 + ], + "angle": 0, + "content": "Input" + }, + { + "type": "image", + "bbox": [ + 0.181, + 0.091, + 0.273, + 0.236 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.207, + 0.237, + 0.242, + 0.247 + ], + "angle": 0, + "content": "\\(\\eta = 0\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.186, + 0.248, + 0.265, + 0.259 + ], + "angle": 0, + "content": "MoreauGrad" + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.091, + 0.368, + 0.236 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.281, + 0.237, + 0.358, + 0.247 + ], + "angle": 0, + "content": "\\(\\eta = 1\\times 10^{-3}\\)" + }, + { + "type": "image", + "bbox": [ + 0.371, + 0.091, + 0.464, + 0.236 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.378, + 0.237, + 0.455, + 0.247 + ], + "angle": 0, + "content": "\\(\\eta = 5\\times 10^{-3}\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.307, + 0.248, + 0.43, + 0.26 + ], + "angle": 0, + "content": "Sparse MoreauGrad" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.264, + 0.468, + 0.292 + ], + "angle": 0, + "content": "Figure 7. Applications of vanilla and sparse MoreauGrad to explain two misclassifications on the ImageNet test set." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.305, + 0.468, + 0.456 + ], + "angle": 0, + "content": "in Figure 5, using the same attack magnitude, the MoreauGrad interpretations are mostly similar before and after the norm-bounded attack. The qualitative robustness of MoreauGrad seems satisfactory compared to the baseline methods. Finally, Figure 6 presents a quantitative comparison of the robustness measures for the baselines and proposed MoreauGrad on CIFAR-10, tiny ImageNet, and ImageNet datasets. As shown by these measures, MoreauGrad outperforms the baselines in terms of the discussed robustness metrics." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.465, + 0.449, + 0.482 + ], + "angle": 0, + "content": "6.5. Applications of MoreauGrad Interpretation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.485, + 0.468, + 0.697 + ], + "angle": 0, + "content": "As shown in Figure 2, MoreauGrad interpretation maps may be further refined to promote sparsity and retain only the salient pixels. The sparsity level could be flexibly adjusted via parameter \\(\\eta\\) in accordance with the target dataset. Moreover, both vanilla and sparse MoreauGrad can be employed for explaining DNN's misclassifications in image recognition tasks. Figure 7 presents two examples of such misclassifications, where \"gas pump\" and \"church\" are erroneously classified as \"tricycle\" and \"restaurant\", respectively. Sparse MoreauGrad identifies the source of these errors and relates them to the presence of \"a person in the middle of two wheels\" and \"people sitting on benches\", respectively. In the Appendix, we present other examples of using MoreauGrad for explaining DNNs' misclassification." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.71, + 0.195, + 0.725 + ], + "angle": 0, + "content": "7. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.468, + 0.901 + ], + "angle": 0, + "content": "In this work, we introduced MoreauGrad as an optimization-based interpretation method for deep neural networks. We demonstrated that MoreauGrad can be flexibly combined with \\( L_{1} \\)-regularization methods to output sparse and group-sparse interpretations. We further showed that the MoreauGrad output will enjoy robustness against input perturbations. While our analysis focuses on the sparsity and robustness of the MoreauGrad explanation, studying the consistency and transferability of MoreauGrad interpretations is an interesting future direction. Moreover, the application of MoreauGrad to convex and norm-regularized" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.138 + ], + "angle": 0, + "content": "neural nets could be another topic for future study. Finally, our analysis of \\(\\ell_1\\)-norm-based Moreau envelope could find independent applications in other deep learning contexts." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.149, + 0.659, + 0.166 + ], + "angle": 0, + "content": "Acknowledgments" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.175, + 0.892, + 0.266 + ], + "angle": 0, + "content": "This work was partially supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China, Project 14209920, and was partially supported by a CUHK Direct Research Grant. Also, the authors would like to thank the anonymous reviewers for their constructive feedback and suggestions." + }, + { + "type": "title", + "bbox": [ + 0.502, + 0.277, + 0.596, + 0.292 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.509, + 0.303, + 0.892, + 0.393 + ], + "angle": 0, + "content": "[1] Aditya Chattopadhy, Anirban Sarkar, Prantik Howlader, and Vineeth N Balasubramanian. Gradcam++: Generalized gradient-based visual explanations for deep convolutional networks. In 2018 IEEE winter conference on applications of computer vision (WACV), pages 839-847. IEEE, 2018. 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.51, + 0.396, + 0.892, + 0.442 + ], + "angle": 0, + "content": "[2] Piotr Dabkowski and Yarin Gal. Real time image saliency for black box classifiers. 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While several gradient-based interpretation schemes have been proposed to reveal the influential variables in a neural net's prediction, standard gradient-based interpretation frameworks have been commonly observed to lack robustness to input perturbations and flexibility for incorporating prior knowledge of sparsity and group-sparsity structures. In this work, we propose MoreauGrad as an interpretation scheme based on the classifier neural net's Moreau envelope. We demonstrate that MoreauGrad results in a smooth and robust interpretation of a multi-layer neural network and can be efficiently computed through first-order optimization methods. Furthermore, we show that MoreauGrad can be naturally combined with $L_{1}$ -norm regularization techniques to output a sparse or group-sparse explanation which are prior conditions applicable to a wide range of deep learning applications. We empirically evaluate the proposed MoreauGrad scheme on standard computer vision datasets, showing the qualitative and quantitative success of the MoreauGrad approach in comparison to standard gradient-based interpretation methods1. + +# 1. Introduction + +Deep neural networks (DNNs) have achieved state-of-the-art performance in many computer vision problems including image classification [11], object detection [29], and medical image analysis [19]. While they manage to attain super-human scores on standard image and speech recognition tasks, a reliable application of deep learning models to real-world problems requires an interpretation of their predictions to help domain experts understand and investigate the basis of their predictions. Over the past few years, developing and analyzing interpretation schemes that reveal + +Farzan Farnia +The Chinese University of Hong Kong +farnia@cse.cuhk.edu.hk + +![](images/fd2a911c589e2c0e855568f2937d08a457cc426946e088004289a3bfa0df39ff.jpg) +Figure 1. Interpretation of Sparse MoreauGrad (ours) vs. standard gradient-based baselines on an ImageNet sample before and after adding a norm-bounded interpretation adversarial attack. + +the influential features in a neural network's prediction have attracted great interest in the computer vision community. + +A standard approach for interpreting neural nets' predictions is to analyze the gradient of their prediction score function at or around an input data point. Such gradient-based interpretation mechanisms result in a feature saliency map revealing the influential variables that locally affect the neural net's assigned prediction score. Three well-known examples of gradient-based interpretation schemes are the simple gradient [21], integrated gradients [24], and + +DeepLIFT [20] methods. While the mentioned methods have found many applications in explaining neural nets' predictions, they have been observed to lack robustness to input perturbations and to output a dense noisy saliency map in their application to computer vision datasets [6, 8]. Consequently, these gradient-based explanations can be considerably altered by minor random or adversarial input noise. + +A widely-used approach to improve the robustness and sharpness of gradient-based interpretations is SmoothGrad [22] which applies Gaussian smoothing to the mentioned gradient-based interpretation methods. As shown by [22], SmoothGrad can significantly boost the visual quality of a neural net's gradient-based saliency map. On the other hand, SmoothGrad typically leads to a dense interpretation vector and remains inflexible to incorporate prior knowledge of sparsity and group-sparsity structures. Since a sparse saliency map is an applicable assumption to several image classification problems where a relatively small group of input variables can completely determine the image label, a counterpart of SmoothGrad which can simultaneously achieve sparse and robust interpretation will be of significant use in computer vision problems. + +In this paper, we propose a novel approach, which we call MoreauGrad, to achieve a provably smooth gradient-based interpretation with potential sparsity or group-sparsity properties. The proposed MoreauGrad outputs the gradient of a classifier's Moreau envelope which is a useful optimization tool for enforcing smoothness in a target function. We leverage convex analysis to show that MoreauGrad behaves smoothly around an input sample and therefore provides an alternative optimization-based approach to SmoothGrad for achieving a smoothly-changing saliency map. As a result, we demonstrate that similar to SmoothGrad, MoreauGrad offers robustness to input perturbations, since a norm-bounded perturbation will only lead to a bounded change to the MoreauGrad interpretation. + +Next, we show that MoreauGrad can be flexibly combined with $L_{1}$ -norm-based regularization penalties to output sparse and group-sparse interpretations. Our proposed combinations, Sparse MoreauGrad and Group-Sparse MoreauGrad, take advantage of elastic-net [31] and group-norm [16] penalty terms to enforce sparse and group-sparse saliency maps, respectively. We show that these extensions of MoreauGrad preserve the smoothness and robustness properties of the original MoreauGrad scheme. Therefore, our discussion demonstrates the adaptable nature of MoreauGrad for incorporating prior knowledge of sparsity structures in the output interpretation. + +Finally, we present the empirical results of our numerical experiments applying MoreauGrad to standard image recognition datasets and neural net architectures. We compare the numerical performance of MoreauGrad with standard gradient-based interpretation baselines. Our numeri + +cal results indicate the satisfactory performance of vanilla and $L_{1}$ -norm-based MoreauGrad in terms of visual quality and robustness. Figure 1 shows the robustness and sparsity of the Sparse MoreauGrad interpretation applied to an ImageNet sample in comparison to standard gradient-based saliency maps. As this and our other empirical findings suggest, MoreauGrad can outperform standard baselines in terms of the sparsity and robustness properties of the output interpretation. In the following, we summarize the main contributions of this paper: + +- Proposing MoreauGrad as an interpretation scheme based on a classifier function's Moreau envelope +- Analyzing the smoothness and robustness properties of MoreauGrad by leveraging convex analysis +- Introducing $L_{1}$ -regularized Sparse MoreauGrad to obtain an interpretation satisfying prior sparsity conditions +- Providing numerical results supporting MoreauGrad over standard image recognition datasets + +# 2. Related Work + +Gradient-based Interpretation. A large body of related works develop gradient-based interpretation methods. Simonyan et al. [21] propose to calculate the gradient of a classifier's output with respect to an input image. The simple gradient approach in [21] has been improved by several related works. Notably, the method of Integrated Gradients [24] is capable of keeping highly relevant pixels in the saliency map by aggregating gradients of image samples. SmoothGrad [22] removes noise in saliency maps by adding Gaussian-random noise to the input image. The CAM method [30] analyzes the information from global average pooling layer for localization, and Grad-CAM++ [1] improves over Grad-CAM [18] and generates coarse heatmaps with improved multi-object localization. The NormGrad [17] focuses on the weight-based gradient to analyze the contribution of each image region. DeepLIFT [20] uses difference from reference to propagate an attribution signal. However, the mentioned gradient-based methods do not obtain a sparse interpretation, and their proper combination with $L_{1}$ -regularization to promote sparsity remains highly non-trivial and challenging. On the other hand, our proposed MoreauGrad can be smoothly equipped with $L_{1}$ -regularization to output sparse interpretations and can further capture group-sparsity structures. + +Mask-based Interpretation. Mask-based interpretation methods rely on adversarial perturbations to interpret neural nets. Applying a mask which perturbs the neural net input, the importance of input pixels is measured by a masked-based method. This approach to explaining neural nets has been successfully applied in References [26, 5, 14, 2] and + +has been shown to benefit from dynamic perturbations [9]. More specifically, Dabkowski and Gal [2] introduce a real-time mask-based detection method; Fong and Vedaldi [5] develop a model-agnostic approach with interpretable perturbations; Wagner et al. [26] propose a method that could generate fine-grained visual interpretations. Moreover, Lim et al. [14] leverage local smoothness to enhance their robustness towards samples attacked by PGD [15]. However, [5] and [2] show that perturbation-based interpretation methods are still vulnerable to adversarial perturbations. + +We note that the discussed methods depend on optimizing perturbation masks for interpretations, and due to the non-convex nature of neural net loss functions, their interpretation remains sensitive to input perturbations. In contrast, our proposed MoreauGrad can provably smooth the neural net score function, and can adapt to non-convex functions using norm regularization. Hence, MoreauGrad can improve both the sparsity and robustness of the interpretation. + +Robust Interpretation. The robustness of interpretation methods has been a subject of great interest in the literature. Ghorbani et al. [6] introduce a gradient-based adversarial attack method to alter the neural nets' interpretation. Dombrowski et al. [4] demonstrate that interpretations could be manipulated, and they suggest improving the robustness via smoothing the neural net classifier. Heo et al. [8] propose a manipulation method that is capable of generalizing across datasets. Subramanya et al. [23] create adversarial patches fooling both the classifier and the interpretation. + +To improve the robustness, Sparsified-SmoothGrad [13] combines a sparsification technique with Gaussian smoothing to achieve certifiable robustness. The related works [26, 28, 5, 14, 2] discuss the application of adversarial defense methods against classification-based attacks to interpret the prediction of neural net classifiers. We note that these papers' main focus is not on defense schemes against interpretation-based attacks. Specifically, [26] filter gradients internally during backpropagation, and [14] leverage local smoothness to integrate more samples. Unlike the mentioned papers, our work proposes a model-agnostic optimization-based method which is capable of generating simultaneously sparse and robust interpretations. + +# 3. Preliminaries + +In this section, we review three standard interpretation methods as well as the notation and definitions in the paper. + +# 3.1. Notation and Definitions + +In the paper, we use notation $\mathbf{X} \in \mathbb{R}^d$ to denote the feature vector and $Y \in \{1, \dots, k\}$ to denote the label of a sample. In addition, $f_{\mathbf{w}}: \mathbb{R}^d \to \mathbb{R}^k$ denotes a neural net classifier with its weights contained in vector $\mathbf{w} \in \mathcal{W}$ where $\mathcal{W}$ is the feasible set of the neural net's weights. Here $f_{\mathbf{w}}$ maps + +the $d$ -dimensional input $\mathbf{x}$ to a $k$ -dimensional prediction vector containing the likelihood of each of the $k$ classes in the classification problem. For every class $c \in \{1, \dots, k\}$ , we use the notation $f_{\mathbf{w}, c}: \mathbb{R}^d \to \mathbb{R}$ to denote the $c$ -th entry of $f_{\mathbf{w}}$ 's output which corresponds to class $c$ . + +We use $\| \mathbf{x}\| _p$ to denote the $\ell_{p}$ -norm of input vector $\mathbf{x}$ . Furthermore, we use notation $\| \mathbf{x}\|_{p,q}$ to denote the $\ell_{p,q}$ group-norm of $\mathbf{x}$ defined in the following equation for given variable subsets $S_{1},\ldots ,S_{t}\subseteq \{1,\dots ,d\}$ : + +$$ +\left\| \mathbf {x} \right\| _ {p, q} = \left\| \left[ \| \mathbf {x} _ {S _ {1}} \| _ {p}, \dots , \| \mathbf {x} _ {S _ {t}} \| _ {p} \right] \right\| _ {q} \tag {1} +$$ + +In other words, $\| \mathbf{x}\|_{p,q}$ is the $\ell_p$ -norm of a vector containing the $\ell_p$ -norms of the subvectors of $\mathbf{x}$ characterized by index subsets $S_{1},\ldots ,S_{t}$ . + +# 3.2. Gradient-based Saliency Maps + +In our theoretical and numerical analysis, we consider the following widely-used gradient-based interpretation baselines which apply to a classifier neural net $f_{\mathbf{w}}$ and predicted class $c$ for input $\mathbf{x}$ : + +1. Simple Gradient: The simple gradient interpretation returns the saliency map of a neural net score function's gradient with respect to input $\mathbf{x}$ : + +$$ +\operatorname {S G} \left(f _ {\mathbf {w}, c}, \mathbf {x}\right) := \nabla_ {\mathbf {x}} f _ {\mathbf {w}, c} (\mathbf {x}). \tag {2} +$$ + +In the applications of the simple gradient approach, $c$ is commonly chosen as the neural net's predicted label with the maximum prediction score. + +2. Integrated Gradients: The integrated gradients approach approximates the integral of the neural net's gradient function between a reference point $\mathbf{x}^0$ and the input $\mathbf{x}$ . Using $m$ intermediate points on the line segment connecting $\mathbf{x}^0$ and $\mathbf{x}$ , the integrated gradient output will be + +$$ +\operatorname {I G} \left(f _ {\mathbf {w}, c}, \mathbf {x}\right) := \frac {\Delta \mathbf {x}}{m} \sum_ {i = 1} ^ {m} \nabla_ {\mathbf {x}} f _ {\mathbf {w}, c} \left(\mathbf {x} ^ {0} + \frac {i}{m} \Delta \mathbf {x}\right). \tag {3} +$$ + +In the above $\Delta \mathbf{x} \coloneqq \mathbf{x} - \mathbf{x}^0$ denotes the difference between the target and reference points $\mathbf{x}, \mathbf{x}^0$ . + +3. SmoothGrad: SmoothGrad considers the averaged simple gradient score over an additive random perturbation $Z$ drawn according to an isotropic Gaussian distribution $Z \sim \mathcal{N}(\mathbf{0}, \sigma^2 I_d)$ . In practice, the SmoothGrad interpretation is estimated over a number $t$ of independently drawn noise vectors $\mathbf{z}_1, \ldots, \mathbf{z}_t \stackrel{\mathrm{i.i.d.}}{\sim} \mathcal{N}(\mathbf{0}, \sigma^2 I_d)$ according to the zero-mean Gaussian distribution: + +$$ +\begin{array}{l} \operatorname {S m o o t h G r a d} \left(f _ {\mathbf {w}, c}, \mathbf {x}\right) := \mathbb {E} \left[ \nabla_ {\mathbf {x}} f _ {\mathbf {w}, c} (\mathbf {x} + Z) \right] \tag {4} \\ \approx \frac {1}{t} \sum_ {i = 1} ^ {t} \nabla_ {\mathbf {x}} f _ {\mathbf {w}, c} (\mathbf {x} + \mathbf {z} _ {i}). \\ \end{array} +$$ + +# 4. MoreauGrad: An Optimization-based Interpretation Framework + +As discussed earlier, smooth classifier functions with a Lipschitz gradient help to obtain a robust explanation of neural nets. Here, we propose an optimization-based smoothing approach based on Moreau-Yosida regularization. To introduce this optimization-based approach, we first define a function's Moreau envelope. + +Definition 1. Given regularization parameter $\rho >0$ , we define the Moreau envelope of a function $g:\mathbb{R}^d\to \mathbb{R}$ as: + +$$ +g ^ {\rho} (\mathbf {x}) := \min _ {\widetilde {\mathbf {x}} \in \mathbb {R} ^ {d}} g (\widetilde {\mathbf {x}}) + \frac {1}{2 \rho} \| \widetilde {\mathbf {x}} - \mathbf {x} \| _ {2} ^ {2}. \tag {5} +$$ + +In the above definition, $\rho > 0$ represents the Moreau-Yosida regularization coefficient. Applying the Moreau envelope, we propose the MoreauGrad interpretation as the gradient of the classifier's Moreau envelope at an input $\mathbf{x}$ . + +Definition 2. Given regularization parameter $\rho >0$ , we define the MoreauGrad interpretation $MG_{\rho}:\mathbb{R}^{d}\to \mathbb{R}^{d}$ of a neural net $f_{\mathbf{w}}$ predicting class $c$ for input $\mathbf{x}$ as + +$$ +M G _ {\rho} \left(f _ {\mathbf {w}, c}, \mathbf {x}\right) := \nabla f _ {\mathbf {w}, c} ^ {\rho} (\mathbf {x}). +$$ + +To compute and analyze the MoreauGrad explanation, we first discuss the optimization-based smoothing enforced by the Moreau envelope. Note that the Moreau envelope is known as an optimization tool to turn non-smooth convex functions (e.g. $\ell_1$ -norm) into smooth functions. Here, we discuss an extension of this result to weakly-convex functions which also apply to non-convex functions. + +Definition 3. A function $g: \mathbb{R}^d \to \mathbb{R}$ is called $\lambda$ -weakly convex if $\Phi(\mathbf{x}) := g(\mathbf{x}) + \frac{\lambda}{2} \| \mathbf{x} \|_2^2$ is a convex function, i.e. for every $\mathbf{x}_1, \mathbf{x}_2 \in \mathbb{R}^d$ and $0 \leq \alpha \leq 1$ we have: + +$$ +\begin{array}{l} g \left(\alpha \mathbf {x} _ {1} + (1 - \alpha) \mathbf {x} _ {2}\right) \leq \alpha g (\mathbf {x} _ {1}) + (1 - \alpha) g (\mathbf {x} _ {2}) \\ + \frac {\lambda \alpha (1 - \alpha)}{2} \| \mathbf {x} _ {1} - \mathbf {x} _ {2} \| _ {2} ^ {2}. \\ \end{array} +$$ + +Theorem 1. Suppose that $g: \mathbb{R}^d \to \mathbb{R}$ is a $\lambda$ -weakly convex function. Assuming that $0 < \rho < \frac{1}{\lambda}$ , the followings hold for the optimization problem of the Moreau envelope $g^\rho$ and the optimal solution $\widetilde{x}_\rho^*(\mathbf{x})$ solving the optimization problem: + +1. For every $\mathbf{x}$ , the gradient of $g^{\rho}$ and Clarke subdifferential of $g$ (denoted by $\partial_0 g$ ) are related as: + +$$ +\nabla g ^ {\rho} (\mathbf {x}) \in \partial_ {0} g \big (\widetilde {x} _ {\rho} ^ {*} (\mathbf {x}) \big), +$$ + +which implies that if $g$ is differentiable at $\widetilde{x}_{\rho}^{*}(\mathbf{x})$ we have $\nabla g^{\rho}(\mathbf{x}) = \nabla g(\widetilde{x}_{\rho}^{*}(\mathbf{x}))$ + +2. The difference $\widetilde{x}_{\rho}^{*}(\mathbf{x}) - \mathbf{x}$ is aligned with $g^{\rho}$ 's gradient: + +$$ +\nabla g ^ {\rho} (\mathbf {x}) = \frac {- 1}{\rho} \left(\widetilde {x} _ {\rho} ^ {*} (\mathbf {x}) - \mathbf {x}\right). +$$ + +3. $g^{\rho}$ will be $\max \left\{\frac{1}{\rho},\frac{\lambda}{1 - \rho\lambda}\right\}$ smooth, i.e. for every $\mathbf{x}_1,\mathbf{x}_2$ + +$$ +\left\| \nabla g ^ {\rho} (\mathbf {x} _ {1}) - \nabla g ^ {\rho} (\mathbf {x} _ {2}) \right\| _ {2} \leq \frac {1}{\min \left\{\rho , \frac {1}{\lambda} - \rho \right\}} \left\| \mathbf {x} _ {1} - \mathbf {x} _ {2} \right\| _ {2}. +$$ + +Proof. This result is well-known for convex functions. In the Appendix, we provide a new proof for the result. $\square$ + +Corollary 1. Assume that the prediction score function $f_{\mathbf{w},c}:\mathbb{R}^d\to \mathbb{R}$ is $\lambda$ -weakly convex. Then, the MoreauGrad interpretation $MG_{\rho}$ will remain robust under an $\epsilon -\ell_2$ -norm bounded perturbation $\| \delta \| _2\leq \epsilon$ as + +$$ +\left\| M G _ {\rho} (\mathbf {x} + \boldsymbol {\delta}) - M G _ {\rho} (\mathbf {x}) \right\| _ {2} \leq \frac {\epsilon}{\min \left\{\rho , \frac {1}{\lambda} - \rho \right\}}. +$$ + +The above results imply that by choosing a small enough coefficient $\rho$ the Moreau envelope will be a differentiable smooth function. Moreover, the computation of the Moreau envelope will reduce to a convex optimization task that can be solved by standard or accelerated gradient descent with global convergence guarantees. Therefore, one can efficiently compute the MoreauGrad interpretation by solving the optimization problem via the gradient descent algorithm. Algorithm 1 applies gradient descent to compute the solution to the Moreau envelope optimization which according to Theorem 1 yields the MoreauGrad explanation. + +As discussed above, MoreauGrad will be provably robust as long as the regularization coefficient will dominate the weakly-convexity degree of the prediction score. In the following proposition, we show this condition can be enforced by applying either Gaussian smoothing. + +Proposition 1. Suppose that $f_{\mathbf{w},c}$ is $L$ -Lipschitz, that is for every $\mathbf{x}_1,\mathbf{x}_2$ $|f_{\mathbf{w},c}(\mathbf{x}_1) - f_{\mathbf{w},c}(\mathbf{x}_2)| \leq L\| \mathbf{x}_2 - \mathbf{x}_1\|_2$ , but could be potentially non-differentiable and nonsmooth. Then, $h_{\mathbf{w},c}(\mathbf{x}) := \mathbb{E}[f_{\mathbf{w},c}(\mathbf{x} + \mathbf{Z})]$ where $\mathbf{Z} \sim \mathcal{N}(0,\sigma^2 I_{d\times d})$ will be $\frac{L}{\sigma}$ -weakly convex. + +Proof. We postpone the proof to the Appendix. + +The above proposition suggests the regularized Moreau-Grad which regularizes the neural net function to satisfy the weakly-convex condition through Gaussian smoothing. + +# 5. Sparse and Group-Sparse MoreauGrad + +To further extend the MoreauGrad approach to output sparsely-structured feature saliency maps, we further include an $L_{1}$ -norm-based penalty term in the Moreau-Yosida regularization and define the following $L_{1}$ -norm-based sparse and group-sparse Moreau envelope. + +Definition 4. For a function $g: \mathbb{R}^d \to \mathbb{R}$ and regularization coefficients $\rho, \eta > 0$ , we define $L_1$ -Moreau envelope $g_{L_1}^{\rho, \eta}$ : + +$$ +g _ {L _ {1}} ^ {\rho , \eta} (\mathbf {x}) := \min _ {\widetilde {\mathbf {x}} \in \mathbb {R} ^ {d}} g (\widetilde {\mathbf {x}}) + \frac {1}{2 \rho} \left\| \widetilde {\mathbf {x}} - \mathbf {x} \right\| _ {2} ^ {2} + \eta \left\| \widetilde {\mathbf {x}} - \mathbf {x} \right\| _ {1}. +$$ + +We also define $L_{2,1}$ -Moreau envelope $g_{L_{2,1}}^{\rho,\eta}$ as + +$$ +g _ {L _ {2, 1}} ^ {\rho , \eta} (\mathbf {x}) := \min _ {\widetilde {\mathbf {x}} \in \mathbb {R} ^ {d}} g (\widetilde {\mathbf {x}}) + \frac {1}{2 \rho} \left\| \widetilde {\mathbf {x}} - \mathbf {x} \right\| _ {2} ^ {2} + \eta \left\| \widetilde {\mathbf {x}} - \mathbf {x} \right\| _ {2, 1}. +$$ + +In the above, the group norm $\| \cdot \|_{2,1}$ is defined as $\| \mathbf{x} \|_{2,1} := \sum_{i=1}^{t} \| \mathbf{x}_{S_i} \|_2$ for given subsets $S_1, \ldots, S_t \subseteq \{1, \ldots, d\}$ . + +Definition 5. Given regularization coefficients $\rho, \eta > 0$ , we define the Sparse MoreauGrad ( $S-MG_{\rho,\eta}$ ) and Group-Sparse MoreauGrad ( $GS-MG_{\rho,\eta}$ ) interpretations as + +$$ +S - M G _ {\rho , \eta} \left(f _ {\mathbf {w}, c}, \mathbf {x}\right) := \frac {1}{\rho} \left(\widetilde {\mathbf {x}} _ {L _ {1}} ^ {*} (\mathbf {x}) - \mathbf {x}\right), +$$ + +$$ +G S - M G _ {\rho , \eta} \left(f _ {\mathbf {w}, c}, \mathbf {x}\right) := \frac {1}{\rho} \left(\widetilde {\mathbf {x}} _ {L _ {2, 1}} ^ {*} (\mathbf {x}) - \mathbf {x}\right), +$$ + +where $\widetilde{\mathbf{x}}_{L_1}^* (\mathbf{x})$ , $\widetilde{\mathbf{x}}_{L_{2,1}}^{*}(\mathbf{x})$ denote the optimal solutions to the optimization tasks of $f_{\mathbf{w},c,L_1}^{\rho ,\eta}(\mathbf{x})$ , $f_{\mathbf{w},c,L_{2,1}}^{\rho ,\eta}(\mathbf{x})$ , respectively. + +In the following theorem, we extend the shown results for the smoothness and robustness of vanilla Moreau envelope to our proposed $L_{1}$ -norm-based extensions of the Moreau envelope. In this theorem, we use the following definitions for the soft-thresholding operators $\mathrm{ST}_{\alpha}$ and $\mathrm{GST}_{\alpha}$ for the sparse and group-sparse cases which are defined entrywise and group-entrywise as follows + +$$ +\mathrm {S T} _ {\alpha} (\mathbf {x}) _ {i} := \left\{ \begin{array}{l l} 0 & \text {i f} | x _ {i} | \leq \alpha \\ x _ {i} - \operatorname {s i g n} (x _ {i}) \alpha & \text {i f} | x _ {i} | > \alpha , \end{array} \right. +$$ + +$$ +\mathrm {G S T} _ {\alpha} (\mathbf {x}) _ {S _ {i}} := \left\{ \begin{array}{l l} \mathbf {0} & \text {i f} \| \mathbf {x} _ {S _ {i}} \| _ {2} \leq \alpha \\ \big (1 - \frac {\alpha}{\| \mathbf {x} _ {S _ {i}} \| _ {2}} \big) \mathbf {x} _ {S _ {i}} & \text {i f} \| \mathbf {x} _ {S _ {i}} \| _ {2} > \alpha . \end{array} \right. +$$ + +Theorem 2. Suppose that $g:\mathbb{R}^d\to \mathbb{R}$ is a $\lambda$ -weakly convex function. Then, assuming that $0 < \rho < \frac{1}{\lambda}$ , Theorem 1's parts 1 and 3 will further hold for the sparse Moreau envelope $g_{L_1}^{\rho ,\eta}$ and group-sparse Moreau envelope $g_{L_{2,1}}^{\rho ,\eta}$ and their optimization problems' optimal solutions $\widetilde{\mathbf{x}}_{\rho ,\eta ,L_1}^* (\mathbf{x})$ and $\widetilde{\mathbf{x}}_{\rho ,\eta ,L_{2,1}}^{*}(\mathbf{x})$ . To parallel Theorem 1's part 2 for $L_{1}$ -Moreau envelope, the followings hold + +$$ +\mathrm {S T} _ {\rho \eta} \left(- \rho \nabla g _ {L _ {1}} ^ {\rho , \eta} (\mathbf {x})\right) = \widetilde {\mathbf {x}} _ {\rho , \eta , L _ {1}} ^ {*} (\mathbf {x}) - \mathbf {x}, +$$ + +$$ +\mathrm {G S T} _ {\rho \eta} \big (- \rho \nabla g _ {L _ {2, 1}} ^ {\rho , \eta} (\mathbf {x}) \big) = \widetilde {\mathbf {x}} _ {\rho , \eta , L _ {2, 1}} ^ {*} (\mathbf {x}) - \mathbf {x}. +$$ + +Proof. We defer the proof to the Appendix. + +Corollary 2. Suppose that the prediction score function $f_{\mathbf{w},c}$ is $\lambda$ -weakly convex. Assuming that $0 < \rho < \frac{1}{\lambda}$ , the Sparse MoreauGrad $S - MG_{\rho, \eta}$ and Group-Sparse MoreauGrad $GS - MG_{\rho, \eta}$ interpretations will be robust to every norm-bounded perturbation $\| \delta \|_2 \leq \epsilon$ as: + +$$ +\left\| S - M G _ {\rho , \eta} (\mathbf {x} + \boldsymbol {\delta}) - S - M G _ {\rho , \eta} (\mathbf {x}) \right\| _ {2} \leq \frac {\epsilon}{\min \left\{\rho , \frac {1}{\lambda} - \rho \right\}}, +$$ + +$$ +\left\| G S - M G _ {\rho , \eta} (\mathbf {x} + \boldsymbol {\delta}) - G S - M G _ {\rho , \eta} (\mathbf {x}) \right\| _ {2} \leq \frac {\epsilon}{\min \left\{\rho , \frac {1}{\lambda} - \rho \right\}}. +$$ + +Algorithm 1 MoreauGrad Interpretation + +Input: data x, label c, classifier $f_{\mathbf{w}}$ , regularization coeff. $\rho$ , stepsize $\gamma$ , noise std. parameter $\sigma$ , number of updates $T$ + +Initialize $\mathbf{x}^{(0)} = \mathbf{x}$ + +for $t = 0,\dots ,T$ do + +if Regularized Mode then + +$$ +\begin{array}{l} \textbf {D r a w n o i s e v e c t o r s z _ {1} , \ldots , z _ {m}} \sim \mathcal {N} (\mathbf {0}, \sigma^ {2} I _ {d \times d}) \\ \textbf {C o m p u t e g} _ {t} = \frac {1}{m} \sum_ {i = 1} ^ {m} \nabla f _ {\mathbf {w}, c} (\mathbf {x} ^ {(t)} + \mathbf {z} _ {i}) \end{array} +$$ + +else + +$$ +\mathbf {C o m p u t e} \mathbf {g} _ {t} = \nabla f _ {\mathbf {w}, c} (\mathbf {x} ^ {(t)}) +$$ + +end + +$$ +\mathbf {d a t e} \mathbf {x} ^ {(t + 1)} \leftarrow (1 - \frac {\gamma}{\rho}) \mathbf {x} ^ {(t)} - \gamma (\mathbf {g} _ {t} - \frac {1}{\rho} \mathbf {x}) +$$ + +if Sparse Mode then + +$$ +\mathbf {U p d a t e} \mathbf {x} ^ {(t + 1)} \leftarrow \text {S o f t T h r e s h o l d} _ {\gamma \eta} \left(\mathbf {x} ^ {(t + 1)} - \mathbf {x}\right) + \mathbf {x} +$$ + +end + +$$ +\operatorname {O u t p u t} \mathrm {M G} (\mathbf {x}) = \frac {1}{\rho} \left(\mathbf {x} ^ {(T)} - \mathbf {x}\right) +$$ + +Based on the above results, we propose applying the proximal gradient descent algorithm as described in Algorithm 1 to compute the Sparse and Group-Sparse Moreau-Grad. We defer discussing Algorithm 1's details to the Appendix. + +# 6. Numerical Results + +We conduct several numerical experiments to evaluate the performance of the proposed MoreauGrad. Our designed experiments focus on the smoothness, sparsity, and robustness properties of MoreauGrad interpretation maps as well as the feature maps of several standard baselines. In the following, we first describe the numerical setup in our experiments and then present the obtained numerical results on the qualitative and quantitative performance of interpretation methods. + +# 6.1. Experiment Setup + +In our numerical evaluation, we use the following benchmark image datasets: CIFAR-10 [10] consisting of 60,000 labeled samples with 10 different labels, tiny-[ImageNet [12] containing 100,000 labels samples with 200 labels, and ImageNet-1K [3] including 1.4 million labeled samples with 1,000 labels. For CIFAR-10 and tiny-[ImageNet experiments, we trained a standard ResNet-18 [7] neural network with the softmax activation on the training set. For ImageNet experiments, we used an EfficientNet-b0 network [25] pre-trained on the ImageNet training data. In our experiments, we compared the MoreauGrad schemes with the following baselines: 1) the simple gradient [21], 2) Integrated Gradients [18], 3) DeepLIFT [20], 4) SmoothGrad + +![](images/671c1d43917eaff991d7ed86bd7415cd1dff33c9797fea167da76d91dcc0436d.jpg) +Input + +![](images/c3e61302d4b5f31c9a26bba9a3e97d257fb78cedcf0b4a9b6bcd9b1c198f6049.jpg) +$\rho = 0$ + +![](images/975545aa5a22e2414b9762064fa3ef0205d7fdb4eb16b1fd641d28c829777cba.jpg) +$\rho = 0.3$ + +![](images/9378d08c7124d38f6bbf39e0ea78c981dc3491693bc0953b5ddcae35857e91bd.jpg) +$\rho = 1$ + +![](images/cd93fd6ef31ca1f01b8d56fe609c8bf2df1506214d47a63ae77272fa80d0a033.jpg) +$\rho = 3$ + +![](images/7cb196ba7cfdef7682fca46154e6d04755116050343fa0a37992a1a619e8b159.jpg) +$\rho = 10$ + +![](images/9d05aa541811591164a6d68f3d25fe01679869414f7cc667e431a40e2a204c27.jpg) +Input + +![](images/960ec559f4a8afd48a170a6107c58d5dcc7fea210ce3dccae6c4f1ea363900ab.jpg) +$\eta = 0$ + +![](images/df89d1dbcee3669e000f3a075a416a3688a14fad3eeb8d51b447e8fd74a64c76.jpg) +$\eta = 0.001$ + +![](images/decaeffb9009eeb64fe54b952a8125beaeaf0e0ecc4db3a3ae428f2aaeba9c2f.jpg) +$\eta = 0.005$ + +![](images/926ef20588d7daf749d7d9725530534ab390a7f3a3420e4af9dfc96fed1a811b.jpg) +$\eta = 0.01$ + +![](images/c5921d16ee8edc49580fb580be95bd2a7d42bb7fcad77cbb88e99aad280ed07f.jpg) +$\eta = 0.015$ + +![](images/a4fa8a36c0346426f936d6463665c79efec6f33941b58e247cd0095509e94339.jpg) +Figure 2. Top: Visualization of MoreauGrad maps with different coefficient $\rho$ 's. $\rho = 0$ reduces to the simple gradient method. Bottom: Visualization of Sparse MoreauGrad maps with different coefficient $\eta$ 's. $\eta = 0$ reduces to the Vanilla MoreauGrad. + +![](images/db61ca39a9d22e252d0a4b8bc7a6bd23005fc8123d0a523bb6833dd153e58b04.jpg) +Figure 3. MoreauGrad vs. SmoothGrad gradient discrepancy, measured via the $l_{2}$ -norm distance from the simple gradient map. + +![](images/1dafd875b6a4d2a8b3d6e9034ff92f193d9eec9d19e80d9c63b7d858baaf7bd5.jpg) + +![](images/5f644c271f3838aa3269e52ae1d3e3cc524cca29feb7e83f75e202993a02ef7c.jpg) + +[22], 5) Sparsified SmoothGrad [13], 6) RelEx [14]. We note that for baseline experiments we adopted the official implementations and conducted the experiments with hyperparameters suggested in their work. We present the full implementation details in the Appendix, and our code is available in the supplementary material. + +# 6.2. Effects of Smoothness and Sparsity Parameters + +We ran the numerical experiments for unregularized Vanilla MoreauGrad with multiple smoothness coefficient $\rho$ values to show the effect of the Moreau envelope's regularization. Figure 2 visualizes the effect of different $\rho$ on the Vanilla MoreauGrad saliency map. As can be seen in this figure, the saliency map qualitatively improves by increasing the value of $\rho$ from 0 to 1. Please note that for $\rho = 0$ , the MoreauGrad simplifies to the simple gradient interpretation. However, as shown in Theorem 1 the proper performance of Vanilla MoreauGrad requires choosing a properly bounded $\rho$ value, which is consistent with our observation that when $\rho$ becomes too large, the Moreau envelope will be computationally difficult to optimize and the quality of interpretation maps could deteriorate to some + +extent. As numerically verified in both CIFAR-10, tinyImageNet, and ImageNet experiments, we used the rule of thumb $\rho = \frac{1}{\sqrt{\mathbb{E}[\|\mathbf{X}\|_2]}}$ measured over the empirical training data to set the value of $\rho$ , which is equal to 1 for the normalized samples in our experiments. + +Regarding the sparsity hyperparameter $\eta$ in Sparse and Group-Sparse MoreauGrad experiments, we ran several experimental tests to properly tune the hyperparameter. Note that a greater coefficient $\eta$ enforces more strict sparsity or group-sparsity in the MoreauGrad interpretation, and the degree of sparsity could be simply adjusted by changing this coefficient $\eta$ . As shown in Figure 2, in our experiments with different $\eta$ coefficients the interpretation map becomes sparser as we increase the $L_{1}$ -norm penalty coefficient $\eta$ . Similarly, to achieve a group-sparse interpretation, we used $L_{2,1}$ -regularization on groups of adjacent pixels as discussed in Definition 4. The effect of the group-sparsity coefficient was similar to the sparse case in our experiments, as fewer pixel groups took non-zero values and the output interpretations showed more structured interpretation maps when choosing a larger coefficient $\eta$ . We defer the results on + +![](images/b2cbe87c06affa0be268735d40a1b75f3619a42318c270756a38b702bb739d52.jpg) + +![](images/7412015ca58d2301c785bd473e46fa705e224d18d6f16e8eeed3d367381fa239.jpg) + +![](images/8053e475ee353c8559f148b7948f40a7f7559606af7575c6e9139a4e8feec0a5.jpg) + +![](images/df169f8da00a64b6e4f712804309cfd9ffdeddd7df0e7d7a04e5e58930e96a69.jpg) +Input + +![](images/0611a7a983bbcc9c2ca583191626dfef36da19eebcdd95aaf84f4c5eb50b0a31.jpg) + +![](images/6941651e523c9774a57e27e61a8b072d987b908b4dd578c349e87cd81c4c5e30.jpg) + +![](images/910f3e3a70cf70ba50e80f07fc985924838d08df95218bbc9e947f56edbd250d.jpg) + +![](images/8c037620033396c42806ac44989bb2b1e4f91c101a393e1c9e34dbb31e40cfc4.jpg) +SmoothGrad + +![](images/6831a3ddd1ae9643dcb070b7d0ebef80f665f122381c9a3346bb3b58d98efa6a.jpg) + +![](images/76e66f3dabed9ddeb7479b61a76b38e8c0d71b4719a22268bcc7cf811a9cdcc3.jpg) + +![](images/86b94df34c13fd344b9ab575588cfcde180020d686e6f34ff8a19369e1c23f91.jpg) + +![](images/7a89027d4d6aa87097412dd86aaf7d39d73b2908a8d159d27a2375c1898c8653.jpg) +Integrated Gradients + +![](images/5f3028e08f999b90382c5c57edc6b97f92671ffd3b1cfc1eab7e2ed97a83f1bc.jpg) + +![](images/284764dfdd65e7824517935c995f20c0335114286f3296997c48406aa1716060.jpg) + +![](images/b2fdace16e61e1417c8988e299c4f08d2c1d404d2d9dc6f60356b96c346fbdf4.jpg) + +![](images/c7674bb26b93caa12b5a76d851093e0f84c1708283a8b651e38152195a857027.jpg) +Vanilla MoreauGrad + +![](images/3f9dc9090a32f1ca99102b0d574efd4ec7c70a7fa4171081c040f93e9c7c67b9.jpg) + +![](images/1e1f9e0677176717ad9f824406a1761b5e095408f2d79d5b39752f49b96ad677.jpg) + +![](images/a033f78c0f6b60eda958cbf97696197419fce3d6d3dd6824e04989248a983e38.jpg) + +![](images/669ba20dd2faf01f6431c045693acaec8a44130d90bec105c44595e7dcd25329.jpg) +Sparsified SmoothGrad +Figure 4. Qualitative comparison between Vanilla, Sparse, Group-Sparse MoreauGrad and the baseline methods. + +![](images/3f04fe0ac36f5f5db24fd8c13045d21692b07dc7b740eb1c3fa2697b1ea49c7f.jpg) + +![](images/9889e6da74a1eb0aae661f660ca70f3793b9449a91f6660c2cfeafef5fc5082c.jpg) + +![](images/2ae76aaa603108d86e8b885213742b76757cb6dee46c8fc72e6a27176beeab11.jpg) + +![](images/5975b09c1ab7abe166861b159b0bd70117b45b011ec5ee9c612f47d2ad61abe5.jpg) +RelEx + +![](images/a6c146c47a6c2ce3b2f1fcd6b339093ba052c946d138b89e9b9f0ea7fbe01bef.jpg) + +![](images/e4f0d510832c4431bd5c4f6736263a4cfb424fcf4e731a72fbd45ac47035c469.jpg) + +![](images/8ffd5a0262fd023f81f8c46b3a9de329f0dfb513138a9841ce3ad01e6a1f9933.jpg) + +![](images/2e1abda7db2b3fb1533a2bc26c6283f23f6ff0534338054751208007cfbf92d9.jpg) +Group-Sparse MoreauGrad + +![](images/95c1b90e13a23e21e3e95fbe97c03d99414afe42af3d303d6ba7d382109a8b45.jpg) + +![](images/b3ab53a0ef4d76dca8a200c7bd5de26a6addb6f6c7f3ad8a31a17cb560a788bb.jpg) + +![](images/d81d52e943bc696a15af0e0646c42299d6c151170377803d80157e82fa328cf8.jpg) + +![](images/c1f5127db324f779d7be44af5e347f325d2438ed8c31d6d3ec2acffcb2428f04.jpg) +Sparse MoreauGrad + +the group-sparsity hyperparameter effect to the Appendix. + +Moreover, to investigate the MoreauGrad's regularization effect, we measured the averaged $\ell_2$ -norm discrepancy between the MoreauGard and simple gradient maps for different smoothness parameter $\rho$ 's. As shown in Figure 3, the $\ell_2$ -norm discrepancy score grows smoothly with coefficient $\rho$ . We also measured the averaged gradient discrepancy for SmoothGrad methods with different smoothness parameter $\sigma$ 's. We adjusted $\eta$ in Sparse MoreauGrad to standardize the sparsity level for fair comparisons with Sparsified SmoothGrad. As Figure 3 shows, SmoothGrad led to similar discrepancy values as in MoreauGrad. Also, Integrated Gradients [24] had a similar averaged gradient discrepancy of 0.34 for CIFAR-10 and 0.40 for ImageNet. As the results suggest, the baselines similarly deviate from the simple gradient maps, which could be linked to improved visual quality and robustness, as also observed by [22, 13]. + +# 6.3. Qualitative Comparison of MoreauGrad vs. Standard Gradient-based Baselines + +In Figure 4, we illustrate the Vanilla, Sparse, and Group-Sparse MoreauGrad interpretation outputs as well as the saliency maps generated by the gradient-based baselines. The results demonstrate that MoreauGrad generates qualitatively sharp and, in the case of Sparse and Group-Sparse MoreauGrad, sparse interpretation maps. As shown in Figure 4, promoting sparsity in the MoreauGrad interpretation maps has improved the visual quality, and managed to erase + +the less relevant pixels like the background ones. Also, the Group-Sparse MoreauGrad maps successfully exhibit both sparsity and connectivity of selected pixels. + +# 6.4. Robustness of Interpretation Maps + +We qualitatively and quantitatively evaluated the robustness of MoreauGrad interpretation. To assess the empirical robustness of interpretation methods, we adopt a $L_{2}$ -bounded interpretation attack method defined by [13]. Also, for quantifying the empirical robustness, we adopt three robustness metrics. The first metric is the Euclidean distance of the normalized interpretations before and after the attack: + +$$ +D \left(I (\mathbf {x}), I \left(\mathbf {x} ^ {\prime}\right)\right) = \left\| \frac {I (\mathbf {x})}{\| I (\mathbf {x}) \| _ {2}} - \frac {I \left(\mathbf {x} ^ {\prime}\right)}{\| I \left(\mathbf {x} ^ {\prime}\right) \| _ {2}} \right\| _ {2} \tag {6} +$$ + +Note that a larger distance between the normalized maps indicates a smaller similarity and a higher vulnerability of the interpretation method to adversarial attacks. + +The second metric is the top-k intersection ratio. This metric is another standard robustness measure used in [6, 13]. This metric measures the ratio of pixels that remain salient after the interpretation attack. A robust interpretation is expected to preserve most of the salient pixels under an attack. The third metric is the structural similarity index measure (SSIM) [27]. A larger SSIM value indicates that the two input maps are more perceptively similar. + +Using the above metrics, we compared the MoreauGrad schemes with the baseline methods. As qualitatively shown + +![](images/81a2ea00f5fe6bd1a3d1777ee65c6bf92a87c399442ab2be2feba864633e5c99.jpg) +Figure 5. Visualization of robustness against interpretation attacks. The top and bottom rows show original and attacked maps. + +![](images/0a9f83b32d63679ba184421719bec217eaade9423b408ff9a30d1d764ccf4f5e.jpg) +Figure 6. Quantitative robustness comparison between MoreauGrad and the baselines. + +![](images/3a6111a1b1708e90d0be507fbafaad5c58e0529357db0bdc80d54d2c11917958.jpg) +Input + +![](images/c4e5fd4260d72c33c6b687501c09fd96e3f3cc6c2398d9e6651bd40eb57abbcd.jpg) +$\eta = 0$ +MoreauGrad + +![](images/2cbda9385ef5f5b3b650fc4ac36f2205979208681b741d3615f2580b14c3d3e4.jpg) +$\eta = 1\times 10^{-3}$ +Sparse MoreauGrad + +![](images/d152693cbc4cda9cada3c37ec6a011402f5a81e04e6e8a56b30980dd831b918e.jpg) +$\eta = 5\times 10^{-3}$ +Figure 7. Applications of vanilla and sparse MoreauGrad to explain two misclassifications on the ImageNet test set. + +in Figure 5, using the same attack magnitude, the MoreauGrad interpretations are mostly similar before and after the norm-bounded attack. The qualitative robustness of MoreauGrad seems satisfactory compared to the baseline methods. Finally, Figure 6 presents a quantitative comparison of the robustness measures for the baselines and proposed MoreauGrad on CIFAR-10, tiny ImageNet, and ImageNet datasets. As shown by these measures, MoreauGrad outperforms the baselines in terms of the discussed robustness metrics. + +# 6.5. Applications of MoreauGrad Interpretation + +As shown in Figure 2, MoreauGrad interpretation maps may be further refined to promote sparsity and retain only the salient pixels. The sparsity level could be flexibly adjusted via parameter $\eta$ in accordance with the target dataset. Moreover, both vanilla and sparse MoreauGrad can be employed for explaining DNN's misclassifications in image recognition tasks. Figure 7 presents two examples of such misclassifications, where "gas pump" and "church" are erroneously classified as "tricycle" and "restaurant", respectively. Sparse MoreauGrad identifies the source of these errors and relates them to the presence of "a person in the middle of two wheels" and "people sitting on benches", respectively. In the Appendix, we present other examples of using MoreauGrad for explaining DNNs' misclassification. + +# 7. Conclusion + +In this work, we introduced MoreauGrad as an optimization-based interpretation method for deep neural networks. We demonstrated that MoreauGrad can be flexibly combined with $L_{1}$ -regularization methods to output sparse and group-sparse interpretations. We further showed that the MoreauGrad output will enjoy robustness against input perturbations. While our analysis focuses on the sparsity and robustness of the MoreauGrad explanation, studying the consistency and transferability of MoreauGrad interpretations is an interesting future direction. Moreover, the application of MoreauGrad to convex and norm-regularized + +neural nets could be another topic for future study. Finally, our analysis of $\ell_1$ -norm-based Moreau envelope could find independent applications in other deep learning contexts. + +# Acknowledgments + +This work was partially supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China, Project 14209920, and was partially supported by a CUHK Direct Research Grant. Also, the authors would like to thank the anonymous reviewers for their constructive feedback and suggestions. + +# References + +[1] Aditya Chattopadhy, Anirban Sarkar, Prantik Howlader, and Vineeth N Balasubramanian. Gradcam++: Generalized gradient-based visual explanations for deep convolutional networks. In 2018 IEEE winter conference on applications of computer vision (WACV), pages 839-847. IEEE, 2018. 2 +[2] Piotr Dabkowski and Yarin Gal. Real time image saliency for black box classifiers. 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Journal of the royal statistical society: series B (statistical methodology), 67(2):301-320, 2005. 2 \ No newline at end of file diff --git a/2023/MoreauGrad_ Sparse and Robust Interpretation of Neural Networks via Moreau Envelope/images.zip b/2023/MoreauGrad_ Sparse and Robust Interpretation of Neural Networks via Moreau Envelope/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..c7cf17ff999fbd2b5e49891d5d83482170991bcc --- /dev/null +++ b/2023/MoreauGrad_ Sparse and Robust Interpretation of Neural Networks via Moreau Envelope/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:995401e3899ebb8592dadc42fb57034aee93abca7b22c034270e49950010140e +size 837221 diff --git a/2023/MoreauGrad_ Sparse and Robust Interpretation of Neural Networks via Moreau Envelope/layout.json b/2023/MoreauGrad_ Sparse and Robust Interpretation of Neural Networks via Moreau Envelope/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..e8aa333a40c124115c77b0ed7984151559b362a9 --- /dev/null +++ b/2023/MoreauGrad_ Sparse and Robust Interpretation of Neural Networks via Moreau Envelope/layout.json @@ -0,0 +1,13003 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 48, + 102, + 545, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 102, + 545, + 140 + ], + "spans": [ + { + "bbox": [ + 48, + 102, + 545, + 140 + ], + "type": "text", + "content": "MoreauGrad: Sparse and Robust Interpretation of Neural Networks via Moreau Envelope" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 95, + 162, + 282, + 203 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 95, + 162, + 282, + 203 + ], + "spans": [ + { + "bbox": [ + 95, + 162, + 282, + 203 + ], + "type": "text", + "content": "Jingwei Zhang \nThe Chinese University of Hong Kong \njwzhang22@cse.cuhk.edu.hk" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "spans": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 256, + 290, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 256, + 290, + 520 + ], + "spans": [ + { + "bbox": [ + 46, + 256, + 290, + 520 + ], + "type": "text", + "content": "Explaining the predictions of deep neural nets has been a topic of great interest in the computer vision literature. While several gradient-based interpretation schemes have been proposed to reveal the influential variables in a neural net's prediction, standard gradient-based interpretation frameworks have been commonly observed to lack robustness to input perturbations and flexibility for incorporating prior knowledge of sparsity and group-sparsity structures. In this work, we propose MoreauGrad as an interpretation scheme based on the classifier neural net's Moreau envelope. We demonstrate that MoreauGrad results in a smooth and robust interpretation of a multi-layer neural network and can be efficiently computed through first-order optimization methods. Furthermore, we show that MoreauGrad can be naturally combined with " + }, + { + "bbox": [ + 46, + 256, + 290, + 520 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 256, + 290, + 520 + ], + "type": "text", + "content": "-norm regularization techniques to output a sparse or group-sparse explanation which are prior conditions applicable to a wide range of deep learning applications. We empirically evaluate the proposed MoreauGrad scheme on standard computer vision datasets, showing the qualitative and quantitative success of the MoreauGrad approach in comparison to standard gradient-based interpretation methods1." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 544, + 128, + 555 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 544, + 128, + 555 + ], + "spans": [ + { + "bbox": [ + 47, + 544, + 128, + 555 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 564, + 287, + 684 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 564, + 287, + 684 + ], + "spans": [ + { + "bbox": [ + 46, + 564, + 287, + 684 + ], + "type": "text", + "content": "Deep neural networks (DNNs) have achieved state-of-the-art performance in many computer vision problems including image classification [11], object detection [29], and medical image analysis [19]. While they manage to attain super-human scores on standard image and speech recognition tasks, a reliable application of deep learning models to real-world problems requires an interpretation of their predictions to help domain experts understand and investigate the basis of their predictions. 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Interpretation of Sparse MoreauGrad (ours) vs. standard gradient-based baselines on an ImageNet sample before and after adding a norm-bounded interpretation adversarial attack." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 592, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 592, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 305, + 592, + 545, + 616 + ], + "type": "text", + "content": "the influential features in a neural network's prediction have attracted great interest in the computer vision community." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 617, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 546, + 714 + ], + "type": "text", + "content": "A standard approach for interpreting neural nets' predictions is to analyze the gradient of their prediction score function at or around an input data point. Such gradient-based interpretation mechanisms result in a feature saliency map revealing the influential variables that locally affect the neural net's assigned prediction score. Three well-known examples of gradient-based interpretation schemes are the simple gradient [21], integrated gradients [24], and" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 693, + 286, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 286, + 713 + ], + "type": "text", + "content": "1The paper's code is available at https://github.com/buyeh1109/MoreauGrad." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 295, + 748, + 314, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 758 + ], + "type": "text", + "content": "2021" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 156 + ], + "type": "text", + "content": "DeepLIFT [20] methods. While the mentioned methods have found many applications in explaining neural nets' predictions, they have been observed to lack robustness to input perturbations and to output a dense noisy saliency map in their application to computer vision datasets [6, 8]. Consequently, these gradient-based explanations can be considerably altered by minor random or adversarial input noise." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 158, + 288, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 158, + 288, + 337 + ], + "spans": [ + { + "bbox": [ + 46, + 158, + 288, + 337 + ], + "type": "text", + "content": "A widely-used approach to improve the robustness and sharpness of gradient-based interpretations is SmoothGrad [22] which applies Gaussian smoothing to the mentioned gradient-based interpretation methods. As shown by [22], SmoothGrad can significantly boost the visual quality of a neural net's gradient-based saliency map. On the other hand, SmoothGrad typically leads to a dense interpretation vector and remains inflexible to incorporate prior knowledge of sparsity and group-sparsity structures. Since a sparse saliency map is an applicable assumption to several image classification problems where a relatively small group of input variables can completely determine the image label, a counterpart of SmoothGrad which can simultaneously achieve sparse and robust interpretation will be of significant use in computer vision problems." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 339, + 287, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 339, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 339, + 287, + 506 + ], + "type": "text", + "content": "In this paper, we propose a novel approach, which we call MoreauGrad, to achieve a provably smooth gradient-based interpretation with potential sparsity or group-sparsity properties. The proposed MoreauGrad outputs the gradient of a classifier's Moreau envelope which is a useful optimization tool for enforcing smoothness in a target function. We leverage convex analysis to show that MoreauGrad behaves smoothly around an input sample and therefore provides an alternative optimization-based approach to SmoothGrad for achieving a smoothly-changing saliency map. As a result, we demonstrate that similar to SmoothGrad, MoreauGrad offers robustness to input perturbations, since a norm-bounded perturbation will only lead to a bounded change to the MoreauGrad interpretation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 508, + 287, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 508, + 287, + 652 + ], + "spans": [ + { + "bbox": [ + 46, + 508, + 287, + 652 + ], + "type": "text", + "content": "Next, we show that MoreauGrad can be flexibly combined with " + }, + { + "bbox": [ + 46, + 508, + 287, + 652 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 508, + 287, + 652 + ], + "type": "text", + "content": "-norm-based regularization penalties to output sparse and group-sparse interpretations. Our proposed combinations, Sparse MoreauGrad and Group-Sparse MoreauGrad, take advantage of elastic-net [31] and group-norm [16] penalty terms to enforce sparse and group-sparse saliency maps, respectively. We show that these extensions of MoreauGrad preserve the smoothness and robustness properties of the original MoreauGrad scheme. Therefore, our discussion demonstrates the adaptable nature of MoreauGrad for incorporating prior knowledge of sparsity structures in the output interpretation." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "Finally, we present the empirical results of our numerical experiments applying MoreauGrad to standard image recognition datasets and neural net architectures. We compare the numerical performance of MoreauGrad with standard gradient-based interpretation baselines. Our numeri" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 545, + 193 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 193 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 193 + ], + "type": "text", + "content": "cal results indicate the satisfactory performance of vanilla and " + }, + { + "bbox": [ + 304, + 72, + 545, + 193 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 304, + 72, + 545, + 193 + ], + "type": "text", + "content": "-norm-based MoreauGrad in terms of visual quality and robustness. Figure 1 shows the robustness and sparsity of the Sparse MoreauGrad interpretation applied to an ImageNet sample in comparison to standard gradient-based saliency maps. As this and our other empirical findings suggest, MoreauGrad can outperform standard baselines in terms of the sparsity and robustness properties of the output interpretation. In the following, we summarize the main contributions of this paper:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 202, + 545, + 323 + ], + "type": "list", + "angle": 0, + "index": 10, + "blocks": [ + { + "bbox": [ + 306, + 202, + 545, + 227 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 202, + 545, + 227 + ], + "spans": [ + { + "bbox": [ + 306, + 202, + 545, + 227 + ], + "type": "text", + "content": "- Proposing MoreauGrad as an interpretation scheme based on a classifier function's Moreau envelope" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 234, + 545, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 234, + 545, + 258 + ], + "spans": [ + { + "bbox": [ + 306, + 234, + 545, + 258 + ], + "type": "text", + "content": "- Analyzing the smoothness and robustness properties of MoreauGrad by leveraging convex analysis" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 266, + 545, + 291 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 266, + 545, + 291 + ], + "spans": [ + { + "bbox": [ + 306, + 266, + 545, + 291 + ], + "type": "text", + "content": "- Introducing " + }, + { + "bbox": [ + 306, + 266, + 545, + 291 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 306, + 266, + 545, + 291 + ], + "type": "text", + "content": "-regularized Sparse MoreauGrad to obtain an interpretation satisfying prior sparsity conditions" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 299, + 545, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 299, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 306, + 299, + 545, + 323 + ], + "type": "text", + "content": "- Providing numerical results supporting MoreauGrad over standard image recognition datasets" + } + ] + } + ], + "index": 9 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 334, + 392, + 346 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 334, + 392, + 346 + ], + "spans": [ + { + "bbox": [ + 306, + 334, + 392, + 346 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 354, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 354, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 354, + 545, + 641 + ], + "type": "text", + "content": "Gradient-based Interpretation. A large body of related works develop gradient-based interpretation methods. Simonyan et al. [21] propose to calculate the gradient of a classifier's output with respect to an input image. The simple gradient approach in [21] has been improved by several related works. Notably, the method of Integrated Gradients [24] is capable of keeping highly relevant pixels in the saliency map by aggregating gradients of image samples. SmoothGrad [22] removes noise in saliency maps by adding Gaussian-random noise to the input image. The CAM method [30] analyzes the information from global average pooling layer for localization, and Grad-CAM++ [1] improves over Grad-CAM [18] and generates coarse heatmaps with improved multi-object localization. The NormGrad [17] focuses on the weight-based gradient to analyze the contribution of each image region. DeepLIFT [20] uses difference from reference to propagate an attribution signal. However, the mentioned gradient-based methods do not obtain a sparse interpretation, and their proper combination with " + }, + { + "bbox": [ + 304, + 354, + 545, + 641 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 304, + 354, + 545, + 641 + ], + "type": "text", + "content": "-regularization to promote sparsity remains highly non-trivial and challenging. On the other hand, our proposed MoreauGrad can be smoothly equipped with " + }, + { + "bbox": [ + 304, + 354, + 545, + 641 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 304, + 354, + 545, + 641 + ], + "type": "text", + "content": "-regularization to output sparse interpretations and can further capture group-sparsity structures." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": "Mask-based Interpretation. Mask-based interpretation methods rely on adversarial perturbations to interpret neural nets. Applying a mask which perturbs the neural net input, the importance of input pixels is measured by a masked-based method. This approach to explaining neural nets has been successfully applied in References [26, 5, 14, 2] and" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2022" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 191 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 191 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 191 + ], + "type": "text", + "content": "has been shown to benefit from dynamic perturbations [9]. More specifically, Dabkowski and Gal [2] introduce a real-time mask-based detection method; Fong and Vedaldi [5] develop a model-agnostic approach with interpretable perturbations; Wagner et al. [26] propose a method that could generate fine-grained visual interpretations. Moreover, Lim et al. [14] leverage local smoothness to enhance their robustness towards samples attacked by PGD [15]. However, [5] and [2] show that perturbation-based interpretation methods are still vulnerable to adversarial perturbations." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 192, + 288, + 297 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 192, + 288, + 297 + ], + "spans": [ + { + "bbox": [ + 46, + 192, + 288, + 297 + ], + "type": "text", + "content": "We note that the discussed methods depend on optimizing perturbation masks for interpretations, and due to the non-convex nature of neural net loss functions, their interpretation remains sensitive to input perturbations. In contrast, our proposed MoreauGrad can provably smooth the neural net score function, and can adapt to non-convex functions using norm regularization. Hence, MoreauGrad can improve both the sparsity and robustness of the interpretation." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 300, + 287, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 300, + 287, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 300, + 287, + 418 + ], + "type": "text", + "content": "Robust Interpretation. The robustness of interpretation methods has been a subject of great interest in the literature. Ghorbani et al. [6] introduce a gradient-based adversarial attack method to alter the neural nets' interpretation. Dombrowski et al. [4] demonstrate that interpretations could be manipulated, and they suggest improving the robustness via smoothing the neural net classifier. Heo et al. [8] propose a manipulation method that is capable of generalizing across datasets. Subramanya et al. [23] create adversarial patches fooling both the classifier and the interpretation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 419, + 288, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 419, + 288, + 574 + ], + "spans": [ + { + "bbox": [ + 46, + 419, + 288, + 574 + ], + "type": "text", + "content": "To improve the robustness, Sparsified-SmoothGrad [13] combines a sparsification technique with Gaussian smoothing to achieve certifiable robustness. The related works [26, 28, 5, 14, 2] discuss the application of adversarial defense methods against classification-based attacks to interpret the prediction of neural net classifiers. We note that these papers' main focus is not on defense schemes against interpretation-based attacks. Specifically, [26] filter gradients internally during backpropagation, and [14] leverage local smoothness to integrate more samples. Unlike the mentioned papers, our work proposes a model-agnostic optimization-based method which is capable of generating simultaneously sparse and robust interpretations." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 584, + 132, + 596 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 584, + 132, + 596 + ], + "spans": [ + { + "bbox": [ + 47, + 584, + 132, + 596 + ], + "type": "text", + "content": "3. Preliminaries" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 605, + 287, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 605, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 47, + 605, + 287, + 628 + ], + "type": "text", + "content": "In this section, we review three standard interpretation methods as well as the notation and definitions in the paper." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 635, + 185, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 635, + 185, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 635, + 185, + 647 + ], + "type": "text", + "content": "3.1. Notation and Definitions" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "content": "In the paper, we use notation " + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{X} \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "content": " to denote the feature vector and " + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "inline_equation", + "content": "Y \\in \\{1, \\dots, k\\}" + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "content": " to denote the label of a sample. In addition, " + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{w}}: \\mathbb{R}^d \\to \\mathbb{R}^k" + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "content": " denotes a neural net classifier with its weights contained in vector " + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{w} \\in \\mathcal{W}" + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "content": " is the feasible set of the neural net's weights. Here " + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{w}}" + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "content": " maps" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "content": "the " + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "content": "-dimensional input " + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "content": " to a " + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "content": "-dimensional prediction vector containing the likelihood of each of the " + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "content": " classes in the classification problem. For every class " + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "inline_equation", + "content": "c \\in \\{1, \\dots, k\\}" + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "content": ", we use the notation " + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{w}, c}: \\mathbb{R}^d \\to \\mathbb{R}" + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "content": " to denote the " + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "content": "-th entry of " + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{w}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "content": "'s output which corresponds to class " + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 72, + 545, + 132 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "spans": [ + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "text", + "content": "We use " + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "inline_equation", + "content": "\\| \\mathbf{x}\\| _p" + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "text", + "content": " to denote the " + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "inline_equation", + "content": "\\ell_{p}" + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "text", + "content": " -norm of input vector " + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "text", + "content": ". Furthermore, we use notation " + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "inline_equation", + "content": "\\| \\mathbf{x}\\|_{p,q}" + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "text", + "content": " to denote the " + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "inline_equation", + "content": "\\ell_{p,q}" + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "text", + "content": " group-norm of " + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "text", + "content": " defined in the following equation for given variable subsets " + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "inline_equation", + "content": "S_{1},\\ldots ,S_{t}\\subseteq \\{1,\\dots ,d\\}" + }, + { + "bbox": [ + 304, + 133, + 545, + 180 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 350, + 186, + 545, + 203 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 186, + 545, + 203 + ], + "spans": [ + { + "bbox": [ + 350, + 186, + 545, + 203 + ], + "type": "interline_equation", + "content": "\\left\\| \\mathbf {x} \\right\\| _ {p, q} = \\left\\| \\left[ \\| \\mathbf {x} _ {S _ {1}} \\| _ {p}, \\dots , \\| \\mathbf {x} _ {S _ {t}} \\| _ {p} \\right] \\right\\| _ {q} \\tag {1}", + "image_path": "9752eaacf430bc68ce56d76413ee98a03333d882ed9cf8f829c12c1a13df2e72.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "spans": [ + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "type": "text", + "content": "In other words, " + }, + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "type": "inline_equation", + "content": "\\| \\mathbf{x}\\|_{p,q}" + }, + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "type": "inline_equation", + "content": "\\ell_p" + }, + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "type": "text", + "content": "-norm of a vector containing the " + }, + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "type": "inline_equation", + "content": "\\ell_p" + }, + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "type": "text", + "content": "-norms of the subvectors of " + }, + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "type": "text", + "content": " characterized by index subsets " + }, + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "type": "inline_equation", + "content": "S_{1},\\ldots ,S_{t}" + }, + { + "bbox": [ + 304, + 209, + 545, + 244 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 251, + 473, + 264 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 251, + 473, + 264 + ], + "spans": [ + { + "bbox": [ + 306, + 251, + 473, + 264 + ], + "type": "text", + "content": "3.2. Gradient-based Saliency Maps" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 270, + 545, + 318 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 270, + 545, + 318 + ], + "spans": [ + { + "bbox": [ + 304, + 270, + 545, + 318 + ], + "type": "text", + "content": "In our theoretical and numerical analysis, we consider the following widely-used gradient-based interpretation baselines which apply to a classifier neural net " + }, + { + "bbox": [ + 304, + 270, + 545, + 318 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{w}}" + }, + { + "bbox": [ + 304, + 270, + 545, + 318 + ], + "type": "text", + "content": " and predicted class " + }, + { + "bbox": [ + 304, + 270, + 545, + 318 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 270, + 545, + 318 + ], + "type": "text", + "content": " for input " + }, + { + "bbox": [ + 304, + 270, + 545, + 318 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 270, + 545, + 318 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 323, + 545, + 360 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 323, + 545, + 360 + ], + "spans": [ + { + "bbox": [ + 306, + 323, + 545, + 360 + ], + "type": "text", + "content": "1. Simple Gradient: The simple gradient interpretation returns the saliency map of a neural net score function's gradient with respect to input " + }, + { + "bbox": [ + 306, + 323, + 545, + 360 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 306, + 323, + 545, + 360 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 371, + 366, + 545, + 380 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 371, + 366, + 545, + 380 + ], + "spans": [ + { + "bbox": [ + 371, + 366, + 545, + 380 + ], + "type": "interline_equation", + "content": "\\operatorname {S G} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\nabla_ {\\mathbf {x}} f _ {\\mathbf {w}, c} (\\mathbf {x}). \\tag {2}", + "image_path": "b8b784364daaa0f8c51ecea9c589837d498e4ac164ea4642ee9b0e02d494044b.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 317, + 387, + 545, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 387, + 545, + 422 + ], + "spans": [ + { + "bbox": [ + 317, + 387, + 545, + 422 + ], + "type": "text", + "content": "In the applications of the simple gradient approach, " + }, + { + "bbox": [ + 317, + 387, + 545, + 422 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 317, + 387, + 545, + 422 + ], + "type": "text", + "content": " is commonly chosen as the neural net's predicted label with the maximum prediction score." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "spans": [ + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "type": "text", + "content": "2. Integrated Gradients: The integrated gradients approach approximates the integral of the neural net's gradient function between a reference point " + }, + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^0" + }, + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "type": "text", + "content": " and the input " + }, + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "type": "text", + "content": ". Using " + }, + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "type": "text", + "content": " intermediate points on the line segment connecting " + }, + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^0" + }, + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 306, + 429, + 545, + 489 + ], + "type": "text", + "content": ", the integrated gradient output will be" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 327, + 506, + 545, + 536 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 327, + 506, + 545, + 536 + ], + "spans": [ + { + "bbox": [ + 327, + 506, + 545, + 536 + ], + "type": "interline_equation", + "content": "\\operatorname {I G} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\frac {\\Delta \\mathbf {x}}{m} \\sum_ {i = 1} ^ {m} \\nabla_ {\\mathbf {x}} f _ {\\mathbf {w}, c} \\left(\\mathbf {x} ^ {0} + \\frac {i}{m} \\Delta \\mathbf {x}\\right). \\tag {3}", + "image_path": "2c291fc79337cdc92383965111da5ac94c04c0b8466aaf7a7df527fb41fd5d91.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 317, + 544, + 545, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 544, + 545, + 568 + ], + "spans": [ + { + "bbox": [ + 317, + 544, + 545, + 568 + ], + "type": "text", + "content": "In the above " + }, + { + "bbox": [ + 317, + 544, + 545, + 568 + ], + "type": "inline_equation", + "content": "\\Delta \\mathbf{x} \\coloneqq \\mathbf{x} - \\mathbf{x}^0" + }, + { + "bbox": [ + 317, + 544, + 545, + 568 + ], + "type": "text", + "content": " denotes the difference between the target and reference points " + }, + { + "bbox": [ + 317, + 544, + 545, + 568 + ], + "type": "inline_equation", + "content": "\\mathbf{x}, \\mathbf{x}^0" + }, + { + "bbox": [ + 317, + 544, + 545, + 568 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 574, + 545, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 574, + 545, + 661 + ], + "spans": [ + { + "bbox": [ + 306, + 574, + 545, + 661 + ], + "type": "text", + "content": "3. SmoothGrad: SmoothGrad considers the averaged simple gradient score over an additive random perturbation " + }, + { + "bbox": [ + 306, + 574, + 545, + 661 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 306, + 574, + 545, + 661 + ], + "type": "text", + "content": " drawn according to an isotropic Gaussian distribution " + }, + { + "bbox": [ + 306, + 574, + 545, + 661 + ], + "type": "inline_equation", + "content": "Z \\sim \\mathcal{N}(\\mathbf{0}, \\sigma^2 I_d)" + }, + { + "bbox": [ + 306, + 574, + 545, + 661 + ], + "type": "text", + "content": ". In practice, the SmoothGrad interpretation is estimated over a number " + }, + { + "bbox": [ + 306, + 574, + 545, + 661 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 306, + 574, + 545, + 661 + ], + "type": "text", + "content": " of independently drawn noise vectors " + }, + { + "bbox": [ + 306, + 574, + 545, + 661 + ], + "type": "inline_equation", + "content": "\\mathbf{z}_1, \\ldots, \\mathbf{z}_t \\stackrel{\\mathrm{i.i.d.}}{\\sim} \\mathcal{N}(\\mathbf{0}, \\sigma^2 I_d)" + }, + { + "bbox": [ + 306, + 574, + 545, + 661 + ], + "type": "text", + "content": " according to the zero-mean Gaussian distribution:" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 330, + 667, + 545, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 330, + 667, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 330, + 667, + 545, + 715 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\operatorname {S m o o t h G r a d} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\mathbb {E} \\left[ \\nabla_ {\\mathbf {x}} f _ {\\mathbf {w}, c} (\\mathbf {x} + Z) \\right] \\tag {4} \\\\ \\approx \\frac {1}{t} \\sum_ {i = 1} ^ {t} \\nabla_ {\\mathbf {x}} f _ {\\mathbf {w}, c} (\\mathbf {x} + \\mathbf {z} _ {i}). \\\\ \\end{array}", + "image_path": "1251d5e0c0f891a021ff408356613c1968f332d3afe3e3ea5cf0a67b8e965f51.jpg" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2023" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 287, + 99 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 287, + 99 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 287, + 99 + ], + "type": "text", + "content": "4. MoreauGrad: An Optimization-based Interpretation Framework" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 105, + 286, + 177 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 105, + 286, + 177 + ], + "spans": [ + { + "bbox": [ + 46, + 105, + 286, + 177 + ], + "type": "text", + "content": "As discussed earlier, smooth classifier functions with a Lipschitz gradient help to obtain a robust explanation of neural nets. Here, we propose an optimization-based smoothing approach based on Moreau-Yosida regularization. To introduce this optimization-based approach, we first define a function's Moreau envelope." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 182, + 286, + 207 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 182, + 286, + 207 + ], + "spans": [ + { + "bbox": [ + 47, + 182, + 286, + 207 + ], + "type": "text", + "content": "Definition 1. Given regularization parameter " + }, + { + "bbox": [ + 47, + 182, + 286, + 207 + ], + "type": "inline_equation", + "content": "\\rho >0" + }, + { + "bbox": [ + 47, + 182, + 286, + 207 + ], + "type": "text", + "content": ", we define the Moreau envelope of a function " + }, + { + "bbox": [ + 47, + 182, + 286, + 207 + ], + "type": "inline_equation", + "content": "g:\\mathbb{R}^d\\to \\mathbb{R}" + }, + { + "bbox": [ + 47, + 182, + 286, + 207 + ], + "type": "text", + "content": " as:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 87, + 213, + 287, + 237 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 87, + 213, + 287, + 237 + ], + "spans": [ + { + "bbox": [ + 87, + 213, + 287, + 237 + ], + "type": "interline_equation", + "content": "g ^ {\\rho} (\\mathbf {x}) := \\min _ {\\widetilde {\\mathbf {x}} \\in \\mathbb {R} ^ {d}} g (\\widetilde {\\mathbf {x}}) + \\frac {1}{2 \\rho} \\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\| _ {2} ^ {2}. \\tag {5}", + "image_path": "5cffb1dcbcccfafc2eebe237e130df640fc7aac51940cb99559e94e53f6dc8df.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 243, + 286, + 292 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 243, + 286, + 292 + ], + "spans": [ + { + "bbox": [ + 47, + 243, + 286, + 292 + ], + "type": "text", + "content": "In the above definition, " + }, + { + "bbox": [ + 47, + 243, + 286, + 292 + ], + "type": "inline_equation", + "content": "\\rho > 0" + }, + { + "bbox": [ + 47, + 243, + 286, + 292 + ], + "type": "text", + "content": " represents the Moreau-Yosida regularization coefficient. Applying the Moreau envelope, we propose the MoreauGrad interpretation as the gradient of the classifier's Moreau envelope at an input " + }, + { + "bbox": [ + 47, + 243, + 286, + 292 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 47, + 243, + 286, + 292 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "spans": [ + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "type": "text", + "content": "Definition 2. Given regularization parameter " + }, + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "type": "inline_equation", + "content": "\\rho >0" + }, + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "type": "text", + "content": ", we define the MoreauGrad interpretation " + }, + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "type": "inline_equation", + "content": "MG_{\\rho}:\\mathbb{R}^{d}\\to \\mathbb{R}^{d}" + }, + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "type": "text", + "content": " of a neural net " + }, + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{w}}" + }, + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "type": "text", + "content": " predicting class " + }, + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "type": "text", + "content": " for input " + }, + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 47, + 297, + 289, + 334 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 105, + 340, + 228, + 354 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 105, + 340, + 228, + 354 + ], + "spans": [ + { + "bbox": [ + 105, + 340, + 228, + 354 + ], + "type": "interline_equation", + "content": "M G _ {\\rho} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\nabla f _ {\\mathbf {w}, c} ^ {\\rho} (\\mathbf {x}).", + "image_path": "8f9a1a710a4e7d0c8f942a85100da45dcf198909bec41064a546e4264076eccd.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 360, + 286, + 444 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 360, + 286, + 444 + ], + "spans": [ + { + "bbox": [ + 46, + 360, + 286, + 444 + ], + "type": "text", + "content": "To compute and analyze the MoreauGrad explanation, we first discuss the optimization-based smoothing enforced by the Moreau envelope. Note that the Moreau envelope is known as an optimization tool to turn non-smooth convex functions (e.g. " + }, + { + "bbox": [ + 46, + 360, + 286, + 444 + ], + "type": "inline_equation", + "content": "\\ell_1" + }, + { + "bbox": [ + 46, + 360, + 286, + 444 + ], + "type": "text", + "content": "-norm) into smooth functions. Here, we discuss an extension of this result to weakly-convex functions which also apply to non-convex functions." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "spans": [ + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "type": "text", + "content": "Definition 3. A function " + }, + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "type": "inline_equation", + "content": "g: \\mathbb{R}^d \\to \\mathbb{R}" + }, + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "type": "text", + "content": " is called " + }, + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "type": "text", + "content": "-weakly convex if " + }, + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "type": "inline_equation", + "content": "\\Phi(\\mathbf{x}) := g(\\mathbf{x}) + \\frac{\\lambda}{2} \\| \\mathbf{x} \\|_2^2" + }, + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "type": "text", + "content": " is a convex function, i.e. for every " + }, + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_1, \\mathbf{x}_2 \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "type": "inline_equation", + "content": "0 \\leq \\alpha \\leq 1" + }, + { + "bbox": [ + 45, + 449, + 286, + 486 + ], + "type": "text", + "content": " we have:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 59, + 492, + 272, + 532 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 492, + 272, + 532 + ], + "spans": [ + { + "bbox": [ + 59, + 492, + 272, + 532 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} g \\left(\\alpha \\mathbf {x} _ {1} + (1 - \\alpha) \\mathbf {x} _ {2}\\right) \\leq \\alpha g (\\mathbf {x} _ {1}) + (1 - \\alpha) g (\\mathbf {x} _ {2}) \\\\ + \\frac {\\lambda \\alpha (1 - \\alpha)}{2} \\| \\mathbf {x} _ {1} - \\mathbf {x} _ {2} \\| _ {2} ^ {2}. \\\\ \\end{array}", + "image_path": "ad1c5b8c9fa5fae700014007a270abdae7df1af122d49fb923b5658838852301.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "spans": [ + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "type": "text", + "content": "Theorem 1. Suppose that " + }, + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "type": "inline_equation", + "content": "g: \\mathbb{R}^d \\to \\mathbb{R}" + }, + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "type": "text", + "content": " is a " + }, + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "type": "text", + "content": "-weakly convex function. Assuming that " + }, + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "type": "inline_equation", + "content": "0 < \\rho < \\frac{1}{\\lambda}" + }, + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "type": "text", + "content": ", the followings hold for the optimization problem of the Moreau envelope " + }, + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "type": "inline_equation", + "content": "g^\\rho" + }, + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "type": "text", + "content": " and the optimal solution " + }, + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "type": "inline_equation", + "content": "\\widetilde{x}_\\rho^*(\\mathbf{x})" + }, + { + "bbox": [ + 46, + 539, + 286, + 588 + ], + "type": "text", + "content": " solving the optimization problem:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 594, + 286, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 594, + 286, + 617 + ], + "spans": [ + { + "bbox": [ + 47, + 594, + 286, + 617 + ], + "type": "text", + "content": "1. For every " + }, + { + "bbox": [ + 47, + 594, + 286, + 617 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 47, + 594, + 286, + 617 + ], + "type": "text", + "content": ", the gradient of " + }, + { + "bbox": [ + 47, + 594, + 286, + 617 + ], + "type": "inline_equation", + "content": "g^{\\rho}" + }, + { + "bbox": [ + 47, + 594, + 286, + 617 + ], + "type": "text", + "content": " and Clarke subdifferential of " + }, + { + "bbox": [ + 47, + 594, + 286, + 617 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 47, + 594, + 286, + 617 + ], + "type": "text", + "content": " (denoted by " + }, + { + "bbox": [ + 47, + 594, + 286, + 617 + ], + "type": "inline_equation", + "content": "\\partial_0 g" + }, + { + "bbox": [ + 47, + 594, + 286, + 617 + ], + "type": "text", + "content": ") are related as:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 123, + 624, + 222, + 639 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 123, + 624, + 222, + 639 + ], + "spans": [ + { + "bbox": [ + 123, + 624, + 222, + 639 + ], + "type": "interline_equation", + "content": "\\nabla g ^ {\\rho} (\\mathbf {x}) \\in \\partial_ {0} g \\big (\\widetilde {x} _ {\\rho} ^ {*} (\\mathbf {x}) \\big),", + "image_path": "0119b05d467a9ed211d653c7a8c1a58e1bd61525448b9b0a814340c994478160.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 59, + 644, + 286, + 669 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 644, + 286, + 669 + ], + "spans": [ + { + "bbox": [ + 59, + 644, + 286, + 669 + ], + "type": "text", + "content": "which implies that if " + }, + { + "bbox": [ + 59, + 644, + 286, + 669 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 59, + 644, + 286, + 669 + ], + "type": "text", + "content": " is differentiable at " + }, + { + "bbox": [ + 59, + 644, + 286, + 669 + ], + "type": "inline_equation", + "content": "\\widetilde{x}_{\\rho}^{*}(\\mathbf{x})" + }, + { + "bbox": [ + 59, + 644, + 286, + 669 + ], + "type": "text", + "content": " we have " + }, + { + "bbox": [ + 59, + 644, + 286, + 669 + ], + "type": "inline_equation", + "content": "\\nabla g^{\\rho}(\\mathbf{x}) = \\nabla g(\\widetilde{x}_{\\rho}^{*}(\\mathbf{x}))" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 672, + 283, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 672, + 283, + 685 + ], + "spans": [ + { + "bbox": [ + 47, + 672, + 283, + 685 + ], + "type": "text", + "content": "2. The difference " + }, + { + "bbox": [ + 47, + 672, + 283, + 685 + ], + "type": "inline_equation", + "content": "\\widetilde{x}_{\\rho}^{*}(\\mathbf{x}) - \\mathbf{x}" + }, + { + "bbox": [ + 47, + 672, + 283, + 685 + ], + "type": "text", + "content": " is aligned with " + }, + { + "bbox": [ + 47, + 672, + 283, + 685 + ], + "type": "inline_equation", + "content": "g^{\\rho}" + }, + { + "bbox": [ + 47, + 672, + 283, + 685 + ], + "type": "text", + "content": "'s gradient:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 112, + 691, + 233, + 716 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 112, + 691, + 233, + 716 + ], + "spans": [ + { + "bbox": [ + 112, + 691, + 233, + 716 + ], + "type": "interline_equation", + "content": "\\nabla g ^ {\\rho} (\\mathbf {x}) = \\frac {- 1}{\\rho} \\left(\\widetilde {x} _ {\\rho} ^ {*} (\\mathbf {x}) - \\mathbf {x}\\right).", + "image_path": "cd5956a019062a85a2725bca9bf5cb183189024754fd0099a4b226b15740a1b4.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 71, + 542, + 87 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 71, + 542, + 87 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 542, + 87 + ], + "type": "text", + "content": "3. " + }, + { + "bbox": [ + 306, + 71, + 542, + 87 + ], + "type": "inline_equation", + "content": "g^{\\rho}" + }, + { + "bbox": [ + 306, + 71, + 542, + 87 + ], + "type": "text", + "content": " will be " + }, + { + "bbox": [ + 306, + 71, + 542, + 87 + ], + "type": "inline_equation", + "content": "\\max \\left\\{\\frac{1}{\\rho},\\frac{\\lambda}{1 - \\rho\\lambda}\\right\\}" + }, + { + "bbox": [ + 306, + 71, + 542, + 87 + ], + "type": "text", + "content": " smooth, i.e. for every " + }, + { + "bbox": [ + 306, + 71, + 542, + 87 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_1,\\mathbf{x}_2" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 318, + 93, + 544, + 119 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 93, + 544, + 119 + ], + "spans": [ + { + "bbox": [ + 318, + 93, + 544, + 119 + ], + "type": "interline_equation", + "content": "\\left\\| \\nabla g ^ {\\rho} (\\mathbf {x} _ {1}) - \\nabla g ^ {\\rho} (\\mathbf {x} _ {2}) \\right\\| _ {2} \\leq \\frac {1}{\\min \\left\\{\\rho , \\frac {1}{\\lambda} - \\rho \\right\\}} \\left\\| \\mathbf {x} _ {1} - \\mathbf {x} _ {2} \\right\\| _ {2}.", + "image_path": "a88cf3ca2964ef595a149eb3f052b9ba6d09dd77fe89bd626fa4f14acf372d45.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 129, + 545, + 153 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 129, + 545, + 153 + ], + "spans": [ + { + "bbox": [ + 305, + 129, + 545, + 153 + ], + "type": "text", + "content": "Proof. This result is well-known for convex functions. In the Appendix, we provide a new proof for the result. " + }, + { + "bbox": [ + 305, + 129, + 545, + 153 + ], + "type": "inline_equation", + "content": "\\square" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "spans": [ + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "type": "text", + "content": "Corollary 1. Assume that the prediction score function " + }, + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{w},c}:\\mathbb{R}^d\\to \\mathbb{R}" + }, + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "type": "text", + "content": "-weakly convex. Then, the MoreauGrad interpretation " + }, + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "type": "inline_equation", + "content": "MG_{\\rho}" + }, + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "type": "text", + "content": " will remain robust under an " + }, + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "type": "inline_equation", + "content": "\\epsilon -\\ell_2" + }, + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "type": "text", + "content": "-norm bounded perturbation " + }, + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "type": "inline_equation", + "content": "\\| \\delta \\| _2\\leq \\epsilon" + }, + { + "bbox": [ + 305, + 160, + 545, + 209 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 327, + 215, + 523, + 239 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 327, + 215, + 523, + 239 + ], + "spans": [ + { + "bbox": [ + 327, + 215, + 523, + 239 + ], + "type": "interline_equation", + "content": "\\left\\| M G _ {\\rho} (\\mathbf {x} + \\boldsymbol {\\delta}) - M G _ {\\rho} (\\mathbf {x}) \\right\\| _ {2} \\leq \\frac {\\epsilon}{\\min \\left\\{\\rho , \\frac {1}{\\lambda} - \\rho \\right\\}}.", + "image_path": "ecb481815d73150a46b47da360875c8043224a5892590b95ab3e0df57b0e62db.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 245, + 545, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 245, + 545, + 376 + ], + "spans": [ + { + "bbox": [ + 304, + 245, + 545, + 376 + ], + "type": "text", + "content": "The above results imply that by choosing a small enough coefficient " + }, + { + "bbox": [ + 304, + 245, + 545, + 376 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 304, + 245, + 545, + 376 + ], + "type": "text", + "content": " the Moreau envelope will be a differentiable smooth function. Moreover, the computation of the Moreau envelope will reduce to a convex optimization task that can be solved by standard or accelerated gradient descent with global convergence guarantees. Therefore, one can efficiently compute the MoreauGrad interpretation by solving the optimization problem via the gradient descent algorithm. Algorithm 1 applies gradient descent to compute the solution to the Moreau envelope optimization which according to Theorem 1 yields the MoreauGrad explanation." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 376, + 545, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 376, + 545, + 437 + ], + "spans": [ + { + "bbox": [ + 304, + 376, + 545, + 437 + ], + "type": "text", + "content": "As discussed above, MoreauGrad will be provably robust as long as the regularization coefficient will dominate the weakly-convexity degree of the prediction score. In the following proposition, we show this condition can be enforced by applying either Gaussian smoothing." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "spans": [ + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "text", + "content": "Proposition 1. Suppose that " + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{w},c}" + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "text", + "content": "-Lipschitz, that is for every " + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_1,\\mathbf{x}_2" + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "inline_equation", + "content": "|f_{\\mathbf{w},c}(\\mathbf{x}_1) - f_{\\mathbf{w},c}(\\mathbf{x}_2)| \\leq L\\| \\mathbf{x}_2 - \\mathbf{x}_1\\|_2" + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "text", + "content": ", but could be potentially non-differentiable and nonsmooth. Then, " + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "inline_equation", + "content": "h_{\\mathbf{w},c}(\\mathbf{x}) := \\mathbb{E}[f_{\\mathbf{w},c}(\\mathbf{x} + \\mathbf{Z})]" + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "inline_equation", + "content": "\\mathbf{Z} \\sim \\mathcal{N}(0,\\sigma^2 I_{d\\times d})" + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "text", + "content": " will be " + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "inline_equation", + "content": "\\frac{L}{\\sigma}" + }, + { + "bbox": [ + 305, + 442, + 545, + 503 + ], + "type": "text", + "content": "-weakly convex." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 508, + 545, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 508, + 545, + 520 + ], + "spans": [ + { + "bbox": [ + 306, + 508, + 545, + 520 + ], + "type": "text", + "content": "Proof. We postpone the proof to the Appendix." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 528, + 545, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 528, + 545, + 564 + ], + "spans": [ + { + "bbox": [ + 304, + 528, + 545, + 564 + ], + "type": "text", + "content": "The above proposition suggests the regularized Moreau-Grad which regularizes the neural net function to satisfy the weakly-convex condition through Gaussian smoothing." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 306, + 574, + 523, + 588 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 574, + 523, + 588 + ], + "spans": [ + { + "bbox": [ + 306, + 574, + 523, + 588 + ], + "type": "text", + "content": "5. Sparse and Group-Sparse MoreauGrad" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 594, + 545, + 654 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 654 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 654 + ], + "type": "text", + "content": "To further extend the MoreauGrad approach to output sparsely-structured feature saliency maps, we further include an " + }, + { + "bbox": [ + 304, + 594, + 545, + 654 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 304, + 594, + 545, + 654 + ], + "type": "text", + "content": "-norm-based penalty term in the Moreau-Yosida regularization and define the following " + }, + { + "bbox": [ + 304, + 594, + 545, + 654 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 304, + 594, + 545, + 654 + ], + "type": "text", + "content": "-norm-based sparse and group-sparse Moreau envelope." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 305, + 659, + 545, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 659, + 545, + 685 + ], + "spans": [ + { + "bbox": [ + 305, + 659, + 545, + 685 + ], + "type": "text", + "content": "Definition 4. For a function " + }, + { + "bbox": [ + 305, + 659, + 545, + 685 + ], + "type": "inline_equation", + "content": "g: \\mathbb{R}^d \\to \\mathbb{R}" + }, + { + "bbox": [ + 305, + 659, + 545, + 685 + ], + "type": "text", + "content": " and regularization coefficients " + }, + { + "bbox": [ + 305, + 659, + 545, + 685 + ], + "type": "inline_equation", + "content": "\\rho, \\eta > 0" + }, + { + "bbox": [ + 305, + 659, + 545, + 685 + ], + "type": "text", + "content": ", we define " + }, + { + "bbox": [ + 305, + 659, + 545, + 685 + ], + "type": "inline_equation", + "content": "L_1" + }, + { + "bbox": [ + 305, + 659, + 545, + 685 + ], + "type": "text", + "content": "-Moreau envelope " + }, + { + "bbox": [ + 305, + 659, + 545, + 685 + ], + "type": "inline_equation", + "content": "g_{L_1}^{\\rho, \\eta}" + }, + { + "bbox": [ + 305, + 659, + 545, + 685 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 315, + 692, + 534, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 692, + 534, + 715 + ], + "spans": [ + { + "bbox": [ + 315, + 692, + 534, + 715 + ], + "type": "interline_equation", + "content": "g _ {L _ {1}} ^ {\\rho , \\eta} (\\mathbf {x}) := \\min _ {\\widetilde {\\mathbf {x}} \\in \\mathbb {R} ^ {d}} g (\\widetilde {\\mathbf {x}}) + \\frac {1}{2 \\rho} \\left\\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\right\\| _ {2} ^ {2} + \\eta \\left\\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\right\\| _ {1}.", + "image_path": "a4af505bba169628e956e6a637b9b31a022495cbd8d69c0f562097dc265fe7a8.jpg" + } + ] + } + ], + "index": 29 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2024" + } + ] + } + ], + "index": 30 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 235, + 87 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 235, + 87 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 235, + 87 + ], + "type": "text", + "content": "We also define " + }, + { + "bbox": [ + 47, + 72, + 235, + 87 + ], + "type": "inline_equation", + "content": "L_{2,1}" + }, + { + "bbox": [ + 47, + 72, + 235, + 87 + ], + "type": "text", + "content": "-Moreau envelope " + }, + { + "bbox": [ + 47, + 72, + 235, + 87 + ], + "type": "inline_equation", + "content": "g_{L_{2,1}}^{\\rho,\\eta}" + }, + { + "bbox": [ + 47, + 72, + 235, + 87 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 51, + 93, + 282, + 118 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 51, + 93, + 282, + 118 + ], + "spans": [ + { + "bbox": [ + 51, + 93, + 282, + 118 + ], + "type": "interline_equation", + "content": "g _ {L _ {2, 1}} ^ {\\rho , \\eta} (\\mathbf {x}) := \\min _ {\\widetilde {\\mathbf {x}} \\in \\mathbb {R} ^ {d}} g (\\widetilde {\\mathbf {x}}) + \\frac {1}{2 \\rho} \\left\\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\right\\| _ {2} ^ {2} + \\eta \\left\\| \\widetilde {\\mathbf {x}} - \\mathbf {x} \\right\\| _ {2, 1}.", + "image_path": "cbfba3a93f9d4e5f8a7180ff614e7cbff7ed3abf583f7a2eb727b8b82407dfeb.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 124, + 287, + 151 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 124, + 287, + 151 + ], + "spans": [ + { + "bbox": [ + 47, + 124, + 287, + 151 + ], + "type": "text", + "content": "In the above, the group norm " + }, + { + "bbox": [ + 47, + 124, + 287, + 151 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\|_{2,1}" + }, + { + "bbox": [ + 47, + 124, + 287, + 151 + ], + "type": "text", + "content": " is defined as " + }, + { + "bbox": [ + 47, + 124, + 287, + 151 + ], + "type": "inline_equation", + "content": "\\| \\mathbf{x} \\|_{2,1} := \\sum_{i=1}^{t} \\| \\mathbf{x}_{S_i} \\|_2" + }, + { + "bbox": [ + 47, + 124, + 287, + 151 + ], + "type": "text", + "content": " for given subsets " + }, + { + "bbox": [ + 47, + 124, + 287, + 151 + ], + "type": "inline_equation", + "content": "S_1, \\ldots, S_t \\subseteq \\{1, \\ldots, d\\}" + }, + { + "bbox": [ + 47, + 124, + 287, + 151 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 156, + 287, + 194 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 156, + 287, + 194 + ], + "spans": [ + { + "bbox": [ + 47, + 156, + 287, + 194 + ], + "type": "text", + "content": "Definition 5. Given regularization coefficients " + }, + { + "bbox": [ + 47, + 156, + 287, + 194 + ], + "type": "inline_equation", + "content": "\\rho, \\eta > 0" + }, + { + "bbox": [ + 47, + 156, + 287, + 194 + ], + "type": "text", + "content": ", we define the Sparse MoreauGrad (" + }, + { + "bbox": [ + 47, + 156, + 287, + 194 + ], + "type": "inline_equation", + "content": "S-MG_{\\rho,\\eta}" + }, + { + "bbox": [ + 47, + 156, + 287, + 194 + ], + "type": "text", + "content": ") and Group-Sparse MoreauGrad (" + }, + { + "bbox": [ + 47, + 156, + 287, + 194 + ], + "type": "inline_equation", + "content": "GS-MG_{\\rho,\\eta}" + }, + { + "bbox": [ + 47, + 156, + 287, + 194 + ], + "type": "text", + "content": ") interpretations as" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 89, + 198, + 252, + 223 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 89, + 198, + 252, + 223 + ], + "spans": [ + { + "bbox": [ + 89, + 198, + 252, + 223 + ], + "type": "interline_equation", + "content": "S - M G _ {\\rho , \\eta} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\frac {1}{\\rho} \\left(\\widetilde {\\mathbf {x}} _ {L _ {1}} ^ {*} (\\mathbf {x}) - \\mathbf {x}\\right),", + "image_path": "8c8af47d7c6b9de06557ef6df0061a342bba1c703d3419e4ca8e408f86f82f29.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 83, + 224, + 257, + 249 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 224, + 257, + 249 + ], + "spans": [ + { + "bbox": [ + 83, + 224, + 257, + 249 + ], + "type": "interline_equation", + "content": "G S - M G _ {\\rho , \\eta} \\left(f _ {\\mathbf {w}, c}, \\mathbf {x}\\right) := \\frac {1}{\\rho} \\left(\\widetilde {\\mathbf {x}} _ {L _ {2, 1}} ^ {*} (\\mathbf {x}) - \\mathbf {x}\\right),", + "image_path": "6f711ac9ce4db0344b5ec2e5b6589ef17a22855821574cd3c38655e26120d417.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 255, + 287, + 284 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 255, + 287, + 284 + ], + "spans": [ + { + "bbox": [ + 47, + 255, + 287, + 284 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 255, + 287, + 284 + ], + "type": "inline_equation", + "content": "\\widetilde{\\mathbf{x}}_{L_1}^* (\\mathbf{x})" + }, + { + "bbox": [ + 47, + 255, + 287, + 284 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 255, + 287, + 284 + ], + "type": "inline_equation", + "content": "\\widetilde{\\mathbf{x}}_{L_{2,1}}^{*}(\\mathbf{x})" + }, + { + "bbox": [ + 47, + 255, + 287, + 284 + ], + "type": "text", + "content": " denote the optimal solutions to the optimization tasks of " + }, + { + "bbox": [ + 47, + 255, + 287, + 284 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{w},c,L_1}^{\\rho ,\\eta}(\\mathbf{x})" + }, + { + "bbox": [ + 47, + 255, + 287, + 284 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 255, + 287, + 284 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{w},c,L_{2,1}}^{\\rho ,\\eta}(\\mathbf{x})" + }, + { + "bbox": [ + 47, + 255, + 287, + 284 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 286, + 287, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 286, + 287, + 371 + ], + "spans": [ + { + "bbox": [ + 46, + 286, + 287, + 371 + ], + "type": "text", + "content": "In the following theorem, we extend the shown results for the smoothness and robustness of vanilla Moreau envelope to our proposed " + }, + { + "bbox": [ + 46, + 286, + 287, + 371 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 286, + 287, + 371 + ], + "type": "text", + "content": "-norm-based extensions of the Moreau envelope. In this theorem, we use the following definitions for the soft-thresholding operators " + }, + { + "bbox": [ + 46, + 286, + 287, + 371 + ], + "type": "inline_equation", + "content": "\\mathrm{ST}_{\\alpha}" + }, + { + "bbox": [ + 46, + 286, + 287, + 371 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 286, + 287, + 371 + ], + "type": "inline_equation", + "content": "\\mathrm{GST}_{\\alpha}" + }, + { + "bbox": [ + 46, + 286, + 287, + 371 + ], + "type": "text", + "content": " for the sparse and group-sparse cases which are defined entrywise and group-entrywise as follows" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 69, + 376, + 253, + 409 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 69, + 376, + 253, + 409 + ], + "spans": [ + { + "bbox": [ + 69, + 376, + 253, + 409 + ], + "type": "interline_equation", + "content": "\\mathrm {S T} _ {\\alpha} (\\mathbf {x}) _ {i} := \\left\\{ \\begin{array}{l l} 0 & \\text {i f} | x _ {i} | \\leq \\alpha \\\\ x _ {i} - \\operatorname {s i g n} (x _ {i}) \\alpha & \\text {i f} | x _ {i} | > \\alpha , \\end{array} \\right.", + "image_path": "90c0a8fc7398d3500ce57fb04c897c321953ce4c34021bf35d9ae84d23d9db92.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 58, + 411, + 275, + 445 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 411, + 275, + 445 + ], + "spans": [ + { + "bbox": [ + 58, + 411, + 275, + 445 + ], + "type": "interline_equation", + "content": "\\mathrm {G S T} _ {\\alpha} (\\mathbf {x}) _ {S _ {i}} := \\left\\{ \\begin{array}{l l} \\mathbf {0} & \\text {i f} \\| \\mathbf {x} _ {S _ {i}} \\| _ {2} \\leq \\alpha \\\\ \\big (1 - \\frac {\\alpha}{\\| \\mathbf {x} _ {S _ {i}} \\| _ {2}} \\big) \\mathbf {x} _ {S _ {i}} & \\text {i f} \\| \\mathbf {x} _ {S _ {i}} \\| _ {2} > \\alpha . \\end{array} \\right.", + "image_path": "a2f4934c1e7fe4fe24641f3c17dd028e575294d2e824eda668197eb79ebdd88b.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "spans": [ + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "text", + "content": "Theorem 2. Suppose that " + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "inline_equation", + "content": "g:\\mathbb{R}^d\\to \\mathbb{R}" + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "text", + "content": " is a " + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "text", + "content": " -weakly convex function. Then, assuming that " + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "inline_equation", + "content": "0 < \\rho < \\frac{1}{\\lambda}" + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "text", + "content": ", Theorem 1's parts 1 and 3 will further hold for the sparse Moreau envelope " + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "inline_equation", + "content": "g_{L_1}^{\\rho ,\\eta}" + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "text", + "content": " and group-sparse Moreau envelope " + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "inline_equation", + "content": "g_{L_{2,1}}^{\\rho ,\\eta}" + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "text", + "content": " and their optimization problems' optimal solutions " + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "inline_equation", + "content": "\\widetilde{\\mathbf{x}}_{\\rho ,\\eta ,L_1}^* (\\mathbf{x})" + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "inline_equation", + "content": "\\widetilde{\\mathbf{x}}_{\\rho ,\\eta ,L_{2,1}}^{*}(\\mathbf{x})" + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "text", + "content": ". To parallel Theorem 1's part 2 for " + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 47, + 451, + 287, + 536 + ], + "type": "text", + "content": "-Moreau envelope, the followings hold" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 86, + 543, + 252, + 558 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 86, + 543, + 252, + 558 + ], + "spans": [ + { + "bbox": [ + 86, + 543, + 252, + 558 + ], + "type": "interline_equation", + "content": "\\mathrm {S T} _ {\\rho \\eta} \\left(- \\rho \\nabla g _ {L _ {1}} ^ {\\rho , \\eta} (\\mathbf {x})\\right) = \\widetilde {\\mathbf {x}} _ {\\rho , \\eta , L _ {1}} ^ {*} (\\mathbf {x}) - \\mathbf {x},", + "image_path": "1bd5f69bce571842b82170e357ef5cfc09f897ea6f289a083bc5cece0c6c6b4c.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 77, + 559, + 258, + 575 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 559, + 258, + 575 + ], + "spans": [ + { + "bbox": [ + 77, + 559, + 258, + 575 + ], + "type": "interline_equation", + "content": "\\mathrm {G S T} _ {\\rho \\eta} \\big (- \\rho \\nabla g _ {L _ {2, 1}} ^ {\\rho , \\eta} (\\mathbf {x}) \\big) = \\widetilde {\\mathbf {x}} _ {\\rho , \\eta , L _ {2, 1}} ^ {*} (\\mathbf {x}) - \\mathbf {x}.", + "image_path": "3c8fedaa31a4fa08d908efbe1c6d2e8cc4f8c6111e2885690cf8342e56f6a8a9.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 580, + 224, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 580, + 224, + 593 + ], + "spans": [ + { + "bbox": [ + 47, + 580, + 224, + 593 + ], + "type": "text", + "content": "Proof. We defer the proof to the Appendix." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "spans": [ + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "text", + "content": "Corollary 2. Suppose that the prediction score function " + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{w},c}" + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "text", + "content": "-weakly convex. Assuming that " + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "inline_equation", + "content": "0 < \\rho < \\frac{1}{\\lambda}" + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "text", + "content": ", the Sparse MoreauGrad " + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "inline_equation", + "content": "S - MG_{\\rho, \\eta}" + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "text", + "content": " and Group-Sparse MoreauGrad " + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "inline_equation", + "content": "GS - MG_{\\rho, \\eta}" + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "text", + "content": " interpretations will be robust to every norm-bounded perturbation " + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "inline_equation", + "content": "\\| \\delta \\|_2 \\leq \\epsilon" + }, + { + "bbox": [ + 47, + 599, + 287, + 660 + ], + "type": "text", + "content": " as:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 61, + 666, + 292, + 691 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 666, + 292, + 691 + ], + "spans": [ + { + "bbox": [ + 61, + 666, + 292, + 691 + ], + "type": "interline_equation", + "content": "\\left\\| S - M G _ {\\rho , \\eta} (\\mathbf {x} + \\boldsymbol {\\delta}) - S - M G _ {\\rho , \\eta} (\\mathbf {x}) \\right\\| _ {2} \\leq \\frac {\\epsilon}{\\min \\left\\{\\rho , \\frac {1}{\\lambda} - \\rho \\right\\}},", + "image_path": "c318c31b55d7fd8311a49896eaef59c47422a7d6a56f811de3063c4a3a794f28.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 48, + 692, + 292, + 717 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 692, + 292, + 717 + ], + "spans": [ + { + "bbox": [ + 48, + 692, + 292, + 717 + ], + "type": "interline_equation", + "content": "\\left\\| G S - M G _ {\\rho , \\eta} (\\mathbf {x} + \\boldsymbol {\\delta}) - G S - M G _ {\\rho , \\eta} (\\mathbf {x}) \\right\\| _ {2} \\leq \\frac {\\epsilon}{\\min \\left\\{\\rho , \\frac {1}{\\lambda} - \\rho \\right\\}}.", + "image_path": "37644efc423ca3376b64db32a94271f5342b1e0a5abf2f0bee13065d71138095.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 83, + 471, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 83, + 471, + 96 + ], + "spans": [ + { + "bbox": [ + 306, + 83, + 471, + 96 + ], + "type": "text", + "content": "Algorithm 1 MoreauGrad Interpretation" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 97, + 545, + 121 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 97, + 545, + 121 + ], + "spans": [ + { + "bbox": [ + 306, + 97, + 545, + 121 + ], + "type": "text", + "content": "Input: data x, label c, classifier " + }, + { + "bbox": [ + 306, + 97, + 545, + 121 + ], + "type": "inline_equation", + "content": "f_{\\mathbf{w}}" + }, + { + "bbox": [ + 306, + 97, + 545, + 121 + ], + "type": "text", + "content": ", regularization coeff. 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\\mathbf {x}\\right)", + "image_path": "e1e0264d8324d68d123185554c1c149975c43808cd2335e2f0823e237e82e57f.jpg" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 304, + 334, + 545, + 394 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 334, + 545, + 394 + ], + "spans": [ + { + "bbox": [ + 304, + 334, + 545, + 394 + ], + "type": "text", + "content": "Based on the above results, we propose applying the proximal gradient descent algorithm as described in Algorithm 1 to compute the Sparse and Group-Sparse Moreau-Grad. We defer discussing Algorithm 1's details to the Appendix." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 306, + 404, + 416, + 417 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 404, + 416, + 417 + ], + "spans": [ + { + "bbox": [ + 306, + 404, + 416, + 417 + ], + "type": "text", + "content": "6. Numerical Results" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 304, + 425, + 545, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 425, + 545, + 532 + ], + "spans": [ + { + "bbox": [ + 304, + 425, + 545, + 532 + ], + "type": "text", + "content": "We conduct several numerical experiments to evaluate the performance of the proposed MoreauGrad. Our designed experiments focus on the smoothness, sparsity, and robustness properties of MoreauGrad interpretation maps as well as the feature maps of several standard baselines. In the following, we first describe the numerical setup in our experiments and then present the obtained numerical results on the qualitative and quantitative performance of interpretation methods." + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 306, + 540, + 413, + 553 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 540, + 413, + 553 + ], + "spans": [ + { + "bbox": [ + 306, + 540, + 413, + 553 + ], + "type": "text", + "content": "6.1. 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Top: Visualization of MoreauGrad maps with different coefficient " + }, + { + "bbox": [ + 47, + 254, + 545, + 277 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 47, + 254, + 545, + 277 + ], + "type": "text", + "content": "'s. " + }, + { + "bbox": [ + 47, + 254, + 545, + 277 + ], + "type": "inline_equation", + "content": "\\rho = 0" + }, + { + "bbox": [ + 47, + 254, + 545, + 277 + ], + "type": "text", + "content": " reduces to the simple gradient method. Bottom: Visualization of Sparse MoreauGrad maps with different coefficient " + }, + { + "bbox": [ + 47, + 254, + 545, + 277 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 47, + 254, + 545, + 277 + ], + "type": "text", + "content": "'s. " + }, + { + "bbox": [ + 47, + 254, + 545, + 277 + ], + "type": "inline_equation", + "content": "\\eta = 0" + }, + { + "bbox": [ + 47, + 254, + 545, + 277 + ], + "type": "text", + "content": " reduces to the Vanilla MoreauGrad." + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 50, + 287, + 178, + 411 + ], + "lines": [ + { + "bbox": [ + 50, + 287, + 178, + 411 + ], + "spans": [ + { + "bbox": [ + 50, + 287, + 178, + 411 + ], + "type": "image", + "image_path": "a4fa8a36c0346426f936d6463665c79efec6f33941b58e247cd0095509e94339.jpg" + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_body" + } + ], + "index": 25 + }, + { + "type": "image", + "bbox": [ + 181, + 287, + 299, + 411 + ], + "blocks": [ + { + "bbox": [ + 181, + 287, + 299, + 411 + ], + "lines": [ + { + "bbox": [ + 181, + 287, + 299, + 411 + ], + "spans": [ + { + "bbox": [ + 181, + 287, + 299, + 411 + ], + "type": "image", + "image_path": "db61ca39a9d22e252d0a4b8bc7a6bd23005fc8123d0a523bb6833dd153e58b04.jpg" + } + ] + } + ], + "index": 26, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 64, + 416, + 523, + 428 + ], + "lines": [ + { + "bbox": [ + 64, + 416, + 523, + 428 + ], + "spans": [ + { + "bbox": [ + 64, + 416, + 523, + 428 + ], + "type": "text", + "content": "Figure 3. MoreauGrad vs. SmoothGrad gradient discrepancy, measured via the " + }, + { + "bbox": [ + 64, + 416, + 523, + 428 + ], + "type": "inline_equation", + "content": "l_{2}" + }, + { + "bbox": [ + 64, + 416, + 523, + 428 + ], + "type": "text", + "content": "-norm distance from the simple gradient map." + } + ] + } + ], + "index": 29, + "angle": 0, + "type": "image_caption" + } + ], + "index": 26 + }, + { + "type": "image", + "bbox": [ + 302, + 287, + 421, + 411 + ], + "blocks": [ + { + "bbox": [ + 302, + 287, + 421, + 411 + ], + "lines": [ + { + "bbox": [ + 302, + 287, + 421, + 411 + ], + "spans": [ + { + "bbox": [ + 302, + 287, + 421, + 411 + ], + "type": "image", + "image_path": "1dafd875b6a4d2a8b3d6e9034ff92f193d9eec9d19e80d9c63b7d858baaf7bd5.jpg" + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_body" + } + ], + "index": 27 + }, + { + "type": "image", + "bbox": [ + 425, + 287, + 543, + 411 + ], + "blocks": [ + { + "bbox": [ + 425, + 287, + 543, + 411 + ], + "lines": [ + { + "bbox": [ + 425, + 287, + 543, + 411 + ], + "spans": [ + { + "bbox": [ + 425, + 287, + 543, + 411 + ], + "type": "image", + "image_path": "5f644c271f3838aa3269e52ae1d3e3cc524cca29feb7e83f75e202993a02ef7c.jpg" + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "image_body" + } + ], + "index": 28 + }, + { + "bbox": [ + 46, + 447, + 287, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 447, + 287, + 519 + ], + "spans": [ + { + "bbox": [ + 46, + 447, + 287, + 519 + ], + "type": "text", + "content": "[22], 5) Sparsified SmoothGrad [13], 6) RelEx [14]. We note that for baseline experiments we adopted the official implementations and conducted the experiments with hyperparameters suggested in their work. We present the full implementation details in the Appendix, and our code is available in the supplementary material." + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 47, + 527, + 287, + 540 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 527, + 287, + 540 + ], + "spans": [ + { + "bbox": [ + 47, + 527, + 287, + 540 + ], + "type": "text", + "content": "6.2. Effects of Smoothness and Sparsity Parameters" + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "We ran the numerical experiments for unregularized Vanilla MoreauGrad with multiple smoothness coefficient " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " values to show the effect of the Moreau envelope's regularization. Figure 2 visualizes the effect of different " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " on the Vanilla MoreauGrad saliency map. As can be seen in this figure, the saliency map qualitatively improves by increasing the value of " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " from 0 to 1. Please note that for " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\rho = 0" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": ", the MoreauGrad simplifies to the simple gradient interpretation. However, as shown in Theorem 1 the proper performance of Vanilla MoreauGrad requires choosing a properly bounded " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " value, which is consistent with our observation that when " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " becomes too large, the Moreau envelope will be computationally difficult to optimize and the quality of interpretation maps could deteriorate to some" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 304, + 447, + 545, + 513 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 447, + 545, + 513 + ], + "spans": [ + { + "bbox": [ + 304, + 447, + 545, + 513 + ], + "type": "text", + "content": "extent. As numerically verified in both CIFAR-10, tinyImageNet, and ImageNet experiments, we used the rule of thumb " + }, + { + "bbox": [ + 304, + 447, + 545, + 513 + ], + "type": "inline_equation", + "content": "\\rho = \\frac{1}{\\sqrt{\\mathbb{E}[\\|\\mathbf{X}\\|_2]}}" + }, + { + "bbox": [ + 304, + 447, + 545, + 513 + ], + "type": "text", + "content": " measured over the empirical training data to set the value of " + }, + { + "bbox": [ + 304, + 447, + 545, + 513 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 304, + 447, + 545, + 513 + ], + "type": "text", + "content": ", which is equal to 1 for the normalized samples in our experiments." + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": "Regarding the sparsity hyperparameter " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": " in Sparse and Group-Sparse MoreauGrad experiments, we ran several experimental tests to properly tune the hyperparameter. Note that a greater coefficient " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": " enforces more strict sparsity or group-sparsity in the MoreauGrad interpretation, and the degree of sparsity could be simply adjusted by changing this coefficient " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": ". As shown in Figure 2, in our experiments with different " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": " coefficients the interpretation map becomes sparser as we increase the " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": "-norm penalty coefficient " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": ". Similarly, to achieve a group-sparse interpretation, we used " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "L_{2,1}" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": "-regularization on groups of adjacent pixels as discussed in Definition 4. The effect of the group-sparsity coefficient was similar to the sparse case in our experiments, as fewer pixel groups took non-zero values and the output interpretations showed more structured interpretation maps when choosing a larger coefficient " + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 304, + 522, + 546, + 713 + ], + "type": "text", + "content": ". 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As shown in Figure 3, the " + }, + { + "bbox": [ + 46, + 386, + 287, + 577 + ], + "type": "inline_equation", + "content": "\\ell_2" + }, + { + "bbox": [ + 46, + 386, + 287, + 577 + ], + "type": "text", + "content": "-norm discrepancy score grows smoothly with coefficient " + }, + { + "bbox": [ + 46, + 386, + 287, + 577 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 46, + 386, + 287, + 577 + ], + "type": "text", + "content": ". We also measured the averaged gradient discrepancy for SmoothGrad methods with different smoothness parameter " + }, + { + "bbox": [ + 46, + 386, + 287, + 577 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 46, + 386, + 287, + 577 + ], + "type": "text", + "content": "'s. We adjusted " + }, + { + "bbox": [ + 46, + 386, + 287, + 577 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 46, + 386, + 287, + 577 + ], + "type": "text", + "content": " in Sparse MoreauGrad to standardize the sparsity level for fair comparisons with Sparsified SmoothGrad. As Figure 3 shows, SmoothGrad led to similar discrepancy values as in MoreauGrad. Also, Integrated Gradients [24] had a similar averaged gradient discrepancy of 0.34 for CIFAR-10 and 0.40 for ImageNet. As the results suggest, the baselines similarly deviate from the simple gradient maps, which could be linked to improved visual quality and robustness, as also observed by [22, 13]." + } + ] + } + ], + "index": 42 + }, + { + "bbox": [ + 47, + 586, + 287, + 610 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 287, + 610 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 287, + 610 + ], + "type": "text", + "content": "6.3. Qualitative Comparison of MoreauGrad vs. Standard Gradient-based Baselines" + } + ] + } + ], + "index": 43 + }, + { + "bbox": [ + 46, + 617, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 714 + ], + "type": "text", + "content": "In Figure 4, we illustrate the Vanilla, Sparse, and Group-Sparse MoreauGrad interpretation outputs as well as the saliency maps generated by the gradient-based baselines. The results demonstrate that MoreauGrad generates qualitatively sharp and, in the case of Sparse and Group-Sparse MoreauGrad, sparse interpretation maps. As shown in Figure 4, promoting sparsity in the MoreauGrad interpretation maps has improved the visual quality, and managed to erase" + } + ] + } + ], + "index": 44 + }, + { + "bbox": [ + 304, + 373, + 545, + 409 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 373, + 545, + 409 + ], + "spans": [ + { + "bbox": [ + 304, + 373, + 545, + 409 + ], + "type": "text", + "content": "the less relevant pixels like the background ones. Also, the Group-Sparse MoreauGrad maps successfully exhibit both sparsity and connectivity of selected pixels." + } + ] + } + ], + "index": 45 + }, + { + "bbox": [ + 306, + 415, + 492, + 427 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 415, + 492, + 427 + ], + "spans": [ + { + "bbox": [ + 306, + 415, + 492, + 427 + ], + "type": "text", + "content": "6.4. Robustness of Interpretation Maps" + } + ] + } + ], + "index": 46 + }, + { + "bbox": [ + 304, + 433, + 545, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 433, + 545, + 517 + ], + "spans": [ + { + "bbox": [ + 304, + 433, + 545, + 517 + ], + "type": "text", + "content": "We qualitatively and quantitatively evaluated the robustness of MoreauGrad interpretation. To assess the empirical robustness of interpretation methods, we adopt a " + }, + { + "bbox": [ + 304, + 433, + 545, + 517 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 304, + 433, + 545, + 517 + ], + "type": "text", + "content": "-bounded interpretation attack method defined by [13]. Also, for quantifying the empirical robustness, we adopt three robustness metrics. The first metric is the Euclidean distance of the normalized interpretations before and after the attack:" + } + ] + } + ], + "index": 47 + }, + { + "bbox": [ + 335, + 526, + 545, + 553 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 335, + 526, + 545, + 553 + ], + "spans": [ + { + "bbox": [ + 335, + 526, + 545, + 553 + ], + "type": "interline_equation", + "content": "D \\left(I (\\mathbf {x}), I \\left(\\mathbf {x} ^ {\\prime}\\right)\\right) = \\left\\| \\frac {I (\\mathbf {x})}{\\| I (\\mathbf {x}) \\| _ {2}} - \\frac {I \\left(\\mathbf {x} ^ {\\prime}\\right)}{\\| I \\left(\\mathbf {x} ^ {\\prime}\\right) \\| _ {2}} \\right\\| _ {2} \\tag {6}", + "image_path": "7754764d52c8001e532626135afd8e48fb278b83b6b5e5fd3e102510c2264b75.jpg" + } + ] + } + ], + "index": 48 + }, + { + "bbox": [ + 304, + 557, + 545, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 545, + 593 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 545, + 593 + ], + "type": "text", + "content": "Note that a larger distance between the normalized maps indicates a smaller similarity and a higher vulnerability of the interpretation method to adversarial attacks." + } + ] + } + ], + "index": 49 + }, + { + "bbox": [ + 304, + 594, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 689 + ], + "type": "text", + "content": "The second metric is the top-k intersection ratio. This metric is another standard robustness measure used in [6, 13]. This metric measures the ratio of pixels that remain salient after the interpretation attack. A robust interpretation is expected to preserve most of the salient pixels under an attack. The third metric is the structural similarity index measure (SSIM) [27]. A larger SSIM value indicates that the two input maps are more perceptively similar." + } + ] + } + ], + "index": 50 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "Using the above metrics, we compared the MoreauGrad schemes with the baseline methods. As qualitatively shown" + } + ] + } + ], + "index": 51 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "2027" + } + ] + } + ], + "index": 52 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 59, + 72, + 537, + 252 + ], + "blocks": [ + { + "bbox": [ + 59, + 72, + 537, + 252 + ], + "lines": [ + { + "bbox": [ + 59, + 72, + 537, + 252 + ], + "spans": [ + { + "bbox": [ + 59, + 72, + 537, + 252 + ], + "type": "image", + "image_path": "81a2ea00f5fe6bd1a3d1777ee65c6bf92a87c399442ab2be2feba864633e5c99.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 66, + 262, + 523, + 274 + ], + "lines": [ + { + "bbox": [ + 66, + 262, + 523, + 274 + ], + "spans": [ + { + "bbox": [ + 66, + 262, + 523, + 274 + ], + "type": "text", + "content": "Figure 5. Visualization of robustness against interpretation attacks. The top and bottom rows show original and attacked maps." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 56, + 287, + 537, + 658 + ], + "blocks": [ + { + "bbox": [ + 56, + 287, + 537, + 658 + ], + "lines": [ + { + "bbox": [ + 56, + 287, + 537, + 658 + ], + "spans": [ + { + "bbox": [ + 56, + 287, + 537, + 658 + ], + "type": "image", + "image_path": "0a9f83b32d63679ba184421719bec217eaade9423b408ff9a30d1d764ccf4f5e.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 138, + 668, + 452, + 679 + ], + "lines": [ + { + "bbox": [ + 138, + 668, + 452, + 679 + ], + "spans": [ + { + "bbox": [ + 138, + 668, + 452, + 679 + ], + "type": "text", + "content": "Figure 6. Quantitative robustness comparison between MoreauGrad and the baselines." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "2028" + } + ] + } + ], + "index": 4 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 72, + 108, + 186 + ], + "blocks": [ + { + "bbox": [ + 51, + 72, + 108, + 186 + ], + "lines": [ + { + "bbox": [ + 51, + 72, + 108, + 186 + ], + "spans": [ + { + "bbox": [ + 51, + 72, + 108, + 186 + ], + "type": "image", + "image_path": "3a6111a1b1708e90d0be507fbafaad5c58e0529357db0bdc80d54d2c11917958.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 70, + 190, + 89, + 200 + ], + "lines": [ + { + "bbox": [ + 70, + 190, + 89, + 200 + ], + "spans": [ + { + "bbox": [ + 70, + 190, + 89, + 200 + ], + "type": "text", + "content": "Input" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 110, + 72, + 167, + 186 + ], + "blocks": [ + { + "bbox": [ + 110, + 72, + 167, + 186 + ], + "lines": [ + { + "bbox": [ + 110, + 72, + 167, + 186 + ], + "spans": [ + { + "bbox": [ + 110, + 72, + 167, + 186 + ], + "type": "image", + "image_path": "c4e5fd4260d72c33c6b687501c09fd96e3f3cc6c2398d9e6651bd40eb57abbcd.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 126, + 187, + 148, + 195 + ], + "lines": [ + { + "bbox": [ + 126, + 187, + 148, + 195 + ], + "spans": [ + { + "bbox": [ + 126, + 187, + 148, + 195 + ], + "type": "inline_equation", + "content": "\\eta = 0" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 113, + 196, + 162, + 205 + ], + "lines": [ + { + "bbox": [ + 113, + 196, + 162, + 205 + ], + "spans": [ + { + "bbox": [ + 113, + 196, + 162, + 205 + ], + "type": "text", + "content": "MoreauGrad" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 168, + 72, + 225, + 186 + ], + "blocks": [ + { + "bbox": [ + 168, + 72, + 225, + 186 + ], + "lines": [ + { + "bbox": [ + 168, + 72, + 225, + 186 + ], + "spans": [ + { + "bbox": [ + 168, + 72, + 225, + 186 + ], + "type": "image", + "image_path": "2cbda9385ef5f5b3b650fc4ac36f2205979208681b741d3615f2580b14c3d3e4.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 171, + 187, + 219, + 195 + ], + "lines": [ + { + "bbox": [ + 171, + 187, + 219, + 195 + ], + "spans": [ + { + "bbox": [ + 171, + 187, + 219, + 195 + ], + "type": "inline_equation", + "content": "\\eta = 1\\times 10^{-3}" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 187, + 196, + 263, + 205 + ], + "lines": [ + { + "bbox": [ + 187, + 196, + 263, + 205 + ], + "spans": [ + { + "bbox": [ + 187, + 196, + 263, + 205 + ], + "type": "text", + "content": "Sparse MoreauGrad" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 227, + 72, + 283, + 186 + ], + "blocks": [ + { + "bbox": [ + 227, + 72, + 283, + 186 + ], + "lines": [ + { + "bbox": [ + 227, + 72, + 283, + 186 + ], + "spans": [ + { + "bbox": [ + 227, + 72, + 283, + 186 + ], + "type": "image", + "image_path": "d152693cbc4cda9cada3c37ec6a011402f5a81e04e6e8a56b30980dd831b918e.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 231, + 187, + 278, + 195 + ], + "lines": [ + { + "bbox": [ + 231, + 187, + 278, + 195 + ], + "spans": [ + { + "bbox": [ + 231, + 187, + 278, + 195 + ], + "type": "inline_equation", + "content": "\\eta = 5\\times 10^{-3}" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 47, + 209, + 286, + 231 + ], + "lines": [ + { + "bbox": [ + 47, + 209, + 286, + 231 + ], + "spans": [ + { + "bbox": [ + 47, + 209, + 286, + 231 + ], + "type": "text", + "content": "Figure 7. Applications of vanilla and sparse MoreauGrad to explain two misclassifications on the ImageNet test set." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 241, + 286, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 241, + 286, + 361 + ], + "spans": [ + { + "bbox": [ + 46, + 241, + 286, + 361 + ], + "type": "text", + "content": "in Figure 5, using the same attack magnitude, the MoreauGrad interpretations are mostly similar before and after the norm-bounded attack. The qualitative robustness of MoreauGrad seems satisfactory compared to the baseline methods. Finally, Figure 6 presents a quantitative comparison of the robustness measures for the baselines and proposed MoreauGrad on CIFAR-10, tiny ImageNet, and ImageNet datasets. As shown by these measures, MoreauGrad outperforms the baselines in terms of the discussed robustness metrics." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 368, + 274, + 381 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 368, + 274, + 381 + ], + "spans": [ + { + "bbox": [ + 47, + 368, + 274, + 381 + ], + "type": "text", + "content": "6.5. Applications of MoreauGrad Interpretation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 384, + 286, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 384, + 286, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 384, + 286, + 552 + ], + "type": "text", + "content": "As shown in Figure 2, MoreauGrad interpretation maps may be further refined to promote sparsity and retain only the salient pixels. The sparsity level could be flexibly adjusted via parameter " + }, + { + "bbox": [ + 46, + 384, + 286, + 552 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 46, + 384, + 286, + 552 + ], + "type": "text", + "content": " in accordance with the target dataset. Moreover, both vanilla and sparse MoreauGrad can be employed for explaining DNN's misclassifications in image recognition tasks. Figure 7 presents two examples of such misclassifications, where \"gas pump\" and \"church\" are erroneously classified as \"tricycle\" and \"restaurant\", respectively. Sparse MoreauGrad identifies the source of these errors and relates them to the presence of \"a person in the middle of two wheels\" and \"people sitting on benches\", respectively. In the Appendix, we present other examples of using MoreauGrad for explaining DNNs' misclassification." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 562, + 119, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 562, + 119, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 562, + 119, + 574 + ], + "type": "text", + "content": "7. Conclusion" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "content": "In this work, we introduced MoreauGrad as an optimization-based interpretation method for deep neural networks. We demonstrated that MoreauGrad can be flexibly combined with " + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "content": "-regularization methods to output sparse and group-sparse interpretations. We further showed that the MoreauGrad output will enjoy robustness against input perturbations. While our analysis focuses on the sparsity and robustness of the MoreauGrad explanation, studying the consistency and transferability of MoreauGrad interpretations is an interesting future direction. Moreover, the application of MoreauGrad to convex and norm-regularized" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 72, + 545, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 109 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 109 + ], + "type": "text", + "content": "neural nets could be another topic for future study. Finally, our analysis of " + }, + { + "bbox": [ + 305, + 72, + 545, + 109 + ], + "type": "inline_equation", + "content": "\\ell_1" + }, + { + "bbox": [ + 305, + 72, + 545, + 109 + ], + "type": "text", + "content": "-norm-based Moreau envelope could find independent applications in other deep learning contexts." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 118, + 403, + 131 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 118, + 403, + 131 + ], + "spans": [ + { + "bbox": [ + 306, + 118, + 403, + 131 + ], + "type": "text", + "content": "Acknowledgments" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 138, + 545, + 210 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 138, + 545, + 210 + ], + "spans": [ + { + "bbox": [ + 305, + 138, + 545, + 210 + ], + "type": "text", + "content": "This work was partially supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China, Project 14209920, and was partially supported by a CUHK Direct Research Grant. Also, the authors would like to thank the anonymous reviewers for their constructive feedback and suggestions." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 307, + 219, + 364, + 231 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 219, + 364, + 231 + ], + "spans": [ + { + "bbox": [ + 307, + 219, + 364, + 231 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 311, + 239, + 545, + 714 + ], + "type": "list", + "angle": 0, + "index": 29, + "blocks": [ + { + "bbox": [ + 311, + 239, + 545, + 311 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 239, + 545, + 311 + ], + "spans": [ + { + "bbox": [ + 311, + 239, + 545, + 311 + ], + "type": "text", + "content": "[1] Aditya Chattopadhy, Anirban Sarkar, Prantik Howlader, and Vineeth N Balasubramanian. Gradcam++: Generalized gradient-based visual explanations for deep convolutional networks. 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Recently, quantum image generation has been explored with many potential advantages over non-quantum techniques; however, previous techniques have suffered from poor quality and robustness. To address these problems, we introduce MosaiQ a high-quality quantum image generation GAN framework that can be executed on today's Near-term Intermediate Scale Quantum (NISQ) computers.", + "bbox": [ + 73, + 376, + 472, + 527 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 556, + 209, + 571 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Generative Adversarial Networks, or GANs, are a type of neural network architecture used in machine learning and computer vision for generative modeling [8, 22, 2, 9]. A classical GAN consists of two neural networks, a generator, and a discriminator, that are trained simultaneously in a competitive process. The generator generates fake data samples, while the discriminator tries to distinguish them from real ones found in the training set, hence serving as an \"adversarial entity\". Classical GANs have received significant attention for generating high-quality images, among other purposes including text generation, data augmentation, and anomaly detection [20, 1, 5].", + "bbox": [ + 75, + 583, + 468, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Naturally, this has spawned interest in the quantum information science community to develop corresponding quantum GANs that run on quantum computers. While recent efforts toward developing quantum GANs have been instrumental and early results have been encouraging, we discovered that existing approaches have severe scalability bottlenecks and have significant room for improvement. This is especially true in the context of generating high-quality image generation on real-system quantum computers.", + "bbox": [ + 75, + 763, + 468, + 902 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Opportunity Gap for Quantum GANs.", + "text_level": 1, + "bbox": [ + 500, + 352, + 799, + 369 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "A recent work by Huang et al. [11], referred to as QGPatch in this paper, is the state-of-the-art demonstration of QuantumGANs on real quantum computers. As our paper also demonstrates, QGPatch can learn different shapes and produce recognizable images in some cases, but can often yield low-quality images. It suffers from the scalability challenge because it breaks the image into \"patches\" and performs a pixel-by-pixel learning. Second, it is not effective at generating a variety of images within the same class – this problem is known as \"mode collapse\" [7]. It is nontrivial to achieve high-quality image generation while also maintaining variety. Motivated by these limitations, MosaicQ's design pushes the state of the art by achieving higher scalability, image quality, and variety.", + "bbox": [ + 496, + 376, + 893, + 589 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Contributions of MosaiQ", + "text_level": 1, + "bbox": [ + 500, + 597, + 697, + 614 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "I. MosaiQ introduces the design and implementation of a novel quantum generative adversarial network for image generation on quantum computers. MosaiQ's approach is a hybrid classical-quantum generation network where a network of low-circuit-depth variational quantum circuits are leveraged to learn and train the model. Upon acceptance, MosaiQ will be available as an open-source contribution.", + "bbox": [ + 496, + 621, + 893, + 727 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "II. MosaiQ's design demonstrates how the extraction of principal components of images enables us to learn and generate higher-quality images, compared to the state-of-the-art approach which is limited in its scalability due to pixel-by-pixel learning [11]. However, exploiting information in principal components to its full potential is non-trivial, and MosaiQ proposes to mitigate those challenges using feature redistribution. Furthermore, MosaiQ introduces a novel adaptive input noise generation technique to improve both the quality and variety of generated images – mitigating the common risk of mode collapse in generative networks.", + "bbox": [ + 496, + 734, + 893, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 805, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "7030", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/f683e1b63e7259faa5591a09880a375e9c2b1ca1ddc5b991ea88dbf45b550cf6.jpg", + "image_caption": [ + "Figure 1. Classical generative adversarial network (GAN) and MosaiQ's hybrid quantum-classical GAN architecture." + ], + "image_footnote": [], + "bbox": [ + 78, + 87, + 467, + 196 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "III. Our evaluation demonstrates that MosaiQ significantly outperforms the state-of-the-art methods [11] on both simulation and real quantum computers with a hardware error. MosaiQ is evaluated on the MNIST [6] and Fashion MNIST datasets [21] – widely-used for QML evaluation on Nearterm Intermediate Scale Quantum (NISQ) machines [15, 11]. MosaiQ outperforms the state-of-the-art methods [11] both visually and quantitatively – for example, over 100 points improvement in image quality generated on IBM Jakarta quantum computer using the FID (Fréchet Inception Distance) score [10], which is popularly used for comparing image quality. MosaiQ is open-sourced at https://github.com/SilverEngineered/MosaiQ.", + "bbox": [ + 75, + 285, + 472, + 482 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. MosaiQ: Challenges and Solution", + "text_level": 1, + "bbox": [ + 76, + 494, + 382, + 512 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this section, we present the design and implementation of MosaiQ, a quantum image generative network. To provide better context for understanding, first, we briefly describe the classical generative adversarial networks (GAN) (depicted in Fig. 1(a)), describe the limitations of the state-of-the-art quantum GANs, and then, provide the details of MosaiQ's quantum GAN design (depicted in Fig. 1(b)).", + "bbox": [ + 75, + 521, + 468, + 627 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Generative Adversarial Networks (GANs)", + "text_level": 1, + "bbox": [ + 76, + 635, + 433, + 651 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Generative Adversarial Networks, or GANs, are a type of neural network architecture used in machine learning for generative modeling [8]. The basic architecture and workflow of a classical (non quantum) GAN are shown in Fig. 1 (a). A classical GAN consists of two neural networks, a generator, and a discriminator, that are trained simultaneously in a competitive process. The generator generates fake data samples, while the discriminator tries to distinguish them from real ones found in the training set, hence serving as the \"ad adversary\". Through training, the generator learns to create increasingly realistic samples that mimic the distribution of the real data in order to better fool an increasingly effective discriminator, eventually reaching an attempt to attain equilibrium with the value function expressed as $\\min_G\\max_D\\mathbb{E}_{x\\sim q_{\\mathrm{data}}(x)}[\\log D(\\pmb {x})] + \\mathbb{E}_{\\pmb {z}\\sim p(\\pmb {z})}[\\log (1 - D(G(\\pmb {z})))]$ . This value function has two", + "bbox": [ + 75, + 659, + 470, + 902 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/ac121dfec9d06b4e9f9ed5a05bd1086fb8572abf31e8be69c54339da83d682e4.jpg", + "image_caption": [ + "Digit 0 (MNIST)", + "Figure 2. State-of-the-art quantum image generator, QG-Patch [11], generates low-quality images for different datasets. However, its quality is still similar to a classical GAN with $25 \\times$ more parameters and iterations." + ], + "image_footnote": [], + "bbox": [ + 501, + 103, + 887, + 164 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "main identifiable components that correspond to the respective optimization objectives of the generator and the discriminator. The use of log provides more numerical stability because it converts the multiplication of multiple small probabilities into addition, and it also allows us to calculate the derivatives more easily during the optimization process.", + "bbox": [ + 496, + 256, + 890, + 347 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Once fully trained, a generator component of the GAN is capable of converting random noise into new data samples (e.g., boots) that conform to the original distribution of the training data. Essentially, the generator, without the use of a discriminator, can be inferred to obtain new data samples. GANs have been shown to be useful in a variety of applications such as image and text generation, data augmentation, and anomaly detection [20, 1, 5]. Naturally, this has spawned interest in the quantum information science community to develop corresponding quantum GANs.", + "bbox": [ + 496, + 347, + 892, + 500 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Quantum GANs follow a similar generator and discriminator structure as classical GANs but use quantum principles to train and infer from the model. Typically, the discriminator functions on classical resources, and the generator is trained on quantum resources. This is expected, as this structure allows the Quantum GANs to leverage quantum resources for generation tasks – the component that persists beyond training; recall that the discriminator is essentially a quality inspector that can be decoupled after training and is not required during inference. While this structure is intuitive and has been demonstrated to be somewhat promising [11], there are multiple open challenges that need to be overcome to achieve higher quality.", + "bbox": [ + 496, + 506, + 890, + 702 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Limitations of Existing Quantum GANs", + "text_level": 1, + "bbox": [ + 500, + 710, + 841, + 727 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "A recent work by Huang et al. [11], referred to as QGPatch, is the most complete, state-of-the-art demonstration of QuantumGANs on real quantum computers. QGPatch follows the Quantum GAN architecture described earlier but achieves limited effectiveness - QGPatch can learn different shapes and produce recognizable images in some cases, but often suffers from low quality. Fig. 2 shows that digit '0' is a reasonable approximation of the ground truth, but the generated boot image is far less recognizable. Despite the imperfect generations, we can see in Fig. 2 how a classical GAN with $25 \\times$ the parameters of QGPatch and", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "7031", + "bbox": [ + 482, + 924, + 513, + 936 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "trained for $25 \\times$ as many iterations is worse or similar to the quantum technique - supporting the potential of quantum machine-learning for image generation tasks as compared to the classical approach with much higher resources and complexity. This independently provides experimental evidence for why the quantum information science community is motivated to accelerate the progress of Quantum GANs, despite its current limitations.", + "bbox": [ + 75, + 90, + 470, + 210 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The reasons for the limited effectiveness of Quatum GANs are multi-fold. The quantum generator component runs on the quantum hardware and requires many qubits to produce high-quality images from random input noise (a qubit is the fundamental unit of computation and information storage on quantum computers). QGPatch addresses this challenge by breaking the image into \"patches\" and employing a generator for different patches. While this is reasonable for smaller resolution images, the \"patch-based\" approach suffers from scalability due to its fundamental nature of learning pixel-by-pixel. For example, a total of 245 qubits are required for images in the full-resolution 784-pixel MNIST dataset.", + "bbox": [ + 75, + 212, + 468, + 406 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The second challenge is performing efficient learning from random input noise – it is critical for the quantum generator to effectively utilize the random input noise to generate a variety of images for the same class. Inability to generate a variety of images within the same class – which even classical GANs suffer from – is popularly known as the “mode collapse” problem [7]. Mode collapse is a side-effect of the generator learning to generate only produce one type of image for a given class because the generator has learned to “fool” the discriminator for this image and saturates in its learning. It is non-trivial to achieve high-quality generating while also maintaining variety. Motivated by these limitations, MosaiQ’s design pushes the state of the art.", + "bbox": [ + 75, + 407, + 468, + 604 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Overview of MosaiQ and Key Ideas", + "text_level": 1, + "bbox": [ + 76, + 613, + 387, + 628 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Hybrid Quantum-Classical Architecture. MosaiQ uses a hybrid quantum-classical architecture for image generation, as summarized in Fig. 1(b). The generator is quantum in nature and trained using quantum simulation, and the discriminator is classical – similar to the construction in [15, 11]. However, there are two key novel architectural changes: (1) to address the scalability and quantum resource bottlenecks for generating high-quality images, MosaiQ applies a transformation on the input image dataset, and (2) MosaiQ employs quantum-style random noise as input to enhance the “variety or mode-collapse” challenge. These two key features are described after a brief description of MosaiQ's generator and discriminator.", + "bbox": [ + 75, + 636, + 468, + 832 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "MosaiQ's Quantum Generator Network. MosaiQ's quantum generator component is a network of multiple subgenerators. Each sub-generator is a variational quantum circuit that is iteratively optimized to train a model. Vari-", + "bbox": [ + 75, + 839, + 470, + 901 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/1fc6b99818042c2e68a4ec0ebbf91ffd7ff1080da655013093ae329a66ecdc95.jpg", + "image_caption": [ + "Figure 3. Circuit ansatz design of MosaiQ's generators. The RY gates in each layer are optimized during training." + ], + "image_footnote": [], + "bbox": [ + 504, + 88, + 887, + 172 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ational quantum circuits are specific types of quantum circuits where some components of the circuits are tunable parameters, which are iteratively optimized. As a background, a quantum circuit is essentially a sequence of quantum gates applied to qubits. The quantum gates are fundamental operations that manipulate the qubit state, and any gate can be represented as a unitary matrix. One-qubit gates, such as the Pauli gates $(\\sigma_x,\\sigma_y,\\sigma_z)$ , apply a rotation to just one qubit and are categorized by the axis around which the rotation takes place, and by how much. Multi-qubit gates, such as the CNOT gate, allow the creation of entanglement.", + "bbox": [ + 496, + 234, + 890, + 400 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Variational quantum circuits in MosaiQ are comprised of two types of sections. The first type, $X$ , has fixed gates that entangle the qubits. The second type, $\\theta$ , has tunable $U_{3}$ gates that are optimized via training. The overall circuit $V$ is therefore an optimization function built of unitary transformations such that $V = U(X,\\theta)$ . One key feature of variational quantum circuits is the ability to leverage many off-the-shelf classical deep-learning techniques for training and optimization. This includes learning through common loss functions such as $L_{2}$ loss and leveraging existing optimizers such as Adam [13] that MosaiQ leverages.", + "bbox": [ + 496, + 402, + 892, + 569 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "All sub-generator circuits in MosaiQ have identical architectures, composed of a five-qubit circuit. Fig. 3 shows an example of the sub-generator circuit. The circuit consists of encoding the input noise as angles using $Rx$ gates and $Ry$ gates. Following the embedding of the noise, the parameterized weights are encoded on each quantum layer alongside $CZ$ gates used to entangle the qubits at each layer. These weights contain the portion of the circuit that is optimized. Following these repeated layers, the Pauli $X$ expected value is taken for each qubit in measurement.", + "bbox": [ + 496, + 571, + 890, + 722 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We note the simplistic design of MosaiQ's generator circuits is intentional; limiting the number of tunable parameters and depth of the circuits enables MosaiQ to mitigate hardware error impact on real quantum machines and maintain high quality, as confirmed by our evaluation (Sec. 3).", + "bbox": [ + 496, + 724, + 890, + 801 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Scalable Learning by Extracting Principal Components. Unlike previous approaches, which learn to construct the pixels of an image directly and consequently, suffer from the scaling bottleneck, MosaiQ demonstrates that extracting and learning the rich features is effective. The principal component analysis (PCA) method enables efficient learn-", + "bbox": [ + 496, + 809, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "7032", + "bbox": [ + 482, + 925, + 514, + 936 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/a2778b8fb35b55e57c33f37354f4438eeb48e82390b7bef825f0548d1a91dab3.jpg", + "image_caption": [ + "Figure 4. MosaiQ divides the PCA features among the eight generator circuits in a manner that the total explained variance is close to equal across all generators." + ], + "image_footnote": [], + "bbox": [ + 86, + 90, + 467, + 200 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ing by focusing on the important features that compromise unique images, as opposed to having to learn to distinguish the important features from the redundant features in an image via the pixel-by-pixel method. PCA maximizes the entropy for a given number of components, concentrating the information of a dataset efficiently.", + "bbox": [ + 75, + 297, + 467, + 388 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The first step in learning principal components is normalizing the input data. Once the images are normalized, MosaiQ decomposes the images into principal components and scales these components between [0, 1] so that the quantum sub-generators can generate throughout the entire space of inputs. As quantum machines rely on only unitary transformations, it is not possible to obtain an output with an absolute value greater than one in measurement. These scaled components are fed into the discriminator as the \"real labels\" and the generator begins to learn how to mimic the distribution throughout the training process. After learning, the outputs are scaled back to the original principal component range, then are inverse transformed to form a unique image that is within the distribution of the original images. This method helps us achieve higher quality in a scalable way. However, experimentally we found that this alone is not sufficient. MosaiQ performs intelligent distribution of features to make the learning more effective and robust.", + "bbox": [ + 75, + 391, + 468, + 662 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Feature Distribution Among Learners. In the conventional implementation of the previously proposed idea, all generated features are distributed among several sub-generators before being concatenated. Recall that the MosaicQ's quantum generator is an ensemble of multiple sub-generators, where each sub-generator is a variation quantum circuit. In the default case where PCA features are aligned one after another to the sub-generators, an unbalanced distribution of explained variance may emerge, where some sub-generators are responsible for significantly more important generations than others. This is because, by definition, the explained variance of PCA features is heavily concentrated on the first few features, and there is often a significant drop-off in explained variance from one PCA feature to the next. Recall that PCA features are entangled within", + "bbox": [ + 75, + 674, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "sub-generators in training to form rich connections for image generation, when some sub-generators do not contain much useful information in any feature, the entire generator does not pose much utility.", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Therefore, while effective in achieving scalability, only performing PCA may not achieve the full potential of MossiQ's quantum image generation as this leads to unbalanced training, likely to quickly discover gradients that ignore many sub-generators and plateaus in training. To mitigate this challenge, we propose a new PCA feature distribution mechanism to counteract the unbalanced nature of assigning principal components to sub-generators (Fig. 4).", + "bbox": [ + 496, + 154, + 890, + 276 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We begin by assigning the first principal component to the first sub-generator, the second principal component to the second, and so on until each sub-generator has one top principal component. We follow this up by assigning the last n-1 principal components to the first generator, where $n$ is the size of each sub-generator. This is followed by assigning the second to last n-1 features to the second sub-generator and repeated on the third generator and so on until all features have been assigned. This creates a much more balanced distribution, which enables us to ensure all sub-generators hold utility during the training process and the learning is not skewed. As an important side-note, MosaiQ's distribution also mitigates the pathological side-effects of hardware errors on NISQ quantum machines where the majority of critical principal component features could be concentrated on a single sub-generator. This sub-generator could be mapped to qubits with higher hardware error rates, and this can potentially make the training less effective. Our evaluation confirms the effectiveness of MosaiQ's principal component feature distribution among learners. Finally, we describe how MosaiQ utilizes the adaptive noise during image generation to increase the variety of images generated to avoid mode collapse.", + "bbox": [ + 496, + 279, + 890, + 627 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Adaptive Input Noise to Improve Variety of Generated Images. Recall that it is critical for the quantum generator to effectively utilize the random input noise to generate a variety of images for the same class. The inability to generate a variety of images within the same class leads to the \"mode collapse\" problem. Therefore, while MosaiQ's previous methods help us achieve high quality, it is critical to achieving high-quality, while also maintaining variety.", + "bbox": [ + 496, + 638, + 890, + 758 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To address this challenge, MosaiQ introduces an adaptive noise range based on the ratio of training loss between the quantum generator and the classical discriminator. The noise range is determined by the current progress of the generator discriminator mini-max game, instead of the traditional fixed range of $[0, \\frac{\\pi}{2}]$ as employed by QGpatch. Formally, the adaptive noise (Noiseadaptive) is defined below in terms of the Generator loss $G_{L}$ and Discriminator loss $D_{L}$ and the Ratio $\\frac{G_{L_0}}{D_{L_0}}$ is the Discriminator/Generator loss ratio", + "bbox": [ + 496, + 763, + 890, + 904 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "7033", + "bbox": [ + 482, + 924, + 514, + 936 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/a9540d1f72372097272222ba4b4c5bd7d921bdb08d0f160c57882d35ab0400b6.jpg", + "image_caption": [ + "Figure 5. MosaiQ's process for training and optimizing the quantum generator circuits using PCA transformation, feature distribution, and adaptive noise generation." + ], + "image_footnote": [], + "bbox": [ + 81, + 87, + 452, + 253 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "observed after the first epoch during training.", + "bbox": [ + 75, + 348, + 375, + 364 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\text {N o i s e} _ {\\text {a d a p t i v e}} = \\frac {\\pi}{8} + \\frac {5 \\pi}{8} R e L U \\left(\\operatorname {T a n h} \\left(\\frac {D _ {L}}{G _ {L}} - \\frac {G _ {L _ {0}}}{D _ {L _ {0}}}\\right)\\right) \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 93, + 373, + 468, + 406 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As the above formula indicates, this adaptive bound enforces a minimum noise range of $\\frac{\\pi}{8}$ and a maximum range of $\\frac{3\\pi}{4}$ for the noise. While the bounds are chosen to be a specific constant, the noise is always distributed within this range and the upper bound automatically adjusts itself based on the relative effectiveness of the generator and the discriminator. MosaiQ does not require tuning the thresholds for the range for different classes, it automatically adjusts itself to adapt to different conditions during training.", + "bbox": [ + 75, + 415, + 468, + 551 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "MosaicQ embeds the adaptive noise using angle embedding on the quantum circuit. The $Tanh$ function is used to scale the adaptive noise to asymptotically approach the range $[-1, 1]$ . MosaiQ chose $Tanh$ because it is a widely-used activation function in deep learning applications which transforms unbounded data into data bound by $[-1, 1]$ . $Tanh$ is defined as $Tanh(x) = \\frac{e^{2x} - 1}{e^{2x} + 1}$ . In practice, we observed that it is not effective to have a noise range lower than $\\frac{\\pi}{8}$ , we leverage $ReLU$ to force negative values to be zero. $ReLU$ is also a commonly used activation function, however, $ReLU$ is used to provide a non-linear transform that makes all negative values 0 (to ensure that the noise is never less than $\\frac{\\pi}{8}$ ), and keeps all positive values the same.", + "bbox": [ + 75, + 551, + 468, + 750 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "While the non-linearity of $\\text{Tanh}$ and $\\text{ReLU}$ are important when used typically as activation functions, the nonlinearity is not the main function in this application. If the generator is not able to catch up with the discriminator for some iterations at this small range, it should learn this smaller range instead of getting even smaller. We set the minimum as $\\frac{\\pi}{8}$ as we discovered that a lower value than $\\frac{\\pi}{8}$ results in mode collapse, with almost no distinction between images generated for a given class.", + "bbox": [ + 75, + 750, + 470, + 885 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Leveraging adaptive noise for input ensures more consis", + "bbox": [ + 96, + 885, + 467, + 900 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/833740fa3d394894cb30493f26cb07620164b5c59cede476c0bf63ac22664881.jpg", + "image_caption": [ + "Figure 6. MosaiQ's inference process to generate new images via running the generators on quantum machines." + ], + "image_footnote": [], + "bbox": [ + 504, + 87, + 883, + 167 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "tent training as the generator can focus on quality when it is doing relatively worse compared to the classical discriminator and expand to generating more variety in high quality as it begins to fool the discriminator more on an easier objective. Overall, the adaptive noise mechanism helps us increase the variety of images for a given class while ensuring that the image quality also remains high. This is further confirmed by our evaluation (Sec. 3).", + "bbox": [ + 496, + 250, + 890, + 369 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "MosaiQ's Classical Discriminator. MosaiQ's discriminator is a classical deep-learning network, designed to aid in the training of the quantum generator. This network is essentially training wheels to guide a difficult-to-train quantum GAN, which can be discarded after training. The discriminator is much larger than the quantum generator, as there is only a single discriminator that must compete in the adversarial game with multiple quantum generators. Typical to its classical counterpart, MosaiQ's discriminator has multiple linear layers with $ReLU$ activation (e.g., 64 layers). MosaiQ has a terminal layer with Sigmoid activation which introduces more non-linearity into the network, which enables it to learn more complex structures. The single value produced at the end of the discriminator network allows it to act as a classifier to distinguish between real and generated data.", + "bbox": [ + 496, + 378, + 892, + 621 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Putting It All Together. The overall workflow for training and inference for MosaiQ are visually summarized in Fig. 5 and 6, respectively. Fig. 5 depicts the continuous feedback-driven process where the discriminator and generator participate in a non-cooperative game to improve the overall quality of MosaiQ. Depending upon the relative loss of the discriminator and generator networks, the random input noise is automatically adjusted to help MosaiQ generators avoid the problem of mode collapse problem and enable it to generate variety. During the training process, the input images are transformed using PCA to encode critical and more information in a compact manner for resource-limited NISQ quantum computers, instead of learning over the input images pixel by pixel. Finally, the five-step inference procedure shown in Fig. 6 highlights that the PCA transformation is inverted to generate new images when running the fully-trained MosaiQ generators on real quantum computers for inference to generate new images.", + "bbox": [ + 496, + 628, + 892, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "7034", + "bbox": [ + 482, + 925, + 514, + 936 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3. Experimental Methodology", + "text_level": 1, + "bbox": [ + 76, + 89, + 331, + 107 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Datasets. MosaiQ is evaluated on the MNIST [6] and Fashion MNIST datasets [21] as they have been widely-used for QML evaluation on NISQ-era quantum machines [15, 11]. MNIST consists of $28 \\times 28$ gray-scale images of handwritten digits from 0 to 9. Fashion MNIST consists of $28 \\times 28$ grayscale images of clothing and accessories. Fashion MNIST provides more challenges for image generation and is chosen to explore more domains of quantum image generation. For both datasets, we split the dataset by image label and train individual models for each data type. This technique has been used in [11] and allows us to interpret the generation process and difficulties isolated for each class of data.", + "bbox": [ + 75, + 114, + 468, + 297 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Experimental Framework and Training Details. The environment for MosaiQ consists of PyTorch [16] acting as a wrapper for Pennylane [3]. MosaiQ is trained on IBM's quantum simulator for speed, but the inference is performed on both the quantum simulator and real quantum machine. For real quantum machine experiments, Pennylane compiles the circuits into a backend compatible with IBM-Qiskit [18]. All real machine runs were performed on the IBM QX Jakarta machine [18]. Images used in training are selected from the training set and decomposed to principal components of size 40. These components are divided across eight five-qubit sub-generators. The discriminator learns to differentiate at the level of principal components and does not need to utilize a full image. Our final FID metrics reported are at the end of the training after 500 iterations (where all methods achieve near-final stability).", + "bbox": [ + 75, + 303, + 470, + 545 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "MosaicQ uses PyTorch's Standard Gradient Descent Optimizer for both the generator and discriminator and Binary Cross Entropy Loss for the shared loss of the generator and discriminator. The Adaptive Noise range is simple to calculate based on the generator and discriminator loss and MosaicQ automatically guides it to adjust itself every training iteration. The generator learning rate is 0.3 and the discriminator learning rate to .05 with a batch size of 8.", + "bbox": [ + 75, + 546, + 468, + 667 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Framework for Competing Techniques. We set up QG-Patch, the state-of-the-art technique [11], using the popular Pennylane framework and choose the parameters used in the original paper [11]. Our QGPatch training is performed using the batch size of eight and it trains until the quality stabilizes (500 iterations). We use the same network size that is mentioned in the original paper, using 4 subgenerators with 5 features each. Evaluating the probabilities in measurement yields a 64-pixel (8x8) image. As MosaicQ's results are based on the original size of the datasets of 784 pixels, we upscale the results of QGPatch using Bilinear Interpolation to allow for direct comparison. We rigorously explored multiple interpolation techniques to provide QGPatch as much as an advantage as possible and experimentally determined that Bilinear interpolation yielded the", + "bbox": [ + 75, + 672, + 470, + 901 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/107b37d4c68a0a689e230222f4981bf8fe9130167ae6e998c9c184c2009d9758.jpg", + "image_caption": [ + "Figure 7. MosaiQ produces visually higher-quality images compared to the state-of-the-art technique, QGPatch, for different classes of MNIST and Fashion-MNIST datasets." + ], + "image_footnote": [], + "bbox": [ + 511, + 88, + 877, + 165 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "highest quality upscaling. For QGPatch, similar to MosaiQ, all metrics scores shown are calculated based on 500 images generated at the end of training compared to the entire distribution of the respective image category.", + "bbox": [ + 496, + 226, + 890, + 287 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We additionally set up other classical experiments to act as ablations for the efficacy of MosaiQ. We introduce two techniques: (1) PCAInverse (using random inputs and PCA inverse transformation to generate images), and (2) ClassicalPCA (a purely-classical GAN using the same number of parameters as MosaiQ, but uses MosaiQ's PCA technique for feature compression). PCAInverse applies the same inverse PCA transformation as MosaiQ, to random noise of size 40. This technique is designed to explore the isolated effects of the inverse PCA transformation procedure since it does not perform any learning. ClassicalPCA trains a purely-classical GAN with an identical number of parameters as MosaiQ and apply the same inverse PCA transformation workflow.", + "bbox": [ + 496, + 287, + 892, + 500 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Figures of Merit. To capture the quality of image generation, our evaluation figures of merit are both qualitative and quantitative. Our primary quantitative figure of merit is FID (Frechet inception distance) score [10]. FID evaluates the distance between two distributions, as defined below for a Gaussian with mean $(m, C)$ and a second Gaussian with mean $(m_w, C_w)$ : FID = $\\| m - m_w\\|_2^2 + Tr(C + C_w - 2(CC_w)^{1/2})$ . A lower FID score between two distributions indicates higher similarity – and hence, lower FID scores imply higher quality. The FID score has been shown to provide a more meaningful comparison over alternative metrics (e.g., Inception Score) for image GANs [10].", + "bbox": [ + 496, + 506, + 890, + 688 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We also evaluate the variance of our images, by evaluating the variance of the pixel values relative to the mean. As defined below, the variance metric gives insight into the distinctness of the images generated for each method. For each pixel in an image row $r$ and column $c$ in an image, we sum the squared difference from the mean value for that respective pixel to achieve our variance score $V$ . We then take the cumulative density function (CDF) of these variance scores for each image generated image $G(z)$ given uniformly distributed noise $z$ from $[0, \\pi/2]$ : $V = \\sum_{r} \\sum_{c} (\\mu_{rc} - G(z)_{rc})^2$ . A higher variance indicates higher variety in generated images for a given class – which is desirable, however, it is also critical that a method should attain a lower FID score before demonstrating higher variety.", + "bbox": [ + 496, + 689, + 892, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "7035", + "bbox": [ + 482, + 925, + 514, + 936 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/71b1c4a505a1b558cb6a7ec561c3e6feb321dbbeda536e4c9a63ed442d03fd79.jpg", + "image_caption": [ + "Figure 8. MosaiQ consistently produces lower FID score images (higher quality images) compared to QGpatch across different classes of the MNIST dataset." + ], + "image_footnote": [], + "bbox": [ + 78, + 88, + 467, + 181 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/08021d7447096302d4be4c84e55ff7aeb45d3e40b35d5f13ac63cb6ab227efa2.jpg", + "image_caption": [ + "Figure 9. MosaiQ consistently produces lower FID score images (higher quality images) compared to QGPatch across different classes of the Fashion-MNIST dataset." + ], + "image_footnote": [], + "bbox": [ + 78, + 260, + 467, + 372 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c0d2012a6d653cd14fe04df72a96896474be224b91937d1ca8b963227ce1ac0f.jpg", + "image_caption": [ + "Figure 10. MosaiQ produces higher quality images on the MNIST and Fashion MNIST dataset as compared to HQCGAN [19]. MosaiQ produces higher quality images than the classical methods: PCAInverse and ClassicalPCA." + ], + "image_footnote": [], + "bbox": [ + 78, + 450, + 464, + 565 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4. Evaluation and Analysis", + "text_level": 1, + "bbox": [ + 76, + 669, + 307, + 686 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we go over the results of MosaiQ and provide an analysis of the key elements of the design.", + "bbox": [ + 75, + 695, + 468, + 726 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "MosaiQ: Key Results and SOTA Comparison. MosaiQ yields significantly better image quality both visually and quantitatively compared to the state-of-the-art (SOTA) method, QGpatch [11]. As discussed earlier, MosaiQ is evaluated on two different datasets to cover diversity across datasets and within a dataset with different shapes and styles (digits and clothing). First, we highlight that MosaiQ provides a significant visual enhancement in the images produces across different classes compared to the SOTA method. In fact, Fig. 7 shows that the SOTA-produced images are almost unrecognizable for sophisticated shapes ('0'", + "bbox": [ + 75, + 734, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/8aad6b6f9380fde982caff74317aa05db518a44ee89a9387ae8e672f7800590c.jpg", + "image_caption": [ + "Figure 11. MosaiQ produces higher quality images on every class of the MNIST dataset as compared to HQCGAN [19] in addition to the classical methods tested." + ], + "image_footnote": [], + "bbox": [ + 500, + 88, + 893, + 181 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/4af3cda8deb329f570a784c36cc5235012d0182e212999cc08518a95f4ec474b.jpg", + "image_caption": [ + "Figure 12. MosaiQ produces higher quality images on every class of the Fashion MNIST dataset as compared to HQCGAN [19] in addition to the classical methods tested." + ], + "image_footnote": [], + "bbox": [ + 500, + 266, + 893, + 378 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "vs. ‘5’ and different types of shoes). In comparison, MosaiQ is effective across different class types – this is further substantiated by lower FID scores of the images generated by MosaiQ (Fig. 8 and 9).", + "bbox": [ + 496, + 477, + 890, + 537 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "As expected, the FID score obtained by MosaiQ varies across different classes for both datasets; this is because of varying degrees of difficulty and shapes of different images. However, the most notable observation is that MosaiQ consistently outperforms QGPatch across all class types by a significant margin (by more than 10 points in many cases). In fact, MNIST digit '7' is quite challenging for QGPatch (FID score is 60), and MosaiQ improves the FID score by approximately 20 points. Similarly, the most challenging class in the Fashion-MNIST dataset (Boot) receives a 45-point improvement by MosaiQ. The key reason MosaiQ outperforms QGPatch is the efficiency of principal components in capturing information. Instead of having to learn pixels one by one, MosaiQ scales more easily by learning a distribution of features that better organize redundancy. For example, most of the background of MNIST and Fashion MNIST images are black, in the case of QGPatch, each pixel must be synthesized, where MosaiQ may be able to build these features with only a few principal components.", + "bbox": [ + 496, + 537, + 892, + 824 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We also compare MosaiQ to other methods, including the PCAInverse technique, the ClassicalPCA technique, and a recent work on hybrid quantum GANs which we refer to as HQCGAN [19]. We sample generated images in Fig. 10 and find the images produced by all methods tested", + "bbox": [ + 496, + 825, + 893, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "7036", + "bbox": [ + 482, + 925, + 514, + 936 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c99ef7fb23a3fc89ab1fba68779abb7165dbad9077592d861aaf015e6bf6fd1b.jpg", + "image_caption": [ + "Figure 13. MosaiQ's PCA feature distribution among learners improves the quality of generated images. The figure shows a distribution of 200 FID scores (comparing 8 images each to the entire data distribution) for the case with and without PCA feature redistribution." + ], + "image_footnote": [], + "bbox": [ + 78, + 87, + 464, + 200 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "are lower quality than MosaiQ, producing images which are far less human-recognizable. We show the corresponding FID scores for MNIST in Fig 11 and Fashion MNIST in Fig. 12. We find that MosaiQ produces higher quality images and significantly improved FID scores in all cases tested compared to the classical methods (PCAInverse and ClassicalPCA), and HQCGAN. Importantly, MosaiQ outperforms ClassicalPCA, demonstrating the power of quantum networks in image generation when compared to equal-sized classical networks. Our results show that while HQCGAN is promising and useful, the final quality may not be as high as MosaiQ – this is because HQCGAN requires significantly more parameters, more training resources, lacks noise-mitigation, and learns noise in a fixed range ([0, 1) instead of MosaiQ's adaptive noise range technique). Next, we dissect the key reasons behind MosaiQ's effectiveness in more detail.", + "bbox": [ + 75, + 310, + 468, + 566 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Why Does MosaiQ Work Effectively? Effect of careful PCA feature distribution among sub-generators. Recall that MosaiQ employs an intelligent PCA feature distribution among sub-generators in the generation phase. The goal is to equalize the explainable PCA feature variance across learners – in an effort to make learners equally capable instead of weaker learners not effectively contributing toward the overall quality. To better understand and demonstrate the effectiveness of this mechanism, Fig. 13 shows the FID score over multiple training iterations with and without this mechanism while keeping all other design elements intact. For easier interpretation, Fig. 13 shows this for class digit '5' for the MNIST dataset. We observe that PCA feature distribution allows MosaiQ to achieve lower (and hence, better) FID score over training compared to without employing this mechanism. A side benefit of this mechanism is that MosaiQ can also mitigate hardware errors on real quantum computers, as discussed later.", + "bbox": [ + 75, + 574, + 468, + 847 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effect of adaptive noise generation during training. Fig. 14 shows the effect of adaptive noise generation that is used by the MosaiQ generators instead of using a constant", + "bbox": [ + 75, + 854, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3eda43be3f6fa41acad06d1bb45f526c5f7479d7fd489872a751d7241a0a33a0.jpg", + "image_caption": [ + "Figure 14. Adaptive noise during generation helps MosaiQ achieve variety (higher variance across images for the same class to mitigate mode-collapse challenge), while achieving lower FID score at the same time, as shown earlier." + ], + "image_footnote": [], + "bbox": [ + 501, + 87, + 883, + 189 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/da7a67d833aabf791be599da57bb470dbb1ee936d1c0bbe12ef017ad1df9882c.jpg", + "image_caption": [ + "Figure 15. Visual image quality of images produced by MosaiQ on real IBM quantum machine (Jakarta) for six representative classes for MNIST and Fashion-MNIST datasets." + ], + "image_footnote": [], + "bbox": [ + 503, + 292, + 885, + 351 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "noise threshold range (i.e., $[0, \\frac{\\pi}{2}]$ ) used by the QGPatch method. Recall that GANs often suffer from intra-class mode-collapse challenges where they can produce a high-quality image for a given class, but there is a possibility that all generated images for a given class appear similar. Therefore, it is critical to ensure that the generated images for a given class have sufficient variety. Fig. 14 confirms that adaptive noise improves variety (class digit '5' used as an example) compared to fixed noise ranges. This is because adaptive noise enables the generators to learn over different distributions more effectively and generate variations. Having an adaptive range allows the generator to improve variety when it is doing comparatively well and focus on stability when it is performing poorly with a smaller range of inputs. Taking advantage of this allows us to have high stability in training and high variety over time.", + "bbox": [ + 496, + 436, + 892, + 679 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "MosaiQ on NISQ Quantum Machines. Our experimental campaign on real superconducting-based IBM NISQ quantum computers confirms MosaiQ produces higher quality images across different datasets with diverse classes of images. Fig. 15 and Table 1 summarize the image quality results for QGPatch and MosaiQ. While MosaiQ's quality remains consistent with simulations, QGPatch's quality degrades considerably on real computers. In fact, our results revealed QGPatch produces lower quality images and sometimes unrecognizable images because QGPatch is more prone to side-effects of prevalent quantum gate errors on real machines, while MosaiQ's simplistic design successfully mitigates those effects as discussed next.", + "bbox": [ + 496, + 686, + 890, + 883 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "First, we observe that MosaiQ produces competitive", + "bbox": [ + 517, + 885, + 890, + 901 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "7037", + "bbox": [ + 482, + 925, + 514, + 936 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/5021b59ab351e7c7373f51fcecc897feea021ac7fe5db3547b7c792accecb97f.jpg", + "table_caption": [ + "Table 1. QGpatch and MosaiQ's FID scores on a real quantum computer for MNIST & Fashion-MNIST datasets.", + "(a) QGPatch" + ], + "table_footnote": [], + "table_body": "
EnvironmentDigit 0Digit 5Digit 9T ShirtPantsShoes
Quantum Simulator525248454282
IBM Jakarta Machine145134131125144124
", + "bbox": [ + 84, + 141, + 472, + 181 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/7e0ead8330b3937d31ce89d23b70ddda406702531a164ccfe1e0450759f38d49.jpg", + "table_caption": [ + "(b) MosaiQ" + ], + "table_footnote": [], + "table_body": "
EnvironmentDigit 0Digit 5Digit 9T ShirtPantsShoes
Quantum Simulator424233342238
IBM Jakarta Machine454435382338
", + "bbox": [ + 84, + 202, + 472, + 241 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "quality images despite hardware errors on real quantum computers. Due to high queue wait time and limited availability of quantum resources, we are presenting results only for selected classes (three from each dataset) which cover a diverse range of intricacies in terms of shape and information. In fact, via visual inspection for different images produced for a given class, we observe that the variety in the produced images by MosaiQ is also high on the quantum computer - effectively mitigating the mode-collapse pitfall in GANs. This is because of MosaiQ's adaptive noise mechanism during the generation phase that improves image variety and avoids mode collapse.", + "bbox": [ + 75, + 273, + 468, + 453 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Second, we observe that the FID scores of MosaiQ on a real quantum computer are similar to error-free simulation results, across different classes. This result demonstrates that MosaiQ's design is effective even when hardware errors are present. In fact, the IBM Jakarta computer has a considerably low quantum volume (higher is better) with a quantum volume of 16. Quantum volume is a useful metric in determining the error rate and capabilities of a quantum computer. For perspective, at the time of writing, IBM has computers available with quantum volumes of 128. We chose a relatively less capable quantum computer for our experiments to demonstrate the portability and robustness of MosaiQ. The reason for MosaiQ's effectiveness is twofold: (1) its simplistic design for generator learners, which avoids a large number of two-qubit gates, and circuits with high depths. which are more prone to hardware noise, and (2) its PCA feature distribution mapping among the ensemble of learners in the generator - this careful redistribution ensures that most critical PCA features are not concentrated on a few qubits, which in the pathological case could be most severely impacted by hardware-errors. MosaiQ's PCA redistribution ensures that the learners do not need to know the error rate of individual qubits on the computer or make assumptions about different error types.", + "bbox": [ + 75, + 454, + 470, + 816 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Related Work", + "text_level": 1, + "bbox": [ + 76, + 829, + 218, + 845 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Demonstration of the Speedup Achieved by Quantum GANs. Quantum GANs were first introduced by Lloyd et al.[14]. This work theoretically proved the potential for ex", + "bbox": [ + 75, + 854, + 468, + 902 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "ponential superiority of Quantum GANs over their classical counterparts. This was later followed by the work of Dallaire-Demers et al. [4], which established a way to design and train variational quantum circuits as the generator component of a Quantum GAN model. Nakaji et al. [15] use a hybrid configuration with a classical discriminator and a quantum generator for classification. Their results demonstrate the potential for quantum GANs to solve problems that are intractable with classical GANs.", + "bbox": [ + 496, + 90, + 890, + 226 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Enchancing Classical GANs using Quantum Components. Approaches such as the work done by Rudolph et al. [17] use a quantum enhancer for large-scale fully-classical generators to enhance the quality of image generation. While the images generated are high quality, this is mostly attributed to the large classical generators. The visual results in these works seem appealing because the classical GAN-based baseline is already high quality, with a quantum preamble which only improves the image quality slightly. This is in contrast to MosaiQ which uses a quantum generator to generate images without a classical generator.", + "bbox": [ + 496, + 238, + 890, + 405 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Fully-Quantum Generators. The work of Huang et al. [12] uses quantum gradients to train quantum GANs to replicate logic gates such as XOR with high fidelity and also generate images from the MNIST dataset. The technique relies on using quantum-based loss functions for their generator and discriminator. This work also shows that quantum GANs have similar performance as classical GANs while using $94.98\\%$ fewer parameters. A succeeding work with higher quality MNIST image generation can be found in QGPatch [11], with a generator split among several subgenerators each responsible for generating a part of the full image. QGPatch trains a quantum generator against a classical discriminator. The quality of generation is the highest among pre-MosaiQ quantum GANs with a purely quantum generative component, at the time of writing. Therefore, we compare MosaiQ against QGPatch in this paper and show that MosaiQ outperforms QGPatch in terms of image quality and variety.", + "bbox": [ + 496, + 416, + 890, + 689 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 715, + 617, + 729 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "MosaicQ is the first quantum GAN to successfully generate high-quality images on real quantum computers. MosaicQ incorporates PCA feature redistribution and adaptive noise to facilitate improved interaction between the quantum generator and classical elements of the model. This integration enhances the quality and variety of the generator's output respectively.", + "bbox": [ + 496, + 744, + 890, + 851 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements We thank the reviewers for constructive feedback. This work was supported by NSF Award 2144540, Northeastern University, and Rice University.", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "7038", + "bbox": [ + 482, + 925, + 514, + 936 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 90, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Samet Akcay, Amir Atapour-Abarghouei, and Toby P. Breckon. Ganomaly: Semi-supervised anomaly detection via adversarial training. In C. V. Jawahar, Hongdong Li, Greg Mori, and Konrad Schindler, editors, Computer Vision - ACCV 2018, pages 622-637, Cham, 2019. Springer International Publishing. 1, 2", + "[2] Martin Arjovsky, Soumith Chintala, and Léon Bottou. Wasserstein gan, 2017. 1", + "[3] Ville Bergholm, Josh Izaac, Maria Schuld, et al. 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Fashion-mnist: a novel image dataset for benchmarking machine learning algorithms, 2017. 2, 6", + "[22] Jun-Yan Zhu, Taesung Park, Phillip Isola, and Alexei A. Efros. Unpaired image-to-image translation using cycle-consistent adversarial networks, 2017. 1" + ], + "bbox": [ + 501, + 92, + 890, + 500 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "7039", + "bbox": [ + 482, + 926, + 514, + 936 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/MosaiQ_ Quantum Generative Adversarial Networks for Image Generation on NISQ Computers/f3fd0f01-346f-46fa-9180-3373ca2881cf_model.json b/2023/MosaiQ_ Quantum Generative Adversarial Networks for Image Generation on NISQ Computers/f3fd0f01-346f-46fa-9180-3373ca2881cf_model.json new file mode 100644 index 0000000000000000000000000000000000000000..e4001282806ae22c02ce5c32dd96450f525f20c4 --- /dev/null +++ b/2023/MosaiQ_ Quantum Generative Adversarial Networks for Image Generation on NISQ Computers/f3fd0f01-346f-46fa-9180-3373ca2881cf_model.json @@ -0,0 +1,1892 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.807, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.218, + 0.131, + 0.756, + 0.177 + ], + "angle": 0, + "content": "MosaiQ: Quantum Generative Adversarial Networks for Image Generation on NISQ Computers" + }, + { + "type": "text", + "bbox": [ + 0.176, + 0.205, + 0.286, + 0.221 + ], + "angle": 0, + "content": "Daniel Silver" + }, + { + "type": "text", + "bbox": [ + 0.135, + 0.223, + 0.327, + 0.24 + ], + "angle": 0, + "content": "Northeastern University" + }, + { + "type": "text", + "bbox": [ + 0.115, + 0.243, + 0.348, + 0.256 + ], + "angle": 0, + "content": "silver.da@northeastern.edu" + }, + { + "type": "text", + "bbox": [ + 0.432, + 0.205, + 0.538, + 0.221 + ], + "angle": 0, + "content": "Tirthak Patel" + }, + { + "type": "text", + "bbox": [ + 0.422, + 0.223, + 0.548, + 0.24 + ], + "angle": 0, + "content": "Rice University" + }, + { + "type": "text", + "bbox": [ + 0.387, + 0.243, + 0.585, + 0.256 + ], + "angle": 0, + "content": "tirthak.patel@rice.edu" + }, + { + "type": "text", + "bbox": [ + 0.678, + 0.205, + 0.803, + 0.221 + ], + "angle": 0, + "content": "William Cutler" + }, + { + "type": "text", + "bbox": [ + 0.645, + 0.223, + 0.836, + 0.24 + ], + "angle": 0, + "content": "Northeastern University" + }, + { + "type": "text", + "bbox": [ + 0.624, + 0.243, + 0.856, + 0.256 + ], + "angle": 0, + "content": "cutler.wi@northeastern.edu" + }, + { + "type": "text", + "bbox": [ + 0.16, + 0.266, + 0.279, + 0.282 + ], + "angle": 0, + "content": "Aditya Ranjan" + }, + { + "type": "text", + "bbox": [ + 0.124, + 0.284, + 0.316, + 0.3 + ], + "angle": 0, + "content": "Northeastern University" + }, + { + "type": "text", + "bbox": [ + 0.104, + 0.304, + 0.336, + 0.317 + ], + "angle": 0, + "content": "ranjan.ad@northeastern.edu" + }, + { + "type": "text", + "bbox": [ + 0.394, + 0.265, + 0.558, + 0.301 + ], + "angle": 0, + "content": "Harshitta Gandhi Northeastern University" + }, + { + "type": "text", + "bbox": [ + 0.374, + 0.304, + 0.606, + 0.317 + ], + "angle": 0, + "content": "gandhi.ha@northeastern.edu" + }, + { + "type": "text", + "bbox": [ + 0.696, + 0.266, + 0.814, + 0.28 + ], + "angle": 0, + "content": "Devesh Tiwari" + }, + { + "type": "text", + "bbox": [ + 0.66, + 0.283, + 0.851, + 0.3 + ], + "angle": 0, + "content": "Northeastern University" + }, + { + "type": "text", + "bbox": [ + 0.644, + 0.304, + 0.867, + 0.316 + ], + "angle": 0, + "content": "d.tiwari@northeastern.edu" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.352, + 0.314, + 0.368 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.377, + 0.473, + 0.528 + ], + "angle": 0, + "content": "Quantum machine learning and vision have come to the fore recently, with hardware advances enabling rapid advancement in the capabilities of quantum machines. Recently, quantum image generation has been explored with many potential advantages over non-quantum techniques; however, previous techniques have suffered from poor quality and robustness. To address these problems, we introduce MosaiQ a high-quality quantum image generation GAN framework that can be executed on today's Near-term Intermediate Scale Quantum (NISQ) computers." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.558, + 0.21, + 0.573 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.47, + 0.765 + ], + "angle": 0, + "content": "Generative Adversarial Networks, or GANs, are a type of neural network architecture used in machine learning and computer vision for generative modeling [8, 22, 2, 9]. A classical GAN consists of two neural networks, a generator, and a discriminator, that are trained simultaneously in a competitive process. The generator generates fake data samples, while the discriminator tries to distinguish them from real ones found in the training set, hence serving as an \"adversarial entity\". Classical GANs have received significant attention for generating high-quality images, among other purposes including text generation, data augmentation, and anomaly detection [20, 1, 5]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Naturally, this has spawned interest in the quantum information science community to develop corresponding quantum GANs that run on quantum computers. While recent efforts toward developing quantum GANs have been instrumental and early results have been encouraging, we discovered that existing approaches have severe scalability bottlenecks and have significant room for improvement. This is especially true in the context of generating high-quality image generation on real-system quantum computers." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.353, + 0.8, + 0.37 + ], + "angle": 0, + "content": "Opportunity Gap for Quantum GANs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.377, + 0.895, + 0.59 + ], + "angle": 0, + "content": "A recent work by Huang et al. [11], referred to as QGPatch in this paper, is the state-of-the-art demonstration of QuantumGANs on real quantum computers. As our paper also demonstrates, QGPatch can learn different shapes and produce recognizable images in some cases, but can often yield low-quality images. It suffers from the scalability challenge because it breaks the image into \"patches\" and performs a pixel-by-pixel learning. Second, it is not effective at generating a variety of images within the same class – this problem is known as \"mode collapse\" [7]. It is nontrivial to achieve high-quality image generation while also maintaining variety. Motivated by these limitations, MosaicQ's design pushes the state of the art by achieving higher scalability, image quality, and variety." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.598, + 0.698, + 0.615 + ], + "angle": 0, + "content": "Contributions of MosaiQ" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.622, + 0.894, + 0.728 + ], + "angle": 0, + "content": "I. MosaiQ introduces the design and implementation of a novel quantum generative adversarial network for image generation on quantum computers. MosaiQ's approach is a hybrid classical-quantum generation network where a network of low-circuit-depth variational quantum circuits are leveraged to learn and train the model. Upon acceptance, MosaiQ will be available as an open-source contribution." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.895, + 0.902 + ], + "angle": 0, + "content": "II. MosaiQ's design demonstrates how the extraction of principal components of images enables us to learn and generate higher-quality images, compared to the state-of-the-art approach which is limited in its scalability due to pixel-by-pixel learning [11]. However, exploiting information in principal components to its full potential is non-trivial, and MosaiQ proposes to mitigate those challenges using feature redistribution. Furthermore, MosaiQ introduces a novel adaptive input noise generation technique to improve both the quality and variety of generated images – mitigating the common risk of mode collapse in generative networks." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.957 + ], + "angle": 0, + "content": "7030" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.079, + 0.088, + 0.468, + 0.197 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.217, + 0.47, + 0.248 + ], + "angle": 0, + "content": "Figure 1. Classical generative adversarial network (GAN) and MosaiQ's hybrid quantum-classical GAN architecture." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.286, + 0.473, + 0.483 + ], + "angle": 0, + "content": "III. Our evaluation demonstrates that MosaiQ significantly outperforms the state-of-the-art methods [11] on both simulation and real quantum computers with a hardware error. MosaiQ is evaluated on the MNIST [6] and Fashion MNIST datasets [21] – widely-used for QML evaluation on Nearterm Intermediate Scale Quantum (NISQ) machines [15, 11]. MosaiQ outperforms the state-of-the-art methods [11] both visually and quantitatively – for example, over 100 points improvement in image quality generated on IBM Jakarta quantum computer using the FID (Fréchet Inception Distance) score [10], which is popularly used for comparing image quality. MosaiQ is open-sourced at https://github.com/SilverEngineered/MosaiQ." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.495, + 0.383, + 0.513 + ], + "angle": 0, + "content": "2. MosaiQ: Challenges and Solution" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.522, + 0.47, + 0.628 + ], + "angle": 0, + "content": "In this section, we present the design and implementation of MosaiQ, a quantum image generative network. To provide better context for understanding, first, we briefly describe the classical generative adversarial networks (GAN) (depicted in Fig. 1(a)), describe the limitations of the state-of-the-art quantum GANs, and then, provide the details of MosaiQ's quantum GAN design (depicted in Fig. 1(b))." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.636, + 0.434, + 0.652 + ], + "angle": 0, + "content": "2.1. Generative Adversarial Networks (GANs)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.66, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Generative Adversarial Networks, or GANs, are a type of neural network architecture used in machine learning for generative modeling [8]. The basic architecture and workflow of a classical (non quantum) GAN are shown in Fig. 1 (a). A classical GAN consists of two neural networks, a generator, and a discriminator, that are trained simultaneously in a competitive process. The generator generates fake data samples, while the discriminator tries to distinguish them from real ones found in the training set, hence serving as the \"ad adversary\". Through training, the generator learns to create increasingly realistic samples that mimic the distribution of the real data in order to better fool an increasingly effective discriminator, eventually reaching an attempt to attain equilibrium with the value function expressed as \\(\\min_G\\max_D\\mathbb{E}_{x\\sim q_{\\mathrm{data}}(x)}[\\log D(\\pmb {x})] + \\mathbb{E}_{\\pmb {z}\\sim p(\\pmb {z})}[\\log (1 - D(G(\\pmb {z})))]\\). This value function has two" + }, + { + "type": "image_caption", + "bbox": [ + 0.556, + 0.089, + 0.646, + 0.102 + ], + "angle": 0, + "content": "Digit 0 (MNIST)" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.104, + 0.888, + 0.165 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.175, + 0.892, + 0.235 + ], + "angle": 0, + "content": "Figure 2. State-of-the-art quantum image generator, QG-Patch [11], generates low-quality images for different datasets. However, its quality is still similar to a classical GAN with \\(25 \\times\\) more parameters and iterations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.257, + 0.892, + 0.348 + ], + "angle": 0, + "content": "main identifiable components that correspond to the respective optimization objectives of the generator and the discriminator. The use of log provides more numerical stability because it converts the multiplication of multiple small probabilities into addition, and it also allows us to calculate the derivatives more easily during the optimization process." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.348, + 0.893, + 0.5 + ], + "angle": 0, + "content": "Once fully trained, a generator component of the GAN is capable of converting random noise into new data samples (e.g., boots) that conform to the original distribution of the training data. Essentially, the generator, without the use of a discriminator, can be inferred to obtain new data samples. GANs have been shown to be useful in a variety of applications such as image and text generation, data augmentation, and anomaly detection [20, 1, 5]. Naturally, this has spawned interest in the quantum information science community to develop corresponding quantum GANs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.507, + 0.892, + 0.703 + ], + "angle": 0, + "content": "Quantum GANs follow a similar generator and discriminator structure as classical GANs but use quantum principles to train and infer from the model. Typically, the discriminator functions on classical resources, and the generator is trained on quantum resources. This is expected, as this structure allows the Quantum GANs to leverage quantum resources for generation tasks – the component that persists beyond training; recall that the discriminator is essentially a quality inspector that can be decoupled after training and is not required during inference. While this structure is intuitive and has been demonstrated to be somewhat promising [11], there are multiple open challenges that need to be overcome to achieve higher quality." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.712, + 0.842, + 0.728 + ], + "angle": 0, + "content": "2.2. Limitations of Existing Quantum GANs" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "A recent work by Huang et al. [11], referred to as QGPatch, is the most complete, state-of-the-art demonstration of QuantumGANs on real quantum computers. QGPatch follows the Quantum GAN architecture described earlier but achieves limited effectiveness - QGPatch can learn different shapes and produce recognizable images in some cases, but often suffers from low quality. Fig. 2 shows that digit '0' is a reasonable approximation of the ground truth, but the generated boot image is far less recognizable. Despite the imperfect generations, we can see in Fig. 2 how a classical GAN with \\(25 \\times\\) the parameters of QGPatch and" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.925, + 0.514, + 0.937 + ], + "angle": 0, + "content": "7031" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.211 + ], + "angle": 0, + "content": "trained for \\(25 \\times\\) as many iterations is worse or similar to the quantum technique - supporting the potential of quantum machine-learning for image generation tasks as compared to the classical approach with much higher resources and complexity. This independently provides experimental evidence for why the quantum information science community is motivated to accelerate the progress of Quantum GANs, despite its current limitations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.213, + 0.47, + 0.407 + ], + "angle": 0, + "content": "The reasons for the limited effectiveness of Quatum GANs are multi-fold. The quantum generator component runs on the quantum hardware and requires many qubits to produce high-quality images from random input noise (a qubit is the fundamental unit of computation and information storage on quantum computers). QGPatch addresses this challenge by breaking the image into \"patches\" and employing a generator for different patches. While this is reasonable for smaller resolution images, the \"patch-based\" approach suffers from scalability due to its fundamental nature of learning pixel-by-pixel. For example, a total of 245 qubits are required for images in the full-resolution 784-pixel MNIST dataset." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.409, + 0.47, + 0.606 + ], + "angle": 0, + "content": "The second challenge is performing efficient learning from random input noise – it is critical for the quantum generator to effectively utilize the random input noise to generate a variety of images for the same class. Inability to generate a variety of images within the same class – which even classical GANs suffer from – is popularly known as the “mode collapse” problem [7]. Mode collapse is a side-effect of the generator learning to generate only produce one type of image for a given class because the generator has learned to “fool” the discriminator for this image and saturates in its learning. It is non-trivial to achieve high-quality generating while also maintaining variety. Motivated by these limitations, MosaiQ’s design pushes the state of the art." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.614, + 0.388, + 0.63 + ], + "angle": 0, + "content": "2.3. Overview of MosaiQ and Key Ideas" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.637, + 0.47, + 0.833 + ], + "angle": 0, + "content": "Hybrid Quantum-Classical Architecture. MosaiQ uses a hybrid quantum-classical architecture for image generation, as summarized in Fig. 1(b). The generator is quantum in nature and trained using quantum simulation, and the discriminator is classical – similar to the construction in [15, 11]. However, there are two key novel architectural changes: (1) to address the scalability and quantum resource bottlenecks for generating high-quality images, MosaiQ applies a transformation on the input image dataset, and (2) MosaiQ employs quantum-style random noise as input to enhance the “variety or mode-collapse” challenge. These two key features are described after a brief description of MosaiQ's generator and discriminator." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.902 + ], + "angle": 0, + "content": "MosaiQ's Quantum Generator Network. MosaiQ's quantum generator component is a network of multiple subgenerators. Each sub-generator is a variational quantum circuit that is iteratively optimized to train a model. Vari-" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.089, + 0.888, + 0.173 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.178, + 0.89, + 0.21 + ], + "angle": 0, + "content": "Figure 3. Circuit ansatz design of MosaiQ's generators. The RY gates in each layer are optimized during training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.235, + 0.892, + 0.401 + ], + "angle": 0, + "content": "ational quantum circuits are specific types of quantum circuits where some components of the circuits are tunable parameters, which are iteratively optimized. As a background, a quantum circuit is essentially a sequence of quantum gates applied to qubits. The quantum gates are fundamental operations that manipulate the qubit state, and any gate can be represented as a unitary matrix. One-qubit gates, such as the Pauli gates \\((\\sigma_x,\\sigma_y,\\sigma_z)\\), apply a rotation to just one qubit and are categorized by the axis around which the rotation takes place, and by how much. Multi-qubit gates, such as the CNOT gate, allow the creation of entanglement." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.403, + 0.893, + 0.57 + ], + "angle": 0, + "content": "Variational quantum circuits in MosaiQ are comprised of two types of sections. The first type, \\( X \\), has fixed gates that entangle the qubits. The second type, \\( \\theta \\), has tunable \\( U_{3} \\) gates that are optimized via training. The overall circuit \\( V \\) is therefore an optimization function built of unitary transformations such that \\( V = U(X,\\theta) \\). One key feature of variational quantum circuits is the ability to leverage many off-the-shelf classical deep-learning techniques for training and optimization. This includes learning through common loss functions such as \\( L_{2} \\) loss and leveraging existing optimizers such as Adam [13] that MosaiQ leverages." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.572, + 0.892, + 0.723 + ], + "angle": 0, + "content": "All sub-generator circuits in MosaiQ have identical architectures, composed of a five-qubit circuit. Fig. 3 shows an example of the sub-generator circuit. The circuit consists of encoding the input noise as angles using \\( Rx \\) gates and \\( Ry \\) gates. Following the embedding of the noise, the parameterized weights are encoded on each quantum layer alongside \\( CZ \\) gates used to entangle the qubits at each layer. These weights contain the portion of the circuit that is optimized. Following these repeated layers, the Pauli \\( X \\) expected value is taken for each qubit in measurement." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.725, + 0.892, + 0.802 + ], + "angle": 0, + "content": "We note the simplistic design of MosaiQ's generator circuits is intentional; limiting the number of tunable parameters and depth of the circuits enables MosaiQ to mitigate hardware error impact on real quantum machines and maintain high quality, as confirmed by our evaluation (Sec. 3)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Scalable Learning by Extracting Principal Components. Unlike previous approaches, which learn to construct the pixels of an image directly and consequently, suffer from the scaling bottleneck, MosaiQ demonstrates that extracting and learning the rich features is effective. The principal component analysis (PCA) method enables efficient learn-" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.926, + 0.516, + 0.938 + ], + "angle": 0, + "content": "7032" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.092, + 0.468, + 0.202 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.208, + 0.47, + 0.253 + ], + "angle": 0, + "content": "Figure 4. MosaiQ divides the PCA features among the eight generator circuits in a manner that the total explained variance is close to equal across all generators." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.299, + 0.468, + 0.389 + ], + "angle": 0, + "content": "ing by focusing on the important features that compromise unique images, as opposed to having to learn to distinguish the important features from the redundant features in an image via the pixel-by-pixel method. PCA maximizes the entropy for a given number of components, concentrating the information of a dataset efficiently." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.392, + 0.47, + 0.664 + ], + "angle": 0, + "content": "The first step in learning principal components is normalizing the input data. Once the images are normalized, MosaiQ decomposes the images into principal components and scales these components between [0, 1] so that the quantum sub-generators can generate throughout the entire space of inputs. As quantum machines rely on only unitary transformations, it is not possible to obtain an output with an absolute value greater than one in measurement. These scaled components are fed into the discriminator as the \"real labels\" and the generator begins to learn how to mimic the distribution throughout the training process. After learning, the outputs are scaled back to the original principal component range, then are inverse transformed to form a unique image that is within the distribution of the original images. This method helps us achieve higher quality in a scalable way. However, experimentally we found that this alone is not sufficient. MosaiQ performs intelligent distribution of features to make the learning more effective and robust." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.675, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Feature Distribution Among Learners. In the conventional implementation of the previously proposed idea, all generated features are distributed among several sub-generators before being concatenated. Recall that the MosaicQ's quantum generator is an ensemble of multiple sub-generators, where each sub-generator is a variation quantum circuit. In the default case where PCA features are aligned one after another to the sub-generators, an unbalanced distribution of explained variance may emerge, where some sub-generators are responsible for significantly more important generations than others. This is because, by definition, the explained variance of PCA features is heavily concentrated on the first few features, and there is often a significant drop-off in explained variance from one PCA feature to the next. Recall that PCA features are entangled within" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "sub-generators in training to form rich connections for image generation, when some sub-generators do not contain much useful information in any feature, the entire generator does not pose much utility." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.155, + 0.892, + 0.277 + ], + "angle": 0, + "content": "Therefore, while effective in achieving scalability, only performing PCA may not achieve the full potential of MossiQ's quantum image generation as this leads to unbalanced training, likely to quickly discover gradients that ignore many sub-generators and plateaus in training. To mitigate this challenge, we propose a new PCA feature distribution mechanism to counteract the unbalanced nature of assigning principal components to sub-generators (Fig. 4)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.28, + 0.892, + 0.628 + ], + "angle": 0, + "content": "We begin by assigning the first principal component to the first sub-generator, the second principal component to the second, and so on until each sub-generator has one top principal component. We follow this up by assigning the last n-1 principal components to the first generator, where \\( n \\) is the size of each sub-generator. This is followed by assigning the second to last n-1 features to the second sub-generator and repeated on the third generator and so on until all features have been assigned. This creates a much more balanced distribution, which enables us to ensure all sub-generators hold utility during the training process and the learning is not skewed. As an important side-note, MosaiQ's distribution also mitigates the pathological side-effects of hardware errors on NISQ quantum machines where the majority of critical principal component features could be concentrated on a single sub-generator. This sub-generator could be mapped to qubits with higher hardware error rates, and this can potentially make the training less effective. Our evaluation confirms the effectiveness of MosaiQ's principal component feature distribution among learners. Finally, we describe how MosaiQ utilizes the adaptive noise during image generation to increase the variety of images generated to avoid mode collapse." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.639, + 0.892, + 0.76 + ], + "angle": 0, + "content": "Adaptive Input Noise to Improve Variety of Generated Images. Recall that it is critical for the quantum generator to effectively utilize the random input noise to generate a variety of images for the same class. The inability to generate a variety of images within the same class leads to the \"mode collapse\" problem. Therefore, while MosaiQ's previous methods help us achieve high quality, it is critical to achieving high-quality, while also maintaining variety." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.764, + 0.892, + 0.905 + ], + "angle": 0, + "content": "To address this challenge, MosaiQ introduces an adaptive noise range based on the ratio of training loss between the quantum generator and the classical discriminator. The noise range is determined by the current progress of the generator discriminator mini-max game, instead of the traditional fixed range of \\([0, \\frac{\\pi}{2}]\\) as employed by QGpatch. Formally, the adaptive noise (Noiseadaptive) is defined below in terms of the Generator loss \\( G_{L} \\) and Discriminator loss \\( D_{L} \\) and the Ratio \\( \\frac{G_{L_0}}{D_{L_0}} \\) is the Discriminator/Generator loss ratio" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.925, + 0.516, + 0.937 + ], + "angle": 0, + "content": "7033" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.088, + 0.454, + 0.254 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.075, + 0.265, + 0.47, + 0.311 + ], + "angle": 0, + "content": "Figure 5. MosaiQ's process for training and optimizing the quantum generator circuits using PCA transformation, feature distribution, and adaptive noise generation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.349, + 0.377, + 0.365 + ], + "angle": 0, + "content": "observed after the first epoch during training." + }, + { + "type": "equation", + "bbox": [ + 0.094, + 0.374, + 0.47, + 0.407 + ], + "angle": 0, + "content": "\\[\n\\text {N o i s e} _ {\\text {a d a p t i v e}} = \\frac {\\pi}{8} + \\frac {5 \\pi}{8} R e L U \\left(\\operatorname {T a n h} \\left(\\frac {D _ {L}}{G _ {L}} - \\frac {G _ {L _ {0}}}{D _ {L _ {0}}}\\right)\\right) \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.416, + 0.47, + 0.552 + ], + "angle": 0, + "content": "As the above formula indicates, this adaptive bound enforces a minimum noise range of \\(\\frac{\\pi}{8}\\) and a maximum range of \\(\\frac{3\\pi}{4}\\) for the noise. While the bounds are chosen to be a specific constant, the noise is always distributed within this range and the upper bound automatically adjusts itself based on the relative effectiveness of the generator and the discriminator. MosaiQ does not require tuning the thresholds for the range for different classes, it automatically adjusts itself to adapt to different conditions during training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.552, + 0.47, + 0.75 + ], + "angle": 0, + "content": "MosaicQ embeds the adaptive noise using angle embedding on the quantum circuit. The \\(Tanh\\) function is used to scale the adaptive noise to asymptotically approach the range \\([-1, 1]\\). MosaiQ chose \\(Tanh\\) because it is a widely-used activation function in deep learning applications which transforms unbounded data into data bound by \\([-1, 1]\\). \\(Tanh\\) is defined as \\(Tanh(x) = \\frac{e^{2x} - 1}{e^{2x} + 1}\\). In practice, we observed that it is not effective to have a noise range lower than \\(\\frac{\\pi}{8}\\), we leverage \\(ReLU\\) to force negative values to be zero. \\(ReLU\\) is also a commonly used activation function, however, \\(ReLU\\) is used to provide a non-linear transform that makes all negative values 0 (to ensure that the noise is never less than \\(\\frac{\\pi}{8}\\)), and keeps all positive values the same." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.471, + 0.886 + ], + "angle": 0, + "content": "While the non-linearity of \\( \\text{Tanh} \\) and \\( \\text{ReLU} \\) are important when used typically as activation functions, the nonlinearity is not the main function in this application. If the generator is not able to catch up with the discriminator for some iterations at this small range, it should learn this smaller range instead of getting even smaller. We set the minimum as \\( \\frac{\\pi}{8} \\) as we discovered that a lower value than \\( \\frac{\\pi}{8} \\) results in mode collapse, with almost no distinction between images generated for a given class." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Leveraging adaptive noise for input ensures more consis" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.088, + 0.885, + 0.168 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.178, + 0.892, + 0.21 + ], + "angle": 0, + "content": "Figure 6. MosaiQ's inference process to generate new images via running the generators on quantum machines." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.251, + 0.892, + 0.371 + ], + "angle": 0, + "content": "tent training as the generator can focus on quality when it is doing relatively worse compared to the classical discriminator and expand to generating more variety in high quality as it begins to fool the discriminator more on an easier objective. Overall, the adaptive noise mechanism helps us increase the variety of images for a given class while ensuring that the image quality also remains high. This is further confirmed by our evaluation (Sec. 3)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.379, + 0.893, + 0.622 + ], + "angle": 0, + "content": "MosaiQ's Classical Discriminator. MosaiQ's discriminator is a classical deep-learning network, designed to aid in the training of the quantum generator. This network is essentially training wheels to guide a difficult-to-train quantum GAN, which can be discarded after training. The discriminator is much larger than the quantum generator, as there is only a single discriminator that must compete in the adversarial game with multiple quantum generators. Typical to its classical counterpart, MosaiQ's discriminator has multiple linear layers with \\(ReLU\\) activation (e.g., 64 layers). MosaiQ has a terminal layer with Sigmoid activation which introduces more non-linearity into the network, which enables it to learn more complex structures. The single value produced at the end of the discriminator network allows it to act as a classifier to distinguish between real and generated data." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Putting It All Together. The overall workflow for training and inference for MosaiQ are visually summarized in Fig. 5 and 6, respectively. Fig. 5 depicts the continuous feedback-driven process where the discriminator and generator participate in a non-cooperative game to improve the overall quality of MosaiQ. Depending upon the relative loss of the discriminator and generator networks, the random input noise is automatically adjusted to help MosaiQ generators avoid the problem of mode collapse problem and enable it to generate variety. During the training process, the input images are transformed using PCA to encode critical and more information in a compact manner for resource-limited NISQ quantum computers, instead of learning over the input images pixel by pixel. Finally, the five-step inference procedure shown in Fig. 6 highlights that the PCA transformation is inverted to generate new images when running the fully-trained MosaiQ generators on real quantum computers for inference to generate new images." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.926, + 0.516, + 0.938 + ], + "angle": 0, + "content": "7034" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.09, + 0.332, + 0.108 + ], + "angle": 0, + "content": "3. Experimental Methodology" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.115, + 0.47, + 0.298 + ], + "angle": 0, + "content": "Datasets. MosaiQ is evaluated on the MNIST [6] and Fashion MNIST datasets [21] as they have been widely-used for QML evaluation on NISQ-era quantum machines [15, 11]. MNIST consists of \\(28 \\times 28\\) gray-scale images of handwritten digits from 0 to 9. Fashion MNIST consists of \\(28 \\times 28\\) grayscale images of clothing and accessories. Fashion MNIST provides more challenges for image generation and is chosen to explore more domains of quantum image generation. For both datasets, we split the dataset by image label and train individual models for each data type. This technique has been used in [11] and allows us to interpret the generation process and difficulties isolated for each class of data." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.304, + 0.471, + 0.546 + ], + "angle": 0, + "content": "Experimental Framework and Training Details. The environment for MosaiQ consists of PyTorch [16] acting as a wrapper for Pennylane [3]. MosaiQ is trained on IBM's quantum simulator for speed, but the inference is performed on both the quantum simulator and real quantum machine. For real quantum machine experiments, Pennylane compiles the circuits into a backend compatible with IBM-Qiskit [18]. All real machine runs were performed on the IBM QX Jakarta machine [18]. Images used in training are selected from the training set and decomposed to principal components of size 40. These components are divided across eight five-qubit sub-generators. The discriminator learns to differentiate at the level of principal components and does not need to utilize a full image. Our final FID metrics reported are at the end of the training after 500 iterations (where all methods achieve near-final stability)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.547, + 0.47, + 0.668 + ], + "angle": 0, + "content": "MosaicQ uses PyTorch's Standard Gradient Descent Optimizer for both the generator and discriminator and Binary Cross Entropy Loss for the shared loss of the generator and discriminator. The Adaptive Noise range is simple to calculate based on the generator and discriminator loss and MosaicQ automatically guides it to adjust itself every training iteration. The generator learning rate is 0.3 and the discriminator learning rate to .05 with a batch size of 8." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.674, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Framework for Competing Techniques. We set up QG-Patch, the state-of-the-art technique [11], using the popular Pennylane framework and choose the parameters used in the original paper [11]. Our QGPatch training is performed using the batch size of eight and it trains until the quality stabilizes (500 iterations). We use the same network size that is mentioned in the original paper, using 4 subgenerators with 5 features each. Evaluating the probabilities in measurement yields a 64-pixel (8x8) image. As MosaicQ's results are based on the original size of the datasets of 784 pixels, we upscale the results of QGPatch using Bilinear Interpolation to allow for direct comparison. We rigorously explored multiple interpolation techniques to provide QGPatch as much as an advantage as possible and experimentally determined that Bilinear interpolation yielded the" + }, + { + "type": "image", + "bbox": [ + 0.512, + 0.089, + 0.878, + 0.166 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.171, + 0.894, + 0.216 + ], + "angle": 0, + "content": "Figure 7. MosaiQ produces visually higher-quality images compared to the state-of-the-art technique, QGPatch, for different classes of MNIST and Fashion-MNIST datasets." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.227, + 0.892, + 0.288 + ], + "angle": 0, + "content": "highest quality upscaling. For QGPatch, similar to MosaiQ, all metrics scores shown are calculated based on 500 images generated at the end of training compared to the entire distribution of the respective image category." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.289, + 0.893, + 0.5 + ], + "angle": 0, + "content": "We additionally set up other classical experiments to act as ablations for the efficacy of MosaiQ. We introduce two techniques: (1) PCAInverse (using random inputs and PCA inverse transformation to generate images), and (2) ClassicalPCA (a purely-classical GAN using the same number of parameters as MosaiQ, but uses MosaiQ's PCA technique for feature compression). PCAInverse applies the same inverse PCA transformation as MosaiQ, to random noise of size 40. This technique is designed to explore the isolated effects of the inverse PCA transformation procedure since it does not perform any learning. ClassicalPCA trains a purely-classical GAN with an identical number of parameters as MosaiQ and apply the same inverse PCA transformation workflow." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.507, + 0.892, + 0.689 + ], + "angle": 0, + "content": "Figures of Merit. To capture the quality of image generation, our evaluation figures of merit are both qualitative and quantitative. Our primary quantitative figure of merit is FID (Frechet inception distance) score [10]. FID evaluates the distance between two distributions, as defined below for a Gaussian with mean \\((m, C)\\) and a second Gaussian with mean \\((m_w, C_w)\\): FID = \\(\\| m - m_w\\|_2^2 + Tr(C + C_w - 2(CC_w)^{1/2})\\). A lower FID score between two distributions indicates higher similarity – and hence, lower FID scores imply higher quality. The FID score has been shown to provide a more meaningful comparison over alternative metrics (e.g., Inception Score) for image GANs [10]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.69, + 0.893, + 0.901 + ], + "angle": 0, + "content": "We also evaluate the variance of our images, by evaluating the variance of the pixel values relative to the mean. As defined below, the variance metric gives insight into the distinctness of the images generated for each method. For each pixel in an image row \\( r \\) and column \\( c \\) in an image, we sum the squared difference from the mean value for that respective pixel to achieve our variance score \\( V \\). We then take the cumulative density function (CDF) of these variance scores for each image generated image \\( G(z) \\) given uniformly distributed noise \\( z \\) from \\( [0, \\pi/2] \\): \\( V = \\sum_{r} \\sum_{c} (\\mu_{rc} - G(z)_{rc})^2 \\). A higher variance indicates higher variety in generated images for a given class – which is desirable, however, it is also critical that a method should attain a lower FID score before demonstrating higher variety." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.926, + 0.516, + 0.938 + ], + "angle": 0, + "content": "7035" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.079, + 0.089, + 0.468, + 0.183 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.187, + 0.472, + 0.234 + ], + "angle": 0, + "content": "Figure 8. MosaiQ consistently produces lower FID score images (higher quality images) compared to QGpatch across different classes of the MNIST dataset." + }, + { + "type": "image", + "bbox": [ + 0.079, + 0.261, + 0.468, + 0.373 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.378, + 0.471, + 0.425 + ], + "angle": 0, + "content": "Figure 9. MosaiQ consistently produces lower FID score images (higher quality images) compared to QGPatch across different classes of the Fashion-MNIST dataset." + }, + { + "type": "image", + "bbox": [ + 0.079, + 0.452, + 0.465, + 0.566 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.569, + 0.471, + 0.63 + ], + "angle": 0, + "content": "Figure 10. MosaiQ produces higher quality images on the MNIST and Fashion MNIST dataset as compared to HQCGAN [19]. MosaiQ produces higher quality images than the classical methods: PCAInverse and ClassicalPCA." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.67, + 0.308, + 0.687 + ], + "angle": 0, + "content": "4. Evaluation and Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.696, + 0.47, + 0.727 + ], + "angle": 0, + "content": "In this section, we go over the results of MosaiQ and provide an analysis of the key elements of the design." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.471, + 0.903 + ], + "angle": 0, + "content": "MosaiQ: Key Results and SOTA Comparison. MosaiQ yields significantly better image quality both visually and quantitatively compared to the state-of-the-art (SOTA) method, QGpatch [11]. As discussed earlier, MosaiQ is evaluated on two different datasets to cover diversity across datasets and within a dataset with different shapes and styles (digits and clothing). First, we highlight that MosaiQ provides a significant visual enhancement in the images produces across different classes compared to the SOTA method. In fact, Fig. 7 shows that the SOTA-produced images are almost unrecognizable for sophisticated shapes ('0'" + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.089, + 0.895, + 0.183 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.202, + 0.895, + 0.248 + ], + "angle": 0, + "content": "Figure 11. MosaiQ produces higher quality images on every class of the MNIST dataset as compared to HQCGAN [19] in addition to the classical methods tested." + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.267, + 0.895, + 0.38 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.399, + 0.894, + 0.446 + ], + "angle": 0, + "content": "Figure 12. MosaiQ produces higher quality images on every class of the Fashion MNIST dataset as compared to HQCGAN [19] in addition to the classical methods tested." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.478, + 0.892, + 0.538 + ], + "angle": 0, + "content": "vs. ‘5’ and different types of shoes). In comparison, MosaiQ is effective across different class types – this is further substantiated by lower FID scores of the images generated by MosaiQ (Fig. 8 and 9)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.539, + 0.893, + 0.825 + ], + "angle": 0, + "content": "As expected, the FID score obtained by MosaiQ varies across different classes for both datasets; this is because of varying degrees of difficulty and shapes of different images. However, the most notable observation is that MosaiQ consistently outperforms QGPatch across all class types by a significant margin (by more than 10 points in many cases). In fact, MNIST digit '7' is quite challenging for QGPatch (FID score is 60), and MosaiQ improves the FID score by approximately 20 points. Similarly, the most challenging class in the Fashion-MNIST dataset (Boot) receives a 45-point improvement by MosaiQ. The key reason MosaiQ outperforms QGPatch is the efficiency of principal components in capturing information. Instead of having to learn pixels one by one, MosaiQ scales more easily by learning a distribution of features that better organize redundancy. For example, most of the background of MNIST and Fashion MNIST images are black, in the case of QGPatch, each pixel must be synthesized, where MosaiQ may be able to build these features with only a few principal components." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.894, + 0.901 + ], + "angle": 0, + "content": "We also compare MosaiQ to other methods, including the PCAInverse technique, the ClassicalPCA technique, and a recent work on hybrid quantum GANs which we refer to as HQCGAN [19]. We sample generated images in Fig. 10 and find the images produced by all methods tested" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.926, + 0.516, + 0.938 + ], + "angle": 0, + "content": "7036" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.088, + 0.465, + 0.202 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.209, + 0.471, + 0.286 + ], + "angle": 0, + "content": "Figure 13. MosaiQ's PCA feature distribution among learners improves the quality of generated images. The figure shows a distribution of 200 FID scores (comparing 8 images each to the entire data distribution) for the case with and without PCA feature redistribution." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.311, + 0.47, + 0.568 + ], + "angle": 0, + "content": "are lower quality than MosaiQ, producing images which are far less human-recognizable. We show the corresponding FID scores for MNIST in Fig 11 and Fashion MNIST in Fig. 12. We find that MosaiQ produces higher quality images and significantly improved FID scores in all cases tested compared to the classical methods (PCAInverse and ClassicalPCA), and HQCGAN. Importantly, MosaiQ outperforms ClassicalPCA, demonstrating the power of quantum networks in image generation when compared to equal-sized classical networks. Our results show that while HQCGAN is promising and useful, the final quality may not be as high as MosaiQ – this is because HQCGAN requires significantly more parameters, more training resources, lacks noise-mitigation, and learns noise in a fixed range ([0, 1) instead of MosaiQ's adaptive noise range technique). Next, we dissect the key reasons behind MosaiQ's effectiveness in more detail." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.575, + 0.47, + 0.848 + ], + "angle": 0, + "content": "Why Does MosaiQ Work Effectively? Effect of careful PCA feature distribution among sub-generators. Recall that MosaiQ employs an intelligent PCA feature distribution among sub-generators in the generation phase. The goal is to equalize the explainable PCA feature variance across learners – in an effort to make learners equally capable instead of weaker learners not effectively contributing toward the overall quality. To better understand and demonstrate the effectiveness of this mechanism, Fig. 13 shows the FID score over multiple training iterations with and without this mechanism while keeping all other design elements intact. For easier interpretation, Fig. 13 shows this for class digit '5' for the MNIST dataset. We observe that PCA feature distribution allows MosaiQ to achieve lower (and hence, better) FID score over training compared to without employing this mechanism. A side benefit of this mechanism is that MosaiQ can also mitigate hardware errors on real quantum computers, as discussed later." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Effect of adaptive noise generation during training. Fig. 14 shows the effect of adaptive noise generation that is used by the MosaiQ generators instead of using a constant" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.088, + 0.885, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.202, + 0.894, + 0.263 + ], + "angle": 0, + "content": "Figure 14. Adaptive noise during generation helps MosaiQ achieve variety (higher variance across images for the same class to mitigate mode-collapse challenge), while achieving lower FID score at the same time, as shown earlier." + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.293, + 0.886, + 0.352 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.363, + 0.893, + 0.409 + ], + "angle": 0, + "content": "Figure 15. Visual image quality of images produced by MosaiQ on real IBM quantum machine (Jakarta) for six representative classes for MNIST and Fashion-MNIST datasets." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.437, + 0.893, + 0.68 + ], + "angle": 0, + "content": "noise threshold range (i.e., \\([0, \\frac{\\pi}{2}]\\)) used by the QGPatch method. Recall that GANs often suffer from intra-class mode-collapse challenges where they can produce a high-quality image for a given class, but there is a possibility that all generated images for a given class appear similar. Therefore, it is critical to ensure that the generated images for a given class have sufficient variety. Fig. 14 confirms that adaptive noise improves variety (class digit '5' used as an example) compared to fixed noise ranges. This is because adaptive noise enables the generators to learn over different distributions more effectively and generate variations. Having an adaptive range allows the generator to improve variety when it is doing comparatively well and focus on stability when it is performing poorly with a smaller range of inputs. Taking advantage of this allows us to have high stability in training and high variety over time." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.687, + 0.892, + 0.884 + ], + "angle": 0, + "content": "MosaiQ on NISQ Quantum Machines. Our experimental campaign on real superconducting-based IBM NISQ quantum computers confirms MosaiQ produces higher quality images across different datasets with diverse classes of images. Fig. 15 and Table 1 summarize the image quality results for QGPatch and MosaiQ. While MosaiQ's quality remains consistent with simulations, QGPatch's quality degrades considerably on real computers. In fact, our results revealed QGPatch produces lower quality images and sometimes unrecognizable images because QGPatch is more prone to side-effects of prevalent quantum gate errors on real machines, while MosaiQ's simplistic design successfully mitigates those effects as discussed next." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "First, we observe that MosaiQ produces competitive" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.926, + 0.516, + 0.938 + ], + "angle": 0, + "content": "7037" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.472, + 0.12 + ], + "angle": 0, + "content": "Table 1. QGpatch and MosaiQ's FID scores on a real quantum computer for MNIST & Fashion-MNIST datasets." + }, + { + "type": "table_caption", + "bbox": [ + 0.241, + 0.127, + 0.312, + 0.139 + ], + "angle": 0, + "content": "(a) QGPatch" + }, + { + "type": "table", + "bbox": [ + 0.086, + 0.142, + 0.473, + 0.182 + ], + "angle": 0, + "content": "
EnvironmentDigit 0Digit 5Digit 9T ShirtPantsShoes
Quantum Simulator525248454282
IBM Jakarta Machine145134131125144124
" + }, + { + "type": "table_caption", + "bbox": [ + 0.244, + 0.186, + 0.308, + 0.198 + ], + "angle": 0, + "content": "(b) MosaiQ" + }, + { + "type": "table", + "bbox": [ + 0.086, + 0.203, + 0.473, + 0.242 + ], + "angle": 0, + "content": "
EnvironmentDigit 0Digit 5Digit 9T ShirtPantsShoes
Quantum Simulator424233342238
IBM Jakarta Machine454435382338
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.274, + 0.47, + 0.454 + ], + "angle": 0, + "content": "quality images despite hardware errors on real quantum computers. Due to high queue wait time and limited availability of quantum resources, we are presenting results only for selected classes (three from each dataset) which cover a diverse range of intricacies in terms of shape and information. In fact, via visual inspection for different images produced for a given class, we observe that the variety in the produced images by MosaiQ is also high on the quantum computer - effectively mitigating the mode-collapse pitfall in GANs. This is because of MosaiQ's adaptive noise mechanism during the generation phase that improves image variety and avoids mode collapse." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.455, + 0.471, + 0.818 + ], + "angle": 0, + "content": "Second, we observe that the FID scores of MosaiQ on a real quantum computer are similar to error-free simulation results, across different classes. This result demonstrates that MosaiQ's design is effective even when hardware errors are present. In fact, the IBM Jakarta computer has a considerably low quantum volume (higher is better) with a quantum volume of 16. Quantum volume is a useful metric in determining the error rate and capabilities of a quantum computer. For perspective, at the time of writing, IBM has computers available with quantum volumes of 128. We chose a relatively less capable quantum computer for our experiments to demonstrate the portability and robustness of MosaiQ. The reason for MosaiQ's effectiveness is twofold: (1) its simplistic design for generator learners, which avoids a large number of two-qubit gates, and circuits with high depths. which are more prone to hardware noise, and (2) its PCA feature distribution mapping among the ensemble of learners in the generator - this careful redistribution ensures that most critical PCA features are not concentrated on a few qubits, which in the pathological case could be most severely impacted by hardware-errors. MosaiQ's PCA redistribution ensures that the learners do not need to know the error rate of individual qubits on the computer or make assumptions about different error types." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.83, + 0.219, + 0.846 + ], + "angle": 0, + "content": "5. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.469, + 0.903 + ], + "angle": 0, + "content": "Demonstration of the Speedup Achieved by Quantum GANs. Quantum GANs were first introduced by Lloyd et al.[14]. This work theoretically proved the potential for ex" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.227 + ], + "angle": 0, + "content": "ponential superiority of Quantum GANs over their classical counterparts. This was later followed by the work of Dallaire-Demers et al. [4], which established a way to design and train variational quantum circuits as the generator component of a Quantum GAN model. Nakaji et al. [15] use a hybrid configuration with a classical discriminator and a quantum generator for classification. Their results demonstrate the potential for quantum GANs to solve problems that are intractable with classical GANs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.239, + 0.892, + 0.406 + ], + "angle": 0, + "content": "Enchancing Classical GANs using Quantum Components. Approaches such as the work done by Rudolph et al. [17] use a quantum enhancer for large-scale fully-classical generators to enhance the quality of image generation. While the images generated are high quality, this is mostly attributed to the large classical generators. The visual results in these works seem appealing because the classical GAN-based baseline is already high quality, with a quantum preamble which only improves the image quality slightly. This is in contrast to MosaiQ which uses a quantum generator to generate images without a classical generator." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.417, + 0.892, + 0.69 + ], + "angle": 0, + "content": "Fully-Quantum Generators. The work of Huang et al. [12] uses quantum gradients to train quantum GANs to replicate logic gates such as XOR with high fidelity and also generate images from the MNIST dataset. The technique relies on using quantum-based loss functions for their generator and discriminator. This work also shows that quantum GANs have similar performance as classical GANs while using \\(94.98\\%\\) fewer parameters. A succeeding work with higher quality MNIST image generation can be found in QGPatch [11], with a generator split among several subgenerators each responsible for generating a part of the full image. QGPatch trains a quantum generator against a classical discriminator. The quality of generation is the highest among pre-MosaiQ quantum GANs with a purely quantum generative component, at the time of writing. Therefore, we compare MosaiQ against QGPatch in this paper and show that MosaiQ outperforms QGPatch in terms of image quality and variety." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.716, + 0.618, + 0.731 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.745, + 0.892, + 0.852 + ], + "angle": 0, + "content": "MosaicQ is the first quantum GAN to successfully generate high-quality images on real quantum computers. MosaicQ incorporates PCA feature redistribution and adaptive noise to facilitate improved interaction between the quantum generator and classical elements of the model. This integration enhances the quality and variety of the generator's output respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgements We thank the reviewers for constructive feedback. This work was supported by NSF Award 2144540, Northeastern University, and Rice University." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.926, + 0.516, + 0.938 + ], + "angle": 0, + "content": "7038" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.091, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.199 + ], + "angle": 0, + "content": "[1] Samet Akcay, Amir Atapour-Abarghouei, and Toby P. Breckon. Ganomaly: Semi-supervised anomaly detection via adversarial training. In C. V. Jawahar, Hongdong Li, Greg Mori, and Konrad Schindler, editors, Computer Vision - ACCV 2018, pages 622-637, Cham, 2019. Springer International Publishing. 1, 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.201, + 0.468, + 0.227 + ], + "angle": 0, + "content": "[2] Martin Arjovsky, Soumith Chintala, and Léon Bottou. 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Unpaired image-to-image translation using cycle-consistent adversarial networks, 2017. 1" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.501 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.927, + 0.516, + 0.938 + ], + "angle": 0, + "content": "7039" + } + ] +] \ No newline at end of file diff --git a/2023/MosaiQ_ Quantum Generative Adversarial Networks for Image Generation on NISQ Computers/f3fd0f01-346f-46fa-9180-3373ca2881cf_origin.pdf b/2023/MosaiQ_ Quantum Generative Adversarial Networks for Image Generation on NISQ Computers/f3fd0f01-346f-46fa-9180-3373ca2881cf_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..3ebd76faa10740fec9c72fc108f864833e7a7f4f --- /dev/null +++ b/2023/MosaiQ_ Quantum Generative Adversarial Networks for Image Generation on NISQ Computers/f3fd0f01-346f-46fa-9180-3373ca2881cf_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:d40a3c5a52e800505467f760e56f8bd55ff1645bc87283bb3abfacbd028ceb66 +size 2366574 diff --git a/2023/MosaiQ_ Quantum Generative Adversarial Networks for Image Generation on NISQ Computers/full.md b/2023/MosaiQ_ Quantum Generative Adversarial Networks for Image Generation on NISQ Computers/full.md new file mode 100644 index 0000000000000000000000000000000000000000..1d6b552889ced97aa91b46e67f42078616c35c2a --- /dev/null +++ b/2023/MosaiQ_ Quantum Generative Adversarial Networks for Image Generation on NISQ Computers/full.md @@ -0,0 +1,276 @@ +# MosaiQ: Quantum Generative Adversarial Networks for Image Generation on NISQ Computers + +Daniel Silver + +Northeastern University + +silver.da@northeastern.edu + +Tirthak Patel + +Rice University + +tirthak.patel@rice.edu + +William Cutler + +Northeastern University + +cutler.wi@northeastern.edu + +Aditya Ranjan + +Northeastern University + +ranjan.ad@northeastern.edu + +Harshitta Gandhi Northeastern University + +gandhi.ha@northeastern.edu + +Devesh Tiwari + +Northeastern University + +d.tiwari@northeastern.edu + +# Abstract + +Quantum machine learning and vision have come to the fore recently, with hardware advances enabling rapid advancement in the capabilities of quantum machines. Recently, quantum image generation has been explored with many potential advantages over non-quantum techniques; however, previous techniques have suffered from poor quality and robustness. To address these problems, we introduce MosaiQ a high-quality quantum image generation GAN framework that can be executed on today's Near-term Intermediate Scale Quantum (NISQ) computers. + +# 1. Introduction + +Generative Adversarial Networks, or GANs, are a type of neural network architecture used in machine learning and computer vision for generative modeling [8, 22, 2, 9]. A classical GAN consists of two neural networks, a generator, and a discriminator, that are trained simultaneously in a competitive process. The generator generates fake data samples, while the discriminator tries to distinguish them from real ones found in the training set, hence serving as an "adversarial entity". Classical GANs have received significant attention for generating high-quality images, among other purposes including text generation, data augmentation, and anomaly detection [20, 1, 5]. + +Naturally, this has spawned interest in the quantum information science community to develop corresponding quantum GANs that run on quantum computers. While recent efforts toward developing quantum GANs have been instrumental and early results have been encouraging, we discovered that existing approaches have severe scalability bottlenecks and have significant room for improvement. This is especially true in the context of generating high-quality image generation on real-system quantum computers. + +# Opportunity Gap for Quantum GANs. + +A recent work by Huang et al. [11], referred to as QGPatch in this paper, is the state-of-the-art demonstration of QuantumGANs on real quantum computers. As our paper also demonstrates, QGPatch can learn different shapes and produce recognizable images in some cases, but can often yield low-quality images. It suffers from the scalability challenge because it breaks the image into "patches" and performs a pixel-by-pixel learning. Second, it is not effective at generating a variety of images within the same class – this problem is known as "mode collapse" [7]. It is nontrivial to achieve high-quality image generation while also maintaining variety. Motivated by these limitations, MosaicQ's design pushes the state of the art by achieving higher scalability, image quality, and variety. + +# Contributions of MosaiQ + +I. MosaiQ introduces the design and implementation of a novel quantum generative adversarial network for image generation on quantum computers. MosaiQ's approach is a hybrid classical-quantum generation network where a network of low-circuit-depth variational quantum circuits are leveraged to learn and train the model. Upon acceptance, MosaiQ will be available as an open-source contribution. + +II. MosaiQ's design demonstrates how the extraction of principal components of images enables us to learn and generate higher-quality images, compared to the state-of-the-art approach which is limited in its scalability due to pixel-by-pixel learning [11]. However, exploiting information in principal components to its full potential is non-trivial, and MosaiQ proposes to mitigate those challenges using feature redistribution. Furthermore, MosaiQ introduces a novel adaptive input noise generation technique to improve both the quality and variety of generated images – mitigating the common risk of mode collapse in generative networks. + +![](images/f683e1b63e7259faa5591a09880a375e9c2b1ca1ddc5b991ea88dbf45b550cf6.jpg) +Figure 1. Classical generative adversarial network (GAN) and MosaiQ's hybrid quantum-classical GAN architecture. + +III. Our evaluation demonstrates that MosaiQ significantly outperforms the state-of-the-art methods [11] on both simulation and real quantum computers with a hardware error. MosaiQ is evaluated on the MNIST [6] and Fashion MNIST datasets [21] – widely-used for QML evaluation on Nearterm Intermediate Scale Quantum (NISQ) machines [15, 11]. MosaiQ outperforms the state-of-the-art methods [11] both visually and quantitatively – for example, over 100 points improvement in image quality generated on IBM Jakarta quantum computer using the FID (Fréchet Inception Distance) score [10], which is popularly used for comparing image quality. MosaiQ is open-sourced at https://github.com/SilverEngineered/MosaiQ. + +# 2. MosaiQ: Challenges and Solution + +In this section, we present the design and implementation of MosaiQ, a quantum image generative network. To provide better context for understanding, first, we briefly describe the classical generative adversarial networks (GAN) (depicted in Fig. 1(a)), describe the limitations of the state-of-the-art quantum GANs, and then, provide the details of MosaiQ's quantum GAN design (depicted in Fig. 1(b)). + +# 2.1. Generative Adversarial Networks (GANs) + +Generative Adversarial Networks, or GANs, are a type of neural network architecture used in machine learning for generative modeling [8]. The basic architecture and workflow of a classical (non quantum) GAN are shown in Fig. 1 (a). A classical GAN consists of two neural networks, a generator, and a discriminator, that are trained simultaneously in a competitive process. The generator generates fake data samples, while the discriminator tries to distinguish them from real ones found in the training set, hence serving as the "ad adversary". Through training, the generator learns to create increasingly realistic samples that mimic the distribution of the real data in order to better fool an increasingly effective discriminator, eventually reaching an attempt to attain equilibrium with the value function expressed as $\min_G\max_D\mathbb{E}_{x\sim q_{\mathrm{data}}(x)}[\log D(\pmb {x})] + \mathbb{E}_{\pmb {z}\sim p(\pmb {z})}[\log (1 - D(G(\pmb {z})))]$ . This value function has two + +![](images/ac121dfec9d06b4e9f9ed5a05bd1086fb8572abf31e8be69c54339da83d682e4.jpg) +Digit 0 (MNIST) +Figure 2. State-of-the-art quantum image generator, QG-Patch [11], generates low-quality images for different datasets. However, its quality is still similar to a classical GAN with $25 \times$ more parameters and iterations. + +main identifiable components that correspond to the respective optimization objectives of the generator and the discriminator. The use of log provides more numerical stability because it converts the multiplication of multiple small probabilities into addition, and it also allows us to calculate the derivatives more easily during the optimization process. + +Once fully trained, a generator component of the GAN is capable of converting random noise into new data samples (e.g., boots) that conform to the original distribution of the training data. Essentially, the generator, without the use of a discriminator, can be inferred to obtain new data samples. GANs have been shown to be useful in a variety of applications such as image and text generation, data augmentation, and anomaly detection [20, 1, 5]. Naturally, this has spawned interest in the quantum information science community to develop corresponding quantum GANs. + +Quantum GANs follow a similar generator and discriminator structure as classical GANs but use quantum principles to train and infer from the model. Typically, the discriminator functions on classical resources, and the generator is trained on quantum resources. This is expected, as this structure allows the Quantum GANs to leverage quantum resources for generation tasks – the component that persists beyond training; recall that the discriminator is essentially a quality inspector that can be decoupled after training and is not required during inference. While this structure is intuitive and has been demonstrated to be somewhat promising [11], there are multiple open challenges that need to be overcome to achieve higher quality. + +# 2.2. Limitations of Existing Quantum GANs + +A recent work by Huang et al. [11], referred to as QGPatch, is the most complete, state-of-the-art demonstration of QuantumGANs on real quantum computers. QGPatch follows the Quantum GAN architecture described earlier but achieves limited effectiveness - QGPatch can learn different shapes and produce recognizable images in some cases, but often suffers from low quality. Fig. 2 shows that digit '0' is a reasonable approximation of the ground truth, but the generated boot image is far less recognizable. Despite the imperfect generations, we can see in Fig. 2 how a classical GAN with $25 \times$ the parameters of QGPatch and + +trained for $25 \times$ as many iterations is worse or similar to the quantum technique - supporting the potential of quantum machine-learning for image generation tasks as compared to the classical approach with much higher resources and complexity. This independently provides experimental evidence for why the quantum information science community is motivated to accelerate the progress of Quantum GANs, despite its current limitations. + +The reasons for the limited effectiveness of Quatum GANs are multi-fold. The quantum generator component runs on the quantum hardware and requires many qubits to produce high-quality images from random input noise (a qubit is the fundamental unit of computation and information storage on quantum computers). QGPatch addresses this challenge by breaking the image into "patches" and employing a generator for different patches. While this is reasonable for smaller resolution images, the "patch-based" approach suffers from scalability due to its fundamental nature of learning pixel-by-pixel. For example, a total of 245 qubits are required for images in the full-resolution 784-pixel MNIST dataset. + +The second challenge is performing efficient learning from random input noise – it is critical for the quantum generator to effectively utilize the random input noise to generate a variety of images for the same class. Inability to generate a variety of images within the same class – which even classical GANs suffer from – is popularly known as the “mode collapse” problem [7]. Mode collapse is a side-effect of the generator learning to generate only produce one type of image for a given class because the generator has learned to “fool” the discriminator for this image and saturates in its learning. It is non-trivial to achieve high-quality generating while also maintaining variety. Motivated by these limitations, MosaiQ’s design pushes the state of the art. + +# 2.3. Overview of MosaiQ and Key Ideas + +Hybrid Quantum-Classical Architecture. MosaiQ uses a hybrid quantum-classical architecture for image generation, as summarized in Fig. 1(b). The generator is quantum in nature and trained using quantum simulation, and the discriminator is classical – similar to the construction in [15, 11]. However, there are two key novel architectural changes: (1) to address the scalability and quantum resource bottlenecks for generating high-quality images, MosaiQ applies a transformation on the input image dataset, and (2) MosaiQ employs quantum-style random noise as input to enhance the “variety or mode-collapse” challenge. These two key features are described after a brief description of MosaiQ's generator and discriminator. + +MosaiQ's Quantum Generator Network. MosaiQ's quantum generator component is a network of multiple subgenerators. Each sub-generator is a variational quantum circuit that is iteratively optimized to train a model. Vari- + +![](images/1fc6b99818042c2e68a4ec0ebbf91ffd7ff1080da655013093ae329a66ecdc95.jpg) +Figure 3. Circuit ansatz design of MosaiQ's generators. The RY gates in each layer are optimized during training. + +ational quantum circuits are specific types of quantum circuits where some components of the circuits are tunable parameters, which are iteratively optimized. As a background, a quantum circuit is essentially a sequence of quantum gates applied to qubits. The quantum gates are fundamental operations that manipulate the qubit state, and any gate can be represented as a unitary matrix. One-qubit gates, such as the Pauli gates $(\sigma_x,\sigma_y,\sigma_z)$ , apply a rotation to just one qubit and are categorized by the axis around which the rotation takes place, and by how much. Multi-qubit gates, such as the CNOT gate, allow the creation of entanglement. + +Variational quantum circuits in MosaiQ are comprised of two types of sections. The first type, $X$ , has fixed gates that entangle the qubits. The second type, $\theta$ , has tunable $U_{3}$ gates that are optimized via training. The overall circuit $V$ is therefore an optimization function built of unitary transformations such that $V = U(X,\theta)$ . One key feature of variational quantum circuits is the ability to leverage many off-the-shelf classical deep-learning techniques for training and optimization. This includes learning through common loss functions such as $L_{2}$ loss and leveraging existing optimizers such as Adam [13] that MosaiQ leverages. + +All sub-generator circuits in MosaiQ have identical architectures, composed of a five-qubit circuit. Fig. 3 shows an example of the sub-generator circuit. The circuit consists of encoding the input noise as angles using $Rx$ gates and $Ry$ gates. Following the embedding of the noise, the parameterized weights are encoded on each quantum layer alongside $CZ$ gates used to entangle the qubits at each layer. These weights contain the portion of the circuit that is optimized. Following these repeated layers, the Pauli $X$ expected value is taken for each qubit in measurement. + +We note the simplistic design of MosaiQ's generator circuits is intentional; limiting the number of tunable parameters and depth of the circuits enables MosaiQ to mitigate hardware error impact on real quantum machines and maintain high quality, as confirmed by our evaluation (Sec. 3). + +Scalable Learning by Extracting Principal Components. Unlike previous approaches, which learn to construct the pixels of an image directly and consequently, suffer from the scaling bottleneck, MosaiQ demonstrates that extracting and learning the rich features is effective. The principal component analysis (PCA) method enables efficient learn- + +![](images/a2778b8fb35b55e57c33f37354f4438eeb48e82390b7bef825f0548d1a91dab3.jpg) +Figure 4. MosaiQ divides the PCA features among the eight generator circuits in a manner that the total explained variance is close to equal across all generators. + +ing by focusing on the important features that compromise unique images, as opposed to having to learn to distinguish the important features from the redundant features in an image via the pixel-by-pixel method. PCA maximizes the entropy for a given number of components, concentrating the information of a dataset efficiently. + +The first step in learning principal components is normalizing the input data. Once the images are normalized, MosaiQ decomposes the images into principal components and scales these components between [0, 1] so that the quantum sub-generators can generate throughout the entire space of inputs. As quantum machines rely on only unitary transformations, it is not possible to obtain an output with an absolute value greater than one in measurement. These scaled components are fed into the discriminator as the "real labels" and the generator begins to learn how to mimic the distribution throughout the training process. After learning, the outputs are scaled back to the original principal component range, then are inverse transformed to form a unique image that is within the distribution of the original images. This method helps us achieve higher quality in a scalable way. However, experimentally we found that this alone is not sufficient. MosaiQ performs intelligent distribution of features to make the learning more effective and robust. + +Feature Distribution Among Learners. In the conventional implementation of the previously proposed idea, all generated features are distributed among several sub-generators before being concatenated. Recall that the MosaicQ's quantum generator is an ensemble of multiple sub-generators, where each sub-generator is a variation quantum circuit. In the default case where PCA features are aligned one after another to the sub-generators, an unbalanced distribution of explained variance may emerge, where some sub-generators are responsible for significantly more important generations than others. This is because, by definition, the explained variance of PCA features is heavily concentrated on the first few features, and there is often a significant drop-off in explained variance from one PCA feature to the next. Recall that PCA features are entangled within + +sub-generators in training to form rich connections for image generation, when some sub-generators do not contain much useful information in any feature, the entire generator does not pose much utility. + +Therefore, while effective in achieving scalability, only performing PCA may not achieve the full potential of MossiQ's quantum image generation as this leads to unbalanced training, likely to quickly discover gradients that ignore many sub-generators and plateaus in training. To mitigate this challenge, we propose a new PCA feature distribution mechanism to counteract the unbalanced nature of assigning principal components to sub-generators (Fig. 4). + +We begin by assigning the first principal component to the first sub-generator, the second principal component to the second, and so on until each sub-generator has one top principal component. We follow this up by assigning the last n-1 principal components to the first generator, where $n$ is the size of each sub-generator. This is followed by assigning the second to last n-1 features to the second sub-generator and repeated on the third generator and so on until all features have been assigned. This creates a much more balanced distribution, which enables us to ensure all sub-generators hold utility during the training process and the learning is not skewed. As an important side-note, MosaiQ's distribution also mitigates the pathological side-effects of hardware errors on NISQ quantum machines where the majority of critical principal component features could be concentrated on a single sub-generator. This sub-generator could be mapped to qubits with higher hardware error rates, and this can potentially make the training less effective. Our evaluation confirms the effectiveness of MosaiQ's principal component feature distribution among learners. Finally, we describe how MosaiQ utilizes the adaptive noise during image generation to increase the variety of images generated to avoid mode collapse. + +Adaptive Input Noise to Improve Variety of Generated Images. Recall that it is critical for the quantum generator to effectively utilize the random input noise to generate a variety of images for the same class. The inability to generate a variety of images within the same class leads to the "mode collapse" problem. Therefore, while MosaiQ's previous methods help us achieve high quality, it is critical to achieving high-quality, while also maintaining variety. + +To address this challenge, MosaiQ introduces an adaptive noise range based on the ratio of training loss between the quantum generator and the classical discriminator. The noise range is determined by the current progress of the generator discriminator mini-max game, instead of the traditional fixed range of $[0, \frac{\pi}{2}]$ as employed by QGpatch. Formally, the adaptive noise (Noiseadaptive) is defined below in terms of the Generator loss $G_{L}$ and Discriminator loss $D_{L}$ and the Ratio $\frac{G_{L_0}}{D_{L_0}}$ is the Discriminator/Generator loss ratio + +![](images/a9540d1f72372097272222ba4b4c5bd7d921bdb08d0f160c57882d35ab0400b6.jpg) +Figure 5. MosaiQ's process for training and optimizing the quantum generator circuits using PCA transformation, feature distribution, and adaptive noise generation. + +observed after the first epoch during training. + +$$ +\text {N o i s e} _ {\text {a d a p t i v e}} = \frac {\pi}{8} + \frac {5 \pi}{8} R e L U \left(\operatorname {T a n h} \left(\frac {D _ {L}}{G _ {L}} - \frac {G _ {L _ {0}}}{D _ {L _ {0}}}\right)\right) \tag {1} +$$ + +As the above formula indicates, this adaptive bound enforces a minimum noise range of $\frac{\pi}{8}$ and a maximum range of $\frac{3\pi}{4}$ for the noise. While the bounds are chosen to be a specific constant, the noise is always distributed within this range and the upper bound automatically adjusts itself based on the relative effectiveness of the generator and the discriminator. MosaiQ does not require tuning the thresholds for the range for different classes, it automatically adjusts itself to adapt to different conditions during training. + +MosaicQ embeds the adaptive noise using angle embedding on the quantum circuit. The $Tanh$ function is used to scale the adaptive noise to asymptotically approach the range $[-1, 1]$ . MosaiQ chose $Tanh$ because it is a widely-used activation function in deep learning applications which transforms unbounded data into data bound by $[-1, 1]$ . $Tanh$ is defined as $Tanh(x) = \frac{e^{2x} - 1}{e^{2x} + 1}$ . In practice, we observed that it is not effective to have a noise range lower than $\frac{\pi}{8}$ , we leverage $ReLU$ to force negative values to be zero. $ReLU$ is also a commonly used activation function, however, $ReLU$ is used to provide a non-linear transform that makes all negative values 0 (to ensure that the noise is never less than $\frac{\pi}{8}$ ), and keeps all positive values the same. + +While the non-linearity of $\text{Tanh}$ and $\text{ReLU}$ are important when used typically as activation functions, the nonlinearity is not the main function in this application. If the generator is not able to catch up with the discriminator for some iterations at this small range, it should learn this smaller range instead of getting even smaller. We set the minimum as $\frac{\pi}{8}$ as we discovered that a lower value than $\frac{\pi}{8}$ results in mode collapse, with almost no distinction between images generated for a given class. + +Leveraging adaptive noise for input ensures more consis + +![](images/833740fa3d394894cb30493f26cb07620164b5c59cede476c0bf63ac22664881.jpg) +Figure 6. MosaiQ's inference process to generate new images via running the generators on quantum machines. + +tent training as the generator can focus on quality when it is doing relatively worse compared to the classical discriminator and expand to generating more variety in high quality as it begins to fool the discriminator more on an easier objective. Overall, the adaptive noise mechanism helps us increase the variety of images for a given class while ensuring that the image quality also remains high. This is further confirmed by our evaluation (Sec. 3). + +MosaiQ's Classical Discriminator. MosaiQ's discriminator is a classical deep-learning network, designed to aid in the training of the quantum generator. This network is essentially training wheels to guide a difficult-to-train quantum GAN, which can be discarded after training. The discriminator is much larger than the quantum generator, as there is only a single discriminator that must compete in the adversarial game with multiple quantum generators. Typical to its classical counterpart, MosaiQ's discriminator has multiple linear layers with $ReLU$ activation (e.g., 64 layers). MosaiQ has a terminal layer with Sigmoid activation which introduces more non-linearity into the network, which enables it to learn more complex structures. The single value produced at the end of the discriminator network allows it to act as a classifier to distinguish between real and generated data. + +Putting It All Together. The overall workflow for training and inference for MosaiQ are visually summarized in Fig. 5 and 6, respectively. Fig. 5 depicts the continuous feedback-driven process where the discriminator and generator participate in a non-cooperative game to improve the overall quality of MosaiQ. Depending upon the relative loss of the discriminator and generator networks, the random input noise is automatically adjusted to help MosaiQ generators avoid the problem of mode collapse problem and enable it to generate variety. During the training process, the input images are transformed using PCA to encode critical and more information in a compact manner for resource-limited NISQ quantum computers, instead of learning over the input images pixel by pixel. Finally, the five-step inference procedure shown in Fig. 6 highlights that the PCA transformation is inverted to generate new images when running the fully-trained MosaiQ generators on real quantum computers for inference to generate new images. + +# 3. Experimental Methodology + +Datasets. MosaiQ is evaluated on the MNIST [6] and Fashion MNIST datasets [21] as they have been widely-used for QML evaluation on NISQ-era quantum machines [15, 11]. MNIST consists of $28 \times 28$ gray-scale images of handwritten digits from 0 to 9. Fashion MNIST consists of $28 \times 28$ grayscale images of clothing and accessories. Fashion MNIST provides more challenges for image generation and is chosen to explore more domains of quantum image generation. For both datasets, we split the dataset by image label and train individual models for each data type. This technique has been used in [11] and allows us to interpret the generation process and difficulties isolated for each class of data. + +Experimental Framework and Training Details. The environment for MosaiQ consists of PyTorch [16] acting as a wrapper for Pennylane [3]. MosaiQ is trained on IBM's quantum simulator for speed, but the inference is performed on both the quantum simulator and real quantum machine. For real quantum machine experiments, Pennylane compiles the circuits into a backend compatible with IBM-Qiskit [18]. All real machine runs were performed on the IBM QX Jakarta machine [18]. Images used in training are selected from the training set and decomposed to principal components of size 40. These components are divided across eight five-qubit sub-generators. The discriminator learns to differentiate at the level of principal components and does not need to utilize a full image. Our final FID metrics reported are at the end of the training after 500 iterations (where all methods achieve near-final stability). + +MosaicQ uses PyTorch's Standard Gradient Descent Optimizer for both the generator and discriminator and Binary Cross Entropy Loss for the shared loss of the generator and discriminator. The Adaptive Noise range is simple to calculate based on the generator and discriminator loss and MosaicQ automatically guides it to adjust itself every training iteration. The generator learning rate is 0.3 and the discriminator learning rate to .05 with a batch size of 8. + +Framework for Competing Techniques. We set up QG-Patch, the state-of-the-art technique [11], using the popular Pennylane framework and choose the parameters used in the original paper [11]. Our QGPatch training is performed using the batch size of eight and it trains until the quality stabilizes (500 iterations). We use the same network size that is mentioned in the original paper, using 4 subgenerators with 5 features each. Evaluating the probabilities in measurement yields a 64-pixel (8x8) image. As MosaicQ's results are based on the original size of the datasets of 784 pixels, we upscale the results of QGPatch using Bilinear Interpolation to allow for direct comparison. We rigorously explored multiple interpolation techniques to provide QGPatch as much as an advantage as possible and experimentally determined that Bilinear interpolation yielded the + +![](images/107b37d4c68a0a689e230222f4981bf8fe9130167ae6e998c9c184c2009d9758.jpg) +Figure 7. MosaiQ produces visually higher-quality images compared to the state-of-the-art technique, QGPatch, for different classes of MNIST and Fashion-MNIST datasets. + +highest quality upscaling. For QGPatch, similar to MosaiQ, all metrics scores shown are calculated based on 500 images generated at the end of training compared to the entire distribution of the respective image category. + +We additionally set up other classical experiments to act as ablations for the efficacy of MosaiQ. We introduce two techniques: (1) PCAInverse (using random inputs and PCA inverse transformation to generate images), and (2) ClassicalPCA (a purely-classical GAN using the same number of parameters as MosaiQ, but uses MosaiQ's PCA technique for feature compression). PCAInverse applies the same inverse PCA transformation as MosaiQ, to random noise of size 40. This technique is designed to explore the isolated effects of the inverse PCA transformation procedure since it does not perform any learning. ClassicalPCA trains a purely-classical GAN with an identical number of parameters as MosaiQ and apply the same inverse PCA transformation workflow. + +Figures of Merit. To capture the quality of image generation, our evaluation figures of merit are both qualitative and quantitative. Our primary quantitative figure of merit is FID (Frechet inception distance) score [10]. FID evaluates the distance between two distributions, as defined below for a Gaussian with mean $(m, C)$ and a second Gaussian with mean $(m_w, C_w)$ : FID = $\| m - m_w\|_2^2 + Tr(C + C_w - 2(CC_w)^{1/2})$ . A lower FID score between two distributions indicates higher similarity – and hence, lower FID scores imply higher quality. The FID score has been shown to provide a more meaningful comparison over alternative metrics (e.g., Inception Score) for image GANs [10]. + +We also evaluate the variance of our images, by evaluating the variance of the pixel values relative to the mean. As defined below, the variance metric gives insight into the distinctness of the images generated for each method. For each pixel in an image row $r$ and column $c$ in an image, we sum the squared difference from the mean value for that respective pixel to achieve our variance score $V$ . We then take the cumulative density function (CDF) of these variance scores for each image generated image $G(z)$ given uniformly distributed noise $z$ from $[0, \pi/2]$ : $V = \sum_{r} \sum_{c} (\mu_{rc} - G(z)_{rc})^2$ . A higher variance indicates higher variety in generated images for a given class – which is desirable, however, it is also critical that a method should attain a lower FID score before demonstrating higher variety. + +![](images/71b1c4a505a1b558cb6a7ec561c3e6feb321dbbeda536e4c9a63ed442d03fd79.jpg) +Figure 8. MosaiQ consistently produces lower FID score images (higher quality images) compared to QGpatch across different classes of the MNIST dataset. + +![](images/08021d7447096302d4be4c84e55ff7aeb45d3e40b35d5f13ac63cb6ab227efa2.jpg) +Figure 9. MosaiQ consistently produces lower FID score images (higher quality images) compared to QGPatch across different classes of the Fashion-MNIST dataset. + +![](images/c0d2012a6d653cd14fe04df72a96896474be224b91937d1ca8b963227ce1ac0f.jpg) +Figure 10. MosaiQ produces higher quality images on the MNIST and Fashion MNIST dataset as compared to HQCGAN [19]. MosaiQ produces higher quality images than the classical methods: PCAInverse and ClassicalPCA. + +# 4. Evaluation and Analysis + +In this section, we go over the results of MosaiQ and provide an analysis of the key elements of the design. + +MosaiQ: Key Results and SOTA Comparison. MosaiQ yields significantly better image quality both visually and quantitatively compared to the state-of-the-art (SOTA) method, QGpatch [11]. As discussed earlier, MosaiQ is evaluated on two different datasets to cover diversity across datasets and within a dataset with different shapes and styles (digits and clothing). First, we highlight that MosaiQ provides a significant visual enhancement in the images produces across different classes compared to the SOTA method. In fact, Fig. 7 shows that the SOTA-produced images are almost unrecognizable for sophisticated shapes ('0' + +![](images/8aad6b6f9380fde982caff74317aa05db518a44ee89a9387ae8e672f7800590c.jpg) +Figure 11. MosaiQ produces higher quality images on every class of the MNIST dataset as compared to HQCGAN [19] in addition to the classical methods tested. + +![](images/4af3cda8deb329f570a784c36cc5235012d0182e212999cc08518a95f4ec474b.jpg) +Figure 12. MosaiQ produces higher quality images on every class of the Fashion MNIST dataset as compared to HQCGAN [19] in addition to the classical methods tested. + +vs. ‘5’ and different types of shoes). In comparison, MosaiQ is effective across different class types – this is further substantiated by lower FID scores of the images generated by MosaiQ (Fig. 8 and 9). + +As expected, the FID score obtained by MosaiQ varies across different classes for both datasets; this is because of varying degrees of difficulty and shapes of different images. However, the most notable observation is that MosaiQ consistently outperforms QGPatch across all class types by a significant margin (by more than 10 points in many cases). In fact, MNIST digit '7' is quite challenging for QGPatch (FID score is 60), and MosaiQ improves the FID score by approximately 20 points. Similarly, the most challenging class in the Fashion-MNIST dataset (Boot) receives a 45-point improvement by MosaiQ. The key reason MosaiQ outperforms QGPatch is the efficiency of principal components in capturing information. Instead of having to learn pixels one by one, MosaiQ scales more easily by learning a distribution of features that better organize redundancy. For example, most of the background of MNIST and Fashion MNIST images are black, in the case of QGPatch, each pixel must be synthesized, where MosaiQ may be able to build these features with only a few principal components. + +We also compare MosaiQ to other methods, including the PCAInverse technique, the ClassicalPCA technique, and a recent work on hybrid quantum GANs which we refer to as HQCGAN [19]. We sample generated images in Fig. 10 and find the images produced by all methods tested + +![](images/c99ef7fb23a3fc89ab1fba68779abb7165dbad9077592d861aaf015e6bf6fd1b.jpg) +Figure 13. MosaiQ's PCA feature distribution among learners improves the quality of generated images. The figure shows a distribution of 200 FID scores (comparing 8 images each to the entire data distribution) for the case with and without PCA feature redistribution. + +are lower quality than MosaiQ, producing images which are far less human-recognizable. We show the corresponding FID scores for MNIST in Fig 11 and Fashion MNIST in Fig. 12. We find that MosaiQ produces higher quality images and significantly improved FID scores in all cases tested compared to the classical methods (PCAInverse and ClassicalPCA), and HQCGAN. Importantly, MosaiQ outperforms ClassicalPCA, demonstrating the power of quantum networks in image generation when compared to equal-sized classical networks. Our results show that while HQCGAN is promising and useful, the final quality may not be as high as MosaiQ – this is because HQCGAN requires significantly more parameters, more training resources, lacks noise-mitigation, and learns noise in a fixed range ([0, 1) instead of MosaiQ's adaptive noise range technique). Next, we dissect the key reasons behind MosaiQ's effectiveness in more detail. + +Why Does MosaiQ Work Effectively? Effect of careful PCA feature distribution among sub-generators. Recall that MosaiQ employs an intelligent PCA feature distribution among sub-generators in the generation phase. The goal is to equalize the explainable PCA feature variance across learners – in an effort to make learners equally capable instead of weaker learners not effectively contributing toward the overall quality. To better understand and demonstrate the effectiveness of this mechanism, Fig. 13 shows the FID score over multiple training iterations with and without this mechanism while keeping all other design elements intact. For easier interpretation, Fig. 13 shows this for class digit '5' for the MNIST dataset. We observe that PCA feature distribution allows MosaiQ to achieve lower (and hence, better) FID score over training compared to without employing this mechanism. A side benefit of this mechanism is that MosaiQ can also mitigate hardware errors on real quantum computers, as discussed later. + +Effect of adaptive noise generation during training. Fig. 14 shows the effect of adaptive noise generation that is used by the MosaiQ generators instead of using a constant + +![](images/3eda43be3f6fa41acad06d1bb45f526c5f7479d7fd489872a751d7241a0a33a0.jpg) +Figure 14. Adaptive noise during generation helps MosaiQ achieve variety (higher variance across images for the same class to mitigate mode-collapse challenge), while achieving lower FID score at the same time, as shown earlier. + +![](images/da7a67d833aabf791be599da57bb470dbb1ee936d1c0bbe12ef017ad1df9882c.jpg) +Figure 15. Visual image quality of images produced by MosaiQ on real IBM quantum machine (Jakarta) for six representative classes for MNIST and Fashion-MNIST datasets. + +noise threshold range (i.e., $[0, \frac{\pi}{2}]$ ) used by the QGPatch method. Recall that GANs often suffer from intra-class mode-collapse challenges where they can produce a high-quality image for a given class, but there is a possibility that all generated images for a given class appear similar. Therefore, it is critical to ensure that the generated images for a given class have sufficient variety. Fig. 14 confirms that adaptive noise improves variety (class digit '5' used as an example) compared to fixed noise ranges. This is because adaptive noise enables the generators to learn over different distributions more effectively and generate variations. Having an adaptive range allows the generator to improve variety when it is doing comparatively well and focus on stability when it is performing poorly with a smaller range of inputs. Taking advantage of this allows us to have high stability in training and high variety over time. + +MosaiQ on NISQ Quantum Machines. Our experimental campaign on real superconducting-based IBM NISQ quantum computers confirms MosaiQ produces higher quality images across different datasets with diverse classes of images. Fig. 15 and Table 1 summarize the image quality results for QGPatch and MosaiQ. While MosaiQ's quality remains consistent with simulations, QGPatch's quality degrades considerably on real computers. In fact, our results revealed QGPatch produces lower quality images and sometimes unrecognizable images because QGPatch is more prone to side-effects of prevalent quantum gate errors on real machines, while MosaiQ's simplistic design successfully mitigates those effects as discussed next. + +First, we observe that MosaiQ produces competitive + +Table 1. QGpatch and MosaiQ's FID scores on a real quantum computer for MNIST & Fashion-MNIST datasets. +(a) QGPatch + +
EnvironmentDigit 0Digit 5Digit 9T ShirtPantsShoes
Quantum Simulator525248454282
IBM Jakarta Machine145134131125144124
+ +(b) MosaiQ + +
EnvironmentDigit 0Digit 5Digit 9T ShirtPantsShoes
Quantum Simulator424233342238
IBM Jakarta Machine454435382338
+ +quality images despite hardware errors on real quantum computers. Due to high queue wait time and limited availability of quantum resources, we are presenting results only for selected classes (three from each dataset) which cover a diverse range of intricacies in terms of shape and information. In fact, via visual inspection for different images produced for a given class, we observe that the variety in the produced images by MosaiQ is also high on the quantum computer - effectively mitigating the mode-collapse pitfall in GANs. This is because of MosaiQ's adaptive noise mechanism during the generation phase that improves image variety and avoids mode collapse. + +Second, we observe that the FID scores of MosaiQ on a real quantum computer are similar to error-free simulation results, across different classes. This result demonstrates that MosaiQ's design is effective even when hardware errors are present. In fact, the IBM Jakarta computer has a considerably low quantum volume (higher is better) with a quantum volume of 16. Quantum volume is a useful metric in determining the error rate and capabilities of a quantum computer. For perspective, at the time of writing, IBM has computers available with quantum volumes of 128. We chose a relatively less capable quantum computer for our experiments to demonstrate the portability and robustness of MosaiQ. The reason for MosaiQ's effectiveness is twofold: (1) its simplistic design for generator learners, which avoids a large number of two-qubit gates, and circuits with high depths. which are more prone to hardware noise, and (2) its PCA feature distribution mapping among the ensemble of learners in the generator - this careful redistribution ensures that most critical PCA features are not concentrated on a few qubits, which in the pathological case could be most severely impacted by hardware-errors. MosaiQ's PCA redistribution ensures that the learners do not need to know the error rate of individual qubits on the computer or make assumptions about different error types. + +# 5. Related Work + +Demonstration of the Speedup Achieved by Quantum GANs. Quantum GANs were first introduced by Lloyd et al.[14]. This work theoretically proved the potential for ex + +ponential superiority of Quantum GANs over their classical counterparts. This was later followed by the work of Dallaire-Demers et al. [4], which established a way to design and train variational quantum circuits as the generator component of a Quantum GAN model. Nakaji et al. [15] use a hybrid configuration with a classical discriminator and a quantum generator for classification. Their results demonstrate the potential for quantum GANs to solve problems that are intractable with classical GANs. + +Enchancing Classical GANs using Quantum Components. Approaches such as the work done by Rudolph et al. [17] use a quantum enhancer for large-scale fully-classical generators to enhance the quality of image generation. While the images generated are high quality, this is mostly attributed to the large classical generators. The visual results in these works seem appealing because the classical GAN-based baseline is already high quality, with a quantum preamble which only improves the image quality slightly. This is in contrast to MosaiQ which uses a quantum generator to generate images without a classical generator. + +Fully-Quantum Generators. The work of Huang et al. [12] uses quantum gradients to train quantum GANs to replicate logic gates such as XOR with high fidelity and also generate images from the MNIST dataset. The technique relies on using quantum-based loss functions for their generator and discriminator. This work also shows that quantum GANs have similar performance as classical GANs while using $94.98\%$ fewer parameters. A succeeding work with higher quality MNIST image generation can be found in QGPatch [11], with a generator split among several subgenerators each responsible for generating a part of the full image. QGPatch trains a quantum generator against a classical discriminator. The quality of generation is the highest among pre-MosaiQ quantum GANs with a purely quantum generative component, at the time of writing. Therefore, we compare MosaiQ against QGPatch in this paper and show that MosaiQ outperforms QGPatch in terms of image quality and variety. + +# 6. Conclusion + +MosaicQ is the first quantum GAN to successfully generate high-quality images on real quantum computers. MosaicQ incorporates PCA feature redistribution and adaptive noise to facilitate improved interaction between the quantum generator and classical elements of the model. This integration enhances the quality and variety of the generator's output respectively. + +Acknowledgements We thank the reviewers for constructive feedback. This work was supported by NSF Award 2144540, Northeastern University, and Rice University. + +# References + +[1] Samet Akcay, Amir Atapour-Abarghouei, and Toby P. Breckon. Ganomaly: Semi-supervised anomaly detection via adversarial training. In C. V. Jawahar, Hongdong Li, Greg Mori, and Konrad Schindler, editors, Computer Vision - ACCV 2018, pages 622-637, Cham, 2019. Springer International Publishing. 1, 2 +[2] Martin Arjovsky, Soumith Chintala, and Léon Bottou. Wasserstein gan, 2017. 1 +[3] Ville Bergholm, Josh Izaac, Maria Schuld, et al. Pennylane: Automatic differentiation of hybrid quantum-classical computations, 2018. 6 +[4] Pierre-Luc Dallaire-Demers and Nathan Killoran. Quantum generative adversarial networks. Phys. Rev. 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298, + 289, + 418 + ], + "spans": [ + { + "bbox": [ + 45, + 298, + 289, + 418 + ], + "type": "text", + "content": "Quantum machine learning and vision have come to the fore recently, with hardware advances enabling rapid advancement in the capabilities of quantum machines. Recently, quantum image generation has been explored with many potential advantages over non-quantum techniques; however, previous techniques have suffered from poor quality and robustness. To address these problems, we introduce MosaiQ a high-quality quantum image generation GAN framework that can be executed on today's Near-term Intermediate Scale Quantum (NISQ) computers." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 47, + 441, + 128, + 453 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 441, + 128, + 453 + ], + "spans": [ + { + "bbox": [ + 47, + 441, + 128, + 453 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 46, + 462, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 462, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 462, + 287, + 605 + ], + "type": "text", + "content": "Generative Adversarial Networks, or GANs, are a type of neural network architecture used in machine learning and computer vision for generative modeling [8, 22, 2, 9]. A classical GAN consists of two neural networks, a generator, and a discriminator, that are trained simultaneously in a competitive process. The generator generates fake data samples, while the discriminator tries to distinguish them from real ones found in the training set, hence serving as an \"adversarial entity\". Classical GANs have received significant attention for generating high-quality images, among other purposes including text generation, data augmentation, and anomaly detection [20, 1, 5]." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "type": "text", + "content": "Naturally, this has spawned interest in the quantum information science community to develop corresponding quantum GANs that run on quantum computers. While recent efforts toward developing quantum GANs have been instrumental and early results have been encouraging, we discovered that existing approaches have severe scalability bottlenecks and have significant room for improvement. This is especially true in the context of generating high-quality image generation on real-system quantum computers." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 306, + 279, + 489, + 293 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 279, + 489, + 293 + ], + "spans": [ + { + "bbox": [ + 306, + 279, + 489, + 293 + ], + "type": "text", + "content": "Opportunity Gap for Quantum GANs." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 304, + 298, + 547, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 298, + 547, + 467 + ], + "spans": [ + { + "bbox": [ + 304, + 298, + 547, + 467 + ], + "type": "text", + "content": "A recent work by Huang et al. [11], referred to as QGPatch in this paper, is the state-of-the-art demonstration of QuantumGANs on real quantum computers. As our paper also demonstrates, QGPatch can learn different shapes and produce recognizable images in some cases, but can often yield low-quality images. It suffers from the scalability challenge because it breaks the image into \"patches\" and performs a pixel-by-pixel learning. Second, it is not effective at generating a variety of images within the same class – this problem is known as \"mode collapse\" [7]. It is nontrivial to achieve high-quality image generation while also maintaining variety. Motivated by these limitations, MosaicQ's design pushes the state of the art by achieving higher scalability, image quality, and variety." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 306, + 473, + 427, + 487 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 473, + 427, + 487 + ], + "spans": [ + { + "bbox": [ + 306, + 473, + 427, + 487 + ], + "type": "text", + "content": "Contributions of MosaiQ" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 304, + 492, + 547, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 492, + 547, + 576 + ], + "spans": [ + { + "bbox": [ + 304, + 492, + 547, + 576 + ], + "type": "text", + "content": "I. MosaiQ introduces the design and implementation of a novel quantum generative adversarial network for image generation on quantum computers. MosaiQ's approach is a hybrid classical-quantum generation network where a network of low-circuit-depth variational quantum circuits are leveraged to learn and train the model. Upon acceptance, MosaiQ will be available as an open-source contribution." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 304, + 582, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 547, + 714 + ], + "type": "text", + "content": "II. MosaiQ's design demonstrates how the extraction of principal components of images enables us to learn and generate higher-quality images, compared to the state-of-the-art approach which is limited in its scalability due to pixel-by-pixel learning [11]. However, exploiting information in principal components to its full potential is non-trivial, and MosaiQ proposes to mitigate those challenges using feature redistribution. Furthermore, MosaiQ introduces a novel adaptive input noise generation technique to improve both the quality and variety of generated images – mitigating the common risk of mode collapse in generative networks." + } + ] + } + ], + "index": 29 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 493, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 493, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 493, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "text", + "content": "7030" + } + ] + } + ], + "index": 30 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 69, + 286, + 156 + ], + "blocks": [ + { + "bbox": [ + 48, + 69, + 286, + 156 + ], + "lines": [ + { + "bbox": [ + 48, + 69, + 286, + 156 + ], + "spans": [ + { + "bbox": [ + 48, + 69, + 286, + 156 + ], + "type": "image", + "image_path": "f683e1b63e7259faa5591a09880a375e9c2b1ca1ddc5b991ea88dbf45b550cf6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 171, + 287, + 196 + ], + "lines": [ + { + "bbox": [ + 46, + 171, + 287, + 196 + ], + "spans": [ + { + "bbox": [ + 46, + 171, + 287, + 196 + ], + "type": "text", + "content": "Figure 1. Classical generative adversarial network (GAN) and MosaiQ's hybrid quantum-classical GAN architecture." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 226, + 289, + 382 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 226, + 289, + 382 + ], + "spans": [ + { + "bbox": [ + 46, + 226, + 289, + 382 + ], + "type": "text", + "content": "III. Our evaluation demonstrates that MosaiQ significantly outperforms the state-of-the-art methods [11] on both simulation and real quantum computers with a hardware error. MosaiQ is evaluated on the MNIST [6] and Fashion MNIST datasets [21] – widely-used for QML evaluation on Nearterm Intermediate Scale Quantum (NISQ) machines [15, 11]. MosaiQ outperforms the state-of-the-art methods [11] both visually and quantitatively – for example, over 100 points improvement in image quality generated on IBM Jakarta quantum computer using the FID (Fréchet Inception Distance) score [10], which is popularly used for comparing image quality. MosaiQ is open-sourced at https://github.com/SilverEngineered/MosaiQ." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 392, + 234, + 406 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 392, + 234, + 406 + ], + "spans": [ + { + "bbox": [ + 47, + 392, + 234, + 406 + ], + "type": "text", + "content": "2. MosaiQ: Challenges and Solution" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 413, + 287, + 497 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 413, + 287, + 497 + ], + "spans": [ + { + "bbox": [ + 46, + 413, + 287, + 497 + ], + "type": "text", + "content": "In this section, we present the design and implementation of MosaiQ, a quantum image generative network. To provide better context for understanding, first, we briefly describe the classical generative adversarial networks (GAN) (depicted in Fig. 1(a)), describe the limitations of the state-of-the-art quantum GANs, and then, provide the details of MosaiQ's quantum GAN design (depicted in Fig. 1(b))." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 503, + 265, + 516 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 503, + 265, + 516 + ], + "spans": [ + { + "bbox": [ + 47, + 503, + 265, + 516 + ], + "type": "text", + "content": "2.1. Generative Adversarial Networks (GANs)" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 522, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 522, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 522, + 288, + 715 + ], + "type": "text", + "content": "Generative Adversarial Networks, or GANs, are a type of neural network architecture used in machine learning for generative modeling [8]. The basic architecture and workflow of a classical (non quantum) GAN are shown in Fig. 1 (a). A classical GAN consists of two neural networks, a generator, and a discriminator, that are trained simultaneously in a competitive process. The generator generates fake data samples, while the discriminator tries to distinguish them from real ones found in the training set, hence serving as the \"ad adversary\". Through training, the generator learns to create increasingly realistic samples that mimic the distribution of the real data in order to better fool an increasingly effective discriminator, eventually reaching an attempt to attain equilibrium with the value function expressed as " + }, + { + "bbox": [ + 46, + 522, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\min_G\\max_D\\mathbb{E}_{x\\sim q_{\\mathrm{data}}(x)}[\\log D(\\pmb {x})] + \\mathbb{E}_{\\pmb {z}\\sim p(\\pmb {z})}[\\log (1 - D(G(\\pmb {z})))]" + }, + { + "bbox": [ + 46, + 522, + 288, + 715 + ], + "type": "text", + "content": ". This value function has two" + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 307, + 82, + 543, + 130 + ], + "blocks": [ + { + "bbox": [ + 340, + 70, + 395, + 80 + ], + "lines": [ + { + "bbox": [ + 340, + 70, + 395, + 80 + ], + "spans": [ + { + "bbox": [ + 340, + 70, + 395, + 80 + ], + "type": "text", + "content": "Digit 0 (MNIST)" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 307, + 82, + 543, + 130 + ], + "lines": [ + { + "bbox": [ + 307, + 82, + 543, + 130 + ], + "spans": [ + { + "bbox": [ + 307, + 82, + 543, + 130 + ], + "type": "image", + "image_path": "ac121dfec9d06b4e9f9ed5a05bd1086fb8572abf31e8be69c54339da83d682e4.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 138, + 545, + 186 + ], + "lines": [ + { + "bbox": [ + 304, + 138, + 545, + 186 + ], + "spans": [ + { + "bbox": [ + 304, + 138, + 545, + 186 + ], + "type": "text", + "content": "Figure 2. State-of-the-art quantum image generator, QG-Patch [11], generates low-quality images for different datasets. However, its quality is still similar to a classical GAN with " + }, + { + "bbox": [ + 304, + 138, + 545, + 186 + ], + "type": "inline_equation", + "content": "25 \\times" + }, + { + "bbox": [ + 304, + 138, + 545, + 186 + ], + "type": "text", + "content": " more parameters and iterations." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 203, + 545, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 203, + 545, + 275 + ], + "spans": [ + { + "bbox": [ + 304, + 203, + 545, + 275 + ], + "type": "text", + "content": "main identifiable components that correspond to the respective optimization objectives of the generator and the discriminator. The use of log provides more numerical stability because it converts the multiplication of multiple small probabilities into addition, and it also allows us to calculate the derivatives more easily during the optimization process." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 275, + 546, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 275, + 546, + 396 + ], + "spans": [ + { + "bbox": [ + 304, + 275, + 546, + 396 + ], + "type": "text", + "content": "Once fully trained, a generator component of the GAN is capable of converting random noise into new data samples (e.g., boots) that conform to the original distribution of the training data. Essentially, the generator, without the use of a discriminator, can be inferred to obtain new data samples. GANs have been shown to be useful in a variety of applications such as image and text generation, data augmentation, and anomaly detection [20, 1, 5]. Naturally, this has spawned interest in the quantum information science community to develop corresponding quantum GANs." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 401, + 545, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 401, + 545, + 556 + ], + "spans": [ + { + "bbox": [ + 304, + 401, + 545, + 556 + ], + "type": "text", + "content": "Quantum GANs follow a similar generator and discriminator structure as classical GANs but use quantum principles to train and infer from the model. Typically, the discriminator functions on classical resources, and the generator is trained on quantum resources. This is expected, as this structure allows the Quantum GANs to leverage quantum resources for generation tasks – the component that persists beyond training; recall that the discriminator is essentially a quality inspector that can be decoupled after training and is not required during inference. While this structure is intuitive and has been demonstrated to be somewhat promising [11], there are multiple open challenges that need to be overcome to achieve higher quality." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 563, + 515, + 576 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 563, + 515, + 576 + ], + "spans": [ + { + "bbox": [ + 306, + 563, + 515, + 576 + ], + "type": "text", + "content": "2.2. Limitations of Existing Quantum GANs" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "A recent work by Huang et al. [11], referred to as QGPatch, is the most complete, state-of-the-art demonstration of QuantumGANs on real quantum computers. QGPatch follows the Quantum GAN architecture described earlier but achieves limited effectiveness - QGPatch can learn different shapes and produce recognizable images in some cases, but often suffers from low quality. Fig. 2 shows that digit '0' is a reasonable approximation of the ground truth, but the generated boot image is far less recognizable. Despite the imperfect generations, we can see in Fig. 2 how a classical GAN with " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "25 \\times" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": " the parameters of QGPatch and" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 732, + 314, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 732, + 314, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 732, + 314, + 742 + ], + "type": "text", + "content": "7031" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 167 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 167 + ], + "type": "text", + "content": "trained for " + }, + { + "bbox": [ + 46, + 72, + 288, + 167 + ], + "type": "inline_equation", + "content": "25 \\times" + }, + { + "bbox": [ + 46, + 72, + 288, + 167 + ], + "type": "text", + "content": " as many iterations is worse or similar to the quantum technique - supporting the potential of quantum machine-learning for image generation tasks as compared to the classical approach with much higher resources and complexity. This independently provides experimental evidence for why the quantum information science community is motivated to accelerate the progress of Quantum GANs, despite its current limitations." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 168, + 287, + 322 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 168, + 287, + 322 + ], + "spans": [ + { + "bbox": [ + 46, + 168, + 287, + 322 + ], + "type": "text", + "content": "The reasons for the limited effectiveness of Quatum GANs are multi-fold. The quantum generator component runs on the quantum hardware and requires many qubits to produce high-quality images from random input noise (a qubit is the fundamental unit of computation and information storage on quantum computers). QGPatch addresses this challenge by breaking the image into \"patches\" and employing a generator for different patches. While this is reasonable for smaller resolution images, the \"patch-based\" approach suffers from scalability due to its fundamental nature of learning pixel-by-pixel. For example, a total of 245 qubits are required for images in the full-resolution 784-pixel MNIST dataset." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 323, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 323, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 323, + 287, + 479 + ], + "type": "text", + "content": "The second challenge is performing efficient learning from random input noise – it is critical for the quantum generator to effectively utilize the random input noise to generate a variety of images for the same class. Inability to generate a variety of images within the same class – which even classical GANs suffer from – is popularly known as the “mode collapse” problem [7]. Mode collapse is a side-effect of the generator learning to generate only produce one type of image for a given class because the generator has learned to “fool” the discriminator for this image and saturates in its learning. It is non-trivial to achieve high-quality generating while also maintaining variety. Motivated by these limitations, MosaiQ’s design pushes the state of the art." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 486, + 237, + 498 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 486, + 237, + 498 + ], + "spans": [ + { + "bbox": [ + 47, + 486, + 237, + 498 + ], + "type": "text", + "content": "2.3. Overview of MosaiQ and Key Ideas" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 504, + 287, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 504, + 287, + 659 + ], + "spans": [ + { + "bbox": [ + 46, + 504, + 287, + 659 + ], + "type": "text", + "content": "Hybrid Quantum-Classical Architecture. MosaiQ uses a hybrid quantum-classical architecture for image generation, as summarized in Fig. 1(b). The generator is quantum in nature and trained using quantum simulation, and the discriminator is classical – similar to the construction in [15, 11]. However, there are two key novel architectural changes: (1) to address the scalability and quantum resource bottlenecks for generating high-quality images, MosaiQ applies a transformation on the input image dataset, and (2) MosaiQ employs quantum-style random noise as input to enhance the “variety or mode-collapse” challenge. These two key features are described after a brief description of MosaiQ's generator and discriminator." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "content": "MosaiQ's Quantum Generator Network. MosaiQ's quantum generator component is a network of multiple subgenerators. Each sub-generator is a variational quantum circuit that is iteratively optimized to train a model. Vari-" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 309, + 70, + 543, + 137 + ], + "blocks": [ + { + "bbox": [ + 309, + 70, + 543, + 137 + ], + "lines": [ + { + "bbox": [ + 309, + 70, + 543, + 137 + ], + "spans": [ + { + "bbox": [ + 309, + 70, + 543, + 137 + ], + "type": "image", + "image_path": "1fc6b99818042c2e68a4ec0ebbf91ffd7ff1080da655013093ae329a66ecdc95.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 140, + 544, + 166 + ], + "lines": [ + { + "bbox": [ + 306, + 140, + 544, + 166 + ], + "spans": [ + { + "bbox": [ + 306, + 140, + 544, + 166 + ], + "type": "text", + "content": "Figure 3. Circuit ansatz design of MosaiQ's generators. The RY gates in each layer are optimized during training." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 186, + 545, + 317 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 186, + 545, + 317 + ], + "spans": [ + { + "bbox": [ + 304, + 186, + 545, + 317 + ], + "type": "text", + "content": "ational quantum circuits are specific types of quantum circuits where some components of the circuits are tunable parameters, which are iteratively optimized. As a background, a quantum circuit is essentially a sequence of quantum gates applied to qubits. The quantum gates are fundamental operations that manipulate the qubit state, and any gate can be represented as a unitary matrix. One-qubit gates, such as the Pauli gates " + }, + { + "bbox": [ + 304, + 186, + 545, + 317 + ], + "type": "inline_equation", + "content": "(\\sigma_x,\\sigma_y,\\sigma_z)" + }, + { + "bbox": [ + 304, + 186, + 545, + 317 + ], + "type": "text", + "content": ", apply a rotation to just one qubit and are categorized by the axis around which the rotation takes place, and by how much. Multi-qubit gates, such as the CNOT gate, allow the creation of entanglement." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "spans": [ + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "text", + "content": "Variational quantum circuits in MosaiQ are comprised of two types of sections. The first type, " + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "text", + "content": ", has fixed gates that entangle the qubits. The second type, " + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "text", + "content": ", has tunable " + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "inline_equation", + "content": "U_{3}" + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "text", + "content": " gates that are optimized via training. The overall circuit " + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "text", + "content": " is therefore an optimization function built of unitary transformations such that " + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "inline_equation", + "content": "V = U(X,\\theta)" + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "text", + "content": ". One key feature of variational quantum circuits is the ability to leverage many off-the-shelf classical deep-learning techniques for training and optimization. This includes learning through common loss functions such as " + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 304, + 319, + 546, + 451 + ], + "type": "text", + "content": " loss and leveraging existing optimizers such as Adam [13] that MosaiQ leverages." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 453, + 545, + 572 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 453, + 545, + 572 + ], + "spans": [ + { + "bbox": [ + 304, + 453, + 545, + 572 + ], + "type": "text", + "content": "All sub-generator circuits in MosaiQ have identical architectures, composed of a five-qubit circuit. Fig. 3 shows an example of the sub-generator circuit. The circuit consists of encoding the input noise as angles using " + }, + { + "bbox": [ + 304, + 453, + 545, + 572 + ], + "type": "inline_equation", + "content": "Rx" + }, + { + "bbox": [ + 304, + 453, + 545, + 572 + ], + "type": "text", + "content": " gates and " + }, + { + "bbox": [ + 304, + 453, + 545, + 572 + ], + "type": "inline_equation", + "content": "Ry" + }, + { + "bbox": [ + 304, + 453, + 545, + 572 + ], + "type": "text", + "content": " gates. Following the embedding of the noise, the parameterized weights are encoded on each quantum layer alongside " + }, + { + "bbox": [ + 304, + 453, + 545, + 572 + ], + "type": "inline_equation", + "content": "CZ" + }, + { + "bbox": [ + 304, + 453, + 545, + 572 + ], + "type": "text", + "content": " gates used to entangle the qubits at each layer. These weights contain the portion of the circuit that is optimized. Following these repeated layers, the Pauli " + }, + { + "bbox": [ + 304, + 453, + 545, + 572 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 304, + 453, + 545, + 572 + ], + "type": "text", + "content": " expected value is taken for each qubit in measurement." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 574, + 545, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 574, + 545, + 635 + ], + "spans": [ + { + "bbox": [ + 304, + 574, + 545, + 635 + ], + "type": "text", + "content": "We note the simplistic design of MosaiQ's generator circuits is intentional; limiting the number of tunable parameters and depth of the circuits enables MosaiQ to mitigate hardware error impact on real quantum machines and maintain high quality, as confirmed by our evaluation (Sec. 3)." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": "Scalable Learning by Extracting Principal Components. Unlike previous approaches, which learn to construct the pixels of an image directly and consequently, suffer from the scaling bottleneck, MosaiQ demonstrates that extracting and learning the rich features is effective. The principal component analysis (PCA) method enables efficient learn-" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "type": "text", + "content": "7032" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 72, + 286, + 159 + ], + "blocks": [ + { + "bbox": [ + 53, + 72, + 286, + 159 + ], + "lines": [ + { + "bbox": [ + 53, + 72, + 286, + 159 + ], + "spans": [ + { + "bbox": [ + 53, + 72, + 286, + 159 + ], + "type": "image", + "image_path": "a2778b8fb35b55e57c33f37354f4438eeb48e82390b7bef825f0548d1a91dab3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 164, + 287, + 200 + ], + "lines": [ + { + "bbox": [ + 47, + 164, + 287, + 200 + ], + "spans": [ + { + "bbox": [ + 47, + 164, + 287, + 200 + ], + "type": "text", + "content": "Figure 4. MosaiQ divides the PCA features among the eight generator circuits in a manner that the total explained variance is close to equal across all generators." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 236, + 286, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 236, + 286, + 308 + ], + "spans": [ + { + "bbox": [ + 46, + 236, + 286, + 308 + ], + "type": "text", + "content": "ing by focusing on the important features that compromise unique images, as opposed to having to learn to distinguish the important features from the redundant features in an image via the pixel-by-pixel method. PCA maximizes the entropy for a given number of components, concentrating the information of a dataset efficiently." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 310, + 287, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 310, + 287, + 525 + ], + "spans": [ + { + "bbox": [ + 46, + 310, + 287, + 525 + ], + "type": "text", + "content": "The first step in learning principal components is normalizing the input data. Once the images are normalized, MosaiQ decomposes the images into principal components and scales these components between [0, 1] so that the quantum sub-generators can generate throughout the entire space of inputs. As quantum machines rely on only unitary transformations, it is not possible to obtain an output with an absolute value greater than one in measurement. These scaled components are fed into the discriminator as the \"real labels\" and the generator begins to learn how to mimic the distribution throughout the training process. After learning, the outputs are scaled back to the original principal component range, then are inverse transformed to form a unique image that is within the distribution of the original images. This method helps us achieve higher quality in a scalable way. However, experimentally we found that this alone is not sufficient. MosaiQ performs intelligent distribution of features to make the learning more effective and robust." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 534, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 534, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 534, + 287, + 713 + ], + "type": "text", + "content": "Feature Distribution Among Learners. In the conventional implementation of the previously proposed idea, all generated features are distributed among several sub-generators before being concatenated. Recall that the MosaicQ's quantum generator is an ensemble of multiple sub-generators, where each sub-generator is a variation quantum circuit. In the default case where PCA features are aligned one after another to the sub-generators, an unbalanced distribution of explained variance may emerge, where some sub-generators are responsible for significantly more important generations than others. This is because, by definition, the explained variance of PCA features is heavily concentrated on the first few features, and there is often a significant drop-off in explained variance from one PCA feature to the next. Recall that PCA features are entangled within" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "sub-generators in training to form rich connections for image generation, when some sub-generators do not contain much useful information in any feature, the entire generator does not pose much utility." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 122, + 545, + 219 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 122, + 545, + 219 + ], + "spans": [ + { + "bbox": [ + 304, + 122, + 545, + 219 + ], + "type": "text", + "content": "Therefore, while effective in achieving scalability, only performing PCA may not achieve the full potential of MossiQ's quantum image generation as this leads to unbalanced training, likely to quickly discover gradients that ignore many sub-generators and plateaus in training. To mitigate this challenge, we propose a new PCA feature distribution mechanism to counteract the unbalanced nature of assigning principal components to sub-generators (Fig. 4)." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 221, + 545, + 497 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 221, + 545, + 497 + ], + "spans": [ + { + "bbox": [ + 304, + 221, + 545, + 497 + ], + "type": "text", + "content": "We begin by assigning the first principal component to the first sub-generator, the second principal component to the second, and so on until each sub-generator has one top principal component. We follow this up by assigning the last n-1 principal components to the first generator, where " + }, + { + "bbox": [ + 304, + 221, + 545, + 497 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 221, + 545, + 497 + ], + "type": "text", + "content": " is the size of each sub-generator. This is followed by assigning the second to last n-1 features to the second sub-generator and repeated on the third generator and so on until all features have been assigned. This creates a much more balanced distribution, which enables us to ensure all sub-generators hold utility during the training process and the learning is not skewed. As an important side-note, MosaiQ's distribution also mitigates the pathological side-effects of hardware errors on NISQ quantum machines where the majority of critical principal component features could be concentrated on a single sub-generator. This sub-generator could be mapped to qubits with higher hardware error rates, and this can potentially make the training less effective. Our evaluation confirms the effectiveness of MosaiQ's principal component feature distribution among learners. Finally, we describe how MosaiQ utilizes the adaptive noise during image generation to increase the variety of images generated to avoid mode collapse." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 506, + 545, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 506, + 545, + 601 + ], + "spans": [ + { + "bbox": [ + 304, + 506, + 545, + 601 + ], + "type": "text", + "content": "Adaptive Input Noise to Improve Variety of Generated Images. Recall that it is critical for the quantum generator to effectively utilize the random input noise to generate a variety of images for the same class. The inability to generate a variety of images within the same class leads to the \"mode collapse\" problem. Therefore, while MosaiQ's previous methods help us achieve high quality, it is critical to achieving high-quality, while also maintaining variety." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 605, + 545, + 716 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 716 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 716 + ], + "type": "text", + "content": "To address this challenge, MosaiQ introduces an adaptive noise range based on the ratio of training loss between the quantum generator and the classical discriminator. The noise range is determined by the current progress of the generator discriminator mini-max game, instead of the traditional fixed range of " + }, + { + "bbox": [ + 304, + 605, + 545, + 716 + ], + "type": "inline_equation", + "content": "[0, \\frac{\\pi}{2}]" + }, + { + "bbox": [ + 304, + 605, + 545, + 716 + ], + "type": "text", + "content": " as employed by QGpatch. Formally, the adaptive noise (Noiseadaptive) is defined below in terms of the Generator loss " + }, + { + "bbox": [ + 304, + 605, + 545, + 716 + ], + "type": "inline_equation", + "content": "G_{L}" + }, + { + "bbox": [ + 304, + 605, + 545, + 716 + ], + "type": "text", + "content": " and Discriminator loss " + }, + { + "bbox": [ + 304, + 605, + 545, + 716 + ], + "type": "inline_equation", + "content": "D_{L}" + }, + { + "bbox": [ + 304, + 605, + 545, + 716 + ], + "type": "text", + "content": " and the Ratio " + }, + { + "bbox": [ + 304, + 605, + 545, + 716 + ], + "type": "inline_equation", + "content": "\\frac{G_{L_0}}{D_{L_0}}" + }, + { + "bbox": [ + 304, + 605, + 545, + 716 + ], + "type": "text", + "content": " is the Discriminator/Generator loss ratio" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 732, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 732, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 732, + 315, + 742 + ], + "type": "text", + "content": "7033" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 69, + 277, + 201 + ], + "blocks": [ + { + "bbox": [ + 50, + 69, + 277, + 201 + ], + "lines": [ + { + "bbox": [ + 50, + 69, + 277, + 201 + ], + "spans": [ + { + "bbox": [ + 50, + 69, + 277, + 201 + ], + "type": "image", + "image_path": "a9540d1f72372097272222ba4b4c5bd7d921bdb08d0f160c57882d35ab0400b6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 209, + 287, + 246 + ], + "lines": [ + { + "bbox": [ + 45, + 209, + 287, + 246 + ], + "spans": [ + { + "bbox": [ + 45, + 209, + 287, + 246 + ], + "type": "text", + "content": "Figure 5. MosaiQ's process for training and optimizing the quantum generator circuits using PCA transformation, feature distribution, and adaptive noise generation." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 276, + 230, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 276, + 230, + 289 + ], + "spans": [ + { + "bbox": [ + 46, + 276, + 230, + 289 + ], + "type": "text", + "content": "observed after the first epoch during training." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 57, + 296, + 287, + 322 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 296, + 287, + 322 + ], + "spans": [ + { + "bbox": [ + 57, + 296, + 287, + 322 + ], + "type": "interline_equation", + "content": "\\text {N o i s e} _ {\\text {a d a p t i v e}} = \\frac {\\pi}{8} + \\frac {5 \\pi}{8} R e L U \\left(\\operatorname {T a n h} \\left(\\frac {D _ {L}}{G _ {L}} - \\frac {G _ {L _ {0}}}{D _ {L _ {0}}}\\right)\\right) \\tag {1}", + "image_path": "995dbc4655fe8799e032ff1aba084b2cf34f343f400fc7254f39702c06efcc91.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 329, + 287, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 329, + 287, + 437 + ], + "spans": [ + { + "bbox": [ + 46, + 329, + 287, + 437 + ], + "type": "text", + "content": "As the above formula indicates, this adaptive bound enforces a minimum noise range of " + }, + { + "bbox": [ + 46, + 329, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\frac{\\pi}{8}" + }, + { + "bbox": [ + 46, + 329, + 287, + 437 + ], + "type": "text", + "content": " and a maximum range of " + }, + { + "bbox": [ + 46, + 329, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\frac{3\\pi}{4}" + }, + { + "bbox": [ + 46, + 329, + 287, + 437 + ], + "type": "text", + "content": " for the noise. While the bounds are chosen to be a specific constant, the noise is always distributed within this range and the upper bound automatically adjusts itself based on the relative effectiveness of the generator and the discriminator. MosaiQ does not require tuning the thresholds for the range for different classes, it automatically adjusts itself to adapt to different conditions during training." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": "MosaicQ embeds the adaptive noise using angle embedding on the quantum circuit. The " + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "inline_equation", + "content": "Tanh" + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": " function is used to scale the adaptive noise to asymptotically approach the range " + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "inline_equation", + "content": "[-1, 1]" + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": ". MosaiQ chose " + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "inline_equation", + "content": "Tanh" + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": " because it is a widely-used activation function in deep learning applications which transforms unbounded data into data bound by " + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "inline_equation", + "content": "[-1, 1]" + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "inline_equation", + "content": "Tanh" + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": " is defined as " + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "inline_equation", + "content": "Tanh(x) = \\frac{e^{2x} - 1}{e^{2x} + 1}" + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": ". In practice, we observed that it is not effective to have a noise range lower than " + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\frac{\\pi}{8}" + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": ", we leverage " + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "inline_equation", + "content": "ReLU" + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": " to force negative values to be zero. " + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "inline_equation", + "content": "ReLU" + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": " is also a commonly used activation function, however, " + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "inline_equation", + "content": "ReLU" + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": " is used to provide a non-linear transform that makes all negative values 0 (to ensure that the noise is never less than " + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "inline_equation", + "content": "\\frac{\\pi}{8}" + }, + { + "bbox": [ + 46, + 437, + 287, + 594 + ], + "type": "text", + "content": "), and keeps all positive values the same." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 594, + 288, + 701 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 701 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 701 + ], + "type": "text", + "content": "While the non-linearity of " + }, + { + "bbox": [ + 46, + 594, + 288, + 701 + ], + "type": "inline_equation", + "content": "\\text{Tanh}" + }, + { + "bbox": [ + 46, + 594, + 288, + 701 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 594, + 288, + 701 + ], + "type": "inline_equation", + "content": "\\text{ReLU}" + }, + { + "bbox": [ + 46, + 594, + 288, + 701 + ], + "type": "text", + "content": " are important when used typically as activation functions, the nonlinearity is not the main function in this application. If the generator is not able to catch up with the discriminator for some iterations at this small range, it should learn this smaller range instead of getting even smaller. We set the minimum as " + }, + { + "bbox": [ + 46, + 594, + 288, + 701 + ], + "type": "inline_equation", + "content": "\\frac{\\pi}{8}" + }, + { + "bbox": [ + 46, + 594, + 288, + 701 + ], + "type": "text", + "content": " as we discovered that a lower value than " + }, + { + "bbox": [ + 46, + 594, + 288, + 701 + ], + "type": "inline_equation", + "content": "\\frac{\\pi}{8}" + }, + { + "bbox": [ + 46, + 594, + 288, + 701 + ], + "type": "text", + "content": " results in mode collapse, with almost no distinction between images generated for a given class." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 59, + 701, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 286, + 713 + ], + "type": "text", + "content": "Leveraging adaptive noise for input ensures more consis" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 309, + 69, + 541, + 133 + ], + "blocks": [ + { + "bbox": [ + 309, + 69, + 541, + 133 + ], + "lines": [ + { + "bbox": [ + 309, + 69, + 541, + 133 + ], + "spans": [ + { + "bbox": [ + 309, + 69, + 541, + 133 + ], + "type": "image", + "image_path": "833740fa3d394894cb30493f26cb07620164b5c59cede476c0bf63ac22664881.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 140, + 545, + 166 + ], + "lines": [ + { + "bbox": [ + 305, + 140, + 545, + 166 + ], + "spans": [ + { + "bbox": [ + 305, + 140, + 545, + 166 + ], + "type": "text", + "content": "Figure 6. MosaiQ's inference process to generate new images via running the generators on quantum machines." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 198, + 545, + 293 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 198, + 545, + 293 + ], + "spans": [ + { + "bbox": [ + 304, + 198, + 545, + 293 + ], + "type": "text", + "content": "tent training as the generator can focus on quality when it is doing relatively worse compared to the classical discriminator and expand to generating more variety in high quality as it begins to fool the discriminator more on an easier objective. Overall, the adaptive noise mechanism helps us increase the variety of images for a given class while ensuring that the image quality also remains high. This is further confirmed by our evaluation (Sec. 3)." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 300, + 546, + 492 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 300, + 546, + 492 + ], + "spans": [ + { + "bbox": [ + 304, + 300, + 546, + 492 + ], + "type": "text", + "content": "MosaiQ's Classical Discriminator. MosaiQ's discriminator is a classical deep-learning network, designed to aid in the training of the quantum generator. This network is essentially training wheels to guide a difficult-to-train quantum GAN, which can be discarded after training. The discriminator is much larger than the quantum generator, as there is only a single discriminator that must compete in the adversarial game with multiple quantum generators. Typical to its classical counterpart, MosaiQ's discriminator has multiple linear layers with " + }, + { + "bbox": [ + 304, + 300, + 546, + 492 + ], + "type": "inline_equation", + "content": "ReLU" + }, + { + "bbox": [ + 304, + 300, + 546, + 492 + ], + "type": "text", + "content": " activation (e.g., 64 layers). MosaiQ has a terminal layer with Sigmoid activation which introduces more non-linearity into the network, which enables it to learn more complex structures. The single value produced at the end of the discriminator network allows it to act as a classifier to distinguish between real and generated data." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 498, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 546, + 713 + ], + "type": "text", + "content": "Putting It All Together. The overall workflow for training and inference for MosaiQ are visually summarized in Fig. 5 and 6, respectively. Fig. 5 depicts the continuous feedback-driven process where the discriminator and generator participate in a non-cooperative game to improve the overall quality of MosaiQ. Depending upon the relative loss of the discriminator and generator networks, the random input noise is automatically adjusted to help MosaiQ generators avoid the problem of mode collapse problem and enable it to generate variety. During the training process, the input images are transformed using PCA to encode critical and more information in a compact manner for resource-limited NISQ quantum computers, instead of learning over the input images pixel by pixel. Finally, the five-step inference procedure shown in Fig. 6 highlights that the PCA transformation is inverted to generate new images when running the fully-trained MosaiQ generators on real quantum computers for inference to generate new images." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "type": "text", + "content": "7034" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 203, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 203, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 203, + 85 + ], + "type": "text", + "content": "3. Experimental Methodology" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 287, + 236 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 287, + 236 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 287, + 236 + ], + "type": "text", + "content": "Datasets. MosaiQ is evaluated on the MNIST [6] and Fashion MNIST datasets [21] as they have been widely-used for QML evaluation on NISQ-era quantum machines [15, 11]. MNIST consists of " + }, + { + "bbox": [ + 46, + 91, + 287, + 236 + ], + "type": "inline_equation", + "content": "28 \\times 28" + }, + { + "bbox": [ + 46, + 91, + 287, + 236 + ], + "type": "text", + "content": " gray-scale images of handwritten digits from 0 to 9. Fashion MNIST consists of " + }, + { + "bbox": [ + 46, + 91, + 287, + 236 + ], + "type": "inline_equation", + "content": "28 \\times 28" + }, + { + "bbox": [ + 46, + 91, + 287, + 236 + ], + "type": "text", + "content": " grayscale images of clothing and accessories. Fashion MNIST provides more challenges for image generation and is chosen to explore more domains of quantum image generation. For both datasets, we split the dataset by image label and train individual models for each data type. This technique has been used in [11] and allows us to interpret the generation process and difficulties isolated for each class of data." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 240, + 288, + 432 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 240, + 288, + 432 + ], + "spans": [ + { + "bbox": [ + 46, + 240, + 288, + 432 + ], + "type": "text", + "content": "Experimental Framework and Training Details. The environment for MosaiQ consists of PyTorch [16] acting as a wrapper for Pennylane [3]. MosaiQ is trained on IBM's quantum simulator for speed, but the inference is performed on both the quantum simulator and real quantum machine. For real quantum machine experiments, Pennylane compiles the circuits into a backend compatible with IBM-Qiskit [18]. All real machine runs were performed on the IBM QX Jakarta machine [18]. Images used in training are selected from the training set and decomposed to principal components of size 40. These components are divided across eight five-qubit sub-generators. The discriminator learns to differentiate at the level of principal components and does not need to utilize a full image. Our final FID metrics reported are at the end of the training after 500 iterations (where all methods achieve near-final stability)." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 433, + 287, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 433, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 433, + 287, + 529 + ], + "type": "text", + "content": "MosaicQ uses PyTorch's Standard Gradient Descent Optimizer for both the generator and discriminator and Binary Cross Entropy Loss for the shared loss of the generator and discriminator. The Adaptive Noise range is simple to calculate based on the generator and discriminator loss and MosaicQ automatically guides it to adjust itself every training iteration. The generator learning rate is 0.3 and the discriminator learning rate to .05 with a batch size of 8." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 288, + 714 + ], + "type": "text", + "content": "Framework for Competing Techniques. We set up QG-Patch, the state-of-the-art technique [11], using the popular Pennylane framework and choose the parameters used in the original paper [11]. Our QGPatch training is performed using the batch size of eight and it trains until the quality stabilizes (500 iterations). We use the same network size that is mentioned in the original paper, using 4 subgenerators with 5 features each. Evaluating the probabilities in measurement yields a 64-pixel (8x8) image. As MosaicQ's results are based on the original size of the datasets of 784 pixels, we upscale the results of QGPatch using Bilinear Interpolation to allow for direct comparison. We rigorously explored multiple interpolation techniques to provide QGPatch as much as an advantage as possible and experimentally determined that Bilinear interpolation yielded the" + } + ] + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 313, + 70, + 537, + 131 + ], + "blocks": [ + { + "bbox": [ + 313, + 70, + 537, + 131 + ], + "lines": [ + { + "bbox": [ + 313, + 70, + 537, + 131 + ], + "spans": [ + { + "bbox": [ + 313, + 70, + 537, + 131 + ], + "type": "image", + "image_path": "107b37d4c68a0a689e230222f4981bf8fe9130167ae6e998c9c184c2009d9758.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 135, + 547, + 171 + ], + "lines": [ + { + "bbox": [ + 305, + 135, + 547, + 171 + ], + "spans": [ + { + "bbox": [ + 305, + 135, + 547, + 171 + ], + "type": "text", + "content": "Figure 7. MosaiQ produces visually higher-quality images compared to the state-of-the-art technique, QGPatch, for different classes of MNIST and Fashion-MNIST datasets." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 179, + 545, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 179, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 304, + 179, + 545, + 228 + ], + "type": "text", + "content": "highest quality upscaling. For QGPatch, similar to MosaiQ, all metrics scores shown are calculated based on 500 images generated at the end of training compared to the entire distribution of the respective image category." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 228, + 546, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 228, + 546, + 396 + ], + "spans": [ + { + "bbox": [ + 304, + 228, + 546, + 396 + ], + "type": "text", + "content": "We additionally set up other classical experiments to act as ablations for the efficacy of MosaiQ. We introduce two techniques: (1) PCAInverse (using random inputs and PCA inverse transformation to generate images), and (2) ClassicalPCA (a purely-classical GAN using the same number of parameters as MosaiQ, but uses MosaiQ's PCA technique for feature compression). PCAInverse applies the same inverse PCA transformation as MosaiQ, to random noise of size 40. This technique is designed to explore the isolated effects of the inverse PCA transformation procedure since it does not perform any learning. ClassicalPCA trains a purely-classical GAN with an identical number of parameters as MosaiQ and apply the same inverse PCA transformation workflow." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 401, + 545, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 401, + 545, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 401, + 545, + 545 + ], + "type": "text", + "content": "Figures of Merit. To capture the quality of image generation, our evaluation figures of merit are both qualitative and quantitative. Our primary quantitative figure of merit is FID (Frechet inception distance) score [10]. FID evaluates the distance between two distributions, as defined below for a Gaussian with mean " + }, + { + "bbox": [ + 304, + 401, + 545, + 545 + ], + "type": "inline_equation", + "content": "(m, C)" + }, + { + "bbox": [ + 304, + 401, + 545, + 545 + ], + "type": "text", + "content": " and a second Gaussian with mean " + }, + { + "bbox": [ + 304, + 401, + 545, + 545 + ], + "type": "inline_equation", + "content": "(m_w, C_w)" + }, + { + "bbox": [ + 304, + 401, + 545, + 545 + ], + "type": "text", + "content": ": FID = " + }, + { + "bbox": [ + 304, + 401, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\| m - m_w\\|_2^2 + Tr(C + C_w - 2(CC_w)^{1/2})" + }, + { + "bbox": [ + 304, + 401, + 545, + 545 + ], + "type": "text", + "content": ". A lower FID score between two distributions indicates higher similarity – and hence, lower FID scores imply higher quality. The FID score has been shown to provide a more meaningful comparison over alternative metrics (e.g., Inception Score) for image GANs [10]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": "We also evaluate the variance of our images, by evaluating the variance of the pixel values relative to the mean. As defined below, the variance metric gives insight into the distinctness of the images generated for each method. For each pixel in an image row " + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": " and column " + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": " in an image, we sum the squared difference from the mean value for that respective pixel to achieve our variance score " + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": ". We then take the cumulative density function (CDF) of these variance scores for each image generated image " + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "inline_equation", + "content": "G(z)" + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": " given uniformly distributed noise " + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "inline_equation", + "content": "[0, \\pi/2]" + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": ": " + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "inline_equation", + "content": "V = \\sum_{r} \\sum_{c} (\\mu_{rc} - G(z)_{rc})^2" + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": ". A higher variance indicates higher variety in generated images for a given class – which is desirable, however, it is also critical that a method should attain a lower FID score before demonstrating higher variety." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "type": "text", + "content": "7035" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 70, + 286, + 144 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 286, + 144 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 286, + 144 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 286, + 144 + ], + "type": "image", + "image_path": "71b1c4a505a1b558cb6a7ec561c3e6feb321dbbeda536e4c9a63ed442d03fd79.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 148, + 288, + 185 + ], + "lines": [ + { + "bbox": [ + 46, + 148, + 288, + 185 + ], + "spans": [ + { + "bbox": [ + 46, + 148, + 288, + 185 + ], + "type": "text", + "content": "Figure 8. MosaiQ consistently produces lower FID score images (higher quality images) compared to QGpatch across different classes of the MNIST dataset." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 48, + 206, + 286, + 295 + ], + "blocks": [ + { + "bbox": [ + 48, + 206, + 286, + 295 + ], + "lines": [ + { + "bbox": [ + 48, + 206, + 286, + 295 + ], + "spans": [ + { + "bbox": [ + 48, + 206, + 286, + 295 + ], + "type": "image", + "image_path": "08021d7447096302d4be4c84e55ff7aeb45d3e40b35d5f13ac63cb6ab227efa2.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 299, + 288, + 336 + ], + "lines": [ + { + "bbox": [ + 46, + 299, + 288, + 336 + ], + "spans": [ + { + "bbox": [ + 46, + 299, + 288, + 336 + ], + "type": "text", + "content": "Figure 9. MosaiQ consistently produces lower FID score images (higher quality images) compared to QGPatch across different classes of the Fashion-MNIST dataset." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 48, + 357, + 284, + 448 + ], + "blocks": [ + { + "bbox": [ + 48, + 357, + 284, + 448 + ], + "lines": [ + { + "bbox": [ + 48, + 357, + 284, + 448 + ], + "spans": [ + { + "bbox": [ + 48, + 357, + 284, + 448 + ], + "type": "image", + "image_path": "c0d2012a6d653cd14fe04df72a96896474be224b91937d1ca8b963227ce1ac0f.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 450, + 288, + 498 + ], + "lines": [ + { + "bbox": [ + 46, + 450, + 288, + 498 + ], + "spans": [ + { + "bbox": [ + 46, + 450, + 288, + 498 + ], + "type": "text", + "content": "Figure 10. MosaiQ produces higher quality images on the MNIST and Fashion MNIST dataset as compared to HQCGAN [19]. MosaiQ produces higher quality images than the classical methods: PCAInverse and ClassicalPCA." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 530, + 188, + 544 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 530, + 188, + 544 + ], + "spans": [ + { + "bbox": [ + 47, + 530, + 188, + 544 + ], + "type": "text", + "content": "4. Evaluation and Analysis" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 551, + 287, + 575 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 551, + 287, + 575 + ], + "spans": [ + { + "bbox": [ + 46, + 551, + 287, + 575 + ], + "type": "text", + "content": "In this section, we go over the results of MosaiQ and provide an analysis of the key elements of the design." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": "MosaiQ: Key Results and SOTA Comparison. MosaiQ yields significantly better image quality both visually and quantitatively compared to the state-of-the-art (SOTA) method, QGpatch [11]. As discussed earlier, MosaiQ is evaluated on two different datasets to cover diversity across datasets and within a dataset with different shapes and styles (digits and clothing). First, we highlight that MosaiQ provides a significant visual enhancement in the images produces across different classes compared to the SOTA method. In fact, Fig. 7 shows that the SOTA-produced images are almost unrecognizable for sophisticated shapes ('0'" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 306, + 70, + 547, + 144 + ], + "blocks": [ + { + "bbox": [ + 306, + 70, + 547, + 144 + ], + "lines": [ + { + "bbox": [ + 306, + 70, + 547, + 144 + ], + "spans": [ + { + "bbox": [ + 306, + 70, + 547, + 144 + ], + "type": "image", + "image_path": "8aad6b6f9380fde982caff74317aa05db518a44ee89a9387ae8e672f7800590c.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 159, + 547, + 196 + ], + "lines": [ + { + "bbox": [ + 305, + 159, + 547, + 196 + ], + "spans": [ + { + "bbox": [ + 305, + 159, + 547, + 196 + ], + "type": "text", + "content": "Figure 11. MosaiQ produces higher quality images on every class of the MNIST dataset as compared to HQCGAN [19] in addition to the classical methods tested." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 306, + 211, + 547, + 300 + ], + "blocks": [ + { + "bbox": [ + 306, + 211, + 547, + 300 + ], + "lines": [ + { + "bbox": [ + 306, + 211, + 547, + 300 + ], + "spans": [ + { + "bbox": [ + 306, + 211, + 547, + 300 + ], + "type": "image", + "image_path": "4af3cda8deb329f570a784c36cc5235012d0182e212999cc08518a95f4ec474b.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 316, + 547, + 353 + ], + "lines": [ + { + "bbox": [ + 305, + 316, + 547, + 353 + ], + "spans": [ + { + "bbox": [ + 305, + 316, + 547, + 353 + ], + "type": "text", + "content": "Figure 12. MosaiQ produces higher quality images on every class of the Fashion MNIST dataset as compared to HQCGAN [19] in addition to the classical methods tested." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 378, + 545, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 378, + 545, + 426 + ], + "spans": [ + { + "bbox": [ + 304, + 378, + 545, + 426 + ], + "type": "text", + "content": "vs. ‘5’ and different types of shoes). In comparison, MosaiQ is effective across different class types – this is further substantiated by lower FID scores of the images generated by MosaiQ (Fig. 8 and 9)." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 426, + 546, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 546, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 546, + 653 + ], + "type": "text", + "content": "As expected, the FID score obtained by MosaiQ varies across different classes for both datasets; this is because of varying degrees of difficulty and shapes of different images. However, the most notable observation is that MosaiQ consistently outperforms QGPatch across all class types by a significant margin (by more than 10 points in many cases). In fact, MNIST digit '7' is quite challenging for QGPatch (FID score is 60), and MosaiQ improves the FID score by approximately 20 points. Similarly, the most challenging class in the Fashion-MNIST dataset (Boot) receives a 45-point improvement by MosaiQ. The key reason MosaiQ outperforms QGPatch is the efficiency of principal components in capturing information. Instead of having to learn pixels one by one, MosaiQ scales more easily by learning a distribution of features that better organize redundancy. For example, most of the background of MNIST and Fashion MNIST images are black, in the case of QGPatch, each pixel must be synthesized, where MosaiQ may be able to build these features with only a few principal components." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 713 + ], + "type": "text", + "content": "We also compare MosaiQ to other methods, including the PCAInverse technique, the ClassicalPCA technique, and a recent work on hybrid quantum GANs which we refer to as HQCGAN [19]. We sample generated images in Fig. 10 and find the images produced by all methods tested" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "type": "text", + "content": "7036" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 69, + 284, + 159 + ], + "blocks": [ + { + "bbox": [ + 48, + 69, + 284, + 159 + ], + "lines": [ + { + "bbox": [ + 48, + 69, + 284, + 159 + ], + "spans": [ + { + "bbox": [ + 48, + 69, + 284, + 159 + ], + "type": "image", + "image_path": "c99ef7fb23a3fc89ab1fba68779abb7165dbad9077592d861aaf015e6bf6fd1b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 165, + 288, + 226 + ], + "lines": [ + { + "bbox": [ + 46, + 165, + 288, + 226 + ], + "spans": [ + { + "bbox": [ + 46, + 165, + 288, + 226 + ], + "type": "text", + "content": "Figure 13. MosaiQ's PCA feature distribution among learners improves the quality of generated images. The figure shows a distribution of 200 FID scores (comparing 8 images each to the entire data distribution) for the case with and without PCA feature redistribution." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 246, + 287, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 246, + 287, + 449 + ], + "spans": [ + { + "bbox": [ + 46, + 246, + 287, + 449 + ], + "type": "text", + "content": "are lower quality than MosaiQ, producing images which are far less human-recognizable. We show the corresponding FID scores for MNIST in Fig 11 and Fashion MNIST in Fig. 12. We find that MosaiQ produces higher quality images and significantly improved FID scores in all cases tested compared to the classical methods (PCAInverse and ClassicalPCA), and HQCGAN. Importantly, MosaiQ outperforms ClassicalPCA, demonstrating the power of quantum networks in image generation when compared to equal-sized classical networks. Our results show that while HQCGAN is promising and useful, the final quality may not be as high as MosaiQ – this is because HQCGAN requires significantly more parameters, more training resources, lacks noise-mitigation, and learns noise in a fixed range ([0, 1) instead of MosaiQ's adaptive noise range technique). Next, we dissect the key reasons behind MosaiQ's effectiveness in more detail." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 455, + 287, + 671 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 455, + 287, + 671 + ], + "spans": [ + { + "bbox": [ + 46, + 455, + 287, + 671 + ], + "type": "text", + "content": "Why Does MosaiQ Work Effectively? Effect of careful PCA feature distribution among sub-generators. Recall that MosaiQ employs an intelligent PCA feature distribution among sub-generators in the generation phase. The goal is to equalize the explainable PCA feature variance across learners – in an effort to make learners equally capable instead of weaker learners not effectively contributing toward the overall quality. To better understand and demonstrate the effectiveness of this mechanism, Fig. 13 shows the FID score over multiple training iterations with and without this mechanism while keeping all other design elements intact. For easier interpretation, Fig. 13 shows this for class digit '5' for the MNIST dataset. We observe that PCA feature distribution allows MosaiQ to achieve lower (and hence, better) FID score over training compared to without employing this mechanism. A side benefit of this mechanism is that MosaiQ can also mitigate hardware errors on real quantum computers, as discussed later." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 677, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 714 + ], + "type": "text", + "content": "Effect of adaptive noise generation during training. Fig. 14 shows the effect of adaptive noise generation that is used by the MosaiQ generators instead of using a constant" + } + ] + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 307, + 69, + 541, + 150 + ], + "blocks": [ + { + "bbox": [ + 307, + 69, + 541, + 150 + ], + "lines": [ + { + "bbox": [ + 307, + 69, + 541, + 150 + ], + "spans": [ + { + "bbox": [ + 307, + 69, + 541, + 150 + ], + "type": "image", + "image_path": "3eda43be3f6fa41acad06d1bb45f526c5f7479d7fd489872a751d7241a0a33a0.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "lines": [ + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "spans": [ + { + "bbox": [ + 305, + 159, + 547, + 208 + ], + "type": "text", + "content": "Figure 14. Adaptive noise during generation helps MosaiQ achieve variety (higher variance across images for the same class to mitigate mode-collapse challenge), while achieving lower FID score at the same time, as shown earlier." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 308, + 232, + 542, + 278 + ], + "blocks": [ + { + "bbox": [ + 308, + 232, + 542, + 278 + ], + "lines": [ + { + "bbox": [ + 308, + 232, + 542, + 278 + ], + "spans": [ + { + "bbox": [ + 308, + 232, + 542, + 278 + ], + "type": "image", + "image_path": "da7a67d833aabf791be599da57bb470dbb1ee936d1c0bbe12ef017ad1df9882c.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 287, + 546, + 323 + ], + "lines": [ + { + "bbox": [ + 305, + 287, + 546, + 323 + ], + "spans": [ + { + "bbox": [ + 305, + 287, + 546, + 323 + ], + "type": "text", + "content": "Figure 15. Visual image quality of images produced by MosaiQ on real IBM quantum machine (Jakarta) for six representative classes for MNIST and Fashion-MNIST datasets." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 346, + 546, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 346, + 546, + 538 + ], + "spans": [ + { + "bbox": [ + 304, + 346, + 546, + 538 + ], + "type": "text", + "content": "noise threshold range (i.e., " + }, + { + "bbox": [ + 304, + 346, + 546, + 538 + ], + "type": "inline_equation", + "content": "[0, \\frac{\\pi}{2}]" + }, + { + "bbox": [ + 304, + 346, + 546, + 538 + ], + "type": "text", + "content": ") used by the QGPatch method. Recall that GANs often suffer from intra-class mode-collapse challenges where they can produce a high-quality image for a given class, but there is a possibility that all generated images for a given class appear similar. Therefore, it is critical to ensure that the generated images for a given class have sufficient variety. Fig. 14 confirms that adaptive noise improves variety (class digit '5' used as an example) compared to fixed noise ranges. This is because adaptive noise enables the generators to learn over different distributions more effectively and generate variations. Having an adaptive range allows the generator to improve variety when it is doing comparatively well and focus on stability when it is performing poorly with a smaller range of inputs. Taking advantage of this allows us to have high stability in training and high variety over time." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 544, + 545, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 544, + 545, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 544, + 545, + 700 + ], + "type": "text", + "content": "MosaiQ on NISQ Quantum Machines. Our experimental campaign on real superconducting-based IBM NISQ quantum computers confirms MosaiQ produces higher quality images across different datasets with diverse classes of images. Fig. 15 and Table 1 summarize the image quality results for QGPatch and MosaiQ. While MosaiQ's quality remains consistent with simulations, QGPatch's quality degrades considerably on real computers. In fact, our results revealed QGPatch produces lower quality images and sometimes unrecognizable images because QGPatch is more prone to side-effects of prevalent quantum gate errors on real machines, while MosaiQ's simplistic design successfully mitigates those effects as discussed next." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "content": "First, we observe that MosaiQ produces competitive" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "type": "text", + "content": "7037" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 52, + 112, + 289, + 144 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 288, + 95 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 288, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 288, + 95 + ], + "type": "text", + "content": "Table 1. QGpatch and MosaiQ's FID scores on a real quantum computer for MNIST & Fashion-MNIST datasets." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 147, + 100, + 190, + 110 + ], + "lines": [ + { + "bbox": [ + 147, + 100, + 190, + 110 + ], + "spans": [ + { + "bbox": [ + 147, + 100, + 190, + 110 + ], + "type": "text", + "content": "(a) QGPatch" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 112, + 289, + 144 + ], + "lines": [ + { + "bbox": [ + 52, + 112, + 289, + 144 + ], + "spans": [ + { + "bbox": [ + 52, + 112, + 289, + 144 + ], + "type": "table", + "html": "
EnvironmentDigit 0Digit 5Digit 9T ShirtPantsShoes
Quantum Simulator525248454282
IBM Jakarta Machine145134131125144124
", + "image_path": "5021b59ab351e7c7373f51fcecc897feea021ac7fe5db3547b7c792accecb97f.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 52, + 160, + 289, + 191 + ], + "blocks": [ + { + "bbox": [ + 149, + 147, + 188, + 156 + ], + "lines": [ + { + "bbox": [ + 149, + 147, + 188, + 156 + ], + "spans": [ + { + "bbox": [ + 149, + 147, + 188, + 156 + ], + "type": "text", + "content": "(b) MosaiQ" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 160, + 289, + 191 + ], + "lines": [ + { + "bbox": [ + 52, + 160, + 289, + 191 + ], + "spans": [ + { + "bbox": [ + 52, + 160, + 289, + 191 + ], + "type": "table", + "html": "
EnvironmentDigit 0Digit 5Digit 9T ShirtPantsShoes
Quantum Simulator424233342238
IBM Jakarta Machine454435382338
", + "image_path": "7e0ead8330b3937d31ce89d23b70ddda406702531a164ccfe1e0450759f38d49.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 217, + 287, + 359 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 217, + 287, + 359 + ], + "spans": [ + { + "bbox": [ + 46, + 217, + 287, + 359 + ], + "type": "text", + "content": "quality images despite hardware errors on real quantum computers. Due to high queue wait time and limited availability of quantum resources, we are presenting results only for selected classes (three from each dataset) which cover a diverse range of intricacies in terms of shape and information. In fact, via visual inspection for different images produced for a given class, we observe that the variety in the produced images by MosaiQ is also high on the quantum computer - effectively mitigating the mode-collapse pitfall in GANs. This is because of MosaiQ's adaptive noise mechanism during the generation phase that improves image variety and avoids mode collapse." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 360, + 288, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 360, + 288, + 647 + ], + "spans": [ + { + "bbox": [ + 46, + 360, + 288, + 647 + ], + "type": "text", + "content": "Second, we observe that the FID scores of MosaiQ on a real quantum computer are similar to error-free simulation results, across different classes. This result demonstrates that MosaiQ's design is effective even when hardware errors are present. In fact, the IBM Jakarta computer has a considerably low quantum volume (higher is better) with a quantum volume of 16. Quantum volume is a useful metric in determining the error rate and capabilities of a quantum computer. For perspective, at the time of writing, IBM has computers available with quantum volumes of 128. We chose a relatively less capable quantum computer for our experiments to demonstrate the portability and robustness of MosaiQ. The reason for MosaiQ's effectiveness is twofold: (1) its simplistic design for generator learners, which avoids a large number of two-qubit gates, and circuits with high depths. which are more prone to hardware noise, and (2) its PCA feature distribution mapping among the ensemble of learners in the generator - this careful redistribution ensures that most critical PCA features are not concentrated on a few qubits, which in the pathological case could be most severely impacted by hardware-errors. MosaiQ's PCA redistribution ensures that the learners do not need to know the error rate of individual qubits on the computer or make assumptions about different error types." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 657, + 134, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 657, + 134, + 670 + ], + "spans": [ + { + "bbox": [ + 47, + 657, + 134, + 670 + ], + "type": "text", + "content": "5. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 715 + ], + "type": "text", + "content": "Demonstration of the Speedup Achieved by Quantum GANs. Quantum GANs were first introduced by Lloyd et al.[14]. This work theoretically proved the potential for ex" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 545, + 179 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 179 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 179 + ], + "type": "text", + "content": "ponential superiority of Quantum GANs over their classical counterparts. This was later followed by the work of Dallaire-Demers et al. [4], which established a way to design and train variational quantum circuits as the generator component of a Quantum GAN model. Nakaji et al. [15] use a hybrid configuration with a classical discriminator and a quantum generator for classification. Their results demonstrate the potential for quantum GANs to solve problems that are intractable with classical GANs." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 189, + 545, + 321 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 189, + 545, + 321 + ], + "spans": [ + { + "bbox": [ + 304, + 189, + 545, + 321 + ], + "type": "text", + "content": "Enchancing Classical GANs using Quantum Components. Approaches such as the work done by Rudolph et al. [17] use a quantum enhancer for large-scale fully-classical generators to enhance the quality of image generation. While the images generated are high quality, this is mostly attributed to the large classical generators. The visual results in these works seem appealing because the classical GAN-based baseline is already high quality, with a quantum preamble which only improves the image quality slightly. This is in contrast to MosaiQ which uses a quantum generator to generate images without a classical generator." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 330, + 545, + 546 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 330, + 545, + 546 + ], + "spans": [ + { + "bbox": [ + 304, + 330, + 545, + 546 + ], + "type": "text", + "content": "Fully-Quantum Generators. The work of Huang et al. [12] uses quantum gradients to train quantum GANs to replicate logic gates such as XOR with high fidelity and also generate images from the MNIST dataset. The technique relies on using quantum-based loss functions for their generator and discriminator. This work also shows that quantum GANs have similar performance as classical GANs while using " + }, + { + "bbox": [ + 304, + 330, + 545, + 546 + ], + "type": "inline_equation", + "content": "94.98\\%" + }, + { + "bbox": [ + 304, + 330, + 545, + 546 + ], + "type": "text", + "content": " fewer parameters. A succeeding work with higher quality MNIST image generation can be found in QGPatch [11], with a generator split among several subgenerators each responsible for generating a part of the full image. QGPatch trains a quantum generator against a classical discriminator. The quality of generation is the highest among pre-MosaiQ quantum GANs with a purely quantum generative component, at the time of writing. Therefore, we compare MosaiQ against QGPatch in this paper and show that MosaiQ outperforms QGPatch in terms of image quality and variety." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 567, + 378, + 578 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 567, + 378, + 578 + ], + "spans": [ + { + "bbox": [ + 306, + 567, + 378, + 578 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 590, + 545, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 590, + 545, + 674 + ], + "spans": [ + { + "bbox": [ + 304, + 590, + 545, + 674 + ], + "type": "text", + "content": "MosaicQ is the first quantum GAN to successfully generate high-quality images on real quantum computers. MosaicQ incorporates PCA feature redistribution and adaptive noise to facilitate improved interaction between the quantum generator and classical elements of the model. This integration enhances the quality and variety of the generator's output respectively." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgements We thank the reviewers for constructive feedback. This work was supported by NSF Award 2144540, Northeastern University, and Rice University." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 733, + 315, + 742 + ], + "type": "text", + "content": "7038" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 72, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 72, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 72, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 287, + 711 + ], + "type": "list", + "angle": 0, + "index": 16, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 157 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 157 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 157 + ], + "type": "text", + "content": "[1] Samet Akcay, Amir Atapour-Abarghouei, and Toby P. 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Unpaired image-to-image translation using cycle-consistent adversarial networks, 2017. 1" + } + ] + } + ], + "index": 23 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 734, + 315, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 734, + 315, + 742 + ], + "spans": [ + { + "bbox": [ + 295, + 734, + 315, + 742 + ], + "type": "text", + "content": "7039" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Most Important Person-Guided Dual-Branch Cross-Patch Attention for Group Affect Recognition/2995ddf2-76d9-45cb-9d66-1a50a95e4d2f_content_list.json b/2023/Most Important Person-Guided Dual-Branch Cross-Patch Attention for Group Affect Recognition/2995ddf2-76d9-45cb-9d66-1a50a95e4d2f_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..0665cdb5995b910ba95ea241f50c3ee2370509da --- /dev/null +++ b/2023/Most Important Person-Guided Dual-Branch Cross-Patch Attention for Group Affect Recognition/2995ddf2-76d9-45cb-9d66-1a50a95e4d2f_content_list.json @@ -0,0 +1,1839 @@ +[ + { + "type": "text", + "text": "Most Important Person-guided Dual-branch Cross-Patch Attention for Group Affect Recognition", + "text_level": 1, + "bbox": [ + 91, + 128, + 879, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Hongxia Xie $^{1}$ , Ming-Xian Lee $^{2}$ , Tzu-Jui Chen $^{2}$ , Hung-Jen Chen $^{1}$ , Hou-I Liu $^{1}$ , Hong-Han Shuai $^{1}$ and Wen-Huang Cheng $^{3}$", + "bbox": [ + 88, + 214, + 880, + 253 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ National Yang Ming Chiao Tung University, hongxiaixie.ee08@nycu.edu.tw", + "bbox": [ + 143, + 263, + 823, + 281 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "2University of Illinois Urbana-Champaign", + "bbox": [ + 318, + 282, + 651, + 299 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{3}$ National Taiwan University, wenhuang@csie.ntu.edu.tw", + "bbox": [ + 228, + 299, + 741, + 316 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 361, + 313, + 378 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Group affect refers to the subjective emotion that is evoked by an external stimulus in a group, which is an important factor that shapes group behavior and outcomes. Recognizing group affect involves identifying important individuals and salient objects among a crowd that can evoke emotions. However, most existing methods lack attention to affective meaning in group dynamics and fail to account for the contextual relevance of faces and objects in group-level images. In this work, we propose a solution by incorporating the psychological concept of the Most Important Person (MIP), which represents the most noteworthy face in a crowd and has affective semantic meaning. We present the Dual-branch Cross-Patch Attention Transformer (DCAT) which uses global image and MIP together as inputs. Specifically, we first learn the informative facial regions produced by the MIP and the global context separately. Then, the Cross-Patch Attention module is proposed to fuse the features of MIP and global context together to complement each other. Our proposed method outperforms state-of-the-art methods on GAF 3.0, GroupEmoW, and HECO datasets. Moreover, we demonstrate the potential for broader applications by showing that our proposed model can be transferred to another group affect task, group cohesion, and achieve comparable results.", + "bbox": [ + 75, + 398, + 473, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 808, + 209, + 824 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Humans are active and social creatures, using multimodal interactions to convey their intentions, attitudes, and feelings. Such physical and emotional interactions between individuals within a group can generate group-level affect", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 0 + }, + { + "type": "table", + "img_path": "images/9542285e489ff9047b917d81c6d15ab8415a640873e95ed44b7cf1d5c468733f.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Global +All3Random3MIPs1RandomMIP
Acc (%)85.0185.4787.4682.3088.86
", + "bbox": [ + 500, + 361, + 897, + 406 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Table 1. Different face selection strategies. The \"3Random\" refers to selecting 3 faces randomly from the detected faces in the image, while the \"3MIPs\" strategy selects the top three detected faces based on their importance ranking. The dataset evaluated here is the GroupEmoW [22].", + "bbox": [ + 498, + 416, + 893, + 486 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "or group-level emotion [2]'.", + "bbox": [ + 500, + 508, + 692, + 526 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/a9e91f77f20a4009fc67e082724119343b01a48265f630131e067e893eb52c23.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 524, + 537, + 635, + 622 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/4d0400e954af0532303fccf14e0928c69db02657a4c8357a2dd2dbdc698f5224.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 640, + 537, + 751, + 622 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3a547c9a6b1eb0a240e5cbc0f81724f8ee3fd73e42fe0e1a7c1a1c0c65b85f51.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 756, + 537, + 867, + 622 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/47aed540efefac8474876d65efc41f41f283ae3aa2dee60cbc0710c65ecac6bf.jpg", + "image_caption": [ + "(a) Input image" + ], + "image_footnote": [], + "bbox": [ + 524, + 628, + 635, + 712 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/73199a18044fa69b79df925fa8d820b67b74b551401bb179c28cbc095d8815bc.jpg", + "image_caption": [ + "(b) Using MIP" + ], + "image_footnote": [], + "bbox": [ + 640, + 628, + 750, + 712 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/63ebafa884cf7425fd532c95f18887f9e73258ac918b40693c097720a2ab11b4.jpg", + "image_caption": [ + "(c) Using all faces", + "Figure 1. Feature map comparison between using MIP and all faces. The yellow box in (a) represents the MIP region." + ], + "image_footnote": [], + "bbox": [ + 756, + 627, + 867, + 712 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "By providing the group-level information, group affect prediction has various real-world applications, e.g., work team outcome prediction [21], social relationship recognition [33], human-machine interaction systems [24]. As a result, the research topics surrounding group affect are di", + "bbox": [ + 496, + 790, + 893, + 867 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "1In this work, groups range in size from two or three individuals up to hundreds.", + "bbox": [ + 500, + 875, + 890, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "20598", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "verse, including categorical analysis, e.g., group valence (positive, negative, neutral) prediction [16, 22], continuous intensity estimation, e.g., group cohesion prediction [15].", + "bbox": [ + 76, + 90, + 468, + 137 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Group affect is influenced by a combination of a group's affective context (e.g., salient objects in the funeral, party) and affective composition (i.e., the combination of a group members' state and trait affect) [2]. Previous methods for group affect recognition mainly adopted a bottom-up approach [9, 44, 16, 22], where features were extracted from individuals separately and then fused to output group-level emotion. This was done by utilizing multi-cues from separate pre-trained detectors, such as facial expressions of individuals, object proposals, and scene features. While these cues can provide valuable information, they may not fully capture the complex interplay of emotions within a group. As indicated in [12], current group-level recognition architectures tend to focus on detecting salient regions, but they may lack an understanding of the affective meaning in the image. Therefore, there is a need for a more holistic approach that considers the most important region in the crowd and how they interact with the scene.", + "bbox": [ + 75, + 138, + 470, + 411 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Hence, in this work, we introduce a crucial psychological concept, namely, Most Important Person (MIP) [2], which goes beyond saliency and considers the importance of individuals for group affect recognition. The MIP of an image is often the group leaders who can influence the emotion of a group [11, 37, 34]. MIP has been explored in many related works in psychology and affective computing, such as the Affective Transfer Process phenomenon in psychology [2], which indicates that the MIP of an image can influence the group's emotion. We conducted a preliminary experiment based on the CrossVit [5] model to demonstrate the effectiveness of the MIP in group affect. Our architecture uses both the global image and faces as two inputs. As depicted in Table 1, the results demonstrate that using all faces is considerably less effective than using the MIP, and even less effective than randomly selecting three facial images. Additionally, as observed in the feature maps illustrated in Figure 1, the model that employs all faces fails to predict accurately due to its focus on irrelevant background regions or faces. In contrast, the network that utilizes MIP can efficiently focus on relevant facial regions, thereby enhancing prediction accuracy. This is mainly due to the fact that in crowded scenes with many blurry faces, the model trained on all faces exhibits dispersed attention, while the model trained on the MIP region concentrates specifically on the relevant area.", + "bbox": [ + 75, + 414, + 470, + 806 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Based on the above observations, we present a dual-pathway vision transformer model, the Dual-branch Cross-Patch Attention Transformer (DCAT), including a global branch and a MIP branch. With the dual-pathway, spatial-wise discriminative clues can be discovered both globally and locally in conjunction with self-attention learning. For", + "bbox": [ + 75, + 810, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "the dual-pathway interaction, since there are many interferences in the group, we propose the Cross-Patch Attention (CPA) module. CPA first utilizes the Token Ranking Module to select the important tokens in each path, and then the cross-attention is calculated between the selected query vectors and the entire key-value vectors from the other path. In this way, global and MIP contexts are able to complement and compensate for each other.", + "bbox": [ + 496, + 90, + 890, + 210 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "This paper makes the following main contributions:", + "bbox": [ + 517, + 212, + 861, + 227 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- In this work, we validate that MIP plays a crucial role in group affect recognition. To the best of our knowledge, this is the first work introducing MIP into the group affect task.", + "- The MIP and global affective context information are integrated into the proposed dual-pathway vision transformer architecture for recognizing group emotions in a context-aware manner. We also propose a novel CPA module that focuses on the interactions among diverse scene contexts and facial informative regions.", + "- Experimental results show that the proposed DCAT outperforms both state-of-the-art group affect works and vision transformer models in terms of accuracy and model parameters. This is also the first work to explore group affect recognition that goes beyond the CNN-based approach. Moreover, our proposed model can be utilized in other group-level affect tasks, i.e., group cohesion analysis." + ], + "bbox": [ + 517, + 233, + 890, + 537 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related works", + "text_level": 1, + "bbox": [ + 500, + 550, + 643, + 566 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Group affect recognition methods", + "text_level": 1, + "bbox": [ + 500, + 575, + 794, + 590 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Current group affect recognition methods primarily analyze the individual members of a group and then assess their contribution to the overall mood of the group by taking into account a variety of cues, such as faces, salient objects, and scenes. Fujii et al. [9] proposed a two-stage classification method, in which the first stage classifies facial expressions, and the second stage adds scene features into consideration to fuse faces and scenes through spectral clustering for further group affect recognition. Khan et al. [22] considered multi-cues, which include all faces, object proposals, and scene information. To achieve such an architecture, additional face detection and object proposal detection detectors are needed. Similarly, Guo et al. [16] also investigated multi-cues using graph neural networks, where the topology of the graph varies as the number of entities varies.", + "bbox": [ + 496, + 598, + 890, + 824 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "However, in large groups, it is not feasible to consider the expressions of all faces and objects individually before aggregating, resulting in lower efficiency and accuracy. As indicated in [9], considering the performance of the main subject estimation is needed, while our work fills the gap.", + "bbox": [ + 496, + 825, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "20599", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Most important person (MIP) detection", + "text_level": 1, + "bbox": [ + 76, + 90, + 415, + 107 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2.1 MIP detection", + "text_level": 1, + "bbox": [ + 76, + 113, + 230, + 128 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "A MIP detection model understands a high-level pattern in a social event image to identify the most important person. Ramanathan et al. [35] used an RNN to learn time-varying attention weights that can be used for event detection and classification. Without any explicit annotations, the person with the highest attendance can be identified as the MIP. In order to overcome the inherent variability of human poses, PersonRank [27] produced a multiple Hyper-Interaction Graph, which treats each individual person as a node. The most active node can be identified using four types of edge message functions. POINT [26] proposed two types of interaction modules, i.e., the person-person interaction module and the event-person interaction module. It then aggregated relation features and person features to form the important feature. To reduce the annotation effort, Hong et al. [19] formulated a POINT-based iterative learning method for semi-supervised important people detection. Thus, we incorporate people awareness into global-level affect analysis in this work.", + "bbox": [ + 75, + 137, + 472, + 425 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Dual attention learning models", + "text_level": 1, + "bbox": [ + 76, + 434, + 349, + 450 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Visual attention with dual-pathway has been widely used to find important contextual regions. Based on the outstanding performance of vision transformers (ViTs) in various visual tasks [8], there are many self-attention-based dual-pathway networks in recent years. Zhu et al. [49] proposed a global-local cross-attention to reinforce the spatial-wise discriminative clues for fine-grained recognition. A pairwise cross-attention was designed to establish the interactions between image pairs. Dual-ViT [46] incorporated a compressed semantic pathway that served as prior information in learning finer pixel-level details. The semantic pathway and pixel pathway are integrated together and trained to spread enhanced self-attention information in parallel.", + "bbox": [ + 75, + 458, + 468, + 652 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The most similar architecture to our work is the CrossViT [5], which was proposed to learn multi-scale features effectively. However, we differ from it in two main ways. Firstly, our network divides at different scales using global images and MIP images, whereas CrossViT divides at different scales using the same input image. Another difference is the cross-attention mechanism. The CrossViT exchanges class tokens, while we designed a Cross-Patch Attention module based on attentive queries from both paths.", + "bbox": [ + 75, + 654, + 468, + 789 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed Dual-branch Cross-Patch Attention Transformer (DCAT)", + "text_level": 1, + "bbox": [ + 76, + 804, + 468, + 838 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overview", + "text_level": 1, + "bbox": [ + 76, + 847, + 187, + 861 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The architecture of our proposed Dual-branch Cross-Patch Attention Transformer (DCAT) for group affect", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "recognition is shown in Figure 2. The model contains two inputs, i.e., the global image and the corresponding MIP image. The two images are tokenized into patches first and sent into a stack of Multi-Scale Transformer Encoder, which consists of dual-path Transformer Encoder, Token Ranking Module, and Cross-Patch Attention (CPA). Specifically, in a dual-path Transformer Encoder, the global image is sent to the coarse-level path to capture long-range information and further refine the encoded tokens for fine-grained details. On the other hand, the MIP image is fed to the fine-level path to obtain high-level semantic tokens. Next, since the global and MIP features are conceptual interdependent, we incorporate dual-path interaction in our model. In particular, we sort tokens according to their importance in each path based on the Token Ranking Module, then calculate the CPA using the key and value vectors from the other path. Finally, the class tokens from two branches are combined and sent into a linear layer for prediction.", + "bbox": [ + 496, + 90, + 890, + 363 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Dual-pathway learning", + "text_level": 1, + "bbox": [ + 500, + 375, + 714, + 392 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To leverage the global information of a group captured by the global image and the local-based semantic prior of the MIP, we propose a dual-pathway feature learning approach for group affect prediction. By integrating self-attention learning into the dual-pathway, our approach enables the discovery of spatial-wise discriminative clues both globally and locally. To validate our assumptions, we compute the CKA similarity [43] to measure the similarity of the intermediate token features in each layer and the final CLS token, follwing [43]. As illustrated in Figure 3, both the MIP and global tokens exhibit a positive correlation with the CLS token as the model depth increases. This suggests that both features are valuable for the final classification task and highlights the rationality and necessity of our dual-pathway input design.", + "bbox": [ + 496, + 398, + 890, + 626 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Firstly, both the global and MIP image are tokenized into patches, then the class token and a learnable position embedding are added to both branches before the MultiScale Transformer Encoder. In order to balance computational costs, our Transformer Encoders in the two pathways include different numbers (i.e., $G = 6$ and $M = 1$ ) inspired by CrossViT [5]. The global branch is the large (primary) branch with a coarse patch size (i.e., 12), with a larger embedding size, and more transformer encoders. The MIP image is the input of a small (complementary) branch with fine-grained patch size (i.e., 16), fewer encoders, and a smaller embedding size.", + "bbox": [ + 496, + 628, + 890, + 808 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As the core of the vision transformer, the Multi-Head Self-Attention (MHSA) maps a query vector into a set of key and value vectors [8]. In the $l$ -th Transformer Encoder block in both pathways (a basic Transformer Encoder is shown in Figure 2b), the output feature map is $X_{l} \\in \\mathbb{R}^{(N + 1)\\times d}$ . The attention matrix $A_{l} \\in \\mathbb{R}^{S \\times (N + 1) \\times (N + 1)}$", + "bbox": [ + 496, + 810, + 890, + 898 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "20600", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/53991e35cece8832602c947d2ddc621319fe330d6874b22b13f2a5821c952765.jpg", + "image_caption": [ + "(a) The overall architecture of our proposed DCAT" + ], + "image_footnote": [], + "bbox": [ + 89, + 88, + 457, + 518 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/6f1bd41b9a0827cc2b0203d63c912bd5fba50d89f8d1be01c9ee04787ee53717.jpg", + "image_caption": [ + "(b) The Transformer Encoder" + ], + "image_footnote": [], + "bbox": [ + 532, + 98, + 890, + 189 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/3975a2d0b19aa136741b2b22c537caf7851c904479d514f1368317b90b6b4466.jpg", + "image_caption": [ + "(c) The Cross-Patch Attention (CPA)" + ], + "image_footnote": [], + "bbox": [ + 550, + 234, + 836, + 513 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/e479b41d4548b5c695fa0aef90257608de731e35f8a35f88b36bc295ecac7143.jpg", + "image_caption": [ + "Figure 2. The overall architecture of our proposed Dual-branch Cross-Patch Attention Transformer (DCAT)." + ], + "image_footnote": [], + "bbox": [ + 78, + 607, + 267, + 715 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/0d8bdb50d819ae26391d919bd6d6be8d46f0ae29fbcedc3e2446a6da1e561cef.jpg", + "image_caption": [ + "Figure 3. CKA similarity in each layer.", + "Figure 4. Different drop ratio of the MIP branch." + ], + "image_footnote": [], + "bbox": [ + 281, + 609, + 465, + 717 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "of MHSA module in the block is computed as:", + "bbox": [ + 76, + 772, + 385, + 787 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nA _ {l} = \\operatorname {S o f t m a x} \\left(\\frac {Q _ {l} * K _ {l} ^ {T}}{\\sqrt {d}}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 176, + 795, + 468, + 830 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $Q_{l}\\in \\mathbb{R}^{(N + 1)\\times d}$ and $K_{l}\\in \\mathbb{R}^{(N + 1)\\times d}$ denote the queries and keys projected by $X_{l}$ of self-attention operation in $(l - 1)$ -th transformer block, respectively. $S$ represents the number of heads, $T$ is a transpose operator, $d$ is the di", + "bbox": [ + 76, + 838, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "mension of the embedding. $N$ is the number of tokenized patches. The input global and MIP images are divided into different patches numbers with different $N$ . The calculation includes 1 class token in addition to the $N$ tokens.", + "bbox": [ + 498, + 609, + 890, + 671 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. The interaction of global and MIP pathways", + "text_level": 1, + "bbox": [ + 500, + 689, + 875, + 707 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Due to the large amount of information in group-level images, extracting features by either global or MIP branch alone is not sufficient, and cross-attention of discriminative tokens from both can provide complementary effects.", + "bbox": [ + 496, + 715, + 890, + 777 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Having obtained global and MIP tokens by the Transformer Encoder, we should consider the dual-path interactions. To achieve this, we propose the Cross-Patch Attention (CPA) mechanism to establish spatial interactions between the global and MIP images. Firstly, we sort the tokens based on their importance in each path using the Token Ranking Module and create a new query matrix by selecting the top $\\eta$ tokens. As depicted in Figure 4, the model's per", + "bbox": [ + 496, + 779, + 892, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "20601", + "bbox": [ + 478, + 944, + 517, + 957 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "formance, taking the MIP branch as an example $^{2}$ , is related to the drop ratio, where dropping a certain percentage of tokens can improve performance. Secondly, we compute the Cross-Patch Attention (CPA) using the new query matrix and key-value from the other branch. It is noteworthy that the gradients propagate through both pathways, which allows it to compensate for information loss on global feature compression through global-to-local interaction. As validated in [49], such cross-attention can also be viewed as a novel regularization method to regularize attention learning, especially for our small datasets.", + "bbox": [ + 75, + 90, + 472, + 257 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3.1 Token Ranking Module", + "text_level": 1, + "bbox": [ + 76, + 275, + 295, + 290 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For Cross-Patch Attention, we need to remove unimportant contents from the complex group images and keep only the tokens that are relevant.", + "bbox": [ + 75, + 299, + 468, + 343 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Our first step is to rank the tokens according to their importance. While the class token attention map $A_{cls} \\in \\mathbb{R}^{1 \\times (N + 1)}$ reflects the importance of features [43, 29], we denote the token importance by the similarity scores between the global class token and each patch token:", + "bbox": [ + 76, + 345, + 468, + 420 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nA _ {c l s} = \\operatorname {S o f t m a x} \\left(\\frac {q _ {c l s} * K ^ {T}}{\\sqrt {d}}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 430, + 468, + 465 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $q_{cls} \\in \\mathbb{R}^{1 \\times d}$ is the query vector of the class token, $K \\in \\mathbb{R}^{(N + 1) \\times d}$ is the key vector, and $d$ is the dimension of the embedding.", + "bbox": [ + 76, + 476, + 468, + 521 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "According to the equation 2, the weights of each patch correlated with the class token are computed. In such a way, the $A_{cls}$ reveals how much each patch contributes to the final classification since it captures the global interactions of the class token to all patches.", + "bbox": [ + 75, + 521, + 468, + 597 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3.2 Cross-Patch Attention (CPA)", + "text_level": 1, + "bbox": [ + 76, + 614, + 333, + 630 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Based on the importance score of each token, we then construct a newly selected query matrix $Q_{sel} \\in \\mathbb{R}^{(\\alpha + 1) \\times d}$ , representing the attentive local embedding, by selecting the top $\\alpha$ query vectors that correspond to the top $\\alpha$ highest responses in the class attention map.", + "bbox": [ + 75, + 638, + 468, + 715 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In each pathway, the Cross-Patch Attention (CPA) vectors is computed as below,", + "bbox": [ + 75, + 715, + 468, + 744 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nf _ {C P A} (Q, K, V) = \\operatorname {S o f t m a x} \\left(\\frac {Q _ {\\text {s e l}} * K ^ {T}}{\\sqrt {d}}\\right) V, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 120, + 756, + 468, + 789 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $K\\in \\mathbb{R}^{(N + 1)\\times d}$ is the key vector, $V\\in \\mathbb{R}^{(N + 1)\\times d}$ is the value vector and $d$ is the dimension of the embedding.", + "bbox": [ + 75, + 800, + 468, + 832 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As shown in Figure 2c, the CPA operation is bidirectional, with each of the two branches providing the selected tokens as the query vector. Both branches are fused together", + "bbox": [ + 75, + 832, + 468, + 878 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$C$ times, which means the selected queries are updated in each CPA.", + "bbox": [ + 500, + 90, + 890, + 119 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Finally, after repeating $L$ Multi-Scale Transformer Encoder, the class tokens from two branches are combined and sent into a linear layer for prediction. The cross-entropy loss is used here for final classification [5, 8].", + "bbox": [ + 498, + 121, + 890, + 181 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 195, + 633, + 212 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Implemental details", + "text_level": 1, + "bbox": [ + 500, + 220, + 689, + 236 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Our model is partly pre-trained with the weight of CrossViT [5] on ImageNet. We train all our models for 300 epochs (30 warm-up epochs) on 2 GPUs (RTX 3090 Ti) with a batch size of 64. The numbers of Transformer Encoder in the dual path, CPA, and Multi-Scale Transformer Encoder are set as $M = 1$ , $G = 6$ , $C = 3$ , and $L = 1$ . For the token selection ratios $\\alpha$ of (global, MIP), we use (0.5, 0.5) for GAF 3.0 and (1, 0.5) for GroupEmoW throughout the paper. More details can be found in our supplementary materials.", + "bbox": [ + 498, + 243, + 890, + 378 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Datasets", + "text_level": 1, + "bbox": [ + 500, + 388, + 601, + 402 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this paper, we utilize several datasets for our experiments, including GroupEmoW [16], GAF 3.0 [13], GAF Cohesion [13, 15], and HECO [44], as presented in Table 2. The GroupEmoW dataset contains images obtained from the web via search engines, using keywords related to various social events such as funerals, birthdays, protests, conferences, and meetings. GAF 3.0 [13] and GAF Cohesion [13, 15] datasets were created through web crawling using a diverse set of keywords related to social events, including world cup winners, weddings, family gatherings, laughing clubs, birthday celebrations, siblings, riots, protests, and violence. The cohesion scores in GAF Cohesion range from strongly agree, agree, disagree to strongly disagree, using a 0-3 scale.", + "bbox": [ + 498, + 412, + 890, + 625 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In our experiments, we utilized the MIP ground truth provided by HECO [44]. However, the ground truth for GAF 3.0 and GroupEmoW was not available. However, since the ground truth for GAF 3.0 and GroupEmoW was not available, we employed the pre-trained POINT model [26] to generate the MIP. The POINT model was trained on the Multi-scene Important People Image Dataset (MS Dataset).3.", + "bbox": [ + 498, + 625, + 890, + 744 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Comparison with state-of-the-art group affect methods and ViTs", + "text_level": 1, + "bbox": [ + 500, + 753, + 890, + 784 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this work, we have built our proposed modules based on CrossViT [5] with vanilla Transformer Encoders [8], which denotes by DCAT-ViT. In addition, since there is a series of ViTs without the class token, e.g., Swin [31] and", + "bbox": [ + 498, + 792, + 890, + 853 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "2The global branch exhibits similar behavior.", + "bbox": [ + 94, + 886, + 334, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "3To evaluate the effectiveness of the pre-trained POINT model, we labeled the MIP on the GAF 3.0 and GroupEmoW datasets, and further details can be found in the supplementary material.", + "bbox": [ + 500, + 862, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "20602", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/35e7517c0475054e767fcdb2ca7695acaf06e88d03c8be317365d0b030012ec6.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DatasetLabelTrain/Val/TestScenarioEvaluation metric
GroupEmoW [13]Neutral, Positive, Negative11,127/3,178/1,589Specific social eventsAcc
GAF 3.0 [13, 15]Neutral, Positive, Negative9,815/4,349/3011Specific social eventsAcc
HECO [44]Surprise, Excitement, Happiness, Peace, Disgust, Anger, Fear, and Sadness6,570/1,877/938In-the-wild images that do not limit scenesmAP
GAF Cohesion [13, 15]0-39,815/4,349/3011Specific social eventsMSE
", + "bbox": [ + 81, + 88, + 890, + 181 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/f76662dc063f1e59ff4afeb130958930b1def33f11024e80663eaf0826c31fe6.jpg", + "image_caption": [ + "Figure 5. Model parameter and accuracy trade-off comparison on the GAF 3.0 dataset. Our proposed models are highlighted by the blue rectangular box." + ], + "image_footnote": [], + "bbox": [ + 84, + 247, + 460, + 449 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "CSwin [7]. In order to prove the generality of our approach, we have added the proposed dual-pathway and CPA module to the CSwin transformer [7], which is denoted by DCAT-CSwin-L.", + "bbox": [ + 75, + 522, + 468, + 580 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "A comparison of the proposed model with the state-of-the-art group affect approaches on GAF 3.0 and GroupEmoW datasets can be found in Figure 5 and Table 3, respectively. Since our proposed DCAT model is based on a vision transformer, we also compare it with recent vision transformer models, such as multiscale-based (CrossViT [5], Focal-B [45], RegionViT-B [4], TCFormaler-L [47]), CNN-transformer hybrid-based (Conformer-L [32]), and lightweight-based models (EvoLeViT [43], DynamicSwin-T [36], DVT [40]).", + "bbox": [ + 75, + 583, + 468, + 733 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparing with state-of-the-art group affect methods. Our DCAT-ViT and DCAT-CSwin-L achieve the best results compared to other group affect recognition methods on the GAF 3.0 dataset. Specifically, our DCAT-ViT achieves $77.29\\%$ accuracy with only 26.70M parameters, which is only about $7.6\\%$ of TMM [9], while our DCAT-CSwin-L with a larger number of parameters (358M) achieves $79.20\\%$ accuracy. On the GroupEmoW dataset, our DCAT-CSwin-L also achieves the best performance compared to other methods. It is worth noting that our proposed method only needs the global image and corre", + "bbox": [ + 75, + 734, + 470, + 901 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/1d4c9f6bf51b19d2543c60b4f394b106c0db3e0613c511624adf03d8c086b5a9.jpg", + "table_caption": [ + "Table 2. Datasets details used in this paper (Acc = Accuracy, mAP = mean average precision, MSE = mean square error)." + ], + "table_footnote": [], + "table_body": "
MethodsAcc (%)Source
Group affect methods
ResNet34 [18]68.13Global, Faces
SE-ResNet-50 [20]69.79Global
Efficientnet-b2 [38]72.33Global, Faces
CAER-Net [25]80.61Global, Faces
GNN [16]82.38Global
GNN [16]84.62Global, Faces, Objects
ConGNN [41]85.59Global, Faces, Objects
WACV 21 [22]89.36Global, Faces
GNN [16]89.93Global, Faces
WACV 21 [22]90.18Global, Faces, Objects
Vision transformers
ViT [8]87.50Global
P2T-base [42]86.50Global
DeepViT [48]83.90Global
Conformer-L [32]83.35Global
Focal-B [45]87.98Global
CrossViT [5]88.48Global
TransFG [17]89.47Global
RegionViT-B [4]89.49Global
CSwin-L [7]89.90Global
DVT [40]87.90Global
Evo-LeViT [43]87.83Global
TCFormer-L [47]89.24Global
DCAT-ViT89.55Global, MIP
DCAT-CSwin-L90.47Global, MIP
", + "bbox": [ + 501, + 239, + 906, + 678 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 3. Overall Accuracy Comparison on the GroupEmoW dataset. \"Source\" refers to the types of features used in each paper.", + "bbox": [ + 498, + 688, + 890, + 717 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "sponding MIP image, while current group affect methods need multiple pre-trained detectors, which may be influenced by imperfect faces and objects. Furthermore, our method learns discriminative clues end-to-end in coordination with self-attention learning.", + "bbox": [ + 496, + 746, + 890, + 823 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparing with single focal attention methods. A comparison is made between our dual-pathway attention model and methods specifically designed for local attention (Focal Transformers [45] and TransFG [17]). This finding highlights the fact that saliency does not always equate to", + "bbox": [ + 496, + 824, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "20603", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/5363207b8a6db59d84d8bf7d38b17ecf57abde02be0e4b8c0f62b25c95e70eda.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodmAP (%)
GCNs [23]48.84
Depth [28]49.02
OpenFace [1]+OpenPose [3]50.28
R-FCN [6]+HOI-Net [30]50.34
HECO [44]50.24
DCAT-ViT53.49
DCAT-CSwin-L58.06
", + "bbox": [ + 125, + 88, + 416, + 214 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "importance, and that our method's attention mechanism can effectively identify and leverage the most critical affective regions.", + "bbox": [ + 75, + 258, + 468, + 303 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Overall, our proposed DCAT-ViT and DCAT-CSwin-L perform better than other group affect recognition models and ViTs in terms of both accuracy and model complexity.", + "bbox": [ + 75, + 304, + 468, + 349 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. The scalability of our method", + "text_level": 1, + "bbox": [ + 76, + 359, + 339, + 376 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Our proposed architecture can be adapted to accommodate the concept of a primary agent, similar to the idea of MIP, which was introduced by HECO [44]. Specifically, we can modify the input to the MIP branch from the MIP image to the primary agent while keeping the global branch unchanged.", + "bbox": [ + 75, + 383, + 468, + 473 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Due to the wide variety of human-object interactions (HOIs) in natural scenes and the fact that interactions of agents' actions with objects can induce emotional arousal of the primary agent in the scene, a useful approach for emotion recognition in images is to detect HOIs. In previous approaches [44, 25], multiple contexts, such as regions of interest (ROIs) and HOIs of all objects, were considered. Our proposed method outperforms previous approaches, as shown in Table 4. Our proposed method achieved superior performance on the dataset, which may be attributed to the wide variety of HOI categories in various challenging scenarios. Previous methods relied on pre-trained HOI models that were limited by predefined interaction categories. In contrast, our Cross-Patch Attention (CPA) module leverages the ability to learn HOI interactions directly from the data, allowing for greater flexibility and adaptability in recognizing new and diverse HOI categories. Moreover, our dual-pathway architecture significantly simplifies the computational process, eliminating the need for a heuristic selection of affective regions.", + "bbox": [ + 75, + 474, + 470, + 777 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5. Transfer learning for group cohesion estimation", + "text_level": 1, + "bbox": [ + 76, + 786, + 468, + 803 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Group cohesion is an affective phenomenon and a measure of agreement between members. Since cohesion and emotion (or valence) are intertwined in social science and affective computing, our DCAT for group valence prediction can be extended to group cohesion estimation. In this work, we finetune our model pre-trained on GroupEmoW", + "bbox": [ + 75, + 809, + 468, + 901 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9490b2888e40456708c3f3c49a87e752d1eae4f48cab7b4cdbe84def2304ea1d.jpg", + "image_caption": [ + "Figure 6. Group cohesion score comparison in the GAF Cohesion dataset (MSE is the evaluation metric, the lower the better)." + ], + "image_footnote": [], + "bbox": [ + 540, + 94, + 857, + 309 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/4bfb5f0deb6ae30d071867c16e57b02200744a8804708317faadd16a10c01dd9.jpg", + "table_caption": [ + "Table 4. Comparison on HECO dataset." + ], + "table_footnote": [], + "table_body": "
ModuleGAF 3.0GroupEmoW
CrossVit75.5688.48
CrossVit+A75.7988.86
CrossVit+A+B76.2188.96
CrossVit+A+B+C77.2989.55
CSwin-L78.0989.90
CSwin-L+A78.9390.12
CSwin-L+A+B79.2090.47
", + "bbox": [ + 532, + 358, + 859, + 500 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 5. The accuracy (\\%) of each proposed module. $A$ , $B$ , and $C$ represent dual-pathway input, CPA module, and Token Ranking Module, respectively. The downsampling operation in each stage of the CSWin-L can be regarded as a token selection mechanism, so the Token Ranking Module is not included in it.", + "bbox": [ + 498, + 512, + 893, + 582 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "for the GAF Cohesion dataset. The results in Figure 6 assure that our models still have good generalization ability rather than only fit to group affect datasets compared to other group affect recognition methods, e.g., EmoticW [13], ICMAI2020 [50], AIST2020 [10], as well as the ViTs, i.e., ViT [8], CSwin [7], Swin transformer [31].", + "bbox": [ + 498, + 621, + 890, + 712 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.6. Ablation study", + "text_level": 1, + "bbox": [ + 500, + 724, + 650, + 739 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The effectiveness of each module. The effectiveness of each module proposed in our work, i.e., dual-pathway input, CPA module, Token Ranking Module, is shown in Table 5. For both the DCAT-ViT and DCAT-CSwin-L, each of the modules contributes to our overall results.", + "bbox": [ + 498, + 748, + 890, + 821 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The effectiveness of dual-input. Hence, we should also dynamically consider the global affective context while learning group affect, as validated in Table 6, where MIP and global inputs together perform better than either alone.", + "bbox": [ + 498, + 823, + 890, + 883 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Cross-Cls-Attention (CCA) vs Our proposed Cross", + "bbox": [ + 519, + 885, + 890, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "20604", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/90412426a6874767e95c8178adda84f7ac0471a7dad53cf20a805ab9254e49e0.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
InputGAF 3.0GroupEmoW
Only MIP68.0280.08
Only global75.5688.48
MIP + global77.2989.55
", + "bbox": [ + 124, + 88, + 423, + 165 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/a3721cce7daad9c702f29d300bcab8b56e13ce8204fa9a03fa4583f394908fb8.jpg", + "table_caption": [ + "Table 6. Effectiveness of dual-input on GAF 3.0 [14] and GroupE-moW [22] dataset (evaluation metric is ACC $(\\%)$ )." + ], + "table_footnote": [], + "table_body": "
GAF 3.0GroupEmoW
CCA75.41%87.86%
CPA77.29%89.55%
", + "bbox": [ + 150, + 231, + 392, + 292 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 7. Comparison between the CCA and our proposed CPA (using the DCAT-ViT) on GAF 3.0 and GroupEmoW dataset.", + "bbox": [ + 76, + 299, + 468, + 327 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/41e676e8d6c448e4d023b99a34636ddc8f42bceda07fc1136e477784ca615045.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 102, + 340, + 209, + 422 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/319584c7d8ec1289cd03619853c4a7c05ec6fc7e0cc866177c276524e01d9885.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 217, + 340, + 325, + 422 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/277095c6d149c752a639b18850e3ab9a042dd5f3612084c3fdf71cc37d176d2a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 333, + 340, + 437, + 422 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/ab1f61f173189414e1fd5d0821ed6ab46d2def2c259e79d73dabf7801c924366.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 102, + 433, + 209, + 513 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b2bfa239c1bfca1d78417bd08364ebd023725574955bb43a54ae3db167b38452.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 217, + 431, + 325, + 513 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b7e707cb71d1dbf1daf7b21b66956a88082b519f125d41fadc1f75d3a0c4bc47.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 334, + 430, + 441, + 513 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/ece99ea8b3f9eed23b527953fbf9e1fbd1f9eca11354478418cc7c1d32e8c376.jpg", + "image_caption": [ + "(a) Input image" + ], + "image_footnote": [], + "bbox": [ + 102, + 525, + 209, + 606 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b3d7a9f91cfd1994453ab671918ecb90742036f67db9c97b2bc1b912a8f1746e.jpg", + "image_caption": [ + "(b) Token dropping" + ], + "image_footnote": [], + "bbox": [ + 217, + 523, + 323, + 607 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8d2cdc9a6939f692b9dff60a10a8961c8f6d10395338e0f05f811844ad28b543.jpg", + "image_caption": [ + "(c) CPA", + "Figure 7. The visualization of the interaction of global and MIP." + ], + "image_footnote": [], + "bbox": [ + 334, + 525, + 437, + 606 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Patch-Attention (CPA). It is worth comparing between Cross-Cls-Attention (CCA) proposed in CrossViT [5] and our proposed CPA (as provided in Table 7). The CCA only exchanges the class token in the cross-attention mechanism, which limits its ability to capture global interactions between class tokens and patches in each branch. In complex scenarios, such as those encountered in group affect recognition, our proposed CPA approach is more effective for modeling the interdependencies between global and MIP features.", + "bbox": [ + 75, + 667, + 468, + 818 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.7. Visualization of the interaction of global and MIP pathways", + "text_level": 1, + "bbox": [ + 76, + 830, + 468, + 862 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The interaction of the global and MIP pathways, including token dropping and CPA, is demonstrated in Fig-", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/00c700bd09a232b104e3d403a533f41280789f4d38bdd5bc1b9ae25236dcc4e4.jpg", + "image_caption": [ + "Figure 8. The performance of average face quality, using all faces and using the MIP under different face count intervals in the image. The GroupEmoW dataset is used here." + ], + "image_footnote": [], + "bbox": [ + 506, + 92, + 882, + 279 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "ure 7. As depicted in column (b), irrelevant background and other facial details are eliminated, while the MIP region and significant background regions (such as banners in protest scenes) are preserved for cross-patch attention. This demonstrates the effectiveness of our MIP-global interaction and highlights its efficacy in capturing discriminative information.", + "bbox": [ + 498, + 352, + 890, + 457 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.8. Case study: the relationship between group size and performance", + "text_level": 1, + "bbox": [ + 500, + 477, + 890, + 508 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Previous studies have suggested that distinguishing between the negative and neutral categories in a group can be challenging [9]. In this paper, we present new insights into this issue. We first analyze the number of individuals in each image and find that as the number of individuals increases, the average quality of their facial features decreases $^{4}$ , as illustrated in Figure 8. This indicates that facial details become increasingly blurred and difficult to extract, posing a significant challenge, particularly when trying to distinguish between negative and neutral categories, which are inherently difficult to distinguish. In contrast to previous works that typically average features across all detected faces [9], our approach selectively focuses on the most informative facial region, i.e., the MIP, and outperforms models that utilize all faces in images with larger populations. This approach avoids interference from low-quality faces and effectively interacts between the features of the MIP and those of the entire global image through our proposed CPA module, enhancing the accuracy of our results. Therefore, our approach yields higher accuracy for distinguishing between the negative and neutral categories compared to previous methods. The exact numerical results can be found in the supplementary material.", + "bbox": [ + 496, + 518, + 892, + 867 + ], + "page_idx": 7 + }, + { + "type": "page_footnote", + "text": "4We quantify face quality based on [39].", + "bbox": [ + 516, + 886, + 733, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "20605", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusions", + "text_level": 1, + "bbox": [ + 80, + 89, + 202, + 106 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this work, by incorporating the MIP concept, we propose a dual-pathway vision transformer model, the Dual-branch Cross-Patch Attention Transformer (DCAT) for group affect recognition. Moreover, we propose the CPA module so that the important tokens from both paths can be interacted with. In terms of accuracy and parameters, the proposed DCAT outperforms both state-of-the-art group affect models and vision transformer models. It is also the first study to explore group affect recognition beyond CNNs. Moreover, our proposed model can be utilized in other group-level affect tasks, i.e., group cohesion analysis.", + "bbox": [ + 80, + 114, + 467, + 294 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 80, + 309, + 235, + 325 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was supported in part by the National Science and Technology Council of Taiwan under Grants NSTC-109-2223-E-002-005-MY3, NSTC-112-2628-E-002-033-MY4 and NSTC-112-2634-F-002-002-MBK.", + "bbox": [ + 80, + 335, + 467, + 393 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "20606", + "bbox": [ + 480, + 946, + 517, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Tadas Baltrusaitis, Peter Robinson, and Louis-Philippe Morency. 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In Proceedings of the 2020 5th International Conference on Mathematics and Artificial Intelligence, pages 24–28, 2020. 7" + ], + "bbox": [ + 501, + 92, + 893, + 811 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "20608", + "bbox": [ + 478, + 945, + 519, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Most Important Person-Guided Dual-Branch Cross-Patch Attention for Group Affect Recognition/2995ddf2-76d9-45cb-9d66-1a50a95e4d2f_model.json b/2023/Most Important Person-Guided Dual-Branch Cross-Patch Attention for Group Affect Recognition/2995ddf2-76d9-45cb-9d66-1a50a95e4d2f_model.json new file mode 100644 index 0000000000000000000000000000000000000000..388a747d429fcd020ab58fc1941e0538fc85fb0d --- /dev/null +++ b/2023/Most Important Person-Guided Dual-Branch Cross-Patch Attention for Group Affect Recognition/2995ddf2-76d9-45cb-9d66-1a50a95e4d2f_model.json @@ -0,0 +1,2488 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.093, + 0.13, + 0.88, + 0.177 + ], + "angle": 0, + "content": "Most Important Person-guided Dual-branch Cross-Patch Attention for Group Affect Recognition" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.215, + 0.882, + 0.254 + ], + "angle": 0, + "content": "Hongxia Xie\\(^{1}\\), Ming-Xian Lee\\(^{2}\\), Tzu-Jui Chen\\(^{2}\\), Hung-Jen Chen\\(^{1}\\), Hou-I Liu\\(^{1}\\), Hong-Han Shuai\\(^{1}\\) and Wen-Huang Cheng\\(^{3}\\)" + }, + { + "type": "text", + "bbox": [ + 0.145, + 0.264, + 0.825, + 0.282 + ], + "angle": 0, + "content": "\\(^{1}\\)National Yang Ming Chiao Tung University, hongxiaixie.ee08@nycu.edu.tw" + }, + { + "type": "text", + "bbox": [ + 0.32, + 0.283, + 0.652, + 0.3 + ], + "angle": 0, + "content": "2University of Illinois Urbana-Champaign" + }, + { + "type": "text", + "bbox": [ + 0.229, + 0.3, + 0.743, + 0.317 + ], + "angle": 0, + "content": "\\(^{3}\\)National Taiwan University, wenhuang@csie.ntu.edu.tw" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.362, + 0.314, + 0.379 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.4, + 0.474, + 0.765 + ], + "angle": 0, + "content": "Group affect refers to the subjective emotion that is evoked by an external stimulus in a group, which is an important factor that shapes group behavior and outcomes. Recognizing group affect involves identifying important individuals and salient objects among a crowd that can evoke emotions. However, most existing methods lack attention to affective meaning in group dynamics and fail to account for the contextual relevance of faces and objects in group-level images. In this work, we propose a solution by incorporating the psychological concept of the Most Important Person (MIP), which represents the most noteworthy face in a crowd and has affective semantic meaning. We present the Dual-branch Cross-Patch Attention Transformer (DCAT) which uses global image and MIP together as inputs. Specifically, we first learn the informative facial regions produced by the MIP and the global context separately. Then, the Cross-Patch Attention module is proposed to fuse the features of MIP and global context together to complement each other. Our proposed method outperforms state-of-the-art methods on GAF 3.0, GroupEmoW, and HECO datasets. Moreover, we demonstrate the potential for broader applications by showing that our proposed model can be transferred to another group affect task, group cohesion, and achieve comparable results." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.809, + 0.21, + 0.825 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Humans are active and social creatures, using multimodal interactions to convey their intentions, attitudes, and feelings. Such physical and emotional interactions between individuals within a group can generate group-level affect" + }, + { + "type": "table", + "bbox": [ + 0.501, + 0.362, + 0.898, + 0.407 + ], + "angle": 0, + "content": "
Global +All3Random3MIPs1RandomMIP
Acc (%)85.0185.4787.4682.3088.86
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.417, + 0.895, + 0.487 + ], + "angle": 0, + "content": "Table 1. Different face selection strategies. The \"3Random\" refers to selecting 3 faces randomly from the detected faces in the image, while the \"3MIPs\" strategy selects the top three detected faces based on their importance ranking. The dataset evaluated here is the GroupEmoW [22]." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.51, + 0.693, + 0.527 + ], + "angle": 0, + "content": "or group-level emotion [2]'." + }, + { + "type": "image", + "bbox": [ + 0.526, + 0.538, + 0.637, + 0.623 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.642, + 0.538, + 0.752, + 0.623 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.757, + 0.538, + 0.868, + 0.623 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.526, + 0.629, + 0.636, + 0.713 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.541, + 0.716, + 0.619, + 0.728 + ], + "angle": 0, + "content": "(a) Input image" + }, + { + "type": "image", + "bbox": [ + 0.642, + 0.629, + 0.751, + 0.713 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.658, + 0.716, + 0.731, + 0.728 + ], + "angle": 0, + "content": "(b) Using MIP" + }, + { + "type": "image", + "bbox": [ + 0.757, + 0.628, + 0.868, + 0.713 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.766, + 0.716, + 0.856, + 0.728 + ], + "angle": 0, + "content": "(c) Using all faces" + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.736, + 0.892, + 0.765 + ], + "angle": 0, + "content": "Figure 1. Feature map comparison between using MIP and all faces. The yellow box in (a) represents the MIP region." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.791, + 0.894, + 0.868 + ], + "angle": 0, + "content": "By providing the group-level information, group affect prediction has various real-world applications, e.g., work team outcome prediction [21], social relationship recognition [33], human-machine interaction systems [24]. As a result, the research topics surrounding group affect are di" + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.892, + 0.9 + ], + "angle": 0, + "content": "1In this work, groups range in size from two or three individuals up to hundreds." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "20598" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.138 + ], + "angle": 0, + "content": "verse, including categorical analysis, e.g., group valence (positive, negative, neutral) prediction [16, 22], continuous intensity estimation, e.g., group cohesion prediction [15]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.14, + 0.471, + 0.412 + ], + "angle": 0, + "content": "Group affect is influenced by a combination of a group's affective context (e.g., salient objects in the funeral, party) and affective composition (i.e., the combination of a group members' state and trait affect) [2]. Previous methods for group affect recognition mainly adopted a bottom-up approach [9, 44, 16, 22], where features were extracted from individuals separately and then fused to output group-level emotion. This was done by utilizing multi-cues from separate pre-trained detectors, such as facial expressions of individuals, object proposals, and scene features. While these cues can provide valuable information, they may not fully capture the complex interplay of emotions within a group. As indicated in [12], current group-level recognition architectures tend to focus on detecting salient regions, but they may lack an understanding of the affective meaning in the image. Therefore, there is a need for a more holistic approach that considers the most important region in the crowd and how they interact with the scene." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.415, + 0.471, + 0.807 + ], + "angle": 0, + "content": "Hence, in this work, we introduce a crucial psychological concept, namely, Most Important Person (MIP) [2], which goes beyond saliency and considers the importance of individuals for group affect recognition. The MIP of an image is often the group leaders who can influence the emotion of a group [11, 37, 34]. MIP has been explored in many related works in psychology and affective computing, such as the Affective Transfer Process phenomenon in psychology [2], which indicates that the MIP of an image can influence the group's emotion. We conducted a preliminary experiment based on the CrossVit [5] model to demonstrate the effectiveness of the MIP in group affect. Our architecture uses both the global image and faces as two inputs. As depicted in Table 1, the results demonstrate that using all faces is considerably less effective than using the MIP, and even less effective than randomly selecting three facial images. Additionally, as observed in the feature maps illustrated in Figure 1, the model that employs all faces fails to predict accurately due to its focus on irrelevant background regions or faces. In contrast, the network that utilizes MIP can efficiently focus on relevant facial regions, thereby enhancing prediction accuracy. This is mainly due to the fact that in crowded scenes with many blurry faces, the model trained on all faces exhibits dispersed attention, while the model trained on the MIP region concentrates specifically on the relevant area." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Based on the above observations, we present a dual-pathway vision transformer model, the Dual-branch Cross-Patch Attention Transformer (DCAT), including a global branch and a MIP branch. With the dual-pathway, spatial-wise discriminative clues can be discovered both globally and locally in conjunction with self-attention learning. For" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.212 + ], + "angle": 0, + "content": "the dual-pathway interaction, since there are many interferences in the group, we propose the Cross-Patch Attention (CPA) module. CPA first utilizes the Token Ranking Module to select the important tokens in each path, and then the cross-attention is calculated between the selected query vectors and the entire key-value vectors from the other path. In this way, global and MIP contexts are able to complement and compensate for each other." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.213, + 0.862, + 0.228 + ], + "angle": 0, + "content": "This paper makes the following main contributions:" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.234, + 0.892, + 0.295 + ], + "angle": 0, + "content": "- In this work, we validate that MIP plays a crucial role in group affect recognition. To the best of our knowledge, this is the first work introducing MIP into the group affect task." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.304, + 0.892, + 0.409 + ], + "angle": 0, + "content": "- The MIP and global affective context information are integrated into the proposed dual-pathway vision transformer architecture for recognizing group emotions in a context-aware manner. We also propose a novel CPA module that focuses on the interactions among diverse scene contexts and facial informative regions." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.418, + 0.892, + 0.539 + ], + "angle": 0, + "content": "- Experimental results show that the proposed DCAT outperforms both state-of-the-art group affect works and vision transformer models in terms of accuracy and model parameters. This is also the first work to explore group affect recognition that goes beyond the CNN-based approach. Moreover, our proposed model can be utilized in other group-level affect tasks, i.e., group cohesion analysis." + }, + { + "type": "list", + "bbox": [ + 0.519, + 0.234, + 0.892, + 0.539 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.551, + 0.645, + 0.567 + ], + "angle": 0, + "content": "2. Related works" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.576, + 0.795, + 0.592 + ], + "angle": 0, + "content": "2.1. Group affect recognition methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.892, + 0.825 + ], + "angle": 0, + "content": "Current group affect recognition methods primarily analyze the individual members of a group and then assess their contribution to the overall mood of the group by taking into account a variety of cues, such as faces, salient objects, and scenes. Fujii et al. [9] proposed a two-stage classification method, in which the first stage classifies facial expressions, and the second stage adds scene features into consideration to fuse faces and scenes through spectral clustering for further group affect recognition. Khan et al. [22] considered multi-cues, which include all faces, object proposals, and scene information. To achieve such an architecture, additional face detection and object proposal detection detectors are needed. Similarly, Guo et al. [16] also investigated multi-cues using graph neural networks, where the topology of the graph varies as the number of entities varies." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.901 + ], + "angle": 0, + "content": "However, in large groups, it is not feasible to consider the expressions of all faces and objects individually before aggregating, resulting in lower efficiency and accuracy. As indicated in [9], considering the performance of the main subject estimation is needed, while our work fills the gap." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "20599" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.091, + 0.416, + 0.108 + ], + "angle": 0, + "content": "2.2. Most important person (MIP) detection" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.114, + 0.232, + 0.129 + ], + "angle": 0, + "content": "2.2.1 MIP detection" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.138, + 0.473, + 0.426 + ], + "angle": 0, + "content": "A MIP detection model understands a high-level pattern in a social event image to identify the most important person. Ramanathan et al. [35] used an RNN to learn time-varying attention weights that can be used for event detection and classification. Without any explicit annotations, the person with the highest attendance can be identified as the MIP. In order to overcome the inherent variability of human poses, PersonRank [27] produced a multiple Hyper-Interaction Graph, which treats each individual person as a node. The most active node can be identified using four types of edge message functions. POINT [26] proposed two types of interaction modules, i.e., the person-person interaction module and the event-person interaction module. It then aggregated relation features and person features to form the important feature. To reduce the annotation effort, Hong et al. [19] formulated a POINT-based iterative learning method for semi-supervised important people detection. Thus, we incorporate people awareness into global-level affect analysis in this work." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.435, + 0.351, + 0.452 + ], + "angle": 0, + "content": "2.3. Dual attention learning models" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.459, + 0.47, + 0.653 + ], + "angle": 0, + "content": "Visual attention with dual-pathway has been widely used to find important contextual regions. Based on the outstanding performance of vision transformers (ViTs) in various visual tasks [8], there are many self-attention-based dual-pathway networks in recent years. Zhu et al. [49] proposed a global-local cross-attention to reinforce the spatial-wise discriminative clues for fine-grained recognition. A pairwise cross-attention was designed to establish the interactions between image pairs. Dual-ViT [46] incorporated a compressed semantic pathway that served as prior information in learning finer pixel-level details. The semantic pathway and pixel pathway are integrated together and trained to spread enhanced self-attention information in parallel." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.655, + 0.47, + 0.79 + ], + "angle": 0, + "content": "The most similar architecture to our work is the CrossViT [5], which was proposed to learn multi-scale features effectively. However, we differ from it in two main ways. Firstly, our network divides at different scales using global images and MIP images, whereas CrossViT divides at different scales using the same input image. Another difference is the cross-attention mechanism. The CrossViT exchanges class tokens, while we designed a Cross-Patch Attention module based on attentive queries from both paths." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.805, + 0.469, + 0.839 + ], + "angle": 0, + "content": "3. Proposed Dual-branch Cross-Patch Attention Transformer (DCAT)" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.848, + 0.188, + 0.862 + ], + "angle": 0, + "content": "3.1. Overview" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.901 + ], + "angle": 0, + "content": "The architecture of our proposed Dual-branch Cross-Patch Attention Transformer (DCAT) for group affect" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.364 + ], + "angle": 0, + "content": "recognition is shown in Figure 2. The model contains two inputs, i.e., the global image and the corresponding MIP image. The two images are tokenized into patches first and sent into a stack of Multi-Scale Transformer Encoder, which consists of dual-path Transformer Encoder, Token Ranking Module, and Cross-Patch Attention (CPA). Specifically, in a dual-path Transformer Encoder, the global image is sent to the coarse-level path to capture long-range information and further refine the encoded tokens for fine-grained details. On the other hand, the MIP image is fed to the fine-level path to obtain high-level semantic tokens. Next, since the global and MIP features are conceptual interdependent, we incorporate dual-path interaction in our model. In particular, we sort tokens according to their importance in each path based on the Token Ranking Module, then calculate the CPA using the key and value vectors from the other path. Finally, the class tokens from two branches are combined and sent into a linear layer for prediction." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.376, + 0.715, + 0.393 + ], + "angle": 0, + "content": "3.2. Dual-pathway learning" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.4, + 0.892, + 0.627 + ], + "angle": 0, + "content": "To leverage the global information of a group captured by the global image and the local-based semantic prior of the MIP, we propose a dual-pathway feature learning approach for group affect prediction. By integrating self-attention learning into the dual-pathway, our approach enables the discovery of spatial-wise discriminative clues both globally and locally. To validate our assumptions, we compute the CKA similarity [43] to measure the similarity of the intermediate token features in each layer and the final CLS token, follwing [43]. As illustrated in Figure 3, both the MIP and global tokens exhibit a positive correlation with the CLS token as the model depth increases. This suggests that both features are valuable for the final classification task and highlights the rationality and necessity of our dual-pathway input design." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.892, + 0.809 + ], + "angle": 0, + "content": "Firstly, both the global and MIP image are tokenized into patches, then the class token and a learnable position embedding are added to both branches before the MultiScale Transformer Encoder. In order to balance computational costs, our Transformer Encoders in the two pathways include different numbers (i.e., \\( G = 6 \\) and \\( M = 1 \\)) inspired by CrossViT [5]. The global branch is the large (primary) branch with a coarse patch size (i.e., 12), with a larger embedding size, and more transformer encoders. The MIP image is the input of a small (complementary) branch with fine-grained patch size (i.e., 16), fewer encoders, and a smaller embedding size." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.9 + ], + "angle": 0, + "content": "As the core of the vision transformer, the Multi-Head Self-Attention (MHSA) maps a query vector into a set of key and value vectors [8]. In the \\(l\\)-th Transformer Encoder block in both pathways (a basic Transformer Encoder is shown in Figure 2b), the output feature map is \\(X_{l} \\in \\mathbb{R}^{(N + 1)\\times d}\\). The attention matrix \\(A_{l} \\in \\mathbb{R}^{S \\times (N + 1) \\times (N + 1)}\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "20600" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.091, + 0.089, + 0.458, + 0.519 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.143, + 0.539, + 0.461, + 0.555 + ], + "angle": 0, + "content": "(a) The overall architecture of our proposed DCAT" + }, + { + "type": "image", + "bbox": [ + 0.534, + 0.099, + 0.892, + 0.19 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.615, + 0.206, + 0.8, + 0.222 + ], + "angle": 0, + "content": "(b) The Transformer Encoder" + }, + { + "type": "image", + "bbox": [ + 0.551, + 0.236, + 0.837, + 0.515 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.584, + 0.54, + 0.815, + 0.555 + ], + "angle": 0, + "content": "(c) The Cross-Patch Attention (CPA)" + }, + { + "type": "image_caption", + "bbox": [ + 0.164, + 0.571, + 0.804, + 0.587 + ], + "angle": 0, + "content": "Figure 2. The overall architecture of our proposed Dual-branch Cross-Patch Attention Transformer (DCAT)." + }, + { + "type": "image", + "bbox": [ + 0.08, + 0.608, + 0.268, + 0.717 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.722, + 0.268, + 0.75 + ], + "angle": 0, + "content": "Figure 3. CKA similarity in each layer." + }, + { + "type": "image", + "bbox": [ + 0.282, + 0.611, + 0.467, + 0.718 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.279, + 0.722, + 0.471, + 0.749 + ], + "angle": 0, + "content": "Figure 4. Different drop ratio of the MIP branch." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.773, + 0.387, + 0.789 + ], + "angle": 0, + "content": "of MHSA module in the block is computed as:" + }, + { + "type": "equation", + "bbox": [ + 0.178, + 0.796, + 0.47, + 0.831 + ], + "angle": 0, + "content": "\\[\nA _ {l} = \\operatorname {S o f t m a x} \\left(\\frac {Q _ {l} * K _ {l} ^ {T}}{\\sqrt {d}}\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.839, + 0.471, + 0.903 + ], + "angle": 0, + "content": "where \\(Q_{l}\\in \\mathbb{R}^{(N + 1)\\times d}\\) and \\(K_{l}\\in \\mathbb{R}^{(N + 1)\\times d}\\) denote the queries and keys projected by \\(X_{l}\\) of self-attention operation in \\((l - 1)\\)-th transformer block, respectively. \\(S\\) represents the number of heads, \\(T\\) is a transpose operator, \\(d\\) is the di" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.61, + 0.892, + 0.672 + ], + "angle": 0, + "content": "mension of the embedding. \\(N\\) is the number of tokenized patches. The input global and MIP images are divided into different patches numbers with different \\(N\\). The calculation includes 1 class token in addition to the \\(N\\) tokens." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.69, + 0.877, + 0.708 + ], + "angle": 0, + "content": "3.3. The interaction of global and MIP pathways" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.717, + 0.892, + 0.778 + ], + "angle": 0, + "content": "Due to the large amount of information in group-level images, extracting features by either global or MIP branch alone is not sufficient, and cross-attention of discriminative tokens from both can provide complementary effects." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.893, + 0.903 + ], + "angle": 0, + "content": "Having obtained global and MIP tokens by the Transformer Encoder, we should consider the dual-path interactions. To achieve this, we propose the Cross-Patch Attention (CPA) mechanism to establish spatial interactions between the global and MIP images. Firstly, we sort the tokens based on their importance in each path using the Token Ranking Module and create a new query matrix by selecting the top \\(\\eta\\) tokens. As depicted in Figure 4, the model's per" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.958 + ], + "angle": 0, + "content": "20601" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.258 + ], + "angle": 0, + "content": "formance, taking the MIP branch as an example \\(^{2}\\), is related to the drop ratio, where dropping a certain percentage of tokens can improve performance. Secondly, we compute the Cross-Patch Attention (CPA) using the new query matrix and key-value from the other branch. It is noteworthy that the gradients propagate through both pathways, which allows it to compensate for information loss on global feature compression through global-to-local interaction. As validated in [49], such cross-attention can also be viewed as a novel regularization method to regularize attention learning, especially for our small datasets." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.276, + 0.296, + 0.291 + ], + "angle": 0, + "content": "3.3.1 Token Ranking Module" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.3, + 0.47, + 0.344 + ], + "angle": 0, + "content": "For Cross-Patch Attention, we need to remove unimportant contents from the complex group images and keep only the tokens that are relevant." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.346, + 0.47, + 0.421 + ], + "angle": 0, + "content": "Our first step is to rank the tokens according to their importance. While the class token attention map \\( A_{cls} \\in \\mathbb{R}^{1 \\times (N + 1)} \\) reflects the importance of features [43, 29], we denote the token importance by the similarity scores between the global class token and each patch token:" + }, + { + "type": "equation", + "bbox": [ + 0.168, + 0.431, + 0.469, + 0.466 + ], + "angle": 0, + "content": "\\[\nA _ {c l s} = \\operatorname {S o f t m a x} \\left(\\frac {q _ {c l s} * K ^ {T}}{\\sqrt {d}}\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.477, + 0.47, + 0.522 + ], + "angle": 0, + "content": "where \\(q_{cls} \\in \\mathbb{R}^{1 \\times d}\\) is the query vector of the class token, \\(K \\in \\mathbb{R}^{(N + 1) \\times d}\\) is the key vector, and \\(d\\) is the dimension of the embedding." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.522, + 0.469, + 0.598 + ], + "angle": 0, + "content": "According to the equation 2, the weights of each patch correlated with the class token are computed. In such a way, the \\( A_{cls} \\) reveals how much each patch contributes to the final classification since it captures the global interactions of the class token to all patches." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.616, + 0.334, + 0.631 + ], + "angle": 0, + "content": "3.3.2 Cross-Patch Attention (CPA)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.64, + 0.469, + 0.716 + ], + "angle": 0, + "content": "Based on the importance score of each token, we then construct a newly selected query matrix \\( Q_{sel} \\in \\mathbb{R}^{(\\alpha + 1) \\times d} \\), representing the attentive local embedding, by selecting the top \\( \\alpha \\) query vectors that correspond to the top \\( \\alpha \\) highest responses in the class attention map." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.716, + 0.469, + 0.745 + ], + "angle": 0, + "content": "In each pathway, the Cross-Patch Attention (CPA) vectors is computed as below," + }, + { + "type": "equation", + "bbox": [ + 0.121, + 0.757, + 0.469, + 0.79 + ], + "angle": 0, + "content": "\\[\nf _ {C P A} (Q, K, V) = \\operatorname {S o f t m a x} \\left(\\frac {Q _ {\\text {s e l}} * K ^ {T}}{\\sqrt {d}}\\right) V, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.801, + 0.469, + 0.833 + ], + "angle": 0, + "content": "where \\(K\\in \\mathbb{R}^{(N + 1)\\times d}\\) is the key vector, \\(V\\in \\mathbb{R}^{(N + 1)\\times d}\\) is the value vector and \\(d\\) is the dimension of the embedding." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.833, + 0.469, + 0.879 + ], + "angle": 0, + "content": "As shown in Figure 2c, the CPA operation is bidirectional, with each of the two branches providing the selected tokens as the query vector. Both branches are fused together" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.892, + 0.121 + ], + "angle": 0, + "content": "\\(C\\) times, which means the selected queries are updated in each CPA." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.122, + 0.892, + 0.182 + ], + "angle": 0, + "content": "Finally, after repeating \\( L \\) Multi-Scale Transformer Encoder, the class tokens from two branches are combined and sent into a linear layer for prediction. The cross-entropy loss is used here for final classification [5, 8]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.196, + 0.634, + 0.213 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.221, + 0.69, + 0.237 + ], + "angle": 0, + "content": "4.1. Implemental details" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.244, + 0.892, + 0.38 + ], + "angle": 0, + "content": "Our model is partly pre-trained with the weight of CrossViT [5] on ImageNet. We train all our models for 300 epochs (30 warm-up epochs) on 2 GPUs (RTX 3090 Ti) with a batch size of 64. The numbers of Transformer Encoder in the dual path, CPA, and Multi-Scale Transformer Encoder are set as \\( M = 1 \\), \\( G = 6 \\), \\( C = 3 \\), and \\( L = 1 \\). For the token selection ratios \\( \\alpha \\) of (global, MIP), we use (0.5, 0.5) for GAF 3.0 and (1, 0.5) for GroupEmoW throughout the paper. More details can be found in our supplementary materials." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.39, + 0.602, + 0.404 + ], + "angle": 0, + "content": "4.2. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.413, + 0.892, + 0.625 + ], + "angle": 0, + "content": "In this paper, we utilize several datasets for our experiments, including GroupEmoW [16], GAF 3.0 [13], GAF Cohesion [13, 15], and HECO [44], as presented in Table 2. The GroupEmoW dataset contains images obtained from the web via search engines, using keywords related to various social events such as funerals, birthdays, protests, conferences, and meetings. GAF 3.0 [13] and GAF Cohesion [13, 15] datasets were created through web crawling using a diverse set of keywords related to social events, including world cup winners, weddings, family gatherings, laughing clubs, birthday celebrations, siblings, riots, protests, and violence. The cohesion scores in GAF Cohesion range from strongly agree, agree, disagree to strongly disagree, using a 0-3 scale." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.625, + 0.892, + 0.745 + ], + "angle": 0, + "content": "In our experiments, we utilized the MIP ground truth provided by HECO [44]. However, the ground truth for GAF 3.0 and GroupEmoW was not available. However, since the ground truth for GAF 3.0 and GroupEmoW was not available, we employed the pre-trained POINT model [26] to generate the MIP. The POINT model was trained on the Multi-scene Important People Image Dataset (MS Dataset).3." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.755, + 0.892, + 0.785 + ], + "angle": 0, + "content": "4.3. Comparison with state-of-the-art group affect methods and ViTs" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.794, + 0.892, + 0.854 + ], + "angle": 0, + "content": "In this work, we have built our proposed modules based on CrossViT [5] with vanilla Transformer Encoders [8], which denotes by DCAT-ViT. In addition, since there is a series of ViTs without the class token, e.g., Swin [31] and" + }, + { + "type": "page_footnote", + "bbox": [ + 0.095, + 0.887, + 0.336, + 0.9 + ], + "angle": 0, + "content": "2The global branch exhibits similar behavior." + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.863, + 0.892, + 0.901 + ], + "angle": 0, + "content": "3To evaluate the effectiveness of the pre-trained POINT model, we labeled the MIP on the GAF 3.0 and GroupEmoW datasets, and further details can be found in the supplementary material." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "20602" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.891, + 0.182 + ], + "angle": 0, + "content": "
DatasetLabelTrain/Val/TestScenarioEvaluation metric
GroupEmoW [13]Neutral, Positive, Negative11,127/3,178/1,589Specific social eventsAcc
GAF 3.0 [13, 15]Neutral, Positive, Negative9,815/4,349/3011Specific social eventsAcc
HECO [44]Surprise, Excitement, Happiness, Peace, Disgust, Anger, Fear, and Sadness6,570/1,877/938In-the-wild images that do not limit scenesmAP
GAF Cohesion [13, 15]0-39,815/4,349/3011Specific social eventsMSE
" + }, + { + "type": "table_caption", + "bbox": [ + 0.127, + 0.192, + 0.842, + 0.207 + ], + "angle": 0, + "content": "Table 2. Datasets details used in this paper (Acc = Accuracy, mAP = mean average precision, MSE = mean square error)." + }, + { + "type": "image", + "bbox": [ + 0.086, + 0.248, + 0.462, + 0.45 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.455, + 0.471, + 0.497 + ], + "angle": 0, + "content": "Figure 5. Model parameter and accuracy trade-off comparison on the GAF 3.0 dataset. Our proposed models are highlighted by the blue rectangular box." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.523, + 0.47, + 0.581 + ], + "angle": 0, + "content": "CSwin [7]. In order to prove the generality of our approach, we have added the proposed dual-pathway and CPA module to the CSwin transformer [7], which is denoted by DCAT-CSwin-L." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.47, + 0.734 + ], + "angle": 0, + "content": "A comparison of the proposed model with the state-of-the-art group affect approaches on GAF 3.0 and GroupEmoW datasets can be found in Figure 5 and Table 3, respectively. Since our proposed DCAT model is based on a vision transformer, we also compare it with recent vision transformer models, such as multiscale-based (CrossViT [5], Focal-B [45], RegionViT-B [4], TCFormaler-L [47]), CNN-transformer hybrid-based (Conformer-L [32]), and lightweight-based models (EvoLeViT [43], DynamicSwin-T [36], DVT [40])." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Comparing with state-of-the-art group affect methods. Our DCAT-ViT and DCAT-CSwin-L achieve the best results compared to other group affect recognition methods on the GAF 3.0 dataset. Specifically, our DCAT-ViT achieves \\(77.29\\%\\) accuracy with only 26.70M parameters, which is only about \\(7.6\\%\\) of TMM [9], while our DCAT-CSwin-L with a larger number of parameters (358M) achieves \\(79.20\\%\\) accuracy. On the GroupEmoW dataset, our DCAT-CSwin-L also achieves the best performance compared to other methods. It is worth noting that our proposed method only needs the global image and corre" + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.241, + 0.907, + 0.679 + ], + "angle": 0, + "content": "
MethodsAcc (%)Source
Group affect methods
ResNet34 [18]68.13Global, Faces
SE-ResNet-50 [20]69.79Global
Efficientnet-b2 [38]72.33Global, Faces
CAER-Net [25]80.61Global, Faces
GNN [16]82.38Global
GNN [16]84.62Global, Faces, Objects
ConGNN [41]85.59Global, Faces, Objects
WACV 21 [22]89.36Global, Faces
GNN [16]89.93Global, Faces
WACV 21 [22]90.18Global, Faces, Objects
Vision transformers
ViT [8]87.50Global
P2T-base [42]86.50Global
DeepViT [48]83.90Global
Conformer-L [32]83.35Global
Focal-B [45]87.98Global
CrossViT [5]88.48Global
TransFG [17]89.47Global
RegionViT-B [4]89.49Global
CSwin-L [7]89.90Global
DVT [40]87.90Global
Evo-LeViT [43]87.83Global
TCFormer-L [47]89.24Global
DCAT-ViT89.55Global, MIP
DCAT-CSwin-L90.47Global, MIP
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.689, + 0.892, + 0.718 + ], + "angle": 0, + "content": "Table 3. Overall Accuracy Comparison on the GroupEmoW dataset. \"Source\" refers to the types of features used in each paper." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.747, + 0.892, + 0.824 + ], + "angle": 0, + "content": "sponding MIP image, while current group affect methods need multiple pre-trained detectors, which may be influenced by imperfect faces and objects. Furthermore, our method learns discriminative clues end-to-end in coordination with self-attention learning." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Comparing with single focal attention methods. A comparison is made between our dual-pathway attention model and methods specifically designed for local attention (Focal Transformers [45] and TransFG [17]). This finding highlights the fact that saliency does not always equate to" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "20603" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.127, + 0.089, + 0.418, + 0.215 + ], + "angle": 0, + "content": "
MethodmAP (%)
GCNs [23]48.84
Depth [28]49.02
OpenFace [1]+OpenPose [3]50.28
R-FCN [6]+HOI-Net [30]50.34
HECO [44]50.24
DCAT-ViT53.49
DCAT-CSwin-L58.06
" + }, + { + "type": "table_caption", + "bbox": [ + 0.155, + 0.22, + 0.393, + 0.233 + ], + "angle": 0, + "content": "Table 4. Comparison on HECO dataset." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.26, + 0.47, + 0.304 + ], + "angle": 0, + "content": "importance, and that our method's attention mechanism can effectively identify and leverage the most critical affective regions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.305, + 0.47, + 0.351 + ], + "angle": 0, + "content": "Overall, our proposed DCAT-ViT and DCAT-CSwin-L perform better than other group affect recognition models and ViTs in terms of both accuracy and model complexity." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.36, + 0.34, + 0.377 + ], + "angle": 0, + "content": "4.4. The scalability of our method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.384, + 0.47, + 0.474 + ], + "angle": 0, + "content": "Our proposed architecture can be adapted to accommodate the concept of a primary agent, similar to the idea of MIP, which was introduced by HECO [44]. Specifically, we can modify the input to the MIP branch from the MIP image to the primary agent while keeping the global branch unchanged." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.476, + 0.471, + 0.779 + ], + "angle": 0, + "content": "Due to the wide variety of human-object interactions (HOIs) in natural scenes and the fact that interactions of agents' actions with objects can induce emotional arousal of the primary agent in the scene, a useful approach for emotion recognition in images is to detect HOIs. In previous approaches [44, 25], multiple contexts, such as regions of interest (ROIs) and HOIs of all objects, were considered. Our proposed method outperforms previous approaches, as shown in Table 4. Our proposed method achieved superior performance on the dataset, which may be attributed to the wide variety of HOI categories in various challenging scenarios. Previous methods relied on pre-trained HOI models that were limited by predefined interaction categories. In contrast, our Cross-Patch Attention (CPA) module leverages the ability to learn HOI interactions directly from the data, allowing for greater flexibility and adaptability in recognizing new and diverse HOI categories. Moreover, our dual-pathway architecture significantly simplifies the computational process, eliminating the need for a heuristic selection of affective regions." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.469, + 0.804 + ], + "angle": 0, + "content": "4.5. Transfer learning for group cohesion estimation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Group cohesion is an affective phenomenon and a measure of agreement between members. Since cohesion and emotion (or valence) are intertwined in social science and affective computing, our DCAT for group valence prediction can be extended to group cohesion estimation. In this work, we finetune our model pre-trained on GroupEmoW" + }, + { + "type": "image", + "bbox": [ + 0.541, + 0.095, + 0.858, + 0.31 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.318, + 0.892, + 0.347 + ], + "angle": 0, + "content": "Figure 6. Group cohesion score comparison in the GAF Cohesion dataset (MSE is the evaluation metric, the lower the better)." + }, + { + "type": "table", + "bbox": [ + 0.534, + 0.359, + 0.86, + 0.501 + ], + "angle": 0, + "content": "
ModuleGAF 3.0GroupEmoW
CrossVit75.5688.48
CrossVit+A75.7988.86
CrossVit+A+B76.2188.96
CrossVit+A+B+C77.2989.55
CSwin-L78.0989.90
CSwin-L+A78.9390.12
CSwin-L+A+B79.2090.47
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.513, + 0.894, + 0.583 + ], + "angle": 0, + "content": "Table 5. The accuracy (\\%) of each proposed module. \\( A \\), \\( B \\), and \\( C \\) represent dual-pathway input, CPA module, and Token Ranking Module, respectively. The downsampling operation in each stage of the CSWin-L can be regarded as a token selection mechanism, so the Token Ranking Module is not included in it." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.622, + 0.892, + 0.713 + ], + "angle": 0, + "content": "for the GAF Cohesion dataset. The results in Figure 6 assure that our models still have good generalization ability rather than only fit to group affect datasets compared to other group affect recognition methods, e.g., EmoticW [13], ICMAI2020 [50], AIST2020 [10], as well as the ViTs, i.e., ViT [8], CSwin [7], Swin transformer [31]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.725, + 0.651, + 0.74 + ], + "angle": 0, + "content": "4.6. Ablation study" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.749, + 0.892, + 0.822 + ], + "angle": 0, + "content": "The effectiveness of each module. The effectiveness of each module proposed in our work, i.e., dual-pathway input, CPA module, Token Ranking Module, is shown in Table 5. For both the DCAT-ViT and DCAT-CSwin-L, each of the modules contributes to our overall results." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.824, + 0.892, + 0.884 + ], + "angle": 0, + "content": "The effectiveness of dual-input. Hence, we should also dynamically consider the global affective context while learning group affect, as validated in Table 6, where MIP and global inputs together perform better than either alone." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Cross-Cls-Attention (CCA) vs Our proposed Cross" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "20604" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.125, + 0.089, + 0.424, + 0.166 + ], + "angle": 0, + "content": "
InputGAF 3.0GroupEmoW
Only MIP68.0280.08
Only global75.5688.48
MIP + global77.2989.55
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.179, + 0.47, + 0.207 + ], + "angle": 0, + "content": "Table 6. Effectiveness of dual-input on GAF 3.0 [14] and GroupE-moW [22] dataset (evaluation metric is ACC \\((\\%)\\))." + }, + { + "type": "table", + "bbox": [ + 0.151, + 0.232, + 0.393, + 0.294 + ], + "angle": 0, + "content": "
GAF 3.0GroupEmoW
CCA75.41%87.86%
CPA77.29%89.55%
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.3, + 0.469, + 0.328 + ], + "angle": 0, + "content": "Table 7. Comparison between the CCA and our proposed CPA (using the DCAT-ViT) on GAF 3.0 and GroupEmoW dataset." + }, + { + "type": "image", + "bbox": [ + 0.103, + 0.342, + 0.21, + 0.424 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.218, + 0.342, + 0.326, + 0.424 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.334, + 0.342, + 0.439, + 0.424 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.103, + 0.434, + 0.21, + 0.515 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.218, + 0.433, + 0.326, + 0.515 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.336, + 0.431, + 0.442, + 0.514 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.104, + 0.526, + 0.21, + 0.607 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.218, + 0.525, + 0.325, + 0.608 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.335, + 0.526, + 0.438, + 0.607 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.11, + 0.613, + 0.193, + 0.625 + ], + "angle": 0, + "content": "(a) Input image" + }, + { + "type": "image_caption", + "bbox": [ + 0.218, + 0.614, + 0.323, + 0.626 + ], + "angle": 0, + "content": "(b) Token dropping" + }, + { + "type": "image_caption", + "bbox": [ + 0.364, + 0.614, + 0.41, + 0.626 + ], + "angle": 0, + "content": "(c) CPA" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.628, + 0.457, + 0.643 + ], + "angle": 0, + "content": "Figure 7. The visualization of the interaction of global and MIP." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.668, + 0.47, + 0.819 + ], + "angle": 0, + "content": "Patch-Attention (CPA). It is worth comparing between Cross-Cls-Attention (CCA) proposed in CrossViT [5] and our proposed CPA (as provided in Table 7). The CCA only exchanges the class token in the cross-attention mechanism, which limits its ability to capture global interactions between class tokens and patches in each branch. In complex scenarios, such as those encountered in group affect recognition, our proposed CPA approach is more effective for modeling the interdependencies between global and MIP features." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.831, + 0.469, + 0.863 + ], + "angle": 0, + "content": "4.7. Visualization of the interaction of global and MIP pathways" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "The interaction of the global and MIP pathways, including token dropping and CPA, is demonstrated in Fig-" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.093, + 0.883, + 0.28 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.281, + 0.892, + 0.322 + ], + "angle": 0, + "content": "Figure 8. The performance of average face quality, using all faces and using the MIP under different face count intervals in the image. The GroupEmoW dataset is used here." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.353, + 0.892, + 0.458 + ], + "angle": 0, + "content": "ure 7. As depicted in column (b), irrelevant background and other facial details are eliminated, while the MIP region and significant background regions (such as banners in protest scenes) are preserved for cross-patch attention. This demonstrates the effectiveness of our MIP-global interaction and highlights its efficacy in capturing discriminative information." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.478, + 0.891, + 0.51 + ], + "angle": 0, + "content": "4.8. Case study: the relationship between group size and performance" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.519, + 0.893, + 0.868 + ], + "angle": 0, + "content": "Previous studies have suggested that distinguishing between the negative and neutral categories in a group can be challenging [9]. In this paper, we present new insights into this issue. We first analyze the number of individuals in each image and find that as the number of individuals increases, the average quality of their facial features decreases \\(^{4}\\), as illustrated in Figure 8. This indicates that facial details become increasingly blurred and difficult to extract, posing a significant challenge, particularly when trying to distinguish between negative and neutral categories, which are inherently difficult to distinguish. In contrast to previous works that typically average features across all detected faces [9], our approach selectively focuses on the most informative facial region, i.e., the MIP, and outperforms models that utilize all faces in images with larger populations. This approach avoids interference from low-quality faces and effectively interacts between the features of the MIP and those of the entire global image through our proposed CPA module, enhancing the accuracy of our results. Therefore, our approach yields higher accuracy for distinguishing between the negative and neutral categories compared to previous methods. The exact numerical results can be found in the supplementary material." + }, + { + "type": "page_footnote", + "bbox": [ + 0.517, + 0.887, + 0.734, + 0.901 + ], + "angle": 0, + "content": "4We quantify face quality based on [39]." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "20605" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.081, + 0.09, + 0.203, + 0.107 + ], + "angle": 0, + "content": "5. Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.115, + 0.468, + 0.295 + ], + "angle": 0, + "content": "In this work, by incorporating the MIP concept, we propose a dual-pathway vision transformer model, the Dual-branch Cross-Patch Attention Transformer (DCAT) for group affect recognition. Moreover, we propose the CPA module so that the important tokens from both paths can be interacted with. In terms of accuracy and parameters, the proposed DCAT outperforms both state-of-the-art group affect models and vision transformer models. It is also the first study to explore group affect recognition beyond CNNs. Moreover, our proposed model can be utilized in other group-level affect tasks, i.e., group cohesion analysis." + }, + { + "type": "title", + "bbox": [ + 0.081, + 0.31, + 0.236, + 0.327 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.336, + 0.468, + 0.395 + ], + "angle": 0, + "content": "This work was supported in part by the National Science and Technology Council of Taiwan under Grants NSTC-109-2223-E-002-005-MY3, NSTC-112-2628-E-002-033-MY4 and NSTC-112-2634-F-002-002-MBK." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.947, + 0.518, + 0.957 + ], + "angle": 0, + "content": "20606" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Tadas Baltrusaitis, Peter Robinson, and Louis-Philippe Morency. 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In Proceedings of the 2020 5th International Conference on Mathematics and Artificial Intelligence, pages 24–28, 2020. 7" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.894, + 0.813 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.52, + 0.957 + ], + "angle": 0, + "content": "20608" + } + ] +] \ No newline at end of file diff --git a/2023/Most Important Person-Guided Dual-Branch Cross-Patch Attention for Group Affect Recognition/2995ddf2-76d9-45cb-9d66-1a50a95e4d2f_origin.pdf b/2023/Most Important Person-Guided Dual-Branch Cross-Patch Attention for Group Affect Recognition/2995ddf2-76d9-45cb-9d66-1a50a95e4d2f_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..c17c91dad6d0b5e599e5a9f46a1ba8e4923c5611 --- /dev/null +++ b/2023/Most Important Person-Guided Dual-Branch Cross-Patch Attention for Group Affect Recognition/2995ddf2-76d9-45cb-9d66-1a50a95e4d2f_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:3fcece950ee646bb0ed5d6fbd26bee3ad75070e73240f30966e141bf1322a9d8 +size 6490679 diff --git a/2023/Most Important Person-Guided Dual-Branch Cross-Patch Attention for Group Affect Recognition/full.md b/2023/Most Important Person-Guided Dual-Branch Cross-Patch Attention for Group Affect Recognition/full.md new file mode 100644 index 0000000000000000000000000000000000000000..cb8534176ea194bfef907aedc97434077719fbd2 --- /dev/null +++ b/2023/Most Important Person-Guided Dual-Branch Cross-Patch Attention for Group Affect Recognition/full.md @@ -0,0 +1,342 @@ +# Most Important Person-guided Dual-branch Cross-Patch Attention for Group Affect Recognition + +Hongxia Xie $^{1}$ , Ming-Xian Lee $^{2}$ , Tzu-Jui Chen $^{2}$ , Hung-Jen Chen $^{1}$ , Hou-I Liu $^{1}$ , Hong-Han Shuai $^{1}$ and Wen-Huang Cheng $^{3}$ + +$^{1}$ National Yang Ming Chiao Tung University, hongxiaixie.ee08@nycu.edu.tw + +2University of Illinois Urbana-Champaign + +$^{3}$ National Taiwan University, wenhuang@csie.ntu.edu.tw + +# Abstract + +Group affect refers to the subjective emotion that is evoked by an external stimulus in a group, which is an important factor that shapes group behavior and outcomes. Recognizing group affect involves identifying important individuals and salient objects among a crowd that can evoke emotions. However, most existing methods lack attention to affective meaning in group dynamics and fail to account for the contextual relevance of faces and objects in group-level images. In this work, we propose a solution by incorporating the psychological concept of the Most Important Person (MIP), which represents the most noteworthy face in a crowd and has affective semantic meaning. We present the Dual-branch Cross-Patch Attention Transformer (DCAT) which uses global image and MIP together as inputs. Specifically, we first learn the informative facial regions produced by the MIP and the global context separately. Then, the Cross-Patch Attention module is proposed to fuse the features of MIP and global context together to complement each other. Our proposed method outperforms state-of-the-art methods on GAF 3.0, GroupEmoW, and HECO datasets. Moreover, we demonstrate the potential for broader applications by showing that our proposed model can be transferred to another group affect task, group cohesion, and achieve comparable results. + +# 1. Introduction + +Humans are active and social creatures, using multimodal interactions to convey their intentions, attitudes, and feelings. Such physical and emotional interactions between individuals within a group can generate group-level affect + +
Global +All3Random3MIPs1RandomMIP
Acc (%)85.0185.4787.4682.3088.86
+ +Table 1. Different face selection strategies. The "3Random" refers to selecting 3 faces randomly from the detected faces in the image, while the "3MIPs" strategy selects the top three detected faces based on their importance ranking. The dataset evaluated here is the GroupEmoW [22]. + +or group-level emotion [2]'. + +![](images/a9e91f77f20a4009fc67e082724119343b01a48265f630131e067e893eb52c23.jpg) + +![](images/4d0400e954af0532303fccf14e0928c69db02657a4c8357a2dd2dbdc698f5224.jpg) + +![](images/3a547c9a6b1eb0a240e5cbc0f81724f8ee3fd73e42fe0e1a7c1a1c0c65b85f51.jpg) + +![](images/47aed540efefac8474876d65efc41f41f283ae3aa2dee60cbc0710c65ecac6bf.jpg) +(a) Input image + +![](images/73199a18044fa69b79df925fa8d820b67b74b551401bb179c28cbc095d8815bc.jpg) +(b) Using MIP + +![](images/63ebafa884cf7425fd532c95f18887f9e73258ac918b40693c097720a2ab11b4.jpg) +(c) Using all faces +Figure 1. Feature map comparison between using MIP and all faces. The yellow box in (a) represents the MIP region. + +By providing the group-level information, group affect prediction has various real-world applications, e.g., work team outcome prediction [21], social relationship recognition [33], human-machine interaction systems [24]. As a result, the research topics surrounding group affect are di + +verse, including categorical analysis, e.g., group valence (positive, negative, neutral) prediction [16, 22], continuous intensity estimation, e.g., group cohesion prediction [15]. + +Group affect is influenced by a combination of a group's affective context (e.g., salient objects in the funeral, party) and affective composition (i.e., the combination of a group members' state and trait affect) [2]. Previous methods for group affect recognition mainly adopted a bottom-up approach [9, 44, 16, 22], where features were extracted from individuals separately and then fused to output group-level emotion. This was done by utilizing multi-cues from separate pre-trained detectors, such as facial expressions of individuals, object proposals, and scene features. While these cues can provide valuable information, they may not fully capture the complex interplay of emotions within a group. As indicated in [12], current group-level recognition architectures tend to focus on detecting salient regions, but they may lack an understanding of the affective meaning in the image. Therefore, there is a need for a more holistic approach that considers the most important region in the crowd and how they interact with the scene. + +Hence, in this work, we introduce a crucial psychological concept, namely, Most Important Person (MIP) [2], which goes beyond saliency and considers the importance of individuals for group affect recognition. The MIP of an image is often the group leaders who can influence the emotion of a group [11, 37, 34]. MIP has been explored in many related works in psychology and affective computing, such as the Affective Transfer Process phenomenon in psychology [2], which indicates that the MIP of an image can influence the group's emotion. We conducted a preliminary experiment based on the CrossVit [5] model to demonstrate the effectiveness of the MIP in group affect. Our architecture uses both the global image and faces as two inputs. As depicted in Table 1, the results demonstrate that using all faces is considerably less effective than using the MIP, and even less effective than randomly selecting three facial images. Additionally, as observed in the feature maps illustrated in Figure 1, the model that employs all faces fails to predict accurately due to its focus on irrelevant background regions or faces. In contrast, the network that utilizes MIP can efficiently focus on relevant facial regions, thereby enhancing prediction accuracy. This is mainly due to the fact that in crowded scenes with many blurry faces, the model trained on all faces exhibits dispersed attention, while the model trained on the MIP region concentrates specifically on the relevant area. + +Based on the above observations, we present a dual-pathway vision transformer model, the Dual-branch Cross-Patch Attention Transformer (DCAT), including a global branch and a MIP branch. With the dual-pathway, spatial-wise discriminative clues can be discovered both globally and locally in conjunction with self-attention learning. For + +the dual-pathway interaction, since there are many interferences in the group, we propose the Cross-Patch Attention (CPA) module. CPA first utilizes the Token Ranking Module to select the important tokens in each path, and then the cross-attention is calculated between the selected query vectors and the entire key-value vectors from the other path. In this way, global and MIP contexts are able to complement and compensate for each other. + +This paper makes the following main contributions: + +- In this work, we validate that MIP plays a crucial role in group affect recognition. To the best of our knowledge, this is the first work introducing MIP into the group affect task. +- The MIP and global affective context information are integrated into the proposed dual-pathway vision transformer architecture for recognizing group emotions in a context-aware manner. We also propose a novel CPA module that focuses on the interactions among diverse scene contexts and facial informative regions. +- Experimental results show that the proposed DCAT outperforms both state-of-the-art group affect works and vision transformer models in terms of accuracy and model parameters. This is also the first work to explore group affect recognition that goes beyond the CNN-based approach. Moreover, our proposed model can be utilized in other group-level affect tasks, i.e., group cohesion analysis. + +# 2. Related works + +# 2.1. Group affect recognition methods + +Current group affect recognition methods primarily analyze the individual members of a group and then assess their contribution to the overall mood of the group by taking into account a variety of cues, such as faces, salient objects, and scenes. Fujii et al. [9] proposed a two-stage classification method, in which the first stage classifies facial expressions, and the second stage adds scene features into consideration to fuse faces and scenes through spectral clustering for further group affect recognition. Khan et al. [22] considered multi-cues, which include all faces, object proposals, and scene information. To achieve such an architecture, additional face detection and object proposal detection detectors are needed. Similarly, Guo et al. [16] also investigated multi-cues using graph neural networks, where the topology of the graph varies as the number of entities varies. + +However, in large groups, it is not feasible to consider the expressions of all faces and objects individually before aggregating, resulting in lower efficiency and accuracy. As indicated in [9], considering the performance of the main subject estimation is needed, while our work fills the gap. + +# 2.2. Most important person (MIP) detection + +# 2.2.1 MIP detection + +A MIP detection model understands a high-level pattern in a social event image to identify the most important person. Ramanathan et al. [35] used an RNN to learn time-varying attention weights that can be used for event detection and classification. Without any explicit annotations, the person with the highest attendance can be identified as the MIP. In order to overcome the inherent variability of human poses, PersonRank [27] produced a multiple Hyper-Interaction Graph, which treats each individual person as a node. The most active node can be identified using four types of edge message functions. POINT [26] proposed two types of interaction modules, i.e., the person-person interaction module and the event-person interaction module. It then aggregated relation features and person features to form the important feature. To reduce the annotation effort, Hong et al. [19] formulated a POINT-based iterative learning method for semi-supervised important people detection. Thus, we incorporate people awareness into global-level affect analysis in this work. + +# 2.3. Dual attention learning models + +Visual attention with dual-pathway has been widely used to find important contextual regions. Based on the outstanding performance of vision transformers (ViTs) in various visual tasks [8], there are many self-attention-based dual-pathway networks in recent years. Zhu et al. [49] proposed a global-local cross-attention to reinforce the spatial-wise discriminative clues for fine-grained recognition. A pairwise cross-attention was designed to establish the interactions between image pairs. Dual-ViT [46] incorporated a compressed semantic pathway that served as prior information in learning finer pixel-level details. The semantic pathway and pixel pathway are integrated together and trained to spread enhanced self-attention information in parallel. + +The most similar architecture to our work is the CrossViT [5], which was proposed to learn multi-scale features effectively. However, we differ from it in two main ways. Firstly, our network divides at different scales using global images and MIP images, whereas CrossViT divides at different scales using the same input image. Another difference is the cross-attention mechanism. The CrossViT exchanges class tokens, while we designed a Cross-Patch Attention module based on attentive queries from both paths. + +# 3. Proposed Dual-branch Cross-Patch Attention Transformer (DCAT) + +# 3.1. Overview + +The architecture of our proposed Dual-branch Cross-Patch Attention Transformer (DCAT) for group affect + +recognition is shown in Figure 2. The model contains two inputs, i.e., the global image and the corresponding MIP image. The two images are tokenized into patches first and sent into a stack of Multi-Scale Transformer Encoder, which consists of dual-path Transformer Encoder, Token Ranking Module, and Cross-Patch Attention (CPA). Specifically, in a dual-path Transformer Encoder, the global image is sent to the coarse-level path to capture long-range information and further refine the encoded tokens for fine-grained details. On the other hand, the MIP image is fed to the fine-level path to obtain high-level semantic tokens. Next, since the global and MIP features are conceptual interdependent, we incorporate dual-path interaction in our model. In particular, we sort tokens according to their importance in each path based on the Token Ranking Module, then calculate the CPA using the key and value vectors from the other path. Finally, the class tokens from two branches are combined and sent into a linear layer for prediction. + +# 3.2. Dual-pathway learning + +To leverage the global information of a group captured by the global image and the local-based semantic prior of the MIP, we propose a dual-pathway feature learning approach for group affect prediction. By integrating self-attention learning into the dual-pathway, our approach enables the discovery of spatial-wise discriminative clues both globally and locally. To validate our assumptions, we compute the CKA similarity [43] to measure the similarity of the intermediate token features in each layer and the final CLS token, follwing [43]. As illustrated in Figure 3, both the MIP and global tokens exhibit a positive correlation with the CLS token as the model depth increases. This suggests that both features are valuable for the final classification task and highlights the rationality and necessity of our dual-pathway input design. + +Firstly, both the global and MIP image are tokenized into patches, then the class token and a learnable position embedding are added to both branches before the MultiScale Transformer Encoder. In order to balance computational costs, our Transformer Encoders in the two pathways include different numbers (i.e., $G = 6$ and $M = 1$ ) inspired by CrossViT [5]. The global branch is the large (primary) branch with a coarse patch size (i.e., 12), with a larger embedding size, and more transformer encoders. The MIP image is the input of a small (complementary) branch with fine-grained patch size (i.e., 16), fewer encoders, and a smaller embedding size. + +As the core of the vision transformer, the Multi-Head Self-Attention (MHSA) maps a query vector into a set of key and value vectors [8]. In the $l$ -th Transformer Encoder block in both pathways (a basic Transformer Encoder is shown in Figure 2b), the output feature map is $X_{l} \in \mathbb{R}^{(N + 1)\times d}$ . The attention matrix $A_{l} \in \mathbb{R}^{S \times (N + 1) \times (N + 1)}$ + +![](images/53991e35cece8832602c947d2ddc621319fe330d6874b22b13f2a5821c952765.jpg) +(a) The overall architecture of our proposed DCAT + +![](images/6f1bd41b9a0827cc2b0203d63c912bd5fba50d89f8d1be01c9ee04787ee53717.jpg) +(b) The Transformer Encoder + +![](images/3975a2d0b19aa136741b2b22c537caf7851c904479d514f1368317b90b6b4466.jpg) +(c) The Cross-Patch Attention (CPA) + +![](images/e479b41d4548b5c695fa0aef90257608de731e35f8a35f88b36bc295ecac7143.jpg) +Figure 2. The overall architecture of our proposed Dual-branch Cross-Patch Attention Transformer (DCAT). + +![](images/0d8bdb50d819ae26391d919bd6d6be8d46f0ae29fbcedc3e2446a6da1e561cef.jpg) +Figure 3. CKA similarity in each layer. +Figure 4. Different drop ratio of the MIP branch. + +of MHSA module in the block is computed as: + +$$ +A _ {l} = \operatorname {S o f t m a x} \left(\frac {Q _ {l} * K _ {l} ^ {T}}{\sqrt {d}}\right), \tag {1} +$$ + +where $Q_{l}\in \mathbb{R}^{(N + 1)\times d}$ and $K_{l}\in \mathbb{R}^{(N + 1)\times d}$ denote the queries and keys projected by $X_{l}$ of self-attention operation in $(l - 1)$ -th transformer block, respectively. $S$ represents the number of heads, $T$ is a transpose operator, $d$ is the di + +mension of the embedding. $N$ is the number of tokenized patches. The input global and MIP images are divided into different patches numbers with different $N$ . The calculation includes 1 class token in addition to the $N$ tokens. + +# 3.3. The interaction of global and MIP pathways + +Due to the large amount of information in group-level images, extracting features by either global or MIP branch alone is not sufficient, and cross-attention of discriminative tokens from both can provide complementary effects. + +Having obtained global and MIP tokens by the Transformer Encoder, we should consider the dual-path interactions. To achieve this, we propose the Cross-Patch Attention (CPA) mechanism to establish spatial interactions between the global and MIP images. Firstly, we sort the tokens based on their importance in each path using the Token Ranking Module and create a new query matrix by selecting the top $\eta$ tokens. As depicted in Figure 4, the model's per + +formance, taking the MIP branch as an example $^{2}$ , is related to the drop ratio, where dropping a certain percentage of tokens can improve performance. Secondly, we compute the Cross-Patch Attention (CPA) using the new query matrix and key-value from the other branch. It is noteworthy that the gradients propagate through both pathways, which allows it to compensate for information loss on global feature compression through global-to-local interaction. As validated in [49], such cross-attention can also be viewed as a novel regularization method to regularize attention learning, especially for our small datasets. + +# 3.3.1 Token Ranking Module + +For Cross-Patch Attention, we need to remove unimportant contents from the complex group images and keep only the tokens that are relevant. + +Our first step is to rank the tokens according to their importance. While the class token attention map $A_{cls} \in \mathbb{R}^{1 \times (N + 1)}$ reflects the importance of features [43, 29], we denote the token importance by the similarity scores between the global class token and each patch token: + +$$ +A _ {c l s} = \operatorname {S o f t m a x} \left(\frac {q _ {c l s} * K ^ {T}}{\sqrt {d}}\right), \tag {2} +$$ + +where $q_{cls} \in \mathbb{R}^{1 \times d}$ is the query vector of the class token, $K \in \mathbb{R}^{(N + 1) \times d}$ is the key vector, and $d$ is the dimension of the embedding. + +According to the equation 2, the weights of each patch correlated with the class token are computed. In such a way, the $A_{cls}$ reveals how much each patch contributes to the final classification since it captures the global interactions of the class token to all patches. + +# 3.3.2 Cross-Patch Attention (CPA) + +Based on the importance score of each token, we then construct a newly selected query matrix $Q_{sel} \in \mathbb{R}^{(\alpha + 1) \times d}$ , representing the attentive local embedding, by selecting the top $\alpha$ query vectors that correspond to the top $\alpha$ highest responses in the class attention map. + +In each pathway, the Cross-Patch Attention (CPA) vectors is computed as below, + +$$ +f _ {C P A} (Q, K, V) = \operatorname {S o f t m a x} \left(\frac {Q _ {\text {s e l}} * K ^ {T}}{\sqrt {d}}\right) V, \tag {3} +$$ + +where $K\in \mathbb{R}^{(N + 1)\times d}$ is the key vector, $V\in \mathbb{R}^{(N + 1)\times d}$ is the value vector and $d$ is the dimension of the embedding. + +As shown in Figure 2c, the CPA operation is bidirectional, with each of the two branches providing the selected tokens as the query vector. Both branches are fused together + +$C$ times, which means the selected queries are updated in each CPA. + +Finally, after repeating $L$ Multi-Scale Transformer Encoder, the class tokens from two branches are combined and sent into a linear layer for prediction. The cross-entropy loss is used here for final classification [5, 8]. + +# 4. Experiments + +# 4.1. Implemental details + +Our model is partly pre-trained with the weight of CrossViT [5] on ImageNet. We train all our models for 300 epochs (30 warm-up epochs) on 2 GPUs (RTX 3090 Ti) with a batch size of 64. The numbers of Transformer Encoder in the dual path, CPA, and Multi-Scale Transformer Encoder are set as $M = 1$ , $G = 6$ , $C = 3$ , and $L = 1$ . For the token selection ratios $\alpha$ of (global, MIP), we use (0.5, 0.5) for GAF 3.0 and (1, 0.5) for GroupEmoW throughout the paper. More details can be found in our supplementary materials. + +# 4.2. Datasets + +In this paper, we utilize several datasets for our experiments, including GroupEmoW [16], GAF 3.0 [13], GAF Cohesion [13, 15], and HECO [44], as presented in Table 2. The GroupEmoW dataset contains images obtained from the web via search engines, using keywords related to various social events such as funerals, birthdays, protests, conferences, and meetings. GAF 3.0 [13] and GAF Cohesion [13, 15] datasets were created through web crawling using a diverse set of keywords related to social events, including world cup winners, weddings, family gatherings, laughing clubs, birthday celebrations, siblings, riots, protests, and violence. The cohesion scores in GAF Cohesion range from strongly agree, agree, disagree to strongly disagree, using a 0-3 scale. + +In our experiments, we utilized the MIP ground truth provided by HECO [44]. However, the ground truth for GAF 3.0 and GroupEmoW was not available. However, since the ground truth for GAF 3.0 and GroupEmoW was not available, we employed the pre-trained POINT model [26] to generate the MIP. The POINT model was trained on the Multi-scene Important People Image Dataset (MS Dataset).3. + +# 4.3. Comparison with state-of-the-art group affect methods and ViTs + +In this work, we have built our proposed modules based on CrossViT [5] with vanilla Transformer Encoders [8], which denotes by DCAT-ViT. In addition, since there is a series of ViTs without the class token, e.g., Swin [31] and + +
DatasetLabelTrain/Val/TestScenarioEvaluation metric
GroupEmoW [13]Neutral, Positive, Negative11,127/3,178/1,589Specific social eventsAcc
GAF 3.0 [13, 15]Neutral, Positive, Negative9,815/4,349/3011Specific social eventsAcc
HECO [44]Surprise, Excitement, Happiness, Peace, Disgust, Anger, Fear, and Sadness6,570/1,877/938In-the-wild images that do not limit scenesmAP
GAF Cohesion [13, 15]0-39,815/4,349/3011Specific social eventsMSE
+ +![](images/f76662dc063f1e59ff4afeb130958930b1def33f11024e80663eaf0826c31fe6.jpg) +Figure 5. Model parameter and accuracy trade-off comparison on the GAF 3.0 dataset. Our proposed models are highlighted by the blue rectangular box. + +CSwin [7]. In order to prove the generality of our approach, we have added the proposed dual-pathway and CPA module to the CSwin transformer [7], which is denoted by DCAT-CSwin-L. + +A comparison of the proposed model with the state-of-the-art group affect approaches on GAF 3.0 and GroupEmoW datasets can be found in Figure 5 and Table 3, respectively. Since our proposed DCAT model is based on a vision transformer, we also compare it with recent vision transformer models, such as multiscale-based (CrossViT [5], Focal-B [45], RegionViT-B [4], TCFormaler-L [47]), CNN-transformer hybrid-based (Conformer-L [32]), and lightweight-based models (EvoLeViT [43], DynamicSwin-T [36], DVT [40]). + +Comparing with state-of-the-art group affect methods. Our DCAT-ViT and DCAT-CSwin-L achieve the best results compared to other group affect recognition methods on the GAF 3.0 dataset. Specifically, our DCAT-ViT achieves $77.29\%$ accuracy with only 26.70M parameters, which is only about $7.6\%$ of TMM [9], while our DCAT-CSwin-L with a larger number of parameters (358M) achieves $79.20\%$ accuracy. On the GroupEmoW dataset, our DCAT-CSwin-L also achieves the best performance compared to other methods. It is worth noting that our proposed method only needs the global image and corre + +Table 2. Datasets details used in this paper (Acc = Accuracy, mAP = mean average precision, MSE = mean square error). + +
MethodsAcc (%)Source
Group affect methods
ResNet34 [18]68.13Global, Faces
SE-ResNet-50 [20]69.79Global
Efficientnet-b2 [38]72.33Global, Faces
CAER-Net [25]80.61Global, Faces
GNN [16]82.38Global
GNN [16]84.62Global, Faces, Objects
ConGNN [41]85.59Global, Faces, Objects
WACV 21 [22]89.36Global, Faces
GNN [16]89.93Global, Faces
WACV 21 [22]90.18Global, Faces, Objects
Vision transformers
ViT [8]87.50Global
P2T-base [42]86.50Global
DeepViT [48]83.90Global
Conformer-L [32]83.35Global
Focal-B [45]87.98Global
CrossViT [5]88.48Global
TransFG [17]89.47Global
RegionViT-B [4]89.49Global
CSwin-L [7]89.90Global
DVT [40]87.90Global
Evo-LeViT [43]87.83Global
TCFormer-L [47]89.24Global
DCAT-ViT89.55Global, MIP
DCAT-CSwin-L90.47Global, MIP
+ +Table 3. Overall Accuracy Comparison on the GroupEmoW dataset. "Source" refers to the types of features used in each paper. + +sponding MIP image, while current group affect methods need multiple pre-trained detectors, which may be influenced by imperfect faces and objects. Furthermore, our method learns discriminative clues end-to-end in coordination with self-attention learning. + +Comparing with single focal attention methods. A comparison is made between our dual-pathway attention model and methods specifically designed for local attention (Focal Transformers [45] and TransFG [17]). This finding highlights the fact that saliency does not always equate to + +
MethodmAP (%)
GCNs [23]48.84
Depth [28]49.02
OpenFace [1]+OpenPose [3]50.28
R-FCN [6]+HOI-Net [30]50.34
HECO [44]50.24
DCAT-ViT53.49
DCAT-CSwin-L58.06
+ +importance, and that our method's attention mechanism can effectively identify and leverage the most critical affective regions. + +Overall, our proposed DCAT-ViT and DCAT-CSwin-L perform better than other group affect recognition models and ViTs in terms of both accuracy and model complexity. + +# 4.4. The scalability of our method + +Our proposed architecture can be adapted to accommodate the concept of a primary agent, similar to the idea of MIP, which was introduced by HECO [44]. Specifically, we can modify the input to the MIP branch from the MIP image to the primary agent while keeping the global branch unchanged. + +Due to the wide variety of human-object interactions (HOIs) in natural scenes and the fact that interactions of agents' actions with objects can induce emotional arousal of the primary agent in the scene, a useful approach for emotion recognition in images is to detect HOIs. In previous approaches [44, 25], multiple contexts, such as regions of interest (ROIs) and HOIs of all objects, were considered. Our proposed method outperforms previous approaches, as shown in Table 4. Our proposed method achieved superior performance on the dataset, which may be attributed to the wide variety of HOI categories in various challenging scenarios. Previous methods relied on pre-trained HOI models that were limited by predefined interaction categories. In contrast, our Cross-Patch Attention (CPA) module leverages the ability to learn HOI interactions directly from the data, allowing for greater flexibility and adaptability in recognizing new and diverse HOI categories. Moreover, our dual-pathway architecture significantly simplifies the computational process, eliminating the need for a heuristic selection of affective regions. + +# 4.5. Transfer learning for group cohesion estimation + +Group cohesion is an affective phenomenon and a measure of agreement between members. Since cohesion and emotion (or valence) are intertwined in social science and affective computing, our DCAT for group valence prediction can be extended to group cohesion estimation. In this work, we finetune our model pre-trained on GroupEmoW + +![](images/9490b2888e40456708c3f3c49a87e752d1eae4f48cab7b4cdbe84def2304ea1d.jpg) +Figure 6. Group cohesion score comparison in the GAF Cohesion dataset (MSE is the evaluation metric, the lower the better). + +Table 4. Comparison on HECO dataset. + +
ModuleGAF 3.0GroupEmoW
CrossVit75.5688.48
CrossVit+A75.7988.86
CrossVit+A+B76.2188.96
CrossVit+A+B+C77.2989.55
CSwin-L78.0989.90
CSwin-L+A78.9390.12
CSwin-L+A+B79.2090.47
+ +Table 5. The accuracy (\%) of each proposed module. $A$ , $B$ , and $C$ represent dual-pathway input, CPA module, and Token Ranking Module, respectively. The downsampling operation in each stage of the CSWin-L can be regarded as a token selection mechanism, so the Token Ranking Module is not included in it. + +for the GAF Cohesion dataset. The results in Figure 6 assure that our models still have good generalization ability rather than only fit to group affect datasets compared to other group affect recognition methods, e.g., EmoticW [13], ICMAI2020 [50], AIST2020 [10], as well as the ViTs, i.e., ViT [8], CSwin [7], Swin transformer [31]. + +# 4.6. Ablation study + +The effectiveness of each module. The effectiveness of each module proposed in our work, i.e., dual-pathway input, CPA module, Token Ranking Module, is shown in Table 5. For both the DCAT-ViT and DCAT-CSwin-L, each of the modules contributes to our overall results. + +The effectiveness of dual-input. Hence, we should also dynamically consider the global affective context while learning group affect, as validated in Table 6, where MIP and global inputs together perform better than either alone. + +Cross-Cls-Attention (CCA) vs Our proposed Cross + +
InputGAF 3.0GroupEmoW
Only MIP68.0280.08
Only global75.5688.48
MIP + global77.2989.55
+ +Table 6. Effectiveness of dual-input on GAF 3.0 [14] and GroupE-moW [22] dataset (evaluation metric is ACC $(\%)$ ). + +
GAF 3.0GroupEmoW
CCA75.41%87.86%
CPA77.29%89.55%
+ +Table 7. Comparison between the CCA and our proposed CPA (using the DCAT-ViT) on GAF 3.0 and GroupEmoW dataset. + +![](images/41e676e8d6c448e4d023b99a34636ddc8f42bceda07fc1136e477784ca615045.jpg) + +![](images/319584c7d8ec1289cd03619853c4a7c05ec6fc7e0cc866177c276524e01d9885.jpg) + +![](images/277095c6d149c752a639b18850e3ab9a042dd5f3612084c3fdf71cc37d176d2a.jpg) + +![](images/ab1f61f173189414e1fd5d0821ed6ab46d2def2c259e79d73dabf7801c924366.jpg) + +![](images/b2bfa239c1bfca1d78417bd08364ebd023725574955bb43a54ae3db167b38452.jpg) + +![](images/b7e707cb71d1dbf1daf7b21b66956a88082b519f125d41fadc1f75d3a0c4bc47.jpg) + +![](images/ece99ea8b3f9eed23b527953fbf9e1fbd1f9eca11354478418cc7c1d32e8c376.jpg) +(a) Input image + +![](images/b3d7a9f91cfd1994453ab671918ecb90742036f67db9c97b2bc1b912a8f1746e.jpg) +(b) Token dropping + +![](images/8d2cdc9a6939f692b9dff60a10a8961c8f6d10395338e0f05f811844ad28b543.jpg) +(c) CPA +Figure 7. The visualization of the interaction of global and MIP. + +Patch-Attention (CPA). It is worth comparing between Cross-Cls-Attention (CCA) proposed in CrossViT [5] and our proposed CPA (as provided in Table 7). The CCA only exchanges the class token in the cross-attention mechanism, which limits its ability to capture global interactions between class tokens and patches in each branch. In complex scenarios, such as those encountered in group affect recognition, our proposed CPA approach is more effective for modeling the interdependencies between global and MIP features. + +# 4.7. Visualization of the interaction of global and MIP pathways + +The interaction of the global and MIP pathways, including token dropping and CPA, is demonstrated in Fig- + +![](images/00c700bd09a232b104e3d403a533f41280789f4d38bdd5bc1b9ae25236dcc4e4.jpg) +Figure 8. The performance of average face quality, using all faces and using the MIP under different face count intervals in the image. The GroupEmoW dataset is used here. + +ure 7. As depicted in column (b), irrelevant background and other facial details are eliminated, while the MIP region and significant background regions (such as banners in protest scenes) are preserved for cross-patch attention. This demonstrates the effectiveness of our MIP-global interaction and highlights its efficacy in capturing discriminative information. + +# 4.8. Case study: the relationship between group size and performance + +Previous studies have suggested that distinguishing between the negative and neutral categories in a group can be challenging [9]. In this paper, we present new insights into this issue. We first analyze the number of individuals in each image and find that as the number of individuals increases, the average quality of their facial features decreases $^{4}$ , as illustrated in Figure 8. This indicates that facial details become increasingly blurred and difficult to extract, posing a significant challenge, particularly when trying to distinguish between negative and neutral categories, which are inherently difficult to distinguish. In contrast to previous works that typically average features across all detected faces [9], our approach selectively focuses on the most informative facial region, i.e., the MIP, and outperforms models that utilize all faces in images with larger populations. This approach avoids interference from low-quality faces and effectively interacts between the features of the MIP and those of the entire global image through our proposed CPA module, enhancing the accuracy of our results. Therefore, our approach yields higher accuracy for distinguishing between the negative and neutral categories compared to previous methods. The exact numerical results can be found in the supplementary material. + +# 5. Conclusions + +In this work, by incorporating the MIP concept, we propose a dual-pathway vision transformer model, the Dual-branch Cross-Patch Attention Transformer (DCAT) for group affect recognition. Moreover, we propose the CPA module so that the important tokens from both paths can be interacted with. In terms of accuracy and parameters, the proposed DCAT outperforms both state-of-the-art group affect models and vision transformer models. It is also the first study to explore group affect recognition beyond CNNs. Moreover, our proposed model can be utilized in other group-level affect tasks, i.e., group cohesion analysis. + +# Acknowledgement + +This work was supported in part by the National Science and Technology Council of Taiwan under Grants NSTC-109-2223-E-002-005-MY3, NSTC-112-2628-E-002-033-MY4 and NSTC-112-2634-F-002-002-MBK. + +# References + +[1] Tadas Baltrusaitis, Peter Robinson, and Louis-Philippe Morency. Openface: an open source facial behavior analysis toolkit. 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Dual vision transformer. arXiv preprint arXiv:2207.04976, 2022. 3 +[47] Wang Zeng, Sheng Jin, Wentao Liu, Chen Qian, Ping Luo, Wanli Ouyang, and Xiaogang Wang. Not all tokens are equal: Human-centric visual analysis via token clustering transformer. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 11101-11111, 2022. 6 +[48] Daquan Zhou, Bingyi Kang, Xiaojie Jin, Linjie Yang, Xiaochen Lian, Zihang Jiang, Qibin Hou, and Jiashi Feng. Deepvit: Towards deeper vision transformer. arXiv preprint arXiv:2103.11886, 2021. 6 +[49] Haowei Zhu, Wenjing Ke, Dong Li, Ji Liu, Lu Tian, and Yi Shan. Dual cross-attention learning for fine-grained visual categorization and object re-identification. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 4692–4702, 2022. 3, 5 +[50] Bochao Zou, Zhifeng Lin, Haoyi Wang, Yingxue Wang, Xiangwen Lyu, and Haiyong Xie. Joint prediction of group-level emotion and cohesiveness with multi-task loss. 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Feature map comparison between using MIP and all faces. The yellow box in (a) represents the MIP region." + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_caption" + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 626, + 547, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 626, + 547, + 687 + ], + "spans": [ + { + "bbox": [ + 304, + 626, + 547, + 687 + ], + "type": "text", + "content": "By providing the group-level information, group affect prediction has various real-world applications, e.g., work team outcome prediction [21], social relationship recognition [33], human-machine interaction systems [24]. As a result, the research topics surrounding group affect are di" + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 306, + 693, + 545, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 545, + 712 + ], + "type": "text", + "content": "1In this work, groups range in size from two or three individuals up to hundreds." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "20598" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "content": "verse, including categorical analysis, e.g., group valence (positive, negative, neutral) prediction [16, 22], continuous intensity estimation, e.g., group cohesion prediction [15]." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 110, + 288, + 326 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 110, + 288, + 326 + ], + "spans": [ + { + "bbox": [ + 46, + 110, + 288, + 326 + ], + "type": "text", + "content": "Group affect is influenced by a combination of a group's affective context (e.g., salient objects in the funeral, party) and affective composition (i.e., the combination of a group members' state and trait affect) [2]. Previous methods for group affect recognition mainly adopted a bottom-up approach [9, 44, 16, 22], where features were extracted from individuals separately and then fused to output group-level emotion. This was done by utilizing multi-cues from separate pre-trained detectors, such as facial expressions of individuals, object proposals, and scene features. While these cues can provide valuable information, they may not fully capture the complex interplay of emotions within a group. As indicated in [12], current group-level recognition architectures tend to focus on detecting salient regions, but they may lack an understanding of the affective meaning in the image. Therefore, there is a need for a more holistic approach that considers the most important region in the crowd and how they interact with the scene." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 328, + 288, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 328, + 288, + 639 + ], + "spans": [ + { + "bbox": [ + 46, + 328, + 288, + 639 + ], + "type": "text", + "content": "Hence, in this work, we introduce a crucial psychological concept, namely, Most Important Person (MIP) [2], which goes beyond saliency and considers the importance of individuals for group affect recognition. The MIP of an image is often the group leaders who can influence the emotion of a group [11, 37, 34]. MIP has been explored in many related works in psychology and affective computing, such as the Affective Transfer Process phenomenon in psychology [2], which indicates that the MIP of an image can influence the group's emotion. We conducted a preliminary experiment based on the CrossVit [5] model to demonstrate the effectiveness of the MIP in group affect. Our architecture uses both the global image and faces as two inputs. As depicted in Table 1, the results demonstrate that using all faces is considerably less effective than using the MIP, and even less effective than randomly selecting three facial images. Additionally, as observed in the feature maps illustrated in Figure 1, the model that employs all faces fails to predict accurately due to its focus on irrelevant background regions or faces. In contrast, the network that utilizes MIP can efficiently focus on relevant facial regions, thereby enhancing prediction accuracy. This is mainly due to the fact that in crowded scenes with many blurry faces, the model trained on all faces exhibits dispersed attention, while the model trained on the MIP region concentrates specifically on the relevant area." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "type": "text", + "content": "Based on the above observations, we present a dual-pathway vision transformer model, the Dual-branch Cross-Patch Attention Transformer (DCAT), including a global branch and a MIP branch. With the dual-pathway, spatial-wise discriminative clues can be discovered both globally and locally in conjunction with self-attention learning. For" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": "the dual-pathway interaction, since there are many interferences in the group, we propose the Cross-Patch Attention (CPA) module. CPA first utilizes the Token Ranking Module to select the important tokens in each path, and then the cross-attention is calculated between the selected query vectors and the entire key-value vectors from the other path. In this way, global and MIP contexts are able to complement and compensate for each other." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 317, + 168, + 527, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 168, + 527, + 180 + ], + "spans": [ + { + "bbox": [ + 317, + 168, + 527, + 180 + ], + "type": "text", + "content": "This paper makes the following main contributions:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 317, + 185, + 545, + 426 + ], + "type": "list", + "angle": 0, + "index": 9, + "blocks": [ + { + "bbox": [ + 317, + 185, + 545, + 233 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 185, + 545, + 233 + ], + "spans": [ + { + "bbox": [ + 317, + 185, + 545, + 233 + ], + "type": "text", + "content": "- In this work, we validate that MIP plays a crucial role in group affect recognition. To the best of our knowledge, this is the first work introducing MIP into the group affect task." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 317, + 240, + 545, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 240, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 317, + 240, + 545, + 323 + ], + "type": "text", + "content": "- The MIP and global affective context information are integrated into the proposed dual-pathway vision transformer architecture for recognizing group emotions in a context-aware manner. We also propose a novel CPA module that focuses on the interactions among diverse scene contexts and facial informative regions." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 331, + 545, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 331, + 545, + 426 + ], + "spans": [ + { + "bbox": [ + 317, + 331, + 545, + 426 + ], + "type": "text", + "content": "- Experimental results show that the proposed DCAT outperforms both state-of-the-art group affect works and vision transformer models in terms of accuracy and model parameters. This is also the first work to explore group affect recognition that goes beyond the CNN-based approach. Moreover, our proposed model can be utilized in other group-level affect tasks, i.e., group cohesion analysis." + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 436, + 394, + 449 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 436, + 394, + 449 + ], + "spans": [ + { + "bbox": [ + 306, + 436, + 394, + 449 + ], + "type": "text", + "content": "2. Related works" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 456, + 486, + 468 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 456, + 486, + 468 + ], + "spans": [ + { + "bbox": [ + 306, + 456, + 486, + 468 + ], + "type": "text", + "content": "2.1. Group affect recognition methods" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 474, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 545, + 653 + ], + "type": "text", + "content": "Current group affect recognition methods primarily analyze the individual members of a group and then assess their contribution to the overall mood of the group by taking into account a variety of cues, such as faces, salient objects, and scenes. Fujii et al. [9] proposed a two-stage classification method, in which the first stage classifies facial expressions, and the second stage adds scene features into consideration to fuse faces and scenes through spectral clustering for further group affect recognition. Khan et al. [22] considered multi-cues, which include all faces, object proposals, and scene information. To achieve such an architecture, additional face detection and object proposal detection detectors are needed. Similarly, Guo et al. [16] also investigated multi-cues using graph neural networks, where the topology of the graph varies as the number of entities varies." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 713 + ], + "type": "text", + "content": "However, in large groups, it is not feasible to consider the expressions of all faces and objects individually before aggregating, resulting in lower efficiency and accuracy. As indicated in [9], considering the performance of the main subject estimation is needed, while our work fills the gap." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "20599" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 254, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 254, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 254, + 85 + ], + "type": "text", + "content": "2.2. Most important person (MIP) detection" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 90, + 141, + 102 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 90, + 141, + 102 + ], + "spans": [ + { + "bbox": [ + 47, + 90, + 141, + 102 + ], + "type": "text", + "content": "2.2.1 MIP detection" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 109, + 289, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 109, + 289, + 337 + ], + "spans": [ + { + "bbox": [ + 46, + 109, + 289, + 337 + ], + "type": "text", + "content": "A MIP detection model understands a high-level pattern in a social event image to identify the most important person. Ramanathan et al. [35] used an RNN to learn time-varying attention weights that can be used for event detection and classification. Without any explicit annotations, the person with the highest attendance can be identified as the MIP. In order to overcome the inherent variability of human poses, PersonRank [27] produced a multiple Hyper-Interaction Graph, which treats each individual person as a node. The most active node can be identified using four types of edge message functions. POINT [26] proposed two types of interaction modules, i.e., the person-person interaction module and the event-person interaction module. It then aggregated relation features and person features to form the important feature. To reduce the annotation effort, Hong et al. [19] formulated a POINT-based iterative learning method for semi-supervised important people detection. Thus, we incorporate people awareness into global-level affect analysis in this work." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 344, + 214, + 357 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 344, + 214, + 357 + ], + "spans": [ + { + "bbox": [ + 47, + 344, + 214, + 357 + ], + "type": "text", + "content": "2.3. Dual attention learning models" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 363, + 287, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 363, + 287, + 517 + ], + "spans": [ + { + "bbox": [ + 46, + 363, + 287, + 517 + ], + "type": "text", + "content": "Visual attention with dual-pathway has been widely used to find important contextual regions. Based on the outstanding performance of vision transformers (ViTs) in various visual tasks [8], there are many self-attention-based dual-pathway networks in recent years. Zhu et al. [49] proposed a global-local cross-attention to reinforce the spatial-wise discriminative clues for fine-grained recognition. A pairwise cross-attention was designed to establish the interactions between image pairs. Dual-ViT [46] incorporated a compressed semantic pathway that served as prior information in learning finer pixel-level details. The semantic pathway and pixel pathway are integrated together and trained to spread enhanced self-attention information in parallel." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 518, + 287, + 625 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 518, + 287, + 625 + ], + "spans": [ + { + "bbox": [ + 46, + 518, + 287, + 625 + ], + "type": "text", + "content": "The most similar architecture to our work is the CrossViT [5], which was proposed to learn multi-scale features effectively. However, we differ from it in two main ways. Firstly, our network divides at different scales using global images and MIP images, whereas CrossViT divides at different scales using the same input image. Another difference is the cross-attention mechanism. The CrossViT exchanges class tokens, while we designed a Cross-Patch Attention module based on attentive queries from both paths." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 637, + 287, + 664 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 637, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 47, + 637, + 287, + 664 + ], + "type": "text", + "content": "3. Proposed Dual-branch Cross-Patch Attention Transformer (DCAT)" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 671, + 115, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 115, + 682 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 115, + 682 + ], + "type": "text", + "content": "3.1. Overview" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "The architecture of our proposed Dual-branch Cross-Patch Attention Transformer (DCAT) for group affect" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "content": "recognition is shown in Figure 2. The model contains two inputs, i.e., the global image and the corresponding MIP image. The two images are tokenized into patches first and sent into a stack of Multi-Scale Transformer Encoder, which consists of dual-path Transformer Encoder, Token Ranking Module, and Cross-Patch Attention (CPA). Specifically, in a dual-path Transformer Encoder, the global image is sent to the coarse-level path to capture long-range information and further refine the encoded tokens for fine-grained details. On the other hand, the MIP image is fed to the fine-level path to obtain high-level semantic tokens. Next, since the global and MIP features are conceptual interdependent, we incorporate dual-path interaction in our model. In particular, we sort tokens according to their importance in each path based on the Token Ranking Module, then calculate the CPA using the key and value vectors from the other path. Finally, the class tokens from two branches are combined and sent into a linear layer for prediction." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 297, + 437, + 311 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 297, + 437, + 311 + ], + "spans": [ + { + "bbox": [ + 306, + 297, + 437, + 311 + ], + "type": "text", + "content": "3.2. Dual-pathway learning" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 316, + 545, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 316, + 545, + 496 + ], + "spans": [ + { + "bbox": [ + 304, + 316, + 545, + 496 + ], + "type": "text", + "content": "To leverage the global information of a group captured by the global image and the local-based semantic prior of the MIP, we propose a dual-pathway feature learning approach for group affect prediction. By integrating self-attention learning into the dual-pathway, our approach enables the discovery of spatial-wise discriminative clues both globally and locally. To validate our assumptions, we compute the CKA similarity [43] to measure the similarity of the intermediate token features in each layer and the final CLS token, follwing [43]. As illustrated in Figure 3, both the MIP and global tokens exhibit a positive correlation with the CLS token as the model depth increases. This suggests that both features are valuable for the final classification task and highlights the rationality and necessity of our dual-pathway input design." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 498, + 545, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 545, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 545, + 640 + ], + "type": "text", + "content": "Firstly, both the global and MIP image are tokenized into patches, then the class token and a learnable position embedding are added to both branches before the MultiScale Transformer Encoder. In order to balance computational costs, our Transformer Encoders in the two pathways include different numbers (i.e., " + }, + { + "bbox": [ + 304, + 498, + 545, + 640 + ], + "type": "inline_equation", + "content": "G = 6" + }, + { + "bbox": [ + 304, + 498, + 545, + 640 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 498, + 545, + 640 + ], + "type": "inline_equation", + "content": "M = 1" + }, + { + "bbox": [ + 304, + 498, + 545, + 640 + ], + "type": "text", + "content": ") inspired by CrossViT [5]. The global branch is the large (primary) branch with a coarse patch size (i.e., 12), with a larger embedding size, and more transformer encoders. The MIP image is the input of a small (complementary) branch with fine-grained patch size (i.e., 16), fewer encoders, and a smaller embedding size." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 712 + ], + "type": "text", + "content": "As the core of the vision transformer, the Multi-Head Self-Attention (MHSA) maps a query vector into a set of key and value vectors [8]. 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" + }, + { + "bbox": [ + 47, + 664, + 288, + 715 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 47, + 664, + 288, + 715 + ], + "type": "text", + "content": " represents the number of heads, " + }, + { + "bbox": [ + 47, + 664, + 288, + 715 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 47, + 664, + 288, + 715 + ], + "type": "text", + "content": " is a transpose operator, " + }, + { + "bbox": [ + 47, + 664, + 288, + 715 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 47, + 664, + 288, + 715 + ], + "type": "text", + "content": " is the di" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 483, + 545, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 483, + 545, + 532 + ], + "spans": [ + { + "bbox": [ + 305, + 483, + 545, + 532 + ], + "type": "text", + "content": "mension of the embedding. " + }, + { + "bbox": [ + 305, + 483, + 545, + 532 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 305, + 483, + 545, + 532 + ], + "type": "text", + "content": " is the number of tokenized patches. The input global and MIP images are divided into different patches numbers with different " + }, + { + "bbox": [ + 305, + 483, + 545, + 532 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 305, + 483, + 545, + 532 + ], + "type": "text", + "content": ". The calculation includes 1 class token in addition to the " + }, + { + "bbox": [ + 305, + 483, + 545, + 532 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 305, + 483, + 545, + 532 + ], + "type": "text", + "content": " tokens." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 546, + 536, + 560 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 546, + 536, + 560 + ], + "spans": [ + { + "bbox": [ + 306, + 546, + 536, + 560 + ], + "type": "text", + "content": "3.3. The interaction of global and MIP pathways" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 567, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 567, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 567, + 545, + 616 + ], + "type": "text", + "content": "Due to the large amount of information in group-level images, extracting features by either global or MIP branch alone is not sufficient, and cross-attention of discriminative tokens from both can provide complementary effects." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 617, + 546, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 546, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 546, + 715 + ], + "type": "text", + "content": "Having obtained global and MIP tokens by the Transformer Encoder, we should consider the dual-path interactions. To achieve this, we propose the Cross-Patch Attention (CPA) mechanism to establish spatial interactions between the global and MIP images. Firstly, we sort the tokens based on their importance in each path using the Token Ranking Module and create a new query matrix by selecting the top " + }, + { + "bbox": [ + 304, + 617, + 546, + 715 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 304, + 617, + 546, + 715 + ], + "type": "text", + "content": " tokens. As depicted in Figure 4, the model's per" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "text", + "content": "20601" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": "formance, taking the MIP branch as an example " + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 46, + 72, + 289, + 204 + ], + "type": "text", + "content": ", is related to the drop ratio, where dropping a certain percentage of tokens can improve performance. Secondly, we compute the Cross-Patch Attention (CPA) using the new query matrix and key-value from the other branch. It is noteworthy that the gradients propagate through both pathways, which allows it to compensate for information loss on global feature compression through global-to-local interaction. As validated in [49], such cross-attention can also be viewed as a novel regularization method to regularize attention learning, especially for our small datasets." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 218, + 181, + 230 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 218, + 181, + 230 + ], + "spans": [ + { + "bbox": [ + 47, + 218, + 181, + 230 + ], + "type": "text", + "content": "3.3.1 Token Ranking Module" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 237, + 287, + 272 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 237, + 287, + 272 + ], + "spans": [ + { + "bbox": [ + 46, + 237, + 287, + 272 + ], + "type": "text", + "content": "For Cross-Patch Attention, we need to remove unimportant contents from the complex group images and keep only the tokens that are relevant." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 274, + 287, + 333 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 274, + 287, + 333 + ], + "spans": [ + { + "bbox": [ + 47, + 274, + 287, + 333 + ], + "type": "text", + "content": "Our first step is to rank the tokens according to their importance. While the class token attention map " + }, + { + "bbox": [ + 47, + 274, + 287, + 333 + ], + "type": "inline_equation", + "content": "A_{cls} \\in \\mathbb{R}^{1 \\times (N + 1)}" + }, + { + "bbox": [ + 47, + 274, + 287, + 333 + ], + "type": "text", + "content": " reflects the importance of features [43, 29], we denote the token importance by the similarity scores between the global class token and each patch token:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 102, + 341, + 287, + 369 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 341, + 287, + 369 + ], + "spans": [ + { + "bbox": [ + 102, + 341, + 287, + 369 + ], + "type": "interline_equation", + "content": "A _ {c l s} = \\operatorname {S o f t m a x} \\left(\\frac {q _ {c l s} * K ^ {T}}{\\sqrt {d}}\\right), \\tag {2}", + "image_path": "665b12d566e40b7a42f40aa2906fe4396f9d96cae53e98f951c68b85d7a629fb.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 377, + 287, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 377, + 287, + 413 + ], + "spans": [ + { + "bbox": [ + 47, + 377, + 287, + 413 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 377, + 287, + 413 + ], + "type": "inline_equation", + "content": "q_{cls} \\in \\mathbb{R}^{1 \\times d}" + }, + { + "bbox": [ + 47, + 377, + 287, + 413 + ], + "type": "text", + "content": " is the query vector of the class token, " + }, + { + "bbox": [ + 47, + 377, + 287, + 413 + ], + "type": "inline_equation", + "content": "K \\in \\mathbb{R}^{(N + 1) \\times d}" + }, + { + "bbox": [ + 47, + 377, + 287, + 413 + ], + "type": "text", + "content": " is the key vector, and " + }, + { + "bbox": [ + 47, + 377, + 287, + 413 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 47, + 377, + 287, + 413 + ], + "type": "text", + "content": " is the dimension of the embedding." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 413, + 287, + 473 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 413, + 287, + 473 + ], + "spans": [ + { + "bbox": [ + 46, + 413, + 287, + 473 + ], + "type": "text", + "content": "According to the equation 2, the weights of each patch correlated with the class token are computed. In such a way, the " + }, + { + "bbox": [ + 46, + 413, + 287, + 473 + ], + "type": "inline_equation", + "content": "A_{cls}" + }, + { + "bbox": [ + 46, + 413, + 287, + 473 + ], + "type": "text", + "content": " reveals how much each patch contributes to the final classification since it captures the global interactions of the class token to all patches." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 487, + 204, + 499 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 487, + 204, + 499 + ], + "spans": [ + { + "bbox": [ + 47, + 487, + 204, + 499 + ], + "type": "text", + "content": "3.3.2 Cross-Patch Attention (CPA)" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 506, + 287, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 506, + 287, + 567 + ], + "spans": [ + { + "bbox": [ + 46, + 506, + 287, + 567 + ], + "type": "text", + "content": "Based on the importance score of each token, we then construct a newly selected query matrix " + }, + { + "bbox": [ + 46, + 506, + 287, + 567 + ], + "type": "inline_equation", + "content": "Q_{sel} \\in \\mathbb{R}^{(\\alpha + 1) \\times d}" + }, + { + "bbox": [ + 46, + 506, + 287, + 567 + ], + "type": "text", + "content": ", representing the attentive local embedding, by selecting the top " + }, + { + "bbox": [ + 46, + 506, + 287, + 567 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 506, + 287, + 567 + ], + "type": "text", + "content": " query vectors that correspond to the top " + }, + { + "bbox": [ + 46, + 506, + 287, + 567 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 506, + 287, + 567 + ], + "type": "text", + "content": " highest responses in the class attention map." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 567, + 287, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 567, + 287, + 590 + ], + "spans": [ + { + "bbox": [ + 46, + 567, + 287, + 590 + ], + "type": "text", + "content": "In each pathway, the Cross-Patch Attention (CPA) vectors is computed as below," + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 74, + 599, + 287, + 625 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 74, + 599, + 287, + 625 + ], + "spans": [ + { + "bbox": [ + 74, + 599, + 287, + 625 + ], + "type": "interline_equation", + "content": "f _ {C P A} (Q, K, V) = \\operatorname {S o f t m a x} \\left(\\frac {Q _ {\\text {s e l}} * K ^ {T}}{\\sqrt {d}}\\right) V, \\tag {3}", + "image_path": "70b4066a4cae62b373ea8e17b93d834058f305f2aafb07f70dcf583a450a6404.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 634, + 287, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 634, + 287, + 659 + ], + "spans": [ + { + "bbox": [ + 46, + 634, + 287, + 659 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 634, + 287, + 659 + ], + "type": "inline_equation", + "content": "K\\in \\mathbb{R}^{(N + 1)\\times d}" + }, + { + "bbox": [ + 46, + 634, + 287, + 659 + ], + "type": "text", + "content": " is the key vector, " + }, + { + "bbox": [ + 46, + 634, + 287, + 659 + ], + "type": "inline_equation", + "content": "V\\in \\mathbb{R}^{(N + 1)\\times d}" + }, + { + "bbox": [ + 46, + 634, + 287, + 659 + ], + "type": "text", + "content": " is the value vector and " + }, + { + "bbox": [ + 46, + 634, + 287, + 659 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 634, + 287, + 659 + ], + "type": "text", + "content": " is the dimension of the embedding." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 659, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 659, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 659, + 287, + 696 + ], + "type": "text", + "content": "As shown in Figure 2c, the CPA operation is bidirectional, with each of the two branches providing the selected tokens as the query vector. Both branches are fused together" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 72, + 545, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 545, + 95 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 306, + 72, + 545, + 95 + ], + "type": "text", + "content": " times, which means the selected queries are updated in each CPA." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 96, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 96, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 305, + 96, + 545, + 144 + ], + "type": "text", + "content": "Finally, after repeating " + }, + { + "bbox": [ + 305, + 96, + 545, + 144 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 305, + 96, + 545, + 144 + ], + "type": "text", + "content": " Multi-Scale Transformer Encoder, the class tokens from two branches are combined and sent into a linear layer for prediction. The cross-entropy loss is used here for final classification [5, 8]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 155, + 388, + 168 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 155, + 388, + 168 + ], + "spans": [ + { + "bbox": [ + 306, + 155, + 388, + 168 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 175, + 422, + 187 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 175, + 422, + 187 + ], + "spans": [ + { + "bbox": [ + 306, + 175, + 422, + 187 + ], + "type": "text", + "content": "4.1. Implemental details" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "type": "text", + "content": "Our model is partly pre-trained with the weight of CrossViT [5] on ImageNet. We train all our models for 300 epochs (30 warm-up epochs) on 2 GPUs (RTX 3090 Ti) with a batch size of 64. The numbers of Transformer Encoder in the dual path, CPA, and Multi-Scale Transformer Encoder are set as " + }, + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "type": "inline_equation", + "content": "M = 1" + }, + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "type": "inline_equation", + "content": "G = 6" + }, + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "type": "inline_equation", + "content": "C = 3" + }, + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "type": "inline_equation", + "content": "L = 1" + }, + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "type": "text", + "content": ". For the token selection ratios " + }, + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 305, + 193, + 545, + 300 + ], + "type": "text", + "content": " of (global, MIP), we use (0.5, 0.5) for GAF 3.0 and (1, 0.5) for GroupEmoW throughout the paper. More details can be found in our supplementary materials." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 308, + 368, + 319 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 308, + 368, + 319 + ], + "spans": [ + { + "bbox": [ + 306, + 308, + 368, + 319 + ], + "type": "text", + "content": "4.2. Datasets" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 327, + 545, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 327, + 545, + 495 + ], + "spans": [ + { + "bbox": [ + 305, + 327, + 545, + 495 + ], + "type": "text", + "content": "In this paper, we utilize several datasets for our experiments, including GroupEmoW [16], GAF 3.0 [13], GAF Cohesion [13, 15], and HECO [44], as presented in Table 2. The GroupEmoW dataset contains images obtained from the web via search engines, using keywords related to various social events such as funerals, birthdays, protests, conferences, and meetings. GAF 3.0 [13] and GAF Cohesion [13, 15] datasets were created through web crawling using a diverse set of keywords related to social events, including world cup winners, weddings, family gatherings, laughing clubs, birthday celebrations, siblings, riots, protests, and violence. The cohesion scores in GAF Cohesion range from strongly agree, agree, disagree to strongly disagree, using a 0-3 scale." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 495, + 545, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 495, + 545, + 590 + ], + "spans": [ + { + "bbox": [ + 305, + 495, + 545, + 590 + ], + "type": "text", + "content": "In our experiments, we utilized the MIP ground truth provided by HECO [44]. However, the ground truth for GAF 3.0 and GroupEmoW was not available. However, since the ground truth for GAF 3.0 and GroupEmoW was not available, we employed the pre-trained POINT model [26] to generate the MIP. The POINT model was trained on the Multi-scene Important People Image Dataset (MS Dataset).3." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 597, + 545, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 597, + 545, + 621 + ], + "spans": [ + { + "bbox": [ + 306, + 597, + 545, + 621 + ], + "type": "text", + "content": "4.3. Comparison with state-of-the-art group affect methods and ViTs" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 628, + 545, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 628, + 545, + 676 + ], + "spans": [ + { + "bbox": [ + 305, + 628, + 545, + 676 + ], + "type": "text", + "content": "In this work, we have built our proposed modules based on CrossViT [5] with vanilla Transformer Encoders [8], which denotes by DCAT-ViT. In addition, since there is a series of ViTs without the class token, e.g., Swin [31] and" + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 58, + 702, + 205, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 205, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 205, + 712 + ], + "type": "text", + "content": "2The global branch exhibits similar behavior." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 683, + 545, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 683, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 683, + 545, + 713 + ], + "type": "text", + "content": "3To evaluate the effectiveness of the pre-trained POINT model, we labeled the MIP on the GAF 3.0 and GroupEmoW datasets, and further details can be found in the supplementary material." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "20602" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 545, + 144 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 545, + 144 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 545, + 144 + ], + "type": "table", + "html": "
DatasetLabelTrain/Val/TestScenarioEvaluation metric
GroupEmoW [13]Neutral, Positive, Negative11,127/3,178/1,589Specific social eventsAcc
GAF 3.0 [13, 15]Neutral, Positive, Negative9,815/4,349/3011Specific social eventsAcc
HECO [44]Surprise, Excitement, Happiness, Peace, Disgust, Anger, Fear, and Sadness6,570/1,877/938In-the-wild images that do not limit scenesmAP
GAF Cohesion [13, 15]0-39,815/4,349/3011Specific social eventsMSE
", + "image_path": "35e7517c0475054e767fcdb2ca7695acaf06e88d03c8be317365d0b030012ec6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 52, + 196, + 282, + 356 + ], + "blocks": [ + { + "bbox": [ + 52, + 196, + 282, + 356 + ], + "lines": [ + { + "bbox": [ + 52, + 196, + 282, + 356 + ], + "spans": [ + { + "bbox": [ + 52, + 196, + 282, + 356 + ], + "type": "image", + "image_path": "f76662dc063f1e59ff4afeb130958930b1def33f11024e80663eaf0826c31fe6.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 360, + 288, + 393 + ], + "lines": [ + { + "bbox": [ + 46, + 360, + 288, + 393 + ], + "spans": [ + { + "bbox": [ + 46, + 360, + 288, + 393 + ], + "type": "text", + "content": "Figure 5. Model parameter and accuracy trade-off comparison on the GAF 3.0 dataset. Our proposed models are highlighted by the blue rectangular box." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 414, + 287, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 414, + 287, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 414, + 287, + 460 + ], + "type": "text", + "content": "CSwin [7]. In order to prove the generality of our approach, we have added the proposed dual-pathway and CPA module to the CSwin transformer [7], which is denoted by DCAT-CSwin-L." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 462, + 287, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 462, + 287, + 581 + ], + "spans": [ + { + "bbox": [ + 46, + 462, + 287, + 581 + ], + "type": "text", + "content": "A comparison of the proposed model with the state-of-the-art group affect approaches on GAF 3.0 and GroupEmoW datasets can be found in Figure 5 and Table 3, respectively. Since our proposed DCAT model is based on a vision transformer, we also compare it with recent vision transformer models, such as multiscale-based (CrossViT [5], Focal-B [45], RegionViT-B [4], TCFormaler-L [47]), CNN-transformer hybrid-based (Conformer-L [32]), and lightweight-based models (EvoLeViT [43], DynamicSwin-T [36], DVT [40])." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 582, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 714 + ], + "type": "text", + "content": "Comparing with state-of-the-art group affect methods. Our DCAT-ViT and DCAT-CSwin-L achieve the best results compared to other group affect recognition methods on the GAF 3.0 dataset. Specifically, our DCAT-ViT achieves " + }, + { + "bbox": [ + 46, + 582, + 288, + 714 + ], + "type": "inline_equation", + "content": "77.29\\%" + }, + { + "bbox": [ + 46, + 582, + 288, + 714 + ], + "type": "text", + "content": " accuracy with only 26.70M parameters, which is only about " + }, + { + "bbox": [ + 46, + 582, + 288, + 714 + ], + "type": "inline_equation", + "content": "7.6\\%" + }, + { + "bbox": [ + 46, + 582, + 288, + 714 + ], + "type": "text", + "content": " of TMM [9], while our DCAT-CSwin-L with a larger number of parameters (358M) achieves " + }, + { + "bbox": [ + 46, + 582, + 288, + 714 + ], + "type": "inline_equation", + "content": "79.20\\%" + }, + { + "bbox": [ + 46, + 582, + 288, + 714 + ], + "type": "text", + "content": " accuracy. On the GroupEmoW dataset, our DCAT-CSwin-L also achieves the best performance compared to other methods. It is worth noting that our proposed method only needs the global image and corre" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 307, + 190, + 555, + 537 + ], + "blocks": [ + { + "bbox": [ + 77, + 152, + 515, + 163 + ], + "lines": [ + { + "bbox": [ + 77, + 152, + 515, + 163 + ], + "spans": [ + { + "bbox": [ + 77, + 152, + 515, + 163 + ], + "type": "text", + "content": "Table 2. Datasets details used in this paper (Acc = Accuracy, mAP = mean average precision, MSE = mean square error)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 190, + 555, + 537 + ], + "lines": [ + { + "bbox": [ + 307, + 190, + 555, + 537 + ], + "spans": [ + { + "bbox": [ + 307, + 190, + 555, + 537 + ], + "type": "table", + "html": "
MethodsAcc (%)Source
Group affect methods
ResNet34 [18]68.13Global, Faces
SE-ResNet-50 [20]69.79Global
Efficientnet-b2 [38]72.33Global, Faces
CAER-Net [25]80.61Global, Faces
GNN [16]82.38Global
GNN [16]84.62Global, Faces, Objects
ConGNN [41]85.59Global, Faces, Objects
WACV 21 [22]89.36Global, Faces
GNN [16]89.93Global, Faces
WACV 21 [22]90.18Global, Faces, Objects
Vision transformers
ViT [8]87.50Global
P2T-base [42]86.50Global
DeepViT [48]83.90Global
Conformer-L [32]83.35Global
Focal-B [45]87.98Global
CrossViT [5]88.48Global
TransFG [17]89.47Global
RegionViT-B [4]89.49Global
CSwin-L [7]89.90Global
DVT [40]87.90Global
Evo-LeViT [43]87.83Global
TCFormer-L [47]89.24Global
DCAT-ViT89.55Global, MIP
DCAT-CSwin-L90.47Global, MIP
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MethodmAP (%)
GCNs [23]48.84
Depth [28]49.02
OpenFace [1]+OpenPose [3]50.28
R-FCN [6]+HOI-Net [30]50.34
HECO [44]50.24
DCAT-ViT53.49
DCAT-CSwin-L58.06
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The scalability of our method" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 304, + 287, + 375 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 287, + 375 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 287, + 375 + ], + "type": "text", + "content": "Our proposed architecture can be adapted to accommodate the concept of a primary agent, similar to the idea of MIP, which was introduced by HECO [44]. Specifically, we can modify the input to the MIP branch from the MIP image to the primary agent while keeping the global branch unchanged." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 376, + 288, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 376, + 288, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 376, + 288, + 616 + ], + "type": "text", + "content": "Due to the wide variety of human-object interactions (HOIs) in natural scenes and the fact that interactions of agents' actions with objects can induce emotional arousal of the primary agent in the scene, a useful approach for emotion recognition in images is to detect HOIs. In previous approaches [44, 25], multiple contexts, such as regions of interest (ROIs) and HOIs of all objects, were considered. Our proposed method outperforms previous approaches, as shown in Table 4. Our proposed method achieved superior performance on the dataset, which may be attributed to the wide variety of HOI categories in various challenging scenarios. Previous methods relied on pre-trained HOI models that were limited by predefined interaction categories. In contrast, our Cross-Patch Attention (CPA) module leverages the ability to learn HOI interactions directly from the data, allowing for greater flexibility and adaptability in recognizing new and diverse HOI categories. Moreover, our dual-pathway architecture significantly simplifies the computational process, eliminating the need for a heuristic selection of affective regions." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 623, + 287, + 636 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 287, + 636 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 287, + 636 + ], + "type": "text", + "content": "4.5. Transfer learning for group cohesion estimation" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 714 + ], + "type": "text", + "content": "Group cohesion is an affective phenomenon and a measure of agreement between members. Since cohesion and emotion (or valence) are intertwined in social science and affective computing, our DCAT for group valence prediction can be extended to group cohesion estimation. In this work, we finetune our model pre-trained on GroupEmoW" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 331, + 75, + 525, + 245 + ], + "blocks": [ + { + "bbox": [ + 331, + 75, + 525, + 245 + ], + "lines": [ + { + "bbox": [ + 331, + 75, + 525, + 245 + ], + "spans": [ + { + "bbox": [ + 331, + 75, + 525, + 245 + ], + "type": "image", + "image_path": "9490b2888e40456708c3f3c49a87e752d1eae4f48cab7b4cdbe84def2304ea1d.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 251, + 545, + 274 + ], + "lines": [ + { + "bbox": [ + 306, + 251, + 545, + 274 + ], + "spans": [ + { + "bbox": [ + 306, + 251, + 545, + 274 + ], + "type": "text", + "content": "Figure 6. Group cohesion score comparison in the GAF Cohesion dataset (MSE is the evaluation metric, the lower the better)." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 326, + 284, + 526, + 396 + ], + "blocks": [ + { + "bbox": [ + 94, + 174, + 240, + 184 + ], + "lines": [ + { + "bbox": [ + 94, + 174, + 240, + 184 + ], + "spans": [ + { + "bbox": [ + 94, + 174, + 240, + 184 + ], + "type": "text", + "content": "Table 4. Comparison on HECO dataset." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 326, + 284, + 526, + 396 + ], + "lines": [ + { + "bbox": [ + 326, + 284, + 526, + 396 + ], + "spans": [ + { + "bbox": [ + 326, + 284, + 526, + 396 + ], + "type": "table", + "html": "
ModuleGAF 3.0GroupEmoW
CrossVit75.5688.48
CrossVit+A75.7988.86
CrossVit+A+B76.2188.96
CrossVit+A+B+C77.2989.55
CSwin-L78.0989.90
CSwin-L+A78.9390.12
CSwin-L+A+B79.2090.47
", + "image_path": "4bfb5f0deb6ae30d071867c16e57b02200744a8804708317faadd16a10c01dd9.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 406, + 547, + 461 + ], + "lines": [ + { + "bbox": [ + 305, + 406, + 547, + 461 + ], + "spans": [ + { + "bbox": [ + 305, + 406, + 547, + 461 + ], + "type": "text", + "content": "Table 5. The accuracy (\\%) of each proposed module. " + }, + { + "bbox": [ + 305, + 406, + 547, + 461 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 305, + 406, + 547, + 461 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 406, + 547, + 461 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 305, + 406, + 547, + 461 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 406, + 547, + 461 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 305, + 406, + 547, + 461 + ], + "type": "text", + "content": " represent dual-pathway input, CPA module, and Token Ranking Module, respectively. The downsampling operation in each stage of the CSWin-L can be regarded as a token selection mechanism, so the Token Ranking Module is not included in it." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 492, + 545, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 492, + 545, + 564 + ], + "spans": [ + { + "bbox": [ + 305, + 492, + 545, + 564 + ], + "type": "text", + "content": "for the GAF Cohesion dataset. The results in Figure 6 assure that our models still have good generalization ability rather than only fit to group affect datasets compared to other group affect recognition methods, e.g., EmoticW [13], ICMAI2020 [50], AIST2020 [10], as well as the ViTs, i.e., ViT [8], CSwin [7], Swin transformer [31]." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 574, + 398, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 574, + 398, + 586 + ], + "spans": [ + { + "bbox": [ + 306, + 574, + 398, + 586 + ], + "type": "text", + "content": "4.6. Ablation study" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 593, + 545, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 593, + 545, + 651 + ], + "spans": [ + { + "bbox": [ + 305, + 593, + 545, + 651 + ], + "type": "text", + "content": "The effectiveness of each module. The effectiveness of each module proposed in our work, i.e., dual-pathway input, CPA module, Token Ranking Module, is shown in Table 5. For both the DCAT-ViT and DCAT-CSwin-L, each of the modules contributes to our overall results." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 652, + 545, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 652, + 545, + 700 + ], + "spans": [ + { + "bbox": [ + 305, + 652, + 545, + 700 + ], + "type": "text", + "content": "The effectiveness of dual-input. Hence, we should also dynamically consider the global affective context while learning group affect, as validated in Table 6, where MIP and global inputs together perform better than either alone." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 318, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 318, + 701, + 545, + 714 + ], + "type": "text", + "content": "Cross-Cls-Attention (CCA) vs Our proposed Cross" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "20604" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 76, + 70, + 259, + 131 + ], + "blocks": [ + { + "bbox": [ + 76, + 70, + 259, + 131 + ], + "lines": [ + { + "bbox": [ + 76, + 70, + 259, + 131 + ], + "spans": [ + { + "bbox": [ + 76, + 70, + 259, + 131 + ], + "type": "table", + "html": "
InputGAF 3.0GroupEmoW
Only MIP68.0280.08
Only global75.5688.48
MIP + global77.2989.55
", + "image_path": "90412426a6874767e95c8178adda84f7ac0471a7dad53cf20a805ab9254e49e0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 92, + 183, + 240, + 232 + ], + "blocks": [ + { + "bbox": [ + 47, + 141, + 287, + 163 + ], + "lines": [ + { + "bbox": [ + 47, + 141, + 287, + 163 + ], + "spans": [ + { + "bbox": [ + 47, + 141, + 287, + 163 + ], + "type": "text", + "content": "Table 6. Effectiveness of dual-input on GAF 3.0 [14] and GroupE-moW [22] dataset (evaluation metric is ACC " + }, + { + "bbox": [ + 47, + 141, + 287, + 163 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 47, + 141, + 287, + 163 + ], + "type": "text", + "content": ")." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 92, + 183, + 240, + 232 + ], + "lines": [ + { + "bbox": [ + 92, + 183, + 240, + 232 + ], + "spans": [ + { + "bbox": [ + 92, + 183, + 240, + 232 + ], + "type": "table", + "html": "
GAF 3.0GroupEmoW
CCA75.41%87.86%
CPA77.29%89.55%
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Comparison between the CCA and our proposed CPA (using the DCAT-ViT) on GAF 3.0 and GroupEmoW dataset." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 63, + 270, + 128, + 335 + ], + "blocks": [ + { + "bbox": [ + 63, + 270, + 128, + 335 + ], + "lines": [ + { + "bbox": [ + 63, + 270, + 128, + 335 + ], + "spans": [ + { + "bbox": [ + 63, + 270, + 128, + 335 + ], + "type": "image", + "image_path": "41e676e8d6c448e4d023b99a34636ddc8f42bceda07fc1136e477784ca615045.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 133, + 270, + 199, + 335 + ], + "blocks": [ + { + "bbox": [ + 133, + 270, + 199, + 335 + ], + "lines": [ + { + "bbox": [ + 133, + 270, + 199, + 335 + ], + "spans": [ + { + "bbox": [ + 133, + 270, + 199, + 335 + ], + "type": "image", + "image_path": "319584c7d8ec1289cd03619853c4a7c05ec6fc7e0cc866177c276524e01d9885.jpg" + } + ] + } + ], + 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"content": "(c) CPA" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 47, + 497, + 279, + 509 + ], + "lines": [ + { + "bbox": [ + 47, + 497, + 279, + 509 + ], + "spans": [ + { + "bbox": [ + 47, + 497, + 279, + 509 + ], + "type": "text", + "content": "Figure 7. The visualization of the interaction of global and MIP." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 529, + 287, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 529, + 287, + 648 + ], + "spans": [ + { + "bbox": [ + 46, + 529, + 287, + 648 + ], + "type": "text", + "content": "Patch-Attention (CPA). It is worth comparing between Cross-Cls-Attention (CCA) proposed in CrossViT [5] and our proposed CPA (as provided in Table 7). The CCA only exchanges the class token in the cross-attention mechanism, which limits its ability to capture global interactions between class tokens and patches in each branch. In complex scenarios, such as those encountered in group affect recognition, our proposed CPA approach is more effective for modeling the interdependencies between global and MIP features." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 47, + 658, + 287, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 658, + 287, + 683 + ], + "spans": [ + { + "bbox": [ + 47, + 658, + 287, + 683 + ], + "type": "text", + "content": "4.7. Visualization of the interaction of global and MIP pathways" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "The interaction of the global and MIP pathways, including token dropping and CPA, is demonstrated in Fig-" + } + ] + } + ], + "index": 19 + }, + { + "type": "image", + "bbox": [ + 310, + 73, + 540, + 221 + ], + "blocks": [ + { + "bbox": [ + 310, + 73, + 540, + 221 + ], + "lines": [ + { + "bbox": [ + 310, + 73, + 540, + 221 + ], + "spans": [ + { + "bbox": [ + 310, + 73, + 540, + 221 + ], + "type": "image", + "image_path": "00c700bd09a232b104e3d403a533f41280789f4d38bdd5bc1b9ae25236dcc4e4.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 222, + 545, + 255 + ], + "lines": [ + { + "bbox": [ + 305, + 222, + 545, + 255 + ], + "spans": [ + { + "bbox": [ + 305, + 222, + 545, + 255 + ], + "type": "text", + "content": "Figure 8. The performance of average face quality, using all faces and using the MIP under different face count intervals in the image. The GroupEmoW dataset is used here." + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_caption" + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 279, + 545, + 362 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 279, + 545, + 362 + ], + "spans": [ + { + "bbox": [ + 305, + 279, + 545, + 362 + ], + "type": "text", + "content": "ure 7. As depicted in column (b), irrelevant background and other facial details are eliminated, while the MIP region and significant background regions (such as banners in protest scenes) are preserved for cross-patch attention. This demonstrates the effectiveness of our MIP-global interaction and highlights its efficacy in capturing discriminative information." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 306, + 378, + 545, + 403 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 378, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 306, + 378, + 545, + 403 + ], + "type": "text", + "content": "4.8. Case study: the relationship between group size and performance" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 411, + 546, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 411, + 546, + 687 + ], + "spans": [ + { + "bbox": [ + 304, + 411, + 546, + 687 + ], + "type": "text", + "content": "Previous studies have suggested that distinguishing between the negative and neutral categories in a group can be challenging [9]. In this paper, we present new insights into this issue. We first analyze the number of individuals in each image and find that as the number of individuals increases, the average quality of their facial features decreases " + }, + { + "bbox": [ + 304, + 411, + 546, + 687 + ], + "type": "inline_equation", + "content": "^{4}" + }, + { + "bbox": [ + 304, + 411, + 546, + 687 + ], + "type": "text", + "content": ", as illustrated in Figure 8. This indicates that facial details become increasingly blurred and difficult to extract, posing a significant challenge, particularly when trying to distinguish between negative and neutral categories, which are inherently difficult to distinguish. In contrast to previous works that typically average features across all detected faces [9], our approach selectively focuses on the most informative facial region, i.e., the MIP, and outperforms models that utilize all faces in images with larger populations. This approach avoids interference from low-quality faces and effectively interacts between the features of the MIP and those of the entire global image through our proposed CPA module, enhancing the accuracy of our results. Therefore, our approach yields higher accuracy for distinguishing between the negative and neutral categories compared to previous methods. The exact numerical results can be found in the supplementary material." + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 316, + 702, + 449, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 702, + 449, + 713 + ], + "spans": [ + { + "bbox": [ + 316, + 702, + 449, + 713 + ], + "type": "text", + "content": "4We quantify face quality based on [39]." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "20605" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 49, + 71, + 124, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 71, + 124, + 84 + ], + "spans": [ + { + "bbox": [ + 49, + 71, + 124, + 84 + ], + "type": "text", + "content": "5. Conclusions" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 49, + 91, + 286, + 233 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 91, + 286, + 233 + ], + "spans": [ + { + "bbox": [ + 49, + 91, + 286, + 233 + ], + "type": "text", + "content": "In this work, by incorporating the MIP concept, we propose a dual-pathway vision transformer model, the Dual-branch Cross-Patch Attention Transformer (DCAT) for group affect recognition. Moreover, we propose the CPA module so that the important tokens from both paths can be interacted with. In terms of accuracy and parameters, the proposed DCAT outperforms both state-of-the-art group affect models and vision transformer models. It is also the first study to explore group affect recognition beyond CNNs. Moreover, our proposed model can be utilized in other group-level affect tasks, i.e., group cohesion analysis." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 49, + 245, + 144, + 258 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 245, + 144, + 258 + ], + "spans": [ + { + "bbox": [ + 49, + 245, + 144, + 258 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 49, + 266, + 286, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 266, + 286, + 312 + ], + "spans": [ + { + "bbox": [ + 49, + 266, + 286, + 312 + ], + "type": "text", + "content": "This work was supported in part by the National Science and Technology Council of Taiwan under Grants NSTC-109-2223-E-002-005-MY3, NSTC-112-2628-E-002-033-MY4 and NSTC-112-2634-F-002-002-MBK." + } + ] + } + ], + "index": 3 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 750, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 750, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 750, + 317, + 757 + ], + "type": "text", + "content": "20606" + } + ] + } + ], + "index": 4 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Tadas Baltrusaitis, Peter Robinson, and Louis-Philippe Morency. 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In Proceedings of the 2020 5th International Conference on Mathematics and Artificial Intelligence, pages 24–28, 2020. 7" + } + ] + } + ], + "index": 24 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "type": "text", + "content": "20608" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Motion-Guided Masking for Spatiotemporal Representation Learning/381ddc28-834d-4797-9d76-2bf9c96fea0c_content_list.json b/2023/Motion-Guided Masking for Spatiotemporal Representation Learning/381ddc28-834d-4797-9d76-2bf9c96fea0c_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..9aa9520daf6f5c1a4eb12872eadd5eba06931326 --- /dev/null +++ b/2023/Motion-Guided Masking for Spatiotemporal Representation Learning/381ddc28-834d-4797-9d76-2bf9c96fea0c_content_list.json @@ -0,0 +1,1909 @@ +[ + { + "type": "text", + "text": "Motion-Guided Masking for Spatiotemporal Representation Learning", + "text_level": 1, + "bbox": [ + 130, + 130, + 839, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "David Fan1 Jue Wang1 Shuai Liao2 Yi Zhu3 Vimal Bhat1 Hector Santos-Villalobos1 Rohith MV1 Xinyu Li1 \n1 Amazon Prime Video 2 Amazon Fulfillment Technology 3 AWS AI Labs {fandavi, juewangn, uliaoshu, yzaws, vimalb, hsantosv, kurohith, xxnl}@amazon.com", + "bbox": [ + 127, + 178, + 844, + 252 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 313, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Several recent works have directly extended the image masked autoencoder (MAE) with random masking into video domain, achieving promising results. However, unlike images, both spatial and temporal information are important for video understanding. This suggests that the random masking strategy that is inherited from the image MAE is less effective for video MAE. This motivates the design of a novel masking algorithm that can more efficiently make use of video saliency. Specifically, we propose a motion-guided masking algorithm (MGM) which leverages motion vectors to guide the position of each mask over time. Crucially, these motion-based correspondences can be directly obtained from information stored in the compressed format of the video, which makes our method efficient and scalable. On two challenging large-scale video benchmarks (Kinetics-400 and Something-Something V2), we equip video MAE with our MGM and achieve up to $+1.3\\%$ improvement compared to previous state-of-the-art methods. Additionally, our MGM achieves equivalent performance to previous video MAE using up to $66\\%$ fewer training epochs. Lastly, we show that MGM generalizes better to downstream transfer learning and domain adaptation tasks on the UCF101, HMDB51, and Diving48 datasets, achieving up to $+4.9\\%$ improvement compared to baseline methods.", + "bbox": [ + 75, + 316, + 473, + 680 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 709, + 209, + 724 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Video transformers [1, 24, 25, 28, 43] have achieved state-of-the-art for a variety of video understanding tasks, mirroring the success of image transformers such as ViT [9]. However, many video transformers heavily rely on large-scale supervised pretraining from image datasets such as ImageNet21K [8] and JFT-300M [35], which is data-inefficient.", + "bbox": [ + 75, + 733, + 470, + 824 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Self-supervised learning (SSL) [5, 15, 17, 29, 42] is one promising paradigm for eliminating the dependency on large-scale supervised pretraining. The denoising / masked autoencoder (MAE) [41], which was originally popularized by BERT [20] for natural language modeling, has recently re", + "bbox": [ + 75, + 824, + 472, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b3e603fe4ab31aa6b677ca87eadc678ae9e632aab57f84455c4a608844429c8e.jpg", + "image_caption": [ + "Figure 1: Top-1 accuracy on Something-Something V2. Our proposed MGM outperforms all previous masked-video methods (M³Video [36], MAM² [33], BEVT [45], OmniMAE [13], MotionMAE [50], and VideoMAE [39]) with improved training efficiency. Marker shape denotes reconstruction target." + ], + "image_footnote": [], + "bbox": [ + 509, + 291, + 895, + 467 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "emerged as a promising representation learning method for vision tasks. Image MAE [2, 16] has achieved state-of-the-art in image domain via learning to reconstruct randomly masked image patches. Recently, similar works [11, 39] that reconstruct randomly masked video have obtained encouraging results in video domain. However, few SSL works focus on effectively learning video saliency. In this paper, we improve upon the previous video MAEs [11, 39] via video saliency.", + "bbox": [ + 496, + 593, + 893, + 731 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We argue that the random masking strategy which is inherited from image MAE is not optimal for video. The optimal random masking ratio for video MAE [11, 39] is higher than that for image MAE [16] (0.9 vs. 0.75). This can be understood as a consequence of the natural temporal coherence within videos, which leads to the existence of similar video patches in other frames. When using random masking, many of these correlated video patches may be visible to the encoder which would make reconstruction easier. This necessitates the use of a high masking ratio in order to reduce redundancy and make the reconstruction task", + "bbox": [ + 496, + 734, + 895, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "5619", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "sufficiently challenging [11]. However, increasing the masking ratio has the side-effect of leaving fewer visible patches for the MAE encoder to learn spatiotemporal saliency from, which we hypothesize limits the learned representation.", + "bbox": [ + 75, + 90, + 470, + 151 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We thus propose to guide the model to learn to reconstruct the most salient regions of video. As humans and objects are key to understanding video, one natural idea is to track the bounding boxes in each video frame and mask the content within. This is also consistent with the observation that video pixels evolve continuously frame-by-frame, and therefore, the MAE should be able to reconstruct this spatiotemporal continuity. However, generating bounding boxes for each frame is impractical for large-scale video datasets.", + "bbox": [ + 75, + 152, + 468, + 286 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To this end, we hypothesize that motion is an effective guide for detecting spatiotemporal saliency. To test this hypothesis, we define the saliency score as $r_{bbox} / r_{non\\_bbox}$ , or the ratio of average motion magnitude within bounding boxes to average motion magnitude outside bounding boxes. The saliency score is 1.47 for Something-Something v2 [14] and 1.28 for Kinetics-400 [19] respectively, suggesting that regions of higher motion overlap with spatially salient regions more often than regions of lesser motion.", + "bbox": [ + 75, + 287, + 470, + 421 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We thus propose an improved masking algorithm, MGM, which uses motion to continuously guide the mask to cover the most salient spatiotemporal regions. MGM obtains cheap motion correspondence by exploiting the H.264 codec [30] which prevails in popular video formats such as MP4. During the encoding phase of H.264, motion vectors are precomputed and stored as part of the codec. Thus during the decoding phase, motion vectors can be obtained \"for free\" along with RGB frames. The use of readily available motion vectors instead of expensive optical flow enables us to efficiently achieve scale. While some supervised works have used motion vectors [21, 43, 47], we are the first to use motion vectors for MAE pretraining.", + "bbox": [ + 75, + 422, + 470, + 619 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our MGM outperforms previous VideoMAE [39] by $1.2\\%$ on Something-Something V2 (SSv2) [14] and $0.2\\%$ on Kinetics-400 (K400) [19], demonstrating that our MGM is effective. MGM can also achieve the same performance as [39] with $50\\%$ fewer training epochs as shown in Fig. 1, further making MAE pretraining more data-efficient. We also show that MGM generalizes well to small datasets (UCF101 [34], HMDB51 [22], and Diving48 [23]) in both full finetune and linear probe evaluation as well as domain adaptation settings with up to $4.9\\%$ performance improvement over VideoMAE [39]. This shows that the features learned by MGM contain richer semantics that transfer well to video recognition tasks. In summary, our contributions are:", + "bbox": [ + 75, + 619, + 470, + 815 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. MGM, an efficient and effective self-supervised algorithm for 3D masking that continuously models motion trajectories.", + "2. Applying motion vectors which are directly available during video decoding - unlike optical flow - to provide" + ], + "bbox": [ + 88, + 824, + 470, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "efficient motion guidance in the MAE framework.", + "bbox": [ + 532, + 90, + 862, + 104 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. New state-of-the-art or comparable results on two large-scale datasets and various downstream tasks on three small datasets, as well as detailed ablations and insights.", + "bbox": [ + 511, + 106, + 893, + 151 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works", + "text_level": 1, + "bbox": [ + 500, + 186, + 650, + 204 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Image Masked Auto-Encoders. iGPT [4] was one of the first recent attempts to revisit masked image modeling using Transformer architecture rather than CNNs. iGPT reconstructs at the pixel-level. Other recent works try different reconstruction targets. Some works such as BEIT [2] explore using tokenization as a prediction target, such as tokens from pretrained dVAE [40]. MaskFeat [46] explores using HoG features [7] as a reconstruction target. ImageMAE [16] reconstructs normalized image patches and focuses on studying decoder design, discovering that larger decoders enable the encoder to process only visible patches, thus enabling the use of a larger masking ratio to achieve both better performance and computational efficiency. Unlike these works, our MGM is designed specifically for video.", + "bbox": [ + 496, + 220, + 893, + 431 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Video Masked Auto-Encoders. Some works such as VIM-PAC [37] and BEVT [45] try to reconstruct video tokens and thus require strong tokenizers using either extra pretraining data or domain-specific knowledge. VideoMAE [11, 39] bypasses this requirement by applying image MAE [16] to reconstruct 3D RGB video patches, achieving promising results on video benchmarks. Other works such as Omni-MAE [13] use both image and video masked modeling to achieve improved performance on both image and video tasks. A line of very recent work tries to improve Video-MAE by designing explicit motion cues by reconstructing optical flow or frame difference based targets [33, 36, 50].", + "bbox": [ + 496, + 439, + 895, + 621 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "These existing video MAE works all inherit random masking from image MAE [16] where the mask is either discontinuous such as in ST-MAE [11] or random tubes such as in VideoMAE [39]. In the former, the mask is randomly distributed both spatially and temporally, and in the latter, the mask is randomly distributed spatially but temporally static. In contrast, we re-examine this assumption and design a new masking algorithm that continuously masks out video motion to force the model to focus on spatiotemporal saliency. We make no changes to the reconstruction target nor model architecture.", + "bbox": [ + 496, + 628, + 893, + 794 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "VideoMAE [39] initially generates a random mask and statically propagates the mask across time. The position of the mask is the same across frames, forming small tubelets which are spatially discontinuous but temporally continuous.", + "bbox": [ + 496, + 801, + 893, + 864 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "ST-MAE [11] independently generates a random mask per-frame which is neither spatially nor temporally continuous.", + "bbox": [ + 496, + 869, + 893, + 901 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "5620", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/82b59bdefe45fd4587f4cd861c8dd2684faf944ff8dc86bb9bc50df929d52e28.jpg", + "image_caption": [ + "Figure 2: An overview of a) the proof-of-concept simulated-motion masking (SMM) vs. b) motion-guided masking (MGM). Our MGM produces 3D masks that achieves both spatial and temporal continuity, while capturing the true motion information in the video. Random masking (left-most) is both spatially and temporally discontinuous." + ], + "image_footnote": [], + "bbox": [ + 81, + 89, + 883, + 280 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 76, + 361, + 212, + 380 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As detailed in Sec. 1, motion is concentrated in salient video regions. Random masking does not effectively cover these regions because motion is not uniformly distributed throughout the video. Furthermore, spatially salient entities such as people and objects are continuous rather than disjoint patches. In general, this leads us to believe random masking may miss certain semantics that are useful for learning spatiotemporal representations. The goal of this work is to address these deficiencies to make masked video modeling more effective for video representation learning. Because video is temporally cohesive, the MAE should be able to reconstruct a continuous spatiotemporal volume comprised of the salient regions. This motivates our following approach.", + "bbox": [ + 75, + 387, + 473, + 585 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Preliminaries", + "text_level": 1, + "bbox": [ + 76, + 592, + 218, + 607 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given a video $V \\in \\mathbb{R}^{T \\times H \\times W \\times C}$ , where $T, H, W, C$ denote the number of frames, height, width, and RGB-channels, the video is typically first split into patches of size $t \\times h \\times w \\times C$ and processed with a patch embedding layer $\\mathcal{P}$ to obtain a sequence of token embeddings $V_{p}$ .", + "bbox": [ + 75, + 613, + 470, + 691 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nV _ {p} = \\mathcal {P} (V); V _ {p} \\in \\mathbb {R} ^ {\\frac {T}{t} \\times \\frac {H}{h} \\times \\frac {W}{w}} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 171, + 700, + 470, + 722 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Next, a masking function $\\eta$ (e.g. random masking [11, 39]) generates a binary mask $M$ which is applied to select a set of visible patches with mask ratio $\\gamma$ .", + "bbox": [ + 76, + 727, + 472, + 772 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nM = \\eta (V _ {p}, \\gamma); d i m (M) = d i m (V _ {p})\n$$\n", + "text_format": "latex", + "bbox": [ + 165, + 792, + 416, + 809 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nV _ {\\mathrm {p} \\text {- v i s i b l e}} = V _ {p} \\cdot (\\sim M) \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 135, + 811, + 468, + 828 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nV _ {\\mathrm {p} \\text {- m a s k e d}} = V _ {p} \\cdot M\n$$\n", + "text_format": "latex", + "bbox": [ + 132, + 830, + 256, + 848 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The encoder $\\phi$ then processes only the visible patches $V_{\\mathrm{p\\_visible}}$ while the decoder $\\xi$ processes the full set of encoded patches and masked tokens $\\phi(V_{\\mathrm{p\\_visible}}) \\cup V_{\\mathrm{p\\_masked}}$ to", + "bbox": [ + 76, + 854, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "reconstruct the video. This work uses the same asymmetric encoder-decoder design as [11, 16, 39].", + "bbox": [ + 498, + 363, + 890, + 393 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nE = \\phi \\left(V _ {\\mathrm {p} - \\text {v i s i b l e}}\\right) \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 638, + 407, + 892, + 426 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nV ^ {\\prime} = \\xi (E \\cup V _ {\\mathrm {p}. \\text {m a s k e d}}) \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 620, + 444, + 892, + 460 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Finally, the model is trained with MSE reconstruction loss between $V$ and $V'$ . The model is then transferred to downstream tasks such as classification via finetuning with cross-entropy loss. Note that this work focuses on the mask generator $\\eta(\\gamma)$ , which is complementary to recent works which look into the loss function and reconstruction targets [33, 36, 45, 50].", + "bbox": [ + 496, + 467, + 893, + 573 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Simulated-Motion Masking (SMM)", + "text_level": 1, + "bbox": [ + 500, + 582, + 808, + 599 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To help the encoder learn spatiotemporal semantics throughout the video, we propose to generate a spatiotemporally continuous moving 3D mask, as shown in Fig. 2. This differs from random masking [11] and random tube masking [39] which break spatiotemporal continuity.", + "bbox": [ + 496, + 604, + 893, + 680 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We define the mask as a vector $[x, y, w, h]$ where $x$ and $y$ define the top-left coordinate and $w$ and $h$ define the width and height of the mask. We first explore the use of random motion to generate a dense moving 3D mask with masking ratio $\\gamma$ . To do this, we initialize a rectangle shaped mask in the first frame with dimensions $w_0 = h_0 = \\sqrt{\\gamma * \\frac{H}{h} * \\frac{W}{w}}$ . $x_0$ and $y_0$ are then randomly initialized in rand(0, H/h - h_0). We then propagate the mask across time using the following recurrent relation:", + "bbox": [ + 496, + 681, + 893, + 824 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n[ x _ {t}, y _ {t}, w _ {t}, h _ {t} ] = [ x _ {t - 1} + v _ {x t}, y _ {t - 1} + v _ {y t},\n$$\n", + "text_format": "latex", + "bbox": [ + 557, + 834, + 831, + 851 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left. w _ {t - 1} + s _ {t}, h _ {t - 1} + s _ {t} \\right] \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 669, + 853, + 890, + 875 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nt \\in [ 1, T), \\sum_ {t} s _ {t} = 0\n$$\n", + "text_format": "latex", + "bbox": [ + 604, + 875, + 750, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "5621", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $v_{xt}, v_{yt}$ are the random horizontal and vertical velocity components, and $s_t$ is a random scaling factor. To ensure that the masking ratio for each video is consistent, we enforce that $\\sum_{t} s_{t} = 0$ ; in other words, the number of masked patches remains fixed for a given $\\gamma$ .", + "bbox": [ + 75, + 90, + 472, + 167 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Motion-Guided Masking (MGM)", + "text_level": 1, + "bbox": [ + 76, + 174, + 369, + 191 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "While SMM leads to an improvement over random masking, SMM generates masks that may not reflect true motion as it is not context-aware. For example in Figure 2, the mask may cover static background rather than the basketball player depending on the random initialization and velocity. The most straightforward approach to address this issue would be to guide the mask using precomputed object bounding boxes or optical flow. However, this requires additional data and cost and would make such a method less scalable.", + "bbox": [ + 75, + 196, + 468, + 332 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We propose to use motion vectors as guidance to ensure that the mask movement consistently covers motion across frames. Motion vectors [30, 47] can be decoded from raw video (with H.264 or H.265 CODECs) with no extra cost, which ensures that our proposed approach adds no additional cost and scales well to larger datasets. A motion vector $M_{t}[x,y]$ for a given pixel position $x,y$ at frame $t$ , is defined as $[d_x,d_y]$ where $d_{x}$ and $d_{y}$ denote the displacement of pixel $x,y$ from frame $t - 1$ . Motion vectors are typically sparsely assigned to $8\\times 8$ pixel grids [30, 47], so the overall motion vector map is similar to optical flow but at a lower resolution. In order to use motion vectors to guide the masking, we need pixel-level correspondence between the motion vectors and the video. We accomplish this by upsampling the motion vector map to match the spatial resolution of the video.", + "bbox": [ + 75, + 334, + 468, + 559 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Given a motion vector map $M_t \\in \\mathbb{R}^{T \\times \\frac{H}{8} \\times \\frac{W}{8}}$ , we first use nearest-neighbor upsampling ( $U_{\\mathrm{nearest}}$ ) to get $M_{\\mathrm{t.scaled}} \\in \\mathbb{R}^{T \\times H \\times W}$ .", + "bbox": [ + 76, + 559, + 468, + 604 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathrm {M} _ {\\text {t . s c a l e d}} = U _ {\\text {n e a r e s t}} \\left(M _ {t}, (H, W)\\right) \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 614, + 468, + 631 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Next, we initialize a dense rectangle mask for frame $t_0$ with dimensions $w_0 = h_0 = \\sqrt{\\gamma * \\frac{H}{h} * \\frac{W}{w}}$ . $x_0$ and $y_0$ are then randomly initialized in $rand(0, \\frac{H}{h} - h_0)$ . The mask is then generated for following time-steps as:", + "bbox": [ + 75, + 638, + 468, + 709 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nx _ {\\mathrm {t} \\text {c e n t e r}}, y _ {\\mathrm {t} \\text {c e n t e r}} = P o o l _ {\\mathrm {t o p K}} (M _ {\\mathrm {t} \\text {s c a l e d}})\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 715, + 331, + 734 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nw _ {t} = w _ {t - 1} + s _ {x t}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 738, + 284, + 751 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nh _ {t} = h _ {t - 1} + s _ {y t}\n$$\n", + "text_format": "latex", + "bbox": [ + 168, + 755, + 282, + 770 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\left[ x _ {t}, y _ {t}, w _ {t}, h _ {t} \\right] = \\left[ x _ {\\mathrm {t} - \\text {c e n t e r}} - \\frac {w _ {t}}{2}, y _ {\\mathrm {t} - \\text {c e n t e r}} - \\frac {y _ {t}}{2}, w _ {t}, h _ {t} \\right] \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 768, + 468, + 799 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nt \\in [ 1, T), \\sum_ {t} s _ {x t} = 0, \\sum_ {t} s _ {y t} = 0\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 801, + 323, + 832 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $Pool_{topK}$ is the topK (top-1 in our work) magnitude pooling operation that gives the argmax indexes $x_{t\\_ center}, y_{t\\_ center}$ , which the mask is centered around. We also apply jitter $s_{xt}, s_{yt}$ to both the mask height and width.", + "bbox": [ + 75, + 839, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In other words, MGM produces a moving 3D mask where the movement of the mask is centered around parts of the video with the highest magnitude of motion, as shown in Fig. 2. This makes the reconstruction task more focused on spatiotemporal semantics than random masking.", + "bbox": [ + 496, + 90, + 893, + 167 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Experimental Results", + "text_level": 1, + "bbox": [ + 498, + 180, + 705, + 196 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Datasets", + "text_level": 1, + "bbox": [ + 500, + 205, + 601, + 220 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We conduct experiments on five commonly used datasets: Something-Something V2 (SSv2) [14] contains 220K videos with 174 action classes. SSv2 is considered a motion heavy dataset, as most of the labels are defined by the motion and directionality of the actual action. Kinetics-400 (K400) [19] is the de-facto standard dataset used to evaluate video recognition. It contains 240K Internet videos with 400 action classes. UCF101 [34] is a dataset containing 13K Internet short videos with 101 action classes. HMDB51 [22] is a dataset containing 5K short movie clips from 51 action classes. Diving48 [23] contains 18K untrimmed video clips from 48 action classes, all of which are types of dives. We report the top-1 accuracy on the evaluation set for all datasets following standard practices [12]. Only UCF101 and HMDB51 have multiple split versions; we use split 1.", + "bbox": [ + 496, + 229, + 893, + 455 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. Implementation Details", + "text_level": 1, + "bbox": [ + 500, + 465, + 718, + 481 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Model Configuration: We experiment with both 2D and 3D transformer backbones. The default backbone is ViT-Base [9] with global joint space-time attention. We also experimented with TimesFormer [3] with divided space-time attention. For fair comparison, we use the same input patch size of $2 \\times 16 \\times 16$ for all models following [39].", + "bbox": [ + 496, + 488, + 893, + 579 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Pre-Processing: We pretrain with clips of 16 frames sampled at a temporal stride of 4 and 2 for K400 and SSv2 respectively following [39]. We use a fixed spatial resolution of $224 \\times 224$ for all experiments. We apply multi-scalecrop and horizontal flip augmentation by default (flip is not applied to SSv2). We follow [39] to use AdamW [27] optimizer with a base learning rate $1.5e - 4$ , weight decay of $0.05$ , $\\beta = [0.9, 0.95]$ , and cosine learning rate decay.", + "bbox": [ + 496, + 580, + 893, + 700 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Finetuning and Evaluation: We use the same 16-frame clip for finetuning and multi-view evaluation protocol following standard practice [12]. We use TSN-style sampling [44] on SSv2 dataset with 2 temporal $\\times$ 3 spatial views during test-time following [39] for fair comparison. For Kinetics-400, UCF101, HMDB51 and Diving48, we use 5 temporal $\\times$ 3 spatial views during test-time following [39] for fair comparison. See the supplementary material for hyperparameter details which are mostly the same as [39].", + "bbox": [ + 496, + 700, + 893, + 837 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.3. Main Results", + "text_level": 1, + "bbox": [ + 500, + 847, + 638, + 861 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Something-Something V2. We first show our MGM's performance on SSv2 in Table 1, and compare with previous", + "bbox": [ + 498, + 869, + 893, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "5622", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/03e17db865682af90b0c510a9fe0927e00c1569ad0ad1db056f5b5d2f849742a.jpg", + "table_caption": [ + "finetune eval on SSv2", + "finetune eval on K400" + ], + "table_footnote": [], + "table_body": "
ModelBackboneGFLOPsEpochsPretrainTop1EpochsPretrainTop1
Supervised
SlowFast [12]R101 + NL106196K40063.1--79.8
TimeSformer [3]ViT-B19615IN21K59.515IN21K78.0
VidTr [51]ViT-B35150K40063.0--79.1
MotionFormer [28]ViT-B37090+35IN21K + K40066.590IN21K79.7
MViTv1 [10]MViT-B455200K40067.7--81.2
MViTv2 [24]MViT-B225200K40070.5--82.9
Self-supervised
BEVT [45]Swin-B282800+150IN1K + K40070.6800+150IN1K + K40080.6
M³Video [36]ViT-B180400SSv269.2400K40079.7
MGMViT-B180400SSv269.6400K40080.3
VideoMAE [39]ViT-B180800SSv269.6800K40080.0
MGMViT-B180800SSv270.6800K40080.8
MAM² [33]ViT-B + VQGAN1801200SSv271.3800K40082.3
MGMViT-B1801200SSv271.61200K40081.2
OmniMAE [13]ViT-B1801600IN1K + SSv269.51600IN1K + K40080.8
VideoMAE [39]ViT-B1801600SSv270.31600K40081.5
VideoMAE [39]ViT-B1802400SSv270.8---
STMAE [11]ViT-B1801600K400N/A1600K40081.3
MotionMAE [50]ViT-B1802400SSv271.81600K40081.7
MGMViT-B1801600SSv271.81600K40081.7
MGMViT-B1802400SSv272.1---
", + "bbox": [ + 89, + 104, + 883, + 429 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1: Results comparison on Something-SomethingV2 (SSv2) and Kinetics-400 (K400). GFLOPs is listed as a single view's. All results are with fine-tuning. We apply repeated augmentation $[18] = 2$ for this table to compare against SOTA.", + "bbox": [ + 75, + 453, + 892, + 484 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "models trained in a supervised manner: Our MGM using vanilla ViT-B pretrained on only SSv2 outperforms previous SOTA such as MViTv1 [10] $(+4.4\\%)$ and MViTv2 [10] $(+1.6\\%)$ which uses a heavy hierarchical 3D transformer backbone and pretrains on Kinetics-400. This demonstrates the efficiency and effectiveness of our proposed method compared to supervised 3D transformer backbones. MGM also significantly outperforms previous supervised learning methods that use the same backbone as us: $+5.6\\%$ over MotionFormer [28] and $+12.6\\%$ over TimeSformer [3]. This demonstrates that the proposed MGM is effective for spatiotemporal modeling.", + "bbox": [ + 75, + 510, + 470, + 691 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We then compare MGM with SOTA video MAE methods. With the same backbone and training schema, MGM achieves $1.3\\%$ higher accuracy comparing to VideoMAE [39]. Note that with $3 \\times$ less training time, our MGM pretrained for 800 epochs is able to achieve nearly the same performance as VideoMAE pretrained for 2400 epochs ( $\\sim 66\\%$ fewer epochs), as illustrated in Fig. 1. This demonstrates that motion-guided masking is a more efficient strategy for self-supervised spatiotemporal learning due to learning video saliency. Compared to OmniMAE [13] which does masked modeling on both images and video, MGM achieves $+2.6\\%$ improvement. Compared to BEVT [45] which also learns from both images and video and additionally uses", + "bbox": [ + 75, + 703, + 470, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Swin Transformer [25, 26] - a heavy 3D Transformer architecture - MGM achieves $+1.5\\%$ improvement. This is despite the fact that our method only uses video and is pretrained from scratch. Note that STMAE [11] only provides results for ViT-Large backbone on SSv2.", + "bbox": [ + 496, + 510, + 893, + 585 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We finally compare our MGM with some most recent works that also utilize motion information for video pretraining. MGM outperforms $\\mathrm{M}^3\\mathrm{Video}$ [36] ( $+0.4\\%$ with the same 400 epochs of pretraining) which reconstructs motion trajectories generated from optical flow. We achieve equivalent performance to MotionMAE [50] using $50\\%$ fewer epochs (1600 vs. 2400) even though it utilizes frame difference as an additional reconstruction target which incorporates explicit motion information. The results show that motion-guided masking alone is sufficient for improving spatiotemporal learning. It is worth reiterating that our MGM uses motion vectors for masking guidance, which is already computed during video encoding, and thus directly available during video decoding [30, 43, 47], making our method more efficient and scalable comparing to works such as [33, 36, 50] which use optical flow and/or frame difference.", + "bbox": [ + 496, + 592, + 895, + 834 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Kinetics-400 (K400). We further conduct experiments on K400 and show results in Table 1. Similar trends are observed. Our MGM is able to outperform supervised models with the same backbone such as TimeSformer [3] by $+3.7\\%$", + "bbox": [ + 496, + 839, + 893, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "5623", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "and MotionFormer [28] by $+2.0\\%$ . MGM slightly underperforms some hierarchical 3D transformer backbones such as MViTv2 [24] by $-1.2\\%$ on K400 but MViTv2 is trained with $2\\times$ more frames (32) and uses significantly more FLOPS.", + "bbox": [ + 75, + 90, + 470, + 151 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparing with other MAE based methods, our MGM consistently outperforms VideoMAE by $+1.4\\%$ at 800 epochs of pretraining. MGM also achieves better performance comparing to other recent works, at no additional cost. Our MGM outperforms $\\mathrm{M}^3\\mathrm{Video}$ [36] at 400 epochs of pretraining by $0.6\\%$ , while being more efficient as our method does not use frame difference nor optical flow. Compared to OmniMAE [13] which uses both images and video, MGM achieves $0.9\\%$ improvement. Compared to BEVT [45], MGM achieves $1.1\\%$ improvement.", + "bbox": [ + 75, + 152, + 470, + 303 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We note that the performance gain MGM obtains over other methods on K400 is slightly lower compared to on SSv2. This can be explained by the fact that a great proportion of actions in K400 dataset can be differentiated by the appearance of a few key frames, for example, \"skiing\" vs. \"tennis\". In contrast, recognising actions in SSv2 dataset, e.g. \"moving something up\" vs. \"moving something down\", requires the model to understand the subtle differences in motion along temporal dimension. Therefore, we hypothesize that spatiotemporal modeling is less impactful on spatial-heavy datasets such as K400 and the strength of MGM is not fully exhibited. Motion serves as a appearance-agnostic differentiator between classes.", + "bbox": [ + 75, + 304, + 470, + 500 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Transfer Learning", + "text_level": 1, + "bbox": [ + 76, + 512, + 256, + 529 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We next evaluate MGM's performance when transferred to smaller datasets: UCF101 [34], HMDB51 [22], and Diving48 [23]. Performance in transfer learning is commonly used as an indicator of feature quality and representativeness [17]. We use ViT-Base model pretrained on K400 and SSv2 by 800 epochs for all transfer learning experiments.", + "bbox": [ + 75, + 536, + 468, + 627 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Finetune on downstream tasks. We first present fine-tuning results from MGM pretrained on unlabeled K400 in Table 2. Our MGM consistently outperforms VideoMAE with same backbone and pretraining setup on all three datasets $(+0.9\\%)$ on UCF101, $+1.1\\%$ on HMDB51, $+4.9\\%$ on Diving48). This shows that our approach learns more representative semantics and thus generalizes better to small-scale downstream tasks. It is worth mentioning that MGM even outperforms K400 supervised pretraining on HMDB51 $(+3.2\\%)$ and on Diving48 $(+7.5\\%)$ , demonstrating the effectiveness of our proposed method.", + "bbox": [ + 75, + 628, + 470, + 792 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Our MGM is also able to consistently outperform VideoMAE [39] with pretraining on unlabeled SSv2 in the finetune setting $(+1.3\\%)$ on UCF101, $+1\\%$ on HMDB51, $+2.6\\%$ on Diving48). Our MGM even outperforms SSv2 supervised pretraining by a large margin $(+14.1\\%)$ on UCF101, $+13.4\\%$ on HMDB51, $+46.9\\%$ on Diving48). Finetuning MGM on SSv2 (same model from Tab. 1) does not lead to a large", + "bbox": [ + 75, + 795, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/aa80afa58cfaf8689483229e28153694e1e2089ec1ff7fbef0ca70c2b62e1977.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
UCFHMDBDiving48
Supervised (K400) †95.171.462.7
VideoMAE [39]93.373.565.3
MGM94.274.670.2
+ K400 Finetune (Tab. 1)97.781.082.6
", + "bbox": [ + 526, + 89, + 867, + 170 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/f33cd6d4dc0fb3da0ad5c40993aaa7115d5935d293a22c4f660f5b4d2fba38dd.jpg", + "table_caption": [ + "(a) Pretrained on K400 and finetuned on downstream tasks." + ], + "table_footnote": [], + "table_body": "
UCFHMDBDiving48
Supervised (SSv2) †77.856.336.2
VideoMAE [39]90.668.780.5
MGM91.969.783.1
+ SSv2 Finetune ( Tab. 1)93.274.783.4
", + "bbox": [ + 521, + 190, + 867, + 271 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/1f821fed843adc5265b58346f0528ffd64186fb6bf72bf0c048536b68a8d8e7d.jpg", + "table_caption": [ + "(b) Pretrained on SSv2 and finetuned on downstream tasks." + ], + "table_footnote": [], + "table_body": "
UCFHMDBDiving48
Supervised (K400) †94.165.425.2
VideoMAE [39]70.545.410.0
MGM77.549.214.2
", + "bbox": [ + 537, + 292, + 854, + 359 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/cb6a228ee1020bb6d1abf400e9f6c04432652e6bd926428cc552ae66eee279d2.jpg", + "table_caption": [ + "(c) Pretrained on K400 and evaluated with linear probing on downstream tasks." + ], + "table_footnote": [], + "table_body": "
UCFHMDBDiving48
Supervised (SSv2) †72.951.813.2
VideoMAE [39]65.341.210.7
MGM69.144.810.2
", + "bbox": [ + 539, + 393, + 854, + 462 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "(d) Pretrained on SSv2 and evaluated with linear probing on downstream tasks.", + "bbox": [ + 527, + 468, + 864, + 496 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2: MGM generalizes well to various downstream datasets (UCF101, HMDB51 and Diving48) on two downstream tasks (finetune, linear-probe). We test VideoMAE and MGM pretrained on Kinetics-400 (K400) for 800 epochs. The supervised baseline is ViT-B trained from scratch on K400 and SSv2 using the recipe from MViT [10, 24].", + "bbox": [ + 496, + 508, + 893, + 599 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "boost, indicating that our model is able to learn the majority of semantics just from unsupervised pretraining, and that unsupervised pretraining is able to make better use of the information in SSv2 than supervised training.", + "bbox": [ + 496, + 628, + 893, + 688 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Linear Probe on downstream tasks. Previous work [2, 11, 16] argues that generative approaches such as MAE generally perform worse on linear probing tasks as there is a larger gap between the reconstruction task and downstream evaluation compared to other pretraining methods. Nevertheless, we compare linear probe performance between MGM and VideoMAE [39] and show that our method achieves significantly better performance. With K400 pretraining, we outperform VideoMAE by $+7\\%$ on UCF101, $+3.8\\%$ on HMDB51, and $+4.2\\%$ on Diving48. With SSv2 pretraining, we outperform by $+3.8\\%$ on UCF101, $+3.6\\%$ on HMDB51, and underperform by $-0.5\\%$ on Diving48. This demonstrates that motion-modeling helps reduce the gap between the reconstruction task and downstream tasks, as linear probe only", + "bbox": [ + 496, + 689, + 893, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "5624", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/135f571ac079d6978cd7840aeb0e8d045982e8285c57ce1aba805344521d957c.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
UCF14 → HMDB7HMDB14 → UCF7
VideoMAE [39]55.769.6
MGM57.671.4
+ K400 Finetune (Tab. 1)79.196.2
", + "bbox": [ + 81, + 88, + 467, + 150 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "trains a linear classifier on top of features extracted from the frozen backbone; linear layers cannot learn new semantics.", + "bbox": [ + 75, + 280, + 468, + 310 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We note that there is a large gap of over $10\\%$ with K400 supervised pretraining on linear probe. This is a general deficiency of generative methods such as MAE-based pretraining [11] and we leave further exploration of this problem to future works. One way to address this would be to combine MAE with discriminative methods such as contrastive learning to obtain a balanced representation.", + "bbox": [ + 75, + 311, + 470, + 416 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Domain adaptation. We further evaluate MGM on partial domain adaptation tasks following [49], in which the labels for the target dataset are a subset of the labels for the source dataset. The model is finetuned on the source dataset and directly evaluated on the target dataset without seeing any samples from the target dataset. This is more challenging than conventional domain adaptation as the model may incorrectly label samples in the target dataset as the labels from the source dataset which are not present in the target dataset (\"negative transfer\") [49]. Previous work has showed that optical flow is useful for action recognition because it is invariant to appearance [32]. Several works such as [6, 31] improve unsupervised domain adaptation in video by reducing background and appearance bias to capture the essence of an action via shuffling and mixup respectively. By similar reasoning, domain adaptation is a good evaluation protocol to assess motion learning as the source and target datasets have very different visual appearances, and motion serves as a common link between classes that is agnostic to spatial appearances.", + "bbox": [ + 75, + 417, + 470, + 718 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We use the training sets provided by [49] for UCF14 $\\rightarrow$ HMDB7 and HMDB14 $\\rightarrow$ UCF7. Our MGM consistently outperform VideoMAE with K400 pretraining in both settings $(+1.9\\%)$ on HMDB7 and $+1.8\\%$ on UCF7) indicating that MGM can also outperform in a domain adaptation setting. While there is a significant gap of over $20\\%$ between Table 3 and Table 2, finetuning our model on K400 labels bridges the gap. This suggests that our model has learned video saliency and can perform well without any large-scale label supervision, but additional label supervision is helpful for challenging settings such as domain adaptation where spatial information is very different and difficult to", + "bbox": [ + 75, + 719, + 472, + 901 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/fd648a874d15a727d3bcd2ee564e90d88f424336ae2801350ba89d2cb430952a.jpg", + "image_caption": [ + "(a) More mask ratios.", + "Figure 3: Ablations on mask ratio 3a and pretraining duration 3b. Mask ratio 0.75 is optimal and performance does not saturate with longer pretraining." + ], + "image_footnote": [], + "bbox": [ + 504, + 90, + 689, + 227 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e45d16a8fae47b9376ca509ac05f77ae6bf24f5d58b28de654365aaf269215ca.jpg", + "image_caption": [ + "(b) Pretrain duration in epochs." + ], + "image_footnote": [], + "bbox": [ + 696, + 90, + 882, + 227 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/287d06c370c9aba2dbaa23ed3015c5cb164b200862f72ab6211d540da5259aa3.jpg", + "table_caption": [ + "Table 3: MGM works well when trained on one dataset and evaluated on another dataset for an overlapping set of classes. The model sees no samples from test dataset, indicating motion understanding as motion is agnostic to spatial appearance. We tested VideoMAE and MGM pretrained on Kinetics-400 (K400) for 800 epochs." + ], + "table_footnote": [], + "table_body": "
backboneSSv2
ViT-S61.1
ViT-B67.3
TimesFormer [3]64.7
", + "bbox": [ + 509, + 325, + 668, + 392 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d4d40bf8008790146f8f1b7ecf8e550f2f3aa98703a6955f88bc431d415cc0f8.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
guidanceSSv2
optical flow66.0
motion vector67.3
", + "bbox": [ + 725, + 339, + 883, + 391 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/5ce3329252f2576acd5bdb4d5a3d5bc00622fdacf06bec9285f6bbdda5f5a54c.jpg", + "table_caption": [ + "(a) Backbone generalization." + ], + "table_footnote": [], + "table_body": "
aspect ratioSSv2
no67.1
yes67.3
", + "bbox": [ + 509, + 411, + 638, + 464 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "(c) Mask jitter.", + "bbox": [ + 527, + 469, + 617, + 483 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/76a4f3c940b93365279831299ae0055b5471f0f861dc912085558708f55ac64a.jpg", + "table_caption": [ + "(b) Source of motion info." + ], + "table_footnote": [], + "table_body": "
pretrain datasamplesK400
Mini-K200 [48]80K78.2
K400 [19]240K78.6
", + "bbox": [ + 668, + 411, + 883, + 464 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/9570f046ebd57b9ea03b86940af7d8c0825990849759a8979b694003358c5c12.jpg", + "table_caption": [ + "(d) Dataset scale generalization." + ], + "table_footnote": [], + "table_body": "
Masktemporal propagationspatial continuity
staticsimulatedmotionsparsedenseAcc
Random Block✓✓62.9
SMM (Sparse)✓✓64.6
Random Tube✓✓65.0
MGM (Sparse)✓✓65.1
SMM (Dense)✓✓65.9
MGM (Dense)✓✓67.3
", + "bbox": [ + 511, + 484, + 883, + 579 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "(e) Masking strategies differentiated by initial position, temporal propagation, and spatial continuity. Spatiotemporally continuous masks with motion guidance perform the best.", + "bbox": [ + 496, + 583, + 893, + 626 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4: Ablations on backbone 4a, source of motion guidance 4b, mask jitter 4c, pretrain data scale 4d, and mask type 4e. All ablations pretrain for 200 epochs on SSv2 unless otherwise indicated.", + "bbox": [ + 496, + 637, + 893, + 698 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "learn from limited samples. There are only $\\sim 1000$ training samples in each setting.", + "bbox": [ + 496, + 727, + 890, + 758 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5. Ablations", + "text_level": 1, + "bbox": [ + 500, + 768, + 611, + 784 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We perform ablations on the Something-Something V2 dataset, with MGM with ViT-B backbone pretrained for 200 epochs using our motion-guided masking, unless otherwise specified.", + "bbox": [ + 496, + 792, + 890, + 853 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Impact of masking ratio. Figure 3a studies the impact of different masking ratio on SSv2. We noticed that 0.75 masking ratio works best for the proposed MGM, which", + "bbox": [ + 496, + 854, + 893, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "5625", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "is lower than that of other works [11, 39]. This is because motion-guided masking leads to a more \"challenging\" reconstruction task compared to random masking, since the masked regions of videos are most informative and therefore cannot be easily inferred from retained regions.", + "bbox": [ + 75, + 90, + 470, + 167 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Impact of pretraining length. We show the impact of different pretraining epochs on SSv2 in Figure 3b. The proposed MGM consistently improves with more training and we achieve state-of-the-art performance on SSv2 with 2400 epochs of pretraining. Performance does not seem to saturate with longer pretraining.", + "bbox": [ + 75, + 167, + 470, + 258 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Generalization to different backbones. MGM also generalizes well to backbones of different sizes and types (Table 4a). We test vanilla ViT-S [9] and ViT-B [9], and TimeSformer [3] with joint space-time attention. Note that our TimeSformer ablation outperforms the supervised result reported by [3] of $59.5\\%$ on SSv2 which uses IN21K pretraining. In contrast, we do not use any extra data. ViT-S's lower performance may be explained by its low model capacity which may not be sufficient for learning spatiotemporal dynamics. As other methods do not use ViT-S, we cannot compare our result to other methods. We thus use ViT-B to compare fairly against other MAE works which use ViT-B.", + "bbox": [ + 75, + 260, + 472, + 441 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Impact of motion source. In Table 4b we compare the performance of MGM when using optical flow vs. motion vectors as the source of motion guidance. Even though optical flow is more fine-grained and precise than motion vectors, performance of MGM drops when the mask is guided by optical flow. This could be related to the fact that optical flow is calculated on a per-pixel basis whereas motion vectors are computed in a block-wise manner and we utilize a block-wise mask strategy. We thus conveniently choose to use motion vector as it is also directly obtainable from compressed video. We extract optical flow using RAFT-Small [38]. On the SSv2 dataset, reading motion vectors is roughly $30 \\times$ faster than computing optical flow (80 milliseconds vs. 2.5 seconds per video on average).", + "bbox": [ + 75, + 443, + 470, + 654 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Impact of mask aspect ratio jitter. In Table 4c we ablate the use of aspect ratio jittering from Eq. (7). We see that aspect ratio jittering gives a small $0.2\\%$ boost in performance but is not a critical component of MGM.", + "bbox": [ + 75, + 656, + 468, + 715 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Impact of pretrain dataset scale. In Table 4d we ablate the amount of pretraining data used to see if MGM can generalize to different dataset scales. We pretrain MGM on MiniKinetics-200 [48] and Kinetics-400 (K400) [19] which contain $\\sim 80\\mathrm{K}$ videos and $\\sim 240\\mathrm{K}$ videos respectively for 200 epochs. MiniKinetics-200 contains videos belonging to a subset of 200 of the most common classes in K400. We then evaluate top-1 accuracy on K400. We find that there is a small $0.4\\%$ drop in performance when pretraining on the smaller MiniKinetics-200. We expect performance to further improve when pretraining on datasets larger than K400.", + "bbox": [ + 75, + 717, + 468, + 883 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effectiveness of 3D motion masking. Table 4e studies", + "bbox": [ + 76, + 885, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "different masking strategies which are broken down into categories based on degree of motion guidance and spatial continuity. We first compare dense to sparse masking, where sparse means that the mask may be spatially discontinuous. The dense variant of SMM and MGM outperform the respective sparse counterpart; dense SMM outperforms sparse SMM by $1.3\\%$ and dense MGM outperforms sparse MGM by $2.2\\%$ . This suggests the importance of maintaining spatial continuity in the masked reconstruction. Next, we compare MGM to SMM. Sparse MGM outperforms sparse SMM by $0.5\\%$ and dense MGM outperforms dense SMM by $1.4\\%$ . When motion is completely removed, performance is the worst even when the mask is spatially continuous (static block gets $62.9\\%$ ). Dense MGM outperforms all masking strategies and specifically the random masking baseline by $2.3\\%$ . All masking strategies except block and sparse SMM outperform random masking. Random masking is spatiotemporally discontinuous. This validates our intuition that forming continuous 3D masks which model the true motion information within video is useful. We thus pick dense MGM for all other experiments and refer to \"MGM\" as the dense variant by default. For a visualization of these masking strategies, see Figure 4.", + "bbox": [ + 496, + 90, + 893, + 439 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/7bdace739ebf35a847db114876ff8b6f48cbf77163604193bb8f329068daa194.jpg", + "image_caption": [ + "Figure 4: Visualization of different mask algorithms." + ], + "image_footnote": [], + "bbox": [ + 506, + 463, + 890, + 616 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.6. Visualization", + "text_level": 1, + "bbox": [ + 500, + 691, + 635, + 705 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In Figure 5, we provide visualizations from two perspectives using MGM pretrained on K400. Note that visualizations are subjective and should not be used as a formal explanation for model behavior. Our intention is to provide additional insight into the model to complement our quantitative results. We first visualize the RGB frames with bounding boxes, motion-guided masks, and motion vectors. We see that the motion-guided masks overlap with the majority of spatiotemporally salient regions. Second, we visualize the attention map using the center patch of the center frame as a query. We observe that the model mostly attends to the salient regions. For more visualizations, see the supplementary.", + "bbox": [ + 496, + 719, + 893, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "5626", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/97aab0482ad9423e7dfd733575229eed50f2dfe182bcb4b1fd41c863a4f1865d.jpg", + "image_caption": [ + "a)" + ], + "image_footnote": [], + "bbox": [ + 138, + 88, + 240, + 169 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/e20ee8d868521dcd20259dc9480785480cf435d11a093ff03d405d1d587aee66.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 245, + 88, + 346, + 169 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/7430f0a27a0ca135b310c9c24469c18aa4beeb2b72f8d769b2c67ccb33bca8fd.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 352, + 88, + 455, + 167 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/89ce736cf1fb41e23f7ffef31d827d32ec165c7e3244d8f2023380c83a70f061.jpg", + "image_caption": [ + "b)" + ], + "image_footnote": [], + "bbox": [ + 138, + 172, + 240, + 252 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/f26e76ef0a9792a6767444f38d188ded069f1fd52f33be30e276de081770d03f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 245, + 172, + 346, + 252 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/9c132fe60ff88e71c5b5487cff34cdbfa8ab6612df3abb278c6f3d31d6d61860.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 352, + 172, + 455, + 252 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/a614dc5acdea4d06eb7211fe51e2e2a271c4fae49a0cbf8ce884fa3f7114d671.jpg", + "image_caption": [ + "c)" + ], + "image_footnote": [], + "bbox": [ + 138, + 255, + 240, + 333 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/f00411b66c812dcb3621412e8a9fb0a9ff222a89eb113bec1017f014d31a6ef0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 245, + 255, + 346, + 334 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/ba385cccba42f6c56809f370a984f9917f5a31181000d20030490547e7e51d8a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 352, + 255, + 455, + 334 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/ec67ddb597ddcb541c1be657b3520b4fb577f8ab861c17619a01bda442a23d70.jpg", + "image_caption": [ + "d)" + ], + "image_footnote": [], + "bbox": [ + 138, + 337, + 240, + 414 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/2cd0a3af7aa4bd63910ebc6f5d0e18fbf142e2e8bcaba7111649c507ac2396f8.jpg", + "image_caption": [ + "Figure 5: a) RGB frames with bounding boxes for visualization. b) Our MGM masks continuously cover the moving hand. c) Motion vector maps. d) Encoder attention map using center patch of center frame as query." + ], + "image_footnote": [], + "bbox": [ + 245, + 337, + 346, + 415 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/faee1514de1aa0a5ac44086a1e67c47729d56f23be49ab6327b55fcb9564368a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 352, + 337, + 455, + 415 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Discussion and Conclusion", + "text_level": 1, + "bbox": [ + 76, + 523, + 323, + 540 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Limitations. Our method efficiently leverages motion cues from compressed video format. However, MGM's effectiveness on the video benchmarks that are not human centric or have tremendous camera motion has yet to be examined. To the best of our knowledge, we did not find such a video benchmark, so we will leave this to future work.", + "bbox": [ + 75, + 556, + 470, + 646 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Potential negative impact. As our model is trained on primarily Internet video datasets, our model will learn the bias inherent to that data. There could be unintended consequences and we advocate for complying with the law.", + "bbox": [ + 75, + 652, + 470, + 714 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Conclusion. This paper introduces motion-guided masking (MGM), an algorithm which produces motion-aware 3D masks to improve spatiotemporal learning. Our use of motion information is much more efficient than previous optical flow as we leverage motion vectors that naturally exist in the video codec. We achieve new state-of-the-art or comparable performance on two challenging large-scale video benchmarks and achieve previous state-of-the-art results with $50\\%$ less pretraining time, making our method more efficient. We also achieve better generalization than previous video MAE works on three small-scale datasets. 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Bevt: Bert pretraining of video transformers. 2022 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), pages 14713-14723, 2022. 1, 2, 3, 5, 6", + "[46] Chen Wei, Haoqi Fan, Saining Xie, Chaoxia Wu, Alan Loddon Yuille, and Christoph Feichtenhofer. Masked feature prediction for self-supervised visual pre-training. 2022 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), pages 14648-14658, 2022. 2", + "[47] Chao-Yuan Wu, Manzil Zaheer, Hexiang Hu, R Manmatha, Alexander J Smola, and Philipp Krahenbuhl. Compressed video action recognition. In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 6026-6035, 2018. 2, 4, 5", + "[48] Saining Xie, Chen Sun, Jonathan Huang, Zhuowen Tu, and Kevin Murphy. Rethinking spatiotemporal feature learning: Speed-accuracy trade-offs in video classification. In Proceedings of the European conference on computer vision (ECCV), pages 305–321, 2018. 7, 8", + "[49] Yuecong Xu, Jianfei Yang, Haozhi Cao, Zhenghua Chen, Qi Li, and Kezhi Mao. Partial video domain adaptation with partial adversarial temporal attentive network. In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 9332-9341, 2021. 7", + "[50] Haosen Yang, Deng Huang, Bin Wen, Jiannan Wu, Hongxun Yao, Yi Jiang, Xiatian Zhu, and Zehuan Yuan. Self-supervised video representation learning with motion-aware masked autoencoders. arXiv preprint arXiv:2210.04154, 2022. 1, 2, 3, 5", + "[51] Yanyi Zhang, Xinyu Li, Chunhui Liu, Bing Shuai, Yi Zhu, Biagio Brattoli, Hao Chen, Ivan Marsic, and Joseph Tighe." + ], + "bbox": [ + 78, + 90, + 470, + 900 + ], + "page_idx": 10 + }, + { + "type": "text", + "text": "Vidtr: Video transformer without convolutions. In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 13577-13587, 2021. 5", + "bbox": [ + 535, + 92, + 893, + 133 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "5629", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Motion-Guided Masking for Spatiotemporal Representation Learning/381ddc28-834d-4797-9d76-2bf9c96fea0c_model.json b/2023/Motion-Guided Masking for Spatiotemporal Representation Learning/381ddc28-834d-4797-9d76-2bf9c96fea0c_model.json new file mode 100644 index 0000000000000000000000000000000000000000..79a96610f4de755c50210a856720310f34411163 --- /dev/null +++ b/2023/Motion-Guided Masking for Spatiotemporal Representation Learning/381ddc28-834d-4797-9d76-2bf9c96fea0c_model.json @@ -0,0 +1,2554 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.044 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.132, + 0.131, + 0.84, + 0.154 + ], + "angle": 0, + "content": "Motion-Guided Masking for Spatiotemporal Representation Learning" + }, + { + "type": "text", + "bbox": [ + 0.129, + 0.179, + 0.845, + 0.253 + ], + "angle": 0, + "content": "David Fan1 Jue Wang1 Shuai Liao2 Yi Zhu3 Vimal Bhat1 Hector Santos-Villalobos1 Rohith MV1 Xinyu Li1 \n1 Amazon Prime Video 2 Amazon Fulfillment Technology 3 AWS AI Labs {fandavi, juewangn, uliaoshu, yzaws, vimalb, hsantosv, kurohith, xxnl}@amazon.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.318, + 0.474, + 0.681 + ], + "angle": 0, + "content": "Several recent works have directly extended the image masked autoencoder (MAE) with random masking into video domain, achieving promising results. However, unlike images, both spatial and temporal information are important for video understanding. This suggests that the random masking strategy that is inherited from the image MAE is less effective for video MAE. This motivates the design of a novel masking algorithm that can more efficiently make use of video saliency. Specifically, we propose a motion-guided masking algorithm (MGM) which leverages motion vectors to guide the position of each mask over time. Crucially, these motion-based correspondences can be directly obtained from information stored in the compressed format of the video, which makes our method efficient and scalable. On two challenging large-scale video benchmarks (Kinetics-400 and Something-Something V2), we equip video MAE with our MGM and achieve up to \\(+1.3\\%\\) improvement compared to previous state-of-the-art methods. Additionally, our MGM achieves equivalent performance to previous video MAE using up to \\(66\\%\\) fewer training epochs. Lastly, we show that MGM generalizes better to downstream transfer learning and domain adaptation tasks on the UCF101, HMDB51, and Diving48 datasets, achieving up to \\(+4.9\\%\\) improvement compared to baseline methods." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.71, + 0.21, + 0.725 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.734, + 0.471, + 0.825 + ], + "angle": 0, + "content": "Video transformers [1, 24, 25, 28, 43] have achieved state-of-the-art for a variety of video understanding tasks, mirroring the success of image transformers such as ViT [9]. However, many video transformers heavily rely on large-scale supervised pretraining from image datasets such as ImageNet21K [8] and JFT-300M [35], which is data-inefficient." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.473, + 0.902 + ], + "angle": 0, + "content": "Self-supervised learning (SSL) [5, 15, 17, 29, 42] is one promising paradigm for eliminating the dependency on large-scale supervised pretraining. The denoising / masked autoencoder (MAE) [41], which was originally popularized by BERT [20] for natural language modeling, has recently re" + }, + { + "type": "image", + "bbox": [ + 0.51, + 0.292, + 0.897, + 0.468 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.484, + 0.896, + 0.576 + ], + "angle": 0, + "content": "Figure 1: Top-1 accuracy on Something-Something V2. Our proposed MGM outperforms all previous masked-video methods (M³Video [36], MAM² [33], BEVT [45], OmniMAE [13], MotionMAE [50], and VideoMAE [39]) with improved training efficiency. Marker shape denotes reconstruction target." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.594, + 0.895, + 0.732 + ], + "angle": 0, + "content": "emerged as a promising representation learning method for vision tasks. Image MAE [2, 16] has achieved state-of-the-art in image domain via learning to reconstruct randomly masked image patches. Recently, similar works [11, 39] that reconstruct randomly masked video have obtained encouraging results in video domain. However, few SSL works focus on effectively learning video saliency. In this paper, we improve upon the previous video MAEs [11, 39] via video saliency." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.896, + 0.901 + ], + "angle": 0, + "content": "We argue that the random masking strategy which is inherited from image MAE is not optimal for video. The optimal random masking ratio for video MAE [11, 39] is higher than that for image MAE [16] (0.9 vs. 0.75). This can be understood as a consequence of the natural temporal coherence within videos, which leads to the existence of similar video patches in other frames. When using random masking, many of these correlated video patches may be visible to the encoder which would make reconstruction easier. This necessitates the use of a high masking ratio in order to reduce redundancy and make the reconstruction task" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5619" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.152 + ], + "angle": 0, + "content": "sufficiently challenging [11]. However, increasing the masking ratio has the side-effect of leaving fewer visible patches for the MAE encoder to learn spatiotemporal saliency from, which we hypothesize limits the learned representation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.153, + 0.47, + 0.287 + ], + "angle": 0, + "content": "We thus propose to guide the model to learn to reconstruct the most salient regions of video. As humans and objects are key to understanding video, one natural idea is to track the bounding boxes in each video frame and mask the content within. This is also consistent with the observation that video pixels evolve continuously frame-by-frame, and therefore, the MAE should be able to reconstruct this spatiotemporal continuity. However, generating bounding boxes for each frame is impractical for large-scale video datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.288, + 0.471, + 0.422 + ], + "angle": 0, + "content": "To this end, we hypothesize that motion is an effective guide for detecting spatiotemporal saliency. To test this hypothesis, we define the saliency score as \\( r_{bbox} / r_{non\\_bbox} \\), or the ratio of average motion magnitude within bounding boxes to average motion magnitude outside bounding boxes. The saliency score is 1.47 for Something-Something v2 [14] and 1.28 for Kinetics-400 [19] respectively, suggesting that regions of higher motion overlap with spatially salient regions more often than regions of lesser motion." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.424, + 0.471, + 0.62 + ], + "angle": 0, + "content": "We thus propose an improved masking algorithm, MGM, which uses motion to continuously guide the mask to cover the most salient spatiotemporal regions. MGM obtains cheap motion correspondence by exploiting the H.264 codec [30] which prevails in popular video formats such as MP4. During the encoding phase of H.264, motion vectors are precomputed and stored as part of the codec. Thus during the decoding phase, motion vectors can be obtained \"for free\" along with RGB frames. The use of readily available motion vectors instead of expensive optical flow enables us to efficiently achieve scale. While some supervised works have used motion vectors [21, 43, 47], we are the first to use motion vectors for MAE pretraining." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.62, + 0.471, + 0.816 + ], + "angle": 0, + "content": "Our MGM outperforms previous VideoMAE [39] by \\(1.2\\%\\) on Something-Something V2 (SSv2) [14] and \\(0.2\\%\\) on Kinetics-400 (K400) [19], demonstrating that our MGM is effective. MGM can also achieve the same performance as [39] with \\(50\\%\\) fewer training epochs as shown in Fig. 1, further making MAE pretraining more data-efficient. We also show that MGM generalizes well to small datasets (UCF101 [34], HMDB51 [22], and Diving48 [23]) in both full finetune and linear probe evaluation as well as domain adaptation settings with up to \\(4.9\\%\\) performance improvement over VideoMAE [39]. This shows that the features learned by MGM contain richer semantics that transfer well to video recognition tasks. In summary, our contributions are:" + }, + { + "type": "text", + "bbox": [ + 0.09, + 0.825, + 0.472, + 0.87 + ], + "angle": 0, + "content": "1. MGM, an efficient and effective self-supervised algorithm for 3D masking that continuously models motion trajectories." + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.871, + 0.471, + 0.902 + ], + "angle": 0, + "content": "2. Applying motion vectors which are directly available during video decoding - unlike optical flow - to provide" + }, + { + "type": "list", + "bbox": [ + 0.089, + 0.825, + 0.472, + 0.902 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.533, + 0.092, + 0.864, + 0.106 + ], + "angle": 0, + "content": "efficient motion guidance in the MAE framework." + }, + { + "type": "text", + "bbox": [ + 0.513, + 0.107, + 0.895, + 0.152 + ], + "angle": 0, + "content": "3. New state-of-the-art or comparable results on two large-scale datasets and various downstream tasks on three small datasets, as well as detailed ablations and insights." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.188, + 0.651, + 0.205 + ], + "angle": 0, + "content": "2. Related Works" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.221, + 0.895, + 0.433 + ], + "angle": 0, + "content": "Image Masked Auto-Encoders. iGPT [4] was one of the first recent attempts to revisit masked image modeling using Transformer architecture rather than CNNs. iGPT reconstructs at the pixel-level. Other recent works try different reconstruction targets. Some works such as BEIT [2] explore using tokenization as a prediction target, such as tokens from pretrained dVAE [40]. MaskFeat [46] explores using HoG features [7] as a reconstruction target. ImageMAE [16] reconstructs normalized image patches and focuses on studying decoder design, discovering that larger decoders enable the encoder to process only visible patches, thus enabling the use of a larger masking ratio to achieve both better performance and computational efficiency. Unlike these works, our MGM is designed specifically for video." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.44, + 0.897, + 0.622 + ], + "angle": 0, + "content": "Video Masked Auto-Encoders. Some works such as VIM-PAC [37] and BEVT [45] try to reconstruct video tokens and thus require strong tokenizers using either extra pretraining data or domain-specific knowledge. VideoMAE [11, 39] bypasses this requirement by applying image MAE [16] to reconstruct 3D RGB video patches, achieving promising results on video benchmarks. Other works such as Omni-MAE [13] use both image and video masked modeling to achieve improved performance on both image and video tasks. A line of very recent work tries to improve Video-MAE by designing explicit motion cues by reconstructing optical flow or frame difference based targets [33, 36, 50]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.895, + 0.795 + ], + "angle": 0, + "content": "These existing video MAE works all inherit random masking from image MAE [16] where the mask is either discontinuous such as in ST-MAE [11] or random tubes such as in VideoMAE [39]. In the former, the mask is randomly distributed both spatially and temporally, and in the latter, the mask is randomly distributed spatially but temporally static. In contrast, we re-examine this assumption and design a new masking algorithm that continuously masks out video motion to force the model to focus on spatiotemporal saliency. We make no changes to the reconstruction target nor model architecture." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.803, + 0.895, + 0.865 + ], + "angle": 0, + "content": "VideoMAE [39] initially generates a random mask and statically propagates the mask across time. The position of the mask is the same across frames, forming small tubelets which are spatially discontinuous but temporally continuous." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.895, + 0.902 + ], + "angle": 0, + "content": "ST-MAE [11] independently generates a random mask per-frame which is neither spatially nor temporally continuous." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5620" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.09, + 0.885, + 0.281 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.292, + 0.897, + 0.34 + ], + "angle": 0, + "content": "Figure 2: An overview of a) the proof-of-concept simulated-motion masking (SMM) vs. b) motion-guided masking (MGM). Our MGM produces 3D masks that achieves both spatial and temporal continuity, while capturing the true motion information in the video. Random masking (left-most) is both spatially and temporally discontinuous." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.362, + 0.214, + 0.381 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.388, + 0.474, + 0.587 + ], + "angle": 0, + "content": "As detailed in Sec. 1, motion is concentrated in salient video regions. Random masking does not effectively cover these regions because motion is not uniformly distributed throughout the video. Furthermore, spatially salient entities such as people and objects are continuous rather than disjoint patches. In general, this leads us to believe random masking may miss certain semantics that are useful for learning spatiotemporal representations. The goal of this work is to address these deficiencies to make masked video modeling more effective for video representation learning. Because video is temporally cohesive, the MAE should be able to reconstruct a continuous spatiotemporal volume comprised of the salient regions. This motivates our following approach." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.593, + 0.22, + 0.608 + ], + "angle": 0, + "content": "3.1. Preliminaries" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.614, + 0.471, + 0.693 + ], + "angle": 0, + "content": "Given a video \\(V \\in \\mathbb{R}^{T \\times H \\times W \\times C}\\), where \\(T, H, W, C\\) denote the number of frames, height, width, and RGB-channels, the video is typically first split into patches of size \\(t \\times h \\times w \\times C\\) and processed with a patch embedding layer \\(\\mathcal{P}\\) to obtain a sequence of token embeddings \\(V_{p}\\)." + }, + { + "type": "equation", + "bbox": [ + 0.173, + 0.702, + 0.472, + 0.723 + ], + "angle": 0, + "content": "\\[\nV _ {p} = \\mathcal {P} (V); V _ {p} \\in \\mathbb {R} ^ {\\frac {T}{t} \\times \\frac {H}{h} \\times \\frac {W}{w}} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.728, + 0.473, + 0.773 + ], + "angle": 0, + "content": "Next, a masking function \\(\\eta\\) (e.g. random masking [11, 39]) generates a binary mask \\(M\\) which is applied to select a set of visible patches with mask ratio \\(\\gamma\\)." + }, + { + "type": "equation", + "bbox": [ + 0.166, + 0.793, + 0.418, + 0.81 + ], + "angle": 0, + "content": "\\[\nM = \\eta (V _ {p}, \\gamma); d i m (M) = d i m (V _ {p})\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.136, + 0.813, + 0.47, + 0.829 + ], + "angle": 0, + "content": "\\[\nV _ {\\mathrm {p} \\text {- v i s i b l e}} = V _ {p} \\cdot (\\sim M) \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.133, + 0.831, + 0.258, + 0.849 + ], + "angle": 0, + "content": "\\[\nV _ {\\mathrm {p} \\text {- m a s k e d}} = V _ {p} \\cdot M\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.473, + 0.903 + ], + "angle": 0, + "content": "The encoder \\(\\phi\\) then processes only the visible patches \\(V_{\\mathrm{p\\_visible}}\\) while the decoder \\(\\xi\\) processes the full set of encoded patches and masked tokens \\(\\phi(V_{\\mathrm{p\\_visible}}) \\cup V_{\\mathrm{p\\_masked}}\\) to" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.364, + 0.892, + 0.395 + ], + "angle": 0, + "content": "reconstruct the video. This work uses the same asymmetric encoder-decoder design as [11, 16, 39]." + }, + { + "type": "equation", + "bbox": [ + 0.64, + 0.409, + 0.893, + 0.427 + ], + "angle": 0, + "content": "\\[\nE = \\phi \\left(V _ {\\mathrm {p} - \\text {v i s i b l e}}\\right) \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.621, + 0.445, + 0.893, + 0.462 + ], + "angle": 0, + "content": "\\[\nV ^ {\\prime} = \\xi (E \\cup V _ {\\mathrm {p}. \\text {m a s k e d}}) \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.468, + 0.895, + 0.574 + ], + "angle": 0, + "content": "Finally, the model is trained with MSE reconstruction loss between \\( V \\) and \\( V' \\). The model is then transferred to downstream tasks such as classification via finetuning with cross-entropy loss. Note that this work focuses on the mask generator \\( \\eta(\\gamma) \\), which is complementary to recent works which look into the loss function and reconstruction targets [33, 36, 45, 50]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.583, + 0.809, + 0.6 + ], + "angle": 0, + "content": "3.2. Simulated-Motion Masking (SMM)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.606, + 0.894, + 0.681 + ], + "angle": 0, + "content": "To help the encoder learn spatiotemporal semantics throughout the video, we propose to generate a spatiotemporally continuous moving 3D mask, as shown in Fig. 2. This differs from random masking [11] and random tube masking [39] which break spatiotemporal continuity." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.682, + 0.895, + 0.825 + ], + "angle": 0, + "content": "We define the mask as a vector \\([x, y, w, h]\\) where \\( x \\) and \\( y \\) define the top-left coordinate and \\( w \\) and \\( h \\) define the width and height of the mask. We first explore the use of random motion to generate a dense moving 3D mask with masking ratio \\( \\gamma \\). To do this, we initialize a rectangle shaped mask in the first frame with dimensions \\( w_0 = h_0 = \\sqrt{\\gamma * \\frac{H}{h} * \\frac{W}{w}} \\). \\( x_0 \\) and \\( y_0 \\) are then randomly initialized in rand(0, H/h - h_0). We then propagate the mask across time using the following recurrent relation:" + }, + { + "type": "equation", + "bbox": [ + 0.558, + 0.835, + 0.833, + 0.852 + ], + "angle": 0, + "content": "\\[\n[ x _ {t}, y _ {t}, w _ {t}, h _ {t} ] = [ x _ {t - 1} + v _ {x t}, y _ {t - 1} + v _ {y t},\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.67, + 0.854, + 0.892, + 0.875 + ], + "angle": 0, + "content": "\\[\n\\left. w _ {t - 1} + s _ {t}, h _ {t - 1} + s _ {t} \\right] \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.606, + 0.875, + 0.75, + 0.904 + ], + "angle": 0, + "content": "\\[\nt \\in [ 1, T), \\sum_ {t} s _ {t} = 0\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "5621" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.168 + ], + "angle": 0, + "content": "where \\( v_{xt}, v_{yt} \\) are the random horizontal and vertical velocity components, and \\( s_t \\) is a random scaling factor. To ensure that the masking ratio for each video is consistent, we enforce that \\( \\sum_{t} s_{t} = 0 \\); in other words, the number of masked patches remains fixed for a given \\( \\gamma \\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.175, + 0.37, + 0.192 + ], + "angle": 0, + "content": "3.3. Motion-Guided Masking (MGM)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.198, + 0.47, + 0.333 + ], + "angle": 0, + "content": "While SMM leads to an improvement over random masking, SMM generates masks that may not reflect true motion as it is not context-aware. For example in Figure 2, the mask may cover static background rather than the basketball player depending on the random initialization and velocity. The most straightforward approach to address this issue would be to guide the mask using precomputed object bounding boxes or optical flow. However, this requires additional data and cost and would make such a method less scalable." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.335, + 0.47, + 0.56 + ], + "angle": 0, + "content": "We propose to use motion vectors as guidance to ensure that the mask movement consistently covers motion across frames. Motion vectors [30, 47] can be decoded from raw video (with H.264 or H.265 CODECs) with no extra cost, which ensures that our proposed approach adds no additional cost and scales well to larger datasets. A motion vector \\( M_{t}[x,y] \\) for a given pixel position \\( x,y \\) at frame \\( t \\), is defined as \\( [d_x,d_y] \\) where \\( d_{x} \\) and \\( d_{y} \\) denote the displacement of pixel \\( x,y \\) from frame \\( t - 1 \\). Motion vectors are typically sparsely assigned to \\( 8\\times 8 \\) pixel grids [30, 47], so the overall motion vector map is similar to optical flow but at a lower resolution. In order to use motion vectors to guide the masking, we need pixel-level correspondence between the motion vectors and the video. We accomplish this by upsampling the motion vector map to match the spatial resolution of the video." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.56, + 0.47, + 0.605 + ], + "angle": 0, + "content": "Given a motion vector map \\( M_t \\in \\mathbb{R}^{T \\times \\frac{H}{8} \\times \\frac{W}{8}} \\), we first use nearest-neighbor upsampling (\\( U_{\\mathrm{nearest}} \\)) to get \\( M_{\\mathrm{t.scaled}} \\in \\mathbb{R}^{T \\times H \\times W} \\)." + }, + { + "type": "equation", + "bbox": [ + 0.165, + 0.615, + 0.47, + 0.632 + ], + "angle": 0, + "content": "\\[\n\\mathrm {M} _ {\\text {t . s c a l e d}} = U _ {\\text {n e a r e s t}} \\left(M _ {t}, (H, W)\\right) \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.64, + 0.47, + 0.71 + ], + "angle": 0, + "content": "Next, we initialize a dense rectangle mask for frame \\( t_0 \\) with dimensions \\( w_0 = h_0 = \\sqrt{\\gamma * \\frac{H}{h} * \\frac{W}{w}} \\). \\( x_0 \\) and \\( y_0 \\) are then randomly initialized in \\( rand(0, \\frac{H}{h} - h_0) \\). The mask is then generated for following time-steps as:" + }, + { + "type": "equation", + "bbox": [ + 0.086, + 0.717, + 0.332, + 0.735 + ], + "angle": 0, + "content": "\\[\nx _ {\\mathrm {t} \\text {c e n t e r}}, y _ {\\mathrm {t} \\text {c e n t e r}} = P o o l _ {\\mathrm {t o p K}} (M _ {\\mathrm {t} \\text {s c a l e d}})\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.168, + 0.739, + 0.285, + 0.752 + ], + "angle": 0, + "content": "\\[\nw _ {t} = w _ {t - 1} + s _ {x t}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.169, + 0.756, + 0.283, + 0.771 + ], + "angle": 0, + "content": "\\[\nh _ {t} = h _ {t - 1} + s _ {y t}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.093, + 0.769, + 0.47, + 0.8 + ], + "angle": 0, + "content": "\\[\n\\left[ x _ {t}, y _ {t}, w _ {t}, h _ {t} \\right] = \\left[ x _ {\\mathrm {t} - \\text {c e n t e r}} - \\frac {w _ {t}}{2}, y _ {\\mathrm {t} - \\text {c e n t e r}} - \\frac {y _ {t}}{2}, w _ {t}, h _ {t} \\right] \\tag {7}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.09, + 0.803, + 0.325, + 0.833 + ], + "angle": 0, + "content": "\\[\nt \\in [ 1, T), \\sum_ {t} s _ {x t} = 0, \\sum_ {t} s _ {y t} = 0\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.902 + ], + "angle": 0, + "content": "where \\( Pool_{topK} \\) is the topK (top-1 in our work) magnitude pooling operation that gives the argmax indexes \\( x_{t\\_ center}, y_{t\\_ center} \\), which the mask is centered around. We also apply jitter \\( s_{xt}, s_{yt} \\) to both the mask height and width." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.894, + 0.168 + ], + "angle": 0, + "content": "In other words, MGM produces a moving 3D mask where the movement of the mask is centered around parts of the video with the highest magnitude of motion, as shown in Fig. 2. This makes the reconstruction task more focused on spatiotemporal semantics than random masking." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.181, + 0.706, + 0.198 + ], + "angle": 0, + "content": "4. Experimental Results" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.206, + 0.602, + 0.221 + ], + "angle": 0, + "content": "4.1. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.23, + 0.895, + 0.457 + ], + "angle": 0, + "content": "We conduct experiments on five commonly used datasets: Something-Something V2 (SSv2) [14] contains 220K videos with 174 action classes. SSv2 is considered a motion heavy dataset, as most of the labels are defined by the motion and directionality of the actual action. Kinetics-400 (K400) [19] is the de-facto standard dataset used to evaluate video recognition. It contains 240K Internet videos with 400 action classes. UCF101 [34] is a dataset containing 13K Internet short videos with 101 action classes. HMDB51 [22] is a dataset containing 5K short movie clips from 51 action classes. Diving48 [23] contains 18K untrimmed video clips from 48 action classes, all of which are types of dives. We report the top-1 accuracy on the evaluation set for all datasets following standard practices [12]. Only UCF101 and HMDB51 have multiple split versions; we use split 1." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.466, + 0.719, + 0.482 + ], + "angle": 0, + "content": "4.2. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.489, + 0.894, + 0.58 + ], + "angle": 0, + "content": "Model Configuration: We experiment with both 2D and 3D transformer backbones. The default backbone is ViT-Base [9] with global joint space-time attention. We also experimented with TimesFormer [3] with divided space-time attention. For fair comparison, we use the same input patch size of \\(2 \\times 16 \\times 16\\) for all models following [39]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.895, + 0.701 + ], + "angle": 0, + "content": "Pre-Processing: We pretrain with clips of 16 frames sampled at a temporal stride of 4 and 2 for K400 and SSv2 respectively following [39]. We use a fixed spatial resolution of \\(224 \\times 224\\) for all experiments. We apply multi-scalecrop and horizontal flip augmentation by default (flip is not applied to SSv2). We follow [39] to use AdamW [27] optimizer with a base learning rate \\(1.5e - 4\\), weight decay of \\(0.05\\), \\(\\beta = [0.9, 0.95]\\), and cosine learning rate decay." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.702, + 0.895, + 0.838 + ], + "angle": 0, + "content": "Finetuning and Evaluation: We use the same 16-frame clip for finetuning and multi-view evaluation protocol following standard practice [12]. We use TSN-style sampling [44] on SSv2 dataset with 2 temporal \\(\\times\\) 3 spatial views during test-time following [39] for fair comparison. For Kinetics-400, UCF101, HMDB51 and Diving48, we use 5 temporal \\(\\times\\) 3 spatial views during test-time following [39] for fair comparison. See the supplementary material for hyperparameter details which are mostly the same as [39]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.848, + 0.64, + 0.862 + ], + "angle": 0, + "content": "4.3. Main Results" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Something-Something V2. We first show our MGM's performance on SSv2 in Table 1, and compare with previous" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5622" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.471, + 0.09, + 0.608, + 0.103 + ], + "angle": 0, + "content": "finetune eval on SSv2" + }, + { + "type": "table_caption", + "bbox": [ + 0.697, + 0.09, + 0.835, + 0.102 + ], + "angle": 0, + "content": "finetune eval on K400" + }, + { + "type": "table", + "bbox": [ + 0.09, + 0.105, + 0.884, + 0.43 + ], + "angle": 0, + "content": "
ModelBackboneGFLOPsEpochsPretrainTop1EpochsPretrainTop1
Supervised
SlowFast [12]R101 + NL106196K40063.1--79.8
TimeSformer [3]ViT-B19615IN21K59.515IN21K78.0
VidTr [51]ViT-B35150K40063.0--79.1
MotionFormer [28]ViT-B37090+35IN21K + K40066.590IN21K79.7
MViTv1 [10]MViT-B455200K40067.7--81.2
MViTv2 [24]MViT-B225200K40070.5--82.9
Self-supervised
BEVT [45]Swin-B282800+150IN1K + K40070.6800+150IN1K + K40080.6
M³Video [36]ViT-B180400SSv269.2400K40079.7
MGMViT-B180400SSv269.6400K40080.3
VideoMAE [39]ViT-B180800SSv269.6800K40080.0
MGMViT-B180800SSv270.6800K40080.8
MAM² [33]ViT-B + VQGAN1801200SSv271.3800K40082.3
MGMViT-B1801200SSv271.61200K40081.2
OmniMAE [13]ViT-B1801600IN1K + SSv269.51600IN1K + K40080.8
VideoMAE [39]ViT-B1801600SSv270.31600K40081.5
VideoMAE [39]ViT-B1802400SSv270.8---
STMAE [11]ViT-B1801600K400N/A1600K40081.3
MotionMAE [50]ViT-B1802400SSv271.81600K40081.7
MGMViT-B1801600SSv271.81600K40081.7
MGMViT-B1802400SSv272.1---
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.454, + 0.893, + 0.486 + ], + "angle": 0, + "content": "Table 1: Results comparison on Something-SomethingV2 (SSv2) and Kinetics-400 (K400). GFLOPs is listed as a single view's. All results are with fine-tuning. We apply repeated augmentation \\([18] = 2\\) for this table to compare against SOTA." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.511, + 0.472, + 0.693 + ], + "angle": 0, + "content": "models trained in a supervised manner: Our MGM using vanilla ViT-B pretrained on only SSv2 outperforms previous SOTA such as MViTv1 [10] \\((+4.4\\%)\\) and MViTv2 [10] \\((+1.6\\%)\\) which uses a heavy hierarchical 3D transformer backbone and pretrains on Kinetics-400. This demonstrates the efficiency and effectiveness of our proposed method compared to supervised 3D transformer backbones. MGM also significantly outperforms previous supervised learning methods that use the same backbone as us: \\(+5.6\\%\\) over MotionFormer [28] and \\(+12.6\\%\\) over TimeSformer [3]. This demonstrates that the proposed MGM is effective for spatiotemporal modeling." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.472, + 0.903 + ], + "angle": 0, + "content": "We then compare MGM with SOTA video MAE methods. With the same backbone and training schema, MGM achieves \\(1.3\\%\\) higher accuracy comparing to VideoMAE [39]. Note that with \\(3 \\times\\) less training time, our MGM pretrained for 800 epochs is able to achieve nearly the same performance as VideoMAE pretrained for 2400 epochs (\\(\\sim 66\\%\\) fewer epochs), as illustrated in Fig. 1. This demonstrates that motion-guided masking is a more efficient strategy for self-supervised spatiotemporal learning due to learning video saliency. Compared to OmniMAE [13] which does masked modeling on both images and video, MGM achieves \\(+2.6\\%\\) improvement. Compared to BEVT [45] which also learns from both images and video and additionally uses" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.511, + 0.895, + 0.587 + ], + "angle": 0, + "content": "Swin Transformer [25, 26] - a heavy 3D Transformer architecture - MGM achieves \\(+1.5\\%\\) improvement. This is despite the fact that our method only uses video and is pretrained from scratch. Note that STMAE [11] only provides results for ViT-Large backbone on SSv2." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.593, + 0.896, + 0.835 + ], + "angle": 0, + "content": "We finally compare our MGM with some most recent works that also utilize motion information for video pretraining. MGM outperforms \\(\\mathrm{M}^3\\mathrm{Video}\\) [36] (\\(+0.4\\%\\) with the same 400 epochs of pretraining) which reconstructs motion trajectories generated from optical flow. We achieve equivalent performance to MotionMAE [50] using \\(50\\%\\) fewer epochs (1600 vs. 2400) even though it utilizes frame difference as an additional reconstruction target which incorporates explicit motion information. The results show that motion-guided masking alone is sufficient for improving spatiotemporal learning. It is worth reiterating that our MGM uses motion vectors for masking guidance, which is already computed during video encoding, and thus directly available during video decoding [30, 43, 47], making our method more efficient and scalable comparing to works such as [33, 36, 50] which use optical flow and/or frame difference." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Kinetics-400 (K400). We further conduct experiments on K400 and show results in Table 1. Similar trends are observed. Our MGM is able to outperform supervised models with the same backbone such as TimeSformer [3] by \\(+3.7\\%\\)" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5623" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.471, + 0.152 + ], + "angle": 0, + "content": "and MotionFormer [28] by \\(+2.0\\%\\). MGM slightly underperforms some hierarchical 3D transformer backbones such as MViTv2 [24] by \\(-1.2\\%\\) on K400 but MViTv2 is trained with \\(2\\times\\) more frames (32) and uses significantly more FLOPS." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.153, + 0.472, + 0.304 + ], + "angle": 0, + "content": "Comparing with other MAE based methods, our MGM consistently outperforms VideoMAE by \\(+1.4\\%\\) at 800 epochs of pretraining. MGM also achieves better performance comparing to other recent works, at no additional cost. Our MGM outperforms \\(\\mathrm{M}^3\\mathrm{Video}\\) [36] at 400 epochs of pretraining by \\(0.6\\%\\), while being more efficient as our method does not use frame difference nor optical flow. Compared to OmniMAE [13] which uses both images and video, MGM achieves \\(0.9\\%\\) improvement. Compared to BEVT [45], MGM achieves \\(1.1\\%\\) improvement." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.305, + 0.472, + 0.501 + ], + "angle": 0, + "content": "We note that the performance gain MGM obtains over other methods on K400 is slightly lower compared to on SSv2. This can be explained by the fact that a great proportion of actions in K400 dataset can be differentiated by the appearance of a few key frames, for example, \"skiing\" vs. \"tennis\". In contrast, recognising actions in SSv2 dataset, e.g. \"moving something up\" vs. \"moving something down\", requires the model to understand the subtle differences in motion along temporal dimension. Therefore, we hypothesize that spatiotemporal modeling is less impactful on spatial-heavy datasets such as K400 and the strength of MGM is not fully exhibited. Motion serves as a appearance-agnostic differentiator between classes." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.513, + 0.258, + 0.53 + ], + "angle": 0, + "content": "4.4. Transfer Learning" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.537, + 0.47, + 0.628 + ], + "angle": 0, + "content": "We next evaluate MGM's performance when transferred to smaller datasets: UCF101 [34], HMDB51 [22], and Diving48 [23]. Performance in transfer learning is commonly used as an indicator of feature quality and representativeness [17]. We use ViT-Base model pretrained on K400 and SSv2 by 800 epochs for all transfer learning experiments." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.471, + 0.794 + ], + "angle": 0, + "content": "Finetune on downstream tasks. We first present fine-tuning results from MGM pretrained on unlabeled K400 in Table 2. Our MGM consistently outperforms VideoMAE with same backbone and pretraining setup on all three datasets \\((+0.9\\%)\\) on UCF101, \\(+1.1\\%\\) on HMDB51, \\(+4.9\\%\\) on Diving48). This shows that our approach learns more representative semantics and thus generalizes better to small-scale downstream tasks. It is worth mentioning that MGM even outperforms K400 supervised pretraining on HMDB51 \\((+3.2\\%)\\) and on Diving48 \\((+7.5\\%)\\), demonstrating the effectiveness of our proposed method." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.472, + 0.903 + ], + "angle": 0, + "content": "Our MGM is also able to consistently outperform VideoMAE [39] with pretraining on unlabeled SSv2 in the finetune setting \\((+1.3\\%)\\) on UCF101, \\(+1\\%\\) on HMDB51, \\(+2.6\\%\\) on Diving48). Our MGM even outperforms SSv2 supervised pretraining by a large margin \\((+14.1\\%)\\) on UCF101, \\(+13.4\\%\\) on HMDB51, \\(+46.9\\%\\) on Diving48). Finetuning MGM on SSv2 (same model from Tab. 1) does not lead to a large" + }, + { + "type": "table", + "bbox": [ + 0.527, + 0.09, + 0.868, + 0.171 + ], + "angle": 0, + "content": "
UCFHMDBDiving48
Supervised (K400) †95.171.462.7
VideoMAE [39]93.373.565.3
MGM94.274.670.2
+ K400 Finetune (Tab. 1)97.781.082.6
" + }, + { + "type": "table_caption", + "bbox": [ + 0.517, + 0.177, + 0.875, + 0.19 + ], + "angle": 0, + "content": "(a) Pretrained on K400 and finetuned on downstream tasks." + }, + { + "type": "table", + "bbox": [ + 0.522, + 0.191, + 0.869, + 0.272 + ], + "angle": 0, + "content": "
UCFHMDBDiving48
Supervised (SSv2) †77.856.336.2
VideoMAE [39]90.668.780.5
MGM91.969.783.1
+ SSv2 Finetune ( Tab. 1)93.274.783.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.517, + 0.278, + 0.875, + 0.292 + ], + "angle": 0, + "content": "(b) Pretrained on SSv2 and finetuned on downstream tasks." + }, + { + "type": "table", + "bbox": [ + 0.539, + 0.293, + 0.855, + 0.361 + ], + "angle": 0, + "content": "
UCFHMDBDiving48
Supervised (K400) †94.165.425.2
VideoMAE [39]70.545.410.0
MGM77.549.214.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.529, + 0.366, + 0.865, + 0.394 + ], + "angle": 0, + "content": "(c) Pretrained on K400 and evaluated with linear probing on downstream tasks." + }, + { + "type": "table", + "bbox": [ + 0.54, + 0.395, + 0.855, + 0.463 + ], + "angle": 0, + "content": "
UCFHMDBDiving48
Supervised (SSv2) †72.951.813.2
VideoMAE [39]65.341.210.7
MGM69.144.810.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.529, + 0.469, + 0.865, + 0.497 + ], + "angle": 0, + "content": "(d) Pretrained on SSv2 and evaluated with linear probing on downstream tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.509, + 0.895, + 0.601 + ], + "angle": 0, + "content": "Table 2: MGM generalizes well to various downstream datasets (UCF101, HMDB51 and Diving48) on two downstream tasks (finetune, linear-probe). We test VideoMAE and MGM pretrained on Kinetics-400 (K400) for 800 epochs. The supervised baseline is ViT-B trained from scratch on K400 and SSv2 using the recipe from MViT [10, 24]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.894, + 0.689 + ], + "angle": 0, + "content": "boost, indicating that our model is able to learn the majority of semantics just from unsupervised pretraining, and that unsupervised pretraining is able to make better use of the information in SSv2 than supervised training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.69, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Linear Probe on downstream tasks. Previous work [2, 11, 16] argues that generative approaches such as MAE generally perform worse on linear probing tasks as there is a larger gap between the reconstruction task and downstream evaluation compared to other pretraining methods. Nevertheless, we compare linear probe performance between MGM and VideoMAE [39] and show that our method achieves significantly better performance. With K400 pretraining, we outperform VideoMAE by \\(+7\\%\\) on UCF101, \\(+3.8\\%\\) on HMDB51, and \\(+4.2\\%\\) on Diving48. With SSv2 pretraining, we outperform by \\(+3.8\\%\\) on UCF101, \\(+3.6\\%\\) on HMDB51, and underperform by \\(-0.5\\%\\) on Diving48. This demonstrates that motion-modeling helps reduce the gap between the reconstruction task and downstream tasks, as linear probe only" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5624" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.468, + 0.151 + ], + "angle": 0, + "content": "
UCF14 → HMDB7HMDB14 → UCF7
VideoMAE [39]55.769.6
MGM57.671.4
+ K400 Finetune (Tab. 1)79.196.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.162, + 0.473, + 0.254 + ], + "angle": 0, + "content": "Table 3: MGM works well when trained on one dataset and evaluated on another dataset for an overlapping set of classes. The model sees no samples from test dataset, indicating motion understanding as motion is agnostic to spatial appearance. We tested VideoMAE and MGM pretrained on Kinetics-400 (K400) for 800 epochs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.281, + 0.47, + 0.311 + ], + "angle": 0, + "content": "trains a linear classifier on top of features extracted from the frozen backbone; linear layers cannot learn new semantics." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.312, + 0.471, + 0.417 + ], + "angle": 0, + "content": "We note that there is a large gap of over \\(10\\%\\) with K400 supervised pretraining on linear probe. This is a general deficiency of generative methods such as MAE-based pretraining [11] and we leave further exploration of this problem to future works. One way to address this would be to combine MAE with discriminative methods such as contrastive learning to obtain a balanced representation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.418, + 0.471, + 0.719 + ], + "angle": 0, + "content": "Domain adaptation. We further evaluate MGM on partial domain adaptation tasks following [49], in which the labels for the target dataset are a subset of the labels for the source dataset. The model is finetuned on the source dataset and directly evaluated on the target dataset without seeing any samples from the target dataset. This is more challenging than conventional domain adaptation as the model may incorrectly label samples in the target dataset as the labels from the source dataset which are not present in the target dataset (\"negative transfer\") [49]. Previous work has showed that optical flow is useful for action recognition because it is invariant to appearance [32]. Several works such as [6, 31] improve unsupervised domain adaptation in video by reducing background and appearance bias to capture the essence of an action via shuffling and mixup respectively. By similar reasoning, domain adaptation is a good evaluation protocol to assess motion learning as the source and target datasets have very different visual appearances, and motion serves as a common link between classes that is agnostic to spatial appearances." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.473, + 0.902 + ], + "angle": 0, + "content": "We use the training sets provided by [49] for UCF14 \\(\\rightarrow\\) HMDB7 and HMDB14 \\(\\rightarrow\\) UCF7. Our MGM consistently outperform VideoMAE with K400 pretraining in both settings \\((+1.9\\%)\\) on HMDB7 and \\(+1.8\\%\\) on UCF7) indicating that MGM can also outperform in a domain adaptation setting. While there is a significant gap of over \\(20\\%\\) between Table 3 and Table 2, finetuning our model on K400 labels bridges the gap. This suggests that our model has learned video saliency and can perform well without any large-scale label supervision, but additional label supervision is helpful for challenging settings such as domain adaptation where spatial information is very different and difficult to" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.091, + 0.69, + 0.228 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.534, + 0.239, + 0.662, + 0.253 + ], + "angle": 0, + "content": "(a) More mask ratios." + }, + { + "type": "image", + "bbox": [ + 0.697, + 0.091, + 0.883, + 0.228 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.699, + 0.239, + 0.884, + 0.254 + ], + "angle": 0, + "content": "(b) Pretrain duration in epochs." + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.265, + 0.895, + 0.312 + ], + "angle": 0, + "content": "Figure 3: Ablations on mask ratio 3a and pretraining duration 3b. Mask ratio 0.75 is optimal and performance does not saturate with longer pretraining." + }, + { + "type": "table", + "bbox": [ + 0.51, + 0.326, + 0.669, + 0.393 + ], + "angle": 0, + "content": "
backboneSSv2
ViT-S61.1
ViT-B67.3
TimesFormer [3]64.7
" + }, + { + "type": "table", + "bbox": [ + 0.726, + 0.34, + 0.884, + 0.392 + ], + "angle": 0, + "content": "
guidanceSSv2
optical flow66.0
motion vector67.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.503, + 0.398, + 0.673, + 0.412 + ], + "angle": 0, + "content": "(a) Backbone generalization." + }, + { + "type": "table", + "bbox": [ + 0.511, + 0.412, + 0.64, + 0.465 + ], + "angle": 0, + "content": "
aspect ratioSSv2
no67.1
yes67.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.529, + 0.47, + 0.619, + 0.484 + ], + "angle": 0, + "content": "(c) Mask jitter." + }, + { + "type": "table_caption", + "bbox": [ + 0.727, + 0.398, + 0.882, + 0.412 + ], + "angle": 0, + "content": "(b) Source of motion info." + }, + { + "type": "table", + "bbox": [ + 0.669, + 0.412, + 0.884, + 0.465 + ], + "angle": 0, + "content": "
pretrain datasamplesK400
Mini-K200 [48]80K78.2
K400 [19]240K78.6
" + }, + { + "type": "table_caption", + "bbox": [ + 0.68, + 0.47, + 0.871, + 0.484 + ], + "angle": 0, + "content": "(d) Dataset scale generalization." + }, + { + "type": "table", + "bbox": [ + 0.512, + 0.485, + 0.884, + 0.58 + ], + "angle": 0, + "content": "
Masktemporal propagationspatial continuity
staticsimulatedmotionsparsedenseAcc
Random Block✓✓62.9
SMM (Sparse)✓✓64.6
Random Tube✓✓65.0
MGM (Sparse)✓✓65.1
SMM (Dense)✓✓65.9
MGM (Dense)✓✓67.3
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.584, + 0.895, + 0.627 + ], + "angle": 0, + "content": "(e) Masking strategies differentiated by initial position, temporal propagation, and spatial continuity. Spatiotemporally continuous masks with motion guidance perform the best." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.638, + 0.895, + 0.699 + ], + "angle": 0, + "content": "Table 4: Ablations on backbone 4a, source of motion guidance 4b, mask jitter 4c, pretrain data scale 4d, and mask type 4e. All ablations pretrain for 200 epochs on SSv2 unless otherwise indicated." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.728, + 0.892, + 0.759 + ], + "angle": 0, + "content": "learn from limited samples. There are only \\(\\sim 1000\\) training samples in each setting." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.77, + 0.612, + 0.785 + ], + "angle": 0, + "content": "4.5. Ablations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.794, + 0.892, + 0.854 + ], + "angle": 0, + "content": "We perform ablations on the Something-Something V2 dataset, with MGM with ViT-B backbone pretrained for 200 epochs using our motion-guided masking, unless otherwise specified." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.895, + 0.902 + ], + "angle": 0, + "content": "Impact of masking ratio. Figure 3a studies the impact of different masking ratio on SSv2. We noticed that 0.75 masking ratio works best for the proposed MGM, which" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5625" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.168 + ], + "angle": 0, + "content": "is lower than that of other works [11, 39]. This is because motion-guided masking leads to a more \"challenging\" reconstruction task compared to random masking, since the masked regions of videos are most informative and therefore cannot be easily inferred from retained regions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.169, + 0.472, + 0.26 + ], + "angle": 0, + "content": "Impact of pretraining length. We show the impact of different pretraining epochs on SSv2 in Figure 3b. The proposed MGM consistently improves with more training and we achieve state-of-the-art performance on SSv2 with 2400 epochs of pretraining. Performance does not seem to saturate with longer pretraining." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.261, + 0.473, + 0.442 + ], + "angle": 0, + "content": "Generalization to different backbones. MGM also generalizes well to backbones of different sizes and types (Table 4a). We test vanilla ViT-S [9] and ViT-B [9], and TimeSformer [3] with joint space-time attention. Note that our TimeSformer ablation outperforms the supervised result reported by [3] of \\(59.5\\%\\) on SSv2 which uses IN21K pretraining. In contrast, we do not use any extra data. ViT-S's lower performance may be explained by its low model capacity which may not be sufficient for learning spatiotemporal dynamics. As other methods do not use ViT-S, we cannot compare our result to other methods. We thus use ViT-B to compare fairly against other MAE works which use ViT-B." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.444, + 0.472, + 0.655 + ], + "angle": 0, + "content": "Impact of motion source. In Table 4b we compare the performance of MGM when using optical flow vs. motion vectors as the source of motion guidance. Even though optical flow is more fine-grained and precise than motion vectors, performance of MGM drops when the mask is guided by optical flow. This could be related to the fact that optical flow is calculated on a per-pixel basis whereas motion vectors are computed in a block-wise manner and we utilize a block-wise mask strategy. We thus conveniently choose to use motion vector as it is also directly obtainable from compressed video. We extract optical flow using RAFT-Small [38]. On the SSv2 dataset, reading motion vectors is roughly \\(30 \\times\\) faster than computing optical flow (80 milliseconds vs. 2.5 seconds per video on average)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.657, + 0.47, + 0.717 + ], + "angle": 0, + "content": "Impact of mask aspect ratio jitter. In Table 4c we ablate the use of aspect ratio jittering from Eq. (7). We see that aspect ratio jittering gives a small \\(0.2\\%\\) boost in performance but is not a critical component of MGM." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.718, + 0.47, + 0.884 + ], + "angle": 0, + "content": "Impact of pretrain dataset scale. In Table 4d we ablate the amount of pretraining data used to see if MGM can generalize to different dataset scales. We pretrain MGM on MiniKinetics-200 [48] and Kinetics-400 (K400) [19] which contain \\(\\sim 80\\mathrm{K}\\) videos and \\(\\sim 240\\mathrm{K}\\) videos respectively for 200 epochs. MiniKinetics-200 contains videos belonging to a subset of 200 of the most common classes in K400. We then evaluate top-1 accuracy on K400. We find that there is a small \\(0.4\\%\\) drop in performance when pretraining on the smaller MiniKinetics-200. We expect performance to further improve when pretraining on datasets larger than K400." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.886, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Effectiveness of 3D motion masking. Table 4e studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.44 + ], + "angle": 0, + "content": "different masking strategies which are broken down into categories based on degree of motion guidance and spatial continuity. We first compare dense to sparse masking, where sparse means that the mask may be spatially discontinuous. The dense variant of SMM and MGM outperform the respective sparse counterpart; dense SMM outperforms sparse SMM by \\(1.3\\%\\) and dense MGM outperforms sparse MGM by \\(2.2\\%\\). This suggests the importance of maintaining spatial continuity in the masked reconstruction. Next, we compare MGM to SMM. Sparse MGM outperforms sparse SMM by \\(0.5\\%\\) and dense MGM outperforms dense SMM by \\(1.4\\%\\). When motion is completely removed, performance is the worst even when the mask is spatially continuous (static block gets \\(62.9\\%\\)). Dense MGM outperforms all masking strategies and specifically the random masking baseline by \\(2.3\\%\\). All masking strategies except block and sparse SMM outperform random masking. Random masking is spatiotemporally discontinuous. This validates our intuition that forming continuous 3D masks which model the true motion information within video is useful. We thus pick dense MGM for all other experiments and refer to \"MGM\" as the dense variant by default. For a visualization of these masking strategies, see Figure 4." + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.464, + 0.891, + 0.617 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.521, + 0.63, + 0.871, + 0.646 + ], + "angle": 0, + "content": "Figure 4: Visualization of different mask algorithms." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.692, + 0.637, + 0.706 + ], + "angle": 0, + "content": "4.6. Visualization" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.901 + ], + "angle": 0, + "content": "In Figure 5, we provide visualizations from two perspectives using MGM pretrained on K400. Note that visualizations are subjective and should not be used as a formal explanation for model behavior. Our intention is to provide additional insight into the model to complement our quantitative results. We first visualize the RGB frames with bounding boxes, motion-guided masks, and motion vectors. We see that the motion-guided masks overlap with the majority of spatiotemporally salient regions. Second, we visualize the attention map using the center patch of the center frame as a query. We observe that the model mostly attends to the salient regions. For more visualizations, see the supplementary." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5626" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.117, + 0.124, + 0.132, + 0.136 + ], + "angle": 0, + "content": "a)" + }, + { + "type": "image", + "bbox": [ + 0.139, + 0.089, + 0.241, + 0.17 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.246, + 0.089, + 0.348, + 0.17 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.354, + 0.089, + 0.457, + 0.169 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.117, + 0.203, + 0.131, + 0.215 + ], + "angle": 0, + "content": "b)" + }, + { + "type": "image", + "bbox": [ + 0.139, + 0.174, + 0.241, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.246, + 0.174, + 0.348, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.354, + 0.174, + 0.456, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.118, + 0.286, + 0.132, + 0.298 + ], + "angle": 0, + "content": "c)" + }, + { + "type": "image", + "bbox": [ + 0.14, + 0.256, + 0.241, + 0.334 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.246, + 0.256, + 0.348, + 0.335 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.354, + 0.256, + 0.456, + 0.335 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.118, + 0.367, + 0.133, + 0.379 + ], + "angle": 0, + "content": "d)" + }, + { + "type": "image", + "bbox": [ + 0.14, + 0.338, + 0.241, + 0.415 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.246, + 0.338, + 0.348, + 0.416 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.354, + 0.338, + 0.456, + 0.416 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.428, + 0.471, + 0.488 + ], + "angle": 0, + "content": "Figure 5: a) RGB frames with bounding boxes for visualization. b) Our MGM masks continuously cover the moving hand. c) Motion vector maps. d) Encoder attention map using center patch of center frame as query." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.525, + 0.325, + 0.541 + ], + "angle": 0, + "content": "5. Discussion and Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.557, + 0.471, + 0.647 + ], + "angle": 0, + "content": "Limitations. Our method efficiently leverages motion cues from compressed video format. However, MGM's effectiveness on the video benchmarks that are not human centric or have tremendous camera motion has yet to be examined. To the best of our knowledge, we did not find such a video benchmark, so we will leave this to future work." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.654, + 0.471, + 0.715 + ], + "angle": 0, + "content": "Potential negative impact. As our model is trained on primarily Internet video datasets, our model will learn the bias inherent to that data. There could be unintended consequences and we advocate for complying with the law." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.473, + 0.902 + ], + "angle": 0, + "content": "Conclusion. This paper introduces motion-guided masking (MGM), an algorithm which produces motion-aware 3D masks to improve spatiotemporal learning. Our use of motion information is much more efficient than previous optical flow as we leverage motion vectors that naturally exist in the video codec. We achieve new state-of-the-art or comparable performance on two challenging large-scale video benchmarks and achieve previous state-of-the-art results with \\(50\\%\\) less pretraining time, making our method more efficient. We also achieve better generalization than previous video MAE works on three small-scale datasets. 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However, unlike images, both spatial and temporal information are important for video understanding. This suggests that the random masking strategy that is inherited from the image MAE is less effective for video MAE. This motivates the design of a novel masking algorithm that can more efficiently make use of video saliency. Specifically, we propose a motion-guided masking algorithm (MGM) which leverages motion vectors to guide the position of each mask over time. Crucially, these motion-based correspondences can be directly obtained from information stored in the compressed format of the video, which makes our method efficient and scalable. On two challenging large-scale video benchmarks (Kinetics-400 and Something-Something V2), we equip video MAE with our MGM and achieve up to $+1.3\%$ improvement compared to previous state-of-the-art methods. Additionally, our MGM achieves equivalent performance to previous video MAE using up to $66\%$ fewer training epochs. Lastly, we show that MGM generalizes better to downstream transfer learning and domain adaptation tasks on the UCF101, HMDB51, and Diving48 datasets, achieving up to $+4.9\%$ improvement compared to baseline methods. + +# 1. Introduction + +Video transformers [1, 24, 25, 28, 43] have achieved state-of-the-art for a variety of video understanding tasks, mirroring the success of image transformers such as ViT [9]. However, many video transformers heavily rely on large-scale supervised pretraining from image datasets such as ImageNet21K [8] and JFT-300M [35], which is data-inefficient. + +Self-supervised learning (SSL) [5, 15, 17, 29, 42] is one promising paradigm for eliminating the dependency on large-scale supervised pretraining. The denoising / masked autoencoder (MAE) [41], which was originally popularized by BERT [20] for natural language modeling, has recently re + +![](images/b3e603fe4ab31aa6b677ca87eadc678ae9e632aab57f84455c4a608844429c8e.jpg) +Figure 1: Top-1 accuracy on Something-Something V2. Our proposed MGM outperforms all previous masked-video methods (M³Video [36], MAM² [33], BEVT [45], OmniMAE [13], MotionMAE [50], and VideoMAE [39]) with improved training efficiency. Marker shape denotes reconstruction target. + +emerged as a promising representation learning method for vision tasks. Image MAE [2, 16] has achieved state-of-the-art in image domain via learning to reconstruct randomly masked image patches. Recently, similar works [11, 39] that reconstruct randomly masked video have obtained encouraging results in video domain. However, few SSL works focus on effectively learning video saliency. In this paper, we improve upon the previous video MAEs [11, 39] via video saliency. + +We argue that the random masking strategy which is inherited from image MAE is not optimal for video. The optimal random masking ratio for video MAE [11, 39] is higher than that for image MAE [16] (0.9 vs. 0.75). This can be understood as a consequence of the natural temporal coherence within videos, which leads to the existence of similar video patches in other frames. When using random masking, many of these correlated video patches may be visible to the encoder which would make reconstruction easier. This necessitates the use of a high masking ratio in order to reduce redundancy and make the reconstruction task + +sufficiently challenging [11]. However, increasing the masking ratio has the side-effect of leaving fewer visible patches for the MAE encoder to learn spatiotemporal saliency from, which we hypothesize limits the learned representation. + +We thus propose to guide the model to learn to reconstruct the most salient regions of video. As humans and objects are key to understanding video, one natural idea is to track the bounding boxes in each video frame and mask the content within. This is also consistent with the observation that video pixels evolve continuously frame-by-frame, and therefore, the MAE should be able to reconstruct this spatiotemporal continuity. However, generating bounding boxes for each frame is impractical for large-scale video datasets. + +To this end, we hypothesize that motion is an effective guide for detecting spatiotemporal saliency. To test this hypothesis, we define the saliency score as $r_{bbox} / r_{non\_bbox}$ , or the ratio of average motion magnitude within bounding boxes to average motion magnitude outside bounding boxes. The saliency score is 1.47 for Something-Something v2 [14] and 1.28 for Kinetics-400 [19] respectively, suggesting that regions of higher motion overlap with spatially salient regions more often than regions of lesser motion. + +We thus propose an improved masking algorithm, MGM, which uses motion to continuously guide the mask to cover the most salient spatiotemporal regions. MGM obtains cheap motion correspondence by exploiting the H.264 codec [30] which prevails in popular video formats such as MP4. During the encoding phase of H.264, motion vectors are precomputed and stored as part of the codec. Thus during the decoding phase, motion vectors can be obtained "for free" along with RGB frames. The use of readily available motion vectors instead of expensive optical flow enables us to efficiently achieve scale. While some supervised works have used motion vectors [21, 43, 47], we are the first to use motion vectors for MAE pretraining. + +Our MGM outperforms previous VideoMAE [39] by $1.2\%$ on Something-Something V2 (SSv2) [14] and $0.2\%$ on Kinetics-400 (K400) [19], demonstrating that our MGM is effective. MGM can also achieve the same performance as [39] with $50\%$ fewer training epochs as shown in Fig. 1, further making MAE pretraining more data-efficient. We also show that MGM generalizes well to small datasets (UCF101 [34], HMDB51 [22], and Diving48 [23]) in both full finetune and linear probe evaluation as well as domain adaptation settings with up to $4.9\%$ performance improvement over VideoMAE [39]. This shows that the features learned by MGM contain richer semantics that transfer well to video recognition tasks. In summary, our contributions are: + +1. MGM, an efficient and effective self-supervised algorithm for 3D masking that continuously models motion trajectories. +2. Applying motion vectors which are directly available during video decoding - unlike optical flow - to provide + +efficient motion guidance in the MAE framework. + +3. New state-of-the-art or comparable results on two large-scale datasets and various downstream tasks on three small datasets, as well as detailed ablations and insights. + +# 2. Related Works + +Image Masked Auto-Encoders. iGPT [4] was one of the first recent attempts to revisit masked image modeling using Transformer architecture rather than CNNs. iGPT reconstructs at the pixel-level. Other recent works try different reconstruction targets. Some works such as BEIT [2] explore using tokenization as a prediction target, such as tokens from pretrained dVAE [40]. MaskFeat [46] explores using HoG features [7] as a reconstruction target. ImageMAE [16] reconstructs normalized image patches and focuses on studying decoder design, discovering that larger decoders enable the encoder to process only visible patches, thus enabling the use of a larger masking ratio to achieve both better performance and computational efficiency. Unlike these works, our MGM is designed specifically for video. + +Video Masked Auto-Encoders. Some works such as VIM-PAC [37] and BEVT [45] try to reconstruct video tokens and thus require strong tokenizers using either extra pretraining data or domain-specific knowledge. VideoMAE [11, 39] bypasses this requirement by applying image MAE [16] to reconstruct 3D RGB video patches, achieving promising results on video benchmarks. Other works such as Omni-MAE [13] use both image and video masked modeling to achieve improved performance on both image and video tasks. A line of very recent work tries to improve Video-MAE by designing explicit motion cues by reconstructing optical flow or frame difference based targets [33, 36, 50]. + +These existing video MAE works all inherit random masking from image MAE [16] where the mask is either discontinuous such as in ST-MAE [11] or random tubes such as in VideoMAE [39]. In the former, the mask is randomly distributed both spatially and temporally, and in the latter, the mask is randomly distributed spatially but temporally static. In contrast, we re-examine this assumption and design a new masking algorithm that continuously masks out video motion to force the model to focus on spatiotemporal saliency. We make no changes to the reconstruction target nor model architecture. + +VideoMAE [39] initially generates a random mask and statically propagates the mask across time. The position of the mask is the same across frames, forming small tubelets which are spatially discontinuous but temporally continuous. + +ST-MAE [11] independently generates a random mask per-frame which is neither spatially nor temporally continuous. + +![](images/82b59bdefe45fd4587f4cd861c8dd2684faf944ff8dc86bb9bc50df929d52e28.jpg) +Figure 2: An overview of a) the proof-of-concept simulated-motion masking (SMM) vs. b) motion-guided masking (MGM). Our MGM produces 3D masks that achieves both spatial and temporal continuity, while capturing the true motion information in the video. Random masking (left-most) is both spatially and temporally discontinuous. + +# 3. Methodology + +As detailed in Sec. 1, motion is concentrated in salient video regions. Random masking does not effectively cover these regions because motion is not uniformly distributed throughout the video. Furthermore, spatially salient entities such as people and objects are continuous rather than disjoint patches. In general, this leads us to believe random masking may miss certain semantics that are useful for learning spatiotemporal representations. The goal of this work is to address these deficiencies to make masked video modeling more effective for video representation learning. Because video is temporally cohesive, the MAE should be able to reconstruct a continuous spatiotemporal volume comprised of the salient regions. This motivates our following approach. + +# 3.1. Preliminaries + +Given a video $V \in \mathbb{R}^{T \times H \times W \times C}$ , where $T, H, W, C$ denote the number of frames, height, width, and RGB-channels, the video is typically first split into patches of size $t \times h \times w \times C$ and processed with a patch embedding layer $\mathcal{P}$ to obtain a sequence of token embeddings $V_{p}$ . + +$$ +V _ {p} = \mathcal {P} (V); V _ {p} \in \mathbb {R} ^ {\frac {T}{t} \times \frac {H}{h} \times \frac {W}{w}} \tag {1} +$$ + +Next, a masking function $\eta$ (e.g. random masking [11, 39]) generates a binary mask $M$ which is applied to select a set of visible patches with mask ratio $\gamma$ . + +$$ +M = \eta (V _ {p}, \gamma); d i m (M) = d i m (V _ {p}) +$$ + +$$ +V _ {\mathrm {p} \text {- v i s i b l e}} = V _ {p} \cdot (\sim M) \tag {2} +$$ + +$$ +V _ {\mathrm {p} \text {- m a s k e d}} = V _ {p} \cdot M +$$ + +The encoder $\phi$ then processes only the visible patches $V_{\mathrm{p\_visible}}$ while the decoder $\xi$ processes the full set of encoded patches and masked tokens $\phi(V_{\mathrm{p\_visible}}) \cup V_{\mathrm{p\_masked}}$ to + +reconstruct the video. This work uses the same asymmetric encoder-decoder design as [11, 16, 39]. + +$$ +E = \phi \left(V _ {\mathrm {p} - \text {v i s i b l e}}\right) \tag {3} +$$ + +$$ +V ^ {\prime} = \xi (E \cup V _ {\mathrm {p}. \text {m a s k e d}}) \tag {4} +$$ + +Finally, the model is trained with MSE reconstruction loss between $V$ and $V'$ . The model is then transferred to downstream tasks such as classification via finetuning with cross-entropy loss. Note that this work focuses on the mask generator $\eta(\gamma)$ , which is complementary to recent works which look into the loss function and reconstruction targets [33, 36, 45, 50]. + +# 3.2. Simulated-Motion Masking (SMM) + +To help the encoder learn spatiotemporal semantics throughout the video, we propose to generate a spatiotemporally continuous moving 3D mask, as shown in Fig. 2. This differs from random masking [11] and random tube masking [39] which break spatiotemporal continuity. + +We define the mask as a vector $[x, y, w, h]$ where $x$ and $y$ define the top-left coordinate and $w$ and $h$ define the width and height of the mask. We first explore the use of random motion to generate a dense moving 3D mask with masking ratio $\gamma$ . To do this, we initialize a rectangle shaped mask in the first frame with dimensions $w_0 = h_0 = \sqrt{\gamma * \frac{H}{h} * \frac{W}{w}}$ . $x_0$ and $y_0$ are then randomly initialized in rand(0, H/h - h_0). We then propagate the mask across time using the following recurrent relation: + +$$ +[ x _ {t}, y _ {t}, w _ {t}, h _ {t} ] = [ x _ {t - 1} + v _ {x t}, y _ {t - 1} + v _ {y t}, +$$ + +$$ +\left. w _ {t - 1} + s _ {t}, h _ {t - 1} + s _ {t} \right] \tag {5} +$$ + +$$ +t \in [ 1, T), \sum_ {t} s _ {t} = 0 +$$ + +where $v_{xt}, v_{yt}$ are the random horizontal and vertical velocity components, and $s_t$ is a random scaling factor. To ensure that the masking ratio for each video is consistent, we enforce that $\sum_{t} s_{t} = 0$ ; in other words, the number of masked patches remains fixed for a given $\gamma$ . + +# 3.3. Motion-Guided Masking (MGM) + +While SMM leads to an improvement over random masking, SMM generates masks that may not reflect true motion as it is not context-aware. For example in Figure 2, the mask may cover static background rather than the basketball player depending on the random initialization and velocity. The most straightforward approach to address this issue would be to guide the mask using precomputed object bounding boxes or optical flow. However, this requires additional data and cost and would make such a method less scalable. + +We propose to use motion vectors as guidance to ensure that the mask movement consistently covers motion across frames. Motion vectors [30, 47] can be decoded from raw video (with H.264 or H.265 CODECs) with no extra cost, which ensures that our proposed approach adds no additional cost and scales well to larger datasets. A motion vector $M_{t}[x,y]$ for a given pixel position $x,y$ at frame $t$ , is defined as $[d_x,d_y]$ where $d_{x}$ and $d_{y}$ denote the displacement of pixel $x,y$ from frame $t - 1$ . Motion vectors are typically sparsely assigned to $8\times 8$ pixel grids [30, 47], so the overall motion vector map is similar to optical flow but at a lower resolution. In order to use motion vectors to guide the masking, we need pixel-level correspondence between the motion vectors and the video. We accomplish this by upsampling the motion vector map to match the spatial resolution of the video. + +Given a motion vector map $M_t \in \mathbb{R}^{T \times \frac{H}{8} \times \frac{W}{8}}$ , we first use nearest-neighbor upsampling ( $U_{\mathrm{nearest}}$ ) to get $M_{\mathrm{t.scaled}} \in \mathbb{R}^{T \times H \times W}$ . + +$$ +\mathrm {M} _ {\text {t . s c a l e d}} = U _ {\text {n e a r e s t}} \left(M _ {t}, (H, W)\right) \tag {6} +$$ + +Next, we initialize a dense rectangle mask for frame $t_0$ with dimensions $w_0 = h_0 = \sqrt{\gamma * \frac{H}{h} * \frac{W}{w}}$ . $x_0$ and $y_0$ are then randomly initialized in $rand(0, \frac{H}{h} - h_0)$ . The mask is then generated for following time-steps as: + +$$ +x _ {\mathrm {t} \text {c e n t e r}}, y _ {\mathrm {t} \text {c e n t e r}} = P o o l _ {\mathrm {t o p K}} (M _ {\mathrm {t} \text {s c a l e d}}) +$$ + +$$ +w _ {t} = w _ {t - 1} + s _ {x t} +$$ + +$$ +h _ {t} = h _ {t - 1} + s _ {y t} +$$ + +$$ +\left[ x _ {t}, y _ {t}, w _ {t}, h _ {t} \right] = \left[ x _ {\mathrm {t} - \text {c e n t e r}} - \frac {w _ {t}}{2}, y _ {\mathrm {t} - \text {c e n t e r}} - \frac {y _ {t}}{2}, w _ {t}, h _ {t} \right] \tag {7} +$$ + +$$ +t \in [ 1, T), \sum_ {t} s _ {x t} = 0, \sum_ {t} s _ {y t} = 0 +$$ + +where $Pool_{topK}$ is the topK (top-1 in our work) magnitude pooling operation that gives the argmax indexes $x_{t\_ center}, y_{t\_ center}$ , which the mask is centered around. We also apply jitter $s_{xt}, s_{yt}$ to both the mask height and width. + +In other words, MGM produces a moving 3D mask where the movement of the mask is centered around parts of the video with the highest magnitude of motion, as shown in Fig. 2. This makes the reconstruction task more focused on spatiotemporal semantics than random masking. + +# 4. Experimental Results + +# 4.1. Datasets + +We conduct experiments on five commonly used datasets: Something-Something V2 (SSv2) [14] contains 220K videos with 174 action classes. SSv2 is considered a motion heavy dataset, as most of the labels are defined by the motion and directionality of the actual action. Kinetics-400 (K400) [19] is the de-facto standard dataset used to evaluate video recognition. It contains 240K Internet videos with 400 action classes. UCF101 [34] is a dataset containing 13K Internet short videos with 101 action classes. HMDB51 [22] is a dataset containing 5K short movie clips from 51 action classes. Diving48 [23] contains 18K untrimmed video clips from 48 action classes, all of which are types of dives. We report the top-1 accuracy on the evaluation set for all datasets following standard practices [12]. Only UCF101 and HMDB51 have multiple split versions; we use split 1. + +# 4.2. Implementation Details + +Model Configuration: We experiment with both 2D and 3D transformer backbones. The default backbone is ViT-Base [9] with global joint space-time attention. We also experimented with TimesFormer [3] with divided space-time attention. For fair comparison, we use the same input patch size of $2 \times 16 \times 16$ for all models following [39]. + +Pre-Processing: We pretrain with clips of 16 frames sampled at a temporal stride of 4 and 2 for K400 and SSv2 respectively following [39]. We use a fixed spatial resolution of $224 \times 224$ for all experiments. We apply multi-scalecrop and horizontal flip augmentation by default (flip is not applied to SSv2). We follow [39] to use AdamW [27] optimizer with a base learning rate $1.5e - 4$ , weight decay of $0.05$ , $\beta = [0.9, 0.95]$ , and cosine learning rate decay. + +Finetuning and Evaluation: We use the same 16-frame clip for finetuning and multi-view evaluation protocol following standard practice [12]. We use TSN-style sampling [44] on SSv2 dataset with 2 temporal $\times$ 3 spatial views during test-time following [39] for fair comparison. For Kinetics-400, UCF101, HMDB51 and Diving48, we use 5 temporal $\times$ 3 spatial views during test-time following [39] for fair comparison. See the supplementary material for hyperparameter details which are mostly the same as [39]. + +# 4.3. Main Results + +Something-Something V2. We first show our MGM's performance on SSv2 in Table 1, and compare with previous + +finetune eval on SSv2 +finetune eval on K400 + +
ModelBackboneGFLOPsEpochsPretrainTop1EpochsPretrainTop1
Supervised
SlowFast [12]R101 + NL106196K40063.1--79.8
TimeSformer [3]ViT-B19615IN21K59.515IN21K78.0
VidTr [51]ViT-B35150K40063.0--79.1
MotionFormer [28]ViT-B37090+35IN21K + K40066.590IN21K79.7
MViTv1 [10]MViT-B455200K40067.7--81.2
MViTv2 [24]MViT-B225200K40070.5--82.9
Self-supervised
BEVT [45]Swin-B282800+150IN1K + K40070.6800+150IN1K + K40080.6
M³Video [36]ViT-B180400SSv269.2400K40079.7
MGMViT-B180400SSv269.6400K40080.3
VideoMAE [39]ViT-B180800SSv269.6800K40080.0
MGMViT-B180800SSv270.6800K40080.8
MAM² [33]ViT-B + VQGAN1801200SSv271.3800K40082.3
MGMViT-B1801200SSv271.61200K40081.2
OmniMAE [13]ViT-B1801600IN1K + SSv269.51600IN1K + K40080.8
VideoMAE [39]ViT-B1801600SSv270.31600K40081.5
VideoMAE [39]ViT-B1802400SSv270.8---
STMAE [11]ViT-B1801600K400N/A1600K40081.3
MotionMAE [50]ViT-B1802400SSv271.81600K40081.7
MGMViT-B1801600SSv271.81600K40081.7
MGMViT-B1802400SSv272.1---
+ +Table 1: Results comparison on Something-SomethingV2 (SSv2) and Kinetics-400 (K400). GFLOPs is listed as a single view's. All results are with fine-tuning. We apply repeated augmentation $[18] = 2$ for this table to compare against SOTA. + +models trained in a supervised manner: Our MGM using vanilla ViT-B pretrained on only SSv2 outperforms previous SOTA such as MViTv1 [10] $(+4.4\%)$ and MViTv2 [10] $(+1.6\%)$ which uses a heavy hierarchical 3D transformer backbone and pretrains on Kinetics-400. This demonstrates the efficiency and effectiveness of our proposed method compared to supervised 3D transformer backbones. MGM also significantly outperforms previous supervised learning methods that use the same backbone as us: $+5.6\%$ over MotionFormer [28] and $+12.6\%$ over TimeSformer [3]. This demonstrates that the proposed MGM is effective for spatiotemporal modeling. + +We then compare MGM with SOTA video MAE methods. With the same backbone and training schema, MGM achieves $1.3\%$ higher accuracy comparing to VideoMAE [39]. Note that with $3 \times$ less training time, our MGM pretrained for 800 epochs is able to achieve nearly the same performance as VideoMAE pretrained for 2400 epochs ( $\sim 66\%$ fewer epochs), as illustrated in Fig. 1. This demonstrates that motion-guided masking is a more efficient strategy for self-supervised spatiotemporal learning due to learning video saliency. Compared to OmniMAE [13] which does masked modeling on both images and video, MGM achieves $+2.6\%$ improvement. Compared to BEVT [45] which also learns from both images and video and additionally uses + +Swin Transformer [25, 26] - a heavy 3D Transformer architecture - MGM achieves $+1.5\%$ improvement. This is despite the fact that our method only uses video and is pretrained from scratch. Note that STMAE [11] only provides results for ViT-Large backbone on SSv2. + +We finally compare our MGM with some most recent works that also utilize motion information for video pretraining. MGM outperforms $\mathrm{M}^3\mathrm{Video}$ [36] ( $+0.4\%$ with the same 400 epochs of pretraining) which reconstructs motion trajectories generated from optical flow. We achieve equivalent performance to MotionMAE [50] using $50\%$ fewer epochs (1600 vs. 2400) even though it utilizes frame difference as an additional reconstruction target which incorporates explicit motion information. The results show that motion-guided masking alone is sufficient for improving spatiotemporal learning. It is worth reiterating that our MGM uses motion vectors for masking guidance, which is already computed during video encoding, and thus directly available during video decoding [30, 43, 47], making our method more efficient and scalable comparing to works such as [33, 36, 50] which use optical flow and/or frame difference. + +Kinetics-400 (K400). We further conduct experiments on K400 and show results in Table 1. Similar trends are observed. Our MGM is able to outperform supervised models with the same backbone such as TimeSformer [3] by $+3.7\%$ + +and MotionFormer [28] by $+2.0\%$ . MGM slightly underperforms some hierarchical 3D transformer backbones such as MViTv2 [24] by $-1.2\%$ on K400 but MViTv2 is trained with $2\times$ more frames (32) and uses significantly more FLOPS. + +Comparing with other MAE based methods, our MGM consistently outperforms VideoMAE by $+1.4\%$ at 800 epochs of pretraining. MGM also achieves better performance comparing to other recent works, at no additional cost. Our MGM outperforms $\mathrm{M}^3\mathrm{Video}$ [36] at 400 epochs of pretraining by $0.6\%$ , while being more efficient as our method does not use frame difference nor optical flow. Compared to OmniMAE [13] which uses both images and video, MGM achieves $0.9\%$ improvement. Compared to BEVT [45], MGM achieves $1.1\%$ improvement. + +We note that the performance gain MGM obtains over other methods on K400 is slightly lower compared to on SSv2. This can be explained by the fact that a great proportion of actions in K400 dataset can be differentiated by the appearance of a few key frames, for example, "skiing" vs. "tennis". In contrast, recognising actions in SSv2 dataset, e.g. "moving something up" vs. "moving something down", requires the model to understand the subtle differences in motion along temporal dimension. Therefore, we hypothesize that spatiotemporal modeling is less impactful on spatial-heavy datasets such as K400 and the strength of MGM is not fully exhibited. Motion serves as a appearance-agnostic differentiator between classes. + +# 4.4. Transfer Learning + +We next evaluate MGM's performance when transferred to smaller datasets: UCF101 [34], HMDB51 [22], and Diving48 [23]. Performance in transfer learning is commonly used as an indicator of feature quality and representativeness [17]. We use ViT-Base model pretrained on K400 and SSv2 by 800 epochs for all transfer learning experiments. + +Finetune on downstream tasks. We first present fine-tuning results from MGM pretrained on unlabeled K400 in Table 2. Our MGM consistently outperforms VideoMAE with same backbone and pretraining setup on all three datasets $(+0.9\%)$ on UCF101, $+1.1\%$ on HMDB51, $+4.9\%$ on Diving48). This shows that our approach learns more representative semantics and thus generalizes better to small-scale downstream tasks. It is worth mentioning that MGM even outperforms K400 supervised pretraining on HMDB51 $(+3.2\%)$ and on Diving48 $(+7.5\%)$ , demonstrating the effectiveness of our proposed method. + +Our MGM is also able to consistently outperform VideoMAE [39] with pretraining on unlabeled SSv2 in the finetune setting $(+1.3\%)$ on UCF101, $+1\%$ on HMDB51, $+2.6\%$ on Diving48). Our MGM even outperforms SSv2 supervised pretraining by a large margin $(+14.1\%)$ on UCF101, $+13.4\%$ on HMDB51, $+46.9\%$ on Diving48). Finetuning MGM on SSv2 (same model from Tab. 1) does not lead to a large + +
UCFHMDBDiving48
Supervised (K400) †95.171.462.7
VideoMAE [39]93.373.565.3
MGM94.274.670.2
+ K400 Finetune (Tab. 1)97.781.082.6
+ +(a) Pretrained on K400 and finetuned on downstream tasks. + +
UCFHMDBDiving48
Supervised (SSv2) †77.856.336.2
VideoMAE [39]90.668.780.5
MGM91.969.783.1
+ SSv2 Finetune ( Tab. 1)93.274.783.4
+ +(b) Pretrained on SSv2 and finetuned on downstream tasks. + +
UCFHMDBDiving48
Supervised (K400) †94.165.425.2
VideoMAE [39]70.545.410.0
MGM77.549.214.2
+ +(c) Pretrained on K400 and evaluated with linear probing on downstream tasks. + +
UCFHMDBDiving48
Supervised (SSv2) †72.951.813.2
VideoMAE [39]65.341.210.7
MGM69.144.810.2
+ +(d) Pretrained on SSv2 and evaluated with linear probing on downstream tasks. + +Table 2: MGM generalizes well to various downstream datasets (UCF101, HMDB51 and Diving48) on two downstream tasks (finetune, linear-probe). We test VideoMAE and MGM pretrained on Kinetics-400 (K400) for 800 epochs. The supervised baseline is ViT-B trained from scratch on K400 and SSv2 using the recipe from MViT [10, 24]. + +boost, indicating that our model is able to learn the majority of semantics just from unsupervised pretraining, and that unsupervised pretraining is able to make better use of the information in SSv2 than supervised training. + +Linear Probe on downstream tasks. Previous work [2, 11, 16] argues that generative approaches such as MAE generally perform worse on linear probing tasks as there is a larger gap between the reconstruction task and downstream evaluation compared to other pretraining methods. Nevertheless, we compare linear probe performance between MGM and VideoMAE [39] and show that our method achieves significantly better performance. With K400 pretraining, we outperform VideoMAE by $+7\%$ on UCF101, $+3.8\%$ on HMDB51, and $+4.2\%$ on Diving48. With SSv2 pretraining, we outperform by $+3.8\%$ on UCF101, $+3.6\%$ on HMDB51, and underperform by $-0.5\%$ on Diving48. This demonstrates that motion-modeling helps reduce the gap between the reconstruction task and downstream tasks, as linear probe only + +
UCF14 → HMDB7HMDB14 → UCF7
VideoMAE [39]55.769.6
MGM57.671.4
+ K400 Finetune (Tab. 1)79.196.2
+ +trains a linear classifier on top of features extracted from the frozen backbone; linear layers cannot learn new semantics. + +We note that there is a large gap of over $10\%$ with K400 supervised pretraining on linear probe. This is a general deficiency of generative methods such as MAE-based pretraining [11] and we leave further exploration of this problem to future works. One way to address this would be to combine MAE with discriminative methods such as contrastive learning to obtain a balanced representation. + +Domain adaptation. We further evaluate MGM on partial domain adaptation tasks following [49], in which the labels for the target dataset are a subset of the labels for the source dataset. The model is finetuned on the source dataset and directly evaluated on the target dataset without seeing any samples from the target dataset. This is more challenging than conventional domain adaptation as the model may incorrectly label samples in the target dataset as the labels from the source dataset which are not present in the target dataset ("negative transfer") [49]. Previous work has showed that optical flow is useful for action recognition because it is invariant to appearance [32]. Several works such as [6, 31] improve unsupervised domain adaptation in video by reducing background and appearance bias to capture the essence of an action via shuffling and mixup respectively. By similar reasoning, domain adaptation is a good evaluation protocol to assess motion learning as the source and target datasets have very different visual appearances, and motion serves as a common link between classes that is agnostic to spatial appearances. + +We use the training sets provided by [49] for UCF14 $\rightarrow$ HMDB7 and HMDB14 $\rightarrow$ UCF7. Our MGM consistently outperform VideoMAE with K400 pretraining in both settings $(+1.9\%)$ on HMDB7 and $+1.8\%$ on UCF7) indicating that MGM can also outperform in a domain adaptation setting. While there is a significant gap of over $20\%$ between Table 3 and Table 2, finetuning our model on K400 labels bridges the gap. This suggests that our model has learned video saliency and can perform well without any large-scale label supervision, but additional label supervision is helpful for challenging settings such as domain adaptation where spatial information is very different and difficult to + +![](images/fd648a874d15a727d3bcd2ee564e90d88f424336ae2801350ba89d2cb430952a.jpg) +(a) More mask ratios. +Figure 3: Ablations on mask ratio 3a and pretraining duration 3b. Mask ratio 0.75 is optimal and performance does not saturate with longer pretraining. + +![](images/e45d16a8fae47b9376ca509ac05f77ae6bf24f5d58b28de654365aaf269215ca.jpg) +(b) Pretrain duration in epochs. + +Table 3: MGM works well when trained on one dataset and evaluated on another dataset for an overlapping set of classes. The model sees no samples from test dataset, indicating motion understanding as motion is agnostic to spatial appearance. We tested VideoMAE and MGM pretrained on Kinetics-400 (K400) for 800 epochs. + +
backboneSSv2
ViT-S61.1
ViT-B67.3
TimesFormer [3]64.7
+ +
guidanceSSv2
optical flow66.0
motion vector67.3
+ +(a) Backbone generalization. + +
aspect ratioSSv2
no67.1
yes67.3
+ +(c) Mask jitter. + +(b) Source of motion info. + +
pretrain datasamplesK400
Mini-K200 [48]80K78.2
K400 [19]240K78.6
+ +(d) Dataset scale generalization. + +
Masktemporal propagationspatial continuity
staticsimulatedmotionsparsedenseAcc
Random Block✓✓62.9
SMM (Sparse)✓✓64.6
Random Tube✓✓65.0
MGM (Sparse)✓✓65.1
SMM (Dense)✓✓65.9
MGM (Dense)✓✓67.3
+ +(e) Masking strategies differentiated by initial position, temporal propagation, and spatial continuity. Spatiotemporally continuous masks with motion guidance perform the best. + +Table 4: Ablations on backbone 4a, source of motion guidance 4b, mask jitter 4c, pretrain data scale 4d, and mask type 4e. All ablations pretrain for 200 epochs on SSv2 unless otherwise indicated. + +learn from limited samples. There are only $\sim 1000$ training samples in each setting. + +# 4.5. Ablations + +We perform ablations on the Something-Something V2 dataset, with MGM with ViT-B backbone pretrained for 200 epochs using our motion-guided masking, unless otherwise specified. + +Impact of masking ratio. Figure 3a studies the impact of different masking ratio on SSv2. We noticed that 0.75 masking ratio works best for the proposed MGM, which + +is lower than that of other works [11, 39]. This is because motion-guided masking leads to a more "challenging" reconstruction task compared to random masking, since the masked regions of videos are most informative and therefore cannot be easily inferred from retained regions. + +Impact of pretraining length. We show the impact of different pretraining epochs on SSv2 in Figure 3b. The proposed MGM consistently improves with more training and we achieve state-of-the-art performance on SSv2 with 2400 epochs of pretraining. Performance does not seem to saturate with longer pretraining. + +Generalization to different backbones. MGM also generalizes well to backbones of different sizes and types (Table 4a). We test vanilla ViT-S [9] and ViT-B [9], and TimeSformer [3] with joint space-time attention. Note that our TimeSformer ablation outperforms the supervised result reported by [3] of $59.5\%$ on SSv2 which uses IN21K pretraining. In contrast, we do not use any extra data. ViT-S's lower performance may be explained by its low model capacity which may not be sufficient for learning spatiotemporal dynamics. As other methods do not use ViT-S, we cannot compare our result to other methods. We thus use ViT-B to compare fairly against other MAE works which use ViT-B. + +Impact of motion source. In Table 4b we compare the performance of MGM when using optical flow vs. motion vectors as the source of motion guidance. Even though optical flow is more fine-grained and precise than motion vectors, performance of MGM drops when the mask is guided by optical flow. This could be related to the fact that optical flow is calculated on a per-pixel basis whereas motion vectors are computed in a block-wise manner and we utilize a block-wise mask strategy. We thus conveniently choose to use motion vector as it is also directly obtainable from compressed video. We extract optical flow using RAFT-Small [38]. On the SSv2 dataset, reading motion vectors is roughly $30 \times$ faster than computing optical flow (80 milliseconds vs. 2.5 seconds per video on average). + +Impact of mask aspect ratio jitter. In Table 4c we ablate the use of aspect ratio jittering from Eq. (7). We see that aspect ratio jittering gives a small $0.2\%$ boost in performance but is not a critical component of MGM. + +Impact of pretrain dataset scale. In Table 4d we ablate the amount of pretraining data used to see if MGM can generalize to different dataset scales. We pretrain MGM on MiniKinetics-200 [48] and Kinetics-400 (K400) [19] which contain $\sim 80\mathrm{K}$ videos and $\sim 240\mathrm{K}$ videos respectively for 200 epochs. MiniKinetics-200 contains videos belonging to a subset of 200 of the most common classes in K400. We then evaluate top-1 accuracy on K400. We find that there is a small $0.4\%$ drop in performance when pretraining on the smaller MiniKinetics-200. We expect performance to further improve when pretraining on datasets larger than K400. + +Effectiveness of 3D motion masking. Table 4e studies + +different masking strategies which are broken down into categories based on degree of motion guidance and spatial continuity. We first compare dense to sparse masking, where sparse means that the mask may be spatially discontinuous. The dense variant of SMM and MGM outperform the respective sparse counterpart; dense SMM outperforms sparse SMM by $1.3\%$ and dense MGM outperforms sparse MGM by $2.2\%$ . This suggests the importance of maintaining spatial continuity in the masked reconstruction. Next, we compare MGM to SMM. Sparse MGM outperforms sparse SMM by $0.5\%$ and dense MGM outperforms dense SMM by $1.4\%$ . When motion is completely removed, performance is the worst even when the mask is spatially continuous (static block gets $62.9\%$ ). Dense MGM outperforms all masking strategies and specifically the random masking baseline by $2.3\%$ . All masking strategies except block and sparse SMM outperform random masking. Random masking is spatiotemporally discontinuous. This validates our intuition that forming continuous 3D masks which model the true motion information within video is useful. We thus pick dense MGM for all other experiments and refer to "MGM" as the dense variant by default. For a visualization of these masking strategies, see Figure 4. + +![](images/7bdace739ebf35a847db114876ff8b6f48cbf77163604193bb8f329068daa194.jpg) +Figure 4: Visualization of different mask algorithms. + +# 4.6. Visualization + +In Figure 5, we provide visualizations from two perspectives using MGM pretrained on K400. Note that visualizations are subjective and should not be used as a formal explanation for model behavior. Our intention is to provide additional insight into the model to complement our quantitative results. We first visualize the RGB frames with bounding boxes, motion-guided masks, and motion vectors. We see that the motion-guided masks overlap with the majority of spatiotemporally salient regions. Second, we visualize the attention map using the center patch of the center frame as a query. We observe that the model mostly attends to the salient regions. For more visualizations, see the supplementary. + +![](images/97aab0482ad9423e7dfd733575229eed50f2dfe182bcb4b1fd41c863a4f1865d.jpg) +a) + +![](images/e20ee8d868521dcd20259dc9480785480cf435d11a093ff03d405d1d587aee66.jpg) + +![](images/7430f0a27a0ca135b310c9c24469c18aa4beeb2b72f8d769b2c67ccb33bca8fd.jpg) + +![](images/89ce736cf1fb41e23f7ffef31d827d32ec165c7e3244d8f2023380c83a70f061.jpg) +b) + +![](images/f26e76ef0a9792a6767444f38d188ded069f1fd52f33be30e276de081770d03f.jpg) + +![](images/9c132fe60ff88e71c5b5487cff34cdbfa8ab6612df3abb278c6f3d31d6d61860.jpg) + +![](images/a614dc5acdea4d06eb7211fe51e2e2a271c4fae49a0cbf8ce884fa3f7114d671.jpg) +c) + +![](images/f00411b66c812dcb3621412e8a9fb0a9ff222a89eb113bec1017f014d31a6ef0.jpg) + +![](images/ba385cccba42f6c56809f370a984f9917f5a31181000d20030490547e7e51d8a.jpg) + +![](images/ec67ddb597ddcb541c1be657b3520b4fb577f8ab861c17619a01bda442a23d70.jpg) +d) + +![](images/2cd0a3af7aa4bd63910ebc6f5d0e18fbf142e2e8bcaba7111649c507ac2396f8.jpg) +Figure 5: a) RGB frames with bounding boxes for visualization. b) Our MGM masks continuously cover the moving hand. c) Motion vector maps. d) Encoder attention map using center patch of center frame as query. + +![](images/faee1514de1aa0a5ac44086a1e67c47729d56f23be49ab6327b55fcb9564368a.jpg) + +# 5. Discussion and Conclusion + +Limitations. Our method efficiently leverages motion cues from compressed video format. However, MGM's effectiveness on the video benchmarks that are not human centric or have tremendous camera motion has yet to be examined. To the best of our knowledge, we did not find such a video benchmark, so we will leave this to future work. + +Potential negative impact. As our model is trained on primarily Internet video datasets, our model will learn the bias inherent to that data. There could be unintended consequences and we advocate for complying with the law. + +Conclusion. This paper introduces motion-guided masking (MGM), an algorithm which produces motion-aware 3D masks to improve spatiotemporal learning. Our use of motion information is much more efficient than previous optical flow as we leverage motion vectors that naturally exist in the video codec. We achieve new state-of-the-art or comparable performance on two challenging large-scale video benchmarks and achieve previous state-of-the-art results with $50\%$ less pretraining time, making our method more efficient. We also achieve better generalization than previous video MAE works on three small-scale datasets. We believe our method has the potential to enable more efficient video training. + +# References + +[1] Anurag Arnab, Mostafa Dehghani, Georg Heigold, Chen Sun, Mario Lučić, and Cordelia Schmid. Vivit: A video vision transformer. In Proceedings of the IEEE/CVF International Conference on Computer Vision (ICCV), pages 6836-6846, October 2021. 1 +[2] Hangbo Bao, Li Dong, Songhao Piao, and Furu Wei. Beit: Bert pre-training of image transformers. In International Conference on Learning Representations, 2021. 1, 2, 6 +[3] Gedas Bertasius, Heng Wang, and Lorenzo Torresani. Is space-time attention all you need for video understanding? 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In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 13577-13587, 2021. 5 \ No newline at end of file diff --git a/2023/Motion-Guided Masking for Spatiotemporal Representation Learning/images.zip b/2023/Motion-Guided Masking for Spatiotemporal Representation Learning/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..5e583b155aaef8bf47210a25339b2805930f1c59 --- /dev/null +++ b/2023/Motion-Guided Masking for Spatiotemporal Representation Learning/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:0e05d95ace7eee5de8cdf7525b535a432d09f90260e3d4c7b3b9c2234cef6399 +size 519688 diff --git a/2023/Motion-Guided Masking for Spatiotemporal Representation Learning/layout.json b/2023/Motion-Guided Masking for Spatiotemporal Representation Learning/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..ec301b69a34450440adc21bef7af098e6438ec83 --- /dev/null +++ b/2023/Motion-Guided Masking for Spatiotemporal Representation Learning/layout.json @@ -0,0 +1,10414 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 80, + 103, + 514, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 103, + 514, + 121 + ], + "spans": [ + { + "bbox": [ + 80, + 103, + 514, + 121 + ], + "type": "text", + "content": "Motion-Guided Masking for Spatiotemporal Representation Learning" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 78, + 141, + 517, + 200 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 78, + 141, + 517, + 200 + ], + "spans": [ + { + "bbox": [ + 78, + 141, + 517, + 200 + ], + "type": "text", + "content": "David Fan1 Jue Wang1 Shuai Liao2 Yi Zhu3 Vimal Bhat1 Hector Santos-Villalobos1 Rohith MV1 Xinyu Li1 \n1 Amazon Prime Video 2 Amazon Fulfillment Technology 3 AWS AI Labs {fandavi, juewangn, uliaoshu, yzaws, vimalb, hsantosv, kurohith, xxnl}@amazon.com" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "spans": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 251, + 290, + 539 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 251, + 290, + 539 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 290, + 539 + ], + "type": "text", + "content": "Several recent works have directly extended the image masked autoencoder (MAE) with random masking into video domain, achieving promising results. However, unlike images, both spatial and temporal information are important for video understanding. This suggests that the random masking strategy that is inherited from the image MAE is less effective for video MAE. This motivates the design of a novel masking algorithm that can more efficiently make use of video saliency. Specifically, we propose a motion-guided masking algorithm (MGM) which leverages motion vectors to guide the position of each mask over time. Crucially, these motion-based correspondences can be directly obtained from information stored in the compressed format of the video, which makes our method efficient and scalable. 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Lastly, we show that MGM generalizes better to downstream transfer learning and domain adaptation tasks on the UCF101, HMDB51, and Diving48 datasets, achieving up to " + }, + { + "bbox": [ + 46, + 251, + 290, + 539 + ], + "type": "inline_equation", + "content": "+4.9\\%" + }, + { + "bbox": [ + 46, + 251, + 290, + 539 + ], + "type": "text", + "content": " improvement compared to baseline methods." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 562, + 128, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 562, + 128, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 562, + 128, + 574 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 581, + 288, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 581, + 288, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 581, + 288, + 653 + ], + "type": "text", + "content": "Video transformers [1, 24, 25, 28, 43] have achieved state-of-the-art for a variety of video understanding tasks, mirroring the success of image transformers such as ViT [9]. However, many video transformers heavily rely on large-scale supervised pretraining from image datasets such as ImageNet21K [8] and JFT-300M [35], which is data-inefficient." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 653, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 289, + 714 + ], + "type": "text", + "content": "Self-supervised learning (SSL) [5, 15, 17, 29, 42] is one promising paradigm for eliminating the dependency on large-scale supervised pretraining. The denoising / masked autoencoder (MAE) [41], which was originally popularized by BERT [20] for natural language modeling, has recently re" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 312, + 231, + 548, + 370 + ], + "blocks": [ + { + "bbox": [ + 312, + 231, + 548, + 370 + ], + "lines": [ + { + "bbox": [ + 312, + 231, + 548, + 370 + ], + "spans": [ + { + "bbox": [ + 312, + 231, + 548, + 370 + ], + "type": "image", + "image_path": "b3e603fe4ab31aa6b677ca87eadc678ae9e632aab57f84455c4a608844429c8e.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 383, + 548, + 456 + ], + "lines": [ + { + "bbox": [ + 304, + 383, + 548, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 383, + 548, + 456 + ], + "type": "text", + "content": "Figure 1: Top-1 accuracy on Something-Something V2. Our proposed MGM outperforms all previous masked-video methods (M³Video [36], MAM² [33], BEVT [45], OmniMAE [13], MotionMAE [50], and VideoMAE [39]) with improved training efficiency. Marker shape denotes reconstruction target." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 470, + 547, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 470, + 547, + 579 + ], + "spans": [ + { + "bbox": [ + 304, + 470, + 547, + 579 + ], + "type": "text", + "content": "emerged as a promising representation learning method for vision tasks. Image MAE [2, 16] has achieved state-of-the-art in image domain via learning to reconstruct randomly masked image patches. Recently, similar works [11, 39] that reconstruct randomly masked video have obtained encouraging results in video domain. However, few SSL works focus on effectively learning video saliency. In this paper, we improve upon the previous video MAEs [11, 39] via video saliency." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 582, + 548, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 548, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 548, + 713 + ], + "type": "text", + "content": "We argue that the random masking strategy which is inherited from image MAE is not optimal for video. The optimal random masking ratio for video MAE [11, 39] is higher than that for image MAE [16] (0.9 vs. 0.75). This can be understood as a consequence of the natural temporal coherence within videos, which leads to the existence of similar video patches in other frames. When using random masking, many of these correlated video patches may be visible to the encoder which would make reconstruction easier. This necessitates the use of a high masking ratio in order to reduce redundancy and make the reconstruction task" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5619" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "text", + "content": "sufficiently challenging [11]. However, increasing the masking ratio has the side-effect of leaving fewer visible patches for the MAE encoder to learn spatiotemporal saliency from, which we hypothesize limits the learned representation." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 121, + 287, + 227 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 121, + 287, + 227 + ], + "spans": [ + { + "bbox": [ + 46, + 121, + 287, + 227 + ], + "type": "text", + "content": "We thus propose to guide the model to learn to reconstruct the most salient regions of video. As humans and objects are key to understanding video, one natural idea is to track the bounding boxes in each video frame and mask the content within. This is also consistent with the observation that video pixels evolve continuously frame-by-frame, and therefore, the MAE should be able to reconstruct this spatiotemporal continuity. However, generating bounding boxes for each frame is impractical for large-scale video datasets." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 228, + 288, + 334 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 228, + 288, + 334 + ], + "spans": [ + { + "bbox": [ + 46, + 228, + 288, + 334 + ], + "type": "text", + "content": "To this end, we hypothesize that motion is an effective guide for detecting spatiotemporal saliency. To test this hypothesis, we define the saliency score as " + }, + { + "bbox": [ + 46, + 228, + 288, + 334 + ], + "type": "inline_equation", + "content": "r_{bbox} / r_{non\\_bbox}" + }, + { + "bbox": [ + 46, + 228, + 288, + 334 + ], + "type": "text", + "content": ", or the ratio of average motion magnitude within bounding boxes to average motion magnitude outside bounding boxes. The saliency score is 1.47 for Something-Something v2 [14] and 1.28 for Kinetics-400 [19] respectively, suggesting that regions of higher motion overlap with spatially salient regions more often than regions of lesser motion." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 335, + 288, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 335, + 288, + 491 + ], + "spans": [ + { + "bbox": [ + 46, + 335, + 288, + 491 + ], + "type": "text", + "content": "We thus propose an improved masking algorithm, MGM, which uses motion to continuously guide the mask to cover the most salient spatiotemporal regions. MGM obtains cheap motion correspondence by exploiting the H.264 codec [30] which prevails in popular video formats such as MP4. During the encoding phase of H.264, motion vectors are precomputed and stored as part of the codec. Thus during the decoding phase, motion vectors can be obtained \"for free\" along with RGB frames. The use of readily available motion vectors instead of expensive optical flow enables us to efficiently achieve scale. While some supervised works have used motion vectors [21, 43, 47], we are the first to use motion vectors for MAE pretraining." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 491, + 288, + 646 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 491, + 288, + 646 + ], + "spans": [ + { + "bbox": [ + 46, + 491, + 288, + 646 + ], + "type": "text", + "content": "Our MGM outperforms previous VideoMAE [39] by " + }, + { + "bbox": [ + 46, + 491, + 288, + 646 + ], + "type": "inline_equation", + "content": "1.2\\%" + }, + { + "bbox": [ + 46, + 491, + 288, + 646 + ], + "type": "text", + "content": " on Something-Something V2 (SSv2) [14] and " + }, + { + "bbox": [ + 46, + 491, + 288, + 646 + ], + "type": "inline_equation", + "content": "0.2\\%" + }, + { + "bbox": [ + 46, + 491, + 288, + 646 + ], + "type": "text", + "content": " on Kinetics-400 (K400) [19], demonstrating that our MGM is effective. MGM can also achieve the same performance as [39] with " + }, + { + "bbox": [ + 46, + 491, + 288, + 646 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 491, + 288, + 646 + ], + "type": "text", + "content": " fewer training epochs as shown in Fig. 1, further making MAE pretraining more data-efficient. We also show that MGM generalizes well to small datasets (UCF101 [34], HMDB51 [22], and Diving48 [23]) in both full finetune and linear probe evaluation as well as domain adaptation settings with up to " + }, + { + "bbox": [ + 46, + 491, + 288, + 646 + ], + "type": "inline_equation", + "content": "4.9\\%" + }, + { + "bbox": [ + 46, + 491, + 288, + 646 + ], + "type": "text", + "content": " performance improvement over VideoMAE [39]. This shows that the features learned by MGM contain richer semantics that transfer well to video recognition tasks. In summary, our contributions are:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 54, + 653, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 55, + 653, + 288, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 653, + 288, + 689 + ], + "spans": [ + { + "bbox": [ + 55, + 653, + 288, + 689 + ], + "type": "text", + "content": "1. MGM, an efficient and effective self-supervised algorithm for 3D masking that continuously models motion trajectories." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 54, + 689, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 689, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 54, + 689, + 288, + 714 + ], + "type": "text", + "content": "2. Applying motion vectors which are directly available during video decoding - unlike optical flow - to provide" + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 326, + 72, + 528, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 326, + 72, + 528, + 83 + ], + "spans": [ + { + "bbox": [ + 326, + 72, + 528, + 83 + ], + "type": "text", + "content": "efficient motion guidance in the MAE framework." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 313, + 84, + 547, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 84, + 547, + 120 + ], + "spans": [ + { + "bbox": [ + 313, + 84, + 547, + 120 + ], + "type": "text", + "content": "3. New state-of-the-art or comparable results on two large-scale datasets and various downstream tasks on three small datasets, as well as detailed ablations and insights." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 148, + 398, + 162 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 148, + 398, + 162 + ], + "spans": [ + { + "bbox": [ + 306, + 148, + 398, + 162 + ], + "type": "text", + "content": "2. Related Works" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 175, + 547, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 175, + 547, + 342 + ], + "spans": [ + { + "bbox": [ + 304, + 175, + 547, + 342 + ], + "type": "text", + "content": "Image Masked Auto-Encoders. iGPT [4] was one of the first recent attempts to revisit masked image modeling using Transformer architecture rather than CNNs. iGPT reconstructs at the pixel-level. Other recent works try different reconstruction targets. Some works such as BEIT [2] explore using tokenization as a prediction target, such as tokens from pretrained dVAE [40]. MaskFeat [46] explores using HoG features [7] as a reconstruction target. ImageMAE [16] reconstructs normalized image patches and focuses on studying decoder design, discovering that larger decoders enable the encoder to process only visible patches, thus enabling the use of a larger masking ratio to achieve both better performance and computational efficiency. Unlike these works, our MGM is designed specifically for video." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 348, + 548, + 492 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 348, + 548, + 492 + ], + "spans": [ + { + "bbox": [ + 304, + 348, + 548, + 492 + ], + "type": "text", + "content": "Video Masked Auto-Encoders. Some works such as VIM-PAC [37] and BEVT [45] try to reconstruct video tokens and thus require strong tokenizers using either extra pretraining data or domain-specific knowledge. VideoMAE [11, 39] bypasses this requirement by applying image MAE [16] to reconstruct 3D RGB video patches, achieving promising results on video benchmarks. Other works such as Omni-MAE [13] use both image and video masked modeling to achieve improved performance on both image and video tasks. A line of very recent work tries to improve Video-MAE by designing explicit motion cues by reconstructing optical flow or frame difference based targets [33, 36, 50]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 498, + 547, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 547, + 629 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 547, + 629 + ], + "type": "text", + "content": "These existing video MAE works all inherit random masking from image MAE [16] where the mask is either discontinuous such as in ST-MAE [11] or random tubes such as in VideoMAE [39]. In the former, the mask is randomly distributed both spatially and temporally, and in the latter, the mask is randomly distributed spatially but temporally static. In contrast, we re-examine this assumption and design a new masking algorithm that continuously masks out video motion to force the model to focus on spatiotemporal saliency. We make no changes to the reconstruction target nor model architecture." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 635, + 547, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 635, + 547, + 685 + ], + "spans": [ + { + "bbox": [ + 304, + 635, + 547, + 685 + ], + "type": "text", + "content": "VideoMAE [39] initially generates a random mask and statically propagates the mask across time. The position of the mask is the same across frames, forming small tubelets which are spatially discontinuous but temporally continuous." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 689, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 547, + 714 + ], + "type": "text", + "content": "ST-MAE [11] independently generates a random mask per-frame which is neither spatially nor temporally continuous." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5620" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 71, + 541, + 222 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 541, + 222 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 541, + 222 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 541, + 222 + ], + "type": "image", + "image_path": "82b59bdefe45fd4587f4cd861c8dd2684faf944ff8dc86bb9bc50df929d52e28.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 231, + 548, + 269 + ], + "lines": [ + { + "bbox": [ + 46, + 231, + 548, + 269 + ], + "spans": [ + { + "bbox": [ + 46, + 231, + 548, + 269 + ], + "type": "text", + "content": "Figure 2: An overview of a) the proof-of-concept simulated-motion masking (SMM) vs. b) motion-guided masking (MGM). Our MGM produces 3D masks that achieves both spatial and temporal continuity, while capturing the true motion information in the video. Random masking (left-most) is both spatially and temporally discontinuous." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 286, + 130, + 301 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 286, + 130, + 301 + ], + "spans": [ + { + "bbox": [ + 47, + 286, + 130, + 301 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 307, + 290, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 307, + 290, + 464 + ], + "spans": [ + { + "bbox": [ + 46, + 307, + 290, + 464 + ], + "type": "text", + "content": "As detailed in Sec. 1, motion is concentrated in salient video regions. Random masking does not effectively cover these regions because motion is not uniformly distributed throughout the video. Furthermore, spatially salient entities such as people and objects are continuous rather than disjoint patches. In general, this leads us to believe random masking may miss certain semantics that are useful for learning spatiotemporal representations. The goal of this work is to address these deficiencies to make masked video modeling more effective for video representation learning. Because video is temporally cohesive, the MAE should be able to reconstruct a continuous spatiotemporal volume comprised of the salient regions. This motivates our following approach." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 469, + 134, + 481 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 469, + 134, + 481 + ], + "spans": [ + { + "bbox": [ + 47, + 469, + 134, + 481 + ], + "type": "text", + "content": "3.1. Preliminaries" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "spans": [ + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "type": "text", + "content": "Given a video " + }, + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "type": "inline_equation", + "content": "V \\in \\mathbb{R}^{T \\times H \\times W \\times C}" + }, + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "type": "inline_equation", + "content": "T, H, W, C" + }, + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "type": "text", + "content": " denote the number of frames, height, width, and RGB-channels, the video is typically first split into patches of size " + }, + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "type": "inline_equation", + "content": "t \\times h \\times w \\times C" + }, + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "type": "text", + "content": " and processed with a patch embedding layer " + }, + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "type": "inline_equation", + "content": "\\mathcal{P}" + }, + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "type": "text", + "content": " to obtain a sequence of token embeddings " + }, + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "type": "inline_equation", + "content": "V_{p}" + }, + { + "bbox": [ + 46, + 486, + 288, + 548 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 105, + 555, + 288, + 572 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 105, + 555, + 288, + 572 + ], + "spans": [ + { + "bbox": [ + 105, + 555, + 288, + 572 + ], + "type": "interline_equation", + "content": "V _ {p} = \\mathcal {P} (V); V _ {p} \\in \\mathbb {R} ^ {\\frac {T}{t} \\times \\frac {H}{h} \\times \\frac {W}{w}} \\tag {1}", + "image_path": "a635e9d467fe2f2d3b25b1dadcac69019375a625bb88f08e763623cfe347bcf9.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 576, + 289, + 612 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 576, + 289, + 612 + ], + "spans": [ + { + "bbox": [ + 47, + 576, + 289, + 612 + ], + "type": "text", + "content": "Next, a masking function " + }, + { + "bbox": [ + 47, + 576, + 289, + 612 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 47, + 576, + 289, + 612 + ], + "type": "text", + "content": " (e.g. random masking [11, 39]) generates a binary mask " + }, + { + "bbox": [ + 47, + 576, + 289, + 612 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 47, + 576, + 289, + 612 + ], + "type": "text", + "content": " which is applied to select a set of visible patches with mask ratio " + }, + { + "bbox": [ + 47, + 576, + 289, + 612 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 47, + 576, + 289, + 612 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 101, + 628, + 255, + 641 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 101, + 628, + 255, + 641 + ], + "spans": [ + { + "bbox": [ + 101, + 628, + 255, + 641 + ], + "type": "interline_equation", + "content": "M = \\eta (V _ {p}, \\gamma); d i m (M) = d i m (V _ {p})", + "image_path": "81dcd8b2878918fcbaeae2f167bf018194888a09d522f258ef676991c34b1284.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 83, + 643, + 287, + 656 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 83, + 643, + 287, + 656 + ], + "spans": [ + { + "bbox": [ + 83, + 643, + 287, + 656 + ], + "type": "interline_equation", + "content": "V _ {\\mathrm {p} \\text {- v i s i b l e}} = V _ {p} \\cdot (\\sim M) \\tag {2}", + "image_path": "5b31645dae25b960113770c75e0a8485f0f8cc52f07d9f79be676b7035c5cba4.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 81, + 658, + 157, + 672 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 81, + 658, + 157, + 672 + ], + "spans": [ + { + "bbox": [ + 81, + 658, + 157, + 672 + ], + "type": "interline_equation", + "content": "V _ {\\mathrm {p} \\text {- m a s k e d}} = V _ {p} \\cdot M", + "image_path": "20aad3803f1169b8c1f30ff944587836232995c9057f600b4cdbc6ad4ce13bba.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 677, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 289, + 715 + ], + "type": "text", + "content": "The encoder " + }, + { + "bbox": [ + 47, + 677, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 47, + 677, + 289, + 715 + ], + "type": "text", + "content": " then processes only the visible patches " + }, + { + "bbox": [ + 47, + 677, + 289, + 715 + ], + "type": "inline_equation", + "content": "V_{\\mathrm{p\\_visible}}" + }, + { + "bbox": [ + 47, + 677, + 289, + 715 + ], + "type": "text", + "content": " while the decoder " + }, + { + "bbox": [ + 47, + 677, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\xi" + }, + { + "bbox": [ + 47, + 677, + 289, + 715 + ], + "type": "text", + "content": " processes the full set of encoded patches and masked tokens " + }, + { + "bbox": [ + 47, + 677, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\phi(V_{\\mathrm{p\\_visible}}) \\cup V_{\\mathrm{p\\_masked}}" + }, + { + "bbox": [ + 47, + 677, + 289, + 715 + ], + "type": "text", + "content": " to" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 288, + 545, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 288, + 545, + 312 + ], + "spans": [ + { + "bbox": [ + 305, + 288, + 545, + 312 + ], + "type": "text", + "content": "reconstruct the video. This work uses the same asymmetric encoder-decoder design as [11, 16, 39]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 391, + 323, + 546, + 338 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 391, + 323, + 546, + 338 + ], + "spans": [ + { + "bbox": [ + 391, + 323, + 546, + 338 + ], + "type": "interline_equation", + "content": "E = \\phi \\left(V _ {\\mathrm {p} - \\text {v i s i b l e}}\\right) \\tag {3}", + "image_path": "f1dbe27b18f73c84d0e8d8e96b5665af35f0a4b97e9f417d00cdafc266329d7b.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 380, + 352, + 546, + 365 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 380, + 352, + 546, + 365 + ], + "spans": [ + { + "bbox": [ + 380, + 352, + 546, + 365 + ], + "type": "interline_equation", + "content": "V ^ {\\prime} = \\xi (E \\cup V _ {\\mathrm {p}. \\text {m a s k e d}}) \\tag {4}", + "image_path": "c203b221410648444c0fd7d69d498cc69d872bb79c8a322c1e5b7998b3e9240c.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 370, + 547, + 454 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 370, + 547, + 454 + ], + "spans": [ + { + "bbox": [ + 304, + 370, + 547, + 454 + ], + "type": "text", + "content": "Finally, the model is trained with MSE reconstruction loss between " + }, + { + "bbox": [ + 304, + 370, + 547, + 454 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 304, + 370, + 547, + 454 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 370, + 547, + 454 + ], + "type": "inline_equation", + "content": "V'" + }, + { + "bbox": [ + 304, + 370, + 547, + 454 + ], + "type": "text", + "content": ". The model is then transferred to downstream tasks such as classification via finetuning with cross-entropy loss. Note that this work focuses on the mask generator " + }, + { + "bbox": [ + 304, + 370, + 547, + 454 + ], + "type": "inline_equation", + "content": "\\eta(\\gamma)" + }, + { + "bbox": [ + 304, + 370, + 547, + 454 + ], + "type": "text", + "content": ", which is complementary to recent works which look into the loss function and reconstruction targets [33, 36, 45, 50]." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 461, + 495, + 475 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 461, + 495, + 475 + ], + "spans": [ + { + "bbox": [ + 306, + 461, + 495, + 475 + ], + "type": "text", + "content": "3.2. Simulated-Motion Masking (SMM)" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 479, + 547, + 539 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 479, + 547, + 539 + ], + "spans": [ + { + "bbox": [ + 304, + 479, + 547, + 539 + ], + "type": "text", + "content": "To help the encoder learn spatiotemporal semantics throughout the video, we propose to generate a spatiotemporally continuous moving 3D mask, as shown in Fig. 2. This differs from random masking [11] and random tube masking [39] which break spatiotemporal continuity." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "text", + "content": "We define the mask as a vector " + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "inline_equation", + "content": "[x, y, w, h]" + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "text", + "content": " define the top-left coordinate and " + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "inline_equation", + "content": "w" + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "text", + "content": " define the width and height of the mask. We first explore the use of random motion to generate a dense moving 3D mask with masking ratio " + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "text", + "content": ". To do this, we initialize a rectangle shaped mask in the first frame with dimensions " + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "inline_equation", + "content": "w_0 = h_0 = \\sqrt{\\gamma * \\frac{H}{h} * \\frac{W}{w}}" + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "inline_equation", + "content": "x_0" + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "inline_equation", + "content": "y_0" + }, + { + "bbox": [ + 304, + 540, + 547, + 653 + ], + "type": "text", + "content": " are then randomly initialized in rand(0, H/h - h_0). We then propagate the mask across time using the following recurrent relation:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 341, + 661, + 509, + 674 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 341, + 661, + 509, + 674 + ], + "spans": [ + { + "bbox": [ + 341, + 661, + 509, + 674 + ], + "type": "interline_equation", + "content": "[ x _ {t}, y _ {t}, w _ {t}, h _ {t} ] = [ x _ {t - 1} + v _ {x t}, y _ {t - 1} + v _ {y t},", + "image_path": "397b8051f579e87e4fb6b7381464b23ade400cd4bc245f6b3fae715784347990.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 410, + 676, + 545, + 693 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 410, + 676, + 545, + 693 + ], + "spans": [ + { + "bbox": [ + 410, + 676, + 545, + 693 + ], + "type": "interline_equation", + "content": "\\left. w _ {t - 1} + s _ {t}, h _ {t - 1} + s _ {t} \\right] \\tag {5}", + "image_path": "421676879ecdb010b1dd73286181f4ea94987a1ffb796c55e0a53aee16181a81.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 370, + 693, + 459, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 370, + 693, + 459, + 715 + ], + "spans": [ + { + "bbox": [ + 370, + 693, + 459, + 715 + ], + "type": "interline_equation", + "content": "t \\in [ 1, T), \\sum_ {t} s _ {t} = 0", + "image_path": "1d6dbaaf3f3474d97fe025525526972412f0703e1b454f0a7f89d0a31cf81c3f.jpg" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "5621" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "inline_equation", + "content": "v_{xt}, v_{yt}" + }, + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "content": " are the random horizontal and vertical velocity components, and " + }, + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "inline_equation", + "content": "s_t" + }, + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "content": " is a random scaling factor. To ensure that the masking ratio for each video is consistent, we enforce that " + }, + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "inline_equation", + "content": "\\sum_{t} s_{t} = 0" + }, + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "content": "; in other words, the number of masked patches remains fixed for a given " + }, + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 138, + 226, + 152 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 138, + 226, + 152 + ], + "spans": [ + { + "bbox": [ + 47, + 138, + 226, + 152 + ], + "type": "text", + "content": "3.3. Motion-Guided Masking (MGM)" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 156, + 287, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 156, + 287, + 263 + ], + "spans": [ + { + "bbox": [ + 46, + 156, + 287, + 263 + ], + "type": "text", + "content": "While SMM leads to an improvement over random masking, SMM generates masks that may not reflect true motion as it is not context-aware. For example in Figure 2, the mask may cover static background rather than the basketball player depending on the random initialization and velocity. The most straightforward approach to address this issue would be to guide the mask using precomputed object bounding boxes or optical flow. However, this requires additional data and cost and would make such a method less scalable." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "spans": [ + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "text", + "content": "We propose to use motion vectors as guidance to ensure that the mask movement consistently covers motion across frames. Motion vectors [30, 47] can be decoded from raw video (with H.264 or H.265 CODECs) with no extra cost, which ensures that our proposed approach adds no additional cost and scales well to larger datasets. A motion vector " + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "inline_equation", + "content": "M_{t}[x,y]" + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "text", + "content": " for a given pixel position " + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "inline_equation", + "content": "x,y" + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "text", + "content": " at frame " + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "text", + "content": ", is defined as " + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "inline_equation", + "content": "[d_x,d_y]" + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "inline_equation", + "content": "d_{x}" + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "inline_equation", + "content": "d_{y}" + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "text", + "content": " denote the displacement of pixel " + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "inline_equation", + "content": "x,y" + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "text", + "content": " from frame " + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "inline_equation", + "content": "t - 1" + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "text", + "content": ". Motion vectors are typically sparsely assigned to " + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "inline_equation", + "content": "8\\times 8" + }, + { + "bbox": [ + 46, + 265, + 287, + 443 + ], + "type": "text", + "content": " pixel grids [30, 47], so the overall motion vector map is similar to optical flow but at a lower resolution. In order to use motion vectors to guide the masking, we need pixel-level correspondence between the motion vectors and the video. We accomplish this by upsampling the motion vector map to match the spatial resolution of the video." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 443, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 443, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 47, + 443, + 287, + 479 + ], + "type": "text", + "content": "Given a motion vector map " + }, + { + "bbox": [ + 47, + 443, + 287, + 479 + ], + "type": "inline_equation", + "content": "M_t \\in \\mathbb{R}^{T \\times \\frac{H}{8} \\times \\frac{W}{8}}" + }, + { + "bbox": [ + 47, + 443, + 287, + 479 + ], + "type": "text", + "content": ", we first use nearest-neighbor upsampling (" + }, + { + "bbox": [ + 47, + 443, + 287, + 479 + ], + "type": "inline_equation", + "content": "U_{\\mathrm{nearest}}" + }, + { + "bbox": [ + 47, + 443, + 287, + 479 + ], + "type": "text", + "content": ") to get " + }, + { + "bbox": [ + 47, + 443, + 287, + 479 + ], + "type": "inline_equation", + "content": "M_{\\mathrm{t.scaled}} \\in \\mathbb{R}^{T \\times H \\times W}" + }, + { + "bbox": [ + 47, + 443, + 287, + 479 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 100, + 487, + 287, + 500 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 487, + 287, + 500 + ], + "spans": [ + { + "bbox": [ + 100, + 487, + 287, + 500 + ], + "type": "interline_equation", + "content": "\\mathrm {M} _ {\\text {t . s c a l e d}} = U _ {\\text {n e a r e s t}} \\left(M _ {t}, (H, W)\\right) \\tag {6}", + "image_path": "736f7c9542eda416f13502e41d62907908ea70f2c20899da754b44f2ef8fe69b.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "spans": [ + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "type": "text", + "content": "Next, we initialize a dense rectangle mask for frame " + }, + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "type": "inline_equation", + "content": "t_0" + }, + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "type": "text", + "content": " with dimensions " + }, + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "type": "inline_equation", + "content": "w_0 = h_0 = \\sqrt{\\gamma * \\frac{H}{h} * \\frac{W}{w}}" + }, + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "type": "inline_equation", + "content": "x_0" + }, + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "type": "inline_equation", + "content": "y_0" + }, + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "type": "text", + "content": " are then randomly initialized in " + }, + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "type": "inline_equation", + "content": "rand(0, \\frac{H}{h} - h_0)" + }, + { + "bbox": [ + 46, + 506, + 287, + 562 + ], + "type": "text", + "content": ". The mask is then generated for following time-steps as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 52, + 567, + 203, + 582 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 567, + 203, + 582 + ], + "spans": [ + { + "bbox": [ + 52, + 567, + 203, + 582 + ], + "type": "interline_equation", + "content": "x _ {\\mathrm {t} \\text {c e n t e r}}, y _ {\\mathrm {t} \\text {c e n t e r}} = P o o l _ {\\mathrm {t o p K}} (M _ {\\mathrm {t} \\text {s c a l e d}})", + "image_path": "c0b43d93030050d431b74440f5f48666dcd611b4f1830d3e8094fe565f4fc1f2.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 102, + 585, + 174, + 595 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 585, + 174, + 595 + ], + "spans": [ + { + "bbox": [ + 102, + 585, + 174, + 595 + ], + "type": "interline_equation", + "content": "w _ {t} = w _ {t - 1} + s _ {x t}", + "image_path": "ee2e923faebe2ac170ac3c77495ca3f2cc9f698e8cd22866e3f32abee57c6c23.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 103, + 598, + 173, + 610 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 103, + 598, + 173, + 610 + ], + "spans": [ + { + "bbox": [ + 103, + 598, + 173, + 610 + ], + "type": "interline_equation", + "content": "h _ {t} = h _ {t - 1} + s _ {y t}", + "image_path": "47e8801a847e849ad93e3deb8167279efd73ad519293f175ac0fdec8d5fcf0ea.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 56, + 609, + 287, + 633 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 609, + 287, + 633 + ], + "spans": [ + { + "bbox": [ + 56, + 609, + 287, + 633 + ], + "type": "interline_equation", + "content": "\\left[ x _ {t}, y _ {t}, w _ {t}, h _ {t} \\right] = \\left[ x _ {\\mathrm {t} - \\text {c e n t e r}} - \\frac {w _ {t}}{2}, y _ {\\mathrm {t} - \\text {c e n t e r}} - \\frac {y _ {t}}{2}, w _ {t}, h _ {t} \\right] \\tag {7}", + "image_path": "fd106b9abcdc9fba5c4761f4ca9e896782e8746709e274b691634024940c5aec.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 55, + 635, + 198, + 659 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 635, + 198, + 659 + ], + "spans": [ + { + "bbox": [ + 55, + 635, + 198, + 659 + ], + "type": "interline_equation", + "content": "t \\in [ 1, T), \\sum_ {t} s _ {x t} = 0, \\sum_ {t} s _ {y t} = 0", + "image_path": "b77bde2fe681b5fa2ee753a28580bd34c1aa0f69179f3aafaacc43ea73e17f82.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "Pool_{topK}" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " is the topK (top-1 in our work) magnitude pooling operation that gives the argmax indexes " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "x_{t\\_ center}, y_{t\\_ center}" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": ", which the mask is centered around. We also apply jitter " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "s_{xt}, s_{yt}" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " to both the mask height and width." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "content": "In other words, MGM produces a moving 3D mask where the movement of the mask is centered around parts of the video with the highest magnitude of motion, as shown in Fig. 2. This makes the reconstruction task more focused on spatiotemporal semantics than random masking." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 143, + 432, + 156 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 143, + 432, + 156 + ], + "spans": [ + { + "bbox": [ + 305, + 143, + 432, + 156 + ], + "type": "text", + "content": "4. Experimental Results" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 163, + 368, + 175 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 163, + 368, + 175 + ], + "spans": [ + { + "bbox": [ + 306, + 163, + 368, + 175 + ], + "type": "text", + "content": "4.1. Datasets" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 182, + 547, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 182, + 547, + 361 + ], + "spans": [ + { + "bbox": [ + 304, + 182, + 547, + 361 + ], + "type": "text", + "content": "We conduct experiments on five commonly used datasets: Something-Something V2 (SSv2) [14] contains 220K videos with 174 action classes. SSv2 is considered a motion heavy dataset, as most of the labels are defined by the motion and directionality of the actual action. Kinetics-400 (K400) [19] is the de-facto standard dataset used to evaluate video recognition. It contains 240K Internet videos with 400 action classes. UCF101 [34] is a dataset containing 13K Internet short videos with 101 action classes. HMDB51 [22] is a dataset containing 5K short movie clips from 51 action classes. Diving48 [23] contains 18K untrimmed video clips from 48 action classes, all of which are types of dives. We report the top-1 accuracy on the evaluation set for all datasets following standard practices [12]. Only UCF101 and HMDB51 have multiple split versions; we use split 1." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 369, + 440, + 381 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 369, + 440, + 381 + ], + "spans": [ + { + "bbox": [ + 306, + 369, + 440, + 381 + ], + "type": "text", + "content": "4.2. Implementation Details" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 387, + 547, + 459 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 387, + 547, + 459 + ], + "spans": [ + { + "bbox": [ + 304, + 387, + 547, + 459 + ], + "type": "text", + "content": "Model Configuration: We experiment with both 2D and 3D transformer backbones. The default backbone is ViT-Base [9] with global joint space-time attention. We also experimented with TimesFormer [3] with divided space-time attention. For fair comparison, we use the same input patch size of " + }, + { + "bbox": [ + 304, + 387, + 547, + 459 + ], + "type": "inline_equation", + "content": "2 \\times 16 \\times 16" + }, + { + "bbox": [ + 304, + 387, + 547, + 459 + ], + "type": "text", + "content": " for all models following [39]." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 460, + 547, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 547, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 547, + 555 + ], + "type": "text", + "content": "Pre-Processing: We pretrain with clips of 16 frames sampled at a temporal stride of 4 and 2 for K400 and SSv2 respectively following [39]. We use a fixed spatial resolution of " + }, + { + "bbox": [ + 304, + 460, + 547, + 555 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 304, + 460, + 547, + 555 + ], + "type": "text", + "content": " for all experiments. We apply multi-scalecrop and horizontal flip augmentation by default (flip is not applied to SSv2). We follow [39] to use AdamW [27] optimizer with a base learning rate " + }, + { + "bbox": [ + 304, + 460, + 547, + 555 + ], + "type": "inline_equation", + "content": "1.5e - 4" + }, + { + "bbox": [ + 304, + 460, + 547, + 555 + ], + "type": "text", + "content": ", weight decay of " + }, + { + "bbox": [ + 304, + 460, + 547, + 555 + ], + "type": "inline_equation", + "content": "0.05" + }, + { + "bbox": [ + 304, + 460, + 547, + 555 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 460, + 547, + 555 + ], + "type": "inline_equation", + "content": "\\beta = [0.9, 0.95]" + }, + { + "bbox": [ + 304, + 460, + 547, + 555 + ], + "type": "text", + "content": ", and cosine learning rate decay." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 555, + 547, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 555, + 547, + 663 + ], + "spans": [ + { + "bbox": [ + 304, + 555, + 547, + 663 + ], + "type": "text", + "content": "Finetuning and Evaluation: We use the same 16-frame clip for finetuning and multi-view evaluation protocol following standard practice [12]. We use TSN-style sampling [44] on SSv2 dataset with 2 temporal " + }, + { + "bbox": [ + 304, + 555, + 547, + 663 + ], + "type": "inline_equation", + "content": "\\times" + }, + { + "bbox": [ + 304, + 555, + 547, + 663 + ], + "type": "text", + "content": " 3 spatial views during test-time following [39] for fair comparison. For Kinetics-400, UCF101, HMDB51 and Diving48, we use 5 temporal " + }, + { + "bbox": [ + 304, + 555, + 547, + 663 + ], + "type": "inline_equation", + "content": "\\times" + }, + { + "bbox": [ + 304, + 555, + 547, + 663 + ], + "type": "text", + "content": " 3 spatial views during test-time following [39] for fair comparison. See the supplementary material for hyperparameter details which are mostly the same as [39]." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 671, + 391, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 671, + 391, + 682 + ], + "spans": [ + { + "bbox": [ + 306, + 671, + 391, + 682 + ], + "type": "text", + "content": "4.3. Main Results" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 689, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 547, + 713 + ], + "type": "text", + "content": "Something-Something V2. We first show our MGM's performance on SSv2 in Table 1, and compare with previous" + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5622" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 55, + 83, + 541, + 340 + ], + "blocks": [ + { + "bbox": [ + 288, + 71, + 372, + 81 + ], + "lines": [ + { + "bbox": [ + 288, + 71, + 372, + 81 + ], + "spans": [ + { + "bbox": [ + 288, + 71, + 372, + 81 + ], + "type": "text", + "content": "finetune eval on SSv2" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 426, + 71, + 511, + 80 + ], + "lines": [ + { + "bbox": [ + 426, + 71, + 511, + 80 + ], + "spans": [ + { + "bbox": [ + 426, + 71, + 511, + 80 + ], + "type": "text", + "content": "finetune eval on K400" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 55, + 83, + 541, + 340 + ], + "lines": [ + { + "bbox": [ + 55, + 83, + 541, + 340 + ], + "spans": [ + { + "bbox": [ + 55, + 83, + 541, + 340 + ], + "type": "table", + "html": "
ModelBackboneGFLOPsEpochsPretrainTop1EpochsPretrainTop1
Supervised
SlowFast [12]R101 + NL106196K40063.1--79.8
TimeSformer [3]ViT-B19615IN21K59.515IN21K78.0
VidTr [51]ViT-B35150K40063.0--79.1
MotionFormer [28]ViT-B37090+35IN21K + K40066.590IN21K79.7
MViTv1 [10]MViT-B455200K40067.7--81.2
MViTv2 [24]MViT-B225200K40070.5--82.9
Self-supervised
BEVT [45]Swin-B282800+150IN1K + K40070.6800+150IN1K + K40080.6
M³Video [36]ViT-B180400SSv269.2400K40079.7
MGMViT-B180400SSv269.6400K40080.3
VideoMAE [39]ViT-B180800SSv269.6800K40080.0
MGMViT-B180800SSv270.6800K40080.8
MAM² [33]ViT-B + VQGAN1801200SSv271.3800K40082.3
MGMViT-B1801200SSv271.61200K40081.2
OmniMAE [13]ViT-B1801600IN1K + SSv269.51600IN1K + K40080.8
VideoMAE [39]ViT-B1801600SSv270.31600K40081.5
VideoMAE [39]ViT-B1802400SSv270.8---
STMAE [11]ViT-B1801600K400N/A1600K40081.3
MotionMAE [50]ViT-B1802400SSv271.81600K40081.7
MGMViT-B1801600SSv271.81600K40081.7
MGMViT-B1802400SSv272.1---
", + "image_path": "03e17db865682af90b0c510a9fe0927e00c1569ad0ad1db056f5b5d2f849742a.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 359, + 546, + 384 + ], + "lines": [ + { + "bbox": [ + 46, + 359, + 546, + 384 + ], + "spans": [ + { + "bbox": [ + 46, + 359, + 546, + 384 + ], + "type": "text", + "content": "Table 1: Results comparison on Something-SomethingV2 (SSv2) and Kinetics-400 (K400). GFLOPs is listed as a single view's. All results are with fine-tuning. We apply repeated augmentation " + }, + { + "bbox": [ + 46, + 359, + 546, + 384 + ], + "type": "inline_equation", + "content": "[18] = 2" + }, + { + "bbox": [ + 46, + 359, + 546, + 384 + ], + "type": "text", + "content": " for this table to compare against SOTA." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 404, + 288, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 404, + 288, + 548 + ], + "spans": [ + { + "bbox": [ + 46, + 404, + 288, + 548 + ], + "type": "text", + "content": "models trained in a supervised manner: Our MGM using vanilla ViT-B pretrained on only SSv2 outperforms previous SOTA such as MViTv1 [10] " + }, + { + "bbox": [ + 46, + 404, + 288, + 548 + ], + "type": "inline_equation", + "content": "(+4.4\\%)" + }, + { + "bbox": [ + 46, + 404, + 288, + 548 + ], + "type": "text", + "content": " and MViTv2 [10] " + }, + { + "bbox": [ + 46, + 404, + 288, + 548 + ], + "type": "inline_equation", + "content": "(+1.6\\%)" + }, + { + "bbox": [ + 46, + 404, + 288, + 548 + ], + "type": "text", + "content": " which uses a heavy hierarchical 3D transformer backbone and pretrains on Kinetics-400. This demonstrates the efficiency and effectiveness of our proposed method compared to supervised 3D transformer backbones. MGM also significantly outperforms previous supervised learning methods that use the same backbone as us: " + }, + { + "bbox": [ + 46, + 404, + 288, + 548 + ], + "type": "inline_equation", + "content": "+5.6\\%" + }, + { + "bbox": [ + 46, + 404, + 288, + 548 + ], + "type": "text", + "content": " over MotionFormer [28] and " + }, + { + "bbox": [ + 46, + 404, + 288, + 548 + ], + "type": "inline_equation", + "content": "+12.6\\%" + }, + { + "bbox": [ + 46, + 404, + 288, + 548 + ], + "type": "text", + "content": " over TimeSformer [3]. This demonstrates that the proposed MGM is effective for spatiotemporal modeling." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 557, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 288, + 715 + ], + "type": "text", + "content": "We then compare MGM with SOTA video MAE methods. With the same backbone and training schema, MGM achieves " + }, + { + "bbox": [ + 46, + 557, + 288, + 715 + ], + "type": "inline_equation", + "content": "1.3\\%" + }, + { + "bbox": [ + 46, + 557, + 288, + 715 + ], + "type": "text", + "content": " higher accuracy comparing to VideoMAE [39]. Note that with " + }, + { + "bbox": [ + 46, + 557, + 288, + 715 + ], + "type": "inline_equation", + "content": "3 \\times" + }, + { + "bbox": [ + 46, + 557, + 288, + 715 + ], + "type": "text", + "content": " less training time, our MGM pretrained for 800 epochs is able to achieve nearly the same performance as VideoMAE pretrained for 2400 epochs (" + }, + { + "bbox": [ + 46, + 557, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\sim 66\\%" + }, + { + "bbox": [ + 46, + 557, + 288, + 715 + ], + "type": "text", + "content": " fewer epochs), as illustrated in Fig. 1. This demonstrates that motion-guided masking is a more efficient strategy for self-supervised spatiotemporal learning due to learning video saliency. Compared to OmniMAE [13] which does masked modeling on both images and video, MGM achieves " + }, + { + "bbox": [ + 46, + 557, + 288, + 715 + ], + "type": "inline_equation", + "content": "+2.6\\%" + }, + { + "bbox": [ + 46, + 557, + 288, + 715 + ], + "type": "text", + "content": " improvement. Compared to BEVT [45] which also learns from both images and video and additionally uses" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 404, + 547, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 404, + 547, + 464 + ], + "spans": [ + { + "bbox": [ + 304, + 404, + 547, + 464 + ], + "type": "text", + "content": "Swin Transformer [25, 26] - a heavy 3D Transformer architecture - MGM achieves " + }, + { + "bbox": [ + 304, + 404, + 547, + 464 + ], + "type": "inline_equation", + "content": "+1.5\\%" + }, + { + "bbox": [ + 304, + 404, + 547, + 464 + ], + "type": "text", + "content": " improvement. This is despite the fact that our method only uses video and is pretrained from scratch. Note that STMAE [11] only provides results for ViT-Large backbone on SSv2." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 469, + 548, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 469, + 548, + 661 + ], + "spans": [ + { + "bbox": [ + 304, + 469, + 548, + 661 + ], + "type": "text", + "content": "We finally compare our MGM with some most recent works that also utilize motion information for video pretraining. MGM outperforms " + }, + { + "bbox": [ + 304, + 469, + 548, + 661 + ], + "type": "inline_equation", + "content": "\\mathrm{M}^3\\mathrm{Video}" + }, + { + "bbox": [ + 304, + 469, + 548, + 661 + ], + "type": "text", + "content": " [36] (" + }, + { + "bbox": [ + 304, + 469, + 548, + 661 + ], + "type": "inline_equation", + "content": "+0.4\\%" + }, + { + "bbox": [ + 304, + 469, + 548, + 661 + ], + "type": "text", + "content": " with the same 400 epochs of pretraining) which reconstructs motion trajectories generated from optical flow. We achieve equivalent performance to MotionMAE [50] using " + }, + { + "bbox": [ + 304, + 469, + 548, + 661 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 304, + 469, + 548, + 661 + ], + "type": "text", + "content": " fewer epochs (1600 vs. 2400) even though it utilizes frame difference as an additional reconstruction target which incorporates explicit motion information. The results show that motion-guided masking alone is sufficient for improving spatiotemporal learning. It is worth reiterating that our MGM uses motion vectors for masking guidance, which is already computed during video encoding, and thus directly available during video decoding [30, 43, 47], making our method more efficient and scalable comparing to works such as [33, 36, 50] which use optical flow and/or frame difference." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "content": "Kinetics-400 (K400). We further conduct experiments on K400 and show results in Table 1. Similar trends are observed. Our MGM is able to outperform supervised models with the same backbone such as TimeSformer [3] by " + }, + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "inline_equation", + "content": "+3.7\\%" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5623" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "text", + "content": "and MotionFormer [28] by " + }, + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "inline_equation", + "content": "+2.0\\%" + }, + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "text", + "content": ". MGM slightly underperforms some hierarchical 3D transformer backbones such as MViTv2 [24] by " + }, + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "inline_equation", + "content": "-1.2\\%" + }, + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "text", + "content": " on K400 but MViTv2 is trained with " + }, + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "inline_equation", + "content": "2\\times" + }, + { + "bbox": [ + 46, + 72, + 288, + 120 + ], + "type": "text", + "content": " more frames (32) and uses significantly more FLOPS." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "type": "text", + "content": "Comparing with other MAE based methods, our MGM consistently outperforms VideoMAE by " + }, + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "type": "inline_equation", + "content": "+1.4\\%" + }, + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "type": "text", + "content": " at 800 epochs of pretraining. MGM also achieves better performance comparing to other recent works, at no additional cost. Our MGM outperforms " + }, + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "type": "inline_equation", + "content": "\\mathrm{M}^3\\mathrm{Video}" + }, + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "type": "text", + "content": " [36] at 400 epochs of pretraining by " + }, + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "type": "inline_equation", + "content": "0.6\\%" + }, + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "type": "text", + "content": ", while being more efficient as our method does not use frame difference nor optical flow. Compared to OmniMAE [13] which uses both images and video, MGM achieves " + }, + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "type": "inline_equation", + "content": "0.9\\%" + }, + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "type": "text", + "content": " improvement. Compared to BEVT [45], MGM achieves " + }, + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "type": "inline_equation", + "content": "1.1\\%" + }, + { + "bbox": [ + 46, + 121, + 288, + 240 + ], + "type": "text", + "content": " improvement." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 241, + 288, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 241, + 288, + 396 + ], + "spans": [ + { + "bbox": [ + 46, + 241, + 288, + 396 + ], + "type": "text", + "content": "We note that the performance gain MGM obtains over other methods on K400 is slightly lower compared to on SSv2. This can be explained by the fact that a great proportion of actions in K400 dataset can be differentiated by the appearance of a few key frames, for example, \"skiing\" vs. \"tennis\". In contrast, recognising actions in SSv2 dataset, e.g. \"moving something up\" vs. \"moving something down\", requires the model to understand the subtle differences in motion along temporal dimension. Therefore, we hypothesize that spatiotemporal modeling is less impactful on spatial-heavy datasets such as K400 and the strength of MGM is not fully exhibited. Motion serves as a appearance-agnostic differentiator between classes." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 406, + 157, + 419 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 406, + 157, + 419 + ], + "spans": [ + { + "bbox": [ + 47, + 406, + 157, + 419 + ], + "type": "text", + "content": "4.4. Transfer Learning" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 425, + 287, + 497 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 425, + 287, + 497 + ], + "spans": [ + { + "bbox": [ + 46, + 425, + 287, + 497 + ], + "type": "text", + "content": "We next evaluate MGM's performance when transferred to smaller datasets: UCF101 [34], HMDB51 [22], and Diving48 [23]. Performance in transfer learning is commonly used as an indicator of feature quality and representativeness [17]. We use ViT-Base model pretrained on K400 and SSv2 by 800 epochs for all transfer learning experiments." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "type": "text", + "content": "Finetune on downstream tasks. We first present fine-tuning results from MGM pretrained on unlabeled K400 in Table 2. Our MGM consistently outperforms VideoMAE with same backbone and pretraining setup on all three datasets " + }, + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "type": "inline_equation", + "content": "(+0.9\\%)" + }, + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "type": "text", + "content": " on UCF101, " + }, + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "type": "inline_equation", + "content": "+1.1\\%" + }, + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "type": "text", + "content": " on HMDB51, " + }, + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "type": "inline_equation", + "content": "+4.9\\%" + }, + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "type": "text", + "content": " on Diving48). This shows that our approach learns more representative semantics and thus generalizes better to small-scale downstream tasks. It is worth mentioning that MGM even outperforms K400 supervised pretraining on HMDB51 " + }, + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "type": "inline_equation", + "content": "(+3.2\\%)" + }, + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "type": "text", + "content": " and on Diving48 " + }, + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "type": "inline_equation", + "content": "(+7.5\\%)" + }, + { + "bbox": [ + 46, + 498, + 288, + 628 + ], + "type": "text", + "content": ", demonstrating the effectiveness of our proposed method." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "content": "Our MGM is also able to consistently outperform VideoMAE [39] with pretraining on unlabeled SSv2 in the finetune setting " + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "inline_equation", + "content": "(+1.3\\%)" + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "content": " on UCF101, " + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "inline_equation", + "content": "+1\\%" + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "content": " on HMDB51, " + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "inline_equation", + "content": "+2.6\\%" + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "content": " on Diving48). Our MGM even outperforms SSv2 supervised pretraining by a large margin " + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "inline_equation", + "content": "(+14.1\\%)" + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "content": " on UCF101, " + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "inline_equation", + "content": "+13.4\\%" + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "content": " on HMDB51, " + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "inline_equation", + "content": "+46.9\\%" + }, + { + "bbox": [ + 46, + 630, + 288, + 715 + ], + "type": "text", + "content": " on Diving48). Finetuning MGM on SSv2 (same model from Tab. 1) does not lead to a large" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 322, + 71, + 531, + 135 + ], + "blocks": [ + { + "bbox": [ + 322, + 71, + 531, + 135 + ], + "lines": [ + { + "bbox": [ + 322, + 71, + 531, + 135 + ], + "spans": [ + { + "bbox": [ + 322, + 71, + 531, + 135 + ], + "type": "table", + "html": "
UCFHMDBDiving48
Supervised (K400) †95.171.462.7
VideoMAE [39]93.373.565.3
MGM94.274.670.2
+ K400 Finetune (Tab. 1)97.781.082.6
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UCFHMDBDiving48
Supervised (SSv2) †77.856.336.2
VideoMAE [39]90.668.780.5
MGM91.969.783.1
+ SSv2 Finetune ( Tab. 1)93.274.783.4
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UCFHMDBDiving48
Supervised (K400) †94.165.425.2
VideoMAE [39]70.545.410.0
MGM77.549.214.2
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UCFHMDBDiving48
Supervised (SSv2) †72.951.813.2
VideoMAE [39]65.341.210.7
MGM69.144.810.2
", + "image_path": "cb6a228ee1020bb6d1abf400e9f6c04432652e6bd926428cc552ae66eee279d2.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_body" + } + ], + "index": 13 + }, + { + "bbox": [ + 323, + 371, + 529, + 393 + ], + "lines": [ + { + "bbox": [ + 323, + 371, + 529, + 393 + ], + "spans": [ + { + "bbox": [ + 323, + 371, + 529, + 393 + ], + "type": "text", + "content": "(d) Pretrained on SSv2 and evaluated with linear probing on downstream tasks." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 403, + 547, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 547, + 475 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 547, + 475 + ], + "type": "text", + "content": "Table 2: MGM generalizes well to various downstream datasets (UCF101, HMDB51 and Diving48) on two downstream tasks (finetune, linear-probe). We test VideoMAE and MGM pretrained on Kinetics-400 (K400) for 800 epochs. The supervised baseline is ViT-B trained from scratch on K400 and SSv2 using the recipe from MViT [10, 24]." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 498, + 547, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 547, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 547, + 545 + ], + "type": "text", + "content": "boost, indicating that our model is able to learn the majority of semantics just from unsupervised pretraining, and that unsupervised pretraining is able to make better use of the information in SSv2 than supervised training." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "text", + "content": "Linear Probe on downstream tasks. Previous work [2, 11, 16] argues that generative approaches such as MAE generally perform worse on linear probing tasks as there is a larger gap between the reconstruction task and downstream evaluation compared to other pretraining methods. Nevertheless, we compare linear probe performance between MGM and VideoMAE [39] and show that our method achieves significantly better performance. With K400 pretraining, we outperform VideoMAE by " + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "inline_equation", + "content": "+7\\%" + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "text", + "content": " on UCF101, " + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "inline_equation", + "content": "+3.8\\%" + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "text", + "content": " on HMDB51, and " + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "inline_equation", + "content": "+4.2\\%" + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "text", + "content": " on Diving48. With SSv2 pretraining, we outperform by " + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "inline_equation", + "content": "+3.8\\%" + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "text", + "content": " on UCF101, " + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "inline_equation", + "content": "+3.6\\%" + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "text", + "content": " on HMDB51, and underperform by " + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "inline_equation", + "content": "-0.5\\%" + }, + { + "bbox": [ + 304, + 546, + 547, + 713 + ], + "type": "text", + "content": " on Diving48. This demonstrates that motion-modeling helps reduce the gap between the reconstruction task and downstream tasks, as linear probe only" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5624" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 286, + 119 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 286, + 119 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 286, + 119 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 286, + 119 + ], + "type": "table", + "html": "
UCF14 → HMDB7HMDB14 → UCF7
VideoMAE [39]55.769.6
MGM57.671.4
+ K400 Finetune (Tab. 1)79.196.2
", + "image_path": "135f571ac079d6978cd7840aeb0e8d045982e8285c57ce1aba805344521d957c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 222, + 287, + 246 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 222, + 287, + 246 + ], + "spans": [ + { + "bbox": [ + 46, + 222, + 287, + 246 + ], + "type": "text", + "content": "trains a linear classifier on top of features extracted from the frozen backbone; linear layers cannot learn new semantics." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 247, + 288, + 330 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 247, + 288, + 330 + ], + "spans": [ + { + "bbox": [ + 46, + 247, + 288, + 330 + ], + "type": "text", + "content": "We note that there is a large gap of over " + }, + { + "bbox": [ + 46, + 247, + 288, + 330 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 247, + 288, + 330 + ], + "type": "text", + "content": " with K400 supervised pretraining on linear probe. This is a general deficiency of generative methods such as MAE-based pretraining [11] and we leave further exploration of this problem to future works. One way to address this would be to combine MAE with discriminative methods such as contrastive learning to obtain a balanced representation." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 331, + 288, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 331, + 288, + 569 + ], + "spans": [ + { + "bbox": [ + 46, + 331, + 288, + 569 + ], + "type": "text", + "content": "Domain adaptation. We further evaluate MGM on partial domain adaptation tasks following [49], in which the labels for the target dataset are a subset of the labels for the source dataset. The model is finetuned on the source dataset and directly evaluated on the target dataset without seeing any samples from the target dataset. This is more challenging than conventional domain adaptation as the model may incorrectly label samples in the target dataset as the labels from the source dataset which are not present in the target dataset (\"negative transfer\") [49]. Previous work has showed that optical flow is useful for action recognition because it is invariant to appearance [32]. Several works such as [6, 31] improve unsupervised domain adaptation in video by reducing background and appearance bias to capture the essence of an action via shuffling and mixup respectively. By similar reasoning, domain adaptation is a good evaluation protocol to assess motion learning as the source and target datasets have very different visual appearances, and motion serves as a common link between classes that is agnostic to spatial appearances." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "content": "We use the training sets provided by [49] for UCF14 " + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "content": " HMDB7 and HMDB14 " + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "content": " UCF7. Our MGM consistently outperform VideoMAE with K400 pretraining in both settings " + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "inline_equation", + "content": "(+1.9\\%)" + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "content": " on HMDB7 and " + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "inline_equation", + "content": "+1.8\\%" + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "content": " on UCF7) indicating that MGM can also outperform in a domain adaptation setting. While there is a significant gap of over " + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "content": " between Table 3 and Table 2, finetuning our model on K400 labels bridges the gap. This suggests that our model has learned video saliency and can perform well without any large-scale label supervision, but additional label supervision is helpful for challenging settings such as domain adaptation where spatial information is very different and difficult to" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 309, + 72, + 422, + 180 + ], + "blocks": [ + { + "bbox": [ + 309, + 72, + 422, + 180 + ], + "lines": [ + { + "bbox": [ + 309, + 72, + 422, + 180 + ], + "spans": [ + { + "bbox": [ + 309, + 72, + 422, + 180 + ], + "type": "image", + "image_path": "fd648a874d15a727d3bcd2ee564e90d88f424336ae2801350ba89d2cb430952a.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 326, + 189, + 405, + 200 + ], + "lines": [ + { + "bbox": [ + 326, + 189, + 405, + 200 + ], + "spans": [ + { + "bbox": [ + 326, + 189, + 405, + 200 + ], + "type": "text", + "content": "(a) More mask ratios." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 209, + 547, + 247 + ], + "lines": [ + { + "bbox": [ + 304, + 209, + 547, + 247 + ], + "spans": [ + { + "bbox": [ + 304, + 209, + 547, + 247 + ], + "type": "text", + "content": "Figure 3: Ablations on mask ratio 3a and pretraining duration 3b. Mask ratio 0.75 is optimal and performance does not saturate with longer pretraining." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 426, + 72, + 540, + 180 + ], + "blocks": [ + { + "bbox": [ + 426, + 72, + 540, + 180 + ], + "lines": [ + { + "bbox": [ + 426, + 72, + 540, + 180 + ], + "spans": [ + { + "bbox": [ + 426, + 72, + 540, + 180 + ], + "type": "image", + "image_path": "e45d16a8fae47b9376ca509ac05f77ae6bf24f5d58b28de654365aaf269215ca.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 427, + 189, + 541, + 201 + ], + "lines": [ + { + "bbox": [ + 427, + 189, + 541, + 201 + ], + "spans": [ + { + "bbox": [ + 427, + 189, + 541, + 201 + ], + "type": "text", + "content": "(b) Pretrain duration in epochs." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 312, + 258, + 409, + 311 + ], + "blocks": [ + { + "bbox": [ + 46, + 128, + 289, + 201 + ], + "lines": [ + { + "bbox": [ + 46, + 128, + 289, + 201 + ], + "spans": [ + { + "bbox": [ + 46, + 128, + 289, + 201 + ], + "type": "text", + "content": "Table 3: MGM works well when trained on one dataset and evaluated on another dataset for an overlapping set of classes. The model sees no samples from test dataset, indicating motion understanding as motion is agnostic to spatial appearance. We tested VideoMAE and MGM pretrained on Kinetics-400 (K400) for 800 epochs." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 312, + 258, + 409, + 311 + ], + "lines": [ + { + "bbox": [ + 312, + 258, + 409, + 311 + ], + "spans": [ + { + "bbox": [ + 312, + 258, + 409, + 311 + ], + "type": "table", + "html": "
backboneSSv2
ViT-S61.1
ViT-B67.3
TimesFormer [3]64.7
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guidanceSSv2
optical flow66.0
motion vector67.3
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aspect ratioSSv2
no67.1
yes67.3
", + "image_path": "5ce3329252f2576acd5bdb4d5a3d5bc00622fdacf06bec9285f6bbdda5f5a54c.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 323, + 372, + 378, + 383 + ], + "lines": [ + { + "bbox": [ + 323, + 372, + 378, + 383 + ], + "spans": [ + { + "bbox": [ + 323, + 372, + 378, + 383 + ], + "type": "text", + "content": "(c) Mask jitter." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "text" + }, + { + "type": "table", + "bbox": [ + 409, + 326, + 541, + 368 + ], + "blocks": [ + { + "bbox": [ + 444, + 315, + 539, + 326 + ], + "lines": [ + { + "bbox": [ + 444, + 315, + 539, + 326 + ], + "spans": [ + { + "bbox": [ + 444, + 315, + 539, + 326 + ], + "type": "text", + "content": "(b) Source of motion info." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 409, + 326, + 541, + 368 + ], + "lines": [ + { + "bbox": [ + 409, + 326, + 541, + 368 + ], + "spans": [ + { + "bbox": [ + 409, + 326, + 541, + 368 + ], + "type": "table", + "html": "
pretrain datasamplesK400
Mini-K200 [48]80K78.2
K400 [19]240K78.6
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Masktemporal propagationspatial continuity
staticsimulatedmotionsparsedenseAcc
Random Block✓✓62.9
SMM (Sparse)✓✓64.6
Random Tube✓✓65.0
MGM (Sparse)✓✓65.1
SMM (Dense)✓✓65.9
MGM (Dense)✓✓67.3
", + "image_path": "9570f046ebd57b9ea03b86940af7d8c0825990849759a8979b694003358c5c12.jpg" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "table_body" + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 462, + 547, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 462, + 547, + 496 + ], + "spans": [ + { + "bbox": [ + 304, + 462, + 547, + 496 + ], + "type": "text", + "content": "(e) Masking strategies differentiated by initial position, temporal propagation, and spatial continuity. Spatiotemporally continuous masks with motion guidance perform the best." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 505, + 547, + 553 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 505, + 547, + 553 + ], + "spans": [ + { + "bbox": [ + 304, + 505, + 547, + 553 + ], + "type": "text", + "content": "Table 4: Ablations on backbone 4a, source of motion guidance 4b, mask jitter 4c, pretrain data scale 4d, and mask type 4e. All ablations pretrain for 200 epochs on SSv2 unless otherwise indicated." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 576, + 545, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 576, + 545, + 601 + ], + "spans": [ + { + "bbox": [ + 304, + 576, + 545, + 601 + ], + "type": "text", + "content": "learn from limited samples. There are only " + }, + { + "bbox": [ + 304, + 576, + 545, + 601 + ], + "type": "inline_equation", + "content": "\\sim 1000" + }, + { + "bbox": [ + 304, + 576, + 545, + 601 + ], + "type": "text", + "content": " training samples in each setting." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 306, + 609, + 374, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 609, + 374, + 621 + ], + "spans": [ + { + "bbox": [ + 306, + 609, + 374, + 621 + ], + "type": "text", + "content": "4.5. Ablations" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 628, + 545, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 628, + 545, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 628, + 545, + 676 + ], + "type": "text", + "content": "We perform ablations on the Something-Something V2 dataset, with MGM with ViT-B backbone pretrained for 200 epochs using our motion-guided masking, unless otherwise specified." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 677, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 714 + ], + "type": "text", + "content": "Impact of masking ratio. Figure 3a studies the impact of different masking ratio on SSv2. We noticed that 0.75 masking ratio works best for the proposed MGM, which" + } + ] + } + ], + "index": 25 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5625" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 133 + ], + "type": "text", + "content": "is lower than that of other works [11, 39]. This is because motion-guided masking leads to a more \"challenging\" reconstruction task compared to random masking, since the masked regions of videos are most informative and therefore cannot be easily inferred from retained regions." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 133, + 288, + 205 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 133, + 288, + 205 + ], + "spans": [ + { + "bbox": [ + 46, + 133, + 288, + 205 + ], + "type": "text", + "content": "Impact of pretraining length. We show the impact of different pretraining epochs on SSv2 in Figure 3b. The proposed MGM consistently improves with more training and we achieve state-of-the-art performance on SSv2 with 2400 epochs of pretraining. Performance does not seem to saturate with longer pretraining." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 206, + 289, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 206, + 289, + 350 + ], + "spans": [ + { + "bbox": [ + 46, + 206, + 289, + 350 + ], + "type": "text", + "content": "Generalization to different backbones. MGM also generalizes well to backbones of different sizes and types (Table 4a). We test vanilla ViT-S [9] and ViT-B [9], and TimeSformer [3] with joint space-time attention. Note that our TimeSformer ablation outperforms the supervised result reported by [3] of " + }, + { + "bbox": [ + 46, + 206, + 289, + 350 + ], + "type": "inline_equation", + "content": "59.5\\%" + }, + { + "bbox": [ + 46, + 206, + 289, + 350 + ], + "type": "text", + "content": " on SSv2 which uses IN21K pretraining. In contrast, we do not use any extra data. ViT-S's lower performance may be explained by its low model capacity which may not be sufficient for learning spatiotemporal dynamics. As other methods do not use ViT-S, we cannot compare our result to other methods. We thus use ViT-B to compare fairly against other MAE works which use ViT-B." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 351, + 288, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 351, + 288, + 518 + ], + "spans": [ + { + "bbox": [ + 46, + 351, + 288, + 518 + ], + "type": "text", + "content": "Impact of motion source. In Table 4b we compare the performance of MGM when using optical flow vs. motion vectors as the source of motion guidance. Even though optical flow is more fine-grained and precise than motion vectors, performance of MGM drops when the mask is guided by optical flow. This could be related to the fact that optical flow is calculated on a per-pixel basis whereas motion vectors are computed in a block-wise manner and we utilize a block-wise mask strategy. We thus conveniently choose to use motion vector as it is also directly obtainable from compressed video. We extract optical flow using RAFT-Small [38]. On the SSv2 dataset, reading motion vectors is roughly " + }, + { + "bbox": [ + 46, + 351, + 288, + 518 + ], + "type": "inline_equation", + "content": "30 \\times" + }, + { + "bbox": [ + 46, + 351, + 288, + 518 + ], + "type": "text", + "content": " faster than computing optical flow (80 milliseconds vs. 2.5 seconds per video on average)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 520, + 287, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 520, + 287, + 567 + ], + "spans": [ + { + "bbox": [ + 46, + 520, + 287, + 567 + ], + "type": "text", + "content": "Impact of mask aspect ratio jitter. In Table 4c we ablate the use of aspect ratio jittering from Eq. (7). We see that aspect ratio jittering gives a small " + }, + { + "bbox": [ + 46, + 520, + 287, + 567 + ], + "type": "inline_equation", + "content": "0.2\\%" + }, + { + "bbox": [ + 46, + 520, + 287, + 567 + ], + "type": "text", + "content": " boost in performance but is not a critical component of MGM." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 568, + 287, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 568, + 287, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 568, + 287, + 700 + ], + "type": "text", + "content": "Impact of pretrain dataset scale. In Table 4d we ablate the amount of pretraining data used to see if MGM can generalize to different dataset scales. We pretrain MGM on MiniKinetics-200 [48] and Kinetics-400 (K400) [19] which contain " + }, + { + "bbox": [ + 46, + 568, + 287, + 700 + ], + "type": "inline_equation", + "content": "\\sim 80\\mathrm{K}" + }, + { + "bbox": [ + 46, + 568, + 287, + 700 + ], + "type": "text", + "content": " videos and " + }, + { + "bbox": [ + 46, + 568, + 287, + 700 + ], + "type": "inline_equation", + "content": "\\sim 240\\mathrm{K}" + }, + { + "bbox": [ + 46, + 568, + 287, + 700 + ], + "type": "text", + "content": " videos respectively for 200 epochs. MiniKinetics-200 contains videos belonging to a subset of 200 of the most common classes in K400. We then evaluate top-1 accuracy on K400. We find that there is a small " + }, + { + "bbox": [ + 46, + 568, + 287, + 700 + ], + "type": "inline_equation", + "content": "0.4\\%" + }, + { + "bbox": [ + 46, + 568, + 287, + 700 + ], + "type": "text", + "content": " drop in performance when pretraining on the smaller MiniKinetics-200. We expect performance to further improve when pretraining on datasets larger than K400." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 701, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 701, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 701, + 287, + 713 + ], + "type": "text", + "content": "Effectiveness of 3D motion masking. Table 4e studies" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "text", + "content": "different masking strategies which are broken down into categories based on degree of motion guidance and spatial continuity. We first compare dense to sparse masking, where sparse means that the mask may be spatially discontinuous. The dense variant of SMM and MGM outperform the respective sparse counterpart; dense SMM outperforms sparse SMM by " + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "inline_equation", + "content": "1.3\\%" + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "text", + "content": " and dense MGM outperforms sparse MGM by " + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "inline_equation", + "content": "2.2\\%" + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "text", + "content": ". This suggests the importance of maintaining spatial continuity in the masked reconstruction. Next, we compare MGM to SMM. Sparse MGM outperforms sparse SMM by " + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "inline_equation", + "content": "0.5\\%" + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "text", + "content": " and dense MGM outperforms dense SMM by " + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "inline_equation", + "content": "1.4\\%" + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "text", + "content": ". When motion is completely removed, performance is the worst even when the mask is spatially continuous (static block gets " + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "inline_equation", + "content": "62.9\\%" + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "text", + "content": "). Dense MGM outperforms all masking strategies and specifically the random masking baseline by " + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "inline_equation", + "content": "2.3\\%" + }, + { + "bbox": [ + 304, + 72, + 547, + 348 + ], + "type": "text", + "content": ". All masking strategies except block and sparse SMM outperform random masking. Random masking is spatiotemporally discontinuous. This validates our intuition that forming continuous 3D masks which model the true motion information within video is useful. We thus pick dense MGM for all other experiments and refer to \"MGM\" as the dense variant by default. For a visualization of these masking strategies, see Figure 4." + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 310, + 367, + 545, + 488 + ], + "blocks": [ + { + "bbox": [ + 310, + 367, + 545, + 488 + ], + "lines": [ + { + "bbox": [ + 310, + 367, + 545, + 488 + ], + "spans": [ + { + "bbox": [ + 310, + 367, + 545, + 488 + ], + "type": "image", + "image_path": "7bdace739ebf35a847db114876ff8b6f48cbf77163604193bb8f329068daa194.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 318, + 498, + 533, + 511 + ], + "lines": [ + { + "bbox": [ + 318, + 498, + 533, + 511 + ], + "spans": [ + { + "bbox": [ + 318, + 498, + 533, + 511 + ], + "type": "text", + "content": "Figure 4: Visualization of different mask algorithms." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 548, + 389, + 559 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 548, + 389, + 559 + ], + "spans": [ + { + "bbox": [ + 306, + 548, + 389, + 559 + ], + "type": "text", + "content": "4.6. Visualization" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 570, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 713 + ], + "type": "text", + "content": "In Figure 5, we provide visualizations from two perspectives using MGM pretrained on K400. Note that visualizations are subjective and should not be used as a formal explanation for model behavior. Our intention is to provide additional insight into the model to complement our quantitative results. We first visualize the RGB frames with bounding boxes, motion-guided masks, and motion vectors. We see that the motion-guided masks overlap with the majority of spatiotemporally salient regions. Second, we visualize the attention map using the center patch of the center frame as a query. We observe that the model mostly attends to the salient regions. For more visualizations, see the supplementary." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5626" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 85, + 70, + 147, + 134 + ], + "blocks": [ + { + "bbox": [ + 71, + 98, + 80, + 107 + ], + "lines": [ + { + "bbox": [ + 71, + 98, + 80, + 107 + ], + "spans": [ + { + "bbox": [ + 71, + 98, + 80, + 107 + ], + "type": "text", + "content": "a)" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 85, + 70, + 147, + 134 + ], + "lines": [ + { + "bbox": [ + 85, + 70, + 147, + 134 + ], + "spans": [ + { + "bbox": [ + 85, + 70, + 147, + 134 + ], + 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], + "index": 13, + "angle": 0, + "type": "image_body" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 150, + 267, + 212, + 329 + ], + "blocks": [ + { + "bbox": [ + 150, + 267, + 212, + 329 + ], + "lines": [ + { + "bbox": [ + 150, + 267, + 212, + 329 + ], + "spans": [ + { + "bbox": [ + 150, + 267, + 212, + 329 + ], + "type": "image", + "image_path": "2cd0a3af7aa4bd63910ebc6f5d0e18fbf142e2e8bcaba7111649c507ac2396f8.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 338, + 288, + 386 + ], + "lines": [ + { + "bbox": [ + 46, + 338, + 288, + 386 + ], + "spans": [ + { + "bbox": [ + 46, + 338, + 288, + 386 + ], + "type": "text", + "content": "Figure 5: a) RGB frames with bounding boxes for visualization. b) Our MGM masks continuously cover the moving hand. c) Motion vector maps. d) Encoder attention map using center patch of center frame as query." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 216, + 267, + 279, + 329 + ], + "blocks": [ + { + "bbox": [ + 216, + 267, + 279, + 329 + ], + "lines": [ + { + "bbox": [ + 216, + 267, + 279, + 329 + ], + "spans": [ + { + "bbox": [ + 216, + 267, + 279, + 329 + ], + "type": "image", + "image_path": "faee1514de1aa0a5ac44086a1e67c47729d56f23be49ab6327b55fcb9564368a.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + } + ], + "index": 15 + }, + { + "bbox": [ + 47, + 415, + 198, + 428 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 415, + 198, + 428 + ], + "spans": [ + { + "bbox": [ + 47, + 415, + 198, + 428 + ], + "type": "text", + "content": "5. Discussion and Conclusion" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 46, + 441, + 288, + 512 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 441, + 288, + 512 + ], + "spans": [ + { + "bbox": [ + 46, + 441, + 288, + 512 + ], + "type": "text", + "content": "Limitations. Our method efficiently leverages motion cues from compressed video format. However, MGM's effectiveness on the video benchmarks that are not human centric or have tremendous camera motion has yet to be examined. To the best of our knowledge, we did not find such a video benchmark, so we will leave this to future work." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 46, + 517, + 288, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 517, + 288, + 566 + ], + "spans": [ + { + "bbox": [ + 46, + 517, + 288, + 566 + ], + "type": "text", + "content": "Potential negative impact. As our model is trained on primarily Internet video datasets, our model will learn the bias inherent to that data. There could be unintended consequences and we advocate for complying with the law." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "content": "Conclusion. This paper introduces motion-guided masking (MGM), an algorithm which produces motion-aware 3D masks to improve spatiotemporal learning. Our use of motion information is much more efficient than previous optical flow as we leverage motion vectors that naturally exist in the video codec. We achieve new state-of-the-art or comparable performance on two challenging large-scale video benchmarks and achieve previous state-of-the-art results with " + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "content": " less pretraining time, making our method more efficient. We also achieve better generalization than previous video MAE works on three small-scale datasets. 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Specifically, we propose a pretraining stage in which a motion encoder is trained to recover the underlying 3D motion from noisy partial 2D observations. The motion representations acquired in this way incorporate geometric, kinematic, and physical knowledge about human motion, which can be easily transferred to multiple downstream tasks. We implement the motion encoder with a Dual-stream Spatio-temporal Transformer (DSTformer) neural network. It could capture long-range spatio-temporal relationships among the skeletal joints comprehensively and adaptively, exemplified by the lowest 3D pose estimation error so far when trained from scratch. Furthermore, our proposed framework achieves state-of-the-art performance on all three downstream tasks by simply finetuning the pretrained motion encoder with a simple regression head (1-2 layers), which demonstrates the versatility of the learned motion representations. Code and models are available at https://motionbert.github.io/", + "bbox": [ + 76, + 353, + 473, + 670 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 702, + 209, + 718 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Perceiving and understanding human activities have long been a core pursuit of machine intelligence. To this end, researchers define various tasks to estimate human-centric semantic labels from videos, e.g. skeleton keypoints [13, 33], action classes [60, 116], and surface meshes [42, 66]. While significant progress has been made in each of these tasks, they tend to be modeled in isolation, rather than as interconnected problems. For example, Spatial Temporal Graph Con", + "bbox": [ + 75, + 728, + 470, + 849 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/56360d2db70b73e01cb534a647d0b0f284177f167c3ee15f582c61819cd2b64b.jpg", + "image_caption": [ + "Figure 1. Framework overview. We utilize a motion encoder to learn human motion representations via recovering 3D human motion from corrupted 2D skeleton sequences. To adapt to different downstream tasks, we finetune the pretrained motion representations with a linear layer or a simple MLP." + ], + "image_footnote": [], + "bbox": [ + 501, + 319, + 885, + 455 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "volitional Networks (ST-GCN) have been applied to modeling spatio-temporal relationship of human joints in both 3D pose estimation [12, 109] and action recognition [89, 116], but their connections have not been fully explored. Intuitively, these models should all have learned to identify typical human motion patterns, despite being designed for different problems. Nonetheless, current methods fail to mine and utilize such commonalities across the tasks. Ideally, we could develop a unified human-centric video representation that can be shared across all relevant tasks.", + "bbox": [ + 496, + 551, + 893, + 703 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "One significant challenge to developing such a representation is the heterogeneity of available data resources. Motion capture (Mocap) systems [36, 71] provide high-fidelity 3D motion data obtained with markers and sensors, but the appearances of captured videos are usually constrained to simple indoor scenes. Action recognition datasets provide annotations of the action semantics, but they either contain no human pose labels [15, 88] or feature limited motion of daily activities [59, 60, 86]. In contrast, in-the-wild human videos offer a vast and diverse range of appearance and motion. However, obtaining precise 2D pose annotations requires considerable effort [3], and acquiring ground-truth (GT) 3D joint locations is almost impossible. Consequently,", + "bbox": [ + 496, + 704, + 895, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Yizhou Wang is with Center on Frontiers of Computing Studies, School of Computer Science, Peking University and Institute for Artificial Intelligence, Peking University.", + "bbox": [ + 75, + 862, + 470, + 901 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "15085", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "most existing studies focus on a specific task using a single type of human motion data, and they are not able to enjoy the advantages of other data resources.", + "bbox": [ + 75, + 90, + 468, + 136 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we provide a new perspective on learning human motion representations. The key idea is that we can learn a versatile human motion representation from heterogeneous data resources in a unified manner, and utilize the representation to handle different downstream tasks in a unified way. We present a two-stage framework, consisting of pretraining and finetuning, as depicted in Figure 1. In the pretraining stage, we extract 2D skeleton sequences from diverse motion data sources and corrupt them with random masks and noises. Subsequently, we train the motion encoder to recover the 3D motion from the corrupted 2D skeletons. This challenging pretext task intrinsically requires the motion encoder to i) infer the underlying 3D human structures from its temporal movements; ii) recover the erroneous and missing observations. In this way, the motion encoder implicitly captures human motion commonsense such as joint linkages, anatomical constraints, and temporal dynamics. In practice, we propose Dual-stream Spatio-temporal Transformer (DSTformer) as the motion encoder to capture the long-range relationship among skeleton keypoints. We suppose that the motion representations learned from large-scale and diversified data resources could be shared across different downstream tasks and benefit their performance. Therefore, for each downstream task, we adapt the pretrained motion representations using task-specific training data and supervisory signals with a simple regression head.", + "bbox": [ + 75, + 137, + 472, + 527 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, the contributions of this work are three-fold: 1) We provide a new perspective on solving various human-centric video tasks through a shared framework of learning human motion representations. 2) We propose a pretraining method to leverage the large-scale yet heterogeneous human motion resources and learn generalizable human motion representations. Our approach could take advantage of the precision of 3D mocap data and the diversity of in-the-wild RGB videos at the same time. 3) We design a dual-stream Transformer network with cascaded spatio-temporal self-attention blocks that could serve as a general backbone for human motion modeling. The experiments demonstrate that the above designs enable a versatile human motion representation that can be transferred to multiple downstream tasks, outperforming the task-specific state-of-the-art methods.", + "bbox": [ + 75, + 529, + 472, + 755 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 768, + 218, + 784 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Learning Human Motion Representations. Early works formulate human motion with Hidden Markov Models [49, 101] and graphical models [47, 92]. Kanazawa et al. [39] design a temporal encoder and a hallucinator to learn representations of 3D human dynamics. Zhang et al. [124] predict future 3D dynamics in a self-supervised manner. Sun et al. [95] further incorporate action labels with an ac", + "bbox": [ + 75, + 794, + 472, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tion memory bank. From the action recognition perspective, a variety of pretext tasks are designed to learn motion representations in a self-supervised manner, including future prediction [93], jigsaw puzzle [56], skeleton-contrastive [100], speed change [94], cross-view consistency [58], and contrast-reconstruction [110]. Similar techniques are also explored in tasks like motion assessment [31, 80] and motion retargeting [119, 130]. These methods leverage homogeneous motion data, design corresponding pretext tasks, and apply them to a specific downstream task. In this work, we propose a unified pretrain-finetune framework to incorporate heterogeneous data resources and demonstrate its versatility in various downstream tasks.", + "bbox": [ + 496, + 90, + 893, + 287 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3D Human Pose Estimation. Recovering 3D human poses from monocular RGB videos is a classical problem, and the methods can be categorized into two categories. The first is to estimate 3D poses with CNN directly from images [77, 97, 128]. However, one limitation of these approaches is that there is a trade-off between 3D pose precision and appearance diversity due to current data collection techniques. The second category is to extract the 2D pose first, then lift the estimated 2D pose to 3D with a separate neural network. The lifting can be achieved via Fully Connected Network [28, 73], Temporal Convolutional Network (TCN) [21, 83], GCN [12, 27, 109], and Transformer [52, 87, 126, 127]. Our framework is built upon the second category as we use the proposed DSTformer to accomplish 2D-to-3D lifting.", + "bbox": [ + 496, + 310, + 895, + 537 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Skeleton-based Action Recognition. The pioneering works [69, 108, 120] point out the inherent connection between action recognition and human pose estimation. Towards modeling the spatio-temporal relationship among human joints, previous studies mainly employ LSTM [91, 129] and GCN [20, 51, 64, 89, 116]. Most recently, PoseC-conv3D [30] proposes to apply 3D-CNN on the stacked 2D joint heatmaps and achieves improved results. In addition to the fully-supervised action recognition task, NTU-RGB+D-120 [60] brings attention to the challenging one-shot action recognition problem. To this end, SL-DML [76] applies deep metric learning to multi-modal signals. Sabater et al. [85] explores one-shot recognition in therapy scenarios with TCN. We demonstrate that the pretrained motion representations could generalize well to action recognition tasks, and the pretrain-finetune framework is a suitable solution for the one-shot challenges.", + "bbox": [ + 496, + 560, + 895, + 816 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Human Mesh Recovery. Based on the parametric human models such as SMPL [66], many research works [38, 70, 78, 115, 125] focus on regressing the human mesh from a single image. SPIN [44] additionally incorporates fitting the body", + "bbox": [ + 496, + 839, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "15086", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/3676fb971eff88d310a197d85cef8ee9330d9586d994ed8369bbfa462f9db7e4.jpg", + "image_caption": [ + "Figure 2. Model architecture. We propose the Dual-stream Spatio-temporal Transformer (DSTformer) as a general backbone for human motion modeling. DSTformer consists of $N$ dual-stream-fusion modules. Each module contains two branches of spatial or temporal MHSA and MLP. The Spatial MHSA models the connection among different joints within a timestep, while the Temporal MHSA models the movement of one joint." + ], + "image_footnote": [], + "bbox": [ + 163, + 89, + 810, + 229 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "model to 2D joints in the training loop. Despite their promising per-frame results, these methods yield jittery and unstable results [42, 123] when applied to videos. To improve their temporal coherence, PoseBERT [7] and SmoothNet [123] propose to employ a denoising and smoothing module to the single-frame predictions. Several works [23, 39, 42, 99] take video clips as input to exploit the temporal cues. Another common problem is that paired images and GT meshes are mostly captured in constrained scenarios, which limits the generalization ability of the above methods. To that end, Pose2Mesh [24] proposes to first extract 2D skeletons using an off-the-shelf pose estimator, then lift them to 3D mesh vertices. Our approach is complementary to state-of-the-art human mesh recovery methods and could further improve their temporal coherence with the pretrained motion representations.", + "bbox": [ + 75, + 316, + 473, + 559 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 604, + 169, + 619 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overview", + "text_level": 1, + "bbox": [ + 76, + 640, + 187, + 654 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As discussed in Section 1, our approach consists of two stages, namely unified pretraining and task-specific finetuning. In the first stage, we train a motion encoder to accomplish the 2D-to-3D lifting task, where we use the proposed DSTformer as the backbone. In the second stage, we finetune the pretrained motion encoder and a few new layers on the downstream tasks. We use 2D skeleton sequences as input for both pretraining and finetuning because they could be reliably extracted from all kinds of motion sources [3,9,71,81,96], and is more robust to variations [18,30]. Existing studies have shown the effectiveness of using 2D skeleton sequences for different downstream tasks [24,30,83,102]. We will first introduce the architecture of DSTformer, and then describe the training scheme in detail.", + "bbox": [ + 75, + 674, + 473, + 898 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Network Architecture", + "text_level": 1, + "bbox": [ + 500, + 316, + 705, + 330 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Figure 2 shows the network architecture for 2D-to-3D lifting. Given an input 2D skeleton sequence $\\mathbf{x} \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{in}}}$ , we first project it to a high-dimensional feature $\\mathbf{F}^0 \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{f}}}$ , then add learnable spatial positional encoding $\\mathbf{P}_{\\mathrm{pos}}^{\\mathrm{S}} \\in \\mathbb{R}^{1 \\times J \\times C_{\\mathrm{f}}}$ and temporal positional encoding $\\mathbf{P}_{\\mathrm{pos}}^{\\mathrm{T}} \\in \\mathbb{R}^{T \\times 1 \\times C_{\\mathrm{f}}}$ to it. We then use the sequence-to-sequence model DSTformer to calculate $\\mathbf{F}^i \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{f}}} (i = 1, \\dots, N)$ where $N$ is the network depth. We apply a linear layer with tanh activation [29] to $\\mathbf{F}^N$ to compute the motion representation $\\mathbf{E} \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{e}}}$ . Finally, we apply a linear transformation to $\\mathbf{E}$ to estimate 3D motion $\\hat{\\mathbf{X}} \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{out}}}$ . Here, $T$ denotes the sequence length, and $J$ denotes the number of body joints. $C_{\\mathrm{in}}, C_{\\mathrm{f}}, C_{\\mathrm{e}}$ , and $C_{\\mathrm{out}}$ denote the channel numbers of input, feature, embedding, and output respectively. We first introduce the basic building blocks of DSTformer, i.e. Spatial and Temporal Blocks with Multi-Head Self-Attention (MHSA), and then explain the DSTformer architecture design.", + "bbox": [ + 496, + 338, + 895, + 613 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Spatial Block. Spatial MHSA (S-MHSA) aims at modeling the relationship among the joints within the same time step. It is defined as", + "bbox": [ + 496, + 631, + 893, + 676 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathrm {S} - \\mathrm {M H S A} \\left(\\mathbf {Q} _ {\\mathrm {S}}, \\mathbf {K} _ {\\mathrm {S}}, \\mathbf {V} _ {\\mathrm {S}}\\right) = \\left[ \\text {h e a d} _ {1}; \\dots ; \\text {h e a d} _ {h} \\right] \\mathbf {W} _ {\\mathrm {S}} ^ {P}, \\\\ \\operatorname {h e a d} _ {i} = \\operatorname {s o f t m a x} \\left(\\frac {\\mathbf {Q} _ {\\mathrm {S}} ^ {i} \\left(\\mathbf {K} _ {\\mathrm {S}} ^ {i}\\right) ^ {\\prime}}{\\sqrt {d _ {K}}}\\right) \\mathbf {V} _ {\\mathrm {S}} ^ {i}, \\tag {1} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 535, + 686, + 890, + 741 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{W}_{\\mathrm{S}}^{P}$ is a projection parameter matrix, $h$ is the number of the heads, $i\\in 1,\\dots ,h$ and ${}^{\\prime}$ denotes matrix transpose. We utilize self-attention to get the query Qs, key $\\mathbf{K}_S$ , and value $\\mathbf{V}_{\\mathrm{S}}$ from input per-frame spatial feature $\\mathbf{F}_{\\mathrm{S}}\\in \\mathbb{R}^{J\\times C_{\\mathrm{e}}}$ for each head,", + "bbox": [ + 496, + 751, + 893, + 827 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Q} _ {\\mathrm {S}} ^ {i} = \\mathbf {F} _ {\\mathrm {S}} \\mathbf {W} _ {\\mathrm {S}} ^ {(Q, i)}, \\mathbf {K} _ {\\mathrm {S}} ^ {i} = \\mathbf {F} _ {\\mathrm {S}} \\mathbf {W} _ {\\mathrm {S}} ^ {(K, i)}, \\mathbf {V} _ {\\mathrm {S}} ^ {i} = \\mathbf {F} _ {\\mathrm {S}} \\mathbf {W} _ {\\mathrm {S}} ^ {(V, i)}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 519, + 837, + 893, + 857 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{W}_{\\mathrm{S}}^{(Q,i)}$ , $\\mathbf{W}_{\\mathrm{S}}^{(K,i)}$ , $\\mathbf{W}_{\\mathrm{S}}^{(V,i)}$ are projection matrices, and $d_{K}$ is the feature dimension of $\\mathbf{K}_{\\mathrm{S}}$ . We apply S-MHSA to", + "bbox": [ + 496, + 866, + 893, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "15087", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "features of different time steps in parallel. Residual connection and layer normalization (LayerNorm) are used to the S-MHSA result, which is further fed into a multilayer perceptron (MLP), and followed by a residual connection and LayerNorm following [105]. We denote the entire spatial block with MHSA, LayerNorm, MLP, and residual connections by $\\mathcal{S}$ .", + "bbox": [ + 75, + 90, + 472, + 196 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Temporal Block. Temporal MHSA (T-MHSA) aims at modeling the relationship across the time steps for a body joint. Its computation process is similar with S-MHSA except that the MHSA is applied to the per-joint temporal feature $\\mathbf{F}_{\\mathrm{T}} \\in \\mathbb{R}^{T \\times C_{\\mathrm{e}}}$ and parallelized over the spatial dimension.", + "bbox": [ + 75, + 215, + 472, + 305 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathrm {T} - \\mathrm {M H S A} \\left(\\mathbf {Q} _ {\\mathrm {T}}, \\mathbf {K} _ {\\mathrm {T}}, \\mathbf {V} _ {\\mathrm {T}}\\right) = \\left[ \\text {h e a d} _ {1}; \\dots ; \\text {h e a d} _ {h} \\right] \\mathbf {W} _ {\\mathrm {T}} ^ {P}, \\\\ \\operatorname {h e a d} _ {i} = \\operatorname {s o f t m a x} \\left(\\frac {\\mathbf {Q} _ {\\mathrm {T}} ^ {i} \\left(\\mathbf {K} _ {\\mathrm {T}} ^ {i}\\right) ^ {\\prime}}{\\sqrt {d _ {K}}}\\right) \\mathbf {V} _ {\\mathrm {T}} ^ {i}, \\tag {3} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 112, + 314, + 468, + 369 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $i \\in 1, \\ldots, h$ , $\\mathbf{Q}_{\\mathrm{T}}$ , $\\mathbf{K}_{\\mathrm{T}}$ , $\\mathbf{V}_{\\mathrm{T}}$ are computed similar with Formula 2. We denote the entire temporal block by $\\mathcal{T}$ .", + "bbox": [ + 76, + 378, + 468, + 409 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Dual-stream Spatio-temporal Transformer. Given spatial and temporal MHSA that captures the intra-frame and inter-frame body joint interactions respectively, we assemble the basic building blocks to fuse the spatial and temporal information in the flow. We design a dual-stream architecture with the following assumptions: 1) Both streams should be capable of modeling the comprehensive spatio-temporal context. 2) Each stream should be specialized in different spatio-temporal aspects. 3) The two streams should be fused together, with the fusion weights dynamically balanced depending on the input spatio-temporal characteristics.", + "bbox": [ + 75, + 428, + 472, + 593 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Hence, we stack the spatial and temporal MHSA blocks in different orders, forming two parallel computation branches. The output features of the two branches are fused using adaptive weights predicted by an attention regressor. The dual-stream-fusion module is then repeated for $N$ times:", + "bbox": [ + 75, + 594, + 470, + 670 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {F} ^ {i} = \\boldsymbol {\\alpha} _ {\\mathrm {S T}} ^ {i} \\circ \\mathcal {T} _ {1} ^ {i} \\left(\\mathcal {S} _ {1} ^ {i} \\left(\\mathbf {F} ^ {i - 1}\\right)\\right) + \\boldsymbol {\\alpha} _ {\\mathrm {T S}} ^ {i} \\circ \\mathcal {S} _ {2} ^ {i} \\left(\\mathcal {T} _ {2} ^ {i} \\left(\\mathbf {F} ^ {i - 1}\\right)\\right), \\quad i \\in 1, \\dots , N, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 676, + 473, + 705 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbf{F}^i$ denotes the feature embedding at depth $i$ , $\\circ$ denotes element-wise production. Orders of $\\mathcal{S}$ and $\\mathcal{T}$ blocks are shown in Figure 2, and different blocks do not share weights. Adaptive fusion weights $\\alpha_{\\mathrm{ST}}, \\alpha_{\\mathrm{TS}} \\in \\mathbb{R}^{N \\times T \\times J}$ are given by", + "bbox": [ + 75, + 708, + 468, + 768 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\alpha_ {\\mathrm {S T}} ^ {i}, \\alpha_ {\\mathrm {T S}} ^ {i} = \\operatorname {s o f t m a x} \\left(\\mathcal {W} \\left(\\left[ \\mathcal {T} _ {1} ^ {i} \\left(\\mathcal {S} _ {1} ^ {i} \\left(\\mathbf {F} ^ {i - 1}\\right)\\right), \\mathcal {S} _ {2} ^ {i} \\left(\\mathcal {T} _ {2} ^ {i} \\left(\\mathbf {F} ^ {i - 1}\\right)\\right) \\right]\\right)\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 776, + 468, + 806 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{W}$ is a learnable linear transformation. $[,]$ denotes concatenation.", + "bbox": [ + 75, + 806, + 468, + 837 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Unified Pretraining", + "text_level": 1, + "bbox": [ + 76, + 847, + 264, + 864 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We address two key challenges when designing the unified pretraining framework: 1) How to learn a powerful", + "bbox": [ + 76, + 869, + 472, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "motion representation with a universal pretext task. 2) How to utilize large-scale but heterogeneous human motion data in all kinds of formats.", + "bbox": [ + 496, + 90, + 890, + 135 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For the first challenge, we follow the successful practices in language [11, 29, 84] and vision [6, 34] modeling to construct the supervision signals, i.e. mask part of the input and use the encoded representations to reconstruct the whole input. Note that such \"cloze\" task naturally exists in human motion analysis, that is to recover the lost depth information from the 2D visual observations, i.e. 3D human pose estimation. Inspired by this, we leverage the large-scale 3D mocap data [71] and design a 2D-to-3D lifting pretext task. We first extract the 2D skeleton sequences $\\mathbf{x}$ by projecting the 3D motion orthographically. Then, we corrupt $\\mathbf{x}$ by randomly masking and adding noise to produce the corrupted 2D skeleton sequences, which also resemble the 2D detection results as it contains occlusions, detection failures, and errors. Both joint-level and frame-level masks are applied with certain probabilities. We use the aforementioned motion encoder to get motion representation $\\mathbf{E}$ and reconstruct 3D motion $\\hat{\\mathbf{X}}$ . We then compute the joint loss $\\mathcal{L}_{3\\mathrm{D}}$ between $\\hat{\\mathbf{X}}$ and GT 3D motion $\\mathbf{X}$ . We also add the velocity loss $\\mathcal{L}_{\\mathrm{O}}$ following previous works [83, 126]. The 3D reconstruction losses are thus given by", + "bbox": [ + 496, + 136, + 893, + 455 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {3 D}} = \\sum_ {t = 1} ^ {T} \\sum_ {j = 1} ^ {J} \\| \\hat {\\mathbf {X}} _ {t, j} - \\mathbf {X} _ {t, j} \\| _ {2}, \\quad \\mathcal {L} _ {\\mathrm {O}} = \\sum_ {t = 2} ^ {T} \\sum_ {j = 1} ^ {J} \\| \\hat {\\mathbf {O}} _ {t, j} - \\mathbf {O} _ {t, j} \\| _ {2}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 498, + 464, + 910, + 513 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\hat{\\mathbf{O}}_t = \\hat{\\mathbf{X}}_t - \\hat{\\mathbf{X}}_{t - 1}$ $\\mathbf{O}_t = \\mathbf{X}_t - \\mathbf{X}_{t - 1}$", + "bbox": [ + 498, + 513, + 795, + 530 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For the second challenge, we notice that 2D skeletons could serve as a universal medium as they can be extracted from all sorts of motion data sources. We further incorporate in-the-wild RGB videos into the 2D-to-3D lifting framework for unified pretraining. For RGB videos, the 2D skeletons $\\mathbf{x}$ could be given by manual annotation [3] or 2D pose estimators [13, 96], and the depth channel of the extracted 2D skeletons is intrinsically \"masked\". Similarly, we add extra masks and noises to degrade $\\mathbf{x}$ (if $\\mathbf{x}$ already contains detection noise, only masking is applied). As 3D motion GT $\\mathbf{X}$ is not available for these data, we apply a weighted 2D re-projection loss which is calculated by", + "bbox": [ + 496, + 530, + 893, + 712 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {2 D}} = \\sum_ {t = 1} ^ {T} \\sum_ {j = 1} ^ {J} \\boldsymbol {\\delta} _ {t, j} \\| \\hat {\\mathbf {x}} _ {t, j} - \\mathbf {x} _ {t, j} \\| _ {2}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 586, + 722, + 890, + 761 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\hat{\\mathbf{x}}$ is the 2D orthogonal projection of the estimated 3D motion $\\hat{\\mathbf{X}}$ , and $\\delta \\in \\mathbb{R}^{T\\times J}$ is given by visibility annotation or 2D detection confidence.", + "bbox": [ + 496, + 771, + 893, + 816 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The total pretraining loss is computed by", + "bbox": [ + 519, + 816, + 790, + 833 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\underbrace {\\mathcal {L} _ {\\mathrm {3 D}} + \\lambda_ {\\mathrm {O}} \\mathcal {L} _ {\\mathrm {O}}} _ {\\text {f o r 3 D d a t a}} + \\underbrace {\\mathcal {L} _ {\\mathrm {2 D}}} _ {\\text {f o r 2 D d a t a}}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 602, + 843, + 890, + 875 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\lambda_{\\mathrm{O}}$ is a constant coefficient to balance the losses.", + "bbox": [ + 500, + 885, + 864, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "15088", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Task-specific Finetuning", + "text_level": 1, + "bbox": [ + 76, + 90, + 302, + 107 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The learned feature embedding $\\mathbf{E}$ serves as a 3D-aware and temporal-aware human motion representation. For downstream tasks, we adopt the minimalist design principle, i.e. implementing a shallow downstream network and training without bells and whistles. In practice, we use an extra linear layer or an MLP with one hidden layer. We then finetune the whole network end-to-end.", + "bbox": [ + 75, + 114, + 470, + 220 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3D Pose Estimation. As we utilize 2D-to-3D lifting as the pretext task, we simply reuse the whole pretrained network. During finetuning, the input 2D skeletons are estimated from videos without extra masks or noises.", + "bbox": [ + 75, + 250, + 470, + 310 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Skeleton-based Action Recognition. We directly apply a global average pooling over different persons and timesteps. The result is then fed into an MLP with one hidden layer. The network is trained with cross-entropy classification loss. For one-shot learning, we apply a linear layer after the pooled features to extract clip-level action representation. We introduce the detailed setup of one-shot learning in Section 4.4.", + "bbox": [ + 75, + 339, + 472, + 445 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Human Mesh Recovery. We use SMPL [66] model to represent the human mesh and regress its parameters. The SMPL model consists of pose parameters $\\theta \\in \\mathbb{R}^{72}$ and shape parameters $\\beta \\in \\mathbb{R}^{10}$ , and calculates the 3D mesh as $\\mathcal{M}(\\theta, \\beta) \\in \\mathbb{R}^{6890 \\times 3}$ . To regress the pose parameters for each frame, we feed the motion embeddings $\\mathbf{E}$ to an MLP with one hidden layer and get $\\hat{\\pmb{\\theta}} \\in \\mathbb{R}^{T \\times 72}$ . To estimate shape parameters, considering that the human shape over a video sequence is supposed to be consistent, we first perform an average pooling of $\\mathbf{E}$ over the temporal dimension and then feed it into another MLP to regress a single $\\hat{\\beta}$ and then expand it to the entire sequence as $\\hat{\\beta} \\in \\mathbb{R}^{T \\times 10}$ . The shape MLP has the same architecture as the pose regression one, and they are initialized with the mean shape and pose, respectively, as in [42]. The overall loss is computed as", + "bbox": [ + 75, + 472, + 472, + 700 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\lambda_ {\\mathrm {3 D}} ^ {\\mathrm {m}} \\mathcal {L} _ {\\mathrm {3 D}} ^ {\\mathrm {m}} + \\lambda_ {\\theta} \\mathcal {L} _ {\\theta} + \\lambda_ {\\beta} \\mathcal {L} _ {\\beta} + \\lambda_ {\\mathrm {n}} \\mathcal {L} _ {\\text {n o r m}} + \\lambda_ {\\mathrm {O}} ^ {\\mathrm {m}} \\mathcal {L} _ {\\mathrm {O}} ^ {\\mathrm {m}}, \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 112, + 713, + 470, + 729 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where each term is calculated as", + "bbox": [ + 76, + 746, + 294, + 760 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {3 D}} ^ {\\mathrm {m}} = \\left\\| \\hat {\\mathbf {X}} ^ {\\mathrm {m}} - \\mathbf {X} ^ {\\mathrm {m}} \\right\\| _ {1}, \\quad \\mathcal {L} _ {\\theta} = \\left\\| \\hat {\\boldsymbol {\\theta}} - \\boldsymbol {\\theta} \\right\\| _ {1}, \\quad \\mathcal {L} _ {\\beta} = \\left\\| \\hat {\\boldsymbol {\\beta}} - \\boldsymbol {\\beta} \\right\\| _ {1},\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 773, + 460, + 791 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {n o r m}} = \\| \\hat {\\boldsymbol {\\theta}} \\| _ {2} + \\| \\hat {\\boldsymbol {\\beta}} \\| _ {2}, \\quad \\mathcal {L} _ {\\mathrm {O}} ^ {\\mathrm {m}} = \\| \\hat {\\mathbf {O}} ^ {\\mathrm {m}} - \\mathbf {O} ^ {\\mathrm {m}} \\| _ {2}. \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 792, + 470, + 821 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Note that each 3D pose in motion $\\mathbf{X}^{\\mathrm{m}}$ at frame $t$ is regressed from mesh vertices by $\\mathbf{X}_t^{\\mathrm{m}} = \\mathbf{J}\\mathcal{M}(\\pmb {\\theta}_t,\\pmb {\\beta}_t)$ , where $\\mathbf{J}\\in \\mathbb{R}^{J\\times 6890}$ is a pre-defined matrix [9]. $\\mathbf{O}^{\\mathrm{m}} = \\mathbf{X}_{t + 1}^{\\mathrm{m}} - \\mathbf{X}_{t}^{\\mathrm{m}}$ , $\\hat{\\mathbf{O}}^{\\mathrm{m}} = \\hat{\\mathbf{X}}_{t + 1}^{\\mathrm{m}} - \\hat{\\mathbf{X}}_t^{\\mathrm{m}}$ . $\\lambda_{3\\mathrm{D}}^{\\mathrm{m}},\\lambda_{\\theta},\\lambda_{\\beta},\\lambda_{\\mathrm{n}}$ and $\\lambda_0^{\\mathrm{m}}$ are constant coefficients to balance the training loss.", + "bbox": [ + 75, + 821, + 472, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 90, + 633, + 107 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Implementation", + "text_level": 1, + "bbox": [ + 500, + 114, + 660, + 131 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We implement the proposed motion encoder DSTformer with depth $N = 5$ , number of heads $h = 8$ , feature size $C_{\\mathrm{f}} = 512$ , embedding size $C_{\\mathrm{e}} = 512$ . For pretraining, we use sequence length $T = 243$ . The pretrained model could handle different input lengths thanks to the Transformer-based backbone. During finetuning, we set the backbone learning rate to be $0.1 \\times$ of the new layer learning rate. We introduce the experiment datasets in the following sections respectively. Please refer to the appendix for more experimental details.", + "bbox": [ + 496, + 138, + 893, + 289 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Pretraining", + "text_level": 1, + "bbox": [ + 500, + 300, + 625, + 316 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We collect diverse and realistic 3D human motion from two datasets, Human3.6M [36] and AMASS [71]. Human3.6M [36] is a commonly used indoor dataset for 3D human pose estimation which contains 3.6 million video frames of professional actors performing daily actions. Following previous works [73, 83], we use subjects 1, 5, 6, 7, 8 for training, and subjects 9, 11 for testing. AMASS [71] integrates most existing marker-based Mocap datasets [1,2,4,10,14,17,32,35,48,65,67,72,79,90,103,104] and parameterizes them with a common representation. We do not use the images or 2D detection results of the two datasets during pretraining as Mocap datasets usually do not provide raw videos. Instead, we use orthographic projection to get the uncorrupted 2D skeletons. We further incorporate two in-the-wild RGB video datasets PoseTrack [3] (annotated) and InstaVariety [39] (unannotated) for higher motion diversity. We align the body keypoint definitions with Human3.6M and calibrate the camera coordinates to pixel coordinates following [26]. We randomly zero out $15\\%$ joints, and sample noises from a mixture of Gaussian and uniform distributions [16]. We first train on 3D data only for 30 epochs, then train on both 3D data and 2D data for 60 epochs, following the curriculum learning practices [8, 111].", + "bbox": [ + 496, + 323, + 893, + 672 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. 3D Pose Estimation", + "text_level": 1, + "bbox": [ + 500, + 680, + 687, + 695 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We evaluate the 3D pose estimation performance on Human3.6M [36] and report the mean per joint position error (MPJPE) in millimeters, which measures the average distance between the predicted joint positions and the GT after aligning the root joint. We also compute the mean per-joint velocity error (MPJVE) to evaluate the temporal smoothness following previous works [126, 127]. We use the Stacked Hourglass (SH) networks [81] to extract the 2D skeletons from videos, and finetune the entire network on Human3.6M [36] training set. In addition, we train a separate model of the same architecture, but with random initialization rather than pretrained weights. As shown in Table 1 (top), the model trained from scratch outperforms", + "bbox": [ + 496, + 704, + 893, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "15089", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/04e0a27d94520649ec2e26314db2bd89480c373df24c9d50046184337ed66a79.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodTDire.Disc.EatGreetPhonePhotoPosePurch.SitSitDSmokeWaitWalkDWalkWalkTAvg
Martinez et al. [73] ICCV'17151.856.258.159.069.578.455.258.174.094.662.359.165.149.552.462.9
Pavlakos et al. [82] CVPR'18148.554.454.452.059.465.349.952.965.871.156.652.960.944.747.856.2
LCN [27] ICCV'19146.852.344.750.452.968.949.646.460.278.951.250.054.840.443.352.7
Xu et al. [114] CVPR'21145.249.947.550.954.966.148.546.359.771.551.448.653.939.944.151.9
VideoPose3D [83] CVPR'1924345.246.743.345.648.155.144.644.357.365.847.144.049.032.833.946.8
Cai et al. [12] ICCV'19744.647.445.648.850.859.047.243.957.961.949.746.651.337.139.448.8
Yeh et al. [122] NeurIPS'1924344.846.143.346.449.055.244.644.058.362.747.143.948.632.733.346.7
Liu et al. [63] CVPR'2024341.844.841.144.947.454.143.442.256.263.645.343.545.331.332.245.1
* Cheng et al. [21] AAAI'2012836.238.142.735.938.245.736.842.045.951.341.841.543.833.128.640.1
* UGCN [109] ECCV'209638.241.045.939.741.451.441.641.452.057.441.844.441.633.130.042.6
† PoseFormer [127] ICCV'218141.544.839.842.546.551.642.142.053.360.745.543.346.131.832.244.3
* Wehrbein et al. [112] ICCV'2120038.542.539.941.746.551.639.940.849.556.845.346.446.837.840.444.3
† MHFormer [52] CVPR'2235139.243.140.140.944.951.240.641.353.560.343.741.143.829.830.643.0
*† MixSTE [126] CVPR'2224336.739.036.539.440.244.939.836.947.954.839.637.839.329.730.639.8
† P-STMO [87] ECCV'2224338.442.139.840.245.248.940.438.353.857.343.941.642.229.329.342.1
† Ours (scratch)24336.338.738.633.642.150.136.235.750.156.641.337.437.725.626.539.2
† Ours (finetune)24336.137.535.832.140.346.336.135.346.953.939.536.335.825.125.337.5
MethodTDire.Disc.EatGreetPhonePhotoPosePurch.SitSitDSmokeWaitWalkDWalkWalkTAvg
Martinez et al. [73] ICCV'17137.744.440.342.148.254.944.442.154.658.045.146.447.636.440.445.5
LCN [27] ICCV'19136.338.829.737.834.642.539.832.536.239.534.438.438.231.334.236.3
Xu et al. [114] CVPR'21135.838.131.035.335.843.237.331.738.445.535.436.736.827.930.735.8
UGCN [109] ECCV'209623.025.722.822.624.130.624.924.531.135.025.624.325.119.818.425.6
† PoseFormer [127] ICCV'218130.033.629.931.030.233.334.831.437.838.631.731.529.023.323.131.3
† MHFormer [52] CVPR'2235127.732.129.128.930.033.933.031.237.039.330.031.029.422.223.030.5
† MixSTE [126] CVPR'2224321.622.020.421.020.824.324.721.926.924.921.221.520.814.715.621.6
† P-STMO [87] ECCV'2224328.530.128.627.929.833.231.327.836.037.429.729.528.121.021.029.3
† Ours (scratch)24316.719.917.116.517.418.819.320.524.022.118.616.816.710.811.517.8
† Ours (finetune)24315.917.316.914.616.818.618.618.422.021.817.316.916.110.511.416.9
MethodTDire.Disc.EatGreetPhonePhotoPosePurch.SitSitDSmokeWaitWalkDWalkWalkTAvg
VideoPose3D [83] CVPR'192433.03.12.23.42.32.72.73.12.12.92.32.43.73.12.82.8
† PoseFormer [127] ICCV'21813.23.42.63.62.63.02.93.22.63.32.72.73.83.22.93.1
*† MixSTE [126] CVPR'222432.52.71.92.81.92.22.32.61.62.21.92.03.12.62.22.3
† Ours (scratch)2431.82.11.52.01.51.91.82.11.21.81.51.42.62.01.71.8
† Ours (finetune)2431.71.91.41.91.41.71.71.91.11.61.41.32.41.91.61.7
", + "bbox": [ + 127, + 88, + 841, + 483 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. Quantitative comparison of 3D human pose estimation on Human3.6M. (Top) MPJPE (mm) using detected 2D pose sequences. (Middle) MPJPE (mm) using GT 2D pose sequences. (Bottom) MPJVE (mm) using detected 2D pose sequences. $T$ denotes the clip length used by the method. We select the best results reported by each work. \\* denotes using HRNet [96] for 2D detection. $\\dagger$ denotes implemented with a spatio-temporal Transformer design. The best and second-best results are highlighted in bold and underlined formats.", + "bbox": [ + 75, + 488, + 893, + 544 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "previous methods including other Transformer-based designs with spatio-temporal modeling. It shows the effectiveness of the proposed DSTformer in terms of learning 3D geometric structures and temporal dynamics. To further evaluate the upper bound of the models' capability, we compare the performance when using 2D GT pose sequences as input, which gets rid of the influence of different 2D detectors. As shown in Table 1 (middle), our models significantly outperform all the previous approaches. Table 1 (bottom) shows that both of our models also surpass previous works in terms of MPJVE, implying better temporal coherence. We attribute the performance advantage of our scratch model to the proposed DSTformer design. We include more comparisons and analysis to demonstrate the advantage of DSTformer with regard to other spatio-temporal architectures in Section 4.6 and supplementary materials. Additionally, our method achieves lower errors with the proposed pretraining stage.", + "bbox": [ + 75, + 569, + 472, + 828 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Skeleton-based Action Recognition", + "text_level": 1, + "bbox": [ + 76, + 844, + 382, + 861 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We further explore the possibility to learn action semantics with the pretrained human motion representations. We", + "bbox": [ + 76, + 869, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "use the human action dataset NTU-RGB+D [86] which contains 57K videos of 60 action classes, and we follow the data splits Cross-subject (X-Sub) and Cross-view (X-View). The dataset has an extended version, NTU-RGB+D-120 [60], which contains 114K videos of 120 action classes. We follow the suggested One-shot action recognition protocol on NTU-RGB+D-120. For both datasets, we use HRNet [96] to extract 2D skeletons following [30]. Similarly, we train a scratch model with random initialization for comparison. As Table 2 (left) shows, our methods are comparable or superior to the state-of-the-art approaches. Notably, the pretraining stage accounts for a large performance gain.", + "bbox": [ + 496, + 569, + 893, + 752 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Additionally, we delve into the one-shot setting which holds significant practical importance. Real-world applications often require fine-grained action recognition in specific domains such as education, sports, and healthcare. Unfortunately, the action classes in these scenarios are not typically defined in public datasets. As a result, only limited annotations for these novel action classes are available, making accurate recognition a challenging task. As proposed in [60], we report the results on the evaluation set of 20 novel classes", + "bbox": [ + 496, + 763, + 895, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "15090", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/51ad21c29c82282f9640cb41cd17642f9342b7ed66d8b5df8fd0782945ae5003.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodX-SubX-View
ST-GCN [116] AAAI'1881.588.3
2s-AGCN [89] CVPR'1988.595.1
MS-G3D [64] CVPR'2091.596.2
Shift-GCN [20] CVPR'2090.796.5
CrosSCLR [58] CVPR'2186.292.5
MCC (finetune) [94] ICCV'2189.796.3
SCC (finetune) [118] ICCV'2188.094.9
UNIK (finetune) [117] BMVC'2186.894.4
CTR-GCN [19] ICCV'2192.496.8
PoseConv3D [30] CVPR'2293.195.7
Ours (scratch)87.794.1
Ours (finetune)93.097.2
", + "bbox": [ + 150, + 88, + 408, + 257 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/22bb6c1cc505a5d1d047a82336c22034440d6e4336de55740e7042697ccd72c0.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodAccuracy
ST-LSTM + AvgPool [61]42.9
ST-LSTM + FC [62]42.1
ST-LSTM + Attention [62]41.0
APSR [60]45.3
TCN OneShot [85]46.5
SL-DML [76]50.9
Skeleton-DML [75]54.2
Ours (scratch)61.0
Ours (finetune)67.4
", + "bbox": [ + 547, + 88, + 805, + 218 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/c7f26adf880b26d3bb38a7c8085b86cc5a78bb7a7f083d1ba306537a21147e1b.jpg", + "table_caption": [ + "Table 2. Quantitative comparison of skeleton-based action recognition accuracy. (Left) Cross-subject and cross-view recognition accuracy on NTU-RGB+D. All the methods are evaluated using only the \"joint\" modality with 1-clip sampling for the fairness of comparison. (Right) One-shot recognition accuracy on NTU-RGB+D-120. All results are top-1 accuracy (\\%)." + ], + "table_footnote": [], + "table_body": "
MethodInputTHuman3.6M3DPW
MPVE↓MPJPE↓PA-MPJPE↓MPVE↓MPJPE↓PA-MPJPE↓
HMR [38] CVPR'18image1-88.056.8-130.081.3
† SPIN [44] ICCV'19image182.359.439.3129.1100.959.1
Pose2Mesh [24] ECCV'202D pose185.364.948.7109.391.460.1
I2L-MeshNet [78] ECCV'20image1-55.741.7110.193.258.6
† HybrIK [50] CVPR'21image158.147.430.182.471.341.9
METRO [54] CVPR'21image1-54.036.788.277.147.9
Mesh Graphormer [55] ICCV'21image1-51.234.587.774.745.6
PARE [43] ICCV'21image1---88.674.546.5
ROMP [98] ICCV'21image1---108.391.354.9
PyMAF [125] ICCV'21image1-57.740.5110.192.858.9
ProHMR [46] ICCV'21image1--41.2--59.8
OCHMR [40] CVPR'22image1---107.189.758.3
3DCrowdNet [25] CVPR'22image1---98.381.751.5
CLIFF [53] ECCV'22image1-47.132.781.269.043.0
FastMETRO [22] ECCV'22image1-52.233.784.173.544.6
VisDB [121] ECCV'22image1-51.034.585.573.544.9
TemporalContext [5] CVPR'19video32-77.854.3--72.2
HMMR [39] CVPR'19video20--56.9139.3116.572.6
DSD-SATN [99] ICCV'19video9-59.142.4--69.5
VIBE [42] CVPR'20video16-65.641.499.182.951.9
TCMR [23] CVPR'21video16-62.341.1102.986.552.7
† MAED [107] ICCV'21video1684.160.438.393.379.045.7
MPS-Net [113] CVPR'22video16-69.447.499.784.352.1
* PoseBERT [7] TPAMI'22 (+SPIN [44])video16-----57.3 ↓ 2.3
* SmoothNet [123] ECCV'22 (+SPIN [44])video32-67.5 ↓ 1.046.3 ↓ 0.2-86.7 ↓ 0.952.7 ↓ 0.6
Ours (scratch)2D motion1675.762.841.099.185.550.2
Ours (finetune)2D motion1665.553.834.988.176.947.2
Ours (finetune) + SPIN [44]video1663.7 ↓ 18.652.2 ↓ 7.235.7 ↓ 3.692.8 ↓ 36.379.6 ↓ 21.348.2 ↓ 10.9
Ours (finetune) + MAED [107]video1666.8 ↓ 17.354.8 ↓ 5.636.4 ↓ 1.984.4 ↓ 8.972.3 ↓ 6.742.3 ↓ 3.4
Ours (finetune) + HybrIK [50]video1652.6 ↓ 5.543.1 ↓ 4.327.8 ↓ 2.379.4 ↓ 3.068.8 ↓ 2.540.6 ↓ 1.3
", + "bbox": [ + 161, + 320, + 810, + 662 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. Quantitative comparison of human mesh recovery on Human3.6M and 3DPW datasets. $T$ denotes the clip length used by the method. $\\dagger$ denotes the results obtained with official model weights. The rest are all officially reported results. The gains in \\* correspond to different re-implemented SPIN [44] results.", + "bbox": [ + 75, + 672, + 892, + 715 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "using only 1 labeled video for each class. The auxiliary set contains the other 100 classes, and all samples of these classes can be used. We train the model on the auxiliary set using the supervised contrastive learning technique [41]. For a batch of auxiliary data, samples of the same class are pulled together, while samples of different classes are pushed away in the action embedding space. During the evaluation, we calculate the cosine distance between the test examples and the exemplars, and use 1-nearest neighbor to determine the class. Table 2 (right) illustrates that the proposed models outperform state-of-the-art by a considerable margin. Moreover,", + "bbox": [ + 75, + 724, + 472, + 892 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "it is noteworthy that our pretrained model achieves optimal performance with only 1-2 epochs of fine-tuning. Our results indicate that the pretraining stage is effective in learning a robust motion representation that generalizes well to novel downstream tasks, even with limited data annotations.", + "bbox": [ + 496, + 724, + 893, + 801 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5. Human Mesh Recovery", + "text_level": 1, + "bbox": [ + 500, + 815, + 718, + 832 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We conduct experiments on Human3.6M [36] and 3DPW [106] datasets and additionally add COCO [57] dataset during training following [42, 54, 107]. We keep the same training and test split for both datasets as in [73] (Section 4.2)", + "bbox": [ + 498, + 839, + 895, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "15091", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/99926cb7f99b2aa12f2d0f82f5a5fb3dc8f26e752f2621502e2ff4ba38572c6c.jpg", + "image_caption": [ + "Figure 3. Learning curves of finetuning and training from scratch." + ], + "image_footnote": [], + "bbox": [ + 86, + 89, + 334, + 229 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4f844dffe3f2829686e24b451db2b92823e16ae4c8a34955ecae190f275bd10e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 359, + 90, + 604, + 229 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8e20cd4f690c14c7f4837e5abfb033bea35a2dbb051291305ea0456e132db5a0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 632, + 90, + 880, + 229 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/380234c85a781908cbfd4dccbcab6cb6d79339e62dd68f54f45cf8aac14867bf.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Backbone (frozen)MPJPE ↓ (3D pose)MPVE ↓ (mesh)Accuracy ↑ (action x-view)Accuracy↑ (action 1-shot)
Random404.4mm114.4mm47.6%46.8%
Pretrained40.3mm72.1mm87.3%60.7%
", + "bbox": [ + 81, + 272, + 470, + 333 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "and [42, 54, 107], respectively. Following the common practice [38, 42, 45, 107], we report MPJPE (mm) and PA-MPJPE (mm) of 14 joints obtained by $\\mathbf{J}\\mathcal{M}(\\theta ,\\beta)$ . PA-MPJPE calculates MPJPE after aligning with GT in translation, rotation, and scale. We further report the mean per vertex error (MPVE) (mm) of the mesh $\\mathcal{M}(\\theta ,\\beta)$ , which measures the average distance between the estimated and GT vertices after aligning the root joint. Note that most previous works [23, 38, 42, 44, 50, 54, 68, 107] use more datasets other than COCO [57] during training, such as LSP [37], MPI-INF-3DHP [74], etc., while we do not. Table 3 demonstrates that our finetuned model delivers competitive results on both Human3.6M and 3DPW datasets, surpassing all the state-of-the-art video-based methods, including MAED [107], especially on the MPVE error. Nonetheless, we note that estimating full-body mesh from sparse 2D keypoints alone [9, 24] is an ill-posed problem because it lacks human shape information. In light of this, we propose a hybrid approach that leverages the strengths of both our framework (coherent motion) and RGB-based methods (accurate shape). We introduce a refiner module that can be easily integrated with existing image/video-based methods, similar to [7, 123]. Specifically, our refiner module is an MLP that takes the combination of our pretrained motion representations and an initial prediction, regressing a residual in joint rotations. Our approach effectively improves the state-of-the-art methods [44, 50, 107] and achieves the lowest error to date.", + "bbox": [ + 76, + 369, + 472, + 777 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.6. Ablation Studies", + "text_level": 1, + "bbox": [ + 76, + 786, + 240, + 801 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Finetune vs. Scratch. We compare the training progress of finetuning the pretrained model and training from scratch. As Figure 3 shows, models initialized with pretrained weights demonstrate superior performance and faster convergence on all three tasks. This observation suggests that the pretrained model learns transferable knowledge about hu", + "bbox": [ + 75, + 809, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/80535bfd0969205d007208be3411ab8df1f0aae9aab1b376274e9f390f2f7698.jpg", + "table_caption": [ + "Table 4. Comparison of partial finetuning." + ], + "table_footnote": [], + "table_body": "
PretrainNoiseMask2DMPJPE↓(3D pose)MPVE↓(mesh)Accuracy↑(action x-sub)
----39.2mm75.7mm87.7%
✓---38.8mm70.6mm89.4%
✓✓--38.1mm68.4mm90.7%
✓✓✓-37.4mm67.8mm91.9%
✓✓✓✓37.5mm65.5mm93.0%
", + "bbox": [ + 504, + 273, + 888, + 373 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Comparison of pretraining strategies.", + "bbox": [ + 549, + 382, + 841, + 397 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "man motion, facilitating the learning of multiple downstream tasks.", + "bbox": [ + 498, + 421, + 890, + 450 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Partial Finetuning. In addition to end-to-end finetuning, we freeze the motion encoder backbone and only train the regression head for each downstream task. To verify the effectiveness of the pretrained motion representations, we compared the pretrained motion encoder with a randomly initialized motion encoder. We report results of 3D pose and mesh on Human3.6M, action on NTU-RGB+D and NTU-RGB+D-120 (same for the tables below). It can be seen in Table 4 that based on the frozen pretrained motion representations, our method still achieves competitive performance on multiple downstream tasks and shows a large improvement compared to the baseline. Pretraining and partial finetuning make it possible for all the downstream tasks to share the same backbone, significantly reducing computation overhead for applications requiring multi-task inference.", + "bbox": [ + 496, + 470, + 893, + 698 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Pretraining Strategies. We evaluate how different pretraining strategies influence the performance of downstream tasks. Starting from the scratch baseline, we apply the proposed strategies one by one. As shown in Table 5, a vanilla 2D-to-3D pretraining stage brings benefits to all the downstream tasks. Introducing corruptions additionally improves the learned motion embeddings. Unified pretraining with in-the-wild videos (w. 2D) enjoys higher motion diversity, which further helps several downstream tasks.", + "bbox": [ + 496, + 715, + 895, + 852 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Pretraining with Different Backbones. We further study the universality of the proposed pretraining approach. We", + "bbox": [ + 498, + 869, + 893, + 902 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "15092", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/26943ad51314ddbfd4a02aad6afacf66d9208cd2af7d11f5278e95d97d8a7be1.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
SettingMPJPE ↓ (3D pose)MPVE ↓ (mesh)Accuracy ↑ (action x-view)Accuracy↑ (action 1-shot)
TCN (scratch)50.1mm92.6mm91.5%52.4%
TCN (finetune)47.9mm86.3mm92.8%59.9%
PoseFormer (scratch)44.8mm85.9mm94.2%57.4%
PoseFormer (finetune)41.5mm80.5mm95.9%60.7%
", + "bbox": [ + 81, + 88, + 467, + 164 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/c5f4324e7dd89ead149bb444ae0d71f41e2d9ce3f27e667f4cd027a4200c14a9.jpg", + "table_caption": [ + "Table 6. Comparison of different backbones." + ], + "table_footnote": [], + "table_body": "
Arch.(a)(b)(c)(d)(e)(f)
DesignS-TT-SS + TST-MHSAS-T + T-S(Average)S-T + T-S(Adaptive)
MPJPE ↓40.58±0.3141.05±0.2441.76±0.2241.54±0.3539.87±0.3239.25±0.27
", + "bbox": [ + 81, + 200, + 465, + 252 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Table 7. Comparison of model architecture variants. All the methods are trained on Human3.6M from scratch over 5 runs and measured by MPJPE (mm) with mean and standard deviation.", + "bbox": [ + 76, + 263, + 468, + 305 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "replace the motion encoder backbone with two variants: TCN [83] and PoseFormer [127]. The models are slightly modified to a seq2seq version, while all the configurations for pretraining and finetuning are simply followed. Table 6 shows that the proposed approach consistently benefits different backbone models on different tasks.", + "bbox": [ + 76, + 329, + 468, + 419 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Model Architecture. Finally, we study the design choices of DSTformer. From (a) to (f) in Table 7, we compare different structure designs of the basic Transformer module. (a) and (b) are single-stream versions with different orders. (a) is conceptually similar to PoseFormer [127], MH-Former [52], and MixSTE [126]. (c) limits each stream to either temporal or spatial modeling before fusion and is similar to MAED [107]. (d) directly connects S-MHSA and T-MHSA without the MLP in between and is similar to the MSA-T variant in MAED [107]. (e) replaces the adaptive fusion with average pooling on two streams. (f) is the proposed DSTformer design. The result statistically confirms our design principles that both streams should be capable and meanwhile complementary, as introduced in Section 3.2. In addition, we find out that pairing each self-attention block with an MLP is crucial, as it could project the learned feature interactions and bring nonlinearity. In general, we design the model architecture for the 3D pose estimation task and apply it to all other tasks without additional adjustment.", + "bbox": [ + 76, + 438, + 468, + 726 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 739, + 194, + 753 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this work, we provide a unified perspective to tackling various human-centric video tasks. We develop a pretraining approach to learn human motion representations from large-scale and heterogeneous data sources. We also propose DSTformer as a universal human motion encoder. Experimental results on multiple benchmarks demonstrate the versatility of the learned motion representations. Future work could explore fusing the learned motion representations with generic video architectures as a human-centric semantic fea", + "bbox": [ + 76, + 763, + 468, + 900 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "ture and applying it to more tasks (e.g., action assessment, segmentation).", + "bbox": [ + 500, + 90, + 890, + 121 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement This work was partially supported by MOST-2022ZD0114900. We would like to thank Hai Ci and Jiefeng Li for their exceptional support.", + "bbox": [ + 500, + 138, + 890, + 186 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "15093", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Advanced Computing Center for the Arts and Design. 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Mocanet: Motion retargeting in-the-wild via canonicalization networks. In AAAI, 2022." + ], + "bbox": [ + 78, + 90, + 470, + 229 + ], + "page_idx": 14 + }, + { + "type": "page_number", + "text": "15099", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 14 + } +] \ No newline at end of file diff --git a/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/57fc0f5c-171f-41a1-94fe-f16ec1d8935d_model.json b/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/57fc0f5c-171f-41a1-94fe-f16ec1d8935d_model.json new file mode 100644 index 0000000000000000000000000000000000000000..302c74e7b0a1c4eee76ba6893e17356c3e1ce9b6 --- /dev/null +++ b/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/57fc0f5c-171f-41a1-94fe-f16ec1d8935d_model.json @@ -0,0 +1,3101 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.131, + 0.895, + 0.155 + ], + "angle": 0, + "content": "MotionBERT: A Unified Perspective on Learning Human Motion Representations" + }, + { + "type": "text", + "bbox": [ + 0.109, + 0.187, + 0.866, + 0.209 + ], + "angle": 0, + "content": "Wentao Zhu\\(^{1}\\) Xiaoxuan Ma\\(^{1}\\) Zhaoyang Liu\\(^{2}\\) Libin Liu\\(^{1}\\) Wayne Wu\\(^{2}\\) Yizhou Wang\\(^{1\\dagger}\\)" + }, + { + "type": "text", + "bbox": [ + 0.284, + 0.218, + 0.686, + 0.239 + ], + "angle": 0, + "content": "\\(^{1}\\) Peking University \\(^{2}\\) Shanghai AI Laboratory" + }, + { + "type": "text", + "bbox": [ + 0.284, + 0.251, + 0.686, + 0.264 + ], + "angle": 0, + "content": "{wtzhu,maxiaoxuan,libin.liu,yizhou.wang}@pku.edu.cn" + }, + { + "type": "text", + "bbox": [ + 0.359, + 0.272, + 0.613, + 0.285 + ], + "angle": 0, + "content": "{zyliumy,wuwenyan0503}@gmail.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.321, + 0.314, + 0.337 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.354, + 0.474, + 0.671 + ], + "angle": 0, + "content": "We present a unified perspective on tackling various human-centric video tasks by learning human motion representations from large-scale and heterogeneous data resources. Specifically, we propose a pretraining stage in which a motion encoder is trained to recover the underlying 3D motion from noisy partial 2D observations. The motion representations acquired in this way incorporate geometric, kinematic, and physical knowledge about human motion, which can be easily transferred to multiple downstream tasks. We implement the motion encoder with a Dual-stream Spatio-temporal Transformer (DSTformer) neural network. It could capture long-range spatio-temporal relationships among the skeletal joints comprehensively and adaptively, exemplified by the lowest 3D pose estimation error so far when trained from scratch. Furthermore, our proposed framework achieves state-of-the-art performance on all three downstream tasks by simply finetuning the pretrained motion encoder with a simple regression head (1-2 layers), which demonstrates the versatility of the learned motion representations. Code and models are available at https://motionbert.github.io/" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.703, + 0.21, + 0.719 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.729, + 0.472, + 0.851 + ], + "angle": 0, + "content": "Perceiving and understanding human activities have long been a core pursuit of machine intelligence. To this end, researchers define various tasks to estimate human-centric semantic labels from videos, e.g. skeleton keypoints [13, 33], action classes [60, 116], and surface meshes [42, 66]. While significant progress has been made in each of these tasks, they tend to be modeled in isolation, rather than as interconnected problems. For example, Spatial Temporal Graph Con" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.32, + 0.887, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.459, + 0.896, + 0.528 + ], + "angle": 0, + "content": "Figure 1. Framework overview. We utilize a motion encoder to learn human motion representations via recovering 3D human motion from corrupted 2D skeleton sequences. To adapt to different downstream tasks, we finetune the pretrained motion representations with a linear layer or a simple MLP." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.895, + 0.704 + ], + "angle": 0, + "content": "volitional Networks (ST-GCN) have been applied to modeling spatio-temporal relationship of human joints in both 3D pose estimation [12, 109] and action recognition [89, 116], but their connections have not been fully explored. Intuitively, these models should all have learned to identify typical human motion patterns, despite being designed for different problems. Nonetheless, current methods fail to mine and utilize such commonalities across the tasks. Ideally, we could develop a unified human-centric video representation that can be shared across all relevant tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.896, + 0.903 + ], + "angle": 0, + "content": "One significant challenge to developing such a representation is the heterogeneity of available data resources. Motion capture (Mocap) systems [36, 71] provide high-fidelity 3D motion data obtained with markers and sensors, but the appearances of captured videos are usually constrained to simple indoor scenes. Action recognition datasets provide annotations of the action semantics, but they either contain no human pose labels [15, 88] or feature limited motion of daily activities [59, 60, 86]. In contrast, in-the-wild human videos offer a vast and diverse range of appearance and motion. However, obtaining precise 2D pose annotations requires considerable effort [3], and acquiring ground-truth (GT) 3D joint locations is almost impossible. Consequently," + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.863, + 0.472, + 0.902 + ], + "angle": 0, + "content": "† Yizhou Wang is with Center on Frontiers of Computing Studies, School of Computer Science, Peking University and Institute for Artificial Intelligence, Peking University." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15085" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.137 + ], + "angle": 0, + "content": "most existing studies focus on a specific task using a single type of human motion data, and they are not able to enjoy the advantages of other data resources." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.138, + 0.473, + 0.529 + ], + "angle": 0, + "content": "In this work, we provide a new perspective on learning human motion representations. The key idea is that we can learn a versatile human motion representation from heterogeneous data resources in a unified manner, and utilize the representation to handle different downstream tasks in a unified way. We present a two-stage framework, consisting of pretraining and finetuning, as depicted in Figure 1. In the pretraining stage, we extract 2D skeleton sequences from diverse motion data sources and corrupt them with random masks and noises. Subsequently, we train the motion encoder to recover the 3D motion from the corrupted 2D skeletons. This challenging pretext task intrinsically requires the motion encoder to i) infer the underlying 3D human structures from its temporal movements; ii) recover the erroneous and missing observations. In this way, the motion encoder implicitly captures human motion commonsense such as joint linkages, anatomical constraints, and temporal dynamics. In practice, we propose Dual-stream Spatio-temporal Transformer (DSTformer) as the motion encoder to capture the long-range relationship among skeleton keypoints. We suppose that the motion representations learned from large-scale and diversified data resources could be shared across different downstream tasks and benefit their performance. Therefore, for each downstream task, we adapt the pretrained motion representations using task-specific training data and supervisory signals with a simple regression head." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.53, + 0.473, + 0.756 + ], + "angle": 0, + "content": "In summary, the contributions of this work are three-fold: 1) We provide a new perspective on solving various human-centric video tasks through a shared framework of learning human motion representations. 2) We propose a pretraining method to leverage the large-scale yet heterogeneous human motion resources and learn generalizable human motion representations. Our approach could take advantage of the precision of 3D mocap data and the diversity of in-the-wild RGB videos at the same time. 3) We design a dual-stream Transformer network with cascaded spatio-temporal self-attention blocks that could serve as a general backbone for human motion modeling. The experiments demonstrate that the above designs enable a versatile human motion representation that can be transferred to multiple downstream tasks, outperforming the task-specific state-of-the-art methods." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.77, + 0.22, + 0.785 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.473, + 0.901 + ], + "angle": 0, + "content": "Learning Human Motion Representations. Early works formulate human motion with Hidden Markov Models [49, 101] and graphical models [47, 92]. Kanazawa et al. [39] design a temporal encoder and a hallucinator to learn representations of 3D human dynamics. Zhang et al. [124] predict future 3D dynamics in a self-supervised manner. Sun et al. [95] further incorporate action labels with an ac" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.288 + ], + "angle": 0, + "content": "tion memory bank. From the action recognition perspective, a variety of pretext tasks are designed to learn motion representations in a self-supervised manner, including future prediction [93], jigsaw puzzle [56], skeleton-contrastive [100], speed change [94], cross-view consistency [58], and contrast-reconstruction [110]. Similar techniques are also explored in tasks like motion assessment [31, 80] and motion retargeting [119, 130]. These methods leverage homogeneous motion data, design corresponding pretext tasks, and apply them to a specific downstream task. In this work, we propose a unified pretrain-finetune framework to incorporate heterogeneous data resources and demonstrate its versatility in various downstream tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.311, + 0.897, + 0.538 + ], + "angle": 0, + "content": "3D Human Pose Estimation. Recovering 3D human poses from monocular RGB videos is a classical problem, and the methods can be categorized into two categories. The first is to estimate 3D poses with CNN directly from images [77, 97, 128]. However, one limitation of these approaches is that there is a trade-off between 3D pose precision and appearance diversity due to current data collection techniques. The second category is to extract the 2D pose first, then lift the estimated 2D pose to 3D with a separate neural network. The lifting can be achieved via Fully Connected Network [28, 73], Temporal Convolutional Network (TCN) [21, 83], GCN [12, 27, 109], and Transformer [52, 87, 126, 127]. Our framework is built upon the second category as we use the proposed DSTformer to accomplish 2D-to-3D lifting." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.561, + 0.897, + 0.818 + ], + "angle": 0, + "content": "Skeleton-based Action Recognition. The pioneering works [69, 108, 120] point out the inherent connection between action recognition and human pose estimation. Towards modeling the spatio-temporal relationship among human joints, previous studies mainly employ LSTM [91, 129] and GCN [20, 51, 64, 89, 116]. Most recently, PoseC-conv3D [30] proposes to apply 3D-CNN on the stacked 2D joint heatmaps and achieves improved results. In addition to the fully-supervised action recognition task, NTU-RGB+D-120 [60] brings attention to the challenging one-shot action recognition problem. To this end, SL-DML [76] applies deep metric learning to multi-modal signals. Sabater et al. [85] explores one-shot recognition in therapy scenarios with TCN. We demonstrate that the pretrained motion representations could generalize well to action recognition tasks, and the pretrain-finetune framework is a suitable solution for the one-shot challenges." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Human Mesh Recovery. Based on the parametric human models such as SMPL [66], many research works [38, 70, 78, 115, 125] focus on regressing the human mesh from a single image. SPIN [44] additionally incorporates fitting the body" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "15086" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.164, + 0.09, + 0.812, + 0.231 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.237, + 0.895, + 0.294 + ], + "angle": 0, + "content": "Figure 2. Model architecture. We propose the Dual-stream Spatio-temporal Transformer (DSTformer) as a general backbone for human motion modeling. DSTformer consists of \\(N\\) dual-stream-fusion modules. Each module contains two branches of spatial or temporal MHSA and MLP. The Spatial MHSA models the connection among different joints within a timestep, while the Temporal MHSA models the movement of one joint." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.317, + 0.475, + 0.56 + ], + "angle": 0, + "content": "model to 2D joints in the training loop. Despite their promising per-frame results, these methods yield jittery and unstable results [42, 123] when applied to videos. To improve their temporal coherence, PoseBERT [7] and SmoothNet [123] propose to employ a denoising and smoothing module to the single-frame predictions. Several works [23, 39, 42, 99] take video clips as input to exploit the temporal cues. Another common problem is that paired images and GT meshes are mostly captured in constrained scenarios, which limits the generalization ability of the above methods. To that end, Pose2Mesh [24] proposes to first extract 2D skeletons using an off-the-shelf pose estimator, then lift them to 3D mesh vertices. Our approach is complementary to state-of-the-art human mesh recovery methods and could further improve their temporal coherence with the pretrained motion representations." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.605, + 0.17, + 0.62 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.641, + 0.188, + 0.655 + ], + "angle": 0, + "content": "3.1. Overview" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.675, + 0.474, + 0.9 + ], + "angle": 0, + "content": "As discussed in Section 1, our approach consists of two stages, namely unified pretraining and task-specific finetuning. In the first stage, we train a motion encoder to accomplish the 2D-to-3D lifting task, where we use the proposed DSTformer as the backbone. In the second stage, we finetune the pretrained motion encoder and a few new layers on the downstream tasks. We use 2D skeleton sequences as input for both pretraining and finetuning because they could be reliably extracted from all kinds of motion sources [3,9,71,81,96], and is more robust to variations [18,30]. Existing studies have shown the effectiveness of using 2D skeleton sequences for different downstream tasks [24,30,83,102]. We will first introduce the architecture of DSTformer, and then describe the training scheme in detail." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.317, + 0.706, + 0.332 + ], + "angle": 0, + "content": "3.2. Network Architecture" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.339, + 0.896, + 0.614 + ], + "angle": 0, + "content": "Figure 2 shows the network architecture for 2D-to-3D lifting. Given an input 2D skeleton sequence \\(\\mathbf{x} \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{in}}}\\), we first project it to a high-dimensional feature \\(\\mathbf{F}^0 \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{f}}}\\), then add learnable spatial positional encoding \\(\\mathbf{P}_{\\mathrm{pos}}^{\\mathrm{S}} \\in \\mathbb{R}^{1 \\times J \\times C_{\\mathrm{f}}}\\) and temporal positional encoding \\(\\mathbf{P}_{\\mathrm{pos}}^{\\mathrm{T}} \\in \\mathbb{R}^{T \\times 1 \\times C_{\\mathrm{f}}}\\) to it. We then use the sequence-to-sequence model DSTformer to calculate \\(\\mathbf{F}^i \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{f}}} (i = 1, \\dots, N)\\) where \\(N\\) is the network depth. We apply a linear layer with tanh activation [29] to \\(\\mathbf{F}^N\\) to compute the motion representation \\(\\mathbf{E} \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{e}}}\\). Finally, we apply a linear transformation to \\(\\mathbf{E}\\) to estimate 3D motion \\(\\hat{\\mathbf{X}} \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{out}}}\\). Here, \\(T\\) denotes the sequence length, and \\(J\\) denotes the number of body joints. \\(C_{\\mathrm{in}}, C_{\\mathrm{f}}, C_{\\mathrm{e}}\\), and \\(C_{\\mathrm{out}}\\) denote the channel numbers of input, feature, embedding, and output respectively. We first introduce the basic building blocks of DSTformer, i.e. Spatial and Temporal Blocks with Multi-Head Self-Attention (MHSA), and then explain the DSTformer architecture design." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.632, + 0.895, + 0.678 + ], + "angle": 0, + "content": "Spatial Block. Spatial MHSA (S-MHSA) aims at modeling the relationship among the joints within the same time step. It is defined as" + }, + { + "type": "equation", + "bbox": [ + 0.537, + 0.687, + 0.892, + 0.742 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathrm {S} - \\mathrm {M H S A} \\left(\\mathbf {Q} _ {\\mathrm {S}}, \\mathbf {K} _ {\\mathrm {S}}, \\mathbf {V} _ {\\mathrm {S}}\\right) = \\left[ \\text {h e a d} _ {1}; \\dots ; \\text {h e a d} _ {h} \\right] \\mathbf {W} _ {\\mathrm {S}} ^ {P}, \\\\ \\operatorname {h e a d} _ {i} = \\operatorname {s o f t m a x} \\left(\\frac {\\mathbf {Q} _ {\\mathrm {S}} ^ {i} \\left(\\mathbf {K} _ {\\mathrm {S}} ^ {i}\\right) ^ {\\prime}}{\\sqrt {d _ {K}}}\\right) \\mathbf {V} _ {\\mathrm {S}} ^ {i}, \\tag {1} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.752, + 0.895, + 0.828 + ], + "angle": 0, + "content": "where \\(\\mathbf{W}_{\\mathrm{S}}^{P}\\) is a projection parameter matrix, \\(h\\) is the number of the heads, \\(i\\in 1,\\dots ,h\\) and \\({}^{\\prime}\\) denotes matrix transpose. We utilize self-attention to get the query Qs, key \\(\\mathbf{K}_S\\) , and value \\(\\mathbf{V}_{\\mathrm{S}}\\) from input per-frame spatial feature \\(\\mathbf{F}_{\\mathrm{S}}\\in \\mathbb{R}^{J\\times C_{\\mathrm{e}}}\\) for each head," + }, + { + "type": "equation", + "bbox": [ + 0.52, + 0.838, + 0.895, + 0.858 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Q} _ {\\mathrm {S}} ^ {i} = \\mathbf {F} _ {\\mathrm {S}} \\mathbf {W} _ {\\mathrm {S}} ^ {(Q, i)}, \\mathbf {K} _ {\\mathrm {S}} ^ {i} = \\mathbf {F} _ {\\mathrm {S}} \\mathbf {W} _ {\\mathrm {S}} ^ {(K, i)}, \\mathbf {V} _ {\\mathrm {S}} ^ {i} = \\mathbf {F} _ {\\mathrm {S}} \\mathbf {W} _ {\\mathrm {S}} ^ {(V, i)}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.867, + 0.895, + 0.902 + ], + "angle": 0, + "content": "where \\(\\mathbf{W}_{\\mathrm{S}}^{(Q,i)}\\), \\(\\mathbf{W}_{\\mathrm{S}}^{(K,i)}\\), \\(\\mathbf{W}_{\\mathrm{S}}^{(V,i)}\\) are projection matrices, and \\(d_{K}\\) is the feature dimension of \\(\\mathbf{K}_{\\mathrm{S}}\\). We apply S-MHSA to" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15087" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.198 + ], + "angle": 0, + "content": "features of different time steps in parallel. Residual connection and layer normalization (LayerNorm) are used to the S-MHSA result, which is further fed into a multilayer perceptron (MLP), and followed by a residual connection and LayerNorm following [105]. We denote the entire spatial block with MHSA, LayerNorm, MLP, and residual connections by \\(\\mathcal{S}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.216, + 0.473, + 0.306 + ], + "angle": 0, + "content": "Temporal Block. Temporal MHSA (T-MHSA) aims at modeling the relationship across the time steps for a body joint. Its computation process is similar with S-MHSA except that the MHSA is applied to the per-joint temporal feature \\(\\mathbf{F}_{\\mathrm{T}} \\in \\mathbb{R}^{T \\times C_{\\mathrm{e}}}\\) and parallelized over the spatial dimension." + }, + { + "type": "equation", + "bbox": [ + 0.113, + 0.315, + 0.47, + 0.37 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathrm {T} - \\mathrm {M H S A} \\left(\\mathbf {Q} _ {\\mathrm {T}}, \\mathbf {K} _ {\\mathrm {T}}, \\mathbf {V} _ {\\mathrm {T}}\\right) = \\left[ \\text {h e a d} _ {1}; \\dots ; \\text {h e a d} _ {h} \\right] \\mathbf {W} _ {\\mathrm {T}} ^ {P}, \\\\ \\operatorname {h e a d} _ {i} = \\operatorname {s o f t m a x} \\left(\\frac {\\mathbf {Q} _ {\\mathrm {T}} ^ {i} \\left(\\mathbf {K} _ {\\mathrm {T}} ^ {i}\\right) ^ {\\prime}}{\\sqrt {d _ {K}}}\\right) \\mathbf {V} _ {\\mathrm {T}} ^ {i}, \\tag {3} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.379, + 0.47, + 0.41 + ], + "angle": 0, + "content": "where \\(i \\in 1, \\ldots, h\\), \\(\\mathbf{Q}_{\\mathrm{T}}\\), \\(\\mathbf{K}_{\\mathrm{T}}\\), \\(\\mathbf{V}_{\\mathrm{T}}\\) are computed similar with Formula 2. We denote the entire temporal block by \\(\\mathcal{T}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.429, + 0.473, + 0.594 + ], + "angle": 0, + "content": "Dual-stream Spatio-temporal Transformer. Given spatial and temporal MHSA that captures the intra-frame and inter-frame body joint interactions respectively, we assemble the basic building blocks to fuse the spatial and temporal information in the flow. We design a dual-stream architecture with the following assumptions: 1) Both streams should be capable of modeling the comprehensive spatio-temporal context. 2) Each stream should be specialized in different spatio-temporal aspects. 3) The two streams should be fused together, with the fusion weights dynamically balanced depending on the input spatio-temporal characteristics." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.595, + 0.472, + 0.671 + ], + "angle": 0, + "content": "Hence, we stack the spatial and temporal MHSA blocks in different orders, forming two parallel computation branches. The output features of the two branches are fused using adaptive weights predicted by an attention regressor. The dual-stream-fusion module is then repeated for \\( N \\) times:" + }, + { + "type": "equation", + "bbox": [ + 0.077, + 0.678, + 0.475, + 0.707 + ], + "angle": 0, + "content": "\\[\n\\mathbf {F} ^ {i} = \\boldsymbol {\\alpha} _ {\\mathrm {S T}} ^ {i} \\circ \\mathcal {T} _ {1} ^ {i} \\left(\\mathcal {S} _ {1} ^ {i} \\left(\\mathbf {F} ^ {i - 1}\\right)\\right) + \\boldsymbol {\\alpha} _ {\\mathrm {T S}} ^ {i} \\circ \\mathcal {S} _ {2} ^ {i} \\left(\\mathcal {T} _ {2} ^ {i} \\left(\\mathbf {F} ^ {i - 1}\\right)\\right), \\quad i \\in 1, \\dots , N, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.709, + 0.47, + 0.77 + ], + "angle": 0, + "content": "where \\(\\mathbf{F}^i\\) denotes the feature embedding at depth \\(i\\), \\(\\circ\\) denotes element-wise production. Orders of \\(\\mathcal{S}\\) and \\(\\mathcal{T}\\) blocks are shown in Figure 2, and different blocks do not share weights. Adaptive fusion weights \\(\\alpha_{\\mathrm{ST}}, \\alpha_{\\mathrm{TS}} \\in \\mathbb{R}^{N \\times T \\times J}\\) are given by" + }, + { + "type": "equation", + "bbox": [ + 0.09, + 0.777, + 0.47, + 0.807 + ], + "angle": 0, + "content": "\\[\n\\alpha_ {\\mathrm {S T}} ^ {i}, \\alpha_ {\\mathrm {T S}} ^ {i} = \\operatorname {s o f t m a x} \\left(\\mathcal {W} \\left(\\left[ \\mathcal {T} _ {1} ^ {i} \\left(\\mathcal {S} _ {1} ^ {i} \\left(\\mathbf {F} ^ {i - 1}\\right)\\right), \\mathcal {S} _ {2} ^ {i} \\left(\\mathcal {T} _ {2} ^ {i} \\left(\\mathbf {F} ^ {i - 1}\\right)\\right) \\right]\\right)\\right), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.808, + 0.469, + 0.838 + ], + "angle": 0, + "content": "where \\(\\mathcal{W}\\) is a learnable linear transformation. \\([,]\\) denotes concatenation." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.848, + 0.265, + 0.865 + ], + "angle": 0, + "content": "3.3. Unified Pretraining" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.473, + 0.902 + ], + "angle": 0, + "content": "We address two key challenges when designing the unified pretraining framework: 1) How to learn a powerful" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.136 + ], + "angle": 0, + "content": "motion representation with a universal pretext task. 2) How to utilize large-scale but heterogeneous human motion data in all kinds of formats." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.137, + 0.895, + 0.456 + ], + "angle": 0, + "content": "For the first challenge, we follow the successful practices in language [11, 29, 84] and vision [6, 34] modeling to construct the supervision signals, i.e. mask part of the input and use the encoded representations to reconstruct the whole input. Note that such \"cloze\" task naturally exists in human motion analysis, that is to recover the lost depth information from the 2D visual observations, i.e. 3D human pose estimation. Inspired by this, we leverage the large-scale 3D mocap data [71] and design a 2D-to-3D lifting pretext task. We first extract the 2D skeleton sequences \\(\\mathbf{x}\\) by projecting the 3D motion orthographically. Then, we corrupt \\(\\mathbf{x}\\) by randomly masking and adding noise to produce the corrupted 2D skeleton sequences, which also resemble the 2D detection results as it contains occlusions, detection failures, and errors. Both joint-level and frame-level masks are applied with certain probabilities. We use the aforementioned motion encoder to get motion representation \\(\\mathbf{E}\\) and reconstruct 3D motion \\(\\hat{\\mathbf{X}}\\). We then compute the joint loss \\(\\mathcal{L}_{3\\mathrm{D}}\\) between \\(\\hat{\\mathbf{X}}\\) and GT 3D motion \\(\\mathbf{X}\\). We also add the velocity loss \\(\\mathcal{L}_{\\mathrm{O}}\\) following previous works [83, 126]. The 3D reconstruction losses are thus given by" + }, + { + "type": "equation", + "bbox": [ + 0.499, + 0.465, + 0.911, + 0.515 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {3 D}} = \\sum_ {t = 1} ^ {T} \\sum_ {j = 1} ^ {J} \\| \\hat {\\mathbf {X}} _ {t, j} - \\mathbf {X} _ {t, j} \\| _ {2}, \\quad \\mathcal {L} _ {\\mathrm {O}} = \\sum_ {t = 2} ^ {T} \\sum_ {j = 1} ^ {J} \\| \\hat {\\mathbf {O}} _ {t, j} - \\mathbf {O} _ {t, j} \\| _ {2}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.515, + 0.797, + 0.531 + ], + "angle": 0, + "content": "where \\(\\hat{\\mathbf{O}}_t = \\hat{\\mathbf{X}}_t - \\hat{\\mathbf{X}}_{t - 1}\\) \\(\\mathbf{O}_t = \\mathbf{X}_t - \\mathbf{X}_{t - 1}\\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.531, + 0.895, + 0.713 + ], + "angle": 0, + "content": "For the second challenge, we notice that 2D skeletons could serve as a universal medium as they can be extracted from all sorts of motion data sources. We further incorporate in-the-wild RGB videos into the 2D-to-3D lifting framework for unified pretraining. For RGB videos, the 2D skeletons \\(\\mathbf{x}\\) could be given by manual annotation [3] or 2D pose estimators [13, 96], and the depth channel of the extracted 2D skeletons is intrinsically \"masked\". Similarly, we add extra masks and noises to degrade \\(\\mathbf{x}\\) (if \\(\\mathbf{x}\\) already contains detection noise, only masking is applied). As 3D motion GT \\(\\mathbf{X}\\) is not available for these data, we apply a weighted 2D re-projection loss which is calculated by" + }, + { + "type": "equation", + "bbox": [ + 0.588, + 0.723, + 0.892, + 0.762 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {2 D}} = \\sum_ {t = 1} ^ {T} \\sum_ {j = 1} ^ {J} \\boldsymbol {\\delta} _ {t, j} \\| \\hat {\\mathbf {x}} _ {t, j} - \\mathbf {x} _ {t, j} \\| _ {2}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.772, + 0.895, + 0.817 + ], + "angle": 0, + "content": "where \\(\\hat{\\mathbf{x}}\\) is the 2D orthogonal projection of the estimated 3D motion \\(\\hat{\\mathbf{X}}\\), and \\(\\delta \\in \\mathbb{R}^{T\\times J}\\) is given by visibility annotation or 2D detection confidence." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.818, + 0.792, + 0.834 + ], + "angle": 0, + "content": "The total pretraining loss is computed by" + }, + { + "type": "equation", + "bbox": [ + 0.603, + 0.844, + 0.892, + 0.876 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\underbrace {\\mathcal {L} _ {\\mathrm {3 D}} + \\lambda_ {\\mathrm {O}} \\mathcal {L} _ {\\mathrm {O}}} _ {\\text {f o r 3 D d a t a}} + \\underbrace {\\mathcal {L} _ {\\mathrm {2 D}}} _ {\\text {f o r 2 D d a t a}}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.886, + 0.866, + 0.901 + ], + "angle": 0, + "content": "where \\(\\lambda_{\\mathrm{O}}\\) is a constant coefficient to balance the losses." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15088" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.091, + 0.303, + 0.108 + ], + "angle": 0, + "content": "3.4. Task-specific Finetuning" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.116, + 0.471, + 0.222 + ], + "angle": 0, + "content": "The learned feature embedding \\(\\mathbf{E}\\) serves as a 3D-aware and temporal-aware human motion representation. For downstream tasks, we adopt the minimalist design principle, i.e. implementing a shallow downstream network and training without bells and whistles. In practice, we use an extra linear layer or an MLP with one hidden layer. We then finetune the whole network end-to-end." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.25, + 0.472, + 0.311 + ], + "angle": 0, + "content": "3D Pose Estimation. As we utilize 2D-to-3D lifting as the pretext task, we simply reuse the whole pretrained network. During finetuning, the input 2D skeletons are estimated from videos without extra masks or noises." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.34, + 0.473, + 0.446 + ], + "angle": 0, + "content": "Skeleton-based Action Recognition. We directly apply a global average pooling over different persons and timesteps. The result is then fed into an MLP with one hidden layer. The network is trained with cross-entropy classification loss. For one-shot learning, we apply a linear layer after the pooled features to extract clip-level action representation. We introduce the detailed setup of one-shot learning in Section 4.4." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.473, + 0.473, + 0.701 + ], + "angle": 0, + "content": "Human Mesh Recovery. We use SMPL [66] model to represent the human mesh and regress its parameters. The SMPL model consists of pose parameters \\(\\theta \\in \\mathbb{R}^{72}\\) and shape parameters \\(\\beta \\in \\mathbb{R}^{10}\\), and calculates the 3D mesh as \\(\\mathcal{M}(\\theta, \\beta) \\in \\mathbb{R}^{6890 \\times 3}\\). To regress the pose parameters for each frame, we feed the motion embeddings \\(\\mathbf{E}\\) to an MLP with one hidden layer and get \\(\\hat{\\pmb{\\theta}} \\in \\mathbb{R}^{T \\times 72}\\). To estimate shape parameters, considering that the human shape over a video sequence is supposed to be consistent, we first perform an average pooling of \\(\\mathbf{E}\\) over the temporal dimension and then feed it into another MLP to regress a single \\(\\hat{\\beta}\\) and then expand it to the entire sequence as \\(\\hat{\\beta} \\in \\mathbb{R}^{T \\times 10}\\). The shape MLP has the same architecture as the pose regression one, and they are initialized with the mean shape and pose, respectively, as in [42]. The overall loss is computed as" + }, + { + "type": "equation", + "bbox": [ + 0.113, + 0.714, + 0.471, + 0.731 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\lambda_ {\\mathrm {3 D}} ^ {\\mathrm {m}} \\mathcal {L} _ {\\mathrm {3 D}} ^ {\\mathrm {m}} + \\lambda_ {\\theta} \\mathcal {L} _ {\\theta} + \\lambda_ {\\beta} \\mathcal {L} _ {\\beta} + \\lambda_ {\\mathrm {n}} \\mathcal {L} _ {\\text {n o r m}} + \\lambda_ {\\mathrm {O}} ^ {\\mathrm {m}} \\mathcal {L} _ {\\mathrm {O}} ^ {\\mathrm {m}}, \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.747, + 0.295, + 0.761 + ], + "angle": 0, + "content": "where each term is calculated as" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.774, + 0.462, + 0.792 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {3 D}} ^ {\\mathrm {m}} = \\left\\| \\hat {\\mathbf {X}} ^ {\\mathrm {m}} - \\mathbf {X} ^ {\\mathrm {m}} \\right\\| _ {1}, \\quad \\mathcal {L} _ {\\theta} = \\left\\| \\hat {\\boldsymbol {\\theta}} - \\boldsymbol {\\theta} \\right\\| _ {1}, \\quad \\mathcal {L} _ {\\beta} = \\left\\| \\hat {\\boldsymbol {\\beta}} - \\boldsymbol {\\beta} \\right\\| _ {1},\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.087, + 0.794, + 0.471, + 0.822 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {n o r m}} = \\| \\hat {\\boldsymbol {\\theta}} \\| _ {2} + \\| \\hat {\\boldsymbol {\\beta}} \\| _ {2}, \\quad \\mathcal {L} _ {\\mathrm {O}} ^ {\\mathrm {m}} = \\| \\hat {\\mathbf {O}} ^ {\\mathrm {m}} - \\mathbf {O} ^ {\\mathrm {m}} \\| _ {2}. \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.823, + 0.473, + 0.902 + ], + "angle": 0, + "content": "Note that each 3D pose in motion \\(\\mathbf{X}^{\\mathrm{m}}\\) at frame \\(t\\) is regressed from mesh vertices by \\(\\mathbf{X}_t^{\\mathrm{m}} = \\mathbf{J}\\mathcal{M}(\\pmb {\\theta}_t,\\pmb {\\beta}_t)\\), where \\(\\mathbf{J}\\in \\mathbb{R}^{J\\times 6890}\\) is a pre-defined matrix [9]. \\(\\mathbf{O}^{\\mathrm{m}} = \\mathbf{X}_{t + 1}^{\\mathrm{m}} - \\mathbf{X}_{t}^{\\mathrm{m}}\\), \\(\\hat{\\mathbf{O}}^{\\mathrm{m}} = \\hat{\\mathbf{X}}_{t + 1}^{\\mathrm{m}} - \\hat{\\mathbf{X}}_t^{\\mathrm{m}}\\). \\(\\lambda_{3\\mathrm{D}}^{\\mathrm{m}},\\lambda_{\\theta},\\lambda_{\\beta},\\lambda_{\\mathrm{n}}\\) and \\(\\lambda_0^{\\mathrm{m}}\\) are constant coefficients to balance the training loss." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.634, + 0.108 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.115, + 0.661, + 0.132 + ], + "angle": 0, + "content": "4.1. Implementation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.139, + 0.895, + 0.29 + ], + "angle": 0, + "content": "We implement the proposed motion encoder DSTformer with depth \\( N = 5 \\), number of heads \\( h = 8 \\), feature size \\( C_{\\mathrm{f}} = 512 \\), embedding size \\( C_{\\mathrm{e}} = 512 \\). For pretraining, we use sequence length \\( T = 243 \\). The pretrained model could handle different input lengths thanks to the Transformer-based backbone. During finetuning, we set the backbone learning rate to be \\( 0.1 \\times \\) of the new layer learning rate. We introduce the experiment datasets in the following sections respectively. Please refer to the appendix for more experimental details." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.301, + 0.627, + 0.317 + ], + "angle": 0, + "content": "4.2. Pretraining" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.324, + 0.895, + 0.673 + ], + "angle": 0, + "content": "We collect diverse and realistic 3D human motion from two datasets, Human3.6M [36] and AMASS [71]. Human3.6M [36] is a commonly used indoor dataset for 3D human pose estimation which contains 3.6 million video frames of professional actors performing daily actions. Following previous works [73, 83], we use subjects 1, 5, 6, 7, 8 for training, and subjects 9, 11 for testing. AMASS [71] integrates most existing marker-based Mocap datasets [1,2,4,10,14,17,32,35,48,65,67,72,79,90,103,104] and parameterizes them with a common representation. We do not use the images or 2D detection results of the two datasets during pretraining as Mocap datasets usually do not provide raw videos. Instead, we use orthographic projection to get the uncorrupted 2D skeletons. We further incorporate two in-the-wild RGB video datasets PoseTrack [3] (annotated) and InstaVariety [39] (unannotated) for higher motion diversity. We align the body keypoint definitions with Human3.6M and calibrate the camera coordinates to pixel coordinates following [26]. We randomly zero out \\(15\\%\\) joints, and sample noises from a mixture of Gaussian and uniform distributions [16]. We first train on 3D data only for 30 epochs, then train on both 3D data and 2D data for 60 epochs, following the curriculum learning practices [8, 111]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.681, + 0.688, + 0.696 + ], + "angle": 0, + "content": "4.3. 3D Pose Estimation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.895, + 0.903 + ], + "angle": 0, + "content": "We evaluate the 3D pose estimation performance on Human3.6M [36] and report the mean per joint position error (MPJPE) in millimeters, which measures the average distance between the predicted joint positions and the GT after aligning the root joint. We also compute the mean per-joint velocity error (MPJVE) to evaluate the temporal smoothness following previous works [126, 127]. We use the Stacked Hourglass (SH) networks [81] to extract the 2D skeletons from videos, and finetune the entire network on Human3.6M [36] training set. In addition, we train a separate model of the same architecture, but with random initialization rather than pretrained weights. As shown in Table 1 (top), the model trained from scratch outperforms" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "15089" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.128, + 0.089, + 0.842, + 0.484 + ], + "angle": 0, + "content": "
MethodTDire.Disc.EatGreetPhonePhotoPosePurch.SitSitDSmokeWaitWalkDWalkWalkTAvg
Martinez et al. [73] ICCV'17151.856.258.159.069.578.455.258.174.094.662.359.165.149.552.462.9
Pavlakos et al. [82] CVPR'18148.554.454.452.059.465.349.952.965.871.156.652.960.944.747.856.2
LCN [27] ICCV'19146.852.344.750.452.968.949.646.460.278.951.250.054.840.443.352.7
Xu et al. [114] CVPR'21145.249.947.550.954.966.148.546.359.771.551.448.653.939.944.151.9
VideoPose3D [83] CVPR'1924345.246.743.345.648.155.144.644.357.365.847.144.049.032.833.946.8
Cai et al. [12] ICCV'19744.647.445.648.850.859.047.243.957.961.949.746.651.337.139.448.8
Yeh et al. [122] NeurIPS'1924344.846.143.346.449.055.244.644.058.362.747.143.948.632.733.346.7
Liu et al. [63] CVPR'2024341.844.841.144.947.454.143.442.256.263.645.343.545.331.332.245.1
* Cheng et al. [21] AAAI'2012836.238.142.735.938.245.736.842.045.951.341.841.543.833.128.640.1
* UGCN [109] ECCV'209638.241.045.939.741.451.441.641.452.057.441.844.441.633.130.042.6
† PoseFormer [127] ICCV'218141.544.839.842.546.551.642.142.053.360.745.543.346.131.832.244.3
* Wehrbein et al. [112] ICCV'2120038.542.539.941.746.551.639.940.849.556.845.346.446.837.840.444.3
† MHFormer [52] CVPR'2235139.243.140.140.944.951.240.641.353.560.343.741.143.829.830.643.0
*† MixSTE [126] CVPR'2224336.739.036.539.440.244.939.836.947.954.839.637.839.329.730.639.8
† P-STMO [87] ECCV'2224338.442.139.840.245.248.940.438.353.857.343.941.642.229.329.342.1
† Ours (scratch)24336.338.738.633.642.150.136.235.750.156.641.337.437.725.626.539.2
† Ours (finetune)24336.137.535.832.140.346.336.135.346.953.939.536.335.825.125.337.5
MethodTDire.Disc.EatGreetPhonePhotoPosePurch.SitSitDSmokeWaitWalkDWalkWalkTAvg
Martinez et al. [73] ICCV'17137.744.440.342.148.254.944.442.154.658.045.146.447.636.440.445.5
LCN [27] ICCV'19136.338.829.737.834.642.539.832.536.239.534.438.438.231.334.236.3
Xu et al. [114] CVPR'21135.838.131.035.335.843.237.331.738.445.535.436.736.827.930.735.8
UGCN [109] ECCV'209623.025.722.822.624.130.624.924.531.135.025.624.325.119.818.425.6
† PoseFormer [127] ICCV'218130.033.629.931.030.233.334.831.437.838.631.731.529.023.323.131.3
† MHFormer [52] CVPR'2235127.732.129.128.930.033.933.031.237.039.330.031.029.422.223.030.5
† MixSTE [126] CVPR'2224321.622.020.421.020.824.324.721.926.924.921.221.520.814.715.621.6
† P-STMO [87] ECCV'2224328.530.128.627.929.833.231.327.836.037.429.729.528.121.021.029.3
† Ours (scratch)24316.719.917.116.517.418.819.320.524.022.118.616.816.710.811.517.8
† Ours (finetune)24315.917.316.914.616.818.618.618.422.021.817.316.916.110.511.416.9
MethodTDire.Disc.EatGreetPhonePhotoPosePurch.SitSitDSmokeWaitWalkDWalkWalkTAvg
VideoPose3D [83] CVPR'192433.03.12.23.42.32.72.73.12.12.92.32.43.73.12.82.8
† PoseFormer [127] ICCV'21813.23.42.63.62.63.02.93.22.63.32.72.73.83.22.93.1
*† MixSTE [126] CVPR'222432.52.71.92.81.92.22.32.61.62.21.92.03.12.62.22.3
† Ours (scratch)2431.82.11.52.01.51.91.82.11.21.81.51.42.62.01.71.8
† Ours (finetune)2431.71.91.41.91.41.71.71.91.11.61.41.32.41.91.61.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.489, + 0.894, + 0.545 + ], + "angle": 0, + "content": "Table 1. Quantitative comparison of 3D human pose estimation on Human3.6M. (Top) MPJPE (mm) using detected 2D pose sequences. (Middle) MPJPE (mm) using GT 2D pose sequences. (Bottom) MPJVE (mm) using detected 2D pose sequences. \\(T\\) denotes the clip length used by the method. We select the best results reported by each work. \\* denotes using HRNet [96] for 2D detection. \\(\\dagger\\) denotes implemented with a spatio-temporal Transformer design. The best and second-best results are highlighted in bold and underlined formats." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.57, + 0.473, + 0.829 + ], + "angle": 0, + "content": "previous methods including other Transformer-based designs with spatio-temporal modeling. It shows the effectiveness of the proposed DSTformer in terms of learning 3D geometric structures and temporal dynamics. To further evaluate the upper bound of the models' capability, we compare the performance when using 2D GT pose sequences as input, which gets rid of the influence of different 2D detectors. As shown in Table 1 (middle), our models significantly outperform all the previous approaches. Table 1 (bottom) shows that both of our models also surpass previous works in terms of MPJVE, implying better temporal coherence. We attribute the performance advantage of our scratch model to the proposed DSTformer design. We include more comparisons and analysis to demonstrate the advantage of DSTformer with regard to other spatio-temporal architectures in Section 4.6 and supplementary materials. Additionally, our method achieves lower errors with the proposed pretraining stage." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.845, + 0.383, + 0.862 + ], + "angle": 0, + "content": "4.4. Skeleton-based Action Recognition" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.472, + 0.903 + ], + "angle": 0, + "content": "We further explore the possibility to learn action semantics with the pretrained human motion representations. We" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.57, + 0.895, + 0.753 + ], + "angle": 0, + "content": "use the human action dataset NTU-RGB+D [86] which contains 57K videos of 60 action classes, and we follow the data splits Cross-subject (X-Sub) and Cross-view (X-View). The dataset has an extended version, NTU-RGB+D-120 [60], which contains 114K videos of 120 action classes. We follow the suggested One-shot action recognition protocol on NTU-RGB+D-120. For both datasets, we use HRNet [96] to extract 2D skeletons following [30]. Similarly, we train a scratch model with random initialization for comparison. As Table 2 (left) shows, our methods are comparable or superior to the state-of-the-art approaches. Notably, the pretraining stage accounts for a large performance gain." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.897, + 0.903 + ], + "angle": 0, + "content": "Additionally, we delve into the one-shot setting which holds significant practical importance. Real-world applications often require fine-grained action recognition in specific domains such as education, sports, and healthcare. Unfortunately, the action classes in these scenarios are not typically defined in public datasets. As a result, only limited annotations for these novel action classes are available, making accurate recognition a challenging task. As proposed in [60], we report the results on the evaluation set of 20 novel classes" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "15090" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.151, + 0.089, + 0.409, + 0.258 + ], + "angle": 0, + "content": "
MethodX-SubX-View
ST-GCN [116] AAAI'1881.588.3
2s-AGCN [89] CVPR'1988.595.1
MS-G3D [64] CVPR'2091.596.2
Shift-GCN [20] CVPR'2090.796.5
CrosSCLR [58] CVPR'2186.292.5
MCC (finetune) [94] ICCV'2189.796.3
SCC (finetune) [118] ICCV'2188.094.9
UNIK (finetune) [117] BMVC'2186.894.4
CTR-GCN [19] ICCV'2192.496.8
PoseConv3D [30] CVPR'2293.195.7
Ours (scratch)87.794.1
Ours (finetune)93.097.2
" + }, + { + "type": "table", + "bbox": [ + 0.549, + 0.089, + 0.807, + 0.219 + ], + "angle": 0, + "content": "
MethodAccuracy
ST-LSTM + AvgPool [61]42.9
ST-LSTM + FC [62]42.1
ST-LSTM + Attention [62]41.0
APSR [60]45.3
TCN OneShot [85]46.5
SL-DML [76]50.9
Skeleton-DML [75]54.2
Ours (scratch)61.0
Ours (finetune)67.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.268, + 0.895, + 0.311 + ], + "angle": 0, + "content": "Table 2. Quantitative comparison of skeleton-based action recognition accuracy. (Left) Cross-subject and cross-view recognition accuracy on NTU-RGB+D. All the methods are evaluated using only the \"joint\" modality with 1-clip sampling for the fairness of comparison. (Right) One-shot recognition accuracy on NTU-RGB+D-120. All results are top-1 accuracy (\\%)." + }, + { + "type": "table", + "bbox": [ + 0.162, + 0.321, + 0.812, + 0.664 + ], + "angle": 0, + "content": "
MethodInputTHuman3.6M3DPW
MPVE↓MPJPE↓PA-MPJPE↓MPVE↓MPJPE↓PA-MPJPE↓
HMR [38] CVPR'18image1-88.056.8-130.081.3
† SPIN [44] ICCV'19image182.359.439.3129.1100.959.1
Pose2Mesh [24] ECCV'202D pose185.364.948.7109.391.460.1
I2L-MeshNet [78] ECCV'20image1-55.741.7110.193.258.6
† HybrIK [50] CVPR'21image158.147.430.182.471.341.9
METRO [54] CVPR'21image1-54.036.788.277.147.9
Mesh Graphormer [55] ICCV'21image1-51.234.587.774.745.6
PARE [43] ICCV'21image1---88.674.546.5
ROMP [98] ICCV'21image1---108.391.354.9
PyMAF [125] ICCV'21image1-57.740.5110.192.858.9
ProHMR [46] ICCV'21image1--41.2--59.8
OCHMR [40] CVPR'22image1---107.189.758.3
3DCrowdNet [25] CVPR'22image1---98.381.751.5
CLIFF [53] ECCV'22image1-47.132.781.269.043.0
FastMETRO [22] ECCV'22image1-52.233.784.173.544.6
VisDB [121] ECCV'22image1-51.034.585.573.544.9
TemporalContext [5] CVPR'19video32-77.854.3--72.2
HMMR [39] CVPR'19video20--56.9139.3116.572.6
DSD-SATN [99] ICCV'19video9-59.142.4--69.5
VIBE [42] CVPR'20video16-65.641.499.182.951.9
TCMR [23] CVPR'21video16-62.341.1102.986.552.7
† MAED [107] ICCV'21video1684.160.438.393.379.045.7
MPS-Net [113] CVPR'22video16-69.447.499.784.352.1
* PoseBERT [7] TPAMI'22 (+SPIN [44])video16-----57.3 ↓ 2.3
* SmoothNet [123] ECCV'22 (+SPIN [44])video32-67.5 ↓ 1.046.3 ↓ 0.2-86.7 ↓ 0.952.7 ↓ 0.6
Ours (scratch)2D motion1675.762.841.099.185.550.2
Ours (finetune)2D motion1665.553.834.988.176.947.2
Ours (finetune) + SPIN [44]video1663.7 ↓ 18.652.2 ↓ 7.235.7 ↓ 3.692.8 ↓ 36.379.6 ↓ 21.348.2 ↓ 10.9
Ours (finetune) + MAED [107]video1666.8 ↓ 17.354.8 ↓ 5.636.4 ↓ 1.984.4 ↓ 8.972.3 ↓ 6.742.3 ↓ 3.4
Ours (finetune) + HybrIK [50]video1652.6 ↓ 5.543.1 ↓ 4.327.8 ↓ 2.379.4 ↓ 3.068.8 ↓ 2.540.6 ↓ 1.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.674, + 0.893, + 0.716 + ], + "angle": 0, + "content": "Table 3. Quantitative comparison of human mesh recovery on Human3.6M and 3DPW datasets. \\(T\\) denotes the clip length used by the method. \\(\\dagger\\) denotes the results obtained with official model weights. The rest are all officially reported results. The gains in \\* correspond to different re-implemented SPIN [44] results." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.726, + 0.473, + 0.893 + ], + "angle": 0, + "content": "using only 1 labeled video for each class. The auxiliary set contains the other 100 classes, and all samples of these classes can be used. We train the model on the auxiliary set using the supervised contrastive learning technique [41]. For a batch of auxiliary data, samples of the same class are pulled together, while samples of different classes are pushed away in the action embedding space. During the evaluation, we calculate the cosine distance between the test examples and the exemplars, and use 1-nearest neighbor to determine the class. Table 2 (right) illustrates that the proposed models outperform state-of-the-art by a considerable margin. Moreover," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.726, + 0.895, + 0.803 + ], + "angle": 0, + "content": "it is noteworthy that our pretrained model achieves optimal performance with only 1-2 epochs of fine-tuning. Our results indicate that the pretraining stage is effective in learning a robust motion representation that generalizes well to novel downstream tasks, even with limited data annotations." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.816, + 0.719, + 0.833 + ], + "angle": 0, + "content": "4.5. Human Mesh Recovery" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.897, + 0.903 + ], + "angle": 0, + "content": "We conduct experiments on Human3.6M [36] and 3DPW [106] datasets and additionally add COCO [57] dataset during training following [42, 54, 107]. We keep the same training and test split for both datasets as in [73] (Section 4.2)" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "15091" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.09, + 0.335, + 0.231 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.361, + 0.091, + 0.605, + 0.23 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.633, + 0.091, + 0.882, + 0.23 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.276, + 0.237, + 0.694, + 0.253 + ], + "angle": 0, + "content": "Figure 3. Learning curves of finetuning and training from scratch." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.273, + 0.472, + 0.334 + ], + "angle": 0, + "content": "
Backbone (frozen)MPJPE ↓ (3D pose)MPVE ↓ (mesh)Accuracy ↑ (action x-view)Accuracy↑ (action 1-shot)
Random404.4mm114.4mm47.6%46.8%
Pretrained40.3mm72.1mm87.3%60.7%
" + }, + { + "type": "table_caption", + "bbox": [ + 0.138, + 0.342, + 0.405, + 0.357 + ], + "angle": 0, + "content": "Table 4. Comparison of partial finetuning." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.37, + 0.473, + 0.779 + ], + "angle": 0, + "content": "and [42, 54, 107], respectively. Following the common practice [38, 42, 45, 107], we report MPJPE (mm) and PA-MPJPE (mm) of 14 joints obtained by \\(\\mathbf{J}\\mathcal{M}(\\theta ,\\beta)\\). PA-MPJPE calculates MPJPE after aligning with GT in translation, rotation, and scale. We further report the mean per vertex error (MPVE) (mm) of the mesh \\(\\mathcal{M}(\\theta ,\\beta)\\), which measures the average distance between the estimated and GT vertices after aligning the root joint. Note that most previous works [23, 38, 42, 44, 50, 54, 68, 107] use more datasets other than COCO [57] during training, such as LSP [37], MPI-INF-3DHP [74], etc., while we do not. Table 3 demonstrates that our finetuned model delivers competitive results on both Human3.6M and 3DPW datasets, surpassing all the state-of-the-art video-based methods, including MAED [107], especially on the MPVE error. Nonetheless, we note that estimating full-body mesh from sparse 2D keypoints alone [9, 24] is an ill-posed problem because it lacks human shape information. In light of this, we propose a hybrid approach that leverages the strengths of both our framework (coherent motion) and RGB-based methods (accurate shape). We introduce a refiner module that can be easily integrated with existing image/video-based methods, similar to [7, 123]. Specifically, our refiner module is an MLP that takes the combination of our pretrained motion representations and an initial prediction, regressing a residual in joint rotations. Our approach effectively improves the state-of-the-art methods [44, 50, 107] and achieves the lowest error to date." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.241, + 0.803 + ], + "angle": 0, + "content": "4.6. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.472, + 0.902 + ], + "angle": 0, + "content": "Finetune vs. Scratch. We compare the training progress of finetuning the pretrained model and training from scratch. As Figure 3 shows, models initialized with pretrained weights demonstrate superior performance and faster convergence on all three tasks. This observation suggests that the pretrained model learns transferable knowledge about hu" + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.275, + 0.89, + 0.374 + ], + "angle": 0, + "content": "
PretrainNoiseMask2DMPJPE↓(3D pose)MPVE↓(mesh)Accuracy↑(action x-sub)
----39.2mm75.7mm87.7%
✓---38.8mm70.6mm89.4%
✓✓--38.1mm68.4mm90.7%
✓✓✓-37.4mm67.8mm91.9%
✓✓✓✓37.5mm65.5mm93.0%
" + }, + { + "type": "table_caption", + "bbox": [ + 0.55, + 0.383, + 0.842, + 0.398 + ], + "angle": 0, + "content": "Table 5. Comparison of pretraining strategies." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.422, + 0.892, + 0.452 + ], + "angle": 0, + "content": "man motion, facilitating the learning of multiple downstream tasks." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.471, + 0.895, + 0.699 + ], + "angle": 0, + "content": "Partial Finetuning. In addition to end-to-end finetuning, we freeze the motion encoder backbone and only train the regression head for each downstream task. To verify the effectiveness of the pretrained motion representations, we compared the pretrained motion encoder with a randomly initialized motion encoder. We report results of 3D pose and mesh on Human3.6M, action on NTU-RGB+D and NTU-RGB+D-120 (same for the tables below). It can be seen in Table 4 that based on the frozen pretrained motion representations, our method still achieves competitive performance on multiple downstream tasks and shows a large improvement compared to the baseline. Pretraining and partial finetuning make it possible for all the downstream tasks to share the same backbone, significantly reducing computation overhead for applications requiring multi-task inference." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.716, + 0.897, + 0.853 + ], + "angle": 0, + "content": "Pretraining Strategies. We evaluate how different pretraining strategies influence the performance of downstream tasks. Starting from the scratch baseline, we apply the proposed strategies one by one. As shown in Table 5, a vanilla 2D-to-3D pretraining stage brings benefits to all the downstream tasks. Introducing corruptions additionally improves the learned motion embeddings. Unified pretraining with in-the-wild videos (w. 2D) enjoys higher motion diversity, which further helps several downstream tasks." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Pretraining with Different Backbones. We further study the universality of the proposed pretraining approach. We" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "15092" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.468, + 0.165 + ], + "angle": 0, + "content": "
SettingMPJPE ↓ (3D pose)MPVE ↓ (mesh)Accuracy ↑ (action x-view)Accuracy↑ (action 1-shot)
TCN (scratch)50.1mm92.6mm91.5%52.4%
TCN (finetune)47.9mm86.3mm92.8%59.9%
PoseFormer (scratch)44.8mm85.9mm94.2%57.4%
PoseFormer (finetune)41.5mm80.5mm95.9%60.7%
" + }, + { + "type": "table_caption", + "bbox": [ + 0.131, + 0.174, + 0.411, + 0.188 + ], + "angle": 0, + "content": "Table 6. Comparison of different backbones." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.201, + 0.466, + 0.253 + ], + "angle": 0, + "content": "
Arch.(a)(b)(c)(d)(e)(f)
DesignS-TT-SS + TST-MHSAS-T + T-S(Average)S-T + T-S(Adaptive)
MPJPE ↓40.58±0.3141.05±0.2441.76±0.2241.54±0.3539.87±0.3239.25±0.27
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.264, + 0.469, + 0.306 + ], + "angle": 0, + "content": "Table 7. Comparison of model architecture variants. All the methods are trained on Human3.6M from scratch over 5 runs and measured by MPJPE (mm) with mean and standard deviation." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.33, + 0.47, + 0.42 + ], + "angle": 0, + "content": "replace the motion encoder backbone with two variants: TCN [83] and PoseFormer [127]. The models are slightly modified to a seq2seq version, while all the configurations for pretraining and finetuning are simply followed. Table 6 shows that the proposed approach consistently benefits different backbone models on different tasks." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.439, + 0.47, + 0.727 + ], + "angle": 0, + "content": "Model Architecture. Finally, we study the design choices of DSTformer. From (a) to (f) in Table 7, we compare different structure designs of the basic Transformer module. (a) and (b) are single-stream versions with different orders. (a) is conceptually similar to PoseFormer [127], MH-Former [52], and MixSTE [126]. (c) limits each stream to either temporal or spatial modeling before fusion and is similar to MAED [107]. (d) directly connects S-MHSA and T-MHSA without the MLP in between and is similar to the MSA-T variant in MAED [107]. (e) replaces the adaptive fusion with average pooling on two streams. (f) is the proposed DSTformer design. The result statistically confirms our design principles that both streams should be capable and meanwhile complementary, as introduced in Section 3.2. In addition, we find out that pairing each self-attention block with an MLP is crucial, as it could project the learned feature interactions and bring nonlinearity. In general, we design the model architecture for the 3D pose estimation task and apply it to all other tasks without additional adjustment." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.74, + 0.195, + 0.755 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.765, + 0.47, + 0.901 + ], + "angle": 0, + "content": "In this work, we provide a unified perspective to tackling various human-centric video tasks. We develop a pretraining approach to learn human motion representations from large-scale and heterogeneous data sources. We also propose DSTformer as a universal human motion encoder. Experimental results on multiple benchmarks demonstrate the versatility of the learned motion representations. Future work could explore fusing the learned motion representations with generic video architectures as a human-centric semantic fea" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "ture and applying it to more tasks (e.g., action assessment, segmentation)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.14, + 0.892, + 0.187 + ], + "angle": 0, + "content": "Acknowledgement This work was partially supported by MOST-2022ZD0114900. We would like to thank Hai Ci and Jiefeng Li for their exceptional support." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "15093" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.096, + 0.116, + 0.47, + 0.146 + ], + "angle": 0, + "content": "[1] Advanced Computing Center for the Arts and Design. 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In AAAI, 2022." + }, + { + "type": "list", + "bbox": [ + 0.079, + 0.092, + 0.472, + 0.23 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.956 + ], + "angle": 0, + "content": "15099" + } + ] +] \ No newline at end of file diff --git a/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/57fc0f5c-171f-41a1-94fe-f16ec1d8935d_origin.pdf b/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/57fc0f5c-171f-41a1-94fe-f16ec1d8935d_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..06171d2696019f4384eaa3094f951583c47f7ea1 --- /dev/null +++ b/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/57fc0f5c-171f-41a1-94fe-f16ec1d8935d_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:91ab62189228bfa827446201a5fcb10224879f83d9296b6d7d6fcfc8773b3055 +size 6417482 diff --git a/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/full.md b/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/full.md new file mode 100644 index 0000000000000000000000000000000000000000..12d793a248c6ce6a50ce67e77209c794277d8f1d --- /dev/null +++ b/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/full.md @@ -0,0 +1,395 @@ +# MotionBERT: A Unified Perspective on Learning Human Motion Representations + +Wentao Zhu $^{1}$ Xiaoxuan Ma $^{1}$ Zhaoyang Liu $^{2}$ Libin Liu $^{1}$ Wayne Wu $^{2}$ Yizhou Wang $^{1\dagger}$ + +$^{1}$ Peking University $^{2}$ Shanghai AI Laboratory + +{wtzhu,maxiaoxuan,libin.liu,yizhou.wang}@pku.edu.cn + +{zyliumy,wuwenyan0503}@gmail.com + +# Abstract + +We present a unified perspective on tackling various human-centric video tasks by learning human motion representations from large-scale and heterogeneous data resources. Specifically, we propose a pretraining stage in which a motion encoder is trained to recover the underlying 3D motion from noisy partial 2D observations. The motion representations acquired in this way incorporate geometric, kinematic, and physical knowledge about human motion, which can be easily transferred to multiple downstream tasks. We implement the motion encoder with a Dual-stream Spatio-temporal Transformer (DSTformer) neural network. It could capture long-range spatio-temporal relationships among the skeletal joints comprehensively and adaptively, exemplified by the lowest 3D pose estimation error so far when trained from scratch. Furthermore, our proposed framework achieves state-of-the-art performance on all three downstream tasks by simply finetuning the pretrained motion encoder with a simple regression head (1-2 layers), which demonstrates the versatility of the learned motion representations. Code and models are available at https://motionbert.github.io/ + +# 1. Introduction + +Perceiving and understanding human activities have long been a core pursuit of machine intelligence. To this end, researchers define various tasks to estimate human-centric semantic labels from videos, e.g. skeleton keypoints [13, 33], action classes [60, 116], and surface meshes [42, 66]. While significant progress has been made in each of these tasks, they tend to be modeled in isolation, rather than as interconnected problems. For example, Spatial Temporal Graph Con + +![](images/56360d2db70b73e01cb534a647d0b0f284177f167c3ee15f582c61819cd2b64b.jpg) +Figure 1. Framework overview. We utilize a motion encoder to learn human motion representations via recovering 3D human motion from corrupted 2D skeleton sequences. To adapt to different downstream tasks, we finetune the pretrained motion representations with a linear layer or a simple MLP. + +volitional Networks (ST-GCN) have been applied to modeling spatio-temporal relationship of human joints in both 3D pose estimation [12, 109] and action recognition [89, 116], but their connections have not been fully explored. Intuitively, these models should all have learned to identify typical human motion patterns, despite being designed for different problems. Nonetheless, current methods fail to mine and utilize such commonalities across the tasks. Ideally, we could develop a unified human-centric video representation that can be shared across all relevant tasks. + +One significant challenge to developing such a representation is the heterogeneity of available data resources. Motion capture (Mocap) systems [36, 71] provide high-fidelity 3D motion data obtained with markers and sensors, but the appearances of captured videos are usually constrained to simple indoor scenes. Action recognition datasets provide annotations of the action semantics, but they either contain no human pose labels [15, 88] or feature limited motion of daily activities [59, 60, 86]. In contrast, in-the-wild human videos offer a vast and diverse range of appearance and motion. However, obtaining precise 2D pose annotations requires considerable effort [3], and acquiring ground-truth (GT) 3D joint locations is almost impossible. Consequently, + +most existing studies focus on a specific task using a single type of human motion data, and they are not able to enjoy the advantages of other data resources. + +In this work, we provide a new perspective on learning human motion representations. The key idea is that we can learn a versatile human motion representation from heterogeneous data resources in a unified manner, and utilize the representation to handle different downstream tasks in a unified way. We present a two-stage framework, consisting of pretraining and finetuning, as depicted in Figure 1. In the pretraining stage, we extract 2D skeleton sequences from diverse motion data sources and corrupt them with random masks and noises. Subsequently, we train the motion encoder to recover the 3D motion from the corrupted 2D skeletons. This challenging pretext task intrinsically requires the motion encoder to i) infer the underlying 3D human structures from its temporal movements; ii) recover the erroneous and missing observations. In this way, the motion encoder implicitly captures human motion commonsense such as joint linkages, anatomical constraints, and temporal dynamics. In practice, we propose Dual-stream Spatio-temporal Transformer (DSTformer) as the motion encoder to capture the long-range relationship among skeleton keypoints. We suppose that the motion representations learned from large-scale and diversified data resources could be shared across different downstream tasks and benefit their performance. Therefore, for each downstream task, we adapt the pretrained motion representations using task-specific training data and supervisory signals with a simple regression head. + +In summary, the contributions of this work are three-fold: 1) We provide a new perspective on solving various human-centric video tasks through a shared framework of learning human motion representations. 2) We propose a pretraining method to leverage the large-scale yet heterogeneous human motion resources and learn generalizable human motion representations. Our approach could take advantage of the precision of 3D mocap data and the diversity of in-the-wild RGB videos at the same time. 3) We design a dual-stream Transformer network with cascaded spatio-temporal self-attention blocks that could serve as a general backbone for human motion modeling. The experiments demonstrate that the above designs enable a versatile human motion representation that can be transferred to multiple downstream tasks, outperforming the task-specific state-of-the-art methods. + +# 2. Related Work + +Learning Human Motion Representations. Early works formulate human motion with Hidden Markov Models [49, 101] and graphical models [47, 92]. Kanazawa et al. [39] design a temporal encoder and a hallucinator to learn representations of 3D human dynamics. Zhang et al. [124] predict future 3D dynamics in a self-supervised manner. Sun et al. [95] further incorporate action labels with an ac + +tion memory bank. From the action recognition perspective, a variety of pretext tasks are designed to learn motion representations in a self-supervised manner, including future prediction [93], jigsaw puzzle [56], skeleton-contrastive [100], speed change [94], cross-view consistency [58], and contrast-reconstruction [110]. Similar techniques are also explored in tasks like motion assessment [31, 80] and motion retargeting [119, 130]. These methods leverage homogeneous motion data, design corresponding pretext tasks, and apply them to a specific downstream task. In this work, we propose a unified pretrain-finetune framework to incorporate heterogeneous data resources and demonstrate its versatility in various downstream tasks. + +3D Human Pose Estimation. Recovering 3D human poses from monocular RGB videos is a classical problem, and the methods can be categorized into two categories. The first is to estimate 3D poses with CNN directly from images [77, 97, 128]. However, one limitation of these approaches is that there is a trade-off between 3D pose precision and appearance diversity due to current data collection techniques. The second category is to extract the 2D pose first, then lift the estimated 2D pose to 3D with a separate neural network. The lifting can be achieved via Fully Connected Network [28, 73], Temporal Convolutional Network (TCN) [21, 83], GCN [12, 27, 109], and Transformer [52, 87, 126, 127]. Our framework is built upon the second category as we use the proposed DSTformer to accomplish 2D-to-3D lifting. + +Skeleton-based Action Recognition. The pioneering works [69, 108, 120] point out the inherent connection between action recognition and human pose estimation. Towards modeling the spatio-temporal relationship among human joints, previous studies mainly employ LSTM [91, 129] and GCN [20, 51, 64, 89, 116]. Most recently, PoseC-conv3D [30] proposes to apply 3D-CNN on the stacked 2D joint heatmaps and achieves improved results. In addition to the fully-supervised action recognition task, NTU-RGB+D-120 [60] brings attention to the challenging one-shot action recognition problem. To this end, SL-DML [76] applies deep metric learning to multi-modal signals. Sabater et al. [85] explores one-shot recognition in therapy scenarios with TCN. We demonstrate that the pretrained motion representations could generalize well to action recognition tasks, and the pretrain-finetune framework is a suitable solution for the one-shot challenges. + +Human Mesh Recovery. Based on the parametric human models such as SMPL [66], many research works [38, 70, 78, 115, 125] focus on regressing the human mesh from a single image. SPIN [44] additionally incorporates fitting the body + +![](images/3676fb971eff88d310a197d85cef8ee9330d9586d994ed8369bbfa462f9db7e4.jpg) +Figure 2. Model architecture. We propose the Dual-stream Spatio-temporal Transformer (DSTformer) as a general backbone for human motion modeling. DSTformer consists of $N$ dual-stream-fusion modules. Each module contains two branches of spatial or temporal MHSA and MLP. The Spatial MHSA models the connection among different joints within a timestep, while the Temporal MHSA models the movement of one joint. + +model to 2D joints in the training loop. Despite their promising per-frame results, these methods yield jittery and unstable results [42, 123] when applied to videos. To improve their temporal coherence, PoseBERT [7] and SmoothNet [123] propose to employ a denoising and smoothing module to the single-frame predictions. Several works [23, 39, 42, 99] take video clips as input to exploit the temporal cues. Another common problem is that paired images and GT meshes are mostly captured in constrained scenarios, which limits the generalization ability of the above methods. To that end, Pose2Mesh [24] proposes to first extract 2D skeletons using an off-the-shelf pose estimator, then lift them to 3D mesh vertices. Our approach is complementary to state-of-the-art human mesh recovery methods and could further improve their temporal coherence with the pretrained motion representations. + +# 3. Method + +# 3.1. Overview + +As discussed in Section 1, our approach consists of two stages, namely unified pretraining and task-specific finetuning. In the first stage, we train a motion encoder to accomplish the 2D-to-3D lifting task, where we use the proposed DSTformer as the backbone. In the second stage, we finetune the pretrained motion encoder and a few new layers on the downstream tasks. We use 2D skeleton sequences as input for both pretraining and finetuning because they could be reliably extracted from all kinds of motion sources [3,9,71,81,96], and is more robust to variations [18,30]. Existing studies have shown the effectiveness of using 2D skeleton sequences for different downstream tasks [24,30,83,102]. We will first introduce the architecture of DSTformer, and then describe the training scheme in detail. + +# 3.2. Network Architecture + +Figure 2 shows the network architecture for 2D-to-3D lifting. Given an input 2D skeleton sequence $\mathbf{x} \in \mathbb{R}^{T \times J \times C_{\mathrm{in}}}$ , we first project it to a high-dimensional feature $\mathbf{F}^0 \in \mathbb{R}^{T \times J \times C_{\mathrm{f}}}$ , then add learnable spatial positional encoding $\mathbf{P}_{\mathrm{pos}}^{\mathrm{S}} \in \mathbb{R}^{1 \times J \times C_{\mathrm{f}}}$ and temporal positional encoding $\mathbf{P}_{\mathrm{pos}}^{\mathrm{T}} \in \mathbb{R}^{T \times 1 \times C_{\mathrm{f}}}$ to it. We then use the sequence-to-sequence model DSTformer to calculate $\mathbf{F}^i \in \mathbb{R}^{T \times J \times C_{\mathrm{f}}} (i = 1, \dots, N)$ where $N$ is the network depth. We apply a linear layer with tanh activation [29] to $\mathbf{F}^N$ to compute the motion representation $\mathbf{E} \in \mathbb{R}^{T \times J \times C_{\mathrm{e}}}$ . Finally, we apply a linear transformation to $\mathbf{E}$ to estimate 3D motion $\hat{\mathbf{X}} \in \mathbb{R}^{T \times J \times C_{\mathrm{out}}}$ . Here, $T$ denotes the sequence length, and $J$ denotes the number of body joints. $C_{\mathrm{in}}, C_{\mathrm{f}}, C_{\mathrm{e}}$ , and $C_{\mathrm{out}}$ denote the channel numbers of input, feature, embedding, and output respectively. We first introduce the basic building blocks of DSTformer, i.e. Spatial and Temporal Blocks with Multi-Head Self-Attention (MHSA), and then explain the DSTformer architecture design. + +Spatial Block. Spatial MHSA (S-MHSA) aims at modeling the relationship among the joints within the same time step. It is defined as + +$$ +\begin{array}{l} \mathrm {S} - \mathrm {M H S A} \left(\mathbf {Q} _ {\mathrm {S}}, \mathbf {K} _ {\mathrm {S}}, \mathbf {V} _ {\mathrm {S}}\right) = \left[ \text {h e a d} _ {1}; \dots ; \text {h e a d} _ {h} \right] \mathbf {W} _ {\mathrm {S}} ^ {P}, \\ \operatorname {h e a d} _ {i} = \operatorname {s o f t m a x} \left(\frac {\mathbf {Q} _ {\mathrm {S}} ^ {i} \left(\mathbf {K} _ {\mathrm {S}} ^ {i}\right) ^ {\prime}}{\sqrt {d _ {K}}}\right) \mathbf {V} _ {\mathrm {S}} ^ {i}, \tag {1} \\ \end{array} +$$ + +where $\mathbf{W}_{\mathrm{S}}^{P}$ is a projection parameter matrix, $h$ is the number of the heads, $i\in 1,\dots ,h$ and ${}^{\prime}$ denotes matrix transpose. We utilize self-attention to get the query Qs, key $\mathbf{K}_S$ , and value $\mathbf{V}_{\mathrm{S}}$ from input per-frame spatial feature $\mathbf{F}_{\mathrm{S}}\in \mathbb{R}^{J\times C_{\mathrm{e}}}$ for each head, + +$$ +\mathbf {Q} _ {\mathrm {S}} ^ {i} = \mathbf {F} _ {\mathrm {S}} \mathbf {W} _ {\mathrm {S}} ^ {(Q, i)}, \mathbf {K} _ {\mathrm {S}} ^ {i} = \mathbf {F} _ {\mathrm {S}} \mathbf {W} _ {\mathrm {S}} ^ {(K, i)}, \mathbf {V} _ {\mathrm {S}} ^ {i} = \mathbf {F} _ {\mathrm {S}} \mathbf {W} _ {\mathrm {S}} ^ {(V, i)}, \tag {2} +$$ + +where $\mathbf{W}_{\mathrm{S}}^{(Q,i)}$ , $\mathbf{W}_{\mathrm{S}}^{(K,i)}$ , $\mathbf{W}_{\mathrm{S}}^{(V,i)}$ are projection matrices, and $d_{K}$ is the feature dimension of $\mathbf{K}_{\mathrm{S}}$ . We apply S-MHSA to + +features of different time steps in parallel. Residual connection and layer normalization (LayerNorm) are used to the S-MHSA result, which is further fed into a multilayer perceptron (MLP), and followed by a residual connection and LayerNorm following [105]. We denote the entire spatial block with MHSA, LayerNorm, MLP, and residual connections by $\mathcal{S}$ . + +Temporal Block. Temporal MHSA (T-MHSA) aims at modeling the relationship across the time steps for a body joint. Its computation process is similar with S-MHSA except that the MHSA is applied to the per-joint temporal feature $\mathbf{F}_{\mathrm{T}} \in \mathbb{R}^{T \times C_{\mathrm{e}}}$ and parallelized over the spatial dimension. + +$$ +\begin{array}{l} \mathrm {T} - \mathrm {M H S A} \left(\mathbf {Q} _ {\mathrm {T}}, \mathbf {K} _ {\mathrm {T}}, \mathbf {V} _ {\mathrm {T}}\right) = \left[ \text {h e a d} _ {1}; \dots ; \text {h e a d} _ {h} \right] \mathbf {W} _ {\mathrm {T}} ^ {P}, \\ \operatorname {h e a d} _ {i} = \operatorname {s o f t m a x} \left(\frac {\mathbf {Q} _ {\mathrm {T}} ^ {i} \left(\mathbf {K} _ {\mathrm {T}} ^ {i}\right) ^ {\prime}}{\sqrt {d _ {K}}}\right) \mathbf {V} _ {\mathrm {T}} ^ {i}, \tag {3} \\ \end{array} +$$ + +where $i \in 1, \ldots, h$ , $\mathbf{Q}_{\mathrm{T}}$ , $\mathbf{K}_{\mathrm{T}}$ , $\mathbf{V}_{\mathrm{T}}$ are computed similar with Formula 2. We denote the entire temporal block by $\mathcal{T}$ . + +Dual-stream Spatio-temporal Transformer. Given spatial and temporal MHSA that captures the intra-frame and inter-frame body joint interactions respectively, we assemble the basic building blocks to fuse the spatial and temporal information in the flow. We design a dual-stream architecture with the following assumptions: 1) Both streams should be capable of modeling the comprehensive spatio-temporal context. 2) Each stream should be specialized in different spatio-temporal aspects. 3) The two streams should be fused together, with the fusion weights dynamically balanced depending on the input spatio-temporal characteristics. + +Hence, we stack the spatial and temporal MHSA blocks in different orders, forming two parallel computation branches. The output features of the two branches are fused using adaptive weights predicted by an attention regressor. The dual-stream-fusion module is then repeated for $N$ times: + +$$ +\mathbf {F} ^ {i} = \boldsymbol {\alpha} _ {\mathrm {S T}} ^ {i} \circ \mathcal {T} _ {1} ^ {i} \left(\mathcal {S} _ {1} ^ {i} \left(\mathbf {F} ^ {i - 1}\right)\right) + \boldsymbol {\alpha} _ {\mathrm {T S}} ^ {i} \circ \mathcal {S} _ {2} ^ {i} \left(\mathcal {T} _ {2} ^ {i} \left(\mathbf {F} ^ {i - 1}\right)\right), \quad i \in 1, \dots , N, \tag {4} +$$ + +where $\mathbf{F}^i$ denotes the feature embedding at depth $i$ , $\circ$ denotes element-wise production. Orders of $\mathcal{S}$ and $\mathcal{T}$ blocks are shown in Figure 2, and different blocks do not share weights. Adaptive fusion weights $\alpha_{\mathrm{ST}}, \alpha_{\mathrm{TS}} \in \mathbb{R}^{N \times T \times J}$ are given by + +$$ +\alpha_ {\mathrm {S T}} ^ {i}, \alpha_ {\mathrm {T S}} ^ {i} = \operatorname {s o f t m a x} \left(\mathcal {W} \left(\left[ \mathcal {T} _ {1} ^ {i} \left(\mathcal {S} _ {1} ^ {i} \left(\mathbf {F} ^ {i - 1}\right)\right), \mathcal {S} _ {2} ^ {i} \left(\mathcal {T} _ {2} ^ {i} \left(\mathbf {F} ^ {i - 1}\right)\right) \right]\right)\right), \tag {5} +$$ + +where $\mathcal{W}$ is a learnable linear transformation. $[,]$ denotes concatenation. + +# 3.3. Unified Pretraining + +We address two key challenges when designing the unified pretraining framework: 1) How to learn a powerful + +motion representation with a universal pretext task. 2) How to utilize large-scale but heterogeneous human motion data in all kinds of formats. + +For the first challenge, we follow the successful practices in language [11, 29, 84] and vision [6, 34] modeling to construct the supervision signals, i.e. mask part of the input and use the encoded representations to reconstruct the whole input. Note that such "cloze" task naturally exists in human motion analysis, that is to recover the lost depth information from the 2D visual observations, i.e. 3D human pose estimation. Inspired by this, we leverage the large-scale 3D mocap data [71] and design a 2D-to-3D lifting pretext task. We first extract the 2D skeleton sequences $\mathbf{x}$ by projecting the 3D motion orthographically. Then, we corrupt $\mathbf{x}$ by randomly masking and adding noise to produce the corrupted 2D skeleton sequences, which also resemble the 2D detection results as it contains occlusions, detection failures, and errors. Both joint-level and frame-level masks are applied with certain probabilities. We use the aforementioned motion encoder to get motion representation $\mathbf{E}$ and reconstruct 3D motion $\hat{\mathbf{X}}$ . We then compute the joint loss $\mathcal{L}_{3\mathrm{D}}$ between $\hat{\mathbf{X}}$ and GT 3D motion $\mathbf{X}$ . We also add the velocity loss $\mathcal{L}_{\mathrm{O}}$ following previous works [83, 126]. The 3D reconstruction losses are thus given by + +$$ +\mathcal {L} _ {\mathrm {3 D}} = \sum_ {t = 1} ^ {T} \sum_ {j = 1} ^ {J} \| \hat {\mathbf {X}} _ {t, j} - \mathbf {X} _ {t, j} \| _ {2}, \quad \mathcal {L} _ {\mathrm {O}} = \sum_ {t = 2} ^ {T} \sum_ {j = 1} ^ {J} \| \hat {\mathbf {O}} _ {t, j} - \mathbf {O} _ {t, j} \| _ {2}, \tag {6} +$$ + +where $\hat{\mathbf{O}}_t = \hat{\mathbf{X}}_t - \hat{\mathbf{X}}_{t - 1}$ $\mathbf{O}_t = \mathbf{X}_t - \mathbf{X}_{t - 1}$ + +For the second challenge, we notice that 2D skeletons could serve as a universal medium as they can be extracted from all sorts of motion data sources. We further incorporate in-the-wild RGB videos into the 2D-to-3D lifting framework for unified pretraining. For RGB videos, the 2D skeletons $\mathbf{x}$ could be given by manual annotation [3] or 2D pose estimators [13, 96], and the depth channel of the extracted 2D skeletons is intrinsically "masked". Similarly, we add extra masks and noises to degrade $\mathbf{x}$ (if $\mathbf{x}$ already contains detection noise, only masking is applied). As 3D motion GT $\mathbf{X}$ is not available for these data, we apply a weighted 2D re-projection loss which is calculated by + +$$ +\mathcal {L} _ {\mathrm {2 D}} = \sum_ {t = 1} ^ {T} \sum_ {j = 1} ^ {J} \boldsymbol {\delta} _ {t, j} \| \hat {\mathbf {x}} _ {t, j} - \mathbf {x} _ {t, j} \| _ {2}, \tag {7} +$$ + +where $\hat{\mathbf{x}}$ is the 2D orthogonal projection of the estimated 3D motion $\hat{\mathbf{X}}$ , and $\delta \in \mathbb{R}^{T\times J}$ is given by visibility annotation or 2D detection confidence. + +The total pretraining loss is computed by + +$$ +\mathcal {L} = \underbrace {\mathcal {L} _ {\mathrm {3 D}} + \lambda_ {\mathrm {O}} \mathcal {L} _ {\mathrm {O}}} _ {\text {f o r 3 D d a t a}} + \underbrace {\mathcal {L} _ {\mathrm {2 D}}} _ {\text {f o r 2 D d a t a}}, \tag {8} +$$ + +where $\lambda_{\mathrm{O}}$ is a constant coefficient to balance the losses. + +# 3.4. Task-specific Finetuning + +The learned feature embedding $\mathbf{E}$ serves as a 3D-aware and temporal-aware human motion representation. For downstream tasks, we adopt the minimalist design principle, i.e. implementing a shallow downstream network and training without bells and whistles. In practice, we use an extra linear layer or an MLP with one hidden layer. We then finetune the whole network end-to-end. + +3D Pose Estimation. As we utilize 2D-to-3D lifting as the pretext task, we simply reuse the whole pretrained network. During finetuning, the input 2D skeletons are estimated from videos without extra masks or noises. + +Skeleton-based Action Recognition. We directly apply a global average pooling over different persons and timesteps. The result is then fed into an MLP with one hidden layer. The network is trained with cross-entropy classification loss. For one-shot learning, we apply a linear layer after the pooled features to extract clip-level action representation. We introduce the detailed setup of one-shot learning in Section 4.4. + +Human Mesh Recovery. We use SMPL [66] model to represent the human mesh and regress its parameters. The SMPL model consists of pose parameters $\theta \in \mathbb{R}^{72}$ and shape parameters $\beta \in \mathbb{R}^{10}$ , and calculates the 3D mesh as $\mathcal{M}(\theta, \beta) \in \mathbb{R}^{6890 \times 3}$ . To regress the pose parameters for each frame, we feed the motion embeddings $\mathbf{E}$ to an MLP with one hidden layer and get $\hat{\pmb{\theta}} \in \mathbb{R}^{T \times 72}$ . To estimate shape parameters, considering that the human shape over a video sequence is supposed to be consistent, we first perform an average pooling of $\mathbf{E}$ over the temporal dimension and then feed it into another MLP to regress a single $\hat{\beta}$ and then expand it to the entire sequence as $\hat{\beta} \in \mathbb{R}^{T \times 10}$ . The shape MLP has the same architecture as the pose regression one, and they are initialized with the mean shape and pose, respectively, as in [42]. The overall loss is computed as + +$$ +\mathcal {L} = \lambda_ {\mathrm {3 D}} ^ {\mathrm {m}} \mathcal {L} _ {\mathrm {3 D}} ^ {\mathrm {m}} + \lambda_ {\theta} \mathcal {L} _ {\theta} + \lambda_ {\beta} \mathcal {L} _ {\beta} + \lambda_ {\mathrm {n}} \mathcal {L} _ {\text {n o r m}} + \lambda_ {\mathrm {O}} ^ {\mathrm {m}} \mathcal {L} _ {\mathrm {O}} ^ {\mathrm {m}}, \tag {9} +$$ + +where each term is calculated as + +$$ +\mathcal {L} _ {\mathrm {3 D}} ^ {\mathrm {m}} = \left\| \hat {\mathbf {X}} ^ {\mathrm {m}} - \mathbf {X} ^ {\mathrm {m}} \right\| _ {1}, \quad \mathcal {L} _ {\theta} = \left\| \hat {\boldsymbol {\theta}} - \boldsymbol {\theta} \right\| _ {1}, \quad \mathcal {L} _ {\beta} = \left\| \hat {\boldsymbol {\beta}} - \boldsymbol {\beta} \right\| _ {1}, +$$ + +$$ +\mathcal {L} _ {\text {n o r m}} = \| \hat {\boldsymbol {\theta}} \| _ {2} + \| \hat {\boldsymbol {\beta}} \| _ {2}, \quad \mathcal {L} _ {\mathrm {O}} ^ {\mathrm {m}} = \| \hat {\mathbf {O}} ^ {\mathrm {m}} - \mathbf {O} ^ {\mathrm {m}} \| _ {2}. \tag {10} +$$ + +Note that each 3D pose in motion $\mathbf{X}^{\mathrm{m}}$ at frame $t$ is regressed from mesh vertices by $\mathbf{X}_t^{\mathrm{m}} = \mathbf{J}\mathcal{M}(\pmb {\theta}_t,\pmb {\beta}_t)$ , where $\mathbf{J}\in \mathbb{R}^{J\times 6890}$ is a pre-defined matrix [9]. $\mathbf{O}^{\mathrm{m}} = \mathbf{X}_{t + 1}^{\mathrm{m}} - \mathbf{X}_{t}^{\mathrm{m}}$ , $\hat{\mathbf{O}}^{\mathrm{m}} = \hat{\mathbf{X}}_{t + 1}^{\mathrm{m}} - \hat{\mathbf{X}}_t^{\mathrm{m}}$ . $\lambda_{3\mathrm{D}}^{\mathrm{m}},\lambda_{\theta},\lambda_{\beta},\lambda_{\mathrm{n}}$ and $\lambda_0^{\mathrm{m}}$ are constant coefficients to balance the training loss. + +# 4. Experiments + +# 4.1. Implementation + +We implement the proposed motion encoder DSTformer with depth $N = 5$ , number of heads $h = 8$ , feature size $C_{\mathrm{f}} = 512$ , embedding size $C_{\mathrm{e}} = 512$ . For pretraining, we use sequence length $T = 243$ . The pretrained model could handle different input lengths thanks to the Transformer-based backbone. During finetuning, we set the backbone learning rate to be $0.1 \times$ of the new layer learning rate. We introduce the experiment datasets in the following sections respectively. Please refer to the appendix for more experimental details. + +# 4.2. Pretraining + +We collect diverse and realistic 3D human motion from two datasets, Human3.6M [36] and AMASS [71]. Human3.6M [36] is a commonly used indoor dataset for 3D human pose estimation which contains 3.6 million video frames of professional actors performing daily actions. Following previous works [73, 83], we use subjects 1, 5, 6, 7, 8 for training, and subjects 9, 11 for testing. AMASS [71] integrates most existing marker-based Mocap datasets [1,2,4,10,14,17,32,35,48,65,67,72,79,90,103,104] and parameterizes them with a common representation. We do not use the images or 2D detection results of the two datasets during pretraining as Mocap datasets usually do not provide raw videos. Instead, we use orthographic projection to get the uncorrupted 2D skeletons. We further incorporate two in-the-wild RGB video datasets PoseTrack [3] (annotated) and InstaVariety [39] (unannotated) for higher motion diversity. We align the body keypoint definitions with Human3.6M and calibrate the camera coordinates to pixel coordinates following [26]. We randomly zero out $15\%$ joints, and sample noises from a mixture of Gaussian and uniform distributions [16]. We first train on 3D data only for 30 epochs, then train on both 3D data and 2D data for 60 epochs, following the curriculum learning practices [8, 111]. + +# 4.3. 3D Pose Estimation + +We evaluate the 3D pose estimation performance on Human3.6M [36] and report the mean per joint position error (MPJPE) in millimeters, which measures the average distance between the predicted joint positions and the GT after aligning the root joint. We also compute the mean per-joint velocity error (MPJVE) to evaluate the temporal smoothness following previous works [126, 127]. We use the Stacked Hourglass (SH) networks [81] to extract the 2D skeletons from videos, and finetune the entire network on Human3.6M [36] training set. In addition, we train a separate model of the same architecture, but with random initialization rather than pretrained weights. As shown in Table 1 (top), the model trained from scratch outperforms + +
MethodTDire.Disc.EatGreetPhonePhotoPosePurch.SitSitDSmokeWaitWalkDWalkWalkTAvg
Martinez et al. [73] ICCV'17151.856.258.159.069.578.455.258.174.094.662.359.165.149.552.462.9
Pavlakos et al. [82] CVPR'18148.554.454.452.059.465.349.952.965.871.156.652.960.944.747.856.2
LCN [27] ICCV'19146.852.344.750.452.968.949.646.460.278.951.250.054.840.443.352.7
Xu et al. [114] CVPR'21145.249.947.550.954.966.148.546.359.771.551.448.653.939.944.151.9
VideoPose3D [83] CVPR'1924345.246.743.345.648.155.144.644.357.365.847.144.049.032.833.946.8
Cai et al. [12] ICCV'19744.647.445.648.850.859.047.243.957.961.949.746.651.337.139.448.8
Yeh et al. [122] NeurIPS'1924344.846.143.346.449.055.244.644.058.362.747.143.948.632.733.346.7
Liu et al. [63] CVPR'2024341.844.841.144.947.454.143.442.256.263.645.343.545.331.332.245.1
* Cheng et al. [21] AAAI'2012836.238.142.735.938.245.736.842.045.951.341.841.543.833.128.640.1
* UGCN [109] ECCV'209638.241.045.939.741.451.441.641.452.057.441.844.441.633.130.042.6
† PoseFormer [127] ICCV'218141.544.839.842.546.551.642.142.053.360.745.543.346.131.832.244.3
* Wehrbein et al. [112] ICCV'2120038.542.539.941.746.551.639.940.849.556.845.346.446.837.840.444.3
† MHFormer [52] CVPR'2235139.243.140.140.944.951.240.641.353.560.343.741.143.829.830.643.0
*† MixSTE [126] CVPR'2224336.739.036.539.440.244.939.836.947.954.839.637.839.329.730.639.8
† P-STMO [87] ECCV'2224338.442.139.840.245.248.940.438.353.857.343.941.642.229.329.342.1
† Ours (scratch)24336.338.738.633.642.150.136.235.750.156.641.337.437.725.626.539.2
† Ours (finetune)24336.137.535.832.140.346.336.135.346.953.939.536.335.825.125.337.5
MethodTDire.Disc.EatGreetPhonePhotoPosePurch.SitSitDSmokeWaitWalkDWalkWalkTAvg
Martinez et al. [73] ICCV'17137.744.440.342.148.254.944.442.154.658.045.146.447.636.440.445.5
LCN [27] ICCV'19136.338.829.737.834.642.539.832.536.239.534.438.438.231.334.236.3
Xu et al. [114] CVPR'21135.838.131.035.335.843.237.331.738.445.535.436.736.827.930.735.8
UGCN [109] ECCV'209623.025.722.822.624.130.624.924.531.135.025.624.325.119.818.425.6
† PoseFormer [127] ICCV'218130.033.629.931.030.233.334.831.437.838.631.731.529.023.323.131.3
† MHFormer [52] CVPR'2235127.732.129.128.930.033.933.031.237.039.330.031.029.422.223.030.5
† MixSTE [126] CVPR'2224321.622.020.421.020.824.324.721.926.924.921.221.520.814.715.621.6
† P-STMO [87] ECCV'2224328.530.128.627.929.833.231.327.836.037.429.729.528.121.021.029.3
† Ours (scratch)24316.719.917.116.517.418.819.320.524.022.118.616.816.710.811.517.8
† Ours (finetune)24315.917.316.914.616.818.618.618.422.021.817.316.916.110.511.416.9
MethodTDire.Disc.EatGreetPhonePhotoPosePurch.SitSitDSmokeWaitWalkDWalkWalkTAvg
VideoPose3D [83] CVPR'192433.03.12.23.42.32.72.73.12.12.92.32.43.73.12.82.8
† PoseFormer [127] ICCV'21813.23.42.63.62.63.02.93.22.63.32.72.73.83.22.93.1
*† MixSTE [126] CVPR'222432.52.71.92.81.92.22.32.61.62.21.92.03.12.62.22.3
† Ours (scratch)2431.82.11.52.01.51.91.82.11.21.81.51.42.62.01.71.8
† Ours (finetune)2431.71.91.41.91.41.71.71.91.11.61.41.32.41.91.61.7
+ +Table 1. Quantitative comparison of 3D human pose estimation on Human3.6M. (Top) MPJPE (mm) using detected 2D pose sequences. (Middle) MPJPE (mm) using GT 2D pose sequences. (Bottom) MPJVE (mm) using detected 2D pose sequences. $T$ denotes the clip length used by the method. We select the best results reported by each work. \* denotes using HRNet [96] for 2D detection. $\dagger$ denotes implemented with a spatio-temporal Transformer design. The best and second-best results are highlighted in bold and underlined formats. + +previous methods including other Transformer-based designs with spatio-temporal modeling. It shows the effectiveness of the proposed DSTformer in terms of learning 3D geometric structures and temporal dynamics. To further evaluate the upper bound of the models' capability, we compare the performance when using 2D GT pose sequences as input, which gets rid of the influence of different 2D detectors. As shown in Table 1 (middle), our models significantly outperform all the previous approaches. Table 1 (bottom) shows that both of our models also surpass previous works in terms of MPJVE, implying better temporal coherence. We attribute the performance advantage of our scratch model to the proposed DSTformer design. We include more comparisons and analysis to demonstrate the advantage of DSTformer with regard to other spatio-temporal architectures in Section 4.6 and supplementary materials. Additionally, our method achieves lower errors with the proposed pretraining stage. + +# 4.4. Skeleton-based Action Recognition + +We further explore the possibility to learn action semantics with the pretrained human motion representations. We + +use the human action dataset NTU-RGB+D [86] which contains 57K videos of 60 action classes, and we follow the data splits Cross-subject (X-Sub) and Cross-view (X-View). The dataset has an extended version, NTU-RGB+D-120 [60], which contains 114K videos of 120 action classes. We follow the suggested One-shot action recognition protocol on NTU-RGB+D-120. For both datasets, we use HRNet [96] to extract 2D skeletons following [30]. Similarly, we train a scratch model with random initialization for comparison. As Table 2 (left) shows, our methods are comparable or superior to the state-of-the-art approaches. Notably, the pretraining stage accounts for a large performance gain. + +Additionally, we delve into the one-shot setting which holds significant practical importance. Real-world applications often require fine-grained action recognition in specific domains such as education, sports, and healthcare. Unfortunately, the action classes in these scenarios are not typically defined in public datasets. As a result, only limited annotations for these novel action classes are available, making accurate recognition a challenging task. As proposed in [60], we report the results on the evaluation set of 20 novel classes + +
MethodX-SubX-View
ST-GCN [116] AAAI'1881.588.3
2s-AGCN [89] CVPR'1988.595.1
MS-G3D [64] CVPR'2091.596.2
Shift-GCN [20] CVPR'2090.796.5
CrosSCLR [58] CVPR'2186.292.5
MCC (finetune) [94] ICCV'2189.796.3
SCC (finetune) [118] ICCV'2188.094.9
UNIK (finetune) [117] BMVC'2186.894.4
CTR-GCN [19] ICCV'2192.496.8
PoseConv3D [30] CVPR'2293.195.7
Ours (scratch)87.794.1
Ours (finetune)93.097.2
+ +
MethodAccuracy
ST-LSTM + AvgPool [61]42.9
ST-LSTM + FC [62]42.1
ST-LSTM + Attention [62]41.0
APSR [60]45.3
TCN OneShot [85]46.5
SL-DML [76]50.9
Skeleton-DML [75]54.2
Ours (scratch)61.0
Ours (finetune)67.4
+ +Table 2. Quantitative comparison of skeleton-based action recognition accuracy. (Left) Cross-subject and cross-view recognition accuracy on NTU-RGB+D. All the methods are evaluated using only the "joint" modality with 1-clip sampling for the fairness of comparison. (Right) One-shot recognition accuracy on NTU-RGB+D-120. All results are top-1 accuracy (\%). + +
MethodInputTHuman3.6M3DPW
MPVE↓MPJPE↓PA-MPJPE↓MPVE↓MPJPE↓PA-MPJPE↓
HMR [38] CVPR'18image1-88.056.8-130.081.3
† SPIN [44] ICCV'19image182.359.439.3129.1100.959.1
Pose2Mesh [24] ECCV'202D pose185.364.948.7109.391.460.1
I2L-MeshNet [78] ECCV'20image1-55.741.7110.193.258.6
† HybrIK [50] CVPR'21image158.147.430.182.471.341.9
METRO [54] CVPR'21image1-54.036.788.277.147.9
Mesh Graphormer [55] ICCV'21image1-51.234.587.774.745.6
PARE [43] ICCV'21image1---88.674.546.5
ROMP [98] ICCV'21image1---108.391.354.9
PyMAF [125] ICCV'21image1-57.740.5110.192.858.9
ProHMR [46] ICCV'21image1--41.2--59.8
OCHMR [40] CVPR'22image1---107.189.758.3
3DCrowdNet [25] CVPR'22image1---98.381.751.5
CLIFF [53] ECCV'22image1-47.132.781.269.043.0
FastMETRO [22] ECCV'22image1-52.233.784.173.544.6
VisDB [121] ECCV'22image1-51.034.585.573.544.9
TemporalContext [5] CVPR'19video32-77.854.3--72.2
HMMR [39] CVPR'19video20--56.9139.3116.572.6
DSD-SATN [99] ICCV'19video9-59.142.4--69.5
VIBE [42] CVPR'20video16-65.641.499.182.951.9
TCMR [23] CVPR'21video16-62.341.1102.986.552.7
† MAED [107] ICCV'21video1684.160.438.393.379.045.7
MPS-Net [113] CVPR'22video16-69.447.499.784.352.1
* PoseBERT [7] TPAMI'22 (+SPIN [44])video16-----57.3 ↓ 2.3
* SmoothNet [123] ECCV'22 (+SPIN [44])video32-67.5 ↓ 1.046.3 ↓ 0.2-86.7 ↓ 0.952.7 ↓ 0.6
Ours (scratch)2D motion1675.762.841.099.185.550.2
Ours (finetune)2D motion1665.553.834.988.176.947.2
Ours (finetune) + SPIN [44]video1663.7 ↓ 18.652.2 ↓ 7.235.7 ↓ 3.692.8 ↓ 36.379.6 ↓ 21.348.2 ↓ 10.9
Ours (finetune) + MAED [107]video1666.8 ↓ 17.354.8 ↓ 5.636.4 ↓ 1.984.4 ↓ 8.972.3 ↓ 6.742.3 ↓ 3.4
Ours (finetune) + HybrIK [50]video1652.6 ↓ 5.543.1 ↓ 4.327.8 ↓ 2.379.4 ↓ 3.068.8 ↓ 2.540.6 ↓ 1.3
+ +Table 3. Quantitative comparison of human mesh recovery on Human3.6M and 3DPW datasets. $T$ denotes the clip length used by the method. $\dagger$ denotes the results obtained with official model weights. The rest are all officially reported results. The gains in \* correspond to different re-implemented SPIN [44] results. + +using only 1 labeled video for each class. The auxiliary set contains the other 100 classes, and all samples of these classes can be used. We train the model on the auxiliary set using the supervised contrastive learning technique [41]. For a batch of auxiliary data, samples of the same class are pulled together, while samples of different classes are pushed away in the action embedding space. During the evaluation, we calculate the cosine distance between the test examples and the exemplars, and use 1-nearest neighbor to determine the class. Table 2 (right) illustrates that the proposed models outperform state-of-the-art by a considerable margin. Moreover, + +it is noteworthy that our pretrained model achieves optimal performance with only 1-2 epochs of fine-tuning. Our results indicate that the pretraining stage is effective in learning a robust motion representation that generalizes well to novel downstream tasks, even with limited data annotations. + +# 4.5. Human Mesh Recovery + +We conduct experiments on Human3.6M [36] and 3DPW [106] datasets and additionally add COCO [57] dataset during training following [42, 54, 107]. We keep the same training and test split for both datasets as in [73] (Section 4.2) + +![](images/99926cb7f99b2aa12f2d0f82f5a5fb3dc8f26e752f2621502e2ff4ba38572c6c.jpg) +Figure 3. Learning curves of finetuning and training from scratch. + +![](images/4f844dffe3f2829686e24b451db2b92823e16ae4c8a34955ecae190f275bd10e.jpg) + +![](images/8e20cd4f690c14c7f4837e5abfb033bea35a2dbb051291305ea0456e132db5a0.jpg) + +
Backbone (frozen)MPJPE ↓ (3D pose)MPVE ↓ (mesh)Accuracy ↑ (action x-view)Accuracy↑ (action 1-shot)
Random404.4mm114.4mm47.6%46.8%
Pretrained40.3mm72.1mm87.3%60.7%
+ +and [42, 54, 107], respectively. Following the common practice [38, 42, 45, 107], we report MPJPE (mm) and PA-MPJPE (mm) of 14 joints obtained by $\mathbf{J}\mathcal{M}(\theta ,\beta)$ . PA-MPJPE calculates MPJPE after aligning with GT in translation, rotation, and scale. We further report the mean per vertex error (MPVE) (mm) of the mesh $\mathcal{M}(\theta ,\beta)$ , which measures the average distance between the estimated and GT vertices after aligning the root joint. Note that most previous works [23, 38, 42, 44, 50, 54, 68, 107] use more datasets other than COCO [57] during training, such as LSP [37], MPI-INF-3DHP [74], etc., while we do not. Table 3 demonstrates that our finetuned model delivers competitive results on both Human3.6M and 3DPW datasets, surpassing all the state-of-the-art video-based methods, including MAED [107], especially on the MPVE error. Nonetheless, we note that estimating full-body mesh from sparse 2D keypoints alone [9, 24] is an ill-posed problem because it lacks human shape information. In light of this, we propose a hybrid approach that leverages the strengths of both our framework (coherent motion) and RGB-based methods (accurate shape). We introduce a refiner module that can be easily integrated with existing image/video-based methods, similar to [7, 123]. Specifically, our refiner module is an MLP that takes the combination of our pretrained motion representations and an initial prediction, regressing a residual in joint rotations. Our approach effectively improves the state-of-the-art methods [44, 50, 107] and achieves the lowest error to date. + +# 4.6. Ablation Studies + +Finetune vs. Scratch. We compare the training progress of finetuning the pretrained model and training from scratch. As Figure 3 shows, models initialized with pretrained weights demonstrate superior performance and faster convergence on all three tasks. This observation suggests that the pretrained model learns transferable knowledge about hu + +Table 4. Comparison of partial finetuning. + +
PretrainNoiseMask2DMPJPE↓(3D pose)MPVE↓(mesh)Accuracy↑(action x-sub)
----39.2mm75.7mm87.7%
✓---38.8mm70.6mm89.4%
✓✓--38.1mm68.4mm90.7%
✓✓✓-37.4mm67.8mm91.9%
✓✓✓✓37.5mm65.5mm93.0%
+ +Table 5. Comparison of pretraining strategies. + +man motion, facilitating the learning of multiple downstream tasks. + +Partial Finetuning. In addition to end-to-end finetuning, we freeze the motion encoder backbone and only train the regression head for each downstream task. To verify the effectiveness of the pretrained motion representations, we compared the pretrained motion encoder with a randomly initialized motion encoder. We report results of 3D pose and mesh on Human3.6M, action on NTU-RGB+D and NTU-RGB+D-120 (same for the tables below). It can be seen in Table 4 that based on the frozen pretrained motion representations, our method still achieves competitive performance on multiple downstream tasks and shows a large improvement compared to the baseline. Pretraining and partial finetuning make it possible for all the downstream tasks to share the same backbone, significantly reducing computation overhead for applications requiring multi-task inference. + +Pretraining Strategies. We evaluate how different pretraining strategies influence the performance of downstream tasks. Starting from the scratch baseline, we apply the proposed strategies one by one. As shown in Table 5, a vanilla 2D-to-3D pretraining stage brings benefits to all the downstream tasks. Introducing corruptions additionally improves the learned motion embeddings. Unified pretraining with in-the-wild videos (w. 2D) enjoys higher motion diversity, which further helps several downstream tasks. + +Pretraining with Different Backbones. We further study the universality of the proposed pretraining approach. We + +
SettingMPJPE ↓ (3D pose)MPVE ↓ (mesh)Accuracy ↑ (action x-view)Accuracy↑ (action 1-shot)
TCN (scratch)50.1mm92.6mm91.5%52.4%
TCN (finetune)47.9mm86.3mm92.8%59.9%
PoseFormer (scratch)44.8mm85.9mm94.2%57.4%
PoseFormer (finetune)41.5mm80.5mm95.9%60.7%
+ +Table 6. Comparison of different backbones. + +
Arch.(a)(b)(c)(d)(e)(f)
DesignS-TT-SS + TST-MHSAS-T + T-S(Average)S-T + T-S(Adaptive)
MPJPE ↓40.58±0.3141.05±0.2441.76±0.2241.54±0.3539.87±0.3239.25±0.27
+ +Table 7. Comparison of model architecture variants. All the methods are trained on Human3.6M from scratch over 5 runs and measured by MPJPE (mm) with mean and standard deviation. + +replace the motion encoder backbone with two variants: TCN [83] and PoseFormer [127]. The models are slightly modified to a seq2seq version, while all the configurations for pretraining and finetuning are simply followed. Table 6 shows that the proposed approach consistently benefits different backbone models on different tasks. + +Model Architecture. Finally, we study the design choices of DSTformer. From (a) to (f) in Table 7, we compare different structure designs of the basic Transformer module. (a) and (b) are single-stream versions with different orders. (a) is conceptually similar to PoseFormer [127], MH-Former [52], and MixSTE [126]. (c) limits each stream to either temporal or spatial modeling before fusion and is similar to MAED [107]. (d) directly connects S-MHSA and T-MHSA without the MLP in between and is similar to the MSA-T variant in MAED [107]. (e) replaces the adaptive fusion with average pooling on two streams. (f) is the proposed DSTformer design. The result statistically confirms our design principles that both streams should be capable and meanwhile complementary, as introduced in Section 3.2. In addition, we find out that pairing each self-attention block with an MLP is crucial, as it could project the learned feature interactions and bring nonlinearity. In general, we design the model architecture for the 3D pose estimation task and apply it to all other tasks without additional adjustment. + +# 5. Conclusion + +In this work, we provide a unified perspective to tackling various human-centric video tasks. We develop a pretraining approach to learn human motion representations from large-scale and heterogeneous data sources. We also propose DSTformer as a universal human motion encoder. Experimental results on multiple benchmarks demonstrate the versatility of the learned motion representations. Future work could explore fusing the learned motion representations with generic video architectures as a human-centric semantic fea + +ture and applying it to more tasks (e.g., action assessment, segmentation). + +Acknowledgement This work was partially supported by MOST-2022ZD0114900. We would like to thank Hai Ci and Jiefeng Li for their exceptional support. + +# References + +[1] Advanced Computing Center for the Arts and Design. ACCAD MoCap Dataset. +[2] Ijaz Akhter and Michael J. Black. Pose-conditioned joint angle limits for 3D human pose reconstruction. In CVPR, pages 1446-1455, June 2015. +[3] Mykhaylo Andriluka, Umar Iqbal, Eldar Insafutdinov, Leonid Pishchulin, Anton Milan, Juergen Gall, and Bernt Schiele. Posetrack: A benchmark for human pose estimation and tracking. In CVPR, pages 5167-5176, 2018. +[4] Andreas Aristidou, Ariel Shamir, and Yiorgos Chrysanthou. 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In AAAI, 2022. \ No newline at end of file diff --git a/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/images.zip b/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..cac858ac222e4718cf598aa8bd84e2caf2643683 --- /dev/null +++ b/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:e07dd86b04f0d0e8110f882bf0f849689132b219a28169e466426150fca763d2 +size 644538 diff --git a/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/layout.json b/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..dc1fb3c5ef23a50e112c60902e4d25ff55e73ec3 --- /dev/null +++ b/2023/MotionBERT_ A Unified Perspective on Learning Human Motion Representations/layout.json @@ -0,0 +1,11324 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 48, + 103, + 547, + 122 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 103, + 547, + 122 + ], + "spans": [ + { + "bbox": [ + 48, + 103, + 547, + 122 + ], + "type": "text", + "content": "MotionBERT: A Unified Perspective on Learning Human Motion Representations" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "spans": [ + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "text", + "content": "Wentao Zhu" + }, + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "text", + "content": " Xiaoxuan Ma" + }, + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "text", + "content": " Zhaoyang Liu" + }, + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "text", + "content": " Libin Liu" + }, + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "text", + "content": " Wayne Wu" + }, + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "text", + "content": " Yizhou Wang" + }, + { + "bbox": [ + 66, + 148, + 529, + 165 + ], + "type": "inline_equation", + "content": "^{1\\dagger}" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 173, + 172, + 419, + 189 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 173, + 172, + 419, + 189 + ], + "spans": [ + { + "bbox": [ + 173, + 172, + 419, + 189 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 173, + 172, + 419, + 189 + ], + "type": "text", + "content": " Peking University " + }, + { + "bbox": [ + 173, + 172, + 419, + 189 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 173, + 172, + 419, + 189 + ], + "type": "text", + "content": " Shanghai AI Laboratory" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 173, + 198, + 419, + 209 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 173, + 198, + 419, + 209 + ], + "spans": [ + { + "bbox": [ + 173, + 198, + 419, + 209 + ], + "type": "text", + "content": "{wtzhu,maxiaoxuan,libin.liu,yizhou.wang}@pku.edu.cn" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 219, + 215, + 375, + 225 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 219, + 215, + 375, + 225 + ], + "spans": [ + { + "bbox": [ + 219, + 215, + 375, + 225 + ], + "type": "text", + "content": "{zyliumy,wuwenyan0503}@gmail.com" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 143, + 254, + 192, + 266 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 254, + 192, + 266 + ], + "spans": [ + { + "bbox": [ + 143, + 254, + 192, + 266 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 280, + 290, + 531 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 280, + 290, + 531 + ], + "spans": [ + { + "bbox": [ + 47, + 280, + 290, + 531 + ], + "type": "text", + "content": "We present a unified perspective on tackling various human-centric video tasks by learning human motion representations from large-scale and heterogeneous data resources. Specifically, we propose a pretraining stage in which a motion encoder is trained to recover the underlying 3D motion from noisy partial 2D observations. The motion representations acquired in this way incorporate geometric, kinematic, and physical knowledge about human motion, which can be easily transferred to multiple downstream tasks. We implement the motion encoder with a Dual-stream Spatio-temporal Transformer (DSTformer) neural network. It could capture long-range spatio-temporal relationships among the skeletal joints comprehensively and adaptively, exemplified by the lowest 3D pose estimation error so far when trained from scratch. Furthermore, our proposed framework achieves state-of-the-art performance on all three downstream tasks by simply finetuning the pretrained motion encoder with a simple regression head (1-2 layers), which demonstrates the versatility of the learned motion representations. Code and models are available at https://motionbert.github.io/" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 556, + 128, + 569 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 556, + 128, + 569 + ], + "spans": [ + { + "bbox": [ + 47, + 556, + 128, + 569 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 577, + 288, + 673 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 577, + 288, + 673 + ], + "spans": [ + { + "bbox": [ + 46, + 577, + 288, + 673 + ], + "type": "text", + "content": "Perceiving and understanding human activities have long been a core pursuit of machine intelligence. To this end, researchers define various tasks to estimate human-centric semantic labels from videos, e.g. skeleton keypoints [13, 33], action classes [60, 116], and surface meshes [42, 66]. While significant progress has been made in each of these tasks, they tend to be modeled in isolation, rather than as interconnected problems. For example, Spatial Temporal Graph Con" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 307, + 253, + 542, + 361 + ], + "blocks": [ + { + "bbox": [ + 307, + 253, + 542, + 361 + ], + "lines": [ + { + "bbox": [ + 307, + 253, + 542, + 361 + ], + "spans": [ + { + "bbox": [ + 307, + 253, + 542, + 361 + ], + "type": "image", + "image_path": "56360d2db70b73e01cb534a647d0b0f284177f167c3ee15f582c61819cd2b64b.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 363, + 548, + 418 + ], + "lines": [ + { + "bbox": [ + 304, + 363, + 548, + 418 + ], + "spans": [ + { + "bbox": [ + 304, + 363, + 548, + 418 + ], + "type": "text", + "content": "Figure 1. Framework overview. We utilize a motion encoder to learn human motion representations via recovering 3D human motion from corrupted 2D skeleton sequences. To adapt to different downstream tasks, we finetune the pretrained motion representations with a linear layer or a simple MLP." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 437, + 547, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 547, + 557 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 547, + 557 + ], + "type": "text", + "content": "volitional Networks (ST-GCN) have been applied to modeling spatio-temporal relationship of human joints in both 3D pose estimation [12, 109] and action recognition [89, 116], but their connections have not been fully explored. Intuitively, these models should all have learned to identify typical human motion patterns, despite being designed for different problems. Nonetheless, current methods fail to mine and utilize such commonalities across the tasks. Ideally, we could develop a unified human-centric video representation that can be shared across all relevant tasks." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 558, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 548, + 715 + ], + "type": "text", + "content": "One significant challenge to developing such a representation is the heterogeneity of available data resources. Motion capture (Mocap) systems [36, 71] provide high-fidelity 3D motion data obtained with markers and sensors, but the appearances of captured videos are usually constrained to simple indoor scenes. Action recognition datasets provide annotations of the action semantics, but they either contain no human pose labels [15, 88] or feature limited motion of daily activities [59, 60, 86]. In contrast, in-the-wild human videos offer a vast and diverse range of appearance and motion. However, obtaining precise 2D pose annotations requires considerable effort [3], and acquiring ground-truth (GT) 3D joint locations is almost impossible. Consequently," + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 683, + 288, + 714 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 683, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 683, + 288, + 714 + ], + "type": "text", + "content": "† Yizhou Wang is with Center on Frontiers of Computing Studies, School of Computer Science, Peking University and Institute for Artificial Intelligence, Peking University." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15085" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "content": "most existing studies focus on a specific task using a single type of human motion data, and they are not able to enjoy the advantages of other data resources." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 109, + 289, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 109, + 289, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 109, + 289, + 418 + ], + "type": "text", + "content": "In this work, we provide a new perspective on learning human motion representations. The key idea is that we can learn a versatile human motion representation from heterogeneous data resources in a unified manner, and utilize the representation to handle different downstream tasks in a unified way. We present a two-stage framework, consisting of pretraining and finetuning, as depicted in Figure 1. In the pretraining stage, we extract 2D skeleton sequences from diverse motion data sources and corrupt them with random masks and noises. Subsequently, we train the motion encoder to recover the 3D motion from the corrupted 2D skeletons. This challenging pretext task intrinsically requires the motion encoder to i) infer the underlying 3D human structures from its temporal movements; ii) recover the erroneous and missing observations. In this way, the motion encoder implicitly captures human motion commonsense such as joint linkages, anatomical constraints, and temporal dynamics. In practice, we propose Dual-stream Spatio-temporal Transformer (DSTformer) as the motion encoder to capture the long-range relationship among skeleton keypoints. We suppose that the motion representations learned from large-scale and diversified data resources could be shared across different downstream tasks and benefit their performance. Therefore, for each downstream task, we adapt the pretrained motion representations using task-specific training data and supervisory signals with a simple regression head." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 419, + 289, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 419, + 289, + 598 + ], + "spans": [ + { + "bbox": [ + 46, + 419, + 289, + 598 + ], + "type": "text", + "content": "In summary, the contributions of this work are three-fold: 1) We provide a new perspective on solving various human-centric video tasks through a shared framework of learning human motion representations. 2) We propose a pretraining method to leverage the large-scale yet heterogeneous human motion resources and learn generalizable human motion representations. Our approach could take advantage of the precision of 3D mocap data and the diversity of in-the-wild RGB videos at the same time. 3) We design a dual-stream Transformer network with cascaded spatio-temporal self-attention blocks that could serve as a general backbone for human motion modeling. The experiments demonstrate that the above designs enable a versatile human motion representation that can be transferred to multiple downstream tasks, outperforming the task-specific state-of-the-art methods." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 609, + 134, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 609, + 134, + 621 + ], + "spans": [ + { + "bbox": [ + 47, + 609, + 134, + 621 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 629, + 289, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 289, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 289, + 713 + ], + "type": "text", + "content": "Learning Human Motion Representations. Early works formulate human motion with Hidden Markov Models [49, 101] and graphical models [47, 92]. Kanazawa et al. [39] design a temporal encoder and a hallucinator to learn representations of 3D human dynamics. Zhang et al. [124] predict future 3D dynamics in a self-supervised manner. Sun et al. [95] further incorporate action labels with an ac" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 547, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 228 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 228 + ], + "type": "text", + "content": "tion memory bank. From the action recognition perspective, a variety of pretext tasks are designed to learn motion representations in a self-supervised manner, including future prediction [93], jigsaw puzzle [56], skeleton-contrastive [100], speed change [94], cross-view consistency [58], and contrast-reconstruction [110]. Similar techniques are also explored in tasks like motion assessment [31, 80] and motion retargeting [119, 130]. These methods leverage homogeneous motion data, design corresponding pretext tasks, and apply them to a specific downstream task. In this work, we propose a unified pretrain-finetune framework to incorporate heterogeneous data resources and demonstrate its versatility in various downstream tasks." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 246, + 548, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 246, + 548, + 426 + ], + "spans": [ + { + "bbox": [ + 304, + 246, + 548, + 426 + ], + "type": "text", + "content": "3D Human Pose Estimation. Recovering 3D human poses from monocular RGB videos is a classical problem, and the methods can be categorized into two categories. The first is to estimate 3D poses with CNN directly from images [77, 97, 128]. However, one limitation of these approaches is that there is a trade-off between 3D pose precision and appearance diversity due to current data collection techniques. The second category is to extract the 2D pose first, then lift the estimated 2D pose to 3D with a separate neural network. The lifting can be achieved via Fully Connected Network [28, 73], Temporal Convolutional Network (TCN) [21, 83], GCN [12, 27, 109], and Transformer [52, 87, 126, 127]. Our framework is built upon the second category as we use the proposed DSTformer to accomplish 2D-to-3D lifting." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 444, + 548, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 444, + 548, + 647 + ], + "spans": [ + { + "bbox": [ + 304, + 444, + 548, + 647 + ], + "type": "text", + "content": "Skeleton-based Action Recognition. The pioneering works [69, 108, 120] point out the inherent connection between action recognition and human pose estimation. Towards modeling the spatio-temporal relationship among human joints, previous studies mainly employ LSTM [91, 129] and GCN [20, 51, 64, 89, 116]. Most recently, PoseC-conv3D [30] proposes to apply 3D-CNN on the stacked 2D joint heatmaps and achieves improved results. In addition to the fully-supervised action recognition task, NTU-RGB+D-120 [60] brings attention to the challenging one-shot action recognition problem. To this end, SL-DML [76] applies deep metric learning to multi-modal signals. Sabater et al. [85] explores one-shot recognition in therapy scenarios with TCN. We demonstrate that the pretrained motion representations could generalize well to action recognition tasks, and the pretrain-finetune framework is a suitable solution for the one-shot challenges." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "content": "Human Mesh Recovery. Based on the parametric human models such as SMPL [66], many research works [38, 70, 78, 115, 125] focus on regressing the human mesh from a single image. SPIN [44] additionally incorporates fitting the body" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "15086" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 100, + 71, + 496, + 182 + ], + "blocks": [ + { + "bbox": [ + 100, + 71, + 496, + 182 + ], + "lines": [ + { + "bbox": [ + 100, + 71, + 496, + 182 + ], + "spans": [ + { + "bbox": [ + 100, + 71, + 496, + 182 + ], + "type": "image", + "image_path": "3676fb971eff88d310a197d85cef8ee9330d9586d994ed8369bbfa462f9db7e4.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 187, + 547, + 232 + ], + "lines": [ + { + "bbox": [ + 46, + 187, + 547, + 232 + ], + "spans": [ + { + "bbox": [ + 46, + 187, + 547, + 232 + ], + "type": "text", + "content": "Figure 2. Model architecture. We propose the Dual-stream Spatio-temporal Transformer (DSTformer) as a general backbone for human motion modeling. DSTformer consists of " + }, + { + "bbox": [ + 46, + 187, + 547, + 232 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 187, + 547, + 232 + ], + "type": "text", + "content": " dual-stream-fusion modules. Each module contains two branches of spatial or temporal MHSA and MLP. The Spatial MHSA models the connection among different joints within a timestep, while the Temporal MHSA models the movement of one joint." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 251, + 290, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 251, + 290, + 443 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 290, + 443 + ], + "type": "text", + "content": "model to 2D joints in the training loop. Despite their promising per-frame results, these methods yield jittery and unstable results [42, 123] when applied to videos. To improve their temporal coherence, PoseBERT [7] and SmoothNet [123] propose to employ a denoising and smoothing module to the single-frame predictions. Several works [23, 39, 42, 99] take video clips as input to exploit the temporal cues. Another common problem is that paired images and GT meshes are mostly captured in constrained scenarios, which limits the generalization ability of the above methods. To that end, Pose2Mesh [24] proposes to first extract 2D skeletons using an off-the-shelf pose estimator, then lift them to 3D mesh vertices. Our approach is complementary to state-of-the-art human mesh recovery methods and could further improve their temporal coherence with the pretrained motion representations." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 479, + 104, + 491 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 479, + 104, + 491 + ], + "spans": [ + { + "bbox": [ + 47, + 479, + 104, + 491 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 507, + 115, + 518 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 507, + 115, + 518 + ], + "spans": [ + { + "bbox": [ + 47, + 507, + 115, + 518 + ], + "type": "text", + "content": "3.1. Overview" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 534, + 290, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 534, + 290, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 534, + 290, + 712 + ], + "type": "text", + "content": "As discussed in Section 1, our approach consists of two stages, namely unified pretraining and task-specific finetuning. In the first stage, we train a motion encoder to accomplish the 2D-to-3D lifting task, where we use the proposed DSTformer as the backbone. In the second stage, we finetune the pretrained motion encoder and a few new layers on the downstream tasks. We use 2D skeleton sequences as input for both pretraining and finetuning because they could be reliably extracted from all kinds of motion sources [3,9,71,81,96], and is more robust to variations [18,30]. Existing studies have shown the effectiveness of using 2D skeleton sequences for different downstream tasks [24,30,83,102]. We will first introduce the architecture of DSTformer, and then describe the training scheme in detail." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 251, + 432, + 262 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 251, + 432, + 262 + ], + "spans": [ + { + "bbox": [ + 306, + 251, + 432, + 262 + ], + "type": "text", + "content": "3.2. Network Architecture" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "spans": [ + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": "Figure 2 shows the network architecture for 2D-to-3D lifting. Given an input 2D skeleton sequence " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "\\mathbf{x} \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{in}}}" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": ", we first project it to a high-dimensional feature " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^0 \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{f}}}" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": ", then add learnable spatial positional encoding " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_{\\mathrm{pos}}^{\\mathrm{S}} \\in \\mathbb{R}^{1 \\times J \\times C_{\\mathrm{f}}}" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": " and temporal positional encoding " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_{\\mathrm{pos}}^{\\mathrm{T}} \\in \\mathbb{R}^{T \\times 1 \\times C_{\\mathrm{f}}}" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": " to it. We then use the sequence-to-sequence model DSTformer to calculate " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^i \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{f}}} (i = 1, \\dots, N)" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": " is the network depth. We apply a linear layer with tanh activation [29] to " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^N" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": " to compute the motion representation " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "\\mathbf{E} \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{e}}}" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": ". Finally, we apply a linear transformation to " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "\\mathbf{E}" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": " to estimate 3D motion " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}} \\in \\mathbb{R}^{T \\times J \\times C_{\\mathrm{out}}}" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": ". Here, " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": " denotes the sequence length, and " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "J" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": " denotes the number of body joints. " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "C_{\\mathrm{in}}, C_{\\mathrm{f}}, C_{\\mathrm{e}}" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "inline_equation", + "content": "C_{\\mathrm{out}}" + }, + { + "bbox": [ + 304, + 268, + 548, + 486 + ], + "type": "text", + "content": " denote the channel numbers of input, feature, embedding, and output respectively. We first introduce the basic building blocks of DSTformer, i.e. Spatial and Temporal Blocks with Multi-Head Self-Attention (MHSA), and then explain the DSTformer architecture design." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 500, + 547, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 500, + 547, + 536 + ], + "spans": [ + { + "bbox": [ + 304, + 500, + 547, + 536 + ], + "type": "text", + "content": "Spatial Block. Spatial MHSA (S-MHSA) aims at modeling the relationship among the joints within the same time step. It is defined as" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 328, + 544, + 545, + 587 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 328, + 544, + 545, + 587 + ], + "spans": [ + { + "bbox": [ + 328, + 544, + 545, + 587 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathrm {S} - \\mathrm {M H S A} \\left(\\mathbf {Q} _ {\\mathrm {S}}, \\mathbf {K} _ {\\mathrm {S}}, \\mathbf {V} _ {\\mathrm {S}}\\right) = \\left[ \\text {h e a d} _ {1}; \\dots ; \\text {h e a d} _ {h} \\right] \\mathbf {W} _ {\\mathrm {S}} ^ {P}, \\\\ \\operatorname {h e a d} _ {i} = \\operatorname {s o f t m a x} \\left(\\frac {\\mathbf {Q} _ {\\mathrm {S}} ^ {i} \\left(\\mathbf {K} _ {\\mathrm {S}} ^ {i}\\right) ^ {\\prime}}{\\sqrt {d _ {K}}}\\right) \\mathbf {V} _ {\\mathrm {S}} ^ {i}, \\tag {1} \\\\ \\end{array}", + "image_path": "a2bbcbe8afcd530dcb28236548593a62b178a3bcfa5e951ea6f71db41db5aa0e.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "spans": [ + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\mathrm{S}}^{P}" + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "text", + "content": " is a projection parameter matrix, " + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "text", + "content": " is the number of the heads, " + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "inline_equation", + "content": "i\\in 1,\\dots ,h" + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "inline_equation", + "content": "{}^{\\prime}" + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "text", + "content": " denotes matrix transpose. We utilize self-attention to get the query Qs, key " + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_S" + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "text", + "content": " , and value " + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "inline_equation", + "content": "\\mathbf{V}_{\\mathrm{S}}" + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "text", + "content": " from input per-frame spatial feature " + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{\\mathrm{S}}\\in \\mathbb{R}^{J\\times C_{\\mathrm{e}}}" + }, + { + "bbox": [ + 304, + 595, + 547, + 655 + ], + "type": "text", + "content": " for each head," + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 318, + 663, + 547, + 679 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 663, + 547, + 679 + ], + "spans": [ + { + "bbox": [ + 318, + 663, + 547, + 679 + ], + "type": "interline_equation", + "content": "\\mathbf {Q} _ {\\mathrm {S}} ^ {i} = \\mathbf {F} _ {\\mathrm {S}} \\mathbf {W} _ {\\mathrm {S}} ^ {(Q, i)}, \\mathbf {K} _ {\\mathrm {S}} ^ {i} = \\mathbf {F} _ {\\mathrm {S}} \\mathbf {W} _ {\\mathrm {S}} ^ {(K, i)}, \\mathbf {V} _ {\\mathrm {S}} ^ {i} = \\mathbf {F} _ {\\mathrm {S}} \\mathbf {W} _ {\\mathrm {S}} ^ {(V, i)}, \\tag {2}", + "image_path": "cd333e0568f830fd3a12b1e286865e6fba701160b5746a8b8d08dde38dfe4cd7.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\mathrm{S}}^{(Q,i)}" + }, + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\mathrm{S}}^{(K,i)}" + }, + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\mathrm{S}}^{(V,i)}" + }, + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "type": "text", + "content": " are projection matrices, and " + }, + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "type": "inline_equation", + "content": "d_{K}" + }, + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "type": "text", + "content": " is the feature dimension of " + }, + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_{\\mathrm{S}}" + }, + { + "bbox": [ + 304, + 686, + 547, + 714 + ], + "type": "text", + "content": ". We apply S-MHSA to" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15087" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "content": "features of different time steps in parallel. Residual connection and layer normalization (LayerNorm) are used to the S-MHSA result, which is further fed into a multilayer perceptron (MLP), and followed by a residual connection and LayerNorm following [105]. We denote the entire spatial block with MHSA, LayerNorm, MLP, and residual connections by " + }, + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "inline_equation", + "content": "\\mathcal{S}" + }, + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 171, + 289, + 242 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 171, + 289, + 242 + ], + "spans": [ + { + "bbox": [ + 46, + 171, + 289, + 242 + ], + "type": "text", + "content": "Temporal Block. Temporal MHSA (T-MHSA) aims at modeling the relationship across the time steps for a body joint. Its computation process is similar with S-MHSA except that the MHSA is applied to the per-joint temporal feature " + }, + { + "bbox": [ + 46, + 171, + 289, + 242 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{\\mathrm{T}} \\in \\mathbb{R}^{T \\times C_{\\mathrm{e}}}" + }, + { + "bbox": [ + 46, + 171, + 289, + 242 + ], + "type": "text", + "content": " and parallelized over the spatial dimension." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 69, + 249, + 287, + 293 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 69, + 249, + 287, + 293 + ], + "spans": [ + { + "bbox": [ + 69, + 249, + 287, + 293 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathrm {T} - \\mathrm {M H S A} \\left(\\mathbf {Q} _ {\\mathrm {T}}, \\mathbf {K} _ {\\mathrm {T}}, \\mathbf {V} _ {\\mathrm {T}}\\right) = \\left[ \\text {h e a d} _ {1}; \\dots ; \\text {h e a d} _ {h} \\right] \\mathbf {W} _ {\\mathrm {T}} ^ {P}, \\\\ \\operatorname {h e a d} _ {i} = \\operatorname {s o f t m a x} \\left(\\frac {\\mathbf {Q} _ {\\mathrm {T}} ^ {i} \\left(\\mathbf {K} _ {\\mathrm {T}} ^ {i}\\right) ^ {\\prime}}{\\sqrt {d _ {K}}}\\right) \\mathbf {V} _ {\\mathrm {T}} ^ {i}, \\tag {3} \\\\ \\end{array}", + "image_path": "a9c0811f7179eaa3e07607a97b8df7636784c5e0e828c57e5f2c54bb8dd678b9.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "spans": [ + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "type": "inline_equation", + "content": "i \\in 1, \\ldots, h" + }, + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "type": "inline_equation", + "content": "\\mathbf{Q}_{\\mathrm{T}}" + }, + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_{\\mathrm{T}}" + }, + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "type": "inline_equation", + "content": "\\mathbf{V}_{\\mathrm{T}}" + }, + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "type": "text", + "content": " are computed similar with Formula 2. We denote the entire temporal block by " + }, + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 47, + 300, + 287, + 324 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 339, + 289, + 470 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 339, + 289, + 470 + ], + "spans": [ + { + "bbox": [ + 46, + 339, + 289, + 470 + ], + "type": "text", + "content": "Dual-stream Spatio-temporal Transformer. Given spatial and temporal MHSA that captures the intra-frame and inter-frame body joint interactions respectively, we assemble the basic building blocks to fuse the spatial and temporal information in the flow. We design a dual-stream architecture with the following assumptions: 1) Both streams should be capable of modeling the comprehensive spatio-temporal context. 2) Each stream should be specialized in different spatio-temporal aspects. 3) The two streams should be fused together, with the fusion weights dynamically balanced depending on the input spatio-temporal characteristics." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 471, + 288, + 531 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 471, + 288, + 531 + ], + "spans": [ + { + "bbox": [ + 46, + 471, + 288, + 531 + ], + "type": "text", + "content": "Hence, we stack the spatial and temporal MHSA blocks in different orders, forming two parallel computation branches. The output features of the two branches are fused using adaptive weights predicted by an attention regressor. The dual-stream-fusion module is then repeated for " + }, + { + "bbox": [ + 46, + 471, + 288, + 531 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 471, + 288, + 531 + ], + "type": "text", + "content": " times:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 536, + 290, + 559 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 536, + 290, + 559 + ], + "spans": [ + { + "bbox": [ + 47, + 536, + 290, + 559 + ], + "type": "interline_equation", + "content": "\\mathbf {F} ^ {i} = \\boldsymbol {\\alpha} _ {\\mathrm {S T}} ^ {i} \\circ \\mathcal {T} _ {1} ^ {i} \\left(\\mathcal {S} _ {1} ^ {i} \\left(\\mathbf {F} ^ {i - 1}\\right)\\right) + \\boldsymbol {\\alpha} _ {\\mathrm {T S}} ^ {i} \\circ \\mathcal {S} _ {2} ^ {i} \\left(\\mathcal {T} _ {2} ^ {i} \\left(\\mathbf {F} ^ {i - 1}\\right)\\right), \\quad i \\in 1, \\dots , N, \\tag {4}", + "image_path": "e5a75178d15a58f7456f6322b6416bbb60751c86fb58c17846d33c0e5f3f5ab0.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "spans": [ + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^i" + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "text", + "content": " denotes the feature embedding at depth " + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "inline_equation", + "content": "\\circ" + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "text", + "content": " denotes element-wise production. Orders of " + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "inline_equation", + "content": "\\mathcal{S}" + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "text", + "content": " blocks are shown in Figure 2, and different blocks do not share weights. Adaptive fusion weights " + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "inline_equation", + "content": "\\alpha_{\\mathrm{ST}}, \\alpha_{\\mathrm{TS}} \\in \\mathbb{R}^{N \\times T \\times J}" + }, + { + "bbox": [ + 46, + 561, + 287, + 609 + ], + "type": "text", + "content": " are given by" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 55, + 615, + 287, + 639 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 615, + 287, + 639 + ], + "spans": [ + { + "bbox": [ + 55, + 615, + 287, + 639 + ], + "type": "interline_equation", + "content": "\\alpha_ {\\mathrm {S T}} ^ {i}, \\alpha_ {\\mathrm {T S}} ^ {i} = \\operatorname {s o f t m a x} \\left(\\mathcal {W} \\left(\\left[ \\mathcal {T} _ {1} ^ {i} \\left(\\mathcal {S} _ {1} ^ {i} \\left(\\mathbf {F} ^ {i - 1}\\right)\\right), \\mathcal {S} _ {2} ^ {i} \\left(\\mathcal {T} _ {2} ^ {i} \\left(\\mathbf {F} ^ {i - 1}\\right)\\right) \\right]\\right)\\right), \\tag {5}", + "image_path": "3bf77b152902ee3857330f963d57eec1fa4a7bf696f91bf18344cf0f964a9442.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 639, + 287, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 639, + 287, + 663 + ], + "spans": [ + { + "bbox": [ + 46, + 639, + 287, + 663 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 639, + 287, + 663 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 46, + 639, + 287, + 663 + ], + "type": "text", + "content": " is a learnable linear transformation. " + }, + { + "bbox": [ + 46, + 639, + 287, + 663 + ], + "type": "inline_equation", + "content": "[,]" + }, + { + "bbox": [ + 46, + 639, + 287, + 663 + ], + "type": "text", + "content": " denotes concatenation." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 671, + 162, + 685 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 162, + 685 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 162, + 685 + ], + "type": "text", + "content": "3.3. Unified Pretraining" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 689, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 289, + 714 + ], + "type": "text", + "content": "We address two key challenges when designing the unified pretraining framework: 1) How to learn a powerful" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 72, + 545, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 107 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 107 + ], + "type": "text", + "content": "motion representation with a universal pretext task. 2) How to utilize large-scale but heterogeneous human motion data in all kinds of formats." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "spans": [ + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "text", + "content": "For the first challenge, we follow the successful practices in language [11, 29, 84] and vision [6, 34] modeling to construct the supervision signals, i.e. mask part of the input and use the encoded representations to reconstruct the whole input. Note that such \"cloze\" task naturally exists in human motion analysis, that is to recover the lost depth information from the 2D visual observations, i.e. 3D human pose estimation. Inspired by this, we leverage the large-scale 3D mocap data [71] and design a 2D-to-3D lifting pretext task. We first extract the 2D skeleton sequences " + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "text", + "content": " by projecting the 3D motion orthographically. Then, we corrupt " + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "text", + "content": " by randomly masking and adding noise to produce the corrupted 2D skeleton sequences, which also resemble the 2D detection results as it contains occlusions, detection failures, and errors. Both joint-level and frame-level masks are applied with certain probabilities. We use the aforementioned motion encoder to get motion representation " + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "inline_equation", + "content": "\\mathbf{E}" + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "text", + "content": " and reconstruct 3D motion " + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}" + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "text", + "content": ". We then compute the joint loss " + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{3\\mathrm{D}}" + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "text", + "content": " between " + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}" + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "text", + "content": " and GT 3D motion " + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "inline_equation", + "content": "\\mathbf{X}" + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "text", + "content": ". We also add the velocity loss " + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{O}}" + }, + { + "bbox": [ + 304, + 108, + 547, + 361 + ], + "type": "text", + "content": " following previous works [83, 126]. The 3D reconstruction losses are thus given by" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 368, + 557, + 407 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 368, + 557, + 407 + ], + "spans": [ + { + "bbox": [ + 305, + 368, + 557, + 407 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {3 D}} = \\sum_ {t = 1} ^ {T} \\sum_ {j = 1} ^ {J} \\| \\hat {\\mathbf {X}} _ {t, j} - \\mathbf {X} _ {t, j} \\| _ {2}, \\quad \\mathcal {L} _ {\\mathrm {O}} = \\sum_ {t = 2} ^ {T} \\sum_ {j = 1} ^ {J} \\| \\hat {\\mathbf {O}} _ {t, j} - \\mathbf {O} _ {t, j} \\| _ {2}, \\tag {6}", + "image_path": "5085ab53b963198b3c20e9733252e57334493da6c3ff796fef7ada5a48984ed9.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 407, + 487, + 420 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 407, + 487, + 420 + ], + "spans": [ + { + "bbox": [ + 305, + 407, + 487, + 420 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 407, + 487, + 420 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{O}}_t = \\hat{\\mathbf{X}}_t - \\hat{\\mathbf{X}}_{t - 1}" + }, + { + "bbox": [ + 305, + 407, + 487, + 420 + ], + "type": "inline_equation", + "content": "\\mathbf{O}_t = \\mathbf{X}_t - \\mathbf{X}_{t - 1}" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 420, + 547, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 420, + 547, + 564 + ], + "spans": [ + { + "bbox": [ + 304, + 420, + 547, + 564 + ], + "type": "text", + "content": "For the second challenge, we notice that 2D skeletons could serve as a universal medium as they can be extracted from all sorts of motion data sources. We further incorporate in-the-wild RGB videos into the 2D-to-3D lifting framework for unified pretraining. For RGB videos, the 2D skeletons " + }, + { + "bbox": [ + 304, + 420, + 547, + 564 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 420, + 547, + 564 + ], + "type": "text", + "content": " could be given by manual annotation [3] or 2D pose estimators [13, 96], and the depth channel of the extracted 2D skeletons is intrinsically \"masked\". Similarly, we add extra masks and noises to degrade " + }, + { + "bbox": [ + 304, + 420, + 547, + 564 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 420, + 547, + 564 + ], + "type": "text", + "content": " (if " + }, + { + "bbox": [ + 304, + 420, + 547, + 564 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 420, + 547, + 564 + ], + "type": "text", + "content": " already contains detection noise, only masking is applied). As 3D motion GT " + }, + { + "bbox": [ + 304, + 420, + 547, + 564 + ], + "type": "inline_equation", + "content": "\\mathbf{X}" + }, + { + "bbox": [ + 304, + 420, + 547, + 564 + ], + "type": "text", + "content": " is not available for these data, we apply a weighted 2D re-projection loss which is calculated by" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 359, + 572, + 545, + 603 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 359, + 572, + 545, + 603 + ], + "spans": [ + { + "bbox": [ + 359, + 572, + 545, + 603 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {2 D}} = \\sum_ {t = 1} ^ {T} \\sum_ {j = 1} ^ {J} \\boldsymbol {\\delta} _ {t, j} \\| \\hat {\\mathbf {x}} _ {t, j} - \\mathbf {x} _ {t, j} \\| _ {2}, \\tag {7}", + "image_path": "9dafe5a29ca17bef312f587eb992d996a653e0a89ca0d2697bcf2da19e98faa2.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 611, + 547, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 611, + 547, + 647 + ], + "spans": [ + { + "bbox": [ + 304, + 611, + 547, + 647 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 611, + 547, + 647 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{x}}" + }, + { + "bbox": [ + 304, + 611, + 547, + 647 + ], + "type": "text", + "content": " is the 2D orthogonal projection of the estimated 3D motion " + }, + { + "bbox": [ + 304, + 611, + 547, + 647 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{X}}" + }, + { + "bbox": [ + 304, + 611, + 547, + 647 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 611, + 547, + 647 + ], + "type": "inline_equation", + "content": "\\delta \\in \\mathbb{R}^{T\\times J}" + }, + { + "bbox": [ + 304, + 611, + 547, + 647 + ], + "type": "text", + "content": " is given by visibility annotation or 2D detection confidence." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 318, + 647, + 484, + 660 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 647, + 484, + 660 + ], + "spans": [ + { + "bbox": [ + 318, + 647, + 484, + 660 + ], + "type": "text", + "content": "The total pretraining loss is computed by" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 369, + 668, + 545, + 693 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 369, + 668, + 545, + 693 + ], + "spans": [ + { + "bbox": [ + 369, + 668, + 545, + 693 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\underbrace {\\mathcal {L} _ {\\mathrm {3 D}} + \\lambda_ {\\mathrm {O}} \\mathcal {L} _ {\\mathrm {O}}} _ {\\text {f o r 3 D d a t a}} + \\underbrace {\\mathcal {L} _ {\\mathrm {2 D}}} _ {\\text {f o r 2 D d a t a}}, \\tag {8}", + "image_path": "d3440fabc91430b41d3527ac8936d67dd5a23ebdd07e89beb9fe1557ce53148d.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 701, + 529, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 701, + 529, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 701, + 529, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 701, + 529, + 713 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{O}}" + }, + { + "bbox": [ + 306, + 701, + 529, + 713 + ], + "type": "text", + "content": " is a constant coefficient to balance the losses." + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15088" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 185, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 185, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 185, + 85 + ], + "type": "text", + "content": "3.4. Task-specific Finetuning" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 288, + 175 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 288, + 175 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 288, + 175 + ], + "type": "text", + "content": "The learned feature embedding " + }, + { + "bbox": [ + 46, + 91, + 288, + 175 + ], + "type": "inline_equation", + "content": "\\mathbf{E}" + }, + { + "bbox": [ + 46, + 91, + 288, + 175 + ], + "type": "text", + "content": " serves as a 3D-aware and temporal-aware human motion representation. For downstream tasks, we adopt the minimalist design principle, i.e. implementing a shallow downstream network and training without bells and whistles. In practice, we use an extra linear layer or an MLP with one hidden layer. We then finetune the whole network end-to-end." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 198, + 288, + 246 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 198, + 288, + 246 + ], + "spans": [ + { + "bbox": [ + 46, + 198, + 288, + 246 + ], + "type": "text", + "content": "3D Pose Estimation. As we utilize 2D-to-3D lifting as the pretext task, we simply reuse the whole pretrained network. During finetuning, the input 2D skeletons are estimated from videos without extra masks or noises." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 269, + 289, + 353 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 269, + 289, + 353 + ], + "spans": [ + { + "bbox": [ + 46, + 269, + 289, + 353 + ], + "type": "text", + "content": "Skeleton-based Action Recognition. We directly apply a global average pooling over different persons and timesteps. The result is then fed into an MLP with one hidden layer. The network is trained with cross-entropy classification loss. For one-shot learning, we apply a linear layer after the pooled features to extract clip-level action representation. We introduce the detailed setup of one-shot learning in Section 4.4." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "spans": [ + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "text", + "content": "Human Mesh Recovery. We use SMPL [66] model to represent the human mesh and regress its parameters. The SMPL model consists of pose parameters " + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "inline_equation", + "content": "\\theta \\in \\mathbb{R}^{72}" + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "text", + "content": " and shape parameters " + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "inline_equation", + "content": "\\beta \\in \\mathbb{R}^{10}" + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "text", + "content": ", and calculates the 3D mesh as " + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "inline_equation", + "content": "\\mathcal{M}(\\theta, \\beta) \\in \\mathbb{R}^{6890 \\times 3}" + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "text", + "content": ". To regress the pose parameters for each frame, we feed the motion embeddings " + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "inline_equation", + "content": "\\mathbf{E}" + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "text", + "content": " to an MLP with one hidden layer and get " + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{\\theta}} \\in \\mathbb{R}^{T \\times 72}" + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "text", + "content": ". To estimate shape parameters, considering that the human shape over a video sequence is supposed to be consistent, we first perform an average pooling of " + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "inline_equation", + "content": "\\mathbf{E}" + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "text", + "content": " over the temporal dimension and then feed it into another MLP to regress a single " + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "inline_equation", + "content": "\\hat{\\beta}" + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "text", + "content": " and then expand it to the entire sequence as " + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "inline_equation", + "content": "\\hat{\\beta} \\in \\mathbb{R}^{T \\times 10}" + }, + { + "bbox": [ + 46, + 374, + 289, + 555 + ], + "type": "text", + "content": ". The shape MLP has the same architecture as the pose regression one, and they are initialized with the mean shape and pose, respectively, as in [42]. The overall loss is computed as" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 69, + 565, + 288, + 578 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 69, + 565, + 288, + 578 + ], + "spans": [ + { + "bbox": [ + 69, + 565, + 288, + 578 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\lambda_ {\\mathrm {3 D}} ^ {\\mathrm {m}} \\mathcal {L} _ {\\mathrm {3 D}} ^ {\\mathrm {m}} + \\lambda_ {\\theta} \\mathcal {L} _ {\\theta} + \\lambda_ {\\beta} \\mathcal {L} _ {\\beta} + \\lambda_ {\\mathrm {n}} \\mathcal {L} _ {\\text {n o r m}} + \\lambda_ {\\mathrm {O}} ^ {\\mathrm {m}} \\mathcal {L} _ {\\mathrm {O}} ^ {\\mathrm {m}}, \\tag {9}", + "image_path": "99399ba91289e32d366934de0d6078b2ff274839542d526db181a53f3b237056.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 591, + 180, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 591, + 180, + 602 + ], + "spans": [ + { + "bbox": [ + 47, + 591, + 180, + 602 + ], + "type": "text", + "content": "where each term is calculated as" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 52, + 613, + 282, + 627 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 613, + 282, + 627 + ], + "spans": [ + { + "bbox": [ + 52, + 613, + 282, + 627 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {3 D}} ^ {\\mathrm {m}} = \\left\\| \\hat {\\mathbf {X}} ^ {\\mathrm {m}} - \\mathbf {X} ^ {\\mathrm {m}} \\right\\| _ {1}, \\quad \\mathcal {L} _ {\\theta} = \\left\\| \\hat {\\boldsymbol {\\theta}} - \\boldsymbol {\\theta} \\right\\| _ {1}, \\quad \\mathcal {L} _ {\\beta} = \\left\\| \\hat {\\boldsymbol {\\beta}} - \\boldsymbol {\\beta} \\right\\| _ {1},", + "image_path": "51cb9d7bf3d322ecda911c8b51bdcce3cf80469ca9d4a44ef1ca2f193d48046c.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 53, + 628, + 288, + 651 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 628, + 288, + 651 + ], + "spans": [ + { + "bbox": [ + 53, + 628, + 288, + 651 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {n o r m}} = \\| \\hat {\\boldsymbol {\\theta}} \\| _ {2} + \\| \\hat {\\boldsymbol {\\beta}} \\| _ {2}, \\quad \\mathcal {L} _ {\\mathrm {O}} ^ {\\mathrm {m}} = \\| \\hat {\\mathbf {O}} ^ {\\mathrm {m}} - \\mathbf {O} ^ {\\mathrm {m}} \\| _ {2}. \\tag {10}", + "image_path": "44f824f69066dee065b7f729967c442f55a9be86d269c2ea912a24dea9025d07.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "text", + "content": "Note that each 3D pose in motion " + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{X}^{\\mathrm{m}}" + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "text", + "content": " at frame " + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "text", + "content": " is regressed from mesh vertices by " + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_t^{\\mathrm{m}} = \\mathbf{J}\\mathcal{M}(\\pmb {\\theta}_t,\\pmb {\\beta}_t)" + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{J}\\in \\mathbb{R}^{J\\times 6890}" + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "text", + "content": " is a pre-defined matrix [9]. " + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{O}^{\\mathrm{m}} = \\mathbf{X}_{t + 1}^{\\mathrm{m}} - \\mathbf{X}_{t}^{\\mathrm{m}}" + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{O}}^{\\mathrm{m}} = \\hat{\\mathbf{X}}_{t + 1}^{\\mathrm{m}} - \\hat{\\mathbf{X}}_t^{\\mathrm{m}}" + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\lambda_{3\\mathrm{D}}^{\\mathrm{m}},\\lambda_{\\theta},\\lambda_{\\beta},\\lambda_{\\mathrm{n}}" + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\lambda_0^{\\mathrm{m}}" + }, + { + "bbox": [ + 46, + 651, + 289, + 714 + ], + "type": "text", + "content": " are constant coefficients to balance the training loss." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 72, + 388, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 388, + 85 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 388, + 85 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 91, + 404, + 104 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 91, + 404, + 104 + ], + "spans": [ + { + "bbox": [ + 306, + 91, + 404, + 104 + ], + "type": "text", + "content": "4.1. Implementation" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "spans": [ + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "text", + "content": "We implement the proposed motion encoder DSTformer with depth " + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "inline_equation", + "content": "N = 5" + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "text", + "content": ", number of heads " + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "inline_equation", + "content": "h = 8" + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "text", + "content": ", feature size " + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "inline_equation", + "content": "C_{\\mathrm{f}} = 512" + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "text", + "content": ", embedding size " + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "inline_equation", + "content": "C_{\\mathrm{e}} = 512" + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "text", + "content": ". For pretraining, we use sequence length " + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "inline_equation", + "content": "T = 243" + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "text", + "content": ". The pretrained model could handle different input lengths thanks to the Transformer-based backbone. During finetuning, we set the backbone learning rate to be " + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "inline_equation", + "content": "0.1 \\times" + }, + { + "bbox": [ + 304, + 110, + 547, + 229 + ], + "type": "text", + "content": " of the new layer learning rate. We introduce the experiment datasets in the following sections respectively. Please refer to the appendix for more experimental details." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 238, + 383, + 251 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 238, + 383, + 251 + ], + "spans": [ + { + "bbox": [ + 306, + 238, + 383, + 251 + ], + "type": "text", + "content": "4.2. Pretraining" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 256, + 547, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 256, + 547, + 533 + ], + "spans": [ + { + "bbox": [ + 304, + 256, + 547, + 533 + ], + "type": "text", + "content": "We collect diverse and realistic 3D human motion from two datasets, Human3.6M [36] and AMASS [71]. Human3.6M [36] is a commonly used indoor dataset for 3D human pose estimation which contains 3.6 million video frames of professional actors performing daily actions. Following previous works [73, 83], we use subjects 1, 5, 6, 7, 8 for training, and subjects 9, 11 for testing. AMASS [71] integrates most existing marker-based Mocap datasets [1,2,4,10,14,17,32,35,48,65,67,72,79,90,103,104] and parameterizes them with a common representation. We do not use the images or 2D detection results of the two datasets during pretraining as Mocap datasets usually do not provide raw videos. Instead, we use orthographic projection to get the uncorrupted 2D skeletons. We further incorporate two in-the-wild RGB video datasets PoseTrack [3] (annotated) and InstaVariety [39] (unannotated) for higher motion diversity. We align the body keypoint definitions with Human3.6M and calibrate the camera coordinates to pixel coordinates following [26]. We randomly zero out " + }, + { + "bbox": [ + 304, + 256, + 547, + 533 + ], + "type": "inline_equation", + "content": "15\\%" + }, + { + "bbox": [ + 304, + 256, + 547, + 533 + ], + "type": "text", + "content": " joints, and sample noises from a mixture of Gaussian and uniform distributions [16]. We first train on 3D data only for 30 epochs, then train on both 3D data and 2D data for 60 epochs, following the curriculum learning practices [8, 111]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 539, + 421, + 551 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 539, + 421, + 551 + ], + "spans": [ + { + "bbox": [ + 306, + 539, + 421, + 551 + ], + "type": "text", + "content": "4.3. 3D Pose Estimation" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 558, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 547, + 715 + ], + "type": "text", + "content": "We evaluate the 3D pose estimation performance on Human3.6M [36] and report the mean per joint position error (MPJPE) in millimeters, which measures the average distance between the predicted joint positions and the GT after aligning the root joint. We also compute the mean per-joint velocity error (MPJVE) to evaluate the temporal smoothness following previous works [126, 127]. We use the Stacked Hourglass (SH) networks [81] to extract the 2D skeletons from videos, and finetune the entire network on Human3.6M [36] training set. In addition, we train a separate model of the same architecture, but with random initialization rather than pretrained weights. As shown in Table 1 (top), the model trained from scratch outperforms" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "15089" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 78, + 70, + 515, + 383 + ], + "blocks": [ + { + "bbox": [ + 78, + 70, + 515, + 383 + ], + "lines": [ + { + "bbox": [ + 78, + 70, + 515, + 383 + ], + "spans": [ + { + "bbox": [ + 78, + 70, + 515, + 383 + ], + "type": "table", + "html": "
MethodTDire.Disc.EatGreetPhonePhotoPosePurch.SitSitDSmokeWaitWalkDWalkWalkTAvg
Martinez et al. [73] ICCV'17151.856.258.159.069.578.455.258.174.094.662.359.165.149.552.462.9
Pavlakos et al. [82] CVPR'18148.554.454.452.059.465.349.952.965.871.156.652.960.944.747.856.2
LCN [27] ICCV'19146.852.344.750.452.968.949.646.460.278.951.250.054.840.443.352.7
Xu et al. [114] CVPR'21145.249.947.550.954.966.148.546.359.771.551.448.653.939.944.151.9
VideoPose3D [83] CVPR'1924345.246.743.345.648.155.144.644.357.365.847.144.049.032.833.946.8
Cai et al. [12] ICCV'19744.647.445.648.850.859.047.243.957.961.949.746.651.337.139.448.8
Yeh et al. [122] NeurIPS'1924344.846.143.346.449.055.244.644.058.362.747.143.948.632.733.346.7
Liu et al. [63] CVPR'2024341.844.841.144.947.454.143.442.256.263.645.343.545.331.332.245.1
* Cheng et al. [21] AAAI'2012836.238.142.735.938.245.736.842.045.951.341.841.543.833.128.640.1
* UGCN [109] ECCV'209638.241.045.939.741.451.441.641.452.057.441.844.441.633.130.042.6
† PoseFormer [127] ICCV'218141.544.839.842.546.551.642.142.053.360.745.543.346.131.832.244.3
* Wehrbein et al. [112] ICCV'2120038.542.539.941.746.551.639.940.849.556.845.346.446.837.840.444.3
† MHFormer [52] CVPR'2235139.243.140.140.944.951.240.641.353.560.343.741.143.829.830.643.0
*† MixSTE [126] CVPR'2224336.739.036.539.440.244.939.836.947.954.839.637.839.329.730.639.8
† P-STMO [87] ECCV'2224338.442.139.840.245.248.940.438.353.857.343.941.642.229.329.342.1
† Ours (scratch)24336.338.738.633.642.150.136.235.750.156.641.337.437.725.626.539.2
† Ours (finetune)24336.137.535.832.140.346.336.135.346.953.939.536.335.825.125.337.5
MethodTDire.Disc.EatGreetPhonePhotoPosePurch.SitSitDSmokeWaitWalkDWalkWalkTAvg
Martinez et al. [73] ICCV'17137.744.440.342.148.254.944.442.154.658.045.146.447.636.440.445.5
LCN [27] ICCV'19136.338.829.737.834.642.539.832.536.239.534.438.438.231.334.236.3
Xu et al. [114] CVPR'21135.838.131.035.335.843.237.331.738.445.535.436.736.827.930.735.8
UGCN [109] ECCV'209623.025.722.822.624.130.624.924.531.135.025.624.325.119.818.425.6
† PoseFormer [127] ICCV'218130.033.629.931.030.233.334.831.437.838.631.731.529.023.323.131.3
† MHFormer [52] CVPR'2235127.732.129.128.930.033.933.031.237.039.330.031.029.422.223.030.5
† MixSTE [126] CVPR'2224321.622.020.421.020.824.324.721.926.924.921.221.520.814.715.621.6
† P-STMO [87] ECCV'2224328.530.128.627.929.833.231.327.836.037.429.729.528.121.021.029.3
† Ours (scratch)24316.719.917.116.517.418.819.320.524.022.118.616.816.710.811.517.8
† Ours (finetune)24315.917.316.914.616.818.618.618.422.021.817.316.916.110.511.416.9
MethodTDire.Disc.EatGreetPhonePhotoPosePurch.SitSitDSmokeWaitWalkDWalkWalkTAvg
VideoPose3D [83] CVPR'192433.03.12.23.42.32.72.73.12.12.92.32.43.73.12.82.8
† PoseFormer [127] ICCV'21813.23.42.63.62.63.02.93.22.63.32.72.73.83.22.93.1
*† MixSTE [126] CVPR'222432.52.71.92.81.92.22.32.61.62.21.92.03.12.62.22.3
† Ours (scratch)2431.82.11.52.01.51.91.82.11.21.81.51.42.62.01.71.8
† Ours (finetune)2431.71.91.41.91.41.71.71.91.11.61.41.32.41.91.61.7
", + "image_path": "04e0a27d94520649ec2e26314db2bd89480c373df24c9d50046184337ed66a79.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 387, + 547, + 431 + ], + "lines": [ + { + "bbox": [ + 46, + 387, + 547, + 431 + ], + "spans": [ + { + "bbox": [ + 46, + 387, + 547, + 431 + ], + "type": "text", + "content": "Table 1. Quantitative comparison of 3D human pose estimation on Human3.6M. (Top) MPJPE (mm) using detected 2D pose sequences. (Middle) MPJPE (mm) using GT 2D pose sequences. (Bottom) MPJVE (mm) using detected 2D pose sequences. " + }, + { + "bbox": [ + 46, + 387, + 547, + 431 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 387, + 547, + 431 + ], + "type": "text", + "content": " denotes the clip length used by the method. We select the best results reported by each work. \\* denotes using HRNet [96] for 2D detection. " + }, + { + "bbox": [ + 46, + 387, + 547, + 431 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 46, + 387, + 547, + 431 + ], + "type": "text", + "content": " denotes implemented with a spatio-temporal Transformer design. The best and second-best results are highlighted in bold and underlined formats." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 451, + 289, + 656 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 451, + 289, + 656 + ], + "spans": [ + { + "bbox": [ + 46, + 451, + 289, + 656 + ], + "type": "text", + "content": "previous methods including other Transformer-based designs with spatio-temporal modeling. It shows the effectiveness of the proposed DSTformer in terms of learning 3D geometric structures and temporal dynamics. To further evaluate the upper bound of the models' capability, we compare the performance when using 2D GT pose sequences as input, which gets rid of the influence of different 2D detectors. As shown in Table 1 (middle), our models significantly outperform all the previous approaches. Table 1 (bottom) shows that both of our models also surpass previous works in terms of MPJVE, implying better temporal coherence. We attribute the performance advantage of our scratch model to the proposed DSTformer design. We include more comparisons and analysis to demonstrate the advantage of DSTformer with regard to other spatio-temporal architectures in Section 4.6 and supplementary materials. Additionally, our method achieves lower errors with the proposed pretraining stage." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 669, + 234, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 669, + 234, + 682 + ], + "spans": [ + { + "bbox": [ + 47, + 669, + 234, + 682 + ], + "type": "text", + "content": "4.4. Skeleton-based Action Recognition" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": "We further explore the possibility to learn action semantics with the pretrained human motion representations. We" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 451, + 547, + 596 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 451, + 547, + 596 + ], + "spans": [ + { + "bbox": [ + 304, + 451, + 547, + 596 + ], + "type": "text", + "content": "use the human action dataset NTU-RGB+D [86] which contains 57K videos of 60 action classes, and we follow the data splits Cross-subject (X-Sub) and Cross-view (X-View). The dataset has an extended version, NTU-RGB+D-120 [60], which contains 114K videos of 120 action classes. We follow the suggested One-shot action recognition protocol on NTU-RGB+D-120. For both datasets, we use HRNet [96] to extract 2D skeletons following [30]. Similarly, we train a scratch model with random initialization for comparison. As Table 2 (left) shows, our methods are comparable or superior to the state-of-the-art approaches. Notably, the pretraining stage accounts for a large performance gain." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 605, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 548, + 715 + ], + "type": "text", + "content": "Additionally, we delve into the one-shot setting which holds significant practical importance. Real-world applications often require fine-grained action recognition in specific domains such as education, sports, and healthcare. Unfortunately, the action classes in these scenarios are not typically defined in public datasets. As a result, only limited annotations for these novel action classes are available, making accurate recognition a challenging task. As proposed in [60], we report the results on the evaluation set of 20 novel classes" + } + ] + } + ], + "index": 6 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "15090" + } + ] + } + ], + "index": 7 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 92, + 70, + 250, + 204 + ], + "blocks": [ + { + "bbox": [ + 92, + 70, + 250, + 204 + ], + "lines": [ + { + "bbox": [ + 92, + 70, + 250, + 204 + ], + "spans": [ + { + "bbox": [ + 92, + 70, + 250, + 204 + ], + "type": "table", + "html": "
MethodX-SubX-View
ST-GCN [116] AAAI'1881.588.3
2s-AGCN [89] CVPR'1988.595.1
MS-G3D [64] CVPR'2091.596.2
Shift-GCN [20] CVPR'2090.796.5
CrosSCLR [58] CVPR'2186.292.5
MCC (finetune) [94] ICCV'2189.796.3
SCC (finetune) [118] ICCV'2188.094.9
UNIK (finetune) [117] BMVC'2186.894.4
CTR-GCN [19] ICCV'2192.496.8
PoseConv3D [30] CVPR'2293.195.7
Ours (scratch)87.794.1
Ours (finetune)93.097.2
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MethodAccuracy
ST-LSTM + AvgPool [61]42.9
ST-LSTM + FC [62]42.1
ST-LSTM + Attention [62]41.0
APSR [60]45.3
TCN OneShot [85]46.5
SL-DML [76]50.9
Skeleton-DML [75]54.2
Ours (scratch)61.0
Ours (finetune)67.4
", + "image_path": "22bb6c1cc505a5d1d047a82336c22034440d6e4336de55740e7042697ccd72c0.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 99, + 254, + 496, + 525 + ], + "blocks": [ + { + "bbox": [ + 46, + 212, + 547, + 246 + ], + "lines": [ + { + "bbox": [ + 46, + 212, + 547, + 246 + ], + "spans": [ + { + "bbox": [ + 46, + 212, + 547, + 246 + ], + "type": "text", + "content": "Table 2. Quantitative comparison of skeleton-based action recognition accuracy. (Left) Cross-subject and cross-view recognition accuracy on NTU-RGB+D. All the methods are evaluated using only the \"joint\" modality with 1-clip sampling for the fairness of comparison. (Right) One-shot recognition accuracy on NTU-RGB+D-120. All results are top-1 accuracy (\\%)." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 99, + 254, + 496, + 525 + ], + "lines": [ + { + "bbox": [ + 99, + 254, + 496, + 525 + ], + "spans": [ + { + "bbox": [ + 99, + 254, + 496, + 525 + ], + "type": "table", + "html": "
MethodInputTHuman3.6M3DPW
MPVE↓MPJPE↓PA-MPJPE↓MPVE↓MPJPE↓PA-MPJPE↓
HMR [38] CVPR'18image1-88.056.8-130.081.3
† SPIN [44] ICCV'19image182.359.439.3129.1100.959.1
Pose2Mesh [24] ECCV'202D pose185.364.948.7109.391.460.1
I2L-MeshNet [78] ECCV'20image1-55.741.7110.193.258.6
† HybrIK [50] CVPR'21image158.147.430.182.471.341.9
METRO [54] CVPR'21image1-54.036.788.277.147.9
Mesh Graphormer [55] ICCV'21image1-51.234.587.774.745.6
PARE [43] ICCV'21image1---88.674.546.5
ROMP [98] ICCV'21image1---108.391.354.9
PyMAF [125] ICCV'21image1-57.740.5110.192.858.9
ProHMR [46] ICCV'21image1--41.2--59.8
OCHMR [40] CVPR'22image1---107.189.758.3
3DCrowdNet [25] CVPR'22image1---98.381.751.5
CLIFF [53] ECCV'22image1-47.132.781.269.043.0
FastMETRO [22] ECCV'22image1-52.233.784.173.544.6
VisDB [121] ECCV'22image1-51.034.585.573.544.9
TemporalContext [5] CVPR'19video32-77.854.3--72.2
HMMR [39] CVPR'19video20--56.9139.3116.572.6
DSD-SATN [99] ICCV'19video9-59.142.4--69.5
VIBE [42] CVPR'20video16-65.641.499.182.951.9
TCMR [23] CVPR'21video16-62.341.1102.986.552.7
† MAED [107] ICCV'21video1684.160.438.393.379.045.7
MPS-Net [113] CVPR'22video16-69.447.499.784.352.1
* PoseBERT [7] TPAMI'22 (+SPIN [44])video16-----57.3 ↓ 2.3
* SmoothNet [123] ECCV'22 (+SPIN [44])video32-67.5 ↓ 1.046.3 ↓ 0.2-86.7 ↓ 0.952.7 ↓ 0.6
Ours (scratch)2D motion1675.762.841.099.185.550.2
Ours (finetune)2D motion1665.553.834.988.176.947.2
Ours (finetune) + SPIN [44]video1663.7 ↓ 18.652.2 ↓ 7.235.7 ↓ 3.692.8 ↓ 36.379.6 ↓ 21.348.2 ↓ 10.9
Ours (finetune) + MAED [107]video1666.8 ↓ 17.354.8 ↓ 5.636.4 ↓ 1.984.4 ↓ 8.972.3 ↓ 6.742.3 ↓ 3.4
Ours (finetune) + HybrIK [50]video1652.6 ↓ 5.543.1 ↓ 4.327.8 ↓ 2.379.4 ↓ 3.068.8 ↓ 2.540.6 ↓ 1.3
", + "image_path": "c7f26adf880b26d3bb38a7c8085b86cc5a78bb7a7f083d1ba306537a21147e1b.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 533, + 546, + 567 + ], + "lines": [ + { + "bbox": [ + 46, + 533, + 546, + 567 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 546, + 567 + ], + "type": "text", + "content": "Table 3. Quantitative comparison of human mesh recovery on Human3.6M and 3DPW datasets. " + }, + { + "bbox": [ + 46, + 533, + 546, + 567 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 533, + 546, + 567 + ], + "type": "text", + "content": " denotes the clip length used by the method. " + }, + { + "bbox": [ + 46, + 533, + 546, + 567 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 46, + 533, + 546, + 567 + ], + "type": "text", + "content": " denotes the results obtained with official model weights. The rest are all officially reported results. The gains in \\* correspond to different re-implemented SPIN [44] results." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 574, + 289, + 707 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 574, + 289, + 707 + ], + "spans": [ + { + "bbox": [ + 46, + 574, + 289, + 707 + ], + "type": "text", + "content": "using only 1 labeled video for each class. The auxiliary set contains the other 100 classes, and all samples of these classes can be used. We train the model on the auxiliary set using the supervised contrastive learning technique [41]. For a batch of auxiliary data, samples of the same class are pulled together, while samples of different classes are pushed away in the action embedding space. During the evaluation, we calculate the cosine distance between the test examples and the exemplars, and use 1-nearest neighbor to determine the class. Table 2 (right) illustrates that the proposed models outperform state-of-the-art by a considerable margin. Moreover," + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 574, + 547, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 574, + 547, + 635 + ], + "spans": [ + { + "bbox": [ + 304, + 574, + 547, + 635 + ], + "type": "text", + "content": "it is noteworthy that our pretrained model achieves optimal performance with only 1-2 epochs of fine-tuning. Our results indicate that the pretraining stage is effective in learning a robust motion representation that generalizes well to novel downstream tasks, even with limited data annotations." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 646, + 440, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 646, + 440, + 659 + ], + "spans": [ + { + "bbox": [ + 306, + 646, + 440, + 659 + ], + "type": "text", + "content": "4.5. Human Mesh Recovery" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 665, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 548, + 715 + ], + "type": "text", + "content": "We conduct experiments on Human3.6M [36] and 3DPW [106] datasets and additionally add COCO [57] dataset during training following [42, 54, 107]. We keep the same training and test split for both datasets as in [73] (Section 4.2)" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15091" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 71, + 205, + 182 + ], + "blocks": [ + { + "bbox": [ + 53, + 71, + 205, + 182 + ], + "lines": [ + { + "bbox": [ + 53, + 71, + 205, + 182 + ], + "spans": [ + { + "bbox": [ + 53, + 71, + 205, + 182 + ], + "type": "image", + "image_path": "99926cb7f99b2aa12f2d0f82f5a5fb3dc8f26e752f2621502e2ff4ba38572c6c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 168, + 187, + 424, + 200 + ], + "lines": [ + { + "bbox": [ + 168, + 187, + 424, + 200 + ], + "spans": [ + { + "bbox": [ + 168, + 187, + 424, + 200 + ], + "type": "text", + "content": "Figure 3. Learning curves of finetuning and training from scratch." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 220, + 72, + 370, + 182 + ], + "blocks": [ + { + "bbox": [ + 220, + 72, + 370, + 182 + ], + "lines": [ + { + "bbox": [ + 220, + 72, + 370, + 182 + ], + "spans": [ + { + "bbox": [ + 220, + 72, + 370, + 182 + ], + "type": "image", + "image_path": "4f844dffe3f2829686e24b451db2b92823e16ae4c8a34955ecae190f275bd10e.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 387, + 72, + 539, + 182 + ], + "blocks": [ + { + "bbox": [ + 387, + 72, + 539, + 182 + ], + "lines": [ + { + "bbox": [ + 387, + 72, + 539, + 182 + ], + "spans": [ + { + "bbox": [ + 387, + 72, + 539, + 182 + ], + "type": "image", + "image_path": "8e20cd4f690c14c7f4837e5abfb033bea35a2dbb051291305ea0456e132db5a0.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 50, + 216, + 288, + 264 + ], + "blocks": [ + { + "bbox": [ + 50, + 216, + 288, + 264 + ], + "lines": [ + { + "bbox": [ + 50, + 216, + 288, + 264 + ], + "spans": [ + { + "bbox": [ + 50, + 216, + 288, + 264 + ], + "type": "table", + "html": "
Backbone (frozen)MPJPE ↓ (3D pose)MPVE ↓ (mesh)Accuracy ↑ (action x-view)Accuracy↑ (action 1-shot)
Random404.4mm114.4mm47.6%46.8%
Pretrained40.3mm72.1mm87.3%60.7%
", + "image_path": "380234c85a781908cbfd4dccbcab6cb6d79339e62dd68f54f45cf8aac14867bf.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 293, + 289, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 293, + 289, + 616 + ], + "spans": [ + { + "bbox": [ + 47, + 293, + 289, + 616 + ], + "type": "text", + "content": "and [42, 54, 107], respectively. Following the common practice [38, 42, 45, 107], we report MPJPE (mm) and PA-MPJPE (mm) of 14 joints obtained by " + }, + { + "bbox": [ + 47, + 293, + 289, + 616 + ], + "type": "inline_equation", + "content": "\\mathbf{J}\\mathcal{M}(\\theta ,\\beta)" + }, + { + "bbox": [ + 47, + 293, + 289, + 616 + ], + "type": "text", + "content": ". PA-MPJPE calculates MPJPE after aligning with GT in translation, rotation, and scale. We further report the mean per vertex error (MPVE) (mm) of the mesh " + }, + { + "bbox": [ + 47, + 293, + 289, + 616 + ], + "type": "inline_equation", + "content": "\\mathcal{M}(\\theta ,\\beta)" + }, + { + "bbox": [ + 47, + 293, + 289, + 616 + ], + "type": "text", + "content": ", which measures the average distance between the estimated and GT vertices after aligning the root joint. Note that most previous works [23, 38, 42, 44, 50, 54, 68, 107] use more datasets other than COCO [57] during training, such as LSP [37], MPI-INF-3DHP [74], etc., while we do not. Table 3 demonstrates that our finetuned model delivers competitive results on both Human3.6M and 3DPW datasets, surpassing all the state-of-the-art video-based methods, including MAED [107], especially on the MPVE error. Nonetheless, we note that estimating full-body mesh from sparse 2D keypoints alone [9, 24] is an ill-posed problem because it lacks human shape information. In light of this, we propose a hybrid approach that leverages the strengths of both our framework (coherent motion) and RGB-based methods (accurate shape). We introduce a refiner module that can be easily integrated with existing image/video-based methods, similar to [7, 123]. Specifically, our refiner module is an MLP that takes the combination of our pretrained motion representations and an initial prediction, regressing a residual in joint rotations. Our approach effectively improves the state-of-the-art methods [44, 50, 107] and achieves the lowest error to date." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 623, + 147, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 147, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 147, + 635 + ], + "type": "text", + "content": "4.6. Ablation Studies" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 288, + 714 + ], + "type": "text", + "content": "Finetune vs. Scratch. We compare the training progress of finetuning the pretrained model and training from scratch. As Figure 3 shows, models initialized with pretrained weights demonstrate superior performance and faster convergence on all three tasks. This observation suggests that the pretrained model learns transferable knowledge about hu" + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 309, + 217, + 544, + 296 + ], + "blocks": [ + { + "bbox": [ + 84, + 270, + 247, + 282 + ], + "lines": [ + { + "bbox": [ + 84, + 270, + 247, + 282 + ], + "spans": [ + { + "bbox": [ + 84, + 270, + 247, + 282 + ], + "type": "text", + "content": "Table 4. Comparison of partial finetuning." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 217, + 544, + 296 + ], + "lines": [ + { + "bbox": [ + 309, + 217, + 544, + 296 + ], + "spans": [ + { + "bbox": [ + 309, + 217, + 544, + 296 + ], + "type": "table", + "html": "
PretrainNoiseMask2DMPJPE↓(3D pose)MPVE↓(mesh)Accuracy↑(action x-sub)
----39.2mm75.7mm87.7%
✓---38.8mm70.6mm89.4%
✓✓--38.1mm68.4mm90.7%
✓✓✓-37.4mm67.8mm91.9%
✓✓✓✓37.5mm65.5mm93.0%
", + "image_path": "80535bfd0969205d007208be3411ab8df1f0aae9aab1b376274e9f390f2f7698.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 336, + 303, + 515, + 315 + ], + "lines": [ + { + "bbox": [ + 336, + 303, + 515, + 315 + ], + "spans": [ + { + "bbox": [ + 336, + 303, + 515, + 315 + ], + "type": "text", + "content": "Table 5. Comparison of pretraining strategies." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 334, + 545, + 357 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 334, + 545, + 357 + ], + "spans": [ + { + "bbox": [ + 305, + 334, + 545, + 357 + ], + "type": "text", + "content": "man motion, facilitating the learning of multiple downstream tasks." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 373, + 547, + 553 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 373, + 547, + 553 + ], + "spans": [ + { + "bbox": [ + 304, + 373, + 547, + 553 + ], + "type": "text", + "content": "Partial Finetuning. In addition to end-to-end finetuning, we freeze the motion encoder backbone and only train the regression head for each downstream task. To verify the effectiveness of the pretrained motion representations, we compared the pretrained motion encoder with a randomly initialized motion encoder. We report results of 3D pose and mesh on Human3.6M, action on NTU-RGB+D and NTU-RGB+D-120 (same for the tables below). It can be seen in Table 4 that based on the frozen pretrained motion representations, our method still achieves competitive performance on multiple downstream tasks and shows a large improvement compared to the baseline. Pretraining and partial finetuning make it possible for all the downstream tasks to share the same backbone, significantly reducing computation overhead for applications requiring multi-task inference." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 567, + 548, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 567, + 548, + 675 + ], + "spans": [ + { + "bbox": [ + 304, + 567, + 548, + 675 + ], + "type": "text", + "content": "Pretraining Strategies. We evaluate how different pretraining strategies influence the performance of downstream tasks. Starting from the scratch baseline, we apply the proposed strategies one by one. As shown in Table 5, a vanilla 2D-to-3D pretraining stage brings benefits to all the downstream tasks. Introducing corruptions additionally improves the learned motion embeddings. Unified pretraining with in-the-wild videos (w. 2D) enjoys higher motion diversity, which further helps several downstream tasks." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 547, + 715 + ], + "type": "text", + "content": "Pretraining with Different Backbones. We further study the universality of the proposed pretraining approach. We" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "15092" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 286, + 130 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 286, + 130 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 286, + 130 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 286, + 130 + ], + "type": "table", + "html": "
SettingMPJPE ↓ (3D pose)MPVE ↓ (mesh)Accuracy ↑ (action x-view)Accuracy↑ (action 1-shot)
TCN (scratch)50.1mm92.6mm91.5%52.4%
TCN (finetune)47.9mm86.3mm92.8%59.9%
PoseFormer (scratch)44.8mm85.9mm94.2%57.4%
PoseFormer (finetune)41.5mm80.5mm95.9%60.7%
", + "image_path": "26943ad51314ddbfd4a02aad6afacf66d9208cd2af7d11f5278e95d97d8a7be1.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 159, + 285, + 200 + ], + "blocks": [ + { + "bbox": [ + 80, + 137, + 251, + 148 + ], + "lines": [ + { + "bbox": [ + 80, + 137, + 251, + 148 + ], + "spans": [ + { + "bbox": [ + 80, + 137, + 251, + 148 + ], + "type": "text", + "content": "Table 6. Comparison of different backbones." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 159, + 285, + 200 + ], + "lines": [ + { + "bbox": [ + 50, + 159, + 285, + 200 + ], + "spans": [ + { + "bbox": [ + 50, + 159, + 285, + 200 + ], + "type": "table", + "html": "
Arch.(a)(b)(c)(d)(e)(f)
DesignS-TT-SS + TST-MHSAS-T + T-S(Average)S-T + T-S(Adaptive)
MPJPE ↓40.58±0.3141.05±0.2441.76±0.2241.54±0.3539.87±0.3239.25±0.27
", + "image_path": "c5f4324e7dd89ead149bb444ae0d71f41e2d9ce3f27e667f4cd027a4200c14a9.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 209, + 287, + 242 + ], + "lines": [ + { + "bbox": [ + 47, + 209, + 287, + 242 + ], + "spans": [ + { + "bbox": [ + 47, + 209, + 287, + 242 + ], + "type": "text", + "content": "Table 7. Comparison of model architecture variants. All the methods are trained on Human3.6M from scratch over 5 runs and measured by MPJPE (mm) with mean and standard deviation." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 261, + 287, + 332 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 261, + 287, + 332 + ], + "spans": [ + { + "bbox": [ + 47, + 261, + 287, + 332 + ], + "type": "text", + "content": "replace the motion encoder backbone with two variants: TCN [83] and PoseFormer [127]. The models are slightly modified to a seq2seq version, while all the configurations for pretraining and finetuning are simply followed. Table 6 shows that the proposed approach consistently benefits different backbone models on different tasks." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 347, + 287, + 575 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 347, + 287, + 575 + ], + "spans": [ + { + "bbox": [ + 47, + 347, + 287, + 575 + ], + "type": "text", + "content": "Model Architecture. Finally, we study the design choices of DSTformer. From (a) to (f) in Table 7, we compare different structure designs of the basic Transformer module. (a) and (b) are single-stream versions with different orders. (a) is conceptually similar to PoseFormer [127], MH-Former [52], and MixSTE [126]. (c) limits each stream to either temporal or spatial modeling before fusion and is similar to MAED [107]. (d) directly connects S-MHSA and T-MHSA without the MLP in between and is similar to the MSA-T variant in MAED [107]. (e) replaces the adaptive fusion with average pooling on two streams. (f) is the proposed DSTformer design. The result statistically confirms our design principles that both streams should be capable and meanwhile complementary, as introduced in Section 3.2. In addition, we find out that pairing each self-attention block with an MLP is crucial, as it could project the learned feature interactions and bring nonlinearity. In general, we design the model architecture for the 3D pose estimation task and apply it to all other tasks without additional adjustment." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 586, + 119, + 597 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 119, + 597 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 119, + 597 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 605, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 605, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 605, + 287, + 713 + ], + "type": "text", + "content": "In this work, we provide a unified perspective to tackling various human-centric video tasks. We develop a pretraining approach to learn human motion representations from large-scale and heterogeneous data sources. We also propose DSTformer as a universal human motion encoder. Experimental results on multiple benchmarks demonstrate the versatility of the learned motion representations. Future work could explore fusing the learned motion representations with generic video architectures as a human-centric semantic fea" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 545, + 96 + ], + "type": "text", + "content": "ture and applying it to more tasks (e.g., action assessment, segmentation)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 110, + 545, + 148 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 110, + 545, + 148 + ], + "spans": [ + { + "bbox": [ + 306, + 110, + 545, + 148 + ], + "type": "text", + "content": "Acknowledgement This work was partially supported by MOST-2022ZD0114900. 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Twigg2", + "bbox": [ + 169, + 202, + 799, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Cem Keskin $^{2}$ Robert Wang $^{2}$ Markus Steinberger $^{1}$", + "bbox": [ + 267, + 220, + 697, + 238 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ Graz University of Technology, $^{2}$ Meta Reality Labs", + "bbox": [ + 276, + 238, + 692, + 256 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ mathias.parger, thomas.neff, steinberger}@icg.tugraz.at", + "bbox": [ + 233, + 257, + 733, + 273 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "2{chengcheng.tang, cdtwigg,cemkeskin, rywang}@meta.com", + "bbox": [ + 241, + 275, + 725, + 292 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/7e4876e45e14b345689377e1c407a97292c76007fbac45cfd2d45efaeca10cab.jpg", + "image_caption": [ + "Figure 1: MotionDeltaCNN leverages temporal continuity to accelerate CNN inference for videos with moving cameras (bottom) by processing only the sparse frame differences based on a two-dimensional ring buffer, spherical buffer (top). Instead of computing each frame individually, we process only the changes (row $b$ ) between the aligned current (row $a$ ) and previous frames. Our padded convolution creates dilated values (top) which allow for seamless attachment of newly unveiled tiles onto the existing spherical buffer (row $c$ ). With these concepts, MotionDeltaCNN speeds up inference by processing only new regions or updated pixels (white areas in row $d$ ) without additional memory allocation." + ], + "image_footnote": [], + "bbox": [ + 81, + 321, + 895, + 508 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 613, + 313, + 628 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Convolutional neural network inference on video input is computationally expensive and requires high memory bandwidth. Recently, DeltaCNN[26] managed to reduce the cost by only processing pixels with significant updates over the previous frame. However, DeltaCNN relies on static camera input. Moving cameras add new challenges in how to fuse newly unveiled image regions with already processed regions efficiently to minimize the update rate - without increasing memory overhead and without knowing the camera extrinsic of future frames. In this work, we propose Motion-DeltaCNN, a sparse CNN inference framework that supports moving cameras. We introduce spherical buffers and padded convolutions to enable seamless fusion of newly unveiled regions and previously processed regions - without increasing memory footprint. Our evaluation shows that we outperform DeltaCNN by up to $90\\%$ for moving camera videos.", + "bbox": [ + 73, + 641, + 472, + 883 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 501, + 613, + 630, + 628 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Real-time inference of convolutional neural networks (CNN) with video streams remains a power-consuming task and is often infeasible on mobile devices due to hardware and thermal limitations, despite recent efforts aiming at efficient CNN inference through pruning [19, 14], quantization [16, 24, 22], specialized hardware [6, 13, 5] or network optimization [28, 31]. Video input allows for performance optimization through temporal similarity between frames. One common method is to use large, slow networks for accurate predictions at key frames, updated with small, fast networks at intermediate frames [34, 33, 20, 18, 9, 21, 12]. However, this approach requires special network design and training and is not suitable for significant frame changes.", + "bbox": [ + 496, + 641, + 893, + 837 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Sparse convolutions, on the other hand, can be used with existing pre-trained models, accelerating the large network to the speed of a smaller network without impacting prediction accuracy significantly [25, 26]. The linearity of convolutions", + "bbox": [ + 496, + 839, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 47 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "17292", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3e06fb17e9095aa8a4cbf5816f435fe46039f0a20aa06419afd29057b41fd6ab.jpg", + "image_caption": [ + "a b", + "Network Input 1" + ], + "image_footnote": [], + "bbox": [ + 114, + 87, + 359, + 247 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/f6e06ff43622846a8745fa5ed9e0f3c17a166429811ee8efbd779fa6c5e81ae9.jpg", + "image_caption": [ + "Network Input 2", + "Figure 2: To support moving camera input in sparse inference of frame differences, a naive approach (a) is to embed the input onto a larger image and only overwrite pixels that are covered in the next frame. This approach comes with large overhead in memory consumption (storing the additional pixels of the embedded frame) and computational cost (checking all pixels for updates). MotionDeltaCNN (b) uses original shape buffers and feature maps – avoiding the memory overhead and reducing the number of pixels that have to be checked for updates." + ], + "image_footnote": [], + "bbox": [ + 367, + 88, + 609, + 250 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/c96b798c7e87534a7e85d8fdaeeec5c65d1dab7b3725de2aaa2a8b0895742904.jpg", + "image_caption": [ + "Accumulated Input" + ], + "image_footnote": [], + "bbox": [ + 617, + 88, + 861, + 250 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "enables the accumulation of updates over consecutive frames. After processing the first frame densely, upcoming frames can be processed using the difference between the current and the previous frame, the Delta, as the network input. Assuming a static camera scenario, this results in large image regions with no frame-to-frame difference. Static elements like background or stationary objects do not require updates after the initial frame. Researchers exploited this sparsity in previous work to reduce the number of FLOPs required for CNN inference [25, 4, 11, 1, 8], but were mostly unable to accelerate inference in practice. With the recent progress in DeltaCNN [26], theoretical FLOP reductions were translated into practical speedups on GPUs, using a custom sparse CNN implementation to exploit sparsity in all layers of the CNN.", + "bbox": [ + 75, + 383, + 472, + 594 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "DeltaCNN achieves speedups on multiple tasks and datasets, but like prior work, it is optimized for static camera inputs. Even small frame-to-frame camera motion necessitates reprocessing large portions, or the entire image. Spatially aligning consecutive frames, e.g., by leveraging camera extrinsics from IMUs or SLAM on mobile devices, can increase per-pixel similarity and thus update sparsity. Due to the change of camera location and orientation, an aligned new frame may \"grow\" beyond the initial field of view - out of the previous-results buffers. One way to solve this issue is to embed inputs in a larger frame by padding the input image and drawing updates on top of it. However, the downside of this approach is that padded input images increase the memory consumption and computational cost significantly, as shown in Figure 2.", + "bbox": [ + 75, + 595, + 472, + 823 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we propose MotionDeltaCNN, a sparse CNN inference framework that allows moving camera input with marginal memory overhead. Compared to previous work, we achieve up to $90\\%$ higher frame rates in videos with moving cameras, indicating a new perspective for CNN", + "bbox": [ + 75, + 824, + 470, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "inference optimization on low-power devices, such as surveillance cameras, smartphones, or VR headsets.", + "bbox": [ + 498, + 383, + 893, + 412 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our main contributions are:", + "bbox": [ + 519, + 414, + 705, + 428 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose MotionDeltaCNN, the first framework that leverages temporal continuity to accelerate CNN inference for videos with moving cameras by processing only the sparse frame differences.", + "- At the core of this work, we propose padded convolutions for seamless integration of newly unveiled pixels without the need of reprocessing seen pixels.", + "- We design a two-dimensional ring buffer, a spherical buffer, with wrapped coordinates. Our buffer allows partial growth, reset and initialization of new tiles without additional memory allocation.", + "- We show how MotionDeltaCNN can also be used for speeding up applications with static cameras when only parts of the image require processing." + ], + "bbox": [ + 517, + 439, + 893, + 685 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 709, + 640, + 724 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The idea of only processing updated pixels in a convolutional layer has been proposed in various ways, with Recurrent Residual Module (RRM) [25] being the first work to apply this concept to videos. RRM uses the difference between current and previous input, the Delta, as input to convolutional layers. RRM demonstrates large theoretical reductions in FLOPs compared to dense inference resulting from skipping computations involving (nearly) zero-valued entries in feature maps. In practice, skipping individual values is infeasible on most inference hardware like GPUs due to their single instruction, multiple data (SIMD) design.", + "bbox": [ + 496, + 734, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "17293", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/fcfdf84748ef11e212b04640f39514379ba1b08a380433269eeadd20cb9236fe.jpg", + "image_caption": [ + "Figure 3: The main concepts of MotionDeltaCNN. We align frame 2 (F2) with frame 1 (F1) using homography matrices. For the intersecting region, we propagate only the aligned frame-to-frame differences (Delta). The newly uncovered regions are propagated directly. The regions in which the buffers store the uncovered regions are reset to zero before processing the current Delta input. After convolving frame 2, we add the bias to all previously unseen regions, and accumulate the result onto our spherical buffer using the offset coordinates for the current frame." + ], + "image_footnote": [], + "bbox": [ + 76, + 85, + 890, + 244 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Furthermore, RRM only processes convolutional layers on sparse Delta input. All remaining layers are processed on the full, dense feature maps and therefore require expensive value-conversions before and after each convolutional layer.", + "bbox": [ + 75, + 354, + 470, + 415 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Skip-Convolution [11] and CBInfer [4] improve the concept of RRM using a per-pixel sparse mask instead of pervalue. Like RRM, CBInfer uses a threshold to truncate insignificant updates in the input feature map. This threshold can be tuned for each layer for maximum sparsity while keeping the accuracy at a desired level. In contrast, Skip-Convolution decides per output pixel whether an update is required or can be skipped. In both cases, only the convolutional layers (and pooling layers in case of CBInfer) are processed sparsely, requiring expensive conversions between dense and sparse features before and after each of these layers, leaving large performance potential unused.", + "bbox": [ + 75, + 416, + 473, + 598 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "DeltaCNN [26] propagates sparse Delta features end-to-end using a sparse Delta feature map together with an update mask. This greatly reduces the memory bandwidth compared to previous work. Propagating sparse updates end-to-end eliminates the necessity of converting the feature maps from dense accumulated values to sparse Deltas, and it speeds up other layers bottlenecked by memory bandwidth like activation, batch normalization, upsampling, etc. Using a custom CUDA implementation, DeltaCNN outperforms cuDNN and CBInfer many times on video input. However, DeltaCNN, as well as all other previous work, assumes static camera input. Even single pixel camera motion between two frames can result in nearly dense updates when the image contains high frequency features.", + "bbox": [ + 75, + 598, + 470, + 809 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Event Neural Networks show that computational savings are strongly impacted by the intensity of camera motion[8]. With slightly shaking cameras, theoretical FLOP savings were reduced by $40\\%$ compared to static camera videos, while moving cameras reduced them by $60\\%$ . Depending on the distribution of the pixel updates, the impact on real", + "bbox": [ + 75, + 810, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "hardware is likely even higher.", + "bbox": [ + 498, + 354, + 702, + 369 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Incremental Sparse Convolution uses sparse convolutions to incrementally update 3D segmentation masks online [23]. They solve a similar problem of reusing results from previously segmented regions, while allowing for new regions to be attached on the fly. Due to their reliance on non-dilating 3D convolutions [10], attaching new regions leads to artifacts along the region borders. We solve this issue using a standard, dilating convolution and by processing all outputs that are affected by the current input.", + "bbox": [ + 496, + 371, + 893, + 507 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We propose MotionDeltaCNN: building upon DeltaCNN, we design and implement a sparse inference extension that supports moving cameras. Compared to DeltaCNN, we add the support for variable resolution inputs, spherical buffers, dynamic buffer allocation & initialization and padded convolutions for seamless attachment of newly unveiled regions.", + "bbox": [ + 496, + 507, + 893, + 599 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 614, + 589, + 628 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "MotionDeltaCNN relies on the following concepts:", + "bbox": [ + 517, + 640, + 857, + 655 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Frame Alignment The current frame is aligned with the initial frame of the sequence to maximize the overlap of consistent features (see Figure 3 Delta).", + "bbox": [ + 496, + 656, + 893, + 700 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Spherical Buffers We use wrapped buffer offset coordinates in all non-linear layers to align them with the input (see Figure 3 Accumulated Output).", + "bbox": [ + 496, + 702, + 893, + 747 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Dynamic Initialization When a new region is first unveiled due to camera motion, MotionDeltaCNN adds biases onto the feature maps on the fly to all newly unveiled pixels to allow for seamless integration with previously processed pixels (see Figure 3 Bias).", + "bbox": [ + 496, + 748, + 893, + 824 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Padded Convolutions We add additional padding to convolutional layers to process all pixels that are affected by the kernel. These dilated pixels are stored in truncated values buffers to enable seamless connection of potentially unveiled neighbor regions in upcoming frames (see Figure 5).", + "bbox": [ + 496, + 825, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "17294", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Background: DeltaCNN", + "text_level": 1, + "bbox": [ + 76, + 90, + 302, + 107 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For a better understanding of our contributions, we first summarize the core concept of DeltaCNN, which accelerates CNN inference by processing only the first frame densely and applying sparse updates to changed pixels in subsequent frames. A sparse input Delta is calculated by subtracting the previously processed input from the current input frame. Pixels whose Delta is smaller than a threshold are truncated to zero to increase sparsity.", + "bbox": [ + 75, + 113, + 470, + 233 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Because of linearity, the output of any convolution layer can be updated by convolving the sparse input Delta, $c(x + \\delta) = c(x) + c(\\delta)$ . This does not hold for non-linear layers like activation (e.g., ReLU) and pooling, which therefore require a separate accumulated values buffer to accumulate the inputs to the respective layers across all previously processed frames. The buffers contain the full, dense layer input of the previous frame, including biases from previous layers.", + "bbox": [ + 75, + 234, + 470, + 354 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Convolutions with kernel sizes larger than 1x1 pixels dilate the updates across the feature map. A single pixel update in the center of the feature map might span over the entire feature map a few convolutional layers later. This can lead to nearly dense updates for the larger part of the network. DeltaCNN solves this by truncating insignificant updates not only on the input image, but at every activation layer. To avoid accumulating errors indefinitely, the truncated values are accumulated in a dedicated truncated values buffer. Once an accumulated, truncated value exceeds a significance threshold, the value is propagated to the next layer.", + "bbox": [ + 75, + 356, + 470, + 521 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Frame Alignment", + "text_level": 1, + "bbox": [ + 76, + 529, + 250, + 544 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Robust frame alignment (or video stabilization) is a fundamental requirement for MotionDeltaCNN to achieve high coherence across consecutive frames. For best alignment between two frames in a 3D space, we use homography matrices with 8 degrees of freedom. Homography matrices align two images in 3D to match a selected set of key features of the initial frame - typically the static background.", + "bbox": [ + 75, + 551, + 470, + 657 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We embed the image in a grid-aligned frame to ensure a pixel-perfect downscale to all layers. For example, in HRNet [29], the highest resolution feature map spans $384 \\times 384$ pixels, whereas the lowest resolution feature map spans only $12 \\times 12$ pixels, resulting in a scaling factor of $32 \\times 32$ . To ensure that all pixels align on all scaling levels, the input to HRNet must be aligned onto a grid of $32 \\times 32$ pixel tiles. E.g., if a frame has a 20-pixel horizontal offset relative to the first frame, we allocate 32 additional pixels, paste the original frame into the grid-aligned frame and set the 20 left-most pixels as well as the 12 right-most pixels to zero.", + "bbox": [ + 75, + 657, + 470, + 825 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Spherical Buffers", + "text_level": 1, + "bbox": [ + 76, + 832, + 248, + 848 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "MotionDeltaCNN enables support for moving cameras by introducing 2D ring buffers, spherical buffers. These buffers align previously processed pixels with pixels of the current", + "bbox": [ + 76, + 854, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/3277034ac1ddff4b6a94a83ed49057830b7354d83626cff1873169253a0b9a5d.jpg", + "image_caption": [ + "Frame 1" + ], + "image_footnote": [], + "bbox": [ + 504, + 88, + 599, + 162 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/94f154ebe1c637c52f65fae4532979295ca263853349e6dfdba8d28a1fa75382.jpg", + "image_caption": [ + "Cropped" + ], + "image_footnote": [], + "bbox": [ + 633, + 102, + 661, + 145 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/12d35fd2c5e2fff9eeda65ae064ef95401138ca6035622f5aed03aa3843a2b5e.jpg", + "image_caption": [ + "Frame 2", + "Cropped", + "Figure 4: MotionDeltaCNN can handle sparse Delta inputs of different crop sizes, and focus only on a fraction of the image, thanks to the concept of spherical buffers. This is not possible for DeltaCNN which always processes sparse Delta inputs of the entire frame." + ], + "image_footnote": [], + "bbox": [ + 694, + 88, + 792, + 162 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/5efb1b34bdfb512ea967d50dccfb777b82765324398e1fdd597348d95a1e5814.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 831, + 109, + 849, + 138 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "frame by translating feature map coordinates to buffer coordinates. Pixel coordinates exceeding image borders are wrapped around the buffer, i.e., mapped to the opposite border using the modulo operator. This enables the reuse of previous results for moving cameras without increasing the memory overhead over DeltaCNN (see Figure 5). Our buffers support 2D offsets relative to the initial frame as well as cropped inputs (see Figure 4). Frame scales can be helpful when only a part of the image is updated in the current frame - for example, when a frame is cropped to the bounding box of a region of interest. Tile offset indices are provided during inference to align features in buffers with the current input. By multiplying tile offset indices with a layer's tile size (in the example above $32 \\times 32$ pixels in highest resolution feature maps, $1 \\times 1$ pixel in the lowest resolution), we get the pixel offset coordinates for buffer access in non-linear layers.", + "bbox": [ + 496, + 297, + 893, + 541 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Dynamic Initialization", + "text_level": 1, + "bbox": [ + 500, + 551, + 709, + 568 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "When the input frame covers a previously unseen area, new tiles are allocated in all buffers before inferring the frame. A new tile is allocated by deleting a previously stored tile at the desired location and resetting respective values to zero. In doing so, we lose information about the accumulated biases inferred in the initial frame. We compensate for this by adding the biases onto reset regions of the Delta feature map during inference.", + "bbox": [ + 496, + 575, + 893, + 699 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.5. Padded Convolutions", + "text_level": 1, + "bbox": [ + 500, + 709, + 700, + 724 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "After the initial frame, MotionDeltaCNN propagates only Delta updates for the remaining sequence. This can cause inconsistencies when mixing previously seen and newly unveiled pixels. Consider a pair of adjacent pixels $\\mathbf{p}_{seen}$ and $\\mathbf{p}_{new}$ across the boundary, the resulting output at $\\mathbf{p}_{new}$ may \"miss\" previously accumulated updates from pixel $\\mathbf{p}_{seen}$ (see Figure 5), since they were \"outside\".", + "bbox": [ + 496, + 733, + 893, + 839 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "MotionDeltaCNN addresses this prospectively by increasing the padding of convolutional layers to include all pixels that could be affected by convolutions on the current input. This leads to an increased output size compared to the input", + "bbox": [ + 496, + 839, + 893, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "17295", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/212787961a0639aeba6131c9f7f0a774396dbe72f7aa82ffb36379258e545a20.jpg", + "image_caption": [ + "Frame 1" + ], + "image_footnote": [], + "bbox": [ + 112, + 146, + 235, + 265 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/0153b386ea13ac3743251599b9ac0caa95261654174e6ad1ede9fef2765a807c.jpg", + "image_caption": [ + "Output 1" + ], + "image_footnote": [], + "bbox": [ + 238, + 147, + 362, + 265 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/6ba5db3b850e1a3cf505117dd8e4779b984d4a96b7d73d92f0ba0b677b681bed.jpg", + "image_caption": [ + "Delta Frame 2", + "Figure 5: Padded convolutions enable fusing images recorded at different perspectives. Naively applying convolutions separately to the initial frame and the Delta of Frame 2, and aggregating the outputs (row b) does not achieve the same results as one would get if the convolution is directly applied to a large fused input buffer (row a). This is because of how the boundary pixels are treated and dropped when applying convolutions and border cropping. To address this issue, we need to cache and pad the output features, as shown in row c. See Section 3.5 for details regarding how to handle this in a practical manner." + ], + "image_footnote": [], + "bbox": [ + 364, + 147, + 486, + 265 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/914a5793d6c4bd84ce6e12479f6784c7300d3dca066a6646197242e0aa3e1957.jpg", + "image_caption": [ + "Output 2" + ], + "image_footnote": [], + "bbox": [ + 490, + 147, + 612, + 265 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/b7fd25abc1903a0717518b9f696cb0cd4ece750f3c17790aa26ee627d5743f09.jpg", + "image_caption": [ + "Accumulated Input" + ], + "image_footnote": [], + "bbox": [ + 614, + 88, + 736, + 265 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/a0c01e0b318c9e43e84f3aa9348f0c3772fce9e5fe1d4272e3c553e9286f5d96.jpg", + "image_caption": [ + "Accumulated Output" + ], + "image_footnote": [], + "bbox": [ + 740, + 88, + 862, + 265 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "when the kernel size is larger than 1x1. For example, a 64x64 pixel input and a 3x3 kernel result in a 66x66 pixel output.", + "bbox": [ + 75, + 402, + 468, + 431 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "With modern CNNs consisting of hundreds of convolutional layers, growing the feature map at each layer could quickly exceed our buffers and computational budget. To prevent this, in practice, we move and stash these output values at dilated pixels, and crop the output feature map of the current buffer to its original shape. Since MotionDeltaCNN already uses truncated values buffers for storing values that were not yet propagated through the activation layer, we only need to increase the size of the buffer slightly to include the dilated values and accumulate them there for later use. Combined with spherical buffers, this allows us to fuse new image regions from all 4 directions seamlessly at the cost of memory and compute overhead for the dilated border pixels. Since most convolutions use kernels of size $3 \\times 3$ and $1 \\times 1$ , the overhead is typically low.", + "bbox": [ + 75, + 431, + 472, + 659 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.6. Buffer management", + "text_level": 1, + "bbox": [ + 76, + 666, + 266, + 681 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We use a buffer manager that is responsible for: keeping track of each tile's state, allocating new regions in the spherical buffer, initializing newly allocated tiles and adding biases to feature maps during inference. As mentioned before, spherical buffers wrap coordinates around image borders to allow for infinite panning. One downside of this approach is that when borders grow in one direction, we overwrite the dilated pixels stored for growing in the opposite direction (see Figure 1). Restoring dilated pixels is non-trivial and would require inferring the negative accumulated values of the deleted tiles - which adds high overhead. Instead, we simply delete the dilated pixels and restrict the growth in the opposite direction. Once the camera moves back over a restricted region, all buffers are reset entirely, and the cur", + "bbox": [ + 75, + 689, + 472, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "rent frame has to be inferred densely - becoming the new reference until the next buffer reset. Restoring the truncated values by only resetting the tiles next to the invalid truncated values does not work, as they would again lack valid truncated values required for seamless attachment to persistent tiles. While a full reset reduces the reuse of previously processed features, in our evaluations, the number of resets is fairly small as camera pans typically last many frames without changing directions. Our buffer manager stores for each tile of the grid the currently held global coordinates and the directions in which the growth is restricted. Every time the camera moves, the buffer manager checks whether the tiles already hold a value from the corresponding coordinates. If not, it resets the respective tiles if possible or requests a buffer reset if growth is restricted.", + "bbox": [ + 496, + 402, + 895, + 628 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.7. Optimizations", + "text_level": 1, + "bbox": [ + 500, + 636, + 645, + 651 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "While the above-mentioned features can already lead to a large speedup in moving camera scenarios, the speedup can be increased significantly with some small optimizations. For the DAVIS 2017 dataset [27], we noticed strong salt-and-pepper style noise in the update masks. Since video stabilization is not perfect, some pixels align incorrectly, especially in high frequency details like leaves of a tree. This leads to a strong color change for some isolated pixels in the image, resulting in a large compute overhead when processing the image in tiles. We mitigate this issue using region-of-interest (ROI) focused sensing and noise suppression. When we know the ROI from previous frames, e.g., in the case of object detection or object segmentation, we can increase the sensitivity around these regions and decrease the sensitivity further away. Additionally, we suppress noise coming from imperfect image alignment by downscaling", + "bbox": [ + 496, + 659, + 893, + 901 + ], + "page_idx": 4 + }, + { + "type": "aside_text", + "text": "a b C", + "bbox": [ + 76, + 114, + 89, + 241 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "17296", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/bd7366fcd3fdcddad7b3fd9caa738805892bab935881bfe77b7650a0244baca2.jpg", + "image_caption": [ + "Frame 1" + ], + "image_footnote": [], + "bbox": [ + 81, + 87, + 210, + 145 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/30f055a0c7820b9fbe69cd1dad65d79aa03d7e40b11ccf56d0317b0d6128ae25.jpg", + "image_caption": [ + "Frame 2" + ], + "image_footnote": [], + "bbox": [ + 215, + 88, + 346, + 146 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/7f3c290fefe098cd20ac85e748b8dba87abb62614e3ee21013920d022a07d649.jpg", + "image_caption": [ + "T", + "Figure 6: We increase update sparsity using noise suppression and region of interest scaling. $T$ uses the original truncation implementation of DeltaCNN. Scaling the Delta further away from the region of interest $(T + S)$ slightly increases sparsity. Using noise suppression $(T + N)$ to eliminate single pixel updates increases sparsity even further. Combining scaling and noise suppression $(T + S + N)$ achieves the highest sparsity, capturing only the most important updates of the moving camel. Note that in all cases, we dilate the update mask by 10 pixels; explaining the low sparsity in case $T$ . Source: DAVIS 2017" + ], + "image_footnote": [], + "bbox": [ + 351, + 97, + 449, + 147 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/331eb80f5b9a668aedc0dfb88565b45f33ac3577e7ef3312e1e276e50275b96e.jpg", + "image_caption": [ + "T+S" + ], + "image_footnote": [], + "bbox": [ + 460, + 87, + 612, + 146 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/51ba846875f5cc2067a574c9639ca129719b82a024a6e052fd14726e4db1d09d.jpg", + "image_caption": [ + "$\\mathrm{T + N}$" + ], + "image_footnote": [], + "bbox": [ + 616, + 89, + 745, + 145 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/93946d9a59b6f75f2d0a0ac9ee3362023d22dbeb5e0769625361110ca3310af6.jpg", + "image_caption": [ + "$\\mathrm{T} + \\mathrm{S} + \\mathrm{N}$" + ], + "image_footnote": [], + "bbox": [ + 750, + 89, + 879, + 145 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "the Delta, processing which pixels exceed the thresholds and suppressing single pixel updates using average pooling. Overall, these steps lead to a significant speedup with only minor impact on accuracy (see Figure 6). Further optimizations can be found in the supplemental material.", + "bbox": [ + 75, + 280, + 470, + 356 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Evaluation", + "text_level": 1, + "bbox": [ + 76, + 373, + 192, + 388 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We evaluate MotionDeltaCNN in two scenarios: a) using video stabilization to align subsequent frames with moving cameras and b) using bounding boxes in a static camera scenario to infer only regions of interest while retaining out-of-interest features from previous frames.", + "bbox": [ + 75, + 398, + 468, + 474 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Video Object Segmentation In task a), we evaluate the video object segmentation model BMVOS [7] on the DAVIS 2017 dataset [27]. BMVOS uses the DenseNet [15] backend for feature encoding, the most computationally expensive part of the model. We use weights pretrained on the DAVIS dataset, which were provided by the authors of BMVOS. The DAVIS 2017 dataset consists of a set of sequences with one or more segmented objects of which the masks are provided only for the first frame - and the model needs to paint the segmentation mask for the remaining frames in the video. Most of the videos are recorded using moving cameras, and are therefore well suited for evaluating MotionDeltaCNN. The DAVIS 2017 dataset does not provide camera extrinsic. Instead, we use OpenCV [2] to estimate homography matrices between two consecutive frames. This simplistic method fails in some cases, e.g., when it does not find good features due to motion blur or with motion parallax. We see the tasks of video stabilization as orthogonal and therefore only evaluate on the set of videos (14 sequences) for which this simple video stabilization approach works reliably.", + "bbox": [ + 75, + 477, + 470, + 779 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In video object segmentation, the segmentation mask from the previous frame can be used to suppress noise in the upcoming frame. We use this mask to lower the update sensitivity further away from the ROI - leading to an increase in sparsity. We deliberately tuned the thresholds for DeltaCNN with a lower accuracy target than for MotionDeltaCNN to show that we achieve higher frame rates even when targeting higher accuracy. The details about threshold tuning and", + "bbox": [ + 75, + 780, + 470, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "ROI-focused sensing are found in the supplemental material.", + "bbox": [ + 500, + 281, + 892, + 295 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Human Pose Estimation In task b), we perform human pose estimation using HRNet [30, 32] on the Human3.6M dataset [3, 17]. Human3.6M uses static cameras and is recorded in a static studio with only a single moving actor in the room. We use this dataset to evaluate a second scenario for MotionDeltaCNN: top-down pose estimation. With top-down pose estimation, humans in the scene are detected first, and then the pose is predicted for each detected human. Each bounding box is cropped and inferred individually - estimating one set of joints per person. Since Human3.6M provides per frame bounding boxes of the actors as part of their labels, we omit the step of detecting humans in the scene. We snap the given bounding boxes onto a $32 \\times 32$ pixel grid and then increase them by 32 pixels on each side where possible. The increased bounding boxes ensure that joint positions are not too close to image borders, as this could negatively impact prediction accuracy. We use the same weights and thresholds as were used in the DeltaCNN paper and evaluate on the same data subset (Subject S11).", + "bbox": [ + 496, + 299, + 893, + 585 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Both scenarios are compared against dense inference of cuDNN and against the original DeltaCNN without moving camera support. In HRNet, we only measure model inference time, without the overhead of post-processing or accuracy evaluation. The input shape is $384 \\times 384$ with a tile size of $32 \\times 32$ pixels unless stated otherwise. In the case of BMVOS, we only measure the duration of the feature encoding model to better highlight the difference of pure CNN inference speeds. For this evaluation, the camera input is embedded into a frame of shape Wx480 pixels, where W depends on the aspect ratio of the video (typically 864px) and is aligned onto a grid with a tile size of $48 \\times 48$ pixels.", + "bbox": [ + 496, + 590, + 893, + 771 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Hardware We conduct our evaluations on two GPUs: Nvidia GTX 1080 Ti and Nvidia RTX 3090 with 3584/10496 CUDA cores and 11GB/24GB of VRAM respectively. The evaluations are performed using 32-bit precision, but our approach can be applied to other data types as well.", + "bbox": [ + 496, + 775, + 893, + 851 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "1The Human3.6M dataset was accessed and used only by the co-authors at Graz University of Technology", + "bbox": [ + 500, + 875, + 892, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "17297", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/0f8ad12cd8facb988f2202557526cdaef44c719ed6835c98caf5733ece614d76.jpg", + "image_caption": [ + "Figure 7: A DAVIS 2017 sequence processed using DeltaCNN (left) and MotionDeltaCNN (right). Row a shows the original input on the left, and the aligned and cropped input on the right. Row b visualizes the Delta between the (aligned) input and the previous input in row c. Row d visualizes the update mask with white pixels indicating an update. MotionDeltaCNN achieves much higher sparsity on the same input by reusing previous results for the aligned, static background." + ], + "image_footnote": [], + "bbox": [ + 89, + 90, + 885, + 178 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5. Results", + "text_level": 1, + "bbox": [ + 76, + 276, + 165, + 292 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We evaluate speedup and accuracy of MotionDeltaCNN compared to DeltaCNN without explicit moving camera support as well as the dense cuDNN backend. In this section, we report the differences on the GTX 1080 Ti - for results on the RTX 3090, please see the respective tables.", + "bbox": [ + 75, + 303, + 470, + 378 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Video Object Segmentation MotionDeltaCNN outperforms state-of-the-art backends in sparse mode by a margin of up to $100\\%$ over the cuDNN baseline (see Table 1). The DAVIS 2017 dataset consists mainly of videos with large bounding boxes and often fast camera motion, leading to a high average update rate of $29\\%$ .", + "bbox": [ + 75, + 380, + 470, + 470 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Excluding videos without camera motion highlights the relative speedup over DeltaCNN without moving camera support with $+85\\%$ speedup over cuDNN instead of $+8\\%$ .", + "bbox": [ + 75, + 473, + 470, + 518 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "MotionDeltaCNN, like DeltaCNN, requires larger workloads with more powerful hardware to show speedups. With 10.496 cores in a RTX 3090, small batch sizes typically do not fully utilize the available hardware resources in most layers - skipping some tiles in this scenario does not affect the overall performance unless all tiles can be skipped altogether. By increasing the batch size, we can fully utilize the GPU - cores that skip a tile can immediately continue processing the next tile, leading to an overall speedup.", + "bbox": [ + 75, + 518, + 470, + 656 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Over the 990 frames in the DAVIS dataset, we had to reset the buffers 9 times because of cameras panning over invalid truncated values. This low number of resets has only a small impact on the overall performance.", + "bbox": [ + 75, + 657, + 468, + 717 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Human Pose Estimation MotionDeltaCNN can outperform cuDNN by up to 11x in the case of HRNet (see Table 2). Please note that the frame rate of cuDNN is $30\\%$ lower than in the DeltaCNN paper since we enforced the use of 32-bit multiplications in all layers - the same accuracy that we also use in our implementation. Furthermore, the accuracies do not match since we always use the full, uncropped images as input. The high sparsity in the Human3.6M dataset together with the efficient implementation allows us to accelerate inference significantly. Compared to DeltaCNN, which does not support varying resolution input or moving cameras, we were able to achieve $13\\%$ higher frame rates with similar", + "bbox": [ + 75, + 719, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "accuracy. We level the playing field in comparisons against the dense cuDNN backend by inferring the same cropped images that we use as input for MotionDeltaCNN. Still, we outperform cuDNN by up to $3.2\\mathrm{x}$ , and achieve a speedup of up to $3.2\\mathrm{x}$ over dense DeltaCNN with full resolution input. For Human3.6M, we know that the actors never cover the entire frame at once. We use this knowledge to lower the size of the buffers by $25\\%$ on each axis - reducing the memory footprint of buffers by $44\\%$ in total. These savings allow us to increase the batch size even further. When fully utilizing all available memory with an increased batch size, we achieve frame rates up to $3.9\\mathrm{x}$ over the cropped cuDNN baseline and $37\\%$ over DeltaCNN.", + "bbox": [ + 496, + 277, + 893, + 474 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation Study We evaluated the individual impact of our contributions in an ablation study (see Table 3). Without dynamic initialization, MotionDeltaCNN always resets the buffers when new image tiles are unveiled. After a reset, the next frame is processed densely. This has a negative impact on the speedup, but slightly increases the accuracy as it regularly flushes accumulated errors. Padded convolutions are key in enabling spherical buffers. Without them, new tiles are not fused into existing buffers correctly, leading to a reduction in accuracy. Our evaluation shows that (ROI) focused sensing enables great speedups without lowering the accuracy of the segmentation. By disabling noise suppression as well, the model becomes more sensitive to errors in image alignment and small changes in the image. To compensate for this, we increase the threshold of the first truncation from 0.15 to 0.35 for this evaluation. However, even with an increased threshold, the speedup is significantly smaller compared to default truncation, while the accuracy is already much lower. Overall, the ablation study shows that all parts of MotionDeltaCNN work in tandem to achieve the best speedup without large impact on accuracy.", + "bbox": [ + 496, + 476, + 893, + 792 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6. Discussion", + "text_level": 1, + "bbox": [ + 500, + 801, + 612, + 816 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Our evaluations prove that MotionDeltaCNN can accelerate CNN video inference with moving cameras where existing sparse methods fail to outperform the dense reference. However, our evaluation also shows that freely moving cameras, especially when combined with dense updates as in", + "bbox": [ + 496, + 825, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "17298", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/cb947a0d7ad17e0718c87af7f3bd687a41e98231b2c5aa75a3fb1260e7aa587d.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
VideosBackendIoUGFLOPsGTX 1080 Ti b=1GTX 1080 Ti b=5RTX 3090 b=1RTX 3090 b=12
FPSspeedupFPSspeedupFPSspeedupFPSspeedup
AllcuDNN76.8522.130.71.040.91.045.41.01031.0
DeltaCNN (dense)76.8522.135.01.1441.21.0166.51.461000.97
MotionDeltaCNN (dense)76.7622.633.51.0940.30.9957.71.2793.60.91
DeltaCNN (sparse)76.1815.542.51.3851.41.2670.01.541251.21
MotionDeltaCNN (sparse)76.326.854.81.7981.92.0065.21.442152.1
MovingcuDNN79.5922.130.71.040.91.045.41.01031.0
DeltaCNN (sparse)79.3818.838.21.2444.11.0870.21.551061.03
MotionDeltaCNN (sparse)79.437.352.31.7075.11.8465.01.432011.95
", + "bbox": [ + 81, + 88, + 890, + 262 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/6998b419d54989396ed5b5075894352b634c329902620ce8281fa45af725785a.jpg", + "table_caption": [ + "Table 1: Results for the task of video object segmentation using BMVOS on the DAVIS dataset. We track only the DenseNet backend for evaluating frames per second (FPS). For accuracy benchmarks, the remaining network is processed densely. GFLOPs are reported as average over the test set. Both devices are evaluated with a batch size $b$ of one, and the maximum batch size each device can hold in memory." + ], + "table_footnote": [], + "table_body": "
BackendPCKh@0.5PCKh@0.2GFLOPsGTX 1080 Ti b=1GTX 1080 Ti b=16RTX 3090 b=1RTX 3090 b=40
FPSspeedupFPSspeedupFPSspeedupFPSspeedup
cuDNN96.03%83.33%47.122.51.024.81.012.31.069.61.0
DeltaCNN (dense)24.21.0841.31.726.02.195.81.4
MotionDeltaCNN (dense)96.00%83.32%17.732.51.4491.43.722.01.82323.3
cuDNN (cropped)95.92%83.11%13.324.01.0771.02.911.81.02093.0
DeltaCNN (sparse)95.95%82.31%3.5544.92.02028.126.22.15477.9
MotionDeltaCNN (sparse)95.95%82.33%3.4541.21.832289.222.61.85848.4
MotionDeltaCNN (sparse †)95.93%82.22%3.4442.51.8927611.122.51.86919.9
", + "bbox": [ + 81, + 345, + 890, + 489 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/19829a5ac6d64a0bbd27f9428f798333d31f230cacffd21175abe67f5ea3b356.jpg", + "table_caption": [ + "Table 2: Speed and accuracy comparisons of different CNN backends used for pose estimation on the Human3.6M dataset. The same set of auto-tuned thresholds for update truncation is used for all devices and batch sizes $b$ . † limits the size of the input from 384x384 to 288x288 pixels - freeing up 44% of the memory used for buffers. The freed-up memory is used to increase the batch size to fully utilize the available VRAM (b=28 on 1080 Ti and b=66 on 3090). cuDNN cropped uses the same, cropped input as ours, instead of the full camera input." + ], + "table_footnote": [], + "table_body": "
FPSIoU# resets
cuDNN40.979.59-
DeltaCNN44.179.38-
MotionDeltaCNN75.179.438
- w/o dynamic init56.479.63110
- w/o padded conv.65.377.898
- w/o ROI scaling63.679.338
- w/o ROI & noise*50.979.068
", + "bbox": [ + 112, + 599, + 434, + 724 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 3: Ablation study. Evaluating BMVOS on DAVIS2017 dataset using a Nvidia GTX 1080 Ti with a batch size of 5. We evaluate on the subset of videos with significant camera motion. * increased threshold on video input.", + "bbox": [ + 75, + 734, + 470, + 797 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "the DAVIS dataset, lead to a much smaller speedup than the static camera setup with sparse motion in Human3.6M. Furthermore, the additional padding slightly increases memory and compute overhead over DeltaCNN.", + "bbox": [ + 75, + 823, + 470, + 883 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Receptive Field While MotionDeltaCNN does achieve", + "bbox": [ + 96, + 885, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "outputs comparable to standard CNN inference, it should be noted that even in dense mode, the results are not identical. This can be observed in Figure 5 where the fused output of MotionDeltaCNN matches the result using the fused input in row $a$ , which includes information from neighbor pixels seen in previous frames. Since we do not actively propagate inverted accumulated values once a previously processed region gets out of view, the receptive field of later layers, also for pixels inside the current view, still contains some information from that now unseen area. This can have positive and negative effects alike. These features might not be valid anymore. At the same time, some out-of-view features can help to make better predictions due to additional context.", + "bbox": [ + 496, + 602, + 893, + 800 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Applications MotionDeltaCNN is a general-purpose framework for video inference and can thus be used with all pre-trained CNNs by replacing the original, dense layers with our sparse equivalent. As additional input, Motion-DeltaCNN requires camera extrinsics for the frame to be processed. While most publicly available datasets do not", + "bbox": [ + 496, + 809, + 895, + 902 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "17299", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "include camera extrinsics and therefore require image stabilization, smartphones, tablets and VR headsets nowadays have built-in support for tracking the camera pose between frames in real-time. Potential applications are not limited to classic computer vision applications like tracking and segmentation, but it could also be used for video up-scaling, filtering, etc. However, applications like image-denoising (diffusion) are likely not a good fit as they provide low levels of spatial update sparsity between iterations and they are very sensitive to noise.", + "bbox": [ + 75, + 90, + 472, + 241 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Limitations One of the main limitations of our approach is its dependency on robust video stabilization. Our experiments with the DAVIS dataset showed that simple video stabilization techniques can break when blur or parallax is involved, or when it fails to find robust features. Parallax can greatly reduce the gains of our method, even when the scene itself is mostly static. When foreground and background layers move at different speeds, frames can only be properly aligned to stabilize one of these layers - leading to dense updates in layers moving at different speeds.", + "bbox": [ + 75, + 242, + 472, + 393 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "MotionDeltaCNN also comes with the trade-off between buffer overallocation and losing information by cropping the input to match the shape of the buffer. In our evaluations, when the camera zooms or rotates around the forward axis (roll), the aligned input can exceed the size of the buffers, and therefore requires slight cropping to fit into the target shape (see Figure 7). Alternatively, the buffers could also be increased to allow for larger inputs in upcoming frames - at the cost of higher memory consumption.", + "bbox": [ + 75, + 393, + 472, + 529 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "7. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 534, + 194, + 549 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We propose MotionDeltaCNN, an extension to the sparse video CNN framework DeltaCNN adding support for moving camera input. To the best of our knowledge, we are the first to propose a solution for moving cameras with sparse inference. MotionDeltaCNN uses spherical buffers, padded convolutions and dynamic initialization of newly unveiled regions to support combining previously processed pixels and newly unveiled pixels together with high sparsity. We test our approach in practice by implementing all kernels natively on the GPU to evaluate the real-world performance with modern hardware. Our experiments show that we outperform DeltaCNN by up to $90\\%$ on moving camera input and that MotionDeltaCNN can also be beneficial to lower the memory footprint in static camera scenarios.", + "bbox": [ + 75, + 554, + 472, + 765 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 76, + 777, + 174, + 792 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Udari De Alwis and Massimo Alioto. TempDiff: Temporal Difference-Based Feature Map-Level Sparsity Induction in CNNs with $< 4\\%$ Memory Overhead. 2021 IEEE 3rd International Conference on Artificial Intelligence Circuits and Systems, AICAS 2021, pages 1-4, Jun 2021.", + "[2] G. Bradski. The OpenCV Library. 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Proceedings - 30th IEEE Conference on Computer Vision and Pattern Recognition, CVPR 2017, 2017-January:4141-4150, 2017." + ], + "bbox": [ + 501, + 92, + 893, + 290 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "17301", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/MotionDeltaCNN_ Sparse CNN Inference of Frame Differences in Moving Camera Videos with Spherical Buffers and Padded Convolutions/60cee84a-76a7-422c-a440-0ab4865a753d_model.json b/2023/MotionDeltaCNN_ Sparse CNN Inference of Frame Differences in Moving Camera Videos with Spherical Buffers and Padded Convolutions/60cee84a-76a7-422c-a440-0ab4865a753d_model.json new file mode 100644 index 0000000000000000000000000000000000000000..df4a988ad24e3622af25da3d06a465eb6f796644 --- /dev/null +++ b/2023/MotionDeltaCNN_ Sparse CNN Inference of Frame Differences in Moving Camera Videos with Spherical Buffers and Padded Convolutions/60cee84a-76a7-422c-a440-0ab4865a753d_model.json @@ -0,0 +1,2167 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.044 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.048 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.13, + 0.895, + 0.177 + ], + "angle": 0, + "content": "MotionDeltaCNN: Sparse CNN Inference of Frame Differences in Moving Camera Videos with Spherical Buffers and Padded Convolutions" + }, + { + "type": "text", + "bbox": [ + 0.171, + 0.203, + 0.8, + 0.222 + ], + "angle": 0, + "content": "Mathias Parger1 Chengcheng Tang2 Thomas Neff1 Christopher D. Twigg2" + }, + { + "type": "text", + "bbox": [ + 0.269, + 0.222, + 0.699, + 0.239 + ], + "angle": 0, + "content": "Cem Keskin\\(^{2}\\) Robert Wang\\(^{2}\\) Markus Steinberger\\(^{1}\\)" + }, + { + "type": "text", + "bbox": [ + 0.277, + 0.239, + 0.694, + 0.257 + ], + "angle": 0, + "content": "\\(^{1}\\)Graz University of Technology, \\(^{2}\\)Meta Reality Labs" + }, + { + "type": "text", + "bbox": [ + 0.235, + 0.258, + 0.734, + 0.275 + ], + "angle": 0, + "content": "\\(^{1}\\)mathias.parger, thomas.neff, steinberger}@icg.tugraz.at" + }, + { + "type": "text", + "bbox": [ + 0.242, + 0.276, + 0.727, + 0.293 + ], + "angle": 0, + "content": "2{chengcheng.tang, cdtwigg,cemkeskin, rywang}@meta.com" + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.323, + 0.896, + 0.51 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.075, + 0.519, + 0.895, + 0.61 + ], + "angle": 0, + "content": "Figure 1: MotionDeltaCNN leverages temporal continuity to accelerate CNN inference for videos with moving cameras (bottom) by processing only the sparse frame differences based on a two-dimensional ring buffer, spherical buffer (top). Instead of computing each frame individually, we process only the changes (row \\( b \\)) between the aligned current (row \\( a \\)) and previous frames. Our padded convolution creates dilated values (top) which allow for seamless attachment of newly unveiled tiles onto the existing spherical buffer (row \\( c \\)). With these concepts, MotionDeltaCNN speeds up inference by processing only new regions or updated pixels (white areas in row \\( d \\)) without additional memory allocation." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.614, + 0.314, + 0.629 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.642, + 0.473, + 0.884 + ], + "angle": 0, + "content": "Convolutional neural network inference on video input is computationally expensive and requires high memory bandwidth. Recently, DeltaCNN[26] managed to reduce the cost by only processing pixels with significant updates over the previous frame. However, DeltaCNN relies on static camera input. Moving cameras add new challenges in how to fuse newly unveiled image regions with already processed regions efficiently to minimize the update rate - without increasing memory overhead and without knowing the camera extrinsic of future frames. In this work, we propose Motion-DeltaCNN, a sparse CNN inference framework that supports moving cameras. We introduce spherical buffers and padded convolutions to enable seamless fusion of newly unveiled regions and previously processed regions - without increasing memory footprint. Our evaluation shows that we outperform DeltaCNN by up to \\(90\\%\\) for moving camera videos." + }, + { + "type": "title", + "bbox": [ + 0.502, + 0.614, + 0.631, + 0.629 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.642, + 0.895, + 0.838 + ], + "angle": 0, + "content": "Real-time inference of convolutional neural networks (CNN) with video streams remains a power-consuming task and is often infeasible on mobile devices due to hardware and thermal limitations, despite recent efforts aiming at efficient CNN inference through pruning [19, 14], quantization [16, 24, 22], specialized hardware [6, 13, 5] or network optimization [28, 31]. Video input allows for performance optimization through temporal similarity between frames. One common method is to use large, slow networks for accurate predictions at key frames, updated with small, fast networks at intermediate frames [34, 33, 20, 18, 9, 21, 12]. However, this approach requires special network design and training and is not suitable for significant frame changes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Sparse convolutions, on the other hand, can be used with existing pre-trained models, accelerating the large network to the speed of a smaller network without impacting prediction accuracy significantly [25, 26]. The linearity of convolutions" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17292" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.078, + 0.137, + 0.091, + 0.226 + ], + "angle": 0, + "content": "a b" + }, + { + "type": "image", + "bbox": [ + 0.116, + 0.088, + 0.36, + 0.248 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.188, + 0.255, + 0.288, + 0.269 + ], + "angle": 0, + "content": "Network Input 1" + }, + { + "type": "image", + "bbox": [ + 0.369, + 0.089, + 0.611, + 0.25 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.439, + 0.255, + 0.541, + 0.269 + ], + "angle": 0, + "content": "Network Input 2" + }, + { + "type": "image", + "bbox": [ + 0.619, + 0.089, + 0.862, + 0.25 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.683, + 0.255, + 0.798, + 0.269 + ], + "angle": 0, + "content": "Accumulated Input" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.281, + 0.895, + 0.358 + ], + "angle": 0, + "content": "Figure 2: To support moving camera input in sparse inference of frame differences, a naive approach (a) is to embed the input onto a larger image and only overwrite pixels that are covered in the next frame. This approach comes with large overhead in memory consumption (storing the additional pixels of the embedded frame) and computational cost (checking all pixels for updates). MotionDeltaCNN (b) uses original shape buffers and feature maps – avoiding the memory overhead and reducing the number of pixels that have to be checked for updates." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.384, + 0.473, + 0.595 + ], + "angle": 0, + "content": "enables the accumulation of updates over consecutive frames. After processing the first frame densely, upcoming frames can be processed using the difference between the current and the previous frame, the Delta, as the network input. Assuming a static camera scenario, this results in large image regions with no frame-to-frame difference. Static elements like background or stationary objects do not require updates after the initial frame. Researchers exploited this sparsity in previous work to reduce the number of FLOPs required for CNN inference [25, 4, 11, 1, 8], but were mostly unable to accelerate inference in practice. With the recent progress in DeltaCNN [26], theoretical FLOP reductions were translated into practical speedups on GPUs, using a custom sparse CNN implementation to exploit sparsity in all layers of the CNN." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.597, + 0.473, + 0.824 + ], + "angle": 0, + "content": "DeltaCNN achieves speedups on multiple tasks and datasets, but like prior work, it is optimized for static camera inputs. Even small frame-to-frame camera motion necessitates reprocessing large portions, or the entire image. Spatially aligning consecutive frames, e.g., by leveraging camera extrinsics from IMUs or SLAM on mobile devices, can increase per-pixel similarity and thus update sparsity. Due to the change of camera location and orientation, an aligned new frame may \"grow\" beyond the initial field of view - out of the previous-results buffers. One way to solve this issue is to embed inputs in a larger frame by padding the input image and drawing updates on top of it. However, the downside of this approach is that padded input images increase the memory consumption and computational cost significantly, as shown in Figure 2." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.471, + 0.903 + ], + "angle": 0, + "content": "In this work, we propose MotionDeltaCNN, a sparse CNN inference framework that allows moving camera input with marginal memory overhead. Compared to previous work, we achieve up to \\(90\\%\\) higher frame rates in videos with moving cameras, indicating a new perspective for CNN" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.384, + 0.895, + 0.414 + ], + "angle": 0, + "content": "inference optimization on low-power devices, such as surveillance cameras, smartphones, or VR headsets." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.415, + 0.706, + 0.429 + ], + "angle": 0, + "content": "Our main contributions are:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.44, + 0.895, + 0.501 + ], + "angle": 0, + "content": "- We propose MotionDeltaCNN, the first framework that leverages temporal continuity to accelerate CNN inference for videos with moving cameras by processing only the sparse frame differences." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.511, + 0.894, + 0.558 + ], + "angle": 0, + "content": "- At the core of this work, we propose padded convolutions for seamless integration of newly unveiled pixels without the need of reprocessing seen pixels." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.567, + 0.895, + 0.629 + ], + "angle": 0, + "content": "- We design a two-dimensional ring buffer, a spherical buffer, with wrapped coordinates. Our buffer allows partial growth, reset and initialization of new tiles without additional memory allocation." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.639, + 0.894, + 0.686 + ], + "angle": 0, + "content": "- We show how MotionDeltaCNN can also be used for speeding up applications with static cameras when only parts of the image require processing." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.44, + 0.895, + 0.686 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.71, + 0.642, + 0.726 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.895, + 0.903 + ], + "angle": 0, + "content": "The idea of only processing updated pixels in a convolutional layer has been proposed in various ways, with Recurrent Residual Module (RRM) [25] being the first work to apply this concept to videos. RRM uses the difference between current and previous input, the Delta, as input to convolutional layers. RRM demonstrates large theoretical reductions in FLOPs compared to dense inference resulting from skipping computations involving (nearly) zero-valued entries in feature maps. In practice, skipping individual values is infeasible on most inference hardware like GPUs due to their single instruction, multiple data (SIMD) design." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17293" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.087, + 0.891, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.253, + 0.897, + 0.33 + ], + "angle": 0, + "content": "Figure 3: The main concepts of MotionDeltaCNN. We align frame 2 (F2) with frame 1 (F1) using homography matrices. For the intersecting region, we propagate only the aligned frame-to-frame differences (Delta). The newly uncovered regions are propagated directly. The regions in which the buffers store the uncovered regions are reset to zero before processing the current Delta input. After convolving frame 2, we add the bias to all previously unseen regions, and accumulate the result onto our spherical buffer using the offset coordinates for the current frame." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.355, + 0.471, + 0.416 + ], + "angle": 0, + "content": "Furthermore, RRM only processes convolutional layers on sparse Delta input. All remaining layers are processed on the full, dense feature maps and therefore require expensive value-conversions before and after each convolutional layer." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.417, + 0.474, + 0.599 + ], + "angle": 0, + "content": "Skip-Convolution [11] and CBInfer [4] improve the concept of RRM using a per-pixel sparse mask instead of pervalue. Like RRM, CBInfer uses a threshold to truncate insignificant updates in the input feature map. This threshold can be tuned for each layer for maximum sparsity while keeping the accuracy at a desired level. In contrast, Skip-Convolution decides per output pixel whether an update is required or can be skipped. In both cases, only the convolutional layers (and pooling layers in case of CBInfer) are processed sparsely, requiring expensive conversions between dense and sparse features before and after each of these layers, leaving large performance potential unused." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.599, + 0.471, + 0.81 + ], + "angle": 0, + "content": "DeltaCNN [26] propagates sparse Delta features end-to-end using a sparse Delta feature map together with an update mask. This greatly reduces the memory bandwidth compared to previous work. Propagating sparse updates end-to-end eliminates the necessity of converting the feature maps from dense accumulated values to sparse Deltas, and it speeds up other layers bottlenecked by memory bandwidth like activation, batch normalization, upsampling, etc. Using a custom CUDA implementation, DeltaCNN outperforms cuDNN and CBInfer many times on video input. However, DeltaCNN, as well as all other previous work, assumes static camera input. Even single pixel camera motion between two frames can result in nearly dense updates when the image contains high frequency features." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.472, + 0.903 + ], + "angle": 0, + "content": "Event Neural Networks show that computational savings are strongly impacted by the intensity of camera motion[8]. With slightly shaking cameras, theoretical FLOP savings were reduced by \\(40\\%\\) compared to static camera videos, while moving cameras reduced them by \\(60\\%\\). Depending on the distribution of the pixel updates, the impact on real" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.355, + 0.704, + 0.371 + ], + "angle": 0, + "content": "hardware is likely even higher." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.372, + 0.895, + 0.508 + ], + "angle": 0, + "content": "Incremental Sparse Convolution uses sparse convolutions to incrementally update 3D segmentation masks online [23]. They solve a similar problem of reusing results from previously segmented regions, while allowing for new regions to be attached on the fly. Due to their reliance on non-dilating 3D convolutions [10], attaching new regions leads to artifacts along the region borders. We solve this issue using a standard, dilating convolution and by processing all outputs that are affected by the current input." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.508, + 0.895, + 0.6 + ], + "angle": 0, + "content": "We propose MotionDeltaCNN: building upon DeltaCNN, we design and implement a sparse inference extension that supports moving cameras. Compared to DeltaCNN, we add the support for variable resolution inputs, spherical buffers, dynamic buffer allocation & initialization and padded convolutions for seamless attachment of newly unveiled regions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.615, + 0.591, + 0.63 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.641, + 0.859, + 0.656 + ], + "angle": 0, + "content": "MotionDeltaCNN relies on the following concepts:" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.657, + 0.894, + 0.702 + ], + "angle": 0, + "content": "Frame Alignment The current frame is aligned with the initial frame of the sequence to maximize the overlap of consistent features (see Figure 3 Delta)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.703, + 0.895, + 0.748 + ], + "angle": 0, + "content": "Spherical Buffers We use wrapped buffer offset coordinates in all non-linear layers to align them with the input (see Figure 3 Accumulated Output)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.749, + 0.895, + 0.825 + ], + "angle": 0, + "content": "Dynamic Initialization When a new region is first unveiled due to camera motion, MotionDeltaCNN adds biases onto the feature maps on the fly to all newly unveiled pixels to allow for seamless integration with previously processed pixels (see Figure 3 Bias)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Padded Convolutions We add additional padding to convolutional layers to process all pixels that are affected by the kernel. These dilated pixels are stored in truncated values buffers to enable seamless connection of potentially unveiled neighbor regions in upcoming frames (see Figure 5)." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17294" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.091, + 0.303, + 0.108 + ], + "angle": 0, + "content": "3.1. Background: DeltaCNN" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.114, + 0.471, + 0.234 + ], + "angle": 0, + "content": "For a better understanding of our contributions, we first summarize the core concept of DeltaCNN, which accelerates CNN inference by processing only the first frame densely and applying sparse updates to changed pixels in subsequent frames. A sparse input Delta is calculated by subtracting the previously processed input from the current input frame. Pixels whose Delta is smaller than a threshold are truncated to zero to increase sparsity." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.236, + 0.472, + 0.356 + ], + "angle": 0, + "content": "Because of linearity, the output of any convolution layer can be updated by convolving the sparse input Delta, \\( c(x + \\delta) = c(x) + c(\\delta) \\). This does not hold for non-linear layers like activation (e.g., ReLU) and pooling, which therefore require a separate accumulated values buffer to accumulate the inputs to the respective layers across all previously processed frames. The buffers contain the full, dense layer input of the previous frame, including biases from previous layers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.357, + 0.472, + 0.522 + ], + "angle": 0, + "content": "Convolutions with kernel sizes larger than 1x1 pixels dilate the updates across the feature map. A single pixel update in the center of the feature map might span over the entire feature map a few convolutional layers later. This can lead to nearly dense updates for the larger part of the network. DeltaCNN solves this by truncating insignificant updates not only on the input image, but at every activation layer. To avoid accumulating errors indefinitely, the truncated values are accumulated in a dedicated truncated values buffer. Once an accumulated, truncated value exceeds a significance threshold, the value is propagated to the next layer." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.53, + 0.251, + 0.545 + ], + "angle": 0, + "content": "3.2. Frame Alignment" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.553, + 0.472, + 0.659 + ], + "angle": 0, + "content": "Robust frame alignment (or video stabilization) is a fundamental requirement for MotionDeltaCNN to achieve high coherence across consecutive frames. For best alignment between two frames in a 3D space, we use homography matrices with 8 degrees of freedom. Homography matrices align two images in 3D to match a selected set of key features of the initial frame - typically the static background." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.472, + 0.826 + ], + "angle": 0, + "content": "We embed the image in a grid-aligned frame to ensure a pixel-perfect downscale to all layers. For example, in HRNet [29], the highest resolution feature map spans \\(384 \\times 384\\) pixels, whereas the lowest resolution feature map spans only \\(12 \\times 12\\) pixels, resulting in a scaling factor of \\(32 \\times 32\\). To ensure that all pixels align on all scaling levels, the input to HRNet must be aligned onto a grid of \\(32 \\times 32\\) pixel tiles. E.g., if a frame has a 20-pixel horizontal offset relative to the first frame, we allocate 32 additional pixels, paste the original frame into the grid-aligned frame and set the 20 left-most pixels as well as the 12 right-most pixels to zero." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.833, + 0.249, + 0.849 + ], + "angle": 0, + "content": "3.3. Spherical Buffers" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.471, + 0.902 + ], + "angle": 0, + "content": "MotionDeltaCNN enables support for moving cameras by introducing 2D ring buffers, spherical buffers. These buffers align previously processed pixels with pixels of the current" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.089, + 0.601, + 0.163 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.526, + 0.168, + 0.577, + 0.181 + ], + "angle": 0, + "content": "Frame 1" + }, + { + "type": "image", + "bbox": [ + 0.635, + 0.103, + 0.662, + 0.146 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.621, + 0.168, + 0.676, + 0.182 + ], + "angle": 0, + "content": "Cropped" + }, + { + "type": "image", + "bbox": [ + 0.696, + 0.089, + 0.793, + 0.163 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.718, + 0.168, + 0.771, + 0.18 + ], + "angle": 0, + "content": "Frame 2" + }, + { + "type": "image", + "bbox": [ + 0.833, + 0.111, + 0.85, + 0.14 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.813, + 0.168, + 0.868, + 0.182 + ], + "angle": 0, + "content": "Cropped" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.194, + 0.895, + 0.271 + ], + "angle": 0, + "content": "Figure 4: MotionDeltaCNN can handle sparse Delta inputs of different crop sizes, and focus only on a fraction of the image, thanks to the concept of spherical buffers. This is not possible for DeltaCNN which always processes sparse Delta inputs of the entire frame." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.299, + 0.895, + 0.542 + ], + "angle": 0, + "content": "frame by translating feature map coordinates to buffer coordinates. Pixel coordinates exceeding image borders are wrapped around the buffer, i.e., mapped to the opposite border using the modulo operator. This enables the reuse of previous results for moving cameras without increasing the memory overhead over DeltaCNN (see Figure 5). Our buffers support 2D offsets relative to the initial frame as well as cropped inputs (see Figure 4). Frame scales can be helpful when only a part of the image is updated in the current frame - for example, when a frame is cropped to the bounding box of a region of interest. Tile offset indices are provided during inference to align features in buffers with the current input. By multiplying tile offset indices with a layer's tile size (in the example above \\(32 \\times 32\\) pixels in highest resolution feature maps, \\(1 \\times 1\\) pixel in the lowest resolution), we get the pixel offset coordinates for buffer access in non-linear layers." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.553, + 0.71, + 0.569 + ], + "angle": 0, + "content": "3.4. Dynamic Initialization" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.577, + 0.895, + 0.7 + ], + "angle": 0, + "content": "When the input frame covers a previously unseen area, new tiles are allocated in all buffers before inferring the frame. A new tile is allocated by deleting a previously stored tile at the desired location and resetting respective values to zero. In doing so, we lose information about the accumulated biases inferred in the initial frame. We compensate for this by adding the biases onto reset regions of the Delta feature map during inference." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.71, + 0.702, + 0.725 + ], + "angle": 0, + "content": "3.5. Padded Convolutions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.734, + 0.894, + 0.84 + ], + "angle": 0, + "content": "After the initial frame, MotionDeltaCNN propagates only Delta updates for the remaining sequence. This can cause inconsistencies when mixing previously seen and newly unveiled pixels. Consider a pair of adjacent pixels \\(\\mathbf{p}_{seen}\\) and \\(\\mathbf{p}_{new}\\) across the boundary, the resulting output at \\(\\mathbf{p}_{new}\\) may \"miss\" previously accumulated updates from pixel \\(\\mathbf{p}_{seen}\\) (see Figure 5), since they were \"outside\"." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.895, + 0.902 + ], + "angle": 0, + "content": "MotionDeltaCNN addresses this prospectively by increasing the padding of convolutional layers to include all pixels that could be affected by convolutions on the current input. This leads to an increased output size compared to the input" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17295" + } + ], + [ + { + "type": "aside_text", + "bbox": [ + 0.078, + 0.115, + 0.091, + 0.242 + ], + "angle": 0, + "content": "a b C" + }, + { + "type": "image", + "bbox": [ + 0.114, + 0.147, + 0.236, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.15, + 0.274, + 0.201, + 0.286 + ], + "angle": 0, + "content": "Frame 1" + }, + { + "type": "image", + "bbox": [ + 0.24, + 0.148, + 0.363, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.274, + 0.274, + 0.328, + 0.287 + ], + "angle": 0, + "content": "Output 1" + }, + { + "type": "image", + "bbox": [ + 0.365, + 0.148, + 0.488, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.383, + 0.274, + 0.471, + 0.286 + ], + "angle": 0, + "content": "Delta Frame 2" + }, + { + "type": "image", + "bbox": [ + 0.491, + 0.148, + 0.613, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.525, + 0.274, + 0.58, + 0.286 + ], + "angle": 0, + "content": "Output 2" + }, + { + "type": "image", + "bbox": [ + 0.616, + 0.089, + 0.738, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.62, + 0.274, + 0.735, + 0.287 + ], + "angle": 0, + "content": "Accumulated Input" + }, + { + "type": "image", + "bbox": [ + 0.741, + 0.089, + 0.864, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.74, + 0.274, + 0.865, + 0.287 + ], + "angle": 0, + "content": "Accumulated Output" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.3, + 0.895, + 0.378 + ], + "angle": 0, + "content": "Figure 5: Padded convolutions enable fusing images recorded at different perspectives. Naively applying convolutions separately to the initial frame and the Delta of Frame 2, and aggregating the outputs (row b) does not achieve the same results as one would get if the convolution is directly applied to a large fused input buffer (row a). This is because of how the boundary pixels are treated and dropped when applying convolutions and border cropping. To address this issue, we need to cache and pad the output features, as shown in row c. See Section 3.5 for details regarding how to handle this in a practical manner." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.403, + 0.469, + 0.432 + ], + "angle": 0, + "content": "when the kernel size is larger than 1x1. For example, a 64x64 pixel input and a 3x3 kernel result in a 66x66 pixel output." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.433, + 0.473, + 0.66 + ], + "angle": 0, + "content": "With modern CNNs consisting of hundreds of convolutional layers, growing the feature map at each layer could quickly exceed our buffers and computational budget. To prevent this, in practice, we move and stash these output values at dilated pixels, and crop the output feature map of the current buffer to its original shape. Since MotionDeltaCNN already uses truncated values buffers for storing values that were not yet propagated through the activation layer, we only need to increase the size of the buffer slightly to include the dilated values and accumulate them there for later use. Combined with spherical buffers, this allows us to fuse new image regions from all 4 directions seamlessly at the cost of memory and compute overhead for the dilated border pixels. Since most convolutions use kernels of size \\(3 \\times 3\\) and \\(1 \\times 1\\), the overhead is typically low." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.667, + 0.267, + 0.683 + ], + "angle": 0, + "content": "3.6. Buffer management" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.69, + 0.473, + 0.901 + ], + "angle": 0, + "content": "We use a buffer manager that is responsible for: keeping track of each tile's state, allocating new regions in the spherical buffer, initializing newly allocated tiles and adding biases to feature maps during inference. As mentioned before, spherical buffers wrap coordinates around image borders to allow for infinite panning. One downside of this approach is that when borders grow in one direction, we overwrite the dilated pixels stored for growing in the opposite direction (see Figure 1). Restoring dilated pixels is non-trivial and would require inferring the negative accumulated values of the deleted tiles - which adds high overhead. Instead, we simply delete the dilated pixels and restrict the growth in the opposite direction. Once the camera moves back over a restricted region, all buffers are reset entirely, and the cur" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.403, + 0.896, + 0.629 + ], + "angle": 0, + "content": "rent frame has to be inferred densely - becoming the new reference until the next buffer reset. Restoring the truncated values by only resetting the tiles next to the invalid truncated values does not work, as they would again lack valid truncated values required for seamless attachment to persistent tiles. While a full reset reduces the reuse of previously processed features, in our evaluations, the number of resets is fairly small as camera pans typically last many frames without changing directions. Our buffer manager stores for each tile of the grid the currently held global coordinates and the directions in which the growth is restricted. Every time the camera moves, the buffer manager checks whether the tiles already hold a value from the corresponding coordinates. If not, it resets the respective tiles if possible or requests a buffer reset if growth is restricted." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.637, + 0.646, + 0.652 + ], + "angle": 0, + "content": "3.7. Optimizations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.66, + 0.895, + 0.902 + ], + "angle": 0, + "content": "While the above-mentioned features can already lead to a large speedup in moving camera scenarios, the speedup can be increased significantly with some small optimizations. For the DAVIS 2017 dataset [27], we noticed strong salt-and-pepper style noise in the update masks. Since video stabilization is not perfect, some pixels align incorrectly, especially in high frequency details like leaves of a tree. This leads to a strong color change for some isolated pixels in the image, resulting in a large compute overhead when processing the image in tiles. We mitigate this issue using region-of-interest (ROI) focused sensing and noise suppression. When we know the ROI from previous frames, e.g., in the case of object detection or object segmentation, we can increase the sensitivity around these regions and decrease the sensitivity further away. Additionally, we suppress noise coming from imperfect image alignment by downscaling" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "17296" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.088, + 0.212, + 0.146 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.122, + 0.153, + 0.172, + 0.164 + ], + "angle": 0, + "content": "Frame 1" + }, + { + "type": "image", + "bbox": [ + 0.217, + 0.089, + 0.348, + 0.147 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.256, + 0.153, + 0.307, + 0.165 + ], + "angle": 0, + "content": "Frame 2" + }, + { + "type": "image", + "bbox": [ + 0.352, + 0.098, + 0.45, + 0.148 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.409, + 0.153, + 0.421, + 0.164 + ], + "angle": 0, + "content": "T" + }, + { + "type": "image", + "bbox": [ + 0.461, + 0.088, + 0.614, + 0.147 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.534, + 0.153, + 0.562, + 0.165 + ], + "angle": 0, + "content": "T+S" + }, + { + "type": "image", + "bbox": [ + 0.617, + 0.09, + 0.746, + 0.146 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.666, + 0.153, + 0.697, + 0.165 + ], + "angle": 0, + "content": "\\(\\mathrm{T + N}\\)" + }, + { + "type": "image", + "bbox": [ + 0.751, + 0.09, + 0.88, + 0.146 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.792, + 0.153, + 0.839, + 0.165 + ], + "angle": 0, + "content": "\\(\\mathrm{T} + \\mathrm{S} + \\mathrm{N}\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.179, + 0.894, + 0.254 + ], + "angle": 0, + "content": "Figure 6: We increase update sparsity using noise suppression and region of interest scaling. \\( T \\) uses the original truncation implementation of DeltaCNN. Scaling the Delta further away from the region of interest \\( (T + S) \\) slightly increases sparsity. Using noise suppression \\( (T + N) \\) to eliminate single pixel updates increases sparsity even further. Combining scaling and noise suppression \\( (T + S + N) \\) achieves the highest sparsity, capturing only the most important updates of the moving camel. Note that in all cases, we dilate the update mask by 10 pixels; explaining the low sparsity in case \\( T \\). Source: DAVIS 2017" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.281, + 0.471, + 0.357 + ], + "angle": 0, + "content": "the Delta, processing which pixels exceed the thresholds and suppressing single pixel updates using average pooling. Overall, these steps lead to a significant speedup with only minor impact on accuracy (see Figure 6). Further optimizations can be found in the supplemental material." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.374, + 0.194, + 0.389 + ], + "angle": 0, + "content": "4. Evaluation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.4, + 0.47, + 0.476 + ], + "angle": 0, + "content": "We evaluate MotionDeltaCNN in two scenarios: a) using video stabilization to align subsequent frames with moving cameras and b) using bounding boxes in a static camera scenario to infer only regions of interest while retaining out-of-interest features from previous frames." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.478, + 0.471, + 0.78 + ], + "angle": 0, + "content": "Video Object Segmentation In task a), we evaluate the video object segmentation model BMVOS [7] on the DAVIS 2017 dataset [27]. BMVOS uses the DenseNet [15] backend for feature encoding, the most computationally expensive part of the model. We use weights pretrained on the DAVIS dataset, which were provided by the authors of BMVOS. The DAVIS 2017 dataset consists of a set of sequences with one or more segmented objects of which the masks are provided only for the first frame - and the model needs to paint the segmentation mask for the remaining frames in the video. Most of the videos are recorded using moving cameras, and are therefore well suited for evaluating MotionDeltaCNN. The DAVIS 2017 dataset does not provide camera extrinsic. Instead, we use OpenCV [2] to estimate homography matrices between two consecutive frames. This simplistic method fails in some cases, e.g., when it does not find good features due to motion blur or with motion parallax. We see the tasks of video stabilization as orthogonal and therefore only evaluate on the set of videos (14 sequences) for which this simple video stabilization approach works reliably." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.471, + 0.902 + ], + "angle": 0, + "content": "In video object segmentation, the segmentation mask from the previous frame can be used to suppress noise in the upcoming frame. We use this mask to lower the update sensitivity further away from the ROI - leading to an increase in sparsity. We deliberately tuned the thresholds for DeltaCNN with a lower accuracy target than for MotionDeltaCNN to show that we achieve higher frame rates even when targeting higher accuracy. The details about threshold tuning and" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.282, + 0.893, + 0.296 + ], + "angle": 0, + "content": "ROI-focused sensing are found in the supplemental material." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.3, + 0.895, + 0.587 + ], + "angle": 0, + "content": "Human Pose Estimation In task b), we perform human pose estimation using HRNet [30, 32] on the Human3.6M dataset [3, 17]. Human3.6M uses static cameras and is recorded in a static studio with only a single moving actor in the room. We use this dataset to evaluate a second scenario for MotionDeltaCNN: top-down pose estimation. With top-down pose estimation, humans in the scene are detected first, and then the pose is predicted for each detected human. Each bounding box is cropped and inferred individually - estimating one set of joints per person. Since Human3.6M provides per frame bounding boxes of the actors as part of their labels, we omit the step of detecting humans in the scene. We snap the given bounding boxes onto a \\(32 \\times 32\\) pixel grid and then increase them by 32 pixels on each side where possible. The increased bounding boxes ensure that joint positions are not too close to image borders, as this could negatively impact prediction accuracy. We use the same weights and thresholds as were used in the DeltaCNN paper and evaluate on the same data subset (Subject S11)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.591, + 0.895, + 0.772 + ], + "angle": 0, + "content": "Both scenarios are compared against dense inference of cuDNN and against the original DeltaCNN without moving camera support. In HRNet, we only measure model inference time, without the overhead of post-processing or accuracy evaluation. The input shape is \\(384 \\times 384\\) with a tile size of \\(32 \\times 32\\) pixels unless stated otherwise. In the case of BMVOS, we only measure the duration of the feature encoding model to better highlight the difference of pure CNN inference speeds. For this evaluation, the camera input is embedded into a frame of shape Wx480 pixels, where W depends on the aspect ratio of the video (typically 864px) and is aligned onto a grid with a tile size of \\(48 \\times 48\\) pixels." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.776, + 0.894, + 0.852 + ], + "angle": 0, + "content": "Hardware We conduct our evaluations on two GPUs: Nvidia GTX 1080 Ti and Nvidia RTX 3090 with 3584/10496 CUDA cores and 11GB/24GB of VRAM respectively. The evaluations are performed using 32-bit precision, but our approach can be applied to other data types as well." + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.893, + 0.901 + ], + "angle": 0, + "content": "1The Human3.6M dataset was accessed and used only by the co-authors at Graz University of Technology" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17297" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.09, + 0.092, + 0.887, + 0.179 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.191, + 0.895, + 0.255 + ], + "angle": 0, + "content": "Figure 7: A DAVIS 2017 sequence processed using DeltaCNN (left) and MotionDeltaCNN (right). Row a shows the original input on the left, and the aligned and cropped input on the right. Row b visualizes the Delta between the (aligned) input and the previous input in row c. Row d visualizes the update mask with white pixels indicating an update. MotionDeltaCNN achieves much higher sparsity on the same input by reusing previous results for the aligned, static background." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.277, + 0.166, + 0.293 + ], + "angle": 0, + "content": "5. Results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.304, + 0.471, + 0.38 + ], + "angle": 0, + "content": "We evaluate speedup and accuracy of MotionDeltaCNN compared to DeltaCNN without explicit moving camera support as well as the dense cuDNN backend. In this section, we report the differences on the GTX 1080 Ti - for results on the RTX 3090, please see the respective tables." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.381, + 0.471, + 0.472 + ], + "angle": 0, + "content": "Video Object Segmentation MotionDeltaCNN outperforms state-of-the-art backends in sparse mode by a margin of up to \\(100\\%\\) over the cuDNN baseline (see Table 1). The DAVIS 2017 dataset consists mainly of videos with large bounding boxes and often fast camera motion, leading to a high average update rate of \\(29\\%\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.474, + 0.471, + 0.519 + ], + "angle": 0, + "content": "Excluding videos without camera motion highlights the relative speedup over DeltaCNN without moving camera support with \\(+85\\%\\) speedup over cuDNN instead of \\(+8\\%\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.52, + 0.471, + 0.657 + ], + "angle": 0, + "content": "MotionDeltaCNN, like DeltaCNN, requires larger workloads with more powerful hardware to show speedups. With 10.496 cores in a RTX 3090, small batch sizes typically do not fully utilize the available hardware resources in most layers - skipping some tiles in this scenario does not affect the overall performance unless all tiles can be skipped altogether. By increasing the batch size, we can fully utilize the GPU - cores that skip a tile can immediately continue processing the next tile, leading to an overall speedup." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.658, + 0.47, + 0.718 + ], + "angle": 0, + "content": "Over the 990 frames in the DAVIS dataset, we had to reset the buffers 9 times because of cameras panning over invalid truncated values. This low number of resets has only a small impact on the overall performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Human Pose Estimation MotionDeltaCNN can outperform cuDNN by up to 11x in the case of HRNet (see Table 2). Please note that the frame rate of cuDNN is \\(30\\%\\) lower than in the DeltaCNN paper since we enforced the use of 32-bit multiplications in all layers - the same accuracy that we also use in our implementation. Furthermore, the accuracies do not match since we always use the full, uncropped images as input. The high sparsity in the Human3.6M dataset together with the efficient implementation allows us to accelerate inference significantly. Compared to DeltaCNN, which does not support varying resolution input or moving cameras, we were able to achieve \\(13\\%\\) higher frame rates with similar" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.279, + 0.895, + 0.475 + ], + "angle": 0, + "content": "accuracy. We level the playing field in comparisons against the dense cuDNN backend by inferring the same cropped images that we use as input for MotionDeltaCNN. Still, we outperform cuDNN by up to \\(3.2\\mathrm{x}\\), and achieve a speedup of up to \\(3.2\\mathrm{x}\\) over dense DeltaCNN with full resolution input. For Human3.6M, we know that the actors never cover the entire frame at once. We use this knowledge to lower the size of the buffers by \\(25\\%\\) on each axis - reducing the memory footprint of buffers by \\(44\\%\\) in total. These savings allow us to increase the batch size even further. When fully utilizing all available memory with an increased batch size, we achieve frame rates up to \\(3.9\\mathrm{x}\\) over the cropped cuDNN baseline and \\(37\\%\\) over DeltaCNN." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.477, + 0.895, + 0.794 + ], + "angle": 0, + "content": "Ablation Study We evaluated the individual impact of our contributions in an ablation study (see Table 3). Without dynamic initialization, MotionDeltaCNN always resets the buffers when new image tiles are unveiled. After a reset, the next frame is processed densely. This has a negative impact on the speedup, but slightly increases the accuracy as it regularly flushes accumulated errors. Padded convolutions are key in enabling spherical buffers. Without them, new tiles are not fused into existing buffers correctly, leading to a reduction in accuracy. Our evaluation shows that (ROI) focused sensing enables great speedups without lowering the accuracy of the segmentation. By disabling noise suppression as well, the model becomes more sensitive to errors in image alignment and small changes in the image. To compensate for this, we increase the threshold of the first truncation from 0.15 to 0.35 for this evaluation. However, even with an increased threshold, the speedup is significantly smaller compared to default truncation, while the accuracy is already much lower. Overall, the ablation study shows that all parts of MotionDeltaCNN work in tandem to achieve the best speedup without large impact on accuracy." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.803, + 0.613, + 0.818 + ], + "angle": 0, + "content": "6. Discussion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Our evaluations prove that MotionDeltaCNN can accelerate CNN video inference with moving cameras where existing sparse methods fail to outperform the dense reference. However, our evaluation also shows that freely moving cameras, especially when combined with dense updates as in" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17298" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.891, + 0.263 + ], + "angle": 0, + "content": "
VideosBackendIoUGFLOPsGTX 1080 Ti b=1GTX 1080 Ti b=5RTX 3090 b=1RTX 3090 b=12
FPSspeedupFPSspeedupFPSspeedupFPSspeedup
AllcuDNN76.8522.130.71.040.91.045.41.01031.0
DeltaCNN (dense)76.8522.135.01.1441.21.0166.51.461000.97
MotionDeltaCNN (dense)76.7622.633.51.0940.30.9957.71.2793.60.91
DeltaCNN (sparse)76.1815.542.51.3851.41.2670.01.541251.21
MotionDeltaCNN (sparse)76.326.854.81.7981.92.0065.21.442152.1
MovingcuDNN79.5922.130.71.040.91.045.41.01031.0
DeltaCNN (sparse)79.3818.838.21.2444.11.0870.21.551061.03
MotionDeltaCNN (sparse)79.437.352.31.7075.11.8465.01.432011.95
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.272, + 0.897, + 0.335 + ], + "angle": 0, + "content": "Table 1: Results for the task of video object segmentation using BMVOS on the DAVIS dataset. We track only the DenseNet backend for evaluating frames per second (FPS). For accuracy benchmarks, the remaining network is processed densely. GFLOPs are reported as average over the test set. Both devices are evaluated with a batch size \\( b \\) of one, and the maximum batch size each device can hold in memory." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.347, + 0.891, + 0.49 + ], + "angle": 0, + "content": "
BackendPCKh@0.5PCKh@0.2GFLOPsGTX 1080 Ti b=1GTX 1080 Ti b=16RTX 3090 b=1RTX 3090 b=40
FPSspeedupFPSspeedupFPSspeedupFPSspeedup
cuDNN96.03%83.33%47.122.51.024.81.012.31.069.61.0
DeltaCNN (dense)24.21.0841.31.726.02.195.81.4
MotionDeltaCNN (dense)96.00%83.32%17.732.51.4491.43.722.01.82323.3
cuDNN (cropped)95.92%83.11%13.324.01.0771.02.911.81.02093.0
DeltaCNN (sparse)95.95%82.31%3.5544.92.02028.126.22.15477.9
MotionDeltaCNN (sparse)95.95%82.33%3.4541.21.832289.222.61.85848.4
MotionDeltaCNN (sparse †)95.93%82.22%3.4442.51.8927611.122.51.86919.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.5, + 0.897, + 0.579 + ], + "angle": 0, + "content": "Table 2: Speed and accuracy comparisons of different CNN backends used for pose estimation on the Human3.6M dataset. The same set of auto-tuned thresholds for update truncation is used for all devices and batch sizes \\( b \\). † limits the size of the input from 384x384 to 288x288 pixels - freeing up 44% of the memory used for buffers. The freed-up memory is used to increase the batch size to fully utilize the available VRAM (b=28 on 1080 Ti and b=66 on 3090). cuDNN cropped uses the same, cropped input as ours, instead of the full camera input." + }, + { + "type": "table", + "bbox": [ + 0.113, + 0.6, + 0.436, + 0.726 + ], + "angle": 0, + "content": "
FPSIoU# resets
cuDNN40.979.59-
DeltaCNN44.179.38-
MotionDeltaCNN75.179.438
- w/o dynamic init56.479.63110
- w/o padded conv.65.377.898
- w/o ROI scaling63.679.338
- w/o ROI & noise*50.979.068
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.735, + 0.472, + 0.798 + ], + "angle": 0, + "content": "Table 3: Ablation study. Evaluating BMVOS on DAVIS2017 dataset using a Nvidia GTX 1080 Ti with a batch size of 5. We evaluate on the subset of videos with significant camera motion. * increased threshold on video input." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.824, + 0.471, + 0.884 + ], + "angle": 0, + "content": "the DAVIS dataset, lead to a much smaller speedup than the static camera setup with sparse motion in Human3.6M. Furthermore, the additional padding slightly increases memory and compute overhead over DeltaCNN." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Receptive Field While MotionDeltaCNN does achieve" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.603, + 0.895, + 0.801 + ], + "angle": 0, + "content": "outputs comparable to standard CNN inference, it should be noted that even in dense mode, the results are not identical. This can be observed in Figure 5 where the fused output of MotionDeltaCNN matches the result using the fused input in row \\( a \\), which includes information from neighbor pixels seen in previous frames. Since we do not actively propagate inverted accumulated values once a previously processed region gets out of view, the receptive field of later layers, also for pixels inside the current view, still contains some information from that now unseen area. This can have positive and negative effects alike. These features might not be valid anymore. At the same time, some out-of-view features can help to make better predictions due to additional context." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.897, + 0.903 + ], + "angle": 0, + "content": "Applications MotionDeltaCNN is a general-purpose framework for video inference and can thus be used with all pre-trained CNNs by replacing the original, dense layers with our sparse equivalent. As additional input, Motion-DeltaCNN requires camera extrinsics for the frame to be processed. While most publicly available datasets do not" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "17299" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.242 + ], + "angle": 0, + "content": "include camera extrinsics and therefore require image stabilization, smartphones, tablets and VR headsets nowadays have built-in support for tracking the camera pose between frames in real-time. Potential applications are not limited to classic computer vision applications like tracking and segmentation, but it could also be used for video up-scaling, filtering, etc. However, applications like image-denoising (diffusion) are likely not a good fit as they provide low levels of spatial update sparsity between iterations and they are very sensitive to noise." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.243, + 0.473, + 0.394 + ], + "angle": 0, + "content": "Limitations One of the main limitations of our approach is its dependency on robust video stabilization. Our experiments with the DAVIS dataset showed that simple video stabilization techniques can break when blur or parallax is involved, or when it fails to find robust features. Parallax can greatly reduce the gains of our method, even when the scene itself is mostly static. When foreground and background layers move at different speeds, frames can only be properly aligned to stabilize one of these layers - leading to dense updates in layers moving at different speeds." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.394, + 0.473, + 0.53 + ], + "angle": 0, + "content": "MotionDeltaCNN also comes with the trade-off between buffer overallocation and losing information by cropping the input to match the shape of the buffer. In our evaluations, when the camera zooms or rotates around the forward axis (roll), the aligned input can exceed the size of the buffers, and therefore requires slight cropping to fit into the target shape (see Figure 7). Alternatively, the buffers could also be increased to allow for larger inputs in upcoming frames - at the cost of higher memory consumption." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.535, + 0.196, + 0.55 + ], + "angle": 0, + "content": "7. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.555, + 0.473, + 0.766 + ], + "angle": 0, + "content": "We propose MotionDeltaCNN, an extension to the sparse video CNN framework DeltaCNN adding support for moving camera input. To the best of our knowledge, we are the first to propose a solution for moving cameras with sparse inference. MotionDeltaCNN uses spherical buffers, padded convolutions and dynamic initialization of newly unveiled regions to support combining previously processed pixels and newly unveiled pixels together with high sparsity. We test our approach in practice by implementing all kernels natively on the GPU to evaluate the real-world performance with modern hardware. Our experiments show that we outperform DeltaCNN by up to \\(90\\%\\) on moving camera input and that MotionDeltaCNN can also be beneficial to lower the memory footprint in static camera scenarios." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.778, + 0.175, + 0.794 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.085, + 0.803, + 0.472, + 0.873 + ], + "angle": 0, + "content": "[1] Udari De Alwis and Massimo Alioto. TempDiff: Temporal Difference-Based Feature Map-Level Sparsity Induction in CNNs with \\(< 4\\%\\) Memory Overhead. 2021 IEEE 3rd International Conference on Artificial Intelligence Circuits and Systems, AICAS 2021, pages 1-4, Jun 2021." + }, + { + "type": "ref_text", + "bbox": [ + 0.085, + 0.874, + 0.473, + 0.901 + ], + "angle": 0, + "content": "[2] G. Bradski. The OpenCV Library. 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Proceedings - 30th IEEE Conference on Computer Vision and Pattern Recognition, CVPR 2017, 2017-January:4141-4150, 2017." + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.894, + 0.291 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.956 + ], + "angle": 0, + "content": "17301" + } + ] +] \ No newline at end of file diff --git a/2023/MotionDeltaCNN_ Sparse CNN Inference of Frame Differences in Moving Camera Videos with Spherical Buffers and Padded Convolutions/60cee84a-76a7-422c-a440-0ab4865a753d_origin.pdf b/2023/MotionDeltaCNN_ Sparse CNN Inference of Frame Differences in Moving Camera Videos with Spherical Buffers and Padded Convolutions/60cee84a-76a7-422c-a440-0ab4865a753d_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..d32eea440c6c6de12b749e8dc3ba2048bc1154b2 --- /dev/null +++ b/2023/MotionDeltaCNN_ Sparse CNN Inference of Frame Differences in Moving Camera Videos with Spherical Buffers and Padded Convolutions/60cee84a-76a7-422c-a440-0ab4865a753d_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:ea32e2d383bed3f3dd1a2d7744b352cb89f7b532d54aee95bb46cf3c923c45ff +size 4678490 diff --git a/2023/MotionDeltaCNN_ Sparse CNN Inference of Frame Differences in Moving Camera Videos with Spherical Buffers and Padded Convolutions/full.md b/2023/MotionDeltaCNN_ Sparse CNN Inference of Frame Differences in Moving Camera Videos with Spherical Buffers and Padded Convolutions/full.md new file mode 100644 index 0000000000000000000000000000000000000000..0119942fac08e1693309ea7da7c51ab7973a654f --- /dev/null +++ b/2023/MotionDeltaCNN_ Sparse CNN Inference of Frame Differences in Moving Camera Videos with Spherical Buffers and Padded Convolutions/full.md @@ -0,0 +1,291 @@ +# MotionDeltaCNN: Sparse CNN Inference of Frame Differences in Moving Camera Videos with Spherical Buffers and Padded Convolutions + +Mathias Parger1 Chengcheng Tang2 Thomas Neff1 Christopher D. Twigg2 + +Cem Keskin $^{2}$ Robert Wang $^{2}$ Markus Steinberger $^{1}$ + +$^{1}$ Graz University of Technology, $^{2}$ Meta Reality Labs + +$^{1}$ mathias.parger, thomas.neff, steinberger}@icg.tugraz.at + +2{chengcheng.tang, cdtwigg,cemkeskin, rywang}@meta.com + +![](images/7e4876e45e14b345689377e1c407a97292c76007fbac45cfd2d45efaeca10cab.jpg) +Figure 1: MotionDeltaCNN leverages temporal continuity to accelerate CNN inference for videos with moving cameras (bottom) by processing only the sparse frame differences based on a two-dimensional ring buffer, spherical buffer (top). Instead of computing each frame individually, we process only the changes (row $b$ ) between the aligned current (row $a$ ) and previous frames. Our padded convolution creates dilated values (top) which allow for seamless attachment of newly unveiled tiles onto the existing spherical buffer (row $c$ ). With these concepts, MotionDeltaCNN speeds up inference by processing only new regions or updated pixels (white areas in row $d$ ) without additional memory allocation. + +# Abstract + +Convolutional neural network inference on video input is computationally expensive and requires high memory bandwidth. Recently, DeltaCNN[26] managed to reduce the cost by only processing pixels with significant updates over the previous frame. However, DeltaCNN relies on static camera input. Moving cameras add new challenges in how to fuse newly unveiled image regions with already processed regions efficiently to minimize the update rate - without increasing memory overhead and without knowing the camera extrinsic of future frames. In this work, we propose Motion-DeltaCNN, a sparse CNN inference framework that supports moving cameras. We introduce spherical buffers and padded convolutions to enable seamless fusion of newly unveiled regions and previously processed regions - without increasing memory footprint. Our evaluation shows that we outperform DeltaCNN by up to $90\%$ for moving camera videos. + +# 1. Introduction + +Real-time inference of convolutional neural networks (CNN) with video streams remains a power-consuming task and is often infeasible on mobile devices due to hardware and thermal limitations, despite recent efforts aiming at efficient CNN inference through pruning [19, 14], quantization [16, 24, 22], specialized hardware [6, 13, 5] or network optimization [28, 31]. Video input allows for performance optimization through temporal similarity between frames. One common method is to use large, slow networks for accurate predictions at key frames, updated with small, fast networks at intermediate frames [34, 33, 20, 18, 9, 21, 12]. However, this approach requires special network design and training and is not suitable for significant frame changes. + +Sparse convolutions, on the other hand, can be used with existing pre-trained models, accelerating the large network to the speed of a smaller network without impacting prediction accuracy significantly [25, 26]. The linearity of convolutions + +![](images/3e06fb17e9095aa8a4cbf5816f435fe46039f0a20aa06419afd29057b41fd6ab.jpg) +a b +Network Input 1 + +![](images/f6e06ff43622846a8745fa5ed9e0f3c17a166429811ee8efbd779fa6c5e81ae9.jpg) +Network Input 2 +Figure 2: To support moving camera input in sparse inference of frame differences, a naive approach (a) is to embed the input onto a larger image and only overwrite pixels that are covered in the next frame. This approach comes with large overhead in memory consumption (storing the additional pixels of the embedded frame) and computational cost (checking all pixels for updates). MotionDeltaCNN (b) uses original shape buffers and feature maps – avoiding the memory overhead and reducing the number of pixels that have to be checked for updates. + +![](images/c96b798c7e87534a7e85d8fdaeeec5c65d1dab7b3725de2aaa2a8b0895742904.jpg) +Accumulated Input + +enables the accumulation of updates over consecutive frames. After processing the first frame densely, upcoming frames can be processed using the difference between the current and the previous frame, the Delta, as the network input. Assuming a static camera scenario, this results in large image regions with no frame-to-frame difference. Static elements like background or stationary objects do not require updates after the initial frame. Researchers exploited this sparsity in previous work to reduce the number of FLOPs required for CNN inference [25, 4, 11, 1, 8], but were mostly unable to accelerate inference in practice. With the recent progress in DeltaCNN [26], theoretical FLOP reductions were translated into practical speedups on GPUs, using a custom sparse CNN implementation to exploit sparsity in all layers of the CNN. + +DeltaCNN achieves speedups on multiple tasks and datasets, but like prior work, it is optimized for static camera inputs. Even small frame-to-frame camera motion necessitates reprocessing large portions, or the entire image. Spatially aligning consecutive frames, e.g., by leveraging camera extrinsics from IMUs or SLAM on mobile devices, can increase per-pixel similarity and thus update sparsity. Due to the change of camera location and orientation, an aligned new frame may "grow" beyond the initial field of view - out of the previous-results buffers. One way to solve this issue is to embed inputs in a larger frame by padding the input image and drawing updates on top of it. However, the downside of this approach is that padded input images increase the memory consumption and computational cost significantly, as shown in Figure 2. + +In this work, we propose MotionDeltaCNN, a sparse CNN inference framework that allows moving camera input with marginal memory overhead. Compared to previous work, we achieve up to $90\%$ higher frame rates in videos with moving cameras, indicating a new perspective for CNN + +inference optimization on low-power devices, such as surveillance cameras, smartphones, or VR headsets. + +Our main contributions are: + +- We propose MotionDeltaCNN, the first framework that leverages temporal continuity to accelerate CNN inference for videos with moving cameras by processing only the sparse frame differences. +- At the core of this work, we propose padded convolutions for seamless integration of newly unveiled pixels without the need of reprocessing seen pixels. +- We design a two-dimensional ring buffer, a spherical buffer, with wrapped coordinates. Our buffer allows partial growth, reset and initialization of new tiles without additional memory allocation. +- We show how MotionDeltaCNN can also be used for speeding up applications with static cameras when only parts of the image require processing. + +# 2. Related Work + +The idea of only processing updated pixels in a convolutional layer has been proposed in various ways, with Recurrent Residual Module (RRM) [25] being the first work to apply this concept to videos. RRM uses the difference between current and previous input, the Delta, as input to convolutional layers. RRM demonstrates large theoretical reductions in FLOPs compared to dense inference resulting from skipping computations involving (nearly) zero-valued entries in feature maps. In practice, skipping individual values is infeasible on most inference hardware like GPUs due to their single instruction, multiple data (SIMD) design. + +![](images/fcfdf84748ef11e212b04640f39514379ba1b08a380433269eeadd20cb9236fe.jpg) +Figure 3: The main concepts of MotionDeltaCNN. We align frame 2 (F2) with frame 1 (F1) using homography matrices. For the intersecting region, we propagate only the aligned frame-to-frame differences (Delta). The newly uncovered regions are propagated directly. The regions in which the buffers store the uncovered regions are reset to zero before processing the current Delta input. After convolving frame 2, we add the bias to all previously unseen regions, and accumulate the result onto our spherical buffer using the offset coordinates for the current frame. + +Furthermore, RRM only processes convolutional layers on sparse Delta input. All remaining layers are processed on the full, dense feature maps and therefore require expensive value-conversions before and after each convolutional layer. + +Skip-Convolution [11] and CBInfer [4] improve the concept of RRM using a per-pixel sparse mask instead of pervalue. Like RRM, CBInfer uses a threshold to truncate insignificant updates in the input feature map. This threshold can be tuned for each layer for maximum sparsity while keeping the accuracy at a desired level. In contrast, Skip-Convolution decides per output pixel whether an update is required or can be skipped. In both cases, only the convolutional layers (and pooling layers in case of CBInfer) are processed sparsely, requiring expensive conversions between dense and sparse features before and after each of these layers, leaving large performance potential unused. + +DeltaCNN [26] propagates sparse Delta features end-to-end using a sparse Delta feature map together with an update mask. This greatly reduces the memory bandwidth compared to previous work. Propagating sparse updates end-to-end eliminates the necessity of converting the feature maps from dense accumulated values to sparse Deltas, and it speeds up other layers bottlenecked by memory bandwidth like activation, batch normalization, upsampling, etc. Using a custom CUDA implementation, DeltaCNN outperforms cuDNN and CBInfer many times on video input. However, DeltaCNN, as well as all other previous work, assumes static camera input. Even single pixel camera motion between two frames can result in nearly dense updates when the image contains high frequency features. + +Event Neural Networks show that computational savings are strongly impacted by the intensity of camera motion[8]. With slightly shaking cameras, theoretical FLOP savings were reduced by $40\%$ compared to static camera videos, while moving cameras reduced them by $60\%$ . Depending on the distribution of the pixel updates, the impact on real + +hardware is likely even higher. + +Incremental Sparse Convolution uses sparse convolutions to incrementally update 3D segmentation masks online [23]. They solve a similar problem of reusing results from previously segmented regions, while allowing for new regions to be attached on the fly. Due to their reliance on non-dilating 3D convolutions [10], attaching new regions leads to artifacts along the region borders. We solve this issue using a standard, dilating convolution and by processing all outputs that are affected by the current input. + +We propose MotionDeltaCNN: building upon DeltaCNN, we design and implement a sparse inference extension that supports moving cameras. Compared to DeltaCNN, we add the support for variable resolution inputs, spherical buffers, dynamic buffer allocation & initialization and padded convolutions for seamless attachment of newly unveiled regions. + +# 3. Method + +MotionDeltaCNN relies on the following concepts: + +Frame Alignment The current frame is aligned with the initial frame of the sequence to maximize the overlap of consistent features (see Figure 3 Delta). + +Spherical Buffers We use wrapped buffer offset coordinates in all non-linear layers to align them with the input (see Figure 3 Accumulated Output). + +Dynamic Initialization When a new region is first unveiled due to camera motion, MotionDeltaCNN adds biases onto the feature maps on the fly to all newly unveiled pixels to allow for seamless integration with previously processed pixels (see Figure 3 Bias). + +Padded Convolutions We add additional padding to convolutional layers to process all pixels that are affected by the kernel. These dilated pixels are stored in truncated values buffers to enable seamless connection of potentially unveiled neighbor regions in upcoming frames (see Figure 5). + +# 3.1. Background: DeltaCNN + +For a better understanding of our contributions, we first summarize the core concept of DeltaCNN, which accelerates CNN inference by processing only the first frame densely and applying sparse updates to changed pixels in subsequent frames. A sparse input Delta is calculated by subtracting the previously processed input from the current input frame. Pixels whose Delta is smaller than a threshold are truncated to zero to increase sparsity. + +Because of linearity, the output of any convolution layer can be updated by convolving the sparse input Delta, $c(x + \delta) = c(x) + c(\delta)$ . This does not hold for non-linear layers like activation (e.g., ReLU) and pooling, which therefore require a separate accumulated values buffer to accumulate the inputs to the respective layers across all previously processed frames. The buffers contain the full, dense layer input of the previous frame, including biases from previous layers. + +Convolutions with kernel sizes larger than 1x1 pixels dilate the updates across the feature map. A single pixel update in the center of the feature map might span over the entire feature map a few convolutional layers later. This can lead to nearly dense updates for the larger part of the network. DeltaCNN solves this by truncating insignificant updates not only on the input image, but at every activation layer. To avoid accumulating errors indefinitely, the truncated values are accumulated in a dedicated truncated values buffer. Once an accumulated, truncated value exceeds a significance threshold, the value is propagated to the next layer. + +# 3.2. Frame Alignment + +Robust frame alignment (or video stabilization) is a fundamental requirement for MotionDeltaCNN to achieve high coherence across consecutive frames. For best alignment between two frames in a 3D space, we use homography matrices with 8 degrees of freedom. Homography matrices align two images in 3D to match a selected set of key features of the initial frame - typically the static background. + +We embed the image in a grid-aligned frame to ensure a pixel-perfect downscale to all layers. For example, in HRNet [29], the highest resolution feature map spans $384 \times 384$ pixels, whereas the lowest resolution feature map spans only $12 \times 12$ pixels, resulting in a scaling factor of $32 \times 32$ . To ensure that all pixels align on all scaling levels, the input to HRNet must be aligned onto a grid of $32 \times 32$ pixel tiles. E.g., if a frame has a 20-pixel horizontal offset relative to the first frame, we allocate 32 additional pixels, paste the original frame into the grid-aligned frame and set the 20 left-most pixels as well as the 12 right-most pixels to zero. + +# 3.3. Spherical Buffers + +MotionDeltaCNN enables support for moving cameras by introducing 2D ring buffers, spherical buffers. These buffers align previously processed pixels with pixels of the current + +![](images/3277034ac1ddff4b6a94a83ed49057830b7354d83626cff1873169253a0b9a5d.jpg) +Frame 1 + +![](images/94f154ebe1c637c52f65fae4532979295ca263853349e6dfdba8d28a1fa75382.jpg) +Cropped + +![](images/12d35fd2c5e2fff9eeda65ae064ef95401138ca6035622f5aed03aa3843a2b5e.jpg) +Frame 2 +Cropped +Figure 4: MotionDeltaCNN can handle sparse Delta inputs of different crop sizes, and focus only on a fraction of the image, thanks to the concept of spherical buffers. This is not possible for DeltaCNN which always processes sparse Delta inputs of the entire frame. + +![](images/5efb1b34bdfb512ea967d50dccfb777b82765324398e1fdd597348d95a1e5814.jpg) + +frame by translating feature map coordinates to buffer coordinates. Pixel coordinates exceeding image borders are wrapped around the buffer, i.e., mapped to the opposite border using the modulo operator. This enables the reuse of previous results for moving cameras without increasing the memory overhead over DeltaCNN (see Figure 5). Our buffers support 2D offsets relative to the initial frame as well as cropped inputs (see Figure 4). Frame scales can be helpful when only a part of the image is updated in the current frame - for example, when a frame is cropped to the bounding box of a region of interest. Tile offset indices are provided during inference to align features in buffers with the current input. By multiplying tile offset indices with a layer's tile size (in the example above $32 \times 32$ pixels in highest resolution feature maps, $1 \times 1$ pixel in the lowest resolution), we get the pixel offset coordinates for buffer access in non-linear layers. + +# 3.4. Dynamic Initialization + +When the input frame covers a previously unseen area, new tiles are allocated in all buffers before inferring the frame. A new tile is allocated by deleting a previously stored tile at the desired location and resetting respective values to zero. In doing so, we lose information about the accumulated biases inferred in the initial frame. We compensate for this by adding the biases onto reset regions of the Delta feature map during inference. + +# 3.5. Padded Convolutions + +After the initial frame, MotionDeltaCNN propagates only Delta updates for the remaining sequence. This can cause inconsistencies when mixing previously seen and newly unveiled pixels. Consider a pair of adjacent pixels $\mathbf{p}_{seen}$ and $\mathbf{p}_{new}$ across the boundary, the resulting output at $\mathbf{p}_{new}$ may "miss" previously accumulated updates from pixel $\mathbf{p}_{seen}$ (see Figure 5), since they were "outside". + +MotionDeltaCNN addresses this prospectively by increasing the padding of convolutional layers to include all pixels that could be affected by convolutions on the current input. This leads to an increased output size compared to the input + +![](images/212787961a0639aeba6131c9f7f0a774396dbe72f7aa82ffb36379258e545a20.jpg) +Frame 1 + +![](images/0153b386ea13ac3743251599b9ac0caa95261654174e6ad1ede9fef2765a807c.jpg) +Output 1 + +![](images/6ba5db3b850e1a3cf505117dd8e4779b984d4a96b7d73d92f0ba0b677b681bed.jpg) +Delta Frame 2 +Figure 5: Padded convolutions enable fusing images recorded at different perspectives. Naively applying convolutions separately to the initial frame and the Delta of Frame 2, and aggregating the outputs (row b) does not achieve the same results as one would get if the convolution is directly applied to a large fused input buffer (row a). This is because of how the boundary pixels are treated and dropped when applying convolutions and border cropping. To address this issue, we need to cache and pad the output features, as shown in row c. See Section 3.5 for details regarding how to handle this in a practical manner. + +![](images/914a5793d6c4bd84ce6e12479f6784c7300d3dca066a6646197242e0aa3e1957.jpg) +Output 2 + +![](images/b7fd25abc1903a0717518b9f696cb0cd4ece750f3c17790aa26ee627d5743f09.jpg) +Accumulated Input + +![](images/a0c01e0b318c9e43e84f3aa9348f0c3772fce9e5fe1d4272e3c553e9286f5d96.jpg) +Accumulated Output + +when the kernel size is larger than 1x1. For example, a 64x64 pixel input and a 3x3 kernel result in a 66x66 pixel output. + +With modern CNNs consisting of hundreds of convolutional layers, growing the feature map at each layer could quickly exceed our buffers and computational budget. To prevent this, in practice, we move and stash these output values at dilated pixels, and crop the output feature map of the current buffer to its original shape. Since MotionDeltaCNN already uses truncated values buffers for storing values that were not yet propagated through the activation layer, we only need to increase the size of the buffer slightly to include the dilated values and accumulate them there for later use. Combined with spherical buffers, this allows us to fuse new image regions from all 4 directions seamlessly at the cost of memory and compute overhead for the dilated border pixels. Since most convolutions use kernels of size $3 \times 3$ and $1 \times 1$ , the overhead is typically low. + +# 3.6. Buffer management + +We use a buffer manager that is responsible for: keeping track of each tile's state, allocating new regions in the spherical buffer, initializing newly allocated tiles and adding biases to feature maps during inference. As mentioned before, spherical buffers wrap coordinates around image borders to allow for infinite panning. One downside of this approach is that when borders grow in one direction, we overwrite the dilated pixels stored for growing in the opposite direction (see Figure 1). Restoring dilated pixels is non-trivial and would require inferring the negative accumulated values of the deleted tiles - which adds high overhead. Instead, we simply delete the dilated pixels and restrict the growth in the opposite direction. Once the camera moves back over a restricted region, all buffers are reset entirely, and the cur + +rent frame has to be inferred densely - becoming the new reference until the next buffer reset. Restoring the truncated values by only resetting the tiles next to the invalid truncated values does not work, as they would again lack valid truncated values required for seamless attachment to persistent tiles. While a full reset reduces the reuse of previously processed features, in our evaluations, the number of resets is fairly small as camera pans typically last many frames without changing directions. Our buffer manager stores for each tile of the grid the currently held global coordinates and the directions in which the growth is restricted. Every time the camera moves, the buffer manager checks whether the tiles already hold a value from the corresponding coordinates. If not, it resets the respective tiles if possible or requests a buffer reset if growth is restricted. + +# 3.7. Optimizations + +While the above-mentioned features can already lead to a large speedup in moving camera scenarios, the speedup can be increased significantly with some small optimizations. For the DAVIS 2017 dataset [27], we noticed strong salt-and-pepper style noise in the update masks. Since video stabilization is not perfect, some pixels align incorrectly, especially in high frequency details like leaves of a tree. This leads to a strong color change for some isolated pixels in the image, resulting in a large compute overhead when processing the image in tiles. We mitigate this issue using region-of-interest (ROI) focused sensing and noise suppression. When we know the ROI from previous frames, e.g., in the case of object detection or object segmentation, we can increase the sensitivity around these regions and decrease the sensitivity further away. Additionally, we suppress noise coming from imperfect image alignment by downscaling + +![](images/bd7366fcd3fdcddad7b3fd9caa738805892bab935881bfe77b7650a0244baca2.jpg) +Frame 1 + +![](images/30f055a0c7820b9fbe69cd1dad65d79aa03d7e40b11ccf56d0317b0d6128ae25.jpg) +Frame 2 + +![](images/7f3c290fefe098cd20ac85e748b8dba87abb62614e3ee21013920d022a07d649.jpg) +T +Figure 6: We increase update sparsity using noise suppression and region of interest scaling. $T$ uses the original truncation implementation of DeltaCNN. Scaling the Delta further away from the region of interest $(T + S)$ slightly increases sparsity. Using noise suppression $(T + N)$ to eliminate single pixel updates increases sparsity even further. Combining scaling and noise suppression $(T + S + N)$ achieves the highest sparsity, capturing only the most important updates of the moving camel. Note that in all cases, we dilate the update mask by 10 pixels; explaining the low sparsity in case $T$ . Source: DAVIS 2017 + +![](images/331eb80f5b9a668aedc0dfb88565b45f33ac3577e7ef3312e1e276e50275b96e.jpg) +T+S + +![](images/51ba846875f5cc2067a574c9639ca129719b82a024a6e052fd14726e4db1d09d.jpg) +$\mathrm{T + N}$ + +![](images/93946d9a59b6f75f2d0a0ac9ee3362023d22dbeb5e0769625361110ca3310af6.jpg) +$\mathrm{T} + \mathrm{S} + \mathrm{N}$ + +the Delta, processing which pixels exceed the thresholds and suppressing single pixel updates using average pooling. Overall, these steps lead to a significant speedup with only minor impact on accuracy (see Figure 6). Further optimizations can be found in the supplemental material. + +# 4. Evaluation + +We evaluate MotionDeltaCNN in two scenarios: a) using video stabilization to align subsequent frames with moving cameras and b) using bounding boxes in a static camera scenario to infer only regions of interest while retaining out-of-interest features from previous frames. + +Video Object Segmentation In task a), we evaluate the video object segmentation model BMVOS [7] on the DAVIS 2017 dataset [27]. BMVOS uses the DenseNet [15] backend for feature encoding, the most computationally expensive part of the model. We use weights pretrained on the DAVIS dataset, which were provided by the authors of BMVOS. The DAVIS 2017 dataset consists of a set of sequences with one or more segmented objects of which the masks are provided only for the first frame - and the model needs to paint the segmentation mask for the remaining frames in the video. Most of the videos are recorded using moving cameras, and are therefore well suited for evaluating MotionDeltaCNN. The DAVIS 2017 dataset does not provide camera extrinsic. Instead, we use OpenCV [2] to estimate homography matrices between two consecutive frames. This simplistic method fails in some cases, e.g., when it does not find good features due to motion blur or with motion parallax. We see the tasks of video stabilization as orthogonal and therefore only evaluate on the set of videos (14 sequences) for which this simple video stabilization approach works reliably. + +In video object segmentation, the segmentation mask from the previous frame can be used to suppress noise in the upcoming frame. We use this mask to lower the update sensitivity further away from the ROI - leading to an increase in sparsity. We deliberately tuned the thresholds for DeltaCNN with a lower accuracy target than for MotionDeltaCNN to show that we achieve higher frame rates even when targeting higher accuracy. The details about threshold tuning and + +ROI-focused sensing are found in the supplemental material. + +Human Pose Estimation In task b), we perform human pose estimation using HRNet [30, 32] on the Human3.6M dataset [3, 17]. Human3.6M uses static cameras and is recorded in a static studio with only a single moving actor in the room. We use this dataset to evaluate a second scenario for MotionDeltaCNN: top-down pose estimation. With top-down pose estimation, humans in the scene are detected first, and then the pose is predicted for each detected human. Each bounding box is cropped and inferred individually - estimating one set of joints per person. Since Human3.6M provides per frame bounding boxes of the actors as part of their labels, we omit the step of detecting humans in the scene. We snap the given bounding boxes onto a $32 \times 32$ pixel grid and then increase them by 32 pixels on each side where possible. The increased bounding boxes ensure that joint positions are not too close to image borders, as this could negatively impact prediction accuracy. We use the same weights and thresholds as were used in the DeltaCNN paper and evaluate on the same data subset (Subject S11). + +Both scenarios are compared against dense inference of cuDNN and against the original DeltaCNN without moving camera support. In HRNet, we only measure model inference time, without the overhead of post-processing or accuracy evaluation. The input shape is $384 \times 384$ with a tile size of $32 \times 32$ pixels unless stated otherwise. In the case of BMVOS, we only measure the duration of the feature encoding model to better highlight the difference of pure CNN inference speeds. For this evaluation, the camera input is embedded into a frame of shape Wx480 pixels, where W depends on the aspect ratio of the video (typically 864px) and is aligned onto a grid with a tile size of $48 \times 48$ pixels. + +Hardware We conduct our evaluations on two GPUs: Nvidia GTX 1080 Ti and Nvidia RTX 3090 with 3584/10496 CUDA cores and 11GB/24GB of VRAM respectively. The evaluations are performed using 32-bit precision, but our approach can be applied to other data types as well. + +![](images/0f8ad12cd8facb988f2202557526cdaef44c719ed6835c98caf5733ece614d76.jpg) +Figure 7: A DAVIS 2017 sequence processed using DeltaCNN (left) and MotionDeltaCNN (right). Row a shows the original input on the left, and the aligned and cropped input on the right. Row b visualizes the Delta between the (aligned) input and the previous input in row c. Row d visualizes the update mask with white pixels indicating an update. MotionDeltaCNN achieves much higher sparsity on the same input by reusing previous results for the aligned, static background. + +# 5. Results + +We evaluate speedup and accuracy of MotionDeltaCNN compared to DeltaCNN without explicit moving camera support as well as the dense cuDNN backend. In this section, we report the differences on the GTX 1080 Ti - for results on the RTX 3090, please see the respective tables. + +Video Object Segmentation MotionDeltaCNN outperforms state-of-the-art backends in sparse mode by a margin of up to $100\%$ over the cuDNN baseline (see Table 1). The DAVIS 2017 dataset consists mainly of videos with large bounding boxes and often fast camera motion, leading to a high average update rate of $29\%$ . + +Excluding videos without camera motion highlights the relative speedup over DeltaCNN without moving camera support with $+85\%$ speedup over cuDNN instead of $+8\%$ . + +MotionDeltaCNN, like DeltaCNN, requires larger workloads with more powerful hardware to show speedups. With 10.496 cores in a RTX 3090, small batch sizes typically do not fully utilize the available hardware resources in most layers - skipping some tiles in this scenario does not affect the overall performance unless all tiles can be skipped altogether. By increasing the batch size, we can fully utilize the GPU - cores that skip a tile can immediately continue processing the next tile, leading to an overall speedup. + +Over the 990 frames in the DAVIS dataset, we had to reset the buffers 9 times because of cameras panning over invalid truncated values. This low number of resets has only a small impact on the overall performance. + +Human Pose Estimation MotionDeltaCNN can outperform cuDNN by up to 11x in the case of HRNet (see Table 2). Please note that the frame rate of cuDNN is $30\%$ lower than in the DeltaCNN paper since we enforced the use of 32-bit multiplications in all layers - the same accuracy that we also use in our implementation. Furthermore, the accuracies do not match since we always use the full, uncropped images as input. The high sparsity in the Human3.6M dataset together with the efficient implementation allows us to accelerate inference significantly. Compared to DeltaCNN, which does not support varying resolution input or moving cameras, we were able to achieve $13\%$ higher frame rates with similar + +accuracy. We level the playing field in comparisons against the dense cuDNN backend by inferring the same cropped images that we use as input for MotionDeltaCNN. Still, we outperform cuDNN by up to $3.2\mathrm{x}$ , and achieve a speedup of up to $3.2\mathrm{x}$ over dense DeltaCNN with full resolution input. For Human3.6M, we know that the actors never cover the entire frame at once. We use this knowledge to lower the size of the buffers by $25\%$ on each axis - reducing the memory footprint of buffers by $44\%$ in total. These savings allow us to increase the batch size even further. When fully utilizing all available memory with an increased batch size, we achieve frame rates up to $3.9\mathrm{x}$ over the cropped cuDNN baseline and $37\%$ over DeltaCNN. + +Ablation Study We evaluated the individual impact of our contributions in an ablation study (see Table 3). Without dynamic initialization, MotionDeltaCNN always resets the buffers when new image tiles are unveiled. After a reset, the next frame is processed densely. This has a negative impact on the speedup, but slightly increases the accuracy as it regularly flushes accumulated errors. Padded convolutions are key in enabling spherical buffers. Without them, new tiles are not fused into existing buffers correctly, leading to a reduction in accuracy. Our evaluation shows that (ROI) focused sensing enables great speedups without lowering the accuracy of the segmentation. By disabling noise suppression as well, the model becomes more sensitive to errors in image alignment and small changes in the image. To compensate for this, we increase the threshold of the first truncation from 0.15 to 0.35 for this evaluation. However, even with an increased threshold, the speedup is significantly smaller compared to default truncation, while the accuracy is already much lower. Overall, the ablation study shows that all parts of MotionDeltaCNN work in tandem to achieve the best speedup without large impact on accuracy. + +# 6. Discussion + +Our evaluations prove that MotionDeltaCNN can accelerate CNN video inference with moving cameras where existing sparse methods fail to outperform the dense reference. However, our evaluation also shows that freely moving cameras, especially when combined with dense updates as in + +
VideosBackendIoUGFLOPsGTX 1080 Ti b=1GTX 1080 Ti b=5RTX 3090 b=1RTX 3090 b=12
FPSspeedupFPSspeedupFPSspeedupFPSspeedup
AllcuDNN76.8522.130.71.040.91.045.41.01031.0
DeltaCNN (dense)76.8522.135.01.1441.21.0166.51.461000.97
MotionDeltaCNN (dense)76.7622.633.51.0940.30.9957.71.2793.60.91
DeltaCNN (sparse)76.1815.542.51.3851.41.2670.01.541251.21
MotionDeltaCNN (sparse)76.326.854.81.7981.92.0065.21.442152.1
MovingcuDNN79.5922.130.71.040.91.045.41.01031.0
DeltaCNN (sparse)79.3818.838.21.2444.11.0870.21.551061.03
MotionDeltaCNN (sparse)79.437.352.31.7075.11.8465.01.432011.95
+ +Table 1: Results for the task of video object segmentation using BMVOS on the DAVIS dataset. We track only the DenseNet backend for evaluating frames per second (FPS). For accuracy benchmarks, the remaining network is processed densely. GFLOPs are reported as average over the test set. Both devices are evaluated with a batch size $b$ of one, and the maximum batch size each device can hold in memory. + +
BackendPCKh@0.5PCKh@0.2GFLOPsGTX 1080 Ti b=1GTX 1080 Ti b=16RTX 3090 b=1RTX 3090 b=40
FPSspeedupFPSspeedupFPSspeedupFPSspeedup
cuDNN96.03%83.33%47.122.51.024.81.012.31.069.61.0
DeltaCNN (dense)24.21.0841.31.726.02.195.81.4
MotionDeltaCNN (dense)96.00%83.32%17.732.51.4491.43.722.01.82323.3
cuDNN (cropped)95.92%83.11%13.324.01.0771.02.911.81.02093.0
DeltaCNN (sparse)95.95%82.31%3.5544.92.02028.126.22.15477.9
MotionDeltaCNN (sparse)95.95%82.33%3.4541.21.832289.222.61.85848.4
MotionDeltaCNN (sparse †)95.93%82.22%3.4442.51.8927611.122.51.86919.9
+ +Table 2: Speed and accuracy comparisons of different CNN backends used for pose estimation on the Human3.6M dataset. The same set of auto-tuned thresholds for update truncation is used for all devices and batch sizes $b$ . † limits the size of the input from 384x384 to 288x288 pixels - freeing up 44% of the memory used for buffers. The freed-up memory is used to increase the batch size to fully utilize the available VRAM (b=28 on 1080 Ti and b=66 on 3090). cuDNN cropped uses the same, cropped input as ours, instead of the full camera input. + +
FPSIoU# resets
cuDNN40.979.59-
DeltaCNN44.179.38-
MotionDeltaCNN75.179.438
- w/o dynamic init56.479.63110
- w/o padded conv.65.377.898
- w/o ROI scaling63.679.338
- w/o ROI & noise*50.979.068
+ +Table 3: Ablation study. Evaluating BMVOS on DAVIS2017 dataset using a Nvidia GTX 1080 Ti with a batch size of 5. We evaluate on the subset of videos with significant camera motion. * increased threshold on video input. + +the DAVIS dataset, lead to a much smaller speedup than the static camera setup with sparse motion in Human3.6M. Furthermore, the additional padding slightly increases memory and compute overhead over DeltaCNN. + +Receptive Field While MotionDeltaCNN does achieve + +outputs comparable to standard CNN inference, it should be noted that even in dense mode, the results are not identical. This can be observed in Figure 5 where the fused output of MotionDeltaCNN matches the result using the fused input in row $a$ , which includes information from neighbor pixels seen in previous frames. Since we do not actively propagate inverted accumulated values once a previously processed region gets out of view, the receptive field of later layers, also for pixels inside the current view, still contains some information from that now unseen area. This can have positive and negative effects alike. These features might not be valid anymore. At the same time, some out-of-view features can help to make better predictions due to additional context. + +Applications MotionDeltaCNN is a general-purpose framework for video inference and can thus be used with all pre-trained CNNs by replacing the original, dense layers with our sparse equivalent. As additional input, Motion-DeltaCNN requires camera extrinsics for the frame to be processed. While most publicly available datasets do not + +include camera extrinsics and therefore require image stabilization, smartphones, tablets and VR headsets nowadays have built-in support for tracking the camera pose between frames in real-time. Potential applications are not limited to classic computer vision applications like tracking and segmentation, but it could also be used for video up-scaling, filtering, etc. However, applications like image-denoising (diffusion) are likely not a good fit as they provide low levels of spatial update sparsity between iterations and they are very sensitive to noise. + +Limitations One of the main limitations of our approach is its dependency on robust video stabilization. Our experiments with the DAVIS dataset showed that simple video stabilization techniques can break when blur or parallax is involved, or when it fails to find robust features. Parallax can greatly reduce the gains of our method, even when the scene itself is mostly static. When foreground and background layers move at different speeds, frames can only be properly aligned to stabilize one of these layers - leading to dense updates in layers moving at different speeds. + +MotionDeltaCNN also comes with the trade-off between buffer overallocation and losing information by cropping the input to match the shape of the buffer. In our evaluations, when the camera zooms or rotates around the forward axis (roll), the aligned input can exceed the size of the buffers, and therefore requires slight cropping to fit into the target shape (see Figure 7). Alternatively, the buffers could also be increased to allow for larger inputs in upcoming frames - at the cost of higher memory consumption. + +# 7. Conclusion + +We propose MotionDeltaCNN, an extension to the sparse video CNN framework DeltaCNN adding support for moving camera input. To the best of our knowledge, we are the first to propose a solution for moving cameras with sparse inference. 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However, this approach requires special network design and training and is not suitable for significant frame changes." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 715 + ], + "type": "text", + "content": "Sparse convolutions, on the other hand, can be used with existing pre-trained models, accelerating the large network to the speed of a smaller network without impacting prediction accuracy significantly [25, 26]. 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After processing the first frame densely, upcoming frames can be processed using the difference between the current and the previous frame, the Delta, as the network input. Assuming a static camera scenario, this results in large image regions with no frame-to-frame difference. Static elements like background or stationary objects do not require updates after the initial frame. Researchers exploited this sparsity in previous work to reduce the number of FLOPs required for CNN inference [25, 4, 11, 1, 8], but were mostly unable to accelerate inference in practice. With the recent progress in DeltaCNN [26], theoretical FLOP reductions were translated into practical speedups on GPUs, using a custom sparse CNN implementation to exploit sparsity in all layers of the CNN." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 472, + 289, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 289, + 652 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 289, + 652 + ], + "type": "text", + "content": "DeltaCNN achieves speedups on multiple tasks and datasets, but like prior work, it is optimized for static camera inputs. Even small frame-to-frame camera motion necessitates reprocessing large portions, or the entire image. Spatially aligning consecutive frames, e.g., by leveraging camera extrinsics from IMUs or SLAM on mobile devices, can increase per-pixel similarity and thus update sparsity. Due to the change of camera location and orientation, an aligned new frame may \"grow\" beyond the initial field of view - out of the previous-results buffers. One way to solve this issue is to embed inputs in a larger frame by padding the input image and drawing updates on top of it. However, the downside of this approach is that padded input images increase the memory consumption and computational cost significantly, as shown in Figure 2." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "content": "In this work, we propose MotionDeltaCNN, a sparse CNN inference framework that allows moving camera input with marginal memory overhead. Compared to previous work, we achieve up to " + }, + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "content": " higher frame rates in videos with moving cameras, indicating a new perspective for CNN" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 304, + 547, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 304, + 547, + 327 + ], + "spans": [ + { + "bbox": [ + 305, + 304, + 547, + 327 + ], + "type": "text", + "content": "inference optimization on low-power devices, such as surveillance cameras, smartphones, or VR headsets." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 318, + 328, + 432, + 339 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 328, + 432, + 339 + ], + "spans": [ + { + "bbox": [ + 318, + 328, + 432, + 339 + ], + "type": "text", + "content": "Our main contributions are:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 317, + 348, + 547, + 543 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 317, + 348, + 547, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 348, + 547, + 396 + ], + "spans": [ + { + "bbox": [ + 317, + 348, + 547, + 396 + ], + "type": "text", + "content": "- We propose MotionDeltaCNN, the first framework that leverages temporal continuity to accelerate CNN inference for videos with moving cameras by processing only the sparse frame differences." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 317, + 404, + 547, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 404, + 547, + 441 + ], + "spans": [ + { + "bbox": [ + 317, + 404, + 547, + 441 + ], + "type": "text", + "content": "- At the core of this work, we propose padded convolutions for seamless integration of newly unveiled pixels without the need of reprocessing seen pixels." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 317, + 449, + 547, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 449, + 547, + 498 + ], + "spans": [ + { + "bbox": [ + 317, + 449, + 547, + 498 + ], + "type": "text", + "content": "- We design a two-dimensional ring buffer, a spherical buffer, with wrapped coordinates. Our buffer allows partial growth, reset and initialization of new tiles without additional memory allocation." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 317, + 506, + 547, + 543 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 506, + 547, + 543 + ], + "spans": [ + { + "bbox": [ + 317, + 506, + 547, + 543 + ], + "type": "text", + "content": "- We show how MotionDeltaCNN can also be used for speeding up applications with static cameras when only parts of the image require processing." + } + ] + } + ], + "index": 16 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 562, + 392, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 562, + 392, + 574 + ], + "spans": [ + { + "bbox": [ + 306, + 562, + 392, + 574 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 547, + 715 + ], + "type": "text", + "content": "The idea of only processing updated pixels in a convolutional layer has been proposed in various ways, with Recurrent Residual Module (RRM) [25] being the first work to apply this concept to videos. RRM uses the difference between current and previous input, the Delta, as input to convolutional layers. RRM demonstrates large theoretical reductions in FLOPs compared to dense inference resulting from skipping computations involving (nearly) zero-valued entries in feature maps. In practice, skipping individual values is infeasible on most inference hardware like GPUs due to their single instruction, multiple data (SIMD) design." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17293" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 68, + 545, + 194 + ], + "blocks": [ + { + "bbox": [ + 47, + 68, + 545, + 194 + ], + "lines": [ + { + "bbox": [ + 47, + 68, + 545, + 194 + ], + "spans": [ + { + "bbox": [ + 47, + 68, + 545, + 194 + ], + "type": "image", + "image_path": "fcfdf84748ef11e212b04640f39514379ba1b08a380433269eeadd20cb9236fe.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 200, + 548, + 261 + ], + "lines": [ + { + "bbox": [ + 46, + 200, + 548, + 261 + ], + "spans": [ + { + "bbox": [ + 46, + 200, + 548, + 261 + ], + "type": "text", + "content": "Figure 3: The main concepts of MotionDeltaCNN. We align frame 2 (F2) with frame 1 (F1) using homography matrices. For the intersecting region, we propagate only the aligned frame-to-frame differences (Delta). The newly uncovered regions are propagated directly. The regions in which the buffers store the uncovered regions are reset to zero before processing the current Delta input. After convolving frame 2, we add the bias to all previously unseen regions, and accumulate the result onto our spherical buffer using the offset coordinates for the current frame." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 281, + 288, + 329 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 281, + 288, + 329 + ], + "spans": [ + { + "bbox": [ + 46, + 281, + 288, + 329 + ], + "type": "text", + "content": "Furthermore, RRM only processes convolutional layers on sparse Delta input. All remaining layers are processed on the full, dense feature maps and therefore require expensive value-conversions before and after each convolutional layer." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 330, + 290, + 474 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 330, + 290, + 474 + ], + "spans": [ + { + "bbox": [ + 46, + 330, + 290, + 474 + ], + "type": "text", + "content": "Skip-Convolution [11] and CBInfer [4] improve the concept of RRM using a per-pixel sparse mask instead of pervalue. Like RRM, CBInfer uses a threshold to truncate insignificant updates in the input feature map. This threshold can be tuned for each layer for maximum sparsity while keeping the accuracy at a desired level. In contrast, Skip-Convolution decides per output pixel whether an update is required or can be skipped. In both cases, only the convolutional layers (and pooling layers in case of CBInfer) are processed sparsely, requiring expensive conversions between dense and sparse features before and after each of these layers, leaving large performance potential unused." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 474, + 288, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 474, + 288, + 641 + ], + "spans": [ + { + "bbox": [ + 46, + 474, + 288, + 641 + ], + "type": "text", + "content": "DeltaCNN [26] propagates sparse Delta features end-to-end using a sparse Delta feature map together with an update mask. This greatly reduces the memory bandwidth compared to previous work. Propagating sparse updates end-to-end eliminates the necessity of converting the feature maps from dense accumulated values to sparse Deltas, and it speeds up other layers bottlenecked by memory bandwidth like activation, batch normalization, upsampling, etc. Using a custom CUDA implementation, DeltaCNN outperforms cuDNN and CBInfer many times on video input. However, DeltaCNN, as well as all other previous work, assumes static camera input. Even single pixel camera motion between two frames can result in nearly dense updates when the image contains high frequency features." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "type": "text", + "content": "Event Neural Networks show that computational savings are strongly impacted by the intensity of camera motion[8]. With slightly shaking cameras, theoretical FLOP savings were reduced by " + }, + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "type": "inline_equation", + "content": "40\\%" + }, + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "type": "text", + "content": " compared to static camera videos, while moving cameras reduced them by " + }, + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "type": "inline_equation", + "content": "60\\%" + }, + { + "bbox": [ + 46, + 642, + 288, + 715 + ], + "type": "text", + "content": ". Depending on the distribution of the pixel updates, the impact on real" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 281, + 430, + 293 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 281, + 430, + 293 + ], + "spans": [ + { + "bbox": [ + 305, + 281, + 430, + 293 + ], + "type": "text", + "content": "hardware is likely even higher." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 294, + 547, + 402 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 294, + 547, + 402 + ], + "spans": [ + { + "bbox": [ + 304, + 294, + 547, + 402 + ], + "type": "text", + "content": "Incremental Sparse Convolution uses sparse convolutions to incrementally update 3D segmentation masks online [23]. They solve a similar problem of reusing results from previously segmented regions, while allowing for new regions to be attached on the fly. Due to their reliance on non-dilating 3D convolutions [10], attaching new regions leads to artifacts along the region borders. We solve this issue using a standard, dilating convolution and by processing all outputs that are affected by the current input." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 402, + 547, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 402, + 547, + 475 + ], + "spans": [ + { + "bbox": [ + 304, + 402, + 547, + 475 + ], + "type": "text", + "content": "We propose MotionDeltaCNN: building upon DeltaCNN, we design and implement a sparse inference extension that supports moving cameras. Compared to DeltaCNN, we add the support for variable resolution inputs, spherical buffers, dynamic buffer allocation & initialization and padded convolutions for seamless attachment of newly unveiled regions." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 487, + 361, + 498 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 487, + 361, + 498 + ], + "spans": [ + { + "bbox": [ + 306, + 487, + 361, + 498 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 507, + 525, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 507, + 525, + 519 + ], + "spans": [ + { + "bbox": [ + 317, + 507, + 525, + 519 + ], + "type": "text", + "content": "MotionDeltaCNN relies on the following concepts:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 520, + 547, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 520, + 547, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 520, + 547, + 555 + ], + "type": "text", + "content": "Frame Alignment The current frame is aligned with the initial frame of the sequence to maximize the overlap of consistent features (see Figure 3 Delta)." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 556, + 547, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 556, + 547, + 592 + ], + "spans": [ + { + "bbox": [ + 304, + 556, + 547, + 592 + ], + "type": "text", + "content": "Spherical Buffers We use wrapped buffer offset coordinates in all non-linear layers to align them with the input (see Figure 3 Accumulated Output)." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 593, + 547, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 593, + 547, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 593, + 547, + 653 + ], + "type": "text", + "content": "Dynamic Initialization When a new region is first unveiled due to camera motion, MotionDeltaCNN adds biases onto the feature maps on the fly to all newly unveiled pixels to allow for seamless integration with previously processed pixels (see Figure 3 Bias)." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": "Padded Convolutions We add additional padding to convolutional layers to process all pixels that are affected by the kernel. These dilated pixels are stored in truncated values buffers to enable seamless connection of potentially unveiled neighbor regions in upcoming frames (see Figure 5)." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17294" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 185, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 185, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 185, + 85 + ], + "type": "text", + "content": "3.1. Background: DeltaCNN" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 90, + 288, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 90, + 288, + 185 + ], + "spans": [ + { + "bbox": [ + 46, + 90, + 288, + 185 + ], + "type": "text", + "content": "For a better understanding of our contributions, we first summarize the core concept of DeltaCNN, which accelerates CNN inference by processing only the first frame densely and applying sparse updates to changed pixels in subsequent frames. A sparse input Delta is calculated by subtracting the previously processed input from the current input frame. Pixels whose Delta is smaller than a threshold are truncated to zero to increase sparsity." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 186, + 288, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 186, + 288, + 281 + ], + "spans": [ + { + "bbox": [ + 46, + 186, + 288, + 281 + ], + "type": "text", + "content": "Because of linearity, the output of any convolution layer can be updated by convolving the sparse input Delta, " + }, + { + "bbox": [ + 46, + 186, + 288, + 281 + ], + "type": "inline_equation", + "content": "c(x + \\delta) = c(x) + c(\\delta)" + }, + { + "bbox": [ + 46, + 186, + 288, + 281 + ], + "type": "text", + "content": ". This does not hold for non-linear layers like activation (e.g., ReLU) and pooling, which therefore require a separate accumulated values buffer to accumulate the inputs to the respective layers across all previously processed frames. The buffers contain the full, dense layer input of the previous frame, including biases from previous layers." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 282, + 288, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 282, + 288, + 413 + ], + "spans": [ + { + "bbox": [ + 46, + 282, + 288, + 413 + ], + "type": "text", + "content": "Convolutions with kernel sizes larger than 1x1 pixels dilate the updates across the feature map. A single pixel update in the center of the feature map might span over the entire feature map a few convolutional layers later. This can lead to nearly dense updates for the larger part of the network. DeltaCNN solves this by truncating insignificant updates not only on the input image, but at every activation layer. To avoid accumulating errors indefinitely, the truncated values are accumulated in a dedicated truncated values buffer. Once an accumulated, truncated value exceeds a significance threshold, the value is propagated to the next layer." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 419, + 153, + 431 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 419, + 153, + 431 + ], + "spans": [ + { + "bbox": [ + 47, + 419, + 153, + 431 + ], + "type": "text", + "content": "3.2. Frame Alignment" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 437, + 288, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 288, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 288, + 521 + ], + "type": "text", + "content": "Robust frame alignment (or video stabilization) is a fundamental requirement for MotionDeltaCNN to achieve high coherence across consecutive frames. For best alignment between two frames in a 3D space, we use homography matrices with 8 degrees of freedom. Homography matrices align two images in 3D to match a selected set of key features of the initial frame - typically the static background." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 521, + 288, + 654 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 288, + 654 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 288, + 654 + ], + "type": "text", + "content": "We embed the image in a grid-aligned frame to ensure a pixel-perfect downscale to all layers. For example, in HRNet [29], the highest resolution feature map spans " + }, + { + "bbox": [ + 46, + 521, + 288, + 654 + ], + "type": "inline_equation", + "content": "384 \\times 384" + }, + { + "bbox": [ + 46, + 521, + 288, + 654 + ], + "type": "text", + "content": " pixels, whereas the lowest resolution feature map spans only " + }, + { + "bbox": [ + 46, + 521, + 288, + 654 + ], + "type": "inline_equation", + "content": "12 \\times 12" + }, + { + "bbox": [ + 46, + 521, + 288, + 654 + ], + "type": "text", + "content": " pixels, resulting in a scaling factor of " + }, + { + "bbox": [ + 46, + 521, + 288, + 654 + ], + "type": "inline_equation", + "content": "32 \\times 32" + }, + { + "bbox": [ + 46, + 521, + 288, + 654 + ], + "type": "text", + "content": ". To ensure that all pixels align on all scaling levels, the input to HRNet must be aligned onto a grid of " + }, + { + "bbox": [ + 46, + 521, + 288, + 654 + ], + "type": "inline_equation", + "content": "32 \\times 32" + }, + { + "bbox": [ + 46, + 521, + 288, + 654 + ], + "type": "text", + "content": " pixel tiles. E.g., if a frame has a 20-pixel horizontal offset relative to the first frame, we allocate 32 additional pixels, paste the original frame into the grid-aligned frame and set the 20 left-most pixels as well as the 12 right-most pixels to zero." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 659, + 152, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 659, + 152, + 672 + ], + "spans": [ + { + "bbox": [ + 47, + 659, + 152, + 672 + ], + "type": "text", + "content": "3.3. Spherical Buffers" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 677, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 288, + 714 + ], + "type": "text", + "content": "MotionDeltaCNN enables support for moving cameras by introducing 2D ring buffers, spherical buffers. These buffers align previously processed pixels with pixels of the current" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 309, + 70, + 367, + 129 + ], + "blocks": [ + { + "bbox": [ + 309, + 70, + 367, + 129 + ], + "lines": [ + { + "bbox": [ + 309, + 70, + 367, + 129 + ], + "spans": [ + { + "bbox": [ + 309, + 70, + 367, + 129 + ], + "type": "image", + "image_path": "3277034ac1ddff4b6a94a83ed49057830b7354d83626cff1873169253a0b9a5d.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 321, + 133, + 353, + 143 + ], + "lines": [ + { + "bbox": [ + 321, + 133, + 353, + 143 + ], + "spans": [ + { + "bbox": [ + 321, + 133, + 353, + 143 + ], + "type": "text", + "content": "Frame 1" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 388, + 81, + 405, + 115 + ], + "blocks": [ + { + "bbox": [ + 388, + 81, + 405, + 115 + ], + "lines": [ + { + "bbox": [ + 388, + 81, + 405, + 115 + ], + "spans": [ + { + "bbox": [ + 388, + 81, + 405, + 115 + ], + "type": "image", + "image_path": "94f154ebe1c637c52f65fae4532979295ca263853349e6dfdba8d28a1fa75382.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 380, + 133, + 413, + 144 + ], + "lines": [ + { + "bbox": [ + 380, + 133, + 413, + 144 + ], + "spans": [ + { + "bbox": [ + 380, + 133, + 413, + 144 + ], + "type": "text", + "content": "Cropped" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 425, + 70, + 485, + 129 + ], + "blocks": [ + { + "bbox": [ + 425, + 70, + 485, + 129 + ], + "lines": [ + { + "bbox": [ + 425, + 70, + 485, + 129 + ], + "spans": [ + { + "bbox": [ + 425, + 70, + 485, + 129 + ], + "type": "image", + "image_path": "12d35fd2c5e2fff9eeda65ae064ef95401138ca6035622f5aed03aa3843a2b5e.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 439, + 133, + 471, + 142 + ], + "lines": [ + { + "bbox": [ + 439, + 133, + 471, + 142 + ], + "spans": [ + { + "bbox": [ + 439, + 133, + 471, + 142 + ], + "type": "text", + "content": "Frame 2" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 497, + 133, + 531, + 144 + ], + "lines": [ + { + "bbox": [ + 497, + 133, + 531, + 144 + ], + "spans": [ + { + "bbox": [ + 497, + 133, + 531, + 144 + ], + "type": "text", + "content": "Cropped" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 153, + 547, + 214 + ], + "lines": [ + { + "bbox": [ + 304, + 153, + 547, + 214 + ], + "spans": [ + { + "bbox": [ + 304, + 153, + 547, + 214 + ], + "type": "text", + "content": "Figure 4: MotionDeltaCNN can handle sparse Delta inputs of different crop sizes, and focus only on a fraction of the image, thanks to the concept of spherical buffers. This is not possible for DeltaCNN which always processes sparse Delta inputs of the entire frame." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 509, + 87, + 520, + 110 + ], + "blocks": [ + { + "bbox": [ + 509, + 87, + 520, + 110 + ], + "lines": [ + { + "bbox": [ + 509, + 87, + 520, + 110 + ], + "spans": [ + { + "bbox": [ + 509, + 87, + 520, + 110 + ], + "type": "image", + "image_path": "5efb1b34bdfb512ea967d50dccfb777b82765324398e1fdd597348d95a1e5814.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 236, + 547, + 429 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 236, + 547, + 429 + ], + "spans": [ + { + "bbox": [ + 304, + 236, + 547, + 429 + ], + "type": "text", + "content": "frame by translating feature map coordinates to buffer coordinates. Pixel coordinates exceeding image borders are wrapped around the buffer, i.e., mapped to the opposite border using the modulo operator. This enables the reuse of previous results for moving cameras without increasing the memory overhead over DeltaCNN (see Figure 5). Our buffers support 2D offsets relative to the initial frame as well as cropped inputs (see Figure 4). Frame scales can be helpful when only a part of the image is updated in the current frame - for example, when a frame is cropped to the bounding box of a region of interest. Tile offset indices are provided during inference to align features in buffers with the current input. By multiplying tile offset indices with a layer's tile size (in the example above " + }, + { + "bbox": [ + 304, + 236, + 547, + 429 + ], + "type": "inline_equation", + "content": "32 \\times 32" + }, + { + "bbox": [ + 304, + 236, + 547, + 429 + ], + "type": "text", + "content": " pixels in highest resolution feature maps, " + }, + { + "bbox": [ + 304, + 236, + 547, + 429 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 304, + 236, + 547, + 429 + ], + "type": "text", + "content": " pixel in the lowest resolution), we get the pixel offset coordinates for buffer access in non-linear layers." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 437, + 434, + 450 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 437, + 434, + 450 + ], + "spans": [ + { + "bbox": [ + 306, + 437, + 434, + 450 + ], + "type": "text", + "content": "3.4. Dynamic Initialization" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 456, + 547, + 554 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 456, + 547, + 554 + ], + "spans": [ + { + "bbox": [ + 304, + 456, + 547, + 554 + ], + "type": "text", + "content": "When the input frame covers a previously unseen area, new tiles are allocated in all buffers before inferring the frame. A new tile is allocated by deleting a previously stored tile at the desired location and resetting respective values to zero. In doing so, we lose information about the accumulated biases inferred in the initial frame. We compensate for this by adding the biases onto reset regions of the Delta feature map during inference." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 562, + 429, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 562, + 429, + 574 + ], + "spans": [ + { + "bbox": [ + 306, + 562, + 429, + 574 + ], + "type": "text", + "content": "3.5. Padded Convolutions" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 581, + 547, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 581, + 547, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 581, + 547, + 665 + ], + "type": "text", + "content": "After the initial frame, MotionDeltaCNN propagates only Delta updates for the remaining sequence. This can cause inconsistencies when mixing previously seen and newly unveiled pixels. Consider a pair of adjacent pixels " + }, + { + "bbox": [ + 304, + 581, + 547, + 665 + ], + "type": "inline_equation", + "content": "\\mathbf{p}_{seen}" + }, + { + "bbox": [ + 304, + 581, + 547, + 665 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 581, + 547, + 665 + ], + "type": "inline_equation", + "content": "\\mathbf{p}_{new}" + }, + { + "bbox": [ + 304, + 581, + 547, + 665 + ], + "type": "text", + "content": " across the boundary, the resulting output at " + }, + { + "bbox": [ + 304, + 581, + 547, + 665 + ], + "type": "inline_equation", + "content": "\\mathbf{p}_{new}" + }, + { + "bbox": [ + 304, + 581, + 547, + 665 + ], + "type": "text", + "content": " may \"miss\" previously accumulated updates from pixel " + }, + { + "bbox": [ + 304, + 581, + 547, + 665 + ], + "type": "inline_equation", + "content": "\\mathbf{p}_{seen}" + }, + { + "bbox": [ + 304, + 581, + 547, + 665 + ], + "type": "text", + "content": " (see Figure 5), since they were \"outside\"." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "text", + "content": "MotionDeltaCNN addresses this prospectively by increasing the padding of convolutional layers to include all pixels that could be affected by convolutions on the current input. 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Naively applying convolutions separately to the initial frame and the Delta of Frame 2, and aggregating the outputs (row b) does not achieve the same results as one would get if the convolution is directly applied to a large fused input buffer (row a). This is because of how the boundary pixels are treated and dropped when applying convolutions and border cropping. To address this issue, we need to cache and pad the output features, as shown in row c. See Section 3.5 for details regarding how to handle this in a practical manner." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 300, + 117, + 375, + 210 + ], + "blocks": [ + { + "bbox": [ + 300, + 117, + 375, + 210 + ], + "lines": [ + { + "bbox": [ + 300, + 117, + 375, + 210 + ], + "spans": [ + { + "bbox": [ + 300, + 117, + 375, + 210 + ], + "type": "image", + "image_path": "914a5793d6c4bd84ce6e12479f6784c7300d3dca066a6646197242e0aa3e1957.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 321, + 217, + 354, + 226 + ], + "lines": [ + { + "bbox": [ + 321, + 217, + 354, + 226 + ], + "spans": [ + { + "bbox": [ + 321, + 217, + 354, + 226 + ], + "type": "text", + "content": "Output 2" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 376, + 70, + 451, + 210 + ], + "blocks": [ + { + "bbox": [ + 376, + 70, + 451, + 210 + ], + "lines": [ + { + "bbox": [ + 376, + 70, + 451, + 210 + ], + "spans": [ + { + "bbox": [ + 376, + 70, + 451, + 210 + ], + "type": "image", + "image_path": "b7fd25abc1903a0717518b9f696cb0cd4ece750f3c17790aa26ee627d5743f09.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 379, + 217, + 449, + 227 + ], + "lines": [ + { + "bbox": [ + 379, + 217, + 449, + 227 + ], + "spans": [ + { + "bbox": [ + 379, + 217, + 449, + 227 + ], + "type": "text", + "content": "Accumulated Input" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 453, + 70, + 528, + 210 + ], + "blocks": [ + { + "bbox": [ + 453, + 70, + 528, + 210 + ], + "lines": [ + { + "bbox": [ + 453, + 70, + 528, + 210 + ], + "spans": [ + { + "bbox": [ + 453, + 70, + 528, + 210 + ], + "type": "image", + "image_path": "a0c01e0b318c9e43e84f3aa9348f0c3772fce9e5fe1d4272e3c553e9286f5d96.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 452, + 217, + 529, + 227 + ], + "lines": [ + { + "bbox": [ + 452, + 217, + 529, + 227 + ], + "spans": [ + { + "bbox": [ + 452, + 217, + 529, + 227 + ], + "type": "text", + "content": "Accumulated Output" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 319, + 287, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 319, + 287, + 342 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 287, + 342 + ], + "type": "text", + "content": "when the kernel size is larger than 1x1. For example, a 64x64 pixel input and a 3x3 kernel result in a 66x66 pixel output." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 342, + 289, + 522 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 342, + 289, + 522 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 289, + 522 + ], + "type": "text", + "content": "With modern CNNs consisting of hundreds of convolutional layers, growing the feature map at each layer could quickly exceed our buffers and computational budget. To prevent this, in practice, we move and stash these output values at dilated pixels, and crop the output feature map of the current buffer to its original shape. Since MotionDeltaCNN already uses truncated values buffers for storing values that were not yet propagated through the activation layer, we only need to increase the size of the buffer slightly to include the dilated values and accumulate them there for later use. Combined with spherical buffers, this allows us to fuse new image regions from all 4 directions seamlessly at the cost of memory and compute overhead for the dilated border pixels. Since most convolutions use kernels of size " + }, + { + "bbox": [ + 46, + 342, + 289, + 522 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 46, + 342, + 289, + 522 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 342, + 289, + 522 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 342, + 289, + 522 + ], + "type": "text", + "content": ", the overhead is typically low." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 47, + 528, + 163, + 540 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 528, + 163, + 540 + ], + "spans": [ + { + "bbox": [ + 47, + 528, + 163, + 540 + ], + "type": "text", + "content": "3.6. Buffer management" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 46, + 546, + 289, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 546, + 289, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 546, + 289, + 713 + ], + "type": "text", + "content": "We use a buffer manager that is responsible for: keeping track of each tile's state, allocating new regions in the spherical buffer, initializing newly allocated tiles and adding biases to feature maps during inference. As mentioned before, spherical buffers wrap coordinates around image borders to allow for infinite panning. One downside of this approach is that when borders grow in one direction, we overwrite the dilated pixels stored for growing in the opposite direction (see Figure 1). Restoring dilated pixels is non-trivial and would require inferring the negative accumulated values of the deleted tiles - which adds high overhead. Instead, we simply delete the dilated pixels and restrict the growth in the opposite direction. Once the camera moves back over a restricted region, all buffers are reset entirely, and the cur" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 319, + 548, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 319, + 548, + 498 + ], + "spans": [ + { + "bbox": [ + 304, + 319, + 548, + 498 + ], + "type": "text", + "content": "rent frame has to be inferred densely - becoming the new reference until the next buffer reset. Restoring the truncated values by only resetting the tiles next to the invalid truncated values does not work, as they would again lack valid truncated values required for seamless attachment to persistent tiles. While a full reset reduces the reuse of previously processed features, in our evaluations, the number of resets is fairly small as camera pans typically last many frames without changing directions. Our buffer manager stores for each tile of the grid the currently held global coordinates and the directions in which the growth is restricted. Every time the camera moves, the buffer manager checks whether the tiles already hold a value from the corresponding coordinates. If not, it resets the respective tiles if possible or requests a buffer reset if growth is restricted." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 504, + 395, + 516 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 504, + 395, + 516 + ], + "spans": [ + { + "bbox": [ + 306, + 504, + 395, + 516 + ], + "type": "text", + "content": "3.7. Optimizations" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 522, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 522, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 522, + 547, + 714 + ], + "type": "text", + "content": "While the above-mentioned features can already lead to a large speedup in moving camera scenarios, the speedup can be increased significantly with some small optimizations. For the DAVIS 2017 dataset [27], we noticed strong salt-and-pepper style noise in the update masks. Since video stabilization is not perfect, some pixels align incorrectly, especially in high frequency details like leaves of a tree. This leads to a strong color change for some isolated pixels in the image, resulting in a large compute overhead when processing the image in tiles. We mitigate this issue using region-of-interest (ROI) focused sensing and noise suppression. When we know the ROI from previous frames, e.g., in the case of object detection or object segmentation, we can increase the sensitivity around these regions and decrease the sensitivity further away. Additionally, we suppress noise coming from imperfect image alignment by downscaling" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 91, + 55, + 191 + ], + "type": "aside_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 91, + 55, + 191 + ], + "spans": [ + { + "bbox": [ + 47, + 91, + 55, + 191 + ], + "type": "text", + "content": "a b C" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "17296" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 69, + 129, + 115 + ], + "blocks": [ + { + "bbox": [ + 50, + 69, + 129, + 115 + ], + "lines": [ + { + "bbox": [ + 50, + 69, + 129, + 115 + ], + "spans": [ + { + "bbox": [ + 50, + 69, + 129, + 115 + ], + "type": "image", + "image_path": "bd7366fcd3fdcddad7b3fd9caa738805892bab935881bfe77b7650a0244baca2.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 74, + 121, + 105, + 129 + ], + "lines": [ + { + "bbox": [ + 74, + 121, + 105, + 129 + ], + "spans": [ + { + "bbox": [ + 74, + 121, + 105, + 129 + ], + "type": "text", + "content": "Frame 1" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 132, + 70, + 212, + 116 + ], + "blocks": [ + { + "bbox": [ + 132, + 70, + 212, + 116 + ], + "lines": [ + { + "bbox": [ + 132, + 70, + 212, + 116 + ], + "spans": [ + { + "bbox": [ + 132, + 70, + 212, + 116 + ], + "type": "image", + "image_path": "30f055a0c7820b9fbe69cd1dad65d79aa03d7e40b11ccf56d0317b0d6128ae25.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 156, + 121, + 187, + 130 + ], + "lines": [ + { + "bbox": [ + 156, + 121, + 187, + 130 + ], + "spans": [ + { + "bbox": [ + 156, + 121, + 187, + 130 + ], + "type": "text", + "content": "Frame 2" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 215, + 77, + 275, + 117 + ], + "blocks": [ + { + "bbox": [ + 215, + 77, + 275, + 117 + ], + "lines": [ + { + "bbox": [ + 215, + 77, + 275, + 117 + ], + "spans": [ + { + "bbox": [ + 215, + 77, + 275, + 117 + ], + "type": "image", + "image_path": "7f3c290fefe098cd20ac85e748b8dba87abb62614e3ee21013920d022a07d649.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 250, + 121, + 257, + 129 + ], + "lines": [ + { + "bbox": [ + 250, + 121, + 257, + 129 + ], + "spans": [ + { + "bbox": [ + 250, + 121, + 257, + 129 + ], + "type": "text", + "content": "T" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "lines": [ + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "spans": [ + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "type": "text", + "content": "Figure 6: We increase update sparsity using noise suppression and region of interest scaling. " + }, + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "type": "text", + "content": " uses the original truncation implementation of DeltaCNN. Scaling the Delta further away from the region of interest " + }, + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "type": "inline_equation", + "content": "(T + S)" + }, + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "type": "text", + "content": " slightly increases sparsity. Using noise suppression " + }, + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "type": "inline_equation", + "content": "(T + N)" + }, + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "type": "text", + "content": " to eliminate single pixel updates increases sparsity even further. Combining scaling and noise suppression " + }, + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "type": "inline_equation", + "content": "(T + S + N)" + }, + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "type": "text", + "content": " achieves the highest sparsity, capturing only the most important updates of the moving camel. Note that in all cases, we dilate the update mask by 10 pixels; explaining the low sparsity in case " + }, + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 141, + 547, + 201 + ], + "type": "text", + "content": ". 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Overall, these steps lead to a significant speedup with only minor impact on accuracy (see Figure 6). Further optimizations can be found in the supplemental material." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 296, + 118, + 308 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 296, + 118, + 308 + ], + "spans": [ + { + "bbox": [ + 47, + 296, + 118, + 308 + ], + "type": "text", + "content": "4. Evaluation" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 316, + 287, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 316, + 287, + 376 + ], + "spans": [ + { + "bbox": [ + 46, + 316, + 287, + 376 + ], + "type": "text", + "content": "We evaluate MotionDeltaCNN in two scenarios: a) using video stabilization to align subsequent frames with moving cameras and b) using bounding boxes in a static camera scenario to infer only regions of interest while retaining out-of-interest features from previous frames." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 46, + 378, + 288, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 378, + 288, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 378, + 288, + 617 + ], + "type": "text", + "content": "Video Object Segmentation In task a), we evaluate the video object segmentation model BMVOS [7] on the DAVIS 2017 dataset [27]. BMVOS uses the DenseNet [15] backend for feature encoding, the most computationally expensive part of the model. We use weights pretrained on the DAVIS dataset, which were provided by the authors of BMVOS. The DAVIS 2017 dataset consists of a set of sequences with one or more segmented objects of which the masks are provided only for the first frame - and the model needs to paint the segmentation mask for the remaining frames in the video. Most of the videos are recorded using moving cameras, and are therefore well suited for evaluating MotionDeltaCNN. The DAVIS 2017 dataset does not provide camera extrinsic. Instead, we use OpenCV [2] to estimate homography matrices between two consecutive frames. This simplistic method fails in some cases, e.g., when it does not find good features due to motion blur or with motion parallax. We see the tasks of video stabilization as orthogonal and therefore only evaluate on the set of videos (14 sequences) for which this simple video stabilization approach works reliably." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 288, + 714 + ], + "type": "text", + "content": "In video object segmentation, the segmentation mask from the previous frame can be used to suppress noise in the upcoming frame. We use this mask to lower the update sensitivity further away from the ROI - leading to an increase in sparsity. We deliberately tuned the thresholds for DeltaCNN with a lower accuracy target than for MotionDeltaCNN to show that we achieve higher frame rates even when targeting higher accuracy. The details about threshold tuning and" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 223, + 546, + 234 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 223, + 546, + 234 + ], + "spans": [ + { + "bbox": [ + 306, + 223, + 546, + 234 + ], + "type": "text", + "content": "ROI-focused sensing are found in the supplemental material." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 237, + 547, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 237, + 547, + 464 + ], + "spans": [ + { + "bbox": [ + 304, + 237, + 547, + 464 + ], + "type": "text", + "content": "Human Pose Estimation In task b), we perform human pose estimation using HRNet [30, 32] on the Human3.6M dataset [3, 17]. Human3.6M uses static cameras and is recorded in a static studio with only a single moving actor in the room. We use this dataset to evaluate a second scenario for MotionDeltaCNN: top-down pose estimation. With top-down pose estimation, humans in the scene are detected first, and then the pose is predicted for each detected human. Each bounding box is cropped and inferred individually - estimating one set of joints per person. Since Human3.6M provides per frame bounding boxes of the actors as part of their labels, we omit the step of detecting humans in the scene. We snap the given bounding boxes onto a " + }, + { + "bbox": [ + 304, + 237, + 547, + 464 + ], + "type": "inline_equation", + "content": "32 \\times 32" + }, + { + "bbox": [ + 304, + 237, + 547, + 464 + ], + "type": "text", + "content": " pixel grid and then increase them by 32 pixels on each side where possible. The increased bounding boxes ensure that joint positions are not too close to image borders, as this could negatively impact prediction accuracy. We use the same weights and thresholds as were used in the DeltaCNN paper and evaluate on the same data subset (Subject S11)." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 468, + 547, + 611 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 468, + 547, + 611 + ], + "spans": [ + { + "bbox": [ + 304, + 468, + 547, + 611 + ], + "type": "text", + "content": "Both scenarios are compared against dense inference of cuDNN and against the original DeltaCNN without moving camera support. In HRNet, we only measure model inference time, without the overhead of post-processing or accuracy evaluation. The input shape is " + }, + { + "bbox": [ + 304, + 468, + 547, + 611 + ], + "type": "inline_equation", + "content": "384 \\times 384" + }, + { + "bbox": [ + 304, + 468, + 547, + 611 + ], + "type": "text", + "content": " with a tile size of " + }, + { + "bbox": [ + 304, + 468, + 547, + 611 + ], + "type": "inline_equation", + "content": "32 \\times 32" + }, + { + "bbox": [ + 304, + 468, + 547, + 611 + ], + "type": "text", + "content": " pixels unless stated otherwise. In the case of BMVOS, we only measure the duration of the feature encoding model to better highlight the difference of pure CNN inference speeds. For this evaluation, the camera input is embedded into a frame of shape Wx480 pixels, where W depends on the aspect ratio of the video (typically 864px) and is aligned onto a grid with a tile size of " + }, + { + "bbox": [ + 304, + 468, + 547, + 611 + ], + "type": "inline_equation", + "content": "48 \\times 48" + }, + { + "bbox": [ + 304, + 468, + 547, + 611 + ], + "type": "text", + "content": " pixels." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 614, + 547, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 614, + 547, + 674 + ], + "spans": [ + { + "bbox": [ + 304, + 614, + 547, + 674 + ], + "type": "text", + "content": "Hardware We conduct our evaluations on two GPUs: Nvidia GTX 1080 Ti and Nvidia RTX 3090 with 3584/10496 CUDA cores and 11GB/24GB of VRAM respectively. The evaluations are performed using 32-bit precision, but our approach can be applied to other data types as well." + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 693, + 546, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 546, + 713 + ], + "type": "text", + "content": "1The Human3.6M dataset was accessed and used only by the co-authors at Graz University of Technology" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17297" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 72, + 542, + 141 + ], + "blocks": [ + { + "bbox": [ + 55, + 72, + 542, + 141 + ], + "lines": [ + { + "bbox": [ + 55, + 72, + 542, + 141 + ], + "spans": [ + { + "bbox": [ + 55, + 72, + 542, + 141 + ], + "type": "image", + "image_path": "0f8ad12cd8facb988f2202557526cdaef44c719ed6835c98caf5733ece614d76.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 151, + 547, + 201 + ], + "lines": [ + { + "bbox": [ + 46, + 151, + 547, + 201 + ], + "spans": [ + { + "bbox": [ + 46, + 151, + 547, + 201 + ], + "type": "text", + "content": "Figure 7: A DAVIS 2017 sequence processed using DeltaCNN (left) and MotionDeltaCNN (right). Row a shows the original input on the left, and the aligned and cropped input on the right. Row b visualizes the Delta between the (aligned) input and the previous input in row c. Row d visualizes the update mask with white pixels indicating an update. MotionDeltaCNN achieves much higher sparsity on the same input by reusing previous results for the aligned, static background." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 219, + 101, + 232 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 219, + 101, + 232 + ], + "spans": [ + { + "bbox": [ + 47, + 219, + 101, + 232 + ], + "type": "text", + "content": "5. Results" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 240, + 288, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 240, + 288, + 300 + ], + "spans": [ + { + "bbox": [ + 46, + 240, + 288, + 300 + ], + "type": "text", + "content": "We evaluate speedup and accuracy of MotionDeltaCNN compared to DeltaCNN without explicit moving camera support as well as the dense cuDNN backend. In this section, we report the differences on the GTX 1080 Ti - for results on the RTX 3090, please see the respective tables." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 301, + 288, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 301, + 288, + 373 + ], + "spans": [ + { + "bbox": [ + 46, + 301, + 288, + 373 + ], + "type": "text", + "content": "Video Object Segmentation MotionDeltaCNN outperforms state-of-the-art backends in sparse mode by a margin of up to " + }, + { + "bbox": [ + 46, + 301, + 288, + 373 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 46, + 301, + 288, + 373 + ], + "type": "text", + "content": " over the cuDNN baseline (see Table 1). The DAVIS 2017 dataset consists mainly of videos with large bounding boxes and often fast camera motion, leading to a high average update rate of " + }, + { + "bbox": [ + 46, + 301, + 288, + 373 + ], + "type": "inline_equation", + "content": "29\\%" + }, + { + "bbox": [ + 46, + 301, + 288, + 373 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 375, + 288, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 375, + 288, + 411 + ], + "spans": [ + { + "bbox": [ + 46, + 375, + 288, + 411 + ], + "type": "text", + "content": "Excluding videos without camera motion highlights the relative speedup over DeltaCNN without moving camera support with " + }, + { + "bbox": [ + 46, + 375, + 288, + 411 + ], + "type": "inline_equation", + "content": "+85\\%" + }, + { + "bbox": [ + 46, + 375, + 288, + 411 + ], + "type": "text", + "content": " speedup over cuDNN instead of " + }, + { + "bbox": [ + 46, + 375, + 288, + 411 + ], + "type": "inline_equation", + "content": "+8\\%" + }, + { + "bbox": [ + 46, + 375, + 288, + 411 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 411, + 288, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 411, + 288, + 520 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 288, + 520 + ], + "type": "text", + "content": "MotionDeltaCNN, like DeltaCNN, requires larger workloads with more powerful hardware to show speedups. With 10.496 cores in a RTX 3090, small batch sizes typically do not fully utilize the available hardware resources in most layers - skipping some tiles in this scenario does not affect the overall performance unless all tiles can be skipped altogether. By increasing the batch size, we can fully utilize the GPU - cores that skip a tile can immediately continue processing the next tile, leading to an overall speedup." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 521, + 287, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 568 + ], + "type": "text", + "content": "Over the 990 frames in the DAVIS dataset, we had to reset the buffers 9 times because of cameras panning over invalid truncated values. This low number of resets has only a small impact on the overall performance." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "text", + "content": "Human Pose Estimation MotionDeltaCNN can outperform cuDNN by up to 11x in the case of HRNet (see Table 2). Please note that the frame rate of cuDNN is " + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "inline_equation", + "content": "30\\%" + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "text", + "content": " lower than in the DeltaCNN paper since we enforced the use of 32-bit multiplications in all layers - the same accuracy that we also use in our implementation. Furthermore, the accuracies do not match since we always use the full, uncropped images as input. The high sparsity in the Human3.6M dataset together with the efficient implementation allows us to accelerate inference significantly. Compared to DeltaCNN, which does not support varying resolution input or moving cameras, we were able to achieve " + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "inline_equation", + "content": "13\\%" + }, + { + "bbox": [ + 46, + 570, + 288, + 713 + ], + "type": "text", + "content": " higher frame rates with similar" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "spans": [ + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "text", + "content": "accuracy. We level the playing field in comparisons against the dense cuDNN backend by inferring the same cropped images that we use as input for MotionDeltaCNN. Still, we outperform cuDNN by up to " + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "inline_equation", + "content": "3.2\\mathrm{x}" + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "text", + "content": ", and achieve a speedup of up to " + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "inline_equation", + "content": "3.2\\mathrm{x}" + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "text", + "content": " over dense DeltaCNN with full resolution input. For Human3.6M, we know that the actors never cover the entire frame at once. We use this knowledge to lower the size of the buffers by " + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "inline_equation", + "content": "25\\%" + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "text", + "content": " on each axis - reducing the memory footprint of buffers by " + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "inline_equation", + "content": "44\\%" + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "text", + "content": " in total. These savings allow us to increase the batch size even further. When fully utilizing all available memory with an increased batch size, we achieve frame rates up to " + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "inline_equation", + "content": "3.9\\mathrm{x}" + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "text", + "content": " over the cropped cuDNN baseline and " + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "inline_equation", + "content": "37\\%" + }, + { + "bbox": [ + 304, + 220, + 547, + 376 + ], + "type": "text", + "content": " over DeltaCNN." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 377, + 547, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 377, + 547, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 377, + 547, + 628 + ], + "type": "text", + "content": "Ablation Study We evaluated the individual impact of our contributions in an ablation study (see Table 3). Without dynamic initialization, MotionDeltaCNN always resets the buffers when new image tiles are unveiled. After a reset, the next frame is processed densely. This has a negative impact on the speedup, but slightly increases the accuracy as it regularly flushes accumulated errors. Padded convolutions are key in enabling spherical buffers. Without them, new tiles are not fused into existing buffers correctly, leading to a reduction in accuracy. Our evaluation shows that (ROI) focused sensing enables great speedups without lowering the accuracy of the segmentation. By disabling noise suppression as well, the model becomes more sensitive to errors in image alignment and small changes in the image. To compensate for this, we increase the threshold of the first truncation from 0.15 to 0.35 for this evaluation. However, even with an increased threshold, the speedup is significantly smaller compared to default truncation, while the accuracy is already much lower. Overall, the ablation study shows that all parts of MotionDeltaCNN work in tandem to achieve the best speedup without large impact on accuracy." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 635, + 375, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 635, + 375, + 647 + ], + "spans": [ + { + "bbox": [ + 306, + 635, + 375, + 647 + ], + "type": "text", + "content": "6. Discussion" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": "Our evaluations prove that MotionDeltaCNN can accelerate CNN video inference with moving cameras where existing sparse methods fail to outperform the dense reference. However, our evaluation also shows that freely moving cameras, especially when combined with dense updates as in" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17298" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 545, + 208 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 545, + 208 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 545, + 208 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 545, + 208 + ], + "type": "table", + "html": "
VideosBackendIoUGFLOPsGTX 1080 Ti b=1GTX 1080 Ti b=5RTX 3090 b=1RTX 3090 b=12
FPSspeedupFPSspeedupFPSspeedupFPSspeedup
AllcuDNN76.8522.130.71.040.91.045.41.01031.0
DeltaCNN (dense)76.8522.135.01.1441.21.0166.51.461000.97
MotionDeltaCNN (dense)76.7622.633.51.0940.30.9957.71.2793.60.91
DeltaCNN (sparse)76.1815.542.51.3851.41.2670.01.541251.21
MotionDeltaCNN (sparse)76.326.854.81.7981.92.0065.21.442152.1
MovingcuDNN79.5922.130.71.040.91.045.41.01031.0
DeltaCNN (sparse)79.3818.838.21.2444.11.0870.21.551061.03
MotionDeltaCNN (sparse)79.437.352.31.7075.11.8465.01.432011.95
", + "image_path": "cb947a0d7ad17e0718c87af7f3bd687a41e98231b2c5aa75a3fb1260e7aa587d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 274, + 545, + 388 + ], + "blocks": [ + { + "bbox": [ + 46, + 215, + 548, + 265 + ], + "lines": [ + { + "bbox": [ + 46, + 215, + 548, + 265 + ], + "spans": [ + { + "bbox": [ + 46, + 215, + 548, + 265 + ], + "type": "text", + "content": "Table 1: Results for the task of video object segmentation using BMVOS on the DAVIS dataset. We track only the DenseNet backend for evaluating frames per second (FPS). For accuracy benchmarks, the remaining network is processed densely. GFLOPs are reported as average over the test set. Both devices are evaluated with a batch size " + }, + { + "bbox": [ + 46, + 215, + 548, + 265 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 46, + 215, + 548, + 265 + ], + "type": "text", + "content": " of one, and the maximum batch size each device can hold in memory." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 274, + 545, + 388 + ], + "lines": [ + { + "bbox": [ + 50, + 274, + 545, + 388 + ], + "spans": [ + { + "bbox": [ + 50, + 274, + 545, + 388 + ], + "type": "table", + "html": "
BackendPCKh@0.5PCKh@0.2GFLOPsGTX 1080 Ti b=1GTX 1080 Ti b=16RTX 3090 b=1RTX 3090 b=40
FPSspeedupFPSspeedupFPSspeedupFPSspeedup
cuDNN96.03%83.33%47.122.51.024.81.012.31.069.61.0
DeltaCNN (dense)24.21.0841.31.726.02.195.81.4
MotionDeltaCNN (dense)96.00%83.32%17.732.51.4491.43.722.01.82323.3
cuDNN (cropped)95.92%83.11%13.324.01.0771.02.911.81.02093.0
DeltaCNN (sparse)95.95%82.31%3.5544.92.02028.126.22.15477.9
MotionDeltaCNN (sparse)95.95%82.33%3.4541.21.832289.222.61.85848.4
MotionDeltaCNN (sparse †)95.93%82.22%3.4442.51.8927611.122.51.86919.9
", + "image_path": "6998b419d54989396ed5b5075894352b634c329902620ce8281fa45af725785a.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 69, + 475, + 266, + 574 + ], + "blocks": [ + { + "bbox": [ + 46, + 396, + 548, + 458 + ], + "lines": [ + { + "bbox": [ + 46, + 396, + 548, + 458 + ], + "spans": [ + { + "bbox": [ + 46, + 396, + 548, + 458 + ], + "type": "text", + "content": "Table 2: Speed and accuracy comparisons of different CNN backends used for pose estimation on the Human3.6M dataset. The same set of auto-tuned thresholds for update truncation is used for all devices and batch sizes " + }, + { + "bbox": [ + 46, + 396, + 548, + 458 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 46, + 396, + 548, + 458 + ], + "type": "text", + "content": ". † limits the size of the input from 384x384 to 288x288 pixels - freeing up 44% of the memory used for buffers. The freed-up memory is used to increase the batch size to fully utilize the available VRAM (b=28 on 1080 Ti and b=66 on 3090). cuDNN cropped uses the same, cropped input as ours, instead of the full camera input." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 69, + 475, + 266, + 574 + ], + "lines": [ + { + "bbox": [ + 69, + 475, + 266, + 574 + ], + "spans": [ + { + "bbox": [ + 69, + 475, + 266, + 574 + ], + "type": "table", + "html": "
FPSIoU# resets
cuDNN40.979.59-
DeltaCNN44.179.38-
MotionDeltaCNN75.179.438
- w/o dynamic init56.479.63110
- w/o padded conv.65.377.898
- w/o ROI scaling63.679.338
- w/o ROI & noise*50.979.068
", + "image_path": "19829a5ac6d64a0bbd27f9428f798333d31f230cacffd21175abe67f5ea3b356.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 582, + 288, + 632 + ], + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 632 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 632 + ], + "type": "text", + "content": "Table 3: Ablation study. Evaluating BMVOS on DAVIS2017 dataset using a Nvidia GTX 1080 Ti with a batch size of 5. We evaluate on the subset of videos with significant camera motion. * increased threshold on video input." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 652, + 288, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 652, + 288, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 652, + 288, + 700 + ], + "type": "text", + "content": "the DAVIS dataset, lead to a much smaller speedup than the static camera setup with sparse motion in Human3.6M. Furthermore, the additional padding slightly increases memory and compute overhead over DeltaCNN." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 59, + 701, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 288, + 714 + ], + "type": "text", + "content": "Receptive Field While MotionDeltaCNN does achieve" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 477, + 547, + 634 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 477, + 547, + 634 + ], + "spans": [ + { + "bbox": [ + 304, + 477, + 547, + 634 + ], + "type": "text", + "content": "outputs comparable to standard CNN inference, it should be noted that even in dense mode, the results are not identical. This can be observed in Figure 5 where the fused output of MotionDeltaCNN matches the result using the fused input in row " + }, + { + "bbox": [ + 304, + 477, + 547, + 634 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 304, + 477, + 547, + 634 + ], + "type": "text", + "content": ", which includes information from neighbor pixels seen in previous frames. Since we do not actively propagate inverted accumulated values once a previously processed region gets out of view, the receptive field of later layers, also for pixels inside the current view, still contains some information from that now unseen area. This can have positive and negative effects alike. These features might not be valid anymore. At the same time, some out-of-view features can help to make better predictions due to additional context." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 641, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 548, + 715 + ], + "type": "text", + "content": "Applications MotionDeltaCNN is a general-purpose framework for video inference and can thus be used with all pre-trained CNNs by replacing the original, dense layers with our sparse equivalent. As additional input, Motion-DeltaCNN requires camera extrinsics for the frame to be processed. While most publicly available datasets do not" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "17299" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 191 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 191 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 191 + ], + "type": "text", + "content": "include camera extrinsics and therefore require image stabilization, smartphones, tablets and VR headsets nowadays have built-in support for tracking the camera pose between frames in real-time. Potential applications are not limited to classic computer vision applications like tracking and segmentation, but it could also be used for video up-scaling, filtering, etc. However, applications like image-denoising (diffusion) are likely not a good fit as they provide low levels of spatial update sparsity between iterations and they are very sensitive to noise." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 192, + 289, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 192, + 289, + 312 + ], + "spans": [ + { + "bbox": [ + 46, + 192, + 289, + 312 + ], + "type": "text", + "content": "Limitations One of the main limitations of our approach is its dependency on robust video stabilization. Our experiments with the DAVIS dataset showed that simple video stabilization techniques can break when blur or parallax is involved, or when it fails to find robust features. Parallax can greatly reduce the gains of our method, even when the scene itself is mostly static. When foreground and background layers move at different speeds, frames can only be properly aligned to stabilize one of these layers - leading to dense updates in layers moving at different speeds." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 312, + 289, + 419 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 312, + 289, + 419 + ], + "spans": [ + { + "bbox": [ + 46, + 312, + 289, + 419 + ], + "type": "text", + "content": "MotionDeltaCNN also comes with the trade-off between buffer overallocation and losing information by cropping the input to match the shape of the buffer. In our evaluations, when the camera zooms or rotates around the forward axis (roll), the aligned input can exceed the size of the buffers, and therefore requires slight cropping to fit into the target shape (see Figure 7). Alternatively, the buffers could also be increased to allow for larger inputs in upcoming frames - at the cost of higher memory consumption." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 423, + 119, + 435 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 423, + 119, + 435 + ], + "spans": [ + { + "bbox": [ + 47, + 423, + 119, + 435 + ], + "type": "text", + "content": "7. Conclusion" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 439, + 289, + 606 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 439, + 289, + 606 + ], + "spans": [ + { + "bbox": [ + 46, + 439, + 289, + 606 + ], + "type": "text", + "content": "We propose MotionDeltaCNN, an extension to the sparse video CNN framework DeltaCNN adding support for moving camera input. To the best of our knowledge, we are the first to propose a solution for moving cameras with sparse inference. MotionDeltaCNN uses spherical buffers, padded convolutions and dynamic initialization of newly unveiled regions to support combining previously processed pixels and newly unveiled pixels together with high sparsity. We test our approach in practice by implementing all kernels natively on the GPU to evaluate the real-world performance with modern hardware. Our experiments show that we outperform DeltaCNN by up to " + }, + { + "bbox": [ + 46, + 439, + 289, + 606 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 46, + 439, + 289, + 606 + ], + "type": "text", + "content": " on moving camera input and that MotionDeltaCNN can also be beneficial to lower the memory footprint in static camera scenarios." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 616, + 107, + 628 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 616, + 107, + 628 + ], + "spans": [ + { + "bbox": [ + 47, + 616, + 107, + 628 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 52, + 635, + 289, + 713 + ], + "type": "list", + "angle": 0, + "index": 8, + "blocks": [ + { + "bbox": [ + 52, + 635, + 288, + 691 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 635, + 288, + 691 + ], + "spans": [ + { + "bbox": [ + 52, + 635, + 288, + 691 + ], + "type": "text", + "content": "[1] Udari De Alwis and Massimo Alioto. 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Refaat Rami Al-Rfou Benjamin Sapp", + "bbox": [ + 135, + 193, + 833, + 229 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Waymo", + "bbox": [ + 450, + 250, + 517, + 266 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 327, + 313, + 343 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Reliable forecasting of the future behavior of road agents is a critical component to safe planning in autonomous vehicles. Here, we represent continuous trajectories as sequences of discrete motion tokens and cast multi-agent motion prediction as a language modeling task over this domain. Our model, MotionLM, provides several advantages: First, it does not require anchors or explicit latent variable optimization to learn multimodal distributions. Instead, we leverage a single standard language modeling objective, maximizing the average log probability over sequence tokens. Second, our approach bypasses post-hoc interaction heuristics where individual agent trajectory generation is conducted prior to interactive scoring. Instead, MotionLM produces joint distributions over interactive agent futures in a single autoregressive decoding process. In addition, the model's sequential factorization enables temporally causal conditional rollouts. The proposed approach establishes new state-of-the-art performance for multi-agent motion prediction on the Waymo Open Motion Dataset, ranking $1^{st}$ on the interactive challenge leaderboard.", + "bbox": [ + 75, + 358, + 473, + 660 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 689, + 209, + 704 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Modern sequence models often employ a next-token prediction objective that incorporates minimal domain-specific assumptions. For example, autoregressive language models [3, 10] are pre-trained to maximize the probability of the next observed subword conditioned on the previous text; there is no predefined notion of parsing or syntax built in. This approach has found success in continuous domains as well, such as audio [2] and image generation [49]. Leveraging the flexibility of arbitrary categorical distributions, the above works represent continuous data with a set of discrete", + "bbox": [ + 75, + 714, + 468, + 864 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/f1f8c965e8223d171350c5c2f689a74abcf109088486c245c461b2530d073257.jpg", + "image_caption": [ + "Figure 1. Our model autoregressively generates sequences of discrete motion tokens for a set of agents to produce consistent interactive trajectory forecasts." + ], + "image_footnote": [], + "bbox": [ + 509, + 309, + 883, + 522 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "tokens, reminiscent of language model vocabularies.", + "bbox": [ + 500, + 607, + 846, + 622 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In driving scenarios, road users may be likened to participants in a constant dialogue, continuously exchanging a dynamic series of actions and reactions mirroring the fluidity and complexity of communication. Navigating this rich web of interactions requires the ability to anticipate the likely maneuvers and responses of the involved actors. Just as today's language models can capture sophisticated distributions over conversations, can we leverage similar sequence models to forecast the behavior of road agents?", + "bbox": [ + 496, + 625, + 890, + 760 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "A common simplification to modeling the full future world state has been to decompose the joint distribution of agent behavior into independent per-agent marginal distributions. Although there has been much progress on this task [8, 47, 12, 25, 31, 5, 6, 21], marginal predictions are insufficient as inputs to a planning system; they do not represent the future dependencies between the actions of different agents, leading to inconsistent scene-level forecasting.", + "bbox": [ + 496, + 762, + 890, + 883 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Of the existing joint prediction approaches, some apply", + "bbox": [ + 517, + 885, + 890, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Work done during an internship at Waymo. Contact: {aseff,bensapp}@waymo.com", + "bbox": [ + 93, + 875, + 354, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "8579", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "a separation between marginal trajectory generation and interactive scoring [40, 42, 29]. For example, Luo et al. [29] initially produce a small set of marginal trajectories for each agent independently, before assigning a learned potential to each inter-agent trajectory pair through a belief propagation algorithm. Sun et al. [42] use a manual heuristic to tag agents as either influencers or reactors, and then pairs marginal and conditional predictions to form joint predictions.", + "bbox": [ + 75, + 90, + 468, + 224 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We also note that because these approaches do not explicitly model temporal dependencies within trajectories, their conditional forecasts may be more susceptible to spurious correlations, leading to less realistic reaction predictions. For example, these models can capture the correlation between a lead agent decelerating and a trailing agent decelerating, but may fail to infer which one is likely causing the other to slow down. In contrast, previous joint models employing an autoregressive factorization, e.g., [36, 43, 39], do respect future temporal dependencies. These models have generally relied on explicit latent variables for diversity, optimized via either an evidence lower bound or normalizing flow.", + "bbox": [ + 75, + 227, + 470, + 422 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we combine trajectory generation and interaction modeling in a single, temporally causal, decoding process over discrete motion tokens (Fig. 1), leveraging a simple training objective inspired by autoregressive language models. Our model, MotionLM, is trained to directly maximize the log probability of these token sequences among interacting agents. At inference time, joint trajectories are produced step-by-step, where interacting agents sample tokens simultaneously, attend to one another, and repeat. In contrast to previous approaches which manually enforce trajectory multimodality during training, our model is entirely latent variable and anchor-free, with multimodality emerging solely as a characteristic of sampling. MotionLM may be applied to several downstream behavior prediction tasks, including marginal, joint, and conditional predictions.", + "bbox": [ + 75, + 424, + 470, + 665 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "This work makes the following contributions:", + "bbox": [ + 96, + 667, + 398, + 681 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. We cast multi-agent motion forecasting as a language modeling task, introducing a temporally causal decoder over discrete motion tokens trained with a causal language modeling loss.", + "2. We pair sampling from our model with a simple rollout aggregation scheme that facilitates weighted mode identification for joint trajectories, establishing new state-of-the-art performance on the Waymo Open Motion Dataset interaction prediction challenge (6% improvement in the ranking joint mAP metric).", + "3. We perform extensive ablations of our approach as well as analysis of its temporally causal conditional" + ], + "bbox": [ + 88, + 694, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "predictions, which are largely unsupported by current joint forecasting models.", + "bbox": [ + 529, + 90, + 890, + 121 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 500, + 136, + 637, + 152 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Marginal trajectory prediction. Behavior predictors are often evaluated on their predictions for individual agents, e.g., in recent motion forecasting benchmarks [14, 9, 4, 51, 37]. Previous methods process the rasterized scene with CNNs [8, 5, 12, 17]; the more recent works represent scenes with points and polygraphs and process them with GNNs [6, 25, 47, 22] or transformers [31, 40, 20]. To handle the multimodality of future trajectories, some models manually enforce diversity via predefined anchors [8, 5] or intention points [40, 52, 28]. Other works learn diverse modes with latent variable modeling, e.g., [24].", + "bbox": [ + 496, + 162, + 890, + 328 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "While these works produce multimodal future trajectories of individual agents, they only capture the marginal distributions of the possible agent futures and do not model the interactions among agents.", + "bbox": [ + 496, + 329, + 890, + 388 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Interactive trajectory prediction. Interactive behavior predictors model the joint distribution of agents' futures. This task has been far less studied than marginal motion prediction. For example, the Waymo Open Motion Dataset (WOMD) [14] challenge leaderboard currently has 71 published entries for marginal prediction compared to only 14 for interaction prediction.", + "bbox": [ + 496, + 411, + 890, + 516 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Ngiam et al. [32] models the distribution of future trajectories with a transformer-based mixture model outputting joint modes. To avoid the exponential blow-up from a full joint model, Luo et al. [29] models pairwise joint distributions. Tolstaya et al. [44], Song et al. [41], Sun et al. [42] consider conditional predictions by exposing the future trajectory of one agent when predicting for another agent. Shi et al. [40] derives joint probabilities by simply multiplying marginal trajectory probabilities, essentially treating agents as independent, which may limit accuracy. Cui et al. [11], Casas et al. [7], Girgis et al. [15] reduce the full-fledged joint distribution using global latent variables. Unlike our autoregressive factorization, the above models typically follow \"one-shot\" (parallel across time) factorizations and do not explicitly model temporally causal interactions.", + "bbox": [ + 496, + 517, + 890, + 743 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Autoregressive trajectory prediction. Autoregressive behavior predictors generate trajectories at intervals to produce scene-consistent multi-agent trajectories. Rhinehart et al. [36], Tang and Salakhutdinov [43], Amirloo et al. [1], Salzmann et al. [39], Yuan et al. [50] predict multiagent future trajectories using latent variable models. Lu et al. [27] explores autoregressively outputting keyframes via mixtures of Gaussians prior to filling in the remaining states. In [18], an adversarial objective is combined with", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "8580", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/a41468b22cc442b27e6d8808b538253d92d7d25c8ba77921ece7977dc072adc6.jpg", + "image_caption": [ + "Figure 2. MotionLM architecture. We first encode heterogeneous scene features relative to each modeled agent (left) as scene embeddings of shape $R, N, \\cdot, H$ . Here, $R$ refers to the number of rollouts, $N$ refers to the number of (jointly modeled) agents, and $H$ is the dimensionality of each embedding. We repeat the embeddings $R$ times in the batch dimension for parallel sampling during inference. Next, a trajectory decoder autoregressively rolls out $T$ discrete motion tokens for multiple agents in a temporally causal manner (center). Finally, representative modes of the rollouts may be recovered via a simple aggregation utilizing k-means clustering initialized with non-maximum suppression (right)." + ], + "image_footnote": [], + "bbox": [ + 86, + 95, + 869, + 275 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "parallel beam search to learn multi-agent rollouts. Unlike most autoregressive trajectory predictors, our method does not rely on latent variables or beam search and generates multimodal joint trajectories by directly sampling from a learned distribution of discrete motion token sequences.", + "bbox": [ + 75, + 407, + 470, + 484 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Discrete sequence modeling in continuous domains. When generating sequences in continuous domains, one effective approach is to discretize the output space and predict categorical distributions at each step.", + "bbox": [ + 75, + 508, + 468, + 568 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For example, in image generation, PixelRNN [45] sequentially predicts the uniformly discretized pixel values for each channel and found this to perform better than outputting continuous values directly. Multiple works on generating images from text such as DALL-E [35] and Parti [49] use a two-stage process with a learned tokenizer to map images to discrete tokens and an autoregressive model to predict the discrete tokens given the text prompt. For audio generation, WaveNet [46] applies a $\\mu$ -law transformation before discretizing. AudioLM [2] learns a hierarchical tokenizer/detokenizer, with the main transformer sequence model operating on the intermediate discrete tokens. When generating polygonal meshes, PolyGen [30] uniformly quantizes the coordinates of each vertex. In MotionLM, we employ a simple uniform quantization of axis-aligned deltas between consecutive waypoints of agent trajectories.", + "bbox": [ + 75, + 570, + 470, + 828 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. MotionLM", + "text_level": 1, + "bbox": [ + 76, + 844, + 194, + 859 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We aim to model a distribution over multi-agent interactions in a general manner that can be applied to distinct", + "bbox": [ + 76, + 869, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "downstream tasks, including marginal, joint, and conditional forecasting. This requires an expressive generative framework capable of capturing the substantial multimodality in driving scenarios. In addition, we take consideration here to preserve temporal dependencies; i.e., inference in our model follows a directed acyclic graph with the parents of every node residing earlier in time and children residing later (Section 3.3, Fig. 4). This enables conditional forecasts that more closely resemble causal interventions [34] by eliminating certain spurious correlations that can otherwise result from disobeying temporal causality $^2$ . We observe that joint models that do not preserve temporal dependencies may have a limited ability to predict realistic agent reactions – a key use in planning (Section 4.6). To this end, we leverage an autoregressive factorization of our future decoder, where agents' motion tokens are conditionally dependent on all previously sampled tokens and trajectories are rolled out sequentially (Fig. 2).", + "bbox": [ + 496, + 407, + 890, + 679 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Let $S$ represent the input data for a given scenario. This may include context such as roadgraph elements, traffic light states, as well as features describing road agents (e.g., vehicles, cyclists, and pedestrians) and their recent histories, all provided at the current timestep $t = 0$ . Our task is to generate predictions for joint agent states $Y_{t} \\doteq \\{y_{t}^{1}, y_{t}^{2}, \\dots, y_{t}^{N}\\}$ for $N$ agents of interest at future timesteps $t = 1, \\dots, T$ . Rather than complete states, these future state targets are typically two-dimensional waypoints (i.e., $(x, y)$ coordinates), with $T$ waypoints forming the full ground", + "bbox": [ + 496, + 681, + 890, + 834 + ], + "page_idx": 2 + }, + { + "type": "page_footnote", + "text": "2We make no claims that our model is capable of directly modeling causal relationships (due to the theoretical limits of purely observational data and unobserved confounders). Here, we solely take care to avoid breaking temporal causality.", + "bbox": [ + 496, + 849, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "8581", + "bbox": [ + 482, + 944, + 513, + 957 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "truth trajectory for an individual agent.", + "bbox": [ + 76, + 90, + 334, + 107 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Joint probabilistic rollouts", + "text_level": 1, + "bbox": [ + 76, + 116, + 316, + 132 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In our modeling framework, we sample a predicted action for each target agent at each future timestep. These actions are formulated as discrete motion tokens from a finite vocabulary, as described later in Section 3.2.2. Let $a_{t}^{n}$ represent the target action (derived from the ground truth waypoints) for the $n$ th agent at time $t$ , with $A_{t} \\doteq \\{a_{t}^{1}, a_{t}^{2}, \\dots, a_{t}^{N}\\}$ representing the set of target actions for all agents at time $t$ .", + "bbox": [ + 76, + 140, + 468, + 261 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Factorization. We factorize the distribution over joint future action sequences as a product of conditionals:", + "bbox": [ + 76, + 280, + 468, + 311 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\np _ {\\theta} \\left(A _ {1}, A _ {2}, \\dots A _ {T} \\mid S\\right) = \\prod_ {t = 1} ^ {T} p _ {\\theta} \\left(A _ {t} \\mid A _ {< t}, S\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 122, + 324, + 468, + 364 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\np _ {\\theta} \\left(A _ {t} \\mid A _ {< t}, S\\right) = \\prod_ {n = 1} ^ {N} p _ {\\theta} \\left(a _ {t} ^ {n} \\mid A _ {< t}, S\\right). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 138, + 377, + 468, + 417 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Similar to [36, 43], Eq. (2) represents the fact that we treat agent actions as conditionally independent at time $t$ , given the previous actions and scene context. This aligns empirically with real-world driving over short time intervals; e.g., non-impaired human drivers generally require at least 500 ms to release the accelerator in response to a vehicle braking ahead ([13]). In our experiments, we find $2\\mathrm{Hz}$ reactions to be sufficient to surpass state-of-the-art joint prediction models.", + "bbox": [ + 75, + 422, + 468, + 556 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We note that our model's factorization is entirely latent variable free; multimodal predictions stem purely from categorical token sampling at each rollout timestep.", + "bbox": [ + 76, + 560, + 468, + 604 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Training objective. MotionLM is formulated as a generative model trained to match the joint distribution of observed agent behavior. Specifically, we follow a maximum likelihood objective over multi-agent action sequences:", + "bbox": [ + 76, + 625, + 468, + 686 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\underset {\\theta} {\\arg \\max } \\prod_ {t = 1} ^ {T} p _ {\\theta} \\left(A _ {t} \\mid A _ {< t}, S\\right) \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 178, + 696, + 468, + 738 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Similar to the typical training setup of modern language models, we utilize \"teacher-forcing\" where previous ground truth (not predicted) tokens are provided at each timestep, which tends to increase stability and avoids sampling during training. We note that this applies to all target agents; in training, each target agent is exposed to ground truth action sequence prefixes for all target agents prior to the current timestep. This naturally allows for temporal parallelization when using modern attention-based architectures such as transformers [48].", + "bbox": [ + 75, + 750, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Our model is subject to the same theoretical limitations as general imitation learning frameworks (e.g., compounding error [38] and self-delusions due to unobserved confounders [33]). However, we find that, in practice, these do not prevent strong performance on forecasting tasks.", + "bbox": [ + 498, + 90, + 890, + 167 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Model implementation", + "text_level": 1, + "bbox": [ + 500, + 176, + 709, + 191 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Our model consists of two main networks, an encoder which processes initial scene elements followed by a trajectory decoder which performs both cross-attention to the scene encodings and self-attention along agent motion tokens, following a transformer architecture [48].", + "bbox": [ + 498, + 200, + 890, + 275 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2.1 Scene encoder", + "text_level": 1, + "bbox": [ + 500, + 295, + 651, + 309 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The scene encoder (Fig. 2, left) is tasked with processing information from several input modalities, including the roadgraph, traffic light states, and history of surrounding agents' trajectories. Here, we follow the design of the early fusion network proposed by [31] as the scene encoding backbone of our model. Early fusion is particularly chosen because of its flexibility to process all modalities together with minimal inductive bias.", + "bbox": [ + 498, + 319, + 890, + 438 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The features above are extracted with respect to each modeled agent's frame of reference. Input tensors are then fed to a stack of self-attention layers that exchange information across all past timesteps and agents. In the first layer, latent queries cross-attend to the original inputs in order to reduce the set of vectors being processed to a manageable number, similar to [23, 19]. For additional details, see [31].", + "bbox": [ + 498, + 440, + 890, + 546 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2.2 Joint trajectory decoder", + "text_level": 1, + "bbox": [ + 500, + 565, + 720, + 580 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Our trajectory decoder (Fig. 2, center) is tasked with generating sequences of motion tokens for multiple agents.", + "bbox": [ + 500, + 589, + 888, + 619 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Discrete motion tokens. We elect to transform trajectories comprised of continuous waypoints into sequences of discrete tokens. This enables treating sampling purely as a classification task at each timestep, implemented via a standard softmax layer. Discretizing continuous targets in this manner has proven effective in other inherently continuous domains, e.g., in audio generation [46] and mesh generation [30]. We suspect that discrete motion tokens also naturally hide some precision from the model, possibly mitigating compounding error effects that could arise from imperfect continuous value prediction. Likewise, we did not find it necessary to manually add any noise to the ground truth teacher-forced trajectories (e.g., as is done in [26]).", + "bbox": [ + 498, + 638, + 890, + 835 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Quantization. To extract target discrete tokens, we begin by normalizing each agent's ground truth trajectory with respect to the position and heading of the agent at", + "bbox": [ + 498, + 854, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "8582", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/825f2e3eea580053724ae5ba734bb572c136be5787218e1cdf276818fc7dc63f.jpg", + "image_caption": [ + "Figure 3. Displayed are the top two predicted joint rollout modes for three WOMD scenes. Color gradients indicate time progression from $t = 0$ s to $t = 8$ s, with the greatest probability joint mode transitioning from green to blue and the secondary joint mode transitioning from orange to purple. Three types of interactions are observed: an agent in the adjacent lane yields to the lane-changing agent according to the timing of the lane change (left), a pedestrian walks behind the passing vehicle according to the progress of the vehicle (center), the turning vehicle either yields to the crossing cyclist (most probable mode) or turns before the cyclist approaches (secondary mode) (right)." + ], + "image_footnote": [], + "bbox": [ + 101, + 90, + 352, + 281 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/17023df7ab3c8a02381296e44f456955ea9c79a3de882c2d31d62dade7b65a42.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 359, + 90, + 609, + 281 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/5c55cb2f881611c58d043dbccfc9f04f81e13abca2cf873cfcee9971085385ea.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 620, + 90, + 870, + 282 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "time $t = 0$ of the scenario. We then parameterize a uniformly quantized $(\\Delta x, \\Delta y)$ vocabulary according to a total number of per-coordinate bins as well as maximum and minimum delta values. A continuous, single-coordinate delta action can then be mapped to a corresponding index $\\in [0, \\text{num\\_bins} - 1]$ , resulting in two indices for a complete $(\\Delta x, \\Delta y)$ action per step. In order to extract actions that accurately reconstruct an entire trajectory, we employ a greedy search, sequentially selecting the quantized actions that reconstruct the next waypoint coordinates with minimum error.", + "bbox": [ + 75, + 392, + 472, + 556 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We wrap the delta actions with a \"Verlet\" step where a zero action indicates that the same delta index should be used as the previous step (as [36] does for continuous states). As agent velocities tend to change smoothly between consecutive timesteps, this helps reduce the total vocabulary size, simplifying the dynamics of training. Finally, to maintain only $T$ sequential predictions, we collapse the per-coordinate actions to a single integer indexing into their Cartesian product. In practice, for the models presented here, we use 13 tokens per coordinate with $13^2 = 169$ total discrete tokens available in the vocabulary (see Appendix A for further details).", + "bbox": [ + 75, + 559, + 468, + 739 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We compute a learned value embedding and two learned positional embeddings (representing the timestep and agent identity) for each discrete motion token, which are combined via an element-wise sum prior to being input to the transformer decoder.", + "bbox": [ + 75, + 741, + 468, + 816 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Flattened agent-time self-attention. We elect to include a single self-attention mechanism in the decoder that operates along flattened sequences of all modeled agents' motion tokens over time. So, given a target sequence of length", + "bbox": [ + 75, + 839, + 468, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$T$ for each of $N$ agents, we perform self-attention over $NT$ elements. While this does mean that these self-attended sequences grow linearly in the number of jointly modeled agents, we note that the absolute sequence length here is still quite small (length 32 for the WOMD interactive split -8 sec. prediction at $2\\mathrm{Hz}$ for 2 agents). Separate passes of factorized agent and time attention are also possible [32], but we use a single pass here for simplicity.", + "bbox": [ + 496, + 392, + 893, + 513 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Ego agent reference frames. To facilitate cross-attention to the agent-centric feature encodings (Section 3.2.1), we represent the flattened token sequence once for each modeled agent. Each modeled agent is treated as the \"ego\" agent once, and cross-attention is performed on that agent's scene features. Collapsing the ego agents into the batch dimension allows parallelization during training and inference.", + "bbox": [ + 496, + 532, + 893, + 638 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Enforcing temporal causality", + "text_level": 1, + "bbox": [ + 500, + 647, + 759, + 664 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Our autoregressive factorization naturally respects temporal dependencies during joint rollouts; motion token sampling for any particular agent is affected only by past tokens (from any agent) and unaffected by future ones. When training, we require a mask to ensure that the self-attention operation only updates representations at each step accordingly. As shown in Fig. 8 (appendix), this attention mask exhibits a blocked, staircase pattern, exposing all agents to each other's histories only up to the preceding step.", + "bbox": [ + 496, + 670, + 890, + 808 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Temporally causal conditioning. As described earlier, a particular benefit of this factorization is the ability to query for temporally causal conditional rollouts (Fig. 4). In this setting, we fix a query agent to take some sequence of actions and only roll out the other agents.", + "bbox": [ + 496, + 825, + 893, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "8583", + "bbox": [ + 482, + 944, + 514, + 957 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/d139ce0bf2cadfa28a152bd716bd38ecc6ed7ac2c5cd973060b1e659f1d31d6d.jpg", + "image_caption": [ + "(a) Causal Bayesian Network for joint rollouts." + ], + "image_footnote": [], + "bbox": [ + 86, + 106, + 328, + 179 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/a7518889e1038dfa6c45c2e9ebdf67015b6a0eec2fb04a570ccaa697650b1d83.jpg", + "image_caption": [ + "Figure 4. A Causal Bayesian network representation for joint rollouts (left), post-intervention Causal Bayesian network (center), and acausal conditioning (right). Solid lines indicate temporally causal dependencies while dashed lines indicate acausal information flow. Models without temporal dependency constraints will support acausal conditioning but not temporally causal conditioning, which can be problematic when attempting to predict agent reactions." + ], + "image_footnote": [], + "bbox": [ + 352, + 104, + 591, + 178 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1037b27a97bf341aaddab4db5f3ffb2acdb06aaf6007c7f70a564a3860973c08.jpg", + "image_caption": [ + "(b) Post-Intervention Causal Bayesian Network.", + "Conditioned Agent Causal conditioning Sampling Agent Acausal conditioning", + "(c) Acausal conditioning." + ], + "image_footnote": [], + "bbox": [ + 635, + 106, + 880, + 176 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We may view this as an approximation of computing causal interventions [34] in the absence of confounders; interventions cannot be learned purely through observational data in general (due to the possible presence of unobserved confounders), but our model's factorization at least eliminates certain spurious correlations arising from breaking temporal causality.", + "bbox": [ + 75, + 313, + 470, + 419 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In Fig. 4 (a), we show an example of a Causal Bayesian network governing joint rollouts. Applying an intervention to nodes $x = 1, \\ldots, T$ , by deleting their incoming edges, results in a post-intervention Bayesian network depicted in Fig. 4 (b), which obeys temporal causality. On the other hand, acausal conditioning (Fig. 4 (c)) results in non-causal information flow, where node $x = i$ affects our belief about node $y = j$ for $i \\geq j$ .", + "bbox": [ + 75, + 419, + 472, + 541 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.4. Rollout aggregation", + "text_level": 1, + "bbox": [ + 76, + 550, + 266, + 566 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Joint motion forecasting benchmark tasks like WOMD [14] require a compact representation of the joint future distribution in the form of a small number of joint \"modes\". Each mode is assigned a probability and might correspond to a specific homotopic outcome (e.g., pass/yield) or more subtle differences in speed/geometry. Here, we aggregate rollouts to achieve two primary goals: 1) uncover the underlying modes of the distribution and 2) estimate the probability of each mode. Specifically, we follow the non-maximum suppression (NMS) aggregation scheme described in [47], but extend it to the joint setting by ensuring that all agent predictions reside within a given distance threshold to the corresponding cluster. In addition, we leverage model ensembling to account for epistemic uncertainty and further improve the quality of the predictions, combining rollouts from independently trained replicas prior to the aggregation step.", + "bbox": [ + 75, + 573, + 472, + 832 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 845, + 209, + 862 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We evaluate MotionLM on marginal and joint motion forecasting benchmarks, examine its conditional predic", + "bbox": [ + 76, + 869, + 470, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "tions and conduct ablations of our modeling choices.", + "bbox": [ + 500, + 313, + 846, + 329 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Datasets", + "text_level": 1, + "bbox": [ + 500, + 343, + 601, + 357 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Waymo Open Motion Dataset (WOMD). WOMD [14] is a collection of 103k 20-second scenarios collected from real-world driving in urban and suburban environments. Segments are divided into 1.1M examples consisting of 9-second windows of interest, where the first second serves as input context and the remaining 8-seconds are the prediction target. Map features such as traffic signal states and lane features are provided along with agent states such as position, velocity, acceleration, and bounding boxes.", + "bbox": [ + 496, + 368, + 890, + 505 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Marginal and interactive prediction challenges. For the marginal prediction challenge, six trajectories must be output by the model for each target agent, along with likelihoods of each mode. For the interactive challenge, two interacting agents are labeled in each test example. In this case, the model must output six weighted joint trajectories.", + "bbox": [ + 496, + 532, + 890, + 625 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Metrics", + "text_level": 1, + "bbox": [ + 500, + 638, + 596, + 652 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The primary evaluation metrics for the marginal and interactive prediction challenges are soft mAP and mAP, respectively, with miss rate as the secondary metric. Distance metrics minADE and minFDE provide additional signal on prediction quality. For the interactive prediction challenge, these metrics refer to scene-level joint calculations. We also use a custom prediction overlap metric (similar to [29]) to assess scene-level consistency for joint models. See Appendix C for details on these metrics.", + "bbox": [ + 496, + 664, + 890, + 800 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Model configuration", + "text_level": 1, + "bbox": [ + 500, + 814, + 692, + 830 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We experiment with up to 8 model replicas and 512 rollouts per replica, assessing performance at various configurations. For complete action space and model hyperparameter details, see Appendices A and B.", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "8584", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/f44cd62d9a91e0484a4fb16b76e9610a434299a142e8f689a549513959e4813c.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelminADE (↓)minFDE (↓)Miss Rate (↓)Soft mAP (↑)
HDGT [20]0.76761.10770.13250.3709
MPA [22]0.59131.25070.16030.3930
MTR [40]0.60501.22070.13510.4216
Wayformer factorized [31]0.54471.12550.12290.4260
Wayformer multi-axis [31]0.54541.12800.12280.4335
MTR-A [40]0.56401.13440.11600.4594
MotionLM (Ours)0.55091.11990.10580.4507
", + "bbox": [ + 215, + 88, + 754, + 209 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/1b90df2d97c64bb48b67aa7a81fbd6a1ee66489ec2bd8c76f03a75c615ae134b.jpg", + "table_caption": [ + "Table 1. Marginal prediction performance on WOMD test set. We display metrics averaged over time steps (3, 5, and 8 seconds) and agent types (vehicles, pedestrians, and cyclists). Greyed columns indicate the official ranking metrics for the marginal prediction challenge." + ], + "table_footnote": [], + "table_body": "
ModelminADE (↓)minFDE (↓)Miss Rate (↓)mAP (↑)
SceneTransformer (J) [32]0.97742.18920.49420.1192
M2I [42]1.35062.83250.55380.1239
DenseTNT [28]1.14172.49040.53500.1647
MTR [40]0.91812.06330.44110.2037
JFP [29]0.88171.99050.42330.2050
MotionLM (Ours)0.89112.00670.41150.2178
", + "bbox": [ + 230, + 262, + 741, + 369 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Quantitative results", + "text_level": 1, + "bbox": [ + 76, + 435, + 264, + 450 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Marginal motion prediction. As shown in Table 1, our model is competitive with the state-of-the-art on WOMD marginal motion prediction (independent per agent). For the main ranking metric of soft mAP, our model ranks second, less than $2\\%$ behind the score achieved by MTRA [40]. In addition, our model attains a substantially improved miss rate over all prior works, with a relative $9\\%$ reduction compared to the previous state-of-the-art. The autoregressive rollouts are able to adequately capture the diversity of multimodal future behavior without reliance on trajectory anchors [8] or static intention points [40].", + "bbox": [ + 75, + 458, + 472, + 625 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Interactive motion prediction. Our model achieves state-of-the-art results for the interactive prediction challenge on WOMD, attaining a $6\\%$ relative improvement in mAP and $3\\%$ relative improvement in miss rate (the two official ranking metrics) over the previous top scoring entry, JFP [29] (see Table 2). In contrast to JFP, our approach does not score pairs of previously constructed marginal trajectories, but generates joint rollouts directly. Fig. 3 displays example interactions predicted by our model.", + "bbox": [ + 75, + 643, + 468, + 779 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3 displays prediction overlap rates for various models on the WOMD interactive test and validation sets (see metric details in Appendix C.2). We obtain test set predictions from the authors of [14, 32, 29]. MotionLM obtains the lowest prediction overlap rate, an indication of scene-consistent predictions. In addition, on the validation set we evaluate two versions of our model: marginal and joint. The marginal version does not perform attention", + "bbox": [ + 75, + 780, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/1f6bf1deb3c442383fd980c6509916552d3d13814b3bd19abe507844c02a8f5b.jpg", + "table_caption": [ + "Table 2. Joint prediction performance on WOMD interactive test set. We display scene-level joint metrics averaged over time steps (3, 5, and 8 seconds) and agent types (vehicles, pedestrians, and cyclists). Greyed columns indicate the official ranking metrics for the challenge." + ], + "table_footnote": [], + "table_body": "
ModelPrediction Overlap (↓)
TestLSTM Baseline [14]0.07462
Scene Transformer [32]0.04336
JFP [29]0.02671
MotionLM (joint)0.02607
ValMotionLM (marginal)0.0404
MotionLM (joint)0.0292
", + "bbox": [ + 522, + 433, + 870, + 547 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3. Prediction overlap rates. Displayed is the custom prediction overlap metric for various model configurations on the WOMD interactive test and validation sets.", + "bbox": [ + 498, + 556, + 890, + 599 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "across the modeled agents during both training and inference rollouts, while the joint version performs $2\\mathrm{Hz}$ interactive attention. We see that the marginal version obtains a relative $38\\%$ higher overlap rate than the joint version. The interactive attention in the joint model allows the agents to more appropriately react to one another.", + "bbox": [ + 498, + 626, + 890, + 717 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5. Ablation studies", + "text_level": 1, + "bbox": [ + 500, + 726, + 661, + 739 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Interactive attention frequency. To assess the importance of inter-agent reactivity during the joint rollouts, we vary the frequency of the interactive attention operation while keeping other architecture details constant. For our leaderboard results, we utilize the greatest frequency studied here, $2\\mathrm{Hz}$ . At the low end of the spectrum, $0.125\\mathrm{Hz}$ corresponds to the agents only observing each other's initial states, and then proceeding with the entire 8-second rollout without communicating again (i.e., marginal rollouts).", + "bbox": [ + 496, + 750, + 890, + 885 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Performance metrics generally improve as agents are", + "bbox": [ + 517, + 886, + 890, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "8585", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1603d7a263732570002c2c9a908ead158fc348f3ee8c1b1551d8dea126a6e3c5.jpg", + "image_caption": [ + "No interactive attention" + ], + "image_footnote": [], + "bbox": [ + 84, + 104, + 269, + 250 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/62e8a5a680bde6e45f9066bf87e75648ae9823fa9cc92b31d0c48eb66a6caac4.jpg", + "image_caption": [ + "16 interaction iterations" + ], + "image_footnote": [], + "bbox": [ + 279, + 106, + 464, + 250 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/967ce5807cfabf79b007a3ef42e0d971a5cc74838c73719949d8179a16e74a6d.jpg", + "image_caption": [ + "Figure 5. Visualization of the top joint rollout mode at the two extremes of the interactive attention frequencies studied here. With no interactive attention (left), the two modeled agents only attend to each other once at the beginning of the 8-second rollout and never again, in contrast to 16 total times for $2\\mathrm{Hz}$ attention (right). The independent rollouts resulting from zero interactive attention can result in scene-inconsistent overlap; e.g., a turning vehicle fails to accommodate a crossing pedestrian (top left) or yield appropriately to a crossing vehicle (bottom left)." + ], + "image_footnote": [], + "bbox": [ + 84, + 255, + 269, + 398 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f26e8aeb300c2e192442d7519aa5c314e13286e76d33025f2debdd0eb3cc0bd6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 279, + 255, + 464, + 398 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "permitted to interact more frequently (Fig. 6 top, Table 5 in appendix). Greater interactive attention frequencies not only lead to more accurate joint predictions, but also reduce implausible overlaps (i.e., collisions) between different agents' predictions. Fig. 5 displays examples where the marginal predictions lead to implausible overlap between agents while the joint predictions lead to appropriately separated trajectories. See supplementary for animated visualizations.", + "bbox": [ + 75, + 571, + 467, + 708 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Number of rollouts. Our rollout aggregation requires that we generate a sufficient number of samples from the model in order to faithfully represent the multimodal future distribution. For this ablation, we vary the number of rollouts generated, but always cluster down to $k = 6$ modes for evaluation. In general, we see performance metrics improve as additional rollouts are utilized (Fig. 6, bottom and Table 6 in appendix). For our final leaderboard results, we use 512 rollouts per replica, although 32 rollouts is sufficient to surpass the previous top entry on joint mAP.", + "bbox": [ + 75, + 750, + 467, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f861862b8e0a966fec108e02259991179672888705f012750157cc619bf2c9ac.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 506, + 90, + 887, + 258 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3bfb396ac9a6e06e72e769d5728758305b233227034c6ddf9acf81c7f569c492.jpg", + "image_caption": [ + "Figure 6. Joint prediction performance across varying interactive attention frequencies (top) and numbers of rollouts per replica (bottom) on the WOMD interactive validation set. Vertical axes display joint (scene-level) metrics for an 8-replica ensemble. See Tables 5 and 6 in the appendix for full parameter ranges and metrics." + ], + "image_footnote": [], + "bbox": [ + 506, + 272, + 885, + 441 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.6. Conditional rollouts", + "text_level": 1, + "bbox": [ + 500, + 569, + 689, + 584 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "As described in Section 3.3, our model naturally supports \"temporally causal\" conditioning, similarly to previous autoregressive efforts such as [36, 43]. In this setting, we fix one query agent to follow a specified trajectory and stochastically roll out the target agent. However, we can also modify the model to leak the query agent's full trajectory, acausally exposing its future to the target agent during conditioning. This resembles the approach to conditional prediction in, e.g., [44], where this acausal conditional distribution is modeled directly, or [29], where this distribution is accessed via inference in an energy-based model.", + "bbox": [ + 496, + 595, + 890, + 762 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Here, we assess predictions from our model across three settings: marginal, temporally causal conditional, and acausal conditional (Fig. 4). Quantitatively, we observe that both types of conditioning lead to more accurate predictions for the target agent (Table 4, Fig. 7). Additionally, we see that acausal conditioning leads to greater improvement than temporally causal conditioning relative to marginal predictions across all metrics, e.g., $8.2\\%$ increase in soft mAP for acausal vs. $3.7\\%$ increase for temporally causal.", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "8586", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/434d86945f52a0a01588e64413c23e8720bf17ce08621276bb0719c1f1f05bc7.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Prediction settingminADE (↓)minFDE (↓)Miss Rate (↓)Soft mAP (↑)
Marginal0.60691.22360.14060.3951
Temporally causal conditional0.59971.20340.13770.4096
Acausal conditional0.58991.18040.13380.4274
", + "bbox": [ + 205, + 88, + 767, + 159 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Table 4. Conditional prediction performance. Displayed are marginal (single-agent) metrics across three prediction settings for our model on the WOMD interactive validation set: marginal, temporally causal conditional, and acausal conditional.", + "bbox": [ + 75, + 167, + 893, + 198 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Intuitively, the greater improvement for acausal conditioning makes sense as it exposes more information to the model. However, the better quantitative scores are largely due to predictions that would be deemed nonsensical if interpreted as predicted reactions to the query agent.", + "bbox": [ + 75, + 222, + 470, + 299 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This can be illustrated in examples where one agent is following another, where typically the lead agent's behavior is causing the trailing agent's reaction, and not vice versa, but this directionality would not be captured with acausal conditioning. This temporally causal modeling is especially important when utilizing the conditional predictions to evaluate safety for an autonomous vehicle's proposed plans. In a scenario where an autonomous vehicle (AV) is stopped behind another agent, planning to move forward into the other agent's current position could be viewed as a safe maneuver with acausal conditioning, as the other agent also moving forward is correlated with (but not caused by) the AV proceeding. However, it is typically the lead agent moving forward that causes the trailing AV to proceed, and the AV moving forward on its own would simply rear-end the lead agent.", + "bbox": [ + 75, + 300, + 473, + 542 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In the supplementary, we compare examples of predictions in various scenarios for the causal and acausal conditioning schemes. Models that ignore temporal dependencies during conditioning (e.g., [44, 29]) may succumb to the same incorrect reasoning that the acausal version of our model does.", + "bbox": [ + 75, + 545, + 470, + 636 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion and future work", + "text_level": 1, + "bbox": [ + 76, + 657, + 336, + 674 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this work, we introduced a method for interactive motion forecasting leveraging multi-agent rollouts over discrete motion tokens, capturing the joint distribution over multimodal futures. The proposed model establishes new state-of-the-art performance on the WOMD interactive prediction challenge.", + "bbox": [ + 75, + 686, + 468, + 777 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Avenues for future work include leveraging the trained model in model-based planning frameworks, allowing a search tree to be formed over the multi-agent action rollouts, or learning amortized value functions from large datasets of scene rollouts. In addition, we plan to explore distillation strategies from large autoregressive teachers, enabling faster student models to be deployed in latency-critical settings.", + "bbox": [ + 75, + 780, + 470, + 902 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/773e7c793696df82720c67d8f67dd99c02aff38e49b7b83b51005341d0a8505c.jpg", + "image_caption": [ + "Figure 7. Visualization of the most likely predicted future for the pedestrian in the marginal setting (left) and temporally causal conditional setting (right). When considering the pedestrian independently, the model assigns greatest probability to a trajectory which crosses the road. When conditioned on the vehicle's ground truth turn (magenta), the pedestrian is instead predicted to yield." + ], + "image_footnote": [], + "bbox": [ + 503, + 218, + 694, + 377 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/83624c9647b22b52ddd04e4c9bce8713bb0a5907030f64ca897cccc0a5e997ac.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 697, + 218, + 888, + 376 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements. We would like to thank David Weiss, Paul Covington, Ashish Venugopal, Piotr Fidkowski, and Minfa Wang for discussions on autoregressive behavior predictors; Cole Gulino and Brandyn White for advising on interactive modeling; Cheol Park, Wenjie Luo, and Scott Ettinger for assistance with evaluation; Drago Anguelov, Kyriacos Shiarlis, and anonymous reviewers for helpful feedback on the manuscript.", + "bbox": [ + 498, + 497, + 893, + 619 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "8587", + "bbox": [ + 482, + 944, + 516, + 957 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Elmira Amirloo, Amir Rasouli, Peter Lakner, Mohsen Rohani, and Jun Luo. 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Refaat, Nigamaa Nayakanti, Andre Cornman, Kan Chen, Bertrand Douillard, Chi-Pang Lam, Dragomir Anguelov, and Benjamin Sapp. Multipath++: Efficient information fusion and trajectory aggregation for behavior prediction. In ICRA, 2022.", + "[48] Ashish Vaswani, Noam Shazeer, Niki Parmar, Jakob Uszkoreit, Llion Jones, Aidan N Gomez, Lukasz Kaiser, and Illia Polosukhin. Attention is all you need. In Advances in Neural Information Processing Systems, 2017.", + "[49] Jiahui Yu, Yuanzhong Xu, Jing Yu Koh, Thang Luong, Gunjan Baid, Zirui Wang, Vijay Vasudevan, Alexander Ku, Yinfei Yang, Burcu Karagol Ayan, Ben Hutchinson, Wei Han, Zarana Parekh, Xin Li, Han Zhang, Jason Baldridge, and Yonghui Wu. Scaling autoregressive models for content-rich text-to-image generation. Transactions on Machine Learning Research, 2022.", + "[50] Ye Yuan, Xinshuo Weng, Yanglan Ou, and Kris M Kitani. Agentformer: Agent-aware transformers for socio-temporal multi-agent forecasting. 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PMLR, 2021." + ], + "bbox": [ + 78, + 90, + 470, + 598 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "8590", + "bbox": [ + 482, + 945, + 516, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/MotionLM_ Multi-Agent Motion Forecasting as Language Modeling/675319b9-5800-4617-9b35-401666d76cde_model.json b/2023/MotionLM_ Multi-Agent Motion Forecasting as Language Modeling/675319b9-5800-4617-9b35-401666d76cde_model.json new file mode 100644 index 0000000000000000000000000000000000000000..25335d00ced5c8f41f24fc49e6d65cba73c1c20c --- /dev/null +++ b/2023/MotionLM_ Multi-Agent Motion Forecasting as Language Modeling/675319b9-5800-4617-9b35-401666d76cde_model.json @@ -0,0 +1,2314 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.141, + 0.131, + 0.83, + 0.154 + ], + "angle": 0, + "content": "MotionLM: Multi-Agent Motion Forecasting as Language Modeling" + }, + { + "type": "text", + "bbox": [ + 0.136, + 0.194, + 0.834, + 0.23 + ], + "angle": 0, + "content": "Ari Seff Brian Cera Dian Chen* Mason Ng Aurick Zhou Nigamaa Nayakanti Khaled S. Refaat Rami Al-Rfou Benjamin Sapp" + }, + { + "type": "text", + "bbox": [ + 0.452, + 0.25, + 0.518, + 0.267 + ], + "angle": 0, + "content": "Waymo" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.328, + 0.314, + 0.344 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.359, + 0.474, + 0.661 + ], + "angle": 0, + "content": "Reliable forecasting of the future behavior of road agents is a critical component to safe planning in autonomous vehicles. Here, we represent continuous trajectories as sequences of discrete motion tokens and cast multi-agent motion prediction as a language modeling task over this domain. Our model, MotionLM, provides several advantages: First, it does not require anchors or explicit latent variable optimization to learn multimodal distributions. Instead, we leverage a single standard language modeling objective, maximizing the average log probability over sequence tokens. Second, our approach bypasses post-hoc interaction heuristics where individual agent trajectory generation is conducted prior to interactive scoring. Instead, MotionLM produces joint distributions over interactive agent futures in a single autoregressive decoding process. In addition, the model's sequential factorization enables temporally causal conditional rollouts. The proposed approach establishes new state-of-the-art performance for multi-agent motion prediction on the Waymo Open Motion Dataset, ranking \\(1^{st}\\) on the interactive challenge leaderboard." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.69, + 0.21, + 0.705 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.715, + 0.47, + 0.866 + ], + "angle": 0, + "content": "Modern sequence models often employ a next-token prediction objective that incorporates minimal domain-specific assumptions. For example, autoregressive language models [3, 10] are pre-trained to maximize the probability of the next observed subword conditioned on the previous text; there is no predefined notion of parsing or syntax built in. This approach has found success in continuous domains as well, such as audio [2] and image generation [49]. Leveraging the flexibility of arbitrary categorical distributions, the above works represent continuous data with a set of discrete" + }, + { + "type": "image", + "bbox": [ + 0.51, + 0.31, + 0.885, + 0.523 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.534, + 0.892, + 0.577 + ], + "angle": 0, + "content": "Figure 1. Our model autoregressively generates sequences of discrete motion tokens for a set of agents to produce consistent interactive trajectory forecasts." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.608, + 0.848, + 0.623 + ], + "angle": 0, + "content": "tokens, reminiscent of language model vocabularies." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.625, + 0.892, + 0.761 + ], + "angle": 0, + "content": "In driving scenarios, road users may be likened to participants in a constant dialogue, continuously exchanging a dynamic series of actions and reactions mirroring the fluidity and complexity of communication. Navigating this rich web of interactions requires the ability to anticipate the likely maneuvers and responses of the involved actors. Just as today's language models can capture sophisticated distributions over conversations, can we leverage similar sequence models to forecast the behavior of road agents?" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.763, + 0.892, + 0.884 + ], + "angle": 0, + "content": "A common simplification to modeling the full future world state has been to decompose the joint distribution of agent behavior into independent per-agent marginal distributions. Although there has been much progress on this task [8, 47, 12, 25, 31, 5, 6, 21], marginal predictions are insufficient as inputs to a planning system; they do not represent the future dependencies between the actions of different agents, leading to inconsistent scene-level forecasting." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Of the existing joint prediction approaches, some apply" + }, + { + "type": "page_footnote", + "bbox": [ + 0.094, + 0.876, + 0.356, + 0.901 + ], + "angle": 0, + "content": "*Work done during an internship at Waymo. Contact: {aseff,bensapp}@waymo.com" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8579" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.226 + ], + "angle": 0, + "content": "a separation between marginal trajectory generation and interactive scoring [40, 42, 29]. For example, Luo et al. [29] initially produce a small set of marginal trajectories for each agent independently, before assigning a learned potential to each inter-agent trajectory pair through a belief propagation algorithm. Sun et al. [42] use a manual heuristic to tag agents as either influencers or reactors, and then pairs marginal and conditional predictions to form joint predictions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.228, + 0.471, + 0.424 + ], + "angle": 0, + "content": "We also note that because these approaches do not explicitly model temporal dependencies within trajectories, their conditional forecasts may be more susceptible to spurious correlations, leading to less realistic reaction predictions. For example, these models can capture the correlation between a lead agent decelerating and a trailing agent decelerating, but may fail to infer which one is likely causing the other to slow down. In contrast, previous joint models employing an autoregressive factorization, e.g., [36, 43, 39], do respect future temporal dependencies. These models have generally relied on explicit latent variables for diversity, optimized via either an evidence lower bound or normalizing flow." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.425, + 0.471, + 0.666 + ], + "angle": 0, + "content": "In this work, we combine trajectory generation and interaction modeling in a single, temporally causal, decoding process over discrete motion tokens (Fig. 1), leveraging a simple training objective inspired by autoregressive language models. Our model, MotionLM, is trained to directly maximize the log probability of these token sequences among interacting agents. At inference time, joint trajectories are produced step-by-step, where interacting agents sample tokens simultaneously, attend to one another, and repeat. In contrast to previous approaches which manually enforce trajectory multimodality during training, our model is entirely latent variable and anchor-free, with multimodality emerging solely as a characteristic of sampling. MotionLM may be applied to several downstream behavior prediction tasks, including marginal, joint, and conditional predictions." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.668, + 0.399, + 0.682 + ], + "angle": 0, + "content": "This work makes the following contributions:" + }, + { + "type": "text", + "bbox": [ + 0.091, + 0.695, + 0.47, + 0.755 + ], + "angle": 0, + "content": "1. We cast multi-agent motion forecasting as a language modeling task, introducing a temporally causal decoder over discrete motion tokens trained with a causal language modeling loss." + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.768, + 0.469, + 0.858 + ], + "angle": 0, + "content": "2. We pair sampling from our model with a simple rollout aggregation scheme that facilitates weighted mode identification for joint trajectories, establishing new state-of-the-art performance on the Waymo Open Motion Dataset interaction prediction challenge (6% improvement in the ranking joint mAP metric)." + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "3. We perform extensive ablations of our approach as well as analysis of its temporally causal conditional" + }, + { + "type": "list", + "bbox": [ + 0.089, + 0.695, + 0.47, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.531, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "predictions, which are largely unsupported by current joint forecasting models." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.137, + 0.638, + 0.153 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.163, + 0.892, + 0.329 + ], + "angle": 0, + "content": "Marginal trajectory prediction. Behavior predictors are often evaluated on their predictions for individual agents, e.g., in recent motion forecasting benchmarks [14, 9, 4, 51, 37]. Previous methods process the rasterized scene with CNNs [8, 5, 12, 17]; the more recent works represent scenes with points and polygraphs and process them with GNNs [6, 25, 47, 22] or transformers [31, 40, 20]. To handle the multimodality of future trajectories, some models manually enforce diversity via predefined anchors [8, 5] or intention points [40, 52, 28]. Other works learn diverse modes with latent variable modeling, e.g., [24]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.33, + 0.892, + 0.39 + ], + "angle": 0, + "content": "While these works produce multimodal future trajectories of individual agents, they only capture the marginal distributions of the possible agent futures and do not model the interactions among agents." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.412, + 0.892, + 0.517 + ], + "angle": 0, + "content": "Interactive trajectory prediction. Interactive behavior predictors model the joint distribution of agents' futures. This task has been far less studied than marginal motion prediction. For example, the Waymo Open Motion Dataset (WOMD) [14] challenge leaderboard currently has 71 published entries for marginal prediction compared to only 14 for interaction prediction." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.518, + 0.892, + 0.744 + ], + "angle": 0, + "content": "Ngiam et al. [32] models the distribution of future trajectories with a transformer-based mixture model outputting joint modes. To avoid the exponential blow-up from a full joint model, Luo et al. [29] models pairwise joint distributions. Tolstaya et al. [44], Song et al. [41], Sun et al. [42] consider conditional predictions by exposing the future trajectory of one agent when predicting for another agent. Shi et al. [40] derives joint probabilities by simply multiplying marginal trajectory probabilities, essentially treating agents as independent, which may limit accuracy. Cui et al. [11], Casas et al. [7], Girgis et al. [15] reduce the full-fledged joint distribution using global latent variables. Unlike our autoregressive factorization, the above models typically follow \"one-shot\" (parallel across time) factorizations and do not explicitly model temporally causal interactions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Autoregressive trajectory prediction. Autoregressive behavior predictors generate trajectories at intervals to produce scene-consistent multi-agent trajectories. Rhinehart et al. [36], Tang and Salakhutdinov [43], Amirloo et al. [1], Salzmann et al. [39], Yuan et al. [50] predict multiagent future trajectories using latent variable models. Lu et al. [27] explores autoregressively outputting keyframes via mixtures of Gaussians prior to filling in the remaining states. In [18], an adversarial objective is combined with" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "8580" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.087, + 0.096, + 0.87, + 0.276 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.298, + 0.896, + 0.385 + ], + "angle": 0, + "content": "Figure 2. MotionLM architecture. We first encode heterogeneous scene features relative to each modeled agent (left) as scene embeddings of shape \\( R, N, \\cdot, H \\). Here, \\( R \\) refers to the number of rollouts, \\( N \\) refers to the number of (jointly modeled) agents, and \\( H \\) is the dimensionality of each embedding. We repeat the embeddings \\( R \\) times in the batch dimension for parallel sampling during inference. Next, a trajectory decoder autoregressively rolls out \\( T \\) discrete motion tokens for multiple agents in a temporally causal manner (center). Finally, representative modes of the rollouts may be recovered via a simple aggregation utilizing k-means clustering initialized with non-maximum suppression (right)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.408, + 0.471, + 0.485 + ], + "angle": 0, + "content": "parallel beam search to learn multi-agent rollouts. Unlike most autoregressive trajectory predictors, our method does not rely on latent variables or beam search and generates multimodal joint trajectories by directly sampling from a learned distribution of discrete motion token sequences." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.509, + 0.47, + 0.569 + ], + "angle": 0, + "content": "Discrete sequence modeling in continuous domains. When generating sequences in continuous domains, one effective approach is to discretize the output space and predict categorical distributions at each step." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.571, + 0.471, + 0.829 + ], + "angle": 0, + "content": "For example, in image generation, PixelRNN [45] sequentially predicts the uniformly discretized pixel values for each channel and found this to perform better than outputting continuous values directly. Multiple works on generating images from text such as DALL-E [35] and Parti [49] use a two-stage process with a learned tokenizer to map images to discrete tokens and an autoregressive model to predict the discrete tokens given the text prompt. For audio generation, WaveNet [46] applies a \\(\\mu\\)-law transformation before discretizing. AudioLM [2] learns a hierarchical tokenizer/detokenizer, with the main transformer sequence model operating on the intermediate discrete tokens. When generating polygonal meshes, PolyGen [30] uniformly quantizes the coordinates of each vertex. In MotionLM, we employ a simple uniform quantization of axis-aligned deltas between consecutive waypoints of agent trajectories." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.845, + 0.195, + 0.86 + ], + "angle": 0, + "content": "3. MotionLM" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.903 + ], + "angle": 0, + "content": "We aim to model a distribution over multi-agent interactions in a general manner that can be applied to distinct" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.408, + 0.892, + 0.68 + ], + "angle": 0, + "content": "downstream tasks, including marginal, joint, and conditional forecasting. This requires an expressive generative framework capable of capturing the substantial multimodality in driving scenarios. In addition, we take consideration here to preserve temporal dependencies; i.e., inference in our model follows a directed acyclic graph with the parents of every node residing earlier in time and children residing later (Section 3.3, Fig. 4). This enables conditional forecasts that more closely resemble causal interventions [34] by eliminating certain spurious correlations that can otherwise result from disobeying temporal causality\\(^2\\). We observe that joint models that do not preserve temporal dependencies may have a limited ability to predict realistic agent reactions – a key use in planning (Section 4.6). To this end, we leverage an autoregressive factorization of our future decoder, where agents' motion tokens are conditionally dependent on all previously sampled tokens and trajectories are rolled out sequentially (Fig. 2)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.682, + 0.892, + 0.835 + ], + "angle": 0, + "content": "Let \\( S \\) represent the input data for a given scenario. This may include context such as roadgraph elements, traffic light states, as well as features describing road agents (e.g., vehicles, cyclists, and pedestrians) and their recent histories, all provided at the current timestep \\( t = 0 \\). Our task is to generate predictions for joint agent states \\( Y_{t} \\doteq \\{y_{t}^{1}, y_{t}^{2}, \\dots, y_{t}^{N}\\} \\) for \\( N \\) agents of interest at future timesteps \\( t = 1, \\dots, T \\). Rather than complete states, these future state targets are typically two-dimensional waypoints (i.e., \\( (x, y) \\) coordinates), with \\( T \\) waypoints forming the full ground" + }, + { + "type": "page_footnote", + "bbox": [ + 0.498, + 0.851, + 0.894, + 0.903 + ], + "angle": 0, + "content": "2We make no claims that our model is capable of directly modeling causal relationships (due to the theoretical limits of purely observational data and unobserved confounders). Here, we solely take care to avoid breaking temporal causality." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.958 + ], + "angle": 0, + "content": "8581" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.336, + 0.108 + ], + "angle": 0, + "content": "truth trajectory for an individual agent." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.117, + 0.317, + 0.133 + ], + "angle": 0, + "content": "3.1. Joint probabilistic rollouts" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.141, + 0.47, + 0.262 + ], + "angle": 0, + "content": "In our modeling framework, we sample a predicted action for each target agent at each future timestep. These actions are formulated as discrete motion tokens from a finite vocabulary, as described later in Section 3.2.2. Let \\(a_{t}^{n}\\) represent the target action (derived from the ground truth waypoints) for the \\(n\\)th agent at time \\(t\\), with \\(A_{t} \\doteq \\{a_{t}^{1}, a_{t}^{2}, \\dots, a_{t}^{N}\\}\\) representing the set of target actions for all agents at time \\(t\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.281, + 0.469, + 0.312 + ], + "angle": 0, + "content": "Factorization. We factorize the distribution over joint future action sequences as a product of conditionals:" + }, + { + "type": "equation", + "bbox": [ + 0.124, + 0.325, + 0.47, + 0.365 + ], + "angle": 0, + "content": "\\[\np _ {\\theta} \\left(A _ {1}, A _ {2}, \\dots A _ {T} \\mid S\\right) = \\prod_ {t = 1} ^ {T} p _ {\\theta} \\left(A _ {t} \\mid A _ {< t}, S\\right), \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.14, + 0.378, + 0.469, + 0.419 + ], + "angle": 0, + "content": "\\[\np _ {\\theta} \\left(A _ {t} \\mid A _ {< t}, S\\right) = \\prod_ {n = 1} ^ {N} p _ {\\theta} \\left(a _ {t} ^ {n} \\mid A _ {< t}, S\\right). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.424, + 0.469, + 0.558 + ], + "angle": 0, + "content": "Similar to [36, 43], Eq. (2) represents the fact that we treat agent actions as conditionally independent at time \\( t \\), given the previous actions and scene context. This aligns empirically with real-world driving over short time intervals; e.g., non-impaired human drivers generally require at least 500 ms to release the accelerator in response to a vehicle braking ahead ([13]). In our experiments, we find \\( 2\\mathrm{Hz} \\) reactions to be sufficient to surpass state-of-the-art joint prediction models." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.561, + 0.469, + 0.606 + ], + "angle": 0, + "content": "We note that our model's factorization is entirely latent variable free; multimodal predictions stem purely from categorical token sampling at each rollout timestep." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.626, + 0.469, + 0.687 + ], + "angle": 0, + "content": "Training objective. MotionLM is formulated as a generative model trained to match the joint distribution of observed agent behavior. Specifically, we follow a maximum likelihood objective over multi-agent action sequences:" + }, + { + "type": "equation", + "bbox": [ + 0.179, + 0.698, + 0.469, + 0.739 + ], + "angle": 0, + "content": "\\[\n\\underset {\\theta} {\\arg \\max } \\prod_ {t = 1} ^ {T} p _ {\\theta} \\left(A _ {t} \\mid A _ {< t}, S\\right) \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Similar to the typical training setup of modern language models, we utilize \"teacher-forcing\" where previous ground truth (not predicted) tokens are provided at each timestep, which tends to increase stability and avoids sampling during training. We note that this applies to all target agents; in training, each target agent is exposed to ground truth action sequence prefixes for all target agents prior to the current timestep. This naturally allows for temporal parallelization when using modern attention-based architectures such as transformers [48]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.168 + ], + "angle": 0, + "content": "Our model is subject to the same theoretical limitations as general imitation learning frameworks (e.g., compounding error [38] and self-delusions due to unobserved confounders [33]). However, we find that, in practice, these do not prevent strong performance on forecasting tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.177, + 0.71, + 0.193 + ], + "angle": 0, + "content": "3.2. Model implementation" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.201, + 0.892, + 0.276 + ], + "angle": 0, + "content": "Our model consists of two main networks, an encoder which processes initial scene elements followed by a trajectory decoder which performs both cross-attention to the scene encodings and self-attention along agent motion tokens, following a transformer architecture [48]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.296, + 0.653, + 0.31 + ], + "angle": 0, + "content": "3.2.1 Scene encoder" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.32, + 0.892, + 0.439 + ], + "angle": 0, + "content": "The scene encoder (Fig. 2, left) is tasked with processing information from several input modalities, including the roadgraph, traffic light states, and history of surrounding agents' trajectories. Here, we follow the design of the early fusion network proposed by [31] as the scene encoding backbone of our model. Early fusion is particularly chosen because of its flexibility to process all modalities together with minimal inductive bias." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.441, + 0.892, + 0.547 + ], + "angle": 0, + "content": "The features above are extracted with respect to each modeled agent's frame of reference. Input tensors are then fed to a stack of self-attention layers that exchange information across all past timesteps and agents. In the first layer, latent queries cross-attend to the original inputs in order to reduce the set of vectors being processed to a manageable number, similar to [23, 19]. For additional details, see [31]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.566, + 0.722, + 0.581 + ], + "angle": 0, + "content": "3.2.2 Joint trajectory decoder" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.59, + 0.89, + 0.621 + ], + "angle": 0, + "content": "Our trajectory decoder (Fig. 2, center) is tasked with generating sequences of motion tokens for multiple agents." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.64, + 0.892, + 0.836 + ], + "angle": 0, + "content": "Discrete motion tokens. We elect to transform trajectories comprised of continuous waypoints into sequences of discrete tokens. This enables treating sampling purely as a classification task at each timestep, implemented via a standard softmax layer. Discretizing continuous targets in this manner has proven effective in other inherently continuous domains, e.g., in audio generation [46] and mesh generation [30]. We suspect that discrete motion tokens also naturally hide some precision from the model, possibly mitigating compounding error effects that could arise from imperfect continuous value prediction. Likewise, we did not find it necessary to manually add any noise to the ground truth teacher-forced trajectories (e.g., as is done in [26])." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Quantization. To extract target discrete tokens, we begin by normalizing each agent's ground truth trajectory with respect to the position and heading of the agent at" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8582" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.102, + 0.091, + 0.353, + 0.282 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.361, + 0.091, + 0.611, + 0.282 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.622, + 0.092, + 0.871, + 0.283 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.296, + 0.895, + 0.368 + ], + "angle": 0, + "content": "Figure 3. Displayed are the top two predicted joint rollout modes for three WOMD scenes. Color gradients indicate time progression from \\( t = 0 \\)s to \\( t = 8 \\)s, with the greatest probability joint mode transitioning from green to blue and the secondary joint mode transitioning from orange to purple. Three types of interactions are observed: an agent in the adjacent lane yields to the lane-changing agent according to the timing of the lane change (left), a pedestrian walks behind the passing vehicle according to the progress of the vehicle (center), the turning vehicle either yields to the crossing cyclist (most probable mode) or turns before the cyclist approaches (secondary mode) (right)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.393, + 0.473, + 0.558 + ], + "angle": 0, + "content": "time \\( t = 0 \\) of the scenario. We then parameterize a uniformly quantized \\( (\\Delta x, \\Delta y) \\) vocabulary according to a total number of per-coordinate bins as well as maximum and minimum delta values. A continuous, single-coordinate delta action can then be mapped to a corresponding index \\( \\in [0, \\text{num\\_bins} - 1] \\), resulting in two indices for a complete \\( (\\Delta x, \\Delta y) \\) action per step. In order to extract actions that accurately reconstruct an entire trajectory, we employ a greedy search, sequentially selecting the quantized actions that reconstruct the next waypoint coordinates with minimum error." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.56, + 0.47, + 0.741 + ], + "angle": 0, + "content": "We wrap the delta actions with a \"Verlet\" step where a zero action indicates that the same delta index should be used as the previous step (as [36] does for continuous states). As agent velocities tend to change smoothly between consecutive timesteps, this helps reduce the total vocabulary size, simplifying the dynamics of training. Finally, to maintain only \\( T \\) sequential predictions, we collapse the per-coordinate actions to a single integer indexing into their Cartesian product. In practice, for the models presented here, we use 13 tokens per coordinate with \\( 13^2 = 169 \\) total discrete tokens available in the vocabulary (see Appendix A for further details)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.742, + 0.47, + 0.817 + ], + "angle": 0, + "content": "We compute a learned value embedding and two learned positional embeddings (representing the timestep and agent identity) for each discrete motion token, which are combined via an element-wise sum prior to being input to the transformer decoder." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Flattened agent-time self-attention. We elect to include a single self-attention mechanism in the decoder that operates along flattened sequences of all modeled agents' motion tokens over time. So, given a target sequence of length" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.393, + 0.895, + 0.514 + ], + "angle": 0, + "content": "\\(T\\) for each of \\(N\\) agents, we perform self-attention over \\(NT\\) elements. While this does mean that these self-attended sequences grow linearly in the number of jointly modeled agents, we note that the absolute sequence length here is still quite small (length 32 for the WOMD interactive split -8 sec. prediction at \\(2\\mathrm{Hz}\\) for 2 agents). Separate passes of factorized agent and time attention are also possible [32], but we use a single pass here for simplicity." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.533, + 0.894, + 0.64 + ], + "angle": 0, + "content": "Ego agent reference frames. To facilitate cross-attention to the agent-centric feature encodings (Section 3.2.1), we represent the flattened token sequence once for each modeled agent. Each modeled agent is treated as the \"ego\" agent once, and cross-attention is performed on that agent's scene features. Collapsing the ego agents into the batch dimension allows parallelization during training and inference." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.648, + 0.761, + 0.665 + ], + "angle": 0, + "content": "3.3. Enforcing temporal causality" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.671, + 0.892, + 0.809 + ], + "angle": 0, + "content": "Our autoregressive factorization naturally respects temporal dependencies during joint rollouts; motion token sampling for any particular agent is affected only by past tokens (from any agent) and unaffected by future ones. When training, we require a mask to ensure that the self-attention operation only updates representations at each step accordingly. As shown in Fig. 8 (appendix), this attention mask exhibits a blocked, staircase pattern, exposing all agents to each other's histories only up to the preceding step." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Temporally causal conditioning. As described earlier, a particular benefit of this factorization is the ability to query for temporally causal conditional rollouts (Fig. 4). In this setting, we fix a query agent to take some sequence of actions and only roll out the other agents." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.958 + ], + "angle": 0, + "content": "8583" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.107, + 0.329, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.105, + 0.208, + 0.324, + 0.22 + ], + "angle": 0, + "content": "(a) Causal Bayesian Network for joint rollouts." + }, + { + "type": "image", + "bbox": [ + 0.354, + 0.106, + 0.592, + 0.179 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.37, + 0.208, + 0.593, + 0.22 + ], + "angle": 0, + "content": "(b) Post-Intervention Causal Bayesian Network." + }, + { + "type": "image", + "bbox": [ + 0.636, + 0.107, + 0.882, + 0.178 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.637, + 0.18, + 0.877, + 0.207 + ], + "angle": 0, + "content": "Conditioned Agent Causal conditioning Sampling Agent Acausal conditioning" + }, + { + "type": "image_caption", + "bbox": [ + 0.689, + 0.208, + 0.807, + 0.22 + ], + "angle": 0, + "content": "(c) Acausal conditioning." + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.231, + 0.895, + 0.288 + ], + "angle": 0, + "content": "Figure 4. A Causal Bayesian network representation for joint rollouts (left), post-intervention Causal Bayesian network (center), and acausal conditioning (right). Solid lines indicate temporally causal dependencies while dashed lines indicate acausal information flow. Models without temporal dependency constraints will support acausal conditioning but not temporally causal conditioning, which can be problematic when attempting to predict agent reactions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.314, + 0.471, + 0.42 + ], + "angle": 0, + "content": "We may view this as an approximation of computing causal interventions [34] in the absence of confounders; interventions cannot be learned purely through observational data in general (due to the possible presence of unobserved confounders), but our model's factorization at least eliminates certain spurious correlations arising from breaking temporal causality." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.42, + 0.473, + 0.542 + ], + "angle": 0, + "content": "In Fig. 4 (a), we show an example of a Causal Bayesian network governing joint rollouts. Applying an intervention to nodes \\( x = 1, \\ldots, T \\), by deleting their incoming edges, results in a post-intervention Bayesian network depicted in Fig. 4 (b), which obeys temporal causality. On the other hand, acausal conditioning (Fig. 4 (c)) results in non-causal information flow, where node \\( x = i \\) affects our belief about node \\( y = j \\) for \\( i \\geq j \\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.551, + 0.267, + 0.567 + ], + "angle": 0, + "content": "3.4. Rollout aggregation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.574, + 0.473, + 0.833 + ], + "angle": 0, + "content": "Joint motion forecasting benchmark tasks like WOMD [14] require a compact representation of the joint future distribution in the form of a small number of joint \"modes\". Each mode is assigned a probability and might correspond to a specific homotopic outcome (e.g., pass/yield) or more subtle differences in speed/geometry. Here, we aggregate rollouts to achieve two primary goals: 1) uncover the underlying modes of the distribution and 2) estimate the probability of each mode. Specifically, we follow the non-maximum suppression (NMS) aggregation scheme described in [47], but extend it to the joint setting by ensuring that all agent predictions reside within a given distance threshold to the corresponding cluster. In addition, we leverage model ensembling to account for epistemic uncertainty and further improve the quality of the predictions, combining rollouts from independently trained replicas prior to the aggregation step." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.846, + 0.21, + 0.863 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.902 + ], + "angle": 0, + "content": "We evaluate MotionLM on marginal and joint motion forecasting benchmarks, examine its conditional predic" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.314, + 0.848, + 0.33 + ], + "angle": 0, + "content": "tions and conduct ablations of our modeling choices." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.344, + 0.602, + 0.358 + ], + "angle": 0, + "content": "4.1. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.369, + 0.892, + 0.506 + ], + "angle": 0, + "content": "Waymo Open Motion Dataset (WOMD). WOMD [14] is a collection of 103k 20-second scenarios collected from real-world driving in urban and suburban environments. Segments are divided into 1.1M examples consisting of 9-second windows of interest, where the first second serves as input context and the remaining 8-seconds are the prediction target. Map features such as traffic signal states and lane features are provided along with agent states such as position, velocity, acceleration, and bounding boxes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.534, + 0.892, + 0.625 + ], + "angle": 0, + "content": "Marginal and interactive prediction challenges. For the marginal prediction challenge, six trajectories must be output by the model for each target agent, along with likelihoods of each mode. For the interactive challenge, two interacting agents are labeled in each test example. In this case, the model must output six weighted joint trajectories." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.64, + 0.597, + 0.654 + ], + "angle": 0, + "content": "4.2. Metrics" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.665, + 0.892, + 0.801 + ], + "angle": 0, + "content": "The primary evaluation metrics for the marginal and interactive prediction challenges are soft mAP and mAP, respectively, with miss rate as the secondary metric. Distance metrics minADE and minFDE provide additional signal on prediction quality. For the interactive prediction challenge, these metrics refer to scene-level joint calculations. We also use a custom prediction overlap metric (similar to [29]) to assess scene-level consistency for joint models. See Appendix C for details on these metrics." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.815, + 0.693, + 0.831 + ], + "angle": 0, + "content": "4.3. Model configuration" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We experiment with up to 8 model replicas and 512 rollouts per replica, assessing performance at various configurations. For complete action space and model hyperparameter details, see Appendices A and B." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8584" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.217, + 0.089, + 0.756, + 0.21 + ], + "angle": 0, + "content": "
ModelminADE (↓)minFDE (↓)Miss Rate (↓)Soft mAP (↑)
HDGT [20]0.76761.10770.13250.3709
MPA [22]0.59131.25070.16030.3930
MTR [40]0.60501.22070.13510.4216
Wayformer factorized [31]0.54471.12550.12290.4260
Wayformer multi-axis [31]0.54541.12800.12280.4335
MTR-A [40]0.56401.13440.11600.4594
MotionLM (Ours)0.55091.11990.10580.4507
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.221, + 0.895, + 0.251 + ], + "angle": 0, + "content": "Table 1. Marginal prediction performance on WOMD test set. We display metrics averaged over time steps (3, 5, and 8 seconds) and agent types (vehicles, pedestrians, and cyclists). Greyed columns indicate the official ranking metrics for the marginal prediction challenge." + }, + { + "type": "table", + "bbox": [ + 0.231, + 0.263, + 0.742, + 0.371 + ], + "angle": 0, + "content": "
ModelminADE (↓)minFDE (↓)Miss Rate (↓)mAP (↑)
SceneTransformer (J) [32]0.97742.18920.49420.1192
M2I [42]1.35062.83250.55380.1239
DenseTNT [28]1.14172.49040.53500.1647
MTR [40]0.91812.06330.44110.2037
JFP [29]0.88171.99050.42330.2050
MotionLM (Ours)0.89112.00670.41150.2178
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.381, + 0.893, + 0.412 + ], + "angle": 0, + "content": "Table 2. Joint prediction performance on WOMD interactive test set. We display scene-level joint metrics averaged over time steps (3, 5, and 8 seconds) and agent types (vehicles, pedestrians, and cyclists). Greyed columns indicate the official ranking metrics for the challenge." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.436, + 0.266, + 0.451 + ], + "angle": 0, + "content": "4.4. Quantitative results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.459, + 0.473, + 0.626 + ], + "angle": 0, + "content": "Marginal motion prediction. As shown in Table 1, our model is competitive with the state-of-the-art on WOMD marginal motion prediction (independent per agent). For the main ranking metric of soft mAP, our model ranks second, less than \\(2\\%\\) behind the score achieved by MTRA [40]. In addition, our model attains a substantially improved miss rate over all prior works, with a relative \\(9\\%\\) reduction compared to the previous state-of-the-art. The autoregressive rollouts are able to adequately capture the diversity of multimodal future behavior without reliance on trajectory anchors [8] or static intention points [40]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.47, + 0.78 + ], + "angle": 0, + "content": "Interactive motion prediction. Our model achieves state-of-the-art results for the interactive prediction challenge on WOMD, attaining a \\(6\\%\\) relative improvement in mAP and \\(3\\%\\) relative improvement in miss rate (the two official ranking metrics) over the previous top scoring entry, JFP [29] (see Table 2). In contrast to JFP, our approach does not score pairs of previously constructed marginal trajectories, but generates joint rollouts directly. Fig. 3 displays example interactions predicted by our model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Table 3 displays prediction overlap rates for various models on the WOMD interactive test and validation sets (see metric details in Appendix C.2). We obtain test set predictions from the authors of [14, 32, 29]. MotionLM obtains the lowest prediction overlap rate, an indication of scene-consistent predictions. In addition, on the validation set we evaluate two versions of our model: marginal and joint. The marginal version does not perform attention" + }, + { + "type": "table", + "bbox": [ + 0.523, + 0.434, + 0.871, + 0.548 + ], + "angle": 0, + "content": "
ModelPrediction Overlap (↓)
TestLSTM Baseline [14]0.07462
Scene Transformer [32]0.04336
JFP [29]0.02671
MotionLM (joint)0.02607
ValMotionLM (marginal)0.0404
MotionLM (joint)0.0292
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.558, + 0.892, + 0.6 + ], + "angle": 0, + "content": "Table 3. Prediction overlap rates. Displayed is the custom prediction overlap metric for various model configurations on the WOMD interactive test and validation sets." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.627, + 0.892, + 0.718 + ], + "angle": 0, + "content": "across the modeled agents during both training and inference rollouts, while the joint version performs \\(2\\mathrm{Hz}\\) interactive attention. We see that the marginal version obtains a relative \\(38\\%\\) higher overlap rate than the joint version. The interactive attention in the joint model allows the agents to more appropriately react to one another." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.727, + 0.663, + 0.741 + ], + "angle": 0, + "content": "4.5. Ablation studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.886 + ], + "angle": 0, + "content": "Interactive attention frequency. To assess the importance of inter-agent reactivity during the joint rollouts, we vary the frequency of the interactive attention operation while keeping other architecture details constant. For our leaderboard results, we utilize the greatest frequency studied here, \\(2\\mathrm{Hz}\\). At the low end of the spectrum, \\(0.125\\mathrm{Hz}\\) corresponds to the agents only observing each other's initial states, and then proceeding with the entire 8-second rollout without communicating again (i.e., marginal rollouts)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.887, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Performance metrics generally improve as agents are" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8585" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.104, + 0.09, + 0.258, + 0.102 + ], + "angle": 0, + "content": "No interactive attention" + }, + { + "type": "image_caption", + "bbox": [ + 0.294, + 0.09, + 0.448, + 0.102 + ], + "angle": 0, + "content": "16 interaction iterations" + }, + { + "type": "image", + "bbox": [ + 0.086, + 0.106, + 0.27, + 0.251 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.28, + 0.107, + 0.465, + 0.251 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.086, + 0.256, + 0.27, + 0.399 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.28, + 0.256, + 0.465, + 0.399 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.413, + 0.47, + 0.538 + ], + "angle": 0, + "content": "Figure 5. Visualization of the top joint rollout mode at the two extremes of the interactive attention frequencies studied here. With no interactive attention (left), the two modeled agents only attend to each other once at the beginning of the 8-second rollout and never again, in contrast to 16 total times for \\(2\\mathrm{Hz}\\) attention (right). The independent rollouts resulting from zero interactive attention can result in scene-inconsistent overlap; e.g., a turning vehicle fails to accommodate a crossing pedestrian (top left) or yield appropriately to a crossing vehicle (bottom left)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.573, + 0.468, + 0.709 + ], + "angle": 0, + "content": "permitted to interact more frequently (Fig. 6 top, Table 5 in appendix). Greater interactive attention frequencies not only lead to more accurate joint predictions, but also reduce implausible overlaps (i.e., collisions) between different agents' predictions. Fig. 5 displays examples where the marginal predictions lead to implausible overlap between agents while the joint predictions lead to appropriately separated trajectories. See supplementary for animated visualizations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Number of rollouts. Our rollout aggregation requires that we generate a sufficient number of samples from the model in order to faithfully represent the multimodal future distribution. For this ablation, we vary the number of rollouts generated, but always cluster down to \\( k = 6 \\) modes for evaluation. In general, we see performance metrics improve as additional rollouts are utilized (Fig. 6, bottom and Table 6 in appendix). For our final leaderboard results, we use 512 rollouts per replica, although 32 rollouts is sufficient to surpass the previous top entry on joint mAP." + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.091, + 0.888, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.273, + 0.886, + 0.443 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.455, + 0.892, + 0.537 + ], + "angle": 0, + "content": "Figure 6. Joint prediction performance across varying interactive attention frequencies (top) and numbers of rollouts per replica (bottom) on the WOMD interactive validation set. Vertical axes display joint (scene-level) metrics for an 8-replica ensemble. See Tables 5 and 6 in the appendix for full parameter ranges and metrics." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.57, + 0.691, + 0.585 + ], + "angle": 0, + "content": "4.6. Conditional rollouts" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.596, + 0.892, + 0.763 + ], + "angle": 0, + "content": "As described in Section 3.3, our model naturally supports \"temporally causal\" conditioning, similarly to previous autoregressive efforts such as [36, 43]. In this setting, we fix one query agent to follow a specified trajectory and stochastically roll out the target agent. However, we can also modify the model to leak the query agent's full trajectory, acausally exposing its future to the target agent during conditioning. This resembles the approach to conditional prediction in, e.g., [44], where this acausal conditional distribution is modeled directly, or [29], where this distribution is accessed via inference in an energy-based model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Here, we assess predictions from our model across three settings: marginal, temporally causal conditional, and acausal conditional (Fig. 4). Quantitatively, we observe that both types of conditioning lead to more accurate predictions for the target agent (Table 4, Fig. 7). Additionally, we see that acausal conditioning leads to greater improvement than temporally causal conditioning relative to marginal predictions across all metrics, e.g., \\(8.2\\%\\) increase in soft mAP for acausal vs. \\(3.7\\%\\) increase for temporally causal." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8586" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.207, + 0.089, + 0.768, + 0.16 + ], + "angle": 0, + "content": "
Prediction settingminADE (↓)minFDE (↓)Miss Rate (↓)Soft mAP (↑)
Marginal0.60691.22360.14060.3951
Temporally causal conditional0.59971.20340.13770.4096
Acausal conditional0.58991.18040.13380.4274
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.168, + 0.895, + 0.199 + ], + "angle": 0, + "content": "Table 4. Conditional prediction performance. Displayed are marginal (single-agent) metrics across three prediction settings for our model on the WOMD interactive validation set: marginal, temporally causal conditional, and acausal conditional." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.223, + 0.471, + 0.3 + ], + "angle": 0, + "content": "Intuitively, the greater improvement for acausal conditioning makes sense as it exposes more information to the model. However, the better quantitative scores are largely due to predictions that would be deemed nonsensical if interpreted as predicted reactions to the query agent." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.301, + 0.474, + 0.543 + ], + "angle": 0, + "content": "This can be illustrated in examples where one agent is following another, where typically the lead agent's behavior is causing the trailing agent's reaction, and not vice versa, but this directionality would not be captured with acausal conditioning. This temporally causal modeling is especially important when utilizing the conditional predictions to evaluate safety for an autonomous vehicle's proposed plans. In a scenario where an autonomous vehicle (AV) is stopped behind another agent, planning to move forward into the other agent's current position could be viewed as a safe maneuver with acausal conditioning, as the other agent also moving forward is correlated with (but not caused by) the AV proceeding. However, it is typically the lead agent moving forward that causes the trailing AV to proceed, and the AV moving forward on its own would simply rear-end the lead agent." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.546, + 0.472, + 0.637 + ], + "angle": 0, + "content": "In the supplementary, we compare examples of predictions in various scenarios for the causal and acausal conditioning schemes. Models that ignore temporal dependencies during conditioning (e.g., [44, 29]) may succumb to the same incorrect reasoning that the acausal version of our model does." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.659, + 0.338, + 0.675 + ], + "angle": 0, + "content": "5. Conclusion and future work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.687, + 0.47, + 0.779 + ], + "angle": 0, + "content": "In this work, we introduced a method for interactive motion forecasting leveraging multi-agent rollouts over discrete motion tokens, capturing the joint distribution over multimodal futures. The proposed model establishes new state-of-the-art performance on the WOMD interactive prediction challenge." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Avenues for future work include leveraging the trained model in model-based planning frameworks, allowing a search tree to be formed over the multi-agent action rollouts, or learning amortized value functions from large datasets of scene rollouts. In addition, we plan to explore distillation strategies from large autoregressive teachers, enabling faster student models to be deployed in latency-critical settings." + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.219, + 0.695, + 0.378 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.699, + 0.219, + 0.89, + 0.377 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.388, + 0.895, + 0.473 + ], + "angle": 0, + "content": "Figure 7. Visualization of the most likely predicted future for the pedestrian in the marginal setting (left) and temporally causal conditional setting (right). When considering the pedestrian independently, the model assigns greatest probability to a trajectory which crosses the road. When conditioned on the vehicle's ground truth turn (magenta), the pedestrian is instead predicted to yield." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.498, + 0.895, + 0.621 + ], + "angle": 0, + "content": "Acknowledgements. We would like to thank David Weiss, Paul Covington, Ashish Venugopal, Piotr Fidkowski, and Minfa Wang for discussions on autoregressive behavior predictors; Cole Gulino and Brandyn White for advising on interactive modeling; Cheol Park, Wenjie Luo, and Scott Ettinger for assistance with evaluation; Drago Anguelov, Kyriacos Shiarlis, and anonymous reviewers for helpful feedback on the manuscript." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.958 + ], + "angle": 0, + "content": "8587" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.157 + ], + "angle": 0, + "content": "[1] Elmira Amirloo, Amir Rasouli, Peter Lakner, Mohsen Rohani, and Jun Luo. 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PMLR, 2021." + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.471, + 0.599 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.517, + 0.957 + ], + "angle": 0, + "content": "8590" + } + ] +] \ No newline at end of file diff --git a/2023/MotionLM_ Multi-Agent Motion Forecasting as Language Modeling/675319b9-5800-4617-9b35-401666d76cde_origin.pdf b/2023/MotionLM_ Multi-Agent Motion Forecasting as Language Modeling/675319b9-5800-4617-9b35-401666d76cde_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..24a2d82fc04de3ff7ab64ed1931e344033ebf43f --- /dev/null +++ b/2023/MotionLM_ Multi-Agent Motion Forecasting as Language Modeling/675319b9-5800-4617-9b35-401666d76cde_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:ba557bdec0f1c63c20cac7ff38fb3614c8ad37f14e1f0eeb20c4f8b0c9012441 +size 1454115 diff --git a/2023/MotionLM_ Multi-Agent Motion Forecasting as Language Modeling/full.md b/2023/MotionLM_ Multi-Agent Motion Forecasting as Language Modeling/full.md new file mode 100644 index 0000000000000000000000000000000000000000..d6a83d463f08b0492900795003aa368f4bf357f2 --- /dev/null +++ b/2023/MotionLM_ Multi-Agent Motion Forecasting as Language Modeling/full.md @@ -0,0 +1,315 @@ +# MotionLM: Multi-Agent Motion Forecasting as Language Modeling + +Ari Seff Brian Cera Dian Chen* Mason Ng Aurick Zhou Nigamaa Nayakanti Khaled S. Refaat Rami Al-Rfou Benjamin Sapp + +Waymo + +# Abstract + +Reliable forecasting of the future behavior of road agents is a critical component to safe planning in autonomous vehicles. Here, we represent continuous trajectories as sequences of discrete motion tokens and cast multi-agent motion prediction as a language modeling task over this domain. Our model, MotionLM, provides several advantages: First, it does not require anchors or explicit latent variable optimization to learn multimodal distributions. Instead, we leverage a single standard language modeling objective, maximizing the average log probability over sequence tokens. Second, our approach bypasses post-hoc interaction heuristics where individual agent trajectory generation is conducted prior to interactive scoring. Instead, MotionLM produces joint distributions over interactive agent futures in a single autoregressive decoding process. In addition, the model's sequential factorization enables temporally causal conditional rollouts. The proposed approach establishes new state-of-the-art performance for multi-agent motion prediction on the Waymo Open Motion Dataset, ranking $1^{st}$ on the interactive challenge leaderboard. + +# 1. Introduction + +Modern sequence models often employ a next-token prediction objective that incorporates minimal domain-specific assumptions. For example, autoregressive language models [3, 10] are pre-trained to maximize the probability of the next observed subword conditioned on the previous text; there is no predefined notion of parsing or syntax built in. This approach has found success in continuous domains as well, such as audio [2] and image generation [49]. Leveraging the flexibility of arbitrary categorical distributions, the above works represent continuous data with a set of discrete + +![](images/f1f8c965e8223d171350c5c2f689a74abcf109088486c245c461b2530d073257.jpg) +Figure 1. Our model autoregressively generates sequences of discrete motion tokens for a set of agents to produce consistent interactive trajectory forecasts. + +tokens, reminiscent of language model vocabularies. + +In driving scenarios, road users may be likened to participants in a constant dialogue, continuously exchanging a dynamic series of actions and reactions mirroring the fluidity and complexity of communication. Navigating this rich web of interactions requires the ability to anticipate the likely maneuvers and responses of the involved actors. Just as today's language models can capture sophisticated distributions over conversations, can we leverage similar sequence models to forecast the behavior of road agents? + +A common simplification to modeling the full future world state has been to decompose the joint distribution of agent behavior into independent per-agent marginal distributions. Although there has been much progress on this task [8, 47, 12, 25, 31, 5, 6, 21], marginal predictions are insufficient as inputs to a planning system; they do not represent the future dependencies between the actions of different agents, leading to inconsistent scene-level forecasting. + +Of the existing joint prediction approaches, some apply + +a separation between marginal trajectory generation and interactive scoring [40, 42, 29]. For example, Luo et al. [29] initially produce a small set of marginal trajectories for each agent independently, before assigning a learned potential to each inter-agent trajectory pair through a belief propagation algorithm. Sun et al. [42] use a manual heuristic to tag agents as either influencers or reactors, and then pairs marginal and conditional predictions to form joint predictions. + +We also note that because these approaches do not explicitly model temporal dependencies within trajectories, their conditional forecasts may be more susceptible to spurious correlations, leading to less realistic reaction predictions. For example, these models can capture the correlation between a lead agent decelerating and a trailing agent decelerating, but may fail to infer which one is likely causing the other to slow down. In contrast, previous joint models employing an autoregressive factorization, e.g., [36, 43, 39], do respect future temporal dependencies. These models have generally relied on explicit latent variables for diversity, optimized via either an evidence lower bound or normalizing flow. + +In this work, we combine trajectory generation and interaction modeling in a single, temporally causal, decoding process over discrete motion tokens (Fig. 1), leveraging a simple training objective inspired by autoregressive language models. Our model, MotionLM, is trained to directly maximize the log probability of these token sequences among interacting agents. At inference time, joint trajectories are produced step-by-step, where interacting agents sample tokens simultaneously, attend to one another, and repeat. In contrast to previous approaches which manually enforce trajectory multimodality during training, our model is entirely latent variable and anchor-free, with multimodality emerging solely as a characteristic of sampling. MotionLM may be applied to several downstream behavior prediction tasks, including marginal, joint, and conditional predictions. + +This work makes the following contributions: + +1. We cast multi-agent motion forecasting as a language modeling task, introducing a temporally causal decoder over discrete motion tokens trained with a causal language modeling loss. +2. We pair sampling from our model with a simple rollout aggregation scheme that facilitates weighted mode identification for joint trajectories, establishing new state-of-the-art performance on the Waymo Open Motion Dataset interaction prediction challenge (6% improvement in the ranking joint mAP metric). +3. We perform extensive ablations of our approach as well as analysis of its temporally causal conditional + +predictions, which are largely unsupported by current joint forecasting models. + +# 2. Related work + +Marginal trajectory prediction. Behavior predictors are often evaluated on their predictions for individual agents, e.g., in recent motion forecasting benchmarks [14, 9, 4, 51, 37]. Previous methods process the rasterized scene with CNNs [8, 5, 12, 17]; the more recent works represent scenes with points and polygraphs and process them with GNNs [6, 25, 47, 22] or transformers [31, 40, 20]. To handle the multimodality of future trajectories, some models manually enforce diversity via predefined anchors [8, 5] or intention points [40, 52, 28]. Other works learn diverse modes with latent variable modeling, e.g., [24]. + +While these works produce multimodal future trajectories of individual agents, they only capture the marginal distributions of the possible agent futures and do not model the interactions among agents. + +Interactive trajectory prediction. Interactive behavior predictors model the joint distribution of agents' futures. This task has been far less studied than marginal motion prediction. For example, the Waymo Open Motion Dataset (WOMD) [14] challenge leaderboard currently has 71 published entries for marginal prediction compared to only 14 for interaction prediction. + +Ngiam et al. [32] models the distribution of future trajectories with a transformer-based mixture model outputting joint modes. To avoid the exponential blow-up from a full joint model, Luo et al. [29] models pairwise joint distributions. Tolstaya et al. [44], Song et al. [41], Sun et al. [42] consider conditional predictions by exposing the future trajectory of one agent when predicting for another agent. Shi et al. [40] derives joint probabilities by simply multiplying marginal trajectory probabilities, essentially treating agents as independent, which may limit accuracy. Cui et al. [11], Casas et al. [7], Girgis et al. [15] reduce the full-fledged joint distribution using global latent variables. Unlike our autoregressive factorization, the above models typically follow "one-shot" (parallel across time) factorizations and do not explicitly model temporally causal interactions. + +Autoregressive trajectory prediction. Autoregressive behavior predictors generate trajectories at intervals to produce scene-consistent multi-agent trajectories. Rhinehart et al. [36], Tang and Salakhutdinov [43], Amirloo et al. [1], Salzmann et al. [39], Yuan et al. [50] predict multiagent future trajectories using latent variable models. Lu et al. [27] explores autoregressively outputting keyframes via mixtures of Gaussians prior to filling in the remaining states. In [18], an adversarial objective is combined with + +![](images/a41468b22cc442b27e6d8808b538253d92d7d25c8ba77921ece7977dc072adc6.jpg) +Figure 2. MotionLM architecture. We first encode heterogeneous scene features relative to each modeled agent (left) as scene embeddings of shape $R, N, \cdot, H$ . Here, $R$ refers to the number of rollouts, $N$ refers to the number of (jointly modeled) agents, and $H$ is the dimensionality of each embedding. We repeat the embeddings $R$ times in the batch dimension for parallel sampling during inference. Next, a trajectory decoder autoregressively rolls out $T$ discrete motion tokens for multiple agents in a temporally causal manner (center). Finally, representative modes of the rollouts may be recovered via a simple aggregation utilizing k-means clustering initialized with non-maximum suppression (right). + +parallel beam search to learn multi-agent rollouts. Unlike most autoregressive trajectory predictors, our method does not rely on latent variables or beam search and generates multimodal joint trajectories by directly sampling from a learned distribution of discrete motion token sequences. + +Discrete sequence modeling in continuous domains. When generating sequences in continuous domains, one effective approach is to discretize the output space and predict categorical distributions at each step. + +For example, in image generation, PixelRNN [45] sequentially predicts the uniformly discretized pixel values for each channel and found this to perform better than outputting continuous values directly. Multiple works on generating images from text such as DALL-E [35] and Parti [49] use a two-stage process with a learned tokenizer to map images to discrete tokens and an autoregressive model to predict the discrete tokens given the text prompt. For audio generation, WaveNet [46] applies a $\mu$ -law transformation before discretizing. AudioLM [2] learns a hierarchical tokenizer/detokenizer, with the main transformer sequence model operating on the intermediate discrete tokens. When generating polygonal meshes, PolyGen [30] uniformly quantizes the coordinates of each vertex. In MotionLM, we employ a simple uniform quantization of axis-aligned deltas between consecutive waypoints of agent trajectories. + +# 3. MotionLM + +We aim to model a distribution over multi-agent interactions in a general manner that can be applied to distinct + +downstream tasks, including marginal, joint, and conditional forecasting. This requires an expressive generative framework capable of capturing the substantial multimodality in driving scenarios. In addition, we take consideration here to preserve temporal dependencies; i.e., inference in our model follows a directed acyclic graph with the parents of every node residing earlier in time and children residing later (Section 3.3, Fig. 4). This enables conditional forecasts that more closely resemble causal interventions [34] by eliminating certain spurious correlations that can otherwise result from disobeying temporal causality $^2$ . We observe that joint models that do not preserve temporal dependencies may have a limited ability to predict realistic agent reactions – a key use in planning (Section 4.6). To this end, we leverage an autoregressive factorization of our future decoder, where agents' motion tokens are conditionally dependent on all previously sampled tokens and trajectories are rolled out sequentially (Fig. 2). + +Let $S$ represent the input data for a given scenario. This may include context such as roadgraph elements, traffic light states, as well as features describing road agents (e.g., vehicles, cyclists, and pedestrians) and their recent histories, all provided at the current timestep $t = 0$ . Our task is to generate predictions for joint agent states $Y_{t} \doteq \{y_{t}^{1}, y_{t}^{2}, \dots, y_{t}^{N}\}$ for $N$ agents of interest at future timesteps $t = 1, \dots, T$ . Rather than complete states, these future state targets are typically two-dimensional waypoints (i.e., $(x, y)$ coordinates), with $T$ waypoints forming the full ground + +truth trajectory for an individual agent. + +# 3.1. Joint probabilistic rollouts + +In our modeling framework, we sample a predicted action for each target agent at each future timestep. These actions are formulated as discrete motion tokens from a finite vocabulary, as described later in Section 3.2.2. Let $a_{t}^{n}$ represent the target action (derived from the ground truth waypoints) for the $n$ th agent at time $t$ , with $A_{t} \doteq \{a_{t}^{1}, a_{t}^{2}, \dots, a_{t}^{N}\}$ representing the set of target actions for all agents at time $t$ . + +Factorization. We factorize the distribution over joint future action sequences as a product of conditionals: + +$$ +p _ {\theta} \left(A _ {1}, A _ {2}, \dots A _ {T} \mid S\right) = \prod_ {t = 1} ^ {T} p _ {\theta} \left(A _ {t} \mid A _ {< t}, S\right), \tag {1} +$$ + +$$ +p _ {\theta} \left(A _ {t} \mid A _ {< t}, S\right) = \prod_ {n = 1} ^ {N} p _ {\theta} \left(a _ {t} ^ {n} \mid A _ {< t}, S\right). \tag {2} +$$ + +Similar to [36, 43], Eq. (2) represents the fact that we treat agent actions as conditionally independent at time $t$ , given the previous actions and scene context. This aligns empirically with real-world driving over short time intervals; e.g., non-impaired human drivers generally require at least 500 ms to release the accelerator in response to a vehicle braking ahead ([13]). In our experiments, we find $2\mathrm{Hz}$ reactions to be sufficient to surpass state-of-the-art joint prediction models. + +We note that our model's factorization is entirely latent variable free; multimodal predictions stem purely from categorical token sampling at each rollout timestep. + +Training objective. MotionLM is formulated as a generative model trained to match the joint distribution of observed agent behavior. Specifically, we follow a maximum likelihood objective over multi-agent action sequences: + +$$ +\underset {\theta} {\arg \max } \prod_ {t = 1} ^ {T} p _ {\theta} \left(A _ {t} \mid A _ {< t}, S\right) \tag {3} +$$ + +Similar to the typical training setup of modern language models, we utilize "teacher-forcing" where previous ground truth (not predicted) tokens are provided at each timestep, which tends to increase stability and avoids sampling during training. We note that this applies to all target agents; in training, each target agent is exposed to ground truth action sequence prefixes for all target agents prior to the current timestep. This naturally allows for temporal parallelization when using modern attention-based architectures such as transformers [48]. + +Our model is subject to the same theoretical limitations as general imitation learning frameworks (e.g., compounding error [38] and self-delusions due to unobserved confounders [33]). However, we find that, in practice, these do not prevent strong performance on forecasting tasks. + +# 3.2. Model implementation + +Our model consists of two main networks, an encoder which processes initial scene elements followed by a trajectory decoder which performs both cross-attention to the scene encodings and self-attention along agent motion tokens, following a transformer architecture [48]. + +# 3.2.1 Scene encoder + +The scene encoder (Fig. 2, left) is tasked with processing information from several input modalities, including the roadgraph, traffic light states, and history of surrounding agents' trajectories. Here, we follow the design of the early fusion network proposed by [31] as the scene encoding backbone of our model. Early fusion is particularly chosen because of its flexibility to process all modalities together with minimal inductive bias. + +The features above are extracted with respect to each modeled agent's frame of reference. Input tensors are then fed to a stack of self-attention layers that exchange information across all past timesteps and agents. In the first layer, latent queries cross-attend to the original inputs in order to reduce the set of vectors being processed to a manageable number, similar to [23, 19]. For additional details, see [31]. + +# 3.2.2 Joint trajectory decoder + +Our trajectory decoder (Fig. 2, center) is tasked with generating sequences of motion tokens for multiple agents. + +Discrete motion tokens. We elect to transform trajectories comprised of continuous waypoints into sequences of discrete tokens. This enables treating sampling purely as a classification task at each timestep, implemented via a standard softmax layer. Discretizing continuous targets in this manner has proven effective in other inherently continuous domains, e.g., in audio generation [46] and mesh generation [30]. We suspect that discrete motion tokens also naturally hide some precision from the model, possibly mitigating compounding error effects that could arise from imperfect continuous value prediction. Likewise, we did not find it necessary to manually add any noise to the ground truth teacher-forced trajectories (e.g., as is done in [26]). + +Quantization. To extract target discrete tokens, we begin by normalizing each agent's ground truth trajectory with respect to the position and heading of the agent at + +![](images/825f2e3eea580053724ae5ba734bb572c136be5787218e1cdf276818fc7dc63f.jpg) +Figure 3. Displayed are the top two predicted joint rollout modes for three WOMD scenes. Color gradients indicate time progression from $t = 0$ s to $t = 8$ s, with the greatest probability joint mode transitioning from green to blue and the secondary joint mode transitioning from orange to purple. Three types of interactions are observed: an agent in the adjacent lane yields to the lane-changing agent according to the timing of the lane change (left), a pedestrian walks behind the passing vehicle according to the progress of the vehicle (center), the turning vehicle either yields to the crossing cyclist (most probable mode) or turns before the cyclist approaches (secondary mode) (right). + +![](images/17023df7ab3c8a02381296e44f456955ea9c79a3de882c2d31d62dade7b65a42.jpg) + +![](images/5c55cb2f881611c58d043dbccfc9f04f81e13abca2cf873cfcee9971085385ea.jpg) + +time $t = 0$ of the scenario. We then parameterize a uniformly quantized $(\Delta x, \Delta y)$ vocabulary according to a total number of per-coordinate bins as well as maximum and minimum delta values. A continuous, single-coordinate delta action can then be mapped to a corresponding index $\in [0, \text{num\_bins} - 1]$ , resulting in two indices for a complete $(\Delta x, \Delta y)$ action per step. In order to extract actions that accurately reconstruct an entire trajectory, we employ a greedy search, sequentially selecting the quantized actions that reconstruct the next waypoint coordinates with minimum error. + +We wrap the delta actions with a "Verlet" step where a zero action indicates that the same delta index should be used as the previous step (as [36] does for continuous states). As agent velocities tend to change smoothly between consecutive timesteps, this helps reduce the total vocabulary size, simplifying the dynamics of training. Finally, to maintain only $T$ sequential predictions, we collapse the per-coordinate actions to a single integer indexing into their Cartesian product. In practice, for the models presented here, we use 13 tokens per coordinate with $13^2 = 169$ total discrete tokens available in the vocabulary (see Appendix A for further details). + +We compute a learned value embedding and two learned positional embeddings (representing the timestep and agent identity) for each discrete motion token, which are combined via an element-wise sum prior to being input to the transformer decoder. + +Flattened agent-time self-attention. We elect to include a single self-attention mechanism in the decoder that operates along flattened sequences of all modeled agents' motion tokens over time. So, given a target sequence of length + +$T$ for each of $N$ agents, we perform self-attention over $NT$ elements. While this does mean that these self-attended sequences grow linearly in the number of jointly modeled agents, we note that the absolute sequence length here is still quite small (length 32 for the WOMD interactive split -8 sec. prediction at $2\mathrm{Hz}$ for 2 agents). Separate passes of factorized agent and time attention are also possible [32], but we use a single pass here for simplicity. + +Ego agent reference frames. To facilitate cross-attention to the agent-centric feature encodings (Section 3.2.1), we represent the flattened token sequence once for each modeled agent. Each modeled agent is treated as the "ego" agent once, and cross-attention is performed on that agent's scene features. Collapsing the ego agents into the batch dimension allows parallelization during training and inference. + +# 3.3. Enforcing temporal causality + +Our autoregressive factorization naturally respects temporal dependencies during joint rollouts; motion token sampling for any particular agent is affected only by past tokens (from any agent) and unaffected by future ones. When training, we require a mask to ensure that the self-attention operation only updates representations at each step accordingly. As shown in Fig. 8 (appendix), this attention mask exhibits a blocked, staircase pattern, exposing all agents to each other's histories only up to the preceding step. + +Temporally causal conditioning. As described earlier, a particular benefit of this factorization is the ability to query for temporally causal conditional rollouts (Fig. 4). In this setting, we fix a query agent to take some sequence of actions and only roll out the other agents. + +![](images/d139ce0bf2cadfa28a152bd716bd38ecc6ed7ac2c5cd973060b1e659f1d31d6d.jpg) +(a) Causal Bayesian Network for joint rollouts. + +![](images/a7518889e1038dfa6c45c2e9ebdf67015b6a0eec2fb04a570ccaa697650b1d83.jpg) +Figure 4. A Causal Bayesian network representation for joint rollouts (left), post-intervention Causal Bayesian network (center), and acausal conditioning (right). Solid lines indicate temporally causal dependencies while dashed lines indicate acausal information flow. Models without temporal dependency constraints will support acausal conditioning but not temporally causal conditioning, which can be problematic when attempting to predict agent reactions. + +![](images/1037b27a97bf341aaddab4db5f3ffb2acdb06aaf6007c7f70a564a3860973c08.jpg) +(b) Post-Intervention Causal Bayesian Network. +Conditioned Agent Causal conditioning Sampling Agent Acausal conditioning +(c) Acausal conditioning. + +We may view this as an approximation of computing causal interventions [34] in the absence of confounders; interventions cannot be learned purely through observational data in general (due to the possible presence of unobserved confounders), but our model's factorization at least eliminates certain spurious correlations arising from breaking temporal causality. + +In Fig. 4 (a), we show an example of a Causal Bayesian network governing joint rollouts. Applying an intervention to nodes $x = 1, \ldots, T$ , by deleting their incoming edges, results in a post-intervention Bayesian network depicted in Fig. 4 (b), which obeys temporal causality. On the other hand, acausal conditioning (Fig. 4 (c)) results in non-causal information flow, where node $x = i$ affects our belief about node $y = j$ for $i \geq j$ . + +# 3.4. Rollout aggregation + +Joint motion forecasting benchmark tasks like WOMD [14] require a compact representation of the joint future distribution in the form of a small number of joint "modes". Each mode is assigned a probability and might correspond to a specific homotopic outcome (e.g., pass/yield) or more subtle differences in speed/geometry. Here, we aggregate rollouts to achieve two primary goals: 1) uncover the underlying modes of the distribution and 2) estimate the probability of each mode. Specifically, we follow the non-maximum suppression (NMS) aggregation scheme described in [47], but extend it to the joint setting by ensuring that all agent predictions reside within a given distance threshold to the corresponding cluster. In addition, we leverage model ensembling to account for epistemic uncertainty and further improve the quality of the predictions, combining rollouts from independently trained replicas prior to the aggregation step. + +# 4. Experiments + +We evaluate MotionLM on marginal and joint motion forecasting benchmarks, examine its conditional predic + +tions and conduct ablations of our modeling choices. + +# 4.1. Datasets + +Waymo Open Motion Dataset (WOMD). WOMD [14] is a collection of 103k 20-second scenarios collected from real-world driving in urban and suburban environments. Segments are divided into 1.1M examples consisting of 9-second windows of interest, where the first second serves as input context and the remaining 8-seconds are the prediction target. Map features such as traffic signal states and lane features are provided along with agent states such as position, velocity, acceleration, and bounding boxes. + +Marginal and interactive prediction challenges. For the marginal prediction challenge, six trajectories must be output by the model for each target agent, along with likelihoods of each mode. For the interactive challenge, two interacting agents are labeled in each test example. In this case, the model must output six weighted joint trajectories. + +# 4.2. Metrics + +The primary evaluation metrics for the marginal and interactive prediction challenges are soft mAP and mAP, respectively, with miss rate as the secondary metric. Distance metrics minADE and minFDE provide additional signal on prediction quality. For the interactive prediction challenge, these metrics refer to scene-level joint calculations. We also use a custom prediction overlap metric (similar to [29]) to assess scene-level consistency for joint models. See Appendix C for details on these metrics. + +# 4.3. Model configuration + +We experiment with up to 8 model replicas and 512 rollouts per replica, assessing performance at various configurations. For complete action space and model hyperparameter details, see Appendices A and B. + +
ModelminADE (↓)minFDE (↓)Miss Rate (↓)Soft mAP (↑)
HDGT [20]0.76761.10770.13250.3709
MPA [22]0.59131.25070.16030.3930
MTR [40]0.60501.22070.13510.4216
Wayformer factorized [31]0.54471.12550.12290.4260
Wayformer multi-axis [31]0.54541.12800.12280.4335
MTR-A [40]0.56401.13440.11600.4594
MotionLM (Ours)0.55091.11990.10580.4507
+ +Table 1. Marginal prediction performance on WOMD test set. We display metrics averaged over time steps (3, 5, and 8 seconds) and agent types (vehicles, pedestrians, and cyclists). Greyed columns indicate the official ranking metrics for the marginal prediction challenge. + +
ModelminADE (↓)minFDE (↓)Miss Rate (↓)mAP (↑)
SceneTransformer (J) [32]0.97742.18920.49420.1192
M2I [42]1.35062.83250.55380.1239
DenseTNT [28]1.14172.49040.53500.1647
MTR [40]0.91812.06330.44110.2037
JFP [29]0.88171.99050.42330.2050
MotionLM (Ours)0.89112.00670.41150.2178
+ +# 4.4. Quantitative results + +Marginal motion prediction. As shown in Table 1, our model is competitive with the state-of-the-art on WOMD marginal motion prediction (independent per agent). For the main ranking metric of soft mAP, our model ranks second, less than $2\%$ behind the score achieved by MTRA [40]. In addition, our model attains a substantially improved miss rate over all prior works, with a relative $9\%$ reduction compared to the previous state-of-the-art. The autoregressive rollouts are able to adequately capture the diversity of multimodal future behavior without reliance on trajectory anchors [8] or static intention points [40]. + +Interactive motion prediction. Our model achieves state-of-the-art results for the interactive prediction challenge on WOMD, attaining a $6\%$ relative improvement in mAP and $3\%$ relative improvement in miss rate (the two official ranking metrics) over the previous top scoring entry, JFP [29] (see Table 2). In contrast to JFP, our approach does not score pairs of previously constructed marginal trajectories, but generates joint rollouts directly. Fig. 3 displays example interactions predicted by our model. + +Table 3 displays prediction overlap rates for various models on the WOMD interactive test and validation sets (see metric details in Appendix C.2). We obtain test set predictions from the authors of [14, 32, 29]. MotionLM obtains the lowest prediction overlap rate, an indication of scene-consistent predictions. In addition, on the validation set we evaluate two versions of our model: marginal and joint. The marginal version does not perform attention + +Table 2. Joint prediction performance on WOMD interactive test set. We display scene-level joint metrics averaged over time steps (3, 5, and 8 seconds) and agent types (vehicles, pedestrians, and cyclists). Greyed columns indicate the official ranking metrics for the challenge. + +
ModelPrediction Overlap (↓)
TestLSTM Baseline [14]0.07462
Scene Transformer [32]0.04336
JFP [29]0.02671
MotionLM (joint)0.02607
ValMotionLM (marginal)0.0404
MotionLM (joint)0.0292
+ +Table 3. Prediction overlap rates. Displayed is the custom prediction overlap metric for various model configurations on the WOMD interactive test and validation sets. + +across the modeled agents during both training and inference rollouts, while the joint version performs $2\mathrm{Hz}$ interactive attention. We see that the marginal version obtains a relative $38\%$ higher overlap rate than the joint version. The interactive attention in the joint model allows the agents to more appropriately react to one another. + +# 4.5. Ablation studies + +Interactive attention frequency. To assess the importance of inter-agent reactivity during the joint rollouts, we vary the frequency of the interactive attention operation while keeping other architecture details constant. For our leaderboard results, we utilize the greatest frequency studied here, $2\mathrm{Hz}$ . At the low end of the spectrum, $0.125\mathrm{Hz}$ corresponds to the agents only observing each other's initial states, and then proceeding with the entire 8-second rollout without communicating again (i.e., marginal rollouts). + +Performance metrics generally improve as agents are + +![](images/1603d7a263732570002c2c9a908ead158fc348f3ee8c1b1551d8dea126a6e3c5.jpg) +No interactive attention + +![](images/62e8a5a680bde6e45f9066bf87e75648ae9823fa9cc92b31d0c48eb66a6caac4.jpg) +16 interaction iterations + +![](images/967ce5807cfabf79b007a3ef42e0d971a5cc74838c73719949d8179a16e74a6d.jpg) +Figure 5. Visualization of the top joint rollout mode at the two extremes of the interactive attention frequencies studied here. With no interactive attention (left), the two modeled agents only attend to each other once at the beginning of the 8-second rollout and never again, in contrast to 16 total times for $2\mathrm{Hz}$ attention (right). The independent rollouts resulting from zero interactive attention can result in scene-inconsistent overlap; e.g., a turning vehicle fails to accommodate a crossing pedestrian (top left) or yield appropriately to a crossing vehicle (bottom left). + +![](images/f26e8aeb300c2e192442d7519aa5c314e13286e76d33025f2debdd0eb3cc0bd6.jpg) + +permitted to interact more frequently (Fig. 6 top, Table 5 in appendix). Greater interactive attention frequencies not only lead to more accurate joint predictions, but also reduce implausible overlaps (i.e., collisions) between different agents' predictions. Fig. 5 displays examples where the marginal predictions lead to implausible overlap between agents while the joint predictions lead to appropriately separated trajectories. See supplementary for animated visualizations. + +Number of rollouts. Our rollout aggregation requires that we generate a sufficient number of samples from the model in order to faithfully represent the multimodal future distribution. For this ablation, we vary the number of rollouts generated, but always cluster down to $k = 6$ modes for evaluation. In general, we see performance metrics improve as additional rollouts are utilized (Fig. 6, bottom and Table 6 in appendix). For our final leaderboard results, we use 512 rollouts per replica, although 32 rollouts is sufficient to surpass the previous top entry on joint mAP. + +![](images/f861862b8e0a966fec108e02259991179672888705f012750157cc619bf2c9ac.jpg) + +![](images/3bfb396ac9a6e06e72e769d5728758305b233227034c6ddf9acf81c7f569c492.jpg) +Figure 6. Joint prediction performance across varying interactive attention frequencies (top) and numbers of rollouts per replica (bottom) on the WOMD interactive validation set. Vertical axes display joint (scene-level) metrics for an 8-replica ensemble. See Tables 5 and 6 in the appendix for full parameter ranges and metrics. + +# 4.6. Conditional rollouts + +As described in Section 3.3, our model naturally supports "temporally causal" conditioning, similarly to previous autoregressive efforts such as [36, 43]. In this setting, we fix one query agent to follow a specified trajectory and stochastically roll out the target agent. However, we can also modify the model to leak the query agent's full trajectory, acausally exposing its future to the target agent during conditioning. This resembles the approach to conditional prediction in, e.g., [44], where this acausal conditional distribution is modeled directly, or [29], where this distribution is accessed via inference in an energy-based model. + +Here, we assess predictions from our model across three settings: marginal, temporally causal conditional, and acausal conditional (Fig. 4). Quantitatively, we observe that both types of conditioning lead to more accurate predictions for the target agent (Table 4, Fig. 7). Additionally, we see that acausal conditioning leads to greater improvement than temporally causal conditioning relative to marginal predictions across all metrics, e.g., $8.2\%$ increase in soft mAP for acausal vs. $3.7\%$ increase for temporally causal. + +
Prediction settingminADE (↓)minFDE (↓)Miss Rate (↓)Soft mAP (↑)
Marginal0.60691.22360.14060.3951
Temporally causal conditional0.59971.20340.13770.4096
Acausal conditional0.58991.18040.13380.4274
+ +Table 4. Conditional prediction performance. Displayed are marginal (single-agent) metrics across three prediction settings for our model on the WOMD interactive validation set: marginal, temporally causal conditional, and acausal conditional. + +Intuitively, the greater improvement for acausal conditioning makes sense as it exposes more information to the model. However, the better quantitative scores are largely due to predictions that would be deemed nonsensical if interpreted as predicted reactions to the query agent. + +This can be illustrated in examples where one agent is following another, where typically the lead agent's behavior is causing the trailing agent's reaction, and not vice versa, but this directionality would not be captured with acausal conditioning. This temporally causal modeling is especially important when utilizing the conditional predictions to evaluate safety for an autonomous vehicle's proposed plans. In a scenario where an autonomous vehicle (AV) is stopped behind another agent, planning to move forward into the other agent's current position could be viewed as a safe maneuver with acausal conditioning, as the other agent also moving forward is correlated with (but not caused by) the AV proceeding. However, it is typically the lead agent moving forward that causes the trailing AV to proceed, and the AV moving forward on its own would simply rear-end the lead agent. + +In the supplementary, we compare examples of predictions in various scenarios for the causal and acausal conditioning schemes. Models that ignore temporal dependencies during conditioning (e.g., [44, 29]) may succumb to the same incorrect reasoning that the acausal version of our model does. + +# 5. Conclusion and future work + +In this work, we introduced a method for interactive motion forecasting leveraging multi-agent rollouts over discrete motion tokens, capturing the joint distribution over multimodal futures. The proposed model establishes new state-of-the-art performance on the WOMD interactive prediction challenge. + +Avenues for future work include leveraging the trained model in model-based planning frameworks, allowing a search tree to be formed over the multi-agent action rollouts, or learning amortized value functions from large datasets of scene rollouts. In addition, we plan to explore distillation strategies from large autoregressive teachers, enabling faster student models to be deployed in latency-critical settings. + +![](images/773e7c793696df82720c67d8f67dd99c02aff38e49b7b83b51005341d0a8505c.jpg) +Figure 7. Visualization of the most likely predicted future for the pedestrian in the marginal setting (left) and temporally causal conditional setting (right). When considering the pedestrian independently, the model assigns greatest probability to a trajectory which crosses the road. When conditioned on the vehicle's ground truth turn (magenta), the pedestrian is instead predicted to yield. + +![](images/83624c9647b22b52ddd04e4c9bce8713bb0a5907030f64ca897cccc0a5e997ac.jpg) + +Acknowledgements. We would like to thank David Weiss, Paul Covington, Ashish Venugopal, Piotr Fidkowski, and Minfa Wang for discussions on autoregressive behavior predictors; Cole Gulino and Brandyn White for advising on interactive modeling; Cheol Park, Wenjie Luo, and Scott Ettinger for assistance with evaluation; Drago Anguelov, Kyriacos Shiarlis, and anonymous reviewers for helpful feedback on the manuscript. + +# References + +[1] Elmira Amirloo, Amir Rasouli, Peter Lakner, Mohsen Rohani, and Jun Luo. LatentFormer: Multi-agent transformer-based interaction modeling and trajectory prediction, 2022. +[2] Zalán Borsos, Raphaël Marinier, Damien Vincent, Eugene Kharitonov, Olivier Pietquin, Matt Sharifi, Dominik Roblek, Olivier Teboul, David Grangier, Marco Tagliasacchi, and Neil Zeghidour. 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Interaction dataset: An international, adversarial and cooperative motion dataset in interactive driving scenarios with semantic maps. arXiv preprint arXiv:1910.03088, 2019. +[52] Hang Zhao, Jiyang Gao, Tian Lan, Chen Sun, Ben Sapp, Balakrishnan Varadarajan, Yue Shen, Yi Shen, Yuning Chai, Cordelia Schmid, et al. Tnt: Target-driven trajectory prediction. In Conference on Robot Learning, pages 895-904. 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Refaat Rami Al-Rfou Benjamin Sapp" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 276, + 198, + 317, + 211 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 198, + 317, + 211 + ], + "spans": [ + { + "bbox": [ + 276, + 198, + 317, + 211 + ], + "type": "text", + "content": "Waymo" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 259, + 192, + 272 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 259, + 192, + 272 + ], + "spans": [ + { + "bbox": [ + 143, + 259, + 192, + 272 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 284, + 290, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 284, + 290, + 523 + ], + "spans": [ + { + "bbox": [ + 46, + 284, + 290, + 523 + ], + "type": "text", + "content": "Reliable forecasting of the future behavior of road agents is a critical component to safe planning in autonomous vehicles. Here, we represent continuous trajectories as sequences of discrete motion tokens and cast multi-agent motion prediction as a language modeling task over this domain. Our model, MotionLM, provides several advantages: First, it does not require anchors or explicit latent variable optimization to learn multimodal distributions. Instead, we leverage a single standard language modeling objective, maximizing the average log probability over sequence tokens. Second, our approach bypasses post-hoc interaction heuristics where individual agent trajectory generation is conducted prior to interactive scoring. Instead, MotionLM produces joint distributions over interactive agent futures in a single autoregressive decoding process. In addition, the model's sequential factorization enables temporally causal conditional rollouts. The proposed approach establishes new state-of-the-art performance for multi-agent motion prediction on the Waymo Open Motion Dataset, ranking " + }, + { + "bbox": [ + 46, + 284, + 290, + 523 + ], + "type": "inline_equation", + "content": "1^{st}" + }, + { + "bbox": [ + 46, + 284, + 290, + 523 + ], + "type": "text", + "content": " on the interactive challenge leaderboard." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 546, + 128, + 558 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 546, + 128, + 558 + ], + "spans": [ + { + "bbox": [ + 47, + 546, + 128, + 558 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 566, + 287, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 566, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 566, + 287, + 685 + ], + "type": "text", + "content": "Modern sequence models often employ a next-token prediction objective that incorporates minimal domain-specific assumptions. For example, autoregressive language models [3, 10] are pre-trained to maximize the probability of the next observed subword conditioned on the previous text; there is no predefined notion of parsing or syntax built in. This approach has found success in continuous domains as well, such as audio [2] and image generation [49]. Leveraging the flexibility of arbitrary categorical distributions, the above works represent continuous data with a set of discrete" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 312, + 245, + 541, + 414 + ], + "blocks": [ + { + "bbox": [ + 312, + 245, + 541, + 414 + ], + "lines": [ + { + "bbox": [ + 312, + 245, + 541, + 414 + ], + "spans": [ + { + "bbox": [ + 312, + 245, + 541, + 414 + ], + "type": "image", + "image_path": "f1f8c965e8223d171350c5c2f689a74abcf109088486c245c461b2530d073257.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 422, + 545, + 456 + ], + "lines": [ + { + "bbox": [ + 305, + 422, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 305, + 422, + 545, + 456 + ], + "type": "text", + "content": "Figure 1. Our model autoregressively generates sequences of discrete motion tokens for a set of agents to produce consistent interactive trajectory forecasts." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 481, + 518, + 493 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 481, + 518, + 493 + ], + "spans": [ + { + "bbox": [ + 306, + 481, + 518, + 493 + ], + "type": "text", + "content": "tokens, reminiscent of language model vocabularies." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 495, + 545, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 545, + 602 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 545, + 602 + ], + "type": "text", + "content": "In driving scenarios, road users may be likened to participants in a constant dialogue, continuously exchanging a dynamic series of actions and reactions mirroring the fluidity and complexity of communication. Navigating this rich web of interactions requires the ability to anticipate the likely maneuvers and responses of the involved actors. Just as today's language models can capture sophisticated distributions over conversations, can we leverage similar sequence models to forecast the behavior of road agents?" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 604, + 545, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 604, + 545, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 604, + 545, + 700 + ], + "type": "text", + "content": "A common simplification to modeling the full future world state has been to decompose the joint distribution of agent behavior into independent per-agent marginal distributions. Although there has been much progress on this task [8, 47, 12, 25, 31, 5, 6, 21], marginal predictions are insufficient as inputs to a planning system; they do not represent the future dependencies between the actions of different agents, leading to inconsistent scene-level forecasting." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "content": "Of the existing joint prediction approaches, some apply" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 57, + 693, + 217, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 693, + 217, + 713 + ], + "spans": [ + { + "bbox": [ + 57, + 693, + 217, + 713 + ], + "type": "text", + "content": "*Work done during an internship at Waymo. Contact: {aseff,bensapp}@waymo.com" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8579" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 178 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 178 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 178 + ], + "type": "text", + "content": "a separation between marginal trajectory generation and interactive scoring [40, 42, 29]. For example, Luo et al. [29] initially produce a small set of marginal trajectories for each agent independently, before assigning a learned potential to each inter-agent trajectory pair through a belief propagation algorithm. Sun et al. [42] use a manual heuristic to tag agents as either influencers or reactors, and then pairs marginal and conditional predictions to form joint predictions." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 180, + 288, + 335 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 180, + 288, + 335 + ], + "spans": [ + { + "bbox": [ + 46, + 180, + 288, + 335 + ], + "type": "text", + "content": "We also note that because these approaches do not explicitly model temporal dependencies within trajectories, their conditional forecasts may be more susceptible to spurious correlations, leading to less realistic reaction predictions. For example, these models can capture the correlation between a lead agent decelerating and a trailing agent decelerating, but may fail to infer which one is likely causing the other to slow down. In contrast, previous joint models employing an autoregressive factorization, e.g., [36, 43, 39], do respect future temporal dependencies. These models have generally relied on explicit latent variables for diversity, optimized via either an evidence lower bound or normalizing flow." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 336, + 288, + 527 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 336, + 288, + 527 + ], + "spans": [ + { + "bbox": [ + 46, + 336, + 288, + 527 + ], + "type": "text", + "content": "In this work, we combine trajectory generation and interaction modeling in a single, temporally causal, decoding process over discrete motion tokens (Fig. 1), leveraging a simple training objective inspired by autoregressive language models. Our model, MotionLM, is trained to directly maximize the log probability of these token sequences among interacting agents. At inference time, joint trajectories are produced step-by-step, where interacting agents sample tokens simultaneously, attend to one another, and repeat. In contrast to previous approaches which manually enforce trajectory multimodality during training, our model is entirely latent variable and anchor-free, with multimodality emerging solely as a characteristic of sampling. MotionLM may be applied to several downstream behavior prediction tasks, including marginal, joint, and conditional predictions." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 529, + 244, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 529, + 244, + 540 + ], + "spans": [ + { + "bbox": [ + 59, + 529, + 244, + 540 + ], + "type": "text", + "content": "This work makes the following contributions:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 54, + 550, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 55, + 550, + 287, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 550, + 287, + 597 + ], + "spans": [ + { + "bbox": [ + 55, + 550, + 287, + 597 + ], + "type": "text", + "content": "1. We cast multi-agent motion forecasting as a language modeling task, introducing a temporally causal decoder over discrete motion tokens trained with a causal language modeling loss." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 54, + 608, + 287, + 679 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 608, + 287, + 679 + ], + "spans": [ + { + "bbox": [ + 54, + 608, + 287, + 679 + ], + "type": "text", + "content": "2. We pair sampling from our model with a simple rollout aggregation scheme that facilitates weighted mode identification for joint trajectories, establishing new state-of-the-art performance on the Waymo Open Motion Dataset interaction prediction challenge (6% improvement in the ranking joint mAP metric)." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 54, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 54, + 689, + 287, + 713 + ], + "type": "text", + "content": "3. We perform extensive ablations of our approach as well as analysis of its temporally causal conditional" + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 324, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 324, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 324, + 72, + 545, + 96 + ], + "type": "text", + "content": "predictions, which are largely unsupported by current joint forecasting models." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 108, + 390, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 108, + 390, + 121 + ], + "spans": [ + { + "bbox": [ + 306, + 108, + 390, + 121 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 129, + 545, + 260 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 129, + 545, + 260 + ], + "spans": [ + { + "bbox": [ + 304, + 129, + 545, + 260 + ], + "type": "text", + "content": "Marginal trajectory prediction. Behavior predictors are often evaluated on their predictions for individual agents, e.g., in recent motion forecasting benchmarks [14, 9, 4, 51, 37]. Previous methods process the rasterized scene with CNNs [8, 5, 12, 17]; the more recent works represent scenes with points and polygraphs and process them with GNNs [6, 25, 47, 22] or transformers [31, 40, 20]. To handle the multimodality of future trajectories, some models manually enforce diversity via predefined anchors [8, 5] or intention points [40, 52, 28]. Other works learn diverse modes with latent variable modeling, e.g., [24]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 261, + 545, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 261, + 545, + 308 + ], + "spans": [ + { + "bbox": [ + 304, + 261, + 545, + 308 + ], + "type": "text", + "content": "While these works produce multimodal future trajectories of individual agents, they only capture the marginal distributions of the possible agent futures and do not model the interactions among agents." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 326, + 545, + 409 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 326, + 545, + 409 + ], + "spans": [ + { + "bbox": [ + 304, + 326, + 545, + 409 + ], + "type": "text", + "content": "Interactive trajectory prediction. Interactive behavior predictors model the joint distribution of agents' futures. This task has been far less studied than marginal motion prediction. For example, the Waymo Open Motion Dataset (WOMD) [14] challenge leaderboard currently has 71 published entries for marginal prediction compared to only 14 for interaction prediction." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 410, + 545, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 410, + 545, + 589 + ], + "spans": [ + { + "bbox": [ + 304, + 410, + 545, + 589 + ], + "type": "text", + "content": "Ngiam et al. [32] models the distribution of future trajectories with a transformer-based mixture model outputting joint modes. To avoid the exponential blow-up from a full joint model, Luo et al. [29] models pairwise joint distributions. Tolstaya et al. [44], Song et al. [41], Sun et al. [42] consider conditional predictions by exposing the future trajectory of one agent when predicting for another agent. Shi et al. [40] derives joint probabilities by simply multiplying marginal trajectory probabilities, essentially treating agents as independent, which may limit accuracy. Cui et al. [11], Casas et al. [7], Girgis et al. [15] reduce the full-fledged joint distribution using global latent variables. Unlike our autoregressive factorization, the above models typically follow \"one-shot\" (parallel across time) factorizations and do not explicitly model temporally causal interactions." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Autoregressive trajectory prediction. Autoregressive behavior predictors generate trajectories at intervals to produce scene-consistent multi-agent trajectories. Rhinehart et al. [36], Tang and Salakhutdinov [43], Amirloo et al. [1], Salzmann et al. [39], Yuan et al. [50] predict multiagent future trajectories using latent variable models. Lu et al. [27] explores autoregressively outputting keyframes via mixtures of Gaussians prior to filling in the remaining states. In [18], an adversarial objective is combined with" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8580" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 76, + 532, + 218 + ], + "blocks": [ + { + "bbox": [ + 53, + 76, + 532, + 218 + ], + "lines": [ + { + "bbox": [ + 53, + 76, + 532, + 218 + ], + "spans": [ + { + "bbox": [ + 53, + 76, + 532, + 218 + ], + "type": "image", + "image_path": "a41468b22cc442b27e6d8808b538253d92d7d25c8ba77921ece7977dc072adc6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "lines": [ + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "spans": [ + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "text", + "content": "Figure 2. MotionLM architecture. We first encode heterogeneous scene features relative to each modeled agent (left) as scene embeddings of shape " + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "inline_equation", + "content": "R, N, \\cdot, H" + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "text", + "content": ". Here, " + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "inline_equation", + "content": "R" + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "text", + "content": " refers to the number of rollouts, " + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "text", + "content": " refers to the number of (jointly modeled) agents, and " + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "text", + "content": " is the dimensionality of each embedding. We repeat the embeddings " + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "inline_equation", + "content": "R" + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "text", + "content": " times in the batch dimension for parallel sampling during inference. Next, a trajectory decoder autoregressively rolls out " + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 236, + 548, + 304 + ], + "type": "text", + "content": " discrete motion tokens for multiple agents in a temporally causal manner (center). Finally, representative modes of the rollouts may be recovered via a simple aggregation utilizing k-means clustering initialized with non-maximum suppression (right)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 323, + 288, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 323, + 288, + 384 + ], + "spans": [ + { + "bbox": [ + 46, + 323, + 288, + 384 + ], + "type": "text", + "content": "parallel beam search to learn multi-agent rollouts. Unlike most autoregressive trajectory predictors, our method does not rely on latent variables or beam search and generates multimodal joint trajectories by directly sampling from a learned distribution of discrete motion token sequences." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 403, + 287, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 403, + 287, + 450 + ], + "spans": [ + { + "bbox": [ + 46, + 403, + 287, + 450 + ], + "type": "text", + "content": "Discrete sequence modeling in continuous domains. When generating sequences in continuous domains, one effective approach is to discretize the output space and predict categorical distributions at each step." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 452, + 288, + 656 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 452, + 288, + 656 + ], + "spans": [ + { + "bbox": [ + 46, + 452, + 288, + 656 + ], + "type": "text", + "content": "For example, in image generation, PixelRNN [45] sequentially predicts the uniformly discretized pixel values for each channel and found this to perform better than outputting continuous values directly. Multiple works on generating images from text such as DALL-E [35] and Parti [49] use a two-stage process with a learned tokenizer to map images to discrete tokens and an autoregressive model to predict the discrete tokens given the text prompt. For audio generation, WaveNet [46] applies a " + }, + { + "bbox": [ + 46, + 452, + 288, + 656 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 46, + 452, + 288, + 656 + ], + "type": "text", + "content": "-law transformation before discretizing. AudioLM [2] learns a hierarchical tokenizer/detokenizer, with the main transformer sequence model operating on the intermediate discrete tokens. When generating polygonal meshes, PolyGen [30] uniformly quantizes the coordinates of each vertex. In MotionLM, we employ a simple uniform quantization of axis-aligned deltas between consecutive waypoints of agent trajectories." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 669, + 119, + 681 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 669, + 119, + 681 + ], + "spans": [ + { + "bbox": [ + 47, + 669, + 119, + 681 + ], + "type": "text", + "content": "3. MotionLM" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": "We aim to model a distribution over multi-agent interactions in a general manner that can be applied to distinct" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 323, + 545, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 323, + 545, + 538 + ], + "spans": [ + { + "bbox": [ + 304, + 323, + 545, + 538 + ], + "type": "text", + "content": "downstream tasks, including marginal, joint, and conditional forecasting. This requires an expressive generative framework capable of capturing the substantial multimodality in driving scenarios. In addition, we take consideration here to preserve temporal dependencies; i.e., inference in our model follows a directed acyclic graph with the parents of every node residing earlier in time and children residing later (Section 3.3, Fig. 4). This enables conditional forecasts that more closely resemble causal interventions [34] by eliminating certain spurious correlations that can otherwise result from disobeying temporal causality" + }, + { + "bbox": [ + 304, + 323, + 545, + 538 + ], + "type": "inline_equation", + "content": "^2" + }, + { + "bbox": [ + 304, + 323, + 545, + 538 + ], + "type": "text", + "content": ". We observe that joint models that do not preserve temporal dependencies may have a limited ability to predict realistic agent reactions – a key use in planning (Section 4.6). To this end, we leverage an autoregressive factorization of our future decoder, where agents' motion tokens are conditionally dependent on all previously sampled tokens and trajectories are rolled out sequentially (Fig. 2)." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "spans": [ + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "content": " represent the input data for a given scenario. This may include context such as roadgraph elements, traffic light states, as well as features describing road agents (e.g., vehicles, cyclists, and pedestrians) and their recent histories, all provided at the current timestep " + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "inline_equation", + "content": "t = 0" + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "content": ". Our task is to generate predictions for joint agent states " + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "inline_equation", + "content": "Y_{t} \\doteq \\{y_{t}^{1}, y_{t}^{2}, \\dots, y_{t}^{N}\\}" + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "content": " agents of interest at future timesteps " + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "inline_equation", + "content": "t = 1, \\dots, T" + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "content": ". Rather than complete states, these future state targets are typically two-dimensional waypoints (i.e., " + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "inline_equation", + "content": "(x, y)" + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "content": " coordinates), with " + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 540, + 545, + 661 + ], + "type": "text", + "content": " waypoints forming the full ground" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 304, + 673, + 547, + 715 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 673, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 673, + 547, + 715 + ], + "type": "text", + "content": "2We make no claims that our model is capable of directly modeling causal relationships (due to the theoretical limits of purely observational data and unobserved confounders). Here, we solely take care to avoid breaking temporal causality." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 295, + 748, + 314, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 758 + ], + "type": "text", + "content": "8581" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 205, + 85 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 205, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 205, + 85 + ], + "type": "text", + "content": "truth trajectory for an individual agent." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 92, + 194, + 105 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 92, + 194, + 105 + ], + "spans": [ + { + "bbox": [ + 47, + 92, + 194, + 105 + ], + "type": "text", + "content": "3.1. Joint probabilistic rollouts" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "spans": [ + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "type": "text", + "content": "In our modeling framework, we sample a predicted action for each target agent at each future timestep. These actions are formulated as discrete motion tokens from a finite vocabulary, as described later in Section 3.2.2. Let " + }, + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "type": "inline_equation", + "content": "a_{t}^{n}" + }, + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "type": "text", + "content": " represent the target action (derived from the ground truth waypoints) for the " + }, + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "type": "text", + "content": "th agent at time " + }, + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "type": "text", + "content": ", with " + }, + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "type": "inline_equation", + "content": "A_{t} \\doteq \\{a_{t}^{1}, a_{t}^{2}, \\dots, a_{t}^{N}\\}" + }, + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "type": "text", + "content": " representing the set of target actions for all agents at time " + }, + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 47, + 111, + 287, + 207 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 222, + 287, + 247 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 222, + 287, + 247 + ], + "spans": [ + { + "bbox": [ + 47, + 222, + 287, + 247 + ], + "type": "text", + "content": "Factorization. We factorize the distribution over joint future action sequences as a product of conditionals:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 75, + 257, + 287, + 289 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 75, + 257, + 287, + 289 + ], + "spans": [ + { + "bbox": [ + 75, + 257, + 287, + 289 + ], + "type": "interline_equation", + "content": "p _ {\\theta} \\left(A _ {1}, A _ {2}, \\dots A _ {T} \\mid S\\right) = \\prod_ {t = 1} ^ {T} p _ {\\theta} \\left(A _ {t} \\mid A _ {< t}, S\\right), \\tag {1}", + "image_path": "254810ac43dc91309b2a551a5c02d8329a6cb290cc1778c345418b2fdd93baac.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 85, + 299, + 287, + 331 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 85, + 299, + 287, + 331 + ], + "spans": [ + { + "bbox": [ + 85, + 299, + 287, + 331 + ], + "type": "interline_equation", + "content": "p _ {\\theta} \\left(A _ {t} \\mid A _ {< t}, S\\right) = \\prod_ {n = 1} ^ {N} p _ {\\theta} \\left(a _ {t} ^ {n} \\mid A _ {< t}, S\\right). \\tag {2}", + "image_path": "596df53e00c8a72d46904024b0f05ca7a57a4f30bcc8a2ca92da7ebb1184f9e3.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 335, + 287, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 335, + 287, + 441 + ], + "spans": [ + { + "bbox": [ + 46, + 335, + 287, + 441 + ], + "type": "text", + "content": "Similar to [36, 43], Eq. (2) represents the fact that we treat agent actions as conditionally independent at time " + }, + { + "bbox": [ + 46, + 335, + 287, + 441 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 335, + 287, + 441 + ], + "type": "text", + "content": ", given the previous actions and scene context. This aligns empirically with real-world driving over short time intervals; e.g., non-impaired human drivers generally require at least 500 ms to release the accelerator in response to a vehicle braking ahead ([13]). In our experiments, we find " + }, + { + "bbox": [ + 46, + 335, + 287, + 441 + ], + "type": "inline_equation", + "content": "2\\mathrm{Hz}" + }, + { + "bbox": [ + 46, + 335, + 287, + 441 + ], + "type": "text", + "content": " reactions to be sufficient to surpass state-of-the-art joint prediction models." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 47, + 444, + 287, + 479 + ], + "type": "text", + "content": "We note that our model's factorization is entirely latent variable free; multimodal predictions stem purely from categorical token sampling at each rollout timestep." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 495, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 495, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 47, + 495, + 287, + 544 + ], + "type": "text", + "content": "Training objective. MotionLM is formulated as a generative model trained to match the joint distribution of observed agent behavior. Specifically, we follow a maximum likelihood objective over multi-agent action sequences:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 109, + 552, + 287, + 585 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 109, + 552, + 287, + 585 + ], + "spans": [ + { + "bbox": [ + 109, + 552, + 287, + 585 + ], + "type": "interline_equation", + "content": "\\underset {\\theta} {\\arg \\max } \\prod_ {t = 1} ^ {T} p _ {\\theta} \\left(A _ {t} \\mid A _ {< t}, S\\right) \\tag {3}", + "image_path": "a390a73285a8bf51092b043158c929cacf8d42f9d7bae08bdfd464b8a127020d.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 287, + 713 + ], + "type": "text", + "content": "Similar to the typical training setup of modern language models, we utilize \"teacher-forcing\" where previous ground truth (not predicted) tokens are provided at each timestep, which tends to increase stability and avoids sampling during training. We note that this applies to all target agents; in training, each target agent is exposed to ground truth action sequence prefixes for all target agents prior to the current timestep. This naturally allows for temporal parallelization when using modern attention-based architectures such as transformers [48]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 72, + 545, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 133 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 133 + ], + "type": "text", + "content": "Our model is subject to the same theoretical limitations as general imitation learning frameworks (e.g., compounding error [38] and self-delusions due to unobserved confounders [33]). However, we find that, in practice, these do not prevent strong performance on forecasting tasks." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 140, + 434, + 152 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 140, + 434, + 152 + ], + "spans": [ + { + "bbox": [ + 306, + 140, + 434, + 152 + ], + "type": "text", + "content": "3.2. Model implementation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 159, + 545, + 218 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 159, + 545, + 218 + ], + "spans": [ + { + "bbox": [ + 305, + 159, + 545, + 218 + ], + "type": "text", + "content": "Our model consists of two main networks, an encoder which processes initial scene elements followed by a trajectory decoder which performs both cross-attention to the scene encodings and self-attention along agent motion tokens, following a transformer architecture [48]." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 234, + 399, + 245 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 234, + 399, + 245 + ], + "spans": [ + { + "bbox": [ + 306, + 234, + 399, + 245 + ], + "type": "text", + "content": "3.2.1 Scene encoder" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 253, + 545, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 253, + 545, + 347 + ], + "spans": [ + { + "bbox": [ + 305, + 253, + 545, + 347 + ], + "type": "text", + "content": "The scene encoder (Fig. 2, left) is tasked with processing information from several input modalities, including the roadgraph, traffic light states, and history of surrounding agents' trajectories. Here, we follow the design of the early fusion network proposed by [31] as the scene encoding backbone of our model. Early fusion is particularly chosen because of its flexibility to process all modalities together with minimal inductive bias." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 349, + 545, + 433 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 349, + 545, + 433 + ], + "spans": [ + { + "bbox": [ + 305, + 349, + 545, + 433 + ], + "type": "text", + "content": "The features above are extracted with respect to each modeled agent's frame of reference. Input tensors are then fed to a stack of self-attention layers that exchange information across all past timesteps and agents. In the first layer, latent queries cross-attend to the original inputs in order to reduce the set of vectors being processed to a manageable number, similar to [23, 19]. For additional details, see [31]." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 448, + 441, + 460 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 448, + 441, + 460 + ], + "spans": [ + { + "bbox": [ + 306, + 448, + 441, + 460 + ], + "type": "text", + "content": "3.2.2 Joint trajectory decoder" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 467, + 544, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 467, + 544, + 491 + ], + "spans": [ + { + "bbox": [ + 306, + 467, + 544, + 491 + ], + "type": "text", + "content": "Our trajectory decoder (Fig. 2, center) is tasked with generating sequences of motion tokens for multiple agents." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 506, + 545, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 506, + 545, + 662 + ], + "spans": [ + { + "bbox": [ + 305, + 506, + 545, + 662 + ], + "type": "text", + "content": "Discrete motion tokens. We elect to transform trajectories comprised of continuous waypoints into sequences of discrete tokens. This enables treating sampling purely as a classification task at each timestep, implemented via a standard softmax layer. Discretizing continuous targets in this manner has proven effective in other inherently continuous domains, e.g., in audio generation [46] and mesh generation [30]. We suspect that discrete motion tokens also naturally hide some precision from the model, possibly mitigating compounding error effects that could arise from imperfect continuous value prediction. Likewise, we did not find it necessary to manually add any noise to the ground truth teacher-forced trajectories (e.g., as is done in [26])." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "content": "Quantization. To extract target discrete tokens, we begin by normalizing each agent's ground truth trajectory with respect to the position and heading of the agent at" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8582" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 62, + 72, + 216, + 223 + ], + "blocks": [ + { + "bbox": [ + 62, + 72, + 216, + 223 + ], + "lines": [ + { + "bbox": [ + 62, + 72, + 216, + 223 + ], + "spans": [ + { + "bbox": [ + 62, + 72, + 216, + 223 + ], + "type": "image", + "image_path": "825f2e3eea580053724ae5ba734bb572c136be5787218e1cdf276818fc7dc63f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 234, + 547, + 291 + ], + "lines": [ + { + "bbox": [ + 46, + 234, + 547, + 291 + ], + "spans": [ + { + "bbox": [ + 46, + 234, + 547, + 291 + ], + "type": "text", + "content": "Figure 3. Displayed are the top two predicted joint rollout modes for three WOMD scenes. Color gradients indicate time progression from " + }, + { + "bbox": [ + 46, + 234, + 547, + 291 + ], + "type": "inline_equation", + "content": "t = 0" + }, + { + "bbox": [ + 46, + 234, + 547, + 291 + ], + "type": "text", + "content": "s to " + }, + { + "bbox": [ + 46, + 234, + 547, + 291 + ], + "type": "inline_equation", + "content": "t = 8" + }, + { + "bbox": [ + 46, + 234, + 547, + 291 + ], + "type": "text", + "content": "s, with the greatest probability joint mode transitioning from green to blue and the secondary joint mode transitioning from orange to purple. Three types of interactions are observed: an agent in the adjacent lane yields to the lane-changing agent according to the timing of the lane change (left), a pedestrian walks behind the passing vehicle according to the progress of the vehicle (center), the turning vehicle either yields to the crossing cyclist (most probable mode) or turns before the cyclist approaches (secondary mode) (right)." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 220, + 72, + 373, + 223 + ], + "blocks": [ + { + "bbox": [ + 220, + 72, + 373, + 223 + ], + "lines": [ + { + "bbox": [ + 220, + 72, + 373, + 223 + ], + "spans": [ + { + "bbox": [ + 220, + 72, + 373, + 223 + ], + "type": "image", + "image_path": "17023df7ab3c8a02381296e44f456955ea9c79a3de882c2d31d62dade7b65a42.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 380, + 72, + 533, + 224 + ], + "blocks": [ + { + "bbox": [ + 380, + 72, + 533, + 224 + ], + "lines": [ + { + "bbox": [ + 380, + 72, + 533, + 224 + ], + "spans": [ + { + "bbox": [ + 380, + 72, + 533, + 224 + ], + "type": "image", + "image_path": "5c55cb2f881611c58d043dbccfc9f04f81e13abca2cf873cfcee9971085385ea.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 311, + 289, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 311, + 289, + 441 + ], + "spans": [ + { + "bbox": [ + 46, + 311, + 289, + 441 + ], + "type": "text", + "content": "time " + }, + { + "bbox": [ + 46, + 311, + 289, + 441 + ], + "type": "inline_equation", + "content": "t = 0" + }, + { + "bbox": [ + 46, + 311, + 289, + 441 + ], + "type": "text", + "content": " of the scenario. We then parameterize a uniformly quantized " + }, + { + "bbox": [ + 46, + 311, + 289, + 441 + ], + "type": "inline_equation", + "content": "(\\Delta x, \\Delta y)" + }, + { + "bbox": [ + 46, + 311, + 289, + 441 + ], + "type": "text", + "content": " vocabulary according to a total number of per-coordinate bins as well as maximum and minimum delta values. A continuous, single-coordinate delta action can then be mapped to a corresponding index " + }, + { + "bbox": [ + 46, + 311, + 289, + 441 + ], + "type": "inline_equation", + "content": "\\in [0, \\text{num\\_bins} - 1]" + }, + { + "bbox": [ + 46, + 311, + 289, + 441 + ], + "type": "text", + "content": ", resulting in two indices for a complete " + }, + { + "bbox": [ + 46, + 311, + 289, + 441 + ], + "type": "inline_equation", + "content": "(\\Delta x, \\Delta y)" + }, + { + "bbox": [ + 46, + 311, + 289, + 441 + ], + "type": "text", + "content": " action per step. In order to extract actions that accurately reconstruct an entire trajectory, we employ a greedy search, sequentially selecting the quantized actions that reconstruct the next waypoint coordinates with minimum error." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 443, + 287, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 443, + 287, + 586 + ], + "spans": [ + { + "bbox": [ + 46, + 443, + 287, + 586 + ], + "type": "text", + "content": "We wrap the delta actions with a \"Verlet\" step where a zero action indicates that the same delta index should be used as the previous step (as [36] does for continuous states). As agent velocities tend to change smoothly between consecutive timesteps, this helps reduce the total vocabulary size, simplifying the dynamics of training. Finally, to maintain only " + }, + { + "bbox": [ + 46, + 443, + 287, + 586 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 443, + 287, + 586 + ], + "type": "text", + "content": " sequential predictions, we collapse the per-coordinate actions to a single integer indexing into their Cartesian product. In practice, for the models presented here, we use 13 tokens per coordinate with " + }, + { + "bbox": [ + 46, + 443, + 287, + 586 + ], + "type": "inline_equation", + "content": "13^2 = 169" + }, + { + "bbox": [ + 46, + 443, + 287, + 586 + ], + "type": "text", + "content": " total discrete tokens available in the vocabulary (see Appendix A for further details)." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "spans": [ + { + "bbox": [ + 46, + 587, + 287, + 647 + ], + "type": "text", + "content": "We compute a learned value embedding and two learned positional embeddings (representing the timestep and agent identity) for each discrete motion token, which are combined via an element-wise sum prior to being input to the transformer decoder." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 715 + ], + "type": "text", + "content": "Flattened agent-time self-attention. We elect to include a single self-attention mechanism in the decoder that operates along flattened sequences of all modeled agents' motion tokens over time. So, given a target sequence of length" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 311, + 547, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 311, + 547, + 407 + ], + "spans": [ + { + "bbox": [ + 304, + 311, + 547, + 407 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 311, + 547, + 407 + ], + "type": "text", + "content": " for each of " + }, + { + "bbox": [ + 304, + 311, + 547, + 407 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 311, + 547, + 407 + ], + "type": "text", + "content": " agents, we perform self-attention over " + }, + { + "bbox": [ + 304, + 311, + 547, + 407 + ], + "type": "inline_equation", + "content": "NT" + }, + { + "bbox": [ + 304, + 311, + 547, + 407 + ], + "type": "text", + "content": " elements. While this does mean that these self-attended sequences grow linearly in the number of jointly modeled agents, we note that the absolute sequence length here is still quite small (length 32 for the WOMD interactive split -8 sec. prediction at " + }, + { + "bbox": [ + 304, + 311, + 547, + 407 + ], + "type": "inline_equation", + "content": "2\\mathrm{Hz}" + }, + { + "bbox": [ + 304, + 311, + 547, + 407 + ], + "type": "text", + "content": " for 2 agents). Separate passes of factorized agent and time attention are also possible [32], but we use a single pass here for simplicity." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 422, + 547, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 422, + 547, + 506 + ], + "spans": [ + { + "bbox": [ + 304, + 422, + 547, + 506 + ], + "type": "text", + "content": "Ego agent reference frames. To facilitate cross-attention to the agent-centric feature encodings (Section 3.2.1), we represent the flattened token sequence once for each modeled agent. Each modeled agent is treated as the \"ego\" agent once, and cross-attention is performed on that agent's scene features. Collapsing the ego agents into the batch dimension allows parallelization during training and inference." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 513, + 465, + 526 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 513, + 465, + 526 + ], + "spans": [ + { + "bbox": [ + 306, + 513, + 465, + 526 + ], + "type": "text", + "content": "3.3. Enforcing temporal causality" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 531, + 545, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 531, + 545, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 531, + 545, + 640 + ], + "type": "text", + "content": "Our autoregressive factorization naturally respects temporal dependencies during joint rollouts; motion token sampling for any particular agent is affected only by past tokens (from any agent) and unaffected by future ones. When training, we require a mask to ensure that the self-attention operation only updates representations at each step accordingly. As shown in Fig. 8 (appendix), this attention mask exhibits a blocked, staircase pattern, exposing all agents to each other's histories only up to the preceding step." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": "Temporally causal conditioning. As described earlier, a particular benefit of this factorization is the ability to query for temporally causal conditional rollouts (Fig. 4). In this setting, we fix a query agent to take some sequence of actions and only roll out the other agents." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "type": "text", + "content": "8583" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 84, + 201, + 142 + ], + "blocks": [ + { + "bbox": [ + 53, + 84, + 201, + 142 + ], + "lines": [ + { + "bbox": [ + 53, + 84, + 201, + 142 + ], + "spans": [ + { + "bbox": [ + 53, + 84, + 201, + 142 + ], + "type": "image", + "image_path": "d139ce0bf2cadfa28a152bd716bd38ecc6ed7ac2c5cd973060b1e659f1d31d6d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 64, + 164, + 198, + 174 + ], + "lines": [ + { + "bbox": [ + 64, + 164, + 198, + 174 + ], + "spans": [ + { + "bbox": [ + 64, + 164, + 198, + 174 + ], + "type": "text", + "content": "(a) Causal Bayesian Network for joint rollouts." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 216, + 83, + 362, + 141 + ], + "blocks": [ + { + "bbox": [ + 216, + 83, + 362, + 141 + ], + "lines": [ + { + "bbox": [ + 216, + 83, + 362, + 141 + ], + "spans": [ + { + "bbox": [ + 216, + 83, + 362, + 141 + ], + "type": "image", + "image_path": "a7518889e1038dfa6c45c2e9ebdf67015b6a0eec2fb04a570ccaa697650b1d83.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 182, + 547, + 228 + ], + "lines": [ + { + "bbox": [ + 46, + 182, + 547, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 182, + 547, + 228 + ], + "type": "text", + "content": "Figure 4. A Causal Bayesian network representation for joint rollouts (left), post-intervention Causal Bayesian network (center), and acausal conditioning (right). Solid lines indicate temporally causal dependencies while dashed lines indicate acausal information flow. Models without temporal dependency constraints will support acausal conditioning but not temporally causal conditioning, which can be problematic when attempting to predict agent reactions." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 389, + 84, + 539, + 140 + ], + "blocks": [ + { + "bbox": [ + 226, + 164, + 362, + 174 + ], + "lines": [ + { + "bbox": [ + 226, + 164, + 362, + 174 + ], + "spans": [ + { + "bbox": [ + 226, + 164, + 362, + 174 + ], + "type": "text", + "content": "(b) Post-Intervention Causal Bayesian Network." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 389, + 84, + 539, + 140 + ], + "lines": [ + { + "bbox": [ + 389, + 84, + 539, + 140 + ], + "spans": [ + { + "bbox": [ + 389, + 84, + 539, + 140 + ], + "type": "image", + "image_path": "1037b27a97bf341aaddab4db5f3ffb2acdb06aaf6007c7f70a564a3860973c08.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 389, + 142, + 536, + 163 + ], + "lines": [ + { + "bbox": [ + 389, + 142, + 536, + 163 + ], + "spans": [ + { + "bbox": [ + 389, + 142, + 536, + 163 + ], + "type": "text", + "content": "Conditioned Agent Causal conditioning Sampling Agent Acausal conditioning" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 421, + 164, + 493, + 174 + ], + "lines": [ + { + "bbox": [ + 421, + 164, + 493, + 174 + ], + "spans": [ + { + "bbox": [ + 421, + 164, + 493, + 174 + ], + "type": "text", + "content": "(c) Acausal conditioning." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 248, + 288, + 332 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 248, + 288, + 332 + ], + "spans": [ + { + "bbox": [ + 46, + 248, + 288, + 332 + ], + "type": "text", + "content": "We may view this as an approximation of computing causal interventions [34] in the absence of confounders; interventions cannot be learned purely through observational data in general (due to the possible presence of unobserved confounders), but our model's factorization at least eliminates certain spurious correlations arising from breaking temporal causality." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 332, + 289, + 429 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 332, + 289, + 429 + ], + "spans": [ + { + "bbox": [ + 46, + 332, + 289, + 429 + ], + "type": "text", + "content": "In Fig. 4 (a), we show an example of a Causal Bayesian network governing joint rollouts. Applying an intervention to nodes " + }, + { + "bbox": [ + 46, + 332, + 289, + 429 + ], + "type": "inline_equation", + "content": "x = 1, \\ldots, T" + }, + { + "bbox": [ + 46, + 332, + 289, + 429 + ], + "type": "text", + "content": ", by deleting their incoming edges, results in a post-intervention Bayesian network depicted in Fig. 4 (b), which obeys temporal causality. On the other hand, acausal conditioning (Fig. 4 (c)) results in non-causal information flow, where node " + }, + { + "bbox": [ + 46, + 332, + 289, + 429 + ], + "type": "inline_equation", + "content": "x = i" + }, + { + "bbox": [ + 46, + 332, + 289, + 429 + ], + "type": "text", + "content": " affects our belief about node " + }, + { + "bbox": [ + 46, + 332, + 289, + 429 + ], + "type": "inline_equation", + "content": "y = j" + }, + { + "bbox": [ + 46, + 332, + 289, + 429 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 332, + 289, + 429 + ], + "type": "inline_equation", + "content": "i \\geq j" + }, + { + "bbox": [ + 46, + 332, + 289, + 429 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 436, + 163, + 449 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 436, + 163, + 449 + ], + "spans": [ + { + "bbox": [ + 47, + 436, + 163, + 449 + ], + "type": "text", + "content": "3.4. Rollout aggregation" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 454, + 289, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 454, + 289, + 659 + ], + "spans": [ + { + "bbox": [ + 46, + 454, + 289, + 659 + ], + "type": "text", + "content": "Joint motion forecasting benchmark tasks like WOMD [14] require a compact representation of the joint future distribution in the form of a small number of joint \"modes\". Each mode is assigned a probability and might correspond to a specific homotopic outcome (e.g., pass/yield) or more subtle differences in speed/geometry. Here, we aggregate rollouts to achieve two primary goals: 1) uncover the underlying modes of the distribution and 2) estimate the probability of each mode. Specifically, we follow the non-maximum suppression (NMS) aggregation scheme described in [47], but extend it to the joint setting by ensuring that all agent predictions reside within a given distance threshold to the corresponding cluster. In addition, we leverage model ensembling to account for epistemic uncertainty and further improve the quality of the predictions, combining rollouts from independently trained replicas prior to the aggregation step." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 670, + 128, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 670, + 128, + 683 + ], + "spans": [ + { + "bbox": [ + 47, + 670, + 128, + 683 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "content": "We evaluate MotionLM on marginal and joint motion forecasting benchmarks, examine its conditional predic" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 248, + 518, + 261 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 248, + 518, + 261 + ], + "spans": [ + { + "bbox": [ + 306, + 248, + 518, + 261 + ], + "type": "text", + "content": "tions and conduct ablations of our modeling choices." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 272, + 368, + 283 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 272, + 368, + 283 + ], + "spans": [ + { + "bbox": [ + 306, + 272, + 368, + 283 + ], + "type": "text", + "content": "4.1. Datasets" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 292, + 545, + 400 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 292, + 545, + 400 + ], + "spans": [ + { + "bbox": [ + 304, + 292, + 545, + 400 + ], + "type": "text", + "content": "Waymo Open Motion Dataset (WOMD). WOMD [14] is a collection of 103k 20-second scenarios collected from real-world driving in urban and suburban environments. Segments are divided into 1.1M examples consisting of 9-second windows of interest, where the first second serves as input context and the remaining 8-seconds are the prediction target. Map features such as traffic signal states and lane features are provided along with agent states such as position, velocity, acceleration, and bounding boxes." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 422, + 545, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 422, + 545, + 495 + ], + "spans": [ + { + "bbox": [ + 304, + 422, + 545, + 495 + ], + "type": "text", + "content": "Marginal and interactive prediction challenges. For the marginal prediction challenge, six trajectories must be output by the model for each target agent, along with likelihoods of each mode. For the interactive challenge, two interacting agents are labeled in each test example. In this case, the model must output six weighted joint trajectories." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 506, + 365, + 517 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 506, + 365, + 517 + ], + "spans": [ + { + "bbox": [ + 306, + 506, + 365, + 517 + ], + "type": "text", + "content": "4.2. Metrics" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 526, + 545, + 634 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 526, + 545, + 634 + ], + "spans": [ + { + "bbox": [ + 304, + 526, + 545, + 634 + ], + "type": "text", + "content": "The primary evaluation metrics for the marginal and interactive prediction challenges are soft mAP and mAP, respectively, with miss rate as the secondary metric. Distance metrics minADE and minFDE provide additional signal on prediction quality. For the interactive prediction challenge, these metrics refer to scene-level joint calculations. We also use a custom prediction overlap metric (similar to [29]) to assess scene-level consistency for joint models. See Appendix C for details on these metrics." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 645, + 424, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 645, + 424, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 645, + 424, + 658 + ], + "type": "text", + "content": "4.3. Model configuration" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "We experiment with up to 8 model replicas and 512 rollouts per replica, assessing performance at various configurations. For complete action space and model hyperparameter details, see Appendices A and B." + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8584" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 132, + 70, + 462, + 166 + ], + "blocks": [ + { + "bbox": [ + 132, + 70, + 462, + 166 + ], + "lines": [ + { + "bbox": [ + 132, + 70, + 462, + 166 + ], + "spans": [ + { + "bbox": [ + 132, + 70, + 462, + 166 + ], + "type": "table", + "html": "
ModelminADE (↓)minFDE (↓)Miss Rate (↓)Soft mAP (↑)
HDGT [20]0.76761.10770.13250.3709
MPA [22]0.59131.25070.16030.3930
MTR [40]0.60501.22070.13510.4216
Wayformer factorized [31]0.54471.12550.12290.4260
Wayformer multi-axis [31]0.54541.12800.12280.4335
MTR-A [40]0.56401.13440.11600.4594
MotionLM (Ours)0.55091.11990.10580.4507
", + "image_path": "f44cd62d9a91e0484a4fb16b76e9610a434299a142e8f689a549513959e4813c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 141, + 208, + 454, + 293 + ], + "blocks": [ + { + "bbox": [ + 46, + 175, + 547, + 198 + ], + "lines": [ + { + "bbox": [ + 46, + 175, + 547, + 198 + ], + "spans": [ + { + "bbox": [ + 46, + 175, + 547, + 198 + ], + "type": "text", + "content": "Table 1. Marginal prediction performance on WOMD test set. We display metrics averaged over time steps (3, 5, and 8 seconds) and agent types (vehicles, pedestrians, and cyclists). Greyed columns indicate the official ranking metrics for the marginal prediction challenge." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 141, + 208, + 454, + 293 + ], + "lines": [ + { + "bbox": [ + 141, + 208, + 454, + 293 + ], + "spans": [ + { + "bbox": [ + 141, + 208, + 454, + 293 + ], + "type": "table", + "html": "
ModelminADE (↓)minFDE (↓)Miss Rate (↓)mAP (↑)
SceneTransformer (J) [32]0.97742.18920.49420.1192
M2I [42]1.35062.83250.55380.1239
DenseTNT [28]1.14172.49040.53500.1647
MTR [40]0.91812.06330.44110.2037
JFP [29]0.88171.99050.42330.2050
MotionLM (Ours)0.89112.00670.41150.2178
", + "image_path": "1b90df2d97c64bb48b67aa7a81fbd6a1ee66489ec2bd8c76f03a75c615ae134b.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 345, + 162, + 357 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 345, + 162, + 357 + ], + "spans": [ + { + "bbox": [ + 47, + 345, + 162, + 357 + ], + "type": "text", + "content": "4.4. Quantitative results" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 363, + 289, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 363, + 289, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 363, + 289, + 495 + ], + "type": "text", + "content": "Marginal motion prediction. As shown in Table 1, our model is competitive with the state-of-the-art on WOMD marginal motion prediction (independent per agent). For the main ranking metric of soft mAP, our model ranks second, less than " + }, + { + "bbox": [ + 46, + 363, + 289, + 495 + ], + "type": "inline_equation", + "content": "2\\%" + }, + { + "bbox": [ + 46, + 363, + 289, + 495 + ], + "type": "text", + "content": " behind the score achieved by MTRA [40]. In addition, our model attains a substantially improved miss rate over all prior works, with a relative " + }, + { + "bbox": [ + 46, + 363, + 289, + 495 + ], + "type": "inline_equation", + "content": "9\\%" + }, + { + "bbox": [ + 46, + 363, + 289, + 495 + ], + "type": "text", + "content": " reduction compared to the previous state-of-the-art. The autoregressive rollouts are able to adequately capture the diversity of multimodal future behavior without reliance on trajectory anchors [8] or static intention points [40]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "text", + "content": "Interactive motion prediction. Our model achieves state-of-the-art results for the interactive prediction challenge on WOMD, attaining a " + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "inline_equation", + "content": "6\\%" + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "text", + "content": " relative improvement in mAP and " + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "inline_equation", + "content": "3\\%" + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "text", + "content": " relative improvement in miss rate (the two official ranking metrics) over the previous top scoring entry, JFP [29] (see Table 2). In contrast to JFP, our approach does not score pairs of previously constructed marginal trajectories, but generates joint rollouts directly. Fig. 3 displays example interactions predicted by our model." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "content": "Table 3 displays prediction overlap rates for various models on the WOMD interactive test and validation sets (see metric details in Appendix C.2). We obtain test set predictions from the authors of [14, 32, 29]. MotionLM obtains the lowest prediction overlap rate, an indication of scene-consistent predictions. In addition, on the validation set we evaluate two versions of our model: marginal and joint. The marginal version does not perform attention" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 320, + 343, + 533, + 434 + ], + "blocks": [ + { + "bbox": [ + 46, + 301, + 546, + 326 + ], + "lines": [ + { + "bbox": [ + 46, + 301, + 546, + 326 + ], + "spans": [ + { + "bbox": [ + 46, + 301, + 546, + 326 + ], + "type": "text", + "content": "Table 2. Joint prediction performance on WOMD interactive test set. We display scene-level joint metrics averaged over time steps (3, 5, and 8 seconds) and agent types (vehicles, pedestrians, and cyclists). Greyed columns indicate the official ranking metrics for the challenge." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 320, + 343, + 533, + 434 + ], + "lines": [ + { + "bbox": [ + 320, + 343, + 533, + 434 + ], + "spans": [ + { + "bbox": [ + 320, + 343, + 533, + 434 + ], + "type": "table", + "html": "
ModelPrediction Overlap (↓)
TestLSTM Baseline [14]0.07462
Scene Transformer [32]0.04336
JFP [29]0.02671
MotionLM (joint)0.02607
ValMotionLM (marginal)0.0404
MotionLM (joint)0.0292
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Displayed is the custom prediction overlap metric for various model configurations on the WOMD interactive test and validation sets." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 496, + 545, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 496, + 545, + 568 + ], + "spans": [ + { + "bbox": [ + 305, + 496, + 545, + 568 + ], + "type": "text", + "content": "across the modeled agents during both training and inference rollouts, while the joint version performs " + }, + { + "bbox": [ + 305, + 496, + 545, + 568 + ], + "type": "inline_equation", + "content": "2\\mathrm{Hz}" + }, + { + "bbox": [ + 305, + 496, + 545, + 568 + ], + "type": "text", + "content": " interactive attention. We see that the marginal version obtains a relative " + }, + { + "bbox": [ + 305, + 496, + 545, + 568 + ], + "type": "inline_equation", + "content": "38\\%" + }, + { + "bbox": [ + 305, + 496, + 545, + 568 + ], + "type": "text", + "content": " higher overlap rate than the joint version. The interactive attention in the joint model allows the agents to more appropriately react to one another." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 575, + 405, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 575, + 405, + 586 + ], + "spans": [ + { + "bbox": [ + 306, + 575, + 405, + 586 + ], + "type": "text", + "content": "4.5. Ablation studies" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 594, + 545, + 701 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 701 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 701 + ], + "type": "text", + "content": "Interactive attention frequency. To assess the importance of inter-agent reactivity during the joint rollouts, we vary the frequency of the interactive attention operation while keeping other architecture details constant. For our leaderboard results, we utilize the greatest frequency studied here, " + }, + { + "bbox": [ + 304, + 594, + 545, + 701 + ], + "type": "inline_equation", + "content": "2\\mathrm{Hz}" + }, + { + "bbox": [ + 304, + 594, + 545, + 701 + ], + "type": "text", + "content": ". At the low end of the spectrum, " + }, + { + "bbox": [ + 304, + 594, + 545, + 701 + ], + "type": "inline_equation", + "content": "0.125\\mathrm{Hz}" + }, + { + "bbox": [ + 304, + 594, + 545, + 701 + ], + "type": "text", + "content": " corresponds to the agents only observing each other's initial states, and then proceeding with the entire 8-second rollout without communicating again (i.e., marginal rollouts)." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 317, + 702, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 702, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 702, + 545, + 714 + ], + "type": "text", + "content": "Performance metrics generally improve as agents are" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8585" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 83, + 165, + 198 + ], + "blocks": [ + { + "bbox": [ + 63, + 71, + 157, + 80 + ], + "lines": [ + { + "bbox": [ + 63, + 71, + 157, + 80 + ], + "spans": [ + { + "bbox": [ + 63, + 71, + 157, + 80 + ], + "type": "text", + "content": "No interactive attention" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 52, + 83, + 165, + 198 + ], + "lines": [ + { + "bbox": [ + 52, + 83, + 165, + 198 + ], + "spans": [ + { + "bbox": [ + 52, + 83, + 165, + 198 + ], + "type": "image", + "image_path": "1603d7a263732570002c2c9a908ead158fc348f3ee8c1b1551d8dea126a6e3c5.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 171, + 84, + 284, + 198 + ], + "blocks": [ + { + "bbox": [ + 179, + 71, + 274, + 80 + ], + "lines": [ + { + "bbox": [ + 179, + 71, + 274, + 80 + ], + "spans": [ + { + "bbox": [ + 179, + 71, + 274, + 80 + ], + "type": "text", + "content": "16 interaction iterations" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 171, + 84, + 284, + 198 + ], + "lines": [ + { + "bbox": [ + 171, + 84, + 284, + 198 + ], + "spans": [ + { + "bbox": [ + 171, + 84, + 284, + 198 + ], + "type": "image", + "image_path": "62e8a5a680bde6e45f9066bf87e75648ae9823fa9cc92b31d0c48eb66a6caac4.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 52, + 202, + 165, + 316 + ], + "blocks": [ + { + "bbox": [ + 52, + 202, + 165, + 316 + ], + "lines": [ + { + "bbox": [ + 52, + 202, + 165, + 316 + ], + "spans": [ + { + "bbox": [ + 52, + 202, + 165, + 316 + ], + "type": "image", + "image_path": "967ce5807cfabf79b007a3ef42e0d971a5cc74838c73719949d8179a16e74a6d.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 327, + 287, + 426 + ], + "lines": [ + { + "bbox": [ + 46, + 327, + 287, + 426 + ], + "spans": [ + { + "bbox": [ + 46, + 327, + 287, + 426 + ], + "type": "text", + "content": "Figure 5. Visualization of the top joint rollout mode at the two extremes of the interactive attention frequencies studied here. With no interactive attention (left), the two modeled agents only attend to each other once at the beginning of the 8-second rollout and never again, in contrast to 16 total times for " + }, + { + "bbox": [ + 46, + 327, + 287, + 426 + ], + "type": "inline_equation", + "content": "2\\mathrm{Hz}" + }, + { + "bbox": [ + 46, + 327, + 287, + 426 + ], + "type": "text", + "content": " attention (right). The independent rollouts resulting from zero interactive attention can result in scene-inconsistent overlap; e.g., a turning vehicle fails to accommodate a crossing pedestrian (top left) or yield appropriately to a crossing vehicle (bottom left)." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 171, + 202, + 284, + 316 + ], + "blocks": [ + { + "bbox": [ + 171, + 202, + 284, + 316 + ], + "lines": [ + { + "bbox": [ + 171, + 202, + 284, + 316 + ], + "spans": [ + { + "bbox": [ + 171, + 202, + 284, + 316 + ], + "type": "image", + "image_path": "f26e8aeb300c2e192442d7519aa5c314e13286e76d33025f2debdd0eb3cc0bd6.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 453, + 286, + 561 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 453, + 286, + 561 + ], + "spans": [ + { + "bbox": [ + 46, + 453, + 286, + 561 + ], + "type": "text", + "content": "permitted to interact more frequently (Fig. 6 top, Table 5 in appendix). Greater interactive attention frequencies not only lead to more accurate joint predictions, but also reduce implausible overlaps (i.e., collisions) between different agents' predictions. Fig. 5 displays examples where the marginal predictions lead to implausible overlap between agents while the joint predictions lead to appropriately separated trajectories. See supplementary for animated visualizations." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "type": "text", + "content": "Number of rollouts. Our rollout aggregation requires that we generate a sufficient number of samples from the model in order to faithfully represent the multimodal future distribution. For this ablation, we vary the number of rollouts generated, but always cluster down to " + }, + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "type": "inline_equation", + "content": "k = 6" + }, + { + "bbox": [ + 46, + 594, + 286, + 713 + ], + "type": "text", + "content": " modes for evaluation. In general, we see performance metrics improve as additional rollouts are utilized (Fig. 6, bottom and Table 6 in appendix). For our final leaderboard results, we use 512 rollouts per replica, although 32 rollouts is sufficient to surpass the previous top entry on joint mAP." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 310, + 72, + 543, + 205 + ], + "blocks": [ + { + "bbox": [ + 310, + 72, + 543, + 205 + ], + "lines": [ + { + "bbox": [ + 310, + 72, + 543, + 205 + ], + "spans": [ + { + "bbox": [ + 310, + 72, + 543, + 205 + ], + "type": "image", + "image_path": "f861862b8e0a966fec108e02259991179672888705f012750157cc619bf2c9ac.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 310, + 216, + 542, + 350 + ], + "blocks": [ + { + "bbox": [ + 310, + 216, + 542, + 350 + ], + "lines": [ + { + "bbox": [ + 310, + 216, + 542, + 350 + ], + "spans": [ + { + "bbox": [ + 310, + 216, + 542, + 350 + ], + "type": "image", + "image_path": "3bfb396ac9a6e06e72e769d5728758305b233227034c6ddf9acf81c7f569c492.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 360, + 545, + 425 + ], + "lines": [ + { + "bbox": [ + 304, + 360, + 545, + 425 + ], + "spans": [ + { + "bbox": [ + 304, + 360, + 545, + 425 + ], + "type": "text", + "content": "Figure 6. Joint prediction performance across varying interactive attention frequencies (top) and numbers of rollouts per replica (bottom) on the WOMD interactive validation set. Vertical axes display joint (scene-level) metrics for an 8-replica ensemble. See Tables 5 and 6 in the appendix for full parameter ranges and metrics." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 451, + 422, + 463 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 451, + 422, + 463 + ], + "spans": [ + { + "bbox": [ + 306, + 451, + 422, + 463 + ], + "type": "text", + "content": "4.6. Conditional rollouts" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 472, + 545, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 472, + 545, + 604 + ], + "spans": [ + { + "bbox": [ + 304, + 472, + 545, + 604 + ], + "type": "text", + "content": "As described in Section 3.3, our model naturally supports \"temporally causal\" conditioning, similarly to previous autoregressive efforts such as [36, 43]. In this setting, we fix one query agent to follow a specified trajectory and stochastically roll out the target agent. However, we can also modify the model to leak the query agent's full trajectory, acausally exposing its future to the target agent during conditioning. This resembles the approach to conditional prediction in, e.g., [44], where this acausal conditional distribution is modeled directly, or [29], where this distribution is accessed via inference in an energy-based model." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Here, we assess predictions from our model across three settings: marginal, temporally causal conditional, and acausal conditional (Fig. 4). Quantitatively, we observe that both types of conditioning lead to more accurate predictions for the target agent (Table 4, Fig. 7). Additionally, we see that acausal conditioning leads to greater improvement than temporally causal conditioning relative to marginal predictions across all metrics, e.g., " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "8.2\\%" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " increase in soft mAP for acausal vs. " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "3.7\\%" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " increase for temporally causal." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8586" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 126, + 70, + 470, + 126 + ], + "blocks": [ + { + "bbox": [ + 126, + 70, + 470, + 126 + ], + "lines": [ + { + "bbox": [ + 126, + 70, + 470, + 126 + ], + "spans": [ + { + "bbox": [ + 126, + 70, + 470, + 126 + ], + "type": "table", + "html": "
Prediction settingminADE (↓)minFDE (↓)Miss Rate (↓)Soft mAP (↑)
Marginal0.60691.22360.14060.3951
Temporally causal conditional0.59971.20340.13770.4096
Acausal conditional0.58991.18040.13380.4274
", + "image_path": "434d86945f52a0a01588e64413c23e8720bf17ce08621276bb0719c1f1f05bc7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 133, + 547, + 157 + ], + "lines": [ + { + "bbox": [ + 46, + 133, + 547, + 157 + ], + "spans": [ + { + "bbox": [ + 46, + 133, + 547, + 157 + ], + "type": "text", + "content": "Table 4. Conditional prediction performance. Displayed are marginal (single-agent) metrics across three prediction settings for our model on the WOMD interactive validation set: marginal, temporally causal conditional, and acausal conditional." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 176, + 288, + 237 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 176, + 288, + 237 + ], + "spans": [ + { + "bbox": [ + 46, + 176, + 288, + 237 + ], + "type": "text", + "content": "Intuitively, the greater improvement for acausal conditioning makes sense as it exposes more information to the model. However, the better quantitative scores are largely due to predictions that would be deemed nonsensical if interpreted as predicted reactions to the query agent." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 238, + 290, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 238, + 290, + 430 + ], + "spans": [ + { + "bbox": [ + 46, + 238, + 290, + 430 + ], + "type": "text", + "content": "This can be illustrated in examples where one agent is following another, where typically the lead agent's behavior is causing the trailing agent's reaction, and not vice versa, but this directionality would not be captured with acausal conditioning. This temporally causal modeling is especially important when utilizing the conditional predictions to evaluate safety for an autonomous vehicle's proposed plans. In a scenario where an autonomous vehicle (AV) is stopped behind another agent, planning to move forward into the other agent's current position could be viewed as a safe maneuver with acausal conditioning, as the other agent also moving forward is correlated with (but not caused by) the AV proceeding. However, it is typically the lead agent moving forward that causes the trailing AV to proceed, and the AV moving forward on its own would simply rear-end the lead agent." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 432, + 288, + 504 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 432, + 288, + 504 + ], + "spans": [ + { + "bbox": [ + 46, + 432, + 288, + 504 + ], + "type": "text", + "content": "In the supplementary, we compare examples of predictions in various scenarios for the causal and acausal conditioning schemes. Models that ignore temporal dependencies during conditioning (e.g., [44, 29]) may succumb to the same incorrect reasoning that the acausal version of our model does." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 521, + 206, + 534 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 521, + 206, + 534 + ], + "spans": [ + { + "bbox": [ + 47, + 521, + 206, + 534 + ], + "type": "text", + "content": "5. Conclusion and future work" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 544, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 544, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 544, + 287, + 616 + ], + "type": "text", + "content": "In this work, we introduced a method for interactive motion forecasting leveraging multi-agent rollouts over discrete motion tokens, capturing the joint distribution over multimodal futures. The proposed model establishes new state-of-the-art performance on the WOMD interactive prediction challenge." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 288, + 715 + ], + "type": "text", + "content": "Avenues for future work include leveraging the trained model in model-based planning frameworks, allowing a search tree to be formed over the multi-agent action rollouts, or learning amortized value functions from large datasets of scene rollouts. In addition, we plan to explore distillation strategies from large autoregressive teachers, enabling faster student models to be deployed in latency-critical settings." + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 308, + 173, + 425, + 299 + ], + "blocks": [ + { + "bbox": [ + 308, + 173, + 425, + 299 + ], + "lines": [ + { + "bbox": [ + 308, + 173, + 425, + 299 + ], + "spans": [ + { + "bbox": [ + 308, + 173, + 425, + 299 + ], + "type": "image", + "image_path": "773e7c793696df82720c67d8f67dd99c02aff38e49b7b83b51005341d0a8505c.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 307, + 547, + 374 + ], + "lines": [ + { + "bbox": [ + 305, + 307, + 547, + 374 + ], + "spans": [ + { + "bbox": [ + 305, + 307, + 547, + 374 + ], + "type": "text", + "content": "Figure 7. Visualization of the most likely predicted future for the pedestrian in the marginal setting (left) and temporally causal conditional setting (right). When considering the pedestrian independently, the model assigns greatest probability to a trajectory which crosses the road. When conditioned on the vehicle's ground truth turn (magenta), the pedestrian is instead predicted to yield." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 427, + 173, + 544, + 298 + ], + "blocks": [ + { + "bbox": [ + 427, + 173, + 544, + 298 + ], + "lines": [ + { + "bbox": [ + 427, + 173, + 544, + 298 + ], + "spans": [ + { + "bbox": [ + 427, + 173, + 544, + 298 + ], + "type": "image", + "image_path": "83624c9647b22b52ddd04e4c9bce8713bb0a5907030f64ca897cccc0a5e997ac.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 394, + 547, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 394, + 547, + 491 + ], + "spans": [ + { + "bbox": [ + 305, + 394, + 547, + 491 + ], + "type": "text", + "content": "Acknowledgements. We would like to thank David Weiss, Paul Covington, Ashish Venugopal, Piotr Fidkowski, and Minfa Wang for discussions on autoregressive behavior predictors; Cole Gulino and Brandyn White for advising on interactive modeling; Cheol Park, Wenjie Luo, and Scott Ettinger for assistance with evaluation; Drago Anguelov, Kyriacos Shiarlis, and anonymous reviewers for helpful feedback on the manuscript." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 316, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 758 + ], + "type": "text", + "content": "8587" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "text", + "content": "[1] Elmira Amirloo, Amir Rasouli, Peter Lakner, Mohsen Rohani, and Jun Luo. 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PMLR, 2021." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 316, + 757 + ], + "type": "text", + "content": "8590" + } + ] + } + ], + "index": 7 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 11 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/d8a8f490-e49c-49c9-b1d9-2afa438fb3bc_content_list.json b/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/d8a8f490-e49c-49c9-b1d9-2afa438fb3bc_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..304c24bb8e91a9b8d195070d1e2904a74cf27e9d --- /dev/null +++ b/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/d8a8f490-e49c-49c9-b1d9-2afa438fb3bc_content_list.json @@ -0,0 +1,1478 @@ +[ + { + "type": "text", + "text": "Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection", + "text_level": 1, + "bbox": [ + 106, + 128, + 867, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Zixuan Zhao Dongqi Wang Xu Zhao* \nDepartment of Automation, Shanghai Jiao Tong University, China \n{zhaozixuan, wangdq0124, zhaoxu}@sjtu.edu.cn", + "bbox": [ + 222, + 203, + 748, + 257 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 291, + 313, + 306 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Boundary localization is a challenging problem in Temporal Action Detection (TAD), in which there are two main issues. First, the submergence of movement feature, i.e. the movement information in a snippet is covered by the scene information. Second, the scale of action, that is, the proportion of action segments in the entire video, is considerably variable. In this work, we first design a Movement Enhance Module (MEM) to highlight movement feature for better action location, and then, we propose a Scale Feature Pyramid Network (SFPN) to detect multi-scale actions in videos. For Movement Enhance Module, firstly, Movement Feature Extractor (MFE) is designed to get the movement feature. Secondly, we propose a Multi-Relation Enhance Module (MREM) to grasp valuable information correlation both locally and temporally. For Scale Feature Pyramid Network, we design a U-Shape Module to model different scale actions, moreover, we design the training and inference strategy of different scales, ensuring that each pyramid layer is only responsible for actions at a specific scale. These two innovations are integrated as the Movement Enhance Network (MENet), and extensive experiments conducted on two challenging benchmarks demonstrate its effectiveness. MENet outperforms other representative TAD methods on ActivityNet-1.3 and THUMOS-14.", + "bbox": [ + 76, + 323, + 473, + 685 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 695, + 209, + 709 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Temporal Action Detection (TAD) is a significant video understanding task, which aims to extract video segments with specific action labels from untrimmed long videos. It remains a challenging problem because action boundaries are difficult to determine precisely, which adversely affects the performance in most works.", + "bbox": [ + 75, + 712, + 468, + 803 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Two critical issues stand in the way of detecting action boundaries robustly from untrimmed videos. The first issue, which could be called as movement feature submergence, exists in where either context but not movement itself dominate feature expression, or movement is small in pixel size.", + "bbox": [ + 75, + 803, + 468, + 878 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/21898c25d4bf84a2c8de184179b6ede51d7afb930520fcb30205e4f4bd58fc11.jpg", + "image_caption": [ + "(a) Strong class-specific context." + ], + "image_footnote": [], + "bbox": [ + 511, + 297, + 696, + 378 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/f391a8a6f1cc42c8c4517192afc16c1ba68b20fe98effe9fb20c187a12d42716.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 702, + 297, + 888, + 377 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/72a3b8daba3973ab538349a34845ff7149ffb32d91d5f8311d714906eac73e69.jpg", + "image_caption": [ + "(b) Small movement in pixel size.", + "(c) Multi-scale actions.", + "Figure 1. Movement feature submergence and multi-scale actions. (a) Strong class-specific context of the accordion leads to video feature generated by TAC lacking the difference between action and background. (b) Small movement of Futsal results in less difference between action area and background area. (c) Multiscale actions have different feature richness and action pattern." + ], + "image_footnote": [], + "bbox": [ + 506, + 417, + 890, + 575 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "For the first case, as shown in Fig 1(a), the action of Playing Accordion can be easily judged by Accordion, while this strong class-specific context causes the real movement information in action area to be submerged. For the second case, as shown in Fig 1(b), for Futsal, the stadium scene takes up a large proportion of pixels in the frame, while the movement information is ignored. This movement feature submergence leads to the feature in background to be similar with the feature in action area, which blues the action boundaries. If the movement information can be highlighted, the boundary will be easier to be located. However, this problem has been ignored by prior works [12, 29, 22].", + "bbox": [ + 496, + 702, + 893, + 883 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The second issue is the multi-scale of actions in an", + "bbox": [ + 519, + 885, + 890, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author", + "bbox": [ + 94, + 887, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "13555", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "untrimmed video. As shown in Fig 1(c), the feature richness varies greatly with the scale. There are rare features for action segments that account for a small proportion of the entire video, that is the small-scale action, and abundant features for those segments that account for a higher proportion, that is the large-scale action. We contend that there are different action patterns between different scales. Specifically, compared with small-scale action, large-scale action contains more obviously action process (i.e. start phase, action phase and end phase). Some researches [13, 7, 11] resort feature pyramid network (FPN) to solve the problem. However, there are two aspects that are ignored. Firstly, these works detect actions at different feature scales, but, they do not adaptively learn action features of different scales. Secondly, the information flow in FPN is insufficient, lacking interactions between different pyramid layers.", + "bbox": [ + 76, + 90, + 472, + 332 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, as an effort to overcome the above challenges, we investigate the feature of TAD. (1) In order to overcome the movement feature submergence, and highlight the difference between foreground and background snippets. We design the Movement Enhance Module (MEM) to enhance the movement information in a video snippet, which includes two crucial parts. First, we propose a siamese network named Movement Feature Extractor (MFE), which uses the dynamic information of the frame sequence and the static information of the frame to extract movement feature from video snippets. And then, we propose the Multi-Relation Enhance Module (MREM) to establish temporal and local correlations between video snippets. (2) In order to learn specific representations for different scale actions, we propose the Scale FPN (SFPN), which uses a U-shaped network to produce multi-scale video features and facilitate the information flow between different layers. Moreover, for each layer in SFPN to take charge of detecting action segments of the corresponding scale, we design a two-stage learning strategy. In the former Generalization stage, each layer is trained with all action segments; in the latter Specialization stage, each layer is biased toward actions in a specific scale range. During inference, every layer takes charge of detecting action segments of the corresponding scale.", + "bbox": [ + 76, + 333, + 472, + 709 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, this work explores feature representation and action segment representation that are more suitable for TAD task. Its contributions are summarized as follows.", + "bbox": [ + 76, + 710, + 468, + 755 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. To alleviate the movement feature submergence, we design the Movement Enhance Module (MEM) to highlight the movement feature in a video snippet, and explore local and temporal relations between snippets.", + "2. For the multi-scale actions in an untrimmed video with different feature patterns, we design the Scale FPN (SFPN) to learn different scale actions respectively, where targeted training and inference strategies are" + ], + "bbox": [ + 88, + 768, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "adopted. Consequently, each layer in the SFPN specializes in actions at a certain scale range.", + "bbox": [ + 531, + 90, + 890, + 121 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Extensive experiments conducted on two datasets verify the effectiveness of our proposed method. On ActivityNet1.3, MENet promotes the best average mAP from $36.6\\%$ to $37.7\\%$ , and boosts the mAP@0.7 from $31.8\\%$ to $34.0\\%$ on THUMOS-14.", + "bbox": [ + 511, + 133, + 893, + 208 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 224, + 640, + 239 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Video Feature for TAD. The pre-trained TAC model is often used as the feature extractor for Temporal Action Detection which receives several frames as a snippet to distill both appearance and motion information from raw video frames. TSN [26], I3D [3], and SlowFast [6] are the most common feature extractors. However, they only focus on the action categories, which results in some actions that are strongly related to the scene having quite similar representations to background segments. To overcome the drawback, TSP [1] adds additional background supervision in the pretraining model to generate the background-sensitive feature. BSP [28] artificially synthesizes different video boundaries and conducts boundary learning in the pretraining model to generate boundary-sensitive feature. However, these works cannot address the problem of movement feature submergence fundamentally. In this paper, MENet uses the Movement Enhance Module (MEM) to magnify the movement feature and the difference between action and background.", + "bbox": [ + 496, + 250, + 893, + 521 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-scale Action Detection. The scale of the action varies dramatically in a video. Compared with the large actions, those small action segments have fewer samples and insufficient features. Some works [13, 7, 11] focus on feature pyramid network (FPN) to generate different temporal resolution features. However, the FPN structure does not learn specific feature representation for a certain action scale, and also lacks sufficient information flow intrinsically. TSI [15] proposes a scale-invariant loss, which balances large and small actions in quantity, but fails to fundamentally solve the scarce feature of small actions. In this work, we propose SFPN to cope with these problems, which establishes associations between different scale features and learns scale-specific feature representations.", + "bbox": [ + 496, + 522, + 893, + 734 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Temporal Action Detection. Benefiting from the successful practice of image object detection and trimmed video action recognition, the two-stage pipeline prevails in TAD task. Specifically, the first stage is to locate candidate action segments in the video, and the second stage uses an action classifier to classify these proposals. The first stage has three main paradigms. (1) Anchor-Based method: Methods [5, 13, 21] put anchors of various scales on the video feature, and then give the final confidence of anchors. However, they cannot produce flexible boundaries. (2) Boundary-Base method: Methods [14, 31, 16]", + "bbox": [ + 496, + 734, + 895, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "13556", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "predict boundary scores on the video feature, which are combined to generate proposals. However, the confidence of the proposal lacks global information. (3) Combined method: Methods [12, 10, 4] combine these two methods to generate precise confidence and flexible boundaries. In this work, we follow the combined method to integrate the start point and end point as a proposal and generate multiscale anchor maps to predict anchor confidence.", + "bbox": [ + 75, + 90, + 472, + 212 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 224, + 168, + 239 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overview", + "text_level": 1, + "bbox": [ + 76, + 248, + 187, + 263 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Problem Definition. Input of the Movement Enhance Network (MENet) is an untrimmed video denoted as $V = \\{v_{i}\\}_{i=1}^{L_{v}}$ , where $v_{i}$ represents the $i$ -th frame of the video and $L_{v}$ is the total frames. The duration of the video is $T_{v}$ . Due to redundancy between video frames, several consecutive frames are usually regarded as a snippet. With the sampling interval $\\sigma$ , the whole video can be defined as snippet sequence $S = \\{s_{i}\\}_{i=1}^{L_{s}}$ , $L_{s} = L_{v} / \\sigma$ representing the number of total snippets. The output of the MENet is $\\{\\psi_{i} | \\psi_{i} = (t_{i,s}, t_{i,e}, c_{i}, score_{i})\\}$ where $t_{i,s}, t_{i,e}, c_{i}$ and $score_{i}$ are start time, end time, action category and confidence score, respectively. The annotations of untrimmed video are action instances $\\{\\Psi_{i} | \\Psi_{i} = (t_{i,s}^{*}, t_{i,e}^{*}, c_{i}^{*})\\}$ .", + "bbox": [ + 75, + 271, + 468, + 469 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Framework Architecture. The framework architecture of MENet is shown in Fig 2. MENet is mainly composed of two parts: Movement Enhance Module (MEM) and Scale FPN (SFPN). MEM is used to extract movement enhanced feature and explore different video relations between snippets. SFPN is proposed to generate feature pyramid and learn specific expression patterns of different action scales. Finally, SFPN gives action boundaries and confidence scores of different scale actions, separately.", + "bbox": [ + 75, + 469, + 468, + 604 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Movement Enhance Module", + "text_level": 1, + "bbox": [ + 76, + 612, + 331, + 626 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To obtain the feature that contains action category information and is sensitive to foreground and background, simultaneously, we propose the Movement Enhance Module, which contains two vital stages: Movement Feature Extractor (MFE) and Multi-Relation Enhance Module (MREM).", + "bbox": [ + 75, + 628, + 468, + 702 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Movement Feature Extractor. In order to amplify the movement information, MFE is proposed. As shown in Fig 3, MFE uses a siamese network to highlight the movement information in a video snippet. We select $\\mathrm{R}(2 + 1)\\mathrm{D}-34$ [24] as backbone with the TAC pretrained weight on Kinetics-400 [9], and two networks share the weight. MFE has two input paths. One path is video snippet path composed of consecutive frames, and the other is frame duplication path, which selects a frame from the snippet and copies it to the length of the snippet. Here, the middle frame is selected for duplication. The feature from the video snippet path contains both static scene and dynamic movement information, which is $F_{Total} \\in \\mathbb{R}^{C' \\times T}$ , but feature from", + "bbox": [ + 75, + 704, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "the frame duplication path only contains static scene information, which is $F_{Static} \\in \\mathbb{R}^{C' \\times T}$ . And then, MFE extracts the movement information in the snippet using the difference between the two features, which is defined as $F_{Movement} \\in \\mathbb{R}^{C' \\times T}$ . Finally, $F_{Movement}$ and $F_{Total}$ are concatenated as $F_{MT} \\in \\mathbb{R}^{2C' \\times T}$ .", + "bbox": [ + 496, + 90, + 890, + 181 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Multi-Relation Enhance Module. To establish relations between snippets and fuse the information at semantic dimension, the Multi-Relation Enhance Module is proposed. As shown in Fig 2, firstly, we use a 1D convolution to fuse information at semantic dimension. Secondly, there are three information paths in MREM. (1) Local Path: 1D convolution can directly establish relations in a local scale $k$ , where $k$ is the kernel size. However, it is difficult for 1D convolutions to establish temporal relationship between snippet features. (2) Forward Path: The LSTM processes each snippet successively according to the input order, with an outstanding ability to model the temporal relation. In forward path, we use LSTM to establish forward information. (3) Backward Path: In backward path, we flip the video sequence, and establish backward information. Finally, the three paths are integrated.", + "bbox": [ + 496, + 181, + 892, + 425 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. Scale Feature Pyramid Network", + "text_level": 1, + "bbox": [ + 498, + 435, + 782, + 450 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We contend different scale actions have different patterns. Therefor, the SFPN is designed to learn patterns of specific scales. SFPN contains U-Shape Module and Detector Head, which aims to generate feature pyramid and final detection results, respectively.", + "bbox": [ + 496, + 459, + 892, + 534 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "U-Shape Module. For feature pyramid generating, as shown in Fig 2, SFPN uses a U-shaped architecture inspired by [20] to generate feature sequences in different temporal resolution. From top to down, SFPN uses multiple temporal convolution layers followed by AvgPooling to downsample the temporal resolution. From bottom to up, to restore the lower layer information, SFPN uses several 1D transpose convolution to restore the feature resolution and features in the same resolution are concatenated.", + "bbox": [ + 496, + 536, + 890, + 671 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Detector Head. As demonstrated in Fig 2, each detector head consists of a Boundary Predictor, an Anchor Feature Align Layer and two Anchor Score Predictor (ASP). The output of the Boundary Predictor and Anchor Score Predictor is used to generate proposals and confidence scores, and the Anchor Feature Align Layer is to generate the feature representation for each anchor.", + "bbox": [ + 496, + 672, + 890, + 777 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Boundary Predictor. Boundary Predictor aims at predicting boundary probabilities $P_{s} = \\{p_{s}^{i}\\}_{i = 1}^{L_{i}}$ , $P_{e} = \\{p_{e}^{i}\\}_{i = 1}^{L_{i}}$ of each snippet by recognizing the boundary pattern.", + "bbox": [ + 496, + 779, + 890, + 824 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Anchor Feature Align Layer. The area between any two snippets can form an anchor, and each anchor consists of several consecutive snippets. Supposing $N_{i}$ anchors are randomly sampled to participate in the forward. The Anchor Feature Align Layer adopts SGAlign designed in [29]", + "bbox": [ + 496, + 825, + 892, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "13557", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/a24ad46a6c7ad8b213ee7318ab063eb7db95c942341d303ae56a872aec0a9d36.jpg", + "image_caption": [ + "Figure 2. Overview of our MENet and the structure of some sub-modules. There are two crucial parts in the framework (Top) of MENet: Movement Enhance Module (MEM) and Scale FPN (SFPN). MEM is designed to generate movement enhanced feature. SFPN is designed to generate multi-scale feature pyramid, and learn action expressions in different layers. The structure of the sub-modules is shown below (Bottom) with the same color in the framework." + ], + "image_footnote": [], + "bbox": [ + 89, + 93, + 870, + 412 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/58226dd19b1a8ccad45382bf78cc29a64131377a34b6b63ab24f7d8c8b3bba52.jpg", + "image_caption": [ + "Figure 3. Illustration of MFE. This module constructs the movement feature in a snippet by the difference between dynamic video snippet and static picture." + ], + "image_footnote": [], + "bbox": [ + 78, + 491, + 477, + 739 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "to generate feature expressions $F_{A}^{i}\\in \\mathbb{R}^{C\\times S\\times N_{i}}$ for anchors from the video feature $F_{v}^{i}$ , where $S$ is the sampling number of snippets within an anchor.", + "bbox": [ + 75, + 805, + 470, + 851 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Anchor Score Predictor. IoU-ASP and Offset-ASP have the same structure to recognize the action pattern within an anchor. For the $i$ -th layer in SFPN, IoU-ASP gener", + "bbox": [ + 75, + 854, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ates two maps $M_{cls}^{i}\\in \\mathbb{R}^{D_{i}\\times L_{i}},M_{reg}^{i}\\in \\mathbb{R}^{D_{i}\\times L_{i}}$ , where $D_{i}$ is predefined maximum anchor duration. In Offset-ASP, two output maps are denoted as $M_{cent}^{i}\\in \\mathbb{R}^{D_{i}\\times L_{i}},M_{dura}^{i}\\in$ $\\mathbb{R}^{D_i\\times L_i}$ . These two maps indicate each anchor's center offset and duration offset respectively.", + "bbox": [ + 500, + 491, + 893, + 570 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Specific action pattern Learning", + "text_level": 1, + "bbox": [ + 500, + 585, + 784, + 602 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Actions of different scales have different feature representations. Correspondingly, different layers in SFPN have different feature granularity and temporal resolution. Therefore, we advocate applying a targeted training strategy for actions at different scales, assuring that each layer in SFPN is only responsible for actions at a specific scale range. Specifically, define the scale $S \\in [0,1]$ as the ratio of action length to video length. Then the first layer (the top layer of the pyramid) with the longest sequence is responsible for small-scale actions whose scale in $[S_{min}^{1}, S_{max}^{1}]$ , and the second layer (the middle layer of the pyramid) with a moderate sequence length is responsible for medium-scale actions whose scale in $[S_{min}^{2}, S_{max}^{2}]$ . The remaining third layer with the shortest sequence is responsible for large-scale actions whose scale belongs to $[S_{min}^{3}, S_{max}^{3}]$ . To implement this idea, a two-stage training strategy is designed.", + "bbox": [ + 496, + 611, + 890, + 852 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Two-stage training strategy. The two-stages of training ASP are Generalization and Specialization, respectively. Due to the different lengths of feature sequences, the to", + "bbox": [ + 496, + 854, + 893, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "13558", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/1649173c50836dba2f4757d1ea10c7fb3d52114b230f06d76908c623b59ece86.jpg", + "image_caption": [ + "Figure 4. The two-stage training strategy (left column and middle column) and the inference strategy (right column) of ASP. Each square represents an anchor map of a layer, the grey area is the invalid region. Other colors represent different sampling ratios in a certain scale range, with white, green, yellow and red representing $0\\%$ , $r_i$ , $2r_i$ and $100\\%$ respectively." + ], + "image_footnote": [], + "bbox": [ + 99, + 97, + 228, + 265 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/0582439aa20faf1e40e2f4294fc9e8899ec276a5177358ba32ef51ebe84baea2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 243, + 98, + 356, + 266 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/3b39d423219f0d6d005fa4ee796746c5e7863dcfdb83e2216d46d86fa403d9ac.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 362, + 99, + 473, + 268 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "tal number of dense anchors contained in each layer varies. In order to ensure that each layer is trained equally and reduce the computational cost, different anchor sampling ratios $r_1$ , $r_2$ , $r_3$ are set for the three layers, where $0\\% < r_1 \\leq r_2 \\leq r_3 \\leq 100\\%$ . (1) In the former Generalization stage, given the sampling ratio $r_i$ , randomly sample $N_i = \\binom{L_i}{2} \\cdot r_i$ anchors from valid region to train the IoU-ASP and Offset-ASP of $i$ -th layer, as shown in the left column of Fig 4. The purpose of this stage is to let ASP learn a general pattern of all actions. (2) In the latter Specialization stage, for the $i$ -th layer in SFPN, the training samples come from two parts, as shown in the middle column in Fig 4. The first part are randomly sampled according to the sampling rate of $\\min(100\\%, 2 \\cdot r_i)$ from anchors whose scale in $[S_{min}^i, S_{max}^i]$ (yellow area in Fig 4). The second part are sampled from the remaining anchors whose scale in $(0, S_{min}^i)$ or $(S_{max}^i, 100\\%)$ , with the sampling rate of $r_i$ (green area in Fig 4). This Specialization stage highlights the effect of anchors at the certain scale range, making the detection head of each layer more specialized.", + "bbox": [ + 75, + 388, + 468, + 691 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.5. Training & Inference", + "text_level": 1, + "bbox": [ + 76, + 705, + 276, + 722 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Label Assignment. Assuming the video duration is $L_{v}$ , each snippet corresponds to a video period. In annotation, a ground-truth action which starts at $t_{s}^{*}$ and ends at $t_{e}^{*}$ . Expanding boundary from moment to region, the start region is defined as $R_{s} = [t_{s}^{*} - 1.5\\frac{T_{v}}{L_{i}}, t_{s}^{*} + 1.5\\frac{T_{v}}{L_{i}}]$ and end region is defined as $R_{e} = [t_{e}^{*} - 1.5\\frac{T_{v}}{L_{i}}, t_{e}^{*} + 1.5\\frac{T_{v}}{L_{i}}]$ . For Boundary Predictor, compute the overlap between each snippet period and $R_{s}$ as the label of start probabilities $G_{s}^{i} \\in \\mathbb{R}^{L_{i}}$ . Similarly, compute the overlap between snippet period and $R_{e}$ as the label of end probabilities $G_{e}^{i}$ . For IoU-ASP, following [12], IoU between each anchor and all actions are", + "bbox": [ + 75, + 729, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "calculated and then arranged into a map $G_{IoU}^{i} \\in \\mathbb{R}^{D_{i} \\times L_{i}}$ . Anchors with tIoU score greater than 0.9 participate in the training of Offset-ASP. For anchor start at $t_{s}$ and end at $t_{e}$ , assuming its corresponding ground-truth action is $[t_{s}^{*}, t_{e}^{*}]$ , the center offset $\\Delta c$ and duration offset $\\Delta d$ are calculated as Eq. (1)-(2), and arranged into maps $G_{cent}^{i} \\in \\mathbb{R}^{D_{i} \\times L_{i}}$ and $G_{dura}^{i} \\in \\mathbb{R}^{D_{i} \\times L_{i}}$ .", + "bbox": [ + 496, + 89, + 890, + 198 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nc = \\frac {t _ {s} + t _ {e}}{2}, d = t _ {e} - t _ {s}, c ^ {*} = \\frac {t _ {s} ^ {*} + t _ {e} ^ {*}}{2}, d ^ {*} = t _ {e} ^ {*} - t _ {s} ^ {*} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 521, + 202, + 890, + 229 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\Delta c = \\frac {c ^ {*} - c}{d}, \\Delta d = \\log \\frac {d ^ {*}}{d} \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 607, + 231, + 890, + 258 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Basic Loss. (1) For the $i$ -th layer, the loss of Boundary-Predictor is the re-weighted binary cross-entropy loss $L_{B}$ Eq. 3, where $P = \\{p_t\\}_{t=1}^{L_i}$ and $G = \\{g_t\\}_{t=1}^{L_i}$ represent the predicted boundary probabilities and its label of all snippets, respectively. Snippets with $g_t > 0.5$ serve as positive samples (i.e., $\\delta \\{g_t > 0.5\\} = 1$ ) and others are negative samples. $T_{i}^{+}$ and $T_{i}^{-}$ are the number of positive and negative samples in this layer respectively. (2) The loss of IoU-ASP is the re-weighted binary cross-entropy loss $L_{asp}$ Eq. 4 and L2 loss $L_{2}$ , where $M = \\{m_j\\}_{j=1}^{N_i}$ and $G = \\{g_j\\}_{j=1}^{N_i}$ represent the predicted value and ground-truth value of each sampled anchor in the $i$ -th layer. $N_{i}, N_{i}^{+}, N_{i}^{-}$ represent the number of sampled anchors, positive anchors whose tIoU greater than 0.9 and negative anchors of this layer, respectively. (3) The loss of Offset-ASP is Smooth L1 loss $L_{1}$ . Note that only those sampled anchors with tIoU greater than 0.9 participate in the training of Offset-ASP. The re-weights in $L_{B}$ and $L_{asp}$ are used to balance the number between positive and negative samples.", + "bbox": [ + 496, + 267, + 892, + 556 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} L _ {B} (P, G) = - \\frac {1}{L _ {i}} \\sum_ {t = 1} ^ {L _ {i}} \\left(\\frac {L _ {i}}{T _ {i} ^ {+}} \\cdot \\delta \\left\\{g _ {t} > 0. 5 \\right\\} \\cdot \\log p _ {t} \\right. \\tag {3} \\\\ + \\frac {L _ {i}}{T _ {i} ^ {-}} (1 - \\delta \\left\\{g _ {t} > 0. 5 \\right\\} \\cdot \\log \\left(1 - p _ {t}\\right)) \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 542, + 564, + 890, + 633 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} L _ {a s p} (M, G) = - \\frac {1}{N _ {i}} \\sum_ {j = 1} ^ {N _ {i}} \\left(\\frac {N _ {i}}{N _ {i} ^ {+}} \\cdot \\delta \\left\\{g _ {j} > 0. 9 \\right\\} \\cdot \\log m _ {j} \\right. \\tag {4} \\\\ + \\frac {N _ {i}}{N _ {i} ^ {-}} (1 - \\delta \\{g _ {j} > 0. 9 \\} \\cdot \\log (1 - m _ {j})) \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 522, + 641, + 890, + 712 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Total Loss. The loss of the $i$ -th layer is composed of three parts: boundary loss, IoU loss and offset loss, as shown in Eq.(5) (6) (7) respectively. The total training objective is the sum of all three layers, formulated as Eq. 8. Besides, in order to balance the value between different terms, the coefficient $\\lambda 1$ and $\\lambda 2$ are set as 5 and 10.", + "bbox": [ + 496, + 720, + 890, + 810 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {\\text {b o u n d}} ^ {i} = L _ {B} \\left(P _ {s} ^ {i}, G _ {s} ^ {i}\\right) + L _ {B} \\left(P _ {e} ^ {i}, G _ {e} ^ {i}\\right) \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 816, + 890, + 834 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {I o U} ^ {i} = L _ {a s p} \\left(M _ {c l s} ^ {i}, G _ {I o U} ^ {i}\\right) + \\lambda_ {1} \\cdot L _ {2} \\left(M _ {r e g} ^ {i}, G _ {I o U} ^ {i}\\right) \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 535, + 847, + 890, + 864 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {o f f} ^ {i} = L _ {1} \\left(M _ {c e n t} ^ {i}, G _ {c e n t} ^ {i}\\right) + L _ {1} \\left(M _ {d u r a} ^ {i}, G _ {d u r a} ^ {i}\\right) \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 545, + 883, + 890, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "13559", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {t o t a l} = \\sum_ {i = 1} ^ {3} \\left(L _ {B} ^ {i} + L _ {I o U} ^ {i} + \\lambda_ {2} \\cdot L _ {o f f} ^ {i}\\right) \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 87, + 468, + 125 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Inference. Each layer outputs $P_{s}^{i}, P_{e}^{i}, M_{cls}^{i}, M_{reg}^{i}, M_{cent}^{i}$ and $M_{dura}^{i}$ from the detector head in inference. Following [14, 12, 15], snippet in boundary probability $P_{s}$ is screened out as candidate start point if it is local peak or its probability is greater than $0.5 \\cdot \\max(P_{s})$ . And snippets can be selected as candidate end point from $P_{e}$ in the same way. Then the candidate start and end points are combined into proposals. In order to produce the more reasonable proposals, as shown in Fig 4, each layer of SFPN only outputs anchors in the corresponding scale range. Specifically, for the $i$ -th layer, its responsible scale range is $[S_{min}^{i}, S_{max}^{i}]$ . Furthermore, in the proposals set, for any start snippet whose index is $sdx$ and centered at time $t_{1}$ , and the end snippet whose index is $edx$ and centered at time $t_{2}$ , we can get its start probability $p_{s} = P_{s}^{i}[sdx]$ , end probability $p_{e} = P_{e}^{i}[edx]$ and tIoU score $p_{IoU} = M_{cls}^{i}[edx - sdx, sdx] \\cdot M_{reg}^{i}[edx - sdx, sdx]$ . Its center is $c = (sdx + edx)/2L_{i}$ and duration is $d = (edx - sdx)/L_{i}$ . Subsequently, to refine the boundary, we can obtain center offset $\\Delta c = M_{cent}^{i}[edx - sdx, sdx]$ and duration offset $\\Delta d = M_{dura}^{i}[edx - sdx, sdx]$ , and adjust the boundary to $(t_{1}', t_{2}')$ as Eq. 9:", + "bbox": [ + 76, + 126, + 472, + 446 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} c ^ {\\prime} = d \\cdot \\Delta c + c, d ^ {\\prime} = d \\cdot e ^ {\\Delta d} \\\\ t _ {1} ^ {\\prime} = c ^ {\\prime} - \\frac {d ^ {\\prime}}{2}, t _ {2} ^ {\\prime} = c ^ {\\prime} + \\frac {d ^ {\\prime}}{2} \\tag {9} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 181, + 454, + 468, + 501 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Finally, proposals generated by each layer are merged together, and the action classifier assigns every proposal with a certain label and a classification score $P_{\\text{label}}$ . The final score for the proposal $(t_1', t_2')$ is shown as Eq. 10. Then Soft-NMS [32] is adopted to remove redundant segments.", + "bbox": [ + 76, + 500, + 468, + 575 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {s c o r e} _ {t _ {1} ^ {\\prime}, t _ {2} ^ {\\prime}} = p _ {s} \\cdot p _ {e} \\cdot p _ {I o U} \\cdot p _ {\\text {l a b e l}} \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 580, + 468, + 597 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 603, + 209, + 619 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Dataset and Settings", + "text_level": 1, + "bbox": [ + 76, + 625, + 269, + 640 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Dataset. In order to verify the effectiveness of MENet, we experiment on two challenging datasets. ActivityNet-1.3 [2] contains 200 categories of daily life, sports, etc. We use the training set for model training and report the performance on the validation set. THUMOS-14 [8] consists of 413 videos with 20 action classes which is almost sports. In THUMOS-14, the validation set contains 200 long videos, including 3007 action segments, and the test set contains 213 videos, including 3358 action segments. Following the standard practice of THUMOS-14, we train MENet on the validation set and valid it on the test set.", + "bbox": [ + 75, + 643, + 468, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Metric. In order to fully demonstrate the advantages of our proposed method, we use two main evaluation metrics: mAP under a certain temporal tIoU threshold (mAP@tIoU) and average recall at a specified average number of proposals (AR@AN). Besides, on ActivityNet, the area under the AR-AN curve (AUC) also serves as a metric.", + "bbox": [ + 75, + 810, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Network Details. We use $\\mathrm{R}(2 + 1)\\mathrm{D} - 34$ as backbone with the TAC pretrained weight on Kinetics-400 serving as the primary feature extractor. The sampling interval $\\sigma$ set as 16 frames and 5 frames for ActivityNet-1.3 and THUMOS-14, respectively. In this way, for the input video with $L_{v}$ frames, video snippet length $L_{s} = L_{v} / \\sigma$ . For ActivityNet-1.3, we use linear interpolation to resize the length of video features $T = 200$ . For a long video in THUMOS-14, a sliding window with a length of 256 and an overlap of $50\\%$ is used to truncate the original video feature. Each window is detected independently, and finally the results of all windows are concatenated as the total result of the entire long video. The scale ranges of each layer in the pyramid are set as: $[S_{min}^{1}, S_{max}^{1}] = [0, 15\\%]$ , $[S_{min}^{2}, S_{max}^{2}] = [10\\%, 75\\%]$ and $[S_{min}^{3}, S_{max}^{3}] = [50\\%, 100\\%]$ . As for the action classifier, following the routine of most two-stage TAD methods, Untrimmed Net [25] serves as the classifier for THUMOS-14, and the recognition model by [32] for ActivityNet-1.3.", + "bbox": [ + 496, + 90, + 890, + 363 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation Details. MENet is trained by Adam algorithm with batch size 8 and learning rate $10^{-3}$ . The sampling ratio of each layer $r_1$ , $r_2$ , $r_3$ are set as $50\\%$ , $40\\%$ , $90\\%$ , respectively. For ActivityNet-1.3, the training process takes 10 epochs, where the first 7 epochs is the Generalization stage and the rest is the Specialization stage. As for THUMOS-14, the total training epoch is 7, and only the first epoch is the Generalization stage. Besides, the learning rate is decayed to $10^{-4}$ after 5 epochs on THUMOS-14 and 7 epochs on ActivityNet-1.3.", + "bbox": [ + 496, + 364, + 890, + 515 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Performance Evaluation On Detection", + "text_level": 1, + "bbox": [ + 498, + 530, + 828, + 545 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We compare MENet with other state-of-the-art methods on ActivityNet-1.3 and THUMOS-14. Table 1 shows the comparison on the validation set of ActivityNet-1.3. The mAP at tIoU thresholds of $\\{0.5, 0.75, 0.95\\}$ are reported, as well as the Avg.mAP which is calculated at tIoU thresholds between 0.5 and 0.95 with the step of 0.05. Impressively, MENet outperforms other representative methods at tIoU thresholds 0.75 and 0.95. MENet promotes the Avg.mAP from $36.6\\%$ to $37.7\\%$ , with an increase of more than $1.1\\%$ . Comparing the methods of different backbones, MENet exceeds others.", + "bbox": [ + 496, + 551, + 890, + 715 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2 presents the detection performance comparison on the test set of THUMOS-14. MENet achieves comparable performance with the best method [30] at low tIoU thresholds. But, MENet outperforms other representative methods at tIoU thresholds 0.6 and 0.7. MENet improves the mAP@0.7 from the current best $31.8\\%$ to $34.0\\%$ . To locate the boundaries more accurately, a higher threshold is usually used to separate the positive and negative samples in training. Therefore MENet has a better response at high tIoU thresholds. Higher tIoU means more precise action boundaries, which is more difficult and more important for action localization. Meanwhile, it is noteworthy", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "13560", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "that MENet shows obvious superiority compared with other FPN-based methods like [11], which substantiates the effectiveness of the SFPN proposed in MENet.", + "bbox": [ + 76, + 90, + 468, + 137 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/eed16e05be0ba05647519cf65cc095f82ab55426080f8e88165a1344fc2fe1a9.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodBackbonemAP@tIoU (%)
0.50.750.95Avg.
GTAN [16]P3D52.634.18.934.3
BSN [14]TSN46.530.08.030.0
BMN [12]TSN50.134.88.333.9
G-TAD [29]TSN50.434.69.034.1
PCMNet [18]TSN51.436.19.535.3
TCA-Net [19]TSN52.336.76.935.5
RTD-Net [23]I3D47.230.78.630.8
ContextLoc [33]I3D56.035.23.634.2
AFSD [11]I3D52.435.36.534.4
TAGS [17]I3D56.336.89.636.5
STPT [27]STPT51.433.76.833.4
ActionFormer [30]R(2+1)D54.737.88.436.6
MENet(ours)R(2+1)D54.738.410.537.7
", + "bbox": [ + 86, + 141, + 460, + 351 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/3658cd4973a9ddc166447557a483c1b6924e060dc7ca0d9dbd7d1ccfaef27360.jpg", + "table_caption": [ + "Table 1. The temporal action detection performance comparison with state-of-art methods on ActivityNet-1.3. Bold text indicates the best results." + ], + "table_footnote": [], + "table_body": "
MethodBackbonemAP@tIoU (%)
0.30.40.50.60.7
GTAN [16]P3D57.847.238.8--
BSN [14]TSN53.545.036.928.420.0
BMN [12]TSN56.047.438.829.720.5
G-TAD [12]TSN54.547.640.230.823.4
PCMNet [18]TSN61.555.447.237.527.3
TCA-Net [19]TSN60.653.244.636.826.7
RTD-Net [23]I3D68.362.351.938.823.7
ContextLoc [33]I3D68.363.854.341.826.2
AFSD [11]I3D67.362.455.543.731.1
TAGS [17]I3D68.663.857.046.331.8
STPT [27]STPT70.665.756.444.630.5
ActionFormer [30]R(2+1)D73.467.459.146.731.5
MENet(ours)R(2+1)D70.765.358.849.134.0
", + "bbox": [ + 86, + 398, + 460, + 609 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Performance Evaluation On Proposal", + "text_level": 1, + "bbox": [ + 76, + 662, + 401, + 678 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To further verify the advantages of MENet, we do not consider action classes of action segments to evaluate its performance on temporal action proposal (TAP) task.", + "bbox": [ + 76, + 679, + 468, + 724 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Through Table 3, we can further discover the performance improvement of AR@100 and the area under the AR-AN curve (AUC) on ActivityNet-1.3. For instance, MENet boosts the AUC from $68.1\\%$ to $70.2\\%$ . As for THUMOS-14, MENet outperforms other methods in all metrics are reported in Table 4, which certifies the effectiveness of MENet once again.", + "bbox": [ + 75, + 724, + 468, + 830 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 839, + 230, + 854 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation studies are performed thoroughly to verify the role of each module in MENet, as well as the impact of different training strategies.", + "bbox": [ + 75, + 854, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/0fd009865288f8aaabaa0a136ee0d03b9433b0700db3e436d700f8b3ce4859f2.jpg", + "table_caption": [ + "Table 2. The temporal action detection performance comparison with state-of-art methods on THUMOS-14. Bold text indicates the best results." + ], + "table_footnote": [], + "table_body": "
MethodAR@100AUC
BSN [14]74.266.2
GTAN [16]74.867.1
BMN [12]75.067.1
RTD-Net [23]73.265.8
TCA-Net [19]76.168.1
MENet(ours)77.070.2
", + "bbox": [ + 570, + 88, + 821, + 204 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/e3c37f52b46eecea386e15d040402bd4f75884dbda65748fb574b1293b9aab94.jpg", + "table_caption": [ + "Table 3. Temporal action proposal performance comparison with other representative methods on ActivityNet-1.3. Bold text indicates the best results." + ], + "table_footnote": [], + "table_body": "
MethodAR@50AR@100AR@200AR@500
BSN [14]37.546.153.260.6
BMN [12]39.447.754.762.1
RTD-Net [23]41.549.3256.4162.91
TCA-Net [19]42.150.557.163.6
MENet(ours)44.252.358.666.0
", + "bbox": [ + 501, + 252, + 893, + 354 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "1). Effectiveness of the MEM: As discussed before, when constructing the movement enhance feature, MFE and MREM are the crucial designs in MEM. To certify the function of these two modules, we design a Base model for comparison, in which the Movement Feature is removed and MREM is replaced by temporal 1D convolution. As shown in Table 5, we can find that compared with the Base model, Movement Feature and MREM both can promote the performance. Besides, the best results emerge when combining them together as the intact MEM.", + "bbox": [ + 498, + 406, + 890, + 556 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/c533832ae48e5e70bdc825b947395e770ec577bb7ca2c63a4a26b2411582bd1e.jpg", + "table_caption": [ + "Table 4. Temporal action proposal performance comparison with other representative methods on THUMOS-14, measured by AR@AN. Bold text indicates the best results." + ], + "table_footnote": [], + "table_body": "
ConstructionmAP@tIoU (%)
0.50.750.95Avg.
Base54.237.310.437.0
Base + Movement Feature54.537.810.637.3
Base + MREM54.437.910.437.3
MEM54.738.410.537.7
", + "bbox": [ + 501, + 561, + 890, + 662 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 5. Ablation study on the MEM. The Detection performance is reported on ActivityNet-1.3. And The best result can be achieved with these two modules are integrated.", + "bbox": [ + 498, + 670, + 890, + 713 + ], + "page_idx": 6 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "2). Effectiveness of the U-shape Module: As discussed before, when constructing the feature pyramid, U-shape Module is designed to establish interactions between different layers. To reveal the validity of this idea, we use 1D convolution with the step of 2 and AvgPooling to downsample the feature sequence respectively. From Table 6, the U-shape Module can promote the performance, which substantiates the importance of this design.", + "3). Effectiveness of feature pyramid structure: For better detection accuracy, MENet makes use of the feature pyramid. To verify the impact of this structure, we only use a single layer feature sequence to conduct experiments" + ], + "bbox": [ + 498, + 719, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "13561", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/a85f145370d12047ebe35e72e4a3675b362c1d141f0b386ba90ed7796b4d74bc.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ConstructionmAP@tIoU (%)
0.50.750.95Avg.
DownSampling (AvgPooling)54.538.210.237.4
DownSampling (Convolution)54.438.110.837.3
U-shape Module54.738.410.537.7
", + "bbox": [ + 84, + 89, + 459, + 172 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "and compare it with the SFPN, keeping other components unchanged. On ActivityNet-1.3, single-layer feature with lengths of 200, 100 and 50 are used. Corresponding results are shown in Table 7. The experimental results exhibit that SFPN performs better than any other single-layer structure, thus justifying the feature pyramid structure is indeed beneficial to the performance.", + "bbox": [ + 75, + 215, + 467, + 321 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/c732fd1239b2e6ea0638c7aa2718458a9e5804d1b8984440abb80594590664d5.jpg", + "table_caption": [ + "Table 6. Ablation study on the U-shape Module. The Detection performance is reported on ActivityNet-1.3." + ], + "table_footnote": [], + "table_body": "
LengthmAP@tIoU (%)
0.50.750.95Avg.
5053.037.110.836.8
10054.138.110.437.1
20054.238.310.537.3
SFPN54.738.410.537.7
", + "bbox": [ + 138, + 329, + 405, + 431 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4). Effectiveness of two-stage training: For efficient training of MENet and ensuring that the $i$ -th layer in SFPN is specialized in actions at a specific scale range $[S_{min}^{i}, S_{max}^{i}]$ , the two-stage training strategy is applied. When training ASP of the $i$ -th layer, in the first Generalization stage, the anchors are randomly selected from all scales according to the sampling ratio $r_i$ , in the second Specialization stage, the sampling ratio inside and outside the range $[S_{min}^{i}, S_{max}^{i}]$ are $2 \\cdot r_i$ and $r_i$ , respectively. In this ablation study, we train MENet using the fully Generalization stage, the fully Specialization stage and the complete two-stage strategy, respectively. In addition, to demonstrate the effectiveness of this training method, we also test a new Bias training strategy that only samples from the range $[S_{min}^{i}, S_{max}^{i}]$ with the sampling ratio of $r_i$ .", + "bbox": [ + 75, + 491, + 467, + 717 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "As shown in Table 8, the performance of the Bias strategy is the worst, indicating that in addition to those samples in the specific scale range, other samples outside this range also play an important role for a better understanding of actions. Further, the training effect is impeded when removing either the Generalization or the Specialization stage, which verifies the effectiveness of the two-stage training strategy.", + "bbox": [ + 75, + 718, + 467, + 824 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5). Qualitative Comparison: To illustrate the edge of MENet more intuitively, we select videos of Javelin Throw and High Jump from ActivityNet-1.3 and compare our results qualitatively with the Base, in which we remove the movement enhanced feature and SFPN. Results with the", + "bbox": [ + 75, + 825, + 467, + 898 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/9f86625fc8edc84f44812348c80a6b23b0ddd689bc5a61f1c8202cf0c1d1be6d.jpg", + "table_caption": [ + "Table 7. Ablation study on the SFPN. \"Length\" means the temporal length of single layer feature sequence. The Detection performance is reported on ActivityNet-1.3." + ], + "table_footnote": [], + "table_body": "
Training StrategymAP@tIoU (%)
0.50.750.95Avg.
only Bias45.829.17.429.4
only Generalization54.338.211.037.4
only Specialization54.638.010.837.4
two-stage54.738.410.537.7
", + "bbox": [ + 521, + 89, + 867, + 188 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 8. Ablation study on the two-stage training strategy. The proposed two-stage training leads to better performance than the single stage method or the Bias method.", + "bbox": [ + 498, + 194, + 890, + 236 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "highest confidence score are visualized in Fig 5. Firstly, Compared with the Base method, MENet uses the movement feature, which enlarges the difference between action and background, making the model more accurate in boundary localization. Secondly, it can be seen the High Jump action contains a large-scale action and a small-scale action. Due to the SFPN in MENet, MENet can better capture actions at different scales. Results of qualitative comparison once again prove the superiority of MENet.", + "bbox": [ + 496, + 244, + 890, + 381 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b0b660d9f12d5764c2ed6ef2d20fa2ba3356685c5f71cefc74c313b3811c4f01.jpg", + "image_caption": [ + "Figure 5. Qualitative Comparison. MENet generates more accurate action segments." + ], + "image_footnote": [], + "bbox": [ + 506, + 398, + 704, + 508 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a7cc00d0cfecdd234bf25ab228c3639146b3a495b6508ab208893300bf9d3655.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 709, + 398, + 905, + 508 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 563, + 617, + 577 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Temporal action detection (TAD) is aimed at localizing the action segment and classifying the action class. Despite the considerable attention and rapid development, TAD is hindered by two critical problems: the movement feature submergence and multi-scale action detection. In an effort to overcome these two challenges, we propose the Movement Enhance Network (MENet) with two crucial designs. Firstly, we propose the Movement Enhance Module (MEM) to extract the movement feature in video snippets and explore the multi-relations between the snippets. Secondly, we propose the Scale FPN (SFPN) to handle the different scale actions, we design the U-shape Module to facilitate the information flow between different scale features. For better performance, we design the training and inference stage, ensuring that each layer in MENet is specialized at a specific scale range. Extensive experiments demonstrate that MENet considerably outperforms other representative TAD methods on ActivityNet-1.3 and THUMOS-14.", + "bbox": [ + 496, + 582, + 890, + 852 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements. This work was supported by National Natural Science Foundation of China (NSFC) No. 62176156.", + "bbox": [ + 498, + 854, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "13562", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Humam Alwassel, Silvio Giancola, and Bernard Ghanem. Tsp: Temporally-sensitive pretraining of video encoders for localization tasks. In ICCV, pages 3173-3183, 2021.", + "[2] Fabian Caba Heilbron, Victor Escorcia, Bernard Ghanem, and Juan Carlos Niebles. 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In ICCV, pages 13516-13525, 2021." + ], + "bbox": [ + 76, + 90, + 468, + 162 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "13564", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/d8a8f490-e49c-49c9-b1d9-2afa438fb3bc_model.json b/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/d8a8f490-e49c-49c9-b1d9-2afa438fb3bc_model.json new file mode 100644 index 0000000000000000000000000000000000000000..178bc2068fd0390e8e45c53ee8b4007aa58812d1 --- /dev/null +++ b/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/d8a8f490-e49c-49c9-b1d9-2afa438fb3bc_model.json @@ -0,0 +1,1925 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.107, + 0.13, + 0.868, + 0.177 + ], + "angle": 0, + "content": "Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection" + }, + { + "type": "text", + "bbox": [ + 0.223, + 0.204, + 0.749, + 0.258 + ], + "angle": 0, + "content": "Zixuan Zhao Dongqi Wang Xu Zhao* \nDepartment of Automation, Shanghai Jiao Tong University, China \n{zhaozixuan, wangdq0124, zhaoxu}@sjtu.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.314, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.324, + 0.474, + 0.686 + ], + "angle": 0, + "content": "Boundary localization is a challenging problem in Temporal Action Detection (TAD), in which there are two main issues. First, the submergence of movement feature, i.e. the movement information in a snippet is covered by the scene information. Second, the scale of action, that is, the proportion of action segments in the entire video, is considerably variable. In this work, we first design a Movement Enhance Module (MEM) to highlight movement feature for better action location, and then, we propose a Scale Feature Pyramid Network (SFPN) to detect multi-scale actions in videos. For Movement Enhance Module, firstly, Movement Feature Extractor (MFE) is designed to get the movement feature. Secondly, we propose a Multi-Relation Enhance Module (MREM) to grasp valuable information correlation both locally and temporally. For Scale Feature Pyramid Network, we design a U-Shape Module to model different scale actions, moreover, we design the training and inference strategy of different scales, ensuring that each pyramid layer is only responsible for actions at a specific scale. These two innovations are integrated as the Movement Enhance Network (MENet), and extensive experiments conducted on two challenging benchmarks demonstrate its effectiveness. MENet outperforms other representative TAD methods on ActivityNet-1.3 and THUMOS-14." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.696, + 0.21, + 0.71 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.713, + 0.47, + 0.804 + ], + "angle": 0, + "content": "Temporal Action Detection (TAD) is a significant video understanding task, which aims to extract video segments with specific action labels from untrimmed long videos. It remains a challenging problem because action boundaries are difficult to determine precisely, which adversely affects the performance in most works." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.804, + 0.47, + 0.88 + ], + "angle": 0, + "content": "Two critical issues stand in the way of detecting action boundaries robustly from untrimmed videos. The first issue, which could be called as movement feature submergence, exists in where either context but not movement itself dominate feature expression, or movement is small in pixel size." + }, + { + "type": "image", + "bbox": [ + 0.513, + 0.298, + 0.697, + 0.379 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.514, + 0.392, + 0.69, + 0.405 + ], + "angle": 0, + "content": "(a) Strong class-specific context." + }, + { + "type": "image", + "bbox": [ + 0.703, + 0.298, + 0.89, + 0.378 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.702, + 0.392, + 0.882, + 0.405 + ], + "angle": 0, + "content": "(b) Small movement in pixel size." + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.418, + 0.892, + 0.577 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.638, + 0.59, + 0.764, + 0.602 + ], + "angle": 0, + "content": "(c) Multi-scale actions." + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.606, + 0.895, + 0.69 + ], + "angle": 0, + "content": "Figure 1. Movement feature submergence and multi-scale actions. (a) Strong class-specific context of the accordion leads to video feature generated by TAC lacking the difference between action and background. (b) Small movement of Futsal results in less difference between action area and background area. (c) Multiscale actions have different feature richness and action pattern." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.703, + 0.895, + 0.884 + ], + "angle": 0, + "content": "For the first case, as shown in Fig 1(a), the action of Playing Accordion can be easily judged by Accordion, while this strong class-specific context causes the real movement information in action area to be submerged. For the second case, as shown in Fig 1(b), for Futsal, the stadium scene takes up a large proportion of pixels in the frame, while the movement information is ignored. This movement feature submergence leads to the feature in background to be similar with the feature in action area, which blues the action boundaries. If the movement information can be highlighted, the boundary will be easier to be located. However, this problem has been ignored by prior works [12, 29, 22]." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.886, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The second issue is the multi-scale of actions in an" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.888, + 0.221, + 0.9 + ], + "angle": 0, + "content": "*Corresponding author" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13555" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.333 + ], + "angle": 0, + "content": "untrimmed video. As shown in Fig 1(c), the feature richness varies greatly with the scale. There are rare features for action segments that account for a small proportion of the entire video, that is the small-scale action, and abundant features for those segments that account for a higher proportion, that is the large-scale action. We contend that there are different action patterns between different scales. Specifically, compared with small-scale action, large-scale action contains more obviously action process (i.e. start phase, action phase and end phase). Some researches [13, 7, 11] resort feature pyramid network (FPN) to solve the problem. However, there are two aspects that are ignored. Firstly, these works detect actions at different feature scales, but, they do not adaptively learn action features of different scales. Secondly, the information flow in FPN is insufficient, lacking interactions between different pyramid layers." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.334, + 0.473, + 0.71 + ], + "angle": 0, + "content": "In this paper, as an effort to overcome the above challenges, we investigate the feature of TAD. (1) In order to overcome the movement feature submergence, and highlight the difference between foreground and background snippets. We design the Movement Enhance Module (MEM) to enhance the movement information in a video snippet, which includes two crucial parts. First, we propose a siamese network named Movement Feature Extractor (MFE), which uses the dynamic information of the frame sequence and the static information of the frame to extract movement feature from video snippets. And then, we propose the Multi-Relation Enhance Module (MREM) to establish temporal and local correlations between video snippets. (2) In order to learn specific representations for different scale actions, we propose the Scale FPN (SFPN), which uses a U-shaped network to produce multi-scale video features and facilitate the information flow between different layers. Moreover, for each layer in SFPN to take charge of detecting action segments of the corresponding scale, we design a two-stage learning strategy. In the former Generalization stage, each layer is trained with all action segments; in the latter Specialization stage, each layer is biased toward actions in a specific scale range. During inference, every layer takes charge of detecting action segments of the corresponding scale." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.711, + 0.47, + 0.756 + ], + "angle": 0, + "content": "In summary, this work explores feature representation and action segment representation that are more suitable for TAD task. Its contributions are summarized as follows." + }, + { + "type": "text", + "bbox": [ + 0.09, + 0.77, + 0.47, + 0.83 + ], + "angle": 0, + "content": "1. To alleviate the movement feature submergence, we design the Movement Enhance Module (MEM) to highlight the movement feature in a video snippet, and explore local and temporal relations between snippets." + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.84, + 0.47, + 0.901 + ], + "angle": 0, + "content": "2. For the multi-scale actions in an untrimmed video with different feature patterns, we design the Scale FPN (SFPN) to learn different scale actions respectively, where targeted training and inference strategies are" + }, + { + "type": "list", + "bbox": [ + 0.089, + 0.77, + 0.47, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.532, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "adopted. Consequently, each layer in the SFPN specializes in actions at a certain scale range." + }, + { + "type": "text", + "bbox": [ + 0.513, + 0.134, + 0.894, + 0.209 + ], + "angle": 0, + "content": "3. Extensive experiments conducted on two datasets verify the effectiveness of our proposed method. On ActivityNet1.3, MENet promotes the best average mAP from \\(36.6\\%\\) to \\(37.7\\%\\), and boosts the mAP@0.7 from \\(31.8\\%\\) to \\(34.0\\%\\) on THUMOS-14." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.225, + 0.642, + 0.241 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.25, + 0.895, + 0.522 + ], + "angle": 0, + "content": "Video Feature for TAD. The pre-trained TAC model is often used as the feature extractor for Temporal Action Detection which receives several frames as a snippet to distill both appearance and motion information from raw video frames. TSN [26], I3D [3], and SlowFast [6] are the most common feature extractors. However, they only focus on the action categories, which results in some actions that are strongly related to the scene having quite similar representations to background segments. To overcome the drawback, TSP [1] adds additional background supervision in the pretraining model to generate the background-sensitive feature. BSP [28] artificially synthesizes different video boundaries and conducts boundary learning in the pretraining model to generate boundary-sensitive feature. However, these works cannot address the problem of movement feature submergence fundamentally. In this paper, MENet uses the Movement Enhance Module (MEM) to magnify the movement feature and the difference between action and background." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.523, + 0.895, + 0.735 + ], + "angle": 0, + "content": "Multi-scale Action Detection. The scale of the action varies dramatically in a video. Compared with the large actions, those small action segments have fewer samples and insufficient features. Some works [13, 7, 11] focus on feature pyramid network (FPN) to generate different temporal resolution features. However, the FPN structure does not learn specific feature representation for a certain action scale, and also lacks sufficient information flow intrinsically. TSI [15] proposes a scale-invariant loss, which balances large and small actions in quantity, but fails to fundamentally solve the scarce feature of small actions. In this work, we propose SFPN to cope with these problems, which establishes associations between different scale features and learns scale-specific feature representations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.897, + 0.903 + ], + "angle": 0, + "content": "Temporal Action Detection. Benefiting from the successful practice of image object detection and trimmed video action recognition, the two-stage pipeline prevails in TAD task. Specifically, the first stage is to locate candidate action segments in the video, and the second stage uses an action classifier to classify these proposals. The first stage has three main paradigms. (1) Anchor-Based method: Methods [5, 13, 21] put anchors of various scales on the video feature, and then give the final confidence of anchors. However, they cannot produce flexible boundaries. (2) Boundary-Base method: Methods [14, 31, 16]" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.521, + 0.957 + ], + "angle": 0, + "content": "13556" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.213 + ], + "angle": 0, + "content": "predict boundary scores on the video feature, which are combined to generate proposals. However, the confidence of the proposal lacks global information. (3) Combined method: Methods [12, 10, 4] combine these two methods to generate precise confidence and flexible boundaries. In this work, we follow the combined method to integrate the start point and end point as a proposal and generate multiscale anchor maps to predict anchor confidence." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.225, + 0.169, + 0.24 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.249, + 0.188, + 0.264 + ], + "angle": 0, + "content": "3.1. Overview" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.272, + 0.47, + 0.47 + ], + "angle": 0, + "content": "Problem Definition. Input of the Movement Enhance Network (MENet) is an untrimmed video denoted as \\( V = \\{v_{i}\\}_{i=1}^{L_{v}} \\), where \\( v_{i} \\) represents the \\( i \\)-th frame of the video and \\( L_{v} \\) is the total frames. The duration of the video is \\( T_{v} \\). Due to redundancy between video frames, several consecutive frames are usually regarded as a snippet. With the sampling interval \\( \\sigma \\), the whole video can be defined as snippet sequence \\( S = \\{s_{i}\\}_{i=1}^{L_{s}} \\), \\( L_{s} = L_{v} / \\sigma \\) representing the number of total snippets. The output of the MENet is \\( \\{\\psi_{i} | \\psi_{i} = (t_{i,s}, t_{i,e}, c_{i}, score_{i})\\} \\) where \\( t_{i,s}, t_{i,e}, c_{i} \\) and \\( score_{i} \\) are start time, end time, action category and confidence score, respectively. The annotations of untrimmed video are action instances \\( \\{\\Psi_{i} | \\Psi_{i} = (t_{i,s}^{*}, t_{i,e}^{*}, c_{i}^{*})\\} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.47, + 0.469, + 0.606 + ], + "angle": 0, + "content": "Framework Architecture. The framework architecture of MENet is shown in Fig 2. MENet is mainly composed of two parts: Movement Enhance Module (MEM) and Scale FPN (SFPN). MEM is used to extract movement enhanced feature and explore different video relations between snippets. SFPN is proposed to generate feature pyramid and learn specific expression patterns of different action scales. Finally, SFPN gives action boundaries and confidence scores of different scale actions, separately." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.613, + 0.332, + 0.627 + ], + "angle": 0, + "content": "3.2. Movement Enhance Module" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.469, + 0.703 + ], + "angle": 0, + "content": "To obtain the feature that contains action category information and is sensitive to foreground and background, simultaneously, we propose the Movement Enhance Module, which contains two vital stages: Movement Feature Extractor (MFE) and Multi-Relation Enhance Module (MREM)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Movement Feature Extractor. In order to amplify the movement information, MFE is proposed. As shown in Fig 3, MFE uses a siamese network to highlight the movement information in a video snippet. We select \\(\\mathrm{R}(2 + 1)\\mathrm{D}-34\\) [24] as backbone with the TAC pretrained weight on Kinetics-400 [9], and two networks share the weight. MFE has two input paths. One path is video snippet path composed of consecutive frames, and the other is frame duplication path, which selects a frame from the snippet and copies it to the length of the snippet. Here, the middle frame is selected for duplication. The feature from the video snippet path contains both static scene and dynamic movement information, which is \\(F_{Total} \\in \\mathbb{R}^{C' \\times T}\\), but feature from" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.182 + ], + "angle": 0, + "content": "the frame duplication path only contains static scene information, which is \\( F_{Static} \\in \\mathbb{R}^{C' \\times T} \\). And then, MFE extracts the movement information in the snippet using the difference between the two features, which is defined as \\( F_{Movement} \\in \\mathbb{R}^{C' \\times T} \\). Finally, \\( F_{Movement} \\) and \\( F_{Total} \\) are concatenated as \\( F_{MT} \\in \\mathbb{R}^{2C' \\times T} \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.183, + 0.893, + 0.426 + ], + "angle": 0, + "content": "Multi-Relation Enhance Module. To establish relations between snippets and fuse the information at semantic dimension, the Multi-Relation Enhance Module is proposed. As shown in Fig 2, firstly, we use a 1D convolution to fuse information at semantic dimension. Secondly, there are three information paths in MREM. (1) Local Path: 1D convolution can directly establish relations in a local scale \\( k \\), where \\( k \\) is the kernel size. However, it is difficult for 1D convolutions to establish temporal relationship between snippet features. (2) Forward Path: The LSTM processes each snippet successively according to the input order, with an outstanding ability to model the temporal relation. In forward path, we use LSTM to establish forward information. (3) Backward Path: In backward path, we flip the video sequence, and establish backward information. Finally, the three paths are integrated." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.436, + 0.783, + 0.452 + ], + "angle": 0, + "content": "3.3. Scale Feature Pyramid Network" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.46, + 0.893, + 0.535 + ], + "angle": 0, + "content": "We contend different scale actions have different patterns. Therefor, the SFPN is designed to learn patterns of specific scales. SFPN contains U-Shape Module and Detector Head, which aims to generate feature pyramid and final detection results, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.537, + 0.892, + 0.672 + ], + "angle": 0, + "content": "U-Shape Module. For feature pyramid generating, as shown in Fig 2, SFPN uses a U-shaped architecture inspired by [20] to generate feature sequences in different temporal resolution. From top to down, SFPN uses multiple temporal convolution layers followed by AvgPooling to downsample the temporal resolution. From bottom to up, to restore the lower layer information, SFPN uses several 1D transpose convolution to restore the feature resolution and features in the same resolution are concatenated." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.673, + 0.892, + 0.779 + ], + "angle": 0, + "content": "Detector Head. As demonstrated in Fig 2, each detector head consists of a Boundary Predictor, an Anchor Feature Align Layer and two Anchor Score Predictor (ASP). The output of the Boundary Predictor and Anchor Score Predictor is used to generate proposals and confidence scores, and the Anchor Feature Align Layer is to generate the feature representation for each anchor." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.825 + ], + "angle": 0, + "content": "Boundary Predictor. Boundary Predictor aims at predicting boundary probabilities \\( P_{s} = \\{p_{s}^{i}\\}_{i = 1}^{L_{i}} \\), \\( P_{e} = \\{p_{e}^{i}\\}_{i = 1}^{L_{i}} \\) of each snippet by recognizing the boundary pattern." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Anchor Feature Align Layer. The area between any two snippets can form an anchor, and each anchor consists of several consecutive snippets. Supposing \\( N_{i} \\) anchors are randomly sampled to participate in the forward. The Anchor Feature Align Layer adopts SGAlign designed in [29]" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13557" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.091, + 0.094, + 0.872, + 0.413 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.424, + 0.896, + 0.482 + ], + "angle": 0, + "content": "Figure 2. Overview of our MENet and the structure of some sub-modules. There are two crucial parts in the framework (Top) of MENet: Movement Enhance Module (MEM) and Scale FPN (SFPN). MEM is designed to generate movement enhanced feature. SFPN is designed to generate multi-scale feature pyramid, and learn action expressions in different layers. The structure of the sub-modules is shown below (Bottom) with the same color in the framework." + }, + { + "type": "image", + "bbox": [ + 0.08, + 0.492, + 0.478, + 0.741 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.75, + 0.471, + 0.793 + ], + "angle": 0, + "content": "Figure 3. Illustration of MFE. This module constructs the movement feature in a snippet by the difference between dynamic video snippet and static picture." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.806, + 0.471, + 0.852 + ], + "angle": 0, + "content": "to generate feature expressions \\(F_{A}^{i}\\in \\mathbb{R}^{C\\times S\\times N_{i}}\\) for anchors from the video feature \\(F_{v}^{i}\\), where \\(S\\) is the sampling number of snippets within an anchor." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Anchor Score Predictor. IoU-ASP and Offset-ASP have the same structure to recognize the action pattern within an anchor. For the \\(i\\)-th layer in SFPN, IoU-ASP gener" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.492, + 0.895, + 0.571 + ], + "angle": 0, + "content": "ates two maps \\(M_{cls}^{i}\\in \\mathbb{R}^{D_{i}\\times L_{i}},M_{reg}^{i}\\in \\mathbb{R}^{D_{i}\\times L_{i}}\\) , where \\(D_{i}\\) is predefined maximum anchor duration. In Offset-ASP, two output maps are denoted as \\(M_{cent}^{i}\\in \\mathbb{R}^{D_{i}\\times L_{i}},M_{dura}^{i}\\in\\) \\(\\mathbb{R}^{D_i\\times L_i}\\) . These two maps indicate each anchor's center offset and duration offset respectively." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.586, + 0.785, + 0.603 + ], + "angle": 0, + "content": "3.4. Specific action pattern Learning" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.612, + 0.892, + 0.853 + ], + "angle": 0, + "content": "Actions of different scales have different feature representations. Correspondingly, different layers in SFPN have different feature granularity and temporal resolution. Therefore, we advocate applying a targeted training strategy for actions at different scales, assuring that each layer in SFPN is only responsible for actions at a specific scale range. Specifically, define the scale \\(S \\in [0,1]\\) as the ratio of action length to video length. Then the first layer (the top layer of the pyramid) with the longest sequence is responsible for small-scale actions whose scale in \\([S_{min}^{1}, S_{max}^{1}]\\), and the second layer (the middle layer of the pyramid) with a moderate sequence length is responsible for medium-scale actions whose scale in \\([S_{min}^{2}, S_{max}^{2}]\\). The remaining third layer with the shortest sequence is responsible for large-scale actions whose scale belongs to \\([S_{min}^{3}, S_{max}^{3}]\\). To implement this idea, a two-stage training strategy is designed." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Two-stage training strategy. The two-stages of training ASP are Generalization and Specialization, respectively. Due to the different lengths of feature sequences, the to" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "13558" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.1, + 0.098, + 0.23, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.245, + 0.099, + 0.357, + 0.267 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.364, + 0.1, + 0.474, + 0.269 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.292, + 0.471, + 0.378 + ], + "angle": 0, + "content": "Figure 4. The two-stage training strategy (left column and middle column) and the inference strategy (right column) of ASP. Each square represents an anchor map of a layer, the grey area is the invalid region. Other colors represent different sampling ratios in a certain scale range, with white, green, yellow and red representing \\(0\\%\\), \\(r_i\\), \\(2r_i\\) and \\(100\\%\\) respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.39, + 0.47, + 0.692 + ], + "angle": 0, + "content": "tal number of dense anchors contained in each layer varies. In order to ensure that each layer is trained equally and reduce the computational cost, different anchor sampling ratios \\( r_1 \\), \\( r_2 \\), \\( r_3 \\) are set for the three layers, where \\( 0\\% < r_1 \\leq r_2 \\leq r_3 \\leq 100\\% \\). (1) In the former Generalization stage, given the sampling ratio \\( r_i \\), randomly sample \\( N_i = \\binom{L_i}{2} \\cdot r_i \\) anchors from valid region to train the IoU-ASP and Offset-ASP of \\( i \\)-th layer, as shown in the left column of Fig 4. The purpose of this stage is to let ASP learn a general pattern of all actions. (2) In the latter Specialization stage, for the \\( i \\)-th layer in SFPN, the training samples come from two parts, as shown in the middle column in Fig 4. The first part are randomly sampled according to the sampling rate of \\( \\min(100\\%, 2 \\cdot r_i) \\) from anchors whose scale in \\( [S_{min}^i, S_{max}^i] \\) (yellow area in Fig 4). The second part are sampled from the remaining anchors whose scale in \\( (0, S_{min}^i) \\) or \\( (S_{max}^i, 100\\%) \\), with the sampling rate of \\( r_i \\) (green area in Fig 4). This Specialization stage highlights the effect of anchors at the certain scale range, making the detection head of each layer more specialized." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.707, + 0.277, + 0.723 + ], + "angle": 0, + "content": "3.5. Training & Inference" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.731, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Label Assignment. Assuming the video duration is \\( L_{v} \\), each snippet corresponds to a video period. In annotation, a ground-truth action which starts at \\( t_{s}^{*} \\) and ends at \\( t_{e}^{*} \\). Expanding boundary from moment to region, the start region is defined as \\( R_{s} = [t_{s}^{*} - 1.5\\frac{T_{v}}{L_{i}}, t_{s}^{*} + 1.5\\frac{T_{v}}{L_{i}}] \\) and end region is defined as \\( R_{e} = [t_{e}^{*} - 1.5\\frac{T_{v}}{L_{i}}, t_{e}^{*} + 1.5\\frac{T_{v}}{L_{i}}] \\). For Boundary Predictor, compute the overlap between each snippet period and \\( R_{s} \\) as the label of start probabilities \\( G_{s}^{i} \\in \\mathbb{R}^{L_{i}} \\). Similarly, compute the overlap between snippet period and \\( R_{e} \\) as the label of end probabilities \\( G_{e}^{i} \\). For IoU-ASP, following [12], IoU between each anchor and all actions are" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.09, + 0.892, + 0.199 + ], + "angle": 0, + "content": "calculated and then arranged into a map \\( G_{IoU}^{i} \\in \\mathbb{R}^{D_{i} \\times L_{i}} \\). Anchors with tIoU score greater than 0.9 participate in the training of Offset-ASP. For anchor start at \\( t_{s} \\) and end at \\( t_{e} \\), assuming its corresponding ground-truth action is \\( [t_{s}^{*}, t_{e}^{*}] \\), the center offset \\( \\Delta c \\) and duration offset \\( \\Delta d \\) are calculated as Eq. (1)-(2), and arranged into maps \\( G_{cent}^{i} \\in \\mathbb{R}^{D_{i} \\times L_{i}} \\) and \\( G_{dura}^{i} \\in \\mathbb{R}^{D_{i} \\times L_{i}} \\)." + }, + { + "type": "equation", + "bbox": [ + 0.522, + 0.203, + 0.892, + 0.231 + ], + "angle": 0, + "content": "\\[\nc = \\frac {t _ {s} + t _ {e}}{2}, d = t _ {e} - t _ {s}, c ^ {*} = \\frac {t _ {s} ^ {*} + t _ {e} ^ {*}}{2}, d ^ {*} = t _ {e} ^ {*} - t _ {s} ^ {*} \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.609, + 0.232, + 0.892, + 0.26 + ], + "angle": 0, + "content": "\\[\n\\Delta c = \\frac {c ^ {*} - c}{d}, \\Delta d = \\log \\frac {d ^ {*}}{d} \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.268, + 0.893, + 0.558 + ], + "angle": 0, + "content": "Basic Loss. (1) For the \\(i\\)-th layer, the loss of Boundary-Predictor is the re-weighted binary cross-entropy loss \\(L_{B}\\) Eq. 3, where \\(P = \\{p_t\\}_{t=1}^{L_i}\\) and \\(G = \\{g_t\\}_{t=1}^{L_i}\\) represent the predicted boundary probabilities and its label of all snippets, respectively. Snippets with \\(g_t > 0.5\\) serve as positive samples (i.e., \\(\\delta \\{g_t > 0.5\\} = 1\\)) and others are negative samples. \\(T_{i}^{+}\\) and \\(T_{i}^{-}\\) are the number of positive and negative samples in this layer respectively. (2) The loss of IoU-ASP is the re-weighted binary cross-entropy loss \\(L_{asp}\\) Eq. 4 and L2 loss \\(L_{2}\\), where \\(M = \\{m_j\\}_{j=1}^{N_i}\\) and \\(G = \\{g_j\\}_{j=1}^{N_i}\\) represent the predicted value and ground-truth value of each sampled anchor in the \\(i\\)-th layer. \\(N_{i}, N_{i}^{+}, N_{i}^{-}\\) represent the number of sampled anchors, positive anchors whose tIoU greater than 0.9 and negative anchors of this layer, respectively. (3) The loss of Offset-ASP is Smooth L1 loss \\(L_{1}\\). Note that only those sampled anchors with tIoU greater than 0.9 participate in the training of Offset-ASP. The re-weights in \\(L_{B}\\) and \\(L_{asp}\\) are used to balance the number between positive and negative samples." + }, + { + "type": "equation", + "bbox": [ + 0.544, + 0.565, + 0.891, + 0.635 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} L _ {B} (P, G) = - \\frac {1}{L _ {i}} \\sum_ {t = 1} ^ {L _ {i}} \\left(\\frac {L _ {i}}{T _ {i} ^ {+}} \\cdot \\delta \\left\\{g _ {t} > 0. 5 \\right\\} \\cdot \\log p _ {t} \\right. \\tag {3} \\\\ + \\frac {L _ {i}}{T _ {i} ^ {-}} (1 - \\delta \\left\\{g _ {t} > 0. 5 \\right\\} \\cdot \\log \\left(1 - p _ {t}\\right)) \\\\ \\end{array}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.523, + 0.642, + 0.891, + 0.713 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} L _ {a s p} (M, G) = - \\frac {1}{N _ {i}} \\sum_ {j = 1} ^ {N _ {i}} \\left(\\frac {N _ {i}}{N _ {i} ^ {+}} \\cdot \\delta \\left\\{g _ {j} > 0. 9 \\right\\} \\cdot \\log m _ {j} \\right. \\tag {4} \\\\ + \\frac {N _ {i}}{N _ {i} ^ {-}} (1 - \\delta \\{g _ {j} > 0. 9 \\} \\cdot \\log (1 - m _ {j})) \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.722, + 0.892, + 0.811 + ], + "angle": 0, + "content": "Total Loss. The loss of the \\(i\\)-th layer is composed of three parts: boundary loss, IoU loss and offset loss, as shown in Eq.(5) (6) (7) respectively. The total training objective is the sum of all three layers, formulated as Eq. 8. Besides, in order to balance the value between different terms, the coefficient \\(\\lambda 1\\) and \\(\\lambda 2\\) are set as 5 and 10." + }, + { + "type": "equation", + "bbox": [ + 0.578, + 0.817, + 0.892, + 0.835 + ], + "angle": 0, + "content": "\\[\nL _ {\\text {b o u n d}} ^ {i} = L _ {B} \\left(P _ {s} ^ {i}, G _ {s} ^ {i}\\right) + L _ {B} \\left(P _ {e} ^ {i}, G _ {e} ^ {i}\\right) \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.537, + 0.848, + 0.892, + 0.866 + ], + "angle": 0, + "content": "\\[\nL _ {I o U} ^ {i} = L _ {a s p} \\left(M _ {c l s} ^ {i}, G _ {I o U} ^ {i}\\right) + \\lambda_ {1} \\cdot L _ {2} \\left(M _ {r e g} ^ {i}, G _ {I o U} ^ {i}\\right) \\tag {6}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.546, + 0.885, + 0.892, + 0.903 + ], + "angle": 0, + "content": "\\[\nL _ {o f f} ^ {i} = L _ {1} \\left(M _ {c e n t} ^ {i}, G _ {c e n t} ^ {i}\\right) + L _ {1} \\left(M _ {d u r a} ^ {i}, G _ {d u r a} ^ {i}\\right) \\tag {7}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13559" + } + ], + [ + { + "type": "equation", + "bbox": [ + 0.152, + 0.088, + 0.47, + 0.125 + ], + "angle": 0, + "content": "\\[\nL _ {t o t a l} = \\sum_ {i = 1} ^ {3} \\left(L _ {B} ^ {i} + L _ {I o U} ^ {i} + \\lambda_ {2} \\cdot L _ {o f f} ^ {i}\\right) \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.127, + 0.473, + 0.448 + ], + "angle": 0, + "content": "Inference. Each layer outputs \\( P_{s}^{i}, P_{e}^{i}, M_{cls}^{i}, M_{reg}^{i}, M_{cent}^{i} \\) and \\( M_{dura}^{i} \\) from the detector head in inference. Following [14, 12, 15], snippet in boundary probability \\( P_{s} \\) is screened out as candidate start point if it is local peak or its probability is greater than \\( 0.5 \\cdot \\max(P_{s}) \\). And snippets can be selected as candidate end point from \\( P_{e} \\) in the same way. Then the candidate start and end points are combined into proposals. In order to produce the more reasonable proposals, as shown in Fig 4, each layer of SFPN only outputs anchors in the corresponding scale range. Specifically, for the \\( i \\)-th layer, its responsible scale range is \\( [S_{min}^{i}, S_{max}^{i}] \\). Furthermore, in the proposals set, for any start snippet whose index is \\( sdx \\) and centered at time \\( t_{1} \\), and the end snippet whose index is \\( edx \\) and centered at time \\( t_{2} \\), we can get its start probability \\( p_{s} = P_{s}^{i}[sdx] \\), end probability \\( p_{e} = P_{e}^{i}[edx] \\) and tIoU score \\( p_{IoU} = M_{cls}^{i}[edx - sdx, sdx] \\cdot M_{reg}^{i}[edx - sdx, sdx] \\). Its center is \\( c = (sdx + edx)/2L_{i} \\) and duration is \\( d = (edx - sdx)/L_{i} \\). Subsequently, to refine the boundary, we can obtain center offset \\( \\Delta c = M_{cent}^{i}[edx - sdx, sdx] \\) and duration offset \\( \\Delta d = M_{dura}^{i}[edx - sdx, sdx] \\), and adjust the boundary to \\( (t_{1}', t_{2}') \\) as Eq. 9:" + }, + { + "type": "equation", + "bbox": [ + 0.182, + 0.455, + 0.469, + 0.502 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} c ^ {\\prime} = d \\cdot \\Delta c + c, d ^ {\\prime} = d \\cdot e ^ {\\Delta d} \\\\ t _ {1} ^ {\\prime} = c ^ {\\prime} - \\frac {d ^ {\\prime}}{2}, t _ {2} ^ {\\prime} = c ^ {\\prime} + \\frac {d ^ {\\prime}}{2} \\tag {9} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.5, + 0.47, + 0.576 + ], + "angle": 0, + "content": "Finally, proposals generated by each layer are merged together, and the action classifier assigns every proposal with a certain label and a classification score \\( P_{\\text{label}} \\). The final score for the proposal \\( (t_1', t_2') \\) is shown as Eq. 10. Then Soft-NMS [32] is adopted to remove redundant segments." + }, + { + "type": "equation", + "bbox": [ + 0.168, + 0.582, + 0.469, + 0.598 + ], + "angle": 0, + "content": "\\[\n\\operatorname {s c o r e} _ {t _ {1} ^ {\\prime}, t _ {2} ^ {\\prime}} = p _ {s} \\cdot p _ {e} \\cdot p _ {I o U} \\cdot p _ {\\text {l a b e l}} \\tag {10}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.604, + 0.21, + 0.62 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.625, + 0.271, + 0.641 + ], + "angle": 0, + "content": "4.1. Dataset and Settings" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.645, + 0.47, + 0.809 + ], + "angle": 0, + "content": "Dataset. In order to verify the effectiveness of MENet, we experiment on two challenging datasets. ActivityNet-1.3 [2] contains 200 categories of daily life, sports, etc. We use the training set for model training and report the performance on the validation set. THUMOS-14 [8] consists of 413 videos with 20 action classes which is almost sports. In THUMOS-14, the validation set contains 200 long videos, including 3007 action segments, and the test set contains 213 videos, including 3358 action segments. Following the standard practice of THUMOS-14, we train MENet on the validation set and valid it on the test set." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Metric. In order to fully demonstrate the advantages of our proposed method, we use two main evaluation metrics: mAP under a certain temporal tIoU threshold (mAP@tIoU) and average recall at a specified average number of proposals (AR@AN). Besides, on ActivityNet, the area under the AR-AN curve (AUC) also serves as a metric." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.364 + ], + "angle": 0, + "content": "Network Details. We use \\(\\mathrm{R}(2 + 1)\\mathrm{D} - 34\\) as backbone with the TAC pretrained weight on Kinetics-400 serving as the primary feature extractor. The sampling interval \\(\\sigma\\) set as 16 frames and 5 frames for ActivityNet-1.3 and THUMOS-14, respectively. In this way, for the input video with \\(L_{v}\\) frames, video snippet length \\(L_{s} = L_{v} / \\sigma\\). For ActivityNet-1.3, we use linear interpolation to resize the length of video features \\(T = 200\\). For a long video in THUMOS-14, a sliding window with a length of 256 and an overlap of \\(50\\%\\) is used to truncate the original video feature. Each window is detected independently, and finally the results of all windows are concatenated as the total result of the entire long video. The scale ranges of each layer in the pyramid are set as: \\([S_{min}^{1}, S_{max}^{1}] = [0, 15\\%]\\), \\([S_{min}^{2}, S_{max}^{2}] = [10\\%, 75\\%]\\) and \\([S_{min}^{3}, S_{max}^{3}] = [50\\%, 100\\%]\\). As for the action classifier, following the routine of most two-stage TAD methods, Untrimmed Net [25] serves as the classifier for THUMOS-14, and the recognition model by [32] for ActivityNet-1.3." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.365, + 0.892, + 0.516 + ], + "angle": 0, + "content": "Implementation Details. MENet is trained by Adam algorithm with batch size 8 and learning rate \\(10^{-3}\\). The sampling ratio of each layer \\(r_1\\), \\(r_2\\), \\(r_3\\) are set as \\(50\\%\\), \\(40\\%\\), \\(90\\%\\), respectively. For ActivityNet-1.3, the training process takes 10 epochs, where the first 7 epochs is the Generalization stage and the rest is the Specialization stage. As for THUMOS-14, the total training epoch is 7, and only the first epoch is the Generalization stage. Besides, the learning rate is decayed to \\(10^{-4}\\) after 5 epochs on THUMOS-14 and 7 epochs on ActivityNet-1.3." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.531, + 0.829, + 0.546 + ], + "angle": 0, + "content": "4.2. Performance Evaluation On Detection" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.552, + 0.892, + 0.717 + ], + "angle": 0, + "content": "We compare MENet with other state-of-the-art methods on ActivityNet-1.3 and THUMOS-14. Table 1 shows the comparison on the validation set of ActivityNet-1.3. The mAP at tIoU thresholds of \\(\\{0.5, 0.75, 0.95\\}\\) are reported, as well as the Avg.mAP which is calculated at tIoU thresholds between 0.5 and 0.95 with the step of 0.05. Impressively, MENet outperforms other representative methods at tIoU thresholds 0.75 and 0.95. MENet promotes the Avg.mAP from \\(36.6\\%\\) to \\(37.7\\%\\), with an increase of more than \\(1.1\\%\\). Comparing the methods of different backbones, MENet exceeds others." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Table 2 presents the detection performance comparison on the test set of THUMOS-14. MENet achieves comparable performance with the best method [30] at low tIoU thresholds. But, MENet outperforms other representative methods at tIoU thresholds 0.6 and 0.7. MENet improves the mAP@0.7 from the current best \\(31.8\\%\\) to \\(34.0\\%\\). To locate the boundaries more accurately, a higher threshold is usually used to separate the positive and negative samples in training. Therefore MENet has a better response at high tIoU thresholds. Higher tIoU means more precise action boundaries, which is more difficult and more important for action localization. Meanwhile, it is noteworthy" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13560" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.138 + ], + "angle": 0, + "content": "that MENet shows obvious superiority compared with other FPN-based methods like [11], which substantiates the effectiveness of the SFPN proposed in MENet." + }, + { + "type": "table", + "bbox": [ + 0.088, + 0.142, + 0.462, + 0.352 + ], + "angle": 0, + "content": "
MethodBackbonemAP@tIoU (%)
0.50.750.95Avg.
GTAN [16]P3D52.634.18.934.3
BSN [14]TSN46.530.08.030.0
BMN [12]TSN50.134.88.333.9
G-TAD [29]TSN50.434.69.034.1
PCMNet [18]TSN51.436.19.535.3
TCA-Net [19]TSN52.336.76.935.5
RTD-Net [23]I3D47.230.78.630.8
ContextLoc [33]I3D56.035.23.634.2
AFSD [11]I3D52.435.36.534.4
TAGS [17]I3D56.336.89.636.5
STPT [27]STPT51.433.76.833.4
ActionFormer [30]R(2+1)D54.737.88.436.6
MENet(ours)R(2+1)D54.738.410.537.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.355, + 0.47, + 0.397 + ], + "angle": 0, + "content": "Table 1. The temporal action detection performance comparison with state-of-art methods on ActivityNet-1.3. Bold text indicates the best results." + }, + { + "type": "table", + "bbox": [ + 0.088, + 0.4, + 0.462, + 0.611 + ], + "angle": 0, + "content": "
MethodBackbonemAP@tIoU (%)
0.30.40.50.60.7
GTAN [16]P3D57.847.238.8--
BSN [14]TSN53.545.036.928.420.0
BMN [12]TSN56.047.438.829.720.5
G-TAD [12]TSN54.547.640.230.823.4
PCMNet [18]TSN61.555.447.237.527.3
TCA-Net [19]TSN60.653.244.636.826.7
RTD-Net [23]I3D68.362.351.938.823.7
ContextLoc [33]I3D68.363.854.341.826.2
AFSD [11]I3D67.362.455.543.731.1
TAGS [17]I3D68.663.857.046.331.8
STPT [27]STPT70.665.756.444.630.5
ActionFormer [30]R(2+1)D73.467.459.146.731.5
MENet(ours)R(2+1)D70.765.358.849.134.0
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.614, + 0.47, + 0.655 + ], + "angle": 0, + "content": "Table 2. The temporal action detection performance comparison with state-of-art methods on THUMOS-14. Bold text indicates the best results." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.663, + 0.403, + 0.679 + ], + "angle": 0, + "content": "4.3. Performance Evaluation On Proposal" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.68, + 0.469, + 0.725 + ], + "angle": 0, + "content": "To further verify the advantages of MENet, we do not consider action classes of action segments to evaluate its performance on temporal action proposal (TAP) task." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.725, + 0.469, + 0.831 + ], + "angle": 0, + "content": "Through Table 3, we can further discover the performance improvement of AR@100 and the area under the AR-AN curve (AUC) on ActivityNet-1.3. For instance, MENet boosts the AUC from \\(68.1\\%\\) to \\(70.2\\%\\). As for THUMOS-14, MENet outperforms other methods in all metrics are reported in Table 4, which certifies the effectiveness of MENet once again." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.84, + 0.231, + 0.855 + ], + "angle": 0, + "content": "4.4. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Ablation studies are performed thoroughly to verify the role of each module in MENet, as well as the impact of different training strategies." + }, + { + "type": "table", + "bbox": [ + 0.571, + 0.089, + 0.822, + 0.205 + ], + "angle": 0, + "content": "
MethodAR@100AUC
BSN [14]74.266.2
GTAN [16]74.867.1
BMN [12]75.067.1
RTD-Net [23]73.265.8
TCA-Net [19]76.168.1
MENet(ours)77.070.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.207, + 0.892, + 0.248 + ], + "angle": 0, + "content": "Table 3. Temporal action proposal performance comparison with other representative methods on ActivityNet-1.3. Bold text indicates the best results." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.253, + 0.895, + 0.355 + ], + "angle": 0, + "content": "
MethodAR@50AR@100AR@200AR@500
BSN [14]37.546.153.260.6
BMN [12]39.447.754.762.1
RTD-Net [23]41.549.3256.4162.91
TCA-Net [19]42.150.557.163.6
MENet(ours)44.252.358.666.0
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.362, + 0.892, + 0.403 + ], + "angle": 0, + "content": "Table 4. Temporal action proposal performance comparison with other representative methods on THUMOS-14, measured by AR@AN. Bold text indicates the best results." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.407, + 0.892, + 0.558 + ], + "angle": 0, + "content": "1). Effectiveness of the MEM: As discussed before, when constructing the movement enhance feature, MFE and MREM are the crucial designs in MEM. To certify the function of these two modules, we design a Base model for comparison, in which the Movement Feature is removed and MREM is replaced by temporal 1D convolution. As shown in Table 5, we can find that compared with the Base model, Movement Feature and MREM both can promote the performance. Besides, the best results emerge when combining them together as the intact MEM." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.563, + 0.892, + 0.664 + ], + "angle": 0, + "content": "
ConstructionmAP@tIoU (%)
0.50.750.95Avg.
Base54.237.310.437.0
Base + Movement Feature54.537.810.637.3
Base + MREM54.437.910.437.3
MEM54.738.410.537.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.671, + 0.892, + 0.714 + ], + "angle": 0, + "content": "Table 5. Ablation study on the MEM. The Detection performance is reported on ActivityNet-1.3. And The best result can be achieved with these two modules are integrated." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.72, + 0.892, + 0.84 + ], + "angle": 0, + "content": "2). Effectiveness of the U-shape Module: As discussed before, when constructing the feature pyramid, U-shape Module is designed to establish interactions between different layers. To reveal the validity of this idea, we use 1D convolution with the step of 2 and AvgPooling to downsample the feature sequence respectively. From Table 6, the U-shape Module can promote the performance, which substantiates the importance of this design." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "3). Effectiveness of feature pyramid structure: For better detection accuracy, MENet makes use of the feature pyramid. To verify the impact of this structure, we only use a single layer feature sequence to conduct experiments" + }, + { + "type": "list", + "bbox": [ + 0.499, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "13561" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.086, + 0.09, + 0.46, + 0.174 + ], + "angle": 0, + "content": "
ConstructionmAP@tIoU (%)
0.50.750.95Avg.
DownSampling (AvgPooling)54.538.210.237.4
DownSampling (Convolution)54.438.110.837.3
U-shape Module54.738.410.537.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.176, + 0.468, + 0.204 + ], + "angle": 0, + "content": "Table 6. Ablation study on the U-shape Module. The Detection performance is reported on ActivityNet-1.3." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.217, + 0.468, + 0.323 + ], + "angle": 0, + "content": "and compare it with the SFPN, keeping other components unchanged. On ActivityNet-1.3, single-layer feature with lengths of 200, 100 and 50 are used. Corresponding results are shown in Table 7. The experimental results exhibit that SFPN performs better than any other single-layer structure, thus justifying the feature pyramid structure is indeed beneficial to the performance." + }, + { + "type": "table", + "bbox": [ + 0.14, + 0.33, + 0.406, + 0.432 + ], + "angle": 0, + "content": "
LengthmAP@tIoU (%)
0.50.750.95Avg.
5053.037.110.836.8
10054.138.110.437.1
20054.238.310.537.3
SFPN54.738.410.537.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.433, + 0.468, + 0.475 + ], + "angle": 0, + "content": "Table 7. Ablation study on the SFPN. \"Length\" means the temporal length of single layer feature sequence. The Detection performance is reported on ActivityNet-1.3." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.492, + 0.468, + 0.718 + ], + "angle": 0, + "content": "4). Effectiveness of two-stage training: For efficient training of MENet and ensuring that the \\(i\\)-th layer in SFPN is specialized in actions at a specific scale range \\([S_{min}^{i}, S_{max}^{i}]\\), the two-stage training strategy is applied. When training ASP of the \\(i\\)-th layer, in the first Generalization stage, the anchors are randomly selected from all scales according to the sampling ratio \\(r_i\\), in the second Specialization stage, the sampling ratio inside and outside the range \\([S_{min}^{i}, S_{max}^{i}]\\) are \\(2 \\cdot r_i\\) and \\(r_i\\), respectively. In this ablation study, we train MENet using the fully Generalization stage, the fully Specialization stage and the complete two-stage strategy, respectively. In addition, to demonstrate the effectiveness of this training method, we also test a new Bias training strategy that only samples from the range \\([S_{min}^{i}, S_{max}^{i}]\\) with the sampling ratio of \\(r_i\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.719, + 0.468, + 0.825 + ], + "angle": 0, + "content": "As shown in Table 8, the performance of the Bias strategy is the worst, indicating that in addition to those samples in the specific scale range, other samples outside this range also play an important role for a better understanding of actions. Further, the training effect is impeded when removing either the Generalization or the Specialization stage, which verifies the effectiveness of the two-stage training strategy." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.468, + 0.9 + ], + "angle": 0, + "content": "5). Qualitative Comparison: To illustrate the edge of MENet more intuitively, we select videos of Javelin Throw and High Jump from ActivityNet-1.3 and compare our results qualitatively with the Base, in which we remove the movement enhanced feature and SFPN. Results with the" + }, + { + "type": "table", + "bbox": [ + 0.522, + 0.09, + 0.868, + 0.189 + ], + "angle": 0, + "content": "
Training StrategymAP@tIoU (%)
0.50.750.95Avg.
only Bias45.829.17.429.4
only Generalization54.338.211.037.4
only Specialization54.638.010.837.4
two-stage54.738.410.537.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.195, + 0.892, + 0.237 + ], + "angle": 0, + "content": "Table 8. Ablation study on the two-stage training strategy. The proposed two-stage training leads to better performance than the single stage method or the Bias method." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.246, + 0.892, + 0.382 + ], + "angle": 0, + "content": "highest confidence score are visualized in Fig 5. Firstly, Compared with the Base method, MENet uses the movement feature, which enlarges the difference between action and background, making the model more accurate in boundary localization. Secondly, it can be seen the High Jump action contains a large-scale action and a small-scale action. Due to the SFPN in MENet, MENet can better capture actions at different scales. Results of qualitative comparison once again prove the superiority of MENet." + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.4, + 0.705, + 0.51 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.71, + 0.4, + 0.906, + 0.51 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.52, + 0.892, + 0.549 + ], + "angle": 0, + "content": "Figure 5. Qualitative Comparison. MENet generates more accurate action segments." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.564, + 0.618, + 0.578 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.583, + 0.892, + 0.853 + ], + "angle": 0, + "content": "Temporal action detection (TAD) is aimed at localizing the action segment and classifying the action class. Despite the considerable attention and rapid development, TAD is hindered by two critical problems: the movement feature submergence and multi-scale action detection. In an effort to overcome these two challenges, we propose the Movement Enhance Network (MENet) with two crucial designs. Firstly, we propose the Movement Enhance Module (MEM) to extract the movement feature in video snippets and explore the multi-relations between the snippets. Secondly, we propose the Scale FPN (SFPN) to handle the different scale actions, we design the U-shape Module to facilitate the information flow between different scale features. For better performance, we design the training and inference stage, ensuring that each layer in MENet is specialized at a specific scale range. Extensive experiments demonstrate that MENet considerably outperforms other representative TAD methods on ActivityNet-1.3 and THUMOS-14." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.891, + 0.9 + ], + "angle": 0, + "content": "Acknowledgements. This work was supported by National Natural Science Foundation of China (NSFC) No. 62176156." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "13562" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.469, + 0.157 + ], + "angle": 0, + "content": "[1] Humam Alwassel, Silvio Giancola, and Bernard Ghanem. Tsp: Temporally-sensitive pretraining of video encoders for localization tasks. In ICCV, pages 3173-3183, 2021." + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.159, + 0.469, + 0.214 + ], + "angle": 0, + "content": "[2] Fabian Caba Heilbron, Victor Escorcia, Bernard Ghanem, and Juan Carlos Niebles. Activitynet: A large-scale video benchmark for human activity understanding. 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In ICCV, pages 13516-13525, 2021." + }, + { + "type": "list", + "bbox": [ + 0.078, + 0.092, + 0.47, + 0.164 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.52, + 0.957 + ], + "angle": 0, + "content": "13564" + } + ] +] \ No newline at end of file diff --git a/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/d8a8f490-e49c-49c9-b1d9-2afa438fb3bc_origin.pdf b/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/d8a8f490-e49c-49c9-b1d9-2afa438fb3bc_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..902b4e989ce6dbcbf4f94af8b508a8caae63d900 --- /dev/null +++ b/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/d8a8f490-e49c-49c9-b1d9-2afa438fb3bc_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:d37fd064ce7a15336052ead4daa5d0d96b807618f4ac27673282dc6025b6eb1b +size 1448655 diff --git a/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/full.md b/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/full.md new file mode 100644 index 0000000000000000000000000000000000000000..80805a391efd28932b68f4efedff16dd5a7db6cc --- /dev/null +++ b/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/full.md @@ -0,0 +1,290 @@ +# Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection + +Zixuan Zhao Dongqi Wang Xu Zhao* +Department of Automation, Shanghai Jiao Tong University, China +{zhaozixuan, wangdq0124, zhaoxu}@sjtu.edu.cn + +# Abstract + +Boundary localization is a challenging problem in Temporal Action Detection (TAD), in which there are two main issues. First, the submergence of movement feature, i.e. the movement information in a snippet is covered by the scene information. Second, the scale of action, that is, the proportion of action segments in the entire video, is considerably variable. In this work, we first design a Movement Enhance Module (MEM) to highlight movement feature for better action location, and then, we propose a Scale Feature Pyramid Network (SFPN) to detect multi-scale actions in videos. For Movement Enhance Module, firstly, Movement Feature Extractor (MFE) is designed to get the movement feature. Secondly, we propose a Multi-Relation Enhance Module (MREM) to grasp valuable information correlation both locally and temporally. For Scale Feature Pyramid Network, we design a U-Shape Module to model different scale actions, moreover, we design the training and inference strategy of different scales, ensuring that each pyramid layer is only responsible for actions at a specific scale. These two innovations are integrated as the Movement Enhance Network (MENet), and extensive experiments conducted on two challenging benchmarks demonstrate its effectiveness. MENet outperforms other representative TAD methods on ActivityNet-1.3 and THUMOS-14. + +# 1. Introduction + +Temporal Action Detection (TAD) is a significant video understanding task, which aims to extract video segments with specific action labels from untrimmed long videos. It remains a challenging problem because action boundaries are difficult to determine precisely, which adversely affects the performance in most works. + +Two critical issues stand in the way of detecting action boundaries robustly from untrimmed videos. The first issue, which could be called as movement feature submergence, exists in where either context but not movement itself dominate feature expression, or movement is small in pixel size. + +![](images/21898c25d4bf84a2c8de184179b6ede51d7afb930520fcb30205e4f4bd58fc11.jpg) +(a) Strong class-specific context. + +![](images/f391a8a6f1cc42c8c4517192afc16c1ba68b20fe98effe9fb20c187a12d42716.jpg) + +![](images/72a3b8daba3973ab538349a34845ff7149ffb32d91d5f8311d714906eac73e69.jpg) +(b) Small movement in pixel size. +(c) Multi-scale actions. +Figure 1. Movement feature submergence and multi-scale actions. (a) Strong class-specific context of the accordion leads to video feature generated by TAC lacking the difference between action and background. (b) Small movement of Futsal results in less difference between action area and background area. (c) Multiscale actions have different feature richness and action pattern. + +For the first case, as shown in Fig 1(a), the action of Playing Accordion can be easily judged by Accordion, while this strong class-specific context causes the real movement information in action area to be submerged. For the second case, as shown in Fig 1(b), for Futsal, the stadium scene takes up a large proportion of pixels in the frame, while the movement information is ignored. This movement feature submergence leads to the feature in background to be similar with the feature in action area, which blues the action boundaries. If the movement information can be highlighted, the boundary will be easier to be located. However, this problem has been ignored by prior works [12, 29, 22]. + +The second issue is the multi-scale of actions in an + +untrimmed video. As shown in Fig 1(c), the feature richness varies greatly with the scale. There are rare features for action segments that account for a small proportion of the entire video, that is the small-scale action, and abundant features for those segments that account for a higher proportion, that is the large-scale action. We contend that there are different action patterns between different scales. Specifically, compared with small-scale action, large-scale action contains more obviously action process (i.e. start phase, action phase and end phase). Some researches [13, 7, 11] resort feature pyramid network (FPN) to solve the problem. However, there are two aspects that are ignored. Firstly, these works detect actions at different feature scales, but, they do not adaptively learn action features of different scales. Secondly, the information flow in FPN is insufficient, lacking interactions between different pyramid layers. + +In this paper, as an effort to overcome the above challenges, we investigate the feature of TAD. (1) In order to overcome the movement feature submergence, and highlight the difference between foreground and background snippets. We design the Movement Enhance Module (MEM) to enhance the movement information in a video snippet, which includes two crucial parts. First, we propose a siamese network named Movement Feature Extractor (MFE), which uses the dynamic information of the frame sequence and the static information of the frame to extract movement feature from video snippets. And then, we propose the Multi-Relation Enhance Module (MREM) to establish temporal and local correlations between video snippets. (2) In order to learn specific representations for different scale actions, we propose the Scale FPN (SFPN), which uses a U-shaped network to produce multi-scale video features and facilitate the information flow between different layers. Moreover, for each layer in SFPN to take charge of detecting action segments of the corresponding scale, we design a two-stage learning strategy. In the former Generalization stage, each layer is trained with all action segments; in the latter Specialization stage, each layer is biased toward actions in a specific scale range. During inference, every layer takes charge of detecting action segments of the corresponding scale. + +In summary, this work explores feature representation and action segment representation that are more suitable for TAD task. Its contributions are summarized as follows. + +1. To alleviate the movement feature submergence, we design the Movement Enhance Module (MEM) to highlight the movement feature in a video snippet, and explore local and temporal relations between snippets. +2. For the multi-scale actions in an untrimmed video with different feature patterns, we design the Scale FPN (SFPN) to learn different scale actions respectively, where targeted training and inference strategies are + +adopted. Consequently, each layer in the SFPN specializes in actions at a certain scale range. + +3. Extensive experiments conducted on two datasets verify the effectiveness of our proposed method. On ActivityNet1.3, MENet promotes the best average mAP from $36.6\%$ to $37.7\%$ , and boosts the mAP@0.7 from $31.8\%$ to $34.0\%$ on THUMOS-14. + +# 2. Related Work + +Video Feature for TAD. The pre-trained TAC model is often used as the feature extractor for Temporal Action Detection which receives several frames as a snippet to distill both appearance and motion information from raw video frames. TSN [26], I3D [3], and SlowFast [6] are the most common feature extractors. However, they only focus on the action categories, which results in some actions that are strongly related to the scene having quite similar representations to background segments. To overcome the drawback, TSP [1] adds additional background supervision in the pretraining model to generate the background-sensitive feature. BSP [28] artificially synthesizes different video boundaries and conducts boundary learning in the pretraining model to generate boundary-sensitive feature. However, these works cannot address the problem of movement feature submergence fundamentally. In this paper, MENet uses the Movement Enhance Module (MEM) to magnify the movement feature and the difference between action and background. + +Multi-scale Action Detection. The scale of the action varies dramatically in a video. Compared with the large actions, those small action segments have fewer samples and insufficient features. Some works [13, 7, 11] focus on feature pyramid network (FPN) to generate different temporal resolution features. However, the FPN structure does not learn specific feature representation for a certain action scale, and also lacks sufficient information flow intrinsically. TSI [15] proposes a scale-invariant loss, which balances large and small actions in quantity, but fails to fundamentally solve the scarce feature of small actions. In this work, we propose SFPN to cope with these problems, which establishes associations between different scale features and learns scale-specific feature representations. + +Temporal Action Detection. Benefiting from the successful practice of image object detection and trimmed video action recognition, the two-stage pipeline prevails in TAD task. Specifically, the first stage is to locate candidate action segments in the video, and the second stage uses an action classifier to classify these proposals. The first stage has three main paradigms. (1) Anchor-Based method: Methods [5, 13, 21] put anchors of various scales on the video feature, and then give the final confidence of anchors. However, they cannot produce flexible boundaries. (2) Boundary-Base method: Methods [14, 31, 16] + +predict boundary scores on the video feature, which are combined to generate proposals. However, the confidence of the proposal lacks global information. (3) Combined method: Methods [12, 10, 4] combine these two methods to generate precise confidence and flexible boundaries. In this work, we follow the combined method to integrate the start point and end point as a proposal and generate multiscale anchor maps to predict anchor confidence. + +# 3. Method + +# 3.1. Overview + +Problem Definition. Input of the Movement Enhance Network (MENet) is an untrimmed video denoted as $V = \{v_{i}\}_{i=1}^{L_{v}}$ , where $v_{i}$ represents the $i$ -th frame of the video and $L_{v}$ is the total frames. The duration of the video is $T_{v}$ . Due to redundancy between video frames, several consecutive frames are usually regarded as a snippet. With the sampling interval $\sigma$ , the whole video can be defined as snippet sequence $S = \{s_{i}\}_{i=1}^{L_{s}}$ , $L_{s} = L_{v} / \sigma$ representing the number of total snippets. The output of the MENet is $\{\psi_{i} | \psi_{i} = (t_{i,s}, t_{i,e}, c_{i}, score_{i})\}$ where $t_{i,s}, t_{i,e}, c_{i}$ and $score_{i}$ are start time, end time, action category and confidence score, respectively. The annotations of untrimmed video are action instances $\{\Psi_{i} | \Psi_{i} = (t_{i,s}^{*}, t_{i,e}^{*}, c_{i}^{*})\}$ . + +Framework Architecture. The framework architecture of MENet is shown in Fig 2. MENet is mainly composed of two parts: Movement Enhance Module (MEM) and Scale FPN (SFPN). MEM is used to extract movement enhanced feature and explore different video relations between snippets. SFPN is proposed to generate feature pyramid and learn specific expression patterns of different action scales. Finally, SFPN gives action boundaries and confidence scores of different scale actions, separately. + +# 3.2. Movement Enhance Module + +To obtain the feature that contains action category information and is sensitive to foreground and background, simultaneously, we propose the Movement Enhance Module, which contains two vital stages: Movement Feature Extractor (MFE) and Multi-Relation Enhance Module (MREM). + +Movement Feature Extractor. In order to amplify the movement information, MFE is proposed. As shown in Fig 3, MFE uses a siamese network to highlight the movement information in a video snippet. We select $\mathrm{R}(2 + 1)\mathrm{D}-34$ [24] as backbone with the TAC pretrained weight on Kinetics-400 [9], and two networks share the weight. MFE has two input paths. One path is video snippet path composed of consecutive frames, and the other is frame duplication path, which selects a frame from the snippet and copies it to the length of the snippet. Here, the middle frame is selected for duplication. The feature from the video snippet path contains both static scene and dynamic movement information, which is $F_{Total} \in \mathbb{R}^{C' \times T}$ , but feature from + +the frame duplication path only contains static scene information, which is $F_{Static} \in \mathbb{R}^{C' \times T}$ . And then, MFE extracts the movement information in the snippet using the difference between the two features, which is defined as $F_{Movement} \in \mathbb{R}^{C' \times T}$ . Finally, $F_{Movement}$ and $F_{Total}$ are concatenated as $F_{MT} \in \mathbb{R}^{2C' \times T}$ . + +Multi-Relation Enhance Module. To establish relations between snippets and fuse the information at semantic dimension, the Multi-Relation Enhance Module is proposed. As shown in Fig 2, firstly, we use a 1D convolution to fuse information at semantic dimension. Secondly, there are three information paths in MREM. (1) Local Path: 1D convolution can directly establish relations in a local scale $k$ , where $k$ is the kernel size. However, it is difficult for 1D convolutions to establish temporal relationship between snippet features. (2) Forward Path: The LSTM processes each snippet successively according to the input order, with an outstanding ability to model the temporal relation. In forward path, we use LSTM to establish forward information. (3) Backward Path: In backward path, we flip the video sequence, and establish backward information. Finally, the three paths are integrated. + +# 3.3. Scale Feature Pyramid Network + +We contend different scale actions have different patterns. Therefor, the SFPN is designed to learn patterns of specific scales. SFPN contains U-Shape Module and Detector Head, which aims to generate feature pyramid and final detection results, respectively. + +U-Shape Module. For feature pyramid generating, as shown in Fig 2, SFPN uses a U-shaped architecture inspired by [20] to generate feature sequences in different temporal resolution. From top to down, SFPN uses multiple temporal convolution layers followed by AvgPooling to downsample the temporal resolution. From bottom to up, to restore the lower layer information, SFPN uses several 1D transpose convolution to restore the feature resolution and features in the same resolution are concatenated. + +Detector Head. As demonstrated in Fig 2, each detector head consists of a Boundary Predictor, an Anchor Feature Align Layer and two Anchor Score Predictor (ASP). The output of the Boundary Predictor and Anchor Score Predictor is used to generate proposals and confidence scores, and the Anchor Feature Align Layer is to generate the feature representation for each anchor. + +Boundary Predictor. Boundary Predictor aims at predicting boundary probabilities $P_{s} = \{p_{s}^{i}\}_{i = 1}^{L_{i}}$ , $P_{e} = \{p_{e}^{i}\}_{i = 1}^{L_{i}}$ of each snippet by recognizing the boundary pattern. + +Anchor Feature Align Layer. The area between any two snippets can form an anchor, and each anchor consists of several consecutive snippets. Supposing $N_{i}$ anchors are randomly sampled to participate in the forward. The Anchor Feature Align Layer adopts SGAlign designed in [29] + +![](images/a24ad46a6c7ad8b213ee7318ab063eb7db95c942341d303ae56a872aec0a9d36.jpg) +Figure 2. Overview of our MENet and the structure of some sub-modules. There are two crucial parts in the framework (Top) of MENet: Movement Enhance Module (MEM) and Scale FPN (SFPN). MEM is designed to generate movement enhanced feature. SFPN is designed to generate multi-scale feature pyramid, and learn action expressions in different layers. The structure of the sub-modules is shown below (Bottom) with the same color in the framework. + +![](images/58226dd19b1a8ccad45382bf78cc29a64131377a34b6b63ab24f7d8c8b3bba52.jpg) +Figure 3. Illustration of MFE. This module constructs the movement feature in a snippet by the difference between dynamic video snippet and static picture. + +to generate feature expressions $F_{A}^{i}\in \mathbb{R}^{C\times S\times N_{i}}$ for anchors from the video feature $F_{v}^{i}$ , where $S$ is the sampling number of snippets within an anchor. + +Anchor Score Predictor. IoU-ASP and Offset-ASP have the same structure to recognize the action pattern within an anchor. For the $i$ -th layer in SFPN, IoU-ASP gener + +ates two maps $M_{cls}^{i}\in \mathbb{R}^{D_{i}\times L_{i}},M_{reg}^{i}\in \mathbb{R}^{D_{i}\times L_{i}}$ , where $D_{i}$ is predefined maximum anchor duration. In Offset-ASP, two output maps are denoted as $M_{cent}^{i}\in \mathbb{R}^{D_{i}\times L_{i}},M_{dura}^{i}\in$ $\mathbb{R}^{D_i\times L_i}$ . These two maps indicate each anchor's center offset and duration offset respectively. + +# 3.4. Specific action pattern Learning + +Actions of different scales have different feature representations. Correspondingly, different layers in SFPN have different feature granularity and temporal resolution. Therefore, we advocate applying a targeted training strategy for actions at different scales, assuring that each layer in SFPN is only responsible for actions at a specific scale range. Specifically, define the scale $S \in [0,1]$ as the ratio of action length to video length. Then the first layer (the top layer of the pyramid) with the longest sequence is responsible for small-scale actions whose scale in $[S_{min}^{1}, S_{max}^{1}]$ , and the second layer (the middle layer of the pyramid) with a moderate sequence length is responsible for medium-scale actions whose scale in $[S_{min}^{2}, S_{max}^{2}]$ . The remaining third layer with the shortest sequence is responsible for large-scale actions whose scale belongs to $[S_{min}^{3}, S_{max}^{3}]$ . To implement this idea, a two-stage training strategy is designed. + +Two-stage training strategy. The two-stages of training ASP are Generalization and Specialization, respectively. Due to the different lengths of feature sequences, the to + +![](images/1649173c50836dba2f4757d1ea10c7fb3d52114b230f06d76908c623b59ece86.jpg) +Figure 4. The two-stage training strategy (left column and middle column) and the inference strategy (right column) of ASP. Each square represents an anchor map of a layer, the grey area is the invalid region. Other colors represent different sampling ratios in a certain scale range, with white, green, yellow and red representing $0\%$ , $r_i$ , $2r_i$ and $100\%$ respectively. + +![](images/0582439aa20faf1e40e2f4294fc9e8899ec276a5177358ba32ef51ebe84baea2.jpg) + +![](images/3b39d423219f0d6d005fa4ee796746c5e7863dcfdb83e2216d46d86fa403d9ac.jpg) + +tal number of dense anchors contained in each layer varies. In order to ensure that each layer is trained equally and reduce the computational cost, different anchor sampling ratios $r_1$ , $r_2$ , $r_3$ are set for the three layers, where $0\% < r_1 \leq r_2 \leq r_3 \leq 100\%$ . (1) In the former Generalization stage, given the sampling ratio $r_i$ , randomly sample $N_i = \binom{L_i}{2} \cdot r_i$ anchors from valid region to train the IoU-ASP and Offset-ASP of $i$ -th layer, as shown in the left column of Fig 4. The purpose of this stage is to let ASP learn a general pattern of all actions. (2) In the latter Specialization stage, for the $i$ -th layer in SFPN, the training samples come from two parts, as shown in the middle column in Fig 4. The first part are randomly sampled according to the sampling rate of $\min(100\%, 2 \cdot r_i)$ from anchors whose scale in $[S_{min}^i, S_{max}^i]$ (yellow area in Fig 4). The second part are sampled from the remaining anchors whose scale in $(0, S_{min}^i)$ or $(S_{max}^i, 100\%)$ , with the sampling rate of $r_i$ (green area in Fig 4). This Specialization stage highlights the effect of anchors at the certain scale range, making the detection head of each layer more specialized. + +# 3.5. Training & Inference + +Label Assignment. Assuming the video duration is $L_{v}$ , each snippet corresponds to a video period. In annotation, a ground-truth action which starts at $t_{s}^{*}$ and ends at $t_{e}^{*}$ . Expanding boundary from moment to region, the start region is defined as $R_{s} = [t_{s}^{*} - 1.5\frac{T_{v}}{L_{i}}, t_{s}^{*} + 1.5\frac{T_{v}}{L_{i}}]$ and end region is defined as $R_{e} = [t_{e}^{*} - 1.5\frac{T_{v}}{L_{i}}, t_{e}^{*} + 1.5\frac{T_{v}}{L_{i}}]$ . For Boundary Predictor, compute the overlap between each snippet period and $R_{s}$ as the label of start probabilities $G_{s}^{i} \in \mathbb{R}^{L_{i}}$ . Similarly, compute the overlap between snippet period and $R_{e}$ as the label of end probabilities $G_{e}^{i}$ . For IoU-ASP, following [12], IoU between each anchor and all actions are + +calculated and then arranged into a map $G_{IoU}^{i} \in \mathbb{R}^{D_{i} \times L_{i}}$ . Anchors with tIoU score greater than 0.9 participate in the training of Offset-ASP. For anchor start at $t_{s}$ and end at $t_{e}$ , assuming its corresponding ground-truth action is $[t_{s}^{*}, t_{e}^{*}]$ , the center offset $\Delta c$ and duration offset $\Delta d$ are calculated as Eq. (1)-(2), and arranged into maps $G_{cent}^{i} \in \mathbb{R}^{D_{i} \times L_{i}}$ and $G_{dura}^{i} \in \mathbb{R}^{D_{i} \times L_{i}}$ . + +$$ +c = \frac {t _ {s} + t _ {e}}{2}, d = t _ {e} - t _ {s}, c ^ {*} = \frac {t _ {s} ^ {*} + t _ {e} ^ {*}}{2}, d ^ {*} = t _ {e} ^ {*} - t _ {s} ^ {*} \tag {1} +$$ + +$$ +\Delta c = \frac {c ^ {*} - c}{d}, \Delta d = \log \frac {d ^ {*}}{d} \tag {2} +$$ + +Basic Loss. (1) For the $i$ -th layer, the loss of Boundary-Predictor is the re-weighted binary cross-entropy loss $L_{B}$ Eq. 3, where $P = \{p_t\}_{t=1}^{L_i}$ and $G = \{g_t\}_{t=1}^{L_i}$ represent the predicted boundary probabilities and its label of all snippets, respectively. Snippets with $g_t > 0.5$ serve as positive samples (i.e., $\delta \{g_t > 0.5\} = 1$ ) and others are negative samples. $T_{i}^{+}$ and $T_{i}^{-}$ are the number of positive and negative samples in this layer respectively. (2) The loss of IoU-ASP is the re-weighted binary cross-entropy loss $L_{asp}$ Eq. 4 and L2 loss $L_{2}$ , where $M = \{m_j\}_{j=1}^{N_i}$ and $G = \{g_j\}_{j=1}^{N_i}$ represent the predicted value and ground-truth value of each sampled anchor in the $i$ -th layer. $N_{i}, N_{i}^{+}, N_{i}^{-}$ represent the number of sampled anchors, positive anchors whose tIoU greater than 0.9 and negative anchors of this layer, respectively. (3) The loss of Offset-ASP is Smooth L1 loss $L_{1}$ . Note that only those sampled anchors with tIoU greater than 0.9 participate in the training of Offset-ASP. The re-weights in $L_{B}$ and $L_{asp}$ are used to balance the number between positive and negative samples. + +$$ +\begin{array}{l} L _ {B} (P, G) = - \frac {1}{L _ {i}} \sum_ {t = 1} ^ {L _ {i}} \left(\frac {L _ {i}}{T _ {i} ^ {+}} \cdot \delta \left\{g _ {t} > 0. 5 \right\} \cdot \log p _ {t} \right. \tag {3} \\ + \frac {L _ {i}}{T _ {i} ^ {-}} (1 - \delta \left\{g _ {t} > 0. 5 \right\} \cdot \log \left(1 - p _ {t}\right)) \\ \end{array} +$$ + +$$ +\begin{array}{l} L _ {a s p} (M, G) = - \frac {1}{N _ {i}} \sum_ {j = 1} ^ {N _ {i}} \left(\frac {N _ {i}}{N _ {i} ^ {+}} \cdot \delta \left\{g _ {j} > 0. 9 \right\} \cdot \log m _ {j} \right. \tag {4} \\ + \frac {N _ {i}}{N _ {i} ^ {-}} (1 - \delta \{g _ {j} > 0. 9 \} \cdot \log (1 - m _ {j})) \\ \end{array} +$$ + +Total Loss. The loss of the $i$ -th layer is composed of three parts: boundary loss, IoU loss and offset loss, as shown in Eq.(5) (6) (7) respectively. The total training objective is the sum of all three layers, formulated as Eq. 8. Besides, in order to balance the value between different terms, the coefficient $\lambda 1$ and $\lambda 2$ are set as 5 and 10. + +$$ +L _ {\text {b o u n d}} ^ {i} = L _ {B} \left(P _ {s} ^ {i}, G _ {s} ^ {i}\right) + L _ {B} \left(P _ {e} ^ {i}, G _ {e} ^ {i}\right) \tag {5} +$$ + +$$ +L _ {I o U} ^ {i} = L _ {a s p} \left(M _ {c l s} ^ {i}, G _ {I o U} ^ {i}\right) + \lambda_ {1} \cdot L _ {2} \left(M _ {r e g} ^ {i}, G _ {I o U} ^ {i}\right) \tag {6} +$$ + +$$ +L _ {o f f} ^ {i} = L _ {1} \left(M _ {c e n t} ^ {i}, G _ {c e n t} ^ {i}\right) + L _ {1} \left(M _ {d u r a} ^ {i}, G _ {d u r a} ^ {i}\right) \tag {7} +$$ + +$$ +L _ {t o t a l} = \sum_ {i = 1} ^ {3} \left(L _ {B} ^ {i} + L _ {I o U} ^ {i} + \lambda_ {2} \cdot L _ {o f f} ^ {i}\right) \tag {8} +$$ + +Inference. Each layer outputs $P_{s}^{i}, P_{e}^{i}, M_{cls}^{i}, M_{reg}^{i}, M_{cent}^{i}$ and $M_{dura}^{i}$ from the detector head in inference. Following [14, 12, 15], snippet in boundary probability $P_{s}$ is screened out as candidate start point if it is local peak or its probability is greater than $0.5 \cdot \max(P_{s})$ . And snippets can be selected as candidate end point from $P_{e}$ in the same way. Then the candidate start and end points are combined into proposals. In order to produce the more reasonable proposals, as shown in Fig 4, each layer of SFPN only outputs anchors in the corresponding scale range. Specifically, for the $i$ -th layer, its responsible scale range is $[S_{min}^{i}, S_{max}^{i}]$ . Furthermore, in the proposals set, for any start snippet whose index is $sdx$ and centered at time $t_{1}$ , and the end snippet whose index is $edx$ and centered at time $t_{2}$ , we can get its start probability $p_{s} = P_{s}^{i}[sdx]$ , end probability $p_{e} = P_{e}^{i}[edx]$ and tIoU score $p_{IoU} = M_{cls}^{i}[edx - sdx, sdx] \cdot M_{reg}^{i}[edx - sdx, sdx]$ . Its center is $c = (sdx + edx)/2L_{i}$ and duration is $d = (edx - sdx)/L_{i}$ . Subsequently, to refine the boundary, we can obtain center offset $\Delta c = M_{cent}^{i}[edx - sdx, sdx]$ and duration offset $\Delta d = M_{dura}^{i}[edx - sdx, sdx]$ , and adjust the boundary to $(t_{1}', t_{2}')$ as Eq. 9: + +$$ +\begin{array}{l} c ^ {\prime} = d \cdot \Delta c + c, d ^ {\prime} = d \cdot e ^ {\Delta d} \\ t _ {1} ^ {\prime} = c ^ {\prime} - \frac {d ^ {\prime}}{2}, t _ {2} ^ {\prime} = c ^ {\prime} + \frac {d ^ {\prime}}{2} \tag {9} \\ \end{array} +$$ + +Finally, proposals generated by each layer are merged together, and the action classifier assigns every proposal with a certain label and a classification score $P_{\text{label}}$ . The final score for the proposal $(t_1', t_2')$ is shown as Eq. 10. Then Soft-NMS [32] is adopted to remove redundant segments. + +$$ +\operatorname {s c o r e} _ {t _ {1} ^ {\prime}, t _ {2} ^ {\prime}} = p _ {s} \cdot p _ {e} \cdot p _ {I o U} \cdot p _ {\text {l a b e l}} \tag {10} +$$ + +# 4. Experiments + +# 4.1. Dataset and Settings + +Dataset. In order to verify the effectiveness of MENet, we experiment on two challenging datasets. ActivityNet-1.3 [2] contains 200 categories of daily life, sports, etc. We use the training set for model training and report the performance on the validation set. THUMOS-14 [8] consists of 413 videos with 20 action classes which is almost sports. In THUMOS-14, the validation set contains 200 long videos, including 3007 action segments, and the test set contains 213 videos, including 3358 action segments. Following the standard practice of THUMOS-14, we train MENet on the validation set and valid it on the test set. + +Metric. In order to fully demonstrate the advantages of our proposed method, we use two main evaluation metrics: mAP under a certain temporal tIoU threshold (mAP@tIoU) and average recall at a specified average number of proposals (AR@AN). Besides, on ActivityNet, the area under the AR-AN curve (AUC) also serves as a metric. + +Network Details. We use $\mathrm{R}(2 + 1)\mathrm{D} - 34$ as backbone with the TAC pretrained weight on Kinetics-400 serving as the primary feature extractor. The sampling interval $\sigma$ set as 16 frames and 5 frames for ActivityNet-1.3 and THUMOS-14, respectively. In this way, for the input video with $L_{v}$ frames, video snippet length $L_{s} = L_{v} / \sigma$ . For ActivityNet-1.3, we use linear interpolation to resize the length of video features $T = 200$ . For a long video in THUMOS-14, a sliding window with a length of 256 and an overlap of $50\%$ is used to truncate the original video feature. Each window is detected independently, and finally the results of all windows are concatenated as the total result of the entire long video. The scale ranges of each layer in the pyramid are set as: $[S_{min}^{1}, S_{max}^{1}] = [0, 15\%]$ , $[S_{min}^{2}, S_{max}^{2}] = [10\%, 75\%]$ and $[S_{min}^{3}, S_{max}^{3}] = [50\%, 100\%]$ . As for the action classifier, following the routine of most two-stage TAD methods, Untrimmed Net [25] serves as the classifier for THUMOS-14, and the recognition model by [32] for ActivityNet-1.3. + +Implementation Details. MENet is trained by Adam algorithm with batch size 8 and learning rate $10^{-3}$ . The sampling ratio of each layer $r_1$ , $r_2$ , $r_3$ are set as $50\%$ , $40\%$ , $90\%$ , respectively. For ActivityNet-1.3, the training process takes 10 epochs, where the first 7 epochs is the Generalization stage and the rest is the Specialization stage. As for THUMOS-14, the total training epoch is 7, and only the first epoch is the Generalization stage. Besides, the learning rate is decayed to $10^{-4}$ after 5 epochs on THUMOS-14 and 7 epochs on ActivityNet-1.3. + +# 4.2. Performance Evaluation On Detection + +We compare MENet with other state-of-the-art methods on ActivityNet-1.3 and THUMOS-14. Table 1 shows the comparison on the validation set of ActivityNet-1.3. The mAP at tIoU thresholds of $\{0.5, 0.75, 0.95\}$ are reported, as well as the Avg.mAP which is calculated at tIoU thresholds between 0.5 and 0.95 with the step of 0.05. Impressively, MENet outperforms other representative methods at tIoU thresholds 0.75 and 0.95. MENet promotes the Avg.mAP from $36.6\%$ to $37.7\%$ , with an increase of more than $1.1\%$ . Comparing the methods of different backbones, MENet exceeds others. + +Table 2 presents the detection performance comparison on the test set of THUMOS-14. MENet achieves comparable performance with the best method [30] at low tIoU thresholds. But, MENet outperforms other representative methods at tIoU thresholds 0.6 and 0.7. MENet improves the mAP@0.7 from the current best $31.8\%$ to $34.0\%$ . To locate the boundaries more accurately, a higher threshold is usually used to separate the positive and negative samples in training. Therefore MENet has a better response at high tIoU thresholds. Higher tIoU means more precise action boundaries, which is more difficult and more important for action localization. Meanwhile, it is noteworthy + +that MENet shows obvious superiority compared with other FPN-based methods like [11], which substantiates the effectiveness of the SFPN proposed in MENet. + +
MethodBackbonemAP@tIoU (%)
0.50.750.95Avg.
GTAN [16]P3D52.634.18.934.3
BSN [14]TSN46.530.08.030.0
BMN [12]TSN50.134.88.333.9
G-TAD [29]TSN50.434.69.034.1
PCMNet [18]TSN51.436.19.535.3
TCA-Net [19]TSN52.336.76.935.5
RTD-Net [23]I3D47.230.78.630.8
ContextLoc [33]I3D56.035.23.634.2
AFSD [11]I3D52.435.36.534.4
TAGS [17]I3D56.336.89.636.5
STPT [27]STPT51.433.76.833.4
ActionFormer [30]R(2+1)D54.737.88.436.6
MENet(ours)R(2+1)D54.738.410.537.7
+ +Table 1. The temporal action detection performance comparison with state-of-art methods on ActivityNet-1.3. Bold text indicates the best results. + +
MethodBackbonemAP@tIoU (%)
0.30.40.50.60.7
GTAN [16]P3D57.847.238.8--
BSN [14]TSN53.545.036.928.420.0
BMN [12]TSN56.047.438.829.720.5
G-TAD [12]TSN54.547.640.230.823.4
PCMNet [18]TSN61.555.447.237.527.3
TCA-Net [19]TSN60.653.244.636.826.7
RTD-Net [23]I3D68.362.351.938.823.7
ContextLoc [33]I3D68.363.854.341.826.2
AFSD [11]I3D67.362.455.543.731.1
TAGS [17]I3D68.663.857.046.331.8
STPT [27]STPT70.665.756.444.630.5
ActionFormer [30]R(2+1)D73.467.459.146.731.5
MENet(ours)R(2+1)D70.765.358.849.134.0
+ +# 4.3. Performance Evaluation On Proposal + +To further verify the advantages of MENet, we do not consider action classes of action segments to evaluate its performance on temporal action proposal (TAP) task. + +Through Table 3, we can further discover the performance improvement of AR@100 and the area under the AR-AN curve (AUC) on ActivityNet-1.3. For instance, MENet boosts the AUC from $68.1\%$ to $70.2\%$ . As for THUMOS-14, MENet outperforms other methods in all metrics are reported in Table 4, which certifies the effectiveness of MENet once again. + +# 4.4. Ablation Study + +Ablation studies are performed thoroughly to verify the role of each module in MENet, as well as the impact of different training strategies. + +Table 2. The temporal action detection performance comparison with state-of-art methods on THUMOS-14. Bold text indicates the best results. + +
MethodAR@100AUC
BSN [14]74.266.2
GTAN [16]74.867.1
BMN [12]75.067.1
RTD-Net [23]73.265.8
TCA-Net [19]76.168.1
MENet(ours)77.070.2
+ +Table 3. Temporal action proposal performance comparison with other representative methods on ActivityNet-1.3. Bold text indicates the best results. + +
MethodAR@50AR@100AR@200AR@500
BSN [14]37.546.153.260.6
BMN [12]39.447.754.762.1
RTD-Net [23]41.549.3256.4162.91
TCA-Net [19]42.150.557.163.6
MENet(ours)44.252.358.666.0
+ +1). Effectiveness of the MEM: As discussed before, when constructing the movement enhance feature, MFE and MREM are the crucial designs in MEM. To certify the function of these two modules, we design a Base model for comparison, in which the Movement Feature is removed and MREM is replaced by temporal 1D convolution. As shown in Table 5, we can find that compared with the Base model, Movement Feature and MREM both can promote the performance. Besides, the best results emerge when combining them together as the intact MEM. + +Table 4. Temporal action proposal performance comparison with other representative methods on THUMOS-14, measured by AR@AN. Bold text indicates the best results. + +
ConstructionmAP@tIoU (%)
0.50.750.95Avg.
Base54.237.310.437.0
Base + Movement Feature54.537.810.637.3
Base + MREM54.437.910.437.3
MEM54.738.410.537.7
+ +Table 5. Ablation study on the MEM. The Detection performance is reported on ActivityNet-1.3. And The best result can be achieved with these two modules are integrated. + +2). Effectiveness of the U-shape Module: As discussed before, when constructing the feature pyramid, U-shape Module is designed to establish interactions between different layers. To reveal the validity of this idea, we use 1D convolution with the step of 2 and AvgPooling to downsample the feature sequence respectively. From Table 6, the U-shape Module can promote the performance, which substantiates the importance of this design. +3). Effectiveness of feature pyramid structure: For better detection accuracy, MENet makes use of the feature pyramid. To verify the impact of this structure, we only use a single layer feature sequence to conduct experiments + +
ConstructionmAP@tIoU (%)
0.50.750.95Avg.
DownSampling (AvgPooling)54.538.210.237.4
DownSampling (Convolution)54.438.110.837.3
U-shape Module54.738.410.537.7
+ +and compare it with the SFPN, keeping other components unchanged. On ActivityNet-1.3, single-layer feature with lengths of 200, 100 and 50 are used. Corresponding results are shown in Table 7. The experimental results exhibit that SFPN performs better than any other single-layer structure, thus justifying the feature pyramid structure is indeed beneficial to the performance. + +Table 6. Ablation study on the U-shape Module. The Detection performance is reported on ActivityNet-1.3. + +
LengthmAP@tIoU (%)
0.50.750.95Avg.
5053.037.110.836.8
10054.138.110.437.1
20054.238.310.537.3
SFPN54.738.410.537.7
+ +4). Effectiveness of two-stage training: For efficient training of MENet and ensuring that the $i$ -th layer in SFPN is specialized in actions at a specific scale range $[S_{min}^{i}, S_{max}^{i}]$ , the two-stage training strategy is applied. When training ASP of the $i$ -th layer, in the first Generalization stage, the anchors are randomly selected from all scales according to the sampling ratio $r_i$ , in the second Specialization stage, the sampling ratio inside and outside the range $[S_{min}^{i}, S_{max}^{i}]$ are $2 \cdot r_i$ and $r_i$ , respectively. In this ablation study, we train MENet using the fully Generalization stage, the fully Specialization stage and the complete two-stage strategy, respectively. In addition, to demonstrate the effectiveness of this training method, we also test a new Bias training strategy that only samples from the range $[S_{min}^{i}, S_{max}^{i}]$ with the sampling ratio of $r_i$ . + +As shown in Table 8, the performance of the Bias strategy is the worst, indicating that in addition to those samples in the specific scale range, other samples outside this range also play an important role for a better understanding of actions. Further, the training effect is impeded when removing either the Generalization or the Specialization stage, which verifies the effectiveness of the two-stage training strategy. + +5). Qualitative Comparison: To illustrate the edge of MENet more intuitively, we select videos of Javelin Throw and High Jump from ActivityNet-1.3 and compare our results qualitatively with the Base, in which we remove the movement enhanced feature and SFPN. Results with the + +Table 7. Ablation study on the SFPN. "Length" means the temporal length of single layer feature sequence. The Detection performance is reported on ActivityNet-1.3. + +
Training StrategymAP@tIoU (%)
0.50.750.95Avg.
only Bias45.829.17.429.4
only Generalization54.338.211.037.4
only Specialization54.638.010.837.4
two-stage54.738.410.537.7
+ +Table 8. Ablation study on the two-stage training strategy. The proposed two-stage training leads to better performance than the single stage method or the Bias method. + +highest confidence score are visualized in Fig 5. Firstly, Compared with the Base method, MENet uses the movement feature, which enlarges the difference between action and background, making the model more accurate in boundary localization. Secondly, it can be seen the High Jump action contains a large-scale action and a small-scale action. Due to the SFPN in MENet, MENet can better capture actions at different scales. Results of qualitative comparison once again prove the superiority of MENet. + +![](images/b0b660d9f12d5764c2ed6ef2d20fa2ba3356685c5f71cefc74c313b3811c4f01.jpg) +Figure 5. Qualitative Comparison. MENet generates more accurate action segments. + +![](images/a7cc00d0cfecdd234bf25ab228c3639146b3a495b6508ab208893300bf9d3655.jpg) + +# 5. Conclusion + +Temporal action detection (TAD) is aimed at localizing the action segment and classifying the action class. Despite the considerable attention and rapid development, TAD is hindered by two critical problems: the movement feature submergence and multi-scale action detection. In an effort to overcome these two challenges, we propose the Movement Enhance Network (MENet) with two crucial designs. Firstly, we propose the Movement Enhance Module (MEM) to extract the movement feature in video snippets and explore the multi-relations between the snippets. Secondly, we propose the Scale FPN (SFPN) to handle the different scale actions, we design the U-shape Module to facilitate the information flow between different scale features. For better performance, we design the training and inference stage, ensuring that each layer in MENet is specialized at a specific scale range. Extensive experiments demonstrate that MENet considerably outperforms other representative TAD methods on ActivityNet-1.3 and THUMOS-14. + +Acknowledgements. This work was supported by National Natural Science Foundation of China (NSFC) No. 62176156. + +# References + +[1] Humam Alwassel, Silvio Giancola, and Bernard Ghanem. Tsp: Temporally-sensitive pretraining of video encoders for localization tasks. In ICCV, pages 3173-3183, 2021. +[2] Fabian Caba Heilbron, Victor Escorcia, Bernard Ghanem, and Juan Carlos Niebles. Activitynet: A large-scale video benchmark for human activity understanding. In CVPR, pages 961-970, 2015. +[3] Joao Carreira and Andrew Zisserman. Quo vadis, action recognition? a new model and the kinetics dataset. In CVPR, pages 6299-6308, 2017. +[4] Guo Chen, Yin-Dong Zheng, Limin Wang, and Tong Lu. Dcan: Improving temporal action detection via dual context aggregation. 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In ICCV, pages 13516-13525, 2021. \ No newline at end of file diff --git a/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/images.zip b/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..058cdefe14e47ee34db0bcdc32b54efa72c1ec42 --- /dev/null +++ b/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:cbd56aeefbc3c8755c3d41edcae42f8dc669134e7303b58305f8cbd3ff8fccce +size 547604 diff --git a/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/layout.json b/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..0982a96dbf7c6ba4411aac0c87fd093d2b3cca3a --- /dev/null +++ b/2023/Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection/layout.json @@ -0,0 +1,8934 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 65, + 102, + 531, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 102, + 531, + 140 + ], + "spans": [ + { + "bbox": [ + 65, + 102, + 531, + 140 + ], + "type": "text", + "content": "Movement Enhancement toward Multi-Scale Video Feature Representation for Temporal Action Detection" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 136, + 161, + 458, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 136, + 161, + 458, + 204 + ], + "spans": [ + { + "bbox": [ + 136, + 161, + 458, + 204 + ], + "type": "text", + "content": "Zixuan Zhao Dongqi Wang Xu Zhao* \nDepartment of Automation, Shanghai Jiao Tong University, China \n{zhaozixuan, wangdq0124, zhaoxu}@sjtu.edu.cn" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "spans": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 256, + 290, + 543 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 256, + 290, + 543 + ], + "spans": [ + { + "bbox": [ + 47, + 256, + 290, + 543 + ], + "type": "text", + "content": "Boundary localization is a challenging problem in Temporal Action Detection (TAD), in which there are two main issues. First, the submergence of movement feature, i.e. the movement information in a snippet is covered by the scene information. Second, the scale of action, that is, the proportion of action segments in the entire video, is considerably variable. In this work, we first design a Movement Enhance Module (MEM) to highlight movement feature for better action location, and then, we propose a Scale Feature Pyramid Network (SFPN) to detect multi-scale actions in videos. For Movement Enhance Module, firstly, Movement Feature Extractor (MFE) is designed to get the movement feature. Secondly, we propose a Multi-Relation Enhance Module (MREM) to grasp valuable information correlation both locally and temporally. For Scale Feature Pyramid Network, we design a U-Shape Module to model different scale actions, moreover, we design the training and inference strategy of different scales, ensuring that each pyramid layer is only responsible for actions at a specific scale. These two innovations are integrated as the Movement Enhance Network (MENet), and extensive experiments conducted on two challenging benchmarks demonstrate its effectiveness. MENet outperforms other representative TAD methods on ActivityNet-1.3 and THUMOS-14." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 551, + 128, + 562 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 551, + 128, + 562 + ], + "spans": [ + { + "bbox": [ + 47, + 551, + 128, + 562 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 564, + 287, + 636 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 564, + 287, + 636 + ], + "spans": [ + { + "bbox": [ + 46, + 564, + 287, + 636 + ], + "type": "text", + "content": "Temporal Action Detection (TAD) is a significant video understanding task, which aims to extract video segments with specific action labels from untrimmed long videos. It remains a challenging problem because action boundaries are difficult to determine precisely, which adversely affects the performance in most works." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 636, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 636, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 636, + 287, + 696 + ], + "type": "text", + "content": "Two critical issues stand in the way of detecting action boundaries robustly from untrimmed videos. The first issue, which could be called as movement feature submergence, exists in where either context but not movement itself dominate feature expression, or movement is small in pixel size." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 313, + 236, + 426, + 300 + ], + "blocks": [ + { + "bbox": [ + 313, + 236, + 426, + 300 + ], + "lines": [ + { + "bbox": [ + 313, + 236, + 426, + 300 + ], + "spans": [ + { + "bbox": [ + 313, + 236, + 426, + 300 + ], + "type": "image", + "image_path": "21898c25d4bf84a2c8de184179b6ede51d7afb930520fcb30205e4f4bd58fc11.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 314, + 310, + 422, + 320 + ], + "lines": [ + { + "bbox": [ + 314, + 310, + 422, + 320 + ], + "spans": [ + { + "bbox": [ + 314, + 310, + 422, + 320 + ], + "type": "text", + "content": "(a) Strong class-specific context." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 430, + 236, + 544, + 299 + ], + "blocks": [ + { + "bbox": [ + 430, + 236, + 544, + 299 + ], + "lines": [ + { + "bbox": [ + 430, + 236, + 544, + 299 + ], + "spans": [ + { + "bbox": [ + 430, + 236, + 544, + 299 + ], + "type": "image", + "image_path": "f391a8a6f1cc42c8c4517192afc16c1ba68b20fe98effe9fb20c187a12d42716.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 310, + 331, + 545, + 456 + ], + "blocks": [ + { + "bbox": [ + 429, + 310, + 539, + 320 + ], + "lines": [ + { + "bbox": [ + 429, + 310, + 539, + 320 + ], + "spans": [ + { + "bbox": [ + 429, + 310, + 539, + 320 + ], + "type": "text", + "content": "(b) Small movement in pixel size." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 310, + 331, + 545, + 456 + ], + "lines": [ + { + "bbox": [ + 310, + 331, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 310, + 331, + 545, + 456 + ], + "type": "image", + "image_path": "72a3b8daba3973ab538349a34845ff7149ffb32d91d5f8311d714906eac73e69.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 390, + 467, + 467, + 476 + ], + "lines": [ + { + "bbox": [ + 390, + 467, + 467, + 476 + ], + "spans": [ + { + "bbox": [ + 390, + 467, + 467, + 476 + ], + "type": "text", + "content": "(c) Multi-scale actions." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 479, + 547, + 546 + ], + "lines": [ + { + "bbox": [ + 304, + 479, + 547, + 546 + ], + "spans": [ + { + "bbox": [ + 304, + 479, + 547, + 546 + ], + "type": "text", + "content": "Figure 1. Movement feature submergence and multi-scale actions. (a) Strong class-specific context of the accordion leads to video feature generated by TAC lacking the difference between action and background. (b) Small movement of Futsal results in less difference between action area and background area. (c) Multiscale actions have different feature richness and action pattern." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 556, + 547, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 556, + 547, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 556, + 547, + 700 + ], + "type": "text", + "content": "For the first case, as shown in Fig 1(a), the action of Playing Accordion can be easily judged by Accordion, while this strong class-specific context causes the real movement information in action area to be submerged. For the second case, as shown in Fig 1(b), for Futsal, the stadium scene takes up a large proportion of pixels in the frame, while the movement information is ignored. This movement feature submergence leads to the feature in background to be similar with the feature in action area, which blues the action boundaries. If the movement information can be highlighted, the boundary will be easier to be located. However, this problem has been ignored by prior works [12, 29, 22]." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 318, + 701, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 701, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 318, + 701, + 545, + 713 + ], + "type": "text", + "content": "The second issue is the multi-scale of actions in an" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 703, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 703, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 703, + 135, + 712 + ], + "type": "text", + "content": "*Corresponding author" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13555" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 263 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 263 + ], + "type": "text", + "content": "untrimmed video. As shown in Fig 1(c), the feature richness varies greatly with the scale. There are rare features for action segments that account for a small proportion of the entire video, that is the small-scale action, and abundant features for those segments that account for a higher proportion, that is the large-scale action. We contend that there are different action patterns between different scales. Specifically, compared with small-scale action, large-scale action contains more obviously action process (i.e. start phase, action phase and end phase). Some researches [13, 7, 11] resort feature pyramid network (FPN) to solve the problem. However, there are two aspects that are ignored. Firstly, these works detect actions at different feature scales, but, they do not adaptively learn action features of different scales. Secondly, the information flow in FPN is insufficient, lacking interactions between different pyramid layers." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 264, + 289, + 562 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 264, + 289, + 562 + ], + "spans": [ + { + "bbox": [ + 47, + 264, + 289, + 562 + ], + "type": "text", + "content": "In this paper, as an effort to overcome the above challenges, we investigate the feature of TAD. (1) In order to overcome the movement feature submergence, and highlight the difference between foreground and background snippets. We design the Movement Enhance Module (MEM) to enhance the movement information in a video snippet, which includes two crucial parts. First, we propose a siamese network named Movement Feature Extractor (MFE), which uses the dynamic information of the frame sequence and the static information of the frame to extract movement feature from video snippets. And then, we propose the Multi-Relation Enhance Module (MREM) to establish temporal and local correlations between video snippets. (2) In order to learn specific representations for different scale actions, we propose the Scale FPN (SFPN), which uses a U-shaped network to produce multi-scale video features and facilitate the information flow between different layers. Moreover, for each layer in SFPN to take charge of detecting action segments of the corresponding scale, we design a two-stage learning strategy. In the former Generalization stage, each layer is trained with all action segments; in the latter Specialization stage, each layer is biased toward actions in a specific scale range. During inference, every layer takes charge of detecting action segments of the corresponding scale." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 563, + 287, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 563, + 287, + 598 + ], + "spans": [ + { + "bbox": [ + 47, + 563, + 287, + 598 + ], + "type": "text", + "content": "In summary, this work explores feature representation and action segment representation that are more suitable for TAD task. Its contributions are summarized as follows." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 54, + 609, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 5, + "blocks": [ + { + "bbox": [ + 55, + 609, + 287, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 609, + 287, + 657 + ], + "spans": [ + { + "bbox": [ + 55, + 609, + 287, + 657 + ], + "type": "text", + "content": "1. To alleviate the movement feature submergence, we design the Movement Enhance Module (MEM) to highlight the movement feature in a video snippet, and explore local and temporal relations between snippets." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 54, + 665, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 665, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 54, + 665, + 287, + 713 + ], + "type": "text", + "content": "2. For the multi-scale actions in an untrimmed video with different feature patterns, we design the Scale FPN (SFPN) to learn different scale actions respectively, where targeted training and inference strategies are" + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 325, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 325, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 325, + 72, + 545, + 96 + ], + "type": "text", + "content": "adopted. Consequently, each layer in the SFPN specializes in actions at a certain scale range." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 313, + 106, + 547, + 165 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 106, + 547, + 165 + ], + "spans": [ + { + "bbox": [ + 313, + 106, + 547, + 165 + ], + "type": "text", + "content": "3. Extensive experiments conducted on two datasets verify the effectiveness of our proposed method. On ActivityNet1.3, MENet promotes the best average mAP from " + }, + { + "bbox": [ + 313, + 106, + 547, + 165 + ], + "type": "inline_equation", + "content": "36.6\\%" + }, + { + "bbox": [ + 313, + 106, + 547, + 165 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 313, + 106, + 547, + 165 + ], + "type": "inline_equation", + "content": "37.7\\%" + }, + { + "bbox": [ + 313, + 106, + 547, + 165 + ], + "type": "text", + "content": ", and boosts the mAP@0.7 from " + }, + { + "bbox": [ + 313, + 106, + 547, + 165 + ], + "type": "inline_equation", + "content": "31.8\\%" + }, + { + "bbox": [ + 313, + 106, + 547, + 165 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 313, + 106, + 547, + 165 + ], + "type": "inline_equation", + "content": "34.0\\%" + }, + { + "bbox": [ + 313, + 106, + 547, + 165 + ], + "type": "text", + "content": " on THUMOS-14." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 178, + 392, + 190 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 178, + 392, + 190 + ], + "spans": [ + { + "bbox": [ + 306, + 178, + 392, + 190 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 198, + 547, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 198, + 547, + 413 + ], + "spans": [ + { + "bbox": [ + 304, + 198, + 547, + 413 + ], + "type": "text", + "content": "Video Feature for TAD. The pre-trained TAC model is often used as the feature extractor for Temporal Action Detection which receives several frames as a snippet to distill both appearance and motion information from raw video frames. TSN [26], I3D [3], and SlowFast [6] are the most common feature extractors. However, they only focus on the action categories, which results in some actions that are strongly related to the scene having quite similar representations to background segments. To overcome the drawback, TSP [1] adds additional background supervision in the pretraining model to generate the background-sensitive feature. BSP [28] artificially synthesizes different video boundaries and conducts boundary learning in the pretraining model to generate boundary-sensitive feature. However, these works cannot address the problem of movement feature submergence fundamentally. In this paper, MENet uses the Movement Enhance Module (MEM) to magnify the movement feature and the difference between action and background." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 414, + 547, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 414, + 547, + 582 + ], + "spans": [ + { + "bbox": [ + 304, + 414, + 547, + 582 + ], + "type": "text", + "content": "Multi-scale Action Detection. The scale of the action varies dramatically in a video. Compared with the large actions, those small action segments have fewer samples and insufficient features. Some works [13, 7, 11] focus on feature pyramid network (FPN) to generate different temporal resolution features. However, the FPN structure does not learn specific feature representation for a certain action scale, and also lacks sufficient information flow intrinsically. TSI [15] proposes a scale-invariant loss, which balances large and small actions in quantity, but fails to fundamentally solve the scarce feature of small actions. In this work, we propose SFPN to cope with these problems, which establishes associations between different scale features and learns scale-specific feature representations." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "type": "text", + "content": "Temporal Action Detection. Benefiting from the successful practice of image object detection and trimmed video action recognition, the two-stage pipeline prevails in TAD task. Specifically, the first stage is to locate candidate action segments in the video, and the second stage uses an action classifier to classify these proposals. The first stage has three main paradigms. (1) Anchor-Based method: Methods [5, 13, 21] put anchors of various scales on the video feature, and then give the final confidence of anchors. However, they cannot produce flexible boundaries. (2) Boundary-Base method: Methods [14, 31, 16]" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "text", + "content": "13556" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 168 + ], + "type": "text", + "content": "predict boundary scores on the video feature, which are combined to generate proposals. However, the confidence of the proposal lacks global information. (3) Combined method: Methods [12, 10, 4] combine these two methods to generate precise confidence and flexible boundaries. In this work, we follow the combined method to integrate the start point and end point as a proposal and generate multiscale anchor maps to predict anchor confidence." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 178, + 103, + 190 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 178, + 103, + 190 + ], + "spans": [ + { + "bbox": [ + 47, + 178, + 103, + 190 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 197, + 115, + 209 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 197, + 115, + 209 + ], + "spans": [ + { + "bbox": [ + 47, + 197, + 115, + 209 + ], + "type": "text", + "content": "3.1. Overview" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "spans": [ + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": "Problem Definition. Input of the Movement Enhance Network (MENet) is an untrimmed video denoted as " + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "inline_equation", + "content": "V = \\{v_{i}\\}_{i=1}^{L_{v}}" + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "inline_equation", + "content": "v_{i}" + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": " represents the " + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": "-th frame of the video and " + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "inline_equation", + "content": "L_{v}" + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": " is the total frames. The duration of the video is " + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "inline_equation", + "content": "T_{v}" + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": ". Due to redundancy between video frames, several consecutive frames are usually regarded as a snippet. With the sampling interval " + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": ", the whole video can be defined as snippet sequence " + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "inline_equation", + "content": "S = \\{s_{i}\\}_{i=1}^{L_{s}}" + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "inline_equation", + "content": "L_{s} = L_{v} / \\sigma" + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": " representing the number of total snippets. The output of the MENet is " + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "inline_equation", + "content": "\\{\\psi_{i} | \\psi_{i} = (t_{i,s}, t_{i,e}, c_{i}, score_{i})\\}" + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "inline_equation", + "content": "t_{i,s}, t_{i,e}, c_{i}" + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "inline_equation", + "content": "score_{i}" + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": " are start time, end time, action category and confidence score, respectively. The annotations of untrimmed video are action instances " + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "inline_equation", + "content": "\\{\\Psi_{i} | \\Psi_{i} = (t_{i,s}^{*}, t_{i,e}^{*}, c_{i}^{*})\\}" + }, + { + "bbox": [ + 46, + 215, + 287, + 372 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 372, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 372, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 372, + 287, + 479 + ], + "type": "text", + "content": "Framework Architecture. The framework architecture of MENet is shown in Fig 2. MENet is mainly composed of two parts: Movement Enhance Module (MEM) and Scale FPN (SFPN). MEM is used to extract movement enhanced feature and explore different video relations between snippets. SFPN is proposed to generate feature pyramid and learn specific expression patterns of different action scales. Finally, SFPN gives action boundaries and confidence scores of different scale actions, separately." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 485, + 203, + 496 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 485, + 203, + 496 + ], + "spans": [ + { + "bbox": [ + 47, + 485, + 203, + 496 + ], + "type": "text", + "content": "3.2. Movement Enhance Module" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 498, + 287, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 287, + 556 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 287, + 556 + ], + "type": "text", + "content": "To obtain the feature that contains action category information and is sensitive to foreground and background, simultaneously, we propose the Movement Enhance Module, which contains two vital stages: Movement Feature Extractor (MFE) and Multi-Relation Enhance Module (MREM)." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "text", + "content": "Movement Feature Extractor. In order to amplify the movement information, MFE is proposed. As shown in Fig 3, MFE uses a siamese network to highlight the movement information in a video snippet. We select " + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{R}(2 + 1)\\mathrm{D}-34" + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "text", + "content": " [24] as backbone with the TAC pretrained weight on Kinetics-400 [9], and two networks share the weight. MFE has two input paths. One path is video snippet path composed of consecutive frames, and the other is frame duplication path, which selects a frame from the snippet and copies it to the length of the snippet. Here, the middle frame is selected for duplication. The feature from the video snippet path contains both static scene and dynamic movement information, which is " + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "inline_equation", + "content": "F_{Total} \\in \\mathbb{R}^{C' \\times T}" + }, + { + "bbox": [ + 46, + 558, + 287, + 714 + ], + "type": "text", + "content": ", but feature from" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": "the frame duplication path only contains static scene information, which is " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "F_{Static} \\in \\mathbb{R}^{C' \\times T}" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": ". And then, MFE extracts the movement information in the snippet using the difference between the two features, which is defined as " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "F_{Movement} \\in \\mathbb{R}^{C' \\times T}" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": ". Finally, " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "F_{Movement}" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "F_{Total}" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " are concatenated as " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "F_{MT} \\in \\mathbb{R}^{2C' \\times T}" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 144, + 546, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 144, + 546, + 337 + ], + "spans": [ + { + "bbox": [ + 304, + 144, + 546, + 337 + ], + "type": "text", + "content": "Multi-Relation Enhance Module. To establish relations between snippets and fuse the information at semantic dimension, the Multi-Relation Enhance Module is proposed. As shown in Fig 2, firstly, we use a 1D convolution to fuse information at semantic dimension. Secondly, there are three information paths in MREM. (1) Local Path: 1D convolution can directly establish relations in a local scale " + }, + { + "bbox": [ + 304, + 144, + 546, + 337 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 144, + 546, + 337 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 144, + 546, + 337 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 144, + 546, + 337 + ], + "type": "text", + "content": " is the kernel size. However, it is difficult for 1D convolutions to establish temporal relationship between snippet features. (2) Forward Path: The LSTM processes each snippet successively according to the input order, with an outstanding ability to model the temporal relation. In forward path, we use LSTM to establish forward information. (3) Backward Path: In backward path, we flip the video sequence, and establish backward information. Finally, the three paths are integrated." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 345, + 479, + 357 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 345, + 479, + 357 + ], + "spans": [ + { + "bbox": [ + 305, + 345, + 479, + 357 + ], + "type": "text", + "content": "3.3. Scale Feature Pyramid Network" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 364, + 546, + 423 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 364, + 546, + 423 + ], + "spans": [ + { + "bbox": [ + 304, + 364, + 546, + 423 + ], + "type": "text", + "content": "We contend different scale actions have different patterns. Therefor, the SFPN is designed to learn patterns of specific scales. SFPN contains U-Shape Module and Detector Head, which aims to generate feature pyramid and final detection results, respectively." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 425, + 545, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 425, + 545, + 532 + ], + "spans": [ + { + "bbox": [ + 304, + 425, + 545, + 532 + ], + "type": "text", + "content": "U-Shape Module. For feature pyramid generating, as shown in Fig 2, SFPN uses a U-shaped architecture inspired by [20] to generate feature sequences in different temporal resolution. From top to down, SFPN uses multiple temporal convolution layers followed by AvgPooling to downsample the temporal resolution. From bottom to up, to restore the lower layer information, SFPN uses several 1D transpose convolution to restore the feature resolution and features in the same resolution are concatenated." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 533, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 533, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 533, + 545, + 616 + ], + "type": "text", + "content": "Detector Head. As demonstrated in Fig 2, each detector head consists of a Boundary Predictor, an Anchor Feature Align Layer and two Anchor Score Predictor (ASP). The output of the Boundary Predictor and Anchor Score Predictor is used to generate proposals and confidence scores, and the Anchor Feature Align Layer is to generate the feature representation for each anchor." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 617, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 653 + ], + "type": "text", + "content": "Boundary Predictor. Boundary Predictor aims at predicting boundary probabilities " + }, + { + "bbox": [ + 304, + 617, + 545, + 653 + ], + "type": "inline_equation", + "content": "P_{s} = \\{p_{s}^{i}\\}_{i = 1}^{L_{i}}" + }, + { + "bbox": [ + 304, + 617, + 545, + 653 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 617, + 545, + 653 + ], + "type": "inline_equation", + "content": "P_{e} = \\{p_{e}^{i}\\}_{i = 1}^{L_{i}}" + }, + { + "bbox": [ + 304, + 617, + 545, + 653 + ], + "type": "text", + "content": " of each snippet by recognizing the boundary pattern." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 654, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 546, + 713 + ], + "type": "text", + "content": "Anchor Feature Align Layer. The area between any two snippets can form an anchor, and each anchor consists of several consecutive snippets. Supposing " + }, + { + "bbox": [ + 304, + 654, + 546, + 713 + ], + "type": "inline_equation", + "content": "N_{i}" + }, + { + "bbox": [ + 304, + 654, + 546, + 713 + ], + "type": "text", + "content": " anchors are randomly sampled to participate in the forward. The Anchor Feature Align Layer adopts SGAlign designed in [29]" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13557" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 74, + 533, + 327 + ], + "blocks": [ + { + "bbox": [ + 55, + 74, + 533, + 327 + ], + "lines": [ + { + "bbox": [ + 55, + 74, + 533, + 327 + ], + "spans": [ + { + "bbox": [ + 55, + 74, + 533, + 327 + ], + "type": "image", + "image_path": "a24ad46a6c7ad8b213ee7318ab063eb7db95c942341d303ae56a872aec0a9d36.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 335, + 548, + 381 + ], + "lines": [ + { + "bbox": [ + 46, + 335, + 548, + 381 + ], + "spans": [ + { + "bbox": [ + 46, + 335, + 548, + 381 + ], + "type": "text", + "content": "Figure 2. Overview of our MENet and the structure of some sub-modules. There are two crucial parts in the framework (Top) of MENet: Movement Enhance Module (MEM) and Scale FPN (SFPN). MEM is designed to generate movement enhanced feature. SFPN is designed to generate multi-scale feature pyramid, and learn action expressions in different layers. The structure of the sub-modules is shown below (Bottom) with the same color in the framework." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 48, + 389, + 292, + 586 + ], + "blocks": [ + { + "bbox": [ + 48, + 389, + 292, + 586 + ], + "lines": [ + { + "bbox": [ + 48, + 389, + 292, + 586 + ], + "spans": [ + { + "bbox": [ + 48, + 389, + 292, + 586 + ], + "type": "image", + "image_path": "58226dd19b1a8ccad45382bf78cc29a64131377a34b6b63ab24f7d8c8b3bba52.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 594, + 288, + 628 + ], + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 628 + ], + "type": "text", + "content": "Figure 3. Illustration of MFE. This module constructs the movement feature in a snippet by the difference between dynamic video snippet and static picture." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 638, + 288, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 638, + 288, + 674 + ], + "spans": [ + { + "bbox": [ + 46, + 638, + 288, + 674 + ], + "type": "text", + "content": "to generate feature expressions " + }, + { + "bbox": [ + 46, + 638, + 288, + 674 + ], + "type": "inline_equation", + "content": "F_{A}^{i}\\in \\mathbb{R}^{C\\times S\\times N_{i}}" + }, + { + "bbox": [ + 46, + 638, + 288, + 674 + ], + "type": "text", + "content": " for anchors from the video feature " + }, + { + "bbox": [ + 46, + 638, + 288, + 674 + ], + "type": "inline_equation", + "content": "F_{v}^{i}" + }, + { + "bbox": [ + 46, + 638, + 288, + 674 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 638, + 288, + 674 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 638, + 288, + 674 + ], + "type": "text", + "content": " is the sampling number of snippets within an anchor." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": "Anchor Score Predictor. IoU-ASP and Offset-ASP have the same structure to recognize the action pattern within an anchor. For the " + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": "-th layer in SFPN, IoU-ASP gener" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 389, + 547, + 452 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 389, + 547, + 452 + ], + "spans": [ + { + "bbox": [ + 306, + 389, + 547, + 452 + ], + "type": "text", + "content": "ates two maps " + }, + { + "bbox": [ + 306, + 389, + 547, + 452 + ], + "type": "inline_equation", + "content": "M_{cls}^{i}\\in \\mathbb{R}^{D_{i}\\times L_{i}},M_{reg}^{i}\\in \\mathbb{R}^{D_{i}\\times L_{i}}" + }, + { + "bbox": [ + 306, + 389, + 547, + 452 + ], + "type": "text", + "content": " , where " + }, + { + "bbox": [ + 306, + 389, + 547, + 452 + ], + "type": "inline_equation", + "content": "D_{i}" + }, + { + "bbox": [ + 306, + 389, + 547, + 452 + ], + "type": "text", + "content": " is predefined maximum anchor duration. In Offset-ASP, two output maps are denoted as " + }, + { + "bbox": [ + 306, + 389, + 547, + 452 + ], + "type": "inline_equation", + "content": "M_{cent}^{i}\\in \\mathbb{R}^{D_{i}\\times L_{i}},M_{dura}^{i}\\in" + }, + { + "bbox": [ + 306, + 389, + 547, + 452 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{D_i\\times L_i}" + }, + { + "bbox": [ + 306, + 389, + 547, + 452 + ], + "type": "text", + "content": " . These two maps indicate each anchor's center offset and duration offset respectively." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 464, + 480, + 477 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 464, + 480, + 477 + ], + "spans": [ + { + "bbox": [ + 306, + 464, + 480, + 477 + ], + "type": "text", + "content": "3.4. Specific action pattern Learning" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "spans": [ + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "type": "text", + "content": "Actions of different scales have different feature representations. Correspondingly, different layers in SFPN have different feature granularity and temporal resolution. Therefore, we advocate applying a targeted training strategy for actions at different scales, assuring that each layer in SFPN is only responsible for actions at a specific scale range. Specifically, define the scale " + }, + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "type": "inline_equation", + "content": "S \\in [0,1]" + }, + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "type": "text", + "content": " as the ratio of action length to video length. Then the first layer (the top layer of the pyramid) with the longest sequence is responsible for small-scale actions whose scale in " + }, + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "type": "inline_equation", + "content": "[S_{min}^{1}, S_{max}^{1}]" + }, + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "type": "text", + "content": ", and the second layer (the middle layer of the pyramid) with a moderate sequence length is responsible for medium-scale actions whose scale in " + }, + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "type": "inline_equation", + "content": "[S_{min}^{2}, S_{max}^{2}]" + }, + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "type": "text", + "content": ". The remaining third layer with the shortest sequence is responsible for large-scale actions whose scale belongs to " + }, + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "type": "inline_equation", + "content": "[S_{min}^{3}, S_{max}^{3}]" + }, + { + "bbox": [ + 304, + 484, + 545, + 675 + ], + "type": "text", + "content": ". To implement this idea, a two-stage training strategy is designed." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "content": "Two-stage training strategy. The two-stages of training ASP are Generalization and Specialization, respectively. Due to the different lengths of feature sequences, the to" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "13558" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 61, + 77, + 140, + 210 + ], + "blocks": [ + { + "bbox": [ + 61, + 77, + 140, + 210 + ], + "lines": [ + { + "bbox": [ + 61, + 77, + 140, + 210 + ], + "spans": [ + { + "bbox": [ + 61, + 77, + 140, + 210 + ], + "type": "image", + "image_path": "1649173c50836dba2f4757d1ea10c7fb3d52114b230f06d76908c623b59ece86.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 231, + 288, + 299 + ], + "lines": [ + { + "bbox": [ + 46, + 231, + 288, + 299 + ], + "spans": [ + { + "bbox": [ + 46, + 231, + 288, + 299 + ], + "type": "text", + "content": "Figure 4. The two-stage training strategy (left column and middle column) and the inference strategy (right column) of ASP. Each square represents an anchor map of a layer, the grey area is the invalid region. Other colors represent different sampling ratios in a certain scale range, with white, green, yellow and red representing " + }, + { + "bbox": [ + 46, + 231, + 288, + 299 + ], + "type": "inline_equation", + "content": "0\\%" + }, + { + "bbox": [ + 46, + 231, + 288, + 299 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 231, + 288, + 299 + ], + "type": "inline_equation", + "content": "r_i" + }, + { + "bbox": [ + 46, + 231, + 288, + 299 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 231, + 288, + 299 + ], + "type": "inline_equation", + "content": "2r_i" + }, + { + "bbox": [ + 46, + 231, + 288, + 299 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 231, + 288, + 299 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 46, + 231, + 288, + 299 + ], + "type": "text", + "content": " respectively." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 149, + 78, + 218, + 211 + ], + "blocks": [ + { + "bbox": [ + 149, + 78, + 218, + 211 + ], + "lines": [ + { + "bbox": [ + 149, + 78, + 218, + 211 + ], + "spans": [ + { + "bbox": [ + 149, + 78, + 218, + 211 + ], + "type": "image", + "image_path": "0582439aa20faf1e40e2f4294fc9e8899ec276a5177358ba32ef51ebe84baea2.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 222, + 79, + 290, + 213 + ], + "blocks": [ + { + "bbox": [ + 222, + 79, + 290, + 213 + ], + "lines": [ + { + "bbox": [ + 222, + 79, + 290, + 213 + ], + "spans": [ + { + "bbox": [ + 222, + 79, + 290, + 213 + ], + "type": "image", + "image_path": "3b39d423219f0d6d005fa4ee796746c5e7863dcfdb83e2216d46d86fa403d9ac.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "spans": [ + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": "tal number of dense anchors contained in each layer varies. In order to ensure that each layer is trained equally and reduce the computational cost, different anchor sampling ratios " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "r_1" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "r_2" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "r_3" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": " are set for the three layers, where " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "0\\% < r_1 \\leq r_2 \\leq r_3 \\leq 100\\%" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": ". (1) In the former Generalization stage, given the sampling ratio " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "r_i" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": ", randomly sample " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "N_i = \\binom{L_i}{2} \\cdot r_i" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": " anchors from valid region to train the IoU-ASP and Offset-ASP of " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": "-th layer, as shown in the left column of Fig 4. The purpose of this stage is to let ASP learn a general pattern of all actions. (2) In the latter Specialization stage, for the " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": "-th layer in SFPN, the training samples come from two parts, as shown in the middle column in Fig 4. The first part are randomly sampled according to the sampling rate of " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "\\min(100\\%, 2 \\cdot r_i)" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": " from anchors whose scale in " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "[S_{min}^i, S_{max}^i]" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": " (yellow area in Fig 4). The second part are sampled from the remaining anchors whose scale in " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "(0, S_{min}^i)" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "(S_{max}^i, 100\\%)" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": ", with the sampling rate of " + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "inline_equation", + "content": "r_i" + }, + { + "bbox": [ + 46, + 308, + 287, + 548 + ], + "type": "text", + "content": " (green area in Fig 4). This Specialization stage highlights the effect of anchors at the certain scale range, making the detection head of each layer more specialized." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 559, + 169, + 572 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 559, + 169, + 572 + ], + "spans": [ + { + "bbox": [ + 47, + 559, + 169, + 572 + ], + "type": "text", + "content": "3.5. Training & Inference" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "text", + "content": "Label Assignment. Assuming the video duration is " + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "inline_equation", + "content": "L_{v}" + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "text", + "content": ", each snippet corresponds to a video period. In annotation, a ground-truth action which starts at " + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "inline_equation", + "content": "t_{s}^{*}" + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "text", + "content": " and ends at " + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "inline_equation", + "content": "t_{e}^{*}" + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "text", + "content": ". Expanding boundary from moment to region, the start region is defined as " + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "inline_equation", + "content": "R_{s} = [t_{s}^{*} - 1.5\\frac{T_{v}}{L_{i}}, t_{s}^{*} + 1.5\\frac{T_{v}}{L_{i}}]" + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "text", + "content": " and end region is defined as " + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "inline_equation", + "content": "R_{e} = [t_{e}^{*} - 1.5\\frac{T_{v}}{L_{i}}, t_{e}^{*} + 1.5\\frac{T_{v}}{L_{i}}]" + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "text", + "content": ". For Boundary Predictor, compute the overlap between each snippet period and " + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "inline_equation", + "content": "R_{s}" + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "text", + "content": " as the label of start probabilities " + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "inline_equation", + "content": "G_{s}^{i} \\in \\mathbb{R}^{L_{i}}" + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "text", + "content": ". Similarly, compute the overlap between snippet period and " + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "inline_equation", + "content": "R_{e}" + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "text", + "content": " as the label of end probabilities " + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "inline_equation", + "content": "G_{e}^{i}" + }, + { + "bbox": [ + 46, + 578, + 287, + 713 + ], + "type": "text", + "content": ". For IoU-ASP, following [12], IoU between each anchor and all actions are" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "spans": [ + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "text", + "content": "calculated and then arranged into a map " + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "inline_equation", + "content": "G_{IoU}^{i} \\in \\mathbb{R}^{D_{i} \\times L_{i}}" + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "text", + "content": ". Anchors with tIoU score greater than 0.9 participate in the training of Offset-ASP. For anchor start at " + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "inline_equation", + "content": "t_{s}" + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "text", + "content": " and end at " + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "inline_equation", + "content": "t_{e}" + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "text", + "content": ", assuming its corresponding ground-truth action is " + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "inline_equation", + "content": "[t_{s}^{*}, t_{e}^{*}]" + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "text", + "content": ", the center offset " + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "inline_equation", + "content": "\\Delta c" + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "text", + "content": " and duration offset " + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "inline_equation", + "content": "\\Delta d" + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "text", + "content": " are calculated as Eq. (1)-(2), and arranged into maps " + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "inline_equation", + "content": "G_{cent}^{i} \\in \\mathbb{R}^{D_{i} \\times L_{i}}" + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "inline_equation", + "content": "G_{dura}^{i} \\in \\mathbb{R}^{D_{i} \\times L_{i}}" + }, + { + "bbox": [ + 304, + 71, + 545, + 157 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 319, + 160, + 545, + 182 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 319, + 160, + 545, + 182 + ], + "spans": [ + { + "bbox": [ + 319, + 160, + 545, + 182 + ], + "type": "interline_equation", + "content": "c = \\frac {t _ {s} + t _ {e}}{2}, d = t _ {e} - t _ {s}, c ^ {*} = \\frac {t _ {s} ^ {*} + t _ {e} ^ {*}}{2}, d ^ {*} = t _ {e} ^ {*} - t _ {s} ^ {*} \\tag {1}", + "image_path": "6b2320add80dca20cfc07e0f15b81a95d5866e6e31351fe3748e261b563b2a2d.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 372, + 183, + 545, + 205 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 372, + 183, + 545, + 205 + ], + "spans": [ + { + "bbox": [ + 372, + 183, + 545, + 205 + ], + "type": "interline_equation", + "content": "\\Delta c = \\frac {c ^ {*} - c}{d}, \\Delta d = \\log \\frac {d ^ {*}}{d} \\tag {2}", + "image_path": "a72c123f9c424aadbd24769fe2ac5746b45722341f6db89ddc36147381bb7f33.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "spans": [ + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": "Basic Loss. (1) For the " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": "-th layer, the loss of Boundary-Predictor is the re-weighted binary cross-entropy loss " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "L_{B}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": " Eq. 3, where " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "P = \\{p_t\\}_{t=1}^{L_i}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "G = \\{g_t\\}_{t=1}^{L_i}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": " represent the predicted boundary probabilities and its label of all snippets, respectively. Snippets with " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "g_t > 0.5" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": " serve as positive samples (i.e., " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "\\delta \\{g_t > 0.5\\} = 1" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": ") and others are negative samples. " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "T_{i}^{+}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "T_{i}^{-}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": " are the number of positive and negative samples in this layer respectively. (2) The loss of IoU-ASP is the re-weighted binary cross-entropy loss " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "L_{asp}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": " Eq. 4 and L2 loss " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "M = \\{m_j\\}_{j=1}^{N_i}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "G = \\{g_j\\}_{j=1}^{N_i}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": " represent the predicted value and ground-truth value of each sampled anchor in the " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": "-th layer. " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "N_{i}, N_{i}^{+}, N_{i}^{-}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": " represent the number of sampled anchors, positive anchors whose tIoU greater than 0.9 and negative anchors of this layer, respectively. (3) The loss of Offset-ASP is Smooth L1 loss " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": ". Note that only those sampled anchors with tIoU greater than 0.9 participate in the training of Offset-ASP. The re-weights in " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "L_{B}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "inline_equation", + "content": "L_{asp}" + }, + { + "bbox": [ + 304, + 212, + 546, + 441 + ], + "type": "text", + "content": " are used to balance the number between positive and negative samples." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 332, + 447, + 545, + 502 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 332, + 447, + 545, + 502 + ], + "spans": [ + { + "bbox": [ + 332, + 447, + 545, + 502 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} L _ {B} (P, G) = - \\frac {1}{L _ {i}} \\sum_ {t = 1} ^ {L _ {i}} \\left(\\frac {L _ {i}}{T _ {i} ^ {+}} \\cdot \\delta \\left\\{g _ {t} > 0. 5 \\right\\} \\cdot \\log p _ {t} \\right. \\tag {3} \\\\ + \\frac {L _ {i}}{T _ {i} ^ {-}} (1 - \\delta \\left\\{g _ {t} > 0. 5 \\right\\} \\cdot \\log \\left(1 - p _ {t}\\right)) \\\\ \\end{array}", + "image_path": "a01de23e454a345e1f14f6ace3de549acc9ff9fc007cff2c01be135c21d54f30.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 320, + 508, + 545, + 564 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 320, + 508, + 545, + 564 + ], + "spans": [ + { + "bbox": [ + 320, + 508, + 545, + 564 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} L _ {a s p} (M, G) = - \\frac {1}{N _ {i}} \\sum_ {j = 1} ^ {N _ {i}} \\left(\\frac {N _ {i}}{N _ {i} ^ {+}} \\cdot \\delta \\left\\{g _ {j} > 0. 9 \\right\\} \\cdot \\log m _ {j} \\right. \\tag {4} \\\\ + \\frac {N _ {i}}{N _ {i} ^ {-}} (1 - \\delta \\{g _ {j} > 0. 9 \\} \\cdot \\log (1 - m _ {j})) \\\\ \\end{array}", + "image_path": "185b60a57d9a537eb98d3bd3a9c30b668ca4bec35ec303c31da2b3862f3f8dd8.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 571, + 545, + 642 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 571, + 545, + 642 + ], + "spans": [ + { + "bbox": [ + 304, + 571, + 545, + 642 + ], + "type": "text", + "content": "Total Loss. The loss of the " + }, + { + "bbox": [ + 304, + 571, + 545, + 642 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 571, + 545, + 642 + ], + "type": "text", + "content": "-th layer is composed of three parts: boundary loss, IoU loss and offset loss, as shown in Eq.(5) (6) (7) respectively. The total training objective is the sum of all three layers, formulated as Eq. 8. Besides, in order to balance the value between different terms, the coefficient " + }, + { + "bbox": [ + 304, + 571, + 545, + 642 + ], + "type": "inline_equation", + "content": "\\lambda 1" + }, + { + "bbox": [ + 304, + 571, + 545, + 642 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 571, + 545, + 642 + ], + "type": "inline_equation", + "content": "\\lambda 2" + }, + { + "bbox": [ + 304, + 571, + 545, + 642 + ], + "type": "text", + "content": " are set as 5 and 10." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 353, + 647, + 545, + 661 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 353, + 647, + 545, + 661 + ], + "spans": [ + { + "bbox": [ + 353, + 647, + 545, + 661 + ], + "type": "interline_equation", + "content": "L _ {\\text {b o u n d}} ^ {i} = L _ {B} \\left(P _ {s} ^ {i}, G _ {s} ^ {i}\\right) + L _ {B} \\left(P _ {e} ^ {i}, G _ {e} ^ {i}\\right) \\tag {5}", + "image_path": "cb911ca08ece2e935805aa54782dfb8e3305e09e1bfc79d8195269776678e95d.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 328, + 671, + 545, + 685 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 328, + 671, + 545, + 685 + ], + "spans": [ + { + "bbox": [ + 328, + 671, + 545, + 685 + ], + "type": "interline_equation", + "content": "L _ {I o U} ^ {i} = L _ {a s p} \\left(M _ {c l s} ^ {i}, G _ {I o U} ^ {i}\\right) + \\lambda_ {1} \\cdot L _ {2} \\left(M _ {r e g} ^ {i}, G _ {I o U} ^ {i}\\right) \\tag {6}", + "image_path": "ba47c65a6bb4d8bb53b45125f3de4cdd34a5eafe38fd9f3e72e9965c845eef89.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 334, + 700, + 545, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 334, + 700, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 334, + 700, + 545, + 715 + ], + "type": "interline_equation", + "content": "L _ {o f f} ^ {i} = L _ {1} \\left(M _ {c e n t} ^ {i}, G _ {c e n t} ^ {i}\\right) + L _ {1} \\left(M _ {d u r a} ^ {i}, G _ {d u r a} ^ {i}\\right) \\tag {7}", + "image_path": "32f8250b2521ef8333f9886bc8ee12199f28edb5268b524eefb48995c4185a7f.jpg" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13559" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 93, + 69, + 287, + 99 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 69, + 287, + 99 + ], + "spans": [ + { + "bbox": [ + 93, + 69, + 287, + 99 + ], + "type": "interline_equation", + "content": "L _ {t o t a l} = \\sum_ {i = 1} ^ {3} \\left(L _ {B} ^ {i} + L _ {I o U} ^ {i} + \\lambda_ {2} \\cdot L _ {o f f} ^ {i}\\right) \\tag {8}", + "image_path": "ddd4ec0d6c366bb99bcce10222b01c80315918a26fae1ff1c174ca8f96714f86.jpg" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "spans": [ + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": "Inference. Each layer outputs " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "P_{s}^{i}, P_{e}^{i}, M_{cls}^{i}, M_{reg}^{i}, M_{cent}^{i}" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "M_{dura}^{i}" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": " from the detector head in inference. Following [14, 12, 15], snippet in boundary probability " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "P_{s}" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": " is screened out as candidate start point if it is local peak or its probability is greater than " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "0.5 \\cdot \\max(P_{s})" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": ". And snippets can be selected as candidate end point from " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "P_{e}" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": " in the same way. Then the candidate start and end points are combined into proposals. In order to produce the more reasonable proposals, as shown in Fig 4, each layer of SFPN only outputs anchors in the corresponding scale range. Specifically, for the " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": "-th layer, its responsible scale range is " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "[S_{min}^{i}, S_{max}^{i}]" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": ". Furthermore, in the proposals set, for any start snippet whose index is " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "sdx" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": " and centered at time " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "t_{1}" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": ", and the end snippet whose index is " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "edx" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": " and centered at time " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "t_{2}" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": ", we can get its start probability " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "p_{s} = P_{s}^{i}[sdx]" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": ", end probability " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "p_{e} = P_{e}^{i}[edx]" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": " and tIoU score " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "p_{IoU} = M_{cls}^{i}[edx - sdx, sdx] \\cdot M_{reg}^{i}[edx - sdx, sdx]" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": ". Its center is " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "c = (sdx + edx)/2L_{i}" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": " and duration is " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "d = (edx - sdx)/L_{i}" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": ". Subsequently, to refine the boundary, we can obtain center offset " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "\\Delta c = M_{cent}^{i}[edx - sdx, sdx]" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": " and duration offset " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "\\Delta d = M_{dura}^{i}[edx - sdx, sdx]" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": ", and adjust the boundary to " + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "inline_equation", + "content": "(t_{1}', t_{2}')" + }, + { + "bbox": [ + 47, + 100, + 289, + 354 + ], + "type": "text", + "content": " as Eq. 9:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 111, + 360, + 287, + 397 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 360, + 287, + 397 + ], + "spans": [ + { + "bbox": [ + 111, + 360, + 287, + 397 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} c ^ {\\prime} = d \\cdot \\Delta c + c, d ^ {\\prime} = d \\cdot e ^ {\\Delta d} \\\\ t _ {1} ^ {\\prime} = c ^ {\\prime} - \\frac {d ^ {\\prime}}{2}, t _ {2} ^ {\\prime} = c ^ {\\prime} + \\frac {d ^ {\\prime}}{2} \\tag {9} \\\\ \\end{array}", + "image_path": "887793e959a88c63090e9032e3389593f0f1b25bf99d47e423739c4ac8f40653.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 396, + 287, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 396, + 287, + 456 + ], + "spans": [ + { + "bbox": [ + 47, + 396, + 287, + 456 + ], + "type": "text", + "content": "Finally, proposals generated by each layer are merged together, and the action classifier assigns every proposal with a certain label and a classification score " + }, + { + "bbox": [ + 47, + 396, + 287, + 456 + ], + "type": "inline_equation", + "content": "P_{\\text{label}}" + }, + { + "bbox": [ + 47, + 396, + 287, + 456 + ], + "type": "text", + "content": ". The final score for the proposal " + }, + { + "bbox": [ + 47, + 396, + 287, + 456 + ], + "type": "inline_equation", + "content": "(t_1', t_2')" + }, + { + "bbox": [ + 47, + 396, + 287, + 456 + ], + "type": "text", + "content": " is shown as Eq. 10. Then Soft-NMS [32] is adopted to remove redundant segments." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 102, + 460, + 287, + 473 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 460, + 287, + 473 + ], + "spans": [ + { + "bbox": [ + 102, + 460, + 287, + 473 + ], + "type": "interline_equation", + "content": "\\operatorname {s c o r e} _ {t _ {1} ^ {\\prime}, t _ {2} ^ {\\prime}} = p _ {s} \\cdot p _ {e} \\cdot p _ {I o U} \\cdot p _ {\\text {l a b e l}} \\tag {10}", + "image_path": "cf88b134cd726a4f8432f16c7a74a7768f92eec3ac1e806eb5c5a894452bebd0.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 478, + 128, + 491 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 478, + 128, + 491 + ], + "spans": [ + { + "bbox": [ + 47, + 478, + 128, + 491 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 495, + 165, + 507 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 495, + 165, + 507 + ], + "spans": [ + { + "bbox": [ + 47, + 495, + 165, + 507 + ], + "type": "text", + "content": "4.1. Dataset and Settings" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 287, + 640 + ], + "type": "text", + "content": "Dataset. In order to verify the effectiveness of MENet, we experiment on two challenging datasets. ActivityNet-1.3 [2] contains 200 categories of daily life, sports, etc. We use the training set for model training and report the performance on the validation set. THUMOS-14 [8] consists of 413 videos with 20 action classes which is almost sports. In THUMOS-14, the validation set contains 200 long videos, including 3007 action segments, and the test set contains 213 videos, including 3358 action segments. Following the standard practice of THUMOS-14, we train MENet on the validation set and valid it on the test set." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 642, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 288, + 713 + ], + "type": "text", + "content": "Metric. In order to fully demonstrate the advantages of our proposed method, we use two main evaluation metrics: mAP under a certain temporal tIoU threshold (mAP@tIoU) and average recall at a specified average number of proposals (AR@AN). Besides, on ActivityNet, the area under the AR-AN curve (AUC) also serves as a metric." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "content": "Network Details. We use " + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "inline_equation", + "content": "\\mathrm{R}(2 + 1)\\mathrm{D} - 34" + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "content": " as backbone with the TAC pretrained weight on Kinetics-400 serving as the primary feature extractor. The sampling interval " + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "content": " set as 16 frames and 5 frames for ActivityNet-1.3 and THUMOS-14, respectively. In this way, for the input video with " + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "inline_equation", + "content": "L_{v}" + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "content": " frames, video snippet length " + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "inline_equation", + "content": "L_{s} = L_{v} / \\sigma" + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "content": ". For ActivityNet-1.3, we use linear interpolation to resize the length of video features " + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "inline_equation", + "content": "T = 200" + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "content": ". For a long video in THUMOS-14, a sliding window with a length of 256 and an overlap of " + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "content": " is used to truncate the original video feature. Each window is detected independently, and finally the results of all windows are concatenated as the total result of the entire long video. The scale ranges of each layer in the pyramid are set as: " + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "inline_equation", + "content": "[S_{min}^{1}, S_{max}^{1}] = [0, 15\\%]" + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "inline_equation", + "content": "[S_{min}^{2}, S_{max}^{2}] = [10\\%, 75\\%]" + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "inline_equation", + "content": "[S_{min}^{3}, S_{max}^{3}] = [50\\%, 100\\%]" + }, + { + "bbox": [ + 304, + 72, + 545, + 288 + ], + "type": "text", + "content": ". As for the action classifier, following the routine of most two-stage TAD methods, Untrimmed Net [25] serves as the classifier for THUMOS-14, and the recognition model by [32] for ActivityNet-1.3." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "spans": [ + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "text", + "content": "Implementation Details. MENet is trained by Adam algorithm with batch size 8 and learning rate " + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "inline_equation", + "content": "10^{-3}" + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "text", + "content": ". The sampling ratio of each layer " + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "inline_equation", + "content": "r_1" + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "inline_equation", + "content": "r_2" + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "inline_equation", + "content": "r_3" + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "text", + "content": " are set as " + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "inline_equation", + "content": "40\\%" + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "text", + "content": ", respectively. For ActivityNet-1.3, the training process takes 10 epochs, where the first 7 epochs is the Generalization stage and the rest is the Specialization stage. As for THUMOS-14, the total training epoch is 7, and only the first epoch is the Generalization stage. Besides, the learning rate is decayed to " + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 304, + 289, + 545, + 408 + ], + "type": "text", + "content": " after 5 epochs on THUMOS-14 and 7 epochs on ActivityNet-1.3." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 420, + 507, + 432 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 420, + 507, + 432 + ], + "spans": [ + { + "bbox": [ + 305, + 420, + 507, + 432 + ], + "type": "text", + "content": "4.2. Performance Evaluation On Detection" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 437, + 545, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 545, + 567 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 545, + 567 + ], + "type": "text", + "content": "We compare MENet with other state-of-the-art methods on ActivityNet-1.3 and THUMOS-14. Table 1 shows the comparison on the validation set of ActivityNet-1.3. The mAP at tIoU thresholds of " + }, + { + "bbox": [ + 304, + 437, + 545, + 567 + ], + "type": "inline_equation", + "content": "\\{0.5, 0.75, 0.95\\}" + }, + { + "bbox": [ + 304, + 437, + 545, + 567 + ], + "type": "text", + "content": " are reported, as well as the Avg.mAP which is calculated at tIoU thresholds between 0.5 and 0.95 with the step of 0.05. Impressively, MENet outperforms other representative methods at tIoU thresholds 0.75 and 0.95. MENet promotes the Avg.mAP from " + }, + { + "bbox": [ + 304, + 437, + 545, + 567 + ], + "type": "inline_equation", + "content": "36.6\\%" + }, + { + "bbox": [ + 304, + 437, + 545, + 567 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 437, + 545, + 567 + ], + "type": "inline_equation", + "content": "37.7\\%" + }, + { + "bbox": [ + 304, + 437, + 545, + 567 + ], + "type": "text", + "content": ", with an increase of more than " + }, + { + "bbox": [ + 304, + 437, + 545, + 567 + ], + "type": "inline_equation", + "content": "1.1\\%" + }, + { + "bbox": [ + 304, + 437, + 545, + 567 + ], + "type": "text", + "content": ". Comparing the methods of different backbones, MENet exceeds others." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "Table 2 presents the detection performance comparison on the test set of THUMOS-14. MENet achieves comparable performance with the best method [30] at low tIoU thresholds. But, MENet outperforms other representative methods at tIoU thresholds 0.6 and 0.7. MENet improves the mAP@0.7 from the current best " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "31.8\\%" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "34.0\\%" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": ". To locate the boundaries more accurately, a higher threshold is usually used to separate the positive and negative samples in training. Therefore MENet has a better response at high tIoU thresholds. Higher tIoU means more precise action boundaries, which is more difficult and more important for action localization. Meanwhile, it is noteworthy" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13560" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "content": "that MENet shows obvious superiority compared with other FPN-based methods like [11], which substantiates the effectiveness of the SFPN proposed in MENet." + } + ] + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 53, + 112, + 282, + 278 + ], + "blocks": [ + { + "bbox": [ + 53, + 112, + 282, + 278 + ], + "lines": [ + { + "bbox": [ + 53, + 112, + 282, + 278 + ], + "spans": [ + { + "bbox": [ + 53, + 112, + 282, + 278 + ], + "type": "table", + "html": "
MethodBackbonemAP@tIoU (%)
0.50.750.95Avg.
GTAN [16]P3D52.634.18.934.3
BSN [14]TSN46.530.08.030.0
BMN [12]TSN50.134.88.333.9
G-TAD [29]TSN50.434.69.034.1
PCMNet [18]TSN51.436.19.535.3
TCA-Net [19]TSN52.336.76.935.5
RTD-Net [23]I3D47.230.78.630.8
ContextLoc [33]I3D56.035.23.634.2
AFSD [11]I3D52.435.36.534.4
TAGS [17]I3D56.336.89.636.5
STPT [27]STPT51.433.76.833.4
ActionFormer [30]R(2+1)D54.737.88.436.6
MENet(ours)R(2+1)D54.738.410.537.7
", + "image_path": "eed16e05be0ba05647519cf65cc095f82ab55426080f8e88165a1344fc2fe1a9.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 53, + 316, + 282, + 483 + ], + "blocks": [ + { + "bbox": [ + 47, + 281, + 287, + 314 + ], + "lines": [ + { + "bbox": [ + 47, + 281, + 287, + 314 + ], + "spans": [ + { + "bbox": [ + 47, + 281, + 287, + 314 + ], + "type": "text", + "content": "Table 1. The temporal action detection performance comparison with state-of-art methods on ActivityNet-1.3. Bold text indicates the best results." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 53, + 316, + 282, + 483 + ], + "lines": [ + { + "bbox": [ + 53, + 316, + 282, + 483 + ], + "spans": [ + { + "bbox": [ + 53, + 316, + 282, + 483 + ], + "type": "table", + "html": "
MethodBackbonemAP@tIoU (%)
0.30.40.50.60.7
GTAN [16]P3D57.847.238.8--
BSN [14]TSN53.545.036.928.420.0
BMN [12]TSN56.047.438.829.720.5
G-TAD [12]TSN54.547.640.230.823.4
PCMNet [18]TSN61.555.447.237.527.3
TCA-Net [19]TSN60.653.244.636.826.7
RTD-Net [23]I3D68.362.351.938.823.7
ContextLoc [33]I3D68.363.854.341.826.2
AFSD [11]I3D67.362.455.543.731.1
TAGS [17]I3D68.663.857.046.331.8
STPT [27]STPT70.665.756.444.630.5
ActionFormer [30]R(2+1)D73.467.459.146.731.5
MENet(ours)R(2+1)D70.765.358.849.134.0
", + "image_path": "3658cd4973a9ddc166447557a483c1b6924e060dc7ca0d9dbd7d1ccfaef27360.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 525, + 246, + 537 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 525, + 246, + 537 + ], + "spans": [ + { + "bbox": [ + 47, + 525, + 246, + 537 + ], + "type": "text", + "content": "4.3. Performance Evaluation On Proposal" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 538, + 287, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 538, + 287, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 538, + 287, + 574 + ], + "type": "text", + "content": "To further verify the advantages of MENet, we do not consider action classes of action segments to evaluate its performance on temporal action proposal (TAP) task." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 574, + 287, + 658 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 574, + 287, + 658 + ], + "spans": [ + { + "bbox": [ + 46, + 574, + 287, + 658 + ], + "type": "text", + "content": "Through Table 3, we can further discover the performance improvement of AR@100 and the area under the AR-AN curve (AUC) on ActivityNet-1.3. For instance, MENet boosts the AUC from " + }, + { + "bbox": [ + 46, + 574, + 287, + 658 + ], + "type": "inline_equation", + "content": "68.1\\%" + }, + { + "bbox": [ + 46, + 574, + 287, + 658 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 574, + 287, + 658 + ], + "type": "inline_equation", + "content": "70.2\\%" + }, + { + "bbox": [ + 46, + 574, + 287, + 658 + ], + "type": "text", + "content": ". As for THUMOS-14, MENet outperforms other methods in all metrics are reported in Table 4, which certifies the effectiveness of MENet once again." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 665, + 141, + 677 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 665, + 141, + 677 + ], + "spans": [ + { + "bbox": [ + 47, + 665, + 141, + 677 + ], + "type": "text", + "content": "4.4. Ablation Study" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": "Ablation studies are performed thoroughly to verify the role of each module in MENet, as well as the impact of different training strategies." + } + ] + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 349, + 70, + 503, + 162 + ], + "blocks": [ + { + "bbox": [ + 47, + 486, + 287, + 518 + ], + "lines": [ + { + "bbox": [ + 47, + 486, + 287, + 518 + ], + "spans": [ + { + "bbox": [ + 47, + 486, + 287, + 518 + ], + "type": "text", + "content": "Table 2. The temporal action detection performance comparison with state-of-art methods on THUMOS-14. Bold text indicates the best results." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 349, + 70, + 503, + 162 + ], + "lines": [ + { + "bbox": [ + 349, + 70, + 503, + 162 + ], + "spans": [ + { + "bbox": [ + 349, + 70, + 503, + 162 + ], + "type": "table", + "html": "
MethodAR@100AUC
BSN [14]74.266.2
GTAN [16]74.867.1
BMN [12]75.067.1
RTD-Net [23]73.265.8
TCA-Net [19]76.168.1
MENet(ours)77.070.2
", + "image_path": "0fd009865288f8aaabaa0a136ee0d03b9433b0700db3e436d700f8b3ce4859f2.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 307, + 200, + 547, + 281 + ], + "blocks": [ + { + "bbox": [ + 305, + 163, + 545, + 196 + ], + "lines": [ + { + "bbox": [ + 305, + 163, + 545, + 196 + ], + "spans": [ + { + "bbox": [ + 305, + 163, + 545, + 196 + ], + "type": "text", + "content": "Table 3. Temporal action proposal performance comparison with other representative methods on ActivityNet-1.3. Bold text indicates the best results." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 200, + 547, + 281 + ], + "lines": [ + { + "bbox": [ + 307, + 200, + 547, + 281 + ], + "spans": [ + { + "bbox": [ + 307, + 200, + 547, + 281 + ], + "type": "table", + "html": "
MethodAR@50AR@100AR@200AR@500
BSN [14]37.546.153.260.6
BMN [12]39.447.754.762.1
RTD-Net [23]41.549.3256.4162.91
TCA-Net [19]42.150.557.163.6
MENet(ours)44.252.358.666.0
", + "image_path": "e3c37f52b46eecea386e15d040402bd4f75884dbda65748fb574b1293b9aab94.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 322, + 545, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 322, + 545, + 441 + ], + "spans": [ + { + "bbox": [ + 305, + 322, + 545, + 441 + ], + "type": "text", + "content": "1). Effectiveness of the MEM: As discussed before, when constructing the movement enhance feature, MFE and MREM are the crucial designs in MEM. To certify the function of these two modules, we design a Base model for comparison, in which the Movement Feature is removed and MREM is replaced by temporal 1D convolution. As shown in Table 5, we can find that compared with the Base model, Movement Feature and MREM both can promote the performance. Besides, the best results emerge when combining them together as the intact MEM." + } + ] + } + ], + "index": 14 + }, + { + "type": "table", + "bbox": [ + 307, + 445, + 545, + 525 + ], + "blocks": [ + { + "bbox": [ + 305, + 286, + 545, + 319 + ], + "lines": [ + { + "bbox": [ + 305, + 286, + 545, + 319 + ], + "spans": [ + { + "bbox": [ + 305, + 286, + 545, + 319 + ], + "type": "text", + "content": "Table 4. Temporal action proposal performance comparison with other representative methods on THUMOS-14, measured by AR@AN. Bold text indicates the best results." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 445, + 545, + 525 + ], + "lines": [ + { + "bbox": [ + 307, + 445, + 545, + 525 + ], + "spans": [ + { + "bbox": [ + 307, + 445, + 545, + 525 + ], + "type": "table", + "html": "
ConstructionmAP@tIoU (%)
0.50.750.95Avg.
Base54.237.310.437.0
Base + Movement Feature54.537.810.637.3
Base + MREM54.437.910.437.3
MEM54.738.410.537.7
", + "image_path": "c533832ae48e5e70bdc825b947395e770ec577bb7ca2c63a4a26b2411582bd1e.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "table_body" + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 531, + 545, + 565 + ], + "lines": [ + { + "bbox": [ + 305, + 531, + 545, + 565 + ], + "spans": [ + { + "bbox": [ + 305, + 531, + 545, + 565 + ], + "type": "text", + "content": "Table 5. Ablation study on the MEM. The Detection performance is reported on ActivityNet-1.3. And The best result can be achieved with these two modules are integrated." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 570, + 545, + 713 + ], + "type": "list", + "angle": 0, + "index": 19, + "blocks": [ + { + "bbox": [ + 305, + 570, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 570, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 305, + 570, + 545, + 665 + ], + "type": "text", + "content": "2). Effectiveness of the U-shape Module: As discussed before, when constructing the feature pyramid, U-shape Module is designed to establish interactions between different layers. To reveal the validity of this idea, we use 1D convolution with the step of 2 and AvgPooling to downsample the feature sequence respectively. From Table 6, the U-shape Module can promote the performance, which substantiates the importance of this design." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "content": "3). Effectiveness of feature pyramid structure: For better detection accuracy, MENet makes use of the feature pyramid. To verify the impact of this structure, we only use a single layer feature sequence to conduct experiments" + } + ] + } + ], + "index": 18 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13561" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 52, + 71, + 281, + 137 + ], + "blocks": [ + { + "bbox": [ + 52, + 71, + 281, + 137 + ], + "lines": [ + { + "bbox": [ + 52, + 71, + 281, + 137 + ], + "spans": [ + { + "bbox": [ + 52, + 71, + 281, + 137 + ], + "type": "table", + "html": "
ConstructionmAP@tIoU (%)
0.50.750.95Avg.
DownSampling (AvgPooling)54.538.210.237.4
DownSampling (Convolution)54.438.110.837.3
U-shape Module54.738.410.537.7
", + "image_path": "a85f145370d12047ebe35e72e4a3675b362c1d141f0b386ba90ed7796b4d74bc.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 171, + 286, + 255 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 171, + 286, + 255 + ], + "spans": [ + { + "bbox": [ + 46, + 171, + 286, + 255 + ], + "type": "text", + "content": "and compare it with the SFPN, keeping other components unchanged. On ActivityNet-1.3, single-layer feature with lengths of 200, 100 and 50 are used. Corresponding results are shown in Table 7. The experimental results exhibit that SFPN performs better than any other single-layer structure, thus justifying the feature pyramid structure is indeed beneficial to the performance." + } + ] + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 85, + 261, + 248, + 342 + ], + "blocks": [ + { + "bbox": [ + 46, + 139, + 286, + 161 + ], + "lines": [ + { + "bbox": [ + 46, + 139, + 286, + 161 + ], + "spans": [ + { + "bbox": [ + 46, + 139, + 286, + 161 + ], + "type": "text", + "content": "Table 6. Ablation study on the U-shape Module. The Detection performance is reported on ActivityNet-1.3." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 85, + 261, + 248, + 342 + ], + "lines": [ + { + "bbox": [ + 85, + 261, + 248, + 342 + ], + "spans": [ + { + "bbox": [ + 85, + 261, + 248, + 342 + ], + "type": "table", + "html": "
LengthmAP@tIoU (%)
0.50.750.95Avg.
5053.037.110.836.8
10054.138.110.437.1
20054.238.310.537.3
SFPN54.738.410.537.7
", + "image_path": "c732fd1239b2e6ea0638c7aa2718458a9e5804d1b8984440abb80594590664d5.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "text", + "content": "4). Effectiveness of two-stage training: For efficient training of MENet and ensuring that the " + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "text", + "content": "-th layer in SFPN is specialized in actions at a specific scale range " + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "inline_equation", + "content": "[S_{min}^{i}, S_{max}^{i}]" + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "text", + "content": ", the two-stage training strategy is applied. When training ASP of the " + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "text", + "content": "-th layer, in the first Generalization stage, the anchors are randomly selected from all scales according to the sampling ratio " + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "inline_equation", + "content": "r_i" + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "text", + "content": ", in the second Specialization stage, the sampling ratio inside and outside the range " + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "inline_equation", + "content": "[S_{min}^{i}, S_{max}^{i}]" + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "text", + "content": " are " + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "inline_equation", + "content": "2 \\cdot r_i" + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "inline_equation", + "content": "r_i" + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "text", + "content": ", respectively. In this ablation study, we train MENet using the fully Generalization stage, the fully Specialization stage and the complete two-stage strategy, respectively. In addition, to demonstrate the effectiveness of this training method, we also test a new Bias training strategy that only samples from the range " + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "inline_equation", + "content": "[S_{min}^{i}, S_{max}^{i}]" + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "text", + "content": " with the sampling ratio of " + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "inline_equation", + "content": "r_i" + }, + { + "bbox": [ + 46, + 389, + 286, + 568 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 569, + 286, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 569, + 286, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 569, + 286, + 653 + ], + "type": "text", + "content": "As shown in Table 8, the performance of the Bias strategy is the worst, indicating that in addition to those samples in the specific scale range, other samples outside this range also play an important role for a better understanding of actions. Further, the training effect is impeded when removing either the Generalization or the Specialization stage, which verifies the effectiveness of the two-stage training strategy." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 654, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 286, + 712 + ], + "type": "text", + "content": "5). Qualitative Comparison: To illustrate the edge of MENet more intuitively, we select videos of Javelin Throw and High Jump from ActivityNet-1.3 and compare our results qualitatively with the Base, in which we remove the movement enhanced feature and SFPN. Results with the" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 319, + 71, + 531, + 149 + ], + "blocks": [ + { + "bbox": [ + 46, + 342, + 286, + 376 + ], + "lines": [ + { + "bbox": [ + 46, + 342, + 286, + 376 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 286, + 376 + ], + "type": "text", + "content": "Table 7. Ablation study on the SFPN. \"Length\" means the temporal length of single layer feature sequence. The Detection performance is reported on ActivityNet-1.3." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 319, + 71, + 531, + 149 + ], + "lines": [ + { + "bbox": [ + 319, + 71, + 531, + 149 + ], + "spans": [ + { + "bbox": [ + 319, + 71, + 531, + 149 + ], + "type": "table", + "html": "
Training StrategymAP@tIoU (%)
0.50.750.95Avg.
only Bias45.829.17.429.4
only Generalization54.338.211.037.4
only Specialization54.638.010.837.4
two-stage54.738.410.537.7
", + "image_path": "9f86625fc8edc84f44812348c80a6b23b0ddd689bc5a61f1c8202cf0c1d1be6d.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 154, + 545, + 187 + ], + "lines": [ + { + "bbox": [ + 305, + 154, + 545, + 187 + ], + "spans": [ + { + "bbox": [ + 305, + 154, + 545, + 187 + ], + "type": "text", + "content": "Table 8. Ablation study on the two-stage training strategy. The proposed two-stage training leads to better performance than the single stage method or the Bias method." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 194, + 545, + 302 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 194, + 545, + 302 + ], + "spans": [ + { + "bbox": [ + 304, + 194, + 545, + 302 + ], + "type": "text", + "content": "highest confidence score are visualized in Fig 5. Firstly, Compared with the Base method, MENet uses the movement feature, which enlarges the difference between action and background, making the model more accurate in boundary localization. Secondly, it can be seen the High Jump action contains a large-scale action and a small-scale action. Due to the SFPN in MENet, MENet can better capture actions at different scales. Results of qualitative comparison once again prove the superiority of MENet." + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 310, + 316, + 431, + 403 + ], + "blocks": [ + { + "bbox": [ + 310, + 316, + 431, + 403 + ], + "lines": [ + { + "bbox": [ + 310, + 316, + 431, + 403 + ], + "spans": [ + { + "bbox": [ + 310, + 316, + 431, + 403 + ], + "type": "image", + "image_path": "b0b660d9f12d5764c2ed6ef2d20fa2ba3356685c5f71cefc74c313b3811c4f01.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 411, + 545, + 434 + ], + "lines": [ + { + "bbox": [ + 305, + 411, + 545, + 434 + ], + "spans": [ + { + "bbox": [ + 305, + 411, + 545, + 434 + ], + "type": "text", + "content": "Figure 5. Qualitative Comparison. MENet generates more accurate action segments." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 434, + 316, + 554, + 403 + ], + "blocks": [ + { + "bbox": [ + 434, + 316, + 554, + 403 + ], + "lines": [ + { + "bbox": [ + 434, + 316, + 554, + 403 + ], + "spans": [ + { + "bbox": [ + 434, + 316, + 554, + 403 + ], + "type": "image", + "image_path": "a7cc00d0cfecdd234bf25ab228c3639146b3a495b6508ab208893300bf9d3655.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 446, + 378, + 457 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 446, + 378, + 457 + ], + "spans": [ + { + "bbox": [ + 306, + 446, + 378, + 457 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 461, + 545, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 461, + 545, + 675 + ], + "spans": [ + { + "bbox": [ + 304, + 461, + 545, + 675 + ], + "type": "text", + "content": "Temporal action detection (TAD) is aimed at localizing the action segment and classifying the action class. Despite the considerable attention and rapid development, TAD is hindered by two critical problems: the movement feature submergence and multi-scale action detection. In an effort to overcome these two challenges, we propose the Movement Enhance Network (MENet) with two crucial designs. Firstly, we propose the Movement Enhance Module (MEM) to extract the movement feature in video snippets and explore the multi-relations between the snippets. Secondly, we propose the Scale FPN (SFPN) to handle the different scale actions, we design the U-shape Module to facilitate the information flow between different scale features. For better performance, we design the training and inference stage, ensuring that each layer in MENet is specialized at a specific scale range. Extensive experiments demonstrate that MENet considerably outperforms other representative TAD methods on ActivityNet-1.3 and THUMOS-14." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 677, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 712 + ], + "type": "text", + "content": "Acknowledgements. This work was supported by National Natural Science Foundation of China (NSFC) No. 62176156." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13562" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "text", + "content": "[1] Humam Alwassel, Silvio Giancola, and Bernard Ghanem. 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Cuhk & ethz & siat submission to activitynet" + } + ] + } + ], + "index": 33 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "13563" + } + ] + } + ], + "index": 35 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 129 + ], + "type": "list", + "angle": 0, + "index": 2, + "blocks": [ + { + "bbox": [ + 66, + 72, + 286, + 94 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 72, + 286, + 94 + ], + "spans": [ + { + "bbox": [ + 66, + 72, + 286, + 94 + ], + "type": "text", + "content": "challenge 2017. arXiv preprint arXiv:1710.08011, 8(8), 2017." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 95, + 287, + 129 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 95, + 287, + 129 + ], + "spans": [ + { + "bbox": [ + 47, + 95, + 287, + 129 + ], + "type": "text", + "content": "[33] Zixin Zhu, Wei Tang, Le Wang, Nanning Zheng, and Gang Hua. Enriching local and global contexts for temporal action localization. In ICCV, pages 13516-13525, 2021." + } + ] + } + ], + "index": 1 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 318, + 757 + ], + "type": "text", + "content": "13564" + } + ] + } + ], + "index": 3 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-Directional Subspace Editing in Style-Space/a84347b3-c2c0-42e5-a59b-c77ba1dcbff7_content_list.json b/2023/Multi-Directional Subspace Editing in Style-Space/a84347b3-c2c0-42e5-a59b-c77ba1dcbff7_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..5434f3c2053ef7439988109ebcab6c8555603dcc --- /dev/null +++ b/2023/Multi-Directional Subspace Editing in Style-Space/a84347b3-c2c0-42e5-a59b-c77ba1dcbff7_content_list.json @@ -0,0 +1,2247 @@ +[ + { + "type": "text", + "text": "Multi-Directional Subspace Editing in Style-Space", + "text_level": 1, + "bbox": [ + 230, + 130, + 740, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Chen Naveh", + "bbox": [ + 433, + 181, + 535, + 196 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "School of Computer Science, Reichman University", + "bbox": [ + 282, + 199, + 686, + 217 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "navehchen1@gmail.com", + "bbox": [ + 393, + 219, + 575, + 233 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e7bc74e7e4686bb092744be81a40227e2cda62c5c76540f74541bced61e381c4.jpg", + "image_caption": [ + "Figure 1: Multi-directional human face editing. Each row indicates changes in a subspace associated with a particular attribute: (top to bottom) gender, age and race." + ], + "image_footnote": [], + "bbox": [ + 102, + 267, + 869, + 599 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 654, + 313, + 670 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "This paper describes a new technique for finding disentangled semantic directions in the latent space of StyleGAN. Our method identifies meaningful orthogonal subspaces that allow editing of one human face attribute, while minimizing undesired changes in other attributes. Our model is capable of editing a single attribute in multiple directions, resulting in a range of possible generated images. We compare our scheme with three state-of-the-art models and show that our method outperforms them in terms of face editing and disentanglement capabilities. Additionally, we suggest quantitative measures for evaluating attribute separation and disentanglement, and exhibit the superiority of", + "bbox": [ + 75, + 719, + 472, + 901 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "our model with respect to those measures1.", + "bbox": [ + 500, + 655, + 784, + 671 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 500, + 700, + 632, + 715 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recent developments in computer vision have enabled the generation of photorealistic, high-resolution synthetic images. The most notable technique is Generative Adversarial Networks (GANs) [11], which have advanced the progress of many applications, including image generation, super-resolution, image inpainting, and more. In particular, the generator of StyleGAN [1], one of the most notable GAN models, has been extensively explored by researchers.", + "bbox": [ + 496, + 726, + 890, + 845 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "StyleGAN samples a latent vector $\\mathbf{z} \\in \\mathbb{R}^{512}$ from a", + "bbox": [ + 517, + 847, + 890, + 864 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "1Project page and code are available at https://chennaveh.github.io/MDSE/", + "bbox": [ + 500, + 875, + 888, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "7138", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Gaussian distribution $\\mathcal{N}(\\mathbf{0},\\mathbf{I})$ , and maps it to an intermediate vector $\\mathbf{w}\\in \\mathcal{W} = \\mathbb{R}^{512}$ using a mapping network. This vector is then used to generate a 1024x1024 RGB image. The vector $\\mathbf{w}$ is inserted into 18 multi-resolution style blocks that control various characteristics of the synthesized image. Vectors at lower resolutions determine high-level features such as pose and hair. Intermediate resolutions affect facial expressions, while vectors at higher resolutions dictate fine details like colors and texture. The original StyleGAN model uses the $\\mathcal{W}$ latent space and the same $\\mathbf{w}$ vector for all 18 style blocks. Subsequent studies [1,2,26,32] utilize the $\\mathcal{W}^{+} = \\mathbb{R}^{18\\cdot 512}$ space, which extends the $\\mathcal{W}$ space, and applies different $\\mathbf{w}$ vectors to different style blocks. This allows for enhanced control over the resulting image. The $\\mathcal{W}^{+}$ latent space is commonly used for inverse mapping, converting an image into $\\mathbf{w}\\in \\mathcal{W}^{+}$ .", + "bbox": [ + 75, + 90, + 472, + 333 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Recent works have explored methods for gaining control over the synthesized images by altering the latent space vectors [3, 7, 12, 25, 28, 29]. For instance, shifting the latent vector of a generated image towards the direction corresponding to \"smile\" can progressively amplify the smile in the output image. While these methods showcase impressive and realistic editing capabilities, pinpointing the attribute directions remains a challenge. One approach is to use vectors in latent space sampled from the GAN model combined with attribute ground truth (either manually labeled or determined using a pre-trained attribute estimator) [10, 16, 28]. A linear classifier in the latent space is then employed. The normal to the classification boundary corresponds to the most significant direction of the attribute. These models often suffer from issues of entangled data and biases in the training set. Such biases might result in attribute correlations, like glasses with age or beard with gender. Consequently, adding glasses to a face may inadvertently age it. Other methods use unsupervised techniques [12, 29], such as PCA, to find meaningful orthogonal directions in the latent space. However, these directions typically require subjective human post-annotation to link directions to attributes in the synthesized images. All these models share the notion of a singular direction for each attribute, despite the possibility of some attributes defined by multiple dimensions (e.g., age might be affected by factors like hair color and skin wrinkles, see Fig. 1).", + "bbox": [ + 75, + 337, + 472, + 744 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we present MDSE, an acronym for Multi-Directional Subspace Editing. This framework aims to identify orthogonal semantics within the latent space of a pre-trained StyleGAN. Our goal is to discover meaningful subspaces that are mutually orthogonal, with each subspace controlling specific facial attributes. \"Multi-directional editing\" means altering a latent vector within a particular subspace in various directions. This approach enables the generation of a wide range of images, each varying in a specific attribute. Furthermore, because the subspaces are", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "mutually orthogonal, modifications in one attribute result in minimal changes to others. We explore the disentanglement capabilities of our model and quantitatively assess its performance in comparison to leading image editing techniques.", + "bbox": [ + 496, + 90, + 893, + 167 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 498, + 181, + 642, + 198 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Generative Adversarial Networks (GANs)", + "text_level": 1, + "bbox": [ + 500, + 205, + 857, + 223 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Generative models have revolutionized the generation of vast amounts of visual content. They can produce visually compelling content with remarkable fidelity, making them indispensable for image editing applications. GAN models learn a mapping from a specific distribution (usually Gaussian or uniform) to the target distribution. The generator $G(\\cdot)$ is trained to fool an adversary $D(\\cdot)$ , which aims to differentiate between the generated images and the real ones. Both models $G(\\cdot)$ and $D(\\cdot)$ are trained concurrently using the min-max loss [11]. The GAN approach is widely recognized and often outperforms other techniques, such as variational autoencoders (VAEs) [21]. Recently, denoising diffusion probabilistic models (DDPM) [15] have risen in prominence and showcased superior results. However, despite their leading performance in image generation, their potential in image editing and semantic interpretation remains relatively unexplored. In this work, our attention is centered on a GAN-based generator, specifically the StyleGAN [18-20], which exhibits exceptional capability in the human face domain.", + "bbox": [ + 496, + 229, + 893, + 531 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "GAN Latent Space. Given a pre-trained generator $\\mathbf{x} = G(\\mathbf{w})$ , GAN inversion $\\hat{\\mathbf{w}} = G^{-1}(\\mathbf{x})$ is the process of inverting a specified image $\\mathbf{x}$ into a latent vector $\\hat{\\mathbf{w}}$ that faithfully reconstructs the image using the generator. In other words, $G(\\hat{\\mathbf{w}})\\approx \\mathbf{x}$ . Most of the common methods either train an encoder [24, 26, 32] from the image space into the latent space or optimize the latent vector, using backpropagation, directly until it generates the desired image [1, 2, 22]. Recent approaches that modify the generator's weight have gained traction, resulting in enhanced image reconstruction [5, 27]. Previous works show that the latent space of a pretrained GAN model encodes image semantics in a meaningful structure. Hence, latent codes corresponding to images with similar semantics tend to cluster closely in the latent space [28]. For instance, within the domain of human face generation, faces sharing characteristics (e.g., being young and blond) will have nearby latent vectors. This foundational insight drives modern image editing techniques.", + "bbox": [ + 496, + 532, + 895, + 806 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Multi-Directional Manipulation in Latent Space", + "text_level": 1, + "bbox": [ + 500, + 815, + 893, + 848 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The idea of editing an image through latent space manipulation has been extensively explored in recent years [7,25]. Such approaches aim to harness the strong capabilities of", + "bbox": [ + 498, + 854, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "7139", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "the generator. Therefore, they keep the generator network static and conduct vector operations solely in the latent space. Recent works primarily rely on a linear latent space assumption and demonstrate pleasing-looking results of image editing by adding or subtracting vectors within the latent space [12, 28, 29]. InterFaceGAN [28] employs pretrained binary classifiers to label images with facial features, such as young-old, male-female, and with/without glasses, among others. It then trains a linear classifier (specifically, a Support Vector Machine or SVM) on the respective latent vectors to derive a classifying hyperplane. The normal to this hyperplane serves as the 1D direction for editing the relevant attribute.", + "bbox": [ + 75, + 90, + 472, + 287 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "GANSpace [12] adopts a data-driven approach, applying PCA on a set of vectors sampled from $\\mathcal{W}$ to find meaningful directions. The eigenvectors associated with the largest eigenvalues serve as the editing directions. Some derived directions can be entangled, such as head rotation and gender. To address this issue, edits are restricted to a specifically selected subset of the generator's layers.", + "bbox": [ + 75, + 289, + 472, + 397 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Another work, SeFa [29], avoids the image sampling pre-processing step. Instead, it determines a closed-form factorization of the latent space by utilizing an eigendecomposition of the generator's weights. For StyleGAN, the style affine transformation matrices are employed for vector decomposition. The eigenvectors corresponding to the greatest variations are selected to define the semantic directions. However, this unsupervised method faces two main issues. Firstly, there's a subjective post-annotation process to match the directions with relevant semantics. Secondly, the directions that are derived often mix several semantics (e.g., age and glasses), a result of biases present in the training data.", + "bbox": [ + 75, + 397, + 472, + 595 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "A distinct set of studies moves away from the linear approach, opting instead to learn non-linear functions to manipulate latent vectors. StyleFlow [3] employs continuous normalizing flows conditioned on the image attribute vector. This attribute vector must be provided using pre-trained networks before every edit. Another non-linear approach is StyleRig [30], which incorporates a 3D semantic network and harnesses it to perform rigid edits such as pose and light. Although non-linear approaches generally perform better, our research primarily emphasizes the more comprehensive linear approach.", + "bbox": [ + 75, + 595, + 472, + 763 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "All previous methods that manipulate the latent space of StyleGAN define a semantic as a singular direction. Both linear and non-linear approaches ultimately derive positive and negative directions for editing a desired attribute. We believe that this oversimplification may restrict the editing capabilities and limit the diversity of the generated images. For example, imagine we want to edit the gender of a given face. One person may argue that hairstyle is a distinguishing factor between men and women, while another might think", + "bbox": [ + 75, + 763, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "of facial structure or the presence of facial hair as a more prominent factor. In this work, we overcome this variability by associating an attribute with an $n$ -dim subspace where $n \\geq 1$ , containing more than a single direction, in the semantic space. We call this a multi-directional subspace, as different vectors within the subspace can affect the resulting image differently, but all affect the associated attribute (see examples in Fig. 1). We also require different attributes to be associated with mutually orthogonal subspaces, to promote disentanglement between attributes.", + "bbox": [ + 496, + 90, + 893, + 242 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We outline our contributions as follows:", + "bbox": [ + 517, + 242, + 785, + 257 + ], + "page_idx": 2 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose MDSE to extend the concept of meaningful latent directions to multi-directional subspaces, thereby diversifying and expanding the capabilities of the editing process.", + "- MDSE identifies orthogonal directions in StyleGAN's latent space, to promote disentanglement. We introduce an orthogonality loss in the model training and demonstrate its significance in preserving some image attributes while editing others. We visualize the results and demonstrate improved results in consecutive edits of multiple attributes (refer to Fig. 4).", + "- We develop a new metric for evaluating the disentanglement properties of image editing. In addition to the conventional approaches of visual comparisons, we suggest using our evaluation metrics as a quantitative measurement of disentanglement capabilities." + ], + "bbox": [ + 517, + 263, + 890, + 522 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 532, + 589, + 547 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given a set of attributes, $B \\triangleq \\{ \\text{gender}, \\text{ glasses}, \\dots \\}$ , we aim to find a subspace for each attribute $b_i \\in B$ so that editing within this subspace leads to changes in the associated attribute $b_i$ . Different directions in each subspace are responsible for distinct visual semantics. To achieve disentanglement, we desire that each subspace solely influences its respective attribute.", + "bbox": [ + 496, + 556, + 890, + 662 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Certain attributes, such as glasses and age, have been observed to correlate with each other [28], making disentangled editing challenging. To overcome this problem, our model seeks to decompose the latent space $\\mathcal{W}^+$ into multiple orthogonal subspaces each of which is associated with a single attribute. This requirement has two main outcomes. Firstly, editing within a subspace facilitates multidirectional edits of a single attribute. Secondly, the orthogonality ensures that altering a specific facial attribute doesn't affect other attributes.", + "bbox": [ + 496, + 664, + 893, + 815 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Latent Space Decomposition", + "text_level": 1, + "bbox": [ + 500, + 821, + 756, + 838 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We decompose $\\mathcal{W}^+$ into $N + 1$ orthogonal subspaces $\\{S_i\\}_{i = 0}^N$ and define each subspace $S_{i}$ as", + "bbox": [ + 500, + 845, + 890, + 878 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nS _ {i} \\triangleq \\operatorname {s p a n} \\left\\{\\mathbf {p} _ {i} ^ {1}, \\mathbf {p} _ {i} ^ {2}, \\dots , \\mathbf {p} _ {i} ^ {n _ {i}} \\right\\}, n _ {i} < \\dim (\\mathcal {W} ^ {+}) \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 526, + 883, + 890, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "7140", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{p}_i^j\\in \\mathcal{W}^+$ , and $\\{\\mathbf{p}_i^j\\}_{j = 1}^{n_i}$ are linearly independent vectors. Therefore, $\\{\\mathbf{p}_i^j\\}_{j = 1}^{n_i}$ form a basis for subspace $S_{i}$ with cardinality $n_i$ . There are $N + 1$ subspaces, where $N = |B|$ is the size of the attribute set $B$ . Each $S_{i}$ corresponds to $b_{i}$ respectively, while $S_0$ is associated with all other information that is not labeled in $B$ . This may include other semantics, e.g., clothing and image background. The correspondence of $S_{i}$ and $b_{i}$ will be elaborated on later in the paper.", + "bbox": [ + 75, + 89, + 468, + 229 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To ensure orthogonality, we require the following conditions:", + "bbox": [ + 75, + 229, + 468, + 258 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nS _ {i} \\subset \\mathcal {W} ^ {+}, \\forall i \\in \\{0, \\dots , N \\} \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 174, + 276, + 468, + 294 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\bigoplus_ {i = 0} ^ {N} S _ {i} = \\mathcal {W} ^ {+} \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 223, + 314, + 468, + 356 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nS _ {i} \\perp S _ {j}, \\forall i \\neq j \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 215, + 369, + 468, + 387 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\bigoplus$ denotes direct sum, and $\\perp$ signifies orthogonal subspaces. Notice that the entire vector set $\\{\\mathbf{p}_i^j\\}$ forms a basis for $\\mathcal{W}^+$ . As a result, we can uniquely express every vector $\\mathbf{w} \\in \\mathbb{R}^{18 \\cdot 512}$ with a set of scalars $\\{a_i^j\\}$ and represent $\\mathbf{w}$ as the following linear combination:", + "bbox": [ + 75, + 395, + 468, + 470 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {w} = \\sum_ {i = 0} ^ {N} \\sum_ {j = 1} ^ {n _ {i}} a _ {i} ^ {j} \\mathbf {p} _ {i} ^ {j} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 210, + 484, + 468, + 526 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "This expression can also be represented in matrix form:", + "bbox": [ + 76, + 532, + 444, + 549 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {w} = \\left[ \\underbrace {\\left[ \\begin{array}{c c c} | & & | \\\\ \\mathbf {p} _ {0} ^ {1} & \\dots & \\mathbf {p} _ {0} ^ {n _ {0}} \\\\ | & & | \\end{array} \\right]} _ {\\mathbf {P} _ {0}} \\dots \\underbrace {\\left[ \\begin{array}{c c c} | & & | \\\\ \\mathbf {p} _ {N} ^ {1} & \\dots & \\mathbf {p} _ {N} ^ {n _ {N}} \\\\ | & & | \\end{array} \\right]} _ {\\mathbf {P} _ {N}} \\right] \\left[ \\begin{array}{c} \\left[ \\begin{array}{c} a _ {0} ^ {1} \\\\ \\vdots \\\\ a _ {0} ^ {n _ {0}} \\end{array} \\right] \\\\ \\vdots \\\\ \\left[ \\begin{array}{c} a _ {N} ^ {1} \\\\ \\vdots \\\\ a _ {N} ^ {n _ {N}} \\end{array} \\right] \\end{array} \\right] \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 571, + 472, + 719 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {w} = \\sum_ {i = 0} ^ {N} \\mathbf {P} _ {i} \\mathbf {a} _ {i} = \\underbrace {\\left[ \\mathbf {P} _ {0} , \\cdots , \\mathbf {P} _ {N} \\right]} _ {\\mathbf {P}} \\underbrace {\\left[ \\begin{array}{c} \\mathbf {a} _ {0} \\\\ \\vdots \\\\ \\mathbf {a} _ {N} \\end{array} \\right]} _ {\\mathbf {a}} \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 138, + 731, + 468, + 806 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbf{P}$ is a matrix defined by:", + "bbox": [ + 76, + 813, + 289, + 828 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {P} = \\left[ \\mathbf {p} _ {0} ^ {1} \\dots \\mathbf {p} _ {0} ^ {n _ {0}} \\dots \\mathbf {p} _ {N} ^ {1} \\dots \\mathbf {p} _ {N} ^ {n _ {N}} \\right] \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 839, + 468, + 859 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "and $\\mathbf{a}^T = [\\mathbf{a}_0^T,\\dots ,\\mathbf{a}_N^T ]$ is a vector of coefficients. Finding $\\mathbf{P}$ that satisfies Eq. (2)-(4) is the core part of our framework.", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Training Procedure", + "text_level": 1, + "bbox": [ + 500, + 90, + 687, + 106 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Our dataset consists of a set of 2,000 vector pairs $\\left\\{(\\mathbf{w}^{(i)},\\mathbf{y}^{(i)})\\right\\}_{i = 1}^{2000}$ . The latent vectors $\\{\\mathbf{w}^{(i)}\\}$ are generated from random vectors sampled from a Gaussian distribution $\\mathbf{z}^{(i)}\\sim \\mathcal{N}(0,1)$ and then mapped to $\\mathcal{W}^+$ space using the StyleGAN mapping function: $\\mathbf{w}^{(i)} = M(\\mathbf{z}^{(i)})$ . Each sample $\\mathbf{w}^{(i)}\\in \\mathbb{R}^{18\\cdot 512}$ is mapped onto the image space using the StyleGAN generator, $\\mathbf{x}^{(i)} = G(\\mathbf{w}^{(i)})$ and then annotated using pre-trained classifiers to determine an attribute score vector:", + "bbox": [ + 498, + 114, + 890, + 252 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {y} ^ {(i)} \\triangleq \\left(y _ {1} ^ {(i)}, \\dots , y _ {N} ^ {(i)}\\right) = \\left(\\mathcal {C} _ {1} \\left(\\mathbf {x} ^ {(i)}\\right), \\dots , \\mathcal {C} _ {N} \\left(\\mathbf {x} ^ {(i)}\\right)\\right) \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 262, + 890, + 287 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here, each $y_{k}^{(i)}$ denotes the $b_{k}$ attribute score for sample $i$ . Depending on the attribute, $y_{k}^{(i)}$ is either a discrete or continuous number. $C_k$ represents the pre-trained classifier for attribute $k$ . For age, smile, gender, and glasses, we used the face attribute classifier from [13] trained on the FFHQ dataset [19]. For the pose attribute, we utilized img2pose [6] for face estimation. Additionally, we employed a race classifier [17] trained on the Yahoo YFCC100M dataset [31].", + "bbox": [ + 498, + 301, + 890, + 441 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The primary goal during the training phase is to determine the matrix $\\mathbf{P}$ and use it to reconstruct all samples from the training set. To satisfy Eq. (5), we jointly learn a vector $\\mathbf{a}^{(i)}$ for each vector $\\mathbf{w}^{(i)}$ such that $\\mathbf{w}^{(i)} = \\mathbf{P}\\mathbf{a}^{(i)}$ . We then introduce the following loss:", + "bbox": [ + 498, + 444, + 890, + 518 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {r e c} ^ {(i)} = \\left\\| \\mathbf {w} ^ {(i)} - \\mathbf {P} \\mathbf {a} ^ {(i)} \\right\\| _ {1} \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 612, + 532, + 890, + 559 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{rec}$ represents the reconstruction loss. Instead of pixel-based image reconstructions, we use a $L_{1}$ loss in the latent space using the original vector $\\mathbf{w}^{(i)} = M(\\mathbf{z}^{(i)})$ as the target value.", + "bbox": [ + 498, + 566, + 890, + 626 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Additionally, to enforce disentanglement, as referred in Eq. (4), we introduce an orthogonality loss:", + "bbox": [ + 498, + 627, + 890, + 657 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {o r t h}} = \\sum_ {i \\neq j} \\left\\| \\mathbf {P} _ {i} ^ {T} \\mathbf {P} _ {j} \\right\\| _ {2} ^ {2} \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 614, + 669, + 890, + 704 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "and require that the columns of matrices $\\mathbf{P}_i, \\mathbf{P}_j$ be orthogonal for $i \\neq j$ , where $\\|\\cdot\\|_2$ is the element-wise Frobenius-norm.", + "bbox": [ + 498, + 715, + 890, + 760 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Since learning disentangled representations is fundamentally impossible without a supervised inductive bias on the data [23], we leverage the attribute vector $\\mathbf{y}^{(i)}$ and introduce a mixing loss to establish the association between $S_{k}$ and $b_{k}$ . Given a vector $\\mathbf{w}^{(i)}$ , we can import attribute $b_{k}$ from a randomly chosen vector $\\mathbf{w}^{(j)}$ , to generate $\\mathbf{w}_{mix}^{(i)}$ :", + "bbox": [ + 498, + 762, + 890, + 857 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {w} _ {m i x} ^ {(i)} = \\mathbf {P} _ {k} \\mathbf {a} _ {k} ^ {(j)} + \\sum_ {l \\neq k} \\mathbf {P} _ {l} \\mathbf {a} _ {l} ^ {(i)} \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 596, + 869, + 890, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "7141", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "and its corresponding image $\\mathbf{x}_{mix}^{(i)}\\triangleq G(\\mathbf{w}_{mix}^{(i)})$ . For the modified image we require $\\mathcal{C}_k(\\mathbf{x}_{mix}^{(i)})$ to be similar to $y_{k}^{(j)}$ while keeping the other attributes unchanged. Thus a mixing loss is added to the network to force changes only in $b_{k}$ :", + "bbox": [ + 75, + 88, + 468, + 170 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {m i x i n g}} ^ {(i)} = L _ {k} \\left(\\mathcal {C} _ {k} \\left(\\mathbf {x} _ {\\text {m i x}} ^ {(i)}\\right), y _ {k} ^ {(j)}\\right) + \\sum_ {l \\neq k} L _ {l} \\left(\\mathcal {C} _ {l} \\left(\\mathbf {x} _ {\\text {m i x}} ^ {(i)}\\right), y _ {l} ^ {(i)}\\right) \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 188, + 467, + 236 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$L_{i}$ are loss functions that vary based on the attribute types. For categorical labels, we use softmax with cross-entropy loss, whereas continuous labels are optimized using the $L_{1}$ loss. In practice, we mix all attributes together from randomly chosen vectors. This introduces complex changes to the image and encourages the association of a single subspace with a single attribute.", + "bbox": [ + 75, + 237, + 467, + 340 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Finally, our model is trained using an objective function comprised of the three losses:", + "bbox": [ + 76, + 342, + 467, + 372 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\lambda_ {\\text {o r t h}} \\mathcal {L} _ {\\text {o r t h}} + \\frac {1}{n} \\sum_ {i} \\mathcal {L} _ {\\text {r e c}} ^ {(i)} + \\lambda_ {\\text {m i x i n g}} \\mathcal {L} _ {\\text {m i x i n g}} ^ {(i)} \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 378, + 468, + 415 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\lambda_{orth}$ , $\\lambda_{mixing}$ are hyperparameters.", + "bbox": [ + 76, + 422, + 362, + 438 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 450, + 209, + 467 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we evaluate the performance of our model compared to state-of-the-art image editing models, all of which utilize the StyleGAN generator for image synthesis.", + "bbox": [ + 76, + 474, + 468, + 521 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To test our model, we generated a source and target latent vector, projected them onto a subspace $S_{k}$ , and replaced the projections of the source vector with those from the target. Since our subspaces are orthogonal, we expect to see changes only in the corresponding attribute $b_{k}$ . Example results are presented in Fig. 2. Notably, if the source face wears glasses, these remain post-edit since we only incorporate pose, smile, and race from the target face.", + "bbox": [ + 75, + 521, + 468, + 642 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Comparison with Previous Methods", + "text_level": 1, + "bbox": [ + 76, + 648, + 387, + 666 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We compared our model with three previous image editing methods: InterFaceGAN [28], StyleFlow [3], and SeFa [29]. We evaluated the editing and disentanglement qualities of these models for a common set of attributes supported by all of them, such as age, gender, smile, pose, and glasses. Additionally, since our method discovers a subspace rather than a single direction, to ensure a fair comparison, we trained a linear SVM inside each subspace. We then used the normal to the hyperplane as the direction for editing. This model is used in Section 4.2 and Section 4.3.", + "bbox": [ + 75, + 672, + 468, + 823 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Qualitative Comparison", + "text_level": 1, + "bbox": [ + 76, + 832, + 297, + 848 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Figure 3 offers a comparative assessment of the quality of real image editing. We inverted the images into StyleGAN's latent space using HyperStyle [4]. Our observations", + "bbox": [ + 75, + 854, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/14384cc1ded0a4abe5cd4f93c02d3b59b4932a9c4eaf6a14fa9b3e1c649a257f.jpg", + "image_caption": [ + "Target" + ], + "image_footnote": [], + "bbox": [ + 606, + 87, + 689, + 150 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/de54c180071dd3ae13b6076da8e4d56986238c97491c304e47ceb36dfc22feb9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 705, + 88, + 785, + 150 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/6b313ae4ede17a9743535dbd3d5ab4261a7fb1436b1dc0d8aa1ef251b908f57d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 802, + 88, + 883, + 150 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/d08a7dafc91efbfa9586a384f8d4373ebdc165bb2e019d502b6114f98275c45d.jpg", + "image_caption": [ + "Source" + ], + "image_footnote": [], + "bbox": [ + 511, + 167, + 591, + 229 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/7825f7968d8679811cd0d5689fb40e0c3cb79e8220ede40a18fb2b20abce398e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 607, + 167, + 689, + 229 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/ffc37c481389a1cc86758e004711e627efcb6b986f26ad58c5aaba5488d8b343.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 705, + 167, + 785, + 229 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/247059b90714da11eb5440083038f2f5d208a3f59b8dc8e72fd72e2b587a7035.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 802, + 167, + 883, + 229 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/ff3409452355ea9c1b6a9fb4fa3a84176780d524ba90b6805c4b71a02b65354f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 511, + 232, + 591, + 294 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/47b5e550e2876f5611aaec0964bcf73a9319ef736548002c0e0ae09589b82c9c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 607, + 232, + 689, + 294 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/bb98f74605d501e84b2ac8bad3cb0fc6163e0d03ed228f84fcae9a10df211904.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 705, + 232, + 785, + 294 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/e33813b6c79e434797a4940f240ee5e85c9c2678536b9298bb31db0a30a62712.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 802, + 232, + 883, + 294 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/4173670af406049c43c578a265e330a4f52918659fcd16b7820e5ecccc6dc799.jpg", + "image_caption": [ + "Figure 2: Image editing capabilities using source images and target attribute images. The attributes derived from the target images include pose, smile, and race." + ], + "image_footnote": [], + "bbox": [ + 511, + 296, + 591, + 358 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/d6a0ac7b46003b37512183beec056c82aba7f884ca507a1155d5d50f1ea10fc7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 607, + 296, + 689, + 358 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/4236c2ac123d4fe47a709a85d7cf971896963d5bb5db2d2667a6128b843126e1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 705, + 296, + 785, + 358 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/c36c3bcc744f653463c535a003dedcb6dd8e9d085239bad14994fc9710e97642.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 802, + 296, + 883, + 358 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "indicate that multiple edits on a single image can significantly diminish its quality, making it more prone to visual artifacts. Moreover, due to biases in the FFHQ dataset [19], some attributes are more correlated in StyleGAN's latent space than others (e.g., younger individuals are less likely to wear glasses). As depicted in Fig. 3, while most models can effectively modify a single attribute, our model outperforms others in terms of accuracy when changing all attributes simultaneously and better maintains each individual attribute edit. Sequential editing is illustrated in Fig. 4, showing that as edits progress, the images retain previous attributes without a loss in quality.", + "bbox": [ + 496, + 445, + 890, + 626 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In Fig. 1 we visualize our model's capability of generating diverse results for different attributes due to its multidirectional nature. The images are generated by shifting the latent vectors to different directions inside the relevant subspace. We found that some attributes (e.g., smile, pose) behave like binary attributes, meaning they contain most of the information in a single direction. Others (e.g., gender, age), however, can be edited in multiple directions resulting in various images. Additional results can be found in the supplementary material.", + "bbox": [ + 496, + 627, + 890, + 777 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3.Quantitative Comparison", + "text_level": 1, + "bbox": [ + 500, + 786, + 732, + 803 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To evaluate our model's disentanglement capabilities, we develop and utilize two different methods: attribute correlation and face preservation. Furthermore, to measure the diversity introduced by multi-directional subspace editing, we utilize the LPIPS score [33] and the Frechet Inception Distance (FID) [14] to evaluate image fidelity.", + "bbox": [ + 496, + 809, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "7142", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/7e869f4bacbf0d82164eabe861c7b88312378c385d335a2dea5af44bc7c62370.jpg", + "image_caption": [ + "Figure 3: Comparison of real image editing between our method and the baseline approaches. The edit direction for each attribute was determined using a linear SVM classifier." + ], + "image_footnote": [], + "bbox": [ + 70, + 87, + 908, + 843 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "7143", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/ac137f7ae88d4f63ee23bce109a63705128733cd10dac47352e1c4cc429d4855.jpg", + "image_caption": [ + "Figure 4: Sequential human face editing result." + ], + "image_footnote": [], + "bbox": [ + 81, + 88, + 472, + 281 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Correlation between edited attributes: We can assign an attribute score to an image $\\mathbf{x}$ using $\\mathcal{C}_k$ as a feature extractor. The activation vector $l(\\mathbf{x})$ , derived from the last hidden layer of $\\mathcal{C}_k$ , is used to compute the distance between the feature vector $l(\\mathbf{x})$ and the classifying hyperplane. This hyperplane is defined by $\\{\\mathbf{v} \\mid \\mathbf{c}_k^T\\mathbf{v} + \\mathbf{t}_k = 0\\}$ .", + "bbox": [ + 76, + 335, + 467, + 426 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The attribute score of an image $\\mathbf{x}$ is given by the distance of $l(\\mathbf{x})$ from the separating hyperplane: $dist_{k}(\\mathbf{x}) = \\frac{\\mathbf{c}_{k}^{T}l(\\mathbf{x}) + \\mathbf{t}_{k}}{|\\mathbf{c}_{k}|}$ .", + "bbox": [ + 76, + 426, + 467, + 477 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To assess the disentanglement capability of our model, we began by generating an evaluation set comprising $1K$", + "bbox": [ + 76, + 477, + 467, + 507 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "pairs of images paired with their desired face attributes. These images were directly sampled from the StyleGAN generator, while the attributes were independently generated for each image. For each image, we manipulated its latent vector $\\mathbf{w} \\in \\mathcal{W}^{+}$ along the learned directions and fed it to the generator to produce an edited version, denoted as $\\mathbf{x}_{edit}$ . It's worth noting that in practice we change all attributes simultaneously.", + "bbox": [ + 496, + 90, + 890, + 210 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Next, we measured the difference in attribute score between the original and the edited images. Taking the attribute \"smile\" as an example, we defined the perceptual distance as: $\\Delta_{smile} = dist_{smile}(\\mathbf{x}_{edit}) - dist_{smile}(\\mathbf{x})$ .", + "bbox": [ + 496, + 212, + 890, + 273 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "For the final assessment, we computed the Pearson correlation between the perceptual distances of every pair of attributes. Each entry in Table 1 displays the absolute correlation value. For instance, for the attributes \"smile\" and \"pose\", we determine the perceptual distances $\\Delta_{smile}$ and $\\Delta_{pose}$ across the entire evaluation set. The correlation value shown in the table is:", + "bbox": [ + 496, + 273, + 890, + 377 + ], + "page_idx": 6 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {c o r r} (\\text {p o s e}, \\text {s m i l e}) = \\left| \\frac {\\operatorname {c o v} \\left(\\Delta_ {\\text {p o s e}} , \\Delta_ {\\text {s m i l e}}\\right)}{E \\left[ \\Delta_ {\\text {p o s e}} \\right] E \\left[ \\Delta_ {\\text {s m i l e}} \\right]} \\right| \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 532, + 387, + 890, + 422 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 1 presents the correlation results of various methods. As previously mentioned [8, 12, 28, 29], we observe that certain attributes exhibit stronger correlations than others. For instance, the glasses-age correlation is consistently higher than the smile-pose correlation across all models.", + "bbox": [ + 496, + 431, + 890, + 507 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/5be5be3dfaeaa42c2f1a81593b6841c572d6ecb7ecb42a2dcdb5b44bd1e04229.jpg", + "table_caption": [ + "Table 1: Attribute correlation matrices of edited images (in absolute values)." + ], + "table_footnote": [], + "table_body": "
(a) SeFa(b) InterFaceGan
PoseSmileAgeGenderGlassesposeSmileAgeGenderGlasses
Pose1.0000.1500.0390.1330.051Pose1.0000.0980.0900.0170.079
Smile0.1501.0000.0010.1700.233Smile0.0981.0000.1540.1980.084
Age0.0390.0011.0000.5330.367Age0.0900.1541.0000.5650.600
Gender0.1330.1700.5331.0000.339Gender0.0170.1980.5651.0000.363
Glasses0.0510.2330.3670.3391.000Glasses0.0790.0840.6000.3631.000
Avg0.0930.1150.2350.2930.247Avg0.0710.1330.3520.2850.281
(c) StyleFlow(d) Ours
PoseSmileAgeGenderGlassesPoseSmileAgeGenderGlasses
Pose1.0000.1130.1260.1030.056Pose1.0000.0180.0080.0290.046
Smile0.1131.0000.2640.0110.074Smile0.0181.0000.1200.0500.100
Age0.1260.2641.0000.5810.494Age0.0080.1201.0000.3880.363
Gender0.1030.0110.5811.0000.338Gender0.0290.0500.3881.0000.203
Glasses0.0560.0740.4940.3381.000Glasses0.0460.1000.3630.2031.000
Avg0.0990.1150.3660.2580.240Avg0.0250.0720.2190.1670.178
", + "bbox": [ + 150, + 553, + 813, + 897 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "7144", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The table's final row sums the off-diagonal columns, representing the average correlation score. Our method's lower scores highlight its superior disentanglement capabilities compared to the other techniques.", + "bbox": [ + 75, + 90, + 470, + 154 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In our previous assessment, all attributes were adjusted simultaneously. To test the stability of attributes when only one is modified, we conducted an experiment editing one attribute at a time and measured the perceptual distances using the classifiers' final layers. Fig. 5 displays results from various methods. The x-axis represents changes in the edited attribute, while the y-axis indicates unintentional changes in other attributes. As edits become more extensive, the inter-attribute effect is more pronounced. Among all models, our approach shows the least deviation, indicating superior attribute disentanglement.", + "bbox": [ + 75, + 157, + 470, + 325 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Face Identity Preservation: Following the approach of the face identity score [3], we assess the edited images using a pre-trained face embedding network [9]. We restricted our edits to attributes that should preserve identity, such as pose, glasses, and smile. After editing, we embedded the images into a latent space using the network. We then calculated", + "bbox": [ + 75, + 330, + 472, + 421 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/3d96dc537995d6b81a12586d307b45e4b8d5876d1c7e04e6ce4408c66968cb46.jpg", + "table_caption": [ + "Table 2: Identity preservation scores by different models." + ], + "table_footnote": [ + "Notation: $C_s$ - Cosine Similarity; $E_d$ - Euclidean Distance." + ], + "table_body": "
EditMetricSeFaInterFaceGanStyleFlowOurs
SmileCs ↑0.9700.9780.9890.991
Ed ↓0.3290.2760.1920.174
PoseCs ↑0.9780.9790.9810.982
Ed ↓0.2830.2790.26620.253
GlassesCs ↑0.9660.9780.9840.985
Ed ↓0.3480.2700.2270.215
AllCs ↑0.9110.9330.9350.948
Ed ↓0.6220.5370.5340.467
", + "bbox": [ + 511, + 114, + 879, + 256 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "the Euclidean distance, $E_{d}$ , and the cosine similarity, $C_s$ , between the original and edited images.", + "bbox": [ + 498, + 313, + 890, + 344 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 2 displays the results for face identity preservation. Our method consistently surpasses other techniques across all types of edits. While StyleFlow shows comparable scores for individual attribute edits, our model excels in preserving identity when multiple edits are combined.", + "bbox": [ + 496, + 345, + 892, + 421 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/80bfee8bd1c8d0472d2955137fa8db024501603106f1e5c73166b491d2eeb793.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 101, + 448, + 243, + 523 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b3b5ba119ab085a14b2efb47a109e06c965ddfd614c790421ff3b4ef3a1d5f59.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 254, + 448, + 398, + 522 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/08386100f31322f2a7f4ae40e4a90aef0c93ff32df3e6e1b675a7f850a4e1cfb.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 408, + 448, + 550, + 522 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": 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"image_caption": [ + "Figure 5: Comparative analysis of the inter-attribute effects exhibited by different models. The upper rows display how changes in one attribute vary as a function of changes in another attribute. The bottom row provides an average of all the rows above." + ], + "image_footnote": [], + "bbox": [ + 101, + 766, + 243, + 839 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/368df0d2e5fd6389feee668a9d19b8e5862a47fb8b52632a0edfc98a54d84cf8.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 256, + 766, + 397, + 839 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/af9b1b6bbf1bcf0b0fe486fb408dae2362fffb702fd16d58326f64cd78983409.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 410, + 766, + 550, + 839 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1090aec8781551c8348baa4f65cf8649ae31bb54599e4c9bc0e5a832eb8bdf20.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 560, + 766, + 702, + 839 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/17f2ccebd0e086385ac8dfbac39b08835a7d9feb163acea905d6ca1eccc5f978.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 715, + 766, + 859, + 839 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "7145", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Diversity Analysis", + "text_level": 1, + "bbox": [ + 76, + 90, + 253, + 107 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In the previous sections, we introduced a single-direction variant of our model. Now, we will explore the performance of our model when multiple directions in the subspace are utilized for editing. To measure the diversity of the images produced by our model, we employed the LPIPS perceptual similarity score [33]. A lower LPIPS score indicates higher similarity between images, whereas a higher score signifies perceptual differences.", + "bbox": [ + 75, + 114, + 468, + 236 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We generated a batch of 1,000 images and applied 5 random edits to each image. For every set of 5 edits, the similarity score between each pair of edited images was computed. Subsequently, all these scores were averaged to derive the final diversity score. We benchmarked our model against StyleFlow and the single-direction variant of our model, referred to as SVM, as detailed in Section 4.1. The FID score was also calculated to assess the visual quality of the generated images.", + "bbox": [ + 75, + 237, + 470, + 373 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "The results, summarized in Table 3, reveal that our approach — when multi-directional subspace editing is employed — not only fosters greater image diversity (as indicated by the LPIPS score) but also ensures superior visual quality (as denoted by the FID score). It's noteworthy that there is a marked enhancement in the multi-directional iteration of our model (subspace) when compared against its single-direction counterpart (SVM) or against StyleFlow.", + "bbox": [ + 75, + 375, + 468, + 494 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/ed239df629613875ba1f483be02de05023dea0be7c4dc8e0c9f94507966846dd.jpg", + "table_caption": [ + "Table 3: Diversity score results for edited images. Our multi-directional model achieves a higher score which indicates its ability to generate more diverse results while maintaining a lower FID score." + ], + "table_footnote": [], + "table_body": "
MethodLPIPS ↑FID ↓
StyleFlow0.21327.467
Our (svm)0.22926.926
Our (subspace)0.32123.648
", + "bbox": [ + 161, + 583, + 387, + 648 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "4.5. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 678, + 230, + 695 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "To validate the importance of our orthogonality loss outlined in Section 3.2, we carried out an ablation study. We trained a version of our model with $\\lambda_{orth} = 0$ , keeping all other configurations, including losses and the training process, consistent. Post-training, we conducted consecutive edits starting from an original image, and the results can be viewed in Fig. 6.", + "bbox": [ + 75, + 702, + 468, + 808 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We found that images edited with the orthogonality loss exhibit crisper details and fewer visual artifacts when subjected to multiple edits. We also carried out the same quantitative evaluations as detailed in Section 4.3. The results in Tables 4 and 5 indicate that our orthogonality loss leads to better attribute disentanglement in our model.", + "bbox": [ + 75, + 810, + 470, + 900 + ], + "page_idx": 8 + }, + { + "type": "equation", + "text": "\n$$\n\\lambda_ {o r t h} = 0\n$$\n", + "text_format": "latex", + "bbox": [ + 666, + 89, + 736, + 104 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/a6a55509796f889dfc4194807bfba2ae7abcea326a401564644b0e611f3b48b6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 511, + 107, + 609, + 170 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/931530730778fb23834ec095f1e128fc1bd8c7bed805ffa7f15963a2f04a9c4b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 617, + 108, + 697, + 170 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/5cd9048da593c74316f1936866c0866c8c0dd1856e6bd75f4cbb998dcb884cd8.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 707, + 107, + 789, + 170 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/5a4113acfd83ae74e57f3cf303ca3b95da0b1ccd066e5d302739db1ac83c1b77.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 799, + 107, + 880, + 170 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/e443c88718da2b9de49b71dd4b681599e7f99bedc76c0bab91a5b40a88be5d3d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 511, + 172, + 609, + 234 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/025d99343bca9277ff2c27c1a62e1deb7bfa6f61e30e5670abb5f8bf5573ab18.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 617, + 172, + 697, + 234 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/425601884dea473c2bbd03f2e8944ae7dbde6b4f528f4668dbe0f156246e8093.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 707, + 172, + 787, + 234 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/1419290e18abac56bb4c412725f2d9449f20b6d54e40490ada753a101c6488e5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 799, + 172, + 880, + 234 + ], + "page_idx": 8 + }, + { + "type": "equation", + "text": "\n$$\n\\lambda_ {o r t h} = 0. 0 0 1\n$$\n", + "text_format": "latex", + "bbox": [ + 655, + 237, + 751, + 252 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/a2be59da0747bf28123fe44c6fb35aeb3400793c70708928ec642976388e9588.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 511, + 251, + 609, + 314 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/7513fa3dc49ef182e172c02f4245982157e7562a02fd5eefd3744ac7f599437c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 617, + 252, + 697, + 314 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/855090fa79d361796ca7750b0b5008d6da8e31cf9fefb6bcfaa0c03eb60ba362.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 707, + 252, + 787, + 314 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/7a700610d150ca6d384f7ac9107b12d1f185d2b1cac03c3bdd9b0618ba85fb8a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 799, + 251, + 880, + 314 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/a8af8ee3a8eaab4d050c4294fd4dbdedcfd15aca9fad84a3652bc74c45308d3f.jpg", + "image_caption": [ + "Figure 6: Comparison using orthogonality loss: First and third rows show reduced pose-glasses entanglement; second and fourth rows show better preservation of hair and shirt color." + ], + "image_footnote": [], + "bbox": [ + 511, + 316, + 609, + 378 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/fe5a0f9968329d0ed413e33e177fa9e68f4916c713e5b30f302db0c7d32c126f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 617, + 316, + 697, + 378 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/757603764b0c2d3ceb800bfe1ce2c13c58b2092e4c5ce7c958735fb038a2d04e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 707, + 316, + 787, + 378 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/b97643186e149553b18a85f47edad7759a21e2016049a7a6c58ced73e1173d58.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 799, + 316, + 880, + 378 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/a2eb021c0dfa21085d3b33645852a306a48e1d7e03a498589f9c12e6088ce3ea.jpg", + "table_caption": [ + "Table 4: Attribute correlation matrices with and without orthogonal loss. The values represent the average correlation between an attribute and others." + ], + "table_footnote": [], + "table_body": "
ModelPoseSmileAgeGenderGlasses
λorth = 00.1490.2420.3420.2830.253
λorth = 0.0010.0250.0720.2190.1670.178
", + "bbox": [ + 500, + 527, + 852, + 578 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/b34e09287cf08eac234f72f8f38100686de4299a5dff99c67a246f4a7987abd4.jpg", + "table_caption": [ + "Table 5: Comparison of identity preservation using orthogonal loss." + ], + "table_footnote": [ + "Notation: $C_s$ - Cosine Similarity; $E_d$ - Euclidean Distance." + ], + "table_body": "
EditMetricλorth=0λorth=0.001
AllCs↑0.9320.948
Ed↓0.5360.467
", + "bbox": [ + 566, + 633, + 826, + 683 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusions", + "text_level": 1, + "bbox": [ + 500, + 738, + 625, + 753 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this work we proposed MDSE, a disentangling generative model for multi-attribute image editing. We introduce the concept of orthogonal subspaces that support multi-directional edits for diverse image generation. Additionally, this model effectively identifies disentangled latent subspaces, allowing precise control over the generated images and the displayed face attributes. We believe that integrating these concepts during the generator's training could further enhance the performance of disentangled models.", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "7146", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 106 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Rameen Abdul, Yipeng Qin, and Peter Wonka. Image2stylegan: How to embed images into the stylegan latent space? In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 4432-4441, 2019. 1, 2", + "[2] Rameen Abdul, Yipeng Qin, and Peter Wonka. Image2stylegan++: How to edit the embedded images? 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Interfacegan: Interpreting the disentangled face representa" + ], + "bbox": [ + 501, + 92, + 893, + 901 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "7147", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "tion learned by gans. IEEE transactions on pattern analysis and machine intelligence, 2020. 2, 3, 5, 7", + "[29] Yujun Shen and Bolei Zhou. Closed-form factorization of latent semantics in gans. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 1532-1540, 2021. 2, 3, 5, 7", + "[30] Ayush Tewari, Mohamed Elgharib, Gaurav Bharaj, Florian Bernard, Hans-Peter Seidel, Patrick Pérez, Michael Zollhofer, and Christian Theobalt. Stylerig: Rigging stylegan for 3d control over portrait images. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 586-595, 2018. 5, 9" + ], + "bbox": [ + 78, + 90, + 470, + 443 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "7148", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multi-Directional Subspace Editing in Style-Space/a84347b3-c2c0-42e5-a59b-c77ba1dcbff7_model.json b/2023/Multi-Directional Subspace Editing in Style-Space/a84347b3-c2c0-42e5-a59b-c77ba1dcbff7_model.json new file mode 100644 index 0000000000000000000000000000000000000000..2065d4d06c2b8fb4dbf1071e6d64496924cd710d --- /dev/null +++ b/2023/Multi-Directional Subspace Editing in Style-Space/a84347b3-c2c0-42e5-a59b-c77ba1dcbff7_model.json @@ -0,0 +1,2609 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.232, + 0.131, + 0.741, + 0.154 + ], + "angle": 0, + "content": "Multi-Directional Subspace Editing in Style-Space" + }, + { + "type": "text", + "bbox": [ + 0.434, + 0.182, + 0.536, + 0.198 + ], + "angle": 0, + "content": "Chen Naveh" + }, + { + "type": "text", + "bbox": [ + 0.283, + 0.2, + 0.687, + 0.218 + ], + "angle": 0, + "content": "School of Computer Science, Reichman University" + }, + { + "type": "text", + "bbox": [ + 0.395, + 0.22, + 0.576, + 0.234 + ], + "angle": 0, + "content": "navehchen1@gmail.com" + }, + { + "type": "image", + "bbox": [ + 0.104, + 0.268, + 0.87, + 0.6 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.611, + 0.895, + 0.644 + ], + "angle": 0, + "content": "Figure 1: Multi-directional human face editing. Each row indicates changes in a subspace associated with a particular attribute: (top to bottom) gender, age and race." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.655, + 0.314, + 0.671 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.473, + 0.902 + ], + "angle": 0, + "content": "This paper describes a new technique for finding disentangled semantic directions in the latent space of StyleGAN. Our method identifies meaningful orthogonal subspaces that allow editing of one human face attribute, while minimizing undesired changes in other attributes. Our model is capable of editing a single attribute in multiple directions, resulting in a range of possible generated images. We compare our scheme with three state-of-the-art models and show that our method outperforms them in terms of face editing and disentanglement capabilities. Additionally, we suggest quantitative measures for evaluating attribute separation and disentanglement, and exhibit the superiority of" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.656, + 0.785, + 0.672 + ], + "angle": 0, + "content": "our model with respect to those measures1." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.702, + 0.633, + 0.717 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.727, + 0.892, + 0.847 + ], + "angle": 0, + "content": "Recent developments in computer vision have enabled the generation of photorealistic, high-resolution synthetic images. The most notable technique is Generative Adversarial Networks (GANs) [11], which have advanced the progress of many applications, including image generation, super-resolution, image inpainting, and more. In particular, the generator of StyleGAN [1], one of the most notable GAN models, has been extensively explored by researchers." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.848, + 0.892, + 0.865 + ], + "angle": 0, + "content": "StyleGAN samples a latent vector \\(\\mathbf{z} \\in \\mathbb{R}^{512}\\) from a" + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.89, + 0.901 + ], + "angle": 0, + "content": "1Project page and code are available at https://chennaveh.github.io/MDSE/" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7138" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.334 + ], + "angle": 0, + "content": "Gaussian distribution \\(\\mathcal{N}(\\mathbf{0},\\mathbf{I})\\), and maps it to an intermediate vector \\(\\mathbf{w}\\in \\mathcal{W} = \\mathbb{R}^{512}\\) using a mapping network. This vector is then used to generate a 1024x1024 RGB image. The vector \\(\\mathbf{w}\\) is inserted into 18 multi-resolution style blocks that control various characteristics of the synthesized image. Vectors at lower resolutions determine high-level features such as pose and hair. Intermediate resolutions affect facial expressions, while vectors at higher resolutions dictate fine details like colors and texture. The original StyleGAN model uses the \\(\\mathcal{W}\\) latent space and the same \\(\\mathbf{w}\\) vector for all 18 style blocks. Subsequent studies [1,2,26,32] utilize the \\(\\mathcal{W}^{+} = \\mathbb{R}^{18\\cdot 512}\\) space, which extends the \\(\\mathcal{W}\\) space, and applies different \\(\\mathbf{w}\\) vectors to different style blocks. This allows for enhanced control over the resulting image. The \\(\\mathcal{W}^{+}\\)latent space is commonly used for inverse mapping, converting an image into \\(\\mathbf{w}\\in \\mathcal{W}^{+}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.338, + 0.473, + 0.746 + ], + "angle": 0, + "content": "Recent works have explored methods for gaining control over the synthesized images by altering the latent space vectors [3, 7, 12, 25, 28, 29]. For instance, shifting the latent vector of a generated image towards the direction corresponding to \"smile\" can progressively amplify the smile in the output image. While these methods showcase impressive and realistic editing capabilities, pinpointing the attribute directions remains a challenge. One approach is to use vectors in latent space sampled from the GAN model combined with attribute ground truth (either manually labeled or determined using a pre-trained attribute estimator) [10, 16, 28]. A linear classifier in the latent space is then employed. The normal to the classification boundary corresponds to the most significant direction of the attribute. These models often suffer from issues of entangled data and biases in the training set. Such biases might result in attribute correlations, like glasses with age or beard with gender. Consequently, adding glasses to a face may inadvertently age it. Other methods use unsupervised techniques [12, 29], such as PCA, to find meaningful orthogonal directions in the latent space. However, these directions typically require subjective human post-annotation to link directions to attributes in the synthesized images. All these models share the notion of a singular direction for each attribute, despite the possibility of some attributes defined by multiple dimensions (e.g., age might be affected by factors like hair color and skin wrinkles, see Fig. 1)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.903 + ], + "angle": 0, + "content": "In this work, we present MDSE, an acronym for Multi-Directional Subspace Editing. This framework aims to identify orthogonal semantics within the latent space of a pre-trained StyleGAN. Our goal is to discover meaningful subspaces that are mutually orthogonal, with each subspace controlling specific facial attributes. \"Multi-directional editing\" means altering a latent vector within a particular subspace in various directions. This approach enables the generation of a wide range of images, each varying in a specific attribute. Furthermore, because the subspaces are" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.168 + ], + "angle": 0, + "content": "mutually orthogonal, modifications in one attribute result in minimal changes to others. We explore the disentanglement capabilities of our model and quantitatively assess its performance in comparison to leading image editing techniques." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.182, + 0.643, + 0.199 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.207, + 0.858, + 0.224 + ], + "angle": 0, + "content": "2.1. Generative Adversarial Networks (GANs)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.231, + 0.895, + 0.532 + ], + "angle": 0, + "content": "Generative models have revolutionized the generation of vast amounts of visual content. They can produce visually compelling content with remarkable fidelity, making them indispensable for image editing applications. GAN models learn a mapping from a specific distribution (usually Gaussian or uniform) to the target distribution. The generator \\(G(\\cdot)\\) is trained to fool an adversary \\(D(\\cdot)\\), which aims to differentiate between the generated images and the real ones. Both models \\(G(\\cdot)\\) and \\(D(\\cdot)\\) are trained concurrently using the min-max loss [11]. The GAN approach is widely recognized and often outperforms other techniques, such as variational autoencoders (VAEs) [21]. Recently, denoising diffusion probabilistic models (DDPM) [15] have risen in prominence and showcased superior results. However, despite their leading performance in image generation, their potential in image editing and semantic interpretation remains relatively unexplored. In this work, our attention is centered on a GAN-based generator, specifically the StyleGAN [18-20], which exhibits exceptional capability in the human face domain." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.534, + 0.896, + 0.807 + ], + "angle": 0, + "content": "GAN Latent Space. Given a pre-trained generator \\(\\mathbf{x} = G(\\mathbf{w})\\), GAN inversion \\(\\hat{\\mathbf{w}} = G^{-1}(\\mathbf{x})\\) is the process of inverting a specified image \\(\\mathbf{x}\\) into a latent vector \\(\\hat{\\mathbf{w}}\\) that faithfully reconstructs the image using the generator. In other words, \\(G(\\hat{\\mathbf{w}})\\approx \\mathbf{x}\\). Most of the common methods either train an encoder [24, 26, 32] from the image space into the latent space or optimize the latent vector, using backpropagation, directly until it generates the desired image [1, 2, 22]. Recent approaches that modify the generator's weight have gained traction, resulting in enhanced image reconstruction [5, 27]. Previous works show that the latent space of a pretrained GAN model encodes image semantics in a meaningful structure. Hence, latent codes corresponding to images with similar semantics tend to cluster closely in the latent space [28]. For instance, within the domain of human face generation, faces sharing characteristics (e.g., being young and blond) will have nearby latent vectors. This foundational insight drives modern image editing techniques." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.816, + 0.895, + 0.849 + ], + "angle": 0, + "content": "2.2. Multi-Directional Manipulation in Latent Space" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.895, + 0.903 + ], + "angle": 0, + "content": "The idea of editing an image through latent space manipulation has been extensively explored in recent years [7,25]. Such approaches aim to harness the strong capabilities of" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.957 + ], + "angle": 0, + "content": "7139" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.288 + ], + "angle": 0, + "content": "the generator. Therefore, they keep the generator network static and conduct vector operations solely in the latent space. Recent works primarily rely on a linear latent space assumption and demonstrate pleasing-looking results of image editing by adding or subtracting vectors within the latent space [12, 28, 29]. InterFaceGAN [28] employs pretrained binary classifiers to label images with facial features, such as young-old, male-female, and with/without glasses, among others. It then trains a linear classifier (specifically, a Support Vector Machine or SVM) on the respective latent vectors to derive a classifying hyperplane. The normal to this hyperplane serves as the 1D direction for editing the relevant attribute." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.29, + 0.473, + 0.398 + ], + "angle": 0, + "content": "GANSpace [12] adopts a data-driven approach, applying PCA on a set of vectors sampled from \\(\\mathcal{W}\\) to find meaningful directions. The eigenvectors associated with the largest eigenvalues serve as the editing directions. Some derived directions can be entangled, such as head rotation and gender. To address this issue, edits are restricted to a specifically selected subset of the generator's layers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.398, + 0.473, + 0.596 + ], + "angle": 0, + "content": "Another work, SeFa [29], avoids the image sampling pre-processing step. Instead, it determines a closed-form factorization of the latent space by utilizing an eigendecomposition of the generator's weights. For StyleGAN, the style affine transformation matrices are employed for vector decomposition. The eigenvectors corresponding to the greatest variations are selected to define the semantic directions. However, this unsupervised method faces two main issues. Firstly, there's a subjective post-annotation process to match the directions with relevant semantics. Secondly, the directions that are derived often mix several semantics (e.g., age and glasses), a result of biases present in the training data." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.597, + 0.473, + 0.764 + ], + "angle": 0, + "content": "A distinct set of studies moves away from the linear approach, opting instead to learn non-linear functions to manipulate latent vectors. StyleFlow [3] employs continuous normalizing flows conditioned on the image attribute vector. This attribute vector must be provided using pre-trained networks before every edit. Another non-linear approach is StyleRig [30], which incorporates a 3D semantic network and harnesses it to perform rigid edits such as pose and light. Although non-linear approaches generally perform better, our research primarily emphasizes the more comprehensive linear approach." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.473, + 0.903 + ], + "angle": 0, + "content": "All previous methods that manipulate the latent space of StyleGAN define a semantic as a singular direction. Both linear and non-linear approaches ultimately derive positive and negative directions for editing a desired attribute. We believe that this oversimplification may restrict the editing capabilities and limit the diversity of the generated images. For example, imagine we want to edit the gender of a given face. One person may argue that hairstyle is a distinguishing factor between men and women, while another might think" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.243 + ], + "angle": 0, + "content": "of facial structure or the presence of facial hair as a more prominent factor. In this work, we overcome this variability by associating an attribute with an \\( n \\)-dim subspace where \\( n \\geq 1 \\), containing more than a single direction, in the semantic space. We call this a multi-directional subspace, as different vectors within the subspace can affect the resulting image differently, but all affect the associated attribute (see examples in Fig. 1). We also require different attributes to be associated with mutually orthogonal subspaces, to promote disentanglement between attributes." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.243, + 0.786, + 0.258 + ], + "angle": 0, + "content": "We outline our contributions as follows:" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.264, + 0.892, + 0.326 + ], + "angle": 0, + "content": "- We propose MDSE to extend the concept of meaningful latent directions to multi-directional subspaces, thereby diversifying and expanding the capabilities of the editing process." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.332, + 0.892, + 0.439 + ], + "angle": 0, + "content": "- MDSE identifies orthogonal directions in StyleGAN's latent space, to promote disentanglement. We introduce an orthogonality loss in the model training and demonstrate its significance in preserving some image attributes while editing others. We visualize the results and demonstrate improved results in consecutive edits of multiple attributes (refer to Fig. 4)." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.446, + 0.892, + 0.523 + ], + "angle": 0, + "content": "- We develop a new metric for evaluating the disentanglement properties of image editing. In addition to the conventional approaches of visual comparisons, we suggest using our evaluation metrics as a quantitative measurement of disentanglement capabilities." + }, + { + "type": "list", + "bbox": [ + 0.519, + 0.264, + 0.892, + 0.523 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.534, + 0.591, + 0.549 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.558, + 0.892, + 0.664 + ], + "angle": 0, + "content": "Given a set of attributes, \\( B \\triangleq \\{ \\text{gender}, \\text{ glasses}, \\dots \\} \\), we aim to find a subspace for each attribute \\( b_i \\in B \\) so that editing within this subspace leads to changes in the associated attribute \\( b_i \\). Different directions in each subspace are responsible for distinct visual semantics. To achieve disentanglement, we desire that each subspace solely influences its respective attribute." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.665, + 0.895, + 0.816 + ], + "angle": 0, + "content": "Certain attributes, such as glasses and age, have been observed to correlate with each other [28], making disentangled editing challenging. To overcome this problem, our model seeks to decompose the latent space \\(\\mathcal{W}^+\\) into multiple orthogonal subspaces each of which is associated with a single attribute. This requirement has two main outcomes. Firstly, editing within a subspace facilitates multidirectional edits of a single attribute. Secondly, the orthogonality ensures that altering a specific facial attribute doesn't affect other attributes." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.823, + 0.757, + 0.839 + ], + "angle": 0, + "content": "3.1. Latent Space Decomposition" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.846, + 0.892, + 0.879 + ], + "angle": 0, + "content": "We decompose \\(\\mathcal{W}^+\\) into \\(N + 1\\) orthogonal subspaces \\(\\{S_i\\}_{i = 0}^N\\) and define each subspace \\(S_{i}\\) as" + }, + { + "type": "equation", + "bbox": [ + 0.527, + 0.884, + 0.892, + 0.904 + ], + "angle": 0, + "content": "\\[\nS _ {i} \\triangleq \\operatorname {s p a n} \\left\\{\\mathbf {p} _ {i} ^ {1}, \\mathbf {p} _ {i} ^ {2}, \\dots , \\mathbf {p} _ {i} ^ {n _ {i}} \\right\\}, n _ {i} < \\dim (\\mathcal {W} ^ {+}) \\tag {1}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7140" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.09, + 0.47, + 0.231 + ], + "angle": 0, + "content": "where \\(\\mathbf{p}_i^j\\in \\mathcal{W}^+\\), and \\(\\{\\mathbf{p}_i^j\\}_{j = 1}^{n_i}\\) are linearly independent vectors. Therefore, \\(\\{\\mathbf{p}_i^j\\}_{j = 1}^{n_i}\\) form a basis for subspace \\(S_{i}\\) with cardinality \\(n_i\\). There are \\(N + 1\\) subspaces, where \\(N = |B|\\) is the size of the attribute set \\(B\\). Each \\(S_{i}\\) corresponds to \\(b_{i}\\) respectively, while \\(S_0\\) is associated with all other information that is not labeled in \\(B\\). This may include other semantics, e.g., clothing and image background. The correspondence of \\(S_{i}\\) and \\(b_{i}\\) will be elaborated on later in the paper." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.231, + 0.469, + 0.26 + ], + "angle": 0, + "content": "To ensure orthogonality, we require the following conditions:" + }, + { + "type": "equation", + "bbox": [ + 0.175, + 0.277, + 0.47, + 0.295 + ], + "angle": 0, + "content": "\\[\nS _ {i} \\subset \\mathcal {W} ^ {+}, \\forall i \\in \\{0, \\dots , N \\} \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.224, + 0.315, + 0.47, + 0.357 + ], + "angle": 0, + "content": "\\[\n\\bigoplus_ {i = 0} ^ {N} S _ {i} = \\mathcal {W} ^ {+} \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.217, + 0.371, + 0.469, + 0.388 + ], + "angle": 0, + "content": "\\[\nS _ {i} \\perp S _ {j}, \\forall i \\neq j \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.396, + 0.47, + 0.471 + ], + "angle": 0, + "content": "where \\(\\bigoplus\\) denotes direct sum, and \\(\\perp\\) signifies orthogonal subspaces. Notice that the entire vector set \\(\\{\\mathbf{p}_i^j\\}\\) forms a basis for \\(\\mathcal{W}^+\\). As a result, we can uniquely express every vector \\(\\mathbf{w} \\in \\mathbb{R}^{18 \\cdot 512}\\) with a set of scalars \\(\\{a_i^j\\}\\) and represent \\(\\mathbf{w}\\) as the following linear combination:" + }, + { + "type": "equation", + "bbox": [ + 0.211, + 0.485, + 0.469, + 0.527 + ], + "angle": 0, + "content": "\\[\n\\mathbf {w} = \\sum_ {i = 0} ^ {N} \\sum_ {j = 1} ^ {n _ {i}} a _ {i} ^ {j} \\mathbf {p} _ {i} ^ {j} \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.534, + 0.445, + 0.55 + ], + "angle": 0, + "content": "This expression can also be represented in matrix form:" + }, + { + "type": "equation", + "bbox": [ + 0.077, + 0.573, + 0.473, + 0.72 + ], + "angle": 0, + "content": "\\[\n\\mathbf {w} = \\left[ \\underbrace {\\left[ \\begin{array}{c c c} | & & | \\\\ \\mathbf {p} _ {0} ^ {1} & \\dots & \\mathbf {p} _ {0} ^ {n _ {0}} \\\\ | & & | \\end{array} \\right]} _ {\\mathbf {P} _ {0}} \\dots \\underbrace {\\left[ \\begin{array}{c c c} | & & | \\\\ \\mathbf {p} _ {N} ^ {1} & \\dots & \\mathbf {p} _ {N} ^ {n _ {N}} \\\\ | & & | \\end{array} \\right]} _ {\\mathbf {P} _ {N}} \\right] \\left[ \\begin{array}{c} \\left[ \\begin{array}{c} a _ {0} ^ {1} \\\\ \\vdots \\\\ a _ {0} ^ {n _ {0}} \\end{array} \\right] \\\\ \\vdots \\\\ \\left[ \\begin{array}{c} a _ {N} ^ {1} \\\\ \\vdots \\\\ a _ {N} ^ {n _ {N}} \\end{array} \\right] \\end{array} \\right] \\tag {6}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.14, + 0.732, + 0.469, + 0.807 + ], + "angle": 0, + "content": "\\[\n\\mathbf {w} = \\sum_ {i = 0} ^ {N} \\mathbf {P} _ {i} \\mathbf {a} _ {i} = \\underbrace {\\left[ \\mathbf {P} _ {0} , \\cdots , \\mathbf {P} _ {N} \\right]} _ {\\mathbf {P}} \\underbrace {\\left[ \\begin{array}{c} \\mathbf {a} _ {0} \\\\ \\vdots \\\\ \\mathbf {a} _ {N} \\end{array} \\right]} _ {\\mathbf {a}} \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.814, + 0.29, + 0.829 + ], + "angle": 0, + "content": "where \\(\\mathbf{P}\\) is a matrix defined by:" + }, + { + "type": "equation", + "bbox": [ + 0.164, + 0.84, + 0.469, + 0.86 + ], + "angle": 0, + "content": "\\[\n\\mathbf {P} = \\left[ \\mathbf {p} _ {0} ^ {1} \\dots \\mathbf {p} _ {0} ^ {n _ {0}} \\dots \\mathbf {p} _ {N} ^ {1} \\dots \\mathbf {p} _ {N} ^ {n _ {N}} \\right] \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.87, + 0.469, + 0.902 + ], + "angle": 0, + "content": "and \\(\\mathbf{a}^T = [\\mathbf{a}_0^T,\\dots ,\\mathbf{a}_N^T ]\\) is a vector of coefficients. Finding \\(\\mathbf{P}\\) that satisfies Eq. (2)-(4) is the core part of our framework." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.091, + 0.688, + 0.107 + ], + "angle": 0, + "content": "3.2. Training Procedure" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.115, + 0.892, + 0.253 + ], + "angle": 0, + "content": "Our dataset consists of a set of 2,000 vector pairs \\(\\left\\{(\\mathbf{w}^{(i)},\\mathbf{y}^{(i)})\\right\\}_{i = 1}^{2000}\\). The latent vectors \\(\\{\\mathbf{w}^{(i)}\\}\\) are generated from random vectors sampled from a Gaussian distribution \\(\\mathbf{z}^{(i)}\\sim \\mathcal{N}(0,1)\\) and then mapped to \\(\\mathcal{W}^+\\) space using the StyleGAN mapping function: \\(\\mathbf{w}^{(i)} = M(\\mathbf{z}^{(i)})\\). Each sample \\(\\mathbf{w}^{(i)}\\in \\mathbb{R}^{18\\cdot 512}\\) is mapped onto the image space using the StyleGAN generator, \\(\\mathbf{x}^{(i)} = G(\\mathbf{w}^{(i)})\\) and then annotated using pre-trained classifiers to determine an attribute score vector:" + }, + { + "type": "equation", + "bbox": [ + 0.515, + 0.263, + 0.892, + 0.289 + ], + "angle": 0, + "content": "\\[\n\\mathbf {y} ^ {(i)} \\triangleq \\left(y _ {1} ^ {(i)}, \\dots , y _ {N} ^ {(i)}\\right) = \\left(\\mathcal {C} _ {1} \\left(\\mathbf {x} ^ {(i)}\\right), \\dots , \\mathcal {C} _ {N} \\left(\\mathbf {x} ^ {(i)}\\right)\\right) \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.303, + 0.892, + 0.443 + ], + "angle": 0, + "content": "Here, each \\( y_{k}^{(i)} \\) denotes the \\( b_{k} \\) attribute score for sample \\( i \\). Depending on the attribute, \\( y_{k}^{(i)} \\) is either a discrete or continuous number. \\( C_k \\) represents the pre-trained classifier for attribute \\( k \\). For age, smile, gender, and glasses, we used the face attribute classifier from [13] trained on the FFHQ dataset [19]. For the pose attribute, we utilized img2pose [6] for face estimation. Additionally, we employed a race classifier [17] trained on the Yahoo YFCC100M dataset [31]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.445, + 0.892, + 0.52 + ], + "angle": 0, + "content": "The primary goal during the training phase is to determine the matrix \\(\\mathbf{P}\\) and use it to reconstruct all samples from the training set. To satisfy Eq. (5), we jointly learn a vector \\(\\mathbf{a}^{(i)}\\) for each vector \\(\\mathbf{w}^{(i)}\\) such that \\(\\mathbf{w}^{(i)} = \\mathbf{P}\\mathbf{a}^{(i)}\\). We then introduce the following loss:" + }, + { + "type": "equation", + "bbox": [ + 0.613, + 0.533, + 0.892, + 0.56 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {r e c} ^ {(i)} = \\left\\| \\mathbf {w} ^ {(i)} - \\mathbf {P} \\mathbf {a} ^ {(i)} \\right\\| _ {1} \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.567, + 0.892, + 0.627 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{rec}\\) represents the reconstruction loss. Instead of pixel-based image reconstructions, we use a \\(L_{1}\\) loss in the latent space using the original vector \\(\\mathbf{w}^{(i)} = M(\\mathbf{z}^{(i)})\\) as the target value." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.628, + 0.892, + 0.658 + ], + "angle": 0, + "content": "Additionally, to enforce disentanglement, as referred in Eq. (4), we introduce an orthogonality loss:" + }, + { + "type": "equation", + "bbox": [ + 0.616, + 0.67, + 0.891, + 0.705 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {o r t h}} = \\sum_ {i \\neq j} \\left\\| \\mathbf {P} _ {i} ^ {T} \\mathbf {P} _ {j} \\right\\| _ {2} ^ {2} \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.717, + 0.891, + 0.761 + ], + "angle": 0, + "content": "and require that the columns of matrices \\(\\mathbf{P}_i, \\mathbf{P}_j\\) be orthogonal for \\(i \\neq j\\), where \\(\\|\\cdot\\|_2\\) is the element-wise Frobenius-norm." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.763, + 0.892, + 0.858 + ], + "angle": 0, + "content": "Since learning disentangled representations is fundamentally impossible without a supervised inductive bias on the data [23], we leverage the attribute vector \\(\\mathbf{y}^{(i)}\\) and introduce a mixing loss to establish the association between \\(S_{k}\\) and \\(b_{k}\\). Given a vector \\(\\mathbf{w}^{(i)}\\), we can import attribute \\(b_{k}\\) from a randomly chosen vector \\(\\mathbf{w}^{(j)}\\), to generate \\(\\mathbf{w}_{mix}^{(i)}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.597, + 0.87, + 0.891, + 0.904 + ], + "angle": 0, + "content": "\\[\n\\mathbf {w} _ {m i x} ^ {(i)} = \\mathbf {P} _ {k} \\mathbf {a} _ {k} ^ {(j)} + \\sum_ {l \\neq k} \\mathbf {P} _ {l} \\mathbf {a} _ {l} ^ {(i)} \\tag {12}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "7141" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.089, + 0.47, + 0.171 + ], + "angle": 0, + "content": "and its corresponding image \\(\\mathbf{x}_{mix}^{(i)}\\triangleq G(\\mathbf{w}_{mix}^{(i)})\\). For the modified image we require \\(\\mathcal{C}_k(\\mathbf{x}_{mix}^{(i)})\\) to be similar to \\(y_{k}^{(j)}\\) while keeping the other attributes unchanged. Thus a mixing loss is added to the network to force changes only in \\(b_{k}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.189, + 0.468, + 0.237 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {m i x i n g}} ^ {(i)} = L _ {k} \\left(\\mathcal {C} _ {k} \\left(\\mathbf {x} _ {\\text {m i x}} ^ {(i)}\\right), y _ {k} ^ {(j)}\\right) + \\sum_ {l \\neq k} L _ {l} \\left(\\mathcal {C} _ {l} \\left(\\mathbf {x} _ {\\text {m i x}} ^ {(i)}\\right), y _ {l} ^ {(i)}\\right) \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.238, + 0.468, + 0.342 + ], + "angle": 0, + "content": "\\(L_{i}\\) are loss functions that vary based on the attribute types. For categorical labels, we use softmax with cross-entropy loss, whereas continuous labels are optimized using the \\(L_{1}\\) loss. In practice, we mix all attributes together from randomly chosen vectors. This introduces complex changes to the image and encourages the association of a single subspace with a single attribute." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.343, + 0.468, + 0.373 + ], + "angle": 0, + "content": "Finally, our model is trained using an objective function comprised of the three losses:" + }, + { + "type": "equation", + "bbox": [ + 0.093, + 0.38, + 0.469, + 0.416 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\lambda_ {\\text {o r t h}} \\mathcal {L} _ {\\text {o r t h}} + \\frac {1}{n} \\sum_ {i} \\mathcal {L} _ {\\text {r e c}} ^ {(i)} + \\lambda_ {\\text {m i x i n g}} \\mathcal {L} _ {\\text {m i x i n g}} ^ {(i)} \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.424, + 0.364, + 0.439 + ], + "angle": 0, + "content": "where \\(\\lambda_{orth}\\), \\(\\lambda_{mixing}\\) are hyperparameters." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.451, + 0.21, + 0.468 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.476, + 0.469, + 0.522 + ], + "angle": 0, + "content": "In this section, we evaluate the performance of our model compared to state-of-the-art image editing models, all of which utilize the StyleGAN generator for image synthesis." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.522, + 0.469, + 0.643 + ], + "angle": 0, + "content": "To test our model, we generated a source and target latent vector, projected them onto a subspace \\( S_{k} \\), and replaced the projections of the source vector with those from the target. Since our subspaces are orthogonal, we expect to see changes only in the corresponding attribute \\( b_{k} \\). Example results are presented in Fig. 2. Notably, if the source face wears glasses, these remain post-edit since we only incorporate pose, smile, and race from the target face." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.65, + 0.388, + 0.667 + ], + "angle": 0, + "content": "4.1. Comparison with Previous Methods" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.674, + 0.469, + 0.824 + ], + "angle": 0, + "content": "We compared our model with three previous image editing methods: InterFaceGAN [28], StyleFlow [3], and SeFa [29]. We evaluated the editing and disentanglement qualities of these models for a common set of attributes supported by all of them, such as age, gender, smile, pose, and glasses. Additionally, since our method discovers a subspace rather than a single direction, to ensure a fair comparison, we trained a linear SVM inside each subspace. We then used the normal to the hyperplane as the direction for editing. This model is used in Section 4.2 and Section 4.3." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.833, + 0.298, + 0.849 + ], + "angle": 0, + "content": "4.2. Qualitative Comparison" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Figure 3 offers a comparative assessment of the quality of real image editing. We inverted the images into StyleGAN's latent space using HyperStyle [4]. Our observations" + }, + { + "type": "image_caption", + "bbox": [ + 0.513, + 0.139, + 0.562, + 0.152 + ], + "angle": 0, + "content": "Source" + }, + { + "type": "image_caption", + "bbox": [ + 0.572, + 0.105, + 0.591, + 0.14 + ], + "angle": 0, + "content": "Target" + }, + { + "type": "image", + "bbox": [ + 0.607, + 0.088, + 0.691, + 0.151 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.706, + 0.089, + 0.787, + 0.151 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.803, + 0.089, + 0.884, + 0.151 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.512, + 0.169, + 0.593, + 0.231 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.609, + 0.168, + 0.691, + 0.231 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.706, + 0.168, + 0.787, + 0.231 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.803, + 0.168, + 0.884, + 0.231 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.512, + 0.233, + 0.593, + 0.295 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.609, + 0.233, + 0.691, + 0.295 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.706, + 0.233, + 0.787, + 0.295 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.803, + 0.233, + 0.884, + 0.295 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.512, + 0.297, + 0.593, + 0.359 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.609, + 0.297, + 0.691, + 0.359 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.706, + 0.297, + 0.787, + 0.359 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.803, + 0.297, + 0.884, + 0.359 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.375, + 0.892, + 0.42 + ], + "angle": 0, + "content": "Figure 2: Image editing capabilities using source images and target attribute images. The attributes derived from the target images include pose, smile, and race." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.446, + 0.892, + 0.627 + ], + "angle": 0, + "content": "indicate that multiple edits on a single image can significantly diminish its quality, making it more prone to visual artifacts. Moreover, due to biases in the FFHQ dataset [19], some attributes are more correlated in StyleGAN's latent space than others (e.g., younger individuals are less likely to wear glasses). As depicted in Fig. 3, while most models can effectively modify a single attribute, our model outperforms others in terms of accuracy when changing all attributes simultaneously and better maintains each individual attribute edit. Sequential editing is illustrated in Fig. 4, showing that as edits progress, the images retain previous attributes without a loss in quality." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.628, + 0.892, + 0.779 + ], + "angle": 0, + "content": "In Fig. 1 we visualize our model's capability of generating diverse results for different attributes due to its multidirectional nature. The images are generated by shifting the latent vectors to different directions inside the relevant subspace. We found that some attributes (e.g., smile, pose) behave like binary attributes, meaning they contain most of the information in a single direction. Others (e.g., gender, age), however, can be edited in multiple directions resulting in various images. Additional results can be found in the supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.787, + 0.733, + 0.804 + ], + "angle": 0, + "content": "4.3.Quantitative Comparison" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.901 + ], + "angle": 0, + "content": "To evaluate our model's disentanglement capabilities, we develop and utilize two different methods: attribute correlation and face preservation. Furthermore, to measure the diversity introduced by multi-directional subspace editing, we utilize the LPIPS score [33] and the Frechet Inception Distance (FID) [14] to evaluate image fidelity." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7142" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.071, + 0.088, + 0.91, + 0.844 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.853, + 0.893, + 0.884 + ], + "angle": 0, + "content": "Figure 3: Comparison of real image editing between our method and the baseline approaches. The edit direction for each attribute was determined using a linear SVM classifier." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7143" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.089, + 0.473, + 0.282 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.117, + 0.293, + 0.428, + 0.309 + ], + "angle": 0, + "content": "Figure 4: Sequential human face editing result." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.336, + 0.468, + 0.427 + ], + "angle": 0, + "content": "Correlation between edited attributes: We can assign an attribute score to an image \\(\\mathbf{x}\\) using \\(\\mathcal{C}_k\\) as a feature extractor. The activation vector \\(l(\\mathbf{x})\\), derived from the last hidden layer of \\(\\mathcal{C}_k\\), is used to compute the distance between the feature vector \\(l(\\mathbf{x})\\) and the classifying hyperplane. This hyperplane is defined by \\(\\{\\mathbf{v} \\mid \\mathbf{c}_k^T\\mathbf{v} + \\mathbf{t}_k = 0\\}\\)." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.428, + 0.468, + 0.478 + ], + "angle": 0, + "content": "The attribute score of an image \\(\\mathbf{x}\\) is given by the distance of \\(l(\\mathbf{x})\\) from the separating hyperplane: \\(dist_{k}(\\mathbf{x}) = \\frac{\\mathbf{c}_{k}^{T}l(\\mathbf{x}) + \\mathbf{t}_{k}}{|\\mathbf{c}_{k}|}\\)." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.478, + 0.468, + 0.508 + ], + "angle": 0, + "content": "To assess the disentanglement capability of our model, we began by generating an evaluation set comprising \\( 1K \\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.212 + ], + "angle": 0, + "content": "pairs of images paired with their desired face attributes. These images were directly sampled from the StyleGAN generator, while the attributes were independently generated for each image. For each image, we manipulated its latent vector \\(\\mathbf{w} \\in \\mathcal{W}^{+}\\) along the learned directions and fed it to the generator to produce an edited version, denoted as \\(\\mathbf{x}_{edit}\\). It's worth noting that in practice we change all attributes simultaneously." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.213, + 0.892, + 0.274 + ], + "angle": 0, + "content": "Next, we measured the difference in attribute score between the original and the edited images. Taking the attribute \"smile\" as an example, we defined the perceptual distance as: \\(\\Delta_{smile} = dist_{smile}(\\mathbf{x}_{edit}) - dist_{smile}(\\mathbf{x})\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.274, + 0.892, + 0.378 + ], + "angle": 0, + "content": "For the final assessment, we computed the Pearson correlation between the perceptual distances of every pair of attributes. Each entry in Table 1 displays the absolute correlation value. For instance, for the attributes \"smile\" and \"pose\", we determine the perceptual distances \\(\\Delta_{smile}\\) and \\(\\Delta_{pose}\\) across the entire evaluation set. The correlation value shown in the table is:" + }, + { + "type": "equation", + "bbox": [ + 0.534, + 0.388, + 0.892, + 0.423 + ], + "angle": 0, + "content": "\\[\n\\operatorname {c o r r} (\\text {p o s e}, \\text {s m i l e}) = \\left| \\frac {\\operatorname {c o v} \\left(\\Delta_ {\\text {p o s e}} , \\Delta_ {\\text {s m i l e}}\\right)}{E \\left[ \\Delta_ {\\text {p o s e}} \\right] E \\left[ \\Delta_ {\\text {s m i l e}} \\right]} \\right| \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.433, + 0.892, + 0.508 + ], + "angle": 0, + "content": "Table 1 presents the correlation results of various methods. As previously mentioned [8, 12, 28, 29], we observe that certain attributes exhibit stronger correlations than others. For instance, the glasses-age correlation is consistently higher than the smile-pose correlation across all models." + }, + { + "type": "table_caption", + "bbox": [ + 0.233, + 0.529, + 0.735, + 0.544 + ], + "angle": 0, + "content": "Table 1: Attribute correlation matrices of edited images (in absolute values)." + }, + { + "type": "table", + "bbox": [ + 0.151, + 0.554, + 0.815, + 0.898 + ], + "angle": 0, + "content": "
(a) SeFa(b) InterFaceGan
PoseSmileAgeGenderGlassesposeSmileAgeGenderGlasses
Pose1.0000.1500.0390.1330.051Pose1.0000.0980.0900.0170.079
Smile0.1501.0000.0010.1700.233Smile0.0981.0000.1540.1980.084
Age0.0390.0011.0000.5330.367Age0.0900.1541.0000.5650.600
Gender0.1330.1700.5331.0000.339Gender0.0170.1980.5651.0000.363
Glasses0.0510.2330.3670.3391.000Glasses0.0790.0840.6000.3631.000
Avg0.0930.1150.2350.2930.247Avg0.0710.1330.3520.2850.281
(c) StyleFlow(d) Ours
PoseSmileAgeGenderGlassesPoseSmileAgeGenderGlasses
Pose1.0000.1130.1260.1030.056Pose1.0000.0180.0080.0290.046
Smile0.1131.0000.2640.0110.074Smile0.0181.0000.1200.0500.100
Age0.1260.2641.0000.5810.494Age0.0080.1201.0000.3880.363
Gender0.1030.0110.5811.0000.338Gender0.0290.0500.3881.0000.203
Glasses0.0560.0740.4940.3381.000Glasses0.0460.1000.3630.2031.000
Avg0.0990.1150.3660.2580.240Avg0.0250.0720.2190.1670.178
" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7144" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.471, + 0.155 + ], + "angle": 0, + "content": "The table's final row sums the off-diagonal columns, representing the average correlation score. Our method's lower scores highlight its superior disentanglement capabilities compared to the other techniques." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.159, + 0.471, + 0.326 + ], + "angle": 0, + "content": "In our previous assessment, all attributes were adjusted simultaneously. To test the stability of attributes when only one is modified, we conducted an experiment editing one attribute at a time and measured the perceptual distances using the classifiers' final layers. Fig. 5 displays results from various methods. The x-axis represents changes in the edited attribute, while the y-axis indicates unintentional changes in other attributes. As edits become more extensive, the inter-attribute effect is more pronounced. Among all models, our approach shows the least deviation, indicating superior attribute disentanglement." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.331, + 0.473, + 0.422 + ], + "angle": 0, + "content": "Face Identity Preservation: Following the approach of the face identity score [3], we assess the edited images using a pre-trained face embedding network [9]. We restricted our edits to attributes that should preserve identity, such as pose, glasses, and smile. After editing, we embedded the images into a latent space using the network. We then calculated" + }, + { + "type": "table_caption", + "bbox": [ + 0.507, + 0.09, + 0.884, + 0.107 + ], + "angle": 0, + "content": "Table 2: Identity preservation scores by different models." + }, + { + "type": "table", + "bbox": [ + 0.513, + 0.116, + 0.88, + 0.257 + ], + "angle": 0, + "content": "
EditMetricSeFaInterFaceGanStyleFlowOurs
SmileCs ↑0.9700.9780.9890.991
Ed ↓0.3290.2760.1920.174
PoseCs ↑0.9780.9790.9810.982
Ed ↓0.2830.2790.26620.253
GlassesCs ↑0.9660.9780.9840.985
Ed ↓0.3480.2700.2270.215
AllCs ↑0.9110.9330.9350.948
Ed ↓0.6220.5370.5340.467
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.5, + 0.258, + 0.89, + 0.273 + ], + "angle": 0, + "content": "Notation: \\( C_s \\) - Cosine Similarity; \\( E_d \\) - Euclidean Distance." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.314, + 0.892, + 0.345 + ], + "angle": 0, + "content": "the Euclidean distance, \\(E_{d}\\), and the cosine similarity, \\(C_s\\), between the original and edited images." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.346, + 0.893, + 0.422 + ], + "angle": 0, + "content": "Table 2 displays the results for face identity preservation. Our method consistently surpasses other techniques across all types of edits. While StyleFlow shows comparable scores for individual attribute edits, our model excels in preserving identity when multiple edits are combined." + }, + { + "type": "image", + "bbox": [ + 0.102, + 0.449, + 0.245, + 0.524 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.256, + 0.449, + 0.4, + 0.523 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.41, + 0.449, + 0.552, + 0.523 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.562, + 0.449, + 0.705, + 0.523 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.717, + 0.449, + 0.86, + 0.523 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.102, + 0.529, + 0.244, + 0.602 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.258, + 0.529, + 0.399, + 0.602 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.411, + 0.529, + 0.552, + 0.602 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.562, + 0.529, + 0.704, + 0.602 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.717, + 0.529, + 0.86, + 0.602 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.102, + 0.608, + 0.244, + 0.681 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.258, + 0.608, + 0.399, + 0.681 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.411, + 0.608, + 0.552, + 0.681 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.562, + 0.608, + 0.704, + 0.681 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.717, + 0.608, + 0.86, + 0.681 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.102, + 0.687, + 0.244, + 0.761 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.258, + 0.687, + 0.399, + 0.761 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.411, + 0.687, + 0.552, + 0.761 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.562, + 0.687, + 0.704, + 0.761 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.717, + 0.687, + 0.86, + 0.761 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.102, + 0.767, + 0.244, + 0.84 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.258, + 0.767, + 0.398, + 0.84 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.411, + 0.767, + 0.552, + 0.84 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.562, + 0.767, + 0.704, + 0.84 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.717, + 0.767, + 0.86, + 0.84 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.075, + 0.851, + 0.894, + 0.898 + ], + "angle": 0, + "content": "Figure 5: Comparative analysis of the inter-attribute effects exhibited by different models. The upper rows display how changes in one attribute vary as a function of changes in another attribute. The bottom row provides an average of all the rows above." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "7145" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.091, + 0.254, + 0.108 + ], + "angle": 0, + "content": "4.4. Diversity Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.115, + 0.47, + 0.237 + ], + "angle": 0, + "content": "In the previous sections, we introduced a single-direction variant of our model. Now, we will explore the performance of our model when multiple directions in the subspace are utilized for editing. To measure the diversity of the images produced by our model, we employed the LPIPS perceptual similarity score [33]. A lower LPIPS score indicates higher similarity between images, whereas a higher score signifies perceptual differences." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.238, + 0.471, + 0.374 + ], + "angle": 0, + "content": "We generated a batch of 1,000 images and applied 5 random edits to each image. For every set of 5 edits, the similarity score between each pair of edited images was computed. Subsequently, all these scores were averaged to derive the final diversity score. We benchmarked our model against StyleFlow and the single-direction variant of our model, referred to as SVM, as detailed in Section 4.1. The FID score was also calculated to assess the visual quality of the generated images." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.375, + 0.47, + 0.496 + ], + "angle": 0, + "content": "The results, summarized in Table 3, reveal that our approach — when multi-directional subspace editing is employed — not only fosters greater image diversity (as indicated by the LPIPS score) but also ensures superior visual quality (as denoted by the FID score). It's noteworthy that there is a marked enhancement in the multi-directional iteration of our model (subspace) when compared against its single-direction counterpart (SVM) or against StyleFlow." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.512, + 0.47, + 0.573 + ], + "angle": 0, + "content": "Table 3: Diversity score results for edited images. Our multi-directional model achieves a higher score which indicates its ability to generate more diverse results while maintaining a lower FID score." + }, + { + "type": "table", + "bbox": [ + 0.163, + 0.584, + 0.388, + 0.649 + ], + "angle": 0, + "content": "
MethodLPIPS ↑FID ↓
StyleFlow0.21327.467
Our (svm)0.22926.926
Our (subspace)0.32123.648
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.679, + 0.231, + 0.696 + ], + "angle": 0, + "content": "4.5. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.703, + 0.47, + 0.809 + ], + "angle": 0, + "content": "To validate the importance of our orthogonality loss outlined in Section 3.2, we carried out an ablation study. We trained a version of our model with \\(\\lambda_{orth} = 0\\), keeping all other configurations, including losses and the training process, consistent. Post-training, we conducted consecutive edits starting from an original image, and the results can be viewed in Fig. 6." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.471, + 0.901 + ], + "angle": 0, + "content": "We found that images edited with the orthogonality loss exhibit crisper details and fewer visual artifacts when subjected to multiple edits. We also carried out the same quantitative evaluations as detailed in Section 4.3. The results in Tables 4 and 5 indicate that our orthogonality loss leads to better attribute disentanglement in our model." + }, + { + "type": "equation", + "bbox": [ + 0.667, + 0.09, + 0.738, + 0.105 + ], + "angle": 0, + "content": "\\[\n\\lambda_ {o r t h} = 0\n\\]" + }, + { + "type": "image", + "bbox": [ + 0.513, + 0.108, + 0.61, + 0.171 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.619, + 0.109, + 0.699, + 0.171 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.709, + 0.108, + 0.79, + 0.171 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.8, + 0.108, + 0.881, + 0.171 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.512, + 0.173, + 0.61, + 0.235 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.619, + 0.173, + 0.699, + 0.235 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.709, + 0.173, + 0.789, + 0.235 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.8, + 0.173, + 0.881, + 0.235 + ], + "angle": 0, + "content": null + }, + { + "type": "equation", + "bbox": [ + 0.656, + 0.238, + 0.752, + 0.253 + ], + "angle": 0, + "content": "\\[\n\\lambda_ {o r t h} = 0. 0 0 1\n\\]" + }, + { + "type": "image", + "bbox": [ + 0.512, + 0.252, + 0.61, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.619, + 0.253, + 0.699, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.709, + 0.253, + 0.789, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.8, + 0.252, + 0.881, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.512, + 0.317, + 0.61, + 0.379 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.619, + 0.317, + 0.699, + 0.379 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.709, + 0.317, + 0.789, + 0.379 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.8, + 0.317, + 0.881, + 0.379 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.393, + 0.893, + 0.454 + ], + "angle": 0, + "content": "Figure 6: Comparison using orthogonality loss: First and third rows show reduced pose-glasses entanglement; second and fourth rows show better preservation of hair and shirt color." + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.471, + 0.892, + 0.515 + ], + "angle": 0, + "content": "Table 4: Attribute correlation matrices with and without orthogonal loss. The values represent the average correlation between an attribute and others." + }, + { + "type": "table", + "bbox": [ + 0.501, + 0.528, + 0.853, + 0.579 + ], + "angle": 0, + "content": "
ModelPoseSmileAgeGenderGlasses
λorth = 00.1490.2420.3420.2830.253
λorth = 0.0010.0250.0720.2190.1670.178
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.593, + 0.89, + 0.622 + ], + "angle": 0, + "content": "Table 5: Comparison of identity preservation using orthogonal loss." + }, + { + "type": "table", + "bbox": [ + 0.567, + 0.635, + 0.828, + 0.684 + ], + "angle": 0, + "content": "
EditMetricλorth=0λorth=0.001
AllCs↑0.9320.948
Ed↓0.5360.467
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.5, + 0.685, + 0.89, + 0.699 + ], + "angle": 0, + "content": "Notation: \\( C_s \\) - Cosine Similarity; \\( E_d \\) - Euclidean Distance." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.739, + 0.627, + 0.755 + ], + "angle": 0, + "content": "5. Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this work we proposed MDSE, a disentangling generative model for multi-attribute image editing. We introduce the concept of orthogonal subspaces that support multi-directional edits for diverse image generation. Additionally, this model effectively identifies disentangled latent subspaces, allowing precise control over the generated images and the displayed face attributes. We believe that integrating these concepts during the generator's training could further enhance the performance of disentangled models." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "7146" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.079, + 0.09, + 0.176, + 0.107 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Rameen Abdul, Yipeng Qin, and Peter Wonka. Image2stylegan: How to embed images into the stylegan latent space? In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 4432-4441, 2019. 1, 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.173, + 0.472, + 0.228 + ], + "angle": 0, + "content": "[2] Rameen Abdul, Yipeng Qin, and Peter Wonka. Image2stylegan++: How to edit the embedded images? 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 586-595, 2018. 5, 9" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.471, + 0.444 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.956 + ], + "angle": 0, + "content": "7148" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-Directional Subspace Editing in Style-Space/a84347b3-c2c0-42e5-a59b-c77ba1dcbff7_origin.pdf b/2023/Multi-Directional Subspace Editing in Style-Space/a84347b3-c2c0-42e5-a59b-c77ba1dcbff7_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..91ee5811970f20de1336edc20d234c7296f8b09d --- /dev/null +++ b/2023/Multi-Directional Subspace Editing in Style-Space/a84347b3-c2c0-42e5-a59b-c77ba1dcbff7_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:202758bd7e9f5e4da009892ae06b8d855f2ef86111e22fd777ea95d0fd06eb10 +size 7121193 diff --git a/2023/Multi-Directional Subspace Editing in Style-Space/full.md b/2023/Multi-Directional Subspace Editing in Style-Space/full.md new file mode 100644 index 0000000000000000000000000000000000000000..243228e881b5db1f5b001a0dd066007b35b4059e --- /dev/null +++ b/2023/Multi-Directional Subspace Editing in Style-Space/full.md @@ -0,0 +1,425 @@ +# Multi-Directional Subspace Editing in Style-Space + +Chen Naveh + +School of Computer Science, Reichman University + +navehchen1@gmail.com + +![](images/e7bc74e7e4686bb092744be81a40227e2cda62c5c76540f74541bced61e381c4.jpg) +Figure 1: Multi-directional human face editing. Each row indicates changes in a subspace associated with a particular attribute: (top to bottom) gender, age and race. + +# Abstract + +This paper describes a new technique for finding disentangled semantic directions in the latent space of StyleGAN. Our method identifies meaningful orthogonal subspaces that allow editing of one human face attribute, while minimizing undesired changes in other attributes. Our model is capable of editing a single attribute in multiple directions, resulting in a range of possible generated images. We compare our scheme with three state-of-the-art models and show that our method outperforms them in terms of face editing and disentanglement capabilities. Additionally, we suggest quantitative measures for evaluating attribute separation and disentanglement, and exhibit the superiority of + +our model with respect to those measures1. + +# 1. Introduction + +Recent developments in computer vision have enabled the generation of photorealistic, high-resolution synthetic images. The most notable technique is Generative Adversarial Networks (GANs) [11], which have advanced the progress of many applications, including image generation, super-resolution, image inpainting, and more. In particular, the generator of StyleGAN [1], one of the most notable GAN models, has been extensively explored by researchers. + +StyleGAN samples a latent vector $\mathbf{z} \in \mathbb{R}^{512}$ from a + +Gaussian distribution $\mathcal{N}(\mathbf{0},\mathbf{I})$ , and maps it to an intermediate vector $\mathbf{w}\in \mathcal{W} = \mathbb{R}^{512}$ using a mapping network. This vector is then used to generate a 1024x1024 RGB image. The vector $\mathbf{w}$ is inserted into 18 multi-resolution style blocks that control various characteristics of the synthesized image. Vectors at lower resolutions determine high-level features such as pose and hair. Intermediate resolutions affect facial expressions, while vectors at higher resolutions dictate fine details like colors and texture. The original StyleGAN model uses the $\mathcal{W}$ latent space and the same $\mathbf{w}$ vector for all 18 style blocks. Subsequent studies [1,2,26,32] utilize the $\mathcal{W}^{+} = \mathbb{R}^{18\cdot 512}$ space, which extends the $\mathcal{W}$ space, and applies different $\mathbf{w}$ vectors to different style blocks. This allows for enhanced control over the resulting image. The $\mathcal{W}^{+}$ latent space is commonly used for inverse mapping, converting an image into $\mathbf{w}\in \mathcal{W}^{+}$ . + +Recent works have explored methods for gaining control over the synthesized images by altering the latent space vectors [3, 7, 12, 25, 28, 29]. For instance, shifting the latent vector of a generated image towards the direction corresponding to "smile" can progressively amplify the smile in the output image. While these methods showcase impressive and realistic editing capabilities, pinpointing the attribute directions remains a challenge. One approach is to use vectors in latent space sampled from the GAN model combined with attribute ground truth (either manually labeled or determined using a pre-trained attribute estimator) [10, 16, 28]. A linear classifier in the latent space is then employed. The normal to the classification boundary corresponds to the most significant direction of the attribute. These models often suffer from issues of entangled data and biases in the training set. Such biases might result in attribute correlations, like glasses with age or beard with gender. Consequently, adding glasses to a face may inadvertently age it. Other methods use unsupervised techniques [12, 29], such as PCA, to find meaningful orthogonal directions in the latent space. However, these directions typically require subjective human post-annotation to link directions to attributes in the synthesized images. All these models share the notion of a singular direction for each attribute, despite the possibility of some attributes defined by multiple dimensions (e.g., age might be affected by factors like hair color and skin wrinkles, see Fig. 1). + +In this work, we present MDSE, an acronym for Multi-Directional Subspace Editing. This framework aims to identify orthogonal semantics within the latent space of a pre-trained StyleGAN. Our goal is to discover meaningful subspaces that are mutually orthogonal, with each subspace controlling specific facial attributes. "Multi-directional editing" means altering a latent vector within a particular subspace in various directions. This approach enables the generation of a wide range of images, each varying in a specific attribute. Furthermore, because the subspaces are + +mutually orthogonal, modifications in one attribute result in minimal changes to others. We explore the disentanglement capabilities of our model and quantitatively assess its performance in comparison to leading image editing techniques. + +# 2. Related Work + +# 2.1. Generative Adversarial Networks (GANs) + +Generative models have revolutionized the generation of vast amounts of visual content. They can produce visually compelling content with remarkable fidelity, making them indispensable for image editing applications. GAN models learn a mapping from a specific distribution (usually Gaussian or uniform) to the target distribution. The generator $G(\cdot)$ is trained to fool an adversary $D(\cdot)$ , which aims to differentiate between the generated images and the real ones. Both models $G(\cdot)$ and $D(\cdot)$ are trained concurrently using the min-max loss [11]. The GAN approach is widely recognized and often outperforms other techniques, such as variational autoencoders (VAEs) [21]. Recently, denoising diffusion probabilistic models (DDPM) [15] have risen in prominence and showcased superior results. However, despite their leading performance in image generation, their potential in image editing and semantic interpretation remains relatively unexplored. In this work, our attention is centered on a GAN-based generator, specifically the StyleGAN [18-20], which exhibits exceptional capability in the human face domain. + +GAN Latent Space. Given a pre-trained generator $\mathbf{x} = G(\mathbf{w})$ , GAN inversion $\hat{\mathbf{w}} = G^{-1}(\mathbf{x})$ is the process of inverting a specified image $\mathbf{x}$ into a latent vector $\hat{\mathbf{w}}$ that faithfully reconstructs the image using the generator. In other words, $G(\hat{\mathbf{w}})\approx \mathbf{x}$ . Most of the common methods either train an encoder [24, 26, 32] from the image space into the latent space or optimize the latent vector, using backpropagation, directly until it generates the desired image [1, 2, 22]. Recent approaches that modify the generator's weight have gained traction, resulting in enhanced image reconstruction [5, 27]. Previous works show that the latent space of a pretrained GAN model encodes image semantics in a meaningful structure. Hence, latent codes corresponding to images with similar semantics tend to cluster closely in the latent space [28]. For instance, within the domain of human face generation, faces sharing characteristics (e.g., being young and blond) will have nearby latent vectors. This foundational insight drives modern image editing techniques. + +# 2.2. Multi-Directional Manipulation in Latent Space + +The idea of editing an image through latent space manipulation has been extensively explored in recent years [7,25]. Such approaches aim to harness the strong capabilities of + +the generator. Therefore, they keep the generator network static and conduct vector operations solely in the latent space. Recent works primarily rely on a linear latent space assumption and demonstrate pleasing-looking results of image editing by adding or subtracting vectors within the latent space [12, 28, 29]. InterFaceGAN [28] employs pretrained binary classifiers to label images with facial features, such as young-old, male-female, and with/without glasses, among others. It then trains a linear classifier (specifically, a Support Vector Machine or SVM) on the respective latent vectors to derive a classifying hyperplane. The normal to this hyperplane serves as the 1D direction for editing the relevant attribute. + +GANSpace [12] adopts a data-driven approach, applying PCA on a set of vectors sampled from $\mathcal{W}$ to find meaningful directions. The eigenvectors associated with the largest eigenvalues serve as the editing directions. Some derived directions can be entangled, such as head rotation and gender. To address this issue, edits are restricted to a specifically selected subset of the generator's layers. + +Another work, SeFa [29], avoids the image sampling pre-processing step. Instead, it determines a closed-form factorization of the latent space by utilizing an eigendecomposition of the generator's weights. For StyleGAN, the style affine transformation matrices are employed for vector decomposition. The eigenvectors corresponding to the greatest variations are selected to define the semantic directions. However, this unsupervised method faces two main issues. Firstly, there's a subjective post-annotation process to match the directions with relevant semantics. Secondly, the directions that are derived often mix several semantics (e.g., age and glasses), a result of biases present in the training data. + +A distinct set of studies moves away from the linear approach, opting instead to learn non-linear functions to manipulate latent vectors. StyleFlow [3] employs continuous normalizing flows conditioned on the image attribute vector. This attribute vector must be provided using pre-trained networks before every edit. Another non-linear approach is StyleRig [30], which incorporates a 3D semantic network and harnesses it to perform rigid edits such as pose and light. Although non-linear approaches generally perform better, our research primarily emphasizes the more comprehensive linear approach. + +All previous methods that manipulate the latent space of StyleGAN define a semantic as a singular direction. Both linear and non-linear approaches ultimately derive positive and negative directions for editing a desired attribute. We believe that this oversimplification may restrict the editing capabilities and limit the diversity of the generated images. For example, imagine we want to edit the gender of a given face. One person may argue that hairstyle is a distinguishing factor between men and women, while another might think + +of facial structure or the presence of facial hair as a more prominent factor. In this work, we overcome this variability by associating an attribute with an $n$ -dim subspace where $n \geq 1$ , containing more than a single direction, in the semantic space. We call this a multi-directional subspace, as different vectors within the subspace can affect the resulting image differently, but all affect the associated attribute (see examples in Fig. 1). We also require different attributes to be associated with mutually orthogonal subspaces, to promote disentanglement between attributes. + +We outline our contributions as follows: + +- We propose MDSE to extend the concept of meaningful latent directions to multi-directional subspaces, thereby diversifying and expanding the capabilities of the editing process. +- MDSE identifies orthogonal directions in StyleGAN's latent space, to promote disentanglement. We introduce an orthogonality loss in the model training and demonstrate its significance in preserving some image attributes while editing others. We visualize the results and demonstrate improved results in consecutive edits of multiple attributes (refer to Fig. 4). +- We develop a new metric for evaluating the disentanglement properties of image editing. In addition to the conventional approaches of visual comparisons, we suggest using our evaluation metrics as a quantitative measurement of disentanglement capabilities. + +# 3. Method + +Given a set of attributes, $B \triangleq \{ \text{gender}, \text{ glasses}, \dots \}$ , we aim to find a subspace for each attribute $b_i \in B$ so that editing within this subspace leads to changes in the associated attribute $b_i$ . Different directions in each subspace are responsible for distinct visual semantics. To achieve disentanglement, we desire that each subspace solely influences its respective attribute. + +Certain attributes, such as glasses and age, have been observed to correlate with each other [28], making disentangled editing challenging. To overcome this problem, our model seeks to decompose the latent space $\mathcal{W}^+$ into multiple orthogonal subspaces each of which is associated with a single attribute. This requirement has two main outcomes. Firstly, editing within a subspace facilitates multidirectional edits of a single attribute. Secondly, the orthogonality ensures that altering a specific facial attribute doesn't affect other attributes. + +# 3.1. Latent Space Decomposition + +We decompose $\mathcal{W}^+$ into $N + 1$ orthogonal subspaces $\{S_i\}_{i = 0}^N$ and define each subspace $S_{i}$ as + +$$ +S _ {i} \triangleq \operatorname {s p a n} \left\{\mathbf {p} _ {i} ^ {1}, \mathbf {p} _ {i} ^ {2}, \dots , \mathbf {p} _ {i} ^ {n _ {i}} \right\}, n _ {i} < \dim (\mathcal {W} ^ {+}) \tag {1} +$$ + +where $\mathbf{p}_i^j\in \mathcal{W}^+$ , and $\{\mathbf{p}_i^j\}_{j = 1}^{n_i}$ are linearly independent vectors. Therefore, $\{\mathbf{p}_i^j\}_{j = 1}^{n_i}$ form a basis for subspace $S_{i}$ with cardinality $n_i$ . There are $N + 1$ subspaces, where $N = |B|$ is the size of the attribute set $B$ . Each $S_{i}$ corresponds to $b_{i}$ respectively, while $S_0$ is associated with all other information that is not labeled in $B$ . This may include other semantics, e.g., clothing and image background. The correspondence of $S_{i}$ and $b_{i}$ will be elaborated on later in the paper. + +To ensure orthogonality, we require the following conditions: + +$$ +S _ {i} \subset \mathcal {W} ^ {+}, \forall i \in \{0, \dots , N \} \tag {2} +$$ + +$$ +\bigoplus_ {i = 0} ^ {N} S _ {i} = \mathcal {W} ^ {+} \tag {3} +$$ + +$$ +S _ {i} \perp S _ {j}, \forall i \neq j \tag {4} +$$ + +where $\bigoplus$ denotes direct sum, and $\perp$ signifies orthogonal subspaces. Notice that the entire vector set $\{\mathbf{p}_i^j\}$ forms a basis for $\mathcal{W}^+$ . As a result, we can uniquely express every vector $\mathbf{w} \in \mathbb{R}^{18 \cdot 512}$ with a set of scalars $\{a_i^j\}$ and represent $\mathbf{w}$ as the following linear combination: + +$$ +\mathbf {w} = \sum_ {i = 0} ^ {N} \sum_ {j = 1} ^ {n _ {i}} a _ {i} ^ {j} \mathbf {p} _ {i} ^ {j} \tag {5} +$$ + +This expression can also be represented in matrix form: + +$$ +\mathbf {w} = \left[ \underbrace {\left[ \begin{array}{c c c} | & & | \\ \mathbf {p} _ {0} ^ {1} & \dots & \mathbf {p} _ {0} ^ {n _ {0}} \\ | & & | \end{array} \right]} _ {\mathbf {P} _ {0}} \dots \underbrace {\left[ \begin{array}{c c c} | & & | \\ \mathbf {p} _ {N} ^ {1} & \dots & \mathbf {p} _ {N} ^ {n _ {N}} \\ | & & | \end{array} \right]} _ {\mathbf {P} _ {N}} \right] \left[ \begin{array}{c} \left[ \begin{array}{c} a _ {0} ^ {1} \\ \vdots \\ a _ {0} ^ {n _ {0}} \end{array} \right] \\ \vdots \\ \left[ \begin{array}{c} a _ {N} ^ {1} \\ \vdots \\ a _ {N} ^ {n _ {N}} \end{array} \right] \end{array} \right] \tag {6} +$$ + +$$ +\mathbf {w} = \sum_ {i = 0} ^ {N} \mathbf {P} _ {i} \mathbf {a} _ {i} = \underbrace {\left[ \mathbf {P} _ {0} , \cdots , \mathbf {P} _ {N} \right]} _ {\mathbf {P}} \underbrace {\left[ \begin{array}{c} \mathbf {a} _ {0} \\ \vdots \\ \mathbf {a} _ {N} \end{array} \right]} _ {\mathbf {a}} \tag {7} +$$ + +where $\mathbf{P}$ is a matrix defined by: + +$$ +\mathbf {P} = \left[ \mathbf {p} _ {0} ^ {1} \dots \mathbf {p} _ {0} ^ {n _ {0}} \dots \mathbf {p} _ {N} ^ {1} \dots \mathbf {p} _ {N} ^ {n _ {N}} \right] \tag {8} +$$ + +and $\mathbf{a}^T = [\mathbf{a}_0^T,\dots ,\mathbf{a}_N^T ]$ is a vector of coefficients. Finding $\mathbf{P}$ that satisfies Eq. (2)-(4) is the core part of our framework. + +# 3.2. Training Procedure + +Our dataset consists of a set of 2,000 vector pairs $\left\{(\mathbf{w}^{(i)},\mathbf{y}^{(i)})\right\}_{i = 1}^{2000}$ . The latent vectors $\{\mathbf{w}^{(i)}\}$ are generated from random vectors sampled from a Gaussian distribution $\mathbf{z}^{(i)}\sim \mathcal{N}(0,1)$ and then mapped to $\mathcal{W}^+$ space using the StyleGAN mapping function: $\mathbf{w}^{(i)} = M(\mathbf{z}^{(i)})$ . Each sample $\mathbf{w}^{(i)}\in \mathbb{R}^{18\cdot 512}$ is mapped onto the image space using the StyleGAN generator, $\mathbf{x}^{(i)} = G(\mathbf{w}^{(i)})$ and then annotated using pre-trained classifiers to determine an attribute score vector: + +$$ +\mathbf {y} ^ {(i)} \triangleq \left(y _ {1} ^ {(i)}, \dots , y _ {N} ^ {(i)}\right) = \left(\mathcal {C} _ {1} \left(\mathbf {x} ^ {(i)}\right), \dots , \mathcal {C} _ {N} \left(\mathbf {x} ^ {(i)}\right)\right) \tag {9} +$$ + +Here, each $y_{k}^{(i)}$ denotes the $b_{k}$ attribute score for sample $i$ . Depending on the attribute, $y_{k}^{(i)}$ is either a discrete or continuous number. $C_k$ represents the pre-trained classifier for attribute $k$ . For age, smile, gender, and glasses, we used the face attribute classifier from [13] trained on the FFHQ dataset [19]. For the pose attribute, we utilized img2pose [6] for face estimation. Additionally, we employed a race classifier [17] trained on the Yahoo YFCC100M dataset [31]. + +The primary goal during the training phase is to determine the matrix $\mathbf{P}$ and use it to reconstruct all samples from the training set. To satisfy Eq. (5), we jointly learn a vector $\mathbf{a}^{(i)}$ for each vector $\mathbf{w}^{(i)}$ such that $\mathbf{w}^{(i)} = \mathbf{P}\mathbf{a}^{(i)}$ . We then introduce the following loss: + +$$ +\mathcal {L} _ {r e c} ^ {(i)} = \left\| \mathbf {w} ^ {(i)} - \mathbf {P} \mathbf {a} ^ {(i)} \right\| _ {1} \tag {10} +$$ + +where $\mathcal{L}_{rec}$ represents the reconstruction loss. Instead of pixel-based image reconstructions, we use a $L_{1}$ loss in the latent space using the original vector $\mathbf{w}^{(i)} = M(\mathbf{z}^{(i)})$ as the target value. + +Additionally, to enforce disentanglement, as referred in Eq. (4), we introduce an orthogonality loss: + +$$ +\mathcal {L} _ {\text {o r t h}} = \sum_ {i \neq j} \left\| \mathbf {P} _ {i} ^ {T} \mathbf {P} _ {j} \right\| _ {2} ^ {2} \tag {11} +$$ + +and require that the columns of matrices $\mathbf{P}_i, \mathbf{P}_j$ be orthogonal for $i \neq j$ , where $\|\cdot\|_2$ is the element-wise Frobenius-norm. + +Since learning disentangled representations is fundamentally impossible without a supervised inductive bias on the data [23], we leverage the attribute vector $\mathbf{y}^{(i)}$ and introduce a mixing loss to establish the association between $S_{k}$ and $b_{k}$ . Given a vector $\mathbf{w}^{(i)}$ , we can import attribute $b_{k}$ from a randomly chosen vector $\mathbf{w}^{(j)}$ , to generate $\mathbf{w}_{mix}^{(i)}$ : + +$$ +\mathbf {w} _ {m i x} ^ {(i)} = \mathbf {P} _ {k} \mathbf {a} _ {k} ^ {(j)} + \sum_ {l \neq k} \mathbf {P} _ {l} \mathbf {a} _ {l} ^ {(i)} \tag {12} +$$ + +and its corresponding image $\mathbf{x}_{mix}^{(i)}\triangleq G(\mathbf{w}_{mix}^{(i)})$ . For the modified image we require $\mathcal{C}_k(\mathbf{x}_{mix}^{(i)})$ to be similar to $y_{k}^{(j)}$ while keeping the other attributes unchanged. Thus a mixing loss is added to the network to force changes only in $b_{k}$ : + +$$ +\mathcal {L} _ {\text {m i x i n g}} ^ {(i)} = L _ {k} \left(\mathcal {C} _ {k} \left(\mathbf {x} _ {\text {m i x}} ^ {(i)}\right), y _ {k} ^ {(j)}\right) + \sum_ {l \neq k} L _ {l} \left(\mathcal {C} _ {l} \left(\mathbf {x} _ {\text {m i x}} ^ {(i)}\right), y _ {l} ^ {(i)}\right) \tag {13} +$$ + +$L_{i}$ are loss functions that vary based on the attribute types. For categorical labels, we use softmax with cross-entropy loss, whereas continuous labels are optimized using the $L_{1}$ loss. In practice, we mix all attributes together from randomly chosen vectors. This introduces complex changes to the image and encourages the association of a single subspace with a single attribute. + +Finally, our model is trained using an objective function comprised of the three losses: + +$$ +\mathcal {L} = \lambda_ {\text {o r t h}} \mathcal {L} _ {\text {o r t h}} + \frac {1}{n} \sum_ {i} \mathcal {L} _ {\text {r e c}} ^ {(i)} + \lambda_ {\text {m i x i n g}} \mathcal {L} _ {\text {m i x i n g}} ^ {(i)} \tag {14} +$$ + +where $\lambda_{orth}$ , $\lambda_{mixing}$ are hyperparameters. + +# 4. Experiments + +In this section, we evaluate the performance of our model compared to state-of-the-art image editing models, all of which utilize the StyleGAN generator for image synthesis. + +To test our model, we generated a source and target latent vector, projected them onto a subspace $S_{k}$ , and replaced the projections of the source vector with those from the target. Since our subspaces are orthogonal, we expect to see changes only in the corresponding attribute $b_{k}$ . Example results are presented in Fig. 2. Notably, if the source face wears glasses, these remain post-edit since we only incorporate pose, smile, and race from the target face. + +# 4.1. Comparison with Previous Methods + +We compared our model with three previous image editing methods: InterFaceGAN [28], StyleFlow [3], and SeFa [29]. We evaluated the editing and disentanglement qualities of these models for a common set of attributes supported by all of them, such as age, gender, smile, pose, and glasses. Additionally, since our method discovers a subspace rather than a single direction, to ensure a fair comparison, we trained a linear SVM inside each subspace. We then used the normal to the hyperplane as the direction for editing. This model is used in Section 4.2 and Section 4.3. + +# 4.2. Qualitative Comparison + +Figure 3 offers a comparative assessment of the quality of real image editing. We inverted the images into StyleGAN's latent space using HyperStyle [4]. Our observations + +![](images/14384cc1ded0a4abe5cd4f93c02d3b59b4932a9c4eaf6a14fa9b3e1c649a257f.jpg) +Target + +![](images/de54c180071dd3ae13b6076da8e4d56986238c97491c304e47ceb36dfc22feb9.jpg) + +![](images/6b313ae4ede17a9743535dbd3d5ab4261a7fb1436b1dc0d8aa1ef251b908f57d.jpg) + +![](images/d08a7dafc91efbfa9586a384f8d4373ebdc165bb2e019d502b6114f98275c45d.jpg) +Source + +![](images/7825f7968d8679811cd0d5689fb40e0c3cb79e8220ede40a18fb2b20abce398e.jpg) + +![](images/ffc37c481389a1cc86758e004711e627efcb6b986f26ad58c5aaba5488d8b343.jpg) + +![](images/247059b90714da11eb5440083038f2f5d208a3f59b8dc8e72fd72e2b587a7035.jpg) + +![](images/ff3409452355ea9c1b6a9fb4fa3a84176780d524ba90b6805c4b71a02b65354f.jpg) + +![](images/47b5e550e2876f5611aaec0964bcf73a9319ef736548002c0e0ae09589b82c9c.jpg) + +![](images/bb98f74605d501e84b2ac8bad3cb0fc6163e0d03ed228f84fcae9a10df211904.jpg) + +![](images/e33813b6c79e434797a4940f240ee5e85c9c2678536b9298bb31db0a30a62712.jpg) + +![](images/4173670af406049c43c578a265e330a4f52918659fcd16b7820e5ecccc6dc799.jpg) +Figure 2: Image editing capabilities using source images and target attribute images. The attributes derived from the target images include pose, smile, and race. + +![](images/d6a0ac7b46003b37512183beec056c82aba7f884ca507a1155d5d50f1ea10fc7.jpg) + +![](images/4236c2ac123d4fe47a709a85d7cf971896963d5bb5db2d2667a6128b843126e1.jpg) + +![](images/c36c3bcc744f653463c535a003dedcb6dd8e9d085239bad14994fc9710e97642.jpg) + +indicate that multiple edits on a single image can significantly diminish its quality, making it more prone to visual artifacts. Moreover, due to biases in the FFHQ dataset [19], some attributes are more correlated in StyleGAN's latent space than others (e.g., younger individuals are less likely to wear glasses). As depicted in Fig. 3, while most models can effectively modify a single attribute, our model outperforms others in terms of accuracy when changing all attributes simultaneously and better maintains each individual attribute edit. Sequential editing is illustrated in Fig. 4, showing that as edits progress, the images retain previous attributes without a loss in quality. + +In Fig. 1 we visualize our model's capability of generating diverse results for different attributes due to its multidirectional nature. The images are generated by shifting the latent vectors to different directions inside the relevant subspace. We found that some attributes (e.g., smile, pose) behave like binary attributes, meaning they contain most of the information in a single direction. Others (e.g., gender, age), however, can be edited in multiple directions resulting in various images. Additional results can be found in the supplementary material. + +# 4.3.Quantitative Comparison + +To evaluate our model's disentanglement capabilities, we develop and utilize two different methods: attribute correlation and face preservation. Furthermore, to measure the diversity introduced by multi-directional subspace editing, we utilize the LPIPS score [33] and the Frechet Inception Distance (FID) [14] to evaluate image fidelity. + +![](images/7e869f4bacbf0d82164eabe861c7b88312378c385d335a2dea5af44bc7c62370.jpg) +Figure 3: Comparison of real image editing between our method and the baseline approaches. The edit direction for each attribute was determined using a linear SVM classifier. + +![](images/ac137f7ae88d4f63ee23bce109a63705128733cd10dac47352e1c4cc429d4855.jpg) +Figure 4: Sequential human face editing result. + +Correlation between edited attributes: We can assign an attribute score to an image $\mathbf{x}$ using $\mathcal{C}_k$ as a feature extractor. The activation vector $l(\mathbf{x})$ , derived from the last hidden layer of $\mathcal{C}_k$ , is used to compute the distance between the feature vector $l(\mathbf{x})$ and the classifying hyperplane. This hyperplane is defined by $\{\mathbf{v} \mid \mathbf{c}_k^T\mathbf{v} + \mathbf{t}_k = 0\}$ . + +The attribute score of an image $\mathbf{x}$ is given by the distance of $l(\mathbf{x})$ from the separating hyperplane: $dist_{k}(\mathbf{x}) = \frac{\mathbf{c}_{k}^{T}l(\mathbf{x}) + \mathbf{t}_{k}}{|\mathbf{c}_{k}|}$ . + +To assess the disentanglement capability of our model, we began by generating an evaluation set comprising $1K$ + +pairs of images paired with their desired face attributes. These images were directly sampled from the StyleGAN generator, while the attributes were independently generated for each image. For each image, we manipulated its latent vector $\mathbf{w} \in \mathcal{W}^{+}$ along the learned directions and fed it to the generator to produce an edited version, denoted as $\mathbf{x}_{edit}$ . It's worth noting that in practice we change all attributes simultaneously. + +Next, we measured the difference in attribute score between the original and the edited images. Taking the attribute "smile" as an example, we defined the perceptual distance as: $\Delta_{smile} = dist_{smile}(\mathbf{x}_{edit}) - dist_{smile}(\mathbf{x})$ . + +For the final assessment, we computed the Pearson correlation between the perceptual distances of every pair of attributes. Each entry in Table 1 displays the absolute correlation value. For instance, for the attributes "smile" and "pose", we determine the perceptual distances $\Delta_{smile}$ and $\Delta_{pose}$ across the entire evaluation set. The correlation value shown in the table is: + +$$ +\operatorname {c o r r} (\text {p o s e}, \text {s m i l e}) = \left| \frac {\operatorname {c o v} \left(\Delta_ {\text {p o s e}} , \Delta_ {\text {s m i l e}}\right)}{E \left[ \Delta_ {\text {p o s e}} \right] E \left[ \Delta_ {\text {s m i l e}} \right]} \right| \tag {15} +$$ + +Table 1 presents the correlation results of various methods. As previously mentioned [8, 12, 28, 29], we observe that certain attributes exhibit stronger correlations than others. For instance, the glasses-age correlation is consistently higher than the smile-pose correlation across all models. + +Table 1: Attribute correlation matrices of edited images (in absolute values). + +
(a) SeFa(b) InterFaceGan
PoseSmileAgeGenderGlassesposeSmileAgeGenderGlasses
Pose1.0000.1500.0390.1330.051Pose1.0000.0980.0900.0170.079
Smile0.1501.0000.0010.1700.233Smile0.0981.0000.1540.1980.084
Age0.0390.0011.0000.5330.367Age0.0900.1541.0000.5650.600
Gender0.1330.1700.5331.0000.339Gender0.0170.1980.5651.0000.363
Glasses0.0510.2330.3670.3391.000Glasses0.0790.0840.6000.3631.000
Avg0.0930.1150.2350.2930.247Avg0.0710.1330.3520.2850.281
(c) StyleFlow(d) Ours
PoseSmileAgeGenderGlassesPoseSmileAgeGenderGlasses
Pose1.0000.1130.1260.1030.056Pose1.0000.0180.0080.0290.046
Smile0.1131.0000.2640.0110.074Smile0.0181.0000.1200.0500.100
Age0.1260.2641.0000.5810.494Age0.0080.1201.0000.3880.363
Gender0.1030.0110.5811.0000.338Gender0.0290.0500.3881.0000.203
Glasses0.0560.0740.4940.3381.000Glasses0.0460.1000.3630.2031.000
Avg0.0990.1150.3660.2580.240Avg0.0250.0720.2190.1670.178
+ +The table's final row sums the off-diagonal columns, representing the average correlation score. Our method's lower scores highlight its superior disentanglement capabilities compared to the other techniques. + +In our previous assessment, all attributes were adjusted simultaneously. To test the stability of attributes when only one is modified, we conducted an experiment editing one attribute at a time and measured the perceptual distances using the classifiers' final layers. Fig. 5 displays results from various methods. The x-axis represents changes in the edited attribute, while the y-axis indicates unintentional changes in other attributes. As edits become more extensive, the inter-attribute effect is more pronounced. Among all models, our approach shows the least deviation, indicating superior attribute disentanglement. + +Face Identity Preservation: Following the approach of the face identity score [3], we assess the edited images using a pre-trained face embedding network [9]. We restricted our edits to attributes that should preserve identity, such as pose, glasses, and smile. After editing, we embedded the images into a latent space using the network. We then calculated + +Table 2: Identity preservation scores by different models. + +
EditMetricSeFaInterFaceGanStyleFlowOurs
SmileCs ↑0.9700.9780.9890.991
Ed ↓0.3290.2760.1920.174
PoseCs ↑0.9780.9790.9810.982
Ed ↓0.2830.2790.26620.253
GlassesCs ↑0.9660.9780.9840.985
Ed ↓0.3480.2700.2270.215
AllCs ↑0.9110.9330.9350.948
Ed ↓0.6220.5370.5340.467
+ +Notation: $C_s$ - Cosine Similarity; $E_d$ - Euclidean Distance. + +the Euclidean distance, $E_{d}$ , and the cosine similarity, $C_s$ , between the original and edited images. + +Table 2 displays the results for face identity preservation. Our method consistently surpasses other techniques across all types of edits. While StyleFlow shows comparable scores for individual attribute edits, our model excels in preserving identity when multiple edits are combined. + +![](images/80bfee8bd1c8d0472d2955137fa8db024501603106f1e5c73166b491d2eeb793.jpg) + +![](images/b3b5ba119ab085a14b2efb47a109e06c965ddfd614c790421ff3b4ef3a1d5f59.jpg) + +![](images/08386100f31322f2a7f4ae40e4a90aef0c93ff32df3e6e1b675a7f850a4e1cfb.jpg) + +![](images/1b5f449357521330a7a3ab63660403889bf3a2f84542215b185c9d08eec922d4.jpg) + +![](images/4362ac282fd9b078ff98226f12b9aeed053094a22df497fd2adbb2c474d26251.jpg) + +![](images/211611a559aad49d9d10465d7c7cef98dd70ad8e63a5f6852bac5900db9b5cdf.jpg) + +![](images/a205eec8d3bab16ecf736807db7feda1292cf0cccaaf9f755dda8a6803862872.jpg) + +![](images/e2b1454267191a1eedb0606d8f03591c20c49454bae7823ac3b30c53fdab4272.jpg) + +![](images/424976fc991ccce3d43176c1d2354e85892d11168137c74bc4d14c5ebde0bd42.jpg) + +![](images/35042f769452a2a4f555bb0c840723297a01aa52b253d2a8ec53876d60586aaa.jpg) + +![](images/891890b1b062e8cb59660c838ad585bb84157839a965492a0ceda2250e960cd7.jpg) + +![](images/1cd89481b0981a662b0841d27bd56758c79ca1973a055ed670a5de111852779c.jpg) + +![](images/e51e81b6aafe06759fbb847ff6b895db1e154009ea9ee29d11f52a699fa83ae7.jpg) + +![](images/3f8f1a05ade3e64e887a157c4be9101b135ddbd9adc85f8e4e3ba05ed994d949.jpg) + +![](images/ee1ee1a1a4b380d2c6c68810859452e8a60ca8b5e52d50a11f62315a0caa1652.jpg) + +![](images/3a32b9b69c2b1dc87ef5c3b5d1572f9060c3ed4e403a51f4331df5872a6ee637.jpg) + +![](images/db6e9f8efc37c88961b85e081e120a48aadfc04af3b7f1c017dd6909bad8767d.jpg) + +![](images/b6c4c7c3e0e52947ff64f3ee4f1729f73d2034bc57db84765bfa70b4eb60b87f.jpg) + +![](images/c644309cebf979cb74c660d6afb8ee7cf844fa34389db08624092006ed59e467.jpg) + +![](images/f2d058070e9e84b034de9644bac06cd35ade26d9286f12c88e33da1f10df3452.jpg) + +![](images/e7297780204ff38f70e1ddb07f91a03d63f44aed434465053d60c1ee48feb897.jpg) +Figure 5: Comparative analysis of the inter-attribute effects exhibited by different models. The upper rows display how changes in one attribute vary as a function of changes in another attribute. The bottom row provides an average of all the rows above. + +![](images/368df0d2e5fd6389feee668a9d19b8e5862a47fb8b52632a0edfc98a54d84cf8.jpg) + +![](images/af9b1b6bbf1bcf0b0fe486fb408dae2362fffb702fd16d58326f64cd78983409.jpg) + +![](images/1090aec8781551c8348baa4f65cf8649ae31bb54599e4c9bc0e5a832eb8bdf20.jpg) + +![](images/17f2ccebd0e086385ac8dfbac39b08835a7d9feb163acea905d6ca1eccc5f978.jpg) + +# 4.4. Diversity Analysis + +In the previous sections, we introduced a single-direction variant of our model. Now, we will explore the performance of our model when multiple directions in the subspace are utilized for editing. To measure the diversity of the images produced by our model, we employed the LPIPS perceptual similarity score [33]. A lower LPIPS score indicates higher similarity between images, whereas a higher score signifies perceptual differences. + +We generated a batch of 1,000 images and applied 5 random edits to each image. For every set of 5 edits, the similarity score between each pair of edited images was computed. Subsequently, all these scores were averaged to derive the final diversity score. We benchmarked our model against StyleFlow and the single-direction variant of our model, referred to as SVM, as detailed in Section 4.1. The FID score was also calculated to assess the visual quality of the generated images. + +The results, summarized in Table 3, reveal that our approach — when multi-directional subspace editing is employed — not only fosters greater image diversity (as indicated by the LPIPS score) but also ensures superior visual quality (as denoted by the FID score). It's noteworthy that there is a marked enhancement in the multi-directional iteration of our model (subspace) when compared against its single-direction counterpart (SVM) or against StyleFlow. + +Table 3: Diversity score results for edited images. Our multi-directional model achieves a higher score which indicates its ability to generate more diverse results while maintaining a lower FID score. + +
MethodLPIPS ↑FID ↓
StyleFlow0.21327.467
Our (svm)0.22926.926
Our (subspace)0.32123.648
+ +# 4.5. Ablation Study + +To validate the importance of our orthogonality loss outlined in Section 3.2, we carried out an ablation study. We trained a version of our model with $\lambda_{orth} = 0$ , keeping all other configurations, including losses and the training process, consistent. Post-training, we conducted consecutive edits starting from an original image, and the results can be viewed in Fig. 6. + +We found that images edited with the orthogonality loss exhibit crisper details and fewer visual artifacts when subjected to multiple edits. We also carried out the same quantitative evaluations as detailed in Section 4.3. The results in Tables 4 and 5 indicate that our orthogonality loss leads to better attribute disentanglement in our model. + +$$ +\lambda_ {o r t h} = 0 +$$ + +![](images/a6a55509796f889dfc4194807bfba2ae7abcea326a401564644b0e611f3b48b6.jpg) + +![](images/931530730778fb23834ec095f1e128fc1bd8c7bed805ffa7f15963a2f04a9c4b.jpg) + +![](images/5cd9048da593c74316f1936866c0866c8c0dd1856e6bd75f4cbb998dcb884cd8.jpg) + +![](images/5a4113acfd83ae74e57f3cf303ca3b95da0b1ccd066e5d302739db1ac83c1b77.jpg) + +![](images/e443c88718da2b9de49b71dd4b681599e7f99bedc76c0bab91a5b40a88be5d3d.jpg) + +![](images/025d99343bca9277ff2c27c1a62e1deb7bfa6f61e30e5670abb5f8bf5573ab18.jpg) + +![](images/425601884dea473c2bbd03f2e8944ae7dbde6b4f528f4668dbe0f156246e8093.jpg) + +![](images/1419290e18abac56bb4c412725f2d9449f20b6d54e40490ada753a101c6488e5.jpg) + +$$ +\lambda_ {o r t h} = 0. 0 0 1 +$$ + +![](images/a2be59da0747bf28123fe44c6fb35aeb3400793c70708928ec642976388e9588.jpg) + +![](images/7513fa3dc49ef182e172c02f4245982157e7562a02fd5eefd3744ac7f599437c.jpg) + +![](images/855090fa79d361796ca7750b0b5008d6da8e31cf9fefb6bcfaa0c03eb60ba362.jpg) + +![](images/7a700610d150ca6d384f7ac9107b12d1f185d2b1cac03c3bdd9b0618ba85fb8a.jpg) + +![](images/a8af8ee3a8eaab4d050c4294fd4dbdedcfd15aca9fad84a3652bc74c45308d3f.jpg) +Figure 6: Comparison using orthogonality loss: First and third rows show reduced pose-glasses entanglement; second and fourth rows show better preservation of hair and shirt color. + +![](images/fe5a0f9968329d0ed413e33e177fa9e68f4916c713e5b30f302db0c7d32c126f.jpg) + +![](images/757603764b0c2d3ceb800bfe1ce2c13c58b2092e4c5ce7c958735fb038a2d04e.jpg) + +![](images/b97643186e149553b18a85f47edad7759a21e2016049a7a6c58ced73e1173d58.jpg) + +Table 4: Attribute correlation matrices with and without orthogonal loss. The values represent the average correlation between an attribute and others. + +
ModelPoseSmileAgeGenderGlasses
λorth = 00.1490.2420.3420.2830.253
λorth = 0.0010.0250.0720.2190.1670.178
+ +Table 5: Comparison of identity preservation using orthogonal loss. + +
EditMetricλorth=0λorth=0.001
AllCs↑0.9320.948
Ed↓0.5360.467
+ +Notation: $C_s$ - Cosine Similarity; $E_d$ - Euclidean Distance. + +# 5. Conclusions + +In this work we proposed MDSE, a disentangling generative model for multi-attribute image editing. We introduce the concept of orthogonal subspaces that support multi-directional edits for diverse image generation. Additionally, this model effectively identifies disentangled latent subspaces, allowing precise control over the generated images and the displayed face attributes. We believe that integrating these concepts during the generator's training could further enhance the performance of disentangled models. + +# References + +[1] Rameen Abdul, Yipeng Qin, and Peter Wonka. Image2stylegan: How to embed images into the stylegan latent space? In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 4432-4441, 2019. 1, 2 +[2] Rameen Abdul, Yipeng Qin, and Peter Wonka. Image2stylegan++: How to edit the embedded images? 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The unreasonable effectiveness of deep features as a perceptual metric. In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 586-595, 2018. 5, 9 \ No newline at end of file diff --git a/2023/Multi-Directional Subspace Editing in Style-Space/images.zip b/2023/Multi-Directional Subspace Editing in Style-Space/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..bfafce7012d749d6ead5dfdd9ffc5db088f1c22e --- /dev/null +++ b/2023/Multi-Directional Subspace Editing in Style-Space/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:91e612c94c44299a2ed899921f4368c71bb1195f2840b66cbbc7705d14bf2118 +size 1139561 diff --git a/2023/Multi-Directional Subspace Editing in Style-Space/layout.json b/2023/Multi-Directional Subspace Editing in Style-Space/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..ef21d2284bec693ef4ade77b52fc04a8b2ea7dd0 --- /dev/null +++ b/2023/Multi-Directional Subspace Editing in Style-Space/layout.json @@ -0,0 +1,10916 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 141, + 103, + 453, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 141, + 103, + 453, + 121 + ], + "spans": [ + { + "bbox": [ + 141, + 103, + 453, + 121 + ], + "type": "text", + "content": "Multi-Directional Subspace Editing in Style-Space" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 265, + 144, + 328, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 265, + 144, + 328, + 156 + ], + "spans": [ + { + "bbox": [ + 265, + 144, + 328, + 156 + ], + "type": "text", + "content": "Chen Naveh" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 173, + 158, + 420, + 172 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 173, + 158, + 420, + 172 + ], + "spans": [ + { + "bbox": [ + 173, + 158, + 420, + 172 + ], + "type": "text", + "content": "School of Computer Science, Reichman University" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 241, + 174, + 352, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 241, + 174, + 352, + 185 + ], + "spans": [ + { + "bbox": [ + 241, + 174, + 352, + 185 + ], + "type": "text", + "content": "navehchen1@gmail.com" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 63, + 212, + 532, + 475 + ], + "blocks": [ + { + "bbox": [ + 63, + 212, + 532, + 475 + ], + "lines": [ + { + "bbox": [ + 63, + 212, + 532, + 475 + ], + "spans": [ + { + "bbox": [ + 63, + 212, + 532, + 475 + ], + "type": "image", + "image_path": "e7bc74e7e4686bb092744be81a40227e2cda62c5c76540f74541bced61e381c4.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 483, + 547, + 510 + ], + "lines": [ + { + "bbox": [ + 46, + 483, + 547, + 510 + ], + "spans": [ + { + "bbox": [ + 46, + 483, + 547, + 510 + ], + "type": "text", + "content": "Figure 1: Multi-directional human face editing. Each row indicates changes in a subspace associated with a particular attribute: (top to bottom) gender, age and race." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "bbox": [ + 143, + 518, + 192, + 531 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 518, + 192, + 531 + ], + "spans": [ + { + "bbox": [ + 143, + 518, + 192, + 531 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 289, + 714 + ], + "type": "text", + "content": "This paper describes a new technique for finding disentangled semantic directions in the latent space of StyleGAN. Our method identifies meaningful orthogonal subspaces that allow editing of one human face attribute, while minimizing undesired changes in other attributes. Our model is capable of editing a single attribute in multiple directions, resulting in a range of possible generated images. We compare our scheme with three state-of-the-art models and show that our method outperforms them in terms of face editing and disentanglement capabilities. Additionally, we suggest quantitative measures for evaluating attribute separation and disentanglement, and exhibit the superiority of" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 519, + 480, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 519, + 480, + 532 + ], + "spans": [ + { + "bbox": [ + 306, + 519, + 480, + 532 + ], + "type": "text", + "content": "our model with respect to those measures1." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 555, + 387, + 567 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 555, + 387, + 567 + ], + "spans": [ + { + "bbox": [ + 306, + 555, + 387, + 567 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 575, + 545, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 575, + 545, + 670 + ], + "spans": [ + { + "bbox": [ + 304, + 575, + 545, + 670 + ], + "type": "text", + "content": "Recent developments in computer vision have enabled the generation of photorealistic, high-resolution synthetic images. The most notable technique is Generative Adversarial Networks (GANs) [11], which have advanced the progress of many applications, including image generation, super-resolution, image inpainting, and more. In particular, the generator of StyleGAN [1], one of the most notable GAN models, has been extensively explored by researchers." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 317, + 671, + 545, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 671, + 545, + 685 + ], + "spans": [ + { + "bbox": [ + 317, + 671, + 545, + 685 + ], + "type": "text", + "content": "StyleGAN samples a latent vector " + }, + { + "bbox": [ + 317, + 671, + 545, + 685 + ], + "type": "inline_equation", + "content": "\\mathbf{z} \\in \\mathbb{R}^{512}" + }, + { + "bbox": [ + 317, + 671, + 545, + 685 + ], + "type": "text", + "content": " from a" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 306, + 693, + 544, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 544, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 544, + 713 + ], + "type": "text", + "content": "1Project page and code are available at https://chennaveh.github.io/MDSE/" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7138" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "text", + "content": "Gaussian distribution " + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "inline_equation", + "content": "\\mathcal{N}(\\mathbf{0},\\mathbf{I})" + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "text", + "content": ", and maps it to an intermediate vector " + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "inline_equation", + "content": "\\mathbf{w}\\in \\mathcal{W} = \\mathbb{R}^{512}" + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "text", + "content": " using a mapping network. This vector is then used to generate a 1024x1024 RGB image. The vector " + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "inline_equation", + "content": "\\mathbf{w}" + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "text", + "content": " is inserted into 18 multi-resolution style blocks that control various characteristics of the synthesized image. Vectors at lower resolutions determine high-level features such as pose and hair. Intermediate resolutions affect facial expressions, while vectors at higher resolutions dictate fine details like colors and texture. The original StyleGAN model uses the " + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "text", + "content": " latent space and the same " + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "inline_equation", + "content": "\\mathbf{w}" + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "text", + "content": " vector for all 18 style blocks. Subsequent studies [1,2,26,32] utilize the " + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "inline_equation", + "content": "\\mathcal{W}^{+} = \\mathbb{R}^{18\\cdot 512}" + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "text", + "content": " space, which extends the " + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "text", + "content": " space, and applies different " + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "inline_equation", + "content": "\\mathbf{w}" + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "text", + "content": " vectors to different style blocks. This allows for enhanced control over the resulting image. The " + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "inline_equation", + "content": "\\mathcal{W}^{+}" + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "text", + "content": "latent space is commonly used for inverse mapping, converting an image into " + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "inline_equation", + "content": "\\mathbf{w}\\in \\mathcal{W}^{+}" + }, + { + "bbox": [ + 46, + 72, + 289, + 264 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 267, + 289, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 267, + 289, + 590 + ], + "spans": [ + { + "bbox": [ + 46, + 267, + 289, + 590 + ], + "type": "text", + "content": "Recent works have explored methods for gaining control over the synthesized images by altering the latent space vectors [3, 7, 12, 25, 28, 29]. For instance, shifting the latent vector of a generated image towards the direction corresponding to \"smile\" can progressively amplify the smile in the output image. While these methods showcase impressive and realistic editing capabilities, pinpointing the attribute directions remains a challenge. One approach is to use vectors in latent space sampled from the GAN model combined with attribute ground truth (either manually labeled or determined using a pre-trained attribute estimator) [10, 16, 28]. A linear classifier in the latent space is then employed. The normal to the classification boundary corresponds to the most significant direction of the attribute. These models often suffer from issues of entangled data and biases in the training set. Such biases might result in attribute correlations, like glasses with age or beard with gender. Consequently, adding glasses to a face may inadvertently age it. Other methods use unsupervised techniques [12, 29], such as PCA, to find meaningful orthogonal directions in the latent space. However, these directions typically require subjective human post-annotation to link directions to attributes in the synthesized images. All these models share the notion of a singular direction for each attribute, despite the possibility of some attributes defined by multiple dimensions (e.g., age might be affected by factors like hair color and skin wrinkles, see Fig. 1)." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "In this work, we present MDSE, an acronym for Multi-Directional Subspace Editing. This framework aims to identify orthogonal semantics within the latent space of a pre-trained StyleGAN. Our goal is to discover meaningful subspaces that are mutually orthogonal, with each subspace controlling specific facial attributes. \"Multi-directional editing\" means altering a latent vector within a particular subspace in various directions. This approach enables the generation of a wide range of images, each varying in a specific attribute. Furthermore, because the subspaces are" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 133 + ], + "type": "text", + "content": "mutually orthogonal, modifications in one attribute result in minimal changes to others. We explore the disentanglement capabilities of our model and quantitatively assess its performance in comparison to leading image editing techniques." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 305, + 144, + 393, + 157 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 144, + 393, + 157 + ], + "spans": [ + { + "bbox": [ + 305, + 144, + 393, + 157 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 163, + 525, + 177 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 163, + 525, + 177 + ], + "spans": [ + { + "bbox": [ + 306, + 163, + 525, + 177 + ], + "type": "text", + "content": "2.1. Generative Adversarial Networks (GANs)" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 182, + 547, + 421 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 182, + 547, + 421 + ], + "spans": [ + { + "bbox": [ + 304, + 182, + 547, + 421 + ], + "type": "text", + "content": "Generative models have revolutionized the generation of vast amounts of visual content. They can produce visually compelling content with remarkable fidelity, making them indispensable for image editing applications. GAN models learn a mapping from a specific distribution (usually Gaussian or uniform) to the target distribution. The generator " + }, + { + "bbox": [ + 304, + 182, + 547, + 421 + ], + "type": "inline_equation", + "content": "G(\\cdot)" + }, + { + "bbox": [ + 304, + 182, + 547, + 421 + ], + "type": "text", + "content": " is trained to fool an adversary " + }, + { + "bbox": [ + 304, + 182, + 547, + 421 + ], + "type": "inline_equation", + "content": "D(\\cdot)" + }, + { + "bbox": [ + 304, + 182, + 547, + 421 + ], + "type": "text", + "content": ", which aims to differentiate between the generated images and the real ones. Both models " + }, + { + "bbox": [ + 304, + 182, + 547, + 421 + ], + "type": "inline_equation", + "content": "G(\\cdot)" + }, + { + "bbox": [ + 304, + 182, + 547, + 421 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 182, + 547, + 421 + ], + "type": "inline_equation", + "content": "D(\\cdot)" + }, + { + "bbox": [ + 304, + 182, + 547, + 421 + ], + "type": "text", + "content": " are trained concurrently using the min-max loss [11]. The GAN approach is widely recognized and often outperforms other techniques, such as variational autoencoders (VAEs) [21]. Recently, denoising diffusion probabilistic models (DDPM) [15] have risen in prominence and showcased superior results. However, despite their leading performance in image generation, their potential in image editing and semantic interpretation remains relatively unexplored. In this work, our attention is centered on a GAN-based generator, specifically the StyleGAN [18-20], which exhibits exceptional capability in the human face domain." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "spans": [ + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "type": "text", + "content": "GAN Latent Space. Given a pre-trained generator " + }, + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "type": "inline_equation", + "content": "\\mathbf{x} = G(\\mathbf{w})" + }, + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "type": "text", + "content": ", GAN inversion " + }, + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{w}} = G^{-1}(\\mathbf{x})" + }, + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "type": "text", + "content": " is the process of inverting a specified image " + }, + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "type": "text", + "content": " into a latent vector " + }, + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{w}}" + }, + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "type": "text", + "content": " that faithfully reconstructs the image using the generator. In other words, " + }, + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "type": "inline_equation", + "content": "G(\\hat{\\mathbf{w}})\\approx \\mathbf{x}" + }, + { + "bbox": [ + 304, + 422, + 548, + 639 + ], + "type": "text", + "content": ". Most of the common methods either train an encoder [24, 26, 32] from the image space into the latent space or optimize the latent vector, using backpropagation, directly until it generates the desired image [1, 2, 22]. Recent approaches that modify the generator's weight have gained traction, resulting in enhanced image reconstruction [5, 27]. Previous works show that the latent space of a pretrained GAN model encodes image semantics in a meaningful structure. Hence, latent codes corresponding to images with similar semantics tend to cluster closely in the latent space [28]. For instance, within the domain of human face generation, faces sharing characteristics (e.g., being young and blond) will have nearby latent vectors. This foundational insight drives modern image editing techniques." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 646, + 547, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 646, + 547, + 672 + ], + "spans": [ + { + "bbox": [ + 306, + 646, + 547, + 672 + ], + "type": "text", + "content": "2.2. Multi-Directional Manipulation in Latent Space" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 677, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 547, + 715 + ], + "type": "text", + "content": "The idea of editing an image through latent space manipulation has been extensively explored in recent years [7,25]. Such approaches aim to harness the strong capabilities of" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "text", + "content": "7139" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 228 + ], + "type": "text", + "content": "the generator. Therefore, they keep the generator network static and conduct vector operations solely in the latent space. Recent works primarily rely on a linear latent space assumption and demonstrate pleasing-looking results of image editing by adding or subtracting vectors within the latent space [12, 28, 29]. InterFaceGAN [28] employs pretrained binary classifiers to label images with facial features, such as young-old, male-female, and with/without glasses, among others. It then trains a linear classifier (specifically, a Support Vector Machine or SVM) on the respective latent vectors to derive a classifying hyperplane. The normal to this hyperplane serves as the 1D direction for editing the relevant attribute." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 229, + 289, + 315 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 229, + 289, + 315 + ], + "spans": [ + { + "bbox": [ + 46, + 229, + 289, + 315 + ], + "type": "text", + "content": "GANSpace [12] adopts a data-driven approach, applying PCA on a set of vectors sampled from " + }, + { + "bbox": [ + 46, + 229, + 289, + 315 + ], + "type": "inline_equation", + "content": "\\mathcal{W}" + }, + { + "bbox": [ + 46, + 229, + 289, + 315 + ], + "type": "text", + "content": " to find meaningful directions. The eigenvectors associated with the largest eigenvalues serve as the editing directions. Some derived directions can be entangled, such as head rotation and gender. To address this issue, edits are restricted to a specifically selected subset of the generator's layers." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 315, + 289, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 315, + 289, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 315, + 289, + 472 + ], + "type": "text", + "content": "Another work, SeFa [29], avoids the image sampling pre-processing step. Instead, it determines a closed-form factorization of the latent space by utilizing an eigendecomposition of the generator's weights. For StyleGAN, the style affine transformation matrices are employed for vector decomposition. The eigenvectors corresponding to the greatest variations are selected to define the semantic directions. However, this unsupervised method faces two main issues. Firstly, there's a subjective post-annotation process to match the directions with relevant semantics. Secondly, the directions that are derived often mix several semantics (e.g., age and glasses), a result of biases present in the training data." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 472, + 289, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 289, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 289, + 605 + ], + "type": "text", + "content": "A distinct set of studies moves away from the linear approach, opting instead to learn non-linear functions to manipulate latent vectors. StyleFlow [3] employs continuous normalizing flows conditioned on the image attribute vector. This attribute vector must be provided using pre-trained networks before every edit. Another non-linear approach is StyleRig [30], which incorporates a 3D semantic network and harnesses it to perform rigid edits such as pose and light. Although non-linear approaches generally perform better, our research primarily emphasizes the more comprehensive linear approach." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": "All previous methods that manipulate the latent space of StyleGAN define a semantic as a singular direction. Both linear and non-linear approaches ultimately derive positive and negative directions for editing a desired attribute. We believe that this oversimplification may restrict the editing capabilities and limit the diversity of the generated images. For example, imagine we want to edit the gender of a given face. One person may argue that hairstyle is a distinguishing factor between men and women, while another might think" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "text", + "content": "of facial structure or the presence of facial hair as a more prominent factor. In this work, we overcome this variability by associating an attribute with an " + }, + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "text", + "content": "-dim subspace where " + }, + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "inline_equation", + "content": "n \\geq 1" + }, + { + "bbox": [ + 304, + 72, + 547, + 192 + ], + "type": "text", + "content": ", containing more than a single direction, in the semantic space. We call this a multi-directional subspace, as different vectors within the subspace can affect the resulting image differently, but all affect the associated attribute (see examples in Fig. 1). We also require different attributes to be associated with mutually orthogonal subspaces, to promote disentanglement between attributes." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 317, + 192, + 481, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 192, + 481, + 204 + ], + "spans": [ + { + "bbox": [ + 317, + 192, + 481, + 204 + ], + "type": "text", + "content": "We outline our contributions as follows:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 317, + 209, + 545, + 414 + ], + "type": "list", + "angle": 0, + "index": 10, + "blocks": [ + { + "bbox": [ + 317, + 209, + 545, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 209, + 545, + 258 + ], + "spans": [ + { + "bbox": [ + 317, + 209, + 545, + 258 + ], + "type": "text", + "content": "- We propose MDSE to extend the concept of meaningful latent directions to multi-directional subspaces, thereby diversifying and expanding the capabilities of the editing process." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 262, + 545, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 262, + 545, + 347 + ], + "spans": [ + { + "bbox": [ + 317, + 262, + 545, + 347 + ], + "type": "text", + "content": "- MDSE identifies orthogonal directions in StyleGAN's latent space, to promote disentanglement. We introduce an orthogonality loss in the model training and demonstrate its significance in preserving some image attributes while editing others. We visualize the results and demonstrate improved results in consecutive edits of multiple attributes (refer to Fig. 4)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 317, + 353, + 545, + 414 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 353, + 545, + 414 + ], + "spans": [ + { + "bbox": [ + 317, + 353, + 545, + 414 + ], + "type": "text", + "content": "- We develop a new metric for evaluating the disentanglement properties of image editing. In addition to the conventional approaches of visual comparisons, we suggest using our evaluation metrics as a quantitative measurement of disentanglement capabilities." + } + ] + } + ], + "index": 9 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 422, + 361, + 434 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 422, + 361, + 434 + ], + "spans": [ + { + "bbox": [ + 306, + 422, + 361, + 434 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 441, + 545, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 441, + 545, + 525 + ], + "spans": [ + { + "bbox": [ + 304, + 441, + 545, + 525 + ], + "type": "text", + "content": "Given a set of attributes, " + }, + { + "bbox": [ + 304, + 441, + 545, + 525 + ], + "type": "inline_equation", + "content": "B \\triangleq \\{ \\text{gender}, \\text{ glasses}, \\dots \\}" + }, + { + "bbox": [ + 304, + 441, + 545, + 525 + ], + "type": "text", + "content": ", we aim to find a subspace for each attribute " + }, + { + "bbox": [ + 304, + 441, + 545, + 525 + ], + "type": "inline_equation", + "content": "b_i \\in B" + }, + { + "bbox": [ + 304, + 441, + 545, + 525 + ], + "type": "text", + "content": " so that editing within this subspace leads to changes in the associated attribute " + }, + { + "bbox": [ + 304, + 441, + 545, + 525 + ], + "type": "inline_equation", + "content": "b_i" + }, + { + "bbox": [ + 304, + 441, + 545, + 525 + ], + "type": "text", + "content": ". Different directions in each subspace are responsible for distinct visual semantics. To achieve disentanglement, we desire that each subspace solely influences its respective attribute." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 526, + 547, + 646 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 526, + 547, + 646 + ], + "spans": [ + { + "bbox": [ + 304, + 526, + 547, + 646 + ], + "type": "text", + "content": "Certain attributes, such as glasses and age, have been observed to correlate with each other [28], making disentangled editing challenging. To overcome this problem, our model seeks to decompose the latent space " + }, + { + "bbox": [ + 304, + 526, + 547, + 646 + ], + "type": "inline_equation", + "content": "\\mathcal{W}^+" + }, + { + "bbox": [ + 304, + 526, + 547, + 646 + ], + "type": "text", + "content": " into multiple orthogonal subspaces each of which is associated with a single attribute. This requirement has two main outcomes. Firstly, editing within a subspace facilitates multidirectional edits of a single attribute. Secondly, the orthogonality ensures that altering a specific facial attribute doesn't affect other attributes." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 651, + 463, + 664 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 651, + 463, + 664 + ], + "spans": [ + { + "bbox": [ + 306, + 651, + 463, + 664 + ], + "type": "text", + "content": "3.1. Latent Space Decomposition" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 670, + 545, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 670, + 545, + 696 + ], + "spans": [ + { + "bbox": [ + 306, + 670, + 545, + 696 + ], + "type": "text", + "content": "We decompose " + }, + { + "bbox": [ + 306, + 670, + 545, + 696 + ], + "type": "inline_equation", + "content": "\\mathcal{W}^+" + }, + { + "bbox": [ + 306, + 670, + 545, + 696 + ], + "type": "text", + "content": " into " + }, + { + "bbox": [ + 306, + 670, + 545, + 696 + ], + "type": "inline_equation", + "content": "N + 1" + }, + { + "bbox": [ + 306, + 670, + 545, + 696 + ], + "type": "text", + "content": " orthogonal subspaces " + }, + { + "bbox": [ + 306, + 670, + 545, + 696 + ], + "type": "inline_equation", + "content": "\\{S_i\\}_{i = 0}^N" + }, + { + "bbox": [ + 306, + 670, + 545, + 696 + ], + "type": "text", + "content": " and define each subspace " + }, + { + "bbox": [ + 306, + 670, + 545, + 696 + ], + "type": "inline_equation", + "content": "S_{i}" + }, + { + "bbox": [ + 306, + 670, + 545, + 696 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 322, + 700, + 545, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 322, + 700, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 322, + 700, + 545, + 715 + ], + "type": "interline_equation", + "content": "S _ {i} \\triangleq \\operatorname {s p a n} \\left\\{\\mathbf {p} _ {i} ^ {1}, \\mathbf {p} _ {i} ^ {2}, \\dots , \\mathbf {p} _ {i} ^ {n _ {i}} \\right\\}, n _ {i} < \\dim (\\mathcal {W} ^ {+}) \\tag {1}", + "image_path": "0bf245851ca3095dcb8f3fe488c9cfaf05bf93d63ed29e167fadadd3bf16413f.jpg" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7140" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "spans": [ + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "\\mathbf{p}_i^j\\in \\mathcal{W}^+" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{p}_i^j\\}_{j = 1}^{n_i}" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": " are linearly independent vectors. Therefore, " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{p}_i^j\\}_{j = 1}^{n_i}" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": " form a basis for subspace " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "S_{i}" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": " with cardinality " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "n_i" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": ". There are " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "N + 1" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": " subspaces, where " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "N = |B|" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": " is the size of the attribute set " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": ". Each " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "S_{i}" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": " corresponds to " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "b_{i}" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": " respectively, while " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "S_0" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": " is associated with all other information that is not labeled in " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": ". This may include other semantics, e.g., clothing and image background. The correspondence of " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "S_{i}" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "inline_equation", + "content": "b_{i}" + }, + { + "bbox": [ + 46, + 71, + 287, + 182 + ], + "type": "text", + "content": " will be elaborated on later in the paper." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 182, + 287, + 205 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 182, + 287, + 205 + ], + "spans": [ + { + "bbox": [ + 46, + 182, + 287, + 205 + ], + "type": "text", + "content": "To ensure orthogonality, we require the following conditions:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 107, + 219, + 287, + 233 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 107, + 219, + 287, + 233 + ], + "spans": [ + { + "bbox": [ + 107, + 219, + 287, + 233 + ], + "type": "interline_equation", + "content": "S _ {i} \\subset \\mathcal {W} ^ {+}, \\forall i \\in \\{0, \\dots , N \\} \\tag {2}", + "image_path": "bdd547900468f42dd34b3566062c427b61e4311848c16ce9fd21ab1257b2522d.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 137, + 249, + 287, + 282 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 137, + 249, + 287, + 282 + ], + "spans": [ + { + "bbox": [ + 137, + 249, + 287, + 282 + ], + "type": "interline_equation", + "content": "\\bigoplus_ {i = 0} ^ {N} S _ {i} = \\mathcal {W} ^ {+} \\tag {3}", + "image_path": "9189a3920891b9d4345e774e748b43c96682b19cc67e2df10f8e1fe8589f3e1f.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 132, + 293, + 287, + 307 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 132, + 293, + 287, + 307 + ], + "spans": [ + { + "bbox": [ + 132, + 293, + 287, + 307 + ], + "type": "interline_equation", + "content": "S _ {i} \\perp S _ {j}, \\forall i \\neq j \\tag {4}", + "image_path": "15d681aa7aa69381536e753ee5ce9f1af63b318a704496f15f7bd85e6efaf9a3.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "spans": [ + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "inline_equation", + "content": "\\bigoplus" + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "text", + "content": " denotes direct sum, and " + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "inline_equation", + "content": "\\perp" + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "text", + "content": " signifies orthogonal subspaces. Notice that the entire vector set " + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{p}_i^j\\}" + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "text", + "content": " forms a basis for " + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "inline_equation", + "content": "\\mathcal{W}^+" + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "text", + "content": ". As a result, we can uniquely express every vector " + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "inline_equation", + "content": "\\mathbf{w} \\in \\mathbb{R}^{18 \\cdot 512}" + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "text", + "content": " with a set of scalars " + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "inline_equation", + "content": "\\{a_i^j\\}" + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "text", + "content": " and represent " + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "inline_equation", + "content": "\\mathbf{w}" + }, + { + "bbox": [ + 46, + 313, + 287, + 373 + ], + "type": "text", + "content": " as the following linear combination:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 129, + 384, + 287, + 417 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 129, + 384, + 287, + 417 + ], + "spans": [ + { + "bbox": [ + 129, + 384, + 287, + 417 + ], + "type": "interline_equation", + "content": "\\mathbf {w} = \\sum_ {i = 0} ^ {N} \\sum_ {j = 1} ^ {n _ {i}} a _ {i} ^ {j} \\mathbf {p} _ {i} ^ {j} \\tag {5}", + "image_path": "f7ce8cd354b348ccbbb17c35b838d2f415e7272db4697a4c7c9aa924031d216f.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 422, + 272, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 422, + 272, + 435 + ], + "spans": [ + { + "bbox": [ + 47, + 422, + 272, + 435 + ], + "type": "text", + "content": "This expression can also be represented in matrix form:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 453, + 289, + 570 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 453, + 289, + 570 + ], + "spans": [ + { + "bbox": [ + 47, + 453, + 289, + 570 + ], + "type": "interline_equation", + "content": "\\mathbf {w} = \\left[ \\underbrace {\\left[ \\begin{array}{c c c} | & & | \\\\ \\mathbf {p} _ {0} ^ {1} & \\dots & \\mathbf {p} _ {0} ^ {n _ {0}} \\\\ | & & | \\end{array} \\right]} _ {\\mathbf {P} _ {0}} \\dots \\underbrace {\\left[ \\begin{array}{c c c} | & & | \\\\ \\mathbf {p} _ {N} ^ {1} & \\dots & \\mathbf {p} _ {N} ^ {n _ {N}} \\\\ | & & | \\end{array} \\right]} _ {\\mathbf {P} _ {N}} \\right] \\left[ \\begin{array}{c} \\left[ \\begin{array}{c} a _ {0} ^ {1} \\\\ \\vdots \\\\ a _ {0} ^ {n _ {0}} \\end{array} \\right] \\\\ \\vdots \\\\ \\left[ \\begin{array}{c} a _ {N} ^ {1} \\\\ \\vdots \\\\ a _ {N} ^ {n _ {N}} \\end{array} \\right] \\end{array} \\right] \\tag {6}", + "image_path": "7516dc4d80b8c8f6e9fd40f6efb04cae8d650e8299271139bbee957df4cf77f4.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 85, + 579, + 287, + 639 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 85, + 579, + 287, + 639 + ], + "spans": [ + { + "bbox": [ + 85, + 579, + 287, + 639 + ], + "type": "interline_equation", + "content": "\\mathbf {w} = \\sum_ {i = 0} ^ {N} \\mathbf {P} _ {i} \\mathbf {a} _ {i} = \\underbrace {\\left[ \\mathbf {P} _ {0} , \\cdots , \\mathbf {P} _ {N} \\right]} _ {\\mathbf {P}} \\underbrace {\\left[ \\begin{array}{c} \\mathbf {a} _ {0} \\\\ \\vdots \\\\ \\mathbf {a} _ {N} \\end{array} \\right]} _ {\\mathbf {a}} \\tag {7}", + "image_path": "d511421322044c98ecb593aa1d83df0b46cc69425d5a0fdadbbd1a5daa875782.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 644, + 177, + 656 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 644, + 177, + 656 + ], + "spans": [ + { + "bbox": [ + 47, + 644, + 177, + 656 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 644, + 177, + 656 + ], + "type": "inline_equation", + "content": "\\mathbf{P}" + }, + { + "bbox": [ + 47, + 644, + 177, + 656 + ], + "type": "text", + "content": " is a matrix defined by:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 100, + 665, + 287, + 681 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 665, + 287, + 681 + ], + "spans": [ + { + "bbox": [ + 100, + 665, + 287, + 681 + ], + "type": "interline_equation", + "content": "\\mathbf {P} = \\left[ \\mathbf {p} _ {0} ^ {1} \\dots \\mathbf {p} _ {0} ^ {n _ {0}} \\dots \\mathbf {p} _ {N} ^ {1} \\dots \\mathbf {p} _ {N} ^ {n _ {N}} \\right] \\tag {8}", + "image_path": "72371e249ac2cc7265644303c178db2485620aa61b50217f8fa09d28ea7e2dcb.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "and " + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{a}^T = [\\mathbf{a}_0^T,\\dots ,\\mathbf{a}_N^T ]" + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": " is a vector of coefficients. Finding " + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{P}" + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": " that satisfies Eq. (2)-(4) is the core part of our framework." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 72, + 421, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 421, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 421, + 84 + ], + "type": "text", + "content": "3.2. Training Procedure" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "spans": [ + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "text", + "content": "Our dataset consists of a set of 2,000 vector pairs " + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "inline_equation", + "content": "\\left\\{(\\mathbf{w}^{(i)},\\mathbf{y}^{(i)})\\right\\}_{i = 1}^{2000}" + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "text", + "content": ". The latent vectors " + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{w}^{(i)}\\}" + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "text", + "content": " are generated from random vectors sampled from a Gaussian distribution " + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "inline_equation", + "content": "\\mathbf{z}^{(i)}\\sim \\mathcal{N}(0,1)" + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "text", + "content": " and then mapped to " + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "inline_equation", + "content": "\\mathcal{W}^+" + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "text", + "content": " space using the StyleGAN mapping function: " + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "inline_equation", + "content": "\\mathbf{w}^{(i)} = M(\\mathbf{z}^{(i)})" + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "text", + "content": ". Each sample " + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "inline_equation", + "content": "\\mathbf{w}^{(i)}\\in \\mathbb{R}^{18\\cdot 512}" + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "text", + "content": " is mapped onto the image space using the StyleGAN generator, " + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "inline_equation", + "content": "\\mathbf{x}^{(i)} = G(\\mathbf{w}^{(i)})" + }, + { + "bbox": [ + 305, + 91, + 545, + 200 + ], + "type": "text", + "content": " and then annotated using pre-trained classifiers to determine an attribute score vector:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 315, + 208, + 545, + 228 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 208, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 315, + 208, + 545, + 228 + ], + "type": "interline_equation", + "content": "\\mathbf {y} ^ {(i)} \\triangleq \\left(y _ {1} ^ {(i)}, \\dots , y _ {N} ^ {(i)}\\right) = \\left(\\mathcal {C} _ {1} \\left(\\mathbf {x} ^ {(i)}\\right), \\dots , \\mathcal {C} _ {N} \\left(\\mathbf {x} ^ {(i)}\\right)\\right) \\tag {9}", + "image_path": "52920735deb9cf61cf76c9e6f1528bf550feb9d0d8bfe376ed5ead41fd113748.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "spans": [ + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "text", + "content": "Here, each " + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "inline_equation", + "content": "y_{k}^{(i)}" + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "text", + "content": " denotes the " + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "inline_equation", + "content": "b_{k}" + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "text", + "content": " attribute score for sample " + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "text", + "content": ". Depending on the attribute, " + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "inline_equation", + "content": "y_{k}^{(i)}" + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "text", + "content": " is either a discrete or continuous number. " + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "inline_equation", + "content": "C_k" + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "text", + "content": " represents the pre-trained classifier for attribute " + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 239, + 545, + 350 + ], + "type": "text", + "content": ". For age, smile, gender, and glasses, we used the face attribute classifier from [13] trained on the FFHQ dataset [19]. For the pose attribute, we utilized img2pose [6] for face estimation. Additionally, we employed a race classifier [17] trained on the Yahoo YFCC100M dataset [31]." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 352, + 545, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 352, + 545, + 411 + ], + "spans": [ + { + "bbox": [ + 305, + 352, + 545, + 411 + ], + "type": "text", + "content": "The primary goal during the training phase is to determine the matrix " + }, + { + "bbox": [ + 305, + 352, + 545, + 411 + ], + "type": "inline_equation", + "content": "\\mathbf{P}" + }, + { + "bbox": [ + 305, + 352, + 545, + 411 + ], + "type": "text", + "content": " and use it to reconstruct all samples from the training set. To satisfy Eq. (5), we jointly learn a vector " + }, + { + "bbox": [ + 305, + 352, + 545, + 411 + ], + "type": "inline_equation", + "content": "\\mathbf{a}^{(i)}" + }, + { + "bbox": [ + 305, + 352, + 545, + 411 + ], + "type": "text", + "content": " for each vector " + }, + { + "bbox": [ + 305, + 352, + 545, + 411 + ], + "type": "inline_equation", + "content": "\\mathbf{w}^{(i)}" + }, + { + "bbox": [ + 305, + 352, + 545, + 411 + ], + "type": "text", + "content": " such that " + }, + { + "bbox": [ + 305, + 352, + 545, + 411 + ], + "type": "inline_equation", + "content": "\\mathbf{w}^{(i)} = \\mathbf{P}\\mathbf{a}^{(i)}" + }, + { + "bbox": [ + 305, + 352, + 545, + 411 + ], + "type": "text", + "content": ". We then introduce the following loss:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 375, + 422, + 545, + 443 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 375, + 422, + 545, + 443 + ], + "spans": [ + { + "bbox": [ + 375, + 422, + 545, + 443 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {r e c} ^ {(i)} = \\left\\| \\mathbf {w} ^ {(i)} - \\mathbf {P} \\mathbf {a} ^ {(i)} \\right\\| _ {1} \\tag {10}", + "image_path": "2d4449ee7dfc1b554f0f21f41cbc700ba88cabaa1f069a032c4acbd13ec08f9f.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 449, + 545, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 449, + 545, + 496 + ], + "spans": [ + { + "bbox": [ + 305, + 449, + 545, + 496 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 449, + 545, + 496 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{rec}" + }, + { + "bbox": [ + 305, + 449, + 545, + 496 + ], + "type": "text", + "content": " represents the reconstruction loss. Instead of pixel-based image reconstructions, we use a " + }, + { + "bbox": [ + 305, + 449, + 545, + 496 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 305, + 449, + 545, + 496 + ], + "type": "text", + "content": " loss in the latent space using the original vector " + }, + { + "bbox": [ + 305, + 449, + 545, + 496 + ], + "type": "inline_equation", + "content": "\\mathbf{w}^{(i)} = M(\\mathbf{z}^{(i)})" + }, + { + "bbox": [ + 305, + 449, + 545, + 496 + ], + "type": "text", + "content": " as the target value." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 497, + 545, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 497, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 305, + 497, + 545, + 521 + ], + "type": "text", + "content": "Additionally, to enforce disentanglement, as referred in Eq. (4), we introduce an orthogonality loss:" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 376, + 530, + 545, + 558 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 376, + 530, + 545, + 558 + ], + "spans": [ + { + "bbox": [ + 376, + 530, + 545, + 558 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {o r t h}} = \\sum_ {i \\neq j} \\left\\| \\mathbf {P} _ {i} ^ {T} \\mathbf {P} _ {j} \\right\\| _ {2} ^ {2} \\tag {11}", + "image_path": "35d775b176a7bc3af0c847d28ad8c1ce5a439e3b3871b1be27a957eeb9ca5c59.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 567, + 545, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 567, + 545, + 602 + ], + "spans": [ + { + "bbox": [ + 305, + 567, + 545, + 602 + ], + "type": "text", + "content": "and require that the columns of matrices " + }, + { + "bbox": [ + 305, + 567, + 545, + 602 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_i, \\mathbf{P}_j" + }, + { + "bbox": [ + 305, + 567, + 545, + 602 + ], + "type": "text", + "content": " be orthogonal for " + }, + { + "bbox": [ + 305, + 567, + 545, + 602 + ], + "type": "inline_equation", + "content": "i \\neq j" + }, + { + "bbox": [ + 305, + 567, + 545, + 602 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 305, + 567, + 545, + 602 + ], + "type": "inline_equation", + "content": "\\|\\cdot\\|_2" + }, + { + "bbox": [ + 305, + 567, + 545, + 602 + ], + "type": "text", + "content": " is the element-wise Frobenius-norm." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "spans": [ + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "text", + "content": "Since learning disentangled representations is fundamentally impossible without a supervised inductive bias on the data [23], we leverage the attribute vector " + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "inline_equation", + "content": "\\mathbf{y}^{(i)}" + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "text", + "content": " and introduce a mixing loss to establish the association between " + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "inline_equation", + "content": "S_{k}" + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "inline_equation", + "content": "b_{k}" + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "text", + "content": ". Given a vector " + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "inline_equation", + "content": "\\mathbf{w}^{(i)}" + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "text", + "content": ", we can import attribute " + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "inline_equation", + "content": "b_{k}" + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "text", + "content": " from a randomly chosen vector " + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "inline_equation", + "content": "\\mathbf{w}^{(j)}" + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "text", + "content": ", to generate " + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "inline_equation", + "content": "\\mathbf{w}_{mix}^{(i)}" + }, + { + "bbox": [ + 305, + 604, + 545, + 679 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 365, + 689, + 545, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 365, + 689, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 365, + 689, + 545, + 715 + ], + "type": "interline_equation", + "content": "\\mathbf {w} _ {m i x} ^ {(i)} = \\mathbf {P} _ {k} \\mathbf {a} _ {k} ^ {(j)} + \\sum_ {l \\neq k} \\mathbf {P} _ {l} \\mathbf {a} _ {l} ^ {(i)} \\tag {12}", + "image_path": "a62d3f99da7291a1eaed0efe548f5b1292600e5fa8b5c6b0d1d3926276c32720.jpg" + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "7141" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 70, + 287, + 135 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 70, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 46, + 70, + 287, + 135 + ], + "type": "text", + "content": "and its corresponding image " + }, + { + "bbox": [ + 46, + 70, + 287, + 135 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{mix}^{(i)}\\triangleq G(\\mathbf{w}_{mix}^{(i)})" + }, + { + "bbox": [ + 46, + 70, + 287, + 135 + ], + "type": "text", + "content": ". For the modified image we require " + }, + { + "bbox": [ + 46, + 70, + 287, + 135 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_k(\\mathbf{x}_{mix}^{(i)})" + }, + { + "bbox": [ + 46, + 70, + 287, + 135 + ], + "type": "text", + "content": " to be similar to " + }, + { + "bbox": [ + 46, + 70, + 287, + 135 + ], + "type": "inline_equation", + "content": "y_{k}^{(j)}" + }, + { + "bbox": [ + 46, + 70, + 287, + 135 + ], + "type": "text", + "content": " while keeping the other attributes unchanged. Thus a mixing loss is added to the network to force changes only in " + }, + { + "bbox": [ + 46, + 70, + 287, + 135 + ], + "type": "inline_equation", + "content": "b_{k}" + }, + { + "bbox": [ + 46, + 70, + 287, + 135 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 149, + 286, + 187 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 149, + 286, + 187 + ], + "spans": [ + { + "bbox": [ + 47, + 149, + 286, + 187 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {m i x i n g}} ^ {(i)} = L _ {k} \\left(\\mathcal {C} _ {k} \\left(\\mathbf {x} _ {\\text {m i x}} ^ {(i)}\\right), y _ {k} ^ {(j)}\\right) + \\sum_ {l \\neq k} L _ {l} \\left(\\mathcal {C} _ {l} \\left(\\mathbf {x} _ {\\text {m i x}} ^ {(i)}\\right), y _ {l} ^ {(i)}\\right) \\tag {13}", + "image_path": "88c51d2e0c4fc74cfe961fc153c0f68e4436676b3134e4b55e6107983c48a392.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 188, + 286, + 270 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 188, + 286, + 270 + ], + "spans": [ + { + "bbox": [ + 46, + 188, + 286, + 270 + ], + "type": "inline_equation", + "content": "L_{i}" + }, + { + "bbox": [ + 46, + 188, + 286, + 270 + ], + "type": "text", + "content": " are loss functions that vary based on the attribute types. For categorical labels, we use softmax with cross-entropy loss, whereas continuous labels are optimized using the " + }, + { + "bbox": [ + 46, + 188, + 286, + 270 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 188, + 286, + 270 + ], + "type": "text", + "content": " loss. In practice, we mix all attributes together from randomly chosen vectors. This introduces complex changes to the image and encourages the association of a single subspace with a single attribute." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 271, + 286, + 295 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 271, + 286, + 295 + ], + "spans": [ + { + "bbox": [ + 47, + 271, + 286, + 295 + ], + "type": "text", + "content": "Finally, our model is trained using an objective function comprised of the three losses:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 56, + 300, + 287, + 329 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 300, + 287, + 329 + ], + "spans": [ + { + "bbox": [ + 56, + 300, + 287, + 329 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\lambda_ {\\text {o r t h}} \\mathcal {L} _ {\\text {o r t h}} + \\frac {1}{n} \\sum_ {i} \\mathcal {L} _ {\\text {r e c}} ^ {(i)} + \\lambda_ {\\text {m i x i n g}} \\mathcal {L} _ {\\text {m i x i n g}} ^ {(i)} \\tag {14}", + "image_path": "4b1e53a030278401e2e7111412632e142d460022b8db37553eceb8eb4a6a37b9.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 335, + 222, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 335, + 222, + 347 + ], + "spans": [ + { + "bbox": [ + 47, + 335, + 222, + 347 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 335, + 222, + 347 + ], + "type": "inline_equation", + "content": "\\lambda_{orth}" + }, + { + "bbox": [ + 47, + 335, + 222, + 347 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 335, + 222, + 347 + ], + "type": "inline_equation", + "content": "\\lambda_{mixing}" + }, + { + "bbox": [ + 47, + 335, + 222, + 347 + ], + "type": "text", + "content": " are hyperparameters." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 357, + 128, + 370 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 357, + 128, + 370 + ], + "spans": [ + { + "bbox": [ + 47, + 357, + 128, + 370 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 376, + 287, + 413 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 376, + 287, + 413 + ], + "spans": [ + { + "bbox": [ + 47, + 376, + 287, + 413 + ], + "type": "text", + "content": "In this section, we evaluate the performance of our model compared to state-of-the-art image editing models, all of which utilize the StyleGAN generator for image synthesis." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 413, + 287, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 413, + 287, + 509 + ], + "spans": [ + { + "bbox": [ + 46, + 413, + 287, + 509 + ], + "type": "text", + "content": "To test our model, we generated a source and target latent vector, projected them onto a subspace " + }, + { + "bbox": [ + 46, + 413, + 287, + 509 + ], + "type": "inline_equation", + "content": "S_{k}" + }, + { + "bbox": [ + 46, + 413, + 287, + 509 + ], + "type": "text", + "content": ", and replaced the projections of the source vector with those from the target. Since our subspaces are orthogonal, we expect to see changes only in the corresponding attribute " + }, + { + "bbox": [ + 46, + 413, + 287, + 509 + ], + "type": "inline_equation", + "content": "b_{k}" + }, + { + "bbox": [ + 46, + 413, + 287, + 509 + ], + "type": "text", + "content": ". Example results are presented in Fig. 2. Notably, if the source face wears glasses, these remain post-edit since we only incorporate pose, smile, and race from the target face." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 514, + 237, + 528 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 514, + 237, + 528 + ], + "spans": [ + { + "bbox": [ + 47, + 514, + 237, + 528 + ], + "type": "text", + "content": "4.1. Comparison with Previous Methods" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 533, + 287, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 287, + 652 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 287, + 652 + ], + "type": "text", + "content": "We compared our model with three previous image editing methods: InterFaceGAN [28], StyleFlow [3], and SeFa [29]. We evaluated the editing and disentanglement qualities of these models for a common set of attributes supported by all of them, such as age, gender, smile, pose, and glasses. Additionally, since our method discovers a subspace rather than a single direction, to ensure a fair comparison, we trained a linear SVM inside each subspace. We then used the normal to the hyperplane as the direction for editing. This model is used in Section 4.2 and Section 4.3." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 659, + 182, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 659, + 182, + 672 + ], + "spans": [ + { + "bbox": [ + 47, + 659, + 182, + 672 + ], + "type": "text", + "content": "4.2. Qualitative Comparison" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": "Figure 3 offers a comparative assessment of the quality of real image editing. We inverted the images into StyleGAN's latent space using HyperStyle [4]. 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The attributes derived from the target images include pose, smile, and race." + } + ] + } + ], + "index": 30, + "angle": 0, + "type": "image_caption" + } + ], + "index": 26 + }, + { + "type": "image", + "bbox": [ + 372, + 235, + 422, + 284 + ], + "blocks": [ + { + "bbox": [ + 372, + 235, + 422, + 284 + ], + "lines": [ + { + "bbox": [ + 372, + 235, + 422, + 284 + ], + "spans": [ + { + "bbox": [ + 372, + 235, + 422, + 284 + ], + "type": "image", + "image_path": "d6a0ac7b46003b37512183beec056c82aba7f884ca507a1155d5d50f1ea10fc7.jpg" + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_body" + } + ], + "index": 27 + }, + { + "type": "image", + "bbox": [ + 432, + 235, + 481, + 284 + ], + "blocks": [ + { + "bbox": [ + 432, + 235, + 481, + 284 + ], + "lines": [ + { + "bbox": [ + 432, + 235, + 481, + 284 + ], + "spans": [ + { + "bbox": [ + 432, + 235, + 481, + 284 + ], + "type": "image", + "image_path": "4236c2ac123d4fe47a709a85d7cf971896963d5bb5db2d2667a6128b843126e1.jpg" + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "image_body" + } + ], + "index": 28 + }, + { + "type": "image", + "bbox": [ + 491, + 235, + 541, + 284 + ], + "blocks": [ + { + "bbox": [ + 491, + 235, + 541, + 284 + ], + "lines": [ + { + "bbox": [ + 491, + 235, + 541, + 284 + ], + "spans": [ + { + "bbox": [ + 491, + 235, + 541, + 284 + ], + "type": "image", + "image_path": "c36c3bcc744f653463c535a003dedcb6dd8e9d085239bad14994fc9710e97642.jpg" + } + ] + } + ], + "index": 29, + "angle": 0, + "type": "image_body" + } + ], + "index": 29 + }, + { + "bbox": [ + 304, + 353, + 545, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 353, + 545, + 496 + ], + "spans": [ + { + "bbox": [ + 304, + 353, + 545, + 496 + ], + "type": "text", + "content": "indicate that multiple edits on a single image can significantly diminish its quality, making it more prone to visual artifacts. Moreover, due to biases in the FFHQ dataset [19], some attributes are more correlated in StyleGAN's latent space than others (e.g., younger individuals are less likely to wear glasses). As depicted in Fig. 3, while most models can effectively modify a single attribute, our model outperforms others in terms of accuracy when changing all attributes simultaneously and better maintains each individual attribute edit. Sequential editing is illustrated in Fig. 4, showing that as edits progress, the images retain previous attributes without a loss in quality." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 304, + 497, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 497, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 497, + 545, + 616 + ], + "type": "text", + "content": "In Fig. 1 we visualize our model's capability of generating diverse results for different attributes due to its multidirectional nature. The images are generated by shifting the latent vectors to different directions inside the relevant subspace. We found that some attributes (e.g., smile, pose) behave like binary attributes, meaning they contain most of the information in a single direction. Others (e.g., gender, age), however, can be edited in multiple directions resulting in various images. Additional results can be found in the supplementary material." + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 306, + 623, + 448, + 636 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 623, + 448, + 636 + ], + "spans": [ + { + "bbox": [ + 306, + 623, + 448, + 636 + ], + "type": "text", + "content": "4.3.Quantitative Comparison" + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": "To evaluate our model's disentanglement capabilities, we develop and utilize two different methods: attribute correlation and face preservation. Furthermore, to measure the diversity introduced by multi-directional subspace editing, we utilize the LPIPS score [33] and the Frechet Inception Distance (FID) [14] to evaluate image fidelity." + } + ] + } + ], + "index": 34 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7142" + } + ] + } + ], + "index": 35 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 43, + 69, + 556, + 668 + ], + "blocks": [ + { + "bbox": [ + 43, + 69, + 556, + 668 + ], + "lines": [ + { + "bbox": [ + 43, + 69, + 556, + 668 + ], + "spans": [ + { + "bbox": [ + 43, + 69, + 556, + 668 + ], + "type": "image", + "image_path": "7e869f4bacbf0d82164eabe861c7b88312378c385d335a2dea5af44bc7c62370.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 675, + 546, + 700 + ], + "lines": [ + { + "bbox": [ + 46, + 675, + 546, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 675, + 546, + 700 + ], + "type": "text", + "content": "Figure 3: Comparison of real image editing between our method and the baseline approaches. The edit direction for each attribute was determined using a linear SVM classifier." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7143" + } + ] + } + ], + "index": 2 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 70, + 289, + 223 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 289, + 223 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 289, + 223 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 289, + 223 + ], + "type": "image", + "image_path": "ac137f7ae88d4f63ee23bce109a63705128733cd10dac47352e1c4cc429d4855.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 71, + 232, + 261, + 244 + ], + "lines": [ + { + "bbox": [ + 71, + 232, + 261, + 244 + ], + "spans": [ + { + "bbox": [ + 71, + 232, + 261, + 244 + ], + "type": "text", + "content": "Figure 4: Sequential human face editing result." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "spans": [ + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "text", + "content": "Correlation between edited attributes: We can assign an attribute score to an image " + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "text", + "content": " using " + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_k" + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "text", + "content": " as a feature extractor. The activation vector " + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "inline_equation", + "content": "l(\\mathbf{x})" + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "text", + "content": ", derived from the last hidden layer of " + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_k" + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "text", + "content": ", is used to compute the distance between the feature vector " + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "inline_equation", + "content": "l(\\mathbf{x})" + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "text", + "content": " and the classifying hyperplane. This hyperplane is defined by " + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{v} \\mid \\mathbf{c}_k^T\\mathbf{v} + \\mathbf{t}_k = 0\\}" + }, + { + "bbox": [ + 47, + 266, + 286, + 338 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 338, + 286, + 378 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 338, + 286, + 378 + ], + "spans": [ + { + "bbox": [ + 47, + 338, + 286, + 378 + ], + "type": "text", + "content": "The attribute score of an image " + }, + { + "bbox": [ + 47, + 338, + 286, + 378 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 47, + 338, + 286, + 378 + ], + "type": "text", + "content": " is given by the distance of " + }, + { + "bbox": [ + 47, + 338, + 286, + 378 + ], + "type": "inline_equation", + "content": "l(\\mathbf{x})" + }, + { + "bbox": [ + 47, + 338, + 286, + 378 + ], + "type": "text", + "content": " from the separating hyperplane: " + }, + { + "bbox": [ + 47, + 338, + 286, + 378 + ], + "type": "inline_equation", + "content": "dist_{k}(\\mathbf{x}) = \\frac{\\mathbf{c}_{k}^{T}l(\\mathbf{x}) + \\mathbf{t}_{k}}{|\\mathbf{c}_{k}|}" + }, + { + "bbox": [ + 47, + 338, + 286, + 378 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 378, + 286, + 402 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 378, + 286, + 402 + ], + "spans": [ + { + "bbox": [ + 47, + 378, + 286, + 402 + ], + "type": "text", + "content": "To assess the disentanglement capability of our model, we began by generating an evaluation set comprising " + }, + { + "bbox": [ + 47, + 378, + 286, + 402 + ], + "type": "inline_equation", + "content": "1K" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": "pairs of images paired with their desired face attributes. These images were directly sampled from the StyleGAN generator, while the attributes were independently generated for each image. For each image, we manipulated its latent vector " + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "inline_equation", + "content": "\\mathbf{w} \\in \\mathcal{W}^{+}" + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": " along the learned directions and fed it to the generator to produce an edited version, denoted as " + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_{edit}" + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": ". It's worth noting that in practice we change all attributes simultaneously." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 168, + 545, + 217 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 168, + 545, + 217 + ], + "spans": [ + { + "bbox": [ + 304, + 168, + 545, + 217 + ], + "type": "text", + "content": "Next, we measured the difference in attribute score between the original and the edited images. Taking the attribute \"smile\" as an example, we defined the perceptual distance as: " + }, + { + "bbox": [ + 304, + 168, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\Delta_{smile} = dist_{smile}(\\mathbf{x}_{edit}) - dist_{smile}(\\mathbf{x})" + }, + { + "bbox": [ + 304, + 168, + 545, + 217 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 217, + 545, + 299 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 217, + 545, + 299 + ], + "spans": [ + { + "bbox": [ + 304, + 217, + 545, + 299 + ], + "type": "text", + "content": "For the final assessment, we computed the Pearson correlation between the perceptual distances of every pair of attributes. Each entry in Table 1 displays the absolute correlation value. For instance, for the attributes \"smile\" and \"pose\", we determine the perceptual distances " + }, + { + "bbox": [ + 304, + 217, + 545, + 299 + ], + "type": "inline_equation", + "content": "\\Delta_{smile}" + }, + { + "bbox": [ + 304, + 217, + 545, + 299 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 217, + 545, + 299 + ], + "type": "inline_equation", + "content": "\\Delta_{pose}" + }, + { + "bbox": [ + 304, + 217, + 545, + 299 + ], + "type": "text", + "content": " across the entire evaluation set. The correlation value shown in the table is:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 326, + 307, + 545, + 335 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 326, + 307, + 545, + 335 + ], + "spans": [ + { + "bbox": [ + 326, + 307, + 545, + 335 + ], + "type": "interline_equation", + "content": "\\operatorname {c o r r} (\\text {p o s e}, \\text {s m i l e}) = \\left| \\frac {\\operatorname {c o v} \\left(\\Delta_ {\\text {p o s e}} , \\Delta_ {\\text {s m i l e}}\\right)}{E \\left[ \\Delta_ {\\text {p o s e}} \\right] E \\left[ \\Delta_ {\\text {s m i l e}} \\right]} \\right| \\tag {15}", + "image_path": "9fe5b3e560bbf079f3a9cbc2f44b9a378f6c7a85f8d599c1bf946b1c1c53bd80.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 342, + 545, + 402 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 342, + 545, + 402 + ], + "spans": [ + { + "bbox": [ + 304, + 342, + 545, + 402 + ], + "type": "text", + "content": "Table 1 presents the correlation results of various methods. As previously mentioned [8, 12, 28, 29], we observe that certain attributes exhibit stronger correlations than others. For instance, the glasses-age correlation is consistently higher than the smile-pose correlation across all models." + } + ] + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 92, + 438, + 498, + 711 + ], + "blocks": [ + { + "bbox": [ + 142, + 418, + 449, + 430 + ], + "lines": [ + { + "bbox": [ + 142, + 418, + 449, + 430 + ], + "spans": [ + { + "bbox": [ + 142, + 418, + 449, + 430 + ], + "type": "text", + "content": "Table 1: Attribute correlation matrices of edited images (in absolute values)." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 92, + 438, + 498, + 711 + ], + "lines": [ + { + "bbox": [ + 92, + 438, + 498, + 711 + ], + "spans": [ + { + "bbox": [ + 92, + 438, + 498, + 711 + ], + "type": "table", + "html": "
(a) SeFa(b) InterFaceGan
PoseSmileAgeGenderGlassesposeSmileAgeGenderGlasses
Pose1.0000.1500.0390.1330.051Pose1.0000.0980.0900.0170.079
Smile0.1501.0000.0010.1700.233Smile0.0981.0000.1540.1980.084
Age0.0390.0011.0000.5330.367Age0.0900.1541.0000.5650.600
Gender0.1330.1700.5331.0000.339Gender0.0170.1980.5651.0000.363
Glasses0.0510.2330.3670.3391.000Glasses0.0790.0840.6000.3631.000
Avg0.0930.1150.2350.2930.247Avg0.0710.1330.3520.2850.281
(c) StyleFlow(d) Ours
PoseSmileAgeGenderGlassesPoseSmileAgeGenderGlasses
Pose1.0000.1130.1260.1030.056Pose1.0000.0180.0080.0290.046
Smile0.1131.0000.2640.0110.074Smile0.0181.0000.1200.0500.100
Age0.1260.2641.0000.5810.494Age0.0080.1201.0000.3880.363
Gender0.1030.0110.5811.0000.338Gender0.0290.0500.3881.0000.203
Glasses0.0560.0740.4940.3381.000Glasses0.0460.1000.3630.2031.000
Avg0.0990.1150.3660.2580.240Avg0.0250.0720.2190.1670.178
", + "image_path": "5be5be3dfaeaa42c2f1a81593b6841c572d6ecb7ecb42a2dcdb5b44bd1e04229.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7144" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 122 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 122 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 122 + ], + "type": "text", + "content": "The table's final row sums the off-diagonal columns, representing the average correlation score. Our method's lower scores highlight its superior disentanglement capabilities compared to the other techniques." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 125, + 288, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 125, + 288, + 258 + ], + "spans": [ + { + "bbox": [ + 46, + 125, + 288, + 258 + ], + "type": "text", + "content": "In our previous assessment, all attributes were adjusted simultaneously. To test the stability of attributes when only one is modified, we conducted an experiment editing one attribute at a time and measured the perceptual distances using the classifiers' final layers. Fig. 5 displays results from various methods. The x-axis represents changes in the edited attribute, while the y-axis indicates unintentional changes in other attributes. As edits become more extensive, the inter-attribute effect is more pronounced. Among all models, our approach shows the least deviation, indicating superior attribute disentanglement." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 262, + 289, + 334 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 262, + 289, + 334 + ], + "spans": [ + { + "bbox": [ + 46, + 262, + 289, + 334 + ], + "type": "text", + "content": "Face Identity Preservation: Following the approach of the face identity score [3], we assess the edited images using a pre-trained face embedding network [9]. We restricted our edits to attributes that should preserve identity, such as pose, glasses, and smile. After editing, we embedded the images into a latent space using the network. We then calculated" + } + ] + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 313, + 91, + 538, + 203 + ], + "blocks": [ + { + "bbox": [ + 310, + 71, + 541, + 84 + ], + "lines": [ + { + "bbox": [ + 310, + 71, + 541, + 84 + ], + "spans": [ + { + "bbox": [ + 310, + 71, + 541, + 84 + ], + "type": "text", + "content": "Table 2: Identity preservation scores by different models." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 313, + 91, + 538, + 203 + ], + "lines": [ + { + "bbox": [ + 313, + 91, + 538, + 203 + ], + "spans": [ + { + "bbox": [ + 313, + 91, + 538, + 203 + ], + "type": "table", + "html": "
EditMetricSeFaInterFaceGanStyleFlowOurs
SmileCs ↑0.9700.9780.9890.991
Ed ↓0.3290.2760.1920.174
PoseCs ↑0.9780.9790.9810.982
Ed ↓0.2830.2790.26620.253
GlassesCs ↑0.9660.9780.9840.985
Ed ↓0.3480.2700.2270.215
AllCs ↑0.9110.9330.9350.948
Ed ↓0.6220.5370.5340.467
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Our method consistently surpasses other techniques across all types of edits. While StyleFlow shows comparable scores for individual attribute edits, our model excels in preserving identity when multiple edits are combined." + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 62, + 355, + 149, + 415 + ], + "blocks": [ + { + "bbox": [ + 62, + 355, + 149, + 415 + ], + "lines": [ + { + "bbox": [ + 62, + 355, + 149, + 415 + ], + "spans": [ + { + "bbox": [ + 62, + 355, + 149, + 415 + ], + "type": "image", + "image_path": "80bfee8bd1c8d0472d2955137fa8db024501603106f1e5c73166b491d2eeb793.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 156, + 355, + 244, + 414 + ], + "blocks": [ + { + "bbox": [ + 156, + 355, + 244, + 414 + ], + "lines": [ + { + "bbox": [ + 156, + 355, + 244, + 414 + ], + "spans": [ + { + "bbox": [ + 156, + 355, + 244, + 414 + ], + "type": "image", + "image_path": "b3b5ba119ab085a14b2efb47a109e06c965ddfd614c790421ff3b4ef3a1d5f59.jpg" + } + ] + } + 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Diversity Analysis" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 287, + 187 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 287, + 187 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 287, + 187 + ], + "type": "text", + "content": "In the previous sections, we introduced a single-direction variant of our model. Now, we will explore the performance of our model when multiple directions in the subspace are utilized for editing. To measure the diversity of the images produced by our model, we employed the LPIPS perceptual similarity score [33]. 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The FID score was also calculated to assess the visual quality of the generated images." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 297, + 287, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 297, + 287, + 392 + ], + "spans": [ + { + "bbox": [ + 46, + 297, + 287, + 392 + ], + "type": "text", + "content": "The results, summarized in Table 3, reveal that our approach — when multi-directional subspace editing is employed — not only fosters greater image diversity (as indicated by the LPIPS score) but also ensures superior visual quality (as denoted by the FID score). It's noteworthy that there is a marked enhancement in the multi-directional iteration of our model (subspace) when compared against its single-direction counterpart (SVM) or against StyleFlow." + } + ] + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 99, + 462, + 237, + 514 + ], + "blocks": [ + { + "bbox": [ + 46, + 405, + 287, + 453 + ], + "lines": [ + { + "bbox": [ + 46, + 405, + 287, + 453 + ], + "spans": [ + { + "bbox": [ + 46, + 405, + 287, + 453 + ], + "type": "text", + "content": "Table 3: Diversity score results for edited images. Our multi-directional model achieves a higher score which indicates its ability to generate more diverse results while maintaining a lower FID score." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 99, + 462, + 237, + 514 + ], + "lines": [ + { + "bbox": [ + 99, + 462, + 237, + 514 + ], + "spans": [ + { + "bbox": [ + 99, + 462, + 237, + 514 + ], + "type": "table", + "html": "
MethodLPIPS ↑FID ↓
StyleFlow0.21327.467
Our (svm)0.22926.926
Our (subspace)0.32123.648
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We trained a version of our model with " + }, + { + "bbox": [ + 46, + 556, + 287, + 640 + ], + "type": "inline_equation", + "content": "\\lambda_{orth} = 0" + }, + { + "bbox": [ + 46, + 556, + 287, + 640 + ], + "type": "text", + "content": ", keeping all other configurations, including losses and the training process, consistent. Post-training, we conducted consecutive edits starting from an original image, and the results can be viewed in Fig. 6." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 642, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 288, + 713 + ], + "type": "text", + "content": "We found that images edited with the orthogonality loss exhibit crisper details and fewer visual artifacts when subjected to multiple edits. We also carried out the same quantitative evaluations as detailed in Section 4.3. The results in Tables 4 and 5 indicate that our orthogonality loss leads to better attribute disentanglement in our model." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 408, + 71, + 451, + 83 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 408, + 71, + 451, + 83 + ], + "spans": [ + { + "bbox": [ + 408, + 71, + 451, + 83 + ], + "type": "interline_equation", + "content": "\\lambda_ {o r t h} = 0", + "image_path": "48b678a39c66acdd4ad109c45c341b4e3564e04926a2fb63b961c43385dec45b.jpg" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 313, + 85, + 373, + 135 + ], + "blocks": [ + { + "bbox": [ + 313, + 85, + 373, + 135 + ], + "lines": [ + { + "bbox": [ + 313, + 85, + 373, + 135 + ], + "spans": [ + { + "bbox": [ + 313, + 85, + 373, + 135 + ], + "type": "image", + "image_path": "a6a55509796f889dfc4194807bfba2ae7abcea326a401564644b0e611f3b48b6.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + } + ], + 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The values represent the average correlation between an attribute and others." + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 306, + 418, + 522, + 458 + ], + "lines": [ + { + "bbox": [ + 306, + 418, + 522, + 458 + ], + "spans": [ + { + "bbox": [ + 306, + 418, + 522, + 458 + ], + "type": "table", + "html": "
ModelPoseSmileAgeGenderGlasses
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EditMetricλorth=0λorth=0.001
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Conclusions" + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "In this work we proposed MDSE, a disentangling generative model for multi-attribute image editing. We introduce the concept of orthogonal subspaces that support multi-directional edits for diverse image generation. Additionally, this model effectively identifies disentangled latent subspaces, allowing precise control over the generated images and the displayed face attributes. We believe that integrating these concepts during the generator's training could further enhance the performance of disentangled models." + } + ] + } + ], + "index": 34 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "7146" + } + ] + } + ], + "index": 35 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 107, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 107, + 84 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 107, + 84 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Rameen Abdul, Yipeng Qin, and Peter Wonka. 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A plethora of work characterized by using a two-stream Vision-Language model architecture that learns a joint representation of video-text pairs has become a prominent approach for the VTR task. However, these models operate under the assumption of bijective video-text correspondences and neglect a more practical scenario where video content usually encompasses multiple events, while texts like user queries or webpage metadata tend to be specific and correspond to single events. This establishes a gap between the previous training objective and real-world applications, leading to the potential performance degradation of earlier models during inference. In this study, we introduce the Multi-event Video-Text Retrieval (MeVTR) task, addressing scenarios in which each video contains multiple different events, as a niche scenario of the conventional Video-Text Retrieval Task. We present a simple model, MeRetriever, which incorporates key event video representation and a new MeVTR loss for the MeVTR task. Comprehensive experiments show that this straightforward framework outperforms other models in the Video-to-Text and Text-to-Video tasks, effectively establishing a robust baseline for the MeVTR task. We believe this work serves as a strong foundation for future studies. Code is available at https://github.com/gengyuanmax/MeVTR.", + "bbox": [ + 76, + 335, + 472, + 729 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 758, + 209, + 773 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "With the proliferation of multimedia data on the Internet every day, Video-Text Retrieval (VTR) task gains increasing importance in searching for desired items from the opposite modality given a video or text query. Over the past years, numerous efforts [49, 33, 9, 14, 31, 3, 7, 30, 16, 12, 51, 17] have been undertaken to improve the", + "bbox": [ + 75, + 784, + 468, + 876 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "multi-modal retrieval performance on both Video-to-Text and Text-to-Video retrieval tasks. Along with the popularity of powerful vision foundation models like CLIP [36] and ALIGN [23] that align the image-text pairs in a joint feature space, two-stream video-text models [30, 16] targeting to learn video-text correspondences have further become a mainstream method for the Video-Text Retrieval task.", + "bbox": [ + 500, + 305, + 890, + 411 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "However, this paradigm neglects that videos usually contain more than a single event, while a single textual caption can only capture a fragment of the entire video content. As depicted in Fig. 1, the example video spans a sequence of unrelated and discontinuous events, and each single textual caption merely corresponds to a video segment. This congruity undoubtedly contradicts the fundamental of the traditional VTR task, which aims to establish a mapping between video-text pair.", + "bbox": [ + 496, + 412, + 892, + 549 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "This fact presents a prevalent scenario in Video-Text Retrieval: videos are intricate, often containing multiple events, whereas texts (typically like search queries or webpage metadata) tend to be specific and fragmentary. Consequently, this dichotomy leads to divergent semantic meanings for a given video-text pair. Such divergence contradicts the conventional training objective of aligning representations for video-text pairs in VTR models, that video features are aligned with the corresponding text feature.", + "bbox": [ + 496, + 550, + 893, + 686 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this study, we formally introduce a new and realistic VTR setting involving multi-event videos, dubbed as Multi-event Video-Text Retrieval (MeVTR). In the introduced MeVTR task, a text describes a single event within a video item, whereas a video corresponds to multiple relevant textual captions, each detailing different events.", + "bbox": [ + 496, + 686, + 893, + 779 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We assess the performance of previous VTR models trained under standard VTR settings that learn a bijective video-text correspondence on the MeVTR task without retraining. Our evaluation reveals distinct levels of performance degradation, as illustrated in Table 1. This observation confirms the presence of a performance gap between training within the conventional VTR framework and real-world MeVTR inference scenarios.", + "bbox": [ + 496, + 779, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author", + "bbox": [ + 94, + 887, + 220, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "22113", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d6fa1a8373a7abedecd5d969a4508e2e36c4dd1128ee74119c5093b6978074b1.jpg", + "image_caption": [ + "Figure 1: An example case of multi-event videos from ActivityNet [4]. The video depicts a sequence of unrelated and discontinuous events, including the progression \"a girl is sitting on the beach\" $\\rightarrow$ \"a young man is practicing tightrope walking\" $\\rightarrow$ \"a scene of sunset by the beach.\" Each textual caption only corresponds to a fragment of the video. Such short and specific textual captions are prevalent in our everyday video data and constitute a common video-text retrieval scenario." + ], + "image_footnote": [], + "bbox": [ + 86, + 103, + 885, + 299 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Besides, we retrain a series of previous models to adapt to the MeVTR task. However, we find that they cannot perform equally well on the Video-to-Text and Text-to-Video. We speculate that this is caused by non-injective videotext correspondences in the MeVTR setting, where previous VTR models embed a video and multiple distinct caption texts into a joint representation space and aim at aligning the video feature with the features of all caption texts. Consequently, distinct texts corresponding to the same video are mapped to the same feature, potentially resulting in suboptimal retrieval performance.", + "bbox": [ + 75, + 405, + 472, + 570 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Under this circumstance, we introduce a new CLIP-based model dubbed Me-Retriever tailored for the MeVTR task. Considering the dichotomy of multi-event video-text pairs, we formulate our approach as follows: (1) representing videos by a bag of key event features and (2) employing a multi-event video-text retrieval loss. This strategy serves the dual purpose of mitigating the collapse of textual features and harmonizing the learning objectives between the Text-to-Video and Video-to-Text tasks.", + "bbox": [ + 75, + 571, + 472, + 705 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our contributions can be summarized as follows:", + "bbox": [ + 96, + 707, + 421, + 720 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. We introduce a new task, Multi-event Video-Text Retrieval for retrieving multi-event video-text pairs, and define new evaluation metrics in MeVTR;", + "2. We propose a new model called Me-Retriever that represents videos with selected key events and a MeVTR loss for training on MeVTR;", + "3. We conduct comprehensive experiments to showcase Me-Retriever's effectiveness and to establish it as a simple yet robust baseline for future research." + ], + "bbox": [ + 88, + 731, + 470, + 888 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 402, + 640, + 419 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Video Language Model A series of work on Vision-Language Models (VLM) has been made like [26, 29, 5, 57, 53] for multi-modal representation learning. Given that videos are a structured sequence of images and typically entail higher computational demands than other visual data formats, the domain of Video-Language models has garnered significant attention. Notable contributions within this category include works by [40, 24, 38, 49, 29, 23, 43, 19, 13] which aim at video foundation models for video tasks. These models represent a subcategory of VLMs, adept at processing video and text inputs.", + "bbox": [ + 496, + 431, + 890, + 599 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Video Representation In a line of work [42, 52, 18, 25], convolutions are performed on videos to fuse spatial and temporal information. Meanwhile, as transformers [44] have achieved success firstly in text [8], and then vision fields [11, 27, 41, 6], attempts to introduce transformers to extract video representations have been made in [39, 2, 47, 56, 32, 28]. The success of pre-trained Vision-Language models has significantly impacted video representation learning. Vision-Language models [29, 38, 31, 36] have demonstrated that textual supervision is conducive to visual representation and to a uniform video-language representation. Among them, the success of representation models [22, 16, 45, 46] has bridged the gap between video and text representations.", + "bbox": [ + 496, + 606, + 892, + 816 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Video-Text Retrieval Video-Text Retrieval is a fundamental task of multi-modal learning, posing a good proxy task for learning joint representations of videos and texts. Two-stream Video-Text models [10, 9, 51, 34] concentrate on processing video-text pairs as inputs and aligning vi", + "bbox": [ + 496, + 824, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "22114", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "table", + "img_path": "images/d754aaef9f808622b5afcdb1a46bc42b642afb2e3b00e71f15ccb26f4ed69427.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Video-to-TextText-to-Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑Median Rank ↓k=1 ↑k=5 ↑k=10 ↑
FROZEN-in-time7.0 ↗ 109.515.3 ↗ 0.843.3 ↗ 3.143.3 ↗ 5.67.0 ↗ 111.015.9 ↗ 1.843.0 ↗ 6.859.01 ↗ 11.7
CLIPBERT4.0 ↗ 449.022.1 ↗ 1.458.2 ↗ 4.769.6 ↗ 7.65.0 ↗ 153.025.9 ↗ 2.655.4 ↗ 9.569.8 ↗ 15.1
CLIP4Clip2.0 ↗ 53.042.5 ↗ 7.574.1 ↗ 19.885.8 ↗ 28.413.0 ↗ 53.014.8 ↗ 7.534.2 ↗ 19.845.6 ↗ 28.4
CenterCLIP2.0 ↗ 51.042.8 ↗ 7.873.8 ↗ 20.885.3 ↗ 29.22.0 ↗ 13.041.8 ↗ 15.173.9 ↗ 34.684.7 ↗ 46.4
", + "bbox": [ + 86, + 88, + 893, + 183 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Table 1: Comparison of model performance on VTR and MeVTR tasks on ActivityNet Captions. We train each model on the ActivityNet Captions with its original codes and evaluate them on MeVTR. We show the performance of VTR on the lefthand of $\\nabla (\\nearrow)$ and the performance of MeVTR on the right. $\\uparrow$ means higher the better, and $\\downarrow$ means lower the better. It is shown that model performance deteriorates to a large extent on both Video-to-Text and Text-to-Video tasks.", + "bbox": [ + 75, + 193, + 893, + 255 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "sual and textual representations within a joint representation space. For instance, Frozen [3] employs a visual encoder that can be adaptively trained on images and videos, incorporating temporal contexts via curriculum learning. TACo [51], in contrast, focuses on aligning content words in texts with corresponding visual content, adding an extra learning objective. With the surge of large Vision-Language foundation models representative of CLIP [36], models [30, 16, 12, 35, 3, 50], leverage the potent pretrained model CLIP and endeavor to extend its capabilities from static images to the domain of videos.", + "bbox": [ + 75, + 281, + 472, + 448 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Problem", + "text_level": 1, + "bbox": [ + 76, + 469, + 174, + 484 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Problem Formulation", + "text_level": 1, + "bbox": [ + 76, + 497, + 279, + 512 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given a video-text dataset with multi-event videos $\\mathcal{V}$ and texts $\\mathcal{T}$ , where a video $v_{i} \\in \\mathcal{V}$ is described by a set of different texts $\\mathcal{T}_{i} \\subset \\mathcal{T}$ and a text is denoted as $t_{j}$ , our task consists in retrieving a video given a text query $t^{q}$ and retrieving all relevant texts given a video query $v^{q}$ . A generic Video-Text Retrieval model is to learn a similarity function $sim(v_{i}, t_{j})$ that scores the similarity between any relevant video-text pair higher and ranks all the candidate items.", + "bbox": [ + 75, + 523, + 470, + 645 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Evaluation Metrics", + "text_level": 1, + "bbox": [ + 76, + 662, + 261, + 678 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Video-Text retrieval is a recall-focused retrieval task. A single item is retrieved in traditional settings, and the average Recall at the top rank $k$ is calculated. Nevertheless, in the MeVTR setting, we also want to evaluate retrieving multiple different text items given one video. Hence we devise the following metrics: (1) Recall@k-Average as the fraction of the number of correspondences ranked at top $k$ ; (2) Recall@k-One-Hit as an indication of whether any of the correspondences will be ranked in the top $k$ ; (3) Recall@k-All-Hit as an indication of whether all items can be retrieved within the top $k$ rank. All metrics are averaged on the whole test set. In the follow-up experiments, we report the Recall for the Text-to-Video tasks and the metrics mentioned above for the Video-to-Text tasks.", + "bbox": [ + 75, + 688, + 470, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. Textual Feature Collapse", + "text_level": 1, + "bbox": [ + 498, + 280, + 728, + 296 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To investigate the textual feature collapse in previous models to elucidate the performance drop by calculating the textual feature's similarity after retraining, we define the average text similarity of a video $v_{i}$ with $n_{v_i}$ captions as:", + "bbox": [ + 496, + 303, + 890, + 364 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {s i m} _ {t} \\left(v _ {i}\\right) = \\sum_ {m = 1} ^ {N _ {v _ {i}}} \\sum_ {n = 1} ^ {N _ {v _ {i}}} \\frac {1}{N _ {v _ {i}} ^ {2}} \\operatorname {s i m} \\left(t _ {m}, t _ {n}\\right) \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 376, + 890, + 421 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In Fig. 3, we attempt to visualize the average text similarity of all videos with a different number of events. Different texts are expected to have lower sentence similarity to retain their meanings due to retraining on MeVTR. We chose CLIP4Clip for comparison in our experiments, as it still performs relatively well in MeVTR tasks compared to other models. As a comparison, we show that Me-R retriever, which will be introduced in the next section, can generate more diverse textual features than CLIP4Clip and effectively avoid textual feature collapse.", + "bbox": [ + 496, + 431, + 890, + 583 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. Method", + "text_level": 1, + "bbox": [ + 498, + 597, + 589, + 612 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We propose Me-Retriever consisting of a Key Event Selection module and MeVTR loss as shown in Fig. 2.", + "bbox": [ + 496, + 622, + 890, + 652 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4.1. Key Event Video Representation", + "text_level": 1, + "bbox": [ + 498, + 662, + 785, + 679 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Intuitively, human brains do not remember experiences with all continuous scenes and consolidate all the details. Instead, brains retain memories of certain discrete events [55]. This insight motivates us to represent a video with a bag of frames as key events. For leveraging frame embeddings extracted from the CLIP visual encoder $\\{\\mathbf{f}_i^1,\\mathbf{f}_i^2,\\dots ,\\mathbf{f}_i^{[v_i]}\\}$ , we define the Key Event Selection module that selects the most distinctive keyframes.", + "bbox": [ + 496, + 686, + 890, + 809 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We employ a classic clustering method, K-Medoids [1]. Compared to other clustering methods, the representative of each cluster given by the K-Medoids algorithm is from the sample points, which corresponds to a particular frame and has explicit interpretation. The criterion is minimizing the distance of all frames in the cluster to its medoid. $K$ frames", + "bbox": [ + 496, + 810, + 893, + 898 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "22115", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/ff7eba4eb35ab607ba87f767e3afdcf0e307a29e1ecbe61359498c7ec562fdd7.jpg", + "image_caption": [ + "Figure 2: The overall framework of Me-Retriever. The model adopts CLIP [36]'s Visual Encoder(VE) and Text Encoder(TE). After the Visual Encoder, [CLASS] tokens in the last hidden layer are taken as frame embeddings. We use a clustering-based Key Event Selection module to aggregate similar frames and extract key events. Each textual caption is fed into Text Encoder, and [EOS] will be used as text embedding. The similarity between these key events of any video $v_{i}$ and any textual caption $t_j$ is measured in the Similarity Calculator. For each video, there are multiple text correspondences as positive samples." + ], + "image_footnote": [], + "bbox": [ + 91, + 98, + 888, + 319 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/306576039b7a18a9c91a583eeae74cfa1e0c5c65c5f0ab6cf7851ff459c92356.jpg", + "image_caption": [ + "Figure 3: We compare the average cosine similarity between all text pairs of videos with a different number of events. Me-Retriever can generate more diverse text features than CLIP4Clip and refrain from text features collapsing, as we discuss in the main part." + ], + "image_footnote": [], + "bbox": [ + 94, + 460, + 455, + 664 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "are chosen as initial medoids; the remaining frames are then assigned to their nearest medoids, and within each cluster, new medoids are again selected based on cosine similarity as a metric function. Video $v_{i}$ can be represented as a sequence of key event embeddings $\\mathbf{K}_i = \\{\\mathbf{k}_i^1,\\mathbf{k}_i^2,\\dots ,\\mathbf{k}_i^K\\}$ . In the loss calculation, we use the pre-computed assignment of all frames as key event video representation.", + "bbox": [ + 75, + 794, + 472, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. MeVTR Loss", + "text_level": 1, + "bbox": [ + 500, + 459, + 638, + 474 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Following the dual learning paradigm of Text-to-Video and Video-to-Text on VTR tasks, we propose MeVTR loss for MeVTR learning. As previously discussed, there is an issue of textual feature collapse during MeVTR training. To address this, we propose disentangling various positive instances within video samples by excluding non-self positive instances from the softmax function. Moreover, considering the dissimilar granularity between multi-event videos and single-event text, we propose adopting a dynamic weighting strategy. This strategy balances the loss scale of both learning objectives during the training process.", + "bbox": [ + 496, + 484, + 890, + 651 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "MeVTR loss is defined as a weighted sum of $\\mathcal{L}_{t2v}$ and $\\mathcal{L}_{v2t}$ as follows:", + "bbox": [ + 500, + 652, + 893, + 683 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {M e V T R} = \\mathcal {L} _ {v 2 t} + \\alpha \\mathcal {L} _ {t 2 v} \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 604, + 698, + 890, + 714 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{v2t}$ and $\\mathcal{L}_{t2v}$ are respectively formulated as:", + "bbox": [ + 517, + 729, + 864, + 746 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {v 2 t} = - \\frac {1}{| \\mathcal {B} |} \\sum_ {i} ^ {| \\mathcal {B} |} \\sum_ {k} ^ {| \\mathcal {T} _ {i} |} \\frac {1}{| \\mathcal {T} _ {i} |} \\log \\frac {\\exp s i m (\\mathbf {K} _ {i} , \\mathbf {w} _ {k}) / \\tau}{\\sum_ {j = 1} ^ {\\mathcal {B} - \\cup \\{k \\}} \\exp s i m (\\mathbf {K} _ {i} , \\mathbf {w} _ {j}) / \\tau},\n$$\n", + "text_format": "latex", + "bbox": [ + 500, + 773, + 913, + 830 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {t 2 v} = - \\frac {1}{| \\mathcal {B} |} \\sum_ {j} ^ {| \\mathcal {B} |} \\log \\frac {\\exp \\operatorname {s i m} \\left(\\mathbf {K} _ {i} , \\mathbf {w} _ {j}\\right) / \\tau}{\\sum_ {i = 1} ^ {\\mathcal {B}} \\exp \\operatorname {s i m} \\left(\\mathbf {K} _ {j} , \\mathbf {w} _ {j}\\right)) / \\tau}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 516, + 859, + 892, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "22116", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/c1e786525cc39871747ad57ec41e244094c21c3bccf0ddf0827a69427d3053d6.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Video-to-Text
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)39.06.60 / 20.74 / -20.32 / 47.02 / 3.4629.37 / 61.26 / 6.7158.41 / 89.77 / 26.24
CLIP4Clip(tight)49.55.23 / 16.45 / -16.74 / 41.94 / 1.7725.50 / 57.37 / 4.2354.22 / 88.00 / 21.52
CenterCLIP38.06.93 / 21.62 / -20.58 / 47.98 / 3.6629.90 / 61.72 / 6.9658.88 / 90.34 / 26.28
FROZEN-in-time330.00.30 / 0.67 / -0.83 / 2.10 / 0.221.60 / 3.37 / 0.675.89 / 12.97 / 2.55
CLIPBERT174.51.80 / 6.10 / -6.48 / 18.97 / 0.1810.93 / 29.00 / 0.8731.34 / 61.42 / 8.72
Singularity64.54.83 / 14.68 / -15.1 / 37.79 / 1.9522.23 / 49.50 / 4.4148.96 / 81.94 / 19.38
Ours(avg)35.08.52 / 26.91 / -23.56 / 54.18 / 3.8632.95 / 67.13 / 7.7961.26 / 92.50 / 27.80
Ours(max)49.06.98 / 22.72 / -18.72 / 46.37 / 2.3027.04 / 60.62 / 5.7654.19 / 88.37 / 20.90
", + "bbox": [ + 96, + 88, + 885, + 258 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/a722a099db0333d12877508fadcba4c0e237bbd79eb7ccd8ab11e944988a256d.jpg", + "table_caption": [ + "Table 2: Results of the Video-to-Text retrieval task on ActivityNet Captions dataset. In each column, we report the Recall@k-Average/One-Hit/All-Hit for each $k = 1,5,10,50$ respectively. The best result in each column is emphasized in bold. We ignore the Recall@1-All-Hit since all models can only achieve a nearly zero result. Ours(avg) maintains its advantage in the text retrieval task and surpasses all other models by a large margin." + ], + "table_footnote": [], + "table_body": "
Video-to-Text
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)441.51.32 / 2.92 / -4.07 / 8.32 / 1.805.65 / 11.84 / 2.5516.84 / 32.01 / 7.65
CLIP4Clip(tight)391.00.80 / 1.80 / -2.45 / 6.30 / 0.754.19 / 10.27 / 1.3515.26 / 30.43 / 6.37
CenterCLIP408.01.32 / 3.00 / -3.71 / 7.87 / 1.576.33 / 13.42 / 2.6217.37 / 33.43 / 7.72
FROZEN-in-time810.00.30 / 0.67 / -0.83 / 2.10 / 0.221.60 / 3.37 / 0.675.89 / 12.97 / 2.55
ClipBERT1339.50.15 / 0.45 / -0.60 / 1.50 / 0.151.19 / 3.30 / 0.225.31 / 11.92 / 1.87
Singularity621.50.95 / 2.17 / -2.84 / 5.92 / 1.424.35 / 9.52 / 1.9512.22 / 25.94 / 4.87
Ours(avg)406.01.39 / 3.22 / -5.04 / 9.90 / 2.477.02 / 13.72 / 3.3717.62 / 32.08 / 8.70
Ours(max)365.61.01 / 2.62 / -4.03 / 9.00 / 1.726.39 / 13.72 / 2.7019.08 / 36.66 / 8.10
", + "bbox": [ + 96, + 344, + 885, + 523 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 3: Results of the Video-to-Text retrieval task on Charades-Event dataset. We use the same notation as in Tab. 2. MeRetriever(avg) and Me-Retriever(max) can achieve best performance.", + "bbox": [ + 75, + 534, + 892, + 566 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$sim(\\cdot)$ is the similarity function, $\\mathcal{B}$ is the set of samples in the training batch, $\\mathcal{B}^{-}$ is the set of negative samples in the batch, $\\tau$ is the temperature coefficient, and $\\mathcal{T}_i$ is the set of positive instances of one sample video in $\\mathcal{L}_{t2v}$ . Notably, given a video item $v_{i}$ , we discard all positive instances in $\\mathcal{T}_i$ other than the current training sample $t_k$ . This encourages similarities between a video and its all positive instances to be increased. In $\\mathcal{L}_{t2v}$ , it degenerates to a normal softmax function.", + "bbox": [ + 75, + 590, + 470, + 727 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We denote $\\alpha$ as the weighting coefficient that balances $\\mathcal{L}_{t2v}$ and $\\mathcal{L}_{v2t}$ . Given that the two losses exhibit differing scales during training, which owes to the positive/negative sample ratio asymmetry, determining the value of $\\alpha$ requires employing certain hyperparameter-tuning techniques to ensure balanced performance on both tasks. We suggest employing a dynamic weighting strategy as opposed to a fixed weight. A dynamic weighting coefficient $\\alpha$ is computed as the ratio of $\\mathcal{L}_{v2t}$ to $\\mathcal{L}_{t2v}$ during training. In Section 5.3, we conduct experimental studies to compare the impact of various weighting strategies.", + "bbox": [ + 75, + 734, + 472, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Similarity function For video-text pairs in bijective correspondences, the similarity between video and text is measured by cosine similarity in the feature space. In MeVTR, we use two approaches are used to measure the similarity between a video $v_{i}$ consisting of key events $\\{\\mathbf{k}_i^1,\\mathbf{k}_i^2,\\dots ,\\mathbf{k}_i^K\\}$ and a text $t_j$ : (1) we average the cosine similarity scores of all key event embeddings and the text as in Eq. 5; (2) we select the maximum cosine similarity of any key event-text pair to represent the similarity between the video to which these medoids belong as in Eq. 6;", + "bbox": [ + 496, + 590, + 893, + 758 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\ns _ {a v g} (v _ {i}, t _ {j}) = \\operatorname {a v g} \\left(\\cos \\left(\\mathbf {k} _ {1} ^ {i}, \\mathbf {w} _ {j}\\right), \\dots , \\cos \\left(\\mathbf {k} _ {k} ^ {i}, \\mathbf {w} _ {j}\\right)\\right) \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 513, + 780, + 892, + 799 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\ns _ {m a x} (v _ {i}, t _ {j}) = \\max (\\cos (\\mathbf {k} _ {1} ^ {i}, \\mathbf {w} _ {j}), \\dots , \\cos (\\mathbf {k} _ {k} ^ {i}, \\mathbf {w} _ {j})) \\quad (6)\n$$\n", + "text_format": "latex", + "bbox": [ + 511, + 830, + 892, + 849 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We denote Me-Retriever with different similarity functions as Me-Retriever(avg) and Me-Retriever(max).", + "bbox": [ + 500, + 869, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "22117", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/e2a66038832c36a09d594f994e5d1a65b28bb7370f558f783cfb52c33adcae76.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Text-to-Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)11.015.2536.4349.1176.64
CLIP4Clip(tight)15.010.1429.0741.9372.50
CenterCLIP11.015.5337.2149.7877.19
FROZEN-in-time111.01.826.8011.7633.86
ClipBERT48.04.2014.5723.3551.02
Singularity(FT)22.09.2924.9636.2665.55
Ours(avg)11.015.9937.1349.6076.66
Ours(max)13.014.9334.4446.3674.65
", + "bbox": [ + 86, + 88, + 470, + 223 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 76, + 359, + 209, + 378 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Experiment Details", + "text_level": 1, + "bbox": [ + 76, + 388, + 261, + 407 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Datasets We perform experiments on two datasets containing multi-event videos: ActivityNet Captions and Charades-Event. It's worth noting that datasets such as MSR-VTT [48], even though videos are accompanied by multiple similar captions, do not align with our multi-event scenario.", + "bbox": [ + 75, + 425, + 468, + 515 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "ActivityNet Captions [20] is a large-scale dataset with 20,000 video-text pairs extracted by web crawling on YouTube based on ActivityNet [4] videos. It covers a wide range of daily scenarios. The training set contains 10,009 videos and 4,917 videos/17,505 texts in the publicly accessible evaluation set 'val1'. Each video has multiple textual descriptions with time-interval annotation. This helps us construct a multi-event scenario for retrieval by taking all textual captions of a video as its associated events.", + "bbox": [ + 75, + 520, + 468, + 656 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Charades-Event is a video dataset of indoor activities with extensive action classes that we adopt from [37]. To create a MeVTR dataset, we filter out all videos with text annotation provided by [15] and interpret each text as an event in our MeVTR setting. There are 5,338 videos/12,408 texts in the training set and 1,334 videos/3,720 texts in the test set.", + "bbox": [ + 75, + 661, + 468, + 752 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Experiment Settings In the key event selection module, we use 60 as the maximum number of iterations and $10^{-5}$ as the distance threshold for clustering. Our model chooses 16 as a fixed number of key events and does not use a smaller or larger number of key events because shorter sequences cannot cover the number of events in part of the videos (the maximum event number in ActivityNet Captions is 27), and longer sequences contradict our intention of clustering. For each experiment, we set the epoch number as 5.", + "bbox": [ + 75, + 763, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/4a4eda5de264fb889181e990d2a1f992fb1f9a89d76983f34cd1945ff579fdd6.jpg", + "table_caption": [ + "Table 4: Results of the Text-to-Video retrieval task on ActivityNet Captions dataset. We compare CLIP4Clip [30], CenterCLIP [54], FROZEN-in-time [3], ClipBERT [22], and [21]. The best result in each column is emphasized in bold, and the second best result is underlined. Our MeRetriever(avg) achieves comparably good performance." + ], + "table_footnote": [], + "table_body": "
Text-to-Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)136.01.536.4810.5429.38
CLIP4Clip(tight)127.01.455.549.3530.11
CenterCLIP131.01.936.6110.6730.13
FRONZEN-in-Time277.00.351.993.8214.52
ClipBERT442.00.351.773.3111.10
Singularity179.51.535.228.5223.87
Ours(avg)126.01.886.6910.5929.97
Ours(max)112.02.027.6112.7434.49
", + "bbox": [ + 509, + 88, + 893, + 220 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 5: Results of Text-to-Video retrieval task on Charades-Event dataset. We use the same notation as Tab. 2. Me-Retriever(max) and Me-Retriever(avg) can achieve the best performance compared to other models.", + "bbox": [ + 496, + 229, + 893, + 292 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. Results", + "text_level": 1, + "bbox": [ + 500, + 320, + 591, + 335 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The experiments show that Me-Retriever performs competitively within the context of MeVTR. On the Video-to-Text task, as presented in Tables 2 and 3, Me-Retriever(avg) surpasses its counterparts. This result underscores our model's capability to address both tasks across different datasets effectively. Additionally, we observe that CLIP4Clip also attains a commendable Recall@1-Average performance on the Video-to-Text task compared to other baseline models. This observation sheds light on the robust transferability of the pre-trained encoder to videos. This indicates that the primary challenge in MeVTR often resides within representation alignment.", + "bbox": [ + 496, + 345, + 890, + 526 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Our model also demonstrates comparable results on both datasets on the Text-to-Video task, as shown in Tab. 4 and Tab. 5. Me-Retriever(avg) demonstrates comparable performance to baseline models like CenterCLIP across numerous metrics on both datasets. Interestingly, we also notice that Me-Retriever(max) performs best on the Charades-Event dataset but not on the ActivityNet Captions dataset. This disparity can be attributed to overfitting, warranting further investigation. The noticeable performance of certain baseline models aligns with our conjecture that prior models can be effectively adapted to the Text-to-Video retrieval task. However, this adaptation might come at the expense of suboptimal results in the Video-to-Text task, as evident in Table 2. This phenomenon can be attributed to the embeddings of different texts collapsing to become more proximate, leading to an unintentional competition among positive instances that ultimately dampens their significance.", + "bbox": [ + 496, + 529, + 892, + 786 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Performance on videos with different subsets In order to reveal the model performance on videos of different properties like video duration and the number of events, we partition the complete ActivityNet Caption test set into two groups of subsets. These subsets are partitioned based on the video duration and the count of events within the videos, respectively:", + "bbox": [ + 496, + 794, + 893, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "22118", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/89d912e2a36435d4ca9a34849f481cb42c4b584b04de14ce4df46235416af1cd.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Text to Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
Ours (Best)11.015.1735.9448.3975.85
w/o Key Event12.015.0335.6747.9475.06
w/o MeVTR loss12.014.4534.9047.2575.24
", + "bbox": [ + 86, + 89, + 470, + 162 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/b2ec37e55c32609b621fad9a17274049218dd980f24f65e67cf68059c05ab7c6.jpg", + "table_caption": [ + "Table 6: Ablation studies on key modules of Me-Retrever training on the Text-to-Video task for ActivityNet Captions. Only the Recall@k-Average is reported in the main part. We find that model performance drops with removing any modules, proving its efficacy." + ], + "table_footnote": [], + "table_body": "
Video to Text
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
Ours (Best)35.08.5223.5632.7961.26
w/o Key Event41.57.4021.0030.2757.71
w/o MeVTR loss41.06.7020.0528.9657.45
", + "bbox": [ + 86, + 263, + 470, + 339 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 7: Ablation studies on key modules of Me-Retriever training on the Video-to-Text task for ActivityNet Captions. Model performance declines to different extents without our modules. We conclude that our model can benefit Video-to-Text retrieval prominently.", + "bbox": [ + 76, + 349, + 468, + 425 + ], + "page_idx": 6 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. Video duration: test-S (Short) with videos shorter than 1 minute, test-M (Medium) with videos between 1-2 minutes, test-L (Long video) with videos between 2-3 minutes, and test-XL (eXtra Long video) with even longer videos than 3 minutes;", + "2. Number of events: test-E1 with videos containing fewer than 4 events, test-E2 with 5-12 events, and test-E3 with more than 12 events." + ], + "bbox": [ + 88, + 455, + 468, + 585 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Comparing performance across datasets of different sizes isn't equitable for a retrieval task, as larger candidate sets exacerbate retrieval difficulties. Therefore, we gauge the average improvement in the model performance of MeRetriever(avg) to the baseline CLIP4Clip(mean) and identify the subsets in which our model showcases notable enhancements. From Fig. 4, we also see that our model usually performs better on test-E1 and test-E2, and improvement slightly decreases for even longer videos. We assume this problem is inevitable since we use a fixed number of clusters and videos containing many events in test-E3, and larger numbers of events increase the retrieval difficulties. Whereas for videos of different duration, model performance slightly varies.", + "bbox": [ + 75, + 595, + 468, + 808 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Ablation Studies", + "text_level": 1, + "bbox": [ + 76, + 816, + 241, + 832 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we conduct various experiments to investigate the effectiveness of different weighting strategies in MeVTR loss and ablate the proposed components of our architecture.", + "bbox": [ + 76, + 839, + 468, + 898 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2fa066806e6d2b5430c7b8d66ae1ad5a83676acf746417c97ec2604da7beb97d.jpg", + "image_caption": [ + "(a) On subsets of different duration" + ], + "image_footnote": [], + "bbox": [ + 552, + 90, + 841, + 256 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6804e5e4ae1f32e9efc29a99d107a0a5982394dd4225444c760e719667463331.jpg", + "image_caption": [ + "(b) On subsets of different event number", + "Figure 4: We compare average performance improvement in percentage(%) for Video-to-Text task on subsets of ActivityNet Captions. It shows how much percentage MeRetriever(avg) is better than CLIP4Clip(mean) on different subsets. Fig. 4a: Video-to-Text results for test-S/M/L/XL; Fig. 4b: Video-to-Text results for test-E1/E2/E3." + ], + "image_footnote": [], + "bbox": [ + 555, + 299, + 841, + 464 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Impact of weighting strategy in MeVTR Loss To study the effect of different weighting strategies of MeVTR loss, i.e., dynamic weighting and fixed weighting, we test our model trained with a set of different weighting coefficients $\\alpha$ as illustrated in Fig. 5 and Fig. 6. On the Video-to-Text task and Text-to-Video Retrieval tasks, we notice that dynamic weighting $\\alpha$ can guarantee us a comparable performance in general and less sensitivity than any fixed coefficient. It is also illustrated that when we choose a smaller coefficient, the Video-to-Text retrieval is favored, while a bigger coefficient benefits the other way around. A cutoff point is empirically between 1.0 and 2.0. The reason is that $\\mathcal{L}_{v2t}$ loss always has a comparably larger scale than $\\mathcal{L}_{t2v}$ loss and dominates training due to the unbalanced number of video-text instances, as we have discussed in Section 4.2. This ensures us that a dynamic weighting strategy can improve the Text-to-Video task by amplifying the influence of $\\mathcal{L}_{t2v}$ and guarantee stable improvements on both tasks.", + "bbox": [ + 496, + 628, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "22119", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/f17a96253965453ffe3479d9734718e8b4554f8d56eadbd26022edba1dde8cec.jpg", + "image_caption": [ + "(a) Average" + ], + "image_footnote": [], + "bbox": [ + 81, + 75, + 343, + 233 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8d7a3b394e53e3bf1c755ead343cbc83454591da0af34cecc2429c90cd747283.jpg", + "image_caption": [ + "(b) One-Hit" + ], + "image_footnote": [], + "bbox": [ + 351, + 75, + 609, + 232 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/024bd25bab93a3be719d0c833fdbc6a8b48a64c23a4a5f045a11ee6bb67d2629.jpg", + "image_caption": [ + "(c) All-Hit" + ], + "image_footnote": [], + "bbox": [ + 620, + 75, + 872, + 232 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/ba34310540d8e3748e548149447b488b07803be6d8e50e50928f2c24d197bc88.jpg", + "image_caption": [ + "Figure 5: We compare the model performance with different weighting strategies, a dynamic weight $\\alpha$ and different choices of fixed weights from a choice of $\\{0.5,1.0,1.5,2.0,3.0\\}$ , in the MeVTR loss on Recall@5 on the Video-to-Text task for ActivityNet Captions. Fig. 5a-5c shows the results of Recall@5-Average/One-Hit/All-Hit respectively. We can find that compared to a fixed weighting coefficient, a dynamic weight $\\alpha$ guarantees more stable and good results in different metrics.", + "Figure 6: We compare the model performance with different weighting coefficients in the MeVTR loss on Recall@5 on the Text-to-Video task for ActivityNet Captions. The same graphical representations are used as Fig. 5. The dynamic weighting coefficient performs better than any other fixed coefficient considering performance and variance." + ], + "image_footnote": [], + "bbox": [ + 135, + 354, + 411, + 523 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effects of different modules We choose our best model Me-Retriever(avg) and ablate the key event selection module by removing the key event selection module and the MeVTR loss by replacing it with the cross-entropy loss, respectively. Results are shown in Tab. 6 and Tab. 7. We display the Recall@k-Average on both tasks in the table and observe that the model performances drop after removing any modules. In particular, our method demonstrates a larger improvement by $1.12\\%$ without the key event selection module and $1.82\\%$ without the MeVTR loss on the Video-to-Text task. This agrees with our assumption that our Me-Retriever model can deal with textual feature collapse in the MeVTR training. On the Text-to-Video task, both modules also show benefits to the performance on all metrics.", + "bbox": [ + 75, + 672, + 472, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Textual features of multi-event videos To show whether Me-Retriever can prevent heterogeneous text features of a multi-event video from collapsing, we calculate the average cosine similarity. If the text features of one video are too similar, then the average cosine similarity among texts is expected to be closer to 1. We find that in Me-Retriever(avg), the cosine similarity averaged on the whole test set is 0.789 with a variance of 0.0059 while in CLIP4Clip(mean), the value is 0.864 with a variance of 0.0028. And as in Fig. 3, Me-Retriever has lower average cosine similarity than CLIP4Clip. This shows that text features of the same video generated by Me-Retriever are more diverse than those by CLIP4Clip, which agrees with our motivation.", + "bbox": [ + 496, + 354, + 893, + 551 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Limitations", + "text_level": 1, + "bbox": [ + 500, + 564, + 622, + 580 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Constrained by time and labor expenses, our experimental studies on the MeVTR task are based on the pre-existing video-text datasets including ActivityNet Captions and Charades. Nonetheless, it is important to recognize the potential bias in these datasets due to their emphasis on human activities and limitations in representing a wider range of videos. We aim to create a more comprehensive MeVTR benchmark encompassing more general videos.", + "bbox": [ + 496, + 590, + 890, + 712 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "7. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 724, + 617, + 739 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We study a practical Video-Text retrieval scenario, Multi-event Video-Text Retrieval, in this paper. We find previous models suffer notable performance degradation in inference on MeVTR and textual feature collapse when retrained on MeVTR. We present a new CLIP-based model, Me-Retriever, to conquer this challenge. In our experimental studies, we demonstrate the efficacy of these techniques on both Text-to-Video and Video-to-Text tasks for ActivityNet Captions and Charades-Event datasets. We believe this can be a strong baseline for future studies.", + "bbox": [ + 496, + 750, + 893, + 902 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "22120", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements", + "text_level": 1, + "bbox": [ + 76, + 90, + 243, + 107 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work has been funded by the German Federal Ministry of Education and Research and the Bavarian State Ministry for Science and the Arts. The authors of this work take full responsibility for its content.", + "bbox": [ + 76, + 114, + 468, + 176 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 191, + 174, + 208 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Partitioning Around Medoids (Program PAM). In Leonard Kaufman and Peter J. 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In Proceedings of the AAAI conference on artificial intelligence, volume 34, pages 13041-13049, 2020. 2" + ], + "bbox": [ + 78, + 90, + 468, + 681 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "22123", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multi-Event Video-Text Retrieval/4a8e429c-a424-42a1-b75b-812c6ff37eb5_model.json b/2023/Multi-Event Video-Text Retrieval/4a8e429c-a424-42a1-b75b-812c6ff37eb5_model.json new file mode 100644 index 0000000000000000000000000000000000000000..87465fac5e7fc40e8332753c9b0069d88ac020eb --- /dev/null +++ b/2023/Multi-Event Video-Text Retrieval/4a8e429c-a424-42a1-b75b-812c6ff37eb5_model.json @@ -0,0 +1,2169 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.318, + 0.131, + 0.654, + 0.151 + ], + "angle": 0, + "content": "Multi-event Video-Text Retrieval" + }, + { + "type": "text", + "bbox": [ + 0.195, + 0.179, + 0.774, + 0.199 + ], + "angle": 0, + "content": "Gengyuan Zhang \\(^{1,2}\\) Jisen Ren \\(^{1}\\) Jindong Gu \\(^{3*}\\) Volker Tresp \\(^{1,2}\\)" + }, + { + "type": "text", + "bbox": [ + 0.348, + 0.199, + 0.624, + 0.218 + ], + "angle": 0, + "content": "\\(^{1}\\) LMU Munich, Munich, Germany" + }, + { + "type": "text", + "bbox": [ + 0.255, + 0.217, + 0.717, + 0.235 + ], + "angle": 0, + "content": "2 Munich Center for Machine Learning, Munich, Germany" + }, + { + "type": "text", + "bbox": [ + 0.291, + 0.235, + 0.679, + 0.253 + ], + "angle": 0, + "content": "3 University of Oxford, Oxford, United Kingdom" + }, + { + "type": "text", + "bbox": [ + 0.287, + 0.255, + 0.684, + 0.269 + ], + "angle": 0, + "content": "zhang@db.s.ifi.lmu.de jindong.gu@outlook.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.305, + 0.313, + 0.32 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.337, + 0.473, + 0.73 + ], + "angle": 0, + "content": "Video-Text Retrieval (VTR) is a crucial multi-modal task in an era of massive video-text data on the Internet. A plethora of work characterized by using a two-stream Vision-Language model architecture that learns a joint representation of video-text pairs has become a prominent approach for the VTR task. However, these models operate under the assumption of bijective video-text correspondences and neglect a more practical scenario where video content usually encompasses multiple events, while texts like user queries or webpage metadata tend to be specific and correspond to single events. This establishes a gap between the previous training objective and real-world applications, leading to the potential performance degradation of earlier models during inference. In this study, we introduce the Multi-event Video-Text Retrieval (MeVTR) task, addressing scenarios in which each video contains multiple different events, as a niche scenario of the conventional Video-Text Retrieval Task. We present a simple model, MeRetriever, which incorporates key event video representation and a new MeVTR loss for the MeVTR task. Comprehensive experiments show that this straightforward framework outperforms other models in the Video-to-Text and Text-to-Video tasks, effectively establishing a robust baseline for the MeVTR task. We believe this work serves as a strong foundation for future studies. Code is available at https://github.com/gengyuanmax/MeVTR." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.76, + 0.21, + 0.775 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.785, + 0.47, + 0.877 + ], + "angle": 0, + "content": "With the proliferation of multimedia data on the Internet every day, Video-Text Retrieval (VTR) task gains increasing importance in searching for desired items from the opposite modality given a video or text query. Over the past years, numerous efforts [49, 33, 9, 14, 31, 3, 7, 30, 16, 12, 51, 17] have been undertaken to improve the" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.306, + 0.892, + 0.412 + ], + "angle": 0, + "content": "multi-modal retrieval performance on both Video-to-Text and Text-to-Video retrieval tasks. Along with the popularity of powerful vision foundation models like CLIP [36] and ALIGN [23] that align the image-text pairs in a joint feature space, two-stream video-text models [30, 16] targeting to learn video-text correspondences have further become a mainstream method for the Video-Text Retrieval task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.413, + 0.893, + 0.55 + ], + "angle": 0, + "content": "However, this paradigm neglects that videos usually contain more than a single event, while a single textual caption can only capture a fragment of the entire video content. As depicted in Fig. 1, the example video spans a sequence of unrelated and discontinuous events, and each single textual caption merely corresponds to a video segment. This congruity undoubtedly contradicts the fundamental of the traditional VTR task, which aims to establish a mapping between video-text pair." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.551, + 0.895, + 0.687 + ], + "angle": 0, + "content": "This fact presents a prevalent scenario in Video-Text Retrieval: videos are intricate, often containing multiple events, whereas texts (typically like search queries or webpage metadata) tend to be specific and fragmentary. Consequently, this dichotomy leads to divergent semantic meanings for a given video-text pair. Such divergence contradicts the conventional training objective of aligning representations for video-text pairs in VTR models, that video features are aligned with the corresponding text feature." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.688, + 0.895, + 0.78 + ], + "angle": 0, + "content": "In this study, we formally introduce a new and realistic VTR setting involving multi-event videos, dubbed as Multi-event Video-Text Retrieval (MeVTR). In the introduced MeVTR task, a text describes a single event within a video item, whereas a video corresponds to multiple relevant textual captions, each detailing different events." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.901 + ], + "angle": 0, + "content": "We assess the performance of previous VTR models trained under standard VTR settings that learn a bijective video-text correspondence on the MeVTR task without retraining. Our evaluation reveals distinct levels of performance degradation, as illustrated in Table 1. This observation confirms the presence of a performance gap between training within the conventional VTR framework and real-world MeVTR inference scenarios." + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.888, + 0.221, + 0.9 + ], + "angle": 0, + "content": "*Corresponding author" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22113" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.104, + 0.887, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.318, + 0.896, + 0.381 + ], + "angle": 0, + "content": "Figure 1: An example case of multi-event videos from ActivityNet [4]. The video depicts a sequence of unrelated and discontinuous events, including the progression \"a girl is sitting on the beach\" \\(\\rightarrow\\) \"a young man is practicing tightrope walking\" \\(\\rightarrow\\) \"a scene of sunset by the beach.\" Each textual caption only corresponds to a fragment of the video. Such short and specific textual captions are prevalent in our everyday video data and constitute a common video-text retrieval scenario." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.406, + 0.473, + 0.571 + ], + "angle": 0, + "content": "Besides, we retrain a series of previous models to adapt to the MeVTR task. However, we find that they cannot perform equally well on the Video-to-Text and Text-to-Video. We speculate that this is caused by non-injective videotext correspondences in the MeVTR setting, where previous VTR models embed a video and multiple distinct caption texts into a joint representation space and aim at aligning the video feature with the features of all caption texts. Consequently, distinct texts corresponding to the same video are mapped to the same feature, potentially resulting in suboptimal retrieval performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.572, + 0.473, + 0.706 + ], + "angle": 0, + "content": "Under this circumstance, we introduce a new CLIP-based model dubbed Me-Retriever tailored for the MeVTR task. Considering the dichotomy of multi-event video-text pairs, we formulate our approach as follows: (1) representing videos by a bag of key event features and (2) employing a multi-event video-text retrieval loss. This strategy serves the dual purpose of mitigating the collapse of textual features and harmonizing the learning objectives between the Text-to-Video and Video-to-Text tasks." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.708, + 0.423, + 0.722 + ], + "angle": 0, + "content": "Our contributions can be summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.091, + 0.732, + 0.47, + 0.778 + ], + "angle": 0, + "content": "1. We introduce a new task, Multi-event Video-Text Retrieval for retrieving multi-event video-text pairs, and define new evaluation metrics in MeVTR;" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.788, + 0.47, + 0.833 + ], + "angle": 0, + "content": "2. We propose a new model called Me-Retriever that represents videos with selected key events and a MeVTR loss for training on MeVTR;" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.844, + 0.471, + 0.889 + ], + "angle": 0, + "content": "3. We conduct comprehensive experiments to showcase Me-Retriever's effectiveness and to establish it as a simple yet robust baseline for future research." + }, + { + "type": "list", + "bbox": [ + 0.089, + 0.732, + 0.471, + 0.889 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.404, + 0.642, + 0.42 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.433, + 0.892, + 0.6 + ], + "angle": 0, + "content": "Video Language Model A series of work on Vision-Language Models (VLM) has been made like [26, 29, 5, 57, 53] for multi-modal representation learning. Given that videos are a structured sequence of images and typically entail higher computational demands than other visual data formats, the domain of Video-Language models has garnered significant attention. Notable contributions within this category include works by [40, 24, 38, 49, 29, 23, 43, 19, 13] which aim at video foundation models for video tasks. These models represent a subcategory of VLMs, adept at processing video and text inputs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.607, + 0.893, + 0.818 + ], + "angle": 0, + "content": "Video Representation In a line of work [42, 52, 18, 25], convolutions are performed on videos to fuse spatial and temporal information. Meanwhile, as transformers [44] have achieved success firstly in text [8], and then vision fields [11, 27, 41, 6], attempts to introduce transformers to extract video representations have been made in [39, 2, 47, 56, 32, 28]. The success of pre-trained Vision-Language models has significantly impacted video representation learning. Vision-Language models [29, 38, 31, 36] have demonstrated that textual supervision is conducive to visual representation and to a uniform video-language representation. Among them, the success of representation models [22, 16, 45, 46] has bridged the gap between video and text representations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Video-Text Retrieval Video-Text Retrieval is a fundamental task of multi-modal learning, posing a good proxy task for learning joint representations of videos and texts. Two-stream Video-Text models [10, 9, 51, 34] concentrate on processing video-text pairs as inputs and aligning vi" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22114" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.088, + 0.089, + 0.894, + 0.184 + ], + "angle": 0, + "content": "
Video-to-TextText-to-Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑Median Rank ↓k=1 ↑k=5 ↑k=10 ↑
FROZEN-in-time7.0 ↗ 109.515.3 ↗ 0.843.3 ↗ 3.143.3 ↗ 5.67.0 ↗ 111.015.9 ↗ 1.843.0 ↗ 6.859.01 ↗ 11.7
CLIPBERT4.0 ↗ 449.022.1 ↗ 1.458.2 ↗ 4.769.6 ↗ 7.65.0 ↗ 153.025.9 ↗ 2.655.4 ↗ 9.569.8 ↗ 15.1
CLIP4Clip2.0 ↗ 53.042.5 ↗ 7.574.1 ↗ 19.885.8 ↗ 28.413.0 ↗ 53.014.8 ↗ 7.534.2 ↗ 19.845.6 ↗ 28.4
CenterCLIP2.0 ↗ 51.042.8 ↗ 7.873.8 ↗ 20.885.3 ↗ 29.22.0 ↗ 13.041.8 ↗ 15.173.9 ↗ 34.684.7 ↗ 46.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.194, + 0.895, + 0.256 + ], + "angle": 0, + "content": "Table 1: Comparison of model performance on VTR and MeVTR tasks on ActivityNet Captions. We train each model on the ActivityNet Captions with its original codes and evaluate them on MeVTR. We show the performance of VTR on the lefthand of \\(\\nabla (\\nearrow)\\) and the performance of MeVTR on the right. \\(\\uparrow\\) means higher the better, and \\(\\downarrow\\) means lower the better. It is shown that model performance deteriorates to a large extent on both Video-to-Text and Text-to-Video tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.282, + 0.473, + 0.449 + ], + "angle": 0, + "content": "sual and textual representations within a joint representation space. For instance, Frozen [3] employs a visual encoder that can be adaptively trained on images and videos, incorporating temporal contexts via curriculum learning. TACo [51], in contrast, focuses on aligning content words in texts with corresponding visual content, adding an extra learning objective. With the surge of large Vision-Language foundation models representative of CLIP [36], models [30, 16, 12, 35, 3, 50], leverage the potent pretrained model CLIP and endeavor to extend its capabilities from static images to the domain of videos." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.47, + 0.175, + 0.485 + ], + "angle": 0, + "content": "3. Problem" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.498, + 0.281, + 0.513 + ], + "angle": 0, + "content": "3.1. Problem Formulation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.524, + 0.471, + 0.646 + ], + "angle": 0, + "content": "Given a video-text dataset with multi-event videos \\(\\mathcal{V}\\) and texts \\(\\mathcal{T}\\), where a video \\(v_{i} \\in \\mathcal{V}\\) is described by a set of different texts \\(\\mathcal{T}_{i} \\subset \\mathcal{T}\\) and a text is denoted as \\(t_{j}\\), our task consists in retrieving a video given a text query \\(t^{q}\\) and retrieving all relevant texts given a video query \\(v^{q}\\). A generic Video-Text Retrieval model is to learn a similarity function \\(sim(v_{i}, t_{j})\\) that scores the similarity between any relevant video-text pair higher and ranks all the candidate items." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.663, + 0.262, + 0.679 + ], + "angle": 0, + "content": "3.2. Evaluation Metrics" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Video-Text retrieval is a recall-focused retrieval task. A single item is retrieved in traditional settings, and the average Recall at the top rank \\( k \\) is calculated. Nevertheless, in the MeVTR setting, we also want to evaluate retrieving multiple different text items given one video. Hence we devise the following metrics: (1) Recall@k-Average as the fraction of the number of correspondences ranked at top \\( k \\); (2) Recall@k-One-Hit as an indication of whether any of the correspondences will be ranked in the top \\( k \\); (3) Recall@k-All-Hit as an indication of whether all items can be retrieved within the top \\( k \\) rank. All metrics are averaged on the whole test set. In the follow-up experiments, we report the Recall for the Text-to-Video tasks and the metrics mentioned above for the Video-to-Text tasks." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.281, + 0.729, + 0.297 + ], + "angle": 0, + "content": "3.3. Textual Feature Collapse" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.304, + 0.892, + 0.366 + ], + "angle": 0, + "content": "To investigate the textual feature collapse in previous models to elucidate the performance drop by calculating the textual feature's similarity after retraining, we define the average text similarity of a video \\( v_{i} \\) with \\( n_{v_i} \\) captions as:" + }, + { + "type": "equation", + "bbox": [ + 0.568, + 0.377, + 0.892, + 0.422 + ], + "angle": 0, + "content": "\\[\n\\operatorname {s i m} _ {t} \\left(v _ {i}\\right) = \\sum_ {m = 1} ^ {N _ {v _ {i}}} \\sum_ {n = 1} ^ {N _ {v _ {i}}} \\frac {1}{N _ {v _ {i}} ^ {2}} \\operatorname {s i m} \\left(t _ {m}, t _ {n}\\right) \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.432, + 0.892, + 0.584 + ], + "angle": 0, + "content": "In Fig. 3, we attempt to visualize the average text similarity of all videos with a different number of events. Different texts are expected to have lower sentence similarity to retain their meanings due to retraining on MeVTR. We chose CLIP4Clip for comparison in our experiments, as it still performs relatively well in MeVTR tasks compared to other models. As a comparison, we show that Me-R retriever, which will be introduced in the next section, can generate more diverse textual features than CLIP4Clip and effectively avoid textual feature collapse." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.598, + 0.591, + 0.613 + ], + "angle": 0, + "content": "4. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.623, + 0.892, + 0.654 + ], + "angle": 0, + "content": "We propose Me-Retriever consisting of a Key Event Selection module and MeVTR loss as shown in Fig. 2." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.664, + 0.787, + 0.68 + ], + "angle": 0, + "content": "4.1. Key Event Video Representation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.687, + 0.892, + 0.81 + ], + "angle": 0, + "content": "Intuitively, human brains do not remember experiences with all continuous scenes and consolidate all the details. Instead, brains retain memories of certain discrete events [55]. This insight motivates us to represent a video with a bag of frames as key events. For leveraging frame embeddings extracted from the CLIP visual encoder \\(\\{\\mathbf{f}_i^1,\\mathbf{f}_i^2,\\dots ,\\mathbf{f}_i^{[v_i]}\\}\\), we define the Key Event Selection module that selects the most distinctive keyframes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.894, + 0.9 + ], + "angle": 0, + "content": "We employ a classic clustering method, K-Medoids [1]. Compared to other clustering methods, the representative of each cluster given by the K-Medoids algorithm is from the sample points, which corresponds to a particular frame and has explicit interpretation. The criterion is minimizing the distance of all frames in the cluster to its medoid. \\(K\\) frames" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22115" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.092, + 0.099, + 0.889, + 0.32 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.358, + 0.896, + 0.437 + ], + "angle": 0, + "content": "Figure 2: The overall framework of Me-Retriever. The model adopts CLIP [36]'s Visual Encoder(VE) and Text Encoder(TE). After the Visual Encoder, [CLASS] tokens in the last hidden layer are taken as frame embeddings. We use a clustering-based Key Event Selection module to aggregate similar frames and extract key events. Each textual caption is fed into Text Encoder, and [EOS] will be used as text embedding. The similarity between these key events of any video \\( v_{i} \\) and any textual caption \\( t_j \\) is measured in the Similarity Calculator. For each video, there are multiple text correspondences as positive samples." + }, + { + "type": "image", + "bbox": [ + 0.096, + 0.462, + 0.456, + 0.665 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.678, + 0.472, + 0.754 + ], + "angle": 0, + "content": "Figure 3: We compare the average cosine similarity between all text pairs of videos with a different number of events. Me-Retriever can generate more diverse text features than CLIP4Clip and refrain from text features collapsing, as we discuss in the main part." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.473, + 0.903 + ], + "angle": 0, + "content": "are chosen as initial medoids; the remaining frames are then assigned to their nearest medoids, and within each cluster, new medoids are again selected based on cosine similarity as a metric function. Video \\( v_{i} \\) can be represented as a sequence of key event embeddings \\( \\mathbf{K}_i = \\{\\mathbf{k}_i^1,\\mathbf{k}_i^2,\\dots ,\\mathbf{k}_i^K\\} \\). In the loss calculation, we use the pre-computed assignment of all frames as key event video representation." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.46, + 0.64, + 0.475 + ], + "angle": 0, + "content": "4.2. MeVTR Loss" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.485, + 0.892, + 0.652 + ], + "angle": 0, + "content": "Following the dual learning paradigm of Text-to-Video and Video-to-Text on VTR tasks, we propose MeVTR loss for MeVTR learning. As previously discussed, there is an issue of textual feature collapse during MeVTR training. To address this, we propose disentangling various positive instances within video samples by excluding non-self positive instances from the softmax function. Moreover, considering the dissimilar granularity between multi-event videos and single-event text, we propose adopting a dynamic weighting strategy. This strategy balances the loss scale of both learning objectives during the training process." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.653, + 0.894, + 0.684 + ], + "angle": 0, + "content": "MeVTR loss is defined as a weighted sum of \\(\\mathcal{L}_{t2v}\\) and \\(\\mathcal{L}_{v2t}\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.606, + 0.699, + 0.892, + 0.715 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {M e V T R} = \\mathcal {L} _ {v 2 t} + \\alpha \\mathcal {L} _ {t 2 v} \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.731, + 0.866, + 0.747 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{v2t}\\) and \\(\\mathcal{L}_{t2v}\\) are respectively formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.5, + 0.774, + 0.914, + 0.832 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {v 2 t} = - \\frac {1}{| \\mathcal {B} |} \\sum_ {i} ^ {| \\mathcal {B} |} \\sum_ {k} ^ {| \\mathcal {T} _ {i} |} \\frac {1}{| \\mathcal {T} _ {i} |} \\log \\frac {\\exp s i m (\\mathbf {K} _ {i} , \\mathbf {w} _ {k}) / \\tau}{\\sum_ {j = 1} ^ {\\mathcal {B} - \\cup \\{k \\}} \\exp s i m (\\mathbf {K} _ {i} , \\mathbf {w} _ {j}) / \\tau},\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.517, + 0.86, + 0.893, + 0.904 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {t 2 v} = - \\frac {1}{| \\mathcal {B} |} \\sum_ {j} ^ {| \\mathcal {B} |} \\log \\frac {\\exp \\operatorname {s i m} \\left(\\mathbf {K} _ {i} , \\mathbf {w} _ {j}\\right) / \\tau}{\\sum_ {i = 1} ^ {\\mathcal {B}} \\exp \\operatorname {s i m} \\left(\\mathbf {K} _ {j} , \\mathbf {w} _ {j}\\right)) / \\tau}, \\tag {4}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22116" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.097, + 0.089, + 0.887, + 0.26 + ], + "angle": 0, + "content": "
Video-to-Text
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)39.06.60 / 20.74 / -20.32 / 47.02 / 3.4629.37 / 61.26 / 6.7158.41 / 89.77 / 26.24
CLIP4Clip(tight)49.55.23 / 16.45 / -16.74 / 41.94 / 1.7725.50 / 57.37 / 4.2354.22 / 88.00 / 21.52
CenterCLIP38.06.93 / 21.62 / -20.58 / 47.98 / 3.6629.90 / 61.72 / 6.9658.88 / 90.34 / 26.28
FROZEN-in-time330.00.30 / 0.67 / -0.83 / 2.10 / 0.221.60 / 3.37 / 0.675.89 / 12.97 / 2.55
CLIPBERT174.51.80 / 6.10 / -6.48 / 18.97 / 0.1810.93 / 29.00 / 0.8731.34 / 61.42 / 8.72
Singularity64.54.83 / 14.68 / -15.1 / 37.79 / 1.9522.23 / 49.50 / 4.4148.96 / 81.94 / 19.38
Ours(avg)35.08.52 / 26.91 / -23.56 / 54.18 / 3.8632.95 / 67.13 / 7.7961.26 / 92.50 / 27.80
Ours(max)49.06.98 / 22.72 / -18.72 / 46.37 / 2.3027.04 / 60.62 / 5.7654.19 / 88.37 / 20.90
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.271, + 0.895, + 0.334 + ], + "angle": 0, + "content": "Table 2: Results of the Video-to-Text retrieval task on ActivityNet Captions dataset. In each column, we report the Recall@k-Average/One-Hit/All-Hit for each \\( k = 1,5,10,50 \\) respectively. The best result in each column is emphasized in bold. We ignore the Recall@1-All-Hit since all models can only achieve a nearly zero result. Ours(avg) maintains its advantage in the text retrieval task and surpasses all other models by a large margin." + }, + { + "type": "table", + "bbox": [ + 0.097, + 0.345, + 0.887, + 0.525 + ], + "angle": 0, + "content": "
Video-to-Text
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)441.51.32 / 2.92 / -4.07 / 8.32 / 1.805.65 / 11.84 / 2.5516.84 / 32.01 / 7.65
CLIP4Clip(tight)391.00.80 / 1.80 / -2.45 / 6.30 / 0.754.19 / 10.27 / 1.3515.26 / 30.43 / 6.37
CenterCLIP408.01.32 / 3.00 / -3.71 / 7.87 / 1.576.33 / 13.42 / 2.6217.37 / 33.43 / 7.72
FROZEN-in-time810.00.30 / 0.67 / -0.83 / 2.10 / 0.221.60 / 3.37 / 0.675.89 / 12.97 / 2.55
ClipBERT1339.50.15 / 0.45 / -0.60 / 1.50 / 0.151.19 / 3.30 / 0.225.31 / 11.92 / 1.87
Singularity621.50.95 / 2.17 / -2.84 / 5.92 / 1.424.35 / 9.52 / 1.9512.22 / 25.94 / 4.87
Ours(avg)406.01.39 / 3.22 / -5.04 / 9.90 / 2.477.02 / 13.72 / 3.3717.62 / 32.08 / 8.70
Ours(max)365.61.01 / 2.62 / -4.03 / 9.00 / 1.726.39 / 13.72 / 2.7019.08 / 36.66 / 8.10
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.535, + 0.893, + 0.568 + ], + "angle": 0, + "content": "Table 3: Results of the Video-to-Text retrieval task on Charades-Event dataset. We use the same notation as in Tab. 2. MeRetriever(avg) and Me-Retriever(max) can achieve best performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.592, + 0.471, + 0.728 + ], + "angle": 0, + "content": "\\(sim(\\cdot)\\) is the similarity function, \\(\\mathcal{B}\\) is the set of samples in the training batch, \\(\\mathcal{B}^{-}\\) is the set of negative samples in the batch, \\(\\tau\\) is the temperature coefficient, and \\(\\mathcal{T}_i\\) is the set of positive instances of one sample video in \\(\\mathcal{L}_{t2v}\\). Notably, given a video item \\(v_{i}\\), we discard all positive instances in \\(\\mathcal{T}_i\\) other than the current training sample \\(t_k\\). This encourages similarities between a video and its all positive instances to be increased. In \\(\\mathcal{L}_{t2v}\\), it degenerates to a normal softmax function." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.473, + 0.903 + ], + "angle": 0, + "content": "We denote \\(\\alpha\\) as the weighting coefficient that balances \\(\\mathcal{L}_{t2v}\\) and \\(\\mathcal{L}_{v2t}\\). Given that the two losses exhibit differing scales during training, which owes to the positive/negative sample ratio asymmetry, determining the value of \\(\\alpha\\) requires employing certain hyperparameter-tuning techniques to ensure balanced performance on both tasks. We suggest employing a dynamic weighting strategy as opposed to a fixed weight. A dynamic weighting coefficient \\(\\alpha\\) is computed as the ratio of \\(\\mathcal{L}_{v2t}\\) to \\(\\mathcal{L}_{t2v}\\) during training. In Section 5.3, we conduct experimental studies to compare the impact of various weighting strategies." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.592, + 0.895, + 0.759 + ], + "angle": 0, + "content": "Similarity function For video-text pairs in bijective correspondences, the similarity between video and text is measured by cosine similarity in the feature space. In MeVTR, we use two approaches are used to measure the similarity between a video \\( v_{i} \\) consisting of key events \\( \\{\\mathbf{k}_i^1,\\mathbf{k}_i^2,\\dots ,\\mathbf{k}_i^K\\} \\) and a text \\( t_j \\): (1) we average the cosine similarity scores of all key event embeddings and the text as in Eq. 5; (2) we select the maximum cosine similarity of any key event-text pair to represent the similarity between the video to which these medoids belong as in Eq. 6;" + }, + { + "type": "equation", + "bbox": [ + 0.514, + 0.781, + 0.893, + 0.8 + ], + "angle": 0, + "content": "\\[\ns _ {a v g} (v _ {i}, t _ {j}) = \\operatorname {a v g} \\left(\\cos \\left(\\mathbf {k} _ {1} ^ {i}, \\mathbf {w} _ {j}\\right), \\dots , \\cos \\left(\\mathbf {k} _ {k} ^ {i}, \\mathbf {w} _ {j}\\right)\\right) \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.512, + 0.832, + 0.893, + 0.851 + ], + "angle": 0, + "content": "\\[\ns _ {m a x} (v _ {i}, t _ {j}) = \\max (\\cos (\\mathbf {k} _ {1} ^ {i}, \\mathbf {w} _ {j}), \\dots , \\cos (\\mathbf {k} _ {k} ^ {i}, \\mathbf {w} _ {j})) \\quad (6)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "We denote Me-Retriever with different similarity functions as Me-Retriever(avg) and Me-Retriever(max)." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22117" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.088, + 0.089, + 0.472, + 0.224 + ], + "angle": 0, + "content": "
Text-to-Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)11.015.2536.4349.1176.64
CLIP4Clip(tight)15.010.1429.0741.9372.50
CenterCLIP11.015.5337.2149.7877.19
FROZEN-in-time111.01.826.8011.7633.86
ClipBERT48.04.2014.5723.3551.02
Singularity(FT)22.09.2924.9636.2665.55
Ours(avg)11.015.9937.1349.6076.66
Ours(max)13.014.9334.4446.3674.65
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.234, + 0.472, + 0.326 + ], + "angle": 0, + "content": "Table 4: Results of the Text-to-Video retrieval task on ActivityNet Captions dataset. We compare CLIP4Clip [30], CenterCLIP [54], FROZEN-in-time [3], ClipBERT [22], and [21]. The best result in each column is emphasized in bold, and the second best result is underlined. Our MeRetriever(avg) achieves comparably good performance." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.361, + 0.21, + 0.379 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.39, + 0.263, + 0.408 + ], + "angle": 0, + "content": "5.1. Experiment Details" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.426, + 0.47, + 0.516 + ], + "angle": 0, + "content": "Datasets We perform experiments on two datasets containing multi-event videos: ActivityNet Captions and Charades-Event. It's worth noting that datasets such as MSR-VTT [48], even though videos are accompanied by multiple similar captions, do not align with our multi-event scenario." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.521, + 0.47, + 0.657 + ], + "angle": 0, + "content": "ActivityNet Captions [20] is a large-scale dataset with 20,000 video-text pairs extracted by web crawling on YouTube based on ActivityNet [4] videos. It covers a wide range of daily scenarios. The training set contains 10,009 videos and 4,917 videos/17,505 texts in the publicly accessible evaluation set 'val1'. Each video has multiple textual descriptions with time-interval annotation. This helps us construct a multi-event scenario for retrieval by taking all textual captions of a video as its associated events." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.662, + 0.47, + 0.753 + ], + "angle": 0, + "content": "Charades-Event is a video dataset of indoor activities with extensive action classes that we adopt from [37]. To create a MeVTR dataset, we filter out all videos with text annotation provided by [15] and interpret each text as an event in our MeVTR setting. There are 5,338 videos/12,408 texts in the training set and 1,334 videos/3,720 texts in the test set." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Experiment Settings In the key event selection module, we use 60 as the maximum number of iterations and \\(10^{-5}\\) as the distance threshold for clustering. Our model chooses 16 as a fixed number of key events and does not use a smaller or larger number of key events because shorter sequences cannot cover the number of events in part of the videos (the maximum event number in ActivityNet Captions is 27), and longer sequences contradict our intention of clustering. For each experiment, we set the epoch number as 5." + }, + { + "type": "table", + "bbox": [ + 0.511, + 0.089, + 0.895, + 0.221 + ], + "angle": 0, + "content": "
Text-to-Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)136.01.536.4810.5429.38
CLIP4Clip(tight)127.01.455.549.3530.11
CenterCLIP131.01.936.6110.6730.13
FRONZEN-in-Time277.00.351.993.8214.52
ClipBERT442.00.351.773.3111.10
Singularity179.51.535.228.5223.87
Ours(avg)126.01.886.6910.5929.97
Ours(max)112.02.027.6112.7434.49
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.231, + 0.895, + 0.293 + ], + "angle": 0, + "content": "Table 5: Results of Text-to-Video retrieval task on Charades-Event dataset. We use the same notation as Tab. 2. Me-Retriever(max) and Me-Retriever(avg) can achieve the best performance compared to other models." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.321, + 0.593, + 0.337 + ], + "angle": 0, + "content": "5.2. Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.347, + 0.892, + 0.527 + ], + "angle": 0, + "content": "The experiments show that Me-Retriever performs competitively within the context of MeVTR. On the Video-to-Text task, as presented in Tables 2 and 3, Me-Retriever(avg) surpasses its counterparts. This result underscores our model's capability to address both tasks across different datasets effectively. Additionally, we observe that CLIP4Clip also attains a commendable Recall@1-Average performance on the Video-to-Text task compared to other baseline models. This observation sheds light on the robust transferability of the pre-trained encoder to videos. This indicates that the primary challenge in MeVTR often resides within representation alignment." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.53, + 0.893, + 0.787 + ], + "angle": 0, + "content": "Our model also demonstrates comparable results on both datasets on the Text-to-Video task, as shown in Tab. 4 and Tab. 5. Me-Retriever(avg) demonstrates comparable performance to baseline models like CenterCLIP across numerous metrics on both datasets. Interestingly, we also notice that Me-Retriever(max) performs best on the Charades-Event dataset but not on the ActivityNet Captions dataset. This disparity can be attributed to overfitting, warranting further investigation. The noticeable performance of certain baseline models aligns with our conjecture that prior models can be effectively adapted to the Text-to-Video retrieval task. However, this adaptation might come at the expense of suboptimal results in the Video-to-Text task, as evident in Table 2. This phenomenon can be attributed to the embeddings of different texts collapsing to become more proximate, leading to an unintentional competition among positive instances that ultimately dampens their significance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Performance on videos with different subsets In order to reveal the model performance on videos of different properties like video duration and the number of events, we partition the complete ActivityNet Caption test set into two groups of subsets. These subsets are partitioned based on the video duration and the count of events within the videos, respectively:" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22118" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.088, + 0.09, + 0.472, + 0.164 + ], + "angle": 0, + "content": "
Text to Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
Ours (Best)11.015.1735.9448.3975.85
w/o Key Event12.015.0335.6747.9475.06
w/o MeVTR loss12.014.4534.9047.2575.24
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.174, + 0.47, + 0.252 + ], + "angle": 0, + "content": "Table 6: Ablation studies on key modules of Me-Retrever training on the Text-to-Video task for ActivityNet Captions. Only the Recall@k-Average is reported in the main part. We find that model performance drops with removing any modules, proving its efficacy." + }, + { + "type": "table", + "bbox": [ + 0.088, + 0.264, + 0.472, + 0.34 + ], + "angle": 0, + "content": "
Video to Text
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
Ours (Best)35.08.5223.5632.7961.26
w/o Key Event41.57.4021.0030.2757.71
w/o MeVTR loss41.06.7020.0528.9657.45
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.35, + 0.47, + 0.426 + ], + "angle": 0, + "content": "Table 7: Ablation studies on key modules of Me-Retriever training on the Video-to-Text task for ActivityNet Captions. Model performance declines to different extents without our modules. We conclude that our model can benefit Video-to-Text retrieval prominently." + }, + { + "type": "text", + "bbox": [ + 0.09, + 0.456, + 0.47, + 0.532 + ], + "angle": 0, + "content": "1. Video duration: test-S (Short) with videos shorter than 1 minute, test-M (Medium) with videos between 1-2 minutes, test-L (Long video) with videos between 2-3 minutes, and test-XL (eXtra Long video) with even longer videos than 3 minutes;" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.541, + 0.47, + 0.587 + ], + "angle": 0, + "content": "2. Number of events: test-E1 with videos containing fewer than 4 events, test-E2 with 5-12 events, and test-E3 with more than 12 events." + }, + { + "type": "list", + "bbox": [ + 0.089, + 0.456, + 0.47, + 0.587 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.597, + 0.47, + 0.809 + ], + "angle": 0, + "content": "Comparing performance across datasets of different sizes isn't equitable for a retrieval task, as larger candidate sets exacerbate retrieval difficulties. Therefore, we gauge the average improvement in the model performance of MeRetriever(avg) to the baseline CLIP4Clip(mean) and identify the subsets in which our model showcases notable enhancements. From Fig. 4, we also see that our model usually performs better on test-E1 and test-E2, and improvement slightly decreases for even longer videos. We assume this problem is inevitable since we use a fixed number of clusters and videos containing many events in test-E3, and larger numbers of events increase the retrieval difficulties. Whereas for videos of different duration, model performance slightly varies." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.818, + 0.242, + 0.833 + ], + "angle": 0, + "content": "5.3. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.84, + 0.47, + 0.9 + ], + "angle": 0, + "content": "In this section, we conduct various experiments to investigate the effectiveness of different weighting strategies in MeVTR loss and ablate the proposed components of our architecture." + }, + { + "type": "image", + "bbox": [ + 0.553, + 0.092, + 0.843, + 0.257 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.59, + 0.266, + 0.8, + 0.28 + ], + "angle": 0, + "content": "(a) On subsets of different duration" + }, + { + "type": "image", + "bbox": [ + 0.556, + 0.3, + 0.843, + 0.465 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.576, + 0.474, + 0.819, + 0.488 + ], + "angle": 0, + "content": "(b) On subsets of different event number" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.501, + 0.895, + 0.592 + ], + "angle": 0, + "content": "Figure 4: We compare average performance improvement in percentage(%) for Video-to-Text task on subsets of ActivityNet Captions. It shows how much percentage MeRetriever(avg) is better than CLIP4Clip(mean) on different subsets. Fig. 4a: Video-to-Text results for test-S/M/L/XL; Fig. 4b: Video-to-Text results for test-E1/E2/E3." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Impact of weighting strategy in MeVTR Loss To study the effect of different weighting strategies of MeVTR loss, i.e., dynamic weighting and fixed weighting, we test our model trained with a set of different weighting coefficients \\(\\alpha\\) as illustrated in Fig. 5 and Fig. 6. On the Video-to-Text task and Text-to-Video Retrieval tasks, we notice that dynamic weighting \\(\\alpha\\) can guarantee us a comparable performance in general and less sensitivity than any fixed coefficient. It is also illustrated that when we choose a smaller coefficient, the Video-to-Text retrieval is favored, while a bigger coefficient benefits the other way around. A cutoff point is empirically between 1.0 and 2.0. The reason is that \\(\\mathcal{L}_{v2t}\\) loss always has a comparably larger scale than \\(\\mathcal{L}_{t2v}\\) loss and dominates training due to the unbalanced number of video-text instances, as we have discussed in Section 4.2. This ensures us that a dynamic weighting strategy can improve the Text-to-Video task by amplifying the influence of \\(\\mathcal{L}_{t2v}\\) and guarantee stable improvements on both tasks." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22119" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.083, + 0.077, + 0.344, + 0.234 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.174, + 0.243, + 0.246, + 0.256 + ], + "angle": 0, + "content": "(a) Average" + }, + { + "type": "image", + "bbox": [ + 0.352, + 0.077, + 0.611, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.443, + 0.243, + 0.515, + 0.256 + ], + "angle": 0, + "content": "(b) One-Hit" + }, + { + "type": "image", + "bbox": [ + 0.622, + 0.077, + 0.874, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.712, + 0.243, + 0.778, + 0.256 + ], + "angle": 0, + "content": "(c) All-Hit" + }, + { + "type": "image_caption", + "bbox": [ + 0.075, + 0.269, + 0.895, + 0.331 + ], + "angle": 0, + "content": "Figure 5: We compare the model performance with different weighting strategies, a dynamic weight \\(\\alpha\\) and different choices of fixed weights from a choice of \\(\\{0.5,1.0,1.5,2.0,3.0\\}\\), in the MeVTR loss on Recall@5 on the Video-to-Text task for ActivityNet Captions. Fig. 5a-5c shows the results of Recall@5-Average/One-Hit/All-Hit respectively. We can find that compared to a fixed weighting coefficient, a dynamic weight \\(\\alpha\\) guarantees more stable and good results in different metrics." + }, + { + "type": "image", + "bbox": [ + 0.137, + 0.356, + 0.413, + 0.524 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.539, + 0.471, + 0.631 + ], + "angle": 0, + "content": "Figure 6: We compare the model performance with different weighting coefficients in the MeVTR loss on Recall@5 on the Text-to-Video task for ActivityNet Captions. The same graphical representations are used as Fig. 5. The dynamic weighting coefficient performs better than any other fixed coefficient considering performance and variance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.674, + 0.473, + 0.901 + ], + "angle": 0, + "content": "Effects of different modules We choose our best model Me-Retriever(avg) and ablate the key event selection module by removing the key event selection module and the MeVTR loss by replacing it with the cross-entropy loss, respectively. Results are shown in Tab. 6 and Tab. 7. We display the Recall@k-Average on both tasks in the table and observe that the model performances drop after removing any modules. In particular, our method demonstrates a larger improvement by \\(1.12\\%\\) without the key event selection module and \\(1.82\\%\\) without the MeVTR loss on the Video-to-Text task. This agrees with our assumption that our Me-Retriever model can deal with textual feature collapse in the MeVTR training. On the Text-to-Video task, both modules also show benefits to the performance on all metrics." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.356, + 0.895, + 0.553 + ], + "angle": 0, + "content": "Textual features of multi-event videos To show whether Me-Retriever can prevent heterogeneous text features of a multi-event video from collapsing, we calculate the average cosine similarity. If the text features of one video are too similar, then the average cosine similarity among texts is expected to be closer to 1. We find that in Me-Retriever(avg), the cosine similarity averaged on the whole test set is 0.789 with a variance of 0.0059 while in CLIP4Clip(mean), the value is 0.864 with a variance of 0.0028. And as in Fig. 3, Me-Retriever has lower average cosine similarity than CLIP4Clip. This shows that text features of the same video generated by Me-Retriever are more diverse than those by CLIP4Clip, which agrees with our motivation." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.565, + 0.623, + 0.581 + ], + "angle": 0, + "content": "6. Limitations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.591, + 0.892, + 0.713 + ], + "angle": 0, + "content": "Constrained by time and labor expenses, our experimental studies on the MeVTR task are based on the pre-existing video-text datasets including ActivityNet Captions and Charades. Nonetheless, it is important to recognize the potential bias in these datasets due to their emphasis on human activities and limitations in representing a wider range of videos. We aim to create a more comprehensive MeVTR benchmark encompassing more general videos." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.725, + 0.619, + 0.74 + ], + "angle": 0, + "content": "7. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.895, + 0.903 + ], + "angle": 0, + "content": "We study a practical Video-Text retrieval scenario, Multi-event Video-Text Retrieval, in this paper. We find previous models suffer notable performance degradation in inference on MeVTR and textual feature collapse when retrained on MeVTR. We present a new CLIP-based model, Me-Retriever, to conquer this challenge. In our experimental studies, we demonstrate the efficacy of these techniques on both Text-to-Video and Video-to-Text tasks for ActivityNet Captions and Charades-Event datasets. We believe this can be a strong baseline for future studies." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22120" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.091, + 0.245, + 0.108 + ], + "angle": 0, + "content": "Acknowledgements" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.116, + 0.47, + 0.177 + ], + "angle": 0, + "content": "This work has been funded by the German Federal Ministry of Education and Research and the Bavarian State Ministry for Science and the Arts. The authors of this work take full responsibility for its content." + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.192, + 0.175, + 0.209 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.217, + 0.47, + 0.273 + ], + "angle": 0, + "content": "[1] Partitioning Around Medoids (Program PAM). In Leonard Kaufman and Peter J. 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In Proceedings of the AAAI conference on artificial intelligence, volume 34, pages 13041-13049, 2020. 2" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.469, + 0.683 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "22123" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-Event Video-Text Retrieval/4a8e429c-a424-42a1-b75b-812c6ff37eb5_origin.pdf b/2023/Multi-Event Video-Text Retrieval/4a8e429c-a424-42a1-b75b-812c6ff37eb5_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..e2a47ad53e085608b369eca22166fb63c45bd503 --- /dev/null +++ b/2023/Multi-Event Video-Text Retrieval/4a8e429c-a424-42a1-b75b-812c6ff37eb5_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:7dea184eec30022c372345eebaf241fb6df747c3425650c2cc1fe24c929f3c59 +size 1394054 diff --git a/2023/Multi-Event Video-Text Retrieval/full.md b/2023/Multi-Event Video-Text Retrieval/full.md new file mode 100644 index 0000000000000000000000000000000000000000..0d79fa72cece5a2168fd5f177e6efed73ad03f1b --- /dev/null +++ b/2023/Multi-Event Video-Text Retrieval/full.md @@ -0,0 +1,289 @@ +# Multi-event Video-Text Retrieval + +Gengyuan Zhang $^{1,2}$ Jisen Ren $^{1}$ Jindong Gu $^{3*}$ Volker Tresp $^{1,2}$ + +$^{1}$ LMU Munich, Munich, Germany + +2 Munich Center for Machine Learning, Munich, Germany + +3 University of Oxford, Oxford, United Kingdom + +zhang@db.s.ifi.lmu.de jindong.gu@outlook.com + +# Abstract + +Video-Text Retrieval (VTR) is a crucial multi-modal task in an era of massive video-text data on the Internet. A plethora of work characterized by using a two-stream Vision-Language model architecture that learns a joint representation of video-text pairs has become a prominent approach for the VTR task. However, these models operate under the assumption of bijective video-text correspondences and neglect a more practical scenario where video content usually encompasses multiple events, while texts like user queries or webpage metadata tend to be specific and correspond to single events. This establishes a gap between the previous training objective and real-world applications, leading to the potential performance degradation of earlier models during inference. In this study, we introduce the Multi-event Video-Text Retrieval (MeVTR) task, addressing scenarios in which each video contains multiple different events, as a niche scenario of the conventional Video-Text Retrieval Task. We present a simple model, MeRetriever, which incorporates key event video representation and a new MeVTR loss for the MeVTR task. Comprehensive experiments show that this straightforward framework outperforms other models in the Video-to-Text and Text-to-Video tasks, effectively establishing a robust baseline for the MeVTR task. We believe this work serves as a strong foundation for future studies. Code is available at https://github.com/gengyuanmax/MeVTR. + +# 1. Introduction + +With the proliferation of multimedia data on the Internet every day, Video-Text Retrieval (VTR) task gains increasing importance in searching for desired items from the opposite modality given a video or text query. Over the past years, numerous efforts [49, 33, 9, 14, 31, 3, 7, 30, 16, 12, 51, 17] have been undertaken to improve the + +multi-modal retrieval performance on both Video-to-Text and Text-to-Video retrieval tasks. Along with the popularity of powerful vision foundation models like CLIP [36] and ALIGN [23] that align the image-text pairs in a joint feature space, two-stream video-text models [30, 16] targeting to learn video-text correspondences have further become a mainstream method for the Video-Text Retrieval task. + +However, this paradigm neglects that videos usually contain more than a single event, while a single textual caption can only capture a fragment of the entire video content. As depicted in Fig. 1, the example video spans a sequence of unrelated and discontinuous events, and each single textual caption merely corresponds to a video segment. This congruity undoubtedly contradicts the fundamental of the traditional VTR task, which aims to establish a mapping between video-text pair. + +This fact presents a prevalent scenario in Video-Text Retrieval: videos are intricate, often containing multiple events, whereas texts (typically like search queries or webpage metadata) tend to be specific and fragmentary. Consequently, this dichotomy leads to divergent semantic meanings for a given video-text pair. Such divergence contradicts the conventional training objective of aligning representations for video-text pairs in VTR models, that video features are aligned with the corresponding text feature. + +In this study, we formally introduce a new and realistic VTR setting involving multi-event videos, dubbed as Multi-event Video-Text Retrieval (MeVTR). In the introduced MeVTR task, a text describes a single event within a video item, whereas a video corresponds to multiple relevant textual captions, each detailing different events. + +We assess the performance of previous VTR models trained under standard VTR settings that learn a bijective video-text correspondence on the MeVTR task without retraining. Our evaluation reveals distinct levels of performance degradation, as illustrated in Table 1. This observation confirms the presence of a performance gap between training within the conventional VTR framework and real-world MeVTR inference scenarios. + +![](images/d6fa1a8373a7abedecd5d969a4508e2e36c4dd1128ee74119c5093b6978074b1.jpg) +Figure 1: An example case of multi-event videos from ActivityNet [4]. The video depicts a sequence of unrelated and discontinuous events, including the progression "a girl is sitting on the beach" $\rightarrow$ "a young man is practicing tightrope walking" $\rightarrow$ "a scene of sunset by the beach." Each textual caption only corresponds to a fragment of the video. Such short and specific textual captions are prevalent in our everyday video data and constitute a common video-text retrieval scenario. + +Besides, we retrain a series of previous models to adapt to the MeVTR task. However, we find that they cannot perform equally well on the Video-to-Text and Text-to-Video. We speculate that this is caused by non-injective videotext correspondences in the MeVTR setting, where previous VTR models embed a video and multiple distinct caption texts into a joint representation space and aim at aligning the video feature with the features of all caption texts. Consequently, distinct texts corresponding to the same video are mapped to the same feature, potentially resulting in suboptimal retrieval performance. + +Under this circumstance, we introduce a new CLIP-based model dubbed Me-Retriever tailored for the MeVTR task. Considering the dichotomy of multi-event video-text pairs, we formulate our approach as follows: (1) representing videos by a bag of key event features and (2) employing a multi-event video-text retrieval loss. This strategy serves the dual purpose of mitigating the collapse of textual features and harmonizing the learning objectives between the Text-to-Video and Video-to-Text tasks. + +Our contributions can be summarized as follows: + +1. We introduce a new task, Multi-event Video-Text Retrieval for retrieving multi-event video-text pairs, and define new evaluation metrics in MeVTR; +2. We propose a new model called Me-Retriever that represents videos with selected key events and a MeVTR loss for training on MeVTR; +3. We conduct comprehensive experiments to showcase Me-Retriever's effectiveness and to establish it as a simple yet robust baseline for future research. + +# 2. Related Work + +Video Language Model A series of work on Vision-Language Models (VLM) has been made like [26, 29, 5, 57, 53] for multi-modal representation learning. Given that videos are a structured sequence of images and typically entail higher computational demands than other visual data formats, the domain of Video-Language models has garnered significant attention. Notable contributions within this category include works by [40, 24, 38, 49, 29, 23, 43, 19, 13] which aim at video foundation models for video tasks. These models represent a subcategory of VLMs, adept at processing video and text inputs. + +Video Representation In a line of work [42, 52, 18, 25], convolutions are performed on videos to fuse spatial and temporal information. Meanwhile, as transformers [44] have achieved success firstly in text [8], and then vision fields [11, 27, 41, 6], attempts to introduce transformers to extract video representations have been made in [39, 2, 47, 56, 32, 28]. The success of pre-trained Vision-Language models has significantly impacted video representation learning. Vision-Language models [29, 38, 31, 36] have demonstrated that textual supervision is conducive to visual representation and to a uniform video-language representation. Among them, the success of representation models [22, 16, 45, 46] has bridged the gap between video and text representations. + +Video-Text Retrieval Video-Text Retrieval is a fundamental task of multi-modal learning, posing a good proxy task for learning joint representations of videos and texts. Two-stream Video-Text models [10, 9, 51, 34] concentrate on processing video-text pairs as inputs and aligning vi + +
Video-to-TextText-to-Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑Median Rank ↓k=1 ↑k=5 ↑k=10 ↑
FROZEN-in-time7.0 ↗ 109.515.3 ↗ 0.843.3 ↗ 3.143.3 ↗ 5.67.0 ↗ 111.015.9 ↗ 1.843.0 ↗ 6.859.01 ↗ 11.7
CLIPBERT4.0 ↗ 449.022.1 ↗ 1.458.2 ↗ 4.769.6 ↗ 7.65.0 ↗ 153.025.9 ↗ 2.655.4 ↗ 9.569.8 ↗ 15.1
CLIP4Clip2.0 ↗ 53.042.5 ↗ 7.574.1 ↗ 19.885.8 ↗ 28.413.0 ↗ 53.014.8 ↗ 7.534.2 ↗ 19.845.6 ↗ 28.4
CenterCLIP2.0 ↗ 51.042.8 ↗ 7.873.8 ↗ 20.885.3 ↗ 29.22.0 ↗ 13.041.8 ↗ 15.173.9 ↗ 34.684.7 ↗ 46.4
+ +Table 1: Comparison of model performance on VTR and MeVTR tasks on ActivityNet Captions. We train each model on the ActivityNet Captions with its original codes and evaluate them on MeVTR. We show the performance of VTR on the lefthand of $\nabla (\nearrow)$ and the performance of MeVTR on the right. $\uparrow$ means higher the better, and $\downarrow$ means lower the better. It is shown that model performance deteriorates to a large extent on both Video-to-Text and Text-to-Video tasks. + +sual and textual representations within a joint representation space. For instance, Frozen [3] employs a visual encoder that can be adaptively trained on images and videos, incorporating temporal contexts via curriculum learning. TACo [51], in contrast, focuses on aligning content words in texts with corresponding visual content, adding an extra learning objective. With the surge of large Vision-Language foundation models representative of CLIP [36], models [30, 16, 12, 35, 3, 50], leverage the potent pretrained model CLIP and endeavor to extend its capabilities from static images to the domain of videos. + +# 3. Problem + +# 3.1. Problem Formulation + +Given a video-text dataset with multi-event videos $\mathcal{V}$ and texts $\mathcal{T}$ , where a video $v_{i} \in \mathcal{V}$ is described by a set of different texts $\mathcal{T}_{i} \subset \mathcal{T}$ and a text is denoted as $t_{j}$ , our task consists in retrieving a video given a text query $t^{q}$ and retrieving all relevant texts given a video query $v^{q}$ . A generic Video-Text Retrieval model is to learn a similarity function $sim(v_{i}, t_{j})$ that scores the similarity between any relevant video-text pair higher and ranks all the candidate items. + +# 3.2. Evaluation Metrics + +Video-Text retrieval is a recall-focused retrieval task. A single item is retrieved in traditional settings, and the average Recall at the top rank $k$ is calculated. Nevertheless, in the MeVTR setting, we also want to evaluate retrieving multiple different text items given one video. Hence we devise the following metrics: (1) Recall@k-Average as the fraction of the number of correspondences ranked at top $k$ ; (2) Recall@k-One-Hit as an indication of whether any of the correspondences will be ranked in the top $k$ ; (3) Recall@k-All-Hit as an indication of whether all items can be retrieved within the top $k$ rank. All metrics are averaged on the whole test set. In the follow-up experiments, we report the Recall for the Text-to-Video tasks and the metrics mentioned above for the Video-to-Text tasks. + +# 3.3. Textual Feature Collapse + +To investigate the textual feature collapse in previous models to elucidate the performance drop by calculating the textual feature's similarity after retraining, we define the average text similarity of a video $v_{i}$ with $n_{v_i}$ captions as: + +$$ +\operatorname {s i m} _ {t} \left(v _ {i}\right) = \sum_ {m = 1} ^ {N _ {v _ {i}}} \sum_ {n = 1} ^ {N _ {v _ {i}}} \frac {1}{N _ {v _ {i}} ^ {2}} \operatorname {s i m} \left(t _ {m}, t _ {n}\right) \tag {1} +$$ + +In Fig. 3, we attempt to visualize the average text similarity of all videos with a different number of events. Different texts are expected to have lower sentence similarity to retain their meanings due to retraining on MeVTR. We chose CLIP4Clip for comparison in our experiments, as it still performs relatively well in MeVTR tasks compared to other models. As a comparison, we show that Me-R retriever, which will be introduced in the next section, can generate more diverse textual features than CLIP4Clip and effectively avoid textual feature collapse. + +# 4. Method + +We propose Me-Retriever consisting of a Key Event Selection module and MeVTR loss as shown in Fig. 2. + +# 4.1. Key Event Video Representation + +Intuitively, human brains do not remember experiences with all continuous scenes and consolidate all the details. Instead, brains retain memories of certain discrete events [55]. This insight motivates us to represent a video with a bag of frames as key events. For leveraging frame embeddings extracted from the CLIP visual encoder $\{\mathbf{f}_i^1,\mathbf{f}_i^2,\dots ,\mathbf{f}_i^{[v_i]}\}$ , we define the Key Event Selection module that selects the most distinctive keyframes. + +We employ a classic clustering method, K-Medoids [1]. Compared to other clustering methods, the representative of each cluster given by the K-Medoids algorithm is from the sample points, which corresponds to a particular frame and has explicit interpretation. The criterion is minimizing the distance of all frames in the cluster to its medoid. $K$ frames + +![](images/ff7eba4eb35ab607ba87f767e3afdcf0e307a29e1ecbe61359498c7ec562fdd7.jpg) +Figure 2: The overall framework of Me-Retriever. The model adopts CLIP [36]'s Visual Encoder(VE) and Text Encoder(TE). After the Visual Encoder, [CLASS] tokens in the last hidden layer are taken as frame embeddings. We use a clustering-based Key Event Selection module to aggregate similar frames and extract key events. Each textual caption is fed into Text Encoder, and [EOS] will be used as text embedding. The similarity between these key events of any video $v_{i}$ and any textual caption $t_j$ is measured in the Similarity Calculator. For each video, there are multiple text correspondences as positive samples. + +![](images/306576039b7a18a9c91a583eeae74cfa1e0c5c65c5f0ab6cf7851ff459c92356.jpg) +Figure 3: We compare the average cosine similarity between all text pairs of videos with a different number of events. Me-Retriever can generate more diverse text features than CLIP4Clip and refrain from text features collapsing, as we discuss in the main part. + +are chosen as initial medoids; the remaining frames are then assigned to their nearest medoids, and within each cluster, new medoids are again selected based on cosine similarity as a metric function. Video $v_{i}$ can be represented as a sequence of key event embeddings $\mathbf{K}_i = \{\mathbf{k}_i^1,\mathbf{k}_i^2,\dots ,\mathbf{k}_i^K\}$ . In the loss calculation, we use the pre-computed assignment of all frames as key event video representation. + +# 4.2. MeVTR Loss + +Following the dual learning paradigm of Text-to-Video and Video-to-Text on VTR tasks, we propose MeVTR loss for MeVTR learning. As previously discussed, there is an issue of textual feature collapse during MeVTR training. To address this, we propose disentangling various positive instances within video samples by excluding non-self positive instances from the softmax function. Moreover, considering the dissimilar granularity between multi-event videos and single-event text, we propose adopting a dynamic weighting strategy. This strategy balances the loss scale of both learning objectives during the training process. + +MeVTR loss is defined as a weighted sum of $\mathcal{L}_{t2v}$ and $\mathcal{L}_{v2t}$ as follows: + +$$ +\mathcal {L} _ {M e V T R} = \mathcal {L} _ {v 2 t} + \alpha \mathcal {L} _ {t 2 v} \tag {2} +$$ + +where $\mathcal{L}_{v2t}$ and $\mathcal{L}_{t2v}$ are respectively formulated as: + +$$ +\mathcal {L} _ {v 2 t} = - \frac {1}{| \mathcal {B} |} \sum_ {i} ^ {| \mathcal {B} |} \sum_ {k} ^ {| \mathcal {T} _ {i} |} \frac {1}{| \mathcal {T} _ {i} |} \log \frac {\exp s i m (\mathbf {K} _ {i} , \mathbf {w} _ {k}) / \tau}{\sum_ {j = 1} ^ {\mathcal {B} - \cup \{k \}} \exp s i m (\mathbf {K} _ {i} , \mathbf {w} _ {j}) / \tau}, +$$ + +$$ +\mathcal {L} _ {t 2 v} = - \frac {1}{| \mathcal {B} |} \sum_ {j} ^ {| \mathcal {B} |} \log \frac {\exp \operatorname {s i m} \left(\mathbf {K} _ {i} , \mathbf {w} _ {j}\right) / \tau}{\sum_ {i = 1} ^ {\mathcal {B}} \exp \operatorname {s i m} \left(\mathbf {K} _ {j} , \mathbf {w} _ {j}\right)) / \tau}, \tag {4} +$$ + +
Video-to-Text
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)39.06.60 / 20.74 / -20.32 / 47.02 / 3.4629.37 / 61.26 / 6.7158.41 / 89.77 / 26.24
CLIP4Clip(tight)49.55.23 / 16.45 / -16.74 / 41.94 / 1.7725.50 / 57.37 / 4.2354.22 / 88.00 / 21.52
CenterCLIP38.06.93 / 21.62 / -20.58 / 47.98 / 3.6629.90 / 61.72 / 6.9658.88 / 90.34 / 26.28
FROZEN-in-time330.00.30 / 0.67 / -0.83 / 2.10 / 0.221.60 / 3.37 / 0.675.89 / 12.97 / 2.55
CLIPBERT174.51.80 / 6.10 / -6.48 / 18.97 / 0.1810.93 / 29.00 / 0.8731.34 / 61.42 / 8.72
Singularity64.54.83 / 14.68 / -15.1 / 37.79 / 1.9522.23 / 49.50 / 4.4148.96 / 81.94 / 19.38
Ours(avg)35.08.52 / 26.91 / -23.56 / 54.18 / 3.8632.95 / 67.13 / 7.7961.26 / 92.50 / 27.80
Ours(max)49.06.98 / 22.72 / -18.72 / 46.37 / 2.3027.04 / 60.62 / 5.7654.19 / 88.37 / 20.90
+ +Table 2: Results of the Video-to-Text retrieval task on ActivityNet Captions dataset. In each column, we report the Recall@k-Average/One-Hit/All-Hit for each $k = 1,5,10,50$ respectively. The best result in each column is emphasized in bold. We ignore the Recall@1-All-Hit since all models can only achieve a nearly zero result. Ours(avg) maintains its advantage in the text retrieval task and surpasses all other models by a large margin. + +
Video-to-Text
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)441.51.32 / 2.92 / -4.07 / 8.32 / 1.805.65 / 11.84 / 2.5516.84 / 32.01 / 7.65
CLIP4Clip(tight)391.00.80 / 1.80 / -2.45 / 6.30 / 0.754.19 / 10.27 / 1.3515.26 / 30.43 / 6.37
CenterCLIP408.01.32 / 3.00 / -3.71 / 7.87 / 1.576.33 / 13.42 / 2.6217.37 / 33.43 / 7.72
FROZEN-in-time810.00.30 / 0.67 / -0.83 / 2.10 / 0.221.60 / 3.37 / 0.675.89 / 12.97 / 2.55
ClipBERT1339.50.15 / 0.45 / -0.60 / 1.50 / 0.151.19 / 3.30 / 0.225.31 / 11.92 / 1.87
Singularity621.50.95 / 2.17 / -2.84 / 5.92 / 1.424.35 / 9.52 / 1.9512.22 / 25.94 / 4.87
Ours(avg)406.01.39 / 3.22 / -5.04 / 9.90 / 2.477.02 / 13.72 / 3.3717.62 / 32.08 / 8.70
Ours(max)365.61.01 / 2.62 / -4.03 / 9.00 / 1.726.39 / 13.72 / 2.7019.08 / 36.66 / 8.10
+ +Table 3: Results of the Video-to-Text retrieval task on Charades-Event dataset. We use the same notation as in Tab. 2. MeRetriever(avg) and Me-Retriever(max) can achieve best performance. + +$sim(\cdot)$ is the similarity function, $\mathcal{B}$ is the set of samples in the training batch, $\mathcal{B}^{-}$ is the set of negative samples in the batch, $\tau$ is the temperature coefficient, and $\mathcal{T}_i$ is the set of positive instances of one sample video in $\mathcal{L}_{t2v}$ . Notably, given a video item $v_{i}$ , we discard all positive instances in $\mathcal{T}_i$ other than the current training sample $t_k$ . This encourages similarities between a video and its all positive instances to be increased. In $\mathcal{L}_{t2v}$ , it degenerates to a normal softmax function. + +We denote $\alpha$ as the weighting coefficient that balances $\mathcal{L}_{t2v}$ and $\mathcal{L}_{v2t}$ . Given that the two losses exhibit differing scales during training, which owes to the positive/negative sample ratio asymmetry, determining the value of $\alpha$ requires employing certain hyperparameter-tuning techniques to ensure balanced performance on both tasks. We suggest employing a dynamic weighting strategy as opposed to a fixed weight. A dynamic weighting coefficient $\alpha$ is computed as the ratio of $\mathcal{L}_{v2t}$ to $\mathcal{L}_{t2v}$ during training. In Section 5.3, we conduct experimental studies to compare the impact of various weighting strategies. + +Similarity function For video-text pairs in bijective correspondences, the similarity between video and text is measured by cosine similarity in the feature space. In MeVTR, we use two approaches are used to measure the similarity between a video $v_{i}$ consisting of key events $\{\mathbf{k}_i^1,\mathbf{k}_i^2,\dots ,\mathbf{k}_i^K\}$ and a text $t_j$ : (1) we average the cosine similarity scores of all key event embeddings and the text as in Eq. 5; (2) we select the maximum cosine similarity of any key event-text pair to represent the similarity between the video to which these medoids belong as in Eq. 6; + +$$ +s _ {a v g} (v _ {i}, t _ {j}) = \operatorname {a v g} \left(\cos \left(\mathbf {k} _ {1} ^ {i}, \mathbf {w} _ {j}\right), \dots , \cos \left(\mathbf {k} _ {k} ^ {i}, \mathbf {w} _ {j}\right)\right) \tag {5} +$$ + +$$ +s _ {m a x} (v _ {i}, t _ {j}) = \max (\cos (\mathbf {k} _ {1} ^ {i}, \mathbf {w} _ {j}), \dots , \cos (\mathbf {k} _ {k} ^ {i}, \mathbf {w} _ {j})) \quad (6) +$$ + +We denote Me-Retriever with different similarity functions as Me-Retriever(avg) and Me-Retriever(max). + +
Text-to-Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)11.015.2536.4349.1176.64
CLIP4Clip(tight)15.010.1429.0741.9372.50
CenterCLIP11.015.5337.2149.7877.19
FROZEN-in-time111.01.826.8011.7633.86
ClipBERT48.04.2014.5723.3551.02
Singularity(FT)22.09.2924.9636.2665.55
Ours(avg)11.015.9937.1349.6076.66
Ours(max)13.014.9334.4446.3674.65
+ +# 5. Experiments + +# 5.1. Experiment Details + +Datasets We perform experiments on two datasets containing multi-event videos: ActivityNet Captions and Charades-Event. It's worth noting that datasets such as MSR-VTT [48], even though videos are accompanied by multiple similar captions, do not align with our multi-event scenario. + +ActivityNet Captions [20] is a large-scale dataset with 20,000 video-text pairs extracted by web crawling on YouTube based on ActivityNet [4] videos. It covers a wide range of daily scenarios. The training set contains 10,009 videos and 4,917 videos/17,505 texts in the publicly accessible evaluation set 'val1'. Each video has multiple textual descriptions with time-interval annotation. This helps us construct a multi-event scenario for retrieval by taking all textual captions of a video as its associated events. + +Charades-Event is a video dataset of indoor activities with extensive action classes that we adopt from [37]. To create a MeVTR dataset, we filter out all videos with text annotation provided by [15] and interpret each text as an event in our MeVTR setting. There are 5,338 videos/12,408 texts in the training set and 1,334 videos/3,720 texts in the test set. + +Experiment Settings In the key event selection module, we use 60 as the maximum number of iterations and $10^{-5}$ as the distance threshold for clustering. Our model chooses 16 as a fixed number of key events and does not use a smaller or larger number of key events because shorter sequences cannot cover the number of events in part of the videos (the maximum event number in ActivityNet Captions is 27), and longer sequences contradict our intention of clustering. For each experiment, we set the epoch number as 5. + +Table 4: Results of the Text-to-Video retrieval task on ActivityNet Captions dataset. We compare CLIP4Clip [30], CenterCLIP [54], FROZEN-in-time [3], ClipBERT [22], and [21]. The best result in each column is emphasized in bold, and the second best result is underlined. Our MeRetriever(avg) achieves comparably good performance. + +
Text-to-Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)136.01.536.4810.5429.38
CLIP4Clip(tight)127.01.455.549.3530.11
CenterCLIP131.01.936.6110.6730.13
FRONZEN-in-Time277.00.351.993.8214.52
ClipBERT442.00.351.773.3111.10
Singularity179.51.535.228.5223.87
Ours(avg)126.01.886.6910.5929.97
Ours(max)112.02.027.6112.7434.49
+ +Table 5: Results of Text-to-Video retrieval task on Charades-Event dataset. We use the same notation as Tab. 2. Me-Retriever(max) and Me-Retriever(avg) can achieve the best performance compared to other models. + +# 5.2. Results + +The experiments show that Me-Retriever performs competitively within the context of MeVTR. On the Video-to-Text task, as presented in Tables 2 and 3, Me-Retriever(avg) surpasses its counterparts. This result underscores our model's capability to address both tasks across different datasets effectively. Additionally, we observe that CLIP4Clip also attains a commendable Recall@1-Average performance on the Video-to-Text task compared to other baseline models. This observation sheds light on the robust transferability of the pre-trained encoder to videos. This indicates that the primary challenge in MeVTR often resides within representation alignment. + +Our model also demonstrates comparable results on both datasets on the Text-to-Video task, as shown in Tab. 4 and Tab. 5. Me-Retriever(avg) demonstrates comparable performance to baseline models like CenterCLIP across numerous metrics on both datasets. Interestingly, we also notice that Me-Retriever(max) performs best on the Charades-Event dataset but not on the ActivityNet Captions dataset. This disparity can be attributed to overfitting, warranting further investigation. The noticeable performance of certain baseline models aligns with our conjecture that prior models can be effectively adapted to the Text-to-Video retrieval task. However, this adaptation might come at the expense of suboptimal results in the Video-to-Text task, as evident in Table 2. This phenomenon can be attributed to the embeddings of different texts collapsing to become more proximate, leading to an unintentional competition among positive instances that ultimately dampens their significance. + +Performance on videos with different subsets In order to reveal the model performance on videos of different properties like video duration and the number of events, we partition the complete ActivityNet Caption test set into two groups of subsets. These subsets are partitioned based on the video duration and the count of events within the videos, respectively: + +
Text to Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
Ours (Best)11.015.1735.9448.3975.85
w/o Key Event12.015.0335.6747.9475.06
w/o MeVTR loss12.014.4534.9047.2575.24
+ +Table 6: Ablation studies on key modules of Me-Retrever training on the Text-to-Video task for ActivityNet Captions. Only the Recall@k-Average is reported in the main part. We find that model performance drops with removing any modules, proving its efficacy. + +
Video to Text
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
Ours (Best)35.08.5223.5632.7961.26
w/o Key Event41.57.4021.0030.2757.71
w/o MeVTR loss41.06.7020.0528.9657.45
+ +Table 7: Ablation studies on key modules of Me-Retriever training on the Video-to-Text task for ActivityNet Captions. Model performance declines to different extents without our modules. We conclude that our model can benefit Video-to-Text retrieval prominently. + +1. Video duration: test-S (Short) with videos shorter than 1 minute, test-M (Medium) with videos between 1-2 minutes, test-L (Long video) with videos between 2-3 minutes, and test-XL (eXtra Long video) with even longer videos than 3 minutes; +2. Number of events: test-E1 with videos containing fewer than 4 events, test-E2 with 5-12 events, and test-E3 with more than 12 events. + +Comparing performance across datasets of different sizes isn't equitable for a retrieval task, as larger candidate sets exacerbate retrieval difficulties. Therefore, we gauge the average improvement in the model performance of MeRetriever(avg) to the baseline CLIP4Clip(mean) and identify the subsets in which our model showcases notable enhancements. From Fig. 4, we also see that our model usually performs better on test-E1 and test-E2, and improvement slightly decreases for even longer videos. We assume this problem is inevitable since we use a fixed number of clusters and videos containing many events in test-E3, and larger numbers of events increase the retrieval difficulties. Whereas for videos of different duration, model performance slightly varies. + +# 5.3. Ablation Studies + +In this section, we conduct various experiments to investigate the effectiveness of different weighting strategies in MeVTR loss and ablate the proposed components of our architecture. + +![](images/2fa066806e6d2b5430c7b8d66ae1ad5a83676acf746417c97ec2604da7beb97d.jpg) +(a) On subsets of different duration + +![](images/6804e5e4ae1f32e9efc29a99d107a0a5982394dd4225444c760e719667463331.jpg) +(b) On subsets of different event number +Figure 4: We compare average performance improvement in percentage(%) for Video-to-Text task on subsets of ActivityNet Captions. It shows how much percentage MeRetriever(avg) is better than CLIP4Clip(mean) on different subsets. Fig. 4a: Video-to-Text results for test-S/M/L/XL; Fig. 4b: Video-to-Text results for test-E1/E2/E3. + +Impact of weighting strategy in MeVTR Loss To study the effect of different weighting strategies of MeVTR loss, i.e., dynamic weighting and fixed weighting, we test our model trained with a set of different weighting coefficients $\alpha$ as illustrated in Fig. 5 and Fig. 6. On the Video-to-Text task and Text-to-Video Retrieval tasks, we notice that dynamic weighting $\alpha$ can guarantee us a comparable performance in general and less sensitivity than any fixed coefficient. It is also illustrated that when we choose a smaller coefficient, the Video-to-Text retrieval is favored, while a bigger coefficient benefits the other way around. A cutoff point is empirically between 1.0 and 2.0. The reason is that $\mathcal{L}_{v2t}$ loss always has a comparably larger scale than $\mathcal{L}_{t2v}$ loss and dominates training due to the unbalanced number of video-text instances, as we have discussed in Section 4.2. This ensures us that a dynamic weighting strategy can improve the Text-to-Video task by amplifying the influence of $\mathcal{L}_{t2v}$ and guarantee stable improvements on both tasks. + +![](images/f17a96253965453ffe3479d9734718e8b4554f8d56eadbd26022edba1dde8cec.jpg) +(a) Average + +![](images/8d7a3b394e53e3bf1c755ead343cbc83454591da0af34cecc2429c90cd747283.jpg) +(b) One-Hit + +![](images/024bd25bab93a3be719d0c833fdbc6a8b48a64c23a4a5f045a11ee6bb67d2629.jpg) +(c) All-Hit + +![](images/ba34310540d8e3748e548149447b488b07803be6d8e50e50928f2c24d197bc88.jpg) +Figure 5: We compare the model performance with different weighting strategies, a dynamic weight $\alpha$ and different choices of fixed weights from a choice of $\{0.5,1.0,1.5,2.0,3.0\}$ , in the MeVTR loss on Recall@5 on the Video-to-Text task for ActivityNet Captions. Fig. 5a-5c shows the results of Recall@5-Average/One-Hit/All-Hit respectively. We can find that compared to a fixed weighting coefficient, a dynamic weight $\alpha$ guarantees more stable and good results in different metrics. +Figure 6: We compare the model performance with different weighting coefficients in the MeVTR loss on Recall@5 on the Text-to-Video task for ActivityNet Captions. The same graphical representations are used as Fig. 5. The dynamic weighting coefficient performs better than any other fixed coefficient considering performance and variance. + +Effects of different modules We choose our best model Me-Retriever(avg) and ablate the key event selection module by removing the key event selection module and the MeVTR loss by replacing it with the cross-entropy loss, respectively. Results are shown in Tab. 6 and Tab. 7. We display the Recall@k-Average on both tasks in the table and observe that the model performances drop after removing any modules. In particular, our method demonstrates a larger improvement by $1.12\%$ without the key event selection module and $1.82\%$ without the MeVTR loss on the Video-to-Text task. This agrees with our assumption that our Me-Retriever model can deal with textual feature collapse in the MeVTR training. On the Text-to-Video task, both modules also show benefits to the performance on all metrics. + +Textual features of multi-event videos To show whether Me-Retriever can prevent heterogeneous text features of a multi-event video from collapsing, we calculate the average cosine similarity. If the text features of one video are too similar, then the average cosine similarity among texts is expected to be closer to 1. We find that in Me-Retriever(avg), the cosine similarity averaged on the whole test set is 0.789 with a variance of 0.0059 while in CLIP4Clip(mean), the value is 0.864 with a variance of 0.0028. And as in Fig. 3, Me-Retriever has lower average cosine similarity than CLIP4Clip. This shows that text features of the same video generated by Me-Retriever are more diverse than those by CLIP4Clip, which agrees with our motivation. + +# 6. Limitations + +Constrained by time and labor expenses, our experimental studies on the MeVTR task are based on the pre-existing video-text datasets including ActivityNet Captions and Charades. Nonetheless, it is important to recognize the potential bias in these datasets due to their emphasis on human activities and limitations in representing a wider range of videos. We aim to create a more comprehensive MeVTR benchmark encompassing more general videos. + +# 7. Conclusion + +We study a practical Video-Text retrieval scenario, Multi-event Video-Text Retrieval, in this paper. We find previous models suffer notable performance degradation in inference on MeVTR and textual feature collapse when retrained on MeVTR. We present a new CLIP-based model, Me-Retriever, to conquer this challenge. 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In Proceedings of the 45th International ACM SIGIR Conference on Research and Development in Information Retrieval, pages 970–981, 2022. 6 +[55] Jie Zheng, Andrea GP Schjetnan, Mar Yebra, Bernard A Gomes, Clayton P Mosher, Suneil K Kalia, Taufik A Valiente, Adam N Mamelak, Gabriel Kreiman, and Ueli Rutishauser. Neurons detect cognitive boundaries to structure episodic memories in humans. Nature neuroscience, 25(3):358-368, 2022. 3 +[56] Daquan Zhou, Bingyi Kang, Xiaojie Jin, Linjie Yang, Xiaochen Lian, Zihang Jiang, Qibin Hou, and Jiashi Feng. Deepvit: Towards deeper vision transformer. arXiv preprint arXiv:2103.11886, 2021. 2 +[57] Luowei Zhou, Hamid Palangi, Lei Zhang, Houdong Hu, Jason Corso, and Jianfeng Gao. Unified vision-language pretraining for image captioning and vqa. In Proceedings of the AAAI conference on artificial intelligence, volume 34, pages 13041-13049, 2020. 2 \ No newline at end of file diff --git a/2023/Multi-Event Video-Text Retrieval/images.zip b/2023/Multi-Event Video-Text Retrieval/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..c9511927a612e26af62a364011c449a7e5f44a1e --- /dev/null +++ b/2023/Multi-Event Video-Text Retrieval/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:304a9c9cd089a9ffb06a76245dbb6c13752d103611bc672e7c978437a8ebf31c +size 586439 diff --git a/2023/Multi-Event Video-Text Retrieval/layout.json b/2023/Multi-Event Video-Text Retrieval/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..9977bfc3e84b144fea50cb4b40cc6b17e9667190 --- /dev/null +++ b/2023/Multi-Event Video-Text Retrieval/layout.json @@ -0,0 +1,7924 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 194, + 103, + 400, + 119 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 194, + 103, + 400, + 119 + ], + "spans": [ + { + "bbox": [ + 194, + 103, + 400, + 119 + ], + "type": "text", + "content": "Multi-event Video-Text Retrieval" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 119, + 141, + 473, + 157 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 119, + 141, + 473, + 157 + ], + "spans": [ + { + "bbox": [ + 119, + 141, + 473, + 157 + ], + "type": "text", + "content": "Gengyuan Zhang " + }, + { + "bbox": [ + 119, + 141, + 473, + 157 + ], + "type": "inline_equation", + "content": "^{1,2}" + }, + { + "bbox": [ + 119, + 141, + 473, + 157 + ], + "type": "text", + "content": " Jisen Ren " + }, + { + "bbox": [ + 119, + 141, + 473, + 157 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 119, + 141, + 473, + 157 + ], + "type": "text", + "content": " Jindong Gu " + }, + { + "bbox": [ + 119, + 141, + 473, + 157 + ], + "type": "inline_equation", + "content": "^{3*}" + }, + { + "bbox": [ + 119, + 141, + 473, + 157 + ], + "type": "text", + "content": " Volker Tresp " + }, + { + "bbox": [ + 119, + 141, + 473, + 157 + ], + "type": "inline_equation", + "content": "^{1,2}" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 212, + 157, + 381, + 172 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 212, + 157, + 381, + 172 + ], + "spans": [ + { + "bbox": [ + 212, + 157, + 381, + 172 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 212, + 157, + 381, + 172 + ], + "type": "text", + "content": " LMU Munich, Munich, Germany" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 156, + 171, + 438, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 156, + 171, + 438, + 186 + ], + "spans": [ + { + "bbox": [ + 156, + 171, + 438, + 186 + ], + "type": "text", + "content": "2 Munich Center for Machine Learning, Munich, Germany" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 178, + 186, + 415, + 200 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 178, + 186, + 415, + 200 + ], + "spans": [ + { + "bbox": [ + 178, + 186, + 415, + 200 + ], + "type": "text", + "content": "3 University of Oxford, Oxford, United Kingdom" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 175, + 201, + 418, + 213 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 175, + 201, + 418, + 213 + ], + "spans": [ + { + "bbox": [ + 175, + 201, + 418, + 213 + ], + "type": "text", + "content": "zhang@db.s.ifi.lmu.de jindong.gu@outlook.com" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 143, + 241, + 191, + 253 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 241, + 191, + 253 + ], + "spans": [ + { + "bbox": [ + 143, + 241, + 191, + 253 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 266, + 289, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 266, + 289, + 578 + ], + "spans": [ + { + "bbox": [ + 47, + 266, + 289, + 578 + ], + "type": "text", + "content": "Video-Text Retrieval (VTR) is a crucial multi-modal task in an era of massive video-text data on the Internet. A plethora of work characterized by using a two-stream Vision-Language model architecture that learns a joint representation of video-text pairs has become a prominent approach for the VTR task. However, these models operate under the assumption of bijective video-text correspondences and neglect a more practical scenario where video content usually encompasses multiple events, while texts like user queries or webpage metadata tend to be specific and correspond to single events. This establishes a gap between the previous training objective and real-world applications, leading to the potential performance degradation of earlier models during inference. In this study, we introduce the Multi-event Video-Text Retrieval (MeVTR) task, addressing scenarios in which each video contains multiple different events, as a niche scenario of the conventional Video-Text Retrieval Task. We present a simple model, MeRetriever, which incorporates key event video representation and a new MeVTR loss for the MeVTR task. Comprehensive experiments show that this straightforward framework outperforms other models in the Video-to-Text and Text-to-Video tasks, effectively establishing a robust baseline for the MeVTR task. We believe this work serves as a strong foundation for future studies. Code is available at https://github.com/gengyuanmax/MeVTR." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 601, + 128, + 613 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 601, + 128, + 613 + ], + "spans": [ + { + "bbox": [ + 47, + 601, + 128, + 613 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 621, + 287, + 694 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 621, + 287, + 694 + ], + "spans": [ + { + "bbox": [ + 46, + 621, + 287, + 694 + ], + "type": "text", + "content": "With the proliferation of multimedia data on the Internet every day, Video-Text Retrieval (VTR) task gains increasing importance in searching for desired items from the opposite modality given a video or text query. Over the past years, numerous efforts [49, 33, 9, 14, 31, 3, 7, 30, 16, 12, 51, 17] have been undertaken to improve the" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 242, + 545, + 326 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 242, + 545, + 326 + ], + "spans": [ + { + "bbox": [ + 306, + 242, + 545, + 326 + ], + "type": "text", + "content": "multi-modal retrieval performance on both Video-to-Text and Text-to-Video retrieval tasks. Along with the popularity of powerful vision foundation models like CLIP [36] and ALIGN [23] that align the image-text pairs in a joint feature space, two-stream video-text models [30, 16] targeting to learn video-text correspondences have further become a mainstream method for the Video-Text Retrieval task." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 327, + 546, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 327, + 546, + 435 + ], + "spans": [ + { + "bbox": [ + 304, + 327, + 546, + 435 + ], + "type": "text", + "content": "However, this paradigm neglects that videos usually contain more than a single event, while a single textual caption can only capture a fragment of the entire video content. As depicted in Fig. 1, the example video spans a sequence of unrelated and discontinuous events, and each single textual caption merely corresponds to a video segment. This congruity undoubtedly contradicts the fundamental of the traditional VTR task, which aims to establish a mapping between video-text pair." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 436, + 547, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 436, + 547, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 436, + 547, + 544 + ], + "type": "text", + "content": "This fact presents a prevalent scenario in Video-Text Retrieval: videos are intricate, often containing multiple events, whereas texts (typically like search queries or webpage metadata) tend to be specific and fragmentary. Consequently, this dichotomy leads to divergent semantic meanings for a given video-text pair. Such divergence contradicts the conventional training objective of aligning representations for video-text pairs in VTR models, that video features are aligned with the corresponding text feature." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 544, + 547, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 544, + 547, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 544, + 547, + 617 + ], + "type": "text", + "content": "In this study, we formally introduce a new and realistic VTR setting involving multi-event videos, dubbed as Multi-event Video-Text Retrieval (MeVTR). In the introduced MeVTR task, a text describes a single event within a video item, whereas a video corresponds to multiple relevant textual captions, each detailing different events." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": "We assess the performance of previous VTR models trained under standard VTR settings that learn a bijective video-text correspondence on the MeVTR task without retraining. Our evaluation reveals distinct levels of performance degradation, as illustrated in Table 1. This observation confirms the presence of a performance gap between training within the conventional VTR framework and real-world MeVTR inference scenarios." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 703, + 135, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 703, + 135, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 703, + 135, + 712 + ], + "type": "text", + "content": "*Corresponding author" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22113" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 82, + 542, + 237 + ], + "blocks": [ + { + "bbox": [ + 53, + 82, + 542, + 237 + ], + "lines": [ + { + "bbox": [ + 53, + 82, + 542, + 237 + ], + "spans": [ + { + "bbox": [ + 53, + 82, + 542, + 237 + ], + "type": "image", + "image_path": "d6fa1a8373a7abedecd5d969a4508e2e36c4dd1128ee74119c5093b6978074b1.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 251, + 548, + 301 + ], + "lines": [ + { + "bbox": [ + 46, + 251, + 548, + 301 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 548, + 301 + ], + "type": "text", + "content": "Figure 1: An example case of multi-event videos from ActivityNet [4]. The video depicts a sequence of unrelated and discontinuous events, including the progression \"a girl is sitting on the beach\" " + }, + { + "bbox": [ + 46, + 251, + 548, + 301 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 251, + 548, + 301 + ], + "type": "text", + "content": " \"a young man is practicing tightrope walking\" " + }, + { + "bbox": [ + 46, + 251, + 548, + 301 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 251, + 548, + 301 + ], + "type": "text", + "content": " \"a scene of sunset by the beach.\" Each textual caption only corresponds to a fragment of the video. Such short and specific textual captions are prevalent in our everyday video data and constitute a common video-text retrieval scenario." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 321, + 289, + 452 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 321, + 289, + 452 + ], + "spans": [ + { + "bbox": [ + 46, + 321, + 289, + 452 + ], + "type": "text", + "content": "Besides, we retrain a series of previous models to adapt to the MeVTR task. However, we find that they cannot perform equally well on the Video-to-Text and Text-to-Video. We speculate that this is caused by non-injective videotext correspondences in the MeVTR setting, where previous VTR models embed a video and multiple distinct caption texts into a joint representation space and aim at aligning the video feature with the features of all caption texts. Consequently, distinct texts corresponding to the same video are mapped to the same feature, potentially resulting in suboptimal retrieval performance." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 453, + 289, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 453, + 289, + 559 + ], + "spans": [ + { + "bbox": [ + 46, + 453, + 289, + 559 + ], + "type": "text", + "content": "Under this circumstance, we introduce a new CLIP-based model dubbed Me-Retriever tailored for the MeVTR task. Considering the dichotomy of multi-event video-text pairs, we formulate our approach as follows: (1) representing videos by a bag of key event features and (2) employing a multi-event video-text retrieval loss. This strategy serves the dual purpose of mitigating the collapse of textual features and harmonizing the learning objectives between the Text-to-Video and Video-to-Text tasks." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 59, + 560, + 258, + 571 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 560, + 258, + 571 + ], + "spans": [ + { + "bbox": [ + 59, + 560, + 258, + 571 + ], + "type": "text", + "content": "Our contributions can be summarized as follows:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 54, + 579, + 288, + 704 + ], + "type": "list", + "angle": 0, + "index": 8, + "blocks": [ + { + "bbox": [ + 55, + 579, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 579, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 55, + 579, + 287, + 616 + ], + "type": "text", + "content": "1. We introduce a new task, Multi-event Video-Text Retrieval for retrieving multi-event video-text pairs, and define new evaluation metrics in MeVTR;" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 54, + 624, + 287, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 624, + 287, + 659 + ], + "spans": [ + { + "bbox": [ + 54, + 624, + 287, + 659 + ], + "type": "text", + "content": "2. We propose a new model called Me-Retriever that represents videos with selected key events and a MeVTR loss for training on MeVTR;" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 54, + 668, + 288, + 704 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 668, + 288, + 704 + ], + "spans": [ + { + "bbox": [ + 54, + 668, + 288, + 704 + ], + "type": "text", + "content": "3. We conduct comprehensive experiments to showcase Me-Retriever's effectiveness and to establish it as a simple yet robust baseline for future research." + } + ] + } + ], + "index": 7 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 319, + 392, + 332 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 319, + 392, + 332 + ], + "spans": [ + { + "bbox": [ + 306, + 319, + 392, + 332 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 342, + 545, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 342, + 545, + 475 + ], + "spans": [ + { + "bbox": [ + 304, + 342, + 545, + 475 + ], + "type": "text", + "content": "Video Language Model A series of work on Vision-Language Models (VLM) has been made like [26, 29, 5, 57, 53] for multi-modal representation learning. Given that videos are a structured sequence of images and typically entail higher computational demands than other visual data formats, the domain of Video-Language models has garnered significant attention. Notable contributions within this category include works by [40, 24, 38, 49, 29, 23, 43, 19, 13] which aim at video foundation models for video tasks. These models represent a subcategory of VLMs, adept at processing video and text inputs." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 480, + 546, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 480, + 546, + 647 + ], + "spans": [ + { + "bbox": [ + 304, + 480, + 546, + 647 + ], + "type": "text", + "content": "Video Representation In a line of work [42, 52, 18, 25], convolutions are performed on videos to fuse spatial and temporal information. Meanwhile, as transformers [44] have achieved success firstly in text [8], and then vision fields [11, 27, 41, 6], attempts to introduce transformers to extract video representations have been made in [39, 2, 47, 56, 32, 28]. The success of pre-trained Vision-Language models has significantly impacted video representation learning. Vision-Language models [29, 38, 31, 36] have demonstrated that textual supervision is conducive to visual representation and to a uniform video-language representation. Among them, the success of representation models [22, 16, 45, 46] has bridged the gap between video and text representations." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "content": "Video-Text Retrieval Video-Text Retrieval is a fundamental task of multi-modal learning, posing a good proxy task for learning joint representations of videos and texts. Two-stream Video-Text models [10, 9, 51, 34] concentrate on processing video-text pairs as inputs and aligning vi" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22114" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 70, + 547, + 145 + ], + "blocks": [ + { + "bbox": [ + 53, + 70, + 547, + 145 + ], + "lines": [ + { + "bbox": [ + 53, + 70, + 547, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 70, + 547, + 145 + ], + "type": "table", + "html": "
Video-to-TextText-to-Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑Median Rank ↓k=1 ↑k=5 ↑k=10 ↑
FROZEN-in-time7.0 ↗ 109.515.3 ↗ 0.843.3 ↗ 3.143.3 ↗ 5.67.0 ↗ 111.015.9 ↗ 1.843.0 ↗ 6.859.01 ↗ 11.7
CLIPBERT4.0 ↗ 449.022.1 ↗ 1.458.2 ↗ 4.769.6 ↗ 7.65.0 ↗ 153.025.9 ↗ 2.655.4 ↗ 9.569.8 ↗ 15.1
CLIP4Clip2.0 ↗ 53.042.5 ↗ 7.574.1 ↗ 19.885.8 ↗ 28.413.0 ↗ 53.014.8 ↗ 7.534.2 ↗ 19.845.6 ↗ 28.4
CenterCLIP2.0 ↗ 51.042.8 ↗ 7.873.8 ↗ 20.885.3 ↗ 29.22.0 ↗ 13.041.8 ↗ 15.173.9 ↗ 34.684.7 ↗ 46.4
", + "image_path": "d754aaef9f808622b5afcdb1a46bc42b642afb2e3b00e71f15ccb26f4ed69427.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 153, + 547, + 202 + ], + "lines": [ + { + "bbox": [ + 46, + 153, + 547, + 202 + ], + "spans": [ + { + "bbox": [ + 46, + 153, + 547, + 202 + ], + "type": "text", + "content": "Table 1: Comparison of model performance on VTR and MeVTR tasks on ActivityNet Captions. We train each model on the ActivityNet Captions with its original codes and evaluate them on MeVTR. We show the performance of VTR on the lefthand of " + }, + { + "bbox": [ + 46, + 153, + 547, + 202 + ], + "type": "inline_equation", + "content": "\\nabla (\\nearrow)" + }, + { + "bbox": [ + 46, + 153, + 547, + 202 + ], + "type": "text", + "content": " and the performance of MeVTR on the right. " + }, + { + "bbox": [ + 46, + 153, + 547, + 202 + ], + "type": "inline_equation", + "content": "\\uparrow" + }, + { + "bbox": [ + 46, + 153, + 547, + 202 + ], + "type": "text", + "content": " means higher the better, and " + }, + { + "bbox": [ + 46, + 153, + 547, + 202 + ], + "type": "inline_equation", + "content": "\\downarrow" + }, + { + "bbox": [ + 46, + 153, + 547, + 202 + ], + "type": "text", + "content": " means lower the better. It is shown that model performance deteriorates to a large extent on both Video-to-Text and Text-to-Video tasks." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 223, + 289, + 355 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 223, + 289, + 355 + ], + "spans": [ + { + "bbox": [ + 46, + 223, + 289, + 355 + ], + "type": "text", + "content": "sual and textual representations within a joint representation space. For instance, Frozen [3] employs a visual encoder that can be adaptively trained on images and videos, incorporating temporal contexts via curriculum learning. TACo [51], in contrast, focuses on aligning content words in texts with corresponding visual content, adding an extra learning objective. With the surge of large Vision-Language foundation models representative of CLIP [36], models [30, 16, 12, 35, 3, 50], leverage the potent pretrained model CLIP and endeavor to extend its capabilities from static images to the domain of videos." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 372, + 107, + 384 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 372, + 107, + 384 + ], + "spans": [ + { + "bbox": [ + 47, + 372, + 107, + 384 + ], + "type": "text", + "content": "3. Problem" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 394, + 171, + 406 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 394, + 171, + 406 + ], + "spans": [ + { + "bbox": [ + 47, + 394, + 171, + 406 + ], + "type": "text", + "content": "3.1. Problem Formulation" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "spans": [ + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "text", + "content": "Given a video-text dataset with multi-event videos " + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "inline_equation", + "content": "\\mathcal{V}" + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "text", + "content": " and texts " + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "text", + "content": ", where a video " + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "inline_equation", + "content": "v_{i} \\in \\mathcal{V}" + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "text", + "content": " is described by a set of different texts " + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{i} \\subset \\mathcal{T}" + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "text", + "content": " and a text is denoted as " + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "inline_equation", + "content": "t_{j}" + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "text", + "content": ", our task consists in retrieving a video given a text query " + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "inline_equation", + "content": "t^{q}" + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "text", + "content": " and retrieving all relevant texts given a video query " + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "inline_equation", + "content": "v^{q}" + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "text", + "content": ". A generic Video-Text Retrieval model is to learn a similarity function " + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "inline_equation", + "content": "sim(v_{i}, t_{j})" + }, + { + "bbox": [ + 46, + 415, + 288, + 511 + ], + "type": "text", + "content": " that scores the similarity between any relevant video-text pair higher and ranks all the candidate items." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 525, + 160, + 537 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 525, + 160, + 537 + ], + "spans": [ + { + "bbox": [ + 47, + 525, + 160, + 537 + ], + "type": "text", + "content": "3.2. Evaluation Metrics" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "Video-Text retrieval is a recall-focused retrieval task. A single item is retrieved in traditional settings, and the average Recall at the top rank " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " is calculated. Nevertheless, in the MeVTR setting, we also want to evaluate retrieving multiple different text items given one video. Hence we devise the following metrics: (1) Recall@k-Average as the fraction of the number of correspondences ranked at top " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "; (2) Recall@k-One-Hit as an indication of whether any of the correspondences will be ranked in the top " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "; (3) Recall@k-All-Hit as an indication of whether all items can be retrieved within the top " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " rank. All metrics are averaged on the whole test set. In the follow-up experiments, we report the Recall for the Text-to-Video tasks and the metrics mentioned above for the Video-to-Text tasks." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 222, + 446, + 235 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 222, + 446, + 235 + ], + "spans": [ + { + "bbox": [ + 305, + 222, + 446, + 235 + ], + "type": "text", + "content": "3.3. Textual Feature Collapse" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 240, + 545, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 240, + 545, + 289 + ], + "spans": [ + { + "bbox": [ + 304, + 240, + 545, + 289 + ], + "type": "text", + "content": "To investigate the textual feature collapse in previous models to elucidate the performance drop by calculating the textual feature's similarity after retraining, we define the average text similarity of a video " + }, + { + "bbox": [ + 304, + 240, + 545, + 289 + ], + "type": "inline_equation", + "content": "v_{i}" + }, + { + "bbox": [ + 304, + 240, + 545, + 289 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 304, + 240, + 545, + 289 + ], + "type": "inline_equation", + "content": "n_{v_i}" + }, + { + "bbox": [ + 304, + 240, + 545, + 289 + ], + "type": "text", + "content": " captions as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 347, + 298, + 545, + 334 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 298, + 545, + 334 + ], + "spans": [ + { + "bbox": [ + 347, + 298, + 545, + 334 + ], + "type": "interline_equation", + "content": "\\operatorname {s i m} _ {t} \\left(v _ {i}\\right) = \\sum_ {m = 1} ^ {N _ {v _ {i}}} \\sum_ {n = 1} ^ {N _ {v _ {i}}} \\frac {1}{N _ {v _ {i}} ^ {2}} \\operatorname {s i m} \\left(t _ {m}, t _ {n}\\right) \\tag {1}", + "image_path": "4a71513d9c6052082a22fa29be129b890ae2bb47d553c3ff19e7c204b62d72bf.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 342, + 545, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 342, + 545, + 462 + ], + "spans": [ + { + "bbox": [ + 304, + 342, + 545, + 462 + ], + "type": "text", + "content": "In Fig. 3, we attempt to visualize the average text similarity of all videos with a different number of events. Different texts are expected to have lower sentence similarity to retain their meanings due to retraining on MeVTR. We chose CLIP4Clip for comparison in our experiments, as it still performs relatively well in MeVTR tasks compared to other models. As a comparison, we show that Me-R retriever, which will be introduced in the next section, can generate more diverse textual features than CLIP4Clip and effectively avoid textual feature collapse." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 473, + 361, + 485 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 473, + 361, + 485 + ], + "spans": [ + { + "bbox": [ + 305, + 473, + 361, + 485 + ], + "type": "text", + "content": "4. Method" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 493, + 545, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 493, + 545, + 517 + ], + "spans": [ + { + "bbox": [ + 304, + 493, + 545, + 517 + ], + "type": "text", + "content": "We propose Me-Retriever consisting of a Key Event Selection module and MeVTR loss as shown in Fig. 2." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 525, + 481, + 538 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 525, + 481, + 538 + ], + "spans": [ + { + "bbox": [ + 305, + 525, + 481, + 538 + ], + "type": "text", + "content": "4.1. Key Event Video Representation" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 544, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 544, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 544, + 545, + 641 + ], + "type": "text", + "content": "Intuitively, human brains do not remember experiences with all continuous scenes and consolidate all the details. Instead, brains retain memories of certain discrete events [55]. This insight motivates us to represent a video with a bag of frames as key events. For leveraging frame embeddings extracted from the CLIP visual encoder " + }, + { + "bbox": [ + 304, + 544, + 545, + 641 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{f}_i^1,\\mathbf{f}_i^2,\\dots ,\\mathbf{f}_i^{[v_i]}\\}" + }, + { + "bbox": [ + 304, + 544, + 545, + 641 + ], + "type": "text", + "content": ", we define the Key Event Selection module that selects the most distinctive keyframes." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 642, + 547, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 547, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 547, + 712 + ], + "type": "text", + "content": "We employ a classic clustering method, K-Medoids [1]. Compared to other clustering methods, the representative of each cluster given by the K-Medoids algorithm is from the sample points, which corresponds to a particular frame and has explicit interpretation. The criterion is minimizing the distance of all frames in the cluster to its medoid. " + }, + { + "bbox": [ + 304, + 642, + 547, + 712 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 642, + 547, + 712 + ], + "type": "text", + "content": " frames" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22115" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 56, + 78, + 544, + 253 + ], + "blocks": [ + { + "bbox": [ + 56, + 78, + 544, + 253 + ], + "lines": [ + { + "bbox": [ + 56, + 78, + 544, + 253 + ], + "spans": [ + { + "bbox": [ + 56, + 78, + 544, + 253 + ], + "type": "image", + "image_path": "ff7eba4eb35ab607ba87f767e3afdcf0e307a29e1ecbe61359498c7ec562fdd7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 283, + 548, + 346 + ], + "lines": [ + { + "bbox": [ + 46, + 283, + 548, + 346 + ], + "spans": [ + { + "bbox": [ + 46, + 283, + 548, + 346 + ], + "type": "text", + "content": "Figure 2: The overall framework of Me-Retriever. The model adopts CLIP [36]'s Visual Encoder(VE) and Text Encoder(TE). After the Visual Encoder, [CLASS] tokens in the last hidden layer are taken as frame embeddings. We use a clustering-based Key Event Selection module to aggregate similar frames and extract key events. Each textual caption is fed into Text Encoder, and [EOS] will be used as text embedding. The similarity between these key events of any video " + }, + { + "bbox": [ + 46, + 283, + 548, + 346 + ], + "type": "inline_equation", + "content": "v_{i}" + }, + { + "bbox": [ + 46, + 283, + 548, + 346 + ], + "type": "text", + "content": " and any textual caption " + }, + { + "bbox": [ + 46, + 283, + 548, + 346 + ], + "type": "inline_equation", + "content": "t_j" + }, + { + "bbox": [ + 46, + 283, + 548, + 346 + ], + "type": "text", + "content": " is measured in the Similarity Calculator. For each video, there are multiple text correspondences as positive samples." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 58, + 365, + 279, + 526 + ], + "blocks": [ + { + "bbox": [ + 58, + 365, + 279, + 526 + ], + "lines": [ + { + "bbox": [ + 58, + 365, + 279, + 526 + ], + "spans": [ + { + "bbox": [ + 58, + 365, + 279, + 526 + ], + "type": "image", + "image_path": "306576039b7a18a9c91a583eeae74cfa1e0c5c65c5f0ab6cf7851ff459c92356.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 536, + 288, + 597 + ], + "lines": [ + { + "bbox": [ + 46, + 536, + 288, + 597 + ], + "spans": [ + { + "bbox": [ + 46, + 536, + 288, + 597 + ], + "type": "text", + "content": "Figure 3: We compare the average cosine similarity between all text pairs of videos with a different number of events. Me-Retriever can generate more diverse text features than CLIP4Clip and refrain from text features collapsing, as we discuss in the main part." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 629, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 289, + 715 + ], + "type": "text", + "content": "are chosen as initial medoids; the remaining frames are then assigned to their nearest medoids, and within each cluster, new medoids are again selected based on cosine similarity as a metric function. Video " + }, + { + "bbox": [ + 46, + 629, + 289, + 715 + ], + "type": "inline_equation", + "content": "v_{i}" + }, + { + "bbox": [ + 46, + 629, + 289, + 715 + ], + "type": "text", + "content": " can be represented as a sequence of key event embeddings " + }, + { + "bbox": [ + 46, + 629, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{K}_i = \\{\\mathbf{k}_i^1,\\mathbf{k}_i^2,\\dots ,\\mathbf{k}_i^K\\}" + }, + { + "bbox": [ + 46, + 629, + 289, + 715 + ], + "type": "text", + "content": ". In the loss calculation, we use the pre-computed assignment of all frames as key event video representation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 364, + 391, + 376 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 364, + 391, + 376 + ], + "spans": [ + { + "bbox": [ + 306, + 364, + 391, + 376 + ], + "type": "text", + "content": "4.2. MeVTR Loss" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 384, + 545, + 516 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 545, + 516 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 545, + 516 + ], + "type": "text", + "content": "Following the dual learning paradigm of Text-to-Video and Video-to-Text on VTR tasks, we propose MeVTR loss for MeVTR learning. As previously discussed, there is an issue of textual feature collapse during MeVTR training. To address this, we propose disentangling various positive instances within video samples by excluding non-self positive instances from the softmax function. Moreover, considering the dissimilar granularity between multi-event videos and single-event text, we propose adopting a dynamic weighting strategy. This strategy balances the loss scale of both learning objectives during the training process." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 517, + 547, + 541 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 517, + 547, + 541 + ], + "spans": [ + { + "bbox": [ + 306, + 517, + 547, + 541 + ], + "type": "text", + "content": "MeVTR loss is defined as a weighted sum of " + }, + { + "bbox": [ + 306, + 517, + 547, + 541 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{t2v}" + }, + { + "bbox": [ + 306, + 517, + 547, + 541 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 517, + 547, + 541 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{v2t}" + }, + { + "bbox": [ + 306, + 517, + 547, + 541 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 370, + 553, + 545, + 566 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 370, + 553, + 545, + 566 + ], + "spans": [ + { + "bbox": [ + 370, + 553, + 545, + 566 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {M e V T R} = \\mathcal {L} _ {v 2 t} + \\alpha \\mathcal {L} _ {t 2 v} \\tag {2}", + "image_path": "ed78f88309941fe4208fc2fcb61fffa274e35c81fb0701788c6bdf21490252c9.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 317, + 578, + 529, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 578, + 529, + 591 + ], + "spans": [ + { + "bbox": [ + 317, + 578, + 529, + 591 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 317, + 578, + 529, + 591 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{v2t}" + }, + { + "bbox": [ + 317, + 578, + 529, + 591 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 317, + 578, + 529, + 591 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{t2v}" + }, + { + "bbox": [ + 317, + 578, + 529, + 591 + ], + "type": "text", + "content": " are respectively formulated as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 613, + 559, + 658 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 613, + 559, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 613, + 559, + 658 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {v 2 t} = - \\frac {1}{| \\mathcal {B} |} \\sum_ {i} ^ {| \\mathcal {B} |} \\sum_ {k} ^ {| \\mathcal {T} _ {i} |} \\frac {1}{| \\mathcal {T} _ {i} |} \\log \\frac {\\exp s i m (\\mathbf {K} _ {i} , \\mathbf {w} _ {k}) / \\tau}{\\sum_ {j = 1} ^ {\\mathcal {B} - \\cup \\{k \\}} \\exp s i m (\\mathbf {K} _ {i} , \\mathbf {w} _ {j}) / \\tau},", + "image_path": "2bcfa013feb292581302f8800b50bccb6429acf2eac8a49daffa52437816e92d.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 316, + 681, + 546, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 681, + 546, + 715 + ], + "spans": [ + { + "bbox": [ + 316, + 681, + 546, + 715 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {t 2 v} = - \\frac {1}{| \\mathcal {B} |} \\sum_ {j} ^ {| \\mathcal {B} |} \\log \\frac {\\exp \\operatorname {s i m} \\left(\\mathbf {K} _ {i} , \\mathbf {w} _ {j}\\right) / \\tau}{\\sum_ {i = 1} ^ {\\mathcal {B}} \\exp \\operatorname {s i m} \\left(\\mathbf {K} _ {j} , \\mathbf {w} _ {j}\\right)) / \\tau}, \\tag {4}", + "image_path": "870c65882e577d5790eaf9be83dff0051ab2eb6c9ce3354e489979ceeef9fd07.jpg" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22116" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 59, + 70, + 542, + 205 + ], + "blocks": [ + { + "bbox": [ + 59, + 70, + 542, + 205 + ], + "lines": [ + { + "bbox": [ + 59, + 70, + 542, + 205 + ], + "spans": [ + { + "bbox": [ + 59, + 70, + 542, + 205 + ], + "type": "table", + "html": "
Video-to-Text
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)39.06.60 / 20.74 / -20.32 / 47.02 / 3.4629.37 / 61.26 / 6.7158.41 / 89.77 / 26.24
CLIP4Clip(tight)49.55.23 / 16.45 / -16.74 / 41.94 / 1.7725.50 / 57.37 / 4.2354.22 / 88.00 / 21.52
CenterCLIP38.06.93 / 21.62 / -20.58 / 47.98 / 3.6629.90 / 61.72 / 6.9658.88 / 90.34 / 26.28
FROZEN-in-time330.00.30 / 0.67 / -0.83 / 2.10 / 0.221.60 / 3.37 / 0.675.89 / 12.97 / 2.55
CLIPBERT174.51.80 / 6.10 / -6.48 / 18.97 / 0.1810.93 / 29.00 / 0.8731.34 / 61.42 / 8.72
Singularity64.54.83 / 14.68 / -15.1 / 37.79 / 1.9522.23 / 49.50 / 4.4148.96 / 81.94 / 19.38
Ours(avg)35.08.52 / 26.91 / -23.56 / 54.18 / 3.8632.95 / 67.13 / 7.7961.26 / 92.50 / 27.80
Ours(max)49.06.98 / 22.72 / -18.72 / 46.37 / 2.3027.04 / 60.62 / 5.7654.19 / 88.37 / 20.90
", + "image_path": "c1e786525cc39871747ad57ec41e244094c21c3bccf0ddf0827a69427d3053d6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 59, + 273, + 542, + 415 + ], + "blocks": [ + { + "bbox": [ + 46, + 214, + 547, + 264 + ], + "lines": [ + { + "bbox": [ + 46, + 214, + 547, + 264 + ], + "spans": [ + { + "bbox": [ + 46, + 214, + 547, + 264 + ], + "type": "text", + "content": "Table 2: Results of the Video-to-Text retrieval task on ActivityNet Captions dataset. In each column, we report the Recall@k-Average/One-Hit/All-Hit for each " + }, + { + "bbox": [ + 46, + 214, + 547, + 264 + ], + "type": "inline_equation", + "content": "k = 1,5,10,50" + }, + { + "bbox": [ + 46, + 214, + 547, + 264 + ], + "type": "text", + "content": " respectively. The best result in each column is emphasized in bold. We ignore the Recall@1-All-Hit since all models can only achieve a nearly zero result. Ours(avg) maintains its advantage in the text retrieval task and surpasses all other models by a large margin." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 59, + 273, + 542, + 415 + ], + "lines": [ + { + "bbox": [ + 59, + 273, + 542, + 415 + ], + "spans": [ + { + "bbox": [ + 59, + 273, + 542, + 415 + ], + "type": "table", + "html": "
Video-to-Text
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)441.51.32 / 2.92 / -4.07 / 8.32 / 1.805.65 / 11.84 / 2.5516.84 / 32.01 / 7.65
CLIP4Clip(tight)391.00.80 / 1.80 / -2.45 / 6.30 / 0.754.19 / 10.27 / 1.3515.26 / 30.43 / 6.37
CenterCLIP408.01.32 / 3.00 / -3.71 / 7.87 / 1.576.33 / 13.42 / 2.6217.37 / 33.43 / 7.72
FROZEN-in-time810.00.30 / 0.67 / -0.83 / 2.10 / 0.221.60 / 3.37 / 0.675.89 / 12.97 / 2.55
ClipBERT1339.50.15 / 0.45 / -0.60 / 1.50 / 0.151.19 / 3.30 / 0.225.31 / 11.92 / 1.87
Singularity621.50.95 / 2.17 / -2.84 / 5.92 / 1.424.35 / 9.52 / 1.9512.22 / 25.94 / 4.87
Ours(avg)406.01.39 / 3.22 / -5.04 / 9.90 / 2.477.02 / 13.72 / 3.3717.62 / 32.08 / 8.70
Ours(max)365.61.01 / 2.62 / -4.03 / 9.00 / 1.726.39 / 13.72 / 2.7019.08 / 36.66 / 8.10
", + "image_path": "a722a099db0333d12877508fadcba4c0e237bbd79eb7ccd8ab11e944988a256d.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 423, + 546, + 449 + ], + "lines": [ + { + "bbox": [ + 46, + 423, + 546, + 449 + ], + "spans": [ + { + "bbox": [ + 46, + 423, + 546, + 449 + ], + "type": "text", + "content": "Table 3: Results of the Video-to-Text retrieval task on Charades-Event dataset. We use the same notation as in Tab. 2. MeRetriever(avg) and Me-Retriever(max) can achieve best performance." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "spans": [ + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "inline_equation", + "content": "sim(\\cdot)" + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "text", + "content": " is the similarity function, " + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "inline_equation", + "content": "\\mathcal{B}" + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "text", + "content": " is the set of samples in the training batch, " + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "inline_equation", + "content": "\\mathcal{B}^{-}" + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "text", + "content": " is the set of negative samples in the batch, " + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "text", + "content": " is the temperature coefficient, and " + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_i" + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "text", + "content": " is the set of positive instances of one sample video in " + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{t2v}" + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "text", + "content": ". Notably, given a video item " + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "inline_equation", + "content": "v_{i}" + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "text", + "content": ", we discard all positive instances in " + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_i" + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "text", + "content": " other than the current training sample " + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "inline_equation", + "content": "t_k" + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "text", + "content": ". This encourages similarities between a video and its all positive instances to be increased. In " + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{t2v}" + }, + { + "bbox": [ + 46, + 468, + 288, + 576 + ], + "type": "text", + "content": ", it degenerates to a normal softmax function." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": "We denote " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " as the weighting coefficient that balances " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{t2v}" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{v2t}" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": ". Given that the two losses exhibit differing scales during training, which owes to the positive/negative sample ratio asymmetry, determining the value of " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " requires employing certain hyperparameter-tuning techniques to ensure balanced performance on both tasks. We suggest employing a dynamic weighting strategy as opposed to a fixed weight. A dynamic weighting coefficient " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " is computed as the ratio of " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{v2t}" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{t2v}" + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": " during training. In Section 5.3, we conduct experimental studies to compare the impact of various weighting strategies." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 468, + 547, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 468, + 547, + 601 + ], + "spans": [ + { + "bbox": [ + 304, + 468, + 547, + 601 + ], + "type": "text", + "content": "Similarity function For video-text pairs in bijective correspondences, the similarity between video and text is measured by cosine similarity in the feature space. In MeVTR, we use two approaches are used to measure the similarity between a video " + }, + { + "bbox": [ + 304, + 468, + 547, + 601 + ], + "type": "inline_equation", + "content": "v_{i}" + }, + { + "bbox": [ + 304, + 468, + 547, + 601 + ], + "type": "text", + "content": " consisting of key events " + }, + { + "bbox": [ + 304, + 468, + 547, + 601 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{k}_i^1,\\mathbf{k}_i^2,\\dots ,\\mathbf{k}_i^K\\}" + }, + { + "bbox": [ + 304, + 468, + 547, + 601 + ], + "type": "text", + "content": " and a text " + }, + { + "bbox": [ + 304, + 468, + 547, + 601 + ], + "type": "inline_equation", + "content": "t_j" + }, + { + "bbox": [ + 304, + 468, + 547, + 601 + ], + "type": "text", + "content": ": (1) we average the cosine similarity scores of all key event embeddings and the text as in Eq. 5; (2) we select the maximum cosine similarity of any key event-text pair to represent the similarity between the video to which these medoids belong as in Eq. 6;" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 314, + 618, + 546, + 633 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 314, + 618, + 546, + 633 + ], + "spans": [ + { + "bbox": [ + 314, + 618, + 546, + 633 + ], + "type": "interline_equation", + "content": "s _ {a v g} (v _ {i}, t _ {j}) = \\operatorname {a v g} \\left(\\cos \\left(\\mathbf {k} _ {1} ^ {i}, \\mathbf {w} _ {j}\\right), \\dots , \\cos \\left(\\mathbf {k} _ {k} ^ {i}, \\mathbf {w} _ {j}\\right)\\right) \\tag {5}", + "image_path": "1c24b58047ec8137cf7b96b38507e49239e90cfcc5688cfd99a72c711ac9e22b.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 313, + 658, + 546, + 673 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 658, + 546, + 673 + ], + "spans": [ + { + "bbox": [ + 313, + 658, + 546, + 673 + ], + "type": "interline_equation", + "content": "s _ {m a x} (v _ {i}, t _ {j}) = \\max (\\cos (\\mathbf {k} _ {1} ^ {i}, \\mathbf {w} _ {j}), \\dots , \\cos (\\mathbf {k} _ {k} ^ {i}, \\mathbf {w} _ {j})) \\quad (6)", + "image_path": "ad1435a7c7eca6ff31e175b69efedeca497515ab2942ed297ffd0ec070ba82f4.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 714 + ], + "type": "text", + "content": "We denote Me-Retriever with different similarity functions as Me-Retriever(avg) and Me-Retriever(max)." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22117" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 70, + 288, + 177 + ], + "blocks": [ + { + "bbox": [ + 53, + 70, + 288, + 177 + ], + "lines": [ + { + "bbox": [ + 53, + 70, + 288, + 177 + ], + "spans": [ + { + "bbox": [ + 53, + 70, + 288, + 177 + ], + "type": "table", + "html": "
Text-to-Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)11.015.2536.4349.1176.64
CLIP4Clip(tight)15.010.1429.0741.9372.50
CenterCLIP11.015.5337.2149.7877.19
FROZEN-in-time111.01.826.8011.7633.86
ClipBERT48.04.2014.5723.3551.02
Singularity(FT)22.09.2924.9636.2665.55
Ours(avg)11.015.9937.1349.6076.66
Ours(max)13.014.9334.4446.3674.65
", + "image_path": "e2a66038832c36a09d594f994e5d1a65b28bb7370f558f783cfb52c33adcae76.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 285, + 128, + 300 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 285, + 128, + 300 + ], + "spans": [ + { + "bbox": [ + 47, + 285, + 128, + 300 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 308, + 160, + 323 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 308, + 160, + 323 + ], + "spans": [ + { + "bbox": [ + 47, + 308, + 160, + 323 + ], + "type": "text", + "content": "5.1. Experiment Details" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 337, + 287, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 337, + 287, + 408 + ], + "spans": [ + { + "bbox": [ + 46, + 337, + 287, + 408 + ], + "type": "text", + "content": "Datasets We perform experiments on two datasets containing multi-event videos: ActivityNet Captions and Charades-Event. It's worth noting that datasets such as MSR-VTT [48], even though videos are accompanied by multiple similar captions, do not align with our multi-event scenario." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 412, + 287, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 412, + 287, + 520 + ], + "spans": [ + { + "bbox": [ + 46, + 412, + 287, + 520 + ], + "type": "text", + "content": "ActivityNet Captions [20] is a large-scale dataset with 20,000 video-text pairs extracted by web crawling on YouTube based on ActivityNet [4] videos. It covers a wide range of daily scenarios. The training set contains 10,009 videos and 4,917 videos/17,505 texts in the publicly accessible evaluation set 'val1'. Each video has multiple textual descriptions with time-interval annotation. This helps us construct a multi-event scenario for retrieval by taking all textual captions of a video as its associated events." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 524, + 287, + 596 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 524, + 287, + 596 + ], + "spans": [ + { + "bbox": [ + 46, + 524, + 287, + 596 + ], + "type": "text", + "content": "Charades-Event is a video dataset of indoor activities with extensive action classes that we adopt from [37]. To create a MeVTR dataset, we filter out all videos with text annotation provided by [15] and interpret each text as an event in our MeVTR setting. There are 5,338 videos/12,408 texts in the training set and 1,334 videos/3,720 texts in the test set." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "Experiment Settings In the key event selection module, we use 60 as the maximum number of iterations and " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "10^{-5}" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " as the distance threshold for clustering. Our model chooses 16 as a fixed number of key events and does not use a smaller or larger number of key events because shorter sequences cannot cover the number of events in part of the videos (the maximum event number in ActivityNet Captions is 27), and longer sequences contradict our intention of clustering. For each experiment, we set the epoch number as 5." + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 312, + 70, + 547, + 175 + ], + "blocks": [ + { + "bbox": [ + 46, + 185, + 288, + 258 + ], + "lines": [ + { + "bbox": [ + 46, + 185, + 288, + 258 + ], + "spans": [ + { + "bbox": [ + 46, + 185, + 288, + 258 + ], + "type": "text", + "content": "Table 4: Results of the Text-to-Video retrieval task on ActivityNet Captions dataset. We compare CLIP4Clip [30], CenterCLIP [54], FROZEN-in-time [3], ClipBERT [22], and [21]. The best result in each column is emphasized in bold, and the second best result is underlined. Our MeRetriever(avg) achieves comparably good performance." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 312, + 70, + 547, + 175 + ], + "lines": [ + { + "bbox": [ + 312, + 70, + 547, + 175 + ], + "spans": [ + { + "bbox": [ + 312, + 70, + 547, + 175 + ], + "type": "table", + "html": "
Text-to-Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
CLIP4Clip(mean)136.01.536.4810.5429.38
CLIP4Clip(tight)127.01.455.549.3530.11
CenterCLIP131.01.936.6110.6730.13
FRONZEN-in-Time277.00.351.993.8214.52
ClipBERT442.00.351.773.3111.10
Singularity179.51.535.228.5223.87
Ours(avg)126.01.886.6910.5929.97
Ours(max)112.02.027.6112.7434.49
", + "image_path": "4a4eda5de264fb889181e990d2a1f992fb1f9a89d76983f34cd1945ff579fdd6.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 182, + 547, + 232 + ], + "lines": [ + { + "bbox": [ + 304, + 182, + 547, + 232 + ], + "spans": [ + { + "bbox": [ + 304, + 182, + 547, + 232 + ], + "type": "text", + "content": "Table 5: Results of Text-to-Video retrieval task on Charades-Event dataset. We use the same notation as Tab. 2. Me-Retriever(max) and Me-Retriever(avg) can achieve the best performance compared to other models." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 254, + 362, + 266 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 254, + 362, + 266 + ], + "spans": [ + { + "bbox": [ + 306, + 254, + 362, + 266 + ], + "type": "text", + "content": "5.2. Results" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 274, + 545, + 417 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 274, + 545, + 417 + ], + "spans": [ + { + "bbox": [ + 304, + 274, + 545, + 417 + ], + "type": "text", + "content": "The experiments show that Me-Retriever performs competitively within the context of MeVTR. On the Video-to-Text task, as presented in Tables 2 and 3, Me-Retriever(avg) surpasses its counterparts. This result underscores our model's capability to address both tasks across different datasets effectively. Additionally, we observe that CLIP4Clip also attains a commendable Recall@1-Average performance on the Video-to-Text task compared to other baseline models. This observation sheds light on the robust transferability of the pre-trained encoder to videos. This indicates that the primary challenge in MeVTR often resides within representation alignment." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 419, + 546, + 623 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 419, + 546, + 623 + ], + "spans": [ + { + "bbox": [ + 304, + 419, + 546, + 623 + ], + "type": "text", + "content": "Our model also demonstrates comparable results on both datasets on the Text-to-Video task, as shown in Tab. 4 and Tab. 5. Me-Retriever(avg) demonstrates comparable performance to baseline models like CenterCLIP across numerous metrics on both datasets. Interestingly, we also notice that Me-Retriever(max) performs best on the Charades-Event dataset but not on the ActivityNet Captions dataset. This disparity can be attributed to overfitting, warranting further investigation. The noticeable performance of certain baseline models aligns with our conjecture that prior models can be effectively adapted to the Text-to-Video retrieval task. However, this adaptation might come at the expense of suboptimal results in the Video-to-Text task, as evident in Table 2. This phenomenon can be attributed to the embeddings of different texts collapsing to become more proximate, leading to an unintentional competition among positive instances that ultimately dampens their significance." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 547, + 715 + ], + "type": "text", + "content": "Performance on videos with different subsets In order to reveal the model performance on videos of different properties like video duration and the number of events, we partition the complete ActivityNet Caption test set into two groups of subsets. These subsets are partitioned based on the video duration and the count of events within the videos, respectively:" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22118" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 71, + 288, + 129 + ], + "blocks": [ + { + "bbox": [ + 53, + 71, + 288, + 129 + ], + "lines": [ + { + "bbox": [ + 53, + 71, + 288, + 129 + ], + "spans": [ + { + "bbox": [ + 53, + 71, + 288, + 129 + ], + "type": "table", + "html": "
Text to Video
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
Ours (Best)11.015.1735.9448.3975.85
w/o Key Event12.015.0335.6747.9475.06
w/o MeVTR loss12.014.4534.9047.2575.24
", + "image_path": "89d912e2a36435d4ca9a34849f481cb42c4b584b04de14ce4df46235416af1cd.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 53, + 209, + 288, + 269 + ], + "blocks": [ + { + "bbox": [ + 47, + 137, + 287, + 199 + ], + "lines": [ + { + "bbox": [ + 47, + 137, + 287, + 199 + ], + "spans": [ + { + "bbox": [ + 47, + 137, + 287, + 199 + ], + "type": "text", + "content": "Table 6: Ablation studies on key modules of Me-Retrever training on the Text-to-Video task for ActivityNet Captions. Only the Recall@k-Average is reported in the main part. We find that model performance drops with removing any modules, proving its efficacy." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 53, + 209, + 288, + 269 + ], + "lines": [ + { + "bbox": [ + 53, + 209, + 288, + 269 + ], + "spans": [ + { + "bbox": [ + 53, + 209, + 288, + 269 + ], + "type": "table", + "html": "
Video to Text
ModelMedian Rank ↓k=1 ↑k=5 ↑k=10 ↑k=50 ↑
Ours (Best)35.08.5223.5632.7961.26
w/o Key Event41.57.4021.0030.2757.71
w/o MeVTR loss41.06.7020.0528.9657.45
", + "image_path": "b2ec37e55c32609b621fad9a17274049218dd980f24f65e67cf68059c05ab7c6.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 277, + 287, + 337 + ], + "lines": [ + { + "bbox": [ + 47, + 277, + 287, + 337 + ], + "spans": [ + { + "bbox": [ + 47, + 277, + 287, + 337 + ], + "type": "text", + "content": "Table 7: Ablation studies on key modules of Me-Retriever training on the Video-to-Text task for ActivityNet Captions. Model performance declines to different extents without our modules. We conclude that our model can benefit Video-to-Text retrieval prominently." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 54, + 361, + 287, + 464 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 55, + 361, + 287, + 421 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 361, + 287, + 421 + ], + "spans": [ + { + "bbox": [ + 55, + 361, + 287, + 421 + ], + "type": "text", + "content": "1. Video duration: test-S (Short) with videos shorter than 1 minute, test-M (Medium) with videos between 1-2 minutes, test-L (Long video) with videos between 2-3 minutes, and test-XL (eXtra Long video) with even longer videos than 3 minutes;" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 54, + 428, + 287, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 428, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 54, + 428, + 287, + 464 + ], + "type": "text", + "content": "2. Number of events: test-E1 with videos containing fewer than 4 events, test-E2 with 5-12 events, and test-E3 with more than 12 events." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 472, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 287, + 640 + ], + "type": "text", + "content": "Comparing performance across datasets of different sizes isn't equitable for a retrieval task, as larger candidate sets exacerbate retrieval difficulties. Therefore, we gauge the average improvement in the model performance of MeRetriever(avg) to the baseline CLIP4Clip(mean) and identify the subsets in which our model showcases notable enhancements. From Fig. 4, we also see that our model usually performs better on test-E1 and test-E2, and improvement slightly decreases for even longer videos. We assume this problem is inevitable since we use a fixed number of clusters and videos containing many events in test-E3, and larger numbers of events increase the retrieval difficulties. Whereas for videos of different duration, model performance slightly varies." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 647, + 148, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 647, + 148, + 659 + ], + "spans": [ + { + "bbox": [ + 47, + 647, + 148, + 659 + ], + "type": "text", + "content": "5.3. Ablation Studies" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 665, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 665, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 665, + 287, + 712 + ], + "type": "text", + "content": "In this section, we conduct various experiments to investigate the effectiveness of different weighting strategies in MeVTR loss and ablate the proposed components of our architecture." + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 338, + 72, + 515, + 203 + ], + "blocks": [ + { + "bbox": [ + 338, + 72, + 515, + 203 + ], + "lines": [ + { + "bbox": [ + 338, + 72, + 515, + 203 + ], + "spans": [ + { + "bbox": [ + 338, + 72, + 515, + 203 + ], + "type": "image", + "image_path": "2fa066806e6d2b5430c7b8d66ae1ad5a83676acf746417c97ec2604da7beb97d.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 361, + 210, + 489, + 221 + ], + "lines": [ + { + "bbox": [ + 361, + 210, + 489, + 221 + ], + "spans": [ + { + "bbox": [ + 361, + 210, + 489, + 221 + ], + "type": "text", + "content": "(a) On subsets of different duration" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 340, + 237, + 515, + 368 + ], + "blocks": [ + { + "bbox": [ + 340, + 237, + 515, + 368 + ], + "lines": [ + { + "bbox": [ + 340, + 237, + 515, + 368 + ], + "spans": [ + { + "bbox": [ + 340, + 237, + 515, + 368 + ], + "type": "image", + "image_path": "6804e5e4ae1f32e9efc29a99d107a0a5982394dd4225444c760e719667463331.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 352, + 375, + 501, + 386 + ], + "lines": [ + { + "bbox": [ + 352, + 375, + 501, + 386 + ], + "spans": [ + { + "bbox": [ + 352, + 375, + 501, + 386 + ], + "type": "text", + "content": "(b) On subsets of different event number" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 396, + 547, + 468 + ], + "lines": [ + { + "bbox": [ + 304, + 396, + 547, + 468 + ], + "spans": [ + { + "bbox": [ + 304, + 396, + 547, + 468 + ], + "type": "text", + "content": "Figure 4: We compare average performance improvement in percentage(%) for Video-to-Text task on subsets of ActivityNet Captions. It shows how much percentage MeRetriever(avg) is better than CLIP4Clip(mean) on different subsets. Fig. 4a: Video-to-Text results for test-S/M/L/XL; Fig. 4b: Video-to-Text results for test-E1/E2/E3." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "text", + "content": "Impact of weighting strategy in MeVTR Loss To study the effect of different weighting strategies of MeVTR loss, i.e., dynamic weighting and fixed weighting, we test our model trained with a set of different weighting coefficients " + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "text", + "content": " as illustrated in Fig. 5 and Fig. 6. On the Video-to-Text task and Text-to-Video Retrieval tasks, we notice that dynamic weighting " + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "text", + "content": " can guarantee us a comparable performance in general and less sensitivity than any fixed coefficient. It is also illustrated that when we choose a smaller coefficient, the Video-to-Text retrieval is favored, while a bigger coefficient benefits the other way around. A cutoff point is empirically between 1.0 and 2.0. The reason is that " + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{v2t}" + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "text", + "content": " loss always has a comparably larger scale than " + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{t2v}" + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "text", + "content": " loss and dominates training due to the unbalanced number of video-text instances, as we have discussed in Section 4.2. This ensures us that a dynamic weighting strategy can improve the Text-to-Video task by amplifying the influence of " + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{t2v}" + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "text", + "content": " and guarantee stable improvements on both tasks." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22119" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 60, + 210, + 185 + ], + "blocks": [ + { + "bbox": [ + 50, + 60, + 210, + 185 + ], + "lines": [ + { + "bbox": [ + 50, + 60, + 210, + 185 + ], + "spans": [ + { + "bbox": [ + 50, + 60, + 210, + 185 + ], + "type": "image", + "image_path": "f17a96253965453ffe3479d9734718e8b4554f8d56eadbd26022edba1dde8cec.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 106, + 192, + 150, + 202 + ], + "lines": [ + { + "bbox": [ + 106, + 192, + 150, + 202 + ], + "spans": [ + { + "bbox": [ + 106, + 192, + 150, + 202 + ], + "type": "text", + "content": "(a) Average" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 215, + 60, + 373, + 184 + ], + "blocks": [ + { + "bbox": [ + 215, + 60, + 373, + 184 + ], + "lines": [ + { + "bbox": [ + 215, + 60, + 373, + 184 + ], + "spans": [ + { + "bbox": [ + 215, + 60, + 373, + 184 + ], + "type": "image", + "image_path": "8d7a3b394e53e3bf1c755ead343cbc83454591da0af34cecc2429c90cd747283.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 271, + 192, + 315, + 202 + ], + "lines": [ + { + "bbox": [ + 271, + 192, + 315, + 202 + ], + "spans": [ + { + "bbox": [ + 271, + 192, + 315, + 202 + ], + "type": "text", + "content": "(b) One-Hit" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 380, + 60, + 534, + 184 + ], + "blocks": [ + { + "bbox": [ + 380, + 60, + 534, + 184 + ], + "lines": [ + { + "bbox": [ + 380, + 60, + 534, + 184 + ], + "spans": [ + { + "bbox": [ + 380, + 60, + 534, + 184 + ], + "type": "image", + "image_path": "024bd25bab93a3be719d0c833fdbc6a8b48a64c23a4a5f045a11ee6bb67d2629.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 435, + 192, + 476, + 202 + ], + "lines": [ + { + "bbox": [ + 435, + 192, + 476, + 202 + ], + "spans": [ + { + "bbox": [ + 435, + 192, + 476, + 202 + ], + "type": "text", + "content": "(c) All-Hit" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 83, + 281, + 252, + 415 + ], + "blocks": [ + { + "bbox": [ + 45, + 213, + 547, + 262 + ], + "lines": [ + { + "bbox": [ + 45, + 213, + 547, + 262 + ], + "spans": [ + { + "bbox": [ + 45, + 213, + 547, + 262 + ], + "type": "text", + "content": "Figure 5: We compare the model performance with different weighting strategies, a dynamic weight " + }, + { + "bbox": [ + 45, + 213, + 547, + 262 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 45, + 213, + 547, + 262 + ], + "type": "text", + "content": " and different choices of fixed weights from a choice of " + }, + { + "bbox": [ + 45, + 213, + 547, + 262 + ], + "type": "inline_equation", + "content": "\\{0.5,1.0,1.5,2.0,3.0\\}" + }, + { + "bbox": [ + 45, + 213, + 547, + 262 + ], + "type": "text", + "content": ", in the MeVTR loss on Recall@5 on the Video-to-Text task for ActivityNet Captions. Fig. 5a-5c shows the results of Recall@5-Average/One-Hit/All-Hit respectively. We can find that compared to a fixed weighting coefficient, a dynamic weight " + }, + { + "bbox": [ + 45, + 213, + 547, + 262 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 45, + 213, + 547, + 262 + ], + "type": "text", + "content": " guarantees more stable and good results in different metrics." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 83, + 281, + 252, + 415 + ], + "lines": [ + { + "bbox": [ + 83, + 281, + 252, + 415 + ], + "spans": [ + { + "bbox": [ + 83, + 281, + 252, + 415 + ], + "type": "image", + "image_path": "ba34310540d8e3748e548149447b488b07803be6d8e50e50928f2c24d197bc88.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 426, + 288, + 499 + ], + "lines": [ + { + "bbox": [ + 46, + 426, + 288, + 499 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 288, + 499 + ], + "type": "text", + "content": "Figure 6: We compare the model performance with different weighting coefficients in the MeVTR loss on Recall@5 on the Text-to-Video task for ActivityNet Captions. The same graphical representations are used as Fig. 5. The dynamic weighting coefficient performs better than any other fixed coefficient considering performance and variance." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 533, + 289, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 289, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 289, + 713 + ], + "type": "text", + "content": "Effects of different modules We choose our best model Me-Retriever(avg) and ablate the key event selection module by removing the key event selection module and the MeVTR loss by replacing it with the cross-entropy loss, respectively. Results are shown in Tab. 6 and Tab. 7. We display the Recall@k-Average on both tasks in the table and observe that the model performances drop after removing any modules. In particular, our method demonstrates a larger improvement by " + }, + { + "bbox": [ + 46, + 533, + 289, + 713 + ], + "type": "inline_equation", + "content": "1.12\\%" + }, + { + "bbox": [ + 46, + 533, + 289, + 713 + ], + "type": "text", + "content": " without the key event selection module and " + }, + { + "bbox": [ + 46, + 533, + 289, + 713 + ], + "type": "inline_equation", + "content": "1.82\\%" + }, + { + "bbox": [ + 46, + 533, + 289, + 713 + ], + "type": "text", + "content": " without the MeVTR loss on the Video-to-Text task. This agrees with our assumption that our Me-Retriever model can deal with textual feature collapse in the MeVTR training. On the Text-to-Video task, both modules also show benefits to the performance on all metrics." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 281, + 547, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 281, + 547, + 437 + ], + "spans": [ + { + "bbox": [ + 304, + 281, + 547, + 437 + ], + "type": "text", + "content": "Textual features of multi-event videos To show whether Me-Retriever can prevent heterogeneous text features of a multi-event video from collapsing, we calculate the average cosine similarity. If the text features of one video are too similar, then the average cosine similarity among texts is expected to be closer to 1. We find that in Me-Retriever(avg), the cosine similarity averaged on the whole test set is 0.789 with a variance of 0.0059 while in CLIP4Clip(mean), the value is 0.864 with a variance of 0.0028. And as in Fig. 3, Me-Retriever has lower average cosine similarity than CLIP4Clip. This shows that text features of the same video generated by Me-Retriever are more diverse than those by CLIP4Clip, which agrees with our motivation." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 447, + 381, + 460 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 447, + 381, + 460 + ], + "spans": [ + { + "bbox": [ + 306, + 447, + 381, + 460 + ], + "type": "text", + "content": "6. Limitations" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 468, + 545, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 468, + 545, + 564 + ], + "spans": [ + { + "bbox": [ + 304, + 468, + 545, + 564 + ], + "type": "text", + "content": "Constrained by time and labor expenses, our experimental studies on the MeVTR task are based on the pre-existing video-text datasets including ActivityNet Captions and Charades. Nonetheless, it is important to recognize the potential bias in these datasets due to their emphasis on human activities and limitations in representing a wider range of videos. We aim to create a more comprehensive MeVTR benchmark encompassing more general videos." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 574, + 378, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 574, + 378, + 586 + ], + "spans": [ + { + "bbox": [ + 306, + 574, + 378, + 586 + ], + "type": "text", + "content": "7. Conclusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "type": "text", + "content": "We study a practical Video-Text retrieval scenario, Multi-event Video-Text Retrieval, in this paper. We find previous models suffer notable performance degradation in inference on MeVTR and textual feature collapse when retrained on MeVTR. We present a new CLIP-based model, Me-Retriever, to conquer this challenge. In our experimental studies, we demonstrate the efficacy of these techniques on both Text-to-Video and Video-to-Text tasks for ActivityNet Captions and Charades-Event datasets. We believe this can be a strong baseline for future studies." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22120" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 149, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 149, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 149, + 85 + ], + "type": "text", + "content": "Acknowledgements" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 91, + 287, + 140 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 91, + 287, + 140 + ], + "spans": [ + { + "bbox": [ + 47, + 91, + 287, + 140 + ], + "type": "text", + "content": "This work has been funded by the German Federal Ministry of Education and Research and the Bavarian State Ministry for Science and the Arts. 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In Proceedings of the AAAI conference on artificial intelligence, volume 34, pages 13041-13049, 2020. 2" + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "22123" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-Frequency Representation Enhancement with Privilege Information for Video Super-Resolution/80575c27-91e5-4c67-9202-9382a183799d_content_list.json b/2023/Multi-Frequency Representation Enhancement with Privilege Information for Video Super-Resolution/80575c27-91e5-4c67-9202-9382a183799d_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..fbd008ebf24c0065787e0de65f463da783257540 --- /dev/null +++ b/2023/Multi-Frequency Representation Enhancement with Privilege Information for Video Super-Resolution/80575c27-91e5-4c67-9202-9382a183799d_content_list.json @@ -0,0 +1,2218 @@ +[ + { + "type": "text", + "text": "Multi-Frequency Representation Enhancement with Privilege Information for Video Super-Resolution", + "text_level": 1, + "bbox": [ + 174, + 161, + 796, + 204 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Fei Li *", + "bbox": [ + 184, + 228, + 250, + 243 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "China Agricultural University", + "bbox": [ + 100, + 245, + 339, + 262 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "leefly072@126.com", + "bbox": [ + 144, + 264, + 297, + 276 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Linfeng Zhang *", + "bbox": [ + 433, + 229, + 568, + 245 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Tsinghua University", + "bbox": [ + 418, + 245, + 584, + 261 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "zhanglinfeng1997@outlook.com", + "bbox": [ + 376, + 264, + 628, + 276 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Zikun Liu", + "bbox": [ + 724, + 229, + 806, + 244 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Samsung Research China", + "bbox": [ + 663, + 245, + 867, + 262 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "zikun.liu@samsung.com", + "bbox": [ + 670, + 264, + 860, + 276 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Juan Lei", + "bbox": [ + 300, + 283, + 371, + 298 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Samsung Research China", + "bbox": [ + 233, + 300, + 438, + 315 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "juan.lei@samsung.com", + "bbox": [ + 247, + 319, + 426, + 332 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Zhenbo Li", + "bbox": [ + 564, + 283, + 668, + 298 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "China Agricultural University", + "bbox": [ + 497, + 300, + 734, + 317 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "lizb@cau.edu.cn", + "bbox": [ + 549, + 319, + 684, + 331 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 364, + 312, + 378 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "CNN's limited receptive field restricts its ability to capture long-range spatial-temporal dependencies, leading to unsatisfactory performance in video super-resolution (VSR). To tackle this challenge, this paper presents a novel multi-frequency representation enhancement module (MFE) that performs spatial-temporal information aggregation in the frequency domain. Specifically, MFE mainly includes a spatial-frequency representation enhancement branch which captures the long-range dependency in the spatial dimension, and an energy frequency representation enhancement branch to obtain the inter-channel feature relationship. Moreover, a novel model training method named privilege training is proposed to encode the privilege information from high-resolution videos to facilitate model training. With these two methods, we introduce a new VSR model named MFPI, which outperforms state-of-the-art methods by a large margin while maintaining good efficiency on various datasets, including REDS4, Kobe, Vid4, and UDM10.", + "bbox": [ + 75, + 393, + 473, + 644 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 77, + 682, + 208, + 698 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Video super-resolution (VSR), which restores high-resolution (HR) video frames from their highly related but unaligned low-resolution (LR) video frames, is well-desired in various real-world applications [11, 2]. Compared with single image super-resolution (SISR), VSR is much more challenging as it aggregates information from multiple related but misaligned frames in the input video. Hence, an ideal VSR model is expected to leverage the spatial information from single images but also integrate the temporal", + "bbox": [ + 75, + 707, + 468, + 833 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/1f29f8aeb33c1b0543b7fd943d6855ae621109df6952db61e8ae4e4595d6f1b8.jpg", + "image_caption": [ + "Figure 1: VSR performance comparison on UDM10 [65] in terms of PSNR (dB), runtime (ms), and parameters (M). MFPI outperforms SOTA methods with high efficiency." + ], + "image_footnote": [], + "bbox": [ + 504, + 362, + 887, + 570 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "semantic features from multiple frames [45, 50, 18, 3].", + "bbox": [ + 499, + 655, + 860, + 669 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "CNN-based models have become the standard choice for VSR due to their simplicity and efficiency. While recent advances in CNN-based VSR, such as residual learning [2, 73], dense connections[59], hierarchical structures [20], and multi-scale frameworks [63, 34, 48], have shown impressive performance, some potential problems still exist. Firstly, CNN's limited receptive field hinders it from modeling long-range spatial dependencies, making it unable to capture complex semantic information. Secondly, convolutional filters have fixed scales and weights, limiting their performance on large motions and adaptability to diverse inputs. In comparison, with the advantages of self-attention layers, ViTs are effective in processing inputs with long-term spatial dependencies. However, the stack", + "bbox": [ + 497, + 672, + 892, + 866 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 129, + 49, + 200, + 84 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation.", + "bbox": [ + 253, + 48, + 789, + 61 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "Except for this watermark, it is identical to the accepted version;", + "bbox": [ + 332, + 62, + 709, + 74 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 304, + 74, + 739, + 87 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "* The first two authors contribute equally. This work is done during the internship of F. Li in Samsung. Z. Li is the corresponding author.", + "bbox": [ + 75, + 842, + 468, + 866 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "12814", + "bbox": [ + 465, + 885, + 505, + 897 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "of self-attention layers is accompanied with a large computation budget, which results in inferior inference efficiency on edge devices [29]; A natural question arises: can CNNs capture long-range dependencies like ViTs?", + "bbox": [ + 75, + 125, + 467, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we propose to answer this question from a frequency perspective. Thanks to their ability to capture global representation, frequency-based models have been widely utilized in single image processing [72, 41, 71]. Unfortunately, their performance in video super-resolution (VSR) is usually limited due to several reasons. (1) Compared with single images, videos are composed of multiple related but misaligned images, which contain both spatial and temporal information. However, traditional frequency methods have fixed paradigms and coefficients [56, 66, 40], making them not able to capture the complex information in videos. (2) Traditional frequency methods are sensitive to the noise in images [64, 14]. This disadvantage becomes more fatal in videos where the noise of different frames can be accumulated.", + "bbox": [ + 75, + 182, + 467, + 389 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address these challenges, we propose a novel module named multi-frequency representation enhancement (MFE), which aggregates information in the frequency domain. Unlike convolutional and self-attention layers that operate in the feature space, MFE directly manipulates the energy feature map in the frequency domain through three branches: 1) a spatial-frequency representation enhancement branch (SFE) that utilizes a Fast Fourier Transform (FFT) and large kernel convolution layer to capture arbitrary interactions among spatial and long-range dependent features, 2) an energy-frequency representation enhancement branch (EFE) that employs a novel energy discrete cosine transform (DCT) to improve representation and explore potentially useful frequency components, and 3) a pair of convolution layers that leverage large kernels to obtain global range-interact features with stronger shape bias. Compared with the previous frequency methods, the learnable filter in SFE enables FFT to capture both spatial and temporal information, and the energy function in EFE can alleviate the noise accumulated in multiple video frames. Moreover, MFE only contains $0.02\\mathrm{M}$ parameters, making it affordable for edge devices.", + "bbox": [ + 75, + 391, + 467, + 695 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Besides MFE, we further propose a novel model training method named privilege training (PT) to facilitate the training of VSR models. Motivated by previous research in learning using privilege information (LUPI) [53], we propose to apply a trainable encoding module to encode the privilege information from HR videos and then employ them to obtain a good initialization for VSR models. Sufficient experiments demonstrate the effectiveness of privilege training on both our model and the other VSR models.", + "bbox": [ + 75, + 698, + 467, + 821 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "With MFE and privilege training, we introduce a novel VSR model referred to as MFPI. Extensive experimental results have demonstrated that MFPI outperforms eighteen", + "bbox": [ + 77, + 824, + 467, + 866 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "previous methods by a clear margin in six VSR benchmarks. For instance, on UDM10, compared with BasicVSR++ [4], which has similar parameters and runtime with MFPI, MFPI achieves 0.36 dB higher PSNR improvements on UDM10 BD degradation, as shown in Figure 1. To sum up, the main contributions in this paper can be summarized as follows:", + "bbox": [ + 497, + 125, + 890, + 209 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose multi-frequency representation enhancement (MFE), a module that effectively aggregates information in the frequency domain by operating the spatial- and energy-frequency components.", + "- We propose privilege training, which encodes the privilege information from the HR videos to boost the performance of VSR models.", + "- Abundant experiments demonstrate the effectiveness of MFPI on four datasets, including REDS4, Vimeo, Vid4, and UDM10 in both BI and BD degradation." + ], + "bbox": [ + 517, + 220, + 890, + 378 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 499, + 391, + 638, + 404 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Video Super Resolution", + "text_level": 1, + "bbox": [ + 499, + 414, + 715, + 428 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Different from SISR, VSR typically produces higher-quality results by utilizing information from neighboring frames. Recently, learning-based approaches have been highly effective in solving the problem of VSR [16, 4]. The main challenge for VSR is how to correctly fuse auxiliary frames in the presence of dynamic content and object motion. To address this problem, abundant methods have been proposed to explicitly use optical flow [55], deformable convolution [57, 50, 3], and homography [18] to align neighbor frames. However, estimating accurate optical flow or transformation is still challenging in large motions. Recently, some methods have been proposed to learn the spatial correspondence across different frames to tackle this challenge [25, 13]. However, these methods have limited performance in VSR since they cannot capture information between adjacent locations or long-range interactions [47, 41]. To address this problem, we introduce a spatial-frequency representation enhancement branch that models long-range spatial and temporal dependencies.", + "bbox": [ + 497, + 435, + 890, + 698 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Learning in Frequency Domain", + "text_level": 1, + "bbox": [ + 499, + 706, + 774, + 720 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Due to the difficulty of distinguishing high-frequency textures from artifacts, fruitful methods [70, 6, 14] have been introduced to decouple them in the frequency space and reconstruct the high-quality textures. For instance, Zhou et al. proposed a deep Fourier up-sampling method to recover the resolution in the frequency domain [72]. Guo et al. utilized the wavelet technique to simplify the mapping between the LR and HR images, reducing the artificial blocks and recovering the edge's information [10]. Motivated by their success, abundant works have tried to", + "bbox": [ + 497, + 726, + 890, + 865 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "12815", + "bbox": [ + 465, + 885, + 504, + 897 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "apply frequency methods to SR. Dario et al. proposed a Fourier space supervision loss to improve restoration results [6]. Qiu et al. designed a fine-grained self-attention module in the space-frequency domain, which reconstructs the real visual texture without artifacts [41]. However, the images that are directly transformed into the frequency domain still face obstacles as follows: (1) Decomposing features into different frequency components usually lacks local correlation information in the channel dimension, making it difficult to utilize the useful frequency components [40]. (2) Non-parametric frequency-based methods are easily susceptible to noise and image scale factors [35]. To address the above problems, this paper proposes to combine the advantages of the energy function and frequency-based representations by using DCT with learnable filters.", + "bbox": [ + 75, + 125, + 472, + 333 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Learning Using Privilege Information", + "text_level": 1, + "bbox": [ + 77, + 353, + 403, + 369 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Learning using privilege information (LUPI) was first proposed by Vapnik et al. to employ the privilege information provided by a teacher model in support vector machine [53]. Generally speaking, LUPI aims to improve the performance of a model by using privilege information, which is utilized during training but not required during inference. Vapnik et al. further utilized LUPI to accelerate the inference speed of SVMs by similarity control and knowledge transfer [52]. Motivated by the success of knowledge distillation [12] on deep neural networks, recently, David et al. proposed generalized distillation, which combines knowledge distillation with learning with privilege information theoretically [32]. Recently, label-guided auxiliary was introduced to apply LUPI to point cloud-based 3D detection by using the privilege information from annotations [15]. Lee et al. proposed PISR, which introduces LUPI to single image super-resolution by using variational knowledge distillation [24]. Moreover, LUPI has also been utilized in semi-supervised learning [7], domain adaptation [37], speech recognition [36] and so on.", + "bbox": [ + 75, + 378, + 472, + 655 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The most related work of the privilege training in our method is PISR [24], which is proposed for knowledge distillation on single image super-resolution. Their main difference is that: (1) PISR is proposed for SISR for model compression while our method is proposed for VSR to improve the quality of restoration. (2) Besides, PISR is a knowledge distillation method which mainly leverages the privilege information with distillation loss. In contrast, our method leverages the privilege information by sharing model weights. (3) PISR implicitly encodes the privilege information via the reconstruction of LR images while our method explicitly encodes privilege information from HR videos with a trainable network. Besides, ablation studies in Table 3 also demonstrate that our method leads to significantly higher performance than PISR.", + "bbox": [ + 75, + 657, + 472, + 866 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 497, + 124, + 636, + 140 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overall Framework for VSR", + "text_level": 1, + "bbox": [ + 497, + 147, + 756, + 162 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Following the previous work [4], we adopt the recurrent bidirectional propagation as the baseline model. Based on its architecture, we propose a novel VSR model termed MFPI, which consists of a multi-frequency representation enhancement module (MFE) to improve the LR frames representation in the frequency domain, and a novel VSR model training method named privilege training which encodes privilege information from HR frames to facilitate model training. The overall architecture is shown in Figure 2: (1) The VSR model extracts features from the LR frames images to reconstruct the HR frames images. (2) Residual blocks and MFE are employed to extract the feature $f_{i}^{j}$ from the LR images, where $f_{i}^{j}$ denotes the feature at $i_{th}$ timestamp in the $j_{th}$ propagation branch. (3) The flow-guided deformable alignment block (FDA) aligns the neighboring features $f_{i-1}^{j}$ and $f_{i-2}^{j}$ . And the pixel-shuffle operator is employed to perform upsampling $4 \\times$ scales from LR to HR frames. Besides, learning privilege information boosts the performance of our VSR models during training, as shown in Figure 3.", + "bbox": [ + 497, + 169, + 890, + 447 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. MFE: A Multi-Frequency Representation Enhancement Module", + "text_level": 1, + "bbox": [ + 497, + 454, + 855, + 484 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As depicted in Figure 2 (b), we design a multi-frequency representation enhancement (MFE) to improve the representation ability and aggregate spatial-temporal information in VSR architecture. MFE is a plug-in-play building block which adopts a multi-branch structure to capture multifrequency representation [9]. Concretely, it first encodes the input features with a depthwise convolution (DWConv) layer [68] and then processes them with three different branches, including 1) a spatial-frequency representation enhancement branch to capture the spatial-frequency information and long-range dependence features, 2) an energy-frequency representation enhancement branch to improve the representation ability and model the inter-channel relationship in the frequency domain, and 3) an auxiliary branch with a pair of $7 \\times 1$ and $1 \\times 7$ DWConv to inject the inductive bias and facilitate training [8, 31]. Finally, a $1 \\times 1$ convolution layer aggregates the diverse features from three branches, and the skip connection is employed to facilitate the convergence of MFE [30].", + "bbox": [ + 497, + 491, + 890, + 755 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2.1 Spatial Frequency Representation Enhancement", + "text_level": 1, + "bbox": [ + 497, + 774, + 890, + 789 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As illustrated in Figure 2 (c), the spatial frequency representation enhancement (SFE) branch first employs a pair of $DWConv$ to generate the feature map $f_{in}$ from the input $x_{in} \\in \\mathbb{R}^{H \\times W \\times C}$ . Then, we split $f_{in}$ into two parts $f_{mid1}, f_{mid2} \\in \\mathbb{R}^{h \\times w \\times c/2}$ [26, 69]. The FFT layer pro", + "bbox": [ + 497, + 796, + 890, + 868 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "12816", + "bbox": [ + 465, + 885, + 505, + 897 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/10daa50da56daf15e6a437f20706144e06c0a737008a7a3bf357bf31cdaed919.jpg", + "image_caption": [ + "(a) The Overall Framework of MFPI", + "(b) MFE: Multi-frequency Representation Enhancement" + ], + "image_footnote": [], + "bbox": [ + 97, + 122, + 803, + 302 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/339c9c6c90b8e24dda7da7134f532a8f0a79543708f9d37fbadf9cd31b05ecb6.jpg", + "image_caption": [ + "(c) SFE: Spatial Frequency Representation Enhancement", + "Figure 2: (a) An overview framework of MFPI. The blue dot line denotes the bilinear upsampling operator. The red curve denotes second-order propagation. \"FDA\" denotes the flow-guided deformable alignment block [4]. The green block denotes the proposed multi-frequency representation enhancement (MFE). (b) An overview of the MFE. (c) The details of the spatial-frequency representation enhancement branch in MFE extract spatial-level and long-range dependencies. (d) The details of the energy-frequency representation enhancement branch. $e_{i,j}^{*}$ denotes the energy feature. Note that the 'FC layer' consists of a sequence of the 'linear-LReLU-linear-LReLU' operator. DWConv denotes the depthwise convolution [68]." + ], + "image_footnote": [], + "bbox": [ + 80, + 321, + 475, + 415 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/648cdb3a3a646446c300915411b8cf7ae18c6c741ad268f0c256e5f8e8588bcb.jpg", + "image_caption": [ + "(d) EFE: Energy Frequency Representation Enhancement" + ], + "image_footnote": [], + "bbox": [ + 485, + 326, + 889, + 409 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "cesses $f_{mid1}$ represents different spatial dependence information as follows:", + "bbox": [ + 75, + 548, + 468, + 574 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nf r e q = \\mathcal {F} \\left[ f _ {\\text {m i d} 1} \\right] \\in \\mathbb {C} ^ {h \\times w \\times c / 2} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 585, + 468, + 602 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $c, h, w$ denote the input channel, height, width of the feature maps, respectively. $\\mathcal{F}[\\cdot]$ denotes the 2D FFT, $freq$ represents the frequency feature of $f_{mid1}$ . To make SFE adaptive to diverse features [43, 54], we modulate the $freq$ multiplies with a learnable filter $L \\in \\mathbb{C}^{h \\times w \\times c/2}$ in the frequency domain: $\\tilde{freq} = freq \\times L$ . The inverse FFT transfers the modulated frequency feature back to the spatial domain:", + "bbox": [ + 75, + 612, + 468, + 720 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {f _ {m i d 1}} \\leftarrow \\mathcal {F} ^ {- 1} \\left[ f \\tilde {r e q} \\right] \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 196, + 720, + 468, + 744 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Finally, the output feature $f_{out}$ is obtained by concatenating with an instance normalization (IN) [51] layer, which prevents covariance shift and preserves the scale information: $f_{out} = \\text{Concat}\\left(f_{mid1}, \\text{IN}\\left(f_{mid2}\\right)\\right)$ .", + "bbox": [ + 75, + 749, + 468, + 809 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "It is also worth noting that in our implementation: (1) SFE utilizes a relatively large local window of $DWConv$ $(e.g., 21 \\times 1, 1 \\times 21)$ to capture the long-range spatial dependencies from features. (2) Besides, a learnable Fourier", + "bbox": [ + 75, + 811, + 468, + 866 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "transform with IN can exhibit clear patterns and generalizations in the frequency domain. Hence, the proposed SFE branch tends to be more efficient than directly utilizing Fourier transforms in the spatial-temporal dimension (Table 2b). (3) Considering that FFT has less computation than DFT, we employ FFT in SFE as the frequency transformation to improve model representation. Moreover, the Fourier domain has the nature of global modeling [54]. Hence, computation on frequency bands implies information aggregation over all the spatial locations of the input images. Specifically, in our SFE, FFT is performed over the whole feature map across all the spatial locations, which is equivalent to the global receptive field of the whole feature. (4) SFE splits features into two branches to improve computational efficiency. Specifically, this split operator enables SFE to capture and combine different aspects or representations of the input data. One part focus on the spatial frequency characteristics or patterns, and the other part act as a form of regularization by introducing additional constraints, such as instance normalization. Their outputs can be concatenated to create a richer and more comprehensive representation. This can enhance the SFE's ability to learn complex relationships and improve its overall performance.", + "bbox": [ + 497, + 548, + 890, + 866 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "12817", + "bbox": [ + 465, + 885, + 504, + 897 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Besides, this two-branch design is also similar to the idea of group convolution and CSN [71], which is a well-known technique of efficient neural networks. Please refer to supplementary materials for theoretical analysis.", + "bbox": [ + 75, + 125, + 468, + 181 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2.2 Energy Frequency Representation Enhancement", + "text_level": 1, + "bbox": [ + 75, + 200, + 468, + 214 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Considering that the frequency methods with a learning filter can be more generic and flexible interactions among spatial locations from diverse images, we introduce an energy function to reweight the input feature and utilize the learnable filter with DCT to represent the rich inter-channel relationship [40]. The architecture of the energy frequency representation enhancement (EFE) is illustrated in Figure 2 (d). More specifically, EFE first utilizes a pair of $DWConv$ (e.g., $11 \\times 1,1 \\times 11$ ) to generate the feature map $f$ . Then, we calculate the mean $\\hat{\\mu}$ and variance $\\hat{\\sigma}^2$ of $f$ , and the energy value [62] can be obtained by minimizing the following:", + "bbox": [ + 75, + 222, + 468, + 375 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\ne _ {i, j} = \\frac {4 (\\hat {\\sigma} ^ {2} + \\delta)}{(t _ {i , j} - \\hat {\\mu}) ^ {2} + 2 \\hat {\\sigma} ^ {2} + 2 \\delta} \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 169, + 385, + 468, + 420 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\delta$ is the hyper-parameter, $e_{i,j}$ denote the energy value of target pixel $t_{i,j}$ , $i\\in \\{0,1,\\dots ,H - 1\\}$ , $j\\in \\{0,1,\\dots ,W - 1\\}$ . The energy feature is obtained by grouping all the $e_{i,j}$ across spatial and channel levels, which rescale the energy value to restrict too large energy value:", + "bbox": [ + 75, + 429, + 468, + 500 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\ne _ {i, j} ^ {*} = \\text {L e a k y R e L U} \\left(\\frac {1}{\\sum_ {i \\neg = 0} ^ {h} \\sum_ {j \\neg = 0} ^ {w} e _ {i , j}}\\right) \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 127, + 510, + 468, + 548 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To further enrich the representation ability of EFE, we employ the DCT technique to convert the energy features into the frequency domain as follows:", + "bbox": [ + 75, + 554, + 468, + 596 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {F} _ {c} (i, j) = \\frac {2}{\\sqrt {H W}} \\alpha (i) \\alpha (j) \\sum_ {h = 0} ^ {H - 1} \\sum_ {w = 0} ^ {W - 1} e _ {i, j} ^ {*} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 134, + 606, + 468, + 646 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {K} _ {h, w} ^ {i, j} = \\cos \\left(\\frac {(2 h + 1) i \\pi}{2 H}\\right) \\cos \\left(\\frac {(2 w + 1) j \\pi}{2 W}\\right) \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 102, + 669, + 468, + 701 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nf _ {c} ^ {h, w} = \\mathcal {K} _ {h, w} ^ {i, j} \\times \\mathcal {F} _ {c} \\left(e _ {i, j} ^ {*}\\right) \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 186, + 717, + 468, + 736 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathcal{F}_c$ denotes DCT operation, $\\kappa$ denotes the basis function of DCT, $\\alpha(x) = 1/\\sqrt{2}$ for $x = 0$ and $\\alpha(x) = 1$ otherwise [46]. Finally, the output refined feature as follows: $f_{out} = f_c^{h,w} \\times x_{i,j}$ . Note that an element-wise multiplication between frequency-domain features and the learnable filters improves the representation ability and makes EFE flexible adaptive to different feature inputs. Besides, the FC layer in Figure 2 (d) consists of a sequence of the 'Linear-LeakyReLU-Linear-LeakyReLU' operators, which", + "bbox": [ + 75, + 741, + 468, + 866 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "convert the channel-wise feature into a scalar representation, which reduces the complexity and improves the effectiveness in the frequency domain. Different from the SFE branch, the EFE branch leverages the merits of the energy function and frequency components to improve the representation power and model the relationship among inter-channel dimensions, as shown in Figure 9.", + "bbox": [ + 497, + 125, + 890, + 222 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Privilege Training", + "text_level": 1, + "bbox": [ + 499, + 230, + 675, + 244 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Learning using privilege information is a well-known theory in machine learning, which shows that one can improve the performance of machine learning by using kinds of privilege information, which is available in training but not accessible during inference. Motivated by its effectiveness, in this paper, we propose a novel neural network training method for VSR, which is shown in Figure 3. By denoting the LR and corresponding HR videos as $x$ and $y$ , respectively, the traditional training method can be formulated as $\\min \\mathbb{E}[|f(x) - y|]$ , where $f(\\cdot)$ denotes the superresolution model. In contrast, in our method, we additionally introduce a lightweight neural network $\\mathcal{D}$ , which aims to encode the privilege information from the HR frames $y$ to a tensor of privilege information $\\mathcal{D}(y)$ which has the same shape with the LR frames $x$ . Then, we can denote a mixture of the LR images and the privilege information as $x^{*} = x + \\gamma \\cdot \\mathcal{D}(y)$ , where $\\gamma \\in [0,1]$ is a parameter to balance the two items. During the training period, we gradually decrease $\\gamma$ from 1 to 0. Hence, the VSR model is able to firstly learn a good representation by using the privilege information, and then gradually get rid of it. Note that since $\\gamma$ is decreased to 0, the VSR model does not require any privilege information during inference. In summary, its objective of privilege training can be written as", + "bbox": [ + 497, + 251, + 890, + 583 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\underset {f, \\mathcal {D}} {\\arg \\min } \\mathbb {E} [ | f (x ^ {*}) - y | + | \\mathcal {D} (y) | ] \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 584, + 590, + 890, + 614 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the first loss item is the common reconstruction loss for VSR training. The second loss item is a regularization item which reduces the energy of privilege information to prevent the model from overusing the privilege information. Note that the regularization item is indispensable since without this item the VSR model may degenerate into a naive auto-encoder which reconstructs the HR images totally based on the privilege information. Note that $\\mathcal{D}$ in our implementation is a stack of three convolutional layers followed with LeakyReLU.", + "bbox": [ + 497, + 621, + 890, + 758 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Why does privilege training work? The effectiveness of privilege information can be understood from the perspective of weight initialization. During the early training iterations, the model can quickly converge to a flat minima by using the privilege information. Then, by reducing $\\gamma$ , the privilege information gradually makes a less influence to the VSR model, and hence the VSR model can converge", + "bbox": [ + 497, + 769, + 890, + 866 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "12818", + "bbox": [ + 465, + 885, + 504, + 897 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/025e5f2b6696c3b849fc9c8b5c31b8468c7e93147c94943109dfa7fb1473aa0c.jpg", + "image_caption": [ + "Figure 3: The paradigm of the proposed learning using privilege information on VSR. $\\oplus$ denotes a weighted addition between the privilege information and the LR frames." + ], + "image_footnote": [], + "bbox": [ + 137, + 123, + 830, + 264 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/62a95eca1968bea6f1e66e2a2433b90308c59cd3364ae503092e02fc1e267ff8.jpg", + "image_caption": [ + "Figure 4: Visualization of the privilege information." + ], + "image_footnote": [], + "bbox": [ + 80, + 324, + 467, + 433 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "stably. Secondly, the success of our method can also be understood as a special case of knowledge distillation, where the teacher model is trained with privilege information, the student model is trained with only the LR frames, and the knowledge distillation is applied by sharing the weights of the student and the teacher. Besides, Figure 4 visualizes the privilege information encoded during the training period. It is observed that most of privilege information concentrates on the pixels belonging to the objects and their edges, which are more important in the assessment of image quality. These privilege information is utilized to help VSR models to converge at the early training period.", + "bbox": [ + 75, + 484, + 468, + 650 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiment", + "text_level": 1, + "bbox": [ + 75, + 667, + 201, + 682 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Experimental Setup", + "text_level": 1, + "bbox": [ + 75, + 691, + 265, + 706 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Our model is trained for each task with $6 \\times 10^{5}$ iterations using randomly cropped patches. We apply data augmentation techniques such as random horizontal and vertical flipping and $90^{\\circ}$ rotation. The Adam optimizer [22] is used with an initial learning rate of $2 \\times 10^{-4}$ , which is steadily decreased to $1 \\times 10^{-7}$ with cosine annealing learning rate decay [33]. $\\delta$ is set to $1 \\times 10^{-6}$ [62]. We employ SPyNet to predict optical flow in videos [42]. Each branch contains 7 residual blocks and 64 feature channels. The batch size is set to 4, and the input low-resolution (LR) frames are of patch size $64 \\times 64$ .", + "bbox": [ + 75, + 713, + 470, + 866 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/6ce13d1e4346a485d76a774eaefadf5e36d998680f636bab80fb5460ee2e6c9b.jpg", + "image_caption": [ + "Figure 5: Challenging scenario on REDS4 [38]. MFPI generates sharp edge in repeated structures of the windows and sharper texts." + ], + "image_footnote": [], + "bbox": [ + 502, + 324, + 890, + 485 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index Measure (SSIM) [58] between ground truth and restored videos are utilized as the metrics in our quantitative comparisons. We follow [4] to utilize REDS [38], Vimeo90K [60] as training set, and REDS4, Vimeo-90K-T [60], Vid4 [28], UDM10 [65], and Vimeo-90K as the test set. REDSval4 is utilized as the validation set. All models are tested with $4 \\times$ downsampling via two degradations - Bicubic (BI) and Blur Downsampling (BD). All experiments are implemented with PyTorch [39] and on two NVIDIA Tesla A100 GPUs.", + "bbox": [ + 497, + 567, + 890, + 718 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparisons with State-of-the-Art Methods", + "text_level": 1, + "bbox": [ + 499, + 732, + 873, + 747 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Qualitative Comparison We show the comparison of visual results in Figure. 5, 6, 7 and 8. It is observed that the results of prior works usually suffer from incomplete artifacts or blurred regions in the image. In contrast, our model restores sharper edges and finer detailed textures of the number plate in Figure 5 and the display board in Figure 6. Besides, MFPI is able to recover the edge of the small object in Figure 6. As shown in Figure 7 and 8, MFPI also shows", + "bbox": [ + 497, + 755, + 890, + 866 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "12819", + "bbox": [ + 465, + 885, + 504, + 897 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/a5990a6fd04e42c682ce830321345a64bc82a7249bc87e3a530b3986a3c6200f.jpg", + "table_caption": [ + "Table 1: Quantitative comparison (PSNR/SSIM). All results are calculated on Y-channel except REDS4 [38] (RGB-channel). The runtime is computed on an LR size of $180 \\times 320$ . A $4 \\times$ upsampling is performed following previous studies. Blanked entries correspond to results not reported in previous works. Numbers in bold indicate the best performance." + ], + "table_footnote": [], + "table_body": "
ModelParams (M)Runtime (ms)BI degradationBD degradation
REDS4 [38]Vimeo-90K-T [60]Vid4[28]UDM10 [65]Vimeo-90-T [60]Vid4 [28]
Bicubic--26.14/0.729231.32/0.868423.78/0.634728.47/0.825331.30/0.868721.80/0.5246
VESPCN [1]----25.35/0.7557---
SPMC [49]----25.88/0.7752---
TOFlow [61]--27.98/0.799033.08/0.905425.89/0.765136.26/0.943834.62/0.9212-
FRVSR [45]5.1137---37.09/0.952235.64/0.931926.69/0.8103
DUF [21]5.897428.63/0.8251--38.48/0.960536.87/0.944727.38/0.8329
RBPN [11]12.2150730.09/0.859037.07/0.943527.12/0.818038.66/0.959637.20/0.9458-
EDVR-M [57]3.311830.53/0.869937.09/0.944627.10/0.818639.40/0.966337.33/0.948427.45/0.8406
EDVR [57]20.637831.09/0.880037.61/0.948927.35/0.826439.89/0.968637.81/0.952327.85/0.8503
PFNL [65]3.029529.63/0.850236.14/0.936326.73/0.802938.74/0.9627-27.16/0.8355
MuCAN [27]--30.88/0.875037.32/0.9465----
TGA [18]5.8384----37.59/0.951627.63/0.8423
RLSP [5]4.249---38.48/0.960636.49/0.940327.48/0.8388
RSDN [17]6.294---39.35/0.965337.23/0.947127.92/0.8505
RRN [19]3.445--38.96/0.9644-27.69/0.8488
BasicVSR [2]6.36331.42/0.890937.18/0.945027.24/0.825139.96/0.969437.53/0.949827.96/0.8553
IconVSR [2]8.77031.67/0.894837.47/0.947627.39/0.827940.03/0.969437.84/0.952428.04/0.8570
BasicVSR++ [4]7.37732.39/0.906937.79/0.953027.79/0.840040.72/0.972238.21/0.955029.04/0.8753
PSRT [47]13.481232.72/0.910638.27/0.953628.07/0.8485---
MFPI (Ours)7.37632.81/0.910638.28/0.953428.11/0.848141.08/0.974138.70/0.957929.34/0.8781
", + "bbox": [ + 77, + 176, + 890, + 444 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/ed43e035659e7bf78be3ce4f53af88054c3c31eb770a2eb98d61554161853d4e.jpg", + "image_caption": [ + "Sequence 00015,Clip 0864" + ], + "image_footnote": [], + "bbox": [ + 82, + 463, + 205, + 532 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/8f5036db1fbc6957713ced9b74bd093b205ff84eafff3dda09f5a738a1d4c658.jpg", + "image_caption": [ + "Bicubic" + ], + "image_footnote": [], + "bbox": [ + 206, + 463, + 337, + 492 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/3ef422b40e86c4b90b8570f9d318e0d1d75e41067dc1aaad0021653a1fd60bae.jpg", + "image_caption": [ + "BasicVSR" + ], + "image_footnote": [], + "bbox": [ + 339, + 463, + 403, + 492 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/960c55cf2960835e10f19f232b26ed7486220df0f62cabda1c573693aa554061.jpg", + "image_caption": [ + "IconVSR" + ], + "image_footnote": [], + "bbox": [ + 405, + 463, + 468, + 492 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "", + "bbox": [ + 82, + 502, + 205, + 530 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/fc6575c7da47fcd7adf3515d94f22112a67986ac6883fe19164f62b4918c832d.jpg", + "image_caption": [ + "BasicVSR++" + ], + "image_footnote": [], + "bbox": [ + 208, + 502, + 245, + 530 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c82fe85cf4fc9f20a984088048d7c41b44235255f5aa5c4f2300ddd12431830e.jpg", + "image_caption": [ + "" + ], + "image_footnote": [], + "bbox": [ + 247, + 502, + 297, + 530 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/319c90478888e7dc004b37183cdda0425d881dffbca69eccaa1f4944e3ef4f3f.jpg", + "image_caption": [ + "" + ], + "image_footnote": [], + "bbox": [ + 299, + 502, + 337, + 530 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/66e0cf9fbd4abc61ab9e342f982ccdd2edf52ede7656af375d0cd241501c7710.jpg", + "image_caption": [ + "MFPI(Ours)" + ], + "image_footnote": [], + "bbox": [ + 341, + 502, + 393, + 530 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/90b62c46ee71b80fd309d60b503d2f5133ae0a07d838dbec69029fa092dcf790.jpg", + "image_caption": [ + "HR" + ], + "image_footnote": [], + "bbox": [ + 405, + 502, + 468, + 530 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2b3c4fbeb8d569ac3f18a42da661b60eb86861259c3bb1d70d13517b6930e9b0.jpg", + "image_caption": [ + "Sequence 00010,Clip 0573", + "Figure 6: Challenging scenario on Vimeo-90K-T [60]. Compared to the other methods, Our method more effectively preserves while recovering the strip-like features in the skirts." + ], + "image_footnote": [], + "bbox": [ + 82, + 545, + 205, + 612 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9e8f57e889ba4eacfc632ff41b1a5b11d20a8b9dab6473e24a619279b1f3f139.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 206, + 545, + 272, + 574 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e2910340ed433e36be77e315673234d17c1aff1cbf3f98c390374c736b131171.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 273, + 545, + 337, + 574 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/bfd292eac0952724e2621d62d36dfcfa0e67d68b823474b7f5b792316f8dccbc.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 341, + 545, + 403, + 574 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/15d6877d39e02b48d71e8a3e0619c72c11aa60828b1500293d007e38f860df1f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 405, + 545, + 468, + 574 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "", + "bbox": [ + 82, + 581, + 205, + 612 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Sequence 00010, Clip 0573", + "bbox": [ + 92, + 612, + 196, + 622 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/3ff8ce0e7fb9cdf6f643177bbd5271d5f772c4d32aa2cd34947c4fb61111e584.jpg", + "image_caption": [ + "Bicubic", + "BasicVSR++" + ], + "image_footnote": [], + "bbox": [ + 206, + 581, + 272, + 612 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b3850d874d0db37115c3a4ba549c6f0c5ea53e1a1795d850dd0c476090c385ee.jpg", + "image_caption": [ + "EDVR", + "PSRT" + ], + "image_footnote": [], + "bbox": [ + 273, + 581, + 337, + 612 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/87fdda86de0d34eeef9a2f7da7ddaafaeb42d1b6d9fb89d7f872558e91068100.jpg", + "image_caption": [ + "BasicVSR", + "MFPI(Ours)" + ], + "image_footnote": [], + "bbox": [ + 341, + 581, + 403, + 612 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/98c6d26d552b4644f34046b7066960b1c9d57b09dbacc219668406caf6cda153.jpg", + "image_caption": [ + "IconVSR", + "HR" + ], + "image_footnote": [], + "bbox": [ + 405, + 581, + 468, + 612 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "significantly better performance than prior works when the camera and the foreground objects are moving, which is a more challenging case in VSR. Moreover, MFPI can recover the scene details more faithfully than other methods, such as pedestrians' feet and text in Figure 7. More visual comparisons are shown in the supplementary material.", + "bbox": [ + 75, + 717, + 468, + 802 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Quantitative Comparison The quantitative results on six test sets with scaling factors 4 are shown in Table 1. It is observed that: (1) Compared with existing approaches that", + "bbox": [ + 75, + 824, + 468, + 866 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9f076478e3bb25daf17862d09c5ac7ac893c2e0e098044af68de90c1c78989ac.jpg", + "image_caption": [ + "Frame 010, Clip city" + ], + "image_footnote": [], + "bbox": [ + 502, + 463, + 626, + 532 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/98bd7e9dc502f6ee8a242effe4fcf481f645e0478a0899e34dfa102a18b533d1.jpg", + "image_caption": [ + "L" + ], + "image_footnote": [], + "bbox": [ + 626, + 463, + 690, + 492 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/324c78426bab7bbee51c3f7be3e306816a469ae1ccf8ff3914da2ed442476c50.jpg", + "image_caption": [ + "EDVR" + ], + "image_footnote": [], + "bbox": [ + 692, + 463, + 757, + 492 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/59d6f23568b63829c4e1cceaaaf5fe8b66f12d8096ff460e8eae63a0134e3eab.jpg", + "image_caption": [ + "BasicVSR" + ], + "image_footnote": [], + "bbox": [ + 759, + 463, + 823, + 492 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/91ac119f618a8e7b381ee9daeefba222058fce8588efa12583f2b42163bae184.jpg", + "image_caption": [ + "IconVSR" + ], + "image_footnote": [], + "bbox": [ + 825, + 463, + 890, + 492 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/554f2baee1f86427cbcad839531f18121d4acf2778a12ecb79b4e9b3f45c709d.jpg", + "image_caption": [ + "Frame 015, Clip walk", + "Figure 7: Challenging scenario on Vid4 [28]. MFPI recovers the clear textures and reduces the produce blurry results." + ], + "image_footnote": [], + "bbox": [ + 502, + 545, + 626, + 614 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/fb88ce50671178c8a1708fdd29bcfe9441fbbbf5255bddaa1aae14ae57a095b5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 626, + 545, + 692, + 574 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/0adf222f7b6ccbcb2fa4a2874c07cbf9bce3fe3aa92d8f414b5e0df0985f15ba.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 692, + 545, + 757, + 574 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/fe50fe54f537401c30cb497f2595bc7bae4264643ae5e207b28aac7b2d8e11dd.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 759, + 545, + 823, + 574 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/33f9d333b8b4a5420f3159e47993d4a31671a95735da0de167800ba4019e1660.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 825, + 545, + 890, + 574 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/86b85a8088fee37ba1b9b4bfb0a7492d05791bfc1add441dbb6fc058fc661d24.jpg", + "image_caption": [ + "L]", + "BasicVSR++" + ], + "image_footnote": [], + "bbox": [ + 499, + 583, + 692, + 614 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e8c518097a6355fe3b1246d30231bea1fcd6694e272f9b6dd97b158f74f33f16.jpg", + "image_caption": [ + "EDVR", + "PSRT" + ], + "image_footnote": [], + "bbox": [ + 692, + 583, + 757, + 614 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1554af292d78842b1ad227ad53b47f67d59b43b9df75e0a93a04ad898849d025.jpg", + "image_caption": [ + "BasicVSR", + "MFPI(Ours)" + ], + "image_footnote": [], + "bbox": [ + 759, + 583, + 823, + 614 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9205bfe011a404cdb2bdf6e4418197afd0d391fb649c96ecd2ebc426baa8d233.jpg", + "image_caption": [ + "IconVSR", + "HR" + ], + "image_footnote": [], + "bbox": [ + 825, + 583, + 890, + 614 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "only perform well on a certain dataset, our MFPI achieves the best performance in all the datasets for both BI and BD degradation. (2) Compared with BasicVSR++ which has very similar parameters and speed to our method, 0.42 dB, 0.49 dB and 0.32 dB PSNR improvements can be achieved on the three datasets in BI degradation experiments, respectively. (3) Compared with PSRT-recurrent which has slightly lower PSNR than our method, our model only has around $54\\%$ parameters, which indicates better efficiency. These observations indicate that our method significantly outperforms the previous VSR models.", + "bbox": [ + 497, + 713, + 892, + 866 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "12820", + "bbox": [ + 465, + 885, + 505, + 897 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6f31a6c8d6cbd358aad9cfe04559fdf1d9de47dc1c19da00c957bd6c30e6fdbf.jpg", + "image_caption": [ + "Frame 024, Clip clap", + "IconVSR" + ], + "image_footnote": [], + "bbox": [ + 80, + 123, + 268, + 191 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/eb1eff36cafd7f58267a91fe01d283d885e92f2d5d2f31a51415ce8eb18a432b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 270, + 123, + 468, + 152 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b46654143542f3e53835e54e75394d3b02fcc0d6cd8d922a69cfe502f1b43a25.jpg", + "image_caption": [ + "EDVR" + ], + "image_footnote": [], + "bbox": [ + 270, + 163, + 468, + 192 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0eb65a248c32dbde15a207a37950293795f15481a17eafa309ea2892002d5e58.jpg", + "image_caption": [ + "EDVR" + ], + "image_footnote": [], + "bbox": [ + 270, + 201, + 468, + 233 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/6f7cd5e8d1f7979a0e26f0f3197d3d2937dcda6ed1a02827ad537be462ecd5eb.jpg", + "image_caption": [ + "IconVSR", + "BasicVSR ++ MFPI(Ours) HR", + "Figure 8: Challenging scenario on UDM10 [65]. Our method produces much clearer text and sharper edges." + ], + "image_footnote": [], + "bbox": [ + 270, + 244, + 468, + 273 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.3. Ablation Studies", + "text_level": 1, + "bbox": [ + 77, + 351, + 240, + 365 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This subsection gives a series of ablation studies to study the effectiveness of each component of MFPI. The evaluations were performed on the REDS4 dataset [38] trained on image patches of size $180 \\times 320$ for $6 \\times 10^{5}$ iterations. BasicVSR++ is utilized as the baseline.", + "bbox": [ + 75, + 374, + 468, + 442 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "A. Individual components. An ablation study is conducted by progressively adding SFE, EFE and the auxiliary branch to study the influence of different network blocks in our MFPI. Besides, we also investigate the effectiveness of the proposed privilege training and compare it with knowledge distillation (KD), which is another popular neural network training method. As shown in Table 2a: (a) $0.16\\mathrm{dB}$ and $0.13\\mathrm{dB}$ PSNR improvements can be obtained by using SFE and EFE individually. Besides, $0.02\\mathrm{dB}$ further PSNR improvements can be obtained by combining the two methods with the auxiliary branch. (b) Privilege training leads to $0.12\\mathrm{PSNR}$ improvements while KD leads to $0.38\\mathrm{dB}$ PSNR reduction, indicating the traditional model training method fails in VSR while our method leads to significant performance benefits. As Table 2a suggests, combining all the components yields the best performance vs. complexity tradeoff $(32.81\\mathrm{dB},7.34\\mathrm{M},$ and $281.25\\mathrm{G})$ compared to employing single or partial components.", + "bbox": [ + 75, + 454, + 468, + 704 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "B. Ablation on SFE. We further study the performance of our proposed SFE in Table 2b with different variants: only FFT, FFT with learnable filter, the split input with FL and original feature, the split operator with FL and batch normalization, the split operator with FL and instance normalization. Then, we incrementally added different DWConv layers on top of the existing components, such as $3 \\times 3$ , $7 \\times 7$ , $11 \\times 11$ , and $21 \\times 21$ . Besides, we only substituted the FFT with the original feature while keeping the LF, IN, and DWConv $21 \\times 21$ (-w/o FFT). Experimental results show that: (i) Only adding FFT to Base leads to 0.04 PSNR drop,", + "bbox": [ + 75, + 713, + 468, + 866 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "indicating that only utilizing Fourier transform cannot boost performance. (ii) Using the learnable filter leads to 0.07 dB improvements, which account for $41\\%$ performance benefits, indicating the learnable filter can improve the representation ability of FFT. (iii) Splitting the features into FFT and IN branches leads to 0.07 dB PSNR benefits, indicating that IN can help the model preserve scale information and prevent covariance shifts. (iv) DWConv with $21 \\times 21$ kernel performs better than other kernels, indicating a larger kernel is necessary. (v) SFE without FFT achieves only 31.93 dB PSNR, indicating FFT plays an essential role in SFE.", + "bbox": [ + 497, + 125, + 890, + 277 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "C. Ablation on EFE. To evaluate different DCT basis functions in the EFE, we have compared our method with four different DCT variants, which are DCT initialization with fixed coefficients (DF), DCT initialization with learnable filter (DL), DF and DL added energy function, respectively. Experimental results show that: (i) Our method achieves the best PSRN, which demonstrates the effectiveness of using a learnable filter and the energy function. (ii) Removing DCT from EFE leads to 0.43 dB PSNR drop, which indicates EFE is necessary. (iii) EFE with DWConv 11x11 kernel achieves the best PSNR than other DWConv kernels, indicating that a relatively larger kernel tends to achieve better performance.", + "bbox": [ + 497, + 287, + 892, + 467 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "D. Privilege Training As shown in Table 2a, 0.12 dB PSNR improvements can be obtained by applying PT to our model, which is 0.50 higher than KD. To further study its effectiveness, we have compared PT with the other six popular model training methods in Table 3 on BasicVSR [2]. It is observed that four of the previous methods do not bring any performance benefits but lead to significant PSNR and SSIM drop. PISR leads to 0.04 dB PSNR and 0.0009 SSIM improvements, which are 0.14 dB and 0.0022 lower than PT in PSNR and SSIM, respectively. Besides, PT can be easily implemented without a pre-trained teacher model.", + "bbox": [ + 497, + 476, + 890, + 629 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "E. Feature Visualization Visualization of intermediate features in MFPI is shown in Figure 9. It is observed that: (1) The feature map significantly reduces noise after MFE, indicating that MFE effectively suppresses noise information. (2) SFE can capture object motion and extract spatial features in the frequency domain. (3) EFE focuses on the fine-grained texture and details of the input feature, as shown in the red arrow and circle. (4) Moreover, the MFE effectively fuses the multi-frequency feature and enhances the representation ability.", + "bbox": [ + 497, + 638, + 890, + 776 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 497, + 787, + 618, + 802 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we have proposed a novel VSR model referred to as MFPI, which consists of a multi-frequency representation enhancement module (MFE) and a privilege training method. MFE is utilized to aggregate informa", + "bbox": [ + 497, + 809, + 890, + 866 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "12821", + "bbox": [ + 465, + 885, + 502, + 897 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/d29518a02d046aad2d3c1c68bd897d34d1afd457eac03ba5e298d06fb9f05ec4.jpg", + "table_caption": [ + "Table 2: Ablation studies. Subtables 2a, 2b, and 2c contain components that are defined in Sec. 3.2 and 3.3. We conduct ablation experiments on various components of SFE and EFE, such as FFT/DCT, split operator, learnable filter, BN/IN, energy function, and different coefficients. We also evaluate the effects of different kernel sizes using DW-Conv. Additionally, we employ knowledge distillation [12] or privilege training (PT) to improve our results." + ], + "table_footnote": [], + "table_body": "
BaseMFETrainingPSNR (dB)Params (M)FLOPs (G)
SFEEFEAuxKDPT
✓32.397.32280.59
✓✓32.557.34280.76
✓✓32.527.33280.68
✓✓✓32.677.34280.86
✓✓✓✓32.697.34281.25
✓✓✓✓✓32.317.34281.25
✓✓✓✓✓32.817.34281.25
", + "bbox": [ + 80, + 245, + 467, + 356 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/caa2452404a354f8cfa898d4543dc10bcd529400c67fa60e13ee294e724ec2d7.jpg", + "table_caption": [ + "(a) Individual components." + ], + "table_footnote": [], + "table_body": "
VariantPSNR
Base + FFT32.35
Base + FFT w/. Learnable filter32.48
Base + FFT w/. Learnable filter + original feature32.49
Base + FFT w/. Learnable filter + BN32.43
Base + FFT w/. Learnable filter + IN32.52
Base + FFT w/. Learnable filter + IN + DWConv 3 × 332.48
Base + FFT w/. Learnable filter + IN + DWConv 7 × 732.52
Base + FFT w/. Learnable filter + IN + DWConv 11 × 1132.51
Base + FFT w/. Learnable filter + IN + DWConv 21 × 21 (Our SFE)32.55
Base + w/. Learnable filter + IN + DWConv 21 × 2131.93
", + "bbox": [ + 80, + 375, + 467, + 497 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/352994fb6f1c80049cf246493577855da85ce7c18056f50f31d337722b244221.jpg", + "table_caption": [ + "(b) Effects of the SFE branch." + ], + "table_footnote": [], + "table_body": "
VariantPSNR
Base + Energy function32.40
Base + DCT w/. Fixed coefficients32.32
Base + DCT w/. Learnable filter32.41
Base + DCT w/. Fixed coefficients + Energy function32.37
Base + DCT w/. Learnable filter + Energy function32.50
Base + DCT w/. Learnable filter + Energy function + DWConv 3 × 332.42
Base + DCT w/. Learnable filter + Energy function + DWConv 7 × 732.40
Base + DCT w/. Learnable filter + Energy function + DWConv 11 × 11 (Our EFE)32.52
Base + DCT w/. Learnable filter + Energy function + DWConv 21 × 2132.43
Base + w/. Learnable filter + Energy function + DWConv 11 × 1132.07
", + "bbox": [ + 80, + 517, + 467, + 621 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/80eed0450f7d8ae9423672e94e957d215863e09366ec6d8a06fe86cafe7b3ae2.jpg", + "table_caption": [ + "(c) Effects of the EFE branch.", + "Table 3: Comparison between the proposed privilege training and previous training methods with BasicVSR on [38]." + ], + "table_footnote": [], + "table_body": "
MethodNeeds Teacher?PSNRSSIM
BasicVSR✓31.580.8940
+ Deep Supervision [23]×31.580.8941
+ Self-KD [67]×31.470.8914
+ Hinton KD [12]✓31.260.8883
+ FitNet [44]✓31.520.8934
+ PISR [24]✓31.620.8949
+ Ours×31.760.8971
", + "bbox": [ + 78, + 694, + 468, + 799 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "tion in the frequency domain by operating the spatial- and energy-frequency components via SFE and EFE. It enables CNN-based VSR models to capture long-range dependen", + "bbox": [ + 75, + 824, + 468, + 866 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/25ccaebb90855998f28169a9c3cb689b3eca65c67ea50dfebb351532de33fcce.jpg", + "image_caption": [ + "Figure 9: Visualization of the features in MFPI on images from REDS4[38]. The red dot curve denotes the change in spatial information at different locations of the same object." + ], + "image_footnote": [], + "bbox": [ + 502, + 125, + 890, + 343 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "cies with very minor additional parameters and computations. Besides, we also propose to improve the performance of VSR from a training perspective by introducing privilege training, which contributes orthogonal effects to our frequency modules. We hope that this paper may promote more research that studies VSR from the perspective of frequency methods and model training methods.", + "bbox": [ + 497, + 427, + 890, + 524 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Future Work", + "text_level": 1, + "bbox": [ + 499, + 549, + 635, + 564 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In the future, exploring MFPI in a real-world scenario would be an exciting direction, which offers a new valuable perspective on our proposed MFEI performance. We speculate that our frequency methods will be useful for real-scenario tasks and a broader investigation of it has provided additional depth to our study. We will continue to (1) evaluate MFPI on more challenging datasets such as RealVSR [63], and (2) deploy MFPI on edge devices and evaluate its performance. We are actively working on conducting the requested experiments that can further strengthen our conclusions.", + "bbox": [ + 497, + 577, + 890, + 729 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 499, + 755, + 660, + 771 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "The authors acknowledge the financial support from the National Key R&D Program of China (No.2021ZD0113805). We appreciate the comments from the seminar participants at the Center for Deep Learning of Computer Vision Research at China Agricultural University, which improves the manuscript significantly.", + "bbox": [ + 497, + 783, + 890, + 866 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "12822", + "bbox": [ + 465, + 885, + 505, + 897 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 124, + 173, + 138 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Jose Caballero, Christian Ledig, Andrew Aitken, Alejandro Acosta, Johannes Totz, Zehan Wang, and Wenzhe Shi. Real-time video super-resolution with spatio-temporal networks and motion compensation. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), pages 4778-4787, 2017. 7", + "[2] Kelvin CK Chan, Xintao Wang, Ke Yu, Chao Dong, and Chen Change Loy. 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In Proceedings of the AAAI Conference on Artificial Intelligence, volume 33, pages 5981-5988, 2019. 1" + ], + "bbox": [ + 502, + 127, + 890, + 755 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "12825", + "bbox": [ + 465, + 887, + 504, + 897 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/Multi-Frequency Representation Enhancement with Privilege Information for Video Super-Resolution/80575c27-91e5-4c67-9202-9382a183799d_model.json b/2023/Multi-Frequency Representation Enhancement with Privilege Information for Video Super-Resolution/80575c27-91e5-4c67-9202-9382a183799d_model.json new file mode 100644 index 0000000000000000000000000000000000000000..efbd3d08f05c47ad9ced3cdccd881085742d605f --- /dev/null +++ b/2023/Multi-Frequency Representation Enhancement with Privilege Information for Video Super-Resolution/80575c27-91e5-4c67-9202-9382a183799d_model.json @@ -0,0 +1,3403 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.13, + 0.051, + 0.201, + 0.085 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.254, + 0.049, + 0.79, + 0.062 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation." + }, + { + "type": "header", + "bbox": [ + 0.334, + 0.063, + 0.71, + 0.075 + ], + "angle": 0, + "content": "Except for this watermark, it is identical to the accepted version;" + }, + { + "type": "header", + "bbox": [ + 0.305, + 0.076, + 0.74, + 0.088 + ], + "angle": 0, + "content": "the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.175, + 0.162, + 0.797, + 0.205 + ], + "angle": 0, + "content": "Multi-Frequency Representation Enhancement with Privilege Information for Video Super-Resolution" + }, + { + "type": "text", + "bbox": [ + 0.186, + 0.229, + 0.251, + 0.244 + ], + "angle": 0, + "content": "Fei Li *" + }, + { + "type": "text", + "bbox": [ + 0.102, + 0.246, + 0.34, + 0.263 + ], + "angle": 0, + "content": "China Agricultural University" + }, + { + "type": "text", + "bbox": [ + 0.145, + 0.265, + 0.298, + 0.277 + ], + "angle": 0, + "content": "leefly072@126.com" + }, + { + "type": "text", + "bbox": [ + 0.435, + 0.23, + 0.569, + 0.246 + ], + "angle": 0, + "content": "Linfeng Zhang *" + }, + { + "type": "text", + "bbox": [ + 0.42, + 0.246, + 0.585, + 0.262 + ], + "angle": 0, + "content": "Tsinghua University" + }, + { + "type": "text", + "bbox": [ + 0.378, + 0.265, + 0.629, + 0.277 + ], + "angle": 0, + "content": "zhanglinfeng1997@outlook.com" + }, + { + "type": "text", + "bbox": [ + 0.725, + 0.23, + 0.808, + 0.245 + ], + "angle": 0, + "content": "Zikun Liu" + }, + { + "type": "text", + "bbox": [ + 0.665, + 0.246, + 0.868, + 0.263 + ], + "angle": 0, + "content": "Samsung Research China" + }, + { + "type": "text", + "bbox": [ + 0.672, + 0.265, + 0.862, + 0.277 + ], + "angle": 0, + "content": "zikun.liu@samsung.com" + }, + { + "type": "text", + "bbox": [ + 0.301, + 0.285, + 0.372, + 0.299 + ], + "angle": 0, + "content": "Juan Lei" + }, + { + "type": "text", + "bbox": [ + 0.235, + 0.301, + 0.439, + 0.317 + ], + "angle": 0, + "content": "Samsung Research China" + }, + { + "type": "text", + "bbox": [ + 0.248, + 0.32, + 0.428, + 0.333 + ], + "angle": 0, + "content": "juan.lei@samsung.com" + }, + { + "type": "text", + "bbox": [ + 0.565, + 0.285, + 0.669, + 0.299 + ], + "angle": 0, + "content": "Zhenbo Li" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.301, + 0.735, + 0.318 + ], + "angle": 0, + "content": "China Agricultural University" + }, + { + "type": "text", + "bbox": [ + 0.55, + 0.32, + 0.685, + 0.332 + ], + "angle": 0, + "content": "lizb@cau.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.365, + 0.314, + 0.38 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.394, + 0.474, + 0.645 + ], + "angle": 0, + "content": "CNN's limited receptive field restricts its ability to capture long-range spatial-temporal dependencies, leading to unsatisfactory performance in video super-resolution (VSR). To tackle this challenge, this paper presents a novel multi-frequency representation enhancement module (MFE) that performs spatial-temporal information aggregation in the frequency domain. Specifically, MFE mainly includes a spatial-frequency representation enhancement branch which captures the long-range dependency in the spatial dimension, and an energy frequency representation enhancement branch to obtain the inter-channel feature relationship. Moreover, a novel model training method named privilege training is proposed to encode the privilege information from high-resolution videos to facilitate model training. With these two methods, we introduce a new VSR model named MFPI, which outperforms state-of-the-art methods by a large margin while maintaining good efficiency on various datasets, including REDS4, Kobe, Vid4, and UDM10." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.684, + 0.21, + 0.699 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.708, + 0.47, + 0.834 + ], + "angle": 0, + "content": "Video super-resolution (VSR), which restores high-resolution (HR) video frames from their highly related but unaligned low-resolution (LR) video frames, is well-desired in various real-world applications [11, 2]. Compared with single image super-resolution (SISR), VSR is much more challenging as it aggregates information from multiple related but misaligned frames in the input video. Hence, an ideal VSR model is expected to leverage the spatial information from single images but also integrate the temporal" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.363, + 0.889, + 0.571 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.584, + 0.892, + 0.627 + ], + "angle": 0, + "content": "Figure 1: VSR performance comparison on UDM10 [65] in terms of PSNR (dB), runtime (ms), and parameters (M). MFPI outperforms SOTA methods with high efficiency." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.656, + 0.862, + 0.671 + ], + "angle": 0, + "content": "semantic features from multiple frames [45, 50, 18, 3]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.673, + 0.893, + 0.868 + ], + "angle": 0, + "content": "CNN-based models have become the standard choice for VSR due to their simplicity and efficiency. While recent advances in CNN-based VSR, such as residual learning [2, 73], dense connections[59], hierarchical structures [20], and multi-scale frameworks [63, 34, 48], have shown impressive performance, some potential problems still exist. Firstly, CNN's limited receptive field hinders it from modeling long-range spatial dependencies, making it unable to capture complex semantic information. Secondly, convolutional filters have fixed scales and weights, limiting their performance on large motions and adaptability to diverse inputs. In comparison, with the advantages of self-attention layers, ViTs are effective in processing inputs with long-term spatial dependencies. However, the stack" + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.843, + 0.47, + 0.867 + ], + "angle": 0, + "content": "* The first two authors contribute equally. This work is done during the internship of F. Li in Samsung. Z. Li is the corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "12814" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.127, + 0.468, + 0.182 + ], + "angle": 0, + "content": "of self-attention layers is accompanied with a large computation budget, which results in inferior inference efficiency on edge devices [29]; A natural question arises: can CNNs capture long-range dependencies like ViTs?" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.184, + 0.468, + 0.39 + ], + "angle": 0, + "content": "In this paper, we propose to answer this question from a frequency perspective. Thanks to their ability to capture global representation, frequency-based models have been widely utilized in single image processing [72, 41, 71]. Unfortunately, their performance in video super-resolution (VSR) is usually limited due to several reasons. (1) Compared with single images, videos are composed of multiple related but misaligned images, which contain both spatial and temporal information. However, traditional frequency methods have fixed paradigms and coefficients [56, 66, 40], making them not able to capture the complex information in videos. (2) Traditional frequency methods are sensitive to the noise in images [64, 14]. This disadvantage becomes more fatal in videos where the noise of different frames can be accumulated." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.393, + 0.468, + 0.697 + ], + "angle": 0, + "content": "To address these challenges, we propose a novel module named multi-frequency representation enhancement (MFE), which aggregates information in the frequency domain. Unlike convolutional and self-attention layers that operate in the feature space, MFE directly manipulates the energy feature map in the frequency domain through three branches: 1) a spatial-frequency representation enhancement branch (SFE) that utilizes a Fast Fourier Transform (FFT) and large kernel convolution layer to capture arbitrary interactions among spatial and long-range dependent features, 2) an energy-frequency representation enhancement branch (EFE) that employs a novel energy discrete cosine transform (DCT) to improve representation and explore potentially useful frequency components, and 3) a pair of convolution layers that leverage large kernels to obtain global range-interact features with stronger shape bias. Compared with the previous frequency methods, the learnable filter in SFE enables FFT to capture both spatial and temporal information, and the energy function in EFE can alleviate the noise accumulated in multiple video frames. Moreover, MFE only contains \\(0.02\\mathrm{M}\\) parameters, making it affordable for edge devices." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.699, + 0.468, + 0.822 + ], + "angle": 0, + "content": "Besides MFE, we further propose a novel model training method named privilege training (PT) to facilitate the training of VSR models. Motivated by previous research in learning using privilege information (LUPI) [53], we propose to apply a trainable encoding module to encode the privilege information from HR videos and then employ them to obtain a good initialization for VSR models. Sufficient experiments demonstrate the effectiveness of privilege training on both our model and the other VSR models." + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.825, + 0.468, + 0.867 + ], + "angle": 0, + "content": "With MFE and privilege training, we introduce a novel VSR model referred to as MFPI. Extensive experimental results have demonstrated that MFPI outperforms eighteen" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.127, + 0.892, + 0.21 + ], + "angle": 0, + "content": "previous methods by a clear margin in six VSR benchmarks. For instance, on UDM10, compared with BasicVSR++ [4], which has similar parameters and runtime with MFPI, MFPI achieves 0.36 dB higher PSNR improvements on UDM10 BD degradation, as shown in Figure 1. To sum up, the main contributions in this paper can be summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.222, + 0.891, + 0.277 + ], + "angle": 0, + "content": "- We propose multi-frequency representation enhancement (MFE), a module that effectively aggregates information in the frequency domain by operating the spatial- and energy-frequency components." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.286, + 0.891, + 0.326 + ], + "angle": 0, + "content": "- We propose privilege training, which encodes the privilege information from the HR videos to boost the performance of VSR models." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.337, + 0.891, + 0.379 + ], + "angle": 0, + "content": "- Abundant experiments demonstrate the effectiveness of MFPI on four datasets, including REDS4, Vimeo, Vid4, and UDM10 in both BI and BD degradation." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.222, + 0.891, + 0.379 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.392, + 0.64, + 0.406 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.415, + 0.717, + 0.429 + ], + "angle": 0, + "content": "2.1. Video Super Resolution" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.436, + 0.892, + 0.699 + ], + "angle": 0, + "content": "Different from SISR, VSR typically produces higher-quality results by utilizing information from neighboring frames. Recently, learning-based approaches have been highly effective in solving the problem of VSR [16, 4]. The main challenge for VSR is how to correctly fuse auxiliary frames in the presence of dynamic content and object motion. To address this problem, abundant methods have been proposed to explicitly use optical flow [55], deformable convolution [57, 50, 3], and homography [18] to align neighbor frames. However, estimating accurate optical flow or transformation is still challenging in large motions. Recently, some methods have been proposed to learn the spatial correspondence across different frames to tackle this challenge [25, 13]. However, these methods have limited performance in VSR since they cannot capture information between adjacent locations or long-range interactions [47, 41]. To address this problem, we introduce a spatial-frequency representation enhancement branch that models long-range spatial and temporal dependencies." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.707, + 0.776, + 0.722 + ], + "angle": 0, + "content": "2.2. Learning in Frequency Domain" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.728, + 0.892, + 0.866 + ], + "angle": 0, + "content": "Due to the difficulty of distinguishing high-frequency textures from artifacts, fruitful methods [70, 6, 14] have been introduced to decouple them in the frequency space and reconstruct the high-quality textures. For instance, Zhou et al. proposed a deep Fourier up-sampling method to recover the resolution in the frequency domain [72]. Guo et al. utilized the wavelet technique to simplify the mapping between the LR and HR images, reducing the artificial blocks and recovering the edge's information [10]. Motivated by their success, abundant works have tried to" + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "12815" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.126, + 0.473, + 0.334 + ], + "angle": 0, + "content": "apply frequency methods to SR. Dario et al. proposed a Fourier space supervision loss to improve restoration results [6]. Qiu et al. designed a fine-grained self-attention module in the space-frequency domain, which reconstructs the real visual texture without artifacts [41]. However, the images that are directly transformed into the frequency domain still face obstacles as follows: (1) Decomposing features into different frequency components usually lacks local correlation information in the channel dimension, making it difficult to utilize the useful frequency components [40]. (2) Non-parametric frequency-based methods are easily susceptible to noise and image scale factors [35]. To address the above problems, this paper proposes to combine the advantages of the energy function and frequency-based representations by using DCT with learnable filters." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.354, + 0.405, + 0.37 + ], + "angle": 0, + "content": "2.3. Learning Using Privilege Information" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.379, + 0.473, + 0.656 + ], + "angle": 0, + "content": "Learning using privilege information (LUPI) was first proposed by Vapnik et al. to employ the privilege information provided by a teacher model in support vector machine [53]. Generally speaking, LUPI aims to improve the performance of a model by using privilege information, which is utilized during training but not required during inference. Vapnik et al. further utilized LUPI to accelerate the inference speed of SVMs by similarity control and knowledge transfer [52]. Motivated by the success of knowledge distillation [12] on deep neural networks, recently, David et al. proposed generalized distillation, which combines knowledge distillation with learning with privilege information theoretically [32]. Recently, label-guided auxiliary was introduced to apply LUPI to point cloud-based 3D detection by using the privilege information from annotations [15]. Lee et al. proposed PISR, which introduces LUPI to single image super-resolution by using variational knowledge distillation [24]. Moreover, LUPI has also been utilized in semi-supervised learning [7], domain adaptation [37], speech recognition [36] and so on." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.473, + 0.868 + ], + "angle": 0, + "content": "The most related work of the privilege training in our method is PISR [24], which is proposed for knowledge distillation on single image super-resolution. Their main difference is that: (1) PISR is proposed for SISR for model compression while our method is proposed for VSR to improve the quality of restoration. (2) Besides, PISR is a knowledge distillation method which mainly leverages the privilege information with distillation loss. In contrast, our method leverages the privilege information by sharing model weights. (3) PISR implicitly encodes the privilege information via the reconstruction of LR images while our method explicitly encodes privilege information from HR videos with a trainable network. Besides, ablation studies in Table 3 also demonstrate that our method leads to significantly higher performance than PISR." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.125, + 0.637, + 0.141 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.148, + 0.757, + 0.163 + ], + "angle": 0, + "content": "3.1. Overall Framework for VSR" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.17, + 0.892, + 0.448 + ], + "angle": 0, + "content": "Following the previous work [4], we adopt the recurrent bidirectional propagation as the baseline model. Based on its architecture, we propose a novel VSR model termed MFPI, which consists of a multi-frequency representation enhancement module (MFE) to improve the LR frames representation in the frequency domain, and a novel VSR model training method named privilege training which encodes privilege information from HR frames to facilitate model training. The overall architecture is shown in Figure 2: (1) The VSR model extracts features from the LR frames images to reconstruct the HR frames images. (2) Residual blocks and MFE are employed to extract the feature \\( f_{i}^{j} \\) from the LR images, where \\( f_{i}^{j} \\) denotes the feature at \\( i_{th} \\) timestamp in the \\( j_{th} \\) propagation branch. (3) The flow-guided deformable alignment block (FDA) aligns the neighboring features \\( f_{i-1}^{j} \\) and \\( f_{i-2}^{j} \\). And the pixel-shuffle operator is employed to perform upsampling \\( 4 \\times \\) scales from LR to HR frames. Besides, learning privilege information boosts the performance of our VSR models during training, as shown in Figure 3." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.456, + 0.857, + 0.485 + ], + "angle": 0, + "content": "3.2. MFE: A Multi-Frequency Representation Enhancement Module" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.492, + 0.892, + 0.756 + ], + "angle": 0, + "content": "As depicted in Figure 2 (b), we design a multi-frequency representation enhancement (MFE) to improve the representation ability and aggregate spatial-temporal information in VSR architecture. MFE is a plug-in-play building block which adopts a multi-branch structure to capture multifrequency representation [9]. Concretely, it first encodes the input features with a depthwise convolution (DWConv) layer [68] and then processes them with three different branches, including 1) a spatial-frequency representation enhancement branch to capture the spatial-frequency information and long-range dependence features, 2) an energy-frequency representation enhancement branch to improve the representation ability and model the inter-channel relationship in the frequency domain, and 3) an auxiliary branch with a pair of \\(7 \\times 1\\) and \\(1 \\times 7\\) DWConv to inject the inductive bias and facilitate training [8, 31]. Finally, a \\(1 \\times 1\\) convolution layer aggregates the diverse features from three branches, and the skip connection is employed to facilitate the convergence of MFE [30]." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.775, + 0.892, + 0.79 + ], + "angle": 0, + "content": "3.2.1 Spatial Frequency Representation Enhancement" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.797, + 0.892, + 0.869 + ], + "angle": 0, + "content": "As illustrated in Figure 2 (c), the spatial frequency representation enhancement (SFE) branch first employs a pair of \\(DWConv\\) to generate the feature map \\(f_{in}\\) from the input \\(x_{in} \\in \\mathbb{R}^{H \\times W \\times C}\\). Then, we split \\(f_{in}\\) into two parts \\(f_{mid1}, f_{mid2} \\in \\mathbb{R}^{h \\times w \\times c/2}\\) [26, 69]. The FFT layer pro" + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "12816" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.099, + 0.123, + 0.805, + 0.304 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.207, + 0.307, + 0.404, + 0.318 + ], + "angle": 0, + "content": "(a) The Overall Framework of MFPI" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.323, + 0.477, + 0.416 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.128, + 0.419, + 0.429, + 0.43 + ], + "angle": 0, + "content": "(c) SFE: Spatial Frequency Representation Enhancement" + }, + { + "type": "image_caption", + "bbox": [ + 0.556, + 0.306, + 0.854, + 0.318 + ], + "angle": 0, + "content": "(b) MFE: Multi-frequency Representation Enhancement" + }, + { + "type": "image", + "bbox": [ + 0.487, + 0.327, + 0.89, + 0.41 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.547, + 0.419, + 0.851, + 0.43 + ], + "angle": 0, + "content": "(d) EFE: Energy Frequency Representation Enhancement" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.441, + 0.893, + 0.525 + ], + "angle": 0, + "content": "Figure 2: (a) An overview framework of MFPI. The blue dot line denotes the bilinear upsampling operator. The red curve denotes second-order propagation. \"FDA\" denotes the flow-guided deformable alignment block [4]. The green block denotes the proposed multi-frequency representation enhancement (MFE). (b) An overview of the MFE. (c) The details of the spatial-frequency representation enhancement branch in MFE extract spatial-level and long-range dependencies. (d) The details of the energy-frequency representation enhancement branch. \\( e_{i,j}^{*} \\) denotes the energy feature. Note that the 'FC layer' consists of a sequence of the 'linear-LReLU-linear-LReLU' operator. DWConv denotes the depthwise convolution [68]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.549, + 0.469, + 0.575 + ], + "angle": 0, + "content": "cesses \\( f_{mid1} \\) represents different spatial dependence information as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.167, + 0.586, + 0.469, + 0.603 + ], + "angle": 0, + "content": "\\[\nf r e q = \\mathcal {F} \\left[ f _ {\\text {m i d} 1} \\right] \\in \\mathbb {C} ^ {h \\times w \\times c / 2} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.614, + 0.469, + 0.721 + ], + "angle": 0, + "content": "where \\(c, h, w\\) denote the input channel, height, width of the feature maps, respectively. \\(\\mathcal{F}[\\cdot]\\) denotes the 2D FFT, \\(freq\\) represents the frequency feature of \\(f_{mid1}\\). To make SFE adaptive to diverse features [43, 54], we modulate the \\(freq\\) multiplies with a learnable filter \\(L \\in \\mathbb{C}^{h \\times w \\times c/2}\\) in the frequency domain: \\(\\tilde{freq} = freq \\times L\\). The inverse FFT transfers the modulated frequency feature back to the spatial domain:" + }, + { + "type": "equation", + "bbox": [ + 0.198, + 0.721, + 0.469, + 0.745 + ], + "angle": 0, + "content": "\\[\n\\tilde {f _ {m i d 1}} \\leftarrow \\mathcal {F} ^ {- 1} \\left[ f \\tilde {r e q} \\right] \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.469, + 0.811 + ], + "angle": 0, + "content": "Finally, the output feature \\( f_{out} \\) is obtained by concatenating with an instance normalization (IN) [51] layer, which prevents covariance shift and preserves the scale information: \\( f_{out} = \\text{Concat}\\left(f_{mid1}, \\text{IN}\\left(f_{mid2}\\right)\\right) \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.812, + 0.469, + 0.867 + ], + "angle": 0, + "content": "It is also worth noting that in our implementation: (1) SFE utilizes a relatively large local window of \\(DWConv\\) \\((e.g., 21 \\times 1, 1 \\times 21)\\) to capture the long-range spatial dependencies from features. (2) Besides, a learnable Fourier" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.549, + 0.892, + 0.867 + ], + "angle": 0, + "content": "transform with IN can exhibit clear patterns and generalizations in the frequency domain. Hence, the proposed SFE branch tends to be more efficient than directly utilizing Fourier transforms in the spatial-temporal dimension (Table 2b). (3) Considering that FFT has less computation than DFT, we employ FFT in SFE as the frequency transformation to improve model representation. Moreover, the Fourier domain has the nature of global modeling [54]. Hence, computation on frequency bands implies information aggregation over all the spatial locations of the input images. Specifically, in our SFE, FFT is performed over the whole feature map across all the spatial locations, which is equivalent to the global receptive field of the whole feature. (4) SFE splits features into two branches to improve computational efficiency. Specifically, this split operator enables SFE to capture and combine different aspects or representations of the input data. One part focus on the spatial frequency characteristics or patterns, and the other part act as a form of regularization by introducing additional constraints, such as instance normalization. Their outputs can be concatenated to create a richer and more comprehensive representation. This can enhance the SFE's ability to learn complex relationships and improve its overall performance." + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "12817" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.126, + 0.47, + 0.182 + ], + "angle": 0, + "content": "Besides, this two-branch design is also similar to the idea of group convolution and CSN [71], which is a well-known technique of efficient neural networks. Please refer to supplementary materials for theoretical analysis." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.201, + 0.469, + 0.215 + ], + "angle": 0, + "content": "3.2.2 Energy Frequency Representation Enhancement" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.223, + 0.469, + 0.376 + ], + "angle": 0, + "content": "Considering that the frequency methods with a learning filter can be more generic and flexible interactions among spatial locations from diverse images, we introduce an energy function to reweight the input feature and utilize the learnable filter with DCT to represent the rich inter-channel relationship [40]. The architecture of the energy frequency representation enhancement (EFE) is illustrated in Figure 2 (d). More specifically, EFE first utilizes a pair of \\(DWConv\\) (e.g., \\(11 \\times 1,1 \\times 11\\)) to generate the feature map \\(f\\). Then, we calculate the mean \\(\\hat{\\mu}\\) and variance \\(\\hat{\\sigma}^2\\) of \\(f\\), and the energy value [62] can be obtained by minimizing the following:" + }, + { + "type": "equation", + "bbox": [ + 0.17, + 0.386, + 0.47, + 0.421 + ], + "angle": 0, + "content": "\\[\ne _ {i, j} = \\frac {4 (\\hat {\\sigma} ^ {2} + \\delta)}{(t _ {i , j} - \\hat {\\mu}) ^ {2} + 2 \\hat {\\sigma} ^ {2} + 2 \\delta} \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.43, + 0.469, + 0.501 + ], + "angle": 0, + "content": "where \\(\\delta\\) is the hyper-parameter, \\(e_{i,j}\\) denote the energy value of target pixel \\(t_{i,j}\\), \\(i\\in \\{0,1,\\dots ,H - 1\\}\\), \\(j\\in \\{0,1,\\dots ,W - 1\\}\\). The energy feature is obtained by grouping all the \\(e_{i,j}\\) across spatial and channel levels, which rescale the energy value to restrict too large energy value:" + }, + { + "type": "equation", + "bbox": [ + 0.129, + 0.511, + 0.469, + 0.549 + ], + "angle": 0, + "content": "\\[\ne _ {i, j} ^ {*} = \\text {L e a k y R e L U} \\left(\\frac {1}{\\sum_ {i \\neg = 0} ^ {h} \\sum_ {j \\neg = 0} ^ {w} e _ {i , j}}\\right) \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.555, + 0.469, + 0.597 + ], + "angle": 0, + "content": "To further enrich the representation ability of EFE, we employ the DCT technique to convert the energy features into the frequency domain as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.135, + 0.608, + 0.469, + 0.647 + ], + "angle": 0, + "content": "\\[\n\\mathcal {F} _ {c} (i, j) = \\frac {2}{\\sqrt {H W}} \\alpha (i) \\alpha (j) \\sum_ {h = 0} ^ {H - 1} \\sum_ {w = 0} ^ {W - 1} e _ {i, j} ^ {*} \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.103, + 0.67, + 0.469, + 0.702 + ], + "angle": 0, + "content": "\\[\n\\mathcal {K} _ {h, w} ^ {i, j} = \\cos \\left(\\frac {(2 h + 1) i \\pi}{2 H}\\right) \\cos \\left(\\frac {(2 w + 1) j \\pi}{2 W}\\right) \\tag {6}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.188, + 0.718, + 0.469, + 0.737 + ], + "angle": 0, + "content": "\\[\nf _ {c} ^ {h, w} = \\mathcal {K} _ {h, w} ^ {i, j} \\times \\mathcal {F} _ {c} \\left(e _ {i, j} ^ {*}\\right) \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.742, + 0.469, + 0.867 + ], + "angle": 0, + "content": "where \\(\\mathcal{F}_c\\) denotes DCT operation, \\(\\kappa\\) denotes the basis function of DCT, \\(\\alpha(x) = 1/\\sqrt{2}\\) for \\(x = 0\\) and \\(\\alpha(x) = 1\\) otherwise [46]. Finally, the output refined feature as follows: \\(f_{out} = f_c^{h,w} \\times x_{i,j}\\). Note that an element-wise multiplication between frequency-domain features and the learnable filters improves the representation ability and makes EFE flexible adaptive to different feature inputs. Besides, the FC layer in Figure 2 (d) consists of a sequence of the 'Linear-LeakyReLU-Linear-LeakyReLU' operators, which" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.127, + 0.892, + 0.223 + ], + "angle": 0, + "content": "convert the channel-wise feature into a scalar representation, which reduces the complexity and improves the effectiveness in the frequency domain. Different from the SFE branch, the EFE branch leverages the merits of the energy function and frequency components to improve the representation power and model the relationship among inter-channel dimensions, as shown in Figure 9." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.231, + 0.676, + 0.245 + ], + "angle": 0, + "content": "3.3. Privilege Training" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.252, + 0.892, + 0.584 + ], + "angle": 0, + "content": "Learning using privilege information is a well-known theory in machine learning, which shows that one can improve the performance of machine learning by using kinds of privilege information, which is available in training but not accessible during inference. Motivated by its effectiveness, in this paper, we propose a novel neural network training method for VSR, which is shown in Figure 3. By denoting the LR and corresponding HR videos as \\( x \\) and \\( y \\), respectively, the traditional training method can be formulated as \\( \\min \\mathbb{E}[|f(x) - y|] \\), where \\( f(\\cdot) \\) denotes the superresolution model. In contrast, in our method, we additionally introduce a lightweight neural network \\( \\mathcal{D} \\), which aims to encode the privilege information from the HR frames \\( y \\) to a tensor of privilege information \\( \\mathcal{D}(y) \\) which has the same shape with the LR frames \\( x \\). Then, we can denote a mixture of the LR images and the privilege information as \\( x^{*} = x + \\gamma \\cdot \\mathcal{D}(y) \\), where \\( \\gamma \\in [0,1] \\) is a parameter to balance the two items. During the training period, we gradually decrease \\( \\gamma \\) from 1 to 0. Hence, the VSR model is able to firstly learn a good representation by using the privilege information, and then gradually get rid of it. Note that since \\( \\gamma \\) is decreased to 0, the VSR model does not require any privilege information during inference. In summary, its objective of privilege training can be written as" + }, + { + "type": "equation", + "bbox": [ + 0.585, + 0.591, + 0.891, + 0.615 + ], + "angle": 0, + "content": "\\[\n\\underset {f, \\mathcal {D}} {\\arg \\min } \\mathbb {E} [ | f (x ^ {*}) - y | + | \\mathcal {D} (y) | ] \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.622, + 0.892, + 0.76 + ], + "angle": 0, + "content": "where the first loss item is the common reconstruction loss for VSR training. The second loss item is a regularization item which reduces the energy of privilege information to prevent the model from overusing the privilege information. Note that the regularization item is indispensable since without this item the VSR model may degenerate into a naive auto-encoder which reconstructs the HR images totally based on the privilege information. Note that \\(\\mathcal{D}\\) in our implementation is a stack of three convolutional layers followed with LeakyReLU." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.77, + 0.892, + 0.867 + ], + "angle": 0, + "content": "Why does privilege training work? The effectiveness of privilege information can be understood from the perspective of weight initialization. During the early training iterations, the model can quickly converge to a flat minima by using the privilege information. Then, by reducing \\(\\gamma\\), the privilege information gradually makes a less influence to the VSR model, and hence the VSR model can converge" + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "12818" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.139, + 0.124, + 0.831, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.275, + 0.893, + 0.304 + ], + "angle": 0, + "content": "Figure 3: The paradigm of the proposed learning using privilege information on VSR. \\(\\oplus\\) denotes a weighted addition between the privilege information and the LR frames." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.325, + 0.468, + 0.434 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.102, + 0.443, + 0.443, + 0.457 + ], + "angle": 0, + "content": "Figure 4: Visualization of the privilege information." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.485, + 0.47, + 0.651 + ], + "angle": 0, + "content": "stably. Secondly, the success of our method can also be understood as a special case of knowledge distillation, where the teacher model is trained with privilege information, the student model is trained with only the LR frames, and the knowledge distillation is applied by sharing the weights of the student and the teacher. Besides, Figure 4 visualizes the privilege information encoded during the training period. It is observed that most of privilege information concentrates on the pixels belonging to the objects and their edges, which are more important in the assessment of image quality. These privilege information is utilized to help VSR models to converge at the early training period." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.668, + 0.202, + 0.683 + ], + "angle": 0, + "content": "4. Experiment" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.692, + 0.267, + 0.707 + ], + "angle": 0, + "content": "4.1. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.714, + 0.471, + 0.867 + ], + "angle": 0, + "content": "Our model is trained for each task with \\(6 \\times 10^{5}\\) iterations using randomly cropped patches. We apply data augmentation techniques such as random horizontal and vertical flipping and \\(90^{\\circ}\\) rotation. The Adam optimizer [22] is used with an initial learning rate of \\(2 \\times 10^{-4}\\), which is steadily decreased to \\(1 \\times 10^{-7}\\) with cosine annealing learning rate decay [33]. \\(\\delta\\) is set to \\(1 \\times 10^{-6}\\) [62]. We employ SPyNet to predict optical flow in videos [42]. Each branch contains 7 residual blocks and 64 feature channels. The batch size is set to 4, and the input low-resolution (LR) frames are of patch size \\(64 \\times 64\\)." + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.325, + 0.892, + 0.486 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.5, + 0.892, + 0.541 + ], + "angle": 0, + "content": "Figure 5: Challenging scenario on REDS4 [38]. MFPI generates sharp edge in repeated structures of the windows and sharper texts." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.568, + 0.892, + 0.719 + ], + "angle": 0, + "content": "Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index Measure (SSIM) [58] between ground truth and restored videos are utilized as the metrics in our quantitative comparisons. We follow [4] to utilize REDS [38], Vimeo90K [60] as training set, and REDS4, Vimeo-90K-T [60], Vid4 [28], UDM10 [65], and Vimeo-90K as the test set. REDSval4 is utilized as the validation set. All models are tested with \\( 4 \\times \\) downsampling via two degradations - Bicubic (BI) and Blur Downsampling (BD). All experiments are implemented with PyTorch [39] and on two NVIDIA Tesla A100 GPUs." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.733, + 0.874, + 0.748 + ], + "angle": 0, + "content": "4.2. Comparisons with State-of-the-Art Methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.756, + 0.892, + 0.867 + ], + "angle": 0, + "content": "Qualitative Comparison We show the comparison of visual results in Figure. 5, 6, 7 and 8. It is observed that the results of prior works usually suffer from incomplete artifacts or blurred regions in the image. In contrast, our model restores sharper edges and finer detailed textures of the number plate in Figure 5 and the display board in Figure 6. Besides, MFPI is able to recover the edge of the small object in Figure 6. As shown in Figure 7 and 8, MFPI also shows" + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "12819" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.124, + 0.894, + 0.167 + ], + "angle": 0, + "content": "Table 1: Quantitative comparison (PSNR/SSIM). All results are calculated on Y-channel except REDS4 [38] (RGB-channel). The runtime is computed on an LR size of \\(180 \\times 320\\). A \\(4 \\times\\) upsampling is performed following previous studies. Blanked entries correspond to results not reported in previous works. Numbers in bold indicate the best performance." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.177, + 0.891, + 0.445 + ], + "angle": 0, + "content": "
ModelParams (M)Runtime (ms)BI degradationBD degradation
REDS4 [38]Vimeo-90K-T [60]Vid4[28]UDM10 [65]Vimeo-90-T [60]Vid4 [28]
Bicubic--26.14/0.729231.32/0.868423.78/0.634728.47/0.825331.30/0.868721.80/0.5246
VESPCN [1]----25.35/0.7557---
SPMC [49]----25.88/0.7752---
TOFlow [61]--27.98/0.799033.08/0.905425.89/0.765136.26/0.943834.62/0.9212-
FRVSR [45]5.1137---37.09/0.952235.64/0.931926.69/0.8103
DUF [21]5.897428.63/0.8251--38.48/0.960536.87/0.944727.38/0.8329
RBPN [11]12.2150730.09/0.859037.07/0.943527.12/0.818038.66/0.959637.20/0.9458-
EDVR-M [57]3.311830.53/0.869937.09/0.944627.10/0.818639.40/0.966337.33/0.948427.45/0.8406
EDVR [57]20.637831.09/0.880037.61/0.948927.35/0.826439.89/0.968637.81/0.952327.85/0.8503
PFNL [65]3.029529.63/0.850236.14/0.936326.73/0.802938.74/0.9627-27.16/0.8355
MuCAN [27]--30.88/0.875037.32/0.9465----
TGA [18]5.8384----37.59/0.951627.63/0.8423
RLSP [5]4.249---38.48/0.960636.49/0.940327.48/0.8388
RSDN [17]6.294---39.35/0.965337.23/0.947127.92/0.8505
RRN [19]3.445--38.96/0.9644-27.69/0.8488
BasicVSR [2]6.36331.42/0.890937.18/0.945027.24/0.825139.96/0.969437.53/0.949827.96/0.8553
IconVSR [2]8.77031.67/0.894837.47/0.947627.39/0.827940.03/0.969437.84/0.952428.04/0.8570
BasicVSR++ [4]7.37732.39/0.906937.79/0.953027.79/0.840040.72/0.972238.21/0.955029.04/0.8753
PSRT [47]13.481232.72/0.910638.27/0.953628.07/0.8485---
MFPI (Ours)7.37632.81/0.910638.28/0.953428.11/0.848141.08/0.974138.70/0.957929.34/0.8781
" + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.464, + 0.206, + 0.533 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.098, + 0.534, + 0.205, + 0.542 + ], + "angle": 0, + "content": "Sequence 00015,Clip 0864" + }, + { + "type": "image", + "bbox": [ + 0.207, + 0.464, + 0.338, + 0.494 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.225, + 0.495, + 0.257, + 0.502 + ], + "angle": 0, + "content": "Bicubic" + }, + { + "type": "image", + "bbox": [ + 0.34, + 0.464, + 0.404, + 0.494 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.35, + 0.495, + 0.394, + 0.502 + ], + "angle": 0, + "content": "BasicVSR" + }, + { + "type": "image", + "bbox": [ + 0.406, + 0.464, + 0.469, + 0.494 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.418, + 0.495, + 0.456, + 0.502 + ], + "angle": 0, + "content": "IconVSR" + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.503, + 0.206, + 0.532 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.21, + 0.503, + 0.246, + 0.532 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.212, + 0.533, + 0.267, + 0.541 + ], + "angle": 0, + "content": "BasicVSR++" + }, + { + "type": "image", + "bbox": [ + 0.248, + 0.503, + 0.299, + 0.532 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.267, + 0.533, + 0.293, + 0.541 + ], + "angle": 0, + "content": "" + }, + { + "type": "image", + "bbox": [ + 0.3, + 0.503, + 0.339, + 0.532 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.319, + 0.533, + 0.345, + 0.541 + ], + "angle": 0, + "content": "" + }, + { + "type": "image", + "bbox": [ + 0.342, + 0.503, + 0.394, + 0.532 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.346, + 0.533, + 0.398, + 0.541 + ], + "angle": 0, + "content": "MFPI(Ours)" + }, + { + "type": "image", + "bbox": [ + 0.406, + 0.503, + 0.469, + 0.532 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.429, + 0.533, + 0.445, + 0.541 + ], + "angle": 0, + "content": "HR" + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.546, + 0.206, + 0.613 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.093, + 0.614, + 0.199, + 0.623 + ], + "angle": 0, + "content": "Sequence 00010,Clip 0573" + }, + { + "type": "image", + "bbox": [ + 0.208, + 0.546, + 0.273, + 0.576 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.226, + 0.577, + 0.256, + 0.583 + ], + "angle": 0, + "content": "Bicubic" + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.546, + 0.338, + 0.576 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.293, + 0.577, + 0.321, + 0.583 + ], + "angle": 0, + "content": "EDVR" + }, + { + "type": "image", + "bbox": [ + 0.342, + 0.546, + 0.404, + 0.576 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.35, + 0.577, + 0.394, + 0.583 + ], + "angle": 0, + "content": "BasicVSR" + }, + { + "type": "image", + "bbox": [ + 0.406, + 0.546, + 0.469, + 0.576 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.419, + 0.577, + 0.455, + 0.583 + ], + "angle": 0, + "content": "IconVSR" + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.583, + 0.206, + 0.613 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.093, + 0.614, + 0.198, + 0.623 + ], + "angle": 0, + "content": "Sequence 00010, Clip 0573" + }, + { + "type": "image", + "bbox": [ + 0.208, + 0.583, + 0.273, + 0.613 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.215, + 0.614, + 0.268, + 0.622 + ], + "angle": 0, + "content": "BasicVSR++" + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.583, + 0.338, + 0.613 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.294, + 0.614, + 0.318, + 0.622 + ], + "angle": 0, + "content": "PSRT" + }, + { + "type": "image", + "bbox": [ + 0.342, + 0.583, + 0.404, + 0.613 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.347, + 0.614, + 0.398, + 0.622 + ], + "angle": 0, + "content": "MFPI(Ours)" + }, + { + "type": "image", + "bbox": [ + 0.406, + 0.583, + 0.469, + 0.613 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.429, + 0.614, + 0.445, + 0.622 + ], + "angle": 0, + "content": "HR" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.636, + 0.47, + 0.69 + ], + "angle": 0, + "content": "Figure 6: Challenging scenario on Vimeo-90K-T [60]. Compared to the other methods, Our method more effectively preserves while recovering the strip-like features in the skirts." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.718, + 0.47, + 0.803 + ], + "angle": 0, + "content": "significantly better performance than prior works when the camera and the foreground objects are moving, which is a more challenging case in VSR. Moreover, MFPI can recover the scene details more faithfully than other methods, such as pedestrians' feet and text in Figure 7. More visual comparisons are shown in the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.868 + ], + "angle": 0, + "content": "Quantitative Comparison The quantitative results on six test sets with scaling factors 4 are shown in Table 1. It is observed that: (1) Compared with existing approaches that" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.464, + 0.627, + 0.533 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.52, + 0.534, + 0.602, + 0.543 + ], + "angle": 0, + "content": "Frame 010, Clip city" + }, + { + "type": "image", + "bbox": [ + 0.628, + 0.464, + 0.692, + 0.494 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.651, + 0.495, + 0.661, + 0.502 + ], + "angle": 0, + "content": "L" + }, + { + "type": "image", + "bbox": [ + 0.693, + 0.464, + 0.758, + 0.494 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.711, + 0.495, + 0.738, + 0.502 + ], + "angle": 0, + "content": "EDVR" + }, + { + "type": "image", + "bbox": [ + 0.76, + 0.464, + 0.824, + 0.494 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.773, + 0.495, + 0.815, + 0.502 + ], + "angle": 0, + "content": "BasicVSR" + }, + { + "type": "image", + "bbox": [ + 0.826, + 0.464, + 0.891, + 0.494 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.839, + 0.495, + 0.877, + 0.502 + ], + "angle": 0, + "content": "IconVSR" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.546, + 0.627, + 0.615 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.516, + 0.616, + 0.603, + 0.624 + ], + "angle": 0, + "content": "Frame 015, Clip walk" + }, + { + "type": "image", + "bbox": [ + 0.628, + 0.546, + 0.693, + 0.576 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.651, + 0.577, + 0.661, + 0.583 + ], + "angle": 0, + "content": "L]" + }, + { + "type": "image", + "bbox": [ + 0.693, + 0.546, + 0.758, + 0.576 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.711, + 0.577, + 0.738, + 0.584 + ], + "angle": 0, + "content": "EDVR" + }, + { + "type": "image", + "bbox": [ + 0.76, + 0.546, + 0.824, + 0.576 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.771, + 0.577, + 0.815, + 0.584 + ], + "angle": 0, + "content": "BasicVSR" + }, + { + "type": "image", + "bbox": [ + 0.826, + 0.546, + 0.891, + 0.576 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.839, + 0.577, + 0.878, + 0.584 + ], + "angle": 0, + "content": "IconVSR" + }, + { + "type": "image", + "bbox": [ + 0.5, + 0.584, + 0.693, + 0.615 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.635, + 0.616, + 0.689, + 0.623 + ], + "angle": 0, + "content": "BasicVSR++" + }, + { + "type": "image", + "bbox": [ + 0.693, + 0.584, + 0.758, + 0.615 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.712, + 0.616, + 0.737, + 0.623 + ], + "angle": 0, + "content": "PSRT" + }, + { + "type": "image", + "bbox": [ + 0.76, + 0.584, + 0.824, + 0.615 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.766, + 0.616, + 0.817, + 0.624 + ], + "angle": 0, + "content": "MFPI(Ours)" + }, + { + "type": "image", + "bbox": [ + 0.826, + 0.584, + 0.891, + 0.615 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.85, + 0.616, + 0.866, + 0.623 + ], + "angle": 0, + "content": "HR" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.636, + 0.892, + 0.666 + ], + "angle": 0, + "content": "Figure 7: Challenging scenario on Vid4 [28]. MFPI recovers the clear textures and reduces the produce blurry results." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.714, + 0.893, + 0.868 + ], + "angle": 0, + "content": "only perform well on a certain dataset, our MFPI achieves the best performance in all the datasets for both BI and BD degradation. (2) Compared with BasicVSR++ which has very similar parameters and speed to our method, 0.42 dB, 0.49 dB and 0.32 dB PSNR improvements can be achieved on the three datasets in BI degradation experiments, respectively. (3) Compared with PSRT-recurrent which has slightly lower PSNR than our method, our model only has around \\(54\\%\\) parameters, which indicates better efficiency. These observations indicate that our method significantly outperforms the previous VSR models." + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "12820" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.124, + 0.27, + 0.192 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.099, + 0.193, + 0.184, + 0.202 + ], + "angle": 0, + "content": "Frame 024, Clip clap" + }, + { + "type": "image", + "bbox": [ + 0.272, + 0.124, + 0.47, + 0.153 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.288, + 0.155, + 0.318, + 0.163 + ], + "angle": 0, + "content": "EDVR" + }, + { + "type": "image", + "bbox": [ + 0.272, + 0.164, + 0.47, + 0.193 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.219, + 0.194, + 0.256, + 0.202 + ], + "angle": 0, + "content": "IconVSR" + }, + { + "type": "image", + "bbox": [ + 0.272, + 0.203, + 0.47, + 0.234 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.288, + 0.236, + 0.318, + 0.244 + ], + "angle": 0, + "content": "EDVR" + }, + { + "type": "image", + "bbox": [ + 0.272, + 0.245, + 0.47, + 0.274 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.219, + 0.275, + 0.256, + 0.282 + ], + "angle": 0, + "content": "IconVSR" + }, + { + "type": "image_caption", + "bbox": [ + 0.272, + 0.274, + 0.47, + 0.283 + ], + "angle": 0, + "content": "BasicVSR ++ MFPI(Ours) HR" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.297, + 0.47, + 0.326 + ], + "angle": 0, + "content": "Figure 8: Challenging scenario on UDM10 [65]. Our method produces much clearer text and sharper edges." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.352, + 0.242, + 0.366 + ], + "angle": 0, + "content": "4.3. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.375, + 0.469, + 0.443 + ], + "angle": 0, + "content": "This subsection gives a series of ablation studies to study the effectiveness of each component of MFPI. The evaluations were performed on the REDS4 dataset [38] trained on image patches of size \\(180 \\times 320\\) for \\(6 \\times 10^{5}\\) iterations. BasicVSR++ is utilized as the baseline." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.455, + 0.47, + 0.705 + ], + "angle": 0, + "content": "A. Individual components. An ablation study is conducted by progressively adding SFE, EFE and the auxiliary branch to study the influence of different network blocks in our MFPI. Besides, we also investigate the effectiveness of the proposed privilege training and compare it with knowledge distillation (KD), which is another popular neural network training method. As shown in Table 2a: (a) \\(0.16\\mathrm{dB}\\) and \\(0.13\\mathrm{dB}\\) PSNR improvements can be obtained by using SFE and EFE individually. Besides, \\(0.02\\mathrm{dB}\\) further PSNR improvements can be obtained by combining the two methods with the auxiliary branch. (b) Privilege training leads to \\(0.12\\mathrm{PSNR}\\) improvements while KD leads to \\(0.38\\mathrm{dB}\\) PSNR reduction, indicating the traditional model training method fails in VSR while our method leads to significant performance benefits. As Table 2a suggests, combining all the components yields the best performance vs. complexity tradeoff \\((32.81\\mathrm{dB},7.34\\mathrm{M},\\) and \\(281.25\\mathrm{G})\\) compared to employing single or partial components." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.714, + 0.47, + 0.867 + ], + "angle": 0, + "content": "B. Ablation on SFE. We further study the performance of our proposed SFE in Table 2b with different variants: only FFT, FFT with learnable filter, the split input with FL and original feature, the split operator with FL and batch normalization, the split operator with FL and instance normalization. Then, we incrementally added different DWConv layers on top of the existing components, such as \\(3 \\times 3\\), \\(7 \\times 7\\), \\(11 \\times 11\\), and \\(21 \\times 21\\). Besides, we only substituted the FFT with the original feature while keeping the LF, IN, and DWConv \\(21 \\times 21\\) (-w/o FFT). Experimental results show that: (i) Only adding FFT to Base leads to 0.04 PSNR drop," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.126, + 0.892, + 0.279 + ], + "angle": 0, + "content": "indicating that only utilizing Fourier transform cannot boost performance. (ii) Using the learnable filter leads to 0.07 dB improvements, which account for \\(41\\%\\) performance benefits, indicating the learnable filter can improve the representation ability of FFT. (iii) Splitting the features into FFT and IN branches leads to 0.07 dB PSNR benefits, indicating that IN can help the model preserve scale information and prevent covariance shifts. (iv) DWConv with \\(21 \\times 21\\) kernel performs better than other kernels, indicating a larger kernel is necessary. (v) SFE without FFT achieves only 31.93 dB PSNR, indicating FFT plays an essential role in SFE." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.288, + 0.893, + 0.468 + ], + "angle": 0, + "content": "C. Ablation on EFE. To evaluate different DCT basis functions in the EFE, we have compared our method with four different DCT variants, which are DCT initialization with fixed coefficients (DF), DCT initialization with learnable filter (DL), DF and DL added energy function, respectively. Experimental results show that: (i) Our method achieves the best PSRN, which demonstrates the effectiveness of using a learnable filter and the energy function. (ii) Removing DCT from EFE leads to 0.43 dB PSNR drop, which indicates EFE is necessary. (iii) EFE with DWConv 11x11 kernel achieves the best PSNR than other DWConv kernels, indicating that a relatively larger kernel tends to achieve better performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.477, + 0.892, + 0.63 + ], + "angle": 0, + "content": "D. Privilege Training As shown in Table 2a, 0.12 dB PSNR improvements can be obtained by applying PT to our model, which is 0.50 higher than KD. To further study its effectiveness, we have compared PT with the other six popular model training methods in Table 3 on BasicVSR [2]. It is observed that four of the previous methods do not bring any performance benefits but lead to significant PSNR and SSIM drop. PISR leads to 0.04 dB PSNR and 0.0009 SSIM improvements, which are 0.14 dB and 0.0022 lower than PT in PSNR and SSIM, respectively. Besides, PT can be easily implemented without a pre-trained teacher model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.639, + 0.892, + 0.777 + ], + "angle": 0, + "content": "E. Feature Visualization Visualization of intermediate features in MFPI is shown in Figure 9. It is observed that: (1) The feature map significantly reduces noise after MFE, indicating that MFE effectively suppresses noise information. (2) SFE can capture object motion and extract spatial features in the frequency domain. (3) EFE focuses on the fine-grained texture and details of the input feature, as shown in the red arrow and circle. (4) Moreover, the MFE effectively fuses the multi-frequency feature and enhances the representation ability." + }, + { + "type": "title", + "bbox": [ + 0.498, + 0.788, + 0.619, + 0.803 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.867 + ], + "angle": 0, + "content": "In this paper, we have proposed a novel VSR model referred to as MFPI, which consists of a multi-frequency representation enhancement module (MFE) and a privilege training method. MFE is utilized to aggregate informa" + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.504, + 0.898 + ], + "angle": 0, + "content": "12821" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.124, + 0.473, + 0.237 + ], + "angle": 0, + "content": "Table 2: Ablation studies. Subtables 2a, 2b, and 2c contain components that are defined in Sec. 3.2 and 3.3. We conduct ablation experiments on various components of SFE and EFE, such as FFT/DCT, split operator, learnable filter, BN/IN, energy function, and different coefficients. We also evaluate the effects of different kernel sizes using DW-Conv. Additionally, we employ knowledge distillation [12] or privilege training (PT) to improve our results." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.246, + 0.468, + 0.357 + ], + "angle": 0, + "content": "
BaseMFETrainingPSNR (dB)Params (M)FLOPs (G)
SFEEFEAuxKDPT
✓32.397.32280.59
✓✓32.557.34280.76
✓✓32.527.33280.68
✓✓✓32.677.34280.86
✓✓✓✓32.697.34281.25
✓✓✓✓✓32.317.34281.25
✓✓✓✓✓32.817.34281.25
" + }, + { + "type": "table_caption", + "bbox": [ + 0.194, + 0.358, + 0.355, + 0.369 + ], + "angle": 0, + "content": "(a) Individual components." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.376, + 0.468, + 0.498 + ], + "angle": 0, + "content": "
VariantPSNR
Base + FFT32.35
Base + FFT w/. Learnable filter32.48
Base + FFT w/. Learnable filter + original feature32.49
Base + FFT w/. Learnable filter + BN32.43
Base + FFT w/. Learnable filter + IN32.52
Base + FFT w/. Learnable filter + IN + DWConv 3 × 332.48
Base + FFT w/. Learnable filter + IN + DWConv 7 × 732.52
Base + FFT w/. Learnable filter + IN + DWConv 11 × 1132.51
Base + FFT w/. Learnable filter + IN + DWConv 21 × 21 (Our SFE)32.55
Base + w/. Learnable filter + IN + DWConv 21 × 2131.93
" + }, + { + "type": "table_caption", + "bbox": [ + 0.185, + 0.499, + 0.362, + 0.51 + ], + "angle": 0, + "content": "(b) Effects of the SFE branch." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.518, + 0.468, + 0.622 + ], + "angle": 0, + "content": "
VariantPSNR
Base + Energy function32.40
Base + DCT w/. Fixed coefficients32.32
Base + DCT w/. Learnable filter32.41
Base + DCT w/. Fixed coefficients + Energy function32.37
Base + DCT w/. Learnable filter + Energy function32.50
Base + DCT w/. Learnable filter + Energy function + DWConv 3 × 332.42
Base + DCT w/. Learnable filter + Energy function + DWConv 7 × 732.40
Base + DCT w/. Learnable filter + Energy function + DWConv 11 × 11 (Our EFE)32.52
Base + DCT w/. Learnable filter + Energy function + DWConv 21 × 2132.43
Base + w/. Learnable filter + Energy function + DWConv 11 × 1132.07
" + }, + { + "type": "table_caption", + "bbox": [ + 0.184, + 0.623, + 0.362, + 0.633 + ], + "angle": 0, + "content": "(c) Effects of the EFE branch." + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.657, + 0.469, + 0.686 + ], + "angle": 0, + "content": "Table 3: Comparison between the proposed privilege training and previous training methods with BasicVSR on [38]." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.695, + 0.469, + 0.8 + ], + "angle": 0, + "content": "
MethodNeeds Teacher?PSNRSSIM
BasicVSR✓31.580.8940
+ Deep Supervision [23]×31.580.8941
+ Self-KD [67]×31.470.8914
+ Hinton KD [12]✓31.260.8883
+ FitNet [44]✓31.520.8934
+ PISR [24]✓31.620.8949
+ Ours×31.760.8971
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.868 + ], + "angle": 0, + "content": "tion in the frequency domain by operating the spatial- and energy-frequency components via SFE and EFE. It enables CNN-based VSR models to capture long-range dependen" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.126, + 0.892, + 0.344 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.352, + 0.893, + 0.395 + ], + "angle": 0, + "content": "Figure 9: Visualization of the features in MFPI on images from REDS4[38]. The red dot curve denotes the change in spatial information at different locations of the same object." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.428, + 0.892, + 0.526 + ], + "angle": 0, + "content": "cies with very minor additional parameters and computations. Besides, we also propose to improve the performance of VSR from a training perspective by introducing privilege training, which contributes orthogonal effects to our frequency modules. We hope that this paper may promote more research that studies VSR from the perspective of frequency methods and model training methods." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.551, + 0.636, + 0.565 + ], + "angle": 0, + "content": "6. Future Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.578, + 0.892, + 0.73 + ], + "angle": 0, + "content": "In the future, exploring MFPI in a real-world scenario would be an exciting direction, which offers a new valuable perspective on our proposed MFEI performance. We speculate that our frequency methods will be useful for real-scenario tasks and a broader investigation of it has provided additional depth to our study. We will continue to (1) evaluate MFPI on more challenging datasets such as RealVSR [63], and (2) deploy MFPI on edge devices and evaluate its performance. We are actively working on conducting the requested experiments that can further strengthen our conclusions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.756, + 0.661, + 0.772 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.784, + 0.892, + 0.868 + ], + "angle": 0, + "content": "The authors acknowledge the financial support from the National Key R&D Program of China (No.2021ZD0113805). We appreciate the comments from the seminar participants at the Center for Deep Learning of Computer Vision Research at China Agricultural University, which improves the manuscript significantly." + }, + { + "type": "page_number", + "bbox": [ + 0.466, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "12822" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.125, + 0.174, + 0.14 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.148, + 0.47, + 0.224 + ], + "angle": 0, + "content": "[1] Jose Caballero, Christian Ledig, Andrew Aitken, Alejandro Acosta, Johannes Totz, Zehan Wang, and Wenzhe Shi. Real-time video super-resolution with spatio-temporal networks and motion compensation. 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To tackle this challenge, this paper presents a novel multi-frequency representation enhancement module (MFE) that performs spatial-temporal information aggregation in the frequency domain. Specifically, MFE mainly includes a spatial-frequency representation enhancement branch which captures the long-range dependency in the spatial dimension, and an energy frequency representation enhancement branch to obtain the inter-channel feature relationship. Moreover, a novel model training method named privilege training is proposed to encode the privilege information from high-resolution videos to facilitate model training. With these two methods, we introduce a new VSR model named MFPI, which outperforms state-of-the-art methods by a large margin while maintaining good efficiency on various datasets, including REDS4, Kobe, Vid4, and UDM10. + +# 1. Introduction + +Video super-resolution (VSR), which restores high-resolution (HR) video frames from their highly related but unaligned low-resolution (LR) video frames, is well-desired in various real-world applications [11, 2]. Compared with single image super-resolution (SISR), VSR is much more challenging as it aggregates information from multiple related but misaligned frames in the input video. Hence, an ideal VSR model is expected to leverage the spatial information from single images but also integrate the temporal + +![](images/1f29f8aeb33c1b0543b7fd943d6855ae621109df6952db61e8ae4e4595d6f1b8.jpg) +Figure 1: VSR performance comparison on UDM10 [65] in terms of PSNR (dB), runtime (ms), and parameters (M). MFPI outperforms SOTA methods with high efficiency. + +semantic features from multiple frames [45, 50, 18, 3]. + +CNN-based models have become the standard choice for VSR due to their simplicity and efficiency. While recent advances in CNN-based VSR, such as residual learning [2, 73], dense connections[59], hierarchical structures [20], and multi-scale frameworks [63, 34, 48], have shown impressive performance, some potential problems still exist. Firstly, CNN's limited receptive field hinders it from modeling long-range spatial dependencies, making it unable to capture complex semantic information. Secondly, convolutional filters have fixed scales and weights, limiting their performance on large motions and adaptability to diverse inputs. In comparison, with the advantages of self-attention layers, ViTs are effective in processing inputs with long-term spatial dependencies. However, the stack + +of self-attention layers is accompanied with a large computation budget, which results in inferior inference efficiency on edge devices [29]; A natural question arises: can CNNs capture long-range dependencies like ViTs? + +In this paper, we propose to answer this question from a frequency perspective. Thanks to their ability to capture global representation, frequency-based models have been widely utilized in single image processing [72, 41, 71]. Unfortunately, their performance in video super-resolution (VSR) is usually limited due to several reasons. (1) Compared with single images, videos are composed of multiple related but misaligned images, which contain both spatial and temporal information. However, traditional frequency methods have fixed paradigms and coefficients [56, 66, 40], making them not able to capture the complex information in videos. (2) Traditional frequency methods are sensitive to the noise in images [64, 14]. This disadvantage becomes more fatal in videos where the noise of different frames can be accumulated. + +To address these challenges, we propose a novel module named multi-frequency representation enhancement (MFE), which aggregates information in the frequency domain. Unlike convolutional and self-attention layers that operate in the feature space, MFE directly manipulates the energy feature map in the frequency domain through three branches: 1) a spatial-frequency representation enhancement branch (SFE) that utilizes a Fast Fourier Transform (FFT) and large kernel convolution layer to capture arbitrary interactions among spatial and long-range dependent features, 2) an energy-frequency representation enhancement branch (EFE) that employs a novel energy discrete cosine transform (DCT) to improve representation and explore potentially useful frequency components, and 3) a pair of convolution layers that leverage large kernels to obtain global range-interact features with stronger shape bias. Compared with the previous frequency methods, the learnable filter in SFE enables FFT to capture both spatial and temporal information, and the energy function in EFE can alleviate the noise accumulated in multiple video frames. Moreover, MFE only contains $0.02\mathrm{M}$ parameters, making it affordable for edge devices. + +Besides MFE, we further propose a novel model training method named privilege training (PT) to facilitate the training of VSR models. Motivated by previous research in learning using privilege information (LUPI) [53], we propose to apply a trainable encoding module to encode the privilege information from HR videos and then employ them to obtain a good initialization for VSR models. Sufficient experiments demonstrate the effectiveness of privilege training on both our model and the other VSR models. + +With MFE and privilege training, we introduce a novel VSR model referred to as MFPI. Extensive experimental results have demonstrated that MFPI outperforms eighteen + +previous methods by a clear margin in six VSR benchmarks. For instance, on UDM10, compared with BasicVSR++ [4], which has similar parameters and runtime with MFPI, MFPI achieves 0.36 dB higher PSNR improvements on UDM10 BD degradation, as shown in Figure 1. To sum up, the main contributions in this paper can be summarized as follows: + +- We propose multi-frequency representation enhancement (MFE), a module that effectively aggregates information in the frequency domain by operating the spatial- and energy-frequency components. +- We propose privilege training, which encodes the privilege information from the HR videos to boost the performance of VSR models. +- Abundant experiments demonstrate the effectiveness of MFPI on four datasets, including REDS4, Vimeo, Vid4, and UDM10 in both BI and BD degradation. + +# 2. Related Work + +# 2.1. Video Super Resolution + +Different from SISR, VSR typically produces higher-quality results by utilizing information from neighboring frames. Recently, learning-based approaches have been highly effective in solving the problem of VSR [16, 4]. The main challenge for VSR is how to correctly fuse auxiliary frames in the presence of dynamic content and object motion. To address this problem, abundant methods have been proposed to explicitly use optical flow [55], deformable convolution [57, 50, 3], and homography [18] to align neighbor frames. However, estimating accurate optical flow or transformation is still challenging in large motions. Recently, some methods have been proposed to learn the spatial correspondence across different frames to tackle this challenge [25, 13]. However, these methods have limited performance in VSR since they cannot capture information between adjacent locations or long-range interactions [47, 41]. To address this problem, we introduce a spatial-frequency representation enhancement branch that models long-range spatial and temporal dependencies. + +# 2.2. Learning in Frequency Domain + +Due to the difficulty of distinguishing high-frequency textures from artifacts, fruitful methods [70, 6, 14] have been introduced to decouple them in the frequency space and reconstruct the high-quality textures. For instance, Zhou et al. proposed a deep Fourier up-sampling method to recover the resolution in the frequency domain [72]. Guo et al. utilized the wavelet technique to simplify the mapping between the LR and HR images, reducing the artificial blocks and recovering the edge's information [10]. Motivated by their success, abundant works have tried to + +apply frequency methods to SR. Dario et al. proposed a Fourier space supervision loss to improve restoration results [6]. Qiu et al. designed a fine-grained self-attention module in the space-frequency domain, which reconstructs the real visual texture without artifacts [41]. However, the images that are directly transformed into the frequency domain still face obstacles as follows: (1) Decomposing features into different frequency components usually lacks local correlation information in the channel dimension, making it difficult to utilize the useful frequency components [40]. (2) Non-parametric frequency-based methods are easily susceptible to noise and image scale factors [35]. To address the above problems, this paper proposes to combine the advantages of the energy function and frequency-based representations by using DCT with learnable filters. + +# 2.3. Learning Using Privilege Information + +Learning using privilege information (LUPI) was first proposed by Vapnik et al. to employ the privilege information provided by a teacher model in support vector machine [53]. Generally speaking, LUPI aims to improve the performance of a model by using privilege information, which is utilized during training but not required during inference. Vapnik et al. further utilized LUPI to accelerate the inference speed of SVMs by similarity control and knowledge transfer [52]. Motivated by the success of knowledge distillation [12] on deep neural networks, recently, David et al. proposed generalized distillation, which combines knowledge distillation with learning with privilege information theoretically [32]. Recently, label-guided auxiliary was introduced to apply LUPI to point cloud-based 3D detection by using the privilege information from annotations [15]. Lee et al. proposed PISR, which introduces LUPI to single image super-resolution by using variational knowledge distillation [24]. Moreover, LUPI has also been utilized in semi-supervised learning [7], domain adaptation [37], speech recognition [36] and so on. + +The most related work of the privilege training in our method is PISR [24], which is proposed for knowledge distillation on single image super-resolution. Their main difference is that: (1) PISR is proposed for SISR for model compression while our method is proposed for VSR to improve the quality of restoration. (2) Besides, PISR is a knowledge distillation method which mainly leverages the privilege information with distillation loss. In contrast, our method leverages the privilege information by sharing model weights. (3) PISR implicitly encodes the privilege information via the reconstruction of LR images while our method explicitly encodes privilege information from HR videos with a trainable network. Besides, ablation studies in Table 3 also demonstrate that our method leads to significantly higher performance than PISR. + +# 3. Methodology + +# 3.1. Overall Framework for VSR + +Following the previous work [4], we adopt the recurrent bidirectional propagation as the baseline model. Based on its architecture, we propose a novel VSR model termed MFPI, which consists of a multi-frequency representation enhancement module (MFE) to improve the LR frames representation in the frequency domain, and a novel VSR model training method named privilege training which encodes privilege information from HR frames to facilitate model training. The overall architecture is shown in Figure 2: (1) The VSR model extracts features from the LR frames images to reconstruct the HR frames images. (2) Residual blocks and MFE are employed to extract the feature $f_{i}^{j}$ from the LR images, where $f_{i}^{j}$ denotes the feature at $i_{th}$ timestamp in the $j_{th}$ propagation branch. (3) The flow-guided deformable alignment block (FDA) aligns the neighboring features $f_{i-1}^{j}$ and $f_{i-2}^{j}$ . And the pixel-shuffle operator is employed to perform upsampling $4 \times$ scales from LR to HR frames. Besides, learning privilege information boosts the performance of our VSR models during training, as shown in Figure 3. + +# 3.2. MFE: A Multi-Frequency Representation Enhancement Module + +As depicted in Figure 2 (b), we design a multi-frequency representation enhancement (MFE) to improve the representation ability and aggregate spatial-temporal information in VSR architecture. MFE is a plug-in-play building block which adopts a multi-branch structure to capture multifrequency representation [9]. Concretely, it first encodes the input features with a depthwise convolution (DWConv) layer [68] and then processes them with three different branches, including 1) a spatial-frequency representation enhancement branch to capture the spatial-frequency information and long-range dependence features, 2) an energy-frequency representation enhancement branch to improve the representation ability and model the inter-channel relationship in the frequency domain, and 3) an auxiliary branch with a pair of $7 \times 1$ and $1 \times 7$ DWConv to inject the inductive bias and facilitate training [8, 31]. Finally, a $1 \times 1$ convolution layer aggregates the diverse features from three branches, and the skip connection is employed to facilitate the convergence of MFE [30]. + +# 3.2.1 Spatial Frequency Representation Enhancement + +As illustrated in Figure 2 (c), the spatial frequency representation enhancement (SFE) branch first employs a pair of $DWConv$ to generate the feature map $f_{in}$ from the input $x_{in} \in \mathbb{R}^{H \times W \times C}$ . Then, we split $f_{in}$ into two parts $f_{mid1}, f_{mid2} \in \mathbb{R}^{h \times w \times c/2}$ [26, 69]. The FFT layer pro + +![](images/10daa50da56daf15e6a437f20706144e06c0a737008a7a3bf357bf31cdaed919.jpg) +(a) The Overall Framework of MFPI +(b) MFE: Multi-frequency Representation Enhancement + +![](images/339c9c6c90b8e24dda7da7134f532a8f0a79543708f9d37fbadf9cd31b05ecb6.jpg) +(c) SFE: Spatial Frequency Representation Enhancement +Figure 2: (a) An overview framework of MFPI. The blue dot line denotes the bilinear upsampling operator. The red curve denotes second-order propagation. "FDA" denotes the flow-guided deformable alignment block [4]. The green block denotes the proposed multi-frequency representation enhancement (MFE). (b) An overview of the MFE. (c) The details of the spatial-frequency representation enhancement branch in MFE extract spatial-level and long-range dependencies. (d) The details of the energy-frequency representation enhancement branch. $e_{i,j}^{*}$ denotes the energy feature. Note that the 'FC layer' consists of a sequence of the 'linear-LReLU-linear-LReLU' operator. DWConv denotes the depthwise convolution [68]. + +![](images/648cdb3a3a646446c300915411b8cf7ae18c6c741ad268f0c256e5f8e8588bcb.jpg) +(d) EFE: Energy Frequency Representation Enhancement + +cesses $f_{mid1}$ represents different spatial dependence information as follows: + +$$ +f r e q = \mathcal {F} \left[ f _ {\text {m i d} 1} \right] \in \mathbb {C} ^ {h \times w \times c / 2} \tag {1} +$$ + +where $c, h, w$ denote the input channel, height, width of the feature maps, respectively. $\mathcal{F}[\cdot]$ denotes the 2D FFT, $freq$ represents the frequency feature of $f_{mid1}$ . To make SFE adaptive to diverse features [43, 54], we modulate the $freq$ multiplies with a learnable filter $L \in \mathbb{C}^{h \times w \times c/2}$ in the frequency domain: $\tilde{freq} = freq \times L$ . The inverse FFT transfers the modulated frequency feature back to the spatial domain: + +$$ +\tilde {f _ {m i d 1}} \leftarrow \mathcal {F} ^ {- 1} \left[ f \tilde {r e q} \right] \tag {2} +$$ + +Finally, the output feature $f_{out}$ is obtained by concatenating with an instance normalization (IN) [51] layer, which prevents covariance shift and preserves the scale information: $f_{out} = \text{Concat}\left(f_{mid1}, \text{IN}\left(f_{mid2}\right)\right)$ . + +It is also worth noting that in our implementation: (1) SFE utilizes a relatively large local window of $DWConv$ $(e.g., 21 \times 1, 1 \times 21)$ to capture the long-range spatial dependencies from features. (2) Besides, a learnable Fourier + +transform with IN can exhibit clear patterns and generalizations in the frequency domain. Hence, the proposed SFE branch tends to be more efficient than directly utilizing Fourier transforms in the spatial-temporal dimension (Table 2b). (3) Considering that FFT has less computation than DFT, we employ FFT in SFE as the frequency transformation to improve model representation. Moreover, the Fourier domain has the nature of global modeling [54]. Hence, computation on frequency bands implies information aggregation over all the spatial locations of the input images. Specifically, in our SFE, FFT is performed over the whole feature map across all the spatial locations, which is equivalent to the global receptive field of the whole feature. (4) SFE splits features into two branches to improve computational efficiency. Specifically, this split operator enables SFE to capture and combine different aspects or representations of the input data. One part focus on the spatial frequency characteristics or patterns, and the other part act as a form of regularization by introducing additional constraints, such as instance normalization. Their outputs can be concatenated to create a richer and more comprehensive representation. This can enhance the SFE's ability to learn complex relationships and improve its overall performance. + +Besides, this two-branch design is also similar to the idea of group convolution and CSN [71], which is a well-known technique of efficient neural networks. Please refer to supplementary materials for theoretical analysis. + +# 3.2.2 Energy Frequency Representation Enhancement + +Considering that the frequency methods with a learning filter can be more generic and flexible interactions among spatial locations from diverse images, we introduce an energy function to reweight the input feature and utilize the learnable filter with DCT to represent the rich inter-channel relationship [40]. The architecture of the energy frequency representation enhancement (EFE) is illustrated in Figure 2 (d). More specifically, EFE first utilizes a pair of $DWConv$ (e.g., $11 \times 1,1 \times 11$ ) to generate the feature map $f$ . Then, we calculate the mean $\hat{\mu}$ and variance $\hat{\sigma}^2$ of $f$ , and the energy value [62] can be obtained by minimizing the following: + +$$ +e _ {i, j} = \frac {4 (\hat {\sigma} ^ {2} + \delta)}{(t _ {i , j} - \hat {\mu}) ^ {2} + 2 \hat {\sigma} ^ {2} + 2 \delta} \tag {3} +$$ + +where $\delta$ is the hyper-parameter, $e_{i,j}$ denote the energy value of target pixel $t_{i,j}$ , $i\in \{0,1,\dots ,H - 1\}$ , $j\in \{0,1,\dots ,W - 1\}$ . The energy feature is obtained by grouping all the $e_{i,j}$ across spatial and channel levels, which rescale the energy value to restrict too large energy value: + +$$ +e _ {i, j} ^ {*} = \text {L e a k y R e L U} \left(\frac {1}{\sum_ {i \neg = 0} ^ {h} \sum_ {j \neg = 0} ^ {w} e _ {i , j}}\right) \tag {4} +$$ + +To further enrich the representation ability of EFE, we employ the DCT technique to convert the energy features into the frequency domain as follows: + +$$ +\mathcal {F} _ {c} (i, j) = \frac {2}{\sqrt {H W}} \alpha (i) \alpha (j) \sum_ {h = 0} ^ {H - 1} \sum_ {w = 0} ^ {W - 1} e _ {i, j} ^ {*} \tag {5} +$$ + +$$ +\mathcal {K} _ {h, w} ^ {i, j} = \cos \left(\frac {(2 h + 1) i \pi}{2 H}\right) \cos \left(\frac {(2 w + 1) j \pi}{2 W}\right) \tag {6} +$$ + +$$ +f _ {c} ^ {h, w} = \mathcal {K} _ {h, w} ^ {i, j} \times \mathcal {F} _ {c} \left(e _ {i, j} ^ {*}\right) \tag {7} +$$ + +where $\mathcal{F}_c$ denotes DCT operation, $\kappa$ denotes the basis function of DCT, $\alpha(x) = 1/\sqrt{2}$ for $x = 0$ and $\alpha(x) = 1$ otherwise [46]. Finally, the output refined feature as follows: $f_{out} = f_c^{h,w} \times x_{i,j}$ . Note that an element-wise multiplication between frequency-domain features and the learnable filters improves the representation ability and makes EFE flexible adaptive to different feature inputs. Besides, the FC layer in Figure 2 (d) consists of a sequence of the 'Linear-LeakyReLU-Linear-LeakyReLU' operators, which + +convert the channel-wise feature into a scalar representation, which reduces the complexity and improves the effectiveness in the frequency domain. Different from the SFE branch, the EFE branch leverages the merits of the energy function and frequency components to improve the representation power and model the relationship among inter-channel dimensions, as shown in Figure 9. + +# 3.3. Privilege Training + +Learning using privilege information is a well-known theory in machine learning, which shows that one can improve the performance of machine learning by using kinds of privilege information, which is available in training but not accessible during inference. Motivated by its effectiveness, in this paper, we propose a novel neural network training method for VSR, which is shown in Figure 3. By denoting the LR and corresponding HR videos as $x$ and $y$ , respectively, the traditional training method can be formulated as $\min \mathbb{E}[|f(x) - y|]$ , where $f(\cdot)$ denotes the superresolution model. In contrast, in our method, we additionally introduce a lightweight neural network $\mathcal{D}$ , which aims to encode the privilege information from the HR frames $y$ to a tensor of privilege information $\mathcal{D}(y)$ which has the same shape with the LR frames $x$ . Then, we can denote a mixture of the LR images and the privilege information as $x^{*} = x + \gamma \cdot \mathcal{D}(y)$ , where $\gamma \in [0,1]$ is a parameter to balance the two items. During the training period, we gradually decrease $\gamma$ from 1 to 0. Hence, the VSR model is able to firstly learn a good representation by using the privilege information, and then gradually get rid of it. Note that since $\gamma$ is decreased to 0, the VSR model does not require any privilege information during inference. In summary, its objective of privilege training can be written as + +$$ +\underset {f, \mathcal {D}} {\arg \min } \mathbb {E} [ | f (x ^ {*}) - y | + | \mathcal {D} (y) | ] \tag {8} +$$ + +where the first loss item is the common reconstruction loss for VSR training. The second loss item is a regularization item which reduces the energy of privilege information to prevent the model from overusing the privilege information. Note that the regularization item is indispensable since without this item the VSR model may degenerate into a naive auto-encoder which reconstructs the HR images totally based on the privilege information. Note that $\mathcal{D}$ in our implementation is a stack of three convolutional layers followed with LeakyReLU. + +Why does privilege training work? The effectiveness of privilege information can be understood from the perspective of weight initialization. During the early training iterations, the model can quickly converge to a flat minima by using the privilege information. Then, by reducing $\gamma$ , the privilege information gradually makes a less influence to the VSR model, and hence the VSR model can converge + +![](images/025e5f2b6696c3b849fc9c8b5c31b8468c7e93147c94943109dfa7fb1473aa0c.jpg) +Figure 3: The paradigm of the proposed learning using privilege information on VSR. $\oplus$ denotes a weighted addition between the privilege information and the LR frames. + +![](images/62a95eca1968bea6f1e66e2a2433b90308c59cd3364ae503092e02fc1e267ff8.jpg) +Figure 4: Visualization of the privilege information. + +stably. Secondly, the success of our method can also be understood as a special case of knowledge distillation, where the teacher model is trained with privilege information, the student model is trained with only the LR frames, and the knowledge distillation is applied by sharing the weights of the student and the teacher. Besides, Figure 4 visualizes the privilege information encoded during the training period. It is observed that most of privilege information concentrates on the pixels belonging to the objects and their edges, which are more important in the assessment of image quality. These privilege information is utilized to help VSR models to converge at the early training period. + +# 4. Experiment + +# 4.1. Experimental Setup + +Our model is trained for each task with $6 \times 10^{5}$ iterations using randomly cropped patches. We apply data augmentation techniques such as random horizontal and vertical flipping and $90^{\circ}$ rotation. The Adam optimizer [22] is used with an initial learning rate of $2 \times 10^{-4}$ , which is steadily decreased to $1 \times 10^{-7}$ with cosine annealing learning rate decay [33]. $\delta$ is set to $1 \times 10^{-6}$ [62]. We employ SPyNet to predict optical flow in videos [42]. Each branch contains 7 residual blocks and 64 feature channels. The batch size is set to 4, and the input low-resolution (LR) frames are of patch size $64 \times 64$ . + +![](images/6ce13d1e4346a485d76a774eaefadf5e36d998680f636bab80fb5460ee2e6c9b.jpg) +Figure 5: Challenging scenario on REDS4 [38]. MFPI generates sharp edge in repeated structures of the windows and sharper texts. + +Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index Measure (SSIM) [58] between ground truth and restored videos are utilized as the metrics in our quantitative comparisons. We follow [4] to utilize REDS [38], Vimeo90K [60] as training set, and REDS4, Vimeo-90K-T [60], Vid4 [28], UDM10 [65], and Vimeo-90K as the test set. REDSval4 is utilized as the validation set. All models are tested with $4 \times$ downsampling via two degradations - Bicubic (BI) and Blur Downsampling (BD). All experiments are implemented with PyTorch [39] and on two NVIDIA Tesla A100 GPUs. + +# 4.2. Comparisons with State-of-the-Art Methods + +Qualitative Comparison We show the comparison of visual results in Figure. 5, 6, 7 and 8. It is observed that the results of prior works usually suffer from incomplete artifacts or blurred regions in the image. In contrast, our model restores sharper edges and finer detailed textures of the number plate in Figure 5 and the display board in Figure 6. Besides, MFPI is able to recover the edge of the small object in Figure 6. As shown in Figure 7 and 8, MFPI also shows + +Table 1: Quantitative comparison (PSNR/SSIM). All results are calculated on Y-channel except REDS4 [38] (RGB-channel). The runtime is computed on an LR size of $180 \times 320$ . A $4 \times$ upsampling is performed following previous studies. Blanked entries correspond to results not reported in previous works. Numbers in bold indicate the best performance. + +
ModelParams (M)Runtime (ms)BI degradationBD degradation
REDS4 [38]Vimeo-90K-T [60]Vid4[28]UDM10 [65]Vimeo-90-T [60]Vid4 [28]
Bicubic--26.14/0.729231.32/0.868423.78/0.634728.47/0.825331.30/0.868721.80/0.5246
VESPCN [1]----25.35/0.7557---
SPMC [49]----25.88/0.7752---
TOFlow [61]--27.98/0.799033.08/0.905425.89/0.765136.26/0.943834.62/0.9212-
FRVSR [45]5.1137---37.09/0.952235.64/0.931926.69/0.8103
DUF [21]5.897428.63/0.8251--38.48/0.960536.87/0.944727.38/0.8329
RBPN [11]12.2150730.09/0.859037.07/0.943527.12/0.818038.66/0.959637.20/0.9458-
EDVR-M [57]3.311830.53/0.869937.09/0.944627.10/0.818639.40/0.966337.33/0.948427.45/0.8406
EDVR [57]20.637831.09/0.880037.61/0.948927.35/0.826439.89/0.968637.81/0.952327.85/0.8503
PFNL [65]3.029529.63/0.850236.14/0.936326.73/0.802938.74/0.9627-27.16/0.8355
MuCAN [27]--30.88/0.875037.32/0.9465----
TGA [18]5.8384----37.59/0.951627.63/0.8423
RLSP [5]4.249---38.48/0.960636.49/0.940327.48/0.8388
RSDN [17]6.294---39.35/0.965337.23/0.947127.92/0.8505
RRN [19]3.445--38.96/0.9644-27.69/0.8488
BasicVSR [2]6.36331.42/0.890937.18/0.945027.24/0.825139.96/0.969437.53/0.949827.96/0.8553
IconVSR [2]8.77031.67/0.894837.47/0.947627.39/0.827940.03/0.969437.84/0.952428.04/0.8570
BasicVSR++ [4]7.37732.39/0.906937.79/0.953027.79/0.840040.72/0.972238.21/0.955029.04/0.8753
PSRT [47]13.481232.72/0.910638.27/0.953628.07/0.8485---
MFPI (Ours)7.37632.81/0.910638.28/0.953428.11/0.848141.08/0.974138.70/0.957929.34/0.8781
+ +![](images/ed43e035659e7bf78be3ce4f53af88054c3c31eb770a2eb98d61554161853d4e.jpg) +Sequence 00015,Clip 0864 + +![](images/8f5036db1fbc6957713ced9b74bd093b205ff84eafff3dda09f5a738a1d4c658.jpg) +Bicubic + +![](images/3ef422b40e86c4b90b8570f9d318e0d1d75e41067dc1aaad0021653a1fd60bae.jpg) +BasicVSR + +![](images/960c55cf2960835e10f19f232b26ed7486220df0f62cabda1c573693aa554061.jpg) +IconVSR + +![](images/fc6575c7da47fcd7adf3515d94f22112a67986ac6883fe19164f62b4918c832d.jpg) +BasicVSR++ + +![](images/c82fe85cf4fc9f20a984088048d7c41b44235255f5aa5c4f2300ddd12431830e.jpg) + +![](images/319c90478888e7dc004b37183cdda0425d881dffbca69eccaa1f4944e3ef4f3f.jpg) + +![](images/66e0cf9fbd4abc61ab9e342f982ccdd2edf52ede7656af375d0cd241501c7710.jpg) +MFPI(Ours) + +![](images/90b62c46ee71b80fd309d60b503d2f5133ae0a07d838dbec69029fa092dcf790.jpg) +HR + +![](images/2b3c4fbeb8d569ac3f18a42da661b60eb86861259c3bb1d70d13517b6930e9b0.jpg) +Sequence 00010,Clip 0573 +Figure 6: Challenging scenario on Vimeo-90K-T [60]. Compared to the other methods, Our method more effectively preserves while recovering the strip-like features in the skirts. + +![](images/9e8f57e889ba4eacfc632ff41b1a5b11d20a8b9dab6473e24a619279b1f3f139.jpg) + +![](images/e2910340ed433e36be77e315673234d17c1aff1cbf3f98c390374c736b131171.jpg) + +![](images/bfd292eac0952724e2621d62d36dfcfa0e67d68b823474b7f5b792316f8dccbc.jpg) + +![](images/15d6877d39e02b48d71e8a3e0619c72c11aa60828b1500293d007e38f860df1f.jpg) + +Sequence 00010, Clip 0573 + +![](images/3ff8ce0e7fb9cdf6f643177bbd5271d5f772c4d32aa2cd34947c4fb61111e584.jpg) +Bicubic +BasicVSR++ + +![](images/b3850d874d0db37115c3a4ba549c6f0c5ea53e1a1795d850dd0c476090c385ee.jpg) +EDVR +PSRT + +![](images/87fdda86de0d34eeef9a2f7da7ddaafaeb42d1b6d9fb89d7f872558e91068100.jpg) +BasicVSR +MFPI(Ours) + +![](images/98c6d26d552b4644f34046b7066960b1c9d57b09dbacc219668406caf6cda153.jpg) +IconVSR +HR + +significantly better performance than prior works when the camera and the foreground objects are moving, which is a more challenging case in VSR. Moreover, MFPI can recover the scene details more faithfully than other methods, such as pedestrians' feet and text in Figure 7. More visual comparisons are shown in the supplementary material. + +Quantitative Comparison The quantitative results on six test sets with scaling factors 4 are shown in Table 1. It is observed that: (1) Compared with existing approaches that + +![](images/9f076478e3bb25daf17862d09c5ac7ac893c2e0e098044af68de90c1c78989ac.jpg) +Frame 010, Clip city + +![](images/98bd7e9dc502f6ee8a242effe4fcf481f645e0478a0899e34dfa102a18b533d1.jpg) +L + +![](images/324c78426bab7bbee51c3f7be3e306816a469ae1ccf8ff3914da2ed442476c50.jpg) +EDVR + +![](images/59d6f23568b63829c4e1cceaaaf5fe8b66f12d8096ff460e8eae63a0134e3eab.jpg) +BasicVSR + +![](images/91ac119f618a8e7b381ee9daeefba222058fce8588efa12583f2b42163bae184.jpg) +IconVSR + +![](images/554f2baee1f86427cbcad839531f18121d4acf2778a12ecb79b4e9b3f45c709d.jpg) +Frame 015, Clip walk +Figure 7: Challenging scenario on Vid4 [28]. MFPI recovers the clear textures and reduces the produce blurry results. + +![](images/fb88ce50671178c8a1708fdd29bcfe9441fbbbf5255bddaa1aae14ae57a095b5.jpg) + +![](images/0adf222f7b6ccbcb2fa4a2874c07cbf9bce3fe3aa92d8f414b5e0df0985f15ba.jpg) + +![](images/fe50fe54f537401c30cb497f2595bc7bae4264643ae5e207b28aac7b2d8e11dd.jpg) + +![](images/33f9d333b8b4a5420f3159e47993d4a31671a95735da0de167800ba4019e1660.jpg) + +![](images/86b85a8088fee37ba1b9b4bfb0a7492d05791bfc1add441dbb6fc058fc661d24.jpg) +L] +BasicVSR++ + +![](images/e8c518097a6355fe3b1246d30231bea1fcd6694e272f9b6dd97b158f74f33f16.jpg) +EDVR +PSRT + +![](images/1554af292d78842b1ad227ad53b47f67d59b43b9df75e0a93a04ad898849d025.jpg) +BasicVSR +MFPI(Ours) + +![](images/9205bfe011a404cdb2bdf6e4418197afd0d391fb649c96ecd2ebc426baa8d233.jpg) +IconVSR +HR + +only perform well on a certain dataset, our MFPI achieves the best performance in all the datasets for both BI and BD degradation. (2) Compared with BasicVSR++ which has very similar parameters and speed to our method, 0.42 dB, 0.49 dB and 0.32 dB PSNR improvements can be achieved on the three datasets in BI degradation experiments, respectively. (3) Compared with PSRT-recurrent which has slightly lower PSNR than our method, our model only has around $54\%$ parameters, which indicates better efficiency. These observations indicate that our method significantly outperforms the previous VSR models. + +![](images/6f31a6c8d6cbd358aad9cfe04559fdf1d9de47dc1c19da00c957bd6c30e6fdbf.jpg) +Frame 024, Clip clap +IconVSR + +![](images/eb1eff36cafd7f58267a91fe01d283d885e92f2d5d2f31a51415ce8eb18a432b.jpg) + +![](images/b46654143542f3e53835e54e75394d3b02fcc0d6cd8d922a69cfe502f1b43a25.jpg) +EDVR + +![](images/0eb65a248c32dbde15a207a37950293795f15481a17eafa309ea2892002d5e58.jpg) +EDVR + +![](images/6f7cd5e8d1f7979a0e26f0f3197d3d2937dcda6ed1a02827ad537be462ecd5eb.jpg) +IconVSR +BasicVSR ++ MFPI(Ours) HR +Figure 8: Challenging scenario on UDM10 [65]. Our method produces much clearer text and sharper edges. + +# 4.3. Ablation Studies + +This subsection gives a series of ablation studies to study the effectiveness of each component of MFPI. The evaluations were performed on the REDS4 dataset [38] trained on image patches of size $180 \times 320$ for $6 \times 10^{5}$ iterations. BasicVSR++ is utilized as the baseline. + +A. Individual components. An ablation study is conducted by progressively adding SFE, EFE and the auxiliary branch to study the influence of different network blocks in our MFPI. Besides, we also investigate the effectiveness of the proposed privilege training and compare it with knowledge distillation (KD), which is another popular neural network training method. As shown in Table 2a: (a) $0.16\mathrm{dB}$ and $0.13\mathrm{dB}$ PSNR improvements can be obtained by using SFE and EFE individually. Besides, $0.02\mathrm{dB}$ further PSNR improvements can be obtained by combining the two methods with the auxiliary branch. (b) Privilege training leads to $0.12\mathrm{PSNR}$ improvements while KD leads to $0.38\mathrm{dB}$ PSNR reduction, indicating the traditional model training method fails in VSR while our method leads to significant performance benefits. As Table 2a suggests, combining all the components yields the best performance vs. complexity tradeoff $(32.81\mathrm{dB},7.34\mathrm{M},$ and $281.25\mathrm{G})$ compared to employing single or partial components. + +B. Ablation on SFE. We further study the performance of our proposed SFE in Table 2b with different variants: only FFT, FFT with learnable filter, the split input with FL and original feature, the split operator with FL and batch normalization, the split operator with FL and instance normalization. Then, we incrementally added different DWConv layers on top of the existing components, such as $3 \times 3$ , $7 \times 7$ , $11 \times 11$ , and $21 \times 21$ . Besides, we only substituted the FFT with the original feature while keeping the LF, IN, and DWConv $21 \times 21$ (-w/o FFT). Experimental results show that: (i) Only adding FFT to Base leads to 0.04 PSNR drop, + +indicating that only utilizing Fourier transform cannot boost performance. (ii) Using the learnable filter leads to 0.07 dB improvements, which account for $41\%$ performance benefits, indicating the learnable filter can improve the representation ability of FFT. (iii) Splitting the features into FFT and IN branches leads to 0.07 dB PSNR benefits, indicating that IN can help the model preserve scale information and prevent covariance shifts. (iv) DWConv with $21 \times 21$ kernel performs better than other kernels, indicating a larger kernel is necessary. (v) SFE without FFT achieves only 31.93 dB PSNR, indicating FFT plays an essential role in SFE. + +C. Ablation on EFE. To evaluate different DCT basis functions in the EFE, we have compared our method with four different DCT variants, which are DCT initialization with fixed coefficients (DF), DCT initialization with learnable filter (DL), DF and DL added energy function, respectively. Experimental results show that: (i) Our method achieves the best PSRN, which demonstrates the effectiveness of using a learnable filter and the energy function. (ii) Removing DCT from EFE leads to 0.43 dB PSNR drop, which indicates EFE is necessary. (iii) EFE with DWConv 11x11 kernel achieves the best PSNR than other DWConv kernels, indicating that a relatively larger kernel tends to achieve better performance. + +D. Privilege Training As shown in Table 2a, 0.12 dB PSNR improvements can be obtained by applying PT to our model, which is 0.50 higher than KD. To further study its effectiveness, we have compared PT with the other six popular model training methods in Table 3 on BasicVSR [2]. It is observed that four of the previous methods do not bring any performance benefits but lead to significant PSNR and SSIM drop. PISR leads to 0.04 dB PSNR and 0.0009 SSIM improvements, which are 0.14 dB and 0.0022 lower than PT in PSNR and SSIM, respectively. Besides, PT can be easily implemented without a pre-trained teacher model. + +E. Feature Visualization Visualization of intermediate features in MFPI is shown in Figure 9. It is observed that: (1) The feature map significantly reduces noise after MFE, indicating that MFE effectively suppresses noise information. (2) SFE can capture object motion and extract spatial features in the frequency domain. (3) EFE focuses on the fine-grained texture and details of the input feature, as shown in the red arrow and circle. (4) Moreover, the MFE effectively fuses the multi-frequency feature and enhances the representation ability. + +# 5. Conclusion + +In this paper, we have proposed a novel VSR model referred to as MFPI, which consists of a multi-frequency representation enhancement module (MFE) and a privilege training method. MFE is utilized to aggregate informa + +Table 2: Ablation studies. Subtables 2a, 2b, and 2c contain components that are defined in Sec. 3.2 and 3.3. We conduct ablation experiments on various components of SFE and EFE, such as FFT/DCT, split operator, learnable filter, BN/IN, energy function, and different coefficients. We also evaluate the effects of different kernel sizes using DW-Conv. Additionally, we employ knowledge distillation [12] or privilege training (PT) to improve our results. + +
BaseMFETrainingPSNR (dB)Params (M)FLOPs (G)
SFEEFEAuxKDPT
✓32.397.32280.59
✓✓32.557.34280.76
✓✓32.527.33280.68
✓✓✓32.677.34280.86
✓✓✓✓32.697.34281.25
✓✓✓✓✓32.317.34281.25
✓✓✓✓✓32.817.34281.25
+ +(a) Individual components. + +
VariantPSNR
Base + FFT32.35
Base + FFT w/. Learnable filter32.48
Base + FFT w/. Learnable filter + original feature32.49
Base + FFT w/. Learnable filter + BN32.43
Base + FFT w/. Learnable filter + IN32.52
Base + FFT w/. Learnable filter + IN + DWConv 3 × 332.48
Base + FFT w/. Learnable filter + IN + DWConv 7 × 732.52
Base + FFT w/. Learnable filter + IN + DWConv 11 × 1132.51
Base + FFT w/. Learnable filter + IN + DWConv 21 × 21 (Our SFE)32.55
Base + w/. Learnable filter + IN + DWConv 21 × 2131.93
+ +(b) Effects of the SFE branch. + +
VariantPSNR
Base + Energy function32.40
Base + DCT w/. Fixed coefficients32.32
Base + DCT w/. Learnable filter32.41
Base + DCT w/. Fixed coefficients + Energy function32.37
Base + DCT w/. Learnable filter + Energy function32.50
Base + DCT w/. Learnable filter + Energy function + DWConv 3 × 332.42
Base + DCT w/. Learnable filter + Energy function + DWConv 7 × 732.40
Base + DCT w/. Learnable filter + Energy function + DWConv 11 × 11 (Our EFE)32.52
Base + DCT w/. Learnable filter + Energy function + DWConv 21 × 2132.43
Base + w/. Learnable filter + Energy function + DWConv 11 × 1132.07
+ +(c) Effects of the EFE branch. +Table 3: Comparison between the proposed privilege training and previous training methods with BasicVSR on [38]. + +
MethodNeeds Teacher?PSNRSSIM
BasicVSR✓31.580.8940
+ Deep Supervision [23]×31.580.8941
+ Self-KD [67]×31.470.8914
+ Hinton KD [12]✓31.260.8883
+ FitNet [44]✓31.520.8934
+ PISR [24]✓31.620.8949
+ Ours×31.760.8971
+ +tion in the frequency domain by operating the spatial- and energy-frequency components via SFE and EFE. It enables CNN-based VSR models to capture long-range dependen + +![](images/25ccaebb90855998f28169a9c3cb689b3eca65c67ea50dfebb351532de33fcce.jpg) +Figure 9: Visualization of the features in MFPI on images from REDS4[38]. The red dot curve denotes the change in spatial information at different locations of the same object. + +cies with very minor additional parameters and computations. Besides, we also propose to improve the performance of VSR from a training perspective by introducing privilege training, which contributes orthogonal effects to our frequency modules. We hope that this paper may promote more research that studies VSR from the perspective of frequency methods and model training methods. + +# 6. Future Work + +In the future, exploring MFPI in a real-world scenario would be an exciting direction, which offers a new valuable perspective on our proposed MFEI performance. We speculate that our frequency methods will be useful for real-scenario tasks and a broader investigation of it has provided additional depth to our study. We will continue to (1) evaluate MFPI on more challenging datasets such as RealVSR [63], and (2) deploy MFPI on edge devices and evaluate its performance. We are actively working on conducting the requested experiments that can further strengthen our conclusions. + +# Acknowledgement + +The authors acknowledge the financial support from the National Key R&D Program of China (No.2021ZD0113805). We appreciate the comments from the seminar participants at the Center for Deep Learning of Computer Vision Research at China Agricultural University, which improves the manuscript significantly. + +# References + +[1] Jose Caballero, Christian Ledig, Andrew Aitken, Alejandro Acosta, Johannes Totz, Zehan Wang, and Wenzhe Shi. Real-time video super-resolution with spatio-temporal networks and motion compensation. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), pages 4778-4787, 2017. 7 +[2] Kelvin CK Chan, Xintao Wang, Ke Yu, Chao Dong, and Chen Change Loy. Basicvsr: The search for essential components in video super-resolution and beyond. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR), pages 4947-4956, 2021. 1, 7, 8 +[3] Kelvin CK Chan, Xintao Wang, Ke Yu, Chao Dong, and Chen Change Loy. Understanding deformable alignment in video super-resolution. 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"lizb@cau.edu.cn" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 139, + 307, + 186, + 319 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 139, + 307, + 186, + 319 + ], + "spans": [ + { + "bbox": [ + 139, + 307, + 186, + 319 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 45, + 331, + 282, + 543 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 331, + 282, + 543 + ], + "spans": [ + { + "bbox": [ + 45, + 331, + 282, + 543 + ], + "type": "text", + "content": "CNN's limited receptive field restricts its ability to capture long-range spatial-temporal dependencies, leading to unsatisfactory performance in video super-resolution (VSR). To tackle this challenge, this paper presents a novel multi-frequency representation enhancement module (MFE) that performs spatial-temporal information aggregation in the frequency domain. Specifically, MFE mainly includes a spatial-frequency representation enhancement branch which captures the long-range dependency in the spatial dimension, and an energy frequency representation enhancement branch to obtain the inter-channel feature relationship. Moreover, a novel model training method named privilege training is proposed to encode the privilege information from high-resolution videos to facilitate model training. With these two methods, we introduce a new VSR model named MFPI, which outperforms state-of-the-art methods by a large margin while maintaining good efficiency on various datasets, including REDS4, Kobe, Vid4, and UDM10." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 46, + 575, + 124, + 588 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 575, + 124, + 588 + ], + "spans": [ + { + "bbox": [ + 46, + 575, + 124, + 588 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 45, + 596, + 279, + 702 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 596, + 279, + 702 + ], + "spans": [ + { + "bbox": [ + 45, + 596, + 279, + 702 + ], + "type": "text", + "content": "Video super-resolution (VSR), which restores high-resolution (HR) video frames from their highly related but unaligned low-resolution (LR) video frames, is well-desired in various real-world applications [11, 2]. Compared with single image super-resolution (SISR), VSR is much more challenging as it aggregates information from multiple related but misaligned frames in the input video. Hence, an ideal VSR model is expected to leverage the spatial information from single images but also integrate the temporal" + } + ] + } + ], + "index": 23 + }, + { + "type": "image", + "bbox": [ + 300, + 305, + 528, + 480 + ], + "blocks": [ + { + "bbox": [ + 300, + 305, + 528, + 480 + ], + "lines": [ + { + "bbox": [ + 300, + 305, + 528, + 480 + ], + "spans": [ + { + "bbox": [ + 300, + 305, + 528, + 480 + ], + "type": "image", + "image_path": "1f29f8aeb33c1b0543b7fd943d6855ae621109df6952db61e8ae4e4595d6f1b8.jpg" + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 296, + 491, + 530, + 527 + ], + "lines": [ + { + "bbox": [ + 296, + 491, + 530, + 527 + ], + "spans": [ + { + "bbox": [ + 296, + 491, + 530, + 527 + ], + "type": "text", + "content": "Figure 1: VSR performance comparison on UDM10 [65] in terms of PSNR (dB), runtime (ms), and parameters (M). MFPI outperforms SOTA methods with high efficiency." + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_caption" + } + ], + "index": 24 + }, + { + "bbox": [ + 297, + 552, + 512, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 552, + 512, + 564 + ], + "spans": [ + { + "bbox": [ + 297, + 552, + 512, + 564 + ], + "type": "text", + "content": "semantic features from multiple frames [45, 50, 18, 3]." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 296, + 566, + 531, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 566, + 531, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 566, + 531, + 730 + ], + "type": "text", + "content": "CNN-based models have become the standard choice for VSR due to their simplicity and efficiency. While recent advances in CNN-based VSR, such as residual learning [2, 73], dense connections[59], hierarchical structures [20], and multi-scale frameworks [63, 34, 48], have shown impressive performance, some potential problems still exist. Firstly, CNN's limited receptive field hinders it from modeling long-range spatial dependencies, making it unable to capture complex semantic information. Secondly, convolutional filters have fixed scales and weights, limiting their performance on large motions and adaptability to diverse inputs. In comparison, with the advantages of self-attention layers, ViTs are effective in processing inputs with long-term spatial dependencies. However, the stack" + } + ] + } + ], + "index": 27 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "spans": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 151, + 41, + 470, + 52 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 151, + 41, + 470, + 52 + ], + "spans": [ + { + "bbox": [ + 151, + 41, + 470, + 52 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 198, + 53, + 422, + 63 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 198, + 53, + 422, + 63 + ], + "spans": [ + { + "bbox": [ + 198, + 53, + 422, + 63 + ], + "type": "text", + "content": "Except for this watermark, it is identical to the accepted version;" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 181, + 63, + 440, + 74 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 181, + 63, + 440, + 74 + ], + "spans": [ + { + "bbox": [ + 181, + 63, + 440, + 74 + ], + "type": "text", + "content": "the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 709, + 279, + 730 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 709, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 709, + 279, + 730 + ], + "type": "text", + "content": "* The first two authors contribute equally. This work is done during the internship of F. Li in Samsung. Z. Li is the corresponding author." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "text", + "content": "12814" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 278, + 153 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 278, + 153 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 278, + 153 + ], + "type": "text", + "content": "of self-attention layers is accompanied with a large computation budget, which results in inferior inference efficiency on edge devices [29]; A natural question arises: can CNNs capture long-range dependencies like ViTs?" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 154, + 278, + 328 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 154, + 278, + 328 + ], + "spans": [ + { + "bbox": [ + 45, + 154, + 278, + 328 + ], + "type": "text", + "content": "In this paper, we propose to answer this question from a frequency perspective. Thanks to their ability to capture global representation, frequency-based models have been widely utilized in single image processing [72, 41, 71]. Unfortunately, their performance in video super-resolution (VSR) is usually limited due to several reasons. (1) Compared with single images, videos are composed of multiple related but misaligned images, which contain both spatial and temporal information. However, traditional frequency methods have fixed paradigms and coefficients [56, 66, 40], making them not able to capture the complex information in videos. (2) Traditional frequency methods are sensitive to the noise in images [64, 14]. This disadvantage becomes more fatal in videos where the noise of different frames can be accumulated." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 330, + 278, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 330, + 278, + 586 + ], + "spans": [ + { + "bbox": [ + 45, + 330, + 278, + 586 + ], + "type": "text", + "content": "To address these challenges, we propose a novel module named multi-frequency representation enhancement (MFE), which aggregates information in the frequency domain. Unlike convolutional and self-attention layers that operate in the feature space, MFE directly manipulates the energy feature map in the frequency domain through three branches: 1) a spatial-frequency representation enhancement branch (SFE) that utilizes a Fast Fourier Transform (FFT) and large kernel convolution layer to capture arbitrary interactions among spatial and long-range dependent features, 2) an energy-frequency representation enhancement branch (EFE) that employs a novel energy discrete cosine transform (DCT) to improve representation and explore potentially useful frequency components, and 3) a pair of convolution layers that leverage large kernels to obtain global range-interact features with stronger shape bias. Compared with the previous frequency methods, the learnable filter in SFE enables FFT to capture both spatial and temporal information, and the energy function in EFE can alleviate the noise accumulated in multiple video frames. Moreover, MFE only contains " + }, + { + "bbox": [ + 45, + 330, + 278, + 586 + ], + "type": "inline_equation", + "content": "0.02\\mathrm{M}" + }, + { + "bbox": [ + 45, + 330, + 278, + 586 + ], + "type": "text", + "content": " parameters, making it affordable for edge devices." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 588, + 278, + 692 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 588, + 278, + 692 + ], + "spans": [ + { + "bbox": [ + 45, + 588, + 278, + 692 + ], + "type": "text", + "content": "Besides MFE, we further propose a novel model training method named privilege training (PT) to facilitate the training of VSR models. Motivated by previous research in learning using privilege information (LUPI) [53], we propose to apply a trainable encoding module to encode the privilege information from HR videos and then employ them to obtain a good initialization for VSR models. Sufficient experiments demonstrate the effectiveness of privilege training on both our model and the other VSR models." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 694, + 278, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 694, + 278, + 730 + ], + "spans": [ + { + "bbox": [ + 46, + 694, + 278, + 730 + ], + "type": "text", + "content": "With MFE and privilege training, we introduce a novel VSR model referred to as MFPI. Extensive experimental results have demonstrated that MFPI outperforms eighteen" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 296, + 106, + 530, + 176 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 106, + 530, + 176 + ], + "spans": [ + { + "bbox": [ + 296, + 106, + 530, + 176 + ], + "type": "text", + "content": "previous methods by a clear margin in six VSR benchmarks. For instance, on UDM10, compared with BasicVSR++ [4], which has similar parameters and runtime with MFPI, MFPI achieves 0.36 dB higher PSNR improvements on UDM10 BD degradation, as shown in Figure 1. To sum up, the main contributions in this paper can be summarized as follows:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 308, + 186, + 530, + 319 + ], + "type": "list", + "angle": 0, + "index": 9, + "blocks": [ + { + "bbox": [ + 308, + 186, + 530, + 233 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 186, + 530, + 233 + ], + "spans": [ + { + "bbox": [ + 308, + 186, + 530, + 233 + ], + "type": "text", + "content": "- We propose multi-frequency representation enhancement (MFE), a module that effectively aggregates information in the frequency domain by operating the spatial- and energy-frequency components." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 308, + 240, + 530, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 240, + 530, + 274 + ], + "spans": [ + { + "bbox": [ + 308, + 240, + 530, + 274 + ], + "type": "text", + "content": "- We propose privilege training, which encodes the privilege information from the HR videos to boost the performance of VSR models." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 308, + 283, + 530, + 319 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 283, + 530, + 319 + ], + "spans": [ + { + "bbox": [ + 308, + 283, + 530, + 319 + ], + "type": "text", + "content": "- Abundant experiments demonstrate the effectiveness of MFPI on four datasets, including REDS4, Vimeo, Vid4, and UDM10 in both BI and BD degradation." + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 297, + 330, + 380, + 341 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 330, + 380, + 341 + ], + "spans": [ + { + "bbox": [ + 297, + 330, + 380, + 341 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 297, + 349, + 426, + 361 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 349, + 426, + 361 + ], + "spans": [ + { + "bbox": [ + 297, + 349, + 426, + 361 + ], + "type": "text", + "content": "2.1. Video Super Resolution" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 367, + 530, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 367, + 530, + 588 + ], + "spans": [ + { + "bbox": [ + 296, + 367, + 530, + 588 + ], + "type": "text", + "content": "Different from SISR, VSR typically produces higher-quality results by utilizing information from neighboring frames. Recently, learning-based approaches have been highly effective in solving the problem of VSR [16, 4]. The main challenge for VSR is how to correctly fuse auxiliary frames in the presence of dynamic content and object motion. To address this problem, abundant methods have been proposed to explicitly use optical flow [55], deformable convolution [57, 50, 3], and homography [18] to align neighbor frames. However, estimating accurate optical flow or transformation is still challenging in large motions. Recently, some methods have been proposed to learn the spatial correspondence across different frames to tackle this challenge [25, 13]. However, these methods have limited performance in VSR since they cannot capture information between adjacent locations or long-range interactions [47, 41]. To address this problem, we introduce a spatial-frequency representation enhancement branch that models long-range spatial and temporal dependencies." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 297, + 595, + 461, + 607 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 595, + 461, + 607 + ], + "spans": [ + { + "bbox": [ + 297, + 595, + 461, + 607 + ], + "type": "text", + "content": "2.2. Learning in Frequency Domain" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 296, + 612, + 530, + 729 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 612, + 530, + 729 + ], + "spans": [ + { + "bbox": [ + 296, + 612, + 530, + 729 + ], + "type": "text", + "content": "Due to the difficulty of distinguishing high-frequency textures from artifacts, fruitful methods [70, 6, 14] have been introduced to decouple them in the frequency space and reconstruct the high-quality textures. For instance, Zhou et al. proposed a deep Fourier up-sampling method to recover the resolution in the frequency domain [72]. Guo et al. utilized the wavelet technique to simplify the mapping between the LR and HR images, reducing the artificial blocks and recovering the edge's information [10]. Motivated by their success, abundant works have tried to" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "type": "text", + "content": "12815" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 281, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 281, + 281 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 281, + 281 + ], + "type": "text", + "content": "apply frequency methods to SR. Dario et al. proposed a Fourier space supervision loss to improve restoration results [6]. Qiu et al. designed a fine-grained self-attention module in the space-frequency domain, which reconstructs the real visual texture without artifacts [41]. However, the images that are directly transformed into the frequency domain still face obstacles as follows: (1) Decomposing features into different frequency components usually lacks local correlation information in the channel dimension, making it difficult to utilize the useful frequency components [40]. (2) Non-parametric frequency-based methods are easily susceptible to noise and image scale factors [35]. To address the above problems, this paper proposes to combine the advantages of the energy function and frequency-based representations by using DCT with learnable filters." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 298, + 240, + 311 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 298, + 240, + 311 + ], + "spans": [ + { + "bbox": [ + 46, + 298, + 240, + 311 + ], + "type": "text", + "content": "2.3. Learning Using Privilege Information" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 319, + 281, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 319, + 281, + 552 + ], + "spans": [ + { + "bbox": [ + 45, + 319, + 281, + 552 + ], + "type": "text", + "content": "Learning using privilege information (LUPI) was first proposed by Vapnik et al. to employ the privilege information provided by a teacher model in support vector machine [53]. Generally speaking, LUPI aims to improve the performance of a model by using privilege information, which is utilized during training but not required during inference. Vapnik et al. further utilized LUPI to accelerate the inference speed of SVMs by similarity control and knowledge transfer [52]. Motivated by the success of knowledge distillation [12] on deep neural networks, recently, David et al. proposed generalized distillation, which combines knowledge distillation with learning with privilege information theoretically [32]. Recently, label-guided auxiliary was introduced to apply LUPI to point cloud-based 3D detection by using the privilege information from annotations [15]. Lee et al. proposed PISR, which introduces LUPI to single image super-resolution by using variational knowledge distillation [24]. Moreover, LUPI has also been utilized in semi-supervised learning [7], domain adaptation [37], speech recognition [36] and so on." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 554, + 281, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 554, + 281, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 554, + 281, + 730 + ], + "type": "text", + "content": "The most related work of the privilege training in our method is PISR [24], which is proposed for knowledge distillation on single image super-resolution. Their main difference is that: (1) PISR is proposed for SISR for model compression while our method is proposed for VSR to improve the quality of restoration. (2) Besides, PISR is a knowledge distillation method which mainly leverages the privilege information with distillation loss. In contrast, our method leverages the privilege information by sharing model weights. (3) PISR implicitly encodes the privilege information via the reconstruction of LR images while our method explicitly encodes privilege information from HR videos with a trainable network. Besides, ablation studies in Table 3 also demonstrate that our method leads to significantly higher performance than PISR." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 296, + 105, + 379, + 118 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 105, + 379, + 118 + ], + "spans": [ + { + "bbox": [ + 296, + 105, + 379, + 118 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 296, + 124, + 450, + 137 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 124, + 450, + 137 + ], + "spans": [ + { + "bbox": [ + 296, + 124, + 450, + 137 + ], + "type": "text", + "content": "3.1. Overall Framework for VSR" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "spans": [ + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "text", + "content": "Following the previous work [4], we adopt the recurrent bidirectional propagation as the baseline model. Based on its architecture, we propose a novel VSR model termed MFPI, which consists of a multi-frequency representation enhancement module (MFE) to improve the LR frames representation in the frequency domain, and a novel VSR model training method named privilege training which encodes privilege information from HR frames to facilitate model training. The overall architecture is shown in Figure 2: (1) The VSR model extracts features from the LR frames images to reconstruct the HR frames images. (2) Residual blocks and MFE are employed to extract the feature " + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "inline_equation", + "content": "f_{i}^{j}" + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "text", + "content": " from the LR images, where " + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "inline_equation", + "content": "f_{i}^{j}" + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "text", + "content": " denotes the feature at " + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "inline_equation", + "content": "i_{th}" + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "text", + "content": " timestamp in the " + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "inline_equation", + "content": "j_{th}" + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "text", + "content": " propagation branch. (3) The flow-guided deformable alignment block (FDA) aligns the neighboring features " + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "inline_equation", + "content": "f_{i-1}^{j}" + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "inline_equation", + "content": "f_{i-2}^{j}" + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "text", + "content": ". And the pixel-shuffle operator is employed to perform upsampling " + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "inline_equation", + "content": "4 \\times" + }, + { + "bbox": [ + 296, + 143, + 530, + 377 + ], + "type": "text", + "content": " scales from LR to HR frames. Besides, learning privilege information boosts the performance of our VSR models during training, as shown in Figure 3." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 296, + 383, + 509, + 408 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 383, + 509, + 408 + ], + "spans": [ + { + "bbox": [ + 296, + 383, + 509, + 408 + ], + "type": "text", + "content": "3.2. MFE: A Multi-Frequency Representation Enhancement Module" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 296, + 414, + 530, + 636 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 414, + 530, + 636 + ], + "spans": [ + { + "bbox": [ + 296, + 414, + 530, + 636 + ], + "type": "text", + "content": "As depicted in Figure 2 (b), we design a multi-frequency representation enhancement (MFE) to improve the representation ability and aggregate spatial-temporal information in VSR architecture. MFE is a plug-in-play building block which adopts a multi-branch structure to capture multifrequency representation [9]. Concretely, it first encodes the input features with a depthwise convolution (DWConv) layer [68] and then processes them with three different branches, including 1) a spatial-frequency representation enhancement branch to capture the spatial-frequency information and long-range dependence features, 2) an energy-frequency representation enhancement branch to improve the representation ability and model the inter-channel relationship in the frequency domain, and 3) an auxiliary branch with a pair of " + }, + { + "bbox": [ + 296, + 414, + 530, + 636 + ], + "type": "inline_equation", + "content": "7 \\times 1" + }, + { + "bbox": [ + 296, + 414, + 530, + 636 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 414, + 530, + 636 + ], + "type": "inline_equation", + "content": "1 \\times 7" + }, + { + "bbox": [ + 296, + 414, + 530, + 636 + ], + "type": "text", + "content": " DWConv to inject the inductive bias and facilitate training [8, 31]. Finally, a " + }, + { + "bbox": [ + 296, + 414, + 530, + 636 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 296, + 414, + 530, + 636 + ], + "type": "text", + "content": " convolution layer aggregates the diverse features from three branches, and the skip connection is employed to facilitate the convergence of MFE [30]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 296, + 652, + 530, + 665 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 652, + 530, + 665 + ], + "spans": [ + { + "bbox": [ + 296, + 652, + 530, + 665 + ], + "type": "text", + "content": "3.2.1 Spatial Frequency Representation Enhancement" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "spans": [ + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "type": "text", + "content": "As illustrated in Figure 2 (c), the spatial frequency representation enhancement (SFE) branch first employs a pair of " + }, + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "type": "inline_equation", + "content": "DWConv" + }, + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "type": "text", + "content": " to generate the feature map " + }, + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "type": "inline_equation", + "content": "f_{in}" + }, + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "type": "text", + "content": " from the input " + }, + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "type": "inline_equation", + "content": "x_{in} \\in \\mathbb{R}^{H \\times W \\times C}" + }, + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "type": "text", + "content": ". Then, we split " + }, + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "type": "inline_equation", + "content": "f_{in}" + }, + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "type": "text", + "content": " into two parts " + }, + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "type": "inline_equation", + "content": "f_{mid1}, f_{mid2} \\in \\mathbb{R}^{h \\times w \\times c/2}" + }, + { + "bbox": [ + 296, + 671, + 530, + 731 + ], + "type": "text", + "content": " [26, 69]. The FFT layer pro" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "text", + "content": "12816" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 58, + 103, + 478, + 255 + ], + "blocks": [ + { + "bbox": [ + 58, + 103, + 478, + 255 + ], + "lines": [ + { + "bbox": [ + 58, + 103, + 478, + 255 + ], + "spans": [ + { + "bbox": [ + 58, + 103, + 478, + 255 + ], + "type": "image", + "image_path": "10daa50da56daf15e6a437f20706144e06c0a737008a7a3bf357bf31cdaed919.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 123, + 258, + 240, + 267 + ], + "lines": [ + { + "bbox": [ + 123, + 258, + 240, + 267 + ], + "spans": [ + { + "bbox": [ + 123, + 258, + 240, + 267 + ], + "type": "text", + "content": "(a) The Overall Framework of MFPI" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 330, + 257, + 508, + 267 + ], + "lines": [ + { + "bbox": [ + 330, + 257, + 508, + 267 + ], + "spans": [ + { + "bbox": [ + 330, + 257, + 508, + 267 + ], + "type": "text", + "content": "(b) MFE: Multi-frequency Representation Enhancement" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 48, + 271, + 283, + 350 + ], + "blocks": [ + { + "bbox": [ + 48, + 271, + 283, + 350 + ], + "lines": [ + { + "bbox": [ + 48, + 271, + 283, + 350 + ], + "spans": [ + { + "bbox": [ + 48, + 271, + 283, + 350 + ], + "type": "image", + "image_path": "339c9c6c90b8e24dda7da7134f532a8f0a79543708f9d37fbadf9cd31b05ecb6.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 76, + 352, + 255, + 362 + ], + "lines": [ + { + "bbox": [ + 76, + 352, + 255, + 362 + ], + "spans": [ + { + "bbox": [ + 76, + 352, + 255, + 362 + ], + "type": "text", + "content": "(c) SFE: Spatial Frequency Representation Enhancement" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 45, + 371, + 531, + 442 + ], + "lines": [ + { + "bbox": [ + 45, + 371, + 531, + 442 + ], + "spans": [ + { + "bbox": [ + 45, + 371, + 531, + 442 + ], + "type": "text", + "content": "Figure 2: (a) An overview framework of MFPI. The blue dot line denotes the bilinear upsampling operator. The red curve denotes second-order propagation. \"FDA\" denotes the flow-guided deformable alignment block [4]. The green block denotes the proposed multi-frequency representation enhancement (MFE). (b) An overview of the MFE. (c) The details of the spatial-frequency representation enhancement branch in MFE extract spatial-level and long-range dependencies. (d) The details of the energy-frequency representation enhancement branch. " + }, + { + "bbox": [ + 45, + 371, + 531, + 442 + ], + "type": "inline_equation", + "content": "e_{i,j}^{*}" + }, + { + "bbox": [ + 45, + 371, + 531, + 442 + ], + "type": "text", + "content": " denotes the energy feature. Note that the 'FC layer' consists of a sequence of the 'linear-LReLU-linear-LReLU' operator. DWConv denotes the depthwise convolution [68]." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 289, + 275, + 529, + 345 + ], + "blocks": [ + { + "bbox": [ + 289, + 275, + 529, + 345 + ], + "lines": [ + { + "bbox": [ + 289, + 275, + 529, + 345 + ], + "spans": [ + { + "bbox": [ + 289, + 275, + 529, + 345 + ], + "type": "image", + "image_path": "648cdb3a3a646446c300915411b8cf7ae18c6c741ad268f0c256e5f8e8588bcb.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 325, + 352, + 506, + 362 + ], + "lines": [ + { + "bbox": [ + 325, + 352, + 506, + 362 + ], + "spans": [ + { + "bbox": [ + 325, + 352, + 506, + 362 + ], + "type": "text", + "content": "(d) EFE: Energy Frequency Representation Enhancement" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 462, + 279, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 462, + 279, + 484 + ], + "spans": [ + { + "bbox": [ + 45, + 462, + 279, + 484 + ], + "type": "text", + "content": "cesses " + }, + { + "bbox": [ + 45, + 462, + 279, + 484 + ], + "type": "inline_equation", + "content": "f_{mid1}" + }, + { + "bbox": [ + 45, + 462, + 279, + 484 + ], + "type": "text", + "content": " represents different spatial dependence information as follows:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 99, + 493, + 279, + 507 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 99, + 493, + 279, + 507 + ], + "spans": [ + { + "bbox": [ + 99, + 493, + 279, + 507 + ], + "type": "interline_equation", + "content": "f r e q = \\mathcal {F} \\left[ f _ {\\text {m i d} 1} \\right] \\in \\mathbb {C} ^ {h \\times w \\times c / 2} \\tag {1}", + "image_path": "13af6c07abba23e4e96c0239ed75bb6290c963836d423bbe31894780d9181d48.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "spans": [ + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "inline_equation", + "content": "c, h, w" + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "text", + "content": " denote the input channel, height, width of the feature maps, respectively. " + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "inline_equation", + "content": "\\mathcal{F}[\\cdot]" + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "text", + "content": " denotes the 2D FFT, " + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "inline_equation", + "content": "freq" + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "text", + "content": " represents the frequency feature of " + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "inline_equation", + "content": "f_{mid1}" + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "text", + "content": ". To make SFE adaptive to diverse features [43, 54], we modulate the " + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "inline_equation", + "content": "freq" + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "text", + "content": " multiplies with a learnable filter " + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "inline_equation", + "content": "L \\in \\mathbb{C}^{h \\times w \\times c/2}" + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "text", + "content": " in the frequency domain: " + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "inline_equation", + "content": "\\tilde{freq} = freq \\times L" + }, + { + "bbox": [ + 45, + 516, + 279, + 607 + ], + "type": "text", + "content": ". The inverse FFT transfers the modulated frequency feature back to the spatial domain:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 117, + 607, + 279, + 627 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 117, + 607, + 279, + 627 + ], + "spans": [ + { + "bbox": [ + 117, + 607, + 279, + 627 + ], + "type": "interline_equation", + "content": "\\tilde {f _ {m i d 1}} \\leftarrow \\mathcal {F} ^ {- 1} \\left[ f \\tilde {r e q} \\right] \\tag {2}", + "image_path": "8fec1eda209e824372418864ea5e693ac63fbe0b03fc012d25a3d9dfc6c36dbb.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 45, + 631, + 279, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 631, + 279, + 682 + ], + "spans": [ + { + "bbox": [ + 45, + 631, + 279, + 682 + ], + "type": "text", + "content": "Finally, the output feature " + }, + { + "bbox": [ + 45, + 631, + 279, + 682 + ], + "type": "inline_equation", + "content": "f_{out}" + }, + { + "bbox": [ + 45, + 631, + 279, + 682 + ], + "type": "text", + "content": " is obtained by concatenating with an instance normalization (IN) [51] layer, which prevents covariance shift and preserves the scale information: " + }, + { + "bbox": [ + 45, + 631, + 279, + 682 + ], + "type": "inline_equation", + "content": "f_{out} = \\text{Concat}\\left(f_{mid1}, \\text{IN}\\left(f_{mid2}\\right)\\right)" + }, + { + "bbox": [ + 45, + 631, + 279, + 682 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 45, + 683, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 683, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 683, + 279, + 730 + ], + "type": "text", + "content": "It is also worth noting that in our implementation: (1) SFE utilizes a relatively large local window of " + }, + { + "bbox": [ + 45, + 683, + 279, + 730 + ], + "type": "inline_equation", + "content": "DWConv" + }, + { + "bbox": [ + 45, + 683, + 279, + 730 + ], + "type": "inline_equation", + "content": "(e.g., 21 \\times 1, 1 \\times 21)" + }, + { + "bbox": [ + 45, + 683, + 279, + 730 + ], + "type": "text", + "content": " to capture the long-range spatial dependencies from features. (2) Besides, a learnable Fourier" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 296, + 462, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 462, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 462, + 530, + 730 + ], + "type": "text", + "content": "transform with IN can exhibit clear patterns and generalizations in the frequency domain. Hence, the proposed SFE branch tends to be more efficient than directly utilizing Fourier transforms in the spatial-temporal dimension (Table 2b). (3) Considering that FFT has less computation than DFT, we employ FFT in SFE as the frequency transformation to improve model representation. Moreover, the Fourier domain has the nature of global modeling [54]. Hence, computation on frequency bands implies information aggregation over all the spatial locations of the input images. Specifically, in our SFE, FFT is performed over the whole feature map across all the spatial locations, which is equivalent to the global receptive field of the whole feature. (4) SFE splits features into two branches to improve computational efficiency. Specifically, this split operator enables SFE to capture and combine different aspects or representations of the input data. One part focus on the spatial frequency characteristics or patterns, and the other part act as a form of regularization by introducing additional constraints, such as instance normalization. Their outputs can be concatenated to create a richer and more comprehensive representation. This can enhance the SFE's ability to learn complex relationships and improve its overall performance." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "type": "text", + "content": "12817" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 279, + 153 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 279, + 153 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 279, + 153 + ], + "type": "text", + "content": "Besides, this two-branch design is also similar to the idea of group convolution and CSN [71], which is a well-known technique of efficient neural networks. Please refer to supplementary materials for theoretical analysis." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 169, + 279, + 181 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 169, + 279, + 181 + ], + "spans": [ + { + "bbox": [ + 45, + 169, + 279, + 181 + ], + "type": "text", + "content": "3.2.2 Energy Frequency Representation Enhancement" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "spans": [ + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "text", + "content": "Considering that the frequency methods with a learning filter can be more generic and flexible interactions among spatial locations from diverse images, we introduce an energy function to reweight the input feature and utilize the learnable filter with DCT to represent the rich inter-channel relationship [40]. The architecture of the energy frequency representation enhancement (EFE) is illustrated in Figure 2 (d). More specifically, EFE first utilizes a pair of " + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "inline_equation", + "content": "DWConv" + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "text", + "content": " (e.g., " + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "inline_equation", + "content": "11 \\times 1,1 \\times 11" + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "text", + "content": ") to generate the feature map " + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "text", + "content": ". Then, we calculate the mean " + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "inline_equation", + "content": "\\hat{\\mu}" + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "text", + "content": " and variance " + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "inline_equation", + "content": "\\hat{\\sigma}^2" + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 45, + 187, + 279, + 316 + ], + "type": "text", + "content": ", and the energy value [62] can be obtained by minimizing the following:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 101, + 325, + 279, + 354 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 101, + 325, + 279, + 354 + ], + "spans": [ + { + "bbox": [ + 101, + 325, + 279, + 354 + ], + "type": "interline_equation", + "content": "e _ {i, j} = \\frac {4 (\\hat {\\sigma} ^ {2} + \\delta)}{(t _ {i , j} - \\hat {\\mu}) ^ {2} + 2 \\hat {\\sigma} ^ {2} + 2 \\delta} \\tag {3}", + "image_path": "b5574f42685ef3a303e12f5d12e9863209cb5d47d6bea042274dd75722418bae.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "spans": [ + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "text", + "content": " is the hyper-parameter, " + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "inline_equation", + "content": "e_{i,j}" + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "text", + "content": " denote the energy value of target pixel " + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "inline_equation", + "content": "t_{i,j}" + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "inline_equation", + "content": "i\\in \\{0,1,\\dots ,H - 1\\}" + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "inline_equation", + "content": "j\\in \\{0,1,\\dots ,W - 1\\}" + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "text", + "content": ". The energy feature is obtained by grouping all the " + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "inline_equation", + "content": "e_{i,j}" + }, + { + "bbox": [ + 45, + 362, + 279, + 421 + ], + "type": "text", + "content": " across spatial and channel levels, which rescale the energy value to restrict too large energy value:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 76, + 430, + 279, + 462 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 76, + 430, + 279, + 462 + ], + "spans": [ + { + "bbox": [ + 76, + 430, + 279, + 462 + ], + "type": "interline_equation", + "content": "e _ {i, j} ^ {*} = \\text {L e a k y R e L U} \\left(\\frac {1}{\\sum_ {i \\neg = 0} ^ {h} \\sum_ {j \\neg = 0} ^ {w} e _ {i , j}}\\right) \\tag {4}", + "image_path": "1fb95a177493f30f44cd22be6ac7d437e0849aa824c5dd8d2e2b3ddd64a80d4e.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 467, + 279, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 467, + 279, + 502 + ], + "spans": [ + { + "bbox": [ + 45, + 467, + 279, + 502 + ], + "type": "text", + "content": "To further enrich the representation ability of EFE, we employ the DCT technique to convert the energy features into the frequency domain as follows:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 80, + 511, + 279, + 544 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 511, + 279, + 544 + ], + "spans": [ + { + "bbox": [ + 80, + 511, + 279, + 544 + ], + "type": "interline_equation", + "content": "\\mathcal {F} _ {c} (i, j) = \\frac {2}{\\sqrt {H W}} \\alpha (i) \\alpha (j) \\sum_ {h = 0} ^ {H - 1} \\sum_ {w = 0} ^ {W - 1} e _ {i, j} ^ {*} \\tag {5}", + "image_path": "29a467407d0347e563298b9cfd65cfe65e991231ef5c153361c3e0107d19139e.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 61, + 564, + 279, + 591 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 564, + 279, + 591 + ], + "spans": [ + { + "bbox": [ + 61, + 564, + 279, + 591 + ], + "type": "interline_equation", + "content": "\\mathcal {K} _ {h, w} ^ {i, j} = \\cos \\left(\\frac {(2 h + 1) i \\pi}{2 H}\\right) \\cos \\left(\\frac {(2 w + 1) j \\pi}{2 W}\\right) \\tag {6}", + "image_path": "4193857d670f2f2bb6305c7b9a4f6f5ea79d37a1ce5ad6ab0527da13e1943479.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 111, + 604, + 279, + 620 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 604, + 279, + 620 + ], + "spans": [ + { + "bbox": [ + 111, + 604, + 279, + 620 + ], + "type": "interline_equation", + "content": "f _ {c} ^ {h, w} = \\mathcal {K} _ {h, w} ^ {i, j} \\times \\mathcal {F} _ {c} \\left(e _ {i, j} ^ {*}\\right) \\tag {7}", + "image_path": "6e37229049c0d4eb9a950641e58eedcddb7d660cb27864e29345eeddbb3c1b90.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_c" + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "text", + "content": " denotes DCT operation, " + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "text", + "content": " denotes the basis function of DCT, " + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "inline_equation", + "content": "\\alpha(x) = 1/\\sqrt{2}" + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "inline_equation", + "content": "x = 0" + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "inline_equation", + "content": "\\alpha(x) = 1" + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "text", + "content": " otherwise [46]. Finally, the output refined feature as follows: " + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "inline_equation", + "content": "f_{out} = f_c^{h,w} \\times x_{i,j}" + }, + { + "bbox": [ + 45, + 624, + 279, + 730 + ], + "type": "text", + "content": ". Note that an element-wise multiplication between frequency-domain features and the learnable filters improves the representation ability and makes EFE flexible adaptive to different feature inputs. Besides, the FC layer in Figure 2 (d) consists of a sequence of the 'Linear-LeakyReLU-Linear-LeakyReLU' operators, which" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 296, + 106, + 530, + 187 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 106, + 530, + 187 + ], + "spans": [ + { + "bbox": [ + 296, + 106, + 530, + 187 + ], + "type": "text", + "content": "convert the channel-wise feature into a scalar representation, which reduces the complexity and improves the effectiveness in the frequency domain. Different from the SFE branch, the EFE branch leverages the merits of the energy function and frequency components to improve the representation power and model the relationship among inter-channel dimensions, as shown in Figure 9." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 297, + 194, + 402, + 206 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 194, + 402, + 206 + ], + "spans": [ + { + "bbox": [ + 297, + 194, + 402, + 206 + ], + "type": "text", + "content": "3.3. Privilege Training" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "spans": [ + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": "Learning using privilege information is a well-known theory in machine learning, which shows that one can improve the performance of machine learning by using kinds of privilege information, which is available in training but not accessible during inference. Motivated by its effectiveness, in this paper, we propose a novel neural network training method for VSR, which is shown in Figure 3. By denoting the LR and corresponding HR videos as " + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": ", respectively, the traditional training method can be formulated as " + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "inline_equation", + "content": "\\min \\mathbb{E}[|f(x) - y|]" + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "inline_equation", + "content": "f(\\cdot)" + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": " denotes the superresolution model. In contrast, in our method, we additionally introduce a lightweight neural network " + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": ", which aims to encode the privilege information from the HR frames " + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": " to a tensor of privilege information " + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "inline_equation", + "content": "\\mathcal{D}(y)" + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": " which has the same shape with the LR frames " + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": ". Then, we can denote a mixture of the LR images and the privilege information as " + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "inline_equation", + "content": "x^{*} = x + \\gamma \\cdot \\mathcal{D}(y)" + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "inline_equation", + "content": "\\gamma \\in [0,1]" + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": " is a parameter to balance the two items. During the training period, we gradually decrease " + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": " from 1 to 0. Hence, the VSR model is able to firstly learn a good representation by using the privilege information, and then gradually get rid of it. Note that since " + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 296, + 212, + 530, + 491 + ], + "type": "text", + "content": " is decreased to 0, the VSR model does not require any privilege information during inference. In summary, its objective of privilege training can be written as" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 348, + 497, + 530, + 517 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 348, + 497, + 530, + 517 + ], + "spans": [ + { + "bbox": [ + 348, + 497, + 530, + 517 + ], + "type": "interline_equation", + "content": "\\underset {f, \\mathcal {D}} {\\arg \\min } \\mathbb {E} [ | f (x ^ {*}) - y | + | \\mathcal {D} (y) | ] \\tag {8}", + "image_path": "018460df135a8172927aa6e50891deb07ddaa3b17777d3554967c2948c9cdc0f.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 296, + 523, + 530, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 523, + 530, + 639 + ], + "spans": [ + { + "bbox": [ + 296, + 523, + 530, + 639 + ], + "type": "text", + "content": "where the first loss item is the common reconstruction loss for VSR training. The second loss item is a regularization item which reduces the energy of privilege information to prevent the model from overusing the privilege information. Note that the regularization item is indispensable since without this item the VSR model may degenerate into a naive auto-encoder which reconstructs the HR images totally based on the privilege information. Note that " + }, + { + "bbox": [ + 296, + 523, + 530, + 639 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 296, + 523, + 530, + 639 + ], + "type": "text", + "content": " in our implementation is a stack of three convolutional layers followed with LeakyReLU." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 296, + 648, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 648, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 648, + 530, + 730 + ], + "type": "text", + "content": "Why does privilege training work? The effectiveness of privilege information can be understood from the perspective of weight initialization. During the early training iterations, the model can quickly converge to a flat minima by using the privilege information. Then, by reducing " + }, + { + "bbox": [ + 296, + 648, + 530, + 730 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 296, + 648, + 530, + 730 + ], + "type": "text", + "content": ", the privilege information gradually makes a less influence to the VSR model, and hence the VSR model can converge" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "type": "text", + "content": "12818" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 82, + 104, + 494, + 223 + ], + "blocks": [ + { + "bbox": [ + 82, + 104, + 494, + 223 + ], + "lines": [ + { + "bbox": [ + 82, + 104, + 494, + 223 + ], + "spans": [ + { + "bbox": [ + 82, + 104, + 494, + 223 + ], + "type": "image", + "image_path": "025e5f2b6696c3b849fc9c8b5c31b8468c7e93147c94943109dfa7fb1473aa0c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 231, + 531, + 255 + ], + "lines": [ + { + "bbox": [ + 45, + 231, + 531, + 255 + ], + "spans": [ + { + "bbox": [ + 45, + 231, + 531, + 255 + ], + "type": "text", + "content": "Figure 3: The paradigm of the proposed learning using privilege information on VSR. " + }, + { + "bbox": [ + 45, + 231, + 531, + 255 + ], + "type": "inline_equation", + "content": "\\oplus" + }, + { + "bbox": [ + 45, + 231, + 531, + 255 + ], + "type": "text", + "content": " denotes a weighted addition between the privilege information and the LR frames." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 48, + 273, + 278, + 365 + ], + "blocks": [ + { + "bbox": [ + 48, + 273, + 278, + 365 + ], + "lines": [ + { + "bbox": [ + 48, + 273, + 278, + 365 + ], + "spans": [ + { + "bbox": [ + 48, + 273, + 278, + 365 + ], + "type": "image", + "image_path": "62a95eca1968bea6f1e66e2a2433b90308c59cd3364ae503092e02fc1e267ff8.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 60, + 373, + 263, + 384 + ], + "lines": [ + { + "bbox": [ + 60, + 373, + 263, + 384 + ], + "spans": [ + { + "bbox": [ + 60, + 373, + 263, + 384 + ], + "type": "text", + "content": "Figure 4: Visualization of the privilege information." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 408, + 279, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 408, + 279, + 548 + ], + "spans": [ + { + "bbox": [ + 45, + 408, + 279, + 548 + ], + "type": "text", + "content": "stably. Secondly, the success of our method can also be understood as a special case of knowledge distillation, where the teacher model is trained with privilege information, the student model is trained with only the LR frames, and the knowledge distillation is applied by sharing the weights of the student and the teacher. Besides, Figure 4 visualizes the privilege information encoded during the training period. It is observed that most of privilege information concentrates on the pixels belonging to the objects and their edges, which are more important in the assessment of image quality. These privilege information is utilized to help VSR models to converge at the early training period." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 562, + 120, + 575 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 562, + 120, + 575 + ], + "spans": [ + { + "bbox": [ + 45, + 562, + 120, + 575 + ], + "type": "text", + "content": "4. Experiment" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 582, + 158, + 595 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 582, + 158, + 595 + ], + "spans": [ + { + "bbox": [ + 45, + 582, + 158, + 595 + ], + "type": "text", + "content": "4.1. Experimental Setup" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "text", + "content": "Our model is trained for each task with " + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "inline_equation", + "content": "6 \\times 10^{5}" + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "text", + "content": " iterations using randomly cropped patches. We apply data augmentation techniques such as random horizontal and vertical flipping and " + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "inline_equation", + "content": "90^{\\circ}" + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "text", + "content": " rotation. The Adam optimizer [22] is used with an initial learning rate of " + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "inline_equation", + "content": "2 \\times 10^{-4}" + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "text", + "content": ", which is steadily decreased to " + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "inline_equation", + "content": "1 \\times 10^{-7}" + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "text", + "content": " with cosine annealing learning rate decay [33]. " + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "text", + "content": " is set to " + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "inline_equation", + "content": "1 \\times 10^{-6}" + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "text", + "content": " [62]. We employ SPyNet to predict optical flow in videos [42]. Each branch contains 7 residual blocks and 64 feature channels. The batch size is set to 4, and the input low-resolution (LR) frames are of patch size " + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "inline_equation", + "content": "64 \\times 64" + }, + { + "bbox": [ + 45, + 601, + 280, + 730 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 299, + 273, + 530, + 409 + ], + "blocks": [ + { + "bbox": [ + 299, + 273, + 530, + 409 + ], + "lines": [ + { + "bbox": [ + 299, + 273, + 530, + 409 + ], + "spans": [ + { + "bbox": [ + 299, + 273, + 530, + 409 + ], + "type": "image", + "image_path": "6ce13d1e4346a485d76a774eaefadf5e36d998680f636bab80fb5460ee2e6c9b.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 296, + 421, + 530, + 455 + ], + "lines": [ + { + "bbox": [ + 296, + 421, + 530, + 455 + ], + "spans": [ + { + "bbox": [ + 296, + 421, + 530, + 455 + ], + "type": "text", + "content": "Figure 5: Challenging scenario on REDS4 [38]. MFPI generates sharp edge in repeated structures of the windows and sharper texts." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 296, + 478, + 530, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 478, + 530, + 605 + ], + "spans": [ + { + "bbox": [ + 296, + 478, + 530, + 605 + ], + "type": "text", + "content": "Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Index Measure (SSIM) [58] between ground truth and restored videos are utilized as the metrics in our quantitative comparisons. We follow [4] to utilize REDS [38], Vimeo90K [60] as training set, and REDS4, Vimeo-90K-T [60], Vid4 [28], UDM10 [65], and Vimeo-90K as the test set. REDSval4 is utilized as the validation set. All models are tested with " + }, + { + "bbox": [ + 296, + 478, + 530, + 605 + ], + "type": "inline_equation", + "content": "4 \\times" + }, + { + "bbox": [ + 296, + 478, + 530, + 605 + ], + "type": "text", + "content": " downsampling via two degradations - Bicubic (BI) and Blur Downsampling (BD). All experiments are implemented with PyTorch [39] and on two NVIDIA Tesla A100 GPUs." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 297, + 617, + 520, + 629 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 617, + 520, + 629 + ], + "spans": [ + { + "bbox": [ + 297, + 617, + 520, + 629 + ], + "type": "text", + "content": "4.2. Comparisons with State-of-the-Art Methods" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 636, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 636, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 636, + 530, + 730 + ], + "type": "text", + "content": "Qualitative Comparison We show the comparison of visual results in Figure. 5, 6, 7 and 8. It is observed that the results of prior works usually suffer from incomplete artifacts or blurred regions in the image. In contrast, our model restores sharper edges and finer detailed textures of the number plate in Figure 5 and the display board in Figure 6. Besides, MFPI is able to recover the edge of the small object in Figure 6. As shown in Figure 7 and 8, MFPI also shows" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 300, + 756 + ], + "type": "text", + "content": "12819" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 46, + 149, + 530, + 374 + ], + "blocks": [ + { + "bbox": [ + 45, + 104, + 531, + 140 + ], + "lines": [ + { + "bbox": [ + 45, + 104, + 531, + 140 + ], + "spans": [ + { + "bbox": [ + 45, + 104, + 531, + 140 + ], + "type": "text", + "content": "Table 1: Quantitative comparison (PSNR/SSIM). All results are calculated on Y-channel except REDS4 [38] (RGB-channel). The runtime is computed on an LR size of " + }, + { + "bbox": [ + 45, + 104, + 531, + 140 + ], + "type": "inline_equation", + "content": "180 \\times 320" + }, + { + "bbox": [ + 45, + 104, + 531, + 140 + ], + "type": "text", + "content": ". A " + }, + { + "bbox": [ + 45, + 104, + 531, + 140 + ], + "type": "inline_equation", + "content": "4 \\times" + }, + { + "bbox": [ + 45, + 104, + 531, + 140 + ], + "type": "text", + "content": " upsampling is performed following previous studies. Blanked entries correspond to results not reported in previous works. Numbers in bold indicate the best performance." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 46, + 149, + 530, + 374 + ], + "lines": [ + { + "bbox": [ + 46, + 149, + 530, + 374 + ], + "spans": [ + { + "bbox": [ + 46, + 149, + 530, + 374 + ], + "type": "table", + "html": "
ModelParams (M)Runtime (ms)BI degradationBD degradation
REDS4 [38]Vimeo-90K-T [60]Vid4[28]UDM10 [65]Vimeo-90-T [60]Vid4 [28]
Bicubic--26.14/0.729231.32/0.868423.78/0.634728.47/0.825331.30/0.868721.80/0.5246
VESPCN [1]----25.35/0.7557---
SPMC [49]----25.88/0.7752---
TOFlow [61]--27.98/0.799033.08/0.905425.89/0.765136.26/0.943834.62/0.9212-
FRVSR [45]5.1137---37.09/0.952235.64/0.931926.69/0.8103
DUF [21]5.897428.63/0.8251--38.48/0.960536.87/0.944727.38/0.8329
RBPN [11]12.2150730.09/0.859037.07/0.943527.12/0.818038.66/0.959637.20/0.9458-
EDVR-M [57]3.311830.53/0.869937.09/0.944627.10/0.818639.40/0.966337.33/0.948427.45/0.8406
EDVR [57]20.637831.09/0.880037.61/0.948927.35/0.826439.89/0.968637.81/0.952327.85/0.8503
PFNL [65]3.029529.63/0.850236.14/0.936326.73/0.802938.74/0.9627-27.16/0.8355
MuCAN [27]--30.88/0.875037.32/0.9465----
TGA [18]5.8384----37.59/0.951627.63/0.8423
RLSP [5]4.249---38.48/0.960636.49/0.940327.48/0.8388
RSDN [17]6.294---39.35/0.965337.23/0.947127.92/0.8505
RRN [19]3.445--38.96/0.9644-27.69/0.8488
BasicVSR [2]6.36331.42/0.890937.18/0.945027.24/0.825139.96/0.969437.53/0.949827.96/0.8553
IconVSR [2]8.77031.67/0.894837.47/0.947627.39/0.827940.03/0.969437.84/0.952428.04/0.8570
BasicVSR++ [4]7.37732.39/0.906937.79/0.953027.79/0.840040.72/0.972238.21/0.955029.04/0.8753
PSRT [47]13.481232.72/0.910638.27/0.953628.07/0.8485---
MFPI (Ours)7.37632.81/0.910638.28/0.953428.11/0.848141.08/0.974138.70/0.957929.34/0.8781
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(2) Compared with BasicVSR++ which has very similar parameters and speed to our method, 0.42 dB, 0.49 dB and 0.32 dB PSNR improvements can be achieved on the three datasets in BI degradation experiments, respectively. (3) Compared with PSRT-recurrent which has slightly lower PSNR than our method, our model only has around " + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "inline_equation", + "content": "54\\%" + }, + { + "bbox": [ + 296, + 601, + 531, + 730 + ], + "type": "text", + "content": " parameters, which indicates better efficiency. These observations indicate that our method significantly outperforms the previous VSR models." + } + ] + } + ], + "index": 73 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "text", + "content": "12820" + } + ] + } + ], + "index": 74 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 104, + 160, + 161 + ], + "blocks": [ + { + "bbox": [ + 48, + 104, + 160, + 161 + ], + "lines": [ + { + "bbox": [ + 48, + 104, + 160, + 161 + ], + "spans": [ + { + "bbox": [ + 48, + 104, + 160, + 161 + ], + "type": "image", + "image_path": "6f31a6c8d6cbd358aad9cfe04559fdf1d9de47dc1c19da00c957bd6c30e6fdbf.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 58, + 162, + 109, + 170 + ], + "lines": [ + { + "bbox": [ + 58, + 162, + 109, + 170 + ], + "spans": [ + { + "bbox": [ + 58, + 162, + 109, + 170 + ], + "type": "text", + "content": "Frame 024, Clip clap" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 130, + 163, + 152, + 170 + ], + "lines": [ + { + "bbox": [ + 130, + 163, + 152, + 170 + ], + "spans": [ + { + "bbox": [ + 130, + 163, + 152, + 170 + ], + "type": "text", + "content": "IconVSR" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 161, + 104, + 279, + 128 + ], + "blocks": [ + { + "bbox": [ + 161, + 104, + 279, + 128 + ], + "lines": [ + { + "bbox": [ + 161, + 104, + 279, + 128 + ], + "spans": [ + { + "bbox": [ + 161, + 104, + 279, + 128 + ], + "type": "image", + "image_path": "eb1eff36cafd7f58267a91fe01d283d885e92f2d5d2f31a51415ce8eb18a432b.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 161, + 138, + 279, + 162 + ], + "blocks": [ + { + "bbox": [ + 171, + 130, + 189, + 137 + ], + "lines": [ + { + "bbox": [ + 171, + 130, + 189, + 137 + ], + "spans": [ + { + "bbox": [ + 171, + 130, + 189, + 137 + ], + "type": "text", + "content": "EDVR" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 161, + 138, + 279, + 162 + ], + "lines": [ + { + "bbox": [ + 161, + 138, + 279, + 162 + ], + "spans": [ + { + "bbox": [ + 161, + 138, + 279, + 162 + ], + "type": "image", + "image_path": "b46654143542f3e53835e54e75394d3b02fcc0d6cd8d922a69cfe502f1b43a25.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 161, + 170, + 279, + 197 + ], + "blocks": [ + { + "bbox": [ + 161, + 170, + 279, + 197 + ], + "lines": [ + { + "bbox": [ + 161, + 170, + 279, + 197 + ], + "spans": [ + { + "bbox": [ + 161, + 170, + 279, + 197 + ], + "type": "image", + "image_path": "0eb65a248c32dbde15a207a37950293795f15481a17eafa309ea2892002d5e58.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 171, + 198, + 189, + 205 + ], + "lines": [ + { + "bbox": [ + 171, + 198, + 189, + 205 + ], + "spans": [ + { + "bbox": [ + 171, + 198, + 189, + 205 + ], + "type": "text", + "content": "EDVR" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 161, + 206, + 279, + 230 + ], + "blocks": [ + { + "bbox": [ + 161, + 206, + 279, + 230 + ], + "lines": [ + { + "bbox": [ + 161, + 206, + 279, + 230 + ], + "spans": [ + { + "bbox": [ + 161, + 206, + 279, + 230 + ], + "type": "image", + "image_path": "6f7cd5e8d1f7979a0e26f0f3197d3d2937dcda6ed1a02827ad537be462ecd5eb.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 130, + 231, + 152, + 237 + ], + "lines": [ + { + "bbox": [ + 130, + 231, + 152, + 237 + ], + "spans": [ + { + "bbox": [ + 130, + 231, + 152, + 237 + ], + "type": "text", + "content": "IconVSR" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 161, + 230, + 279, + 238 + ], + "lines": [ + { + "bbox": [ + 161, + 230, + 279, + 238 + ], + "spans": [ + { + "bbox": [ + 161, + 230, + 279, + 238 + ], + "type": "text", + "content": "BasicVSR ++ MFPI(Ours) HR" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 45, + 250, + 279, + 274 + ], + "lines": [ + { + "bbox": [ + 45, + 250, + 279, + 274 + ], + "spans": [ + { + "bbox": [ + 45, + 250, + 279, + 274 + ], + "type": "text", + "content": "Figure 8: Challenging scenario on UDM10 [65]. Our method produces much clearer text and sharper edges." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 296, + 143, + 308 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 296, + 143, + 308 + ], + "spans": [ + { + "bbox": [ + 46, + 296, + 143, + 308 + ], + "type": "text", + "content": "4.3. Ablation Studies" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 45, + 315, + 279, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 315, + 279, + 373 + ], + "spans": [ + { + "bbox": [ + 45, + 315, + 279, + 373 + ], + "type": "text", + "content": "This subsection gives a series of ablation studies to study the effectiveness of each component of MFPI. The evaluations were performed on the REDS4 dataset [38] trained on image patches of size " + }, + { + "bbox": [ + 45, + 315, + 279, + 373 + ], + "type": "inline_equation", + "content": "180 \\times 320" + }, + { + "bbox": [ + 45, + 315, + 279, + 373 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 45, + 315, + 279, + 373 + ], + "type": "inline_equation", + "content": "6 \\times 10^{5}" + }, + { + "bbox": [ + 45, + 315, + 279, + 373 + ], + "type": "text", + "content": " iterations. BasicVSR++ is utilized as the baseline." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "spans": [ + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "text", + "content": "A. Individual components. An ablation study is conducted by progressively adding SFE, EFE and the auxiliary branch to study the influence of different network blocks in our MFPI. Besides, we also investigate the effectiveness of the proposed privilege training and compare it with knowledge distillation (KD), which is another popular neural network training method. As shown in Table 2a: (a) " + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "inline_equation", + "content": "0.16\\mathrm{dB}" + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "inline_equation", + "content": "0.13\\mathrm{dB}" + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "text", + "content": " PSNR improvements can be obtained by using SFE and EFE individually. Besides, " + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "inline_equation", + "content": "0.02\\mathrm{dB}" + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "text", + "content": " further PSNR improvements can be obtained by combining the two methods with the auxiliary branch. (b) Privilege training leads to " + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "inline_equation", + "content": "0.12\\mathrm{PSNR}" + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "text", + "content": " improvements while KD leads to " + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "inline_equation", + "content": "0.38\\mathrm{dB}" + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "text", + "content": " PSNR reduction, indicating the traditional model training method fails in VSR while our method leads to significant performance benefits. As Table 2a suggests, combining all the components yields the best performance vs. complexity tradeoff " + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "inline_equation", + "content": "(32.81\\mathrm{dB},7.34\\mathrm{M}," + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "inline_equation", + "content": "281.25\\mathrm{G})" + }, + { + "bbox": [ + 45, + 383, + 279, + 593 + ], + "type": "text", + "content": " compared to employing single or partial components." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "type": "text", + "content": "B. Ablation on SFE. We further study the performance of our proposed SFE in Table 2b with different variants: only FFT, FFT with learnable filter, the split input with FL and original feature, the split operator with FL and batch normalization, the split operator with FL and instance normalization. Then, we incrementally added different DWConv layers on top of the existing components, such as " + }, + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "type": "inline_equation", + "content": "7 \\times 7" + }, + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "type": "inline_equation", + "content": "11 \\times 11" + }, + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "type": "inline_equation", + "content": "21 \\times 21" + }, + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "type": "text", + "content": ". Besides, we only substituted the FFT with the original feature while keeping the LF, IN, and DWConv " + }, + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "type": "inline_equation", + "content": "21 \\times 21" + }, + { + "bbox": [ + 45, + 601, + 279, + 730 + ], + "type": "text", + "content": " (-w/o FFT). Experimental results show that: (i) Only adding FFT to Base leads to 0.04 PSNR drop," + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 296, + 106, + 530, + 234 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 106, + 530, + 234 + ], + "spans": [ + { + "bbox": [ + 296, + 106, + 530, + 234 + ], + "type": "text", + "content": "indicating that only utilizing Fourier transform cannot boost performance. (ii) Using the learnable filter leads to 0.07 dB improvements, which account for " + }, + { + "bbox": [ + 296, + 106, + 530, + 234 + ], + "type": "inline_equation", + "content": "41\\%" + }, + { + "bbox": [ + 296, + 106, + 530, + 234 + ], + "type": "text", + "content": " performance benefits, indicating the learnable filter can improve the representation ability of FFT. (iii) Splitting the features into FFT and IN branches leads to 0.07 dB PSNR benefits, indicating that IN can help the model preserve scale information and prevent covariance shifts. (iv) DWConv with " + }, + { + "bbox": [ + 296, + 106, + 530, + 234 + ], + "type": "inline_equation", + "content": "21 \\times 21" + }, + { + "bbox": [ + 296, + 106, + 530, + 234 + ], + "type": "text", + "content": " kernel performs better than other kernels, indicating a larger kernel is necessary. (v) SFE without FFT achieves only 31.93 dB PSNR, indicating FFT plays an essential role in SFE." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 296, + 242, + 531, + 394 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 242, + 531, + 394 + ], + "spans": [ + { + "bbox": [ + 296, + 242, + 531, + 394 + ], + "type": "text", + "content": "C. Ablation on EFE. To evaluate different DCT basis functions in the EFE, we have compared our method with four different DCT variants, which are DCT initialization with fixed coefficients (DF), DCT initialization with learnable filter (DL), DF and DL added energy function, respectively. Experimental results show that: (i) Our method achieves the best PSRN, which demonstrates the effectiveness of using a learnable filter and the energy function. (ii) Removing DCT from EFE leads to 0.43 dB PSNR drop, which indicates EFE is necessary. (iii) EFE with DWConv 11x11 kernel achieves the best PSNR than other DWConv kernels, indicating that a relatively larger kernel tends to achieve better performance." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 296, + 401, + 530, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 401, + 530, + 530 + ], + "spans": [ + { + "bbox": [ + 296, + 401, + 530, + 530 + ], + "type": "text", + "content": "D. Privilege Training As shown in Table 2a, 0.12 dB PSNR improvements can be obtained by applying PT to our model, which is 0.50 higher than KD. To further study its effectiveness, we have compared PT with the other six popular model training methods in Table 3 on BasicVSR [2]. It is observed that four of the previous methods do not bring any performance benefits but lead to significant PSNR and SSIM drop. PISR leads to 0.04 dB PSNR and 0.0009 SSIM improvements, which are 0.14 dB and 0.0022 lower than PT in PSNR and SSIM, respectively. Besides, PT can be easily implemented without a pre-trained teacher model." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 296, + 538, + 530, + 654 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 538, + 530, + 654 + ], + "spans": [ + { + "bbox": [ + 296, + 538, + 530, + 654 + ], + "type": "text", + "content": "E. Feature Visualization Visualization of intermediate features in MFPI is shown in Figure 9. It is observed that: (1) The feature map significantly reduces noise after MFE, indicating that MFE effectively suppresses noise information. (2) SFE can capture object motion and extract spatial features in the frequency domain. (3) EFE focuses on the fine-grained texture and details of the input feature, as shown in the red arrow and circle. (4) Moreover, the MFE effectively fuses the multi-frequency feature and enhances the representation ability." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 296, + 663, + 368, + 676 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 663, + 368, + 676 + ], + "spans": [ + { + "bbox": [ + 296, + 663, + 368, + 676 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 296, + 682, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 682, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 682, + 530, + 730 + ], + "type": "text", + "content": "In this paper, we have proposed a novel VSR model referred to as MFPI, which consists of a multi-frequency representation enhancement module (MFE) and a privilege training method. MFE is utilized to aggregate informa" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 299, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 299, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 299, + 756 + ], + "type": "text", + "content": "12821" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 207, + 278, + 300 + ], + "blocks": [ + { + "bbox": [ + 45, + 104, + 281, + 199 + ], + "lines": [ + { + "bbox": [ + 45, + 104, + 281, + 199 + ], + "spans": [ + { + "bbox": [ + 45, + 104, + 281, + 199 + ], + "type": "text", + "content": "Table 2: Ablation studies. Subtables 2a, 2b, and 2c contain components that are defined in Sec. 3.2 and 3.3. We conduct ablation experiments on various components of SFE and EFE, such as FFT/DCT, split operator, learnable filter, BN/IN, energy function, and different coefficients. We also evaluate the effects of different kernel sizes using DW-Conv. Additionally, we employ knowledge distillation [12] or privilege training (PT) to improve our results." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 207, + 278, + 300 + ], + "lines": [ + { + "bbox": [ + 48, + 207, + 278, + 300 + ], + "spans": [ + { + "bbox": [ + 48, + 207, + 278, + 300 + ], + "type": "table", + "html": "
BaseMFETrainingPSNR (dB)Params (M)FLOPs (G)
SFEEFEAuxKDPT
✓32.397.32280.59
✓✓32.557.34280.76
✓✓32.527.33280.68
✓✓✓32.677.34280.86
✓✓✓✓32.697.34281.25
✓✓✓✓✓32.317.34281.25
✓✓✓✓✓32.817.34281.25
", + "image_path": "d29518a02d046aad2d3c1c68bd897d34d1afd457eac03ba5e298d06fb9f05ec4.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 48, + 316, + 278, + 419 + ], + "blocks": [ + { + "bbox": [ + 115, + 301, + 211, + 310 + ], + "lines": [ + { + "bbox": [ + 115, + 301, + 211, + 310 + ], + "spans": [ + { + "bbox": [ + 115, + 301, + 211, + 310 + ], + "type": "text", + "content": "(a) Individual components." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 316, + 278, + 419 + ], + "lines": [ + { + "bbox": [ + 48, + 316, + 278, + 419 + ], + "spans": [ + { + "bbox": [ + 48, + 316, + 278, + 419 + ], + "type": "table", + "html": "
VariantPSNR
Base + FFT32.35
Base + FFT w/. Learnable filter32.48
Base + FFT w/. Learnable filter + original feature32.49
Base + FFT w/. Learnable filter + BN32.43
Base + FFT w/. Learnable filter + IN32.52
Base + FFT w/. Learnable filter + IN + DWConv 3 × 332.48
Base + FFT w/. Learnable filter + IN + DWConv 7 × 732.52
Base + FFT w/. Learnable filter + IN + DWConv 11 × 1132.51
Base + FFT w/. Learnable filter + IN + DWConv 21 × 21 (Our SFE)32.55
Base + w/. Learnable filter + IN + DWConv 21 × 2131.93
", + "image_path": "caa2452404a354f8cfa898d4543dc10bcd529400c67fa60e13ee294e724ec2d7.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 48, + 436, + 278, + 523 + ], + "blocks": [ + { + "bbox": [ + 110, + 420, + 215, + 429 + ], + "lines": [ + { + "bbox": [ + 110, + 420, + 215, + 429 + ], + "spans": [ + { + "bbox": [ + 110, + 420, + 215, + 429 + ], + "type": "text", + "content": "(b) Effects of the SFE branch." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 436, + 278, + 523 + ], + "lines": [ + { + "bbox": [ + 48, + 436, + 278, + 523 + ], + "spans": [ + { + "bbox": [ + 48, + 436, + 278, + 523 + ], + "type": "table", + "html": "
VariantPSNR
Base + Energy function32.40
Base + DCT w/. Fixed coefficients32.32
Base + DCT w/. Learnable filter32.41
Base + DCT w/. Fixed coefficients + Energy function32.37
Base + DCT w/. Learnable filter + Energy function32.50
Base + DCT w/. Learnable filter + Energy function + DWConv 3 × 332.42
Base + DCT w/. Learnable filter + Energy function + DWConv 7 × 732.40
Base + DCT w/. Learnable filter + Energy function + DWConv 11 × 11 (Our EFE)32.52
Base + DCT w/. Learnable filter + Energy function + DWConv 21 × 2132.43
Base + w/. Learnable filter + Energy function + DWConv 11 × 1132.07
", + "image_path": "352994fb6f1c80049cf246493577855da85ce7c18056f50f31d337722b244221.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 47, + 585, + 279, + 673 + ], + "blocks": [ + { + "bbox": [ + 109, + 524, + 215, + 532 + ], + "lines": [ + { + "bbox": [ + 109, + 524, + 215, + 532 + ], + "spans": [ + { + "bbox": [ + 109, + 524, + 215, + 532 + ], + "type": "text", + "content": "(c) Effects of the EFE branch." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 45, + 553, + 279, + 577 + ], + "lines": [ + { + "bbox": [ + 45, + 553, + 279, + 577 + ], + "spans": [ + { + "bbox": [ + 45, + 553, + 279, + 577 + ], + "type": "text", + "content": "Table 3: Comparison between the proposed privilege training and previous training methods with BasicVSR on [38]." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 47, + 585, + 279, + 673 + ], + "lines": [ + { + "bbox": [ + 47, + 585, + 279, + 673 + ], + "spans": [ + { + "bbox": [ + 47, + 585, + 279, + 673 + ], + "type": "table", + "html": "
MethodNeeds Teacher?PSNRSSIM
BasicVSR✓31.580.8940
+ Deep Supervision [23]×31.580.8941
+ Self-KD [67]×31.470.8914
+ Hinton KD [12]✓31.260.8883
+ FitNet [44]✓31.520.8934
+ PISR [24]✓31.620.8949
+ Ours×31.760.8971
", + "image_path": "80eed0450f7d8ae9423672e94e957d215863e09366ec6d8a06fe86cafe7b3ae2.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 45, + 694, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 694, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 694, + 279, + 730 + ], + "type": "text", + "content": "tion in the frequency domain by operating the spatial- and energy-frequency components via SFE and EFE. It enables CNN-based VSR models to capture long-range dependen" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 299, + 106, + 530, + 289 + ], + "blocks": [ + { + "bbox": [ + 299, + 106, + 530, + 289 + ], + "lines": [ + { + "bbox": [ + 299, + 106, + 530, + 289 + ], + "spans": [ + { + "bbox": [ + 299, + 106, + 530, + 289 + ], + "type": "image", + "image_path": "25ccaebb90855998f28169a9c3cb689b3eca65c67ea50dfebb351532de33fcce.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 296, + 296, + 531, + 332 + ], + "lines": [ + { + "bbox": [ + 296, + 296, + 531, + 332 + ], + "spans": [ + { + "bbox": [ + 296, + 296, + 531, + 332 + ], + "type": "text", + "content": "Figure 9: Visualization of the features in MFPI on images from REDS4[38]. The red dot curve denotes the change in spatial information at different locations of the same object." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 296, + 360, + 530, + 442 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 360, + 530, + 442 + ], + "spans": [ + { + "bbox": [ + 296, + 360, + 530, + 442 + ], + "type": "text", + "content": "cies with very minor additional parameters and computations. Besides, we also propose to improve the performance of VSR from a training perspective by introducing privilege training, which contributes orthogonal effects to our frequency modules. We hope that this paper may promote more research that studies VSR from the perspective of frequency methods and model training methods." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 297, + 463, + 378, + 475 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 463, + 378, + 475 + ], + "spans": [ + { + "bbox": [ + 297, + 463, + 378, + 475 + ], + "type": "text", + "content": "6. Future Work" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 296, + 486, + 530, + 614 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 486, + 530, + 614 + ], + "spans": [ + { + "bbox": [ + 296, + 486, + 530, + 614 + ], + "type": "text", + "content": "In the future, exploring MFPI in a real-world scenario would be an exciting direction, which offers a new valuable perspective on our proposed MFEI performance. We speculate that our frequency methods will be useful for real-scenario tasks and a broader investigation of it has provided additional depth to our study. We will continue to (1) evaluate MFPI on more challenging datasets such as RealVSR [63], and (2) deploy MFPI on edge devices and evaluate its performance. We are actively working on conducting the requested experiments that can further strengthen our conclusions." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 297, + 636, + 393, + 650 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 636, + 393, + 650 + ], + "spans": [ + { + "bbox": [ + 297, + 636, + 393, + 650 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 296, + 660, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 660, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 660, + 530, + 730 + ], + "type": "text", + "content": "The authors acknowledge the financial support from the National Key R&D Program of China (No.2021ZD0113805). We appreciate the comments from the seminar participants at the Center for Deep Learning of Computer Vision Research at China Agricultural University, which improves the manuscript significantly." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 746, + 301, + 756 + ], + "type": "text", + "content": "12822" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 105, + 103, + 117 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 105, + 103, + 117 + ], + "spans": [ + { + "bbox": [ + 47, + 105, + 103, + 117 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 124, + 280, + 729 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 51, + 124, + 279, + 188 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 51, + 124, + 279, + 188 + ], + "spans": [ + { + "bbox": [ + 51, + 124, + 279, + 188 + ], + "type": "text", + "content": "[1] Jose Caballero, Christian Ledig, Andrew Aitken, Alejandro Acosta, Johannes Totz, Zehan Wang, and Wenzhe Shi. 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In Proceedings of the AAAI Conference on Artificial Intelligence, volume 33, pages 5981-5988, 2019. 1" + } + ] + } + ], + "index": 24 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 277, + 747, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 277, + 747, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 277, + 747, + 300, + 756 + ], + "type": "text", + "content": "12825" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 11 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-Label Knowledge Distillation/3f3ec8fe-1476-4cc1-910f-9ce888c57a74_content_list.json b/2023/Multi-Label Knowledge Distillation/3f3ec8fe-1476-4cc1-910f-9ce888c57a74_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..2bf0aa612ea0a2ed16b2c59e9aacfa3ec3db6ef8 --- /dev/null +++ b/2023/Multi-Label Knowledge Distillation/3f3ec8fe-1476-4cc1-910f-9ce888c57a74_content_list.json @@ -0,0 +1,1857 @@ +[ + { + "type": "text", + "text": "Multi-Label Knowledge Distillation", + "text_level": 1, + "bbox": [ + 303, + 130, + 665, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Penghui Yang $^{1,2*}$ , Ming-Kun Xie $^{1,2*}$ , Chen-Chen Zong $^{1,2}$ , Lei Feng $^{3}$ , Gang Niu $^{4}$ , Masashi Sugiyama $^{4,5}$ , Sheng-Jun Huang $^{1,2\\dagger}$", + "bbox": [ + 210, + 179, + 758, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1College of Computer Science and Technology, Nanjing University of Aeronautics and Astronautics,", + "bbox": [ + 89, + 215, + 880, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{2}$ MIIT Key Laboratory of Pattern Analysis and Machine Intelligence, Nanjing, China", + "bbox": [ + 148, + 233, + 820, + 251 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{3}$ School of Computer Science and Engineering, Nanyang Technological University, Singapore", + "bbox": [ + 114, + 251, + 854, + 268 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{4}$ RIKEN Center for Advanced Intelligence Project, $^{5}$ The University of Tokyo, Tokyo, Japan", + "bbox": [ + 125, + 268, + 844, + 287 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "phyang.cs@gmail.com, mkxie@nuaa.edu.cn, chencz@nuaa.edu.cn, lfengqaq@gmail.com,", + "bbox": [ + 133, + 289, + 831, + 304 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "gang.niu.ml@gmail.com, sugi@k.u-tokyo.ac.jp, huangsj@nuaa.edu.cn", + "bbox": [ + 200, + 306, + 767, + 321 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 356, + 312, + 372 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Existing knowledge distillation methods typically work by imparting the knowledge of output logits or intermediate feature maps from the teacher network to the student network, which is very successful in multi-class single-label learning. However, these methods can hardly be extended to the multi-label learning scenario, where each instance is associated with multiple semantic labels, because the prediction probabilities do not sum to one and feature maps of the whole example may ignore minor classes in such a scenario. In this paper, we propose a novel multi-label knowledge distillation method. On one hand, it exploits the informative semantic knowledge from the logits by dividing the multi-label learning problem into a set of binary classification problems; on the other hand, it enhances the distinctiveness of the learned feature representations by leveraging the structural information of label-wise embeddings. Experimental results on multiple benchmark datasets validate that the proposed method can avoid knowledge counteraction among labels, thus achieving superior performance against diverse comparing methods. Our code is available at: https://github.com/penghui-yang/L2D.", + "bbox": [ + 75, + 388, + 473, + 705 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 734, + 209, + 750 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Multi-label learning (MLL) addresses problems where each instance is assigned with multiple class labels simultaneously [32]. For example, as shown in Figure 1, an image of a street scene may be annotated with labels bus, car and person. To learn the complex object-label mapping, there is always necessity of training large models to obtain desirable performance in MLL. While the remarkable successes", + "bbox": [ + 75, + 758, + 468, + 864 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/f8ae256cc43ff760ad524458b691c83cb160bb80a84a1a3d19e8e9f3671ae346.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 501, + 354, + 689, + 500 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/f95be211c4353b66d7fefb317f00e97b28efb9c3516335438d9fe8e3a294a679.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 705, + 354, + 797, + 425 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/794790ff89ef70edd2ae25d11b4b80ccd82ea4bb7060f59d2506b58a0496ed4b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 802, + 354, + 893, + 425 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e94ae6ac6c0749eef97a8c73e368145b5ad1d85513af9c4ea6e9cb58f199338c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 501, + 513, + 593, + 583 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/6e8b20205be9a25b7c2d9f3cb60e38e9da757cb89bd1caf3b0f7514999144f78.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 596, + 513, + 687, + 582 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/9cad36313e012f96ec63c8e9bb3eef6028ae89a05d1c87d43c8226c2a7aee27b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 705, + 428, + 797, + 500 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/7a1cbb892f0ad70da593c380d70032b2beacf2e8b7e3081e69f8ab2cfb31f211.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 802, + 428, + 893, + 500 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/06216606a3900e2d039d98a2d118b10b602a67bc74bd405b76bceeb868916034.jpg", + "image_caption": [ + "Car" + ], + "image_footnote": [], + "bbox": [ + 501, + 587, + 593, + 657 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/0e432b67fd1dee463adc65245945020ec0038fe88bd822523d17914f4c3bd9f0.jpg", + "image_caption": [ + "Figure 1. Visualization of attention maps on different classes. We compare our method with the following three baselines: 1) Vanilla: the student trained without distillation; 2) ReviewKD [1]: a feature-based method that achieves the state-of-the-art performance; 3) Teacher: the pretrained model used in distillation. It can be observed that: on the classes bus and car, L2D captures semantic objects more precisely than the conventional KD method; on the class person, although all of the methods focus on people, only our method focuses on the same person as the teacher, which validates that L2D can distill the \"dark\" knowledge [27] from the teacher more effectively. The backbones of the teacher and student models are respectively ResNet-101 and ResNet-34. More visualization of attention maps can be found in Appendix." + ], + "image_footnote": [], + "bbox": [ + 596, + 587, + 687, + 657 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/0ef4dd21797681db4dd5d1f83f1cdbcc9e58caaa331a44799f3e0ea36b5b5d1d.jpg", + "image_caption": [ + "Person" + ], + "image_footnote": [], + "bbox": [ + 705, + 587, + 797, + 657 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/78835a24b77ccf85e75c8b830c20d71bef48c6ce67d78cf51bfe8bffad270774.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 802, + 587, + 893, + 657 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "have been made in MLL through the training of deep neural networks (DNNs) [14, 23], it is hard to deploy these large", + "bbox": [ + 500, + 869, + 892, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Both authors contributed equally to this research.", + "bbox": [ + 93, + 875, + 362, + 887 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "$^{\\dagger}$ Correspondence to: Sheng-Jun Huang (huangsj@nuaa.edu.cn).", + "bbox": [ + 96, + 887, + 433, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "17271", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "models on lightweight terminals, e.g., mobile phones, under the constraint of computational resource or requirement of short inference time.", + "bbox": [ + 76, + 90, + 468, + 135 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To mitigate this issue, knowledge distillation (KD) [10] is needed which aims to improve the performance of a small network (also known as the \"student\") by requiring the knowledge from a large network (also known as the \"teacher\") to guide the training of the student network. Typical KD methods focus on the multi-class classification, and can be roughly divided into two categories: logits-based methods and feature-based methods. The former minimizes the difference between logits of the teacher model and the student model [10, 34], while the latter distills knowledge from feature maps of intermediate layers [19, 28, 1].", + "bbox": [ + 75, + 138, + 467, + 305 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Although KD has been proven to be effective for improving the performance of the student network in single-label classification, it is still a challenging problem to directly extend existing KD methods to solve multi-label knowledge distillation (MLKD) problems. Specifically, logits-based methods often obtain the predicted probabilities based on the softmax function; this function is not suitable for MLKD, because the sum of predicted probabilities may not equal one in MLL. Feature-based methods often perform KD based on the feature maps of a whole image with multiple semantics, which makes the model focus on the major objects while neglect minor objects. For example, in Figure 1, Vanilla and ReviewKD wrongly focused on the bus when the model queried the label car. Such a phenomenon would cause the model to obtain sub-optimal even undesirable distillation performance.", + "bbox": [ + 75, + 306, + 467, + 547 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Recently, several attempts have been made to utilize KD techniques for improving the performance of MLL [15, 29, 25]. There are mainly two differences between these works and our work. Firstly, these methods often required specifically-designed network architectures [15, 25] or training strategies [29] to train the teacher and student models, while our method focuses on studying MLKD in general scenarios without any extra requirement. Secondly, unlike the previous methods utilized KD as an auxiliary technique to improve the performance of MLL, our goal is to develop a tailored approach for MLKD. As a result, previous methods were mainly compared with MLL methods in their original papers, we evaluate the KD performance of our method by comparing it with state-of-the-art KD methods.", + "bbox": [ + 75, + 550, + 467, + 775 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, to perform MLKD, we propose a new method consisting of multi-label logits distillation and label-wise embedding distillation (L2D for short). Specifically, to exploit informative semantic knowledge compressed in the logits, L2D employs the one-versus-all reduction strategy to obtain a set of binary classification problems and perform logits distillation for each one. To enhance the distinctiveness of learned feature representations,", + "bbox": [ + 75, + 780, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "L2D encourages the student model to maintain a consistent structure of intra-class and intra-instance (inter-class) label-wise embeddings with the teacher model. By leveraging the structural information of the teacher model, these two structural consistencies respectively enhance the compactness of intra-class embeddings and dispersion of inter-class embeddings for the student model. Both of these two components lead L2D to achieve better distillation performance than conventional KD methods as shown in Figure 1.", + "bbox": [ + 496, + 90, + 890, + 224 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our main contributions can be summarized as follows:", + "bbox": [ + 517, + 227, + 879, + 241 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- A general framework called MLKD is proposed. To our best knowledge, the framework is the first study specially designed for knowledge distillation in the multi-label learning scenario.", + "- A new approach for MLKD called L2D is proposed. It performs multi-label logits distillation and label-wise embedding distillation simultaneously. The former provides informative semantic knowledge while the latter encourages the student model to learn more distinctive feature representations.", + "- Extensive experimental results on benchmark datasets demonstrate the effectiveness of our proposed method." + ], + "bbox": [ + 500, + 253, + 890, + 454 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 467, + 638, + 483 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The concept of knowledge distillation (KD) proposed by Geoffrey Hinton et al. [10] defines a learning framework that transfers knowledge from a large teacher network to a small student network. Existing works can be roughly divided into two groups, i.e., logits-based methods and feature-based methods. Logits-based methods mainly focus on designing effective distillation losses to distill knowledge from logits and softmax scores after logits. DML [33] introduces a mutual learning method to train both teachers and students simultaneously. TAKD [18] proposes a new architecture called \"teacher assistant\", which is an intermediate-sized network bridging the gap between teachers and students. Besides, a recent study [34] proposes a novel logits-based method to reformulate the classical KD loss into two parts and achieves the state-of-the-art performance by adjusting weights for these two parts. Some other methods focus on distilling knowledge from intermediate feature layers. FitNet [24] is the first approach to distill knowledge from intermediate features by measuring the distance between feature maps. Attention transfer [31] achieves better performance than FitNet by distilling knowledge from the attention maps. PKT [20] measures the KL divergence between features by treating them as probability distributions. RKD [19] utilizes the relations among instances to guide the training process of the student model. CRD [28] incorporates contrastive learning into knowledge distillation. ReviewKD [1] proposes a review mechanism", + "bbox": [ + 496, + 493, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "17272", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "which uses multiple layers in the teacher to supervise one layer in the student. ITRD [17] aims to maximize the correlation and mutual information between the students' and teachers' representations.", + "bbox": [ + 75, + 90, + 468, + 151 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Multi-label learning has increasingly attracted a lot of interest recently. Existing solutions for solving MLL problems can be categorized into three directions. The first type attempts to design novel loss functions for tackling the intrinsic positive-negative imbalance issue in multi-label classification tasks. For example, ASL [22] uses different weights to re-weight positive and negative examples for the balanced training. The second type focuses on modeling the label correlations, which provides prior knowledge for multi-label classification. Among them, MLGCN [3] is a representative method that employs a graph convolutional network to model correlation matrix. CADM [2] constructs a similar graph based on class-aware maps. To handle the multiple semantic objects contained in an image, the last type of methods aims to locate areas of interest related to semantic labels by using attention techniques. Among them, C-Tran [12] first utilizes the transformer to retrieve embeddings from visual features for each label. Query2Label [14] uses several stacked transformer encoders to identify interesting areas. ML-Decoder [23] simplifies transformer encoders in Query2Label. ADDS [30] introduces encoders from CLIP [21] in order to get better textual and visual embedding inputs to the classification head. In addition, ADDS adds a multi-head cross-attention layer and a skipping connection from the query input to the query output based on ML-Decoder.", + "bbox": [ + 75, + 151, + 472, + 542 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Several previous studies have applied KD techniques to improve the performance of MLL. For example, Yongcheng Liu et al. [15] and Jiazhi Xu et al. [29] simply minimized mean squared error (MSE) loss between teacher logits and student logits. Liangchen Song et al. [25] designed a partial softmax function by combining a positive label with all other negative labels. Then, the conventional KD loss can be computed for each positive label. Although these methods made the pioneering attempts of combining KD and MLL, they cannot be directly applied general MLKD scenarios, and also fail to evaluate their KD performance by comparing with KD methods.", + "bbox": [ + 75, + 544, + 468, + 724 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. The Proposed Approach", + "text_level": 1, + "bbox": [ + 76, + 739, + 305, + 757 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Let $\\pmb{x} \\in \\mathcal{X}$ be an instance and $\\pmb{y} \\in \\mathcal{Y}$ be its corresponding label vector, where $\\mathcal{X} \\subset \\mathbb{R}^d$ is the input space with $d$ dimensions and $\\mathcal{Y} \\subset \\{0,1\\}^q$ is the target space with $q$ class labels. We further use $y_{j}$ to denote the $j$ -th component of $\\pmb{y}$ . For a given instance $\\pmb{x}$ , $y_{j} = 1$ indicates the $j$ -th label is relevant to the instance; $y_{j} = 0$ , otherwise. In multi-label learning, each instance may be assigned with more than one label, which means $\\sum_{j=1}^{q} \\mathbb{I}(y_{j} = 1) \\geq 1$ , where $\\mathbb{I}(\\cdot)$ is the indicator function. We also denote by $[q]$ the integer set", + "bbox": [ + 75, + 763, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\{1, 2, \\dots , q \\}.\n$$\n", + "text_format": "latex", + "bbox": [ + 500, + 90, + 596, + 106 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this paper, we use a classification model consisting of three components, i.e., a visual backbone $f$ , which extracts a feature map $f(\\pmb{x})$ for the input $\\pmb{x}$ , a label-wise embedding encoder $g$ [12, 14], which produces a label-wise embedding $e_k = g_k(f(\\pmb{x}))$ with respect to the $k$ -th class based on the feature map $f(\\pmb{x})$ , and a multi-label classifier $h$ , which predicts multi-label probabilities $\\hat{y} = [\\sigma(h_1(e_1)), \\sigma(h_2(e_2)), \\dots, \\sigma(h_q(e_q))]$ , where $\\sigma(\\cdot)$ denotes the sigmoid function. It is noteworthy that the used model is very general, which can be built by equipping commonly used backbones, e.g., ResNet [9], with a label-wise embedding encoder $g$ . For the notations mentioned above, we use the superscripts $\\mathcal{T}$ (or $S$ ) to denote the teacher (or student) model. For example, we use $e_k^T$ and $e_k^S$ to denote the label-wise embeddings for teacher and student models.", + "bbox": [ + 496, + 107, + 890, + 330 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In multi-label learning, a popular method is to employ the one-versus-all reduction strategy to transform the original task into multiple binary problems. Among the various loss functions, the most commonly used one is the binary cross entropy (BCE) loss. Specifically, given a batch of examples $\\{(x_i,y_i)\\}_{i = 1}^b$ and the predicted probabilities $\\hat{\\pmb{y}}$ , the BCE loss can be defined as follows:", + "bbox": [ + 496, + 332, + 890, + 436 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {B C E}} = - \\frac {1}{b} \\sum_ {i = 1} ^ {b} \\sum_ {k = 1} ^ {q} y _ {i k} \\log \\left(\\hat {y} _ {i k}\\right) + (1 - y _ {i k}) \\log \\left(1 - \\hat {y} _ {i k}\\right). \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 500, + 445, + 890, + 500 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Figure 2 illustrates the distillation process of the proposed L2D framework. For a batch of training examples, we feed them into the teacher/student model to obtain the label-wise embeddings and predicted probabilities. In order to train the student model, besides the BCE loss, we design the following two distillation losses: 1) multi-label logits distillation loss $\\mathcal{L}_{\\mathrm{MLD}}$ to exploit informative semantic knowledge compressed in the logits, 2) label-wise embedding distillation loss $\\mathcal{L}_{\\mathrm{LED}}$ to leverage structural information for enhancing the distinctiveness of learned feature representations. The overall objective function can be presented as", + "bbox": [ + 496, + 500, + 890, + 679 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {L 2 D}} = \\mathcal {L} _ {\\mathrm {B C E}} + \\lambda_ {\\mathrm {M L D}} \\mathcal {L} _ {\\mathrm {M L D}} + \\lambda_ {\\mathrm {L E D}} \\mathcal {L} _ {\\mathrm {L E D}}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 555, + 681, + 890, + 696 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\lambda_{\\mathrm{MLD}}$ and $\\lambda_{\\mathrm{LED}}$ are two balancing parameters.", + "bbox": [ + 498, + 703, + 846, + 718 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Multi-Label Logits Distillation", + "text_level": 1, + "bbox": [ + 500, + 726, + 769, + 742 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Traditional logits-based distillation normally minimizes the Kullback-Leibler (KL) divergence between the predicted probabilities, i.e., the logits after the softmax function, of teacher and student model. However, the method cannot be directly applied to the MLL scenario, since it depends on a basic assumption that the predicted probabilities of all classes should sum to one, which hardly holds for MLL examples.", + "bbox": [ + 496, + 750, + 890, + 869 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To mitigate this issue, inspired by the idea of one-versus-all reduction, we propose a multi-label logits distillation", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "17273", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/f0117610615eb2a33b54d4846bd2dc7dc885cc2b30c71b681c633caec31fba67.jpg", + "image_caption": [ + "Figure 2. An illustration of the L2D framework. The framework simultaneously performs multi-label logits distillation and label-wise embedding distillation to improve the performance of the student model." + ], + "image_footnote": [], + "bbox": [ + 106, + 95, + 885, + 330 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "(MLD) loss, which decomposes the original multi-label task into multiple binary classification problems and minimizes the divergence between the binary predicted probabilities of two models. Formally, the MLD loss can be formulated as follows:", + "bbox": [ + 75, + 392, + 473, + 467 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {M L D}} = \\frac {1}{b} \\sum_ {i = 1} ^ {b} \\sum_ {k = 1} ^ {q} \\mathcal {D} \\left(\\left[ \\hat {y} _ {i k} ^ {\\mathcal {T}}, 1 - \\hat {y} _ {i k} ^ {\\mathcal {T}} \\right] \\mid \\mid [ \\hat {y} _ {i k} ^ {\\mathcal {S}}, 1 - \\hat {y} _ {i k} ^ {\\mathcal {S}} ]\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 473, + 472, + 513 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $[\\cdot, \\cdot]$ is an operator used to concatenate two scalars into a vector, and $\\mathcal{D}$ is a divergence function. The most common choice is the KL divergence $\\mathcal{D}_{\\mathrm{KL}}(P \\| Q) = \\sum_{x \\in \\mathcal{X}} P(x) \\log \\left(\\frac{P(x)}{Q(x)}\\right)$ , where $P$ and $Q$ are two different probability distributions. The MLD loss aims to improve the performance of student model by sufficiently exploiting informative knowledge from logits.", + "bbox": [ + 75, + 515, + 470, + 628 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Label-wise Embedding Distillation", + "text_level": 1, + "bbox": [ + 76, + 635, + 380, + 651 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The MLD loss performs distillation on the predicted probabilities that can be regarded as a high-level representation, i.e., the final outputs of model. The knowledge distilled from the teacher model by only using the MLD loss would be insufficient to train a student model with desirable performance due to the limited information carried by the logits. To further strengthen the effectiveness of distillation, we design the label-wise embedding distillation (LED) loss, which aims to explore the structural knowledge from label-wise embeddings. The main idea is to capture two types of structural relations among label-wise embeddings: 1) class-aware label-wise embedding distillation (CD) loss $\\mathcal{L}_{\\mathrm{CD}}$ , which captures the structural relation between any two intra-class label-wise embeddings from different examples; 2) instance-aware label-wise embedding distillation (ID) loss $\\mathcal{L}_{\\mathrm{ID}}$ , which models the structural re", + "bbox": [ + 75, + 657, + 472, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "lation between any two inter-class label-wise embeddings from the same example. In the following content, we introduce these two distillation losses in detail.", + "bbox": [ + 498, + 392, + 892, + 436 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2.1 Class-Aware Label-Wise Embedding Distillation", + "text_level": 1, + "bbox": [ + 498, + 464, + 890, + 479 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Class-aware label-wise embedding distillation aims to improve the distillation performance by exploiting the structural relations among intra-class label-wise embeddings. Generally, the same semantic objects from two different images often differ from each other by their individual characteristics, such as two cars with different colors and diverse styles (see the left side in Figure 3). Since our goal is to distinguish between car and other semantic classes instead of identifying different cars, these distinctiveness would be confusing information for the corresponding classification task. Due to the powerful learning capacity, the large model is able to capture the highly abstract semantic representations for each class label by neglecting the useless individual information. From the perspective of learned feature representations, as shown in the left side of Figure 3, the teacher model tends to obtain a more compact structure of intra-class label-wise embedding, which often leads to better classification performance. By transferring the structural knowledge from the teacher model to the student model, CD encourages the student model to enhance the compactness of intra-class label-wise embeddings, which can improve its classification performance.", + "bbox": [ + 496, + 489, + 892, + 823 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For a batch of examples, let $\\{e_{ik}^{\\mathcal{T}}\\}_{i = 1}^{b}$ and $\\{e_{ik}^{\\mathcal{S}}\\}_{i = 1}^{b}$ respectively denote the intra-class label-wise embeddings with respect to class $k\\in [q]$ generated by the teacher and student models. Then, we can capture the structural relation between any two intra-class label-wise embeddings $e_{ik}^{\\mathcal{T}}$ and", + "bbox": [ + 496, + 823, + 893, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "17274", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/be49ff750de031fa6b78dfc5acaa32c0cb6ff0bafac4722c0f10b5cea9861270.jpg", + "image_caption": [ + "Figure 3. An illustration of class/instance-aware label-wise embedding distillation. Class-aware label-wise embedding distillation (CD) captures structural relations among intra-class label-wise embeddings from different examples, while instance-aware label-wise embedding distillation (ID) explores structural relations among intra-instance (inter-class) label-wise embeddings." + ], + "image_footnote": [], + "bbox": [ + 106, + 102, + 854, + 335 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$\\pmb{e}_{jk}^{\\mathcal{T}}$ by measuring their distance in the embedding space:", + "bbox": [ + 76, + 420, + 450, + 440 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\phi_ {\\mathrm {C D}} \\left(\\boldsymbol {e} _ {i k} ^ {\\mathcal {T}}, \\boldsymbol {e} _ {j k} ^ {\\mathcal {T}}\\right) = \\left\\{ \\begin{array}{l l} \\| \\boldsymbol {e} _ {i k} ^ {\\mathcal {T}} - \\boldsymbol {e} _ {j k} ^ {\\mathcal {T}} \\| _ {2} & y _ {i k} = 1, y _ {j k} = 1, \\\\ 0 & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 448, + 468, + 488 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "It is worth to note that we only consider the structural relation between any two valid label-wise embeddings, i.e., the embeddings with respect to positive labels. Similar to Eq.(4), for any two intra-class label-wise embeddings $e_{ik}^S$ and $e_{jk}^S$ , we can obtain the structural relation $\\phi_{\\mathrm{CD}}(e_{ik}^S, e_{jk}^S)$ for the student model.", + "bbox": [ + 76, + 497, + 468, + 585 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "By enforcing the teacher and student structural relations to maintain the consistency for each pair of intra-class label-wise embeddings, we can achieve the class-aware structural consistency as follows:", + "bbox": [ + 76, + 587, + 468, + 647 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {C D}} = \\sum_ {k = 1} ^ {q} \\sum_ {i, j \\in [ b ]} \\ell \\left(\\phi_ {\\mathrm {C D}} \\left(e _ {i k} ^ {\\mathcal {T}}, e _ {j k} ^ {\\mathcal {T}}\\right), \\phi_ {\\mathrm {C D}} \\left(e _ {i k} ^ {\\mathcal {S}}, e _ {j k} ^ {\\mathcal {S}}\\right)\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 80, + 656, + 468, + 694 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\ell$ is a function to measure the consistency between the teacher and student structural relations. In experiments, we use the following Huber loss function as a measurement:", + "bbox": [ + 76, + 695, + 468, + 742 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\ell (a, b) = \\left\\{ \\begin{array}{l l} \\frac {1}{2} (a - b) ^ {2} & | a - b | \\leq 1, \\\\ | a - b | - \\frac {1}{2} & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 143, + 750, + 468, + 789 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $a$ and $b$ are two different structural relations.", + "bbox": [ + 76, + 799, + 415, + 811 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2.2 Instance-Aware Label-Wise Embedding Distillation", + "text_level": 1, + "bbox": [ + 76, + 830, + 468, + 861 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Instance-aware label-wise embedding distillation (ID) aims to improve the distillation performance by exploring the", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "structural relations among inter-class label-wise embeddings from the same image. Generally, one can hardly distinguish between two different semantic objects occurring in an image due to the high similarities they share. For example, in the upper left corner of Figure 3, an image annotated with both sky and sea makes it difficult to distinguish between the semantic objects, as they share the same color and similar texture. A feasible solution is to exploit other useful information, such as their spatial relation, i.e., sky is always above sea. Due to the powerful learning capacity, the large model is able to distinguish between the similar semantic objects by exploiting such implicit supervised information. From the perspective of learned feature representations, as shown in the right side of 3, the teacher model tends to learn a dispersed structure of inter-class label-wise embedding, which is beneficial for improving its discrimination ability. By distilling the structural knowledge from the teacher model, ID enforces the student model to enhance the dispersion of inter-class label-wise embeddings, which can improve its discrimination ability.", + "bbox": [ + 496, + 421, + 890, + 720 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For a given instance $\\pmb{x}_i$ , let $\\{e_{ik}^{\\mathcal{T}}\\}_{k=1}^{q}$ and $\\{e_{ik}^S\\}_{k=1}^{q}$ respectively denote the label-wise embeddings generated by teacher and student models. Then, we can capture the structural relation between any two inter-class label-wise embeddings $e_{ik}^{\\mathcal{T}}$ and $e_{il}^{\\mathcal{T}}$ by measuring their distance in the embedding space:", + "bbox": [ + 496, + 722, + 890, + 814 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\phi_ {\\mathrm {I D}} \\left(e _ {i k} ^ {\\mathcal {T}}, e _ {i l} ^ {\\mathcal {T}}\\right) = \\left\\{ \\begin{array}{l l} \\| e _ {i k} ^ {\\mathcal {T}} - e _ {i l} ^ {\\mathcal {T}} \\| _ {2} & y _ {i k} = 1, y _ {i l} = 1, \\\\ 0 & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 516, + 821, + 890, + 862 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Note that in Eq.(7), we only consider the structural relation between any two valid label-wise embeddings, i.e.,", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "17275", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/898a37fd0bb7a59f399d632ee7ac68ca7982245acb0830ffe613885e9f641821.jpg", + "table_caption": [ + "Table 1. Results on MS-COCO where teacher and student models are in the same architectures." + ], + "table_footnote": [], + "table_body": "
TeacherRepVGG-A2ResNet-101WRN-101Swin-S
StudentRepVGG-A0ResNet-34WRN-50Swin-T
MetricsmAPOF1CF1mAPOF1CF1mAPOF1CF1mAPOF1CF1
Teacher72.7174.1168.6373.6273.8968.6174.7075.5670.7381.7080.4877.12
Student70.0272.4966.7770.3172.4966.8274.4575.4370.6179.5979.1875.42
RKD70.0872.3966.7370.1372.4466.7874.7075.7170.8479.6379.1975.57
PKT70.1172.4766.8070.4372.6466.6874.5475.4770.5879.6479.0975.39
ReviewKD70.0072.3566.8270.3972.6266.7674.0375.2970.3679.8179.1875.55
MSE70.2672.5466.9970.5472.7566.8574.5375.6070.7179.6779.2075.52
PS70.6572.8967.6070.8672.6667.1275.1276.0571.6379.9679.6476.20
MLD70.7472.8167.4670.6872.6967.1974.9275.7571.2180.1179.6876.44
L2D72.8174.5969.4972.8774.4569.4376.6177.0872.7981.5981.0377.86
", + "bbox": [ + 81, + 99, + 888, + 311 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/47ba0d8d2f9fe2916bba6b7d8da724f5ddedb7221e24ff2a4f88e381ac7cf0fd.jpg", + "table_caption": [ + "Table 2. Results on MS-COCO where teacher and student models are in the different architectures." + ], + "table_footnote": [], + "table_body": "
TeacherResNet-101Swin-TResNet-101Swin-T
StudentRepVGG-A0ResNet-34MobileNet v2MobileNet v2
MetricsmAPOF1CF1mAPOF1CF1mAPOF1CF1mAPOF1CF1
Teacher73.6273.8968.6179.4378.7775.0773.6273.8968.6179.4378.7775.07
Student70.0272.4966.7770.3172.4966.8271.8573.5968.2671.8573.5968.26
RKD70.0872.3566.7270.0072.3466.6471.7673.6868.4071.7473.6868.37
PKT69.9972.3566.5670.2672.3966.8271.8873.6068.3571.8473.7668.37
ReviewKD70.0072.3366.6270.2972.3966.5871.9273.7368.4871.7373.7168.36
MSE70.0772.5066.8570.3372.5766.7271.9173.6868.2871.8073.7468.38
PS70.3072.6167.1070.9472.9367.5772.1173.8968.4272.4274.1468.94
MLD70.4872.7767.1071.1472.9967.6372.1773.8468.5272.3574.1068.91
L2D72.1474.0868.7873.4274.9770.2073.2474.8569.7274.2175.7270.87
", + "bbox": [ + 81, + 334, + 888, + 547 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "the embedding with respect to positive labels. Similar to Eq.(7), for any two inter-class label-wise embeddings $e_{ik}^S$ and $e_{il}^S$ , we can obtain the structural relation $\\phi_{\\mathrm{ID}}(e_{ik}^S, e_{il}^S)$ for the student model.", + "bbox": [ + 75, + 571, + 468, + 631 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "By encouraging the teacher and student model to maintain the consistent structure of intra-instance label-wise embeddings, we can minimize the following $\\mathcal{L}_{\\mathrm{ID}}$ loss to achieve the instance-aware structural consistency where $\\ell(.)$ is Huber loss as defined in Eq.(6):", + "bbox": [ + 75, + 632, + 468, + 708 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {I D}} = \\sum_ {i = 1} ^ {b} \\sum_ {k, l \\in [ q ]} \\ell \\left(\\phi_ {\\mathrm {I D}} \\left(\\boldsymbol {e} _ {i k} ^ {\\mathcal {T}}, \\boldsymbol {e} _ {i l} ^ {\\mathcal {T}}\\right), \\phi_ {\\mathrm {I D}} \\left(\\boldsymbol {e} _ {i k} ^ {\\mathcal {S}}, \\boldsymbol {e} _ {i l} ^ {\\mathcal {S}}\\right)\\right). \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 714, + 468, + 755 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Finally, the overall objective function of L2D (Eq.(2)) can be re-written as follows:", + "bbox": [ + 75, + 756, + 468, + 785 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {L 2 D}} = \\mathcal {L} _ {\\mathrm {B C E}} + \\lambda_ {\\mathrm {M L D}} \\mathcal {L} _ {\\mathrm {M L D}} + \\lambda_ {\\mathrm {C D}} \\mathcal {L} _ {\\mathrm {C D}} + \\lambda_ {\\mathrm {I D}} \\mathcal {L} _ {\\mathrm {I D}}, \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 96, + 792, + 468, + 811 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\lambda_{\\mathrm{MLD}}$ , $\\lambda_{\\mathrm{CD}}$ and $\\lambda_{\\mathrm{ID}}$ are all balancing parameters.", + "bbox": [ + 76, + 818, + 441, + 834 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 844, + 209, + 861 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Datasets. We perform experiments on three benchmark datasets Pascal VOC2007 [8] (VOC for short), MS-", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "COCO2014 [13] (MS-COCO for short) and NUS-WIDE [4]. VOC contains 5,011 images in the train-val set, and 4,952 images in the test set. It covers 20 common objects, with an average of 1.6 labels per image. MS-COCO contains 82,081 training images and 40,137 test images. It covers 80 common objects, with an average of 2.9 labels per image. NUS-WIDE contains 161,789 training images and 107,859 test images. It covers 81 visual concepts, with an average of 1.9 labels per image.", + "bbox": [ + 496, + 571, + 890, + 708 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Metrics. Following existing works [32, 14, 26], we adopt the mean average precision (mAP) over all classes, overall F1-score (OF1) and average per-class F1-score (CF1) to evaluate the performance. We choose OF1 and CF1, since they consider both recall and precision and thus are more comprehensive.", + "bbox": [ + 496, + 713, + 890, + 805 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comparing Methods. To validate the proposed method, we compare it with the following sota KD methods: RKD [19], which captures the relations among instances to guide the training of the student model; PKT [20], which measures KL divergence between features by treating them as probability distributions; ReviewKD [1], which transfers", + "bbox": [ + 496, + 809, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "17276", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "knowledge across different stages instead of just focusing on features in the same levels; as well as the modified KD techniques that have been applied to MLL: MSE [29], which minimizes the MSE loss between logits of teacher and student model; PS [25], which minimizes KL divergence of logits after a partial softmax function.", + "bbox": [ + 75, + 90, + 470, + 181 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Implementation Details. We use the models pretrained on ImageNet [6] as the backbones. We resize the resolution of all images to $224 \\times 224$ and set the batch size as 64. For each training image, we adopt a weak augmentation consisting of random horizontal flipping and a strong augmentation consisting of Cutout [7] and RandAugment [5]. We use the Adam optimization method [11] to train the model for 80 epochs. The one-cycle policy is used with a maximal learning rate of 0.0001 and the weight decay [16] of 0.0001. For all experiments, we set $\\lambda_{\\mathrm{MLD}} = 10$ , $\\lambda_{\\mathrm{CD}} = 100$ , and $\\lambda_{\\mathrm{ID}} = 1000$ . Parameter sensitivity analysis in Appendix shows that the performance of L2D are insensitive to all of our balancing parameters. For the comparing methods, we set their parameters as suggested in the original papers. Especially, for all feature-based methods, we just deploy them on the feature maps which is output from the visual backbone $f$ . All the experiments are conducted on GeForce RTX 2080 GPUs. More details about the used models and implementation of the label-wise embedding encoder are attached in Appendix.", + "bbox": [ + 75, + 183, + 473, + 484 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.1. Comparison Results", + "text_level": 1, + "bbox": [ + 76, + 498, + 269, + 513 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 1 and Table 2 report comparison results on MS-COCO with the same and different architectures of student and teacher models. From Table 1, it can be observed that: 1) Conventional feature-based distillation methods only achieve minor improvements in performance when compared with the student model (without distillation). This indicates these methods do not work in multi-label scenarios due to their disability to capture multiple semantics occurred in feature maps. 2) MLD can outperform conventional feature-based distillation methods in most cases, which indicates by performing one-versus-all reduction, the logits-based distillation can be adapted into multi-label knowledge distillation. 3) The proposed L2D significantly outperforms all other methods and achieves comparable performance with the teacher model. In particular, when WRN is used as the backbone, the performance of L2D is even better than that of teacher model. One possible reason is that L2D can effectively alleviate the over-fitting issue occurred to the teacher model. More results about reversed knowledge distillation where the Vanilla student model outperforms the teacher can be found in Appendix. From Table 2, we can see that compared with the same architecture, the performance gap between teacher and student model is larger for different architectures, which indicates the corresponding distillation task becomes harder. Our method sig", + "bbox": [ + 75, + 523, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/05662685c24221e05810063f638d4a8df577a609050b2c87c2cc1e1b5ced884f.jpg", + "table_caption": [ + "Table 3. Comparison results of the comparing methods on VOC in terms of AP and mAP (\\%), where the backbones of teacher and student model are respectively ResNet-50 and ResNet-18. The best performance is highlighted in red, and second best performance is highlighted in blue." + ], + "table_footnote": [], + "table_body": "
MethodsVanillaRKDPKTMSEMLDL2D
bottle57.1859.0157.2958.2658.3259.71
pottedplant67.4367.0166.1668.0268.8870.52
chair70.3571.3171.1670.6871.1274.77
sofa73.1772.8673.2272.0673.7775.01
diningtable76.1476.9076.8977.9378.6578.93
cow82.6581.1181.7581.0684.6083.87
tvmonitor82.3081.7081.9582.3682.4284.13
bus85.5384.7985.0686.0386.4185.45
sheep84.1684.7783.6683.7283.7785.67
motorbike88.3888.8688.7388.3088.5889.83
dog90.1890.0390.1090.4690.7890.60
bird90.6591.6591.3190.6091.0291.48
bicycle91.4091.5391.7791.5891.9291.90
cat90.6791.8691.8391.0791.6392.14
boat92.5492.5392.3591.6492.2592.57
car92.7292.0692.0792.0192.3493.40
horse94.2293.9793.1294.0594.5394.67
person95.7395.8895.8095.6996.0496.46
train96.0997.0896.9997.1396.9796.81
aeroplane97.2797.0097.0997.1097.3097.39
mAP84.0184.1883.8684.2384.4885.71
", + "bbox": [ + 504, + 156, + 890, + 463 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/14a1d6b944baa7195927ca189f881ab973dbcc42bf456521f532129b67e48566.jpg", + "table_caption": [ + "Table 4. Ablation studies on MS-COCO." + ], + "table_footnote": [], + "table_body": "
MLDCDIDmAPOF1CF1
70.3172.4966.82
✓70.6872.6967.19
✓✓71.9173.7468.76
✓✓71.7973.6268.43
✓✓✓72.8774.4569.43
", + "bbox": [ + 535, + 488, + 859, + 588 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "nificantly outperforms all the comparing methods by a significant margin in all cases. These results provide a strong empirical validation for the effectiveness of the proposed method.", + "bbox": [ + 496, + 613, + 890, + 672 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3 illustrates the performance of the proposed methods and other comparing methods on VOC in terms of AP and mAP. It is noteworthy that the performance is ranked in descending according to the performance of student model. From the figure, it can be observed that: 1) Our proposed L2D achieves the best performance and significantly outperforms the comparing methods in terms of mAP. 2) L2D consistently achieves superior performance to the comparing methods in most classes and the performance gap is large especially for classes that the student model achieves poor performance. This observation discloses that L2D improves the performance of hard classes by enhancing the distinctiveness of feature representations. These experimental results demonstrate the practical usefulness of the proposed method. More results on VOC and NUS-WIDE", + "bbox": [ + 496, + 674, + 892, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "17277", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/65833ff6bde88244d7c41a87dfdedc25b1d42c7300c287b8ebbbd3fd310ffbd5.jpg", + "image_caption": [ + "Query" + ], + "image_footnote": [], + "bbox": [ + 86, + 107, + 153, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2568c26758369e2217844c9936e9fefa52a734a19a2100e5d7acc5fd919d7af6.jpg", + "image_caption": [ + "Dog, Fire Hydrant" + ], + "image_footnote": [], + "bbox": [ + 86, + 160, + 153, + 217 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/ba6ccfddf2cbdf04a63ff203a4f1424cbcc0e4e4f6e0e2cf11f0f4c4287d109f.jpg", + "image_caption": [ + "Book, Person, Remote" + ], + "image_footnote": [], + "bbox": [ + 168, + 107, + 236, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f43e19ae9bb7f1a6cfcfd6c62777462d3cfd6dcc226ed286c4c6b1904dd32134.jpg", + "image_caption": [ + "Dog, Fire Hydrant" + ], + "image_footnote": [], + "bbox": [ + 168, + 165, + 236, + 217 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2d9a59d7b49706ebb214109e5c95ea532a66c9a21d7a1c2570d785bcc05aa6c6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 241, + 107, + 308, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/bbde36c2ec96960a5ed7377348303041ab3e9950535c61a88ba05e8da1609ae7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 310, + 107, + 377, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/386d2e3290b63a78a3bd7fba0d269b9423083fc5e5f277899e4d9f52ea03be53.jpg", + "image_caption": [ + "Dog, Fire Hydrant", + "Figure 4. Top-5 returned images with the query image. The returned results on the left are based on ReviewKD, while the results on the right are based on L2D. All results are sorted in the ascending order according to the distance from the query image. Red labels indicate that they are not included in the returned images' labels, while green labels are shared by the query image and the returned one." + ], + "image_footnote": [], + "bbox": [ + 310, + 164, + 377, + 217 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8517187a115732c1b7938c104301b29f03e7cb59a2aed73f2ecfacb6eea8dbf2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 380, + 107, + 447, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/cd6819e3013168cf3c7a9e1ccf2ae8a1555bb3bcfd831f2ada38fbed385b50de.jpg", + "image_caption": [ + "Dog, Fire Hydrant" + ], + "image_footnote": [], + "bbox": [ + 380, + 165, + 447, + 217 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/30c37cf3229283eb99d3d157be02194afb7c5bfb48268d12e67728ab33c2148e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 450, + 107, + 517, + 162 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/acf59acdeb50469f183497608ff935b3a8410364fb37be182eef530a287cc920.jpg", + "image_caption": [ + "Dog, Fire Hydrant" + ], + "image_footnote": [], + "bbox": [ + 450, + 165, + 517, + 217 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2ba5393ede6b9e9cf5efa22b7e0d800507d4b75158a82806aa8112da8c8f1fcf.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 534, + 107, + 601, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3fb608fcb54080456845ab5ad29bbc0b5573a124cdba15ef2c5f70a7ff8cba0f.jpg", + "image_caption": [ + "Dog, Fire Hydrant" + ], + "image_footnote": [], + "bbox": [ + 534, + 164, + 601, + 217 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/bb2cc5b68c0464ffea80876cdf34bf5594da2e6f21f1127370b7a9df3b6f7560.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 604, + 107, + 671, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a194dc4502018fa92c416e875eee8b5ae42f12a3c49a71811455ee2548bb0fb4.jpg", + "image_caption": [ + "Dog, Fire Hydrant" + ], + "image_footnote": [], + "bbox": [ + 604, + 165, + 671, + 217 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/199fdbef6c8e0f26677e84ac0b6975b7a035bc8d727fa95657d3ea2874586201.jpg", + "image_caption": [ + "L2D" + ], + "image_footnote": [], + "bbox": [ + 676, + 107, + 743, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0f93ebf7b4a459e26e9528dea9c46465994483d833977b66e660d115d6924863.jpg", + "image_caption": [ + "Dog, Fire Hydrant" + ], + "image_footnote": [], + "bbox": [ + 676, + 165, + 741, + 217 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/902acbc6969f27a9e74dd356062935f5cff75941e98c0c8bc3fe04cf6d388e62.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 746, + 107, + 812, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/440c04035c9b12cd3555aa786f12aa8d067b8dd55becbcef223fbf2c40e6c62c.jpg", + "image_caption": [ + "Dog, Fire Hydrant" + ], + "image_footnote": [], + "bbox": [ + 745, + 164, + 812, + 217 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/53aa6f5c1b84954029201491a6ff97984cc1ef64a50fa15ba91715abcb4e91ed.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 816, + 107, + 883, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/5403ea8c23c65ce99222f725c13818e191371440684ca5aaf683f76792dd6a67.jpg", + "image_caption": [ + "Dog, Fire Hydrant" + ], + "image_footnote": [], + "bbox": [ + 816, + 165, + 882, + 217 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "can be found in Appendix.", + "bbox": [ + 76, + 291, + 254, + 306 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.2. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 327, + 228, + 343 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this section, to further analyze how the proposed method improves distillation performance, Table 4 reports results of ablation studies on MS-COCO (teacher: ResNet-101, student: ResNet-34). The first line in Table 4 reports the performance of student model without knowledge distillation. It can be observed that the distillation performance is improved slightly by only conducting multi-label logits distillation. Compared with MLD, label-wise embeddings distillation achieves the major improvement for the proposed method. It can be observed that by performing CD and ID, the mAP performance achieves $1.6\\%$ and $1.48\\%$ increments, respectively. Finally, we also examine the combination of these techniques. By incorporating these components together, the fusing method achieves the best performance and significantly outperforms each other method. These results demonstrate that all of three components are of great importance to the performance of the proposed L2D.", + "bbox": [ + 75, + 354, + 470, + 625 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.3. Performance on Image Retrieval", + "text_level": 1, + "bbox": [ + 76, + 647, + 362, + 662 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To further evaluate if our method can learn better representations, we conduct an image retrieval experiment. Specifically, we use the $k$ -NN algorithm to perform content-based image retrieval, and choose the student model trained by ReviewKD as the baseline, which has achieved the best performance among all conventional KD methods. Figure 4 illustrates the top-5 images returned by both methods. The labels under each image are colored in green if they are shared by both the query image and the returned one, and otherwise in red. These images are sorted in the ascending order based on the distance to the query image in the representation space. From the figures, we can see that our method returns the images that match the query image better than ReviewKD. This indicates our approach can obtain better representations than conventional KD methods.", + "bbox": [ + 75, + 674, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/34399b7617cb08cc09ee12414a67f9c56ed93184e7482468a3fbc66c13ab9aee.jpg", + "image_caption": [ + "(a) Vanilla" + ], + "image_footnote": [], + "bbox": [ + 529, + 297, + 666, + 405 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c0ed09ee2c68dbf988d7c8d6777addd52f0f73dfba83cc84c419744d7dc7b9bd.jpg", + "image_caption": [ + "(b) ReviewKD" + ], + "image_footnote": [], + "bbox": [ + 671, + 297, + 864, + 406 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1d6b94802552b84e92a3da23e6682ab23d76f7a07e4612c4b419120f9de41417.jpg", + "image_caption": [ + "(c)MLD" + ], + "image_footnote": [], + "bbox": [ + 527, + 438, + 666, + 546 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1dc8d39aa155d8503165787594e7bc07af96e2becde5353a5b74d11a51288802.jpg", + "image_caption": [ + "(d) L2D", + "Figure 5. The differences between correlation matrices of student and teacher predicted probabilities on MS-COCO." + ], + "image_footnote": [], + "bbox": [ + 669, + 436, + 864, + 547 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Distilling Inter-class Correlations", + "text_level": 1, + "bbox": [ + 500, + 604, + 792, + 619 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "As discussed in the previous works [10], the conventional supervised learning losses, e.g., BCE loss, often neglects the correlations among class predictions, which act as a foundational element in MLL. To validate whether the correlations can be captured by L2D effectively, Figure 5 illustrates the differences between correlation matrices of student and teacher predicted probabilities on MS-COCO. From the figure, it can be observed that: 1) The representative comparing method ReviewKD shows a large difference, which discloses that the conventional KD methods are ineffective to capture the correlations in multi-label scenarios. 2) MLD does not show a reduced difference, which indicates that the information of logits is not enough for capturing precise correlations. 3) L2D shows significant matching between the teacher and student correlations. By enhancing the distinctiveness of label-wise embeddings, L2D can obtain more correct predicted probabilities, leading to a more precise correlation estimation.", + "bbox": [ + 496, + 628, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "17278", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 89, + 194, + 104 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "The paper studies the problem of multi-label knowledge distillation. In the proposed method, the multi-label logits distillation explores the informative semantic knowledge compressed in the teacher logits to obtain more semantic supervision. Furthermore, the label-wise embedding distillation exploits the structural knowledge from label-wise embeddings to learn more distinctive feature representations. Experimental results on benchmark datasets validate the effectiveness of the proposed method. In future, we plan to improve the performance of MLKD by exploiting other abundant structural information.", + "bbox": [ + 75, + 117, + 472, + 282 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 76, + 305, + 236, + 321 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Sheng-Jun Huang was supported by, the National Key R&D Program of China (2020AAA0107000), the Natural Science Foundation of Jiangsu Province of China (BK20222012, BK20211517), and NSFC (62222605). Lei Feng was supported by the Joint NTU-WeBank Research Centre on Fintech (Award No: NWJ-2021-005), Nanyang Technological University, Singapore, Chongqing Overseas Chinese Entrepreneurship and Innovation Support Program, Chongqing Artificial Intelligence Innovation Center, and CAAI-Huawei MindSpore Open Fund. Masashi Sugiyama was supported by JST CREST Grant Number JP-MJCR18A2.", + "bbox": [ + 75, + 333, + 472, + 513 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 76, + 535, + 174, + 550 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Pengguang Chen, Shu Liu, Hengshuang Zhao, and Jiaya Jia. Distilling knowledge via knowledge review. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 5008-5017, 2021. 1, 2, 6", + "[2] Zhao-Min Chen, Xiu-Shen Wei, Xin Jin, and Yanwen Guo. Multi-label image recognition with joint class-aware map disentangling and label correlation embedding. In Proceedings of the IEEE International Conference on Multimedia and Expo, pages 622-627, 2019. 3", + "[3] Zhao-Min Chen, Xiu-Shen Wei, Peng Wang, and Yanwen Guo. Multi-label image recognition with graph convolutional networks. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 11953-11962, 2022. 2" + ], + "bbox": [ + 78, + 90, + 468, + 837 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "17280", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Multi-Label Knowledge Distillation/3f3ec8fe-1476-4cc1-910f-9ce888c57a74_model.json b/2023/Multi-Label Knowledge Distillation/3f3ec8fe-1476-4cc1-910f-9ce888c57a74_model.json new file mode 100644 index 0000000000000000000000000000000000000000..73f2dfa5c395dbc0d13641adec06dc601f85cc03 --- /dev/null +++ b/2023/Multi-Label Knowledge Distillation/3f3ec8fe-1476-4cc1-910f-9ce888c57a74_model.json @@ -0,0 +1,2409 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.305, + 0.131, + 0.666, + 0.154 + ], + "angle": 0, + "content": "Multi-Label Knowledge Distillation" + }, + { + "type": "text", + "bbox": [ + 0.211, + 0.18, + 0.759, + 0.217 + ], + "angle": 0, + "content": "Penghui Yang\\(^{1,2*}\\), Ming-Kun Xie\\(^{1,2*}\\), Chen-Chen Zong\\(^{1,2}\\), Lei Feng\\(^{3}\\), Gang Niu\\(^{4}\\), Masashi Sugiyama\\(^{4,5}\\), Sheng-Jun Huang\\(^{1,2\\dagger}\\)" + }, + { + "type": "text", + "bbox": [ + 0.09, + 0.217, + 0.882, + 0.234 + ], + "angle": 0, + "content": "1College of Computer Science and Technology, Nanjing University of Aeronautics and Astronautics," + }, + { + "type": "text", + "bbox": [ + 0.15, + 0.234, + 0.821, + 0.252 + ], + "angle": 0, + "content": "\\(^{2}\\)MIIT Key Laboratory of Pattern Analysis and Machine Intelligence, Nanjing, China" + }, + { + "type": "text", + "bbox": [ + 0.115, + 0.252, + 0.855, + 0.27 + ], + "angle": 0, + "content": "\\(^{3}\\)School of Computer Science and Engineering, Nanyang Technological University, Singapore" + }, + { + "type": "text", + "bbox": [ + 0.126, + 0.27, + 0.845, + 0.288 + ], + "angle": 0, + "content": "\\(^{4}\\)RIKEN Center for Advanced Intelligence Project, \\(^{5}\\)The University of Tokyo, Tokyo, Japan" + }, + { + "type": "text", + "bbox": [ + 0.134, + 0.29, + 0.832, + 0.305 + ], + "angle": 0, + "content": "phyang.cs@gmail.com, mkxie@nuaa.edu.cn, chencz@nuaa.edu.cn, lfengqaq@gmail.com," + }, + { + "type": "text", + "bbox": [ + 0.202, + 0.308, + 0.769, + 0.322 + ], + "angle": 0, + "content": "gang.niu.ml@gmail.com, sugi@k.u-tokyo.ac.jp, huangsj@nuaa.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.357, + 0.313, + 0.373 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.389, + 0.474, + 0.707 + ], + "angle": 0, + "content": "Existing knowledge distillation methods typically work by imparting the knowledge of output logits or intermediate feature maps from the teacher network to the student network, which is very successful in multi-class single-label learning. However, these methods can hardly be extended to the multi-label learning scenario, where each instance is associated with multiple semantic labels, because the prediction probabilities do not sum to one and feature maps of the whole example may ignore minor classes in such a scenario. In this paper, we propose a novel multi-label knowledge distillation method. On one hand, it exploits the informative semantic knowledge from the logits by dividing the multi-label learning problem into a set of binary classification problems; on the other hand, it enhances the distinctiveness of the learned feature representations by leveraging the structural information of label-wise embeddings. Experimental results on multiple benchmark datasets validate that the proposed method can avoid knowledge counteraction among labels, thus achieving superior performance against diverse comparing methods. Our code is available at: https://github.com/penghui-yang/L2D." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.735, + 0.21, + 0.751 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.76, + 0.47, + 0.866 + ], + "angle": 0, + "content": "Multi-label learning (MLL) addresses problems where each instance is assigned with multiple class labels simultaneously [32]. For example, as shown in Figure 1, an image of a street scene may be annotated with labels bus, car and person. To learn the complex object-label mapping, there is always necessity of training large models to obtain desirable performance in MLL. While the remarkable successes" + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.355, + 0.691, + 0.501 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.707, + 0.355, + 0.798, + 0.426 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.803, + 0.355, + 0.895, + 0.426 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.514, + 0.594, + 0.584 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.598, + 0.514, + 0.689, + 0.583 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.707, + 0.429, + 0.798, + 0.5 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.803, + 0.429, + 0.895, + 0.5 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.588, + 0.594, + 0.658 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.598, + 0.588, + 0.689, + 0.658 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.707, + 0.588, + 0.798, + 0.658 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.803, + 0.588, + 0.895, + 0.658 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.584, + 0.66, + 0.608, + 0.671 + ], + "angle": 0, + "content": "Car" + }, + { + "type": "image_caption", + "bbox": [ + 0.779, + 0.66, + 0.822, + 0.671 + ], + "angle": 0, + "content": "Person" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.678, + 0.892, + 0.859 + ], + "angle": 0, + "content": "Figure 1. Visualization of attention maps on different classes. We compare our method with the following three baselines: 1) Vanilla: the student trained without distillation; 2) ReviewKD [1]: a feature-based method that achieves the state-of-the-art performance; 3) Teacher: the pretrained model used in distillation. It can be observed that: on the classes bus and car, L2D captures semantic objects more precisely than the conventional KD method; on the class person, although all of the methods focus on people, only our method focuses on the same person as the teacher, which validates that L2D can distill the \"dark\" knowledge [27] from the teacher more effectively. The backbones of the teacher and student models are respectively ResNet-101 and ResNet-34. More visualization of attention maps can be found in Appendix." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.893, + 0.902 + ], + "angle": 0, + "content": "have been made in MLL through the training of deep neural networks (DNNs) [14, 23], it is hard to deploy these large" + }, + { + "type": "page_footnote", + "bbox": [ + 0.094, + 0.875, + 0.363, + 0.888 + ], + "angle": 0, + "content": "*Both authors contributed equally to this research." + }, + { + "type": "page_footnote", + "bbox": [ + 0.097, + 0.888, + 0.434, + 0.901 + ], + "angle": 0, + "content": "\\(^{\\dagger}\\) Correspondence to: Sheng-Jun Huang (huangsj@nuaa.edu.cn)." + }, + { + "type": "list", + "bbox": [ + 0.094, + 0.871, + 0.434, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "17271" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.136 + ], + "angle": 0, + "content": "models on lightweight terminals, e.g., mobile phones, under the constraint of computational resource or requirement of short inference time." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.139, + 0.468, + 0.306 + ], + "angle": 0, + "content": "To mitigate this issue, knowledge distillation (KD) [10] is needed which aims to improve the performance of a small network (also known as the \"student\") by requiring the knowledge from a large network (also known as the \"teacher\") to guide the training of the student network. Typical KD methods focus on the multi-class classification, and can be roughly divided into two categories: logits-based methods and feature-based methods. The former minimizes the difference between logits of the teacher model and the student model [10, 34], while the latter distills knowledge from feature maps of intermediate layers [19, 28, 1]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.308, + 0.468, + 0.549 + ], + "angle": 0, + "content": "Although KD has been proven to be effective for improving the performance of the student network in single-label classification, it is still a challenging problem to directly extend existing KD methods to solve multi-label knowledge distillation (MLKD) problems. Specifically, logits-based methods often obtain the predicted probabilities based on the softmax function; this function is not suitable for MLKD, because the sum of predicted probabilities may not equal one in MLL. Feature-based methods often perform KD based on the feature maps of a whole image with multiple semantics, which makes the model focus on the major objects while neglect minor objects. For example, in Figure 1, Vanilla and ReviewKD wrongly focused on the bus when the model queried the label car. Such a phenomenon would cause the model to obtain sub-optimal even undesirable distillation performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.551, + 0.468, + 0.776 + ], + "angle": 0, + "content": "Recently, several attempts have been made to utilize KD techniques for improving the performance of MLL [15, 29, 25]. There are mainly two differences between these works and our work. Firstly, these methods often required specifically-designed network architectures [15, 25] or training strategies [29] to train the teacher and student models, while our method focuses on studying MLKD in general scenarios without any extra requirement. Secondly, unlike the previous methods utilized KD as an auxiliary technique to improve the performance of MLL, our goal is to develop a tailored approach for MLKD. As a result, previous methods were mainly compared with MLL methods in their original papers, we evaluate the KD performance of our method by comparing it with state-of-the-art KD methods." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.781, + 0.468, + 0.901 + ], + "angle": 0, + "content": "In this paper, to perform MLKD, we propose a new method consisting of multi-label logits distillation and label-wise embedding distillation (L2D for short). Specifically, to exploit informative semantic knowledge compressed in the logits, L2D employs the one-versus-all reduction strategy to obtain a set of binary classification problems and perform logits distillation for each one. To enhance the distinctiveness of learned feature representations," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.226 + ], + "angle": 0, + "content": "L2D encourages the student model to maintain a consistent structure of intra-class and intra-instance (inter-class) label-wise embeddings with the teacher model. By leveraging the structural information of the teacher model, these two structural consistencies respectively enhance the compactness of intra-class embeddings and dispersion of inter-class embeddings for the student model. Both of these two components lead L2D to achieve better distillation performance than conventional KD methods as shown in Figure 1." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.228, + 0.88, + 0.242 + ], + "angle": 0, + "content": "Our main contributions can be summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.255, + 0.891, + 0.314 + ], + "angle": 0, + "content": "- A general framework called MLKD is proposed. To our best knowledge, the framework is the first study specially designed for knowledge distillation in the multi-label learning scenario." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.324, + 0.891, + 0.414 + ], + "angle": 0, + "content": "- A new approach for MLKD called L2D is proposed. It performs multi-label logits distillation and label-wise embedding distillation simultaneously. The former provides informative semantic knowledge while the latter encourages the student model to learn more distinctive feature representations." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.425, + 0.89, + 0.455 + ], + "angle": 0, + "content": "- Extensive experimental results on benchmark datasets demonstrate the effectiveness of our proposed method." + }, + { + "type": "list", + "bbox": [ + 0.5, + 0.255, + 0.891, + 0.455 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.468, + 0.64, + 0.484 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.494, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The concept of knowledge distillation (KD) proposed by Geoffrey Hinton et al. [10] defines a learning framework that transfers knowledge from a large teacher network to a small student network. Existing works can be roughly divided into two groups, i.e., logits-based methods and feature-based methods. Logits-based methods mainly focus on designing effective distillation losses to distill knowledge from logits and softmax scores after logits. DML [33] introduces a mutual learning method to train both teachers and students simultaneously. TAKD [18] proposes a new architecture called \"teacher assistant\", which is an intermediate-sized network bridging the gap between teachers and students. Besides, a recent study [34] proposes a novel logits-based method to reformulate the classical KD loss into two parts and achieves the state-of-the-art performance by adjusting weights for these two parts. Some other methods focus on distilling knowledge from intermediate feature layers. FitNet [24] is the first approach to distill knowledge from intermediate features by measuring the distance between feature maps. Attention transfer [31] achieves better performance than FitNet by distilling knowledge from the attention maps. PKT [20] measures the KL divergence between features by treating them as probability distributions. RKD [19] utilizes the relations among instances to guide the training process of the student model. CRD [28] incorporates contrastive learning into knowledge distillation. ReviewKD [1] proposes a review mechanism" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17272" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "which uses multiple layers in the teacher to supervise one layer in the student. ITRD [17] aims to maximize the correlation and mutual information between the students' and teachers' representations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.152, + 0.473, + 0.543 + ], + "angle": 0, + "content": "Multi-label learning has increasingly attracted a lot of interest recently. Existing solutions for solving MLL problems can be categorized into three directions. The first type attempts to design novel loss functions for tackling the intrinsic positive-negative imbalance issue in multi-label classification tasks. For example, ASL [22] uses different weights to re-weight positive and negative examples for the balanced training. The second type focuses on modeling the label correlations, which provides prior knowledge for multi-label classification. Among them, MLGCN [3] is a representative method that employs a graph convolutional network to model correlation matrix. CADM [2] constructs a similar graph based on class-aware maps. To handle the multiple semantic objects contained in an image, the last type of methods aims to locate areas of interest related to semantic labels by using attention techniques. Among them, C-Tran [12] first utilizes the transformer to retrieve embeddings from visual features for each label. Query2Label [14] uses several stacked transformer encoders to identify interesting areas. ML-Decoder [23] simplifies transformer encoders in Query2Label. ADDS [30] introduces encoders from CLIP [21] in order to get better textual and visual embedding inputs to the classification head. In addition, ADDS adds a multi-head cross-attention layer and a skipping connection from the query input to the query output based on ML-Decoder." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.545, + 0.47, + 0.726 + ], + "angle": 0, + "content": "Several previous studies have applied KD techniques to improve the performance of MLL. For example, Yongcheng Liu et al. [15] and Jiazhi Xu et al. [29] simply minimized mean squared error (MSE) loss between teacher logits and student logits. Liangchen Song et al. [25] designed a partial softmax function by combining a positive label with all other negative labels. Then, the conventional KD loss can be computed for each positive label. Although these methods made the pioneering attempts of combining KD and MLL, they cannot be directly applied general MLKD scenarios, and also fail to evaluate their KD performance by comparing with KD methods." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.74, + 0.307, + 0.758 + ], + "angle": 0, + "content": "3. The Proposed Approach" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Let \\( \\pmb{x} \\in \\mathcal{X} \\) be an instance and \\( \\pmb{y} \\in \\mathcal{Y} \\) be its corresponding label vector, where \\( \\mathcal{X} \\subset \\mathbb{R}^d \\) is the input space with \\( d \\) dimensions and \\( \\mathcal{Y} \\subset \\{0,1\\}^q \\) is the target space with \\( q \\) class labels. We further use \\( y_{j} \\) to denote the \\( j \\)-th component of \\( \\pmb{y} \\). For a given instance \\( \\pmb{x} \\), \\( y_{j} = 1 \\) indicates the \\( j \\)-th label is relevant to the instance; \\( y_{j} = 0 \\), otherwise. In multi-label learning, each instance may be assigned with more than one label, which means \\( \\sum_{j=1}^{q} \\mathbb{I}(y_{j} = 1) \\geq 1 \\), where \\( \\mathbb{I}(\\cdot) \\) is the indicator function. We also denote by \\( [q] \\) the integer set" + }, + { + "type": "equation", + "bbox": [ + 0.5, + 0.092, + 0.597, + 0.107 + ], + "angle": 0, + "content": "\\[\n\\{1, 2, \\dots , q \\}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.108, + 0.892, + 0.332 + ], + "angle": 0, + "content": "In this paper, we use a classification model consisting of three components, i.e., a visual backbone \\( f \\), which extracts a feature map \\( f(\\pmb{x}) \\) for the input \\( \\pmb{x} \\), a label-wise embedding encoder \\( g \\) [12, 14], which produces a label-wise embedding \\( e_k = g_k(f(\\pmb{x})) \\) with respect to the \\( k \\)-th class based on the feature map \\( f(\\pmb{x}) \\), and a multi-label classifier \\( h \\), which predicts multi-label probabilities \\( \\hat{y} = [\\sigma(h_1(e_1)), \\sigma(h_2(e_2)), \\dots, \\sigma(h_q(e_q))] \\), where \\( \\sigma(\\cdot) \\) denotes the sigmoid function. It is noteworthy that the used model is very general, which can be built by equipping commonly used backbones, e.g., ResNet [9], with a label-wise embedding encoder \\( g \\). For the notations mentioned above, we use the superscripts \\( \\mathcal{T} \\) (or \\( S \\)) to denote the teacher (or student) model. For example, we use \\( e_k^T \\) and \\( e_k^S \\) to denote the label-wise embeddings for teacher and student models." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.333, + 0.892, + 0.438 + ], + "angle": 0, + "content": "In multi-label learning, a popular method is to employ the one-versus-all reduction strategy to transform the original task into multiple binary problems. Among the various loss functions, the most commonly used one is the binary cross entropy (BCE) loss. Specifically, given a batch of examples \\(\\{(x_i,y_i)\\}_{i = 1}^b\\) and the predicted probabilities \\(\\hat{\\pmb{y}}\\), the BCE loss can be defined as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.5, + 0.446, + 0.892, + 0.5 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {B C E}} = - \\frac {1}{b} \\sum_ {i = 1} ^ {b} \\sum_ {k = 1} ^ {q} y _ {i k} \\log \\left(\\hat {y} _ {i k}\\right) + (1 - y _ {i k}) \\log \\left(1 - \\hat {y} _ {i k}\\right). \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.501, + 0.892, + 0.68 + ], + "angle": 0, + "content": "Figure 2 illustrates the distillation process of the proposed L2D framework. For a batch of training examples, we feed them into the teacher/student model to obtain the label-wise embeddings and predicted probabilities. In order to train the student model, besides the BCE loss, we design the following two distillation losses: 1) multi-label logits distillation loss \\(\\mathcal{L}_{\\mathrm{MLD}}\\) to exploit informative semantic knowledge compressed in the logits, 2) label-wise embedding distillation loss \\(\\mathcal{L}_{\\mathrm{LED}}\\) to leverage structural information for enhancing the distinctiveness of learned feature representations. The overall objective function can be presented as" + }, + { + "type": "equation", + "bbox": [ + 0.557, + 0.682, + 0.891, + 0.697 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {L 2 D}} = \\mathcal {L} _ {\\mathrm {B C E}} + \\lambda_ {\\mathrm {M L D}} \\mathcal {L} _ {\\mathrm {M L D}} + \\lambda_ {\\mathrm {L E D}} \\mathcal {L} _ {\\mathrm {L E D}}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.704, + 0.848, + 0.719 + ], + "angle": 0, + "content": "where \\(\\lambda_{\\mathrm{MLD}}\\) and \\(\\lambda_{\\mathrm{LED}}\\) are two balancing parameters." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.727, + 0.771, + 0.743 + ], + "angle": 0, + "content": "3.1. Multi-Label Logits Distillation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.87 + ], + "angle": 0, + "content": "Traditional logits-based distillation normally minimizes the Kullback-Leibler (KL) divergence between the predicted probabilities, i.e., the logits after the softmax function, of teacher and student model. However, the method cannot be directly applied to the MLL scenario, since it depends on a basic assumption that the predicted probabilities of all classes should sum to one, which hardly holds for MLL examples." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "To mitigate this issue, inspired by the idea of one-versus-all reduction, we propose a multi-label logits distillation" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17273" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.107, + 0.096, + 0.887, + 0.331 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.339, + 0.895, + 0.371 + ], + "angle": 0, + "content": "Figure 2. An illustration of the L2D framework. The framework simultaneously performs multi-label logits distillation and label-wise embedding distillation to improve the performance of the student model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.393, + 0.475, + 0.468 + ], + "angle": 0, + "content": "(MLD) loss, which decomposes the original multi-label task into multiple binary classification problems and minimizes the divergence between the binary predicted probabilities of two models. Formally, the MLD loss can be formulated as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.077, + 0.474, + 0.473, + 0.514 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {M L D}} = \\frac {1}{b} \\sum_ {i = 1} ^ {b} \\sum_ {k = 1} ^ {q} \\mathcal {D} \\left(\\left[ \\hat {y} _ {i k} ^ {\\mathcal {T}}, 1 - \\hat {y} _ {i k} ^ {\\mathcal {T}} \\right] \\mid \\mid [ \\hat {y} _ {i k} ^ {\\mathcal {S}}, 1 - \\hat {y} _ {i k} ^ {\\mathcal {S}} ]\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.516, + 0.472, + 0.63 + ], + "angle": 0, + "content": "where \\([\\cdot, \\cdot]\\) is an operator used to concatenate two scalars into a vector, and \\(\\mathcal{D}\\) is a divergence function. The most common choice is the KL divergence \\(\\mathcal{D}_{\\mathrm{KL}}(P \\| Q) = \\sum_{x \\in \\mathcal{X}} P(x) \\log \\left(\\frac{P(x)}{Q(x)}\\right)\\), where \\(P\\) and \\(Q\\) are two different probability distributions. The MLD loss aims to improve the performance of student model by sufficiently exploiting informative knowledge from logits." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.636, + 0.381, + 0.652 + ], + "angle": 0, + "content": "3.2. Label-wise Embedding Distillation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.473, + 0.903 + ], + "angle": 0, + "content": "The MLD loss performs distillation on the predicted probabilities that can be regarded as a high-level representation, i.e., the final outputs of model. The knowledge distilled from the teacher model by only using the MLD loss would be insufficient to train a student model with desirable performance due to the limited information carried by the logits. To further strengthen the effectiveness of distillation, we design the label-wise embedding distillation (LED) loss, which aims to explore the structural knowledge from label-wise embeddings. The main idea is to capture two types of structural relations among label-wise embeddings: 1) class-aware label-wise embedding distillation (CD) loss \\(\\mathcal{L}_{\\mathrm{CD}}\\), which captures the structural relation between any two intra-class label-wise embeddings from different examples; 2) instance-aware label-wise embedding distillation (ID) loss \\(\\mathcal{L}_{\\mathrm{ID}}\\), which models the structural re" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.393, + 0.893, + 0.438 + ], + "angle": 0, + "content": "lation between any two inter-class label-wise embeddings from the same example. In the following content, we introduce these two distillation losses in detail." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.465, + 0.892, + 0.481 + ], + "angle": 0, + "content": "3.2.1 Class-Aware Label-Wise Embedding Distillation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.491, + 0.893, + 0.824 + ], + "angle": 0, + "content": "Class-aware label-wise embedding distillation aims to improve the distillation performance by exploiting the structural relations among intra-class label-wise embeddings. Generally, the same semantic objects from two different images often differ from each other by their individual characteristics, such as two cars with different colors and diverse styles (see the left side in Figure 3). Since our goal is to distinguish between car and other semantic classes instead of identifying different cars, these distinctiveness would be confusing information for the corresponding classification task. Due to the powerful learning capacity, the large model is able to capture the highly abstract semantic representations for each class label by neglecting the useless individual information. From the perspective of learned feature representations, as shown in the left side of Figure 3, the teacher model tends to obtain a more compact structure of intra-class label-wise embedding, which often leads to better classification performance. By transferring the structural knowledge from the teacher model to the student model, CD encourages the student model to enhance the compactness of intra-class label-wise embeddings, which can improve its classification performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.824, + 0.895, + 0.903 + ], + "angle": 0, + "content": "For a batch of examples, let \\(\\{e_{ik}^{\\mathcal{T}}\\}_{i = 1}^{b}\\) and \\(\\{e_{ik}^{\\mathcal{S}}\\}_{i = 1}^{b}\\) respectively denote the intra-class label-wise embeddings with respect to class \\(k\\in [q]\\) generated by the teacher and student models. Then, we can capture the structural relation between any two intra-class label-wise embeddings \\(e_{ik}^{\\mathcal{T}}\\) and" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "17274" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.107, + 0.103, + 0.855, + 0.337 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.355, + 0.895, + 0.398 + ], + "angle": 0, + "content": "Figure 3. An illustration of class/instance-aware label-wise embedding distillation. Class-aware label-wise embedding distillation (CD) captures structural relations among intra-class label-wise embeddings from different examples, while instance-aware label-wise embedding distillation (ID) explores structural relations among intra-instance (inter-class) label-wise embeddings." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.421, + 0.452, + 0.441 + ], + "angle": 0, + "content": "\\(\\pmb{e}_{jk}^{\\mathcal{T}}\\) by measuring their distance in the embedding space:" + }, + { + "type": "equation", + "bbox": [ + 0.087, + 0.449, + 0.47, + 0.489 + ], + "angle": 0, + "content": "\\[\n\\phi_ {\\mathrm {C D}} \\left(\\boldsymbol {e} _ {i k} ^ {\\mathcal {T}}, \\boldsymbol {e} _ {j k} ^ {\\mathcal {T}}\\right) = \\left\\{ \\begin{array}{l l} \\| \\boldsymbol {e} _ {i k} ^ {\\mathcal {T}} - \\boldsymbol {e} _ {j k} ^ {\\mathcal {T}} \\| _ {2} & y _ {i k} = 1, y _ {j k} = 1, \\\\ 0 & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.498, + 0.47, + 0.587 + ], + "angle": 0, + "content": "It is worth to note that we only consider the structural relation between any two valid label-wise embeddings, i.e., the embeddings with respect to positive labels. Similar to Eq.(4), for any two intra-class label-wise embeddings \\( e_{ik}^S \\) and \\( e_{jk}^S \\), we can obtain the structural relation \\( \\phi_{\\mathrm{CD}}(e_{ik}^S, e_{jk}^S) \\) for the student model." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.588, + 0.47, + 0.648 + ], + "angle": 0, + "content": "By enforcing the teacher and student structural relations to maintain the consistency for each pair of intra-class label-wise embeddings, we can achieve the class-aware structural consistency as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.081, + 0.657, + 0.469, + 0.695 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {C D}} = \\sum_ {k = 1} ^ {q} \\sum_ {i, j \\in [ b ]} \\ell \\left(\\phi_ {\\mathrm {C D}} \\left(e _ {i k} ^ {\\mathcal {T}}, e _ {j k} ^ {\\mathcal {T}}\\right), \\phi_ {\\mathrm {C D}} \\left(e _ {i k} ^ {\\mathcal {S}}, e _ {j k} ^ {\\mathcal {S}}\\right)\\right), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.696, + 0.47, + 0.743 + ], + "angle": 0, + "content": "where \\(\\ell\\) is a function to measure the consistency between the teacher and student structural relations. In experiments, we use the following Huber loss function as a measurement:" + }, + { + "type": "equation", + "bbox": [ + 0.145, + 0.751, + 0.469, + 0.79 + ], + "angle": 0, + "content": "\\[\n\\ell (a, b) = \\left\\{ \\begin{array}{l l} \\frac {1}{2} (a - b) ^ {2} & | a - b | \\leq 1, \\\\ | a - b | - \\frac {1}{2} & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.8, + 0.416, + 0.813 + ], + "angle": 0, + "content": "where \\(a\\) and \\(b\\) are two different structural relations." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.832, + 0.47, + 0.862 + ], + "angle": 0, + "content": "3.2.2 Instance-Aware Label-Wise Embedding Distillation" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Instance-aware label-wise embedding distillation (ID) aims to improve the distillation performance by exploring the" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.422, + 0.892, + 0.722 + ], + "angle": 0, + "content": "structural relations among inter-class label-wise embeddings from the same image. Generally, one can hardly distinguish between two different semantic objects occurring in an image due to the high similarities they share. For example, in the upper left corner of Figure 3, an image annotated with both sky and sea makes it difficult to distinguish between the semantic objects, as they share the same color and similar texture. A feasible solution is to exploit other useful information, such as their spatial relation, i.e., sky is always above sea. Due to the powerful learning capacity, the large model is able to distinguish between the similar semantic objects by exploiting such implicit supervised information. From the perspective of learned feature representations, as shown in the right side of 3, the teacher model tends to learn a dispersed structure of inter-class label-wise embedding, which is beneficial for improving its discrimination ability. By distilling the structural knowledge from the teacher model, ID enforces the student model to enhance the dispersion of inter-class label-wise embeddings, which can improve its discrimination ability." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.723, + 0.892, + 0.815 + ], + "angle": 0, + "content": "For a given instance \\( \\pmb{x}_i \\), let \\( \\{e_{ik}^{\\mathcal{T}}\\}_{k=1}^{q} \\) and \\( \\{e_{ik}^S\\}_{k=1}^{q} \\) respectively denote the label-wise embeddings generated by teacher and student models. Then, we can capture the structural relation between any two inter-class label-wise embeddings \\( e_{ik}^{\\mathcal{T}} \\) and \\( e_{il}^{\\mathcal{T}} \\) by measuring their distance in the embedding space:" + }, + { + "type": "equation", + "bbox": [ + 0.517, + 0.823, + 0.892, + 0.863 + ], + "angle": 0, + "content": "\\[\n\\phi_ {\\mathrm {I D}} \\left(e _ {i k} ^ {\\mathcal {T}}, e _ {i l} ^ {\\mathcal {T}}\\right) = \\left\\{ \\begin{array}{l l} \\| e _ {i k} ^ {\\mathcal {T}} - e _ {i l} ^ {\\mathcal {T}} \\| _ {2} & y _ {i k} = 1, y _ {i l} = 1, \\\\ 0 & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Note that in Eq.(7), we only consider the structural relation between any two valid label-wise embeddings, i.e.," + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17275" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.198, + 0.088, + 0.769, + 0.1 + ], + "angle": 0, + "content": "Table 1. Results on MS-COCO where teacher and student models are in the same architectures." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.1, + 0.89, + 0.312 + ], + "angle": 0, + "content": "
TeacherRepVGG-A2ResNet-101WRN-101Swin-S
StudentRepVGG-A0ResNet-34WRN-50Swin-T
MetricsmAPOF1CF1mAPOF1CF1mAPOF1CF1mAPOF1CF1
Teacher72.7174.1168.6373.6273.8968.6174.7075.5670.7381.7080.4877.12
Student70.0272.4966.7770.3172.4966.8274.4575.4370.6179.5979.1875.42
RKD70.0872.3966.7370.1372.4466.7874.7075.7170.8479.6379.1975.57
PKT70.1172.4766.8070.4372.6466.6874.5475.4770.5879.6479.0975.39
ReviewKD70.0072.3566.8270.3972.6266.7674.0375.2970.3679.8179.1875.55
MSE70.2672.5466.9970.5472.7566.8574.5375.6070.7179.6779.2075.52
PS70.6572.8967.6070.8672.6667.1275.1276.0571.6379.9679.6476.20
MLD70.7472.8167.4670.6872.6967.1974.9275.7571.2180.1179.6876.44
L2D72.8174.5969.4972.8774.4569.4376.6177.0872.7981.5981.0377.86
" + }, + { + "type": "table_caption", + "bbox": [ + 0.185, + 0.323, + 0.782, + 0.335 + ], + "angle": 0, + "content": "Table 2. Results on MS-COCO where teacher and student models are in the different architectures." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.335, + 0.89, + 0.548 + ], + "angle": 0, + "content": "
TeacherResNet-101Swin-TResNet-101Swin-T
StudentRepVGG-A0ResNet-34MobileNet v2MobileNet v2
MetricsmAPOF1CF1mAPOF1CF1mAPOF1CF1mAPOF1CF1
Teacher73.6273.8968.6179.4378.7775.0773.6273.8968.6179.4378.7775.07
Student70.0272.4966.7770.3172.4966.8271.8573.5968.2671.8573.5968.26
RKD70.0872.3566.7270.0072.3466.6471.7673.6868.4071.7473.6868.37
PKT69.9972.3566.5670.2672.3966.8271.8873.6068.3571.8473.7668.37
ReviewKD70.0072.3366.6270.2972.3966.5871.9273.7368.4871.7373.7168.36
MSE70.0772.5066.8570.3372.5766.7271.9173.6868.2871.8073.7468.38
PS70.3072.6167.1070.9472.9367.5772.1173.8968.4272.4274.1468.94
MLD70.4872.7767.1071.1472.9967.6372.1773.8468.5272.3574.1068.91
L2D72.1474.0868.7873.4274.9770.2073.2474.8569.7274.2175.7270.87
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.572, + 0.469, + 0.632 + ], + "angle": 0, + "content": "the embedding with respect to positive labels. Similar to Eq.(7), for any two inter-class label-wise embeddings \\( e_{ik}^S \\) and \\( e_{il}^S \\), we can obtain the structural relation \\( \\phi_{\\mathrm{ID}}(e_{ik}^S, e_{il}^S) \\) for the student model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.633, + 0.469, + 0.709 + ], + "angle": 0, + "content": "By encouraging the teacher and student model to maintain the consistent structure of intra-instance label-wise embeddings, we can minimize the following \\(\\mathcal{L}_{\\mathrm{ID}}\\) loss to achieve the instance-aware structural consistency where \\(\\ell(.)\\) is Huber loss as defined in Eq.(6):" + }, + { + "type": "equation", + "bbox": [ + 0.091, + 0.715, + 0.469, + 0.756 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {I D}} = \\sum_ {i = 1} ^ {b} \\sum_ {k, l \\in [ q ]} \\ell \\left(\\phi_ {\\mathrm {I D}} \\left(\\boldsymbol {e} _ {i k} ^ {\\mathcal {T}}, \\boldsymbol {e} _ {i l} ^ {\\mathcal {T}}\\right), \\phi_ {\\mathrm {I D}} \\left(\\boldsymbol {e} _ {i k} ^ {\\mathcal {S}}, \\boldsymbol {e} _ {i l} ^ {\\mathcal {S}}\\right)\\right). \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.757, + 0.469, + 0.786 + ], + "angle": 0, + "content": "Finally, the overall objective function of L2D (Eq.(2)) can be re-written as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.097, + 0.794, + 0.469, + 0.812 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {L 2 D}} = \\mathcal {L} _ {\\mathrm {B C E}} + \\lambda_ {\\mathrm {M L D}} \\mathcal {L} _ {\\mathrm {M L D}} + \\lambda_ {\\mathrm {C D}} \\mathcal {L} _ {\\mathrm {C D}} + \\lambda_ {\\mathrm {I D}} \\mathcal {L} _ {\\mathrm {I D}}, \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.819, + 0.442, + 0.835 + ], + "angle": 0, + "content": "where \\(\\lambda_{\\mathrm{MLD}}\\), \\(\\lambda_{\\mathrm{CD}}\\) and \\(\\lambda_{\\mathrm{ID}}\\) are all balancing parameters." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.845, + 0.21, + 0.862 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Datasets. We perform experiments on three benchmark datasets Pascal VOC2007 [8] (VOC for short), MS-" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.572, + 0.892, + 0.709 + ], + "angle": 0, + "content": "COCO2014 [13] (MS-COCO for short) and NUS-WIDE [4]. VOC contains 5,011 images in the train-val set, and 4,952 images in the test set. It covers 20 common objects, with an average of 1.6 labels per image. MS-COCO contains 82,081 training images and 40,137 test images. It covers 80 common objects, with an average of 2.9 labels per image. NUS-WIDE contains 161,789 training images and 107,859 test images. It covers 81 visual concepts, with an average of 1.9 labels per image." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.714, + 0.892, + 0.806 + ], + "angle": 0, + "content": "Metrics. Following existing works [32, 14, 26], we adopt the mean average precision (mAP) over all classes, overall F1-score (OF1) and average per-class F1-score (CF1) to evaluate the performance. We choose OF1 and CF1, since they consider both recall and precision and thus are more comprehensive." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Comparing Methods. To validate the proposed method, we compare it with the following sota KD methods: RKD [19], which captures the relations among instances to guide the training of the student model; PKT [20], which measures KL divergence between features by treating them as probability distributions; ReviewKD [1], which transfers" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "17276" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.471, + 0.182 + ], + "angle": 0, + "content": "knowledge across different stages instead of just focusing on features in the same levels; as well as the modified KD techniques that have been applied to MLL: MSE [29], which minimizes the MSE loss between logits of teacher and student model; PS [25], which minimizes KL divergence of logits after a partial softmax function." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.184, + 0.474, + 0.486 + ], + "angle": 0, + "content": "Implementation Details. We use the models pretrained on ImageNet [6] as the backbones. We resize the resolution of all images to \\(224 \\times 224\\) and set the batch size as 64. For each training image, we adopt a weak augmentation consisting of random horizontal flipping and a strong augmentation consisting of Cutout [7] and RandAugment [5]. We use the Adam optimization method [11] to train the model for 80 epochs. The one-cycle policy is used with a maximal learning rate of 0.0001 and the weight decay [16] of 0.0001. For all experiments, we set \\(\\lambda_{\\mathrm{MLD}} = 10\\), \\(\\lambda_{\\mathrm{CD}} = 100\\), and \\(\\lambda_{\\mathrm{ID}} = 1000\\). Parameter sensitivity analysis in Appendix shows that the performance of L2D are insensitive to all of our balancing parameters. For the comparing methods, we set their parameters as suggested in the original papers. Especially, for all feature-based methods, we just deploy them on the feature maps which is output from the visual backbone \\(f\\). All the experiments are conducted on GeForce RTX 2080 GPUs. More details about the used models and implementation of the label-wise embedding encoder are attached in Appendix." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.499, + 0.27, + 0.515 + ], + "angle": 0, + "content": "4.1. Comparison Results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.524, + 0.472, + 0.903 + ], + "angle": 0, + "content": "Table 1 and Table 2 report comparison results on MS-COCO with the same and different architectures of student and teacher models. From Table 1, it can be observed that: 1) Conventional feature-based distillation methods only achieve minor improvements in performance when compared with the student model (without distillation). This indicates these methods do not work in multi-label scenarios due to their disability to capture multiple semantics occurred in feature maps. 2) MLD can outperform conventional feature-based distillation methods in most cases, which indicates by performing one-versus-all reduction, the logits-based distillation can be adapted into multi-label knowledge distillation. 3) The proposed L2D significantly outperforms all other methods and achieves comparable performance with the teacher model. In particular, when WRN is used as the backbone, the performance of L2D is even better than that of teacher model. One possible reason is that L2D can effectively alleviate the over-fitting issue occurred to the teacher model. More results about reversed knowledge distillation where the Vanilla student model outperforms the teacher can be found in Appendix. From Table 2, we can see that compared with the same architecture, the performance gap between teacher and student model is larger for different architectures, which indicates the corresponding distillation task becomes harder. Our method sig" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.088, + 0.892, + 0.156 + ], + "angle": 0, + "content": "Table 3. Comparison results of the comparing methods on VOC in terms of AP and mAP (\\%), where the backbones of teacher and student model are respectively ResNet-50 and ResNet-18. The best performance is highlighted in red, and second best performance is highlighted in blue." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.157, + 0.892, + 0.464 + ], + "angle": 0, + "content": "
MethodsVanillaRKDPKTMSEMLDL2D
bottle57.1859.0157.2958.2658.3259.71
pottedplant67.4367.0166.1668.0268.8870.52
chair70.3571.3171.1670.6871.1274.77
sofa73.1772.8673.2272.0673.7775.01
diningtable76.1476.9076.8977.9378.6578.93
cow82.6581.1181.7581.0684.6083.87
tvmonitor82.3081.7081.9582.3682.4284.13
bus85.5384.7985.0686.0386.4185.45
sheep84.1684.7783.6683.7283.7785.67
motorbike88.3888.8688.7388.3088.5889.83
dog90.1890.0390.1090.4690.7890.60
bird90.6591.6591.3190.6091.0291.48
bicycle91.4091.5391.7791.5891.9291.90
cat90.6791.8691.8391.0791.6392.14
boat92.5492.5392.3591.6492.2592.57
car92.7292.0692.0792.0192.3493.40
horse94.2293.9793.1294.0594.5394.67
person95.7395.8895.8095.6996.0496.46
train96.0997.0896.9997.1396.9796.81
aeroplane97.2797.0097.0997.1097.3097.39
mAP84.0184.1883.8684.2384.4885.71
" + }, + { + "type": "table_caption", + "bbox": [ + 0.574, + 0.477, + 0.816, + 0.489 + ], + "angle": 0, + "content": "Table 4. Ablation studies on MS-COCO." + }, + { + "type": "table", + "bbox": [ + 0.536, + 0.489, + 0.861, + 0.589 + ], + "angle": 0, + "content": "
MLDCDIDmAPOF1CF1
70.3172.4966.82
✓70.6872.6967.19
✓✓71.9173.7468.76
✓✓71.7973.6268.43
✓✓✓72.8774.4569.43
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.892, + 0.673 + ], + "angle": 0, + "content": "nificantly outperforms all the comparing methods by a significant margin in all cases. These results provide a strong empirical validation for the effectiveness of the proposed method." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.893, + 0.902 + ], + "angle": 0, + "content": "Table 3 illustrates the performance of the proposed methods and other comparing methods on VOC in terms of AP and mAP. It is noteworthy that the performance is ranked in descending according to the performance of student model. From the figure, it can be observed that: 1) Our proposed L2D achieves the best performance and significantly outperforms the comparing methods in terms of mAP. 2) L2D consistently achieves superior performance to the comparing methods in most classes and the performance gap is large especially for classes that the student model achieves poor performance. This observation discloses that L2D improves the performance of hard classes by enhancing the distinctiveness of feature representations. These experimental results demonstrate the practical usefulness of the proposed method. More results on VOC and NUS-WIDE" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17277" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.104, + 0.093, + 0.138, + 0.104 + ], + "angle": 0, + "content": "Query" + }, + { + "type": "image", + "bbox": [ + 0.087, + 0.108, + 0.155, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.087, + 0.161, + 0.155, + 0.218 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.1, + 0.22, + 0.142, + 0.225 + ], + "angle": 0, + "content": "Dog, Fire Hydrant" + }, + { + "type": "image", + "bbox": [ + 0.169, + 0.108, + 0.238, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.169, + 0.166, + 0.238, + 0.218 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.185, + 0.22, + 0.227, + 0.225 + ], + "angle": 0, + "content": "Dog, Fire Hydrant" + }, + { + "type": "image", + "bbox": [ + 0.242, + 0.108, + 0.309, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.245, + 0.161, + 0.307, + 0.165 + ], + "angle": 0, + "content": "Book, Person, Remote" + }, + { + "type": "image", + "bbox": [ + 0.312, + 0.108, + 0.378, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.312, + 0.165, + 0.378, + 0.218 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.325, + 0.22, + 0.367, + 0.225 + ], + "angle": 0, + "content": "Dog, Fire Hydrant" + }, + { + "type": "image", + "bbox": [ + 0.382, + 0.108, + 0.448, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.382, + 0.166, + 0.448, + 0.218 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.394, + 0.22, + 0.437, + 0.225 + ], + "angle": 0, + "content": "Dog, Fire Hydrant" + }, + { + "type": "image", + "bbox": [ + 0.452, + 0.108, + 0.519, + 0.164 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.452, + 0.166, + 0.518, + 0.218 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.465, + 0.22, + 0.507, + 0.225 + ], + "angle": 0, + "content": "Dog, Fire Hydrant" + }, + { + "type": "image_caption", + "bbox": [ + 0.696, + 0.093, + 0.722, + 0.102 + ], + "angle": 0, + "content": "L2D" + }, + { + "type": "image", + "bbox": [ + 0.535, + 0.108, + 0.602, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.535, + 0.165, + 0.602, + 0.218 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.548, + 0.22, + 0.589, + 0.225 + ], + "angle": 0, + "content": "Dog, Fire Hydrant" + }, + { + "type": "image", + "bbox": [ + 0.606, + 0.108, + 0.672, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.606, + 0.166, + 0.672, + 0.218 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.619, + 0.22, + 0.661, + 0.225 + ], + "angle": 0, + "content": "Dog, Fire Hydrant" + }, + { + "type": "image", + "bbox": [ + 0.677, + 0.108, + 0.744, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.677, + 0.166, + 0.743, + 0.218 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.688, + 0.22, + 0.73, + 0.225 + ], + "angle": 0, + "content": "Dog, Fire Hydrant" + }, + { + "type": "image", + "bbox": [ + 0.747, + 0.108, + 0.813, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.746, + 0.165, + 0.813, + 0.218 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.759, + 0.22, + 0.8, + 0.225 + ], + "angle": 0, + "content": "Dog, Fire Hydrant" + }, + { + "type": "image", + "bbox": [ + 0.817, + 0.108, + 0.884, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.817, + 0.166, + 0.883, + 0.218 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.829, + 0.22, + 0.871, + 0.225 + ], + "angle": 0, + "content": "Dog, Fire Hydrant" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.233, + 0.892, + 0.275 + ], + "angle": 0, + "content": "Figure 4. Top-5 returned images with the query image. The returned results on the left are based on ReviewKD, while the results on the right are based on L2D. All results are sorted in the ascending order according to the distance from the query image. Red labels indicate that they are not included in the returned images' labels, while green labels are shared by the query image and the returned one." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.292, + 0.255, + 0.307 + ], + "angle": 0, + "content": "can be found in Appendix." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.328, + 0.23, + 0.344 + ], + "angle": 0, + "content": "4.2. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.355, + 0.471, + 0.626 + ], + "angle": 0, + "content": "In this section, to further analyze how the proposed method improves distillation performance, Table 4 reports results of ablation studies on MS-COCO (teacher: ResNet-101, student: ResNet-34). The first line in Table 4 reports the performance of student model without knowledge distillation. It can be observed that the distillation performance is improved slightly by only conducting multi-label logits distillation. Compared with MLD, label-wise embeddings distillation achieves the major improvement for the proposed method. It can be observed that by performing CD and ID, the mAP performance achieves \\(1.6\\%\\) and \\(1.48\\%\\) increments, respectively. Finally, we also examine the combination of these techniques. By incorporating these components together, the fusing method achieves the best performance and significantly outperforms each other method. These results demonstrate that all of three components are of great importance to the performance of the proposed L2D." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.648, + 0.364, + 0.664 + ], + "angle": 0, + "content": "4.3. Performance on Image Retrieval" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.675, + 0.47, + 0.901 + ], + "angle": 0, + "content": "To further evaluate if our method can learn better representations, we conduct an image retrieval experiment. Specifically, we use the \\(k\\)-NN algorithm to perform content-based image retrieval, and choose the student model trained by ReviewKD as the baseline, which has achieved the best performance among all conventional KD methods. Figure 4 illustrates the top-5 images returned by both methods. The labels under each image are colored in green if they are shared by both the query image and the returned one, and otherwise in red. These images are sorted in the ascending order based on the distance to the query image in the representation space. From the figures, we can see that our method returns the images that match the query image better than ReviewKD. This indicates our approach can obtain better representations than conventional KD methods." + }, + { + "type": "image", + "bbox": [ + 0.53, + 0.298, + 0.667, + 0.406 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.58, + 0.414, + 0.64, + 0.424 + ], + "angle": 0, + "content": "(a) Vanilla" + }, + { + "type": "image", + "bbox": [ + 0.672, + 0.298, + 0.866, + 0.407 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.743, + 0.414, + 0.825, + 0.424 + ], + "angle": 0, + "content": "(b) ReviewKD" + }, + { + "type": "image", + "bbox": [ + 0.529, + 0.439, + 0.667, + 0.547 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.584, + 0.555, + 0.636, + 0.566 + ], + "angle": 0, + "content": "(c)MLD" + }, + { + "type": "image", + "bbox": [ + 0.671, + 0.438, + 0.866, + 0.548 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.761, + 0.555, + 0.807, + 0.566 + ], + "angle": 0, + "content": "(d) L2D" + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.57, + 0.891, + 0.598 + ], + "angle": 0, + "content": "Figure 5. The differences between correlation matrices of student and teacher predicted probabilities on MS-COCO." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.606, + 0.794, + 0.621 + ], + "angle": 0, + "content": "4.4. Distilling Inter-class Correlations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.892, + 0.901 + ], + "angle": 0, + "content": "As discussed in the previous works [10], the conventional supervised learning losses, e.g., BCE loss, often neglects the correlations among class predictions, which act as a foundational element in MLL. To validate whether the correlations can be captured by L2D effectively, Figure 5 illustrates the differences between correlation matrices of student and teacher predicted probabilities on MS-COCO. From the figure, it can be observed that: 1) The representative comparing method ReviewKD shows a large difference, which discloses that the conventional KD methods are ineffective to capture the correlations in multi-label scenarios. 2) MLD does not show a reduced difference, which indicates that the information of logits is not enough for capturing precise correlations. 3) L2D shows significant matching between the teacher and student correlations. By enhancing the distinctiveness of label-wise embeddings, L2D can obtain more correct predicted probabilities, leading to a more precise correlation estimation." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17278" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.09, + 0.196, + 0.106 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.118, + 0.473, + 0.284 + ], + "angle": 0, + "content": "The paper studies the problem of multi-label knowledge distillation. In the proposed method, the multi-label logits distillation explores the informative semantic knowledge compressed in the teacher logits to obtain more semantic supervision. Furthermore, the label-wise embedding distillation exploits the structural knowledge from label-wise embeddings to learn more distinctive feature representations. Experimental results on benchmark datasets validate the effectiveness of the proposed method. In future, we plan to improve the performance of MLKD by exploiting other abundant structural information." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.306, + 0.238, + 0.323 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.334, + 0.473, + 0.514 + ], + "angle": 0, + "content": "Sheng-Jun Huang was supported by, the National Key R&D Program of China (2020AAA0107000), the Natural Science Foundation of Jiangsu Province of China (BK20222012, BK20211517), and NSFC (62222605). Lei Feng was supported by the Joint NTU-WeBank Research Centre on Fintech (Award No: NWJ-2021-005), Nanyang Technological University, Singapore, Chongqing Overseas Chinese Entrepreneurship and Innovation Support Program, Chongqing Artificial Intelligence Innovation Center, and CAAI-Huawei MindSpore Open Fund. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 11953-11962, 2022. 2" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.838 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "17280" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-Label Knowledge Distillation/3f3ec8fe-1476-4cc1-910f-9ce888c57a74_origin.pdf b/2023/Multi-Label Knowledge Distillation/3f3ec8fe-1476-4cc1-910f-9ce888c57a74_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..c909bea8f22e546e52663efd3244d9fbcff7c07d --- /dev/null +++ b/2023/Multi-Label Knowledge Distillation/3f3ec8fe-1476-4cc1-910f-9ce888c57a74_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:0c8912d868cae33502fc36cd52cf293849db4a38be60b356b6a14166209e91a5 +size 2847747 diff --git a/2023/Multi-Label Knowledge Distillation/full.md b/2023/Multi-Label Knowledge Distillation/full.md new file mode 100644 index 0000000000000000000000000000000000000000..9966ae021b4d100670dffe3ef8b0c47790c4da26 --- /dev/null +++ b/2023/Multi-Label Knowledge Distillation/full.md @@ -0,0 +1,356 @@ +# Multi-Label Knowledge Distillation + +Penghui Yang $^{1,2*}$ , Ming-Kun Xie $^{1,2*}$ , Chen-Chen Zong $^{1,2}$ , Lei Feng $^{3}$ , Gang Niu $^{4}$ , Masashi Sugiyama $^{4,5}$ , Sheng-Jun Huang $^{1,2\dagger}$ + +1College of Computer Science and Technology, Nanjing University of Aeronautics and Astronautics, + +$^{2}$ MIIT Key Laboratory of Pattern Analysis and Machine Intelligence, Nanjing, China + +$^{3}$ School of Computer Science and Engineering, Nanyang Technological University, Singapore + +$^{4}$ RIKEN Center for Advanced Intelligence Project, $^{5}$ The University of Tokyo, Tokyo, Japan + +phyang.cs@gmail.com, mkxie@nuaa.edu.cn, chencz@nuaa.edu.cn, lfengqaq@gmail.com, + +gang.niu.ml@gmail.com, sugi@k.u-tokyo.ac.jp, huangsj@nuaa.edu.cn + +# Abstract + +Existing knowledge distillation methods typically work by imparting the knowledge of output logits or intermediate feature maps from the teacher network to the student network, which is very successful in multi-class single-label learning. However, these methods can hardly be extended to the multi-label learning scenario, where each instance is associated with multiple semantic labels, because the prediction probabilities do not sum to one and feature maps of the whole example may ignore minor classes in such a scenario. In this paper, we propose a novel multi-label knowledge distillation method. On one hand, it exploits the informative semantic knowledge from the logits by dividing the multi-label learning problem into a set of binary classification problems; on the other hand, it enhances the distinctiveness of the learned feature representations by leveraging the structural information of label-wise embeddings. Experimental results on multiple benchmark datasets validate that the proposed method can avoid knowledge counteraction among labels, thus achieving superior performance against diverse comparing methods. Our code is available at: https://github.com/penghui-yang/L2D. + +# 1. Introduction + +Multi-label learning (MLL) addresses problems where each instance is assigned with multiple class labels simultaneously [32]. For example, as shown in Figure 1, an image of a street scene may be annotated with labels bus, car and person. To learn the complex object-label mapping, there is always necessity of training large models to obtain desirable performance in MLL. While the remarkable successes + +![](images/f8ae256cc43ff760ad524458b691c83cb160bb80a84a1a3d19e8e9f3671ae346.jpg) + +![](images/f95be211c4353b66d7fefb317f00e97b28efb9c3516335438d9fe8e3a294a679.jpg) + +![](images/794790ff89ef70edd2ae25d11b4b80ccd82ea4bb7060f59d2506b58a0496ed4b.jpg) + +![](images/e94ae6ac6c0749eef97a8c73e368145b5ad1d85513af9c4ea6e9cb58f199338c.jpg) + +![](images/6e8b20205be9a25b7c2d9f3cb60e38e9da757cb89bd1caf3b0f7514999144f78.jpg) + +![](images/9cad36313e012f96ec63c8e9bb3eef6028ae89a05d1c87d43c8226c2a7aee27b.jpg) + +![](images/7a1cbb892f0ad70da593c380d70032b2beacf2e8b7e3081e69f8ab2cfb31f211.jpg) + +![](images/06216606a3900e2d039d98a2d118b10b602a67bc74bd405b76bceeb868916034.jpg) +Car + +![](images/0e432b67fd1dee463adc65245945020ec0038fe88bd822523d17914f4c3bd9f0.jpg) +Figure 1. Visualization of attention maps on different classes. We compare our method with the following three baselines: 1) Vanilla: the student trained without distillation; 2) ReviewKD [1]: a feature-based method that achieves the state-of-the-art performance; 3) Teacher: the pretrained model used in distillation. It can be observed that: on the classes bus and car, L2D captures semantic objects more precisely than the conventional KD method; on the class person, although all of the methods focus on people, only our method focuses on the same person as the teacher, which validates that L2D can distill the "dark" knowledge [27] from the teacher more effectively. The backbones of the teacher and student models are respectively ResNet-101 and ResNet-34. More visualization of attention maps can be found in Appendix. + +![](images/0ef4dd21797681db4dd5d1f83f1cdbcc9e58caaa331a44799f3e0ea36b5b5d1d.jpg) +Person + +![](images/78835a24b77ccf85e75c8b830c20d71bef48c6ce67d78cf51bfe8bffad270774.jpg) + +have been made in MLL through the training of deep neural networks (DNNs) [14, 23], it is hard to deploy these large + +models on lightweight terminals, e.g., mobile phones, under the constraint of computational resource or requirement of short inference time. + +To mitigate this issue, knowledge distillation (KD) [10] is needed which aims to improve the performance of a small network (also known as the "student") by requiring the knowledge from a large network (also known as the "teacher") to guide the training of the student network. Typical KD methods focus on the multi-class classification, and can be roughly divided into two categories: logits-based methods and feature-based methods. The former minimizes the difference between logits of the teacher model and the student model [10, 34], while the latter distills knowledge from feature maps of intermediate layers [19, 28, 1]. + +Although KD has been proven to be effective for improving the performance of the student network in single-label classification, it is still a challenging problem to directly extend existing KD methods to solve multi-label knowledge distillation (MLKD) problems. Specifically, logits-based methods often obtain the predicted probabilities based on the softmax function; this function is not suitable for MLKD, because the sum of predicted probabilities may not equal one in MLL. Feature-based methods often perform KD based on the feature maps of a whole image with multiple semantics, which makes the model focus on the major objects while neglect minor objects. For example, in Figure 1, Vanilla and ReviewKD wrongly focused on the bus when the model queried the label car. Such a phenomenon would cause the model to obtain sub-optimal even undesirable distillation performance. + +Recently, several attempts have been made to utilize KD techniques for improving the performance of MLL [15, 29, 25]. There are mainly two differences between these works and our work. Firstly, these methods often required specifically-designed network architectures [15, 25] or training strategies [29] to train the teacher and student models, while our method focuses on studying MLKD in general scenarios without any extra requirement. Secondly, unlike the previous methods utilized KD as an auxiliary technique to improve the performance of MLL, our goal is to develop a tailored approach for MLKD. As a result, previous methods were mainly compared with MLL methods in their original papers, we evaluate the KD performance of our method by comparing it with state-of-the-art KD methods. + +In this paper, to perform MLKD, we propose a new method consisting of multi-label logits distillation and label-wise embedding distillation (L2D for short). Specifically, to exploit informative semantic knowledge compressed in the logits, L2D employs the one-versus-all reduction strategy to obtain a set of binary classification problems and perform logits distillation for each one. To enhance the distinctiveness of learned feature representations, + +L2D encourages the student model to maintain a consistent structure of intra-class and intra-instance (inter-class) label-wise embeddings with the teacher model. By leveraging the structural information of the teacher model, these two structural consistencies respectively enhance the compactness of intra-class embeddings and dispersion of inter-class embeddings for the student model. Both of these two components lead L2D to achieve better distillation performance than conventional KD methods as shown in Figure 1. + +Our main contributions can be summarized as follows: + +- A general framework called MLKD is proposed. To our best knowledge, the framework is the first study specially designed for knowledge distillation in the multi-label learning scenario. +- A new approach for MLKD called L2D is proposed. It performs multi-label logits distillation and label-wise embedding distillation simultaneously. The former provides informative semantic knowledge while the latter encourages the student model to learn more distinctive feature representations. +- Extensive experimental results on benchmark datasets demonstrate the effectiveness of our proposed method. + +# 2. Related Work + +The concept of knowledge distillation (KD) proposed by Geoffrey Hinton et al. [10] defines a learning framework that transfers knowledge from a large teacher network to a small student network. Existing works can be roughly divided into two groups, i.e., logits-based methods and feature-based methods. Logits-based methods mainly focus on designing effective distillation losses to distill knowledge from logits and softmax scores after logits. DML [33] introduces a mutual learning method to train both teachers and students simultaneously. TAKD [18] proposes a new architecture called "teacher assistant", which is an intermediate-sized network bridging the gap between teachers and students. Besides, a recent study [34] proposes a novel logits-based method to reformulate the classical KD loss into two parts and achieves the state-of-the-art performance by adjusting weights for these two parts. Some other methods focus on distilling knowledge from intermediate feature layers. FitNet [24] is the first approach to distill knowledge from intermediate features by measuring the distance between feature maps. Attention transfer [31] achieves better performance than FitNet by distilling knowledge from the attention maps. PKT [20] measures the KL divergence between features by treating them as probability distributions. RKD [19] utilizes the relations among instances to guide the training process of the student model. CRD [28] incorporates contrastive learning into knowledge distillation. ReviewKD [1] proposes a review mechanism + +which uses multiple layers in the teacher to supervise one layer in the student. ITRD [17] aims to maximize the correlation and mutual information between the students' and teachers' representations. + +Multi-label learning has increasingly attracted a lot of interest recently. Existing solutions for solving MLL problems can be categorized into three directions. The first type attempts to design novel loss functions for tackling the intrinsic positive-negative imbalance issue in multi-label classification tasks. For example, ASL [22] uses different weights to re-weight positive and negative examples for the balanced training. The second type focuses on modeling the label correlations, which provides prior knowledge for multi-label classification. Among them, MLGCN [3] is a representative method that employs a graph convolutional network to model correlation matrix. CADM [2] constructs a similar graph based on class-aware maps. To handle the multiple semantic objects contained in an image, the last type of methods aims to locate areas of interest related to semantic labels by using attention techniques. Among them, C-Tran [12] first utilizes the transformer to retrieve embeddings from visual features for each label. Query2Label [14] uses several stacked transformer encoders to identify interesting areas. ML-Decoder [23] simplifies transformer encoders in Query2Label. ADDS [30] introduces encoders from CLIP [21] in order to get better textual and visual embedding inputs to the classification head. In addition, ADDS adds a multi-head cross-attention layer and a skipping connection from the query input to the query output based on ML-Decoder. + +Several previous studies have applied KD techniques to improve the performance of MLL. For example, Yongcheng Liu et al. [15] and Jiazhi Xu et al. [29] simply minimized mean squared error (MSE) loss between teacher logits and student logits. Liangchen Song et al. [25] designed a partial softmax function by combining a positive label with all other negative labels. Then, the conventional KD loss can be computed for each positive label. Although these methods made the pioneering attempts of combining KD and MLL, they cannot be directly applied general MLKD scenarios, and also fail to evaluate their KD performance by comparing with KD methods. + +# 3. The Proposed Approach + +Let $\pmb{x} \in \mathcal{X}$ be an instance and $\pmb{y} \in \mathcal{Y}$ be its corresponding label vector, where $\mathcal{X} \subset \mathbb{R}^d$ is the input space with $d$ dimensions and $\mathcal{Y} \subset \{0,1\}^q$ is the target space with $q$ class labels. We further use $y_{j}$ to denote the $j$ -th component of $\pmb{y}$ . For a given instance $\pmb{x}$ , $y_{j} = 1$ indicates the $j$ -th label is relevant to the instance; $y_{j} = 0$ , otherwise. In multi-label learning, each instance may be assigned with more than one label, which means $\sum_{j=1}^{q} \mathbb{I}(y_{j} = 1) \geq 1$ , where $\mathbb{I}(\cdot)$ is the indicator function. We also denote by $[q]$ the integer set + +$$ +\{1, 2, \dots , q \}. +$$ + +In this paper, we use a classification model consisting of three components, i.e., a visual backbone $f$ , which extracts a feature map $f(\pmb{x})$ for the input $\pmb{x}$ , a label-wise embedding encoder $g$ [12, 14], which produces a label-wise embedding $e_k = g_k(f(\pmb{x}))$ with respect to the $k$ -th class based on the feature map $f(\pmb{x})$ , and a multi-label classifier $h$ , which predicts multi-label probabilities $\hat{y} = [\sigma(h_1(e_1)), \sigma(h_2(e_2)), \dots, \sigma(h_q(e_q))]$ , where $\sigma(\cdot)$ denotes the sigmoid function. It is noteworthy that the used model is very general, which can be built by equipping commonly used backbones, e.g., ResNet [9], with a label-wise embedding encoder $g$ . For the notations mentioned above, we use the superscripts $\mathcal{T}$ (or $S$ ) to denote the teacher (or student) model. For example, we use $e_k^T$ and $e_k^S$ to denote the label-wise embeddings for teacher and student models. + +In multi-label learning, a popular method is to employ the one-versus-all reduction strategy to transform the original task into multiple binary problems. Among the various loss functions, the most commonly used one is the binary cross entropy (BCE) loss. Specifically, given a batch of examples $\{(x_i,y_i)\}_{i = 1}^b$ and the predicted probabilities $\hat{\pmb{y}}$ , the BCE loss can be defined as follows: + +$$ +\mathcal {L} _ {\mathrm {B C E}} = - \frac {1}{b} \sum_ {i = 1} ^ {b} \sum_ {k = 1} ^ {q} y _ {i k} \log \left(\hat {y} _ {i k}\right) + (1 - y _ {i k}) \log \left(1 - \hat {y} _ {i k}\right). \tag {1} +$$ + +Figure 2 illustrates the distillation process of the proposed L2D framework. For a batch of training examples, we feed them into the teacher/student model to obtain the label-wise embeddings and predicted probabilities. In order to train the student model, besides the BCE loss, we design the following two distillation losses: 1) multi-label logits distillation loss $\mathcal{L}_{\mathrm{MLD}}$ to exploit informative semantic knowledge compressed in the logits, 2) label-wise embedding distillation loss $\mathcal{L}_{\mathrm{LED}}$ to leverage structural information for enhancing the distinctiveness of learned feature representations. The overall objective function can be presented as + +$$ +\mathcal {L} _ {\mathrm {L 2 D}} = \mathcal {L} _ {\mathrm {B C E}} + \lambda_ {\mathrm {M L D}} \mathcal {L} _ {\mathrm {M L D}} + \lambda_ {\mathrm {L E D}} \mathcal {L} _ {\mathrm {L E D}}, \tag {2} +$$ + +where $\lambda_{\mathrm{MLD}}$ and $\lambda_{\mathrm{LED}}$ are two balancing parameters. + +# 3.1. Multi-Label Logits Distillation + +Traditional logits-based distillation normally minimizes the Kullback-Leibler (KL) divergence between the predicted probabilities, i.e., the logits after the softmax function, of teacher and student model. However, the method cannot be directly applied to the MLL scenario, since it depends on a basic assumption that the predicted probabilities of all classes should sum to one, which hardly holds for MLL examples. + +To mitigate this issue, inspired by the idea of one-versus-all reduction, we propose a multi-label logits distillation + +![](images/f0117610615eb2a33b54d4846bd2dc7dc885cc2b30c71b681c633caec31fba67.jpg) +Figure 2. An illustration of the L2D framework. The framework simultaneously performs multi-label logits distillation and label-wise embedding distillation to improve the performance of the student model. + +(MLD) loss, which decomposes the original multi-label task into multiple binary classification problems and minimizes the divergence between the binary predicted probabilities of two models. Formally, the MLD loss can be formulated as follows: + +$$ +\mathcal {L} _ {\mathrm {M L D}} = \frac {1}{b} \sum_ {i = 1} ^ {b} \sum_ {k = 1} ^ {q} \mathcal {D} \left(\left[ \hat {y} _ {i k} ^ {\mathcal {T}}, 1 - \hat {y} _ {i k} ^ {\mathcal {T}} \right] \mid \mid [ \hat {y} _ {i k} ^ {\mathcal {S}}, 1 - \hat {y} _ {i k} ^ {\mathcal {S}} ]\right), \tag {3} +$$ + +where $[\cdot, \cdot]$ is an operator used to concatenate two scalars into a vector, and $\mathcal{D}$ is a divergence function. The most common choice is the KL divergence $\mathcal{D}_{\mathrm{KL}}(P \| Q) = \sum_{x \in \mathcal{X}} P(x) \log \left(\frac{P(x)}{Q(x)}\right)$ , where $P$ and $Q$ are two different probability distributions. The MLD loss aims to improve the performance of student model by sufficiently exploiting informative knowledge from logits. + +# 3.2. Label-wise Embedding Distillation + +The MLD loss performs distillation on the predicted probabilities that can be regarded as a high-level representation, i.e., the final outputs of model. The knowledge distilled from the teacher model by only using the MLD loss would be insufficient to train a student model with desirable performance due to the limited information carried by the logits. To further strengthen the effectiveness of distillation, we design the label-wise embedding distillation (LED) loss, which aims to explore the structural knowledge from label-wise embeddings. The main idea is to capture two types of structural relations among label-wise embeddings: 1) class-aware label-wise embedding distillation (CD) loss $\mathcal{L}_{\mathrm{CD}}$ , which captures the structural relation between any two intra-class label-wise embeddings from different examples; 2) instance-aware label-wise embedding distillation (ID) loss $\mathcal{L}_{\mathrm{ID}}$ , which models the structural re + +lation between any two inter-class label-wise embeddings from the same example. In the following content, we introduce these two distillation losses in detail. + +# 3.2.1 Class-Aware Label-Wise Embedding Distillation + +Class-aware label-wise embedding distillation aims to improve the distillation performance by exploiting the structural relations among intra-class label-wise embeddings. Generally, the same semantic objects from two different images often differ from each other by their individual characteristics, such as two cars with different colors and diverse styles (see the left side in Figure 3). Since our goal is to distinguish between car and other semantic classes instead of identifying different cars, these distinctiveness would be confusing information for the corresponding classification task. Due to the powerful learning capacity, the large model is able to capture the highly abstract semantic representations for each class label by neglecting the useless individual information. From the perspective of learned feature representations, as shown in the left side of Figure 3, the teacher model tends to obtain a more compact structure of intra-class label-wise embedding, which often leads to better classification performance. By transferring the structural knowledge from the teacher model to the student model, CD encourages the student model to enhance the compactness of intra-class label-wise embeddings, which can improve its classification performance. + +For a batch of examples, let $\{e_{ik}^{\mathcal{T}}\}_{i = 1}^{b}$ and $\{e_{ik}^{\mathcal{S}}\}_{i = 1}^{b}$ respectively denote the intra-class label-wise embeddings with respect to class $k\in [q]$ generated by the teacher and student models. Then, we can capture the structural relation between any two intra-class label-wise embeddings $e_{ik}^{\mathcal{T}}$ and + +![](images/be49ff750de031fa6b78dfc5acaa32c0cb6ff0bafac4722c0f10b5cea9861270.jpg) +Figure 3. An illustration of class/instance-aware label-wise embedding distillation. Class-aware label-wise embedding distillation (CD) captures structural relations among intra-class label-wise embeddings from different examples, while instance-aware label-wise embedding distillation (ID) explores structural relations among intra-instance (inter-class) label-wise embeddings. + +$\pmb{e}_{jk}^{\mathcal{T}}$ by measuring their distance in the embedding space: + +$$ +\phi_ {\mathrm {C D}} \left(\boldsymbol {e} _ {i k} ^ {\mathcal {T}}, \boldsymbol {e} _ {j k} ^ {\mathcal {T}}\right) = \left\{ \begin{array}{l l} \| \boldsymbol {e} _ {i k} ^ {\mathcal {T}} - \boldsymbol {e} _ {j k} ^ {\mathcal {T}} \| _ {2} & y _ {i k} = 1, y _ {j k} = 1, \\ 0 & \text {o t h e r w i s e .} \end{array} \right. \tag {4} +$$ + +It is worth to note that we only consider the structural relation between any two valid label-wise embeddings, i.e., the embeddings with respect to positive labels. Similar to Eq.(4), for any two intra-class label-wise embeddings $e_{ik}^S$ and $e_{jk}^S$ , we can obtain the structural relation $\phi_{\mathrm{CD}}(e_{ik}^S, e_{jk}^S)$ for the student model. + +By enforcing the teacher and student structural relations to maintain the consistency for each pair of intra-class label-wise embeddings, we can achieve the class-aware structural consistency as follows: + +$$ +\mathcal {L} _ {\mathrm {C D}} = \sum_ {k = 1} ^ {q} \sum_ {i, j \in [ b ]} \ell \left(\phi_ {\mathrm {C D}} \left(e _ {i k} ^ {\mathcal {T}}, e _ {j k} ^ {\mathcal {T}}\right), \phi_ {\mathrm {C D}} \left(e _ {i k} ^ {\mathcal {S}}, e _ {j k} ^ {\mathcal {S}}\right)\right), \tag {5} +$$ + +where $\ell$ is a function to measure the consistency between the teacher and student structural relations. In experiments, we use the following Huber loss function as a measurement: + +$$ +\ell (a, b) = \left\{ \begin{array}{l l} \frac {1}{2} (a - b) ^ {2} & | a - b | \leq 1, \\ | a - b | - \frac {1}{2} & \text {o t h e r w i s e .} \end{array} \right. \tag {6} +$$ + +where $a$ and $b$ are two different structural relations. + +# 3.2.2 Instance-Aware Label-Wise Embedding Distillation + +Instance-aware label-wise embedding distillation (ID) aims to improve the distillation performance by exploring the + +structural relations among inter-class label-wise embeddings from the same image. Generally, one can hardly distinguish between two different semantic objects occurring in an image due to the high similarities they share. For example, in the upper left corner of Figure 3, an image annotated with both sky and sea makes it difficult to distinguish between the semantic objects, as they share the same color and similar texture. A feasible solution is to exploit other useful information, such as their spatial relation, i.e., sky is always above sea. Due to the powerful learning capacity, the large model is able to distinguish between the similar semantic objects by exploiting such implicit supervised information. From the perspective of learned feature representations, as shown in the right side of 3, the teacher model tends to learn a dispersed structure of inter-class label-wise embedding, which is beneficial for improving its discrimination ability. By distilling the structural knowledge from the teacher model, ID enforces the student model to enhance the dispersion of inter-class label-wise embeddings, which can improve its discrimination ability. + +For a given instance $\pmb{x}_i$ , let $\{e_{ik}^{\mathcal{T}}\}_{k=1}^{q}$ and $\{e_{ik}^S\}_{k=1}^{q}$ respectively denote the label-wise embeddings generated by teacher and student models. Then, we can capture the structural relation between any two inter-class label-wise embeddings $e_{ik}^{\mathcal{T}}$ and $e_{il}^{\mathcal{T}}$ by measuring their distance in the embedding space: + +$$ +\phi_ {\mathrm {I D}} \left(e _ {i k} ^ {\mathcal {T}}, e _ {i l} ^ {\mathcal {T}}\right) = \left\{ \begin{array}{l l} \| e _ {i k} ^ {\mathcal {T}} - e _ {i l} ^ {\mathcal {T}} \| _ {2} & y _ {i k} = 1, y _ {i l} = 1, \\ 0 & \text {o t h e r w i s e .} \end{array} \right. \tag {7} +$$ + +Note that in Eq.(7), we only consider the structural relation between any two valid label-wise embeddings, i.e., + +Table 1. Results on MS-COCO where teacher and student models are in the same architectures. + +
TeacherRepVGG-A2ResNet-101WRN-101Swin-S
StudentRepVGG-A0ResNet-34WRN-50Swin-T
MetricsmAPOF1CF1mAPOF1CF1mAPOF1CF1mAPOF1CF1
Teacher72.7174.1168.6373.6273.8968.6174.7075.5670.7381.7080.4877.12
Student70.0272.4966.7770.3172.4966.8274.4575.4370.6179.5979.1875.42
RKD70.0872.3966.7370.1372.4466.7874.7075.7170.8479.6379.1975.57
PKT70.1172.4766.8070.4372.6466.6874.5475.4770.5879.6479.0975.39
ReviewKD70.0072.3566.8270.3972.6266.7674.0375.2970.3679.8179.1875.55
MSE70.2672.5466.9970.5472.7566.8574.5375.6070.7179.6779.2075.52
PS70.6572.8967.6070.8672.6667.1275.1276.0571.6379.9679.6476.20
MLD70.7472.8167.4670.6872.6967.1974.9275.7571.2180.1179.6876.44
L2D72.8174.5969.4972.8774.4569.4376.6177.0872.7981.5981.0377.86
+ +Table 2. Results on MS-COCO where teacher and student models are in the different architectures. + +
TeacherResNet-101Swin-TResNet-101Swin-T
StudentRepVGG-A0ResNet-34MobileNet v2MobileNet v2
MetricsmAPOF1CF1mAPOF1CF1mAPOF1CF1mAPOF1CF1
Teacher73.6273.8968.6179.4378.7775.0773.6273.8968.6179.4378.7775.07
Student70.0272.4966.7770.3172.4966.8271.8573.5968.2671.8573.5968.26
RKD70.0872.3566.7270.0072.3466.6471.7673.6868.4071.7473.6868.37
PKT69.9972.3566.5670.2672.3966.8271.8873.6068.3571.8473.7668.37
ReviewKD70.0072.3366.6270.2972.3966.5871.9273.7368.4871.7373.7168.36
MSE70.0772.5066.8570.3372.5766.7271.9173.6868.2871.8073.7468.38
PS70.3072.6167.1070.9472.9367.5772.1173.8968.4272.4274.1468.94
MLD70.4872.7767.1071.1472.9967.6372.1773.8468.5272.3574.1068.91
L2D72.1474.0868.7873.4274.9770.2073.2474.8569.7274.2175.7270.87
+ +the embedding with respect to positive labels. Similar to Eq.(7), for any two inter-class label-wise embeddings $e_{ik}^S$ and $e_{il}^S$ , we can obtain the structural relation $\phi_{\mathrm{ID}}(e_{ik}^S, e_{il}^S)$ for the student model. + +By encouraging the teacher and student model to maintain the consistent structure of intra-instance label-wise embeddings, we can minimize the following $\mathcal{L}_{\mathrm{ID}}$ loss to achieve the instance-aware structural consistency where $\ell(.)$ is Huber loss as defined in Eq.(6): + +$$ +\mathcal {L} _ {\mathrm {I D}} = \sum_ {i = 1} ^ {b} \sum_ {k, l \in [ q ]} \ell \left(\phi_ {\mathrm {I D}} \left(\boldsymbol {e} _ {i k} ^ {\mathcal {T}}, \boldsymbol {e} _ {i l} ^ {\mathcal {T}}\right), \phi_ {\mathrm {I D}} \left(\boldsymbol {e} _ {i k} ^ {\mathcal {S}}, \boldsymbol {e} _ {i l} ^ {\mathcal {S}}\right)\right). \tag {8} +$$ + +Finally, the overall objective function of L2D (Eq.(2)) can be re-written as follows: + +$$ +\mathcal {L} _ {\mathrm {L 2 D}} = \mathcal {L} _ {\mathrm {B C E}} + \lambda_ {\mathrm {M L D}} \mathcal {L} _ {\mathrm {M L D}} + \lambda_ {\mathrm {C D}} \mathcal {L} _ {\mathrm {C D}} + \lambda_ {\mathrm {I D}} \mathcal {L} _ {\mathrm {I D}}, \tag {9} +$$ + +where $\lambda_{\mathrm{MLD}}$ , $\lambda_{\mathrm{CD}}$ and $\lambda_{\mathrm{ID}}$ are all balancing parameters. + +# 4. Experiments + +Datasets. We perform experiments on three benchmark datasets Pascal VOC2007 [8] (VOC for short), MS- + +COCO2014 [13] (MS-COCO for short) and NUS-WIDE [4]. VOC contains 5,011 images in the train-val set, and 4,952 images in the test set. It covers 20 common objects, with an average of 1.6 labels per image. MS-COCO contains 82,081 training images and 40,137 test images. It covers 80 common objects, with an average of 2.9 labels per image. NUS-WIDE contains 161,789 training images and 107,859 test images. It covers 81 visual concepts, with an average of 1.9 labels per image. + +Metrics. Following existing works [32, 14, 26], we adopt the mean average precision (mAP) over all classes, overall F1-score (OF1) and average per-class F1-score (CF1) to evaluate the performance. We choose OF1 and CF1, since they consider both recall and precision and thus are more comprehensive. + +Comparing Methods. To validate the proposed method, we compare it with the following sota KD methods: RKD [19], which captures the relations among instances to guide the training of the student model; PKT [20], which measures KL divergence between features by treating them as probability distributions; ReviewKD [1], which transfers + +knowledge across different stages instead of just focusing on features in the same levels; as well as the modified KD techniques that have been applied to MLL: MSE [29], which minimizes the MSE loss between logits of teacher and student model; PS [25], which minimizes KL divergence of logits after a partial softmax function. + +Implementation Details. We use the models pretrained on ImageNet [6] as the backbones. We resize the resolution of all images to $224 \times 224$ and set the batch size as 64. For each training image, we adopt a weak augmentation consisting of random horizontal flipping and a strong augmentation consisting of Cutout [7] and RandAugment [5]. We use the Adam optimization method [11] to train the model for 80 epochs. The one-cycle policy is used with a maximal learning rate of 0.0001 and the weight decay [16] of 0.0001. For all experiments, we set $\lambda_{\mathrm{MLD}} = 10$ , $\lambda_{\mathrm{CD}} = 100$ , and $\lambda_{\mathrm{ID}} = 1000$ . Parameter sensitivity analysis in Appendix shows that the performance of L2D are insensitive to all of our balancing parameters. For the comparing methods, we set their parameters as suggested in the original papers. Especially, for all feature-based methods, we just deploy them on the feature maps which is output from the visual backbone $f$ . All the experiments are conducted on GeForce RTX 2080 GPUs. More details about the used models and implementation of the label-wise embedding encoder are attached in Appendix. + +# 4.1. Comparison Results + +Table 1 and Table 2 report comparison results on MS-COCO with the same and different architectures of student and teacher models. From Table 1, it can be observed that: 1) Conventional feature-based distillation methods only achieve minor improvements in performance when compared with the student model (without distillation). This indicates these methods do not work in multi-label scenarios due to their disability to capture multiple semantics occurred in feature maps. 2) MLD can outperform conventional feature-based distillation methods in most cases, which indicates by performing one-versus-all reduction, the logits-based distillation can be adapted into multi-label knowledge distillation. 3) The proposed L2D significantly outperforms all other methods and achieves comparable performance with the teacher model. In particular, when WRN is used as the backbone, the performance of L2D is even better than that of teacher model. One possible reason is that L2D can effectively alleviate the over-fitting issue occurred to the teacher model. More results about reversed knowledge distillation where the Vanilla student model outperforms the teacher can be found in Appendix. From Table 2, we can see that compared with the same architecture, the performance gap between teacher and student model is larger for different architectures, which indicates the corresponding distillation task becomes harder. Our method sig + +Table 3. Comparison results of the comparing methods on VOC in terms of AP and mAP (\%), where the backbones of teacher and student model are respectively ResNet-50 and ResNet-18. The best performance is highlighted in red, and second best performance is highlighted in blue. + +
MethodsVanillaRKDPKTMSEMLDL2D
bottle57.1859.0157.2958.2658.3259.71
pottedplant67.4367.0166.1668.0268.8870.52
chair70.3571.3171.1670.6871.1274.77
sofa73.1772.8673.2272.0673.7775.01
diningtable76.1476.9076.8977.9378.6578.93
cow82.6581.1181.7581.0684.6083.87
tvmonitor82.3081.7081.9582.3682.4284.13
bus85.5384.7985.0686.0386.4185.45
sheep84.1684.7783.6683.7283.7785.67
motorbike88.3888.8688.7388.3088.5889.83
dog90.1890.0390.1090.4690.7890.60
bird90.6591.6591.3190.6091.0291.48
bicycle91.4091.5391.7791.5891.9291.90
cat90.6791.8691.8391.0791.6392.14
boat92.5492.5392.3591.6492.2592.57
car92.7292.0692.0792.0192.3493.40
horse94.2293.9793.1294.0594.5394.67
person95.7395.8895.8095.6996.0496.46
train96.0997.0896.9997.1396.9796.81
aeroplane97.2797.0097.0997.1097.3097.39
mAP84.0184.1883.8684.2384.4885.71
+ +Table 4. Ablation studies on MS-COCO. + +
MLDCDIDmAPOF1CF1
70.3172.4966.82
✓70.6872.6967.19
✓✓71.9173.7468.76
✓✓71.7973.6268.43
✓✓✓72.8774.4569.43
+ +nificantly outperforms all the comparing methods by a significant margin in all cases. These results provide a strong empirical validation for the effectiveness of the proposed method. + +Table 3 illustrates the performance of the proposed methods and other comparing methods on VOC in terms of AP and mAP. It is noteworthy that the performance is ranked in descending according to the performance of student model. From the figure, it can be observed that: 1) Our proposed L2D achieves the best performance and significantly outperforms the comparing methods in terms of mAP. 2) L2D consistently achieves superior performance to the comparing methods in most classes and the performance gap is large especially for classes that the student model achieves poor performance. This observation discloses that L2D improves the performance of hard classes by enhancing the distinctiveness of feature representations. These experimental results demonstrate the practical usefulness of the proposed method. More results on VOC and NUS-WIDE + +![](images/65833ff6bde88244d7c41a87dfdedc25b1d42c7300c287b8ebbbd3fd310ffbd5.jpg) +Query + +![](images/2568c26758369e2217844c9936e9fefa52a734a19a2100e5d7acc5fd919d7af6.jpg) +Dog, Fire Hydrant + +![](images/ba6ccfddf2cbdf04a63ff203a4f1424cbcc0e4e4f6e0e2cf11f0f4c4287d109f.jpg) +Book, Person, Remote + +![](images/f43e19ae9bb7f1a6cfcfd6c62777462d3cfd6dcc226ed286c4c6b1904dd32134.jpg) +Dog, Fire Hydrant + +![](images/2d9a59d7b49706ebb214109e5c95ea532a66c9a21d7a1c2570d785bcc05aa6c6.jpg) + +![](images/bbde36c2ec96960a5ed7377348303041ab3e9950535c61a88ba05e8da1609ae7.jpg) + +![](images/386d2e3290b63a78a3bd7fba0d269b9423083fc5e5f277899e4d9f52ea03be53.jpg) +Dog, Fire Hydrant +Figure 4. Top-5 returned images with the query image. The returned results on the left are based on ReviewKD, while the results on the right are based on L2D. All results are sorted in the ascending order according to the distance from the query image. Red labels indicate that they are not included in the returned images' labels, while green labels are shared by the query image and the returned one. + +![](images/8517187a115732c1b7938c104301b29f03e7cb59a2aed73f2ecfacb6eea8dbf2.jpg) + +![](images/cd6819e3013168cf3c7a9e1ccf2ae8a1555bb3bcfd831f2ada38fbed385b50de.jpg) +Dog, Fire Hydrant + +![](images/30c37cf3229283eb99d3d157be02194afb7c5bfb48268d12e67728ab33c2148e.jpg) + +![](images/acf59acdeb50469f183497608ff935b3a8410364fb37be182eef530a287cc920.jpg) +Dog, Fire Hydrant + +![](images/2ba5393ede6b9e9cf5efa22b7e0d800507d4b75158a82806aa8112da8c8f1fcf.jpg) + +![](images/3fb608fcb54080456845ab5ad29bbc0b5573a124cdba15ef2c5f70a7ff8cba0f.jpg) +Dog, Fire Hydrant + +![](images/bb2cc5b68c0464ffea80876cdf34bf5594da2e6f21f1127370b7a9df3b6f7560.jpg) + +![](images/a194dc4502018fa92c416e875eee8b5ae42f12a3c49a71811455ee2548bb0fb4.jpg) +Dog, Fire Hydrant + +![](images/199fdbef6c8e0f26677e84ac0b6975b7a035bc8d727fa95657d3ea2874586201.jpg) +L2D + +![](images/0f93ebf7b4a459e26e9528dea9c46465994483d833977b66e660d115d6924863.jpg) +Dog, Fire Hydrant + +![](images/902acbc6969f27a9e74dd356062935f5cff75941e98c0c8bc3fe04cf6d388e62.jpg) + +![](images/440c04035c9b12cd3555aa786f12aa8d067b8dd55becbcef223fbf2c40e6c62c.jpg) +Dog, Fire Hydrant + +![](images/53aa6f5c1b84954029201491a6ff97984cc1ef64a50fa15ba91715abcb4e91ed.jpg) + +![](images/5403ea8c23c65ce99222f725c13818e191371440684ca5aaf683f76792dd6a67.jpg) +Dog, Fire Hydrant + +can be found in Appendix. + +# 4.2. Ablation Study + +In this section, to further analyze how the proposed method improves distillation performance, Table 4 reports results of ablation studies on MS-COCO (teacher: ResNet-101, student: ResNet-34). The first line in Table 4 reports the performance of student model without knowledge distillation. It can be observed that the distillation performance is improved slightly by only conducting multi-label logits distillation. Compared with MLD, label-wise embeddings distillation achieves the major improvement for the proposed method. It can be observed that by performing CD and ID, the mAP performance achieves $1.6\%$ and $1.48\%$ increments, respectively. Finally, we also examine the combination of these techniques. By incorporating these components together, the fusing method achieves the best performance and significantly outperforms each other method. These results demonstrate that all of three components are of great importance to the performance of the proposed L2D. + +# 4.3. Performance on Image Retrieval + +To further evaluate if our method can learn better representations, we conduct an image retrieval experiment. Specifically, we use the $k$ -NN algorithm to perform content-based image retrieval, and choose the student model trained by ReviewKD as the baseline, which has achieved the best performance among all conventional KD methods. Figure 4 illustrates the top-5 images returned by both methods. The labels under each image are colored in green if they are shared by both the query image and the returned one, and otherwise in red. These images are sorted in the ascending order based on the distance to the query image in the representation space. From the figures, we can see that our method returns the images that match the query image better than ReviewKD. This indicates our approach can obtain better representations than conventional KD methods. + +![](images/34399b7617cb08cc09ee12414a67f9c56ed93184e7482468a3fbc66c13ab9aee.jpg) +(a) Vanilla + +![](images/c0ed09ee2c68dbf988d7c8d6777addd52f0f73dfba83cc84c419744d7dc7b9bd.jpg) +(b) ReviewKD + +![](images/1d6b94802552b84e92a3da23e6682ab23d76f7a07e4612c4b419120f9de41417.jpg) +(c)MLD + +![](images/1dc8d39aa155d8503165787594e7bc07af96e2becde5353a5b74d11a51288802.jpg) +(d) L2D +Figure 5. The differences between correlation matrices of student and teacher predicted probabilities on MS-COCO. + +# 4.4. Distilling Inter-class Correlations + +As discussed in the previous works [10], the conventional supervised learning losses, e.g., BCE loss, often neglects the correlations among class predictions, which act as a foundational element in MLL. To validate whether the correlations can be captured by L2D effectively, Figure 5 illustrates the differences between correlation matrices of student and teacher predicted probabilities on MS-COCO. From the figure, it can be observed that: 1) The representative comparing method ReviewKD shows a large difference, which discloses that the conventional KD methods are ineffective to capture the correlations in multi-label scenarios. 2) MLD does not show a reduced difference, which indicates that the information of logits is not enough for capturing precise correlations. 3) L2D shows significant matching between the teacher and student correlations. By enhancing the distinctiveness of label-wise embeddings, L2D can obtain more correct predicted probabilities, leading to a more precise correlation estimation. + +# 5. Conclusion + +The paper studies the problem of multi-label knowledge distillation. In the proposed method, the multi-label logits distillation explores the informative semantic knowledge compressed in the teacher logits to obtain more semantic supervision. Furthermore, the label-wise embedding distillation exploits the structural knowledge from label-wise embeddings to learn more distinctive feature representations. Experimental results on benchmark datasets validate the effectiveness of the proposed method. In future, we plan to improve the performance of MLKD by exploiting other abundant structural information. + +# Acknowledgement + +Sheng-Jun Huang was supported by, the National Key R&D Program of China (2020AAA0107000), the Natural Science Foundation of Jiangsu Province of China (BK20222012, BK20211517), and NSFC (62222605). Lei Feng was supported by the Joint NTU-WeBank Research Centre on Fintech (Award No: NWJ-2021-005), Nanyang Technological University, Singapore, Chongqing Overseas Chinese Entrepreneurship and Innovation Support Program, Chongqing Artificial Intelligence Innovation Center, and CAAI-Huawei MindSpore Open Fund. Masashi Sugiyama was supported by JST CREST Grant Number JP-MJCR18A2. + +# References + +[1] Pengguang Chen, Shu Liu, Hengshuang Zhao, and Jiaya Jia. Distilling knowledge via knowledge review. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 5008-5017, 2021. 1, 2, 6 +[2] Zhao-Min Chen, Xiu-Shen Wei, Xin Jin, and Yanwen Guo. Multi-label image recognition with joint class-aware map disentangling and label correlation embedding. In Proceedings of the IEEE International Conference on Multimedia and Expo, pages 622-627, 2019. 3 +[3] Zhao-Min Chen, Xiu-Shen Wei, Peng Wang, and Yanwen Guo. 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"type": "text", + "content": "phyang.cs@gmail.com, mkxie@nuaa.edu.cn, chencz@nuaa.edu.cn, lfengqaq@gmail.com," + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 123, + 243, + 470, + 255 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 123, + 243, + 470, + 255 + ], + "spans": [ + { + "bbox": [ + 123, + 243, + 470, + 255 + ], + "type": "text", + "content": "gang.niu.ml@gmail.com, sugi@k.u-tokyo.ac.jp, huangsj@nuaa.edu.cn" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 143, + 282, + 191, + 295 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 282, + 191, + 295 + ], + "spans": [ + { + "bbox": [ + 143, + 282, + 191, + 295 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 308, + 290, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 308, + 290, + 559 + ], + "spans": [ + { + "bbox": [ + 46, + 308, + 290, + 559 + ], + "type": "text", + "content": "Existing knowledge distillation methods typically work by imparting the knowledge of output logits or intermediate feature maps from the teacher network to the student network, which is very successful in multi-class single-label learning. However, these methods can hardly be extended to the multi-label learning scenario, where each instance is associated with multiple semantic labels, because the prediction probabilities do not sum to one and feature maps of the whole example may ignore minor classes in such a scenario. In this paper, we propose a novel multi-label knowledge distillation method. On one hand, it exploits the informative semantic knowledge from the logits by dividing the multi-label learning problem into a set of binary classification problems; on the other hand, it enhances the distinctiveness of the learned feature representations by leveraging the structural information of label-wise embeddings. Experimental results on multiple benchmark datasets validate that the proposed method can avoid knowledge counteraction among labels, thus achieving superior performance against diverse comparing methods. Our code is available at: https://github.com/penghui-yang/L2D." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 582, + 128, + 594 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 582, + 128, + 594 + ], + "spans": [ + { + "bbox": [ + 47, + 582, + 128, + 594 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 601, + 287, + 685 + ], + "type": "text", + "content": "Multi-label learning (MLL) addresses problems where each instance is assigned with multiple class labels simultaneously [32]. For example, as shown in Figure 1, an image of a street scene may be annotated with labels bus, car and person. To learn the complex object-label mapping, there is always necessity of training large models to obtain desirable performance in MLL. While the remarkable successes" + } + ] + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 307, + 281, + 422, + 396 + ], + "blocks": [ + { + "bbox": [ + 307, + 281, + 422, + 396 + ], + "lines": [ + { + "bbox": [ + 307, + 281, + 422, + 396 + ], + "spans": [ + { + "bbox": [ + 307, + 281, + 422, + 396 + ], + "type": "image", + "image_path": "f8ae256cc43ff760ad524458b691c83cb160bb80a84a1a3d19e8e9f3671ae346.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 432, + 281, + 488, + 337 + ], + "blocks": [ + { + "bbox": [ + 432, + 281, + 488, + 337 + ], + "lines": [ + { + "bbox": [ + 432, + 281, + 488, + 337 + ], + "spans": [ + { + "bbox": [ + 432, + 281, + 488, + 337 + ], + "type": "image", + "image_path": "f95be211c4353b66d7fefb317f00e97b28efb9c3516335438d9fe8e3a294a679.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + } + ], + "index": 15 + }, + { + "type": "image", + "bbox": [ + 491, + 281, + 547, + 337 + ], + "blocks": [ + { + "bbox": [ + 491, + 281, + 547, + 337 + ], + "lines": [ + { + "bbox": [ + 491, + 281, + 547, + 337 + ], + "spans": [ + { + "bbox": [ + 491, + 281, + 547, + 337 + ], + "type": "image", + "image_path": "794790ff89ef70edd2ae25d11b4b80ccd82ea4bb7060f59d2506b58a0496ed4b.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 307, + 407, + 363, + 462 + ], + "blocks": [ + { + "bbox": [ + 307, + 407, + 363, + 462 + ], + "lines": [ + { + "bbox": [ + 307, + 407, + 363, + 462 + ], + "spans": [ + { + "bbox": [ + 307, + 407, + 363, + 462 + ], + "type": "image", + "image_path": "e94ae6ac6c0749eef97a8c73e368145b5ad1d85513af9c4ea6e9cb58f199338c.jpg" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_body" + } + ], + "index": 17 + }, + { + "type": "image", + "bbox": [ + 365, + 407, + 421, + 461 + ], + "blocks": [ + { + "bbox": [ + 365, + 407, + 421, + 461 + ], + "lines": [ + { + "bbox": [ + 365, + 407, + 421, + 461 + ], + "spans": [ + { + "bbox": [ + 365, + 407, + 421, + 461 + ], + "type": "image", + "image_path": "6e8b20205be9a25b7c2d9f3cb60e38e9da757cb89bd1caf3b0f7514999144f78.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + } + ], + "index": 18 + }, + { + "type": "image", + "bbox": [ + 432, + 339, + 488, + 396 + ], + "blocks": [ + { + "bbox": [ + 432, + 339, + 488, + 396 + ], + "lines": [ + { + "bbox": [ + 432, + 339, + 488, + 396 + ], + "spans": [ + { + "bbox": [ + 432, + 339, + 488, + 396 + ], + "type": "image", + "image_path": "9cad36313e012f96ec63c8e9bb3eef6028ae89a05d1c87d43c8226c2a7aee27b.jpg" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_body" + } + ], + "index": 19 + }, + { + "type": "image", + "bbox": [ + 491, + 339, + 547, + 396 + ], + "blocks": [ + { + "bbox": [ + 491, + 339, + 547, + 396 + ], + "lines": [ + { + "bbox": [ + 491, + 339, + 547, + 396 + ], + "spans": [ + { + "bbox": [ + 491, + 339, + 547, + 396 + ], + "type": "image", + "image_path": "7a1cbb892f0ad70da593c380d70032b2beacf2e8b7e3081e69f8ab2cfb31f211.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + } + ], + "index": 20 + }, + { + "type": "image", + "bbox": [ + 307, + 465, + 363, + 521 + ], + "blocks": [ + { + "bbox": [ + 307, + 465, + 363, + 521 + ], + "lines": [ + { + "bbox": [ + 307, + 465, + 363, + 521 + ], + "spans": [ + { + "bbox": [ + 307, + 465, + 363, + 521 + ], + "type": "image", + "image_path": "06216606a3900e2d039d98a2d118b10b602a67bc74bd405b76bceeb868916034.jpg" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 357, + 522, + 372, + 531 + ], + "lines": [ + { + "bbox": [ + 357, + 522, + 372, + 531 + ], + "spans": [ + { + "bbox": [ + 357, + 522, + 372, + 531 + ], + "type": "text", + "content": "Car" + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_caption" + } + ], + "index": 21 + }, + { + "type": "image", + "bbox": [ + 365, + 465, + 421, + 521 + ], + "blocks": [ + { + "bbox": [ + 365, + 465, + 421, + 521 + ], + "lines": [ + { + "bbox": [ + 365, + 465, + 421, + 521 + ], + "spans": [ + { + "bbox": [ + 365, + 465, + 421, + 521 + ], + "type": "image", + "image_path": "0e432b67fd1dee463adc65245945020ec0038fe88bd822523d17914f4c3bd9f0.jpg" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 536, + 545, + 680 + ], + "lines": [ + { + "bbox": [ + 304, + 536, + 545, + 680 + ], + "spans": [ + { + "bbox": [ + 304, + 536, + 545, + 680 + ], + "type": "text", + "content": "Figure 1. Visualization of attention maps on different classes. We compare our method with the following three baselines: 1) Vanilla: the student trained without distillation; 2) ReviewKD [1]: a feature-based method that achieves the state-of-the-art performance; 3) Teacher: the pretrained model used in distillation. It can be observed that: on the classes bus and car, L2D captures semantic objects more precisely than the conventional KD method; on the class person, although all of the methods focus on people, only our method focuses on the same person as the teacher, which validates that L2D can distill the \"dark\" knowledge [27] from the teacher more effectively. The backbones of the teacher and student models are respectively ResNet-101 and ResNet-34. More visualization of attention maps can be found in Appendix." + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_caption" + } + ], + "index": 22 + }, + { + "type": "image", + "bbox": [ + 432, + 465, + 488, + 521 + ], + "blocks": [ + { + "bbox": [ + 432, + 465, + 488, + 521 + ], + "lines": [ + { + "bbox": [ + 432, + 465, + 488, + 521 + ], + "spans": [ + { + "bbox": [ + 432, + 465, + 488, + 521 + ], + "type": "image", + "image_path": "0ef4dd21797681db4dd5d1f83f1cdbcc9e58caaa331a44799f3e0ea36b5b5d1d.jpg" + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 476, + 522, + 503, + 531 + ], + "lines": [ + { + "bbox": [ + 476, + 522, + 503, + 531 + ], + "spans": [ + { + "bbox": [ + 476, + 522, + 503, + 531 + ], + "type": "text", + "content": "Person" + } + ] + } + ], + "index": 26, + "angle": 0, + "type": "image_caption" + } + ], + "index": 23 + }, + { + "type": "image", + "bbox": [ + 491, + 465, + 547, + 521 + ], + "blocks": [ + { + "bbox": [ + 491, + 465, + 547, + 521 + ], + "lines": [ + { + "bbox": [ + 491, + 465, + 547, + 521 + ], + "spans": [ + { + "bbox": [ + 491, + 465, + 547, + 521 + ], + "type": "image", + "image_path": "78835a24b77ccf85e75c8b830c20d71bef48c6ce67d78cf51bfe8bffad270774.jpg" + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_body" + } + ], + "index": 24 + }, + { + "bbox": [ + 306, + 689, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 546, + 714 + ], + "type": "text", + "content": "have been made in MLL through the training of deep neural networks (DNNs) [14, 23], it is hard to deploy these large" + } + ] + } + ], + "index": 28 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 57, + 693, + 222, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 693, + 222, + 703 + ], + "spans": [ + { + "bbox": [ + 57, + 693, + 222, + 703 + ], + "type": "text", + "content": "*Both authors contributed equally to this research." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 59, + 703, + 265, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 703, + 265, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 703, + 265, + 713 + ], + "type": "inline_equation", + "content": "^{\\dagger}" + }, + { + "bbox": [ + 59, + 703, + 265, + 713 + ], + "type": "text", + "content": " Correspondence to: Sheng-Jun Huang (huangsj@nuaa.edu.cn)." + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17271" + } + ] + } + ], + "index": 32 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 107 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 107 + ], + "type": "text", + "content": "models on lightweight terminals, e.g., mobile phones, under the constraint of computational resource or requirement of short inference time." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 110, + 286, + 242 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 110, + 286, + 242 + ], + "spans": [ + { + "bbox": [ + 46, + 110, + 286, + 242 + ], + "type": "text", + "content": "To mitigate this issue, knowledge distillation (KD) [10] is needed which aims to improve the performance of a small network (also known as the \"student\") by requiring the knowledge from a large network (also known as the \"teacher\") to guide the training of the student network. Typical KD methods focus on the multi-class classification, and can be roughly divided into two categories: logits-based methods and feature-based methods. The former minimizes the difference between logits of the teacher model and the student model [10, 34], while the latter distills knowledge from feature maps of intermediate layers [19, 28, 1]." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 243, + 286, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 243, + 286, + 434 + ], + "spans": [ + { + "bbox": [ + 46, + 243, + 286, + 434 + ], + "type": "text", + "content": "Although KD has been proven to be effective for improving the performance of the student network in single-label classification, it is still a challenging problem to directly extend existing KD methods to solve multi-label knowledge distillation (MLKD) problems. Specifically, logits-based methods often obtain the predicted probabilities based on the softmax function; this function is not suitable for MLKD, because the sum of predicted probabilities may not equal one in MLL. Feature-based methods often perform KD based on the feature maps of a whole image with multiple semantics, which makes the model focus on the major objects while neglect minor objects. For example, in Figure 1, Vanilla and ReviewKD wrongly focused on the bus when the model queried the label car. Such a phenomenon would cause the model to obtain sub-optimal even undesirable distillation performance." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 436, + 286, + 614 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 436, + 286, + 614 + ], + "spans": [ + { + "bbox": [ + 46, + 436, + 286, + 614 + ], + "type": "text", + "content": "Recently, several attempts have been made to utilize KD techniques for improving the performance of MLL [15, 29, 25]. There are mainly two differences between these works and our work. Firstly, these methods often required specifically-designed network architectures [15, 25] or training strategies [29] to train the teacher and student models, while our method focuses on studying MLKD in general scenarios without any extra requirement. Secondly, unlike the previous methods utilized KD as an auxiliary technique to improve the performance of MLL, our goal is to develop a tailored approach for MLKD. As a result, previous methods were mainly compared with MLL methods in their original papers, we evaluate the KD performance of our method by comparing it with state-of-the-art KD methods." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 618, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 286, + 713 + ], + "type": "text", + "content": "In this paper, to perform MLKD, we propose a new method consisting of multi-label logits distillation and label-wise embedding distillation (L2D for short). Specifically, to exploit informative semantic knowledge compressed in the logits, L2D employs the one-versus-all reduction strategy to obtain a set of binary classification problems and perform logits distillation for each one. To enhance the distinctiveness of learned feature representations," + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 545, + 178 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 178 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 178 + ], + "type": "text", + "content": "L2D encourages the student model to maintain a consistent structure of intra-class and intra-instance (inter-class) label-wise embeddings with the teacher model. By leveraging the structural information of the teacher model, these two structural consistencies respectively enhance the compactness of intra-class embeddings and dispersion of inter-class embeddings for the student model. Both of these two components lead L2D to achieve better distillation performance than conventional KD methods as shown in Figure 1." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 317, + 180, + 538, + 191 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 180, + 538, + 191 + ], + "spans": [ + { + "bbox": [ + 317, + 180, + 538, + 191 + ], + "type": "text", + "content": "Our main contributions can be summarized as follows:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 201, + 545, + 360 + ], + "type": "list", + "angle": 0, + "index": 10, + "blocks": [ + { + "bbox": [ + 306, + 201, + 545, + 248 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 201, + 545, + 248 + ], + "spans": [ + { + "bbox": [ + 306, + 201, + 545, + 248 + ], + "type": "text", + "content": "- A general framework called MLKD is proposed. To our best knowledge, the framework is the first study specially designed for knowledge distillation in the multi-label learning scenario." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 256, + 545, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 256, + 545, + 327 + ], + "spans": [ + { + "bbox": [ + 306, + 256, + 545, + 327 + ], + "type": "text", + "content": "- A new approach for MLKD called L2D is proposed. It performs multi-label logits distillation and label-wise embedding distillation simultaneously. The former provides informative semantic knowledge while the latter encourages the student model to learn more distinctive feature representations." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 336, + 544, + 360 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 336, + 544, + 360 + ], + "spans": [ + { + "bbox": [ + 306, + 336, + 544, + 360 + ], + "type": "text", + "content": "- Extensive experimental results on benchmark datasets demonstrate the effectiveness of our proposed method." + } + ] + } + ], + "index": 9 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 370, + 391, + 383 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 370, + 391, + 383 + ], + "spans": [ + { + "bbox": [ + 306, + 370, + 391, + 383 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 391, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 391, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 391, + 545, + 713 + ], + "type": "text", + "content": "The concept of knowledge distillation (KD) proposed by Geoffrey Hinton et al. [10] defines a learning framework that transfers knowledge from a large teacher network to a small student network. Existing works can be roughly divided into two groups, i.e., logits-based methods and feature-based methods. Logits-based methods mainly focus on designing effective distillation losses to distill knowledge from logits and softmax scores after logits. DML [33] introduces a mutual learning method to train both teachers and students simultaneously. TAKD [18] proposes a new architecture called \"teacher assistant\", which is an intermediate-sized network bridging the gap between teachers and students. Besides, a recent study [34] proposes a novel logits-based method to reformulate the classical KD loss into two parts and achieves the state-of-the-art performance by adjusting weights for these two parts. Some other methods focus on distilling knowledge from intermediate feature layers. FitNet [24] is the first approach to distill knowledge from intermediate features by measuring the distance between feature maps. Attention transfer [31] achieves better performance than FitNet by distilling knowledge from the attention maps. PKT [20] measures the KL divergence between features by treating them as probability distributions. RKD [19] utilizes the relations among instances to guide the training process of the student model. CRD [28] incorporates contrastive learning into knowledge distillation. ReviewKD [1] proposes a review mechanism" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17272" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": "which uses multiple layers in the teacher to supervise one layer in the student. ITRD [17] aims to maximize the correlation and mutual information between the students' and teachers' representations." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 120, + 289, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 120, + 289, + 430 + ], + "spans": [ + { + "bbox": [ + 46, + 120, + 289, + 430 + ], + "type": "text", + "content": "Multi-label learning has increasingly attracted a lot of interest recently. Existing solutions for solving MLL problems can be categorized into three directions. The first type attempts to design novel loss functions for tackling the intrinsic positive-negative imbalance issue in multi-label classification tasks. For example, ASL [22] uses different weights to re-weight positive and negative examples for the balanced training. The second type focuses on modeling the label correlations, which provides prior knowledge for multi-label classification. Among them, MLGCN [3] is a representative method that employs a graph convolutional network to model correlation matrix. CADM [2] constructs a similar graph based on class-aware maps. To handle the multiple semantic objects contained in an image, the last type of methods aims to locate areas of interest related to semantic labels by using attention techniques. Among them, C-Tran [12] first utilizes the transformer to retrieve embeddings from visual features for each label. Query2Label [14] uses several stacked transformer encoders to identify interesting areas. ML-Decoder [23] simplifies transformer encoders in Query2Label. ADDS [30] introduces encoders from CLIP [21] in order to get better textual and visual embedding inputs to the classification head. In addition, ADDS adds a multi-head cross-attention layer and a skipping connection from the query input to the query output based on ML-Decoder." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 431, + 287, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 431, + 287, + 574 + ], + "spans": [ + { + "bbox": [ + 46, + 431, + 287, + 574 + ], + "type": "text", + "content": "Several previous studies have applied KD techniques to improve the performance of MLL. For example, Yongcheng Liu et al. [15] and Jiazhi Xu et al. [29] simply minimized mean squared error (MSE) loss between teacher logits and student logits. Liangchen Song et al. [25] designed a partial softmax function by combining a positive label with all other negative labels. Then, the conventional KD loss can be computed for each positive label. Although these methods made the pioneering attempts of combining KD and MLL, they cannot be directly applied general MLKD scenarios, and also fail to evaluate their KD performance by comparing with KD methods." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 586, + 187, + 600 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 187, + 600 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 187, + 600 + ], + "type": "text", + "content": "3. The Proposed Approach" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\pmb{x} \\in \\mathcal{X}" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " be an instance and " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\pmb{y} \\in \\mathcal{Y}" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " be its corresponding label vector, where " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{X} \\subset \\mathbb{R}^d" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " is the input space with " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " dimensions and " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{Y} \\subset \\{0,1\\}^q" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " is the target space with " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " class labels. We further use " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "y_{j}" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " to denote the " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "-th component of " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\pmb{y}" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": ". For a given instance " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\pmb{x}" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "y_{j} = 1" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " indicates the " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "-th label is relevant to the instance; " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "y_{j} = 0" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": ", otherwise. In multi-label learning, each instance may be assigned with more than one label, which means " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\sum_{j=1}^{q} \\mathbb{I}(y_{j} = 1) \\geq 1" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbb{I}(\\cdot)" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " is the indicator function. We also denote by " + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "inline_equation", + "content": "[q]" + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": " the integer set" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 72, + 365, + 84 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 365, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 365, + 84 + ], + "type": "interline_equation", + "content": "\\{1, 2, \\dots , q \\}.", + "image_path": "46fbf7f301e4561ba93706fec231b8763a46d68feead91e9803eaba55688f3ef.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "spans": [ + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": "In this paper, we use a classification model consisting of three components, i.e., a visual backbone " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": ", which extracts a feature map " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "f(\\pmb{x})" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": " for the input " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "\\pmb{x}" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": ", a label-wise embedding encoder " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": " [12, 14], which produces a label-wise embedding " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "e_k = g_k(f(\\pmb{x}))" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": " with respect to the " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": "-th class based on the feature map " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "f(\\pmb{x})" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": ", and a multi-label classifier " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": ", which predicts multi-label probabilities " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "\\hat{y} = [\\sigma(h_1(e_1)), \\sigma(h_2(e_2)), \\dots, \\sigma(h_q(e_q))]" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "\\sigma(\\cdot)" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": " denotes the sigmoid function. It is noteworthy that the used model is very general, which can be built by equipping commonly used backbones, e.g., ResNet [9], with a label-wise embedding encoder " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": ". For the notations mentioned above, we use the superscripts " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": " (or " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": ") to denote the teacher (or student) model. For example, we use " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "e_k^T" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "inline_equation", + "content": "e_k^S" + }, + { + "bbox": [ + 304, + 85, + 545, + 262 + ], + "type": "text", + "content": " to denote the label-wise embeddings for teacher and student models." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 263, + 545, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 263, + 545, + 346 + ], + "spans": [ + { + "bbox": [ + 304, + 263, + 545, + 346 + ], + "type": "text", + "content": "In multi-label learning, a popular method is to employ the one-versus-all reduction strategy to transform the original task into multiple binary problems. Among the various loss functions, the most commonly used one is the binary cross entropy (BCE) loss. Specifically, given a batch of examples " + }, + { + "bbox": [ + 304, + 263, + 545, + 346 + ], + "type": "inline_equation", + "content": "\\{(x_i,y_i)\\}_{i = 1}^b" + }, + { + "bbox": [ + 304, + 263, + 545, + 346 + ], + "type": "text", + "content": " and the predicted probabilities " + }, + { + "bbox": [ + 304, + 263, + 545, + 346 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{y}}" + }, + { + "bbox": [ + 304, + 263, + 545, + 346 + ], + "type": "text", + "content": ", the BCE loss can be defined as follows:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 353, + 545, + 396 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 353, + 545, + 396 + ], + "spans": [ + { + "bbox": [ + 306, + 353, + 545, + 396 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {B C E}} = - \\frac {1}{b} \\sum_ {i = 1} ^ {b} \\sum_ {k = 1} ^ {q} y _ {i k} \\log \\left(\\hat {y} _ {i k}\\right) + (1 - y _ {i k}) \\log \\left(1 - \\hat {y} _ {i k}\\right). \\tag {1}", + "image_path": "18540a931c6d55007086e95d09635f37b943fed0a5a586a4abf40e23dee34b73.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 396, + 545, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 396, + 545, + 538 + ], + "spans": [ + { + "bbox": [ + 304, + 396, + 545, + 538 + ], + "type": "text", + "content": "Figure 2 illustrates the distillation process of the proposed L2D framework. For a batch of training examples, we feed them into the teacher/student model to obtain the label-wise embeddings and predicted probabilities. In order to train the student model, besides the BCE loss, we design the following two distillation losses: 1) multi-label logits distillation loss " + }, + { + "bbox": [ + 304, + 396, + 545, + 538 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{MLD}}" + }, + { + "bbox": [ + 304, + 396, + 545, + 538 + ], + "type": "text", + "content": " to exploit informative semantic knowledge compressed in the logits, 2) label-wise embedding distillation loss " + }, + { + "bbox": [ + 304, + 396, + 545, + 538 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{LED}}" + }, + { + "bbox": [ + 304, + 396, + 545, + 538 + ], + "type": "text", + "content": " to leverage structural information for enhancing the distinctiveness of learned feature representations. The overall objective function can be presented as" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 340, + 540, + 545, + 552 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 340, + 540, + 545, + 552 + ], + "spans": [ + { + "bbox": [ + 340, + 540, + 545, + 552 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {L 2 D}} = \\mathcal {L} _ {\\mathrm {B C E}} + \\lambda_ {\\mathrm {M L D}} \\mathcal {L} _ {\\mathrm {M L D}} + \\lambda_ {\\mathrm {L E D}} \\mathcal {L} _ {\\mathrm {L E D}}, \\tag {2}", + "image_path": "9c908c7337247ce4c2334abc7b8e74aa2c6c97ece04907b2f40ce7f01b31816f.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 557, + 518, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 557, + 518, + 569 + ], + "spans": [ + { + "bbox": [ + 305, + 557, + 518, + 569 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 557, + 518, + 569 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{MLD}}" + }, + { + "bbox": [ + 305, + 557, + 518, + 569 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 557, + 518, + 569 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{LED}}" + }, + { + "bbox": [ + 305, + 557, + 518, + 569 + ], + "type": "text", + "content": " are two balancing parameters." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 575, + 471, + 588 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 575, + 471, + 588 + ], + "spans": [ + { + "bbox": [ + 306, + 575, + 471, + 588 + ], + "type": "text", + "content": "3.1. Multi-Label Logits Distillation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 594, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 689 + ], + "type": "text", + "content": "Traditional logits-based distillation normally minimizes the Kullback-Leibler (KL) divergence between the predicted probabilities, i.e., the logits after the softmax function, of teacher and student model. However, the method cannot be directly applied to the MLL scenario, since it depends on a basic assumption that the predicted probabilities of all classes should sum to one, which hardly holds for MLL examples." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "To mitigate this issue, inspired by the idea of one-versus-all reduction, we propose a multi-label logits distillation" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17273" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 65, + 76, + 542, + 262 + ], + "blocks": [ + { + "bbox": [ + 65, + 76, + 542, + 262 + ], + "lines": [ + { + "bbox": [ + 65, + 76, + 542, + 262 + ], + "spans": [ + { + "bbox": [ + 65, + 76, + 542, + 262 + ], + "type": "image", + "image_path": "f0117610615eb2a33b54d4846bd2dc7dc885cc2b30c71b681c633caec31fba67.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 268, + 547, + 293 + ], + "lines": [ + { + "bbox": [ + 46, + 268, + 547, + 293 + ], + "spans": [ + { + "bbox": [ + 46, + 268, + 547, + 293 + ], + "type": "text", + "content": "Figure 2. An illustration of the L2D framework. The framework simultaneously performs multi-label logits distillation and label-wise embedding distillation to improve the performance of the student model." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 311, + 290, + 370 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 311, + 290, + 370 + ], + "spans": [ + { + "bbox": [ + 46, + 311, + 290, + 370 + ], + "type": "text", + "content": "(MLD) loss, which decomposes the original multi-label task into multiple binary classification problems and minimizes the divergence between the binary predicted probabilities of two models. Formally, the MLD loss can be formulated as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 375, + 289, + 407 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 375, + 289, + 407 + ], + "spans": [ + { + "bbox": [ + 47, + 375, + 289, + 407 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {M L D}} = \\frac {1}{b} \\sum_ {i = 1} ^ {b} \\sum_ {k = 1} ^ {q} \\mathcal {D} \\left(\\left[ \\hat {y} _ {i k} ^ {\\mathcal {T}}, 1 - \\hat {y} _ {i k} ^ {\\mathcal {T}} \\right] \\mid \\mid [ \\hat {y} _ {i k} ^ {\\mathcal {S}}, 1 - \\hat {y} _ {i k} ^ {\\mathcal {S}} ]\\right), \\tag {3}", + "image_path": "85351c3ca088e0ad60ab6342848322730ed9701827d1e36beb2bb5795dd593df.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "spans": [ + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "type": "inline_equation", + "content": "[\\cdot, \\cdot]" + }, + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "type": "text", + "content": " is an operator used to concatenate two scalars into a vector, and " + }, + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "type": "text", + "content": " is a divergence function. The most common choice is the KL divergence " + }, + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_{\\mathrm{KL}}(P \\| Q) = \\sum_{x \\in \\mathcal{X}} P(x) \\log \\left(\\frac{P(x)}{Q(x)}\\right)" + }, + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "type": "inline_equation", + "content": "Q" + }, + { + "bbox": [ + 46, + 408, + 288, + 498 + ], + "type": "text", + "content": " are two different probability distributions. The MLD loss aims to improve the performance of student model by sufficiently exploiting informative knowledge from logits." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 503, + 233, + 516 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 503, + 233, + 516 + ], + "spans": [ + { + "bbox": [ + 47, + 503, + 233, + 516 + ], + "type": "text", + "content": "3.2. Label-wise Embedding Distillation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "text", + "content": "The MLD loss performs distillation on the predicted probabilities that can be regarded as a high-level representation, i.e., the final outputs of model. The knowledge distilled from the teacher model by only using the MLD loss would be insufficient to train a student model with desirable performance due to the limited information carried by the logits. To further strengthen the effectiveness of distillation, we design the label-wise embedding distillation (LED) loss, which aims to explore the structural knowledge from label-wise embeddings. The main idea is to capture two types of structural relations among label-wise embeddings: 1) class-aware label-wise embedding distillation (CD) loss " + }, + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{CD}}" + }, + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "text", + "content": ", which captures the structural relation between any two intra-class label-wise embeddings from different examples; 2) instance-aware label-wise embedding distillation (ID) loss " + }, + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{ID}}" + }, + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "text", + "content": ", which models the structural re" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 311, + 546, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 311, + 546, + 346 + ], + "spans": [ + { + "bbox": [ + 305, + 311, + 546, + 346 + ], + "type": "text", + "content": "lation between any two inter-class label-wise embeddings from the same example. In the following content, we introduce these two distillation losses in detail." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 368, + 545, + 380 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 368, + 545, + 380 + ], + "spans": [ + { + "bbox": [ + 305, + 368, + 545, + 380 + ], + "type": "text", + "content": "3.2.1 Class-Aware Label-Wise Embedding Distillation" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 388, + 546, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 388, + 546, + 652 + ], + "spans": [ + { + "bbox": [ + 304, + 388, + 546, + 652 + ], + "type": "text", + "content": "Class-aware label-wise embedding distillation aims to improve the distillation performance by exploiting the structural relations among intra-class label-wise embeddings. Generally, the same semantic objects from two different images often differ from each other by their individual characteristics, such as two cars with different colors and diverse styles (see the left side in Figure 3). Since our goal is to distinguish between car and other semantic classes instead of identifying different cars, these distinctiveness would be confusing information for the corresponding classification task. Due to the powerful learning capacity, the large model is able to capture the highly abstract semantic representations for each class label by neglecting the useless individual information. From the perspective of learned feature representations, as shown in the left side of Figure 3, the teacher model tends to obtain a more compact structure of intra-class label-wise embedding, which often leads to better classification performance. By transferring the structural knowledge from the teacher model to the student model, CD encourages the student model to enhance the compactness of intra-class label-wise embeddings, which can improve its classification performance." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 652, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 652, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 652, + 547, + 715 + ], + "type": "text", + "content": "For a batch of examples, let " + }, + { + "bbox": [ + 304, + 652, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\{e_{ik}^{\\mathcal{T}}\\}_{i = 1}^{b}" + }, + { + "bbox": [ + 304, + 652, + 547, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 652, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\{e_{ik}^{\\mathcal{S}}\\}_{i = 1}^{b}" + }, + { + "bbox": [ + 304, + 652, + 547, + 715 + ], + "type": "text", + "content": " respectively denote the intra-class label-wise embeddings with respect to class " + }, + { + "bbox": [ + 304, + 652, + 547, + 715 + ], + "type": "inline_equation", + "content": "k\\in [q]" + }, + { + "bbox": [ + 304, + 652, + 547, + 715 + ], + "type": "text", + "content": " generated by the teacher and student models. Then, we can capture the structural relation between any two intra-class label-wise embeddings " + }, + { + "bbox": [ + 304, + 652, + 547, + 715 + ], + "type": "inline_equation", + "content": "e_{ik}^{\\mathcal{T}}" + }, + { + "bbox": [ + 304, + 652, + 547, + 715 + ], + "type": "text", + "content": " and" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "17274" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 65, + 81, + 523, + 266 + ], + "blocks": [ + { + "bbox": [ + 65, + 81, + 523, + 266 + ], + "lines": [ + { + "bbox": [ + 65, + 81, + 523, + 266 + ], + "spans": [ + { + "bbox": [ + 65, + 81, + 523, + 266 + ], + "type": "image", + "image_path": "be49ff750de031fa6b78dfc5acaa32c0cb6ff0bafac4722c0f10b5cea9861270.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 281, + 547, + 315 + ], + "lines": [ + { + "bbox": [ + 46, + 281, + 547, + 315 + ], + "spans": [ + { + "bbox": [ + 46, + 281, + 547, + 315 + ], + "type": "text", + "content": "Figure 3. An illustration of class/instance-aware label-wise embedding distillation. Class-aware label-wise embedding distillation (CD) captures structural relations among intra-class label-wise embeddings from different examples, while instance-aware label-wise embedding distillation (ID) explores structural relations among intra-instance (inter-class) label-wise embeddings." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 333, + 276, + 349 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 333, + 276, + 349 + ], + "spans": [ + { + "bbox": [ + 47, + 333, + 276, + 349 + ], + "type": "inline_equation", + "content": "\\pmb{e}_{jk}^{\\mathcal{T}}" + }, + { + "bbox": [ + 47, + 333, + 276, + 349 + ], + "type": "text", + "content": " by measuring their distance in the embedding space:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 53, + 355, + 287, + 387 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 355, + 287, + 387 + ], + "spans": [ + { + "bbox": [ + 53, + 355, + 287, + 387 + ], + "type": "interline_equation", + "content": "\\phi_ {\\mathrm {C D}} \\left(\\boldsymbol {e} _ {i k} ^ {\\mathcal {T}}, \\boldsymbol {e} _ {j k} ^ {\\mathcal {T}}\\right) = \\left\\{ \\begin{array}{l l} \\| \\boldsymbol {e} _ {i k} ^ {\\mathcal {T}} - \\boldsymbol {e} _ {j k} ^ {\\mathcal {T}} \\| _ {2} & y _ {i k} = 1, y _ {j k} = 1, \\\\ 0 & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {4}", + "image_path": "7e4ed07f97634265c70d7e277dfd9c8e6e9e48cc809c64ba5b2289563201dcb3.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 394, + 287, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 394, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 47, + 394, + 287, + 464 + ], + "type": "text", + "content": "It is worth to note that we only consider the structural relation between any two valid label-wise embeddings, i.e., the embeddings with respect to positive labels. Similar to Eq.(4), for any two intra-class label-wise embeddings " + }, + { + "bbox": [ + 47, + 394, + 287, + 464 + ], + "type": "inline_equation", + "content": "e_{ik}^S" + }, + { + "bbox": [ + 47, + 394, + 287, + 464 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 394, + 287, + 464 + ], + "type": "inline_equation", + "content": "e_{jk}^S" + }, + { + "bbox": [ + 47, + 394, + 287, + 464 + ], + "type": "text", + "content": ", we can obtain the structural relation " + }, + { + "bbox": [ + 47, + 394, + 287, + 464 + ], + "type": "inline_equation", + "content": "\\phi_{\\mathrm{CD}}(e_{ik}^S, e_{jk}^S)" + }, + { + "bbox": [ + 47, + 394, + 287, + 464 + ], + "type": "text", + "content": " for the student model." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 465, + 287, + 513 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 465, + 287, + 513 + ], + "spans": [ + { + "bbox": [ + 47, + 465, + 287, + 513 + ], + "type": "text", + "content": "By enforcing the teacher and student structural relations to maintain the consistency for each pair of intra-class label-wise embeddings, we can achieve the class-aware structural consistency as follows:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 49, + 520, + 287, + 550 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 520, + 287, + 550 + ], + "spans": [ + { + "bbox": [ + 49, + 520, + 287, + 550 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {C D}} = \\sum_ {k = 1} ^ {q} \\sum_ {i, j \\in [ b ]} \\ell \\left(\\phi_ {\\mathrm {C D}} \\left(e _ {i k} ^ {\\mathcal {T}}, e _ {j k} ^ {\\mathcal {T}}\\right), \\phi_ {\\mathrm {C D}} \\left(e _ {i k} ^ {\\mathcal {S}}, e _ {j k} ^ {\\mathcal {S}}\\right)\\right), \\tag {5}", + "image_path": "077789b51366379df01ad02ce1da5558fd702d996fdb0372f0cb42f3feea1b91.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 551, + 287, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 551, + 287, + 588 + ], + "spans": [ + { + "bbox": [ + 47, + 551, + 287, + 588 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 551, + 287, + 588 + ], + "type": "inline_equation", + "content": "\\ell" + }, + { + "bbox": [ + 47, + 551, + 287, + 588 + ], + "type": "text", + "content": " is a function to measure the consistency between the teacher and student structural relations. In experiments, we use the following Huber loss function as a measurement:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 88, + 594, + 287, + 625 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 594, + 287, + 625 + ], + "spans": [ + { + "bbox": [ + 88, + 594, + 287, + 625 + ], + "type": "interline_equation", + "content": "\\ell (a, b) = \\left\\{ \\begin{array}{l l} \\frac {1}{2} (a - b) ^ {2} & | a - b | \\leq 1, \\\\ | a - b | - \\frac {1}{2} & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {6}", + "image_path": "2a41209870fd2c6066bda77f11f457dafee85f8f54939b44988facb1cb39f409.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 633, + 254, + 643 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 633, + 254, + 643 + ], + "spans": [ + { + "bbox": [ + 47, + 633, + 254, + 643 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 633, + 254, + 643 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 47, + 633, + 254, + 643 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 633, + 254, + 643 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 47, + 633, + 254, + 643 + ], + "type": "text", + "content": " are two different structural relations." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 658, + 287, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 658, + 287, + 682 + ], + "spans": [ + { + "bbox": [ + 47, + 658, + 287, + 682 + ], + "type": "text", + "content": "3.2.2 Instance-Aware Label-Wise Embedding Distillation" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "Instance-aware label-wise embedding distillation (ID) aims to improve the distillation performance by exploring the" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 334, + 545, + 571 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 334, + 545, + 571 + ], + "spans": [ + { + "bbox": [ + 304, + 334, + 545, + 571 + ], + "type": "text", + "content": "structural relations among inter-class label-wise embeddings from the same image. Generally, one can hardly distinguish between two different semantic objects occurring in an image due to the high similarities they share. For example, in the upper left corner of Figure 3, an image annotated with both sky and sea makes it difficult to distinguish between the semantic objects, as they share the same color and similar texture. A feasible solution is to exploit other useful information, such as their spatial relation, i.e., sky is always above sea. Due to the powerful learning capacity, the large model is able to distinguish between the similar semantic objects by exploiting such implicit supervised information. From the perspective of learned feature representations, as shown in the right side of 3, the teacher model tends to learn a dispersed structure of inter-class label-wise embedding, which is beneficial for improving its discrimination ability. By distilling the structural knowledge from the teacher model, ID enforces the student model to enhance the dispersion of inter-class label-wise embeddings, which can improve its discrimination ability." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "spans": [ + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "type": "text", + "content": "For a given instance " + }, + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "type": "inline_equation", + "content": "\\pmb{x}_i" + }, + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "type": "text", + "content": ", let " + }, + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "type": "inline_equation", + "content": "\\{e_{ik}^{\\mathcal{T}}\\}_{k=1}^{q}" + }, + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "type": "inline_equation", + "content": "\\{e_{ik}^S\\}_{k=1}^{q}" + }, + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "type": "text", + "content": " respectively denote the label-wise embeddings generated by teacher and student models. Then, we can capture the structural relation between any two inter-class label-wise embeddings " + }, + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "type": "inline_equation", + "content": "e_{ik}^{\\mathcal{T}}" + }, + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "type": "inline_equation", + "content": "e_{il}^{\\mathcal{T}}" + }, + { + "bbox": [ + 304, + 572, + 545, + 645 + ], + "type": "text", + "content": " by measuring their distance in the embedding space:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 316, + 651, + 545, + 683 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 316, + 651, + 545, + 683 + ], + "spans": [ + { + "bbox": [ + 316, + 651, + 545, + 683 + ], + "type": "interline_equation", + "content": "\\phi_ {\\mathrm {I D}} \\left(e _ {i k} ^ {\\mathcal {T}}, e _ {i l} ^ {\\mathcal {T}}\\right) = \\left\\{ \\begin{array}{l l} \\| e _ {i k} ^ {\\mathcal {T}} - e _ {i l} ^ {\\mathcal {T}} \\| _ {2} & y _ {i k} = 1, y _ {i l} = 1, \\\\ 0 & \\text {o t h e r w i s e .} \\end{array} \\right. \\tag {7}", + "image_path": "9c16500e9e258120793d984467b159cb69613d2d42bea31165c0be723b39db38.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "Note that in Eq.(7), we only consider the structural relation between any two valid label-wise embeddings, i.e.," + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17275" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 79, + 544, + 247 + ], + "blocks": [ + { + "bbox": [ + 121, + 69, + 470, + 79 + ], + "lines": [ + { + "bbox": [ + 121, + 69, + 470, + 79 + ], + "spans": [ + { + "bbox": [ + 121, + 69, + 470, + 79 + ], + "type": "text", + "content": "Table 1. Results on MS-COCO where teacher and student models are in the same architectures." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 79, + 544, + 247 + ], + "lines": [ + { + "bbox": [ + 50, + 79, + 544, + 247 + ], + "spans": [ + { + "bbox": [ + 50, + 79, + 544, + 247 + ], + "type": "table", + "html": "
TeacherRepVGG-A2ResNet-101WRN-101Swin-S
StudentRepVGG-A0ResNet-34WRN-50Swin-T
MetricsmAPOF1CF1mAPOF1CF1mAPOF1CF1mAPOF1CF1
Teacher72.7174.1168.6373.6273.8968.6174.7075.5670.7381.7080.4877.12
Student70.0272.4966.7770.3172.4966.8274.4575.4370.6179.5979.1875.42
RKD70.0872.3966.7370.1372.4466.7874.7075.7170.8479.6379.1975.57
PKT70.1172.4766.8070.4372.6466.6874.5475.4770.5879.6479.0975.39
ReviewKD70.0072.3566.8270.3972.6266.7674.0375.2970.3679.8179.1875.55
MSE70.2672.5466.9970.5472.7566.8574.5375.6070.7179.6779.2075.52
PS70.6572.8967.6070.8672.6667.1275.1276.0571.6379.9679.6476.20
MLD70.7472.8167.4670.6872.6967.1974.9275.7571.2180.1179.6876.44
L2D72.8174.5969.4972.8774.4569.4376.6177.0872.7981.5981.0377.86
", + "image_path": "898a37fd0bb7a59f399d632ee7ac68ca7982245acb0830ffe613885e9f641821.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 50, + 265, + 544, + 434 + ], + "blocks": [ + { + "bbox": [ + 113, + 255, + 478, + 265 + ], + "lines": [ + { + "bbox": [ + 113, + 255, + 478, + 265 + ], + "spans": [ + { + "bbox": [ + 113, + 255, + 478, + 265 + ], + "type": "text", + "content": "Table 2. Results on MS-COCO where teacher and student models are in the different architectures." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 265, + 544, + 434 + ], + "lines": [ + { + "bbox": [ + 50, + 265, + 544, + 434 + ], + "spans": [ + { + "bbox": [ + 50, + 265, + 544, + 434 + ], + "type": "table", + "html": "
TeacherResNet-101Swin-TResNet-101Swin-T
StudentRepVGG-A0ResNet-34MobileNet v2MobileNet v2
MetricsmAPOF1CF1mAPOF1CF1mAPOF1CF1mAPOF1CF1
Teacher73.6273.8968.6179.4378.7775.0773.6273.8968.6179.4378.7775.07
Student70.0272.4966.7770.3172.4966.8271.8573.5968.2671.8573.5968.26
RKD70.0872.3566.7270.0072.3466.6471.7673.6868.4071.7473.6868.37
PKT69.9972.3566.5670.2672.3966.8271.8873.6068.3571.8473.7668.37
ReviewKD70.0072.3366.6270.2972.3966.5871.9273.7368.4871.7373.7168.36
MSE70.0772.5066.8570.3372.5766.7271.9173.6868.2871.8073.7468.38
PS70.3072.6167.1070.9472.9367.5772.1173.8968.4272.4274.1468.94
MLD70.4872.7767.1071.1472.9967.6372.1773.8468.5272.3574.1068.91
L2D72.1474.0868.7873.4274.9770.2073.2474.8569.7274.2175.7270.87
", + "image_path": "47ba0d8d2f9fe2916bba6b7d8da724f5ddedb7221e24ff2a4f88e381ac7cf0fd.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 453, + 287, + 500 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 453, + 287, + 500 + ], + "spans": [ + { + "bbox": [ + 46, + 453, + 287, + 500 + ], + "type": "text", + "content": "the embedding with respect to positive labels. Similar to Eq.(7), for any two inter-class label-wise embeddings " + }, + { + "bbox": [ + 46, + 453, + 287, + 500 + ], + "type": "inline_equation", + "content": "e_{ik}^S" + }, + { + "bbox": [ + 46, + 453, + 287, + 500 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 453, + 287, + 500 + ], + "type": "inline_equation", + "content": "e_{il}^S" + }, + { + "bbox": [ + 46, + 453, + 287, + 500 + ], + "type": "text", + "content": ", we can obtain the structural relation " + }, + { + "bbox": [ + 46, + 453, + 287, + 500 + ], + "type": "inline_equation", + "content": "\\phi_{\\mathrm{ID}}(e_{ik}^S, e_{il}^S)" + }, + { + "bbox": [ + 46, + 453, + 287, + 500 + ], + "type": "text", + "content": " for the student model." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 501, + 287, + 561 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 501, + 287, + 561 + ], + "spans": [ + { + "bbox": [ + 46, + 501, + 287, + 561 + ], + "type": "text", + "content": "By encouraging the teacher and student model to maintain the consistent structure of intra-instance label-wise embeddings, we can minimize the following " + }, + { + "bbox": [ + 46, + 501, + 287, + 561 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{ID}}" + }, + { + "bbox": [ + 46, + 501, + 287, + 561 + ], + "type": "text", + "content": " loss to achieve the instance-aware structural consistency where " + }, + { + "bbox": [ + 46, + 501, + 287, + 561 + ], + "type": "inline_equation", + "content": "\\ell(.)" + }, + { + "bbox": [ + 46, + 501, + 287, + 561 + ], + "type": "text", + "content": " is Huber loss as defined in Eq.(6):" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 55, + 566, + 287, + 598 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 566, + 287, + 598 + ], + "spans": [ + { + "bbox": [ + 55, + 566, + 287, + 598 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {I D}} = \\sum_ {i = 1} ^ {b} \\sum_ {k, l \\in [ q ]} \\ell \\left(\\phi_ {\\mathrm {I D}} \\left(\\boldsymbol {e} _ {i k} ^ {\\mathcal {T}}, \\boldsymbol {e} _ {i l} ^ {\\mathcal {T}}\\right), \\phi_ {\\mathrm {I D}} \\left(\\boldsymbol {e} _ {i k} ^ {\\mathcal {S}}, \\boldsymbol {e} _ {i l} ^ {\\mathcal {S}}\\right)\\right). \\tag {8}", + "image_path": "3eef0e24750ab09dcd1638fe6e10f1005e01ccba7ed4b7b79367e460be23de11.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 599, + 287, + 622 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 599, + 287, + 622 + ], + "spans": [ + { + "bbox": [ + 46, + 599, + 287, + 622 + ], + "type": "text", + "content": "Finally, the overall objective function of L2D (Eq.(2)) can be re-written as follows:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 59, + 628, + 287, + 643 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 628, + 287, + 643 + ], + "spans": [ + { + "bbox": [ + 59, + 628, + 287, + 643 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {L 2 D}} = \\mathcal {L} _ {\\mathrm {B C E}} + \\lambda_ {\\mathrm {M L D}} \\mathcal {L} _ {\\mathrm {M L D}} + \\lambda_ {\\mathrm {C D}} \\mathcal {L} _ {\\mathrm {C D}} + \\lambda_ {\\mathrm {I D}} \\mathcal {L} _ {\\mathrm {I D}}, \\tag {9}", + "image_path": "9e3cbe92aec6e01508a436c522047320fb065507f89e4322a8ca99645fe40cda.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 648, + 270, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 648, + 270, + 661 + ], + "spans": [ + { + "bbox": [ + 47, + 648, + 270, + 661 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 648, + 270, + 661 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{MLD}}" + }, + { + "bbox": [ + 47, + 648, + 270, + 661 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 648, + 270, + 661 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{CD}}" + }, + { + "bbox": [ + 47, + 648, + 270, + 661 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 648, + 270, + 661 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{ID}}" + }, + { + "bbox": [ + 47, + 648, + 270, + 661 + ], + "type": "text", + "content": " are all balancing parameters." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 669, + 128, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 669, + 128, + 682 + ], + "spans": [ + { + "bbox": [ + 47, + 669, + 128, + 682 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "Datasets. We perform experiments on three benchmark datasets Pascal VOC2007 [8] (VOC for short), MS-" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 453, + 545, + 561 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 453, + 545, + 561 + ], + "spans": [ + { + "bbox": [ + 304, + 453, + 545, + 561 + ], + "type": "text", + "content": "COCO2014 [13] (MS-COCO for short) and NUS-WIDE [4]. VOC contains 5,011 images in the train-val set, and 4,952 images in the test set. It covers 20 common objects, with an average of 1.6 labels per image. MS-COCO contains 82,081 training images and 40,137 test images. It covers 80 common objects, with an average of 2.9 labels per image. NUS-WIDE contains 161,789 training images and 107,859 test images. It covers 81 visual concepts, with an average of 1.9 labels per image." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 565, + 545, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 565, + 545, + 638 + ], + "spans": [ + { + "bbox": [ + 304, + 565, + 545, + 638 + ], + "type": "text", + "content": "Metrics. Following existing works [32, 14, 26], we adopt the mean average precision (mAP) over all classes, overall F1-score (OF1) and average per-class F1-score (CF1) to evaluate the performance. We choose OF1 and CF1, since they consider both recall and precision and thus are more comprehensive." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": "Comparing Methods. To validate the proposed method, we compare it with the following sota KD methods: RKD [19], which captures the relations among instances to guide the training of the student model; PKT [20], which measures KL divergence between features by treating them as probability distributions; ReviewKD [1], which transfers" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "17276" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "content": "knowledge across different stages instead of just focusing on features in the same levels; as well as the modified KD techniques that have been applied to MLL: MSE [29], which minimizes the MSE loss between logits of teacher and student model; PS [25], which minimizes KL divergence of logits after a partial softmax function." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "spans": [ + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "type": "text", + "content": "Implementation Details. We use the models pretrained on ImageNet [6] as the backbones. We resize the resolution of all images to " + }, + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "type": "text", + "content": " and set the batch size as 64. For each training image, we adopt a weak augmentation consisting of random horizontal flipping and a strong augmentation consisting of Cutout [7] and RandAugment [5]. We use the Adam optimization method [11] to train the model for 80 epochs. The one-cycle policy is used with a maximal learning rate of 0.0001 and the weight decay [16] of 0.0001. For all experiments, we set " + }, + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{MLD}} = 10" + }, + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{CD}} = 100" + }, + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{ID}} = 1000" + }, + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "type": "text", + "content": ". Parameter sensitivity analysis in Appendix shows that the performance of L2D are insensitive to all of our balancing parameters. For the comparing methods, we set their parameters as suggested in the original papers. Especially, for all feature-based methods, we just deploy them on the feature maps which is output from the visual backbone " + }, + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 145, + 290, + 384 + ], + "type": "text", + "content": ". All the experiments are conducted on GeForce RTX 2080 GPUs. More details about the used models and implementation of the label-wise embedding encoder are attached in Appendix." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 395, + 165, + 407 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 395, + 165, + 407 + ], + "spans": [ + { + "bbox": [ + 47, + 395, + 165, + 407 + ], + "type": "text", + "content": "4.1. Comparison Results" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 415, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 415, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 415, + 288, + 715 + ], + "type": "text", + "content": "Table 1 and Table 2 report comparison results on MS-COCO with the same and different architectures of student and teacher models. From Table 1, it can be observed that: 1) Conventional feature-based distillation methods only achieve minor improvements in performance when compared with the student model (without distillation). This indicates these methods do not work in multi-label scenarios due to their disability to capture multiple semantics occurred in feature maps. 2) MLD can outperform conventional feature-based distillation methods in most cases, which indicates by performing one-versus-all reduction, the logits-based distillation can be adapted into multi-label knowledge distillation. 3) The proposed L2D significantly outperforms all other methods and achieves comparable performance with the teacher model. In particular, when WRN is used as the backbone, the performance of L2D is even better than that of teacher model. One possible reason is that L2D can effectively alleviate the over-fitting issue occurred to the teacher model. More results about reversed knowledge distillation where the Vanilla student model outperforms the teacher can be found in Appendix. From Table 2, we can see that compared with the same architecture, the performance gap between teacher and student model is larger for different architectures, which indicates the corresponding distillation task becomes harder. Our method sig" + } + ] + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 309, + 124, + 545, + 367 + ], + "blocks": [ + { + "bbox": [ + 304, + 69, + 545, + 123 + ], + "lines": [ + { + "bbox": [ + 304, + 69, + 545, + 123 + ], + "spans": [ + { + "bbox": [ + 304, + 69, + 545, + 123 + ], + "type": "text", + "content": "Table 3. Comparison results of the comparing methods on VOC in terms of AP and mAP (\\%), where the backbones of teacher and student model are respectively ResNet-50 and ResNet-18. The best performance is highlighted in red, and second best performance is highlighted in blue." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 124, + 545, + 367 + ], + "lines": [ + { + "bbox": [ + 309, + 124, + 545, + 367 + ], + "spans": [ + { + "bbox": [ + 309, + 124, + 545, + 367 + ], + "type": "table", + "html": "
MethodsVanillaRKDPKTMSEMLDL2D
bottle57.1859.0157.2958.2658.3259.71
pottedplant67.4367.0166.1668.0268.8870.52
chair70.3571.3171.1670.6871.1274.77
sofa73.1772.8673.2272.0673.7775.01
diningtable76.1476.9076.8977.9378.6578.93
cow82.6581.1181.7581.0684.6083.87
tvmonitor82.3081.7081.9582.3682.4284.13
bus85.5384.7985.0686.0386.4185.45
sheep84.1684.7783.6683.7283.7785.67
motorbike88.3888.8688.7388.3088.5889.83
dog90.1890.0390.1090.4690.7890.60
bird90.6591.6591.3190.6091.0291.48
bicycle91.4091.5391.7791.5891.9291.90
cat90.6791.8691.8391.0791.6392.14
boat92.5492.5392.3591.6492.2592.57
car92.7292.0692.0792.0192.3493.40
horse94.2293.9793.1294.0594.5394.67
person95.7395.8895.8095.6996.0496.46
train96.0997.0896.9997.1396.9796.81
aeroplane97.2797.0097.0997.1097.3097.39
mAP84.0184.1883.8684.2384.4885.71
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It is noteworthy that the performance is ranked in descending according to the performance of student model. From the figure, it can be observed that: 1) Our proposed L2D achieves the best performance and significantly outperforms the comparing methods in terms of mAP. 2) L2D consistently achieves superior performance to the comparing methods in most classes and the performance gap is large especially for classes that the student model achieves poor performance. This observation discloses that L2D improves the performance of hard classes by enhancing the distinctiveness of feature representations. These experimental results demonstrate the practical usefulness of the proposed method. More results on VOC and NUS-WIDE" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "17277" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 85, + 94, + 125 + ], + "blocks": [ + { + "bbox": [ + 63, + 73, + 84, + 82 + ], + "lines": [ + { + "bbox": [ + 63, + 73, + 84, + 82 + ], + "spans": [ + { + "bbox": [ + 63, + 73, + 84, + 82 + ], + "type": "text", + "content": "Query" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 53, + 85, + 94, + 125 + ], + "lines": [ + { + "bbox": [ + 53, + 85, + 94, + 125 + ], + "spans": [ + { + "bbox": [ + 53, + 85, + 94, + 125 + ], + "type": "image", + 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Ablation Study" + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 46, + 281, + 288, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 281, + 288, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 281, + 288, + 495 + ], + "type": "text", + "content": "In this section, to further analyze how the proposed method improves distillation performance, Table 4 reports results of ablation studies on MS-COCO (teacher: ResNet-101, student: ResNet-34). The first line in Table 4 reports the performance of student model without knowledge distillation. It can be observed that the distillation performance is improved slightly by only conducting multi-label logits distillation. Compared with MLD, label-wise embeddings distillation achieves the major improvement for the proposed method. It can be observed that by performing CD and ID, the mAP performance achieves " + }, + { + "bbox": [ + 46, + 281, + 288, + 495 + ], + "type": "inline_equation", + "content": "1.6\\%" + }, + { + "bbox": [ + 46, + 281, + 288, + 495 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 281, + 288, + 495 + ], + "type": "inline_equation", + "content": "1.48\\%" + }, + { + "bbox": [ + 46, + 281, + 288, + 495 + ], + "type": "text", + "content": " increments, respectively. Finally, we also examine the combination of these techniques. By incorporating these components together, the fusing method achieves the best performance and significantly outperforms each other method. These results demonstrate that all of three components are of great importance to the performance of the proposed L2D." + } + ] + } + ], + "index": 37 + }, + { + "bbox": [ + 47, + 513, + 222, + 525 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 513, + 222, + 525 + ], + "spans": [ + { + "bbox": [ + 47, + 513, + 222, + 525 + ], + "type": "text", + "content": "4.3. Performance on Image Retrieval" + } + ] + } + ], + "index": 38 + }, + { + "bbox": [ + 46, + 534, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 534, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 534, + 287, + 713 + ], + "type": "text", + "content": "To further evaluate if our method can learn better representations, we conduct an image retrieval experiment. Specifically, we use the " + }, + { + "bbox": [ + 46, + 534, + 287, + 713 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 534, + 287, + 713 + ], + "type": "text", + "content": "-NN algorithm to perform content-based image retrieval, and choose the student model trained by ReviewKD as the baseline, which has achieved the best performance among all conventional KD methods. Figure 4 illustrates the top-5 images returned by both methods. The labels under each image are colored in green if they are shared by both the query image and the returned one, and otherwise in red. These images are sorted in the ascending order based on the distance to the query image in the representation space. From the figures, we can see that our method returns the images that match the query image better than ReviewKD. This indicates our approach can obtain better representations than conventional KD methods." + } + ] + } + ], + "index": 39 + }, + { + "type": "image", + "bbox": [ + 324, + 236, + 408, + 321 + ], + "blocks": [ + { + "bbox": [ + 324, + 236, + 408, + 321 + ], + "lines": [ + { + "bbox": [ + 324, + 236, + 408, + 321 + ], + "spans": [ + { + "bbox": [ + 324, + 236, + 408, + 321 + ], + "type": "image", + "image_path": "34399b7617cb08cc09ee12414a67f9c56ed93184e7482468a3fbc66c13ab9aee.jpg" + } + ] + } + ], + "index": 40, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 354, + 327, + 391, + 335 + ], + "lines": [ + { + "bbox": [ + 354, + 327, + 391, + 335 + ], + "spans": [ + { + "bbox": [ + 354, + 327, + 391, + 335 + ], + "type": "text", + "content": "(a) Vanilla" + } + ] + } + ], + "index": 41, + "angle": 0, + "type": "image_caption" + } + ], + "index": 40 + }, + { + "type": "image", + "bbox": [ + 411, + 236, + 529, + 322 + ], + "blocks": [ + { + "bbox": [ + 411, + 236, + 529, + 322 + ], + "lines": [ + { + "bbox": [ + 411, + 236, + 529, + 322 + ], + "spans": [ + { + "bbox": [ + 411, + 236, + 529, + 322 + ], + "type": "image", + "image_path": "c0ed09ee2c68dbf988d7c8d6777addd52f0f73dfba83cc84c419744d7dc7b9bd.jpg" + } + ] + } + ], + "index": 42, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 454, + 327, + 504, + 335 + ], + "lines": [ + { + "bbox": [ + 454, + 327, + 504, + 335 + ], + "spans": [ + { + "bbox": [ + 454, + 327, + 504, + 335 + ], + "type": "text", + "content": "(b) ReviewKD" + } + ] + } + ], + "index": 43, + "angle": 0, + "type": "image_caption" + } + ], + "index": 42 + }, + { + "type": "image", + "bbox": [ + 323, + 347, + 408, + 433 + ], + "blocks": [ + { + "bbox": [ + 323, + 347, + 408, + 433 + ], + "lines": [ + { + "bbox": [ + 323, + 347, + 408, + 433 + ], + "spans": [ + { + "bbox": [ + 323, + 347, + 408, + 433 + ], + "type": "image", + "image_path": "1d6b94802552b84e92a3da23e6682ab23d76f7a07e4612c4b419120f9de41417.jpg" + } + ] + } + ], + "index": 44, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 357, + 439, + 389, + 448 + ], + "lines": [ + { + "bbox": [ + 357, + 439, + 389, + 448 + ], + "spans": [ + { + "bbox": [ + 357, + 439, + 389, + 448 + ], + "type": "text", + "content": "(c)MLD" + } + ] + } + ], + "index": 45, + "angle": 0, + "type": "image_caption" + } + ], + "index": 44 + }, + { + "type": "image", + "bbox": [ + 410, + 346, + 529, + 434 + ], + "blocks": [ + { + "bbox": [ + 410, + 346, + 529, + 434 + ], + "lines": [ + { + "bbox": [ + 410, + 346, + 529, + 434 + ], + "spans": [ + { + "bbox": [ + 410, + 346, + 529, + 434 + ], + "type": "image", + "image_path": "1dc8d39aa155d8503165787594e7bc07af96e2becde5353a5b74d11a51288802.jpg" + } + ] + } + ], + "index": 46, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 465, + 439, + 493, + 448 + ], + "lines": [ + { + "bbox": [ + 465, + 439, + 493, + 448 + ], + "spans": [ + { + "bbox": [ + 465, + 439, + 493, + 448 + ], + "type": "text", + "content": "(d) L2D" + } + ] + } + ], + "index": 47, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 306, + 451, + 545, + 473 + ], + "lines": [ + { + "bbox": [ + 306, + 451, + 545, + 473 + ], + "spans": [ + { + "bbox": [ + 306, + 451, + 545, + 473 + ], + "type": "text", + "content": "Figure 5. The differences between correlation matrices of student and teacher predicted probabilities on MS-COCO." + } + ] + } + ], + "index": 48, + "angle": 0, + "type": "image_caption" + } + ], + "index": 46 + }, + { + "bbox": [ + 306, + 479, + 485, + 491 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 479, + 485, + 491 + ], + "spans": [ + { + "bbox": [ + 306, + 479, + 485, + 491 + ], + "type": "text", + "content": "4.4. Distilling Inter-class Correlations" + } + ] + } + ], + "index": 49 + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "content": "As discussed in the previous works [10], the conventional supervised learning losses, e.g., BCE loss, often neglects the correlations among class predictions, which act as a foundational element in MLL. To validate whether the correlations can be captured by L2D effectively, Figure 5 illustrates the differences between correlation matrices of student and teacher predicted probabilities on MS-COCO. From the figure, it can be observed that: 1) The representative comparing method ReviewKD shows a large difference, which discloses that the conventional KD methods are ineffective to capture the correlations in multi-label scenarios. 2) MLD does not show a reduced difference, which indicates that the information of logits is not enough for capturing precise correlations. 3) L2D shows significant matching between the teacher and student correlations. By enhancing the distinctiveness of label-wise embeddings, L2D can obtain more correct predicted probabilities, leading to a more precise correlation estimation." + } + ] + } + ], + "index": 50 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17278" + } + ] + } + ], + "index": 51 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 119, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 119, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 119, + 83 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 93, + 289, + 224 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 93, + 289, + 224 + ], + "spans": [ + { + "bbox": [ + 46, + 93, + 289, + 224 + ], + "type": "text", + "content": "The paper studies the problem of multi-label knowledge distillation. In the proposed method, the multi-label logits distillation explores the informative semantic knowledge compressed in the teacher logits to obtain more semantic supervision. Furthermore, the label-wise embedding distillation exploits the structural knowledge from label-wise embeddings to learn more distinctive feature representations. Experimental results on benchmark datasets validate the effectiveness of the proposed method. In future, we plan to improve the performance of MLKD by exploiting other abundant structural information." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 242, + 145, + 255 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 242, + 145, + 255 + ], + "spans": [ + { + "bbox": [ + 47, + 242, + 145, + 255 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 264, + 289, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 264, + 289, + 407 + ], + "spans": [ + { + "bbox": [ + 46, + 264, + 289, + 407 + ], + "type": "text", + "content": "Sheng-Jun Huang was supported by, the National Key R&D Program of China (2020AAA0107000), the Natural Science Foundation of Jiangsu Province of China (BK20222012, BK20211517), and NSFC (62222605). Lei Feng was supported by the Joint NTU-WeBank Research Centre on Fintech (Award No: NWJ-2021-005), Nanyang Technological University, Singapore, Chongqing Overseas Chinese Entrepreneurship and Innovation Support Program, Chongqing Artificial Intelligence Innovation Center, and CAAI-Huawei MindSpore Open Fund. Masashi Sugiyama was supported by JST CREST Grant Number JP-MJCR18A2." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 424, + 107, + 436 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 424, + 107, + 436 + ], + "spans": [ + { + "bbox": [ + 47, + 424, + 107, + 436 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 53, + 444, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 53, + 444, + 287, + 487 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 444, + 287, + 487 + ], + "spans": [ + { + "bbox": [ + 53, + 444, + 287, + 487 + ], + "type": "text", + "content": "[1] Pengguang Chen, Shu Liu, Hengshuang Zhao, and Jiaya Jia. Distilling knowledge via knowledge review. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 11953-11962, 2022. 2" + } + ] + } + ], + "index": 13 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "17280" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-Label Self-Supervised Learning with Scene Images/d8308065-1607-45e1-b7cf-dd3679dcb186_content_list.json b/2023/Multi-Label Self-Supervised Learning with Scene Images/d8308065-1607-45e1-b7cf-dd3679dcb186_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..a9bd624b9c1a29cd17136791dab1207c4163a6fd --- /dev/null +++ b/2023/Multi-Label Self-Supervised Learning with Scene Images/d8308065-1607-45e1-b7cf-dd3679dcb186_content_list.json @@ -0,0 +1,1948 @@ +[ + { + "type": "text", + "text": "Multi-Label Self-Supervised Learning with Scene Images", + "text_level": 1, + "bbox": [ + 196, + 130, + 774, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Ke Zhu Minghao Fu Jianxin Wu* \nState Key Laboratory for Novel Software Technology \nNanjing University, China", + "bbox": [ + 272, + 180, + 696, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "zhuk@lamda.nju.edu.cn, fumh@lamda.nju.edu.cn, wujx2001@nju.edu.cn", + "bbox": [ + 196, + 237, + 772, + 250 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 313, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Self-supervised learning (SSL) methods targeting scene images have seen a rapid growth recently, and they mostly rely on either a dedicated dense matching mechanism or a costly unsupervised object discovery module. This paper shows that instead of hinging on these strenuous operations, quality image representations can be learned by treating scene/multi-label image SSL simply as a multi-label classification problem, which greatly simplifies the learning framework. Specifically, multiple binary pseudo-labels are assigned for each input image by comparing its embeddings with those in two dictionaries, and the network is optimized using the binary cross entropy loss. The proposed method is named Multi-Label Self-supervised learning (MLS). Visualizations qualitatively show that clearly the pseudo-labels by MLS can automatically find semantically similar pseudo-positive pairs across different images to facilitate contrastive learning. MLS learns high quality representations on MS-COCO and achieves state-of-the-art results on classification, detection and segmentation benchmarks. At the same time, MLS is much simpler than existing methods, making it easier to deploy and for further exploration.", + "bbox": [ + 75, + 316, + 473, + 650 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 678, + 209, + 694 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Self-supervised learning (SSL) methods based on contrastive learning [4, 3] have facilitated numerous downstream tasks. Those [16, 6, 14, 13] that target object-centric images (e.g., ImageNet) are already relatively mature, but inventing SSL methods for scene images (e.g., MS-COCO [23]) gains popularity recently. Since unlabeled scene images (or multi-label images) are more natural [46] and richer in semantics, various SSL methods [39, 45, 19, 40, 20, 44] have successively emerged.", + "bbox": [ + 75, + 703, + 468, + 838 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "SSL methods focusing on scene/multi-label images can", + "bbox": [ + 96, + 839, + 468, + 854 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/8a89928182d88d08553e7739a6be98cb8179207c88e6de7702b21823f2834190.jpg", + "image_caption": [ + "Figure 1. Illustrating our motivation. An image patch cropped from a multi-label image comprises multiple objects. Each object can find similar ('pos') and dissimilar ('neg') images from a large dictionary. The whole image patch is pulled closer to those positive ones and pushed away from the negatives using a BCE loss. See Fig. 4 for positives and negatives chosen by our algorithm." + ], + "image_footnote": [], + "bbox": [ + 526, + 287, + 870, + 444 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "be summarized into two categories. One is dense matching, such as DenseCL [39], MaskCo [51] and Self-EMD [24]. They take the features' locations into account to improve the performance on dense prediction tasks. They mostly differ in how the heuristic matching metric is designed. Another branch of work like SoCo [41] and ORL [46] resort to unsupervised object discovery to find local object contents, and learn quality representation with both object- and scene-level semantics. However, they usually involve multi-stage SSL pretraining on top of expensive box generation [35].", + "bbox": [ + 496, + 565, + 893, + 717 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "These scene image SSL methods are generally based on the contrastive loss (e.g., InfoNCE [27]), where two randomly augmented views of the same image are forced to be close to each other, and optionally push away views from different images. The loss assumes single-label images [27], but the input are in fact multi-label: hence there is a mismatch between the loss and the data. On one hand, it can be difficult for two views randomly cropped from the same scene image to be exactly matched [39, 47]. On the other hand, there is only one matched positive pair in InfoNCE, while more positive pairs are naturally preferred: a view cropped from a multi-label image likely contains mul", + "bbox": [ + 496, + 719, + 895, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*J. Wu is the corresponding author. This paper was partly supported by the National Natural Science Foundation of China under Grant 62276123 and Grant 61921006.", + "bbox": [ + 75, + 862, + 468, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "6694", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "tiple semantic concepts or objects.", + "bbox": [ + 78, + 90, + 305, + 106 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Therefore, this paper proposes a simple yet direct approach towards scene image SSL, named as Multi-Label Self-supervised learning (MLS). We treat each image (or randomly cropped patch) as a semantic bag with multiple objects, then retrieve images sharing similar semantics with any object in the bag from a large image dictionary. Note that an object in a bag is not necessarily within the set of human-annotated categories. As illustrated in Fig. 1, the cropped patch contains person, horse, road and bus, which will be pulled closer to similar images containing any of these objects and be pushed away from those dissimilar ones. Specifically, the patch's embedding produced by a backbone network will select top $k$ similar embeddings as $k$ (pseudo) positive images from a dictionary, and the rest will be negatives. In another dictionary containing images in the same order as the first one, the BCE (binary cross entropy) loss plus these binary pseudo-labels will classify the patch's embedding after an MLP projector using all the images in this second dictionary as classifiers, and generates gradients that optimize the backbone network. This framework is illustrated in Fig. 2.", + "bbox": [ + 80, + 107, + 467, + 422 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our framework has two benefits. First, the large dictionary has diverse positive samples for any given input, hence provides many quality positive pairs with deformations or intra-class variations [11]. Second, unlike InfoNCE, the BCE loss is not mutually exclusive among classes, hence allows the co-occurrence of multiple classes in one scene image. By applying our SSL method to scene images (e.g., MS-COCO), we achieve state-of-the-art results on object detection, instance segmentation and various classification benchmarks. Our contributions are summarized as follows:", + "bbox": [ + 80, + 425, + 467, + 574 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. For the first time, we formulate scene image SSL as a multi-label classification, and propose our Multi-Label Self-supervised (MLS) learning approach.", + "2. Unlike previous methods that adopt dense matching or unsupervised object discovery, MLS is simple in concept, and enjoys intuitive visualizations (c.f. Fig. 4) which clearly verifies our motivation.", + "3. Extensive experiments of object detection, instance segmentation and classification on various benchmark datasets, together with ablation studies, clearly demonstrate the effectiveness of our method." + ], + "bbox": [ + 91, + 590, + 467, + 780 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 80, + 800, + 215, + 814 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Traditional SSL methods. Self-supervised learning (SSL) has emerged as a promising direction towards unsupervised representation learning [6]. Early SSL methods [27, 33] are mainly derived from noise contrastive estimation [15]. Later, SSL methods based on contrastive", + "bbox": [ + 80, + 825, + 467, + 898 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "learning and clustering paradigms have been proved effective, too. Representative methods such as SimCLR [4], MoCo [16], BYOL [14] and SwAV [3] have exhibited both simplicity and generalization ability [36] to various downstream tasks. A set of variants such as Simsiam [7], InfoMin [34] and NNCLR [11] try to simplify, analyze and optimize traditional SSL methods from different aspects. However, all of them mainly focus on pretraining on object-centric images like the ImageNet dataset [32] for image classification (e.g., ImageNet linear evaluation), but pay less attention to dense prediction tasks.", + "bbox": [ + 501, + 90, + 888, + 256 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Scene-image SSL methods. The development of scene (multi-label) image SSL is a diversified process, which mainly contains two branches: dedicated dense feature matching and multi-stage pretraining with unsupervised object discovery. DenseCL [39], PixPro [47], ReSim [44], LEWEL [20] and SetSim [40] all apply the InfoNCE loss in a dense matching manner. They propose dense loss functions in addition to the traditional InfoNCE loss, and their pipelines differ in how the matching metrics are (probably manually) selected. Another branch of methods such as SoCo [41] and ORL [46] try to learn quality feature representation with both scene- and object-level information: they utilize multi-stage pretraining to find correspondence across images with the help of unsupervised object generation methods [35, 54], which suffers from huge computation costs. A recent SSL method [36] that is close to our work proposed kNN-MoCo as an extra module. But, this method is still in a single-label InfoNCE manner and the improvement is small compared to our multi-label MLS (c.f. Table 6). Compared to existing methods, our MLS is novel in concept and simple in implementation.", + "bbox": [ + 503, + 258, + 888, + 571 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-label classification. Multi-label recognition aims to predict the presence or absence of each object class in an input image [48]. Traditional methods are based on three aspects: attention modules [53, 52], correlation matrix [8, 5] and unsupervised box generation [42, 38]. The loss function adopted in this task is mostly binary cross entropy (BCE), which is not mutually exclusive among classes [48], such that the presence of one class does not suppress the existence of others. In this paper, we inherit this unique property of multi-label classification and try to integrate BCE into self-supervised learning on scene images. We adopt the joint image embedding to generate $k$ pseudo-labels, together with the classification logits to calculate the final loss term, which effectively guides the multi-label self-supervised learning.", + "bbox": [ + 503, + 575, + 888, + 799 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 503, + 816, + 588, + 830 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this section, we start by describing the preliminaries of self-supervised learning, including the InfoNCE loss and its variants. We will then describe the proposed Multi-Label Self-supervised (MLS) learning methods and how the over", + "bbox": [ + 503, + 840, + 888, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "6695", + "bbox": [ + 483, + 946, + 513, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "all loss function is formulated and optimized.", + "bbox": [ + 76, + 90, + 377, + 106 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Preliminaries", + "text_level": 1, + "bbox": [ + 76, + 113, + 217, + 128 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Self-supervised learning methods, whether contrastive based [16, 14] or clustering based [3], usually rely on the InfoNCE loss [27] or its variants [33]:", + "bbox": [ + 76, + 137, + 468, + 183 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {n c e} = - \\log \\frac {\\exp (q \\cdot k _ {+} / \\tau)}{\\exp (q \\cdot k _ {+} / \\tau) + \\sum_ {k _ {-}} \\exp (q \\cdot k _ {-} / \\tau)}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 186, + 468, + 234 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $q$ and $k_{+}$ are positive embeddings (similar to $z_{1}$ and $z_{2}$ in Fig. 2) after the multi-layer perception (MLP) projector of two encoders. The negative features $k_{-}$ may come from a memory bank [43], a large dictionary or a queue [6], or the current mini-batch [4]. Negatives may be removed by using additional techniques (e.g., the stop gradient adopted in BYOL [14] and SimSiam [7]).", + "bbox": [ + 76, + 236, + 468, + 340 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Similar with the form of a normal softmax function [53] that is popular in single-label classification, InfoNCE is mutually exclusive among all classes, such that there can only be one positive out of all pseudo concepts. There are variants of InfoNCE (such as SupCon [21]) where more positive pairs are excavated and accumulated, with each item being a sole InfoNCE form. These variants can be summarized as follows:", + "bbox": [ + 75, + 340, + 468, + 460 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n- \\frac {1}{N _ {p o s}} \\sum_ {i = 1} ^ {N _ {p o s}} \\log \\frac {\\exp \\left(q \\cdot k _ {+} ^ {i} / \\tau\\right)}{\\exp \\left(q \\cdot k _ {+} ^ {i} / \\tau\\right) + \\sum_ {k _ {-}} \\exp \\left(q \\cdot k _ {-} / \\tau\\right)}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 465, + 468, + 520 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "in which the total $N_{pos}$ positives are enumerated over $k_{+}^{i}$ . It can indeed alleviate the dilemma of the traditional form by involving more positives, but all these methods mainly focus on supervised learning [21] or lack extensive experiments on large dense prediction tasks [36].", + "bbox": [ + 75, + 521, + 468, + 595 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "More importantly, the concept of multi-label learning is not introduced, that is, the classes are still mutually exclusive, which hinders the model from learning quality representations from scene image self-supervised learning.", + "bbox": [ + 75, + 597, + 468, + 657 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Multi-label self-supervised learning", + "text_level": 1, + "bbox": [ + 76, + 664, + 385, + 681 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Now, we will introduce the proposed MLS method in detail. As discussed above, previous SSL methods who targeted scene images all adopt loss functions in the single-label form, while in this paper, we aim to reduce the gap between the optimization objective and the unique property of multi-label images.", + "bbox": [ + 75, + 686, + 468, + 777 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We adopt MoCo-v2 [6] as our base structure. Specifically, given an input image $I$ , it is first cropped and augmented into two different views:", + "bbox": [ + 75, + 777, + 468, + 823 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nv _ {1} = \\mathcal {T} (I), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 232, + 828, + 468, + 851 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nv _ {2} = \\mathcal {T} ^ {\\prime} (I),\n$$\n", + "text_format": "latex", + "bbox": [ + 230, + 848, + 316, + 863 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathcal{T}$ and $\\mathcal{T}'$ are two randomly sampled data augmentations. These two views are then passed through the base", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "encoder $\\phi (\\cdot)$ and a momentum encoder $\\phi^m (\\cdot)$ to get the backbone features $g_{1}$ and $g_{2}$ :", + "bbox": [ + 498, + 90, + 890, + 121 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ng _ {1} = \\phi (v _ {1}), g _ {2} = \\phi^ {m} (v _ {2}), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 602, + 135, + 890, + 152 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "in which $g_{1}, g_{2} \\in \\mathbb{R}^{d_{g}}$ (e.g., $d_{g} = 2048$ in ResNet-50 [18]). Next, the backbone features are both passed through a multi-layer perceptron (MLP) projector $f(\\cdot)$ or $f^{m}(\\cdot)$", + "bbox": [ + 498, + 165, + 890, + 213 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nz _ {1} = f \\left(g _ {1}\\right), z _ {2} = f ^ {m} \\left(g _ {2}\\right) \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 607, + 226, + 890, + 243 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "to get the final embeddings $z_{1},z_{2}\\in \\mathbb{R}^{d_{z}}$ . Similar to MoCo $\\mathrm{v}2$ that retains a large dictionary $Q_{z}$ (shown in Fig. 2), here we keep two queues $Q_{g}\\in \\mathbb{R}^{D\\times d_{g}}$ and $Q_{z}\\in \\mathbb{R}^{D\\times d_{z}}$ with normalized embeddings coming from $g_{2}$ and $z_{2}$ , respectively.", + "bbox": [ + 496, + 257, + 890, + 332 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\frac {g _ {2}}{| | g _ {2} | |} \\stackrel {{E n q u e u e}} {{\\Longrightarrow}} Q _ {g}, \\tag {6} \\\\ \\begin{array}{c} \\frac {z _ {2}}{| | z _ {2} | |} \\overset {E n q u e u e} {\\Longrightarrow} Q _ {z}. \\end{array} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 630, + 335, + 890, + 397 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Note that for simplicity the enqueue and deque operations are not shown in Fig. 2, and that features stored in $Q_{g}$ and $Q_{z}$ are all kept in the same order. embeddings in both queues are L2 normalized.", + "bbox": [ + 498, + 406, + 890, + 465 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Then, the backbone feature $g_{1}$ of view $v_{1}$ picks its top $k$ nearest neighbors from $Q_{g}$ and treats them as containing similar semantics as that in the input image's view $v_{1}$ (e.g., containing at least one object that appears in the input view $v_{1}$ ). These nearest neighbors are given pseudo positive labels and all the rest items in $Q_{g}$ are pseudo negatives. This step forms multiple binary pseudo-labels $y \\in \\mathbb{R}^{D}$ :", + "bbox": [ + 498, + 468, + 890, + 574 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ny = I s T o p k \\left(g _ {1} \\odot Q _ {g}\\right), \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 612, + 588, + 890, + 606 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\odot$ is the matrix multiplication operation.", + "bbox": [ + 500, + 619, + 812, + 633 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the next step, the normalized embeddings inside $Q_{z}$ are treated as normalized classifiers. They are multiplied by the feature $z_{1}$ to produce the logits $p \\in \\mathbb{R}^{D}$ , which classify $z_{1}$ into the $D$ pseudo categories:", + "bbox": [ + 498, + 636, + 890, + 696 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\np = z _ {1} \\odot Q _ {z}. \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 645, + 710, + 890, + 727 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Finally, the pseudo labels $y$ and the classified logits interact with each other, and are optimized using the binary cross entropy (BCE) loss,", + "bbox": [ + 498, + 741, + 890, + 787 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {m l} = \\frac {- 1}{D} \\sum_ {i = 1} ^ {D} \\left[ y _ {i} \\log \\sigma \\left(\\frac {p _ {i}}{\\tau}\\right) + (1 - y _ {i}) \\log \\left(1 - \\sigma \\left(\\frac {p _ {i}}{\\tau}\\right)\\right) \\right], \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 501, + 801, + 890, + 854 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "in which $\\tau$ is a temperature hyperparameter (following MoCo-v2's), and $\\sigma(\\cdot)$ is the sigmoid function [52] that maps the scores to the range $[0,1]$ .", + "bbox": [ + 498, + 854, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "6696", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/2293a6938d28b81f00dfbd3c7be4c30f4340095502356a2a4f254a90be8947c8.jpg", + "image_caption": [ + "Figure 2. The proposed MLS method. An image $I$ is first augmented to two views and sent to two encoders. The embeddings $g_{1}, g_{2} \\in \\mathbb{R}^{d_{g}}$ and $z_{1}, z_{2} \\in \\mathbb{R}^{d_{z}}$ are features after the backbone and the MLP, respectively. View 2's features ( $g_{2}$ and $z_{2}$ ) are enqueued to form two dictionaries $Q_{g} \\in \\mathbb{R}^{D \\times d_{g}}$ and $Q_{z} \\in \\mathbb{R}^{D \\times d_{z}}$ in the same order. As shown in the right half, the embedding $g_{1}$ picks its top $k$ nearest embeddings from the queue $Q_{g}$ to produce binary pseudo labels $y \\in \\mathbb{R}^{D}$ . Then, the embeddings from $Q_{z}$ are treated as classifiers that calculate the logit $p \\in \\mathbb{R}^{D}$ of $z_{1}$ , which is compared against the pseudo-labels $y$ by a BCE loss. Best viewed in color." + ], + "image_footnote": [], + "bbox": [ + 122, + 89, + 519, + 237 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/67b31838b4a5e8842f421ef80f76de4a07419b5bb607a66a4fff72ade9c8a2a9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 566, + 108, + 844, + 232 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Optimization", + "text_level": 1, + "bbox": [ + 76, + 343, + 215, + 359 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "When we use the multi-label loss $\\mathcal{L}_{ml}$ as the only loss function, we found that empirically the optimization process often faces an unstable training issue. We believe this unstable optimization should be attributed to the adverse interaction between assigning pseudo-labels and learning representations from a poor starting point. High quality embeddings from the queues $Q_{g}$ and $Q_{z}$ cannot be obtained if the pseudo-labels are incorrect. At the same time picking nearest neighbors and classification will surely fail if the enqueued embeddings are misleading (a point which was mentioned in DenseCL [39], too).", + "bbox": [ + 75, + 367, + 470, + 532 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Two strategies easily stabilize the multi-label SSL learning. One is to use InfoNCE alone in the first few epochs to warmup the dictionary $Q_{g}$ and $Q_{z}$ . The other remedy is to combine InfoNCE with our multi-label BCE loss during the whole training process, which is widely used in previous methods [39, 1, 40] and easier in implementation. Hence, we adopt this strategy and our overall loss function is formulated as:", + "bbox": [ + 75, + 534, + 468, + 652 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathcal {L} _ {n c e} + \\lambda \\mathcal {L} _ {m l}, \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 205, + 655, + 468, + 670 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{nce}$ is the InfoNCE loss that is adopted in MoCo-v2 (c.f. Eq. 1) and along with many multi-label SSL methods. $\\mathcal{L}_{ml}$ is our multi-label BCE loss (c.f. Eq. 9). The value of combination weight $\\lambda$ is fixed at $\\lambda = 0.5$ .", + "bbox": [ + 76, + 678, + 468, + 738 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The proposed method is abbreviated as MLS (multi-label self-supervised) learning.", + "bbox": [ + 76, + 739, + 468, + 768 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 784, + 207, + 800 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Now we validate the effectiveness of MLS through extensive experiments. We first describe the settings of our experiments, including datasets for upstream pretraining and downstream finetuning, training details, and the architecture for object detection, instance/semantic segmentation and image classification.", + "bbox": [ + 75, + 809, + 468, + 898 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Experimental settings", + "text_level": 1, + "bbox": [ + 500, + 343, + 702, + 359 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Datasets. We adopted the MS-COCO train2017 set [23] for SSL pretraining, which is widely applied in the study of scene image SSL [46, 41, 39]. Note that we did not use ImageNet. For downstream tasks, we conducted experiments on MS-COCO, VOC0712 [12], CityScapes [10] as well as 7 small classification datasets (CUB200 [37], Flowers [26], Cars [22], Aircraft [25], Indoor67 [30], Pets [28] and DTD [9]) following previous SSL methods [2]. Specifically, MS-COCO contains 118,287 and 5000 images for training and validation, respectively. VOC2007 has 5011 and 4952 images in the trainval and test sets, respectively. CityScapes is a semantic segmentation dataset containing 2975 and 500 images for training and validation, respectively. For more information about the 7 small classification datasets, please refer to [2] for a more detailed description.", + "bbox": [ + 496, + 368, + 890, + 595 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Pretraining. We adopted ResNet-50 [18] as our base encoder (c.f. Fig. 2) and mostly follow the structure of MoCoV2. We pretrained our models for 400 or 800 epochs on MSCOCO, set learning rate as 0.3, weight decay as 0.0001. For data augmentation, we adopted random resized crop, color distortion, random gray scale, random flip, etc, following [36, 3]. The queue size $D$ of $Q_{g}$ and $Q_{z}$ was 4096. The temperature $\\tau$ was set as 0.2 and was shared between the InfoNCE loss and our multi-label BCE loss. The dimensionalities of the embeddings $g_{1}$ and $z_{1}$ were 2048 and 256, respectively. For faster convergence, we adjusted the momentum update coefficient to 0.995. With regard to our multi-label BCE loss, the parameter $k$ was set as 20, and the combination coefficient $\\lambda$ was 0.5.", + "bbox": [ + 496, + 597, + 890, + 806 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Downstream. We finetuned the pretrained model on various benchmarks, including MS-COCO object detection and instance segmentation, CityScapes semantic segmentation, VOC0712 detection and other classification benchmarks. Specifically, we finetuned on MS-COCO using the Mask-RCNN R50-FPN/C4 [17] architecture for 90k itera", + "bbox": [ + 496, + 809, + 890, + 898 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "6697", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/32e16244eb49207e11ebcfe1c03de18b7d08211b6a5fd9fb282dfb4bce6cb02e.jpg", + "table_caption": [ + "Table 1. Results of COCO detection and segmentation. All SSL models (except those pretrained on ImageNet) were first pretrained on MS-COCO and then finetuned on COCO with Mask R-CNN R50-FPN [17]. Our MLS was pretrained for 400 or 800 epochs for fair comparisons. We reproduced $\\mathrm{SoCo}^*$ with the settings in [41]. Note that SetSim [40] and ReSim [44] are adaptable to scene image pretraining, but only reported ImageNet pretraining results. The column 'Epochs' means the number of pretraining epochs. ORL $^{+}$ [46] needs two pretraining stages (800 epochs each), so the total training time is doubled." + ], + "table_footnote": [], + "table_body": "
MethodDataEpochsDetectionSegmentation
APbboxAPbbox50APbbox75APsegAPseg50APseg75
Supervised [41]ImageNet9038.959.642.735.456.538.1
ReSim-C4 [44]ImageNet20039.359.743.135.756.738.1
LEWELM [20]ImageNet20040.059.843.736.157.038.7
SetSim [40]ImageNet20040.260.743.936.457.739.0
SoCo* [41]COCO40039.159.142.735.456.037.8
Self-EMD [24]COCO80039.360.142.8---
MoCo-v2 [6]COCO80038.558.142.134.855.337.3
BYOL [14]COCO80038.858.542.235.055.938.1
DenseCL [39]COCO80039.659.343.335.756.538.4
ORL+ [46]COCO160040.360.244.436.357.338.9
MLSCOCO40040.160.243.936.257.338.6
MLSCOCO80040.560.744.536.557.739.1
", + "bbox": [ + 155, + 157, + 816, + 397 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "tions. For VOC0712, we finetuned for 24k iterations with Faster-RCNN R50-C4 [31]. For CityScapes semantic segmentation, we adopted PSANet [50] and PSPNet [49] for 40k iterations. For classification, we chose VOC2007 for multi-label recognition and finetuned 120 epochs on 7 small classification datasets. We ran 3 times on VOC detection and 2 runs on CityScapes since these results have relatively large variations. Following previous studies, the evaluation metrics for detection, segmentation and classification are AP, mIoU/mAcc and top-1 accuracy, respectively. All the experiments were conducted with RTX 3090 GPUs in the PyTorch [29] framework.", + "bbox": [ + 75, + 421, + 472, + 604 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. COCO detection and segmentation results", + "text_level": 1, + "bbox": [ + 76, + 617, + 437, + 633 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We first evaluated downstream performance on MS-COCO object detection and instance segmentation. Following previous work, we used Mask R-CNN R50-FPN for finetuning. The results is in Table 1. DenseCL [39] and Self-EMD [24] are those adopting dense matching, while SoCo [41] and ORL [46] both resort to the unsupervised object discovery method Selective Search [35]. For a fair comparison, we reproduced SoCo's results since it was originally pretrained on $\\mathrm{COCO + }$ [41] (which is based on COCO but has more unlabeled data). Note that ReSim-C4 [44] and SetSim [40] are suitable for scene image pretraining, but only ImageNet results were reported.", + "bbox": [ + 75, + 642, + 468, + 824 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As shown in Table 1, with only 400 epochs of pretraining, our MLS is almost better than all counterparts (e.g., DenseCL, SoCo, LEWEL [20]) and surpasses supervised results by $1.2\\%$ APbbox and $0.8\\%$ APseg. With the standard 800 epochs of pretraining, MLS is better than all previous", + "bbox": [ + 75, + 824, + 470, + 902 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/9749705d77837b5891262062ad7c36fac57b6f06552f0fc233b862cb36941823.jpg", + "table_caption": [ + "Table 2. Results on COCO with the Mask R-CNN R50-C4 detector. 'Data' stands for the pretraining dataset. 'CC' and 'IN' means COCO and ImageNet, respectively. All SSL models were pretrained for 400 epochs on MS-COCO." + ], + "table_footnote": [], + "table_body": "
MethodDataDetectionSegmentation
APbboxAPbbox50APbbox75APsegAPseg50APseg75
Random-26.444.027.829.346.930.8
SupervisedIN38.158.141.133.254.835.0
BYOLCC36.956.739.432.453.534.3
MoCo-v2CC37.356.740.432.853.534.9
SoCo*CC36.956.239.732.453.034.5
DenseCLCC38.357.941.433.554.435.7
MLSCC38.658.341.533.855.136.0
", + "bbox": [ + 504, + 473, + 887, + 621 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "scene image SSL methods. This further verifies our motivation: formulating scene image self-supervised learning as a multi-label classification is both simpler in concept and effective in performance.", + "bbox": [ + 496, + 652, + 890, + 714 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We also tried the Mask R-CNN R50-C4 structure. Since there are relatively less SSL results based on this structure, we reproduced supervised learning, BYOL [14], MoCoV2 [6], SoCo [41] and DenseCL [39] methods by pretraining and finetuning on MS-COCO. To compare fairly, all these SSL models were pretrained for 400 epochs.", + "bbox": [ + 496, + 715, + 890, + 808 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As can be found in Table 2, our MLS surpasses all previous self-supervised learning methods like SoCo [41] and DenseCL [39], despite being much simpler than them. Note that SoCo needs unsupervised box generation and multiple auxiliary loss functions. Our MLS also achieves better results than supervised ImageNet pretraining, with an", + "bbox": [ + 496, + 809, + 893, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "6698", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/fc8d0501d961b3f258868e87a660dcd10d51367d95a7e74a336fa9a9a4d720e5.jpg", + "table_caption": [ + "Table 3. Results of CityScapes semantic segmentation using two different segmentation pipelines (PSANet [50] and PSPNet [49]). 'Data' stands for the pretraining dataset. 'CC' and 'IN' means COCO and ImageNet, respectively." + ], + "table_footnote": [], + "table_body": "
MethodDataPSANetPSPNet
mIoUmAccaAccmIoUmAccaAcc
SupervisedIN77.586.695.977.886.795.9
BYOLCC77.686.695.976.985.995.9
MoCo-v2CC76.885.895.876.885.495.8
DenseCLCC77.686.696.077.686.395.9
SoCoCC76.385.395.876.585.395.8
MLSCC79.087.396.278.586.696.1
", + "bbox": [ + 91, + 142, + 454, + 281 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/18cf1a68e05ee7f60257a1ae38ae0ae091fbb7036cdc1b30100ef20bd95db522.jpg", + "table_caption": [ + "Table 4. Results of VOC0712 object detection using the Faster-RCNN R50-C4 object detector. All SSL models were pretrained on MS-COCO for 800 epochs. BYOL and MoCo-v2 results were reproduced by us." + ], + "table_footnote": [], + "table_body": "
MethodDataAP\\( AP_{50} \\)\\( AP_{75} \\)
Random-32.859.031.6
SupervisedImageNet53.381.058.8
SwAV [3]ImageNet45.177.446.5
SimCLR [4]ImageNet51.579.455.6
SoCo* [41]COCO51.778.657.2
Self-EMD [24]COCO53.080.058.6
BYOLCOCO51.780.256.4
MoCo-v2COCO53.780.059.5
MLSCOCO55.081.661.2
", + "bbox": [ + 91, + 347, + 454, + 526 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "improvement of $0.5\\%$ $\\mathrm{AP}^{bbox}$ and $0.6\\%$ $\\mathrm{AP}^{seg}$ for object detection and instance segmentation, respectively.", + "bbox": [ + 76, + 550, + 468, + 582 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Transfer learning", + "text_level": 1, + "bbox": [ + 76, + 590, + 250, + 607 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Next, we test how our MLS method performs on various transfer learning tasks, including CityScapes semantic segmentation, VOC0712 object detection and (multi-label) classification.", + "bbox": [ + 76, + 613, + 468, + 672 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "CityScapes semantic segmentation. We first transferred pretrained models to CityScapes [10] semantic segmentation. Because relatively few SSL methods worked on this benchmark and the segmentation architecture generally differed, we first reproduced several SSL methods (BYOL, MoCo-v2, DenseCL and SoCo), then finetuned them in the same setting. It is clearly demonstrated in Table 3 that our multi-label self-supervised learning method is superior than all of them, surpassing state-of-the-art dense matching approach DenseCL [39] and object discovery method SoCo [41], both by significant margins. Our MLS also improves supervised learning from $77.5\\%$ mIoU to $79.0\\%$ mIoU and from $77.8\\%$ mIoU to $78.5\\%$ mIoU with PSANet [50] and PSPNet [49], respectively.", + "bbox": [ + 75, + 674, + 468, + 885 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "VOC0712 object detection. Moving on to other dense", + "bbox": [ + 96, + 885, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "prediction tasks, we evaluated the effectiveness of MLS on VOC0712 object detection with Faster R-CNN R50-C4. Since there were missing results for BYOL and MoCo-v2 in this experimental setting, we reproduced both of them for a fair comparison. As shown in Table 4, our MLS surpasses all previous object-centric SSL methods by a large margin. For example, our method is higher than SimCLR by $3.5\\%$ AP and $5.6\\%$ $\\mathrm{AP}_{75}$ metrics. MLS is also better than supervised ImageNet results (an improvement of $1.7\\%$ AP and $2.4\\%$ $\\mathrm{AP}_{75}$ ), showing again the great potential of multi-label self-supervised learning.", + "bbox": [ + 496, + 90, + 890, + 256 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Single- and multi-label classification. Then, we explore how our proposed method behaves on image classification benchmarks. As pointed out by a previous SSL research work [45], various dense matching or unsupervised object discovery based SSL methods usually sacrifice the performance of image classification, in return for high accuracy in dense prediction tasks. In other words, classification is tough for these SSL methods. Therefore, we evaluated MLS on both multi-label (e.g., VOC2007) and single-label classification tasks. As discussed above, we also reproduced the results of MoCo-v2 and DenseCL because MLS has the same architecture with them. It can be found in Table 5 that MLS is consistently better than previous SSL methods, surpassing our baseline MoCo-v2 by a noticeable margin—an improvement of $5.3\\%$ mAP for VOC07 and $3.0\\%$ accuracy for Indoor67. We attribute this gain to the joint embedding property of MLS: since our method is optimized with global features, it can be naturally easier for us to capture image-level information, thus suitable for image classification tasks. However, all SSL methods are generally worse than supervised ImageNet pretraining, showing that supervised pretraining with more pretraining data (ImageNet vs. COCO) still remains a powerful technique for general image classification.", + "bbox": [ + 496, + 258, + 892, + 619 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Ablation studies", + "text_level": 1, + "bbox": [ + 500, + 633, + 661, + 648 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Compare with other loss functions. We first explore if there are other alternatives besides multi-label BCE that can also achieve similar or even better results. An alternative, however, needs to produce multiple positive paradigms in the loss term. We consider kNN softmax adopted in [21, 36], and propose a variant of BCE by disregarding the negative term in Eq. 9 (calling it 'BCE-pos'). As can be seen in Table 6, adding kNN softmax and the BCE-pos loss function besides the InfoNCE loss used in [36] both lead to consistent improvements in all metrics, demonstrating the effectiveness of our hypothesis. Still, they are both inferior to our proposed MLS, showing that pure BCE works better than the variant in scene image self-supervised learning.", + "bbox": [ + 496, + 657, + 890, + 853 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Why keeping two dictionaries? There are two dictionaries $Q_{g}$ and $Q_{z}$ in our pipeline with different functionalities: one for pseudo-labeling and the other for classification.", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "6699", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/85dbcf3644c4e8d1e2329277c74f643a1bbafa309b6036d02310e038bc8c06b3.jpg", + "table_caption": [ + "Table 5. Results on downstream classification, including VOC2007 multi-label and 7 small single-label classification datasets. We reproduced the baseline MoCo-v2 and dense matching approach DenseCL for a fair comparison. The evaluation metric for VOC2007 is mAP while for others is top-1 accuracy. All models were pretrained for 400 epochs on the MS-COCO dataset." + ], + "table_footnote": [], + "table_body": "
MethodDataVOC07CUB200FlowersCarsAircraftIndoorPetsDTD
SupervisedImageNet89.081.396.790.686.758.164.474.7
MoCo-v2COCO80.568.889.687.580.464.179.460.9
DenseCLCOCO83.769.388.688.379.965.480.061.8
MLSCOCO85.871.791.288.581.267.181.963.0
", + "bbox": [ + 142, + 128, + 828, + 227 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/1a49863bf138be562c67d08fa91b1ec77efa36d5fbf25038c2bbc3964ddb7232.jpg", + "table_caption": [ + "Table 6. MS-COCO detection and segmentation results using different pretraining loss functions. The 'kNN' loss was adopted in [36] and the 'BCE-pos' loss means only positive terms of binary cross entropy in Eq. 9 were considered." + ], + "table_footnote": [], + "table_body": "
MethodDetectionSegmentation
APbboxAPbbox50APbbox75APsegAPseg50APseg75
Baseline38.858.342.535.555.537.5
+kNN39.158.742.635.355.837.9
+BCE-pos39.659.443.135.756.538.1
+BCE (ours)40.160.243.936.257.338.6
", + "bbox": [ + 83, + 303, + 464, + 402 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Why not keeping only one for simplicity? We explain this problem through both visualization and quantitative experiments. First, we plot the histogram of scores in Fig. 3, with $g_{1} \\odot Q_{g}$ and $z_{1} \\odot Q_{z}$ representing the backbone and MLP scores, respectively. The backbone scores have witnessed a dramatic change after training, indicating some information the network potentially obtained by SSL. On the other hand, the MLP scores almost always follow a normal distribution, with only slight changes in the mean and variance statistics. Hence, we choose to use the backbone queue $Q_{g}$ for pseudo labeling. The MLP dictionary $Q_{z}$ is used for classification, following the common practice in previous SSL methods [16, 39]. Our choice is also verified by the experiments in Table 7, where using only $Q_{g}$ or $Q_{z}$ is clearly sub-optimal, and worse than our MLS where they are jointly adopted.", + "bbox": [ + 75, + 429, + 468, + 671 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Effect of $k$ . Now we examine how different $k$ values (the number of pseudo positive labels generated) affect the final results of our MLS method. The downstream results of MS-COCO detection and segmentation can be found in Table 8, where a too small and a too large $k$ value both lead to a performance drop. A small $k$ means semantically related images may become false negatives in BCE classification, while a large $k$ will similarly lead to false positives. Our MLS is relatively more robust when $k$ is small. But when $k$ is too large, the accuracy drop is significant. Based on this observation, we choose $k = 20$ by default.", + "bbox": [ + 75, + 672, + 468, + 838 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Effect of queue size and $\\lambda$ . The fourth module we evaluated is the dictionary (queue) size and the combination weight $\\lambda$ in Eq. 10. We pretrained the models on the MS-COCO dataset using MLS and finetuned them for COCO", + "bbox": [ + 75, + 839, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/7a9c9eca5e3cf4a8ba6f7a58e88782c2801610ca2220fc2fdd6b68362370b665.jpg", + "table_caption": [ + "Table 7. Effect of using different dictionaries. $Q_{g}$ only' means the embeddings in $Q_{g}$ and $g_{1}$ are used twice to both generate the pseudo labels $y$ and the logits $p$ (c.f. Fig. 2). $Q_{z}$ only' means only using $Q_{z}$ and $z_{1}$ ." + ], + "table_footnote": [], + "table_body": "
MethodAPbboxAPseg
Qg only39.535.7
Qz only39.836.0
Both Qg and Qz (ours)40.136.2
", + "bbox": [ + 544, + 303, + 848, + 380 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/80074f54810a3d017effe49cfb2ebec578b63fc263a33db80440ea9c3eccf60d.jpg", + "image_caption": [ + "(a) Backbone- and MLP-scores before MLS training" + ], + "image_footnote": [], + "bbox": [ + 514, + 397, + 692, + 486 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2a19ff9a513a71f5cf7da37d8245bbfbc2cec83e335a3c93c7cc03dec0980eb6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 700, + 397, + 879, + 486 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/a94c52afff05cbd64803039d55b779844c5333eeddeb93d421f0eb74964c5255.jpg", + "image_caption": [ + "(b) Backbone- and MLP-scores after MLS training" + ], + "image_footnote": [], + "bbox": [ + 514, + 522, + 692, + 612 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6f0128a02fc4e34003c35bdf99fadcd40b8bb6037709d4d7a3be4a07c69f90e8.jpg", + "image_caption": [ + "Figure 3. Visualization of the score distribution of one sampled COCO image before and after training. The backbone scores and MLS scores are $g_{1} \\odot Q_{g}$ and $z_{1} \\odot Q_{z}$ , respectively. The backbone scores are more indicative compared with MLP scores, thus suitable for pseudo label generation." + ], + "image_footnote": [], + "bbox": [ + 700, + 522, + 879, + 612 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "object detection with Mask R-CNN R50-FPN. As demonstrated in Fig. 5 (a), a too small queue size (e.g., 1024) is detrimental for SSL pretraining, since a small queue means limited representations stored, which is not enough for an image to retrieve its positive neighbors. An overly large dictionary also obtains sub-optimal results, because dictionaries that are too large probably contain many out-of-date embeddings (due to the deque and enqueue mechanism [6]) and might lead to incorrect pseudo labels. And, we also validate the robustness of our MLS by trying multiple $\\lambda$ values. It can be seen in Figure 5 (b) that all $\\lambda$ leads to consistent", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "6700", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/7f3d8336de7861bdc8c1725f779cd6f6ee2aff9bd30c628ba8bb5bb0a3a21bff.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 84, + 93, + 163, + 154 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/ca3be5a0189c0eab400e6dd3b7b772cce4b50ab294fcdcf212fc238c255b8507.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 163, + 93, + 238, + 152 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f5469d6504edab281df347d91c63c13030a8dcf4899eb4121a7a7e3501826bd4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 238, + 93, + 316, + 152 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b1835565a8890d0e8806c0268338ac691fbac84c10a899cd32b709ba1320245f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 316, + 93, + 393, + 152 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/be57618f0d8011c1ea202b09dc8ef24a0a05d1ec67f1881034430f64c474b621.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 393, + 93, + 470, + 152 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9ac278a9144a5ddc059f33cef3fbe89e698e81598119c8f6f7f7825e04defe46.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 84, + 164, + 161, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8e0d4a67b6e247898c8c17c1d8facd672686b5a4a819d56ff8634fadaa25ad49.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 163, + 164, + 238, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c4916859d31468ff6ad8c584dd31f22b2e7b24767f1a019488a68ec6c3e1f8a7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 238, + 164, + 316, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/6a4fe22b409e29c6708f5be2f8f8e32cb2ccf341dbbc07dc03829234e26e0bca.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 316, + 164, + 393, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2312f3659acfa80997667f1057c961a2406567db37eb90678637ebd2db7a489a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 393, + 164, + 470, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/60612bb044c17718cf1e8e0ade96fdcd618d58263465e5e5dc4fa7577d425abe.jpg", + "image_caption": [ + "Figure 4. Visualization of positive pseudo-labels picked up by MLS across images in COCO. For each randomly cropped query image patch, we find the top-4 of its NNs from the dictionary $Q_{g}$ (shown in yellow rectangles). All these rectangles are generated by the random resized crop data augmentation, a standard component in SSL. We record the cropped boxes' coordinates of the embeddings (the query $g_{1}$ and those stored in the dictionary $Q_{g}$ during data augmentation). To be more precise, we first randomly sampled 60 query images. We then randomly sampled 5 query images out of the set of 60 and found their top-4 NNs. In addition, we manually select the worst query image (i.e., semantically most different from its top-4 NNs), which is the right half of the last row. This figure is best viewed in color." + ], + "image_footnote": [], + "bbox": [ + 84, + 234, + 161, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/fddc09f6adb17821e268c1461e8a9ea481547d20c5a4079d732b3b73f2f4bdc9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 163, + 234, + 238, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/84f9fbf1fb314364fac6172849811cefff0dfa22415c24716675703712517f05.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 238, + 234, + 316, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/41d24fb909d35539352cfb1ab38bc84e5f920f640538d6c1388ed75520f738d1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 316, + 234, + 393, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/7996abc27f68f2db0d2b053353a02f5339fa8ea11ca2689f7d09178fb80c3e54.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 393, + 234, + 470, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/d1c2db78e80ba41cdd517092fd292898d98f7f62e7913ce5fa005851d1902d13.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 498, + 93, + 575, + 152 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2524b3d8ab9a7106845fa91c47d6aa0c76084414f61263c5ee005ac110106268.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 576, + 93, + 651, + 152 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e73ec75961cee0f91a764f737bee452a3f3ba060acb0a3de7573dd7492e217b9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 653, + 93, + 728, + 152 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/84fd8e364dde62689201cef0ccd82b7f14c1935363723d274dbfc21269852fda.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 728, + 93, + 805, + 152 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1a3305670d75185600397ada41e1e0224a9726ebd9efe0d86534fa0b50564e13.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 808, + 93, + 883, + 152 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3c337f76ffb327c7abff513255de8b4b508acace0f3ad33d59da48b373242e1b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 498, + 164, + 575, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/69c0a091690357f81696cc8f6a8310bad3c93d55dcf0c4593f01c4c78c28e91c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 576, + 164, + 651, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3dd2b92ec0fe4974d8484cf377a28420dac1b03789cbfae37785184083cab802.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 653, + 164, + 728, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0eda076d75948cba1c47314cf23493f7d40fee4a00523557ce8bc9f4b8e50ef5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 728, + 164, + 805, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/d353752f7ae8901a0c5d7464436a22892cffe8633c6d1aaa2ce9708f7b3b5f70.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 807, + 164, + 883, + 223 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/fca9a93916c41d72ca97b27ac475dd10ea763c472c273fa14c966f9c34ace69e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 498, + 234, + 575, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9cbae051ca70a5af45f0e07a29a58fb9788ba995ee0e2b76e12cae11d424024c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 576, + 234, + 651, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/99b97fca04f959c72918a625c418bf1a608bd2b3ca53b3da67ae599a5d1aa9c3.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 653, + 234, + 728, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/07131323b211613a36fde366dfd55d04f3331c3eaefc88ba550689f55ffdc82e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 728, + 234, + 805, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/dbbc53b140ca3613d6eba5c914ff437195ba2bf31f181872a98cffa620dfa98c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 807, + 234, + 883, + 292 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/c3ffc257d9a48edab5f4f64ce94765018369653fad49bda6d89db796f4b73fab.jpg", + "table_caption": [ + "Table 8. The effect of different $k$ in pseudo label generation as illustrated in Fig. 2 and Eq. 7. All models were pretrained on MS-COCO and finetuned for detection and segmentation." + ], + "table_footnote": [], + "table_body": "
Top kk=1k=5k=20k=40
APbbox39.740.040.139.2
APseg35.936.136.235.4
", + "bbox": [ + 112, + 443, + 433, + 503 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/065d7b6042c005db2a88d0783520b360e157ad692a1863eef03c948215952498.jpg", + "image_caption": [ + "(a) Effect of Queue size", + "Figure 5. Effect of different queue size and $\\lambda$ values (c.f. Eq. 10) in terms of downstream tasks' results. In this paper, we choose 4096 queue size and $\\lambda = 0.5$ by default." + ], + "image_footnote": [], + "bbox": [ + 94, + 527, + 267, + 625 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a61c6b9df60600c11a510b9b79be01ad5746caf678c0b0453c52533a1ac5a7ed.jpg", + "image_caption": [ + "(b) Effect of $\\lambda$" + ], + "image_footnote": [], + "bbox": [ + 279, + 527, + 452, + 625 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "improvement over the baseline $(c.f.$ Table 6), and there is a sweet spot in the choice of $\\lambda$ . Thus, in this paper we choose $\\lambda = 0.5$ by default in our experiment.", + "bbox": [ + 75, + 718, + 467, + 762 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Visualization of positive pseudo-labels. Last but not least, we validate the effectiveness of our MLS pipeline by visualization: are the top $k$ nearest neighbors (NN) picked up from the dictionary $Q_{g}$ indeed semantically similar to the input? Because random resized crop is applied in the SSL pipeline (it is the cropped patch that is sent to the network), we record the cropped location of each image during data augmentation. Then, for each query $g_{1}$ in Fig. 2, we find its top-4 NNs stored in the queue $Q_{g}$ . All these queries", + "bbox": [ + 75, + 763, + 467, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "and NNs are associated with a certain cropped patch, and thus we visualize them with red and yellow rectangles, respectively. As shown in Fig. 4, our MLS backbone effectively captures semantically similar correspondences across the dataset. Specifically, intra-class variance (the first row) and multiple positive partial concepts (the second and third rows) are clearly demonstrated, showing that our motivation in Sec. 1 is valid and that MLS is not only suitable for scene image SSL, but might also be adaptable to image retrieval, as well.", + "bbox": [ + 496, + 405, + 890, + 555 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusions and Limitations", + "text_level": 1, + "bbox": [ + 500, + 571, + 763, + 587 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we argued that scene image self-supervised learning does not necessarily rely on dense matching or unsupervised object discovery methods, and instead proposed our Multi-Label Self-supervised (MLS) learning approach. The key idea in MLS is that a multi-label image contains multiple concepts or objects, hence we need to have multiple positive pairs corresponding to different objects in the input image. Specifically, we create two dictionaries, one for creating pseudo-labels (positive or negative pairs) and the other for distinguishing between them (i.e., a multi-label classification problem). This is the first time that multi-label SSL is cast as a multi-label classification problem, and MLS has been validated by extensive experiments on various benchmarks (e.g., MS-COCO, CityScapes, VOC0712, etc.) and tasks (object detection, image segmentation, single- and multi-label classification).", + "bbox": [ + 496, + 598, + 890, + 838 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "As for limitations, it still remains unclear why the BCE loss alone will cause an unstable training issue. This is a long-lasting and open question as numerous scene image SSL methods [39, 44, 40, 1] also struggle if the InfoNCE", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "6701", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "loss is removed. Hence, these methods (including our MLS) always use their proposed modules in combination with InfoNCE. In the future, we will explore how and why the collapsing phenomenon exists without the normal contrastive loss, and will apply our MLS to single-label image SSL to further explore the adaptability of our method.", + "bbox": [ + 76, + 90, + 472, + 183 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 196, + 174, + 213 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Yutong Bai, Xinlei Chen, Alexander Kirillov, Alan Yuille, and Alexander C. Berg. Point-level region contrast for object detection pre-training. In CVPR, pages 16061-16070, 2022.", + "[2] Yun-Hao Cao and Jianxin Wu. A random CNN sees objects: One inductive bias of CNN and its applications. In AAAI, pages 194-202, 2021.", + "[3] Mathilde Caron, Ishan Misra, Julien Mairal, Priya Goyal, Piotr Bojanowski, and Armand Joulin. Unsupervised learning of visual features by contrasting cluster assignments. 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Springer, 2014." + ], + "bbox": [ + 501, + 92, + 890, + 613 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "6703", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Multi-Label Self-Supervised Learning with Scene Images/d8308065-1607-45e1-b7cf-dd3679dcb186_model.json b/2023/Multi-Label Self-Supervised Learning with Scene Images/d8308065-1607-45e1-b7cf-dd3679dcb186_model.json new file mode 100644 index 0000000000000000000000000000000000000000..f1b07cb46c9481fe8b86355624c0ee7bfec88a68 --- /dev/null +++ b/2023/Multi-Label Self-Supervised Learning with Scene Images/d8308065-1607-45e1-b7cf-dd3679dcb186_model.json @@ -0,0 +1,2574 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.197, + 0.131, + 0.775, + 0.154 + ], + "angle": 0, + "content": "Multi-Label Self-Supervised Learning with Scene Images" + }, + { + "type": "text", + "bbox": [ + 0.273, + 0.181, + 0.697, + 0.234 + ], + "angle": 0, + "content": "Ke Zhu Minghao Fu Jianxin Wu* \nState Key Laboratory for Novel Software Technology \nNanjing University, China" + }, + { + "type": "text", + "bbox": [ + 0.197, + 0.238, + 0.773, + 0.251 + ], + "angle": 0, + "content": "zhuk@lamda.nju.edu.cn, fumh@lamda.nju.edu.cn, wujx2001@nju.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.318, + 0.474, + 0.651 + ], + "angle": 0, + "content": "Self-supervised learning (SSL) methods targeting scene images have seen a rapid growth recently, and they mostly rely on either a dedicated dense matching mechanism or a costly unsupervised object discovery module. This paper shows that instead of hinging on these strenuous operations, quality image representations can be learned by treating scene/multi-label image SSL simply as a multi-label classification problem, which greatly simplifies the learning framework. Specifically, multiple binary pseudo-labels are assigned for each input image by comparing its embeddings with those in two dictionaries, and the network is optimized using the binary cross entropy loss. The proposed method is named Multi-Label Self-supervised learning (MLS). Visualizations qualitatively show that clearly the pseudo-labels by MLS can automatically find semantically similar pseudo-positive pairs across different images to facilitate contrastive learning. MLS learns high quality representations on MS-COCO and achieves state-of-the-art results on classification, detection and segmentation benchmarks. At the same time, MLS is much simpler than existing methods, making it easier to deploy and for further exploration." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.679, + 0.21, + 0.695 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.47, + 0.839 + ], + "angle": 0, + "content": "Self-supervised learning (SSL) methods based on contrastive learning [4, 3] have facilitated numerous downstream tasks. Those [16, 6, 14, 13] that target object-centric images (e.g., ImageNet) are already relatively mature, but inventing SSL methods for scene images (e.g., MS-COCO [23]) gains popularity recently. Since unlabeled scene images (or multi-label images) are more natural [46] and richer in semantics, various SSL methods [39, 45, 19, 40, 20, 44] have successively emerged." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.84, + 0.47, + 0.856 + ], + "angle": 0, + "content": "SSL methods focusing on scene/multi-label images can" + }, + { + "type": "image", + "bbox": [ + 0.527, + 0.288, + 0.871, + 0.445 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.451, + 0.895, + 0.537 + ], + "angle": 0, + "content": "Figure 1. Illustrating our motivation. An image patch cropped from a multi-label image comprises multiple objects. Each object can find similar ('pos') and dissimilar ('neg') images from a large dictionary. The whole image patch is pulled closer to those positive ones and pushed away from the negatives using a BCE loss. See Fig. 4 for positives and negatives chosen by our algorithm." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.566, + 0.895, + 0.718 + ], + "angle": 0, + "content": "be summarized into two categories. One is dense matching, such as DenseCL [39], MaskCo [51] and Self-EMD [24]. They take the features' locations into account to improve the performance on dense prediction tasks. They mostly differ in how the heuristic matching metric is designed. Another branch of work like SoCo [41] and ORL [46] resort to unsupervised object discovery to find local object contents, and learn quality representation with both object- and scene-level semantics. However, they usually involve multi-stage SSL pretraining on top of expensive box generation [35]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.896, + 0.902 + ], + "angle": 0, + "content": "These scene image SSL methods are generally based on the contrastive loss (e.g., InfoNCE [27]), where two randomly augmented views of the same image are forced to be close to each other, and optionally push away views from different images. The loss assumes single-label images [27], but the input are in fact multi-label: hence there is a mismatch between the loss and the data. On one hand, it can be difficult for two views randomly cropped from the same scene image to be exactly matched [39, 47]. On the other hand, there is only one matched positive pair in InfoNCE, while more positive pairs are naturally preferred: a view cropped from a multi-label image likely contains mul" + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.863, + 0.47, + 0.9 + ], + "angle": 0, + "content": "*J. Wu is the corresponding author. This paper was partly supported by the National Natural Science Foundation of China under Grant 62276123 and Grant 61921006." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6694" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.08, + 0.092, + 0.306, + 0.107 + ], + "angle": 0, + "content": "tiple semantic concepts or objects." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.108, + 0.468, + 0.424 + ], + "angle": 0, + "content": "Therefore, this paper proposes a simple yet direct approach towards scene image SSL, named as Multi-Label Self-supervised learning (MLS). We treat each image (or randomly cropped patch) as a semantic bag with multiple objects, then retrieve images sharing similar semantics with any object in the bag from a large image dictionary. Note that an object in a bag is not necessarily within the set of human-annotated categories. As illustrated in Fig. 1, the cropped patch contains person, horse, road and bus, which will be pulled closer to similar images containing any of these objects and be pushed away from those dissimilar ones. Specifically, the patch's embedding produced by a backbone network will select top \\( k \\) similar embeddings as \\( k \\) (pseudo) positive images from a dictionary, and the rest will be negatives. In another dictionary containing images in the same order as the first one, the BCE (binary cross entropy) loss plus these binary pseudo-labels will classify the patch's embedding after an MLP projector using all the images in this second dictionary as classifiers, and generates gradients that optimize the backbone network. This framework is illustrated in Fig. 2." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.426, + 0.468, + 0.575 + ], + "angle": 0, + "content": "Our framework has two benefits. First, the large dictionary has diverse positive samples for any given input, hence provides many quality positive pairs with deformations or intra-class variations [11]. Second, unlike InfoNCE, the BCE loss is not mutually exclusive among classes, hence allows the co-occurrence of multiple classes in one scene image. By applying our SSL method to scene images (e.g., MS-COCO), we achieve state-of-the-art results on object detection, instance segmentation and various classification benchmarks. Our contributions are summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.094, + 0.592, + 0.468, + 0.636 + ], + "angle": 0, + "content": "1. For the first time, we formulate scene image SSL as a multi-label classification, and propose our Multi-Label Self-supervised (MLS) learning approach." + }, + { + "type": "text", + "bbox": [ + 0.093, + 0.651, + 0.468, + 0.708 + ], + "angle": 0, + "content": "2. Unlike previous methods that adopt dense matching or unsupervised object discovery, MLS is simple in concept, and enjoys intuitive visualizations (c.f. Fig. 4) which clearly verifies our motivation." + }, + { + "type": "text", + "bbox": [ + 0.093, + 0.724, + 0.468, + 0.781 + ], + "angle": 0, + "content": "3. Extensive experiments of object detection, instance segmentation and classification on various benchmark datasets, together with ablation studies, clearly demonstrate the effectiveness of our method." + }, + { + "type": "list", + "bbox": [ + 0.093, + 0.592, + 0.468, + 0.781 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.081, + 0.801, + 0.217, + 0.815 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.827, + 0.468, + 0.899 + ], + "angle": 0, + "content": "Traditional SSL methods. Self-supervised learning (SSL) has emerged as a promising direction towards unsupervised representation learning [6]. Early SSL methods [27, 33] are mainly derived from noise contrastive estimation [15]. Later, SSL methods based on contrastive" + }, + { + "type": "text", + "bbox": [ + 0.503, + 0.092, + 0.89, + 0.257 + ], + "angle": 0, + "content": "learning and clustering paradigms have been proved effective, too. Representative methods such as SimCLR [4], MoCo [16], BYOL [14] and SwAV [3] have exhibited both simplicity and generalization ability [36] to various downstream tasks. A set of variants such as Simsiam [7], InfoMin [34] and NNCLR [11] try to simplify, analyze and optimize traditional SSL methods from different aspects. However, all of them mainly focus on pretraining on object-centric images like the ImageNet dataset [32] for image classification (e.g., ImageNet linear evaluation), but pay less attention to dense prediction tasks." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.259, + 0.89, + 0.573 + ], + "angle": 0, + "content": "Scene-image SSL methods. The development of scene (multi-label) image SSL is a diversified process, which mainly contains two branches: dedicated dense feature matching and multi-stage pretraining with unsupervised object discovery. DenseCL [39], PixPro [47], ReSim [44], LEWEL [20] and SetSim [40] all apply the InfoNCE loss in a dense matching manner. They propose dense loss functions in addition to the traditional InfoNCE loss, and their pipelines differ in how the matching metrics are (probably manually) selected. Another branch of methods such as SoCo [41] and ORL [46] try to learn quality feature representation with both scene- and object-level information: they utilize multi-stage pretraining to find correspondence across images with the help of unsupervised object generation methods [35, 54], which suffers from huge computation costs. A recent SSL method [36] that is close to our work proposed kNN-MoCo as an extra module. But, this method is still in a single-label InfoNCE manner and the improvement is small compared to our multi-label MLS (c.f. Table 6). Compared to existing methods, our MLS is novel in concept and simple in implementation." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.576, + 0.89, + 0.8 + ], + "angle": 0, + "content": "Multi-label classification. Multi-label recognition aims to predict the presence or absence of each object class in an input image [48]. Traditional methods are based on three aspects: attention modules [53, 52], correlation matrix [8, 5] and unsupervised box generation [42, 38]. The loss function adopted in this task is mostly binary cross entropy (BCE), which is not mutually exclusive among classes [48], such that the presence of one class does not suppress the existence of others. In this paper, we inherit this unique property of multi-label classification and try to integrate BCE into self-supervised learning on scene images. We adopt the joint image embedding to generate \\(k\\) pseudo-labels, together with the classification logits to calculate the final loss term, which effectively guides the multi-label self-supervised learning." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.817, + 0.589, + 0.831 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.842, + 0.89, + 0.899 + ], + "angle": 0, + "content": "In this section, we start by describing the preliminaries of self-supervised learning, including the InfoNCE loss and its variants. We will then describe the proposed Multi-Label Self-supervised (MLS) learning methods and how the over" + }, + { + "type": "page_number", + "bbox": [ + 0.485, + 0.947, + 0.514, + 0.957 + ], + "angle": 0, + "content": "6695" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.092, + 0.378, + 0.107 + ], + "angle": 0, + "content": "all loss function is formulated and optimized." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.114, + 0.218, + 0.129 + ], + "angle": 0, + "content": "3.1. Preliminaries" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.138, + 0.47, + 0.184 + ], + "angle": 0, + "content": "Self-supervised learning methods, whether contrastive based [16, 14] or clustering based [3], usually rely on the InfoNCE loss [27] or its variants [33]:" + }, + { + "type": "equation", + "bbox": [ + 0.093, + 0.188, + 0.47, + 0.235 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {n c e} = - \\log \\frac {\\exp (q \\cdot k _ {+} / \\tau)}{\\exp (q \\cdot k _ {+} / \\tau) + \\sum_ {k _ {-}} \\exp (q \\cdot k _ {-} / \\tau)}, \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.237, + 0.469, + 0.341 + ], + "angle": 0, + "content": "where \\(q\\) and \\(k_{+}\\) are positive embeddings (similar to \\(z_{1}\\) and \\(z_{2}\\) in Fig. 2) after the multi-layer perception (MLP) projector of two encoders. The negative features \\(k_{-}\\) may come from a memory bank [43], a large dictionary or a queue [6], or the current mini-batch [4]. Negatives may be removed by using additional techniques (e.g., the stop gradient adopted in BYOL [14] and SimSiam [7])." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.342, + 0.469, + 0.462 + ], + "angle": 0, + "content": "Similar with the form of a normal softmax function [53] that is popular in single-label classification, InfoNCE is mutually exclusive among all classes, such that there can only be one positive out of all pseudo concepts. There are variants of InfoNCE (such as SupCon [21]) where more positive pairs are excavated and accumulated, with each item being a sole InfoNCE form. These variants can be summarized as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.467, + 0.469, + 0.521 + ], + "angle": 0, + "content": "\\[\n- \\frac {1}{N _ {p o s}} \\sum_ {i = 1} ^ {N _ {p o s}} \\log \\frac {\\exp \\left(q \\cdot k _ {+} ^ {i} / \\tau\\right)}{\\exp \\left(q \\cdot k _ {+} ^ {i} / \\tau\\right) + \\sum_ {k _ {-}} \\exp \\left(q \\cdot k _ {-} / \\tau\\right)}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.522, + 0.469, + 0.597 + ], + "angle": 0, + "content": "in which the total \\(N_{pos}\\) positives are enumerated over \\(k_{+}^{i}\\). It can indeed alleviate the dilemma of the traditional form by involving more positives, but all these methods mainly focus on supervised learning [21] or lack extensive experiments on large dense prediction tasks [36]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.598, + 0.469, + 0.658 + ], + "angle": 0, + "content": "More importantly, the concept of multi-label learning is not introduced, that is, the classes are still mutually exclusive, which hinders the model from learning quality representations from scene image self-supervised learning." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.665, + 0.387, + 0.682 + ], + "angle": 0, + "content": "3.2. Multi-label self-supervised learning" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.688, + 0.469, + 0.779 + ], + "angle": 0, + "content": "Now, we will introduce the proposed MLS method in detail. As discussed above, previous SSL methods who targeted scene images all adopt loss functions in the single-label form, while in this paper, we aim to reduce the gap between the optimization objective and the unique property of multi-label images." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.779, + 0.469, + 0.824 + ], + "angle": 0, + "content": "We adopt MoCo-v2 [6] as our base structure. Specifically, given an input image \\(I\\), it is first cropped and augmented into two different views:" + }, + { + "type": "equation", + "bbox": [ + 0.233, + 0.829, + 0.469, + 0.852 + ], + "angle": 0, + "content": "\\[\nv _ {1} = \\mathcal {T} (I), \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.231, + 0.849, + 0.317, + 0.864 + ], + "angle": 0, + "content": "\\[\nv _ {2} = \\mathcal {T} ^ {\\prime} (I),\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "where \\(\\mathcal{T}\\) and \\(\\mathcal{T}'\\) are two randomly sampled data augmentations. These two views are then passed through the base" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "encoder \\(\\phi (\\cdot)\\) and a momentum encoder \\(\\phi^m (\\cdot)\\) to get the backbone features \\(g_{1}\\) and \\(g_{2}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.604, + 0.136, + 0.892, + 0.154 + ], + "angle": 0, + "content": "\\[\ng _ {1} = \\phi (v _ {1}), g _ {2} = \\phi^ {m} (v _ {2}), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.166, + 0.892, + 0.214 + ], + "angle": 0, + "content": "in which \\( g_{1}, g_{2} \\in \\mathbb{R}^{d_{g}} \\) (e.g., \\( d_{g} = 2048 \\) in ResNet-50 [18]). Next, the backbone features are both passed through a multi-layer perceptron (MLP) projector \\( f(\\cdot) \\) or \\( f^{m}(\\cdot) \\)" + }, + { + "type": "equation", + "bbox": [ + 0.608, + 0.227, + 0.892, + 0.244 + ], + "angle": 0, + "content": "\\[\nz _ {1} = f \\left(g _ {1}\\right), z _ {2} = f ^ {m} \\left(g _ {2}\\right) \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.258, + 0.892, + 0.333 + ], + "angle": 0, + "content": "to get the final embeddings \\(z_{1},z_{2}\\in \\mathbb{R}^{d_{z}}\\) . Similar to MoCo\\(\\mathrm{v}2\\) that retains a large dictionary \\(Q_{z}\\) (shown in Fig. 2), here we keep two queues \\(Q_{g}\\in \\mathbb{R}^{D\\times d_{g}}\\) and \\(Q_{z}\\in \\mathbb{R}^{D\\times d_{z}}\\) with normalized embeddings coming from \\(g_{2}\\) and \\(z_{2}\\) , respectively." + }, + { + "type": "equation", + "bbox": [ + 0.631, + 0.336, + 0.892, + 0.398 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\frac {g _ {2}}{| | g _ {2} | |} \\stackrel {{E n q u e u e}} {{\\Longrightarrow}} Q _ {g}, \\tag {6} \\\\ \\begin{array}{c} \\frac {z _ {2}}{| | z _ {2} | |} \\overset {E n q u e u e} {\\Longrightarrow} Q _ {z}. \\end{array} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.407, + 0.892, + 0.467 + ], + "angle": 0, + "content": "Note that for simplicity the enqueue and deque operations are not shown in Fig. 2, and that features stored in \\( Q_{g} \\) and \\( Q_{z} \\) are all kept in the same order. embeddings in both queues are L2 normalized." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.469, + 0.892, + 0.575 + ], + "angle": 0, + "content": "Then, the backbone feature \\( g_{1} \\) of view \\( v_{1} \\) picks its top \\( k \\) nearest neighbors from \\( Q_{g} \\) and treats them as containing similar semantics as that in the input image's view \\( v_{1} \\) (e.g., containing at least one object that appears in the input view \\( v_{1} \\)). These nearest neighbors are given pseudo positive labels and all the rest items in \\( Q_{g} \\) are pseudo negatives. This step forms multiple binary pseudo-labels \\( y \\in \\mathbb{R}^{D} \\):" + }, + { + "type": "equation", + "bbox": [ + 0.614, + 0.589, + 0.892, + 0.607 + ], + "angle": 0, + "content": "\\[\ny = I s T o p k \\left(g _ {1} \\odot Q _ {g}\\right), \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.621, + 0.813, + 0.635 + ], + "angle": 0, + "content": "where \\(\\odot\\) is the matrix multiplication operation." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.637, + 0.892, + 0.697 + ], + "angle": 0, + "content": "In the next step, the normalized embeddings inside \\( Q_{z} \\) are treated as normalized classifiers. They are multiplied by the feature \\( z_{1} \\) to produce the logits \\( p \\in \\mathbb{R}^{D} \\), which classify \\( z_{1} \\) into the \\( D \\) pseudo categories:" + }, + { + "type": "equation", + "bbox": [ + 0.646, + 0.712, + 0.892, + 0.728 + ], + "angle": 0, + "content": "\\[\np = z _ {1} \\odot Q _ {z}. \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.742, + 0.892, + 0.788 + ], + "angle": 0, + "content": "Finally, the pseudo labels \\( y \\) and the classified logits interact with each other, and are optimized using the binary cross entropy (BCE) loss," + }, + { + "type": "equation", + "bbox": [ + 0.502, + 0.802, + 0.892, + 0.855 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {m l} = \\frac {- 1}{D} \\sum_ {i = 1} ^ {D} \\left[ y _ {i} \\log \\sigma \\left(\\frac {p _ {i}}{\\tau}\\right) + (1 - y _ {i}) \\log \\left(1 - \\sigma \\left(\\frac {p _ {i}}{\\tau}\\right)\\right) \\right], \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.892, + 0.902 + ], + "angle": 0, + "content": "in which \\(\\tau\\) is a temperature hyperparameter (following MoCo-v2's), and \\(\\sigma(\\cdot)\\) is the sigmoid function [52] that maps the scores to the range \\([0,1]\\)." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6696" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.123, + 0.09, + 0.52, + 0.238 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.568, + 0.109, + 0.846, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.25, + 0.895, + 0.321 + ], + "angle": 0, + "content": "Figure 2. The proposed MLS method. An image \\(I\\) is first augmented to two views and sent to two encoders. The embeddings \\(g_{1}, g_{2} \\in \\mathbb{R}^{d_{g}}\\) and \\(z_{1}, z_{2} \\in \\mathbb{R}^{d_{z}}\\) are features after the backbone and the MLP, respectively. View 2's features (\\(g_{2}\\) and \\(z_{2}\\)) are enqueued to form two dictionaries \\(Q_{g} \\in \\mathbb{R}^{D \\times d_{g}}\\) and \\(Q_{z} \\in \\mathbb{R}^{D \\times d_{z}}\\) in the same order. As shown in the right half, the embedding \\(g_{1}\\) picks its top \\(k\\) nearest embeddings from the queue \\(Q_{g}\\) to produce binary pseudo labels \\(y \\in \\mathbb{R}^{D}\\). Then, the embeddings from \\(Q_{z}\\) are treated as classifiers that calculate the logit \\(p \\in \\mathbb{R}^{D}\\) of \\(z_{1}\\), which is compared against the pseudo-labels \\(y\\) by a BCE loss. Best viewed in color." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.344, + 0.216, + 0.36 + ], + "angle": 0, + "content": "3.3. Optimization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.368, + 0.471, + 0.534 + ], + "angle": 0, + "content": "When we use the multi-label loss \\(\\mathcal{L}_{ml}\\) as the only loss function, we found that empirically the optimization process often faces an unstable training issue. We believe this unstable optimization should be attributed to the adverse interaction between assigning pseudo-labels and learning representations from a poor starting point. High quality embeddings from the queues \\(Q_{g}\\) and \\(Q_{z}\\) cannot be obtained if the pseudo-labels are incorrect. At the same time picking nearest neighbors and classification will surely fail if the enqueued embeddings are misleading (a point which was mentioned in DenseCL [39], too)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.535, + 0.47, + 0.653 + ], + "angle": 0, + "content": "Two strategies easily stabilize the multi-label SSL learning. One is to use InfoNCE alone in the first few epochs to warmup the dictionary \\( Q_{g} \\) and \\( Q_{z} \\). The other remedy is to combine InfoNCE with our multi-label BCE loss during the whole training process, which is widely used in previous methods [39, 1, 40] and easier in implementation. Hence, we adopt this strategy and our overall loss function is formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.206, + 0.656, + 0.469, + 0.671 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathcal {L} _ {n c e} + \\lambda \\mathcal {L} _ {m l}, \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.679, + 0.47, + 0.739 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{nce}\\) is the InfoNCE loss that is adopted in MoCo-v2 (c.f. Eq. 1) and along with many multi-label SSL methods. \\(\\mathcal{L}_{ml}\\) is our multi-label BCE loss (c.f. Eq. 9). The value of combination weight \\(\\lambda\\) is fixed at \\(\\lambda = 0.5\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.74, + 0.469, + 0.77 + ], + "angle": 0, + "content": "The proposed method is abbreviated as MLS (multi-label self-supervised) learning." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.785, + 0.208, + 0.801 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.469, + 0.9 + ], + "angle": 0, + "content": "Now we validate the effectiveness of MLS through extensive experiments. We first describe the settings of our experiments, including datasets for upstream pretraining and downstream finetuning, training details, and the architecture for object detection, instance/semantic segmentation and image classification." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.344, + 0.704, + 0.361 + ], + "angle": 0, + "content": "4.1. Experimental settings" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.369, + 0.892, + 0.596 + ], + "angle": 0, + "content": "Datasets. We adopted the MS-COCO train2017 set [23] for SSL pretraining, which is widely applied in the study of scene image SSL [46, 41, 39]. Note that we did not use ImageNet. For downstream tasks, we conducted experiments on MS-COCO, VOC0712 [12], CityScapes [10] as well as 7 small classification datasets (CUB200 [37], Flowers [26], Cars [22], Aircraft [25], Indoor67 [30], Pets [28] and DTD [9]) following previous SSL methods [2]. Specifically, MS-COCO contains 118,287 and 5000 images for training and validation, respectively. VOC2007 has 5011 and 4952 images in the trainval and test sets, respectively. CityScapes is a semantic segmentation dataset containing 2975 and 500 images for training and validation, respectively. For more information about the 7 small classification datasets, please refer to [2] for a more detailed description." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.598, + 0.892, + 0.808 + ], + "angle": 0, + "content": "Pretraining. We adopted ResNet-50 [18] as our base encoder (c.f. Fig. 2) and mostly follow the structure of MoCoV2. We pretrained our models for 400 or 800 epochs on MSCOCO, set learning rate as 0.3, weight decay as 0.0001. For data augmentation, we adopted random resized crop, color distortion, random gray scale, random flip, etc, following [36, 3]. The queue size \\( D \\) of \\( Q_{g} \\) and \\( Q_{z} \\) was 4096. The temperature \\( \\tau \\) was set as 0.2 and was shared between the InfoNCE loss and our multi-label BCE loss. The dimensionalities of the embeddings \\( g_{1} \\) and \\( z_{1} \\) were 2048 and 256, respectively. For faster convergence, we adjusted the momentum update coefficient to 0.995. With regard to our multi-label BCE loss, the parameter \\( k \\) was set as 20, and the combination coefficient \\( \\lambda \\) was 0.5." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Downstream. We finetuned the pretrained model on various benchmarks, including MS-COCO object detection and instance segmentation, CityScapes semantic segmentation, VOC0712 detection and other classification benchmarks. Specifically, we finetuned on MS-COCO using the Mask-RCNN R50-FPN/C4 [17] architecture for 90k itera" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6697" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.087, + 0.895, + 0.158 + ], + "angle": 0, + "content": "Table 1. Results of COCO detection and segmentation. All SSL models (except those pretrained on ImageNet) were first pretrained on MS-COCO and then finetuned on COCO with Mask R-CNN R50-FPN [17]. Our MLS was pretrained for 400 or 800 epochs for fair comparisons. We reproduced \\(\\mathrm{SoCo}^*\\) with the settings in [41]. Note that SetSim [40] and ReSim [44] are adaptable to scene image pretraining, but only reported ImageNet pretraining results. The column 'Epochs' means the number of pretraining epochs. ORL \\(^{+}\\) [46] needs two pretraining stages (800 epochs each), so the total training time is doubled." + }, + { + "type": "table", + "bbox": [ + 0.156, + 0.159, + 0.817, + 0.398 + ], + "angle": 0, + "content": "
MethodDataEpochsDetectionSegmentation
APbboxAPbbox50APbbox75APsegAPseg50APseg75
Supervised [41]ImageNet9038.959.642.735.456.538.1
ReSim-C4 [44]ImageNet20039.359.743.135.756.738.1
LEWELM [20]ImageNet20040.059.843.736.157.038.7
SetSim [40]ImageNet20040.260.743.936.457.739.0
SoCo* [41]COCO40039.159.142.735.456.037.8
Self-EMD [24]COCO80039.360.142.8---
MoCo-v2 [6]COCO80038.558.142.134.855.337.3
BYOL [14]COCO80038.858.542.235.055.938.1
DenseCL [39]COCO80039.659.343.335.756.538.4
ORL+ [46]COCO160040.360.244.436.357.338.9
MLSCOCO40040.160.243.936.257.338.6
MLSCOCO80040.560.744.536.557.739.1
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.422, + 0.473, + 0.606 + ], + "angle": 0, + "content": "tions. For VOC0712, we finetuned for 24k iterations with Faster-RCNN R50-C4 [31]. For CityScapes semantic segmentation, we adopted PSANet [50] and PSPNet [49] for 40k iterations. For classification, we chose VOC2007 for multi-label recognition and finetuned 120 epochs on 7 small classification datasets. We ran 3 times on VOC detection and 2 runs on CityScapes since these results have relatively large variations. Following previous studies, the evaluation metrics for detection, segmentation and classification are AP, mIoU/mAcc and top-1 accuracy, respectively. All the experiments were conducted with RTX 3090 GPUs in the PyTorch [29] framework." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.618, + 0.438, + 0.635 + ], + "angle": 0, + "content": "4.2. COCO detection and segmentation results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.643, + 0.47, + 0.825 + ], + "angle": 0, + "content": "We first evaluated downstream performance on MS-COCO object detection and instance segmentation. Following previous work, we used Mask R-CNN R50-FPN for finetuning. The results is in Table 1. DenseCL [39] and Self-EMD [24] are those adopting dense matching, while SoCo [41] and ORL [46] both resort to the unsupervised object discovery method Selective Search [35]. For a fair comparison, we reproduced SoCo's results since it was originally pretrained on \\(\\mathrm{COCO + }\\) [41] (which is based on COCO but has more unlabeled data). Note that ReSim-C4 [44] and SetSim [40] are suitable for scene image pretraining, but only ImageNet results were reported." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.471, + 0.903 + ], + "angle": 0, + "content": "As shown in Table 1, with only 400 epochs of pretraining, our MLS is almost better than all counterparts (e.g., DenseCL, SoCo, LEWEL [20]) and surpasses supervised results by \\(1.2\\%\\) APbbox and \\(0.8\\%\\) APseg. With the standard 800 epochs of pretraining, MLS is better than all previous" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.419, + 0.892, + 0.474 + ], + "angle": 0, + "content": "Table 2. Results on COCO with the Mask R-CNN R50-C4 detector. 'Data' stands for the pretraining dataset. 'CC' and 'IN' means COCO and ImageNet, respectively. All SSL models were pretrained for 400 epochs on MS-COCO." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.474, + 0.888, + 0.622 + ], + "angle": 0, + "content": "
MethodDataDetectionSegmentation
APbboxAPbbox50APbbox75APsegAPseg50APseg75
Random-26.444.027.829.346.930.8
SupervisedIN38.158.141.133.254.835.0
BYOLCC36.956.739.432.453.534.3
MoCo-v2CC37.356.740.432.853.534.9
SoCo*CC36.956.239.732.453.034.5
DenseCLCC38.357.941.433.554.435.7
MLSCC38.658.341.533.855.136.0
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.653, + 0.892, + 0.715 + ], + "angle": 0, + "content": "scene image SSL methods. This further verifies our motivation: formulating scene image self-supervised learning as a multi-label classification is both simpler in concept and effective in performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.716, + 0.892, + 0.809 + ], + "angle": 0, + "content": "We also tried the Mask R-CNN R50-C4 structure. Since there are relatively less SSL results based on this structure, we reproduced supervised learning, BYOL [14], MoCoV2 [6], SoCo [41] and DenseCL [39] methods by pretraining and finetuning on MS-COCO. To compare fairly, all these SSL models were pretrained for 400 epochs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.895, + 0.903 + ], + "angle": 0, + "content": "As can be found in Table 2, our MLS surpasses all previous self-supervised learning methods like SoCo [41] and DenseCL [39], despite being much simpler than them. Note that SoCo needs unsupervised box generation and multiple auxiliary loss functions. Our MLS also achieves better results than supervised ImageNet pretraining, with an" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6698" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.088, + 0.47, + 0.143 + ], + "angle": 0, + "content": "Table 3. Results of CityScapes semantic segmentation using two different segmentation pipelines (PSANet [50] and PSPNet [49]). 'Data' stands for the pretraining dataset. 'CC' and 'IN' means COCO and ImageNet, respectively." + }, + { + "type": "table", + "bbox": [ + 0.093, + 0.143, + 0.455, + 0.282 + ], + "angle": 0, + "content": "
MethodDataPSANetPSPNet
mIoUmAccaAccmIoUmAccaAcc
SupervisedIN77.586.695.977.886.795.9
BYOLCC77.686.695.976.985.995.9
MoCo-v2CC76.885.895.876.885.495.8
DenseCLCC77.686.696.077.686.395.9
SoCoCC76.385.395.876.585.395.8
MLSCC79.087.396.278.586.696.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.293, + 0.47, + 0.348 + ], + "angle": 0, + "content": "Table 4. Results of VOC0712 object detection using the Faster-RCNN R50-C4 object detector. All SSL models were pretrained on MS-COCO for 800 epochs. BYOL and MoCo-v2 results were reproduced by us." + }, + { + "type": "table", + "bbox": [ + 0.093, + 0.348, + 0.455, + 0.527 + ], + "angle": 0, + "content": "
MethodDataAP\\( AP_{50} \\)\\( AP_{75} \\)
Random-32.859.031.6
SupervisedImageNet53.381.058.8
SwAV [3]ImageNet45.177.446.5
SimCLR [4]ImageNet51.579.455.6
SoCo* [41]COCO51.778.657.2
Self-EMD [24]COCO53.080.058.6
BYOLCOCO51.780.256.4
MoCo-v2COCO53.780.059.5
MLSCOCO55.081.661.2
" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.551, + 0.47, + 0.583 + ], + "angle": 0, + "content": "improvement of \\(0.5\\%\\) \\(\\mathrm{AP}^{bbox}\\) and \\(0.6\\%\\) \\(\\mathrm{AP}^{seg}\\) for object detection and instance segmentation, respectively." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.591, + 0.25, + 0.608 + ], + "angle": 0, + "content": "4.3. Transfer learning" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.614, + 0.469, + 0.674 + ], + "angle": 0, + "content": "Next, we test how our MLS method performs on various transfer learning tasks, including CityScapes semantic segmentation, VOC0712 object detection and (multi-label) classification." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.675, + 0.469, + 0.886 + ], + "angle": 0, + "content": "CityScapes semantic segmentation. We first transferred pretrained models to CityScapes [10] semantic segmentation. Because relatively few SSL methods worked on this benchmark and the segmentation architecture generally differed, we first reproduced several SSL methods (BYOL, MoCo-v2, DenseCL and SoCo), then finetuned them in the same setting. It is clearly demonstrated in Table 3 that our multi-label self-supervised learning method is superior than all of them, surpassing state-of-the-art dense matching approach DenseCL [39] and object discovery method SoCo [41], both by significant margins. Our MLS also improves supervised learning from \\(77.5\\%\\) mIoU to \\(79.0\\%\\) mIoU and from \\(77.8\\%\\) mIoU to \\(78.5\\%\\) mIoU with PSANet [50] and PSPNet [49], respectively." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.469, + 0.901 + ], + "angle": 0, + "content": "VOC0712 object detection. Moving on to other dense" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.257 + ], + "angle": 0, + "content": "prediction tasks, we evaluated the effectiveness of MLS on VOC0712 object detection with Faster R-CNN R50-C4. Since there were missing results for BYOL and MoCo-v2 in this experimental setting, we reproduced both of them for a fair comparison. As shown in Table 4, our MLS surpasses all previous object-centric SSL methods by a large margin. For example, our method is higher than SimCLR by \\(3.5\\%\\) AP and \\(5.6\\%\\) \\(\\mathrm{AP}_{75}\\) metrics. MLS is also better than supervised ImageNet results (an improvement of \\(1.7\\%\\) AP and \\(2.4\\%\\) \\(\\mathrm{AP}_{75}\\)), showing again the great potential of multi-label self-supervised learning." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.259, + 0.893, + 0.621 + ], + "angle": 0, + "content": "Single- and multi-label classification. Then, we explore how our proposed method behaves on image classification benchmarks. As pointed out by a previous SSL research work [45], various dense matching or unsupervised object discovery based SSL methods usually sacrifice the performance of image classification, in return for high accuracy in dense prediction tasks. In other words, classification is tough for these SSL methods. Therefore, we evaluated MLS on both multi-label (e.g., VOC2007) and single-label classification tasks. As discussed above, we also reproduced the results of MoCo-v2 and DenseCL because MLS has the same architecture with them. It can be found in Table 5 that MLS is consistently better than previous SSL methods, surpassing our baseline MoCo-v2 by a noticeable margin—an improvement of \\(5.3\\%\\) mAP for VOC07 and \\(3.0\\%\\) accuracy for Indoor67. We attribute this gain to the joint embedding property of MLS: since our method is optimized with global features, it can be naturally easier for us to capture image-level information, thus suitable for image classification tasks. However, all SSL methods are generally worse than supervised ImageNet pretraining, showing that supervised pretraining with more pretraining data (ImageNet vs. COCO) still remains a powerful technique for general image classification." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.634, + 0.662, + 0.649 + ], + "angle": 0, + "content": "4.4. Ablation studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.658, + 0.892, + 0.854 + ], + "angle": 0, + "content": "Compare with other loss functions. We first explore if there are other alternatives besides multi-label BCE that can also achieve similar or even better results. An alternative, however, needs to produce multiple positive paradigms in the loss term. We consider kNN softmax adopted in [21, 36], and propose a variant of BCE by disregarding the negative term in Eq. 9 (calling it 'BCE-pos'). As can be seen in Table 6, adding kNN softmax and the BCE-pos loss function besides the InfoNCE loss used in [36] both lead to consistent improvements in all metrics, demonstrating the effectiveness of our hypothesis. Still, they are both inferior to our proposed MLS, showing that pure BCE works better than the variant in scene image self-supervised learning." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Why keeping two dictionaries? There are two dictionaries \\( Q_{g} \\) and \\( Q_{z} \\) in our pipeline with different functionalities: one for pseudo-labeling and the other for classification." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6699" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.087, + 0.895, + 0.129 + ], + "angle": 0, + "content": "Table 5. Results on downstream classification, including VOC2007 multi-label and 7 small single-label classification datasets. We reproduced the baseline MoCo-v2 and dense matching approach DenseCL for a fair comparison. The evaluation metric for VOC2007 is mAP while for others is top-1 accuracy. All models were pretrained for 400 epochs on the MS-COCO dataset." + }, + { + "type": "table", + "bbox": [ + 0.143, + 0.13, + 0.83, + 0.228 + ], + "angle": 0, + "content": "
MethodDataVOC07CUB200FlowersCarsAircraftIndoorPetsDTD
SupervisedImageNet89.081.396.790.686.758.164.474.7
MoCo-v2COCO80.568.889.687.580.464.179.460.9
DenseCLCOCO83.769.388.688.379.965.480.061.8
MLSCOCO85.871.791.288.581.267.181.963.0
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.248, + 0.47, + 0.304 + ], + "angle": 0, + "content": "Table 6. MS-COCO detection and segmentation results using different pretraining loss functions. The 'kNN' loss was adopted in [36] and the 'BCE-pos' loss means only positive terms of binary cross entropy in Eq. 9 were considered." + }, + { + "type": "table", + "bbox": [ + 0.084, + 0.304, + 0.465, + 0.404 + ], + "angle": 0, + "content": "
MethodDetectionSegmentation
APbboxAPbbox50APbbox75APsegAPseg50APseg75
Baseline38.858.342.535.555.537.5
+kNN39.158.742.635.355.837.9
+BCE-pos39.659.443.135.756.538.1
+BCE (ours)40.160.243.936.257.338.6
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.43, + 0.47, + 0.672 + ], + "angle": 0, + "content": "Why not keeping only one for simplicity? We explain this problem through both visualization and quantitative experiments. First, we plot the histogram of scores in Fig. 3, with \\( g_{1} \\odot Q_{g} \\) and \\( z_{1} \\odot Q_{z} \\) representing the backbone and MLP scores, respectively. The backbone scores have witnessed a dramatic change after training, indicating some information the network potentially obtained by SSL. On the other hand, the MLP scores almost always follow a normal distribution, with only slight changes in the mean and variance statistics. Hence, we choose to use the backbone queue \\( Q_{g} \\) for pseudo labeling. The MLP dictionary \\( Q_{z} \\) is used for classification, following the common practice in previous SSL methods [16, 39]. Our choice is also verified by the experiments in Table 7, where using only \\( Q_{g} \\) or \\( Q_{z} \\) is clearly sub-optimal, and worse than our MLS where they are jointly adopted." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.673, + 0.47, + 0.839 + ], + "angle": 0, + "content": "Effect of \\( k \\). Now we examine how different \\( k \\) values (the number of pseudo positive labels generated) affect the final results of our MLS method. The downstream results of MS-COCO detection and segmentation can be found in Table 8, where a too small and a too large \\( k \\) value both lead to a performance drop. A small \\( k \\) means semantically related images may become false negatives in BCE classification, while a large \\( k \\) will similarly lead to false positives. Our MLS is relatively more robust when \\( k \\) is small. But when \\( k \\) is too large, the accuracy drop is significant. Based on this observation, we choose \\( k = 20 \\) by default." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Effect of queue size and \\(\\lambda\\). The fourth module we evaluated is the dictionary (queue) size and the combination weight \\(\\lambda\\) in Eq. 10. We pretrained the models on the MS-COCO dataset using MLS and finetuned them for COCO" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.248, + 0.892, + 0.304 + ], + "angle": 0, + "content": "Table 7. Effect of using different dictionaries. \\( Q_{g} \\) only' means the embeddings in \\( Q_{g} \\) and \\( g_{1} \\) are used twice to both generate the pseudo labels \\( y \\) and the logits \\( p \\) (c.f. Fig. 2). \\( Q_{z} \\) only' means only using \\( Q_{z} \\) and \\( z_{1} \\)." + }, + { + "type": "table", + "bbox": [ + 0.545, + 0.304, + 0.849, + 0.381 + ], + "angle": 0, + "content": "
MethodAPbboxAPseg
Qg only39.535.7
Qz only39.836.0
Both Qg and Qz (ours)40.136.2
" + }, + { + "type": "image", + "bbox": [ + 0.515, + 0.398, + 0.693, + 0.487 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.702, + 0.398, + 0.88, + 0.487 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.557, + 0.497, + 0.836, + 0.51 + ], + "angle": 0, + "content": "(a) Backbone- and MLP-scores before MLS training" + }, + { + "type": "image", + "bbox": [ + 0.515, + 0.523, + 0.693, + 0.613 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.702, + 0.523, + 0.88, + 0.613 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.561, + 0.622, + 0.833, + 0.635 + ], + "angle": 0, + "content": "(b) Backbone- and MLP-scores after MLS training" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.638, + 0.892, + 0.709 + ], + "angle": 0, + "content": "Figure 3. Visualization of the score distribution of one sampled COCO image before and after training. The backbone scores and MLS scores are \\( g_{1} \\odot Q_{g} \\) and \\( z_{1} \\odot Q_{z} \\), respectively. The backbone scores are more indicative compared with MLP scores, thus suitable for pseudo label generation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "object detection with Mask R-CNN R50-FPN. As demonstrated in Fig. 5 (a), a too small queue size (e.g., 1024) is detrimental for SSL pretraining, since a small queue means limited representations stored, which is not enough for an image to retrieve its positive neighbors. An overly large dictionary also obtains sub-optimal results, because dictionaries that are too large probably contain many out-of-date embeddings (due to the deque and enqueue mechanism [6]) and might lead to incorrect pseudo labels. And, we also validate the robustness of our MLS by trying multiple \\(\\lambda\\) values. It can be seen in Figure 5 (b) that all \\(\\lambda\\) leads to consistent" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "6700" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.094, + 0.165, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.165, + 0.094, + 0.24, + 0.154 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.24, + 0.094, + 0.317, + 0.154 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.318, + 0.094, + 0.394, + 0.154 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.395, + 0.094, + 0.472, + 0.154 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.086, + 0.165, + 0.163, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.164, + 0.165, + 0.24, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.24, + 0.165, + 0.317, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.318, + 0.165, + 0.394, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.395, + 0.165, + 0.472, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.086, + 0.235, + 0.163, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.164, + 0.235, + 0.24, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.24, + 0.235, + 0.317, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.318, + 0.235, + 0.394, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.395, + 0.235, + 0.472, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.499, + 0.094, + 0.576, + 0.154 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.577, + 0.094, + 0.653, + 0.154 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.654, + 0.094, + 0.729, + 0.154 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.73, + 0.094, + 0.807, + 0.154 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.81, + 0.094, + 0.885, + 0.154 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.499, + 0.165, + 0.576, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.577, + 0.165, + 0.653, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.654, + 0.165, + 0.729, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.73, + 0.165, + 0.806, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.808, + 0.165, + 0.884, + 0.224 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.499, + 0.235, + 0.576, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.577, + 0.235, + 0.653, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.654, + 0.235, + 0.729, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.73, + 0.235, + 0.806, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.808, + 0.235, + 0.884, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.298, + 0.892, + 0.381 + ], + "angle": 0, + "content": "Figure 4. Visualization of positive pseudo-labels picked up by MLS across images in COCO. For each randomly cropped query image patch, we find the top-4 of its NNs from the dictionary \\( Q_{g} \\) (shown in yellow rectangles). All these rectangles are generated by the random resized crop data augmentation, a standard component in SSL. We record the cropped boxes' coordinates of the embeddings (the query \\( g_{1} \\) and those stored in the dictionary \\( Q_{g} \\) during data augmentation). To be more precise, we first randomly sampled 60 query images. We then randomly sampled 5 query images out of the set of 60 and found their top-4 NNs. In addition, we manually select the worst query image (i.e., semantically most different from its top-4 NNs), which is the right half of the last row. This figure is best viewed in color." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.403, + 0.468, + 0.444 + ], + "angle": 0, + "content": "Table 8. The effect of different \\( k \\) in pseudo label generation as illustrated in Fig. 2 and Eq. 7. All models were pretrained on MS-COCO and finetuned for detection and segmentation." + }, + { + "type": "table", + "bbox": [ + 0.114, + 0.444, + 0.434, + 0.505 + ], + "angle": 0, + "content": "
Top kk=1k=5k=20k=40
APbbox39.740.040.139.2
APseg35.936.136.235.4
" + }, + { + "type": "image", + "bbox": [ + 0.095, + 0.528, + 0.268, + 0.626 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.116, + 0.634, + 0.246, + 0.646 + ], + "angle": 0, + "content": "(a) Effect of Queue size" + }, + { + "type": "image", + "bbox": [ + 0.28, + 0.528, + 0.453, + 0.626 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.326, + 0.634, + 0.408, + 0.645 + ], + "angle": 0, + "content": "(b) Effect of \\(\\lambda\\)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.65, + 0.468, + 0.692 + ], + "angle": 0, + "content": "Figure 5. Effect of different queue size and \\(\\lambda\\) values (c.f. Eq. 10) in terms of downstream tasks' results. In this paper, we choose 4096 queue size and \\(\\lambda = 0.5\\) by default." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.719, + 0.468, + 0.763 + ], + "angle": 0, + "content": "improvement over the baseline \\((c.f.\\) Table 6), and there is a sweet spot in the choice of \\(\\lambda\\). Thus, in this paper we choose \\(\\lambda = 0.5\\) by default in our experiment." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.468, + 0.902 + ], + "angle": 0, + "content": "Visualization of positive pseudo-labels. Last but not least, we validate the effectiveness of our MLS pipeline by visualization: are the top \\(k\\) nearest neighbors (NN) picked up from the dictionary \\(Q_{g}\\) indeed semantically similar to the input? Because random resized crop is applied in the SSL pipeline (it is the cropped patch that is sent to the network), we record the cropped location of each image during data augmentation. Then, for each query \\(g_{1}\\) in Fig. 2, we find its top-4 NNs stored in the queue \\(Q_{g}\\). All these queries" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.406, + 0.892, + 0.556 + ], + "angle": 0, + "content": "and NNs are associated with a certain cropped patch, and thus we visualize them with red and yellow rectangles, respectively. As shown in Fig. 4, our MLS backbone effectively captures semantically similar correspondences across the dataset. Specifically, intra-class variance (the first row) and multiple positive partial concepts (the second and third rows) are clearly demonstrated, showing that our motivation in Sec. 1 is valid and that MLS is not only suitable for scene image SSL, but might also be adaptable to image retrieval, as well." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.572, + 0.764, + 0.588 + ], + "angle": 0, + "content": "5. Conclusions and Limitations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.892, + 0.839 + ], + "angle": 0, + "content": "In this paper, we argued that scene image self-supervised learning does not necessarily rely on dense matching or unsupervised object discovery methods, and instead proposed our Multi-Label Self-supervised (MLS) learning approach. The key idea in MLS is that a multi-label image contains multiple concepts or objects, hence we need to have multiple positive pairs corresponding to different objects in the input image. Specifically, we create two dictionaries, one for creating pseudo-labels (positive or negative pairs) and the other for distinguishing between them (i.e., a multi-label classification problem). This is the first time that multi-label SSL is cast as a multi-label classification problem, and MLS has been validated by extensive experiments on various benchmarks (e.g., MS-COCO, CityScapes, VOC0712, etc.) and tasks (object detection, image segmentation, single- and multi-label classification)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "As for limitations, it still remains unclear why the BCE loss alone will cause an unstable training issue. This is a long-lasting and open question as numerous scene image SSL methods [39, 44, 40, 1] also struggle if the InfoNCE" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "6701" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.184 + ], + "angle": 0, + "content": "loss is removed. Hence, these methods (including our MLS) always use their proposed modules in combination with InfoNCE. In the future, we will explore how and why the collapsing phenomenon exists without the normal contrastive loss, and will apply our MLS to single-label image SSL to further explore the adaptability of our method." + }, + { + "type": "title", + "bbox": [ + 0.08, + 0.198, + 0.175, + 0.214 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.224, + 0.47, + 0.266 + ], + "angle": 0, + "content": "[1] Yutong Bai, Xinlei Chen, Alexander Kirillov, Alan Yuille, and Alexander C. Berg. Point-level region contrast for object detection pre-training. In CVPR, pages 16061-16070, 2022." + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.268, + 0.469, + 0.31 + ], + "angle": 0, + "content": "[2] Yun-Hao Cao and Jianxin Wu. A random CNN sees objects: One inductive bias of CNN and its applications. 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Springer, 2014." + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.614 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.515, + 0.956 + ], + "angle": 0, + "content": "6703" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-Label Self-Supervised Learning with Scene Images/d8308065-1607-45e1-b7cf-dd3679dcb186_origin.pdf b/2023/Multi-Label Self-Supervised Learning with Scene Images/d8308065-1607-45e1-b7cf-dd3679dcb186_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..b50f0c8069a0dfbdfd5a9e4a7c86be6637d525e7 --- /dev/null +++ b/2023/Multi-Label Self-Supervised Learning with Scene Images/d8308065-1607-45e1-b7cf-dd3679dcb186_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:93f281c39e65eb1b3d288b6e7d15f43879b126f89b5fcd8d4eaf76948a422cb8 +size 2599100 diff --git a/2023/Multi-Label Self-Supervised Learning with Scene Images/full.md b/2023/Multi-Label Self-Supervised Learning with Scene Images/full.md new file mode 100644 index 0000000000000000000000000000000000000000..3695e3a59400a51aa186575d1b5fac4b86c7fcdb --- /dev/null +++ b/2023/Multi-Label Self-Supervised Learning with Scene Images/full.md @@ -0,0 +1,388 @@ +# Multi-Label Self-Supervised Learning with Scene Images + +Ke Zhu Minghao Fu Jianxin Wu* +State Key Laboratory for Novel Software Technology +Nanjing University, China + +zhuk@lamda.nju.edu.cn, fumh@lamda.nju.edu.cn, wujx2001@nju.edu.cn + +# Abstract + +Self-supervised learning (SSL) methods targeting scene images have seen a rapid growth recently, and they mostly rely on either a dedicated dense matching mechanism or a costly unsupervised object discovery module. This paper shows that instead of hinging on these strenuous operations, quality image representations can be learned by treating scene/multi-label image SSL simply as a multi-label classification problem, which greatly simplifies the learning framework. Specifically, multiple binary pseudo-labels are assigned for each input image by comparing its embeddings with those in two dictionaries, and the network is optimized using the binary cross entropy loss. The proposed method is named Multi-Label Self-supervised learning (MLS). Visualizations qualitatively show that clearly the pseudo-labels by MLS can automatically find semantically similar pseudo-positive pairs across different images to facilitate contrastive learning. MLS learns high quality representations on MS-COCO and achieves state-of-the-art results on classification, detection and segmentation benchmarks. At the same time, MLS is much simpler than existing methods, making it easier to deploy and for further exploration. + +# 1. Introduction + +Self-supervised learning (SSL) methods based on contrastive learning [4, 3] have facilitated numerous downstream tasks. Those [16, 6, 14, 13] that target object-centric images (e.g., ImageNet) are already relatively mature, but inventing SSL methods for scene images (e.g., MS-COCO [23]) gains popularity recently. Since unlabeled scene images (or multi-label images) are more natural [46] and richer in semantics, various SSL methods [39, 45, 19, 40, 20, 44] have successively emerged. + +SSL methods focusing on scene/multi-label images can + +![](images/8a89928182d88d08553e7739a6be98cb8179207c88e6de7702b21823f2834190.jpg) +Figure 1. Illustrating our motivation. An image patch cropped from a multi-label image comprises multiple objects. Each object can find similar ('pos') and dissimilar ('neg') images from a large dictionary. The whole image patch is pulled closer to those positive ones and pushed away from the negatives using a BCE loss. See Fig. 4 for positives and negatives chosen by our algorithm. + +be summarized into two categories. One is dense matching, such as DenseCL [39], MaskCo [51] and Self-EMD [24]. They take the features' locations into account to improve the performance on dense prediction tasks. They mostly differ in how the heuristic matching metric is designed. Another branch of work like SoCo [41] and ORL [46] resort to unsupervised object discovery to find local object contents, and learn quality representation with both object- and scene-level semantics. However, they usually involve multi-stage SSL pretraining on top of expensive box generation [35]. + +These scene image SSL methods are generally based on the contrastive loss (e.g., InfoNCE [27]), where two randomly augmented views of the same image are forced to be close to each other, and optionally push away views from different images. The loss assumes single-label images [27], but the input are in fact multi-label: hence there is a mismatch between the loss and the data. On one hand, it can be difficult for two views randomly cropped from the same scene image to be exactly matched [39, 47]. On the other hand, there is only one matched positive pair in InfoNCE, while more positive pairs are naturally preferred: a view cropped from a multi-label image likely contains mul + +tiple semantic concepts or objects. + +Therefore, this paper proposes a simple yet direct approach towards scene image SSL, named as Multi-Label Self-supervised learning (MLS). We treat each image (or randomly cropped patch) as a semantic bag with multiple objects, then retrieve images sharing similar semantics with any object in the bag from a large image dictionary. Note that an object in a bag is not necessarily within the set of human-annotated categories. As illustrated in Fig. 1, the cropped patch contains person, horse, road and bus, which will be pulled closer to similar images containing any of these objects and be pushed away from those dissimilar ones. Specifically, the patch's embedding produced by a backbone network will select top $k$ similar embeddings as $k$ (pseudo) positive images from a dictionary, and the rest will be negatives. In another dictionary containing images in the same order as the first one, the BCE (binary cross entropy) loss plus these binary pseudo-labels will classify the patch's embedding after an MLP projector using all the images in this second dictionary as classifiers, and generates gradients that optimize the backbone network. This framework is illustrated in Fig. 2. + +Our framework has two benefits. First, the large dictionary has diverse positive samples for any given input, hence provides many quality positive pairs with deformations or intra-class variations [11]. Second, unlike InfoNCE, the BCE loss is not mutually exclusive among classes, hence allows the co-occurrence of multiple classes in one scene image. By applying our SSL method to scene images (e.g., MS-COCO), we achieve state-of-the-art results on object detection, instance segmentation and various classification benchmarks. Our contributions are summarized as follows: + +1. For the first time, we formulate scene image SSL as a multi-label classification, and propose our Multi-Label Self-supervised (MLS) learning approach. +2. Unlike previous methods that adopt dense matching or unsupervised object discovery, MLS is simple in concept, and enjoys intuitive visualizations (c.f. Fig. 4) which clearly verifies our motivation. +3. Extensive experiments of object detection, instance segmentation and classification on various benchmark datasets, together with ablation studies, clearly demonstrate the effectiveness of our method. + +# 2. Related Work + +Traditional SSL methods. Self-supervised learning (SSL) has emerged as a promising direction towards unsupervised representation learning [6]. Early SSL methods [27, 33] are mainly derived from noise contrastive estimation [15]. Later, SSL methods based on contrastive + +learning and clustering paradigms have been proved effective, too. Representative methods such as SimCLR [4], MoCo [16], BYOL [14] and SwAV [3] have exhibited both simplicity and generalization ability [36] to various downstream tasks. A set of variants such as Simsiam [7], InfoMin [34] and NNCLR [11] try to simplify, analyze and optimize traditional SSL methods from different aspects. However, all of them mainly focus on pretraining on object-centric images like the ImageNet dataset [32] for image classification (e.g., ImageNet linear evaluation), but pay less attention to dense prediction tasks. + +Scene-image SSL methods. The development of scene (multi-label) image SSL is a diversified process, which mainly contains two branches: dedicated dense feature matching and multi-stage pretraining with unsupervised object discovery. DenseCL [39], PixPro [47], ReSim [44], LEWEL [20] and SetSim [40] all apply the InfoNCE loss in a dense matching manner. They propose dense loss functions in addition to the traditional InfoNCE loss, and their pipelines differ in how the matching metrics are (probably manually) selected. Another branch of methods such as SoCo [41] and ORL [46] try to learn quality feature representation with both scene- and object-level information: they utilize multi-stage pretraining to find correspondence across images with the help of unsupervised object generation methods [35, 54], which suffers from huge computation costs. A recent SSL method [36] that is close to our work proposed kNN-MoCo as an extra module. But, this method is still in a single-label InfoNCE manner and the improvement is small compared to our multi-label MLS (c.f. Table 6). Compared to existing methods, our MLS is novel in concept and simple in implementation. + +Multi-label classification. Multi-label recognition aims to predict the presence or absence of each object class in an input image [48]. Traditional methods are based on three aspects: attention modules [53, 52], correlation matrix [8, 5] and unsupervised box generation [42, 38]. The loss function adopted in this task is mostly binary cross entropy (BCE), which is not mutually exclusive among classes [48], such that the presence of one class does not suppress the existence of others. In this paper, we inherit this unique property of multi-label classification and try to integrate BCE into self-supervised learning on scene images. We adopt the joint image embedding to generate $k$ pseudo-labels, together with the classification logits to calculate the final loss term, which effectively guides the multi-label self-supervised learning. + +# 3. Method + +In this section, we start by describing the preliminaries of self-supervised learning, including the InfoNCE loss and its variants. We will then describe the proposed Multi-Label Self-supervised (MLS) learning methods and how the over + +all loss function is formulated and optimized. + +# 3.1. Preliminaries + +Self-supervised learning methods, whether contrastive based [16, 14] or clustering based [3], usually rely on the InfoNCE loss [27] or its variants [33]: + +$$ +\mathcal {L} _ {n c e} = - \log \frac {\exp (q \cdot k _ {+} / \tau)}{\exp (q \cdot k _ {+} / \tau) + \sum_ {k _ {-}} \exp (q \cdot k _ {-} / \tau)}, \tag {1} +$$ + +where $q$ and $k_{+}$ are positive embeddings (similar to $z_{1}$ and $z_{2}$ in Fig. 2) after the multi-layer perception (MLP) projector of two encoders. The negative features $k_{-}$ may come from a memory bank [43], a large dictionary or a queue [6], or the current mini-batch [4]. Negatives may be removed by using additional techniques (e.g., the stop gradient adopted in BYOL [14] and SimSiam [7]). + +Similar with the form of a normal softmax function [53] that is popular in single-label classification, InfoNCE is mutually exclusive among all classes, such that there can only be one positive out of all pseudo concepts. There are variants of InfoNCE (such as SupCon [21]) where more positive pairs are excavated and accumulated, with each item being a sole InfoNCE form. These variants can be summarized as follows: + +$$ +- \frac {1}{N _ {p o s}} \sum_ {i = 1} ^ {N _ {p o s}} \log \frac {\exp \left(q \cdot k _ {+} ^ {i} / \tau\right)}{\exp \left(q \cdot k _ {+} ^ {i} / \tau\right) + \sum_ {k _ {-}} \exp \left(q \cdot k _ {-} / \tau\right)}, \tag {2} +$$ + +in which the total $N_{pos}$ positives are enumerated over $k_{+}^{i}$ . It can indeed alleviate the dilemma of the traditional form by involving more positives, but all these methods mainly focus on supervised learning [21] or lack extensive experiments on large dense prediction tasks [36]. + +More importantly, the concept of multi-label learning is not introduced, that is, the classes are still mutually exclusive, which hinders the model from learning quality representations from scene image self-supervised learning. + +# 3.2. Multi-label self-supervised learning + +Now, we will introduce the proposed MLS method in detail. As discussed above, previous SSL methods who targeted scene images all adopt loss functions in the single-label form, while in this paper, we aim to reduce the gap between the optimization objective and the unique property of multi-label images. + +We adopt MoCo-v2 [6] as our base structure. Specifically, given an input image $I$ , it is first cropped and augmented into two different views: + +$$ +v _ {1} = \mathcal {T} (I), \tag {3} +$$ + +$$ +v _ {2} = \mathcal {T} ^ {\prime} (I), +$$ + +where $\mathcal{T}$ and $\mathcal{T}'$ are two randomly sampled data augmentations. These two views are then passed through the base + +encoder $\phi (\cdot)$ and a momentum encoder $\phi^m (\cdot)$ to get the backbone features $g_{1}$ and $g_{2}$ : + +$$ +g _ {1} = \phi (v _ {1}), g _ {2} = \phi^ {m} (v _ {2}), \tag {4} +$$ + +in which $g_{1}, g_{2} \in \mathbb{R}^{d_{g}}$ (e.g., $d_{g} = 2048$ in ResNet-50 [18]). Next, the backbone features are both passed through a multi-layer perceptron (MLP) projector $f(\cdot)$ or $f^{m}(\cdot)$ + +$$ +z _ {1} = f \left(g _ {1}\right), z _ {2} = f ^ {m} \left(g _ {2}\right) \tag {5} +$$ + +to get the final embeddings $z_{1},z_{2}\in \mathbb{R}^{d_{z}}$ . Similar to MoCo $\mathrm{v}2$ that retains a large dictionary $Q_{z}$ (shown in Fig. 2), here we keep two queues $Q_{g}\in \mathbb{R}^{D\times d_{g}}$ and $Q_{z}\in \mathbb{R}^{D\times d_{z}}$ with normalized embeddings coming from $g_{2}$ and $z_{2}$ , respectively. + +$$ +\begin{array}{l} \frac {g _ {2}}{| | g _ {2} | |} \stackrel {{E n q u e u e}} {{\Longrightarrow}} Q _ {g}, \tag {6} \\ \begin{array}{c} \frac {z _ {2}}{| | z _ {2} | |} \overset {E n q u e u e} {\Longrightarrow} Q _ {z}. \end{array} \\ \end{array} +$$ + +Note that for simplicity the enqueue and deque operations are not shown in Fig. 2, and that features stored in $Q_{g}$ and $Q_{z}$ are all kept in the same order. embeddings in both queues are L2 normalized. + +Then, the backbone feature $g_{1}$ of view $v_{1}$ picks its top $k$ nearest neighbors from $Q_{g}$ and treats them as containing similar semantics as that in the input image's view $v_{1}$ (e.g., containing at least one object that appears in the input view $v_{1}$ ). These nearest neighbors are given pseudo positive labels and all the rest items in $Q_{g}$ are pseudo negatives. This step forms multiple binary pseudo-labels $y \in \mathbb{R}^{D}$ : + +$$ +y = I s T o p k \left(g _ {1} \odot Q _ {g}\right), \tag {7} +$$ + +where $\odot$ is the matrix multiplication operation. + +In the next step, the normalized embeddings inside $Q_{z}$ are treated as normalized classifiers. They are multiplied by the feature $z_{1}$ to produce the logits $p \in \mathbb{R}^{D}$ , which classify $z_{1}$ into the $D$ pseudo categories: + +$$ +p = z _ {1} \odot Q _ {z}. \tag {8} +$$ + +Finally, the pseudo labels $y$ and the classified logits interact with each other, and are optimized using the binary cross entropy (BCE) loss, + +$$ +\mathcal {L} _ {m l} = \frac {- 1}{D} \sum_ {i = 1} ^ {D} \left[ y _ {i} \log \sigma \left(\frac {p _ {i}}{\tau}\right) + (1 - y _ {i}) \log \left(1 - \sigma \left(\frac {p _ {i}}{\tau}\right)\right) \right], \tag {9} +$$ + +in which $\tau$ is a temperature hyperparameter (following MoCo-v2's), and $\sigma(\cdot)$ is the sigmoid function [52] that maps the scores to the range $[0,1]$ . + +![](images/2293a6938d28b81f00dfbd3c7be4c30f4340095502356a2a4f254a90be8947c8.jpg) +Figure 2. The proposed MLS method. An image $I$ is first augmented to two views and sent to two encoders. The embeddings $g_{1}, g_{2} \in \mathbb{R}^{d_{g}}$ and $z_{1}, z_{2} \in \mathbb{R}^{d_{z}}$ are features after the backbone and the MLP, respectively. View 2's features ( $g_{2}$ and $z_{2}$ ) are enqueued to form two dictionaries $Q_{g} \in \mathbb{R}^{D \times d_{g}}$ and $Q_{z} \in \mathbb{R}^{D \times d_{z}}$ in the same order. As shown in the right half, the embedding $g_{1}$ picks its top $k$ nearest embeddings from the queue $Q_{g}$ to produce binary pseudo labels $y \in \mathbb{R}^{D}$ . Then, the embeddings from $Q_{z}$ are treated as classifiers that calculate the logit $p \in \mathbb{R}^{D}$ of $z_{1}$ , which is compared against the pseudo-labels $y$ by a BCE loss. Best viewed in color. + +![](images/67b31838b4a5e8842f421ef80f76de4a07419b5bb607a66a4fff72ade9c8a2a9.jpg) + +# 3.3. Optimization + +When we use the multi-label loss $\mathcal{L}_{ml}$ as the only loss function, we found that empirically the optimization process often faces an unstable training issue. We believe this unstable optimization should be attributed to the adverse interaction between assigning pseudo-labels and learning representations from a poor starting point. High quality embeddings from the queues $Q_{g}$ and $Q_{z}$ cannot be obtained if the pseudo-labels are incorrect. At the same time picking nearest neighbors and classification will surely fail if the enqueued embeddings are misleading (a point which was mentioned in DenseCL [39], too). + +Two strategies easily stabilize the multi-label SSL learning. One is to use InfoNCE alone in the first few epochs to warmup the dictionary $Q_{g}$ and $Q_{z}$ . The other remedy is to combine InfoNCE with our multi-label BCE loss during the whole training process, which is widely used in previous methods [39, 1, 40] and easier in implementation. Hence, we adopt this strategy and our overall loss function is formulated as: + +$$ +\mathcal {L} = \mathcal {L} _ {n c e} + \lambda \mathcal {L} _ {m l}, \tag {10} +$$ + +where $\mathcal{L}_{nce}$ is the InfoNCE loss that is adopted in MoCo-v2 (c.f. Eq. 1) and along with many multi-label SSL methods. $\mathcal{L}_{ml}$ is our multi-label BCE loss (c.f. Eq. 9). The value of combination weight $\lambda$ is fixed at $\lambda = 0.5$ . + +The proposed method is abbreviated as MLS (multi-label self-supervised) learning. + +# 4. Experiments + +Now we validate the effectiveness of MLS through extensive experiments. We first describe the settings of our experiments, including datasets for upstream pretraining and downstream finetuning, training details, and the architecture for object detection, instance/semantic segmentation and image classification. + +# 4.1. Experimental settings + +Datasets. We adopted the MS-COCO train2017 set [23] for SSL pretraining, which is widely applied in the study of scene image SSL [46, 41, 39]. Note that we did not use ImageNet. For downstream tasks, we conducted experiments on MS-COCO, VOC0712 [12], CityScapes [10] as well as 7 small classification datasets (CUB200 [37], Flowers [26], Cars [22], Aircraft [25], Indoor67 [30], Pets [28] and DTD [9]) following previous SSL methods [2]. Specifically, MS-COCO contains 118,287 and 5000 images for training and validation, respectively. VOC2007 has 5011 and 4952 images in the trainval and test sets, respectively. CityScapes is a semantic segmentation dataset containing 2975 and 500 images for training and validation, respectively. For more information about the 7 small classification datasets, please refer to [2] for a more detailed description. + +Pretraining. We adopted ResNet-50 [18] as our base encoder (c.f. Fig. 2) and mostly follow the structure of MoCoV2. We pretrained our models for 400 or 800 epochs on MSCOCO, set learning rate as 0.3, weight decay as 0.0001. For data augmentation, we adopted random resized crop, color distortion, random gray scale, random flip, etc, following [36, 3]. The queue size $D$ of $Q_{g}$ and $Q_{z}$ was 4096. The temperature $\tau$ was set as 0.2 and was shared between the InfoNCE loss and our multi-label BCE loss. The dimensionalities of the embeddings $g_{1}$ and $z_{1}$ were 2048 and 256, respectively. For faster convergence, we adjusted the momentum update coefficient to 0.995. With regard to our multi-label BCE loss, the parameter $k$ was set as 20, and the combination coefficient $\lambda$ was 0.5. + +Downstream. We finetuned the pretrained model on various benchmarks, including MS-COCO object detection and instance segmentation, CityScapes semantic segmentation, VOC0712 detection and other classification benchmarks. Specifically, we finetuned on MS-COCO using the Mask-RCNN R50-FPN/C4 [17] architecture for 90k itera + +Table 1. Results of COCO detection and segmentation. All SSL models (except those pretrained on ImageNet) were first pretrained on MS-COCO and then finetuned on COCO with Mask R-CNN R50-FPN [17]. Our MLS was pretrained for 400 or 800 epochs for fair comparisons. We reproduced $\mathrm{SoCo}^*$ with the settings in [41]. Note that SetSim [40] and ReSim [44] are adaptable to scene image pretraining, but only reported ImageNet pretraining results. The column 'Epochs' means the number of pretraining epochs. ORL $^{+}$ [46] needs two pretraining stages (800 epochs each), so the total training time is doubled. + +
MethodDataEpochsDetectionSegmentation
APbboxAPbbox50APbbox75APsegAPseg50APseg75
Supervised [41]ImageNet9038.959.642.735.456.538.1
ReSim-C4 [44]ImageNet20039.359.743.135.756.738.1
LEWELM [20]ImageNet20040.059.843.736.157.038.7
SetSim [40]ImageNet20040.260.743.936.457.739.0
SoCo* [41]COCO40039.159.142.735.456.037.8
Self-EMD [24]COCO80039.360.142.8---
MoCo-v2 [6]COCO80038.558.142.134.855.337.3
BYOL [14]COCO80038.858.542.235.055.938.1
DenseCL [39]COCO80039.659.343.335.756.538.4
ORL+ [46]COCO160040.360.244.436.357.338.9
MLSCOCO40040.160.243.936.257.338.6
MLSCOCO80040.560.744.536.557.739.1
+ +tions. For VOC0712, we finetuned for 24k iterations with Faster-RCNN R50-C4 [31]. For CityScapes semantic segmentation, we adopted PSANet [50] and PSPNet [49] for 40k iterations. For classification, we chose VOC2007 for multi-label recognition and finetuned 120 epochs on 7 small classification datasets. We ran 3 times on VOC detection and 2 runs on CityScapes since these results have relatively large variations. Following previous studies, the evaluation metrics for detection, segmentation and classification are AP, mIoU/mAcc and top-1 accuracy, respectively. All the experiments were conducted with RTX 3090 GPUs in the PyTorch [29] framework. + +# 4.2. COCO detection and segmentation results + +We first evaluated downstream performance on MS-COCO object detection and instance segmentation. Following previous work, we used Mask R-CNN R50-FPN for finetuning. The results is in Table 1. DenseCL [39] and Self-EMD [24] are those adopting dense matching, while SoCo [41] and ORL [46] both resort to the unsupervised object discovery method Selective Search [35]. For a fair comparison, we reproduced SoCo's results since it was originally pretrained on $\mathrm{COCO + }$ [41] (which is based on COCO but has more unlabeled data). Note that ReSim-C4 [44] and SetSim [40] are suitable for scene image pretraining, but only ImageNet results were reported. + +As shown in Table 1, with only 400 epochs of pretraining, our MLS is almost better than all counterparts (e.g., DenseCL, SoCo, LEWEL [20]) and surpasses supervised results by $1.2\%$ APbbox and $0.8\%$ APseg. With the standard 800 epochs of pretraining, MLS is better than all previous + +Table 2. Results on COCO with the Mask R-CNN R50-C4 detector. 'Data' stands for the pretraining dataset. 'CC' and 'IN' means COCO and ImageNet, respectively. All SSL models were pretrained for 400 epochs on MS-COCO. + +
MethodDataDetectionSegmentation
APbboxAPbbox50APbbox75APsegAPseg50APseg75
Random-26.444.027.829.346.930.8
SupervisedIN38.158.141.133.254.835.0
BYOLCC36.956.739.432.453.534.3
MoCo-v2CC37.356.740.432.853.534.9
SoCo*CC36.956.239.732.453.034.5
DenseCLCC38.357.941.433.554.435.7
MLSCC38.658.341.533.855.136.0
+ +scene image SSL methods. This further verifies our motivation: formulating scene image self-supervised learning as a multi-label classification is both simpler in concept and effective in performance. + +We also tried the Mask R-CNN R50-C4 structure. Since there are relatively less SSL results based on this structure, we reproduced supervised learning, BYOL [14], MoCoV2 [6], SoCo [41] and DenseCL [39] methods by pretraining and finetuning on MS-COCO. To compare fairly, all these SSL models were pretrained for 400 epochs. + +As can be found in Table 2, our MLS surpasses all previous self-supervised learning methods like SoCo [41] and DenseCL [39], despite being much simpler than them. Note that SoCo needs unsupervised box generation and multiple auxiliary loss functions. Our MLS also achieves better results than supervised ImageNet pretraining, with an + +Table 3. Results of CityScapes semantic segmentation using two different segmentation pipelines (PSANet [50] and PSPNet [49]). 'Data' stands for the pretraining dataset. 'CC' and 'IN' means COCO and ImageNet, respectively. + +
MethodDataPSANetPSPNet
mIoUmAccaAccmIoUmAccaAcc
SupervisedIN77.586.695.977.886.795.9
BYOLCC77.686.695.976.985.995.9
MoCo-v2CC76.885.895.876.885.495.8
DenseCLCC77.686.696.077.686.395.9
SoCoCC76.385.395.876.585.395.8
MLSCC79.087.396.278.586.696.1
+ +Table 4. Results of VOC0712 object detection using the Faster-RCNN R50-C4 object detector. All SSL models were pretrained on MS-COCO for 800 epochs. BYOL and MoCo-v2 results were reproduced by us. + +
MethodDataAP\( AP_{50} \)\( AP_{75} \)
Random-32.859.031.6
SupervisedImageNet53.381.058.8
SwAV [3]ImageNet45.177.446.5
SimCLR [4]ImageNet51.579.455.6
SoCo* [41]COCO51.778.657.2
Self-EMD [24]COCO53.080.058.6
BYOLCOCO51.780.256.4
MoCo-v2COCO53.780.059.5
MLSCOCO55.081.661.2
+ +improvement of $0.5\%$ $\mathrm{AP}^{bbox}$ and $0.6\%$ $\mathrm{AP}^{seg}$ for object detection and instance segmentation, respectively. + +# 4.3. Transfer learning + +Next, we test how our MLS method performs on various transfer learning tasks, including CityScapes semantic segmentation, VOC0712 object detection and (multi-label) classification. + +CityScapes semantic segmentation. We first transferred pretrained models to CityScapes [10] semantic segmentation. Because relatively few SSL methods worked on this benchmark and the segmentation architecture generally differed, we first reproduced several SSL methods (BYOL, MoCo-v2, DenseCL and SoCo), then finetuned them in the same setting. It is clearly demonstrated in Table 3 that our multi-label self-supervised learning method is superior than all of them, surpassing state-of-the-art dense matching approach DenseCL [39] and object discovery method SoCo [41], both by significant margins. Our MLS also improves supervised learning from $77.5\%$ mIoU to $79.0\%$ mIoU and from $77.8\%$ mIoU to $78.5\%$ mIoU with PSANet [50] and PSPNet [49], respectively. + +VOC0712 object detection. Moving on to other dense + +prediction tasks, we evaluated the effectiveness of MLS on VOC0712 object detection with Faster R-CNN R50-C4. Since there were missing results for BYOL and MoCo-v2 in this experimental setting, we reproduced both of them for a fair comparison. As shown in Table 4, our MLS surpasses all previous object-centric SSL methods by a large margin. For example, our method is higher than SimCLR by $3.5\%$ AP and $5.6\%$ $\mathrm{AP}_{75}$ metrics. MLS is also better than supervised ImageNet results (an improvement of $1.7\%$ AP and $2.4\%$ $\mathrm{AP}_{75}$ ), showing again the great potential of multi-label self-supervised learning. + +Single- and multi-label classification. Then, we explore how our proposed method behaves on image classification benchmarks. As pointed out by a previous SSL research work [45], various dense matching or unsupervised object discovery based SSL methods usually sacrifice the performance of image classification, in return for high accuracy in dense prediction tasks. In other words, classification is tough for these SSL methods. Therefore, we evaluated MLS on both multi-label (e.g., VOC2007) and single-label classification tasks. As discussed above, we also reproduced the results of MoCo-v2 and DenseCL because MLS has the same architecture with them. It can be found in Table 5 that MLS is consistently better than previous SSL methods, surpassing our baseline MoCo-v2 by a noticeable margin—an improvement of $5.3\%$ mAP for VOC07 and $3.0\%$ accuracy for Indoor67. We attribute this gain to the joint embedding property of MLS: since our method is optimized with global features, it can be naturally easier for us to capture image-level information, thus suitable for image classification tasks. However, all SSL methods are generally worse than supervised ImageNet pretraining, showing that supervised pretraining with more pretraining data (ImageNet vs. COCO) still remains a powerful technique for general image classification. + +# 4.4. Ablation studies + +Compare with other loss functions. We first explore if there are other alternatives besides multi-label BCE that can also achieve similar or even better results. An alternative, however, needs to produce multiple positive paradigms in the loss term. We consider kNN softmax adopted in [21, 36], and propose a variant of BCE by disregarding the negative term in Eq. 9 (calling it 'BCE-pos'). As can be seen in Table 6, adding kNN softmax and the BCE-pos loss function besides the InfoNCE loss used in [36] both lead to consistent improvements in all metrics, demonstrating the effectiveness of our hypothesis. Still, they are both inferior to our proposed MLS, showing that pure BCE works better than the variant in scene image self-supervised learning. + +Why keeping two dictionaries? There are two dictionaries $Q_{g}$ and $Q_{z}$ in our pipeline with different functionalities: one for pseudo-labeling and the other for classification. + +Table 5. Results on downstream classification, including VOC2007 multi-label and 7 small single-label classification datasets. We reproduced the baseline MoCo-v2 and dense matching approach DenseCL for a fair comparison. The evaluation metric for VOC2007 is mAP while for others is top-1 accuracy. All models were pretrained for 400 epochs on the MS-COCO dataset. + +
MethodDataVOC07CUB200FlowersCarsAircraftIndoorPetsDTD
SupervisedImageNet89.081.396.790.686.758.164.474.7
MoCo-v2COCO80.568.889.687.580.464.179.460.9
DenseCLCOCO83.769.388.688.379.965.480.061.8
MLSCOCO85.871.791.288.581.267.181.963.0
+ +Table 6. MS-COCO detection and segmentation results using different pretraining loss functions. The 'kNN' loss was adopted in [36] and the 'BCE-pos' loss means only positive terms of binary cross entropy in Eq. 9 were considered. + +
MethodDetectionSegmentation
APbboxAPbbox50APbbox75APsegAPseg50APseg75
Baseline38.858.342.535.555.537.5
+kNN39.158.742.635.355.837.9
+BCE-pos39.659.443.135.756.538.1
+BCE (ours)40.160.243.936.257.338.6
+ +Why not keeping only one for simplicity? We explain this problem through both visualization and quantitative experiments. First, we plot the histogram of scores in Fig. 3, with $g_{1} \odot Q_{g}$ and $z_{1} \odot Q_{z}$ representing the backbone and MLP scores, respectively. The backbone scores have witnessed a dramatic change after training, indicating some information the network potentially obtained by SSL. On the other hand, the MLP scores almost always follow a normal distribution, with only slight changes in the mean and variance statistics. Hence, we choose to use the backbone queue $Q_{g}$ for pseudo labeling. The MLP dictionary $Q_{z}$ is used for classification, following the common practice in previous SSL methods [16, 39]. Our choice is also verified by the experiments in Table 7, where using only $Q_{g}$ or $Q_{z}$ is clearly sub-optimal, and worse than our MLS where they are jointly adopted. + +Effect of $k$ . Now we examine how different $k$ values (the number of pseudo positive labels generated) affect the final results of our MLS method. The downstream results of MS-COCO detection and segmentation can be found in Table 8, where a too small and a too large $k$ value both lead to a performance drop. A small $k$ means semantically related images may become false negatives in BCE classification, while a large $k$ will similarly lead to false positives. Our MLS is relatively more robust when $k$ is small. But when $k$ is too large, the accuracy drop is significant. Based on this observation, we choose $k = 20$ by default. + +Effect of queue size and $\lambda$ . The fourth module we evaluated is the dictionary (queue) size and the combination weight $\lambda$ in Eq. 10. We pretrained the models on the MS-COCO dataset using MLS and finetuned them for COCO + +Table 7. Effect of using different dictionaries. $Q_{g}$ only' means the embeddings in $Q_{g}$ and $g_{1}$ are used twice to both generate the pseudo labels $y$ and the logits $p$ (c.f. Fig. 2). $Q_{z}$ only' means only using $Q_{z}$ and $z_{1}$ . + +
MethodAPbboxAPseg
Qg only39.535.7
Qz only39.836.0
Both Qg and Qz (ours)40.136.2
+ +![](images/80074f54810a3d017effe49cfb2ebec578b63fc263a33db80440ea9c3eccf60d.jpg) +(a) Backbone- and MLP-scores before MLS training + +![](images/2a19ff9a513a71f5cf7da37d8245bbfbc2cec83e335a3c93c7cc03dec0980eb6.jpg) + +![](images/a94c52afff05cbd64803039d55b779844c5333eeddeb93d421f0eb74964c5255.jpg) +(b) Backbone- and MLP-scores after MLS training + +![](images/6f0128a02fc4e34003c35bdf99fadcd40b8bb6037709d4d7a3be4a07c69f90e8.jpg) +Figure 3. Visualization of the score distribution of one sampled COCO image before and after training. The backbone scores and MLS scores are $g_{1} \odot Q_{g}$ and $z_{1} \odot Q_{z}$ , respectively. The backbone scores are more indicative compared with MLP scores, thus suitable for pseudo label generation. + +object detection with Mask R-CNN R50-FPN. As demonstrated in Fig. 5 (a), a too small queue size (e.g., 1024) is detrimental for SSL pretraining, since a small queue means limited representations stored, which is not enough for an image to retrieve its positive neighbors. An overly large dictionary also obtains sub-optimal results, because dictionaries that are too large probably contain many out-of-date embeddings (due to the deque and enqueue mechanism [6]) and might lead to incorrect pseudo labels. And, we also validate the robustness of our MLS by trying multiple $\lambda$ values. It can be seen in Figure 5 (b) that all $\lambda$ leads to consistent + +![](images/7f3d8336de7861bdc8c1725f779cd6f6ee2aff9bd30c628ba8bb5bb0a3a21bff.jpg) + +![](images/ca3be5a0189c0eab400e6dd3b7b772cce4b50ab294fcdcf212fc238c255b8507.jpg) + +![](images/f5469d6504edab281df347d91c63c13030a8dcf4899eb4121a7a7e3501826bd4.jpg) + +![](images/b1835565a8890d0e8806c0268338ac691fbac84c10a899cd32b709ba1320245f.jpg) + +![](images/be57618f0d8011c1ea202b09dc8ef24a0a05d1ec67f1881034430f64c474b621.jpg) + +![](images/9ac278a9144a5ddc059f33cef3fbe89e698e81598119c8f6f7f7825e04defe46.jpg) + +![](images/8e0d4a67b6e247898c8c17c1d8facd672686b5a4a819d56ff8634fadaa25ad49.jpg) + +![](images/c4916859d31468ff6ad8c584dd31f22b2e7b24767f1a019488a68ec6c3e1f8a7.jpg) + +![](images/6a4fe22b409e29c6708f5be2f8f8e32cb2ccf341dbbc07dc03829234e26e0bca.jpg) + +![](images/2312f3659acfa80997667f1057c961a2406567db37eb90678637ebd2db7a489a.jpg) + +![](images/60612bb044c17718cf1e8e0ade96fdcd618d58263465e5e5dc4fa7577d425abe.jpg) +Figure 4. Visualization of positive pseudo-labels picked up by MLS across images in COCO. For each randomly cropped query image patch, we find the top-4 of its NNs from the dictionary $Q_{g}$ (shown in yellow rectangles). All these rectangles are generated by the random resized crop data augmentation, a standard component in SSL. We record the cropped boxes' coordinates of the embeddings (the query $g_{1}$ and those stored in the dictionary $Q_{g}$ during data augmentation). To be more precise, we first randomly sampled 60 query images. We then randomly sampled 5 query images out of the set of 60 and found their top-4 NNs. In addition, we manually select the worst query image (i.e., semantically most different from its top-4 NNs), which is the right half of the last row. This figure is best viewed in color. + +![](images/fddc09f6adb17821e268c1461e8a9ea481547d20c5a4079d732b3b73f2f4bdc9.jpg) + +![](images/84f9fbf1fb314364fac6172849811cefff0dfa22415c24716675703712517f05.jpg) + +![](images/41d24fb909d35539352cfb1ab38bc84e5f920f640538d6c1388ed75520f738d1.jpg) + +![](images/7996abc27f68f2db0d2b053353a02f5339fa8ea11ca2689f7d09178fb80c3e54.jpg) + +![](images/d1c2db78e80ba41cdd517092fd292898d98f7f62e7913ce5fa005851d1902d13.jpg) + +![](images/2524b3d8ab9a7106845fa91c47d6aa0c76084414f61263c5ee005ac110106268.jpg) + +![](images/e73ec75961cee0f91a764f737bee452a3f3ba060acb0a3de7573dd7492e217b9.jpg) + +![](images/84fd8e364dde62689201cef0ccd82b7f14c1935363723d274dbfc21269852fda.jpg) + +![](images/1a3305670d75185600397ada41e1e0224a9726ebd9efe0d86534fa0b50564e13.jpg) + +![](images/3c337f76ffb327c7abff513255de8b4b508acace0f3ad33d59da48b373242e1b.jpg) + +![](images/69c0a091690357f81696cc8f6a8310bad3c93d55dcf0c4593f01c4c78c28e91c.jpg) + +![](images/3dd2b92ec0fe4974d8484cf377a28420dac1b03789cbfae37785184083cab802.jpg) + +![](images/0eda076d75948cba1c47314cf23493f7d40fee4a00523557ce8bc9f4b8e50ef5.jpg) + +![](images/d353752f7ae8901a0c5d7464436a22892cffe8633c6d1aaa2ce9708f7b3b5f70.jpg) + +![](images/fca9a93916c41d72ca97b27ac475dd10ea763c472c273fa14c966f9c34ace69e.jpg) + +![](images/9cbae051ca70a5af45f0e07a29a58fb9788ba995ee0e2b76e12cae11d424024c.jpg) + +![](images/99b97fca04f959c72918a625c418bf1a608bd2b3ca53b3da67ae599a5d1aa9c3.jpg) + +![](images/07131323b211613a36fde366dfd55d04f3331c3eaefc88ba550689f55ffdc82e.jpg) + +![](images/dbbc53b140ca3613d6eba5c914ff437195ba2bf31f181872a98cffa620dfa98c.jpg) + +Table 8. The effect of different $k$ in pseudo label generation as illustrated in Fig. 2 and Eq. 7. All models were pretrained on MS-COCO and finetuned for detection and segmentation. + +
Top kk=1k=5k=20k=40
APbbox39.740.040.139.2
APseg35.936.136.235.4
+ +![](images/065d7b6042c005db2a88d0783520b360e157ad692a1863eef03c948215952498.jpg) +(a) Effect of Queue size +Figure 5. Effect of different queue size and $\lambda$ values (c.f. Eq. 10) in terms of downstream tasks' results. In this paper, we choose 4096 queue size and $\lambda = 0.5$ by default. + +![](images/a61c6b9df60600c11a510b9b79be01ad5746caf678c0b0453c52533a1ac5a7ed.jpg) +(b) Effect of $\lambda$ + +improvement over the baseline $(c.f.$ Table 6), and there is a sweet spot in the choice of $\lambda$ . Thus, in this paper we choose $\lambda = 0.5$ by default in our experiment. + +Visualization of positive pseudo-labels. Last but not least, we validate the effectiveness of our MLS pipeline by visualization: are the top $k$ nearest neighbors (NN) picked up from the dictionary $Q_{g}$ indeed semantically similar to the input? Because random resized crop is applied in the SSL pipeline (it is the cropped patch that is sent to the network), we record the cropped location of each image during data augmentation. Then, for each query $g_{1}$ in Fig. 2, we find its top-4 NNs stored in the queue $Q_{g}$ . All these queries + +and NNs are associated with a certain cropped patch, and thus we visualize them with red and yellow rectangles, respectively. As shown in Fig. 4, our MLS backbone effectively captures semantically similar correspondences across the dataset. Specifically, intra-class variance (the first row) and multiple positive partial concepts (the second and third rows) are clearly demonstrated, showing that our motivation in Sec. 1 is valid and that MLS is not only suitable for scene image SSL, but might also be adaptable to image retrieval, as well. + +# 5. Conclusions and Limitations + +In this paper, we argued that scene image self-supervised learning does not necessarily rely on dense matching or unsupervised object discovery methods, and instead proposed our Multi-Label Self-supervised (MLS) learning approach. The key idea in MLS is that a multi-label image contains multiple concepts or objects, hence we need to have multiple positive pairs corresponding to different objects in the input image. Specifically, we create two dictionaries, one for creating pseudo-labels (positive or negative pairs) and the other for distinguishing between them (i.e., a multi-label classification problem). This is the first time that multi-label SSL is cast as a multi-label classification problem, and MLS has been validated by extensive experiments on various benchmarks (e.g., MS-COCO, CityScapes, VOC0712, etc.) and tasks (object detection, image segmentation, single- and multi-label classification). + +As for limitations, it still remains unclear why the BCE loss alone will cause an unstable training issue. This is a long-lasting and open question as numerous scene image SSL methods [39, 44, 40, 1] also struggle if the InfoNCE + +loss is removed. Hence, these methods (including our MLS) always use their proposed modules in combination with InfoNCE. In the future, we will explore how and why the collapsing phenomenon exists without the normal contrastive loss, and will apply our MLS to single-label image SSL to further explore the adaptability of our method. + +# References + +[1] Yutong Bai, Xinlei Chen, Alexander Kirillov, Alan Yuille, and Alexander C. Berg. 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This paper shows that instead of hinging on these strenuous operations, quality image representations can be learned by treating scene/multi-label image SSL simply as a multi-label classification problem, which greatly simplifies the learning framework. Specifically, multiple binary pseudo-labels are assigned for each input image by comparing its embeddings with those in two dictionaries, and the network is optimized using the binary cross entropy loss. The proposed method is named Multi-Label Self-supervised learning (MLS). Visualizations qualitatively show that clearly the pseudo-labels by MLS can automatically find semantically similar pseudo-positive pairs across different images to facilitate contrastive learning. MLS learns high quality representations on MS-COCO and achieves state-of-the-art results on classification, detection and segmentation benchmarks. At the same time, MLS is much simpler than existing methods, making it easier to deploy and for further exploration." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 537, + 128, + 550 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 537, + 128, + 550 + ], + "spans": [ + { + "bbox": [ + 47, + 537, + 128, + 550 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 557, + 287, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 287, + 664 + ], + "type": "text", + "content": "Self-supervised learning (SSL) methods based on contrastive learning [4, 3] have facilitated numerous downstream tasks. Those [16, 6, 14, 13] that target object-centric images (e.g., ImageNet) are already relatively mature, but inventing SSL methods for scene images (e.g., MS-COCO [23]) gains popularity recently. Since unlabeled scene images (or multi-label images) are more natural [46] and richer in semantics, various SSL methods [39, 45, 19, 40, 20, 44] have successively emerged." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 59, + 665, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 665, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 59, + 665, + 287, + 677 + ], + "type": "text", + "content": "SSL methods focusing on scene/multi-label images can" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 322, + 228, + 533, + 352 + ], + "blocks": [ + { + "bbox": [ + 322, + 228, + 533, + 352 + ], + "lines": [ + { + "bbox": [ + 322, + 228, + 533, + 352 + ], + "spans": [ + { + "bbox": [ + 322, + 228, + 533, + 352 + ], + "type": "image", + "image_path": "8a89928182d88d08553e7739a6be98cb8179207c88e6de7702b21823f2834190.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 357, + 547, + 425 + ], + "lines": [ + { + "bbox": [ + 305, + 357, + 547, + 425 + ], + "spans": [ + { + "bbox": [ + 305, + 357, + 547, + 425 + ], + "type": "text", + "content": "Figure 1. Illustrating our motivation. An image patch cropped from a multi-label image comprises multiple objects. Each object can find similar ('pos') and dissimilar ('neg') images from a large dictionary. The whole image patch is pulled closer to those positive ones and pushed away from the negatives using a BCE loss. See Fig. 4 for positives and negatives chosen by our algorithm." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 448, + 547, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 448, + 547, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 547, + 568 + ], + "type": "text", + "content": "be summarized into two categories. One is dense matching, such as DenseCL [39], MaskCo [51] and Self-EMD [24]. They take the features' locations into account to improve the performance on dense prediction tasks. They mostly differ in how the heuristic matching metric is designed. Another branch of work like SoCo [41] and ORL [46] resort to unsupervised object discovery to find local object contents, and learn quality representation with both object- and scene-level semantics. However, they usually involve multi-stage SSL pretraining on top of expensive box generation [35]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "text", + "content": "These scene image SSL methods are generally based on the contrastive loss (e.g., InfoNCE [27]), where two randomly augmented views of the same image are forced to be close to each other, and optionally push away views from different images. The loss assumes single-label images [27], but the input are in fact multi-label: hence there is a mismatch between the loss and the data. On one hand, it can be difficult for two views randomly cropped from the same scene image to be exactly matched [39, 47]. On the other hand, there is only one matched positive pair in InfoNCE, while more positive pairs are naturally preferred: a view cropped from a multi-label image likely contains mul" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 683, + 287, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 683, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 683, + 287, + 712 + ], + "type": "text", + "content": "*J. Wu is the corresponding author. This paper was partly supported by the National Natural Science Foundation of China under Grant 62276123 and Grant 61921006." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6694" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 72, + 187, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 72, + 187, + 84 + ], + "spans": [ + { + "bbox": [ + 48, + 72, + 187, + 84 + ], + "type": "text", + "content": "tiple semantic concepts or objects." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 49, + 85, + 286, + 335 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 85, + 286, + 335 + ], + "spans": [ + { + "bbox": [ + 49, + 85, + 286, + 335 + ], + "type": "text", + "content": "Therefore, this paper proposes a simple yet direct approach towards scene image SSL, named as Multi-Label Self-supervised learning (MLS). We treat each image (or randomly cropped patch) as a semantic bag with multiple objects, then retrieve images sharing similar semantics with any object in the bag from a large image dictionary. Note that an object in a bag is not necessarily within the set of human-annotated categories. As illustrated in Fig. 1, the cropped patch contains person, horse, road and bus, which will be pulled closer to similar images containing any of these objects and be pushed away from those dissimilar ones. Specifically, the patch's embedding produced by a backbone network will select top " + }, + { + "bbox": [ + 49, + 85, + 286, + 335 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 49, + 85, + 286, + 335 + ], + "type": "text", + "content": " similar embeddings as " + }, + { + "bbox": [ + 49, + 85, + 286, + 335 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 49, + 85, + 286, + 335 + ], + "type": "text", + "content": " (pseudo) positive images from a dictionary, and the rest will be negatives. In another dictionary containing images in the same order as the first one, the BCE (binary cross entropy) loss plus these binary pseudo-labels will classify the patch's embedding after an MLP projector using all the images in this second dictionary as classifiers, and generates gradients that optimize the backbone network. This framework is illustrated in Fig. 2." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 49, + 337, + 286, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 337, + 286, + 455 + ], + "spans": [ + { + "bbox": [ + 49, + 337, + 286, + 455 + ], + "type": "text", + "content": "Our framework has two benefits. First, the large dictionary has diverse positive samples for any given input, hence provides many quality positive pairs with deformations or intra-class variations [11]. Second, unlike InfoNCE, the BCE loss is not mutually exclusive among classes, hence allows the co-occurrence of multiple classes in one scene image. By applying our SSL method to scene images (e.g., MS-COCO), we achieve state-of-the-art results on object detection, instance segmentation and various classification benchmarks. Our contributions are summarized as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 56, + 468, + 286, + 618 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 57, + 468, + 286, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 468, + 286, + 503 + ], + "spans": [ + { + "bbox": [ + 57, + 468, + 286, + 503 + ], + "type": "text", + "content": "1. For the first time, we formulate scene image SSL as a multi-label classification, and propose our Multi-Label Self-supervised (MLS) learning approach." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 56, + 515, + 286, + 560 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 515, + 286, + 560 + ], + "spans": [ + { + "bbox": [ + 56, + 515, + 286, + 560 + ], + "type": "text", + "content": "2. Unlike previous methods that adopt dense matching or unsupervised object discovery, MLS is simple in concept, and enjoys intuitive visualizations (c.f. Fig. 4) which clearly verifies our motivation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 56, + 573, + 286, + 618 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 573, + 286, + 618 + ], + "spans": [ + { + "bbox": [ + 56, + 573, + 286, + 618 + ], + "type": "text", + "content": "3. Extensive experiments of object detection, instance segmentation and classification on various benchmark datasets, together with ablation studies, clearly demonstrate the effectiveness of our method." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 49, + 634, + 132, + 645 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 634, + 132, + 645 + ], + "spans": [ + { + "bbox": [ + 49, + 634, + 132, + 645 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 49, + 654, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 654, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 49, + 654, + 286, + 712 + ], + "type": "text", + "content": "Traditional SSL methods. Self-supervised learning (SSL) has emerged as a promising direction towards unsupervised representation learning [6]. Early SSL methods [27, 33] are mainly derived from noise contrastive estimation [15]. Later, SSL methods based on contrastive" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 307, + 72, + 544, + 203 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 72, + 544, + 203 + ], + "spans": [ + { + "bbox": [ + 307, + 72, + 544, + 203 + ], + "type": "text", + "content": "learning and clustering paradigms have been proved effective, too. Representative methods such as SimCLR [4], MoCo [16], BYOL [14] and SwAV [3] have exhibited both simplicity and generalization ability [36] to various downstream tasks. A set of variants such as Simsiam [7], InfoMin [34] and NNCLR [11] try to simplify, analyze and optimize traditional SSL methods from different aspects. However, all of them mainly focus on pretraining on object-centric images like the ImageNet dataset [32] for image classification (e.g., ImageNet linear evaluation), but pay less attention to dense prediction tasks." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 308, + 205, + 544, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 205, + 544, + 453 + ], + "spans": [ + { + "bbox": [ + 308, + 205, + 544, + 453 + ], + "type": "text", + "content": "Scene-image SSL methods. The development of scene (multi-label) image SSL is a diversified process, which mainly contains two branches: dedicated dense feature matching and multi-stage pretraining with unsupervised object discovery. DenseCL [39], PixPro [47], ReSim [44], LEWEL [20] and SetSim [40] all apply the InfoNCE loss in a dense matching manner. They propose dense loss functions in addition to the traditional InfoNCE loss, and their pipelines differ in how the matching metrics are (probably manually) selected. Another branch of methods such as SoCo [41] and ORL [46] try to learn quality feature representation with both scene- and object-level information: they utilize multi-stage pretraining to find correspondence across images with the help of unsupervised object generation methods [35, 54], which suffers from huge computation costs. A recent SSL method [36] that is close to our work proposed kNN-MoCo as an extra module. But, this method is still in a single-label InfoNCE manner and the improvement is small compared to our multi-label MLS (c.f. Table 6). Compared to existing methods, our MLS is novel in concept and simple in implementation." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 308, + 456, + 544, + 633 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 456, + 544, + 633 + ], + "spans": [ + { + "bbox": [ + 308, + 456, + 544, + 633 + ], + "type": "text", + "content": "Multi-label classification. Multi-label recognition aims to predict the presence or absence of each object class in an input image [48]. Traditional methods are based on three aspects: attention modules [53, 52], correlation matrix [8, 5] and unsupervised box generation [42, 38]. The loss function adopted in this task is mostly binary cross entropy (BCE), which is not mutually exclusive among classes [48], such that the presence of one class does not suppress the existence of others. In this paper, we inherit this unique property of multi-label classification and try to integrate BCE into self-supervised learning on scene images. We adopt the joint image embedding to generate " + }, + { + "bbox": [ + 308, + 456, + 544, + 633 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 308, + 456, + 544, + 633 + ], + "type": "text", + "content": " pseudo-labels, together with the classification logits to calculate the final loss term, which effectively guides the multi-label self-supervised learning." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 308, + 647, + 360, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 647, + 360, + 658 + ], + "spans": [ + { + "bbox": [ + 308, + 647, + 360, + 658 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 308, + 666, + 544, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 666, + 544, + 712 + ], + "spans": [ + { + "bbox": [ + 308, + 666, + 544, + 712 + ], + "type": "text", + "content": "In this section, we start by describing the preliminaries of self-supervised learning, including the InfoNCE loss and its variants. We will then describe the proposed Multi-Label Self-supervised (MLS) learning methods and how the over" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 750, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 750, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 750, + 314, + 757 + ], + "type": "text", + "content": "6695" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 231, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 231, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 231, + 84 + ], + "type": "text", + "content": "all loss function is formulated and optimized." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 90, + 133, + 102 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 90, + 133, + 102 + ], + "spans": [ + { + "bbox": [ + 47, + 90, + 133, + 102 + ], + "type": "text", + "content": "3.1. Preliminaries" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 109, + 287, + 145 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 109, + 287, + 145 + ], + "spans": [ + { + "bbox": [ + 47, + 109, + 287, + 145 + ], + "type": "text", + "content": "Self-supervised learning methods, whether contrastive based [16, 14] or clustering based [3], usually rely on the InfoNCE loss [27] or its variants [33]:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 56, + 148, + 287, + 186 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 148, + 287, + 186 + ], + "spans": [ + { + "bbox": [ + 56, + 148, + 287, + 186 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {n c e} = - \\log \\frac {\\exp (q \\cdot k _ {+} / \\tau)}{\\exp (q \\cdot k _ {+} / \\tau) + \\sum_ {k _ {-}} \\exp (q \\cdot k _ {-} / \\tau)}, \\tag {1}", + "image_path": "f24117cb00768cc62e9a58e9e1af8b4ddd3c9c129cc696c3f3535e5e6b470f49.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "spans": [ + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "type": "inline_equation", + "content": "k_{+}" + }, + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "type": "text", + "content": " are positive embeddings (similar to " + }, + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "type": "inline_equation", + "content": "z_{1}" + }, + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "type": "inline_equation", + "content": "z_{2}" + }, + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "type": "text", + "content": " in Fig. 2) after the multi-layer perception (MLP) projector of two encoders. The negative features " + }, + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "type": "inline_equation", + "content": "k_{-}" + }, + { + "bbox": [ + 47, + 187, + 287, + 270 + ], + "type": "text", + "content": " may come from a memory bank [43], a large dictionary or a queue [6], or the current mini-batch [4]. Negatives may be removed by using additional techniques (e.g., the stop gradient adopted in BYOL [14] and SimSiam [7])." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 270, + 287, + 365 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 270, + 287, + 365 + ], + "spans": [ + { + "bbox": [ + 46, + 270, + 287, + 365 + ], + "type": "text", + "content": "Similar with the form of a normal softmax function [53] that is popular in single-label classification, InfoNCE is mutually exclusive among all classes, such that there can only be one positive out of all pseudo concepts. There are variants of InfoNCE (such as SupCon [21]) where more positive pairs are excavated and accumulated, with each item being a sole InfoNCE form. These variants can be summarized as follows:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 52, + 369, + 287, + 412 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 369, + 287, + 412 + ], + "spans": [ + { + "bbox": [ + 52, + 369, + 287, + 412 + ], + "type": "interline_equation", + "content": "- \\frac {1}{N _ {p o s}} \\sum_ {i = 1} ^ {N _ {p o s}} \\log \\frac {\\exp \\left(q \\cdot k _ {+} ^ {i} / \\tau\\right)}{\\exp \\left(q \\cdot k _ {+} ^ {i} / \\tau\\right) + \\sum_ {k _ {-}} \\exp \\left(q \\cdot k _ {-} / \\tau\\right)}, \\tag {2}", + "image_path": "f5e05d1ffa4d63b18ddf9ff8b698d8064fda9f8c587e95d5bc52c04ec20e90ca.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 413, + 287, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 413, + 287, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 413, + 287, + 472 + ], + "type": "text", + "content": "in which the total " + }, + { + "bbox": [ + 46, + 413, + 287, + 472 + ], + "type": "inline_equation", + "content": "N_{pos}" + }, + { + "bbox": [ + 46, + 413, + 287, + 472 + ], + "type": "text", + "content": " positives are enumerated over " + }, + { + "bbox": [ + 46, + 413, + 287, + 472 + ], + "type": "inline_equation", + "content": "k_{+}^{i}" + }, + { + "bbox": [ + 46, + 413, + 287, + 472 + ], + "type": "text", + "content": ". It can indeed alleviate the dilemma of the traditional form by involving more positives, but all these methods mainly focus on supervised learning [21] or lack extensive experiments on large dense prediction tasks [36]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 473, + 287, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 473, + 287, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 473, + 287, + 521 + ], + "type": "text", + "content": "More importantly, the concept of multi-label learning is not introduced, that is, the classes are still mutually exclusive, which hinders the model from learning quality representations from scene image self-supervised learning." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 526, + 236, + 540 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 526, + 236, + 540 + ], + "spans": [ + { + "bbox": [ + 47, + 526, + 236, + 540 + ], + "type": "text", + "content": "3.2. Multi-label self-supervised learning" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 544, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 544, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 544, + 287, + 616 + ], + "type": "text", + "content": "Now, we will introduce the proposed MLS method in detail. As discussed above, previous SSL methods who targeted scene images all adopt loss functions in the single-label form, while in this paper, we aim to reduce the gap between the optimization objective and the unique property of multi-label images." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 616, + 287, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 616, + 287, + 652 + ], + "spans": [ + { + "bbox": [ + 46, + 616, + 287, + 652 + ], + "type": "text", + "content": "We adopt MoCo-v2 [6] as our base structure. Specifically, given an input image " + }, + { + "bbox": [ + 46, + 616, + 287, + 652 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 46, + 616, + 287, + 652 + ], + "type": "text", + "content": ", it is first cropped and augmented into two different views:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 142, + 656, + 287, + 674 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 142, + 656, + 287, + 674 + ], + "spans": [ + { + "bbox": [ + 142, + 656, + 287, + 674 + ], + "type": "interline_equation", + "content": "v _ {1} = \\mathcal {T} (I), \\tag {3}", + "image_path": "85d1109c01ca9cc8e6374309ad3d0aec24b431bd06ab2e014b17b06519803bb6.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 141, + 672, + 194, + 684 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 141, + 672, + 194, + 684 + ], + "spans": [ + { + "bbox": [ + 141, + 672, + 194, + 684 + ], + "type": "interline_equation", + "content": "v _ {2} = \\mathcal {T} ^ {\\prime} (I),", + "image_path": "d940d5692a95efecf65b43aebae4723ec762980f5505b13282fb427e654b5b71.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{T}'" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " are two randomly sampled data augmentations. These two views are then passed through the base" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": "encoder " + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "\\phi (\\cdot)" + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": " and a momentum encoder " + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "\\phi^m (\\cdot)" + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": " to get the backbone features " + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "g_{1}" + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "g_{2}" + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 369, + 107, + 545, + 121 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 369, + 107, + 545, + 121 + ], + "spans": [ + { + "bbox": [ + 369, + 107, + 545, + 121 + ], + "type": "interline_equation", + "content": "g _ {1} = \\phi (v _ {1}), g _ {2} = \\phi^ {m} (v _ {2}), \\tag {4}", + "image_path": "eb3b60b9d4f9e0a83c604cb6db6862be6117550277bd6c3a546a4360b6cf6c50.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 131, + 545, + 169 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 131, + 545, + 169 + ], + "spans": [ + { + "bbox": [ + 305, + 131, + 545, + 169 + ], + "type": "text", + "content": "in which " + }, + { + "bbox": [ + 305, + 131, + 545, + 169 + ], + "type": "inline_equation", + "content": "g_{1}, g_{2} \\in \\mathbb{R}^{d_{g}}" + }, + { + "bbox": [ + 305, + 131, + 545, + 169 + ], + "type": "text", + "content": " (e.g., " + }, + { + "bbox": [ + 305, + 131, + 545, + 169 + ], + "type": "inline_equation", + "content": "d_{g} = 2048" + }, + { + "bbox": [ + 305, + 131, + 545, + 169 + ], + "type": "text", + "content": " in ResNet-50 [18]). Next, the backbone features are both passed through a multi-layer perceptron (MLP) projector " + }, + { + "bbox": [ + 305, + 131, + 545, + 169 + ], + "type": "inline_equation", + "content": "f(\\cdot)" + }, + { + "bbox": [ + 305, + 131, + 545, + 169 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 305, + 131, + 545, + 169 + ], + "type": "inline_equation", + "content": "f^{m}(\\cdot)" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 372, + 179, + 545, + 193 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 372, + 179, + 545, + 193 + ], + "spans": [ + { + "bbox": [ + 372, + 179, + 545, + 193 + ], + "type": "interline_equation", + "content": "z _ {1} = f \\left(g _ {1}\\right), z _ {2} = f ^ {m} \\left(g _ {2}\\right) \\tag {5}", + "image_path": "3b8e7620b16649e2cfbd53e22edd31a198d98d1b689f81a5c9bfc3c587168ad6.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "spans": [ + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "text", + "content": "to get the final embeddings " + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "inline_equation", + "content": "z_{1},z_{2}\\in \\mathbb{R}^{d_{z}}" + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "text", + "content": " . Similar to MoCo" + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "inline_equation", + "content": "\\mathrm{v}2" + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "text", + "content": " that retains a large dictionary " + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "inline_equation", + "content": "Q_{z}" + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "text", + "content": " (shown in Fig. 2), here we keep two queues " + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "inline_equation", + "content": "Q_{g}\\in \\mathbb{R}^{D\\times d_{g}}" + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "inline_equation", + "content": "Q_{z}\\in \\mathbb{R}^{D\\times d_{z}}" + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "text", + "content": " with normalized embeddings coming from " + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "inline_equation", + "content": "g_{2}" + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "inline_equation", + "content": "z_{2}" + }, + { + "bbox": [ + 304, + 204, + 545, + 263 + ], + "type": "text", + "content": " , respectively." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 386, + 266, + 545, + 315 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 386, + 266, + 545, + 315 + ], + "spans": [ + { + "bbox": [ + 386, + 266, + 545, + 315 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\frac {g _ {2}}{| | g _ {2} | |} \\stackrel {{E n q u e u e}} {{\\Longrightarrow}} Q _ {g}, \\tag {6} \\\\ \\begin{array}{c} \\frac {z _ {2}}{| | z _ {2} | |} \\overset {E n q u e u e} {\\Longrightarrow} Q _ {z}. \\end{array} \\\\ \\end{array}", + "image_path": "cdb28be94e5451d038afaeb923047bb417945f2d899c6d047ba0542a33660e9e.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 322, + 545, + 369 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 322, + 545, + 369 + ], + "spans": [ + { + "bbox": [ + 305, + 322, + 545, + 369 + ], + "type": "text", + "content": "Note that for simplicity the enqueue and deque operations are not shown in Fig. 2, and that features stored in " + }, + { + "bbox": [ + 305, + 322, + 545, + 369 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 305, + 322, + 545, + 369 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 322, + 545, + 369 + ], + "type": "inline_equation", + "content": "Q_{z}" + }, + { + "bbox": [ + 305, + 322, + 545, + 369 + ], + "type": "text", + "content": " are all kept in the same order. embeddings in both queues are L2 normalized." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "spans": [ + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "text", + "content": "Then, the backbone feature " + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "inline_equation", + "content": "g_{1}" + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "text", + "content": " of view " + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "inline_equation", + "content": "v_{1}" + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "text", + "content": " picks its top " + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "text", + "content": " nearest neighbors from " + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "text", + "content": " and treats them as containing similar semantics as that in the input image's view " + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "inline_equation", + "content": "v_{1}" + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "text", + "content": " (e.g., containing at least one object that appears in the input view " + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "inline_equation", + "content": "v_{1}" + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "text", + "content": "). These nearest neighbors are given pseudo positive labels and all the rest items in " + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "text", + "content": " are pseudo negatives. This step forms multiple binary pseudo-labels " + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "inline_equation", + "content": "y \\in \\mathbb{R}^{D}" + }, + { + "bbox": [ + 305, + 371, + 545, + 455 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 375, + 466, + 545, + 480 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 375, + 466, + 545, + 480 + ], + "spans": [ + { + "bbox": [ + 375, + 466, + 545, + 480 + ], + "type": "interline_equation", + "content": "y = I s T o p k \\left(g _ {1} \\odot Q _ {g}\\right), \\tag {7}", + "image_path": "b20f508a1a290cd8602492b20a0ee356ff43ab5e5a36fa0f75d474c63eae03f4.jpg" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 491, + 497, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 491, + 497, + 502 + ], + "spans": [ + { + "bbox": [ + 306, + 491, + 497, + 502 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 491, + 497, + 502 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 306, + 491, + 497, + 502 + ], + "type": "text", + "content": " is the matrix multiplication operation." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "spans": [ + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "type": "text", + "content": "In the next step, the normalized embeddings inside " + }, + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "type": "inline_equation", + "content": "Q_{z}" + }, + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "type": "text", + "content": " are treated as normalized classifiers. They are multiplied by the feature " + }, + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "type": "inline_equation", + "content": "z_{1}" + }, + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "type": "text", + "content": " to produce the logits " + }, + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "type": "inline_equation", + "content": "p \\in \\mathbb{R}^{D}" + }, + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "type": "text", + "content": ", which classify " + }, + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "type": "inline_equation", + "content": "z_{1}" + }, + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "type": "text", + "content": " into the " + }, + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 305, + 504, + 545, + 552 + ], + "type": "text", + "content": " pseudo categories:" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 395, + 563, + 545, + 576 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 395, + 563, + 545, + 576 + ], + "spans": [ + { + "bbox": [ + 395, + 563, + 545, + 576 + ], + "type": "interline_equation", + "content": "p = z _ {1} \\odot Q _ {z}. \\tag {8}", + "image_path": "1935396bfd936de5ad0677e32cf62da9100382f81811a181d2b0da0c8215bb7e.jpg" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 305, + 587, + 545, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 587, + 545, + 624 + ], + "spans": [ + { + "bbox": [ + 305, + 587, + 545, + 624 + ], + "type": "text", + "content": "Finally, the pseudo labels " + }, + { + "bbox": [ + 305, + 587, + 545, + 624 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 305, + 587, + 545, + 624 + ], + "type": "text", + "content": " and the classified logits interact with each other, and are optimized using the binary cross entropy (BCE) loss," + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 307, + 635, + 545, + 677 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 635, + 545, + 677 + ], + "spans": [ + { + "bbox": [ + 307, + 635, + 545, + 677 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {m l} = \\frac {- 1}{D} \\sum_ {i = 1} ^ {D} \\left[ y _ {i} \\log \\sigma \\left(\\frac {p _ {i}}{\\tau}\\right) + (1 - y _ {i}) \\log \\left(1 - \\sigma \\left(\\frac {p _ {i}}{\\tau}\\right)\\right) \\right], \\tag {9}", + "image_path": "cc0cb9ddf31c86668653058d4d2fa47d20ce396cd089c5c0b45ea5ab60bf5d65.jpg" + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "type": "text", + "content": "in which " + }, + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "type": "text", + "content": " is a temperature hyperparameter (following MoCo-v2's), and " + }, + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\sigma(\\cdot)" + }, + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "type": "text", + "content": " is the sigmoid function [52] that maps the scores to the range " + }, + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "[0,1]" + }, + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 29 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "6696" + } + ] + } + ], + "index": 30 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 75, + 71, + 318, + 188 + ], + "blocks": [ + { + "bbox": [ + 75, + 71, + 318, + 188 + ], + "lines": [ + { + "bbox": [ + 75, + 71, + 318, + 188 + ], + "spans": [ + { + "bbox": [ + 75, + 71, + 318, + 188 + ], + "type": "image", + "image_path": "2293a6938d28b81f00dfbd3c7be4c30f4340095502356a2a4f254a90be8947c8.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "lines": [ + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "spans": [ + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": "Figure 2. The proposed MLS method. An image " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": " is first augmented to two views and sent to two encoders. The embeddings " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "g_{1}, g_{2} \\in \\mathbb{R}^{d_{g}}" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "z_{1}, z_{2} \\in \\mathbb{R}^{d_{z}}" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": " are features after the backbone and the MLP, respectively. View 2's features (" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "g_{2}" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "z_{2}" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": ") are enqueued to form two dictionaries " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "Q_{g} \\in \\mathbb{R}^{D \\times d_{g}}" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "Q_{z} \\in \\mathbb{R}^{D \\times d_{z}}" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": " in the same order. As shown in the right half, the embedding " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "g_{1}" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": " picks its top " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": " nearest embeddings from the queue " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": " to produce binary pseudo labels " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "y \\in \\mathbb{R}^{D}" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": ". Then, the embeddings from " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "Q_{z}" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": " are treated as classifiers that calculate the logit " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "p \\in \\mathbb{R}^{D}" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "z_{1}" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": ", which is compared against the pseudo-labels " + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 198, + 547, + 254 + ], + "type": "text", + "content": " by a BCE loss. Best viewed in color." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 347, + 86, + 517, + 184 + ], + "blocks": [ + { + "bbox": [ + 347, + 86, + 517, + 184 + ], + "lines": [ + { + "bbox": [ + 347, + 86, + 517, + 184 + ], + "spans": [ + { + "bbox": [ + 347, + 86, + 517, + 184 + ], + "type": "image", + "image_path": "67b31838b4a5e8842f421ef80f76de4a07419b5bb607a66a4fff72ade9c8a2a9.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 272, + 132, + 285 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 272, + 132, + 285 + ], + "spans": [ + { + "bbox": [ + 47, + 272, + 132, + 285 + ], + "type": "text", + "content": "3.3. Optimization" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 291, + 288, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 291, + 288, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 291, + 288, + 422 + ], + "type": "text", + "content": "When we use the multi-label loss " + }, + { + "bbox": [ + 46, + 291, + 288, + 422 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{ml}" + }, + { + "bbox": [ + 46, + 291, + 288, + 422 + ], + "type": "text", + "content": " as the only loss function, we found that empirically the optimization process often faces an unstable training issue. We believe this unstable optimization should be attributed to the adverse interaction between assigning pseudo-labels and learning representations from a poor starting point. High quality embeddings from the queues " + }, + { + "bbox": [ + 46, + 291, + 288, + 422 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 46, + 291, + 288, + 422 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 291, + 288, + 422 + ], + "type": "inline_equation", + "content": "Q_{z}" + }, + { + "bbox": [ + 46, + 291, + 288, + 422 + ], + "type": "text", + "content": " cannot be obtained if the pseudo-labels are incorrect. At the same time picking nearest neighbors and classification will surely fail if the enqueued embeddings are misleading (a point which was mentioned in DenseCL [39], too)." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 423, + 287, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 423, + 287, + 517 + ], + "spans": [ + { + "bbox": [ + 46, + 423, + 287, + 517 + ], + "type": "text", + "content": "Two strategies easily stabilize the multi-label SSL learning. One is to use InfoNCE alone in the first few epochs to warmup the dictionary " + }, + { + "bbox": [ + 46, + 423, + 287, + 517 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 46, + 423, + 287, + 517 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 423, + 287, + 517 + ], + "type": "inline_equation", + "content": "Q_{z}" + }, + { + "bbox": [ + 46, + 423, + 287, + 517 + ], + "type": "text", + "content": ". The other remedy is to combine InfoNCE with our multi-label BCE loss during the whole training process, which is widely used in previous methods [39, 1, 40] and easier in implementation. Hence, we adopt this strategy and our overall loss function is formulated as:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 126, + 519, + 287, + 531 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 126, + 519, + 287, + 531 + ], + "spans": [ + { + "bbox": [ + 126, + 519, + 287, + 531 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathcal {L} _ {n c e} + \\lambda \\mathcal {L} _ {m l}, \\tag {10}", + "image_path": "5718b07afc1d89e1eacaf55c0a1c8c9f2586a4440add76de9cba115e6ef81fd8.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 537, + 287, + 585 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 537, + 287, + 585 + ], + "spans": [ + { + "bbox": [ + 47, + 537, + 287, + 585 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 537, + 287, + 585 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{nce}" + }, + { + "bbox": [ + 47, + 537, + 287, + 585 + ], + "type": "text", + "content": " is the InfoNCE loss that is adopted in MoCo-v2 (c.f. Eq. 1) and along with many multi-label SSL methods. " + }, + { + "bbox": [ + 47, + 537, + 287, + 585 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{ml}" + }, + { + "bbox": [ + 47, + 537, + 287, + 585 + ], + "type": "text", + "content": " is our multi-label BCE loss (c.f. Eq. 9). The value of combination weight " + }, + { + "bbox": [ + 47, + 537, + 287, + 585 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 47, + 537, + 287, + 585 + ], + "type": "text", + "content": " is fixed at " + }, + { + "bbox": [ + 47, + 537, + 287, + 585 + ], + "type": "inline_equation", + "content": "\\lambda = 0.5" + }, + { + "bbox": [ + 47, + 537, + 287, + 585 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 586, + 287, + 609 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 287, + 609 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 287, + 609 + ], + "type": "text", + "content": "The proposed method is abbreviated as MLS (multi-label self-supervised) learning." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 621, + 127, + 634 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 621, + 127, + 634 + ], + "spans": [ + { + "bbox": [ + 47, + 621, + 127, + 634 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 641, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 712 + ], + "type": "text", + "content": "Now we validate the effectiveness of MLS through extensive experiments. We first describe the settings of our experiments, including datasets for upstream pretraining and downstream finetuning, training details, and the architecture for object detection, instance/semantic segmentation and image classification." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 272, + 430, + 285 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 272, + 430, + 285 + ], + "spans": [ + { + "bbox": [ + 306, + 272, + 430, + 285 + ], + "type": "text", + "content": "4.1. Experimental settings" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 292, + 545, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 292, + 545, + 472 + ], + "spans": [ + { + "bbox": [ + 304, + 292, + 545, + 472 + ], + "type": "text", + "content": "Datasets. We adopted the MS-COCO train2017 set [23] for SSL pretraining, which is widely applied in the study of scene image SSL [46, 41, 39]. Note that we did not use ImageNet. For downstream tasks, we conducted experiments on MS-COCO, VOC0712 [12], CityScapes [10] as well as 7 small classification datasets (CUB200 [37], Flowers [26], Cars [22], Aircraft [25], Indoor67 [30], Pets [28] and DTD [9]) following previous SSL methods [2]. Specifically, MS-COCO contains 118,287 and 5000 images for training and validation, respectively. VOC2007 has 5011 and 4952 images in the trainval and test sets, respectively. CityScapes is a semantic segmentation dataset containing 2975 and 500 images for training and validation, respectively. For more information about the 7 small classification datasets, please refer to [2] for a more detailed description." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "spans": [ + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "text", + "content": "Pretraining. We adopted ResNet-50 [18] as our base encoder (c.f. Fig. 2) and mostly follow the structure of MoCoV2. We pretrained our models for 400 or 800 epochs on MSCOCO, set learning rate as 0.3, weight decay as 0.0001. For data augmentation, we adopted random resized crop, color distortion, random gray scale, random flip, etc, following [36, 3]. The queue size " + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "inline_equation", + "content": "Q_{z}" + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "text", + "content": " was 4096. The temperature " + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "text", + "content": " was set as 0.2 and was shared between the InfoNCE loss and our multi-label BCE loss. The dimensionalities of the embeddings " + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "inline_equation", + "content": "g_{1}" + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "inline_equation", + "content": "z_{1}" + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "text", + "content": " were 2048 and 256, respectively. For faster convergence, we adjusted the momentum update coefficient to 0.995. With regard to our multi-label BCE loss, the parameter " + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "text", + "content": " was set as 20, and the combination coefficient " + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 473, + 545, + 639 + ], + "type": "text", + "content": " was 0.5." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 641, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 712 + ], + "type": "text", + "content": "Downstream. We finetuned the pretrained model on various benchmarks, including MS-COCO object detection and instance segmentation, CityScapes semantic segmentation, VOC0712 detection and other classification benchmarks. Specifically, we finetuned on MS-COCO using the Mask-RCNN R50-FPN/C4 [17] architecture for 90k itera" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6697" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 95, + 125, + 500, + 315 + ], + "blocks": [ + { + "bbox": [ + 46, + 68, + 547, + 125 + ], + "lines": [ + { + "bbox": [ + 46, + 68, + 547, + 125 + ], + "spans": [ + { + "bbox": [ + 46, + 68, + 547, + 125 + ], + "type": "text", + "content": "Table 1. Results of COCO detection and segmentation. All SSL models (except those pretrained on ImageNet) were first pretrained on MS-COCO and then finetuned on COCO with Mask R-CNN R50-FPN [17]. Our MLS was pretrained for 400 or 800 epochs for fair comparisons. We reproduced " + }, + { + "bbox": [ + 46, + 68, + 547, + 125 + ], + "type": "inline_equation", + "content": "\\mathrm{SoCo}^*" + }, + { + "bbox": [ + 46, + 68, + 547, + 125 + ], + "type": "text", + "content": " with the settings in [41]. Note that SetSim [40] and ReSim [44] are adaptable to scene image pretraining, but only reported ImageNet pretraining results. The column 'Epochs' means the number of pretraining epochs. ORL " + }, + { + "bbox": [ + 46, + 68, + 547, + 125 + ], + "type": "inline_equation", + "content": "^{+}" + }, + { + "bbox": [ + 46, + 68, + 547, + 125 + ], + "type": "text", + "content": " [46] needs two pretraining stages (800 epochs each), so the total training time is doubled." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 95, + 125, + 500, + 315 + ], + "lines": [ + { + "bbox": [ + 95, + 125, + 500, + 315 + ], + "spans": [ + { + "bbox": [ + 95, + 125, + 500, + 315 + ], + "type": "table", + "html": "
MethodDataEpochsDetectionSegmentation
APbboxAPbbox50APbbox75APsegAPseg50APseg75
Supervised [41]ImageNet9038.959.642.735.456.538.1
ReSim-C4 [44]ImageNet20039.359.743.135.756.738.1
LEWELM [20]ImageNet20040.059.843.736.157.038.7
SetSim [40]ImageNet20040.260.743.936.457.739.0
SoCo* [41]COCO40039.159.142.735.456.037.8
Self-EMD [24]COCO80039.360.142.8---
MoCo-v2 [6]COCO80038.558.142.134.855.337.3
BYOL [14]COCO80038.858.542.235.055.938.1
DenseCL [39]COCO80039.659.343.335.756.538.4
ORL+ [46]COCO160040.360.244.436.357.338.9
MLSCOCO40040.160.243.936.257.338.6
MLSCOCO80040.560.744.536.557.739.1
", + "image_path": "32e16244eb49207e11ebcfe1c03de18b7d08211b6a5fd9fb282dfb4bce6cb02e.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 334, + 289, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 334, + 289, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 334, + 289, + 479 + ], + "type": "text", + "content": "tions. For VOC0712, we finetuned for 24k iterations with Faster-RCNN R50-C4 [31]. For CityScapes semantic segmentation, we adopted PSANet [50] and PSPNet [49] for 40k iterations. For classification, we chose VOC2007 for multi-label recognition and finetuned 120 epochs on 7 small classification datasets. We ran 3 times on VOC detection and 2 runs on CityScapes since these results have relatively large variations. Following previous studies, the evaluation metrics for detection, segmentation and classification are AP, mIoU/mAcc and top-1 accuracy, respectively. All the experiments were conducted with RTX 3090 GPUs in the PyTorch [29] framework." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 489, + 268, + 502 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 489, + 268, + 502 + ], + "spans": [ + { + "bbox": [ + 47, + 489, + 268, + 502 + ], + "type": "text", + "content": "4.2. COCO detection and segmentation results" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 509, + 287, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 509, + 287, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 509, + 287, + 653 + ], + "type": "text", + "content": "We first evaluated downstream performance on MS-COCO object detection and instance segmentation. Following previous work, we used Mask R-CNN R50-FPN for finetuning. The results is in Table 1. DenseCL [39] and Self-EMD [24] are those adopting dense matching, while SoCo [41] and ORL [46] both resort to the unsupervised object discovery method Selective Search [35]. For a fair comparison, we reproduced SoCo's results since it was originally pretrained on " + }, + { + "bbox": [ + 46, + 509, + 287, + 653 + ], + "type": "inline_equation", + "content": "\\mathrm{COCO + }" + }, + { + "bbox": [ + 46, + 509, + 287, + 653 + ], + "type": "text", + "content": " [41] (which is based on COCO but has more unlabeled data). Note that ReSim-C4 [44] and SetSim [40] are suitable for scene image pretraining, but only ImageNet results were reported." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "content": "As shown in Table 1, with only 400 epochs of pretraining, our MLS is almost better than all counterparts (e.g., DenseCL, SoCo, LEWEL [20]) and surpasses supervised results by " + }, + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "inline_equation", + "content": "1.2\\%" + }, + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "content": " APbbox and " + }, + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "inline_equation", + "content": "0.8\\%" + }, + { + "bbox": [ + 46, + 653, + 288, + 715 + ], + "type": "text", + "content": " APseg. With the standard 800 epochs of pretraining, MLS is better than all previous" + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 309, + 375, + 543, + 492 + ], + "blocks": [ + { + "bbox": [ + 305, + 331, + 545, + 375 + ], + "lines": [ + { + "bbox": [ + 305, + 331, + 545, + 375 + ], + "spans": [ + { + "bbox": [ + 305, + 331, + 545, + 375 + ], + "type": "text", + "content": "Table 2. Results on COCO with the Mask R-CNN R50-C4 detector. 'Data' stands for the pretraining dataset. 'CC' and 'IN' means COCO and ImageNet, respectively. All SSL models were pretrained for 400 epochs on MS-COCO." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 375, + 543, + 492 + ], + "lines": [ + { + "bbox": [ + 309, + 375, + 543, + 492 + ], + "spans": [ + { + "bbox": [ + 309, + 375, + 543, + 492 + ], + "type": "table", + "html": "
MethodDataDetectionSegmentation
APbboxAPbbox50APbbox75APsegAPseg50APseg75
Random-26.444.027.829.346.930.8
SupervisedIN38.158.141.133.254.835.0
BYOLCC36.956.739.432.453.534.3
MoCo-v2CC37.356.740.432.853.534.9
SoCo*CC36.956.239.732.453.034.5
DenseCLCC38.357.941.433.554.435.7
MLSCC38.658.341.533.855.136.0
", + "image_path": "9749705d77837b5891262062ad7c36fac57b6f06552f0fc233b862cb36941823.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 517, + 545, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 517, + 545, + 566 + ], + "spans": [ + { + "bbox": [ + 304, + 517, + 545, + 566 + ], + "type": "text", + "content": "scene image SSL methods. This further verifies our motivation: formulating scene image self-supervised learning as a multi-label classification is both simpler in concept and effective in performance." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 567, + 545, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 567, + 545, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 567, + 545, + 640 + ], + "type": "text", + "content": "We also tried the Mask R-CNN R50-C4 structure. Since there are relatively less SSL results based on this structure, we reproduced supervised learning, BYOL [14], MoCoV2 [6], SoCo [41] and DenseCL [39] methods by pretraining and finetuning on MS-COCO. To compare fairly, all these SSL models were pretrained for 400 epochs." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "type": "text", + "content": "As can be found in Table 2, our MLS surpasses all previous self-supervised learning methods like SoCo [41] and DenseCL [39], despite being much simpler than them. Note that SoCo needs unsupervised box generation and multiple auxiliary loss functions. Our MLS also achieves better results than supervised ImageNet pretraining, with an" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "6698" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 56, + 113, + 278, + 223 + ], + "blocks": [ + { + "bbox": [ + 47, + 69, + 287, + 113 + ], + "lines": [ + { + "bbox": [ + 47, + 69, + 287, + 113 + ], + "spans": [ + { + "bbox": [ + 47, + 69, + 287, + 113 + ], + "type": "text", + "content": "Table 3. Results of CityScapes semantic segmentation using two different segmentation pipelines (PSANet [50] and PSPNet [49]). 'Data' stands for the pretraining dataset. 'CC' and 'IN' means COCO and ImageNet, respectively." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 56, + 113, + 278, + 223 + ], + "lines": [ + { + "bbox": [ + 56, + 113, + 278, + 223 + ], + "spans": [ + { + "bbox": [ + 56, + 113, + 278, + 223 + ], + "type": "table", + "html": "
MethodDataPSANetPSPNet
mIoUmAccaAccmIoUmAccaAcc
SupervisedIN77.586.695.977.886.795.9
BYOLCC77.686.695.976.985.995.9
MoCo-v2CC76.885.895.876.885.495.8
DenseCLCC77.686.696.077.686.395.9
SoCoCC76.385.395.876.585.395.8
MLSCC79.087.396.278.586.696.1
", + "image_path": "fc8d0501d961b3f258868e87a660dcd10d51367d95a7e74a336fa9a9a4d720e5.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 56, + 275, + 278, + 417 + ], + "blocks": [ + { + "bbox": [ + 47, + 232, + 287, + 275 + ], + "lines": [ + { + "bbox": [ + 47, + 232, + 287, + 275 + ], + "spans": [ + { + "bbox": [ + 47, + 232, + 287, + 275 + ], + "type": "text", + "content": "Table 4. Results of VOC0712 object detection using the Faster-RCNN R50-C4 object detector. All SSL models were pretrained on MS-COCO for 800 epochs. BYOL and MoCo-v2 results were reproduced by us." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 56, + 275, + 278, + 417 + ], + "lines": [ + { + "bbox": [ + 56, + 275, + 278, + 417 + ], + "spans": [ + { + "bbox": [ + 56, + 275, + 278, + 417 + ], + "type": "table", + "html": "
MethodDataAP\\( AP_{50} \\)\\( AP_{75} \\)
Random-32.859.031.6
SupervisedImageNet53.381.058.8
SwAV [3]ImageNet45.177.446.5
SimCLR [4]ImageNet51.579.455.6
SoCo* [41]COCO51.778.657.2
Self-EMD [24]COCO53.080.058.6
BYOLCOCO51.780.256.4
MoCo-v2COCO53.780.059.5
MLSCOCO55.081.661.2
", + "image_path": "18cf1a68e05ee7f60257a1ae38ae0ae091fbb7036cdc1b30100ef20bd95db522.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 436, + 287, + 461 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 436, + 287, + 461 + ], + "spans": [ + { + "bbox": [ + 47, + 436, + 287, + 461 + ], + "type": "text", + "content": "improvement of " + }, + { + "bbox": [ + 47, + 436, + 287, + 461 + ], + "type": "inline_equation", + "content": "0.5\\%" + }, + { + "bbox": [ + 47, + 436, + 287, + 461 + ], + "type": "inline_equation", + "content": "\\mathrm{AP}^{bbox}" + }, + { + "bbox": [ + 47, + 436, + 287, + 461 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 436, + 287, + 461 + ], + "type": "inline_equation", + "content": "0.6\\%" + }, + { + "bbox": [ + 47, + 436, + 287, + 461 + ], + "type": "inline_equation", + "content": "\\mathrm{AP}^{seg}" + }, + { + "bbox": [ + 47, + 436, + 287, + 461 + ], + "type": "text", + "content": " for object detection and instance segmentation, respectively." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 468, + 153, + 481 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 468, + 153, + 481 + ], + "spans": [ + { + "bbox": [ + 47, + 468, + 153, + 481 + ], + "type": "text", + "content": "4.3. Transfer learning" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 486, + 287, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 486, + 287, + 533 + ], + "spans": [ + { + "bbox": [ + 47, + 486, + 287, + 533 + ], + "type": "text", + "content": "Next, we test how our MLS method performs on various transfer learning tasks, including CityScapes semantic segmentation, VOC0712 object detection and (multi-label) classification." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 534, + 287, + 701 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 534, + 287, + 701 + ], + "spans": [ + { + "bbox": [ + 46, + 534, + 287, + 701 + ], + "type": "text", + "content": "CityScapes semantic segmentation. We first transferred pretrained models to CityScapes [10] semantic segmentation. Because relatively few SSL methods worked on this benchmark and the segmentation architecture generally differed, we first reproduced several SSL methods (BYOL, MoCo-v2, DenseCL and SoCo), then finetuned them in the same setting. It is clearly demonstrated in Table 3 that our multi-label self-supervised learning method is superior than all of them, surpassing state-of-the-art dense matching approach DenseCL [39] and object discovery method SoCo [41], both by significant margins. Our MLS also improves supervised learning from " + }, + { + "bbox": [ + 46, + 534, + 287, + 701 + ], + "type": "inline_equation", + "content": "77.5\\%" + }, + { + "bbox": [ + 46, + 534, + 287, + 701 + ], + "type": "text", + "content": " mIoU to " + }, + { + "bbox": [ + 46, + 534, + 287, + 701 + ], + "type": "inline_equation", + "content": "79.0\\%" + }, + { + "bbox": [ + 46, + 534, + 287, + 701 + ], + "type": "text", + "content": " mIoU and from " + }, + { + "bbox": [ + 46, + 534, + 287, + 701 + ], + "type": "inline_equation", + "content": "77.8\\%" + }, + { + "bbox": [ + 46, + 534, + 287, + 701 + ], + "type": "text", + "content": " mIoU to " + }, + { + "bbox": [ + 46, + 534, + 287, + 701 + ], + "type": "inline_equation", + "content": "78.5\\%" + }, + { + "bbox": [ + 46, + 534, + 287, + 701 + ], + "type": "text", + "content": " mIoU with PSANet [50] and PSPNet [49], respectively." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "content": "VOC0712 object detection. Moving on to other dense" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "type": "text", + "content": "prediction tasks, we evaluated the effectiveness of MLS on VOC0712 object detection with Faster R-CNN R50-C4. Since there were missing results for BYOL and MoCo-v2 in this experimental setting, we reproduced both of them for a fair comparison. As shown in Table 4, our MLS surpasses all previous object-centric SSL methods by a large margin. For example, our method is higher than SimCLR by " + }, + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "type": "inline_equation", + "content": "3.5\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "type": "text", + "content": " AP and " + }, + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "type": "inline_equation", + "content": "5.6\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "type": "inline_equation", + "content": "\\mathrm{AP}_{75}" + }, + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "type": "text", + "content": " metrics. MLS is also better than supervised ImageNet results (an improvement of " + }, + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "type": "inline_equation", + "content": "1.7\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "type": "text", + "content": " AP and " + }, + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "type": "inline_equation", + "content": "2.4\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "type": "inline_equation", + "content": "\\mathrm{AP}_{75}" + }, + { + "bbox": [ + 304, + 72, + 545, + 203 + ], + "type": "text", + "content": "), showing again the great potential of multi-label self-supervised learning." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 205, + 546, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 205, + 546, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 205, + 546, + 491 + ], + "type": "text", + "content": "Single- and multi-label classification. Then, we explore how our proposed method behaves on image classification benchmarks. As pointed out by a previous SSL research work [45], various dense matching or unsupervised object discovery based SSL methods usually sacrifice the performance of image classification, in return for high accuracy in dense prediction tasks. In other words, classification is tough for these SSL methods. Therefore, we evaluated MLS on both multi-label (e.g., VOC2007) and single-label classification tasks. As discussed above, we also reproduced the results of MoCo-v2 and DenseCL because MLS has the same architecture with them. It can be found in Table 5 that MLS is consistently better than previous SSL methods, surpassing our baseline MoCo-v2 by a noticeable margin—an improvement of " + }, + { + "bbox": [ + 304, + 205, + 546, + 491 + ], + "type": "inline_equation", + "content": "5.3\\%" + }, + { + "bbox": [ + 304, + 205, + 546, + 491 + ], + "type": "text", + "content": " mAP for VOC07 and " + }, + { + "bbox": [ + 304, + 205, + 546, + 491 + ], + "type": "inline_equation", + "content": "3.0\\%" + }, + { + "bbox": [ + 304, + 205, + 546, + 491 + ], + "type": "text", + "content": " accuracy for Indoor67. We attribute this gain to the joint embedding property of MLS: since our method is optimized with global features, it can be naturally easier for us to capture image-level information, thus suitable for image classification tasks. However, all SSL methods are generally worse than supervised ImageNet pretraining, showing that supervised pretraining with more pretraining data (ImageNet vs. COCO) still remains a powerful technique for general image classification." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 502, + 405, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 502, + 405, + 514 + ], + "spans": [ + { + "bbox": [ + 306, + 502, + 405, + 514 + ], + "type": "text", + "content": "4.4. Ablation studies" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 521, + 545, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 545, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 545, + 676 + ], + "type": "text", + "content": "Compare with other loss functions. We first explore if there are other alternatives besides multi-label BCE that can also achieve similar or even better results. An alternative, however, needs to produce multiple positive paradigms in the loss term. We consider kNN softmax adopted in [21, 36], and propose a variant of BCE by disregarding the negative term in Eq. 9 (calling it 'BCE-pos'). As can be seen in Table 6, adding kNN softmax and the BCE-pos loss function besides the InfoNCE loss used in [36] both lead to consistent improvements in all metrics, demonstrating the effectiveness of our hypothesis. Still, they are both inferior to our proposed MLS, showing that pure BCE works better than the variant in scene image self-supervised learning." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "Why keeping two dictionaries? There are two dictionaries " + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "inline_equation", + "content": "Q_{z}" + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": " in our pipeline with different functionalities: one for pseudo-labeling and the other for classification." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "6699" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 87, + 102, + 507, + 180 + ], + "blocks": [ + { + "bbox": [ + 46, + 68, + 547, + 102 + ], + "lines": [ + { + "bbox": [ + 46, + 68, + 547, + 102 + ], + "spans": [ + { + "bbox": [ + 46, + 68, + 547, + 102 + ], + "type": "text", + "content": "Table 5. Results on downstream classification, including VOC2007 multi-label and 7 small single-label classification datasets. We reproduced the baseline MoCo-v2 and dense matching approach DenseCL for a fair comparison. The evaluation metric for VOC2007 is mAP while for others is top-1 accuracy. All models were pretrained for 400 epochs on the MS-COCO dataset." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 87, + 102, + 507, + 180 + ], + "lines": [ + { + "bbox": [ + 87, + 102, + 507, + 180 + ], + "spans": [ + { + "bbox": [ + 87, + 102, + 507, + 180 + ], + "type": "table", + "html": "
MethodDataVOC07CUB200FlowersCarsAircraftIndoorPetsDTD
SupervisedImageNet89.081.396.790.686.758.164.474.7
MoCo-v2COCO80.568.889.687.580.464.179.460.9
DenseCLCOCO83.769.388.688.379.965.480.061.8
MLSCOCO85.871.791.288.581.267.181.963.0
", + "image_path": "85dbcf3644c4e8d1e2329277c74f643a1bbafa309b6036d02310e038bc8c06b3.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 51, + 240, + 284, + 319 + ], + "blocks": [ + { + "bbox": [ + 47, + 196, + 287, + 240 + ], + "lines": [ + { + "bbox": [ + 47, + 196, + 287, + 240 + ], + "spans": [ + { + "bbox": [ + 47, + 196, + 287, + 240 + ], + "type": "text", + "content": "Table 6. MS-COCO detection and segmentation results using different pretraining loss functions. The 'kNN' loss was adopted in [36] and the 'BCE-pos' loss means only positive terms of binary cross entropy in Eq. 9 were considered." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 51, + 240, + 284, + 319 + ], + "lines": [ + { + "bbox": [ + 51, + 240, + 284, + 319 + ], + "spans": [ + { + "bbox": [ + 51, + 240, + 284, + 319 + ], + "type": "table", + "html": "
MethodDetectionSegmentation
APbboxAPbbox50APbbox75APsegAPseg50APseg75
Baseline38.858.342.535.555.537.5
+kNN39.158.742.635.355.837.9
+BCE-pos39.659.443.135.756.538.1
+BCE (ours)40.160.243.936.257.338.6
", + "image_path": "1a49863bf138be562c67d08fa91b1ec77efa36d5fbf25038c2bbc3964ddb7232.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "spans": [ + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "text", + "content": "Why not keeping only one for simplicity? We explain this problem through both visualization and quantitative experiments. First, we plot the histogram of scores in Fig. 3, with " + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "inline_equation", + "content": "g_{1} \\odot Q_{g}" + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "inline_equation", + "content": "z_{1} \\odot Q_{z}" + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "text", + "content": " representing the backbone and MLP scores, respectively. The backbone scores have witnessed a dramatic change after training, indicating some information the network potentially obtained by SSL. On the other hand, the MLP scores almost always follow a normal distribution, with only slight changes in the mean and variance statistics. Hence, we choose to use the backbone queue " + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "text", + "content": " for pseudo labeling. The MLP dictionary " + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "inline_equation", + "content": "Q_{z}" + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "text", + "content": " is used for classification, following the common practice in previous SSL methods [16, 39]. Our choice is also verified by the experiments in Table 7, where using only " + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "inline_equation", + "content": "Q_{z}" + }, + { + "bbox": [ + 46, + 340, + 287, + 532 + ], + "type": "text", + "content": " is clearly sub-optimal, and worse than our MLS where they are jointly adopted." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "text", + "content": "Effect of " + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "text", + "content": ". Now we examine how different " + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "text", + "content": " values (the number of pseudo positive labels generated) affect the final results of our MLS method. The downstream results of MS-COCO detection and segmentation can be found in Table 8, where a too small and a too large " + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "text", + "content": " value both lead to a performance drop. A small " + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "text", + "content": " means semantically related images may become false negatives in BCE classification, while a large " + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "text", + "content": " will similarly lead to false positives. Our MLS is relatively more robust when " + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "text", + "content": " is small. But when " + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "text", + "content": " is too large, the accuracy drop is significant. Based on this observation, we choose " + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "inline_equation", + "content": "k = 20" + }, + { + "bbox": [ + 46, + 533, + 287, + 664 + ], + "type": "text", + "content": " by default." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": "Effect of queue size and " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": ". The fourth module we evaluated is the dictionary (queue) size and the combination weight " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": " in Eq. 10. We pretrained the models on the MS-COCO dataset using MLS and finetuned them for COCO" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 333, + 240, + 519, + 301 + ], + "blocks": [ + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "lines": [ + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "spans": [ + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "text", + "content": "Table 7. Effect of using different dictionaries. " + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "text", + "content": " only' means the embeddings in " + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "inline_equation", + "content": "g_{1}" + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "text", + "content": " are used twice to both generate the pseudo labels " + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "text", + "content": " and the logits " + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "text", + "content": " (c.f. Fig. 2). " + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "inline_equation", + "content": "Q_{z}" + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "text", + "content": " only' means only using " + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "inline_equation", + "content": "Q_{z}" + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "inline_equation", + "content": "z_{1}" + }, + { + "bbox": [ + 304, + 196, + 545, + 240 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 333, + 240, + 519, + 301 + ], + "lines": [ + { + "bbox": [ + 333, + 240, + 519, + 301 + ], + "spans": [ + { + "bbox": [ + 333, + 240, + 519, + 301 + ], + "type": "table", + "html": "
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Visualization of the score distribution of one sampled COCO image before and after training. The backbone scores and MLS scores are " + }, + { + "bbox": [ + 304, + 505, + 545, + 561 + ], + "type": "inline_equation", + "content": "g_{1} \\odot Q_{g}" + }, + { + "bbox": [ + 304, + 505, + 545, + 561 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 505, + 545, + 561 + ], + "type": "inline_equation", + "content": "z_{1} \\odot Q_{z}" + }, + { + "bbox": [ + 304, + 505, + 545, + 561 + ], + "type": "text", + "content": ", respectively. The backbone scores are more indicative compared with MLP scores, thus suitable for pseudo label generation." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "object detection with Mask R-CNN R50-FPN. As demonstrated in Fig. 5 (a), a too small queue size (e.g., 1024) is detrimental for SSL pretraining, since a small queue means limited representations stored, which is not enough for an image to retrieve its positive neighbors. An overly large dictionary also obtains sub-optimal results, because dictionaries that are too large probably contain many out-of-date embeddings (due to the deque and enqueue mechanism [6]) and might lead to incorrect pseudo labels. 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It can be seen in Figure 5 (b) that all " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": " leads to consistent" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "6700" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 74, + 100, + 122 + ], + "blocks": [ + { + "bbox": [ + 52, + 74, + 100, + 122 + ], + "lines": [ + { + "bbox": [ + 52, + 74, + 100, + 122 + ], + "spans": [ + { + "bbox": [ + 52, + 74, + 100, + 122 + ], + "type": "image", + "image_path": 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Visualization of positive pseudo-labels picked up by MLS across images in COCO. For each randomly cropped query image patch, we find the top-4 of its NNs from the dictionary " + }, + { + "bbox": [ + 46, + 236, + 545, + 301 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 46, + 236, + 545, + 301 + ], + "type": "text", + "content": " (shown in yellow rectangles). All these rectangles are generated by the random resized crop data augmentation, a standard component in SSL. We record the cropped boxes' coordinates of the embeddings (the query " + }, + { + "bbox": [ + 46, + 236, + 545, + 301 + ], + "type": "inline_equation", + "content": "g_{1}" + }, + { + "bbox": [ + 46, + 236, + 545, + 301 + ], + "type": "text", + "content": " and those stored in the dictionary " + }, + { + "bbox": [ + 46, + 236, + 545, + 301 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 46, + 236, + 545, + 301 + ], + "type": "text", + "content": " during data augmentation). To be more precise, we first randomly sampled 60 query images. We then randomly sampled 5 query images out of the set of 60 and found their top-4 NNs. In addition, we manually select the worst query image (i.e., semantically most different from its top-4 NNs), which is the right half of the last row. 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Effect of different queue size and " + }, + { + "bbox": [ + 46, + 514, + 286, + 548 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 514, + 286, + 548 + ], + "type": "text", + "content": " values (c.f. Eq. 10) in terms of downstream tasks' results. In this paper, we choose 4096 queue size and " + }, + { + "bbox": [ + 46, + 514, + 286, + 548 + ], + "type": "inline_equation", + "content": "\\lambda = 0.5" + }, + { + "bbox": [ + 46, + 514, + 286, + 548 + ], + "type": "text", + "content": " by default." + } + ] + } + ], + "index": 37, + "angle": 0, + "type": "image_caption" + } + ], + "index": 33 + }, + { + "type": "image", + "bbox": [ + 171, + 418, + 277, + 495 + ], + "blocks": [ + { + "bbox": [ + 171, + 418, + 277, + 495 + ], + "lines": [ + { + "bbox": [ + 171, + 418, + 277, + 495 + ], + "spans": [ + { + "bbox": [ + 171, + 418, + 277, + 495 + ], + "type": "image", + "image_path": "a61c6b9df60600c11a510b9b79be01ad5746caf678c0b0453c52533a1ac5a7ed.jpg" + } + ] + } + ], + "index": 35, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 199, + 502, + 249, + 510 + ], + "lines": [ + { + "bbox": [ + 199, + 502, + 249, + 510 + ], + "spans": [ + { + "bbox": [ + 199, + 502, + 249, + 510 + ], + "type": "text", + "content": "(b) Effect of " + }, + { + "bbox": [ + 199, + 502, + 249, + 510 + ], + "type": "inline_equation", + "content": "\\lambda" + } + ] + } + ], + "index": 36, + "angle": 0, + "type": "image_caption" + } + ], + "index": 35 + }, + { + "bbox": [ + 46, + 569, + 286, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 569, + 286, + 604 + ], + "spans": [ + { + "bbox": [ + 46, + 569, + 286, + 604 + ], + "type": "text", + "content": "improvement over the baseline " + }, + { + "bbox": [ + 46, + 569, + 286, + 604 + ], + "type": "inline_equation", + "content": "(c.f." + }, + { + "bbox": [ + 46, + 569, + 286, + 604 + ], + "type": "text", + "content": " Table 6), and there is a sweet spot in the choice of " + }, + { + "bbox": [ + 46, + 569, + 286, + 604 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 569, + 286, + 604 + ], + "type": "text", + "content": ". Thus, in this paper we choose " + }, + { + "bbox": [ + 46, + 569, + 286, + 604 + ], + "type": "inline_equation", + "content": "\\lambda = 0.5" + }, + { + "bbox": [ + 46, + 569, + 286, + 604 + ], + "type": "text", + "content": " by default in our experiment." + } + ] + } + ], + "index": 38 + }, + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "type": "text", + "content": "Visualization of positive pseudo-labels. Last but not least, we validate the effectiveness of our MLS pipeline by visualization: are the top " + }, + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "type": "text", + "content": " nearest neighbors (NN) picked up from the dictionary " + }, + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "type": "text", + "content": " indeed semantically similar to the input? Because random resized crop is applied in the SSL pipeline (it is the cropped patch that is sent to the network), we record the cropped location of each image during data augmentation. Then, for each query " + }, + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "type": "inline_equation", + "content": "g_{1}" + }, + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "type": "text", + "content": " in Fig. 2, we find its top-4 NNs stored in the queue " + }, + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "type": "inline_equation", + "content": "Q_{g}" + }, + { + "bbox": [ + 46, + 605, + 286, + 714 + ], + "type": "text", + "content": ". All these queries" + } + ] + } + ], + "index": 39 + }, + { + "bbox": [ + 304, + 321, + 545, + 440 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 321, + 545, + 440 + ], + "spans": [ + { + "bbox": [ + 304, + 321, + 545, + 440 + ], + "type": "text", + "content": "and NNs are associated with a certain cropped patch, and thus we visualize them with red and yellow rectangles, respectively. As shown in Fig. 4, our MLS backbone effectively captures semantically similar correspondences across the dataset. Specifically, intra-class variance (the first row) and multiple positive partial concepts (the second and third rows) are clearly demonstrated, showing that our motivation in Sec. 1 is valid and that MLS is not only suitable for scene image SSL, but might also be adaptable to image retrieval, as well." + } + ] + } + ], + "index": 40 + }, + { + "bbox": [ + 306, + 453, + 467, + 465 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 453, + 467, + 465 + ], + "spans": [ + { + "bbox": [ + 306, + 453, + 467, + 465 + ], + "type": "text", + "content": "5. Conclusions and Limitations" + } + ] + } + ], + "index": 41 + }, + { + "bbox": [ + 304, + 474, + 545, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 545, + 664 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 545, + 664 + ], + "type": "text", + "content": "In this paper, we argued that scene image self-supervised learning does not necessarily rely on dense matching or unsupervised object discovery methods, and instead proposed our Multi-Label Self-supervised (MLS) learning approach. The key idea in MLS is that a multi-label image contains multiple concepts or objects, hence we need to have multiple positive pairs corresponding to different objects in the input image. Specifically, we create two dictionaries, one for creating pseudo-labels (positive or negative pairs) and the other for distinguishing between them (i.e., a multi-label classification problem). This is the first time that multi-label SSL is cast as a multi-label classification problem, and MLS has been validated by extensive experiments on various benchmarks (e.g., MS-COCO, CityScapes, VOC0712, etc.) and tasks (object detection, image segmentation, single- and multi-label classification)." + } + ] + } + ], + "index": 42 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "As for limitations, it still remains unclear why the BCE loss alone will cause an unstable training issue. This is a long-lasting and open question as numerous scene image SSL methods [39, 44, 40, 1] also struggle if the InfoNCE" + } + ] + } + ], + "index": 43 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "6701" + } + ] + } + ], + "index": 44 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 145 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 145 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 145 + ], + "type": "text", + "content": "loss is removed. Hence, these methods (including our MLS) always use their proposed modules in combination with InfoNCE. In the future, we will explore how and why the collapsing phenomenon exists without the normal contrastive loss, and will apply our MLS to single-label image SSL to further explore the adaptability of our method." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 156, + 107, + 169 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 156, + 107, + 169 + ], + "spans": [ + { + "bbox": [ + 48, + 156, + 107, + 169 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 48, + 177, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 16, + "blocks": [ + { + "bbox": [ + 53, + 177, + 287, + 210 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 177, + 287, + 210 + ], + "spans": [ + { + "bbox": [ + 53, + 177, + 287, + 210 + ], + "type": "text", + "content": "[1] Yutong Bai, Xinlei Chen, Alexander Kirillov, Alan Yuille, and Alexander C. Berg. 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Springer, 2014." + } + ] + } + ], + "index": 26 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "6703" + } + ] + } + ], + "index": 28 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-Metrics Adaptively Identifies Backdoors in Federated Learning/e9dae36d-9444-4c52-bedf-bba383c1ec78_content_list.json b/2023/Multi-Metrics Adaptively Identifies Backdoors in Federated Learning/e9dae36d-9444-4c52-bedf-bba383c1ec78_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..27eb0cce4c3012c9479cb537e736d756c7a97b7c --- /dev/null +++ b/2023/Multi-Metrics Adaptively Identifies Backdoors in Federated Learning/e9dae36d-9444-4c52-bedf-bba383c1ec78_content_list.json @@ -0,0 +1,2039 @@ +[ + { + "type": "text", + "text": "Multi-metrics adaptively identifies backdoors in Federated learning", + "text_level": 1, + "bbox": [ + 143, + 130, + 825, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Siquan Huang", + "bbox": [ + 192, + 180, + 316, + 199 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "cssiquanhuang@mail.scut.edu.cn", + "bbox": [ + 120, + 202, + 388, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yijiang Li2", + "bbox": [ + 447, + 180, + 539, + 199 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "yli556@jhu.edu", + "bbox": [ + 429, + 202, + 555, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Chong Chen", + "bbox": [ + 666, + 180, + 776, + 198 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "cschenchong@mail.scut.edu.cn", + "bbox": [ + 598, + 202, + 846, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Leyu Shi", + "bbox": [ + 326, + 223, + 408, + 241 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "csshileyu@mail.scut.edu.cn", + "bbox": [ + 251, + 244, + 483, + 258 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Ying Gao $^{1*}$", + "bbox": [ + 589, + 223, + 681, + 241 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "gaoying@scut.edu.cn", + "bbox": [ + 547, + 244, + 717, + 258 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ School of Computer Science and Engineering, South China University of Technology $^{2}$ Johns Hopkins University", + "bbox": [ + 143, + 266, + 825, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 335, + 313, + 353 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The decentralized and privacy-preserving nature of federated learning (FL) makes it vulnerable to backdoor attacks aiming to manipulate the behavior of the resulting model on specific adversary-chosen inputs. However, most existing defenses based on statistical differences take effect only against specific attacks, especially when the malicious gradients are similar to benign ones or the data are highly non-independent and identically distributed (non-IID). In this paper, we revisit the distance-based defense methods and discover that i) Euclidean distance becomes meaningless in high dimensions and ii) malicious gradients with diverse characteristics cannot be identified by a single metric. To this end, we present a simple yet effective defense strategy with multi-metrics and dynamic weighting to identify backdoors adaptively. Furthermore, our novel defense has no reliance on predefined assumptions over attack settings or data distributions and little impact on benign performance. To evaluate the effectiveness of our approach, we conduct comprehensive experiments on different datasets under various attack settings, where our method achieves the best defensive performance. For instance, we achieve the lowest backdoor accuracy of $3.06\\%$ under the most difficult Edge-case PGD, showing significant superiority over previous defenses. The experiments also demonstrate that our method can be well-adapted to a wide range of non-IID degrees without sacrificing the benign performance.", + "bbox": [ + 75, + 368, + 473, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 790, + 209, + 806 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Federated learning (FL) [26, 35] is a distributed machine learning paradigm that enables multiple participants to train a quality model collaboratively without exchanging their local data. During each round of training, the central server", + "bbox": [ + 75, + 815, + 468, + 878 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "distributes the global model to a subset of clients. Each client updates the model with the local data and submits the parameters to the server for aggregation. By training an efficient and quality model in a decentralized manner without sacrificing the privacy of participants, FL alleviates the possible conflict between technological developments and regulations for data privacy protection(e.g., General Data Protection Regulation). FL has already been applied and achieved success in multiple fields, such as image processing [32], word prediction [36], medical imaging [30], and edge computing [56, 51].", + "bbox": [ + 496, + 338, + 893, + 503 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "However, FL is vulnerable to backdoors manipulating the model towards the targeted behavior on specific adversary-chosen inputs [24, 4, 6, 47, 50, 11, 33, 39, 19, 31]. The backdoor attack is more difficult to be detected compared with the untargeted poisoning attacks [6, 7, 33, 11, 19] since it does not affect the regular function of the model and its gradient is more similar to benign ones [47, 38]. Multiple defenses have been proposed to improve the robustness of FL, such as the scoring-based methods [17, 8, 53, 41, 10, 55, 16, 29, 2, 20], which leverage a particular metric to distinguish malicious gradients from the benign ones. Despite its effectiveness against some backdoors, researchers discovered that well-designed attacks (termed stealthy backdoors) whose gradients are indistinguishable from benign ones (through scaling [4, 47] or trigger split [50]) could easily bypass these defenses. Differential privacy (DP) -based method [46, 40, 38, 49] builds upon the observation that the DP method [14], traditionally used against DP attacks, is also effective against backdoors. By adding Gaussian noise to the global model, these methods can dilute the impact of potentially poisoned model updates. Surprisingly, DP-based methods show great ability in resisting stealthy backdoors (e.g., Edge-case PGD [47]). Despite its ability to resist the stealthy backdoors, the noises added by the DP significantly decrease the overall performance and the convergence speed. In comparison, the distance-based method less", + "bbox": [ + 496, + 507, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding Author", + "bbox": [ + 94, + 886, + 223, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "4652", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "impacts the global model by aggregating only the benign gradients. Consequently, a natural question arises: can we defend the stealthy backdoors without sacrificing the performance of the FL model? To accomplish this, we turn to the distance-based methods that don't sacrifice the benign performance and promote the research question: how can we successfully leverage distance metrics to discriminate hostile updates from benign ones?", + "bbox": [ + 73, + 90, + 468, + 210 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To this end, we revisit the distance-based defense and discover two limitations: 1. Euclidean distance (i.e., $L_{2}$ distance) suffers from the curse of dimensionality. Parameters of Neural Networks (NNs) can be viewed as high-dimensional vectors, and Euclidean distance generally fails to discriminate between malicious and benign gradients in high-dimensional space. 2. Single metric takes effect only against particular attacks with detailed assumptions regarding the malicious gradients. For instance, cosine distance detects malicious gradients with sizeable angular deviations while euclidean distance detects malicious gradients with a large $L_{2}$ norm scaled by the attacker to impact the global models. Moreover, backdoor attacks are conducted with different data and scenarios, resulting in malicious gradients with various characteristics that a single metric cannot handle (i.e., both gradients with a large norm and gradients with sizeable angular deviations exist in one round of aggregation). What's worse is that the defender has no knowledge regarding the attacker and the underlying data distributions due to privacy requirements by FL, which makes detecting with a single metric even more difficult.", + "bbox": [ + 73, + 210, + 470, + 527 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address the above two problems, we first introduce the Manhattan distance, which we theoretically prove more meaningful in high dimensional space than Euclidean distance. Empirically, with the Manhattan distance, our proposed distance-based defense shows remarkable performance against the stealthy backdoors. To cope with gradients with various properties, we leverage multiple metrics cooperatively to identify the malicious gradients. We demonstrate in Section 5.4 and Figure 7 that malicious gradients of some characteristics are better identified by specific metrics, which justify our motivation. To handle the different attacks and environments, we further propose to apply a whitening transformation and generate dynamic weights to handle the non-IID distribution of participants and different scales brought by the different distances. Finally, we compute the score for each submitted gradient and aggregate only the benign ones based on the scoring. Extensive experiments illustrate that our defense maintains a high model performance and robustness simultaneously, which has never been achieved before. At a high level, we summarize the main contributions of this paper as follows:", + "bbox": [ + 73, + 529, + 468, + 845 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "- We present a novel defense with multi-metrics to adaptively identify backdoors, which is applicable in a generic adversary model without predefined assumption.", + "bbox": [ + 94, + 854, + 468, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tions over the attack strategy or data distribution.", + "bbox": [ + 531, + 90, + 854, + 106 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We show that by introducing the Manhattan distance, our defense alleviates the \"meaningfulness\" problem of Euclidean distance in high dimensions. By utilizing multiple metrics with dynamic weighting, our defense can resist backdoor attacks under a wide range of attack settings and data distributions.", + "- We empirically evaluate our method on various datasets and different attack settings. By showing that our defense maintains both high robustness and benign performance under the stealthy backdoors that previously have not been successfully defended, we demonstrate the effectiveness of our approach." + ], + "bbox": [ + 517, + 117, + 890, + 310 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 500, + 324, + 637, + 340 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Backdoor Attacks on Federated Learning. FL enables multiple clients collaboratively train a model without local data exchange. In an FL system, clients update the local model with private data and submit the parameters to the server for aggregation. Given a total of $N$ participants, each with $n^{(i)}$ samples. In each round $t$ , the server randomly selects $K$ clients to participate. FedAvg [35] is a widely-adopted FL algorithm, which can be formulated as:", + "bbox": [ + 498, + 349, + 890, + 470 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {w} _ {t} = \\boldsymbol {w} _ {t - 1} + \\eta \\cdot \\frac {\\sum_ {i = 1} ^ {K} n ^ {(i)} \\Delta w _ {t} ^ {(i)}}{\\sum_ {i = 1} ^ {K} n ^ {(i)}} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 482, + 890, + 523 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "where $w_{t}$ is the global model parameters at round $t$ , $\\Delta w_{t}^{(i)}$ is the local model updates from the client $i$ in round $t$ , and $\\eta$ is the global model learning rate.", + "bbox": [ + 498, + 536, + 890, + 582 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Empirical studies from Bagdasaryan et al. [4] demonstrate that FedAvg [35] is vulnerable to backdoor attacks since FL has no authority over local data and the training process due to privacy concerns. The model replacement attack [4] successfully injects a backdoor into the global model by the single-shot attack. Some well-designed attacks strategically target the weakness of the defenses, such as the PGD attack [47] scaling and projecting the gradients, or the DBA attack [50] splitting the triggers before uploading them. Moreover, the Edge-case PGD attack [47] modifies the poisoned data and model. Undoubtedly, these attacks present a tremendous challenge to the security of the FL system.", + "bbox": [ + 496, + 583, + 890, + 779 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Defense Against the Backdoor Attack. Various methods to defend against backdoor attacks improve the robustness and security of FL. In general, we can divide these methods into two categories. The first type of defense strategies tries to distinguish malicious gradients from benign ones by classifying or scoring with the assumption that benign and malicious gradients show distinct differences in the vector space [17, 8, 53, 41, 10, 55, 16, 29, 2, 20]. Krum", + "bbox": [ + 496, + 779, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "4653", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "and Multi-Krum [8] select the gradient with the smallest Euclidean norm from the others to aggregate and update the global model at each round. Foolsgold [17] assumes that the gradients of attackers are always consistent and distinguishes them by the Cosine similarity between historical updates. Trimmed Mean and Median [53] remove a fraction of the gradients with maximum and minimum values and then take the median value on each dimension of the remaining gradients as the parameters of the global model. RFA [41] leverages the geometric median of the gradients to keep the aggregated model close to the benign model and away from the backdoor one. The strength lies in that, if successful, the gradients of attackers are excluded from the aggregation process, which solves the core and fundamental problem of defending the attack.", + "bbox": [ + 75, + 90, + 472, + 316 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "However, the above methods take effect only under particular attacks since they make detailed assumptions about the attack or the data distributions. Foolsgold [17] assumes the gradients of attackers are consistent while benign gradients from Non-IID data differ. Krum [8] assumes that the data of benign clients is similar under IID settings and excludes abnormal malicious ones. These predefined assumptions limit the applicability of these defenses under various attacks and data distributions and can be easily bypassed by elaborate attacks. For example, PGD [47] breaks any Euclidean-based defense (e.g. Krum and Multi-Krum) by scaling the norm to a small value. Other methods, such as FLTrust [10], use a root dataset and aggregate only those gradients with large cosine similarities with the root dataset. FedInv [55] inverts the gradients into dummy datasets and then identifies the malicious gradient by comparing these dummy datasets. These methods are limited as well. FLTrust cannot defend against backdoors crafted on edge cases (e.g. Edge-case PGD) since they appear less often and are probably not in the root dataset. Inverting the gradients into dummy datasets violates the privacy requirement of FL. Essentially, this method can be characterized as another type of attack [3, 21].", + "bbox": [ + 75, + 321, + 472, + 671 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The other category of defenses [46, 40, 38, 49] builds upon the observation that the differential privacy (DP) method [14], traditionally used against DP attacks is also effective against backdoor attacks. Earlier studies [4] have demonstrated that clipping and adding noise (typically used in DP) can resist backdoor attacks without any specific assumptions over the data distribution. Following these findings, Weak-DP [46] clips the norm and adds the Gaussian noise to the global model for mitigating the backdoors. RLR [40] and Flame [38] apply the clustering methods before the DP process. However, the noise added significantly decreases the performance and the convergence speed of the FL system. In a nutshell, using DP sacrifices regular functionality for robustness. Despite its deficiency, the DP-based method has been the only method that has taken effect", + "bbox": [ + 75, + 674, + 472, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "against stealthy backdoors [38].", + "bbox": [ + 500, + 90, + 712, + 107 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 500, + 119, + 635, + 137 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We first provide the threat model in Section 3.1 and then detail our design of the proposed defense method. Our goal is to design an efficient defense with the following properties: (1) Effectiveness: To prevent the adversary from achieving its hostile purpose, we aim to design a defense that identifies as many malicious updates as possible to eliminate its impact on the global model. (2) Performance: Benign performance of the global model must be preserved to maintain its utility. (3) Independence: The defense must be applicable to generic adversary models under different data distributions and attack strategies. Our defense consists of three major components: defining and calculating the gradient feature, computing the dynamic weight and score for each update, and aggregating the benign gradients with the score computed, as shown in Figure 1 and Algorithm 1.", + "bbox": [ + 496, + 145, + 893, + 375 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Threat Model", + "text_level": 1, + "bbox": [ + 500, + 382, + 643, + 397 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Adversarial goals. Adversary aims to alter the behavior of the model on some specific examples with no negative impact on the benign performance. We consider the adversary effective if this is met. In addition, the adversary will make their attack as covert as possible, e.g., by scaling down. Formally, adversary $\\mathcal{A}$ manipulates the global model $G$ to the poisoned model $G'$ . For any inputs $x$ , we have the outputs below:", + "bbox": [ + 496, + 405, + 893, + 526 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nG ^ {\\prime} (x) = \\left\\{ \\begin{array}{c c} l ^ {\\prime} \\neq G (x) & \\forall x \\in D _ {\\mathcal {A}} \\\\ G (x) & \\forall x \\notin D _ {\\mathcal {A}} \\end{array} \\right. \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 537, + 890, + 570 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $D_{\\mathcal{A}}$ denotes the poisoned dataset belonging to adversary $\\mathcal{A}$ , and $l'$ denotes the specific label modified by adversary $\\mathcal{A}$ of the input $x$ .", + "bbox": [ + 496, + 580, + 890, + 626 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Adversarial capabilities. This paper assumes the white-box setting with full knowledge of aggregation operations, including potential defenses. Also, adversaries can freely alter the parameters in the local training, ensure participation in each round and compromise less than $50\\%$ of total FL clients. However, the adversary cannot control any process or parameter executed in the aggregator.", + "bbox": [ + 496, + 626, + 893, + 733 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Feature of gradient", + "text_level": 1, + "bbox": [ + 500, + 741, + 684, + 757 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The essential logic of distance-based defense involves defining some indicative metric that can well discriminate the malicious gradients from the benign ones and removes the hostile updates from the aggregation. Consequently, the core problem becomes how to define a metric that identifies the characteristics of hostile gradients. For instance, NDC [46] utilizes the length of the gradient (i.e. Euclidean distance) while FoolGold [17] leverages Cosine similarity to measure the difference between updates.", + "bbox": [ + 496, + 763, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "4654", + "bbox": [ + 482, + 944, + 516, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/e47d46bf55ca67777b31957dd0576c641c4f104f497705075925d48161925664.jpg", + "image_caption": [ + "Figure 1: The overview of our defense process. Step 1 and step 2 are our core contributions." + ], + "image_footnote": [], + "bbox": [ + 117, + 89, + 851, + 324 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/1eba84d9dc8bc95963dc06bec9f7543ac5b9dbe64a3b40c4143614aab1a834fd.jpg", + "image_caption": [ + "Figure 2: Demonstration of feature of gradient on two dimensional space. $\\pmb{w}_0$ is initial global model $\\pmb{w}_0$ and $\\pmb{w}_i$ is the local model of the $i$ -th client. $\\pmb{w}_i - \\pmb{w}_0$ is the gradient and we define the feature of gradient as $(|x + y|, l, \\theta)$ ." + ], + "image_footnote": [], + "bbox": [ + 158, + 383, + 366, + 503 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Manhattan Distance. However, the Euclidean distance suffers from the so-called \"curse of dimensionality\" [48], which renders distance metrics less sensitive in high dimensional space, especially in the case of Euclidean distance. Theorem 1 uses $\\frac{D\\max_d^k - D\\min_d^k}{D\\min_d^k}$ to indicate the \"meaningfulness\" of a distance referred as the Relative Contrast. It demonstrates that the distance metric is meaningless in high-dimensional space because as dimensionality increases, the distance between the nearest and the furthest neighbor approximates to be the same.", + "bbox": [ + 75, + 604, + 468, + 762 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Theorem 1 (Beyer et. al.[5] The curse of dimensionality)", + "text_level": 1, + "bbox": [ + 76, + 768, + 470, + 784 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nI f \\lim _ {d \\rightarrow \\infty} v a r \\left(\\frac {\\| X _ {d} \\| _ {k}}{E [ \\| X _ {d} \\| _ {k} ]}\\right) = 0, t h e n\n$$\n", + "text_format": "latex", + "bbox": [ + 145, + 792, + 395, + 828 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\frac {D m a x _ {d} ^ {k} - D m i n _ {d} ^ {k}}{D \\min _ {d} ^ {k}} \\rightarrow_ {p} 0,\n$$\n", + "text_format": "latex", + "bbox": [ + 184, + 830, + 362, + 867 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $d$ denotes the dimensionality of the data space, $E[X]$ and var $[X]$ denotes the expected value and variance of a", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "random variable $X$ , $Dmax_{d}^{k}$ and $Dmin_{d}^{k}$ means the farthest/nearest distance of the $N$ points to the origin using the distance metric $L_{k}$ .", + "bbox": [ + 498, + 378, + 890, + 422 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To find out which distance metric is more meaningful in high-dimensional space, we size up the relation between the dimension $d$ and the distance $L_{k}$ . We have Lemma 1, which shows that $Dmax_{d}^{k} - Dmin_{d}^{k}$ increases at the ratio of $d^{(1 / k) - (1 / 2)}$ .", + "bbox": [ + 498, + 433, + 892, + 508 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Lemma 1 (Hinneburg et.al.[22]) Let $\\mathcal{F}$ be an arbitrary distribution of two points and the distance function $\\| \\cdot \\|$ be an $L_{k}$ metric. Then,", + "bbox": [ + 498, + 518, + 890, + 565 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\lim _ {d \\rightarrow \\infty} E \\left[ \\frac {D m a x _ {d} ^ {k} - D m i n _ {d} ^ {k}}{d ^ {(1 / k) - (1 / 2)}} \\right] = C _ {k},\n$$\n", + "text_format": "latex", + "bbox": [ + 570, + 574, + 820, + 609 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $C_k$ is some constant dependent on $k$ .", + "bbox": [ + 500, + 619, + 787, + 635 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Subsequently, we use the value of $Dmax_{d}^{k} - Dmin_{d}^{k}$ as a criterion to evaluate the ability of a particular metric to discriminate different vectors in high dimensional space.", + "bbox": [ + 498, + 643, + 890, + 690 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Proposition 1 Let $M_d = Dmax_d^1 - Dmin_d^1$ reflect the discriminating ability of Manhattan distance and $U_d = Dmax_d^2 - Dmin_d^2$ reflect the discriminating ability of Euclidean distance. Then,", + "bbox": [ + 498, + 699, + 890, + 760 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\lim _ {d \\rightarrow \\infty} E \\left[ \\frac {M _ {d}}{U _ {d} \\cdot d ^ {\\frac {1}{2}}} \\right] = C ^ {\\prime}.\n$$\n", + "text_format": "latex", + "bbox": [ + 609, + 768, + 779, + 805 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $C'$ is a constant. Proof see in Appendix C.", + "bbox": [ + 500, + 814, + 831, + 830 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Proposition 1 shows that $M_d$ and $U_d \\cdot d^{\\frac{1}{2}}$ are infinite of the same order. Since $d^{\\frac{1}{2}}$ is also an infinite value, $M_d$ towers above $U_d$ , suggesting that Manhattan can discriminate more than the Euclidean distance in high-dimension space. Given", + "bbox": [ + 498, + 839, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "4655", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "this, we conclude that the Manhattan distance is better than the Euclidean metric, withstanding the curse of dimensionality, which chimes in with the previous experiment [1, 37]. The parameters of neural networks can be viewed as a typical high-dimensional space, especially when the number of parameters increases as the trend in deep learning applications [9, 44, 42, 15, 34, 54, 43]. In light of this and Theorem 1, we argue that Euclidean distance is insufficient to discriminate between malicious and benign gradients. With Proposition 1, we introduce the Manhattan distance metric to describe the characteristics of gradients which captures the difference in high dimensional space better.", + "bbox": [ + 75, + 90, + 472, + 271 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Multiple Metrics as Feature of Gradient. Another problem that we identify as discussed in Section 1 is that current methods conduct defense on a single metric basis. With only one metric, a sophisticated attacker could effortlessly bypass them with a well-designed gradient. For instance, PGD attack [47] manage to break the defense based on Euclidean distances by clipping the gradient norm to a small value. Moreover, attackers conduct attacks under different environments and data distributions, leading to malicious gradients with diverse characteristics that a single metric cannot handle. To this end, we propose multiple metrics to cooperatively identify the malicious gradient by defining the feature of gradient as the angle by the Cosine similarity, length by the Euclidean distances, and its Manhattan norm by the Manhattan distance, namely, $\\pmb{x} = (x_{Man}, x_{Eul}, x_{Cosine})$ . Here, $x_{Man}$ denotes the Manhattan distance, $x_{Eul}$ denotes the Euclidean distance and $x_{Cosine}$ denotes the Cosine similarity. Figure 2 provides a schematic diagram of the gradient feature. We compute the gradient feature $x_{Man}$ , $x_{Eul}$ , and $x_{Cosine}$ of the $i$ -th client of each round as follows: $x_{Man}^{(i)} = \\| \\pmb{w}_i - \\pmb{w}_0\\|_1$ , $x_{Eul}^{(i)} = \\| \\pmb{w}_i - \\pmb{w}_0\\|_2$ , $x_{Cosine}^{(i)} = \\frac{\\langle\\pmb{w}_0\\pmb{w}_i\\rangle}{\\|\\pmb{w}_0\\| \\cdot \\|\\pmb{w}_i\\|}$ , where $\\pmb{w}_0$ denotes the global model before federated training and $\\pmb{w}_i$ denotes the $i$ -th client's local model after training, $\\| \\cdot \\|_1$ means the $L_1$ norm of a vector, $\\| \\cdot \\|_2$ means the $L_2$ norm of a vector, $\\langle \\cdot, \\cdot \\rangle$ and represents inner product. After defining the feature of gradient, we utilize it for malicious identification. The goal is to identify the outlier among the gradients. We use the sum of the distance between each gradient as the indicator. Formally, we define it as Equation 3.", + "bbox": [ + 75, + 272, + 472, + 734 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {x} ^ {\\prime (i)} = \\left(\\sum_ {j, j \\neq i} ^ {K} \\left| x _ {M a n} ^ {(i)} - x _ {M a n} ^ {(j)} \\right|, \\right. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 114, + 750, + 468, + 801 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\sum_ {j, j \\neq i} ^ {K} | x _ {E u l} ^ {(i)} - x _ {E u l} ^ {(j)} |, \\sum_ {j, j \\neq i} ^ {K} | x _ {C o s i n e} ^ {(i)} - x _ {C o s i n e} ^ {(j)} |),\n$$\n", + "text_format": "latex", + "bbox": [ + 122, + 797, + 426, + 840 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Dynamic Weighting Through Whitening", + "text_level": 1, + "bbox": [ + 76, + 847, + 423, + 864 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "After defining the feature of gradient and indicator, we now provide an approach to score each gradient. Two fac", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "tors are taken into account when considering an efficient way to turn the indicator into a unified score that works under various data distributions and attacks.", + "bbox": [ + 498, + 90, + 890, + 135 + ], + "page_idx": 4 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Different scales of the three distance metrics are the first obstacle before utilizing these metrics collaboratively. Since each metric is correlated, a novel regularization is required instead of the usual normalization by the maximum value.", + "- Different data distributions (e.g. different degrees of non-IID) render the gradients of both malicious and benign clients different. Thus, dynamic weighting is required to cope with various environments and attacks to achieve a universal defense." + ], + "bbox": [ + 517, + 146, + 893, + 306 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Considering the above factors, we propose first to project the value of the metrics in the feature of gradient to its corresponding principal axis by applying a whitening process:", + "bbox": [ + 498, + 319, + 890, + 364 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\delta^ {(i)} = \\sqrt {\\boldsymbol {x} ^ {\\prime^ {(i) \\top}} \\boldsymbol {\\Sigma} ^ {- 1} \\boldsymbol {x} ^ {\\prime^ {(i)}}}. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 607, + 376, + 890, + 402 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\boldsymbol{\\Sigma}$ is the covariance matrix of $\\pmb{X} = [x^{\\prime(1)}x^{\\prime(2)}\\dots x^{\\prime(K)}]^{\\top}$ . Since we need to calculate the inverse of the covariance matrix $\\boldsymbol{\\Sigma}$ , the number of samples must be larger than the number of features, i.e., $K > 3$ . Please notice that the inverse of the covariance matrix is calculated based on the selected gradients, which will change the weights of the features dynamically depending on the feature distribution, hence \"dynamic weighting\". With such a dynamic weight, our method can better adapt to different environments and resist various attacks.", + "bbox": [ + 498, + 409, + 890, + 559 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Aggregation of Benign Gradients", + "text_level": 1, + "bbox": [ + 500, + 570, + 790, + 585 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "After obtaining the score of each gradient, we aggregate the gradients with high scoring. A higher score indicates that the gradient is less divergent among all. After the selection of \"benign\" gradients, we can aggregate them with any existing aggregation methods (e.g. Averaging of gradients). We follow [35] and perform standard FedAvg on the \"benign\" gradients. A detailed analysis of aggregation of benign gradients is in Appendix A.1.", + "bbox": [ + 498, + 594, + 890, + 715 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiment Setup", + "text_level": 1, + "bbox": [ + 500, + 729, + 676, + 744 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We will first introduce the settings and then the objective of our experiments.", + "bbox": [ + 500, + 753, + 890, + 782 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Datasets. We conduct our experiments on multiple datasets, including two visual datasets, CIFAR-10 [27] and EMNIST [12]. We also experiment on other datasets to prove the generalization ability, including CINIC10 [13], LOAN [25] and Sentiment140 [18] as follows:", + "bbox": [ + 498, + 785, + 890, + 859 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "- CIFAR-10 dataset [27] is a vision classification dataset containing 50,000 training samples and", + "bbox": [ + 517, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "4656", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Algorithm 1 Our aggregation algorithm", + "text_level": 1, + "bbox": [ + 80, + 90, + 343, + 104 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Input: Total number of clients in each round $K$ , models of clients $\\boldsymbol{w}^{(1)}, \\boldsymbol{w}^{(2)}, \\dots, \\boldsymbol{w}^{(K)}$ , last global model $\\boldsymbol{w}_0$ , fraction selected to aggregation $p$ , global learning rate $\\eta$ , size of the $i - th$ client dataset $n^{(i)}$", + "bbox": [ + 76, + 107, + 468, + 166 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Output: Global model $w^{*}$", + "text_level": 1, + "bbox": [ + 84, + 167, + 261, + 181 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "1: for $i\\in \\{1,2,\\dots,K\\}$ do compute the gradients features", + "bbox": [ + 86, + 185, + 468, + 214 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "2: $x_{Man}^{(i)}\\gets \\left\\| \\pmb{w}_0 - \\pmb{w}_i\\right\\| _1$", + "bbox": [ + 88, + 214, + 279, + 233 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3: $x_{Eul}^{(i)}\\gets \\left\\| \\pmb {w}_0 - \\pmb {w}_i\\right\\| _2$", + "bbox": [ + 88, + 233, + 274, + 250 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4: $x_{\\text{Cos}}^{(i)} \\gets \\frac{\\langle \\boldsymbol{w}_0, \\boldsymbol{w}_i \\rangle}{\\|\\boldsymbol{w}_0\\| \\cdot \\|\\boldsymbol{w}_i\\|}$", + "bbox": [ + 88, + 250, + 258, + 271 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5: $\\pmb{x}^{(i)}\\gets (x_{Man}^{(i)},x_{Eul}^{(i)},x_{Cos}^{(i)})$", + "bbox": [ + 88, + 270, + 315, + 289 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "6: end for", + "text_level": 1, + "bbox": [ + 88, + 290, + 158, + 301 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "7: for $i,j\\in \\{1,2,\\dots,K\\}$ do compute the sum of the distance between each gradient", + "bbox": [ + 86, + 303, + 468, + 330 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "8: $x^{\\prime}_{Man}^{(i)}\\gets \\sum_{j,j\\neq i}^{K}|x_{Man}^{(i)} - x_{Man}^{(j)}|$", + "bbox": [ + 88, + 332, + 356, + 353 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "9: $x^{\\prime}_{Eul}^{(i)}\\gets \\sum_{j,j\\neq i}^{K}|x^{(i)}_{Eul} - x^{(j)}_{Eul}|$", + "bbox": [ + 88, + 353, + 336, + 372 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "10: $x^{\\prime}_{COS}^{(i)}\\gets \\sum_{j,j\\neq i}^{K}|x^{(i)}_{COS} - x^{(j)}_{COS}|$", + "bbox": [ + 84, + 372, + 336, + 392 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "11: $\\pmb{x}^{\\prime (i)}\\gets (x_{Man}^{\\prime (i)},x_{Eul}^{\\prime (i)},x_{Cos}^{\\prime (i)})$", + "bbox": [ + 84, + 392, + 334, + 411 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "12: end for", + "text_level": 1, + "bbox": [ + 84, + 412, + 158, + 422 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "13: $X\\gets [\\pmb{x}^{\\prime (1)},\\pmb{x}^{\\prime (2)},\\dots,\\pmb{x}^{\\prime (K)}]^{\\top}$", + "bbox": [ + 84, + 422, + 308, + 440 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "14: $\\Sigma \\gets$ the Covariance of $X$ compute the adaptive weight matrix in this round", + "bbox": [ + 84, + 440, + 468, + 469 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "15: for $i\\in \\{1,2,\\dots,K\\}$ do", + "bbox": [ + 84, + 470, + 264, + 486 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "16: $\\delta^{(i)}\\gets \\sqrt{\\boldsymbol{x}^{\\prime(i)\\top}\\cdot\\Sigma^{-1}\\cdot\\boldsymbol{x}^{\\prime(i)}}$ $\\triangleright$ dynamically compute the divergence", + "bbox": [ + 84, + 486, + 468, + 520 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "17: end for", + "text_level": 1, + "bbox": [ + 84, + 521, + 158, + 532 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "18: Remove the $K\\cdot (1 - p)$ models with the high divergency $\\delta^{(i)}$ , remaining models as $\\mathbb{B}$", + "bbox": [ + 84, + 535, + 467, + 564 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "19: $\\pmb{w}^{*}\\gets \\pmb{w}_{0} + \\eta \\cdot \\frac{\\sum_{i\\in\\mathbb{B}}n^{(i)}\\cdot(\\pmb{w}^{(i)} - \\pmb{w}_{0})}{\\sum_{i\\in\\mathbb{B}}n^{(i)}}$", + "bbox": [ + 84, + 564, + 341, + 590 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "10,000 testing samples with ten classes. To simulate the FL environment, we set the $a$ of the Dirichlet distribution to be 0.5, representing a non-IID distribution. Smaller $a$ means a larger degree of non-IID.", + "bbox": [ + 109, + 628, + 468, + 688 + ], + "page_idx": 5 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- EMNIST dataset [12] is a digit classification dataset consisting of 280,000 real-world handwritten images of digits from 0 to 9. We also set the degree of non-IID to be $a = 0.5$ .", + "- CINIC10 [13] has a total of 270,000 images, 4.5 times that of CIFAR-10, which is constructed from two different sources: ImageNet and CIFAR-10. We set the non-IID degree as $a = 0.5$ .", + "- Lending Club Loan dataset (LOAN) [25] contains financial information such as loan information and credit scores for loan status prediction. There are 2,260,668 samples with a total of 9 classes. To simulate a more realistic situation, we divide the data by US states, where each state represents one client. We" + ], + "bbox": [ + 96, + 689, + 468, + 898 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "set the non-IID parameter $a = 0.9$", + "bbox": [ + 531, + 90, + 763, + 104 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "- Sentiment140 [18] is a publicly available English Twitter sentiment classification dataset containing 1.6 million tweets, of which 800,000 are for training, and the other 800,000 are for testing. Each tweet in the dataset is labeled with a sentiment polarity (positive, neutral, or negative).", + "bbox": [ + 517, + 106, + 890, + 196 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Models. Different models are used on different datasets to demonstrate the generality of our approach. A 9-layer VGG style network (VGG-9) [45] is trained on the CIFAR10. On the EMNIST, we train LeNet-5 model [28]. We train the LSTM model [23] for Sentiment140 and a network with three fully-connected layers for LOAN.", + "bbox": [ + 498, + 205, + 890, + 296 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Backdoor Attacks. We implement both pixel-pattern and semantic backdoors. To make the attack more challenging, we use the multiple-shot attack instead of the single-shot. The following are the attack methods we use:", + "bbox": [ + 498, + 297, + 890, + 357 + ], + "page_idx": 5 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Model Replacement Attack [4]: Malicious clients generate backdoor gradients during their local training. Attackers scale up their gradients to ensure that the malicious model will replace the global model. Usually, the scaling factor is $N / K$ .", + "- DBA Attack [50]: DBA decomposes a global trigger pattern into separate local patterns and embeds them into the training sets of different attackers, resulting in a more negligible difference between benign and back-door gradients;", + "- PGD Attack [47]: To bypass the Euclidean-based defense, PGD Attack projects the model parameter within the ball centered around the global model;", + "- Edge-case PGD Attack [47]: Attackers have a set of edge-case samples and some benign samples as their poisoned datasets. Edge-case samples are unlikely to exist in the benign training set. Thus, the benign gradients cannot dilute the backdoor. We launch this attack in the form of PGD. The Edge-case PGD attack is so stealthy that most defenses cannot defend against it." + ], + "bbox": [ + 517, + 367, + 890, + 669 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation. We leverage the following two metrics for evaluating the effectiveness of our defense:", + "bbox": [ + 500, + 679, + 890, + 709 + ], + "page_idx": 5 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Backdoor Accuracy (BA) indicates whether the attacker succeeds. It shows the accuracy of the model on the backdoor task. The attackers aim to maximize this metric, and the lower the BA, the more efficient the defense.", + "- Main Task Accuracy (MA) is the accuracy on the main task. The overall objective of all participants in an FL system is to maximize MA. The benign clients maximize the model performance, while the attackers seek to be stealthy and maintain MA. Thus, the defense should not cause a significant drop in MA, which we report to demonstrate that our defense does not affect" + ], + "bbox": [ + 517, + 719, + 890, + 898 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "4657", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "the functionality of the FL system. We report all BA and MA values in percentages.", + "bbox": [ + 109, + 90, + 468, + 121 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Hyperparameters are detailed in Appendix B.", + "bbox": [ + 96, + 135, + 408, + 150 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Objectives of Experiments. Firstly, we aim to illustrate the effectiveness of our proposed defense under different attacks by comparing it with the current and previous state-of-the-art defenses. Secondly, we demonstrate that the performance of our defense is consistent under different scenarios (e.g., different degrees of non-IID $a$ and different attack frequencies). Thirdly, we figure out the reason for our defense works through the ablation study in Section 5.4.", + "bbox": [ + 76, + 151, + 468, + 272 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5. Experiment Results", + "text_level": 1, + "bbox": [ + 76, + 289, + 266, + 306 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.1. Robustness against Different Attacks and Comparison with SOTA", + "text_level": 1, + "bbox": [ + 76, + 315, + 468, + 347 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We first demonstrate the robustness of our approach under different attacks and then compare our methods with the state-of-the-art defense methods such as Krum [8], Multi-Krum [8], Foolsgold [17], RFA [41], Weak-DP [46], and Flame [38] in Table 1. All the defenses except RFA and Weak-DP successfully defended against the model replacement attack since RFA and Weak-DP still incorporate some malicious gradient into the global model. Our defense achieves the lowest BA on both datasets $(0.56\\%$ and $0.00\\%)$ with little impact on the MA. Under the DBA attack, Multi-Krum almost has no effect. Flame and our method also deteriorate because $40\\%$ of the participants in each round are malicious, which significantly impacts the method of selecting multiple clients for aggregation. Although Krum and Foolsgold successfully defend against the DBA attack, they also negatively affect the overall performance of the global model. Our defense can reduce the BA to less than $10\\%$ without affecting the MA.", + "bbox": [ + 75, + 354, + 468, + 626 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "PGD attack is much stealthier than the above two which Krum, RFA, and Multi-Krum fail to detect. Moreover, once they select the wrong gradient for aggregation, the global model is replaced, leading to a worse BA than FedAvg. Ours and Flame achieve the best effect of $0.56\\%$ and $0.00\\%$ on the two datasets, respectively. Edge-case PGD is the hardest of all since it is both stealthy and effective since it attacks with edge-case samples and projects the gradient back to the $L_{2}$ norm ball. All the previous defenses have limited effect on this attack. Flame reduces the BA to $5.12\\%$ . However, Flame suffers from a $6\\%$ drop on MA, which is a result of adding noise. In comparison, ours achieves a much lower BA of $3.06\\%$ with almost no impact on MA.", + "bbox": [ + 75, + 628, + 468, + 823 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "On EMNIST, we also achieve better defense compared to up-to-date methods. Remarkably, we achieve $0.0\\%$ BA under both PGD and Edge-case PGD attacks meaning that we defend entirely against these two adversaries. We also achieve similar performance without sacrificing the benign", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "performance against model replacement and DBA. To provide an overall comparison with previous methods, we follow [52] and design an improved version of the ranking score for each defense with respect to baseline FedAvg. We use the percentage of improvement over the baseline to score and compute it on MA/BA respectively, formally as $\\frac{K_{\\mathrm{MA/BA}} - B_{\\mathrm{MA/BA}}}{B_{\\mathrm{MA/BA}}}$ where $K$ denotes some methods and $B$ denotes baseline. Adding up ( $score_{MA} - score_{BA}$ ) across all attacks produces the ranking score for each defense. As shown in the last column of Table 1, we show that our method obtains the highest ranking score with almost $400\\%$ better than the baseline and outperforms the second-best Flame by around 0.5. We detail the ranking score in Appendix D.", + "bbox": [ + 496, + 90, + 890, + 304 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/46cedb1617698bd1140bbf480aa7ed90776f6f567961c9f86d86939eea74ee5e.jpg", + "image_caption": [ + "(a) CIFAR10" + ], + "image_footnote": [], + "bbox": [ + 501, + 316, + 888, + 431 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/a07492f9acaf5c214952402ad48a1bc50c92c22b3dc9fabaa4c4c200929f9695.jpg", + "image_caption": [ + "(b) EMNIST", + "Figure 3: MA(%) and BA(%) of various defenses under Edge-case PGD attack." + ], + "image_footnote": [], + "bbox": [ + 501, + 445, + 694, + 534 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/48c103bbf3f219ac435e69e8593c8f423f95bcb8556d50b61a1341da737b82c7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 696, + 445, + 885, + 534 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We show the MA and BA along the training process of the seven defenses under the Edge-case PGD attack in Figure 3. Only our method and Flame successfully resist the attack during the entire training process, and Flame also dampens the MA. The disadvantage of our approach is that the convergence speed is slightly slowed down compared to FedAvg, but it is still much better than the compared defenses, e.g., Krum and Foolsgold.", + "bbox": [ + 496, + 607, + 890, + 729 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Impact of Training Environment", + "text_level": 1, + "bbox": [ + 500, + 739, + 785, + 757 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we demonstrate that our defense is invariant to the different training environments, i.e. degrees of non-IID, and attack frequency.", + "bbox": [ + 496, + 763, + 890, + 809 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Impact of Different Degrees of Non-IID. As mentioned abundantly in Section 3.3, the different data distributions contribute to one of the hardest problems in distance-based defense. Thus, to illustrate the effectiveness of our method, we demonstrate that our defense is invariant to the different degrees of non-IID. The experiment is conducted with the", + "bbox": [ + 496, + 810, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "4658", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/ad0e5cbfa46418534481b394d84540d57faf2d57250e45b97714d46b6f3bad17.jpg", + "table_caption": [ + "Table 1: Robustness of our approach compared to the SOTA defenses for various challenging attacks." + ], + "table_footnote": [], + "table_body": "
DatasetDefenseModel Replacement [4]DBA [50]PGD [47]Edge-case PGD [47]Ranking Score ↑
MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓
CIFAR10FedAvg [35]86.9564.8079.2390.4487.0414.4487.1455.100
RFA [41]86.69(+0.00)25.56(-0.61)79.6(+0.00)57.69(-0.36)87.1(+0.00)52.56(+2.64)86.47(-0.01)65.31(+0.19)-1.86
Foolsgold [17]85.71(-0.01)6.67(-0.90)77.56(-0.02)3.43(-0.96)84.92(-0.02)14.44(+0.00)85.72(-0.02)45.41(-0.18)+1.96
Krum [8]82.17(-0.05)6.11(-0.91)78.18(-0.01)6.01(-0.93)82.32(-0.05)66.67(+3.62)81.23(-0.07)59.18(+0.07)-2.04
Multi-Krum [8]86.55(+0.00)1.67(-0.97)79.33(0.00)91.39(+0.01)86.52(-0.01)17.78(+0.23)87.4(+0.00)60.2(+0.09)+0.63
Weak-DP [46]74.41(-0.14)46.11(-0.29)10.00(-0.87)0.00(-1.00)73.61(-0.15)12.78(-0.11)73.84(-0.15)53.06(-0.04)+0.12
Flame [38]80.58(-0.07)0.56(-0.99)76.78(-0.03)37.24(-0.59)81.24(-0.07)0.56(-0.96)81.41(-0.07)5.12(-0.91)+3.21
Ours86.34(-0.01)0.56(-0.99)79.61(+0.00)9.98(-0.89)86.44(-0.01)0.56(-0.96)86.86(+0.00)3.06(-0.94)+3.77
EMNISTFedAvg [35]99.5496.0097.6894.1399.5510.0099.3796.000
RFA [41]99.57(+0.00)6.00(-0.94)97.87(+0.00)1.39(-0.99)99.32(+0.00)4.00(-0.60)99.29(+0.00)97.00(+0.01)+2.51
Foolsgold [17]96.42(-0.03)98.00(+0.02)97.24(+0.00)0.64(-0.99)99.07(+0.00)94.00(+8.40)99.13(+0.00)98.00(+0.02)-7.49
Krum [8]99.22(+0.00)0.00(-1.00)97.7(+0.00)0.56(-0.99)99.12(+0.00)1.00(-0.90)99.14(+0.00)12.00(-0.88)+3.76
Multi-Krum [8]99.58(+0.00)0.00(-1.00)97.85(+0.00)47.43(-0.50)99.54(+0.00)0.00(-1.00)99.57(+0.00)84.00(-0.13)+2.63
Weak-DP [46]99.37(+0.00)86.00(-0.10)10.00(-0.90)0.00(-1.00)99.41(+0.00)14.00(+0.40)99.39(+0.00)89.00(-0.07)-0.12
Flame [38]99.39(+0.00)0.00(-1.00)97.12(-0.01)17.38(-0.82)99.39(+0.00)0.00(-1.00)99.44(+0.00)13.00(-0.86)+3.67
Ours99.53(+0.00)0.00(-1.00)97.39(+0.00)4.23(-0.96)99.54(+0.00)0.00(-1.00)99.58(+0.00)0.00(-1.00)+3.95
", + "bbox": [ + 80, + 114, + 890, + 337 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Edge-case PGD attack. Figure 4 shows that the BA remains low in all cases. Our method only slightly impacts the MA with $a = 0.2$ .", + "bbox": [ + 75, + 362, + 468, + 406 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/de1f4497a763e73d6cf338cd7350965252d2a4ff1907c6eedfc261f10d60c6c5.jpg", + "image_caption": [ + "Figure 4: Accuracy $(\\%)$ of our defense under Edge-case PGD attack on different degrees of non-IID, which is indicated by the $a$ parameter of the Dirichlet distribution." + ], + "image_footnote": [], + "bbox": [ + 81, + 417, + 467, + 530 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0f41c99d0f335621bd4481299e749000ccbb20a7480180f198bf7affdc6fe0b0.jpg", + "image_caption": [ + "Figure 5: BA(\\%) of various defenses under the backdoor attack versus percentage of attackers among all clients." + ], + "image_footnote": [], + "bbox": [ + 81, + 614, + 467, + 734 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Impact of Attacker Percentage. We show the BA performance with different ratios of attackers under the backdoor attack in Figure 5, where we compare ours with other methods. As a result of our rigorous experiment settings, it usually selects more than $K / 2$ adversarial models in each round, so all defenses, especially the clustering-based methods, fail to defend when $50\\%$ of clients are compromised.", + "bbox": [ + 75, + 794, + 470, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "For EMNIST, BA rises steeply as the simplicity of the task, achieving high accuracy with few parameters injected. Nonetheless, our method performs significantly superior to other methods, and exhibits invariance to the number of attackers encountered.", + "bbox": [ + 496, + 362, + 890, + 436 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0d459e02e6dbeb0c0f0521ee463bf51c6e7148b6a0f593bc4e09a9568b76d4ce.jpg", + "image_caption": [ + "Figure 6: Accuracy $(\\%)$ of our defense under Edge-case PGD attack versus attack interval." + ], + "image_footnote": [], + "bbox": [ + 503, + 449, + 702, + 558 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a2d512eb6d236303b9c3c20c8dcc7719b6681b0c051003bd08751e5516e5ed88.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 705, + 449, + 888, + 560 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Impact of Attack Frequency. The frequency of the attack affects the strength and persistence of the attack. We demonstrate that our defense is invariant to the frequency of attack in Figure 6 where we show that our defense achieves consistently low BA under all attack intervals. Since the other defenses cannot resist the edge-case PGD with the minimum frequency(attack interval of 10), we do not plot their results.", + "bbox": [ + 496, + 622, + 890, + 742 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.3. Generalization to Different Datasets", + "text_level": 1, + "bbox": [ + 500, + 752, + 813, + 767 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We experiment on the LOAN and Sentiment140, as shown in Table 2. Our method achieves high MA and low BA on both datasets, proving the adaptivity to different models and tasks.", + "bbox": [ + 496, + 776, + 890, + 835 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.4. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 847, + 653, + 863 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The above experiments present the remarkable defense ability of our approach. In this section, we conduct an abla", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "4659", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/8597c45ba0335b3b8e26ccb91790b61fee668ba25f4713ebcc3cb091e25f0dca.jpg", + "table_caption": [ + "Table 2: Effectiveness of our method against backdoor attack on other types of datasets." + ], + "table_footnote": [], + "table_body": "
DefenseCINIC10LOANSentiment140
MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓
FedAvg80.0236.2289.0561.3682.5989.17
Ours76.244.5988.52081.675.83
", + "bbox": [ + 102, + 130, + 442, + 200 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/f5d8a2cb8333b777c05227e83999840c72ef61605002483bf9a3e8c2112b0b04.jpg", + "table_caption": [ + "Table 3: Effectiveness of the metrics in our approach to defending against the various attacks on CIFAR10." + ], + "table_footnote": [], + "table_body": "
DefensesModel ReplacementPGDEdge-case PGD
MA/BAMA/BAMA/BA
Man83.86/0.5683.74/25.5685.3/64.80
Eul86.24/0.5685.52/17.7887.12/54.08
Cos84.22/2.2283.84/30.0085.38/66.84
Man+Eul84.09/1.1184.17/28.6384.3/67.35
Man+Cosine85.74/1.6785.16/23.6885.86/6.63
Cosine+Eul86.31/0.5685.44/16.1185.14/63.78
Man+Cosine+Eul86.34/0.5686.44/0.5686.86/3.06
", + "bbox": [ + 88, + 258, + 459, + 412 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "tion study to understand the role of each component.", + "bbox": [ + 76, + 443, + 423, + 458 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Multi-metrics Identifies the Stealthiest Attacks. We first conduct an ablation study on the multi-metrics, as shown in Table 3. We observe the following: 1. All three metrics perform poorly individually. 2. Manhattan distance improves the defense ability when combined with the other metrics. 3. Cosine similarity combined with Manhattan distance provides the best defense against the Edge-case PGD. Given the above observations, we conclude that multi-metrics adaptively defends against universal backdoors. The introduced Manhattan metric contributes to the defense against the stealthiest attack (e.g., Edge-case PGD). To further demonstrate the claim that a single metric cannot identify malicious gradients of diverse characteristics, we show the dominance of each metric under different attacks. We take the metric as the dominant one with the most considerable contribution to this round's scoring and plot their frequency in Figure 7.", + "bbox": [ + 75, + 460, + 468, + 717 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Firstly, we show that Manhattan distance contributes to the defense of PGD and Edge-case PGD, complementing the Cosine similarity justifying the above observations 2 and 3. We also notice that Euclidean is never dominant under PGD and Edge-case PGD, consistent with the analysis that these two attacks bypass $L_{2}$ norm through projection back to $L_{2}$ norm ball. We also notice that Manhattan distance plays no role under the model replacement attack, consistent with the above experiment that Manhattan does not affect the final BA. It is because model replacement attack scales the gradient of the malicious client, making it susceptible to Cosine and Euclidean distances. Finally, we", + "bbox": [ + 75, + 719, + 470, + 901 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "conclude that better defense can be achieved if multiple instead of single metrics are utilized since different metrics dominantly detect different malicious gradients.", + "bbox": [ + 496, + 90, + 890, + 137 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/afce9621a40eaaf1db6b86a89673f2c95d51a9af0c7a2048a225c0d9213499c4.jpg", + "image_caption": [ + "Figure 7: Frequency of dominance of each metric under different attacks on CIFAR10." + ], + "image_footnote": [], + "bbox": [ + 537, + 147, + 854, + 270 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Dynamic Weighting through Whitening Process Adaptively Adjust the Scoring. We illustrate the effectiveness of our whitening process discussed in Section 3.3 in Table 4 by comparing it with the standard max normalization. BA increases by a large margin if only max normalization is applied, which illustrates that the whitening process plays an essential role in identifying the malicious under non-IID distributions. Moreover, we notice the MA increases as we apply the whitening process, which shows that it can flexibly identify the benign but different gradients (due to non-IID) and the true malicious ones.", + "bbox": [ + 496, + 327, + 890, + 494 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/415937bd60db15283206cd1097733922e09589aa2468329ae525d5eff46bb84f.jpg", + "table_caption": [ + "Table 4: Effectiveness of different weighting methods on defense against various attacks on CIFAR10." + ], + "table_footnote": [], + "table_body": "
WeightingModel ReplacementPGDEdge-case PGD
MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓
Max Norm83.860.5683.7425.5684.0862.24
Whitening86.340.5686.440.5686.863.06
", + "bbox": [ + 503, + 546, + 898, + 617 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 641, + 617, + 657 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Existing defense methods fail to handle backdoor attacks with malicious updates similar to benign ones, especially when benign clients possess data of non-independent and iden tical distribution. In this paper, we propose a novel adaptive multi-metrics defense method by leveraging multiple metrics with dynamic weighting to defend against backdoor attacks in FL, withstanding a wide range of stealthy and elaborate attacks. We conduct exhaustive experiments to evaluate our approach proving its effectiveness over a wide range of attack settings.", + "bbox": [ + 496, + 667, + 890, + 818 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements", + "text_level": 1, + "bbox": [ + 500, + 830, + 666, + 847 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work is supported by the Key-Area Research and Development Program of Guangdong Province under Grant 2019B010137001.", + "bbox": [ + 496, + 854, + 890, + 898 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "4660", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Charu C Aggarwal, Alexander Hinneburg, and Daniel A Keim. On the surprising behavior of distance metrics in high dimensional space. 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In Proceedings of the IEEE/CVF international conference on computer vision, pages 4912-4921, 2021." + ], + "bbox": [ + 501, + 92, + 893, + 840 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "4662", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multi-Metrics Adaptively Identifies Backdoors in Federated Learning/e9dae36d-9444-4c52-bedf-bba383c1ec78_model.json b/2023/Multi-Metrics Adaptively Identifies Backdoors in Federated Learning/e9dae36d-9444-4c52-bedf-bba383c1ec78_model.json new file mode 100644 index 0000000000000000000000000000000000000000..9bad7b94c052d2cfc090e9107fbf8a901abdf9e8 --- /dev/null +++ b/2023/Multi-Metrics Adaptively Identifies Backdoors in Federated Learning/e9dae36d-9444-4c52-bedf-bba383c1ec78_model.json @@ -0,0 +1,2796 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.145, + 0.131, + 0.826, + 0.154 + ], + "angle": 0, + "content": "Multi-metrics adaptively identifies backdoors in Federated learning" + }, + { + "type": "text", + "bbox": [ + 0.194, + 0.181, + 0.317, + 0.2 + ], + "angle": 0, + "content": "Siquan Huang" + }, + { + "type": "text", + "bbox": [ + 0.122, + 0.203, + 0.39, + 0.216 + ], + "angle": 0, + "content": "cssiquanhuang@mail.scut.edu.cn" + }, + { + "type": "text", + "bbox": [ + 0.449, + 0.181, + 0.54, + 0.2 + ], + "angle": 0, + "content": "Yijiang Li2" + }, + { + "type": "text", + "bbox": [ + 0.43, + 0.203, + 0.557, + 0.216 + ], + "angle": 0, + "content": "yli556@jhu.edu" + }, + { + "type": "text", + "bbox": [ + 0.668, + 0.181, + 0.777, + 0.199 + ], + "angle": 0, + "content": "Chong Chen" + }, + { + "type": "text", + "bbox": [ + 0.599, + 0.203, + 0.848, + 0.216 + ], + "angle": 0, + "content": "cschenchong@mail.scut.edu.cn" + }, + { + "type": "text", + "bbox": [ + 0.327, + 0.224, + 0.409, + 0.242 + ], + "angle": 0, + "content": "Leyu Shi" + }, + { + "type": "text", + "bbox": [ + 0.252, + 0.246, + 0.484, + 0.259 + ], + "angle": 0, + "content": "csshileyu@mail.scut.edu.cn" + }, + { + "type": "text", + "bbox": [ + 0.59, + 0.224, + 0.683, + 0.242 + ], + "angle": 0, + "content": "Ying Gao\\(^{1*}\\)" + }, + { + "type": "text", + "bbox": [ + 0.548, + 0.246, + 0.718, + 0.259 + ], + "angle": 0, + "content": "gaoying@scut.edu.cn" + }, + { + "type": "text", + "bbox": [ + 0.145, + 0.267, + 0.826, + 0.303 + ], + "angle": 0, + "content": "\\(^{1}\\)School of Computer Science and Engineering, South China University of Technology \\(^{2}\\)Johns Hopkins University" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.337, + 0.314, + 0.354 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.369, + 0.474, + 0.764 + ], + "angle": 0, + "content": "The decentralized and privacy-preserving nature of federated learning (FL) makes it vulnerable to backdoor attacks aiming to manipulate the behavior of the resulting model on specific adversary-chosen inputs. However, most existing defenses based on statistical differences take effect only against specific attacks, especially when the malicious gradients are similar to benign ones or the data are highly non-independent and identically distributed (non-IID). In this paper, we revisit the distance-based defense methods and discover that i) Euclidean distance becomes meaningless in high dimensions and ii) malicious gradients with diverse characteristics cannot be identified by a single metric. To this end, we present a simple yet effective defense strategy with multi-metrics and dynamic weighting to identify backdoors adaptively. Furthermore, our novel defense has no reliance on predefined assumptions over attack settings or data distributions and little impact on benign performance. To evaluate the effectiveness of our approach, we conduct comprehensive experiments on different datasets under various attack settings, where our method achieves the best defensive performance. For instance, we achieve the lowest backdoor accuracy of \\(3.06\\%\\) under the most difficult Edge-case PGD, showing significant superiority over previous defenses. The experiments also demonstrate that our method can be well-adapted to a wide range of non-IID degrees without sacrificing the benign performance." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.791, + 0.21, + 0.807 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.816, + 0.47, + 0.879 + ], + "angle": 0, + "content": "Federated learning (FL) [26, 35] is a distributed machine learning paradigm that enables multiple participants to train a quality model collaboratively without exchanging their local data. During each round of training, the central server" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.339, + 0.895, + 0.505 + ], + "angle": 0, + "content": "distributes the global model to a subset of clients. Each client updates the model with the local data and submits the parameters to the server for aggregation. By training an efficient and quality model in a decentralized manner without sacrificing the privacy of participants, FL alleviates the possible conflict between technological developments and regulations for data privacy protection(e.g., General Data Protection Regulation). FL has already been applied and achieved success in multiple fields, such as image processing [32], word prediction [36], medical imaging [30], and edge computing [56, 51]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.508, + 0.895, + 0.903 + ], + "angle": 0, + "content": "However, FL is vulnerable to backdoors manipulating the model towards the targeted behavior on specific adversary-chosen inputs [24, 4, 6, 47, 50, 11, 33, 39, 19, 31]. The backdoor attack is more difficult to be detected compared with the untargeted poisoning attacks [6, 7, 33, 11, 19] since it does not affect the regular function of the model and its gradient is more similar to benign ones [47, 38]. Multiple defenses have been proposed to improve the robustness of FL, such as the scoring-based methods [17, 8, 53, 41, 10, 55, 16, 29, 2, 20], which leverage a particular metric to distinguish malicious gradients from the benign ones. Despite its effectiveness against some backdoors, researchers discovered that well-designed attacks (termed stealthy backdoors) whose gradients are indistinguishable from benign ones (through scaling [4, 47] or trigger split [50]) could easily bypass these defenses. Differential privacy (DP) -based method [46, 40, 38, 49] builds upon the observation that the DP method [14], traditionally used against DP attacks, is also effective against backdoors. By adding Gaussian noise to the global model, these methods can dilute the impact of potentially poisoned model updates. Surprisingly, DP-based methods show great ability in resisting stealthy backdoors (e.g., Edge-case PGD [47]). Despite its ability to resist the stealthy backdoors, the noises added by the DP significantly decrease the overall performance and the convergence speed. In comparison, the distance-based method less" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.225, + 0.9 + ], + "angle": 0, + "content": "*Corresponding Author" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4652" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.075, + 0.092, + 0.47, + 0.212 + ], + "angle": 0, + "content": "impacts the global model by aggregating only the benign gradients. Consequently, a natural question arises: can we defend the stealthy backdoors without sacrificing the performance of the FL model? To accomplish this, we turn to the distance-based methods that don't sacrifice the benign performance and promote the research question: how can we successfully leverage distance metrics to discriminate hostile updates from benign ones?" + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.212, + 0.471, + 0.529 + ], + "angle": 0, + "content": "To this end, we revisit the distance-based defense and discover two limitations: 1. Euclidean distance (i.e., \\( L_{2} \\) distance) suffers from the curse of dimensionality. Parameters of Neural Networks (NNs) can be viewed as high-dimensional vectors, and Euclidean distance generally fails to discriminate between malicious and benign gradients in high-dimensional space. 2. Single metric takes effect only against particular attacks with detailed assumptions regarding the malicious gradients. For instance, cosine distance detects malicious gradients with sizeable angular deviations while euclidean distance detects malicious gradients with a large \\( L_{2} \\) norm scaled by the attacker to impact the global models. Moreover, backdoor attacks are conducted with different data and scenarios, resulting in malicious gradients with various characteristics that a single metric cannot handle (i.e., both gradients with a large norm and gradients with sizeable angular deviations exist in one round of aggregation). What's worse is that the defender has no knowledge regarding the attacker and the underlying data distributions due to privacy requirements by FL, which makes detecting with a single metric even more difficult." + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.53, + 0.47, + 0.846 + ], + "angle": 0, + "content": "To address the above two problems, we first introduce the Manhattan distance, which we theoretically prove more meaningful in high dimensional space than Euclidean distance. Empirically, with the Manhattan distance, our proposed distance-based defense shows remarkable performance against the stealthy backdoors. To cope with gradients with various properties, we leverage multiple metrics cooperatively to identify the malicious gradients. We demonstrate in Section 5.4 and Figure 7 that malicious gradients of some characteristics are better identified by specific metrics, which justify our motivation. To handle the different attacks and environments, we further propose to apply a whitening transformation and generate dynamic weights to handle the non-IID distribution of participants and different scales brought by the different distances. Finally, we compute the score for each submitted gradient and aggregate only the benign ones based on the scoring. Extensive experiments illustrate that our defense maintains a high model performance and robustness simultaneously, which has never been achieved before. At a high level, we summarize the main contributions of this paper as follows:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.856, + 0.47, + 0.902 + ], + "angle": 0, + "content": "- We present a novel defense with multi-metrics to adaptively identify backdoors, which is applicable in a generic adversary model without predefined assumption." + }, + { + "type": "text", + "bbox": [ + 0.532, + 0.092, + 0.855, + 0.107 + ], + "angle": 0, + "content": "tions over the attack strategy or data distribution." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.118, + 0.892, + 0.209 + ], + "angle": 0, + "content": "- We show that by introducing the Manhattan distance, our defense alleviates the \"meaningfulness\" problem of Euclidean distance in high dimensions. By utilizing multiple metrics with dynamic weighting, our defense can resist backdoor attacks under a wide range of attack settings and data distributions." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.22, + 0.892, + 0.311 + ], + "angle": 0, + "content": "- We empirically evaluate our method on various datasets and different attack settings. By showing that our defense maintains both high robustness and benign performance under the stealthy backdoors that previously have not been successfully defended, we demonstrate the effectiveness of our approach." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.118, + 0.892, + 0.311 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.325, + 0.638, + 0.341 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.351, + 0.892, + 0.472 + ], + "angle": 0, + "content": "Backdoor Attacks on Federated Learning. FL enables multiple clients collaboratively train a model without local data exchange. In an FL system, clients update the local model with private data and submit the parameters to the server for aggregation. Given a total of \\( N \\) participants, each with \\( n^{(i)} \\) samples. In each round \\( t \\), the server randomly selects \\( K \\) clients to participate. FedAvg [35] is a widely-adopted FL algorithm, which can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.577, + 0.483, + 0.892, + 0.524 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {w} _ {t} = \\boldsymbol {w} _ {t - 1} + \\eta \\cdot \\frac {\\sum_ {i = 1} ^ {K} n ^ {(i)} \\Delta w _ {t} ^ {(i)}}{\\sum_ {i = 1} ^ {K} n ^ {(i)}} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.537, + 0.892, + 0.583 + ], + "angle": 0, + "content": "where \\( w_{t} \\) is the global model parameters at round \\( t \\), \\( \\Delta w_{t}^{(i)} \\) is the local model updates from the client \\( i \\) in round \\( t \\), and \\( \\eta \\) is the global model learning rate." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.584, + 0.892, + 0.78 + ], + "angle": 0, + "content": "Empirical studies from Bagdasaryan et al. [4] demonstrate that FedAvg [35] is vulnerable to backdoor attacks since FL has no authority over local data and the training process due to privacy concerns. The model replacement attack [4] successfully injects a backdoor into the global model by the single-shot attack. Some well-designed attacks strategically target the weakness of the defenses, such as the PGD attack [47] scaling and projecting the gradients, or the DBA attack [50] splitting the triggers before uploading them. Moreover, the Edge-case PGD attack [47] modifies the poisoned data and model. Undoubtedly, these attacks present a tremendous challenge to the security of the FL system." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Defense Against the Backdoor Attack. Various methods to defend against backdoor attacks improve the robustness and security of FL. In general, we can divide these methods into two categories. The first type of defense strategies tries to distinguish malicious gradients from benign ones by classifying or scoring with the assumption that benign and malicious gradients show distinct differences in the vector space [17, 8, 53, 41, 10, 55, 16, 29, 2, 20]. Krum" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4653" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.318 + ], + "angle": 0, + "content": "and Multi-Krum [8] select the gradient with the smallest Euclidean norm from the others to aggregate and update the global model at each round. Foolsgold [17] assumes that the gradients of attackers are always consistent and distinguishes them by the Cosine similarity between historical updates. Trimmed Mean and Median [53] remove a fraction of the gradients with maximum and minimum values and then take the median value on each dimension of the remaining gradients as the parameters of the global model. RFA [41] leverages the geometric median of the gradients to keep the aggregated model close to the benign model and away from the backdoor one. The strength lies in that, if successful, the gradients of attackers are excluded from the aggregation process, which solves the core and fundamental problem of defending the attack." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.323, + 0.473, + 0.672 + ], + "angle": 0, + "content": "However, the above methods take effect only under particular attacks since they make detailed assumptions about the attack or the data distributions. Foolsgold [17] assumes the gradients of attackers are consistent while benign gradients from Non-IID data differ. Krum [8] assumes that the data of benign clients is similar under IID settings and excludes abnormal malicious ones. These predefined assumptions limit the applicability of these defenses under various attacks and data distributions and can be easily bypassed by elaborate attacks. For example, PGD [47] breaks any Euclidean-based defense (e.g. Krum and Multi-Krum) by scaling the norm to a small value. Other methods, such as FLTrust [10], use a root dataset and aggregate only those gradients with large cosine similarities with the root dataset. FedInv [55] inverts the gradients into dummy datasets and then identifies the malicious gradient by comparing these dummy datasets. These methods are limited as well. FLTrust cannot defend against backdoors crafted on edge cases (e.g. Edge-case PGD) since they appear less often and are probably not in the root dataset. Inverting the gradients into dummy datasets violates the privacy requirement of FL. Essentially, this method can be characterized as another type of attack [3, 21]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.675, + 0.473, + 0.902 + ], + "angle": 0, + "content": "The other category of defenses [46, 40, 38, 49] builds upon the observation that the differential privacy (DP) method [14], traditionally used against DP attacks is also effective against backdoor attacks. Earlier studies [4] have demonstrated that clipping and adding noise (typically used in DP) can resist backdoor attacks without any specific assumptions over the data distribution. Following these findings, Weak-DP [46] clips the norm and adds the Gaussian noise to the global model for mitigating the backdoors. RLR [40] and Flame [38] apply the clustering methods before the DP process. However, the noise added significantly decreases the performance and the convergence speed of the FL system. In a nutshell, using DP sacrifices regular functionality for robustness. Despite its deficiency, the DP-based method has been the only method that has taken effect" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.714, + 0.108 + ], + "angle": 0, + "content": "against stealthy backdoors [38]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.12, + 0.637, + 0.138 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.146, + 0.895, + 0.375 + ], + "angle": 0, + "content": "We first provide the threat model in Section 3.1 and then detail our design of the proposed defense method. Our goal is to design an efficient defense with the following properties: (1) Effectiveness: To prevent the adversary from achieving its hostile purpose, we aim to design a defense that identifies as many malicious updates as possible to eliminate its impact on the global model. (2) Performance: Benign performance of the global model must be preserved to maintain its utility. (3) Independence: The defense must be applicable to generic adversary models under different data distributions and attack strategies. Our defense consists of three major components: defining and calculating the gradient feature, computing the dynamic weight and score for each update, and aggregating the benign gradients with the score computed, as shown in Figure 1 and Algorithm 1." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.383, + 0.644, + 0.398 + ], + "angle": 0, + "content": "3.1. Threat Model" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.406, + 0.895, + 0.527 + ], + "angle": 0, + "content": "Adversarial goals. Adversary aims to alter the behavior of the model on some specific examples with no negative impact on the benign performance. We consider the adversary effective if this is met. In addition, the adversary will make their attack as covert as possible, e.g., by scaling down. Formally, adversary \\(\\mathcal{A}\\) manipulates the global model \\(G\\) to the poisoned model \\(G'\\). For any inputs \\(x\\), we have the outputs below:" + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.538, + 0.892, + 0.571 + ], + "angle": 0, + "content": "\\[\nG ^ {\\prime} (x) = \\left\\{ \\begin{array}{c c} l ^ {\\prime} \\neq G (x) & \\forall x \\in D _ {\\mathcal {A}} \\\\ G (x) & \\forall x \\notin D _ {\\mathcal {A}} \\end{array} \\right. \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.892, + 0.627 + ], + "angle": 0, + "content": "where \\(D_{\\mathcal{A}}\\) denotes the poisoned dataset belonging to adversary \\(\\mathcal{A}\\), and \\(l'\\) denotes the specific label modified by adversary \\(\\mathcal{A}\\) of the input \\(x\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.627, + 0.895, + 0.734 + ], + "angle": 0, + "content": "Adversarial capabilities. This paper assumes the white-box setting with full knowledge of aggregation operations, including potential defenses. Also, adversaries can freely alter the parameters in the local training, ensure participation in each round and compromise less than \\(50\\%\\) of total FL clients. However, the adversary cannot control any process or parameter executed in the aggregator." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.742, + 0.686, + 0.758 + ], + "angle": 0, + "content": "3.2. Feature of gradient" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.903 + ], + "angle": 0, + "content": "The essential logic of distance-based defense involves defining some indicative metric that can well discriminate the malicious gradients from the benign ones and removes the hostile updates from the aggregation. Consequently, the core problem becomes how to define a metric that identifies the characteristics of hostile gradients. For instance, NDC [46] utilizes the length of the gradient (i.e. Euclidean distance) while FoolGold [17] leverages Cosine similarity to measure the difference between updates." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.517, + 0.957 + ], + "angle": 0, + "content": "4654" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.119, + 0.09, + 0.852, + 0.325 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.181, + 0.337, + 0.788, + 0.353 + ], + "angle": 0, + "content": "Figure 1: The overview of our defense process. Step 1 and step 2 are our core contributions." + }, + { + "type": "image", + "bbox": [ + 0.159, + 0.384, + 0.367, + 0.505 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.52, + 0.471, + 0.582 + ], + "angle": 0, + "content": "Figure 2: Demonstration of feature of gradient on two dimensional space. \\(\\pmb{w}_0\\) is initial global model \\(\\pmb{w}_0\\) and \\(\\pmb{w}_i\\) is the local model of the \\(i\\)-th client. \\(\\pmb{w}_i - \\pmb{w}_0\\) is the gradient and we define the feature of gradient as \\((|x + y|, l, \\theta)\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.605, + 0.47, + 0.763 + ], + "angle": 0, + "content": "Manhattan Distance. However, the Euclidean distance suffers from the so-called \"curse of dimensionality\" [48], which renders distance metrics less sensitive in high dimensional space, especially in the case of Euclidean distance. Theorem 1 uses \\(\\frac{D\\max_d^k - D\\min_d^k}{D\\min_d^k}\\) to indicate the \"meaningfulness\" of a distance referred as the Relative Contrast. It demonstrates that the distance metric is meaningless in high-dimensional space because as dimensionality increases, the distance between the nearest and the furthest neighbor approximates to be the same." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.769, + 0.472, + 0.785 + ], + "angle": 0, + "content": "Theorem 1 (Beyer et. al.[5] The curse of dimensionality)" + }, + { + "type": "equation", + "bbox": [ + 0.146, + 0.794, + 0.397, + 0.829 + ], + "angle": 0, + "content": "\\[\nI f \\lim _ {d \\rightarrow \\infty} v a r \\left(\\frac {\\| X _ {d} \\| _ {k}}{E [ \\| X _ {d} \\| _ {k} ]}\\right) = 0, t h e n\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.185, + 0.831, + 0.364, + 0.868 + ], + "angle": 0, + "content": "\\[\n\\frac {D m a x _ {d} ^ {k} - D m i n _ {d} ^ {k}}{D \\min _ {d} ^ {k}} \\rightarrow_ {p} 0,\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.87, + 0.47, + 0.902 + ], + "angle": 0, + "content": "where \\(d\\) denotes the dimensionality of the data space, \\(E[X]\\) and var \\([X]\\) denotes the expected value and variance of a" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.379, + 0.892, + 0.424 + ], + "angle": 0, + "content": "random variable \\( X \\), \\( Dmax_{d}^{k} \\) and \\( Dmin_{d}^{k} \\) means the farthest/nearest distance of the \\( N \\) points to the origin using the distance metric \\( L_{k} \\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.434, + 0.893, + 0.509 + ], + "angle": 0, + "content": "To find out which distance metric is more meaningful in high-dimensional space, we size up the relation between the dimension \\(d\\) and the distance \\(L_{k}\\). We have Lemma 1, which shows that \\(Dmax_{d}^{k} - Dmin_{d}^{k}\\) increases at the ratio of \\(d^{(1 / k) - (1 / 2)}\\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.52, + 0.892, + 0.566 + ], + "angle": 0, + "content": "Lemma 1 (Hinneburg et.al.[22]) Let \\(\\mathcal{F}\\) be an arbitrary distribution of two points and the distance function \\(\\| \\cdot \\|\\) be an \\(L_{k}\\) metric. Then," + }, + { + "type": "equation", + "bbox": [ + 0.571, + 0.575, + 0.821, + 0.61 + ], + "angle": 0, + "content": "\\[\n\\lim _ {d \\rightarrow \\infty} E \\left[ \\frac {D m a x _ {d} ^ {k} - D m i n _ {d} ^ {k}}{d ^ {(1 / k) - (1 / 2)}} \\right] = C _ {k},\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.62, + 0.788, + 0.636 + ], + "angle": 0, + "content": "where \\(C_k\\) is some constant dependent on \\(k\\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.644, + 0.892, + 0.691 + ], + "angle": 0, + "content": "Subsequently, we use the value of \\( Dmax_{d}^{k} - Dmin_{d}^{k} \\) as a criterion to evaluate the ability of a particular metric to discriminate different vectors in high dimensional space." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.7, + 0.892, + 0.761 + ], + "angle": 0, + "content": "Proposition 1 Let \\( M_d = Dmax_d^1 - Dmin_d^1 \\) reflect the discriminating ability of Manhattan distance and \\( U_d = Dmax_d^2 - Dmin_d^2 \\) reflect the discriminating ability of Euclidean distance. Then," + }, + { + "type": "equation", + "bbox": [ + 0.611, + 0.77, + 0.78, + 0.806 + ], + "angle": 0, + "content": "\\[\n\\lim _ {d \\rightarrow \\infty} E \\left[ \\frac {M _ {d}}{U _ {d} \\cdot d ^ {\\frac {1}{2}}} \\right] = C ^ {\\prime}.\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.815, + 0.833, + 0.831 + ], + "angle": 0, + "content": "where \\(C'\\) is a constant. Proof see in Appendix C." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Proposition 1 shows that \\( M_d \\) and \\( U_d \\cdot d^{\\frac{1}{2}} \\) are infinite of the same order. Since \\( d^{\\frac{1}{2}} \\) is also an infinite value, \\( M_d \\) towers above \\( U_d \\), suggesting that Manhattan can discriminate more than the Euclidean distance in high-dimension space. Given" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4655" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.272 + ], + "angle": 0, + "content": "this, we conclude that the Manhattan distance is better than the Euclidean metric, withstanding the curse of dimensionality, which chimes in with the previous experiment [1, 37]. The parameters of neural networks can be viewed as a typical high-dimensional space, especially when the number of parameters increases as the trend in deep learning applications [9, 44, 42, 15, 34, 54, 43]. In light of this and Theorem 1, we argue that Euclidean distance is insufficient to discriminate between malicious and benign gradients. With Proposition 1, we introduce the Manhattan distance metric to describe the characteristics of gradients which captures the difference in high dimensional space better." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.273, + 0.473, + 0.735 + ], + "angle": 0, + "content": "Multiple Metrics as Feature of Gradient. Another problem that we identify as discussed in Section 1 is that current methods conduct defense on a single metric basis. With only one metric, a sophisticated attacker could effortlessly bypass them with a well-designed gradient. For instance, PGD attack [47] manage to break the defense based on Euclidean distances by clipping the gradient norm to a small value. Moreover, attackers conduct attacks under different environments and data distributions, leading to malicious gradients with diverse characteristics that a single metric cannot handle. To this end, we propose multiple metrics to cooperatively identify the malicious gradient by defining the feature of gradient as the angle by the Cosine similarity, length by the Euclidean distances, and its Manhattan norm by the Manhattan distance, namely, \\(\\pmb{x} = (x_{Man}, x_{Eul}, x_{Cosine})\\). Here, \\(x_{Man}\\) denotes the Manhattan distance, \\(x_{Eul}\\) denotes the Euclidean distance and \\(x_{Cosine}\\) denotes the Cosine similarity. Figure 2 provides a schematic diagram of the gradient feature. We compute the gradient feature \\(x_{Man}\\), \\(x_{Eul}\\), and \\(x_{Cosine}\\) of the \\(i\\)-th client of each round as follows: \\(x_{Man}^{(i)} = \\| \\pmb{w}_i - \\pmb{w}_0\\|_1\\), \\(x_{Eul}^{(i)} = \\| \\pmb{w}_i - \\pmb{w}_0\\|_2\\), \\(x_{Cosine}^{(i)} = \\frac{\\langle\\pmb{w}_0\\pmb{w}_i\\rangle}{\\|\\pmb{w}_0\\| \\cdot \\|\\pmb{w}_i\\|}\\), where \\(\\pmb{w}_0\\) denotes the global model before federated training and \\(\\pmb{w}_i\\) denotes the \\(i\\)-th client's local model after training, \\(\\| \\cdot \\|_1\\) means the \\(L_1\\) norm of a vector, \\(\\| \\cdot \\|_2\\) means the \\(L_2\\) norm of a vector, \\(\\langle \\cdot, \\cdot \\rangle\\) and represents inner product. After defining the feature of gradient, we utilize it for malicious identification. The goal is to identify the outlier among the gradients. We use the sum of the distance between each gradient as the indicator. Formally, we define it as Equation 3." + }, + { + "type": "equation", + "bbox": [ + 0.116, + 0.751, + 0.469, + 0.803 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {x} ^ {\\prime (i)} = \\left(\\sum_ {j, j \\neq i} ^ {K} \\left| x _ {M a n} ^ {(i)} - x _ {M a n} ^ {(j)} \\right|, \\right. \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.123, + 0.799, + 0.428, + 0.842 + ], + "angle": 0, + "content": "\\[\n\\sum_ {j, j \\neq i} ^ {K} | x _ {E u l} ^ {(i)} - x _ {E u l} ^ {(j)} |, \\sum_ {j, j \\neq i} ^ {K} | x _ {C o s i n e} ^ {(i)} - x _ {C o s i n e} ^ {(j)} |),\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.848, + 0.424, + 0.865 + ], + "angle": 0, + "content": "3.3. Dynamic Weighting Through Whitening" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.902 + ], + "angle": 0, + "content": "After defining the feature of gradient and indicator, we now provide an approach to score each gradient. Two fac" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.136 + ], + "angle": 0, + "content": "tors are taken into account when considering an efficient way to turn the indicator into a unified score that works under various data distributions and attacks." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.147, + 0.892, + 0.222 + ], + "angle": 0, + "content": "- Different scales of the three distance metrics are the first obstacle before utilizing these metrics collaboratively. Since each metric is correlated, a novel regularization is required instead of the usual normalization by the maximum value." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.233, + 0.894, + 0.308 + ], + "angle": 0, + "content": "- Different data distributions (e.g. different degrees of non-IID) render the gradients of both malicious and benign clients different. Thus, dynamic weighting is required to cope with various environments and attacks to achieve a universal defense." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.147, + 0.894, + 0.308 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.32, + 0.892, + 0.366 + ], + "angle": 0, + "content": "Considering the above factors, we propose first to project the value of the metrics in the feature of gradient to its corresponding principal axis by applying a whitening process:" + }, + { + "type": "equation", + "bbox": [ + 0.608, + 0.377, + 0.892, + 0.403 + ], + "angle": 0, + "content": "\\[\n\\delta^ {(i)} = \\sqrt {\\boldsymbol {x} ^ {\\prime^ {(i) \\top}} \\boldsymbol {\\Sigma} ^ {- 1} \\boldsymbol {x} ^ {\\prime^ {(i)}}}. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.41, + 0.892, + 0.56 + ], + "angle": 0, + "content": "where \\(\\boldsymbol{\\Sigma}\\) is the covariance matrix of \\(\\pmb{X} = [x^{\\prime(1)}x^{\\prime(2)}\\dots x^{\\prime(K)}]^{\\top}\\). Since we need to calculate the inverse of the covariance matrix \\(\\boldsymbol{\\Sigma}\\), the number of samples must be larger than the number of features, i.e., \\(K > 3\\). Please notice that the inverse of the covariance matrix is calculated based on the selected gradients, which will change the weights of the features dynamically depending on the feature distribution, hence \"dynamic weighting\". With such a dynamic weight, our method can better adapt to different environments and resist various attacks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.571, + 0.791, + 0.587 + ], + "angle": 0, + "content": "3.4. Aggregation of Benign Gradients" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.595, + 0.892, + 0.716 + ], + "angle": 0, + "content": "After obtaining the score of each gradient, we aggregate the gradients with high scoring. A higher score indicates that the gradient is less divergent among all. After the selection of \"benign\" gradients, we can aggregate them with any existing aggregation methods (e.g. Averaging of gradients). We follow [35] and perform standard FedAvg on the \"benign\" gradients. A detailed analysis of aggregation of benign gradients is in Appendix A.1." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.73, + 0.677, + 0.746 + ], + "angle": 0, + "content": "4. Experiment Setup" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.755, + 0.891, + 0.784 + ], + "angle": 0, + "content": "We will first introduce the settings and then the objective of our experiments." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.786, + 0.892, + 0.86 + ], + "angle": 0, + "content": "Datasets. We conduct our experiments on multiple datasets, including two visual datasets, CIFAR-10 [27] and EMNIST [12]. We also experiment on other datasets to prove the generalization ability, including CINIC10 [13], LOAN [25] and Sentiment140 [18] as follows:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "- CIFAR-10 dataset [27] is a vision classification dataset containing 50,000 training samples and" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "4656" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.081, + 0.092, + 0.344, + 0.106 + ], + "angle": 0, + "content": "Algorithm 1 Our aggregation algorithm" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.108, + 0.469, + 0.167 + ], + "angle": 0, + "content": "Input: Total number of clients in each round \\(K\\), models of clients \\(\\boldsymbol{w}^{(1)}, \\boldsymbol{w}^{(2)}, \\dots, \\boldsymbol{w}^{(K)}\\), last global model \\(\\boldsymbol{w}_0\\), fraction selected to aggregation \\(p\\), global learning rate \\(\\eta\\), size of the \\(i - th\\) client dataset \\(n^{(i)}\\)" + }, + { + "type": "title", + "bbox": [ + 0.086, + 0.169, + 0.262, + 0.183 + ], + "angle": 0, + "content": "Output: Global model \\( w^{*} \\)" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.186, + 0.469, + 0.215 + ], + "angle": 0, + "content": "1: for \\(i\\in \\{1,2,\\dots,K\\}\\) do compute the gradients features" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.215, + 0.281, + 0.234 + ], + "angle": 0, + "content": "2: \\(x_{Man}^{(i)}\\gets \\left\\| \\pmb{w}_0 - \\pmb{w}_i\\right\\| _1\\)" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.234, + 0.276, + 0.251 + ], + "angle": 0, + "content": "3: \\(x_{Eul}^{(i)}\\gets \\left\\| \\pmb {w}_0 - \\pmb {w}_i\\right\\| _2\\)" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.251, + 0.259, + 0.272 + ], + "angle": 0, + "content": "4: \\(x_{\\text{Cos}}^{(i)} \\gets \\frac{\\langle \\boldsymbol{w}_0, \\boldsymbol{w}_i \\rangle}{\\|\\boldsymbol{w}_0\\| \\cdot \\|\\boldsymbol{w}_i\\|}\\)" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.271, + 0.316, + 0.29 + ], + "angle": 0, + "content": "5: \\(\\pmb{x}^{(i)}\\gets (x_{Man}^{(i)},x_{Eul}^{(i)},x_{Cos}^{(i)})\\)" + }, + { + "type": "title", + "bbox": [ + 0.089, + 0.291, + 0.16, + 0.302 + ], + "angle": 0, + "content": "6: end for" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.304, + 0.469, + 0.332 + ], + "angle": 0, + "content": "7: for \\(i,j\\in \\{1,2,\\dots,K\\}\\) do compute the sum of the distance between each gradient" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.333, + 0.357, + 0.354 + ], + "angle": 0, + "content": "8: \\(x^{\\prime}_{Man}^{(i)}\\gets \\sum_{j,j\\neq i}^{K}|x_{Man}^{(i)} - x_{Man}^{(j)}|\\)" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.354, + 0.337, + 0.373 + ], + "angle": 0, + "content": "9: \\(x^{\\prime}_{Eul}^{(i)}\\gets \\sum_{j,j\\neq i}^{K}|x^{(i)}_{Eul} - x^{(j)}_{Eul}|\\)" + }, + { + "type": "text", + "bbox": [ + 0.085, + 0.373, + 0.338, + 0.393 + ], + "angle": 0, + "content": "10: \\(x^{\\prime}_{COS}^{(i)}\\gets \\sum_{j,j\\neq i}^{K}|x^{(i)}_{COS} - x^{(j)}_{COS}|\\)" + }, + { + "type": "text", + "bbox": [ + 0.085, + 0.393, + 0.336, + 0.412 + ], + "angle": 0, + "content": "11: \\( \\pmb{x}^{\\prime (i)}\\gets (x_{Man}^{\\prime (i)},x_{Eul}^{\\prime (i)},x_{Cos}^{\\prime (i)}) \\)" + }, + { + "type": "title", + "bbox": [ + 0.085, + 0.413, + 0.16, + 0.423 + ], + "angle": 0, + "content": "12: end for" + }, + { + "type": "text", + "bbox": [ + 0.085, + 0.423, + 0.309, + 0.441 + ], + "angle": 0, + "content": "13: \\(X\\gets [\\pmb{x}^{\\prime (1)},\\pmb{x}^{\\prime (2)},\\dots,\\pmb{x}^{\\prime (K)}]^{\\top}\\)" + }, + { + "type": "text", + "bbox": [ + 0.085, + 0.441, + 0.469, + 0.47 + ], + "angle": 0, + "content": "14: \\(\\Sigma \\gets\\) the Covariance of \\(X\\) compute the adaptive weight matrix in this round" + }, + { + "type": "text", + "bbox": [ + 0.085, + 0.471, + 0.265, + 0.487 + ], + "angle": 0, + "content": "15: for \\(i\\in \\{1,2,\\dots,K\\}\\) do" + }, + { + "type": "text", + "bbox": [ + 0.085, + 0.487, + 0.469, + 0.521 + ], + "angle": 0, + "content": "16: \\(\\delta^{(i)}\\gets \\sqrt{\\boldsymbol{x}^{\\prime(i)\\top}\\cdot\\Sigma^{-1}\\cdot\\boldsymbol{x}^{\\prime(i)}}\\) \\(\\triangleright\\) dynamically compute the divergence" + }, + { + "type": "title", + "bbox": [ + 0.085, + 0.522, + 0.16, + 0.533 + ], + "angle": 0, + "content": "17: end for" + }, + { + "type": "text", + "bbox": [ + 0.085, + 0.536, + 0.468, + 0.565 + ], + "angle": 0, + "content": "18: Remove the \\(K\\cdot (1 - p)\\) models with the high divergency \\(\\delta^{(i)}\\), remaining models as \\(\\mathbb{B}\\)" + }, + { + "type": "text", + "bbox": [ + 0.085, + 0.565, + 0.343, + 0.592 + ], + "angle": 0, + "content": "19: \\(\\pmb{w}^{*}\\gets \\pmb{w}_{0} + \\eta \\cdot \\frac{\\sum_{i\\in\\mathbb{B}}n^{(i)}\\cdot(\\pmb{w}^{(i)} - \\pmb{w}_{0})}{\\sum_{i\\in\\mathbb{B}}n^{(i)}}\\)" + }, + { + "type": "text", + "bbox": [ + 0.11, + 0.629, + 0.469, + 0.689 + ], + "angle": 0, + "content": "10,000 testing samples with ten classes. To simulate the FL environment, we set the \\( a \\) of the Dirichlet distribution to be 0.5, representing a non-IID distribution. Smaller \\( a \\) means a larger degree of non-IID." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.69, + 0.469, + 0.748 + ], + "angle": 0, + "content": "- EMNIST dataset [12] is a digit classification dataset consisting of 280,000 real-world handwritten images of digits from 0 to 9. We also set the degree of non-IID to be \\(a = 0.5\\)." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.75, + 0.469, + 0.81 + ], + "angle": 0, + "content": "- CINIC10 [13] has a total of 270,000 images, 4.5 times that of CIFAR-10, which is constructed from two different sources: ImageNet and CIFAR-10. We set the non-IID degree as \\(a = 0.5\\)." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.811, + 0.469, + 0.9 + ], + "angle": 0, + "content": "- Lending Club Loan dataset (LOAN) [25] contains financial information such as loan information and credit scores for loan status prediction. There are 2,260,668 samples with a total of 9 classes. To simulate a more realistic situation, we divide the data by US states, where each state represents one client. We" + }, + { + "type": "list", + "bbox": [ + 0.097, + 0.69, + 0.469, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.532, + 0.092, + 0.764, + 0.106 + ], + "angle": 0, + "content": "set the non-IID parameter \\(a = 0.9\\)" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.107, + 0.892, + 0.197 + ], + "angle": 0, + "content": "- Sentiment140 [18] is a publicly available English Twitter sentiment classification dataset containing 1.6 million tweets, of which 800,000 are for training, and the other 800,000 are for testing. Each tweet in the dataset is labeled with a sentiment polarity (positive, neutral, or negative)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.207, + 0.892, + 0.297 + ], + "angle": 0, + "content": "Models. Different models are used on different datasets to demonstrate the generality of our approach. A 9-layer VGG style network (VGG-9) [45] is trained on the CIFAR10. On the EMNIST, we train LeNet-5 model [28]. We train the LSTM model [23] for Sentiment140 and a network with three fully-connected layers for LOAN." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.298, + 0.892, + 0.358 + ], + "angle": 0, + "content": "Backdoor Attacks. We implement both pixel-pattern and semantic backdoors. To make the attack more challenging, we use the multiple-shot attack instead of the single-shot. The following are the attack methods we use:" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.368, + 0.891, + 0.443 + ], + "angle": 0, + "content": "- Model Replacement Attack [4]: Malicious clients generate backdoor gradients during their local training. Attackers scale up their gradients to ensure that the malicious model will replace the global model. Usually, the scaling factor is \\( N / K \\)." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.444, + 0.891, + 0.518 + ], + "angle": 0, + "content": "- DBA Attack [50]: DBA decomposes a global trigger pattern into separate local patterns and embeds them into the training sets of different attackers, resulting in a more negligible difference between benign and back-door gradients;" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.519, + 0.891, + 0.564 + ], + "angle": 0, + "content": "- PGD Attack [47]: To bypass the Euclidean-based defense, PGD Attack projects the model parameter within the ball centered around the global model;" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.564, + 0.892, + 0.67 + ], + "angle": 0, + "content": "- Edge-case PGD Attack [47]: Attackers have a set of edge-case samples and some benign samples as their poisoned datasets. Edge-case samples are unlikely to exist in the benign training set. Thus, the benign gradients cannot dilute the backdoor. We launch this attack in the form of PGD. The Edge-case PGD attack is so stealthy that most defenses cannot defend against it." + }, + { + "type": "list", + "bbox": [ + 0.519, + 0.368, + 0.892, + 0.67 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.68, + 0.892, + 0.71 + ], + "angle": 0, + "content": "Evaluation. We leverage the following two metrics for evaluating the effectiveness of our defense:" + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.72, + 0.891, + 0.794 + ], + "angle": 0, + "content": "- Backdoor Accuracy (BA) indicates whether the attacker succeeds. It shows the accuracy of the model on the backdoor task. The attackers aim to maximize this metric, and the lower the BA, the more efficient the defense." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.796, + 0.892, + 0.9 + ], + "angle": 0, + "content": "- Main Task Accuracy (MA) is the accuracy on the main task. The overall objective of all participants in an FL system is to maximize MA. The benign clients maximize the model performance, while the attackers seek to be stealthy and maintain MA. Thus, the defense should not cause a significant drop in MA, which we report to demonstrate that our defense does not affect" + }, + { + "type": "list", + "bbox": [ + 0.519, + 0.72, + 0.892, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.515, + 0.957 + ], + "angle": 0, + "content": "4657" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.11, + 0.092, + 0.47, + 0.122 + ], + "angle": 0, + "content": "the functionality of the FL system. We report all BA and MA values in percentages." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.136, + 0.41, + 0.151 + ], + "angle": 0, + "content": "Hyperparameters are detailed in Appendix B." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.152, + 0.47, + 0.273 + ], + "angle": 0, + "content": "Objectives of Experiments. Firstly, we aim to illustrate the effectiveness of our proposed defense under different attacks by comparing it with the current and previous state-of-the-art defenses. Secondly, we demonstrate that the performance of our defense is consistent under different scenarios (e.g., different degrees of non-IID \\( a \\) and different attack frequencies). Thirdly, we figure out the reason for our defense works through the ablation study in Section 5.4." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.29, + 0.267, + 0.307 + ], + "angle": 0, + "content": "5. Experiment Results" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.316, + 0.469, + 0.348 + ], + "angle": 0, + "content": "5.1. Robustness against Different Attacks and Comparison with SOTA" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.355, + 0.47, + 0.627 + ], + "angle": 0, + "content": "We first demonstrate the robustness of our approach under different attacks and then compare our methods with the state-of-the-art defense methods such as Krum [8], Multi-Krum [8], Foolsgold [17], RFA [41], Weak-DP [46], and Flame [38] in Table 1. All the defenses except RFA and Weak-DP successfully defended against the model replacement attack since RFA and Weak-DP still incorporate some malicious gradient into the global model. Our defense achieves the lowest BA on both datasets \\((0.56\\%\\) and \\(0.00\\%)\\) with little impact on the MA. Under the DBA attack, Multi-Krum almost has no effect. Flame and our method also deteriorate because \\(40\\%\\) of the participants in each round are malicious, which significantly impacts the method of selecting multiple clients for aggregation. Although Krum and Foolsgold successfully defend against the DBA attack, they also negatively affect the overall performance of the global model. Our defense can reduce the BA to less than \\(10\\%\\) without affecting the MA." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.469, + 0.824 + ], + "angle": 0, + "content": "PGD attack is much stealthier than the above two which Krum, RFA, and Multi-Krum fail to detect. Moreover, once they select the wrong gradient for aggregation, the global model is replaced, leading to a worse BA than FedAvg. Ours and Flame achieve the best effect of \\(0.56\\%\\) and \\(0.00\\%\\) on the two datasets, respectively. Edge-case PGD is the hardest of all since it is both stealthy and effective since it attacks with edge-case samples and projects the gradient back to the \\(L_{2}\\) norm ball. All the previous defenses have limited effect on this attack. Flame reduces the BA to \\(5.12\\%\\). However, Flame suffers from a \\(6\\%\\) drop on MA, which is a result of adding noise. In comparison, ours achieves a much lower BA of \\(3.06\\%\\) with almost no impact on MA." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "On EMNIST, we also achieve better defense compared to up-to-date methods. Remarkably, we achieve \\(0.0\\%\\) BA under both PGD and Edge-case PGD attacks meaning that we defend entirely against these two adversaries. We also achieve similar performance without sacrificing the benign" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.305 + ], + "angle": 0, + "content": "performance against model replacement and DBA. To provide an overall comparison with previous methods, we follow [52] and design an improved version of the ranking score for each defense with respect to baseline FedAvg. We use the percentage of improvement over the baseline to score and compute it on MA/BA respectively, formally as \\(\\frac{K_{\\mathrm{MA/BA}} - B_{\\mathrm{MA/BA}}}{B_{\\mathrm{MA/BA}}}\\) where \\(K\\) denotes some methods and \\(B\\) denotes baseline. Adding up (\\(score_{MA} - score_{BA}\\)) across all attacks produces the ranking score for each defense. As shown in the last column of Table 1, we show that our method obtains the highest ranking score with almost \\(400\\%\\) better than the baseline and outperforms the second-best Flame by around 0.5. We detail the ranking score in Appendix D." + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.318, + 0.889, + 0.432 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.655, + 0.432, + 0.741, + 0.445 + ], + "angle": 0, + "content": "(a) CIFAR10" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.446, + 0.695, + 0.535 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.655, + 0.534, + 0.74, + 0.547 + ], + "angle": 0, + "content": "(b) EMNIST" + }, + { + "type": "image", + "bbox": [ + 0.697, + 0.446, + 0.886, + 0.535 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.559, + 0.892, + 0.59 + ], + "angle": 0, + "content": "Figure 3: MA(%) and BA(%) of various defenses under Edge-case PGD attack." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.608, + 0.892, + 0.73 + ], + "angle": 0, + "content": "We show the MA and BA along the training process of the seven defenses under the Edge-case PGD attack in Figure 3. Only our method and Flame successfully resist the attack during the entire training process, and Flame also dampens the MA. The disadvantage of our approach is that the convergence speed is slightly slowed down compared to FedAvg, but it is still much better than the compared defenses, e.g., Krum and Foolsgold." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.741, + 0.787, + 0.758 + ], + "angle": 0, + "content": "5.2. Impact of Training Environment" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.891, + 0.81 + ], + "angle": 0, + "content": "In this section, we demonstrate that our defense is invariant to the different training environments, i.e. degrees of non-IID, and attack frequency." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Impact of Different Degrees of Non-IID. As mentioned abundantly in Section 3.3, the different data distributions contribute to one of the hardest problems in distance-based defense. Thus, to illustrate the effectiveness of our method, we demonstrate that our defense is invariant to the different degrees of non-IID. The experiment is conducted with the" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4658" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.152, + 0.09, + 0.816, + 0.105 + ], + "angle": 0, + "content": "Table 1: Robustness of our approach compared to the SOTA defenses for various challenging attacks." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.116, + 0.892, + 0.338 + ], + "angle": 0, + "content": "
DatasetDefenseModel Replacement [4]DBA [50]PGD [47]Edge-case PGD [47]Ranking Score ↑
MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓
CIFAR10FedAvg [35]86.9564.8079.2390.4487.0414.4487.1455.100
RFA [41]86.69(+0.00)25.56(-0.61)79.6(+0.00)57.69(-0.36)87.1(+0.00)52.56(+2.64)86.47(-0.01)65.31(+0.19)-1.86
Foolsgold [17]85.71(-0.01)6.67(-0.90)77.56(-0.02)3.43(-0.96)84.92(-0.02)14.44(+0.00)85.72(-0.02)45.41(-0.18)+1.96
Krum [8]82.17(-0.05)6.11(-0.91)78.18(-0.01)6.01(-0.93)82.32(-0.05)66.67(+3.62)81.23(-0.07)59.18(+0.07)-2.04
Multi-Krum [8]86.55(+0.00)1.67(-0.97)79.33(0.00)91.39(+0.01)86.52(-0.01)17.78(+0.23)87.4(+0.00)60.2(+0.09)+0.63
Weak-DP [46]74.41(-0.14)46.11(-0.29)10.00(-0.87)0.00(-1.00)73.61(-0.15)12.78(-0.11)73.84(-0.15)53.06(-0.04)+0.12
Flame [38]80.58(-0.07)0.56(-0.99)76.78(-0.03)37.24(-0.59)81.24(-0.07)0.56(-0.96)81.41(-0.07)5.12(-0.91)+3.21
Ours86.34(-0.01)0.56(-0.99)79.61(+0.00)9.98(-0.89)86.44(-0.01)0.56(-0.96)86.86(+0.00)3.06(-0.94)+3.77
EMNISTFedAvg [35]99.5496.0097.6894.1399.5510.0099.3796.000
RFA [41]99.57(+0.00)6.00(-0.94)97.87(+0.00)1.39(-0.99)99.32(+0.00)4.00(-0.60)99.29(+0.00)97.00(+0.01)+2.51
Foolsgold [17]96.42(-0.03)98.00(+0.02)97.24(+0.00)0.64(-0.99)99.07(+0.00)94.00(+8.40)99.13(+0.00)98.00(+0.02)-7.49
Krum [8]99.22(+0.00)0.00(-1.00)97.7(+0.00)0.56(-0.99)99.12(+0.00)1.00(-0.90)99.14(+0.00)12.00(-0.88)+3.76
Multi-Krum [8]99.58(+0.00)0.00(-1.00)97.85(+0.00)47.43(-0.50)99.54(+0.00)0.00(-1.00)99.57(+0.00)84.00(-0.13)+2.63
Weak-DP [46]99.37(+0.00)86.00(-0.10)10.00(-0.90)0.00(-1.00)99.41(+0.00)14.00(+0.40)99.39(+0.00)89.00(-0.07)-0.12
Flame [38]99.39(+0.00)0.00(-1.00)97.12(-0.01)17.38(-0.82)99.39(+0.00)0.00(-1.00)99.44(+0.00)13.00(-0.86)+3.67
Ours99.53(+0.00)0.00(-1.00)97.39(+0.00)4.23(-0.96)99.54(+0.00)0.00(-1.00)99.58(+0.00)0.00(-1.00)+3.95
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.363, + 0.47, + 0.407 + ], + "angle": 0, + "content": "Edge-case PGD attack. Figure 4 shows that the BA remains low in all cases. Our method only slightly impacts the MA with \\( a = 0.2 \\)." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.419, + 0.468, + 0.531 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.542, + 0.47, + 0.587 + ], + "angle": 0, + "content": "Figure 4: Accuracy \\((\\%)\\) of our defense under Edge-case PGD attack on different degrees of non-IID, which is indicated by the \\(a\\) parameter of the Dirichlet distribution." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.616, + 0.468, + 0.735 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.746, + 0.47, + 0.777 + ], + "angle": 0, + "content": "Figure 5: BA(\\%) of various defenses under the backdoor attack versus percentage of attackers among all clients." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Impact of Attacker Percentage. We show the BA performance with different ratios of attackers under the backdoor attack in Figure 5, where we compare ours with other methods. As a result of our rigorous experiment settings, it usually selects more than \\( K / 2 \\) adversarial models in each round, so all defenses, especially the clustering-based methods, fail to defend when \\( 50\\% \\) of clients are compromised." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.363, + 0.892, + 0.437 + ], + "angle": 0, + "content": "For EMNIST, BA rises steeply as the simplicity of the task, achieving high accuracy with few parameters injected. Nonetheless, our method performs significantly superior to other methods, and exhibits invariance to the number of attackers encountered." + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.45, + 0.703, + 0.559 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.706, + 0.45, + 0.89, + 0.561 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.573, + 0.892, + 0.602 + ], + "angle": 0, + "content": "Figure 6: Accuracy \\((\\%)\\) of our defense under Edge-case PGD attack versus attack interval." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.623, + 0.892, + 0.743 + ], + "angle": 0, + "content": "Impact of Attack Frequency. The frequency of the attack affects the strength and persistence of the attack. We demonstrate that our defense is invariant to the frequency of attack in Figure 6 where we show that our defense achieves consistently low BA under all attack intervals. Since the other defenses cannot resist the edge-case PGD with the minimum frequency(attack interval of 10), we do not plot their results." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.753, + 0.814, + 0.768 + ], + "angle": 0, + "content": "5.3. Generalization to Different Datasets" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.777, + 0.892, + 0.837 + ], + "angle": 0, + "content": "We experiment on the LOAN and Sentiment140, as shown in Table 2. Our method achieves high MA and low BA on both datasets, proving the adaptivity to different models and tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.848, + 0.654, + 0.864 + ], + "angle": 0, + "content": "5.4. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The above experiments present the remarkable defense ability of our approach. In this section, we conduct an abla" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4659" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.09, + 0.47, + 0.12 + ], + "angle": 0, + "content": "Table 2: Effectiveness of our method against backdoor attack on other types of datasets." + }, + { + "type": "table", + "bbox": [ + 0.104, + 0.131, + 0.444, + 0.202 + ], + "angle": 0, + "content": "
DefenseCINIC10LOANSentiment140
MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓
FedAvg80.0236.2289.0561.3682.5989.17
Ours76.244.5988.52081.675.83
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.219, + 0.468, + 0.25 + ], + "angle": 0, + "content": "Table 3: Effectiveness of the metrics in our approach to defending against the various attacks on CIFAR10." + }, + { + "type": "table", + "bbox": [ + 0.089, + 0.26, + 0.46, + 0.414 + ], + "angle": 0, + "content": "
DefensesModel ReplacementPGDEdge-case PGD
MA/BAMA/BAMA/BA
Man83.86/0.5683.74/25.5685.3/64.80
Eul86.24/0.5685.52/17.7887.12/54.08
Cos84.22/2.2283.84/30.0085.38/66.84
Man+Eul84.09/1.1184.17/28.6384.3/67.35
Man+Cosine85.74/1.6785.16/23.6885.86/6.63
Cosine+Eul86.31/0.5685.44/16.1185.14/63.78
Man+Cosine+Eul86.34/0.5686.44/0.5686.86/3.06
" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.444, + 0.424, + 0.459 + ], + "angle": 0, + "content": "tion study to understand the role of each component." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.461, + 0.47, + 0.718 + ], + "angle": 0, + "content": "Multi-metrics Identifies the Stealthiest Attacks. We first conduct an ablation study on the multi-metrics, as shown in Table 3. We observe the following: 1. All three metrics perform poorly individually. 2. Manhattan distance improves the defense ability when combined with the other metrics. 3. Cosine similarity combined with Manhattan distance provides the best defense against the Edge-case PGD. Given the above observations, we conclude that multi-metrics adaptively defends against universal backdoors. The introduced Manhattan metric contributes to the defense against the stealthiest attack (e.g., Edge-case PGD). To further demonstrate the claim that a single metric cannot identify malicious gradients of diverse characteristics, we show the dominance of each metric under different attacks. We take the metric as the dominant one with the most considerable contribution to this round's scoring and plot their frequency in Figure 7." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Firstly, we show that Manhattan distance contributes to the defense of PGD and Edge-case PGD, complementing the Cosine similarity justifying the above observations 2 and 3. We also notice that Euclidean is never dominant under PGD and Edge-case PGD, consistent with the analysis that these two attacks bypass \\( L_{2} \\) norm through projection back to \\( L_{2} \\) norm ball. We also notice that Manhattan distance plays no role under the model replacement attack, consistent with the above experiment that Manhattan does not affect the final BA. It is because model replacement attack scales the gradient of the malicious client, making it susceptible to Cosine and Euclidean distances. Finally, we" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.138 + ], + "angle": 0, + "content": "conclude that better defense can be achieved if multiple instead of single metrics are utilized since different metrics dominantly detect different malicious gradients." + }, + { + "type": "image", + "bbox": [ + 0.538, + 0.148, + 0.856, + 0.271 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.283, + 0.892, + 0.314 + ], + "angle": 0, + "content": "Figure 7: Frequency of dominance of each metric under different attacks on CIFAR10." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.328, + 0.892, + 0.495 + ], + "angle": 0, + "content": "Dynamic Weighting through Whitening Process Adaptively Adjust the Scoring. We illustrate the effectiveness of our whitening process discussed in Section 3.3 in Table 4 by comparing it with the standard max normalization. BA increases by a large margin if only max normalization is applied, which illustrates that the whitening process plays an essential role in identifying the malicious under non-IID distributions. Moreover, we notice the MA increases as we apply the whitening process, which shows that it can flexibly identify the benign but different gradients (due to non-IID) and the true malicious ones." + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.505, + 0.892, + 0.536 + ], + "angle": 0, + "content": "Table 4: Effectiveness of different weighting methods on defense against various attacks on CIFAR10." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.547, + 0.899, + 0.618 + ], + "angle": 0, + "content": "
WeightingModel ReplacementPGDEdge-case PGD
MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓
Max Norm83.860.5683.7425.5684.0862.24
Whitening86.340.5686.440.5686.863.06
" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.642, + 0.619, + 0.658 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.668, + 0.892, + 0.819 + ], + "angle": 0, + "content": "Existing defense methods fail to handle backdoor attacks with malicious updates similar to benign ones, especially when benign clients possess data of non-independent and iden tical distribution. In this paper, we propose a novel adaptive multi-metrics defense method by leveraging multiple metrics with dynamic weighting to defend against backdoor attacks in FL, withstanding a wide range of stealthy and elaborate attacks. We conduct exhaustive experiments to evaluate our approach proving its effectiveness over a wide range of attack settings." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.831, + 0.667, + 0.848 + ], + "angle": 0, + "content": "Acknowledgements" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.9 + ], + "angle": 0, + "content": "This work is supported by the Key-Area Research and Development Program of Guangdong Province under Grant 2019B010137001." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "4660" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Charu C Aggarwal, Alexander Hinneburg, and Daniel A Keim. On the surprising behavior of distance metrics in high dimensional space. 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In Proceedings of the IEEE/CVF international conference on computer vision, pages 4912-4921, 2021." + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.894, + 0.842 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.956 + ], + "angle": 0, + "content": "4662" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-Metrics Adaptively Identifies Backdoors in Federated Learning/e9dae36d-9444-4c52-bedf-bba383c1ec78_origin.pdf b/2023/Multi-Metrics Adaptively Identifies Backdoors in Federated Learning/e9dae36d-9444-4c52-bedf-bba383c1ec78_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..e60d5ce65aa8edf080ddd33335ebddaa7cee84ef --- /dev/null +++ b/2023/Multi-Metrics Adaptively Identifies Backdoors in Federated Learning/e9dae36d-9444-4c52-bedf-bba383c1ec78_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:e20ff5915367c43e060d8fa93b4ef227e66b319a92f1be47a81555079b6a30b4 +size 2075697 diff --git a/2023/Multi-Metrics Adaptively Identifies Backdoors in Federated Learning/full.md b/2023/Multi-Metrics Adaptively Identifies Backdoors in Federated Learning/full.md new file mode 100644 index 0000000000000000000000000000000000000000..5f85743cb438f2016049705631f0dccac4627be2 --- /dev/null +++ b/2023/Multi-Metrics Adaptively Identifies Backdoors in Federated Learning/full.md @@ -0,0 +1,405 @@ +# Multi-metrics adaptively identifies backdoors in Federated learning + +Siquan Huang + +cssiquanhuang@mail.scut.edu.cn + +Yijiang Li2 + +yli556@jhu.edu + +Chong Chen + +cschenchong@mail.scut.edu.cn + +Leyu Shi + +csshileyu@mail.scut.edu.cn + +Ying Gao $^{1*}$ + +gaoying@scut.edu.cn + +$^{1}$ School of Computer Science and Engineering, South China University of Technology $^{2}$ Johns Hopkins University + +# Abstract + +The decentralized and privacy-preserving nature of federated learning (FL) makes it vulnerable to backdoor attacks aiming to manipulate the behavior of the resulting model on specific adversary-chosen inputs. However, most existing defenses based on statistical differences take effect only against specific attacks, especially when the malicious gradients are similar to benign ones or the data are highly non-independent and identically distributed (non-IID). In this paper, we revisit the distance-based defense methods and discover that i) Euclidean distance becomes meaningless in high dimensions and ii) malicious gradients with diverse characteristics cannot be identified by a single metric. To this end, we present a simple yet effective defense strategy with multi-metrics and dynamic weighting to identify backdoors adaptively. Furthermore, our novel defense has no reliance on predefined assumptions over attack settings or data distributions and little impact on benign performance. To evaluate the effectiveness of our approach, we conduct comprehensive experiments on different datasets under various attack settings, where our method achieves the best defensive performance. For instance, we achieve the lowest backdoor accuracy of $3.06\%$ under the most difficult Edge-case PGD, showing significant superiority over previous defenses. The experiments also demonstrate that our method can be well-adapted to a wide range of non-IID degrees without sacrificing the benign performance. + +# 1. Introduction + +Federated learning (FL) [26, 35] is a distributed machine learning paradigm that enables multiple participants to train a quality model collaboratively without exchanging their local data. During each round of training, the central server + +distributes the global model to a subset of clients. Each client updates the model with the local data and submits the parameters to the server for aggregation. By training an efficient and quality model in a decentralized manner without sacrificing the privacy of participants, FL alleviates the possible conflict between technological developments and regulations for data privacy protection(e.g., General Data Protection Regulation). FL has already been applied and achieved success in multiple fields, such as image processing [32], word prediction [36], medical imaging [30], and edge computing [56, 51]. + +However, FL is vulnerable to backdoors manipulating the model towards the targeted behavior on specific adversary-chosen inputs [24, 4, 6, 47, 50, 11, 33, 39, 19, 31]. The backdoor attack is more difficult to be detected compared with the untargeted poisoning attacks [6, 7, 33, 11, 19] since it does not affect the regular function of the model and its gradient is more similar to benign ones [47, 38]. Multiple defenses have been proposed to improve the robustness of FL, such as the scoring-based methods [17, 8, 53, 41, 10, 55, 16, 29, 2, 20], which leverage a particular metric to distinguish malicious gradients from the benign ones. Despite its effectiveness against some backdoors, researchers discovered that well-designed attacks (termed stealthy backdoors) whose gradients are indistinguishable from benign ones (through scaling [4, 47] or trigger split [50]) could easily bypass these defenses. Differential privacy (DP) -based method [46, 40, 38, 49] builds upon the observation that the DP method [14], traditionally used against DP attacks, is also effective against backdoors. By adding Gaussian noise to the global model, these methods can dilute the impact of potentially poisoned model updates. Surprisingly, DP-based methods show great ability in resisting stealthy backdoors (e.g., Edge-case PGD [47]). Despite its ability to resist the stealthy backdoors, the noises added by the DP significantly decrease the overall performance and the convergence speed. In comparison, the distance-based method less + +impacts the global model by aggregating only the benign gradients. Consequently, a natural question arises: can we defend the stealthy backdoors without sacrificing the performance of the FL model? To accomplish this, we turn to the distance-based methods that don't sacrifice the benign performance and promote the research question: how can we successfully leverage distance metrics to discriminate hostile updates from benign ones? + +To this end, we revisit the distance-based defense and discover two limitations: 1. Euclidean distance (i.e., $L_{2}$ distance) suffers from the curse of dimensionality. Parameters of Neural Networks (NNs) can be viewed as high-dimensional vectors, and Euclidean distance generally fails to discriminate between malicious and benign gradients in high-dimensional space. 2. Single metric takes effect only against particular attacks with detailed assumptions regarding the malicious gradients. For instance, cosine distance detects malicious gradients with sizeable angular deviations while euclidean distance detects malicious gradients with a large $L_{2}$ norm scaled by the attacker to impact the global models. Moreover, backdoor attacks are conducted with different data and scenarios, resulting in malicious gradients with various characteristics that a single metric cannot handle (i.e., both gradients with a large norm and gradients with sizeable angular deviations exist in one round of aggregation). What's worse is that the defender has no knowledge regarding the attacker and the underlying data distributions due to privacy requirements by FL, which makes detecting with a single metric even more difficult. + +To address the above two problems, we first introduce the Manhattan distance, which we theoretically prove more meaningful in high dimensional space than Euclidean distance. Empirically, with the Manhattan distance, our proposed distance-based defense shows remarkable performance against the stealthy backdoors. To cope with gradients with various properties, we leverage multiple metrics cooperatively to identify the malicious gradients. We demonstrate in Section 5.4 and Figure 7 that malicious gradients of some characteristics are better identified by specific metrics, which justify our motivation. To handle the different attacks and environments, we further propose to apply a whitening transformation and generate dynamic weights to handle the non-IID distribution of participants and different scales brought by the different distances. Finally, we compute the score for each submitted gradient and aggregate only the benign ones based on the scoring. Extensive experiments illustrate that our defense maintains a high model performance and robustness simultaneously, which has never been achieved before. At a high level, we summarize the main contributions of this paper as follows: + +- We present a novel defense with multi-metrics to adaptively identify backdoors, which is applicable in a generic adversary model without predefined assumption. + +tions over the attack strategy or data distribution. + +- We show that by introducing the Manhattan distance, our defense alleviates the "meaningfulness" problem of Euclidean distance in high dimensions. By utilizing multiple metrics with dynamic weighting, our defense can resist backdoor attacks under a wide range of attack settings and data distributions. +- We empirically evaluate our method on various datasets and different attack settings. By showing that our defense maintains both high robustness and benign performance under the stealthy backdoors that previously have not been successfully defended, we demonstrate the effectiveness of our approach. + +# 2. Related work + +Backdoor Attacks on Federated Learning. FL enables multiple clients collaboratively train a model without local data exchange. In an FL system, clients update the local model with private data and submit the parameters to the server for aggregation. Given a total of $N$ participants, each with $n^{(i)}$ samples. In each round $t$ , the server randomly selects $K$ clients to participate. FedAvg [35] is a widely-adopted FL algorithm, which can be formulated as: + +$$ +\boldsymbol {w} _ {t} = \boldsymbol {w} _ {t - 1} + \eta \cdot \frac {\sum_ {i = 1} ^ {K} n ^ {(i)} \Delta w _ {t} ^ {(i)}}{\sum_ {i = 1} ^ {K} n ^ {(i)}} \tag {1} +$$ + +where $w_{t}$ is the global model parameters at round $t$ , $\Delta w_{t}^{(i)}$ is the local model updates from the client $i$ in round $t$ , and $\eta$ is the global model learning rate. + +Empirical studies from Bagdasaryan et al. [4] demonstrate that FedAvg [35] is vulnerable to backdoor attacks since FL has no authority over local data and the training process due to privacy concerns. The model replacement attack [4] successfully injects a backdoor into the global model by the single-shot attack. Some well-designed attacks strategically target the weakness of the defenses, such as the PGD attack [47] scaling and projecting the gradients, or the DBA attack [50] splitting the triggers before uploading them. Moreover, the Edge-case PGD attack [47] modifies the poisoned data and model. Undoubtedly, these attacks present a tremendous challenge to the security of the FL system. + +Defense Against the Backdoor Attack. Various methods to defend against backdoor attacks improve the robustness and security of FL. In general, we can divide these methods into two categories. The first type of defense strategies tries to distinguish malicious gradients from benign ones by classifying or scoring with the assumption that benign and malicious gradients show distinct differences in the vector space [17, 8, 53, 41, 10, 55, 16, 29, 2, 20]. Krum + +and Multi-Krum [8] select the gradient with the smallest Euclidean norm from the others to aggregate and update the global model at each round. Foolsgold [17] assumes that the gradients of attackers are always consistent and distinguishes them by the Cosine similarity between historical updates. Trimmed Mean and Median [53] remove a fraction of the gradients with maximum and minimum values and then take the median value on each dimension of the remaining gradients as the parameters of the global model. RFA [41] leverages the geometric median of the gradients to keep the aggregated model close to the benign model and away from the backdoor one. The strength lies in that, if successful, the gradients of attackers are excluded from the aggregation process, which solves the core and fundamental problem of defending the attack. + +However, the above methods take effect only under particular attacks since they make detailed assumptions about the attack or the data distributions. Foolsgold [17] assumes the gradients of attackers are consistent while benign gradients from Non-IID data differ. Krum [8] assumes that the data of benign clients is similar under IID settings and excludes abnormal malicious ones. These predefined assumptions limit the applicability of these defenses under various attacks and data distributions and can be easily bypassed by elaborate attacks. For example, PGD [47] breaks any Euclidean-based defense (e.g. Krum and Multi-Krum) by scaling the norm to a small value. Other methods, such as FLTrust [10], use a root dataset and aggregate only those gradients with large cosine similarities with the root dataset. FedInv [55] inverts the gradients into dummy datasets and then identifies the malicious gradient by comparing these dummy datasets. These methods are limited as well. FLTrust cannot defend against backdoors crafted on edge cases (e.g. Edge-case PGD) since they appear less often and are probably not in the root dataset. Inverting the gradients into dummy datasets violates the privacy requirement of FL. Essentially, this method can be characterized as another type of attack [3, 21]. + +The other category of defenses [46, 40, 38, 49] builds upon the observation that the differential privacy (DP) method [14], traditionally used against DP attacks is also effective against backdoor attacks. Earlier studies [4] have demonstrated that clipping and adding noise (typically used in DP) can resist backdoor attacks without any specific assumptions over the data distribution. Following these findings, Weak-DP [46] clips the norm and adds the Gaussian noise to the global model for mitigating the backdoors. RLR [40] and Flame [38] apply the clustering methods before the DP process. However, the noise added significantly decreases the performance and the convergence speed of the FL system. In a nutshell, using DP sacrifices regular functionality for robustness. Despite its deficiency, the DP-based method has been the only method that has taken effect + +against stealthy backdoors [38]. + +# 3. Methodology + +We first provide the threat model in Section 3.1 and then detail our design of the proposed defense method. Our goal is to design an efficient defense with the following properties: (1) Effectiveness: To prevent the adversary from achieving its hostile purpose, we aim to design a defense that identifies as many malicious updates as possible to eliminate its impact on the global model. (2) Performance: Benign performance of the global model must be preserved to maintain its utility. (3) Independence: The defense must be applicable to generic adversary models under different data distributions and attack strategies. Our defense consists of three major components: defining and calculating the gradient feature, computing the dynamic weight and score for each update, and aggregating the benign gradients with the score computed, as shown in Figure 1 and Algorithm 1. + +# 3.1. Threat Model + +Adversarial goals. Adversary aims to alter the behavior of the model on some specific examples with no negative impact on the benign performance. We consider the adversary effective if this is met. In addition, the adversary will make their attack as covert as possible, e.g., by scaling down. Formally, adversary $\mathcal{A}$ manipulates the global model $G$ to the poisoned model $G'$ . For any inputs $x$ , we have the outputs below: + +$$ +G ^ {\prime} (x) = \left\{ \begin{array}{c c} l ^ {\prime} \neq G (x) & \forall x \in D _ {\mathcal {A}} \\ G (x) & \forall x \notin D _ {\mathcal {A}} \end{array} \right. \tag {2} +$$ + +where $D_{\mathcal{A}}$ denotes the poisoned dataset belonging to adversary $\mathcal{A}$ , and $l'$ denotes the specific label modified by adversary $\mathcal{A}$ of the input $x$ . + +Adversarial capabilities. This paper assumes the white-box setting with full knowledge of aggregation operations, including potential defenses. Also, adversaries can freely alter the parameters in the local training, ensure participation in each round and compromise less than $50\%$ of total FL clients. However, the adversary cannot control any process or parameter executed in the aggregator. + +# 3.2. Feature of gradient + +The essential logic of distance-based defense involves defining some indicative metric that can well discriminate the malicious gradients from the benign ones and removes the hostile updates from the aggregation. Consequently, the core problem becomes how to define a metric that identifies the characteristics of hostile gradients. For instance, NDC [46] utilizes the length of the gradient (i.e. Euclidean distance) while FoolGold [17] leverages Cosine similarity to measure the difference between updates. + +![](images/e47d46bf55ca67777b31957dd0576c641c4f104f497705075925d48161925664.jpg) +Figure 1: The overview of our defense process. Step 1 and step 2 are our core contributions. + +![](images/1eba84d9dc8bc95963dc06bec9f7543ac5b9dbe64a3b40c4143614aab1a834fd.jpg) +Figure 2: Demonstration of feature of gradient on two dimensional space. $\pmb{w}_0$ is initial global model $\pmb{w}_0$ and $\pmb{w}_i$ is the local model of the $i$ -th client. $\pmb{w}_i - \pmb{w}_0$ is the gradient and we define the feature of gradient as $(|x + y|, l, \theta)$ . + +Manhattan Distance. However, the Euclidean distance suffers from the so-called "curse of dimensionality" [48], which renders distance metrics less sensitive in high dimensional space, especially in the case of Euclidean distance. Theorem 1 uses $\frac{D\max_d^k - D\min_d^k}{D\min_d^k}$ to indicate the "meaningfulness" of a distance referred as the Relative Contrast. It demonstrates that the distance metric is meaningless in high-dimensional space because as dimensionality increases, the distance between the nearest and the furthest neighbor approximates to be the same. + +# Theorem 1 (Beyer et. al.[5] The curse of dimensionality) + +$$ +I f \lim _ {d \rightarrow \infty} v a r \left(\frac {\| X _ {d} \| _ {k}}{E [ \| X _ {d} \| _ {k} ]}\right) = 0, t h e n +$$ + +$$ +\frac {D m a x _ {d} ^ {k} - D m i n _ {d} ^ {k}}{D \min _ {d} ^ {k}} \rightarrow_ {p} 0, +$$ + +where $d$ denotes the dimensionality of the data space, $E[X]$ and var $[X]$ denotes the expected value and variance of a + +random variable $X$ , $Dmax_{d}^{k}$ and $Dmin_{d}^{k}$ means the farthest/nearest distance of the $N$ points to the origin using the distance metric $L_{k}$ . + +To find out which distance metric is more meaningful in high-dimensional space, we size up the relation between the dimension $d$ and the distance $L_{k}$ . We have Lemma 1, which shows that $Dmax_{d}^{k} - Dmin_{d}^{k}$ increases at the ratio of $d^{(1 / k) - (1 / 2)}$ . + +Lemma 1 (Hinneburg et.al.[22]) Let $\mathcal{F}$ be an arbitrary distribution of two points and the distance function $\| \cdot \|$ be an $L_{k}$ metric. Then, + +$$ +\lim _ {d \rightarrow \infty} E \left[ \frac {D m a x _ {d} ^ {k} - D m i n _ {d} ^ {k}}{d ^ {(1 / k) - (1 / 2)}} \right] = C _ {k}, +$$ + +where $C_k$ is some constant dependent on $k$ . + +Subsequently, we use the value of $Dmax_{d}^{k} - Dmin_{d}^{k}$ as a criterion to evaluate the ability of a particular metric to discriminate different vectors in high dimensional space. + +Proposition 1 Let $M_d = Dmax_d^1 - Dmin_d^1$ reflect the discriminating ability of Manhattan distance and $U_d = Dmax_d^2 - Dmin_d^2$ reflect the discriminating ability of Euclidean distance. Then, + +$$ +\lim _ {d \rightarrow \infty} E \left[ \frac {M _ {d}}{U _ {d} \cdot d ^ {\frac {1}{2}}} \right] = C ^ {\prime}. +$$ + +where $C'$ is a constant. Proof see in Appendix C. + +Proposition 1 shows that $M_d$ and $U_d \cdot d^{\frac{1}{2}}$ are infinite of the same order. Since $d^{\frac{1}{2}}$ is also an infinite value, $M_d$ towers above $U_d$ , suggesting that Manhattan can discriminate more than the Euclidean distance in high-dimension space. Given + +this, we conclude that the Manhattan distance is better than the Euclidean metric, withstanding the curse of dimensionality, which chimes in with the previous experiment [1, 37]. The parameters of neural networks can be viewed as a typical high-dimensional space, especially when the number of parameters increases as the trend in deep learning applications [9, 44, 42, 15, 34, 54, 43]. In light of this and Theorem 1, we argue that Euclidean distance is insufficient to discriminate between malicious and benign gradients. With Proposition 1, we introduce the Manhattan distance metric to describe the characteristics of gradients which captures the difference in high dimensional space better. + +Multiple Metrics as Feature of Gradient. Another problem that we identify as discussed in Section 1 is that current methods conduct defense on a single metric basis. With only one metric, a sophisticated attacker could effortlessly bypass them with a well-designed gradient. For instance, PGD attack [47] manage to break the defense based on Euclidean distances by clipping the gradient norm to a small value. Moreover, attackers conduct attacks under different environments and data distributions, leading to malicious gradients with diverse characteristics that a single metric cannot handle. To this end, we propose multiple metrics to cooperatively identify the malicious gradient by defining the feature of gradient as the angle by the Cosine similarity, length by the Euclidean distances, and its Manhattan norm by the Manhattan distance, namely, $\pmb{x} = (x_{Man}, x_{Eul}, x_{Cosine})$ . Here, $x_{Man}$ denotes the Manhattan distance, $x_{Eul}$ denotes the Euclidean distance and $x_{Cosine}$ denotes the Cosine similarity. Figure 2 provides a schematic diagram of the gradient feature. We compute the gradient feature $x_{Man}$ , $x_{Eul}$ , and $x_{Cosine}$ of the $i$ -th client of each round as follows: $x_{Man}^{(i)} = \| \pmb{w}_i - \pmb{w}_0\|_1$ , $x_{Eul}^{(i)} = \| \pmb{w}_i - \pmb{w}_0\|_2$ , $x_{Cosine}^{(i)} = \frac{\langle\pmb{w}_0\pmb{w}_i\rangle}{\|\pmb{w}_0\| \cdot \|\pmb{w}_i\|}$ , where $\pmb{w}_0$ denotes the global model before federated training and $\pmb{w}_i$ denotes the $i$ -th client's local model after training, $\| \cdot \|_1$ means the $L_1$ norm of a vector, $\| \cdot \|_2$ means the $L_2$ norm of a vector, $\langle \cdot, \cdot \rangle$ and represents inner product. After defining the feature of gradient, we utilize it for malicious identification. The goal is to identify the outlier among the gradients. We use the sum of the distance between each gradient as the indicator. Formally, we define it as Equation 3. + +$$ +\boldsymbol {x} ^ {\prime (i)} = \left(\sum_ {j, j \neq i} ^ {K} \left| x _ {M a n} ^ {(i)} - x _ {M a n} ^ {(j)} \right|, \right. \tag {3} +$$ + +$$ +\sum_ {j, j \neq i} ^ {K} | x _ {E u l} ^ {(i)} - x _ {E u l} ^ {(j)} |, \sum_ {j, j \neq i} ^ {K} | x _ {C o s i n e} ^ {(i)} - x _ {C o s i n e} ^ {(j)} |), +$$ + +# 3.3. Dynamic Weighting Through Whitening + +After defining the feature of gradient and indicator, we now provide an approach to score each gradient. Two fac + +tors are taken into account when considering an efficient way to turn the indicator into a unified score that works under various data distributions and attacks. + +- Different scales of the three distance metrics are the first obstacle before utilizing these metrics collaboratively. Since each metric is correlated, a novel regularization is required instead of the usual normalization by the maximum value. +- Different data distributions (e.g. different degrees of non-IID) render the gradients of both malicious and benign clients different. Thus, dynamic weighting is required to cope with various environments and attacks to achieve a universal defense. + +Considering the above factors, we propose first to project the value of the metrics in the feature of gradient to its corresponding principal axis by applying a whitening process: + +$$ +\delta^ {(i)} = \sqrt {\boldsymbol {x} ^ {\prime^ {(i) \top}} \boldsymbol {\Sigma} ^ {- 1} \boldsymbol {x} ^ {\prime^ {(i)}}}. \tag {4} +$$ + +where $\boldsymbol{\Sigma}$ is the covariance matrix of $\pmb{X} = [x^{\prime(1)}x^{\prime(2)}\dots x^{\prime(K)}]^{\top}$ . Since we need to calculate the inverse of the covariance matrix $\boldsymbol{\Sigma}$ , the number of samples must be larger than the number of features, i.e., $K > 3$ . Please notice that the inverse of the covariance matrix is calculated based on the selected gradients, which will change the weights of the features dynamically depending on the feature distribution, hence "dynamic weighting". With such a dynamic weight, our method can better adapt to different environments and resist various attacks. + +# 3.4. Aggregation of Benign Gradients + +After obtaining the score of each gradient, we aggregate the gradients with high scoring. A higher score indicates that the gradient is less divergent among all. After the selection of "benign" gradients, we can aggregate them with any existing aggregation methods (e.g. Averaging of gradients). We follow [35] and perform standard FedAvg on the "benign" gradients. A detailed analysis of aggregation of benign gradients is in Appendix A.1. + +# 4. Experiment Setup + +We will first introduce the settings and then the objective of our experiments. + +Datasets. We conduct our experiments on multiple datasets, including two visual datasets, CIFAR-10 [27] and EMNIST [12]. We also experiment on other datasets to prove the generalization ability, including CINIC10 [13], LOAN [25] and Sentiment140 [18] as follows: + +- CIFAR-10 dataset [27] is a vision classification dataset containing 50,000 training samples and + +# Algorithm 1 Our aggregation algorithm + +Input: Total number of clients in each round $K$ , models of clients $\boldsymbol{w}^{(1)}, \boldsymbol{w}^{(2)}, \dots, \boldsymbol{w}^{(K)}$ , last global model $\boldsymbol{w}_0$ , fraction selected to aggregation $p$ , global learning rate $\eta$ , size of the $i - th$ client dataset $n^{(i)}$ + +# Output: Global model $w^{*}$ + +1: for $i\in \{1,2,\dots,K\}$ do compute the gradients features + +2: $x_{Man}^{(i)}\gets \left\| \pmb{w}_0 - \pmb{w}_i\right\| _1$ + +3: $x_{Eul}^{(i)}\gets \left\| \pmb {w}_0 - \pmb {w}_i\right\| _2$ + +4: $x_{\text{Cos}}^{(i)} \gets \frac{\langle \boldsymbol{w}_0, \boldsymbol{w}_i \rangle}{\|\boldsymbol{w}_0\| \cdot \|\boldsymbol{w}_i\|}$ + +5: $\pmb{x}^{(i)}\gets (x_{Man}^{(i)},x_{Eul}^{(i)},x_{Cos}^{(i)})$ + +# 6: end for + +7: for $i,j\in \{1,2,\dots,K\}$ do compute the sum of the distance between each gradient + +8: $x^{\prime}_{Man}^{(i)}\gets \sum_{j,j\neq i}^{K}|x_{Man}^{(i)} - x_{Man}^{(j)}|$ + +9: $x^{\prime}_{Eul}^{(i)}\gets \sum_{j,j\neq i}^{K}|x^{(i)}_{Eul} - x^{(j)}_{Eul}|$ + +10: $x^{\prime}_{COS}^{(i)}\gets \sum_{j,j\neq i}^{K}|x^{(i)}_{COS} - x^{(j)}_{COS}|$ + +11: $\pmb{x}^{\prime (i)}\gets (x_{Man}^{\prime (i)},x_{Eul}^{\prime (i)},x_{Cos}^{\prime (i)})$ + +# 12: end for + +13: $X\gets [\pmb{x}^{\prime (1)},\pmb{x}^{\prime (2)},\dots,\pmb{x}^{\prime (K)}]^{\top}$ + +14: $\Sigma \gets$ the Covariance of $X$ compute the adaptive weight matrix in this round + +15: for $i\in \{1,2,\dots,K\}$ do + +16: $\delta^{(i)}\gets \sqrt{\boldsymbol{x}^{\prime(i)\top}\cdot\Sigma^{-1}\cdot\boldsymbol{x}^{\prime(i)}}$ $\triangleright$ dynamically compute the divergence + +# 17: end for + +18: Remove the $K\cdot (1 - p)$ models with the high divergency $\delta^{(i)}$ , remaining models as $\mathbb{B}$ + +19: $\pmb{w}^{*}\gets \pmb{w}_{0} + \eta \cdot \frac{\sum_{i\in\mathbb{B}}n^{(i)}\cdot(\pmb{w}^{(i)} - \pmb{w}_{0})}{\sum_{i\in\mathbb{B}}n^{(i)}}$ + +10,000 testing samples with ten classes. To simulate the FL environment, we set the $a$ of the Dirichlet distribution to be 0.5, representing a non-IID distribution. Smaller $a$ means a larger degree of non-IID. + +- EMNIST dataset [12] is a digit classification dataset consisting of 280,000 real-world handwritten images of digits from 0 to 9. We also set the degree of non-IID to be $a = 0.5$ . +- CINIC10 [13] has a total of 270,000 images, 4.5 times that of CIFAR-10, which is constructed from two different sources: ImageNet and CIFAR-10. We set the non-IID degree as $a = 0.5$ . +- Lending Club Loan dataset (LOAN) [25] contains financial information such as loan information and credit scores for loan status prediction. There are 2,260,668 samples with a total of 9 classes. To simulate a more realistic situation, we divide the data by US states, where each state represents one client. We + +set the non-IID parameter $a = 0.9$ + +- Sentiment140 [18] is a publicly available English Twitter sentiment classification dataset containing 1.6 million tweets, of which 800,000 are for training, and the other 800,000 are for testing. Each tweet in the dataset is labeled with a sentiment polarity (positive, neutral, or negative). + +Models. Different models are used on different datasets to demonstrate the generality of our approach. A 9-layer VGG style network (VGG-9) [45] is trained on the CIFAR10. On the EMNIST, we train LeNet-5 model [28]. We train the LSTM model [23] for Sentiment140 and a network with three fully-connected layers for LOAN. + +Backdoor Attacks. We implement both pixel-pattern and semantic backdoors. To make the attack more challenging, we use the multiple-shot attack instead of the single-shot. The following are the attack methods we use: + +- Model Replacement Attack [4]: Malicious clients generate backdoor gradients during their local training. Attackers scale up their gradients to ensure that the malicious model will replace the global model. Usually, the scaling factor is $N / K$ . +- DBA Attack [50]: DBA decomposes a global trigger pattern into separate local patterns and embeds them into the training sets of different attackers, resulting in a more negligible difference between benign and back-door gradients; +- PGD Attack [47]: To bypass the Euclidean-based defense, PGD Attack projects the model parameter within the ball centered around the global model; +- Edge-case PGD Attack [47]: Attackers have a set of edge-case samples and some benign samples as their poisoned datasets. Edge-case samples are unlikely to exist in the benign training set. Thus, the benign gradients cannot dilute the backdoor. We launch this attack in the form of PGD. The Edge-case PGD attack is so stealthy that most defenses cannot defend against it. + +Evaluation. We leverage the following two metrics for evaluating the effectiveness of our defense: + +- Backdoor Accuracy (BA) indicates whether the attacker succeeds. It shows the accuracy of the model on the backdoor task. The attackers aim to maximize this metric, and the lower the BA, the more efficient the defense. +- Main Task Accuracy (MA) is the accuracy on the main task. The overall objective of all participants in an FL system is to maximize MA. The benign clients maximize the model performance, while the attackers seek to be stealthy and maintain MA. Thus, the defense should not cause a significant drop in MA, which we report to demonstrate that our defense does not affect + +the functionality of the FL system. We report all BA and MA values in percentages. + +Hyperparameters are detailed in Appendix B. + +Objectives of Experiments. Firstly, we aim to illustrate the effectiveness of our proposed defense under different attacks by comparing it with the current and previous state-of-the-art defenses. Secondly, we demonstrate that the performance of our defense is consistent under different scenarios (e.g., different degrees of non-IID $a$ and different attack frequencies). Thirdly, we figure out the reason for our defense works through the ablation study in Section 5.4. + +# 5. Experiment Results + +# 5.1. Robustness against Different Attacks and Comparison with SOTA + +We first demonstrate the robustness of our approach under different attacks and then compare our methods with the state-of-the-art defense methods such as Krum [8], Multi-Krum [8], Foolsgold [17], RFA [41], Weak-DP [46], and Flame [38] in Table 1. All the defenses except RFA and Weak-DP successfully defended against the model replacement attack since RFA and Weak-DP still incorporate some malicious gradient into the global model. Our defense achieves the lowest BA on both datasets $(0.56\%$ and $0.00\%)$ with little impact on the MA. Under the DBA attack, Multi-Krum almost has no effect. Flame and our method also deteriorate because $40\%$ of the participants in each round are malicious, which significantly impacts the method of selecting multiple clients for aggregation. Although Krum and Foolsgold successfully defend against the DBA attack, they also negatively affect the overall performance of the global model. Our defense can reduce the BA to less than $10\%$ without affecting the MA. + +PGD attack is much stealthier than the above two which Krum, RFA, and Multi-Krum fail to detect. Moreover, once they select the wrong gradient for aggregation, the global model is replaced, leading to a worse BA than FedAvg. Ours and Flame achieve the best effect of $0.56\%$ and $0.00\%$ on the two datasets, respectively. Edge-case PGD is the hardest of all since it is both stealthy and effective since it attacks with edge-case samples and projects the gradient back to the $L_{2}$ norm ball. All the previous defenses have limited effect on this attack. Flame reduces the BA to $5.12\%$ . However, Flame suffers from a $6\%$ drop on MA, which is a result of adding noise. In comparison, ours achieves a much lower BA of $3.06\%$ with almost no impact on MA. + +On EMNIST, we also achieve better defense compared to up-to-date methods. Remarkably, we achieve $0.0\%$ BA under both PGD and Edge-case PGD attacks meaning that we defend entirely against these two adversaries. We also achieve similar performance without sacrificing the benign + +performance against model replacement and DBA. To provide an overall comparison with previous methods, we follow [52] and design an improved version of the ranking score for each defense with respect to baseline FedAvg. We use the percentage of improvement over the baseline to score and compute it on MA/BA respectively, formally as $\frac{K_{\mathrm{MA/BA}} - B_{\mathrm{MA/BA}}}{B_{\mathrm{MA/BA}}}$ where $K$ denotes some methods and $B$ denotes baseline. Adding up ( $score_{MA} - score_{BA}$ ) across all attacks produces the ranking score for each defense. As shown in the last column of Table 1, we show that our method obtains the highest ranking score with almost $400\%$ better than the baseline and outperforms the second-best Flame by around 0.5. We detail the ranking score in Appendix D. + +![](images/46cedb1617698bd1140bbf480aa7ed90776f6f567961c9f86d86939eea74ee5e.jpg) +(a) CIFAR10 + +![](images/a07492f9acaf5c214952402ad48a1bc50c92c22b3dc9fabaa4c4c200929f9695.jpg) +(b) EMNIST +Figure 3: MA(%) and BA(%) of various defenses under Edge-case PGD attack. + +![](images/48c103bbf3f219ac435e69e8593c8f423f95bcb8556d50b61a1341da737b82c7.jpg) + +We show the MA and BA along the training process of the seven defenses under the Edge-case PGD attack in Figure 3. Only our method and Flame successfully resist the attack during the entire training process, and Flame also dampens the MA. The disadvantage of our approach is that the convergence speed is slightly slowed down compared to FedAvg, but it is still much better than the compared defenses, e.g., Krum and Foolsgold. + +# 5.2. Impact of Training Environment + +In this section, we demonstrate that our defense is invariant to the different training environments, i.e. degrees of non-IID, and attack frequency. + +Impact of Different Degrees of Non-IID. As mentioned abundantly in Section 3.3, the different data distributions contribute to one of the hardest problems in distance-based defense. Thus, to illustrate the effectiveness of our method, we demonstrate that our defense is invariant to the different degrees of non-IID. The experiment is conducted with the + +Table 1: Robustness of our approach compared to the SOTA defenses for various challenging attacks. + +
DatasetDefenseModel Replacement [4]DBA [50]PGD [47]Edge-case PGD [47]Ranking Score ↑
MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓
CIFAR10FedAvg [35]86.9564.8079.2390.4487.0414.4487.1455.100
RFA [41]86.69(+0.00)25.56(-0.61)79.6(+0.00)57.69(-0.36)87.1(+0.00)52.56(+2.64)86.47(-0.01)65.31(+0.19)-1.86
Foolsgold [17]85.71(-0.01)6.67(-0.90)77.56(-0.02)3.43(-0.96)84.92(-0.02)14.44(+0.00)85.72(-0.02)45.41(-0.18)+1.96
Krum [8]82.17(-0.05)6.11(-0.91)78.18(-0.01)6.01(-0.93)82.32(-0.05)66.67(+3.62)81.23(-0.07)59.18(+0.07)-2.04
Multi-Krum [8]86.55(+0.00)1.67(-0.97)79.33(0.00)91.39(+0.01)86.52(-0.01)17.78(+0.23)87.4(+0.00)60.2(+0.09)+0.63
Weak-DP [46]74.41(-0.14)46.11(-0.29)10.00(-0.87)0.00(-1.00)73.61(-0.15)12.78(-0.11)73.84(-0.15)53.06(-0.04)+0.12
Flame [38]80.58(-0.07)0.56(-0.99)76.78(-0.03)37.24(-0.59)81.24(-0.07)0.56(-0.96)81.41(-0.07)5.12(-0.91)+3.21
Ours86.34(-0.01)0.56(-0.99)79.61(+0.00)9.98(-0.89)86.44(-0.01)0.56(-0.96)86.86(+0.00)3.06(-0.94)+3.77
EMNISTFedAvg [35]99.5496.0097.6894.1399.5510.0099.3796.000
RFA [41]99.57(+0.00)6.00(-0.94)97.87(+0.00)1.39(-0.99)99.32(+0.00)4.00(-0.60)99.29(+0.00)97.00(+0.01)+2.51
Foolsgold [17]96.42(-0.03)98.00(+0.02)97.24(+0.00)0.64(-0.99)99.07(+0.00)94.00(+8.40)99.13(+0.00)98.00(+0.02)-7.49
Krum [8]99.22(+0.00)0.00(-1.00)97.7(+0.00)0.56(-0.99)99.12(+0.00)1.00(-0.90)99.14(+0.00)12.00(-0.88)+3.76
Multi-Krum [8]99.58(+0.00)0.00(-1.00)97.85(+0.00)47.43(-0.50)99.54(+0.00)0.00(-1.00)99.57(+0.00)84.00(-0.13)+2.63
Weak-DP [46]99.37(+0.00)86.00(-0.10)10.00(-0.90)0.00(-1.00)99.41(+0.00)14.00(+0.40)99.39(+0.00)89.00(-0.07)-0.12
Flame [38]99.39(+0.00)0.00(-1.00)97.12(-0.01)17.38(-0.82)99.39(+0.00)0.00(-1.00)99.44(+0.00)13.00(-0.86)+3.67
Ours99.53(+0.00)0.00(-1.00)97.39(+0.00)4.23(-0.96)99.54(+0.00)0.00(-1.00)99.58(+0.00)0.00(-1.00)+3.95
+ +Edge-case PGD attack. Figure 4 shows that the BA remains low in all cases. Our method only slightly impacts the MA with $a = 0.2$ . + +![](images/de1f4497a763e73d6cf338cd7350965252d2a4ff1907c6eedfc261f10d60c6c5.jpg) +Figure 4: Accuracy $(\%)$ of our defense under Edge-case PGD attack on different degrees of non-IID, which is indicated by the $a$ parameter of the Dirichlet distribution. + +![](images/0f41c99d0f335621bd4481299e749000ccbb20a7480180f198bf7affdc6fe0b0.jpg) +Figure 5: BA(\%) of various defenses under the backdoor attack versus percentage of attackers among all clients. + +Impact of Attacker Percentage. We show the BA performance with different ratios of attackers under the backdoor attack in Figure 5, where we compare ours with other methods. As a result of our rigorous experiment settings, it usually selects more than $K / 2$ adversarial models in each round, so all defenses, especially the clustering-based methods, fail to defend when $50\%$ of clients are compromised. + +For EMNIST, BA rises steeply as the simplicity of the task, achieving high accuracy with few parameters injected. Nonetheless, our method performs significantly superior to other methods, and exhibits invariance to the number of attackers encountered. + +![](images/0d459e02e6dbeb0c0f0521ee463bf51c6e7148b6a0f593bc4e09a9568b76d4ce.jpg) +Figure 6: Accuracy $(\%)$ of our defense under Edge-case PGD attack versus attack interval. + +![](images/a2d512eb6d236303b9c3c20c8dcc7719b6681b0c051003bd08751e5516e5ed88.jpg) + +Impact of Attack Frequency. The frequency of the attack affects the strength and persistence of the attack. We demonstrate that our defense is invariant to the frequency of attack in Figure 6 where we show that our defense achieves consistently low BA under all attack intervals. Since the other defenses cannot resist the edge-case PGD with the minimum frequency(attack interval of 10), we do not plot their results. + +# 5.3. Generalization to Different Datasets + +We experiment on the LOAN and Sentiment140, as shown in Table 2. Our method achieves high MA and low BA on both datasets, proving the adaptivity to different models and tasks. + +# 5.4. Ablation Study + +The above experiments present the remarkable defense ability of our approach. In this section, we conduct an abla + +Table 2: Effectiveness of our method against backdoor attack on other types of datasets. + +
DefenseCINIC10LOANSentiment140
MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓
FedAvg80.0236.2289.0561.3682.5989.17
Ours76.244.5988.52081.675.83
+ +Table 3: Effectiveness of the metrics in our approach to defending against the various attacks on CIFAR10. + +
DefensesModel ReplacementPGDEdge-case PGD
MA/BAMA/BAMA/BA
Man83.86/0.5683.74/25.5685.3/64.80
Eul86.24/0.5685.52/17.7887.12/54.08
Cos84.22/2.2283.84/30.0085.38/66.84
Man+Eul84.09/1.1184.17/28.6384.3/67.35
Man+Cosine85.74/1.6785.16/23.6885.86/6.63
Cosine+Eul86.31/0.5685.44/16.1185.14/63.78
Man+Cosine+Eul86.34/0.5686.44/0.5686.86/3.06
+ +tion study to understand the role of each component. + +Multi-metrics Identifies the Stealthiest Attacks. We first conduct an ablation study on the multi-metrics, as shown in Table 3. We observe the following: 1. All three metrics perform poorly individually. 2. Manhattan distance improves the defense ability when combined with the other metrics. 3. Cosine similarity combined with Manhattan distance provides the best defense against the Edge-case PGD. Given the above observations, we conclude that multi-metrics adaptively defends against universal backdoors. The introduced Manhattan metric contributes to the defense against the stealthiest attack (e.g., Edge-case PGD). To further demonstrate the claim that a single metric cannot identify malicious gradients of diverse characteristics, we show the dominance of each metric under different attacks. We take the metric as the dominant one with the most considerable contribution to this round's scoring and plot their frequency in Figure 7. + +Firstly, we show that Manhattan distance contributes to the defense of PGD and Edge-case PGD, complementing the Cosine similarity justifying the above observations 2 and 3. We also notice that Euclidean is never dominant under PGD and Edge-case PGD, consistent with the analysis that these two attacks bypass $L_{2}$ norm through projection back to $L_{2}$ norm ball. We also notice that Manhattan distance plays no role under the model replacement attack, consistent with the above experiment that Manhattan does not affect the final BA. It is because model replacement attack scales the gradient of the malicious client, making it susceptible to Cosine and Euclidean distances. Finally, we + +conclude that better defense can be achieved if multiple instead of single metrics are utilized since different metrics dominantly detect different malicious gradients. + +![](images/afce9621a40eaaf1db6b86a89673f2c95d51a9af0c7a2048a225c0d9213499c4.jpg) +Figure 7: Frequency of dominance of each metric under different attacks on CIFAR10. + +Dynamic Weighting through Whitening Process Adaptively Adjust the Scoring. We illustrate the effectiveness of our whitening process discussed in Section 3.3 in Table 4 by comparing it with the standard max normalization. BA increases by a large margin if only max normalization is applied, which illustrates that the whitening process plays an essential role in identifying the malicious under non-IID distributions. Moreover, we notice the MA increases as we apply the whitening process, which shows that it can flexibly identify the benign but different gradients (due to non-IID) and the true malicious ones. + +Table 4: Effectiveness of different weighting methods on defense against various attacks on CIFAR10. + +
WeightingModel ReplacementPGDEdge-case PGD
MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓
Max Norm83.860.5683.7425.5684.0862.24
Whitening86.340.5686.440.5686.863.06
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However, most existing defenses based on statistical differences take effect only against specific attacks, especially when the malicious gradients are similar to benign ones or the data are highly non-independent and identically distributed (non-IID). In this paper, we revisit the distance-based defense methods and discover that i) Euclidean distance becomes meaningless in high dimensions and ii) malicious gradients with diverse characteristics cannot be identified by a single metric. To this end, we present a simple yet effective defense strategy with multi-metrics and dynamic weighting to identify backdoors adaptively. Furthermore, our novel defense has no reliance on predefined assumptions over attack settings or data distributions and little impact on benign performance. To evaluate the effectiveness of our approach, we conduct comprehensive experiments on different datasets under various attack settings, where our method achieves the best defensive performance. For instance, we achieve the lowest backdoor accuracy of " + }, + { + "bbox": [ + 46, + 292, + 290, + 605 + ], + "type": "inline_equation", + "content": "3.06\\%" + }, + { + "bbox": [ + 46, + 292, + 290, + 605 + ], + "type": "text", + "content": " under the most difficult Edge-case PGD, showing significant superiority over previous defenses. The experiments also demonstrate that our method can be well-adapted to a wide range of non-IID degrees without sacrificing the benign performance." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 47, + 626, + 128, + 639 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 626, + 128, + 639 + ], + "spans": [ + { + "bbox": [ + 47, + 626, + 128, + 639 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 46, + 646, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 646, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 646, + 287, + 696 + ], + "type": "text", + "content": "Federated learning (FL) [26, 35] is a distributed machine learning paradigm that enables multiple participants to train a quality model collaboratively without exchanging their local data. During each round of training, the central server" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 268, + 547, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 268, + 547, + 399 + ], + "spans": [ + { + "bbox": [ + 304, + 268, + 547, + 399 + ], + "type": "text", + "content": "distributes the global model to a subset of clients. Each client updates the model with the local data and submits the parameters to the server for aggregation. By training an efficient and quality model in a decentralized manner without sacrificing the privacy of participants, FL alleviates the possible conflict between technological developments and regulations for data privacy protection(e.g., General Data Protection Regulation). FL has already been applied and achieved success in multiple fields, such as image processing [32], word prediction [36], medical imaging [30], and edge computing [56, 51]." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 402, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 402, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 402, + 547, + 715 + ], + "type": "text", + "content": "However, FL is vulnerable to backdoors manipulating the model towards the targeted behavior on specific adversary-chosen inputs [24, 4, 6, 47, 50, 11, 33, 39, 19, 31]. The backdoor attack is more difficult to be detected compared with the untargeted poisoning attacks [6, 7, 33, 11, 19] since it does not affect the regular function of the model and its gradient is more similar to benign ones [47, 38]. Multiple defenses have been proposed to improve the robustness of FL, such as the scoring-based methods [17, 8, 53, 41, 10, 55, 16, 29, 2, 20], which leverage a particular metric to distinguish malicious gradients from the benign ones. Despite its effectiveness against some backdoors, researchers discovered that well-designed attacks (termed stealthy backdoors) whose gradients are indistinguishable from benign ones (through scaling [4, 47] or trigger split [50]) could easily bypass these defenses. Differential privacy (DP) -based method [46, 40, 38, 49] builds upon the observation that the DP method [14], traditionally used against DP attacks, is also effective against backdoors. By adding Gaussian noise to the global model, these methods can dilute the impact of potentially poisoned model updates. Surprisingly, DP-based methods show great ability in resisting stealthy backdoors (e.g., Edge-case PGD [47]). Despite its ability to resist the stealthy backdoors, the noises added by the DP significantly decrease the overall performance and the convergence speed. In comparison, the distance-based method less" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 137, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 137, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 137, + 712 + ], + "type": "text", + "content": "*Corresponding Author" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4652" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 72, + 287, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 72, + 287, + 167 + ], + "spans": [ + { + "bbox": [ + 45, + 72, + 287, + 167 + ], + "type": "text", + "content": "impacts the global model by aggregating only the benign gradients. Consequently, a natural question arises: can we defend the stealthy backdoors without sacrificing the performance of the FL model? To accomplish this, we turn to the distance-based methods that don't sacrifice the benign performance and promote the research question: how can we successfully leverage distance metrics to discriminate hostile updates from benign ones?" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 167, + 288, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 167, + 288, + 418 + ], + "spans": [ + { + "bbox": [ + 45, + 167, + 288, + 418 + ], + "type": "text", + "content": "To this end, we revisit the distance-based defense and discover two limitations: 1. Euclidean distance (i.e., " + }, + { + "bbox": [ + 45, + 167, + 288, + 418 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 45, + 167, + 288, + 418 + ], + "type": "text", + "content": " distance) suffers from the curse of dimensionality. Parameters of Neural Networks (NNs) can be viewed as high-dimensional vectors, and Euclidean distance generally fails to discriminate between malicious and benign gradients in high-dimensional space. 2. Single metric takes effect only against particular attacks with detailed assumptions regarding the malicious gradients. For instance, cosine distance detects malicious gradients with sizeable angular deviations while euclidean distance detects malicious gradients with a large " + }, + { + "bbox": [ + 45, + 167, + 288, + 418 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 45, + 167, + 288, + 418 + ], + "type": "text", + "content": " norm scaled by the attacker to impact the global models. Moreover, backdoor attacks are conducted with different data and scenarios, resulting in malicious gradients with various characteristics that a single metric cannot handle (i.e., both gradients with a large norm and gradients with sizeable angular deviations exist in one round of aggregation). What's worse is that the defender has no knowledge regarding the attacker and the underlying data distributions due to privacy requirements by FL, which makes detecting with a single metric even more difficult." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 419, + 287, + 670 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 419, + 287, + 670 + ], + "spans": [ + { + "bbox": [ + 45, + 419, + 287, + 670 + ], + "type": "text", + "content": "To address the above two problems, we first introduce the Manhattan distance, which we theoretically prove more meaningful in high dimensional space than Euclidean distance. Empirically, with the Manhattan distance, our proposed distance-based defense shows remarkable performance against the stealthy backdoors. To cope with gradients with various properties, we leverage multiple metrics cooperatively to identify the malicious gradients. We demonstrate in Section 5.4 and Figure 7 that malicious gradients of some characteristics are better identified by specific metrics, which justify our motivation. To handle the different attacks and environments, we further propose to apply a whitening transformation and generate dynamic weights to handle the non-IID distribution of participants and different scales brought by the different distances. Finally, we compute the score for each submitted gradient and aggregate only the benign ones based on the scoring. Extensive experiments illustrate that our defense maintains a high model performance and robustness simultaneously, which has never been achieved before. At a high level, we summarize the main contributions of this paper as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 677, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 677, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 58, + 677, + 287, + 714 + ], + "type": "text", + "content": "- We present a novel defense with multi-metrics to adaptively identify backdoors, which is applicable in a generic adversary model without predefined assumption." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 325, + 72, + 523, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 325, + 72, + 523, + 84 + ], + "spans": [ + { + "bbox": [ + 325, + 72, + 523, + 84 + ], + "type": "text", + "content": "tions over the attack strategy or data distribution." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 317, + 93, + 545, + 246 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 317, + 93, + 545, + 165 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 93, + 545, + 165 + ], + "spans": [ + { + "bbox": [ + 317, + 93, + 545, + 165 + ], + "type": "text", + "content": "- We show that by introducing the Manhattan distance, our defense alleviates the \"meaningfulness\" problem of Euclidean distance in high dimensions. By utilizing multiple metrics with dynamic weighting, our defense can resist backdoor attacks under a wide range of attack settings and data distributions." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 317, + 174, + 545, + 246 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 174, + 545, + 246 + ], + "spans": [ + { + "bbox": [ + 317, + 174, + 545, + 246 + ], + "type": "text", + "content": "- We empirically evaluate our method on various datasets and different attack settings. By showing that our defense maintains both high robustness and benign performance under the stealthy backdoors that previously have not been successfully defended, we demonstrate the effectiveness of our approach." + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 257, + 390, + 270 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 257, + 390, + 270 + ], + "spans": [ + { + "bbox": [ + 306, + 257, + 390, + 270 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 277, + 545, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 277, + 545, + 373 + ], + "spans": [ + { + "bbox": [ + 305, + 277, + 545, + 373 + ], + "type": "text", + "content": "Backdoor Attacks on Federated Learning. FL enables multiple clients collaboratively train a model without local data exchange. In an FL system, clients update the local model with private data and submit the parameters to the server for aggregation. Given a total of " + }, + { + "bbox": [ + 305, + 277, + 545, + 373 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 305, + 277, + 545, + 373 + ], + "type": "text", + "content": " participants, each with " + }, + { + "bbox": [ + 305, + 277, + 545, + 373 + ], + "type": "inline_equation", + "content": "n^{(i)}" + }, + { + "bbox": [ + 305, + 277, + 545, + 373 + ], + "type": "text", + "content": " samples. In each round " + }, + { + "bbox": [ + 305, + 277, + 545, + 373 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 305, + 277, + 545, + 373 + ], + "type": "text", + "content": ", the server randomly selects " + }, + { + "bbox": [ + 305, + 277, + 545, + 373 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 305, + 277, + 545, + 373 + ], + "type": "text", + "content": " clients to participate. FedAvg [35] is a widely-adopted FL algorithm, which can be formulated as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 353, + 382, + 545, + 415 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 353, + 382, + 545, + 415 + ], + "spans": [ + { + "bbox": [ + 353, + 382, + 545, + 415 + ], + "type": "interline_equation", + "content": "\\boldsymbol {w} _ {t} = \\boldsymbol {w} _ {t - 1} + \\eta \\cdot \\frac {\\sum_ {i = 1} ^ {K} n ^ {(i)} \\Delta w _ {t} ^ {(i)}}{\\sum_ {i = 1} ^ {K} n ^ {(i)}} \\tag {1}", + "image_path": "ee888ed283c5808863fb531cf498b1ebfa46f7061d168f4d6766865405cfd225.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "spans": [ + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "inline_equation", + "content": "w_{t}" + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "text", + "content": " is the global model parameters at round " + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "inline_equation", + "content": "\\Delta w_{t}^{(i)}" + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "text", + "content": " is the local model updates from the client " + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "text", + "content": " in round " + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 305, + 425, + 545, + 461 + ], + "type": "text", + "content": " is the global model learning rate." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 462, + 545, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 462, + 545, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 462, + 545, + 617 + ], + "type": "text", + "content": "Empirical studies from Bagdasaryan et al. [4] demonstrate that FedAvg [35] is vulnerable to backdoor attacks since FL has no authority over local data and the training process due to privacy concerns. The model replacement attack [4] successfully injects a backdoor into the global model by the single-shot attack. Some well-designed attacks strategically target the weakness of the defenses, such as the PGD attack [47] scaling and projecting the gradients, or the DBA attack [50] splitting the triggers before uploading them. Moreover, the Edge-case PGD attack [47] modifies the poisoned data and model. Undoubtedly, these attacks present a tremendous challenge to the security of the FL system." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": "Defense Against the Backdoor Attack. Various methods to defend against backdoor attacks improve the robustness and security of FL. In general, we can divide these methods into two categories. The first type of defense strategies tries to distinguish malicious gradients from benign ones by classifying or scoring with the assumption that benign and malicious gradients show distinct differences in the vector space [17, 8, 53, 41, 10, 55, 16, 29, 2, 20]. Krum" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4653" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": "and Multi-Krum [8] select the gradient with the smallest Euclidean norm from the others to aggregate and update the global model at each round. Foolsgold [17] assumes that the gradients of attackers are always consistent and distinguishes them by the Cosine similarity between historical updates. Trimmed Mean and Median [53] remove a fraction of the gradients with maximum and minimum values and then take the median value on each dimension of the remaining gradients as the parameters of the global model. RFA [41] leverages the geometric median of the gradients to keep the aggregated model close to the benign model and away from the backdoor one. The strength lies in that, if successful, the gradients of attackers are excluded from the aggregation process, which solves the core and fundamental problem of defending the attack." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 255, + 289, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 255, + 289, + 532 + ], + "spans": [ + { + "bbox": [ + 46, + 255, + 289, + 532 + ], + "type": "text", + "content": "However, the above methods take effect only under particular attacks since they make detailed assumptions about the attack or the data distributions. Foolsgold [17] assumes the gradients of attackers are consistent while benign gradients from Non-IID data differ. Krum [8] assumes that the data of benign clients is similar under IID settings and excludes abnormal malicious ones. These predefined assumptions limit the applicability of these defenses under various attacks and data distributions and can be easily bypassed by elaborate attacks. For example, PGD [47] breaks any Euclidean-based defense (e.g. Krum and Multi-Krum) by scaling the norm to a small value. Other methods, such as FLTrust [10], use a root dataset and aggregate only those gradients with large cosine similarities with the root dataset. FedInv [55] inverts the gradients into dummy datasets and then identifies the malicious gradient by comparing these dummy datasets. These methods are limited as well. FLTrust cannot defend against backdoors crafted on edge cases (e.g. Edge-case PGD) since they appear less often and are probably not in the root dataset. Inverting the gradients into dummy datasets violates the privacy requirement of FL. Essentially, this method can be characterized as another type of attack [3, 21]." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 534, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 534, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 534, + 289, + 714 + ], + "type": "text", + "content": "The other category of defenses [46, 40, 38, 49] builds upon the observation that the differential privacy (DP) method [14], traditionally used against DP attacks is also effective against backdoor attacks. Earlier studies [4] have demonstrated that clipping and adding noise (typically used in DP) can resist backdoor attacks without any specific assumptions over the data distribution. Following these findings, Weak-DP [46] clips the norm and adds the Gaussian noise to the global model for mitigating the backdoors. RLR [40] and Flame [38] apply the clustering methods before the DP process. However, the noise added significantly decreases the performance and the convergence speed of the FL system. In a nutshell, using DP sacrifices regular functionality for robustness. Despite its deficiency, the DP-based method has been the only method that has taken effect" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 306, + 72, + 436, + 85 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 436, + 85 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 436, + 85 + ], + "type": "text", + "content": "against stealthy backdoors [38]." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 306, + 95, + 389, + 109 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 95, + 389, + 109 + ], + "spans": [ + { + "bbox": [ + 306, + 95, + 389, + 109 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 115, + 547, + 297 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 115, + 547, + 297 + ], + "spans": [ + { + "bbox": [ + 304, + 115, + 547, + 297 + ], + "type": "text", + "content": "We first provide the threat model in Section 3.1 and then detail our design of the proposed defense method. Our goal is to design an efficient defense with the following properties: (1) Effectiveness: To prevent the adversary from achieving its hostile purpose, we aim to design a defense that identifies as many malicious updates as possible to eliminate its impact on the global model. (2) Performance: Benign performance of the global model must be preserved to maintain its utility. (3) Independence: The defense must be applicable to generic adversary models under different data distributions and attack strategies. Our defense consists of three major components: defining and calculating the gradient feature, computing the dynamic weight and score for each update, and aggregating the benign gradients with the score computed, as shown in Figure 1 and Algorithm 1." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 303, + 394, + 315 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 303, + 394, + 315 + ], + "spans": [ + { + "bbox": [ + 306, + 303, + 394, + 315 + ], + "type": "text", + "content": "3.1. Threat Model" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 321, + 547, + 417 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 321, + 547, + 417 + ], + "spans": [ + { + "bbox": [ + 304, + 321, + 547, + 417 + ], + "type": "text", + "content": "Adversarial goals. Adversary aims to alter the behavior of the model on some specific examples with no negative impact on the benign performance. We consider the adversary effective if this is met. In addition, the adversary will make their attack as covert as possible, e.g., by scaling down. Formally, adversary " + }, + { + "bbox": [ + 304, + 321, + 547, + 417 + ], + "type": "inline_equation", + "content": "\\mathcal{A}" + }, + { + "bbox": [ + 304, + 321, + 547, + 417 + ], + "type": "text", + "content": " manipulates the global model " + }, + { + "bbox": [ + 304, + 321, + 547, + 417 + ], + "type": "inline_equation", + "content": "G" + }, + { + "bbox": [ + 304, + 321, + 547, + 417 + ], + "type": "text", + "content": " to the poisoned model " + }, + { + "bbox": [ + 304, + 321, + 547, + 417 + ], + "type": "inline_equation", + "content": "G'" + }, + { + "bbox": [ + 304, + 321, + 547, + 417 + ], + "type": "text", + "content": ". For any inputs " + }, + { + "bbox": [ + 304, + 321, + 547, + 417 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 321, + 547, + 417 + ], + "type": "text", + "content": ", we have the outputs below:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 350, + 426, + 545, + 452 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 426, + 545, + 452 + ], + "spans": [ + { + "bbox": [ + 350, + 426, + 545, + 452 + ], + "type": "interline_equation", + "content": "G ^ {\\prime} (x) = \\left\\{ \\begin{array}{c c} l ^ {\\prime} \\neq G (x) & \\forall x \\in D _ {\\mathcal {A}} \\\\ G (x) & \\forall x \\notin D _ {\\mathcal {A}} \\end{array} \\right. \\tag {2}", + "image_path": "887a6f1d79fc4f69781e3c479ec935b5cd400daa203c01343b1499ce450eb5c8.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "inline_equation", + "content": "D_{\\mathcal{A}}" + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "text", + "content": " denotes the poisoned dataset belonging to adversary " + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "inline_equation", + "content": "\\mathcal{A}" + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "inline_equation", + "content": "l'" + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "text", + "content": " denotes the specific label modified by adversary " + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "inline_equation", + "content": "\\mathcal{A}" + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "text", + "content": " of the input " + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 460, + 545, + 496 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 496, + 547, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 496, + 547, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 496, + 547, + 581 + ], + "type": "text", + "content": "Adversarial capabilities. This paper assumes the white-box setting with full knowledge of aggregation operations, including potential defenses. Also, adversaries can freely alter the parameters in the local training, ensure participation in each round and compromise less than " + }, + { + "bbox": [ + 304, + 496, + 547, + 581 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 304, + 496, + 547, + 581 + ], + "type": "text", + "content": " of total FL clients. However, the adversary cannot control any process or parameter executed in the aggregator." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 587, + 419, + 600 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 587, + 419, + 600 + ], + "spans": [ + { + "bbox": [ + 306, + 587, + 419, + 600 + ], + "type": "text", + "content": "3.2. Feature of gradient" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "content": "The essential logic of distance-based defense involves defining some indicative metric that can well discriminate the malicious gradients from the benign ones and removes the hostile updates from the aggregation. Consequently, the core problem becomes how to define a metric that identifies the characteristics of hostile gradients. For instance, NDC [46] utilizes the length of the gradient (i.e. Euclidean distance) while FoolGold [17] leverages Cosine similarity to measure the difference between updates." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 316, + 757 + ], + "type": "text", + "content": "4654" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 72, + 71, + 521, + 257 + ], + "blocks": [ + { + "bbox": [ + 72, + 71, + 521, + 257 + ], + "lines": [ + { + "bbox": [ + 72, + 71, + 521, + 257 + ], + "spans": [ + { + "bbox": [ + 72, + 71, + 521, + 257 + ], + "type": "image", + "image_path": "e47d46bf55ca67777b31957dd0576c641c4f104f497705075925d48161925664.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 110, + 266, + 482, + 279 + ], + "lines": [ + { + "bbox": [ + 110, + 266, + 482, + 279 + ], + "spans": [ + { + "bbox": [ + 110, + 266, + 482, + 279 + ], + "type": "text", + "content": "Figure 1: The overview of our defense process. Step 1 and step 2 are our core contributions." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 97, + 304, + 224, + 399 + ], + "blocks": [ + { + "bbox": [ + 97, + 304, + 224, + 399 + ], + "lines": [ + { + "bbox": [ + 97, + 304, + 224, + 399 + ], + "spans": [ + { + "bbox": [ + 97, + 304, + 224, + 399 + ], + "type": "image", + "image_path": "1eba84d9dc8bc95963dc06bec9f7543ac5b9dbe64a3b40c4143614aab1a834fd.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "lines": [ + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "text", + "content": "Figure 2: Demonstration of feature of gradient on two dimensional space. " + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "inline_equation", + "content": "\\pmb{w}_0" + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "text", + "content": " is initial global model " + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "inline_equation", + "content": "\\pmb{w}_0" + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "inline_equation", + "content": "\\pmb{w}_i" + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "text", + "content": " is the local model of the " + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "text", + "content": "-th client. " + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "inline_equation", + "content": "\\pmb{w}_i - \\pmb{w}_0" + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "text", + "content": " is the gradient and we define the feature of gradient as " + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "inline_equation", + "content": "(|x + y|, l, \\theta)" + }, + { + "bbox": [ + 46, + 411, + 288, + 460 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 479, + 287, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 479, + 287, + 604 + ], + "spans": [ + { + "bbox": [ + 46, + 479, + 287, + 604 + ], + "type": "text", + "content": "Manhattan Distance. However, the Euclidean distance suffers from the so-called \"curse of dimensionality\" [48], which renders distance metrics less sensitive in high dimensional space, especially in the case of Euclidean distance. Theorem 1 uses " + }, + { + "bbox": [ + 46, + 479, + 287, + 604 + ], + "type": "inline_equation", + "content": "\\frac{D\\max_d^k - D\\min_d^k}{D\\min_d^k}" + }, + { + "bbox": [ + 46, + 479, + 287, + 604 + ], + "type": "text", + "content": " to indicate the \"meaningfulness\" of a distance referred as the Relative Contrast. It demonstrates that the distance metric is meaningless in high-dimensional space because as dimensionality increases, the distance between the nearest and the furthest neighbor approximates to be the same." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 609, + 288, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 609, + 288, + 621 + ], + "spans": [ + { + "bbox": [ + 47, + 609, + 288, + 621 + ], + "type": "text", + "content": "Theorem 1 (Beyer et. al.[5] The curse of dimensionality)" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 89, + 628, + 242, + 656 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 89, + 628, + 242, + 656 + ], + "spans": [ + { + "bbox": [ + 89, + 628, + 242, + 656 + ], + "type": "interline_equation", + "content": "I f \\lim _ {d \\rightarrow \\infty} v a r \\left(\\frac {\\| X _ {d} \\| _ {k}}{E [ \\| X _ {d} \\| _ {k} ]}\\right) = 0, t h e n", + "image_path": "4d1b0d0af579916d3e3ba0e74e34bb888b99176b3fefa910553a866ea8b282ca.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 113, + 658, + 222, + 687 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 113, + 658, + 222, + 687 + ], + "spans": [ + { + "bbox": [ + 113, + 658, + 222, + 687 + ], + "type": "interline_equation", + "content": "\\frac {D m a x _ {d} ^ {k} - D m i n _ {d} ^ {k}}{D \\min _ {d} ^ {k}} \\rightarrow_ {p} 0,", + "image_path": "e2570ed3a3ce4e573a4219cd784829b7b59fa348d00bf3dc433fa70f84deced1.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": " denotes the dimensionality of the data space, " + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "E[X]" + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": " and var " + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "[X]" + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": " denotes the expected value and variance of a" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "spans": [ + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "type": "text", + "content": "random variable " + }, + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "type": "inline_equation", + "content": "Dmax_{d}^{k}" + }, + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "type": "inline_equation", + "content": "Dmin_{d}^{k}" + }, + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "type": "text", + "content": " means the farthest/nearest distance of the " + }, + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "type": "text", + "content": " points to the origin using the distance metric " + }, + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "type": "inline_equation", + "content": "L_{k}" + }, + { + "bbox": [ + 305, + 300, + 545, + 335 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 343, + 546, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 343, + 546, + 403 + ], + "spans": [ + { + "bbox": [ + 305, + 343, + 546, + 403 + ], + "type": "text", + "content": "To find out which distance metric is more meaningful in high-dimensional space, we size up the relation between the dimension " + }, + { + "bbox": [ + 305, + 343, + 546, + 403 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 305, + 343, + 546, + 403 + ], + "type": "text", + "content": " and the distance " + }, + { + "bbox": [ + 305, + 343, + 546, + 403 + ], + "type": "inline_equation", + "content": "L_{k}" + }, + { + "bbox": [ + 305, + 343, + 546, + 403 + ], + "type": "text", + "content": ". We have Lemma 1, which shows that " + }, + { + "bbox": [ + 305, + 343, + 546, + 403 + ], + "type": "inline_equation", + "content": "Dmax_{d}^{k} - Dmin_{d}^{k}" + }, + { + "bbox": [ + 305, + 343, + 546, + 403 + ], + "type": "text", + "content": " increases at the ratio of " + }, + { + "bbox": [ + 305, + 343, + 546, + 403 + ], + "type": "inline_equation", + "content": "d^{(1 / k) - (1 / 2)}" + }, + { + "bbox": [ + 305, + 343, + 546, + 403 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 411, + 545, + 448 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 411, + 545, + 448 + ], + "spans": [ + { + "bbox": [ + 305, + 411, + 545, + 448 + ], + "type": "text", + "content": "Lemma 1 (Hinneburg et.al.[22]) Let " + }, + { + "bbox": [ + 305, + 411, + 545, + 448 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 305, + 411, + 545, + 448 + ], + "type": "text", + "content": " be an arbitrary distribution of two points and the distance function " + }, + { + "bbox": [ + 305, + 411, + 545, + 448 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\|" + }, + { + "bbox": [ + 305, + 411, + 545, + 448 + ], + "type": "text", + "content": " be an " + }, + { + "bbox": [ + 305, + 411, + 545, + 448 + ], + "type": "inline_equation", + "content": "L_{k}" + }, + { + "bbox": [ + 305, + 411, + 545, + 448 + ], + "type": "text", + "content": " metric. Then," + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 349, + 455, + 502, + 483 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 349, + 455, + 502, + 483 + ], + "spans": [ + { + "bbox": [ + 349, + 455, + 502, + 483 + ], + "type": "interline_equation", + "content": "\\lim _ {d \\rightarrow \\infty} E \\left[ \\frac {D m a x _ {d} ^ {k} - D m i n _ {d} ^ {k}}{d ^ {(1 / k) - (1 / 2)}} \\right] = C _ {k},", + "image_path": "d6dfd51bb055d2adc63f542fd67bea046ca1053bb2939d28dc59407c4ba68cd2.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 491, + 482, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 491, + 482, + 503 + ], + "spans": [ + { + "bbox": [ + 306, + 491, + 482, + 503 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 491, + 482, + 503 + ], + "type": "inline_equation", + "content": "C_k" + }, + { + "bbox": [ + 306, + 491, + 482, + 503 + ], + "type": "text", + "content": " is some constant dependent on " + }, + { + "bbox": [ + 306, + 491, + 482, + 503 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 306, + 491, + 482, + 503 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 510, + 545, + 547 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 510, + 545, + 547 + ], + "spans": [ + { + "bbox": [ + 305, + 510, + 545, + 547 + ], + "type": "text", + "content": "Subsequently, we use the value of " + }, + { + "bbox": [ + 305, + 510, + 545, + 547 + ], + "type": "inline_equation", + "content": "Dmax_{d}^{k} - Dmin_{d}^{k}" + }, + { + "bbox": [ + 305, + 510, + 545, + 547 + ], + "type": "text", + "content": " as a criterion to evaluate the ability of a particular metric to discriminate different vectors in high dimensional space." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 554, + 545, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 554, + 545, + 602 + ], + "spans": [ + { + "bbox": [ + 305, + 554, + 545, + 602 + ], + "type": "text", + "content": "Proposition 1 Let " + }, + { + "bbox": [ + 305, + 554, + 545, + 602 + ], + "type": "inline_equation", + "content": "M_d = Dmax_d^1 - Dmin_d^1" + }, + { + "bbox": [ + 305, + 554, + 545, + 602 + ], + "type": "text", + "content": " reflect the discriminating ability of Manhattan distance and " + }, + { + "bbox": [ + 305, + 554, + 545, + 602 + ], + "type": "inline_equation", + "content": "U_d = Dmax_d^2 - Dmin_d^2" + }, + { + "bbox": [ + 305, + 554, + 545, + 602 + ], + "type": "text", + "content": " reflect the discriminating ability of Euclidean distance. Then," + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 373, + 609, + 477, + 638 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 373, + 609, + 477, + 638 + ], + "spans": [ + { + "bbox": [ + 373, + 609, + 477, + 638 + ], + "type": "interline_equation", + "content": "\\lim _ {d \\rightarrow \\infty} E \\left[ \\frac {M _ {d}}{U _ {d} \\cdot d ^ {\\frac {1}{2}}} \\right] = C ^ {\\prime}.", + "image_path": "801bfadc4cc71d0bbb6ecb22e74cff88166a0c50ac6ca5ddc877ba9de1042ffc.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 645, + 509, + 658 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 645, + 509, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 645, + 509, + 658 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 645, + 509, + 658 + ], + "type": "inline_equation", + "content": "C'" + }, + { + "bbox": [ + 306, + 645, + 509, + 658 + ], + "type": "text", + "content": " is a constant. Proof see in Appendix C." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "content": "Proposition 1 shows that " + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "M_d" + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "U_d \\cdot d^{\\frac{1}{2}}" + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "content": " are infinite of the same order. Since " + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "d^{\\frac{1}{2}}" + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "content": " is also an infinite value, " + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "M_d" + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "content": " towers above " + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "inline_equation", + "content": "U_d" + }, + { + "bbox": [ + 305, + 665, + 545, + 713 + ], + "type": "text", + "content": ", suggesting that Manhattan can discriminate more than the Euclidean distance in high-dimension space. Given" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4655" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 215 + ], + "type": "text", + "content": "this, we conclude that the Manhattan distance is better than the Euclidean metric, withstanding the curse of dimensionality, which chimes in with the previous experiment [1, 37]. The parameters of neural networks can be viewed as a typical high-dimensional space, especially when the number of parameters increases as the trend in deep learning applications [9, 44, 42, 15, 34, 54, 43]. In light of this and Theorem 1, we argue that Euclidean distance is insufficient to discriminate between malicious and benign gradients. With Proposition 1, we introduce the Manhattan distance metric to describe the characteristics of gradients which captures the difference in high dimensional space better." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "spans": [ + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": "Multiple Metrics as Feature of Gradient. Another problem that we identify as discussed in Section 1 is that current methods conduct defense on a single metric basis. With only one metric, a sophisticated attacker could effortlessly bypass them with a well-designed gradient. For instance, PGD attack [47] manage to break the defense based on Euclidean distances by clipping the gradient norm to a small value. Moreover, attackers conduct attacks under different environments and data distributions, leading to malicious gradients with diverse characteristics that a single metric cannot handle. To this end, we propose multiple metrics to cooperatively identify the malicious gradient by defining the feature of gradient as the angle by the Cosine similarity, length by the Euclidean distances, and its Manhattan norm by the Manhattan distance, namely, " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "\\pmb{x} = (x_{Man}, x_{Eul}, x_{Cosine})" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": ". Here, " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "x_{Man}" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": " denotes the Manhattan distance, " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "x_{Eul}" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": " denotes the Euclidean distance and " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "x_{Cosine}" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": " denotes the Cosine similarity. Figure 2 provides a schematic diagram of the gradient feature. We compute the gradient feature " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "x_{Man}" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "x_{Eul}" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "x_{Cosine}" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": " of the " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": "-th client of each round as follows: " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "x_{Man}^{(i)} = \\| \\pmb{w}_i - \\pmb{w}_0\\|_1" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "x_{Eul}^{(i)} = \\| \\pmb{w}_i - \\pmb{w}_0\\|_2" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "x_{Cosine}^{(i)} = \\frac{\\langle\\pmb{w}_0\\pmb{w}_i\\rangle}{\\|\\pmb{w}_0\\| \\cdot \\|\\pmb{w}_i\\|}" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "\\pmb{w}_0" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": " denotes the global model before federated training and " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "\\pmb{w}_i" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": " denotes the " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": "-th client's local model after training, " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\|_1" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": " means the " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "L_1" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": " norm of a vector, " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\|_2" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": " means the " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "L_2" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": " norm of a vector, " + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "inline_equation", + "content": "\\langle \\cdot, \\cdot \\rangle" + }, + { + "bbox": [ + 46, + 216, + 289, + 582 + ], + "type": "text", + "content": " and represents inner product. After defining the feature of gradient, we utilize it for malicious identification. The goal is to identify the outlier among the gradients. We use the sum of the distance between each gradient as the indicator. Formally, we define it as Equation 3." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 70, + 594, + 287, + 635 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 70, + 594, + 287, + 635 + ], + "spans": [ + { + "bbox": [ + 70, + 594, + 287, + 635 + ], + "type": "interline_equation", + "content": "\\boldsymbol {x} ^ {\\prime (i)} = \\left(\\sum_ {j, j \\neq i} ^ {K} \\left| x _ {M a n} ^ {(i)} - x _ {M a n} ^ {(j)} \\right|, \\right. \\tag {3}", + "image_path": "c41621368316d12d5d3c64d2fcb1988416ba49e53c8f8bd0cce071f2143503cf.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 75, + 632, + 261, + 666 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 75, + 632, + 261, + 666 + ], + "spans": [ + { + "bbox": [ + 75, + 632, + 261, + 666 + ], + "type": "interline_equation", + "content": "\\sum_ {j, j \\neq i} ^ {K} | x _ {E u l} ^ {(i)} - x _ {E u l} ^ {(j)} |, \\sum_ {j, j \\neq i} ^ {K} | x _ {C o s i n e} ^ {(i)} - x _ {C o s i n e} ^ {(j)} |),", + "image_path": "45938e489fe42ae597669e758c9ed8b4376dcb28be0e7669fce3704e26c740c4.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 671, + 259, + 685 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 259, + 685 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 259, + 685 + ], + "type": "text", + "content": "3.3. Dynamic Weighting Through Whitening" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "After defining the feature of gradient and indicator, we now provide an approach to score each gradient. Two fac" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 107 + ], + "type": "text", + "content": "tors are taken into account when considering an efficient way to turn the indicator into a unified score that works under various data distributions and attacks." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 317, + 116, + 547, + 243 + ], + "type": "list", + "angle": 0, + "index": 9, + "blocks": [ + { + "bbox": [ + 317, + 116, + 545, + 175 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 116, + 545, + 175 + ], + "spans": [ + { + "bbox": [ + 317, + 116, + 545, + 175 + ], + "type": "text", + "content": "- Different scales of the three distance metrics are the first obstacle before utilizing these metrics collaboratively. Since each metric is correlated, a novel regularization is required instead of the usual normalization by the maximum value." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 184, + 547, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 184, + 547, + 243 + ], + "spans": [ + { + "bbox": [ + 317, + 184, + 547, + 243 + ], + "type": "text", + "content": "- Different data distributions (e.g. different degrees of non-IID) render the gradients of both malicious and benign clients different. Thus, dynamic weighting is required to cope with various environments and attacks to achieve a universal defense." + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 305, + 253, + 545, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 253, + 545, + 289 + ], + "spans": [ + { + "bbox": [ + 305, + 253, + 545, + 289 + ], + "type": "text", + "content": "Considering the above factors, we propose first to project the value of the metrics in the feature of gradient to its corresponding principal axis by applying a whitening process:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 372, + 298, + 545, + 319 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 372, + 298, + 545, + 319 + ], + "spans": [ + { + "bbox": [ + 372, + 298, + 545, + 319 + ], + "type": "interline_equation", + "content": "\\delta^ {(i)} = \\sqrt {\\boldsymbol {x} ^ {\\prime^ {(i) \\top}} \\boldsymbol {\\Sigma} ^ {- 1} \\boldsymbol {x} ^ {\\prime^ {(i)}}}. \\tag {4}", + "image_path": "94c35efeee9b496266227aee1c245d41f0ae84b1bc9c894a4a54aabfbf76a46b.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 324, + 545, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 324, + 545, + 443 + ], + "spans": [ + { + "bbox": [ + 305, + 324, + 545, + 443 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 324, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\boldsymbol{\\Sigma}" + }, + { + "bbox": [ + 305, + 324, + 545, + 443 + ], + "type": "text", + "content": " is the covariance matrix of " + }, + { + "bbox": [ + 305, + 324, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\pmb{X} = [x^{\\prime(1)}x^{\\prime(2)}\\dots x^{\\prime(K)}]^{\\top}" + }, + { + "bbox": [ + 305, + 324, + 545, + 443 + ], + "type": "text", + "content": ". Since we need to calculate the inverse of the covariance matrix " + }, + { + "bbox": [ + 305, + 324, + 545, + 443 + ], + "type": "inline_equation", + "content": "\\boldsymbol{\\Sigma}" + }, + { + "bbox": [ + 305, + 324, + 545, + 443 + ], + "type": "text", + "content": ", the number of samples must be larger than the number of features, i.e., " + }, + { + "bbox": [ + 305, + 324, + 545, + 443 + ], + "type": "inline_equation", + "content": "K > 3" + }, + { + "bbox": [ + 305, + 324, + 545, + 443 + ], + "type": "text", + "content": ". Please notice that the inverse of the covariance matrix is calculated based on the selected gradients, which will change the weights of the features dynamically depending on the feature distribution, hence \"dynamic weighting\". With such a dynamic weight, our method can better adapt to different environments and resist various attacks." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 452, + 484, + 464 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 452, + 484, + 464 + ], + "spans": [ + { + "bbox": [ + 306, + 452, + 484, + 464 + ], + "type": "text", + "content": "3.4. Aggregation of Benign Gradients" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 471, + 545, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 471, + 545, + 567 + ], + "spans": [ + { + "bbox": [ + 305, + 471, + 545, + 567 + ], + "type": "text", + "content": "After obtaining the score of each gradient, we aggregate the gradients with high scoring. A higher score indicates that the gradient is less divergent among all. After the selection of \"benign\" gradients, we can aggregate them with any existing aggregation methods (e.g. Averaging of gradients). We follow [35] and perform standard FedAvg on the \"benign\" gradients. A detailed analysis of aggregation of benign gradients is in Appendix A.1." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 578, + 414, + 590 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 578, + 414, + 590 + ], + "spans": [ + { + "bbox": [ + 306, + 578, + 414, + 590 + ], + "type": "text", + "content": "4. Experiment Setup" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 597, + 545, + 620 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 597, + 545, + 620 + ], + "spans": [ + { + "bbox": [ + 306, + 597, + 545, + 620 + ], + "type": "text", + "content": "We will first introduce the settings and then the objective of our experiments." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 622, + 545, + 681 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 622, + 545, + 681 + ], + "spans": [ + { + "bbox": [ + 305, + 622, + 545, + 681 + ], + "type": "text", + "content": "Datasets. We conduct our experiments on multiple datasets, including two visual datasets, CIFAR-10 [27] and EMNIST [12]. We also experiment on other datasets to prove the generalization ability, including CINIC10 [13], LOAN [25] and Sentiment140 [18] as follows:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 317, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 317, + 689, + 545, + 713 + ], + "type": "text", + "content": "- CIFAR-10 dataset [27] is a vision classification dataset containing 50,000 training samples and" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4656" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 49, + 72, + 210, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 72, + 210, + 83 + ], + "spans": [ + { + "bbox": [ + 49, + 72, + 210, + 83 + ], + "type": "text", + "content": "Algorithm 1 Our aggregation algorithm" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "spans": [ + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "text", + "content": "Input: Total number of clients in each round " + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "text", + "content": ", models of clients " + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "inline_equation", + "content": "\\boldsymbol{w}^{(1)}, \\boldsymbol{w}^{(2)}, \\dots, \\boldsymbol{w}^{(K)}" + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "text", + "content": ", last global model " + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "inline_equation", + "content": "\\boldsymbol{w}_0" + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "text", + "content": ", fraction selected to aggregation " + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "text", + "content": ", global learning rate " + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "text", + "content": ", size of the " + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "inline_equation", + "content": "i - th" + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "text", + "content": " client dataset " + }, + { + "bbox": [ + 47, + 85, + 287, + 132 + ], + "type": "inline_equation", + "content": "n^{(i)}" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 52, + 133, + 160, + 144 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 133, + 160, + 144 + ], + "spans": [ + { + "bbox": [ + 52, + 133, + 160, + 144 + ], + "type": "text", + "content": "Output: Global model " + }, + { + "bbox": [ + 52, + 133, + 160, + 144 + ], + "type": "inline_equation", + "content": "w^{*}" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 53, + 147, + 287, + 170 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 147, + 287, + 170 + ], + "spans": [ + { + "bbox": [ + 53, + 147, + 287, + 170 + ], + "type": "text", + "content": "1: for " + }, + { + "bbox": [ + 53, + 147, + 287, + 170 + ], + "type": "inline_equation", + "content": "i\\in \\{1,2,\\dots,K\\}" + }, + { + "bbox": [ + 53, + 147, + 287, + 170 + ], + "type": "text", + "content": " do compute the gradients features" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 54, + 170, + 171, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 170, + 171, + 185 + ], + "spans": [ + { + "bbox": [ + 54, + 170, + 171, + 185 + ], + "type": "text", + "content": "2: " + }, + { + "bbox": [ + 54, + 170, + 171, + 185 + ], + "type": "inline_equation", + "content": "x_{Man}^{(i)}\\gets \\left\\| \\pmb{w}_0 - \\pmb{w}_i\\right\\| _1" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 54, + 185, + 168, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 185, + 168, + 198 + ], + "spans": [ + { + "bbox": [ + 54, + 185, + 168, + 198 + ], + "type": "text", + "content": "3: " + }, + { + "bbox": [ + 54, + 185, + 168, + 198 + ], + "type": "inline_equation", + "content": "x_{Eul}^{(i)}\\gets \\left\\| \\pmb {w}_0 - \\pmb {w}_i\\right\\| _2" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 54, + 198, + 158, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 198, + 158, + 215 + ], + "spans": [ + { + "bbox": [ + 54, + 198, + 158, + 215 + ], + "type": "text", + "content": "4: " + }, + { + "bbox": [ + 54, + 198, + 158, + 215 + ], + "type": "inline_equation", + "content": "x_{\\text{Cos}}^{(i)} \\gets \\frac{\\langle \\boldsymbol{w}_0, \\boldsymbol{w}_i \\rangle}{\\|\\boldsymbol{w}_0\\| \\cdot \\|\\boldsymbol{w}_i\\|}" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 54, + 214, + 193, + 229 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 214, + 193, + 229 + ], + "spans": [ + { + "bbox": [ + 54, + 214, + 193, + 229 + ], + "type": "text", + "content": "5: " + }, + { + "bbox": [ + 54, + 214, + 193, + 229 + ], + "type": "inline_equation", + "content": "\\pmb{x}^{(i)}\\gets (x_{Man}^{(i)},x_{Eul}^{(i)},x_{Cos}^{(i)})" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 54, + 230, + 97, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 230, + 97, + 239 + ], + "spans": [ + { + "bbox": [ + 54, + 230, + 97, + 239 + ], + "type": "text", + "content": "6: end for" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 53, + 240, + 287, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 240, + 287, + 262 + ], + "spans": [ + { + "bbox": [ + 53, + 240, + 287, + 262 + ], + "type": "text", + "content": "7: for " + }, + { + "bbox": [ + 53, + 240, + 287, + 262 + ], + "type": "inline_equation", + "content": "i,j\\in \\{1,2,\\dots,K\\}" + }, + { + "bbox": [ + 53, + 240, + 287, + 262 + ], + "type": "text", + "content": " do compute the sum of the distance between each gradient" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 54, + 263, + 218, + 280 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 263, + 218, + 280 + ], + "spans": [ + { + "bbox": [ + 54, + 263, + 218, + 280 + ], + "type": "text", + "content": "8: " + }, + { + "bbox": [ + 54, + 263, + 218, + 280 + ], + "type": "inline_equation", + "content": "x^{\\prime}_{Man}^{(i)}\\gets \\sum_{j,j\\neq i}^{K}|x_{Man}^{(i)} - x_{Man}^{(j)}|" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 54, + 280, + 206, + 295 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 280, + 206, + 295 + ], + "spans": [ + { + "bbox": [ + 54, + 280, + 206, + 295 + ], + "type": "text", + "content": "9: " + }, + { + "bbox": [ + 54, + 280, + 206, + 295 + ], + "type": "inline_equation", + "content": "x^{\\prime}_{Eul}^{(i)}\\gets \\sum_{j,j\\neq i}^{K}|x^{(i)}_{Eul} - x^{(j)}_{Eul}|" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 52, + 295, + 206, + 311 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 295, + 206, + 311 + ], + "spans": [ + { + "bbox": [ + 52, + 295, + 206, + 311 + ], + "type": "text", + "content": "10: " + }, + { + "bbox": [ + 52, + 295, + 206, + 311 + ], + "type": "inline_equation", + "content": "x^{\\prime}_{COS}^{(i)}\\gets \\sum_{j,j\\neq i}^{K}|x^{(i)}_{COS} - x^{(j)}_{COS}|" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 52, + 311, + 205, + 326 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 311, + 205, + 326 + ], + "spans": [ + { + "bbox": [ + 52, + 311, + 205, + 326 + ], + "type": "text", + "content": "11: " + }, + { + "bbox": [ + 52, + 311, + 205, + 326 + ], + "type": "inline_equation", + "content": "\\pmb{x}^{\\prime (i)}\\gets (x_{Man}^{\\prime (i)},x_{Eul}^{\\prime (i)},x_{Cos}^{\\prime (i)})" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 52, + 327, + 97, + 335 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 327, + 97, + 335 + ], + "spans": [ + { + "bbox": [ + 52, + 327, + 97, + 335 + ], + "type": "text", + "content": "12: end for" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 52, + 335, + 189, + 349 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 335, + 189, + 349 + ], + "spans": [ + { + "bbox": [ + 52, + 335, + 189, + 349 + ], + "type": "text", + "content": "13: " + }, + { + "bbox": [ + 52, + 335, + 189, + 349 + ], + "type": "inline_equation", + "content": "X\\gets [\\pmb{x}^{\\prime (1)},\\pmb{x}^{\\prime (2)},\\dots,\\pmb{x}^{\\prime (K)}]^{\\top}" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 52, + 349, + 287, + 372 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 349, + 287, + 372 + ], + "spans": [ + { + "bbox": [ + 52, + 349, + 287, + 372 + ], + "type": "text", + "content": "14: " + }, + { + "bbox": [ + 52, + 349, + 287, + 372 + ], + "type": "inline_equation", + "content": "\\Sigma \\gets" + }, + { + "bbox": [ + 52, + 349, + 287, + 372 + ], + "type": "text", + "content": " the Covariance of " + }, + { + "bbox": [ + 52, + 349, + 287, + 372 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 52, + 349, + 287, + 372 + ], + "type": "text", + "content": " compute the adaptive weight matrix in this round" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 52, + 373, + 162, + 385 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 373, + 162, + 385 + ], + "spans": [ + { + "bbox": [ + 52, + 373, + 162, + 385 + ], + "type": "text", + "content": "15: for " + }, + { + "bbox": [ + 52, + 373, + 162, + 385 + ], + "type": "inline_equation", + "content": "i\\in \\{1,2,\\dots,K\\}" + }, + { + "bbox": [ + 52, + 373, + 162, + 385 + ], + "type": "text", + "content": " do" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 52, + 385, + 287, + 412 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 385, + 287, + 412 + ], + "spans": [ + { + "bbox": [ + 52, + 385, + 287, + 412 + ], + "type": "text", + "content": "16: " + }, + { + "bbox": [ + 52, + 385, + 287, + 412 + ], + "type": "inline_equation", + "content": "\\delta^{(i)}\\gets \\sqrt{\\boldsymbol{x}^{\\prime(i)\\top}\\cdot\\Sigma^{-1}\\cdot\\boldsymbol{x}^{\\prime(i)}}" + }, + { + "bbox": [ + 52, + 385, + 287, + 412 + ], + "type": "inline_equation", + "content": "\\triangleright" + }, + { + "bbox": [ + 52, + 385, + 287, + 412 + ], + "type": "text", + "content": " dynamically compute the divergence" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 52, + 413, + 97, + 422 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 413, + 97, + 422 + ], + "spans": [ + { + "bbox": [ + 52, + 413, + 97, + 422 + ], + "type": "text", + "content": "17: end for" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 52, + 424, + 286, + 447 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 424, + 286, + 447 + ], + "spans": [ + { + "bbox": [ + 52, + 424, + 286, + 447 + ], + "type": "text", + "content": "18: Remove the " + }, + { + "bbox": [ + 52, + 424, + 286, + 447 + ], + "type": "inline_equation", + "content": "K\\cdot (1 - p)" + }, + { + "bbox": [ + 52, + 424, + 286, + 447 + ], + "type": "text", + "content": " models with the high divergency " + }, + { + "bbox": [ + 52, + 424, + 286, + 447 + ], + "type": "inline_equation", + "content": "\\delta^{(i)}" + }, + { + "bbox": [ + 52, + 424, + 286, + 447 + ], + "type": "text", + "content": ", remaining models as " + }, + { + "bbox": [ + 52, + 424, + 286, + 447 + ], + "type": "inline_equation", + "content": "\\mathbb{B}" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 52, + 447, + 209, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 447, + 209, + 468 + ], + "spans": [ + { + "bbox": [ + 52, + 447, + 209, + 468 + ], + "type": "text", + "content": "19: " + }, + { + "bbox": [ + 52, + 447, + 209, + 468 + ], + "type": "inline_equation", + "content": "\\pmb{w}^{*}\\gets \\pmb{w}_{0} + \\eta \\cdot \\frac{\\sum_{i\\in\\mathbb{B}}n^{(i)}\\cdot(\\pmb{w}^{(i)} - \\pmb{w}_{0})}{\\sum_{i\\in\\mathbb{B}}n^{(i)}}" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 67, + 498, + 287, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 498, + 287, + 545 + ], + "spans": [ + { + "bbox": [ + 67, + 498, + 287, + 545 + ], + "type": "text", + "content": "10,000 testing samples with ten classes. To simulate the FL environment, we set the " + }, + { + "bbox": [ + 67, + 498, + 287, + 545 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 67, + 498, + 287, + 545 + ], + "type": "text", + "content": " of the Dirichlet distribution to be 0.5, representing a non-IID distribution. Smaller " + }, + { + "bbox": [ + 67, + 498, + 287, + 545 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 67, + 498, + 287, + 545 + ], + "type": "text", + "content": " means a larger degree of non-IID." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 59, + 546, + 287, + 712 + ], + "type": "list", + "angle": 0, + "index": 26, + "blocks": [ + { + "bbox": [ + 59, + 546, + 287, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 546, + 287, + 592 + ], + "spans": [ + { + "bbox": [ + 59, + 546, + 287, + 592 + ], + "type": "text", + "content": "- EMNIST dataset [12] is a digit classification dataset consisting of 280,000 real-world handwritten images of digits from 0 to 9. We also set the degree of non-IID to be " + }, + { + "bbox": [ + 59, + 546, + 287, + 592 + ], + "type": "inline_equation", + "content": "a = 0.5" + }, + { + "bbox": [ + 59, + 546, + 287, + 592 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 59, + 594, + 287, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 594, + 287, + 641 + ], + "spans": [ + { + "bbox": [ + 59, + 594, + 287, + 641 + ], + "type": "text", + "content": "- CINIC10 [13] has a total of 270,000 images, 4.5 times that of CIFAR-10, which is constructed from two different sources: ImageNet and CIFAR-10. We set the non-IID degree as " + }, + { + "bbox": [ + 59, + 594, + 287, + 641 + ], + "type": "inline_equation", + "content": "a = 0.5" + }, + { + "bbox": [ + 59, + 594, + 287, + 641 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 59, + 642, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 642, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 59, + 642, + 287, + 712 + ], + "type": "text", + "content": "- Lending Club Loan dataset (LOAN) [25] contains financial information such as loan information and credit scores for loan status prediction. There are 2,260,668 samples with a total of 9 classes. To simulate a more realistic situation, we divide the data by US states, where each state represents one client. We" + } + ] + } + ], + "index": 25 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 325, + 72, + 467, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 325, + 72, + 467, + 83 + ], + "spans": [ + { + "bbox": [ + 325, + 72, + 467, + 83 + ], + "type": "text", + "content": "set the non-IID parameter " + }, + { + "bbox": [ + 325, + 72, + 467, + 83 + ], + "type": "inline_equation", + "content": "a = 0.9" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 317, + 84, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 84, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 317, + 84, + 545, + 156 + ], + "type": "text", + "content": "- Sentiment140 [18] is a publicly available English Twitter sentiment classification dataset containing 1.6 million tweets, of which 800,000 are for training, and the other 800,000 are for testing. Each tweet in the dataset is labeled with a sentiment polarity (positive, neutral, or negative)." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 305, + 163, + 545, + 235 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 163, + 545, + 235 + ], + "spans": [ + { + "bbox": [ + 305, + 163, + 545, + 235 + ], + "type": "text", + "content": "Models. Different models are used on different datasets to demonstrate the generality of our approach. A 9-layer VGG style network (VGG-9) [45] is trained on the CIFAR10. On the EMNIST, we train LeNet-5 model [28]. We train the LSTM model [23] for Sentiment140 and a network with three fully-connected layers for LOAN." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 305, + 236, + 545, + 283 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 236, + 545, + 283 + ], + "spans": [ + { + "bbox": [ + 305, + 236, + 545, + 283 + ], + "type": "text", + "content": "Backdoor Attacks. We implement both pixel-pattern and semantic backdoors. To make the attack more challenging, we use the multiple-shot attack instead of the single-shot. The following are the attack methods we use:" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 317, + 291, + 545, + 530 + ], + "type": "list", + "angle": 0, + "index": 35, + "blocks": [ + { + "bbox": [ + 317, + 291, + 545, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 291, + 545, + 350 + ], + "spans": [ + { + "bbox": [ + 317, + 291, + 545, + 350 + ], + "type": "text", + "content": "- Model Replacement Attack [4]: Malicious clients generate backdoor gradients during their local training. Attackers scale up their gradients to ensure that the malicious model will replace the global model. Usually, the scaling factor is " + }, + { + "bbox": [ + 317, + 291, + 545, + 350 + ], + "type": "inline_equation", + "content": "N / K" + }, + { + "bbox": [ + 317, + 291, + 545, + 350 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 317, + 351, + 545, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 351, + 545, + 410 + ], + "spans": [ + { + "bbox": [ + 317, + 351, + 545, + 410 + ], + "type": "text", + "content": "- DBA Attack [50]: DBA decomposes a global trigger pattern into separate local patterns and embeds them into the training sets of different attackers, resulting in a more negligible difference between benign and back-door gradients;" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 317, + 411, + 545, + 446 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 411, + 545, + 446 + ], + "spans": [ + { + "bbox": [ + 317, + 411, + 545, + 446 + ], + "type": "text", + "content": "- PGD Attack [47]: To bypass the Euclidean-based defense, PGD Attack projects the model parameter within the ball centered around the global model;" + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 317, + 446, + 545, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 446, + 545, + 530 + ], + "spans": [ + { + "bbox": [ + 317, + 446, + 545, + 530 + ], + "type": "text", + "content": "- Edge-case PGD Attack [47]: Attackers have a set of edge-case samples and some benign samples as their poisoned datasets. Edge-case samples are unlikely to exist in the benign training set. Thus, the benign gradients cannot dilute the backdoor. We launch this attack in the form of PGD. The Edge-case PGD attack is so stealthy that most defenses cannot defend against it." + } + ] + } + ], + "index": 34 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 538, + 545, + 562 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 538, + 545, + 562 + ], + "spans": [ + { + "bbox": [ + 306, + 538, + 545, + 562 + ], + "type": "text", + "content": "Evaluation. We leverage the following two metrics for evaluating the effectiveness of our defense:" + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 317, + 570, + 545, + 712 + ], + "type": "list", + "angle": 0, + "index": 39, + "blocks": [ + { + "bbox": [ + 317, + 570, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 570, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 317, + 570, + 545, + 628 + ], + "type": "text", + "content": "- Backdoor Accuracy (BA) indicates whether the attacker succeeds. It shows the accuracy of the model on the backdoor task. The attackers aim to maximize this metric, and the lower the BA, the more efficient the defense." + } + ] + } + ], + "index": 37 + }, + { + "bbox": [ + 317, + 630, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 630, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 317, + 630, + 545, + 712 + ], + "type": "text", + "content": "- Main Task Accuracy (MA) is the accuracy on the main task. The overall objective of all participants in an FL system is to maximize MA. The benign clients maximize the model performance, while the attackers seek to be stealthy and maintain MA. Thus, the defense should not cause a significant drop in MA, which we report to demonstrate that our defense does not affect" + } + ] + } + ], + "index": 38 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4657" + } + ] + } + ], + "index": 40 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 67, + 72, + 287, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 72, + 287, + 96 + ], + "spans": [ + { + "bbox": [ + 67, + 72, + 287, + 96 + ], + "type": "text", + "content": "the functionality of the FL system. We report all BA and MA values in percentages." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 59, + 107, + 250, + 119 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 107, + 250, + 119 + ], + "spans": [ + { + "bbox": [ + 59, + 107, + 250, + 119 + ], + "type": "text", + "content": "Hyperparameters are detailed in Appendix B." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 120, + 287, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 120, + 287, + 216 + ], + "spans": [ + { + "bbox": [ + 47, + 120, + 287, + 216 + ], + "type": "text", + "content": "Objectives of Experiments. Firstly, we aim to illustrate the effectiveness of our proposed defense under different attacks by comparing it with the current and previous state-of-the-art defenses. Secondly, we demonstrate that the performance of our defense is consistent under different scenarios (e.g., different degrees of non-IID " + }, + { + "bbox": [ + 47, + 120, + 287, + 216 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 47, + 120, + 287, + 216 + ], + "type": "text", + "content": " and different attack frequencies). Thirdly, we figure out the reason for our defense works through the ablation study in Section 5.4." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 229, + 163, + 243 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 229, + 163, + 243 + ], + "spans": [ + { + "bbox": [ + 47, + 229, + 163, + 243 + ], + "type": "text", + "content": "5. Experiment Results" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 250, + 287, + 275 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 250, + 287, + 275 + ], + "spans": [ + { + "bbox": [ + 47, + 250, + 287, + 275 + ], + "type": "text", + "content": "5.1. Robustness against Different Attacks and Comparison with SOTA" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 281, + 287, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 281, + 287, + 496 + ], + "spans": [ + { + "bbox": [ + 46, + 281, + 287, + 496 + ], + "type": "text", + "content": "We first demonstrate the robustness of our approach under different attacks and then compare our methods with the state-of-the-art defense methods such as Krum [8], Multi-Krum [8], Foolsgold [17], RFA [41], Weak-DP [46], and Flame [38] in Table 1. All the defenses except RFA and Weak-DP successfully defended against the model replacement attack since RFA and Weak-DP still incorporate some malicious gradient into the global model. Our defense achieves the lowest BA on both datasets " + }, + { + "bbox": [ + 46, + 281, + 287, + 496 + ], + "type": "inline_equation", + "content": "(0.56\\%" + }, + { + "bbox": [ + 46, + 281, + 287, + 496 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 281, + 287, + 496 + ], + "type": "inline_equation", + "content": "0.00\\%)" + }, + { + "bbox": [ + 46, + 281, + 287, + 496 + ], + "type": "text", + "content": " with little impact on the MA. Under the DBA attack, Multi-Krum almost has no effect. Flame and our method also deteriorate because " + }, + { + "bbox": [ + 46, + 281, + 287, + 496 + ], + "type": "inline_equation", + "content": "40\\%" + }, + { + "bbox": [ + 46, + 281, + 287, + 496 + ], + "type": "text", + "content": " of the participants in each round are malicious, which significantly impacts the method of selecting multiple clients for aggregation. Although Krum and Foolsgold successfully defend against the DBA attack, they also negatively affect the overall performance of the global model. Our defense can reduce the BA to less than " + }, + { + "bbox": [ + 46, + 281, + 287, + 496 + ], + "type": "inline_equation", + "content": "10\\%" + }, + { + "bbox": [ + 46, + 281, + 287, + 496 + ], + "type": "text", + "content": " without affecting the MA." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "text", + "content": "PGD attack is much stealthier than the above two which Krum, RFA, and Multi-Krum fail to detect. Moreover, once they select the wrong gradient for aggregation, the global model is replaced, leading to a worse BA than FedAvg. Ours and Flame achieve the best effect of " + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "inline_equation", + "content": "0.56\\%" + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "inline_equation", + "content": "0.00\\%" + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "text", + "content": " on the two datasets, respectively. Edge-case PGD is the hardest of all since it is both stealthy and effective since it attacks with edge-case samples and projects the gradient back to the " + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "text", + "content": " norm ball. All the previous defenses have limited effect on this attack. Flame reduces the BA to " + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "inline_equation", + "content": "5.12\\%" + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "text", + "content": ". However, Flame suffers from a " + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "inline_equation", + "content": "6\\%" + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "text", + "content": " drop on MA, which is a result of adding noise. In comparison, ours achieves a much lower BA of " + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "inline_equation", + "content": "3.06\\%" + }, + { + "bbox": [ + 46, + 498, + 287, + 652 + ], + "type": "text", + "content": " with almost no impact on MA." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "On EMNIST, we also achieve better defense compared to up-to-date methods. Remarkably, we achieve " + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "inline_equation", + "content": "0.0\\%" + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": " BA under both PGD and Edge-case PGD attacks meaning that we defend entirely against these two adversaries. We also achieve similar performance without sacrificing the benign" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "type": "text", + "content": "performance against model replacement and DBA. To provide an overall comparison with previous methods, we follow [52] and design an improved version of the ranking score for each defense with respect to baseline FedAvg. We use the percentage of improvement over the baseline to score and compute it on MA/BA respectively, formally as " + }, + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "type": "inline_equation", + "content": "\\frac{K_{\\mathrm{MA/BA}} - B_{\\mathrm{MA/BA}}}{B_{\\mathrm{MA/BA}}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "type": "text", + "content": " denotes some methods and " + }, + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "type": "text", + "content": " denotes baseline. Adding up (" + }, + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "type": "inline_equation", + "content": "score_{MA} - score_{BA}" + }, + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "type": "text", + "content": ") across all attacks produces the ranking score for each defense. As shown in the last column of Table 1, we show that our method obtains the highest ranking score with almost " + }, + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "type": "inline_equation", + "content": "400\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 241 + ], + "type": "text", + "content": " better than the baseline and outperforms the second-best Flame by around 0.5. We detail the ranking score in Appendix D." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 307, + 251, + 544, + 342 + ], + "blocks": [ + { + "bbox": [ + 307, + 251, + 544, + 342 + ], + "lines": [ + { + "bbox": [ + 307, + 251, + 544, + 342 + ], + "spans": [ + { + "bbox": [ + 307, + 251, + 544, + 342 + ], + "type": "image", + "image_path": "46cedb1617698bd1140bbf480aa7ed90776f6f567961c9f86d86939eea74ee5e.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 400, + 342, + 453, + 352 + ], + "lines": [ + { + "bbox": [ + 400, + 342, + 453, + 352 + ], + "spans": [ + { + "bbox": [ + 400, + 342, + 453, + 352 + ], + "type": "text", + "content": "(a) CIFAR10" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 307, + 353, + 425, + 423 + ], + "blocks": [ + { + "bbox": [ + 307, + 353, + 425, + 423 + ], + "lines": [ + { + "bbox": [ + 307, + 353, + 425, + 423 + ], + "spans": [ + { + "bbox": [ + 307, + 353, + 425, + 423 + ], + "type": "image", + "image_path": "a07492f9acaf5c214952402ad48a1bc50c92c22b3dc9fabaa4c4c200929f9695.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 400, + 422, + 452, + 433 + ], + "lines": [ + { + "bbox": [ + 400, + 422, + 452, + 433 + ], + "spans": [ + { + "bbox": [ + 400, + 422, + 452, + 433 + ], + "type": "text", + "content": "(b) EMNIST" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 306, + 442, + 545, + 467 + ], + "lines": [ + { + "bbox": [ + 306, + 442, + 545, + 467 + ], + "spans": [ + { + "bbox": [ + 306, + 442, + 545, + 467 + ], + "type": "text", + "content": "Figure 3: MA(%) and BA(%) of various defenses under Edge-case PGD attack." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 426, + 353, + 542, + 423 + ], + "blocks": [ + { + "bbox": [ + 426, + 353, + 542, + 423 + ], + "lines": [ + { + "bbox": [ + 426, + 353, + 542, + 423 + ], + "spans": [ + { + "bbox": [ + 426, + 353, + 542, + 423 + ], + "type": "image", + "image_path": "48c103bbf3f219ac435e69e8593c8f423f95bcb8556d50b61a1341da737b82c7.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 481, + 545, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 481, + 545, + 578 + ], + "spans": [ + { + "bbox": [ + 304, + 481, + 545, + 578 + ], + "type": "text", + "content": "We show the MA and BA along the training process of the seven defenses under the Edge-case PGD attack in Figure 3. Only our method and Flame successfully resist the attack during the entire training process, and Flame also dampens the MA. The disadvantage of our approach is that the convergence speed is slightly slowed down compared to FedAvg, but it is still much better than the compared defenses, e.g., Krum and Foolsgold." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 586, + 481, + 600 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 586, + 481, + 600 + ], + "spans": [ + { + "bbox": [ + 306, + 586, + 481, + 600 + ], + "type": "text", + "content": "5.2. Impact of Training Environment" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 605, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 641 + ], + "type": "text", + "content": "In this section, we demonstrate that our defense is invariant to the different training environments, i.e. degrees of non-IID, and attack frequency." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": "Impact of Different Degrees of Non-IID. As mentioned abundantly in Section 3.3, the different data distributions contribute to one of the hardest problems in distance-based defense. Thus, to illustrate the effectiveness of our method, we demonstrate that our defense is invariant to the different degrees of non-IID. The experiment is conducted with the" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4658" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 91, + 545, + 267 + ], + "blocks": [ + { + "bbox": [ + 93, + 71, + 499, + 83 + ], + "lines": [ + { + "bbox": [ + 93, + 71, + 499, + 83 + ], + "spans": [ + { + "bbox": [ + 93, + 71, + 499, + 83 + ], + "type": "text", + "content": "Table 1: Robustness of our approach compared to the SOTA defenses for various challenging attacks." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 91, + 545, + 267 + ], + "lines": [ + { + "bbox": [ + 49, + 91, + 545, + 267 + ], + "spans": [ + { + "bbox": [ + 49, + 91, + 545, + 267 + ], + "type": "table", + "html": "
DatasetDefenseModel Replacement [4]DBA [50]PGD [47]Edge-case PGD [47]Ranking Score ↑
MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓
CIFAR10FedAvg [35]86.9564.8079.2390.4487.0414.4487.1455.100
RFA [41]86.69(+0.00)25.56(-0.61)79.6(+0.00)57.69(-0.36)87.1(+0.00)52.56(+2.64)86.47(-0.01)65.31(+0.19)-1.86
Foolsgold [17]85.71(-0.01)6.67(-0.90)77.56(-0.02)3.43(-0.96)84.92(-0.02)14.44(+0.00)85.72(-0.02)45.41(-0.18)+1.96
Krum [8]82.17(-0.05)6.11(-0.91)78.18(-0.01)6.01(-0.93)82.32(-0.05)66.67(+3.62)81.23(-0.07)59.18(+0.07)-2.04
Multi-Krum [8]86.55(+0.00)1.67(-0.97)79.33(0.00)91.39(+0.01)86.52(-0.01)17.78(+0.23)87.4(+0.00)60.2(+0.09)+0.63
Weak-DP [46]74.41(-0.14)46.11(-0.29)10.00(-0.87)0.00(-1.00)73.61(-0.15)12.78(-0.11)73.84(-0.15)53.06(-0.04)+0.12
Flame [38]80.58(-0.07)0.56(-0.99)76.78(-0.03)37.24(-0.59)81.24(-0.07)0.56(-0.96)81.41(-0.07)5.12(-0.91)+3.21
Ours86.34(-0.01)0.56(-0.99)79.61(+0.00)9.98(-0.89)86.44(-0.01)0.56(-0.96)86.86(+0.00)3.06(-0.94)+3.77
EMNISTFedAvg [35]99.5496.0097.6894.1399.5510.0099.3796.000
RFA [41]99.57(+0.00)6.00(-0.94)97.87(+0.00)1.39(-0.99)99.32(+0.00)4.00(-0.60)99.29(+0.00)97.00(+0.01)+2.51
Foolsgold [17]96.42(-0.03)98.00(+0.02)97.24(+0.00)0.64(-0.99)99.07(+0.00)94.00(+8.40)99.13(+0.00)98.00(+0.02)-7.49
Krum [8]99.22(+0.00)0.00(-1.00)97.7(+0.00)0.56(-0.99)99.12(+0.00)1.00(-0.90)99.14(+0.00)12.00(-0.88)+3.76
Multi-Krum [8]99.58(+0.00)0.00(-1.00)97.85(+0.00)47.43(-0.50)99.54(+0.00)0.00(-1.00)99.57(+0.00)84.00(-0.13)+2.63
Weak-DP [46]99.37(+0.00)86.00(-0.10)10.00(-0.90)0.00(-1.00)99.41(+0.00)14.00(+0.40)99.39(+0.00)89.00(-0.07)-0.12
Flame [38]99.39(+0.00)0.00(-1.00)97.12(-0.01)17.38(-0.82)99.39(+0.00)0.00(-1.00)99.44(+0.00)13.00(-0.86)+3.67
Ours99.53(+0.00)0.00(-1.00)97.39(+0.00)4.23(-0.96)99.54(+0.00)0.00(-1.00)99.58(+0.00)0.00(-1.00)+3.95
", + "image_path": "ad0e5cbfa46418534481b394d84540d57faf2d57250e45b97714d46b6f3bad17.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 287, + 287, + 322 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 287, + 287, + 322 + ], + "spans": [ + { + "bbox": [ + 46, + 287, + 287, + 322 + ], + "type": "text", + "content": "Edge-case PGD attack. Figure 4 shows that the BA remains low in all cases. Our method only slightly impacts the MA with " + }, + { + "bbox": [ + 46, + 287, + 287, + 322 + ], + "type": "inline_equation", + "content": "a = 0.2" + }, + { + "bbox": [ + 46, + 287, + 287, + 322 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 50, + 331, + 286, + 420 + ], + "blocks": [ + { + "bbox": [ + 50, + 331, + 286, + 420 + ], + "lines": [ + { + "bbox": [ + 50, + 331, + 286, + 420 + ], + "spans": [ + { + "bbox": [ + 50, + 331, + 286, + 420 + ], + "type": "image", + "image_path": "de1f4497a763e73d6cf338cd7350965252d2a4ff1907c6eedfc261f10d60c6c5.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 429, + 287, + 464 + ], + "lines": [ + { + "bbox": [ + 46, + 429, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 46, + 429, + 287, + 464 + ], + "type": "text", + "content": "Figure 4: Accuracy " + }, + { + "bbox": [ + 46, + 429, + 287, + 464 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 46, + 429, + 287, + 464 + ], + "type": "text", + "content": " of our defense under Edge-case PGD attack on different degrees of non-IID, which is indicated by the " + }, + { + "bbox": [ + 46, + 429, + 287, + 464 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 46, + 429, + 287, + 464 + ], + "type": "text", + "content": " parameter of the Dirichlet distribution." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 50, + 487, + 286, + 582 + ], + "blocks": [ + { + "bbox": [ + 50, + 487, + 286, + 582 + ], + "lines": [ + { + "bbox": [ + 50, + 487, + 286, + 582 + ], + "spans": [ + { + "bbox": [ + 50, + 487, + 286, + 582 + ], + "type": "image", + "image_path": "0f41c99d0f335621bd4481299e749000ccbb20a7480180f198bf7affdc6fe0b0.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 590, + 287, + 615 + ], + "lines": [ + { + "bbox": [ + 46, + 590, + 287, + 615 + ], + "spans": [ + { + "bbox": [ + 46, + 590, + 287, + 615 + ], + "type": "text", + "content": "Figure 5: BA(\\%) of various defenses under the backdoor attack versus percentage of attackers among all clients." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 629, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 288, + 713 + ], + "type": "text", + "content": "Impact of Attacker Percentage. We show the BA performance with different ratios of attackers under the backdoor attack in Figure 5, where we compare ours with other methods. As a result of our rigorous experiment settings, it usually selects more than " + }, + { + "bbox": [ + 46, + 629, + 288, + 713 + ], + "type": "inline_equation", + "content": "K / 2" + }, + { + "bbox": [ + 46, + 629, + 288, + 713 + ], + "type": "text", + "content": " adversarial models in each round, so all defenses, especially the clustering-based methods, fail to defend when " + }, + { + "bbox": [ + 46, + 629, + 288, + 713 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 46, + 629, + 288, + 713 + ], + "type": "text", + "content": " of clients are compromised." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 287, + 545, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 287, + 545, + 346 + ], + "spans": [ + { + "bbox": [ + 304, + 287, + 545, + 346 + ], + "type": "text", + "content": "For EMNIST, BA rises steeply as the simplicity of the task, achieving high accuracy with few parameters injected. Nonetheless, our method performs significantly superior to other methods, and exhibits invariance to the number of attackers encountered." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 308, + 356, + 430, + 442 + ], + "blocks": [ + { + "bbox": [ + 308, + 356, + 430, + 442 + ], + "lines": [ + { + "bbox": [ + 308, + 356, + 430, + 442 + ], + "spans": [ + { + "bbox": [ + 308, + 356, + 430, + 442 + ], + "type": "image", + "image_path": "0d459e02e6dbeb0c0f0521ee463bf51c6e7148b6a0f593bc4e09a9568b76d4ce.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 453, + 545, + 476 + ], + "lines": [ + { + "bbox": [ + 305, + 453, + 545, + 476 + ], + "spans": [ + { + "bbox": [ + 305, + 453, + 545, + 476 + ], + "type": "text", + "content": "Figure 6: Accuracy " + }, + { + "bbox": [ + 305, + 453, + 545, + 476 + ], + "type": "inline_equation", + "content": "(\\%)" + }, + { + "bbox": [ + 305, + 453, + 545, + 476 + ], + "type": "text", + "content": " of our defense under Edge-case PGD attack versus attack interval." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 432, + 356, + 544, + 444 + ], + "blocks": [ + { + "bbox": [ + 432, + 356, + 544, + 444 + ], + "lines": [ + { + "bbox": [ + 432, + 356, + 544, + 444 + ], + "spans": [ + { + "bbox": [ + 432, + 356, + 544, + 444 + ], + "type": "image", + "image_path": "a2d512eb6d236303b9c3c20c8dcc7719b6681b0c051003bd08751e5516e5ed88.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 493, + 545, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 493, + 545, + 588 + ], + "spans": [ + { + "bbox": [ + 304, + 493, + 545, + 588 + ], + "type": "text", + "content": "Impact of Attack Frequency. The frequency of the attack affects the strength and persistence of the attack. We demonstrate that our defense is invariant to the frequency of attack in Figure 6 where we show that our defense achieves consistently low BA under all attack intervals. Since the other defenses cannot resist the edge-case PGD with the minimum frequency(attack interval of 10), we do not plot their results." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 596, + 498, + 608 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 596, + 498, + 608 + ], + "spans": [ + { + "bbox": [ + 306, + 596, + 498, + 608 + ], + "type": "text", + "content": "5.3. Generalization to Different Datasets" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 615, + 545, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 615, + 545, + 662 + ], + "spans": [ + { + "bbox": [ + 304, + 615, + 545, + 662 + ], + "type": "text", + "content": "We experiment on the LOAN and Sentiment140, as shown in Table 2. Our method achieves high MA and low BA on both datasets, proving the adaptivity to different models and tasks." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 671, + 400, + 684 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 671, + 400, + 684 + ], + "spans": [ + { + "bbox": [ + 306, + 671, + 400, + 684 + ], + "type": "text", + "content": "5.4. Ablation Study" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "The above experiments present the remarkable defense ability of our approach. In this section, we conduct an abla" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4659" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 63, + 103, + 271, + 159 + ], + "blocks": [ + { + "bbox": [ + 47, + 71, + 287, + 95 + ], + "lines": [ + { + "bbox": [ + 47, + 71, + 287, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 287, + 95 + ], + "type": "text", + "content": "Table 2: Effectiveness of our method against backdoor attack on other types of datasets." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 63, + 103, + 271, + 159 + ], + "lines": [ + { + "bbox": [ + 63, + 103, + 271, + 159 + ], + "spans": [ + { + "bbox": [ + 63, + 103, + 271, + 159 + ], + "type": "table", + "html": "
DefenseCINIC10LOANSentiment140
MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓
FedAvg80.0236.2289.0561.3682.5989.17
Ours76.244.5988.52081.675.83
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DefensesModel ReplacementPGDEdge-case PGD
MA/BAMA/BAMA/BA
Man83.86/0.5683.74/25.5685.3/64.80
Eul86.24/0.5685.52/17.7887.12/54.08
Cos84.22/2.2283.84/30.0085.38/66.84
Man+Eul84.09/1.1184.17/28.6384.3/67.35
Man+Cosine85.74/1.6785.16/23.6885.86/6.63
Cosine+Eul86.31/0.5685.44/16.1185.14/63.78
Man+Cosine+Eul86.34/0.5686.44/0.5686.86/3.06
", + "image_path": "f5d8a2cb8333b777c05227e83999840c72ef61605002483bf9a3e8c2112b0b04.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 351, + 259, + 363 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 351, + 259, + 363 + ], + "spans": [ + { + "bbox": [ + 47, + 351, + 259, + 363 + ], + "type": "text", + "content": "tion study to understand the role of each component." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 365, + 287, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 287, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 287, + 568 + ], + "type": "text", + "content": "Multi-metrics Identifies the Stealthiest Attacks. We first conduct an ablation study on the multi-metrics, as shown in Table 3. We observe the following: 1. All three metrics perform poorly individually. 2. Manhattan distance improves the defense ability when combined with the other metrics. 3. Cosine similarity combined with Manhattan distance provides the best defense against the Edge-case PGD. Given the above observations, we conclude that multi-metrics adaptively defends against universal backdoors. The introduced Manhattan metric contributes to the defense against the stealthiest attack (e.g., Edge-case PGD). To further demonstrate the claim that a single metric cannot identify malicious gradients of diverse characteristics, we show the dominance of each metric under different attacks. We take the metric as the dominant one with the most considerable contribution to this round's scoring and plot their frequency in Figure 7." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": "Firstly, we show that Manhattan distance contributes to the defense of PGD and Edge-case PGD, complementing the Cosine similarity justifying the above observations 2 and 3. We also notice that Euclidean is never dominant under PGD and Edge-case PGD, consistent with the analysis that these two attacks bypass " + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": " norm through projection back to " + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": " norm ball. We also notice that Manhattan distance plays no role under the model replacement attack, consistent with the above experiment that Manhattan does not affect the final BA. It is because model replacement attack scales the gradient of the malicious client, making it susceptible to Cosine and Euclidean distances. Finally, we" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 109 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 109 + ], + "type": "text", + "content": "conclude that better defense can be achieved if multiple instead of single metrics are utilized since different metrics dominantly detect different malicious gradients." + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 329, + 117, + 523, + 214 + ], + "blocks": [ + { + "bbox": [ + 329, + 117, + 523, + 214 + ], + "lines": [ + { + "bbox": [ + 329, + 117, + 523, + 214 + ], + "spans": [ + { + "bbox": [ + 329, + 117, + 523, + 214 + ], + "type": "image", + "image_path": "afce9621a40eaaf1db6b86a89673f2c95d51a9af0c7a2048a225c0d9213499c4.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 224, + 545, + 248 + ], + "lines": [ + { + "bbox": [ + 304, + 224, + 545, + 248 + ], + "spans": [ + { + "bbox": [ + 304, + 224, + 545, + 248 + ], + "type": "text", + "content": "Figure 7: Frequency of dominance of each metric under different attacks on CIFAR10." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 259, + 545, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 259, + 545, + 392 + ], + "spans": [ + { + "bbox": [ + 304, + 259, + 545, + 392 + ], + "type": "text", + "content": "Dynamic Weighting through Whitening Process Adaptively Adjust the Scoring. We illustrate the effectiveness of our whitening process discussed in Section 3.3 in Table 4 by comparing it with the standard max normalization. BA increases by a large margin if only max normalization is applied, which illustrates that the whitening process plays an essential role in identifying the malicious under non-IID distributions. Moreover, we notice the MA increases as we apply the whitening process, which shows that it can flexibly identify the benign but different gradients (due to non-IID) and the true malicious ones." + } + ] + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 308, + 433, + 550, + 489 + ], + "blocks": [ + { + "bbox": [ + 304, + 399, + 545, + 424 + ], + "lines": [ + { + "bbox": [ + 304, + 399, + 545, + 424 + ], + "spans": [ + { + "bbox": [ + 304, + 399, + 545, + 424 + ], + "type": "text", + "content": "Table 4: Effectiveness of different weighting methods on defense against various attacks on CIFAR10." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 433, + 550, + 489 + ], + "lines": [ + { + "bbox": [ + 308, + 433, + 550, + 489 + ], + "spans": [ + { + "bbox": [ + 308, + 433, + 550, + 489 + ], + "type": "table", + "html": "
WeightingModel ReplacementPGDEdge-case PGD
MA ↑BA ↓MA ↑BA ↓MA ↑BA ↓
Max Norm83.860.5683.7425.5684.0862.24
Whitening86.340.5686.440.5686.863.06
", + "image_path": "415937bd60db15283206cd1097733922e09589aa2468329ae525d5eff46bb84f.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 508, + 378, + 521 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 508, + 378, + 521 + ], + "spans": [ + { + "bbox": [ + 306, + 508, + 378, + 521 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 529, + 545, + 648 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 529, + 545, + 648 + ], + "spans": [ + { + "bbox": [ + 304, + 529, + 545, + 648 + ], + "type": "text", + "content": "Existing defense methods fail to handle backdoor attacks with malicious updates similar to benign ones, especially when benign clients possess data of non-independent and iden tical distribution. In this paper, we propose a novel adaptive multi-metrics defense method by leveraging multiple metrics with dynamic weighting to defend against backdoor attacks in FL, withstanding a wide range of stealthy and elaborate attacks. We conduct exhaustive experiments to evaluate our approach proving its effectiveness over a wide range of attack settings." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 658, + 408, + 671 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 658, + 408, + 671 + ], + "spans": [ + { + "bbox": [ + 306, + 658, + 408, + 671 + ], + "type": "text", + "content": "Acknowledgements" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "type": "text", + "content": "This work is supported by the Key-Area Research and Development Program of Guangdong Province under Grant 2019B010137001." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4660" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Charu C Aggarwal, Alexander Hinneburg, and Daniel A Keim. 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In Proceedings of the IEEE/CVF international conference on computer vision, pages 4912-4921, 2021." + } + ] + } + ], + "index": 27 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "4662" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-Modal Continual Test-Time Adaptation for 3D Semantic Segmentation/7a008f21-91bc-4a63-ae49-b60252dec431_content_list.json b/2023/Multi-Modal Continual Test-Time Adaptation for 3D Semantic Segmentation/7a008f21-91bc-4a63-ae49-b60252dec431_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..983f6007945961af284880e85ca8668fecc35b36 --- /dev/null +++ b/2023/Multi-Modal Continual Test-Time Adaptation for 3D Semantic Segmentation/7a008f21-91bc-4a63-ae49-b60252dec431_content_list.json @@ -0,0 +1,1653 @@ +[ + { + "type": "text", + "text": "Multi-Modal Continual Test-Time Adaptation for 3D Semantic Segmentation", + "text_level": 1, + "bbox": [ + 96, + 130, + 872, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Haozhi Cao $^{1*}$ Yuecong Xu $^{2*}$ Jianfei Yang $^{1\\dagger}$ Pengyu Yin $^{1}$ Shenghai Yuan $^{1}$ Lihua Xie $^{1}$ $^{1}$ Nanyang Technological University $^{2}$ Institute for Infocomm Research, A*STAR, Singapore \n{haozhi002, xuyu0014, yang0478, pengyu001, syuan003}@e.ntu.edu.sg elhxie@ntu.edu.sg", + "bbox": [ + 109, + 179, + 854, + 234 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Continual Test-Time Adaptation (CTTA) generalizes conventional Test-Time Adaptation (TTA) by assuming that the target domain is dynamic over time rather than stationary. In this paper, we explore Multi-Modal Continua! tual Test-Time Adaptation (MM-CTTA) as a new extension of CTTA for 3D semantic segmentation. The key to MMCTTA is to adaptively attend to the reliable modality while avoiding catastrophic forgetting during continual domain shifts, which is out of the capability of previous TTA or CTTA methods. To fulfill this gap, we propose an MM-CTTA method called Continua! Cross-Modal Adaptive Clustering (CoMAC) that addresses this task from two perspectives. On one hand, we propose an adaptive dual-stage mechanism to generate reliable cross-modal predictions by attending to the reliable modality based on the class-wise featurecentroid distance in the latent space. On the other hand, to perform test-time adaptation without catastrophic forgetting, we design class-wise momentum queues that capture confident target features for adaptation while stochastically restoring pseudo-source features to revisit source knowledge. We further introduce two new benchmarks to facilitate the exploration of MM-CTTA in the future. Our experimental results show that our method achieves state-of-the-art performance on both benchmarks. Visit our project website at https://sites.google.com/view/mmcotta.", + "bbox": [ + 76, + 300, + 473, + 680 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 705, + 209, + 720 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Test-Time Adaptation (TTA) proposes a realistic domain adaptation scenario, which adapts pre-trained models to the target domain during the testing process. Unlike previous Unsupervised Domain Adaptation (UDA) [17, 45, 52, 47], TTA performs adaptation online without accessing the data from the source domain. Typical TTA [40, 35, 36] methods assume a stationary target domain, while real-world scenarios are dynamic over time. To fulfill this gap, a previous work [42] proposes a general extension of TTA named Con-", + "bbox": [ + 75, + 729, + 468, + 867 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/1a6a931f2d306fe37710fa4c6f83d16348abd78073280614f500b3629bd4a2c9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 506, + 272, + 890, + 335 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/aaada682dd055f130be65cba221c5dc7fd1e823b07d039a46162d76e8148c56e.jpg", + "image_caption": [ + "Figure 1. Illustration of how continual domain shifts affect multimodal segmentation and our method. Unlike the source domain where predictions from both modalities are reliable, the reliability of each modality varies in MM-CTTA due to different domain shifts. CoMAC tackles MM-CTTA by attending to the reliable modality $(\\checkmark)$ rather than the noisy one $(\\chi)$ . Meanwhile, source knowledge is stochastically revisited to avoid catastrophic forgetting. Figure best viewed in color and zoomed in." + ], + "image_footnote": [], + "bbox": [ + 506, + 337, + 890, + 472 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "tual Test-Time Adaptation (CTTA) which assumes that the target domain is continually changing rather than static. Compared to TTA, CTTA is more challenging since the performance is easily affected by error accumulation [6] and catastrophic forgetting [27] during the continual adaptation.", + "bbox": [ + 496, + 625, + 890, + 700 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "For 3D semantic segmentation, multi-modal sensors are frequently leveraged in different tasks, such as scene understanding [4, 28] and semantic map construction [29, 43]. For some specific applications like semantic-based localization [8] and autonomous driving [46, 44], multi-modal information is the key to robust performance under adverse conditions. However, their collaboration has been proven to be sensitive toward domain drifts [1, 35]. In real-world scenarios, such collaboration deterioration could be more severe considering that the target domain is continually changing as in CTTA (e.g., the operating environments of 24/7 AGVs are continually changing due to altering weather or illumination conditions). Hence, it is essential for multi-", + "bbox": [ + 496, + 704, + 892, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Equal contributions. †Corresponding author.", + "bbox": [ + 93, + 875, + 220, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "18809", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "modal networks to adapt to the dynamic target domain in an online manner. In this work, we aim to study MultiModal Continual Test-Time Adaptation (MM-CTTA) for 3D semantic segmentation, where networks are continually adapted to a changing target domain taking 3D point clouds and 2D images as input without accessing the source data.", + "bbox": [ + 75, + 90, + 468, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Intuitively, one can address MM-CTTA by utilizing CTTA [30, 42] or TTA [3, 38] methods on 2D and 3D networks separately. However, this simple extension can not achieve satisfactory performance since it cannot correctly attend to the reliable modality for adaptation when others suffer from severe domain shifts. Take Fig. 1 as an example: predictions from the 2D image are more accurate at the beginning of the target domain, while 2D results become unreliable and 3D predictions prevail as the illumination level significantly changes over time. Although previous CTTA or TTA methods have attempted to mitigate this intra-modal prediction noise by augmentations [42] or entropy minimization [40, 30], the domain drift in Fig. 1 is too severe to be effectively rectified by image input itself, leading to inevitable error accumulation. Previous works have proposed different cross-modal fusion methods to mitigate the effect of the noisy modality during adaptation, such as cross-modal consistency [18] for UDA or pseudo-label fusion based on student-teacher consistency [35] for TTA. However, their methods rely on the premise that the target domain is static, and therefore suffer from catastrophic forgetting in MM-CTTA, leading to degenerated results.", + "bbox": [ + 75, + 186, + 470, + 518 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "For MM-CTTA, an ideal solution is to suppress the contribution from the noisy modality and attend more to the reliable one in an online manner. Typically, the reliability of prediction can be estimated based on its corresponding feature location in the latent space. A prediction with features close to the centroid is more likely to be reliable, suffering less from the domain shift and vice versa. On the other hand, to ensure the validity of centroid-based reliability estimation, class-wise centroids should actively adapt to the continually changing target domain while stochastically revisiting the source knowledge to avoid catastrophic forgetting. To this end, we propose an MM-CTTA method called Continual Cross-Modal Adaptive Clustering (CoMAC) for 3D semantic segmentation. CoMAC consists of three main modules: (i) Intra-Modal Prediction Aggregation (iMPA), (ii) Inter-Modal Pseudo-Label Fusion (xMPF), and (iii) Class-Wise Momentum Queues (CMQs). On one hand, the proposed iMPA and xMPF are utilized to suppress prediction noise based on the centroid-based reliability estimation from intra-modal and inter-modal perspectives, respectively. On the other hand, CMQs are designed to actively adapt class-wise centroids for iMPA and xMPF while avoiding catastrophic forgetting. Additionally, a class-wise contrastive loss is introduced to regularize the extracted features from drifting too far from centroids.", + "bbox": [ + 75, + 523, + 468, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, our main contributions are three-fold. (i) We explore a new task MM-CTTA where multi-modal input is utilized to perform continual test-time adaptation for 3D semantic segmentation and propose an effective method named CoMAC to leverage multi-modal information for MM-CTTA. (ii) We propose iMPA and xMPF to generate accurate cross-modal pseudo-labels by attending to a reliable modality. CMQs are introduced to actively adapt to the target domain without catastrophic forgetting. (iii) We introduce two 3D semantic segmentation benchmarks to facilitate the future exploration of MM-CTTA. Extensive experiments show that our method achieves state-of-the-art performance, outperforming previous methods significantly by $6.9\\%$ on the challenging benchmark.", + "bbox": [ + 496, + 90, + 890, + 303 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works", + "text_level": 1, + "bbox": [ + 500, + 316, + 648, + 333 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Test-Time Adaptation Describing a more realistic adaptation scenario, Test-Time Adaptation (TTA) is receiving more and more attention. Different from previous Unsupervised Domain Adaptation (UDA), TTA forbids access to raw source data and adapts the source pre-trained model during test time. As one of the primary works, TENT [40] highlights the fully test-time setting and proposes to update the batch normalization layers by entropy minimization. The following works mainly address TTA by aligning batch normalization statistics [30, 23, 51], self-training with pseudo labeling [13, 41], feature alignment [25], or augmentation invariance [50, 21]. The aforementioned TTA methods strictly follow the one-pass protocol as mentioned in [36], where networks immediately infer each sample in an online manner and forbid multiple training epochs. On the other hand, some previous works [22, 10, 7, 48] follow the multi-pass protocol by adapting the model for multiple epochs in an offline manner. As one of the primary works, Source Hypothesis Transfer (SHOT) [22] proposes to update only the encoder parameters and align source and target representation by entropy minimization and pseudolabeling. While most existing TTA methods are proposed for image classification, some recent works [10, 20, 26] aim to explore TTA for image semantic segmentation. Specifically, [10] proposes to minimize the prediction entropy while maximizing its robustness toward feature noise. [20] divides the TTA problem into source domain generalization and target domain adaptation. [26] proposes a dual attention distillation method to transfer contextual knowledge and patch-level pseudo labels for self-supervised learning.", + "bbox": [ + 496, + 340, + 890, + 792 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Continual Test-Time Adaptation The definition of Continual Test-Time Adaptation (CTTA) is first proposed in CoTTA[42], which aims to adapt the model to continually changing target domains in an online manner without any source data. Specifically, CoTTA proposes to use the moving teacher model and augmentation-average predictions for noise suppression and the model stochastic", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "18810", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "restoration to avoid catastrophic forgetting. Following the scheme of CoTTA, some recent works [11, 12, 30] have addressed CTTA from different perspectives. Specifically, [12] leverages the temporal correlations of streamed input by reservoir sampling and instance-aware batch normalization. [11] proposes domain-specific prompts and domain-agnostic prompts to preserve domain-specific and domain-shared knowledge, respectively. EATA [30] performs adaptation on non-redundant samples for an efficient update.", + "bbox": [ + 75, + 90, + 472, + 226 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Multi-Modal Adaptation for Segmentation Thanks to the emerging multi-modal datasets [2, 5, 37, 33, 49], recent works start to explore how to leverage multi-modal information between 2D images and 3D point clouds to perform domain adaptation under different settings. xMUDA [18] proposes the first Multi-Modal Unsupervised Domain Adaptation (MM-UDA) method for 3D semantic segmentation. Specifically, it leverages the cross-modal prediction consistency by minimizing the prediction discrepancy from additional classifiers. Following the scheme of cross-modal learning, DsCML [31] designs a deformable mapping between pixel-point correlation for MM-UDA while [24] introduces adversarial training to mitigate domain discrepancy. In addition to UDA settings, [35] proposes the first multi-modal test-time adaptation for semantic segmentation which generates intra-modal and inter-modal pseudo labels by attending to the one with more consistent predictions across student and teacher models.", + "bbox": [ + 75, + 227, + 472, + 498 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this work, we propose MM-CTTA as a new extension of CTTA with a specific method CoMAC. While our proposed dual-stage modules (i.e., iMPA and xMPA) and CMQs share some similar merit with previous TTA methods [35, 36], our method is explicitly designed for MM-CTTA. Unlike previous work [35] measuring prediction reliability by teacher-student consistency, our reliability measurement relies on the feature-centroid distance to encourage feature clustering around the adapting centroids. Different from [36] utilizing queues to measure target distribution, the objective of our CMQs is to actively update class-wise centroids to ensure the validity of iMPA and xMPA while avoiding catastrophic forgetting.", + "bbox": [ + 75, + 500, + 472, + 696 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed Method", + "text_level": 1, + "bbox": [ + 76, + 707, + 250, + 724 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Problem definition and notations. At timestamp $t$ , the 2D image $x_{\\mathcal{T},t}^{2\\mathrm{D}} \\in \\mathbb{R}^{H \\times W \\times 3}$ and the 3D point cloud $x_{\\mathcal{T},t}^{3\\mathrm{D}} \\in \\mathbb{R}^{N \\times 4}$ are observed in the target domain $\\mathcal{T}$ , where $N$ denotes the number of 3D points located in the camera FOV. Modal-specific pre-trained networks $\\phi_{\\theta, t}^{m}(\\cdot) = f_{t}^{m}(g_{t}^{m}(\\cdot)), m \\in \\{2\\mathrm{D}, 3\\mathrm{D}\\}$ consisting of the feature extractor $f_{t}^{m}$ and the classifier $g_{t}^{m}$ are used to predict the semantic labels for each point. Inspired by the fact that moving average models can provide more stable predictions [39], we utilize a fast student network $\\phi_{\\theta}^{m}(\\cdot) = f_{\\theta}^{m}(g_{\\theta}^{m}(\\cdot))$ and a slow teacher network $\\phi_{\\theta'}^{m}(\\cdot) = f_{\\theta'}^{m}(g_{\\theta'}^{m}(\\cdot))$ for each modal-", + "bbox": [ + 75, + 732, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ity similar to previous works [35, 42]. Given $x_{\\mathcal{T},t}^{m}$ as input, the features extracted by $f_{t}^{m}$ is denoted as $z_{\\mathcal{T},t}^{m} \\in \\mathcal{R}^{N \\times F^{m}}$ where $F^{m}$ denotes the channel number. Here we adopt the same projection protocol of previous works [18, 35] for cross-modal alignment, which projects features from the 2D branch back to 3D points, resulting in the 2D feature $z_{\\mathcal{T},t}^{2\\mathrm{D}}$ of shape $N \\times F^{2\\mathrm{D}}$ . By default, the subscript of the target domain $\\mathcal{T}$ and the timestamp $t$ are omitted for clarity. Given the multi-modal input $x_{\\mathcal{T},t}^{2\\mathrm{D}}, x_{\\mathcal{T},t}^{3\\mathrm{D}}$ , the goal of MM-CTTA is to output reliable cross-modal predictions by continuously adapting to the changing target domain. In this work, we interpret the core of MM-CTTA as two-fold: (i) attending to the reliable modality for noisy suppression, and (ii) revisiting source knowledge to prevent catastrophic forgetting.", + "bbox": [ + 496, + 90, + 890, + 306 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To this end, we propose Continual Cross-Modal Adaptive Clustering (CoMAC) to tackle MM-CTTA from the aforementioned perspectives. Specifically, as shown in Fig. 2, the class-wise centroids are initialized from the source domain and pseudo-source features are randomly sampled around the centroids as source knowledge (Sec. 3.1). Given the raw and augmentation-average predictions from the teacher models as input, Intra-Modal Prediction Aggregation (iMPA) generates stable intra-modal predictions as their weighted sum based on their feature distance to the class-wise centroids (Sec. 3.2). Inter-Modal Pseudo-Label Fusion (xMPF) then combines the intramodal predictions from each modality based on their reliability and output cross-modal pseudo-labels as supervision signals for student networks (Sec. 3.3). Given raw samples as input, confident target features from student networks are utilized to update Class-Wise Momentum Queues (CMQs), while pseudo-source features are stochastically restored to avoid catastrophic forgetting (Sec. 3.4).", + "bbox": [ + 496, + 306, + 892, + 594 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Source Models and Class-Wise Centroids", + "text_level": 1, + "bbox": [ + 498, + 603, + 852, + 618 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To effectively avoid catastrophic forgetting and inspired by previous TTA methods [9, 36] which preserve trivial source domain information, we utilize pseudo-source features sampled around source offline feature centroids as source representatives. The source offline centroids and pseudo-source features are treated as the prior knowledge from the source domain, which plays an essential role in preventing catastrophic forgetting detailed in Sec. 3.4. Specifically, given a specific semantic category $k$ , the corresponding source offline centroid is modeled as Gaussian distribution, and pseudo-source features are denoted as:", + "bbox": [ + 496, + 626, + 890, + 792 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nC _ {s r c} ^ {m, k} = \\mathcal {N} \\left(\\mu_ {s r c} ^ {m, k}, \\sigma_ {s r c} ^ {m, k}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 563, + 801, + 890, + 820 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {Z} _ {s r c} ^ {m, k} = \\left\\{z _ {s r c, i} ^ {m, k} \\sim C _ {s r c} ^ {m, k} \\mid i \\in [ 1, N _ {q} ] \\right\\}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 565, + 823, + 890, + 842 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $N_{q}$ is the number of pseudo-source features. $\\mu_{src}^{m,k}$ and $\\sigma_{src}^{m,k}$ denote the mean and standard deviation of normalized source features from the category $k$ , respectively.", + "bbox": [ + 500, + 854, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "18811", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/4729166c77b5ad3bfb7e63261500f887e0a634172cbf74decb581f35c039cc56.jpg", + "image_caption": [ + "Figure 2. The main structure of our proposed method. From the source domain, we preserve the source centroids and the pre-trained model for each modality as the initialization of the class-wise centroids and all the models in the target domain, respectively. To generate reliable intra-modal predictions, Intra-Modal Prediction Aggregation (iMPA) attends to the reliable prediction whose feature shares a closer distance with the class-wise centroids in an intra-modal manner. Inter-Modal Pseudo-Label Fusion (xMPF) then fuses the intramodal predictions by estimating the reliability of predictions from each modality for noise suppression. Class-Wise Momentum Queues (CMQs) are designed to achieve a good balance between target domain adaptation and source knowledge preservation." + ], + "image_footnote": [], + "bbox": [ + 98, + 89, + 867, + 362 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here we use the features generated by the pre-trained extractor $g_0^m(\\cdot)$ for the centroid construction.", + "bbox": [ + 75, + 473, + 468, + 505 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Intra-Modal Prediction Aggregation", + "text_level": 1, + "bbox": [ + 76, + 511, + 392, + 527 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In MM-CTTA, the prediction from each modality could be unreliable due to continual domain shifts, causing severe noise to the multi-modal fusion. To mitigate the intramodal noise, iMPA aims to generate reliable intra-modal predictions for each modality. Although previous methods [42, 38] regard the augmentation-average prediction as a more stable alternative, we argue that its superiority is not certain since test-time augmentations may introduce inductive bias to the prediction [34] (e.g., resizing image as in [42] could cause ambiguity to small-scale classes). Unlike the previous work [42], we propose an adaptive mechanism to fuse the raw and the augmentation-average prediction as the weighted sum based on their feature distance between class-wise centroids. Given the input sample $x^{m}$ and its augmented variants $\\{\\widetilde{x}_i^m\\mid i\\in [1,N_{aug}^m]\\}$ , the features and predictions are extracted by the teacher model $\\phi_{\\theta^{\\prime}}^{m}$ as:", + "bbox": [ + 75, + 534, + 473, + 777 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\np \\left(x ^ {m}\\right) = f _ {\\theta^ {\\prime}} ^ {m} \\left(g _ {\\theta^ {\\prime}} ^ {m} \\left(x ^ {m}\\right)\\right) = f _ {\\theta^ {\\prime}} ^ {m} \\left(z ^ {m}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 782, + 468, + 800 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\widetilde {p} \\left(x ^ {m}\\right) = \\frac {1}{N _ {a u g} ^ {m}} \\sum_ {i = 1} ^ {N _ {a u g} ^ {m}} f _ {\\theta^ {\\prime}} ^ {m} \\left(g _ {\\theta^ {\\prime}} ^ {m} \\left(\\widetilde {x} _ {i} ^ {m}\\right)\\right), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 804, + 468, + 848 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $p(x^{m})$ and $\\widetilde{p} (x^m)$ represent the raw and the augmentation-average prediction, respectively. Both predictions are of shape $N\\times N_{c}$ , where $N_{C}$ is the number", + "bbox": [ + 75, + 854, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "of classes and $N_{aug}^{m}$ denotes the number of augmentations. The normalized augmentation-average feature is computed as $\\widetilde{z}^m = \\sum_{i=1}^{N_{aug}^m} g^m(\\widetilde{x}_i^m) / (\\|g^m(\\widetilde{x}_i^m)\\| \\cdot N_{aug}^m)$ . Subsequently, the weights for predictions $p(x^m), \\widetilde{p}(x^m)$ are computed based on their corresponding feature distance to the class-wise centroid in a point-wise manner, so that each point of the intra-modal prediction $\\hat{p}(x^m)$ can attend more to the confident prediction located closer to the cluster in the latent space. Taking a point $(j)$ as an example, given its predictions $p_{(j)}(x^m), \\widetilde{p}_{(j)}(x^m)$ and features $z_{(j)}^m, \\widetilde{z}_{(j)}^m$ :", + "bbox": [ + 496, + 473, + 890, + 632 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nw _ {(j)} ^ {m} = \\frac {\\exp \\left(\\left\\langle \\mu^ {m , k} , z _ {(j)} ^ {m} \\right\\rangle\\right)}{\\sum_ {i \\in N _ {c}} \\exp \\left(\\left\\langle \\mu^ {m , i} , z _ {(j)} ^ {m} \\right\\rangle\\right)}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 583, + 641, + 890, + 680 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\widetilde {w} _ {(j)} ^ {m} = \\frac {\\exp \\left(\\left\\langle \\mu^ {m , \\widetilde {k}} , \\widetilde {z} _ {(j)} ^ {m} \\right\\rangle\\right)}{\\sum_ {i \\in N _ {c}} \\exp \\left(\\left\\langle \\mu^ {m , i} , \\widetilde {z} _ {(j)} ^ {m} \\right\\rangle\\right)}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 584, + 683, + 890, + 724 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {p} _ {(j)} \\left(x ^ {m}\\right) = \\frac {w _ {(j)} ^ {m} p _ {(j)} \\left(x ^ {m}\\right) + \\widetilde {w} _ {(j)} ^ {m} \\widetilde {p} _ {(j)} \\left(x ^ {m}\\right)}{w _ {(j)} ^ {m} + \\widetilde {w} _ {(j)} ^ {m}}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 550, + 727, + 890, + 767 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $w_{(j)}^m, \\widetilde{w}_{(j)}^m$ are termed as the raw weight and augmentation-average weight, respectively. $k, \\widetilde{k}$ are the largest element locations of $p_{(j)}(x^m), \\widetilde{p}_{(j)}(x^m)$ . $\\mu^{m,k}$ denotes the mean of class $k$ centroid, which is actively updated as shown in Sec. 3.4. $\\langle a,b\\rangle$ represents the inner product of vectors $a$ and $b$ . Our empirical results show that this adaptive fusion between the raw and augmentation-average predictions results in more stable intra-modal predictions.", + "bbox": [ + 496, + 773, + 893, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "18812", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Inter-Modal Pseudo-Label Fusion", + "text_level": 1, + "bbox": [ + 76, + 90, + 374, + 104 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Given the output of iMPA, the goal of xMPF is to generate pseudo-labels by estimating their reliability in a cross-modal manner. Since domain shifts can affect the reliability of each modality variously (e.g., images in day and night), the cross-modal pseudo-label should adaptively attend to the reliable modality for noise suppression. Motivated by this idea, the proposed xMPF generates the cross-modal pseudo-labels as the weighted sum of intra-modal predictions from iMPA. Specifically, taking point $(j)$ as an example, the inter-modal weight $\\hat{w}_{(j)}^{m}$ is computed as the summation of both weights if their corresponding predictions indicate the same class, or the maximum one otherwise. This can be viewed as an implicit way to encourage point-wise prediction consistency for each modality. Formally, the inter-modal weight $\\hat{w}_{(j)}^{m}$ is computed as follows:", + "bbox": [ + 75, + 113, + 472, + 344 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {w} _ {(j)} ^ {m} = \\left\\{ \\begin{array}{l} w _ {(j)} ^ {m} + \\widetilde {w} _ {(j)} ^ {m}, \\text {i f} k = \\widetilde {k} \\\\ \\max \\left(w _ {(j)} ^ {m}, \\widetilde {w} _ {(j)} ^ {m}\\right), \\text {i f} k \\neq \\widetilde {k} \\end{array} \\right. \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 133, + 352, + 468, + 396 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The cross-modal prediction is then computed as the weighted sum in a cross-modal manner:", + "bbox": [ + 76, + 402, + 468, + 433 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {p} _ {(j)} ^ {\\mathrm {X M}} (x) = \\frac {\\hat {w} _ {(j)} ^ {\\mathrm {2 D}} \\hat {p} _ {(j)} ^ {\\mathrm {2 D}} (x) + \\hat {w} _ {(j)} ^ {\\mathrm {3 D}} \\hat {p} _ {(j)} ^ {\\mathrm {3 D}} (x)}{\\hat {w} _ {(j)} ^ {\\mathrm {2 D}} + \\hat {w} _ {(j)} ^ {\\mathrm {3 D}}}, \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 143, + 441, + 468, + 484 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {y} _ {(j)} = \\arg \\max _ {k \\in N _ {c}} \\left(\\hat {p} _ {(j)} ^ {\\mathbf {x M}} (x) ^ {(k)}\\right), \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 484, + 468, + 510 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\hat{p}_{(j)}^{\\mathrm{xM}}(x),\\hat{y}_{(j)}$ denote the cross-modal prediction and pseudo-label, respectively. The cross-modal pseudo-label can therefore attend to the more reliable modality with confident intra-modal predictions.", + "bbox": [ + 76, + 520, + 468, + 580 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Class-Wise Moving Queues", + "text_level": 1, + "bbox": [ + 76, + 590, + 323, + 606 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Both iMPA and xMPF greatly depend on the quality of class-wise centroids. Initialized from the source offline centroids as in Eq. 1, the class-wise centroids should continually adapt to the target domain to ensure the validity of iMPA and xMPF. Meanwhile, the source knowledge should be occasionally played back during the centroid adaptation so that it can be revisited during the reliability estimation in iMPA and xMPF without catastrophic forgetting. To achieve a balance between adaptation and source knowledge preservation, we propose CMQs which utilize momentum queues [15] to actively estimate feature clustering of the target domain by capturing confident target features while stochastically restoring pseudo-source features for each modality. Specifically, the CMQ of the class $k$ is initialized by the pseudo-source features $\\mathcal{Z}_{src}^{m,k}$ as in Eq. 2. For each iteration, taking the raw sample as input, the normalized point features from the student network $\\phi_{\\theta}^{m}$ with confident predictions are preserved by threshold-based filtering. Given the CMQ of class $k$ from the previous step", + "bbox": [ + 75, + 613, + 472, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "denoted as $\\hat{\\mathcal{Q}}_{t - 1}^{m,k}$ , the CMQ of current step is updated as:", + "bbox": [ + 500, + 89, + 877, + 108 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {Z} _ {c f} ^ {m, k} = \\mathbb {1} _ {c f} ^ {k} \\left[ g _ {\\theta} ^ {m} \\left(x ^ {m}\\right) / \\| g _ {\\theta} ^ {m} \\left(x ^ {m}\\right) \\| \\right], \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 527, + 119, + 890, + 140 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\widetilde {\\mathcal {Q}} _ {t} ^ {m, k} = \\Phi \\left(\\hat {\\mathcal {Q}} _ {t - 1} ^ {m, k}, \\mathcal {Z} _ {c f} ^ {m, k}\\right), \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 527, + 141, + 890, + 162 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathcal {Q}} _ {t} ^ {m, k} = \\left\\{ \\begin{array}{l l} \\widetilde {\\mathcal {Q}} _ {t} ^ {m, k}, & \\text {i f} \\gamma_ {t} > p _ {r s} \\\\ \\Phi \\left(\\hat {\\mathcal {Q}} _ {t - 1} ^ {m, k}, \\mathbb {1} _ {r s} ^ {k} \\mathcal {Z} _ {s r c} ^ {m, k}\\right), & \\text {i f} \\gamma_ {t} \\leq p _ {r s} \\end{array} , \\right. \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 527, + 165, + 890, + 205 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbb{1}_{cf}^k$ is the confidence index for class $k$ where $\\mathbb{1}_{cf}^k\\phi_\\theta^m (x^m)^{(k)}\\geq \\tau_{cf}$ and $\\mathbb{1}_{rs}^k$ denotes the source restoring index which randomly samples $N_{enq}$ pseudo-source features from $\\mathcal{Z}_{src}^{m,k}$ . $\\Phi (a,b)$ denotes the operation of enqueuing $b$ in $a$ as in [15]. $\\gamma_{t}$ is a restoring flag uniformly sampled from [0, 1] at timestamp $t$ and $p_{rs}$ denotes the hyperparameter of restoring probability. Different from the image classification problem which can capture all confident samples [36], the number of confident points from each class can be huge (i.e., more than 1,000), which is too aggressive and expensive to enqueue all points. Therefore, we limit the index number of $\\mathbb{1}_{cf}^k$ by an upper bound $N_{enq}$ through selecting features with the top $N_{enq}$ confident predictions.", + "bbox": [ + 498, + 217, + 890, + 417 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For each optimization step, the mean of the class-wise centroid for the next step $\\mu_{t + 1}^{m,k}$ is updated as the average of CMQ of the current timestamp $\\hat{\\mathcal{Q}}_t^{m,k}$ so that the class-wise centroids can adapt to the feature clustering of target domain without catastrophic forgetting. Additionally, we propose a class-wise contrastive loss modified from [19] as a regularizer so that the target confident features can revisit source knowledge through clustering around the class-wise centroids. Specifically, given any confident target feature from Eq. 11 as the anchor, the positive samples are the features from the CMQ that shares the same modality and semantic class, denoted as $P(k) = \\{\\hat{q}_p\\mid \\hat{q}_p\\in \\hat{\\mathcal{Q}}_t^{m,k}\\}$ . The negative samples are the features from the CMQs of the same modality but different classes denoted as $A(k) = \\{\\hat{q}_n\\mid \\hat{q}_n\\in \\hat{\\mathcal{Q}}_t^{m,a},\\forall a\\neq k\\bigcap a\\in N_c\\}$ . The class-wise contrastive loss $\\mathcal{L}_{cts}^m$ is computed as:", + "bbox": [ + 498, + 417, + 892, + 662 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {L} _ {c t s} ^ {m} = \\sum_ {i \\in | \\mathcal {Z} _ {c f} ^ {m, k} |} \\frac {- 1}{| P (k) |} \\\\ \\sum_ {q _ {p} \\in P (k)} \\frac {\\exp \\left(\\hat {z} _ {t , (i)} ^ {m , k} \\cdot q _ {p}\\right)}{\\sum_ {q _ {n} \\in N (k)} \\exp \\left(\\hat {z} _ {t , (i)} ^ {m , k} \\cdot q _ {n}\\right)}. \\tag {14} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 537, + 672, + 890, + 763 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.5. Main Structure and Optimization", + "text_level": 1, + "bbox": [ + 500, + 786, + 795, + 801 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The main structure of our proposed method is shown in Fig. 2. Given the multi-modal input $x^{m}$ , the teacher model is used to infer $x^{m}$ and its augmented variants $\\{\\widetilde{x}_i^m | i \\in [1, N_{\\text{aug}}^m]\\}$ and then generate reliable cross-modal pseudolabels denoted as $\\hat{y}$ through iMPA and xMPF. The student model is directly updated by minimizing the weighted sum", + "bbox": [ + 498, + 810, + 893, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "18813", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Algorithm 1: The proposed CoMAC", + "text_level": 1, + "bbox": [ + 78, + 94, + 326, + 109 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Init Model: Teacher $\\phi_{\\theta}^{m}$ , student $\\phi_{\\theta}^{m}$ , $m \\in \\{2D, 3D\\}$", + "bbox": [ + 76, + 112, + 429, + 128 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Init CMQ: $\\hat{\\mathcal{Q}}_0^{m,k} = \\mathcal{Z}_{src}^{m,k}$ , $m\\in \\{2\\mathrm{D},3\\mathrm{D}\\}$ , $k\\in N_{c}$", + "bbox": [ + 78, + 128, + 416, + 145 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "for $t\\in |\\mathcal{X}_{\\mathcal{T}}|$ $x = (x^{2D},x^{3D})\\in \\mathcal{X}_{\\mathcal{T}}$ do", + "bbox": [ + 78, + 145, + 334, + 160 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "for $m\\in \\{2D,3D\\}$ do", + "bbox": [ + 84, + 161, + 232, + 174 + ], + "page_idx": 5 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. Augmented input to get $\\{\\widetilde{x}_i^m\\mid i\\in N_{aug}^m\\}$", + "2. Get predictions and features with $\\phi_{\\theta'}^m$ by Eq. 3-4", + "3. Get intra-modal $\\hat{p}^m (x^m)$ by iMPA through Eq. 5-7" + ], + "bbox": [ + 91, + 175, + 442, + 222 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "end", + "text_level": 1, + "bbox": [ + 84, + 224, + 112, + 234 + ], + "page_idx": 5 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "4. Get inter-modal $\\hat{y}$ by xMPF through Eq. 8-10", + "5. Update CMQs and compute $\\mathcal{L}_{cts}^{m}$ by Eq. 11-14", + "6. Update $\\phi_{\\theta}^{m}$ by Eq. 16 and $\\phi_{\\theta^{\\prime}}^{m}$ by Eq. 17" + ], + "bbox": [ + 84, + 238, + 408, + 284 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "end", + "text_level": 1, + "bbox": [ + 78, + 286, + 107, + 297 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "of the standard cross-entropy loss between its prediction and the pseudo-label $\\hat{y}$ , and the contrastive loss in Eq. 14. The teacher model is updated as the exponential moving average of the student's weights as in previous works [35, 42]:", + "bbox": [ + 75, + 335, + 468, + 397 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {c e} ^ {m} = \\mathbb {1} _ {\\tilde {y}} \\log \\phi^ {m} \\left(x ^ {m}\\right), \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 173, + 409, + 468, + 426 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\{2 D, 3 D \\}\n$$\n", + "text_format": "latex", + "bbox": [ + 222, + 430, + 267, + 441 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {t o t a l}} = \\sum_ {m} \\left(\\mathcal {L} _ {c e} ^ {m} + \\lambda_ {c t s} \\mathcal {L} _ {c t s} ^ {m}\\right), \\tag {16}\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 441, + 468, + 472 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\theta_ {t + 1} ^ {\\prime} = \\left(1 - \\lambda_ {s}\\right) \\theta + \\lambda_ {s} \\theta^ {\\prime}, \\tag {17}\n$$\n", + "text_format": "latex", + "bbox": [ + 168, + 474, + 468, + 492 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\lambda_{cts}$ and $\\lambda_s$ are the hyper-parameters denoting the coefficient of the contrastive loss and the momentum factor. Our adaptation process is summarized as Algorithm 1.", + "bbox": [ + 75, + 505, + 468, + 551 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 566, + 209, + 583 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this section, we present our experimental results based on two new benchmarks. The details of our proposed benchmarks, baselines, and implementation are first introduced in Sec. 4.1. Sec. 4.2 presents our overall results and Sec. 4.3 justifies our method by extensive ablation studies.", + "bbox": [ + 75, + 592, + 468, + 669 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Benchmarks and Settings", + "text_level": 1, + "bbox": [ + 76, + 680, + 308, + 696 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Proposed benchmarks. To evaluate the performance under MM-CTTA settings, we proposed two benchmarks in this work, including (i) SemanticKITTI-to-Synthia (S-to-S) and (ii) SemanticKITTI-to-Waymo (S-to-W). Both benchmarks leverage SemanticKITTI [2] as the source-domain dataset, which utilizes a 0.7MP camera and a 64-line LiDAR. For the target domain, we utilize two different datasets including Synthia [33] and Waymo [37] thanks to the various environmental conditions they cover. The former shares a larger domain gap with more diverse seasons, weather, and illumination conditions while the latter is less challenging but closer to the real-world application. For S-to-S, it is constructed by a sequence of different videos", + "bbox": [ + 75, + 703, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "from Synthia [33] without any repetition. Since Synthia includes depth images instead of 3D point clouds, we generate a simulated point cloud for each sample by randomly sampling depth pixels as 3D points following the structural characteristic of LiDAR. For each sequence, all samples are included for adaptation and we use \"No.-Conditions\" to indicate their corresponding video sequence in Synthia (i.e., \"01-Spring\" indicates video sequence 01 under Spring condition). Different from the previous CTTA benchmark [42] which only includes 4 different unique sequences, the proposed S-to-S consists of 12 different sequences recorded under various environmental conditions without repetition. By default, we organize the sequences following the order of seasons $\\rightarrow$ illumination $\\rightarrow$ weathers as a challenge ascending order. For S-to-W, we sort out the illumination conditions of each sequence in Waymo dataset [37] based on the sequence descriptions and divide all samples into three types, including Day (D), Dawn-Dusk (DD), and Night (N). Since the number of sequences of D is much larger than others, we further split the sequence of D based on their recording location, including Phoenix (P), San Francisco (S), and Others (O). Each sequence is separated in two halves to simulate the revisiting situation as in [42] but without repeated samples (i.e., \"D-O-1\" indicates the first half of the D-O sequence). Similar to S-to-S, S-to-W also follows a challenge ascending order. For both datasets, we adopt the images of the front-view camera similar to the source-domain dataset. We utilize a similar class mapping strategy as [18, 35] with slight modification since some classes are missing in the target domain. More details are illustrated in the appendix.", + "bbox": [ + 496, + 90, + 890, + 545 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Baselines. Previous TTA, MM-TTA, and CTTA methods are evaluated on both S-to-S and S-to-M as baselines. For TTA methods, we compare with pseudo-labels with threshold filtering (Plabel), TENT [40] and LAME [3], while xMUDA with pseudo-labels (xMUDA-pl) [18] and MMTTA [43] are regarded as the representatives of MMTTA methods. CoTTA [42] and EATA [30] are the recent works that focus on CTTA problems. Specifically, xMUDA-pl is originally designed for UDA, whereas we modify it into a TTA version by discarding the source data during adaptation. Considering our CoMAC is the only MM-CTTA method, we implement an MM-CTTA version of MMTTA [35] integrated with model-based stochastic restoration in [42] for a fair comparison. We report the softmax-average mIoU of 2D and 3D predictions as results.", + "bbox": [ + 496, + 547, + 890, + 776 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation details. Following previous works [18, 35], we utilize UNet [32] with ResNet-34 [16] encoder as the 2D backbone and SCN [14] based on UNet as the 3D backbone for all baselines. The pre-training procedures on SemanticKITTI dataset follow [18]. For our method, we empirically choose resizing and z-rotation as the 2D and 3D augmentations following previous works [42, 18]. Specifically, we utilize multiple resizing factors of [0.5,", + "bbox": [ + 496, + 779, + 890, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "18814", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/0a871873ade4464ea0e435a8c4a9654ca543d8f5d62048d329cb9eac995cde86.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Timet →t →
MethodsDA TypeSemanticKITTI-to-SynthiaSemanticKITTI-to-Waymo
01-Spring02-Summer04-Full05-Winter01-Dawn02-Night04-Sunset05-Wnight01-Fog02-S-Rain04-R-Night05-RainAvgD-O-1D-P-1D-S-1DD-1N-1D-O-2D-P-2D-S-2DD-2N-2Avg
Source-28.330.737.727.323.127.338.226.527.021.627.816.427.733.236.929.528.314.032.838.030.428.414.628.6
PlabelTTA29.627.136.428.421.426.632.326.127.421.825.018.026.739.141.937.036.825.738.543.737.637.624.636.9
TENT [40]TTA35.424.924.920.718.716.616.013.613.611.58.49.117.833.622.318.816.910.815.712.99.811.310.616.3
LAME [3]TTA14.012.417.313.012.611.617.013.219.27.77.86.012.711.910.413.49.28.713.411.212.29.78.612.7
xMUDA-pl [18]MM-TTA28.826.935.928.221.326.532.226.027.021.624.917.926.439.342.137.437.025.938.743.937.937.725.036.5
MMTTA [35]MM-TTA31.124.430.725.828.324.226.823.229.620.722.120.625.639.940.030.931.529.630.632.223.926.423.830.9
CoTTA [42]CTTA29.727.234.727.026.425.633.027.328.118.022.718.426.532.928.022.922.220.326.124.923.624.719.724.5
EATA [30]CTTA34.030.038.630.230.228.436.530.132.221.325.320.129.740.140.836.334.328.939.341.736.537.928.836.5
MMTTA-rs [35]MM-CTTA31.928.137.729.328.727.635.229.730.220.425.620.328.740.441.536.334.730.239.941.536.438.329.936.9
CoMAC (Ours)MM-CTTA34.034.744.938.135.037.845.139.039.129.435.127.136.641.443.738.837.832.242.241.840.738.930.438.8
Timet ←t ←
TENT [40]TTA10.28.88.69.010.29.59.811.418.313.216.918.912.112.011.59.29.89.712.613.012.519.821.213.1
MMTTA-rs [35]MM-CTTA31.427.437.228.726.227.233.129.028.519.922.319.727.640.441.436.431.629.137.640.235.435.227.835.5
CoMAC (Ours)MM-CTTA34.632.840.933.231.832.439.233.233.825.130.323.332.440.841.937.733.230.339.643.638.838.630.037.5
", + "bbox": [ + 81, + 88, + 890, + 291 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 1. Performance (mIoU) of SemanticKITTI-to-Synthia. Here we report the softmax-average mIoU of 2D and 3D prediction.", + "bbox": [ + 101, + 297, + 864, + 313 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/ead5781acdec926235eb580f3f6fe4bddd607acace7c96163bc5351df486c466.jpg", + "image_caption": [ + "Figure 3. Ablation studies to justify our design of CoMAC. Specifically, (a) compares CoMAC with variants only using raw or augmented samples as input of iMPA and (b) justifies the necessity of weighting mechanisms in iMPA and xMPF. (c) compares CoMAC with variants without either target feature enqueuing or pseudo-source features restoring in CMQs. Scores within the parentheses are the average mIoU." + ], + "image_footnote": [], + "bbox": [ + 83, + 329, + 321, + 411 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/28511b9a214e92153d5cb718a56fab981c18bea8aafff6d44056368a3b46001c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 362, + 329, + 606, + 410 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/65ce37e2c261a5b748a0cf18c5e62dc1a12b5ef4b527a6204af49873838b0857.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 648, + 329, + 888, + 410 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "0.625, 0.75, 0.875] and z-rotation of $[60^{\\circ}, 120^{\\circ}, 180^{\\circ}, 240^{\\circ}, 300^{\\circ}]$ . $N_{q}$ and $N_{enq}$ are set to 4096 and 200, respectively. We utilize a restore rate $p_{rs}$ of 0.5 and a momentum factor $\\lambda_{s}$ of 0.999 with a coefficient $\\lambda_{cts}$ of 1. All methods strictly follow the one-pass protocol [36] (i.e., the training epoch is one where inference is conducted immediately for each sample). More details are included in the appendix.", + "bbox": [ + 75, + 483, + 468, + 590 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Overall Results", + "text_level": 1, + "bbox": [ + 76, + 604, + 232, + 618 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "As shown in Table 1, our CoMAC achieves SOTA performance on the average mIoU of all sequences for both benchmarks. Specifically, the proposed CoMAC significantly outperforms previous methods by more than $6.9\\%$ on S-to-S and $1.9\\%$ on S-to-W, which justifies the effectiveness of our method. It can also be observed that most TTA methods (TENT [40] and LAME [3]) are outperformed by CTTA methods, which reveals the importance of avoiding catastrophic forgetting. Additionally, previous MM-TTA (i.e., xMUDA and MMTTA) methods can not consistently outperform previous single-modal methods (e.g., EATA [30]), which suggests the sensitivity of multi-modal collaboration toward continual domain shifts. In fact, by intuitively utilizing model-based stochastic restoration, MMTTA-rs can achieve a noticeable improvement of $3.1\\%$ and $6.0\\%$ on S-to-S and S-to-W, respectively. Yet MMTTA-rs is still outperformed by our method. To justify the effect of the sequence arrangement, we conduct additional experiments by", + "bbox": [ + 75, + 628, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "reversing the sequences of S-to-S and S-to-W for TENT, MMTTA-ms, and our CoMAC. While the performance of all methods decreases, the improvement of CoMAC compared to others can be observed across all sequences.", + "bbox": [ + 496, + 484, + 890, + 545 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "For S-to-S, we notice that our method achieves the second-best performance at the first sequence 01-Spring and then surpasses all previous methods in the following sequences since we utilize CMQs to gradually adapt to the changing target domain without forgetting. Compared with TTA methods, our method consistently prevails with an increasing gap as they struggle with error accumulation. A similar observation can be found at D-O-2 of S-to-W. Interestingly, xMUDA-pl as well as Plabel perform competitively on S-to-W and outperform CoMAC in D-P-2 mainly because is less challenging and simply filtering pseudolabels can effectively mitigate the prediction noise. Nevertheless, this performance gap is trivial as our CoMAC surpasses both xMUDA-pl and Plabel on all other sequences.", + "bbox": [ + 496, + 546, + 890, + 758 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Studies", + "text_level": 1, + "bbox": [ + 500, + 768, + 663, + 784 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we provide our ablation studies on S-to-S to justify our design of CoMAC.", + "bbox": [ + 496, + 794, + 890, + 824 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Utilization of raw and augmented input. In Sec. 3.2, a key hypothesis is that while the augmentation-average prediction can be a potential reliable alternative, it may introduce inductive bias to the result. To justify this assumption, we conduct experiments by simply using the pure raw", + "bbox": [ + 496, + 825, + 890, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "18815", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9b5afb25a3f5b42dbfb78cb4fa1ff13d93019bfc0c1395f82edba9b31b9c7837.jpg", + "image_caption": [ + "Figure 4. Visualization of online segmentation results. Here we present the cross-modal pseudo-labels from xMPF (Ours) as well as the individual prediction from 2D and 3D teachers in comparison with the ground truth (GT)." + ], + "image_footnote": [], + "bbox": [ + 122, + 88, + 851, + 281 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "or augmentation-average prediction as the intra-modal prediction as in Eq. 7. As shown in Fig. 3(a), both variants achieve inferior performance compared to CoMAC and these performance gaps are consistent across most sequences. Specifically, using pure augmentation-average predictions lead to serious degradation of $5.8\\%$ , which justifies the necessity of mitigating the inductive noise brought by test-time augmentations and our motivation for iMPA.", + "bbox": [ + 75, + 342, + 468, + 462 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Weighting mechanisms of iMPA and xMPF. The proposed iMPA and xMPF utilize centroid-based weighting mechanisms to attend to the reliable modality. To justify their effectiveness, we compared CoMAC with variants by replacing either Eq. 7 or Eq. 8 with a simple average fusion (indicated as w/o iMPA and w/o xMPF). As presented in Fig. 3(b), CoMAC outperforms both variants by more than $2.5\\%$ . This performance gap justifies that both iMPA and xMPF play an important part in noise suppression.", + "bbox": [ + 75, + 468, + 468, + 604 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Updating mechanisms of CMQs. The goal of CMQs is to achieve a good balance between adaptation and knowledge preservation. To justify the role of CMQs, we compared CoMAC with variants without enqueuing target features or restoring pseudo-source features, respectively. For the variant without enqueuing target features, the corresponding class-wise centroids are identical to the source centroids across the whole testing process. As in Fig. 3(c), disabling enqueuing target features (w/o Update) causes a significant performance decrease of $6.1\\%$ , which justifies the necessity of adapting class-wise centroids for the validity of iMPA and xMPF. On the other hand, while disabling restoring pseudo-source features (w/o Restore) leads to a quicker adaptation at the first two sequences, it eventually causes catastrophic forgetting after the third sequence, resulting in a noticeable gap of $8.4\\%$ . Overall, the performance gain brought by CMQs justifies their effectiveness.", + "bbox": [ + 75, + 608, + 468, + 864 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Number of Augmentations. To investigate the effect of augmentations, we conduct a grid search by utilizing differ-", + "bbox": [ + 76, + 869, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/091bec5db9788da354ccb99119d893cfcf88a5ea78788d2be6c559e99dbee3fc.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
CoMACNo. of 2D Aug
12345Avg
No. of 3D Aug133.033.133.233.233.333.2
234.134.234.334.434.434.3
335.235.235.435.335.535.3
436.436.436.536.536.536.5
536.436.536.736.636.736.6
Avg35.035.135.235.235.335.2
", + "bbox": [ + 527, + 339, + 864, + 422 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/f72d2bf341ede54a42db46eab41748a17c2f086b29a40d969b1cc0c2002d9afe.jpg", + "table_caption": [ + "Table 2. Augmentation analysis of CoMAC. CoMAC is evaluated with different numbers of augmentations." + ], + "table_footnote": [], + "table_body": "
CoMAC\\( p_{rs} \\)\\( (\\tau_{cf},\\lambda_{cts}) \\)Avg\\( \\tau_{cf} \\)\\( (p_{rs},\\lambda_{cts}) \\)Avg\\( \\lambda_{cts} \\)\\( (p_{rs},\\tau_{cf}) \\)Avg
0.5(0.8,1.0)36.60.8(0.5,1.0)36.61.0(0.5,0.8)36.6
0.3-34.50.0-34.80.0-35.8
0.7-36.40.5-36.50.01-36.4
1.0-36.30.9-36.40.1-36.4
", + "bbox": [ + 504, + 465, + 890, + 521 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 3. Sensitivity analysis of CoMAC. Here \"xM\" is the softmax-average of 2D and 3D predictions. The parameter value with \"-\" indicates the same value as default settings.", + "bbox": [ + 500, + 527, + 890, + 570 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "ent numbers of 2D and 3D augmentations. Specifically, we adopt resize and rotation as 2D and 3D augmentation, respectively. The factor range for 2D scaling is [0.5, 1) while 3D one is set to $(0^{\\circ}, 360^{\\circ})$ , where the list of augmentations is computed as evenly spaced factors given the number of augmentations. As shown in Table 2, increasing the number of either 2D or 3D augmentations leads to performance improvement, while the 2D improvement is less noticeable compared to 3D probably due to the inductive bias brought by 2D augmentations. While all settings perform competitively, we adopt the combination of three 2D augmentations and five 3D augmentations to achieve the best result.", + "bbox": [ + 496, + 597, + 890, + 777 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Sensitivity analysis. We perform sensitivity analysis over the hyper-parameters of CoMAC as shown in Table 3. There are some extreme cases that can lead to the performance degeneration of CoMAC. For restoring rate $p_{rs}$ , the performance relatively drops about $5.7\\%$ when $p_{rs} = 0.3$ , indicating the restoring rate is too low to prevent forgetting. Nevertheless, when $p_{rs} \\geq 0.5$ , CoMAC is robust to the arbitrary choice of $p_{rs}$ . Similar observations can be found when", + "bbox": [ + 496, + 779, + 892, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "18816", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/0b5c68bfd19e040ad8a5a493d7d6d9e694635bcbda125c96df189987534092f7.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodAug SamplesInf. Time (s)/samplemIoU
meanstd
TENT [40]X0.3790.01017.8
CoTTA [42]✓7.2200.39926.5
Ours✓1.8880.08236.6
Ours (less augs)✓1.0040.03833.0
", + "bbox": [ + 99, + 75, + 446, + 151 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Table 4. Comparison of processing time per sample.", + "bbox": [ + 117, + 152, + 426, + 167 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/7a0eafe200e0d567cd3254c3fb45cfdf5c598993d0c005ae607bea40c81b7dc0.jpg", + "image_caption": [ + "Figure 5. Processing time of CoMAC components per sample (left) and GPU RAM with or without CMQs (right). Experiments are conducted on S-to-S with the default backbones and settings." + ], + "image_footnote": [], + "bbox": [ + 81, + 183, + 251, + 281 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/2befc8781f28844b7e564d1e8d33d7bbe86a23dc52d7e59e15dfb52386e24d6b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 263, + 183, + 457, + 281 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "$\\tau_{cf} = 0.0$ or $\\lambda_{cts} = 0.0$ , where the performance decreases relatively by $4.9\\%$ and $2.2\\%$ . This performance degeneration indicates the importance of confident feature filtering and class-wise contrastive loss. Overall, when $\\tau_{cf} \\geq 0.0$ and $\\lambda_{cts} \\geq 0.01$ , the performance of CoMAC is also robust to the hyper-parameter settings, falling into a relative margin of $0.5\\%$ . Note that all settings of CoMAC surpass the previous SOTA method EATA [30] by more than $4.8\\%$ .", + "bbox": [ + 75, + 357, + 467, + 477 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Visualization of segmentation. To further justify the effectiveness of our proposed CoMAC, we provide some visualization results as shown in Fig. 4. Specifically, we visualize the 2D and 3D predictions from teacher models and our cross-modal pseudo-labels from xMPF. Compared to single-modal predictions, our cross-modal pseudo-labels can achieve better segmentation results by attending to the reliable modality, such as the first row in Fig. 4, where the sidewalk prediction attends more to the 2D image while the car prediction attends to the reliable 3D point cloud.", + "bbox": [ + 75, + 478, + 467, + 628 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Computational and storage overhead. To investigate the computational and storage overhead of CoMAC, we analyze the processing time and GPU occupancy when online testing with our CoMAC as illustrated in Table 4 and Fig. 5. Similar to previous augmentation-based methods, our proposed CoMAC is limited by the computational overhead brought by multiple augmentations. However, compared to the augmentation-based SOTA method CoTTA [42], our method outperforms it in terms of performance and efficiency (a relative performance improvement of $38.1\\%$ with $73.9\\%$ less processing time). Compared to the single-sample-based method TENT, despite a computational overhead of 1.51s, our method significantly improves relatively by more than $100\\%$ . The computational overhead can be further lessened by using fewer augmentations, reducing the processing time relatively by more than $46.8\\%$ with a minor performance drop of $3.6\\%$ . Besides augmentations, another potential source of overhead lies in the utilization of", + "bbox": [ + 75, + 628, + 467, + 900 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "CMQs as they capture class-wise features for each iteration. As shown in Fig .5, however, the computational overhead brought by CMQs is rather trivial, which takes less than 0.05s to update and process each frame. Moreover, since CMQs only preserve the high-level features instead of raw samples, the storage cost is also acceptable with a minor usage increase (less than $800\\mathrm{MB}$ ) of GPU RAM compared to the CoMAC invariant without CMQs.", + "bbox": [ + 496, + 90, + 890, + 212 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 228, + 617, + 243 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this paper, we present a new task, named multi-modal continual test-time adaptation (MM-CTTA) for 3D semantic segmentation. We further propose a novel method called CoMAC that tackles MM-CTTA from two perspectives. On one hand, reliable cross-modal pseudo-labels are generated by iMPA and xMPF by adaptively attending to the more reliable modality in a dual-stage manner. On the other hand, CMQs are proposed to leverage pseudo-source features and reliable target features to perform adaptation without catastrophic forgetting. We introduce two new benchmarks for MM-CTTA and our methods outperform previous works by a noticeable margin in both benchmarks. In the future, we hope both our method and benchmarks can facilitate the exploration of MM-CTTA and promote the development of reliable multi-modal systems in altering environments.", + "bbox": [ + 496, + 255, + 890, + 482 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 500, + 498, + 658, + 515 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This research is supported by the National Research Foundation, Singapore under its Medium Sized Center for Advanced Robotics Technology Innovation. This research is jointly supported by the National Research Foundation, Singapore under its AI Singapore Programme (AISG Award No: AISG2-RP-2021-027).", + "bbox": [ + 496, + 523, + 890, + 614 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 500, + 632, + 596, + 647 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Khaled Bayoudh, Raja Knani, Fayçal Hamdaoui, and Abdellatif Mtibaa. A survey on deep multimodal learning for computer vision: advances, trends, applications, and datasets. The Visual Computer, pages 1-32, 2021. 1", + "[2] Jens Behley, Martin Garbade, Andres Milioto, Jan Quenzel, Sven Behnke, Cyril Stachniss, and Jurgen Gall. Semantickitti: A dataset for semantic scene understanding of lidar sequences. 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In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 5982-5991, 2019. 1" + ], + "bbox": [ + 501, + 92, + 893, + 869 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "18819", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multi-Modal Continual Test-Time Adaptation for 3D Semantic Segmentation/7a008f21-91bc-4a63-ae49-b60252dec431_model.json b/2023/Multi-Modal Continual Test-Time Adaptation for 3D Semantic Segmentation/7a008f21-91bc-4a63-ae49-b60252dec431_model.json new file mode 100644 index 0000000000000000000000000000000000000000..75e69a2de6202e434d49326bfdab460a576e8bbc --- /dev/null +++ b/2023/Multi-Modal Continual Test-Time Adaptation for 3D Semantic Segmentation/7a008f21-91bc-4a63-ae49-b60252dec431_model.json @@ -0,0 +1,2257 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.097, + 0.131, + 0.873, + 0.153 + ], + "angle": 0, + "content": "Multi-Modal Continual Test-Time Adaptation for 3D Semantic Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.11, + 0.18, + 0.856, + 0.235 + ], + "angle": 0, + "content": "Haozhi Cao\\(^{1*}\\) Yuecong Xu\\(^{2*}\\) Jianfei Yang\\(^{1\\dagger}\\) Pengyu Yin\\(^{1}\\) Shenghai Yuan\\(^{1}\\) Lihua Xie\\(^{1}\\) \n\\(^{1}\\)Nanyang Technological University \\(^{2}\\)Institute for Infocomm Research, A*STAR, Singapore \n{haozhi002, xuyu0014, yang0478, pengyu001, syuan003}@e.ntu.edu.sg elhxie@ntu.edu.sg" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.301, + 0.474, + 0.681 + ], + "angle": 0, + "content": "Continual Test-Time Adaptation (CTTA) generalizes conventional Test-Time Adaptation (TTA) by assuming that the target domain is dynamic over time rather than stationary. In this paper, we explore Multi-Modal Continua! tual Test-Time Adaptation (MM-CTTA) as a new extension of CTTA for 3D semantic segmentation. The key to MMCTTA is to adaptively attend to the reliable modality while avoiding catastrophic forgetting during continual domain shifts, which is out of the capability of previous TTA or CTTA methods. To fulfill this gap, we propose an MM-CTTA method called Continua! Cross-Modal Adaptive Clustering (CoMAC) that addresses this task from two perspectives. On one hand, we propose an adaptive dual-stage mechanism to generate reliable cross-modal predictions by attending to the reliable modality based on the class-wise featurecentroid distance in the latent space. On the other hand, to perform test-time adaptation without catastrophic forgetting, we design class-wise momentum queues that capture confident target features for adaptation while stochastically restoring pseudo-source features to revisit source knowledge. We further introduce two new benchmarks to facilitate the exploration of MM-CTTA in the future. Our experimental results show that our method achieves state-of-the-art performance on both benchmarks. Visit our project website at https://sites.google.com/view/mmcotta." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.706, + 0.21, + 0.721 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.731, + 0.47, + 0.868 + ], + "angle": 0, + "content": "Test-Time Adaptation (TTA) proposes a realistic domain adaptation scenario, which adapts pre-trained models to the target domain during the testing process. Unlike previous Unsupervised Domain Adaptation (UDA) [17, 45, 52, 47], TTA performs adaptation online without accessing the data from the source domain. Typical TTA [40, 35, 36] methods assume a stationary target domain, while real-world scenarios are dynamic over time. To fulfill this gap, a previous work [42] proposes a general extension of TTA named Con-" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.273, + 0.892, + 0.337 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.338, + 0.892, + 0.473 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.48, + 0.893, + 0.592 + ], + "angle": 0, + "content": "Figure 1. Illustration of how continual domain shifts affect multimodal segmentation and our method. Unlike the source domain where predictions from both modalities are reliable, the reliability of each modality varies in MM-CTTA due to different domain shifts. CoMAC tackles MM-CTTA by attending to the reliable modality \\((\\checkmark)\\) rather than the noisy one \\((\\chi)\\). Meanwhile, source knowledge is stochastically revisited to avoid catastrophic forgetting. Figure best viewed in color and zoomed in." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.625, + 0.892, + 0.701 + ], + "angle": 0, + "content": "tual Test-Time Adaptation (CTTA) which assumes that the target domain is continually changing rather than static. Compared to TTA, CTTA is more challenging since the performance is easily affected by error accumulation [6] and catastrophic forgetting [27] during the continual adaptation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.893, + 0.901 + ], + "angle": 0, + "content": "For 3D semantic segmentation, multi-modal sensors are frequently leveraged in different tasks, such as scene understanding [4, 28] and semantic map construction [29, 43]. For some specific applications like semantic-based localization [8] and autonomous driving [46, 44], multi-modal information is the key to robust performance under adverse conditions. However, their collaboration has been proven to be sensitive toward domain drifts [1, 35]. In real-world scenarios, such collaboration deterioration could be more severe considering that the target domain is continually changing as in CTTA (e.g., the operating environments of 24/7 AGVs are continually changing due to altering weather or illumination conditions). Hence, it is essential for multi-" + }, + { + "type": "page_footnote", + "bbox": [ + 0.094, + 0.875, + 0.221, + 0.901 + ], + "angle": 0, + "content": "*Equal contributions. †Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18809" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.182 + ], + "angle": 0, + "content": "modal networks to adapt to the dynamic target domain in an online manner. In this work, we aim to study MultiModal Continual Test-Time Adaptation (MM-CTTA) for 3D semantic segmentation, where networks are continually adapted to a changing target domain taking 3D point clouds and 2D images as input without accessing the source data." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.187, + 0.471, + 0.519 + ], + "angle": 0, + "content": "Intuitively, one can address MM-CTTA by utilizing CTTA [30, 42] or TTA [3, 38] methods on 2D and 3D networks separately. However, this simple extension can not achieve satisfactory performance since it cannot correctly attend to the reliable modality for adaptation when others suffer from severe domain shifts. Take Fig. 1 as an example: predictions from the 2D image are more accurate at the beginning of the target domain, while 2D results become unreliable and 3D predictions prevail as the illumination level significantly changes over time. Although previous CTTA or TTA methods have attempted to mitigate this intra-modal prediction noise by augmentations [42] or entropy minimization [40, 30], the domain drift in Fig. 1 is too severe to be effectively rectified by image input itself, leading to inevitable error accumulation. Previous works have proposed different cross-modal fusion methods to mitigate the effect of the noisy modality during adaptation, such as cross-modal consistency [18] for UDA or pseudo-label fusion based on student-teacher consistency [35] for TTA. However, their methods rely on the premise that the target domain is static, and therefore suffer from catastrophic forgetting in MM-CTTA, leading to degenerated results." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.524, + 0.47, + 0.901 + ], + "angle": 0, + "content": "For MM-CTTA, an ideal solution is to suppress the contribution from the noisy modality and attend more to the reliable one in an online manner. Typically, the reliability of prediction can be estimated based on its corresponding feature location in the latent space. A prediction with features close to the centroid is more likely to be reliable, suffering less from the domain shift and vice versa. On the other hand, to ensure the validity of centroid-based reliability estimation, class-wise centroids should actively adapt to the continually changing target domain while stochastically revisiting the source knowledge to avoid catastrophic forgetting. To this end, we propose an MM-CTTA method called Continual Cross-Modal Adaptive Clustering (CoMAC) for 3D semantic segmentation. CoMAC consists of three main modules: (i) Intra-Modal Prediction Aggregation (iMPA), (ii) Inter-Modal Pseudo-Label Fusion (xMPF), and (iii) Class-Wise Momentum Queues (CMQs). On one hand, the proposed iMPA and xMPF are utilized to suppress prediction noise based on the centroid-based reliability estimation from intra-modal and inter-modal perspectives, respectively. On the other hand, CMQs are designed to actively adapt class-wise centroids for iMPA and xMPF while avoiding catastrophic forgetting. Additionally, a class-wise contrastive loss is introduced to regularize the extracted features from drifting too far from centroids." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.304 + ], + "angle": 0, + "content": "In summary, our main contributions are three-fold. (i) We explore a new task MM-CTTA where multi-modal input is utilized to perform continual test-time adaptation for 3D semantic segmentation and propose an effective method named CoMAC to leverage multi-modal information for MM-CTTA. (ii) We propose iMPA and xMPF to generate accurate cross-modal pseudo-labels by attending to a reliable modality. CMQs are introduced to actively adapt to the target domain without catastrophic forgetting. (iii) We introduce two 3D semantic segmentation benchmarks to facilitate the future exploration of MM-CTTA. Extensive experiments show that our method achieves state-of-the-art performance, outperforming previous methods significantly by \\(6.9\\%\\) on the challenging benchmark." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.317, + 0.65, + 0.334 + ], + "angle": 0, + "content": "2. Related Works" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.342, + 0.892, + 0.794 + ], + "angle": 0, + "content": "Test-Time Adaptation Describing a more realistic adaptation scenario, Test-Time Adaptation (TTA) is receiving more and more attention. Different from previous Unsupervised Domain Adaptation (UDA), TTA forbids access to raw source data and adapts the source pre-trained model during test time. As one of the primary works, TENT [40] highlights the fully test-time setting and proposes to update the batch normalization layers by entropy minimization. The following works mainly address TTA by aligning batch normalization statistics [30, 23, 51], self-training with pseudo labeling [13, 41], feature alignment [25], or augmentation invariance [50, 21]. The aforementioned TTA methods strictly follow the one-pass protocol as mentioned in [36], where networks immediately infer each sample in an online manner and forbid multiple training epochs. On the other hand, some previous works [22, 10, 7, 48] follow the multi-pass protocol by adapting the model for multiple epochs in an offline manner. As one of the primary works, Source Hypothesis Transfer (SHOT) [22] proposes to update only the encoder parameters and align source and target representation by entropy minimization and pseudolabeling. While most existing TTA methods are proposed for image classification, some recent works [10, 20, 26] aim to explore TTA for image semantic segmentation. Specifically, [10] proposes to minimize the prediction entropy while maximizing its robustness toward feature noise. [20] divides the TTA problem into source domain generalization and target domain adaptation. [26] proposes a dual attention distillation method to transfer contextual knowledge and patch-level pseudo labels for self-supervised learning." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Continual Test-Time Adaptation The definition of Continual Test-Time Adaptation (CTTA) is first proposed in CoTTA[42], which aims to adapt the model to continually changing target domains in an online manner without any source data. Specifically, CoTTA proposes to use the moving teacher model and augmentation-average predictions for noise suppression and the model stochastic" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "18810" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.227 + ], + "angle": 0, + "content": "restoration to avoid catastrophic forgetting. Following the scheme of CoTTA, some recent works [11, 12, 30] have addressed CTTA from different perspectives. Specifically, [12] leverages the temporal correlations of streamed input by reservoir sampling and instance-aware batch normalization. [11] proposes domain-specific prompts and domain-agnostic prompts to preserve domain-specific and domain-shared knowledge, respectively. EATA [30] performs adaptation on non-redundant samples for an efficient update." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.228, + 0.473, + 0.499 + ], + "angle": 0, + "content": "Multi-Modal Adaptation for Segmentation Thanks to the emerging multi-modal datasets [2, 5, 37, 33, 49], recent works start to explore how to leverage multi-modal information between 2D images and 3D point clouds to perform domain adaptation under different settings. xMUDA [18] proposes the first Multi-Modal Unsupervised Domain Adaptation (MM-UDA) method for 3D semantic segmentation. Specifically, it leverages the cross-modal prediction consistency by minimizing the prediction discrepancy from additional classifiers. Following the scheme of cross-modal learning, DsCML [31] designs a deformable mapping between pixel-point correlation for MM-UDA while [24] introduces adversarial training to mitigate domain discrepancy. In addition to UDA settings, [35] proposes the first multi-modal test-time adaptation for semantic segmentation which generates intra-modal and inter-modal pseudo labels by attending to the one with more consistent predictions across student and teacher models." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.5, + 0.473, + 0.698 + ], + "angle": 0, + "content": "In this work, we propose MM-CTTA as a new extension of CTTA with a specific method CoMAC. While our proposed dual-stage modules (i.e., iMPA and xMPA) and CMQs share some similar merit with previous TTA methods [35, 36], our method is explicitly designed for MM-CTTA. Unlike previous work [35] measuring prediction reliability by teacher-student consistency, our reliability measurement relies on the feature-centroid distance to encourage feature clustering around the adapting centroids. Different from [36] utilizing queues to measure target distribution, the objective of our CMQs is to actively update class-wise centroids to ensure the validity of iMPA and xMPA while avoiding catastrophic forgetting." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.708, + 0.251, + 0.725 + ], + "angle": 0, + "content": "3. Proposed Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.733, + 0.473, + 0.904 + ], + "angle": 0, + "content": "Problem definition and notations. At timestamp \\(t\\), the 2D image \\(x_{\\mathcal{T},t}^{2\\mathrm{D}} \\in \\mathbb{R}^{H \\times W \\times 3}\\) and the 3D point cloud \\(x_{\\mathcal{T},t}^{3\\mathrm{D}} \\in \\mathbb{R}^{N \\times 4}\\) are observed in the target domain \\(\\mathcal{T}\\), where \\(N\\) denotes the number of 3D points located in the camera FOV. Modal-specific pre-trained networks \\(\\phi_{\\theta, t}^{m}(\\cdot) = f_{t}^{m}(g_{t}^{m}(\\cdot)), m \\in \\{2\\mathrm{D}, 3\\mathrm{D}\\}\\) consisting of the feature extractor \\(f_{t}^{m}\\) and the classifier \\(g_{t}^{m}\\) are used to predict the semantic labels for each point. Inspired by the fact that moving average models can provide more stable predictions [39], we utilize a fast student network \\(\\phi_{\\theta}^{m}(\\cdot) = f_{\\theta}^{m}(g_{\\theta}^{m}(\\cdot))\\) and a slow teacher network \\(\\phi_{\\theta'}^{m}(\\cdot) = f_{\\theta'}^{m}(g_{\\theta'}^{m}(\\cdot))\\) for each modal-" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.307 + ], + "angle": 0, + "content": "ity similar to previous works [35, 42]. Given \\(x_{\\mathcal{T},t}^{m}\\) as input, the features extracted by \\(f_{t}^{m}\\) is denoted as \\(z_{\\mathcal{T},t}^{m} \\in \\mathcal{R}^{N \\times F^{m}}\\) where \\(F^{m}\\) denotes the channel number. Here we adopt the same projection protocol of previous works [18, 35] for cross-modal alignment, which projects features from the 2D branch back to 3D points, resulting in the 2D feature \\(z_{\\mathcal{T},t}^{2\\mathrm{D}}\\) of shape \\(N \\times F^{2\\mathrm{D}}\\). By default, the subscript of the target domain \\(\\mathcal{T}\\) and the timestamp \\(t\\) are omitted for clarity. Given the multi-modal input \\(x_{\\mathcal{T},t}^{2\\mathrm{D}}, x_{\\mathcal{T},t}^{3\\mathrm{D}}\\), the goal of MM-CTTA is to output reliable cross-modal predictions by continuously adapting to the changing target domain. In this work, we interpret the core of MM-CTTA as two-fold: (i) attending to the reliable modality for noisy suppression, and (ii) revisiting source knowledge to prevent catastrophic forgetting." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.308, + 0.893, + 0.595 + ], + "angle": 0, + "content": "To this end, we propose Continual Cross-Modal Adaptive Clustering (CoMAC) to tackle MM-CTTA from the aforementioned perspectives. Specifically, as shown in Fig. 2, the class-wise centroids are initialized from the source domain and pseudo-source features are randomly sampled around the centroids as source knowledge (Sec. 3.1). Given the raw and augmentation-average predictions from the teacher models as input, Intra-Modal Prediction Aggregation (iMPA) generates stable intra-modal predictions as their weighted sum based on their feature distance to the class-wise centroids (Sec. 3.2). Inter-Modal Pseudo-Label Fusion (xMPF) then combines the intramodal predictions from each modality based on their reliability and output cross-modal pseudo-labels as supervision signals for student networks (Sec. 3.3). Given raw samples as input, confident target features from student networks are utilized to update Class-Wise Momentum Queues (CMQs), while pseudo-source features are stochastically restored to avoid catastrophic forgetting (Sec. 3.4)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.604, + 0.854, + 0.619 + ], + "angle": 0, + "content": "3.1. Source Models and Class-Wise Centroids" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.627, + 0.892, + 0.793 + ], + "angle": 0, + "content": "To effectively avoid catastrophic forgetting and inspired by previous TTA methods [9, 36] which preserve trivial source domain information, we utilize pseudo-source features sampled around source offline feature centroids as source representatives. The source offline centroids and pseudo-source features are treated as the prior knowledge from the source domain, which plays an essential role in preventing catastrophic forgetting detailed in Sec. 3.4. Specifically, given a specific semantic category \\( k \\), the corresponding source offline centroid is modeled as Gaussian distribution, and pseudo-source features are denoted as:" + }, + { + "type": "equation", + "bbox": [ + 0.565, + 0.802, + 0.891, + 0.821 + ], + "angle": 0, + "content": "\\[\nC _ {s r c} ^ {m, k} = \\mathcal {N} \\left(\\mu_ {s r c} ^ {m, k}, \\sigma_ {s r c} ^ {m, k}\\right), \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.566, + 0.824, + 0.891, + 0.843 + ], + "angle": 0, + "content": "\\[\n\\mathcal {Z} _ {s r c} ^ {m, k} = \\left\\{z _ {s r c, i} ^ {m, k} \\sim C _ {s r c} ^ {m, k} \\mid i \\in [ 1, N _ {q} ] \\right\\}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.855, + 0.892, + 0.902 + ], + "angle": 0, + "content": "where \\(N_{q}\\) is the number of pseudo-source features. \\(\\mu_{src}^{m,k}\\) and \\(\\sigma_{src}^{m,k}\\) denote the mean and standard deviation of normalized source features from the category \\(k\\), respectively." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "18811" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.099, + 0.09, + 0.868, + 0.363 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.366, + 0.892, + 0.451 + ], + "angle": 0, + "content": "Figure 2. The main structure of our proposed method. From the source domain, we preserve the source centroids and the pre-trained model for each modality as the initialization of the class-wise centroids and all the models in the target domain, respectively. To generate reliable intra-modal predictions, Intra-Modal Prediction Aggregation (iMPA) attends to the reliable prediction whose feature shares a closer distance with the class-wise centroids in an intra-modal manner. Inter-Modal Pseudo-Label Fusion (xMPF) then fuses the intramodal predictions by estimating the reliability of predictions from each modality for noise suppression. Class-Wise Momentum Queues (CMQs) are designed to achieve a good balance between target domain adaptation and source knowledge preservation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.474, + 0.47, + 0.506 + ], + "angle": 0, + "content": "Here we use the features generated by the pre-trained extractor \\(g_0^m(\\cdot)\\) for the centroid construction." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.512, + 0.393, + 0.529 + ], + "angle": 0, + "content": "3.2. Intra-Modal Prediction Aggregation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.535, + 0.474, + 0.779 + ], + "angle": 0, + "content": "In MM-CTTA, the prediction from each modality could be unreliable due to continual domain shifts, causing severe noise to the multi-modal fusion. To mitigate the intramodal noise, iMPA aims to generate reliable intra-modal predictions for each modality. Although previous methods [42, 38] regard the augmentation-average prediction as a more stable alternative, we argue that its superiority is not certain since test-time augmentations may introduce inductive bias to the prediction [34] (e.g., resizing image as in [42] could cause ambiguity to small-scale classes). Unlike the previous work [42], we propose an adaptive mechanism to fuse the raw and the augmentation-average prediction as the weighted sum based on their feature distance between class-wise centroids. Given the input sample \\( x^{m} \\) and its augmented variants \\( \\{\\widetilde{x}_i^m\\mid i\\in [1,N_{aug}^m]\\} \\), the features and predictions are extracted by the teacher model \\( \\phi_{\\theta^{\\prime}}^{m} \\) as:" + }, + { + "type": "equation", + "bbox": [ + 0.152, + 0.784, + 0.47, + 0.801 + ], + "angle": 0, + "content": "\\[\np \\left(x ^ {m}\\right) = f _ {\\theta^ {\\prime}} ^ {m} \\left(g _ {\\theta^ {\\prime}} ^ {m} \\left(x ^ {m}\\right)\\right) = f _ {\\theta^ {\\prime}} ^ {m} \\left(z ^ {m}\\right), \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.152, + 0.805, + 0.469, + 0.849 + ], + "angle": 0, + "content": "\\[\n\\widetilde {p} \\left(x ^ {m}\\right) = \\frac {1}{N _ {a u g} ^ {m}} \\sum_ {i = 1} ^ {N _ {a u g} ^ {m}} f _ {\\theta^ {\\prime}} ^ {m} \\left(g _ {\\theta^ {\\prime}} ^ {m} \\left(\\widetilde {x} _ {i} ^ {m}\\right)\\right), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.903 + ], + "angle": 0, + "content": "where \\(p(x^{m})\\) and \\(\\widetilde{p} (x^m)\\) represent the raw and the augmentation-average prediction, respectively. Both predictions are of shape \\(N\\times N_{c}\\), where \\(N_{C}\\) is the number" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.474, + 0.892, + 0.633 + ], + "angle": 0, + "content": "of classes and \\(N_{aug}^{m}\\) denotes the number of augmentations. The normalized augmentation-average feature is computed as \\(\\widetilde{z}^m = \\sum_{i=1}^{N_{aug}^m} g^m(\\widetilde{x}_i^m) / (\\|g^m(\\widetilde{x}_i^m)\\| \\cdot N_{aug}^m)\\). Subsequently, the weights for predictions \\(p(x^m), \\widetilde{p}(x^m)\\) are computed based on their corresponding feature distance to the class-wise centroid in a point-wise manner, so that each point of the intra-modal prediction \\(\\hat{p}(x^m)\\) can attend more to the confident prediction located closer to the cluster in the latent space. Taking a point \\((j)\\) as an example, given its predictions \\(p_{(j)}(x^m), \\widetilde{p}_{(j)}(x^m)\\) and features \\(z_{(j)}^m, \\widetilde{z}_{(j)}^m\\):" + }, + { + "type": "equation", + "bbox": [ + 0.584, + 0.642, + 0.892, + 0.681 + ], + "angle": 0, + "content": "\\[\nw _ {(j)} ^ {m} = \\frac {\\exp \\left(\\left\\langle \\mu^ {m , k} , z _ {(j)} ^ {m} \\right\\rangle\\right)}{\\sum_ {i \\in N _ {c}} \\exp \\left(\\left\\langle \\mu^ {m , i} , z _ {(j)} ^ {m} \\right\\rangle\\right)}, \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.585, + 0.684, + 0.892, + 0.726 + ], + "angle": 0, + "content": "\\[\n\\widetilde {w} _ {(j)} ^ {m} = \\frac {\\exp \\left(\\left\\langle \\mu^ {m , \\widetilde {k}} , \\widetilde {z} _ {(j)} ^ {m} \\right\\rangle\\right)}{\\sum_ {i \\in N _ {c}} \\exp \\left(\\left\\langle \\mu^ {m , i} , \\widetilde {z} _ {(j)} ^ {m} \\right\\rangle\\right)}, \\tag {6}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.552, + 0.728, + 0.892, + 0.768 + ], + "angle": 0, + "content": "\\[\n\\hat {p} _ {(j)} \\left(x ^ {m}\\right) = \\frac {w _ {(j)} ^ {m} p _ {(j)} \\left(x ^ {m}\\right) + \\widetilde {w} _ {(j)} ^ {m} \\widetilde {p} _ {(j)} \\left(x ^ {m}\\right)}{w _ {(j)} ^ {m} + \\widetilde {w} _ {(j)} ^ {m}}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.775, + 0.895, + 0.903 + ], + "angle": 0, + "content": "where \\( w_{(j)}^m, \\widetilde{w}_{(j)}^m \\) are termed as the raw weight and augmentation-average weight, respectively. \\( k, \\widetilde{k} \\) are the largest element locations of \\( p_{(j)}(x^m), \\widetilde{p}_{(j)}(x^m) \\). \\( \\mu^{m,k} \\) denotes the mean of class \\( k \\) centroid, which is actively updated as shown in Sec. 3.4. \\( \\langle a,b\\rangle \\) represents the inner product of vectors \\( a \\) and \\( b \\). Our empirical results show that this adaptive fusion between the raw and augmentation-average predictions results in more stable intra-modal predictions." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "18812" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.091, + 0.375, + 0.106 + ], + "angle": 0, + "content": "3.3. Inter-Modal Pseudo-Label Fusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.114, + 0.473, + 0.345 + ], + "angle": 0, + "content": "Given the output of iMPA, the goal of xMPF is to generate pseudo-labels by estimating their reliability in a cross-modal manner. Since domain shifts can affect the reliability of each modality variously (e.g., images in day and night), the cross-modal pseudo-label should adaptively attend to the reliable modality for noise suppression. Motivated by this idea, the proposed xMPF generates the cross-modal pseudo-labels as the weighted sum of intra-modal predictions from iMPA. Specifically, taking point \\((j)\\) as an example, the inter-modal weight \\(\\hat{w}_{(j)}^{m}\\) is computed as the summation of both weights if their corresponding predictions indicate the same class, or the maximum one otherwise. This can be viewed as an implicit way to encourage point-wise prediction consistency for each modality. Formally, the inter-modal weight \\(\\hat{w}_{(j)}^{m}\\) is computed as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.135, + 0.353, + 0.47, + 0.397 + ], + "angle": 0, + "content": "\\[\n\\hat {w} _ {(j)} ^ {m} = \\left\\{ \\begin{array}{l} w _ {(j)} ^ {m} + \\widetilde {w} _ {(j)} ^ {m}, \\text {i f} k = \\widetilde {k} \\\\ \\max \\left(w _ {(j)} ^ {m}, \\widetilde {w} _ {(j)} ^ {m}\\right), \\text {i f} k \\neq \\widetilde {k} \\end{array} \\right. \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.403, + 0.47, + 0.434 + ], + "angle": 0, + "content": "The cross-modal prediction is then computed as the weighted sum in a cross-modal manner:" + }, + { + "type": "equation", + "bbox": [ + 0.144, + 0.442, + 0.47, + 0.485 + ], + "angle": 0, + "content": "\\[\n\\hat {p} _ {(j)} ^ {\\mathrm {X M}} (x) = \\frac {\\hat {w} _ {(j)} ^ {\\mathrm {2 D}} \\hat {p} _ {(j)} ^ {\\mathrm {2 D}} (x) + \\hat {w} _ {(j)} ^ {\\mathrm {3 D}} \\hat {p} _ {(j)} ^ {\\mathrm {3 D}} (x)}{\\hat {w} _ {(j)} ^ {\\mathrm {2 D}} + \\hat {w} _ {(j)} ^ {\\mathrm {3 D}}}, \\tag {9}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.168, + 0.486, + 0.47, + 0.511 + ], + "angle": 0, + "content": "\\[\n\\hat {y} _ {(j)} = \\arg \\max _ {k \\in N _ {c}} \\left(\\hat {p} _ {(j)} ^ {\\mathbf {x M}} (x) ^ {(k)}\\right), \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.521, + 0.47, + 0.582 + ], + "angle": 0, + "content": "where \\(\\hat{p}_{(j)}^{\\mathrm{xM}}(x),\\hat{y}_{(j)}\\) denote the cross-modal prediction and pseudo-label, respectively. The cross-modal pseudo-label can therefore attend to the more reliable modality with confident intra-modal predictions." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.591, + 0.325, + 0.607 + ], + "angle": 0, + "content": "3.4. Class-Wise Moving Queues" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.614, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Both iMPA and xMPF greatly depend on the quality of class-wise centroids. Initialized from the source offline centroids as in Eq. 1, the class-wise centroids should continually adapt to the target domain to ensure the validity of iMPA and xMPF. Meanwhile, the source knowledge should be occasionally played back during the centroid adaptation so that it can be revisited during the reliability estimation in iMPA and xMPF without catastrophic forgetting. To achieve a balance between adaptation and source knowledge preservation, we propose CMQs which utilize momentum queues [15] to actively estimate feature clustering of the target domain by capturing confident target features while stochastically restoring pseudo-source features for each modality. Specifically, the CMQ of the class \\( k \\) is initialized by the pseudo-source features \\( \\mathcal{Z}_{src}^{m,k} \\) as in Eq. 2. For each iteration, taking the raw sample as input, the normalized point features from the student network \\( \\phi_{\\theta}^{m} \\) with confident predictions are preserved by threshold-based filtering. Given the CMQ of class \\( k \\) from the previous step" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.09, + 0.878, + 0.109 + ], + "angle": 0, + "content": "denoted as \\(\\hat{\\mathcal{Q}}_{t - 1}^{m,k}\\), the CMQ of current step is updated as:" + }, + { + "type": "equation", + "bbox": [ + 0.528, + 0.12, + 0.892, + 0.141 + ], + "angle": 0, + "content": "\\[\n\\mathcal {Z} _ {c f} ^ {m, k} = \\mathbb {1} _ {c f} ^ {k} \\left[ g _ {\\theta} ^ {m} \\left(x ^ {m}\\right) / \\| g _ {\\theta} ^ {m} \\left(x ^ {m}\\right) \\| \\right], \\tag {11}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.528, + 0.142, + 0.892, + 0.163 + ], + "angle": 0, + "content": "\\[\n\\widetilde {\\mathcal {Q}} _ {t} ^ {m, k} = \\Phi \\left(\\hat {\\mathcal {Q}} _ {t - 1} ^ {m, k}, \\mathcal {Z} _ {c f} ^ {m, k}\\right), \\tag {12}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.528, + 0.166, + 0.892, + 0.207 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathcal {Q}} _ {t} ^ {m, k} = \\left\\{ \\begin{array}{l l} \\widetilde {\\mathcal {Q}} _ {t} ^ {m, k}, & \\text {i f} \\gamma_ {t} > p _ {r s} \\\\ \\Phi \\left(\\hat {\\mathcal {Q}} _ {t - 1} ^ {m, k}, \\mathbb {1} _ {r s} ^ {k} \\mathcal {Z} _ {s r c} ^ {m, k}\\right), & \\text {i f} \\gamma_ {t} \\leq p _ {r s} \\end{array} , \\right. \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.218, + 0.892, + 0.419 + ], + "angle": 0, + "content": "where \\(\\mathbb{1}_{cf}^k\\) is the confidence index for class \\(k\\) where \\(\\mathbb{1}_{cf}^k\\phi_\\theta^m (x^m)^{(k)}\\geq \\tau_{cf}\\) and \\(\\mathbb{1}_{rs}^k\\) denotes the source restoring index which randomly samples \\(N_{enq}\\) pseudo-source features from \\(\\mathcal{Z}_{src}^{m,k}\\). \\(\\Phi (a,b)\\) denotes the operation of enqueuing \\(b\\) in \\(a\\) as in [15]. \\(\\gamma_{t}\\) is a restoring flag uniformly sampled from [0, 1] at timestamp \\(t\\) and \\(p_{rs}\\) denotes the hyperparameter of restoring probability. Different from the image classification problem which can capture all confident samples [36], the number of confident points from each class can be huge (i.e., more than 1,000), which is too aggressive and expensive to enqueue all points. Therefore, we limit the index number of \\(\\mathbb{1}_{cf}^k\\) by an upper bound \\(N_{enq}\\) through selecting features with the top \\(N_{enq}\\) confident predictions." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.419, + 0.893, + 0.664 + ], + "angle": 0, + "content": "For each optimization step, the mean of the class-wise centroid for the next step \\(\\mu_{t + 1}^{m,k}\\) is updated as the average of CMQ of the current timestamp \\(\\hat{\\mathcal{Q}}_t^{m,k}\\) so that the class-wise centroids can adapt to the feature clustering of target domain without catastrophic forgetting. Additionally, we propose a class-wise contrastive loss modified from [19] as a regularizer so that the target confident features can revisit source knowledge through clustering around the class-wise centroids. Specifically, given any confident target feature from Eq. 11 as the anchor, the positive samples are the features from the CMQ that shares the same modality and semantic class, denoted as \\(P(k) = \\{\\hat{q}_p\\mid \\hat{q}_p\\in \\hat{\\mathcal{Q}}_t^{m,k}\\}\\). The negative samples are the features from the CMQs of the same modality but different classes denoted as \\(A(k) = \\{\\hat{q}_n\\mid \\hat{q}_n\\in \\hat{\\mathcal{Q}}_t^{m,a},\\forall a\\neq k\\bigcap a\\in N_c\\}\\). The class-wise contrastive loss \\(\\mathcal{L}_{cts}^m\\) is computed as:" + }, + { + "type": "equation", + "bbox": [ + 0.538, + 0.674, + 0.892, + 0.765 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {L} _ {c t s} ^ {m} = \\sum_ {i \\in | \\mathcal {Z} _ {c f} ^ {m, k} |} \\frac {- 1}{| P (k) |} \\\\ \\sum_ {q _ {p} \\in P (k)} \\frac {\\exp \\left(\\hat {z} _ {t , (i)} ^ {m , k} \\cdot q _ {p}\\right)}{\\sum_ {q _ {n} \\in N (k)} \\exp \\left(\\hat {z} _ {t , (i)} ^ {m , k} \\cdot q _ {n}\\right)}. \\tag {14} \\\\ \\end{array}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.787, + 0.796, + 0.803 + ], + "angle": 0, + "content": "3.5. Main Structure and Optimization" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.811, + 0.894, + 0.902 + ], + "angle": 0, + "content": "The main structure of our proposed method is shown in Fig. 2. Given the multi-modal input \\( x^{m} \\), the teacher model is used to infer \\( x^{m} \\) and its augmented variants \\( \\{\\widetilde{x}_i^m | i \\in [1, N_{\\text{aug}}^m]\\} \\) and then generate reliable cross-modal pseudolabels denoted as \\( \\hat{y} \\) through iMPA and xMPF. The student model is directly updated by minimizing the weighted sum" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18813" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.079, + 0.095, + 0.327, + 0.11 + ], + "angle": 0, + "content": "Algorithm 1: The proposed CoMAC" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.113, + 0.43, + 0.129 + ], + "angle": 0, + "content": "Init Model: Teacher \\(\\phi_{\\theta}^{m}\\), student \\(\\phi_{\\theta}^{m}\\), \\(m \\in \\{2D, 3D\\}\\)" + }, + { + "type": "text", + "bbox": [ + 0.079, + 0.129, + 0.418, + 0.146 + ], + "angle": 0, + "content": "Init CMQ: \\(\\hat{\\mathcal{Q}}_0^{m,k} = \\mathcal{Z}_{src}^{m,k}\\), \\(m\\in \\{2\\mathrm{D},3\\mathrm{D}\\}\\), \\(k\\in N_{c}\\)" + }, + { + "type": "text", + "bbox": [ + 0.08, + 0.146, + 0.336, + 0.161 + ], + "angle": 0, + "content": "for \\(t\\in |\\mathcal{X}_{\\mathcal{T}}|\\) \\(x = (x^{2D},x^{3D})\\in \\mathcal{X}_{\\mathcal{T}}\\) do" + }, + { + "type": "text", + "bbox": [ + 0.086, + 0.162, + 0.233, + 0.175 + ], + "angle": 0, + "content": "for \\(m\\in \\{2D,3D\\}\\) do" + }, + { + "type": "text", + "bbox": [ + 0.094, + 0.176, + 0.383, + 0.193 + ], + "angle": 0, + "content": "1. Augmented input to get \\(\\{\\widetilde{x}_i^m\\mid i\\in N_{aug}^m\\}\\)" + }, + { + "type": "text", + "bbox": [ + 0.093, + 0.193, + 0.428, + 0.208 + ], + "angle": 0, + "content": "2. Get predictions and features with \\(\\phi_{\\theta'}^m\\) by Eq. 3-4" + }, + { + "type": "text", + "bbox": [ + 0.093, + 0.208, + 0.443, + 0.223 + ], + "angle": 0, + "content": "3. Get intra-modal \\(\\hat{p}^m (x^m)\\) by iMPA through Eq. 5-7" + }, + { + "type": "list", + "bbox": [ + 0.093, + 0.176, + 0.443, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.086, + 0.225, + 0.114, + 0.236 + ], + "angle": 0, + "content": "end" + }, + { + "type": "text", + "bbox": [ + 0.086, + 0.239, + 0.402, + 0.254 + ], + "angle": 0, + "content": "4. Get inter-modal \\(\\hat{y}\\) by xMPF through Eq. 8-10" + }, + { + "type": "text", + "bbox": [ + 0.086, + 0.254, + 0.41, + 0.269 + ], + "angle": 0, + "content": "5. Update CMQs and compute \\(\\mathcal{L}_{cts}^{m}\\) by Eq. 11-14" + }, + { + "type": "text", + "bbox": [ + 0.086, + 0.27, + 0.367, + 0.285 + ], + "angle": 0, + "content": "6. Update \\(\\phi_{\\theta}^{m}\\) by Eq. 16 and \\(\\phi_{\\theta^{\\prime}}^{m}\\) by Eq. 17" + }, + { + "type": "list", + "bbox": [ + 0.086, + 0.239, + 0.41, + 0.285 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.287, + 0.108, + 0.299 + ], + "angle": 0, + "content": "end" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.336, + 0.47, + 0.398 + ], + "angle": 0, + "content": "of the standard cross-entropy loss between its prediction and the pseudo-label \\(\\hat{y}\\), and the contrastive loss in Eq. 14. The teacher model is updated as the exponential moving average of the student's weights as in previous works [35, 42]:" + }, + { + "type": "equation", + "bbox": [ + 0.174, + 0.41, + 0.469, + 0.427 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {c e} ^ {m} = \\mathbb {1} _ {\\tilde {y}} \\log \\phi^ {m} \\left(x ^ {m}\\right), \\tag {15}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.223, + 0.431, + 0.269, + 0.443 + ], + "angle": 0, + "content": "\\[\n\\{2 D, 3 D \\}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.443, + 0.469, + 0.473 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {t o t a l}} = \\sum_ {m} \\left(\\mathcal {L} _ {c e} ^ {m} + \\lambda_ {c t s} \\mathcal {L} _ {c t s} ^ {m}\\right), \\tag {16}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.169, + 0.476, + 0.469, + 0.493 + ], + "angle": 0, + "content": "\\[\n\\theta_ {t + 1} ^ {\\prime} = \\left(1 - \\lambda_ {s}\\right) \\theta + \\lambda_ {s} \\theta^ {\\prime}, \\tag {17}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.506, + 0.469, + 0.552 + ], + "angle": 0, + "content": "where \\(\\lambda_{cts}\\) and \\(\\lambda_s\\) are the hyper-parameters denoting the coefficient of the contrastive loss and the momentum factor. Our adaptation process is summarized as Algorithm 1." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.567, + 0.21, + 0.584 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.593, + 0.47, + 0.67 + ], + "angle": 0, + "content": "In this section, we present our experimental results based on two new benchmarks. The details of our proposed benchmarks, baselines, and implementation are first introduced in Sec. 4.1. Sec. 4.2 presents our overall results and Sec. 4.3 justifies our method by extensive ablation studies." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.681, + 0.31, + 0.697 + ], + "angle": 0, + "content": "4.1. Benchmarks and Settings" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Proposed benchmarks. To evaluate the performance under MM-CTTA settings, we proposed two benchmarks in this work, including (i) SemanticKITTI-to-Synthia (S-to-S) and (ii) SemanticKITTI-to-Waymo (S-to-W). Both benchmarks leverage SemanticKITTI [2] as the source-domain dataset, which utilizes a 0.7MP camera and a 64-line LiDAR. For the target domain, we utilize two different datasets including Synthia [33] and Waymo [37] thanks to the various environmental conditions they cover. The former shares a larger domain gap with more diverse seasons, weather, and illumination conditions while the latter is less challenging but closer to the real-world application. For S-to-S, it is constructed by a sequence of different videos" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.091, + 0.892, + 0.546 + ], + "angle": 0, + "content": "from Synthia [33] without any repetition. Since Synthia includes depth images instead of 3D point clouds, we generate a simulated point cloud for each sample by randomly sampling depth pixels as 3D points following the structural characteristic of LiDAR. For each sequence, all samples are included for adaptation and we use \"No.-Conditions\" to indicate their corresponding video sequence in Synthia (i.e., \"01-Spring\" indicates video sequence 01 under Spring condition). Different from the previous CTTA benchmark [42] which only includes 4 different unique sequences, the proposed S-to-S consists of 12 different sequences recorded under various environmental conditions without repetition. By default, we organize the sequences following the order of seasons \\(\\rightarrow\\) illumination \\(\\rightarrow\\) weathers as a challenge ascending order. For S-to-W, we sort out the illumination conditions of each sequence in Waymo dataset [37] based on the sequence descriptions and divide all samples into three types, including Day (D), Dawn-Dusk (DD), and Night (N). Since the number of sequences of D is much larger than others, we further split the sequence of D based on their recording location, including Phoenix (P), San Francisco (S), and Others (O). Each sequence is separated in two halves to simulate the revisiting situation as in [42] but without repeated samples (i.e., \"D-O-1\" indicates the first half of the D-O sequence). Similar to S-to-S, S-to-W also follows a challenge ascending order. For both datasets, we adopt the images of the front-view camera similar to the source-domain dataset. We utilize a similar class mapping strategy as [18, 35] with slight modification since some classes are missing in the target domain. More details are illustrated in the appendix." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.549, + 0.892, + 0.777 + ], + "angle": 0, + "content": "Baselines. Previous TTA, MM-TTA, and CTTA methods are evaluated on both S-to-S and S-to-M as baselines. For TTA methods, we compare with pseudo-labels with threshold filtering (Plabel), TENT [40] and LAME [3], while xMUDA with pseudo-labels (xMUDA-pl) [18] and MMTTA [43] are regarded as the representatives of MMTTA methods. CoTTA [42] and EATA [30] are the recent works that focus on CTTA problems. Specifically, xMUDA-pl is originally designed for UDA, whereas we modify it into a TTA version by discarding the source data during adaptation. Considering our CoMAC is the only MM-CTTA method, we implement an MM-CTTA version of MMTTA [35] integrated with model-based stochastic restoration in [42] for a fair comparison. We report the softmax-average mIoU of 2D and 3D predictions as results." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Implementation details. Following previous works [18, 35], we utilize UNet [32] with ResNet-34 [16] encoder as the 2D backbone and SCN [14] based on UNet as the 3D backbone for all baselines. The pre-training procedures on SemanticKITTI dataset follow [18]. For our method, we empirically choose resizing and z-rotation as the 2D and 3D augmentations following previous works [42, 18]. Specifically, we utilize multiple resizing factors of [0.5," + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18814" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.891, + 0.292 + ], + "angle": 0, + "content": "
Timet →t →
MethodsDA TypeSemanticKITTI-to-SynthiaSemanticKITTI-to-Waymo
01-Spring02-Summer04-Full05-Winter01-Dawn02-Night04-Sunset05-Wnight01-Fog02-S-Rain04-R-Night05-RainAvgD-O-1D-P-1D-S-1DD-1N-1D-O-2D-P-2D-S-2DD-2N-2Avg
Source-28.330.737.727.323.127.338.226.527.021.627.816.427.733.236.929.528.314.032.838.030.428.414.628.6
PlabelTTA29.627.136.428.421.426.632.326.127.421.825.018.026.739.141.937.036.825.738.543.737.637.624.636.9
TENT [40]TTA35.424.924.920.718.716.616.013.613.611.58.49.117.833.622.318.816.910.815.712.99.811.310.616.3
LAME [3]TTA14.012.417.313.012.611.617.013.219.27.77.86.012.711.910.413.49.28.713.411.212.29.78.612.7
xMUDA-pl [18]MM-TTA28.826.935.928.221.326.532.226.027.021.624.917.926.439.342.137.437.025.938.743.937.937.725.036.5
MMTTA [35]MM-TTA31.124.430.725.828.324.226.823.229.620.722.120.625.639.940.030.931.529.630.632.223.926.423.830.9
CoTTA [42]CTTA29.727.234.727.026.425.633.027.328.118.022.718.426.532.928.022.922.220.326.124.923.624.719.724.5
EATA [30]CTTA34.030.038.630.230.228.436.530.132.221.325.320.129.740.140.836.334.328.939.341.736.537.928.836.5
MMTTA-rs [35]MM-CTTA31.928.137.729.328.727.635.229.730.220.425.620.328.740.441.536.334.730.239.941.536.438.329.936.9
CoMAC (Ours)MM-CTTA34.034.744.938.135.037.845.139.039.129.435.127.136.641.443.738.837.832.242.241.840.738.930.438.8
Timet ←t ←
TENT [40]TTA10.28.88.69.010.29.59.811.418.313.216.918.912.112.011.59.29.89.712.613.012.519.821.213.1
MMTTA-rs [35]MM-CTTA31.427.437.228.726.227.233.129.028.519.922.319.727.640.441.436.431.629.137.640.235.435.227.835.5
CoMAC (Ours)MM-CTTA34.632.840.933.231.832.439.233.233.825.130.323.332.440.841.937.733.230.339.643.638.838.630.037.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.102, + 0.299, + 0.866, + 0.314 + ], + "angle": 0, + "content": "Table 1. Performance (mIoU) of SemanticKITTI-to-Synthia. Here we report the softmax-average mIoU of 2D and 3D prediction." + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.33, + 0.322, + 0.412 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.364, + 0.33, + 0.607, + 0.411 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.649, + 0.33, + 0.89, + 0.411 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.418, + 0.893, + 0.461 + ], + "angle": 0, + "content": "Figure 3. Ablation studies to justify our design of CoMAC. Specifically, (a) compares CoMAC with variants only using raw or augmented samples as input of iMPA and (b) justifies the necessity of weighting mechanisms in iMPA and xMPF. (c) compares CoMAC with variants without either target feature enqueuing or pseudo-source features restoring in CMQs. Scores within the parentheses are the average mIoU." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.484, + 0.47, + 0.592 + ], + "angle": 0, + "content": "0.625, 0.75, 0.875] and z-rotation of \\([60^{\\circ}, 120^{\\circ}, 180^{\\circ}, 240^{\\circ}, 300^{\\circ}]\\). \\(N_{q}\\) and \\(N_{enq}\\) are set to 4096 and 200, respectively. We utilize a restore rate \\(p_{rs}\\) of 0.5 and a momentum factor \\(\\lambda_{s}\\) of 0.999 with a coefficient \\(\\lambda_{cts}\\) of 1. All methods strictly follow the one-pass protocol [36] (i.e., the training epoch is one where inference is conducted immediately for each sample). More details are included in the appendix." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.605, + 0.233, + 0.619 + ], + "angle": 0, + "content": "4.2. Overall Results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.471, + 0.903 + ], + "angle": 0, + "content": "As shown in Table 1, our CoMAC achieves SOTA performance on the average mIoU of all sequences for both benchmarks. Specifically, the proposed CoMAC significantly outperforms previous methods by more than \\(6.9\\%\\) on S-to-S and \\(1.9\\%\\) on S-to-W, which justifies the effectiveness of our method. It can also be observed that most TTA methods (TENT [40] and LAME [3]) are outperformed by CTTA methods, which reveals the importance of avoiding catastrophic forgetting. Additionally, previous MM-TTA (i.e., xMUDA and MMTTA) methods can not consistently outperform previous single-modal methods (e.g., EATA [30]), which suggests the sensitivity of multi-modal collaboration toward continual domain shifts. In fact, by intuitively utilizing model-based stochastic restoration, MMTTA-rs can achieve a noticeable improvement of \\(3.1\\%\\) and \\(6.0\\%\\) on S-to-S and S-to-W, respectively. Yet MMTTA-rs is still outperformed by our method. To justify the effect of the sequence arrangement, we conduct additional experiments by" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.485, + 0.892, + 0.546 + ], + "angle": 0, + "content": "reversing the sequences of S-to-S and S-to-W for TENT, MMTTA-ms, and our CoMAC. While the performance of all methods decreases, the improvement of CoMAC compared to others can be observed across all sequences." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.547, + 0.892, + 0.759 + ], + "angle": 0, + "content": "For S-to-S, we notice that our method achieves the second-best performance at the first sequence 01-Spring and then surpasses all previous methods in the following sequences since we utilize CMQs to gradually adapt to the changing target domain without forgetting. Compared with TTA methods, our method consistently prevails with an increasing gap as they struggle with error accumulation. A similar observation can be found at D-O-2 of S-to-W. Interestingly, xMUDA-pl as well as Plabel perform competitively on S-to-W and outperform CoMAC in D-P-2 mainly because is less challenging and simply filtering pseudolabels can effectively mitigate the prediction noise. Nevertheless, this performance gap is trivial as our CoMAC surpasses both xMUDA-pl and Plabel on all other sequences." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.77, + 0.665, + 0.785 + ], + "angle": 0, + "content": "4.3. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.891, + 0.825 + ], + "angle": 0, + "content": "In this section, we provide our ablation studies on S-to-S to justify our design of CoMAC." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Utilization of raw and augmented input. In Sec. 3.2, a key hypothesis is that while the augmentation-average prediction can be a potential reliable alternative, it may introduce inductive bias to the result. To justify this assumption, we conduct experiments by simply using the pure raw" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18815" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.123, + 0.089, + 0.852, + 0.282 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.29, + 0.893, + 0.318 + ], + "angle": 0, + "content": "Figure 4. Visualization of online segmentation results. Here we present the cross-modal pseudo-labels from xMPF (Ours) as well as the individual prediction from 2D and 3D teachers in comparison with the ground truth (GT)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.343, + 0.47, + 0.463 + ], + "angle": 0, + "content": "or augmentation-average prediction as the intra-modal prediction as in Eq. 7. As shown in Fig. 3(a), both variants achieve inferior performance compared to CoMAC and these performance gaps are consistent across most sequences. Specifically, using pure augmentation-average predictions lead to serious degradation of \\(5.8\\%\\), which justifies the necessity of mitigating the inductive noise brought by test-time augmentations and our motivation for iMPA." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.469, + 0.47, + 0.606 + ], + "angle": 0, + "content": "Weighting mechanisms of iMPA and xMPF. The proposed iMPA and xMPF utilize centroid-based weighting mechanisms to attend to the reliable modality. To justify their effectiveness, we compared CoMAC with variants by replacing either Eq. 7 or Eq. 8 with a simple average fusion (indicated as w/o iMPA and w/o xMPF). As presented in Fig. 3(b), CoMAC outperforms both variants by more than \\(2.5\\%\\). This performance gap justifies that both iMPA and xMPF play an important part in noise suppression." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.609, + 0.47, + 0.866 + ], + "angle": 0, + "content": "Updating mechanisms of CMQs. The goal of CMQs is to achieve a good balance between adaptation and knowledge preservation. To justify the role of CMQs, we compared CoMAC with variants without enqueuing target features or restoring pseudo-source features, respectively. For the variant without enqueuing target features, the corresponding class-wise centroids are identical to the source centroids across the whole testing process. As in Fig. 3(c), disabling enqueuing target features (w/o Update) causes a significant performance decrease of \\(6.1\\%\\), which justifies the necessity of adapting class-wise centroids for the validity of iMPA and xMPF. On the other hand, while disabling restoring pseudo-source features (w/o Restore) leads to a quicker adaptation at the first two sequences, it eventually causes catastrophic forgetting after the third sequence, resulting in a noticeable gap of \\(8.4\\%\\). Overall, the performance gain brought by CMQs justifies their effectiveness." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Number of Augmentations. To investigate the effect of augmentations, we conduct a grid search by utilizing differ-" + }, + { + "type": "table", + "bbox": [ + 0.528, + 0.34, + 0.866, + 0.423 + ], + "angle": 0, + "content": "
CoMACNo. of 2D Aug
12345Avg
No. of 3D Aug133.033.133.233.233.333.2
234.134.234.334.434.434.3
335.235.235.435.335.535.3
436.436.436.536.536.536.5
536.436.536.736.636.736.6
Avg35.035.135.235.235.335.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.425, + 0.892, + 0.453 + ], + "angle": 0, + "content": "Table 2. Augmentation analysis of CoMAC. CoMAC is evaluated with different numbers of augmentations." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.467, + 0.892, + 0.522 + ], + "angle": 0, + "content": "
CoMAC\\( p_{rs} \\)\\( (\\tau_{cf},\\lambda_{cts}) \\)Avg\\( \\tau_{cf} \\)\\( (p_{rs},\\lambda_{cts}) \\)Avg\\( \\lambda_{cts} \\)\\( (p_{rs},\\tau_{cf}) \\)Avg
0.5(0.8,1.0)36.60.8(0.5,1.0)36.61.0(0.5,0.8)36.6
0.3-34.50.0-34.80.0-35.8
0.7-36.40.5-36.50.01-36.4
1.0-36.30.9-36.40.1-36.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.529, + 0.892, + 0.571 + ], + "angle": 0, + "content": "Table 3. Sensitivity analysis of CoMAC. Here \"xM\" is the softmax-average of 2D and 3D predictions. The parameter value with \"-\" indicates the same value as default settings." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.598, + 0.892, + 0.779 + ], + "angle": 0, + "content": "ent numbers of 2D and 3D augmentations. Specifically, we adopt resize and rotation as 2D and 3D augmentation, respectively. The factor range for 2D scaling is [0.5, 1) while 3D one is set to \\((0^{\\circ}, 360^{\\circ})\\), where the list of augmentations is computed as evenly spaced factors given the number of augmentations. As shown in Table 2, increasing the number of either 2D or 3D augmentations leads to performance improvement, while the 2D improvement is less noticeable compared to 3D probably due to the inductive bias brought by 2D augmentations. While all settings perform competitively, we adopt the combination of three 2D augmentations and five 3D augmentations to achieve the best result." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Sensitivity analysis. We perform sensitivity analysis over the hyper-parameters of CoMAC as shown in Table 3. There are some extreme cases that can lead to the performance degeneration of CoMAC. For restoring rate \\( p_{rs} \\), the performance relatively drops about \\( 5.7\\% \\) when \\( p_{rs} = 0.3 \\), indicating the restoring rate is too low to prevent forgetting. Nevertheless, when \\( p_{rs} \\geq 0.5 \\), CoMAC is robust to the arbitrary choice of \\( p_{rs} \\). Similar observations can be found when" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.956 + ], + "angle": 0, + "content": "18816" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.1, + 0.077, + 0.447, + 0.152 + ], + "angle": 0, + "content": "
MethodAug SamplesInf. Time (s)/samplemIoU
meanstd
TENT [40]X0.3790.01017.8
CoTTA [42]✓7.2200.39926.5
Ours✓1.8880.08236.6
Ours (less augs)✓1.0040.03833.0
" + }, + { + "type": "table_caption", + "bbox": [ + 0.118, + 0.154, + 0.428, + 0.168 + ], + "angle": 0, + "content": "Table 4. Comparison of processing time per sample." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.184, + 0.252, + 0.282 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.264, + 0.184, + 0.459, + 0.282 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.286, + 0.47, + 0.328 + ], + "angle": 0, + "content": "Figure 5. Processing time of CoMAC components per sample (left) and GPU RAM with or without CMQs (right). Experiments are conducted on S-to-S with the default backbones and settings." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.358, + 0.468, + 0.478 + ], + "angle": 0, + "content": "\\(\\tau_{cf} = 0.0\\) or \\(\\lambda_{cts} = 0.0\\), where the performance decreases relatively by \\(4.9\\%\\) and \\(2.2\\%\\). This performance degeneration indicates the importance of confident feature filtering and class-wise contrastive loss. Overall, when \\(\\tau_{cf} \\geq 0.0\\) and \\(\\lambda_{cts} \\geq 0.01\\), the performance of CoMAC is also robust to the hyper-parameter settings, falling into a relative margin of \\(0.5\\%\\). Note that all settings of CoMAC surpass the previous SOTA method EATA [30] by more than \\(4.8\\%\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.479, + 0.468, + 0.629 + ], + "angle": 0, + "content": "Visualization of segmentation. To further justify the effectiveness of our proposed CoMAC, we provide some visualization results as shown in Fig. 4. Specifically, we visualize the 2D and 3D predictions from teacher models and our cross-modal pseudo-labels from xMPF. Compared to single-modal predictions, our cross-modal pseudo-labels can achieve better segmentation results by attending to the reliable modality, such as the first row in Fig. 4, where the sidewalk prediction attends more to the 2D image while the car prediction attends to the reliable 3D point cloud." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.63, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Computational and storage overhead. To investigate the computational and storage overhead of CoMAC, we analyze the processing time and GPU occupancy when online testing with our CoMAC as illustrated in Table 4 and Fig. 5. Similar to previous augmentation-based methods, our proposed CoMAC is limited by the computational overhead brought by multiple augmentations. However, compared to the augmentation-based SOTA method CoTTA [42], our method outperforms it in terms of performance and efficiency (a relative performance improvement of \\(38.1\\%\\) with \\(73.9\\%\\) less processing time). Compared to the single-sample-based method TENT, despite a computational overhead of 1.51s, our method significantly improves relatively by more than \\(100\\%\\). The computational overhead can be further lessened by using fewer augmentations, reducing the processing time relatively by more than \\(46.8\\%\\) with a minor performance drop of \\(3.6\\%\\). Besides augmentations, another potential source of overhead lies in the utilization of" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.213 + ], + "angle": 0, + "content": "CMQs as they capture class-wise features for each iteration. As shown in Fig .5, however, the computational overhead brought by CMQs is rather trivial, which takes less than 0.05s to update and process each frame. Moreover, since CMQs only preserve the high-level features instead of raw samples, the storage cost is also acceptable with a minor usage increase (less than \\(800\\mathrm{MB}\\)) of GPU RAM compared to the CoMAC invariant without CMQs." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.229, + 0.618, + 0.244 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.256, + 0.892, + 0.483 + ], + "angle": 0, + "content": "In this paper, we present a new task, named multi-modal continual test-time adaptation (MM-CTTA) for 3D semantic segmentation. We further propose a novel method called CoMAC that tackles MM-CTTA from two perspectives. On one hand, reliable cross-modal pseudo-labels are generated by iMPA and xMPF by adaptively attending to the more reliable modality in a dual-stage manner. On the other hand, CMQs are proposed to leverage pseudo-source features and reliable target features to perform adaptation without catastrophic forgetting. We introduce two new benchmarks for MM-CTTA and our methods outperform previous works by a noticeable margin in both benchmarks. In the future, we hope both our method and benchmarks can facilitate the exploration of MM-CTTA and promote the development of reliable multi-modal systems in altering environments." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.499, + 0.66, + 0.516 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.525, + 0.892, + 0.615 + ], + "angle": 0, + "content": "This research is supported by the National Research Foundation, Singapore under its Medium Sized Center for Advanced Robotics Technology Innovation. 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In this paper, we explore Multi-Modal Continua! tual Test-Time Adaptation (MM-CTTA) as a new extension of CTTA for 3D semantic segmentation. The key to MMCTTA is to adaptively attend to the reliable modality while avoiding catastrophic forgetting during continual domain shifts, which is out of the capability of previous TTA or CTTA methods. To fulfill this gap, we propose an MM-CTTA method called Continua! Cross-Modal Adaptive Clustering (CoMAC) that addresses this task from two perspectives. On one hand, we propose an adaptive dual-stage mechanism to generate reliable cross-modal predictions by attending to the reliable modality based on the class-wise featurecentroid distance in the latent space. On the other hand, to perform test-time adaptation without catastrophic forgetting, we design class-wise momentum queues that capture confident target features for adaptation while stochastically restoring pseudo-source features to revisit source knowledge. We further introduce two new benchmarks to facilitate the exploration of MM-CTTA in the future. Our experimental results show that our method achieves state-of-the-art performance on both benchmarks. Visit our project website at https://sites.google.com/view/mmcotta. + +# 1. Introduction + +Test-Time Adaptation (TTA) proposes a realistic domain adaptation scenario, which adapts pre-trained models to the target domain during the testing process. Unlike previous Unsupervised Domain Adaptation (UDA) [17, 45, 52, 47], TTA performs adaptation online without accessing the data from the source domain. Typical TTA [40, 35, 36] methods assume a stationary target domain, while real-world scenarios are dynamic over time. To fulfill this gap, a previous work [42] proposes a general extension of TTA named Con- + +![](images/1a6a931f2d306fe37710fa4c6f83d16348abd78073280614f500b3629bd4a2c9.jpg) + +![](images/aaada682dd055f130be65cba221c5dc7fd1e823b07d039a46162d76e8148c56e.jpg) +Figure 1. Illustration of how continual domain shifts affect multimodal segmentation and our method. Unlike the source domain where predictions from both modalities are reliable, the reliability of each modality varies in MM-CTTA due to different domain shifts. CoMAC tackles MM-CTTA by attending to the reliable modality $(\checkmark)$ rather than the noisy one $(\chi)$ . Meanwhile, source knowledge is stochastically revisited to avoid catastrophic forgetting. Figure best viewed in color and zoomed in. + +tual Test-Time Adaptation (CTTA) which assumes that the target domain is continually changing rather than static. Compared to TTA, CTTA is more challenging since the performance is easily affected by error accumulation [6] and catastrophic forgetting [27] during the continual adaptation. + +For 3D semantic segmentation, multi-modal sensors are frequently leveraged in different tasks, such as scene understanding [4, 28] and semantic map construction [29, 43]. For some specific applications like semantic-based localization [8] and autonomous driving [46, 44], multi-modal information is the key to robust performance under adverse conditions. However, their collaboration has been proven to be sensitive toward domain drifts [1, 35]. In real-world scenarios, such collaboration deterioration could be more severe considering that the target domain is continually changing as in CTTA (e.g., the operating environments of 24/7 AGVs are continually changing due to altering weather or illumination conditions). Hence, it is essential for multi- + +modal networks to adapt to the dynamic target domain in an online manner. In this work, we aim to study MultiModal Continual Test-Time Adaptation (MM-CTTA) for 3D semantic segmentation, where networks are continually adapted to a changing target domain taking 3D point clouds and 2D images as input without accessing the source data. + +Intuitively, one can address MM-CTTA by utilizing CTTA [30, 42] or TTA [3, 38] methods on 2D and 3D networks separately. However, this simple extension can not achieve satisfactory performance since it cannot correctly attend to the reliable modality for adaptation when others suffer from severe domain shifts. Take Fig. 1 as an example: predictions from the 2D image are more accurate at the beginning of the target domain, while 2D results become unreliable and 3D predictions prevail as the illumination level significantly changes over time. Although previous CTTA or TTA methods have attempted to mitigate this intra-modal prediction noise by augmentations [42] or entropy minimization [40, 30], the domain drift in Fig. 1 is too severe to be effectively rectified by image input itself, leading to inevitable error accumulation. Previous works have proposed different cross-modal fusion methods to mitigate the effect of the noisy modality during adaptation, such as cross-modal consistency [18] for UDA or pseudo-label fusion based on student-teacher consistency [35] for TTA. However, their methods rely on the premise that the target domain is static, and therefore suffer from catastrophic forgetting in MM-CTTA, leading to degenerated results. + +For MM-CTTA, an ideal solution is to suppress the contribution from the noisy modality and attend more to the reliable one in an online manner. Typically, the reliability of prediction can be estimated based on its corresponding feature location in the latent space. A prediction with features close to the centroid is more likely to be reliable, suffering less from the domain shift and vice versa. On the other hand, to ensure the validity of centroid-based reliability estimation, class-wise centroids should actively adapt to the continually changing target domain while stochastically revisiting the source knowledge to avoid catastrophic forgetting. To this end, we propose an MM-CTTA method called Continual Cross-Modal Adaptive Clustering (CoMAC) for 3D semantic segmentation. CoMAC consists of three main modules: (i) Intra-Modal Prediction Aggregation (iMPA), (ii) Inter-Modal Pseudo-Label Fusion (xMPF), and (iii) Class-Wise Momentum Queues (CMQs). On one hand, the proposed iMPA and xMPF are utilized to suppress prediction noise based on the centroid-based reliability estimation from intra-modal and inter-modal perspectives, respectively. On the other hand, CMQs are designed to actively adapt class-wise centroids for iMPA and xMPF while avoiding catastrophic forgetting. Additionally, a class-wise contrastive loss is introduced to regularize the extracted features from drifting too far from centroids. + +In summary, our main contributions are three-fold. (i) We explore a new task MM-CTTA where multi-modal input is utilized to perform continual test-time adaptation for 3D semantic segmentation and propose an effective method named CoMAC to leverage multi-modal information for MM-CTTA. (ii) We propose iMPA and xMPF to generate accurate cross-modal pseudo-labels by attending to a reliable modality. CMQs are introduced to actively adapt to the target domain without catastrophic forgetting. (iii) We introduce two 3D semantic segmentation benchmarks to facilitate the future exploration of MM-CTTA. Extensive experiments show that our method achieves state-of-the-art performance, outperforming previous methods significantly by $6.9\%$ on the challenging benchmark. + +# 2. Related Works + +Test-Time Adaptation Describing a more realistic adaptation scenario, Test-Time Adaptation (TTA) is receiving more and more attention. Different from previous Unsupervised Domain Adaptation (UDA), TTA forbids access to raw source data and adapts the source pre-trained model during test time. As one of the primary works, TENT [40] highlights the fully test-time setting and proposes to update the batch normalization layers by entropy minimization. The following works mainly address TTA by aligning batch normalization statistics [30, 23, 51], self-training with pseudo labeling [13, 41], feature alignment [25], or augmentation invariance [50, 21]. The aforementioned TTA methods strictly follow the one-pass protocol as mentioned in [36], where networks immediately infer each sample in an online manner and forbid multiple training epochs. On the other hand, some previous works [22, 10, 7, 48] follow the multi-pass protocol by adapting the model for multiple epochs in an offline manner. As one of the primary works, Source Hypothesis Transfer (SHOT) [22] proposes to update only the encoder parameters and align source and target representation by entropy minimization and pseudolabeling. While most existing TTA methods are proposed for image classification, some recent works [10, 20, 26] aim to explore TTA for image semantic segmentation. Specifically, [10] proposes to minimize the prediction entropy while maximizing its robustness toward feature noise. [20] divides the TTA problem into source domain generalization and target domain adaptation. [26] proposes a dual attention distillation method to transfer contextual knowledge and patch-level pseudo labels for self-supervised learning. + +Continual Test-Time Adaptation The definition of Continual Test-Time Adaptation (CTTA) is first proposed in CoTTA[42], which aims to adapt the model to continually changing target domains in an online manner without any source data. Specifically, CoTTA proposes to use the moving teacher model and augmentation-average predictions for noise suppression and the model stochastic + +restoration to avoid catastrophic forgetting. Following the scheme of CoTTA, some recent works [11, 12, 30] have addressed CTTA from different perspectives. Specifically, [12] leverages the temporal correlations of streamed input by reservoir sampling and instance-aware batch normalization. [11] proposes domain-specific prompts and domain-agnostic prompts to preserve domain-specific and domain-shared knowledge, respectively. EATA [30] performs adaptation on non-redundant samples for an efficient update. + +Multi-Modal Adaptation for Segmentation Thanks to the emerging multi-modal datasets [2, 5, 37, 33, 49], recent works start to explore how to leverage multi-modal information between 2D images and 3D point clouds to perform domain adaptation under different settings. xMUDA [18] proposes the first Multi-Modal Unsupervised Domain Adaptation (MM-UDA) method for 3D semantic segmentation. Specifically, it leverages the cross-modal prediction consistency by minimizing the prediction discrepancy from additional classifiers. Following the scheme of cross-modal learning, DsCML [31] designs a deformable mapping between pixel-point correlation for MM-UDA while [24] introduces adversarial training to mitigate domain discrepancy. In addition to UDA settings, [35] proposes the first multi-modal test-time adaptation for semantic segmentation which generates intra-modal and inter-modal pseudo labels by attending to the one with more consistent predictions across student and teacher models. + +In this work, we propose MM-CTTA as a new extension of CTTA with a specific method CoMAC. While our proposed dual-stage modules (i.e., iMPA and xMPA) and CMQs share some similar merit with previous TTA methods [35, 36], our method is explicitly designed for MM-CTTA. Unlike previous work [35] measuring prediction reliability by teacher-student consistency, our reliability measurement relies on the feature-centroid distance to encourage feature clustering around the adapting centroids. Different from [36] utilizing queues to measure target distribution, the objective of our CMQs is to actively update class-wise centroids to ensure the validity of iMPA and xMPA while avoiding catastrophic forgetting. + +# 3. Proposed Method + +Problem definition and notations. At timestamp $t$ , the 2D image $x_{\mathcal{T},t}^{2\mathrm{D}} \in \mathbb{R}^{H \times W \times 3}$ and the 3D point cloud $x_{\mathcal{T},t}^{3\mathrm{D}} \in \mathbb{R}^{N \times 4}$ are observed in the target domain $\mathcal{T}$ , where $N$ denotes the number of 3D points located in the camera FOV. Modal-specific pre-trained networks $\phi_{\theta, t}^{m}(\cdot) = f_{t}^{m}(g_{t}^{m}(\cdot)), m \in \{2\mathrm{D}, 3\mathrm{D}\}$ consisting of the feature extractor $f_{t}^{m}$ and the classifier $g_{t}^{m}$ are used to predict the semantic labels for each point. Inspired by the fact that moving average models can provide more stable predictions [39], we utilize a fast student network $\phi_{\theta}^{m}(\cdot) = f_{\theta}^{m}(g_{\theta}^{m}(\cdot))$ and a slow teacher network $\phi_{\theta'}^{m}(\cdot) = f_{\theta'}^{m}(g_{\theta'}^{m}(\cdot))$ for each modal- + +ity similar to previous works [35, 42]. Given $x_{\mathcal{T},t}^{m}$ as input, the features extracted by $f_{t}^{m}$ is denoted as $z_{\mathcal{T},t}^{m} \in \mathcal{R}^{N \times F^{m}}$ where $F^{m}$ denotes the channel number. Here we adopt the same projection protocol of previous works [18, 35] for cross-modal alignment, which projects features from the 2D branch back to 3D points, resulting in the 2D feature $z_{\mathcal{T},t}^{2\mathrm{D}}$ of shape $N \times F^{2\mathrm{D}}$ . By default, the subscript of the target domain $\mathcal{T}$ and the timestamp $t$ are omitted for clarity. Given the multi-modal input $x_{\mathcal{T},t}^{2\mathrm{D}}, x_{\mathcal{T},t}^{3\mathrm{D}}$ , the goal of MM-CTTA is to output reliable cross-modal predictions by continuously adapting to the changing target domain. In this work, we interpret the core of MM-CTTA as two-fold: (i) attending to the reliable modality for noisy suppression, and (ii) revisiting source knowledge to prevent catastrophic forgetting. + +To this end, we propose Continual Cross-Modal Adaptive Clustering (CoMAC) to tackle MM-CTTA from the aforementioned perspectives. Specifically, as shown in Fig. 2, the class-wise centroids are initialized from the source domain and pseudo-source features are randomly sampled around the centroids as source knowledge (Sec. 3.1). Given the raw and augmentation-average predictions from the teacher models as input, Intra-Modal Prediction Aggregation (iMPA) generates stable intra-modal predictions as their weighted sum based on their feature distance to the class-wise centroids (Sec. 3.2). Inter-Modal Pseudo-Label Fusion (xMPF) then combines the intramodal predictions from each modality based on their reliability and output cross-modal pseudo-labels as supervision signals for student networks (Sec. 3.3). Given raw samples as input, confident target features from student networks are utilized to update Class-Wise Momentum Queues (CMQs), while pseudo-source features are stochastically restored to avoid catastrophic forgetting (Sec. 3.4). + +# 3.1. Source Models and Class-Wise Centroids + +To effectively avoid catastrophic forgetting and inspired by previous TTA methods [9, 36] which preserve trivial source domain information, we utilize pseudo-source features sampled around source offline feature centroids as source representatives. The source offline centroids and pseudo-source features are treated as the prior knowledge from the source domain, which plays an essential role in preventing catastrophic forgetting detailed in Sec. 3.4. Specifically, given a specific semantic category $k$ , the corresponding source offline centroid is modeled as Gaussian distribution, and pseudo-source features are denoted as: + +$$ +C _ {s r c} ^ {m, k} = \mathcal {N} \left(\mu_ {s r c} ^ {m, k}, \sigma_ {s r c} ^ {m, k}\right), \tag {1} +$$ + +$$ +\mathcal {Z} _ {s r c} ^ {m, k} = \left\{z _ {s r c, i} ^ {m, k} \sim C _ {s r c} ^ {m, k} \mid i \in [ 1, N _ {q} ] \right\}, \tag {2} +$$ + +where $N_{q}$ is the number of pseudo-source features. $\mu_{src}^{m,k}$ and $\sigma_{src}^{m,k}$ denote the mean and standard deviation of normalized source features from the category $k$ , respectively. + +![](images/4729166c77b5ad3bfb7e63261500f887e0a634172cbf74decb581f35c039cc56.jpg) +Figure 2. The main structure of our proposed method. From the source domain, we preserve the source centroids and the pre-trained model for each modality as the initialization of the class-wise centroids and all the models in the target domain, respectively. To generate reliable intra-modal predictions, Intra-Modal Prediction Aggregation (iMPA) attends to the reliable prediction whose feature shares a closer distance with the class-wise centroids in an intra-modal manner. Inter-Modal Pseudo-Label Fusion (xMPF) then fuses the intramodal predictions by estimating the reliability of predictions from each modality for noise suppression. Class-Wise Momentum Queues (CMQs) are designed to achieve a good balance between target domain adaptation and source knowledge preservation. + +Here we use the features generated by the pre-trained extractor $g_0^m(\cdot)$ for the centroid construction. + +# 3.2. Intra-Modal Prediction Aggregation + +In MM-CTTA, the prediction from each modality could be unreliable due to continual domain shifts, causing severe noise to the multi-modal fusion. To mitigate the intramodal noise, iMPA aims to generate reliable intra-modal predictions for each modality. Although previous methods [42, 38] regard the augmentation-average prediction as a more stable alternative, we argue that its superiority is not certain since test-time augmentations may introduce inductive bias to the prediction [34] (e.g., resizing image as in [42] could cause ambiguity to small-scale classes). Unlike the previous work [42], we propose an adaptive mechanism to fuse the raw and the augmentation-average prediction as the weighted sum based on their feature distance between class-wise centroids. Given the input sample $x^{m}$ and its augmented variants $\{\widetilde{x}_i^m\mid i\in [1,N_{aug}^m]\}$ , the features and predictions are extracted by the teacher model $\phi_{\theta^{\prime}}^{m}$ as: + +$$ +p \left(x ^ {m}\right) = f _ {\theta^ {\prime}} ^ {m} \left(g _ {\theta^ {\prime}} ^ {m} \left(x ^ {m}\right)\right) = f _ {\theta^ {\prime}} ^ {m} \left(z ^ {m}\right), \tag {3} +$$ + +$$ +\widetilde {p} \left(x ^ {m}\right) = \frac {1}{N _ {a u g} ^ {m}} \sum_ {i = 1} ^ {N _ {a u g} ^ {m}} f _ {\theta^ {\prime}} ^ {m} \left(g _ {\theta^ {\prime}} ^ {m} \left(\widetilde {x} _ {i} ^ {m}\right)\right), \tag {4} +$$ + +where $p(x^{m})$ and $\widetilde{p} (x^m)$ represent the raw and the augmentation-average prediction, respectively. Both predictions are of shape $N\times N_{c}$ , where $N_{C}$ is the number + +of classes and $N_{aug}^{m}$ denotes the number of augmentations. The normalized augmentation-average feature is computed as $\widetilde{z}^m = \sum_{i=1}^{N_{aug}^m} g^m(\widetilde{x}_i^m) / (\|g^m(\widetilde{x}_i^m)\| \cdot N_{aug}^m)$ . Subsequently, the weights for predictions $p(x^m), \widetilde{p}(x^m)$ are computed based on their corresponding feature distance to the class-wise centroid in a point-wise manner, so that each point of the intra-modal prediction $\hat{p}(x^m)$ can attend more to the confident prediction located closer to the cluster in the latent space. Taking a point $(j)$ as an example, given its predictions $p_{(j)}(x^m), \widetilde{p}_{(j)}(x^m)$ and features $z_{(j)}^m, \widetilde{z}_{(j)}^m$ : + +$$ +w _ {(j)} ^ {m} = \frac {\exp \left(\left\langle \mu^ {m , k} , z _ {(j)} ^ {m} \right\rangle\right)}{\sum_ {i \in N _ {c}} \exp \left(\left\langle \mu^ {m , i} , z _ {(j)} ^ {m} \right\rangle\right)}, \tag {5} +$$ + +$$ +\widetilde {w} _ {(j)} ^ {m} = \frac {\exp \left(\left\langle \mu^ {m , \widetilde {k}} , \widetilde {z} _ {(j)} ^ {m} \right\rangle\right)}{\sum_ {i \in N _ {c}} \exp \left(\left\langle \mu^ {m , i} , \widetilde {z} _ {(j)} ^ {m} \right\rangle\right)}, \tag {6} +$$ + +$$ +\hat {p} _ {(j)} \left(x ^ {m}\right) = \frac {w _ {(j)} ^ {m} p _ {(j)} \left(x ^ {m}\right) + \widetilde {w} _ {(j)} ^ {m} \widetilde {p} _ {(j)} \left(x ^ {m}\right)}{w _ {(j)} ^ {m} + \widetilde {w} _ {(j)} ^ {m}}, \tag {7} +$$ + +where $w_{(j)}^m, \widetilde{w}_{(j)}^m$ are termed as the raw weight and augmentation-average weight, respectively. $k, \widetilde{k}$ are the largest element locations of $p_{(j)}(x^m), \widetilde{p}_{(j)}(x^m)$ . $\mu^{m,k}$ denotes the mean of class $k$ centroid, which is actively updated as shown in Sec. 3.4. $\langle a,b\rangle$ represents the inner product of vectors $a$ and $b$ . Our empirical results show that this adaptive fusion between the raw and augmentation-average predictions results in more stable intra-modal predictions. + +# 3.3. Inter-Modal Pseudo-Label Fusion + +Given the output of iMPA, the goal of xMPF is to generate pseudo-labels by estimating their reliability in a cross-modal manner. Since domain shifts can affect the reliability of each modality variously (e.g., images in day and night), the cross-modal pseudo-label should adaptively attend to the reliable modality for noise suppression. Motivated by this idea, the proposed xMPF generates the cross-modal pseudo-labels as the weighted sum of intra-modal predictions from iMPA. Specifically, taking point $(j)$ as an example, the inter-modal weight $\hat{w}_{(j)}^{m}$ is computed as the summation of both weights if their corresponding predictions indicate the same class, or the maximum one otherwise. This can be viewed as an implicit way to encourage point-wise prediction consistency for each modality. Formally, the inter-modal weight $\hat{w}_{(j)}^{m}$ is computed as follows: + +$$ +\hat {w} _ {(j)} ^ {m} = \left\{ \begin{array}{l} w _ {(j)} ^ {m} + \widetilde {w} _ {(j)} ^ {m}, \text {i f} k = \widetilde {k} \\ \max \left(w _ {(j)} ^ {m}, \widetilde {w} _ {(j)} ^ {m}\right), \text {i f} k \neq \widetilde {k} \end{array} \right. \tag {8} +$$ + +The cross-modal prediction is then computed as the weighted sum in a cross-modal manner: + +$$ +\hat {p} _ {(j)} ^ {\mathrm {X M}} (x) = \frac {\hat {w} _ {(j)} ^ {\mathrm {2 D}} \hat {p} _ {(j)} ^ {\mathrm {2 D}} (x) + \hat {w} _ {(j)} ^ {\mathrm {3 D}} \hat {p} _ {(j)} ^ {\mathrm {3 D}} (x)}{\hat {w} _ {(j)} ^ {\mathrm {2 D}} + \hat {w} _ {(j)} ^ {\mathrm {3 D}}}, \tag {9} +$$ + +$$ +\hat {y} _ {(j)} = \arg \max _ {k \in N _ {c}} \left(\hat {p} _ {(j)} ^ {\mathbf {x M}} (x) ^ {(k)}\right), \tag {10} +$$ + +where $\hat{p}_{(j)}^{\mathrm{xM}}(x),\hat{y}_{(j)}$ denote the cross-modal prediction and pseudo-label, respectively. The cross-modal pseudo-label can therefore attend to the more reliable modality with confident intra-modal predictions. + +# 3.4. Class-Wise Moving Queues + +Both iMPA and xMPF greatly depend on the quality of class-wise centroids. Initialized from the source offline centroids as in Eq. 1, the class-wise centroids should continually adapt to the target domain to ensure the validity of iMPA and xMPF. Meanwhile, the source knowledge should be occasionally played back during the centroid adaptation so that it can be revisited during the reliability estimation in iMPA and xMPF without catastrophic forgetting. To achieve a balance between adaptation and source knowledge preservation, we propose CMQs which utilize momentum queues [15] to actively estimate feature clustering of the target domain by capturing confident target features while stochastically restoring pseudo-source features for each modality. Specifically, the CMQ of the class $k$ is initialized by the pseudo-source features $\mathcal{Z}_{src}^{m,k}$ as in Eq. 2. For each iteration, taking the raw sample as input, the normalized point features from the student network $\phi_{\theta}^{m}$ with confident predictions are preserved by threshold-based filtering. Given the CMQ of class $k$ from the previous step + +denoted as $\hat{\mathcal{Q}}_{t - 1}^{m,k}$ , the CMQ of current step is updated as: + +$$ +\mathcal {Z} _ {c f} ^ {m, k} = \mathbb {1} _ {c f} ^ {k} \left[ g _ {\theta} ^ {m} \left(x ^ {m}\right) / \| g _ {\theta} ^ {m} \left(x ^ {m}\right) \| \right], \tag {11} +$$ + +$$ +\widetilde {\mathcal {Q}} _ {t} ^ {m, k} = \Phi \left(\hat {\mathcal {Q}} _ {t - 1} ^ {m, k}, \mathcal {Z} _ {c f} ^ {m, k}\right), \tag {12} +$$ + +$$ +\hat {\mathcal {Q}} _ {t} ^ {m, k} = \left\{ \begin{array}{l l} \widetilde {\mathcal {Q}} _ {t} ^ {m, k}, & \text {i f} \gamma_ {t} > p _ {r s} \\ \Phi \left(\hat {\mathcal {Q}} _ {t - 1} ^ {m, k}, \mathbb {1} _ {r s} ^ {k} \mathcal {Z} _ {s r c} ^ {m, k}\right), & \text {i f} \gamma_ {t} \leq p _ {r s} \end{array} , \right. \tag {13} +$$ + +where $\mathbb{1}_{cf}^k$ is the confidence index for class $k$ where $\mathbb{1}_{cf}^k\phi_\theta^m (x^m)^{(k)}\geq \tau_{cf}$ and $\mathbb{1}_{rs}^k$ denotes the source restoring index which randomly samples $N_{enq}$ pseudo-source features from $\mathcal{Z}_{src}^{m,k}$ . $\Phi (a,b)$ denotes the operation of enqueuing $b$ in $a$ as in [15]. $\gamma_{t}$ is a restoring flag uniformly sampled from [0, 1] at timestamp $t$ and $p_{rs}$ denotes the hyperparameter of restoring probability. Different from the image classification problem which can capture all confident samples [36], the number of confident points from each class can be huge (i.e., more than 1,000), which is too aggressive and expensive to enqueue all points. Therefore, we limit the index number of $\mathbb{1}_{cf}^k$ by an upper bound $N_{enq}$ through selecting features with the top $N_{enq}$ confident predictions. + +For each optimization step, the mean of the class-wise centroid for the next step $\mu_{t + 1}^{m,k}$ is updated as the average of CMQ of the current timestamp $\hat{\mathcal{Q}}_t^{m,k}$ so that the class-wise centroids can adapt to the feature clustering of target domain without catastrophic forgetting. Additionally, we propose a class-wise contrastive loss modified from [19] as a regularizer so that the target confident features can revisit source knowledge through clustering around the class-wise centroids. Specifically, given any confident target feature from Eq. 11 as the anchor, the positive samples are the features from the CMQ that shares the same modality and semantic class, denoted as $P(k) = \{\hat{q}_p\mid \hat{q}_p\in \hat{\mathcal{Q}}_t^{m,k}\}$ . The negative samples are the features from the CMQs of the same modality but different classes denoted as $A(k) = \{\hat{q}_n\mid \hat{q}_n\in \hat{\mathcal{Q}}_t^{m,a},\forall a\neq k\bigcap a\in N_c\}$ . The class-wise contrastive loss $\mathcal{L}_{cts}^m$ is computed as: + +$$ +\begin{array}{l} \mathcal {L} _ {c t s} ^ {m} = \sum_ {i \in | \mathcal {Z} _ {c f} ^ {m, k} |} \frac {- 1}{| P (k) |} \\ \sum_ {q _ {p} \in P (k)} \frac {\exp \left(\hat {z} _ {t , (i)} ^ {m , k} \cdot q _ {p}\right)}{\sum_ {q _ {n} \in N (k)} \exp \left(\hat {z} _ {t , (i)} ^ {m , k} \cdot q _ {n}\right)}. \tag {14} \\ \end{array} +$$ + +# 3.5. Main Structure and Optimization + +The main structure of our proposed method is shown in Fig. 2. Given the multi-modal input $x^{m}$ , the teacher model is used to infer $x^{m}$ and its augmented variants $\{\widetilde{x}_i^m | i \in [1, N_{\text{aug}}^m]\}$ and then generate reliable cross-modal pseudolabels denoted as $\hat{y}$ through iMPA and xMPF. The student model is directly updated by minimizing the weighted sum + +# Algorithm 1: The proposed CoMAC + +Init Model: Teacher $\phi_{\theta}^{m}$ , student $\phi_{\theta}^{m}$ , $m \in \{2D, 3D\}$ + +Init CMQ: $\hat{\mathcal{Q}}_0^{m,k} = \mathcal{Z}_{src}^{m,k}$ , $m\in \{2\mathrm{D},3\mathrm{D}\}$ , $k\in N_{c}$ + +for $t\in |\mathcal{X}_{\mathcal{T}}|$ $x = (x^{2D},x^{3D})\in \mathcal{X}_{\mathcal{T}}$ do + +for $m\in \{2D,3D\}$ do + +1. Augmented input to get $\{\widetilde{x}_i^m\mid i\in N_{aug}^m\}$ +2. Get predictions and features with $\phi_{\theta'}^m$ by Eq. 3-4 +3. Get intra-modal $\hat{p}^m (x^m)$ by iMPA through Eq. 5-7 + +# end + +4. Get inter-modal $\hat{y}$ by xMPF through Eq. 8-10 +5. Update CMQs and compute $\mathcal{L}_{cts}^{m}$ by Eq. 11-14 +6. Update $\phi_{\theta}^{m}$ by Eq. 16 and $\phi_{\theta^{\prime}}^{m}$ by Eq. 17 + +# end + +of the standard cross-entropy loss between its prediction and the pseudo-label $\hat{y}$ , and the contrastive loss in Eq. 14. The teacher model is updated as the exponential moving average of the student's weights as in previous works [35, 42]: + +$$ +\mathcal {L} _ {c e} ^ {m} = \mathbb {1} _ {\tilde {y}} \log \phi^ {m} \left(x ^ {m}\right), \tag {15} +$$ + +$$ +\{2 D, 3 D \} +$$ + +$$ +\mathcal {L} _ {\text {t o t a l}} = \sum_ {m} \left(\mathcal {L} _ {c e} ^ {m} + \lambda_ {c t s} \mathcal {L} _ {c t s} ^ {m}\right), \tag {16} +$$ + +$$ +\theta_ {t + 1} ^ {\prime} = \left(1 - \lambda_ {s}\right) \theta + \lambda_ {s} \theta^ {\prime}, \tag {17} +$$ + +where $\lambda_{cts}$ and $\lambda_s$ are the hyper-parameters denoting the coefficient of the contrastive loss and the momentum factor. Our adaptation process is summarized as Algorithm 1. + +# 4. Experiments + +In this section, we present our experimental results based on two new benchmarks. The details of our proposed benchmarks, baselines, and implementation are first introduced in Sec. 4.1. Sec. 4.2 presents our overall results and Sec. 4.3 justifies our method by extensive ablation studies. + +# 4.1. Benchmarks and Settings + +Proposed benchmarks. To evaluate the performance under MM-CTTA settings, we proposed two benchmarks in this work, including (i) SemanticKITTI-to-Synthia (S-to-S) and (ii) SemanticKITTI-to-Waymo (S-to-W). Both benchmarks leverage SemanticKITTI [2] as the source-domain dataset, which utilizes a 0.7MP camera and a 64-line LiDAR. For the target domain, we utilize two different datasets including Synthia [33] and Waymo [37] thanks to the various environmental conditions they cover. The former shares a larger domain gap with more diverse seasons, weather, and illumination conditions while the latter is less challenging but closer to the real-world application. For S-to-S, it is constructed by a sequence of different videos + +from Synthia [33] without any repetition. Since Synthia includes depth images instead of 3D point clouds, we generate a simulated point cloud for each sample by randomly sampling depth pixels as 3D points following the structural characteristic of LiDAR. For each sequence, all samples are included for adaptation and we use "No.-Conditions" to indicate their corresponding video sequence in Synthia (i.e., "01-Spring" indicates video sequence 01 under Spring condition). Different from the previous CTTA benchmark [42] which only includes 4 different unique sequences, the proposed S-to-S consists of 12 different sequences recorded under various environmental conditions without repetition. By default, we organize the sequences following the order of seasons $\rightarrow$ illumination $\rightarrow$ weathers as a challenge ascending order. For S-to-W, we sort out the illumination conditions of each sequence in Waymo dataset [37] based on the sequence descriptions and divide all samples into three types, including Day (D), Dawn-Dusk (DD), and Night (N). Since the number of sequences of D is much larger than others, we further split the sequence of D based on their recording location, including Phoenix (P), San Francisco (S), and Others (O). Each sequence is separated in two halves to simulate the revisiting situation as in [42] but without repeated samples (i.e., "D-O-1" indicates the first half of the D-O sequence). Similar to S-to-S, S-to-W also follows a challenge ascending order. For both datasets, we adopt the images of the front-view camera similar to the source-domain dataset. We utilize a similar class mapping strategy as [18, 35] with slight modification since some classes are missing in the target domain. More details are illustrated in the appendix. + +Baselines. Previous TTA, MM-TTA, and CTTA methods are evaluated on both S-to-S and S-to-M as baselines. For TTA methods, we compare with pseudo-labels with threshold filtering (Plabel), TENT [40] and LAME [3], while xMUDA with pseudo-labels (xMUDA-pl) [18] and MMTTA [43] are regarded as the representatives of MMTTA methods. CoTTA [42] and EATA [30] are the recent works that focus on CTTA problems. Specifically, xMUDA-pl is originally designed for UDA, whereas we modify it into a TTA version by discarding the source data during adaptation. Considering our CoMAC is the only MM-CTTA method, we implement an MM-CTTA version of MMTTA [35] integrated with model-based stochastic restoration in [42] for a fair comparison. We report the softmax-average mIoU of 2D and 3D predictions as results. + +Implementation details. Following previous works [18, 35], we utilize UNet [32] with ResNet-34 [16] encoder as the 2D backbone and SCN [14] based on UNet as the 3D backbone for all baselines. The pre-training procedures on SemanticKITTI dataset follow [18]. For our method, we empirically choose resizing and z-rotation as the 2D and 3D augmentations following previous works [42, 18]. Specifically, we utilize multiple resizing factors of [0.5, + +
Timet →t →
MethodsDA TypeSemanticKITTI-to-SynthiaSemanticKITTI-to-Waymo
01-Spring02-Summer04-Full05-Winter01-Dawn02-Night04-Sunset05-Wnight01-Fog02-S-Rain04-R-Night05-RainAvgD-O-1D-P-1D-S-1DD-1N-1D-O-2D-P-2D-S-2DD-2N-2Avg
Source-28.330.737.727.323.127.338.226.527.021.627.816.427.733.236.929.528.314.032.838.030.428.414.628.6
PlabelTTA29.627.136.428.421.426.632.326.127.421.825.018.026.739.141.937.036.825.738.543.737.637.624.636.9
TENT [40]TTA35.424.924.920.718.716.616.013.613.611.58.49.117.833.622.318.816.910.815.712.99.811.310.616.3
LAME [3]TTA14.012.417.313.012.611.617.013.219.27.77.86.012.711.910.413.49.28.713.411.212.29.78.612.7
xMUDA-pl [18]MM-TTA28.826.935.928.221.326.532.226.027.021.624.917.926.439.342.137.437.025.938.743.937.937.725.036.5
MMTTA [35]MM-TTA31.124.430.725.828.324.226.823.229.620.722.120.625.639.940.030.931.529.630.632.223.926.423.830.9
CoTTA [42]CTTA29.727.234.727.026.425.633.027.328.118.022.718.426.532.928.022.922.220.326.124.923.624.719.724.5
EATA [30]CTTA34.030.038.630.230.228.436.530.132.221.325.320.129.740.140.836.334.328.939.341.736.537.928.836.5
MMTTA-rs [35]MM-CTTA31.928.137.729.328.727.635.229.730.220.425.620.328.740.441.536.334.730.239.941.536.438.329.936.9
CoMAC (Ours)MM-CTTA34.034.744.938.135.037.845.139.039.129.435.127.136.641.443.738.837.832.242.241.840.738.930.438.8
Timet ←t ←
TENT [40]TTA10.28.88.69.010.29.59.811.418.313.216.918.912.112.011.59.29.89.712.613.012.519.821.213.1
MMTTA-rs [35]MM-CTTA31.427.437.228.726.227.233.129.028.519.922.319.727.640.441.436.431.629.137.640.235.435.227.835.5
CoMAC (Ours)MM-CTTA34.632.840.933.231.832.439.233.233.825.130.323.332.440.841.937.733.230.339.643.638.838.630.037.5
+ +Table 1. Performance (mIoU) of SemanticKITTI-to-Synthia. Here we report the softmax-average mIoU of 2D and 3D prediction. + +![](images/ead5781acdec926235eb580f3f6fe4bddd607acace7c96163bc5351df486c466.jpg) +Figure 3. Ablation studies to justify our design of CoMAC. Specifically, (a) compares CoMAC with variants only using raw or augmented samples as input of iMPA and (b) justifies the necessity of weighting mechanisms in iMPA and xMPF. (c) compares CoMAC with variants without either target feature enqueuing or pseudo-source features restoring in CMQs. Scores within the parentheses are the average mIoU. + +![](images/28511b9a214e92153d5cb718a56fab981c18bea8aafff6d44056368a3b46001c.jpg) + +![](images/65ce37e2c261a5b748a0cf18c5e62dc1a12b5ef4b527a6204af49873838b0857.jpg) + +0.625, 0.75, 0.875] and z-rotation of $[60^{\circ}, 120^{\circ}, 180^{\circ}, 240^{\circ}, 300^{\circ}]$ . $N_{q}$ and $N_{enq}$ are set to 4096 and 200, respectively. We utilize a restore rate $p_{rs}$ of 0.5 and a momentum factor $\lambda_{s}$ of 0.999 with a coefficient $\lambda_{cts}$ of 1. All methods strictly follow the one-pass protocol [36] (i.e., the training epoch is one where inference is conducted immediately for each sample). More details are included in the appendix. + +# 4.2. Overall Results + +As shown in Table 1, our CoMAC achieves SOTA performance on the average mIoU of all sequences for both benchmarks. Specifically, the proposed CoMAC significantly outperforms previous methods by more than $6.9\%$ on S-to-S and $1.9\%$ on S-to-W, which justifies the effectiveness of our method. It can also be observed that most TTA methods (TENT [40] and LAME [3]) are outperformed by CTTA methods, which reveals the importance of avoiding catastrophic forgetting. Additionally, previous MM-TTA (i.e., xMUDA and MMTTA) methods can not consistently outperform previous single-modal methods (e.g., EATA [30]), which suggests the sensitivity of multi-modal collaboration toward continual domain shifts. In fact, by intuitively utilizing model-based stochastic restoration, MMTTA-rs can achieve a noticeable improvement of $3.1\%$ and $6.0\%$ on S-to-S and S-to-W, respectively. Yet MMTTA-rs is still outperformed by our method. To justify the effect of the sequence arrangement, we conduct additional experiments by + +reversing the sequences of S-to-S and S-to-W for TENT, MMTTA-ms, and our CoMAC. While the performance of all methods decreases, the improvement of CoMAC compared to others can be observed across all sequences. + +For S-to-S, we notice that our method achieves the second-best performance at the first sequence 01-Spring and then surpasses all previous methods in the following sequences since we utilize CMQs to gradually adapt to the changing target domain without forgetting. Compared with TTA methods, our method consistently prevails with an increasing gap as they struggle with error accumulation. A similar observation can be found at D-O-2 of S-to-W. Interestingly, xMUDA-pl as well as Plabel perform competitively on S-to-W and outperform CoMAC in D-P-2 mainly because is less challenging and simply filtering pseudolabels can effectively mitigate the prediction noise. Nevertheless, this performance gap is trivial as our CoMAC surpasses both xMUDA-pl and Plabel on all other sequences. + +# 4.3. Ablation Studies + +In this section, we provide our ablation studies on S-to-S to justify our design of CoMAC. + +Utilization of raw and augmented input. In Sec. 3.2, a key hypothesis is that while the augmentation-average prediction can be a potential reliable alternative, it may introduce inductive bias to the result. To justify this assumption, we conduct experiments by simply using the pure raw + +![](images/9b5afb25a3f5b42dbfb78cb4fa1ff13d93019bfc0c1395f82edba9b31b9c7837.jpg) +Figure 4. Visualization of online segmentation results. Here we present the cross-modal pseudo-labels from xMPF (Ours) as well as the individual prediction from 2D and 3D teachers in comparison with the ground truth (GT). + +or augmentation-average prediction as the intra-modal prediction as in Eq. 7. As shown in Fig. 3(a), both variants achieve inferior performance compared to CoMAC and these performance gaps are consistent across most sequences. Specifically, using pure augmentation-average predictions lead to serious degradation of $5.8\%$ , which justifies the necessity of mitigating the inductive noise brought by test-time augmentations and our motivation for iMPA. + +Weighting mechanisms of iMPA and xMPF. The proposed iMPA and xMPF utilize centroid-based weighting mechanisms to attend to the reliable modality. To justify their effectiveness, we compared CoMAC with variants by replacing either Eq. 7 or Eq. 8 with a simple average fusion (indicated as w/o iMPA and w/o xMPF). As presented in Fig. 3(b), CoMAC outperforms both variants by more than $2.5\%$ . This performance gap justifies that both iMPA and xMPF play an important part in noise suppression. + +Updating mechanisms of CMQs. The goal of CMQs is to achieve a good balance between adaptation and knowledge preservation. To justify the role of CMQs, we compared CoMAC with variants without enqueuing target features or restoring pseudo-source features, respectively. For the variant without enqueuing target features, the corresponding class-wise centroids are identical to the source centroids across the whole testing process. As in Fig. 3(c), disabling enqueuing target features (w/o Update) causes a significant performance decrease of $6.1\%$ , which justifies the necessity of adapting class-wise centroids for the validity of iMPA and xMPF. On the other hand, while disabling restoring pseudo-source features (w/o Restore) leads to a quicker adaptation at the first two sequences, it eventually causes catastrophic forgetting after the third sequence, resulting in a noticeable gap of $8.4\%$ . Overall, the performance gain brought by CMQs justifies their effectiveness. + +Number of Augmentations. To investigate the effect of augmentations, we conduct a grid search by utilizing differ- + +
CoMACNo. of 2D Aug
12345Avg
No. of 3D Aug133.033.133.233.233.333.2
234.134.234.334.434.434.3
335.235.235.435.335.535.3
436.436.436.536.536.536.5
536.436.536.736.636.736.6
Avg35.035.135.235.235.335.2
+ +Table 2. Augmentation analysis of CoMAC. CoMAC is evaluated with different numbers of augmentations. + +
CoMAC\( p_{rs} \)\( (\tau_{cf},\lambda_{cts}) \)Avg\( \tau_{cf} \)\( (p_{rs},\lambda_{cts}) \)Avg\( \lambda_{cts} \)\( (p_{rs},\tau_{cf}) \)Avg
0.5(0.8,1.0)36.60.8(0.5,1.0)36.61.0(0.5,0.8)36.6
0.3-34.50.0-34.80.0-35.8
0.7-36.40.5-36.50.01-36.4
1.0-36.30.9-36.40.1-36.4
+ +Table 3. Sensitivity analysis of CoMAC. Here "xM" is the softmax-average of 2D and 3D predictions. The parameter value with "-" indicates the same value as default settings. + +ent numbers of 2D and 3D augmentations. Specifically, we adopt resize and rotation as 2D and 3D augmentation, respectively. The factor range for 2D scaling is [0.5, 1) while 3D one is set to $(0^{\circ}, 360^{\circ})$ , where the list of augmentations is computed as evenly spaced factors given the number of augmentations. As shown in Table 2, increasing the number of either 2D or 3D augmentations leads to performance improvement, while the 2D improvement is less noticeable compared to 3D probably due to the inductive bias brought by 2D augmentations. While all settings perform competitively, we adopt the combination of three 2D augmentations and five 3D augmentations to achieve the best result. + +Sensitivity analysis. We perform sensitivity analysis over the hyper-parameters of CoMAC as shown in Table 3. There are some extreme cases that can lead to the performance degeneration of CoMAC. For restoring rate $p_{rs}$ , the performance relatively drops about $5.7\%$ when $p_{rs} = 0.3$ , indicating the restoring rate is too low to prevent forgetting. Nevertheless, when $p_{rs} \geq 0.5$ , CoMAC is robust to the arbitrary choice of $p_{rs}$ . Similar observations can be found when + +
MethodAug SamplesInf. Time (s)/samplemIoU
meanstd
TENT [40]X0.3790.01017.8
CoTTA [42]✓7.2200.39926.5
Ours✓1.8880.08236.6
Ours (less augs)✓1.0040.03833.0
+ +Table 4. Comparison of processing time per sample. + +![](images/7a0eafe200e0d567cd3254c3fb45cfdf5c598993d0c005ae607bea40c81b7dc0.jpg) +Figure 5. Processing time of CoMAC components per sample (left) and GPU RAM with or without CMQs (right). Experiments are conducted on S-to-S with the default backbones and settings. + +![](images/2befc8781f28844b7e564d1e8d33d7bbe86a23dc52d7e59e15dfb52386e24d6b.jpg) + +$\tau_{cf} = 0.0$ or $\lambda_{cts} = 0.0$ , where the performance decreases relatively by $4.9\%$ and $2.2\%$ . This performance degeneration indicates the importance of confident feature filtering and class-wise contrastive loss. Overall, when $\tau_{cf} \geq 0.0$ and $\lambda_{cts} \geq 0.01$ , the performance of CoMAC is also robust to the hyper-parameter settings, falling into a relative margin of $0.5\%$ . Note that all settings of CoMAC surpass the previous SOTA method EATA [30] by more than $4.8\%$ . + +Visualization of segmentation. To further justify the effectiveness of our proposed CoMAC, we provide some visualization results as shown in Fig. 4. Specifically, we visualize the 2D and 3D predictions from teacher models and our cross-modal pseudo-labels from xMPF. Compared to single-modal predictions, our cross-modal pseudo-labels can achieve better segmentation results by attending to the reliable modality, such as the first row in Fig. 4, where the sidewalk prediction attends more to the 2D image while the car prediction attends to the reliable 3D point cloud. + +Computational and storage overhead. To investigate the computational and storage overhead of CoMAC, we analyze the processing time and GPU occupancy when online testing with our CoMAC as illustrated in Table 4 and Fig. 5. Similar to previous augmentation-based methods, our proposed CoMAC is limited by the computational overhead brought by multiple augmentations. However, compared to the augmentation-based SOTA method CoTTA [42], our method outperforms it in terms of performance and efficiency (a relative performance improvement of $38.1\%$ with $73.9\%$ less processing time). Compared to the single-sample-based method TENT, despite a computational overhead of 1.51s, our method significantly improves relatively by more than $100\%$ . The computational overhead can be further lessened by using fewer augmentations, reducing the processing time relatively by more than $46.8\%$ with a minor performance drop of $3.6\%$ . Besides augmentations, another potential source of overhead lies in the utilization of + +CMQs as they capture class-wise features for each iteration. As shown in Fig .5, however, the computational overhead brought by CMQs is rather trivial, which takes less than 0.05s to update and process each frame. Moreover, since CMQs only preserve the high-level features instead of raw samples, the storage cost is also acceptable with a minor usage increase (less than $800\mathrm{MB}$ ) of GPU RAM compared to the CoMAC invariant without CMQs. + +# 5. Conclusion + +In this paper, we present a new task, named multi-modal continual test-time adaptation (MM-CTTA) for 3D semantic segmentation. We further propose a novel method called CoMAC that tackles MM-CTTA from two perspectives. On one hand, reliable cross-modal pseudo-labels are generated by iMPA and xMPF by adaptively attending to the more reliable modality in a dual-stage manner. On the other hand, CMQs are proposed to leverage pseudo-source features and reliable target features to perform adaptation without catastrophic forgetting. We introduce two new benchmarks for MM-CTTA and our methods outperform previous works by a noticeable margin in both benchmarks. In the future, we hope both our method and benchmarks can facilitate the exploration of MM-CTTA and promote the development of reliable multi-modal systems in altering environments. + +# Acknowledgement + +This research is supported by the National Research Foundation, Singapore under its Medium Sized Center for Advanced Robotics Technology Innovation. This research is jointly supported by the National Research Foundation, Singapore under its AI Singapore Programme (AISG Award No: AISG2-RP-2021-027). + +# References + +[1] Khaled Bayoudh, Raja Knani, Fayçal Hamdaoui, and Abdellatif Mtibaa. A survey on deep multimodal learning for computer vision: advances, trends, applications, and datasets. The Visual Computer, pages 1-32, 2021. 1 +[2] Jens Behley, Martin Garbade, Andres Milioto, Jan Quenzel, Sven Behnke, Cyril Stachniss, and Jurgen Gall. Semantickitti: A dataset for semantic scene understanding of lidar sequences. 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In this paper, we explore Multi-Modal Continua! tual Test-Time Adaptation (MM-CTTA) as a new extension of CTTA for 3D semantic segmentation. The key to MMCTTA is to adaptively attend to the reliable modality while avoiding catastrophic forgetting during continual domain shifts, which is out of the capability of previous TTA or CTTA methods. To fulfill this gap, we propose an MM-CTTA method called Continua! Cross-Modal Adaptive Clustering (CoMAC) that addresses this task from two perspectives. On one hand, we propose an adaptive dual-stage mechanism to generate reliable cross-modal predictions by attending to the reliable modality based on the class-wise featurecentroid distance in the latent space. On the other hand, to perform test-time adaptation without catastrophic forgetting, we design class-wise momentum queues that capture confident target features for adaptation while stochastically restoring pseudo-source features to revisit source knowledge. We further introduce two new benchmarks to facilitate the exploration of MM-CTTA in the future. Our experimental results show that our method achieves state-of-the-art performance on both benchmarks. Visit our project website at https://sites.google.com/view/mmcotta." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 559, + 128, + 571 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 559, + 128, + 571 + ], + "spans": [ + { + "bbox": [ + 47, + 559, + 128, + 571 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 578, + 287, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 578, + 287, + 687 + ], + "spans": [ + { + "bbox": [ + 46, + 578, + 287, + 687 + ], + "type": "text", + "content": "Test-Time Adaptation (TTA) proposes a realistic domain adaptation scenario, which adapts pre-trained models to the target domain during the testing process. 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Illustration of how continual domain shifts affect multimodal segmentation and our method. Unlike the source domain where predictions from both modalities are reliable, the reliability of each modality varies in MM-CTTA due to different domain shifts. CoMAC tackles MM-CTTA by attending to the reliable modality " + }, + { + "bbox": [ + 304, + 380, + 546, + 468 + ], + "type": "inline_equation", + "content": "(\\checkmark)" + }, + { + "bbox": [ + 304, + 380, + 546, + 468 + ], + "type": "text", + "content": " rather than the noisy one " + }, + { + "bbox": [ + 304, + 380, + 546, + 468 + ], + "type": "inline_equation", + "content": "(\\chi)" + }, + { + "bbox": [ + 304, + 380, + 546, + 468 + ], + "type": "text", + "content": ". Meanwhile, source knowledge is stochastically revisited to avoid catastrophic forgetting. Figure best viewed in color and zoomed in." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 495, + 545, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 495, + 545, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 495, + 545, + 555 + ], + "type": "text", + "content": "tual Test-Time Adaptation (CTTA) which assumes that the target domain is continually changing rather than static. Compared to TTA, CTTA is more challenging since the performance is easily affected by error accumulation [6] and catastrophic forgetting [27] during the continual adaptation." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 558, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 546, + 713 + ], + "type": "text", + "content": "For 3D semantic segmentation, multi-modal sensors are frequently leveraged in different tasks, such as scene understanding [4, 28] and semantic map construction [29, 43]. For some specific applications like semantic-based localization [8] and autonomous driving [46, 44], multi-modal information is the key to robust performance under adverse conditions. However, their collaboration has been proven to be sensitive toward domain drifts [1, 35]. In real-world scenarios, such collaboration deterioration could be more severe considering that the target domain is continually changing as in CTTA (e.g., the operating environments of 24/7 AGVs are continually changing due to altering weather or illumination conditions). Hence, it is essential for multi-" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 57, + 693, + 135, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 693, + 135, + 713 + ], + "spans": [ + { + "bbox": [ + 57, + 693, + 135, + 713 + ], + "type": "text", + "content": "*Equal contributions. †Corresponding author." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18809" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "modal networks to adapt to the dynamic target domain in an online manner. In this work, we aim to study MultiModal Continual Test-Time Adaptation (MM-CTTA) for 3D semantic segmentation, where networks are continually adapted to a changing target domain taking 3D point clouds and 2D images as input without accessing the source data." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 148, + 288, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 148, + 288, + 411 + ], + "spans": [ + { + "bbox": [ + 46, + 148, + 288, + 411 + ], + "type": "text", + "content": "Intuitively, one can address MM-CTTA by utilizing CTTA [30, 42] or TTA [3, 38] methods on 2D and 3D networks separately. However, this simple extension can not achieve satisfactory performance since it cannot correctly attend to the reliable modality for adaptation when others suffer from severe domain shifts. Take Fig. 1 as an example: predictions from the 2D image are more accurate at the beginning of the target domain, while 2D results become unreliable and 3D predictions prevail as the illumination level significantly changes over time. Although previous CTTA or TTA methods have attempted to mitigate this intra-modal prediction noise by augmentations [42] or entropy minimization [40, 30], the domain drift in Fig. 1 is too severe to be effectively rectified by image input itself, leading to inevitable error accumulation. Previous works have proposed different cross-modal fusion methods to mitigate the effect of the noisy modality during adaptation, such as cross-modal consistency [18] for UDA or pseudo-label fusion based on student-teacher consistency [35] for TTA. However, their methods rely on the premise that the target domain is static, and therefore suffer from catastrophic forgetting in MM-CTTA, leading to degenerated results." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 415, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 415, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 415, + 287, + 713 + ], + "type": "text", + "content": "For MM-CTTA, an ideal solution is to suppress the contribution from the noisy modality and attend more to the reliable one in an online manner. Typically, the reliability of prediction can be estimated based on its corresponding feature location in the latent space. A prediction with features close to the centroid is more likely to be reliable, suffering less from the domain shift and vice versa. On the other hand, to ensure the validity of centroid-based reliability estimation, class-wise centroids should actively adapt to the continually changing target domain while stochastically revisiting the source knowledge to avoid catastrophic forgetting. To this end, we propose an MM-CTTA method called Continual Cross-Modal Adaptive Clustering (CoMAC) for 3D semantic segmentation. CoMAC consists of three main modules: (i) Intra-Modal Prediction Aggregation (iMPA), (ii) Inter-Modal Pseudo-Label Fusion (xMPF), and (iii) Class-Wise Momentum Queues (CMQs). On one hand, the proposed iMPA and xMPF are utilized to suppress prediction noise based on the centroid-based reliability estimation from intra-modal and inter-modal perspectives, respectively. On the other hand, CMQs are designed to actively adapt class-wise centroids for iMPA and xMPF while avoiding catastrophic forgetting. Additionally, a class-wise contrastive loss is introduced to regularize the extracted features from drifting too far from centroids." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 304, + 72, + 545, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 240 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 240 + ], + "type": "text", + "content": "In summary, our main contributions are three-fold. (i) We explore a new task MM-CTTA where multi-modal input is utilized to perform continual test-time adaptation for 3D semantic segmentation and propose an effective method named CoMAC to leverage multi-modal information for MM-CTTA. (ii) We propose iMPA and xMPF to generate accurate cross-modal pseudo-labels by attending to a reliable modality. CMQs are introduced to actively adapt to the target domain without catastrophic forgetting. (iii) We introduce two 3D semantic segmentation benchmarks to facilitate the future exploration of MM-CTTA. Extensive experiments show that our method achieves state-of-the-art performance, outperforming previous methods significantly by " + }, + { + "bbox": [ + 304, + 72, + 545, + 240 + ], + "type": "inline_equation", + "content": "6.9\\%" + }, + { + "bbox": [ + 304, + 72, + 545, + 240 + ], + "type": "text", + "content": " on the challenging benchmark." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 306, + 251, + 397, + 264 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 251, + 397, + 264 + ], + "spans": [ + { + "bbox": [ + 306, + 251, + 397, + 264 + ], + "type": "text", + "content": "2. Related Works" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 270, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 270, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 270, + 545, + 628 + ], + "type": "text", + "content": "Test-Time Adaptation Describing a more realistic adaptation scenario, Test-Time Adaptation (TTA) is receiving more and more attention. Different from previous Unsupervised Domain Adaptation (UDA), TTA forbids access to raw source data and adapts the source pre-trained model during test time. As one of the primary works, TENT [40] highlights the fully test-time setting and proposes to update the batch normalization layers by entropy minimization. The following works mainly address TTA by aligning batch normalization statistics [30, 23, 51], self-training with pseudo labeling [13, 41], feature alignment [25], or augmentation invariance [50, 21]. The aforementioned TTA methods strictly follow the one-pass protocol as mentioned in [36], where networks immediately infer each sample in an online manner and forbid multiple training epochs. On the other hand, some previous works [22, 10, 7, 48] follow the multi-pass protocol by adapting the model for multiple epochs in an offline manner. As one of the primary works, Source Hypothesis Transfer (SHOT) [22] proposes to update only the encoder parameters and align source and target representation by entropy minimization and pseudolabeling. While most existing TTA methods are proposed for image classification, some recent works [10, 20, 26] aim to explore TTA for image semantic segmentation. Specifically, [10] proposes to minimize the prediction entropy while maximizing its robustness toward feature noise. [20] divides the TTA problem into source domain generalization and target domain adaptation. [26] proposes a dual attention distillation method to transfer contextual knowledge and patch-level pseudo labels for self-supervised learning." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "Continual Test-Time Adaptation The definition of Continual Test-Time Adaptation (CTTA) is first proposed in CoTTA[42], which aims to adapt the model to continually changing target domains in an online manner without any source data. Specifically, CoTTA proposes to use the moving teacher model and augmentation-average predictions for noise suppression and the model stochastic" + } + ] + } + ], + "index": 6 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "18810" + } + ] + } + ], + "index": 7 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 179 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 179 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 179 + ], + "type": "text", + "content": "restoration to avoid catastrophic forgetting. Following the scheme of CoTTA, some recent works [11, 12, 30] have addressed CTTA from different perspectives. Specifically, [12] leverages the temporal correlations of streamed input by reservoir sampling and instance-aware batch normalization. [11] proposes domain-specific prompts and domain-agnostic prompts to preserve domain-specific and domain-shared knowledge, respectively. EATA [30] performs adaptation on non-redundant samples for an efficient update." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 180, + 289, + 395 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 180, + 289, + 395 + ], + "spans": [ + { + "bbox": [ + 46, + 180, + 289, + 395 + ], + "type": "text", + "content": "Multi-Modal Adaptation for Segmentation Thanks to the emerging multi-modal datasets [2, 5, 37, 33, 49], recent works start to explore how to leverage multi-modal information between 2D images and 3D point clouds to perform domain adaptation under different settings. xMUDA [18] proposes the first Multi-Modal Unsupervised Domain Adaptation (MM-UDA) method for 3D semantic segmentation. Specifically, it leverages the cross-modal prediction consistency by minimizing the prediction discrepancy from additional classifiers. Following the scheme of cross-modal learning, DsCML [31] designs a deformable mapping between pixel-point correlation for MM-UDA while [24] introduces adversarial training to mitigate domain discrepancy. In addition to UDA settings, [35] proposes the first multi-modal test-time adaptation for semantic segmentation which generates intra-modal and inter-modal pseudo labels by attending to the one with more consistent predictions across student and teacher models." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 396, + 289, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 396, + 289, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 396, + 289, + 552 + ], + "type": "text", + "content": "In this work, we propose MM-CTTA as a new extension of CTTA with a specific method CoMAC. While our proposed dual-stage modules (i.e., iMPA and xMPA) and CMQs share some similar merit with previous TTA methods [35, 36], our method is explicitly designed for MM-CTTA. Unlike previous work [35] measuring prediction reliability by teacher-student consistency, our reliability measurement relies on the feature-centroid distance to encourage feature clustering around the adapting centroids. Different from [36] utilizing queues to measure target distribution, the objective of our CMQs is to actively update class-wise centroids to ensure the validity of iMPA and xMPA while avoiding catastrophic forgetting." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 560, + 153, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 560, + 153, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 560, + 153, + 574 + ], + "type": "text", + "content": "3. Proposed Method" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "text", + "content": "Problem definition and notations. At timestamp " + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "text", + "content": ", the 2D image " + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "inline_equation", + "content": "x_{\\mathcal{T},t}^{2\\mathrm{D}} \\in \\mathbb{R}^{H \\times W \\times 3}" + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "text", + "content": " and the 3D point cloud " + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "inline_equation", + "content": "x_{\\mathcal{T},t}^{3\\mathrm{D}} \\in \\mathbb{R}^{N \\times 4}" + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "text", + "content": " are observed in the target domain " + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "text", + "content": " denotes the number of 3D points located in the camera FOV. Modal-specific pre-trained networks " + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\phi_{\\theta, t}^{m}(\\cdot) = f_{t}^{m}(g_{t}^{m}(\\cdot)), m \\in \\{2\\mathrm{D}, 3\\mathrm{D}\\}" + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "text", + "content": " consisting of the feature extractor " + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "inline_equation", + "content": "f_{t}^{m}" + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "text", + "content": " and the classifier " + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "inline_equation", + "content": "g_{t}^{m}" + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "text", + "content": " are used to predict the semantic labels for each point. Inspired by the fact that moving average models can provide more stable predictions [39], we utilize a fast student network " + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\phi_{\\theta}^{m}(\\cdot) = f_{\\theta}^{m}(g_{\\theta}^{m}(\\cdot))" + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "text", + "content": " and a slow teacher network " + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\phi_{\\theta'}^{m}(\\cdot) = f_{\\theta'}^{m}(g_{\\theta'}^{m}(\\cdot))" + }, + { + "bbox": [ + 46, + 580, + 289, + 715 + ], + "type": "text", + "content": " for each modal-" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "text", + "content": "ity similar to previous works [35, 42]. Given " + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "inline_equation", + "content": "x_{\\mathcal{T},t}^{m}" + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "text", + "content": " as input, the features extracted by " + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "inline_equation", + "content": "f_{t}^{m}" + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "text", + "content": " is denoted as " + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "inline_equation", + "content": "z_{\\mathcal{T},t}^{m} \\in \\mathcal{R}^{N \\times F^{m}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "inline_equation", + "content": "F^{m}" + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "text", + "content": " denotes the channel number. Here we adopt the same projection protocol of previous works [18, 35] for cross-modal alignment, which projects features from the 2D branch back to 3D points, resulting in the 2D feature " + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "inline_equation", + "content": "z_{\\mathcal{T},t}^{2\\mathrm{D}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "text", + "content": " of shape " + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "inline_equation", + "content": "N \\times F^{2\\mathrm{D}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "text", + "content": ". By default, the subscript of the target domain " + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "text", + "content": " and the timestamp " + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "text", + "content": " are omitted for clarity. Given the multi-modal input " + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "inline_equation", + "content": "x_{\\mathcal{T},t}^{2\\mathrm{D}}, x_{\\mathcal{T},t}^{3\\mathrm{D}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 243 + ], + "type": "text", + "content": ", the goal of MM-CTTA is to output reliable cross-modal predictions by continuously adapting to the changing target domain. In this work, we interpret the core of MM-CTTA as two-fold: (i) attending to the reliable modality for noisy suppression, and (ii) revisiting source knowledge to prevent catastrophic forgetting." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 243, + 546, + 471 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 243, + 546, + 471 + ], + "spans": [ + { + "bbox": [ + 304, + 243, + 546, + 471 + ], + "type": "text", + "content": "To this end, we propose Continual Cross-Modal Adaptive Clustering (CoMAC) to tackle MM-CTTA from the aforementioned perspectives. Specifically, as shown in Fig. 2, the class-wise centroids are initialized from the source domain and pseudo-source features are randomly sampled around the centroids as source knowledge (Sec. 3.1). Given the raw and augmentation-average predictions from the teacher models as input, Intra-Modal Prediction Aggregation (iMPA) generates stable intra-modal predictions as their weighted sum based on their feature distance to the class-wise centroids (Sec. 3.2). Inter-Modal Pseudo-Label Fusion (xMPF) then combines the intramodal predictions from each modality based on their reliability and output cross-modal pseudo-labels as supervision signals for student networks (Sec. 3.3). Given raw samples as input, confident target features from student networks are utilized to update Class-Wise Momentum Queues (CMQs), while pseudo-source features are stochastically restored to avoid catastrophic forgetting (Sec. 3.4)." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 478, + 522, + 490 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 478, + 522, + 490 + ], + "spans": [ + { + "bbox": [ + 305, + 478, + 522, + 490 + ], + "type": "text", + "content": "3.1. Source Models and Class-Wise Centroids" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 496, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 496, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 496, + 545, + 628 + ], + "type": "text", + "content": "To effectively avoid catastrophic forgetting and inspired by previous TTA methods [9, 36] which preserve trivial source domain information, we utilize pseudo-source features sampled around source offline feature centroids as source representatives. The source offline centroids and pseudo-source features are treated as the prior knowledge from the source domain, which plays an essential role in preventing catastrophic forgetting detailed in Sec. 3.4. Specifically, given a specific semantic category " + }, + { + "bbox": [ + 304, + 496, + 545, + 628 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 496, + 545, + 628 + ], + "type": "text", + "content": ", the corresponding source offline centroid is modeled as Gaussian distribution, and pseudo-source features are denoted as:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 345, + 635, + 545, + 650 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 345, + 635, + 545, + 650 + ], + "spans": [ + { + "bbox": [ + 345, + 635, + 545, + 650 + ], + "type": "interline_equation", + "content": "C _ {s r c} ^ {m, k} = \\mathcal {N} \\left(\\mu_ {s r c} ^ {m, k}, \\sigma_ {s r c} ^ {m, k}\\right), \\tag {1}", + "image_path": "aa6279b992752620540cec2769fad9878ead3b0744cd04d33245d9557812b6e2.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 346, + 652, + 545, + 667 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 346, + 652, + 545, + 667 + ], + "spans": [ + { + "bbox": [ + 346, + 652, + 545, + 667 + ], + "type": "interline_equation", + "content": "\\mathcal {Z} _ {s r c} ^ {m, k} = \\left\\{z _ {s r c, i} ^ {m, k} \\sim C _ {s r c} ^ {m, k} \\mid i \\in [ 1, N _ {q} ] \\right\\}, \\tag {2}", + "image_path": "2180de8d581753d58a7c66c2ca7b0403931d72b1a7a7fbff9b3c5b919230104f.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 677, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 677, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 306, + 677, + 545, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "N_{q}" + }, + { + "bbox": [ + 306, + 677, + 545, + 714 + ], + "type": "text", + "content": " is the number of pseudo-source features. " + }, + { + "bbox": [ + 306, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mu_{src}^{m,k}" + }, + { + "bbox": [ + 306, + 677, + 545, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\sigma_{src}^{m,k}" + }, + { + "bbox": [ + 306, + 677, + 545, + 714 + ], + "type": "text", + "content": " denote the mean and standard deviation of normalized source features from the category " + }, + { + "bbox": [ + 306, + 677, + 545, + 714 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 306, + 677, + 545, + 714 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18811" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 60, + 71, + 531, + 287 + ], + "blocks": [ + { + "bbox": [ + 60, + 71, + 531, + 287 + ], + "lines": [ + { + "bbox": [ + 60, + 71, + 531, + 287 + ], + "spans": [ + { + "bbox": [ + 60, + 71, + 531, + 287 + ], + "type": "image", + "image_path": "4729166c77b5ad3bfb7e63261500f887e0a634172cbf74decb581f35c039cc56.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 289, + 545, + 357 + ], + "lines": [ + { + "bbox": [ + 46, + 289, + 545, + 357 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 545, + 357 + ], + "type": "text", + "content": "Figure 2. The main structure of our proposed method. From the source domain, we preserve the source centroids and the pre-trained model for each modality as the initialization of the class-wise centroids and all the models in the target domain, respectively. To generate reliable intra-modal predictions, Intra-Modal Prediction Aggregation (iMPA) attends to the reliable prediction whose feature shares a closer distance with the class-wise centroids in an intra-modal manner. Inter-Modal Pseudo-Label Fusion (xMPF) then fuses the intramodal predictions by estimating the reliability of predictions from each modality for noise suppression. Class-Wise Momentum Queues (CMQs) are designed to achieve a good balance between target domain adaptation and source knowledge preservation." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 375, + 287, + 400 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 375, + 287, + 400 + ], + "spans": [ + { + "bbox": [ + 46, + 375, + 287, + 400 + ], + "type": "text", + "content": "Here we use the features generated by the pre-trained extractor " + }, + { + "bbox": [ + 46, + 375, + 287, + 400 + ], + "type": "inline_equation", + "content": "g_0^m(\\cdot)" + }, + { + "bbox": [ + 46, + 375, + 287, + 400 + ], + "type": "text", + "content": " for the centroid construction." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 405, + 240, + 418 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 405, + 240, + 418 + ], + "spans": [ + { + "bbox": [ + 47, + 405, + 240, + 418 + ], + "type": "text", + "content": "3.2. Intra-Modal Prediction Aggregation" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 423, + 290, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 423, + 290, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 423, + 290, + 616 + ], + "type": "text", + "content": "In MM-CTTA, the prediction from each modality could be unreliable due to continual domain shifts, causing severe noise to the multi-modal fusion. To mitigate the intramodal noise, iMPA aims to generate reliable intra-modal predictions for each modality. Although previous methods [42, 38] regard the augmentation-average prediction as a more stable alternative, we argue that its superiority is not certain since test-time augmentations may introduce inductive bias to the prediction [34] (e.g., resizing image as in [42] could cause ambiguity to small-scale classes). Unlike the previous work [42], we propose an adaptive mechanism to fuse the raw and the augmentation-average prediction as the weighted sum based on their feature distance between class-wise centroids. Given the input sample " + }, + { + "bbox": [ + 46, + 423, + 290, + 616 + ], + "type": "inline_equation", + "content": "x^{m}" + }, + { + "bbox": [ + 46, + 423, + 290, + 616 + ], + "type": "text", + "content": " and its augmented variants " + }, + { + "bbox": [ + 46, + 423, + 290, + 616 + ], + "type": "inline_equation", + "content": "\\{\\widetilde{x}_i^m\\mid i\\in [1,N_{aug}^m]\\}" + }, + { + "bbox": [ + 46, + 423, + 290, + 616 + ], + "type": "text", + "content": ", the features and predictions are extracted by the teacher model " + }, + { + "bbox": [ + 46, + 423, + 290, + 616 + ], + "type": "inline_equation", + "content": "\\phi_{\\theta^{\\prime}}^{m}" + }, + { + "bbox": [ + 46, + 423, + 290, + 616 + ], + "type": "text", + "content": " as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 93, + 620, + 287, + 634 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 620, + 287, + 634 + ], + "spans": [ + { + "bbox": [ + 93, + 620, + 287, + 634 + ], + "type": "interline_equation", + "content": "p \\left(x ^ {m}\\right) = f _ {\\theta^ {\\prime}} ^ {m} \\left(g _ {\\theta^ {\\prime}} ^ {m} \\left(x ^ {m}\\right)\\right) = f _ {\\theta^ {\\prime}} ^ {m} \\left(z ^ {m}\\right), \\tag {3}", + "image_path": "0f2cc14791c4be35dcf972ff1f75d2d43fb72564221cbbe3afbdf265818ed0c2.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 93, + 637, + 287, + 672 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 637, + 287, + 672 + ], + "spans": [ + { + "bbox": [ + 93, + 637, + 287, + 672 + ], + "type": "interline_equation", + "content": "\\widetilde {p} \\left(x ^ {m}\\right) = \\frac {1}{N _ {a u g} ^ {m}} \\sum_ {i = 1} ^ {N _ {a u g} ^ {m}} f _ {\\theta^ {\\prime}} ^ {m} \\left(g _ {\\theta^ {\\prime}} ^ {m} \\left(\\widetilde {x} _ {i} ^ {m}\\right)\\right), \\tag {4}", + "image_path": "c5b7d4ac9b9d0c48e9e6280345d560b523ef64af783843d1686dc455d0ffa1df.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "inline_equation", + "content": "p(x^{m})" + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\widetilde{p} (x^m)" + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": " represent the raw and the augmentation-average prediction, respectively. Both predictions are of shape " + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "inline_equation", + "content": "N\\times N_{c}" + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "inline_equation", + "content": "N_{C}" + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": " is the number" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "spans": [ + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "text", + "content": "of classes and " + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "inline_equation", + "content": "N_{aug}^{m}" + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "text", + "content": " denotes the number of augmentations. The normalized augmentation-average feature is computed as " + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "inline_equation", + "content": "\\widetilde{z}^m = \\sum_{i=1}^{N_{aug}^m} g^m(\\widetilde{x}_i^m) / (\\|g^m(\\widetilde{x}_i^m)\\| \\cdot N_{aug}^m)" + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "text", + "content": ". Subsequently, the weights for predictions " + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "inline_equation", + "content": "p(x^m), \\widetilde{p}(x^m)" + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "text", + "content": " are computed based on their corresponding feature distance to the class-wise centroid in a point-wise manner, so that each point of the intra-modal prediction " + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "inline_equation", + "content": "\\hat{p}(x^m)" + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "text", + "content": " can attend more to the confident prediction located closer to the cluster in the latent space. Taking a point " + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "inline_equation", + "content": "(j)" + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "text", + "content": " as an example, given its predictions " + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "inline_equation", + "content": "p_{(j)}(x^m), \\widetilde{p}_{(j)}(x^m)" + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "text", + "content": " and features " + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "inline_equation", + "content": "z_{(j)}^m, \\widetilde{z}_{(j)}^m" + }, + { + "bbox": [ + 304, + 375, + 545, + 501 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 357, + 508, + 545, + 539 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 357, + 508, + 545, + 539 + ], + "spans": [ + { + "bbox": [ + 357, + 508, + 545, + 539 + ], + "type": "interline_equation", + "content": "w _ {(j)} ^ {m} = \\frac {\\exp \\left(\\left\\langle \\mu^ {m , k} , z _ {(j)} ^ {m} \\right\\rangle\\right)}{\\sum_ {i \\in N _ {c}} \\exp \\left(\\left\\langle \\mu^ {m , i} , z _ {(j)} ^ {m} \\right\\rangle\\right)}, \\tag {5}", + "image_path": "e9c720448df0f66caf01b9622a10ff432d90343166958c6c7beaa79739dc68b6.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 358, + 541, + 545, + 574 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 358, + 541, + 545, + 574 + ], + "spans": [ + { + "bbox": [ + 358, + 541, + 545, + 574 + ], + "type": "interline_equation", + "content": "\\widetilde {w} _ {(j)} ^ {m} = \\frac {\\exp \\left(\\left\\langle \\mu^ {m , \\widetilde {k}} , \\widetilde {z} _ {(j)} ^ {m} \\right\\rangle\\right)}{\\sum_ {i \\in N _ {c}} \\exp \\left(\\left\\langle \\mu^ {m , i} , \\widetilde {z} _ {(j)} ^ {m} \\right\\rangle\\right)}, \\tag {6}", + "image_path": "d02f67565456a7d8505c5e640c56b97f4443f6ca1ab37de7026ae33d826d3460.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 337, + 576, + 545, + 608 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 337, + 576, + 545, + 608 + ], + "spans": [ + { + "bbox": [ + 337, + 576, + 545, + 608 + ], + "type": "interline_equation", + "content": "\\hat {p} _ {(j)} \\left(x ^ {m}\\right) = \\frac {w _ {(j)} ^ {m} p _ {(j)} \\left(x ^ {m}\\right) + \\widetilde {w} _ {(j)} ^ {m} \\widetilde {p} _ {(j)} \\left(x ^ {m}\\right)}{w _ {(j)} ^ {m} + \\widetilde {w} _ {(j)} ^ {m}}, \\tag {7}", + "image_path": "f834251135b85a5326ebfcd01ee1ed3bf4479f14d17e91285c4d775681c047b1.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "inline_equation", + "content": "w_{(j)}^m, \\widetilde{w}_{(j)}^m" + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "text", + "content": " are termed as the raw weight and augmentation-average weight, respectively. " + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "inline_equation", + "content": "k, \\widetilde{k}" + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "text", + "content": " are the largest element locations of " + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "inline_equation", + "content": "p_{(j)}(x^m), \\widetilde{p}_{(j)}(x^m)" + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\mu^{m,k}" + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "text", + "content": " denotes the mean of class " + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "text", + "content": " centroid, which is actively updated as shown in Sec. 3.4. " + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\langle a,b\\rangle" + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "text", + "content": " represents the inner product of vectors " + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 304, + 613, + 547, + 715 + ], + "type": "text", + "content": ". Our empirical results show that this adaptive fusion between the raw and augmentation-average predictions results in more stable intra-modal predictions." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "18812" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 229, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 229, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 229, + 83 + ], + "type": "text", + "content": "3.3. Inter-Modal Pseudo-Label Fusion" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 90, + 289, + 273 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 90, + 289, + 273 + ], + "spans": [ + { + "bbox": [ + 46, + 90, + 289, + 273 + ], + "type": "text", + "content": "Given the output of iMPA, the goal of xMPF is to generate pseudo-labels by estimating their reliability in a cross-modal manner. Since domain shifts can affect the reliability of each modality variously (e.g., images in day and night), the cross-modal pseudo-label should adaptively attend to the reliable modality for noise suppression. Motivated by this idea, the proposed xMPF generates the cross-modal pseudo-labels as the weighted sum of intra-modal predictions from iMPA. Specifically, taking point " + }, + { + "bbox": [ + 46, + 90, + 289, + 273 + ], + "type": "inline_equation", + "content": "(j)" + }, + { + "bbox": [ + 46, + 90, + 289, + 273 + ], + "type": "text", + "content": " as an example, the inter-modal weight " + }, + { + "bbox": [ + 46, + 90, + 289, + 273 + ], + "type": "inline_equation", + "content": "\\hat{w}_{(j)}^{m}" + }, + { + "bbox": [ + 46, + 90, + 289, + 273 + ], + "type": "text", + "content": " is computed as the summation of both weights if their corresponding predictions indicate the same class, or the maximum one otherwise. This can be viewed as an implicit way to encourage point-wise prediction consistency for each modality. Formally, the inter-modal weight " + }, + { + "bbox": [ + 46, + 90, + 289, + 273 + ], + "type": "inline_equation", + "content": "\\hat{w}_{(j)}^{m}" + }, + { + "bbox": [ + 46, + 90, + 289, + 273 + ], + "type": "text", + "content": " is computed as follows:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 82, + 279, + 287, + 314 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 82, + 279, + 287, + 314 + ], + "spans": [ + { + "bbox": [ + 82, + 279, + 287, + 314 + ], + "type": "interline_equation", + "content": "\\hat {w} _ {(j)} ^ {m} = \\left\\{ \\begin{array}{l} w _ {(j)} ^ {m} + \\widetilde {w} _ {(j)} ^ {m}, \\text {i f} k = \\widetilde {k} \\\\ \\max \\left(w _ {(j)} ^ {m}, \\widetilde {w} _ {(j)} ^ {m}\\right), \\text {i f} k \\neq \\widetilde {k} \\end{array} \\right. \\tag {8}", + "image_path": "48d15e4b81e44cd41675f74368ba5f2dadfee6e9207158b130979b3c0e0b2331.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 319, + 287, + 343 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 319, + 287, + 343 + ], + "spans": [ + { + "bbox": [ + 47, + 319, + 287, + 343 + ], + "type": "text", + "content": "The cross-modal prediction is then computed as the weighted sum in a cross-modal manner:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 88, + 350, + 287, + 384 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 350, + 287, + 384 + ], + "spans": [ + { + "bbox": [ + 88, + 350, + 287, + 384 + ], + "type": "interline_equation", + "content": "\\hat {p} _ {(j)} ^ {\\mathrm {X M}} (x) = \\frac {\\hat {w} _ {(j)} ^ {\\mathrm {2 D}} \\hat {p} _ {(j)} ^ {\\mathrm {2 D}} (x) + \\hat {w} _ {(j)} ^ {\\mathrm {3 D}} \\hat {p} _ {(j)} ^ {\\mathrm {3 D}} (x)}{\\hat {w} _ {(j)} ^ {\\mathrm {2 D}} + \\hat {w} _ {(j)} ^ {\\mathrm {3 D}}}, \\tag {9}", + "image_path": "4a15127fd923d71706bd53c0a3accfc5a45a7b8554514ea2e008425ee792b602.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 102, + 384, + 287, + 404 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 384, + 287, + 404 + ], + "spans": [ + { + "bbox": [ + 102, + 384, + 287, + 404 + ], + "type": "interline_equation", + "content": "\\hat {y} _ {(j)} = \\arg \\max _ {k \\in N _ {c}} \\left(\\hat {p} _ {(j)} ^ {\\mathbf {x M}} (x) ^ {(k)}\\right), \\tag {10}", + "image_path": "bb04c83798b86242653bbec824a1cbb7ea964c6a8b308568e69232cb03071d79.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 412, + 287, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 412, + 287, + 460 + ], + "spans": [ + { + "bbox": [ + 47, + 412, + 287, + 460 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 412, + 287, + 460 + ], + "type": "inline_equation", + "content": "\\hat{p}_{(j)}^{\\mathrm{xM}}(x),\\hat{y}_{(j)}" + }, + { + "bbox": [ + 47, + 412, + 287, + 460 + ], + "type": "text", + "content": " denote the cross-modal prediction and pseudo-label, respectively. The cross-modal pseudo-label can therefore attend to the more reliable modality with confident intra-modal predictions." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 468, + 198, + 480 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 468, + 198, + 480 + ], + "spans": [ + { + "bbox": [ + 47, + 468, + 198, + 480 + ], + "type": "text", + "content": "3.4. Class-Wise Moving Queues" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "type": "text", + "content": "Both iMPA and xMPF greatly depend on the quality of class-wise centroids. Initialized from the source offline centroids as in Eq. 1, the class-wise centroids should continually adapt to the target domain to ensure the validity of iMPA and xMPF. Meanwhile, the source knowledge should be occasionally played back during the centroid adaptation so that it can be revisited during the reliability estimation in iMPA and xMPF without catastrophic forgetting. To achieve a balance between adaptation and source knowledge preservation, we propose CMQs which utilize momentum queues [15] to actively estimate feature clustering of the target domain by capturing confident target features while stochastically restoring pseudo-source features for each modality. Specifically, the CMQ of the class " + }, + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "type": "text", + "content": " is initialized by the pseudo-source features " + }, + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}_{src}^{m,k}" + }, + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "type": "text", + "content": " as in Eq. 2. For each iteration, taking the raw sample as input, the normalized point features from the student network " + }, + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\phi_{\\theta}^{m}" + }, + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "type": "text", + "content": " with confident predictions are preserved by threshold-based filtering. Given the CMQ of class " + }, + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "type": "text", + "content": " from the previous step" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 71, + 537, + 86 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 71, + 537, + 86 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 537, + 86 + ], + "type": "text", + "content": "denoted as " + }, + { + "bbox": [ + 306, + 71, + 537, + 86 + ], + "type": "inline_equation", + "content": "\\hat{\\mathcal{Q}}_{t - 1}^{m,k}" + }, + { + "bbox": [ + 306, + 71, + 537, + 86 + ], + "type": "text", + "content": ", the CMQ of current step is updated as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 323, + 95, + 545, + 111 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 323, + 95, + 545, + 111 + ], + "spans": [ + { + "bbox": [ + 323, + 95, + 545, + 111 + ], + "type": "interline_equation", + "content": "\\mathcal {Z} _ {c f} ^ {m, k} = \\mathbb {1} _ {c f} ^ {k} \\left[ g _ {\\theta} ^ {m} \\left(x ^ {m}\\right) / \\| g _ {\\theta} ^ {m} \\left(x ^ {m}\\right) \\| \\right], \\tag {11}", + "image_path": "6e0b96bed29cca4389b96a9e6a7d2fd97c533d9fe81e2b3e7fbc067895f49e93.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 323, + 112, + 545, + 129 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 323, + 112, + 545, + 129 + ], + "spans": [ + { + "bbox": [ + 323, + 112, + 545, + 129 + ], + "type": "interline_equation", + "content": "\\widetilde {\\mathcal {Q}} _ {t} ^ {m, k} = \\Phi \\left(\\hat {\\mathcal {Q}} _ {t - 1} ^ {m, k}, \\mathcal {Z} _ {c f} ^ {m, k}\\right), \\tag {12}", + "image_path": "cb9412aa7884af8a44503892ef0e486b215124da76edf3aeaf4582fae04bf176.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 323, + 131, + 545, + 163 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 323, + 131, + 545, + 163 + ], + "spans": [ + { + "bbox": [ + 323, + 131, + 545, + 163 + ], + "type": "interline_equation", + "content": "\\hat {\\mathcal {Q}} _ {t} ^ {m, k} = \\left\\{ \\begin{array}{l l} \\widetilde {\\mathcal {Q}} _ {t} ^ {m, k}, & \\text {i f} \\gamma_ {t} > p _ {r s} \\\\ \\Phi \\left(\\hat {\\mathcal {Q}} _ {t - 1} ^ {m, k}, \\mathbb {1} _ {r s} ^ {k} \\mathcal {Z} _ {s r c} ^ {m, k}\\right), & \\text {i f} \\gamma_ {t} \\leq p _ {r s} \\end{array} , \\right. \\tag {13}", + "image_path": "ff40893030c96b10d29a923e690dbd40bd623c59c9b9fa9d3cc5e4e9d0612fcd.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "spans": [ + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "\\mathbb{1}_{cf}^k" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " is the confidence index for class " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "\\mathbb{1}_{cf}^k\\phi_\\theta^m (x^m)^{(k)}\\geq \\tau_{cf}" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "\\mathbb{1}_{rs}^k" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " denotes the source restoring index which randomly samples " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "N_{enq}" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " pseudo-source features from " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}_{src}^{m,k}" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "\\Phi (a,b)" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " denotes the operation of enqueuing " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " as in [15]. " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "\\gamma_{t}" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " is a restoring flag uniformly sampled from [0, 1] at timestamp " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "p_{rs}" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " denotes the hyperparameter of restoring probability. Different from the image classification problem which can capture all confident samples [36], the number of confident points from each class can be huge (i.e., more than 1,000), which is too aggressive and expensive to enqueue all points. Therefore, we limit the index number of " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "\\mathbb{1}_{cf}^k" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " by an upper bound " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "N_{enq}" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " through selecting features with the top " + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "inline_equation", + "content": "N_{enq}" + }, + { + "bbox": [ + 305, + 172, + 545, + 331 + ], + "type": "text", + "content": " confident predictions." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "spans": [ + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "type": "text", + "content": "For each optimization step, the mean of the class-wise centroid for the next step " + }, + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "type": "inline_equation", + "content": "\\mu_{t + 1}^{m,k}" + }, + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "type": "text", + "content": " is updated as the average of CMQ of the current timestamp " + }, + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "type": "inline_equation", + "content": "\\hat{\\mathcal{Q}}_t^{m,k}" + }, + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "type": "text", + "content": " so that the class-wise centroids can adapt to the feature clustering of target domain without catastrophic forgetting. Additionally, we propose a class-wise contrastive loss modified from [19] as a regularizer so that the target confident features can revisit source knowledge through clustering around the class-wise centroids. Specifically, given any confident target feature from Eq. 11 as the anchor, the positive samples are the features from the CMQ that shares the same modality and semantic class, denoted as " + }, + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "type": "inline_equation", + "content": "P(k) = \\{\\hat{q}_p\\mid \\hat{q}_p\\in \\hat{\\mathcal{Q}}_t^{m,k}\\}" + }, + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "type": "text", + "content": ". The negative samples are the features from the CMQs of the same modality but different classes denoted as " + }, + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "type": "inline_equation", + "content": "A(k) = \\{\\hat{q}_n\\mid \\hat{q}_n\\in \\hat{\\mathcal{Q}}_t^{m,a},\\forall a\\neq k\\bigcap a\\in N_c\\}" + }, + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "type": "text", + "content": ". The class-wise contrastive loss " + }, + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{cts}^m" + }, + { + "bbox": [ + 305, + 331, + 546, + 525 + ], + "type": "text", + "content": " is computed as:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 329, + 533, + 545, + 605 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 329, + 533, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 329, + 533, + 545, + 605 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {L} _ {c t s} ^ {m} = \\sum_ {i \\in | \\mathcal {Z} _ {c f} ^ {m, k} |} \\frac {- 1}{| P (k) |} \\\\ \\sum_ {q _ {p} \\in P (k)} \\frac {\\exp \\left(\\hat {z} _ {t , (i)} ^ {m , k} \\cdot q _ {p}\\right)}{\\sum_ {q _ {n} \\in N (k)} \\exp \\left(\\hat {z} _ {t , (i)} ^ {m , k} \\cdot q _ {n}\\right)}. \\tag {14} \\\\ \\end{array}", + "image_path": "01f4cfa1b8cf357951f39f5340e7baffe4c6489986b038042b36fa1de223607a.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 623, + 487, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 623, + 487, + 635 + ], + "spans": [ + { + "bbox": [ + 306, + 623, + 487, + 635 + ], + "type": "text", + "content": "3.5. Main Structure and Optimization" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 642, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 642, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 642, + 547, + 714 + ], + "type": "text", + "content": "The main structure of our proposed method is shown in Fig. 2. Given the multi-modal input " + }, + { + "bbox": [ + 305, + 642, + 547, + 714 + ], + "type": "inline_equation", + "content": "x^{m}" + }, + { + "bbox": [ + 305, + 642, + 547, + 714 + ], + "type": "text", + "content": ", the teacher model is used to infer " + }, + { + "bbox": [ + 305, + 642, + 547, + 714 + ], + "type": "inline_equation", + "content": "x^{m}" + }, + { + "bbox": [ + 305, + 642, + 547, + 714 + ], + "type": "text", + "content": " and its augmented variants " + }, + { + "bbox": [ + 305, + 642, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\{\\widetilde{x}_i^m | i \\in [1, N_{\\text{aug}}^m]\\}" + }, + { + "bbox": [ + 305, + 642, + 547, + 714 + ], + "type": "text", + "content": " and then generate reliable cross-modal pseudolabels denoted as " + }, + { + "bbox": [ + 305, + 642, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\hat{y}" + }, + { + "bbox": [ + 305, + 642, + 547, + 714 + ], + "type": "text", + "content": " through iMPA and xMPF. The student model is directly updated by minimizing the weighted sum" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18813" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 75, + 200, + 87 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 75, + 200, + 87 + ], + "spans": [ + { + "bbox": [ + 48, + 75, + 200, + 87 + ], + "type": "text", + "content": "Algorithm 1: The proposed CoMAC" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 89, + 263, + 102 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 89, + 263, + 102 + ], + "spans": [ + { + "bbox": [ + 47, + 89, + 263, + 102 + ], + "type": "text", + "content": "Init Model: Teacher " + }, + { + "bbox": [ + 47, + 89, + 263, + 102 + ], + "type": "inline_equation", + "content": "\\phi_{\\theta}^{m}" + }, + { + "bbox": [ + 47, + 89, + 263, + 102 + ], + "type": "text", + "content": ", student " + }, + { + "bbox": [ + 47, + 89, + 263, + 102 + ], + "type": "inline_equation", + "content": "\\phi_{\\theta}^{m}" + }, + { + "bbox": [ + 47, + 89, + 263, + 102 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 89, + 263, + 102 + ], + "type": "inline_equation", + "content": "m \\in \\{2D, 3D\\}" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 48, + 102, + 255, + 115 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 102, + 255, + 115 + ], + "spans": [ + { + "bbox": [ + 48, + 102, + 255, + 115 + ], + "type": "text", + "content": "Init CMQ: " + }, + { + "bbox": [ + 48, + 102, + 255, + 115 + ], + "type": "inline_equation", + "content": "\\hat{\\mathcal{Q}}_0^{m,k} = \\mathcal{Z}_{src}^{m,k}" + }, + { + "bbox": [ + 48, + 102, + 255, + 115 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 48, + 102, + 255, + 115 + ], + "type": "inline_equation", + "content": "m\\in \\{2\\mathrm{D},3\\mathrm{D}\\}" + }, + { + "bbox": [ + 48, + 102, + 255, + 115 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 48, + 102, + 255, + 115 + ], + "type": "inline_equation", + "content": "k\\in N_{c}" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 48, + 115, + 205, + 127 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 115, + 205, + 127 + ], + "spans": [ + { + "bbox": [ + 48, + 115, + 205, + 127 + ], + "type": "text", + "content": "for " + }, + { + "bbox": [ + 48, + 115, + 205, + 127 + ], + "type": "inline_equation", + "content": "t\\in |\\mathcal{X}_{\\mathcal{T}}|" + }, + { + "bbox": [ + 48, + 115, + 205, + 127 + ], + "type": "inline_equation", + "content": "x = (x^{2D},x^{3D})\\in \\mathcal{X}_{\\mathcal{T}}" + }, + { + "bbox": [ + 48, + 115, + 205, + 127 + ], + "type": "text", + "content": " do" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 52, + 128, + 142, + 138 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 128, + 142, + 138 + ], + "spans": [ + { + "bbox": [ + 52, + 128, + 142, + 138 + ], + "type": "text", + "content": "for " + }, + { + "bbox": [ + 52, + 128, + 142, + 138 + ], + "type": "inline_equation", + "content": "m\\in \\{2D,3D\\}" + }, + { + "bbox": [ + 52, + 128, + 142, + 138 + ], + "type": "text", + "content": " do" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 56, + 139, + 271, + 176 + ], + "type": "list", + "angle": 0, + "index": 8, + "blocks": [ + { + "bbox": [ + 57, + 139, + 234, + 152 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 139, + 234, + 152 + ], + "spans": [ + { + "bbox": [ + 57, + 139, + 234, + 152 + ], + "type": "text", + "content": "1. Augmented input to get " + }, + { + "bbox": [ + 57, + 139, + 234, + 152 + ], + "type": "inline_equation", + "content": "\\{\\widetilde{x}_i^m\\mid i\\in N_{aug}^m\\}" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 56, + 152, + 261, + 164 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 152, + 261, + 164 + ], + "spans": [ + { + "bbox": [ + 56, + 152, + 261, + 164 + ], + "type": "text", + "content": "2. Get predictions and features with " + }, + { + "bbox": [ + 56, + 152, + 261, + 164 + ], + "type": "inline_equation", + "content": "\\phi_{\\theta'}^m" + }, + { + "bbox": [ + 56, + 152, + 261, + 164 + ], + "type": "text", + "content": " by Eq. 3-4" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 56, + 164, + 271, + 176 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 164, + 271, + 176 + ], + "spans": [ + { + "bbox": [ + 56, + 164, + 271, + 176 + ], + "type": "text", + "content": "3. Get intra-modal " + }, + { + "bbox": [ + 56, + 164, + 271, + 176 + ], + "type": "inline_equation", + "content": "\\hat{p}^m (x^m)" + }, + { + "bbox": [ + 56, + 164, + 271, + 176 + ], + "type": "text", + "content": " by iMPA through Eq. 5-7" + } + ] + } + ], + "index": 7 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 52, + 178, + 69, + 186 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 178, + 69, + 186 + ], + "spans": [ + { + "bbox": [ + 52, + 178, + 69, + 186 + ], + "type": "text", + "content": "end" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 52, + 189, + 250, + 225 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 52, + 189, + 246, + 201 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 189, + 246, + 201 + ], + "spans": [ + { + "bbox": [ + 52, + 189, + 246, + 201 + ], + "type": "text", + "content": "4. Get inter-modal " + }, + { + "bbox": [ + 52, + 189, + 246, + 201 + ], + "type": "inline_equation", + "content": "\\hat{y}" + }, + { + "bbox": [ + 52, + 189, + 246, + 201 + ], + "type": "text", + "content": " by xMPF through Eq. 8-10" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 52, + 201, + 250, + 213 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 201, + 250, + 213 + ], + "spans": [ + { + "bbox": [ + 52, + 201, + 250, + 213 + ], + "type": "text", + "content": "5. Update CMQs and compute " + }, + { + "bbox": [ + 52, + 201, + 250, + 213 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{cts}^{m}" + }, + { + "bbox": [ + 52, + 201, + 250, + 213 + ], + "type": "text", + "content": " by Eq. 11-14" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 52, + 213, + 224, + 225 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 213, + 224, + 225 + ], + "spans": [ + { + "bbox": [ + 52, + 213, + 224, + 225 + ], + "type": "text", + "content": "6. Update " + }, + { + "bbox": [ + 52, + 213, + 224, + 225 + ], + "type": "inline_equation", + "content": "\\phi_{\\theta}^{m}" + }, + { + "bbox": [ + 52, + 213, + 224, + 225 + ], + "type": "text", + "content": " by Eq. 16 and " + }, + { + "bbox": [ + 52, + 213, + 224, + 225 + ], + "type": "inline_equation", + "content": "\\phi_{\\theta^{\\prime}}^{m}" + }, + { + "bbox": [ + 52, + 213, + 224, + 225 + ], + "type": "text", + "content": " by Eq. 17" + } + ] + } + ], + "index": 12 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 48, + 227, + 66, + 236 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 227, + 66, + 236 + ], + "spans": [ + { + "bbox": [ + 48, + 227, + 66, + 236 + ], + "type": "text", + "content": "end" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 266, + 287, + 315 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 266, + 287, + 315 + ], + "spans": [ + { + "bbox": [ + 46, + 266, + 287, + 315 + ], + "type": "text", + "content": "of the standard cross-entropy loss between its prediction and the pseudo-label " + }, + { + "bbox": [ + 46, + 266, + 287, + 315 + ], + "type": "inline_equation", + "content": "\\hat{y}" + }, + { + "bbox": [ + 46, + 266, + 287, + 315 + ], + "type": "text", + "content": ", and the contrastive loss in Eq. 14. The teacher model is updated as the exponential moving average of the student's weights as in previous works [35, 42]:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 106, + 324, + 287, + 338 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 106, + 324, + 287, + 338 + ], + "spans": [ + { + "bbox": [ + 106, + 324, + 287, + 338 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {c e} ^ {m} = \\mathbb {1} _ {\\tilde {y}} \\log \\phi^ {m} \\left(x ^ {m}\\right), \\tag {15}", + "image_path": "fa8f54aeceab1ce7a46cf3009b164d1ffc7dc9848e342f15e19a12a102c1f129.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 136, + 341, + 164, + 350 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 136, + 341, + 164, + 350 + ], + "spans": [ + { + "bbox": [ + 136, + 341, + 164, + 350 + ], + "type": "interline_equation", + "content": "\\{2 D, 3 D \\}", + "image_path": "491372a8a4ddbbf442f3e831ab40e9476e27aab2e88f8554b9c673f570d2d5a8.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 97, + 350, + 287, + 374 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 350, + 287, + 374 + ], + "spans": [ + { + "bbox": [ + 97, + 350, + 287, + 374 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {t o t a l}} = \\sum_ {m} \\left(\\mathcal {L} _ {c e} ^ {m} + \\lambda_ {c t s} \\mathcal {L} _ {c t s} ^ {m}\\right), \\tag {16}", + "image_path": "11bf8e1113b406eae9e5536588cd5de418dc7c4e7e5f1a720a581cb4c0b78f53.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 103, + 376, + 287, + 390 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 103, + 376, + 287, + 390 + ], + "spans": [ + { + "bbox": [ + 103, + 376, + 287, + 390 + ], + "type": "interline_equation", + "content": "\\theta_ {t + 1} ^ {\\prime} = \\left(1 - \\lambda_ {s}\\right) \\theta + \\lambda_ {s} \\theta^ {\\prime}, \\tag {17}", + "image_path": "066847cc4e1f02ddf59453b9698f7a3dfe062f87ee80cf5ead8180073de58579.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 46, + 400, + 287, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 400, + 287, + 437 + ], + "spans": [ + { + "bbox": [ + 46, + 400, + 287, + 437 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 400, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\lambda_{cts}" + }, + { + "bbox": [ + 46, + 400, + 287, + 437 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 400, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\lambda_s" + }, + { + "bbox": [ + 46, + 400, + 287, + 437 + ], + "type": "text", + "content": " are the hyper-parameters denoting the coefficient of the contrastive loss and the momentum factor. Our adaptation process is summarized as Algorithm 1." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 47, + 449, + 128, + 462 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 449, + 128, + 462 + ], + "spans": [ + { + "bbox": [ + 47, + 449, + 128, + 462 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 46, + 469, + 287, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 469, + 287, + 530 + ], + "spans": [ + { + "bbox": [ + 46, + 469, + 287, + 530 + ], + "type": "text", + "content": "In this section, we present our experimental results based on two new benchmarks. The details of our proposed benchmarks, baselines, and implementation are first introduced in Sec. 4.1. Sec. 4.2 presents our overall results and Sec. 4.3 justifies our method by extensive ablation studies." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 47, + 539, + 189, + 552 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 539, + 189, + 552 + ], + "spans": [ + { + "bbox": [ + 47, + 539, + 189, + 552 + ], + "type": "text", + "content": "4.1. Benchmarks and Settings" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 46, + 557, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 288, + 713 + ], + "type": "text", + "content": "Proposed benchmarks. To evaluate the performance under MM-CTTA settings, we proposed two benchmarks in this work, including (i) SemanticKITTI-to-Synthia (S-to-S) and (ii) SemanticKITTI-to-Waymo (S-to-W). Both benchmarks leverage SemanticKITTI [2] as the source-domain dataset, which utilizes a 0.7MP camera and a 64-line LiDAR. For the target domain, we utilize two different datasets including Synthia [33] and Waymo [37] thanks to the various environmental conditions they cover. The former shares a larger domain gap with more diverse seasons, weather, and illumination conditions while the latter is less challenging but closer to the real-world application. For S-to-S, it is constructed by a sequence of different videos" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 72, + 545, + 432 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 432 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 432 + ], + "type": "text", + "content": "from Synthia [33] without any repetition. Since Synthia includes depth images instead of 3D point clouds, we generate a simulated point cloud for each sample by randomly sampling depth pixels as 3D points following the structural characteristic of LiDAR. For each sequence, all samples are included for adaptation and we use \"No.-Conditions\" to indicate their corresponding video sequence in Synthia (i.e., \"01-Spring\" indicates video sequence 01 under Spring condition). Different from the previous CTTA benchmark [42] which only includes 4 different unique sequences, the proposed S-to-S consists of 12 different sequences recorded under various environmental conditions without repetition. By default, we organize the sequences following the order of seasons " + }, + { + "bbox": [ + 304, + 72, + 545, + 432 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 304, + 72, + 545, + 432 + ], + "type": "text", + "content": " illumination " + }, + { + "bbox": [ + 304, + 72, + 545, + 432 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 304, + 72, + 545, + 432 + ], + "type": "text", + "content": " weathers as a challenge ascending order. For S-to-W, we sort out the illumination conditions of each sequence in Waymo dataset [37] based on the sequence descriptions and divide all samples into three types, including Day (D), Dawn-Dusk (DD), and Night (N). Since the number of sequences of D is much larger than others, we further split the sequence of D based on their recording location, including Phoenix (P), San Francisco (S), and Others (O). Each sequence is separated in two halves to simulate the revisiting situation as in [42] but without repeated samples (i.e., \"D-O-1\" indicates the first half of the D-O sequence). Similar to S-to-S, S-to-W also follows a challenge ascending order. For both datasets, we adopt the images of the front-view camera similar to the source-domain dataset. We utilize a similar class mapping strategy as [18, 35] with slight modification since some classes are missing in the target domain. More details are illustrated in the appendix." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 304, + 434, + 545, + 615 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 434, + 545, + 615 + ], + "spans": [ + { + "bbox": [ + 304, + 434, + 545, + 615 + ], + "type": "text", + "content": "Baselines. Previous TTA, MM-TTA, and CTTA methods are evaluated on both S-to-S and S-to-M as baselines. For TTA methods, we compare with pseudo-labels with threshold filtering (Plabel), TENT [40] and LAME [3], while xMUDA with pseudo-labels (xMUDA-pl) [18] and MMTTA [43] are regarded as the representatives of MMTTA methods. CoTTA [42] and EATA [30] are the recent works that focus on CTTA problems. Specifically, xMUDA-pl is originally designed for UDA, whereas we modify it into a TTA version by discarding the source data during adaptation. Considering our CoMAC is the only MM-CTTA method, we implement an MM-CTTA version of MMTTA [35] integrated with model-based stochastic restoration in [42] for a fair comparison. We report the softmax-average mIoU of 2D and 3D predictions as results." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 714 + ], + "type": "text", + "content": "Implementation details. Following previous works [18, 35], we utilize UNet [32] with ResNet-34 [16] encoder as the 2D backbone and SCN [14] based on UNet as the 3D backbone for all baselines. The pre-training procedures on SemanticKITTI dataset follow [18]. For our method, we empirically choose resizing and z-rotation as the 2D and 3D augmentations following previous works [42, 18]. Specifically, we utilize multiple resizing factors of [0.5," + } + ] + } + ], + "index": 27 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18814" + } + ] + } + ], + "index": 28 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 545, + 231 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 545, + 231 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 545, + 231 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 545, + 231 + ], + "type": "table", + "html": "
Timet →t →
MethodsDA TypeSemanticKITTI-to-SynthiaSemanticKITTI-to-Waymo
01-Spring02-Summer04-Full05-Winter01-Dawn02-Night04-Sunset05-Wnight01-Fog02-S-Rain04-R-Night05-RainAvgD-O-1D-P-1D-S-1DD-1N-1D-O-2D-P-2D-S-2DD-2N-2Avg
Source-28.330.737.727.323.127.338.226.527.021.627.816.427.733.236.929.528.314.032.838.030.428.414.628.6
PlabelTTA29.627.136.428.421.426.632.326.127.421.825.018.026.739.141.937.036.825.738.543.737.637.624.636.9
TENT [40]TTA35.424.924.920.718.716.616.013.613.611.58.49.117.833.622.318.816.910.815.712.99.811.310.616.3
LAME [3]TTA14.012.417.313.012.611.617.013.219.27.77.86.012.711.910.413.49.28.713.411.212.29.78.612.7
xMUDA-pl [18]MM-TTA28.826.935.928.221.326.532.226.027.021.624.917.926.439.342.137.437.025.938.743.937.937.725.036.5
MMTTA [35]MM-TTA31.124.430.725.828.324.226.823.229.620.722.120.625.639.940.030.931.529.630.632.223.926.423.830.9
CoTTA [42]CTTA29.727.234.727.026.425.633.027.328.118.022.718.426.532.928.022.922.220.326.124.923.624.719.724.5
EATA [30]CTTA34.030.038.630.230.228.436.530.132.221.325.320.129.740.140.836.334.328.939.341.736.537.928.836.5
MMTTA-rs [35]MM-CTTA31.928.137.729.328.727.635.229.730.220.425.620.328.740.441.536.334.730.239.941.536.438.329.936.9
CoMAC (Ours)MM-CTTA34.034.744.938.135.037.845.139.039.129.435.127.136.641.443.738.837.832.242.241.840.738.930.438.8
Timet ←t ←
TENT [40]TTA10.28.88.69.010.29.59.811.418.313.216.918.912.112.011.59.29.89.712.613.012.519.821.213.1
MMTTA-rs [35]MM-CTTA31.427.437.228.726.227.233.129.028.519.922.319.727.640.441.436.431.629.137.640.235.435.227.835.5
CoMAC (Ours)MM-CTTA34.632.840.933.231.832.439.233.233.825.130.323.332.440.841.937.733.230.339.643.638.838.630.037.5
", + "image_path": "0a871873ade4464ea0e435a8c4a9654ca543d8f5d62048d329cb9eac995cde86.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 62, + 236, + 529, + 248 + ], + "lines": [ + { + "bbox": [ + 62, + 236, + 529, + 248 + ], + "spans": [ + { + "bbox": [ + 62, + 236, + 529, + 248 + ], + "type": "text", + "content": "Table 1. Performance (mIoU) of SemanticKITTI-to-Synthia. Here we report the softmax-average mIoU of 2D and 3D prediction." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 51, + 261, + 197, + 326 + ], + "blocks": [ + { + "bbox": [ + 51, + 261, + 197, + 326 + ], + "lines": [ + { + "bbox": [ + 51, + 261, + 197, + 326 + ], + "spans": [ + { + "bbox": [ + 51, + 261, + 197, + 326 + ], + "type": "image", + "image_path": "ead5781acdec926235eb580f3f6fe4bddd607acace7c96163bc5351df486c466.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 331, + 546, + 365 + ], + "lines": [ + { + "bbox": [ + 46, + 331, + 546, + 365 + ], + "spans": [ + { + "bbox": [ + 46, + 331, + 546, + 365 + ], + "type": "text", + "content": "Figure 3. Ablation studies to justify our design of CoMAC. Specifically, (a) compares CoMAC with variants only using raw or augmented samples as input of iMPA and (b) justifies the necessity of weighting mechanisms in iMPA and xMPF. (c) compares CoMAC with variants without either target feature enqueuing or pseudo-source features restoring in CMQs. Scores within the parentheses are the average mIoU." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 222, + 261, + 371, + 325 + ], + "blocks": [ + { + "bbox": [ + 222, + 261, + 371, + 325 + ], + "lines": [ + { + "bbox": [ + 222, + 261, + 371, + 325 + ], + "spans": [ + { + "bbox": [ + 222, + 261, + 371, + 325 + ], + "type": "image", + "image_path": "28511b9a214e92153d5cb718a56fab981c18bea8aafff6d44056368a3b46001c.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 397, + 261, + 544, + 325 + ], + "blocks": [ + { + "bbox": [ + 397, + 261, + 544, + 325 + ], + "lines": [ + { + "bbox": [ + 397, + 261, + 544, + 325 + ], + "spans": [ + { + "bbox": [ + 397, + 261, + 544, + 325 + ], + "type": "image", + "image_path": "65ce37e2c261a5b748a0cf18c5e62dc1a12b5ef4b527a6204af49873838b0857.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "spans": [ + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "text", + "content": "0.625, 0.75, 0.875] and z-rotation of " + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "inline_equation", + "content": "[60^{\\circ}, 120^{\\circ}, 180^{\\circ}, 240^{\\circ}, 300^{\\circ}]" + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "inline_equation", + "content": "N_{q}" + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "inline_equation", + "content": "N_{enq}" + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "text", + "content": " are set to 4096 and 200, respectively. We utilize a restore rate " + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "inline_equation", + "content": "p_{rs}" + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "text", + "content": " of 0.5 and a momentum factor " + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "inline_equation", + "content": "\\lambda_{s}" + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "text", + "content": " of 0.999 with a coefficient " + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "inline_equation", + "content": "\\lambda_{cts}" + }, + { + "bbox": [ + 46, + 383, + 287, + 468 + ], + "type": "text", + "content": " of 1. All methods strictly follow the one-pass protocol [36] (i.e., the training epoch is one where inference is conducted immediately for each sample). More details are included in the appendix." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 479, + 142, + 490 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 479, + 142, + 490 + ], + "spans": [ + { + "bbox": [ + 47, + 479, + 142, + 490 + ], + "type": "text", + "content": "4.2. Overall Results" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "type": "text", + "content": "As shown in Table 1, our CoMAC achieves SOTA performance on the average mIoU of all sequences for both benchmarks. Specifically, the proposed CoMAC significantly outperforms previous methods by more than " + }, + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "type": "inline_equation", + "content": "6.9\\%" + }, + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "type": "text", + "content": " on S-to-S and " + }, + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "type": "inline_equation", + "content": "1.9\\%" + }, + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "type": "text", + "content": " on S-to-W, which justifies the effectiveness of our method. It can also be observed that most TTA methods (TENT [40] and LAME [3]) are outperformed by CTTA methods, which reveals the importance of avoiding catastrophic forgetting. Additionally, previous MM-TTA (i.e., xMUDA and MMTTA) methods can not consistently outperform previous single-modal methods (e.g., EATA [30]), which suggests the sensitivity of multi-modal collaboration toward continual domain shifts. In fact, by intuitively utilizing model-based stochastic restoration, MMTTA-rs can achieve a noticeable improvement of " + }, + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "type": "inline_equation", + "content": "3.1\\%" + }, + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "type": "inline_equation", + "content": "6.0\\%" + }, + { + "bbox": [ + 46, + 498, + 288, + 715 + ], + "type": "text", + "content": " on S-to-S and S-to-W, respectively. Yet MMTTA-rs is still outperformed by our method. To justify the effect of the sequence arrangement, we conduct additional experiments by" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 384, + 545, + 432 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 545, + 432 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 545, + 432 + ], + "type": "text", + "content": "reversing the sequences of S-to-S and S-to-W for TENT, MMTTA-ms, and our CoMAC. While the performance of all methods decreases, the improvement of CoMAC compared to others can be observed across all sequences." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 433, + 545, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 433, + 545, + 601 + ], + "spans": [ + { + "bbox": [ + 304, + 433, + 545, + 601 + ], + "type": "text", + "content": "For S-to-S, we notice that our method achieves the second-best performance at the first sequence 01-Spring and then surpasses all previous methods in the following sequences since we utilize CMQs to gradually adapt to the changing target domain without forgetting. Compared with TTA methods, our method consistently prevails with an increasing gap as they struggle with error accumulation. A similar observation can be found at D-O-2 of S-to-W. Interestingly, xMUDA-pl as well as Plabel perform competitively on S-to-W and outperform CoMAC in D-P-2 mainly because is less challenging and simply filtering pseudolabels can effectively mitigate the prediction noise. Nevertheless, this performance gap is trivial as our CoMAC surpasses both xMUDA-pl and Plabel on all other sequences." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 609, + 406, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 609, + 406, + 621 + ], + "spans": [ + { + "bbox": [ + 306, + 609, + 406, + 621 + ], + "type": "text", + "content": "4.3. Ablation Studies" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 629, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 653 + ], + "type": "text", + "content": "In this section, we provide our ablation studies on S-to-S to justify our design of CoMAC." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 714 + ], + "type": "text", + "content": "Utilization of raw and augmented input. In Sec. 3.2, a key hypothesis is that while the augmentation-average prediction can be a potential reliable alternative, it may introduce inductive bias to the result. To justify this assumption, we conduct experiments by simply using the pure raw" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18815" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 75, + 70, + 521, + 223 + ], + "blocks": [ + { + "bbox": [ + 75, + 70, + 521, + 223 + ], + "lines": [ + { + "bbox": [ + 75, + 70, + 521, + 223 + ], + "spans": [ + { + "bbox": [ + 75, + 70, + 521, + 223 + ], + "type": "image", + "image_path": "9b5afb25a3f5b42dbfb78cb4fa1ff13d93019bfc0c1395f82edba9b31b9c7837.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 229, + 546, + 251 + ], + "lines": [ + { + "bbox": [ + 46, + 229, + 546, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 229, + 546, + 251 + ], + "type": "text", + "content": "Figure 4. Visualization of online segmentation results. Here we present the cross-modal pseudo-labels from xMPF (Ours) as well as the individual prediction from 2D and 3D teachers in comparison with the ground truth (GT)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 271, + 287, + 366 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 271, + 287, + 366 + ], + "spans": [ + { + "bbox": [ + 46, + 271, + 287, + 366 + ], + "type": "text", + "content": "or augmentation-average prediction as the intra-modal prediction as in Eq. 7. As shown in Fig. 3(a), both variants achieve inferior performance compared to CoMAC and these performance gaps are consistent across most sequences. Specifically, using pure augmentation-average predictions lead to serious degradation of " + }, + { + "bbox": [ + 46, + 271, + 287, + 366 + ], + "type": "inline_equation", + "content": "5.8\\%" + }, + { + "bbox": [ + 46, + 271, + 287, + 366 + ], + "type": "text", + "content": ", which justifies the necessity of mitigating the inductive noise brought by test-time augmentations and our motivation for iMPA." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 371, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 371, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 371, + 287, + 479 + ], + "type": "text", + "content": "Weighting mechanisms of iMPA and xMPF. The proposed iMPA and xMPF utilize centroid-based weighting mechanisms to attend to the reliable modality. To justify their effectiveness, we compared CoMAC with variants by replacing either Eq. 7 or Eq. 8 with a simple average fusion (indicated as w/o iMPA and w/o xMPF). As presented in Fig. 3(b), CoMAC outperforms both variants by more than " + }, + { + "bbox": [ + 46, + 371, + 287, + 479 + ], + "type": "inline_equation", + "content": "2.5\\%" + }, + { + "bbox": [ + 46, + 371, + 287, + 479 + ], + "type": "text", + "content": ". This performance gap justifies that both iMPA and xMPF play an important part in noise suppression." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 482, + 287, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 482, + 287, + 685 + ], + "spans": [ + { + "bbox": [ + 46, + 482, + 287, + 685 + ], + "type": "text", + "content": "Updating mechanisms of CMQs. The goal of CMQs is to achieve a good balance between adaptation and knowledge preservation. To justify the role of CMQs, we compared CoMAC with variants without enqueuing target features or restoring pseudo-source features, respectively. For the variant without enqueuing target features, the corresponding class-wise centroids are identical to the source centroids across the whole testing process. As in Fig. 3(c), disabling enqueuing target features (w/o Update) causes a significant performance decrease of " + }, + { + "bbox": [ + 46, + 482, + 287, + 685 + ], + "type": "inline_equation", + "content": "6.1\\%" + }, + { + "bbox": [ + 46, + 482, + 287, + 685 + ], + "type": "text", + "content": ", which justifies the necessity of adapting class-wise centroids for the validity of iMPA and xMPF. On the other hand, while disabling restoring pseudo-source features (w/o Restore) leads to a quicker adaptation at the first two sequences, it eventually causes catastrophic forgetting after the third sequence, resulting in a noticeable gap of " + }, + { + "bbox": [ + 46, + 482, + 287, + 685 + ], + "type": "inline_equation", + "content": "8.4\\%" + }, + { + "bbox": [ + 46, + 482, + 287, + 685 + ], + "type": "text", + "content": ". Overall, the performance gain brought by CMQs justifies their effectiveness." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "content": "Number of Augmentations. To investigate the effect of augmentations, we conduct a grid search by utilizing differ-" + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 323, + 269, + 529, + 335 + ], + "blocks": [ + { + "bbox": [ + 323, + 269, + 529, + 335 + ], + "lines": [ + { + "bbox": [ + 323, + 269, + 529, + 335 + ], + "spans": [ + { + "bbox": [ + 323, + 269, + 529, + 335 + ], + "type": "table", + "html": "
CoMACNo. of 2D Aug
12345Avg
No. of 3D Aug133.033.133.233.233.333.2
234.134.234.334.434.434.3
335.235.235.435.335.535.3
436.436.436.536.536.536.5
536.436.536.736.636.736.6
Avg35.035.135.235.235.335.2
", + "image_path": "091bec5db9788da354ccb99119d893cfcf88a5ea78788d2be6c559e99dbee3fc.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 309, + 369, + 545, + 413 + ], + "blocks": [ + { + "bbox": [ + 306, + 336, + 545, + 358 + ], + "lines": [ + { + "bbox": [ + 306, + 336, + 545, + 358 + ], + "spans": [ + { + "bbox": [ + 306, + 336, + 545, + 358 + ], + "type": "text", + "content": "Table 2. Augmentation analysis of CoMAC. CoMAC is evaluated with different numbers of augmentations." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 369, + 545, + 413 + ], + "lines": [ + { + "bbox": [ + 309, + 369, + 545, + 413 + ], + "spans": [ + { + "bbox": [ + 309, + 369, + 545, + 413 + ], + "type": "table", + "html": "
CoMAC\\( p_{rs} \\)\\( (\\tau_{cf},\\lambda_{cts}) \\)Avg\\( \\tau_{cf} \\)\\( (p_{rs},\\lambda_{cts}) \\)Avg\\( \\lambda_{cts} \\)\\( (p_{rs},\\tau_{cf}) \\)Avg
0.5(0.8,1.0)36.60.8(0.5,1.0)36.61.0(0.5,0.8)36.6
0.3-34.50.0-34.80.0-35.8
0.7-36.40.5-36.50.01-36.4
1.0-36.30.9-36.40.1-36.4
", + "image_path": "f72d2bf341ede54a42db46eab41748a17c2f086b29a40d969b1cc0c2002d9afe.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 418, + 545, + 452 + ], + "lines": [ + { + "bbox": [ + 306, + 418, + 545, + 452 + ], + "spans": [ + { + "bbox": [ + 306, + 418, + 545, + 452 + ], + "type": "text", + "content": "Table 3. Sensitivity analysis of CoMAC. Here \"xM\" is the softmax-average of 2D and 3D predictions. The parameter value with \"-\" indicates the same value as default settings." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 473, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 473, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 473, + 545, + 616 + ], + "type": "text", + "content": "ent numbers of 2D and 3D augmentations. Specifically, we adopt resize and rotation as 2D and 3D augmentation, respectively. The factor range for 2D scaling is [0.5, 1) while 3D one is set to " + }, + { + "bbox": [ + 304, + 473, + 545, + 616 + ], + "type": "inline_equation", + "content": "(0^{\\circ}, 360^{\\circ})" + }, + { + "bbox": [ + 304, + 473, + 545, + 616 + ], + "type": "text", + "content": ", where the list of augmentations is computed as evenly spaced factors given the number of augmentations. As shown in Table 2, increasing the number of either 2D or 3D augmentations leads to performance improvement, while the 2D improvement is less noticeable compared to 3D probably due to the inductive bias brought by 2D augmentations. While all settings perform competitively, we adopt the combination of three 2D augmentations and five 3D augmentations to achieve the best result." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "content": "Sensitivity analysis. We perform sensitivity analysis over the hyper-parameters of CoMAC as shown in Table 3. There are some extreme cases that can lead to the performance degeneration of CoMAC. For restoring rate " + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "inline_equation", + "content": "p_{rs}" + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "content": ", the performance relatively drops about " + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "inline_equation", + "content": "5.7\\%" + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "content": " when " + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "inline_equation", + "content": "p_{rs} = 0.3" + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "content": ", indicating the restoring rate is too low to prevent forgetting. Nevertheless, when " + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "inline_equation", + "content": "p_{rs} \\geq 0.5" + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "content": ", CoMAC is robust to the arbitrary choice of " + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "inline_equation", + "content": "p_{rs}" + }, + { + "bbox": [ + 304, + 617, + 546, + 713 + ], + "type": "text", + "content": ". Similar observations can be found when" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18816" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 61, + 60, + 273, + 120 + ], + "blocks": [ + { + "bbox": [ + 61, + 60, + 273, + 120 + ], + "lines": [ + { + "bbox": [ + 61, + 60, + 273, + 120 + ], + "spans": [ + { + "bbox": [ + 61, + 60, + 273, + 120 + ], + "type": "table", + "html": "
MethodAug SamplesInf. Time (s)/samplemIoU
meanstd
TENT [40]X0.3790.01017.8
CoTTA [42]✓7.2200.39926.5
Ours✓1.8880.08236.6
Ours (less augs)✓1.0040.03833.0
", + "image_path": "0b5c68bfd19e040ad8a5a493d7d6d9e694635bcbda125c96df189987534092f7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 72, + 121, + 261, + 133 + ], + "lines": [ + { + "bbox": [ + 72, + 121, + 261, + 133 + ], + "spans": [ + { + "bbox": [ + 72, + 121, + 261, + 133 + ], + "type": "text", + "content": "Table 4. Comparison of processing time per sample." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 50, + 145, + 154, + 223 + ], + "blocks": [ + { + "bbox": [ + 50, + 145, + 154, + 223 + ], + "lines": [ + { + "bbox": [ + 50, + 145, + 154, + 223 + ], + "spans": [ + { + "bbox": [ + 50, + 145, + 154, + 223 + ], + "type": "image", + "image_path": "7a0eafe200e0d567cd3254c3fb45cfdf5c598993d0c005ae607bea40c81b7dc0.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 226, + 287, + 259 + ], + "lines": [ + { + "bbox": [ + 46, + 226, + 287, + 259 + ], + "spans": [ + { + "bbox": [ + 46, + 226, + 287, + 259 + ], + "type": "text", + "content": "Figure 5. Processing time of CoMAC components per sample (left) and GPU RAM with or without CMQs (right). Experiments are conducted on S-to-S with the default backbones and settings." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 161, + 145, + 280, + 223 + ], + "blocks": [ + { + "bbox": [ + 161, + 145, + 280, + 223 + ], + "lines": [ + { + "bbox": [ + 161, + 145, + 280, + 223 + ], + "spans": [ + { + "bbox": [ + 161, + 145, + 280, + 223 + ], + "type": "image", + "image_path": "2befc8781f28844b7e564d1e8d33d7bbe86a23dc52d7e59e15dfb52386e24d6b.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "spans": [ + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "inline_equation", + "content": "\\tau_{cf} = 0.0" + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "inline_equation", + "content": "\\lambda_{cts} = 0.0" + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "text", + "content": ", where the performance decreases relatively by " + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "inline_equation", + "content": "4.9\\%" + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "inline_equation", + "content": "2.2\\%" + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "text", + "content": ". This performance degeneration indicates the importance of confident feature filtering and class-wise contrastive loss. Overall, when " + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "inline_equation", + "content": "\\tau_{cf} \\geq 0.0" + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "inline_equation", + "content": "\\lambda_{cts} \\geq 0.01" + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "text", + "content": ", the performance of CoMAC is also robust to the hyper-parameter settings, falling into a relative margin of " + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "inline_equation", + "content": "0.5\\%" + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "text", + "content": ". Note that all settings of CoMAC surpass the previous SOTA method EATA [30] by more than " + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "inline_equation", + "content": "4.8\\%" + }, + { + "bbox": [ + 46, + 283, + 286, + 378 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 379, + 286, + 498 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 379, + 286, + 498 + ], + "spans": [ + { + "bbox": [ + 46, + 379, + 286, + 498 + ], + "type": "text", + "content": "Visualization of segmentation. To further justify the effectiveness of our proposed CoMAC, we provide some visualization results as shown in Fig. 4. Specifically, we visualize the 2D and 3D predictions from teacher models and our cross-modal pseudo-labels from xMPF. Compared to single-modal predictions, our cross-modal pseudo-labels can achieve better segmentation results by attending to the reliable modality, such as the first row in Fig. 4, where the sidewalk prediction attends more to the 2D image while the car prediction attends to the reliable 3D point cloud." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": "Computational and storage overhead. To investigate the computational and storage overhead of CoMAC, we analyze the processing time and GPU occupancy when online testing with our CoMAC as illustrated in Table 4 and Fig. 5. Similar to previous augmentation-based methods, our proposed CoMAC is limited by the computational overhead brought by multiple augmentations. However, compared to the augmentation-based SOTA method CoTTA [42], our method outperforms it in terms of performance and efficiency (a relative performance improvement of " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "38.1\\%" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "73.9\\%" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": " less processing time). Compared to the single-sample-based method TENT, despite a computational overhead of 1.51s, our method significantly improves relatively by more than " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": ". The computational overhead can be further lessened by using fewer augmentations, reducing the processing time relatively by more than " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "46.8\\%" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": " with a minor performance drop of " + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "inline_equation", + "content": "3.6\\%" + }, + { + "bbox": [ + 46, + 498, + 286, + 713 + ], + "type": "text", + "content": ". Besides augmentations, another potential source of overhead lies in the utilization of" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "content": "CMQs as they capture class-wise features for each iteration. As shown in Fig .5, however, the computational overhead brought by CMQs is rather trivial, which takes less than 0.05s to update and process each frame. Moreover, since CMQs only preserve the high-level features instead of raw samples, the storage cost is also acceptable with a minor usage increase (less than " + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "inline_equation", + "content": "800\\mathrm{MB}" + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "content": ") of GPU RAM compared to the CoMAC invariant without CMQs." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 181, + 378, + 193 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 181, + 378, + 193 + ], + "spans": [ + { + "bbox": [ + 306, + 181, + 378, + 193 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 202, + 545, + 382 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 202, + 545, + 382 + ], + "spans": [ + { + "bbox": [ + 304, + 202, + 545, + 382 + ], + "type": "text", + "content": "In this paper, we present a new task, named multi-modal continual test-time adaptation (MM-CTTA) for 3D semantic segmentation. We further propose a novel method called CoMAC that tackles MM-CTTA from two perspectives. On one hand, reliable cross-modal pseudo-labels are generated by iMPA and xMPF by adaptively attending to the more reliable modality in a dual-stage manner. On the other hand, CMQs are proposed to leverage pseudo-source features and reliable target features to perform adaptation without catastrophic forgetting. We introduce two new benchmarks for MM-CTTA and our methods outperform previous works by a noticeable margin in both benchmarks. In the future, we hope both our method and benchmarks can facilitate the exploration of MM-CTTA and promote the development of reliable multi-modal systems in altering environments." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 395, + 403, + 408 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 395, + 403, + 408 + ], + "spans": [ + { + "bbox": [ + 306, + 395, + 403, + 408 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 415, + 545, + 487 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 545, + 487 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 545, + 487 + ], + "type": "text", + "content": "This research is supported by the National Research Foundation, Singapore under its Medium Sized Center for Advanced Robotics Technology Innovation. 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In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 5982-5991, 2019. 1" + } + ] + } + ], + "index": 25 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "18819" + } + ] + } + ], + "index": 27 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/6e316164-78c4-4054-8879-22d243fd30bc_content_list.json b/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/6e316164-78c4-4054-8879-22d243fd30bc_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..d33700e96cf1a21af6dde258d949b865cb713d11 --- /dev/null +++ b/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/6e316164-78c4-4054-8879-22d243fd30bc_content_list.json @@ -0,0 +1,2363 @@ +[ + { + "type": "text", + "text": "Multi-modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion", + "text_level": 1, + "bbox": [ + 186, + 161, + 783, + 204 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Bing Cao*, Yiming Sun*; Pengfei Zhu†; Qinghua Hu", + "bbox": [ + 297, + 228, + 699, + 245 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Tianjin Key Lab of Machine Learning, College of Intelligence and Computing, Tianjin University, China \nHaihe Laboratory of Information Technology Application Innovation, China", + "bbox": [ + 87, + 245, + 910, + 277 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{caobing,sunyiming1895,zhupengfei,huqinghua}@tju.edu.cn", + "bbox": [ + 255, + 277, + 741, + 293 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 324, + 312, + 339 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Infrared and visible image fusion aims to integrate comprehensive information from multiple sources to achieve superior performances on various practical tasks, such as detection, over that of a single modality. However, most existing methods directly combined the texture details and object contrast of different modalities, ignoring the dynamic changes in reality, which diminishes the visible texture in good lighting conditions and the infrared contrast in low lighting conditions. To fill this gap, we propose a dynamic image fusion framework with a multi-modal gated mixture of local-to-global experts, termed MoE-Fusion, to dynamically extract effective and comprehensive information from the respective modalities. Our model consists of a Mixture of Local Experts (MoLE) and a Mixture of Global Experts (MoGE) guided by a multi-modal gate. The MoLE performs specialized learning of multi-modal local features, prompting the fused images to retain the local information in a sample-adaptive manner, while the MoGE focuses on the global information that complements the fused image with overall texture detail and contrast. Extensive experiments show that our MoE-Fusion outperforms state-of-the-art methods in preserving multi-modal image texture and contrast through the local-to-global dynamic learning paradigm, and also achieves superior performance on detection tasks. Our code is available: https://github.com/SunYM2020/MoE-Fusion.", + "bbox": [ + 75, + 353, + 472, + 713 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 77, + 739, + 208, + 754 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Infrared and visible image fusion focus on generating appealing and informative fused images that enable superior performance in practical downstream tasks over that of using single modality alone [24, 45, 41, 21]. In recent years, infrared-visible image fusion has been widely used", + "bbox": [ + 75, + 763, + 468, + 834 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/0b5d17b7a2825f752da3b7202735e6b72ba60b7e69ce4e53e8d450517bb81eea.jpg", + "image_caption": [ + "Visible image" + ], + "image_footnote": [], + "bbox": [ + 504, + 325, + 630, + 416 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/f64abab0c497c8006b16841a3fbc8bb8998cc17578cbf715be93d73371b511a3.jpg", + "image_caption": [ + "Infrared image" + ], + "image_footnote": [], + "bbox": [ + 630, + 326, + 759, + 416 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/f6de8f6583bd4695f646a763e1ae74a6f1975f78deeaa83543536fc8b35bff7b.jpg", + "image_caption": [ + "DF (IEEE TIP'19)" + ], + "image_footnote": [], + "bbox": [ + 759, + 326, + 887, + 416 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e4e2c8207de2da83d13686fbebb3d079af12315737998f4e52be0c6d1eaae9c8.jpg", + "image_caption": [ + "DIDF (IJCAI'20)", + "Figure 1. The importance of dynamic image fusion. In the SOTA methods (DF [16], DIDF [49], and TDL [18]), the texture details of objects (e.g., car, truck, and traffic sign) in the fused image are suppressed by the contrast of infrared image, leading to terrible detection results. Benefiting from the dynamic fusion, our method can preserve clear texture details without being interrupted by unsuitable contrast, achieving the best performance." + ], + "image_footnote": [], + "bbox": [ + 504, + 428, + 631, + 517 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/39c39590ad33fc78280bc05df289c3228c5899acb48a387a4fa730613f9c02d2.jpg", + "image_caption": [ + "TDL (CVPR'22)" + ], + "image_footnote": [], + "bbox": [ + 631, + 428, + 759, + 517 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/701b980a9afc580b032828191bb4a52e7303e239e2ca3e259f071362907aa5a4.jpg", + "image_caption": [ + "MoE-Fusion (Ours)" + ], + "image_footnote": [], + "bbox": [ + 759, + 428, + 887, + 517 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "in many applications, such as autonomous vehicles [9] and unmanned aerial vehicles [34]. According to the thermal infrared imaging mechanism, infrared images can be adapted to various lighting conditions but has the disadvantage of few texture details [25, 50, 19]. By contrast, visible images contain rich texture detail information, but cannot provide clear information in low light conditions. Therefore, how to design advanced fusion methods such that the fused images preserve sufficient texture details and valuable thermal information has attracted a lot of research attention.", + "bbox": [ + 497, + 654, + 890, + 792 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Existing infrared-visible fusion methods [46, 38, 33, 42] can be mainly categorized to traditional approaches (image decomposition [15], sparse representation [47], etc.) and deep learning-based approaches (autoencoder based methods [16, 49, 17], generative adversarial network based", + "bbox": [ + 497, + 796, + 890, + 866 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 129, + 49, + 200, + 84 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 253, + 48, + 789, + 86 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Equal contribution", + "bbox": [ + 95, + 843, + 203, + 853 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Corresponding author", + "bbox": [ + 97, + 853, + 218, + 865 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "23555", + "bbox": [ + 463, + 885, + 504, + 897 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "approaches [18, 26], transformer based approaches [40, 36], etc.). However, most of these methods directly combined the texture details and object contrast of different modalities, ignoring the dynamic changes in reality, leading to poor fusion results and even weaker downstream task performance than that of a single modality. As shown in Fig. 1, the infrared image should adaptively enhance cars in dim light while avoiding compromising the textural detail of truck in bright light. However, the object textures in these state-of-the-art fusion methods are significantly disturbed by the infrared thermal information due to the lack of dynamic learning of multi-modal local and global information, resulting in terrible object detection performance.", + "bbox": [ + 75, + 125, + 472, + 305 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In complex scenes, different modalities have different characteristics: under good lighting conditions, the texture of an object should not be disturbed by thermal infrared information; under low lighting conditions, the contrast of an object also should not be suppressed by the darkness of the visible image. Most existing methods perform image fusion in a fixed correlation paradigm, ignoring the dominant modality changes dynamically in reality, and often fall into domain bias. To break the traditional fixed fusion paradigm, we pioneered sample-adaptive local-to-global experts to dynamically enhance the dominant modality for image fusion. Fig. 1 show that the proposed method not only eliminates domain bias but also achieves sample-adaptive dynamic fusion, yielding the best detection results. Specifically, we propose a dynamic image fusion framework with a multi-modal gated mixture of local-to-global experts, termed MoE-Fusion, which consists of a Mixture of Local Experts (MoLE) and a Mixture of Global Experts (MoGE) guided by a multi-modal gate. In MoLE, we introduce the attention map generated by an auxiliary network to construct multi-modal local priors and perform dynamic learning of multi-modal local features guided by multimodal gating, achieving sample-adaptive multi-modal local feature fusion. Moreover, MoGE performs dynamic learning of multi-modal global features to achieve a balance of texture details and contrasts globally in the fused images. With the proposed dynamic fusion paradigm from local to global, our model is capable of performing a reliable fusion of different modal images.", + "bbox": [ + 75, + 305, + 472, + 705 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We summarize our main contributions as follows:", + "bbox": [ + 95, + 706, + 423, + 720 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a dynamic image fusion model, providing a new multi-modal gated mixture of local-to-global experts for reliable infrared and visible image fusion (benefiting from the dynamically integrating effective information from the respective modalities).", + "- The proposed model is an effective and robust framework for sample-adaptive infrared-visible fusion from local to global. Further, it prompts the fused images to dynamically balance the texture details and contrasts." + ], + "bbox": [ + 95, + 730, + 468, + 866 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "- We conduct extensive experiments on multiple infrared-visible datasets, which clearly validate our superiority, quantitatively and qualitatively. Moreover, we also demonstrate our effectiveness in object detection.", + "bbox": [ + 517, + 125, + 890, + 194 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works", + "text_level": 1, + "bbox": [ + 499, + 209, + 650, + 223 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Infrared and Visible Image Fusion", + "text_level": 1, + "bbox": [ + 499, + 232, + 801, + 247 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The infrared and visible image fusion task focuses on generating a fused image containing sufficient information through the learning of multi-modal features [24, 45, 20, 22, 12, 8]. Ma et al. [23] defined the goal of image fusion as preserving more intensity information in infrared images as well as gradient information in visible images. Li et al. [16] use the autoencoder to extract multi-modal overall features and fuse them by designed fusion rules, which inspired a series of subsequent works [14, 17]. Zhao et al. [49, 50] proposed the deep learning-based image decomposition methods, which decompose images into background and detail images by high- and low-frequency information, respectively, and then fuse them by designed fusion rules. Recently, some GAN-based methods [26, 25, 18] and Transformer-based methods [40, 36] have also attracted wide attention. These works, despite the different approaches adopted, all focus on learning on the representation of the overall multi-modal features. However, they ignore the dynamic changes in reality, which diminishes the visible texture in good lighting conditions and the infrared contrast in low lighting conditions. We propose a dynamic image fusion framework that enables sample-adaptive fusion from local to global. This approach prompts the fused images to balance the texture details and contrast with specialized experts dynamically.", + "bbox": [ + 497, + 252, + 890, + 599 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Mixture-of-Experts", + "text_level": 1, + "bbox": [ + 499, + 609, + 685, + 624 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Mixture-of-Experts (MoE) [10, 30, 27] can dynamically adjust its structure according to different inputs. Shazeer et al. [32] constructed a sparsely-gated MoE layer that uses a gate network to select multiple experts and assign weights to each selected expert. The final result of the MoE is a weighted sum of the outputs of the different experts. This work also serves as the basis for subsequent research. Recently, some researchers [13, 27] have focused on exploring learning mechanisms in MoE, trying to solve the problems of unbalanced expert load and the number of activated experts faced by MoE during training. Other researchers [6, 52, 3, 39] focuses on the combination of MoE and Transformer. They expect to use MoE to build sparse models. Zhu et al. [52] introduced Conditional MoE into the generalist model and proposed different routing strategies to mitigate the interference between tasks and modalities. Existing MoE-related methods focus on modeling", + "bbox": [ + 497, + 631, + 890, + 866 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "23556", + "bbox": [ + 463, + 885, + 505, + 897 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/905586731212f212619fd3abf50674b87333b3eee8ee946daa4859b8bb942c12.jpg", + "image_caption": [ + "(a)" + ], + "image_footnote": [], + "bbox": [ + 80, + 124, + 336, + 296 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/02f3373c793f4046f9a0cb5f730dc45a8ba2b06713a03828dd325c59c88cc4f8.jpg", + "image_caption": [ + "(b)" + ], + "image_footnote": [], + "bbox": [ + 342, + 124, + 630, + 306 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/4f5c3fd9f8c873e844d46a221d0de910714c17851e1a52f9a6b9224e07a951fd.jpg", + "image_caption": [ + "Figure 2. The architecture of MoE-Fusion. MoE-Fusion consists of a Mixture of Local Experts (MoLE), a Mixture of Global Experts (MoGE) guided by the multi-modal gate, a set of infrared and visible feature encoders, and the auxiliary network." + ], + "image_footnote": [], + "bbox": [ + 631, + 128, + 890, + 305 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "generic knowledge by using the dynamicity and sparsity of MoE, resulting in each expert does not know what they should be expert in. In contrast, we extend the idea of MoE to image fusion tasks for the first time, constructing a multimodal gated mixture of local-to-global experts, assigning specific tasks to each expert, and enabling sample-adaptive specialized learning, which yields superior performance.", + "bbox": [ + 75, + 369, + 468, + 467 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 75, + 477, + 166, + 491 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overall Architecture", + "text_level": 1, + "bbox": [ + 75, + 500, + 272, + 511 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this paper, we propose a dynamic image fusion framework with a multi-modal gated mixture of local-to-global experts, termed MoE-Fusion. In Fig. 2, MoE-Fusion contains two encoders, a Mixture of Local Experts, a Mixture of Global Experts, and the auxiliary network.", + "bbox": [ + 75, + 521, + 468, + 589 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In Fig. 2 (b), we send a pair of infrared image $I_{\\mathcal{I}} \\in \\mathbb{R}^{H \\times W \\times 1}$ and visible image $I_{\\mathcal{V}} \\in \\mathbb{R}^{H \\times W \\times 3}$ into the infrared and visible encoders ( $Enc_{\\mathcal{I}}$ and $Enc_{\\mathcal{V}}$ ) to extract the features, respectively. The structure of encoders follows [16]. The output of the encoder has two parts: the feature maps of the last layer ( $x_{enc}^{\\mathcal{I}}$ and $x_{enc}^{\\mathcal{V}}$ ) and the dense feature maps ( $x_{dense}^{\\mathcal{I}}$ and $x_{dense}^{\\mathcal{V}}$ ). More details of the structure are provided in the supplementary material. We send the $x_{enc}^{\\mathcal{I}}$ and $x_{enc}^{\\mathcal{V}}$ to the MoLE along with the attention map which is learning from the auxiliary network. In this paper, we use Faster-RCNN [29] as the auxiliary network. In MoLE, we send visible and infrared features to specific local experts separately to achieve dynamic integration of local features under the guidance of multi-modal gating. We concatenate the outputs of MoLE with the dense feature maps as the input to the MoGE. Each expert in MoGE has the ability to decode global features, and a multi-modal gate network is used to dynamic select which experts are activated to decode multi-modal fusion features. The final fused image $I_{\\mathcal{F}} \\in \\mathbb{R}^{H \\times W \\times 1}$ is generated by a weighted", + "bbox": [ + 75, + 590, + 468, + 866 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "sum mechanism of the different global experts.", + "bbox": [ + 499, + 370, + 810, + 383 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The MoE-Fusion is optimized mainly by calculating the pixel loss and gradient loss between the fused image $I_{\\mathcal{F}}$ and two source images $(I_{\\mathcal{I}}$ and $I_{\\mathcal{V}}$ ). In addition, we also introduce the load loss to motivate each expert to receive roughly equal numbers of training images. The auxiliary detection networks are optimized independently by the detection loss.", + "bbox": [ + 497, + 385, + 890, + 467 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Mixture of Local Experts", + "text_level": 1, + "bbox": [ + 499, + 482, + 729, + 496 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In infrared-visible image fusion tasks, specialized learning of multi-modal local information by a sample adaptive manner helps to overcome the challenge of multi-modal fusion failure in complex scenes. To realize this vision, we need to address two questions: (1) How to find local regions in multi-modal images; (2) How to learn the local features dynamically due to the differences in various samples.", + "bbox": [ + 497, + 505, + 890, + 602 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As shown in Fig. 2 (a), we propose a Mixture of Local Experts (MoLE) to dynamically learning the multi-modal local features. We use the auxiliary detection networks with a spatial attention module to learn the attention maps. Then we can find the local regions in multi-modal images according to the guidance of the learned attention maps. Specifically, we introduce attention modules in two auxiliary detection networks for extracting visible attention maps and infrared attention maps, respectively. The modal-specific attention map $Att_{\\mathcal{V}} / Att_{\\mathcal{I}}$ is generated by the attention module between the feature extractor and the detection head in the detection networks, which consists of a Conv(1 × 1)-BN-ReLU layer and a Conv(1 × 1)-BN-Sigmoid layer. The $Att_{\\mathcal{V}}$ and $Att_{\\mathcal{I}}$ are concatenated and fed into 2 convolutional layers, the maximum of which output is the Att. In MoLE, we multiply the $x_{enc}^{\\mathcal{V}}$ and $x_{enc}^{\\mathcal{I}}$ with Att to obtain $x_{local}^{\\mathcal{V}}$ and $x_{local}^{\\mathcal{I}}$ , respectively. Then we concatenate the $x_{local}^{\\mathcal{V}}$ and $x_{local}^{\\mathcal{I}}$ to get the $x_{local}$ , which is the input of the multi-modal gating network. The MoLE is consist of", + "bbox": [ + 497, + 603, + 892, + 866 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "23557", + "bbox": [ + 463, + 885, + 504, + 897 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/e024336abe7041ca2000ffec0dd36a96f5d1ada233c745e65338dc2e6596d829.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 80, + 124, + 176, + 175 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/76d10daf4c8b2ee9279662f7fc9b09f49e016e19f08cb76c07fb6d2020486775.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 176, + 125, + 273, + 175 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/86cadb6249db4f301535eac120c746748ee27185f54ad79aa2178d95ad8d3e8e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 275, + 125, + 369, + 175 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/820bec065e86d5b899f7ad3a1b22c231bb0f040d5b3e0bfa8712957acc3d7055.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 371, + 125, + 467, + 175 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/2227b3b768393f1a08e79cb69e511e4e7d9467dac2c59117a16a4e7984d8e156.jpg", + "image_caption": [ + "Visible image", + "AUIF" + ], + "image_footnote": [], + "bbox": [ + 80, + 182, + 176, + 233 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/e2872cc0151a3eec46671deebfc5d9a856e9c4a4f7d1d0347708763223997131.jpg", + "image_caption": [ + "Infrared image", + "DIDFuse" + ], + "image_footnote": [], + "bbox": [ + 176, + 182, + 273, + 233 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/27051783c5af4fd81bd822796b25f2a2ffbc11c52e7abbf212bebcd2a46da534.jpg", + "image_caption": [ + "RFN-Nest", + "TarDAL" + ], + "image_footnote": [], + "bbox": [ + 275, + 182, + 369, + 233 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/7f981afba8b36e17b1a99895defd181fdcbda430bfee899356b1897741317ae6.jpg", + "image_caption": [ + "DenseFuse", + "PIAFusion" + ], + "image_footnote": [], + "bbox": [ + 371, + 182, + 467, + 233 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/d1fb650c9076d004457cf777c6bf884a49dbbc6ba24a81b77ddd0498684319b3.jpg", + "image_caption": [ + "IFCNN", + "Figure 3. Qualitative comparisons of various methods on representative images selected from the $\\mathbf{M}^3\\mathrm{FD}$ dataset." + ], + "image_footnote": [], + "bbox": [ + 80, + 243, + 176, + 292 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/3a51d82871ea82212aadff8c74add6a53f0fb5b0504a02a2d457f32cb96e3c84.jpg", + "image_caption": [ + "SwinFuse" + ], + "image_footnote": [], + "bbox": [ + 176, + 243, + 273, + 292 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/12bb8bea6cd9cc7924aee48d8d0bc58dfa4821f6fe407a5ab960db8d16022812.jpg", + "image_caption": [ + "YDTR" + ], + "image_footnote": [], + "bbox": [ + 275, + 243, + 369, + 292 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/18ea2312da937e0ab865cfa4af58a6d2ac61948451bfe0eb01c52e97c15b646d.jpg", + "image_caption": [ + "MoE-Fusion (Ours)" + ], + "image_footnote": [], + "bbox": [ + 371, + 243, + 467, + 292 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "a multi-modal gating network $G_{local}$ and a set of $N$ expert networks $\\{E_1^{local},\\dots,E_N^{local}\\}$ . The structure of each expert network is 2 convolution layers and 1 ReLU layers.", + "bbox": [ + 75, + 353, + 468, + 393 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In MoLE, we flatten the input $x_{local} \\in \\mathbb{R}^{H \\times W \\times C}$ to $s_{local} \\in \\mathbb{R}^D$ . The gate network $G_{local}$ takes the vector $s_{local}$ as input and produces the probability of it with respective to $N$ experts. The formalization of the gate network is as follows,", + "bbox": [ + 75, + 394, + 468, + 463 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nG _ {\\text {l o c a l}} \\left(s _ {\\text {l o c a l}}\\right) = \\operatorname {s o f t m a x} \\left(\\operatorname {t o p K} \\left(s _ {\\text {l o c a l}} \\cdot W _ {\\text {l o c a l}}\\right)\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 94, + 473, + 468, + 488 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $W_{local} \\in \\mathbb{R}^{D \\times N}$ is a learnable weight matrix and the top $K$ outputs are normalized via softmax function.", + "bbox": [ + 75, + 498, + 468, + 526 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To achieve specialized learning of different modalities, we input visible local features $x_{local}^{\\nu}$ into one set of expert networks $\\{E_1^{local},\\dots,E_{N / 2}^{local}\\}$ and infrared local features $x_{local}^{\\mathcal{I}}$ into another set of non-overlapping expert networks $\\{E_{(N / 2) + 1}^{local},\\dots,E_N^{local}\\}$ . Each expert network produces its own output $E_i^{local}(x_{local}^j)$ . The final output $y_{local}$ of the MoLE is calculated as follows,", + "bbox": [ + 75, + 527, + 468, + 629 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ny _ {l o c a l} = \\sum_ {i = 1} ^ {N} G _ {l o c a l} \\left(s _ {l o c a l}\\right) _ {i} E _ {i} ^ {l o c a l} \\left(x _ {l o c a l} ^ {j}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 131, + 638, + 468, + 675 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $j$ represents $\\mathcal{I}$ or $\\nu$ . Then we concatenate the $y_{local}$ , $x_{dense}^{\\mathcal{I}}$ , and $x_{dense}^{\\nu}$ to obtain the global multi-modal fusion feature $x_{f}$ .", + "bbox": [ + 75, + 684, + 468, + 726 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Mixture of Global Experts", + "text_level": 1, + "bbox": [ + 77, + 733, + 315, + 749 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Traditional image fusion algorithms use the same network structure and parameters to learn the fusion features of different samples. In contrast, we propose the MoGE to dynamically integrate multi-modal global features, which can adaptively adjust its own structure and parameters when dealing with different samples, thus showing superior advantages in terms of model expressiveness and self-adaptability. The main components of the MoGE include a", + "bbox": [ + 75, + 755, + 468, + 866 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/02fe1e6e840e6e7661ea400e685efd4238e5687e1b988e04f050a93481e5bfab.jpg", + "table_caption": [ + "Table 1. Quantitative comparison of our MoE-Fusion with 9 state-of-the-art methods. Bold red indicates the best, Bold blue indicates the second best, and Bold cyan indicates the third best." + ], + "table_footnote": [], + "table_body": "
M3FD Dataset [18]
ENSFSDMIVIFAGSCDQabf
DenseFuse [16]6.41340.03648.59872.95240.65723.07001.50690.3838
RFN-Nest [17]6.92080.03459.29842.93010.78063.16981.54100.3772
IFCNN [48]6.65550.05999.24562.99540.75225.09321.54480.5755
PIAfusion [35]6.81670.070710.12283.83370.84475.65601.30650.5540
DIDFuse [49]6.61160.04209.34092.99550.73823.56681.58750.4342
AUIF [50]6.52330.03998.87592.97930.67963.32241.53140.4124
SwinFuse [40]6.98190.06969.64003.20040.91145.62341.53950.5166
YDTR [36]6.53970.04969.26313.21280.72763.89511.50760.4812
TarDAL [18]7.13470.05289.68203.28530.83474.19981.53340.3858
MoE-Fusion7.00180.071510.14064.19491.00345.67421.54330.6661
FLIR Dataset [44]
ENSFSDMIVIFAGSCDQabf
DenseFuse [16]6.94790.030410.59282.92540.64133.05241.31320.2947
RFN-Nest [17]7.42770.026710.87472.96690.72602.76641.67310.2603
IFCNN [48]7.13670.063810.66682.92630.75676.10811.35210.4894
PIAfusion [35]6.99680.055110.65633.09270.81785.18491.16150.4388
DIDFuse [49]7.27540.067011.63182.50220.66495.88151.49130.3469
AUIF [50]7.28530.046310.21082.88930.70994.44711.58230.3240
SwinFuse [40]7.41630.058210.60772.94040.81045.75871.67390.3751
YDTR [36]6.89480.036410.65713.08200.67493.29931.33790.3333
TarDAL [18]7.48660.058810.69483.02280.76655.19551.31820.3896
MoE-Fusion7.49250.060310.70073.12090.82125.76041.68180.4991
LLVIP Dataset [11]
ENSFSDMIVIFAGSCDQabf
DenseFuse [16]6.83140.04269.38002.67640.68943.26401.21090.3093
RFN-Nest [17]7.14080.03009.71842.50420.72942.78531.46120.2287
IFCNN [48]7.21390.06889.76332.94790.77975.41361.42690.5845
PIAfusion [35]7.39540.07879.73203.36900.88606.08461.53000.5789
DIDFuse [49]6.03720.05507.80742.51370.50543.44741.25740.2436
AUIF [50]6.19470.06367.84182.39660.55333.85881.28400.2764
SwinFuse [40]5.99730.06087.65252.18460.59623.73441.26290.2620
YDTR [36]6.69220.04748.87012.91520.63223.20431.08810.2907
TarDAL [18]7.35040.06479.76763.46550.77694.60941.36070.4431
MoE-Fusion7.35230.08629.86643.10610.92026.13161.78410.5932
", + "bbox": [ + 502, + 159, + 890, + 454 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "global multi-modal gating network $G_{global}$ and a set of $N$ expert networks $\\{E_1^{global},\\dots,E_N^{global}\\}$ . In MoGE, we flatten $x_{f}$ to get $s_f$ and feed it into $G_{global}$ . The corresponding gating weights of the $N$ expert networks are calculated as follows,", + "bbox": [ + 497, + 480, + 890, + 549 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nG _ {\\text {g l o b a l}} \\left(s _ {f}\\right) = \\operatorname {s o f t m a x} \\left(\\operatorname {t o p} K \\left(s _ {f} \\cdot W _ {\\text {g l o b a l}}\\right)\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 537, + 566, + 890, + 581 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $W_{global}$ is a learnable weight matrix and the top $K$ outputs are normalized via softmax distribution.", + "bbox": [ + 497, + 593, + 889, + 622 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The structure of each expert network consists of 4 convolution layers. Each expert takes the global multimodal fusion feature $x_{f}$ as input to produce its own output $E_{i}^{global}(x_{f})$ . The final output $I_{\\mathcal{F}}$ of MoGE is the linearly weighted combination of each expert's output with the corresponding gating weights. The formalization is as follows,", + "bbox": [ + 497, + 624, + 890, + 709 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nI _ {\\mathcal {F}} = \\sum_ {i = 1} ^ {N} G _ {\\text {g l o b a l}} \\left(s _ {f}\\right) _ {i} E _ {i} ^ {\\text {g l o b a l}} \\left(x _ {f}\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 724, + 890, + 761 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Loss Function", + "text_level": 1, + "bbox": [ + 499, + 774, + 643, + 787 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In MoE-Fusion, we use the fusion loss $\\mathcal{L}_{fusion}$ to guide the optimization of the image fusion network, and the auxiliary detection networks are optimized by their respective detection loss [29] ( $\\mathcal{L}_{det}^{\\mathcal{V}}$ or $\\mathcal{L}_{det}^{\\mathcal{T}}$ ). We end-to-end train the entire framework through these three loss functions. Specif", + "bbox": [ + 497, + 796, + 890, + 866 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "23558", + "bbox": [ + 463, + 885, + 504, + 897 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/625c14882b44f3347339224615551ede477a1003434541f35e034c05062fba81.jpg", + "image_caption": [ + "Visible image" + ], + "image_footnote": [], + "bbox": [ + 80, + 124, + 176, + 229 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/c3a35f3d2b785c0c52edbeb898803df6c6a6242414a985510bc47466c04c9fcf.jpg", + "image_caption": [ + "Infrared image" + ], + "image_footnote": [], + "bbox": [ + 176, + 124, + 273, + 229 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/95769e906d42b575b185de5449ddd516141bba192e3909568819fda98cecd20a.jpg", + "image_caption": [ + "RFN-Nest" + ], + "image_footnote": [], + "bbox": [ + 275, + 124, + 369, + 229 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/63153df40f90e3d439510360daa582c179fa57c0b4fc18b8bb6218f2eb57a673.jpg", + "image_caption": [ + "DenseFuse" + ], + "image_footnote": [], + "bbox": [ + 371, + 124, + 467, + 229 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/378d11e9483a0ec7bcb76e2d7de90c00863d0edc00ce5cb9bc90be90aacb034b.jpg", + "image_caption": [ + "AUF" + ], + "image_footnote": [], + "bbox": [ + 80, + 239, + 176, + 342 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/d3817e68f204d08c13b8e1c73175f0ccffbda2fea975042766e9f7182881b2c5.jpg", + "image_caption": [ + "DIDFuse" + ], + "image_footnote": [], + "bbox": [ + 178, + 239, + 273, + 342 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/955cf0fe17023b0c1c11f978f254579076a4c436700acd4ef7f84a4f101861d3.jpg", + "image_caption": [ + "TarDAL" + ], + "image_footnote": [], + "bbox": [ + 275, + 239, + 369, + 342 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/6a0e9e2cfacb7bc195a4440facb8c4c04f31027d8567b83eeaab5eacd88d18f1.jpg", + "image_caption": [ + "PIAFusion" + ], + "image_footnote": [], + "bbox": [ + 371, + 238, + 467, + 342 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/65cc427fdeff94767fa4d18d8e4a054c456bf7e590e488c471b8717d91f1e4e4.jpg", + "image_caption": [ + "IFCNN", + "Figure 4. Qualitative comparisons of various methods on representative images selected from the FLIR dataset." + ], + "image_footnote": [], + "bbox": [ + 80, + 352, + 176, + 456 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/96661590a4cea0bb9e705b839a6634b1f093ce8f7a2711117954fea71cfac8b9.jpg", + "image_caption": [ + "SwinFuse" + ], + "image_footnote": [], + "bbox": [ + 176, + 352, + 273, + 456 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/869f29f190bd4d753d1d10670ad9006753fd0fcda11ba5cc81831dbff9f8d5d1.jpg", + "image_caption": [ + "YDTR" + ], + "image_footnote": [], + "bbox": [ + 275, + 352, + 369, + 456 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/942506bec986b3d695539c7a0407bbe59efe7bf5729fd8214a3abaad4672dc16.jpg", + "image_caption": [ + "MoE-Fusion (Ours)" + ], + "image_footnote": [], + "bbox": [ + 371, + 352, + 467, + 456 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "ically, the formula of fusion loss is as follows,", + "bbox": [ + 75, + 517, + 381, + 532 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {f u s i o n}} = \\mathcal {L} _ {\\text {p i x e l}} + \\alpha \\mathcal {L} _ {\\text {g r a d}} + \\mathcal {L} _ {\\text {l o a d}}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 147, + 545, + 468, + 560 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the pixel loss $\\mathcal{L}_{pixel}$ constrains the fused image to preserve more significant pixel intensities originating from the target images, while the gradient loss $\\mathcal{L}_{grad}$ forces the fused image to contain more texture details from different modalities. $\\mathcal{L}_{load}$ represents load loss, which encourages experts to receive roughly equal numbers of training examples [32]. More details about pixel loss, gradient loss and load loss are provided in the supplementary material. $\\alpha$ is used to strike a balance between the different loss functions.", + "bbox": [ + 75, + 571, + 468, + 695 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 75, + 709, + 206, + 724 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental Setting", + "text_level": 1, + "bbox": [ + 75, + 732, + 275, + 748 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Datasets and Partition Protocol. We conducted experiments on three publicly available datasets: $(\\mathbf{M}^{3}\\mathrm{FD}$ [18], LLVIP [11] and FLIR [37]).", + "bbox": [ + 75, + 754, + 467, + 795 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$\\mathbf{M}^3\\mathbf{FD}$ : It contains 4,200 infrared-visible image pairs captured by on-board cameras. We used 3,900 pairs of images for training and the remaining 300 pairs for evaluation.", + "bbox": [ + 75, + 796, + 467, + 837 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "FLIR: We used the \"aligned\" version [44] of FLIR in this work. It contains 5,142 infrared-visible image pairs", + "bbox": [ + 75, + 838, + 467, + 866 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "captured by on-board cameras. We used 4, 129 image pairs for training and 1, 013 image pairs for evaluation.", + "bbox": [ + 497, + 125, + 889, + 153 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "LLVIP: The LLVIP dataset contains 15,488 aligned infrared-visible image pairs, which is captured by the surveillance cameras in different street scenes. We trained the model with 12,025 image pairs and performed evaluation on 3,463 image pairs.", + "bbox": [ + 497, + 154, + 890, + 223 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Competing methods. We compared the 9 state-of-the-art methods on three publicly available datasets $(\\mathrm{M}^3\\mathrm{FD}$ [18], LLVIP [11] and FLIR [37]). In these comparison methods, DenseFuse [16] and RFN-Nest [17] are the autoencoder-based methods, PIAFusion [35] and IFCNN [48] are the CNN-based methods, TarDAL [18] is the GAN-based methods. DIDFuse [49] and AUIF [50] are the deep learning-based image decomposition methods. SwinFuse [40] and YDTR [36] are the Transformer-based methods.", + "bbox": [ + 497, + 224, + 890, + 347 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Implementation Details. We performed experiments on a computing platform with two NVIDIA GeForce RTX 3090 GPUs. We used Adam Optimization to update the overall network parameters with the learning rate of $1.0 \\times 10^{-4}$ . The auxiliary network Faster R-CNN [29] is also trained along with the image fusion pipeline. The training epoch is set to 24 and the batch size is 4. The tuning parameter $\\alpha$ is set to 10. For MoLE and MoGE, we set the number of experts is 4, and sparsely activate the top 2 experts.", + "bbox": [ + 497, + 349, + 890, + 473 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluation Metrics. We evaluated the performance of the proposed method based on qualitative and quantitative results. The qualitative evaluation is mainly based on the visual effect of the fused image. A good fused image needs to have complementary information of multi-modal images. The quantitative evaluation mainly uses quality evaluation metrics to measure the performance of image fusion. We selected 8 popular metrics, including the entropy (EN) [31], spatial frequency (SF) [4], standard deviation (SD), mutual information (MI) [28], visual information fidelity (VIF) [7], average gradient (AG) [2], the sum of the correlations of differences (SCD) [1], and gradient-based similarity measurement $(Q_{abf})$ [43]. We also evaluate the performance of the different methods on the typical downstream task, infrared-visible object detection.", + "bbox": [ + 497, + 473, + 890, + 681 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Evaluation on the $\\mathbf{M}^3\\mathrm{FD}$ dataset", + "text_level": 1, + "bbox": [ + 499, + 692, + 781, + 706 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Quantitative Comparisons. Table 1 presents the results of the quantitative evaluation on the $\\mathrm{M}^3\\mathrm{FD}$ dataset, where our method achieves the best in 7 metrics and the second and third best performance in the remaining metrics, respectively. In particular, it shows overwhelming advantages on VIF, MI,and $Q_{abf}$ , which indicates that our fusion results contain more valuable information and are more beneficial to the visual perception effect of human eyes. The highest SF, SD and AG also indicate that our fusion results preserve sufficient texture detail and contrast. Such superior performance is attributed to the proposed dynamic learning frame", + "bbox": [ + 497, + 713, + 890, + 866 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "23559", + "bbox": [ + 463, + 885, + 504, + 897 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/4582124d584a7a2d7b58f506001857863fb300734564b740228733612e2f8a71.jpg", + "image_caption": [ + "Visible image" + ], + "image_footnote": [], + "bbox": [ + 80, + 125, + 176, + 232 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/f162f3e8fab87b722ee1c9841f7bfdebe3cfadbd3ef70acb724d6fda368effda.jpg", + "image_caption": [ + "Infrared image" + ], + "image_footnote": [], + "bbox": [ + 176, + 125, + 270, + 232 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/cd06c6cbf4d5e520b58d29dd4cd7fecef0675e7311a7bcb0e935a0780d89e4f8.jpg", + "image_caption": [ + "RFN-Nest" + ], + "image_footnote": [], + "bbox": [ + 273, + 125, + 368, + 232 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/dc37122cec68a3f7f409926d305125b057db854e3214bf6ae35c405a520d7fbc.jpg", + "image_caption": [ + "DenseFuse" + ], + "image_footnote": [], + "bbox": [ + 369, + 125, + 463, + 232 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/16e472ad00ef22f27a5e8bf146c891501df86937f98485c117a2ecb065b10545.jpg", + "image_caption": [ + "AUE" + ], + "image_footnote": [], + "bbox": [ + 80, + 243, + 176, + 349 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/5a23e6e8d64a0700b2c4970312928701e6d110d82ce59d6c0c58d821e48e1e5c.jpg", + "image_caption": [ + "DIDFuse" + ], + "image_footnote": [], + "bbox": [ + 176, + 243, + 270, + 349 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/602a1706bdd4e41b2f588777aef29146864e43412aebdb519bb5000dbf60425e.jpg", + "image_caption": [ + "TarDAL" + ], + "image_footnote": [], + "bbox": [ + 273, + 243, + 368, + 349 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/30d5b61e75162edae8fb9ca382d65a9b42fd33d2fb6ac29d28b53c3a562c73b8.jpg", + "image_caption": [ + "PIAFusion" + ], + "image_footnote": [], + "bbox": [ + 369, + 243, + 463, + 349 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1e78f30902a89aa1f74287384d9b578b1482ba94aacb4b3eed208254057901f5.jpg", + "image_caption": [ + "IFCNN" + ], + "image_footnote": [], + "bbox": [ + 80, + 359, + 176, + 466 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/ca4a9d54db9ba84ce297ba42971764e763c760f19be5428bbabe4507ae0e42e8.jpg", + "image_caption": [ + "SwinFuse" + ], + "image_footnote": [], + "bbox": [ + 176, + 359, + 270, + 465 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/cf6e7ce48e8b8e1afa5fa170343922597e07a3d60684f14a03d8c05ffc9cd86c.jpg", + "image_caption": [ + "YDTR" + ], + "image_footnote": [], + "bbox": [ + 273, + 359, + 366, + 465 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/408245e02820900b990e14af2f17595e37e6c41ead1584b5f15606001ae7e11c.jpg", + "image_caption": [ + "MoE-Fusion (Ours)", + "Figure 5. Qualitative comparisons of various methods on representative images selected from the LLVIP dataset." + ], + "image_footnote": [], + "bbox": [ + 369, + 359, + 463, + 465 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "work from local to global, which achieves state-of-the-art fusion performance through the sample adaptive approach.", + "bbox": [ + 75, + 533, + 467, + 560 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Qualitative Comparisons. To better show the superiority of our model, we assigned the color information of the 3-channel visible image to the single-channel fused image through the color space conversion between RGB and YCbCr. We mark the background region with the green rectangular box and the foreground region with the red rectangular box. As shown in Fig. 3, our fusion results have the best results in both local and global regions. Compared to PIAFusion, YDTR, AUIF, IFCNN and DIDFuse, our fusion results show better contrast, and our fusion results show better texture details compared to TarDAL and SwinFuse. In daytime scenes, our model adaptively learned sufficient texture detail and significant contrast, such as containers and people. Especially for people, our method significantly avoids the effect of smoke and preserves the contrast information of infrared. In local regions, we successfully preserve the rich texture information of containers, outperforming other methods. In global regions such as mountains, grass and sky, our fusion results also effectively retain texture information, indicating that our method has better visual effects due to dynamic learning of local and global information of different modalities.", + "bbox": [ + 75, + 561, + 468, + 865 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Evaluation on the FLIR dataset", + "text_level": 1, + "bbox": [ + 499, + 125, + 778, + 138 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Quantitative Comparisons. Table 1 reports the performance of the different methods on the FLIR dataset for 8 metrics. Our method achieves the best results in 5 metrics. Among them, the highest EN and MI indicate that our method can preserve abundant information of the multimodal images well. The best performance of our method on SCD and $Q_{abf}$ also indicates that our fusion results can better learn the multi-modal complementary information and edge information, which makes our fusion results have better foreground-background contrast and richer texture details. Moreover, the highest VIF also demonstrates that our method can generate fused images with better visual effects that are beneficial to human observation. In addition, the third best results on SF, SD, and AG also indicate that our method is highly competitive. The quantitative results on the FLIR dataset also validate the superiority of our method in dynamically fusing multi-modal complementary information from the local to the global.", + "bbox": [ + 497, + 146, + 890, + 394 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Qualitative Comparisons. We mark the background region with the green rectangular box and the foreground region with the red rectangular box. We also show their zoomed-in effects for easier comparison. As shown in Fig. 4, our fusion results have the best results in both local and global regions. In night scenes, our fusion results adaptively learn sufficient texture detail and contrast, for example on buildings, trees, mountains and traffic lights. Especially for the traffic lights, our method effectively avoids the effects of glare and best preserves the entire outline of the traffic lights. On the local regions, our fusion results preserve the best contrast information of the pedestrians and the rich detail information of the vehicles. These comparisons illustrate that our method has better visual effects due to the effective dynamic learning of local information from different modalities. The superiority of the proposed MoE-Fusion also reveals that specialized knowledge of multimodal local and global in fusion networks can effectively improve fusion performance.", + "bbox": [ + 497, + 395, + 890, + 657 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Evaluation on the LLVIP dataset", + "text_level": 1, + "bbox": [ + 499, + 665, + 786, + 678 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Quantitative Comparisons. The quantitative results of the different methods on the LLVIP dataset are reported in Table 1. Our method outperforms all the compared methods on 6 metrics and achieved the second and third best results on the remaining 2 metrics, respectively. Specifically, the highest SF and AG we achieved indicate that the proposed method preserves richer texture details in the multi-modal images. As well as the highest SD also indicates that our fusion results can contain the highest contrast information between the foreground and the background. SCD and $Q_{abf}$ denote the complementary information and edge information transferred from multi-modal images to fused image, respectively, and our highest results on these two metrics", + "bbox": [ + 497, + 686, + 890, + 866 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "23560", + "bbox": [ + 463, + 885, + 504, + 897 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/78214219ee33ccd14a6df2b3bf793846902cc09f46bffd57ce69296ad9b08bdc.jpg", + "table_caption": [ + "Table 2. Ablation studies on three infrared-visible datasets." + ], + "table_footnote": [], + "table_body": "
M3FD Dataset [18]
ENSFSDMIVIFAGSCDQabf
w/o MoLE6.78560.06929.16362.72140.81005.55091.51530.6535
w/o MoGE6.83510.06959.24912.81380.82615.65211.53460.6375
Att-Local6.86560.06939.18942.73200.82715.58091.51900.6390
MoE-Fusion7.00180.071510.14064.19491.00345.67421.54330.6661
FLIR Dataset [44]
ENSFSDMIVIFAGSCDQabf
w/o MoLE6.90210.058710.28592.36660.53715.69611.09760.3187
w/o MoGE7.31720.054810.66542.92080.77475.25251.66290.4796
Att-Local7.30700.060210.64032.66730.74485.72651.47880.4838
MoE-Fusion7.49250.060310.70073.12090.82125.76041.68180.4991
LLVIP Dataset [11]
ENSFSDMIVIFAGSCDQabf
w/o MoLE6.90770.06619.80902.50390.58124.93581.17390.4732
w/o MoGE7.27400.08479.60342.70670.76215.59601.62600.5110
Att-Local7.25280.08589.54832.71290.85996.10991.63930.5735
MoE-Fusion7.35230.08629.86643.10610.92026.13161.78410.5932
", + "bbox": [ + 80, + 131, + 467, + 293 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "indicate that our method can learn more valuable information from multi-modal images. Moreover, the highest VIF also means that our method can generate the most appealing fused images that are more suitable for human vision. These quantitative results demonstrate that the proposed MoE-Fusion can effectively learn multi-modal knowledge and generate informative and appealing fusion results.", + "bbox": [ + 75, + 318, + 467, + 415 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Qualitative Comparisons. We mark the background region with the green rectangular box and the foreground region with the red rectangular box. We also show their zoomed-in effects for easier comparison. As shown in Fig. 5, we can find that the proposed method best preserves the texture details of the local and global in the multi-modal image compared with the state-of-the-art methods, while highlighting the contrast information of the local dynamically. Specifically, for the background region, our fusion results show the sharpest effect on the edge texture of the zebra crossing. For the foreground region, our fusion results preserve the most significant contrast and the richest texture detail in pedestrians and cyclists. Qualitative comparisons show that our MoE-Fusion can balance the texture details and contrasts with the specialized experts dynamically.", + "bbox": [ + 75, + 416, + 467, + 623 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5. Ablation Study", + "text_level": 1, + "bbox": [ + 75, + 635, + 228, + 649 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We conducted ablation studies on the $\\mathbf{M}^3\\mathrm{FD}$ , LLVIP, and FLIR datasets and reported the results in Table 2.", + "bbox": [ + 75, + 657, + 467, + 684 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "MoLE. To verify the effectiveness of MoLE, we removed MoLE from MoE-Fusion and then extracted multi-modal features by two encoders only, and they were sent to MoGE after concatenation. As shown in Table 2, all the metrics show a significant decrease after removing MoLE, indicating that MoLE is very effective in learning multi-modal texture details and contrast information. Among others, the decrease on SCD also shows it is difficult to learn complementary multi-modal local information sufficiently without MoLE, which strongly supports our motivation to design MoLE. The local dynamic experts of MoLE adaptively boost dominant local (foreground and background) information induced from the auxiliary detector of different", + "bbox": [ + 75, + 686, + 467, + 865 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/11c3599880800f496dfc5ce26ef100396b90c07efbb586e873eb80768cdc77f3.jpg", + "image_caption": [ + "Visible image" + ], + "image_footnote": [], + "bbox": [ + 504, + 124, + 601, + 179 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/4b681e6d63a46589f003264b912becd89bafcba583f379397989c9c104ea06e2.jpg", + "image_caption": [ + "Infrared image" + ], + "image_footnote": [], + "bbox": [ + 601, + 124, + 695, + 179 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b12d946c68aef3da04bcf3ffb7cf1a8a9bd480b30e801e07a0214cba54682437.jpg", + "image_caption": [ + "Fusion Feature" + ], + "image_footnote": [], + "bbox": [ + 695, + 124, + 791, + 179 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/66722b06e1f99123d19a26b498a49c36a5b5162fd1c2f0b1d591250cb1185bfa.jpg", + "image_caption": [ + "Fusion result" + ], + "image_footnote": [], + "bbox": [ + 793, + 124, + 889, + 179 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1b4bf8665cd4558d881c85da036168c26267b50011e70459bb360d643088d88b.jpg", + "image_caption": [ + "FG Expert #1" + ], + "image_footnote": [], + "bbox": [ + 504, + 190, + 600, + 245 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2656e4480a22dfe9a86be20be2ca61690a9929bc33a832670ac82ab39ed038bc.jpg", + "image_caption": [ + "FG Expert #2" + ], + "image_footnote": [], + "bbox": [ + 600, + 190, + 695, + 245 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/a159f61568437d9e70bbb641c8382d8ed8f24271ea570e287adb7c2cd7539f9a.jpg", + "image_caption": [ + "FG Expert #3" + ], + "image_footnote": [], + "bbox": [ + 695, + 190, + 791, + 245 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/0c9980161262760aa35d6bd26f0121f7bb1b886f4f066bf1b70028e7e1e731fc.jpg", + "image_caption": [ + "FG Expert # 4" + ], + "image_footnote": [], + "bbox": [ + 793, + 190, + 889, + 245 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/1c62152a9a246ccc54639ce301b19235ca3bf8743ff788d5149d79bce5b84090.jpg", + "image_caption": [ + "BG Expert #1", + "Figure 6. Visualization of the features learned by each expert in MoLE. FG denotes foreground, BG denotes background." + ], + "image_footnote": [], + "bbox": [ + 504, + 258, + 600, + 312 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e6d5714d590b55e527c8b0f3ba15b0f51b97a17ac78b84b2f1d3c810c842be89.jpg", + "image_caption": [ + "BG Expert #2" + ], + "image_footnote": [], + "bbox": [ + 600, + 258, + 695, + 312 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b907bcdb6b50e400f48a8864c3ce584cdecfc1851c541c9afca529cf0d86349e.jpg", + "image_caption": [ + "BG Expert #3" + ], + "image_footnote": [], + "bbox": [ + 695, + 258, + 791, + 312 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6f12694d2613e3416bfbb0ea59de354b45848bdd50492ca0943ffa163b46ac5c.jpg", + "image_caption": [ + "BG Expert # 4" + ], + "image_footnote": [], + "bbox": [ + 793, + 258, + 889, + 312 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "modalities for dynamic fusion, specialized to local regions. MoGE. We replaced the MoGE with a common decoder with the same structure as that of a single expert in the MoGE. As shown in Table 2, all the metrics appear to be significantly decreased, strongly verifying that the MoGE can help fused images preserve more contrast and texture detail information. Moreover, these results also demonstrate that MoGE can effectively motivate the image fusion network to dynamically adapt to different samples, learning better feature representations, and thus achieving better fusion performance. The global dynamic experts of MoGE further enhance the dominant modality from a global perspective while refining the potential errors that may occur in local fusion.", + "bbox": [ + 497, + 376, + 890, + 568 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Attention-based Local Feature. We want to explore how the fusion performance changes when dynamic learning is not performed for local features and only local feature priors constructed by attention maps are used as local features. We designed an attention-based local feature learning module (Att-Local), and to keep the output channels consistent, we followed the Att-Local module with a $1 \\times 1$ convolution layers. In Table 2, all metrics cannot exceed the results of MoE-Fusion with the use of Att-Local, but most of them are higher than w/o MoLE, which demonstrates on the one hand that our proposed MoLE is indeed effective, and on the other hand that the dynamic integration of the effective information from the respective modalities is beneficial to improve the performance of multi-modal image fusion.", + "bbox": [ + 497, + 570, + 890, + 764 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.6. Analysis and Discussion", + "text_level": 1, + "bbox": [ + 499, + 775, + 719, + 789 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Visualization of MoLE. In the MoLE, we can obtain local feature priors according to the attention map Att, which we define as foreground local features (FG), and we also use $1 - \\text{Att}$ to obtain background local features (BG). We visualize what each expert has learned in MoLE. As shown", + "bbox": [ + 497, + 796, + 890, + 866 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "23561", + "bbox": [ + 463, + 885, + 502, + 897 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/f9b0037caf79546a943a30f572f06cb704f497a6cd4ab8bc63e94c707dd69540.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 80, + 122, + 171, + 187 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/56b4926f448cbef341f47aacddc5e630fb194fd2363a857a325bef175bf44cc1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 176, + 122, + 268, + 186 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/cae6071f418c33656bfb288d50b6cbc35031efeb468e1564c6908efc456f865a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 275, + 122, + 368, + 186 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/36bc9e6705d66343027c74470bd2c1c18e6f3d224c59d3c758554a822ac6aa4a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 376, + 122, + 467, + 186 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8ae2f20afd10beedaa7c63dabb70fa262a9b5e20a1334a86c4a9b557ec23886c.jpg", + "image_caption": [ + "Figure 7. Experiments on the number of experts." + ], + "image_footnote": [], + "bbox": [ + 78, + 191, + 171, + 254 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f667dafd16422b0543d507b77a4f68f27ecaa5f04d006b091525655cc4b19a7b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 176, + 191, + 268, + 254 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b450399a689ff0ecff9c23fe231984c94d9bf85eef2025dedcadd580b90ceea0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 275, + 191, + 368, + 254 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/768b577ddff32aefbba13443e2147efcca4c7634f0c7c2b560460893bf2992ec.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 374, + 191, + 467, + 254 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/84a795cad70ff0be8858d1e83e7386e379b066408e9a113dffe9b08c94f9ba54.jpg", + "table_caption": [ + "Table 3. Object detection evaluation on the FLIR dataset." + ], + "table_footnote": [], + "table_body": "
MethodscarpersonbicyclemAP
Visible55.9027.2033.2038.70
Infrared68.7045.6030.8048.40
DenseFuse [16]65.8044.7031.4047.30
RFN-Nest [17]58.8036.5026.2040.50
IFCNN [48]67.8045.7034.7049.40
PIAFusion [35]62.6040.9031.5045.00
DIDFuse [49]64.2041.7032.1046.00
AUIF [50]61.7036.8029.6042.70
SwinFuse [40]65.6041.3029.7045.60
YDTR [36]65.0044.2032.5047.20
TarDAL [18]62.5035.4030.8042.90
MoE-Fusion72.9055.0039.5055.80
", + "bbox": [ + 105, + 296, + 440, + 477 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "in Fig. 6, we see that the four foreground local experts can clearly learn foreground information, while the four background local experts can also learn rich background features. These results show that MoLE can successfully let each expert know what it should specialize in.", + "bbox": [ + 75, + 503, + 468, + 572 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Detection Evaluation. Good fused images should have better performance in downstream tasks. For different image fusion methods, we perform the evaluation on the object detection task and use the mean average precision (mAP) [5] as the metric. Following [51], we first train the object detection model using infrared images and visible images, and then we input the fused images generated by different image fusion methods into the object detection model for inference and evaluate their detection performance. In this paper, we use Faster R-CNN [29] as the object detection algorithm and set the IoU (Intersection over Union) threshold for evaluation to 0.5. According to Table 3, our MoE-Fusion outperforms all the compared methods and achieves the highest mAP. It is worth noting that our method has an overwhelming advantage on all categories, which demonstrate the proposed dynamic image fusion method is more beneficial for downstream tasks. The detection evaluation on other datasets is provided in the supplementary material.", + "bbox": [ + 75, + 574, + 468, + 823 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Number of Experts. In Fig. 7, we performed 4 sets of experiments on the FLIR dataset, E2k2, E4K2, E6K2, and E8K2, to explore the effect of the number of experts on the", + "bbox": [ + 75, + 824, + 468, + 866 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8b63cc1bbfc3acf1d959a067e0c12ee951e0522341321bb8f751d3c181852d0c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 504, + 122, + 589, + 182 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/96686f89c872c3a83dce2acdc7a220264a651e2cdc8b96e47fee0669ce2624a7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 601, + 123, + 687, + 182 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8edb6a25b8cabfe1a6e1c509a06d4a21ca2da148d8fe6a7d052d3c2c9a4e61ff.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 700, + 123, + 784, + 182 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a914c564327785233c91921d9bfeb1318cf7392555eee76976432abead1ce107.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 798, + 123, + 882, + 182 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0fbcef3f26b393d3e0364e69bf72849df4469d8f8fdcd68245237303fc276c2d.jpg", + "image_caption": [ + "Figure 8. Hyperparameter sensitivity analysis on the FLIR dataset." + ], + "image_footnote": [], + "bbox": [ + 502, + 191, + 589, + 252 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e9a6c81ac9d154157c9f3d43c04c5658b0bf5e82c72f385a3dc5a81ce769f685.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 601, + 191, + 687, + 252 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b388d7ea6436b2e32aac4288e51ebea520d9744876d5db5d25a70bc1f9106b5d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 700, + 191, + 784, + 252 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9eb45e4b27983eb307a49b03f55e4ab609db75576b592234116d2afb77c35e77.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 798, + 191, + 882, + 252 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "fusion results. As an example, E4K2 means that the MoE contains 4 experts and sparsely selects top 2 experts for integration. We found that E4K2 was higher than E2K2 in 7 metrics, E6K2 in 6 metrics, and E8K2 in 5 metrics, suggesting that a higher number of experts may not be better. In addition, we also set up 3 sets of experiments, E4K1, E4K3 and E4K4, to verify the effect of sparse selection of experts in MoE on the fusion results. In Fig. 7, we find that E4K2 can outperform E4K1 and E4K3 in 7 metrics and E4K4 in all metrics. Therefore, in this work, we set 4 experts for each MoE and sparsely select 2 experts for integration.", + "bbox": [ + 497, + 300, + 890, + 453 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Hyperparameter. As shown in Fig. 8, we choose five values for tuning parameter $\\alpha$ (1, 5, 10, 20, and 40) and experiment with them in turn. When $\\alpha$ is less than 10, the fusion results fail to exceed the performance on all metrics with $\\alpha$ equal to 10. When $\\alpha$ is greater than 10, there is an improvement in only 2 metrics (SF and AG) compared to $\\alpha$ equal to 10, but the other 6 metrics show a decrease. Therefore, in this work, we set $\\alpha$ to 10 to obtain better results.", + "bbox": [ + 497, + 456, + 892, + 566 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 499, + 590, + 616, + 604 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose a novel dynamic image fusion framework with a multi-modal gated mixture of locally-global experts (MoE-Fusion), which can produce reliable infrared-visible image fusion results. Our framework focuses on dynamically integrating effective information from different source modalities by performing sample-adaptive infrared-visible fusion from local to global. The MoE-Fusion model dynamically balances the texture details and contrasts with the specialized local experts and global experts. The experimental results on three challenging datasets demonstrate that the proposed MoE-Fusion outperforms state-of-the-art methods in terms of visual effects and quantitative metrics. Moreover, we also validate the superiority of our MoE-Fusion in the object detection task. In future work, we will explore leveraging the uncertainty of different images to guide the fusion, and investigate developing an uncertainty-gated MoE paradigm for dynamic image fusion.", + "bbox": [ + 497, + 617, + 890, + 866 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "23562", + "bbox": [ + 463, + 885, + 504, + 897 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments", + "text_level": 1, + "bbox": [ + 78, + 124, + 235, + 140 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was supported in part by the National Key R&D Program of China 2022ZD0116500, in part by the National Natural Science Foundation of China under Grant 62222608, 62106171, and 61925602, in part by the Haihe Lab of ITAI under Grant 22HHXCJC00002, and in part by the Tianjin Natural Science Foundation under Grant 21JCYBJC00580.", + "bbox": [ + 75, + 148, + 468, + 243 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 258, + 171, + 271 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] V Aslantas and Emre Bendes. 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NeurIPS, 2022." + ], + "bbox": [ + 502, + 127, + 890, + 861 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "23564", + "bbox": [ + 463, + 887, + 504, + 897 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/6e316164-78c4-4054-8879-22d243fd30bc_model.json b/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/6e316164-78c4-4054-8879-22d243fd30bc_model.json new file mode 100644 index 0000000000000000000000000000000000000000..3f0c28abdd1e3f4da64882459da1e54c8a812e66 --- /dev/null +++ b/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/6e316164-78c4-4054-8879-22d243fd30bc_model.json @@ -0,0 +1,3355 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.13, + 0.051, + 0.201, + 0.085 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.254, + 0.049, + 0.79, + 0.087 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.188, + 0.162, + 0.784, + 0.205 + ], + "angle": 0, + "content": "Multi-modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion" + }, + { + "type": "text", + "bbox": [ + 0.298, + 0.229, + 0.7, + 0.246 + ], + "angle": 0, + "content": "Bing Cao*, Yiming Sun*; Pengfei Zhu†; Qinghua Hu" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.246, + 0.912, + 0.278 + ], + "angle": 0, + "content": "Tianjin Key Lab of Machine Learning, College of Intelligence and Computing, Tianjin University, China \nHaihe Laboratory of Information Technology Application Innovation, China" + }, + { + "type": "text", + "bbox": [ + 0.257, + 0.279, + 0.742, + 0.294 + ], + "angle": 0, + "content": "{caobing,sunyiming1895,zhupengfei,huqinghua}@tju.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.325, + 0.313, + 0.34 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.355, + 0.473, + 0.714 + ], + "angle": 0, + "content": "Infrared and visible image fusion aims to integrate comprehensive information from multiple sources to achieve superior performances on various practical tasks, such as detection, over that of a single modality. However, most existing methods directly combined the texture details and object contrast of different modalities, ignoring the dynamic changes in reality, which diminishes the visible texture in good lighting conditions and the infrared contrast in low lighting conditions. To fill this gap, we propose a dynamic image fusion framework with a multi-modal gated mixture of local-to-global experts, termed MoE-Fusion, to dynamically extract effective and comprehensive information from the respective modalities. Our model consists of a Mixture of Local Experts (MoLE) and a Mixture of Global Experts (MoGE) guided by a multi-modal gate. The MoLE performs specialized learning of multi-modal local features, prompting the fused images to retain the local information in a sample-adaptive manner, while the MoGE focuses on the global information that complements the fused image with overall texture detail and contrast. Extensive experiments show that our MoE-Fusion outperforms state-of-the-art methods in preserving multi-modal image texture and contrast through the local-to-global dynamic learning paradigm, and also achieves superior performance on detection tasks. Our code is available: https://github.com/SunYM2020/MoE-Fusion." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.741, + 0.21, + 0.755 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.764, + 0.47, + 0.835 + ], + "angle": 0, + "content": "Infrared and visible image fusion focus on generating appealing and informative fused images that enable superior performance in practical downstream tasks over that of using single modality alone [24, 45, 41, 21]. In recent years, infrared-visible image fusion has been widely used" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.326, + 0.631, + 0.417 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.526, + 0.418, + 0.608, + 0.428 + ], + "angle": 0, + "content": "Visible image" + }, + { + "type": "image", + "bbox": [ + 0.631, + 0.327, + 0.76, + 0.417 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.651, + 0.418, + 0.737, + 0.428 + ], + "angle": 0, + "content": "Infrared image" + }, + { + "type": "image", + "bbox": [ + 0.761, + 0.327, + 0.888, + 0.417 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.77, + 0.418, + 0.879, + 0.428 + ], + "angle": 0, + "content": "DF (IEEE TIP'19)" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.429, + 0.632, + 0.519 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.518, + 0.52, + 0.621, + 0.53 + ], + "angle": 0, + "content": "DIDF (IJCAI'20)" + }, + { + "type": "image", + "bbox": [ + 0.632, + 0.429, + 0.761, + 0.519 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.648, + 0.52, + 0.746, + 0.531 + ], + "angle": 0, + "content": "TDL (CVPR'22)" + }, + { + "type": "image", + "bbox": [ + 0.761, + 0.429, + 0.888, + 0.519 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.769, + 0.52, + 0.884, + 0.531 + ], + "angle": 0, + "content": "MoE-Fusion (Ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.535, + 0.892, + 0.625 + ], + "angle": 0, + "content": "Figure 1. The importance of dynamic image fusion. In the SOTA methods (DF [16], DIDF [49], and TDL [18]), the texture details of objects (e.g., car, truck, and traffic sign) in the fused image are suppressed by the contrast of infrared image, leading to terrible detection results. Benefiting from the dynamic fusion, our method can preserve clear texture details without being interrupted by unsuitable contrast, achieving the best performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.655, + 0.892, + 0.793 + ], + "angle": 0, + "content": "in many applications, such as autonomous vehicles [9] and unmanned aerial vehicles [34]. According to the thermal infrared imaging mechanism, infrared images can be adapted to various lighting conditions but has the disadvantage of few texture details [25, 50, 19]. By contrast, visible images contain rich texture detail information, but cannot provide clear information in low light conditions. Therefore, how to design advanced fusion methods such that the fused images preserve sufficient texture details and valuable thermal information has attracted a lot of research attention." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.798, + 0.892, + 0.867 + ], + "angle": 0, + "content": "Existing infrared-visible fusion methods [46, 38, 33, 42] can be mainly categorized to traditional approaches (image decomposition [15], sparse representation [47], etc.) and deep learning-based approaches (autoencoder based methods [16, 49, 17], generative adversarial network based" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.844, + 0.204, + 0.854 + ], + "angle": 0, + "content": "*Equal contribution" + }, + { + "type": "page_footnote", + "bbox": [ + 0.098, + 0.855, + 0.22, + 0.866 + ], + "angle": 0, + "content": "† Corresponding author" + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.844, + 0.22, + 0.866 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "23555" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.126, + 0.473, + 0.306 + ], + "angle": 0, + "content": "approaches [18, 26], transformer based approaches [40, 36], etc.). However, most of these methods directly combined the texture details and object contrast of different modalities, ignoring the dynamic changes in reality, leading to poor fusion results and even weaker downstream task performance than that of a single modality. As shown in Fig. 1, the infrared image should adaptively enhance cars in dim light while avoiding compromising the textural detail of truck in bright light. However, the object textures in these state-of-the-art fusion methods are significantly disturbed by the infrared thermal information due to the lack of dynamic learning of multi-modal local and global information, resulting in terrible object detection performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.306, + 0.473, + 0.706 + ], + "angle": 0, + "content": "In complex scenes, different modalities have different characteristics: under good lighting conditions, the texture of an object should not be disturbed by thermal infrared information; under low lighting conditions, the contrast of an object also should not be suppressed by the darkness of the visible image. Most existing methods perform image fusion in a fixed correlation paradigm, ignoring the dominant modality changes dynamically in reality, and often fall into domain bias. To break the traditional fixed fusion paradigm, we pioneered sample-adaptive local-to-global experts to dynamically enhance the dominant modality for image fusion. Fig. 1 show that the proposed method not only eliminates domain bias but also achieves sample-adaptive dynamic fusion, yielding the best detection results. Specifically, we propose a dynamic image fusion framework with a multi-modal gated mixture of local-to-global experts, termed MoE-Fusion, which consists of a Mixture of Local Experts (MoLE) and a Mixture of Global Experts (MoGE) guided by a multi-modal gate. In MoLE, we introduce the attention map generated by an auxiliary network to construct multi-modal local priors and perform dynamic learning of multi-modal local features guided by multimodal gating, achieving sample-adaptive multi-modal local feature fusion. Moreover, MoGE performs dynamic learning of multi-modal global features to achieve a balance of texture details and contrasts globally in the fused images. With the proposed dynamic fusion paradigm from local to global, our model is capable of performing a reliable fusion of different modal images." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.707, + 0.425, + 0.721 + ], + "angle": 0, + "content": "We summarize our main contributions as follows:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.731, + 0.47, + 0.801 + ], + "angle": 0, + "content": "- We propose a dynamic image fusion model, providing a new multi-modal gated mixture of local-to-global experts for reliable infrared and visible image fusion (benefiting from the dynamically integrating effective information from the respective modalities)." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.811, + 0.47, + 0.867 + ], + "angle": 0, + "content": "- The proposed model is an effective and robust framework for sample-adaptive infrared-visible fusion from local to global. Further, it prompts the fused images to dynamically balance the texture details and contrasts." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.731, + 0.47, + 0.867 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.127, + 0.892, + 0.195 + ], + "angle": 0, + "content": "- We conduct extensive experiments on multiple infrared-visible datasets, which clearly validate our superiority, quantitatively and qualitatively. Moreover, we also demonstrate our effectiveness in object detection." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.21, + 0.651, + 0.224 + ], + "angle": 0, + "content": "2. Related Works" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.233, + 0.802, + 0.248 + ], + "angle": 0, + "content": "2.1. Infrared and Visible Image Fusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.254, + 0.892, + 0.6 + ], + "angle": 0, + "content": "The infrared and visible image fusion task focuses on generating a fused image containing sufficient information through the learning of multi-modal features [24, 45, 20, 22, 12, 8]. Ma et al. [23] defined the goal of image fusion as preserving more intensity information in infrared images as well as gradient information in visible images. Li et al. [16] use the autoencoder to extract multi-modal overall features and fuse them by designed fusion rules, which inspired a series of subsequent works [14, 17]. Zhao et al. [49, 50] proposed the deep learning-based image decomposition methods, which decompose images into background and detail images by high- and low-frequency information, respectively, and then fuse them by designed fusion rules. Recently, some GAN-based methods [26, 25, 18] and Transformer-based methods [40, 36] have also attracted wide attention. These works, despite the different approaches adopted, all focus on learning on the representation of the overall multi-modal features. However, they ignore the dynamic changes in reality, which diminishes the visible texture in good lighting conditions and the infrared contrast in low lighting conditions. We propose a dynamic image fusion framework that enables sample-adaptive fusion from local to global. This approach prompts the fused images to balance the texture details and contrast with specialized experts dynamically." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.61, + 0.687, + 0.625 + ], + "angle": 0, + "content": "2.2. Mixture-of-Experts" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.632, + 0.892, + 0.868 + ], + "angle": 0, + "content": "Mixture-of-Experts (MoE) [10, 30, 27] can dynamically adjust its structure according to different inputs. Shazeer et al. [32] constructed a sparsely-gated MoE layer that uses a gate network to select multiple experts and assign weights to each selected expert. The final result of the MoE is a weighted sum of the outputs of the different experts. This work also serves as the basis for subsequent research. Recently, some researchers [13, 27] have focused on exploring learning mechanisms in MoE, trying to solve the problems of unbalanced expert load and the number of activated experts faced by MoE during training. Other researchers [6, 52, 3, 39] focuses on the combination of MoE and Transformer. They expect to use MoE to build sparse models. Zhu et al. [52] introduced Conditional MoE into the generalist model and proposed different routing strategies to mitigate the interference between tasks and modalities. Existing MoE-related methods focus on modeling" + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "23556" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.125, + 0.337, + 0.297 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.202, + 0.306, + 0.221, + 0.317 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.344, + 0.125, + 0.631, + 0.307 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.589, + 0.306, + 0.608, + 0.318 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image", + "bbox": [ + 0.633, + 0.129, + 0.891, + 0.306 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.322, + 0.893, + 0.348 + ], + "angle": 0, + "content": "Figure 2. The architecture of MoE-Fusion. MoE-Fusion consists of a Mixture of Local Experts (MoLE), a Mixture of Global Experts (MoGE) guided by the multi-modal gate, a set of infrared and visible feature encoders, and the auxiliary network." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.37, + 0.47, + 0.468 + ], + "angle": 0, + "content": "generic knowledge by using the dynamicity and sparsity of MoE, resulting in each expert does not know what they should be expert in. In contrast, we extend the idea of MoE to image fusion tasks for the first time, constructing a multimodal gated mixture of local-to-global experts, assigning specific tasks to each expert, and enabling sample-adaptive specialized learning, which yields superior performance." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.478, + 0.168, + 0.492 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.5, + 0.273, + 0.513 + ], + "angle": 0, + "content": "3.1. Overall Architecture" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.522, + 0.469, + 0.59 + ], + "angle": 0, + "content": "In this paper, we propose a dynamic image fusion framework with a multi-modal gated mixture of local-to-global experts, termed MoE-Fusion. In Fig. 2, MoE-Fusion contains two encoders, a Mixture of Local Experts, a Mixture of Global Experts, and the auxiliary network." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.591, + 0.47, + 0.867 + ], + "angle": 0, + "content": "In Fig. 2 (b), we send a pair of infrared image \\( I_{\\mathcal{I}} \\in \\mathbb{R}^{H \\times W \\times 1} \\) and visible image \\( I_{\\mathcal{V}} \\in \\mathbb{R}^{H \\times W \\times 3} \\) into the infrared and visible encoders (\\( Enc_{\\mathcal{I}} \\) and \\( Enc_{\\mathcal{V}} \\)) to extract the features, respectively. The structure of encoders follows [16]. The output of the encoder has two parts: the feature maps of the last layer (\\( x_{enc}^{\\mathcal{I}} \\) and \\( x_{enc}^{\\mathcal{V}} \\)) and the dense feature maps (\\( x_{dense}^{\\mathcal{I}} \\) and \\( x_{dense}^{\\mathcal{V}} \\)). More details of the structure are provided in the supplementary material. We send the \\( x_{enc}^{\\mathcal{I}} \\) and \\( x_{enc}^{\\mathcal{V}} \\) to the MoLE along with the attention map which is learning from the auxiliary network. In this paper, we use Faster-RCNN [29] as the auxiliary network. In MoLE, we send visible and infrared features to specific local experts separately to achieve dynamic integration of local features under the guidance of multi-modal gating. We concatenate the outputs of MoLE with the dense feature maps as the input to the MoGE. Each expert in MoGE has the ability to decode global features, and a multi-modal gate network is used to dynamic select which experts are activated to decode multi-modal fusion features. The final fused image \\( I_{\\mathcal{F}} \\in \\mathbb{R}^{H \\times W \\times 1} \\) is generated by a weighted" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.371, + 0.811, + 0.384 + ], + "angle": 0, + "content": "sum mechanism of the different global experts." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.386, + 0.892, + 0.469 + ], + "angle": 0, + "content": "The MoE-Fusion is optimized mainly by calculating the pixel loss and gradient loss between the fused image \\( I_{\\mathcal{F}} \\) and two source images \\( (I_{\\mathcal{I}} \\) and \\( I_{\\mathcal{V}} \\)). In addition, we also introduce the load loss to motivate each expert to receive roughly equal numbers of training images. The auxiliary detection networks are optimized independently by the detection loss." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.483, + 0.73, + 0.497 + ], + "angle": 0, + "content": "3.2. Mixture of Local Experts" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.506, + 0.891, + 0.603 + ], + "angle": 0, + "content": "In infrared-visible image fusion tasks, specialized learning of multi-modal local information by a sample adaptive manner helps to overcome the challenge of multi-modal fusion failure in complex scenes. To realize this vision, we need to address two questions: (1) How to find local regions in multi-modal images; (2) How to learn the local features dynamically due to the differences in various samples." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.604, + 0.893, + 0.867 + ], + "angle": 0, + "content": "As shown in Fig. 2 (a), we propose a Mixture of Local Experts (MoLE) to dynamically learning the multi-modal local features. We use the auxiliary detection networks with a spatial attention module to learn the attention maps. Then we can find the local regions in multi-modal images according to the guidance of the learned attention maps. Specifically, we introduce attention modules in two auxiliary detection networks for extracting visible attention maps and infrared attention maps, respectively. The modal-specific attention map \\( Att_{\\mathcal{V}} / Att_{\\mathcal{I}} \\) is generated by the attention module between the feature extractor and the detection head in the detection networks, which consists of a Conv(1 × 1)-BN-ReLU layer and a Conv(1 × 1)-BN-Sigmoid layer. The \\( Att_{\\mathcal{V}} \\) and \\( Att_{\\mathcal{I}} \\) are concatenated and fed into 2 convolutional layers, the maximum of which output is the Att. In MoLE, we multiply the \\( x_{enc}^{\\mathcal{V}} \\) and \\( x_{enc}^{\\mathcal{I}} \\) with Att to obtain \\( x_{local}^{\\mathcal{V}} \\) and \\( x_{local}^{\\mathcal{I}} \\), respectively. Then we concatenate the \\( x_{local}^{\\mathcal{V}} \\) and \\( x_{local}^{\\mathcal{I}} \\) to get the \\( x_{local} \\), which is the input of the multi-modal gating network. The MoLE is consist of" + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "23557" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.125, + 0.177, + 0.176 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.098, + 0.177, + 0.158, + 0.184 + ], + "angle": 0, + "content": "Visible image" + }, + { + "type": "image", + "bbox": [ + 0.178, + 0.126, + 0.275, + 0.176 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.191, + 0.177, + 0.256, + 0.184 + ], + "angle": 0, + "content": "Infrared image" + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.126, + 0.371, + 0.176 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.296, + 0.177, + 0.341, + 0.184 + ], + "angle": 0, + "content": "RFN-Nest" + }, + { + "type": "image", + "bbox": [ + 0.372, + 0.126, + 0.468, + 0.176 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.391, + 0.177, + 0.438, + 0.184 + ], + "angle": 0, + "content": "DenseFuse" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.184, + 0.177, + 0.235 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.119, + 0.236, + 0.143, + 0.242 + ], + "angle": 0, + "content": "AUIF" + }, + { + "type": "image", + "bbox": [ + 0.178, + 0.184, + 0.274, + 0.235 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.207, + 0.236, + 0.248, + 0.243 + ], + "angle": 0, + "content": "DIDFuse" + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.184, + 0.371, + 0.235 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.306, + 0.236, + 0.34, + 0.243 + ], + "angle": 0, + "content": "TarDAL" + }, + { + "type": "image", + "bbox": [ + 0.372, + 0.184, + 0.468, + 0.235 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.395, + 0.236, + 0.442, + 0.243 + ], + "angle": 0, + "content": "PIAFusion" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.244, + 0.177, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.116, + 0.295, + 0.148, + 0.301 + ], + "angle": 0, + "content": "IFCNN" + }, + { + "type": "image", + "bbox": [ + 0.178, + 0.244, + 0.275, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.207, + 0.295, + 0.249, + 0.302 + ], + "angle": 0, + "content": "SwinFuse" + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.244, + 0.371, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.309, + 0.295, + 0.338, + 0.301 + ], + "angle": 0, + "content": "YDTR" + }, + { + "type": "image", + "bbox": [ + 0.372, + 0.244, + 0.468, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.378, + 0.295, + 0.462, + 0.302 + ], + "angle": 0, + "content": "MoE-Fusion (Ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.306, + 0.468, + 0.332 + ], + "angle": 0, + "content": "Figure 3. Qualitative comparisons of various methods on representative images selected from the \\(\\mathbf{M}^3\\mathrm{FD}\\) dataset." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.354, + 0.469, + 0.394 + ], + "angle": 0, + "content": "a multi-modal gating network \\( G_{local} \\) and a set of \\( N \\) expert networks \\( \\{E_1^{local},\\dots,E_N^{local}\\} \\). The structure of each expert network is 2 convolution layers and 1 ReLU layers." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.395, + 0.469, + 0.464 + ], + "angle": 0, + "content": "In MoLE, we flatten the input \\( x_{local} \\in \\mathbb{R}^{H \\times W \\times C} \\) to \\( s_{local} \\in \\mathbb{R}^D \\). The gate network \\( G_{local} \\) takes the vector \\( s_{local} \\) as input and produces the probability of it with respective to \\( N \\) experts. The formalization of the gate network is as follows," + }, + { + "type": "equation", + "bbox": [ + 0.095, + 0.474, + 0.469, + 0.489 + ], + "angle": 0, + "content": "\\[\nG _ {\\text {l o c a l}} \\left(s _ {\\text {l o c a l}}\\right) = \\operatorname {s o f t m a x} \\left(\\operatorname {t o p K} \\left(s _ {\\text {l o c a l}} \\cdot W _ {\\text {l o c a l}}\\right)\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.499, + 0.469, + 0.527 + ], + "angle": 0, + "content": "where \\( W_{local} \\in \\mathbb{R}^{D \\times N} \\) is a learnable weight matrix and the top \\( K \\) outputs are normalized via softmax function." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.528, + 0.469, + 0.63 + ], + "angle": 0, + "content": "To achieve specialized learning of different modalities, we input visible local features \\(x_{local}^{\\nu}\\) into one set of expert networks \\(\\{E_1^{local},\\dots,E_{N / 2}^{local}\\}\\) and infrared local features \\(x_{local}^{\\mathcal{I}}\\) into another set of non-overlapping expert networks \\(\\{E_{(N / 2) + 1}^{local},\\dots,E_N^{local}\\}\\). Each expert network produces its own output \\(E_i^{local}(x_{local}^j)\\). The final output \\(y_{local}\\) of the MoLE is calculated as follows," + }, + { + "type": "equation", + "bbox": [ + 0.132, + 0.64, + 0.469, + 0.676 + ], + "angle": 0, + "content": "\\[\ny _ {l o c a l} = \\sum_ {i = 1} ^ {N} G _ {l o c a l} \\left(s _ {l o c a l}\\right) _ {i} E _ {i} ^ {l o c a l} \\left(x _ {l o c a l} ^ {j}\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.685, + 0.469, + 0.727 + ], + "angle": 0, + "content": "where \\(j\\) represents \\(\\mathcal{I}\\) or \\(\\nu\\). Then we concatenate the \\(y_{local}\\), \\(x_{dense}^{\\mathcal{I}}\\), and \\(x_{dense}^{\\nu}\\) to obtain the global multi-modal fusion feature \\(x_{f}\\)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.735, + 0.316, + 0.75 + ], + "angle": 0, + "content": "3.3. Mixture of Global Experts" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.756, + 0.469, + 0.867 + ], + "angle": 0, + "content": "Traditional image fusion algorithms use the same network structure and parameters to learn the fusion features of different samples. In contrast, we propose the MoGE to dynamically integrate multi-modal global features, which can adaptively adjust its own structure and parameters when dealing with different samples, thus showing superior advantages in terms of model expressiveness and self-adaptability. The main components of the MoGE include a" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.123, + 0.892, + 0.159 + ], + "angle": 0, + "content": "Table 1. Quantitative comparison of our MoE-Fusion with 9 state-of-the-art methods. Bold red indicates the best, Bold blue indicates the second best, and Bold cyan indicates the third best." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.16, + 0.892, + 0.455 + ], + "angle": 0, + "content": "
M3FD Dataset [18]
ENSFSDMIVIFAGSCDQabf
DenseFuse [16]6.41340.03648.59872.95240.65723.07001.50690.3838
RFN-Nest [17]6.92080.03459.29842.93010.78063.16981.54100.3772
IFCNN [48]6.65550.05999.24562.99540.75225.09321.54480.5755
PIAfusion [35]6.81670.070710.12283.83370.84475.65601.30650.5540
DIDFuse [49]6.61160.04209.34092.99550.73823.56681.58750.4342
AUIF [50]6.52330.03998.87592.97930.67963.32241.53140.4124
SwinFuse [40]6.98190.06969.64003.20040.91145.62341.53950.5166
YDTR [36]6.53970.04969.26313.21280.72763.89511.50760.4812
TarDAL [18]7.13470.05289.68203.28530.83474.19981.53340.3858
MoE-Fusion7.00180.071510.14064.19491.00345.67421.54330.6661
FLIR Dataset [44]
ENSFSDMIVIFAGSCDQabf
DenseFuse [16]6.94790.030410.59282.92540.64133.05241.31320.2947
RFN-Nest [17]7.42770.026710.87472.96690.72602.76641.67310.2603
IFCNN [48]7.13670.063810.66682.92630.75676.10811.35210.4894
PIAfusion [35]6.99680.055110.65633.09270.81785.18491.16150.4388
DIDFuse [49]7.27540.067011.63182.50220.66495.88151.49130.3469
AUIF [50]7.28530.046310.21082.88930.70994.44711.58230.3240
SwinFuse [40]7.41630.058210.60772.94040.81045.75871.67390.3751
YDTR [36]6.89480.036410.65713.08200.67493.29931.33790.3333
TarDAL [18]7.48660.058810.69483.02280.76655.19551.31820.3896
MoE-Fusion7.49250.060310.70073.12090.82125.76041.68180.4991
LLVIP Dataset [11]
ENSFSDMIVIFAGSCDQabf
DenseFuse [16]6.83140.04269.38002.67640.68943.26401.21090.3093
RFN-Nest [17]7.14080.03009.71842.50420.72942.78531.46120.2287
IFCNN [48]7.21390.06889.76332.94790.77975.41361.42690.5845
PIAfusion [35]7.39540.07879.73203.36900.88606.08461.53000.5789
DIDFuse [49]6.03720.05507.80742.51370.50543.44741.25740.2436
AUIF [50]6.19470.06367.84182.39660.55333.85881.28400.2764
SwinFuse [40]5.99730.06087.65252.18460.59623.73441.26290.2620
YDTR [36]6.69220.04748.87012.91520.63223.20431.08810.2907
TarDAL [18]7.35040.06479.76763.46550.77694.60941.36070.4431
MoE-Fusion7.35230.08629.86643.10610.92026.13161.78410.5932
" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.481, + 0.892, + 0.551 + ], + "angle": 0, + "content": "global multi-modal gating network \\( G_{global} \\) and a set of \\( N \\) expert networks \\( \\{E_1^{global},\\dots,E_N^{global}\\} \\). In MoGE, we flatten \\( x_{f} \\) to get \\( s_f \\) and feed it into \\( G_{global} \\). The corresponding gating weights of the \\( N \\) expert networks are calculated as follows," + }, + { + "type": "equation", + "bbox": [ + 0.539, + 0.567, + 0.891, + 0.583 + ], + "angle": 0, + "content": "\\[\nG _ {\\text {g l o b a l}} \\left(s _ {f}\\right) = \\operatorname {s o f t m a x} \\left(\\operatorname {t o p} K \\left(s _ {f} \\cdot W _ {\\text {g l o b a l}}\\right)\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.595, + 0.89, + 0.623 + ], + "angle": 0, + "content": "where \\( W_{global} \\) is a learnable weight matrix and the top \\( K \\) outputs are normalized via softmax distribution." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.625, + 0.892, + 0.71 + ], + "angle": 0, + "content": "The structure of each expert network consists of 4 convolution layers. Each expert takes the global multimodal fusion feature \\( x_{f} \\) as input to produce its own output \\( E_{i}^{global}(x_{f}) \\). The final output \\( I_{\\mathcal{F}} \\) of MoGE is the linearly weighted combination of each expert's output with the corresponding gating weights. The formalization is as follows," + }, + { + "type": "equation", + "bbox": [ + 0.577, + 0.725, + 0.891, + 0.762 + ], + "angle": 0, + "content": "\\[\nI _ {\\mathcal {F}} = \\sum_ {i = 1} ^ {N} G _ {\\text {g l o b a l}} \\left(s _ {f}\\right) _ {i} E _ {i} ^ {\\text {g l o b a l}} \\left(x _ {f}\\right). \\tag {4}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.775, + 0.644, + 0.788 + ], + "angle": 0, + "content": "3.4. Loss Function" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.797, + 0.892, + 0.867 + ], + "angle": 0, + "content": "In MoE-Fusion, we use the fusion loss \\(\\mathcal{L}_{fusion}\\) to guide the optimization of the image fusion network, and the auxiliary detection networks are optimized by their respective detection loss [29] (\\(\\mathcal{L}_{det}^{\\mathcal{V}}\\) or \\(\\mathcal{L}_{det}^{\\mathcal{T}}\\)). We end-to-end train the entire framework through these three loss functions. Specif" + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "23558" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.125, + 0.177, + 0.23 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.1, + 0.23, + 0.16, + 0.238 + ], + "angle": 0, + "content": "Visible image" + }, + { + "type": "image", + "bbox": [ + 0.178, + 0.125, + 0.274, + 0.23 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.194, + 0.23, + 0.259, + 0.238 + ], + "angle": 0, + "content": "Infrared image" + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.125, + 0.371, + 0.23 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.299, + 0.23, + 0.345, + 0.238 + ], + "angle": 0, + "content": "RFN-Nest" + }, + { + "type": "image", + "bbox": [ + 0.372, + 0.125, + 0.468, + 0.23 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.394, + 0.23, + 0.443, + 0.238 + ], + "angle": 0, + "content": "DenseFuse" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.24, + 0.178, + 0.343 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.116, + 0.343, + 0.142, + 0.351 + ], + "angle": 0, + "content": "AUF" + }, + { + "type": "image", + "bbox": [ + 0.179, + 0.24, + 0.274, + 0.343 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.205, + 0.343, + 0.247, + 0.351 + ], + "angle": 0, + "content": "DIDFuse" + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.24, + 0.371, + 0.343 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.304, + 0.343, + 0.341, + 0.351 + ], + "angle": 0, + "content": "TarDAL" + }, + { + "type": "image", + "bbox": [ + 0.372, + 0.239, + 0.468, + 0.343 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.394, + 0.343, + 0.442, + 0.351 + ], + "angle": 0, + "content": "PIAFusion" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.353, + 0.177, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.113, + 0.457, + 0.146, + 0.465 + ], + "angle": 0, + "content": "IFCNN" + }, + { + "type": "image", + "bbox": [ + 0.178, + 0.353, + 0.274, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.204, + 0.457, + 0.248, + 0.465 + ], + "angle": 0, + "content": "SwinFuse" + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.353, + 0.371, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.308, + 0.457, + 0.338, + 0.465 + ], + "angle": 0, + "content": "YDTR" + }, + { + "type": "image", + "bbox": [ + 0.372, + 0.353, + 0.468, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.377, + 0.457, + 0.463, + 0.466 + ], + "angle": 0, + "content": "MoE-Fusion (Ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.47, + 0.468, + 0.495 + ], + "angle": 0, + "content": "Figure 4. Qualitative comparisons of various methods on representative images selected from the FLIR dataset." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.519, + 0.382, + 0.533 + ], + "angle": 0, + "content": "ically, the formula of fusion loss is as follows," + }, + { + "type": "equation", + "bbox": [ + 0.148, + 0.546, + 0.469, + 0.561 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {f u s i o n}} = \\mathcal {L} _ {\\text {p i x e l}} + \\alpha \\mathcal {L} _ {\\text {g r a d}} + \\mathcal {L} _ {\\text {l o a d}}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.572, + 0.469, + 0.696 + ], + "angle": 0, + "content": "where the pixel loss \\(\\mathcal{L}_{pixel}\\) constrains the fused image to preserve more significant pixel intensities originating from the target images, while the gradient loss \\(\\mathcal{L}_{grad}\\) forces the fused image to contain more texture details from different modalities. \\(\\mathcal{L}_{load}\\) represents load loss, which encourages experts to receive roughly equal numbers of training examples [32]. More details about pixel loss, gradient loss and load loss are provided in the supplementary material. \\(\\alpha\\) is used to strike a balance between the different loss functions." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.71, + 0.208, + 0.725 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.733, + 0.277, + 0.749 + ], + "angle": 0, + "content": "4.1. Experimental Setting" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.755, + 0.468, + 0.796 + ], + "angle": 0, + "content": "Datasets and Partition Protocol. We conducted experiments on three publicly available datasets: \\((\\mathbf{M}^{3}\\mathrm{FD}\\) [18], LLVIP [11] and FLIR [37])." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.797, + 0.468, + 0.838 + ], + "angle": 0, + "content": "\\(\\mathbf{M}^3\\mathbf{FD}\\): It contains 4,200 infrared-visible image pairs captured by on-board cameras. We used 3,900 pairs of images for training and the remaining 300 pairs for evaluation." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.839, + 0.468, + 0.867 + ], + "angle": 0, + "content": "FLIR: We used the \"aligned\" version [44] of FLIR in this work. It contains 5,142 infrared-visible image pairs" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.127, + 0.89, + 0.154 + ], + "angle": 0, + "content": "captured by on-board cameras. We used 4, 129 image pairs for training and 1, 013 image pairs for evaluation." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.155, + 0.891, + 0.224 + ], + "angle": 0, + "content": "LLVIP: The LLVIP dataset contains 15,488 aligned infrared-visible image pairs, which is captured by the surveillance cameras in different street scenes. We trained the model with 12,025 image pairs and performed evaluation on 3,463 image pairs." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.225, + 0.891, + 0.348 + ], + "angle": 0, + "content": "Competing methods. We compared the 9 state-of-the-art methods on three publicly available datasets \\((\\mathrm{M}^3\\mathrm{FD}\\) [18], LLVIP [11] and FLIR [37]). In these comparison methods, DenseFuse [16] and RFN-Nest [17] are the autoencoder-based methods, PIAFusion [35] and IFCNN [48] are the CNN-based methods, TarDAL [18] is the GAN-based methods. DIDFuse [49] and AUIF [50] are the deep learning-based image decomposition methods. SwinFuse [40] and YDTR [36] are the Transformer-based methods." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.35, + 0.892, + 0.474 + ], + "angle": 0, + "content": "Implementation Details. We performed experiments on a computing platform with two NVIDIA GeForce RTX 3090 GPUs. We used Adam Optimization to update the overall network parameters with the learning rate of \\(1.0 \\times 10^{-4}\\). The auxiliary network Faster R-CNN [29] is also trained along with the image fusion pipeline. The training epoch is set to 24 and the batch size is 4. The tuning parameter \\(\\alpha\\) is set to 10. For MoLE and MoGE, we set the number of experts is 4, and sparsely activate the top 2 experts." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.475, + 0.892, + 0.682 + ], + "angle": 0, + "content": "Evaluation Metrics. We evaluated the performance of the proposed method based on qualitative and quantitative results. The qualitative evaluation is mainly based on the visual effect of the fused image. A good fused image needs to have complementary information of multi-modal images. The quantitative evaluation mainly uses quality evaluation metrics to measure the performance of image fusion. We selected 8 popular metrics, including the entropy (EN) [31], spatial frequency (SF) [4], standard deviation (SD), mutual information (MI) [28], visual information fidelity (VIF) [7], average gradient (AG) [2], the sum of the correlations of differences (SCD) [1], and gradient-based similarity measurement \\((Q_{abf})\\) [43]. We also evaluate the performance of the different methods on the typical downstream task, infrared-visible object detection." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.693, + 0.783, + 0.707 + ], + "angle": 0, + "content": "4.2. Evaluation on the \\(\\mathbf{M}^3\\mathrm{FD}\\) dataset" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.714, + 0.892, + 0.867 + ], + "angle": 0, + "content": "Quantitative Comparisons. Table 1 presents the results of the quantitative evaluation on the \\(\\mathrm{M}^3\\mathrm{FD}\\) dataset, where our method achieves the best in 7 metrics and the second and third best performance in the remaining metrics, respectively. In particular, it shows overwhelming advantages on VIF, MI,and \\(Q_{abf}\\), which indicates that our fusion results contain more valuable information and are more beneficial to the visual perception effect of human eyes. The highest SF, SD and AG also indicate that our fusion results preserve sufficient texture detail and contrast. Such superior performance is attributed to the proposed dynamic learning frame" + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "23559" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.126, + 0.177, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.1, + 0.234, + 0.16, + 0.242 + ], + "angle": 0, + "content": "Visible image" + }, + { + "type": "image", + "bbox": [ + 0.178, + 0.127, + 0.272, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.194, + 0.234, + 0.258, + 0.242 + ], + "angle": 0, + "content": "Infrared image" + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.127, + 0.369, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.299, + 0.234, + 0.344, + 0.242 + ], + "angle": 0, + "content": "RFN-Nest" + }, + { + "type": "image", + "bbox": [ + 0.371, + 0.127, + 0.465, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.393, + 0.234, + 0.441, + 0.242 + ], + "angle": 0, + "content": "DenseFuse" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.244, + 0.177, + 0.35 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.117, + 0.352, + 0.141, + 0.358 + ], + "angle": 0, + "content": "AUE" + }, + { + "type": "image", + "bbox": [ + 0.178, + 0.244, + 0.272, + 0.35 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.205, + 0.352, + 0.246, + 0.359 + ], + "angle": 0, + "content": "DIDFuse" + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.244, + 0.369, + 0.35 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.304, + 0.352, + 0.339, + 0.359 + ], + "angle": 0, + "content": "TarDAL" + }, + { + "type": "image", + "bbox": [ + 0.371, + 0.244, + 0.465, + 0.35 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.394, + 0.352, + 0.441, + 0.359 + ], + "angle": 0, + "content": "PIAFusion" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.361, + 0.177, + 0.467 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.113, + 0.469, + 0.146, + 0.475 + ], + "angle": 0, + "content": "IFCNN" + }, + { + "type": "image", + "bbox": [ + 0.178, + 0.361, + 0.272, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.204, + 0.469, + 0.247, + 0.476 + ], + "angle": 0, + "content": "SwinFuse" + }, + { + "type": "image", + "bbox": [ + 0.275, + 0.361, + 0.368, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.307, + 0.469, + 0.336, + 0.476 + ], + "angle": 0, + "content": "YDTR" + }, + { + "type": "image", + "bbox": [ + 0.371, + 0.361, + 0.465, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.375, + 0.469, + 0.461, + 0.477 + ], + "angle": 0, + "content": "MoE-Fusion (Ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.482, + 0.468, + 0.507 + ], + "angle": 0, + "content": "Figure 5. Qualitative comparisons of various methods on representative images selected from the LLVIP dataset." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.534, + 0.468, + 0.561 + ], + "angle": 0, + "content": "work from local to global, which achieves state-of-the-art fusion performance through the sample adaptive approach." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.562, + 0.469, + 0.866 + ], + "angle": 0, + "content": "Qualitative Comparisons. To better show the superiority of our model, we assigned the color information of the 3-channel visible image to the single-channel fused image through the color space conversion between RGB and YCbCr. We mark the background region with the green rectangular box and the foreground region with the red rectangular box. As shown in Fig. 3, our fusion results have the best results in both local and global regions. Compared to PIAFusion, YDTR, AUIF, IFCNN and DIDFuse, our fusion results show better contrast, and our fusion results show better texture details compared to TarDAL and SwinFuse. In daytime scenes, our model adaptively learned sufficient texture detail and significant contrast, such as containers and people. Especially for people, our method significantly avoids the effect of smoke and preserves the contrast information of infrared. In local regions, we successfully preserve the rich texture information of containers, outperforming other methods. In global regions such as mountains, grass and sky, our fusion results also effectively retain texture information, indicating that our method has better visual effects due to dynamic learning of local and global information of different modalities." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.126, + 0.779, + 0.139 + ], + "angle": 0, + "content": "4.3. Evaluation on the FLIR dataset" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.147, + 0.892, + 0.395 + ], + "angle": 0, + "content": "Quantitative Comparisons. Table 1 reports the performance of the different methods on the FLIR dataset for 8 metrics. Our method achieves the best results in 5 metrics. Among them, the highest EN and MI indicate that our method can preserve abundant information of the multimodal images well. The best performance of our method on SCD and \\( Q_{abf} \\) also indicates that our fusion results can better learn the multi-modal complementary information and edge information, which makes our fusion results have better foreground-background contrast and richer texture details. Moreover, the highest VIF also demonstrates that our method can generate fused images with better visual effects that are beneficial to human observation. In addition, the third best results on SF, SD, and AG also indicate that our method is highly competitive. The quantitative results on the FLIR dataset also validate the superiority of our method in dynamically fusing multi-modal complementary information from the local to the global." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.396, + 0.892, + 0.658 + ], + "angle": 0, + "content": "Qualitative Comparisons. We mark the background region with the green rectangular box and the foreground region with the red rectangular box. We also show their zoomed-in effects for easier comparison. As shown in Fig. 4, our fusion results have the best results in both local and global regions. In night scenes, our fusion results adaptively learn sufficient texture detail and contrast, for example on buildings, trees, mountains and traffic lights. Especially for the traffic lights, our method effectively avoids the effects of glare and best preserves the entire outline of the traffic lights. On the local regions, our fusion results preserve the best contrast information of the pedestrians and the rich detail information of the vehicles. These comparisons illustrate that our method has better visual effects due to the effective dynamic learning of local information from different modalities. The superiority of the proposed MoE-Fusion also reveals that specialized knowledge of multimodal local and global in fusion networks can effectively improve fusion performance." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.666, + 0.788, + 0.679 + ], + "angle": 0, + "content": "4.4. Evaluation on the LLVIP dataset" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.687, + 0.892, + 0.867 + ], + "angle": 0, + "content": "Quantitative Comparisons. The quantitative results of the different methods on the LLVIP dataset are reported in Table 1. Our method outperforms all the compared methods on 6 metrics and achieved the second and third best results on the remaining 2 metrics, respectively. Specifically, the highest SF and AG we achieved indicate that the proposed method preserves richer texture details in the multi-modal images. As well as the highest SD also indicates that our fusion results can contain the highest contrast information between the foreground and the background. SCD and \\( Q_{abf} \\) denote the complementary information and edge information transferred from multi-modal images to fused image, respectively, and our highest results on these two metrics" + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "23560" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.099, + 0.123, + 0.446, + 0.134 + ], + "angle": 0, + "content": "Table 2. Ablation studies on three infrared-visible datasets." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.133, + 0.468, + 0.294 + ], + "angle": 0, + "content": "
M3FD Dataset [18]
ENSFSDMIVIFAGSCDQabf
w/o MoLE6.78560.06929.16362.72140.81005.55091.51530.6535
w/o MoGE6.83510.06959.24912.81380.82615.65211.53460.6375
Att-Local6.86560.06939.18942.73200.82715.58091.51900.6390
MoE-Fusion7.00180.071510.14064.19491.00345.67421.54330.6661
FLIR Dataset [44]
ENSFSDMIVIFAGSCDQabf
w/o MoLE6.90210.058710.28592.36660.53715.69611.09760.3187
w/o MoGE7.31720.054810.66542.92080.77475.25251.66290.4796
Att-Local7.30700.060210.64032.66730.74485.72651.47880.4838
MoE-Fusion7.49250.060310.70073.12090.82125.76041.68180.4991
LLVIP Dataset [11]
ENSFSDMIVIFAGSCDQabf
w/o MoLE6.90770.06619.80902.50390.58124.93581.17390.4732
w/o MoGE7.27400.08479.60342.70670.76215.59601.62600.5110
Att-Local7.25280.08589.54832.71290.85996.10991.63930.5735
MoE-Fusion7.35230.08629.86643.10610.92026.13161.78410.5932
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.319, + 0.468, + 0.416 + ], + "angle": 0, + "content": "indicate that our method can learn more valuable information from multi-modal images. Moreover, the highest VIF also means that our method can generate the most appealing fused images that are more suitable for human vision. These quantitative results demonstrate that the proposed MoE-Fusion can effectively learn multi-modal knowledge and generate informative and appealing fusion results." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.417, + 0.468, + 0.624 + ], + "angle": 0, + "content": "Qualitative Comparisons. We mark the background region with the green rectangular box and the foreground region with the red rectangular box. We also show their zoomed-in effects for easier comparison. As shown in Fig. 5, we can find that the proposed method best preserves the texture details of the local and global in the multi-modal image compared with the state-of-the-art methods, while highlighting the contrast information of the local dynamically. Specifically, for the background region, our fusion results show the sharpest effect on the edge texture of the zebra crossing. For the foreground region, our fusion results preserve the most significant contrast and the richest texture detail in pedestrians and cyclists. Qualitative comparisons show that our MoE-Fusion can balance the texture details and contrasts with the specialized experts dynamically." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.636, + 0.229, + 0.65 + ], + "angle": 0, + "content": "4.5. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.658, + 0.468, + 0.685 + ], + "angle": 0, + "content": "We conducted ablation studies on the \\(\\mathbf{M}^3\\mathrm{FD}\\), LLVIP, and FLIR datasets and reported the results in Table 2." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.687, + 0.468, + 0.866 + ], + "angle": 0, + "content": "MoLE. To verify the effectiveness of MoLE, we removed MoLE from MoE-Fusion and then extracted multi-modal features by two encoders only, and they were sent to MoGE after concatenation. As shown in Table 2, all the metrics show a significant decrease after removing MoLE, indicating that MoLE is very effective in learning multi-modal texture details and contrast information. Among others, the decrease on SCD also shows it is difficult to learn complementary multi-modal local information sufficiently without MoLE, which strongly supports our motivation to design MoLE. The local dynamic experts of MoLE adaptively boost dominant local (foreground and background) information induced from the auxiliary detector of different" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.125, + 0.603, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.521, + 0.181, + 0.584, + 0.19 + ], + "angle": 0, + "content": "Visible image" + }, + { + "type": "image", + "bbox": [ + 0.603, + 0.125, + 0.696, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.616, + 0.181, + 0.682, + 0.19 + ], + "angle": 0, + "content": "Infrared image" + }, + { + "type": "image", + "bbox": [ + 0.697, + 0.125, + 0.793, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.713, + 0.181, + 0.78, + 0.189 + ], + "angle": 0, + "content": "Fusion Feature" + }, + { + "type": "image", + "bbox": [ + 0.794, + 0.125, + 0.89, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.812, + 0.181, + 0.871, + 0.189 + ], + "angle": 0, + "content": "Fusion result" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.191, + 0.601, + 0.246 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.522, + 0.247, + 0.583, + 0.256 + ], + "angle": 0, + "content": "FG Expert #1" + }, + { + "type": "image", + "bbox": [ + 0.601, + 0.191, + 0.696, + 0.246 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.617, + 0.247, + 0.678, + 0.257 + ], + "angle": 0, + "content": "FG Expert #2" + }, + { + "type": "image", + "bbox": [ + 0.697, + 0.191, + 0.793, + 0.246 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.714, + 0.247, + 0.775, + 0.257 + ], + "angle": 0, + "content": "FG Expert #3" + }, + { + "type": "image", + "bbox": [ + 0.794, + 0.191, + 0.89, + 0.246 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.81, + 0.247, + 0.874, + 0.257 + ], + "angle": 0, + "content": "FG Expert # 4" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.259, + 0.601, + 0.313 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.521, + 0.314, + 0.583, + 0.323 + ], + "angle": 0, + "content": "BG Expert #1" + }, + { + "type": "image", + "bbox": [ + 0.601, + 0.26, + 0.696, + 0.313 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.617, + 0.314, + 0.678, + 0.323 + ], + "angle": 0, + "content": "BG Expert #2" + }, + { + "type": "image", + "bbox": [ + 0.697, + 0.26, + 0.793, + 0.313 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.714, + 0.314, + 0.776, + 0.323 + ], + "angle": 0, + "content": "BG Expert #3" + }, + { + "type": "image", + "bbox": [ + 0.794, + 0.26, + 0.89, + 0.313 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.81, + 0.314, + 0.875, + 0.323 + ], + "angle": 0, + "content": "BG Expert # 4" + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.327, + 0.892, + 0.353 + ], + "angle": 0, + "content": "Figure 6. Visualization of the features learned by each expert in MoLE. FG denotes foreground, BG denotes background." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.377, + 0.892, + 0.57 + ], + "angle": 0, + "content": "modalities for dynamic fusion, specialized to local regions. MoGE. We replaced the MoGE with a common decoder with the same structure as that of a single expert in the MoGE. As shown in Table 2, all the metrics appear to be significantly decreased, strongly verifying that the MoGE can help fused images preserve more contrast and texture detail information. Moreover, these results also demonstrate that MoGE can effectively motivate the image fusion network to dynamically adapt to different samples, learning better feature representations, and thus achieving better fusion performance. The global dynamic experts of MoGE further enhance the dominant modality from a global perspective while refining the potential errors that may occur in local fusion." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.571, + 0.892, + 0.765 + ], + "angle": 0, + "content": "Attention-based Local Feature. We want to explore how the fusion performance changes when dynamic learning is not performed for local features and only local feature priors constructed by attention maps are used as local features. We designed an attention-based local feature learning module (Att-Local), and to keep the output channels consistent, we followed the Att-Local module with a \\(1 \\times 1\\) convolution layers. In Table 2, all metrics cannot exceed the results of MoE-Fusion with the use of Att-Local, but most of them are higher than w/o MoLE, which demonstrates on the one hand that our proposed MoLE is indeed effective, and on the other hand that the dynamic integration of the effective information from the respective modalities is beneficial to improve the performance of multi-modal image fusion." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.776, + 0.72, + 0.79 + ], + "angle": 0, + "content": "4.6. Analysis and Discussion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.797, + 0.892, + 0.867 + ], + "angle": 0, + "content": "Visualization of MoLE. In the MoLE, we can obtain local feature priors according to the attention map Att, which we define as foreground local features (FG), and we also use \\(1 - \\text{Att}\\) to obtain background local features (BG). We visualize what each expert has learned in MoLE. As shown" + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.503, + 0.898 + ], + "angle": 0, + "content": "23561" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.123, + 0.172, + 0.188 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.178, + 0.123, + 0.27, + 0.187 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.123, + 0.369, + 0.187 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.377, + 0.123, + 0.468, + 0.187 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.08, + 0.192, + 0.172, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.178, + 0.192, + 0.27, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.277, + 0.192, + 0.369, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.376, + 0.192, + 0.468, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.128, + 0.26, + 0.416, + 0.273 + ], + "angle": 0, + "content": "Figure 7. Experiments on the number of experts." + }, + { + "type": "table_caption", + "bbox": [ + 0.104, + 0.286, + 0.442, + 0.298 + ], + "angle": 0, + "content": "Table 3. Object detection evaluation on the FLIR dataset." + }, + { + "type": "table", + "bbox": [ + 0.106, + 0.298, + 0.442, + 0.478 + ], + "angle": 0, + "content": "
MethodscarpersonbicyclemAP
Visible55.9027.2033.2038.70
Infrared68.7045.6030.8048.40
DenseFuse [16]65.8044.7031.4047.30
RFN-Nest [17]58.8036.5026.2040.50
IFCNN [48]67.8045.7034.7049.40
PIAFusion [35]62.6040.9031.5045.00
DIDFuse [49]64.2041.7032.1046.00
AUIF [50]61.7036.8029.6042.70
SwinFuse [40]65.6041.3029.7045.60
YDTR [36]65.0044.2032.5047.20
TarDAL [18]62.5035.4030.8042.90
MoE-Fusion72.9055.0039.5055.80
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.504, + 0.47, + 0.573 + ], + "angle": 0, + "content": "in Fig. 6, we see that the four foreground local experts can clearly learn foreground information, while the four background local experts can also learn rich background features. These results show that MoLE can successfully let each expert know what it should specialize in." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.575, + 0.469, + 0.824 + ], + "angle": 0, + "content": "Detection Evaluation. Good fused images should have better performance in downstream tasks. For different image fusion methods, we perform the evaluation on the object detection task and use the mean average precision (mAP) [5] as the metric. Following [51], we first train the object detection model using infrared images and visible images, and then we input the fused images generated by different image fusion methods into the object detection model for inference and evaluate their detection performance. In this paper, we use Faster R-CNN [29] as the object detection algorithm and set the IoU (Intersection over Union) threshold for evaluation to 0.5. According to Table 3, our MoE-Fusion outperforms all the compared methods and achieves the highest mAP. It is worth noting that our method has an overwhelming advantage on all categories, which demonstrate the proposed dynamic image fusion method is more beneficial for downstream tasks. The detection evaluation on other datasets is provided in the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.867 + ], + "angle": 0, + "content": "Number of Experts. In Fig. 7, we performed 4 sets of experiments on the FLIR dataset, E2k2, E4K2, E6K2, and E8K2, to explore the effect of the number of experts on the" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.123, + 0.59, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.603, + 0.124, + 0.688, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.701, + 0.124, + 0.785, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.799, + 0.124, + 0.884, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.192, + 0.59, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.603, + 0.192, + 0.688, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.701, + 0.192, + 0.785, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.799, + 0.192, + 0.884, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.258, + 0.892, + 0.271 + ], + "angle": 0, + "content": "Figure 8. Hyperparameter sensitivity analysis on the FLIR dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.301, + 0.892, + 0.454 + ], + "angle": 0, + "content": "fusion results. As an example, E4K2 means that the MoE contains 4 experts and sparsely selects top 2 experts for integration. We found that E4K2 was higher than E2K2 in 7 metrics, E6K2 in 6 metrics, and E8K2 in 5 metrics, suggesting that a higher number of experts may not be better. In addition, we also set up 3 sets of experiments, E4K1, E4K3 and E4K4, to verify the effect of sparse selection of experts in MoE on the fusion results. In Fig. 7, we find that E4K2 can outperform E4K1 and E4K3 in 7 metrics and E4K4 in all metrics. Therefore, in this work, we set 4 experts for each MoE and sparsely select 2 experts for integration." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.457, + 0.893, + 0.567 + ], + "angle": 0, + "content": "Hyperparameter. As shown in Fig. 8, we choose five values for tuning parameter \\(\\alpha\\) (1, 5, 10, 20, and 40) and experiment with them in turn. When \\(\\alpha\\) is less than 10, the fusion results fail to exceed the performance on all metrics with \\(\\alpha\\) equal to 10. When \\(\\alpha\\) is greater than 10, there is an improvement in only 2 metrics (SF and AG) compared to \\(\\alpha\\) equal to 10, but the other 6 metrics show a decrease. Therefore, in this work, we set \\(\\alpha\\) to 10 to obtain better results." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.591, + 0.618, + 0.605 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.618, + 0.892, + 0.867 + ], + "angle": 0, + "content": "In this paper, we propose a novel dynamic image fusion framework with a multi-modal gated mixture of locally-global experts (MoE-Fusion), which can produce reliable infrared-visible image fusion results. Our framework focuses on dynamically integrating effective information from different source modalities by performing sample-adaptive infrared-visible fusion from local to global. The MoE-Fusion model dynamically balances the texture details and contrasts with the specialized local experts and global experts. The experimental results on three challenging datasets demonstrate that the proposed MoE-Fusion outperforms state-of-the-art methods in terms of visual effects and quantitative metrics. Moreover, we also validate the superiority of our MoE-Fusion in the object detection task. In future work, we will explore leveraging the uncertainty of different images to guide the fusion, and investigate developing an uncertainty-gated MoE paradigm for dynamic image fusion." + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "23562" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.079, + 0.125, + 0.236, + 0.141 + ], + "angle": 0, + "content": "Acknowledgments" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.149, + 0.47, + 0.244 + ], + "angle": 0, + "content": "This work was supported in part by the National Key R&D Program of China 2022ZD0116500, in part by the National Natural Science Foundation of China under Grant 62222608, 62106171, and 61925602, in part by the Haihe Lab of ITAI under Grant 22HHXCJC00002, and in part by the Tianjin Natural Science Foundation under Grant 21JCYBJC00580." + }, + { + "type": "title", + "bbox": [ + 0.08, + 0.259, + 0.173, + 0.273 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.282, + 0.47, + 0.332 + ], + "angle": 0, + "content": "[1] V Aslantas and Emre Bendes. 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NeurIPS, 2022." + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.128, + 0.892, + 0.862 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.888, + 0.505, + 0.898 + ], + "angle": 0, + "content": "23564" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/6e316164-78c4-4054-8879-22d243fd30bc_origin.pdf b/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/6e316164-78c4-4054-8879-22d243fd30bc_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..37b042ec1d5fe0a22f54b5d66f33f213fdedcb59 --- /dev/null +++ b/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/6e316164-78c4-4054-8879-22d243fd30bc_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:d27ffd170101a6caee86f91904f662b31fd84ef08a84a29389f4fc456372ac9e +size 5851154 diff --git a/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/full.md b/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/full.md new file mode 100644 index 0000000000000000000000000000000000000000..9c432bc4ec170b40c231ce8c72f11ec3d05c5fd2 --- /dev/null +++ b/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/full.md @@ -0,0 +1,463 @@ +# Multi-modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion + +Bing Cao*, Yiming Sun*; Pengfei Zhu†; Qinghua Hu + +Tianjin Key Lab of Machine Learning, College of Intelligence and Computing, Tianjin University, China +Haihe Laboratory of Information Technology Application Innovation, China + +{caobing,sunyiming1895,zhupengfei,huqinghua}@tju.edu.cn + +# Abstract + +Infrared and visible image fusion aims to integrate comprehensive information from multiple sources to achieve superior performances on various practical tasks, such as detection, over that of a single modality. However, most existing methods directly combined the texture details and object contrast of different modalities, ignoring the dynamic changes in reality, which diminishes the visible texture in good lighting conditions and the infrared contrast in low lighting conditions. To fill this gap, we propose a dynamic image fusion framework with a multi-modal gated mixture of local-to-global experts, termed MoE-Fusion, to dynamically extract effective and comprehensive information from the respective modalities. Our model consists of a Mixture of Local Experts (MoLE) and a Mixture of Global Experts (MoGE) guided by a multi-modal gate. The MoLE performs specialized learning of multi-modal local features, prompting the fused images to retain the local information in a sample-adaptive manner, while the MoGE focuses on the global information that complements the fused image with overall texture detail and contrast. Extensive experiments show that our MoE-Fusion outperforms state-of-the-art methods in preserving multi-modal image texture and contrast through the local-to-global dynamic learning paradigm, and also achieves superior performance on detection tasks. Our code is available: https://github.com/SunYM2020/MoE-Fusion. + +# 1. Introduction + +Infrared and visible image fusion focus on generating appealing and informative fused images that enable superior performance in practical downstream tasks over that of using single modality alone [24, 45, 41, 21]. In recent years, infrared-visible image fusion has been widely used + +![](images/0b5d17b7a2825f752da3b7202735e6b72ba60b7e69ce4e53e8d450517bb81eea.jpg) +Visible image + +![](images/f64abab0c497c8006b16841a3fbc8bb8998cc17578cbf715be93d73371b511a3.jpg) +Infrared image + +![](images/f6de8f6583bd4695f646a763e1ae74a6f1975f78deeaa83543536fc8b35bff7b.jpg) +DF (IEEE TIP'19) + +![](images/e4e2c8207de2da83d13686fbebb3d079af12315737998f4e52be0c6d1eaae9c8.jpg) +DIDF (IJCAI'20) +Figure 1. The importance of dynamic image fusion. In the SOTA methods (DF [16], DIDF [49], and TDL [18]), the texture details of objects (e.g., car, truck, and traffic sign) in the fused image are suppressed by the contrast of infrared image, leading to terrible detection results. Benefiting from the dynamic fusion, our method can preserve clear texture details without being interrupted by unsuitable contrast, achieving the best performance. + +![](images/39c39590ad33fc78280bc05df289c3228c5899acb48a387a4fa730613f9c02d2.jpg) +TDL (CVPR'22) + +![](images/701b980a9afc580b032828191bb4a52e7303e239e2ca3e259f071362907aa5a4.jpg) +MoE-Fusion (Ours) + +in many applications, such as autonomous vehicles [9] and unmanned aerial vehicles [34]. According to the thermal infrared imaging mechanism, infrared images can be adapted to various lighting conditions but has the disadvantage of few texture details [25, 50, 19]. By contrast, visible images contain rich texture detail information, but cannot provide clear information in low light conditions. Therefore, how to design advanced fusion methods such that the fused images preserve sufficient texture details and valuable thermal information has attracted a lot of research attention. + +Existing infrared-visible fusion methods [46, 38, 33, 42] can be mainly categorized to traditional approaches (image decomposition [15], sparse representation [47], etc.) and deep learning-based approaches (autoencoder based methods [16, 49, 17], generative adversarial network based + +approaches [18, 26], transformer based approaches [40, 36], etc.). However, most of these methods directly combined the texture details and object contrast of different modalities, ignoring the dynamic changes in reality, leading to poor fusion results and even weaker downstream task performance than that of a single modality. As shown in Fig. 1, the infrared image should adaptively enhance cars in dim light while avoiding compromising the textural detail of truck in bright light. However, the object textures in these state-of-the-art fusion methods are significantly disturbed by the infrared thermal information due to the lack of dynamic learning of multi-modal local and global information, resulting in terrible object detection performance. + +In complex scenes, different modalities have different characteristics: under good lighting conditions, the texture of an object should not be disturbed by thermal infrared information; under low lighting conditions, the contrast of an object also should not be suppressed by the darkness of the visible image. Most existing methods perform image fusion in a fixed correlation paradigm, ignoring the dominant modality changes dynamically in reality, and often fall into domain bias. To break the traditional fixed fusion paradigm, we pioneered sample-adaptive local-to-global experts to dynamically enhance the dominant modality for image fusion. Fig. 1 show that the proposed method not only eliminates domain bias but also achieves sample-adaptive dynamic fusion, yielding the best detection results. Specifically, we propose a dynamic image fusion framework with a multi-modal gated mixture of local-to-global experts, termed MoE-Fusion, which consists of a Mixture of Local Experts (MoLE) and a Mixture of Global Experts (MoGE) guided by a multi-modal gate. In MoLE, we introduce the attention map generated by an auxiliary network to construct multi-modal local priors and perform dynamic learning of multi-modal local features guided by multimodal gating, achieving sample-adaptive multi-modal local feature fusion. Moreover, MoGE performs dynamic learning of multi-modal global features to achieve a balance of texture details and contrasts globally in the fused images. With the proposed dynamic fusion paradigm from local to global, our model is capable of performing a reliable fusion of different modal images. + +We summarize our main contributions as follows: + +- We propose a dynamic image fusion model, providing a new multi-modal gated mixture of local-to-global experts for reliable infrared and visible image fusion (benefiting from the dynamically integrating effective information from the respective modalities). +- The proposed model is an effective and robust framework for sample-adaptive infrared-visible fusion from local to global. Further, it prompts the fused images to dynamically balance the texture details and contrasts. + +- We conduct extensive experiments on multiple infrared-visible datasets, which clearly validate our superiority, quantitatively and qualitatively. Moreover, we also demonstrate our effectiveness in object detection. + +# 2. Related Works + +# 2.1. Infrared and Visible Image Fusion + +The infrared and visible image fusion task focuses on generating a fused image containing sufficient information through the learning of multi-modal features [24, 45, 20, 22, 12, 8]. Ma et al. [23] defined the goal of image fusion as preserving more intensity information in infrared images as well as gradient information in visible images. Li et al. [16] use the autoencoder to extract multi-modal overall features and fuse them by designed fusion rules, which inspired a series of subsequent works [14, 17]. Zhao et al. [49, 50] proposed the deep learning-based image decomposition methods, which decompose images into background and detail images by high- and low-frequency information, respectively, and then fuse them by designed fusion rules. Recently, some GAN-based methods [26, 25, 18] and Transformer-based methods [40, 36] have also attracted wide attention. These works, despite the different approaches adopted, all focus on learning on the representation of the overall multi-modal features. However, they ignore the dynamic changes in reality, which diminishes the visible texture in good lighting conditions and the infrared contrast in low lighting conditions. We propose a dynamic image fusion framework that enables sample-adaptive fusion from local to global. This approach prompts the fused images to balance the texture details and contrast with specialized experts dynamically. + +# 2.2. Mixture-of-Experts + +Mixture-of-Experts (MoE) [10, 30, 27] can dynamically adjust its structure according to different inputs. Shazeer et al. [32] constructed a sparsely-gated MoE layer that uses a gate network to select multiple experts and assign weights to each selected expert. The final result of the MoE is a weighted sum of the outputs of the different experts. This work also serves as the basis for subsequent research. Recently, some researchers [13, 27] have focused on exploring learning mechanisms in MoE, trying to solve the problems of unbalanced expert load and the number of activated experts faced by MoE during training. Other researchers [6, 52, 3, 39] focuses on the combination of MoE and Transformer. They expect to use MoE to build sparse models. Zhu et al. [52] introduced Conditional MoE into the generalist model and proposed different routing strategies to mitigate the interference between tasks and modalities. Existing MoE-related methods focus on modeling + +![](images/905586731212f212619fd3abf50674b87333b3eee8ee946daa4859b8bb942c12.jpg) +(a) + +![](images/02f3373c793f4046f9a0cb5f730dc45a8ba2b06713a03828dd325c59c88cc4f8.jpg) +(b) + +![](images/4f5c3fd9f8c873e844d46a221d0de910714c17851e1a52f9a6b9224e07a951fd.jpg) +Figure 2. The architecture of MoE-Fusion. MoE-Fusion consists of a Mixture of Local Experts (MoLE), a Mixture of Global Experts (MoGE) guided by the multi-modal gate, a set of infrared and visible feature encoders, and the auxiliary network. + +generic knowledge by using the dynamicity and sparsity of MoE, resulting in each expert does not know what they should be expert in. In contrast, we extend the idea of MoE to image fusion tasks for the first time, constructing a multimodal gated mixture of local-to-global experts, assigning specific tasks to each expert, and enabling sample-adaptive specialized learning, which yields superior performance. + +# 3. Method + +# 3.1. Overall Architecture + +In this paper, we propose a dynamic image fusion framework with a multi-modal gated mixture of local-to-global experts, termed MoE-Fusion. In Fig. 2, MoE-Fusion contains two encoders, a Mixture of Local Experts, a Mixture of Global Experts, and the auxiliary network. + +In Fig. 2 (b), we send a pair of infrared image $I_{\mathcal{I}} \in \mathbb{R}^{H \times W \times 1}$ and visible image $I_{\mathcal{V}} \in \mathbb{R}^{H \times W \times 3}$ into the infrared and visible encoders ( $Enc_{\mathcal{I}}$ and $Enc_{\mathcal{V}}$ ) to extract the features, respectively. The structure of encoders follows [16]. The output of the encoder has two parts: the feature maps of the last layer ( $x_{enc}^{\mathcal{I}}$ and $x_{enc}^{\mathcal{V}}$ ) and the dense feature maps ( $x_{dense}^{\mathcal{I}}$ and $x_{dense}^{\mathcal{V}}$ ). More details of the structure are provided in the supplementary material. We send the $x_{enc}^{\mathcal{I}}$ and $x_{enc}^{\mathcal{V}}$ to the MoLE along with the attention map which is learning from the auxiliary network. In this paper, we use Faster-RCNN [29] as the auxiliary network. In MoLE, we send visible and infrared features to specific local experts separately to achieve dynamic integration of local features under the guidance of multi-modal gating. We concatenate the outputs of MoLE with the dense feature maps as the input to the MoGE. Each expert in MoGE has the ability to decode global features, and a multi-modal gate network is used to dynamic select which experts are activated to decode multi-modal fusion features. The final fused image $I_{\mathcal{F}} \in \mathbb{R}^{H \times W \times 1}$ is generated by a weighted + +sum mechanism of the different global experts. + +The MoE-Fusion is optimized mainly by calculating the pixel loss and gradient loss between the fused image $I_{\mathcal{F}}$ and two source images $(I_{\mathcal{I}}$ and $I_{\mathcal{V}}$ ). In addition, we also introduce the load loss to motivate each expert to receive roughly equal numbers of training images. The auxiliary detection networks are optimized independently by the detection loss. + +# 3.2. Mixture of Local Experts + +In infrared-visible image fusion tasks, specialized learning of multi-modal local information by a sample adaptive manner helps to overcome the challenge of multi-modal fusion failure in complex scenes. To realize this vision, we need to address two questions: (1) How to find local regions in multi-modal images; (2) How to learn the local features dynamically due to the differences in various samples. + +As shown in Fig. 2 (a), we propose a Mixture of Local Experts (MoLE) to dynamically learning the multi-modal local features. We use the auxiliary detection networks with a spatial attention module to learn the attention maps. Then we can find the local regions in multi-modal images according to the guidance of the learned attention maps. Specifically, we introduce attention modules in two auxiliary detection networks for extracting visible attention maps and infrared attention maps, respectively. The modal-specific attention map $Att_{\mathcal{V}} / Att_{\mathcal{I}}$ is generated by the attention module between the feature extractor and the detection head in the detection networks, which consists of a Conv(1 × 1)-BN-ReLU layer and a Conv(1 × 1)-BN-Sigmoid layer. The $Att_{\mathcal{V}}$ and $Att_{\mathcal{I}}$ are concatenated and fed into 2 convolutional layers, the maximum of which output is the Att. In MoLE, we multiply the $x_{enc}^{\mathcal{V}}$ and $x_{enc}^{\mathcal{I}}$ with Att to obtain $x_{local}^{\mathcal{V}}$ and $x_{local}^{\mathcal{I}}$ , respectively. Then we concatenate the $x_{local}^{\mathcal{V}}$ and $x_{local}^{\mathcal{I}}$ to get the $x_{local}$ , which is the input of the multi-modal gating network. The MoLE is consist of + +![](images/e024336abe7041ca2000ffec0dd36a96f5d1ada233c745e65338dc2e6596d829.jpg) + +![](images/76d10daf4c8b2ee9279662f7fc9b09f49e016e19f08cb76c07fb6d2020486775.jpg) + +![](images/86cadb6249db4f301535eac120c746748ee27185f54ad79aa2178d95ad8d3e8e.jpg) + +![](images/820bec065e86d5b899f7ad3a1b22c231bb0f040d5b3e0bfa8712957acc3d7055.jpg) + +![](images/2227b3b768393f1a08e79cb69e511e4e7d9467dac2c59117a16a4e7984d8e156.jpg) +Visible image +AUIF + +![](images/e2872cc0151a3eec46671deebfc5d9a856e9c4a4f7d1d0347708763223997131.jpg) +Infrared image +DIDFuse + +![](images/27051783c5af4fd81bd822796b25f2a2ffbc11c52e7abbf212bebcd2a46da534.jpg) +RFN-Nest +TarDAL + +![](images/7f981afba8b36e17b1a99895defd181fdcbda430bfee899356b1897741317ae6.jpg) +DenseFuse +PIAFusion + +![](images/d1fb650c9076d004457cf777c6bf884a49dbbc6ba24a81b77ddd0498684319b3.jpg) +IFCNN +Figure 3. Qualitative comparisons of various methods on representative images selected from the $\mathbf{M}^3\mathrm{FD}$ dataset. + +![](images/3a51d82871ea82212aadff8c74add6a53f0fb5b0504a02a2d457f32cb96e3c84.jpg) +SwinFuse + +![](images/12bb8bea6cd9cc7924aee48d8d0bc58dfa4821f6fe407a5ab960db8d16022812.jpg) +YDTR + +![](images/18ea2312da937e0ab865cfa4af58a6d2ac61948451bfe0eb01c52e97c15b646d.jpg) +MoE-Fusion (Ours) + +a multi-modal gating network $G_{local}$ and a set of $N$ expert networks $\{E_1^{local},\dots,E_N^{local}\}$ . The structure of each expert network is 2 convolution layers and 1 ReLU layers. + +In MoLE, we flatten the input $x_{local} \in \mathbb{R}^{H \times W \times C}$ to $s_{local} \in \mathbb{R}^D$ . The gate network $G_{local}$ takes the vector $s_{local}$ as input and produces the probability of it with respective to $N$ experts. The formalization of the gate network is as follows, + +$$ +G _ {\text {l o c a l}} \left(s _ {\text {l o c a l}}\right) = \operatorname {s o f t m a x} \left(\operatorname {t o p K} \left(s _ {\text {l o c a l}} \cdot W _ {\text {l o c a l}}\right)\right), \tag {1} +$$ + +where $W_{local} \in \mathbb{R}^{D \times N}$ is a learnable weight matrix and the top $K$ outputs are normalized via softmax function. + +To achieve specialized learning of different modalities, we input visible local features $x_{local}^{\nu}$ into one set of expert networks $\{E_1^{local},\dots,E_{N / 2}^{local}\}$ and infrared local features $x_{local}^{\mathcal{I}}$ into another set of non-overlapping expert networks $\{E_{(N / 2) + 1}^{local},\dots,E_N^{local}\}$ . Each expert network produces its own output $E_i^{local}(x_{local}^j)$ . The final output $y_{local}$ of the MoLE is calculated as follows, + +$$ +y _ {l o c a l} = \sum_ {i = 1} ^ {N} G _ {l o c a l} \left(s _ {l o c a l}\right) _ {i} E _ {i} ^ {l o c a l} \left(x _ {l o c a l} ^ {j}\right), \tag {2} +$$ + +where $j$ represents $\mathcal{I}$ or $\nu$ . Then we concatenate the $y_{local}$ , $x_{dense}^{\mathcal{I}}$ , and $x_{dense}^{\nu}$ to obtain the global multi-modal fusion feature $x_{f}$ . + +# 3.3. Mixture of Global Experts + +Traditional image fusion algorithms use the same network structure and parameters to learn the fusion features of different samples. In contrast, we propose the MoGE to dynamically integrate multi-modal global features, which can adaptively adjust its own structure and parameters when dealing with different samples, thus showing superior advantages in terms of model expressiveness and self-adaptability. The main components of the MoGE include a + +Table 1. Quantitative comparison of our MoE-Fusion with 9 state-of-the-art methods. Bold red indicates the best, Bold blue indicates the second best, and Bold cyan indicates the third best. + +
M3FD Dataset [18]
ENSFSDMIVIFAGSCDQabf
DenseFuse [16]6.41340.03648.59872.95240.65723.07001.50690.3838
RFN-Nest [17]6.92080.03459.29842.93010.78063.16981.54100.3772
IFCNN [48]6.65550.05999.24562.99540.75225.09321.54480.5755
PIAfusion [35]6.81670.070710.12283.83370.84475.65601.30650.5540
DIDFuse [49]6.61160.04209.34092.99550.73823.56681.58750.4342
AUIF [50]6.52330.03998.87592.97930.67963.32241.53140.4124
SwinFuse [40]6.98190.06969.64003.20040.91145.62341.53950.5166
YDTR [36]6.53970.04969.26313.21280.72763.89511.50760.4812
TarDAL [18]7.13470.05289.68203.28530.83474.19981.53340.3858
MoE-Fusion7.00180.071510.14064.19491.00345.67421.54330.6661
FLIR Dataset [44]
ENSFSDMIVIFAGSCDQabf
DenseFuse [16]6.94790.030410.59282.92540.64133.05241.31320.2947
RFN-Nest [17]7.42770.026710.87472.96690.72602.76641.67310.2603
IFCNN [48]7.13670.063810.66682.92630.75676.10811.35210.4894
PIAfusion [35]6.99680.055110.65633.09270.81785.18491.16150.4388
DIDFuse [49]7.27540.067011.63182.50220.66495.88151.49130.3469
AUIF [50]7.28530.046310.21082.88930.70994.44711.58230.3240
SwinFuse [40]7.41630.058210.60772.94040.81045.75871.67390.3751
YDTR [36]6.89480.036410.65713.08200.67493.29931.33790.3333
TarDAL [18]7.48660.058810.69483.02280.76655.19551.31820.3896
MoE-Fusion7.49250.060310.70073.12090.82125.76041.68180.4991
LLVIP Dataset [11]
ENSFSDMIVIFAGSCDQabf
DenseFuse [16]6.83140.04269.38002.67640.68943.26401.21090.3093
RFN-Nest [17]7.14080.03009.71842.50420.72942.78531.46120.2287
IFCNN [48]7.21390.06889.76332.94790.77975.41361.42690.5845
PIAfusion [35]7.39540.07879.73203.36900.88606.08461.53000.5789
DIDFuse [49]6.03720.05507.80742.51370.50543.44741.25740.2436
AUIF [50]6.19470.06367.84182.39660.55333.85881.28400.2764
SwinFuse [40]5.99730.06087.65252.18460.59623.73441.26290.2620
YDTR [36]6.69220.04748.87012.91520.63223.20431.08810.2907
TarDAL [18]7.35040.06479.76763.46550.77694.60941.36070.4431
MoE-Fusion7.35230.08629.86643.10610.92026.13161.78410.5932
+ +global multi-modal gating network $G_{global}$ and a set of $N$ expert networks $\{E_1^{global},\dots,E_N^{global}\}$ . In MoGE, we flatten $x_{f}$ to get $s_f$ and feed it into $G_{global}$ . The corresponding gating weights of the $N$ expert networks are calculated as follows, + +$$ +G _ {\text {g l o b a l}} \left(s _ {f}\right) = \operatorname {s o f t m a x} \left(\operatorname {t o p} K \left(s _ {f} \cdot W _ {\text {g l o b a l}}\right)\right), \tag {3} +$$ + +where $W_{global}$ is a learnable weight matrix and the top $K$ outputs are normalized via softmax distribution. + +The structure of each expert network consists of 4 convolution layers. Each expert takes the global multimodal fusion feature $x_{f}$ as input to produce its own output $E_{i}^{global}(x_{f})$ . The final output $I_{\mathcal{F}}$ of MoGE is the linearly weighted combination of each expert's output with the corresponding gating weights. The formalization is as follows, + +$$ +I _ {\mathcal {F}} = \sum_ {i = 1} ^ {N} G _ {\text {g l o b a l}} \left(s _ {f}\right) _ {i} E _ {i} ^ {\text {g l o b a l}} \left(x _ {f}\right). \tag {4} +$$ + +# 3.4. Loss Function + +In MoE-Fusion, we use the fusion loss $\mathcal{L}_{fusion}$ to guide the optimization of the image fusion network, and the auxiliary detection networks are optimized by their respective detection loss [29] ( $\mathcal{L}_{det}^{\mathcal{V}}$ or $\mathcal{L}_{det}^{\mathcal{T}}$ ). We end-to-end train the entire framework through these three loss functions. Specif + +![](images/625c14882b44f3347339224615551ede477a1003434541f35e034c05062fba81.jpg) +Visible image + +![](images/c3a35f3d2b785c0c52edbeb898803df6c6a6242414a985510bc47466c04c9fcf.jpg) +Infrared image + +![](images/95769e906d42b575b185de5449ddd516141bba192e3909568819fda98cecd20a.jpg) +RFN-Nest + +![](images/63153df40f90e3d439510360daa582c179fa57c0b4fc18b8bb6218f2eb57a673.jpg) +DenseFuse + +![](images/378d11e9483a0ec7bcb76e2d7de90c00863d0edc00ce5cb9bc90be90aacb034b.jpg) +AUF + +![](images/d3817e68f204d08c13b8e1c73175f0ccffbda2fea975042766e9f7182881b2c5.jpg) +DIDFuse + +![](images/955cf0fe17023b0c1c11f978f254579076a4c436700acd4ef7f84a4f101861d3.jpg) +TarDAL + +![](images/6a0e9e2cfacb7bc195a4440facb8c4c04f31027d8567b83eeaab5eacd88d18f1.jpg) +PIAFusion + +![](images/65cc427fdeff94767fa4d18d8e4a054c456bf7e590e488c471b8717d91f1e4e4.jpg) +IFCNN +Figure 4. Qualitative comparisons of various methods on representative images selected from the FLIR dataset. + +![](images/96661590a4cea0bb9e705b839a6634b1f093ce8f7a2711117954fea71cfac8b9.jpg) +SwinFuse + +![](images/869f29f190bd4d753d1d10670ad9006753fd0fcda11ba5cc81831dbff9f8d5d1.jpg) +YDTR + +![](images/942506bec986b3d695539c7a0407bbe59efe7bf5729fd8214a3abaad4672dc16.jpg) +MoE-Fusion (Ours) + +ically, the formula of fusion loss is as follows, + +$$ +\mathcal {L} _ {\text {f u s i o n}} = \mathcal {L} _ {\text {p i x e l}} + \alpha \mathcal {L} _ {\text {g r a d}} + \mathcal {L} _ {\text {l o a d}}, \tag {5} +$$ + +where the pixel loss $\mathcal{L}_{pixel}$ constrains the fused image to preserve more significant pixel intensities originating from the target images, while the gradient loss $\mathcal{L}_{grad}$ forces the fused image to contain more texture details from different modalities. $\mathcal{L}_{load}$ represents load loss, which encourages experts to receive roughly equal numbers of training examples [32]. More details about pixel loss, gradient loss and load loss are provided in the supplementary material. $\alpha$ is used to strike a balance between the different loss functions. + +# 4. Experiments + +# 4.1. Experimental Setting + +Datasets and Partition Protocol. We conducted experiments on three publicly available datasets: $(\mathbf{M}^{3}\mathrm{FD}$ [18], LLVIP [11] and FLIR [37]). + +$\mathbf{M}^3\mathbf{FD}$ : It contains 4,200 infrared-visible image pairs captured by on-board cameras. We used 3,900 pairs of images for training and the remaining 300 pairs for evaluation. + +FLIR: We used the "aligned" version [44] of FLIR in this work. It contains 5,142 infrared-visible image pairs + +captured by on-board cameras. We used 4, 129 image pairs for training and 1, 013 image pairs for evaluation. + +LLVIP: The LLVIP dataset contains 15,488 aligned infrared-visible image pairs, which is captured by the surveillance cameras in different street scenes. We trained the model with 12,025 image pairs and performed evaluation on 3,463 image pairs. + +Competing methods. We compared the 9 state-of-the-art methods on three publicly available datasets $(\mathrm{M}^3\mathrm{FD}$ [18], LLVIP [11] and FLIR [37]). In these comparison methods, DenseFuse [16] and RFN-Nest [17] are the autoencoder-based methods, PIAFusion [35] and IFCNN [48] are the CNN-based methods, TarDAL [18] is the GAN-based methods. DIDFuse [49] and AUIF [50] are the deep learning-based image decomposition methods. SwinFuse [40] and YDTR [36] are the Transformer-based methods. + +Implementation Details. We performed experiments on a computing platform with two NVIDIA GeForce RTX 3090 GPUs. We used Adam Optimization to update the overall network parameters with the learning rate of $1.0 \times 10^{-4}$ . The auxiliary network Faster R-CNN [29] is also trained along with the image fusion pipeline. The training epoch is set to 24 and the batch size is 4. The tuning parameter $\alpha$ is set to 10. For MoLE and MoGE, we set the number of experts is 4, and sparsely activate the top 2 experts. + +Evaluation Metrics. We evaluated the performance of the proposed method based on qualitative and quantitative results. The qualitative evaluation is mainly based on the visual effect of the fused image. A good fused image needs to have complementary information of multi-modal images. The quantitative evaluation mainly uses quality evaluation metrics to measure the performance of image fusion. We selected 8 popular metrics, including the entropy (EN) [31], spatial frequency (SF) [4], standard deviation (SD), mutual information (MI) [28], visual information fidelity (VIF) [7], average gradient (AG) [2], the sum of the correlations of differences (SCD) [1], and gradient-based similarity measurement $(Q_{abf})$ [43]. We also evaluate the performance of the different methods on the typical downstream task, infrared-visible object detection. + +# 4.2. Evaluation on the $\mathbf{M}^3\mathrm{FD}$ dataset + +Quantitative Comparisons. Table 1 presents the results of the quantitative evaluation on the $\mathrm{M}^3\mathrm{FD}$ dataset, where our method achieves the best in 7 metrics and the second and third best performance in the remaining metrics, respectively. In particular, it shows overwhelming advantages on VIF, MI,and $Q_{abf}$ , which indicates that our fusion results contain more valuable information and are more beneficial to the visual perception effect of human eyes. The highest SF, SD and AG also indicate that our fusion results preserve sufficient texture detail and contrast. Such superior performance is attributed to the proposed dynamic learning frame + +![](images/4582124d584a7a2d7b58f506001857863fb300734564b740228733612e2f8a71.jpg) +Visible image + +![](images/f162f3e8fab87b722ee1c9841f7bfdebe3cfadbd3ef70acb724d6fda368effda.jpg) +Infrared image + +![](images/cd06c6cbf4d5e520b58d29dd4cd7fecef0675e7311a7bcb0e935a0780d89e4f8.jpg) +RFN-Nest + +![](images/dc37122cec68a3f7f409926d305125b057db854e3214bf6ae35c405a520d7fbc.jpg) +DenseFuse + +![](images/16e472ad00ef22f27a5e8bf146c891501df86937f98485c117a2ecb065b10545.jpg) +AUE + +![](images/5a23e6e8d64a0700b2c4970312928701e6d110d82ce59d6c0c58d821e48e1e5c.jpg) +DIDFuse + +![](images/602a1706bdd4e41b2f588777aef29146864e43412aebdb519bb5000dbf60425e.jpg) +TarDAL + +![](images/30d5b61e75162edae8fb9ca382d65a9b42fd33d2fb6ac29d28b53c3a562c73b8.jpg) +PIAFusion + +![](images/1e78f30902a89aa1f74287384d9b578b1482ba94aacb4b3eed208254057901f5.jpg) +IFCNN + +![](images/ca4a9d54db9ba84ce297ba42971764e763c760f19be5428bbabe4507ae0e42e8.jpg) +SwinFuse + +![](images/cf6e7ce48e8b8e1afa5fa170343922597e07a3d60684f14a03d8c05ffc9cd86c.jpg) +YDTR + +![](images/408245e02820900b990e14af2f17595e37e6c41ead1584b5f15606001ae7e11c.jpg) +MoE-Fusion (Ours) +Figure 5. Qualitative comparisons of various methods on representative images selected from the LLVIP dataset. + +work from local to global, which achieves state-of-the-art fusion performance through the sample adaptive approach. + +Qualitative Comparisons. To better show the superiority of our model, we assigned the color information of the 3-channel visible image to the single-channel fused image through the color space conversion between RGB and YCbCr. We mark the background region with the green rectangular box and the foreground region with the red rectangular box. As shown in Fig. 3, our fusion results have the best results in both local and global regions. Compared to PIAFusion, YDTR, AUIF, IFCNN and DIDFuse, our fusion results show better contrast, and our fusion results show better texture details compared to TarDAL and SwinFuse. In daytime scenes, our model adaptively learned sufficient texture detail and significant contrast, such as containers and people. Especially for people, our method significantly avoids the effect of smoke and preserves the contrast information of infrared. In local regions, we successfully preserve the rich texture information of containers, outperforming other methods. In global regions such as mountains, grass and sky, our fusion results also effectively retain texture information, indicating that our method has better visual effects due to dynamic learning of local and global information of different modalities. + +# 4.3. Evaluation on the FLIR dataset + +Quantitative Comparisons. Table 1 reports the performance of the different methods on the FLIR dataset for 8 metrics. Our method achieves the best results in 5 metrics. Among them, the highest EN and MI indicate that our method can preserve abundant information of the multimodal images well. The best performance of our method on SCD and $Q_{abf}$ also indicates that our fusion results can better learn the multi-modal complementary information and edge information, which makes our fusion results have better foreground-background contrast and richer texture details. Moreover, the highest VIF also demonstrates that our method can generate fused images with better visual effects that are beneficial to human observation. In addition, the third best results on SF, SD, and AG also indicate that our method is highly competitive. The quantitative results on the FLIR dataset also validate the superiority of our method in dynamically fusing multi-modal complementary information from the local to the global. + +Qualitative Comparisons. We mark the background region with the green rectangular box and the foreground region with the red rectangular box. We also show their zoomed-in effects for easier comparison. As shown in Fig. 4, our fusion results have the best results in both local and global regions. In night scenes, our fusion results adaptively learn sufficient texture detail and contrast, for example on buildings, trees, mountains and traffic lights. Especially for the traffic lights, our method effectively avoids the effects of glare and best preserves the entire outline of the traffic lights. On the local regions, our fusion results preserve the best contrast information of the pedestrians and the rich detail information of the vehicles. These comparisons illustrate that our method has better visual effects due to the effective dynamic learning of local information from different modalities. The superiority of the proposed MoE-Fusion also reveals that specialized knowledge of multimodal local and global in fusion networks can effectively improve fusion performance. + +# 4.4. Evaluation on the LLVIP dataset + +Quantitative Comparisons. The quantitative results of the different methods on the LLVIP dataset are reported in Table 1. Our method outperforms all the compared methods on 6 metrics and achieved the second and third best results on the remaining 2 metrics, respectively. Specifically, the highest SF and AG we achieved indicate that the proposed method preserves richer texture details in the multi-modal images. As well as the highest SD also indicates that our fusion results can contain the highest contrast information between the foreground and the background. SCD and $Q_{abf}$ denote the complementary information and edge information transferred from multi-modal images to fused image, respectively, and our highest results on these two metrics + +Table 2. Ablation studies on three infrared-visible datasets. + +
M3FD Dataset [18]
ENSFSDMIVIFAGSCDQabf
w/o MoLE6.78560.06929.16362.72140.81005.55091.51530.6535
w/o MoGE6.83510.06959.24912.81380.82615.65211.53460.6375
Att-Local6.86560.06939.18942.73200.82715.58091.51900.6390
MoE-Fusion7.00180.071510.14064.19491.00345.67421.54330.6661
FLIR Dataset [44]
ENSFSDMIVIFAGSCDQabf
w/o MoLE6.90210.058710.28592.36660.53715.69611.09760.3187
w/o MoGE7.31720.054810.66542.92080.77475.25251.66290.4796
Att-Local7.30700.060210.64032.66730.74485.72651.47880.4838
MoE-Fusion7.49250.060310.70073.12090.82125.76041.68180.4991
LLVIP Dataset [11]
ENSFSDMIVIFAGSCDQabf
w/o MoLE6.90770.06619.80902.50390.58124.93581.17390.4732
w/o MoGE7.27400.08479.60342.70670.76215.59601.62600.5110
Att-Local7.25280.08589.54832.71290.85996.10991.63930.5735
MoE-Fusion7.35230.08629.86643.10610.92026.13161.78410.5932
+ +indicate that our method can learn more valuable information from multi-modal images. Moreover, the highest VIF also means that our method can generate the most appealing fused images that are more suitable for human vision. These quantitative results demonstrate that the proposed MoE-Fusion can effectively learn multi-modal knowledge and generate informative and appealing fusion results. + +Qualitative Comparisons. We mark the background region with the green rectangular box and the foreground region with the red rectangular box. We also show their zoomed-in effects for easier comparison. As shown in Fig. 5, we can find that the proposed method best preserves the texture details of the local and global in the multi-modal image compared with the state-of-the-art methods, while highlighting the contrast information of the local dynamically. Specifically, for the background region, our fusion results show the sharpest effect on the edge texture of the zebra crossing. For the foreground region, our fusion results preserve the most significant contrast and the richest texture detail in pedestrians and cyclists. Qualitative comparisons show that our MoE-Fusion can balance the texture details and contrasts with the specialized experts dynamically. + +# 4.5. Ablation Study + +We conducted ablation studies on the $\mathbf{M}^3\mathrm{FD}$ , LLVIP, and FLIR datasets and reported the results in Table 2. + +MoLE. To verify the effectiveness of MoLE, we removed MoLE from MoE-Fusion and then extracted multi-modal features by two encoders only, and they were sent to MoGE after concatenation. As shown in Table 2, all the metrics show a significant decrease after removing MoLE, indicating that MoLE is very effective in learning multi-modal texture details and contrast information. Among others, the decrease on SCD also shows it is difficult to learn complementary multi-modal local information sufficiently without MoLE, which strongly supports our motivation to design MoLE. The local dynamic experts of MoLE adaptively boost dominant local (foreground and background) information induced from the auxiliary detector of different + +![](images/11c3599880800f496dfc5ce26ef100396b90c07efbb586e873eb80768cdc77f3.jpg) +Visible image + +![](images/4b681e6d63a46589f003264b912becd89bafcba583f379397989c9c104ea06e2.jpg) +Infrared image + +![](images/b12d946c68aef3da04bcf3ffb7cf1a8a9bd480b30e801e07a0214cba54682437.jpg) +Fusion Feature + +![](images/66722b06e1f99123d19a26b498a49c36a5b5162fd1c2f0b1d591250cb1185bfa.jpg) +Fusion result + +![](images/1b4bf8665cd4558d881c85da036168c26267b50011e70459bb360d643088d88b.jpg) +FG Expert #1 + +![](images/2656e4480a22dfe9a86be20be2ca61690a9929bc33a832670ac82ab39ed038bc.jpg) +FG Expert #2 + +![](images/a159f61568437d9e70bbb641c8382d8ed8f24271ea570e287adb7c2cd7539f9a.jpg) +FG Expert #3 + +![](images/0c9980161262760aa35d6bd26f0121f7bb1b886f4f066bf1b70028e7e1e731fc.jpg) +FG Expert # 4 + +![](images/1c62152a9a246ccc54639ce301b19235ca3bf8743ff788d5149d79bce5b84090.jpg) +BG Expert #1 +Figure 6. Visualization of the features learned by each expert in MoLE. FG denotes foreground, BG denotes background. + +![](images/e6d5714d590b55e527c8b0f3ba15b0f51b97a17ac78b84b2f1d3c810c842be89.jpg) +BG Expert #2 + +![](images/b907bcdb6b50e400f48a8864c3ce584cdecfc1851c541c9afca529cf0d86349e.jpg) +BG Expert #3 + +![](images/6f12694d2613e3416bfbb0ea59de354b45848bdd50492ca0943ffa163b46ac5c.jpg) +BG Expert # 4 + +modalities for dynamic fusion, specialized to local regions. MoGE. We replaced the MoGE with a common decoder with the same structure as that of a single expert in the MoGE. As shown in Table 2, all the metrics appear to be significantly decreased, strongly verifying that the MoGE can help fused images preserve more contrast and texture detail information. Moreover, these results also demonstrate that MoGE can effectively motivate the image fusion network to dynamically adapt to different samples, learning better feature representations, and thus achieving better fusion performance. The global dynamic experts of MoGE further enhance the dominant modality from a global perspective while refining the potential errors that may occur in local fusion. + +Attention-based Local Feature. We want to explore how the fusion performance changes when dynamic learning is not performed for local features and only local feature priors constructed by attention maps are used as local features. We designed an attention-based local feature learning module (Att-Local), and to keep the output channels consistent, we followed the Att-Local module with a $1 \times 1$ convolution layers. In Table 2, all metrics cannot exceed the results of MoE-Fusion with the use of Att-Local, but most of them are higher than w/o MoLE, which demonstrates on the one hand that our proposed MoLE is indeed effective, and on the other hand that the dynamic integration of the effective information from the respective modalities is beneficial to improve the performance of multi-modal image fusion. + +# 4.6. Analysis and Discussion + +Visualization of MoLE. In the MoLE, we can obtain local feature priors according to the attention map Att, which we define as foreground local features (FG), and we also use $1 - \text{Att}$ to obtain background local features (BG). We visualize what each expert has learned in MoLE. As shown + +![](images/f9b0037caf79546a943a30f572f06cb704f497a6cd4ab8bc63e94c707dd69540.jpg) + +![](images/56b4926f448cbef341f47aacddc5e630fb194fd2363a857a325bef175bf44cc1.jpg) + +![](images/cae6071f418c33656bfb288d50b6cbc35031efeb468e1564c6908efc456f865a.jpg) + +![](images/36bc9e6705d66343027c74470bd2c1c18e6f3d224c59d3c758554a822ac6aa4a.jpg) + +![](images/8ae2f20afd10beedaa7c63dabb70fa262a9b5e20a1334a86c4a9b557ec23886c.jpg) +Figure 7. Experiments on the number of experts. + +![](images/f667dafd16422b0543d507b77a4f68f27ecaa5f04d006b091525655cc4b19a7b.jpg) + +![](images/b450399a689ff0ecff9c23fe231984c94d9bf85eef2025dedcadd580b90ceea0.jpg) + +![](images/768b577ddff32aefbba13443e2147efcca4c7634f0c7c2b560460893bf2992ec.jpg) + +Table 3. Object detection evaluation on the FLIR dataset. + +
MethodscarpersonbicyclemAP
Visible55.9027.2033.2038.70
Infrared68.7045.6030.8048.40
DenseFuse [16]65.8044.7031.4047.30
RFN-Nest [17]58.8036.5026.2040.50
IFCNN [48]67.8045.7034.7049.40
PIAFusion [35]62.6040.9031.5045.00
DIDFuse [49]64.2041.7032.1046.00
AUIF [50]61.7036.8029.6042.70
SwinFuse [40]65.6041.3029.7045.60
YDTR [36]65.0044.2032.5047.20
TarDAL [18]62.5035.4030.8042.90
MoE-Fusion72.9055.0039.5055.80
+ +in Fig. 6, we see that the four foreground local experts can clearly learn foreground information, while the four background local experts can also learn rich background features. These results show that MoLE can successfully let each expert know what it should specialize in. + +Detection Evaluation. Good fused images should have better performance in downstream tasks. For different image fusion methods, we perform the evaluation on the object detection task and use the mean average precision (mAP) [5] as the metric. Following [51], we first train the object detection model using infrared images and visible images, and then we input the fused images generated by different image fusion methods into the object detection model for inference and evaluate their detection performance. In this paper, we use Faster R-CNN [29] as the object detection algorithm and set the IoU (Intersection over Union) threshold for evaluation to 0.5. According to Table 3, our MoE-Fusion outperforms all the compared methods and achieves the highest mAP. It is worth noting that our method has an overwhelming advantage on all categories, which demonstrate the proposed dynamic image fusion method is more beneficial for downstream tasks. The detection evaluation on other datasets is provided in the supplementary material. + +Number of Experts. In Fig. 7, we performed 4 sets of experiments on the FLIR dataset, E2k2, E4K2, E6K2, and E8K2, to explore the effect of the number of experts on the + +![](images/8b63cc1bbfc3acf1d959a067e0c12ee951e0522341321bb8f751d3c181852d0c.jpg) + +![](images/96686f89c872c3a83dce2acdc7a220264a651e2cdc8b96e47fee0669ce2624a7.jpg) + +![](images/8edb6a25b8cabfe1a6e1c509a06d4a21ca2da148d8fe6a7d052d3c2c9a4e61ff.jpg) + +![](images/a914c564327785233c91921d9bfeb1318cf7392555eee76976432abead1ce107.jpg) + +![](images/0fbcef3f26b393d3e0364e69bf72849df4469d8f8fdcd68245237303fc276c2d.jpg) +Figure 8. Hyperparameter sensitivity analysis on the FLIR dataset. + +![](images/e9a6c81ac9d154157c9f3d43c04c5658b0bf5e82c72f385a3dc5a81ce769f685.jpg) + +![](images/b388d7ea6436b2e32aac4288e51ebea520d9744876d5db5d25a70bc1f9106b5d.jpg) + +![](images/9eb45e4b27983eb307a49b03f55e4ab609db75576b592234116d2afb77c35e77.jpg) + +fusion results. As an example, E4K2 means that the MoE contains 4 experts and sparsely selects top 2 experts for integration. We found that E4K2 was higher than E2K2 in 7 metrics, E6K2 in 6 metrics, and E8K2 in 5 metrics, suggesting that a higher number of experts may not be better. In addition, we also set up 3 sets of experiments, E4K1, E4K3 and E4K4, to verify the effect of sparse selection of experts in MoE on the fusion results. In Fig. 7, we find that E4K2 can outperform E4K1 and E4K3 in 7 metrics and E4K4 in all metrics. Therefore, in this work, we set 4 experts for each MoE and sparsely select 2 experts for integration. + +Hyperparameter. As shown in Fig. 8, we choose five values for tuning parameter $\alpha$ (1, 5, 10, 20, and 40) and experiment with them in turn. When $\alpha$ is less than 10, the fusion results fail to exceed the performance on all metrics with $\alpha$ equal to 10. When $\alpha$ is greater than 10, there is an improvement in only 2 metrics (SF and AG) compared to $\alpha$ equal to 10, but the other 6 metrics show a decrease. Therefore, in this work, we set $\alpha$ to 10 to obtain better results. + +# 5. Conclusion + +In this paper, we propose a novel dynamic image fusion framework with a multi-modal gated mixture of locally-global experts (MoE-Fusion), which can produce reliable infrared-visible image fusion results. Our framework focuses on dynamically integrating effective information from different source modalities by performing sample-adaptive infrared-visible fusion from local to global. The MoE-Fusion model dynamically balances the texture details and contrasts with the specialized local experts and global experts. The experimental results on three challenging datasets demonstrate that the proposed MoE-Fusion outperforms state-of-the-art methods in terms of visual effects and quantitative metrics. Moreover, we also validate the superiority of our MoE-Fusion in the object detection task. In future work, we will explore leveraging the uncertainty of different images to guide the fusion, and investigate developing an uncertainty-gated MoE paradigm for dynamic image fusion. + +# Acknowledgments + +This work was supported in part by the National Key R&D Program of China 2022ZD0116500, in part by the National Natural Science Foundation of China under Grant 62222608, 62106171, and 61925602, in part by the Haihe Lab of ITAI under Grant 22HHXCJC00002, and in part by the Tianjin Natural Science Foundation under Grant 21JCYBJC00580. + +# References + +[1] V Aslantas and Emre Bendes. A new image quality metric for image fusion: the sum of the correlations of differences. Aeu-international Journal of electronics and communications, 69(12):1890-1896, 2015. +[2] Guangmang Cui, Huajun Feng, Zhi hai Xu, Qi Li, and Yue ting Chen. Detail preserved fusion of visible and infrared images using regional saliency extraction and multi-scale image decomposition. 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NeurIPS, 2022. \ No newline at end of file diff --git a/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/images.zip b/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..e2c90dd46a3e5f674e5acc0c2af677132c3759ec --- /dev/null +++ b/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:74b45482e08bcd899369659867e56ff1b337f3492d3c6608abf214ef5bb89be5 +size 756339 diff --git a/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/layout.json b/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..39a77bc1d9c147a66f14f9c0a14bcbb75e7744c8 --- /dev/null +++ b/2023/Multi-Modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion/layout.json @@ -0,0 +1,12637 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 111, + 136, + 466, + 172 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 136, + 466, + 172 + ], + "spans": [ + { + "bbox": [ + 111, + 136, + 466, + 172 + ], + "type": "text", + "content": "Multi-modal Gated Mixture of Local-to-Global Experts for Dynamic Image Fusion" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 177, + 192, + 416, + 207 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 177, + 192, + 416, + 207 + ], + "spans": [ + { + "bbox": [ + 177, + 192, + 416, + 207 + ], + "type": "text", + "content": "Bing Cao*, Yiming Sun*; Pengfei Zhu†; Qinghua Hu" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 52, + 207, + 542, + 234 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 207, + 542, + 234 + ], + "spans": [ + { + "bbox": [ + 52, + 207, + 542, + 234 + ], + "type": "text", + "content": "Tianjin Key Lab of Machine Learning, College of Intelligence and Computing, Tianjin University, China \nHaihe Laboratory of Information Technology Application Innovation, China" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 152, + 234, + 441, + 247 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 152, + 234, + 441, + 247 + ], + "spans": [ + { + "bbox": [ + 152, + 234, + 441, + 247 + ], + "type": "text", + "content": "{caobing,sunyiming1895,zhupengfei,huqinghua}@tju.edu.cn" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 139, + 273, + 186, + 286 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 139, + 273, + 186, + 286 + ], + "spans": [ + { + "bbox": [ + 139, + 273, + 186, + 286 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 298, + 281, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 298, + 281, + 601 + ], + "spans": [ + { + "bbox": [ + 45, + 298, + 281, + 601 + ], + "type": "text", + "content": "Infrared and visible image fusion aims to integrate comprehensive information from multiple sources to achieve superior performances on various practical tasks, such as detection, over that of a single modality. However, most existing methods directly combined the texture details and object contrast of different modalities, ignoring the dynamic changes in reality, which diminishes the visible texture in good lighting conditions and the infrared contrast in low lighting conditions. To fill this gap, we propose a dynamic image fusion framework with a multi-modal gated mixture of local-to-global experts, termed MoE-Fusion, to dynamically extract effective and comprehensive information from the respective modalities. Our model consists of a Mixture of Local Experts (MoLE) and a Mixture of Global Experts (MoGE) guided by a multi-modal gate. The MoLE performs specialized learning of multi-modal local features, prompting the fused images to retain the local information in a sample-adaptive manner, while the MoGE focuses on the global information that complements the fused image with overall texture detail and contrast. 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The importance of dynamic image fusion. In the SOTA methods (DF [16], DIDF [49], and TDL [18]), the texture details of objects (e.g., car, truck, and traffic sign) in the fused image are suppressed by the contrast of infrared image, leading to terrible detection results. Benefiting from the dynamic fusion, our method can preserve clear texture details without being interrupted by unsuitable contrast, achieving the best performance." + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 376, + 361, + 452, + 436 + ], + "blocks": [ + { + "bbox": [ + 376, + 361, + 452, + 436 + ], + "lines": [ + { + "bbox": [ + 376, + 361, + 452, + 436 + ], + "spans": [ + { + "bbox": [ + 376, + 361, + 452, + 436 + ], + "type": "image", + "image_path": "39c39590ad33fc78280bc05df289c3228c5899acb48a387a4fa730613f9c02d2.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 385, + 437, + 443, + 447 + ], + "lines": [ + { + "bbox": [ + 385, + 437, + 443, + 447 + ], + "spans": [ + { + "bbox": [ + 385, + 437, + 443, + 447 + ], + "type": "text", + "content": "TDL (CVPR'22)" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "type": "image", + "bbox": [ + 452, + 361, + 528, + 436 + ], + "blocks": [ + { + "bbox": [ + 452, + 361, + 528, + 436 + ], + "lines": [ + { + "bbox": [ + 452, + 361, + 528, + 436 + ], + "spans": [ + { + "bbox": [ + 452, + 361, + 528, + 436 + ], + "type": "image", + "image_path": "701b980a9afc580b032828191bb4a52e7303e239e2ca3e259f071362907aa5a4.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 457, + 437, + 525, + 447 + ], + "lines": [ + { + "bbox": [ + 457, + 437, + 525, + 447 + ], + "spans": [ + { + "bbox": [ + 457, + 437, + 525, + 447 + ], + "type": "text", + "content": "MoE-Fusion (Ours)" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_caption" + } + ], + "index": 20 + }, + { + "bbox": [ + 296, + 551, + 530, + 667 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 551, + 530, + 667 + ], + "spans": [ + { + "bbox": [ + 296, + 551, + 530, + 667 + ], + "type": "text", + "content": "in many applications, such as autonomous vehicles [9] and unmanned aerial vehicles [34]. According to the thermal infrared imaging mechanism, infrared images can be adapted to various lighting conditions but has the disadvantage of few texture details [25, 50, 19]. By contrast, visible images contain rich texture detail information, but cannot provide clear information in low light conditions. Therefore, how to design advanced fusion methods such that the fused images preserve sufficient texture details and valuable thermal information has attracted a lot of research attention." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "text", + "content": "Existing infrared-visible fusion methods [46, 38, 33, 42] can be mainly categorized to traditional approaches (image decomposition [15], sparse representation [47], etc.) and deep learning-based approaches (autoencoder based methods [16, 49, 17], generative adversarial network based" + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "spans": [ + { + "bbox": [ + 77, + 42, + 119, + 71 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 151, + 41, + 470, + 73 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 151, + 41, + 470, + 73 + ], + "spans": [ + { + "bbox": [ + 151, + 41, + 470, + 73 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 57, + 710, + 121, + 719 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 710, + 121, + 719 + ], + "spans": [ + { + "bbox": [ + 57, + 710, + 121, + 719 + ], + "type": "text", + "content": "*Equal contribution" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 58, + 719, + 130, + 729 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 719, + 130, + 729 + ], + "spans": [ + { + "bbox": [ + 58, + 719, + 130, + 729 + ], + "type": "text", + "content": "† Corresponding author" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "text", + "content": "23555" + } + ] + } + ], + "index": 28 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 281, + 257 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 281, + 257 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 281, + 257 + ], + "type": "text", + "content": "approaches [18, 26], transformer based approaches [40, 36], etc.). However, most of these methods directly combined the texture details and object contrast of different modalities, ignoring the dynamic changes in reality, leading to poor fusion results and even weaker downstream task performance than that of a single modality. As shown in Fig. 1, the infrared image should adaptively enhance cars in dim light while avoiding compromising the textural detail of truck in bright light. However, the object textures in these state-of-the-art fusion methods are significantly disturbed by the infrared thermal information due to the lack of dynamic learning of multi-modal local and global information, resulting in terrible object detection performance." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 257, + 281, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 257, + 281, + 594 + ], + "spans": [ + { + "bbox": [ + 45, + 257, + 281, + 594 + ], + "type": "text", + "content": "In complex scenes, different modalities have different characteristics: under good lighting conditions, the texture of an object should not be disturbed by thermal infrared information; under low lighting conditions, the contrast of an object also should not be suppressed by the darkness of the visible image. Most existing methods perform image fusion in a fixed correlation paradigm, ignoring the dominant modality changes dynamically in reality, and often fall into domain bias. To break the traditional fixed fusion paradigm, we pioneered sample-adaptive local-to-global experts to dynamically enhance the dominant modality for image fusion. Fig. 1 show that the proposed method not only eliminates domain bias but also achieves sample-adaptive dynamic fusion, yielding the best detection results. Specifically, we propose a dynamic image fusion framework with a multi-modal gated mixture of local-to-global experts, termed MoE-Fusion, which consists of a Mixture of Local Experts (MoLE) and a Mixture of Global Experts (MoGE) guided by a multi-modal gate. In MoLE, we introduce the attention map generated by an auxiliary network to construct multi-modal local priors and perform dynamic learning of multi-modal local features guided by multimodal gating, achieving sample-adaptive multi-modal local feature fusion. Moreover, MoGE performs dynamic learning of multi-modal global features to achieve a balance of texture details and contrasts globally in the fused images. With the proposed dynamic fusion paradigm from local to global, our model is capable of performing a reliable fusion of different modal images." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 57, + 595, + 252, + 607 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 595, + 252, + 607 + ], + "spans": [ + { + "bbox": [ + 57, + 595, + 252, + 607 + ], + "type": "text", + "content": "We summarize our main contributions as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 57, + 615, + 279, + 730 + ], + "type": "list", + "angle": 0, + "index": 5, + "blocks": [ + { + "bbox": [ + 57, + 615, + 279, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 615, + 279, + 674 + ], + "spans": [ + { + "bbox": [ + 57, + 615, + 279, + 674 + ], + "type": "text", + "content": "- We propose a dynamic image fusion model, providing a new multi-modal gated mixture of local-to-global experts for reliable infrared and visible image fusion (benefiting from the dynamically integrating effective information from the respective modalities)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 57, + 682, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 682, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 57, + 682, + 279, + 730 + ], + "type": "text", + "content": "- The proposed model is an effective and robust framework for sample-adaptive infrared-visible fusion from local to global. Further, it prompts the fused images to dynamically balance the texture details and contrasts." + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 308, + 106, + 530, + 164 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 106, + 530, + 164 + ], + "spans": [ + { + "bbox": [ + 308, + 106, + 530, + 164 + ], + "type": "text", + "content": "- We conduct extensive experiments on multiple infrared-visible datasets, which clearly validate our superiority, quantitatively and qualitatively. Moreover, we also demonstrate our effectiveness in object detection." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 297, + 176, + 387, + 188 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 176, + 387, + 188 + ], + "spans": [ + { + "bbox": [ + 297, + 176, + 387, + 188 + ], + "type": "text", + "content": "2. Related Works" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 297, + 196, + 477, + 208 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 196, + 477, + 208 + ], + "spans": [ + { + "bbox": [ + 297, + 196, + 477, + 208 + ], + "type": "text", + "content": "2.1. Infrared and Visible Image Fusion" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 296, + 213, + 530, + 505 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 213, + 530, + 505 + ], + "spans": [ + { + "bbox": [ + 296, + 213, + 530, + 505 + ], + "type": "text", + "content": "The infrared and visible image fusion task focuses on generating a fused image containing sufficient information through the learning of multi-modal features [24, 45, 20, 22, 12, 8]. Ma et al. [23] defined the goal of image fusion as preserving more intensity information in infrared images as well as gradient information in visible images. Li et al. [16] use the autoencoder to extract multi-modal overall features and fuse them by designed fusion rules, which inspired a series of subsequent works [14, 17]. Zhao et al. [49, 50] proposed the deep learning-based image decomposition methods, which decompose images into background and detail images by high- and low-frequency information, respectively, and then fuse them by designed fusion rules. Recently, some GAN-based methods [26, 25, 18] and Transformer-based methods [40, 36] have also attracted wide attention. These works, despite the different approaches adopted, all focus on learning on the representation of the overall multi-modal features. However, they ignore the dynamic changes in reality, which diminishes the visible texture in good lighting conditions and the infrared contrast in low lighting conditions. We propose a dynamic image fusion framework that enables sample-adaptive fusion from local to global. This approach prompts the fused images to balance the texture details and contrast with specialized experts dynamically." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 297, + 513, + 408, + 526 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 513, + 408, + 526 + ], + "spans": [ + { + "bbox": [ + 297, + 513, + 408, + 526 + ], + "type": "text", + "content": "2.2. Mixture-of-Experts" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 296, + 532, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 532, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 532, + 530, + 730 + ], + "type": "text", + "content": "Mixture-of-Experts (MoE) [10, 30, 27] can dynamically adjust its structure according to different inputs. Shazeer et al. [32] constructed a sparsely-gated MoE layer that uses a gate network to select multiple experts and assign weights to each selected expert. The final result of the MoE is a weighted sum of the outputs of the different experts. This work also serves as the basis for subsequent research. Recently, some researchers [13, 27] have focused on exploring learning mechanisms in MoE, trying to solve the problems of unbalanced expert load and the number of activated experts faced by MoE during training. Other researchers [6, 52, 3, 39] focuses on the combination of MoE and Transformer. They expect to use MoE to build sparse models. Zhu et al. [52] introduced Conditional MoE into the generalist model and proposed different routing strategies to mitigate the interference between tasks and modalities. Existing MoE-related methods focus on modeling" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 301, + 756 + ], + "type": "text", + "content": "23556" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 105, + 200, + 250 + ], + "blocks": [ + { + "bbox": [ + 48, + 105, + 200, + 250 + ], + "lines": [ + { + "bbox": [ + 48, + 105, + 200, + 250 + ], + "spans": [ + { + "bbox": [ + 48, + 105, + 200, + 250 + ], + "type": "image", + "image_path": "905586731212f212619fd3abf50674b87333b3eee8ee946daa4859b8bb942c12.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 120, + 257, + 131, + 266 + ], + "lines": [ + { + "bbox": [ + 120, + 257, + 131, + 266 + ], + "spans": [ + { + "bbox": [ + 120, + 257, + 131, + 266 + ], + "type": "text", + "content": "(a)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 204, + 105, + 375, + 258 + ], + "blocks": [ + { + "bbox": [ + 204, + 105, + 375, + 258 + ], + "lines": [ + { + "bbox": [ + 204, + 105, + 375, + 258 + ], + "spans": [ + { + "bbox": [ + 204, + 105, + 375, + 258 + ], + "type": "image", + "image_path": "02f3373c793f4046f9a0cb5f730dc45a8ba2b06713a03828dd325c59c88cc4f8.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 350, + 257, + 361, + 267 + ], + "lines": [ + { + "bbox": [ + 350, + 257, + 361, + 267 + ], + "spans": [ + { + "bbox": [ + 350, + 257, + 361, + 267 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 376, + 108, + 530, + 257 + ], + "blocks": [ + { + "bbox": [ + 376, + 108, + 530, + 257 + ], + "lines": [ + { + "bbox": [ + 376, + 108, + 530, + 257 + ], + "spans": [ + { + "bbox": [ + 376, + 108, + 530, + 257 + ], + "type": "image", + "image_path": "4f5c3fd9f8c873e844d46a221d0de910714c17851e1a52f9a6b9224e07a951fd.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 271, + 531, + 293 + ], + "lines": [ + { + "bbox": [ + 45, + 271, + 531, + 293 + ], + "spans": [ + { + "bbox": [ + 45, + 271, + 531, + 293 + ], + "type": "text", + "content": "Figure 2. The architecture of MoE-Fusion. MoE-Fusion consists of a Mixture of Local Experts (MoLE), a Mixture of Global Experts (MoGE) guided by the multi-modal gate, a set of infrared and visible feature encoders, and the auxiliary network." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 311, + 279, + 394 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 311, + 279, + 394 + ], + "spans": [ + { + "bbox": [ + 45, + 311, + 279, + 394 + ], + "type": "text", + "content": "generic knowledge by using the dynamicity and sparsity of MoE, resulting in each expert does not know what they should be expert in. In contrast, we extend the idea of MoE to image fusion tasks for the first time, constructing a multimodal gated mixture of local-to-global experts, assigning specific tasks to each expert, and enabling sample-adaptive specialized learning, which yields superior performance." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 402, + 99, + 414 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 402, + 99, + 414 + ], + "spans": [ + { + "bbox": [ + 45, + 402, + 99, + 414 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 45, + 421, + 162, + 431 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 421, + 162, + 431 + ], + "spans": [ + { + "bbox": [ + 45, + 421, + 162, + 431 + ], + "type": "text", + "content": "3.1. Overall Architecture" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 45, + 439, + 279, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 439, + 279, + 496 + ], + "spans": [ + { + "bbox": [ + 45, + 439, + 279, + 496 + ], + "type": "text", + "content": "In this paper, we propose a dynamic image fusion framework with a multi-modal gated mixture of local-to-global experts, termed MoE-Fusion. In Fig. 2, MoE-Fusion contains two encoders, a Mixture of Local Experts, a Mixture of Global Experts, and the auxiliary network." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "content": "In Fig. 2 (b), we send a pair of infrared image " + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "inline_equation", + "content": "I_{\\mathcal{I}} \\in \\mathbb{R}^{H \\times W \\times 1}" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "content": " and visible image " + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "inline_equation", + "content": "I_{\\mathcal{V}} \\in \\mathbb{R}^{H \\times W \\times 3}" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "content": " into the infrared and visible encoders (" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "inline_equation", + "content": "Enc_{\\mathcal{I}}" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "inline_equation", + "content": "Enc_{\\mathcal{V}}" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "content": ") to extract the features, respectively. The structure of encoders follows [16]. The output of the encoder has two parts: the feature maps of the last layer (" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "inline_equation", + "content": "x_{enc}^{\\mathcal{I}}" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "inline_equation", + "content": "x_{enc}^{\\mathcal{V}}" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "content": ") and the dense feature maps (" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "inline_equation", + "content": "x_{dense}^{\\mathcal{I}}" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "inline_equation", + "content": "x_{dense}^{\\mathcal{V}}" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "content": "). More details of the structure are provided in the supplementary material. We send the " + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "inline_equation", + "content": "x_{enc}^{\\mathcal{I}}" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "inline_equation", + "content": "x_{enc}^{\\mathcal{V}}" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "content": " to the MoLE along with the attention map which is learning from the auxiliary network. In this paper, we use Faster-RCNN [29] as the auxiliary network. In MoLE, we send visible and infrared features to specific local experts separately to achieve dynamic integration of local features under the guidance of multi-modal gating. We concatenate the outputs of MoLE with the dense feature maps as the input to the MoGE. Each expert in MoGE has the ability to decode global features, and a multi-modal gate network is used to dynamic select which experts are activated to decode multi-modal fusion features. The final fused image " + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "inline_equation", + "content": "I_{\\mathcal{F}} \\in \\mathbb{R}^{H \\times W \\times 1}" + }, + { + "bbox": [ + 45, + 497, + 279, + 730 + ], + "type": "text", + "content": " is generated by a weighted" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 297, + 312, + 482, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 312, + 482, + 323 + ], + "spans": [ + { + "bbox": [ + 297, + 312, + 482, + 323 + ], + "type": "text", + "content": "sum mechanism of the different global experts." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 325, + 530, + 394 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 325, + 530, + 394 + ], + "spans": [ + { + "bbox": [ + 296, + 325, + 530, + 394 + ], + "type": "text", + "content": "The MoE-Fusion is optimized mainly by calculating the pixel loss and gradient loss between the fused image " + }, + { + "bbox": [ + 296, + 325, + 530, + 394 + ], + "type": "inline_equation", + "content": "I_{\\mathcal{F}}" + }, + { + "bbox": [ + 296, + 325, + 530, + 394 + ], + "type": "text", + "content": " and two source images " + }, + { + "bbox": [ + 296, + 325, + 530, + 394 + ], + "type": "inline_equation", + "content": "(I_{\\mathcal{I}}" + }, + { + "bbox": [ + 296, + 325, + 530, + 394 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 325, + 530, + 394 + ], + "type": "inline_equation", + "content": "I_{\\mathcal{V}}" + }, + { + "bbox": [ + 296, + 325, + 530, + 394 + ], + "type": "text", + "content": "). In addition, we also introduce the load loss to motivate each expert to receive roughly equal numbers of training images. The auxiliary detection networks are optimized independently by the detection loss." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 297, + 406, + 434, + 418 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 406, + 434, + 418 + ], + "spans": [ + { + "bbox": [ + 297, + 406, + 434, + 418 + ], + "type": "text", + "content": "3.2. Mixture of Local Experts" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 296, + 426, + 530, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 426, + 530, + 507 + ], + "spans": [ + { + "bbox": [ + 296, + 426, + 530, + 507 + ], + "type": "text", + "content": "In infrared-visible image fusion tasks, specialized learning of multi-modal local information by a sample adaptive manner helps to overcome the challenge of multi-modal fusion failure in complex scenes. To realize this vision, we need to address two questions: (1) How to find local regions in multi-modal images; (2) How to learn the local features dynamically due to the differences in various samples." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "text", + "content": "As shown in Fig. 2 (a), we propose a Mixture of Local Experts (MoLE) to dynamically learning the multi-modal local features. We use the auxiliary detection networks with a spatial attention module to learn the attention maps. Then we can find the local regions in multi-modal images according to the guidance of the learned attention maps. Specifically, we introduce attention modules in two auxiliary detection networks for extracting visible attention maps and infrared attention maps, respectively. The modal-specific attention map " + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "inline_equation", + "content": "Att_{\\mathcal{V}} / Att_{\\mathcal{I}}" + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "text", + "content": " is generated by the attention module between the feature extractor and the detection head in the detection networks, which consists of a Conv(1 × 1)-BN-ReLU layer and a Conv(1 × 1)-BN-Sigmoid layer. The " + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "inline_equation", + "content": "Att_{\\mathcal{V}}" + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "inline_equation", + "content": "Att_{\\mathcal{I}}" + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "text", + "content": " are concatenated and fed into 2 convolutional layers, the maximum of which output is the Att. In MoLE, we multiply the " + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "inline_equation", + "content": "x_{enc}^{\\mathcal{V}}" + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "inline_equation", + "content": "x_{enc}^{\\mathcal{I}}" + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "text", + "content": " with Att to obtain " + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "inline_equation", + "content": "x_{local}^{\\mathcal{V}}" + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "inline_equation", + "content": "x_{local}^{\\mathcal{I}}" + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "text", + "content": ", respectively. Then we concatenate the " + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "inline_equation", + "content": "x_{local}^{\\mathcal{V}}" + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "inline_equation", + "content": "x_{local}^{\\mathcal{I}}" + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "text", + "content": " to get the " + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "inline_equation", + "content": "x_{local}" + }, + { + "bbox": [ + 296, + 508, + 531, + 730 + ], + "type": "text", + "content": ", which is the input of the multi-modal gating network. 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The structure of each expert network is 2 convolution layers and 1 ReLU layers." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "spans": [ + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "type": "text", + "content": "In MoLE, we flatten the input " + }, + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "type": "inline_equation", + "content": "x_{local} \\in \\mathbb{R}^{H \\times W \\times C}" + }, + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "type": "inline_equation", + "content": "s_{local} \\in \\mathbb{R}^D" + }, + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "type": "text", + "content": ". The gate network " + }, + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "type": "inline_equation", + "content": "G_{local}" + }, + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "type": "text", + "content": " takes the vector " + }, + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "type": "inline_equation", + "content": "s_{local}" + }, + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "type": "text", + "content": " as input and produces the probability of it with respective to " + }, + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 45, + 332, + 279, + 390 + ], + "type": "text", + "content": " experts. The formalization of the gate network is as follows," + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 56, + 399, + 279, + 411 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 399, + 279, + 411 + ], + "spans": [ + { + "bbox": [ + 56, + 399, + 279, + 411 + ], + "type": "interline_equation", + "content": "G _ {\\text {l o c a l}} \\left(s _ {\\text {l o c a l}}\\right) = \\operatorname {s o f t m a x} \\left(\\operatorname {t o p K} \\left(s _ {\\text {l o c a l}} \\cdot W _ {\\text {l o c a l}}\\right)\\right), \\tag {1}", + "image_path": "a860af370a6f1af36fb7aff8deca393ec1136fb254088c0cd68f9ce2ec760444.jpg" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 45, + 420, + 279, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 420, + 279, + 443 + ], + "spans": [ + { + "bbox": [ + 45, + 420, + 279, + 443 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 420, + 279, + 443 + ], + "type": "inline_equation", + "content": "W_{local} \\in \\mathbb{R}^{D \\times N}" + }, + { + "bbox": [ + 45, + 420, + 279, + 443 + ], + "type": "text", + "content": " is a learnable weight matrix and the top " + }, + { + "bbox": [ + 45, + 420, + 279, + 443 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 45, + 420, + 279, + 443 + ], + "type": "text", + "content": " outputs are normalized via softmax function." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "spans": [ + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "text", + "content": "To achieve specialized learning of different modalities, we input visible local features " + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "inline_equation", + "content": "x_{local}^{\\nu}" + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "text", + "content": " into one set of expert networks " + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "inline_equation", + "content": "\\{E_1^{local},\\dots,E_{N / 2}^{local}\\}" + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "text", + "content": " and infrared local features " + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "inline_equation", + "content": "x_{local}^{\\mathcal{I}}" + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "text", + "content": " into another set of non-overlapping expert networks " + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "inline_equation", + "content": "\\{E_{(N / 2) + 1}^{local},\\dots,E_N^{local}\\}" + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "text", + "content": ". Each expert network produces its own output " + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "inline_equation", + "content": "E_i^{local}(x_{local}^j)" + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "text", + "content": ". The final output " + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "inline_equation", + "content": "y_{local}" + }, + { + "bbox": [ + 45, + 444, + 279, + 530 + ], + "type": "text", + "content": " of the MoLE is calculated as follows," + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 78, + 538, + 279, + 569 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 78, + 538, + 279, + 569 + ], + "spans": [ + { + "bbox": [ + 78, + 538, + 279, + 569 + ], + "type": "interline_equation", + "content": "y _ {l o c a l} = \\sum_ {i = 1} ^ {N} G _ {l o c a l} \\left(s _ {l o c a l}\\right) _ {i} E _ {i} ^ {l o c a l} \\left(x _ {l o c a l} ^ {j}\\right), \\tag {2}", + "image_path": "ffdc780e6f0d615158b1199b96d513db51965f9ba0eadf36c546688de82bb3dd.jpg" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "spans": [ + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "text", + "content": " represents " + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "inline_equation", + "content": "\\mathcal{I}" + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "inline_equation", + "content": "\\nu" + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "text", + "content": ". Then we concatenate the " + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "inline_equation", + "content": "y_{local}" + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "inline_equation", + "content": "x_{dense}^{\\mathcal{I}}" + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "inline_equation", + "content": "x_{dense}^{\\nu}" + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "text", + "content": " to obtain the global multi-modal fusion feature " + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "inline_equation", + "content": "x_{f}" + }, + { + "bbox": [ + 45, + 576, + 279, + 612 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 46, + 618, + 188, + 631 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 618, + 188, + 631 + ], + "spans": [ + { + "bbox": [ + 46, + 618, + 188, + 631 + ], + "type": "text", + "content": "3.3. Mixture of Global Experts" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 45, + 636, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 636, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 636, + 279, + 730 + ], + "type": "text", + "content": "Traditional image fusion algorithms use the same network structure and parameters to learn the fusion features of different samples. In contrast, we propose the MoGE to dynamically integrate multi-modal global features, which can adaptively adjust its own structure and parameters when dealing with different samples, thus showing superior advantages in terms of model expressiveness and self-adaptability. The main components of the MoGE include a" + } + ] + } + ], + "index": 33 + }, + { + "type": "table", + "bbox": [ + 299, + 134, + 530, + 383 + ], + "blocks": [ + { + "bbox": [ + 297, + 103, + 530, + 133 + ], + "lines": [ + { + "bbox": [ + 297, + 103, + 530, + 133 + ], + "spans": [ + { + "bbox": [ + 297, + 103, + 530, + 133 + ], + "type": "text", + "content": "Table 1. Quantitative comparison of our MoE-Fusion with 9 state-of-the-art methods. Bold red indicates the best, Bold blue indicates the second best, and Bold cyan indicates the third best." + } + ] + } + ], + "index": 34, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 299, + 134, + 530, + 383 + ], + "lines": [ + { + "bbox": [ + 299, + 134, + 530, + 383 + ], + "spans": [ + { + "bbox": [ + 299, + 134, + 530, + 383 + ], + "type": "table", + "html": "
M3FD Dataset [18]
ENSFSDMIVIFAGSCDQabf
DenseFuse [16]6.41340.03648.59872.95240.65723.07001.50690.3838
RFN-Nest [17]6.92080.03459.29842.93010.78063.16981.54100.3772
IFCNN [48]6.65550.05999.24562.99540.75225.09321.54480.5755
PIAfusion [35]6.81670.070710.12283.83370.84475.65601.30650.5540
DIDFuse [49]6.61160.04209.34092.99550.73823.56681.58750.4342
AUIF [50]6.52330.03998.87592.97930.67963.32241.53140.4124
SwinFuse [40]6.98190.06969.64003.20040.91145.62341.53950.5166
YDTR [36]6.53970.04969.26313.21280.72763.89511.50760.4812
TarDAL [18]7.13470.05289.68203.28530.83474.19981.53340.3858
MoE-Fusion7.00180.071510.14064.19491.00345.67421.54330.6661
FLIR Dataset [44]
ENSFSDMIVIFAGSCDQabf
DenseFuse [16]6.94790.030410.59282.92540.64133.05241.31320.2947
RFN-Nest [17]7.42770.026710.87472.96690.72602.76641.67310.2603
IFCNN [48]7.13670.063810.66682.92630.75676.10811.35210.4894
PIAfusion [35]6.99680.055110.65633.09270.81785.18491.16150.4388
DIDFuse [49]7.27540.067011.63182.50220.66495.88151.49130.3469
AUIF [50]7.28530.046310.21082.88930.70994.44711.58230.3240
SwinFuse [40]7.41630.058210.60772.94040.81045.75871.67390.3751
YDTR [36]6.89480.036410.65713.08200.67493.29931.33790.3333
TarDAL [18]7.48660.058810.69483.02280.76655.19551.31820.3896
MoE-Fusion7.49250.060310.70073.12090.82125.76041.68180.4991
LLVIP Dataset [11]
ENSFSDMIVIFAGSCDQabf
DenseFuse [16]6.83140.04269.38002.67640.68943.26401.21090.3093
RFN-Nest [17]7.14080.03009.71842.50420.72942.78531.46120.2287
IFCNN [48]7.21390.06889.76332.94790.77975.41361.42690.5845
PIAfusion [35]7.39540.07879.73203.36900.88606.08461.53000.5789
DIDFuse [49]6.03720.05507.80742.51370.50543.44741.25740.2436
AUIF [50]6.19470.06367.84182.39660.55333.85881.28400.2764
SwinFuse [40]5.99730.06087.65252.18460.59623.73441.26290.2620
YDTR [36]6.69220.04748.87012.91520.63223.20431.08810.2907
TarDAL [18]7.35040.06479.76763.46550.77694.60941.36070.4431
MoE-Fusion7.35230.08629.86643.10610.92026.13161.78410.5932
", + "image_path": "02fe1e6e840e6e7661ea400e685efd4238e5687e1b988e04f050a93481e5bfab.jpg" + } + ] + } + ], + "index": 35, + "angle": 0, + "type": "table_body" + } + ], + "index": 35 + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "spans": [ + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "text", + "content": "global multi-modal gating network " + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "inline_equation", + "content": "G_{global}" + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "text", + "content": " and a set of " + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "text", + "content": " expert networks " + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "inline_equation", + "content": "\\{E_1^{global},\\dots,E_N^{global}\\}" + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "text", + "content": ". In MoGE, we flatten " + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "inline_equation", + "content": "x_{f}" + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "text", + "content": " to get " + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "inline_equation", + "content": "s_f" + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "text", + "content": " and feed it into " + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "inline_equation", + "content": "G_{global}" + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "text", + "content": ". The corresponding gating weights of the " + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 296, + 405, + 530, + 463 + ], + "type": "text", + "content": " expert networks are calculated as follows," + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 320, + 477, + 530, + 490 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 320, + 477, + 530, + 490 + ], + "spans": [ + { + "bbox": [ + 320, + 477, + 530, + 490 + ], + "type": "interline_equation", + "content": "G _ {\\text {g l o b a l}} \\left(s _ {f}\\right) = \\operatorname {s o f t m a x} \\left(\\operatorname {t o p} K \\left(s _ {f} \\cdot W _ {\\text {g l o b a l}}\\right)\\right), \\tag {3}", + "image_path": "064669b34f392b880a5af0904a71b8188d751a9c580ea10c1a604c73b03f7764.jpg" + } + ] + } + ], + "index": 37 + }, + { + "bbox": [ + 296, + 500, + 529, + 524 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 500, + 529, + 524 + ], + "spans": [ + { + "bbox": [ + 296, + 500, + 529, + 524 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 296, + 500, + 529, + 524 + ], + "type": "inline_equation", + "content": "W_{global}" + }, + { + "bbox": [ + 296, + 500, + 529, + 524 + ], + "type": "text", + "content": " is a learnable weight matrix and the top " + }, + { + "bbox": [ + 296, + 500, + 529, + 524 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 296, + 500, + 529, + 524 + ], + "type": "text", + "content": " outputs are normalized via softmax distribution." + } + ] + } + ], + "index": 38 + }, + { + "bbox": [ + 296, + 526, + 530, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 526, + 530, + 597 + ], + "spans": [ + { + "bbox": [ + 296, + 526, + 530, + 597 + ], + "type": "text", + "content": "The structure of each expert network consists of 4 convolution layers. Each expert takes the global multimodal fusion feature " + }, + { + "bbox": [ + 296, + 526, + 530, + 597 + ], + "type": "inline_equation", + "content": "x_{f}" + }, + { + "bbox": [ + 296, + 526, + 530, + 597 + ], + "type": "text", + "content": " as input to produce its own output " + }, + { + "bbox": [ + 296, + 526, + 530, + 597 + ], + "type": "inline_equation", + "content": "E_{i}^{global}(x_{f})" + }, + { + "bbox": [ + 296, + 526, + 530, + 597 + ], + "type": "text", + "content": ". The final output " + }, + { + "bbox": [ + 296, + 526, + 530, + 597 + ], + "type": "inline_equation", + "content": "I_{\\mathcal{F}}" + }, + { + "bbox": [ + 296, + 526, + 530, + 597 + ], + "type": "text", + "content": " of MoGE is the linearly weighted combination of each expert's output with the corresponding gating weights. The formalization is as follows," + } + ] + } + ], + "index": 39 + }, + { + "bbox": [ + 343, + 610, + 530, + 641 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 610, + 530, + 641 + ], + "spans": [ + { + "bbox": [ + 343, + 610, + 530, + 641 + ], + "type": "interline_equation", + "content": "I _ {\\mathcal {F}} = \\sum_ {i = 1} ^ {N} G _ {\\text {g l o b a l}} \\left(s _ {f}\\right) _ {i} E _ {i} ^ {\\text {g l o b a l}} \\left(x _ {f}\\right). \\tag {4}", + "image_path": "018ecbdcb143767c47a73278d3b26525a7d7ea9ede0f96647302d1c52c1928f8.jpg" + } + ] + } + ], + "index": 40 + }, + { + "bbox": [ + 297, + 652, + 383, + 663 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 652, + 383, + 663 + ], + "spans": [ + { + "bbox": [ + 297, + 652, + 383, + 663 + ], + "type": "text", + "content": "3.4. Loss Function" + } + ] + } + ], + "index": 41 + }, + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "text", + "content": "In MoE-Fusion, we use the fusion loss " + }, + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{fusion}" + }, + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "text", + "content": " to guide the optimization of the image fusion network, and the auxiliary detection networks are optimized by their respective detection loss [29] (" + }, + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{det}^{\\mathcal{V}}" + }, + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{det}^{\\mathcal{T}}" + }, + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "text", + "content": "). 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" + }, + { + "bbox": [ + 45, + 481, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{load}" + }, + { + "bbox": [ + 45, + 481, + 279, + 586 + ], + "type": "text", + "content": " represents load loss, which encourages experts to receive roughly equal numbers of training examples [32]. More details about pixel loss, gradient loss and load loss are provided in the supplementary material. " + }, + { + "bbox": [ + 45, + 481, + 279, + 586 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 45, + 481, + 279, + 586 + ], + "type": "text", + "content": " is used to strike a balance between the different loss functions." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 45, + 597, + 123, + 610 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 597, + 123, + 610 + ], + "spans": [ + { + "bbox": [ + 45, + 597, + 123, + 610 + ], + "type": "text", + "content": "4. 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We conducted experiments on three publicly available datasets: " + }, + { + "bbox": [ + 45, + 635, + 278, + 670 + ], + "type": "inline_equation", + "content": "(\\mathbf{M}^{3}\\mathrm{FD}" + }, + { + "bbox": [ + 45, + 635, + 278, + 670 + ], + "type": "text", + "content": " [18], LLVIP [11] and FLIR [37])." + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 45, + 671, + 278, + 705 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 671, + 278, + 705 + ], + "spans": [ + { + "bbox": [ + 45, + 671, + 278, + 705 + ], + "type": "inline_equation", + "content": "\\mathbf{M}^3\\mathbf{FD}" + }, + { + "bbox": [ + 45, + 671, + 278, + 705 + ], + "type": "text", + "content": ": It contains 4,200 infrared-visible image pairs captured by on-board cameras. We used 3,900 pairs of images for training and the remaining 300 pairs for evaluation." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 45, + 706, + 278, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 706, + 278, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 706, + 278, + 730 + ], + "type": "text", + "content": "FLIR: We used the \"aligned\" version [44] of FLIR in this work. It contains 5,142 infrared-visible image pairs" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 296, + 106, + 529, + 129 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 106, + 529, + 129 + ], + "spans": [ + { + "bbox": [ + 296, + 106, + 529, + 129 + ], + "type": "text", + "content": "captured by on-board cameras. We used 4, 129 image pairs for training and 1, 013 image pairs for evaluation." + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 296, + 130, + 530, + 188 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 130, + 530, + 188 + ], + "spans": [ + { + "bbox": [ + 296, + 130, + 530, + 188 + ], + "type": "text", + "content": "LLVIP: The LLVIP dataset contains 15,488 aligned infrared-visible image pairs, which is captured by the surveillance cameras in different street scenes. We trained the model with 12,025 image pairs and performed evaluation on 3,463 image pairs." + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 296, + 189, + 530, + 293 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 189, + 530, + 293 + ], + "spans": [ + { + "bbox": [ + 296, + 189, + 530, + 293 + ], + "type": "text", + "content": "Competing methods. We compared the 9 state-of-the-art methods on three publicly available datasets " + }, + { + "bbox": [ + 296, + 189, + 530, + 293 + ], + "type": "inline_equation", + "content": "(\\mathrm{M}^3\\mathrm{FD}" + }, + { + "bbox": [ + 296, + 189, + 530, + 293 + ], + "type": "text", + "content": " [18], LLVIP [11] and FLIR [37]). In these comparison methods, DenseFuse [16] and RFN-Nest [17] are the autoencoder-based methods, PIAFusion [35] and IFCNN [48] are the CNN-based methods, TarDAL [18] is the GAN-based methods. DIDFuse [49] and AUIF [50] are the deep learning-based image decomposition methods. SwinFuse [40] and YDTR [36] are the Transformer-based methods." + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 296, + 294, + 530, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 294, + 530, + 399 + ], + "spans": [ + { + "bbox": [ + 296, + 294, + 530, + 399 + ], + "type": "text", + "content": "Implementation Details. We performed experiments on a computing platform with two NVIDIA GeForce RTX 3090 GPUs. We used Adam Optimization to update the overall network parameters with the learning rate of " + }, + { + "bbox": [ + 296, + 294, + 530, + 399 + ], + "type": "inline_equation", + "content": "1.0 \\times 10^{-4}" + }, + { + "bbox": [ + 296, + 294, + 530, + 399 + ], + "type": "text", + "content": ". The auxiliary network Faster R-CNN [29] is also trained along with the image fusion pipeline. The training epoch is set to 24 and the batch size is 4. The tuning parameter " + }, + { + "bbox": [ + 296, + 294, + 530, + 399 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 296, + 294, + 530, + 399 + ], + "type": "text", + "content": " is set to 10. For MoLE and MoGE, we set the number of experts is 4, and sparsely activate the top 2 experts." + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 296, + 399, + 530, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 399, + 530, + 574 + ], + "spans": [ + { + "bbox": [ + 296, + 399, + 530, + 574 + ], + "type": "text", + "content": "Evaluation Metrics. We evaluated the performance of the proposed method based on qualitative and quantitative results. The qualitative evaluation is mainly based on the visual effect of the fused image. A good fused image needs to have complementary information of multi-modal images. The quantitative evaluation mainly uses quality evaluation metrics to measure the performance of image fusion. We selected 8 popular metrics, including the entropy (EN) [31], spatial frequency (SF) [4], standard deviation (SD), mutual information (MI) [28], visual information fidelity (VIF) [7], average gradient (AG) [2], the sum of the correlations of differences (SCD) [1], and gradient-based similarity measurement " + }, + { + "bbox": [ + 296, + 399, + 530, + 574 + ], + "type": "inline_equation", + "content": "(Q_{abf})" + }, + { + "bbox": [ + 296, + 399, + 530, + 574 + ], + "type": "text", + "content": " [43]. We also evaluate the performance of the different methods on the typical downstream task, infrared-visible object detection." + } + ] + } + ], + "index": 37 + }, + { + "bbox": [ + 297, + 583, + 465, + 595 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 583, + 465, + 595 + ], + "spans": [ + { + "bbox": [ + 297, + 583, + 465, + 595 + ], + "type": "text", + "content": "4.2. Evaluation on the " + }, + { + "bbox": [ + 297, + 583, + 465, + 595 + ], + "type": "inline_equation", + "content": "\\mathbf{M}^3\\mathrm{FD}" + }, + { + "bbox": [ + 297, + 583, + 465, + 595 + ], + "type": "text", + "content": " dataset" + } + ] + } + ], + "index": 38 + }, + { + "bbox": [ + 296, + 601, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 601, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 601, + 530, + 730 + ], + "type": "text", + "content": "Quantitative Comparisons. Table 1 presents the results of the quantitative evaluation on the " + }, + { + "bbox": [ + 296, + 601, + 530, + 730 + ], + "type": "inline_equation", + "content": "\\mathrm{M}^3\\mathrm{FD}" + }, + { + "bbox": [ + 296, + 601, + 530, + 730 + ], + "type": "text", + "content": " dataset, where our method achieves the best in 7 metrics and the second and third best performance in the remaining metrics, respectively. In particular, it shows overwhelming advantages on VIF, MI,and " + }, + { + "bbox": [ + 296, + 601, + 530, + 730 + ], + "type": "inline_equation", + "content": "Q_{abf}" + }, + { + "bbox": [ + 296, + 601, + 530, + 730 + ], + "type": "text", + "content": ", which indicates that our fusion results contain more valuable information and are more beneficial to the visual perception effect of human eyes. The highest SF, SD and AG also indicate that our fusion results preserve sufficient texture detail and contrast. 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Qualitative comparisons of various methods on representative images selected from the LLVIP dataset." + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_caption" + } + ], + "index": 22 + }, + { + "bbox": [ + 45, + 449, + 278, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 449, + 278, + 472 + ], + "spans": [ + { + "bbox": [ + 45, + 449, + 278, + 472 + ], + "type": "text", + "content": "work from local to global, which achieves state-of-the-art fusion performance through the sample adaptive approach." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 45, + 473, + 279, + 729 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 473, + 279, + 729 + ], + "spans": [ + { + "bbox": [ + 45, + 473, + 279, + 729 + ], + "type": "text", + "content": "Qualitative Comparisons. To better show the superiority of our model, we assigned the color information of the 3-channel visible image to the single-channel fused image through the color space conversion between RGB and YCbCr. We mark the background region with the green rectangular box and the foreground region with the red rectangular box. As shown in Fig. 3, our fusion results have the best results in both local and global regions. Compared to PIAFusion, YDTR, AUIF, IFCNN and DIDFuse, our fusion results show better contrast, and our fusion results show better texture details compared to TarDAL and SwinFuse. In daytime scenes, our model adaptively learned sufficient texture detail and significant contrast, such as containers and people. Especially for people, our method significantly avoids the effect of smoke and preserves the contrast information of infrared. In local regions, we successfully preserve the rich texture information of containers, outperforming other methods. In global regions such as mountains, grass and sky, our fusion results also effectively retain texture information, indicating that our method has better visual effects due to dynamic learning of local and global information of different modalities." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 297, + 106, + 463, + 117 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 106, + 463, + 117 + ], + "spans": [ + { + "bbox": [ + 297, + 106, + 463, + 117 + ], + "type": "text", + "content": "4.3. Evaluation on the FLIR dataset" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 296, + 123, + 530, + 332 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 123, + 530, + 332 + ], + "spans": [ + { + "bbox": [ + 296, + 123, + 530, + 332 + ], + "type": "text", + "content": "Quantitative Comparisons. Table 1 reports the performance of the different methods on the FLIR dataset for 8 metrics. Our method achieves the best results in 5 metrics. Among them, the highest EN and MI indicate that our method can preserve abundant information of the multimodal images well. The best performance of our method on SCD and " + }, + { + "bbox": [ + 296, + 123, + 530, + 332 + ], + "type": "inline_equation", + "content": "Q_{abf}" + }, + { + "bbox": [ + 296, + 123, + 530, + 332 + ], + "type": "text", + "content": " also indicates that our fusion results can better learn the multi-modal complementary information and edge information, which makes our fusion results have better foreground-background contrast and richer texture details. Moreover, the highest VIF also demonstrates that our method can generate fused images with better visual effects that are beneficial to human observation. In addition, the third best results on SF, SD, and AG also indicate that our method is highly competitive. The quantitative results on the FLIR dataset also validate the superiority of our method in dynamically fusing multi-modal complementary information from the local to the global." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 296, + 333, + 530, + 554 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 333, + 530, + 554 + ], + "spans": [ + { + "bbox": [ + 296, + 333, + 530, + 554 + ], + "type": "text", + "content": "Qualitative Comparisons. We mark the background region with the green rectangular box and the foreground region with the red rectangular box. We also show their zoomed-in effects for easier comparison. As shown in Fig. 4, our fusion results have the best results in both local and global regions. In night scenes, our fusion results adaptively learn sufficient texture detail and contrast, for example on buildings, trees, mountains and traffic lights. Especially for the traffic lights, our method effectively avoids the effects of glare and best preserves the entire outline of the traffic lights. On the local regions, our fusion results preserve the best contrast information of the pedestrians and the rich detail information of the vehicles. These comparisons illustrate that our method has better visual effects due to the effective dynamic learning of local information from different modalities. The superiority of the proposed MoE-Fusion also reveals that specialized knowledge of multimodal local and global in fusion networks can effectively improve fusion performance." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 297, + 560, + 468, + 571 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 560, + 468, + 571 + ], + "spans": [ + { + "bbox": [ + 297, + 560, + 468, + 571 + ], + "type": "text", + "content": "4.4. Evaluation on the LLVIP dataset" + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 296, + 578, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 578, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 578, + 530, + 730 + ], + "type": "text", + "content": "Quantitative Comparisons. The quantitative results of the different methods on the LLVIP dataset are reported in Table 1. Our method outperforms all the compared methods on 6 metrics and achieved the second and third best results on the remaining 2 metrics, respectively. Specifically, the highest SF and AG we achieved indicate that the proposed method preserves richer texture details in the multi-modal images. As well as the highest SD also indicates that our fusion results can contain the highest contrast information between the foreground and the background. SCD and " + }, + { + "bbox": [ + 296, + 578, + 530, + 730 + ], + "type": "inline_equation", + "content": "Q_{abf}" + }, + { + "bbox": [ + 296, + 578, + 530, + 730 + ], + "type": "text", + "content": " denote the complementary information and edge information transferred from multi-modal images to fused image, respectively, and our highest results on these two metrics" + } + ] + } + ], + "index": 31 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "text", + "content": "23560" + } + ] + } + ], + "index": 32 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 111, + 278, + 247 + ], + "blocks": [ + { + "bbox": [ + 58, + 103, + 265, + 112 + ], + "lines": [ + { + "bbox": [ + 58, + 103, + 265, + 112 + ], + "spans": [ + { + "bbox": [ + 58, + 103, + 265, + 112 + ], + "type": "text", + "content": "Table 2. Ablation studies on three infrared-visible datasets." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 111, + 278, + 247 + ], + "lines": [ + { + "bbox": [ + 48, + 111, + 278, + 247 + ], + "spans": [ + { + "bbox": [ + 48, + 111, + 278, + 247 + ], + "type": "table", + "html": "
M3FD Dataset [18]
ENSFSDMIVIFAGSCDQabf
w/o MoLE6.78560.06929.16362.72140.81005.55091.51530.6535
w/o MoGE6.83510.06959.24912.81380.82615.65211.53460.6375
Att-Local6.86560.06939.18942.73200.82715.58091.51900.6390
MoE-Fusion7.00180.071510.14064.19491.00345.67421.54330.6661
FLIR Dataset [44]
ENSFSDMIVIFAGSCDQabf
w/o MoLE6.90210.058710.28592.36660.53715.69611.09760.3187
w/o MoGE7.31720.054810.66542.92080.77475.25251.66290.4796
Att-Local7.30700.060210.64032.66730.74485.72651.47880.4838
MoE-Fusion7.49250.060310.70073.12090.82125.76041.68180.4991
LLVIP Dataset [11]
ENSFSDMIVIFAGSCDQabf
w/o MoLE6.90770.06619.80902.50390.58124.93581.17390.4732
w/o MoGE7.27400.08479.60342.70670.76215.59601.62600.5110
Att-Local7.25280.08589.54832.71290.85996.10991.63930.5735
MoE-Fusion7.35230.08629.86643.10610.92026.13161.78410.5932
", + "image_path": "78214219ee33ccd14a6df2b3bf793846902cc09f46bffd57ce69296ad9b08bdc.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 268, + 278, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 268, + 278, + 350 + ], + "spans": [ + { + "bbox": [ + 45, + 268, + 278, + 350 + ], + "type": "text", + "content": "indicate that our method can learn more valuable information from multi-modal images. Moreover, the highest VIF also means that our method can generate the most appealing fused images that are more suitable for human vision. These quantitative results demonstrate that the proposed MoE-Fusion can effectively learn multi-modal knowledge and generate informative and appealing fusion results." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 351, + 278, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 351, + 278, + 525 + ], + "spans": [ + { + "bbox": [ + 45, + 351, + 278, + 525 + ], + "type": "text", + "content": "Qualitative Comparisons. We mark the background region with the green rectangular box and the foreground region with the red rectangular box. We also show their zoomed-in effects for easier comparison. As shown in Fig. 5, we can find that the proposed method best preserves the texture details of the local and global in the multi-modal image compared with the state-of-the-art methods, while highlighting the contrast information of the local dynamically. Specifically, for the background region, our fusion results show the sharpest effect on the edge texture of the zebra crossing. For the foreground region, our fusion results preserve the most significant contrast and the richest texture detail in pedestrians and cyclists. Qualitative comparisons show that our MoE-Fusion can balance the texture details and contrasts with the specialized experts dynamically." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 535, + 136, + 547 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 535, + 136, + 547 + ], + "spans": [ + { + "bbox": [ + 45, + 535, + 136, + 547 + ], + "type": "text", + "content": "4.5. Ablation Study" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 554, + 278, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 554, + 278, + 576 + ], + "spans": [ + { + "bbox": [ + 45, + 554, + 278, + 576 + ], + "type": "text", + "content": "We conducted ablation studies on the " + }, + { + "bbox": [ + 45, + 554, + 278, + 576 + ], + "type": "inline_equation", + "content": "\\mathbf{M}^3\\mathrm{FD}" + }, + { + "bbox": [ + 45, + 554, + 278, + 576 + ], + "type": "text", + "content": ", LLVIP, and FLIR datasets and reported the results in Table 2." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 578, + 278, + 729 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 578, + 278, + 729 + ], + "spans": [ + { + "bbox": [ + 45, + 578, + 278, + 729 + ], + "type": "text", + "content": "MoLE. To verify the effectiveness of MoLE, we removed MoLE from MoE-Fusion and then extracted multi-modal features by two encoders only, and they were sent to MoGE after concatenation. As shown in Table 2, all the metrics show a significant decrease after removing MoLE, indicating that MoLE is very effective in learning multi-modal texture details and contrast information. Among others, the decrease on SCD also shows it is difficult to learn complementary multi-modal local information sufficiently without MoLE, which strongly supports our motivation to design MoLE. 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FG denotes foreground, BG denotes background." + } + ] + } + ], + "index": 31, + "angle": 0, + "type": "image_caption" + } + ], + "index": 23 + }, + { + "type": "image", + "bbox": [ + 357, + 218, + 414, + 263 + ], + "blocks": [ + { + "bbox": [ + 357, + 218, + 414, + 263 + ], + "lines": [ + { + "bbox": [ + 357, + 218, + 414, + 263 + ], + "spans": [ + { + "bbox": [ + 357, + 218, + 414, + 263 + ], + "type": "image", + "image_path": "e6d5714d590b55e527c8b0f3ba15b0f51b97a17ac78b84b2f1d3c810c842be89.jpg" + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 367, + 264, + 403, + 271 + ], + "lines": [ + { + "bbox": [ + 367, + 264, + 403, + 271 + ], + "spans": [ + { + "bbox": [ + 367, + 264, + 403, + 271 + ], + "type": "text", + "content": "BG Expert #2" + } + ] + } + ], + "index": 26, + "angle": 0, + "type": "image_caption" + } + ], + "index": 25 + }, + { + "type": "image", + "bbox": [ + 414, + 218, + 471, + 263 + ], + "blocks": [ + { + "bbox": [ + 414, + 218, + 471, + 263 + ], + "lines": [ + { + "bbox": [ + 414, + 218, + 471, + 263 + ], + "spans": [ + { + "bbox": [ + 414, + 218, + 471, + 263 + ], + "type": "image", + "image_path": "b907bcdb6b50e400f48a8864c3ce584cdecfc1851c541c9afca529cf0d86349e.jpg" + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 424, + 264, + 461, + 271 + ], + "lines": [ + { + "bbox": [ + 424, + 264, + 461, + 271 + ], + "spans": [ + { + "bbox": [ + 424, + 264, + 461, + 271 + ], + "type": "text", + "content": "BG Expert #3" + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "image_caption" + } + ], + "index": 27 + }, + { + "type": "image", + "bbox": [ + 472, + 218, + 529, + 263 + ], + "blocks": [ + { + "bbox": [ + 472, + 218, + 529, + 263 + ], + "lines": [ + { + "bbox": [ + 472, + 218, + 529, + 263 + ], + "spans": [ + { + "bbox": [ + 472, + 218, + 529, + 263 + ], + "type": "image", + "image_path": "6f12694d2613e3416bfbb0ea59de354b45848bdd50492ca0943ffa163b46ac5c.jpg" + } + ] + } + ], + "index": 29, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 481, + 264, + 520, + 271 + ], + "lines": [ + { + "bbox": [ + 481, + 264, + 520, + 271 + ], + "spans": [ + { + "bbox": [ + 481, + 264, + 520, + 271 + ], + "type": "text", + "content": "BG Expert # 4" + } + ] + } + ], + "index": 30, + "angle": 0, + "type": "image_caption" + } + ], + "index": 29 + }, + { + "bbox": [ + 296, + 317, + 530, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 317, + 530, + 479 + ], + "spans": [ + { + "bbox": [ + 296, + 317, + 530, + 479 + ], + "type": "text", + "content": "modalities for dynamic fusion, specialized to local regions. MoGE. We replaced the MoGE with a common decoder with the same structure as that of a single expert in the MoGE. As shown in Table 2, all the metrics appear to be significantly decreased, strongly verifying that the MoGE can help fused images preserve more contrast and texture detail information. Moreover, these results also demonstrate that MoGE can effectively motivate the image fusion network to dynamically adapt to different samples, learning better feature representations, and thus achieving better fusion performance. The global dynamic experts of MoGE further enhance the dominant modality from a global perspective while refining the potential errors that may occur in local fusion." + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 296, + 480, + 530, + 644 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 480, + 530, + 644 + ], + "spans": [ + { + "bbox": [ + 296, + 480, + 530, + 644 + ], + "type": "text", + "content": "Attention-based Local Feature. We want to explore how the fusion performance changes when dynamic learning is not performed for local features and only local feature priors constructed by attention maps are used as local features. We designed an attention-based local feature learning module (Att-Local), and to keep the output channels consistent, we followed the Att-Local module with a " + }, + { + "bbox": [ + 296, + 480, + 530, + 644 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 296, + 480, + 530, + 644 + ], + "type": "text", + "content": " convolution layers. In Table 2, all metrics cannot exceed the results of MoE-Fusion with the use of Att-Local, but most of them are higher than w/o MoLE, which demonstrates on the one hand that our proposed MoLE is indeed effective, and on the other hand that the dynamic integration of the effective information from the respective modalities is beneficial to improve the performance of multi-modal image fusion." + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 297, + 653, + 428, + 665 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 653, + 428, + 665 + ], + "spans": [ + { + "bbox": [ + 297, + 653, + 428, + 665 + ], + "type": "text", + "content": "4.6. Analysis and Discussion" + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "text", + "content": "Visualization of MoLE. In the MoLE, we can obtain local feature priors according to the attention map Att, which we define as foreground local features (FG), and we also use " + }, + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "inline_equation", + "content": "1 - \\text{Att}" + }, + { + "bbox": [ + 296, + 671, + 530, + 730 + ], + "type": "text", + "content": " to obtain background local features (BG). We visualize what each expert has learned in MoLE. As shown" + } + ] + } + ], + "index": 35 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 746, + 299, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 299, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 299, + 756 + ], + "type": "text", + "content": "23561" + } + ] + } + ], + "index": 36 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 103, + 102, + 158 + ], + "blocks": [ + { + "bbox": [ + 48, + 103, + 102, + 158 + ], + "lines": [ + { + "bbox": [ + 48, + 103, + 102, + 158 + ], + "spans": [ + { + "bbox": [ + 48, + 103, + 102, + 158 + ], + "type": "image", + "image_path": "f9b0037caf79546a943a30f572f06cb704f497a6cd4ab8bc63e94c707dd69540.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 105, + 103, + 160, + 157 + ], + "blocks": [ + { + "bbox": [ + 105, + 103, + 160, + 157 + ], + "lines": [ + { + "bbox": [ + 105, + 103, + 160, + 157 + ], + "spans": [ + { + "bbox": [ + 105, + 103, + 160, + 157 + ], + "type": "image", + "image_path": "56b4926f448cbef341f47aacddc5e630fb194fd2363a857a325bef175bf44cc1.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 164, + 103, + 219, + 157 + ], + "blocks": [ + { + "bbox": [ + 164, + 103, + 219, + 157 + ], + "lines": [ + { + "bbox": [ + 164, + 103, + 219, + 157 + ], + "spans": [ + { + "bbox": [ + 164, + 103, + 219, + 157 + ], + "type": "image", + "image_path": "cae6071f418c33656bfb288d50b6cbc35031efeb468e1564c6908efc456f865a.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 224, + 103, + 278, + 157 + ], + "blocks": [ + { + "bbox": [ + 224, + 103, + 278, + 157 + ], + "lines": [ + { + "bbox": [ + 224, + 103, + 278, + 157 + ], + "spans": [ + { + "bbox": [ + 224, + 103, + 278, + 157 + ], + "type": "image", + "image_path": "36bc9e6705d66343027c74470bd2c1c18e6f3d224c59d3c758554a822ac6aa4a.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 47, + 161, + 102, + 214 + ], + "blocks": [ + { + "bbox": [ + 47, + 161, + 102, + 214 + ], + "lines": [ + { + "bbox": [ + 47, + 161, + 102, + 214 + ], + "spans": [ + { + "bbox": [ + 47, + 161, + 102, + 214 + ], + "type": "image", + "image_path": "8ae2f20afd10beedaa7c63dabb70fa262a9b5e20a1334a86c4a9b557ec23886c.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 76, + 218, + 247, + 229 + ], + "lines": [ + { + "bbox": [ + 76, + 218, + 247, + 229 + ], + "spans": [ + { + "bbox": [ + 76, + 218, + 247, + 229 + ], + "type": "text", + "content": "Figure 7. Experiments on the number of experts." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 105, + 161, + 160, + 214 + ], + "blocks": [ + { + "bbox": [ + 105, + 161, + 160, + 214 + ], + "lines": [ + { + "bbox": [ + 105, + 161, + 160, + 214 + ], + "spans": [ + { + "bbox": [ + 105, + 161, + 160, + 214 + ], + "type": "image", + "image_path": "f667dafd16422b0543d507b77a4f68f27ecaa5f04d006b091525655cc4b19a7b.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 164, + 161, + 219, + 214 + ], + "blocks": [ + { + "bbox": [ + 164, + 161, + 219, + 214 + ], + "lines": [ + { + "bbox": [ + 164, + 161, + 219, + 214 + ], + "spans": [ + { + "bbox": [ + 164, + 161, + 219, + 214 + ], + "type": "image", + "image_path": "b450399a689ff0ecff9c23fe231984c94d9bf85eef2025dedcadd580b90ceea0.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 223, + 161, + 278, + 214 + ], + "blocks": [ + { + "bbox": [ + 223, + 161, + 278, + 214 + ], + "lines": [ + { + "bbox": [ + 223, + 161, + 278, + 214 + ], + "spans": [ + { + "bbox": [ + 223, + 161, + 278, + 214 + ], + "type": "image", + "image_path": "768b577ddff32aefbba13443e2147efcca4c7634f0c7c2b560460893bf2992ec.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 63, + 250, + 262, + 402 + ], + "blocks": [ + { + "bbox": [ + 61, + 240, + 262, + 250 + ], + "lines": [ + { + "bbox": [ + 61, + 240, + 262, + 250 + ], + "spans": [ + { + "bbox": [ + 61, + 240, + 262, + 250 + ], + "type": "text", + "content": "Table 3. Object detection evaluation on the FLIR dataset." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 63, + 250, + 262, + 402 + ], + "lines": [ + { + "bbox": [ + 63, + 250, + 262, + 402 + ], + "spans": [ + { + "bbox": [ + 63, + 250, + 262, + 402 + ], + "type": "table", + "html": "
MethodscarpersonbicyclemAP
Visible55.9027.2033.2038.70
Infrared68.7045.6030.8048.40
DenseFuse [16]65.8044.7031.4047.30
RFN-Nest [17]58.8036.5026.2040.50
IFCNN [48]67.8045.7034.7049.40
PIAFusion [35]62.6040.9031.5045.00
DIDFuse [49]64.2041.7032.1046.00
AUIF [50]61.7036.8029.6042.70
SwinFuse [40]65.6041.3029.7045.60
YDTR [36]65.0044.2032.5047.20
TarDAL [18]62.5035.4030.8042.90
MoE-Fusion72.9055.0039.5055.80
", + "image_path": "84a795cad70ff0be8858d1e83e7386e379b066408e9a113dffe9b08c94f9ba54.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 45, + 424, + 279, + 482 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 424, + 279, + 482 + ], + "spans": [ + { + "bbox": [ + 45, + 424, + 279, + 482 + ], + "type": "text", + "content": "in Fig. 6, we see that the four foreground local experts can clearly learn foreground information, while the four background local experts can also learn rich background features. These results show that MoLE can successfully let each expert know what it should specialize in." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 45, + 484, + 279, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 484, + 279, + 693 + ], + "spans": [ + { + "bbox": [ + 45, + 484, + 279, + 693 + ], + "type": "text", + "content": "Detection Evaluation. Good fused images should have better performance in downstream tasks. For different image fusion methods, we perform the evaluation on the object detection task and use the mean average precision (mAP) [5] as the metric. Following [51], we first train the object detection model using infrared images and visible images, and then we input the fused images generated by different image fusion methods into the object detection model for inference and evaluate their detection performance. In this paper, we use Faster R-CNN [29] as the object detection algorithm and set the IoU (Intersection over Union) threshold for evaluation to 0.5. According to Table 3, our MoE-Fusion outperforms all the compared methods and achieves the highest mAP. It is worth noting that our method has an overwhelming advantage on all categories, which demonstrate the proposed dynamic image fusion method is more beneficial for downstream tasks. The detection evaluation on other datasets is provided in the supplementary material." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 45, + 694, + 279, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 694, + 279, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 694, + 279, + 730 + ], + "type": "text", + "content": "Number of Experts. In Fig. 7, we performed 4 sets of experiments on the FLIR dataset, E2k2, E4K2, E6K2, and E8K2, to explore the effect of the number of experts on the" + } + ] + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 300, + 103, + 351, + 154 + ], + "blocks": [ + { + "bbox": [ + 300, + 103, + 351, + 154 + ], + "lines": [ + { + "bbox": [ + 300, + 103, + 351, + 154 + ], + "spans": [ + { + "bbox": [ + 300, + 103, + 351, + 154 + ], + "type": "image", + "image_path": "8b63cc1bbfc3acf1d959a067e0c12ee951e0522341321bb8f751d3c181852d0c.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 358, + 104, + 409, + 154 + ], + "blocks": [ + { + "bbox": [ + 358, + 104, + 409, + 154 + ], + "lines": [ + { + "bbox": [ + 358, + 104, + 409, + 154 + ], + "spans": [ + { + "bbox": [ + 358, + 104, + 409, + 154 + ], + "type": "image", + "image_path": "96686f89c872c3a83dce2acdc7a220264a651e2cdc8b96e47fee0669ce2624a7.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + } + ], + "index": 15 + }, + { + "type": "image", + "bbox": [ + 417, + 104, + 467, + 154 + ], + "blocks": [ + { + "bbox": [ + 417, + 104, + 467, + 154 + ], + "lines": [ + { + "bbox": [ + 417, + 104, + 467, + 154 + ], + "spans": [ + { + "bbox": [ + 417, + 104, + 467, + 154 + ], + "type": "image", + "image_path": "8edb6a25b8cabfe1a6e1c509a06d4a21ca2da148d8fe6a7d052d3c2c9a4e61ff.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 475, + 104, + 525, + 154 + ], + "blocks": [ + { + "bbox": [ + 475, + 104, + 525, + 154 + ], + "lines": [ + { + "bbox": [ + 475, + 104, + 525, + 154 + ], + "spans": [ + { + "bbox": [ + 475, + 104, + 525, + 154 + ], + "type": "image", + "image_path": "a914c564327785233c91921d9bfeb1318cf7392555eee76976432abead1ce107.jpg" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_body" + } + ], + "index": 17 + }, + { + "type": "image", + "bbox": [ + 299, + 161, + 351, + 213 + ], + "blocks": [ + { + "bbox": [ + 299, + 161, + 351, + 213 + ], + "lines": [ + { + "bbox": [ + 299, + 161, + 351, + 213 + ], + "spans": [ + { + "bbox": [ + 299, + 161, + 351, + 213 + ], + "type": "image", + "image_path": "0fbcef3f26b393d3e0364e69bf72849df4469d8f8fdcd68245237303fc276c2d.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 297, + 217, + 530, + 228 + ], + "lines": [ + { + "bbox": [ + 297, + 217, + 530, + 228 + ], + "spans": [ + { + "bbox": [ + 297, + 217, + 530, + 228 + ], + "type": "text", + "content": "Figure 8. Hyperparameter sensitivity analysis on the FLIR dataset." + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "type": "image", + "bbox": [ + 358, + 161, + 409, + 213 + ], + "blocks": [ + { + "bbox": [ + 358, + 161, + 409, + 213 + ], + "lines": [ + { + "bbox": [ + 358, + 161, + 409, + 213 + ], + "spans": [ + { + "bbox": [ + 358, + 161, + 409, + 213 + ], + "type": "image", + "image_path": "e9a6c81ac9d154157c9f3d43c04c5658b0bf5e82c72f385a3dc5a81ce769f685.jpg" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_body" + } + ], + "index": 19 + }, + { + "type": "image", + "bbox": [ + 417, + 161, + 467, + 213 + ], + "blocks": [ + { + "bbox": [ + 417, + 161, + 467, + 213 + ], + "lines": [ + { + "bbox": [ + 417, + 161, + 467, + 213 + ], + "spans": [ + { + "bbox": [ + 417, + 161, + 467, + 213 + ], + "type": "image", + "image_path": "b388d7ea6436b2e32aac4288e51ebea520d9744876d5db5d25a70bc1f9106b5d.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + } + ], + "index": 20 + }, + { + "type": "image", + "bbox": [ + 475, + 161, + 525, + 213 + ], + "blocks": [ + { + "bbox": [ + 475, + 161, + 525, + 213 + ], + "lines": [ + { + "bbox": [ + 475, + 161, + 525, + 213 + ], + "spans": [ + { + "bbox": [ + 475, + 161, + 525, + 213 + ], + "type": "image", + "image_path": "9eb45e4b27983eb307a49b03f55e4ab609db75576b592234116d2afb77c35e77.jpg" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_body" + } + ], + "index": 21 + }, + { + "bbox": [ + 296, + 253, + 530, + 382 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 253, + 530, + 382 + ], + "spans": [ + { + "bbox": [ + 296, + 253, + 530, + 382 + ], + "type": "text", + "content": "fusion results. As an example, E4K2 means that the MoE contains 4 experts and sparsely selects top 2 experts for integration. We found that E4K2 was higher than E2K2 in 7 metrics, E6K2 in 6 metrics, and E8K2 in 5 metrics, suggesting that a higher number of experts may not be better. In addition, we also set up 3 sets of experiments, E4K1, E4K3 and E4K4, to verify the effect of sparse selection of experts in MoE on the fusion results. In Fig. 7, we find that E4K2 can outperform E4K1 and E4K3 in 7 metrics and E4K4 in all metrics. Therefore, in this work, we set 4 experts for each MoE and sparsely select 2 experts for integration." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "spans": [ + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "text", + "content": "Hyperparameter. As shown in Fig. 8, we choose five values for tuning parameter " + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "text", + "content": " (1, 5, 10, 20, and 40) and experiment with them in turn. When " + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "text", + "content": " is less than 10, the fusion results fail to exceed the performance on all metrics with " + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "text", + "content": " equal to 10. When " + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "text", + "content": " is greater than 10, there is an improvement in only 2 metrics (SF and AG) compared to " + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "text", + "content": " equal to 10, but the other 6 metrics show a decrease. Therefore, in this work, we set " + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 296, + 384, + 531, + 477 + ], + "type": "text", + "content": " to 10 to obtain better results." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 297, + 497, + 367, + 509 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 497, + 367, + 509 + ], + "spans": [ + { + "bbox": [ + 297, + 497, + 367, + 509 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 296, + 520, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 520, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 520, + 530, + 730 + ], + "type": "text", + "content": "In this paper, we propose a novel dynamic image fusion framework with a multi-modal gated mixture of locally-global experts (MoE-Fusion), which can produce reliable infrared-visible image fusion results. Our framework focuses on dynamically integrating effective information from different source modalities by performing sample-adaptive infrared-visible fusion from local to global. The MoE-Fusion model dynamically balances the texture details and contrasts with the specialized local experts and global experts. The experimental results on three challenging datasets demonstrate that the proposed MoE-Fusion outperforms state-of-the-art methods in terms of visual effects and quantitative metrics. Moreover, we also validate the superiority of our MoE-Fusion in the object detection task. In future work, we will explore leveraging the uncertainty of different images to guide the fusion, and investigate developing an uncertainty-gated MoE paradigm for dynamic image fusion." + } + ] + } + ], + "index": 26 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "text", + "content": "23562" + } + ] + } + ], + "index": 27 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 105, + 140, + 118 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 105, + 140, + 118 + ], + "spans": [ + { + "bbox": [ + 47, + 105, + 140, + 118 + ], + "type": "text", + "content": "Acknowledgments" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 125, + 279, + 205 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 125, + 279, + 205 + ], + "spans": [ + { + "bbox": [ + 45, + 125, + 279, + 205 + ], + "type": "text", + "content": "This work was supported in part by the National Key R&D Program of China 2022ZD0116500, in part by the National Natural Science Foundation of China under Grant 62222608, 62106171, and 61925602, in part by the Haihe Lab of ITAI under Grant 22HHXCJC00002, and in part by the Tianjin Natural Science Foundation under Grant 21JCYBJC00580." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 218, + 102, + 229 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 218, + 102, + 229 + ], + "spans": [ + { + "bbox": [ + 47, + 218, + 102, + 229 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 237, + 279, + 729 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 51, + 237, + 279, + 279 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 51, + 237, + 279, + 279 + ], + "spans": [ + { + "bbox": [ + 51, + 237, + 279, + 279 + ], + "type": "text", + "content": "[1] V Aslantas and Emre Bendes. 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NeurIPS, 2022." + } + ] + } + ], + "index": 29 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 747, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 747, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 747, + 300, + 756 + ], + "type": "text", + "content": "23564" + } + ] + } + ], + "index": 31 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-Modal Neural Radiance Field for Monocular Dense SLAM with a Light-Weight ToF Sensor/d9ac6102-d7cb-4a42-a50b-5549d5aea3c8_content_list.json b/2023/Multi-Modal Neural Radiance Field for Monocular Dense SLAM with a Light-Weight ToF Sensor/d9ac6102-d7cb-4a42-a50b-5549d5aea3c8_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..f7eaf207d80c95604c623c818a601003d8556e2c --- /dev/null +++ b/2023/Multi-Modal Neural Radiance Field for Monocular Dense SLAM with a Light-Weight ToF Sensor/d9ac6102-d7cb-4a42-a50b-5549d5aea3c8_content_list.json @@ -0,0 +1,1576 @@ +[ + { + "type": "text", + "text": "Multi-Modal Neural Radiance Field for Monocular Dense SLAM with a Light-Weight ToF Sensor", + "text_level": 1, + "bbox": [ + 156, + 130, + 816, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Xinyang Liu $^{1}$ , Yijin Li $^{1}$ , Yanbin Teng $^{1}$ , Hujun Bao $^{1}$ , Guofeng Zhang $^{1}$ , Yinda Zhang $^{2}$ , Zhaopeng Cui $^{1*}$ $^{1}$ State Key Lab of CAD&CG, Zhejiang University $^{2}$ Google", + "bbox": [ + 86, + 202, + 893, + 239 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 273, + 313, + 289 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Light-weight time-of-flight (ToF) depth sensors are compact and cost-efficient, and thus widely used on mobile devices for tasks such as autofocus and obstacle detection. However, due to the sparse and noisy depth measurements, these sensors have rarely been considered for dense geometry reconstruction. In this work, we present the first dense SLAM system with a monocular camera and a lightweight ToF sensor. Specifically, we propose a multi-modal implicit scene representation that supports rendering both the signals from the RGB camera and light-weight ToF sensor which drives the optimization by comparing with the raw sensor inputs. Moreover, in order to guarantee successful pose tracking and reconstruction, we exploit a predicted depth as an intermediate supervision and develop a coarse-to-fine optimization strategy for efficient learning of the implicit representation. At last, the temporal information is explicitly exploited to deal with the noisy signals from light-weight ToF sensors to improve the accuracy and robustness of the system. Experiments demonstrate that our system well exploits the signals of lightweight ToF sensors and achieves competitive results both on camera tracking and dense scene reconstruction. Project page: https://zju3dv.github.io/tof_slam/.", + "bbox": [ + 76, + 305, + 473, + 654 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 679, + 209, + 695 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Dense simultaneous localization and mapping (dense SLAM) [38, 8, 9, 44] has extensive applications in augmented reality [13, 17], indoor robotics, etc. It usually relies on high-precision and high-resolution depth sensors, such as time-of-flight (ToF) sensors or structured light sensors. Due to the size, weight, and price issues, these depth sensors are only used in a few high-end mobile devices until recent years. In contrast, light-weight ToF sensors, which are cost-effective, compact, and energy-efficient, were integrated into hundreds of smartphone models1. As a result,", + "bbox": [ + 75, + 704, + 468, + 857 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/77bc33968a493fc838c60c0f1e4ada2d380593bc6e4ae5141b583f480367b426.jpg", + "image_caption": [ + "Figure 1. Monocular Dense SLAM with Our Multi-Modal Implicit Representation. We present a novel SLAM system based on implicit scene representation. The system does not require high-precision and high-resolution depth sensors and only takes RGB images and the signals of light-weight ToF sensors as input." + ], + "image_footnote": [], + "bbox": [ + 506, + 273, + 888, + 532 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "it would be valuable if we could fully utilize these lightweight sensors for dense SLAM, which further facilitates other applications like AR/VR and micro-Robot.", + "bbox": [ + 496, + 643, + 892, + 688 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Unfortunately, limited by the compact electronic design, the light-weight ToF sensor can only provide coarse measurement in the form of depth distribution in an extremely low resolution as illustrated in Fig. 2. Existing RGB-D dense SLAM systems [38, 46, 31] are designed for accurate and pixel-wise depth inputs, thus cannot work with the light-weight ToF signals directly. They will also fail if we simply consider the light-weight ToF signals as a low-resolution depth (i.e., mean depth values in each zone).", + "bbox": [ + 496, + 689, + 893, + 824 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we aim to design a novel learning-based dense SLAM system that provides accurate pose tracking and dense reconstruction taking the RGB sequences from a color camera and the sparse signals of light-weight ToF as input (Fig. 1). However, it is non-trivial to design such", + "bbox": [ + 496, + 825, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author.", + "bbox": [ + 94, + 863, + 222, + 875 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "1https://www.st.com/content/st_com/en/about/", + "bbox": [ + 96, + 875, + 441, + 887 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "media-center/press-item.html/t4210.html", + "bbox": [ + 78, + 888, + 387, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "1", + "bbox": [ + 493, + 945, + 503, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b05aba552881eca49556599d94593055f46606e06b1b0b65e58e42eb386a95da.jpg", + "image_caption": [ + "Figure 2. L5 Sensing Principle. Instead of pixel-wise depth measurement, L5 measures the depth distribution of a large zone and returns its depth mean and variance. Specifically, L5 measures $8 \\times 8$ zones in total. The figure is adapted from [14]." + ], + "image_footnote": [], + "bbox": [ + 99, + 90, + 444, + 305 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "a system. At first, motivated by the recent achievements in the field of neural rendering [20, 2, 40, 39, 41] and grid-based feature encoding [46, 36, 18], we propose to design our system based on a novel implicit representation from which we can render both the RGB image and original ToF signal. In this way, we can define the losses directly against the multi-domain input, which can be utilized to optimize camera poses and 3D scenes. However, we find that this cannot guarantee plausible tracking and reconstruction results because of low-quality raw depth signals from the sensor. Inspired by recent works [31, 46] that high-resolution accurate depth maps play an important role in the implicit SLAM systems, we further exploit the depth estimation model [14] for the light-weight ToF sensor to predict an intermediate high-resolution depth as additional supervision. Based on all the above insights, we develop a multimodal implicit scene representation with multi-level feature grids, which is able to generate both the zone-level signals of light-weight ToF sensors and pixel-wise RGB/depth images via the differentiable rendering for the camera tracking and reconstruction. For efficient network convergence, we also design a coarse-to-fine optimization process for this novel implicit scene representation, i.e., firstly using zone-level ToF signals to optimize the scene at the coarse level, then adding pixel-wise RGB/depth supervisions to recover geometry details.", + "bbox": [ + 75, + 402, + 468, + 792 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Moreover, although the predicted per-pixel depth is generally smooth and provides reasonable supervision as intermediate signals, it may also produce severe artifacts when there is a large portion of missing L5 signals since it is hard for the network to handle such cases due to the inherent depth ambiguity in the missing regions. As a result, we further develop a temporal filtering technique to enhance depth", + "bbox": [ + 75, + 795, + 467, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "prediction. Specifically, when a new signal is captured, we render a zone-level light-weight ToF signal from our multimodal scene representation with an initialized pose and fuse it with that new observation signal, which serves as the input of the depth prediction network. Such an explicit filtering technique improves the depth estimation performance significantly, particularly in extreme cases where the raw L5 signals are very noisy or contain large amounts of missing data, and therefore further benefits the whole SLAM system.", + "bbox": [ + 496, + 90, + 890, + 239 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our contributions can be summarized as follows. At first, to our best knowledge, we present the first dense SLAM system by only taking the monocular images and the signals from a light-weight ToF sensor as input. Moreover, we propose a multi-modal implicit scene representation which supports rendering both the zone-level signals of light-weight ToF sensors and pixel-wise RGB/depth images. By minimizing the re-rendering loss of these signals in a coarse-to-fine strategy, we can recover the camera pose and the scene geometry via differentiable neural rendering. Furthermore, we propose a temporal filtering technique to enhance the signals of light-weight ToF sensors and corresponding depth prediction which significantly improve the proposed SLAM system in extreme cases. Experiments on the real datasets demonstrate that the proposed system well exploits the signals of light-weight ToF sensors and achieves competitive results both on camera tracking and dense scene reconstruction compared to existing methods.", + "bbox": [ + 496, + 242, + 892, + 513 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 527, + 640, + 542 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Visual SLAM. Sparse visual SLAM systems [13, 23, 16] focus on solving accurate camera poses based on the tracking of sparse keypoint [28, 25]. These types of methods usually struggle in texture-less environments and cannot provide a complete reconstruction result of the scene. In comparison, dense visual SLAM systems [10, 38, 11, 24] perform much more robust but usually require depth images as input. More recently, many methods emerged to estimate the dense depth map and camera pose simultaneously from RGB sequences only using deep neural networks [3, 6, 34, 35] and reconstruct the scene through fusing the estimated depth maps. Unlike these previous methods optimizing depth maps per frame, we follow iMAP [31] and NICE-SLAM [46] and use an implicit scene representation. However, unlike iMAP and NICE-SLAM, we do not require the depth camera and take the light-weight ToF signals as input instead.", + "bbox": [ + 496, + 551, + 890, + 809 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Neural Implicit Representation. Neural implicit representations are widely used in various kinds of tasks, including novel view synthesis [20, 45, 2, 19] and scene reconstruction [1, 36, 26]. While showing promising results, these methods require precise camera poses as input which greatly limits their application scenarios. Some re", + "bbox": [ + 496, + 810, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "2", + "bbox": [ + 493, + 945, + 503, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/beb9a7d4e20dce5d4a526f16b2b557f9c77a3ccaec9ec5957228986d7994b517.jpg", + "image_caption": [ + "Figure 3. System Overview. Our method uses a monocular camera and a light-weight ToF sensor as input and recovers both camera motion and the scene structures. Through differentiable rendering, our method can render multi-modal signals, including color images, depth images and zone-level L5 signals. Both the scene structure and the camera poses are optimized by minimizing the re-rendering loss." + ], + "image_footnote": [], + "bbox": [ + 81, + 94, + 883, + 368 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "cent works [15, 42] propose to optimize camera pose with the scene representation simultaneously. Lately, iMAP [31] and NICE-SLAM [46] bring neural implicit representations into visual SLAM systems. Nevertheless, requirements of RGB-D sequences as input significantly constrain their applications, especially on mobile devices with tight power budgets. In contrast, we propose a visual SLAM method using only an RGB camera and a light-weight ToF sensor, which commonly co-exists on mobile devices.", + "bbox": [ + 75, + 450, + 468, + 585 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Neural Grid Optimization. Typically, a single multi-layer perceptron (MLP) is employed to represent the entire scene in earlier neural implicit methods [20, 2, 31]. However, these methods perform poorly when applied to large scenes and need an extremely long time for training. To address this issue, recent works [33, 22, 5] try to optimize neural features on an explicit volumetric grid. These methods, however, are only capable of pixel-level rendering and do not accommodate L5 signals as it has extremely low resolution and measures the depth distribution of a large area. To this end, we introduce a multi-modal feature grid representation that enables rendering multi-modal information at different resolutions and can deal with zone-level depth distribution data measured by light-weight ToF sensors.", + "bbox": [ + 75, + 587, + 468, + 800 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 814, + 168, + 829 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we provide an overview of the sensing principle of light-weight ToF sensors (e.g., L5) in Sec. 3.1. Based on the characteristics of L5's signals, we design the first dense SLAM system with a monocular camera and a", + "bbox": [ + 76, + 840, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "light-weight ToF sensor as shown in Fig. 3. Specifically, we first propose a multi-modal implicit scene representation which enables rendering L5 signals together with the common RGB image and depth maps (Sec. 3.2). To guarantee successful tracking and mapping, we exploit a depth prediction model [14] to predict intermediate per-pixel depth maps as additional supervision. By minimizing the difference between the rendered signals and input/predicted ones, we can simultaneously optimize the camera pose and scene structure in a coarse-to-fine way. Furthermore, since the depth prediction may contain severe artifacts when there is a large portion of missing L5 signals, we propose to refine the L5 signals with temporal filtering techniques to enhance the depth prediction module (Sec. 3.3). Finally, we describe the system implementation detail in Sec. 3.4.", + "bbox": [ + 496, + 450, + 890, + 678 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Preliminaries: L5 Sensing Principle", + "text_level": 1, + "bbox": [ + 500, + 693, + 812, + 710 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Light-weight ToF sensors are designed to be low-cost, small, and low-energy and have been massively deployed on mobile devices. Compared with conventional ToF sensors, which provide high-resolution depth measurement and measure the per-pixel distance to the scene, light-weight ToF sensors usually have extremely low resolution (e.g., $8 \\times 8$ zones) and measure the depth distribution for each zone. Here we take ST VL53L5CX [29] (denoted as L5), a representative product of light-weight ToF sensors, as an example to declare the sensing principle of these sensors. As shown in Fig. 2, L5 measures the depth distribution by counting the received photon number within specific time", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "3", + "bbox": [ + 493, + 945, + 503, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "intervals. The result is then fitted with a Gaussian distribution, and L5 only transmits the mean and variance to decrease both the energy consumption and broadband load. None of the previous studies have explored the usage of L5 for downstream applications like SLAM due to its low resolution and high uncertainty.", + "bbox": [ + 75, + 90, + 468, + 181 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Multi-Modal Implicit Scene Representation", + "text_level": 1, + "bbox": [ + 76, + 193, + 446, + 209 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The combination of neural rendering and grid-based feature encoding has found broad utilization in applications like SLAM and surface reconstruction. [46, 36, 43]. By minimizing the loss between the rendered image/depth and the input image/depth, they achieve accurate 6-DoF camera pose tracking and the reconstruction of scene geometry. In this paper, we propose a multi-modal implicit scene representation, which supports the rendering of zone-level L5 signals apart from the common RGB and depth images. Specifically, we encode the geometry and color separately and propose the masked rendering technique in the geometry encoding for the rendering of both zone-level L5 signals and pixel-level depth images.", + "bbox": [ + 75, + 217, + 468, + 414 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Geometry Encoding with Masked Rendering. The idea of the proposed masked rendering is inspired by the integrated positional encoding(IPE) theory proposed in MipNeRF [2], but we promote it to the grid-based scene representation. The core idea of IPE is that the input features are passed through a low pass filter, i.e., if the frequency of a particular feature has a larger period than the ray, then the feature is unaffected; otherwise, the feature is scaled down towards zero. The original method represents the scene using a single MLP and achieves the low pass filtering by calculating an integral of the positional encoding as input. In our grid-based case, we concatenate features from different-level feature grids and use a rendering mask to mask out features extracted from overly high spatial frequency grids based on the current rendering scale.", + "bbox": [ + 75, + 415, + 468, + 641 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To be more specific, we encode the scene geometry into a multi-level feature grid containing four layers $\\mathcal{V}_{\\theta} = \\{V^0,V^1,V^2,V^3\\}$ . The zone-level feature grid $V^{\\mathrm{zone}}$ contains the coarser feature grids $\\{V^0,V^1\\}$ while the pixel-level feature grid $V^{\\mathrm{pix}}$ contains the finer feature grids $\\{V^2,V^3\\}$ . For a given point $\\mathbf{x}\\in \\mathbb{R}^3$ , its whole geometry feature $\\mathcal{F}$ is extracted by tri-linearly interpolating features at each grid level and concatenating these features together. The feature can be decoded into SDF values in both pixel-level $\\phi_{pix}(\\mathbf{x})$ and zone-level $\\phi_{zone}(\\mathbf{x})$ via the same geometry decoder $f_{\\omega}(\\cdot)$ switched by the rendering mask. We use all the features for rendering pixel-level results $\\phi_{pix}$ , and mask out the features extracted from the finer grids for zone-level rendering results $\\phi_{zone}$ :", + "bbox": [ + 75, + 643, + 470, + 854 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\phi_ {p i x} (\\mathbf {x}) = f _ {\\omega} \\left(\\left[ V ^ {z o n e} (\\mathbf {x}), V ^ {p i x} (\\mathbf {x}) \\right]\\right), \\\\ \\phi_ {z o n e} (\\mathbf {x}) = f _ {\\omega} \\left(\\left[ V ^ {z o n e} (\\mathbf {x}), \\mathbf {0} \\right]\\right). \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 142, + 867, + 403, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "This mask operation also makes the corresponding neurons in the geometry decoder inactive. The SDF values from both branches are used in the tracking and mapping process corresponding to the pixel-level and zone-level supervision, and only the pixel-level SDF values are used for the final mesh extraction.", + "bbox": [ + 496, + 90, + 890, + 180 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Color Encoding. For color information, we encode it only at the finest level using a separate set of feature grid $\\mathcal{W}_{\\beta}$ and decoder $g_{\\gamma}(\\cdot)$ as [46, 36]. When decoding color, we additionally use the ray direction $\\mathbf{r}$ , so the color value for a 3D point is given by:", + "bbox": [ + 496, + 181, + 890, + 257 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {c} = g _ {\\gamma} \\left(\\mathcal {W} _ {\\beta} (\\mathbf {x}), \\mathbf {r}\\right). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 625, + 270, + 890, + 287 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Rendering of L5 Signals, Color and Depth Images. We render color and depth values with the volumetric rendering technique [37]. Specifically, to render a color pixel, we sample $N$ points along the corresponding emitted ray, denoted as $\\mathbf{x}_i = \\mathbf{o} + d_i\\mathbf{r}, i \\in \\{1,2,\\dots,N\\}$ where $\\mathbf{o}$ is the camera center, $\\mathbf{r}$ is the direction of this ray and $d_i$ is the distance of the sampled point $\\mathbf{x}_i$ along the ray. We then accumulate the color value along the ray through:", + "bbox": [ + 496, + 297, + 890, + 419 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {c}} = \\sum_ {i = 1} ^ {N} T _ {i} \\alpha_ {i} \\mathbf {c} _ {i}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 638, + 431, + 890, + 470 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $T_{i} = \\prod_{j = 1}^{i - 1}\\left(1 - \\alpha_{j}\\right)$ is the accumulated transmittance, and $\\alpha_{i}$ is the opacity value converted from the SDF prediction $\\phi_{pix}$ . The conversion follows the original definition in NeuS [37].", + "bbox": [ + 496, + 484, + 890, + 561 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The process of rendering the L5 signals is similar to rendering the color. The differences are that for rendering the mean depth value $\\hat{d}_z$ of an L5 zone, we emit the ray from the center of that zone and accumulate the distance along the ray through:", + "bbox": [ + 496, + 561, + 890, + 638 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {d} _ {z} = \\sum_ {i = 1} ^ {N} T _ {i} \\alpha_ {i} d _ {i}. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 635, + 648, + 890, + 690 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The zone-level opacity $\\alpha_{i}$ is derived in the same manner as color rendering but using $\\phi_{zone}$ instead of $\\phi_{pix}$ . Intuitively, we can optimize the camera pose and scene structure by only supervising the rendered color images and L5 signals. However, in our experiment (Sec. 4.3), we show that the results are far from satisfactory. As a result, we also render the pixel-wise depth maps using Eq. 4 with $\\phi_{pix}$ and supervise it with the depth prediction from [14].", + "bbox": [ + 496, + 700, + 890, + 821 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Temporal Filtering of L5 Signals", + "text_level": 1, + "bbox": [ + 500, + 830, + 785, + 848 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As mentioned before, we use DELTAR [14] to predict a pixel-wise depth map as additional supervision. DELTAR is a pre-trained neural network that takes L5 signals and RGB", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "4", + "bbox": [ + 493, + 946, + 503, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/25e881c9f86476ee4504f924530a95db7dcd416599d09fa438f54d5032b9894f.jpg", + "image_caption": [ + "Figure 4. Temporal Filtering of L5 Signals. By fusing the latest ToF measurement with a rendered one, we can significantly improve the signal quality and the corresponding predicted depth." + ], + "image_footnote": [], + "bbox": [ + 80, + 93, + 467, + 205 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "images as input and predicts corresponding depth maps. We observe that when there are a large number of missing or noisy L5 signals, the depth map predicted by DELTAR may contain severe artifacts due to the inherent depth ambiguities of missing or noisy regions, thus further contaminating the learning of implicit features and degrading the SLAM system's performance.", + "bbox": [ + 75, + 289, + 467, + 393 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "This motivates us to develop an explicit temporal filtering technique (Fig. 4) to enhance the L5 signals before feeding into DELTAR. Since the past observations are stored implicitly in our scene representation, we can leverage this information to refine the current observation. Specifically, the proposed filtering algorithm contains two steps: the prediction step and the update step. In the prediction step, we predict the per-zone ToF measurement $X_{k} = \\{\\mu_{1},\\sigma_{1}\\}$ in the timestamp $k$ using neural rendering (Eq. 4) with an initialized pose. Then we update $X_{k}$ to $X_{k}^{\\prime}$ with the current L5 measurement $Z_{k} = \\{\\mu_{2},\\sigma_{2}\\}$ :", + "bbox": [ + 75, + 395, + 467, + 561 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mu_ {X _ {k ^ {\\prime}}} = \\frac {\\mu_ {1} \\sigma_ {2} ^ {2} + \\mu_ {2} \\sigma_ {1} ^ {2}}{\\sigma_ {1} ^ {2} + \\sigma_ {2} ^ {2}}, \\quad \\sigma_ {X _ {k ^ {\\prime}}} ^ {2} = \\frac {\\sigma_ {1} ^ {2} \\sigma_ {2} ^ {2}}{\\sigma_ {1} ^ {2} + \\sigma_ {2} ^ {2}}. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 125, + 569, + 467, + 604 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As for the zones with no valid raw L5 signals, we simply use the predicted L5 signals. Finally, the enhanced signals $X_{k}^{\\prime}$ are fed into the depth prediction network with corresponding RGB image [14] to obtain a high-resolution depth estimation.", + "bbox": [ + 76, + 611, + 467, + 686 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. SLAM System Implementation", + "text_level": 1, + "bbox": [ + 76, + 696, + 352, + 712 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Initialization. Since we do not have reliable depth maps as input, we need to perform initialization in order to build a local map for our system to bootstrap. The first $N_{i}$ frames are added to the initialization process with a fixed interval $I_{skip}$ sequentially. The pose of each newly added frame is initialized by the previous frame. During this process, the feature grids, decoders and camera poses are jointly optimized using the same loss function as in the mapping process. Finally, when all the frames are added, we optimize the whole frame set for $N_{e}$ iterations.", + "bbox": [ + 75, + 719, + 467, + 869 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Coarse-to-Fine Mapping. To optimize the scene representation mentioned in Sec. 3.2, we uniformly sample total", + "bbox": [ + 75, + 869, + 467, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$M$ pixels and $Z$ zones and perform optimization to minimize the photometric loss, geometric loss and SDF regularization. The zones and pixels are sampled from the current optimization window, which consists of two types of frames: neighbor frames (the nearest $N_{n}$ frames with an interval of 4) and global frames (chosen from all the past co-visible mapping frames). The photometric loss is the average color difference of all the sampled pixels:", + "bbox": [ + 498, + 90, + 890, + 212 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {c} = \\frac {1}{M} \\sum_ {m = 1} ^ {M} | I [ u _ {m}, v _ {m} ] - \\hat {\\mathbf {c}} _ {m} |, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 584, + 223, + 890, + 263 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $u_{m}, v_{m}$ represents for the image coordinate of pixel $m$ . The geometric loss is calculated on both pixel-level and zone-level. For zone-level loss, only zones with valid L5 signals $Z_{d}$ are considered. We also add SDF supervision on pixel-level as in [36, 26] to add robustness to the optimization. The whole geometric loss is defined as:", + "bbox": [ + 498, + 276, + 890, + 366 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {g} = \\mathcal {L} _ {d} + \\mathcal {L} _ {z} + \\lambda_ {s d f} \\mathcal {L} _ {s d f},\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 378, + 769, + 396 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {d} = \\frac {1}{M} \\sum_ {m = 1} ^ {M} | \\widetilde {D} [ u _ {m}, v _ {m} ] - \\hat {d} _ {m} |, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 398, + 890, + 439 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {z} = \\frac {1}{| Z _ {d} |} \\sum_ {z \\in Z _ {d}} | \\bar {D} _ {z} - \\hat {d} _ {z} |,\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 441, + 766, + 479 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\overline{D} \\in \\mathbb{R}^{8 \\times 8}$ represents the mean depth value measured by L5 and $\\widetilde{D}$ represents the pixel-wise depth prediction. Since we do not have high-quality depth as input and there are many texture-less areas in typical indoor scenes, directly optimizing the feature volume and camera poses is an ill-posed problem. Therefore, we employ two regularizations on the SDF values during pixel-level rendering as [36], namely the eikonal term $\\mathcal{L}_{eik}$ and the smoothness term $\\mathcal{L}_s$ :", + "bbox": [ + 498, + 491, + 890, + 613 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {r} = \\lambda_ {e i k} \\mathcal {L} _ {e i k} + \\lambda_ {s} \\mathcal {L} _ {s}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 614, + 631, + 890, + 646 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the eikonal regularization is employed to ensure the network produces valid SDF values [37, 36], the smoothness regularization is used to encourage neighbor points to have similar normal directions, and $\\lambda_{eik}$ and $\\lambda_s$ are weights to balance the two regularization terms.", + "bbox": [ + 498, + 654, + 890, + 729 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "During the mapping process, we perform a coarse-to-fine optimization process, bringing better convergence since pixel-wise optimization can rely on the already initialized coarse grids. We first optimize the scene at the coarse level using zone-level ToF signals. Then, pixel-wise RGB/depth supervisions are added to jointly optimize the decoders, feature grids and camera poses by minimizing the mentioned losses for $N_{m}$ iterations with a local BA to cover geometry details.", + "bbox": [ + 496, + 731, + 890, + 864 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\theta , \\omega , \\beta , \\gamma , \\left\\{\\mathbf {R} _ {i}, \\mathbf {t} _ {i} \\right\\}} \\lambda_ {c} \\mathcal {L} _ {c} + \\lambda_ {g} \\mathcal {L} _ {g} + \\lambda_ {r} \\mathcal {L} _ {r}. \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 878, + 890, + 902 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "5", + "bbox": [ + 493, + 945, + 503, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/2a39c9be56d585f42ddb2a9eb1aea1d00cafc14fd1c4f86f268df6f791fe5d53.jpg", + "image_caption": [ + "Figure 5. Qualitative Reconstruction Results. Compared to other methods, our approach produces high-quality reconstructions with smooth surfaces and fewer artifacts." + ], + "image_footnote": [], + "bbox": [ + 101, + 88, + 869, + 460 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We also conduct a global BA every $N_g$ frame by adding all the past mapping frames to the optimization window and jointly optimize them to globally optimize the camera poses and scene geometry. We provide the details of losses in the supplementary material.", + "bbox": [ + 75, + 523, + 468, + 599 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Tracking. During tracking, the feature grid and the decoders remain fixed, while only the 6-DoF pose of the current frame is optimized. Similar to previous methods [46, 31], $M_t$ pixels are sampled in the current frame to calculate both the pixel-level photometric loss and geometric loss as previously described. The camera pose is then updated iteratively via back-propagation. Tracking with only pixel-level supervision is susceptible to a suboptimal solution, so we leverage our multi-modal scene representation and apply zone-level supervision in the early stage. Specifically, we additionally sample $Z$ zones in the current frame and use the L5 signal to minimize zone depth loss as well, which leads to a more robust tracking result.", + "bbox": [ + 75, + 602, + 470, + 799 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 818, + 209, + 834 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Experimental Setup", + "text_level": 1, + "bbox": [ + 76, + 844, + 267, + 861 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Datasets. Since no public SLAM benchmarks take the L5 signals as input, we build a data capture device as in [14]", + "bbox": [ + 75, + 869, + 468, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "and use it to create an indoor SLAM dataset, which contains 7 sequences captured in 5 typical indoor scenes. We record color images $(640\\times 480)$ , L5 signals and depth maps for each sequence. Note that we only use the color images and L5 signals as the input to our SLAM system. The depth maps are used to obtain the ground truth 6-DoF camera poses and 3D surface mesh. We follow the automated capture pipeline proposed in ScanNet [7] to compute the ground truth data.", + "bbox": [ + 496, + 523, + 890, + 660 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Baselines. We compare our method with two categories of baselines: (a) learning-based SLAM methods including iMAP [31] (re-implemented by [46]) and NICE-SLAM [46]; (b) traditional SLAM methods including ORBSLAM3 [4], KinectFusion [10], ElasticFusion [38] and BundleFusion [8]. For the methods that only support RGB-D input, including iMAP, NICE-SLAM, KinectFusion, ElasticFusion and BundleFusion, we use the RGB image and the predicted depth map by [14] as the system input. For ORB-SLAM3, we evaluate it in both the RGB version (given only RGB image as input) and the RGB-D version (using the predicted depth, marked as $\\widetilde{D}$ ). Note that none of these methods can work well with only raw L5 zone-level depths or take it as additional inputs. We evaluate both the scene reconstruction and the camera tracking results. Since", + "bbox": [ + 496, + 674, + 892, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "6", + "bbox": [ + 493, + 946, + 503, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/d79e79c4bdf57a36153d98e520cfed7de766ab7ecaaf868cabdb38662ddd2517.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Scene NameKitchenSofaOfficeReceptionLiving roomOffice2Sofa2Avg.
KinectFusion[10]Acc.↓-0.1900.2110.261-0.2670.1350.213
Comp.↓-0.0480.0460.064-0.0780.0640.060
F-score-0.2780.2880.285-0.2740.3810.301
ElasticFusion[38]Acc.↓0.0920.1350.0840.2970.1510.0960.1220.140
Comp.↓0.0650.0480.0820.3050.2160.1470.0470.130
F-score0.5530.4200.5290.2740.3820.4160.4810.436
BundleFusion[8]Acc.↓0.1700.1000.1030.122-0.1210.1230.123
Comp.↓0.0880.0300.0380.057-0.2140.0340.077
F-score0.3730.5710.4740.470-0.4420.5270.476
iMAP[31]Acc.↓-0.1350.2290.3650.2250.2330.1390.221
Comp.↓-0.0540.1030.2450.2910.1390.0690.150
F-score-0.4450.3150.2380.1700.2550.4160.307
NICE-SLAM[46]Acc.↓0.3030.1190.1160.2160.1030.1560.4640.211
Comp.↓0.4560.0420.0700.1990.0890.1630.0450.152
F-score0.2210.5540.4110.4020.4000.2730.4010.380
OursAcc.↓0.0810.0680.0670.0790.0780.1130.1210.087
Comp.↓0.0710.0410.0450.0620.1220.0850.0330.066
F-score0.5590.6610.6460.6430.4960.5570.6560.604
", + "bbox": [ + 130, + 88, + 841, + 362 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/f9ea8432ce6007589d04c4945b2c3d64d32625bb6a56823e6db2ace19bccbe90.jpg", + "table_caption": [ + "Table 1. Quantitative Comparison on Reconstruction. We perform the mapping evaluation on 7 indoor sequences and report results of three metrics including accuracy (Acc.), completion (Comp.) and F-score. The failure cases are marked as “-”." + ], + "table_footnote": [], + "table_body": "
Scene NameKitchenSofaOfficeReceptionLiving roomOffice2Sofa2
ORB-SLAM3 [4]0.054-0.0170.025-0.022-
ORB-SLAM3(with D) [4]0.0820.0350.0190.049-0.058-
KinectFusion [10]-0.1460.2090.157-0.3210.125
ElasticFusion [38]0.2530.1100.0700.1930.5300.1210.146
BundleFusion [8]0.1760.1020.1350.101-0.1630.120
iMAP [31]-1.6580.3380.6480.6790.3440.214
NICE-SLAM [46]0.7450.1440.1550.2510.2890.2280.421
Ours0.1130.0810.0560.1140.2000.1010.085
", + "bbox": [ + 163, + 402, + 805, + 537 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2. Camera Tracking Results. ATE RMSE [m] (↓) is used as the evaluation metric. The failure cases are marked as “-”. For the variations of ORB-SLAM3, we only mark the best one in each sequence. Our approach outperforms all the other methods except for ORB-SLAM3 [4]. However, ORB-SLAM3 fails on 3 of the 7 sequences due to the textureless indoor environment while our approach tracks successfully on all of the sequences.", + "bbox": [ + 75, + 537, + 893, + 594 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ORB-SLAM3 cannot output dense models, we exclude it from the mapping evaluation.", + "bbox": [ + 75, + 617, + 470, + 648 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Implementation Details. Our SLAM system is executed on a desktop PC equipped with an Intel i7-9700K CPU and an NVIDIA RTX 3090 GPU. In all our experiments, we set the grid sizes to [3, 6, 24, 96] cm and the number of sampling pixels $M$ to 5000. Our method is implemented using PyTorch [27] with ADAM [12] optimizer. The decoders, multi-modal feature grids, and camera poses are trained with learning rates of 0.001, 0.01, and 0.0005, respectively. The loss weights are set to 10 for $\\lambda_{c}$ and $\\lambda_{sdf}$ and 1 for the others. Inspired by instant-ngp [22], we use the tiny-cuda-nn [21] library to implement the proposed multimodal grid encoding, which significantly accelerates the optimization process. We follow DELTAR [14] to pre-train the multi-modal depth prediction network on NYU-V2 with simulated L5 signals. For more details, please refer to the supplementary material.", + "bbox": [ + 75, + 657, + 472, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Evaluation of Mapping and Tracking", + "text_level": 1, + "bbox": [ + 498, + 617, + 821, + 633 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Mapping. We use three metrics to evaluate the reconstruction result including accuracy (Acc.), completion (Comp.) and F-score following the previous work [32]. For detailed descriptions of these metrics, please refer to the supplementary material. As shown in Table 1, our method outperforms all the baseline methods by a large margin (ours 0.604 vs. the second-best 0.476 in terms of F-score). We also show qualitative results in Fig. 5. Our method is able to produce high-quality 3D models with smooth surfaces and high accuracy. It is easy to notice that our reconstruction result has much fewer artifacts and noisy points. Since NICE-SLAM [46] relies on high-quality depth input, its performance is poor given the noisy and unreliable depth input.", + "bbox": [ + 496, + 642, + 890, + 839 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Tracking. We use ATE RMSE [30] to evaluate the camera tracking. As shown in Table 2, our method outperforms all other methods except for ORB-SLAM3 [4]. However, ORB-SLAM3 is much less robust and tracks lost on 3 of", + "bbox": [ + 496, + 839, + 893, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "7", + "bbox": [ + 493, + 945, + 504, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/1ec41855dceffa5c4dd534f8da5ebd0bb18da321a31eec3759858bc6fe6b2540.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
EMKitchenSofaOfficeReceptionLiving roomOffice2Sofa2Avg.
0.2030.0880.0630.1430.2160.1200.0940.132
✓0.1350.0850.0600.1440.2110.1080.0890.119
✓✓0.1130.0810.0560.1140.2000.1010.0850.107
", + "bbox": [ + 192, + 88, + 777, + 151 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/188260e69dbca5e59bd57bdf47750987a58648c1dcbcba4f3774f74478eaa173.jpg", + "table_caption": [ + "Table 3. Ablation Study. We explore the efficiency of multi-modal scene representation (marked as “M”) and L5 signal temporal filtering (marked as “E”). We use ATE RMSE [m] (↓) as the evaluation metric." + ], + "table_footnote": [], + "table_body": "
TrackingMapping
Learning-based MethodsiMAP [31]101 ms448 ms
NICE-SLAM [46]470 ms1300 ms
Ours116 ms380 ms
Classical MethodsORB-SLAM3 [4]31 ms159 ms
ElasticFusion [38]31 ms-
", + "bbox": [ + 78, + 202, + 467, + 292 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 4. Runtime Comparison. Different from NICE-SLAM [46] that measures one iteration of optimization, we report the averaging total runtime for tracking and mapping respectively for better comparison with classic methods. ElasticFusion does not have an explicit mapping process thus it is labeled as “-”.", + "bbox": [ + 76, + 294, + 467, + 363 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9d91c5f5f5b0daf6f2cbb3fb71fe82d5db633b251a37770ed00d963e7ee06f50.jpg", + "image_caption": [ + "Figure 6. Results without Pixel-Wise Depth Supervision. It cannot guarantee plausible reconstruction results without the pixel-wise depth maps as additional supervision." + ], + "image_footnote": [], + "bbox": [ + 81, + 376, + 467, + 498 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "the 7 sequences, while our method successfully tracks all the sequences. This is because that ORB-SLAM3, as a keypoint-based method, struggles in texture-less regions, which are commonly seen in indoor environments. Given the predicted depth, ORB-SLAM3 can reduce the lost ratio from $42.8\\%$ to $28.5\\%$ but leads to worse camera tracking results since the predicted depth is not accurate enough.", + "bbox": [ + 75, + 580, + 468, + 686 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Runtime Analysis. We compare the runtime of tracking and mapping in Table 4 for both classical methods and learning-based methods. The runtime of our method is similar to iMAP, but it is faster than NICE-SLAM due to our implementation optimization inspired by instant-ngp [22].", + "bbox": [ + 75, + 686, + 468, + 762 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 771, + 230, + 787 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this section, we first study the effectiveness of using pixel-wise depth prediction as additional supervision, then investigate the importance of the proposed multi-modal feature grid representation and the temporal filtering technique. Impact of the Pixel-Wise Depth Supervision. We try using only the L5 raw signals and RGB images for supervision. Removing the pixel-wise depth supervision makes", + "bbox": [ + 75, + 794, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0b0967ef6aa79f3e79d2c967dce6bd7811854a552316828a14fc0a4d0979fe14.jpg", + "image_caption": [ + "RGB/GT" + ], + "image_footnote": [], + "bbox": [ + 503, + 203, + 604, + 321 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/815fc6ec20f282c6c31787913c7156c60ceb1589a9411f55cb5a0c8e92154f5d.jpg", + "image_caption": [ + "L5 Signal" + ], + "image_footnote": [], + "bbox": [ + 607, + 203, + 687, + 321 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4356fefe6895ecad8bd3df299fb0c9538dc95c63ac3ba18b1ed18381eed5d558.jpg", + "image_caption": [ + "Predicted Depth" + ], + "image_footnote": [], + "bbox": [ + 692, + 203, + 789, + 321 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/25726e2eeab16b6483ecea7627b9c7125a016ed979959caf5a51cf56a430536d.jpg", + "image_caption": [ + "Error Map", + "Figure 7. Qualitative Study of the Effect of Temporal Filtering on Depth Prediction. We compare the depth prediction result obtained through two methods: solely employing raw L5 signals (top row) and incorporating our temporal filtering technique (bottom row). Our temporal filtering technique enhances the raw L5 signals and fills up the missing regions, leading to a better depth prediction result." + ], + "image_footnote": [], + "bbox": [ + 792, + 203, + 890, + 321 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "the optimization problem harder, which is more obvious when the problem size grows. In Fig. 6 we show the rendered depth when optimizing the first frame and the first 150 frames. The latter contains serious errors. As a result, it leads to a distorted reconstruction, i.e., the \"Baseline\" result in the upper right.", + "bbox": [ + 498, + 484, + 890, + 575 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Impact of the Multi-Modal Feature Grid. We verify the effectiveness of our multi-modal feature grid representation (denoted as “M”) in terms of camera tracking and show the result in Table 3. With the multi-modal feature grid representation, we are able to use raw L5 signal as supervision. As a result, we can optimize the camera poses on both pixel-level and zone-level, leading to better trajectory accuracy.", + "bbox": [ + 498, + 577, + 890, + 683 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Impact of the Temporal Filtering. In Fig. 7 we show the qualitative comparison with and without the proposed temporal filtering. It can be seen that the large portion of missing L5 signals leads to severe errors on the corresponding regions of the predicted depth map. The error reduces significantly with the proposed temporal filtering technique.", + "bbox": [ + 496, + 686, + 890, + 777 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We also study the quantitative impact of temporal filtering (marked as \"E\") on both the depth prediction (Table 5) and the camera tracking (Table 3). We divide the testing sequences into normal and hard cases according to the quality of L5 signals. As shown in Table 5, the temporal filtering technique improves the predicted depth in general and significantly in hard cases. Such an improvement benefits the final SLAM system and leads to more accurate camera", + "bbox": [ + 496, + 779, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "8", + "bbox": [ + 493, + 945, + 503, + 955 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/5f8aa80438a45ee867806ef78e1d899d29b2adec867c708ef2ffffc4fb754b3c.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
δ1↑δ2↑δ3↑REL↓RMSE↓
Hw/o E0.7730.9100.9690.1590.513
w E0.9250.9720.9830.0930.366
Nw/o E0.9540.9890.9970.0650.151
w E0.9560.9920.9980.0650.145
", + "bbox": [ + 78, + 88, + 446, + 164 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Table 5. Ablation Study on Temporal Filtering for Depth Prediction. “H”/“N” stands for the hard/normal cases and “E” represents the temporal filtering. We report the quantitative result of depth maps predicted from L5 raw signals and our refined signals.", + "bbox": [ + 76, + 166, + 468, + 222 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/46aa0e638c670513eff902d702630d2c70fc879ac55cc13049d58593959e1627.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 91, + 238, + 245, + 325 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/0222d4b2428a33cfa30cfc614c67a4eb032d595f0101284736054e590c856ea1.jpg", + "image_caption": [ + "Outdoor Scene" + ], + "image_footnote": [], + "bbox": [ + 91, + 325, + 243, + 412 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/b102b3c1fb96c20abb8e283d0c49cdbed6c45f3f6f25649811de8cba6c3d4901.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 248, + 237, + 454, + 323 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/c25cef289f243897dbccf2c137f0551911bdb5a1655fc717059a6de4fbd064f9.jpg", + "image_caption": [ + "Our Reconstruction", + "Figure 8. Qualitative Results of Outdoor Reconstruction. The proposed method can recover a complete scene model in outdoor scenes but missing more details than that in indoor due to the poor L5 signals." + ], + "image_footnote": [], + "bbox": [ + 253, + 327, + 450, + 414 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "tracking, as shown in Table 3 (marked as “E”). Please refer to the supplementary material for the definition of the normal/hard cases and the depth evaluation metrics.", + "bbox": [ + 75, + 527, + 468, + 574 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "4.4. Performance in Outdoor Scenes", + "text_level": 1, + "bbox": [ + 76, + 582, + 357, + 595 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Currently, we focus on indoor scenes as other NeRF-based SLAM systems [31, 46] due to the optical interference limitation of depth sensors. Actually, the sunlight has a stronger interference on the L5 sensor for its low-power emitter. In Fig. 8, we show two examples of outdoor scene reconstruction using our proposed methods. The recovered mesh is complete but missing more details than that in indoor scenes due to the poor L5 signals.", + "bbox": [ + 75, + 604, + 468, + 726 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 739, + 194, + 753 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We introduce a novel dense visual SLAM framework working with RGB cameras and light-weight ToF sensors using neural implicit scene representation. To accommodate this new input modality, we propose a novel multimodal feature grid that enables both zone-level rendering for the ToF sensors and pixel-level rendering for other high-resolution signals. To guarantee robust tracking and mapping, we exploit a per-pixel depth prediction as additional supervision, which is further improved by a novel tempo", + "bbox": [ + 75, + 763, + 468, + 902 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "ral filtering strategy. Our experiments demonstrate that the proposed method can provide accurate camera tracking and high-quality reconstruction result on indoor scenes. Similar to other NeRF-based RGB-D SLAM systems, as future work we plan to further improve the system to overcome the limitation of ToF sensors in outdoor scenarios and make it efficient enough to run on mobile robots.", + "bbox": [ + 496, + 90, + 890, + 196 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements: This work was partially supported by NSF of China (No. 62102356).", + "bbox": [ + 498, + 198, + 890, + 227 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 500, + 244, + 596, + 260 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Dejan Azinović, Ricardo Martin-Brualla, Dan B Goldman, Matthias Nießner, and Justus Thies. Neural RGB-D surface reconstruction. 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In Proceedings of the IEEE/CVF Conference on" + ], + "bbox": [ + 78, + 92, + 468, + 900 + ], + "page_idx": 10 + }, + { + "type": "text", + "text": "Computer Vision and Pattern Recognition, pages 12786-12796, 2022.", + "bbox": [ + 535, + 92, + 890, + 119 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "11", + "bbox": [ + 491, + 946, + 504, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multi-Modal Neural Radiance Field for Monocular Dense SLAM with a Light-Weight ToF Sensor/d9ac6102-d7cb-4a42-a50b-5549d5aea3c8_model.json b/2023/Multi-Modal Neural Radiance Field for Monocular Dense SLAM with a Light-Weight ToF Sensor/d9ac6102-d7cb-4a42-a50b-5549d5aea3c8_model.json new file mode 100644 index 0000000000000000000000000000000000000000..aec6703f28b5957b7b9fb57fbfb307ebbd1d9a0a --- /dev/null +++ b/2023/Multi-Modal Neural Radiance Field for Monocular Dense SLAM with a Light-Weight ToF Sensor/d9ac6102-d7cb-4a42-a50b-5549d5aea3c8_model.json @@ -0,0 +1,2147 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.157, + 0.131, + 0.817, + 0.177 + ], + "angle": 0, + "content": "Multi-Modal Neural Radiance Field for Monocular Dense SLAM with a Light-Weight ToF Sensor" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.203, + 0.894, + 0.24 + ], + "angle": 0, + "content": "Xinyang Liu\\(^{1}\\), Yijin Li\\(^{1}\\), Yanbin Teng\\(^{1}\\), Hujun Bao\\(^{1}\\), Guofeng Zhang\\(^{1}\\), Yinda Zhang\\(^{2}\\), Zhaopeng Cui\\(^{1*}\\) \n\\(^{1}\\)State Key Lab of CAD&CG, Zhejiang University \\(^{2}\\)Google" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.274, + 0.314, + 0.29 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.306, + 0.474, + 0.655 + ], + "angle": 0, + "content": "Light-weight time-of-flight (ToF) depth sensors are compact and cost-efficient, and thus widely used on mobile devices for tasks such as autofocus and obstacle detection. However, due to the sparse and noisy depth measurements, these sensors have rarely been considered for dense geometry reconstruction. In this work, we present the first dense SLAM system with a monocular camera and a lightweight ToF sensor. Specifically, we propose a multi-modal implicit scene representation that supports rendering both the signals from the RGB camera and light-weight ToF sensor which drives the optimization by comparing with the raw sensor inputs. Moreover, in order to guarantee successful pose tracking and reconstruction, we exploit a predicted depth as an intermediate supervision and develop a coarse-to-fine optimization strategy for efficient learning of the implicit representation. At last, the temporal information is explicitly exploited to deal with the noisy signals from light-weight ToF sensors to improve the accuracy and robustness of the system. Experiments demonstrate that our system well exploits the signals of lightweight ToF sensors and achieves competitive results both on camera tracking and dense scene reconstruction. Project page: https://zju3dv.github.io/tof_slam/." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.68, + 0.21, + 0.696 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.47, + 0.858 + ], + "angle": 0, + "content": "Dense simultaneous localization and mapping (dense SLAM) [38, 8, 9, 44] has extensive applications in augmented reality [13, 17], indoor robotics, etc. It usually relies on high-precision and high-resolution depth sensors, such as time-of-flight (ToF) sensors or structured light sensors. Due to the size, weight, and price issues, these depth sensors are only used in a few high-end mobile devices until recent years. In contrast, light-weight ToF sensors, which are cost-effective, compact, and energy-efficient, were integrated into hundreds of smartphone models1. As a result," + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.275, + 0.889, + 0.534 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.549, + 0.895, + 0.621 + ], + "angle": 0, + "content": "Figure 1. Monocular Dense SLAM with Our Multi-Modal Implicit Representation. We present a novel SLAM system based on implicit scene representation. The system does not require high-precision and high-resolution depth sensors and only takes RGB images and the signals of light-weight ToF sensors as input." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.893, + 0.689 + ], + "angle": 0, + "content": "it would be valuable if we could fully utilize these lightweight sensors for dense SLAM, which further facilitates other applications like AR/VR and micro-Robot." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.69, + 0.895, + 0.825 + ], + "angle": 0, + "content": "Unfortunately, limited by the compact electronic design, the light-weight ToF sensor can only provide coarse measurement in the form of depth distribution in an extremely low resolution as illustrated in Fig. 2. Existing RGB-D dense SLAM systems [38, 46, 31] are designed for accurate and pixel-wise depth inputs, thus cannot work with the light-weight ToF signals directly. They will also fail if we simply consider the light-weight ToF signals as a low-resolution depth (i.e., mean depth values in each zone)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.895, + 0.903 + ], + "angle": 0, + "content": "In this paper, we aim to design a novel learning-based dense SLAM system that provides accurate pose tracking and dense reconstruction taking the RGB sequences from a color camera and the sparse signals of light-weight ToF as input (Fig. 1). However, it is non-trivial to design such" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.864, + 0.223, + 0.876 + ], + "angle": 0, + "content": "*Corresponding author." + }, + { + "type": "page_footnote", + "bbox": [ + 0.097, + 0.876, + 0.442, + 0.888 + ], + "angle": 0, + "content": "1https://www.st.com/content/st_com/en/about/" + }, + { + "type": "page_footnote", + "bbox": [ + 0.079, + 0.889, + 0.388, + 0.9 + ], + "angle": 0, + "content": "media-center/press-item.html/t4210.html" + }, + { + "type": "list", + "bbox": [ + 0.079, + 0.864, + 0.442, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.495, + 0.946, + 0.504, + 0.956 + ], + "angle": 0, + "content": "1" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.1, + 0.092, + 0.446, + 0.306 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.319, + 0.471, + 0.378 + ], + "angle": 0, + "content": "Figure 2. L5 Sensing Principle. Instead of pixel-wise depth measurement, L5 measures the depth distribution of a large zone and returns its depth mean and variance. Specifically, L5 measures \\(8 \\times 8\\) zones in total. The figure is adapted from [14]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.403, + 0.47, + 0.794 + ], + "angle": 0, + "content": "a system. At first, motivated by the recent achievements in the field of neural rendering [20, 2, 40, 39, 41] and grid-based feature encoding [46, 36, 18], we propose to design our system based on a novel implicit representation from which we can render both the RGB image and original ToF signal. In this way, we can define the losses directly against the multi-domain input, which can be utilized to optimize camera poses and 3D scenes. However, we find that this cannot guarantee plausible tracking and reconstruction results because of low-quality raw depth signals from the sensor. Inspired by recent works [31, 46] that high-resolution accurate depth maps play an important role in the implicit SLAM systems, we further exploit the depth estimation model [14] for the light-weight ToF sensor to predict an intermediate high-resolution depth as additional supervision. Based on all the above insights, we develop a multimodal implicit scene representation with multi-level feature grids, which is able to generate both the zone-level signals of light-weight ToF sensors and pixel-wise RGB/depth images via the differentiable rendering for the camera tracking and reconstruction. For efficient network convergence, we also design a coarse-to-fine optimization process for this novel implicit scene representation, i.e., firstly using zone-level ToF signals to optimize the scene at the coarse level, then adding pixel-wise RGB/depth supervisions to recover geometry details." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.796, + 0.468, + 0.903 + ], + "angle": 0, + "content": "Moreover, although the predicted per-pixel depth is generally smooth and provides reasonable supervision as intermediate signals, it may also produce severe artifacts when there is a large portion of missing L5 signals since it is hard for the network to handle such cases due to the inherent depth ambiguity in the missing regions. As a result, we further develop a temporal filtering technique to enhance depth" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.241 + ], + "angle": 0, + "content": "prediction. Specifically, when a new signal is captured, we render a zone-level light-weight ToF signal from our multimodal scene representation with an initialized pose and fuse it with that new observation signal, which serves as the input of the depth prediction network. Such an explicit filtering technique improves the depth estimation performance significantly, particularly in extreme cases where the raw L5 signals are very noisy or contain large amounts of missing data, and therefore further benefits the whole SLAM system." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.243, + 0.893, + 0.515 + ], + "angle": 0, + "content": "Our contributions can be summarized as follows. At first, to our best knowledge, we present the first dense SLAM system by only taking the monocular images and the signals from a light-weight ToF sensor as input. Moreover, we propose a multi-modal implicit scene representation which supports rendering both the zone-level signals of light-weight ToF sensors and pixel-wise RGB/depth images. By minimizing the re-rendering loss of these signals in a coarse-to-fine strategy, we can recover the camera pose and the scene geometry via differentiable neural rendering. Furthermore, we propose a temporal filtering technique to enhance the signals of light-weight ToF sensors and corresponding depth prediction which significantly improve the proposed SLAM system in extreme cases. Experiments on the real datasets demonstrate that the proposed system well exploits the signals of light-weight ToF sensors and achieves competitive results both on camera tracking and dense scene reconstruction compared to existing methods." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.528, + 0.642, + 0.543 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.892, + 0.81 + ], + "angle": 0, + "content": "Visual SLAM. Sparse visual SLAM systems [13, 23, 16] focus on solving accurate camera poses based on the tracking of sparse keypoint [28, 25]. These types of methods usually struggle in texture-less environments and cannot provide a complete reconstruction result of the scene. In comparison, dense visual SLAM systems [10, 38, 11, 24] perform much more robust but usually require depth images as input. More recently, many methods emerged to estimate the dense depth map and camera pose simultaneously from RGB sequences only using deep neural networks [3, 6, 34, 35] and reconstruct the scene through fusing the estimated depth maps. Unlike these previous methods optimizing depth maps per frame, we follow iMAP [31] and NICE-SLAM [46] and use an implicit scene representation. However, unlike iMAP and NICE-SLAM, we do not require the depth camera and take the light-weight ToF signals as input instead." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Neural Implicit Representation. Neural implicit representations are widely used in various kinds of tasks, including novel view synthesis [20, 45, 2, 19] and scene reconstruction [1, 36, 26]. While showing promising results, these methods require precise camera poses as input which greatly limits their application scenarios. Some re" + }, + { + "type": "page_number", + "bbox": [ + 0.494, + 0.946, + 0.504, + 0.956 + ], + "angle": 0, + "content": "2" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.095, + 0.885, + 0.369 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.384, + 0.893, + 0.427 + ], + "angle": 0, + "content": "Figure 3. System Overview. Our method uses a monocular camera and a light-weight ToF sensor as input and recovers both camera motion and the scene structures. Through differentiable rendering, our method can render multi-modal signals, including color images, depth images and zone-level L5 signals. Both the scene structure and the camera poses are optimized by minimizing the re-rendering loss." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.451, + 0.47, + 0.587 + ], + "angle": 0, + "content": "cent works [15, 42] propose to optimize camera pose with the scene representation simultaneously. Lately, iMAP [31] and NICE-SLAM [46] bring neural implicit representations into visual SLAM systems. Nevertheless, requirements of RGB-D sequences as input significantly constrain their applications, especially on mobile devices with tight power budgets. In contrast, we propose a visual SLAM method using only an RGB camera and a light-weight ToF sensor, which commonly co-exists on mobile devices." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.588, + 0.47, + 0.801 + ], + "angle": 0, + "content": "Neural Grid Optimization. Typically, a single multi-layer perceptron (MLP) is employed to represent the entire scene in earlier neural implicit methods [20, 2, 31]. However, these methods perform poorly when applied to large scenes and need an extremely long time for training. To address this issue, recent works [33, 22, 5] try to optimize neural features on an explicit volumetric grid. These methods, however, are only capable of pixel-level rendering and do not accommodate L5 signals as it has extremely low resolution and measures the depth distribution of a large area. To this end, we introduce a multi-modal feature grid representation that enables rendering multi-modal information at different resolutions and can deal with zone-level depth distribution data measured by light-weight ToF sensors." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.815, + 0.169, + 0.83 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.841, + 0.47, + 0.901 + ], + "angle": 0, + "content": "In this section, we provide an overview of the sensing principle of light-weight ToF sensors (e.g., L5) in Sec. 3.1. Based on the characteristics of L5's signals, we design the first dense SLAM system with a monocular camera and a" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.451, + 0.892, + 0.679 + ], + "angle": 0, + "content": "light-weight ToF sensor as shown in Fig. 3. Specifically, we first propose a multi-modal implicit scene representation which enables rendering L5 signals together with the common RGB image and depth maps (Sec. 3.2). To guarantee successful tracking and mapping, we exploit a depth prediction model [14] to predict intermediate per-pixel depth maps as additional supervision. By minimizing the difference between the rendered signals and input/predicted ones, we can simultaneously optimize the camera pose and scene structure in a coarse-to-fine way. Furthermore, since the depth prediction may contain severe artifacts when there is a large portion of missing L5 signals, we propose to refine the L5 signals with temporal filtering techniques to enhance the depth prediction module (Sec. 3.3). Finally, we describe the system implementation detail in Sec. 3.4." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.694, + 0.813, + 0.712 + ], + "angle": 0, + "content": "3.1. Preliminaries: L5 Sensing Principle" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Light-weight ToF sensors are designed to be low-cost, small, and low-energy and have been massively deployed on mobile devices. Compared with conventional ToF sensors, which provide high-resolution depth measurement and measure the per-pixel distance to the scene, light-weight ToF sensors usually have extremely low resolution (e.g., \\(8 \\times 8\\) zones) and measure the depth distribution for each zone. Here we take ST VL53L5CX [29] (denoted as L5), a representative product of light-weight ToF sensors, as an example to declare the sensing principle of these sensors. As shown in Fig. 2, L5 measures the depth distribution by counting the received photon number within specific time" + }, + { + "type": "page_number", + "bbox": [ + 0.494, + 0.946, + 0.504, + 0.956 + ], + "angle": 0, + "content": "3" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.182 + ], + "angle": 0, + "content": "intervals. The result is then fitted with a Gaussian distribution, and L5 only transmits the mean and variance to decrease both the energy consumption and broadband load. None of the previous studies have explored the usage of L5 for downstream applications like SLAM due to its low resolution and high uncertainty." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.194, + 0.447, + 0.21 + ], + "angle": 0, + "content": "3.2. Multi-Modal Implicit Scene Representation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.218, + 0.47, + 0.415 + ], + "angle": 0, + "content": "The combination of neural rendering and grid-based feature encoding has found broad utilization in applications like SLAM and surface reconstruction. [46, 36, 43]. By minimizing the loss between the rendered image/depth and the input image/depth, they achieve accurate 6-DoF camera pose tracking and the reconstruction of scene geometry. In this paper, we propose a multi-modal implicit scene representation, which supports the rendering of zone-level L5 signals apart from the common RGB and depth images. Specifically, we encode the geometry and color separately and propose the masked rendering technique in the geometry encoding for the rendering of both zone-level L5 signals and pixel-level depth images." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.416, + 0.47, + 0.642 + ], + "angle": 0, + "content": "Geometry Encoding with Masked Rendering. The idea of the proposed masked rendering is inspired by the integrated positional encoding(IPE) theory proposed in MipNeRF [2], but we promote it to the grid-based scene representation. The core idea of IPE is that the input features are passed through a low pass filter, i.e., if the frequency of a particular feature has a larger period than the ray, then the feature is unaffected; otherwise, the feature is scaled down towards zero. The original method represents the scene using a single MLP and achieves the low pass filtering by calculating an integral of the positional encoding as input. In our grid-based case, we concatenate features from different-level feature grids and use a rendering mask to mask out features extracted from overly high spatial frequency grids based on the current rendering scale." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.471, + 0.855 + ], + "angle": 0, + "content": "To be more specific, we encode the scene geometry into a multi-level feature grid containing four layers \\(\\mathcal{V}_{\\theta} = \\{V^0,V^1,V^2,V^3\\}\\). The zone-level feature grid \\(V^{\\mathrm{zone}}\\) contains the coarser feature grids \\(\\{V^0,V^1\\}\\) while the pixel-level feature grid \\(V^{\\mathrm{pix}}\\) contains the finer feature grids \\(\\{V^2,V^3\\}\\). For a given point \\(\\mathbf{x}\\in \\mathbb{R}^3\\), its whole geometry feature \\(\\mathcal{F}\\) is extracted by tri-linearly interpolating features at each grid level and concatenating these features together. The feature can be decoded into SDF values in both pixel-level \\(\\phi_{pix}(\\mathbf{x})\\) and zone-level \\(\\phi_{zone}(\\mathbf{x})\\) via the same geometry decoder \\(f_{\\omega}(\\cdot)\\) switched by the rendering mask. We use all the features for rendering pixel-level results \\(\\phi_{pix}\\), and mask out the features extracted from the finer grids for zone-level rendering results \\(\\phi_{zone}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.143, + 0.868, + 0.405, + 0.904 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\phi_ {p i x} (\\mathbf {x}) = f _ {\\omega} \\left(\\left[ V ^ {z o n e} (\\mathbf {x}), V ^ {p i x} (\\mathbf {x}) \\right]\\right), \\\\ \\phi_ {z o n e} (\\mathbf {x}) = f _ {\\omega} \\left(\\left[ V ^ {z o n e} (\\mathbf {x}), \\mathbf {0} \\right]\\right). \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.181 + ], + "angle": 0, + "content": "This mask operation also makes the corresponding neurons in the geometry decoder inactive. The SDF values from both branches are used in the tracking and mapping process corresponding to the pixel-level and zone-level supervision, and only the pixel-level SDF values are used for the final mesh extraction." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.182, + 0.892, + 0.258 + ], + "angle": 0, + "content": "Color Encoding. For color information, we encode it only at the finest level using a separate set of feature grid \\(\\mathcal{W}_{\\beta}\\) and decoder \\(g_{\\gamma}(\\cdot)\\) as [46, 36]. When decoding color, we additionally use the ray direction \\(\\mathbf{r}\\), so the color value for a 3D point is given by:" + }, + { + "type": "equation", + "bbox": [ + 0.627, + 0.271, + 0.892, + 0.288 + ], + "angle": 0, + "content": "\\[\n\\mathbf {c} = g _ {\\gamma} \\left(\\mathcal {W} _ {\\beta} (\\mathbf {x}), \\mathbf {r}\\right). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.299, + 0.892, + 0.42 + ], + "angle": 0, + "content": "Rendering of L5 Signals, Color and Depth Images. We render color and depth values with the volumetric rendering technique [37]. Specifically, to render a color pixel, we sample \\(N\\) points along the corresponding emitted ray, denoted as \\(\\mathbf{x}_i = \\mathbf{o} + d_i\\mathbf{r}, i \\in \\{1,2,\\dots,N\\}\\) where \\(\\mathbf{o}\\) is the camera center, \\(\\mathbf{r}\\) is the direction of this ray and \\(d_i\\) is the distance of the sampled point \\(\\mathbf{x}_i\\) along the ray. We then accumulate the color value along the ray through:" + }, + { + "type": "equation", + "bbox": [ + 0.64, + 0.432, + 0.892, + 0.472 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {c}} = \\sum_ {i = 1} ^ {N} T _ {i} \\alpha_ {i} \\mathbf {c} _ {i}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.485, + 0.892, + 0.562 + ], + "angle": 0, + "content": "where \\( T_{i} = \\prod_{j = 1}^{i - 1}\\left(1 - \\alpha_{j}\\right) \\) is the accumulated transmittance, and \\( \\alpha_{i} \\) is the opacity value converted from the SDF prediction \\( \\phi_{pix} \\). The conversion follows the original definition in NeuS [37]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.563, + 0.892, + 0.639 + ], + "angle": 0, + "content": "The process of rendering the L5 signals is similar to rendering the color. The differences are that for rendering the mean depth value \\(\\hat{d}_z\\) of an L5 zone, we emit the ray from the center of that zone and accumulate the distance along the ray through:" + }, + { + "type": "equation", + "bbox": [ + 0.636, + 0.65, + 0.892, + 0.691 + ], + "angle": 0, + "content": "\\[\n\\hat {d} _ {z} = \\sum_ {i = 1} ^ {N} T _ {i} \\alpha_ {i} d _ {i}. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.702, + 0.892, + 0.822 + ], + "angle": 0, + "content": "The zone-level opacity \\(\\alpha_{i}\\) is derived in the same manner as color rendering but using \\(\\phi_{zone}\\) instead of \\(\\phi_{pix}\\). Intuitively, we can optimize the camera pose and scene structure by only supervising the rendered color images and L5 signals. However, in our experiment (Sec. 4.3), we show that the results are far from satisfactory. As a result, we also render the pixel-wise depth maps using Eq. 4 with \\(\\phi_{pix}\\) and supervise it with the depth prediction from [14]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.832, + 0.787, + 0.849 + ], + "angle": 0, + "content": "3.3. Temporal Filtering of L5 Signals" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "As mentioned before, we use DELTAR [14] to predict a pixel-wise depth map as additional supervision. DELTAR is a pre-trained neural network that takes L5 signals and RGB" + }, + { + "type": "page_number", + "bbox": [ + 0.494, + 0.947, + 0.504, + 0.956 + ], + "angle": 0, + "content": "4" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.094, + 0.468, + 0.207 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.224, + 0.47, + 0.267 + ], + "angle": 0, + "content": "Figure 4. Temporal Filtering of L5 Signals. By fusing the latest ToF measurement with a rendered one, we can significantly improve the signal quality and the corresponding predicted depth." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.29, + 0.468, + 0.395 + ], + "angle": 0, + "content": "images as input and predicts corresponding depth maps. We observe that when there are a large number of missing or noisy L5 signals, the depth map predicted by DELTAR may contain severe artifacts due to the inherent depth ambiguities of missing or noisy regions, thus further contaminating the learning of implicit features and degrading the SLAM system's performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.396, + 0.468, + 0.562 + ], + "angle": 0, + "content": "This motivates us to develop an explicit temporal filtering technique (Fig. 4) to enhance the L5 signals before feeding into DELTAR. Since the past observations are stored implicitly in our scene representation, we can leverage this information to refine the current observation. Specifically, the proposed filtering algorithm contains two steps: the prediction step and the update step. In the prediction step, we predict the per-zone ToF measurement \\( X_{k} = \\{\\mu_{1},\\sigma_{1}\\} \\) in the timestamp \\( k \\) using neural rendering (Eq. 4) with an initialized pose. Then we update \\( X_{k} \\) to \\( X_{k}^{\\prime} \\) with the current L5 measurement \\( Z_{k} = \\{\\mu_{2},\\sigma_{2}\\} \\):" + }, + { + "type": "equation", + "bbox": [ + 0.126, + 0.57, + 0.468, + 0.605 + ], + "angle": 0, + "content": "\\[\n\\mu_ {X _ {k ^ {\\prime}}} = \\frac {\\mu_ {1} \\sigma_ {2} ^ {2} + \\mu_ {2} \\sigma_ {1} ^ {2}}{\\sigma_ {1} ^ {2} + \\sigma_ {2} ^ {2}}, \\quad \\sigma_ {X _ {k ^ {\\prime}}} ^ {2} = \\frac {\\sigma_ {1} ^ {2} \\sigma_ {2} ^ {2}}{\\sigma_ {1} ^ {2} + \\sigma_ {2} ^ {2}}. \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.612, + 0.468, + 0.687 + ], + "angle": 0, + "content": "As for the zones with no valid raw L5 signals, we simply use the predicted L5 signals. Finally, the enhanced signals \\(X_{k}^{\\prime}\\) are fed into the depth prediction network with corresponding RGB image [14] to obtain a high-resolution depth estimation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.697, + 0.353, + 0.713 + ], + "angle": 0, + "content": "3.4. SLAM System Implementation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.468, + 0.87 + ], + "angle": 0, + "content": "Initialization. Since we do not have reliable depth maps as input, we need to perform initialization in order to build a local map for our system to bootstrap. The first \\( N_{i} \\) frames are added to the initialization process with a fixed interval \\( I_{skip} \\) sequentially. The pose of each newly added frame is initialized by the previous frame. During this process, the feature grids, decoders and camera poses are jointly optimized using the same loss function as in the mapping process. Finally, when all the frames are added, we optimize the whole frame set for \\( N_{e} \\) iterations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Coarse-to-Fine Mapping. To optimize the scene representation mentioned in Sec. 3.2, we uniformly sample total" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.213 + ], + "angle": 0, + "content": "\\(M\\) pixels and \\(Z\\) zones and perform optimization to minimize the photometric loss, geometric loss and SDF regularization. The zones and pixels are sampled from the current optimization window, which consists of two types of frames: neighbor frames (the nearest \\(N_{n}\\) frames with an interval of 4) and global frames (chosen from all the past co-visible mapping frames). The photometric loss is the average color difference of all the sampled pixels:" + }, + { + "type": "equation", + "bbox": [ + 0.585, + 0.224, + 0.892, + 0.265 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {c} = \\frac {1}{M} \\sum_ {m = 1} ^ {M} | I [ u _ {m}, v _ {m} ] - \\hat {\\mathbf {c}} _ {m} |, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.277, + 0.892, + 0.367 + ], + "angle": 0, + "content": "where \\( u_{m}, v_{m} \\) represents for the image coordinate of pixel \\( m \\). The geometric loss is calculated on both pixel-level and zone-level. For zone-level loss, only zones with valid L5 signals \\( Z_{d} \\) are considered. We also add SDF supervision on pixel-level as in [36, 26] to add robustness to the optimization. The whole geometric loss is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.582, + 0.38, + 0.77, + 0.397 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {g} = \\mathcal {L} _ {d} + \\mathcal {L} _ {z} + \\lambda_ {s d f} \\mathcal {L} _ {s d f},\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.582, + 0.4, + 0.891, + 0.44 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {d} = \\frac {1}{M} \\sum_ {m = 1} ^ {M} | \\widetilde {D} [ u _ {m}, v _ {m} ] - \\hat {d} _ {m} |, \\tag {7}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.582, + 0.442, + 0.767, + 0.48 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {z} = \\frac {1}{| Z _ {d} |} \\sum_ {z \\in Z _ {d}} | \\bar {D} _ {z} - \\hat {d} _ {z} |,\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.492, + 0.892, + 0.614 + ], + "angle": 0, + "content": "where \\(\\overline{D} \\in \\mathbb{R}^{8 \\times 8}\\) represents the mean depth value measured by L5 and \\(\\widetilde{D}\\) represents the pixel-wise depth prediction. Since we do not have high-quality depth as input and there are many texture-less areas in typical indoor scenes, directly optimizing the feature volume and camera poses is an ill-posed problem. Therefore, we employ two regularizations on the SDF values during pixel-level rendering as [36], namely the eikonal term \\(\\mathcal{L}_{eik}\\) and the smoothness term \\(\\mathcal{L}_s\\):" + }, + { + "type": "equation", + "bbox": [ + 0.615, + 0.632, + 0.891, + 0.647 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {r} = \\lambda_ {e i k} \\mathcal {L} _ {e i k} + \\lambda_ {s} \\mathcal {L} _ {s}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.655, + 0.891, + 0.731 + ], + "angle": 0, + "content": "where the eikonal regularization is employed to ensure the network produces valid SDF values [37, 36], the smoothness regularization is used to encourage neighbor points to have similar normal directions, and \\(\\lambda_{eik}\\) and \\(\\lambda_s\\) are weights to balance the two regularization terms." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.732, + 0.892, + 0.865 + ], + "angle": 0, + "content": "During the mapping process, we perform a coarse-to-fine optimization process, bringing better convergence since pixel-wise optimization can rely on the already initialized coarse grids. We first optimize the scene at the coarse level using zone-level ToF signals. Then, pixel-wise RGB/depth supervisions are added to jointly optimize the decoders, feature grids and camera poses by minimizing the mentioned losses for \\( N_{m} \\) iterations with a local BA to cover geometry details." + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.88, + 0.891, + 0.904 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\theta , \\omega , \\beta , \\gamma , \\left\\{\\mathbf {R} _ {i}, \\mathbf {t} _ {i} \\right\\}} \\lambda_ {c} \\mathcal {L} _ {c} + \\lambda_ {g} \\mathcal {L} _ {g} + \\lambda_ {r} \\mathcal {L} _ {r}. \\tag {9}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.494, + 0.946, + 0.504, + 0.956 + ], + "angle": 0, + "content": "5" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.102, + 0.089, + 0.87, + 0.462 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.474, + 0.893, + 0.503 + ], + "angle": 0, + "content": "Figure 5. Qualitative Reconstruction Results. Compared to other methods, our approach produces high-quality reconstructions with smooth surfaces and fewer artifacts." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.525, + 0.47, + 0.601 + ], + "angle": 0, + "content": "We also conduct a global BA every \\(N_g\\) frame by adding all the past mapping frames to the optimization window and jointly optimize them to globally optimize the camera poses and scene geometry. We provide the details of losses in the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.603, + 0.471, + 0.8 + ], + "angle": 0, + "content": "Tracking. During tracking, the feature grid and the decoders remain fixed, while only the 6-DoF pose of the current frame is optimized. Similar to previous methods [46, 31], \\( M_t \\) pixels are sampled in the current frame to calculate both the pixel-level photometric loss and geometric loss as previously described. The camera pose is then updated iteratively via back-propagation. Tracking with only pixel-level supervision is susceptible to a suboptimal solution, so we leverage our multi-modal scene representation and apply zone-level supervision in the early stage. Specifically, we additionally sample \\( Z \\) zones in the current frame and use the L5 signal to minimize zone depth loss as well, which leads to a more robust tracking result." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.819, + 0.21, + 0.835 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.845, + 0.268, + 0.862 + ], + "angle": 0, + "content": "4.1. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Datasets. Since no public SLAM benchmarks take the L5 signals as input, we build a data capture device as in [14]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.525, + 0.892, + 0.661 + ], + "angle": 0, + "content": "and use it to create an indoor SLAM dataset, which contains 7 sequences captured in 5 typical indoor scenes. We record color images \\((640\\times 480)\\), L5 signals and depth maps for each sequence. Note that we only use the color images and L5 signals as the input to our SLAM system. The depth maps are used to obtain the ground truth 6-DoF camera poses and 3D surface mesh. We follow the automated capture pipeline proposed in ScanNet [7] to compute the ground truth data." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Baselines. We compare our method with two categories of baselines: (a) learning-based SLAM methods including iMAP [31] (re-implemented by [46]) and NICE-SLAM [46]; (b) traditional SLAM methods including ORBSLAM3 [4], KinectFusion [10], ElasticFusion [38] and BundleFusion [8]. For the methods that only support RGB-D input, including iMAP, NICE-SLAM, KinectFusion, ElasticFusion and BundleFusion, we use the RGB image and the predicted depth map by [14] as the system input. For ORB-SLAM3, we evaluate it in both the RGB version (given only RGB image as input) and the RGB-D version (using the predicted depth, marked as \\(\\widetilde{D}\\)). Note that none of these methods can work well with only raw L5 zone-level depths or take it as additional inputs. We evaluate both the scene reconstruction and the camera tracking results. Since" + }, + { + "type": "page_number", + "bbox": [ + 0.494, + 0.947, + 0.504, + 0.956 + ], + "angle": 0, + "content": "6" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.131, + 0.089, + 0.842, + 0.363 + ], + "angle": 0, + "content": "
Scene NameKitchenSofaOfficeReceptionLiving roomOffice2Sofa2Avg.
KinectFusion[10]Acc.↓-0.1900.2110.261-0.2670.1350.213
Comp.↓-0.0480.0460.064-0.0780.0640.060
F-score-0.2780.2880.285-0.2740.3810.301
ElasticFusion[38]Acc.↓0.0920.1350.0840.2970.1510.0960.1220.140
Comp.↓0.0650.0480.0820.3050.2160.1470.0470.130
F-score0.5530.4200.5290.2740.3820.4160.4810.436
BundleFusion[8]Acc.↓0.1700.1000.1030.122-0.1210.1230.123
Comp.↓0.0880.0300.0380.057-0.2140.0340.077
F-score0.3730.5710.4740.470-0.4420.5270.476
iMAP[31]Acc.↓-0.1350.2290.3650.2250.2330.1390.221
Comp.↓-0.0540.1030.2450.2910.1390.0690.150
F-score-0.4450.3150.2380.1700.2550.4160.307
NICE-SLAM[46]Acc.↓0.3030.1190.1160.2160.1030.1560.4640.211
Comp.↓0.4560.0420.0700.1990.0890.1630.0450.152
F-score0.2210.5540.4110.4020.4000.2730.4010.380
OursAcc.↓0.0810.0680.0670.0790.0780.1130.1210.087
Comp.↓0.0710.0410.0450.0620.1220.0850.0330.066
F-score0.5590.6610.6460.6430.4960.5570.6560.604
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.364, + 0.895, + 0.391 + ], + "angle": 0, + "content": "Table 1. Quantitative Comparison on Reconstruction. We perform the mapping evaluation on 7 indoor sequences and report results of three metrics including accuracy (Acc.), completion (Comp.) and F-score. The failure cases are marked as “-”." + }, + { + "type": "table", + "bbox": [ + 0.165, + 0.403, + 0.806, + 0.538 + ], + "angle": 0, + "content": "
Scene NameKitchenSofaOfficeReceptionLiving roomOffice2Sofa2
ORB-SLAM3 [4]0.054-0.0170.025-0.022-
ORB-SLAM3(with D) [4]0.0820.0350.0190.049-0.058-
KinectFusion [10]-0.1460.2090.157-0.3210.125
ElasticFusion [38]0.2530.1100.0700.1930.5300.1210.146
BundleFusion [8]0.1760.1020.1350.101-0.1630.120
iMAP [31]-1.6580.3380.6480.6790.3440.214
NICE-SLAM [46]0.7450.1440.1550.2510.2890.2280.421
Ours0.1130.0810.0560.1140.2000.1010.085
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.538, + 0.895, + 0.595 + ], + "angle": 0, + "content": "Table 2. Camera Tracking Results. ATE RMSE [m] (↓) is used as the evaluation metric. The failure cases are marked as “-”. For the variations of ORB-SLAM3, we only mark the best one in each sequence. Our approach outperforms all the other methods except for ORB-SLAM3 [4]. However, ORB-SLAM3 fails on 3 of the 7 sequences due to the textureless indoor environment while our approach tracks successfully on all of the sequences." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.618, + 0.471, + 0.65 + ], + "angle": 0, + "content": "ORB-SLAM3 cannot output dense models, we exclude it from the mapping evaluation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Implementation Details. Our SLAM system is executed on a desktop PC equipped with an Intel i7-9700K CPU and an NVIDIA RTX 3090 GPU. In all our experiments, we set the grid sizes to [3, 6, 24, 96] cm and the number of sampling pixels \\(M\\) to 5000. Our method is implemented using PyTorch [27] with ADAM [12] optimizer. The decoders, multi-modal feature grids, and camera poses are trained with learning rates of 0.001, 0.01, and 0.0005, respectively. The loss weights are set to 10 for \\(\\lambda_{c}\\) and \\(\\lambda_{sdf}\\) and 1 for the others. Inspired by instant-ngp [22], we use the tiny-cuda-nn [21] library to implement the proposed multimodal grid encoding, which significantly accelerates the optimization process. We follow DELTAR [14] to pre-train the multi-modal depth prediction network on NYU-V2 with simulated L5 signals. For more details, please refer to the supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.618, + 0.822, + 0.635 + ], + "angle": 0, + "content": "4.2. Evaluation of Mapping and Tracking" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.643, + 0.892, + 0.84 + ], + "angle": 0, + "content": "Mapping. We use three metrics to evaluate the reconstruction result including accuracy (Acc.), completion (Comp.) and F-score following the previous work [32]. For detailed descriptions of these metrics, please refer to the supplementary material. As shown in Table 1, our method outperforms all the baseline methods by a large margin (ours 0.604 vs. the second-best 0.476 in terms of F-score). We also show qualitative results in Fig. 5. Our method is able to produce high-quality 3D models with smooth surfaces and high accuracy. It is easy to notice that our reconstruction result has much fewer artifacts and noisy points. Since NICE-SLAM [46] relies on high-quality depth input, its performance is poor given the noisy and unreliable depth input." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Tracking. We use ATE RMSE [30] to evaluate the camera tracking. As shown in Table 2, our method outperforms all other methods except for ORB-SLAM3 [4]. However, ORB-SLAM3 is much less robust and tracks lost on 3 of" + }, + { + "type": "page_number", + "bbox": [ + 0.494, + 0.946, + 0.505, + 0.956 + ], + "angle": 0, + "content": "7" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.194, + 0.089, + 0.778, + 0.152 + ], + "angle": 0, + "content": "
EMKitchenSofaOfficeReceptionLiving roomOffice2Sofa2Avg.
0.2030.0880.0630.1430.2160.1200.0940.132
✓0.1350.0850.0600.1440.2110.1080.0890.119
✓✓0.1130.0810.0560.1140.2000.1010.0850.107
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.153, + 0.894, + 0.181 + ], + "angle": 0, + "content": "Table 3. Ablation Study. We explore the efficiency of multi-modal scene representation (marked as “M”) and L5 signal temporal filtering (marked as “E”). We use ATE RMSE [m] (↓) as the evaluation metric." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.203, + 0.468, + 0.294 + ], + "angle": 0, + "content": "
TrackingMapping
Learning-based MethodsiMAP [31]101 ms448 ms
NICE-SLAM [46]470 ms1300 ms
Ours116 ms380 ms
Classical MethodsORB-SLAM3 [4]31 ms159 ms
ElasticFusion [38]31 ms-
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.295, + 0.468, + 0.364 + ], + "angle": 0, + "content": "Table 4. Runtime Comparison. Different from NICE-SLAM [46] that measures one iteration of optimization, we report the averaging total runtime for tracking and mapping respectively for better comparison with classic methods. ElasticFusion does not have an explicit mapping process thus it is labeled as “-”." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.377, + 0.468, + 0.499 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.514, + 0.47, + 0.556 + ], + "angle": 0, + "content": "Figure 6. Results without Pixel-Wise Depth Supervision. It cannot guarantee plausible reconstruction results without the pixel-wise depth maps as additional supervision." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.469, + 0.687 + ], + "angle": 0, + "content": "the 7 sequences, while our method successfully tracks all the sequences. This is because that ORB-SLAM3, as a keypoint-based method, struggles in texture-less regions, which are commonly seen in indoor environments. Given the predicted depth, ORB-SLAM3 can reduce the lost ratio from \\(42.8\\%\\) to \\(28.5\\%\\) but leads to worse camera tracking results since the predicted depth is not accurate enough." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.687, + 0.469, + 0.763 + ], + "angle": 0, + "content": "Runtime Analysis. We compare the runtime of tracking and mapping in Table 4 for both classical methods and learning-based methods. The runtime of our method is similar to iMAP, but it is faster than NICE-SLAM due to our implementation optimization inspired by instant-ngp [22]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.772, + 0.231, + 0.789 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.469, + 0.901 + ], + "angle": 0, + "content": "In this section, we first study the effectiveness of using pixel-wise depth prediction as additional supervision, then investigate the importance of the proposed multi-modal feature grid representation and the temporal filtering technique. Impact of the Pixel-Wise Depth Supervision. We try using only the L5 raw signals and RGB images for supervision. Removing the pixel-wise depth supervision makes" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.204, + 0.605, + 0.322 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.529, + 0.327, + 0.582, + 0.338 + ], + "angle": 0, + "content": "RGB/GT" + }, + { + "type": "image", + "bbox": [ + 0.608, + 0.204, + 0.689, + 0.322 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.62, + 0.326, + 0.675, + 0.338 + ], + "angle": 0, + "content": "L5 Signal" + }, + { + "type": "image", + "bbox": [ + 0.693, + 0.204, + 0.79, + 0.322 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.697, + 0.326, + 0.786, + 0.338 + ], + "angle": 0, + "content": "Predicted Depth" + }, + { + "type": "image", + "bbox": [ + 0.793, + 0.204, + 0.892, + 0.322 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.812, + 0.327, + 0.871, + 0.339 + ], + "angle": 0, + "content": "Error Map" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.356, + 0.892, + 0.453 + ], + "angle": 0, + "content": "Figure 7. Qualitative Study of the Effect of Temporal Filtering on Depth Prediction. We compare the depth prediction result obtained through two methods: solely employing raw L5 signals (top row) and incorporating our temporal filtering technique (bottom row). Our temporal filtering technique enhances the raw L5 signals and fills up the missing regions, leading to a better depth prediction result." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.485, + 0.892, + 0.576 + ], + "angle": 0, + "content": "the optimization problem harder, which is more obvious when the problem size grows. In Fig. 6 we show the rendered depth when optimizing the first frame and the first 150 frames. The latter contains serious errors. As a result, it leads to a distorted reconstruction, i.e., the \"Baseline\" result in the upper right." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.578, + 0.892, + 0.684 + ], + "angle": 0, + "content": "Impact of the Multi-Modal Feature Grid. We verify the effectiveness of our multi-modal feature grid representation (denoted as “M”) in terms of camera tracking and show the result in Table 3. With the multi-modal feature grid representation, we are able to use raw L5 signal as supervision. As a result, we can optimize the camera poses on both pixel-level and zone-level, leading to better trajectory accuracy." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.687, + 0.892, + 0.778 + ], + "angle": 0, + "content": "Impact of the Temporal Filtering. In Fig. 7 we show the qualitative comparison with and without the proposed temporal filtering. It can be seen that the large portion of missing L5 signals leads to severe errors on the corresponding regions of the predicted depth map. The error reduces significantly with the proposed temporal filtering technique." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We also study the quantitative impact of temporal filtering (marked as \"E\") on both the depth prediction (Table 5) and the camera tracking (Table 3). We divide the testing sequences into normal and hard cases according to the quality of L5 signals. As shown in Table 5, the temporal filtering technique improves the predicted depth in general and significantly in hard cases. Such an improvement benefits the final SLAM system and leads to more accurate camera" + }, + { + "type": "page_number", + "bbox": [ + 0.494, + 0.946, + 0.504, + 0.956 + ], + "angle": 0, + "content": "8" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.079, + 0.089, + 0.447, + 0.165 + ], + "angle": 0, + "content": "
δ1↑δ2↑δ3↑REL↓RMSE↓
Hw/o E0.7730.9100.9690.1590.513
w E0.9250.9720.9830.0930.366
Nw/o E0.9540.9890.9970.0650.151
w E0.9560.9920.9980.0650.145
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.167, + 0.47, + 0.223 + ], + "angle": 0, + "content": "Table 5. Ablation Study on Temporal Filtering for Depth Prediction. “H”/“N” stands for the hard/normal cases and “E” represents the temporal filtering. We report the quantitative result of depth maps predicted from L5 raw signals and our refined signals." + }, + { + "type": "image", + "bbox": [ + 0.093, + 0.239, + 0.246, + 0.326 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.093, + 0.327, + 0.245, + 0.414 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.124, + 0.418, + 0.213, + 0.43 + ], + "angle": 0, + "content": "Outdoor Scene" + }, + { + "type": "image", + "bbox": [ + 0.249, + 0.238, + 0.455, + 0.324 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.254, + 0.328, + 0.451, + 0.415 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.296, + 0.419, + 0.413, + 0.431 + ], + "angle": 0, + "content": "Our Reconstruction" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.448, + 0.47, + 0.504 + ], + "angle": 0, + "content": "Figure 8. Qualitative Results of Outdoor Reconstruction. The proposed method can recover a complete scene model in outdoor scenes but missing more details than that in indoor due to the poor L5 signals." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.528, + 0.47, + 0.575 + ], + "angle": 0, + "content": "tracking, as shown in Table 3 (marked as “E”). Please refer to the supplementary material for the definition of the normal/hard cases and the depth evaluation metrics." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.583, + 0.358, + 0.597 + ], + "angle": 0, + "content": "4.4. Performance in Outdoor Scenes" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.606, + 0.47, + 0.727 + ], + "angle": 0, + "content": "Currently, we focus on indoor scenes as other NeRF-based SLAM systems [31, 46] due to the optical interference limitation of depth sensors. Actually, the sunlight has a stronger interference on the L5 sensor for its low-power emitter. In Fig. 8, we show two examples of outdoor scene reconstruction using our proposed methods. The recovered mesh is complete but missing more details than that in indoor scenes due to the poor L5 signals." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.74, + 0.196, + 0.755 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.903 + ], + "angle": 0, + "content": "We introduce a novel dense visual SLAM framework working with RGB cameras and light-weight ToF sensors using neural implicit scene representation. To accommodate this new input modality, we propose a novel multimodal feature grid that enables both zone-level rendering for the ToF sensors and pixel-level rendering for other high-resolution signals. To guarantee robust tracking and mapping, we exploit a per-pixel depth prediction as additional supervision, which is further improved by a novel tempo" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.198 + ], + "angle": 0, + "content": "ral filtering strategy. Our experiments demonstrate that the proposed method can provide accurate camera tracking and high-quality reconstruction result on indoor scenes. Similar to other NeRF-based RGB-D SLAM systems, as future work we plan to further improve the system to overcome the limitation of ToF sensors in outdoor scenarios and make it efficient enough to run on mobile robots." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.199, + 0.892, + 0.228 + ], + "angle": 0, + "content": "Acknowledgements: This work was partially supported by NSF of China (No. 62102356)." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.246, + 0.597, + 0.261 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.508, + 0.272, + 0.892, + 0.34 + ], + "angle": 0, + "content": "[1] Dejan Azinović, Ricardo Martin-Brualla, Dan B Goldman, Matthias Nießner, and Justus Thies. Neural RGB-D surface reconstruction. 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However, due to the sparse and noisy depth measurements, these sensors have rarely been considered for dense geometry reconstruction. In this work, we present the first dense SLAM system with a monocular camera and a lightweight ToF sensor. Specifically, we propose a multi-modal implicit scene representation that supports rendering both the signals from the RGB camera and light-weight ToF sensor which drives the optimization by comparing with the raw sensor inputs. Moreover, in order to guarantee successful pose tracking and reconstruction, we exploit a predicted depth as an intermediate supervision and develop a coarse-to-fine optimization strategy for efficient learning of the implicit representation. At last, the temporal information is explicitly exploited to deal with the noisy signals from light-weight ToF sensors to improve the accuracy and robustness of the system. Experiments demonstrate that our system well exploits the signals of lightweight ToF sensors and achieves competitive results both on camera tracking and dense scene reconstruction. Project page: https://zju3dv.github.io/tof_slam/. + +# 1. Introduction + +Dense simultaneous localization and mapping (dense SLAM) [38, 8, 9, 44] has extensive applications in augmented reality [13, 17], indoor robotics, etc. It usually relies on high-precision and high-resolution depth sensors, such as time-of-flight (ToF) sensors or structured light sensors. Due to the size, weight, and price issues, these depth sensors are only used in a few high-end mobile devices until recent years. In contrast, light-weight ToF sensors, which are cost-effective, compact, and energy-efficient, were integrated into hundreds of smartphone models1. As a result, + +![](images/77bc33968a493fc838c60c0f1e4ada2d380593bc6e4ae5141b583f480367b426.jpg) +Figure 1. Monocular Dense SLAM with Our Multi-Modal Implicit Representation. We present a novel SLAM system based on implicit scene representation. The system does not require high-precision and high-resolution depth sensors and only takes RGB images and the signals of light-weight ToF sensors as input. + +it would be valuable if we could fully utilize these lightweight sensors for dense SLAM, which further facilitates other applications like AR/VR and micro-Robot. + +Unfortunately, limited by the compact electronic design, the light-weight ToF sensor can only provide coarse measurement in the form of depth distribution in an extremely low resolution as illustrated in Fig. 2. Existing RGB-D dense SLAM systems [38, 46, 31] are designed for accurate and pixel-wise depth inputs, thus cannot work with the light-weight ToF signals directly. They will also fail if we simply consider the light-weight ToF signals as a low-resolution depth (i.e., mean depth values in each zone). + +In this paper, we aim to design a novel learning-based dense SLAM system that provides accurate pose tracking and dense reconstruction taking the RGB sequences from a color camera and the sparse signals of light-weight ToF as input (Fig. 1). However, it is non-trivial to design such + +![](images/b05aba552881eca49556599d94593055f46606e06b1b0b65e58e42eb386a95da.jpg) +Figure 2. L5 Sensing Principle. Instead of pixel-wise depth measurement, L5 measures the depth distribution of a large zone and returns its depth mean and variance. Specifically, L5 measures $8 \times 8$ zones in total. The figure is adapted from [14]. + +a system. At first, motivated by the recent achievements in the field of neural rendering [20, 2, 40, 39, 41] and grid-based feature encoding [46, 36, 18], we propose to design our system based on a novel implicit representation from which we can render both the RGB image and original ToF signal. In this way, we can define the losses directly against the multi-domain input, which can be utilized to optimize camera poses and 3D scenes. However, we find that this cannot guarantee plausible tracking and reconstruction results because of low-quality raw depth signals from the sensor. Inspired by recent works [31, 46] that high-resolution accurate depth maps play an important role in the implicit SLAM systems, we further exploit the depth estimation model [14] for the light-weight ToF sensor to predict an intermediate high-resolution depth as additional supervision. Based on all the above insights, we develop a multimodal implicit scene representation with multi-level feature grids, which is able to generate both the zone-level signals of light-weight ToF sensors and pixel-wise RGB/depth images via the differentiable rendering for the camera tracking and reconstruction. For efficient network convergence, we also design a coarse-to-fine optimization process for this novel implicit scene representation, i.e., firstly using zone-level ToF signals to optimize the scene at the coarse level, then adding pixel-wise RGB/depth supervisions to recover geometry details. + +Moreover, although the predicted per-pixel depth is generally smooth and provides reasonable supervision as intermediate signals, it may also produce severe artifacts when there is a large portion of missing L5 signals since it is hard for the network to handle such cases due to the inherent depth ambiguity in the missing regions. As a result, we further develop a temporal filtering technique to enhance depth + +prediction. Specifically, when a new signal is captured, we render a zone-level light-weight ToF signal from our multimodal scene representation with an initialized pose and fuse it with that new observation signal, which serves as the input of the depth prediction network. Such an explicit filtering technique improves the depth estimation performance significantly, particularly in extreme cases where the raw L5 signals are very noisy or contain large amounts of missing data, and therefore further benefits the whole SLAM system. + +Our contributions can be summarized as follows. At first, to our best knowledge, we present the first dense SLAM system by only taking the monocular images and the signals from a light-weight ToF sensor as input. Moreover, we propose a multi-modal implicit scene representation which supports rendering both the zone-level signals of light-weight ToF sensors and pixel-wise RGB/depth images. By minimizing the re-rendering loss of these signals in a coarse-to-fine strategy, we can recover the camera pose and the scene geometry via differentiable neural rendering. Furthermore, we propose a temporal filtering technique to enhance the signals of light-weight ToF sensors and corresponding depth prediction which significantly improve the proposed SLAM system in extreme cases. Experiments on the real datasets demonstrate that the proposed system well exploits the signals of light-weight ToF sensors and achieves competitive results both on camera tracking and dense scene reconstruction compared to existing methods. + +# 2. Related Work + +Visual SLAM. Sparse visual SLAM systems [13, 23, 16] focus on solving accurate camera poses based on the tracking of sparse keypoint [28, 25]. These types of methods usually struggle in texture-less environments and cannot provide a complete reconstruction result of the scene. In comparison, dense visual SLAM systems [10, 38, 11, 24] perform much more robust but usually require depth images as input. More recently, many methods emerged to estimate the dense depth map and camera pose simultaneously from RGB sequences only using deep neural networks [3, 6, 34, 35] and reconstruct the scene through fusing the estimated depth maps. Unlike these previous methods optimizing depth maps per frame, we follow iMAP [31] and NICE-SLAM [46] and use an implicit scene representation. However, unlike iMAP and NICE-SLAM, we do not require the depth camera and take the light-weight ToF signals as input instead. + +Neural Implicit Representation. Neural implicit representations are widely used in various kinds of tasks, including novel view synthesis [20, 45, 2, 19] and scene reconstruction [1, 36, 26]. While showing promising results, these methods require precise camera poses as input which greatly limits their application scenarios. Some re + +![](images/beb9a7d4e20dce5d4a526f16b2b557f9c77a3ccaec9ec5957228986d7994b517.jpg) +Figure 3. System Overview. Our method uses a monocular camera and a light-weight ToF sensor as input and recovers both camera motion and the scene structures. Through differentiable rendering, our method can render multi-modal signals, including color images, depth images and zone-level L5 signals. Both the scene structure and the camera poses are optimized by minimizing the re-rendering loss. + +cent works [15, 42] propose to optimize camera pose with the scene representation simultaneously. Lately, iMAP [31] and NICE-SLAM [46] bring neural implicit representations into visual SLAM systems. Nevertheless, requirements of RGB-D sequences as input significantly constrain their applications, especially on mobile devices with tight power budgets. In contrast, we propose a visual SLAM method using only an RGB camera and a light-weight ToF sensor, which commonly co-exists on mobile devices. + +Neural Grid Optimization. Typically, a single multi-layer perceptron (MLP) is employed to represent the entire scene in earlier neural implicit methods [20, 2, 31]. However, these methods perform poorly when applied to large scenes and need an extremely long time for training. To address this issue, recent works [33, 22, 5] try to optimize neural features on an explicit volumetric grid. These methods, however, are only capable of pixel-level rendering and do not accommodate L5 signals as it has extremely low resolution and measures the depth distribution of a large area. To this end, we introduce a multi-modal feature grid representation that enables rendering multi-modal information at different resolutions and can deal with zone-level depth distribution data measured by light-weight ToF sensors. + +# 3. Method + +In this section, we provide an overview of the sensing principle of light-weight ToF sensors (e.g., L5) in Sec. 3.1. Based on the characteristics of L5's signals, we design the first dense SLAM system with a monocular camera and a + +light-weight ToF sensor as shown in Fig. 3. Specifically, we first propose a multi-modal implicit scene representation which enables rendering L5 signals together with the common RGB image and depth maps (Sec. 3.2). To guarantee successful tracking and mapping, we exploit a depth prediction model [14] to predict intermediate per-pixel depth maps as additional supervision. By minimizing the difference between the rendered signals and input/predicted ones, we can simultaneously optimize the camera pose and scene structure in a coarse-to-fine way. Furthermore, since the depth prediction may contain severe artifacts when there is a large portion of missing L5 signals, we propose to refine the L5 signals with temporal filtering techniques to enhance the depth prediction module (Sec. 3.3). Finally, we describe the system implementation detail in Sec. 3.4. + +# 3.1. Preliminaries: L5 Sensing Principle + +Light-weight ToF sensors are designed to be low-cost, small, and low-energy and have been massively deployed on mobile devices. Compared with conventional ToF sensors, which provide high-resolution depth measurement and measure the per-pixel distance to the scene, light-weight ToF sensors usually have extremely low resolution (e.g., $8 \times 8$ zones) and measure the depth distribution for each zone. Here we take ST VL53L5CX [29] (denoted as L5), a representative product of light-weight ToF sensors, as an example to declare the sensing principle of these sensors. As shown in Fig. 2, L5 measures the depth distribution by counting the received photon number within specific time + +intervals. The result is then fitted with a Gaussian distribution, and L5 only transmits the mean and variance to decrease both the energy consumption and broadband load. None of the previous studies have explored the usage of L5 for downstream applications like SLAM due to its low resolution and high uncertainty. + +# 3.2. Multi-Modal Implicit Scene Representation + +The combination of neural rendering and grid-based feature encoding has found broad utilization in applications like SLAM and surface reconstruction. [46, 36, 43]. By minimizing the loss between the rendered image/depth and the input image/depth, they achieve accurate 6-DoF camera pose tracking and the reconstruction of scene geometry. In this paper, we propose a multi-modal implicit scene representation, which supports the rendering of zone-level L5 signals apart from the common RGB and depth images. Specifically, we encode the geometry and color separately and propose the masked rendering technique in the geometry encoding for the rendering of both zone-level L5 signals and pixel-level depth images. + +Geometry Encoding with Masked Rendering. The idea of the proposed masked rendering is inspired by the integrated positional encoding(IPE) theory proposed in MipNeRF [2], but we promote it to the grid-based scene representation. The core idea of IPE is that the input features are passed through a low pass filter, i.e., if the frequency of a particular feature has a larger period than the ray, then the feature is unaffected; otherwise, the feature is scaled down towards zero. The original method represents the scene using a single MLP and achieves the low pass filtering by calculating an integral of the positional encoding as input. In our grid-based case, we concatenate features from different-level feature grids and use a rendering mask to mask out features extracted from overly high spatial frequency grids based on the current rendering scale. + +To be more specific, we encode the scene geometry into a multi-level feature grid containing four layers $\mathcal{V}_{\theta} = \{V^0,V^1,V^2,V^3\}$ . The zone-level feature grid $V^{\mathrm{zone}}$ contains the coarser feature grids $\{V^0,V^1\}$ while the pixel-level feature grid $V^{\mathrm{pix}}$ contains the finer feature grids $\{V^2,V^3\}$ . For a given point $\mathbf{x}\in \mathbb{R}^3$ , its whole geometry feature $\mathcal{F}$ is extracted by tri-linearly interpolating features at each grid level and concatenating these features together. The feature can be decoded into SDF values in both pixel-level $\phi_{pix}(\mathbf{x})$ and zone-level $\phi_{zone}(\mathbf{x})$ via the same geometry decoder $f_{\omega}(\cdot)$ switched by the rendering mask. We use all the features for rendering pixel-level results $\phi_{pix}$ , and mask out the features extracted from the finer grids for zone-level rendering results $\phi_{zone}$ : + +$$ +\begin{array}{l} \phi_ {p i x} (\mathbf {x}) = f _ {\omega} \left(\left[ V ^ {z o n e} (\mathbf {x}), V ^ {p i x} (\mathbf {x}) \right]\right), \\ \phi_ {z o n e} (\mathbf {x}) = f _ {\omega} \left(\left[ V ^ {z o n e} (\mathbf {x}), \mathbf {0} \right]\right). \\ \end{array} +$$ + +This mask operation also makes the corresponding neurons in the geometry decoder inactive. The SDF values from both branches are used in the tracking and mapping process corresponding to the pixel-level and zone-level supervision, and only the pixel-level SDF values are used for the final mesh extraction. + +Color Encoding. For color information, we encode it only at the finest level using a separate set of feature grid $\mathcal{W}_{\beta}$ and decoder $g_{\gamma}(\cdot)$ as [46, 36]. When decoding color, we additionally use the ray direction $\mathbf{r}$ , so the color value for a 3D point is given by: + +$$ +\mathbf {c} = g _ {\gamma} \left(\mathcal {W} _ {\beta} (\mathbf {x}), \mathbf {r}\right). \tag {2} +$$ + +Rendering of L5 Signals, Color and Depth Images. We render color and depth values with the volumetric rendering technique [37]. Specifically, to render a color pixel, we sample $N$ points along the corresponding emitted ray, denoted as $\mathbf{x}_i = \mathbf{o} + d_i\mathbf{r}, i \in \{1,2,\dots,N\}$ where $\mathbf{o}$ is the camera center, $\mathbf{r}$ is the direction of this ray and $d_i$ is the distance of the sampled point $\mathbf{x}_i$ along the ray. We then accumulate the color value along the ray through: + +$$ +\hat {\mathbf {c}} = \sum_ {i = 1} ^ {N} T _ {i} \alpha_ {i} \mathbf {c} _ {i}, \tag {3} +$$ + +where $T_{i} = \prod_{j = 1}^{i - 1}\left(1 - \alpha_{j}\right)$ is the accumulated transmittance, and $\alpha_{i}$ is the opacity value converted from the SDF prediction $\phi_{pix}$ . The conversion follows the original definition in NeuS [37]. + +The process of rendering the L5 signals is similar to rendering the color. The differences are that for rendering the mean depth value $\hat{d}_z$ of an L5 zone, we emit the ray from the center of that zone and accumulate the distance along the ray through: + +$$ +\hat {d} _ {z} = \sum_ {i = 1} ^ {N} T _ {i} \alpha_ {i} d _ {i}. \tag {4} +$$ + +The zone-level opacity $\alpha_{i}$ is derived in the same manner as color rendering but using $\phi_{zone}$ instead of $\phi_{pix}$ . Intuitively, we can optimize the camera pose and scene structure by only supervising the rendered color images and L5 signals. However, in our experiment (Sec. 4.3), we show that the results are far from satisfactory. As a result, we also render the pixel-wise depth maps using Eq. 4 with $\phi_{pix}$ and supervise it with the depth prediction from [14]. + +# 3.3. Temporal Filtering of L5 Signals + +As mentioned before, we use DELTAR [14] to predict a pixel-wise depth map as additional supervision. DELTAR is a pre-trained neural network that takes L5 signals and RGB + +![](images/25e881c9f86476ee4504f924530a95db7dcd416599d09fa438f54d5032b9894f.jpg) +Figure 4. Temporal Filtering of L5 Signals. By fusing the latest ToF measurement with a rendered one, we can significantly improve the signal quality and the corresponding predicted depth. + +images as input and predicts corresponding depth maps. We observe that when there are a large number of missing or noisy L5 signals, the depth map predicted by DELTAR may contain severe artifacts due to the inherent depth ambiguities of missing or noisy regions, thus further contaminating the learning of implicit features and degrading the SLAM system's performance. + +This motivates us to develop an explicit temporal filtering technique (Fig. 4) to enhance the L5 signals before feeding into DELTAR. Since the past observations are stored implicitly in our scene representation, we can leverage this information to refine the current observation. Specifically, the proposed filtering algorithm contains two steps: the prediction step and the update step. In the prediction step, we predict the per-zone ToF measurement $X_{k} = \{\mu_{1},\sigma_{1}\}$ in the timestamp $k$ using neural rendering (Eq. 4) with an initialized pose. Then we update $X_{k}$ to $X_{k}^{\prime}$ with the current L5 measurement $Z_{k} = \{\mu_{2},\sigma_{2}\}$ : + +$$ +\mu_ {X _ {k ^ {\prime}}} = \frac {\mu_ {1} \sigma_ {2} ^ {2} + \mu_ {2} \sigma_ {1} ^ {2}}{\sigma_ {1} ^ {2} + \sigma_ {2} ^ {2}}, \quad \sigma_ {X _ {k ^ {\prime}}} ^ {2} = \frac {\sigma_ {1} ^ {2} \sigma_ {2} ^ {2}}{\sigma_ {1} ^ {2} + \sigma_ {2} ^ {2}}. \tag {5} +$$ + +As for the zones with no valid raw L5 signals, we simply use the predicted L5 signals. Finally, the enhanced signals $X_{k}^{\prime}$ are fed into the depth prediction network with corresponding RGB image [14] to obtain a high-resolution depth estimation. + +# 3.4. SLAM System Implementation + +Initialization. Since we do not have reliable depth maps as input, we need to perform initialization in order to build a local map for our system to bootstrap. The first $N_{i}$ frames are added to the initialization process with a fixed interval $I_{skip}$ sequentially. The pose of each newly added frame is initialized by the previous frame. During this process, the feature grids, decoders and camera poses are jointly optimized using the same loss function as in the mapping process. Finally, when all the frames are added, we optimize the whole frame set for $N_{e}$ iterations. + +Coarse-to-Fine Mapping. To optimize the scene representation mentioned in Sec. 3.2, we uniformly sample total + +$M$ pixels and $Z$ zones and perform optimization to minimize the photometric loss, geometric loss and SDF regularization. The zones and pixels are sampled from the current optimization window, which consists of two types of frames: neighbor frames (the nearest $N_{n}$ frames with an interval of 4) and global frames (chosen from all the past co-visible mapping frames). The photometric loss is the average color difference of all the sampled pixels: + +$$ +\mathcal {L} _ {c} = \frac {1}{M} \sum_ {m = 1} ^ {M} | I [ u _ {m}, v _ {m} ] - \hat {\mathbf {c}} _ {m} |, \tag {6} +$$ + +where $u_{m}, v_{m}$ represents for the image coordinate of pixel $m$ . The geometric loss is calculated on both pixel-level and zone-level. For zone-level loss, only zones with valid L5 signals $Z_{d}$ are considered. We also add SDF supervision on pixel-level as in [36, 26] to add robustness to the optimization. The whole geometric loss is defined as: + +$$ +\mathcal {L} _ {g} = \mathcal {L} _ {d} + \mathcal {L} _ {z} + \lambda_ {s d f} \mathcal {L} _ {s d f}, +$$ + +$$ +\mathcal {L} _ {d} = \frac {1}{M} \sum_ {m = 1} ^ {M} | \widetilde {D} [ u _ {m}, v _ {m} ] - \hat {d} _ {m} |, \tag {7} +$$ + +$$ +\mathcal {L} _ {z} = \frac {1}{| Z _ {d} |} \sum_ {z \in Z _ {d}} | \bar {D} _ {z} - \hat {d} _ {z} |, +$$ + +where $\overline{D} \in \mathbb{R}^{8 \times 8}$ represents the mean depth value measured by L5 and $\widetilde{D}$ represents the pixel-wise depth prediction. Since we do not have high-quality depth as input and there are many texture-less areas in typical indoor scenes, directly optimizing the feature volume and camera poses is an ill-posed problem. Therefore, we employ two regularizations on the SDF values during pixel-level rendering as [36], namely the eikonal term $\mathcal{L}_{eik}$ and the smoothness term $\mathcal{L}_s$ : + +$$ +\mathcal {L} _ {r} = \lambda_ {e i k} \mathcal {L} _ {e i k} + \lambda_ {s} \mathcal {L} _ {s}, \tag {8} +$$ + +where the eikonal regularization is employed to ensure the network produces valid SDF values [37, 36], the smoothness regularization is used to encourage neighbor points to have similar normal directions, and $\lambda_{eik}$ and $\lambda_s$ are weights to balance the two regularization terms. + +During the mapping process, we perform a coarse-to-fine optimization process, bringing better convergence since pixel-wise optimization can rely on the already initialized coarse grids. We first optimize the scene at the coarse level using zone-level ToF signals. Then, pixel-wise RGB/depth supervisions are added to jointly optimize the decoders, feature grids and camera poses by minimizing the mentioned losses for $N_{m}$ iterations with a local BA to cover geometry details. + +$$ +\min _ {\theta , \omega , \beta , \gamma , \left\{\mathbf {R} _ {i}, \mathbf {t} _ {i} \right\}} \lambda_ {c} \mathcal {L} _ {c} + \lambda_ {g} \mathcal {L} _ {g} + \lambda_ {r} \mathcal {L} _ {r}. \tag {9} +$$ + +![](images/2a39c9be56d585f42ddb2a9eb1aea1d00cafc14fd1c4f86f268df6f791fe5d53.jpg) +Figure 5. Qualitative Reconstruction Results. Compared to other methods, our approach produces high-quality reconstructions with smooth surfaces and fewer artifacts. + +We also conduct a global BA every $N_g$ frame by adding all the past mapping frames to the optimization window and jointly optimize them to globally optimize the camera poses and scene geometry. We provide the details of losses in the supplementary material. + +Tracking. During tracking, the feature grid and the decoders remain fixed, while only the 6-DoF pose of the current frame is optimized. Similar to previous methods [46, 31], $M_t$ pixels are sampled in the current frame to calculate both the pixel-level photometric loss and geometric loss as previously described. The camera pose is then updated iteratively via back-propagation. Tracking with only pixel-level supervision is susceptible to a suboptimal solution, so we leverage our multi-modal scene representation and apply zone-level supervision in the early stage. Specifically, we additionally sample $Z$ zones in the current frame and use the L5 signal to minimize zone depth loss as well, which leads to a more robust tracking result. + +# 4. Experiments + +# 4.1. Experimental Setup + +Datasets. Since no public SLAM benchmarks take the L5 signals as input, we build a data capture device as in [14] + +and use it to create an indoor SLAM dataset, which contains 7 sequences captured in 5 typical indoor scenes. We record color images $(640\times 480)$ , L5 signals and depth maps for each sequence. Note that we only use the color images and L5 signals as the input to our SLAM system. The depth maps are used to obtain the ground truth 6-DoF camera poses and 3D surface mesh. We follow the automated capture pipeline proposed in ScanNet [7] to compute the ground truth data. + +Baselines. We compare our method with two categories of baselines: (a) learning-based SLAM methods including iMAP [31] (re-implemented by [46]) and NICE-SLAM [46]; (b) traditional SLAM methods including ORBSLAM3 [4], KinectFusion [10], ElasticFusion [38] and BundleFusion [8]. For the methods that only support RGB-D input, including iMAP, NICE-SLAM, KinectFusion, ElasticFusion and BundleFusion, we use the RGB image and the predicted depth map by [14] as the system input. For ORB-SLAM3, we evaluate it in both the RGB version (given only RGB image as input) and the RGB-D version (using the predicted depth, marked as $\widetilde{D}$ ). Note that none of these methods can work well with only raw L5 zone-level depths or take it as additional inputs. We evaluate both the scene reconstruction and the camera tracking results. Since + +
Scene NameKitchenSofaOfficeReceptionLiving roomOffice2Sofa2Avg.
KinectFusion[10]Acc.↓-0.1900.2110.261-0.2670.1350.213
Comp.↓-0.0480.0460.064-0.0780.0640.060
F-score-0.2780.2880.285-0.2740.3810.301
ElasticFusion[38]Acc.↓0.0920.1350.0840.2970.1510.0960.1220.140
Comp.↓0.0650.0480.0820.3050.2160.1470.0470.130
F-score0.5530.4200.5290.2740.3820.4160.4810.436
BundleFusion[8]Acc.↓0.1700.1000.1030.122-0.1210.1230.123
Comp.↓0.0880.0300.0380.057-0.2140.0340.077
F-score0.3730.5710.4740.470-0.4420.5270.476
iMAP[31]Acc.↓-0.1350.2290.3650.2250.2330.1390.221
Comp.↓-0.0540.1030.2450.2910.1390.0690.150
F-score-0.4450.3150.2380.1700.2550.4160.307
NICE-SLAM[46]Acc.↓0.3030.1190.1160.2160.1030.1560.4640.211
Comp.↓0.4560.0420.0700.1990.0890.1630.0450.152
F-score0.2210.5540.4110.4020.4000.2730.4010.380
OursAcc.↓0.0810.0680.0670.0790.0780.1130.1210.087
Comp.↓0.0710.0410.0450.0620.1220.0850.0330.066
F-score0.5590.6610.6460.6430.4960.5570.6560.604
+ +Table 1. Quantitative Comparison on Reconstruction. We perform the mapping evaluation on 7 indoor sequences and report results of three metrics including accuracy (Acc.), completion (Comp.) and F-score. The failure cases are marked as “-”. + +
Scene NameKitchenSofaOfficeReceptionLiving roomOffice2Sofa2
ORB-SLAM3 [4]0.054-0.0170.025-0.022-
ORB-SLAM3(with D) [4]0.0820.0350.0190.049-0.058-
KinectFusion [10]-0.1460.2090.157-0.3210.125
ElasticFusion [38]0.2530.1100.0700.1930.5300.1210.146
BundleFusion [8]0.1760.1020.1350.101-0.1630.120
iMAP [31]-1.6580.3380.6480.6790.3440.214
NICE-SLAM [46]0.7450.1440.1550.2510.2890.2280.421
Ours0.1130.0810.0560.1140.2000.1010.085
+ +Table 2. Camera Tracking Results. ATE RMSE [m] (↓) is used as the evaluation metric. The failure cases are marked as “-”. For the variations of ORB-SLAM3, we only mark the best one in each sequence. Our approach outperforms all the other methods except for ORB-SLAM3 [4]. However, ORB-SLAM3 fails on 3 of the 7 sequences due to the textureless indoor environment while our approach tracks successfully on all of the sequences. + +ORB-SLAM3 cannot output dense models, we exclude it from the mapping evaluation. + +Implementation Details. Our SLAM system is executed on a desktop PC equipped with an Intel i7-9700K CPU and an NVIDIA RTX 3090 GPU. In all our experiments, we set the grid sizes to [3, 6, 24, 96] cm and the number of sampling pixels $M$ to 5000. Our method is implemented using PyTorch [27] with ADAM [12] optimizer. The decoders, multi-modal feature grids, and camera poses are trained with learning rates of 0.001, 0.01, and 0.0005, respectively. The loss weights are set to 10 for $\lambda_{c}$ and $\lambda_{sdf}$ and 1 for the others. Inspired by instant-ngp [22], we use the tiny-cuda-nn [21] library to implement the proposed multimodal grid encoding, which significantly accelerates the optimization process. We follow DELTAR [14] to pre-train the multi-modal depth prediction network on NYU-V2 with simulated L5 signals. For more details, please refer to the supplementary material. + +# 4.2. Evaluation of Mapping and Tracking + +Mapping. We use three metrics to evaluate the reconstruction result including accuracy (Acc.), completion (Comp.) and F-score following the previous work [32]. For detailed descriptions of these metrics, please refer to the supplementary material. As shown in Table 1, our method outperforms all the baseline methods by a large margin (ours 0.604 vs. the second-best 0.476 in terms of F-score). We also show qualitative results in Fig. 5. Our method is able to produce high-quality 3D models with smooth surfaces and high accuracy. It is easy to notice that our reconstruction result has much fewer artifacts and noisy points. Since NICE-SLAM [46] relies on high-quality depth input, its performance is poor given the noisy and unreliable depth input. + +Tracking. We use ATE RMSE [30] to evaluate the camera tracking. As shown in Table 2, our method outperforms all other methods except for ORB-SLAM3 [4]. However, ORB-SLAM3 is much less robust and tracks lost on 3 of + +
EMKitchenSofaOfficeReceptionLiving roomOffice2Sofa2Avg.
0.2030.0880.0630.1430.2160.1200.0940.132
✓0.1350.0850.0600.1440.2110.1080.0890.119
✓✓0.1130.0810.0560.1140.2000.1010.0850.107
+ +Table 3. Ablation Study. We explore the efficiency of multi-modal scene representation (marked as “M”) and L5 signal temporal filtering (marked as “E”). We use ATE RMSE [m] (↓) as the evaluation metric. + +
TrackingMapping
Learning-based MethodsiMAP [31]101 ms448 ms
NICE-SLAM [46]470 ms1300 ms
Ours116 ms380 ms
Classical MethodsORB-SLAM3 [4]31 ms159 ms
ElasticFusion [38]31 ms-
+ +Table 4. Runtime Comparison. Different from NICE-SLAM [46] that measures one iteration of optimization, we report the averaging total runtime for tracking and mapping respectively for better comparison with classic methods. ElasticFusion does not have an explicit mapping process thus it is labeled as “-”. + +![](images/9d91c5f5f5b0daf6f2cbb3fb71fe82d5db633b251a37770ed00d963e7ee06f50.jpg) +Figure 6. Results without Pixel-Wise Depth Supervision. It cannot guarantee plausible reconstruction results without the pixel-wise depth maps as additional supervision. + +the 7 sequences, while our method successfully tracks all the sequences. This is because that ORB-SLAM3, as a keypoint-based method, struggles in texture-less regions, which are commonly seen in indoor environments. Given the predicted depth, ORB-SLAM3 can reduce the lost ratio from $42.8\%$ to $28.5\%$ but leads to worse camera tracking results since the predicted depth is not accurate enough. + +Runtime Analysis. We compare the runtime of tracking and mapping in Table 4 for both classical methods and learning-based methods. The runtime of our method is similar to iMAP, but it is faster than NICE-SLAM due to our implementation optimization inspired by instant-ngp [22]. + +# 4.3. Ablation Study + +In this section, we first study the effectiveness of using pixel-wise depth prediction as additional supervision, then investigate the importance of the proposed multi-modal feature grid representation and the temporal filtering technique. Impact of the Pixel-Wise Depth Supervision. We try using only the L5 raw signals and RGB images for supervision. Removing the pixel-wise depth supervision makes + +![](images/0b0967ef6aa79f3e79d2c967dce6bd7811854a552316828a14fc0a4d0979fe14.jpg) +RGB/GT + +![](images/815fc6ec20f282c6c31787913c7156c60ceb1589a9411f55cb5a0c8e92154f5d.jpg) +L5 Signal + +![](images/4356fefe6895ecad8bd3df299fb0c9538dc95c63ac3ba18b1ed18381eed5d558.jpg) +Predicted Depth + +![](images/25726e2eeab16b6483ecea7627b9c7125a016ed979959caf5a51cf56a430536d.jpg) +Error Map +Figure 7. Qualitative Study of the Effect of Temporal Filtering on Depth Prediction. We compare the depth prediction result obtained through two methods: solely employing raw L5 signals (top row) and incorporating our temporal filtering technique (bottom row). Our temporal filtering technique enhances the raw L5 signals and fills up the missing regions, leading to a better depth prediction result. + +the optimization problem harder, which is more obvious when the problem size grows. In Fig. 6 we show the rendered depth when optimizing the first frame and the first 150 frames. The latter contains serious errors. As a result, it leads to a distorted reconstruction, i.e., the "Baseline" result in the upper right. + +Impact of the Multi-Modal Feature Grid. We verify the effectiveness of our multi-modal feature grid representation (denoted as “M”) in terms of camera tracking and show the result in Table 3. With the multi-modal feature grid representation, we are able to use raw L5 signal as supervision. As a result, we can optimize the camera poses on both pixel-level and zone-level, leading to better trajectory accuracy. + +Impact of the Temporal Filtering. In Fig. 7 we show the qualitative comparison with and without the proposed temporal filtering. It can be seen that the large portion of missing L5 signals leads to severe errors on the corresponding regions of the predicted depth map. The error reduces significantly with the proposed temporal filtering technique. + +We also study the quantitative impact of temporal filtering (marked as "E") on both the depth prediction (Table 5) and the camera tracking (Table 3). We divide the testing sequences into normal and hard cases according to the quality of L5 signals. As shown in Table 5, the temporal filtering technique improves the predicted depth in general and significantly in hard cases. Such an improvement benefits the final SLAM system and leads to more accurate camera + +
δ1↑δ2↑δ3↑REL↓RMSE↓
Hw/o E0.7730.9100.9690.1590.513
w E0.9250.9720.9830.0930.366
Nw/o E0.9540.9890.9970.0650.151
w E0.9560.9920.9980.0650.145
+ +Table 5. Ablation Study on Temporal Filtering for Depth Prediction. “H”/“N” stands for the hard/normal cases and “E” represents the temporal filtering. We report the quantitative result of depth maps predicted from L5 raw signals and our refined signals. + +![](images/46aa0e638c670513eff902d702630d2c70fc879ac55cc13049d58593959e1627.jpg) + +![](images/0222d4b2428a33cfa30cfc614c67a4eb032d595f0101284736054e590c856ea1.jpg) +Outdoor Scene + +![](images/b102b3c1fb96c20abb8e283d0c49cdbed6c45f3f6f25649811de8cba6c3d4901.jpg) + +![](images/c25cef289f243897dbccf2c137f0551911bdb5a1655fc717059a6de4fbd064f9.jpg) +Our Reconstruction +Figure 8. Qualitative Results of Outdoor Reconstruction. The proposed method can recover a complete scene model in outdoor scenes but missing more details than that in indoor due to the poor L5 signals. + +tracking, as shown in Table 3 (marked as “E”). Please refer to the supplementary material for the definition of the normal/hard cases and the depth evaluation metrics. + +# 4.4. Performance in Outdoor Scenes + +Currently, we focus on indoor scenes as other NeRF-based SLAM systems [31, 46] due to the optical interference limitation of depth sensors. Actually, the sunlight has a stronger interference on the L5 sensor for its low-power emitter. In Fig. 8, we show two examples of outdoor scene reconstruction using our proposed methods. The recovered mesh is complete but missing more details than that in indoor scenes due to the poor L5 signals. + +# 5. Conclusion + +We introduce a novel dense visual SLAM framework working with RGB cameras and light-weight ToF sensors using neural implicit scene representation. To accommodate this new input modality, we propose a novel multimodal feature grid that enables both zone-level rendering for the ToF sensors and pixel-level rendering for other high-resolution signals. To guarantee robust tracking and mapping, we exploit a per-pixel depth prediction as additional supervision, which is further improved by a novel tempo + +ral filtering strategy. Our experiments demonstrate that the proposed method can provide accurate camera tracking and high-quality reconstruction result on indoor scenes. Similar to other NeRF-based RGB-D SLAM systems, as future work we plan to further improve the system to overcome the limitation of ToF sensors in outdoor scenarios and make it efficient enough to run on mobile robots. + +Acknowledgements: This work was partially supported by NSF of China (No. 62102356). + +# References + +[1] Dejan Azinović, Ricardo Martin-Brualla, Dan B Goldman, Matthias Nießner, and Justus Thies. Neural RGB-D surface reconstruction. 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IEEE, 2022. +[37] Peng Wang, Lingjie Liu, Yuan Liu, Christian Theobalt, Taku Komura, and Wenping Wang. NeuS: Learning neural implicit surfaces by volume rendering for multi-view reconstruction. Advances in Neural Information Processing Systems, 34:27171-27183, 2021. +[38] Thomas Whelan, Renato F Salas-Moreno, Ben Glocker, Andrew J Davison, and Stefan Leutenegger. ElasticFusion: Real-time dense SLAM and light source estimation. The International Journal of Robotics Research, 35(14):1697-1716, 2016. +[39] Bangbang Yang, Chong Bao, Junyi Zeng, Hujun Bao, Yinda Zhang, Zhaopeng Cui, and Guofeng Zhang. NeuMesh: Learning disentangled neural mesh-based implicit field for geometry and texture editing. In Proceedings of the European Conference on Computer Vision, pages 597-614. Springer, 2022. +[40] Bangbang Yang, Yinda Zhang, Yijin Li, Zhaopeng Cui, Sean Fanello, Hujun Bao, and Guofeng Zhang. Neural rendering in a room: amodal 3d understanding and free-viewpoint rendering for the closed scene composed of pre-captured objects. ACM Transactions on Graphics (TOG), 41(4):1-10, 2022. +[41] Bangbang Yang, Yinda Zhang, Yinghao Xu, Yijin Li, Han Zhou, Hujun Bao, Guofeng Zhang, and Zhaopeng Cui. Learning object-compositional neural radiance field for ed-itable scene rendering. In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 13779-13788, 2021. +[42] Lin Yen-Chen, Pete Florence, Jonathan T Barron, Alberto Rodriguez, Phillip Isola, and Tsung-Yi Lin. iNeRF: Inverting neural radiance fields for pose estimation. in 2021 IEEE. In Proceedings of the RSJ International Conference on Intelligent Robots and Systems (IROS), pages 1323-1330, 2021. +[43] Zehao Yu, Songyou Peng, Michael Niemeyer, Torsten Sattler, and Andreas Geiger. MonoSDF: Exploring monocular geometric cues for neural implicit surface reconstruction. Advances in Neural Information Processing Systems, 35:25018-25032, 2022. +[44] Guofeng Zhang, Jiaya Jia, Tien-Tsin Wong, and Hujun Bao. Recovering consistent video depth maps via bundle optimization. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 1-8. IEEE, 2008. +[45] Kai Zhang, Gernot Riegler, Noah Snavely, and Vladlen Koltun. NeRF++: Analyzing and improving neural radiance fields. arXiv preprint arXiv:2010.07492, 2020. +[46] Zihan Zhu, Songyou Peng, Viktor Larsson, Weiwei Xu, Hujun Bao, Zhaopeng Cui, Martin R Oswald, and Marc Pollefeys. NICE-SLAM: Neural implicit scalable encoding for SLAM. 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However, due to the sparse and noisy depth measurements, these sensors have rarely been considered for dense geometry reconstruction. In this work, we present the first dense SLAM system with a monocular camera and a lightweight ToF sensor. Specifically, we propose a multi-modal implicit scene representation that supports rendering both the signals from the RGB camera and light-weight ToF sensor which drives the optimization by comparing with the raw sensor inputs. Moreover, in order to guarantee successful pose tracking and reconstruction, we exploit a predicted depth as an intermediate supervision and develop a coarse-to-fine optimization strategy for efficient learning of the implicit representation. At last, the temporal information is explicitly exploited to deal with the noisy signals from light-weight ToF sensors to improve the accuracy and robustness of the system. Experiments demonstrate that our system well exploits the signals of lightweight ToF sensors and achieves competitive results both on camera tracking and dense scene reconstruction. Project page: https://zju3dv.github.io/tof_slam/." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 538, + 128, + 551 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 538, + 128, + 551 + ], + "spans": [ + { + "bbox": [ + 47, + 538, + 128, + 551 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 558, + 287, + 679 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 287, + 679 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 287, + 679 + ], + "type": "text", + "content": "Dense simultaneous localization and mapping (dense SLAM) [38, 8, 9, 44] has extensive applications in augmented reality [13, 17], indoor robotics, etc. It usually relies on high-precision and high-resolution depth sensors, such as time-of-flight (ToF) sensors or structured light sensors. Due to the size, weight, and price issues, these depth sensors are only used in a few high-end mobile devices until recent years. In contrast, light-weight ToF sensors, which are cost-effective, compact, and energy-efficient, were integrated into hundreds of smartphone models1. As a result," + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 310, + 217, + 544, + 422 + ], + "blocks": [ + { + "bbox": [ + 310, + 217, + 544, + 422 + ], + "lines": [ + { + "bbox": [ + 310, + 217, + 544, + 422 + ], + "spans": [ + { + "bbox": [ + 310, + 217, + 544, + 422 + ], + "type": "image", + "image_path": "77bc33968a493fc838c60c0f1e4ada2d380593bc6e4ae5141b583f480367b426.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 434, + 547, + 491 + ], + "lines": [ + { + "bbox": [ + 304, + 434, + 547, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 434, + 547, + 491 + ], + "type": "text", + "content": "Figure 1. Monocular Dense SLAM with Our Multi-Modal Implicit Representation. We present a novel SLAM system based on implicit scene representation. The system does not require high-precision and high-resolution depth sensors and only takes RGB images and the signals of light-weight ToF sensors as input." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 510, + 546, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 546, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 546, + 545 + ], + "type": "text", + "content": "it would be valuable if we could fully utilize these lightweight sensors for dense SLAM, which further facilitates other applications like AR/VR and micro-Robot." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 546, + 547, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 546, + 547, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 546, + 547, + 653 + ], + "type": "text", + "content": "Unfortunately, limited by the compact electronic design, the light-weight ToF sensor can only provide coarse measurement in the form of depth distribution in an extremely low resolution as illustrated in Fig. 2. Existing RGB-D dense SLAM systems [38, 46, 31] are designed for accurate and pixel-wise depth inputs, thus cannot work with the light-weight ToF signals directly. They will also fail if we simply consider the light-weight ToF signals as a low-resolution depth (i.e., mean depth values in each zone)." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 547, + 715 + ], + "type": "text", + "content": "In this paper, we aim to design a novel learning-based dense SLAM system that provides accurate pose tracking and dense reconstruction taking the RGB sequences from a color camera and the sparse signals of light-weight ToF as input (Fig. 1). However, it is non-trivial to design such" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 684, + 136, + 693 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 684, + 136, + 693 + ], + "spans": [ + { + "bbox": [ + 58, + 684, + 136, + 693 + ], + "type": "text", + "content": "*Corresponding author." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 59, + 693, + 270, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 693, + 270, + 703 + ], + "spans": [ + { + "bbox": [ + 59, + 693, + 270, + 703 + ], + "type": "text", + "content": "1https://www.st.com/content/st_com/en/about/" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 48, + 704, + 237, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 704, + 237, + 712 + ], + "spans": [ + { + "bbox": [ + 48, + 704, + 237, + 712 + ], + "type": "text", + "content": "media-center/press-item.html/t4210.html" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "spans": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "type": "text", + "content": "1" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 61, + 72, + 272, + 242 + ], + "blocks": [ + { + "bbox": [ + 61, + 72, + 272, + 242 + ], + "lines": [ + { + "bbox": [ + 61, + 72, + 272, + 242 + ], + "spans": [ + { + "bbox": [ + 61, + 72, + 272, + 242 + ], + "type": "image", + "image_path": "b05aba552881eca49556599d94593055f46606e06b1b0b65e58e42eb386a95da.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 252, + 288, + 299 + ], + "lines": [ + { + "bbox": [ + 46, + 252, + 288, + 299 + ], + "spans": [ + { + "bbox": [ + 46, + 252, + 288, + 299 + ], + "type": "text", + "content": "Figure 2. L5 Sensing Principle. Instead of pixel-wise depth measurement, L5 measures the depth distribution of a large zone and returns its depth mean and variance. Specifically, L5 measures " + }, + { + "bbox": [ + 46, + 252, + 288, + 299 + ], + "type": "inline_equation", + "content": "8 \\times 8" + }, + { + "bbox": [ + 46, + 252, + 288, + 299 + ], + "type": "text", + "content": " zones in total. The figure is adapted from [14]." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 319, + 287, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 319, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 287, + 628 + ], + "type": "text", + "content": "a system. At first, motivated by the recent achievements in the field of neural rendering [20, 2, 40, 39, 41] and grid-based feature encoding [46, 36, 18], we propose to design our system based on a novel implicit representation from which we can render both the RGB image and original ToF signal. In this way, we can define the losses directly against the multi-domain input, which can be utilized to optimize camera poses and 3D scenes. However, we find that this cannot guarantee plausible tracking and reconstruction results because of low-quality raw depth signals from the sensor. Inspired by recent works [31, 46] that high-resolution accurate depth maps play an important role in the implicit SLAM systems, we further exploit the depth estimation model [14] for the light-weight ToF sensor to predict an intermediate high-resolution depth as additional supervision. Based on all the above insights, we develop a multimodal implicit scene representation with multi-level feature grids, which is able to generate both the zone-level signals of light-weight ToF sensors and pixel-wise RGB/depth images via the differentiable rendering for the camera tracking and reconstruction. For efficient network convergence, we also design a coarse-to-fine optimization process for this novel implicit scene representation, i.e., firstly using zone-level ToF signals to optimize the scene at the coarse level, then adding pixel-wise RGB/depth supervisions to recover geometry details." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 630, + 286, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 630, + 286, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 630, + 286, + 715 + ], + "type": "text", + "content": "Moreover, although the predicted per-pixel depth is generally smooth and provides reasonable supervision as intermediate signals, it may also produce severe artifacts when there is a large portion of missing L5 signals since it is hard for the network to handle such cases due to the inherent depth ambiguity in the missing regions. As a result, we further develop a temporal filtering technique to enhance depth" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 545, + 190 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 190 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 190 + ], + "type": "text", + "content": "prediction. Specifically, when a new signal is captured, we render a zone-level light-weight ToF signal from our multimodal scene representation with an initialized pose and fuse it with that new observation signal, which serves as the input of the depth prediction network. Such an explicit filtering technique improves the depth estimation performance significantly, particularly in extreme cases where the raw L5 signals are very noisy or contain large amounts of missing data, and therefore further benefits the whole SLAM system." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 192, + 546, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 192, + 546, + 407 + ], + "spans": [ + { + "bbox": [ + 304, + 192, + 546, + 407 + ], + "type": "text", + "content": "Our contributions can be summarized as follows. At first, to our best knowledge, we present the first dense SLAM system by only taking the monocular images and the signals from a light-weight ToF sensor as input. Moreover, we propose a multi-modal implicit scene representation which supports rendering both the zone-level signals of light-weight ToF sensors and pixel-wise RGB/depth images. By minimizing the re-rendering loss of these signals in a coarse-to-fine strategy, we can recover the camera pose and the scene geometry via differentiable neural rendering. Furthermore, we propose a temporal filtering technique to enhance the signals of light-weight ToF sensors and corresponding depth prediction which significantly improve the proposed SLAM system in extreme cases. Experiments on the real datasets demonstrate that the proposed system well exploits the signals of light-weight ToF sensors and achieves competitive results both on camera tracking and dense scene reconstruction compared to existing methods." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 418, + 392, + 430 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 418, + 392, + 430 + ], + "spans": [ + { + "bbox": [ + 306, + 418, + 392, + 430 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 437, + 545, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 545, + 641 + ], + "type": "text", + "content": "Visual SLAM. Sparse visual SLAM systems [13, 23, 16] focus on solving accurate camera poses based on the tracking of sparse keypoint [28, 25]. These types of methods usually struggle in texture-less environments and cannot provide a complete reconstruction result of the scene. In comparison, dense visual SLAM systems [10, 38, 11, 24] perform much more robust but usually require depth images as input. More recently, many methods emerged to estimate the dense depth map and camera pose simultaneously from RGB sequences only using deep neural networks [3, 6, 34, 35] and reconstruct the scene through fusing the estimated depth maps. Unlike these previous methods optimizing depth maps per frame, we follow iMAP [31] and NICE-SLAM [46] and use an implicit scene representation. However, unlike iMAP and NICE-SLAM, we do not require the depth camera and take the light-weight ToF signals as input instead." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": "Neural Implicit Representation. Neural implicit representations are widely used in various kinds of tasks, including novel view synthesis [20, 45, 2, 19] and scene reconstruction [1, 36, 26]. While showing promising results, these methods require precise camera poses as input which greatly limits their application scenarios. Some re" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "spans": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "type": "text", + "content": "2" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 75, + 541, + 292 + ], + "blocks": [ + { + "bbox": [ + 50, + 75, + 541, + 292 + ], + "lines": [ + { + "bbox": [ + 50, + 75, + 541, + 292 + ], + "spans": [ + { + "bbox": [ + 50, + 75, + 541, + 292 + ], + "type": "image", + "image_path": "beb9a7d4e20dce5d4a526f16b2b557f9c77a3ccaec9ec5957228986d7994b517.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 304, + 546, + 338 + ], + "lines": [ + { + "bbox": [ + 46, + 304, + 546, + 338 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 546, + 338 + ], + "type": "text", + "content": "Figure 3. System Overview. Our method uses a monocular camera and a light-weight ToF sensor as input and recovers both camera motion and the scene structures. Through differentiable rendering, our method can render multi-modal signals, including color images, depth images and zone-level L5 signals. Both the scene structure and the camera poses are optimized by minimizing the re-rendering loss." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 357, + 287, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 357, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 46, + 357, + 287, + 464 + ], + "type": "text", + "content": "cent works [15, 42] propose to optimize camera pose with the scene representation simultaneously. Lately, iMAP [31] and NICE-SLAM [46] bring neural implicit representations into visual SLAM systems. Nevertheless, requirements of RGB-D sequences as input significantly constrain their applications, especially on mobile devices with tight power budgets. In contrast, we propose a visual SLAM method using only an RGB camera and a light-weight ToF sensor, which commonly co-exists on mobile devices." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 465, + 287, + 634 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 465, + 287, + 634 + ], + "spans": [ + { + "bbox": [ + 46, + 465, + 287, + 634 + ], + "type": "text", + "content": "Neural Grid Optimization. Typically, a single multi-layer perceptron (MLP) is employed to represent the entire scene in earlier neural implicit methods [20, 2, 31]. However, these methods perform poorly when applied to large scenes and need an extremely long time for training. To address this issue, recent works [33, 22, 5] try to optimize neural features on an explicit volumetric grid. These methods, however, are only capable of pixel-level rendering and do not accommodate L5 signals as it has extremely low resolution and measures the depth distribution of a large area. To this end, we introduce a multi-modal feature grid representation that enables rendering multi-modal information at different resolutions and can deal with zone-level depth distribution data measured by light-weight ToF sensors." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 645, + 103, + 657 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 645, + 103, + 657 + ], + "spans": [ + { + "bbox": [ + 47, + 645, + 103, + 657 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 666, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 666, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 666, + 287, + 713 + ], + "type": "text", + "content": "In this section, we provide an overview of the sensing principle of light-weight ToF sensors (e.g., L5) in Sec. 3.1. Based on the characteristics of L5's signals, we design the first dense SLAM system with a monocular camera and a" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 357, + 545, + 537 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 357, + 545, + 537 + ], + "spans": [ + { + "bbox": [ + 304, + 357, + 545, + 537 + ], + "type": "text", + "content": "light-weight ToF sensor as shown in Fig. 3. Specifically, we first propose a multi-modal implicit scene representation which enables rendering L5 signals together with the common RGB image and depth maps (Sec. 3.2). To guarantee successful tracking and mapping, we exploit a depth prediction model [14] to predict intermediate per-pixel depth maps as additional supervision. By minimizing the difference between the rendered signals and input/predicted ones, we can simultaneously optimize the camera pose and scene structure in a coarse-to-fine way. Furthermore, since the depth prediction may contain severe artifacts when there is a large portion of missing L5 signals, we propose to refine the L5 signals with temporal filtering techniques to enhance the depth prediction module (Sec. 3.3). Finally, we describe the system implementation detail in Sec. 3.4." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 549, + 497, + 563 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 549, + 497, + 563 + ], + "spans": [ + { + "bbox": [ + 306, + 549, + 497, + 563 + ], + "type": "text", + "content": "3.1. Preliminaries: L5 Sensing Principle" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "Light-weight ToF sensors are designed to be low-cost, small, and low-energy and have been massively deployed on mobile devices. Compared with conventional ToF sensors, which provide high-resolution depth measurement and measure the per-pixel distance to the scene, light-weight ToF sensors usually have extremely low resolution (e.g., " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "8 \\times 8" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " zones) and measure the depth distribution for each zone. Here we take ST VL53L5CX [29] (denoted as L5), a representative product of light-weight ToF sensors, as an example to declare the sensing principle of these sensors. As shown in Fig. 2, L5 measures the depth distribution by counting the received photon number within specific time" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "spans": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "type": "text", + "content": "3" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 144 + ], + "type": "text", + "content": "intervals. The result is then fitted with a Gaussian distribution, and L5 only transmits the mean and variance to decrease both the energy consumption and broadband load. None of the previous studies have explored the usage of L5 for downstream applications like SLAM due to its low resolution and high uncertainty." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 153, + 273, + 166 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 153, + 273, + 166 + ], + "spans": [ + { + "bbox": [ + 47, + 153, + 273, + 166 + ], + "type": "text", + "content": "3.2. Multi-Modal Implicit Scene Representation" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 172, + 287, + 328 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 172, + 287, + 328 + ], + "spans": [ + { + "bbox": [ + 46, + 172, + 287, + 328 + ], + "type": "text", + "content": "The combination of neural rendering and grid-based feature encoding has found broad utilization in applications like SLAM and surface reconstruction. [46, 36, 43]. By minimizing the loss between the rendered image/depth and the input image/depth, they achieve accurate 6-DoF camera pose tracking and the reconstruction of scene geometry. In this paper, we propose a multi-modal implicit scene representation, which supports the rendering of zone-level L5 signals apart from the common RGB and depth images. Specifically, we encode the geometry and color separately and propose the masked rendering technique in the geometry encoding for the rendering of both zone-level L5 signals and pixel-level depth images." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 329, + 287, + 508 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 329, + 287, + 508 + ], + "spans": [ + { + "bbox": [ + 46, + 329, + 287, + 508 + ], + "type": "text", + "content": "Geometry Encoding with Masked Rendering. The idea of the proposed masked rendering is inspired by the integrated positional encoding(IPE) theory proposed in MipNeRF [2], but we promote it to the grid-based scene representation. The core idea of IPE is that the input features are passed through a low pass filter, i.e., if the frequency of a particular feature has a larger period than the ray, then the feature is unaffected; otherwise, the feature is scaled down towards zero. The original method represents the scene using a single MLP and achieves the low pass filtering by calculating an integral of the positional encoding as input. In our grid-based case, we concatenate features from different-level feature grids and use a rendering mask to mask out features extracted from overly high spatial frequency grids based on the current rendering scale." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": "To be more specific, we encode the scene geometry into a multi-level feature grid containing four layers " + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_{\\theta} = \\{V^0,V^1,V^2,V^3\\}" + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": ". The zone-level feature grid " + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "inline_equation", + "content": "V^{\\mathrm{zone}}" + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": " contains the coarser feature grids " + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "inline_equation", + "content": "\\{V^0,V^1\\}" + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": " while the pixel-level feature grid " + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "inline_equation", + "content": "V^{\\mathrm{pix}}" + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": " contains the finer feature grids " + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "inline_equation", + "content": "\\{V^2,V^3\\}" + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": ". For a given point " + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "inline_equation", + "content": "\\mathbf{x}\\in \\mathbb{R}^3" + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": ", its whole geometry feature " + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": " is extracted by tri-linearly interpolating features at each grid level and concatenating these features together. The feature can be decoded into SDF values in both pixel-level " + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "inline_equation", + "content": "\\phi_{pix}(\\mathbf{x})" + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": " and zone-level " + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "inline_equation", + "content": "\\phi_{zone}(\\mathbf{x})" + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": " via the same geometry decoder " + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "inline_equation", + "content": "f_{\\omega}(\\cdot)" + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": " switched by the rendering mask. We use all the features for rendering pixel-level results " + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "inline_equation", + "content": "\\phi_{pix}" + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": ", and mask out the features extracted from the finer grids for zone-level rendering results " + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "inline_equation", + "content": "\\phi_{zone}" + }, + { + "bbox": [ + 46, + 510, + 288, + 677 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 87, + 687, + 247, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 87, + 687, + 247, + 715 + ], + "spans": [ + { + "bbox": [ + 87, + 687, + 247, + 715 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\phi_ {p i x} (\\mathbf {x}) = f _ {\\omega} \\left(\\left[ V ^ {z o n e} (\\mathbf {x}), V ^ {p i x} (\\mathbf {x}) \\right]\\right), \\\\ \\phi_ {z o n e} (\\mathbf {x}) = f _ {\\omega} \\left(\\left[ V ^ {z o n e} (\\mathbf {x}), \\mathbf {0} \\right]\\right). \\\\ \\end{array}", + "image_path": "5c7926326669736a243bdb4c8e67fc37a7fc3cbe7593d058b1f29aecdd297149.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 143 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 143 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 143 + ], + "type": "text", + "content": "This mask operation also makes the corresponding neurons in the geometry decoder inactive. The SDF values from both branches are used in the tracking and mapping process corresponding to the pixel-level and zone-level supervision, and only the pixel-level SDF values are used for the final mesh extraction." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 144, + 545, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 144, + 545, + 204 + ], + "spans": [ + { + "bbox": [ + 304, + 144, + 545, + 204 + ], + "type": "text", + "content": "Color Encoding. For color information, we encode it only at the finest level using a separate set of feature grid " + }, + { + "bbox": [ + 304, + 144, + 545, + 204 + ], + "type": "inline_equation", + "content": "\\mathcal{W}_{\\beta}" + }, + { + "bbox": [ + 304, + 144, + 545, + 204 + ], + "type": "text", + "content": " and decoder " + }, + { + "bbox": [ + 304, + 144, + 545, + 204 + ], + "type": "inline_equation", + "content": "g_{\\gamma}(\\cdot)" + }, + { + "bbox": [ + 304, + 144, + 545, + 204 + ], + "type": "text", + "content": " as [46, 36]. When decoding color, we additionally use the ray direction " + }, + { + "bbox": [ + 304, + 144, + 545, + 204 + ], + "type": "inline_equation", + "content": "\\mathbf{r}" + }, + { + "bbox": [ + 304, + 144, + 545, + 204 + ], + "type": "text", + "content": ", so the color value for a 3D point is given by:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 383, + 214, + 545, + 228 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 383, + 214, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 383, + 214, + 545, + 228 + ], + "type": "interline_equation", + "content": "\\mathbf {c} = g _ {\\gamma} \\left(\\mathcal {W} _ {\\beta} (\\mathbf {x}), \\mathbf {r}\\right). \\tag {2}", + "image_path": "73874bbd53d26b5e72b6620b1dd2083a94ad7cd63d2090054d39afbe58f637ae.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "spans": [ + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "text", + "content": "Rendering of L5 Signals, Color and Depth Images. We render color and depth values with the volumetric rendering technique [37]. Specifically, to render a color pixel, we sample " + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "text", + "content": " points along the corresponding emitted ray, denoted as " + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i = \\mathbf{o} + d_i\\mathbf{r}, i \\in \\{1,2,\\dots,N\\}" + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "inline_equation", + "content": "\\mathbf{o}" + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "text", + "content": " is the camera center, " + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "inline_equation", + "content": "\\mathbf{r}" + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "text", + "content": " is the direction of this ray and " + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "inline_equation", + "content": "d_i" + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "text", + "content": " is the distance of the sampled point " + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i" + }, + { + "bbox": [ + 304, + 236, + 545, + 332 + ], + "type": "text", + "content": " along the ray. We then accumulate the color value along the ray through:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 391, + 342, + 545, + 373 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 391, + 342, + 545, + 373 + ], + "spans": [ + { + "bbox": [ + 391, + 342, + 545, + 373 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {c}} = \\sum_ {i = 1} ^ {N} T _ {i} \\alpha_ {i} \\mathbf {c} _ {i}, \\tag {3}", + "image_path": "1b3e73ea55e85f93a75c30dddcf4ddad5ea33c0f1b4a88dbc1cd07dba76d2e9b.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 384, + 545, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 384, + 545, + 445 + ], + "spans": [ + { + "bbox": [ + 304, + 384, + 545, + 445 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 384, + 545, + 445 + ], + "type": "inline_equation", + "content": "T_{i} = \\prod_{j = 1}^{i - 1}\\left(1 - \\alpha_{j}\\right)" + }, + { + "bbox": [ + 304, + 384, + 545, + 445 + ], + "type": "text", + "content": " is the accumulated transmittance, and " + }, + { + "bbox": [ + 304, + 384, + 545, + 445 + ], + "type": "inline_equation", + "content": "\\alpha_{i}" + }, + { + "bbox": [ + 304, + 384, + 545, + 445 + ], + "type": "text", + "content": " is the opacity value converted from the SDF prediction " + }, + { + "bbox": [ + 304, + 384, + 545, + 445 + ], + "type": "inline_equation", + "content": "\\phi_{pix}" + }, + { + "bbox": [ + 304, + 384, + 545, + 445 + ], + "type": "text", + "content": ". The conversion follows the original definition in NeuS [37]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 445, + 545, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 445, + 545, + 506 + ], + "spans": [ + { + "bbox": [ + 304, + 445, + 545, + 506 + ], + "type": "text", + "content": "The process of rendering the L5 signals is similar to rendering the color. The differences are that for rendering the mean depth value " + }, + { + "bbox": [ + 304, + 445, + 545, + 506 + ], + "type": "inline_equation", + "content": "\\hat{d}_z" + }, + { + "bbox": [ + 304, + 445, + 545, + 506 + ], + "type": "text", + "content": " of an L5 zone, we emit the ray from the center of that zone and accumulate the distance along the ray through:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 389, + 514, + 545, + 547 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 389, + 514, + 545, + 547 + ], + "spans": [ + { + "bbox": [ + 389, + 514, + 545, + 547 + ], + "type": "interline_equation", + "content": "\\hat {d} _ {z} = \\sum_ {i = 1} ^ {N} T _ {i} \\alpha_ {i} d _ {i}. \\tag {4}", + "image_path": "8d128a4dc78ab41c935b171765e2641acb1c10e4caae18934b3616b287af0b71.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 555, + 545, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 555, + 545, + 651 + ], + "spans": [ + { + "bbox": [ + 304, + 555, + 545, + 651 + ], + "type": "text", + "content": "The zone-level opacity " + }, + { + "bbox": [ + 304, + 555, + 545, + 651 + ], + "type": "inline_equation", + "content": "\\alpha_{i}" + }, + { + "bbox": [ + 304, + 555, + 545, + 651 + ], + "type": "text", + "content": " is derived in the same manner as color rendering but using " + }, + { + "bbox": [ + 304, + 555, + 545, + 651 + ], + "type": "inline_equation", + "content": "\\phi_{zone}" + }, + { + "bbox": [ + 304, + 555, + 545, + 651 + ], + "type": "text", + "content": " instead of " + }, + { + "bbox": [ + 304, + 555, + 545, + 651 + ], + "type": "inline_equation", + "content": "\\phi_{pix}" + }, + { + "bbox": [ + 304, + 555, + 545, + 651 + ], + "type": "text", + "content": ". Intuitively, we can optimize the camera pose and scene structure by only supervising the rendered color images and L5 signals. However, in our experiment (Sec. 4.3), we show that the results are far from satisfactory. As a result, we also render the pixel-wise depth maps using Eq. 4 with " + }, + { + "bbox": [ + 304, + 555, + 545, + 651 + ], + "type": "inline_equation", + "content": "\\phi_{pix}" + }, + { + "bbox": [ + 304, + 555, + 545, + 651 + ], + "type": "text", + "content": " and supervise it with the depth prediction from [14]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 658, + 481, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 658, + 481, + 672 + ], + "spans": [ + { + "bbox": [ + 306, + 658, + 481, + 672 + ], + "type": "text", + "content": "3.3. Temporal Filtering of L5 Signals" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "As mentioned before, we use DELTAR [14] to predict a pixel-wise depth map as additional supervision. DELTAR is a pre-trained neural network that takes L5 signals and RGB" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 302, + 750, + 308, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 302, + 750, + 308, + 757 + ], + "spans": [ + { + "bbox": [ + 302, + 750, + 308, + 757 + ], + "type": "text", + "content": "4" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 74, + 286, + 163 + ], + "blocks": [ + { + "bbox": [ + 49, + 74, + 286, + 163 + ], + "lines": [ + { + "bbox": [ + 49, + 74, + 286, + 163 + ], + "spans": [ + { + "bbox": [ + 49, + 74, + 286, + 163 + ], + "type": "image", + "image_path": "25e881c9f86476ee4504f924530a95db7dcd416599d09fa438f54d5032b9894f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 177, + 287, + 211 + ], + "lines": [ + { + "bbox": [ + 46, + 177, + 287, + 211 + ], + "spans": [ + { + "bbox": [ + 46, + 177, + 287, + 211 + ], + "type": "text", + "content": "Figure 4. Temporal Filtering of L5 Signals. By fusing the latest ToF measurement with a rendered one, we can significantly improve the signal quality and the corresponding predicted depth." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 229, + 286, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 229, + 286, + 312 + ], + "spans": [ + { + "bbox": [ + 46, + 229, + 286, + 312 + ], + "type": "text", + "content": "images as input and predicts corresponding depth maps. We observe that when there are a large number of missing or noisy L5 signals, the depth map predicted by DELTAR may contain severe artifacts due to the inherent depth ambiguities of missing or noisy regions, thus further contaminating the learning of implicit features and degrading the SLAM system's performance." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "spans": [ + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "type": "text", + "content": "This motivates us to develop an explicit temporal filtering technique (Fig. 4) to enhance the L5 signals before feeding into DELTAR. Since the past observations are stored implicitly in our scene representation, we can leverage this information to refine the current observation. Specifically, the proposed filtering algorithm contains two steps: the prediction step and the update step. In the prediction step, we predict the per-zone ToF measurement " + }, + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "type": "inline_equation", + "content": "X_{k} = \\{\\mu_{1},\\sigma_{1}\\}" + }, + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "type": "text", + "content": " in the timestamp " + }, + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "type": "text", + "content": " using neural rendering (Eq. 4) with an initialized pose. Then we update " + }, + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "type": "inline_equation", + "content": "X_{k}" + }, + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "type": "inline_equation", + "content": "X_{k}^{\\prime}" + }, + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "type": "text", + "content": " with the current L5 measurement " + }, + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "type": "inline_equation", + "content": "Z_{k} = \\{\\mu_{2},\\sigma_{2}\\}" + }, + { + "bbox": [ + 46, + 313, + 286, + 445 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 77, + 451, + 286, + 479 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 77, + 451, + 286, + 479 + ], + "spans": [ + { + "bbox": [ + 77, + 451, + 286, + 479 + ], + "type": "interline_equation", + "content": "\\mu_ {X _ {k ^ {\\prime}}} = \\frac {\\mu_ {1} \\sigma_ {2} ^ {2} + \\mu_ {2} \\sigma_ {1} ^ {2}}{\\sigma_ {1} ^ {2} + \\sigma_ {2} ^ {2}}, \\quad \\sigma_ {X _ {k ^ {\\prime}}} ^ {2} = \\frac {\\sigma_ {1} ^ {2} \\sigma_ {2} ^ {2}}{\\sigma_ {1} ^ {2} + \\sigma_ {2} ^ {2}}. \\tag {5}", + "image_path": "13f34749fe066d58dbd2f6a9c4119e3ad372794b95edb0e22239026592be9197.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 484, + 286, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 484, + 286, + 544 + ], + "spans": [ + { + "bbox": [ + 47, + 484, + 286, + 544 + ], + "type": "text", + "content": "As for the zones with no valid raw L5 signals, we simply use the predicted L5 signals. Finally, the enhanced signals " + }, + { + "bbox": [ + 47, + 484, + 286, + 544 + ], + "type": "inline_equation", + "content": "X_{k}^{\\prime}" + }, + { + "bbox": [ + 47, + 484, + 286, + 544 + ], + "type": "text", + "content": " are fed into the depth prediction network with corresponding RGB image [14] to obtain a high-resolution depth estimation." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 552, + 216, + 564 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 552, + 216, + 564 + ], + "spans": [ + { + "bbox": [ + 47, + 552, + 216, + 564 + ], + "type": "text", + "content": "3.4. SLAM System Implementation" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 570, + 286, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 286, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 286, + 689 + ], + "type": "text", + "content": "Initialization. Since we do not have reliable depth maps as input, we need to perform initialization in order to build a local map for our system to bootstrap. The first " + }, + { + "bbox": [ + 46, + 570, + 286, + 689 + ], + "type": "inline_equation", + "content": "N_{i}" + }, + { + "bbox": [ + 46, + 570, + 286, + 689 + ], + "type": "text", + "content": " frames are added to the initialization process with a fixed interval " + }, + { + "bbox": [ + 46, + 570, + 286, + 689 + ], + "type": "inline_equation", + "content": "I_{skip}" + }, + { + "bbox": [ + 46, + 570, + 286, + 689 + ], + "type": "text", + "content": " sequentially. The pose of each newly added frame is initialized by the previous frame. During this process, the feature grids, decoders and camera poses are jointly optimized using the same loss function as in the mapping process. Finally, when all the frames are added, we optimize the whole frame set for " + }, + { + "bbox": [ + 46, + 570, + 286, + 689 + ], + "type": "inline_equation", + "content": "N_{e}" + }, + { + "bbox": [ + 46, + 570, + 286, + 689 + ], + "type": "text", + "content": " iterations." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 689, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 286, + 713 + ], + "type": "text", + "content": "Coarse-to-Fine Mapping. To optimize the scene representation mentioned in Sec. 3.2, we uniformly sample total" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 72, + 545, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 168 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 168 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 305, + 72, + 545, + 168 + ], + "type": "text", + "content": " pixels and " + }, + { + "bbox": [ + 305, + 72, + 545, + 168 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 305, + 72, + 545, + 168 + ], + "type": "text", + "content": " zones and perform optimization to minimize the photometric loss, geometric loss and SDF regularization. The zones and pixels are sampled from the current optimization window, which consists of two types of frames: neighbor frames (the nearest " + }, + { + "bbox": [ + 305, + 72, + 545, + 168 + ], + "type": "inline_equation", + "content": "N_{n}" + }, + { + "bbox": [ + 305, + 72, + 545, + 168 + ], + "type": "text", + "content": " frames with an interval of 4) and global frames (chosen from all the past co-visible mapping frames). The photometric loss is the average color difference of all the sampled pixels:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 358, + 177, + 545, + 209 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 358, + 177, + 545, + 209 + ], + "spans": [ + { + "bbox": [ + 358, + 177, + 545, + 209 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {c} = \\frac {1}{M} \\sum_ {m = 1} ^ {M} | I [ u _ {m}, v _ {m} ] - \\hat {\\mathbf {c}} _ {m} |, \\tag {6}", + "image_path": "a24b9281700fa6a3235a2143bda0c7fcf217e32ec850fe88080e1fd5c06dfdfd.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 219, + 545, + 290 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 219, + 545, + 290 + ], + "spans": [ + { + "bbox": [ + 305, + 219, + 545, + 290 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 219, + 545, + 290 + ], + "type": "inline_equation", + "content": "u_{m}, v_{m}" + }, + { + "bbox": [ + 305, + 219, + 545, + 290 + ], + "type": "text", + "content": " represents for the image coordinate of pixel " + }, + { + "bbox": [ + 305, + 219, + 545, + 290 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 305, + 219, + 545, + 290 + ], + "type": "text", + "content": ". The geometric loss is calculated on both pixel-level and zone-level. For zone-level loss, only zones with valid L5 signals " + }, + { + "bbox": [ + 305, + 219, + 545, + 290 + ], + "type": "inline_equation", + "content": "Z_{d}" + }, + { + "bbox": [ + 305, + 219, + 545, + 290 + ], + "type": "text", + "content": " are considered. We also add SDF supervision on pixel-level as in [36, 26] to add robustness to the optimization. The whole geometric loss is defined as:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 356, + 300, + 471, + 314 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 300, + 471, + 314 + ], + "spans": [ + { + "bbox": [ + 356, + 300, + 471, + 314 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {g} = \\mathcal {L} _ {d} + \\mathcal {L} _ {z} + \\lambda_ {s d f} \\mathcal {L} _ {s d f},", + "image_path": "ba76e0e0ecc3d833f1ca400e499fb03fb31a1f0dbd84dfc876cb68c0000988c6.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 356, + 316, + 545, + 348 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 316, + 545, + 348 + ], + "spans": [ + { + "bbox": [ + 356, + 316, + 545, + 348 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {d} = \\frac {1}{M} \\sum_ {m = 1} ^ {M} | \\widetilde {D} [ u _ {m}, v _ {m} ] - \\hat {d} _ {m} |, \\tag {7}", + "image_path": "8e5195523963538664b435f995120578c42c203a5108dbb1735e2a38625a0f65.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 356, + 350, + 469, + 380 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 350, + 469, + 380 + ], + "spans": [ + { + "bbox": [ + 356, + 350, + 469, + 380 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {z} = \\frac {1}{| Z _ {d} |} \\sum_ {z \\in Z _ {d}} | \\bar {D} _ {z} - \\hat {d} _ {z} |,", + "image_path": "954e41b15bd426197cc6cd1260134fa890eec4a4b691419361afe6b6b7f1f23a.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 389, + 545, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 389, + 545, + 486 + ], + "spans": [ + { + "bbox": [ + 305, + 389, + 545, + 486 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 389, + 545, + 486 + ], + "type": "inline_equation", + "content": "\\overline{D} \\in \\mathbb{R}^{8 \\times 8}" + }, + { + "bbox": [ + 305, + 389, + 545, + 486 + ], + "type": "text", + "content": " represents the mean depth value measured by L5 and " + }, + { + "bbox": [ + 305, + 389, + 545, + 486 + ], + "type": "inline_equation", + "content": "\\widetilde{D}" + }, + { + "bbox": [ + 305, + 389, + 545, + 486 + ], + "type": "text", + "content": " represents the pixel-wise depth prediction. Since we do not have high-quality depth as input and there are many texture-less areas in typical indoor scenes, directly optimizing the feature volume and camera poses is an ill-posed problem. Therefore, we employ two regularizations on the SDF values during pixel-level rendering as [36], namely the eikonal term " + }, + { + "bbox": [ + 305, + 389, + 545, + 486 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{eik}" + }, + { + "bbox": [ + 305, + 389, + 545, + 486 + ], + "type": "text", + "content": " and the smoothness term " + }, + { + "bbox": [ + 305, + 389, + 545, + 486 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_s" + }, + { + "bbox": [ + 305, + 389, + 545, + 486 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 376, + 500, + 545, + 512 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 376, + 500, + 545, + 512 + ], + "spans": [ + { + "bbox": [ + 376, + 500, + 545, + 512 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {r} = \\lambda_ {e i k} \\mathcal {L} _ {e i k} + \\lambda_ {s} \\mathcal {L} _ {s}, \\tag {8}", + "image_path": "c8770553441934b318773e0bd4b6cf54084f9ba7f9fd7867ed19b108647a0727.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 518, + 545, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 518, + 545, + 578 + ], + "spans": [ + { + "bbox": [ + 305, + 518, + 545, + 578 + ], + "type": "text", + "content": "where the eikonal regularization is employed to ensure the network produces valid SDF values [37, 36], the smoothness regularization is used to encourage neighbor points to have similar normal directions, and " + }, + { + "bbox": [ + 305, + 518, + 545, + 578 + ], + "type": "inline_equation", + "content": "\\lambda_{eik}" + }, + { + "bbox": [ + 305, + 518, + 545, + 578 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 518, + 545, + 578 + ], + "type": "inline_equation", + "content": "\\lambda_s" + }, + { + "bbox": [ + 305, + 518, + 545, + 578 + ], + "type": "text", + "content": " are weights to balance the two regularization terms." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 579, + 545, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 579, + 545, + 685 + ], + "spans": [ + { + "bbox": [ + 304, + 579, + 545, + 685 + ], + "type": "text", + "content": "During the mapping process, we perform a coarse-to-fine optimization process, bringing better convergence since pixel-wise optimization can rely on the already initialized coarse grids. We first optimize the scene at the coarse level using zone-level ToF signals. Then, pixel-wise RGB/depth supervisions are added to jointly optimize the decoders, feature grids and camera poses by minimizing the mentioned losses for " + }, + { + "bbox": [ + 304, + 579, + 545, + 685 + ], + "type": "inline_equation", + "content": "N_{m}" + }, + { + "bbox": [ + 304, + 579, + 545, + 685 + ], + "type": "text", + "content": " iterations with a local BA to cover geometry details." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 350, + 696, + 545, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 696, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 350, + 696, + 545, + 715 + ], + "type": "interline_equation", + "content": "\\min _ {\\theta , \\omega , \\beta , \\gamma , \\left\\{\\mathbf {R} _ {i}, \\mathbf {t} _ {i} \\right\\}} \\lambda_ {c} \\mathcal {L} _ {c} + \\lambda_ {g} \\mathcal {L} _ {g} + \\lambda_ {r} \\mathcal {L} _ {r}. \\tag {9}", + "image_path": "a46034be56e850613069dc2e74437232a4e5189bb410d3f5a3d56ecc65a78f1b.jpg" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "spans": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "type": "text", + "content": "5" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 62, + 70, + 532, + 365 + ], + "blocks": [ + { + "bbox": [ + 62, + 70, + 532, + 365 + ], + "lines": [ + { + "bbox": [ + 62, + 70, + 532, + 365 + ], + "spans": [ + { + "bbox": [ + 62, + 70, + 532, + 365 + ], + "type": "image", + "image_path": "2a39c9be56d585f42ddb2a9eb1aea1d00cafc14fd1c4f86f268df6f791fe5d53.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 375, + 546, + 398 + ], + "lines": [ + { + "bbox": [ + 46, + 375, + 546, + 398 + ], + "spans": [ + { + "bbox": [ + 46, + 375, + 546, + 398 + ], + "type": "text", + "content": "Figure 5. Qualitative Reconstruction Results. Compared to other methods, our approach produces high-quality reconstructions with smooth surfaces and fewer artifacts." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 415, + 287, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 415, + 287, + 475 + ], + "spans": [ + { + "bbox": [ + 46, + 415, + 287, + 475 + ], + "type": "text", + "content": "We also conduct a global BA every " + }, + { + "bbox": [ + 46, + 415, + 287, + 475 + ], + "type": "inline_equation", + "content": "N_g" + }, + { + "bbox": [ + 46, + 415, + 287, + 475 + ], + "type": "text", + "content": " frame by adding all the past mapping frames to the optimization window and jointly optimize them to globally optimize the camera poses and scene geometry. We provide the details of losses in the supplementary material." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 477, + 288, + 633 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 477, + 288, + 633 + ], + "spans": [ + { + "bbox": [ + 46, + 477, + 288, + 633 + ], + "type": "text", + "content": "Tracking. During tracking, the feature grid and the decoders remain fixed, while only the 6-DoF pose of the current frame is optimized. Similar to previous methods [46, 31], " + }, + { + "bbox": [ + 46, + 477, + 288, + 633 + ], + "type": "inline_equation", + "content": "M_t" + }, + { + "bbox": [ + 46, + 477, + 288, + 633 + ], + "type": "text", + "content": " pixels are sampled in the current frame to calculate both the pixel-level photometric loss and geometric loss as previously described. The camera pose is then updated iteratively via back-propagation. Tracking with only pixel-level supervision is susceptible to a suboptimal solution, so we leverage our multi-modal scene representation and apply zone-level supervision in the early stage. Specifically, we additionally sample " + }, + { + "bbox": [ + 46, + 477, + 288, + 633 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 46, + 477, + 288, + 633 + ], + "type": "text", + "content": " zones in the current frame and use the L5 signal to minimize zone depth loss as well, which leads to a more robust tracking result." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 648, + 128, + 661 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 648, + 128, + 661 + ], + "spans": [ + { + "bbox": [ + 47, + 648, + 128, + 661 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 669, + 164, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 669, + 164, + 682 + ], + "spans": [ + { + "bbox": [ + 47, + 669, + 164, + 682 + ], + "type": "text", + "content": "4.1. Experimental Setup" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 689, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 715 + ], + "type": "text", + "content": "Datasets. Since no public SLAM benchmarks take the L5 signals as input, we build a data capture device as in [14]" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 415, + 545, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 545, + 523 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 545, + 523 + ], + "type": "text", + "content": "and use it to create an indoor SLAM dataset, which contains 7 sequences captured in 5 typical indoor scenes. We record color images " + }, + { + "bbox": [ + 304, + 415, + 545, + 523 + ], + "type": "inline_equation", + "content": "(640\\times 480)" + }, + { + "bbox": [ + 304, + 415, + 545, + 523 + ], + "type": "text", + "content": ", L5 signals and depth maps for each sequence. Note that we only use the color images and L5 signals as the input to our SLAM system. The depth maps are used to obtain the ground truth 6-DoF camera poses and 3D surface mesh. We follow the automated capture pipeline proposed in ScanNet [7] to compute the ground truth data." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "content": "Baselines. We compare our method with two categories of baselines: (a) learning-based SLAM methods including iMAP [31] (re-implemented by [46]) and NICE-SLAM [46]; (b) traditional SLAM methods including ORBSLAM3 [4], KinectFusion [10], ElasticFusion [38] and BundleFusion [8]. For the methods that only support RGB-D input, including iMAP, NICE-SLAM, KinectFusion, ElasticFusion and BundleFusion, we use the RGB image and the predicted depth map by [14] as the system input. For ORB-SLAM3, we evaluate it in both the RGB version (given only RGB image as input) and the RGB-D version (using the predicted depth, marked as " + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\widetilde{D}" + }, + { + "bbox": [ + 304, + 534, + 546, + 713 + ], + "type": "text", + "content": "). Note that none of these methods can work well with only raw L5 zone-level depths or take it as additional inputs. We evaluate both the scene reconstruction and the camera tracking results. Since" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 302, + 750, + 308, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 302, + 750, + 308, + 757 + ], + "spans": [ + { + "bbox": [ + 302, + 750, + 308, + 757 + ], + "type": "text", + "content": "6" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 80, + 70, + 515, + 287 + ], + "blocks": [ + { + "bbox": [ + 80, + 70, + 515, + 287 + ], + "lines": [ + { + "bbox": [ + 80, + 70, + 515, + 287 + ], + "spans": [ + { + "bbox": [ + 80, + 70, + 515, + 287 + ], + "type": "table", + "html": "
Scene NameKitchenSofaOfficeReceptionLiving roomOffice2Sofa2Avg.
KinectFusion[10]Acc.↓-0.1900.2110.261-0.2670.1350.213
Comp.↓-0.0480.0460.064-0.0780.0640.060
F-score-0.2780.2880.285-0.2740.3810.301
ElasticFusion[38]Acc.↓0.0920.1350.0840.2970.1510.0960.1220.140
Comp.↓0.0650.0480.0820.3050.2160.1470.0470.130
F-score0.5530.4200.5290.2740.3820.4160.4810.436
BundleFusion[8]Acc.↓0.1700.1000.1030.122-0.1210.1230.123
Comp.↓0.0880.0300.0380.057-0.2140.0340.077
F-score0.3730.5710.4740.470-0.4420.5270.476
iMAP[31]Acc.↓-0.1350.2290.3650.2250.2330.1390.221
Comp.↓-0.0540.1030.2450.2910.1390.0690.150
F-score-0.4450.3150.2380.1700.2550.4160.307
NICE-SLAM[46]Acc.↓0.3030.1190.1160.2160.1030.1560.4640.211
Comp.↓0.4560.0420.0700.1990.0890.1630.0450.152
F-score0.2210.5540.4110.4020.4000.2730.4010.380
OursAcc.↓0.0810.0680.0670.0790.0780.1130.1210.087
Comp.↓0.0710.0410.0450.0620.1220.0850.0330.066
F-score0.5590.6610.6460.6430.4960.5570.6560.604
", + "image_path": "d79e79c4bdf57a36153d98e520cfed7de766ab7ecaaf868cabdb38662ddd2517.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 100, + 319, + 493, + 426 + ], + "blocks": [ + { + "bbox": [ + 46, + 288, + 547, + 309 + ], + "lines": [ + { + "bbox": [ + 46, + 288, + 547, + 309 + ], + "spans": [ + { + "bbox": [ + 46, + 288, + 547, + 309 + ], + "type": "text", + "content": "Table 1. Quantitative Comparison on Reconstruction. We perform the mapping evaluation on 7 indoor sequences and report results of three metrics including accuracy (Acc.), completion (Comp.) and F-score. The failure cases are marked as “-”." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 100, + 319, + 493, + 426 + ], + "lines": [ + { + "bbox": [ + 100, + 319, + 493, + 426 + ], + "spans": [ + { + "bbox": [ + 100, + 319, + 493, + 426 + ], + "type": "table", + "html": "
Scene NameKitchenSofaOfficeReceptionLiving roomOffice2Sofa2
ORB-SLAM3 [4]0.054-0.0170.025-0.022-
ORB-SLAM3(with D) [4]0.0820.0350.0190.049-0.058-
KinectFusion [10]-0.1460.2090.157-0.3210.125
ElasticFusion [38]0.2530.1100.0700.1930.5300.1210.146
BundleFusion [8]0.1760.1020.1350.101-0.1630.120
iMAP [31]-1.6580.3380.6480.6790.3440.214
NICE-SLAM [46]0.7450.1440.1550.2510.2890.2280.421
Ours0.1130.0810.0560.1140.2000.1010.085
", + "image_path": "f9ea8432ce6007589d04c4945b2c3d64d32625bb6a56823e6db2ace19bccbe90.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 426, + 547, + 471 + ], + "lines": [ + { + "bbox": [ + 46, + 426, + 547, + 471 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 547, + 471 + ], + "type": "text", + "content": "Table 2. Camera Tracking Results. ATE RMSE [m] (↓) is used as the evaluation metric. The failure cases are marked as “-”. For the variations of ORB-SLAM3, we only mark the best one in each sequence. Our approach outperforms all the other methods except for ORB-SLAM3 [4]. However, ORB-SLAM3 fails on 3 of the 7 sequences due to the textureless indoor environment while our approach tracks successfully on all of the sequences." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 489, + 288, + 514 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 489, + 288, + 514 + ], + "spans": [ + { + "bbox": [ + 46, + 489, + 288, + 514 + ], + "type": "text", + "content": "ORB-SLAM3 cannot output dense models, we exclude it from the mapping evaluation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "text", + "content": "Implementation Details. Our SLAM system is executed on a desktop PC equipped with an Intel i7-9700K CPU and an NVIDIA RTX 3090 GPU. In all our experiments, we set the grid sizes to [3, 6, 24, 96] cm and the number of sampling pixels " + }, + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "text", + "content": " to 5000. Our method is implemented using PyTorch [27] with ADAM [12] optimizer. The decoders, multi-modal feature grids, and camera poses are trained with learning rates of 0.001, 0.01, and 0.0005, respectively. The loss weights are set to 10 for " + }, + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\lambda_{c}" + }, + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\lambda_{sdf}" + }, + { + "bbox": [ + 46, + 521, + 289, + 715 + ], + "type": "text", + "content": " and 1 for the others. Inspired by instant-ngp [22], we use the tiny-cuda-nn [21] library to implement the proposed multimodal grid encoding, which significantly accelerates the optimization process. We follow DELTAR [14] to pre-train the multi-modal depth prediction network on NYU-V2 with simulated L5 signals. For more details, please refer to the supplementary material." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 489, + 503, + 502 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 489, + 503, + 502 + ], + "spans": [ + { + "bbox": [ + 305, + 489, + 503, + 502 + ], + "type": "text", + "content": "4.2. Evaluation of Mapping and Tracking" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 509, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 509, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 509, + 545, + 665 + ], + "type": "text", + "content": "Mapping. We use three metrics to evaluate the reconstruction result including accuracy (Acc.), completion (Comp.) and F-score following the previous work [32]. For detailed descriptions of these metrics, please refer to the supplementary material. As shown in Table 1, our method outperforms all the baseline methods by a large margin (ours 0.604 vs. the second-best 0.476 in terms of F-score). We also show qualitative results in Fig. 5. Our method is able to produce high-quality 3D models with smooth surfaces and high accuracy. It is easy to notice that our reconstruction result has much fewer artifacts and noisy points. Since NICE-SLAM [46] relies on high-quality depth input, its performance is poor given the noisy and unreliable depth input." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": "Tracking. We use ATE RMSE [30] to evaluate the camera tracking. As shown in Table 2, our method outperforms all other methods except for ORB-SLAM3 [4]. However, ORB-SLAM3 is much less robust and tracks lost on 3 of" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 302, + 749, + 309, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 302, + 749, + 309, + 757 + ], + "spans": [ + { + "bbox": [ + 302, + 749, + 309, + 757 + ], + "type": "text", + "content": "7" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 118, + 70, + 476, + 120 + ], + "blocks": [ + { + "bbox": [ + 118, + 70, + 476, + 120 + ], + "lines": [ + { + "bbox": [ + 118, + 70, + 476, + 120 + ], + "spans": [ + { + "bbox": [ + 118, + 70, + 476, + 120 + ], + "type": "table", + "html": "
EMKitchenSofaOfficeReceptionLiving roomOffice2Sofa2Avg.
0.2030.0880.0630.1430.2160.1200.0940.132
✓0.1350.0850.0600.1440.2110.1080.0890.119
✓✓0.1130.0810.0560.1140.2000.1010.0850.107
", + "image_path": "1ec41855dceffa5c4dd534f8da5ebd0bb18da321a31eec3759858bc6fe6b2540.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 160, + 286, + 232 + ], + "blocks": [ + { + "bbox": [ + 47, + 121, + 547, + 143 + ], + "lines": [ + { + "bbox": [ + 47, + 121, + 547, + 143 + ], + "spans": [ + { + "bbox": [ + 47, + 121, + 547, + 143 + ], + "type": "text", + "content": "Table 3. Ablation Study. We explore the efficiency of multi-modal scene representation (marked as “M”) and L5 signal temporal filtering (marked as “E”). We use ATE RMSE [m] (↓) as the evaluation metric." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 160, + 286, + 232 + ], + "lines": [ + { + "bbox": [ + 48, + 160, + 286, + 232 + ], + "spans": [ + { + "bbox": [ + 48, + 160, + 286, + 232 + ], + "type": "table", + "html": "
TrackingMapping
Learning-based MethodsiMAP [31]101 ms448 ms
NICE-SLAM [46]470 ms1300 ms
Ours116 ms380 ms
Classical MethodsORB-SLAM3 [4]31 ms159 ms
ElasticFusion [38]31 ms-
", + "image_path": "188260e69dbca5e59bd57bdf47750987a58648c1dcbcba4f3774f74478eaa173.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 233, + 286, + 288 + ], + "lines": [ + { + "bbox": [ + 47, + 233, + 286, + 288 + ], + "spans": [ + { + "bbox": [ + 47, + 233, + 286, + 288 + ], + "type": "text", + "content": "Table 4. Runtime Comparison. Different from NICE-SLAM [46] that measures one iteration of optimization, we report the averaging total runtime for tracking and mapping respectively for better comparison with classic methods. ElasticFusion does not have an explicit mapping process thus it is labeled as “-”." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 50, + 298, + 286, + 395 + ], + "blocks": [ + { + "bbox": [ + 50, + 298, + 286, + 395 + ], + "lines": [ + { + "bbox": [ + 50, + 298, + 286, + 395 + ], + "spans": [ + { + "bbox": [ + 50, + 298, + 286, + 395 + ], + "type": "image", + "image_path": "9d91c5f5f5b0daf6f2cbb3fb71fe82d5db633b251a37770ed00d963e7ee06f50.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 407, + 287, + 440 + ], + "lines": [ + { + "bbox": [ + 47, + 407, + 287, + 440 + ], + "spans": [ + { + "bbox": [ + 47, + 407, + 287, + 440 + ], + "type": "text", + "content": "Figure 6. Results without Pixel-Wise Depth Supervision. It cannot guarantee plausible reconstruction results without the pixel-wise depth maps as additional supervision." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 460, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 287, + 544 + ], + "type": "text", + "content": "the 7 sequences, while our method successfully tracks all the sequences. This is because that ORB-SLAM3, as a keypoint-based method, struggles in texture-less regions, which are commonly seen in indoor environments. Given the predicted depth, ORB-SLAM3 can reduce the lost ratio from " + }, + { + "bbox": [ + 46, + 460, + 287, + 544 + ], + "type": "inline_equation", + "content": "42.8\\%" + }, + { + "bbox": [ + 46, + 460, + 287, + 544 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 460, + 287, + 544 + ], + "type": "inline_equation", + "content": "28.5\\%" + }, + { + "bbox": [ + 46, + 460, + 287, + 544 + ], + "type": "text", + "content": " but leads to worse camera tracking results since the predicted depth is not accurate enough." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 544, + 287, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 544, + 287, + 604 + ], + "spans": [ + { + "bbox": [ + 46, + 544, + 287, + 604 + ], + "type": "text", + "content": "Runtime Analysis. We compare the runtime of tracking and mapping in Table 4 for both classical methods and learning-based methods. The runtime of our method is similar to iMAP, but it is faster than NICE-SLAM due to our implementation optimization inspired by instant-ngp [22]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 611, + 141, + 624 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 611, + 141, + 624 + ], + "spans": [ + { + "bbox": [ + 47, + 611, + 141, + 624 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "content": "In this section, we first study the effectiveness of using pixel-wise depth prediction as additional supervision, then investigate the importance of the proposed multi-modal feature grid representation and the temporal filtering technique. Impact of the Pixel-Wise Depth Supervision. We try using only the L5 raw signals and RGB images for supervision. Removing the pixel-wise depth supervision makes" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 308, + 161, + 370, + 255 + ], + "blocks": [ + { + "bbox": [ + 308, + 161, + 370, + 255 + ], + "lines": [ + { + "bbox": [ + 308, + 161, + 370, + 255 + ], + "spans": [ + { + "bbox": [ + 308, + 161, + 370, + 255 + ], + "type": "image", + "image_path": "0b0967ef6aa79f3e79d2c967dce6bd7811854a552316828a14fc0a4d0979fe14.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 323, + 258, + 356, + 267 + ], + "lines": [ + { + "bbox": [ + 323, + 258, + 356, + 267 + ], + "spans": [ + { + "bbox": [ + 323, + 258, + 356, + 267 + ], + "type": "text", + "content": "RGB/GT" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 372, + 161, + 421, + 255 + ], + "blocks": [ + { + "bbox": [ + 372, + 161, + 421, + 255 + ], + "lines": [ + { + "bbox": [ + 372, + 161, + 421, + 255 + ], + "spans": [ + { + "bbox": [ + 372, + 161, + 421, + 255 + ], + "type": "image", + "image_path": "815fc6ec20f282c6c31787913c7156c60ceb1589a9411f55cb5a0c8e92154f5d.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 379, + 258, + 413, + 267 + ], + "lines": [ + { + "bbox": [ + 379, + 258, + 413, + 267 + ], + "spans": [ + { + "bbox": [ + 379, + 258, + 413, + 267 + ], + "type": "text", + "content": "L5 Signal" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 424, + 161, + 483, + 255 + ], + "blocks": [ + { + "bbox": [ + 424, + 161, + 483, + 255 + ], + "lines": [ + { + "bbox": [ + 424, + 161, + 483, + 255 + ], + "spans": [ + { + "bbox": [ + 424, + 161, + 483, + 255 + ], + "type": "image", + "image_path": "4356fefe6895ecad8bd3df299fb0c9538dc95c63ac3ba18b1ed18381eed5d558.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 426, + 258, + 481, + 267 + ], + "lines": [ + { + "bbox": [ + 426, + 258, + 481, + 267 + ], + "spans": [ + { + "bbox": [ + 426, + 258, + 481, + 267 + ], + "type": "text", + "content": "Predicted Depth" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 485, + 161, + 545, + 255 + ], + "blocks": [ + { + "bbox": [ + 485, + 161, + 545, + 255 + ], + "lines": [ + { + "bbox": [ + 485, + 161, + 545, + 255 + ], + "spans": [ + { + "bbox": [ + 485, + 161, + 545, + 255 + ], + "type": "image", + "image_path": "25726e2eeab16b6483ecea7627b9c7125a016ed979959caf5a51cf56a430536d.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 496, + 258, + 533, + 268 + ], + "lines": [ + { + "bbox": [ + 496, + 258, + 533, + 268 + ], + "spans": [ + { + "bbox": [ + 496, + 258, + 533, + 268 + ], + "type": "text", + "content": "Error Map" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 281, + 545, + 358 + ], + "lines": [ + { + "bbox": [ + 305, + 281, + 545, + 358 + ], + "spans": [ + { + "bbox": [ + 305, + 281, + 545, + 358 + ], + "type": "text", + "content": "Figure 7. Qualitative Study of the Effect of Temporal Filtering on Depth Prediction. We compare the depth prediction result obtained through two methods: solely employing raw L5 signals (top row) and incorporating our temporal filtering technique (bottom row). Our temporal filtering technique enhances the raw L5 signals and fills up the missing regions, leading to a better depth prediction result." + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 384, + 545, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 384, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 305, + 384, + 545, + 456 + ], + "type": "text", + "content": "the optimization problem harder, which is more obvious when the problem size grows. In Fig. 6 we show the rendered depth when optimizing the first frame and the first 150 frames. The latter contains serious errors. As a result, it leads to a distorted reconstruction, i.e., the \"Baseline\" result in the upper right." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 457, + 545, + 541 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 457, + 545, + 541 + ], + "spans": [ + { + "bbox": [ + 305, + 457, + 545, + 541 + ], + "type": "text", + "content": "Impact of the Multi-Modal Feature Grid. We verify the effectiveness of our multi-modal feature grid representation (denoted as “M”) in terms of camera tracking and show the result in Table 3. With the multi-modal feature grid representation, we are able to use raw L5 signal as supervision. As a result, we can optimize the camera poses on both pixel-level and zone-level, leading to better trajectory accuracy." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 544, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 544, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 544, + 545, + 616 + ], + "type": "text", + "content": "Impact of the Temporal Filtering. In Fig. 7 we show the qualitative comparison with and without the proposed temporal filtering. It can be seen that the large portion of missing L5 signals leads to severe errors on the corresponding regions of the predicted depth map. The error reduces significantly with the proposed temporal filtering technique." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": "We also study the quantitative impact of temporal filtering (marked as \"E\") on both the depth prediction (Table 5) and the camera tracking (Table 3). We divide the testing sequences into normal and hard cases according to the quality of L5 signals. As shown in Table 5, the temporal filtering technique improves the predicted depth in general and significantly in hard cases. Such an improvement benefits the final SLAM system and leads to more accurate camera" + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "spans": [ + { + "bbox": [ + 302, + 749, + 308, + 757 + ], + "type": "text", + "content": "8" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 70, + 273, + 130 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 273, + 130 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 273, + 130 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 273, + 130 + ], + "type": "table", + "html": "
δ1↑δ2↑δ3↑REL↓RMSE↓
Hw/o E0.7730.9100.9690.1590.513
w E0.9250.9720.9830.0930.366
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We report the quantitative result of depth maps predicted from L5 raw signals and our refined signals." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 56, + 189, + 150, + 258 + ], + "blocks": [ + { + "bbox": [ + 56, + 189, + 150, + 258 + ], + "lines": [ + { + "bbox": [ + 56, + 189, + 150, + 258 + ], + "spans": [ + { + "bbox": [ + 56, + 189, + 150, + 258 + ], + "type": "image", + "image_path": "46aa0e638c670513eff902d702630d2c70fc879ac55cc13049d58593959e1627.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 56, + 258, + 149, + 327 + ], + "blocks": [ + { + "bbox": [ + 56, + 258, + 149, + 327 + ], + "lines": [ + { + "bbox": [ + 56, + 258, + 149, + 327 + ], + "spans": [ + { + "bbox": [ + 56, + 258, + 149, + 327 + ], + "type": "image", + "image_path": "0222d4b2428a33cfa30cfc614c67a4eb032d595f0101284736054e590c856ea1.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 75, + 331, + 130, + 340 + ], + "lines": [ + { + "bbox": [ + 75, + 331, + 130, + 340 + ], + "spans": [ + { + "bbox": [ + 75, + 331, + 130, + 340 + ], + "type": "text", + "content": "Outdoor Scene" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 152, + 188, + 278, + 256 + ], + "blocks": [ + { + "bbox": [ + 152, + 188, + 278, + 256 + ], + "lines": [ + { + "bbox": [ + 152, + 188, + 278, + 256 + ], + "spans": [ + { + "bbox": [ + 152, + 188, + 278, + 256 + ], + "type": "image", + "image_path": "b102b3c1fb96c20abb8e283d0c49cdbed6c45f3f6f25649811de8cba6c3d4901.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 155, + 259, + 276, + 328 + ], + "blocks": [ + { + "bbox": [ + 155, + 259, + 276, + 328 + ], + "lines": [ + { + "bbox": [ + 155, + 259, + 276, + 328 + ], + "spans": [ + { + "bbox": [ + 155, + 259, + 276, + 328 + ], + "type": "image", + "image_path": "c25cef289f243897dbccf2c137f0551911bdb5a1655fc717059a6de4fbd064f9.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 181, + 331, + 252, + 341 + ], + "lines": [ + { + "bbox": [ + 181, + 331, + 252, + 341 + ], + "spans": [ + { + "bbox": [ + 181, + 331, + 252, + 341 + ], + "type": "text", + "content": "Our Reconstruction" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 354, + 287, + 399 + ], + "lines": [ + { + "bbox": [ + 46, + 354, + 287, + 399 + ], + "spans": [ + { + "bbox": [ + 46, + 354, + 287, + 399 + ], + "type": "text", + "content": "Figure 8. Qualitative Results of Outdoor Reconstruction. The proposed method can recover a complete scene model in outdoor scenes but missing more details than that in indoor due to the poor L5 signals." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 418, + 287, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 418, + 287, + 455 + ], + "spans": [ + { + "bbox": [ + 46, + 418, + 287, + 455 + ], + "type": "text", + "content": "tracking, as shown in Table 3 (marked as “E”). Please refer to the supplementary material for the definition of the normal/hard cases and the depth evaluation metrics." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 461, + 219, + 472 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 461, + 219, + 472 + ], + "spans": [ + { + "bbox": [ + 47, + 461, + 219, + 472 + ], + "type": "text", + "content": "4.4. Performance in Outdoor Scenes" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 479, + 287, + 575 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 479, + 287, + 575 + ], + "spans": [ + { + "bbox": [ + 46, + 479, + 287, + 575 + ], + "type": "text", + "content": "Currently, we focus on indoor scenes as other NeRF-based SLAM systems [31, 46] due to the optical interference limitation of depth sensors. Actually, the sunlight has a stronger interference on the L5 sensor for its low-power emitter. In Fig. 8, we show two examples of outdoor scene reconstruction using our proposed methods. The recovered mesh is complete but missing more details than that in indoor scenes due to the poor L5 signals." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 586, + 119, + 597 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 119, + 597 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 119, + 597 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "type": "text", + "content": "We introduce a novel dense visual SLAM framework working with RGB cameras and light-weight ToF sensors using neural implicit scene representation. To accommodate this new input modality, we propose a novel multimodal feature grid that enables both zone-level rendering for the ToF sensors and pixel-level rendering for other high-resolution signals. To guarantee robust tracking and mapping, we exploit a per-pixel depth prediction as additional supervision, which is further improved by a novel tempo" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": "ral filtering strategy. Our experiments demonstrate that the proposed method can provide accurate camera tracking and high-quality reconstruction result on indoor scenes. Similar to other NeRF-based RGB-D SLAM systems, as future work we plan to further improve the system to overcome the limitation of ToF sensors in outdoor scenarios and make it efficient enough to run on mobile robots." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 157, + 545, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 157, + 545, + 180 + ], + "spans": [ + { + "bbox": [ + 305, + 157, + 545, + 180 + ], + "type": "text", + "content": "Acknowledgements: This work was partially supported by NSF of China (No. 62102356)." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 194, + 365, + 206 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 194, + 365, + 206 + ], + "spans": [ + { + "bbox": [ + 306, + 194, + 365, + 206 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 310, + 215, + 547, + 713 + ], + "type": "list", + "angle": 0, + "index": 26, + "blocks": [ + { + "bbox": [ + 310, + 215, + 545, + 269 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 215, + 545, + 269 + ], + "spans": [ + { + "bbox": [ + 310, + 215, + 545, + 269 + ], + "type": "text", + "content": "[1] Dejan Azinović, Ricardo Martin-Brualla, Dan B Goldman, Matthias Nießner, and Justus Thies. 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In Proceedings of the IEEE/CVF Conference on" + } + ] + } + ], + "index": 11 + } + ], + "sub_type": "ref_text" + }, + { + "bbox": [ + 328, + 73, + 545, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 328, + 73, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 328, + 73, + 545, + 95 + ], + "type": "text", + "content": "Computer Vision and Pattern Recognition, pages 12786-12796, 2022." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 301, + 750, + 309, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 301, + 750, + 309, + 757 + ], + "spans": [ + { + "bbox": [ + 301, + 750, + 309, + 757 + ], + "type": "text", + "content": "11" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-Object Discovery by Low-Dimensional Object Motion/063ca8bc-3b85-47f8-b8af-3f433d446bab_content_list.json b/2023/Multi-Object Discovery by Low-Dimensional Object Motion/063ca8bc-3b85-47f8-b8af-3f433d446bab_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..123a6f9f6934ddf3cb0392e1ca1d83e891f14fe4 --- /dev/null +++ b/2023/Multi-Object Discovery by Low-Dimensional Object Motion/063ca8bc-3b85-47f8-b8af-3f433d446bab_content_list.json @@ -0,0 +1,1396 @@ +[ + { + "type": "text", + "text": "Multi-Object Discovery by Low-Dimensional Object Motion", + "text_level": 1, + "bbox": [ + 181, + 130, + 789, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Sadra Safadoust Fatma Güney \nKUIS AI Center and Department of Computer Engineering, Koç University \nssafadoust20@ku.edu.tr fguney@ku.edu.tr", + "bbox": [ + 186, + 181, + 781, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recent work in unsupervised multi-object segmentation shows impressive results by predicting motion from a single image despite the inherent ambiguity in predicting motion without the next image. On the other hand, the set of possible motions for an image can be constrained to a low-dimensional space by considering the scene structure and moving objects in it. We propose to model pixel-wise geometry and object motion to remove ambiguity in reconstructing flow from a single image. Specifically, we divide the image into coherently moving regions and use depth to construct flow bases that best explain the observed flow in each region. We achieve state-of-the-art results in unsupervised multi-object segmentation on synthetic and real-world datasets by modeling the scene structure and object motion. Our evaluation of the predicted depth maps shows reliable performance in monocular depth estimation.", + "bbox": [ + 75, + 301, + 473, + 542 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 571, + 209, + 588 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Finding objects on visual data is one of the oldest problems in computer vision, which has been shown to work to great extent in the presence of labeled data. Achieving it without supervision is important given the difficulty of obtaining pixel-precise masks for the variety of objects encountered in everyday life. In the absence of labels, motion provides important cues to group pixels corresponding to objects. The existing solutions use motion either as input to perform grouping or as output to reconstruct as a way of verifying the predicted grouping. The current methodology fails to incorporate the underlying 3D geometry creating the observed motion. In this work, we show that modeling geometry together with object motion significantly improves the segmentation of multiple objects without supervision.", + "bbox": [ + 75, + 598, + 470, + 809 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Unsupervised multi-object discovery is significantly more challenging than the single-object case due to mutual occlusions. Therefore, earlier methods in unsupervised segmentation focused on separating a foreground object from the background whereas multi-object methods have been mostly limited to synthetic datasets or resorted to additional", + "bbox": [ + 75, + 810, + 470, + 901 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "supervision on real-world data such as sparse depth [15].", + "bbox": [ + 498, + 270, + 874, + 285 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "While sparse-depth supervision can be applied to driving scenarios [15], depth information is not typically available on common video datasets. Moreover, video segmentation datasets such as DAVIS [48, 49] contain a wide variety of categories under challenging conditions such as appearance changes due to lighting conditions or motion blur. The motion information can be obtained from video sequences via optical flow. Optical flow not only provides motion cues for grouping [64] but can also be used for training on synthetic data without suffering from the domain gap while transferring to real data [63]. The problems in optical flow prediction on real-world data can be mitigated to some extent by relating flow predictions from multiple frames [63].", + "bbox": [ + 496, + 287, + 890, + 484 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In addition to problems in predicting optical flow, requiring flow as input prohibits the application of the method on static images. Another line of work [11, 33] uses motion for supervision at train time only. Based on the observation that objects create distinctive patterns in flow, initial work [11] fits a simple parametric model to the flow in each object region to capture the object motion. This way, the network can predict object regions that can potentially move coherently from a single image at test time. There is an inherent ambiguity in predicting motion from a single image. Therefore, the follow-up work [33] predicts a distribution of possible motion patterns to reduce this ambiguity. This also allows extending it to the multi-object case by mitigating the over-segmentation problem of the initial work [11].", + "bbox": [ + 496, + 489, + 892, + 700 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this work, we propose to model pixel-wise geometry to remove ambiguity in reconstructing flow from a single image. Optical flow is the difference between the 2D projections of the 3D world in consecutive time steps. By modeling the 3D geometry creating these projections, we directly address the mutual occlusion problem due to interactions of multiple objects. This problem has been crudely addressed by previous work with a depth-ordered layer representation [63]. Instead of assuming a single depth layer per object, we predict pixel-wise depth which provides more expressive power in explaining the observed motion. Furthermore, we do not use flow as input during inference, allowing us to evaluate our method on single-image datasets.", + "bbox": [ + 496, + 704, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 805, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "734", + "bbox": [ + 485, + 944, + 509, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recent work [5] showed that motion resides in a low-dimensional subspace, and its reconstruction can be used to supervise monocular depth prediction. Despite many possible flow fields, the space of possible flow fields is spanned by a small number of basis flow fields related to depth and independently moving objects. While [5] focuses on modeling camera motion for quantitatively evaluating depth in static scenes, it also points to the fact that the object motion can be similarly modeled in a low-dimensional subspace by simply masking the points in the object region. Given the difficulty of predicting pixel-wise masks, simple object embeddings are used to cluster independently moving objects. We instead predict the object regions jointly with depth to find the low-dimensional object motion that best explains the observed flow in each region.", + "bbox": [ + 75, + 90, + 472, + 316 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our approach works extremely well on synthetic Multi-Object Video (MOVi) datasets [23], significantly outperforming previous work, especially in more challenging MOVi-{C,D,E} partitions and performing comparably on visually simpler MOVi-A due to difficulty of estimating depth. We use motion only for supervision at train time, therefore our method can be successfully applied to still images of CLEVR [31] and CLEVRTEX [34] and shows state-of-the-art performance. More impressively, our method can segment multiple objects on real-world videos of DAVIS2017 [49] from a single image at test time, exceeding the performance of the state-of-the-art that uses flow from multiple frames as input [63]. In addition to evaluating segmentation, we show that our method can also reliably predict depth in real-world self-driving scenarios on KITTI [21].", + "bbox": [ + 75, + 316, + 472, + 544 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 558, + 218, + 574 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Basis Learning. Early work showed that optical flow estimation due to camera motion can be constrained using a subspace formulation for flow [28]. Basis learning has been used as a regularization in low-level vision, unifying tasks such as depth, flow, and segmentation [55]. PCA-Flow [61] builds a higher dimensional flow subspace from movies to represent flow as a weighted sum of flow bases. Recent work [67] learns the coefficients to combine eight pre-defined flow bases for homography estimation.", + "bbox": [ + 75, + 590, + 468, + 727 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Motion as Input. Most of the work in motion segmentation focuses on the single-object case. While earlier work uses traditional methods to cluster pixels into similar motion groups [6, 35, 47, 62], later methods train deep neural networks which take flow as input and predict segmentation as output [13, 57, 58]. Another work [66] uses the distinctiveness of motion in the case of foreground objects by proposing an adversarial setting to predict motion from context. Segmenting objects in camouflaged settings can be achieved by modeling background motion to remove its effect and highlight the moving foreground object [3, 4, 38].", + "bbox": [ + 75, + 734, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Recent work uses consistency between two flow fields computed under different frame gaps for self-supervision [64].", + "bbox": [ + 498, + 90, + 890, + 121 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The most relevant to our work is OCLR [63] which extends motion segmentation to multiple objects by relating motion extracted from multiple frames using a transformer in a layered representation. In this work, we show that better results can be achieved on real data even from a single image by modeling pixel-wise geometry.", + "bbox": [ + 496, + 123, + 893, + 214 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Motion for Supervision. While using motion only as input works well where appearance fails, e.g. the camouflage datasets, RGB carries important information that might be missing in flow. DyStaB [65] trains a dynamic model by exploiting motion for temporal consistency and then uses it to bootstrap a static model which takes a single image as input. A single image network is used to predict a segmentation in [40] and then the motion of each segment is predicted with a two-frame motion network. While image warping loss is used in [40] for self-supervision, recent work [11, 33] uses flow reconstruction loss by assuming the availability of flow at train time only. GWM [11] segments foreground objects by fitting an approximate motion model to each segment and then merging them using spectral clustering. The follow-up work [33] extends it to multiple objects by predicting probable motion patterns for each segment with a distribution. We also reconstruct flow for supervision but differently, we account for 3D to remove the ambiguity in reconstructing motion from a single image.", + "bbox": [ + 496, + 222, + 892, + 508 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The most relevant to our work is the previous work that uses flow as a source of supervision for depth [5] or segmentation [11, 34]. In this work, we model both depth and segmentation with supervision from motion.", + "bbox": [ + 496, + 511, + 893, + 571 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-Object Scene Decomposition. Our work is also related to scene decomposition approaches which are mostly evaluated on synthetic datasets. The earlier image-based decomposition approaches such as MONet [7] and IO-DINE [24] use a sequential VAE structure where the decomposition at a step can affect the remaining parts to be explained in the next step. GENESIS [17] follows an object-centric approach by accounting for component interactions, which is extended to more realistic scenarios with an autoregressive prior in the follow-up work [18]. Slot Attention [42] uses an iterative attention mechanism to decompose the image into a set of slot representations. A hierarchical VAE is used in [16] to extract symmetric and disentangled representations.", + "bbox": [ + 496, + 580, + 890, + 792 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "There are also video-based approaches to multi-object scene decomposition. SCALOR [30] focuses on scaling generative approaches to crowded scenes in terms of object density. SIMONE [32] learns a factorized latent space to separate object semantics that is constant in the sequence from the background which changes at each frame according to camera motion. SAVi [36] extends Slot Attention [42]", + "bbox": [ + 496, + 795, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "735", + "bbox": [ + 486, + 945, + 509, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/329808514883619822e691004d9df586b32f5ddb884d44ddf9d84e0a4f955e32.jpg", + "image_caption": [ + "Figure 1: Overview of our Approach. From a single image, we use a segmentation and a depth network to predict a segmentation mask $\\mathbf{m}$ and a disparity map $\\mathbf{d}$ . Based on these predictions, we construct the bases for the space of the possible optical flows for $K$ distinctly moving regions on the image. Each moving region $i$ is represented with a separate basis $\\mathcal{B}_i$ . Given optical flow $\\mathbf{F}$ as input, either ground truth or estimated by an off-the-shelf method, we project it into $\\mathrm{span}(\\bigcup_{i=1}^{K} \\mathcal{B}_i)$ . We use the distance between the input flow $\\mathbf{F}$ and the projected flow $\\hat{\\mathbf{F}}$ to supervise depth and segmentation. During inference, our networks can be used to predict depth and segmentation from a single image." + ], + "image_footnote": [], + "bbox": [ + 81, + 85, + 831, + 316 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "to videos and $\\mathrm{SAVi}++$ [15] extends it to real-world driving scenarios with sparse depth supervision.", + "bbox": [ + 75, + 448, + 468, + 479 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Self-Supervised Monocular Depth Estimation. Zhou et al. [69] train a pose network to estimate the pose between the frames in a sequence and jointly train it with the depth network. Godard et al. [22] improves the results with a better loss function and other design choices. Guizilini et al. [25] learn detail-preserving representations using 3D packing and unpacking blocks. Given instance segmentation masks, a line of work [9, 39] models the motion of objects in the scene in addition to the camera motion to go beyond the static-scene assumption. While the object masks are supervised using ground truth masks in [37], the masks are learned without supervision as an auxiliary output in [53] for better depth estimation. While they require multiple frames during inference, our approach can estimate masks from a single image. Additionally, our method does not use camera intrinsics.", + "bbox": [ + 75, + 484, + 470, + 727 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Depth-Aware Multi-Object Segmentation", + "text_level": 1, + "bbox": [ + 76, + 739, + 446, + 757 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The observed motion in 2D is the result of 3D scene structure and independently moving objects. By predicting the scene structure in terms of depth and locating independently moving objects, we can accurately reconstruct the optical flow corresponding to the observed motion in 2D. Towards this purpose, we use a low-dimensional parameterization of optical flow based on depth (Section 3.1). In this low-dimensional representation, we can accurately reconstruct flow from a rigid motion. We extend this parametriza", + "bbox": [ + 75, + 763, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "tion to a number of rigidly moving objects to find the regions corresponding to objects (Section 3.2). See Fig. 1 for an overview of our approach.", + "bbox": [ + 498, + 448, + 890, + 494 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Low-Dimensional Motion Representation", + "text_level": 1, + "bbox": [ + 498, + 501, + 852, + 517 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The space of all possible optical flow fields is very high-dimensional, i.e. in $\\mathbb{R}^{H\\times W\\times 2}$ . However, conditioned on the scene structure, only a small fraction of all flow fields are possible. Previous work [27, 5] has shown that the set of possible instantaneous flows for a moving camera in a static scene forms a linear space with six basis vectors:", + "bbox": [ + 496, + 523, + 890, + 614 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {B} _ {0} = \\left\\{\\mathbf {b} _ {\\mathbf {T} x}, \\mathbf {b} _ {\\mathbf {T} y}, \\mathbf {b} _ {\\mathbf {T} z}, \\mathbf {b} _ {\\mathbf {R} x}, \\mathbf {b} _ {\\mathbf {R} y}, \\mathbf {b} _ {\\mathbf {R} z} \\right\\} \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 558, + 623, + 890, + 640 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "These basis vectors correspond to translation and rotation along the $x, y$ , and $z$ axes, respectively. For an image $\\mathbf{I} \\in \\mathbb{R}^{H \\times W \\times 3}$ , the values of each basis vector $\\mathbf{b}_i \\in \\mathbb{R}^{H \\times W \\times 2}$ for a given pixel $(u, v)$ can be calculated as follows:", + "bbox": [ + 498, + 646, + 890, + 707 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {b} _ {\\mathbf {T} x} = \\left[ \\begin{array}{c} f _ {x} d \\\\ 0 \\end{array} \\right], \\quad \\mathbf {b} _ {\\mathbf {R} x} = \\left[ \\begin{array}{c} f _ {y} ^ {- 1} \\bar {u} \\bar {v} \\\\ f _ {y} + f _ {y} ^ {- 1} \\bar {v} ^ {2} \\end{array} \\right]\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 713, + 841, + 750 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {b} _ {\\mathbf {T} y} = \\left[ \\begin{array}{c} 0 \\\\ f _ {y} d \\end{array} \\right], \\quad \\mathbf {b} _ {\\mathbf {R} y} = \\left[ \\begin{array}{c} f _ {x} + f _ {x} ^ {- 1} \\bar {u} ^ {2} \\\\ f _ {x} ^ {- 1} \\bar {u} \\bar {v} \\end{array} \\right]\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 756, + 843, + 792 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {b} _ {\\mathbf {T} z} = \\left[ \\begin{array}{l} - \\bar {u} d \\\\ - \\bar {v} d \\end{array} \\right], \\quad \\mathbf {b} _ {\\mathbf {R} z} = \\left[ \\begin{array}{l} f _ {x} f _ {y} ^ {- 1} \\bar {v} \\\\ - f _ {y} f _ {x} ^ {- 1} \\bar {u} \\end{array} \\right] \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 557, + 799, + 890, + 834 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $f_{x}, f_{y}$ are the focal lengths of the camera. For brevity, we define $\\bar{u} = u - c_{x}$ and $\\bar{v} = v - c_{y}$ to be the centered pixel coordinates according to $(c_{x}, c_{y})$ , the principal point of the camera. With a slight abuse of notation, we", + "bbox": [ + 496, + 840, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "736", + "bbox": [ + 485, + 944, + 511, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "do not write the basis vectors as a function of $(u,v)$ and use $d$ to denote the disparity $\\mathbf{d}(u,v)$ at a pixel $(u,v)$ .", + "bbox": [ + 75, + 90, + 468, + 119 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We train a monocular depth network to predict inverse depth, disparity $\\mathbf{d}$ from a single image. Then, the predicted disparity at each pixel is used to form the translation part of the basis vectors as shown in Eq. (2). Note that predicted disparity values do not affect the rotation but form the low-dimensional motion representation via translation. The depth network receives gradients directly from the flow reconstruction loss as explained next in Section 3.2.", + "bbox": [ + 75, + 121, + 467, + 241 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In Eq. (2), camera parameters including the principal point $(c_x, c_y)$ and the focal lengths $f_x$ , $f_y$ are required to calculate the basis vectors. We assume the principal points to be at the center of the image. However, we do not assume to know the values of focal lengths. Instead, we only assume that $f_x = f_y$ . In this case, as demonstrated by [5], we can rewrite $\\mathcal{B}_0$ as a set of 8 vectors that do not depend on the values of $f_x$ and $f_y$ . For more details, please see Supplementary. Even without knowing the actual values of the focal lengths, we can obtain quite accurate depth predictions with supervision from flow (Section 4).", + "bbox": [ + 75, + 242, + 468, + 407 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Segmentation by Object Motion", + "text_level": 1, + "bbox": [ + 76, + 417, + 357, + 431 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We extend the formulation introduced in Section 3.1 to handle the instantaneous flow from multiple object motion. As stated in [5], for a rigidly moving object in the scene, there is an equivalent camera motion. Therefore the space of optical flow from a rigidly moving object is the same as the space of optical flow from camera motion restricted to points in the object. Consider a scene with $K$ regions corresponding to moving parts including the background and multiple objects. If we represent each region $i \\in \\{1, \\dots, K\\}$ with ones on a binary mask $\\mathbf{m}_i \\in \\{0, 1\\}^{H \\times W \\times 1}$ , then a basis for the space of possible flows can be defined as follows:", + "bbox": [ + 75, + 440, + 467, + 619 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {B} = \\left\\{\\mathcal {B} _ {1} \\cup \\mathcal {B} _ {2} \\cup \\dots \\mathcal {B} _ {K} \\right\\} \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 186, + 632, + 467, + 648 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{B}_i$ refers to the basis for the space of possible flows restricted to region $i$ as:", + "bbox": [ + 75, + 659, + 467, + 689 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {B} _ {i} = \\left\\{\\mathbf {m} _ {i} \\mathbf {b} \\mid \\mathbf {b} \\in \\mathcal {B} _ {0} \\right\\}. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 192, + 700, + 467, + 715 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We train a segmentation network to divide the image into coherently moving regions $\\mathbf{m} \\in [0,1]^{H \\times W \\times K}$ , representing soft assignments over $K$ regions. We use the predicted mask $\\mathbf{m}_i \\in [0,1]^{H \\times W \\times 1}$ of the region $i$ to obtain the basis corresponding to that region according to Eq. (4).", + "bbox": [ + 75, + 727, + 467, + 801 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Training Objective. Based on the predicted disparity map $\\mathbf{d}$ and the segmentation map $\\mathbf{m}$ , we form the basis $\\mathcal{B}$ for the space of possible optical flows for the image according to Eq. (3) and Eq. (4). We denote the optical flow where the input image is the source frame as $\\mathbf{F} \\in \\mathbb{R}^{H \\times W \\times 2}$ . It can be either ground truth flow or the output of a two-frame flow", + "bbox": [ + 75, + 809, + 467, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "network such as RAFT [56]. We project $\\mathbf{F}$ into the space spanned by $\\mathcal{B}$ in a differentiable manner to obtain $\\hat{\\mathbf{F}}$ . For the details of the projection, please refer to Supplementary. We define our loss function as the $L_{2}$ distance between the given flow $\\mathbf{F}$ and the reconstructed flow $\\hat{\\mathbf{F}}$ and use it to train depth and segmentation networks jointly:", + "bbox": [ + 496, + 90, + 890, + 181 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\left\\| \\mathbf {F} - \\hat {\\mathbf {F}} \\right\\| _ {2} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 642, + 190, + 890, + 208 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 498, + 219, + 630, + 234 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Datasets", + "text_level": 1, + "bbox": [ + 498, + 243, + 601, + 258 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Synthetic Datasets. For comparison to image-based methods, we evaluate our method on the CLEVR [31] and CLEVRTEX [34] datasets. CLEVR is a dataset of still images depicting multiple objects of random shape, size, color, and position. CLEVRTEX is similar to CLEVR but contains more diverse textures and shapes. Because our method needs optical flow for training, we train our model on the MOVINGCLEVR and MOVINGCLEVRTEX datasets [33], which are video extensions of CLEVR and CLEVRTEX scenes. We train on the video versions but evaluate on the original test sets of CLEVR and CLEVRTEX.", + "bbox": [ + 496, + 273, + 890, + 439 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For comparison to video-based methods, we use the Multi-Object Video (MOVi) datasets [23]. Similar to [33], we use the MOVi-{A, C, D, E} variants. MOVi-A is based on CLEVR [31] and contains scenes with a static camera and multiple objects with simple textures and uniform colors tossed on a gray floor. MOVi-C is more challenging due to realistic everyday objects with rich textures on a more complex background. MOVi-D increases the complexity by increasing the number of objects. MOVi-E is even more challenging as it features camera motion as well.", + "bbox": [ + 496, + 440, + 890, + 590 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In all our experiments on synthetic datasets, we use a resolution of $128 \\times 128$ and the ground truth optical flow.", + "bbox": [ + 498, + 590, + 890, + 621 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Real-World Datasets. We use the common video segmentation dataset DAVIS-2017 [49] containing 90 video sequences where each sequence has one or more moving objects. We follow the evaluation protocol of [63] where the ground truth objects are reannotated by assigning the same label to the jointly moving objects. We resize the images to a resolution of $128 \\times 224$ during training and use the flow from RAFT [56] with $\\{-8, -4, 4, 8\\}$ gaps between frames.", + "bbox": [ + 496, + 628, + 890, + 750 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Additionally, we evaluate our method on the KITTI driving dataset [21, 20]. Following [2], we train on the whole training set and evaluate the segmentation results on the instance segmentation benchmark consisting of 200 frames. We use a resolution of $128 \\times 416$ and the flow from RAFT [56] with a gap of $+1$ . Additionally, we evaluate our depth results on KITTI. Following prior work [69, 22], we evaluate depth on the Eigen split [14] of the KITTI dataset using improved ground truth [59] to be comparable to self-supervised monocular depth estimation approaches.", + "bbox": [ + 496, + 750, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "737", + "bbox": [ + 486, + 945, + 509, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/2c62286bfee8aaa8447521c058acf80d2ffec3cb53fdd8f2805943bb38105671.jpg", + "image_caption": [ + "Figure 2: Visualization of Depth and Segmentation Results on MOVi datasets. Our method performs accurate segmentations, while PPMP suffers from over-segmentation and also mistakenly segments parts of the background as objects." + ], + "image_footnote": [], + "bbox": [ + 145, + 85, + 823, + 468 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Architecture Details", + "text_level": 1, + "bbox": [ + 76, + 523, + 269, + 537 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We use the same architecture used in [50] for depth and Mask2Former [10] for segmentation, using only the segmentation head. We use different backbones for the segmentation network on the synthetic and real datasets. On synthetic datasets, we follow [33, 36, 42] and utilize a 6-layer CNN. On real-world datasets, following [11], we use a ViT-B/8 transformer pre-trained self-supervised using DINO [8] on ImageNet [52]. On all of the datasets, we use 6 object queries in the segmentation network, which translates to $K = 6$ , except for CLEVR, where we use $K = 8$ .", + "bbox": [ + 75, + 547, + 468, + 699 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We use a fixed learning rate of $5 \\times 10^{-5}$ for the depth network and use $1.5 \\times 10^{-4}$ with a linear warm-up for the first 5K iterations for the segmentation network, reduced to $1.5 \\times 10^{-5}$ after 200K iterations. We train both networks with AdamW optimizer [43] for 250K iterations. See Supplementary for further details, we will also share the code.", + "bbox": [ + 75, + 700, + 468, + 792 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Evaluation Details", + "text_level": 1, + "bbox": [ + 76, + 806, + 254, + 821 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Metrics. Following prior work [34, 36, 33], we evaluate segmentation on synthetic datasets using Adjusted Rand Index on foreground pixels (FG-ARI) and mean Intersection over Union (mIoU). ARI measures how well predicted and", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "ground truth segmentation masks match in a permutation-invariant manner. For mIoU, we first apply Hungarian matching and calculate the mean over the maximum between the number of ground-truth and predicted segments.", + "bbox": [ + 496, + 523, + 890, + 583 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "On DAVIS-2017 [49], we use the standard $\\mathcal{I}$ , $\\mathcal{F}$ metrics and perform the Hungarian matching per frame, similar to other datasets. Note that we focus on the multi-object segmentation task without using any labels for segmentation at train or test time. For KITTI, we use the FG-ARI metric, following [33, 2]. For evaluating depth, we use the standard metrics used in monocular depth estimation [14, 19].", + "bbox": [ + 496, + 584, + 892, + 691 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Post-processing. We also report the results on segmentation using the post-processing method introduced in [33]. They extract the connected components in the model output and choose the largest $K$ masks and discard any masks that take up less than $0.1\\%$ of the image. Then they combine the discarded masks with the largest mask. The results with post-processing are marked with $^{\\dagger}$ in the tables.", + "bbox": [ + 496, + 698, + 893, + 805 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.4. Results on Synthetic Datasets", + "text_level": 1, + "bbox": [ + 500, + 816, + 761, + 832 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We evaluate our method on synthetic datasets and compare its performance to both image-based and video-based methods. Our method uses motion during training only. Therefore, it can also be evaluated on the image datasets.", + "bbox": [ + 496, + 839, + 893, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "738", + "bbox": [ + 486, + 945, + 509, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/2f853ac780e21a40df7d12b6087b11b70949505a83377c42e74ed89d692e2a97.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MOVi-AMOVi-CMOVi-DMOVi-E
FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑
GWM [10]70.3042.2749.9830.1739.7818.3842.5018.74
SCALOR [30]59.5744.4140.4322.54----
SAVi [36]88.3062.6943.2631.9243.4510.6017.395.75
PPMP [33]84.0160.0861.1834.7255.7423.5062.6225.78
\\( PPMP^† \\)85.4176.1961.2437.2655.1825.2163.1128.59
\\( PPMP^† (Swin) \\)90.0884.7667.6752.1766.4130.4072.7335.30
Ours56.0936.4873.8054.4876.4158.8278.3347.38
\\( Ours^† \\)70.1546.2674.6459.2477.1559.6880.8350.48
", + "bbox": [ + 127, + 88, + 843, + 262 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Video-Based Methods. We compare our method to other video-based methods on the MOVi video datasets in Table 1 and Fig. 2. All of the methods in Table 1 use optical flow for supervision. Differently, SCALOR [30] and SAVi [36] use all frames in a video, whereas PPMP [33] and our method perform single-image segmentation, one frame at a time without using any motion information at test time. On the simpler MOVi-A dataset, the performance of our method falls behind SAVi [36] and PPMP [33]. PPMP with Swin transformer [41] performs the best overall. With the same 6-layer CNN backbone and without post-processing, SAVi performs the best. Despite the advantage of motion information, the success of SCALOR [30] and SAVi [36] is limited to visually simpler MOVi-A.", + "bbox": [ + 75, + 321, + 472, + 534 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "On the more challenging MOVi- $\\{\\mathrm{C},\\mathrm{D},\\mathrm{E}\\}$ datasets, our method, even without post-processing, significantly outperforms all the previous methods in both metrics, with or without post-processing. The previous state-of-the-art, PPMP [33] uses the same backbone in their segmentation network as ours. Even with a more powerful backbone (Swin transformer [41]) and post-processing, the results of PPMP are still far behind our results without any post-processing. From MOVi-C to MOVi-E, the performance gap between our method and the others increases as the complexity of the dataset increases. Please see Supplementary for qualitative results with post-processing and evaluation of our estimated depth for objects in these datasets.", + "bbox": [ + 75, + 539, + 472, + 738 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Image-Based Methods. We compare our method to other image-based methods on the CLEVR and CLEVRTEX datasets in Table 2. Our method outperforms the state-of-the-art method PPMP [33] in all metrics on both datasets except for mIoU on CLEVR without postprocessing and mIoU on CLEVRTEX with postprocessing. We point to +9.01 improvement in mIoU on the more challenging CLEVRTEX dataset without postprocessing. See Supplementary for qualitative results on CLEVR and CLEVRTEX.", + "bbox": [ + 75, + 763, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.5. Results on Real-World Datasets", + "text_level": 1, + "bbox": [ + 498, + 321, + 779, + 338 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We compare our method to multi-object segmentation methods on real-world datasets including driving scenarios on KITTI and unconstrained videos on DAVIS-2017.", + "bbox": [ + 496, + 349, + 892, + 393 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Results on DAVIS. Our method is the first image-based method to report performance in multi-object segmentation without using any labels during training or testing on", + "bbox": [ + 496, + 402, + 892, + 450 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/1006bfbbfade51a41cefae7cab64a22c032921df27c52e011590079a28786ae1.jpg", + "table_caption": [ + "Table 1: Segmentation Results on MOVi Datasets. The best result in each column is shown in bold, and the second best is underlined. $\\dagger$ indicates post-processing, and (Swin) denotes using a Swin transformer as the backbone." + ], + "table_footnote": [], + "table_body": "
CLEVRCLEVRTEX
FG-ARI↑mIoU↑FG-ARI↑mIoU↑
SPAIR [12]77.1365.950.000.00
MN [54]72.1256.8138.3110.46
MONet [7]54.4730.6636.6619.78
SA [42]95.8936.6162.4022.58
IODINE [24]93.8145.1459.5229.17
DTI-S [46]59.5448.7479.9033.79
GNM [29]65.0559.9253.3742.25
SAVi [36]--49.5431.88
PPMP [32]91.6966.7090.8055.07
Ours95.0363.3694.6664.08
SPAIR†[12]77.0566.870.000.00
MN†[54]72.0857.6138.3410.34
MONet†[7]61.3645.6135.6423.59
SA†[42]94.8837.6861.6021.96
IODINE†[24]93.6844.2060.6329.40
DTI-S†[46]89.8653.3879.8632.20
GNM†[29]65.6763.3853.3844.30
PPMP†[33]95.9484.8692.6177.67
Ours†96.9586.3895.3270.28
", + "bbox": [ + 498, + 477, + 906, + 825 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2: Segmentation Results on CLEVR and CLEVRTex Datasets. The lower part with $\\dagger$ shows the results with post-processing. The best result in each column is shown in bold, and the second best is underlined.", + "bbox": [ + 496, + 834, + 893, + 897 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "739", + "bbox": [ + 485, + 944, + 509, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/4cb046bd9b344cd30a5892551a9b4f31bda5980bb36e585f347dee4b568bf301.jpg", + "image_caption": [ + "Figure 3: Qualitative Comparison on DAVIS-2017. While OCLR [63] misses some objects completely and suffers from relying on only optical flow as input, our method can segment a wide variety of multiple objects in everyday scenes." + ], + "image_footnote": [], + "bbox": [ + 86, + 87, + 883, + 426 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "DAVIS-2017. Therefore, in Table 3, we compare it to video-based approaches which use motion as input. We also compare to a simple baseline proposed in [63] based on Mask R-CNN [26] using optical flow as input. We use the labels re-annotated by [63] for evaluation, as explained in Section 4.1. Motion Grouping refers to [64] trained on DAVIS-2017. Motion Grouping (sup.), Mask R-CNN (flow) and OCLR are models trained on synthetic data from [63] in a supervised way using optical flow as input. Our method, which uses a single RGB image as input at test time, outperforms previous methods, including the state-of-the-art OCLR [63] that uses flow from multiple time steps. Ours-M refers to a version of our model where we adapt the spectral clustering approach of [11] to merge our predicted regions into the ground truth number of regions in each frame.", + "bbox": [ + 75, + 479, + 472, + 708 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/7dcc5de8b4c56951785c110d1a99ea53257456c0f651cf5ae2b06825d366d319.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelJ& F↑J↑F↑
Motion Grouping [64]35.838.433.2
Motion Grouping (sup.)39.544.934.2
Mask R-CNN (flow)50.350.450.2
OCLR [63]55.154.555.7
Ours55.355.355.3
Ours-M59.259.359.2
", + "bbox": [ + 106, + 733, + 439, + 854 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 3: Multi-Object Segmentation Results on DAVIS-2017. We evaluate by using the motion labels from [63].", + "bbox": [ + 76, + 864, + 468, + 896 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Although not necessary to achieve state-of-the-art, this improves the results significantly.", + "bbox": [ + 500, + 481, + 888, + 511 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We visualize the results of our model in comparison to OCLR [63] in Fig. 3. Our method can correctly segment a wide variety of objects such as the bike and the person in the first column and the multiple fish in the third, multiple people walking or fighting in the second and fourth. OCLR is highly affected by the inaccuracies in flow, unlike our method, as can be seen from the last two columns.", + "bbox": [ + 496, + 513, + 890, + 618 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results on KITTI. Since KITTI has ground truth depth, we evaluate our method in terms of both segmentation and monocular depth prediction on KITTI. The segmentation results on KITTI are presented in Table 4a. Our method is among the top-performing methods, outperforming earlier approaches. In addition to segmentation, our method can also predict depth from a single image. We present the evaluation of our depth predictions in comparison to self-supervised monocular depth estimation methods in Table 4b. Our depth network can predict reliable depth maps even without camera intrinsics with comparable results to recent self-supervised monocular depth estimation approaches [22, 25] that are specifically designed for that task and that use camera intrinsics.", + "bbox": [ + 496, + 626, + 892, + 837 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We visualize our segmentation and depth results on KITTI in Supplementary. Our method can segment multiple moving objects such as car, bike, bus without using any semantic labels for training or motion information at test", + "bbox": [ + 496, + 839, + 893, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "740", + "bbox": [ + 486, + 944, + 511, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/cdd2840a27c5895357fd8a9fc576454df7d4e270c7cb582eb1b770ddb2ff43e5.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelFG-ARI ↑
SA [42]13.8
MONet [7]14.9
SCALAR [30]21.1
S-IODINE [24]14.4
MCG [1]40.9
Ours42.3
Bao et al. [2]47.1
PPMP [33]50.8
", + "bbox": [ + 76, + 93, + 250, + 219 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/619f1e6200265f36af0bc491d81e3c09943530fab85e8bdcd184d984dfc635bf.jpg", + "table_caption": [ + "(a) Segmentation" + ], + "table_footnote": [], + "table_body": "
Abs Rel ↓Sq Rel ↓RSME ↓RMSE log ↓δ < 1.25 ↑δ < 1.252 ↑δ < 1.253 ↑
Zhou et al. [69]0.1761.5326.1290.2440.7580.9210.971
Mahjourian et al. [45]0.1340.9835.5010.2030.8270.9440.981
GeoNet [68]0.1320.9945.2400.1930.8330.9530.985
DDVO [60]0.1260.8664.9320.1850.8510.9580.986
Ranjan et al. [51]0.1230.8814.8340.1810.8600.9590.985
EPC++ [44]0.1200.7894.7550.1770.8560.9610.987
Ours0.1071.5394.0270.1490.9110.9710.989
Monodepth2 [22]0.0900.5453.9420.1370.9140.9830.998
PackNet-SfM [25]0.0780.4203.4850.1210.9340.9860.996
", + "bbox": [ + 258, + 88, + 918, + 224 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/0a3604d5ab63fb31234cdd83874c678425da4ee736ddcf56012631677e6c22c2.jpg", + "table_caption": [ + "(b) Depth", + "Table 4: Results on KITTI. We evaluate the segmentation on the instance segmentation benchmark, and the depth on the KITTI Eigen split [14] with improved ground truth [59]." + ], + "table_footnote": [], + "table_body": "
MOVi-AMOVi-CMOVi-DMOVi-E
FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑
Only-T31.1317.7269.6925.8468.6822.7464.6928.26
Only-R90.4375.6368.5153.0070.5756.9773.0340.34
Full56.0936.4873.8054.4876.4158.8278.3347.38
Only-T†47.9629.9269.9426.3168.6622.7669.9430.71
Only-R†92.0984.6069.2355.5471.2058.4176.2042.96
Full†70.1546.2674.6459.2477.1559.6880.8350.48
", + "bbox": [ + 196, + 290, + 774, + 417 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5: Ablation Study. We perform an ablation study by using only the translation (Only-T) or rotation (Only-R) component and compare it to our model with both (Full). See text for details.", + "bbox": [ + 75, + 428, + 888, + 459 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "time. Furthermore, it can predict high-quality depth, capturing thin structures and sharp boundaries around objects.", + "bbox": [ + 75, + 474, + 468, + 505 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.6. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 523, + 230, + 540 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To evaluate the contribution of different types of flow basis, we perform an experiment by considering only translation or rotation and compare it to the full model on MOVi datasets in Table 5. Note that in the rotation-only case (Only-R), the depth predictions are not used and the depth network is not trained. Overall, the rotation-only model outperforms the translation-only model and the full model with both rotation and translation works the best on MOVi-{C, D, E} datasets with reliable depth predictions.", + "bbox": [ + 75, + 550, + 468, + 686 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The trend is different on the simpler MOVi-A dataset. Only-R outperforms all models including the state-of-the-art in Table 1. We found that in the translation-only case, the depth cannot be predicted on MOVi-A due to missing texture and enough detail for the depth network to learn a mapping from a single image to depth. The rotation-only model, on the other hand, learns to group pixels in a region, based on their rotational motion which does not depend on depth. This ability explains the success of Only-R on simpler datasets. The importance of pixel-wise depth increases with the complexity of the dataset. On MOVi-E, for example, which has the most complex setup with a large number of objects and camera motion, predicting depth, from Only-R to Full, improves the performance the most.", + "bbox": [ + 75, + 688, + 470, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion and Future Work", + "text_level": 1, + "bbox": [ + 500, + 473, + 769, + 489 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We presented a motion-supervised approach for multi-object segmentation that can work with a single RGB image at test time, therefore still applicable to image datasets. Our method is the first to consider geometry to remove ambiguity for multi-object segmentation from a single image without using any labels for segmentation. Modeling geometry significantly advances the state-of-the-art on commonly used synthetic datasets. We also evaluated our method on real-world datasets. Our method is the first image-based multi-object segmentation method to report state-of-the-art results on DAVIS-2017 without using motion at test time. We also report comparable results for depth prediction on KITTI and MOVi datasets where depth can be evaluated.", + "bbox": [ + 496, + 498, + 890, + 694 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Predicting objects that can potentially move independently from a single image requires observing examples of various objects moving in the training set. Moreover, static objects send a mixed signal to the model. The coherent changes in the flow can be captured with the help of geometry as shown in our work. The remaining uncertainty can be addressed with a probabilistic formulation as done in previous state-of-the-art [33]. Another problem is scenes without enough information to predict depth as we observed on textureless MOVi-A. However, the lack of information to this extent rarely happens on real-world data.", + "bbox": [ + 496, + 695, + 892, + 861 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements. Sadra Safadoust was supported by KUIS AI Fellowship and UNVEST R&D Center.", + "bbox": [ + 500, + 868, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "741", + "bbox": [ + 486, + 945, + 509, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] P. Arbeláez, J. Pont-Tuset, J. Barron, F. Marques, and J. Malik. Multiscale combinatorial grouping. In CVPR, 2014. 8", + "[2] Zhipeng Bao, Pavel Tokmakov, Allan Jabri, Yu-Xiong Wang, Adrien Gaidon, and Martial Hebert. Discovering objects that can move. In CVPR, pages 11789-11798, 2022. 4, 5, 8", + "[3] Pia Bideau and Erik G. Learned-Miller. 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In CVPR, 2019. 2" + ], + "bbox": [ + 501, + 92, + 890, + 900 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "743", + "bbox": [ + 486, + 945, + 509, + 955 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[67] Nianjin Ye, Chuan Wang, Haoqiang Fan, and Shuaicheng Liu. Motion basis learning for unsupervised deep homography estimation with subspace projection. In ICCV, 2021. 2", + "[68] Zhichao Yin and Jianping Shi. GeoNet: Unsupervised learning of dense depth, optical flow and camera pose. In CVPR, 2018. 8", + "[69] Tinghui Zhou, Matthew Brown, Noah Snavely, and David G Lowe. Unsupervised learning of depth and ego-motion from video. In CVPR, 2017. 3, 4, 8" + ], + "bbox": [ + 78, + 90, + 468, + 232 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "744", + "bbox": [ + 486, + 945, + 509, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multi-Object Discovery by Low-Dimensional Object Motion/063ca8bc-3b85-47f8-b8af-3f433d446bab_model.json b/2023/Multi-Object Discovery by Low-Dimensional Object Motion/063ca8bc-3b85-47f8-b8af-3f433d446bab_model.json new file mode 100644 index 0000000000000000000000000000000000000000..93fbab9f43d1e30e2aa55138b01277862fa1ea94 --- /dev/null +++ b/2023/Multi-Object Discovery by Low-Dimensional Object Motion/063ca8bc-3b85-47f8-b8af-3f433d446bab_model.json @@ -0,0 +1,2125 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.807, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.182, + 0.131, + 0.79, + 0.153 + ], + "angle": 0, + "content": "Multi-Object Discovery by Low-Dimensional Object Motion" + }, + { + "type": "text", + "bbox": [ + 0.187, + 0.182, + 0.782, + 0.234 + ], + "angle": 0, + "content": "Sadra Safadoust Fatma Güney \nKUIS AI Center and Department of Computer Engineering, Koç University \nssafadoust20@ku.edu.tr fguney@ku.edu.tr" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.302, + 0.474, + 0.543 + ], + "angle": 0, + "content": "Recent work in unsupervised multi-object segmentation shows impressive results by predicting motion from a single image despite the inherent ambiguity in predicting motion without the next image. On the other hand, the set of possible motions for an image can be constrained to a low-dimensional space by considering the scene structure and moving objects in it. We propose to model pixel-wise geometry and object motion to remove ambiguity in reconstructing flow from a single image. Specifically, we divide the image into coherently moving regions and use depth to construct flow bases that best explain the observed flow in each region. We achieve state-of-the-art results in unsupervised multi-object segmentation on synthetic and real-world datasets by modeling the scene structure and object motion. Our evaluation of the predicted depth maps shows reliable performance in monocular depth estimation." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.573, + 0.21, + 0.589 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.599, + 0.471, + 0.81 + ], + "angle": 0, + "content": "Finding objects on visual data is one of the oldest problems in computer vision, which has been shown to work to great extent in the presence of labeled data. Achieving it without supervision is important given the difficulty of obtaining pixel-precise masks for the variety of objects encountered in everyday life. In the absence of labels, motion provides important cues to group pixels corresponding to objects. The existing solutions use motion either as input to perform grouping or as output to reconstruct as a way of verifying the predicted grouping. The current methodology fails to incorporate the underlying 3D geometry creating the observed motion. In this work, we show that modeling geometry together with object motion significantly improves the segmentation of multiple objects without supervision." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Unsupervised multi-object discovery is significantly more challenging than the single-object case due to mutual occlusions. Therefore, earlier methods in unsupervised segmentation focused on separating a foreground object from the background whereas multi-object methods have been mostly limited to synthetic datasets or resorted to additional" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.271, + 0.875, + 0.286 + ], + "angle": 0, + "content": "supervision on real-world data such as sparse depth [15]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.289, + 0.892, + 0.486 + ], + "angle": 0, + "content": "While sparse-depth supervision can be applied to driving scenarios [15], depth information is not typically available on common video datasets. Moreover, video segmentation datasets such as DAVIS [48, 49] contain a wide variety of categories under challenging conditions such as appearance changes due to lighting conditions or motion blur. The motion information can be obtained from video sequences via optical flow. Optical flow not only provides motion cues for grouping [64] but can also be used for training on synthetic data without suffering from the domain gap while transferring to real data [63]. The problems in optical flow prediction on real-world data can be mitigated to some extent by relating flow predictions from multiple frames [63]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.49, + 0.893, + 0.701 + ], + "angle": 0, + "content": "In addition to problems in predicting optical flow, requiring flow as input prohibits the application of the method on static images. Another line of work [11, 33] uses motion for supervision at train time only. Based on the observation that objects create distinctive patterns in flow, initial work [11] fits a simple parametric model to the flow in each object region to capture the object motion. This way, the network can predict object regions that can potentially move coherently from a single image at test time. There is an inherent ambiguity in predicting motion from a single image. Therefore, the follow-up work [33] predicts a distribution of possible motion patterns to reduce this ambiguity. This also allows extending it to the multi-object case by mitigating the over-segmentation problem of the initial work [11]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.895, + 0.903 + ], + "angle": 0, + "content": "In this work, we propose to model pixel-wise geometry to remove ambiguity in reconstructing flow from a single image. Optical flow is the difference between the 2D projections of the 3D world in consecutive time steps. By modeling the 3D geometry creating these projections, we directly address the mutual occlusion problem due to interactions of multiple objects. This problem has been crudely addressed by previous work with a depth-ordered layer representation [63]. Instead of assuming a single depth layer per object, we predict pixel-wise depth which provides more expressive power in explaining the observed motion. Furthermore, we do not use flow as input during inference, allowing us to evaluate our method on single-image datasets." + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.945, + 0.511, + 0.957 + ], + "angle": 0, + "content": "734" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.318 + ], + "angle": 0, + "content": "Recent work [5] showed that motion resides in a low-dimensional subspace, and its reconstruction can be used to supervise monocular depth prediction. Despite many possible flow fields, the space of possible flow fields is spanned by a small number of basis flow fields related to depth and independently moving objects. While [5] focuses on modeling camera motion for quantitatively evaluating depth in static scenes, it also points to the fact that the object motion can be similarly modeled in a low-dimensional subspace by simply masking the points in the object region. Given the difficulty of predicting pixel-wise masks, simple object embeddings are used to cluster independently moving objects. We instead predict the object regions jointly with depth to find the low-dimensional object motion that best explains the observed flow in each region." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.318, + 0.473, + 0.545 + ], + "angle": 0, + "content": "Our approach works extremely well on synthetic Multi-Object Video (MOVi) datasets [23], significantly outperforming previous work, especially in more challenging MOVi-{C,D,E} partitions and performing comparably on visually simpler MOVi-A due to difficulty of estimating depth. We use motion only for supervision at train time, therefore our method can be successfully applied to still images of CLEVR [31] and CLEVRTEX [34] and shows state-of-the-art performance. More impressively, our method can segment multiple objects on real-world videos of DAVIS2017 [49] from a single image at test time, exceeding the performance of the state-of-the-art that uses flow from multiple frames as input [63]. In addition to evaluating segmentation, we show that our method can also reliably predict depth in real-world self-driving scenarios on KITTI [21]." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.559, + 0.22, + 0.575 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.592, + 0.47, + 0.728 + ], + "angle": 0, + "content": "Basis Learning. Early work showed that optical flow estimation due to camera motion can be constrained using a subspace formulation for flow [28]. Basis learning has been used as a regularization in low-level vision, unifying tasks such as depth, flow, and segmentation [55]. PCA-Flow [61] builds a higher dimensional flow subspace from movies to represent flow as a weighted sum of flow bases. Recent work [67] learns the coefficients to combine eight pre-defined flow bases for homography estimation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Motion as Input. Most of the work in motion segmentation focuses on the single-object case. While earlier work uses traditional methods to cluster pixels into similar motion groups [6, 35, 47, 62], later methods train deep neural networks which take flow as input and predict segmentation as output [13, 57, 58]. Another work [66] uses the distinctiveness of motion in the case of foreground objects by proposing an adversarial setting to predict motion from context. Segmenting objects in camouflaged settings can be achieved by modeling background motion to remove its effect and highlight the moving foreground object [3, 4, 38]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "Recent work uses consistency between two flow fields computed under different frame gaps for self-supervision [64]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.124, + 0.894, + 0.215 + ], + "angle": 0, + "content": "The most relevant to our work is OCLR [63] which extends motion segmentation to multiple objects by relating motion extracted from multiple frames using a transformer in a layered representation. In this work, we show that better results can be achieved on real data even from a single image by modeling pixel-wise geometry." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.223, + 0.893, + 0.51 + ], + "angle": 0, + "content": "Motion for Supervision. While using motion only as input works well where appearance fails, e.g. the camouflage datasets, RGB carries important information that might be missing in flow. DyStaB [65] trains a dynamic model by exploiting motion for temporal consistency and then uses it to bootstrap a static model which takes a single image as input. A single image network is used to predict a segmentation in [40] and then the motion of each segment is predicted with a two-frame motion network. While image warping loss is used in [40] for self-supervision, recent work [11, 33] uses flow reconstruction loss by assuming the availability of flow at train time only. GWM [11] segments foreground objects by fitting an approximate motion model to each segment and then merging them using spectral clustering. The follow-up work [33] extends it to multiple objects by predicting probable motion patterns for each segment with a distribution. We also reconstruct flow for supervision but differently, we account for 3D to remove the ambiguity in reconstructing motion from a single image." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.512, + 0.894, + 0.573 + ], + "angle": 0, + "content": "The most relevant to our work is the previous work that uses flow as a source of supervision for depth [5] or segmentation [11, 34]. In this work, we model both depth and segmentation with supervision from motion." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.582, + 0.892, + 0.793 + ], + "angle": 0, + "content": "Multi-Object Scene Decomposition. Our work is also related to scene decomposition approaches which are mostly evaluated on synthetic datasets. The earlier image-based decomposition approaches such as MONet [7] and IO-DINE [24] use a sequential VAE structure where the decomposition at a step can affect the remaining parts to be explained in the next step. GENESIS [17] follows an object-centric approach by accounting for component interactions, which is extended to more realistic scenarios with an autoregressive prior in the follow-up work [18]. Slot Attention [42] uses an iterative attention mechanism to decompose the image into a set of slot representations. A hierarchical VAE is used in [16] to extract symmetric and disentangled representations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.894, + 0.903 + ], + "angle": 0, + "content": "There are also video-based approaches to multi-object scene decomposition. SCALOR [30] focuses on scaling generative approaches to crowded scenes in terms of object density. SIMONE [32] learns a factorized latent space to separate object semantics that is constant in the sequence from the background which changes at each frame according to camera motion. SAVi [36] extends Slot Attention [42]" + }, + { + "type": "page_number", + "bbox": [ + 0.487, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "735" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.086, + 0.833, + 0.318 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.33, + 0.892, + 0.424 + ], + "angle": 0, + "content": "Figure 1: Overview of our Approach. From a single image, we use a segmentation and a depth network to predict a segmentation mask \\(\\mathbf{m}\\) and a disparity map \\(\\mathbf{d}\\). Based on these predictions, we construct the bases for the space of the possible optical flows for \\(K\\) distinctly moving regions on the image. Each moving region \\(i\\) is represented with a separate basis \\(\\mathcal{B}_i\\). Given optical flow \\(\\mathbf{F}\\) as input, either ground truth or estimated by an off-the-shelf method, we project it into \\(\\mathrm{span}(\\bigcup_{i=1}^{K} \\mathcal{B}_i)\\). We use the distance between the input flow \\(\\mathbf{F}\\) and the projected flow \\(\\hat{\\mathbf{F}}\\) to supervise depth and segmentation. During inference, our networks can be used to predict depth and segmentation from a single image." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.449, + 0.47, + 0.48 + ], + "angle": 0, + "content": "to videos and \\(\\mathrm{SAVi}++\\) [15] extends it to real-world driving scenarios with sparse depth supervision." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.486, + 0.471, + 0.728 + ], + "angle": 0, + "content": "Self-Supervised Monocular Depth Estimation. Zhou et al. [69] train a pose network to estimate the pose between the frames in a sequence and jointly train it with the depth network. Godard et al. [22] improves the results with a better loss function and other design choices. Guizilini et al. [25] learn detail-preserving representations using 3D packing and unpacking blocks. Given instance segmentation masks, a line of work [9, 39] models the motion of objects in the scene in addition to the camera motion to go beyond the static-scene assumption. While the object masks are supervised using ground truth masks in [37], the masks are learned without supervision as an auxiliary output in [53] for better depth estimation. While they require multiple frames during inference, our approach can estimate masks from a single image. Additionally, our method does not use camera intrinsics." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.74, + 0.447, + 0.758 + ], + "angle": 0, + "content": "3. Depth-Aware Multi-Object Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.902 + ], + "angle": 0, + "content": "The observed motion in 2D is the result of 3D scene structure and independently moving objects. By predicting the scene structure in terms of depth and locating independently moving objects, we can accurately reconstruct the optical flow corresponding to the observed motion in 2D. Towards this purpose, we use a low-dimensional parameterization of optical flow based on depth (Section 3.1). In this low-dimensional representation, we can accurately reconstruct flow from a rigid motion. We extend this parametriza" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.449, + 0.892, + 0.495 + ], + "angle": 0, + "content": "tion to a number of rigidly moving objects to find the regions corresponding to objects (Section 3.2). See Fig. 1 for an overview of our approach." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.502, + 0.854, + 0.518 + ], + "angle": 0, + "content": "3.1. Low-Dimensional Motion Representation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.525, + 0.892, + 0.616 + ], + "angle": 0, + "content": "The space of all possible optical flow fields is very high-dimensional, i.e. in \\(\\mathbb{R}^{H\\times W\\times 2}\\). However, conditioned on the scene structure, only a small fraction of all flow fields are possible. Previous work [27, 5] has shown that the set of possible instantaneous flows for a moving camera in a static scene forms a linear space with six basis vectors:" + }, + { + "type": "equation", + "bbox": [ + 0.56, + 0.624, + 0.891, + 0.641 + ], + "angle": 0, + "content": "\\[\n\\mathcal {B} _ {0} = \\left\\{\\mathbf {b} _ {\\mathbf {T} x}, \\mathbf {b} _ {\\mathbf {T} y}, \\mathbf {b} _ {\\mathbf {T} z}, \\mathbf {b} _ {\\mathbf {R} x}, \\mathbf {b} _ {\\mathbf {R} y}, \\mathbf {b} _ {\\mathbf {R} z} \\right\\} \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.647, + 0.892, + 0.708 + ], + "angle": 0, + "content": "These basis vectors correspond to translation and rotation along the \\(x, y\\), and \\(z\\) axes, respectively. For an image \\(\\mathbf{I} \\in \\mathbb{R}^{H \\times W \\times 3}\\), the values of each basis vector \\(\\mathbf{b}_i \\in \\mathbb{R}^{H \\times W \\times 2}\\) for a given pixel \\((u, v)\\) can be calculated as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.561, + 0.714, + 0.843, + 0.75 + ], + "angle": 0, + "content": "\\[\n\\mathbf {b} _ {\\mathbf {T} x} = \\left[ \\begin{array}{c} f _ {x} d \\\\ 0 \\end{array} \\right], \\quad \\mathbf {b} _ {\\mathbf {R} x} = \\left[ \\begin{array}{c} f _ {y} ^ {- 1} \\bar {u} \\bar {v} \\\\ f _ {y} + f _ {y} ^ {- 1} \\bar {v} ^ {2} \\end{array} \\right]\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.561, + 0.757, + 0.844, + 0.793 + ], + "angle": 0, + "content": "\\[\n\\mathbf {b} _ {\\mathbf {T} y} = \\left[ \\begin{array}{c} 0 \\\\ f _ {y} d \\end{array} \\right], \\quad \\mathbf {b} _ {\\mathbf {R} y} = \\left[ \\begin{array}{c} f _ {x} + f _ {x} ^ {- 1} \\bar {u} ^ {2} \\\\ f _ {x} ^ {- 1} \\bar {u} \\bar {v} \\end{array} \\right]\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.558, + 0.8, + 0.892, + 0.835 + ], + "angle": 0, + "content": "\\[\n\\mathbf {b} _ {\\mathbf {T} z} = \\left[ \\begin{array}{l} - \\bar {u} d \\\\ - \\bar {v} d \\end{array} \\right], \\quad \\mathbf {b} _ {\\mathbf {R} z} = \\left[ \\begin{array}{l} f _ {x} f _ {y} ^ {- 1} \\bar {v} \\\\ - f _ {y} f _ {x} ^ {- 1} \\bar {u} \\end{array} \\right] \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.841, + 0.892, + 0.902 + ], + "angle": 0, + "content": "where \\( f_{x}, f_{y} \\) are the focal lengths of the camera. For brevity, we define \\( \\bar{u} = u - c_{x} \\) and \\( \\bar{v} = v - c_{y} \\) to be the centered pixel coordinates according to \\( (c_{x}, c_{y}) \\), the principal point of the camera. With a slight abuse of notation, we" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.945, + 0.512, + 0.957 + ], + "angle": 0, + "content": "736" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.121 + ], + "angle": 0, + "content": "do not write the basis vectors as a function of \\((u,v)\\) and use \\(d\\) to denote the disparity \\(\\mathbf{d}(u,v)\\) at a pixel \\((u,v)\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.122, + 0.468, + 0.242 + ], + "angle": 0, + "content": "We train a monocular depth network to predict inverse depth, disparity \\( \\mathbf{d} \\) from a single image. Then, the predicted disparity at each pixel is used to form the translation part of the basis vectors as shown in Eq. (2). Note that predicted disparity values do not affect the rotation but form the low-dimensional motion representation via translation. The depth network receives gradients directly from the flow reconstruction loss as explained next in Section 3.2." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.243, + 0.47, + 0.409 + ], + "angle": 0, + "content": "In Eq. (2), camera parameters including the principal point \\((c_x, c_y)\\) and the focal lengths \\(f_x\\), \\(f_y\\) are required to calculate the basis vectors. We assume the principal points to be at the center of the image. However, we do not assume to know the values of focal lengths. Instead, we only assume that \\(f_x = f_y\\). In this case, as demonstrated by [5], we can rewrite \\(\\mathcal{B}_0\\) as a set of 8 vectors that do not depend on the values of \\(f_x\\) and \\(f_y\\). For more details, please see Supplementary. Even without knowing the actual values of the focal lengths, we can obtain quite accurate depth predictions with supervision from flow (Section 4)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.418, + 0.358, + 0.433 + ], + "angle": 0, + "content": "3.2. Segmentation by Object Motion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.441, + 0.468, + 0.621 + ], + "angle": 0, + "content": "We extend the formulation introduced in Section 3.1 to handle the instantaneous flow from multiple object motion. As stated in [5], for a rigidly moving object in the scene, there is an equivalent camera motion. Therefore the space of optical flow from a rigidly moving object is the same as the space of optical flow from camera motion restricted to points in the object. Consider a scene with \\(K\\) regions corresponding to moving parts including the background and multiple objects. If we represent each region \\(i \\in \\{1, \\dots, K\\}\\) with ones on a binary mask \\(\\mathbf{m}_i \\in \\{0, 1\\}^{H \\times W \\times 1}\\), then a basis for the space of possible flows can be defined as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.187, + 0.633, + 0.468, + 0.649 + ], + "angle": 0, + "content": "\\[\n\\mathcal {B} = \\left\\{\\mathcal {B} _ {1} \\cup \\mathcal {B} _ {2} \\cup \\dots \\mathcal {B} _ {K} \\right\\} \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.66, + 0.468, + 0.69 + ], + "angle": 0, + "content": "where \\(\\mathcal{B}_i\\) refers to the basis for the space of possible flows restricted to region \\(i\\) as:" + }, + { + "type": "equation", + "bbox": [ + 0.194, + 0.701, + 0.468, + 0.717 + ], + "angle": 0, + "content": "\\[\n\\mathcal {B} _ {i} = \\left\\{\\mathbf {m} _ {i} \\mathbf {b} \\mid \\mathbf {b} \\in \\mathcal {B} _ {0} \\right\\}. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.728, + 0.468, + 0.803 + ], + "angle": 0, + "content": "We train a segmentation network to divide the image into coherently moving regions \\(\\mathbf{m} \\in [0,1]^{H \\times W \\times K}\\), representing soft assignments over \\(K\\) regions. We use the predicted mask \\(\\mathbf{m}_i \\in [0,1]^{H \\times W \\times 1}\\) of the region \\(i\\) to obtain the basis corresponding to that region according to Eq. (4)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Training Objective. Based on the predicted disparity map \\(\\mathbf{d}\\) and the segmentation map \\(\\mathbf{m}\\), we form the basis \\(\\mathcal{B}\\) for the space of possible optical flows for the image according to Eq. (3) and Eq. (4). We denote the optical flow where the input image is the source frame as \\(\\mathbf{F} \\in \\mathbb{R}^{H \\times W \\times 2}\\). It can be either ground truth flow or the output of a two-frame flow" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.183 + ], + "angle": 0, + "content": "network such as RAFT [56]. We project \\(\\mathbf{F}\\) into the space spanned by \\(\\mathcal{B}\\) in a differentiable manner to obtain \\(\\hat{\\mathbf{F}}\\). For the details of the projection, please refer to Supplementary. We define our loss function as the \\(L_{2}\\) distance between the given flow \\(\\mathbf{F}\\) and the reconstructed flow \\(\\hat{\\mathbf{F}}\\) and use it to train depth and segmentation networks jointly:" + }, + { + "type": "equation", + "bbox": [ + 0.643, + 0.191, + 0.892, + 0.209 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\left\\| \\mathbf {F} - \\hat {\\mathbf {F}} \\right\\| _ {2} \\tag {5}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.22, + 0.632, + 0.236 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.244, + 0.602, + 0.259 + ], + "angle": 0, + "content": "4.1. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.275, + 0.892, + 0.44 + ], + "angle": 0, + "content": "Synthetic Datasets. For comparison to image-based methods, we evaluate our method on the CLEVR [31] and CLEVRTEX [34] datasets. CLEVR is a dataset of still images depicting multiple objects of random shape, size, color, and position. CLEVRTEX is similar to CLEVR but contains more diverse textures and shapes. Because our method needs optical flow for training, we train our model on the MOVINGCLEVR and MOVINGCLEVRTEX datasets [33], which are video extensions of CLEVR and CLEVRTEX scenes. We train on the video versions but evaluate on the original test sets of CLEVR and CLEVRTEX." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.441, + 0.892, + 0.592 + ], + "angle": 0, + "content": "For comparison to video-based methods, we use the Multi-Object Video (MOVi) datasets [23]. Similar to [33], we use the MOVi-{A, C, D, E} variants. MOVi-A is based on CLEVR [31] and contains scenes with a static camera and multiple objects with simple textures and uniform colors tossed on a gray floor. MOVi-C is more challenging due to realistic everyday objects with rich textures on a more complex background. MOVi-D increases the complexity by increasing the number of objects. MOVi-E is even more challenging as it features camera motion as well." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.592, + 0.892, + 0.622 + ], + "angle": 0, + "content": "In all our experiments on synthetic datasets, we use a resolution of \\(128 \\times 128\\) and the ground truth optical flow." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.892, + 0.75 + ], + "angle": 0, + "content": "Real-World Datasets. We use the common video segmentation dataset DAVIS-2017 [49] containing 90 video sequences where each sequence has one or more moving objects. We follow the evaluation protocol of [63] where the ground truth objects are reannotated by assigning the same label to the jointly moving objects. We resize the images to a resolution of \\(128 \\times 224\\) during training and use the flow from RAFT [56] with \\(\\{-8, -4, 4, 8\\}\\) gaps between frames." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.751, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Additionally, we evaluate our method on the KITTI driving dataset [21, 20]. Following [2], we train on the whole training set and evaluate the segmentation results on the instance segmentation benchmark consisting of 200 frames. We use a resolution of \\(128 \\times 416\\) and the flow from RAFT [56] with a gap of \\(+1\\). Additionally, we evaluate our depth results on KITTI. Following prior work [69, 22], we evaluate depth on the Eigen split [14] of the KITTI dataset using improved ground truth [59] to be comparable to self-supervised monocular depth estimation approaches." + }, + { + "type": "page_number", + "bbox": [ + 0.487, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "737" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.147, + 0.087, + 0.825, + 0.469 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.478, + 0.893, + 0.51 + ], + "angle": 0, + "content": "Figure 2: Visualization of Depth and Segmentation Results on MOVi datasets. Our method performs accurate segmentations, while PPMP suffers from over-segmentation and also mistakenly segments parts of the background as objects." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.524, + 0.27, + 0.538 + ], + "angle": 0, + "content": "4.2. Architecture Details" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.549, + 0.47, + 0.7 + ], + "angle": 0, + "content": "We use the same architecture used in [50] for depth and Mask2Former [10] for segmentation, using only the segmentation head. We use different backbones for the segmentation network on the synthetic and real datasets. On synthetic datasets, we follow [33, 36, 42] and utilize a 6-layer CNN. On real-world datasets, following [11], we use a ViT-B/8 transformer pre-trained self-supervised using DINO [8] on ImageNet [52]. On all of the datasets, we use 6 object queries in the segmentation network, which translates to \\( K = 6 \\), except for CLEVR, where we use \\( K = 8 \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.701, + 0.47, + 0.793 + ], + "angle": 0, + "content": "We use a fixed learning rate of \\(5 \\times 10^{-5}\\) for the depth network and use \\(1.5 \\times 10^{-4}\\) with a linear warm-up for the first 5K iterations for the segmentation network, reduced to \\(1.5 \\times 10^{-5}\\) after 200K iterations. We train both networks with AdamW optimizer [43] for 250K iterations. See Supplementary for further details, we will also share the code." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.808, + 0.255, + 0.823 + ], + "angle": 0, + "content": "4.3. Evaluation Details" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Metrics. Following prior work [34, 36, 33], we evaluate segmentation on synthetic datasets using Adjusted Rand Index on foreground pixels (FG-ARI) and mean Intersection over Union (mIoU). ARI measures how well predicted and" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.524, + 0.892, + 0.584 + ], + "angle": 0, + "content": "ground truth segmentation masks match in a permutation-invariant manner. For mIoU, we first apply Hungarian matching and calculate the mean over the maximum between the number of ground-truth and predicted segments." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.585, + 0.893, + 0.692 + ], + "angle": 0, + "content": "On DAVIS-2017 [49], we use the standard \\(\\mathcal{I}\\), \\(\\mathcal{F}\\) metrics and perform the Hungarian matching per frame, similar to other datasets. Note that we focus on the multi-object segmentation task without using any labels for segmentation at train or test time. For KITTI, we use the FG-ARI metric, following [33, 2]. For evaluating depth, we use the standard metrics used in monocular depth estimation [14, 19]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.699, + 0.895, + 0.806 + ], + "angle": 0, + "content": "Post-processing. We also report the results on segmentation using the post-processing method introduced in [33]. They extract the connected components in the model output and choose the largest \\( K \\) masks and discard any masks that take up less than \\( 0.1\\% \\) of the image. Then they combine the discarded masks with the largest mask. The results with post-processing are marked with \\( ^{\\dagger} \\) in the tables." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.817, + 0.762, + 0.833 + ], + "angle": 0, + "content": "4.4. Results on Synthetic Datasets" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.894, + 0.902 + ], + "angle": 0, + "content": "We evaluate our method on synthetic datasets and compare its performance to both image-based and video-based methods. Our method uses motion during training only. Therefore, it can also be evaluated on the image datasets." + }, + { + "type": "page_number", + "bbox": [ + 0.487, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "738" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.128, + 0.089, + 0.844, + 0.263 + ], + "angle": 0, + "content": "
MOVi-AMOVi-CMOVi-DMOVi-E
FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑
GWM [10]70.3042.2749.9830.1739.7818.3842.5018.74
SCALOR [30]59.5744.4140.4322.54----
SAVi [36]88.3062.6943.2631.9243.4510.6017.395.75
PPMP [33]84.0160.0861.1834.7255.7423.5062.6225.78
\\( PPMP^† \\)85.4176.1961.2437.2655.1825.2163.1128.59
\\( PPMP^† (Swin) \\)90.0884.7667.6752.1766.4130.4072.7335.30
Ours56.0936.4873.8054.4876.4158.8278.3347.38
\\( Ours^† \\)70.1546.2674.6459.2477.1559.6880.8350.48
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.273, + 0.893, + 0.306 + ], + "angle": 0, + "content": "Table 1: Segmentation Results on MOVi Datasets. The best result in each column is shown in bold, and the second best is underlined. \\(\\dagger\\) indicates post-processing, and (Swin) denotes using a Swin transformer as the backbone." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.323, + 0.473, + 0.535 + ], + "angle": 0, + "content": "Video-Based Methods. We compare our method to other video-based methods on the MOVi video datasets in Table 1 and Fig. 2. All of the methods in Table 1 use optical flow for supervision. Differently, SCALOR [30] and SAVi [36] use all frames in a video, whereas PPMP [33] and our method perform single-image segmentation, one frame at a time without using any motion information at test time. On the simpler MOVi-A dataset, the performance of our method falls behind SAVi [36] and PPMP [33]. PPMP with Swin transformer [41] performs the best overall. With the same 6-layer CNN backbone and without post-processing, SAVi performs the best. Despite the advantage of motion information, the success of SCALOR [30] and SAVi [36] is limited to visually simpler MOVi-A." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.54, + 0.473, + 0.739 + ], + "angle": 0, + "content": "On the more challenging MOVi-\\(\\{\\mathrm{C},\\mathrm{D},\\mathrm{E}\\}\\) datasets, our method, even without post-processing, significantly outperforms all the previous methods in both metrics, with or without post-processing. The previous state-of-the-art, PPMP [33] uses the same backbone in their segmentation network as ours. Even with a more powerful backbone (Swin transformer [41]) and post-processing, the results of PPMP are still far behind our results without any post-processing. From MOVi-C to MOVi-E, the performance gap between our method and the others increases as the complexity of the dataset increases. Please see Supplementary for qualitative results with post-processing and evaluation of our estimated depth for objects in these datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.472, + 0.903 + ], + "angle": 0, + "content": "Image-Based Methods. We compare our method to other image-based methods on the CLEVR and CLEVRTEX datasets in Table 2. Our method outperforms the state-of-the-art method PPMP [33] in all metrics on both datasets except for mIoU on CLEVR without postprocessing and mIoU on CLEVRTEX with postprocessing. We point to +9.01 improvement in mIoU on the more challenging CLEVRTEX dataset without postprocessing. See Supplementary for qualitative results on CLEVR and CLEVRTEX." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.323, + 0.78, + 0.339 + ], + "angle": 0, + "content": "4.5. Results on Real-World Datasets" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.35, + 0.893, + 0.395 + ], + "angle": 0, + "content": "We compare our method to multi-object segmentation methods on real-world datasets including driving scenarios on KITTI and unconstrained videos on DAVIS-2017." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.404, + 0.893, + 0.452 + ], + "angle": 0, + "content": "Results on DAVIS. Our method is the first image-based method to report performance in multi-object segmentation without using any labels during training or testing on" + }, + { + "type": "table", + "bbox": [ + 0.499, + 0.478, + 0.908, + 0.826 + ], + "angle": 0, + "content": "
CLEVRCLEVRTEX
FG-ARI↑mIoU↑FG-ARI↑mIoU↑
SPAIR [12]77.1365.950.000.00
MN [54]72.1256.8138.3110.46
MONet [7]54.4730.6636.6619.78
SA [42]95.8936.6162.4022.58
IODINE [24]93.8145.1459.5229.17
DTI-S [46]59.5448.7479.9033.79
GNM [29]65.0559.9253.3742.25
SAVi [36]--49.5431.88
PPMP [32]91.6966.7090.8055.07
Ours95.0363.3694.6664.08
SPAIR†[12]77.0566.870.000.00
MN†[54]72.0857.6138.3410.34
MONet†[7]61.3645.6135.6423.59
SA†[42]94.8837.6861.6021.96
IODINE†[24]93.6844.2060.6329.40
DTI-S†[46]89.8653.3879.8632.20
GNM†[29]65.6763.3853.3844.30
PPMP†[33]95.9484.8692.6177.67
Ours†96.9586.3895.3270.28
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.835, + 0.895, + 0.898 + ], + "angle": 0, + "content": "Table 2: Segmentation Results on CLEVR and CLEVRTex Datasets. The lower part with \\(\\dagger\\) shows the results with post-processing. The best result in each column is shown in bold, and the second best is underlined." + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.945, + 0.511, + 0.957 + ], + "angle": 0, + "content": "739" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.087, + 0.088, + 0.885, + 0.427 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.435, + 0.895, + 0.467 + ], + "angle": 0, + "content": "Figure 3: Qualitative Comparison on DAVIS-2017. While OCLR [63] misses some objects completely and suffers from relying on only optical flow as input, our method can segment a wide variety of multiple objects in everyday scenes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.481, + 0.473, + 0.709 + ], + "angle": 0, + "content": "DAVIS-2017. Therefore, in Table 3, we compare it to video-based approaches which use motion as input. We also compare to a simple baseline proposed in [63] based on Mask R-CNN [26] using optical flow as input. We use the labels re-annotated by [63] for evaluation, as explained in Section 4.1. Motion Grouping refers to [64] trained on DAVIS-2017. Motion Grouping (sup.), Mask R-CNN (flow) and OCLR are models trained on synthetic data from [63] in a supervised way using optical flow as input. Our method, which uses a single RGB image as input at test time, outperforms previous methods, including the state-of-the-art OCLR [63] that uses flow from multiple time steps. Ours-M refers to a version of our model where we adapt the spectral clustering approach of [11] to merge our predicted regions into the ground truth number of regions in each frame." + }, + { + "type": "table", + "bbox": [ + 0.107, + 0.734, + 0.441, + 0.855 + ], + "angle": 0, + "content": "
ModelJ& F↑J↑F↑
Motion Grouping [64]35.838.433.2
Motion Grouping (sup.)39.544.934.2
Mask R-CNN (flow)50.350.450.2
OCLR [63]55.154.555.7
Ours55.355.355.3
Ours-M59.259.359.2
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.866, + 0.47, + 0.897 + ], + "angle": 0, + "content": "Table 3: Multi-Object Segmentation Results on DAVIS-2017. We evaluate by using the motion labels from [63]." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.482, + 0.89, + 0.512 + ], + "angle": 0, + "content": "Although not necessary to achieve state-of-the-art, this improves the results significantly." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.514, + 0.892, + 0.619 + ], + "angle": 0, + "content": "We visualize the results of our model in comparison to OCLR [63] in Fig. 3. Our method can correctly segment a wide variety of objects such as the bike and the person in the first column and the multiple fish in the third, multiple people walking or fighting in the second and fourth. OCLR is highly affected by the inaccuracies in flow, unlike our method, as can be seen from the last two columns." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.627, + 0.893, + 0.838 + ], + "angle": 0, + "content": "Results on KITTI. Since KITTI has ground truth depth, we evaluate our method in terms of both segmentation and monocular depth prediction on KITTI. The segmentation results on KITTI are presented in Table 4a. Our method is among the top-performing methods, outperforming earlier approaches. In addition to segmentation, our method can also predict depth from a single image. We present the evaluation of our depth predictions in comparison to self-supervised monocular depth estimation methods in Table 4b. Our depth network can predict reliable depth maps even without camera intrinsics with comparable results to recent self-supervised monocular depth estimation approaches [22, 25] that are specifically designed for that task and that use camera intrinsics." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.894, + 0.901 + ], + "angle": 0, + "content": "We visualize our segmentation and depth results on KITTI in Supplementary. Our method can segment multiple moving objects such as car, bike, bus without using any semantic labels for training or motion information at test" + }, + { + "type": "page_number", + "bbox": [ + 0.487, + 0.945, + 0.512, + 0.956 + ], + "angle": 0, + "content": "740" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.078, + 0.094, + 0.251, + 0.22 + ], + "angle": 0, + "content": "
ModelFG-ARI ↑
SA [42]13.8
MONet [7]14.9
SCALAR [30]21.1
S-IODINE [24]14.4
MCG [1]40.9
Ours42.3
Bao et al. [2]47.1
PPMP [33]50.8
" + }, + { + "type": "table_caption", + "bbox": [ + 0.11, + 0.226, + 0.214, + 0.239 + ], + "angle": 0, + "content": "(a) Segmentation" + }, + { + "type": "table", + "bbox": [ + 0.259, + 0.089, + 0.919, + 0.226 + ], + "angle": 0, + "content": "
Abs Rel ↓Sq Rel ↓RSME ↓RMSE log ↓δ < 1.25 ↑δ < 1.252 ↑δ < 1.253 ↑
Zhou et al. [69]0.1761.5326.1290.2440.7580.9210.971
Mahjourian et al. [45]0.1340.9835.5010.2030.8270.9440.981
GeoNet [68]0.1320.9945.2400.1930.8330.9530.985
DDVO [60]0.1260.8664.9320.1850.8510.9580.986
Ranjan et al. [51]0.1230.8814.8340.1810.8600.9590.985
EPC++ [44]0.1200.7894.7550.1770.8560.9610.987
Ours0.1071.5394.0270.1490.9110.9710.989
Monodepth2 [22]0.0900.5453.9420.1370.9140.9830.998
PackNet-SfM [25]0.0780.4203.4850.1210.9340.9860.996
" + }, + { + "type": "table_caption", + "bbox": [ + 0.556, + 0.231, + 0.617, + 0.245 + ], + "angle": 0, + "content": "(b) Depth" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.248, + 0.892, + 0.278 + ], + "angle": 0, + "content": "Table 4: Results on KITTI. We evaluate the segmentation on the instance segmentation benchmark, and the depth on the KITTI Eigen split [14] with improved ground truth [59]." + }, + { + "type": "table", + "bbox": [ + 0.197, + 0.291, + 0.776, + 0.419 + ], + "angle": 0, + "content": "
MOVi-AMOVi-CMOVi-DMOVi-E
FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑
Only-T31.1317.7269.6925.8468.6822.7464.6928.26
Only-R90.4375.6368.5153.0070.5756.9773.0340.34
Full56.0936.4873.8054.4876.4158.8278.3347.38
Only-T†47.9629.9269.9426.3168.6622.7669.9430.71
Only-R†92.0984.6069.2355.5471.2058.4176.2042.96
Full†70.1546.2674.6459.2477.1559.6880.8350.48
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.429, + 0.89, + 0.46 + ], + "angle": 0, + "content": "Table 5: Ablation Study. We perform an ablation study by using only the translation (Only-T) or rotation (Only-R) component and compare it to our model with both (Full). See text for details." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.475, + 0.469, + 0.506 + ], + "angle": 0, + "content": "time. Furthermore, it can predict high-quality depth, capturing thin structures and sharp boundaries around objects." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.524, + 0.231, + 0.541 + ], + "angle": 0, + "content": "4.6. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.551, + 0.47, + 0.687 + ], + "angle": 0, + "content": "To evaluate the contribution of different types of flow basis, we perform an experiment by considering only translation or rotation and compare it to the full model on MOVi datasets in Table 5. Note that in the rotation-only case (Only-R), the depth predictions are not used and the depth network is not trained. Overall, the rotation-only model outperforms the translation-only model and the full model with both rotation and translation works the best on MOVi-{C, D, E} datasets with reliable depth predictions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.901 + ], + "angle": 0, + "content": "The trend is different on the simpler MOVi-A dataset. Only-R outperforms all models including the state-of-the-art in Table 1. We found that in the translation-only case, the depth cannot be predicted on MOVi-A due to missing texture and enough detail for the depth network to learn a mapping from a single image to depth. The rotation-only model, on the other hand, learns to group pixels in a region, based on their rotational motion which does not depend on depth. This ability explains the success of Only-R on simpler datasets. The importance of pixel-wise depth increases with the complexity of the dataset. On MOVi-E, for example, which has the most complex setup with a large number of objects and camera motion, predicting depth, from Only-R to Full, improves the performance the most." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.474, + 0.771, + 0.49 + ], + "angle": 0, + "content": "5. Conclusion and Future Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.499, + 0.892, + 0.695 + ], + "angle": 0, + "content": "We presented a motion-supervised approach for multi-object segmentation that can work with a single RGB image at test time, therefore still applicable to image datasets. Our method is the first to consider geometry to remove ambiguity for multi-object segmentation from a single image without using any labels for segmentation. Modeling geometry significantly advances the state-of-the-art on commonly used synthetic datasets. We also evaluated our method on real-world datasets. Our method is the first image-based multi-object segmentation method to report state-of-the-art results on DAVIS-2017 without using motion at test time. We also report comparable results for depth prediction on KITTI and MOVi datasets where depth can be evaluated." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.696, + 0.893, + 0.862 + ], + "angle": 0, + "content": "Predicting objects that can potentially move independently from a single image requires observing examples of various objects moving in the training set. Moreover, static objects send a mixed signal to the model. The coherent changes in the flow can be captured with the help of geometry as shown in our work. The remaining uncertainty can be addressed with a probabilistic formulation as done in previous state-of-the-art [33]. Another problem is scenes without enough information to predict depth as we observed on textureless MOVi-A. However, the lack of information to this extent rarely happens on real-world data." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.869, + 0.892, + 0.899 + ], + "angle": 0, + "content": "Acknowledgements. Sadra Safadoust was supported by KUIS AI Fellowship and UNVEST R&D Center." + }, + { + "type": "page_number", + "bbox": [ + 0.487, + 0.946, + 0.51, + 0.957 + ], + "angle": 0, + "content": "741" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.468, + 0.143 + ], + "angle": 0, + "content": "[1] P. Arbeláez, J. Pont-Tuset, J. Barron, F. Marques, and J. Malik. Multiscale combinatorial grouping. In CVPR, 2014. 8" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.146, + 0.468, + 0.186 + ], + "angle": 0, + "content": "[2] Zhipeng Bao, Pavel Tokmakov, Allan Jabri, Yu-Xiong Wang, Adrien Gaidon, and Martial Hebert. 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On the other hand, the set of possible motions for an image can be constrained to a low-dimensional space by considering the scene structure and moving objects in it. We propose to model pixel-wise geometry and object motion to remove ambiguity in reconstructing flow from a single image. Specifically, we divide the image into coherently moving regions and use depth to construct flow bases that best explain the observed flow in each region. We achieve state-of-the-art results in unsupervised multi-object segmentation on synthetic and real-world datasets by modeling the scene structure and object motion. Our evaluation of the predicted depth maps shows reliable performance in monocular depth estimation. + +# 1. Introduction + +Finding objects on visual data is one of the oldest problems in computer vision, which has been shown to work to great extent in the presence of labeled data. Achieving it without supervision is important given the difficulty of obtaining pixel-precise masks for the variety of objects encountered in everyday life. In the absence of labels, motion provides important cues to group pixels corresponding to objects. The existing solutions use motion either as input to perform grouping or as output to reconstruct as a way of verifying the predicted grouping. The current methodology fails to incorporate the underlying 3D geometry creating the observed motion. In this work, we show that modeling geometry together with object motion significantly improves the segmentation of multiple objects without supervision. + +Unsupervised multi-object discovery is significantly more challenging than the single-object case due to mutual occlusions. Therefore, earlier methods in unsupervised segmentation focused on separating a foreground object from the background whereas multi-object methods have been mostly limited to synthetic datasets or resorted to additional + +supervision on real-world data such as sparse depth [15]. + +While sparse-depth supervision can be applied to driving scenarios [15], depth information is not typically available on common video datasets. Moreover, video segmentation datasets such as DAVIS [48, 49] contain a wide variety of categories under challenging conditions such as appearance changes due to lighting conditions or motion blur. The motion information can be obtained from video sequences via optical flow. Optical flow not only provides motion cues for grouping [64] but can also be used for training on synthetic data without suffering from the domain gap while transferring to real data [63]. The problems in optical flow prediction on real-world data can be mitigated to some extent by relating flow predictions from multiple frames [63]. + +In addition to problems in predicting optical flow, requiring flow as input prohibits the application of the method on static images. Another line of work [11, 33] uses motion for supervision at train time only. Based on the observation that objects create distinctive patterns in flow, initial work [11] fits a simple parametric model to the flow in each object region to capture the object motion. This way, the network can predict object regions that can potentially move coherently from a single image at test time. There is an inherent ambiguity in predicting motion from a single image. Therefore, the follow-up work [33] predicts a distribution of possible motion patterns to reduce this ambiguity. This also allows extending it to the multi-object case by mitigating the over-segmentation problem of the initial work [11]. + +In this work, we propose to model pixel-wise geometry to remove ambiguity in reconstructing flow from a single image. Optical flow is the difference between the 2D projections of the 3D world in consecutive time steps. By modeling the 3D geometry creating these projections, we directly address the mutual occlusion problem due to interactions of multiple objects. This problem has been crudely addressed by previous work with a depth-ordered layer representation [63]. Instead of assuming a single depth layer per object, we predict pixel-wise depth which provides more expressive power in explaining the observed motion. Furthermore, we do not use flow as input during inference, allowing us to evaluate our method on single-image datasets. + +Recent work [5] showed that motion resides in a low-dimensional subspace, and its reconstruction can be used to supervise monocular depth prediction. Despite many possible flow fields, the space of possible flow fields is spanned by a small number of basis flow fields related to depth and independently moving objects. While [5] focuses on modeling camera motion for quantitatively evaluating depth in static scenes, it also points to the fact that the object motion can be similarly modeled in a low-dimensional subspace by simply masking the points in the object region. Given the difficulty of predicting pixel-wise masks, simple object embeddings are used to cluster independently moving objects. We instead predict the object regions jointly with depth to find the low-dimensional object motion that best explains the observed flow in each region. + +Our approach works extremely well on synthetic Multi-Object Video (MOVi) datasets [23], significantly outperforming previous work, especially in more challenging MOVi-{C,D,E} partitions and performing comparably on visually simpler MOVi-A due to difficulty of estimating depth. We use motion only for supervision at train time, therefore our method can be successfully applied to still images of CLEVR [31] and CLEVRTEX [34] and shows state-of-the-art performance. More impressively, our method can segment multiple objects on real-world videos of DAVIS2017 [49] from a single image at test time, exceeding the performance of the state-of-the-art that uses flow from multiple frames as input [63]. In addition to evaluating segmentation, we show that our method can also reliably predict depth in real-world self-driving scenarios on KITTI [21]. + +# 2. Related Work + +Basis Learning. Early work showed that optical flow estimation due to camera motion can be constrained using a subspace formulation for flow [28]. Basis learning has been used as a regularization in low-level vision, unifying tasks such as depth, flow, and segmentation [55]. PCA-Flow [61] builds a higher dimensional flow subspace from movies to represent flow as a weighted sum of flow bases. Recent work [67] learns the coefficients to combine eight pre-defined flow bases for homography estimation. + +Motion as Input. Most of the work in motion segmentation focuses on the single-object case. While earlier work uses traditional methods to cluster pixels into similar motion groups [6, 35, 47, 62], later methods train deep neural networks which take flow as input and predict segmentation as output [13, 57, 58]. Another work [66] uses the distinctiveness of motion in the case of foreground objects by proposing an adversarial setting to predict motion from context. Segmenting objects in camouflaged settings can be achieved by modeling background motion to remove its effect and highlight the moving foreground object [3, 4, 38]. + +Recent work uses consistency between two flow fields computed under different frame gaps for self-supervision [64]. + +The most relevant to our work is OCLR [63] which extends motion segmentation to multiple objects by relating motion extracted from multiple frames using a transformer in a layered representation. In this work, we show that better results can be achieved on real data even from a single image by modeling pixel-wise geometry. + +Motion for Supervision. While using motion only as input works well where appearance fails, e.g. the camouflage datasets, RGB carries important information that might be missing in flow. DyStaB [65] trains a dynamic model by exploiting motion for temporal consistency and then uses it to bootstrap a static model which takes a single image as input. A single image network is used to predict a segmentation in [40] and then the motion of each segment is predicted with a two-frame motion network. While image warping loss is used in [40] for self-supervision, recent work [11, 33] uses flow reconstruction loss by assuming the availability of flow at train time only. GWM [11] segments foreground objects by fitting an approximate motion model to each segment and then merging them using spectral clustering. The follow-up work [33] extends it to multiple objects by predicting probable motion patterns for each segment with a distribution. We also reconstruct flow for supervision but differently, we account for 3D to remove the ambiguity in reconstructing motion from a single image. + +The most relevant to our work is the previous work that uses flow as a source of supervision for depth [5] or segmentation [11, 34]. In this work, we model both depth and segmentation with supervision from motion. + +Multi-Object Scene Decomposition. Our work is also related to scene decomposition approaches which are mostly evaluated on synthetic datasets. The earlier image-based decomposition approaches such as MONet [7] and IO-DINE [24] use a sequential VAE structure where the decomposition at a step can affect the remaining parts to be explained in the next step. GENESIS [17] follows an object-centric approach by accounting for component interactions, which is extended to more realistic scenarios with an autoregressive prior in the follow-up work [18]. Slot Attention [42] uses an iterative attention mechanism to decompose the image into a set of slot representations. A hierarchical VAE is used in [16] to extract symmetric and disentangled representations. + +There are also video-based approaches to multi-object scene decomposition. SCALOR [30] focuses on scaling generative approaches to crowded scenes in terms of object density. SIMONE [32] learns a factorized latent space to separate object semantics that is constant in the sequence from the background which changes at each frame according to camera motion. SAVi [36] extends Slot Attention [42] + +![](images/329808514883619822e691004d9df586b32f5ddb884d44ddf9d84e0a4f955e32.jpg) +Figure 1: Overview of our Approach. From a single image, we use a segmentation and a depth network to predict a segmentation mask $\mathbf{m}$ and a disparity map $\mathbf{d}$ . Based on these predictions, we construct the bases for the space of the possible optical flows for $K$ distinctly moving regions on the image. Each moving region $i$ is represented with a separate basis $\mathcal{B}_i$ . Given optical flow $\mathbf{F}$ as input, either ground truth or estimated by an off-the-shelf method, we project it into $\mathrm{span}(\bigcup_{i=1}^{K} \mathcal{B}_i)$ . We use the distance between the input flow $\mathbf{F}$ and the projected flow $\hat{\mathbf{F}}$ to supervise depth and segmentation. During inference, our networks can be used to predict depth and segmentation from a single image. + +to videos and $\mathrm{SAVi}++$ [15] extends it to real-world driving scenarios with sparse depth supervision. + +Self-Supervised Monocular Depth Estimation. Zhou et al. [69] train a pose network to estimate the pose between the frames in a sequence and jointly train it with the depth network. Godard et al. [22] improves the results with a better loss function and other design choices. Guizilini et al. [25] learn detail-preserving representations using 3D packing and unpacking blocks. Given instance segmentation masks, a line of work [9, 39] models the motion of objects in the scene in addition to the camera motion to go beyond the static-scene assumption. While the object masks are supervised using ground truth masks in [37], the masks are learned without supervision as an auxiliary output in [53] for better depth estimation. While they require multiple frames during inference, our approach can estimate masks from a single image. Additionally, our method does not use camera intrinsics. + +# 3. Depth-Aware Multi-Object Segmentation + +The observed motion in 2D is the result of 3D scene structure and independently moving objects. By predicting the scene structure in terms of depth and locating independently moving objects, we can accurately reconstruct the optical flow corresponding to the observed motion in 2D. Towards this purpose, we use a low-dimensional parameterization of optical flow based on depth (Section 3.1). In this low-dimensional representation, we can accurately reconstruct flow from a rigid motion. We extend this parametriza + +tion to a number of rigidly moving objects to find the regions corresponding to objects (Section 3.2). See Fig. 1 for an overview of our approach. + +# 3.1. Low-Dimensional Motion Representation + +The space of all possible optical flow fields is very high-dimensional, i.e. in $\mathbb{R}^{H\times W\times 2}$ . However, conditioned on the scene structure, only a small fraction of all flow fields are possible. Previous work [27, 5] has shown that the set of possible instantaneous flows for a moving camera in a static scene forms a linear space with six basis vectors: + +$$ +\mathcal {B} _ {0} = \left\{\mathbf {b} _ {\mathbf {T} x}, \mathbf {b} _ {\mathbf {T} y}, \mathbf {b} _ {\mathbf {T} z}, \mathbf {b} _ {\mathbf {R} x}, \mathbf {b} _ {\mathbf {R} y}, \mathbf {b} _ {\mathbf {R} z} \right\} \tag {1} +$$ + +These basis vectors correspond to translation and rotation along the $x, y$ , and $z$ axes, respectively. For an image $\mathbf{I} \in \mathbb{R}^{H \times W \times 3}$ , the values of each basis vector $\mathbf{b}_i \in \mathbb{R}^{H \times W \times 2}$ for a given pixel $(u, v)$ can be calculated as follows: + +$$ +\mathbf {b} _ {\mathbf {T} x} = \left[ \begin{array}{c} f _ {x} d \\ 0 \end{array} \right], \quad \mathbf {b} _ {\mathbf {R} x} = \left[ \begin{array}{c} f _ {y} ^ {- 1} \bar {u} \bar {v} \\ f _ {y} + f _ {y} ^ {- 1} \bar {v} ^ {2} \end{array} \right] +$$ + +$$ +\mathbf {b} _ {\mathbf {T} y} = \left[ \begin{array}{c} 0 \\ f _ {y} d \end{array} \right], \quad \mathbf {b} _ {\mathbf {R} y} = \left[ \begin{array}{c} f _ {x} + f _ {x} ^ {- 1} \bar {u} ^ {2} \\ f _ {x} ^ {- 1} \bar {u} \bar {v} \end{array} \right] +$$ + +$$ +\mathbf {b} _ {\mathbf {T} z} = \left[ \begin{array}{l} - \bar {u} d \\ - \bar {v} d \end{array} \right], \quad \mathbf {b} _ {\mathbf {R} z} = \left[ \begin{array}{l} f _ {x} f _ {y} ^ {- 1} \bar {v} \\ - f _ {y} f _ {x} ^ {- 1} \bar {u} \end{array} \right] \tag {2} +$$ + +where $f_{x}, f_{y}$ are the focal lengths of the camera. For brevity, we define $\bar{u} = u - c_{x}$ and $\bar{v} = v - c_{y}$ to be the centered pixel coordinates according to $(c_{x}, c_{y})$ , the principal point of the camera. With a slight abuse of notation, we + +do not write the basis vectors as a function of $(u,v)$ and use $d$ to denote the disparity $\mathbf{d}(u,v)$ at a pixel $(u,v)$ . + +We train a monocular depth network to predict inverse depth, disparity $\mathbf{d}$ from a single image. Then, the predicted disparity at each pixel is used to form the translation part of the basis vectors as shown in Eq. (2). Note that predicted disparity values do not affect the rotation but form the low-dimensional motion representation via translation. The depth network receives gradients directly from the flow reconstruction loss as explained next in Section 3.2. + +In Eq. (2), camera parameters including the principal point $(c_x, c_y)$ and the focal lengths $f_x$ , $f_y$ are required to calculate the basis vectors. We assume the principal points to be at the center of the image. However, we do not assume to know the values of focal lengths. Instead, we only assume that $f_x = f_y$ . In this case, as demonstrated by [5], we can rewrite $\mathcal{B}_0$ as a set of 8 vectors that do not depend on the values of $f_x$ and $f_y$ . For more details, please see Supplementary. Even without knowing the actual values of the focal lengths, we can obtain quite accurate depth predictions with supervision from flow (Section 4). + +# 3.2. Segmentation by Object Motion + +We extend the formulation introduced in Section 3.1 to handle the instantaneous flow from multiple object motion. As stated in [5], for a rigidly moving object in the scene, there is an equivalent camera motion. Therefore the space of optical flow from a rigidly moving object is the same as the space of optical flow from camera motion restricted to points in the object. Consider a scene with $K$ regions corresponding to moving parts including the background and multiple objects. If we represent each region $i \in \{1, \dots, K\}$ with ones on a binary mask $\mathbf{m}_i \in \{0, 1\}^{H \times W \times 1}$ , then a basis for the space of possible flows can be defined as follows: + +$$ +\mathcal {B} = \left\{\mathcal {B} _ {1} \cup \mathcal {B} _ {2} \cup \dots \mathcal {B} _ {K} \right\} \tag {3} +$$ + +where $\mathcal{B}_i$ refers to the basis for the space of possible flows restricted to region $i$ as: + +$$ +\mathcal {B} _ {i} = \left\{\mathbf {m} _ {i} \mathbf {b} \mid \mathbf {b} \in \mathcal {B} _ {0} \right\}. \tag {4} +$$ + +We train a segmentation network to divide the image into coherently moving regions $\mathbf{m} \in [0,1]^{H \times W \times K}$ , representing soft assignments over $K$ regions. We use the predicted mask $\mathbf{m}_i \in [0,1]^{H \times W \times 1}$ of the region $i$ to obtain the basis corresponding to that region according to Eq. (4). + +Training Objective. Based on the predicted disparity map $\mathbf{d}$ and the segmentation map $\mathbf{m}$ , we form the basis $\mathcal{B}$ for the space of possible optical flows for the image according to Eq. (3) and Eq. (4). We denote the optical flow where the input image is the source frame as $\mathbf{F} \in \mathbb{R}^{H \times W \times 2}$ . It can be either ground truth flow or the output of a two-frame flow + +network such as RAFT [56]. We project $\mathbf{F}$ into the space spanned by $\mathcal{B}$ in a differentiable manner to obtain $\hat{\mathbf{F}}$ . For the details of the projection, please refer to Supplementary. We define our loss function as the $L_{2}$ distance between the given flow $\mathbf{F}$ and the reconstructed flow $\hat{\mathbf{F}}$ and use it to train depth and segmentation networks jointly: + +$$ +\mathcal {L} = \left\| \mathbf {F} - \hat {\mathbf {F}} \right\| _ {2} \tag {5} +$$ + +# 4. Experiments + +# 4.1. Datasets + +Synthetic Datasets. For comparison to image-based methods, we evaluate our method on the CLEVR [31] and CLEVRTEX [34] datasets. CLEVR is a dataset of still images depicting multiple objects of random shape, size, color, and position. CLEVRTEX is similar to CLEVR but contains more diverse textures and shapes. Because our method needs optical flow for training, we train our model on the MOVINGCLEVR and MOVINGCLEVRTEX datasets [33], which are video extensions of CLEVR and CLEVRTEX scenes. We train on the video versions but evaluate on the original test sets of CLEVR and CLEVRTEX. + +For comparison to video-based methods, we use the Multi-Object Video (MOVi) datasets [23]. Similar to [33], we use the MOVi-{A, C, D, E} variants. MOVi-A is based on CLEVR [31] and contains scenes with a static camera and multiple objects with simple textures and uniform colors tossed on a gray floor. MOVi-C is more challenging due to realistic everyday objects with rich textures on a more complex background. MOVi-D increases the complexity by increasing the number of objects. MOVi-E is even more challenging as it features camera motion as well. + +In all our experiments on synthetic datasets, we use a resolution of $128 \times 128$ and the ground truth optical flow. + +Real-World Datasets. We use the common video segmentation dataset DAVIS-2017 [49] containing 90 video sequences where each sequence has one or more moving objects. We follow the evaluation protocol of [63] where the ground truth objects are reannotated by assigning the same label to the jointly moving objects. We resize the images to a resolution of $128 \times 224$ during training and use the flow from RAFT [56] with $\{-8, -4, 4, 8\}$ gaps between frames. + +Additionally, we evaluate our method on the KITTI driving dataset [21, 20]. Following [2], we train on the whole training set and evaluate the segmentation results on the instance segmentation benchmark consisting of 200 frames. We use a resolution of $128 \times 416$ and the flow from RAFT [56] with a gap of $+1$ . Additionally, we evaluate our depth results on KITTI. Following prior work [69, 22], we evaluate depth on the Eigen split [14] of the KITTI dataset using improved ground truth [59] to be comparable to self-supervised monocular depth estimation approaches. + +![](images/2c62286bfee8aaa8447521c058acf80d2ffec3cb53fdd8f2805943bb38105671.jpg) +Figure 2: Visualization of Depth and Segmentation Results on MOVi datasets. Our method performs accurate segmentations, while PPMP suffers from over-segmentation and also mistakenly segments parts of the background as objects. + +# 4.2. Architecture Details + +We use the same architecture used in [50] for depth and Mask2Former [10] for segmentation, using only the segmentation head. We use different backbones for the segmentation network on the synthetic and real datasets. On synthetic datasets, we follow [33, 36, 42] and utilize a 6-layer CNN. On real-world datasets, following [11], we use a ViT-B/8 transformer pre-trained self-supervised using DINO [8] on ImageNet [52]. On all of the datasets, we use 6 object queries in the segmentation network, which translates to $K = 6$ , except for CLEVR, where we use $K = 8$ . + +We use a fixed learning rate of $5 \times 10^{-5}$ for the depth network and use $1.5 \times 10^{-4}$ with a linear warm-up for the first 5K iterations for the segmentation network, reduced to $1.5 \times 10^{-5}$ after 200K iterations. We train both networks with AdamW optimizer [43] for 250K iterations. See Supplementary for further details, we will also share the code. + +# 4.3. Evaluation Details + +Metrics. Following prior work [34, 36, 33], we evaluate segmentation on synthetic datasets using Adjusted Rand Index on foreground pixels (FG-ARI) and mean Intersection over Union (mIoU). ARI measures how well predicted and + +ground truth segmentation masks match in a permutation-invariant manner. For mIoU, we first apply Hungarian matching and calculate the mean over the maximum between the number of ground-truth and predicted segments. + +On DAVIS-2017 [49], we use the standard $\mathcal{I}$ , $\mathcal{F}$ metrics and perform the Hungarian matching per frame, similar to other datasets. Note that we focus on the multi-object segmentation task without using any labels for segmentation at train or test time. For KITTI, we use the FG-ARI metric, following [33, 2]. For evaluating depth, we use the standard metrics used in monocular depth estimation [14, 19]. + +Post-processing. We also report the results on segmentation using the post-processing method introduced in [33]. They extract the connected components in the model output and choose the largest $K$ masks and discard any masks that take up less than $0.1\%$ of the image. Then they combine the discarded masks with the largest mask. The results with post-processing are marked with $^{\dagger}$ in the tables. + +# 4.4. Results on Synthetic Datasets + +We evaluate our method on synthetic datasets and compare its performance to both image-based and video-based methods. Our method uses motion during training only. Therefore, it can also be evaluated on the image datasets. + +
MOVi-AMOVi-CMOVi-DMOVi-E
FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑
GWM [10]70.3042.2749.9830.1739.7818.3842.5018.74
SCALOR [30]59.5744.4140.4322.54----
SAVi [36]88.3062.6943.2631.9243.4510.6017.395.75
PPMP [33]84.0160.0861.1834.7255.7423.5062.6225.78
\( PPMP^† \)85.4176.1961.2437.2655.1825.2163.1128.59
\( PPMP^† (Swin) \)90.0884.7667.6752.1766.4130.4072.7335.30
Ours56.0936.4873.8054.4876.4158.8278.3347.38
\( Ours^† \)70.1546.2674.6459.2477.1559.6880.8350.48
+ +Video-Based Methods. We compare our method to other video-based methods on the MOVi video datasets in Table 1 and Fig. 2. All of the methods in Table 1 use optical flow for supervision. Differently, SCALOR [30] and SAVi [36] use all frames in a video, whereas PPMP [33] and our method perform single-image segmentation, one frame at a time without using any motion information at test time. On the simpler MOVi-A dataset, the performance of our method falls behind SAVi [36] and PPMP [33]. PPMP with Swin transformer [41] performs the best overall. With the same 6-layer CNN backbone and without post-processing, SAVi performs the best. Despite the advantage of motion information, the success of SCALOR [30] and SAVi [36] is limited to visually simpler MOVi-A. + +On the more challenging MOVi- $\{\mathrm{C},\mathrm{D},\mathrm{E}\}$ datasets, our method, even without post-processing, significantly outperforms all the previous methods in both metrics, with or without post-processing. The previous state-of-the-art, PPMP [33] uses the same backbone in their segmentation network as ours. Even with a more powerful backbone (Swin transformer [41]) and post-processing, the results of PPMP are still far behind our results without any post-processing. From MOVi-C to MOVi-E, the performance gap between our method and the others increases as the complexity of the dataset increases. Please see Supplementary for qualitative results with post-processing and evaluation of our estimated depth for objects in these datasets. + +Image-Based Methods. We compare our method to other image-based methods on the CLEVR and CLEVRTEX datasets in Table 2. Our method outperforms the state-of-the-art method PPMP [33] in all metrics on both datasets except for mIoU on CLEVR without postprocessing and mIoU on CLEVRTEX with postprocessing. We point to +9.01 improvement in mIoU on the more challenging CLEVRTEX dataset without postprocessing. See Supplementary for qualitative results on CLEVR and CLEVRTEX. + +# 4.5. Results on Real-World Datasets + +We compare our method to multi-object segmentation methods on real-world datasets including driving scenarios on KITTI and unconstrained videos on DAVIS-2017. + +Results on DAVIS. Our method is the first image-based method to report performance in multi-object segmentation without using any labels during training or testing on + +Table 1: Segmentation Results on MOVi Datasets. The best result in each column is shown in bold, and the second best is underlined. $\dagger$ indicates post-processing, and (Swin) denotes using a Swin transformer as the backbone. + +
CLEVRCLEVRTEX
FG-ARI↑mIoU↑FG-ARI↑mIoU↑
SPAIR [12]77.1365.950.000.00
MN [54]72.1256.8138.3110.46
MONet [7]54.4730.6636.6619.78
SA [42]95.8936.6162.4022.58
IODINE [24]93.8145.1459.5229.17
DTI-S [46]59.5448.7479.9033.79
GNM [29]65.0559.9253.3742.25
SAVi [36]--49.5431.88
PPMP [32]91.6966.7090.8055.07
Ours95.0363.3694.6664.08
SPAIR†[12]77.0566.870.000.00
MN†[54]72.0857.6138.3410.34
MONet†[7]61.3645.6135.6423.59
SA†[42]94.8837.6861.6021.96
IODINE†[24]93.6844.2060.6329.40
DTI-S†[46]89.8653.3879.8632.20
GNM†[29]65.6763.3853.3844.30
PPMP†[33]95.9484.8692.6177.67
Ours†96.9586.3895.3270.28
+ +Table 2: Segmentation Results on CLEVR and CLEVRTex Datasets. The lower part with $\dagger$ shows the results with post-processing. The best result in each column is shown in bold, and the second best is underlined. + +![](images/4cb046bd9b344cd30a5892551a9b4f31bda5980bb36e585f347dee4b568bf301.jpg) +Figure 3: Qualitative Comparison on DAVIS-2017. While OCLR [63] misses some objects completely and suffers from relying on only optical flow as input, our method can segment a wide variety of multiple objects in everyday scenes. + +DAVIS-2017. Therefore, in Table 3, we compare it to video-based approaches which use motion as input. We also compare to a simple baseline proposed in [63] based on Mask R-CNN [26] using optical flow as input. We use the labels re-annotated by [63] for evaluation, as explained in Section 4.1. Motion Grouping refers to [64] trained on DAVIS-2017. Motion Grouping (sup.), Mask R-CNN (flow) and OCLR are models trained on synthetic data from [63] in a supervised way using optical flow as input. Our method, which uses a single RGB image as input at test time, outperforms previous methods, including the state-of-the-art OCLR [63] that uses flow from multiple time steps. Ours-M refers to a version of our model where we adapt the spectral clustering approach of [11] to merge our predicted regions into the ground truth number of regions in each frame. + +
ModelJ& F↑J↑F↑
Motion Grouping [64]35.838.433.2
Motion Grouping (sup.)39.544.934.2
Mask R-CNN (flow)50.350.450.2
OCLR [63]55.154.555.7
Ours55.355.355.3
Ours-M59.259.359.2
+ +Table 3: Multi-Object Segmentation Results on DAVIS-2017. We evaluate by using the motion labels from [63]. + +Although not necessary to achieve state-of-the-art, this improves the results significantly. + +We visualize the results of our model in comparison to OCLR [63] in Fig. 3. Our method can correctly segment a wide variety of objects such as the bike and the person in the first column and the multiple fish in the third, multiple people walking or fighting in the second and fourth. OCLR is highly affected by the inaccuracies in flow, unlike our method, as can be seen from the last two columns. + +Results on KITTI. Since KITTI has ground truth depth, we evaluate our method in terms of both segmentation and monocular depth prediction on KITTI. The segmentation results on KITTI are presented in Table 4a. Our method is among the top-performing methods, outperforming earlier approaches. In addition to segmentation, our method can also predict depth from a single image. We present the evaluation of our depth predictions in comparison to self-supervised monocular depth estimation methods in Table 4b. Our depth network can predict reliable depth maps even without camera intrinsics with comparable results to recent self-supervised monocular depth estimation approaches [22, 25] that are specifically designed for that task and that use camera intrinsics. + +We visualize our segmentation and depth results on KITTI in Supplementary. Our method can segment multiple moving objects such as car, bike, bus without using any semantic labels for training or motion information at test + +
ModelFG-ARI ↑
SA [42]13.8
MONet [7]14.9
SCALAR [30]21.1
S-IODINE [24]14.4
MCG [1]40.9
Ours42.3
Bao et al. [2]47.1
PPMP [33]50.8
+ +(a) Segmentation + +
Abs Rel ↓Sq Rel ↓RSME ↓RMSE log ↓δ < 1.25 ↑δ < 1.252 ↑δ < 1.253 ↑
Zhou et al. [69]0.1761.5326.1290.2440.7580.9210.971
Mahjourian et al. [45]0.1340.9835.5010.2030.8270.9440.981
GeoNet [68]0.1320.9945.2400.1930.8330.9530.985
DDVO [60]0.1260.8664.9320.1850.8510.9580.986
Ranjan et al. [51]0.1230.8814.8340.1810.8600.9590.985
EPC++ [44]0.1200.7894.7550.1770.8560.9610.987
Ours0.1071.5394.0270.1490.9110.9710.989
Monodepth2 [22]0.0900.5453.9420.1370.9140.9830.998
PackNet-SfM [25]0.0780.4203.4850.1210.9340.9860.996
+ +(b) Depth +Table 4: Results on KITTI. We evaluate the segmentation on the instance segmentation benchmark, and the depth on the KITTI Eigen split [14] with improved ground truth [59]. + +
MOVi-AMOVi-CMOVi-DMOVi-E
FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑
Only-T31.1317.7269.6925.8468.6822.7464.6928.26
Only-R90.4375.6368.5153.0070.5756.9773.0340.34
Full56.0936.4873.8054.4876.4158.8278.3347.38
Only-T†47.9629.9269.9426.3168.6622.7669.9430.71
Only-R†92.0984.6069.2355.5471.2058.4176.2042.96
Full†70.1546.2674.6459.2477.1559.6880.8350.48
+ +Table 5: Ablation Study. We perform an ablation study by using only the translation (Only-T) or rotation (Only-R) component and compare it to our model with both (Full). See text for details. + +time. Furthermore, it can predict high-quality depth, capturing thin structures and sharp boundaries around objects. + +# 4.6. Ablation Study + +To evaluate the contribution of different types of flow basis, we perform an experiment by considering only translation or rotation and compare it to the full model on MOVi datasets in Table 5. Note that in the rotation-only case (Only-R), the depth predictions are not used and the depth network is not trained. Overall, the rotation-only model outperforms the translation-only model and the full model with both rotation and translation works the best on MOVi-{C, D, E} datasets with reliable depth predictions. + +The trend is different on the simpler MOVi-A dataset. Only-R outperforms all models including the state-of-the-art in Table 1. We found that in the translation-only case, the depth cannot be predicted on MOVi-A due to missing texture and enough detail for the depth network to learn a mapping from a single image to depth. The rotation-only model, on the other hand, learns to group pixels in a region, based on their rotational motion which does not depend on depth. This ability explains the success of Only-R on simpler datasets. The importance of pixel-wise depth increases with the complexity of the dataset. On MOVi-E, for example, which has the most complex setup with a large number of objects and camera motion, predicting depth, from Only-R to Full, improves the performance the most. + +# 5. Conclusion and Future Work + +We presented a motion-supervised approach for multi-object segmentation that can work with a single RGB image at test time, therefore still applicable to image datasets. Our method is the first to consider geometry to remove ambiguity for multi-object segmentation from a single image without using any labels for segmentation. Modeling geometry significantly advances the state-of-the-art on commonly used synthetic datasets. We also evaluated our method on real-world datasets. Our method is the first image-based multi-object segmentation method to report state-of-the-art results on DAVIS-2017 without using motion at test time. We also report comparable results for depth prediction on KITTI and MOVi datasets where depth can be evaluated. + +Predicting objects that can potentially move independently from a single image requires observing examples of various objects moving in the training set. Moreover, static objects send a mixed signal to the model. The coherent changes in the flow can be captured with the help of geometry as shown in our work. The remaining uncertainty can be addressed with a probabilistic formulation as done in previous state-of-the-art [33]. Another problem is scenes without enough information to predict depth as we observed on textureless MOVi-A. However, the lack of information to this extent rarely happens on real-world data. + +Acknowledgements. Sadra Safadoust was supported by KUIS AI Fellowship and UNVEST R&D Center. + +# References + +[1] P. Arbeláez, J. Pont-Tuset, J. Barron, F. Marques, and J. Malik. Multiscale combinatorial grouping. In CVPR, 2014. 8 +[2] Zhipeng Bao, Pavel Tokmakov, Allan Jabri, Yu-Xiong Wang, Adrien Gaidon, and Martial Hebert. Discovering objects that can move. In CVPR, pages 11789-11798, 2022. 4, 5, 8 +[3] Pia Bideau and Erik G. Learned-Miller. It's moving! a probabilistic model for causal motion segmentation in moving camera videos. In ECCV, 2016. 2 +[4] Pia Bideau, Aruni RoyChowdhury, Rakesh R. Menon, and Erik Learned-Miller. 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In CVPR, 2017. 3, 4, 8 \ No newline at end of file diff --git a/2023/Multi-Object Discovery by Low-Dimensional Object Motion/images.zip b/2023/Multi-Object Discovery by Low-Dimensional Object Motion/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..b933f2a1bf03c72500f20e7704c46f74c2627203 --- /dev/null +++ b/2023/Multi-Object Discovery by Low-Dimensional Object Motion/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:8b0ae2c097378ee3b9da65e8b14e65a17c4a7059094d16306e1742c2b105c0b1 +size 642473 diff --git a/2023/Multi-Object Discovery by Low-Dimensional Object Motion/layout.json b/2023/Multi-Object Discovery by Low-Dimensional Object Motion/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..aa7eb4c0a4bd1afe65c90ec548cb23446c699d3b --- /dev/null +++ b/2023/Multi-Object Discovery by Low-Dimensional Object Motion/layout.json @@ -0,0 +1,7856 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 111, + 103, + 483, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 103, + 483, + 121 + ], + "spans": [ + { + "bbox": [ + 111, + 103, + 483, + 121 + ], + "type": "text", + "content": "Multi-Object Discovery by Low-Dimensional Object Motion" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 114, + 144, + 478, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 114, + 144, + 478, + 185 + ], + "spans": [ + { + "bbox": [ + 114, + 144, + 478, + 185 + ], + "type": "text", + "content": "Sadra Safadoust Fatma Güney \nKUIS AI Center and Department of Computer Engineering, Koç University \nssafadoust20@ku.edu.tr fguney@ku.edu.tr" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "spans": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 239, + 290, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 290, + 430 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 290, + 430 + ], + "type": "text", + "content": "Recent work in unsupervised multi-object segmentation shows impressive results by predicting motion from a single image despite the inherent ambiguity in predicting motion without the next image. On the other hand, the set of possible motions for an image can be constrained to a low-dimensional space by considering the scene structure and moving objects in it. We propose to model pixel-wise geometry and object motion to remove ambiguity in reconstructing flow from a single image. Specifically, we divide the image into coherently moving regions and use depth to construct flow bases that best explain the observed flow in each region. We achieve state-of-the-art results in unsupervised multi-object segmentation on synthetic and real-world datasets by modeling the scene structure and object motion. Our evaluation of the predicted depth maps shows reliable performance in monocular depth estimation." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 453, + 128, + 466 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 453, + 128, + 466 + ], + "spans": [ + { + "bbox": [ + 47, + 453, + 128, + 466 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 474, + 288, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 474, + 288, + 641 + ], + "spans": [ + { + "bbox": [ + 46, + 474, + 288, + 641 + ], + "type": "text", + "content": "Finding objects on visual data is one of the oldest problems in computer vision, which has been shown to work to great extent in the presence of labeled data. Achieving it without supervision is important given the difficulty of obtaining pixel-precise masks for the variety of objects encountered in everyday life. In the absence of labels, motion provides important cues to group pixels corresponding to objects. The existing solutions use motion either as input to perform grouping or as output to reconstruct as a way of verifying the predicted grouping. The current methodology fails to incorporate the underlying 3D geometry creating the observed motion. In this work, we show that modeling geometry together with object motion significantly improves the segmentation of multiple objects without supervision." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": "Unsupervised multi-object discovery is significantly more challenging than the single-object case due to mutual occlusions. Therefore, earlier methods in unsupervised segmentation focused on separating a foreground object from the background whereas multi-object methods have been mostly limited to synthetic datasets or resorted to additional" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 214, + 535, + 226 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 214, + 535, + 226 + ], + "spans": [ + { + "bbox": [ + 305, + 214, + 535, + 226 + ], + "type": "text", + "content": "supervision on real-world data such as sparse depth [15]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 228, + 545, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 228, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 304, + 228, + 545, + 384 + ], + "type": "text", + "content": "While sparse-depth supervision can be applied to driving scenarios [15], depth information is not typically available on common video datasets. Moreover, video segmentation datasets such as DAVIS [48, 49] contain a wide variety of categories under challenging conditions such as appearance changes due to lighting conditions or motion blur. The motion information can be obtained from video sequences via optical flow. Optical flow not only provides motion cues for grouping [64] but can also be used for training on synthetic data without suffering from the domain gap while transferring to real data [63]. The problems in optical flow prediction on real-world data can be mitigated to some extent by relating flow predictions from multiple frames [63]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 388, + 546, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 388, + 546, + 555 + ], + "spans": [ + { + "bbox": [ + 304, + 388, + 546, + 555 + ], + "type": "text", + "content": "In addition to problems in predicting optical flow, requiring flow as input prohibits the application of the method on static images. Another line of work [11, 33] uses motion for supervision at train time only. Based on the observation that objects create distinctive patterns in flow, initial work [11] fits a simple parametric model to the flow in each object region to capture the object motion. This way, the network can predict object regions that can potentially move coherently from a single image at test time. There is an inherent ambiguity in predicting motion from a single image. Therefore, the follow-up work [33] predicts a distribution of possible motion patterns to reduce this ambiguity. This also allows extending it to the multi-object case by mitigating the over-segmentation problem of the initial work [11]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 558, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 547, + 715 + ], + "type": "text", + "content": "In this work, we propose to model pixel-wise geometry to remove ambiguity in reconstructing flow from a single image. Optical flow is the difference between the 2D projections of the 3D world in consecutive time steps. By modeling the 3D geometry creating these projections, we directly address the mutual occlusion problem due to interactions of multiple objects. This problem has been crudely addressed by previous work with a depth-ordered layer representation [63]. Instead of assuming a single depth layer per object, we predict pixel-wise depth which provides more expressive power in explaining the observed motion. Furthermore, we do not use flow as input during inference, allowing us to evaluate our method on single-image datasets." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 493, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 493, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 493, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "text", + "content": "734" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": "Recent work [5] showed that motion resides in a low-dimensional subspace, and its reconstruction can be used to supervise monocular depth prediction. Despite many possible flow fields, the space of possible flow fields is spanned by a small number of basis flow fields related to depth and independently moving objects. While [5] focuses on modeling camera motion for quantitatively evaluating depth in static scenes, it also points to the fact that the object motion can be similarly modeled in a low-dimensional subspace by simply masking the points in the object region. Given the difficulty of predicting pixel-wise masks, simple object embeddings are used to cluster independently moving objects. We instead predict the object regions jointly with depth to find the low-dimensional object motion that best explains the observed flow in each region." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 251, + 289, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 251, + 289, + 431 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 289, + 431 + ], + "type": "text", + "content": "Our approach works extremely well on synthetic Multi-Object Video (MOVi) datasets [23], significantly outperforming previous work, especially in more challenging MOVi-{C,D,E} partitions and performing comparably on visually simpler MOVi-A due to difficulty of estimating depth. We use motion only for supervision at train time, therefore our method can be successfully applied to still images of CLEVR [31] and CLEVRTEX [34] and shows state-of-the-art performance. More impressively, our method can segment multiple objects on real-world videos of DAVIS2017 [49] from a single image at test time, exceeding the performance of the state-of-the-art that uses flow from multiple frames as input [63]. In addition to evaluating segmentation, we show that our method can also reliably predict depth in real-world self-driving scenarios on KITTI [21]." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 442, + 134, + 455 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 442, + 134, + 455 + ], + "spans": [ + { + "bbox": [ + 47, + 442, + 134, + 455 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 468, + 287, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 468, + 287, + 576 + ], + "spans": [ + { + "bbox": [ + 46, + 468, + 287, + 576 + ], + "type": "text", + "content": "Basis Learning. Early work showed that optical flow estimation due to camera motion can be constrained using a subspace formulation for flow [28]. Basis learning has been used as a regularization in low-level vision, unifying tasks such as depth, flow, and segmentation [55]. PCA-Flow [61] builds a higher dimensional flow subspace from movies to represent flow as a weighted sum of flow bases. Recent work [67] learns the coefficients to combine eight pre-defined flow bases for homography estimation." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 582, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 287, + 715 + ], + "type": "text", + "content": "Motion as Input. Most of the work in motion segmentation focuses on the single-object case. While earlier work uses traditional methods to cluster pixels into similar motion groups [6, 35, 47, 62], later methods train deep neural networks which take flow as input and predict segmentation as output [13, 57, 58]. Another work [66] uses the distinctiveness of motion in the case of foreground objects by proposing an adversarial setting to predict motion from context. Segmenting objects in camouflaged settings can be achieved by modeling background motion to remove its effect and highlight the moving foreground object [3, 4, 38]." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": "Recent work uses consistency between two flow fields computed under different frame gaps for self-supervision [64]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "spans": [ + { + "bbox": [ + 304, + 98, + 547, + 170 + ], + "type": "text", + "content": "The most relevant to our work is OCLR [63] which extends motion segmentation to multiple objects by relating motion extracted from multiple frames using a transformer in a layered representation. In this work, we show that better results can be achieved on real data even from a single image by modeling pixel-wise geometry." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 176, + 546, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 176, + 546, + 403 + ], + "spans": [ + { + "bbox": [ + 304, + 176, + 546, + 403 + ], + "type": "text", + "content": "Motion for Supervision. While using motion only as input works well where appearance fails, e.g. the camouflage datasets, RGB carries important information that might be missing in flow. DyStaB [65] trains a dynamic model by exploiting motion for temporal consistency and then uses it to bootstrap a static model which takes a single image as input. A single image network is used to predict a segmentation in [40] and then the motion of each segment is predicted with a two-frame motion network. While image warping loss is used in [40] for self-supervision, recent work [11, 33] uses flow reconstruction loss by assuming the availability of flow at train time only. GWM [11] segments foreground objects by fitting an approximate motion model to each segment and then merging them using spectral clustering. The follow-up work [33] extends it to multiple objects by predicting probable motion patterns for each segment with a distribution. We also reconstruct flow for supervision but differently, we account for 3D to remove the ambiguity in reconstructing motion from a single image." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 405, + 547, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 405, + 547, + 453 + ], + "spans": [ + { + "bbox": [ + 304, + 405, + 547, + 453 + ], + "type": "text", + "content": "The most relevant to our work is the previous work that uses flow as a source of supervision for depth [5] or segmentation [11, 34]. In this work, we model both depth and segmentation with supervision from motion." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 460, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 545, + 628 + ], + "type": "text", + "content": "Multi-Object Scene Decomposition. Our work is also related to scene decomposition approaches which are mostly evaluated on synthetic datasets. The earlier image-based decomposition approaches such as MONet [7] and IO-DINE [24] use a sequential VAE structure where the decomposition at a step can affect the remaining parts to be explained in the next step. GENESIS [17] follows an object-centric approach by accounting for component interactions, which is extended to more realistic scenarios with an autoregressive prior in the follow-up work [18]. Slot Attention [42] uses an iterative attention mechanism to decompose the image into a set of slot representations. A hierarchical VAE is used in [16] to extract symmetric and disentangled representations." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "content": "There are also video-based approaches to multi-object scene decomposition. SCALOR [30] focuses on scaling generative approaches to crowded scenes in terms of object density. SIMONE [32] learns a factorized latent space to separate object semantics that is constant in the sequence from the background which changes at each frame according to camera motion. SAVi [36] extends Slot Attention [42]" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "text", + "content": "735" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 68, + 509, + 251 + ], + "blocks": [ + { + "bbox": [ + 50, + 68, + 509, + 251 + ], + "lines": [ + { + "bbox": [ + 50, + 68, + 509, + 251 + ], + "spans": [ + { + "bbox": [ + 50, + 68, + 509, + 251 + ], + "type": "image", + "image_path": "329808514883619822e691004d9df586b32f5ddb884d44ddf9d84e0a4f955e32.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "lines": [ + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "spans": [ + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "text", + "content": "Figure 1: Overview of our Approach. From a single image, we use a segmentation and a depth network to predict a segmentation mask " + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "inline_equation", + "content": "\\mathbf{m}" + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "text", + "content": " and a disparity map " + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "inline_equation", + "content": "\\mathbf{d}" + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "text", + "content": ". Based on these predictions, we construct the bases for the space of the possible optical flows for " + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "text", + "content": " distinctly moving regions on the image. Each moving region " + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "text", + "content": " is represented with a separate basis " + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "inline_equation", + "content": "\\mathcal{B}_i" + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "text", + "content": ". Given optical flow " + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "inline_equation", + "content": "\\mathbf{F}" + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "text", + "content": " as input, either ground truth or estimated by an off-the-shelf method, we project it into " + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "inline_equation", + "content": "\\mathrm{span}(\\bigcup_{i=1}^{K} \\mathcal{B}_i)" + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "text", + "content": ". We use the distance between the input flow " + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "inline_equation", + "content": "\\mathbf{F}" + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "text", + "content": " and the projected flow " + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{F}}" + }, + { + "bbox": [ + 46, + 261, + 545, + 335 + ], + "type": "text", + "content": " to supervise depth and segmentation. During inference, our networks can be used to predict depth and segmentation from a single image." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 355, + 287, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 355, + 287, + 380 + ], + "spans": [ + { + "bbox": [ + 46, + 355, + 287, + 380 + ], + "type": "text", + "content": "to videos and " + }, + { + "bbox": [ + 46, + 355, + 287, + 380 + ], + "type": "inline_equation", + "content": "\\mathrm{SAVi}++" + }, + { + "bbox": [ + 46, + 355, + 287, + 380 + ], + "type": "text", + "content": " [15] extends it to real-world driving scenarios with sparse depth supervision." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 384, + 288, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 384, + 288, + 576 + ], + "spans": [ + { + "bbox": [ + 46, + 384, + 288, + 576 + ], + "type": "text", + "content": "Self-Supervised Monocular Depth Estimation. Zhou et al. [69] train a pose network to estimate the pose between the frames in a sequence and jointly train it with the depth network. Godard et al. [22] improves the results with a better loss function and other design choices. Guizilini et al. [25] learn detail-preserving representations using 3D packing and unpacking blocks. Given instance segmentation masks, a line of work [9, 39] models the motion of objects in the scene in addition to the camera motion to go beyond the static-scene assumption. While the object masks are supervised using ground truth masks in [37], the masks are learned without supervision as an auxiliary output in [53] for better depth estimation. While they require multiple frames during inference, our approach can estimate masks from a single image. Additionally, our method does not use camera intrinsics." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 586, + 273, + 600 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 273, + 600 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 273, + 600 + ], + "type": "text", + "content": "3. Depth-Aware Multi-Object Segmentation" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 605, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 714 + ], + "type": "text", + "content": "The observed motion in 2D is the result of 3D scene structure and independently moving objects. By predicting the scene structure in terms of depth and locating independently moving objects, we can accurately reconstruct the optical flow corresponding to the observed motion in 2D. Towards this purpose, we use a low-dimensional parameterization of optical flow based on depth (Section 3.1). In this low-dimensional representation, we can accurately reconstruct flow from a rigid motion. We extend this parametriza" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 355, + 545, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 355, + 545, + 392 + ], + "spans": [ + { + "bbox": [ + 305, + 355, + 545, + 392 + ], + "type": "text", + "content": "tion to a number of rigidly moving objects to find the regions corresponding to objects (Section 3.2). See Fig. 1 for an overview of our approach." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 397, + 522, + 410 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 397, + 522, + 410 + ], + "spans": [ + { + "bbox": [ + 305, + 397, + 522, + 410 + ], + "type": "text", + "content": "3.1. Low-Dimensional Motion Representation" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 415, + 545, + 487 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 545, + 487 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 545, + 487 + ], + "type": "text", + "content": "The space of all possible optical flow fields is very high-dimensional, i.e. in " + }, + { + "bbox": [ + 304, + 415, + 545, + 487 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{H\\times W\\times 2}" + }, + { + "bbox": [ + 304, + 415, + 545, + 487 + ], + "type": "text", + "content": ". However, conditioned on the scene structure, only a small fraction of all flow fields are possible. Previous work [27, 5] has shown that the set of possible instantaneous flows for a moving camera in a static scene forms a linear space with six basis vectors:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 342, + 494, + 545, + 507 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 342, + 494, + 545, + 507 + ], + "spans": [ + { + "bbox": [ + 342, + 494, + 545, + 507 + ], + "type": "interline_equation", + "content": "\\mathcal {B} _ {0} = \\left\\{\\mathbf {b} _ {\\mathbf {T} x}, \\mathbf {b} _ {\\mathbf {T} y}, \\mathbf {b} _ {\\mathbf {T} z}, \\mathbf {b} _ {\\mathbf {R} x}, \\mathbf {b} _ {\\mathbf {R} y}, \\mathbf {b} _ {\\mathbf {R} z} \\right\\} \\tag {1}", + "image_path": "45179d74cd6058f7377791495687428f4c56774fe045bc92765c1bd860750c57.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "spans": [ + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "type": "text", + "content": "These basis vectors correspond to translation and rotation along the " + }, + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "type": "inline_equation", + "content": "x, y" + }, + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "type": "text", + "content": " axes, respectively. For an image " + }, + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "type": "inline_equation", + "content": "\\mathbf{I} \\in \\mathbb{R}^{H \\times W \\times 3}" + }, + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "type": "text", + "content": ", the values of each basis vector " + }, + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "type": "inline_equation", + "content": "\\mathbf{b}_i \\in \\mathbb{R}^{H \\times W \\times 2}" + }, + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "type": "text", + "content": " for a given pixel " + }, + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "type": "inline_equation", + "content": "(u, v)" + }, + { + "bbox": [ + 305, + 512, + 545, + 560 + ], + "type": "text", + "content": " can be calculated as follows:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 343, + 565, + 515, + 594 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 565, + 515, + 594 + ], + "spans": [ + { + "bbox": [ + 343, + 565, + 515, + 594 + ], + "type": "interline_equation", + "content": "\\mathbf {b} _ {\\mathbf {T} x} = \\left[ \\begin{array}{c} f _ {x} d \\\\ 0 \\end{array} \\right], \\quad \\mathbf {b} _ {\\mathbf {R} x} = \\left[ \\begin{array}{c} f _ {y} ^ {- 1} \\bar {u} \\bar {v} \\\\ f _ {y} + f _ {y} ^ {- 1} \\bar {v} ^ {2} \\end{array} \\right]", + "image_path": "7c9a940fd2c1f7e1e34f41a4630c85fa55ccb9fe5b759f4f63b6fbbbfc12b7fb.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 343, + 599, + 516, + 628 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 599, + 516, + 628 + ], + "spans": [ + { + "bbox": [ + 343, + 599, + 516, + 628 + ], + "type": "interline_equation", + "content": "\\mathbf {b} _ {\\mathbf {T} y} = \\left[ \\begin{array}{c} 0 \\\\ f _ {y} d \\end{array} \\right], \\quad \\mathbf {b} _ {\\mathbf {R} y} = \\left[ \\begin{array}{c} f _ {x} + f _ {x} ^ {- 1} \\bar {u} ^ {2} \\\\ f _ {x} ^ {- 1} \\bar {u} \\bar {v} \\end{array} \\right]", + "image_path": "4ac0e1968dd5f996f9874336c47d3348752b53b3f2a3d7a2f43b508e2984bb92.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 341, + 633, + 545, + 661 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 341, + 633, + 545, + 661 + ], + "spans": [ + { + "bbox": [ + 341, + 633, + 545, + 661 + ], + "type": "interline_equation", + "content": "\\mathbf {b} _ {\\mathbf {T} z} = \\left[ \\begin{array}{l} - \\bar {u} d \\\\ - \\bar {v} d \\end{array} \\right], \\quad \\mathbf {b} _ {\\mathbf {R} z} = \\left[ \\begin{array}{l} f _ {x} f _ {y} ^ {- 1} \\bar {v} \\\\ - f _ {y} f _ {x} ^ {- 1} \\bar {u} \\end{array} \\right] \\tag {2}", + "image_path": "db9abe5a08fadd55a1c8967efb987ec3b9df3156f460520dad5045dca463b87d.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "inline_equation", + "content": "f_{x}, f_{y}" + }, + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "text", + "content": " are the focal lengths of the camera. For brevity, we define " + }, + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\bar{u} = u - c_{x}" + }, + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\bar{v} = v - c_{y}" + }, + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "text", + "content": " to be the centered pixel coordinates according to " + }, + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "inline_equation", + "content": "(c_{x}, c_{y})" + }, + { + "bbox": [ + 304, + 666, + 545, + 714 + ], + "type": "text", + "content": ", the principal point of the camera. With a slight abuse of notation, we" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 748, + 313, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 748, + 313, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 748, + 313, + 757 + ], + "type": "text", + "content": "736" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "type": "text", + "content": "do not write the basis vectors as a function of " + }, + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "type": "inline_equation", + "content": "(u,v)" + }, + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "type": "text", + "content": " and use " + }, + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "type": "text", + "content": " to denote the disparity " + }, + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "type": "inline_equation", + "content": "\\mathbf{d}(u,v)" + }, + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "type": "text", + "content": " at a pixel " + }, + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "type": "inline_equation", + "content": "(u,v)" + }, + { + "bbox": [ + 46, + 72, + 287, + 95 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 96, + 286, + 191 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 96, + 286, + 191 + ], + "spans": [ + { + "bbox": [ + 46, + 96, + 286, + 191 + ], + "type": "text", + "content": "We train a monocular depth network to predict inverse depth, disparity " + }, + { + "bbox": [ + 46, + 96, + 286, + 191 + ], + "type": "inline_equation", + "content": "\\mathbf{d}" + }, + { + "bbox": [ + 46, + 96, + 286, + 191 + ], + "type": "text", + "content": " from a single image. Then, the predicted disparity at each pixel is used to form the translation part of the basis vectors as shown in Eq. (2). Note that predicted disparity values do not affect the rotation but form the low-dimensional motion representation via translation. The depth network receives gradients directly from the flow reconstruction loss as explained next in Section 3.2." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "spans": [ + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "text", + "content": "In Eq. (2), camera parameters including the principal point " + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "inline_equation", + "content": "(c_x, c_y)" + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "text", + "content": " and the focal lengths " + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "inline_equation", + "content": "f_x" + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "inline_equation", + "content": "f_y" + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "text", + "content": " are required to calculate the basis vectors. We assume the principal points to be at the center of the image. However, we do not assume to know the values of focal lengths. Instead, we only assume that " + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "inline_equation", + "content": "f_x = f_y" + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "text", + "content": ". In this case, as demonstrated by [5], we can rewrite " + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "inline_equation", + "content": "\\mathcal{B}_0" + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "text", + "content": " as a set of 8 vectors that do not depend on the values of " + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "inline_equation", + "content": "f_x" + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "inline_equation", + "content": "f_y" + }, + { + "bbox": [ + 46, + 192, + 287, + 323 + ], + "type": "text", + "content": ". For more details, please see Supplementary. Even without knowing the actual values of the focal lengths, we can obtain quite accurate depth predictions with supervision from flow (Section 4)." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 331, + 219, + 342 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 331, + 219, + 342 + ], + "spans": [ + { + "bbox": [ + 47, + 331, + 219, + 342 + ], + "type": "text", + "content": "3.2. Segmentation by Object Motion" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 349, + 286, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 349, + 286, + 491 + ], + "spans": [ + { + "bbox": [ + 46, + 349, + 286, + 491 + ], + "type": "text", + "content": "We extend the formulation introduced in Section 3.1 to handle the instantaneous flow from multiple object motion. As stated in [5], for a rigidly moving object in the scene, there is an equivalent camera motion. Therefore the space of optical flow from a rigidly moving object is the same as the space of optical flow from camera motion restricted to points in the object. Consider a scene with " + }, + { + "bbox": [ + 46, + 349, + 286, + 491 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 349, + 286, + 491 + ], + "type": "text", + "content": " regions corresponding to moving parts including the background and multiple objects. If we represent each region " + }, + { + "bbox": [ + 46, + 349, + 286, + 491 + ], + "type": "inline_equation", + "content": "i \\in \\{1, \\dots, K\\}" + }, + { + "bbox": [ + 46, + 349, + 286, + 491 + ], + "type": "text", + "content": " with ones on a binary mask " + }, + { + "bbox": [ + 46, + 349, + 286, + 491 + ], + "type": "inline_equation", + "content": "\\mathbf{m}_i \\in \\{0, 1\\}^{H \\times W \\times 1}" + }, + { + "bbox": [ + 46, + 349, + 286, + 491 + ], + "type": "text", + "content": ", then a basis for the space of possible flows can be defined as follows:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 114, + 501, + 286, + 514 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 114, + 501, + 286, + 514 + ], + "spans": [ + { + "bbox": [ + 114, + 501, + 286, + 514 + ], + "type": "interline_equation", + "content": "\\mathcal {B} = \\left\\{\\mathcal {B} _ {1} \\cup \\mathcal {B} _ {2} \\cup \\dots \\mathcal {B} _ {K} \\right\\} \\tag {3}", + "image_path": "9f47fda17d9170e803510255c1578d2c16447322c4a77fae0cd404655519ffcd.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 522, + 286, + 546 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 522, + 286, + 546 + ], + "spans": [ + { + "bbox": [ + 46, + 522, + 286, + 546 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 522, + 286, + 546 + ], + "type": "inline_equation", + "content": "\\mathcal{B}_i" + }, + { + "bbox": [ + 46, + 522, + 286, + 546 + ], + "type": "text", + "content": " refers to the basis for the space of possible flows restricted to region " + }, + { + "bbox": [ + 46, + 522, + 286, + 546 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 522, + 286, + 546 + ], + "type": "text", + "content": " as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 118, + 555, + 286, + 567 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 118, + 555, + 286, + 567 + ], + "spans": [ + { + "bbox": [ + 118, + 555, + 286, + 567 + ], + "type": "interline_equation", + "content": "\\mathcal {B} _ {i} = \\left\\{\\mathbf {m} _ {i} \\mathbf {b} \\mid \\mathbf {b} \\in \\mathcal {B} _ {0} \\right\\}. \\tag {4}", + "image_path": "7478cd74ff7a2650669b97d64a96d2b9c8796642011b304c2e99faa28a7ae165.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 576, + 286, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 576, + 286, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 576, + 286, + 635 + ], + "type": "text", + "content": "We train a segmentation network to divide the image into coherently moving regions " + }, + { + "bbox": [ + 46, + 576, + 286, + 635 + ], + "type": "inline_equation", + "content": "\\mathbf{m} \\in [0,1]^{H \\times W \\times K}" + }, + { + "bbox": [ + 46, + 576, + 286, + 635 + ], + "type": "text", + "content": ", representing soft assignments over " + }, + { + "bbox": [ + 46, + 576, + 286, + 635 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 576, + 286, + 635 + ], + "type": "text", + "content": " regions. We use the predicted mask " + }, + { + "bbox": [ + 46, + 576, + 286, + 635 + ], + "type": "inline_equation", + "content": "\\mathbf{m}_i \\in [0,1]^{H \\times W \\times 1}" + }, + { + "bbox": [ + 46, + 576, + 286, + 635 + ], + "type": "text", + "content": " of the region " + }, + { + "bbox": [ + 46, + 576, + 286, + 635 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 576, + 286, + 635 + ], + "type": "text", + "content": " to obtain the basis corresponding to that region according to Eq. (4)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "text", + "content": "Training Objective. Based on the predicted disparity map " + }, + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{d}" + }, + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "text", + "content": " and the segmentation map " + }, + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{m}" + }, + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "text", + "content": ", we form the basis " + }, + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{B}" + }, + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "text", + "content": " for the space of possible optical flows for the image according to Eq. (3) and Eq. (4). We denote the optical flow where the input image is the source frame as " + }, + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{F} \\in \\mathbb{R}^{H \\times W \\times 2}" + }, + { + "bbox": [ + 46, + 641, + 286, + 713 + ], + "type": "text", + "content": ". It can be either ground truth flow or the output of a two-frame flow" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": "network such as RAFT [56]. We project " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\mathbf{F}" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " into the space spanned by " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\mathcal{B}" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " in a differentiable manner to obtain " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{F}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": ". For the details of the projection, please refer to Supplementary. We define our loss function as the " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " distance between the given flow " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\mathbf{F}" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " and the reconstructed flow " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{F}}" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " and use it to train depth and segmentation networks jointly:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 393, + 151, + 545, + 165 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 393, + 151, + 545, + 165 + ], + "spans": [ + { + "bbox": [ + 393, + 151, + 545, + 165 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\left\\| \\mathbf {F} - \\hat {\\mathbf {F}} \\right\\| _ {2} \\tag {5}", + "image_path": "92ffea96e4c97a9d5f01282544ed120ade665aa0c7848f62fcd2244cb7ee66c6.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 174, + 386, + 186 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 174, + 386, + 186 + ], + "spans": [ + { + "bbox": [ + 305, + 174, + 386, + 186 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 193, + 368, + 205 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 193, + 368, + 205 + ], + "spans": [ + { + "bbox": [ + 305, + 193, + 368, + 205 + ], + "type": "text", + "content": "4.1. Datasets" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 217, + 545, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 217, + 545, + 348 + ], + "spans": [ + { + "bbox": [ + 304, + 217, + 545, + 348 + ], + "type": "text", + "content": "Synthetic Datasets. For comparison to image-based methods, we evaluate our method on the CLEVR [31] and CLEVRTEX [34] datasets. CLEVR is a dataset of still images depicting multiple objects of random shape, size, color, and position. CLEVRTEX is similar to CLEVR but contains more diverse textures and shapes. Because our method needs optical flow for training, we train our model on the MOVINGCLEVR and MOVINGCLEVRTEX datasets [33], which are video extensions of CLEVR and CLEVRTEX scenes. We train on the video versions but evaluate on the original test sets of CLEVR and CLEVRTEX." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 349, + 545, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 349, + 545, + 468 + ], + "spans": [ + { + "bbox": [ + 304, + 349, + 545, + 468 + ], + "type": "text", + "content": "For comparison to video-based methods, we use the Multi-Object Video (MOVi) datasets [23]. Similar to [33], we use the MOVi-{A, C, D, E} variants. MOVi-A is based on CLEVR [31] and contains scenes with a static camera and multiple objects with simple textures and uniform colors tossed on a gray floor. MOVi-C is more challenging due to realistic everyday objects with rich textures on a more complex background. MOVi-D increases the complexity by increasing the number of objects. MOVi-E is even more challenging as it features camera motion as well." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 468, + 545, + 492 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 468, + 545, + 492 + ], + "spans": [ + { + "bbox": [ + 305, + 468, + 545, + 492 + ], + "type": "text", + "content": "In all our experiments on synthetic datasets, we use a resolution of " + }, + { + "bbox": [ + 305, + 468, + 545, + 492 + ], + "type": "inline_equation", + "content": "128 \\times 128" + }, + { + "bbox": [ + 305, + 468, + 545, + 492 + ], + "type": "text", + "content": " and the ground truth optical flow." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 498, + 545, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 545, + 594 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 545, + 594 + ], + "type": "text", + "content": "Real-World Datasets. We use the common video segmentation dataset DAVIS-2017 [49] containing 90 video sequences where each sequence has one or more moving objects. We follow the evaluation protocol of [63] where the ground truth objects are reannotated by assigning the same label to the jointly moving objects. We resize the images to a resolution of " + }, + { + "bbox": [ + 304, + 498, + 545, + 594 + ], + "type": "inline_equation", + "content": "128 \\times 224" + }, + { + "bbox": [ + 304, + 498, + 545, + 594 + ], + "type": "text", + "content": " during training and use the flow from RAFT [56] with " + }, + { + "bbox": [ + 304, + 498, + 545, + 594 + ], + "type": "inline_equation", + "content": "\\{-8, -4, 4, 8\\}" + }, + { + "bbox": [ + 304, + 498, + 545, + 594 + ], + "type": "text", + "content": " gaps between frames." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": "Additionally, we evaluate our method on the KITTI driving dataset [21, 20]. Following [2], we train on the whole training set and evaluate the segmentation results on the instance segmentation benchmark consisting of 200 frames. We use a resolution of " + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "inline_equation", + "content": "128 \\times 416" + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": " and the flow from RAFT [56] with a gap of " + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "inline_equation", + "content": "+1" + }, + { + "bbox": [ + 304, + 594, + 545, + 713 + ], + "type": "text", + "content": ". Additionally, we evaluate our depth results on KITTI. Following prior work [69, 22], we evaluate depth on the Eigen split [14] of the KITTI dataset using improved ground truth [59] to be comparable to self-supervised monocular depth estimation approaches." + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "text", + "content": "737" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 89, + 68, + 504, + 371 + ], + "blocks": [ + { + "bbox": [ + 89, + 68, + 504, + 371 + ], + "lines": [ + { + "bbox": [ + 89, + 68, + 504, + 371 + ], + "spans": [ + { + "bbox": [ + 89, + 68, + 504, + 371 + ], + "type": "image", + "image_path": "2c62286bfee8aaa8447521c058acf80d2ffec3cb53fdd8f2805943bb38105671.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 378, + 546, + 403 + ], + "lines": [ + { + "bbox": [ + 46, + 378, + 546, + 403 + ], + "spans": [ + { + "bbox": [ + 46, + 378, + 546, + 403 + ], + "type": "text", + "content": "Figure 2: Visualization of Depth and Segmentation Results on MOVi datasets. Our method performs accurate segmentations, while PPMP suffers from over-segmentation and also mistakenly segments parts of the background as objects." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 415, + 165, + 426 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 415, + 165, + 426 + ], + "spans": [ + { + "bbox": [ + 47, + 415, + 165, + 426 + ], + "type": "text", + "content": "4.2. Architecture Details" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 434, + 287, + 554 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 434, + 287, + 554 + ], + "spans": [ + { + "bbox": [ + 46, + 434, + 287, + 554 + ], + "type": "text", + "content": "We use the same architecture used in [50] for depth and Mask2Former [10] for segmentation, using only the segmentation head. We use different backbones for the segmentation network on the synthetic and real datasets. On synthetic datasets, we follow [33, 36, 42] and utilize a 6-layer CNN. On real-world datasets, following [11], we use a ViT-B/8 transformer pre-trained self-supervised using DINO [8] on ImageNet [52]. On all of the datasets, we use 6 object queries in the segmentation network, which translates to " + }, + { + "bbox": [ + 46, + 434, + 287, + 554 + ], + "type": "inline_equation", + "content": "K = 6" + }, + { + "bbox": [ + 46, + 434, + 287, + 554 + ], + "type": "text", + "content": ", except for CLEVR, where we use " + }, + { + "bbox": [ + 46, + 434, + 287, + 554 + ], + "type": "inline_equation", + "content": "K = 8" + }, + { + "bbox": [ + 46, + 434, + 287, + 554 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 555, + 287, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 555, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 555, + 287, + 628 + ], + "type": "text", + "content": "We use a fixed learning rate of " + }, + { + "bbox": [ + 46, + 555, + 287, + 628 + ], + "type": "inline_equation", + "content": "5 \\times 10^{-5}" + }, + { + "bbox": [ + 46, + 555, + 287, + 628 + ], + "type": "text", + "content": " for the depth network and use " + }, + { + "bbox": [ + 46, + 555, + 287, + 628 + ], + "type": "inline_equation", + "content": "1.5 \\times 10^{-4}" + }, + { + "bbox": [ + 46, + 555, + 287, + 628 + ], + "type": "text", + "content": " with a linear warm-up for the first 5K iterations for the segmentation network, reduced to " + }, + { + "bbox": [ + 46, + 555, + 287, + 628 + ], + "type": "inline_equation", + "content": "1.5 \\times 10^{-5}" + }, + { + "bbox": [ + 46, + 555, + 287, + 628 + ], + "type": "text", + "content": " after 200K iterations. We train both networks with AdamW optimizer [43] for 250K iterations. See Supplementary for further details, we will also share the code." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 639, + 156, + 651 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 639, + 156, + 651 + ], + "spans": [ + { + "bbox": [ + 47, + 639, + 156, + 651 + ], + "type": "text", + "content": "4.3. Evaluation Details" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": "Metrics. Following prior work [34, 36, 33], we evaluate segmentation on synthetic datasets using Adjusted Rand Index on foreground pixels (FG-ARI) and mean Intersection over Union (mIoU). ARI measures how well predicted and" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 415, + 545, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 415, + 545, + 462 + ], + "spans": [ + { + "bbox": [ + 304, + 415, + 545, + 462 + ], + "type": "text", + "content": "ground truth segmentation masks match in a permutation-invariant manner. For mIoU, we first apply Hungarian matching and calculate the mean over the maximum between the number of ground-truth and predicted segments." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 463, + 546, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 463, + 546, + 548 + ], + "spans": [ + { + "bbox": [ + 304, + 463, + 546, + 548 + ], + "type": "text", + "content": "On DAVIS-2017 [49], we use the standard " + }, + { + "bbox": [ + 304, + 463, + 546, + 548 + ], + "type": "inline_equation", + "content": "\\mathcal{I}" + }, + { + "bbox": [ + 304, + 463, + 546, + 548 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 463, + 546, + 548 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 304, + 463, + 546, + 548 + ], + "type": "text", + "content": " metrics and perform the Hungarian matching per frame, similar to other datasets. Note that we focus on the multi-object segmentation task without using any labels for segmentation at train or test time. For KITTI, we use the FG-ARI metric, following [33, 2]. For evaluating depth, we use the standard metrics used in monocular depth estimation [14, 19]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 553, + 547, + 638 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 553, + 547, + 638 + ], + "spans": [ + { + "bbox": [ + 304, + 553, + 547, + 638 + ], + "type": "text", + "content": "Post-processing. We also report the results on segmentation using the post-processing method introduced in [33]. They extract the connected components in the model output and choose the largest " + }, + { + "bbox": [ + 304, + 553, + 547, + 638 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 553, + 547, + 638 + ], + "type": "text", + "content": " masks and discard any masks that take up less than " + }, + { + "bbox": [ + 304, + 553, + 547, + 638 + ], + "type": "inline_equation", + "content": "0.1\\%" + }, + { + "bbox": [ + 304, + 553, + 547, + 638 + ], + "type": "text", + "content": " of the image. Then they combine the discarded masks with the largest mask. The results with post-processing are marked with " + }, + { + "bbox": [ + 304, + 553, + 547, + 638 + ], + "type": "inline_equation", + "content": "^{\\dagger}" + }, + { + "bbox": [ + 304, + 553, + 547, + 638 + ], + "type": "text", + "content": " in the tables." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 647, + 466, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 647, + 466, + 659 + ], + "spans": [ + { + "bbox": [ + 306, + 647, + 466, + 659 + ], + "type": "text", + "content": "4.4. Results on Synthetic Datasets" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 714 + ], + "type": "text", + "content": "We evaluate our method on synthetic datasets and compare its performance to both image-based and video-based methods. Our method uses motion during training only. Therefore, it can also be evaluated on the image datasets." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "text", + "content": "738" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 78, + 70, + 516, + 208 + ], + "blocks": [ + { + "bbox": [ + 78, + 70, + 516, + 208 + ], + "lines": [ + { + "bbox": [ + 78, + 70, + 516, + 208 + ], + "spans": [ + { + "bbox": [ + 78, + 70, + 516, + 208 + ], + "type": "table", + "html": "
MOVi-AMOVi-CMOVi-DMOVi-E
FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑
GWM [10]70.3042.2749.9830.1739.7818.3842.5018.74
SCALOR [30]59.5744.4140.4322.54----
SAVi [36]88.3062.6943.2631.9243.4510.6017.395.75
PPMP [33]84.0160.0861.1834.7255.7423.5062.6225.78
\\( PPMP^† \\)85.4176.1961.2437.2655.1825.2163.1128.59
\\( PPMP^† (Swin) \\)90.0884.7667.6752.1766.4130.4072.7335.30
Ours56.0936.4873.8054.4876.4158.8278.3347.38
\\( Ours^† \\)70.1546.2674.6459.2477.1559.6880.8350.48
", + "image_path": "2f853ac780e21a40df7d12b6087b11b70949505a83377c42e74ed89d692e2a97.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 255, + 289, + 423 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 255, + 289, + 423 + ], + "spans": [ + { + "bbox": [ + 46, + 255, + 289, + 423 + ], + "type": "text", + "content": "Video-Based Methods. We compare our method to other video-based methods on the MOVi video datasets in Table 1 and Fig. 2. All of the methods in Table 1 use optical flow for supervision. Differently, SCALOR [30] and SAVi [36] use all frames in a video, whereas PPMP [33] and our method perform single-image segmentation, one frame at a time without using any motion information at test time. On the simpler MOVi-A dataset, the performance of our method falls behind SAVi [36] and PPMP [33]. PPMP with Swin transformer [41] performs the best overall. With the same 6-layer CNN backbone and without post-processing, SAVi performs the best. Despite the advantage of motion information, the success of SCALOR [30] and SAVi [36] is limited to visually simpler MOVi-A." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 427, + 289, + 585 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 427, + 289, + 585 + ], + "spans": [ + { + "bbox": [ + 46, + 427, + 289, + 585 + ], + "type": "text", + "content": "On the more challenging MOVi-" + }, + { + "bbox": [ + 46, + 427, + 289, + 585 + ], + "type": "inline_equation", + "content": "\\{\\mathrm{C},\\mathrm{D},\\mathrm{E}\\}" + }, + { + "bbox": [ + 46, + 427, + 289, + 585 + ], + "type": "text", + "content": " datasets, our method, even without post-processing, significantly outperforms all the previous methods in both metrics, with or without post-processing. The previous state-of-the-art, PPMP [33] uses the same backbone in their segmentation network as ours. Even with a more powerful backbone (Swin transformer [41]) and post-processing, the results of PPMP are still far behind our results without any post-processing. From MOVi-C to MOVi-E, the performance gap between our method and the others increases as the complexity of the dataset increases. Please see Supplementary for qualitative results with post-processing and evaluation of our estimated depth for objects in these datasets." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "Image-Based Methods. We compare our method to other image-based methods on the CLEVR and CLEVRTEX datasets in Table 2. Our method outperforms the state-of-the-art method PPMP [33] in all metrics on both datasets except for mIoU on CLEVR without postprocessing and mIoU on CLEVRTEX with postprocessing. We point to +9.01 improvement in mIoU on the more challenging CLEVRTEX dataset without postprocessing. See Supplementary for qualitative results on CLEVR and CLEVRTEX." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 255, + 477, + 268 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 255, + 477, + 268 + ], + "spans": [ + { + "bbox": [ + 305, + 255, + 477, + 268 + ], + "type": "text", + "content": "4.5. Results on Real-World Datasets" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 277, + 546, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 277, + 546, + 312 + ], + "spans": [ + { + "bbox": [ + 304, + 277, + 546, + 312 + ], + "type": "text", + "content": "We compare our method to multi-object segmentation methods on real-world datasets including driving scenarios on KITTI and unconstrained videos on DAVIS-2017." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 319, + 546, + 357 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 319, + 546, + 357 + ], + "spans": [ + { + "bbox": [ + 304, + 319, + 546, + 357 + ], + "type": "text", + "content": "Results on DAVIS. Our method is the first image-based method to report performance in multi-object segmentation without using any labels during training or testing on" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 305, + 378, + 555, + 654 + ], + "blocks": [ + { + "bbox": [ + 46, + 216, + 546, + 242 + ], + "lines": [ + { + "bbox": [ + 46, + 216, + 546, + 242 + ], + "spans": [ + { + "bbox": [ + 46, + 216, + 546, + 242 + ], + "type": "text", + "content": "Table 1: Segmentation Results on MOVi Datasets. The best result in each column is shown in bold, and the second best is underlined. " + }, + { + "bbox": [ + 46, + 216, + 546, + 242 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 46, + 216, + 546, + 242 + ], + "type": "text", + "content": " indicates post-processing, and (Swin) denotes using a Swin transformer as the backbone." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 305, + 378, + 555, + 654 + ], + "lines": [ + { + "bbox": [ + 305, + 378, + 555, + 654 + ], + "spans": [ + { + "bbox": [ + 305, + 378, + 555, + 654 + ], + "type": "table", + "html": "
CLEVRCLEVRTEX
FG-ARI↑mIoU↑FG-ARI↑mIoU↑
SPAIR [12]77.1365.950.000.00
MN [54]72.1256.8138.3110.46
MONet [7]54.4730.6636.6619.78
SA [42]95.8936.6162.4022.58
IODINE [24]93.8145.1459.5229.17
DTI-S [46]59.5448.7479.9033.79
GNM [29]65.0559.9253.3742.25
SAVi [36]--49.5431.88
PPMP [32]91.6966.7090.8055.07
Ours95.0363.3694.6664.08
SPAIR†[12]77.0566.870.000.00
MN†[54]72.0857.6138.3410.34
MONet†[7]61.3645.6135.6423.59
SA†[42]94.8837.6861.6021.96
IODINE†[24]93.6844.2060.6329.40
DTI-S†[46]89.8653.3879.8632.20
GNM†[29]65.6763.3853.3844.30
PPMP†[33]95.9484.8692.6177.67
Ours†96.9586.3895.3270.28
", + "image_path": "1006bfbbfade51a41cefae7cab64a22c032921df27c52e011590079a28786ae1.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 661, + 547, + 711 + ], + "lines": [ + { + "bbox": [ + 304, + 661, + 547, + 711 + ], + "spans": [ + { + "bbox": [ + 304, + 661, + 547, + 711 + ], + "type": "text", + "content": "Table 2: Segmentation Results on CLEVR and CLEVRTex Datasets. The lower part with " + }, + { + "bbox": [ + 304, + 661, + 547, + 711 + ], + "type": "inline_equation", + "content": "\\dagger" + }, + { + "bbox": [ + 304, + 661, + 547, + 711 + ], + "type": "text", + "content": " shows the results with post-processing. The best result in each column is shown in bold, and the second best is underlined." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "text", + "content": "739" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 69, + 541, + 338 + ], + "blocks": [ + { + "bbox": [ + 53, + 69, + 541, + 338 + ], + "lines": [ + { + "bbox": [ + 53, + 69, + 541, + 338 + ], + "spans": [ + { + "bbox": [ + 53, + 69, + 541, + 338 + ], + "type": "image", + "image_path": "4cb046bd9b344cd30a5892551a9b4f31bda5980bb36e585f347dee4b568bf301.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 344, + 547, + 369 + ], + "lines": [ + { + "bbox": [ + 46, + 344, + 547, + 369 + ], + "spans": [ + { + "bbox": [ + 46, + 344, + 547, + 369 + ], + "type": "text", + "content": "Figure 3: Qualitative Comparison on DAVIS-2017. While OCLR [63] misses some objects completely and suffers from relying on only optical flow as input, our method can segment a wide variety of multiple objects in everyday scenes." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 380, + 289, + 561 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 380, + 289, + 561 + ], + "spans": [ + { + "bbox": [ + 46, + 380, + 289, + 561 + ], + "type": "text", + "content": "DAVIS-2017. Therefore, in Table 3, we compare it to video-based approaches which use motion as input. We also compare to a simple baseline proposed in [63] based on Mask R-CNN [26] using optical flow as input. We use the labels re-annotated by [63] for evaluation, as explained in Section 4.1. Motion Grouping refers to [64] trained on DAVIS-2017. Motion Grouping (sup.), Mask R-CNN (flow) and OCLR are models trained on synthetic data from [63] in a supervised way using optical flow as input. Our method, which uses a single RGB image as input at test time, outperforms previous methods, including the state-of-the-art OCLR [63] that uses flow from multiple time steps. Ours-M refers to a version of our model where we adapt the spectral clustering approach of [11] to merge our predicted regions into the ground truth number of regions in each frame." + } + ] + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 65, + 581, + 269, + 677 + ], + "blocks": [ + { + "bbox": [ + 65, + 581, + 269, + 677 + ], + "lines": [ + { + "bbox": [ + 65, + 581, + 269, + 677 + ], + "spans": [ + { + "bbox": [ + 65, + 581, + 269, + 677 + ], + "type": "table", + "html": "
ModelJ& F↑J↑F↑
Motion Grouping [64]35.838.433.2
Motion Grouping (sup.)39.544.934.2
Mask R-CNN (flow)50.350.450.2
OCLR [63]55.154.555.7
Ours55.355.355.3
Ours-M59.259.359.2
", + "image_path": "7dcc5de8b4c56951785c110d1a99ea53257456c0f651cf5ae2b06825d366d319.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 685, + 287, + 710 + ], + "lines": [ + { + "bbox": [ + 47, + 685, + 287, + 710 + ], + "spans": [ + { + "bbox": [ + 47, + 685, + 287, + 710 + ], + "type": "text", + "content": "Table 3: Multi-Object Segmentation Results on DAVIS-2017. We evaluate by using the motion labels from [63]." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 381, + 544, + 405 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 381, + 544, + 405 + ], + "spans": [ + { + "bbox": [ + 306, + 381, + 544, + 405 + ], + "type": "text", + "content": "Although not necessary to achieve state-of-the-art, this improves the results significantly." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 407, + 545, + 490 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 407, + 545, + 490 + ], + "spans": [ + { + "bbox": [ + 304, + 407, + 545, + 490 + ], + "type": "text", + "content": "We visualize the results of our model in comparison to OCLR [63] in Fig. 3. Our method can correctly segment a wide variety of objects such as the bike and the person in the first column and the multiple fish in the third, multiple people walking or fighting in the second and fourth. OCLR is highly affected by the inaccuracies in flow, unlike our method, as can be seen from the last two columns." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 496, + 546, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 496, + 546, + 663 + ], + "spans": [ + { + "bbox": [ + 304, + 496, + 546, + 663 + ], + "type": "text", + "content": "Results on KITTI. Since KITTI has ground truth depth, we evaluate our method in terms of both segmentation and monocular depth prediction on KITTI. The segmentation results on KITTI are presented in Table 4a. Our method is among the top-performing methods, outperforming earlier approaches. In addition to segmentation, our method can also predict depth from a single image. We present the evaluation of our depth predictions in comparison to self-supervised monocular depth estimation methods in Table 4b. Our depth network can predict reliable depth maps even without camera intrinsics with comparable results to recent self-supervised monocular depth estimation approaches [22, 25] that are specifically designed for that task and that use camera intrinsics." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": "We visualize our segmentation and depth results on KITTI in Supplementary. Our method can segment multiple moving objects such as car, bike, bus without using any semantic labels for training or motion information at test" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 298, + 748, + 313, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 748, + 313, + 757 + ], + "spans": [ + { + "bbox": [ + 298, + 748, + 313, + 757 + ], + "type": "text", + "content": "740" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 74, + 153, + 174 + ], + "blocks": [ + { + "bbox": [ + 47, + 74, + 153, + 174 + ], + "lines": [ + { + "bbox": [ + 47, + 74, + 153, + 174 + ], + "spans": [ + { + "bbox": [ + 47, + 74, + 153, + 174 + ], + "type": "table", + "html": "
ModelFG-ARI ↑
SA [42]13.8
MONet [7]14.9
SCALAR [30]21.1
S-IODINE [24]14.4
MCG [1]40.9
Ours42.3
Bao et al. [2]47.1
PPMP [33]50.8
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Abs Rel ↓Sq Rel ↓RSME ↓RMSE log ↓δ < 1.25 ↑δ < 1.252 ↑δ < 1.253 ↑
Zhou et al. [69]0.1761.5326.1290.2440.7580.9210.971
Mahjourian et al. [45]0.1340.9835.5010.2030.8270.9440.981
GeoNet [68]0.1320.9945.2400.1930.8330.9530.985
DDVO [60]0.1260.8664.9320.1850.8510.9580.986
Ranjan et al. [51]0.1230.8814.8340.1810.8600.9590.985
EPC++ [44]0.1200.7894.7550.1770.8560.9610.987
Ours0.1071.5394.0270.1490.9110.9710.989
Monodepth2 [22]0.0900.5453.9420.1370.9140.9830.998
PackNet-SfM [25]0.0780.4203.4850.1210.9340.9860.996
", + "image_path": "619f1e6200265f36af0bc491d81e3c09943530fab85e8bdcd184d984dfc635bf.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 120, + 230, + 474, + 331 + ], + "blocks": [ + { + "bbox": [ + 340, + 182, + 377, + 194 + ], + "lines": [ + { + "bbox": [ + 340, + 182, + 377, + 194 + ], + "spans": [ + { + "bbox": [ + 340, + 182, + 377, + 194 + ], + "type": "text", + "content": "(b) Depth" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 46, + 196, + 545, + 220 + ], + "lines": [ + { + "bbox": [ + 46, + 196, + 545, + 220 + ], + "spans": [ + { + "bbox": [ + 46, + 196, + 545, + 220 + ], + "type": "text", + "content": "Table 4: Results on KITTI. We evaluate the segmentation on the instance segmentation benchmark, and the depth on the KITTI Eigen split [14] with improved ground truth [59]." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 120, + 230, + 474, + 331 + ], + "lines": [ + { + "bbox": [ + 120, + 230, + 474, + 331 + ], + "spans": [ + { + "bbox": [ + 120, + 230, + 474, + 331 + ], + "type": "table", + "html": "
MOVi-AMOVi-CMOVi-DMOVi-E
FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑FG-ARI↑mIoU↑
Only-T31.1317.7269.6925.8468.6822.7464.6928.26
Only-R90.4375.6368.5153.0070.5756.9773.0340.34
Full56.0936.4873.8054.4876.4158.8278.3347.38
Only-T†47.9629.9269.9426.3168.6622.7669.9430.71
Only-R†92.0984.6069.2355.5471.2058.4176.2042.96
Full†70.1546.2674.6459.2477.1559.6880.8350.48
", + "image_path": "0a3604d5ab63fb31234cdd83874c678425da4ee736ddcf56012631677e6c22c2.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 339, + 544, + 364 + ], + "lines": [ + { + "bbox": [ + 46, + 339, + 544, + 364 + ], + "spans": [ + { + "bbox": [ + 46, + 339, + 544, + 364 + ], + "type": "text", + "content": "Table 5: Ablation Study. We perform an ablation study by using only the translation (Only-T) or rotation (Only-R) component and compare it to our model with both (Full). See text for details." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 376, + 287, + 400 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 376, + 287, + 400 + ], + "spans": [ + { + "bbox": [ + 46, + 376, + 287, + 400 + ], + "type": "text", + "content": "time. Furthermore, it can predict high-quality depth, capturing thin structures and sharp boundaries around objects." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 415, + 141, + 428 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 415, + 141, + 428 + ], + "spans": [ + { + "bbox": [ + 47, + 415, + 141, + 428 + ], + "type": "text", + "content": "4.6. Ablation Study" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 436, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 436, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 436, + 287, + 544 + ], + "type": "text", + "content": "To evaluate the contribution of different types of flow basis, we perform an experiment by considering only translation or rotation and compare it to the full model on MOVi datasets in Table 5. Note that in the rotation-only case (Only-R), the depth predictions are not used and the depth network is not trained. Overall, the rotation-only model outperforms the translation-only model and the full model with both rotation and translation works the best on MOVi-{C, D, E} datasets with reliable depth predictions." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "The trend is different on the simpler MOVi-A dataset. Only-R outperforms all models including the state-of-the-art in Table 1. We found that in the translation-only case, the depth cannot be predicted on MOVi-A due to missing texture and enough detail for the depth network to learn a mapping from a single image to depth. The rotation-only model, on the other hand, learns to group pixels in a region, based on their rotational motion which does not depend on depth. This ability explains the success of Only-R on simpler datasets. The importance of pixel-wise depth increases with the complexity of the dataset. On MOVi-E, for example, which has the most complex setup with a large number of objects and camera motion, predicting depth, from Only-R to Full, improves the performance the most." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 375, + 471, + 388 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 375, + 471, + 388 + ], + "spans": [ + { + "bbox": [ + 306, + 375, + 471, + 388 + ], + "type": "text", + "content": "5. Conclusion and Future Work" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 395, + 545, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 395, + 545, + 550 + ], + "spans": [ + { + "bbox": [ + 304, + 395, + 545, + 550 + ], + "type": "text", + "content": "We presented a motion-supervised approach for multi-object segmentation that can work with a single RGB image at test time, therefore still applicable to image datasets. Our method is the first to consider geometry to remove ambiguity for multi-object segmentation from a single image without using any labels for segmentation. Modeling geometry significantly advances the state-of-the-art on commonly used synthetic datasets. We also evaluated our method on real-world datasets. Our method is the first image-based multi-object segmentation method to report state-of-the-art results on DAVIS-2017 without using motion at test time. We also report comparable results for depth prediction on KITTI and MOVi datasets where depth can be evaluated." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 551, + 546, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 551, + 546, + 682 + ], + "spans": [ + { + "bbox": [ + 304, + 551, + 546, + 682 + ], + "type": "text", + "content": "Predicting objects that can potentially move independently from a single image requires observing examples of various objects moving in the training set. Moreover, static objects send a mixed signal to the model. The coherent changes in the flow can be captured with the help of geometry as shown in our work. The remaining uncertainty can be addressed with a probabilistic formulation as done in previous state-of-the-art [33]. Another problem is scenes without enough information to predict depth as we observed on textureless MOVi-A. However, the lack of information to this extent rarely happens on real-world data." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 688, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 688, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 306, + 688, + 545, + 712 + ], + "type": "text", + "content": "Acknowledgements. Sadra Safadoust was supported by KUIS AI Fellowship and UNVEST R&D Center." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "text", + "content": "741" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 286, + 712 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 53, + 91, + 286, + 113 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 286, + 113 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 286, + 113 + ], + "type": "text", + "content": "[1] P. 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In CVPR, 2017. 3, 4, 8" + } + ] + } + ], + "index": 2 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "text", + "content": "744" + } + ] + } + ], + "index": 4 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-Object Navigation with Dynamically Learned Neural Implicit Representations/8c2cacd0-618b-43fb-afc2-cdc6e282531c_content_list.json b/2023/Multi-Object Navigation with Dynamically Learned Neural Implicit Representations/8c2cacd0-618b-43fb-afc2-cdc6e282531c_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..f4064e509d8ff58b334f302aa18ea8856f801d89 --- /dev/null +++ b/2023/Multi-Object Navigation with Dynamically Learned Neural Implicit Representations/8c2cacd0-618b-43fb-afc2-cdc6e282531c_content_list.json @@ -0,0 +1,1648 @@ +[ + { + "type": "text", + "text": "Multi-Object Navigation with dynamically learned neural implicit representations", + "text_level": 1, + "bbox": [ + 76, + 130, + 893, + 155 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Pierre Marza", + "bbox": [ + 151, + 178, + 272, + 196 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Laetitia Matignon", + "bbox": [ + 312, + 180, + 465, + 198 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Olivier Simonin", + "bbox": [ + 504, + 180, + 640, + 196 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Christian Wolf3", + "bbox": [ + 681, + 180, + 808, + 196 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ INSA Lyon $^{2}$ UCBL $^{3}$ Naver Labs Europe", + "bbox": [ + 323, + 199, + 642, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{pierre.marza, olivier.simonin}@insa-lyon.fr", + "bbox": [ + 292, + 219, + 679, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "laetitia.matignon@univ-lyon1.fr,christian.wolf@naverlabs.com", + "bbox": [ + 217, + 237, + 751, + 250 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Project Page: https://pierremarza.github.io/projects/dynamicImplicit Representations/", + "bbox": [ + 199, + 253, + 767, + 268 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 304, + 313, + 319 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Understanding and mapping a new environment are core abilities of any autonomously navigating agent. While classical robotics usually estimates maps in a stand-alone manner with SLAM variants, which maintain a topological or metric representation, end-to-end learning of navigation keeps some form of memory in a neural network. Networks are typically imbued with inductive biases, which can range from vectorial representations to birds-eye metric tensors or topological structures. In this work, we propose to structure neural networks with two neural implicit representations, which are learned dynamically during each episode and map the content of the scene: (i) the Semantic Finder predicts the position of a previously seen queried object; (ii) the Occupancy and Exploration Implicit Representation encapsulates information about explored area and obstacles, and is queried with a novel global read mechanism which directly maps from function space to a usable embedding space. Both representations are leveraged by an agent trained with Reinforcement Learning (RL) and learned online during each episode. We evaluate the agent on Multi-Object Navigation and show the high impact of using neural implicit representations as a memory source.", + "bbox": [ + 75, + 335, + 473, + 667 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 694, + 207, + 709 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Autonomous navigation in complex unknown 3D environments from visual observations requires building a suitable representation of the environment, in particular when the targeted navigation task requires high-level reasoning. Whereas classical robotics builds these representations explicitly through reconstructions, possibly supported through machine learning, end-to-end training learns them automatically either from reward, by imitation learning or through self-supervised objectives.", + "bbox": [ + 75, + 719, + 470, + 854 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "While spatial representations can emerge even in unstructured agents, as shown in the form of grid-cells in artificial [16, 3] and biological agents [25], spatial inductive biases", + "bbox": [ + 75, + 854, + 470, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/144ebf5cffe83e827aaa6aab122b204f8e358b1c78a7708974780bc1f7677047.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 519, + 304, + 691, + 417 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b6a8d8ca0c67bc06343318487d79ebd8dbf333b8a10c93efc970f3b9eedb6031.jpg", + "image_caption": [ + "Figure 1. We propose two implicit representations as inductive biases for autonomous agents — both are learned online during each episode. (2) a semantic representation $f_{s}$ predicts positions $\\mathbf{x}$ from goals $\\mathbf{g}$ given as semantic codes. We show Ground Truth object positions (rectangles) and predictions (round; radius shows uncertainty, unit-less, as an illustration). Blue and pink objects have been observed, but not the yellow target. (3) A structural representation $f_{o}$ predicts occupancy and exploration $s$ from positions $\\mathbf{x}$ ; we provide a global read which directly maps from function space $f_{o}$ (represented by trainable weights $\\theta_{o}$ ) to a context embedding $e$ used by the agent. (4) shows the reconstruction produced by a decoder $Dec$ during training. Orange=navigable, Green=Obstacles, Blue=Unexplored. (1) a ground-truth map is shown for reference, simulating a fully explored scene." + ], + "image_footnote": [], + "bbox": [ + 521, + 422, + 691, + 558 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d7c41b2f305540784b7781daef92e7834cc50784c2dcf584aef83a069d63be99.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 696, + 301, + 870, + 412 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ea753e9360e2e2bf2130e678eb0d9019d1929bd6f7ba07b30373a2564bc9172c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 699, + 422, + 870, + 558 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "can support learning actionable spatial representations and decrease sample complexity. Popular inductive biases are metric maps [44, 5, 26], topological maps [6, 12] and recently, self-attention, adapting transformers [55] to sequential decision making and navigation [20, 18, 13, 47]. The chosen representation should support robust estimation of navigable space even in difficult conditions, mapping fea", + "bbox": [ + 496, + 794, + 895, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "11004", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "tures and objects of interest, as well as querying and reusing this information at a later time. The representation should be as detailed as required, span the full (observed) scene, easy to query, and efficient to read and write to, in particular when training is done in large-scale simulations.", + "bbox": [ + 75, + 90, + 470, + 167 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our work builds on neural fields and implicit representations, a category of models which represent the scene geometry, and eventually the semantics, by the weights of a trained neural network [57]. They have the advantage of avoiding the explicit choice of scene representation (e.g. volume, surface, point cloud etc.) and inherently benefit from the generalization abilities of deep networks to interpolate and complete unobserved information. Implicit representations have demonstrated impressive capabilities in novel view synthesis [40, 51], and have potential as a competitive representation for robotics [42, 32, 52, 1]. Their continuous nature allows them to handle level of detail efficiently through a budget given as the amount of trainable weights. This allows to span large environments without the need of discretizing the environment and handling growing maps.", + "bbox": [ + 75, + 169, + 470, + 396 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We explore and study the potential of implicit representations as inductive biases for visual navigation. Similar to recent work in implicit SLAM [52], our representations are dynamically learned in each episode. Going beyond, we exploit the representation dynamically in one of the most challenging visual navigation tasks, Multi-Object Navigation [56]. We introduce two complementary representations, namely a query-able Semantic Finder trained to predict the scene coordinates of an object of interest specified as input, and an Occupancy and Exploration Implicit Representation, which maps 2D coordinates to occupancy information, see Figure 1. We address the issue of the efficiency of querying an implicit representation globally by introducing a new global read mechanism, which directly maps from function space, represented through its trainable parameters, to an embedding summarizing the current status of occupancy and exploration information, useful for navigation. Invariance w.r.t. reparametrization of the queried network is favored (but not enforced) through a transformer based solution. Our method does not require previous rollouts on the scene for pre-training or building a representation.", + "bbox": [ + 75, + 397, + 470, + 715 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our work targets a fundamental aspect of visual and semantic navigation, the mapping of key objects of interest. MultiON is currently one of the few benchmarks which evaluates it. As argued in previous literature [5, 56], only sequential tasks, where objects have to be found in a given order, allow object level mapping to emerge directly from reward. This follows from the observation that an agent trained to find and retrieve a single object per episode (from reward) is not required to map seen target objects, as observing them directly leads to a reactive motion towards them.", + "bbox": [ + 75, + 717, + 470, + 867 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our contributions can be summarized as follows: (i) We propose two implicit representations for semantic, occupancy", + "bbox": [ + 76, + 869, + 470, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "and exploration information, which are trained online during each episode; (ii) We introduce a new global read procedure which can extract summarizing context information directly from the function itself; (iii) We show that the representations obtain performance gains compared to classical neural agents; (iv) We evaluate and analyze key design choices, the representation's scaling laws and its capabilities of lifelong learning.", + "bbox": [ + 496, + 90, + 893, + 212 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 224, + 640, + 242 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Visual Navigation — is a rich problem that involves perception, mapping and decision making, with required capacities being highly dependent on the specific task. A summary of reasoning in navigation has been given in [2], differentiating, for instance, between waypoint navigation (Pointgoal) [2] or finding objects of semantic categories (ObjectGoal) [2]. More recent tasks have been explicitly designed to evaluate and encourage mapping objects of interest during navigation itself [4, 56]. They are of sequential nature and use external objects, which are not part of the scanned 3D scenes but randomly placed. In this work we address Multi-Object Navigation (MultiON) [56].", + "bbox": [ + 496, + 251, + 893, + 431 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Mapping and Representations — Classical methods often rely on SLAM [8, 34] which has been proposed in different variants (2D or 3D metric, topological, eventually with semantics) and observations (LIDAR, visual etc.). The objective is to integrate observations and odometry estimates over a trajectory and reconstruct the scene. Differentiable variants have been proposed recently [28, 30]. Mapping can also be discovered through interactions by a blind agent [7]. Visual Navigation can also be framed as an end-to-end learning problem, where representations are learned automatically from different signals, in particular RL. Memory can take the form of vectorial representations in recurrent units [41, 27, 62], with hybrid variants including mapping [12, 48, 17]. Recent work tends to augment agents with more structured memories. Examples are spatial metric tensors, which can contain occupancy [11], semantics [10] or be fully latent, effectively corresponding to inductive biases of the neural agents [44, 5, 26]. Other alternatives are topological maps [6, 12] or self-attention and transformers [55] adapted to navigation [20, 18, 13, 47].", + "bbox": [ + 496, + 433, + 893, + 734 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Implicit representations — were initially targeting 3D reconstruction [39, 45, 14]. The core idea is to replace the need for discretizing 3D space into voxels [38], 3D points [19] or meshes [23], by an implicit representation of the 3D structure of the scene through the parameters of a learned neural network. Recent work [40, 51] achieved state-of-the-art performance on novel view synthesis with neural implicit representations. The NeRF paper introduced a differentiable volume rendering loss allowing to supervise 3D scene reconstruction from only 2D supervision [40]. For a more detailed overview of recent advances in the rapidly", + "bbox": [ + 496, + 734, + 895, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "11005", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "growing field, we refer the reader to [57].", + "bbox": [ + 76, + 90, + 352, + 104 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Implicit representations in robotics — are a recent phenomenon, used to represent density [1] or to perform visuomotor control [33]. Related to goal-oriented navigation, some work targets SLAM with neural implicit representations [52], follow-up adding semantics [59], learned from sparse semantic annotations of the scene. [60] is also built on top of [52] and allows a user to interactively provide semantic annotation for the implicit representation to be trained on in real time. [63] proposes a hierarchical implicit representation of a scene to scale to larger environments and obtain a more detailed reconstruction. [15] combines feature-based SLAM and NeRF. Our work goes beyond implicit SLAM and does not stop at reconstructing a scene. We not only build implicit representations dynamically during the episode, we also use them in a down-stream navigation task without requiring any initial rollout for pre-training or building a representation. We also combine two different implicit representations targeting semantics vs. scene structure.", + "bbox": [ + 75, + 106, + 470, + 378 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Analyzing the neural network function space — implicit representations are instances of function spaces, which are represented through their trainable parameters. Previous work performed analyses by predicting accuracy from network weights [54, 35, 36] or the generality gap between train and test performance from hidden activations [29, 58]. A direction pioneered by Hypernetworks [24] directly predict the network weights. Recently, [61] generate the weights of a CNN from support samples in the context of few-shot learning. More related to our work, [43] learns to predict the weights of an implicit representation based on external factors in the context of spatio-temporal dynamics encoding. In this work, we learn a direct mapping between an implicit representation, represented by its weights, to an actionable embedding summarizing the scene globally.", + "bbox": [ + 75, + 378, + 470, + 604 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Navigating with implicit representations", + "text_level": 1, + "bbox": [ + 76, + 618, + 437, + 636 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We target the Multi-Object Navigation task [56], which requires an agent to navigate in a photo realistic 3D environment from RGB-D observations $\\mathbf{o}_t$ and reach a sequence of target objects (colored cylinders) in a particular order. Goal categories $\\mathbf{g}_t$ are given at each time step $t$ . In an RL setting, the agent receives positive reward for each successfully reached object as well as when the geodesic distance towards the goal decreases, and a small negative reward for each step, favoring short paths.", + "bbox": [ + 75, + 643, + 468, + 779 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We follow and augment a base end-to-end architecture used in many recent RL approaches, including [56, 37, 41], with the RGB-D observation, class of the current target and previous action as input to the agent. Temporal information is aggregated with a GRU unit whose output is fed to actor and critic heads. We equip this agent with two implicit representations, trained to hold and map essential information necessary for navigation: the positions of different objects of", + "bbox": [ + 75, + 779, + 470, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "interest, and occupancy / exploration information, as shown in Figure 1,", + "bbox": [ + 498, + 90, + 890, + 121 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The goal of the Semantic Finder $f_{s}(:,\\theta_{s})$ parameterized by trainable weights $\\theta_{s}$ is to predict the absolute position of an object as $\\mathbf{x} = [\\mathbf{x}_x\\mathbf{x}_y\\mathbf{x}_z] = f_s(\\mathbf{q};\\theta_s)$ specified through an input query vector $\\mathbf{q}$ . Uncertainty $u$ is also estimated — see Section 3.1 for details. $\\mathbf{x}$ is then converted into coordinates relative to the agent to be fed to the GRU. Compared to classical metric representations [26, 44, 12, 5], querying the location of an object can be done through a single forward pass.", + "bbox": [ + 517, + 133, + 893, + 272 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The Occupancy and Exploration Representation $f_{o}(:,\\theta_{o})$ parameterized by trainable weights $\\theta_{o}$ encodes information about free navigable space and obstacles. It predicts occupancy $\\mathbf{s}$ as a classification problem with three classes {Obstacle, Navigable, Unexplored}, as $\\mathbf{s} = f_{o}(\\phi ;\\theta_{o})$ , where $\\phi$ is a position feature vector encoded from coordinates $\\mathbf{x}$ — see Section 3.2 for details.", + "bbox": [ + 517, + 281, + 893, + 404 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The Occupancy and Exploration Representation can in principle be queried directly for a single position, but reading out information over a large area directly this way would require multiple reads. We propose to compress this procedure by providing a trainable global read operation $r(:, \\theta_g)$ , which predicts an embedding $\\mathbf{e}$ containing a global context about what has already been explored, and positions of navigable space. The prediction is done directly from the trainable parameters of the implicit representation, as $\\mathbf{e} = r(\\theta_o; \\theta_r)$ . Here $\\theta_o$ is input to $r$ , whereas $\\theta_r$ are its parameters.", + "bbox": [ + 496, + 417, + 893, + 568 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given representations $f_{s}$ and $f_{o}$ , a single forward pass of the agent at time step $t$ and for a goal $g_{t}$ involves reading the representations and providing the input to the policy. The current RGB-D observation $o_{t}$ is also encoded by the convolutional network $c$ (different from the projection module $p$ used to generate samples for training the Semantic Finder). Previous action $a_{t-1}$ and current goal $g_{t}$ are passed through embedding layers, named $L(\\cdot)$ in the following equations. These different outputs are fed to the policy,", + "bbox": [ + 496, + 569, + 893, + 705 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {x} _ {t} = f _ {s} \\left(g _ {t}; \\theta_ {s, t}\\right), \\mathbf {e} _ {t} = r \\left(\\theta_ {o, t}; \\theta_ {r}\\right), \\mathbf {c} _ {t} = c \\left(o _ {t}; \\theta_ {c}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 713, + 893, + 729 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {h} _ {t} = G R U \\left(\\mathbf {h} _ {t - 1}, \\mathbf {x} _ {t}, u _ {t}, \\mathbf {e} _ {t}, L \\left(a _ {t - 1}\\right), L \\left(g _ {t}\\right), \\mathbf {c} _ {t}; \\theta_ {G}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 732, + 890, + 750 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\na _ {t} = \\pi \\left(\\mathbf {h} _ {t}; \\theta_ {\\pi}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 752, + 890, + 768 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where we added indices $\\cdot_t$ to relevant variables to indicate time. Please note that the trainable parameters $\\theta_{s,t}$ and $\\theta_{o,t}$ of the two implicit representations are time dependent, as they depend on the observed scene and are updated dynamically, whereas the parameters of the policy $\\pi$ and the global reader $r$ are not. Here, GRU corresponds to the update equations of a GRU network, where we omitted gates for ease of notation. The notation $a_t = \\pi(.)$ predicting action $a_t$ is", + "bbox": [ + 496, + 779, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "11006", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/ca3b92b49c6a8c8eb936223f8b452dca3325d55d7eb923dc4ba0d0cd0e619939.jpg", + "image_caption": [ + "Figure 2. Navigating with implicit representations. Red connections $\\longrightarrow$ indicate the training process of the two implicit representations (= mapping), which is also done during agent deployment. Black connections $\\longrightarrow$ show the forward pass of the agent. ■ are discrete learned embeddings (LUT). Policy training is not shown in this figure." + ], + "image_footnote": [], + "bbox": [ + 161, + 87, + 816, + 378 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "also a simplification, as we train the agent with PPO, an actor-critic method — see Section 3.4.", + "bbox": [ + 75, + 450, + 470, + 479 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Mapping means training! — The implicit representations $f_{s}$ and $f_{o}$ maintain a compact and actionable representation of the observed scene, and as such need to be updated at each time step from the current observation $o_{t}$ . Given their implicit nature and implementation as neural networks, updates are gradient based and done with SGD. The implicit representations are therefore trained from scratch at each episode even after deployment.", + "bbox": [ + 75, + 483, + 470, + 604 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Training a representation from observations obtained sequentially during an episode also raises a serious issue of catastrophic forgetting [22], as places of the scene observed early might be forgotten later in the episode [52, 59]. We solve this by maintaining two replay buffers throughout the episode, one for each representation. Training samples are generated from each new observation and added to the replay buffers at each time step. Both representations are then trained for a number of gradient steps ( $n_s$ for the Semantic Finder and $n_o$ for the Exploration and Occupancy Representation). Details on the two representations and their training are given in Sections 3.1 and 3.2. The global reader $r$ is not trained or finetuned online but rather trained once offline.", + "bbox": [ + 75, + 604, + 470, + 801 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. The Semantic Finder $f_{s}$", + "text_level": 1, + "bbox": [ + 76, + 815, + 294, + 832 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "While recent work on implicit representations for robotics focused on signed distance functions [42, 32], occupancy [52] or density, assuming light density approximates mass density [1], the aim of this model is to localize an object", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "of interest within the scene, which can be seen as inverse operation to classical work. From a query vector given as input, the Semantic Finder predicts the position of the object, which is particularly useful for an agent interacting with an environment in the context of a goal conditioned task. It is implemented as a 3-layer MLP with ReLu activations in the intermediate layers and a sigmoid activation for the output. Hidden layers have 512 neurons. The query vector $\\mathbf{q}$ corresponds to the 1-in-K encoding of the target object class, which during navigation is directly determined by the object goal $g_{t}$ provided by the task.", + "bbox": [ + 496, + 450, + 893, + 618 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Mapping/Training - The implicit representation is updated minimizing the L1 loss between the prediction $\\mathbf{x}_i = f_s(\\mathbf{q}_i, \\theta_s)$ and the supervised coordinates $\\mathbf{x}_i^*$ (we avoided the term \"ground-truth\" here on purpose), $\\mathcal{L}_s = \\sum_i \\| \\mathbf{x}_i^* - \\mathbf{x}_i \\|_1$ , where the sum goes over the batch sampled from the scene replay buffer. Coordinates $\\mathbf{x}_i^*$ are normalized $\\in [0, 1]$ .", + "bbox": [ + 496, + 623, + 893, + 715 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The data pairs $(x_{i}^{*}, q_{i})$ for training are created from each observation $o_{t}$ during each time step, each data point corresponding to an observed point. Pixels in $o_{t}$ are inversely projected into 3D coordinates in the scene using the depth channel, the camera intrinsics, as well as agent's coordinates and heading that are assumed to be available, as in [56]. The query vector $\\mathbf{q}$ corresponds to a 9-dimensional vector encoding a distribution over object classes (8 target objects and the \"background\" class). Let us recall that while the training of the representation is supervised, this supervision cannot use \"ground-truth\" information available only during training. All supervision information is required to be", + "bbox": [ + 496, + 719, + 895, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "11007", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "predicted from the data available to the agent even after deployment. We predict object class information through a semantic segmentation model $p$ , which is applied to each current RGB-D observation $o_t \\in \\mathbb{R}^{h \\times w \\times 4}$ , recovering the output segmentation map $m_t \\in \\mathbb{R}^{k \\times l \\times 9}$ . The model has been pre-trained on the segmentation of the different target objects, i.e. coloured cylinders, and is not fine-tuned during training of the agent itself.", + "bbox": [ + 75, + 90, + 472, + 210 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Training data pairs $(x_{i}^{*}, q_{i})$ are sampled from this output. The supervised coordinates $x_{i}^{*}$ are simply the mean 3D coordinates of each feature map cell, after inverse projection. The query vector $\\mathbf{q}_{i}$ is the distribution over semantic classes. After the replay buffer is updated, a training batch must be sampled to update the neural field. One fourth of the samples in the batch of size $b$ correspond to the $b/4$ last steps. The rest are sampled from the previous steps in the replay buffer. Uniform sampling is also performed among pairs collected at a given time step.", + "bbox": [ + 75, + 212, + 473, + 364 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Estimating uncertainty — is an essential component, as querying yet unseen objects will lead to wrong predictions, which the agent needs to recognize as such, and discard. The estimation of uncertainty in neural networks is an open problem, which has been previously addressed through different means, including drop out as a Bayesian approximation [21], variational information bottlenecks [50], density estimation [31], and others. In this work, we approximate a density estimate in the scene replay buffer by calculating the minimum Euclidean distance between the input query and all embeddings in the replay buffer at the current time step. The method is simple and efficient and does not require explicitly fitting a model to estimate the marginal distribution $p(\\mathbf{q})$ , in particular as the uncertainty representation is latent, can be un-normalized as not required to be a probability.", + "bbox": [ + 75, + 380, + 473, + 609 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2. Occupancy and Exploration Implicit Representation $f_{o}$", + "text_level": 1, + "bbox": [ + 76, + 614, + 470, + 647 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Unlike $f_{s}$ , the occupancy representation $f_{o}$ is closer to classical implicit representations in robotics, e.g. [52, 42, 32, 1], which map spatial coordinates to variables encoding information on navigable area like occupancy or signed distances. Different to previous work, our representation also includes exploration information, which changes over time during the episode. Once explored, a position changes its class, which makes our neural field dynamic. Another difference with $f_{s}$ is that the latter deals with 3D coordinates while $f_{o}$ is a topdown 2D representation. Inspired by [57, 53], the model uses Fourier features $\\phi$ extracted from the 2D coordinates $\\mathbf{x}$ previously normalized $\\in [0,1]$ ,", + "bbox": [ + 75, + 652, + 472, + 835 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\phi = (\\cos (\\mathbf {x} 2 ^ {0}), \\sin (\\mathbf {x} 2 ^ {0}), \\dots , \\cos (\\mathbf {x} 2 ^ {\\frac {p}{4}}), \\sin (\\mathbf {x} 2 ^ {\\frac {p}{4}})). (4)\n$$\n", + "text_format": "latex", + "bbox": [ + 94, + 843, + 472, + 864 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The network $f_{o}$ is a 3-layer MLP with ReLu intermediate activations and a softmax function at the output layer. Hidden", + "bbox": [ + 75, + 869, + 472, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "layers have 512 neurons, and $p = 40$ .", + "bbox": [ + 498, + 90, + 746, + 106 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Mapping/Training — The implicit representation is updated minimizing the Cross Entropy loss between the prediction $\\mathbf{s}$ of the neural field and the supervised label $\\mathbf{s}^*$ of three classes $\\{\\text{Obstacle, Navigable, Unexplored}\\}$ , as $\\mathcal{L}_o = -\\sum_{c=1}^{3} \\mathbf{s}_c^* \\log \\mathbf{s}_c$ . As for the Semantic Finder, training data pairs $(\\mathbf{s}^*, \\mathbf{s})$ are created through inverse perspective projection of the pixels of the observation $o_t$ into 3D scene coordinates. Thresholding the $z$ (height) coordinate decides between Navigable and Obstacle classes. Points with a $z$ coordinate higher than a certain threshold are discarded. The replay buffer is balanced between both classes, and only samples of the last 1000 steps are kept. Samples of the Unexplored class are not stored.", + "bbox": [ + 496, + 107, + 893, + 303 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The replay buffer is sampled similarly to the one for the Semantic Finder. However, additional samples for the Unexplored class are created by sampling uniformly inside the scene, for speed reasons simply ignoring conflicts with explored areas and treating them as noisy labels.", + "bbox": [ + 496, + 303, + 893, + 380 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Global Occupancy Read $r$ — handling reparametrization invariance", + "text_level": 1, + "bbox": [ + 498, + 391, + 892, + 422 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The global Occupancy reader $r$ allows to query the occupancy information of the scene globally, beyond point-wise information, and as such is a trainable mapping from the space of functions $f_{o}(:,.)$ to an embedding space $e$ . In particular, two functions $f_{o}$ and $f_{o}'$ s.t. $f_{o}(\\mathbf{x}) = f_{o}'(\\mathbf{x}) \\forall \\mathbf{x}$ should be mapped to identical or close embeddings. However, as the occupancy networks $f_{o}$ are implemented as MLPs, any given instance $f_{o}(:,;\\theta_{o})$ parameterized by trainable weights $\\theta_{o}$ can be reparametrized by any permutation of hidden units, which leads to permutations of the rows and columns, respectively, of two weight matrices, its own and the one of the preceding layer. This reparameterization keeps the represented functions identical, although their representations as weight vectors are different.", + "bbox": [ + 496, + 430, + 893, + 641 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To favor learning a global occupancy reader which is invariant w.r.t these transformations, we implement it as a transformer model with self-attention [55] — this, however, does not enforce full invariance. The model takes as input a sequence of tokens $(w_{1},\\dots,w_{N})$ , where $w_{i}\\in \\mathbb{R}^{a}$ is a learned linear embedding of the incoming weights of one neuron within the implicit representation $f_{o}$ , and $N$ is the number of neurons of $f_{o}$ . Each token is summed with a positional encoding in the form of Fourier features. An additional \"CLS\" token with learned embedding is concatenated to the input sequence. The reader is composed of 4 self-attention layers, with 8 attention heads. The output representation of the \"CLS\" token is used as the global embedding of the implicit representation.", + "bbox": [ + 496, + 643, + 895, + 853 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Training - The global reader $r$ is trained with full supervision from a dataset of $25k$ trajectories composed of MLP weights $\\theta_{o,i}$ and absolute maps $\\mathbf{M}_i$ , $i..1..25k$ . Each", + "bbox": [ + 498, + 854, + 893, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "11008", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "map is a metric tensor providing occupancy information extracted from the corresponding implicit representation, i.e. $\\mathbf{M}_i(\\mathbf{x}_y,\\mathbf{x}_x) = f_o(\\mathbf{x},\\theta_{o,i})$ . The dataset also contains an egocentric version $\\mathbf{M}_i^{\\prime}$ of each map, which is centered on the agent and oriented depending on its current heading. The reader $r$ is trained in an Encoder-Decoder fashion, where $r$ plays the role of the encoder,", + "bbox": [ + 75, + 90, + 472, + 196 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {e} _ {i} = r \\left(\\theta_ {o, i}\\right), \\quad \\hat {\\mathbf {M}} _ {i} = D e c \\left(e _ {i}, p _ {i}\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 155, + 208, + 470, + 226 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $p_i$ is the agent pose (position and heading), necessary to decode ego-centric information. We minimize a cross entropy loss on the prediction of ego-centric maps,", + "bbox": [ + 75, + 237, + 468, + 282 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {g} = - \\sum_ {i} \\sum_ {k} \\sum_ {l} \\sum_ {c = 1} ^ {3} \\mathbf {M} _ {i, c} ^ {\\prime *} (k, l) \\log \\mathbf {M} _ {i, c} ^ {\\prime} (k, l) (6)\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 292, + 470, + 311 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Directly training this prediction proved to be difficult. We propose a procedure involving several steps, detailed in section 3.5. After the training phase, the reader $g$ is used in the perception + mapping module of the agent as given in equation (1), and kept frozen during agent RL training.", + "bbox": [ + 75, + 321, + 472, + 398 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.4. Training the Agent", + "text_level": 1, + "bbox": [ + 76, + 407, + 261, + 422 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The agent is trained with RL, more precisely Proximal Policy Optimization (PPO) [49]. The inner training loops of the implicit representations are supervised (red arrows in Figure 2) and occur at each time step in the forward pass, whereas the RL-based outer training loop of the agent occurs after $N$ acting steps (black arrows in Figure 2). As the perception module used to generate training data from RGBD-observations for the Semantic Finder $f_{s}$ is independent of the visual encoder $c$ in the agent (see Figure 2), and as its query $\\mathbf{q}_t$ is fixed to the navigation goal $\\mathbf{g}_t$ , there is no need to track the weights $\\theta_{s}$ at each time step in order to backpropagate the PPO loss (outer training). This is a key design choice of our method.", + "bbox": [ + 75, + 429, + 472, + 625 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training assumptions — We do not rely on the existence of global GT maps for occupancy, as $f_{o}()$ and $r()$ were trained on observation data from agent trajectories only. However, similar to [37, 46], we exploit object positions in simulation, during training only; Moreover, we require pixel-wise segmentation masks during training. We believe that this does not change requirements, as the goal is to fully exploit 3D photo-realistic simulators as a data source and see how far the field can go with this. Generalization requirements are unchanged: we require our agent to be able to generalize to new unseen scenes. Generalization to unseen object categories is not targeted, and in MultiON task setup not possible for any agent, as object positions and labels are required for reward calculation.", + "bbox": [ + 75, + 627, + 472, + 838 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.5. Training the global reader", + "text_level": 1, + "bbox": [ + 76, + 847, + 316, + 863 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The proposed training procedure for the global reader $r$ (performed before training the agent) can be split into 3 phases.", + "bbox": [ + 75, + 869, + 472, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The architecture for the convolutional decoder $Dec()$ is kept the same in all of them. The hyperparameters of its different layers are detailed in the Supplementary Material. It is composed of 6 transpose convolution layers along with batch norm layers and ReLU activations, except for the last layer with a softmax activation. Figure 3 provides an overview of the 3 steps involved in the training of the global reader.", + "bbox": [ + 496, + 90, + 893, + 198 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Fully convolutional autoencoder — The first step is to train a fully convolutional autoencoder on the set of absolute maps $\\mathbf{M}_i$ , $i..1..25k$ . Only the decoder weights are kept.", + "bbox": [ + 500, + 213, + 893, + 273 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Global reader training on absolute maps — The second step consists in training the global reader to output embeddings fed to the frozen decoder from the previous step. The objective is to reconstruct absolute maps from the weights of the implicit representation. The global reader weights are kept after this training phase.", + "bbox": [ + 500, + 287, + 893, + 378 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Global reader finetuning on egocentric maps The global reader, whose weights are initialized from the weights obtained in the previous step, is now trained along with the same decoder from the first step (also used in the second step) on the set of egocentric maps $\\mathbf{M}_i^{\\prime}$ , $i..1..25k$ . Both global reader and decoder are finetuned. The output of the global reader is not directly fed to the decoder, but is passed through linear layers in order to fuse information about first the position of the agent, and then its heading because this time the right operations of shift and rotation must be applied in order to reconstruct egocentric maps.", + "bbox": [ + 500, + 391, + 893, + 574 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Integrating the pre-trained global reader into the agent After this pre-training in 3 steps, the weights of the global reader are frozen and not updated during the RL training. However, a linear layer is learnt to project the 576-dim embedding from the global reader into a 256-dim representation fed to the GRU. This linear layer is trained from reward signals.", + "bbox": [ + 500, + 585, + 890, + 691 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 723, + 633, + 739 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "MultiON task — we target the 3-ON version of the MultiON task [56], where the agent deals with sequences of 3 objects, each belonging to one of 8 classes (cylinders of different colors). At each step, the observation $\\mathbf{o}_t$ is an RGB-D image of size $256 \\times 256 \\times 4$ and the target class is a one-in-K ( $K = 8$ ) vector. The action space is discrete: {Move forward $0.25m$ , Turn left $30^\\circ$ , Turn right $30^\\circ$ , Found}. An episode is considered successful if the agent finds all of the targets before the time limit (2, 500 environment steps), and chooses the Found action for each one at a distance closer to", + "bbox": [ + 496, + 750, + 893, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "11009", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/dd8b87e0f90df7252d5d672360cb58d2efa026066632578ff554280eef087a72.jpg", + "image_caption": [ + "Figure 3. Training the Global Reader in 3 steps: $①$ training a convolutional auto-encoder on absolute maps; $②$ extension to inputs equal to weights $\\theta_{o} =$ the gobal reader; $③$ extension to predicting ego-centric maps, better suited to navigation problems." + ], + "image_footnote": [], + "bbox": [ + 127, + 89, + 843, + 441 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/a666675f04a35cd820c14f1d9cd31ba9c01a97bd04fe657aec2ab01ce34e3115.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
0 - 3030 - 5050 - 70— Val —— Test —
SOSOSOSuccessProgressSPLPPLSuccessProgressSPLPPL
------33.2±1.249.0±1.121.2±0.531.6±1.242.3±1.556.7±0.928.1±1.037.8±1.8
μ--✓-✓37.8±1.652.3±0.926.35±1.536.5±0.847.0±1.760.5±1.634.5±0.844.2±1.0
--✓-✓✓38.5±4.652.5±4.828.2±2.138.3±1.746.7±3.060.1±3.135.1±1.444.8±1.0
------32.147.721.632.641.055.928.939.0
↑--✓-✓38.151.927.337.148.661.535.244.2
--✓-✓✓43.156.830.540.149.763.436.445.9
", + "bbox": [ + 168, + 493, + 802, + 612 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 1. Impact of the implicit representations: navigation performance on MultiON val and MultiON test. S=f_s activated, O=f_o activated in the corresponding training period (see text). Top/μ: means over 3 runs; Bottom/↑: best validation seeds over 3 runs.", + "bbox": [ + 75, + 619, + 893, + 648 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "$1.5m$ . Calling Found incorrectly terminates episode as a failure. An access to perfect odometry information (localization and heading) was assumed in [56] as the standard protocol.", + "bbox": [ + 75, + 672, + 470, + 717 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Dataset and metrics — The agent is trained on the Mutterport3d [9] dataset. We followed the standard train/val/test split over scenes (denoted MultiON train, MultiON val, MultiON test): 61 training, 11 validation and 18 test scenes. The train, val and test splits are respectively composed of 50,000, 12,500 and 12,500 episodes per scene. Reported results on the val and test sets (Tables 1 and 2) were computed on a subset of 1,000 randomly sampled episodes. We report standard metrics as used in the navigation literature (and in [56]): Success: percentage of successful episodes — all objects are reached respecting order, time; Progress: percentage of objects successfully found (respecting order,", + "bbox": [ + 73, + 719, + 473, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "time); SPL: Success weighted by Path Length, extending the original SPL metric [2] to MultiON; PPL: Progress weighted By Path Length (the official MultiON challenge metric).", + "bbox": [ + 496, + 672, + 890, + 717 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Global reader dataset — The Global reader $r$ was trained on a dataset of $25k$ trajectories obtained from rollouts performed by a baseline agent [37]. $95\\%$ was used for training and the rest for validation. On these trajectories we first trained the occupancy representation $f_{o}$ \"in-situ\", i.e. as if it were deployed on the agent, and we recorded training samples $i$ for training the reader $r$ : pairs of network weights $\\theta_{o,i}$ and associated maps $M_{i}$ obtained by iteratively querying the implicit representation. Ego-centric maps were generated from the absolute ones and both were cropped around their center.", + "bbox": [ + 496, + 718, + 893, + 883 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Perception module dataset — The perception module", + "bbox": [ + 517, + 885, + 890, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "11010", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/c0f89d4ed9b1447f6e4b6673d01c04de5d8f0c95833364e311e2dae578e3a599.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
AgentραγSuccessProgressSPLPPLAUXORC
(a)OracleMap† [56]-✓50.4±3.560.5±3.140.7±2.248.8±1.9-✓
(b)OracleEgoMap† [56]-✓32.8±5.247.7±5.226.1±4.537.6±4.7-✓
(c)NoMap† [56]-✓16.7±3.633.7±3.313.1±2.426.0±1.7--
(d)ProjNMap† [26]-✓25.9±1.143.4±1.018.3±0.630.9±0.7--
(e)NoMap✓-42.3±1.556.7±0.928.1±1.037.8±1.8--
(f)ProjNMap [26]✓-39.7±2.355.4±1.428.7±1.140.1±1.9--
(g)Implicit (Ours) w/ curriculum w/pre-train✓--46.7±3.060.1±3.135.1±1.444.8±1.0--
(h)ProjNMap + AUX [37]N/A✓N/A57.7±3.770.2±2.737.5±2.045.9±1.9✓-
(i)Implicit (Ours) w/o curriculum w/pre-train + AUX✓✓✓58.3±0.869.4±1.143.8±1.052.1±1.6✓-
(j)Implicit (Ours) w/o curriculum w/o pre-train-✓✓54.8±3.668.0±3.441.7±1.951.3±1.6--
(k)Implicit (Ours) w/o curriculum w/o pre-train + AUX-✓✓57.9±2.069.5±0.643.3±2.251.9±3.7✓-
", + "bbox": [ + 117, + 88, + 849, + 262 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/a1bd20ce4b2bb7269b0077180272cbc0d924f0432a0828ff743cc8bd14512550.jpg", + "table_caption": [ + "Table 2. Comparison with SOTA methods on MultiON test. †=performance taken from [37]. “AUX” = auxiliary losses using privileged information [37]. “ORC” = non-comparable, uses oracle information. ρ = pre-training of input encoders from [37]. α = finetuning of input encoders with RL. γ = implicit representations are accessible to the agent since the beginning of RL training (w/o curriculum)." + ], + "table_footnote": [], + "table_body": "
UncertaintySuccessProgressSPLPPL
-35.4±3.049.7±3.329.4±2.040.9±2.4
✓43.4±3.158.0±3.035.1±0.846.4±1.0
", + "bbox": [ + 114, + 334, + 431, + 383 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 3. Uncertainty: comparing training w/ semantic input only, no occupancy, from the beg. of training, w/ and w/o uncertainty.", + "bbox": [ + 75, + 390, + 470, + 419 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "$p$ was trained to segment the different target objects. The generated dataset is composed of $132k$ pairs of RGB-D observations and segmentation masks. Samples for 4 scenes were kept as a validation set.", + "bbox": [ + 75, + 429, + 468, + 489 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Training details - We use the reward function given in [56] for RL/PPO training (see supplementary material), and train all agents for $70M$ steps as in [37]. For all agents in Table 1 and some in Table 2 ( $w/$ pre-train: $\\sqrt{}$ in $\\rho$ column), the encoders (visual encoder $c$ , as well as goal and previous action embedding layers, see Figure 2) are pre-trained with a baseline, which corresponds to the ProjNeuralMap agent trained with auxiliary losses [37]. This is done to faster training, as it will be shown later (in Table 2) that the same final performance can be reached without this initial pre-training of encoders. Training and evaluation hyper-parameters, as well as architecture details have been taken from [56]. All reported quantitative results are obtained after 3 training runs for each model.", + "bbox": [ + 75, + 491, + 470, + 700 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Impact of the implicit representations — Table 1 shows the impact of the two implicit representations on navigation (top: means over 3 runs; bottom: best validation seeds over 3 runs). To keep compute requirements limited and decrease sample complexity, in these ablations we do not train the full agent from scratch, in particular since the early stages of training are spent on learning basic interactions. We decompose training into three phases: $0 - 30M$ steps (no implicit representations, i.e. all entries to the agent related to $f_{s}$ and $f_{o}$ are set to 0); $30M - 50M$ steps (training includes the Semantic Finder $f_{s}$ ) and finally $50M - 70M$ steps (full model). This 3-steps approach is used to train all agents in Table 1, and will be denoted as curriculum (See", + "bbox": [ + 75, + 704, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 2, $w/$ curriculum: - in $\\gamma$ column). All metrics on both val and test sets are improved, with the biggest impact provided by the Semantic Finder, which was expected. We conjecture that mapping object positions is a more difficult task, which is less easily delegated to the vectorial GRU representation, than occupancy. We also see an impact of the occupancy representation, which not only confirms the choice of the implicit representation ${f}_{o}$ itself,but also its global read through $r\\left( {\\theta }_{o}\\right)$ . Training curves are given in the supplementary material.", + "bbox": [ + 496, + 337, + 893, + 489 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Uncertainty — has an impact on agent performance, as we show in the ablation in Table 3. Indeed, when training an agent with the semantic input since the beginning of training (w/o curriculum) and no occupancy input (as the uncertainty is only related to semantic information), feeding the agent with the computed uncertainty about the output of the Semantic Finder brings a boost in performance.", + "bbox": [ + 496, + 489, + 893, + 597 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Comparison with previous SOTA methods — is done in Table 2. The performance entries of these baselines are taken from [37], which describes the winning entry of the CVPR 2021 MultiON competition. Our method outperforms the different competing representations, even when they benefit from the same pre-training scheme and are thus completely comparable. NoMap with pre-training corresponds to the first row of Table 1. The difference between (g) and (i) is the use of the auxiliary tasks in [37], but also that the implicit representations are available to the agent during the whole training period for (i), i.e. no decomposition into 3 phases as in the ablations in Table 1 (w/o curriculum). Moreover, compared to (g), in (i) the weights of the pre-trained encoders are finetuned. We see that the gains of our representations are complementary to the auxiliary losses in [37]. (j) and (k) confirm this finding, showing that most of the gain compared with (h) comes from the implicit representations, with the auxiliary losses bringing an additional boost. (j) and (k) also show that, even though pre-training can help speed up RL training, similar test performance is achieved without it.", + "bbox": [ + 496, + 598, + 895, + 902 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "11011", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/51ab0aad70199eb725cd6276a1201454493fe702d3fa84e1f71484bfecf95f17.jpg", + "image_caption": [ + "(a)", + "Figure 4. Capacity of the semantic representation: we report mean distance prediction error (normalized $\\in [0,1]$ ) as a function of the number of stored objects. Replay buffers are composed of dummy queries: (a) one-hot queries with same dimension as number of objects; (b) random query with dimension 9; (c) random query with same dimension as number of objects." + ], + "image_footnote": [], + "bbox": [ + 83, + 98, + 263, + 224 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/e6d048fe9ed4f1aa772de290b8753026734f33cfc043a212e079ec178133a457.jpg", + "image_caption": [ + "(b)" + ], + "image_footnote": [], + "bbox": [ + 271, + 97, + 428, + 215 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/1b285e3496fbf412969e0c87a2fa5d3cf51a2bc545a012f7eb7eb52f2aa17a12.jpg", + "image_caption": [ + "(c)" + ], + "image_footnote": [], + "bbox": [ + 429, + 97, + 593, + 215 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/b7c808453ab0ff7fdda121b7234baf9e9252ff9fb76c4c1ddeaae3c4bbc6a72a.jpg", + "image_caption": [ + "Figure 5. Lifelong learning of the semantic repr. $f_{s}$ : we report mean error in meters, test set, 600 episodes, as a function of the number of time steps since the object was first seen in the episode (t=0). The error falls immediately and stays low over the episode." + ], + "image_footnote": [], + "bbox": [ + 638, + 99, + 870, + 224 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Reconstruction performance of the Global Reader $r$ — although the task of reconstructing egocentric maps from occupancy functions $f_{o}$ (represented by $\\theta_{o}$ ) is only used as a proxy task to train the Global reader $r$ , we see it is a reliable proxy for the quality of extracting the global latent vector $\\mathbf{e}$ fed to the agent.", + "bbox": [ + 73, + 325, + 467, + 416 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/d1981c309bff3ed05262d36b04bc4176349ec662d09dc21f16cf9e04bf69fbaf.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
AccuracyJaccard Index
83.456.5
", + "bbox": [ + 81, + 438, + 243, + 467 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Table 4. Performance of the global reader $r$ : We report accuracy and Jaccard index.", + "bbox": [ + 76, + 479, + 254, + 522 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In Table 4 we report reconstruction performance measured as accuracy and mean Jaccard Index on the validation split of the dataset used to train the reader. We judge that an accuracy of $83.4\\%$ is surprisingly high, given that", + "bbox": [ + 284, + 417, + 470, + 537 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "the global reader needs to reconstruct the content of the representation directly from its parameters $\\theta_{o}$ , that each implicit representation has been initialized randomly, and that the reader is required to be invariant w.r.t. to reparameterization (see Section 4). The task is even made harder as neural weights can be considered as an absolute representation of the env. and the reader must combine it with information about the agent pose to reconstruct an egocentric map.", + "bbox": [ + 75, + 537, + 468, + 657 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Capacity of the Semantic Finder — Unlike all other results presented in this paper, this experiment is performed independently of the official MultiON benchmark. We construct a synthetic dataset to evaluate the capacity of the Semantic Finder. More details about the generated data can be found in the supplementary material. As the granularity of the implicit representations is handled through the budget in terms of trainable parameters, we evaluate the capacity of the Semantic Finder $f_{s}$ to store large numbers of objects in Figure 4: In (a), we can see that increasing the number of objects up to 1000 does not increase error with sufficient gradient updates. However, since inputs are 1-in-K, increasing the number of objects also increases capacity. In (c), we see that this does not hold for random objects (not 1-in-K), whose less structured storage requires more capacity. In (b), we keep the input dimension fixed for random objects, which", + "bbox": [ + 75, + 659, + 470, + 900 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "further increases error.", + "bbox": [ + 500, + 325, + 651, + 340 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Evaluating catastrophic forgetting — we evaluate the capacity of the Semantic Finder $f_{s}$ to hold the learned information over the full length of the sequence in spite of the fact that it is continuously trained. Figure 5 shows the evolution of the mean error in distance for the predicted position of queried target objects as a function of time. The error quickly goes below $1.5m$ once the object has been seen the first time ( $t = 0$ in the plot), which is distance threshold required by the MultiON task, and stays there, providing evidence that the model does not suffer from catastrophic forgetting.", + "bbox": [ + 496, + 344, + 893, + 496 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Runtime performance — inspite of requiring to continuously train the representations, we achieve 45 fps during parallelized RL training, including the environment steps (simulator rendering), forward passes, representation training and RL training on a single V100 GPU. The average time of one agent forward pass, including updates of implicit representations is 20ms on a V100 GPU, which is equivalent to 50 fps, enough for real-time performance.", + "bbox": [ + 496, + 500, + 893, + 619 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 643, + 617, + 659 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We introduce two implicit representations to map semantic, occupancy and exploration information. The first estimates the position of an object of interest from a vector query, while the second encapsulates information about occupancy and explored area in the current environment. We also introduce a global read directly from the trainable weights of this representation. Our experiments show that both implicit representations have a positive impact on the navigation performance of the agent. We also studied the scaling laws of the semantic representation and its behavior in the targeted lifelong learning problem. Future work will target differentiating through the implicit representations all the way back to the perception modules.", + "bbox": [ + 496, + 672, + 893, + 868 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement - We thank ANR for support through AI-chair grant \"Remember\" (ANR-20-CHIA-0018).", + "bbox": [ + 500, + 871, + 890, + 900 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "11012", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Michal Adamkiewicz, Timothy Chen, Adam Caccavale, Rachel Gardner, Preston Culbertson, Jeannette Bohg, and Mac Schwager. Vision-only robot navigation in a neural radiance world. IEEE Robotics and Automation Letters, 2022. 2, 3, 4, 5", + "[2] Peter Anderson, Angel X. 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In ICRA, 2017. 2" + ], + "bbox": [ + 503, + 92, + 893, + 900 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "11014", + "bbox": [ + 480, + 945, + 519, + 955 + ], + "page_idx": 10 + }, + { + "type": "ref_text", + "text": "[63] Zihan Zhu, Songyou Peng, Viktor Larsson, Weiwei Xu, Hujun Bao, Zhaopeng Cui, Martin R Oswald, and Marc Pollefeys. Nice-slam: Neural implicit scalable encoding for slam. CVPR, 2022. 3", + "bbox": [ + 78, + 90, + 470, + 146 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "11015", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/Multi-Object Navigation with Dynamically Learned Neural Implicit Representations/8c2cacd0-618b-43fb-afc2-cdc6e282531c_model.json b/2023/Multi-Object Navigation with Dynamically Learned Neural Implicit Representations/8c2cacd0-618b-43fb-afc2-cdc6e282531c_model.json new file mode 100644 index 0000000000000000000000000000000000000000..3a0802da4945da39d84f12023316d781fec9c44e --- /dev/null +++ b/2023/Multi-Object Navigation with Dynamically Learned Neural Implicit Representations/8c2cacd0-618b-43fb-afc2-cdc6e282531c_model.json @@ -0,0 +1,2325 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.131, + 0.895, + 0.156 + ], + "angle": 0, + "content": "Multi-Object Navigation with dynamically learned neural implicit representations" + }, + { + "type": "text", + "bbox": [ + 0.153, + 0.179, + 0.273, + 0.198 + ], + "angle": 0, + "content": "Pierre Marza" + }, + { + "type": "text", + "bbox": [ + 0.313, + 0.181, + 0.466, + 0.199 + ], + "angle": 0, + "content": "Laetitia Matignon" + }, + { + "type": "text", + "bbox": [ + 0.505, + 0.181, + 0.641, + 0.198 + ], + "angle": 0, + "content": "Olivier Simonin" + }, + { + "type": "text", + "bbox": [ + 0.683, + 0.181, + 0.81, + 0.198 + ], + "angle": 0, + "content": "Christian Wolf3" + }, + { + "type": "text", + "bbox": [ + 0.324, + 0.2, + 0.643, + 0.217 + ], + "angle": 0, + "content": "\\(^{1}\\)INSA Lyon \\(^{2}\\)UCBL \\(^{3}\\)Naver Labs Europe" + }, + { + "type": "text", + "bbox": [ + 0.293, + 0.22, + 0.68, + 0.234 + ], + "angle": 0, + "content": "{pierre.marza, olivier.simonin}@insa-lyon.fr" + }, + { + "type": "text", + "bbox": [ + 0.218, + 0.238, + 0.752, + 0.251 + ], + "angle": 0, + "content": "laetitia.matignon@univ-lyon1.fr,christian.wolf@naverlabs.com" + }, + { + "type": "text", + "bbox": [ + 0.2, + 0.254, + 0.769, + 0.27 + ], + "angle": 0, + "content": "Project Page: https://pierremarza.github.io/projects/dynamicImplicit Representations/" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.305, + 0.314, + 0.32 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.336, + 0.474, + 0.669 + ], + "angle": 0, + "content": "Understanding and mapping a new environment are core abilities of any autonomously navigating agent. While classical robotics usually estimates maps in a stand-alone manner with SLAM variants, which maintain a topological or metric representation, end-to-end learning of navigation keeps some form of memory in a neural network. Networks are typically imbued with inductive biases, which can range from vectorial representations to birds-eye metric tensors or topological structures. In this work, we propose to structure neural networks with two neural implicit representations, which are learned dynamically during each episode and map the content of the scene: (i) the Semantic Finder predicts the position of a previously seen queried object; (ii) the Occupancy and Exploration Implicit Representation encapsulates information about explored area and obstacles, and is queried with a novel global read mechanism which directly maps from function space to a usable embedding space. Both representations are leveraged by an agent trained with Reinforcement Learning (RL) and learned online during each episode. We evaluate the agent on Multi-Object Navigation and show the high impact of using neural implicit representations as a memory source." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.695, + 0.208, + 0.71 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.471, + 0.856 + ], + "angle": 0, + "content": "Autonomous navigation in complex unknown 3D environments from visual observations requires building a suitable representation of the environment, in particular when the targeted navigation task requires high-level reasoning. Whereas classical robotics builds these representations explicitly through reconstructions, possibly supported through machine learning, end-to-end training learns them automatically either from reward, by imitation learning or through self-supervised objectives." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.902 + ], + "angle": 0, + "content": "While spatial representations can emerge even in unstructured agents, as shown in the form of grid-cells in artificial [16, 3] and biological agents [25], spatial inductive biases" + }, + { + "type": "image", + "bbox": [ + 0.52, + 0.305, + 0.692, + 0.418 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.522, + 0.423, + 0.692, + 0.559 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.697, + 0.303, + 0.871, + 0.414 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.7, + 0.423, + 0.872, + 0.559 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.569, + 0.895, + 0.765 + ], + "angle": 0, + "content": "Figure 1. We propose two implicit representations as inductive biases for autonomous agents — both are learned online during each episode. (2) a semantic representation \\( f_{s} \\) predicts positions \\( \\mathbf{x} \\) from goals \\( \\mathbf{g} \\) given as semantic codes. We show Ground Truth object positions (rectangles) and predictions (round; radius shows uncertainty, unit-less, as an illustration). Blue and pink objects have been observed, but not the yellow target. (3) A structural representation \\( f_{o} \\) predicts occupancy and exploration \\( s \\) from positions \\( \\mathbf{x} \\); we provide a global read which directly maps from function space \\( f_{o} \\) (represented by trainable weights \\( \\theta_{o} \\)) to a context embedding \\( e \\) used by the agent. (4) shows the reconstruction produced by a decoder \\( Dec \\) during training. Orange=navigable, Green=Obstacles, Blue=Unexplored. (1) a ground-truth map is shown for reference, simulating a fully explored scene." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.897, + 0.903 + ], + "angle": 0, + "content": "can support learning actionable spatial representations and decrease sample complexity. Popular inductive biases are metric maps [44, 5, 26], topological maps [6, 12] and recently, self-attention, adapting transformers [55] to sequential decision making and navigation [20, 18, 13, 47]. The chosen representation should support robust estimation of navigable space even in difficult conditions, mapping fea" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "11004" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.168 + ], + "angle": 0, + "content": "tures and objects of interest, as well as querying and reusing this information at a later time. The representation should be as detailed as required, span the full (observed) scene, easy to query, and efficient to read and write to, in particular when training is done in large-scale simulations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.17, + 0.472, + 0.397 + ], + "angle": 0, + "content": "Our work builds on neural fields and implicit representations, a category of models which represent the scene geometry, and eventually the semantics, by the weights of a trained neural network [57]. They have the advantage of avoiding the explicit choice of scene representation (e.g. volume, surface, point cloud etc.) and inherently benefit from the generalization abilities of deep networks to interpolate and complete unobserved information. Implicit representations have demonstrated impressive capabilities in novel view synthesis [40, 51], and have potential as a competitive representation for robotics [42, 32, 52, 1]. Their continuous nature allows them to handle level of detail efficiently through a budget given as the amount of trainable weights. This allows to span large environments without the need of discretizing the environment and handling growing maps." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.398, + 0.472, + 0.716 + ], + "angle": 0, + "content": "We explore and study the potential of implicit representations as inductive biases for visual navigation. Similar to recent work in implicit SLAM [52], our representations are dynamically learned in each episode. Going beyond, we exploit the representation dynamically in one of the most challenging visual navigation tasks, Multi-Object Navigation [56]. We introduce two complementary representations, namely a query-able Semantic Finder trained to predict the scene coordinates of an object of interest specified as input, and an Occupancy and Exploration Implicit Representation, which maps 2D coordinates to occupancy information, see Figure 1. We address the issue of the efficiency of querying an implicit representation globally by introducing a new global read mechanism, which directly maps from function space, represented through its trainable parameters, to an embedding summarizing the current status of occupancy and exploration information, useful for navigation. Invariance w.r.t. reparametrization of the queried network is favored (but not enforced) through a transformer based solution. Our method does not require previous rollouts on the scene for pre-training or building a representation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.718, + 0.472, + 0.868 + ], + "angle": 0, + "content": "Our work targets a fundamental aspect of visual and semantic navigation, the mapping of key objects of interest. MultiON is currently one of the few benchmarks which evaluates it. As argued in previous literature [5, 56], only sequential tasks, where objects have to be found in a given order, allow object level mapping to emerge directly from reward. This follows from the observation that an agent trained to find and retrieve a single object per episode (from reward) is not required to map seen target objects, as observing them directly leads to a reactive motion towards them." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Our contributions can be summarized as follows: (i) We propose two implicit representations for semantic, occupancy" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.213 + ], + "angle": 0, + "content": "and exploration information, which are trained online during each episode; (ii) We introduce a new global read procedure which can extract summarizing context information directly from the function itself; (iii) We show that the representations obtain performance gains compared to classical neural agents; (iv) We evaluate and analyze key design choices, the representation's scaling laws and its capabilities of lifelong learning." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.226, + 0.642, + 0.243 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.252, + 0.895, + 0.433 + ], + "angle": 0, + "content": "Visual Navigation — is a rich problem that involves perception, mapping and decision making, with required capacities being highly dependent on the specific task. A summary of reasoning in navigation has been given in [2], differentiating, for instance, between waypoint navigation (Pointgoal) [2] or finding objects of semantic categories (ObjectGoal) [2]. More recent tasks have been explicitly designed to evaluate and encourage mapping objects of interest during navigation itself [4, 56]. They are of sequential nature and use external objects, which are not part of the scanned 3D scenes but randomly placed. In this work we address Multi-Object Navigation (MultiON) [56]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.434, + 0.895, + 0.735 + ], + "angle": 0, + "content": "Mapping and Representations — Classical methods often rely on SLAM [8, 34] which has been proposed in different variants (2D or 3D metric, topological, eventually with semantics) and observations (LIDAR, visual etc.). The objective is to integrate observations and odometry estimates over a trajectory and reconstruct the scene. Differentiable variants have been proposed recently [28, 30]. Mapping can also be discovered through interactions by a blind agent [7]. Visual Navigation can also be framed as an end-to-end learning problem, where representations are learned automatically from different signals, in particular RL. Memory can take the form of vectorial representations in recurrent units [41, 27, 62], with hybrid variants including mapping [12, 48, 17]. Recent work tends to augment agents with more structured memories. Examples are spatial metric tensors, which can contain occupancy [11], semantics [10] or be fully latent, effectively corresponding to inductive biases of the neural agents [44, 5, 26]. Other alternatives are topological maps [6, 12] or self-attention and transformers [55] adapted to navigation [20, 18, 13, 47]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.736, + 0.897, + 0.903 + ], + "angle": 0, + "content": "Implicit representations — were initially targeting 3D reconstruction [39, 45, 14]. The core idea is to replace the need for discretizing 3D space into voxels [38], 3D points [19] or meshes [23], by an implicit representation of the 3D structure of the scene through the parameters of a learned neural network. Recent work [40, 51] achieved state-of-the-art performance on novel view synthesis with neural implicit representations. The NeRF paper introduced a differentiable volume rendering loss allowing to supervise 3D scene reconstruction from only 2D supervision [40]. For a more detailed overview of recent advances in the rapidly" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "11005" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.354, + 0.106 + ], + "angle": 0, + "content": "growing field, we refer the reader to [57]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.107, + 0.471, + 0.379 + ], + "angle": 0, + "content": "Implicit representations in robotics — are a recent phenomenon, used to represent density [1] or to perform visuomotor control [33]. Related to goal-oriented navigation, some work targets SLAM with neural implicit representations [52], follow-up adding semantics [59], learned from sparse semantic annotations of the scene. [60] is also built on top of [52] and allows a user to interactively provide semantic annotation for the implicit representation to be trained on in real time. [63] proposes a hierarchical implicit representation of a scene to scale to larger environments and obtain a more detailed reconstruction. [15] combines feature-based SLAM and NeRF. Our work goes beyond implicit SLAM and does not stop at reconstructing a scene. We not only build implicit representations dynamically during the episode, we also use them in a down-stream navigation task without requiring any initial rollout for pre-training or building a representation. We also combine two different implicit representations targeting semantics vs. scene structure." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.379, + 0.471, + 0.606 + ], + "angle": 0, + "content": "Analyzing the neural network function space — implicit representations are instances of function spaces, which are represented through their trainable parameters. Previous work performed analyses by predicting accuracy from network weights [54, 35, 36] or the generality gap between train and test performance from hidden activations [29, 58]. A direction pioneered by Hypernetworks [24] directly predict the network weights. Recently, [61] generate the weights of a CNN from support samples in the context of few-shot learning. More related to our work, [43] learns to predict the weights of an implicit representation based on external factors in the context of spatio-temporal dynamics encoding. In this work, we learn a direct mapping between an implicit representation, represented by its weights, to an actionable embedding summarizing the scene globally." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.619, + 0.438, + 0.637 + ], + "angle": 0, + "content": "3. Navigating with implicit representations" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.47, + 0.78 + ], + "angle": 0, + "content": "We target the Multi-Object Navigation task [56], which requires an agent to navigate in a photo realistic 3D environment from RGB-D observations \\(\\mathbf{o}_t\\) and reach a sequence of target objects (colored cylinders) in a particular order. Goal categories \\(\\mathbf{g}_t\\) are given at each time step \\(t\\). In an RL setting, the agent receives positive reward for each successfully reached object as well as when the geodesic distance towards the goal decreases, and a small negative reward for each step, favoring short paths." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.471, + 0.902 + ], + "angle": 0, + "content": "We follow and augment a base end-to-end architecture used in many recent RL approaches, including [56, 37, 41], with the RGB-D observation, class of the current target and previous action as input to the agent. Temporal information is aggregated with a GRU unit whose output is fed to actor and critic heads. We equip this agent with two implicit representations, trained to hold and map essential information necessary for navigation: the positions of different objects of" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "interest, and occupancy / exploration information, as shown in Figure 1," + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.134, + 0.895, + 0.273 + ], + "angle": 0, + "content": "The goal of the Semantic Finder \\( f_{s}(:,\\theta_{s}) \\) parameterized by trainable weights \\( \\theta_{s} \\) is to predict the absolute position of an object as \\( \\mathbf{x} = [\\mathbf{x}_x\\mathbf{x}_y\\mathbf{x}_z] = f_s(\\mathbf{q};\\theta_s) \\) specified through an input query vector \\( \\mathbf{q} \\). Uncertainty \\( u \\) is also estimated — see Section 3.1 for details. \\( \\mathbf{x} \\) is then converted into coordinates relative to the agent to be fed to the GRU. Compared to classical metric representations [26, 44, 12, 5], querying the location of an object can be done through a single forward pass." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.282, + 0.895, + 0.405 + ], + "angle": 0, + "content": "The Occupancy and Exploration Representation \\( f_{o}(:,\\theta_{o}) \\) parameterized by trainable weights \\( \\theta_{o} \\) encodes information about free navigable space and obstacles. It predicts occupancy \\( \\mathbf{s} \\) as a classification problem with three classes {Obstacle, Navigable, Unexplored}, as \\( \\mathbf{s} = f_{o}(\\phi ;\\theta_{o}) \\), where \\( \\phi \\) is a position feature vector encoded from coordinates \\( \\mathbf{x} \\) — see Section 3.2 for details." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.418, + 0.895, + 0.569 + ], + "angle": 0, + "content": "The Occupancy and Exploration Representation can in principle be queried directly for a single position, but reading out information over a large area directly this way would require multiple reads. We propose to compress this procedure by providing a trainable global read operation \\( r(:, \\theta_g) \\), which predicts an embedding \\( \\mathbf{e} \\) containing a global context about what has already been explored, and positions of navigable space. The prediction is done directly from the trainable parameters of the implicit representation, as \\( \\mathbf{e} = r(\\theta_o; \\theta_r) \\). Here \\( \\theta_o \\) is input to \\( r \\), whereas \\( \\theta_r \\) are its parameters." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.57, + 0.895, + 0.706 + ], + "angle": 0, + "content": "Given representations \\( f_{s} \\) and \\( f_{o} \\), a single forward pass of the agent at time step \\( t \\) and for a goal \\( g_{t} \\) involves reading the representations and providing the input to the policy. The current RGB-D observation \\( o_{t} \\) is also encoded by the convolutional network \\( c \\) (different from the projection module \\( p \\) used to generate samples for training the Semantic Finder). Previous action \\( a_{t-1} \\) and current goal \\( g_{t} \\) are passed through embedding layers, named \\( L(\\cdot) \\) in the following equations. These different outputs are fed to the policy," + }, + { + "type": "equation", + "bbox": [ + 0.511, + 0.714, + 0.894, + 0.731 + ], + "angle": 0, + "content": "\\[\n\\mathbf {x} _ {t} = f _ {s} \\left(g _ {t}; \\theta_ {s, t}\\right), \\mathbf {e} _ {t} = r \\left(\\theta_ {o, t}; \\theta_ {r}\\right), \\mathbf {c} _ {t} = c \\left(o _ {t}; \\theta_ {c}\\right), \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.511, + 0.733, + 0.892, + 0.75 + ], + "angle": 0, + "content": "\\[\n\\mathbf {h} _ {t} = G R U \\left(\\mathbf {h} _ {t - 1}, \\mathbf {x} _ {t}, u _ {t}, \\mathbf {e} _ {t}, L \\left(a _ {t - 1}\\right), L \\left(g _ {t}\\right), \\mathbf {c} _ {t}; \\theta_ {G}\\right), \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.515, + 0.753, + 0.892, + 0.769 + ], + "angle": 0, + "content": "\\[\na _ {t} = \\pi \\left(\\mathbf {h} _ {t}; \\theta_ {\\pi}\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.894, + 0.901 + ], + "angle": 0, + "content": "where we added indices \\(\\cdot_t\\) to relevant variables to indicate time. Please note that the trainable parameters \\(\\theta_{s,t}\\) and \\(\\theta_{o,t}\\) of the two implicit representations are time dependent, as they depend on the observed scene and are updated dynamically, whereas the parameters of the policy \\(\\pi\\) and the global reader \\(r\\) are not. Here, GRU corresponds to the update equations of a GRU network, where we omitted gates for ease of notation. The notation \\(a_t = \\pi(.)\\) predicting action \\(a_t\\) is" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "11006" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.162, + 0.088, + 0.817, + 0.379 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.385, + 0.895, + 0.43 + ], + "angle": 0, + "content": "Figure 2. Navigating with implicit representations. Red connections \\(\\longrightarrow\\) indicate the training process of the two implicit representations (= mapping), which is also done during agent deployment. Black connections \\(\\longrightarrow\\) show the forward pass of the agent. ■ are discrete learned embeddings (LUT). Policy training is not shown in this figure." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.452, + 0.471, + 0.481 + ], + "angle": 0, + "content": "also a simplification, as we train the agent with PPO, an actor-critic method — see Section 3.4." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.484, + 0.472, + 0.605 + ], + "angle": 0, + "content": "Mapping means training! — The implicit representations \\( f_{s} \\) and \\( f_{o} \\) maintain a compact and actionable representation of the observed scene, and as such need to be updated at each time step from the current observation \\( o_{t} \\). Given their implicit nature and implementation as neural networks, updates are gradient based and done with SGD. The implicit representations are therefore trained from scratch at each episode even after deployment." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.606, + 0.472, + 0.803 + ], + "angle": 0, + "content": "Training a representation from observations obtained sequentially during an episode also raises a serious issue of catastrophic forgetting [22], as places of the scene observed early might be forgotten later in the episode [52, 59]. We solve this by maintaining two replay buffers throughout the episode, one for each representation. Training samples are generated from each new observation and added to the replay buffers at each time step. Both representations are then trained for a number of gradient steps (\\( n_s \\) for the Semantic Finder and \\( n_o \\) for the Exploration and Occupancy Representation). Details on the two representations and their training are given in Sections 3.1 and 3.2. The global reader \\( r \\) is not trained or finetuned online but rather trained once offline." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.816, + 0.295, + 0.833 + ], + "angle": 0, + "content": "3.1. The Semantic Finder \\( f_{s} \\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.903 + ], + "angle": 0, + "content": "While recent work on implicit representations for robotics focused on signed distance functions [42, 32], occupancy [52] or density, assuming light density approximates mass density [1], the aim of this model is to localize an object" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.452, + 0.895, + 0.619 + ], + "angle": 0, + "content": "of interest within the scene, which can be seen as inverse operation to classical work. From a query vector given as input, the Semantic Finder predicts the position of the object, which is particularly useful for an agent interacting with an environment in the context of a goal conditioned task. It is implemented as a 3-layer MLP with ReLu activations in the intermediate layers and a sigmoid activation for the output. Hidden layers have 512 neurons. The query vector \\(\\mathbf{q}\\) corresponds to the 1-in-K encoding of the target object class, which during navigation is directly determined by the object goal \\(g_{t}\\) provided by the task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.624, + 0.895, + 0.716 + ], + "angle": 0, + "content": "Mapping/Training - The implicit representation is updated minimizing the L1 loss between the prediction \\(\\mathbf{x}_i = f_s(\\mathbf{q}_i, \\theta_s)\\) and the supervised coordinates \\(\\mathbf{x}_i^*\\) (we avoided the term \"ground-truth\" here on purpose), \\(\\mathcal{L}_s = \\sum_i \\| \\mathbf{x}_i^* - \\mathbf{x}_i \\|_1\\), where the sum goes over the batch sampled from the scene replay buffer. Coordinates \\(\\mathbf{x}_i^*\\) are normalized \\(\\in [0, 1]\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.897, + 0.902 + ], + "angle": 0, + "content": "The data pairs \\((x_{i}^{*}, q_{i})\\) for training are created from each observation \\(o_{t}\\) during each time step, each data point corresponding to an observed point. Pixels in \\(o_{t}\\) are inversely projected into 3D coordinates in the scene using the depth channel, the camera intrinsics, as well as agent's coordinates and heading that are assumed to be available, as in [56]. The query vector \\(\\mathbf{q}\\) corresponds to a 9-dimensional vector encoding a distribution over object classes (8 target objects and the \"background\" class). Let us recall that while the training of the representation is supervised, this supervision cannot use \"ground-truth\" information available only during training. All supervision information is required to be" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "11007" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.212 + ], + "angle": 0, + "content": "predicted from the data available to the agent even after deployment. We predict object class information through a semantic segmentation model \\( p \\), which is applied to each current RGB-D observation \\( o_t \\in \\mathbb{R}^{h \\times w \\times 4} \\), recovering the output segmentation map \\( m_t \\in \\mathbb{R}^{k \\times l \\times 9} \\). The model has been pre-trained on the segmentation of the different target objects, i.e. coloured cylinders, and is not fine-tuned during training of the agent itself." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.213, + 0.474, + 0.365 + ], + "angle": 0, + "content": "Training data pairs \\((x_{i}^{*}, q_{i})\\) are sampled from this output. The supervised coordinates \\(x_{i}^{*}\\) are simply the mean 3D coordinates of each feature map cell, after inverse projection. The query vector \\(\\mathbf{q}_{i}\\) is the distribution over semantic classes. After the replay buffer is updated, a training batch must be sampled to update the neural field. One fourth of the samples in the batch of size \\(b\\) correspond to the \\(b/4\\) last steps. The rest are sampled from the previous steps in the replay buffer. Uniform sampling is also performed among pairs collected at a given time step." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.381, + 0.474, + 0.61 + ], + "angle": 0, + "content": "Estimating uncertainty — is an essential component, as querying yet unseen objects will lead to wrong predictions, which the agent needs to recognize as such, and discard. The estimation of uncertainty in neural networks is an open problem, which has been previously addressed through different means, including drop out as a Bayesian approximation [21], variational information bottlenecks [50], density estimation [31], and others. In this work, we approximate a density estimate in the scene replay buffer by calculating the minimum Euclidean distance between the input query and all embeddings in the replay buffer at the current time step. The method is simple and efficient and does not require explicitly fitting a model to estimate the marginal distribution \\( p(\\mathbf{q}) \\), in particular as the uncertainty representation is latent, can be un-normalized as not required to be a probability." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.616, + 0.471, + 0.648 + ], + "angle": 0, + "content": "3.2. Occupancy and Exploration Implicit Representation \\( f_{o} \\)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.654, + 0.473, + 0.837 + ], + "angle": 0, + "content": "Unlike \\( f_{s} \\), the occupancy representation \\( f_{o} \\) is closer to classical implicit representations in robotics, e.g. [52, 42, 32, 1], which map spatial coordinates to variables encoding information on navigable area like occupancy or signed distances. Different to previous work, our representation also includes exploration information, which changes over time during the episode. Once explored, a position changes its class, which makes our neural field dynamic. Another difference with \\( f_{s} \\) is that the latter deals with 3D coordinates while \\( f_{o} \\) is a topdown 2D representation. Inspired by [57, 53], the model uses Fourier features \\( \\phi \\) extracted from the 2D coordinates \\( \\mathbf{x} \\) previously normalized \\( \\in [0,1] \\)," + }, + { + "type": "equation", + "bbox": [ + 0.095, + 0.844, + 0.473, + 0.865 + ], + "angle": 0, + "content": "\\[\n\\phi = (\\cos (\\mathbf {x} 2 ^ {0}), \\sin (\\mathbf {x} 2 ^ {0}), \\dots , \\cos (\\mathbf {x} 2 ^ {\\frac {p}{4}}), \\sin (\\mathbf {x} 2 ^ {\\frac {p}{4}})). (4)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.473, + 0.902 + ], + "angle": 0, + "content": "The network \\( f_{o} \\) is a 3-layer MLP with ReLu intermediate activations and a softmax function at the output layer. Hidden" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.748, + 0.107 + ], + "angle": 0, + "content": "layers have 512 neurons, and \\( p = 40 \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.108, + 0.895, + 0.304 + ], + "angle": 0, + "content": "Mapping/Training — The implicit representation is updated minimizing the Cross Entropy loss between the prediction \\(\\mathbf{s}\\) of the neural field and the supervised label \\(\\mathbf{s}^*\\) of three classes \\(\\{\\text{Obstacle, Navigable, Unexplored}\\}\\), as \\(\\mathcal{L}_o = -\\sum_{c=1}^{3} \\mathbf{s}_c^* \\log \\mathbf{s}_c\\). As for the Semantic Finder, training data pairs \\((\\mathbf{s}^*, \\mathbf{s})\\) are created through inverse perspective projection of the pixels of the observation \\(o_t\\) into 3D scene coordinates. Thresholding the \\(z\\) (height) coordinate decides between Navigable and Obstacle classes. Points with a \\(z\\) coordinate higher than a certain threshold are discarded. The replay buffer is balanced between both classes, and only samples of the last 1000 steps are kept. Samples of the Unexplored class are not stored." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.304, + 0.894, + 0.381 + ], + "angle": 0, + "content": "The replay buffer is sampled similarly to the one for the Semantic Finder. However, additional samples for the Unexplored class are created by sampling uniformly inside the scene, for speed reasons simply ignoring conflicts with explored areas and treating them as noisy labels." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.392, + 0.893, + 0.423 + ], + "angle": 0, + "content": "3.3. Global Occupancy Read \\( r \\) — handling reparametrization invariance" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.431, + 0.895, + 0.642 + ], + "angle": 0, + "content": "The global Occupancy reader \\( r \\) allows to query the occupancy information of the scene globally, beyond point-wise information, and as such is a trainable mapping from the space of functions \\( f_{o}(:,.) \\) to an embedding space \\( e \\). In particular, two functions \\( f_{o} \\) and \\( f_{o}' \\) s.t. \\( f_{o}(\\mathbf{x}) = f_{o}'(\\mathbf{x}) \\forall \\mathbf{x} \\) should be mapped to identical or close embeddings. However, as the occupancy networks \\( f_{o} \\) are implemented as MLPs, any given instance \\( f_{o}(:,;\\theta_{o}) \\) parameterized by trainable weights \\( \\theta_{o} \\) can be reparametrized by any permutation of hidden units, which leads to permutations of the rows and columns, respectively, of two weight matrices, its own and the one of the preceding layer. This reparameterization keeps the represented functions identical, although their representations as weight vectors are different." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.896, + 0.854 + ], + "angle": 0, + "content": "To favor learning a global occupancy reader which is invariant w.r.t these transformations, we implement it as a transformer model with self-attention [55] — this, however, does not enforce full invariance. The model takes as input a sequence of tokens \\((w_{1},\\dots,w_{N})\\), where \\(w_{i}\\in \\mathbb{R}^{a}\\) is a learned linear embedding of the incoming weights of one neuron within the implicit representation \\(f_{o}\\), and \\(N\\) is the number of neurons of \\(f_{o}\\). Each token is summed with a positional encoding in the form of Fourier features. An additional \"CLS\" token with learned embedding is concatenated to the input sequence. The reader is composed of 4 self-attention layers, with 8 attention heads. The output representation of the \"CLS\" token is used as the global embedding of the implicit representation." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Training - The global reader \\( r \\) is trained with full supervision from a dataset of \\( 25k \\) trajectories composed of MLP weights \\( \\theta_{o,i} \\) and absolute maps \\( \\mathbf{M}_i \\), \\( i..1..25k \\). Each" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "11008" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.198 + ], + "angle": 0, + "content": "map is a metric tensor providing occupancy information extracted from the corresponding implicit representation, i.e. \\(\\mathbf{M}_i(\\mathbf{x}_y,\\mathbf{x}_x) = f_o(\\mathbf{x},\\theta_{o,i})\\) . The dataset also contains an egocentric version \\(\\mathbf{M}_i^{\\prime}\\) of each map, which is centered on the agent and oriented depending on its current heading. The reader \\(r\\) is trained in an Encoder-Decoder fashion, where \\(r\\) plays the role of the encoder," + }, + { + "type": "equation", + "bbox": [ + 0.156, + 0.209, + 0.472, + 0.227 + ], + "angle": 0, + "content": "\\[\n\\mathbf {e} _ {i} = r \\left(\\theta_ {o, i}\\right), \\quad \\hat {\\mathbf {M}} _ {i} = D e c \\left(e _ {i}, p _ {i}\\right), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.238, + 0.47, + 0.283 + ], + "angle": 0, + "content": "where \\( p_i \\) is the agent pose (position and heading), necessary to decode ego-centric information. We minimize a cross entropy loss on the prediction of ego-centric maps," + }, + { + "type": "equation", + "bbox": [ + 0.093, + 0.293, + 0.472, + 0.313 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {g} = - \\sum_ {i} \\sum_ {k} \\sum_ {l} \\sum_ {c = 1} ^ {3} \\mathbf {M} _ {i, c} ^ {\\prime *} (k, l) \\log \\mathbf {M} _ {i, c} ^ {\\prime} (k, l) (6)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.322, + 0.473, + 0.399 + ], + "angle": 0, + "content": "Directly training this prediction proved to be difficult. We propose a procedure involving several steps, detailed in section 3.5. After the training phase, the reader \\( g \\) is used in the perception + mapping module of the agent as given in equation (1), and kept frozen during agent RL training." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.408, + 0.262, + 0.423 + ], + "angle": 0, + "content": "3.4. Training the Agent" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.43, + 0.473, + 0.626 + ], + "angle": 0, + "content": "The agent is trained with RL, more precisely Proximal Policy Optimization (PPO) [49]. The inner training loops of the implicit representations are supervised (red arrows in Figure 2) and occur at each time step in the forward pass, whereas the RL-based outer training loop of the agent occurs after \\( N \\) acting steps (black arrows in Figure 2). As the perception module used to generate training data from RGBD-observations for the Semantic Finder \\( f_{s} \\) is independent of the visual encoder \\( c \\) in the agent (see Figure 2), and as its query \\( \\mathbf{q}_t \\) is fixed to the navigation goal \\( \\mathbf{g}_t \\), there is no need to track the weights \\( \\theta_{s} \\) at each time step in order to backpropagate the PPO loss (outer training). This is a key design choice of our method." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.628, + 0.473, + 0.839 + ], + "angle": 0, + "content": "Training assumptions — We do not rely on the existence of global GT maps for occupancy, as \\( f_{o}() \\) and \\( r() \\) were trained on observation data from agent trajectories only. However, similar to [37, 46], we exploit object positions in simulation, during training only; Moreover, we require pixel-wise segmentation masks during training. We believe that this does not change requirements, as the goal is to fully exploit 3D photo-realistic simulators as a data source and see how far the field can go with this. Generalization requirements are unchanged: we require our agent to be able to generalize to new unseen scenes. Generalization to unseen object categories is not targeted, and in MultiON task setup not possible for any agent, as object positions and labels are required for reward calculation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.848, + 0.317, + 0.864 + ], + "angle": 0, + "content": "3.5. Training the global reader" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.473, + 0.902 + ], + "angle": 0, + "content": "The proposed training procedure for the global reader \\( r \\) (performed before training the agent) can be split into 3 phases." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.199 + ], + "angle": 0, + "content": "The architecture for the convolutional decoder \\(Dec()\\) is kept the same in all of them. The hyperparameters of its different layers are detailed in the Supplementary Material. It is composed of 6 transpose convolution layers along with batch norm layers and ReLU activations, except for the last layer with a softmax activation. Figure 3 provides an overview of the 3 steps involved in the training of the global reader." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.214, + 0.895, + 0.275 + ], + "angle": 0, + "content": "Fully convolutional autoencoder — The first step is to train a fully convolutional autoencoder on the set of absolute maps \\(\\mathbf{M}_i\\), \\(i..1..25k\\). Only the decoder weights are kept." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.288, + 0.894, + 0.38 + ], + "angle": 0, + "content": "Global reader training on absolute maps — The second step consists in training the global reader to output embeddings fed to the frozen decoder from the previous step. The objective is to reconstruct absolute maps from the weights of the implicit representation. The global reader weights are kept after this training phase." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.392, + 0.894, + 0.575 + ], + "angle": 0, + "content": "Global reader finetuning on egocentric maps The global reader, whose weights are initialized from the weights obtained in the previous step, is now trained along with the same decoder from the first step (also used in the second step) on the set of egocentric maps \\(\\mathbf{M}_i^{\\prime}\\), \\(i..1..25k\\). Both global reader and decoder are finetuned. The output of the global reader is not directly fed to the decoder, but is passed through linear layers in order to fuse information about first the position of the agent, and then its heading because this time the right operations of shift and rotation must be applied in order to reconstruct egocentric maps." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.587, + 0.892, + 0.693 + ], + "angle": 0, + "content": "Integrating the pre-trained global reader into the agent After this pre-training in 3 steps, the weights of the global reader are frozen and not updated during the RL training. However, a linear layer is learnt to project the 576-dim embedding from the global reader into a 256-dim representation fed to the GRU. This linear layer is trained from reward signals." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.724, + 0.634, + 0.741 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.895, + 0.901 + ], + "angle": 0, + "content": "MultiON task — we target the 3-ON version of the MultiON task [56], where the agent deals with sequences of 3 objects, each belonging to one of 8 classes (cylinders of different colors). At each step, the observation \\(\\mathbf{o}_t\\) is an RGB-D image of size \\(256 \\times 256 \\times 4\\) and the target class is a one-in-K (\\(K = 8\\)) vector. The action space is discrete: {Move forward \\(0.25m\\), Turn left \\(30^\\circ\\), Turn right \\(30^\\circ\\), Found}. An episode is considered successful if the agent finds all of the targets before the time limit (2, 500 environment steps), and chooses the Found action for each one at a distance closer to" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "11009" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.129, + 0.09, + 0.844, + 0.442 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.454, + 0.895, + 0.484 + ], + "angle": 0, + "content": "Figure 3. Training the Global Reader in 3 steps: \\(①\\) training a convolutional auto-encoder on absolute maps; \\(②\\) extension to inputs equal to weights \\(\\theta_{o} =\\) the gobal reader; \\(③\\) extension to predicting ego-centric maps, better suited to navigation problems." + }, + { + "type": "table", + "bbox": [ + 0.169, + 0.494, + 0.803, + 0.613 + ], + "angle": 0, + "content": "
0 - 3030 - 5050 - 70— Val —— Test —
SOSOSOSuccessProgressSPLPPLSuccessProgressSPLPPL
------33.2±1.249.0±1.121.2±0.531.6±1.242.3±1.556.7±0.928.1±1.037.8±1.8
μ--✓-✓37.8±1.652.3±0.926.35±1.536.5±0.847.0±1.760.5±1.634.5±0.844.2±1.0
--✓-✓✓38.5±4.652.5±4.828.2±2.138.3±1.746.7±3.060.1±3.135.1±1.444.8±1.0
------32.147.721.632.641.055.928.939.0
↑--✓-✓38.151.927.337.148.661.535.244.2
--✓-✓✓43.156.830.540.149.763.436.445.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.62, + 0.895, + 0.65 + ], + "angle": 0, + "content": "Table 1. Impact of the implicit representations: navigation performance on MultiON val and MultiON test. S=f_s activated, O=f_o activated in the corresponding training period (see text). Top/μ: means over 3 runs; Bottom/↑: best validation seeds over 3 runs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.673, + 0.471, + 0.718 + ], + "angle": 0, + "content": "\\(1.5m\\). Calling Found incorrectly terminates episode as a failure. An access to perfect odometry information (localization and heading) was assumed in [56] as the standard protocol." + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.72, + 0.474, + 0.903 + ], + "angle": 0, + "content": "Dataset and metrics — The agent is trained on the Mutterport3d [9] dataset. We followed the standard train/val/test split over scenes (denoted MultiON train, MultiON val, MultiON test): 61 training, 11 validation and 18 test scenes. The train, val and test splits are respectively composed of 50,000, 12,500 and 12,500 episodes per scene. Reported results on the val and test sets (Tables 1 and 2) were computed on a subset of 1,000 randomly sampled episodes. We report standard metrics as used in the navigation literature (and in [56]): Success: percentage of successful episodes — all objects are reached respecting order, time; Progress: percentage of objects successfully found (respecting order," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.673, + 0.892, + 0.718 + ], + "angle": 0, + "content": "time); SPL: Success weighted by Path Length, extending the original SPL metric [2] to MultiON; PPL: Progress weighted By Path Length (the official MultiON challenge metric)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.719, + 0.895, + 0.884 + ], + "angle": 0, + "content": "Global reader dataset — The Global reader \\( r \\) was trained on a dataset of \\( 25k \\) trajectories obtained from rollouts performed by a baseline agent [37]. \\( 95\\% \\) was used for training and the rest for validation. On these trajectories we first trained the occupancy representation \\( f_{o} \\) \"in-situ\", i.e. as if it were deployed on the agent, and we recorded training samples \\( i \\) for training the reader \\( r \\): pairs of network weights \\( \\theta_{o,i} \\) and associated maps \\( M_{i} \\) obtained by iteratively querying the implicit representation. Ego-centric maps were generated from the absolute ones and both were cropped around their center." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Perception module dataset — The perception module" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "11010" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.118, + 0.089, + 0.85, + 0.263 + ], + "angle": 0, + "content": "
AgentραγSuccessProgressSPLPPLAUXORC
(a)OracleMap† [56]-✓50.4±3.560.5±3.140.7±2.248.8±1.9-✓
(b)OracleEgoMap† [56]-✓32.8±5.247.7±5.226.1±4.537.6±4.7-✓
(c)NoMap† [56]-✓16.7±3.633.7±3.313.1±2.426.0±1.7--
(d)ProjNMap† [26]-✓25.9±1.143.4±1.018.3±0.630.9±0.7--
(e)NoMap✓-42.3±1.556.7±0.928.1±1.037.8±1.8--
(f)ProjNMap [26]✓-39.7±2.355.4±1.428.7±1.140.1±1.9--
(g)Implicit (Ours) w/ curriculum w/pre-train✓--46.7±3.060.1±3.135.1±1.444.8±1.0--
(h)ProjNMap + AUX [37]N/A✓N/A57.7±3.770.2±2.737.5±2.045.9±1.9✓-
(i)Implicit (Ours) w/o curriculum w/pre-train + AUX✓✓✓58.3±0.869.4±1.143.8±1.052.1±1.6✓-
(j)Implicit (Ours) w/o curriculum w/o pre-train-✓✓54.8±3.668.0±3.441.7±1.951.3±1.6--
(k)Implicit (Ours) w/o curriculum w/o pre-train + AUX-✓✓57.9±2.069.5±0.643.3±2.251.9±3.7✓-
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.271, + 0.895, + 0.315 + ], + "angle": 0, + "content": "Table 2. Comparison with SOTA methods on MultiON test. †=performance taken from [37]. “AUX” = auxiliary losses using privileged information [37]. “ORC” = non-comparable, uses oracle information. ρ = pre-training of input encoders from [37]. α = finetuning of input encoders with RL. γ = implicit representations are accessible to the agent since the beginning of RL training (w/o curriculum)." + }, + { + "type": "table", + "bbox": [ + 0.116, + 0.335, + 0.432, + 0.384 + ], + "angle": 0, + "content": "
UncertaintySuccessProgressSPLPPL
-35.4±3.049.7±3.329.4±2.040.9±2.4
✓43.4±3.158.0±3.035.1±0.846.4±1.0
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.391, + 0.471, + 0.42 + ], + "angle": 0, + "content": "Table 3. Uncertainty: comparing training w/ semantic input only, no occupancy, from the beg. of training, w/ and w/o uncertainty." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.43, + 0.47, + 0.49 + ], + "angle": 0, + "content": "\\(p\\) was trained to segment the different target objects. The generated dataset is composed of \\(132k\\) pairs of RGB-D observations and segmentation masks. Samples for 4 scenes were kept as a validation set." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.492, + 0.471, + 0.702 + ], + "angle": 0, + "content": "Training details - We use the reward function given in [56] for RL/PPO training (see supplementary material), and train all agents for \\(70M\\) steps as in [37]. For all agents in Table 1 and some in Table 2 (\\(w/\\) pre-train: \\(\\sqrt{}\\) in \\(\\rho\\) column), the encoders (visual encoder \\(c\\), as well as goal and previous action embedding layers, see Figure 2) are pre-trained with a baseline, which corresponds to the ProjNeuralMap agent trained with auxiliary losses [37]. This is done to faster training, as it will be shown later (in Table 2) that the same final performance can be reached without this initial pre-training of encoders. Training and evaluation hyper-parameters, as well as architecture details have been taken from [56]. All reported quantitative results are obtained after 3 training runs for each model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Impact of the implicit representations — Table 1 shows the impact of the two implicit representations on navigation (top: means over 3 runs; bottom: best validation seeds over 3 runs). To keep compute requirements limited and decrease sample complexity, in these ablations we do not train the full agent from scratch, in particular since the early stages of training are spent on learning basic interactions. We decompose training into three phases: \\(0 - 30M\\) steps (no implicit representations, i.e. all entries to the agent related to \\(f_{s}\\) and \\(f_{o}\\) are set to 0); \\(30M - 50M\\) steps (training includes the Semantic Finder \\(f_{s}\\)) and finally \\(50M - 70M\\) steps (full model). This 3-steps approach is used to train all agents in Table 1, and will be denoted as curriculum (See" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.338, + 0.895, + 0.49 + ], + "angle": 0, + "content": "Table 2, \\( w/ \\) curriculum: - in \\( \\gamma \\) column). All metrics on both val and test sets are improved, with the biggest impact provided by the Semantic Finder, which was expected. We conjecture that mapping object positions is a more difficult task, which is less easily delegated to the vectorial GRU representation, than occupancy. We also see an impact of the occupancy representation, which not only confirms the choice of the implicit representation \\( {f}_{o} \\) itself,but also its global read through \\( r\\left( {\\theta }_{o}\\right) \\) . Training curves are given in the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.491, + 0.895, + 0.598 + ], + "angle": 0, + "content": "Uncertainty — has an impact on agent performance, as we show in the ablation in Table 3. Indeed, when training an agent with the semantic input since the beginning of training (w/o curriculum) and no occupancy input (as the uncertainty is only related to semantic information), feeding the agent with the computed uncertainty about the output of the Semantic Finder brings a boost in performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.897, + 0.903 + ], + "angle": 0, + "content": "Comparison with previous SOTA methods — is done in Table 2. The performance entries of these baselines are taken from [37], which describes the winning entry of the CVPR 2021 MultiON competition. Our method outperforms the different competing representations, even when they benefit from the same pre-training scheme and are thus completely comparable. NoMap with pre-training corresponds to the first row of Table 1. The difference between (g) and (i) is the use of the auxiliary tasks in [37], but also that the implicit representations are available to the agent during the whole training period for (i), i.e. no decomposition into 3 phases as in the ablations in Table 1 (w/o curriculum). Moreover, compared to (g), in (i) the weights of the pre-trained encoders are finetuned. We see that the gains of our representations are complementary to the auxiliary losses in [37]. (j) and (k) confirm this finding, showing that most of the gain compared with (h) comes from the implicit representations, with the auxiliary losses bringing an additional boost. (j) and (k) also show that, even though pre-training can help speed up RL training, similar test performance is achieved without it." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11011" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.186, + 0.09, + 0.204, + 0.101 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.099, + 0.264, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.351, + 0.091, + 0.369, + 0.101 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image", + "bbox": [ + 0.272, + 0.098, + 0.429, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.515, + 0.091, + 0.532, + 0.101 + ], + "angle": 0, + "content": "(c)" + }, + { + "type": "image", + "bbox": [ + 0.43, + 0.098, + 0.594, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.08, + 0.236, + 0.597, + 0.306 + ], + "angle": 0, + "content": "Figure 4. Capacity of the semantic representation: we report mean distance prediction error (normalized \\(\\in [0,1]\\)) as a function of the number of stored objects. Replay buffers are composed of dummy queries: (a) one-hot queries with same dimension as number of objects; (b) random query with dimension 9; (c) random query with same dimension as number of objects." + }, + { + "type": "image", + "bbox": [ + 0.639, + 0.1, + 0.871, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.627, + 0.236, + 0.89, + 0.32 + ], + "angle": 0, + "content": "Figure 5. Lifelong learning of the semantic repr. \\( f_{s} \\): we report mean error in meters, test set, 600 episodes, as a function of the number of time steps since the object was first seen in the episode (t=0). The error falls immediately and stays low over the episode." + }, + { + "type": "text", + "bbox": [ + 0.074, + 0.327, + 0.468, + 0.417 + ], + "angle": 0, + "content": "Reconstruction performance of the Global Reader \\( r \\) — although the task of reconstructing egocentric maps from occupancy functions \\( f_{o} \\) (represented by \\( \\theta_{o} \\)) is only used as a proxy task to train the Global reader \\( r \\), we see it is a reliable proxy for the quality of extracting the global latent vector \\( \\mathbf{e} \\) fed to the agent." + }, + { + "type": "table", + "bbox": [ + 0.083, + 0.439, + 0.245, + 0.468 + ], + "angle": 0, + "content": "
AccuracyJaccard Index
83.456.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.481, + 0.255, + 0.523 + ], + "angle": 0, + "content": "Table 4. Performance of the global reader \\( r \\) : We report accuracy and Jaccard index." + }, + { + "type": "text", + "bbox": [ + 0.285, + 0.418, + 0.471, + 0.538 + ], + "angle": 0, + "content": "In Table 4 we report reconstruction performance measured as accuracy and mean Jaccard Index on the validation split of the dataset used to train the reader. We judge that an accuracy of \\(83.4\\%\\) is surprisingly high, given that" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.539, + 0.47, + 0.659 + ], + "angle": 0, + "content": "the global reader needs to reconstruct the content of the representation directly from its parameters \\(\\theta_{o}\\), that each implicit representation has been initialized randomly, and that the reader is required to be invariant w.r.t. to reparameterization (see Section 4). The task is even made harder as neural weights can be considered as an absolute representation of the env. and the reader must combine it with information about the agent pose to reconstruct an egocentric map." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.66, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Capacity of the Semantic Finder — Unlike all other results presented in this paper, this experiment is performed independently of the official MultiON benchmark. We construct a synthetic dataset to evaluate the capacity of the Semantic Finder. More details about the generated data can be found in the supplementary material. As the granularity of the implicit representations is handled through the budget in terms of trainable parameters, we evaluate the capacity of the Semantic Finder \\( f_{s} \\) to store large numbers of objects in Figure 4: In (a), we can see that increasing the number of objects up to 1000 does not increase error with sufficient gradient updates. However, since inputs are 1-in-K, increasing the number of objects also increases capacity. In (c), we see that this does not hold for random objects (not 1-in-K), whose less structured storage requires more capacity. In (b), we keep the input dimension fixed for random objects, which" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.327, + 0.652, + 0.341 + ], + "angle": 0, + "content": "further increases error." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.345, + 0.894, + 0.497 + ], + "angle": 0, + "content": "Evaluating catastrophic forgetting — we evaluate the capacity of the Semantic Finder \\( f_{s} \\) to hold the learned information over the full length of the sequence in spite of the fact that it is continuously trained. Figure 5 shows the evolution of the mean error in distance for the predicted position of queried target objects as a function of time. The error quickly goes below \\( 1.5m \\) once the object has been seen the first time (\\( t = 0 \\) in the plot), which is distance threshold required by the MultiON task, and stays there, providing evidence that the model does not suffer from catastrophic forgetting." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.5, + 0.894, + 0.621 + ], + "angle": 0, + "content": "Runtime performance — inspite of requiring to continuously train the representations, we achieve 45 fps during parallelized RL training, including the environment steps (simulator rendering), forward passes, representation training and RL training on a single V100 GPU. The average time of one agent forward pass, including updates of implicit representations is 20ms on a V100 GPU, which is equivalent to 50 fps, enough for real-time performance." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.645, + 0.619, + 0.66 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.674, + 0.895, + 0.869 + ], + "angle": 0, + "content": "We introduce two implicit representations to map semantic, occupancy and exploration information. The first estimates the position of an object of interest from a vector query, while the second encapsulates information about occupancy and explored area in the current environment. We also introduce a global read directly from the trainable weights of this representation. Our experiments show that both implicit representations have a positive impact on the navigation performance of the agent. We also studied the scaling laws of the semantic representation and its behavior in the targeted lifelong learning problem. Future work will target differentiating through the implicit representations all the way back to the perception modules." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.872, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgement - We thank ANR for support through AI-chair grant \"Remember\" (ANR-20-CHIA-0018)." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "11012" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.473, + 0.184 + ], + "angle": 0, + "content": "[1] Michal Adamkiewicz, Timothy Chen, Adam Caccavale, Rachel Gardner, Preston Culbertson, Jeannette Bohg, and Mac Schwager. Vision-only robot navigation in a neural radiance world. 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CVPR, 2022. 3" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.956 + ], + "angle": 0, + "content": "11015" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-Object Navigation with Dynamically Learned Neural Implicit Representations/8c2cacd0-618b-43fb-afc2-cdc6e282531c_origin.pdf b/2023/Multi-Object Navigation with Dynamically Learned Neural Implicit Representations/8c2cacd0-618b-43fb-afc2-cdc6e282531c_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..c4957f3ec6da8db149ee2abcdb0193a83bebf89d --- /dev/null +++ b/2023/Multi-Object Navigation with Dynamically Learned Neural Implicit Representations/8c2cacd0-618b-43fb-afc2-cdc6e282531c_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:683981a975b3995ce9e56e7f5f617004c574990ca4a2c98abab298ed7a4b81cb +size 1773907 diff --git a/2023/Multi-Object Navigation with Dynamically Learned Neural Implicit Representations/full.md b/2023/Multi-Object Navigation with Dynamically Learned Neural Implicit Representations/full.md new file mode 100644 index 0000000000000000000000000000000000000000..477ffb5b7ce54b09cd93a0ee3aebfd69cd157882 --- /dev/null +++ b/2023/Multi-Object Navigation with Dynamically Learned Neural Implicit Representations/full.md @@ -0,0 +1,326 @@ +# Multi-Object Navigation with dynamically learned neural implicit representations + +Pierre Marza + +Laetitia Matignon + +Olivier Simonin + +Christian Wolf3 + +$^{1}$ INSA Lyon $^{2}$ UCBL $^{3}$ Naver Labs Europe + +{pierre.marza, olivier.simonin}@insa-lyon.fr + +laetitia.matignon@univ-lyon1.fr,christian.wolf@naverlabs.com + +Project Page: https://pierremarza.github.io/projects/dynamicImplicit Representations/ + +# Abstract + +Understanding and mapping a new environment are core abilities of any autonomously navigating agent. While classical robotics usually estimates maps in a stand-alone manner with SLAM variants, which maintain a topological or metric representation, end-to-end learning of navigation keeps some form of memory in a neural network. Networks are typically imbued with inductive biases, which can range from vectorial representations to birds-eye metric tensors or topological structures. In this work, we propose to structure neural networks with two neural implicit representations, which are learned dynamically during each episode and map the content of the scene: (i) the Semantic Finder predicts the position of a previously seen queried object; (ii) the Occupancy and Exploration Implicit Representation encapsulates information about explored area and obstacles, and is queried with a novel global read mechanism which directly maps from function space to a usable embedding space. Both representations are leveraged by an agent trained with Reinforcement Learning (RL) and learned online during each episode. We evaluate the agent on Multi-Object Navigation and show the high impact of using neural implicit representations as a memory source. + +# 1. Introduction + +Autonomous navigation in complex unknown 3D environments from visual observations requires building a suitable representation of the environment, in particular when the targeted navigation task requires high-level reasoning. Whereas classical robotics builds these representations explicitly through reconstructions, possibly supported through machine learning, end-to-end training learns them automatically either from reward, by imitation learning or through self-supervised objectives. + +While spatial representations can emerge even in unstructured agents, as shown in the form of grid-cells in artificial [16, 3] and biological agents [25], spatial inductive biases + +![](images/144ebf5cffe83e827aaa6aab122b204f8e358b1c78a7708974780bc1f7677047.jpg) + +![](images/b6a8d8ca0c67bc06343318487d79ebd8dbf333b8a10c93efc970f3b9eedb6031.jpg) +Figure 1. We propose two implicit representations as inductive biases for autonomous agents — both are learned online during each episode. (2) a semantic representation $f_{s}$ predicts positions $\mathbf{x}$ from goals $\mathbf{g}$ given as semantic codes. We show Ground Truth object positions (rectangles) and predictions (round; radius shows uncertainty, unit-less, as an illustration). Blue and pink objects have been observed, but not the yellow target. (3) A structural representation $f_{o}$ predicts occupancy and exploration $s$ from positions $\mathbf{x}$ ; we provide a global read which directly maps from function space $f_{o}$ (represented by trainable weights $\theta_{o}$ ) to a context embedding $e$ used by the agent. (4) shows the reconstruction produced by a decoder $Dec$ during training. Orange=navigable, Green=Obstacles, Blue=Unexplored. (1) a ground-truth map is shown for reference, simulating a fully explored scene. + +![](images/d7c41b2f305540784b7781daef92e7834cc50784c2dcf584aef83a069d63be99.jpg) + +![](images/ea753e9360e2e2bf2130e678eb0d9019d1929bd6f7ba07b30373a2564bc9172c.jpg) + +can support learning actionable spatial representations and decrease sample complexity. Popular inductive biases are metric maps [44, 5, 26], topological maps [6, 12] and recently, self-attention, adapting transformers [55] to sequential decision making and navigation [20, 18, 13, 47]. The chosen representation should support robust estimation of navigable space even in difficult conditions, mapping fea + +tures and objects of interest, as well as querying and reusing this information at a later time. The representation should be as detailed as required, span the full (observed) scene, easy to query, and efficient to read and write to, in particular when training is done in large-scale simulations. + +Our work builds on neural fields and implicit representations, a category of models which represent the scene geometry, and eventually the semantics, by the weights of a trained neural network [57]. They have the advantage of avoiding the explicit choice of scene representation (e.g. volume, surface, point cloud etc.) and inherently benefit from the generalization abilities of deep networks to interpolate and complete unobserved information. Implicit representations have demonstrated impressive capabilities in novel view synthesis [40, 51], and have potential as a competitive representation for robotics [42, 32, 52, 1]. Their continuous nature allows them to handle level of detail efficiently through a budget given as the amount of trainable weights. This allows to span large environments without the need of discretizing the environment and handling growing maps. + +We explore and study the potential of implicit representations as inductive biases for visual navigation. Similar to recent work in implicit SLAM [52], our representations are dynamically learned in each episode. Going beyond, we exploit the representation dynamically in one of the most challenging visual navigation tasks, Multi-Object Navigation [56]. We introduce two complementary representations, namely a query-able Semantic Finder trained to predict the scene coordinates of an object of interest specified as input, and an Occupancy and Exploration Implicit Representation, which maps 2D coordinates to occupancy information, see Figure 1. We address the issue of the efficiency of querying an implicit representation globally by introducing a new global read mechanism, which directly maps from function space, represented through its trainable parameters, to an embedding summarizing the current status of occupancy and exploration information, useful for navigation. Invariance w.r.t. reparametrization of the queried network is favored (but not enforced) through a transformer based solution. Our method does not require previous rollouts on the scene for pre-training or building a representation. + +Our work targets a fundamental aspect of visual and semantic navigation, the mapping of key objects of interest. MultiON is currently one of the few benchmarks which evaluates it. As argued in previous literature [5, 56], only sequential tasks, where objects have to be found in a given order, allow object level mapping to emerge directly from reward. This follows from the observation that an agent trained to find and retrieve a single object per episode (from reward) is not required to map seen target objects, as observing them directly leads to a reactive motion towards them. + +Our contributions can be summarized as follows: (i) We propose two implicit representations for semantic, occupancy + +and exploration information, which are trained online during each episode; (ii) We introduce a new global read procedure which can extract summarizing context information directly from the function itself; (iii) We show that the representations obtain performance gains compared to classical neural agents; (iv) We evaluate and analyze key design choices, the representation's scaling laws and its capabilities of lifelong learning. + +# 2. Related Work + +Visual Navigation — is a rich problem that involves perception, mapping and decision making, with required capacities being highly dependent on the specific task. A summary of reasoning in navigation has been given in [2], differentiating, for instance, between waypoint navigation (Pointgoal) [2] or finding objects of semantic categories (ObjectGoal) [2]. More recent tasks have been explicitly designed to evaluate and encourage mapping objects of interest during navigation itself [4, 56]. They are of sequential nature and use external objects, which are not part of the scanned 3D scenes but randomly placed. In this work we address Multi-Object Navigation (MultiON) [56]. + +Mapping and Representations — Classical methods often rely on SLAM [8, 34] which has been proposed in different variants (2D or 3D metric, topological, eventually with semantics) and observations (LIDAR, visual etc.). The objective is to integrate observations and odometry estimates over a trajectory and reconstruct the scene. Differentiable variants have been proposed recently [28, 30]. Mapping can also be discovered through interactions by a blind agent [7]. Visual Navigation can also be framed as an end-to-end learning problem, where representations are learned automatically from different signals, in particular RL. Memory can take the form of vectorial representations in recurrent units [41, 27, 62], with hybrid variants including mapping [12, 48, 17]. Recent work tends to augment agents with more structured memories. Examples are spatial metric tensors, which can contain occupancy [11], semantics [10] or be fully latent, effectively corresponding to inductive biases of the neural agents [44, 5, 26]. Other alternatives are topological maps [6, 12] or self-attention and transformers [55] adapted to navigation [20, 18, 13, 47]. + +Implicit representations — were initially targeting 3D reconstruction [39, 45, 14]. The core idea is to replace the need for discretizing 3D space into voxels [38], 3D points [19] or meshes [23], by an implicit representation of the 3D structure of the scene through the parameters of a learned neural network. Recent work [40, 51] achieved state-of-the-art performance on novel view synthesis with neural implicit representations. The NeRF paper introduced a differentiable volume rendering loss allowing to supervise 3D scene reconstruction from only 2D supervision [40]. For a more detailed overview of recent advances in the rapidly + +growing field, we refer the reader to [57]. + +Implicit representations in robotics — are a recent phenomenon, used to represent density [1] or to perform visuomotor control [33]. Related to goal-oriented navigation, some work targets SLAM with neural implicit representations [52], follow-up adding semantics [59], learned from sparse semantic annotations of the scene. [60] is also built on top of [52] and allows a user to interactively provide semantic annotation for the implicit representation to be trained on in real time. [63] proposes a hierarchical implicit representation of a scene to scale to larger environments and obtain a more detailed reconstruction. [15] combines feature-based SLAM and NeRF. Our work goes beyond implicit SLAM and does not stop at reconstructing a scene. We not only build implicit representations dynamically during the episode, we also use them in a down-stream navigation task without requiring any initial rollout for pre-training or building a representation. We also combine two different implicit representations targeting semantics vs. scene structure. + +Analyzing the neural network function space — implicit representations are instances of function spaces, which are represented through their trainable parameters. Previous work performed analyses by predicting accuracy from network weights [54, 35, 36] or the generality gap between train and test performance from hidden activations [29, 58]. A direction pioneered by Hypernetworks [24] directly predict the network weights. Recently, [61] generate the weights of a CNN from support samples in the context of few-shot learning. More related to our work, [43] learns to predict the weights of an implicit representation based on external factors in the context of spatio-temporal dynamics encoding. In this work, we learn a direct mapping between an implicit representation, represented by its weights, to an actionable embedding summarizing the scene globally. + +# 3. Navigating with implicit representations + +We target the Multi-Object Navigation task [56], which requires an agent to navigate in a photo realistic 3D environment from RGB-D observations $\mathbf{o}_t$ and reach a sequence of target objects (colored cylinders) in a particular order. Goal categories $\mathbf{g}_t$ are given at each time step $t$ . In an RL setting, the agent receives positive reward for each successfully reached object as well as when the geodesic distance towards the goal decreases, and a small negative reward for each step, favoring short paths. + +We follow and augment a base end-to-end architecture used in many recent RL approaches, including [56, 37, 41], with the RGB-D observation, class of the current target and previous action as input to the agent. Temporal information is aggregated with a GRU unit whose output is fed to actor and critic heads. We equip this agent with two implicit representations, trained to hold and map essential information necessary for navigation: the positions of different objects of + +interest, and occupancy / exploration information, as shown in Figure 1, + +The goal of the Semantic Finder $f_{s}(:,\theta_{s})$ parameterized by trainable weights $\theta_{s}$ is to predict the absolute position of an object as $\mathbf{x} = [\mathbf{x}_x\mathbf{x}_y\mathbf{x}_z] = f_s(\mathbf{q};\theta_s)$ specified through an input query vector $\mathbf{q}$ . Uncertainty $u$ is also estimated — see Section 3.1 for details. $\mathbf{x}$ is then converted into coordinates relative to the agent to be fed to the GRU. Compared to classical metric representations [26, 44, 12, 5], querying the location of an object can be done through a single forward pass. + +The Occupancy and Exploration Representation $f_{o}(:,\theta_{o})$ parameterized by trainable weights $\theta_{o}$ encodes information about free navigable space and obstacles. It predicts occupancy $\mathbf{s}$ as a classification problem with three classes {Obstacle, Navigable, Unexplored}, as $\mathbf{s} = f_{o}(\phi ;\theta_{o})$ , where $\phi$ is a position feature vector encoded from coordinates $\mathbf{x}$ — see Section 3.2 for details. + +The Occupancy and Exploration Representation can in principle be queried directly for a single position, but reading out information over a large area directly this way would require multiple reads. We propose to compress this procedure by providing a trainable global read operation $r(:, \theta_g)$ , which predicts an embedding $\mathbf{e}$ containing a global context about what has already been explored, and positions of navigable space. The prediction is done directly from the trainable parameters of the implicit representation, as $\mathbf{e} = r(\theta_o; \theta_r)$ . Here $\theta_o$ is input to $r$ , whereas $\theta_r$ are its parameters. + +Given representations $f_{s}$ and $f_{o}$ , a single forward pass of the agent at time step $t$ and for a goal $g_{t}$ involves reading the representations and providing the input to the policy. The current RGB-D observation $o_{t}$ is also encoded by the convolutional network $c$ (different from the projection module $p$ used to generate samples for training the Semantic Finder). Previous action $a_{t-1}$ and current goal $g_{t}$ are passed through embedding layers, named $L(\cdot)$ in the following equations. These different outputs are fed to the policy, + +$$ +\mathbf {x} _ {t} = f _ {s} \left(g _ {t}; \theta_ {s, t}\right), \mathbf {e} _ {t} = r \left(\theta_ {o, t}; \theta_ {r}\right), \mathbf {c} _ {t} = c \left(o _ {t}; \theta_ {c}\right), \tag {1} +$$ + +$$ +\mathbf {h} _ {t} = G R U \left(\mathbf {h} _ {t - 1}, \mathbf {x} _ {t}, u _ {t}, \mathbf {e} _ {t}, L \left(a _ {t - 1}\right), L \left(g _ {t}\right), \mathbf {c} _ {t}; \theta_ {G}\right), \tag {2} +$$ + +$$ +a _ {t} = \pi \left(\mathbf {h} _ {t}; \theta_ {\pi}\right), \tag {3} +$$ + +where we added indices $\cdot_t$ to relevant variables to indicate time. Please note that the trainable parameters $\theta_{s,t}$ and $\theta_{o,t}$ of the two implicit representations are time dependent, as they depend on the observed scene and are updated dynamically, whereas the parameters of the policy $\pi$ and the global reader $r$ are not. Here, GRU corresponds to the update equations of a GRU network, where we omitted gates for ease of notation. The notation $a_t = \pi(.)$ predicting action $a_t$ is + +![](images/ca3b92b49c6a8c8eb936223f8b452dca3325d55d7eb923dc4ba0d0cd0e619939.jpg) +Figure 2. Navigating with implicit representations. Red connections $\longrightarrow$ indicate the training process of the two implicit representations (= mapping), which is also done during agent deployment. Black connections $\longrightarrow$ show the forward pass of the agent. ■ are discrete learned embeddings (LUT). Policy training is not shown in this figure. + +also a simplification, as we train the agent with PPO, an actor-critic method — see Section 3.4. + +Mapping means training! — The implicit representations $f_{s}$ and $f_{o}$ maintain a compact and actionable representation of the observed scene, and as such need to be updated at each time step from the current observation $o_{t}$ . Given their implicit nature and implementation as neural networks, updates are gradient based and done with SGD. The implicit representations are therefore trained from scratch at each episode even after deployment. + +Training a representation from observations obtained sequentially during an episode also raises a serious issue of catastrophic forgetting [22], as places of the scene observed early might be forgotten later in the episode [52, 59]. We solve this by maintaining two replay buffers throughout the episode, one for each representation. Training samples are generated from each new observation and added to the replay buffers at each time step. Both representations are then trained for a number of gradient steps ( $n_s$ for the Semantic Finder and $n_o$ for the Exploration and Occupancy Representation). Details on the two representations and their training are given in Sections 3.1 and 3.2. The global reader $r$ is not trained or finetuned online but rather trained once offline. + +# 3.1. The Semantic Finder $f_{s}$ + +While recent work on implicit representations for robotics focused on signed distance functions [42, 32], occupancy [52] or density, assuming light density approximates mass density [1], the aim of this model is to localize an object + +of interest within the scene, which can be seen as inverse operation to classical work. From a query vector given as input, the Semantic Finder predicts the position of the object, which is particularly useful for an agent interacting with an environment in the context of a goal conditioned task. It is implemented as a 3-layer MLP with ReLu activations in the intermediate layers and a sigmoid activation for the output. Hidden layers have 512 neurons. The query vector $\mathbf{q}$ corresponds to the 1-in-K encoding of the target object class, which during navigation is directly determined by the object goal $g_{t}$ provided by the task. + +Mapping/Training - The implicit representation is updated minimizing the L1 loss between the prediction $\mathbf{x}_i = f_s(\mathbf{q}_i, \theta_s)$ and the supervised coordinates $\mathbf{x}_i^*$ (we avoided the term "ground-truth" here on purpose), $\mathcal{L}_s = \sum_i \| \mathbf{x}_i^* - \mathbf{x}_i \|_1$ , where the sum goes over the batch sampled from the scene replay buffer. Coordinates $\mathbf{x}_i^*$ are normalized $\in [0, 1]$ . + +The data pairs $(x_{i}^{*}, q_{i})$ for training are created from each observation $o_{t}$ during each time step, each data point corresponding to an observed point. Pixels in $o_{t}$ are inversely projected into 3D coordinates in the scene using the depth channel, the camera intrinsics, as well as agent's coordinates and heading that are assumed to be available, as in [56]. The query vector $\mathbf{q}$ corresponds to a 9-dimensional vector encoding a distribution over object classes (8 target objects and the "background" class). Let us recall that while the training of the representation is supervised, this supervision cannot use "ground-truth" information available only during training. All supervision information is required to be + +predicted from the data available to the agent even after deployment. We predict object class information through a semantic segmentation model $p$ , which is applied to each current RGB-D observation $o_t \in \mathbb{R}^{h \times w \times 4}$ , recovering the output segmentation map $m_t \in \mathbb{R}^{k \times l \times 9}$ . The model has been pre-trained on the segmentation of the different target objects, i.e. coloured cylinders, and is not fine-tuned during training of the agent itself. + +Training data pairs $(x_{i}^{*}, q_{i})$ are sampled from this output. The supervised coordinates $x_{i}^{*}$ are simply the mean 3D coordinates of each feature map cell, after inverse projection. The query vector $\mathbf{q}_{i}$ is the distribution over semantic classes. After the replay buffer is updated, a training batch must be sampled to update the neural field. One fourth of the samples in the batch of size $b$ correspond to the $b/4$ last steps. The rest are sampled from the previous steps in the replay buffer. Uniform sampling is also performed among pairs collected at a given time step. + +Estimating uncertainty — is an essential component, as querying yet unseen objects will lead to wrong predictions, which the agent needs to recognize as such, and discard. The estimation of uncertainty in neural networks is an open problem, which has been previously addressed through different means, including drop out as a Bayesian approximation [21], variational information bottlenecks [50], density estimation [31], and others. In this work, we approximate a density estimate in the scene replay buffer by calculating the minimum Euclidean distance between the input query and all embeddings in the replay buffer at the current time step. The method is simple and efficient and does not require explicitly fitting a model to estimate the marginal distribution $p(\mathbf{q})$ , in particular as the uncertainty representation is latent, can be un-normalized as not required to be a probability. + +# 3.2. Occupancy and Exploration Implicit Representation $f_{o}$ + +Unlike $f_{s}$ , the occupancy representation $f_{o}$ is closer to classical implicit representations in robotics, e.g. [52, 42, 32, 1], which map spatial coordinates to variables encoding information on navigable area like occupancy or signed distances. Different to previous work, our representation also includes exploration information, which changes over time during the episode. Once explored, a position changes its class, which makes our neural field dynamic. Another difference with $f_{s}$ is that the latter deals with 3D coordinates while $f_{o}$ is a topdown 2D representation. Inspired by [57, 53], the model uses Fourier features $\phi$ extracted from the 2D coordinates $\mathbf{x}$ previously normalized $\in [0,1]$ , + +$$ +\phi = (\cos (\mathbf {x} 2 ^ {0}), \sin (\mathbf {x} 2 ^ {0}), \dots , \cos (\mathbf {x} 2 ^ {\frac {p}{4}}), \sin (\mathbf {x} 2 ^ {\frac {p}{4}})). (4) +$$ + +The network $f_{o}$ is a 3-layer MLP with ReLu intermediate activations and a softmax function at the output layer. Hidden + +layers have 512 neurons, and $p = 40$ . + +Mapping/Training — The implicit representation is updated minimizing the Cross Entropy loss between the prediction $\mathbf{s}$ of the neural field and the supervised label $\mathbf{s}^*$ of three classes $\{\text{Obstacle, Navigable, Unexplored}\}$ , as $\mathcal{L}_o = -\sum_{c=1}^{3} \mathbf{s}_c^* \log \mathbf{s}_c$ . As for the Semantic Finder, training data pairs $(\mathbf{s}^*, \mathbf{s})$ are created through inverse perspective projection of the pixels of the observation $o_t$ into 3D scene coordinates. Thresholding the $z$ (height) coordinate decides between Navigable and Obstacle classes. Points with a $z$ coordinate higher than a certain threshold are discarded. The replay buffer is balanced between both classes, and only samples of the last 1000 steps are kept. Samples of the Unexplored class are not stored. + +The replay buffer is sampled similarly to the one for the Semantic Finder. However, additional samples for the Unexplored class are created by sampling uniformly inside the scene, for speed reasons simply ignoring conflicts with explored areas and treating them as noisy labels. + +# 3.3. Global Occupancy Read $r$ — handling reparametrization invariance + +The global Occupancy reader $r$ allows to query the occupancy information of the scene globally, beyond point-wise information, and as such is a trainable mapping from the space of functions $f_{o}(:,.)$ to an embedding space $e$ . In particular, two functions $f_{o}$ and $f_{o}'$ s.t. $f_{o}(\mathbf{x}) = f_{o}'(\mathbf{x}) \forall \mathbf{x}$ should be mapped to identical or close embeddings. However, as the occupancy networks $f_{o}$ are implemented as MLPs, any given instance $f_{o}(:,;\theta_{o})$ parameterized by trainable weights $\theta_{o}$ can be reparametrized by any permutation of hidden units, which leads to permutations of the rows and columns, respectively, of two weight matrices, its own and the one of the preceding layer. This reparameterization keeps the represented functions identical, although their representations as weight vectors are different. + +To favor learning a global occupancy reader which is invariant w.r.t these transformations, we implement it as a transformer model with self-attention [55] — this, however, does not enforce full invariance. The model takes as input a sequence of tokens $(w_{1},\dots,w_{N})$ , where $w_{i}\in \mathbb{R}^{a}$ is a learned linear embedding of the incoming weights of one neuron within the implicit representation $f_{o}$ , and $N$ is the number of neurons of $f_{o}$ . Each token is summed with a positional encoding in the form of Fourier features. An additional "CLS" token with learned embedding is concatenated to the input sequence. The reader is composed of 4 self-attention layers, with 8 attention heads. The output representation of the "CLS" token is used as the global embedding of the implicit representation. + +Training - The global reader $r$ is trained with full supervision from a dataset of $25k$ trajectories composed of MLP weights $\theta_{o,i}$ and absolute maps $\mathbf{M}_i$ , $i..1..25k$ . Each + +map is a metric tensor providing occupancy information extracted from the corresponding implicit representation, i.e. $\mathbf{M}_i(\mathbf{x}_y,\mathbf{x}_x) = f_o(\mathbf{x},\theta_{o,i})$ . The dataset also contains an egocentric version $\mathbf{M}_i^{\prime}$ of each map, which is centered on the agent and oriented depending on its current heading. The reader $r$ is trained in an Encoder-Decoder fashion, where $r$ plays the role of the encoder, + +$$ +\mathbf {e} _ {i} = r \left(\theta_ {o, i}\right), \quad \hat {\mathbf {M}} _ {i} = D e c \left(e _ {i}, p _ {i}\right), \tag {5} +$$ + +where $p_i$ is the agent pose (position and heading), necessary to decode ego-centric information. We minimize a cross entropy loss on the prediction of ego-centric maps, + +$$ +\mathcal {L} _ {g} = - \sum_ {i} \sum_ {k} \sum_ {l} \sum_ {c = 1} ^ {3} \mathbf {M} _ {i, c} ^ {\prime *} (k, l) \log \mathbf {M} _ {i, c} ^ {\prime} (k, l) (6) +$$ + +Directly training this prediction proved to be difficult. We propose a procedure involving several steps, detailed in section 3.5. After the training phase, the reader $g$ is used in the perception + mapping module of the agent as given in equation (1), and kept frozen during agent RL training. + +# 3.4. Training the Agent + +The agent is trained with RL, more precisely Proximal Policy Optimization (PPO) [49]. The inner training loops of the implicit representations are supervised (red arrows in Figure 2) and occur at each time step in the forward pass, whereas the RL-based outer training loop of the agent occurs after $N$ acting steps (black arrows in Figure 2). As the perception module used to generate training data from RGBD-observations for the Semantic Finder $f_{s}$ is independent of the visual encoder $c$ in the agent (see Figure 2), and as its query $\mathbf{q}_t$ is fixed to the navigation goal $\mathbf{g}_t$ , there is no need to track the weights $\theta_{s}$ at each time step in order to backpropagate the PPO loss (outer training). This is a key design choice of our method. + +Training assumptions — We do not rely on the existence of global GT maps for occupancy, as $f_{o}()$ and $r()$ were trained on observation data from agent trajectories only. However, similar to [37, 46], we exploit object positions in simulation, during training only; Moreover, we require pixel-wise segmentation masks during training. We believe that this does not change requirements, as the goal is to fully exploit 3D photo-realistic simulators as a data source and see how far the field can go with this. Generalization requirements are unchanged: we require our agent to be able to generalize to new unseen scenes. Generalization to unseen object categories is not targeted, and in MultiON task setup not possible for any agent, as object positions and labels are required for reward calculation. + +# 3.5. Training the global reader + +The proposed training procedure for the global reader $r$ (performed before training the agent) can be split into 3 phases. + +The architecture for the convolutional decoder $Dec()$ is kept the same in all of them. The hyperparameters of its different layers are detailed in the Supplementary Material. It is composed of 6 transpose convolution layers along with batch norm layers and ReLU activations, except for the last layer with a softmax activation. Figure 3 provides an overview of the 3 steps involved in the training of the global reader. + +Fully convolutional autoencoder — The first step is to train a fully convolutional autoencoder on the set of absolute maps $\mathbf{M}_i$ , $i..1..25k$ . Only the decoder weights are kept. + +Global reader training on absolute maps — The second step consists in training the global reader to output embeddings fed to the frozen decoder from the previous step. The objective is to reconstruct absolute maps from the weights of the implicit representation. The global reader weights are kept after this training phase. + +Global reader finetuning on egocentric maps The global reader, whose weights are initialized from the weights obtained in the previous step, is now trained along with the same decoder from the first step (also used in the second step) on the set of egocentric maps $\mathbf{M}_i^{\prime}$ , $i..1..25k$ . Both global reader and decoder are finetuned. The output of the global reader is not directly fed to the decoder, but is passed through linear layers in order to fuse information about first the position of the agent, and then its heading because this time the right operations of shift and rotation must be applied in order to reconstruct egocentric maps. + +Integrating the pre-trained global reader into the agent After this pre-training in 3 steps, the weights of the global reader are frozen and not updated during the RL training. However, a linear layer is learnt to project the 576-dim embedding from the global reader into a 256-dim representation fed to the GRU. This linear layer is trained from reward signals. + +# 4. Experiments + +MultiON task — we target the 3-ON version of the MultiON task [56], where the agent deals with sequences of 3 objects, each belonging to one of 8 classes (cylinders of different colors). At each step, the observation $\mathbf{o}_t$ is an RGB-D image of size $256 \times 256 \times 4$ and the target class is a one-in-K ( $K = 8$ ) vector. The action space is discrete: {Move forward $0.25m$ , Turn left $30^\circ$ , Turn right $30^\circ$ , Found}. An episode is considered successful if the agent finds all of the targets before the time limit (2, 500 environment steps), and chooses the Found action for each one at a distance closer to + +![](images/dd8b87e0f90df7252d5d672360cb58d2efa026066632578ff554280eef087a72.jpg) +Figure 3. Training the Global Reader in 3 steps: $①$ training a convolutional auto-encoder on absolute maps; $②$ extension to inputs equal to weights $\theta_{o} =$ the gobal reader; $③$ extension to predicting ego-centric maps, better suited to navigation problems. + +
0 - 3030 - 5050 - 70— Val —— Test —
SOSOSOSuccessProgressSPLPPLSuccessProgressSPLPPL
------33.2±1.249.0±1.121.2±0.531.6±1.242.3±1.556.7±0.928.1±1.037.8±1.8
μ--✓-✓37.8±1.652.3±0.926.35±1.536.5±0.847.0±1.760.5±1.634.5±0.844.2±1.0
--✓-✓✓38.5±4.652.5±4.828.2±2.138.3±1.746.7±3.060.1±3.135.1±1.444.8±1.0
------32.147.721.632.641.055.928.939.0
↑--✓-✓38.151.927.337.148.661.535.244.2
--✓-✓✓43.156.830.540.149.763.436.445.9
+ +Table 1. Impact of the implicit representations: navigation performance on MultiON val and MultiON test. S=f_s activated, O=f_o activated in the corresponding training period (see text). Top/μ: means over 3 runs; Bottom/↑: best validation seeds over 3 runs. + +$1.5m$ . Calling Found incorrectly terminates episode as a failure. An access to perfect odometry information (localization and heading) was assumed in [56] as the standard protocol. + +Dataset and metrics — The agent is trained on the Mutterport3d [9] dataset. We followed the standard train/val/test split over scenes (denoted MultiON train, MultiON val, MultiON test): 61 training, 11 validation and 18 test scenes. The train, val and test splits are respectively composed of 50,000, 12,500 and 12,500 episodes per scene. Reported results on the val and test sets (Tables 1 and 2) were computed on a subset of 1,000 randomly sampled episodes. We report standard metrics as used in the navigation literature (and in [56]): Success: percentage of successful episodes — all objects are reached respecting order, time; Progress: percentage of objects successfully found (respecting order, + +time); SPL: Success weighted by Path Length, extending the original SPL metric [2] to MultiON; PPL: Progress weighted By Path Length (the official MultiON challenge metric). + +Global reader dataset — The Global reader $r$ was trained on a dataset of $25k$ trajectories obtained from rollouts performed by a baseline agent [37]. $95\%$ was used for training and the rest for validation. On these trajectories we first trained the occupancy representation $f_{o}$ "in-situ", i.e. as if it were deployed on the agent, and we recorded training samples $i$ for training the reader $r$ : pairs of network weights $\theta_{o,i}$ and associated maps $M_{i}$ obtained by iteratively querying the implicit representation. Ego-centric maps were generated from the absolute ones and both were cropped around their center. + +Perception module dataset — The perception module + +
AgentραγSuccessProgressSPLPPLAUXORC
(a)OracleMap† [56]-✓50.4±3.560.5±3.140.7±2.248.8±1.9-✓
(b)OracleEgoMap† [56]-✓32.8±5.247.7±5.226.1±4.537.6±4.7-✓
(c)NoMap† [56]-✓16.7±3.633.7±3.313.1±2.426.0±1.7--
(d)ProjNMap† [26]-✓25.9±1.143.4±1.018.3±0.630.9±0.7--
(e)NoMap✓-42.3±1.556.7±0.928.1±1.037.8±1.8--
(f)ProjNMap [26]✓-39.7±2.355.4±1.428.7±1.140.1±1.9--
(g)Implicit (Ours) w/ curriculum w/pre-train✓--46.7±3.060.1±3.135.1±1.444.8±1.0--
(h)ProjNMap + AUX [37]N/A✓N/A57.7±3.770.2±2.737.5±2.045.9±1.9✓-
(i)Implicit (Ours) w/o curriculum w/pre-train + AUX✓✓✓58.3±0.869.4±1.143.8±1.052.1±1.6✓-
(j)Implicit (Ours) w/o curriculum w/o pre-train-✓✓54.8±3.668.0±3.441.7±1.951.3±1.6--
(k)Implicit (Ours) w/o curriculum w/o pre-train + AUX-✓✓57.9±2.069.5±0.643.3±2.251.9±3.7✓-
+ +Table 2. Comparison with SOTA methods on MultiON test. †=performance taken from [37]. “AUX” = auxiliary losses using privileged information [37]. “ORC” = non-comparable, uses oracle information. ρ = pre-training of input encoders from [37]. α = finetuning of input encoders with RL. γ = implicit representations are accessible to the agent since the beginning of RL training (w/o curriculum). + +
UncertaintySuccessProgressSPLPPL
-35.4±3.049.7±3.329.4±2.040.9±2.4
✓43.4±3.158.0±3.035.1±0.846.4±1.0
+ +Table 3. Uncertainty: comparing training w/ semantic input only, no occupancy, from the beg. of training, w/ and w/o uncertainty. + +$p$ was trained to segment the different target objects. The generated dataset is composed of $132k$ pairs of RGB-D observations and segmentation masks. Samples for 4 scenes were kept as a validation set. + +Training details - We use the reward function given in [56] for RL/PPO training (see supplementary material), and train all agents for $70M$ steps as in [37]. For all agents in Table 1 and some in Table 2 ( $w/$ pre-train: $\sqrt{}$ in $\rho$ column), the encoders (visual encoder $c$ , as well as goal and previous action embedding layers, see Figure 2) are pre-trained with a baseline, which corresponds to the ProjNeuralMap agent trained with auxiliary losses [37]. This is done to faster training, as it will be shown later (in Table 2) that the same final performance can be reached without this initial pre-training of encoders. Training and evaluation hyper-parameters, as well as architecture details have been taken from [56]. All reported quantitative results are obtained after 3 training runs for each model. + +Impact of the implicit representations — Table 1 shows the impact of the two implicit representations on navigation (top: means over 3 runs; bottom: best validation seeds over 3 runs). To keep compute requirements limited and decrease sample complexity, in these ablations we do not train the full agent from scratch, in particular since the early stages of training are spent on learning basic interactions. We decompose training into three phases: $0 - 30M$ steps (no implicit representations, i.e. all entries to the agent related to $f_{s}$ and $f_{o}$ are set to 0); $30M - 50M$ steps (training includes the Semantic Finder $f_{s}$ ) and finally $50M - 70M$ steps (full model). This 3-steps approach is used to train all agents in Table 1, and will be denoted as curriculum (See + +Table 2, $w/$ curriculum: - in $\gamma$ column). All metrics on both val and test sets are improved, with the biggest impact provided by the Semantic Finder, which was expected. We conjecture that mapping object positions is a more difficult task, which is less easily delegated to the vectorial GRU representation, than occupancy. We also see an impact of the occupancy representation, which not only confirms the choice of the implicit representation ${f}_{o}$ itself,but also its global read through $r\left( {\theta }_{o}\right)$ . Training curves are given in the supplementary material. + +Uncertainty — has an impact on agent performance, as we show in the ablation in Table 3. Indeed, when training an agent with the semantic input since the beginning of training (w/o curriculum) and no occupancy input (as the uncertainty is only related to semantic information), feeding the agent with the computed uncertainty about the output of the Semantic Finder brings a boost in performance. + +Comparison with previous SOTA methods — is done in Table 2. The performance entries of these baselines are taken from [37], which describes the winning entry of the CVPR 2021 MultiON competition. Our method outperforms the different competing representations, even when they benefit from the same pre-training scheme and are thus completely comparable. NoMap with pre-training corresponds to the first row of Table 1. The difference between (g) and (i) is the use of the auxiliary tasks in [37], but also that the implicit representations are available to the agent during the whole training period for (i), i.e. no decomposition into 3 phases as in the ablations in Table 1 (w/o curriculum). Moreover, compared to (g), in (i) the weights of the pre-trained encoders are finetuned. We see that the gains of our representations are complementary to the auxiliary losses in [37]. (j) and (k) confirm this finding, showing that most of the gain compared with (h) comes from the implicit representations, with the auxiliary losses bringing an additional boost. (j) and (k) also show that, even though pre-training can help speed up RL training, similar test performance is achieved without it. + +![](images/51ab0aad70199eb725cd6276a1201454493fe702d3fa84e1f71484bfecf95f17.jpg) +(a) +Figure 4. Capacity of the semantic representation: we report mean distance prediction error (normalized $\in [0,1]$ ) as a function of the number of stored objects. Replay buffers are composed of dummy queries: (a) one-hot queries with same dimension as number of objects; (b) random query with dimension 9; (c) random query with same dimension as number of objects. + +![](images/e6d048fe9ed4f1aa772de290b8753026734f33cfc043a212e079ec178133a457.jpg) +(b) + +![](images/1b285e3496fbf412969e0c87a2fa5d3cf51a2bc545a012f7eb7eb52f2aa17a12.jpg) +(c) + +![](images/b7c808453ab0ff7fdda121b7234baf9e9252ff9fb76c4c1ddeaae3c4bbc6a72a.jpg) +Figure 5. Lifelong learning of the semantic repr. $f_{s}$ : we report mean error in meters, test set, 600 episodes, as a function of the number of time steps since the object was first seen in the episode (t=0). The error falls immediately and stays low over the episode. + +Reconstruction performance of the Global Reader $r$ — although the task of reconstructing egocentric maps from occupancy functions $f_{o}$ (represented by $\theta_{o}$ ) is only used as a proxy task to train the Global reader $r$ , we see it is a reliable proxy for the quality of extracting the global latent vector $\mathbf{e}$ fed to the agent. + +
AccuracyJaccard Index
83.456.5
+ +Table 4. Performance of the global reader $r$ : We report accuracy and Jaccard index. + +In Table 4 we report reconstruction performance measured as accuracy and mean Jaccard Index on the validation split of the dataset used to train the reader. We judge that an accuracy of $83.4\%$ is surprisingly high, given that + +the global reader needs to reconstruct the content of the representation directly from its parameters $\theta_{o}$ , that each implicit representation has been initialized randomly, and that the reader is required to be invariant w.r.t. to reparameterization (see Section 4). The task is even made harder as neural weights can be considered as an absolute representation of the env. and the reader must combine it with information about the agent pose to reconstruct an egocentric map. + +Capacity of the Semantic Finder — Unlike all other results presented in this paper, this experiment is performed independently of the official MultiON benchmark. We construct a synthetic dataset to evaluate the capacity of the Semantic Finder. More details about the generated data can be found in the supplementary material. As the granularity of the implicit representations is handled through the budget in terms of trainable parameters, we evaluate the capacity of the Semantic Finder $f_{s}$ to store large numbers of objects in Figure 4: In (a), we can see that increasing the number of objects up to 1000 does not increase error with sufficient gradient updates. However, since inputs are 1-in-K, increasing the number of objects also increases capacity. In (c), we see that this does not hold for random objects (not 1-in-K), whose less structured storage requires more capacity. In (b), we keep the input dimension fixed for random objects, which + +further increases error. + +Evaluating catastrophic forgetting — we evaluate the capacity of the Semantic Finder $f_{s}$ to hold the learned information over the full length of the sequence in spite of the fact that it is continuously trained. Figure 5 shows the evolution of the mean error in distance for the predicted position of queried target objects as a function of time. The error quickly goes below $1.5m$ once the object has been seen the first time ( $t = 0$ in the plot), which is distance threshold required by the MultiON task, and stays there, providing evidence that the model does not suffer from catastrophic forgetting. + +Runtime performance — inspite of requiring to continuously train the representations, we achieve 45 fps during parallelized RL training, including the environment steps (simulator rendering), forward passes, representation training and RL training on a single V100 GPU. The average time of one agent forward pass, including updates of implicit representations is 20ms on a V100 GPU, which is equivalent to 50 fps, enough for real-time performance. + +# 5. Conclusion + +We introduce two implicit representations to map semantic, occupancy and exploration information. The first estimates the position of an object of interest from a vector query, while the second encapsulates information about occupancy and explored area in the current environment. We also introduce a global read directly from the trainable weights of this representation. Our experiments show that both implicit representations have a positive impact on the navigation performance of the agent. We also studied the scaling laws of the semantic representation and its behavior in the targeted lifelong learning problem. Future work will target differentiating through the implicit representations all the way back to the perception modules. + +Acknowledgement - We thank ANR for support through AI-chair grant "Remember" (ANR-20-CHIA-0018). + +# References + +[1] Michal Adamkiewicz, Timothy Chen, Adam Caccavale, Rachel Gardner, Preston Culbertson, Jeannette Bohg, and Mac Schwager. Vision-only robot navigation in a neural radiance world. IEEE Robotics and Automation Letters, 2022. 2, 3, 4, 5 +[2] Peter Anderson, Angel X. Chang, Devendra Singh Chaplot, Alexey Dosovitskiy, Saurabh Gupta, Vladlen Koltun, Jana Kosecka, Jitendra Malik, Roozbeh Mottaghi, Manolis Savva, and Amir Roshan Zamir. On evaluation of embodied navigation agents. arXiv preprint, 2018. 2, 7 +[3] A. Banino, C. Barry, B. Uria, C. Blundell, T. Lillicrap, P. Mirowski, A. Pritzel, M.J. Chadwick, T. Degris, J. Modayil, G. Wayne, H. Soyer, F. Viola, B. Zhang, R. Goroshin, N. Rabinowitz, R. Pascanu, C. Beattie, S. Petersen, A. Sadik, S. 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While classical robotics usually estimates maps in a stand-alone manner with SLAM variants, which maintain a topological or metric representation, end-to-end learning of navigation keeps some form of memory in a neural network. Networks are typically imbued with inductive biases, which can range from vectorial representations to birds-eye metric tensors or topological structures. In this work, we propose to structure neural networks with two neural implicit representations, which are learned dynamically during each episode and map the content of the scene: (i) the Semantic Finder predicts the position of a previously seen queried object; (ii) the Occupancy and Exploration Implicit Representation encapsulates information about explored area and obstacles, and is queried with a novel global read mechanism which directly maps from function space to a usable embedding space. 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We propose two implicit representations as inductive biases for autonomous agents — both are learned online during each episode. (2) a semantic representation " + }, + { + "bbox": [ + 304, + 450, + 547, + 605 + ], + "type": "inline_equation", + "content": "f_{s}" + }, + { + "bbox": [ + 304, + 450, + 547, + 605 + ], + "type": "text", + "content": " predicts positions " + }, + { + "bbox": [ + 304, + 450, + 547, + 605 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 450, + 547, + 605 + ], + "type": "text", + "content": " from goals " + }, + { + "bbox": [ + 304, + 450, + 547, + 605 + ], + "type": "inline_equation", + "content": "\\mathbf{g}" + }, + { + "bbox": [ + 304, + 450, + 547, + 605 + ], + "type": "text", + "content": " given as semantic codes. We show Ground Truth object positions (rectangles) and predictions (round; radius shows uncertainty, unit-less, as an illustration). 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(1) a ground-truth map is shown for reference, simulating a fully explored scene." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + } + ], + "index": 17 + }, + { + "type": "image", + "bbox": [ + 426, + 239, + 533, + 327 + ], + "blocks": [ + { + "bbox": [ + 426, + 239, + 533, + 327 + ], + "lines": [ + { + "bbox": [ + 426, + 239, + 533, + 327 + ], + "spans": [ + { + "bbox": [ + 426, + 239, + 533, + 327 + ], + "type": "image", + "image_path": "d7c41b2f305540784b7781daef92e7834cc50784c2dcf584aef83a069d63be99.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + } + ], + "index": 18 + }, + { + "type": "image", + "bbox": [ + 428, + 335, + 533, + 442 + ], + "blocks": [ + { + "bbox": [ + 428, + 335, + 533, + 442 + ], + "lines": [ + { + "bbox": [ + 428, + 335, + 533, + 442 + ], + "spans": [ + { + "bbox": [ + 428, + 335, + 533, + 442 + ], + "type": "image", + "image_path": "ea753e9360e2e2bf2130e678eb0d9019d1929bd6f7ba07b30373a2564bc9172c.jpg" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_body" + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 629, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 548, + 715 + ], + "type": "text", + "content": "can support learning actionable spatial representations and decrease sample complexity. Popular inductive biases are metric maps [44, 5, 26], topological maps [6, 12] and recently, self-attention, adapting transformers [55] to sequential decision making and navigation [20, 18, 13, 47]. The chosen representation should support robust estimation of navigable space even in difficult conditions, mapping fea" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "11004" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 133 + ], + "type": "text", + "content": "tures and objects of interest, as well as querying and reusing this information at a later time. The representation should be as detailed as required, span the full (observed) scene, easy to query, and efficient to read and write to, in particular when training is done in large-scale simulations." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 134, + 288, + 314 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 134, + 288, + 314 + ], + "spans": [ + { + "bbox": [ + 46, + 134, + 288, + 314 + ], + "type": "text", + "content": "Our work builds on neural fields and implicit representations, a category of models which represent the scene geometry, and eventually the semantics, by the weights of a trained neural network [57]. They have the advantage of avoiding the explicit choice of scene representation (e.g. volume, surface, point cloud etc.) and inherently benefit from the generalization abilities of deep networks to interpolate and complete unobserved information. Implicit representations have demonstrated impressive capabilities in novel view synthesis [40, 51], and have potential as a competitive representation for robotics [42, 32, 52, 1]. Their continuous nature allows them to handle level of detail efficiently through a budget given as the amount of trainable weights. This allows to span large environments without the need of discretizing the environment and handling growing maps." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 315, + 288, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 315, + 288, + 567 + ], + "spans": [ + { + "bbox": [ + 46, + 315, + 288, + 567 + ], + "type": "text", + "content": "We explore and study the potential of implicit representations as inductive biases for visual navigation. Similar to recent work in implicit SLAM [52], our representations are dynamically learned in each episode. Going beyond, we exploit the representation dynamically in one of the most challenging visual navigation tasks, Multi-Object Navigation [56]. We introduce two complementary representations, namely a query-able Semantic Finder trained to predict the scene coordinates of an object of interest specified as input, and an Occupancy and Exploration Implicit Representation, which maps 2D coordinates to occupancy information, see Figure 1. We address the issue of the efficiency of querying an implicit representation globally by introducing a new global read mechanism, which directly maps from function space, represented through its trainable parameters, to an embedding summarizing the current status of occupancy and exploration information, useful for navigation. Invariance w.r.t. reparametrization of the queried network is favored (but not enforced) through a transformer based solution. Our method does not require previous rollouts on the scene for pre-training or building a representation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 568, + 288, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 568, + 288, + 687 + ], + "spans": [ + { + "bbox": [ + 46, + 568, + 288, + 687 + ], + "type": "text", + "content": "Our work targets a fundamental aspect of visual and semantic navigation, the mapping of key objects of interest. MultiON is currently one of the few benchmarks which evaluates it. As argued in previous literature [5, 56], only sequential tasks, where objects have to be found in a given order, allow object level mapping to emerge directly from reward. This follows from the observation that an agent trained to find and retrieve a single object per episode (from reward) is not required to map seen target objects, as observing them directly leads to a reactive motion towards them." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": "Our contributions can be summarized as follows: (i) We propose two implicit representations for semantic, occupancy" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 547, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 168 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 168 + ], + "type": "text", + "content": "and exploration information, which are trained online during each episode; (ii) We introduce a new global read procedure which can extract summarizing context information directly from the function itself; (iii) We show that the representations obtain performance gains compared to classical neural agents; (iv) We evaluate and analyze key design choices, the representation's scaling laws and its capabilities of lifelong learning." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 178, + 392, + 192 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 178, + 392, + 192 + ], + "spans": [ + { + "bbox": [ + 306, + 178, + 392, + 192 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 199, + 547, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 199, + 547, + 342 + ], + "spans": [ + { + "bbox": [ + 304, + 199, + 547, + 342 + ], + "type": "text", + "content": "Visual Navigation — is a rich problem that involves perception, mapping and decision making, with required capacities being highly dependent on the specific task. A summary of reasoning in navigation has been given in [2], differentiating, for instance, between waypoint navigation (Pointgoal) [2] or finding objects of semantic categories (ObjectGoal) [2]. More recent tasks have been explicitly designed to evaluate and encourage mapping objects of interest during navigation itself [4, 56]. They are of sequential nature and use external objects, which are not part of the scanned 3D scenes but randomly placed. In this work we address Multi-Object Navigation (MultiON) [56]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 343, + 547, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 343, + 547, + 582 + ], + "spans": [ + { + "bbox": [ + 304, + 343, + 547, + 582 + ], + "type": "text", + "content": "Mapping and Representations — Classical methods often rely on SLAM [8, 34] which has been proposed in different variants (2D or 3D metric, topological, eventually with semantics) and observations (LIDAR, visual etc.). The objective is to integrate observations and odometry estimates over a trajectory and reconstruct the scene. Differentiable variants have been proposed recently [28, 30]. Mapping can also be discovered through interactions by a blind agent [7]. Visual Navigation can also be framed as an end-to-end learning problem, where representations are learned automatically from different signals, in particular RL. Memory can take the form of vectorial representations in recurrent units [41, 27, 62], with hybrid variants including mapping [12, 48, 17]. Recent work tends to augment agents with more structured memories. Examples are spatial metric tensors, which can contain occupancy [11], semantics [10] or be fully latent, effectively corresponding to inductive biases of the neural agents [44, 5, 26]. Other alternatives are topological maps [6, 12] or self-attention and transformers [55] adapted to navigation [20, 18, 13, 47]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "type": "text", + "content": "Implicit representations — were initially targeting 3D reconstruction [39, 45, 14]. The core idea is to replace the need for discretizing 3D space into voxels [38], 3D points [19] or meshes [23], by an implicit representation of the 3D structure of the scene through the parameters of a learned neural network. Recent work [40, 51] achieved state-of-the-art performance on novel view synthesis with neural implicit representations. The NeRF paper introduced a differentiable volume rendering loss allowing to supervise 3D scene reconstruction from only 2D supervision [40]. For a more detailed overview of recent advances in the rapidly" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "11005" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 216, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 216, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 216, + 83 + ], + "type": "text", + "content": "growing field, we refer the reader to [57]." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 84, + 288, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 84, + 288, + 300 + ], + "spans": [ + { + "bbox": [ + 46, + 84, + 288, + 300 + ], + "type": "text", + "content": "Implicit representations in robotics — are a recent phenomenon, used to represent density [1] or to perform visuomotor control [33]. Related to goal-oriented navigation, some work targets SLAM with neural implicit representations [52], follow-up adding semantics [59], learned from sparse semantic annotations of the scene. [60] is also built on top of [52] and allows a user to interactively provide semantic annotation for the implicit representation to be trained on in real time. [63] proposes a hierarchical implicit representation of a scene to scale to larger environments and obtain a more detailed reconstruction. [15] combines feature-based SLAM and NeRF. Our work goes beyond implicit SLAM and does not stop at reconstructing a scene. We not only build implicit representations dynamically during the episode, we also use them in a down-stream navigation task without requiring any initial rollout for pre-training or building a representation. We also combine two different implicit representations targeting semantics vs. scene structure." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 300, + 288, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 300, + 288, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 300, + 288, + 479 + ], + "type": "text", + "content": "Analyzing the neural network function space — implicit representations are instances of function spaces, which are represented through their trainable parameters. Previous work performed analyses by predicting accuracy from network weights [54, 35, 36] or the generality gap between train and test performance from hidden activations [29, 58]. A direction pioneered by Hypernetworks [24] directly predict the network weights. Recently, [61] generate the weights of a CNN from support samples in the context of few-shot learning. More related to our work, [43] learns to predict the weights of an implicit representation based on external factors in the context of spatio-temporal dynamics encoding. In this work, we learn a direct mapping between an implicit representation, represented by its weights, to an actionable embedding summarizing the scene globally." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 490, + 268, + 504 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 490, + 268, + 504 + ], + "spans": [ + { + "bbox": [ + 47, + 490, + 268, + 504 + ], + "type": "text", + "content": "3. Navigating with implicit representations" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "text", + "content": "We target the Multi-Object Navigation task [56], which requires an agent to navigate in a photo realistic 3D environment from RGB-D observations " + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "inline_equation", + "content": "\\mathbf{o}_t" + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "text", + "content": " and reach a sequence of target objects (colored cylinders) in a particular order. Goal categories " + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "inline_equation", + "content": "\\mathbf{g}_t" + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "text", + "content": " are given at each time step " + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 510, + 287, + 617 + ], + "type": "text", + "content": ". In an RL setting, the agent receives positive reward for each successfully reached object as well as when the geodesic distance towards the goal decreases, and a small negative reward for each step, favoring short paths." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "type": "text", + "content": "We follow and augment a base end-to-end architecture used in many recent RL approaches, including [56, 37, 41], with the RGB-D observation, class of the current target and previous action as input to the agent. Temporal information is aggregated with a GRU unit whose output is fed to actor and critic heads. We equip this agent with two implicit representations, trained to hold and map essential information necessary for navigation: the positions of different objects of" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": "interest, and occupancy / exploration information, as shown in Figure 1," + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "spans": [ + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "text", + "content": "The goal of the Semantic Finder " + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "inline_equation", + "content": "f_{s}(:,\\theta_{s})" + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "text", + "content": " parameterized by trainable weights " + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "inline_equation", + "content": "\\theta_{s}" + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "text", + "content": " is to predict the absolute position of an object as " + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "inline_equation", + "content": "\\mathbf{x} = [\\mathbf{x}_x\\mathbf{x}_y\\mathbf{x}_z] = f_s(\\mathbf{q};\\theta_s)" + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "text", + "content": " specified through an input query vector " + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "inline_equation", + "content": "\\mathbf{q}" + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "text", + "content": ". Uncertainty " + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "inline_equation", + "content": "u" + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "text", + "content": " is also estimated — see Section 3.1 for details. " + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 317, + 106, + 547, + 216 + ], + "type": "text", + "content": " is then converted into coordinates relative to the agent to be fed to the GRU. Compared to classical metric representations [26, 44, 12, 5], querying the location of an object can be done through a single forward pass." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "spans": [ + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "text", + "content": "The Occupancy and Exploration Representation " + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "inline_equation", + "content": "f_{o}(:,\\theta_{o})" + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "text", + "content": " parameterized by trainable weights " + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "inline_equation", + "content": "\\theta_{o}" + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "text", + "content": " encodes information about free navigable space and obstacles. It predicts occupancy " + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "inline_equation", + "content": "\\mathbf{s}" + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "text", + "content": " as a classification problem with three classes {Obstacle, Navigable, Unexplored}, as " + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "inline_equation", + "content": "\\mathbf{s} = f_{o}(\\phi ;\\theta_{o})" + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "text", + "content": " is a position feature vector encoded from coordinates " + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 317, + 223, + 547, + 320 + ], + "type": "text", + "content": " — see Section 3.2 for details." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "spans": [ + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "text", + "content": "The Occupancy and Exploration Representation can in principle be queried directly for a single position, but reading out information over a large area directly this way would require multiple reads. We propose to compress this procedure by providing a trainable global read operation " + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "inline_equation", + "content": "r(:, \\theta_g)" + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "text", + "content": ", which predicts an embedding " + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "inline_equation", + "content": "\\mathbf{e}" + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "text", + "content": " containing a global context about what has already been explored, and positions of navigable space. The prediction is done directly from the trainable parameters of the implicit representation, as " + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "inline_equation", + "content": "\\mathbf{e} = r(\\theta_o; \\theta_r)" + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "text", + "content": ". Here " + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "inline_equation", + "content": "\\theta_o" + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "text", + "content": " is input to " + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "text", + "content": ", whereas " + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "inline_equation", + "content": "\\theta_r" + }, + { + "bbox": [ + 304, + 331, + 547, + 450 + ], + "type": "text", + "content": " are its parameters." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "spans": [ + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "text", + "content": "Given representations " + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "inline_equation", + "content": "f_{s}" + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "inline_equation", + "content": "f_{o}" + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "text", + "content": ", a single forward pass of the agent at time step " + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "text", + "content": " and for a goal " + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "inline_equation", + "content": "g_{t}" + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "text", + "content": " involves reading the representations and providing the input to the policy. The current RGB-D observation " + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "inline_equation", + "content": "o_{t}" + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "text", + "content": " is also encoded by the convolutional network " + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "text", + "content": " (different from the projection module " + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "text", + "content": " used to generate samples for training the Semantic Finder). Previous action " + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "inline_equation", + "content": "a_{t-1}" + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "text", + "content": " and current goal " + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "inline_equation", + "content": "g_{t}" + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "text", + "content": " are passed through embedding layers, named " + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "inline_equation", + "content": "L(\\cdot)" + }, + { + "bbox": [ + 304, + 451, + 547, + 559 + ], + "type": "text", + "content": " in the following equations. These different outputs are fed to the policy," + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 312, + 565, + 547, + 578 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 565, + 547, + 578 + ], + "spans": [ + { + "bbox": [ + 312, + 565, + 547, + 578 + ], + "type": "interline_equation", + "content": "\\mathbf {x} _ {t} = f _ {s} \\left(g _ {t}; \\theta_ {s, t}\\right), \\mathbf {e} _ {t} = r \\left(\\theta_ {o, t}; \\theta_ {r}\\right), \\mathbf {c} _ {t} = c \\left(o _ {t}; \\theta_ {c}\\right), \\tag {1}", + "image_path": "75459cdc0f3266200fb08ebe18bc7637a70ddc80bf7c89c9c85a83c58e005445.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 312, + 580, + 545, + 594 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 580, + 545, + 594 + ], + "spans": [ + { + "bbox": [ + 312, + 580, + 545, + 594 + ], + "type": "interline_equation", + "content": "\\mathbf {h} _ {t} = G R U \\left(\\mathbf {h} _ {t - 1}, \\mathbf {x} _ {t}, u _ {t}, \\mathbf {e} _ {t}, L \\left(a _ {t - 1}\\right), L \\left(g _ {t}\\right), \\mathbf {c} _ {t}; \\theta_ {G}\\right), \\tag {2}", + "image_path": "c8eebad4dd8dea333910b2b3b0e99f11e74ee80ca236b51e5ca5d7b85b9f2ab4.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 315, + 596, + 545, + 609 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 596, + 545, + 609 + ], + "spans": [ + { + "bbox": [ + 315, + 596, + 545, + 609 + ], + "type": "interline_equation", + "content": "a _ {t} = \\pi \\left(\\mathbf {h} _ {t}; \\theta_ {\\pi}\\right), \\tag {3}", + "image_path": "90a27299892e67b4923d2fe134c3b63e43cc471d51989f00a024685960f5f6a8.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": "where we added indices " + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\cdot_t" + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": " to relevant variables to indicate time. Please note that the trainable parameters " + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\theta_{s,t}" + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\theta_{o,t}" + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": " of the two implicit representations are time dependent, as they depend on the observed scene and are updated dynamically, whereas the parameters of the policy " + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\pi" + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": " and the global reader " + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": " are not. Here, GRU corresponds to the update equations of a GRU network, where we omitted gates for ease of notation. The notation " + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "inline_equation", + "content": "a_t = \\pi(.)" + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": " predicting action " + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "inline_equation", + "content": "a_t" + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": " is" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "11006" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 99, + 69, + 500, + 300 + ], + "blocks": [ + { + "bbox": [ + 99, + 69, + 500, + 300 + ], + "lines": [ + { + "bbox": [ + 99, + 69, + 500, + 300 + ], + "spans": [ + { + "bbox": [ + 99, + 69, + 500, + 300 + ], + "type": "image", + "image_path": "ca3b92b49c6a8c8eb936223f8b452dca3325d55d7eb923dc4ba0d0cd0e619939.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 304, + 547, + 340 + ], + "lines": [ + { + "bbox": [ + 46, + 304, + 547, + 340 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 547, + 340 + ], + "type": "text", + "content": "Figure 2. Navigating with implicit representations. Red connections " + }, + { + "bbox": [ + 46, + 304, + 547, + 340 + ], + "type": "inline_equation", + "content": "\\longrightarrow" + }, + { + "bbox": [ + 46, + 304, + 547, + 340 + ], + "type": "text", + "content": " indicate the training process of the two implicit representations (= mapping), which is also done during agent deployment. Black connections " + }, + { + "bbox": [ + 46, + 304, + 547, + 340 + ], + "type": "inline_equation", + "content": "\\longrightarrow" + }, + { + "bbox": [ + 46, + 304, + 547, + 340 + ], + "type": "text", + "content": " show the forward pass of the agent. ■ are discrete learned embeddings (LUT). Policy training is not shown in this figure." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 357, + 288, + 380 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 357, + 288, + 380 + ], + "spans": [ + { + "bbox": [ + 46, + 357, + 288, + 380 + ], + "type": "text", + "content": "also a simplification, as we train the agent with PPO, an actor-critic method — see Section 3.4." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 383, + 288, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 383, + 288, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 383, + 288, + 479 + ], + "type": "text", + "content": "Mapping means training! — The implicit representations " + }, + { + "bbox": [ + 46, + 383, + 288, + 479 + ], + "type": "inline_equation", + "content": "f_{s}" + }, + { + "bbox": [ + 46, + 383, + 288, + 479 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 383, + 288, + 479 + ], + "type": "inline_equation", + "content": "f_{o}" + }, + { + "bbox": [ + 46, + 383, + 288, + 479 + ], + "type": "text", + "content": " maintain a compact and actionable representation of the observed scene, and as such need to be updated at each time step from the current observation " + }, + { + "bbox": [ + 46, + 383, + 288, + 479 + ], + "type": "inline_equation", + "content": "o_{t}" + }, + { + "bbox": [ + 46, + 383, + 288, + 479 + ], + "type": "text", + "content": ". Given their implicit nature and implementation as neural networks, updates are gradient based and done with SGD. The implicit representations are therefore trained from scratch at each episode even after deployment." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 479, + 288, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 479, + 288, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 479, + 288, + 635 + ], + "type": "text", + "content": "Training a representation from observations obtained sequentially during an episode also raises a serious issue of catastrophic forgetting [22], as places of the scene observed early might be forgotten later in the episode [52, 59]. We solve this by maintaining two replay buffers throughout the episode, one for each representation. Training samples are generated from each new observation and added to the replay buffers at each time step. Both representations are then trained for a number of gradient steps (" + }, + { + "bbox": [ + 46, + 479, + 288, + 635 + ], + "type": "inline_equation", + "content": "n_s" + }, + { + "bbox": [ + 46, + 479, + 288, + 635 + ], + "type": "text", + "content": " for the Semantic Finder and " + }, + { + "bbox": [ + 46, + 479, + 288, + 635 + ], + "type": "inline_equation", + "content": "n_o" + }, + { + "bbox": [ + 46, + 479, + 288, + 635 + ], + "type": "text", + "content": " for the Exploration and Occupancy Representation). Details on the two representations and their training are given in Sections 3.1 and 3.2. The global reader " + }, + { + "bbox": [ + 46, + 479, + 288, + 635 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 479, + 288, + 635 + ], + "type": "text", + "content": " is not trained or finetuned online but rather trained once offline." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 646, + 180, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 646, + 180, + 659 + ], + "spans": [ + { + "bbox": [ + 47, + 646, + 180, + 659 + ], + "type": "text", + "content": "3.1. The Semantic Finder " + }, + { + "bbox": [ + 47, + 646, + 180, + 659 + ], + "type": "inline_equation", + "content": "f_{s}" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": "While recent work on implicit representations for robotics focused on signed distance functions [42, 32], occupancy [52] or density, assuming light density approximates mass density [1], the aim of this model is to localize an object" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 357, + 547, + 490 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 357, + 547, + 490 + ], + "spans": [ + { + "bbox": [ + 304, + 357, + 547, + 490 + ], + "type": "text", + "content": "of interest within the scene, which can be seen as inverse operation to classical work. From a query vector given as input, the Semantic Finder predicts the position of the object, which is particularly useful for an agent interacting with an environment in the context of a goal conditioned task. It is implemented as a 3-layer MLP with ReLu activations in the intermediate layers and a sigmoid activation for the output. Hidden layers have 512 neurons. The query vector " + }, + { + "bbox": [ + 304, + 357, + 547, + 490 + ], + "type": "inline_equation", + "content": "\\mathbf{q}" + }, + { + "bbox": [ + 304, + 357, + 547, + 490 + ], + "type": "text", + "content": " corresponds to the 1-in-K encoding of the target object class, which during navigation is directly determined by the object goal " + }, + { + "bbox": [ + 304, + 357, + 547, + 490 + ], + "type": "inline_equation", + "content": "g_{t}" + }, + { + "bbox": [ + 304, + 357, + 547, + 490 + ], + "type": "text", + "content": " provided by the task." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "spans": [ + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "type": "text", + "content": "Mapping/Training - The implicit representation is updated minimizing the L1 loss between the prediction " + }, + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i = f_s(\\mathbf{q}_i, \\theta_s)" + }, + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "type": "text", + "content": " and the supervised coordinates " + }, + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i^*" + }, + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "type": "text", + "content": " (we avoided the term \"ground-truth\" here on purpose), " + }, + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_s = \\sum_i \\| \\mathbf{x}_i^* - \\mathbf{x}_i \\|_1" + }, + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "type": "text", + "content": ", where the sum goes over the batch sampled from the scene replay buffer. Coordinates " + }, + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i^*" + }, + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "type": "text", + "content": " are normalized " + }, + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "type": "inline_equation", + "content": "\\in [0, 1]" + }, + { + "bbox": [ + 304, + 494, + 547, + 567 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "text", + "content": "The data pairs " + }, + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "inline_equation", + "content": "(x_{i}^{*}, q_{i})" + }, + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "text", + "content": " for training are created from each observation " + }, + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "inline_equation", + "content": "o_{t}" + }, + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "text", + "content": " during each time step, each data point corresponding to an observed point. Pixels in " + }, + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "inline_equation", + "content": "o_{t}" + }, + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "text", + "content": " are inversely projected into 3D coordinates in the scene using the depth channel, the camera intrinsics, as well as agent's coordinates and heading that are assumed to be available, as in [56]. The query vector " + }, + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{q}" + }, + { + "bbox": [ + 304, + 570, + 548, + 714 + ], + "type": "text", + "content": " corresponds to a 9-dimensional vector encoding a distribution over object classes (8 target objects and the \"background\" class). Let us recall that while the training of the representation is supervised, this supervision cannot use \"ground-truth\" information available only during training. All supervision information is required to be" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "11007" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 167 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 167 + ], + "type": "text", + "content": "predicted from the data available to the agent even after deployment. We predict object class information through a semantic segmentation model " + }, + { + "bbox": [ + 46, + 72, + 289, + 167 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 72, + 289, + 167 + ], + "type": "text", + "content": ", which is applied to each current RGB-D observation " + }, + { + "bbox": [ + 46, + 72, + 289, + 167 + ], + "type": "inline_equation", + "content": "o_t \\in \\mathbb{R}^{h \\times w \\times 4}" + }, + { + "bbox": [ + 46, + 72, + 289, + 167 + ], + "type": "text", + "content": ", recovering the output segmentation map " + }, + { + "bbox": [ + 46, + 72, + 289, + 167 + ], + "type": "inline_equation", + "content": "m_t \\in \\mathbb{R}^{k \\times l \\times 9}" + }, + { + "bbox": [ + 46, + 72, + 289, + 167 + ], + "type": "text", + "content": ". The model has been pre-trained on the segmentation of the different target objects, i.e. coloured cylinders, and is not fine-tuned during training of the agent itself." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "spans": [ + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "type": "text", + "content": "Training data pairs " + }, + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "type": "inline_equation", + "content": "(x_{i}^{*}, q_{i})" + }, + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "type": "text", + "content": " are sampled from this output. The supervised coordinates " + }, + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "type": "inline_equation", + "content": "x_{i}^{*}" + }, + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "type": "text", + "content": " are simply the mean 3D coordinates of each feature map cell, after inverse projection. The query vector " + }, + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "type": "inline_equation", + "content": "\\mathbf{q}_{i}" + }, + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "type": "text", + "content": " is the distribution over semantic classes. After the replay buffer is updated, a training batch must be sampled to update the neural field. One fourth of the samples in the batch of size " + }, + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "type": "text", + "content": " correspond to the " + }, + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "type": "inline_equation", + "content": "b/4" + }, + { + "bbox": [ + 46, + 168, + 290, + 289 + ], + "type": "text", + "content": " last steps. The rest are sampled from the previous steps in the replay buffer. Uniform sampling is also performed among pairs collected at a given time step." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 301, + 290, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 301, + 290, + 483 + ], + "spans": [ + { + "bbox": [ + 46, + 301, + 290, + 483 + ], + "type": "text", + "content": "Estimating uncertainty — is an essential component, as querying yet unseen objects will lead to wrong predictions, which the agent needs to recognize as such, and discard. The estimation of uncertainty in neural networks is an open problem, which has been previously addressed through different means, including drop out as a Bayesian approximation [21], variational information bottlenecks [50], density estimation [31], and others. In this work, we approximate a density estimate in the scene replay buffer by calculating the minimum Euclidean distance between the input query and all embeddings in the replay buffer at the current time step. The method is simple and efficient and does not require explicitly fitting a model to estimate the marginal distribution " + }, + { + "bbox": [ + 46, + 301, + 290, + 483 + ], + "type": "inline_equation", + "content": "p(\\mathbf{q})" + }, + { + "bbox": [ + 46, + 301, + 290, + 483 + ], + "type": "text", + "content": ", in particular as the uncertainty representation is latent, can be un-normalized as not required to be a probability." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 487, + 288, + 513 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 487, + 288, + 513 + ], + "spans": [ + { + "bbox": [ + 47, + 487, + 288, + 513 + ], + "type": "text", + "content": "3.2. Occupancy and Exploration Implicit Representation " + }, + { + "bbox": [ + 47, + 487, + 288, + 513 + ], + "type": "inline_equation", + "content": "f_{o}" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "spans": [ + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "text", + "content": "Unlike " + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "inline_equation", + "content": "f_{s}" + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "text", + "content": ", the occupancy representation " + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "inline_equation", + "content": "f_{o}" + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "text", + "content": " is closer to classical implicit representations in robotics, e.g. [52, 42, 32, 1], which map spatial coordinates to variables encoding information on navigable area like occupancy or signed distances. Different to previous work, our representation also includes exploration information, which changes over time during the episode. Once explored, a position changes its class, which makes our neural field dynamic. Another difference with " + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "inline_equation", + "content": "f_{s}" + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "text", + "content": " is that the latter deals with 3D coordinates while " + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "inline_equation", + "content": "f_{o}" + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "text", + "content": " is a topdown 2D representation. Inspired by [57, 53], the model uses Fourier features " + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "text", + "content": " extracted from the 2D coordinates " + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "text", + "content": " previously normalized " + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "inline_equation", + "content": "\\in [0,1]" + }, + { + "bbox": [ + 46, + 517, + 289, + 662 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 668, + 289, + 685 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 668, + 289, + 685 + ], + "spans": [ + { + "bbox": [ + 58, + 668, + 289, + 685 + ], + "type": "interline_equation", + "content": "\\phi = (\\cos (\\mathbf {x} 2 ^ {0}), \\sin (\\mathbf {x} 2 ^ {0}), \\dots , \\cos (\\mathbf {x} 2 ^ {\\frac {p}{4}}), \\sin (\\mathbf {x} 2 ^ {\\frac {p}{4}})). (4)", + "image_path": "8c2994fd8bd547a1ea6e67bf5f76f4c2ca8b9cc8707a335bbd9230f72b6a35b6.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 689, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 289, + 714 + ], + "type": "text", + "content": "The network " + }, + { + "bbox": [ + 46, + 689, + 289, + 714 + ], + "type": "inline_equation", + "content": "f_{o}" + }, + { + "bbox": [ + 46, + 689, + 289, + 714 + ], + "type": "text", + "content": " is a 3-layer MLP with ReLu intermediate activations and a softmax function at the output layer. Hidden" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 72, + 457, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 457, + 84 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 457, + 84 + ], + "type": "text", + "content": "layers have 512 neurons, and " + }, + { + "bbox": [ + 305, + 72, + 457, + 84 + ], + "type": "inline_equation", + "content": "p = 40" + }, + { + "bbox": [ + 305, + 72, + 457, + 84 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "spans": [ + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "text", + "content": "Mapping/Training — The implicit representation is updated minimizing the Cross Entropy loss between the prediction " + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "inline_equation", + "content": "\\mathbf{s}" + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "text", + "content": " of the neural field and the supervised label " + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "inline_equation", + "content": "\\mathbf{s}^*" + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "text", + "content": " of three classes " + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "inline_equation", + "content": "\\{\\text{Obstacle, Navigable, Unexplored}\\}" + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "text", + "content": ", as " + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_o = -\\sum_{c=1}^{3} \\mathbf{s}_c^* \\log \\mathbf{s}_c" + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "text", + "content": ". As for the Semantic Finder, training data pairs " + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "inline_equation", + "content": "(\\mathbf{s}^*, \\mathbf{s})" + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "text", + "content": " are created through inverse perspective projection of the pixels of the observation " + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "inline_equation", + "content": "o_t" + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "text", + "content": " into 3D scene coordinates. Thresholding the " + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "text", + "content": " (height) coordinate decides between Navigable and Obstacle classes. Points with a " + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 304, + 85, + 547, + 240 + ], + "type": "text", + "content": " coordinate higher than a certain threshold are discarded. The replay buffer is balanced between both classes, and only samples of the last 1000 steps are kept. Samples of the Unexplored class are not stored." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 240, + 547, + 301 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 240, + 547, + 301 + ], + "spans": [ + { + "bbox": [ + 304, + 240, + 547, + 301 + ], + "type": "text", + "content": "The replay buffer is sampled similarly to the one for the Semantic Finder. However, additional samples for the Unexplored class are created by sampling uniformly inside the scene, for speed reasons simply ignoring conflicts with explored areas and treating them as noisy labels." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 310, + 546, + 335 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 310, + 546, + 335 + ], + "spans": [ + { + "bbox": [ + 305, + 310, + 546, + 335 + ], + "type": "text", + "content": "3.3. Global Occupancy Read " + }, + { + "bbox": [ + 305, + 310, + 546, + 335 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 305, + 310, + 546, + 335 + ], + "type": "text", + "content": " — handling reparametrization invariance" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "spans": [ + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "text", + "content": "The global Occupancy reader " + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "text", + "content": " allows to query the occupancy information of the scene globally, beyond point-wise information, and as such is a trainable mapping from the space of functions " + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "inline_equation", + "content": "f_{o}(:,.)" + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "text", + "content": " to an embedding space " + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "inline_equation", + "content": "e" + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "text", + "content": ". In particular, two functions " + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "inline_equation", + "content": "f_{o}" + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "inline_equation", + "content": "f_{o}'" + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "text", + "content": " s.t. " + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "inline_equation", + "content": "f_{o}(\\mathbf{x}) = f_{o}'(\\mathbf{x}) \\forall \\mathbf{x}" + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "text", + "content": " should be mapped to identical or close embeddings. However, as the occupancy networks " + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "inline_equation", + "content": "f_{o}" + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "text", + "content": " are implemented as MLPs, any given instance " + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "inline_equation", + "content": "f_{o}(:,;\\theta_{o})" + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "text", + "content": " parameterized by trainable weights " + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "inline_equation", + "content": "\\theta_{o}" + }, + { + "bbox": [ + 304, + 341, + 547, + 508 + ], + "type": "text", + "content": " can be reparametrized by any permutation of hidden units, which leads to permutations of the rows and columns, respectively, of two weight matrices, its own and the one of the preceding layer. This reparameterization keeps the represented functions identical, although their representations as weight vectors are different." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "type": "text", + "content": "To favor learning a global occupancy reader which is invariant w.r.t these transformations, we implement it as a transformer model with self-attention [55] — this, however, does not enforce full invariance. The model takes as input a sequence of tokens " + }, + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "type": "inline_equation", + "content": "(w_{1},\\dots,w_{N})" + }, + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "type": "inline_equation", + "content": "w_{i}\\in \\mathbb{R}^{a}" + }, + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "type": "text", + "content": " is a learned linear embedding of the incoming weights of one neuron within the implicit representation " + }, + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "type": "inline_equation", + "content": "f_{o}" + }, + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "type": "text", + "content": " is the number of neurons of " + }, + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "type": "inline_equation", + "content": "f_{o}" + }, + { + "bbox": [ + 304, + 510, + 548, + 676 + ], + "type": "text", + "content": ". Each token is summed with a positional encoding in the form of Fourier features. An additional \"CLS\" token with learned embedding is concatenated to the input sequence. The reader is composed of 4 self-attention layers, with 8 attention heads. The output representation of the \"CLS\" token is used as the global embedding of the implicit representation." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "content": "Training - The global reader " + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "content": " is trained with full supervision from a dataset of " + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "inline_equation", + "content": "25k" + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "content": " trajectories composed of MLP weights " + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\theta_{o,i}" + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "content": " and absolute maps " + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i" + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "inline_equation", + "content": "i..1..25k" + }, + { + "bbox": [ + 305, + 677, + 547, + 713 + ], + "type": "text", + "content": ". Each" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "11008" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "content": "map is a metric tensor providing occupancy information extracted from the corresponding implicit representation, i.e. " + }, + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i(\\mathbf{x}_y,\\mathbf{x}_x) = f_o(\\mathbf{x},\\theta_{o,i})" + }, + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "content": " . The dataset also contains an egocentric version " + }, + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i^{\\prime}" + }, + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "content": " of each map, which is centered on the agent and oriented depending on its current heading. The reader " + }, + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "content": " is trained in an Encoder-Decoder fashion, where " + }, + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "content": " plays the role of the encoder," + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 95, + 165, + 288, + 179 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 95, + 165, + 288, + 179 + ], + "spans": [ + { + "bbox": [ + 95, + 165, + 288, + 179 + ], + "type": "interline_equation", + "content": "\\mathbf {e} _ {i} = r \\left(\\theta_ {o, i}\\right), \\quad \\hat {\\mathbf {M}} _ {i} = D e c \\left(e _ {i}, p _ {i}\\right), \\tag {5}", + "image_path": "81bd6862856be89cb07f35b885df80cb44d434dfec3fdeaa4c484151b8d8fd3f.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 188, + 287, + 224 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 188, + 287, + 224 + ], + "spans": [ + { + "bbox": [ + 46, + 188, + 287, + 224 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 188, + 287, + 224 + ], + "type": "inline_equation", + "content": "p_i" + }, + { + "bbox": [ + 46, + 188, + 287, + 224 + ], + "type": "text", + "content": " is the agent pose (position and heading), necessary to decode ego-centric information. We minimize a cross entropy loss on the prediction of ego-centric maps," + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 56, + 232, + 288, + 247 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 232, + 288, + 247 + ], + "spans": [ + { + "bbox": [ + 56, + 232, + 288, + 247 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {g} = - \\sum_ {i} \\sum_ {k} \\sum_ {l} \\sum_ {c = 1} ^ {3} \\mathbf {M} _ {i, c} ^ {\\prime *} (k, l) \\log \\mathbf {M} _ {i, c} ^ {\\prime} (k, l) (6)", + "image_path": "ed67302f3c65dbdcd8522d0c7bb2eb1b0c05a6dcc04702866bfa9de4ff9d376a.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 255, + 289, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 255, + 289, + 316 + ], + "spans": [ + { + "bbox": [ + 46, + 255, + 289, + 316 + ], + "type": "text", + "content": "Directly training this prediction proved to be difficult. We propose a procedure involving several steps, detailed in section 3.5. After the training phase, the reader " + }, + { + "bbox": [ + 46, + 255, + 289, + 316 + ], + "type": "inline_equation", + "content": "g" + }, + { + "bbox": [ + 46, + 255, + 289, + 316 + ], + "type": "text", + "content": " is used in the perception + mapping module of the agent as given in equation (1), and kept frozen during agent RL training." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 323, + 160, + 335 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 323, + 160, + 335 + ], + "spans": [ + { + "bbox": [ + 47, + 323, + 160, + 335 + ], + "type": "text", + "content": "3.4. Training the Agent" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "text", + "content": "The agent is trained with RL, more precisely Proximal Policy Optimization (PPO) [49]. The inner training loops of the implicit representations are supervised (red arrows in Figure 2) and occur at each time step in the forward pass, whereas the RL-based outer training loop of the agent occurs after " + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "text", + "content": " acting steps (black arrows in Figure 2). As the perception module used to generate training data from RGBD-observations for the Semantic Finder " + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "inline_equation", + "content": "f_{s}" + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "text", + "content": " is independent of the visual encoder " + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "text", + "content": " in the agent (see Figure 2), and as its query " + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "inline_equation", + "content": "\\mathbf{q}_t" + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "text", + "content": " is fixed to the navigation goal " + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "inline_equation", + "content": "\\mathbf{g}_t" + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "text", + "content": ", there is no need to track the weights " + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "inline_equation", + "content": "\\theta_{s}" + }, + { + "bbox": [ + 46, + 340, + 289, + 495 + ], + "type": "text", + "content": " at each time step in order to backpropagate the PPO loss (outer training). This is a key design choice of our method." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 497, + 289, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 497, + 289, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 497, + 289, + 664 + ], + "type": "text", + "content": "Training assumptions — We do not rely on the existence of global GT maps for occupancy, as " + }, + { + "bbox": [ + 46, + 497, + 289, + 664 + ], + "type": "inline_equation", + "content": "f_{o}()" + }, + { + "bbox": [ + 46, + 497, + 289, + 664 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 497, + 289, + 664 + ], + "type": "inline_equation", + "content": "r()" + }, + { + "bbox": [ + 46, + 497, + 289, + 664 + ], + "type": "text", + "content": " were trained on observation data from agent trajectories only. However, similar to [37, 46], we exploit object positions in simulation, during training only; Moreover, we require pixel-wise segmentation masks during training. We believe that this does not change requirements, as the goal is to fully exploit 3D photo-realistic simulators as a data source and see how far the field can go with this. Generalization requirements are unchanged: we require our agent to be able to generalize to new unseen scenes. Generalization to unseen object categories is not targeted, and in MultiON task setup not possible for any agent, as object positions and labels are required for reward calculation." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 671, + 194, + 684 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 194, + 684 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 194, + 684 + ], + "type": "text", + "content": "3.5. Training the global reader" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 689, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 289, + 714 + ], + "type": "text", + "content": "The proposed training procedure for the global reader " + }, + { + "bbox": [ + 46, + 689, + 289, + 714 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 46, + 689, + 289, + 714 + ], + "type": "text", + "content": " (performed before training the agent) can be split into 3 phases." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 547, + 157 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 157 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 157 + ], + "type": "text", + "content": "The architecture for the convolutional decoder " + }, + { + "bbox": [ + 304, + 72, + 547, + 157 + ], + "type": "inline_equation", + "content": "Dec()" + }, + { + "bbox": [ + 304, + 72, + 547, + 157 + ], + "type": "text", + "content": " is kept the same in all of them. The hyperparameters of its different layers are detailed in the Supplementary Material. It is composed of 6 transpose convolution layers along with batch norm layers and ReLU activations, except for the last layer with a softmax activation. Figure 3 provides an overview of the 3 steps involved in the training of the global reader." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 169, + 547, + 217 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 169, + 547, + 217 + ], + "spans": [ + { + "bbox": [ + 306, + 169, + 547, + 217 + ], + "type": "text", + "content": "Fully convolutional autoencoder — The first step is to train a fully convolutional autoencoder on the set of absolute maps " + }, + { + "bbox": [ + 306, + 169, + 547, + 217 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i" + }, + { + "bbox": [ + 306, + 169, + 547, + 217 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 306, + 169, + 547, + 217 + ], + "type": "inline_equation", + "content": "i..1..25k" + }, + { + "bbox": [ + 306, + 169, + 547, + 217 + ], + "type": "text", + "content": ". Only the decoder weights are kept." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 228, + 547, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 228, + 547, + 300 + ], + "spans": [ + { + "bbox": [ + 306, + 228, + 547, + 300 + ], + "type": "text", + "content": "Global reader training on absolute maps — The second step consists in training the global reader to output embeddings fed to the frozen decoder from the previous step. The objective is to reconstruct absolute maps from the weights of the implicit representation. The global reader weights are kept after this training phase." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 310, + 547, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 310, + 547, + 455 + ], + "spans": [ + { + "bbox": [ + 306, + 310, + 547, + 455 + ], + "type": "text", + "content": "Global reader finetuning on egocentric maps The global reader, whose weights are initialized from the weights obtained in the previous step, is now trained along with the same decoder from the first step (also used in the second step) on the set of egocentric maps " + }, + { + "bbox": [ + 306, + 310, + 547, + 455 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i^{\\prime}" + }, + { + "bbox": [ + 306, + 310, + 547, + 455 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 306, + 310, + 547, + 455 + ], + "type": "inline_equation", + "content": "i..1..25k" + }, + { + "bbox": [ + 306, + 310, + 547, + 455 + ], + "type": "text", + "content": ". Both global reader and decoder are finetuned. The output of the global reader is not directly fed to the decoder, but is passed through linear layers in order to fuse information about first the position of the agent, and then its heading because this time the right operations of shift and rotation must be applied in order to reconstruct egocentric maps." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 464, + 545, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 464, + 545, + 548 + ], + "spans": [ + { + "bbox": [ + 306, + 464, + 545, + 548 + ], + "type": "text", + "content": "Integrating the pre-trained global reader into the agent After this pre-training in 3 steps, the weights of the global reader are frozen and not updated during the RL training. However, a linear layer is learnt to project the 576-dim embedding from the global reader into a 256-dim representation fed to the GRU. This linear layer is trained from reward signals." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 573, + 388, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 573, + 388, + 586 + ], + "spans": [ + { + "bbox": [ + 306, + 573, + 388, + 586 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": "MultiON task — we target the 3-ON version of the MultiON task [56], where the agent deals with sequences of 3 objects, each belonging to one of 8 classes (cylinders of different colors). At each step, the observation " + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{o}_t" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": " is an RGB-D image of size " + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "inline_equation", + "content": "256 \\times 256 \\times 4" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": " and the target class is a one-in-K (" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "inline_equation", + "content": "K = 8" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": ") vector. The action space is discrete: {Move forward " + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "inline_equation", + "content": "0.25m" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": ", Turn left " + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "inline_equation", + "content": "30^\\circ" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": ", Turn right " + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "inline_equation", + "content": "30^\\circ" + }, + { + "bbox": [ + 304, + 594, + 547, + 713 + ], + "type": "text", + "content": ", Found}. An episode is considered successful if the agent finds all of the targets before the time limit (2, 500 environment steps), and chooses the Found action for each one at a distance closer to" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "11009" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 78, + 71, + 516, + 350 + ], + "blocks": [ + { + "bbox": [ + 78, + 71, + 516, + 350 + ], + "lines": [ + { + "bbox": [ + 78, + 71, + 516, + 350 + ], + "spans": [ + { + "bbox": [ + 78, + 71, + 516, + 350 + ], + "type": "image", + "image_path": "dd8b87e0f90df7252d5d672360cb58d2efa026066632578ff554280eef087a72.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 359, + 547, + 383 + ], + "lines": [ + { + "bbox": [ + 46, + 359, + 547, + 383 + ], + "spans": [ + { + "bbox": [ + 46, + 359, + 547, + 383 + ], + "type": "text", + "content": "Figure 3. Training the Global Reader in 3 steps: " + }, + { + "bbox": [ + 46, + 359, + 547, + 383 + ], + "type": "inline_equation", + "content": "①" + }, + { + "bbox": [ + 46, + 359, + 547, + 383 + ], + "type": "text", + "content": " training a convolutional auto-encoder on absolute maps; " + }, + { + "bbox": [ + 46, + 359, + 547, + 383 + ], + "type": "inline_equation", + "content": "②" + }, + { + "bbox": [ + 46, + 359, + 547, + 383 + ], + "type": "text", + "content": " extension to inputs equal to weights " + }, + { + "bbox": [ + 46, + 359, + 547, + 383 + ], + "type": "inline_equation", + "content": "\\theta_{o} =" + }, + { + "bbox": [ + 46, + 359, + 547, + 383 + ], + "type": "text", + "content": " the gobal reader; " + }, + { + "bbox": [ + 46, + 359, + 547, + 383 + ], + "type": "inline_equation", + "content": "③" + }, + { + "bbox": [ + 46, + 359, + 547, + 383 + ], + "type": "text", + "content": " extension to predicting ego-centric maps, better suited to navigation problems." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 103, + 391, + 491, + 485 + ], + "blocks": [ + { + "bbox": [ + 103, + 391, + 491, + 485 + ], + "lines": [ + { + "bbox": [ + 103, + 391, + 491, + 485 + ], + "spans": [ + { + "bbox": [ + 103, + 391, + 491, + 485 + ], + "type": "table", + "html": "
0 - 3030 - 5050 - 70— Val —— Test —
SOSOSOSuccessProgressSPLPPLSuccessProgressSPLPPL
------33.2±1.249.0±1.121.2±0.531.6±1.242.3±1.556.7±0.928.1±1.037.8±1.8
μ--✓-✓37.8±1.652.3±0.926.35±1.536.5±0.847.0±1.760.5±1.634.5±0.844.2±1.0
--✓-✓✓38.5±4.652.5±4.828.2±2.138.3±1.746.7±3.060.1±3.135.1±1.444.8±1.0
------32.147.721.632.641.055.928.939.0
↑--✓-✓38.151.927.337.148.661.535.244.2
--✓-✓✓43.156.830.540.149.763.436.445.9
", + "image_path": "a666675f04a35cd820c14f1d9cd31ba9c01a97bd04fe657aec2ab01ce34e3115.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 491, + 547, + 514 + ], + "lines": [ + { + "bbox": [ + 46, + 491, + 547, + 514 + ], + "spans": [ + { + "bbox": [ + 46, + 491, + 547, + 514 + ], + "type": "text", + "content": "Table 1. Impact of the implicit representations: navigation performance on MultiON val and MultiON test. S=f_s activated, O=f_o activated in the corresponding training period (see text). Top/μ: means over 3 runs; Bottom/↑: best validation seeds over 3 runs." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 533, + 288, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 288, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 288, + 568 + ], + "type": "inline_equation", + "content": "1.5m" + }, + { + "bbox": [ + 46, + 533, + 288, + 568 + ], + "type": "text", + "content": ". Calling Found incorrectly terminates episode as a failure. An access to perfect odometry information (localization and heading) was assumed in [56] as the standard protocol." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 570, + 290, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 570, + 290, + 715 + ], + "spans": [ + { + "bbox": [ + 45, + 570, + 290, + 715 + ], + "type": "text", + "content": "Dataset and metrics — The agent is trained on the Mutterport3d [9] dataset. We followed the standard train/val/test split over scenes (denoted MultiON train, MultiON val, MultiON test): 61 training, 11 validation and 18 test scenes. The train, val and test splits are respectively composed of 50,000, 12,500 and 12,500 episodes per scene. Reported results on the val and test sets (Tables 1 and 2) were computed on a subset of 1,000 randomly sampled episodes. We report standard metrics as used in the navigation literature (and in [56]): Success: percentage of successful episodes — all objects are reached respecting order, time; Progress: percentage of objects successfully found (respecting order," + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 533, + 545, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 533, + 545, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 533, + 545, + 568 + ], + "type": "text", + "content": "time); SPL: Success weighted by Path Length, extending the original SPL metric [2] to MultiON; PPL: Progress weighted By Path Length (the official MultiON challenge metric)." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "spans": [ + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "text", + "content": "Global reader dataset — The Global reader " + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "text", + "content": " was trained on a dataset of " + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "inline_equation", + "content": "25k" + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "text", + "content": " trajectories obtained from rollouts performed by a baseline agent [37]. " + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "inline_equation", + "content": "95\\%" + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "text", + "content": " was used for training and the rest for validation. On these trajectories we first trained the occupancy representation " + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "inline_equation", + "content": "f_{o}" + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "text", + "content": " \"in-situ\", i.e. as if it were deployed on the agent, and we recorded training samples " + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "text", + "content": " for training the reader " + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "text", + "content": ": pairs of network weights " + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "inline_equation", + "content": "\\theta_{o,i}" + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "text", + "content": " and associated maps " + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "inline_equation", + "content": "M_{i}" + }, + { + "bbox": [ + 304, + 569, + 547, + 700 + ], + "type": "text", + "content": " obtained by iteratively querying the implicit representation. Ego-centric maps were generated from the absolute ones and both were cropped around their center." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 714 + ], + "type": "text", + "content": "Perception module dataset — The perception module" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "11010" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 72, + 70, + 520, + 208 + ], + "blocks": [ + { + "bbox": [ + 72, + 70, + 520, + 208 + ], + "lines": [ + { + "bbox": [ + 72, + 70, + 520, + 208 + ], + "spans": [ + { + "bbox": [ + 72, + 70, + 520, + 208 + ], + "type": "table", + "html": "
AgentραγSuccessProgressSPLPPLAUXORC
(a)OracleMap† [56]-✓50.4±3.560.5±3.140.7±2.248.8±1.9-✓
(b)OracleEgoMap† [56]-✓32.8±5.247.7±5.226.1±4.537.6±4.7-✓
(c)NoMap† [56]-✓16.7±3.633.7±3.313.1±2.426.0±1.7--
(d)ProjNMap† [26]-✓25.9±1.143.4±1.018.3±0.630.9±0.7--
(e)NoMap✓-42.3±1.556.7±0.928.1±1.037.8±1.8--
(f)ProjNMap [26]✓-39.7±2.355.4±1.428.7±1.140.1±1.9--
(g)Implicit (Ours) w/ curriculum w/pre-train✓--46.7±3.060.1±3.135.1±1.444.8±1.0--
(h)ProjNMap + AUX [37]N/A✓N/A57.7±3.770.2±2.737.5±2.045.9±1.9✓-
(i)Implicit (Ours) w/o curriculum w/pre-train + AUX✓✓✓58.3±0.869.4±1.143.8±1.052.1±1.6✓-
(j)Implicit (Ours) w/o curriculum w/o pre-train-✓✓54.8±3.668.0±3.441.7±1.951.3±1.6--
(k)Implicit (Ours) w/o curriculum w/o pre-train + AUX-✓✓57.9±2.069.5±0.643.3±2.251.9±3.7✓-
", + "image_path": "c0f89d4ed9b1447f6e4b6673d01c04de5d8f0c95833364e311e2dae578e3a599.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 70, + 265, + 264, + 304 + ], + "blocks": [ + { + "bbox": [ + 46, + 214, + 547, + 249 + ], + "lines": [ + { + "bbox": [ + 46, + 214, + 547, + 249 + ], + "spans": [ + { + "bbox": [ + 46, + 214, + 547, + 249 + ], + "type": "text", + "content": "Table 2. Comparison with SOTA methods on MultiON test. †=performance taken from [37]. “AUX” = auxiliary losses using privileged information [37]. “ORC” = non-comparable, uses oracle information. ρ = pre-training of input encoders from [37]. α = finetuning of input encoders with RL. γ = implicit representations are accessible to the agent since the beginning of RL training (w/o curriculum)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 70, + 265, + 264, + 304 + ], + "lines": [ + { + "bbox": [ + 70, + 265, + 264, + 304 + ], + "spans": [ + { + "bbox": [ + 70, + 265, + 264, + 304 + ], + "type": "table", + "html": "
UncertaintySuccessProgressSPLPPL
-35.4±3.049.7±3.329.4±2.040.9±2.4
✓43.4±3.158.0±3.035.1±0.846.4±1.0
", + "image_path": "a1bd20ce4b2bb7269b0077180272cbc0d924f0432a0828ff743cc8bd14512550.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 309, + 288, + 332 + ], + "lines": [ + { + "bbox": [ + 46, + 309, + 288, + 332 + ], + "spans": [ + { + "bbox": [ + 46, + 309, + 288, + 332 + ], + "type": "text", + "content": "Table 3. Uncertainty: comparing training w/ semantic input only, no occupancy, from the beg. of training, w/ and w/o uncertainty." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 340, + 287, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 340, + 287, + 388 + ], + "spans": [ + { + "bbox": [ + 46, + 340, + 287, + 388 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 340, + 287, + 388 + ], + "type": "text", + "content": " was trained to segment the different target objects. The generated dataset is composed of " + }, + { + "bbox": [ + 46, + 340, + 287, + 388 + ], + "type": "inline_equation", + "content": "132k" + }, + { + "bbox": [ + 46, + 340, + 287, + 388 + ], + "type": "text", + "content": " pairs of RGB-D observations and segmentation masks. Samples for 4 scenes were kept as a validation set." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "spans": [ + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "type": "text", + "content": "Training details - We use the reward function given in [56] for RL/PPO training (see supplementary material), and train all agents for " + }, + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "type": "inline_equation", + "content": "70M" + }, + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "type": "text", + "content": " steps as in [37]. For all agents in Table 1 and some in Table 2 (" + }, + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "type": "inline_equation", + "content": "w/" + }, + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "type": "text", + "content": " pre-train: " + }, + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "type": "inline_equation", + "content": "\\sqrt{}" + }, + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "type": "text", + "content": " column), the encoders (visual encoder " + }, + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 46, + 389, + 288, + 555 + ], + "type": "text", + "content": ", as well as goal and previous action embedding layers, see Figure 2) are pre-trained with a baseline, which corresponds to the ProjNeuralMap agent trained with auxiliary losses [37]. This is done to faster training, as it will be shown later (in Table 2) that the same final performance can be reached without this initial pre-training of encoders. Training and evaluation hyper-parameters, as well as architecture details have been taken from [56]. All reported quantitative results are obtained after 3 training runs for each model." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "text", + "content": "Impact of the implicit representations — Table 1 shows the impact of the two implicit representations on navigation (top: means over 3 runs; bottom: best validation seeds over 3 runs). To keep compute requirements limited and decrease sample complexity, in these ablations we do not train the full agent from scratch, in particular since the early stages of training are spent on learning basic interactions. We decompose training into three phases: " + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "inline_equation", + "content": "0 - 30M" + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "text", + "content": " steps (no implicit representations, i.e. all entries to the agent related to " + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{s}" + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{o}" + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "text", + "content": " are set to 0); " + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "inline_equation", + "content": "30M - 50M" + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "text", + "content": " steps (training includes the Semantic Finder " + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{s}" + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "text", + "content": ") and finally " + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "inline_equation", + "content": "50M - 70M" + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "text", + "content": " steps (full model). This 3-steps approach is used to train all agents in Table 1, and will be denoted as curriculum (See" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 267, + 547, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 267, + 547, + 388 + ], + "spans": [ + { + "bbox": [ + 304, + 267, + 547, + 388 + ], + "type": "text", + "content": "Table 2, " + }, + { + "bbox": [ + 304, + 267, + 547, + 388 + ], + "type": "inline_equation", + "content": "w/" + }, + { + "bbox": [ + 304, + 267, + 547, + 388 + ], + "type": "text", + "content": " curriculum: - in " + }, + { + "bbox": [ + 304, + 267, + 547, + 388 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 267, + 547, + 388 + ], + "type": "text", + "content": " column). All metrics on both val and test sets are improved, with the biggest impact provided by the Semantic Finder, which was expected. We conjecture that mapping object positions is a more difficult task, which is less easily delegated to the vectorial GRU representation, than occupancy. We also see an impact of the occupancy representation, which not only confirms the choice of the implicit representation " + }, + { + "bbox": [ + 304, + 267, + 547, + 388 + ], + "type": "inline_equation", + "content": "{f}_{o}" + }, + { + "bbox": [ + 304, + 267, + 547, + 388 + ], + "type": "text", + "content": " itself,but also its global read through " + }, + { + "bbox": [ + 304, + 267, + 547, + 388 + ], + "type": "inline_equation", + "content": "r\\left( {\\theta }_{o}\\right)" + }, + { + "bbox": [ + 304, + 267, + 547, + 388 + ], + "type": "text", + "content": " . Training curves are given in the supplementary material." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 388, + 547, + 473 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 388, + 547, + 473 + ], + "spans": [ + { + "bbox": [ + 304, + 388, + 547, + 473 + ], + "type": "text", + "content": "Uncertainty — has an impact on agent performance, as we show in the ablation in Table 3. Indeed, when training an agent with the semantic input since the beginning of training (w/o curriculum) and no occupancy input (as the uncertainty is only related to semantic information), feeding the agent with the computed uncertainty about the output of the Semantic Finder brings a boost in performance." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 474, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 548, + 715 + ], + "type": "text", + "content": "Comparison with previous SOTA methods — is done in Table 2. The performance entries of these baselines are taken from [37], which describes the winning entry of the CVPR 2021 MultiON competition. Our method outperforms the different competing representations, even when they benefit from the same pre-training scheme and are thus completely comparable. NoMap with pre-training corresponds to the first row of Table 1. The difference between (g) and (i) is the use of the auxiliary tasks in [37], but also that the implicit representations are available to the agent during the whole training period for (i), i.e. no decomposition into 3 phases as in the ablations in Table 1 (w/o curriculum). Moreover, compared to (g), in (i) the weights of the pre-trained encoders are finetuned. We see that the gains of our representations are complementary to the auxiliary losses in [37]. (j) and (k) confirm this finding, showing that most of the gain compared with (h) comes from the implicit representations, with the auxiliary losses bringing an additional boost. (j) and (k) also show that, even though pre-training can help speed up RL training, similar test performance is achieved without it." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11011" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 78, + 161, + 178 + ], + "blocks": [ + { + "bbox": [ + 113, + 71, + 124, + 79 + ], + "lines": [ + { + "bbox": [ + 113, + 71, + 124, + 79 + ], + "spans": [ + { + "bbox": [ + 113, + 71, + 124, + 79 + ], + "type": "text", + "content": "(a)" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 51, + 78, + 161, + 178 + ], + "lines": [ + { + "bbox": [ + 51, + 78, + 161, + 178 + ], + "spans": [ + { + "bbox": [ + 51, + 78, + 161, + 178 + ], + "type": "image", + "image_path": "51ab0aad70199eb725cd6276a1201454493fe702d3fa84e1f71484bfecf95f17.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 48, + 186, + 365, + 242 + ], + "lines": [ + { + "bbox": [ + 48, + 186, + 365, + 242 + ], + "spans": [ + { + "bbox": [ + 48, + 186, + 365, + 242 + ], + "type": "text", + "content": "Figure 4. Capacity of the semantic representation: we report mean distance prediction error (normalized " + }, + { + "bbox": [ + 48, + 186, + 365, + 242 + ], + "type": "inline_equation", + "content": "\\in [0,1]" + }, + { + "bbox": [ + 48, + 186, + 365, + 242 + ], + "type": "text", + "content": ") as a function of the number of stored objects. Replay buffers are composed of dummy queries: (a) one-hot queries with same dimension as number of objects; (b) random query with dimension 9; (c) random query with same dimension as number of objects." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 166, + 77, + 262, + 171 + ], + "blocks": [ + { + "bbox": [ + 214, + 72, + 225, + 79 + ], + "lines": [ + { + "bbox": [ + 214, + 72, + 225, + 79 + ], + "spans": [ + { + "bbox": [ + 214, + 72, + 225, + 79 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 166, + 77, + 262, + 171 + ], + "lines": [ + { + "bbox": [ + 166, + 77, + 262, + 171 + ], + "spans": [ + { + "bbox": [ + 166, + 77, + 262, + 171 + ], + "type": "image", + "image_path": "e6d048fe9ed4f1aa772de290b8753026734f33cfc043a212e079ec178133a457.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 263, + 77, + 363, + 171 + ], + "blocks": [ + { + "bbox": [ + 315, + 72, + 325, + 79 + ], + "lines": [ + { + "bbox": [ + 315, + 72, + 325, + 79 + ], + "spans": [ + { + "bbox": [ + 315, + 72, + 325, + 79 + ], + "type": "text", + "content": "(c)" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 263, + 77, + 363, + 171 + ], + "lines": [ + { + "bbox": [ + 263, + 77, + 363, + 171 + ], + "spans": [ + { + "bbox": [ + 263, + 77, + 363, + 171 + ], + "type": "image", + "image_path": "1b285e3496fbf412969e0c87a2fa5d3cf51a2bc545a012f7eb7eb52f2aa17a12.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 391, + 79, + 533, + 178 + ], + "blocks": [ + { + "bbox": [ + 391, + 79, + 533, + 178 + ], + "lines": [ + { + "bbox": [ + 391, + 79, + 533, + 178 + ], + "spans": [ + { + "bbox": [ + 391, + 79, + 533, + 178 + ], + "type": "image", + "image_path": "b7c808453ab0ff7fdda121b7234baf9e9252ff9fb76c4c1ddeaae3c4bbc6a72a.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 383, + 186, + 544, + 253 + ], + "lines": [ + { + "bbox": [ + 383, + 186, + 544, + 253 + ], + "spans": [ + { + "bbox": [ + 383, + 186, + 544, + 253 + ], + "type": "text", + "content": "Figure 5. Lifelong learning of the semantic repr. " + }, + { + "bbox": [ + 383, + 186, + 544, + 253 + ], + "type": "inline_equation", + "content": "f_{s}" + }, + { + "bbox": [ + 383, + 186, + 544, + 253 + ], + "type": "text", + "content": ": we report mean error in meters, test set, 600 episodes, as a function of the number of time steps since the object was first seen in the episode (t=0). The error falls immediately and stays low over the episode." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "spans": [ + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "type": "text", + "content": "Reconstruction performance of the Global Reader " + }, + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "type": "text", + "content": " — although the task of reconstructing egocentric maps from occupancy functions " + }, + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "type": "inline_equation", + "content": "f_{o}" + }, + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "type": "text", + "content": " (represented by " + }, + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "type": "inline_equation", + "content": "\\theta_{o}" + }, + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "type": "text", + "content": ") is only used as a proxy task to train the Global reader " + }, + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "type": "text", + "content": ", we see it is a reliable proxy for the quality of extracting the global latent vector " + }, + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "type": "inline_equation", + "content": "\\mathbf{e}" + }, + { + "bbox": [ + 45, + 258, + 286, + 330 + ], + "type": "text", + "content": " fed to the agent." + } + ] + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 50, + 347, + 149, + 370 + ], + "blocks": [ + { + "bbox": [ + 50, + 347, + 149, + 370 + ], + "lines": [ + { + "bbox": [ + 50, + 347, + 149, + 370 + ], + "spans": [ + { + "bbox": [ + 50, + 347, + 149, + 370 + ], + "type": "table", + "html": "
AccuracyJaccard Index
83.456.5
", + "image_path": "d1981c309bff3ed05262d36b04bc4176349ec662d09dc21f16cf9e04bf69fbaf.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 380, + 156, + 414 + ], + "lines": [ + { + "bbox": [ + 47, + 380, + 156, + 414 + ], + "spans": [ + { + "bbox": [ + 47, + 380, + 156, + 414 + ], + "type": "text", + "content": "Table 4. Performance of the global reader " + }, + { + "bbox": [ + 47, + 380, + 156, + 414 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 47, + 380, + 156, + 414 + ], + "type": "text", + "content": " : We report accuracy and Jaccard index." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 174, + 331, + 288, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 174, + 331, + 288, + 426 + ], + "spans": [ + { + "bbox": [ + 174, + 331, + 288, + 426 + ], + "type": "text", + "content": "In Table 4 we report reconstruction performance measured as accuracy and mean Jaccard Index on the validation split of the dataset used to train the reader. We judge that an accuracy of " + }, + { + "bbox": [ + 174, + 331, + 288, + 426 + ], + "type": "inline_equation", + "content": "83.4\\%" + }, + { + "bbox": [ + 174, + 331, + 288, + 426 + ], + "type": "text", + "content": " is surprisingly high, given that" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 426, + 287, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 287, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 287, + 521 + ], + "type": "text", + "content": "the global reader needs to reconstruct the content of the representation directly from its parameters " + }, + { + "bbox": [ + 46, + 426, + 287, + 521 + ], + "type": "inline_equation", + "content": "\\theta_{o}" + }, + { + "bbox": [ + 46, + 426, + 287, + 521 + ], + "type": "text", + "content": ", that each implicit representation has been initialized randomly, and that the reader is required to be invariant w.r.t. to reparameterization (see Section 4). The task is even made harder as neural weights can be considered as an absolute representation of the env. and the reader must combine it with information about the agent pose to reconstruct an egocentric map." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "content": "Capacity of the Semantic Finder — Unlike all other results presented in this paper, this experiment is performed independently of the official MultiON benchmark. We construct a synthetic dataset to evaluate the capacity of the Semantic Finder. More details about the generated data can be found in the supplementary material. As the granularity of the implicit representations is handled through the budget in terms of trainable parameters, we evaluate the capacity of the Semantic Finder " + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "inline_equation", + "content": "f_{s}" + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "content": " to store large numbers of objects in Figure 4: In (a), we can see that increasing the number of objects up to 1000 does not increase error with sufficient gradient updates. However, since inputs are 1-in-K, increasing the number of objects also increases capacity. In (c), we see that this does not hold for random objects (not 1-in-K), whose less structured storage requires more capacity. In (b), we keep the input dimension fixed for random objects, which" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 258, + 399, + 270 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 258, + 399, + 270 + ], + "spans": [ + { + "bbox": [ + 306, + 258, + 399, + 270 + ], + "type": "text", + "content": "further increases error." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 273, + 547, + 393 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 273, + 547, + 393 + ], + "spans": [ + { + "bbox": [ + 304, + 273, + 547, + 393 + ], + "type": "text", + "content": "Evaluating catastrophic forgetting — we evaluate the capacity of the Semantic Finder " + }, + { + "bbox": [ + 304, + 273, + 547, + 393 + ], + "type": "inline_equation", + "content": "f_{s}" + }, + { + "bbox": [ + 304, + 273, + 547, + 393 + ], + "type": "text", + "content": " to hold the learned information over the full length of the sequence in spite of the fact that it is continuously trained. Figure 5 shows the evolution of the mean error in distance for the predicted position of queried target objects as a function of time. The error quickly goes below " + }, + { + "bbox": [ + 304, + 273, + 547, + 393 + ], + "type": "inline_equation", + "content": "1.5m" + }, + { + "bbox": [ + 304, + 273, + 547, + 393 + ], + "type": "text", + "content": " once the object has been seen the first time (" + }, + { + "bbox": [ + 304, + 273, + 547, + 393 + ], + "type": "inline_equation", + "content": "t = 0" + }, + { + "bbox": [ + 304, + 273, + 547, + 393 + ], + "type": "text", + "content": " in the plot), which is distance threshold required by the MultiON task, and stays there, providing evidence that the model does not suffer from catastrophic forgetting." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 396, + 547, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 396, + 547, + 491 + ], + "spans": [ + { + "bbox": [ + 304, + 396, + 547, + 491 + ], + "type": "text", + "content": "Runtime performance — inspite of requiring to continuously train the representations, we achieve 45 fps during parallelized RL training, including the environment steps (simulator rendering), forward passes, representation training and RL training on a single V100 GPU. The average time of one agent forward pass, including updates of implicit representations is 20ms on a V100 GPU, which is equivalent to 50 fps, enough for real-time performance." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 510, + 378, + 522 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 510, + 378, + 522 + ], + "spans": [ + { + "bbox": [ + 306, + 510, + 378, + 522 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 533, + 547, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 533, + 547, + 688 + ], + "spans": [ + { + "bbox": [ + 304, + 533, + 547, + 688 + ], + "type": "text", + "content": "We introduce two implicit representations to map semantic, occupancy and exploration information. The first estimates the position of an object of interest from a vector query, while the second encapsulates information about occupancy and explored area in the current environment. We also introduce a global read directly from the trainable weights of this representation. Our experiments show that both implicit representations have a positive impact on the navigation performance of the agent. We also studied the scaling laws of the semantic representation and its behavior in the targeted lifelong learning problem. Future work will target differentiating through the implicit representations all the way back to the perception modules." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 690, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 690, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 690, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgement - We thank ANR for support through AI-chair grant \"Remember\" (ANR-20-CHIA-0018)." + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "11012" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 289, + 715 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 289, + 145 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 289, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 289, + 145 + ], + "type": "text", + "content": "[1] Michal Adamkiewicz, Timothy Chen, Adam Caccavale, Rachel Gardner, Preston Culbertson, Jeannette Bohg, and Mac Schwager. 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In this paper, we propose a novel multi-scale bidirectional recurrent architecture that iteratively optimizes the coarse-to-fine scene flow estimation. In each resolution scale of estimation, a novel bidirectional gated recurrent unit is proposed to bidirectionally and iteratively augment point features and produce progressively optimized scene flow. The optimization of each iteration is integrated with the hybrid correlation that captures not only local correlation but also semantic correlation for more accurate estimation. Experimental results indicate that our proposed architecture significantly outperforms the existing state-of-the-art approaches on both FlyingThings3D and KITTI benchmarks while maintaining superior time efficiency. Codes and pre-trained models are publicly available at https://github.com/cwc1260/MSBRN.", + "bbox": [ + 75, + 340, + 473, + 613 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 646, + 209, + 662 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Scene flow estimation is a fundamental task that estimates the dense 3D motion field of points from two consecutive frames [32, 19]. As it provides the basic motion understanding of a dynamic environment, it is meaningful in a variety of high-level applications such as autonomous driving, augmented reality, and robotics [15].", + "bbox": [ + 75, + 672, + 468, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Early scene flow estimation approaches rely on 2D representations such as RGB images [14, 11, 13, 28, 12]. They basically estimate optical flow and disparity map separately in the 2D space instead of directly estimating scene flow vectors in the 3D space. Recently, with the advances in LiDAR sensors and point cloud-based learning technologies, learning scene flow directly from point clouds has been extensively studied. The pioneering work known as FlowNet3D [19] is the first to introduce hierarchical Point-", + "bbox": [ + 75, + 763, + 470, + 901 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/820978a1b7801a6eeb9540813f9ba603965a8cfe472872e245fae135ff5f4c87.jpg", + "image_caption": [ + "Figure 1. Illustration of the multi-scale bidirectional recurrent network for scene flow estimation. The multi-scale features extracted from each input frame are fed into novel bidirectional gated recurrent units (BGRUs) that respectively iterates $K$ times for optimizing scene flows on each scale. Introducing hybrid correlation (HC) further improves the performance by searching correspondence in both the Euclidean and latent feature space. The estimated scene flows are warped with the source frame for a clear comparison with the target frame." + ], + "image_footnote": [], + "bbox": [ + 521, + 309, + 879, + 448 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$\\mathrm{Net}++$ [26] to directly predict the 3D scene flow based on the point cloud. Following this work, a diverse variety of architectures [33, 36, 9, 32, 15] have been proposed and significantly enhanced performance.", + "bbox": [ + 498, + 609, + 893, + 672 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recently, there is a rising trend of iteratively optimizing estimated scene flow by utilizing the recurrent scheme [15, 9, 31] to progressively improve the estimation accuracy. However, they only focus on optimizing single resolution scale which causes large computation latency. On the other hand, another series of works [28, 4] presented their superior efficiency by estimating multi-scale scene flow in a coarse-to-fine manner. However, their single-shot estimation on each scale restricts their performance. To achieve high estimation accuracy while holding high efficiency, we propose an effective and efficient architecture, Multi-Scale Bidirectional Recurrent Network (MSBRN), that iteratively optimizes coarse-to-fine scene flow. Moreover, in our view, the optimization phases of scene flow can be regarded as temporal sequences, which can benefit from the bidirectional", + "bbox": [ + 496, + 674, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "10041", + "bbox": [ + 480, + 944, + 517, + 957 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/98f0da9118b1948bde152eedbbef2668155b5a6b2b9b3efcb8c9a5ab0393b79b.jpg", + "image_caption": [ + "Figure 2. Examples of two variants of correlation extraction. The bold red and green points are the grouped correlated points of the bold blue source point through the feature-induced correlation and Euclidean distance-based correlation, respectively." + ], + "image_footnote": [], + "bbox": [ + 78, + 89, + 465, + 212 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tional recurrent architecture [27, 8, 5, 16]. In each specific resolution scale, thus, we apply a novel bidirectional gated recurrent unit (BGRU) to bidirectionally and iteratively augment point features and produce progressively optimized scene flow.", + "bbox": [ + 75, + 305, + 467, + 380 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Moreover, we also noticed a common limitation of current point cloud-based flow estimation approaches. They aggregate the grouped neighboring points in the Euclidean space when generating the correspondence features between two point frames. The correspondence grouping used in these methods generally exploits $k$ -nearest-neighbor (kNN) that only focuses on a specific local region. Thus, these methods may be harmed by nearby non-correlated points in Euclidean space, as shown in Figure 2. To resolve these issues, we first proposed a feature-induced correlation that collects the nearest neighbor points in the latent feature space. Thus, the grouped points from the feature space are semantically related regardless of their distances in Euclidean space. Afterwards, we combined the proposed correlation with the conventional Euclidean distance-based correlation forming the hybrid correlation. Therefore, the network is able to capture distance-insensitive correspondences as well as local correlations.", + "bbox": [ + 75, + 383, + 467, + 654 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We evaluated MSBRN on two challenging benchmarks, the synthetic dataset FlyingThings3D [22] and the real-world LiDAR scan dataset KITTI [23], under both occluded and non-occluded settings. Following the evaluation settings of previous studies, the proposed model is trained only on the FlyingThings3D dataset and evaluated on both datasets to confirm the accuracy and generalization performance. The experimental results show that MSBRN outperforms all other approaches on the FlyingThings3D dataset with $46\\%$ and $27\\%$ lower errors under the occluded and non-occluded conditions, respectively. Moreover, MSBRN achieves improved generality on the real-world KITTI dataset with $66\\%$ and $32\\%$ lower errors under the occluded and non-occluded conditions, respectively. Our MSBRN also shows better time efficiency while maintaining higher accuracy compared to other iterative state-of-the-arts.", + "bbox": [ + 75, + 659, + 467, + 898 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The key contributions of this paper are summarized as follows:", + "bbox": [ + 500, + 90, + 890, + 119 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a novel multi-scale bidirectional recurrent architecture used for a 3D scene flow estimation task based on point cloud. The model can iteratively and bidirectionally enhance features and scene flow estimations in a coarse-to-fine manner in order to significantly improve the performance while maintaining high efficiency.", + "- We propose a hybrid correspondence grouping that collects corresponding points from the other point frame in both the latent feature space and Euclidean space.", + "- The proposed model achieves state-of-the-art performance and generality on the synthetic FlyingThings3D and real-world KITTI benchmarks under both occluded and non-occluded conditions." + ], + "bbox": [ + 517, + 132, + 890, + 378 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 395, + 640, + 410 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Scene Flow Estimation on Point Clouds", + "text_level": 1, + "bbox": [ + 500, + 420, + 836, + 434 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The first study in solving flow estimation on raw point clouds with learning-based methods was FlowNet3D [19]. FlowNet3D exploited hierarchical PointNet++ [26] and a local correlation learning layer to estimate the scene flow from two raw point cloud frames. Following this scheme, FlowNet3D++ [33] and HCRF-Flow [18] were proposed to further refine the final estimation by introducing auxiliary geometric constraints and high-order CRFs, respectively. However, the performance of these FlowNet3D-based models was restricted by the single-scale flow correlation. To address this flaw, HPLFlownet [10] was proposed in order to capture multi-scale correlations. PointPWC-Net [36] further suggested a coarse-to-fine architecture to regress multi-scale scene flow by applying local correlation extraction hierarchically. Based on the coarse-to-fine design, OGSFNet [24] additionally estimated occlusion masks with an occlusion-aware correlation layer. Furthermore, Bi-PointFlowNet [4] introduced a bidirectional mechanism to bidirectionally propagate point features for informative correlation extraction.", + "bbox": [ + 496, + 443, + 890, + 743 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Nevertheless, the above-mentioned approaches all rely on the local correlation, which has a limit on estimation accuracy when corresponding points are out of the local region. However, the hybrid correlation proposed in this work can alleviate this limitation by considering both local correlation and semantic correlation.", + "bbox": [ + 496, + 744, + 890, + 835 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Recurrent Models for Flow Estimation", + "text_level": 1, + "bbox": [ + 500, + 845, + 831, + 861 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Many recent studies have demonstrated a reasonable performance by employing a recurrent architecture to itera-", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "10042", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/4af0d04d3e60bec9789e420426df78fd6d0ab5047520a645e732ecf911f33906.jpg", + "image_caption": [ + "Figure 3. Architecture of MSBRN for scene flow estimation. First, the two consecutive input point frames are fed into the shared hierarchical feature extraction module for multi-level features. At each level, a novel BGRU bidirectionally augments point features and iteratively optimizes correlations and flow predictions. The upsampling layers are adopted between adjacent levels for propagating features and flows from high levels to low levels. The figure is best viewed in color." + ], + "image_footnote": [], + "bbox": [ + 81, + 94, + 895, + 250 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "tively refine the estimations [13, 21, 30, 31, 34, 15]. Inspired by the previous iterative refinement models [14, 28, 11, 9, 6], IRR [13] reused its whole architecture as a recurrent unit to iteratively optimize the optical flow. Lv et. al. proposed a approach that iterates a learning-based Inverse Compositional algorithm to optimize dense 3D rigid motion. To further improve the efficiency and convergence, RAFT [30] developed a 4D all-to-all correlation volume with the use of a gated recurrent unit (GRU). Based on RAFT, RAFT-3D [31] promoted the recurrent scheme into scene flow estimation by iteratively estimating a dense field of per-pixel SE(3) motion. Afterward, PV-RAFT [34] was proposed to iteratively capture the point-voxel correlation for scene flow estimation from the point cloud inputs. Different from the RAFT-series methods, FlowStep3D [15] and RCP [9] iteratively optimized the correlation that gradually aligns point clouds based on the iterative closest point (ICP) algorithm [3, 1]. FlowStep3D [15] deployed a gated recurrent unit and the source frame warping for iterative updates correlation at a single dense resolution. Similarly, RCP [9] performed iterative point-wise optimization and subsequently introduced the GRU for regularization. Dong et al. [6] introduced direct multi-body rigidity constraints to a GRU-based recurrent neural network for robust iterative optimization of scene flow estimation. There are several other approaches [25, 17] that treated scene flow estimation as solving an optimal transport problem. They typically required point-wise features to iteratively optimize the all-to-all correlation.", + "bbox": [ + 76, + 335, + 472, + 773 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Nevertheless, the existing iterative methods proceed with the optimization only at a single resolution. To achieve acceptable accuracy, they typically optimize dense resolution, which severely restricts the estimation efficiency. Therefore, we introduce a multi-scale iterative optimization to achieve high accuracy while maintaining high efficiency.", + "bbox": [ + 75, + 810, + 468, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. MSBRN Architecture", + "text_level": 1, + "bbox": [ + 498, + 335, + 705, + 349 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The goal of the scene flow estimation task is to estimate 3D point-wise motion vectors representing the non-rigid transformation from two consecutive point frames sampled from a dynamic scene. To solve this task, we propose MSBRN, a coarse-to-fine bidirectional recurrent architecture with the feature-induced correlation, as shown in Figure 3. MSBRN accepts as input the consecutive source and target frames that are represented by only 3D coordinates, $S = \\{s_i \\in \\mathbb{R}^3\\}_{i=1}^N$ and $T = \\{t_j \\in \\mathbb{R}^3\\}_{j=1}^M$ , where $N$ and $M$ denote the number of points in the source and target frame, respectively. Note that, $N$ and $M$ are not necessarily to be equal because of the sparsity and occlusion in a point cloud. The expected output of MSBRN are 3D scene flow vectors $V = \\{v_i \\in \\mathbb{R}^3\\}_{i=1}^N$ that describe the 3D displacement for every point in the source frame aligning with the target frame.", + "bbox": [ + 496, + 362, + 890, + 603 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Similar to the previous studies [36, 4], MSBRN is implemented as a coarse-to-fine architecture (Sec. 3.3) with the assistance of two existing modules: a multi-scale feature extraction module that extracts multi-scale point features and an upsampling layer that propagates features from higher scales to lower scales. At each upsampled scale, we deploy a novel BGRU (Sec. 3.1) to iteratively augment correlations and optimize scene flows. BGRU also applies a novel hybrid correlation (Sec. 3.2) in order to enhance the quality of the captured correlations.", + "bbox": [ + 496, + 604, + 892, + 755 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Bidirectional Gated Recurrent Unit", + "text_level": 1, + "bbox": [ + 500, + 770, + 808, + 784 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We propose a novel BGRU that not only optimizes correlations but also augments point features of both frames bidirectionally and iteratively in various scales, as shown in Figure 4. In contrast, the previous methods [15, 9] that only apply conventional recurrent units to iteratively optimize only correlations for flow estimation in only one single scale. For each specific scale $l$ , the BGRU accepts source", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "10043", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/d319ee33d0987d0f1b98f95fa61c49617eeec2197fa0080c97b41c081e4c3bea.jpg", + "image_caption": [ + "Figure 4. Structure of the bidirectional gated recurrent unit (BGRU). The proposed BGRU accepts source/target point features, flow estimations and correlations from the previous scale as input and hidden states. The source/target point features are first bidirectionally updated and fed to the proposed hybrid correlation for the candidate correlation generation. Subsequent GRU utilizes the candidate correlations for iteratively updating the correlation states." + ], + "image_footnote": [], + "bbox": [ + 86, + 87, + 893, + 309 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "point coordinates and features $S^{l,0} = \\{(s^l,f^{(l,0)})\\}$ , target point coordinates and features $T^{l,0} = \\{(t^l,g^{(l,0)})\\}$ , correlations $E^{l,0}$ and flow $V^{l,0}$ as input as well as hidden state variables that will be iteratively updated. After $K$ iterations, updated $P^{l,K}, Q^{l,K}, E^{l,K}$ and $V^{l,K}$ are sent to the subsequent scale. In this section, we focus on one specific scale and omit the notation $l$ for clarity.", + "bbox": [ + 75, + 396, + 468, + 503 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Warping: Warping enables the source points to progressively approach the target frame. The estimated scene flows of upsampling layers (for the first iteration only) or previous iterations are immediately accumulated to the source frame, i.e. $s = v^{k - 1} + s$ . The warped source points are further fed to the subsequent feature augmentation for more accurate correlation extraction.", + "bbox": [ + 75, + 505, + 468, + 609 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Iterative Bidirectional Feature Augmentation (IBFA): IBFA accepts as input two frames of point coordinates and corresponding features from the previous $(k - 1)$ -th iteration, $S^{k - 1} = \\{(s,f^{k - 1})\\}$ and $T^{k - 1} = \\{(t,g^{k - 1})\\}$ . For each point in both frames, the features are augmented bidirectionally for the current $k$ -th iteration by aggregating features from the other frame as follows:", + "bbox": [ + 75, + 609, + 468, + 715 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nf ^ {k} = \\underset {\\left(t _ {i}, g _ {i} ^ {k - 1}\\right) \\in \\mathcal {N} _ {T} ^ {k - 1} \\left\\{\\left(s, f ^ {k - 1}\\right) \\right\\}} {\\operatorname {S e t C o n v}} \\left(\\left[ t _ {i} - s, g _ {i} ^ {k - 1}, f ^ {k - 1} \\right]\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 726, + 468, + 757 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ng ^ {k} = \\underset {\\left(s _ {j}, f _ {j} ^ {k - 1}\\right) \\in \\mathcal {N} _ {S} ^ {k - 1} \\{(t, g ^ {k - 1}) \\}} {\\operatorname {S e t C o n v}} \\left(\\left[ s _ {j} - t, f _ {j} ^ {k - 1}, g ^ {k - 1} \\right]\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 782, + 468, + 813 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where SetConv [19] is composed of a shared multi-layer perceptron and a maxpooling layer, $\\mathcal{N}_T\\{(s,\\cdot)\\}$ denotes the nearest neighbor points of $s$ in $T$ , subscript $i,j$ indicate the indices of points in the neighbor group $\\mathcal{N}$ , and $[\\cdot ,\\cdot ]$ denotes the channel concatenation operator. Note that, the", + "bbox": [ + 75, + 824, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "SetConv in Equation (1) and (2) share the equivalent parameters. The output are buffered as hidden states for the subsequent iteration or scale.", + "bbox": [ + 496, + 398, + 890, + 443 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Iterative Correlation Update: The bidirectionally-augmented features are fed to the hybrid correlation extraction module (Sec. 3.2) to generate candidate correlation features. The candidate correlations serve as the input to a GRU in order to update the state correlation features from the previous iteration. Formally, the correlation features updated by the current iteration is denoted as:", + "bbox": [ + 496, + 443, + 892, + 547 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nz = \\sigma \\left(\\underset {\\left(s _ {i}, \\tilde {e} _ {i} ^ {k}\\right) \\in \\mathcal {N} _ {\\tilde {S}} ^ {k - 1} \\{(s, e ^ {k - 1}) \\}} {\\operatorname {S e t C o n v} _ {z}} \\left([ s _ {i} - s, e ^ {k - 1}, \\tilde {e} _ {i} ^ {k} ]\\right)\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 519, + 556, + 890, + 589 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nr _ {i} = \\sigma (M L P _ {r} ([ s _ {i} - s, e ^ {k - 1}, \\widetilde {e} _ {i} ^ {k} ])), \\qquad (4)\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 603, + 890, + 622 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {e} ^ {k} = \\tanh \\left(\\underset {\\left(s _ {i}, \\tilde {e} _ {i} ^ {k}\\right) \\in \\mathcal {N} _ {\\tilde {S}} ^ {k - 1} \\left\\{\\left(s, e ^ {k - 1}\\right) \\right\\}} {\\operatorname {S e t C o n v} _ {h}} \\left(\\left[ s _ {i} - s, e ^ {k - 1} \\odot r _ {i}, \\tilde {e} _ {i} ^ {k}\\right)\\right), \\right. \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 500, + 650, + 890, + 695 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ne ^ {k} = (1 - z) \\odot e ^ {k - 1} + z \\odot \\hat {e} ^ {k}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 589, + 709, + 890, + 727 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\odot$ denotes the Hadamard product.", + "bbox": [ + 500, + 732, + 769, + 747 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Scene Flow Estimation: Given the updated correlation feature of each point, an MLP is followed to transform the correlation into a flow vector. Additionally, we introduce a residual mechanism by estimating the flow vector refinement $\\Delta V_{k}$ . The final flow estimation is then accumulated as $V^{k} = V^{k - 1} + \\Delta V^{k}$ .", + "bbox": [ + 496, + 747, + 890, + 837 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Hybrid Correlation", + "text_level": 1, + "bbox": [ + 500, + 847, + 687, + 863 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Feature-induced Correlation: Instead of capturing neighbor points in the conventional Euclidean space, we fetch", + "bbox": [ + 496, + 869, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "10044", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "neighbor points from the latent feature space in order to acquire semantically correlative points. For instance, Figure 2 shows that the proposed correlation can capture semantically similar points (front windscreen) even if they are far away. Thus, the proposed correlation is different from the Euclidean-based correlation that may capture semantically unrelated points (bumper). Formally, given two point sets consisted of 3-dimensional coordinates and $C$ -dimensional features $S = \\{(s,f)|s\\in \\mathbb{R}^3,f\\in \\mathbb{R}^C\\}$ and $T = \\{(t,g)|t\\in \\mathbb{R}^3,g\\in \\mathbb{R}^C\\}$ , for each point $(s,f)\\in S$ , its collected neighbor points $\\mathcal{N}_T\\{(s,f)\\}$ from $T$ satisfy $\\delta (f,g_i) < \\delta (f,g_j)$ , when $\\forall (t_i,g_i)\\subset \\mathcal{N}_T\\{(s,f)\\}$ and $(t_j,g_j)\\subset Q\\backslash \\mathcal{N}_T\\{(p,f)\\}$ . Note that, $|\\mathcal{N}_T\\{(s,f)\\}| = K$ is the hyperparameter that defines the amount of the top-K neighbor points, and $\\delta (\\cdot ,\\cdot)$ is the cosine similarity measure.", + "bbox": [ + 75, + 90, + 472, + 316 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "After the corresponding points are collected, the features of the collected points are further aggregated by a learnable symmetric function. Hence, the correlation feature for each point $(p,f)\\in P$ is formally denoted as:", + "bbox": [ + 75, + 318, + 470, + 378 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\widetilde {e} = \\underset {\\left(t _ {i}, g _ {i}\\right) \\in \\mathcal {N} _ {T} \\left\\{\\left(s, f\\right) \\right\\}} {\\operatorname {S e t C o n v}} \\left(\\left[ t _ {i} - s, g _ {i}, f \\right]\\right). \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 148, + 390, + 468, + 416 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Hybrid Correlation: Considering that the conventional grouping can capture fine-grained local motion and the proposed feature-induced grouping can capture correspondence regardless of distances, we integrate the two techniques to take advantage of both correlation extraction strategies. Thus, we fuse the collected points with the feature-induced grouping and conventional grouping as a hybrid neighbor set $\\mathcal{N}_T\\{(s,f)\\}$ in Equation (7) for the subsequent correlation aggregation.", + "bbox": [ + 75, + 426, + 472, + 565 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Coarse-to-Fine Architecture", + "text_level": 1, + "bbox": [ + 76, + 574, + 331, + 589 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we thus introduce two existing layers [36] to construct a coarse-to-fine network for multi-scale feature generation and propagation.", + "bbox": [ + 75, + 597, + 468, + 643 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Multi-scale Feature Extraction: The multi-scale feature extraction follows the design that is commonly used in point cloud processing [26, 35]. The feature extraction generates $L$ -level pyramid of point features, where the top level is the input point clouds. At each level $l$ , dense input points and their corresponding features are first subsampled through the furthest point sampling, which forms a sparse point set. Then, for each subsampled sparse point, the $k$ -nearest neighbor groups dense points locally forming a local region for the feature extraction. Afterwards, a Pointconv [35] layer is applied to aggregate the features from the grouped local points through dynamic weights learned on their local coordinates, and produced the local feature for each sparse point.", + "bbox": [ + 75, + 643, + 472, + 853 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Upsampling Layer: Since each level produces scene flows and iteratively augmented bidirectional features and correlations, we introduced the upsampling layer to propagate", + "bbox": [ + 75, + 854, + 472, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "these features to the following level for a denser optimization. Following the previous works [36, 4], the upsampling layer adopts the 3D interpolation that aggregates $k$ nearest neighbors with their inverse distances as weights. Specifically, in the case of upsampling correlations from the $l$ -th level to the $(l - 1)$ -th level, the input to the upsampling layer are $l$ -th level's sparse coordinates $\\{x_j^l\\}_{j = 1}^{N^l}$ , $l$ -th level's correlations $\\{e_j^l\\}_{j = 1}^{N^l}$ and $(l - 1)$ -th level's dense coordinates $\\{x_i^{l - 1}\\}_{i = 1}^{N^{l - 1}}$ , where $N^{l - 1}$ and $N^l$ are the number of points and $N^{l - 1} > N^l$ . The interpolated feature for each point $x_{i}^{l}$ in the dense $(l - 1)$ -th level is defined as:", + "bbox": [ + 496, + 90, + 893, + 268 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\ne _ {i} ^ {l - 1} = \\frac {\\sum_ {j = 1} ^ {k} w \\left(x _ {j} ^ {l} , x _ {i} ^ {l - 1}\\right) e _ {j} ^ {l}}{\\sum_ {j = 1} ^ {k} w \\left(x _ {j} ^ {l} , x _ {i} ^ {l - 1}\\right)}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 593, + 277, + 890, + 321 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $w(x_{j}^{l},x_{i}^{l - 1}) = 1 / ||x_{j}^{l} - x_{i}^{l - 1}||_{2}$ , and $k = 3$ as suggested by the previous studies [4, 36].", + "bbox": [ + 496, + 323, + 893, + 356 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Loss Function", + "text_level": 1, + "bbox": [ + 498, + 363, + 645, + 378 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Following the previous studies for optical flow estimation [7, 29] and scene flow estimation [32, 36, 4], we train the proposed model in the multi-scale supervision manner. Furthermore, we also supervise the estimations of all intermediate iterations at each scale. All the estimated flows are supervised by the ground truth with the L2 measure. Let $\\{v_i^{l,k}\\}_{i=1}^N$ denote the scene flow vectors estimated from the $k$ -th iteration at the $l$ -th level and $\\{\\hat{v}_i^l\\}_{i=1}^N$ denote the ground truth scene flow vectors of the $l$ -th scale. The training loss is defined as:", + "bbox": [ + 496, + 386, + 893, + 541 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\sum_ {l = 0} ^ {L - 1} \\alpha^ {l} \\sum_ {k = 1} ^ {K} \\sum_ {i = 1} ^ {N ^ {l}} \\| \\hat {v} _ {i} ^ {l} - v _ {i} ^ {l, k} \\| _ {2}, \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 583, + 547, + 890, + 590 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\alpha^l$ is the weight for scale $l$ . The weights are $\\alpha^0 = 0.16, \\alpha^1 = 0.08, \\alpha^2 = 0.04, \\alpha^3 = 0.02$ by default.", + "bbox": [ + 496, + 598, + 893, + 630 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 498, + 641, + 633, + 657 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental Settings", + "text_level": 1, + "bbox": [ + 498, + 665, + 707, + 681 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As shown in Fig. 3, we implemented a hierarchical model with $L = 4$ scales. We used $N = M = 8$ , 192 points as inputs. The point numbers of each scale are defined as $N^1 = 2$ , 048, $N^2 = 512$ , $N^3 = 256$ , and $N^4 = 64$ . We adopted the synthetic FlyingThings3D [22] dataset and the real-world KITTI Scene Flow 2015 [23] dataset to evaluate our model. As in the previous methods, we trained networks only on the synthetic FlyingThings3D dataset and validated the performance on the FlyingThings3D dataset (Sec. 4.3). Finally, we directly evaluated the model trained on FlyingThings3D without any fine-tuning to validate the generalization ability on the real-world KITTI dataset (Sec. 4.4). The experiments are conducted on an NVIDIA Titan RTX GPU with PyTorch.", + "bbox": [ + 496, + 688, + 893, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "10045", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/37702c74032a6605c68594c260219ae15630c3e56520208ce808d9f650cc2385.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DatasetMethodEPE3D (m) ↓ACC3DS ↑ACC3DR ↑Outliers3D ↓EPE2D (px) ↓ACC2D ↑
FT3DsFlowNet3D [19]0.1130.4120.7710.6025.9740.569
HPLFlowNet [10]0.0800.6140.8550.4294.6720.676
PointPWC [36]0.0590.7380.9280.3423.2390.799
FLOT [25]0.0520.7320.9270.357--
HCRF-Flow [18]0.0480.8350.9500.2612.5650.870
PV-RAFT [34]0.0460.8160.9570.292--
FlowStep3D [15]0.0450.8160.9610.216--
RCP [9]0.0400.8560.9630.197--
Bi-PointFlowNet [4]0.0280.9180.9780.1431.5820.929
Ours0.0150.9730.9920.0560.8330.970
KITTsFlowNet3D [19]0.1770.3740.6680.5277.2140.509
HPLFlowNet [10]0.1170.4780.7780.4104.8050.593
PointPWC [36]0.0690.7280.8880.2651.9020.866
FLOT [25]0.0560.7550.9080.242--
HCRF-Flow [18]0.0530.8630.9440.1792.0700.865
PV-RAFT [34]0.0560.8220.9370.216--
FlowStep3D [15]0.0540.8050.9250.149--
RCP [9]0.0480.8490.9440.122--
Bi-PointFlowNet [4]0.0300.9200.9600.1411.0560.949
Ours0.0110.9710.9890.0850.4430.985
", + "bbox": [ + 102, + 88, + 870, + 393 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. Comparison of the proposed method with previous state-of-the-art methods on the non-occluded FT3D ${}_{s}$ and KITTI ${}_{s}$ datasets. All methods are trained only on the FT3D ${}_{s}$ dataset.", + "bbox": [ + 75, + 402, + 893, + 433 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Evaluation Measures", + "text_level": 1, + "bbox": [ + 76, + 455, + 277, + 470 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For a fair comparison, we adopted the same evaluation measures that are used in the related works [10, 36, 25, 15, 18, 4].", + "bbox": [ + 76, + 479, + 468, + 525 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "EPE3D, EPE3Dfull (m): the main evaluation measure measuring 3D end-point-error $\\| \\hat{v}_i^l - v_i^l\\|_2$ averaged over non-occluded points and all points, respectively.", + "bbox": [ + 76, + 526, + 468, + 571 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "ACC3DS: the percentage of points that satisfy EPE3D $< 0.05\\mathrm{m}$ or relative error $< 5\\%$ .", + "bbox": [ + 76, + 571, + 468, + 601 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "ACC3DR: the percentage of points that satisfy EPE3D $< 0.1\\mathrm{m}$ or relative error $< 10\\%$ .", + "bbox": [ + 76, + 603, + 468, + 633 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Outliers3D: the percentage of points that satisfy EPE3D $>0.3\\mathrm{m}$ or relative error $>10\\%$ .", + "bbox": [ + 76, + 635, + 468, + 664 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "EPE2D (px): 2D end-point-error measured by projecting points back to the 2D image plane, which is a common measure for optical flow evaluation.", + "bbox": [ + 76, + 666, + 468, + 710 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "ACC2D: the percentage of points that satisfy EPE2D $< 3\\mathrm{px}$ or relative error $< 5\\%$ .", + "bbox": [ + 76, + 712, + 468, + 742 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Training and Evaluation on FlyingThings3D", + "text_level": 1, + "bbox": [ + 76, + 753, + 454, + 772 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Due to the challenge with labeling for dense point cloud scenes, recent models [10, 36, 25, 15, 18, 4] only utilized the synthetic FlyingThing3D dataset for training. The FlyingThing3D [22] dataset provides 19,640 pairs of frames for training and 3,824 pairs of frames for testing. Each frame contains synthetic stereo and RGB-D images rendered from virtual scenes with multiple moving objects sampled from the ShapeNet [2] dataset. We follow the same preprocessing", + "bbox": [ + 75, + 779, + 470, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "that generates two subsets: $\\mathrm{FT3D}_o$ that includes occluded points and $\\mathrm{FT3D}_s$ that excludes the occluded points, as suggested in [10, 36, 25, 4]. The consecutive input frames are formed by randomly sampling $N = 8$ , 192 of points from the dataset with non-correspondence.", + "bbox": [ + 496, + 455, + 890, + 531 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For training, we used the AdamW optimizer [20] with beta1 = 0.9, beta2 = 0.999. The learning rate is initially set as $\\alpha = 0.0001$ and reduced by half every 80 epochs. We trained the model for a total of 560 epochs. The numbers of iterations for all BGRUs are set to $K_{tr} = 4$ during training and $K_{in} = 4$ during testing.", + "bbox": [ + 496, + 532, + 890, + 623 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Results. We compared the performance of the proposed model with other state-of-the-art approaches based on point cloud [19, 10, 36, 25, 15, 24, 9, 4]. As presented in Table 1, the proposed method significantly outperforms all recent state-of-the-art methods with more than $46\\%$ reduction of estimation error under the non-occluded condition. When compared to the related iterative methods FlowStep3D [15] and RCP [9], our model achieves an error reduction of $62\\%$ .", + "bbox": [ + 496, + 623, + 890, + 744 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Generalization on KITTI", + "text_level": 1, + "bbox": [ + 498, + 755, + 732, + 770 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Following the same evaluation strategy as in the recent studies [19, 10, 36, 25, 15, 24, 4], we evaluated the generalization ability of MSBRN on the real-world KITTI [23] dataset with the model that was only trained on the synthetic dataset. The KITTI dataset provides 200 scenes for training and 200 scenes for testing. However, the disparities were missing in the testing scene and parts of the training scenes. Thus, 142 non-occluded scenes (KITTI $_s$ , re", + "bbox": [ + 496, + 779, + 890, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "10046", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/0c05347bf3441d8ae389ecefedf538612881cde64cb12eb05c83f9d8ebd198f9.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DatasetMethodEPE3Dfull (m) ↓EPE3D (m) ↓ACC3DS ↑ACC3DR ↑Outliers3D ↓
FT3DoFlowNet3D [19]0.2110.1570.2280.5820.804
HPLFlowNet [10]0.2010.1680.2620.5740.812
FLOT [25]0.2500.1530.3960.6600.662
PointPWC [36]0.1950.1550.4160.6990.638
OGSFNet [24]0.1630.1210.5510.7760.518
Bi-PointFlowNet [4]0.1020.0730.7910.8960.274
Ours0.0800.0530.8360.9260.231
KITTIoFlowNet3D [19]0.183-0.0980.3940.799
HPLFlowNet [10]0.343-0.1030.3860.814
FLOT [25]0.130-0.2780.6670.529
PointPWC [36]0.118-0.4030.7570.496
OGSFNet [24]0.075-0.7060.8690.327
Bi-PointFlowNet [4]0.065-0.7690.9060.264
Ours0.044-0.8730.9500.208
", + "bbox": [ + 133, + 89, + 838, + 310 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2. Comparison of the proposed method with previous state-of-the-art methods on the occluded FT3DO and KITTIO datasets. All methods are trained only on the FT3DO dataset.", + "bbox": [ + 75, + 320, + 892, + 349 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/fff2732f2eabc30e696b353368435ff79df34285d8218c14033e602128e60a0e.jpg", + "image_caption": [ + "Figure 5. Qualitative results of MSBRN on the non-occluded KITTI dataset. Points are colored to indicate points as from source frame, target frame or as MSBRN estimated points (source frame + scene flow)." + ], + "image_footnote": [], + "bbox": [ + 89, + 359, + 888, + 583 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "moving occluded points) and 150 occluded scenes (KITTI $_o$ , remaining occluded points) were available for evaluation with raw point clouds. We removed ground points by height $< 0.3$ m as suggested by the previous approaches [19, 10, 36, 25, 15, 24] for a fair comparison.", + "bbox": [ + 75, + 641, + 468, + 717 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results. We compared the generalization ability of MSBRN with the existing state-of-the-art methods based on point cloud [19, 10, 36, 25, 15, 24, 9, 4]. As shown in Table 1 and 2, our proposed method represented the state-of-the-art generality when the model is trained on the synthetic datasets and tested on and real-world KITTI dataset. Our method significantly outperforms other methods by a large margin. Focusing on the main EPE3D measure, our method outperforms the recent state-of-the-art with $63\\%$ of error reduction on the non-occluded scenes. Compared to the similar iterative methods FlowStep3D [15] and RCP [9], our method shows over $77\\%$ of error reduction. Moreover, our", + "bbox": [ + 75, + 719, + 472, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "model shows the superior generality on the occluded scenes, as shown in Table 2. Our model shows an over $32\\%$ reduction of $\\mathrm{EPE3D_{full}}$ .", + "bbox": [ + 496, + 641, + 890, + 688 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 696, + 653, + 712 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Number of Iterations. The iteration number of the BGRU is a significant factor that affects the estimation accuracy. It is worth noting that the iteration configuration can be different between the training stage $(K_{tr})$ and the evaluation stage $(K_{in})$ . Therefore, we trained and evaluated our method with the different iteration numbers. Note that, all levels proceed with the same iteration number as configured. Table 3 reports the performance comparison between models with the different numbers of BGRU iterations. The result shows that iteratively adopting the proposed BGRU effectively reduces the estimation error on both the synthetic dataset and the real-world dataset. The model delivers", + "bbox": [ + 496, + 719, + 893, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "10047", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/23d81f3297cf692f2c88e29da83c26d1ca6bb79f67363d7bfd585adc096af737.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
\\(K_{tr}\\)EPE3D (m) @ \\(K_{in}\\)
123456
FT3\\(d_s\\)10.0260.0710.1010.1490.2040.281
20.0330.0210.0300.0370.0460.049
30.0380.0200.0160.0160.0160.018
40.0400.0240.0170.0150.0150.015
50.0490.0270.0190.0150.0140.014
KITTLs10.0380.1290.1120.1460.1720.230
20.0390.0220.0400.0690.0570.076
30.0390.0210.0150.0140.0130.013
40.0400.0220.0150.0110.0100.009
50.0570.0310.0210.0170.0130.012
", + "bbox": [ + 86, + 89, + 460, + 266 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/5ab590e89fea91b3eba73b9dccd22375cf94ee462a45b035881b26c0d47e776b.jpg", + "table_caption": [ + "Table 3. Comparison on the EPE2D metric between different training/inference iteration configurations. The model is first trained under a specific $K_{tr}$ on the FT3Ds dataset and then evaluated with various $K_{ins}$ on both FT3Ds and KITTIs dataset." + ], + "table_footnote": [], + "table_body": "
Correlation type\n# neighbor (dist:feat)Euclidean\n(32:0)Hybrid\n(16:16)Feature\n(0:32)
EPE3D (m)FT3Ds0.0190.0160.022
KITTs0.0180.0150.036
", + "bbox": [ + 86, + 344, + 460, + 412 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/7e8642563e41286706b963a1728a2b09fd2b18133973d6008273685cc65b28fa.jpg", + "table_caption": [ + "Table 4. Comparison between different numbers of the neighbor points for the correlation extraction. 'Dist' and 'feat' indicate the Euclidean distance-based neighbor points and the feature-induced neighbor points, respectively." + ], + "table_footnote": [], + "table_body": "
IBFAHCGRUFT3Ds EPE3D (m)KITTIs EPE3D (m)
×××0.0290.030
✓××0.0250.025
×✓×0.0290.038
✓×✓0.0190.018
✓✓×0.0210.018
×✓✓0.0270.033
✓✓✓0.0160.015
", + "bbox": [ + 120, + 491, + 426, + 626 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "the optimal estimation performance when $K_{tr} = 4$ . Moreover, the model also demonstrated that the performance is saturated at $K_{tr} = 5$ . On the other hand, we observe that the model keeps improving for a few more iterations even though the inference $K_{in}$ is larger than the training when the training $K_{tr} \\geq 3$ . However, the improvement is negligible thus we stop evaluating at $K_{in} = K_{tr}$ .", + "bbox": [ + 75, + 733, + 467, + 839 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Hybrid Correlation. As mentioned in Section 3.2, the hybrid correlation consists of the Euclidean distance-based correlation and the proposed feature-induced correlation, thus can benefit from both of their advantages. To val", + "bbox": [ + 75, + 839, + 467, + 900 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/caefe2dfd99b2026e4644dd92a5cc4a01646334f66ce9c6ba234f14ff26cf8e2.jpg", + "table_caption": [ + "Table 5. Ablations of different components. IBFA, HC and GRU represent whether the iterative bidirectional feature augmentation, hybrid correlation and GRU are deployed in the model, respectively. The iterative models are trained and evaluated with $K_{tr} = K_{in} = 3$ ." + ], + "table_footnote": [], + "table_body": "
MethodRuntimeMethodRuntime
PV-RAFT [34]781.1msOurs (Kin=2)209.6ms
FlowStep3D [15]972.7msOurs (Kin=3)287.6ms
RCP [9]2854.6msOurs (Kin=4)365.8ms
", + "bbox": [ + 506, + 89, + 883, + 156 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 6. Runtime comparison of iterative methods. The results are evaluated on a single TITAN RTX GPU. PV-RAFT, FlowStep3D and RCP are evaluated with their optimal iteration configurations which are 32, 4 and 14, respectively.", + "bbox": [ + 498, + 166, + 890, + 222 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "idate the effectiveness of the hybrid correlation (16:16), we implemented two ablation experiments: a model with only the Euclidean distance-based correlation (32:0) and a model with only the proposed feature-induced correlation (0:32). Note that, the numbers in brackets indicate the number of Euclidean neighbor points and the number of feature-induced neighbor points, respectively. The total number of neighbor points is fixed at 32 for all experiments for a fair comparison. As demonstrated in Table 4, introducing our feature-induced correlation in the conventional Euclidean distance-based approaches can boost performance. However, the proposed feature-induced correlation must work with the Euclidean distance-based correlation. It is because the feature-induced correlation can capture semantically similar points from other instances located far away. Additionally applying the Euclidean distance-based correlation can introduce a proper constraint on the range.", + "bbox": [ + 496, + 251, + 890, + 508 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Analysis of different BGRU configurations. To verify the contributions of the proposed components in the BGRU, we incrementally adopted the IBFA, hybrid correlation, and GRU based on a baseline model. Note that, the baseline model replaces IBFA and the hybrid correlation with BFP [4] and the distance-based correlation, respectively, and removes GRU. As shown in Table 5, IBFA, hybrid correlation and GRU all contribute considerably to the effective estimation. In particular, IBFA improves the accuracy by 0.5 mm on KITTI. Furthermore, using the hybrid correlation and GRU mechanism further reduces the estimation error by $0.7\\mathrm{mm}$ and $0.3\\mathrm{mm}$ on KITTI, respectively. However, Table 5 also reveals that the hybrid correlation and GRU must cooperate with IBFA to get convincing improvement.", + "bbox": [ + 496, + 510, + 890, + 723 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.6. Runtime", + "text_level": 1, + "bbox": [ + 500, + 738, + 602, + 753 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We compare the running time of our proposed methods to other state-of-the-art iterative approaches [34, 15, 9] in Table 6. All methods are measured on a single NVIDIA Titan RTX GPU. Table 6 and 1 show that our proposed method outperforms by a large margin in terms of running time while achieving superior accuracy and generality. Even under $K_{in} = 2$ , our method also presents outperformed accuracy with faster speed compared to the existing iterative approaches.", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "10048", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 89, + 194, + 104 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This paper presented MSBRN, a novel recurrent bidirectional architecture that is capable of iteratively estimating progressively accurate multi-scale 3D scene flows from two consecutive point cloud frames. Our proposed network also utilized the hybrid correlation for improved flow estimation performance. Experimental results showed that our network significantly outperforms previous state-of-the-art methods on two challenging benchmarks. The proposed method also showed superior efficiency compared to existing iterative state-of-the-art. Extensive experiments also demonstrated the excellent effectiveness of the novel components proposed in this work.", + "bbox": [ + 75, + 114, + 472, + 297 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 76, + 308, + 236, + 325 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was supported by the Ministry of Science and ICT (MSIT) of Korea under the National Research Foundation (NRF) grant (2022R1A4A3032913) and the Institute of Information and Communication Technology Planning Evaluation (IITP) grants (IITP-2019-0-00421, IITP-2023-2020-0-01821, IITP-2021-0-02052, IITP-2021-0-02068), and by the Technology Innovation Program (RS-2023-00235718) funded by the Ministry of Trade, Industry & Energy (1415187474). Wencan Cheng was partly supported by the China Scholarship Council (CSC).", + "bbox": [ + 75, + 333, + 472, + 486 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 76, + 497, + 174, + 513 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Paul J Besl and Neil D McKay. Method for registration of 3-d shapes. In Sensor fusion IV: control paradigms and data structures, volume 1611, pages 586-606. International Society for Optics and Photonics, 1992. 3", + "[2] Angel X Chang, Thomas Funkhouser, Leonidas Guibas, Pat Hanrahan, Qixing Huang, Zimo Li, Silvio Savarese, Manolis Savva, Shuran Song, Hao Su, et al. Shapenet: An information-rich 3d model repository. arXiv preprint arXiv:1512.03012, 2015. 6", + "[3] Yang Chen and Gérard Medioni. Object modelling by registration of multiple range images. Image and vision computing, 10(3):145-155, 1992. 3", + "[4] Wencan Cheng and Jong Hwan Ko. 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Springer, 2020. 3", + "[31] Zachary Teed and Jia Deng. Raft-3d: Scene flow using rigid-motion embeddings. In IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 8375–8384, 2021. 1, 3", + "[32] Guangming Wang, Xinrui Wu, Zhe Liu, and Hesheng Wang. Hierarchical attention learning of scene flow in 3d point clouds. IEEE Transactions on Image Processing, 30:5168-5181, 2021. 1, 5", + "[33] Zirui Wang, Shuda Li, Henry Howard-Jenkins, Victor Prisacariu, and Min Chen. Flownet3d++: Geometric losses" + ], + "bbox": [ + 78, + 90, + 468, + 898 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "for deep scene flow estimation. In Proceedings of the IEEE/CVF winter conference on applications of computer vision, pages 91-98, 2020. 1, 2", + "[34] Yi Wei, Ziyi Wang, Yongming Rao, Jiwen Lu, and Jie Zhou. Pv-raft: point-voxel correlation fields for scene flow estimation of point clouds. In Proceedings of the IEEE/CVF conference on computer vision and pattern recognition, pages 6954–6963, 2021. 3, 6, 8", + "[35] Wenxuan Wu, Zhongang Qi, and Li Fuxin. Pointconv: Deep convolutional networks on 3d point clouds. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 9621-9630, 2019. 5", + "[36] Wenxuan Wu, Zhi Yuan Wang, Zhuwen Li, Wei Liu, and Li Fuxin. Pointpwc-net: Cost volume on point clouds for (self-) supervised scene flow estimation. In European Conference on Computer Vision, pages 88-107. Springer, 2020. 1, 2, 3, 5, 6, 7" + ], + "bbox": [ + 501, + 92, + 890, + 329 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "10050", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Multi-Scale Bidirectional Recurrent Network with Hybrid Correlation for Point Cloud Based Scene Flow Estimation/2097692e-e492-4ed9-98c6-50cba1cdd9a7_model.json b/2023/Multi-Scale Bidirectional Recurrent Network with Hybrid Correlation for Point Cloud Based Scene Flow Estimation/2097692e-e492-4ed9-98c6-50cba1cdd9a7_model.json new file mode 100644 index 0000000000000000000000000000000000000000..bd5a68a58d6ed24003bef702469aa0d271403437 --- /dev/null +++ b/2023/Multi-Scale Bidirectional Recurrent Network with Hybrid Correlation for Point Cloud Based Scene Flow Estimation/2097692e-e492-4ed9-98c6-50cba1cdd9a7_model.json @@ -0,0 +1,1969 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.085, + 0.13, + 0.888, + 0.175 + ], + "angle": 0, + "content": "Multi-Scale Bidirectional Recurrent Network with Hybrid Correlation for Point Cloud Based Scene Flow Estimation" + }, + { + "type": "text", + "bbox": [ + 0.18, + 0.205, + 0.305, + 0.222 + ], + "angle": 0, + "content": "Wencan Cheng" + }, + { + "type": "text", + "bbox": [ + 0.098, + 0.223, + 0.388, + 0.258 + ], + "angle": 0, + "content": "Department of Artificial Intelligence Sungkyunkwan University" + }, + { + "type": "text", + "bbox": [ + 0.171, + 0.261, + 0.316, + 0.273 + ], + "angle": 0, + "content": "cwc1260@skku.edu" + }, + { + "type": "text", + "bbox": [ + 0.424, + 0.205, + 0.71, + 0.222 + ], + "angle": 0, + "content": "Jong Hwan Ko" + }, + { + "type": "text", + "bbox": [ + 0.424, + 0.223, + 0.872, + 0.258 + ], + "angle": 0, + "content": "College of Information and Communication Engineering Sungkyunkwan University" + }, + { + "type": "text", + "bbox": [ + 0.591, + 0.261, + 0.708, + 0.274 + ], + "angle": 0, + "content": "jhko@skku.edu" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.309, + 0.314, + 0.327 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.342, + 0.474, + 0.614 + ], + "angle": 0, + "content": "Scene flow estimation provides the fundamental motion perception of a dynamic scene, which is of practical importance in many computer vision applications. In this paper, we propose a novel multi-scale bidirectional recurrent architecture that iteratively optimizes the coarse-to-fine scene flow estimation. In each resolution scale of estimation, a novel bidirectional gated recurrent unit is proposed to bidirectionally and iteratively augment point features and produce progressively optimized scene flow. The optimization of each iteration is integrated with the hybrid correlation that captures not only local correlation but also semantic correlation for more accurate estimation. Experimental results indicate that our proposed architecture significantly outperforms the existing state-of-the-art approaches on both FlyingThings3D and KITTI benchmarks while maintaining superior time efficiency. Codes and pre-trained models are publicly available at https://github.com/cwc1260/MSBRN." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.647, + 0.21, + 0.663 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.673, + 0.47, + 0.764 + ], + "angle": 0, + "content": "Scene flow estimation is a fundamental task that estimates the dense 3D motion field of points from two consecutive frames [32, 19]. As it provides the basic motion understanding of a dynamic environment, it is meaningful in a variety of high-level applications such as autonomous driving, augmented reality, and robotics [15]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Early scene flow estimation approaches rely on 2D representations such as RGB images [14, 11, 13, 28, 12]. They basically estimate optical flow and disparity map separately in the 2D space instead of directly estimating scene flow vectors in the 3D space. Recently, with the advances in LiDAR sensors and point cloud-based learning technologies, learning scene flow directly from point clouds has been extensively studied. The pioneering work known as FlowNet3D [19] is the first to introduce hierarchical Point-" + }, + { + "type": "image", + "bbox": [ + 0.522, + 0.31, + 0.88, + 0.449 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.454, + 0.895, + 0.581 + ], + "angle": 0, + "content": "Figure 1. Illustration of the multi-scale bidirectional recurrent network for scene flow estimation. The multi-scale features extracted from each input frame are fed into novel bidirectional gated recurrent units (BGRUs) that respectively iterates \\( K \\) times for optimizing scene flows on each scale. Introducing hybrid correlation (HC) further improves the performance by searching correspondence in both the Euclidean and latent feature space. The estimated scene flows are warped with the source frame for a clear comparison with the target frame." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.611, + 0.895, + 0.673 + ], + "angle": 0, + "content": "\\(\\mathrm{Net}++\\) [26] to directly predict the 3D scene flow based on the point cloud. Following this work, a diverse variety of architectures [33, 36, 9, 32, 15] have been proposed and significantly enhanced performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Recently, there is a rising trend of iteratively optimizing estimated scene flow by utilizing the recurrent scheme [15, 9, 31] to progressively improve the estimation accuracy. However, they only focus on optimizing single resolution scale which causes large computation latency. On the other hand, another series of works [28, 4] presented their superior efficiency by estimating multi-scale scene flow in a coarse-to-fine manner. However, their single-shot estimation on each scale restricts their performance. To achieve high estimation accuracy while holding high efficiency, we propose an effective and efficient architecture, Multi-Scale Bidirectional Recurrent Network (MSBRN), that iteratively optimizes coarse-to-fine scene flow. Moreover, in our view, the optimization phases of scene flow can be regarded as temporal sequences, which can benefit from the bidirectional" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.958 + ], + "angle": 0, + "content": "10041" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.09, + 0.466, + 0.213 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.219, + 0.47, + 0.276 + ], + "angle": 0, + "content": "Figure 2. Examples of two variants of correlation extraction. The bold red and green points are the grouped correlated points of the bold blue source point through the feature-induced correlation and Euclidean distance-based correlation, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.306, + 0.468, + 0.381 + ], + "angle": 0, + "content": "tional recurrent architecture [27, 8, 5, 16]. In each specific resolution scale, thus, we apply a novel bidirectional gated recurrent unit (BGRU) to bidirectionally and iteratively augment point features and produce progressively optimized scene flow." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.385, + 0.468, + 0.655 + ], + "angle": 0, + "content": "Moreover, we also noticed a common limitation of current point cloud-based flow estimation approaches. They aggregate the grouped neighboring points in the Euclidean space when generating the correspondence features between two point frames. The correspondence grouping used in these methods generally exploits \\( k \\)-nearest-neighbor (kNN) that only focuses on a specific local region. Thus, these methods may be harmed by nearby non-correlated points in Euclidean space, as shown in Figure 2. To resolve these issues, we first proposed a feature-induced correlation that collects the nearest neighbor points in the latent feature space. Thus, the grouped points from the feature space are semantically related regardless of their distances in Euclidean space. Afterwards, we combined the proposed correlation with the conventional Euclidean distance-based correlation forming the hybrid correlation. Therefore, the network is able to capture distance-insensitive correspondences as well as local correlations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.66, + 0.468, + 0.9 + ], + "angle": 0, + "content": "We evaluated MSBRN on two challenging benchmarks, the synthetic dataset FlyingThings3D [22] and the real-world LiDAR scan dataset KITTI [23], under both occluded and non-occluded settings. Following the evaluation settings of previous studies, the proposed model is trained only on the FlyingThings3D dataset and evaluated on both datasets to confirm the accuracy and generalization performance. The experimental results show that MSBRN outperforms all other approaches on the FlyingThings3D dataset with \\(46\\%\\) and \\(27\\%\\) lower errors under the occluded and non-occluded conditions, respectively. Moreover, MSBRN achieves improved generality on the real-world KITTI dataset with \\(66\\%\\) and \\(32\\%\\) lower errors under the occluded and non-occluded conditions, respectively. Our MSBRN also shows better time efficiency while maintaining higher accuracy compared to other iterative state-of-the-arts." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.892, + 0.121 + ], + "angle": 0, + "content": "The key contributions of this paper are summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.133, + 0.892, + 0.239 + ], + "angle": 0, + "content": "- We propose a novel multi-scale bidirectional recurrent architecture used for a 3D scene flow estimation task based on point cloud. The model can iteratively and bidirectionally enhance features and scene flow estimations in a coarse-to-fine manner in order to significantly improve the performance while maintaining high efficiency." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.25, + 0.892, + 0.31 + ], + "angle": 0, + "content": "- We propose a hybrid correspondence grouping that collects corresponding points from the other point frame in both the latent feature space and Euclidean space." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.321, + 0.892, + 0.38 + ], + "angle": 0, + "content": "- The proposed model achieves state-of-the-art performance and generality on the synthetic FlyingThings3D and real-world KITTI benchmarks under both occluded and non-occluded conditions." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.133, + 0.892, + 0.38 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.396, + 0.642, + 0.411 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.421, + 0.838, + 0.435 + ], + "angle": 0, + "content": "2.1. Scene Flow Estimation on Point Clouds" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.444, + 0.892, + 0.744 + ], + "angle": 0, + "content": "The first study in solving flow estimation on raw point clouds with learning-based methods was FlowNet3D [19]. FlowNet3D exploited hierarchical PointNet++ [26] and a local correlation learning layer to estimate the scene flow from two raw point cloud frames. Following this scheme, FlowNet3D++ [33] and HCRF-Flow [18] were proposed to further refine the final estimation by introducing auxiliary geometric constraints and high-order CRFs, respectively. However, the performance of these FlowNet3D-based models was restricted by the single-scale flow correlation. To address this flaw, HPLFlownet [10] was proposed in order to capture multi-scale correlations. PointPWC-Net [36] further suggested a coarse-to-fine architecture to regress multi-scale scene flow by applying local correlation extraction hierarchically. Based on the coarse-to-fine design, OGSFNet [24] additionally estimated occlusion masks with an occlusion-aware correlation layer. Furthermore, Bi-PointFlowNet [4] introduced a bidirectional mechanism to bidirectionally propagate point features for informative correlation extraction." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.746, + 0.892, + 0.836 + ], + "angle": 0, + "content": "Nevertheless, the above-mentioned approaches all rely on the local correlation, which has a limit on estimation accuracy when corresponding points are out of the local region. However, the hybrid correlation proposed in this work can alleviate this limitation by considering both local correlation and semantic correlation." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.847, + 0.833, + 0.862 + ], + "angle": 0, + "content": "2.2. Recurrent Models for Flow Estimation" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Many recent studies have demonstrated a reasonable performance by employing a recurrent architecture to itera-" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "10042" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.083, + 0.095, + 0.896, + 0.25 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.256, + 0.895, + 0.314 + ], + "angle": 0, + "content": "Figure 3. Architecture of MSBRN for scene flow estimation. First, the two consecutive input point frames are fed into the shared hierarchical feature extraction module for multi-level features. At each level, a novel BGRU bidirectionally augments point features and iteratively optimizes correlations and flow predictions. The upsampling layers are adopted between adjacent levels for propagating features and flows from high levels to low levels. The figure is best viewed in color." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.337, + 0.473, + 0.775 + ], + "angle": 0, + "content": "tively refine the estimations [13, 21, 30, 31, 34, 15]. Inspired by the previous iterative refinement models [14, 28, 11, 9, 6], IRR [13] reused its whole architecture as a recurrent unit to iteratively optimize the optical flow. Lv et. al. proposed a approach that iterates a learning-based Inverse Compositional algorithm to optimize dense 3D rigid motion. To further improve the efficiency and convergence, RAFT [30] developed a 4D all-to-all correlation volume with the use of a gated recurrent unit (GRU). Based on RAFT, RAFT-3D [31] promoted the recurrent scheme into scene flow estimation by iteratively estimating a dense field of per-pixel SE(3) motion. Afterward, PV-RAFT [34] was proposed to iteratively capture the point-voxel correlation for scene flow estimation from the point cloud inputs. Different from the RAFT-series methods, FlowStep3D [15] and RCP [9] iteratively optimized the correlation that gradually aligns point clouds based on the iterative closest point (ICP) algorithm [3, 1]. FlowStep3D [15] deployed a gated recurrent unit and the source frame warping for iterative updates correlation at a single dense resolution. Similarly, RCP [9] performed iterative point-wise optimization and subsequently introduced the GRU for regularization. Dong et al. [6] introduced direct multi-body rigidity constraints to a GRU-based recurrent neural network for robust iterative optimization of scene flow estimation. There are several other approaches [25, 17] that treated scene flow estimation as solving an optimal transport problem. They typically required point-wise features to iteratively optimize the all-to-all correlation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Nevertheless, the existing iterative methods proceed with the optimization only at a single resolution. To achieve acceptable accuracy, they typically optimize dense resolution, which severely restricts the estimation efficiency. Therefore, we introduce a multi-scale iterative optimization to achieve high accuracy while maintaining high efficiency." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.336, + 0.707, + 0.351 + ], + "angle": 0, + "content": "3. MSBRN Architecture" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.363, + 0.892, + 0.604 + ], + "angle": 0, + "content": "The goal of the scene flow estimation task is to estimate 3D point-wise motion vectors representing the non-rigid transformation from two consecutive point frames sampled from a dynamic scene. To solve this task, we propose MSBRN, a coarse-to-fine bidirectional recurrent architecture with the feature-induced correlation, as shown in Figure 3. MSBRN accepts as input the consecutive source and target frames that are represented by only 3D coordinates, \\( S = \\{s_i \\in \\mathbb{R}^3\\}_{i=1}^N \\) and \\( T = \\{t_j \\in \\mathbb{R}^3\\}_{j=1}^M \\), where \\( N \\) and \\( M \\) denote the number of points in the source and target frame, respectively. Note that, \\( N \\) and \\( M \\) are not necessarily to be equal because of the sparsity and occlusion in a point cloud. The expected output of MSBRN are 3D scene flow vectors \\( V = \\{v_i \\in \\mathbb{R}^3\\}_{i=1}^N \\) that describe the 3D displacement for every point in the source frame aligning with the target frame." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.606, + 0.893, + 0.756 + ], + "angle": 0, + "content": "Similar to the previous studies [36, 4], MSBRN is implemented as a coarse-to-fine architecture (Sec. 3.3) with the assistance of two existing modules: a multi-scale feature extraction module that extracts multi-scale point features and an upsampling layer that propagates features from higher scales to lower scales. At each upsampled scale, we deploy a novel BGRU (Sec. 3.1) to iteratively augment correlations and optimize scene flows. BGRU also applies a novel hybrid correlation (Sec. 3.2) in order to enhance the quality of the captured correlations." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.771, + 0.809, + 0.785 + ], + "angle": 0, + "content": "3.1. Bidirectional Gated Recurrent Unit" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We propose a novel BGRU that not only optimizes correlations but also augments point features of both frames bidirectionally and iteratively in various scales, as shown in Figure 4. In contrast, the previous methods [15, 9] that only apply conventional recurrent units to iteratively optimize only correlations for flow estimation in only one single scale. For each specific scale \\( l \\), the BGRU accepts source" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "10043" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.087, + 0.088, + 0.895, + 0.31 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.318, + 0.895, + 0.377 + ], + "angle": 0, + "content": "Figure 4. Structure of the bidirectional gated recurrent unit (BGRU). The proposed BGRU accepts source/target point features, flow estimations and correlations from the previous scale as input and hidden states. The source/target point features are first bidirectionally updated and fed to the proposed hybrid correlation for the candidate correlation generation. Subsequent GRU utilizes the candidate correlations for iteratively updating the correlation states." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.397, + 0.47, + 0.505 + ], + "angle": 0, + "content": "point coordinates and features \\( S^{l,0} = \\{(s^l,f^{(l,0)})\\} \\), target point coordinates and features \\( T^{l,0} = \\{(t^l,g^{(l,0)})\\} \\), correlations \\( E^{l,0} \\) and flow \\( V^{l,0} \\) as input as well as hidden state variables that will be iteratively updated. After \\( K \\) iterations, updated \\( P^{l,K}, Q^{l,K}, E^{l,K} \\) and \\( V^{l,K} \\) are sent to the subsequent scale. In this section, we focus on one specific scale and omit the notation \\( l \\) for clarity." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.506, + 0.47, + 0.61 + ], + "angle": 0, + "content": "Warping: Warping enables the source points to progressively approach the target frame. The estimated scene flows of upsampling layers (for the first iteration only) or previous iterations are immediately accumulated to the source frame, i.e. \\( s = v^{k - 1} + s \\). The warped source points are further fed to the subsequent feature augmentation for more accurate correlation extraction." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.611, + 0.47, + 0.716 + ], + "angle": 0, + "content": "Iterative Bidirectional Feature Augmentation (IBFA): IBFA accepts as input two frames of point coordinates and corresponding features from the previous \\((k - 1)\\)-th iteration, \\(S^{k - 1} = \\{(s,f^{k - 1})\\}\\) and \\(T^{k - 1} = \\{(t,g^{k - 1})\\}\\). For each point in both frames, the features are augmented bidirectionally for the current \\(k\\)-th iteration by aggregating features from the other frame as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.727, + 0.47, + 0.758 + ], + "angle": 0, + "content": "\\[\nf ^ {k} = \\underset {\\left(t _ {i}, g _ {i} ^ {k - 1}\\right) \\in \\mathcal {N} _ {T} ^ {k - 1} \\left\\{\\left(s, f ^ {k - 1}\\right) \\right\\}} {\\operatorname {S e t C o n v}} \\left(\\left[ t _ {i} - s, g _ {i} ^ {k - 1}, f ^ {k - 1} \\right]\\right), \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.784, + 0.469, + 0.814 + ], + "angle": 0, + "content": "\\[\ng ^ {k} = \\underset {\\left(s _ {j}, f _ {j} ^ {k - 1}\\right) \\in \\mathcal {N} _ {S} ^ {k - 1} \\{(t, g ^ {k - 1}) \\}} {\\operatorname {S e t C o n v}} \\left(\\left[ s _ {j} - t, f _ {j} ^ {k - 1}, g ^ {k - 1} \\right]\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.471, + 0.902 + ], + "angle": 0, + "content": "where SetConv [19] is composed of a shared multi-layer perceptron and a maxpooling layer, \\(\\mathcal{N}_T\\{(s,\\cdot)\\}\\) denotes the nearest neighbor points of \\(s\\) in \\(T\\), subscript \\(i,j\\) indicate the indices of points in the neighbor group \\(\\mathcal{N}\\), and \\([\\cdot ,\\cdot ]\\) denotes the channel concatenation operator. Note that, the" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.399, + 0.892, + 0.444 + ], + "angle": 0, + "content": "SetConv in Equation (1) and (2) share the equivalent parameters. The output are buffered as hidden states for the subsequent iteration or scale." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.444, + 0.893, + 0.549 + ], + "angle": 0, + "content": "Iterative Correlation Update: The bidirectionally-augmented features are fed to the hybrid correlation extraction module (Sec. 3.2) to generate candidate correlation features. The candidate correlations serve as the input to a GRU in order to update the state correlation features from the previous iteration. Formally, the correlation features updated by the current iteration is denoted as:" + }, + { + "type": "equation", + "bbox": [ + 0.521, + 0.558, + 0.892, + 0.59 + ], + "angle": 0, + "content": "\\[\nz = \\sigma \\left(\\underset {\\left(s _ {i}, \\tilde {e} _ {i} ^ {k}\\right) \\in \\mathcal {N} _ {\\tilde {S}} ^ {k - 1} \\{(s, e ^ {k - 1}) \\}} {\\operatorname {S e t C o n v} _ {z}} \\left([ s _ {i} - s, e ^ {k - 1}, \\tilde {e} _ {i} ^ {k} ]\\right)\\right), \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.577, + 0.604, + 0.892, + 0.623 + ], + "angle": 0, + "content": "\\[\nr _ {i} = \\sigma (M L P _ {r} ([ s _ {i} - s, e ^ {k - 1}, \\widetilde {e} _ {i} ^ {k} ])), \\qquad (4)\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.501, + 0.651, + 0.891, + 0.696 + ], + "angle": 0, + "content": "\\[\n\\hat {e} ^ {k} = \\tanh \\left(\\underset {\\left(s _ {i}, \\tilde {e} _ {i} ^ {k}\\right) \\in \\mathcal {N} _ {\\tilde {S}} ^ {k - 1} \\left\\{\\left(s, e ^ {k - 1}\\right) \\right\\}} {\\operatorname {S e t C o n v} _ {h}} \\left(\\left[ s _ {i} - s, e ^ {k - 1} \\odot r _ {i}, \\tilde {e} _ {i} ^ {k}\\right)\\right), \\right. \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.59, + 0.71, + 0.891, + 0.728 + ], + "angle": 0, + "content": "\\[\ne ^ {k} = (1 - z) \\odot e ^ {k - 1} + z \\odot \\hat {e} ^ {k}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.733, + 0.771, + 0.748 + ], + "angle": 0, + "content": "where \\(\\odot\\) denotes the Hadamard product." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.748, + 0.892, + 0.838 + ], + "angle": 0, + "content": "Scene Flow Estimation: Given the updated correlation feature of each point, an MLP is followed to transform the correlation into a flow vector. Additionally, we introduce a residual mechanism by estimating the flow vector refinement \\(\\Delta V_{k}\\). The final flow estimation is then accumulated as \\(V^{k} = V^{k - 1} + \\Delta V^{k}\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.848, + 0.688, + 0.864 + ], + "angle": 0, + "content": "3.2. Hybrid Correlation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Feature-induced Correlation: Instead of capturing neighbor points in the conventional Euclidean space, we fetch" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "10044" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.318 + ], + "angle": 0, + "content": "neighbor points from the latent feature space in order to acquire semantically correlative points. For instance, Figure 2 shows that the proposed correlation can capture semantically similar points (front windscreen) even if they are far away. Thus, the proposed correlation is different from the Euclidean-based correlation that may capture semantically unrelated points (bumper). Formally, given two point sets consisted of 3-dimensional coordinates and \\( C \\)-dimensional features \\( S = \\{(s,f)|s\\in \\mathbb{R}^3,f\\in \\mathbb{R}^C\\} \\) and \\( T = \\{(t,g)|t\\in \\mathbb{R}^3,g\\in \\mathbb{R}^C\\} \\), for each point \\( (s,f)\\in S \\), its collected neighbor points \\( \\mathcal{N}_T\\{(s,f)\\} \\) from \\( T \\) satisfy \\( \\delta (f,g_i) < \\delta (f,g_j) \\), when \\( \\forall (t_i,g_i)\\subset \\mathcal{N}_T\\{(s,f)\\} \\) and \\( (t_j,g_j)\\subset Q\\backslash \\mathcal{N}_T\\{(p,f)\\} \\). Note that, \\( |\\mathcal{N}_T\\{(s,f)\\}| = K \\) is the hyperparameter that defines the amount of the top-K neighbor points, and \\( \\delta (\\cdot ,\\cdot) \\) is the cosine similarity measure." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.319, + 0.472, + 0.38 + ], + "angle": 0, + "content": "After the corresponding points are collected, the features of the collected points are further aggregated by a learnable symmetric function. Hence, the correlation feature for each point \\((p,f)\\in P\\) is formally denoted as:" + }, + { + "type": "equation", + "bbox": [ + 0.15, + 0.391, + 0.47, + 0.417 + ], + "angle": 0, + "content": "\\[\n\\widetilde {e} = \\underset {\\left(t _ {i}, g _ {i}\\right) \\in \\mathcal {N} _ {T} \\left\\{\\left(s, f\\right) \\right\\}} {\\operatorname {S e t C o n v}} \\left(\\left[ t _ {i} - s, g _ {i}, f \\right]\\right). \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.428, + 0.473, + 0.566 + ], + "angle": 0, + "content": "Hybrid Correlation: Considering that the conventional grouping can capture fine-grained local motion and the proposed feature-induced grouping can capture correspondence regardless of distances, we integrate the two techniques to take advantage of both correlation extraction strategies. Thus, we fuse the collected points with the feature-induced grouping and conventional grouping as a hybrid neighbor set \\(\\mathcal{N}_T\\{(s,f)\\}\\) in Equation (7) for the subsequent correlation aggregation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.575, + 0.332, + 0.59 + ], + "angle": 0, + "content": "3.3. Coarse-to-Fine Architecture" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.598, + 0.47, + 0.644 + ], + "angle": 0, + "content": "In this section, we thus introduce two existing layers [36] to construct a coarse-to-fine network for multi-scale feature generation and propagation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.645, + 0.473, + 0.854 + ], + "angle": 0, + "content": "Multi-scale Feature Extraction: The multi-scale feature extraction follows the design that is commonly used in point cloud processing [26, 35]. The feature extraction generates \\( L \\)-level pyramid of point features, where the top level is the input point clouds. At each level \\( l \\), dense input points and their corresponding features are first subsampled through the furthest point sampling, which forms a sparse point set. Then, for each subsampled sparse point, the \\( k \\)-nearest neighbor groups dense points locally forming a local region for the feature extraction. Afterwards, a Pointconv [35] layer is applied to aggregate the features from the grouped local points through dynamic weights learned on their local coordinates, and produced the local feature for each sparse point." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Upsampling Layer: Since each level produces scene flows and iteratively augmented bidirectional features and correlations, we introduced the upsampling layer to propagate" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.269 + ], + "angle": 0, + "content": "these features to the following level for a denser optimization. Following the previous works [36, 4], the upsampling layer adopts the 3D interpolation that aggregates \\( k \\) nearest neighbors with their inverse distances as weights. Specifically, in the case of upsampling correlations from the \\( l \\)-th level to the \\( (l - 1) \\)-th level, the input to the upsampling layer are \\( l \\)-th level's sparse coordinates \\( \\{x_j^l\\}_{j = 1}^{N^l} \\), \\( l \\)-th level's correlations \\( \\{e_j^l\\}_{j = 1}^{N^l} \\) and \\( (l - 1) \\)-th level's dense coordinates \\( \\{x_i^{l - 1}\\}_{i = 1}^{N^{l - 1}} \\), where \\( N^{l - 1} \\) and \\( N^l \\) are the number of points and \\( N^{l - 1} > N^l \\). The interpolated feature for each point \\( x_{i}^{l} \\) in the dense \\( (l - 1) \\)-th level is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.594, + 0.278, + 0.892, + 0.322 + ], + "angle": 0, + "content": "\\[\ne _ {i} ^ {l - 1} = \\frac {\\sum_ {j = 1} ^ {k} w \\left(x _ {j} ^ {l} , x _ {i} ^ {l - 1}\\right) e _ {j} ^ {l}}{\\sum_ {j = 1} ^ {k} w \\left(x _ {j} ^ {l} , x _ {i} ^ {l - 1}\\right)}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.324, + 0.895, + 0.357 + ], + "angle": 0, + "content": "where \\( w(x_{j}^{l},x_{i}^{l - 1}) = 1 / ||x_{j}^{l} - x_{i}^{l - 1}||_{2} \\), and \\( k = 3 \\) as suggested by the previous studies [4, 36]." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.364, + 0.646, + 0.379 + ], + "angle": 0, + "content": "3.4. Loss Function" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.387, + 0.895, + 0.542 + ], + "angle": 0, + "content": "Following the previous studies for optical flow estimation [7, 29] and scene flow estimation [32, 36, 4], we train the proposed model in the multi-scale supervision manner. Furthermore, we also supervise the estimations of all intermediate iterations at each scale. All the estimated flows are supervised by the ground truth with the L2 measure. Let \\(\\{v_i^{l,k}\\}_{i=1}^N\\) denote the scene flow vectors estimated from the \\(k\\)-th iteration at the \\(l\\)-th level and \\(\\{\\hat{v}_i^l\\}_{i=1}^N\\) denote the ground truth scene flow vectors of the \\(l\\)-th scale. The training loss is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.584, + 0.548, + 0.892, + 0.592 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\sum_ {l = 0} ^ {L - 1} \\alpha^ {l} \\sum_ {k = 1} ^ {K} \\sum_ {i = 1} ^ {N ^ {l}} \\| \\hat {v} _ {i} ^ {l} - v _ {i} ^ {l, k} \\| _ {2}, \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.895, + 0.631 + ], + "angle": 0, + "content": "where \\(\\alpha^l\\) is the weight for scale \\(l\\). The weights are \\(\\alpha^0 = 0.16, \\alpha^1 = 0.08, \\alpha^2 = 0.04, \\alpha^3 = 0.02\\) by default." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.642, + 0.634, + 0.659 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.666, + 0.709, + 0.683 + ], + "angle": 0, + "content": "4.1. Experimental Settings" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.895, + 0.902 + ], + "angle": 0, + "content": "As shown in Fig. 3, we implemented a hierarchical model with \\( L = 4 \\) scales. We used \\( N = M = 8 \\), 192 points as inputs. The point numbers of each scale are defined as \\( N^1 = 2 \\), 048, \\( N^2 = 512 \\), \\( N^3 = 256 \\), and \\( N^4 = 64 \\). We adopted the synthetic FlyingThings3D [22] dataset and the real-world KITTI Scene Flow 2015 [23] dataset to evaluate our model. As in the previous methods, we trained networks only on the synthetic FlyingThings3D dataset and validated the performance on the FlyingThings3D dataset (Sec. 4.3). Finally, we directly evaluated the model trained on FlyingThings3D without any fine-tuning to validate the generalization ability on the real-world KITTI dataset (Sec. 4.4). The experiments are conducted on an NVIDIA Titan RTX GPU with PyTorch." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "10045" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.104, + 0.089, + 0.872, + 0.395 + ], + "angle": 0, + "content": "
DatasetMethodEPE3D (m) ↓ACC3DS ↑ACC3DR ↑Outliers3D ↓EPE2D (px) ↓ACC2D ↑
FT3DsFlowNet3D [19]0.1130.4120.7710.6025.9740.569
HPLFlowNet [10]0.0800.6140.8550.4294.6720.676
PointPWC [36]0.0590.7380.9280.3423.2390.799
FLOT [25]0.0520.7320.9270.357--
HCRF-Flow [18]0.0480.8350.9500.2612.5650.870
PV-RAFT [34]0.0460.8160.9570.292--
FlowStep3D [15]0.0450.8160.9610.216--
RCP [9]0.0400.8560.9630.197--
Bi-PointFlowNet [4]0.0280.9180.9780.1431.5820.929
Ours0.0150.9730.9920.0560.8330.970
KITTsFlowNet3D [19]0.1770.3740.6680.5277.2140.509
HPLFlowNet [10]0.1170.4780.7780.4104.8050.593
PointPWC [36]0.0690.7280.8880.2651.9020.866
FLOT [25]0.0560.7550.9080.242--
HCRF-Flow [18]0.0530.8630.9440.1792.0700.865
PV-RAFT [34]0.0560.8220.9370.216--
FlowStep3D [15]0.0540.8050.9250.149--
RCP [9]0.0480.8490.9440.122--
Bi-PointFlowNet [4]0.0300.9200.9600.1411.0560.949
Ours0.0110.9710.9890.0850.4430.985
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.403, + 0.895, + 0.434 + ], + "angle": 0, + "content": "Table 1. Comparison of the proposed method with previous state-of-the-art methods on the non-occluded FT3D \\( {}_{s} \\) and KITTI \\( {}_{s} \\) datasets. All methods are trained only on the FT3D \\( {}_{s} \\) dataset." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.456, + 0.279, + 0.472 + ], + "angle": 0, + "content": "4.2. Evaluation Measures" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.48, + 0.47, + 0.526 + ], + "angle": 0, + "content": "For a fair comparison, we adopted the same evaluation measures that are used in the related works [10, 36, 25, 15, 18, 4]." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.527, + 0.47, + 0.572 + ], + "angle": 0, + "content": "EPE3D, EPE3Dfull (m): the main evaluation measure measuring 3D end-point-error \\(\\| \\hat{v}_i^l - v_i^l\\|_2\\) averaged over non-occluded points and all points, respectively." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.573, + 0.47, + 0.602 + ], + "angle": 0, + "content": "ACC3DS: the percentage of points that satisfy EPE3D \\(< 0.05\\mathrm{m}\\) or relative error \\(< 5\\%\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.604, + 0.47, + 0.634 + ], + "angle": 0, + "content": "ACC3DR: the percentage of points that satisfy EPE3D \\(< 0.1\\mathrm{m}\\) or relative error \\(< 10\\%\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.636, + 0.469, + 0.665 + ], + "angle": 0, + "content": "Outliers3D: the percentage of points that satisfy EPE3D \\(>0.3\\mathrm{m}\\) or relative error \\(>10\\%\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.667, + 0.47, + 0.712 + ], + "angle": 0, + "content": "EPE2D (px): 2D end-point-error measured by projecting points back to the 2D image plane, which is a common measure for optical flow evaluation." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.713, + 0.47, + 0.743 + ], + "angle": 0, + "content": "ACC2D: the percentage of points that satisfy EPE2D \\(< 3\\mathrm{px}\\) or relative error \\(< 5\\%\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.755, + 0.455, + 0.773 + ], + "angle": 0, + "content": "4.3. Training and Evaluation on FlyingThings3D" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Due to the challenge with labeling for dense point cloud scenes, recent models [10, 36, 25, 15, 18, 4] only utilized the synthetic FlyingThing3D dataset for training. The FlyingThing3D [22] dataset provides 19,640 pairs of frames for training and 3,824 pairs of frames for testing. Each frame contains synthetic stereo and RGB-D images rendered from virtual scenes with multiple moving objects sampled from the ShapeNet [2] dataset. We follow the same preprocessing" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.456, + 0.892, + 0.532 + ], + "angle": 0, + "content": "that generates two subsets: \\(\\mathrm{FT3D}_o\\) that includes occluded points and \\(\\mathrm{FT3D}_s\\) that excludes the occluded points, as suggested in [10, 36, 25, 4]. The consecutive input frames are formed by randomly sampling \\(N = 8\\), 192 of points from the dataset with non-correspondence." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.533, + 0.892, + 0.624 + ], + "angle": 0, + "content": "For training, we used the AdamW optimizer [20] with beta1 = 0.9, beta2 = 0.999. The learning rate is initially set as \\(\\alpha = 0.0001\\) and reduced by half every 80 epochs. We trained the model for a total of 560 epochs. The numbers of iterations for all BGRUs are set to \\(K_{tr} = 4\\) during training and \\(K_{in} = 4\\) during testing." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.624, + 0.892, + 0.745 + ], + "angle": 0, + "content": "Results. We compared the performance of the proposed model with other state-of-the-art approaches based on point cloud [19, 10, 36, 25, 15, 24, 9, 4]. As presented in Table 1, the proposed method significantly outperforms all recent state-of-the-art methods with more than \\(46\\%\\) reduction of estimation error under the non-occluded condition. When compared to the related iterative methods FlowStep3D [15] and RCP [9], our model achieves an error reduction of \\(62\\%\\)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.756, + 0.733, + 0.771 + ], + "angle": 0, + "content": "4.4. Generalization on KITTI" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Following the same evaluation strategy as in the recent studies [19, 10, 36, 25, 15, 24, 4], we evaluated the generalization ability of MSBRN on the real-world KITTI [23] dataset with the model that was only trained on the synthetic dataset. The KITTI dataset provides 200 scenes for training and 200 scenes for testing. However, the disparities were missing in the testing scene and parts of the training scenes. Thus, 142 non-occluded scenes (KITTI\\(_s\\), re" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "10046" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.134, + 0.09, + 0.839, + 0.311 + ], + "angle": 0, + "content": "
DatasetMethodEPE3Dfull (m) ↓EPE3D (m) ↓ACC3DS ↑ACC3DR ↑Outliers3D ↓
FT3DoFlowNet3D [19]0.2110.1570.2280.5820.804
HPLFlowNet [10]0.2010.1680.2620.5740.812
FLOT [25]0.2500.1530.3960.6600.662
PointPWC [36]0.1950.1550.4160.6990.638
OGSFNet [24]0.1630.1210.5510.7760.518
Bi-PointFlowNet [4]0.1020.0730.7910.8960.274
Ours0.0800.0530.8360.9260.231
KITTIoFlowNet3D [19]0.183-0.0980.3940.799
HPLFlowNet [10]0.343-0.1030.3860.814
FLOT [25]0.130-0.2780.6670.529
PointPWC [36]0.118-0.4030.7570.496
OGSFNet [24]0.075-0.7060.8690.327
Bi-PointFlowNet [4]0.065-0.7690.9060.264
Ours0.044-0.8730.9500.208
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.321, + 0.893, + 0.351 + ], + "angle": 0, + "content": "Table 2. Comparison of the proposed method with previous state-of-the-art methods on the occluded FT3DO and KITTIO datasets. All methods are trained only on the FT3DO dataset." + }, + { + "type": "image", + "bbox": [ + 0.09, + 0.361, + 0.889, + 0.584 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.589, + 0.893, + 0.618 + ], + "angle": 0, + "content": "Figure 5. Qualitative results of MSBRN on the non-occluded KITTI dataset. Points are colored to indicate points as from source frame, target frame or as MSBRN estimated points (source frame + scene flow)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.642, + 0.47, + 0.718 + ], + "angle": 0, + "content": "moving occluded points) and 150 occluded scenes (KITTI\\(_o\\), remaining occluded points) were available for evaluation with raw point clouds. We removed ground points by height \\(< 0.3\\) m as suggested by the previous approaches [19, 10, 36, 25, 15, 24] for a fair comparison." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.473, + 0.901 + ], + "angle": 0, + "content": "Results. We compared the generalization ability of MSBRN with the existing state-of-the-art methods based on point cloud [19, 10, 36, 25, 15, 24, 9, 4]. As shown in Table 1 and 2, our proposed method represented the state-of-the-art generality when the model is trained on the synthetic datasets and tested on and real-world KITTI dataset. Our method significantly outperforms other methods by a large margin. Focusing on the main EPE3D measure, our method outperforms the recent state-of-the-art with \\(63\\%\\) of error reduction on the non-occluded scenes. Compared to the similar iterative methods FlowStep3D [15] and RCP [9], our method shows over \\(77\\%\\) of error reduction. Moreover, our" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.642, + 0.892, + 0.689 + ], + "angle": 0, + "content": "model shows the superior generality on the occluded scenes, as shown in Table 2. Our model shows an over \\(32\\%\\) reduction of \\(\\mathrm{EPE3D_{full}}\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.697, + 0.655, + 0.713 + ], + "angle": 0, + "content": "4.5. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Number of Iterations. The iteration number of the BGRU is a significant factor that affects the estimation accuracy. It is worth noting that the iteration configuration can be different between the training stage \\((K_{tr})\\) and the evaluation stage \\((K_{in})\\). Therefore, we trained and evaluated our method with the different iteration numbers. Note that, all levels proceed with the same iteration number as configured. Table 3 reports the performance comparison between models with the different numbers of BGRU iterations. The result shows that iteratively adopting the proposed BGRU effectively reduces the estimation error on both the synthetic dataset and the real-world dataset. The model delivers" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "10047" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.087, + 0.09, + 0.462, + 0.267 + ], + "angle": 0, + "content": "
\\(K_{tr}\\)EPE3D (m) @ \\(K_{in}\\)
123456
FT3\\(d_s\\)10.0260.0710.1010.1490.2040.281
20.0330.0210.0300.0370.0460.049
30.0380.0200.0160.0160.0160.018
40.0400.0240.0170.0150.0150.015
50.0490.0270.0190.0150.0140.014
KITTLs10.0380.1290.1120.1460.1720.230
20.0390.0220.0400.0690.0570.076
30.0390.0210.0150.0140.0130.013
40.0400.0220.0150.0110.0100.009
50.0570.0310.0210.0170.0130.012
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.278, + 0.47, + 0.334 + ], + "angle": 0, + "content": "Table 3. Comparison on the EPE2D metric between different training/inference iteration configurations. The model is first trained under a specific \\( K_{tr} \\) on the FT3Ds dataset and then evaluated with various \\( K_{ins} \\) on both FT3Ds and KITTIs dataset." + }, + { + "type": "table", + "bbox": [ + 0.088, + 0.345, + 0.462, + 0.414 + ], + "angle": 0, + "content": "
Correlation type\n# neighbor (dist:feat)Euclidean\n(32:0)Hybrid\n(16:16)Feature\n(0:32)
EPE3D (m)FT3Ds0.0190.0160.022
KITTs0.0180.0150.036
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.423, + 0.47, + 0.48 + ], + "angle": 0, + "content": "Table 4. Comparison between different numbers of the neighbor points for the correlation extraction. 'Dist' and 'feat' indicate the Euclidean distance-based neighbor points and the feature-induced neighbor points, respectively." + }, + { + "type": "table", + "bbox": [ + 0.121, + 0.492, + 0.428, + 0.627 + ], + "angle": 0, + "content": "
IBFAHCGRUFT3Ds EPE3D (m)KITTIs EPE3D (m)
×××0.0290.030
✓××0.0250.025
×✓×0.0290.038
✓×✓0.0190.018
✓✓×0.0210.018
×✓✓0.0270.033
✓✓✓0.0160.015
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.64, + 0.47, + 0.71 + ], + "angle": 0, + "content": "Table 5. Ablations of different components. IBFA, HC and GRU represent whether the iterative bidirectional feature augmentation, hybrid correlation and GRU are deployed in the model, respectively. The iterative models are trained and evaluated with \\( K_{tr} = K_{in} = 3 \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.734, + 0.468, + 0.84 + ], + "angle": 0, + "content": "the optimal estimation performance when \\( K_{tr} = 4 \\). Moreover, the model also demonstrated that the performance is saturated at \\( K_{tr} = 5 \\). On the other hand, we observe that the model keeps improving for a few more iterations even though the inference \\( K_{in} \\) is larger than the training when the training \\( K_{tr} \\geq 3 \\). However, the improvement is negligible thus we stop evaluating at \\( K_{in} = K_{tr} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Hybrid Correlation. As mentioned in Section 3.2, the hybrid correlation consists of the Euclidean distance-based correlation and the proposed feature-induced correlation, thus can benefit from both of their advantages. To val" + }, + { + "type": "table", + "bbox": [ + 0.508, + 0.09, + 0.885, + 0.157 + ], + "angle": 0, + "content": "
MethodRuntimeMethodRuntime
PV-RAFT [34]781.1msOurs (Kin=2)209.6ms
FlowStep3D [15]972.7msOurs (Kin=3)287.6ms
RCP [9]2854.6msOurs (Kin=4)365.8ms
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.167, + 0.892, + 0.223 + ], + "angle": 0, + "content": "Table 6. Runtime comparison of iterative methods. The results are evaluated on a single TITAN RTX GPU. PV-RAFT, FlowStep3D and RCP are evaluated with their optimal iteration configurations which are 32, 4 and 14, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.252, + 0.892, + 0.509 + ], + "angle": 0, + "content": "idate the effectiveness of the hybrid correlation (16:16), we implemented two ablation experiments: a model with only the Euclidean distance-based correlation (32:0) and a model with only the proposed feature-induced correlation (0:32). Note that, the numbers in brackets indicate the number of Euclidean neighbor points and the number of feature-induced neighbor points, respectively. The total number of neighbor points is fixed at 32 for all experiments for a fair comparison. As demonstrated in Table 4, introducing our feature-induced correlation in the conventional Euclidean distance-based approaches can boost performance. However, the proposed feature-induced correlation must work with the Euclidean distance-based correlation. It is because the feature-induced correlation can capture semantically similar points from other instances located far away. Additionally applying the Euclidean distance-based correlation can introduce a proper constraint on the range." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.511, + 0.892, + 0.724 + ], + "angle": 0, + "content": "Analysis of different BGRU configurations. To verify the contributions of the proposed components in the BGRU, we incrementally adopted the IBFA, hybrid correlation, and GRU based on a baseline model. Note that, the baseline model replaces IBFA and the hybrid correlation with BFP [4] and the distance-based correlation, respectively, and removes GRU. As shown in Table 5, IBFA, hybrid correlation and GRU all contribute considerably to the effective estimation. In particular, IBFA improves the accuracy by 0.5 mm on KITTI. Furthermore, using the hybrid correlation and GRU mechanism further reduces the estimation error by \\(0.7\\mathrm{mm}\\) and \\(0.3\\mathrm{mm}\\) on KITTI, respectively. However, Table 5 also reveals that the hybrid correlation and GRU must cooperate with IBFA to get convincing improvement." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.739, + 0.604, + 0.754 + ], + "angle": 0, + "content": "4.6. Runtime" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We compare the running time of our proposed methods to other state-of-the-art iterative approaches [34, 15, 9] in Table 6. All methods are measured on a single NVIDIA Titan RTX GPU. Table 6 and 1 show that our proposed method outperforms by a large margin in terms of running time while achieving superior accuracy and generality. Even under \\( K_{in} = 2 \\), our method also presents outperformed accuracy with faster speed compared to the existing iterative approaches." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "10048" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.09, + 0.196, + 0.106 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.115, + 0.473, + 0.298 + ], + "angle": 0, + "content": "This paper presented MSBRN, a novel recurrent bidirectional architecture that is capable of iteratively estimating progressively accurate multi-scale 3D scene flows from two consecutive point cloud frames. Our proposed network also utilized the hybrid correlation for improved flow estimation performance. Experimental results showed that our network significantly outperforms previous state-of-the-art methods on two challenging benchmarks. The proposed method also showed superior efficiency compared to existing iterative state-of-the-art. Extensive experiments also demonstrated the excellent effectiveness of the novel components proposed in this work." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.309, + 0.238, + 0.327 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.334, + 0.473, + 0.487 + ], + "angle": 0, + "content": "This work was supported by the Ministry of Science and ICT (MSIT) of Korea under the National Research Foundation (NRF) grant (2022R1A4A3032913) and the Institute of Information and Communication Technology Planning Evaluation (IITP) grants (IITP-2019-0-00421, IITP-2023-2020-0-01821, IITP-2021-0-02052, IITP-2021-0-02068), and by the Technology Innovation Program (RS-2023-00235718) funded by the Ministry of Trade, Industry & Energy (1415187474). Wencan Cheng was partly supported by the China Scholarship Council (CSC)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.498, + 0.175, + 0.515 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.523, + 0.47, + 0.579 + ], + "angle": 0, + "content": "[1] Paul J Besl and Neil D McKay. Method for registration of 3-d shapes. In Sensor fusion IV: control paradigms and data structures, volume 1611, pages 586-606. International Society for Optics and Photonics, 1992. 3" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.58, + 0.47, + 0.648 + ], + "angle": 0, + "content": "[2] Angel X Chang, Thomas Funkhouser, Leonidas Guibas, Pat Hanrahan, Qixing Huang, Zimo Li, Silvio Savarese, Manolis Savva, Shuran Song, Hao Su, et al. 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Springer, 2020. 1, 2, 3, 5, 6, 7" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.33 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.956 + ], + "angle": 0, + "content": "10050" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-Scale Bidirectional Recurrent Network with Hybrid Correlation for Point Cloud Based Scene Flow Estimation/2097692e-e492-4ed9-98c6-50cba1cdd9a7_origin.pdf b/2023/Multi-Scale Bidirectional Recurrent Network with Hybrid Correlation for Point Cloud Based Scene Flow Estimation/2097692e-e492-4ed9-98c6-50cba1cdd9a7_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..fe34afbf702d344152603ecd4cc9c4bfa185c7a6 --- /dev/null +++ b/2023/Multi-Scale Bidirectional Recurrent Network with Hybrid Correlation for Point Cloud Based Scene Flow Estimation/2097692e-e492-4ed9-98c6-50cba1cdd9a7_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:530b8489452ded08955797168f566607eb18a9ba904cebdf30fdaee4ae124b3b +size 724014 diff --git a/2023/Multi-Scale Bidirectional Recurrent Network with Hybrid Correlation for Point Cloud Based Scene Flow Estimation/full.md b/2023/Multi-Scale Bidirectional Recurrent Network with Hybrid Correlation for Point Cloud Based Scene Flow Estimation/full.md new file mode 100644 index 0000000000000000000000000000000000000000..a7bd93fa8312e930ae41d3ab61a2397ceecb9ab5 --- /dev/null +++ b/2023/Multi-Scale Bidirectional Recurrent Network with Hybrid Correlation for Point Cloud Based Scene Flow Estimation/full.md @@ -0,0 +1,299 @@ +# Multi-Scale Bidirectional Recurrent Network with Hybrid Correlation for Point Cloud Based Scene Flow Estimation + +Wencan Cheng + +Department of Artificial Intelligence Sungkyunkwan University + +cwc1260@skku.edu + +Jong Hwan Ko + +College of Information and Communication Engineering Sungkyunkwan University + +jhko@skku.edu + +# Abstract + +Scene flow estimation provides the fundamental motion perception of a dynamic scene, which is of practical importance in many computer vision applications. In this paper, we propose a novel multi-scale bidirectional recurrent architecture that iteratively optimizes the coarse-to-fine scene flow estimation. In each resolution scale of estimation, a novel bidirectional gated recurrent unit is proposed to bidirectionally and iteratively augment point features and produce progressively optimized scene flow. The optimization of each iteration is integrated with the hybrid correlation that captures not only local correlation but also semantic correlation for more accurate estimation. Experimental results indicate that our proposed architecture significantly outperforms the existing state-of-the-art approaches on both FlyingThings3D and KITTI benchmarks while maintaining superior time efficiency. Codes and pre-trained models are publicly available at https://github.com/cwc1260/MSBRN. + +# 1. Introduction + +Scene flow estimation is a fundamental task that estimates the dense 3D motion field of points from two consecutive frames [32, 19]. As it provides the basic motion understanding of a dynamic environment, it is meaningful in a variety of high-level applications such as autonomous driving, augmented reality, and robotics [15]. + +Early scene flow estimation approaches rely on 2D representations such as RGB images [14, 11, 13, 28, 12]. They basically estimate optical flow and disparity map separately in the 2D space instead of directly estimating scene flow vectors in the 3D space. Recently, with the advances in LiDAR sensors and point cloud-based learning technologies, learning scene flow directly from point clouds has been extensively studied. The pioneering work known as FlowNet3D [19] is the first to introduce hierarchical Point- + +![](images/820978a1b7801a6eeb9540813f9ba603965a8cfe472872e245fae135ff5f4c87.jpg) +Figure 1. Illustration of the multi-scale bidirectional recurrent network for scene flow estimation. The multi-scale features extracted from each input frame are fed into novel bidirectional gated recurrent units (BGRUs) that respectively iterates $K$ times for optimizing scene flows on each scale. Introducing hybrid correlation (HC) further improves the performance by searching correspondence in both the Euclidean and latent feature space. The estimated scene flows are warped with the source frame for a clear comparison with the target frame. + +$\mathrm{Net}++$ [26] to directly predict the 3D scene flow based on the point cloud. Following this work, a diverse variety of architectures [33, 36, 9, 32, 15] have been proposed and significantly enhanced performance. + +Recently, there is a rising trend of iteratively optimizing estimated scene flow by utilizing the recurrent scheme [15, 9, 31] to progressively improve the estimation accuracy. However, they only focus on optimizing single resolution scale which causes large computation latency. On the other hand, another series of works [28, 4] presented their superior efficiency by estimating multi-scale scene flow in a coarse-to-fine manner. However, their single-shot estimation on each scale restricts their performance. To achieve high estimation accuracy while holding high efficiency, we propose an effective and efficient architecture, Multi-Scale Bidirectional Recurrent Network (MSBRN), that iteratively optimizes coarse-to-fine scene flow. Moreover, in our view, the optimization phases of scene flow can be regarded as temporal sequences, which can benefit from the bidirectional + +![](images/98f0da9118b1948bde152eedbbef2668155b5a6b2b9b3efcb8c9a5ab0393b79b.jpg) +Figure 2. Examples of two variants of correlation extraction. The bold red and green points are the grouped correlated points of the bold blue source point through the feature-induced correlation and Euclidean distance-based correlation, respectively. + +tional recurrent architecture [27, 8, 5, 16]. In each specific resolution scale, thus, we apply a novel bidirectional gated recurrent unit (BGRU) to bidirectionally and iteratively augment point features and produce progressively optimized scene flow. + +Moreover, we also noticed a common limitation of current point cloud-based flow estimation approaches. They aggregate the grouped neighboring points in the Euclidean space when generating the correspondence features between two point frames. The correspondence grouping used in these methods generally exploits $k$ -nearest-neighbor (kNN) that only focuses on a specific local region. Thus, these methods may be harmed by nearby non-correlated points in Euclidean space, as shown in Figure 2. To resolve these issues, we first proposed a feature-induced correlation that collects the nearest neighbor points in the latent feature space. Thus, the grouped points from the feature space are semantically related regardless of their distances in Euclidean space. Afterwards, we combined the proposed correlation with the conventional Euclidean distance-based correlation forming the hybrid correlation. Therefore, the network is able to capture distance-insensitive correspondences as well as local correlations. + +We evaluated MSBRN on two challenging benchmarks, the synthetic dataset FlyingThings3D [22] and the real-world LiDAR scan dataset KITTI [23], under both occluded and non-occluded settings. Following the evaluation settings of previous studies, the proposed model is trained only on the FlyingThings3D dataset and evaluated on both datasets to confirm the accuracy and generalization performance. The experimental results show that MSBRN outperforms all other approaches on the FlyingThings3D dataset with $46\%$ and $27\%$ lower errors under the occluded and non-occluded conditions, respectively. Moreover, MSBRN achieves improved generality on the real-world KITTI dataset with $66\%$ and $32\%$ lower errors under the occluded and non-occluded conditions, respectively. Our MSBRN also shows better time efficiency while maintaining higher accuracy compared to other iterative state-of-the-arts. + +The key contributions of this paper are summarized as follows: + +- We propose a novel multi-scale bidirectional recurrent architecture used for a 3D scene flow estimation task based on point cloud. The model can iteratively and bidirectionally enhance features and scene flow estimations in a coarse-to-fine manner in order to significantly improve the performance while maintaining high efficiency. +- We propose a hybrid correspondence grouping that collects corresponding points from the other point frame in both the latent feature space and Euclidean space. +- The proposed model achieves state-of-the-art performance and generality on the synthetic FlyingThings3D and real-world KITTI benchmarks under both occluded and non-occluded conditions. + +# 2. Related Work + +# 2.1. Scene Flow Estimation on Point Clouds + +The first study in solving flow estimation on raw point clouds with learning-based methods was FlowNet3D [19]. FlowNet3D exploited hierarchical PointNet++ [26] and a local correlation learning layer to estimate the scene flow from two raw point cloud frames. Following this scheme, FlowNet3D++ [33] and HCRF-Flow [18] were proposed to further refine the final estimation by introducing auxiliary geometric constraints and high-order CRFs, respectively. However, the performance of these FlowNet3D-based models was restricted by the single-scale flow correlation. To address this flaw, HPLFlownet [10] was proposed in order to capture multi-scale correlations. PointPWC-Net [36] further suggested a coarse-to-fine architecture to regress multi-scale scene flow by applying local correlation extraction hierarchically. Based on the coarse-to-fine design, OGSFNet [24] additionally estimated occlusion masks with an occlusion-aware correlation layer. Furthermore, Bi-PointFlowNet [4] introduced a bidirectional mechanism to bidirectionally propagate point features for informative correlation extraction. + +Nevertheless, the above-mentioned approaches all rely on the local correlation, which has a limit on estimation accuracy when corresponding points are out of the local region. However, the hybrid correlation proposed in this work can alleviate this limitation by considering both local correlation and semantic correlation. + +# 2.2. Recurrent Models for Flow Estimation + +Many recent studies have demonstrated a reasonable performance by employing a recurrent architecture to itera- + +![](images/4af0d04d3e60bec9789e420426df78fd6d0ab5047520a645e732ecf911f33906.jpg) +Figure 3. Architecture of MSBRN for scene flow estimation. First, the two consecutive input point frames are fed into the shared hierarchical feature extraction module for multi-level features. At each level, a novel BGRU bidirectionally augments point features and iteratively optimizes correlations and flow predictions. The upsampling layers are adopted between adjacent levels for propagating features and flows from high levels to low levels. The figure is best viewed in color. + +tively refine the estimations [13, 21, 30, 31, 34, 15]. Inspired by the previous iterative refinement models [14, 28, 11, 9, 6], IRR [13] reused its whole architecture as a recurrent unit to iteratively optimize the optical flow. Lv et. al. proposed a approach that iterates a learning-based Inverse Compositional algorithm to optimize dense 3D rigid motion. To further improve the efficiency and convergence, RAFT [30] developed a 4D all-to-all correlation volume with the use of a gated recurrent unit (GRU). Based on RAFT, RAFT-3D [31] promoted the recurrent scheme into scene flow estimation by iteratively estimating a dense field of per-pixel SE(3) motion. Afterward, PV-RAFT [34] was proposed to iteratively capture the point-voxel correlation for scene flow estimation from the point cloud inputs. Different from the RAFT-series methods, FlowStep3D [15] and RCP [9] iteratively optimized the correlation that gradually aligns point clouds based on the iterative closest point (ICP) algorithm [3, 1]. FlowStep3D [15] deployed a gated recurrent unit and the source frame warping for iterative updates correlation at a single dense resolution. Similarly, RCP [9] performed iterative point-wise optimization and subsequently introduced the GRU for regularization. Dong et al. [6] introduced direct multi-body rigidity constraints to a GRU-based recurrent neural network for robust iterative optimization of scene flow estimation. There are several other approaches [25, 17] that treated scene flow estimation as solving an optimal transport problem. They typically required point-wise features to iteratively optimize the all-to-all correlation. + +Nevertheless, the existing iterative methods proceed with the optimization only at a single resolution. To achieve acceptable accuracy, they typically optimize dense resolution, which severely restricts the estimation efficiency. Therefore, we introduce a multi-scale iterative optimization to achieve high accuracy while maintaining high efficiency. + +# 3. MSBRN Architecture + +The goal of the scene flow estimation task is to estimate 3D point-wise motion vectors representing the non-rigid transformation from two consecutive point frames sampled from a dynamic scene. To solve this task, we propose MSBRN, a coarse-to-fine bidirectional recurrent architecture with the feature-induced correlation, as shown in Figure 3. MSBRN accepts as input the consecutive source and target frames that are represented by only 3D coordinates, $S = \{s_i \in \mathbb{R}^3\}_{i=1}^N$ and $T = \{t_j \in \mathbb{R}^3\}_{j=1}^M$ , where $N$ and $M$ denote the number of points in the source and target frame, respectively. Note that, $N$ and $M$ are not necessarily to be equal because of the sparsity and occlusion in a point cloud. The expected output of MSBRN are 3D scene flow vectors $V = \{v_i \in \mathbb{R}^3\}_{i=1}^N$ that describe the 3D displacement for every point in the source frame aligning with the target frame. + +Similar to the previous studies [36, 4], MSBRN is implemented as a coarse-to-fine architecture (Sec. 3.3) with the assistance of two existing modules: a multi-scale feature extraction module that extracts multi-scale point features and an upsampling layer that propagates features from higher scales to lower scales. At each upsampled scale, we deploy a novel BGRU (Sec. 3.1) to iteratively augment correlations and optimize scene flows. BGRU also applies a novel hybrid correlation (Sec. 3.2) in order to enhance the quality of the captured correlations. + +# 3.1. Bidirectional Gated Recurrent Unit + +We propose a novel BGRU that not only optimizes correlations but also augments point features of both frames bidirectionally and iteratively in various scales, as shown in Figure 4. In contrast, the previous methods [15, 9] that only apply conventional recurrent units to iteratively optimize only correlations for flow estimation in only one single scale. For each specific scale $l$ , the BGRU accepts source + +![](images/d319ee33d0987d0f1b98f95fa61c49617eeec2197fa0080c97b41c081e4c3bea.jpg) +Figure 4. Structure of the bidirectional gated recurrent unit (BGRU). The proposed BGRU accepts source/target point features, flow estimations and correlations from the previous scale as input and hidden states. The source/target point features are first bidirectionally updated and fed to the proposed hybrid correlation for the candidate correlation generation. Subsequent GRU utilizes the candidate correlations for iteratively updating the correlation states. + +point coordinates and features $S^{l,0} = \{(s^l,f^{(l,0)})\}$ , target point coordinates and features $T^{l,0} = \{(t^l,g^{(l,0)})\}$ , correlations $E^{l,0}$ and flow $V^{l,0}$ as input as well as hidden state variables that will be iteratively updated. After $K$ iterations, updated $P^{l,K}, Q^{l,K}, E^{l,K}$ and $V^{l,K}$ are sent to the subsequent scale. In this section, we focus on one specific scale and omit the notation $l$ for clarity. + +Warping: Warping enables the source points to progressively approach the target frame. The estimated scene flows of upsampling layers (for the first iteration only) or previous iterations are immediately accumulated to the source frame, i.e. $s = v^{k - 1} + s$ . The warped source points are further fed to the subsequent feature augmentation for more accurate correlation extraction. + +Iterative Bidirectional Feature Augmentation (IBFA): IBFA accepts as input two frames of point coordinates and corresponding features from the previous $(k - 1)$ -th iteration, $S^{k - 1} = \{(s,f^{k - 1})\}$ and $T^{k - 1} = \{(t,g^{k - 1})\}$ . For each point in both frames, the features are augmented bidirectionally for the current $k$ -th iteration by aggregating features from the other frame as follows: + +$$ +f ^ {k} = \underset {\left(t _ {i}, g _ {i} ^ {k - 1}\right) \in \mathcal {N} _ {T} ^ {k - 1} \left\{\left(s, f ^ {k - 1}\right) \right\}} {\operatorname {S e t C o n v}} \left(\left[ t _ {i} - s, g _ {i} ^ {k - 1}, f ^ {k - 1} \right]\right), \tag {1} +$$ + +$$ +g ^ {k} = \underset {\left(s _ {j}, f _ {j} ^ {k - 1}\right) \in \mathcal {N} _ {S} ^ {k - 1} \{(t, g ^ {k - 1}) \}} {\operatorname {S e t C o n v}} \left(\left[ s _ {j} - t, f _ {j} ^ {k - 1}, g ^ {k - 1} \right]\right), \tag {2} +$$ + +where SetConv [19] is composed of a shared multi-layer perceptron and a maxpooling layer, $\mathcal{N}_T\{(s,\cdot)\}$ denotes the nearest neighbor points of $s$ in $T$ , subscript $i,j$ indicate the indices of points in the neighbor group $\mathcal{N}$ , and $[\cdot ,\cdot ]$ denotes the channel concatenation operator. Note that, the + +SetConv in Equation (1) and (2) share the equivalent parameters. The output are buffered as hidden states for the subsequent iteration or scale. + +Iterative Correlation Update: The bidirectionally-augmented features are fed to the hybrid correlation extraction module (Sec. 3.2) to generate candidate correlation features. The candidate correlations serve as the input to a GRU in order to update the state correlation features from the previous iteration. Formally, the correlation features updated by the current iteration is denoted as: + +$$ +z = \sigma \left(\underset {\left(s _ {i}, \tilde {e} _ {i} ^ {k}\right) \in \mathcal {N} _ {\tilde {S}} ^ {k - 1} \{(s, e ^ {k - 1}) \}} {\operatorname {S e t C o n v} _ {z}} \left([ s _ {i} - s, e ^ {k - 1}, \tilde {e} _ {i} ^ {k} ]\right)\right), \tag {3} +$$ + +$$ +r _ {i} = \sigma (M L P _ {r} ([ s _ {i} - s, e ^ {k - 1}, \widetilde {e} _ {i} ^ {k} ])), \qquad (4) +$$ + +$$ +\hat {e} ^ {k} = \tanh \left(\underset {\left(s _ {i}, \tilde {e} _ {i} ^ {k}\right) \in \mathcal {N} _ {\tilde {S}} ^ {k - 1} \left\{\left(s, e ^ {k - 1}\right) \right\}} {\operatorname {S e t C o n v} _ {h}} \left(\left[ s _ {i} - s, e ^ {k - 1} \odot r _ {i}, \tilde {e} _ {i} ^ {k}\right)\right), \right. \tag {5} +$$ + +$$ +e ^ {k} = (1 - z) \odot e ^ {k - 1} + z \odot \hat {e} ^ {k}, \tag {6} +$$ + +where $\odot$ denotes the Hadamard product. + +Scene Flow Estimation: Given the updated correlation feature of each point, an MLP is followed to transform the correlation into a flow vector. Additionally, we introduce a residual mechanism by estimating the flow vector refinement $\Delta V_{k}$ . The final flow estimation is then accumulated as $V^{k} = V^{k - 1} + \Delta V^{k}$ . + +# 3.2. Hybrid Correlation + +Feature-induced Correlation: Instead of capturing neighbor points in the conventional Euclidean space, we fetch + +neighbor points from the latent feature space in order to acquire semantically correlative points. For instance, Figure 2 shows that the proposed correlation can capture semantically similar points (front windscreen) even if they are far away. Thus, the proposed correlation is different from the Euclidean-based correlation that may capture semantically unrelated points (bumper). Formally, given two point sets consisted of 3-dimensional coordinates and $C$ -dimensional features $S = \{(s,f)|s\in \mathbb{R}^3,f\in \mathbb{R}^C\}$ and $T = \{(t,g)|t\in \mathbb{R}^3,g\in \mathbb{R}^C\}$ , for each point $(s,f)\in S$ , its collected neighbor points $\mathcal{N}_T\{(s,f)\}$ from $T$ satisfy $\delta (f,g_i) < \delta (f,g_j)$ , when $\forall (t_i,g_i)\subset \mathcal{N}_T\{(s,f)\}$ and $(t_j,g_j)\subset Q\backslash \mathcal{N}_T\{(p,f)\}$ . Note that, $|\mathcal{N}_T\{(s,f)\}| = K$ is the hyperparameter that defines the amount of the top-K neighbor points, and $\delta (\cdot ,\cdot)$ is the cosine similarity measure. + +After the corresponding points are collected, the features of the collected points are further aggregated by a learnable symmetric function. Hence, the correlation feature for each point $(p,f)\in P$ is formally denoted as: + +$$ +\widetilde {e} = \underset {\left(t _ {i}, g _ {i}\right) \in \mathcal {N} _ {T} \left\{\left(s, f\right) \right\}} {\operatorname {S e t C o n v}} \left(\left[ t _ {i} - s, g _ {i}, f \right]\right). \tag {7} +$$ + +Hybrid Correlation: Considering that the conventional grouping can capture fine-grained local motion and the proposed feature-induced grouping can capture correspondence regardless of distances, we integrate the two techniques to take advantage of both correlation extraction strategies. Thus, we fuse the collected points with the feature-induced grouping and conventional grouping as a hybrid neighbor set $\mathcal{N}_T\{(s,f)\}$ in Equation (7) for the subsequent correlation aggregation. + +# 3.3. Coarse-to-Fine Architecture + +In this section, we thus introduce two existing layers [36] to construct a coarse-to-fine network for multi-scale feature generation and propagation. + +Multi-scale Feature Extraction: The multi-scale feature extraction follows the design that is commonly used in point cloud processing [26, 35]. The feature extraction generates $L$ -level pyramid of point features, where the top level is the input point clouds. At each level $l$ , dense input points and their corresponding features are first subsampled through the furthest point sampling, which forms a sparse point set. Then, for each subsampled sparse point, the $k$ -nearest neighbor groups dense points locally forming a local region for the feature extraction. Afterwards, a Pointconv [35] layer is applied to aggregate the features from the grouped local points through dynamic weights learned on their local coordinates, and produced the local feature for each sparse point. + +Upsampling Layer: Since each level produces scene flows and iteratively augmented bidirectional features and correlations, we introduced the upsampling layer to propagate + +these features to the following level for a denser optimization. Following the previous works [36, 4], the upsampling layer adopts the 3D interpolation that aggregates $k$ nearest neighbors with their inverse distances as weights. Specifically, in the case of upsampling correlations from the $l$ -th level to the $(l - 1)$ -th level, the input to the upsampling layer are $l$ -th level's sparse coordinates $\{x_j^l\}_{j = 1}^{N^l}$ , $l$ -th level's correlations $\{e_j^l\}_{j = 1}^{N^l}$ and $(l - 1)$ -th level's dense coordinates $\{x_i^{l - 1}\}_{i = 1}^{N^{l - 1}}$ , where $N^{l - 1}$ and $N^l$ are the number of points and $N^{l - 1} > N^l$ . The interpolated feature for each point $x_{i}^{l}$ in the dense $(l - 1)$ -th level is defined as: + +$$ +e _ {i} ^ {l - 1} = \frac {\sum_ {j = 1} ^ {k} w \left(x _ {j} ^ {l} , x _ {i} ^ {l - 1}\right) e _ {j} ^ {l}}{\sum_ {j = 1} ^ {k} w \left(x _ {j} ^ {l} , x _ {i} ^ {l - 1}\right)}, \tag {8} +$$ + +where $w(x_{j}^{l},x_{i}^{l - 1}) = 1 / ||x_{j}^{l} - x_{i}^{l - 1}||_{2}$ , and $k = 3$ as suggested by the previous studies [4, 36]. + +# 3.4. Loss Function + +Following the previous studies for optical flow estimation [7, 29] and scene flow estimation [32, 36, 4], we train the proposed model in the multi-scale supervision manner. Furthermore, we also supervise the estimations of all intermediate iterations at each scale. All the estimated flows are supervised by the ground truth with the L2 measure. Let $\{v_i^{l,k}\}_{i=1}^N$ denote the scene flow vectors estimated from the $k$ -th iteration at the $l$ -th level and $\{\hat{v}_i^l\}_{i=1}^N$ denote the ground truth scene flow vectors of the $l$ -th scale. The training loss is defined as: + +$$ +\mathcal {L} = \sum_ {l = 0} ^ {L - 1} \alpha^ {l} \sum_ {k = 1} ^ {K} \sum_ {i = 1} ^ {N ^ {l}} \| \hat {v} _ {i} ^ {l} - v _ {i} ^ {l, k} \| _ {2}, \tag {9} +$$ + +where $\alpha^l$ is the weight for scale $l$ . The weights are $\alpha^0 = 0.16, \alpha^1 = 0.08, \alpha^2 = 0.04, \alpha^3 = 0.02$ by default. + +# 4. Experiments + +# 4.1. Experimental Settings + +As shown in Fig. 3, we implemented a hierarchical model with $L = 4$ scales. We used $N = M = 8$ , 192 points as inputs. The point numbers of each scale are defined as $N^1 = 2$ , 048, $N^2 = 512$ , $N^3 = 256$ , and $N^4 = 64$ . We adopted the synthetic FlyingThings3D [22] dataset and the real-world KITTI Scene Flow 2015 [23] dataset to evaluate our model. As in the previous methods, we trained networks only on the synthetic FlyingThings3D dataset and validated the performance on the FlyingThings3D dataset (Sec. 4.3). Finally, we directly evaluated the model trained on FlyingThings3D without any fine-tuning to validate the generalization ability on the real-world KITTI dataset (Sec. 4.4). The experiments are conducted on an NVIDIA Titan RTX GPU with PyTorch. + +
DatasetMethodEPE3D (m) ↓ACC3DS ↑ACC3DR ↑Outliers3D ↓EPE2D (px) ↓ACC2D ↑
FT3DsFlowNet3D [19]0.1130.4120.7710.6025.9740.569
HPLFlowNet [10]0.0800.6140.8550.4294.6720.676
PointPWC [36]0.0590.7380.9280.3423.2390.799
FLOT [25]0.0520.7320.9270.357--
HCRF-Flow [18]0.0480.8350.9500.2612.5650.870
PV-RAFT [34]0.0460.8160.9570.292--
FlowStep3D [15]0.0450.8160.9610.216--
RCP [9]0.0400.8560.9630.197--
Bi-PointFlowNet [4]0.0280.9180.9780.1431.5820.929
Ours0.0150.9730.9920.0560.8330.970
KITTsFlowNet3D [19]0.1770.3740.6680.5277.2140.509
HPLFlowNet [10]0.1170.4780.7780.4104.8050.593
PointPWC [36]0.0690.7280.8880.2651.9020.866
FLOT [25]0.0560.7550.9080.242--
HCRF-Flow [18]0.0530.8630.9440.1792.0700.865
PV-RAFT [34]0.0560.8220.9370.216--
FlowStep3D [15]0.0540.8050.9250.149--
RCP [9]0.0480.8490.9440.122--
Bi-PointFlowNet [4]0.0300.9200.9600.1411.0560.949
Ours0.0110.9710.9890.0850.4430.985
+ +Table 1. Comparison of the proposed method with previous state-of-the-art methods on the non-occluded FT3D ${}_{s}$ and KITTI ${}_{s}$ datasets. All methods are trained only on the FT3D ${}_{s}$ dataset. + +# 4.2. Evaluation Measures + +For a fair comparison, we adopted the same evaluation measures that are used in the related works [10, 36, 25, 15, 18, 4]. + +EPE3D, EPE3Dfull (m): the main evaluation measure measuring 3D end-point-error $\| \hat{v}_i^l - v_i^l\|_2$ averaged over non-occluded points and all points, respectively. + +ACC3DS: the percentage of points that satisfy EPE3D $< 0.05\mathrm{m}$ or relative error $< 5\%$ . + +ACC3DR: the percentage of points that satisfy EPE3D $< 0.1\mathrm{m}$ or relative error $< 10\%$ . + +Outliers3D: the percentage of points that satisfy EPE3D $>0.3\mathrm{m}$ or relative error $>10\%$ . + +EPE2D (px): 2D end-point-error measured by projecting points back to the 2D image plane, which is a common measure for optical flow evaluation. + +ACC2D: the percentage of points that satisfy EPE2D $< 3\mathrm{px}$ or relative error $< 5\%$ . + +# 4.3. Training and Evaluation on FlyingThings3D + +Due to the challenge with labeling for dense point cloud scenes, recent models [10, 36, 25, 15, 18, 4] only utilized the synthetic FlyingThing3D dataset for training. The FlyingThing3D [22] dataset provides 19,640 pairs of frames for training and 3,824 pairs of frames for testing. Each frame contains synthetic stereo and RGB-D images rendered from virtual scenes with multiple moving objects sampled from the ShapeNet [2] dataset. We follow the same preprocessing + +that generates two subsets: $\mathrm{FT3D}_o$ that includes occluded points and $\mathrm{FT3D}_s$ that excludes the occluded points, as suggested in [10, 36, 25, 4]. The consecutive input frames are formed by randomly sampling $N = 8$ , 192 of points from the dataset with non-correspondence. + +For training, we used the AdamW optimizer [20] with beta1 = 0.9, beta2 = 0.999. The learning rate is initially set as $\alpha = 0.0001$ and reduced by half every 80 epochs. We trained the model for a total of 560 epochs. The numbers of iterations for all BGRUs are set to $K_{tr} = 4$ during training and $K_{in} = 4$ during testing. + +Results. We compared the performance of the proposed model with other state-of-the-art approaches based on point cloud [19, 10, 36, 25, 15, 24, 9, 4]. As presented in Table 1, the proposed method significantly outperforms all recent state-of-the-art methods with more than $46\%$ reduction of estimation error under the non-occluded condition. When compared to the related iterative methods FlowStep3D [15] and RCP [9], our model achieves an error reduction of $62\%$ . + +# 4.4. Generalization on KITTI + +Following the same evaluation strategy as in the recent studies [19, 10, 36, 25, 15, 24, 4], we evaluated the generalization ability of MSBRN on the real-world KITTI [23] dataset with the model that was only trained on the synthetic dataset. The KITTI dataset provides 200 scenes for training and 200 scenes for testing. However, the disparities were missing in the testing scene and parts of the training scenes. Thus, 142 non-occluded scenes (KITTI $_s$ , re + +
DatasetMethodEPE3Dfull (m) ↓EPE3D (m) ↓ACC3DS ↑ACC3DR ↑Outliers3D ↓
FT3DoFlowNet3D [19]0.2110.1570.2280.5820.804
HPLFlowNet [10]0.2010.1680.2620.5740.812
FLOT [25]0.2500.1530.3960.6600.662
PointPWC [36]0.1950.1550.4160.6990.638
OGSFNet [24]0.1630.1210.5510.7760.518
Bi-PointFlowNet [4]0.1020.0730.7910.8960.274
Ours0.0800.0530.8360.9260.231
KITTIoFlowNet3D [19]0.183-0.0980.3940.799
HPLFlowNet [10]0.343-0.1030.3860.814
FLOT [25]0.130-0.2780.6670.529
PointPWC [36]0.118-0.4030.7570.496
OGSFNet [24]0.075-0.7060.8690.327
Bi-PointFlowNet [4]0.065-0.7690.9060.264
Ours0.044-0.8730.9500.208
+ +Table 2. Comparison of the proposed method with previous state-of-the-art methods on the occluded FT3DO and KITTIO datasets. All methods are trained only on the FT3DO dataset. + +![](images/fff2732f2eabc30e696b353368435ff79df34285d8218c14033e602128e60a0e.jpg) +Figure 5. Qualitative results of MSBRN on the non-occluded KITTI dataset. Points are colored to indicate points as from source frame, target frame or as MSBRN estimated points (source frame + scene flow). + +moving occluded points) and 150 occluded scenes (KITTI $_o$ , remaining occluded points) were available for evaluation with raw point clouds. We removed ground points by height $< 0.3$ m as suggested by the previous approaches [19, 10, 36, 25, 15, 24] for a fair comparison. + +Results. We compared the generalization ability of MSBRN with the existing state-of-the-art methods based on point cloud [19, 10, 36, 25, 15, 24, 9, 4]. As shown in Table 1 and 2, our proposed method represented the state-of-the-art generality when the model is trained on the synthetic datasets and tested on and real-world KITTI dataset. Our method significantly outperforms other methods by a large margin. Focusing on the main EPE3D measure, our method outperforms the recent state-of-the-art with $63\%$ of error reduction on the non-occluded scenes. Compared to the similar iterative methods FlowStep3D [15] and RCP [9], our method shows over $77\%$ of error reduction. Moreover, our + +model shows the superior generality on the occluded scenes, as shown in Table 2. Our model shows an over $32\%$ reduction of $\mathrm{EPE3D_{full}}$ . + +# 4.5. Ablation Study + +Number of Iterations. The iteration number of the BGRU is a significant factor that affects the estimation accuracy. It is worth noting that the iteration configuration can be different between the training stage $(K_{tr})$ and the evaluation stage $(K_{in})$ . Therefore, we trained and evaluated our method with the different iteration numbers. Note that, all levels proceed with the same iteration number as configured. Table 3 reports the performance comparison between models with the different numbers of BGRU iterations. The result shows that iteratively adopting the proposed BGRU effectively reduces the estimation error on both the synthetic dataset and the real-world dataset. The model delivers + +
\(K_{tr}\)EPE3D (m) @ \(K_{in}\)
123456
FT3\(d_s\)10.0260.0710.1010.1490.2040.281
20.0330.0210.0300.0370.0460.049
30.0380.0200.0160.0160.0160.018
40.0400.0240.0170.0150.0150.015
50.0490.0270.0190.0150.0140.014
KITTLs10.0380.1290.1120.1460.1720.230
20.0390.0220.0400.0690.0570.076
30.0390.0210.0150.0140.0130.013
40.0400.0220.0150.0110.0100.009
50.0570.0310.0210.0170.0130.012
+ +Table 3. Comparison on the EPE2D metric between different training/inference iteration configurations. The model is first trained under a specific $K_{tr}$ on the FT3Ds dataset and then evaluated with various $K_{ins}$ on both FT3Ds and KITTIs dataset. + +
Correlation type +# neighbor (dist:feat)Euclidean +(32:0)Hybrid +(16:16)Feature +(0:32)
EPE3D (m)FT3Ds0.0190.0160.022
KITTs0.0180.0150.036
+ +Table 4. Comparison between different numbers of the neighbor points for the correlation extraction. 'Dist' and 'feat' indicate the Euclidean distance-based neighbor points and the feature-induced neighbor points, respectively. + +
IBFAHCGRUFT3Ds EPE3D (m)KITTIs EPE3D (m)
×××0.0290.030
✓××0.0250.025
×✓×0.0290.038
✓×✓0.0190.018
✓✓×0.0210.018
×✓✓0.0270.033
✓✓✓0.0160.015
+ +the optimal estimation performance when $K_{tr} = 4$ . Moreover, the model also demonstrated that the performance is saturated at $K_{tr} = 5$ . On the other hand, we observe that the model keeps improving for a few more iterations even though the inference $K_{in}$ is larger than the training when the training $K_{tr} \geq 3$ . However, the improvement is negligible thus we stop evaluating at $K_{in} = K_{tr}$ . + +Hybrid Correlation. As mentioned in Section 3.2, the hybrid correlation consists of the Euclidean distance-based correlation and the proposed feature-induced correlation, thus can benefit from both of their advantages. To val + +Table 5. Ablations of different components. IBFA, HC and GRU represent whether the iterative bidirectional feature augmentation, hybrid correlation and GRU are deployed in the model, respectively. The iterative models are trained and evaluated with $K_{tr} = K_{in} = 3$ . + +
MethodRuntimeMethodRuntime
PV-RAFT [34]781.1msOurs (Kin=2)209.6ms
FlowStep3D [15]972.7msOurs (Kin=3)287.6ms
RCP [9]2854.6msOurs (Kin=4)365.8ms
+ +Table 6. Runtime comparison of iterative methods. The results are evaluated on a single TITAN RTX GPU. PV-RAFT, FlowStep3D and RCP are evaluated with their optimal iteration configurations which are 32, 4 and 14, respectively. + +idate the effectiveness of the hybrid correlation (16:16), we implemented two ablation experiments: a model with only the Euclidean distance-based correlation (32:0) and a model with only the proposed feature-induced correlation (0:32). Note that, the numbers in brackets indicate the number of Euclidean neighbor points and the number of feature-induced neighbor points, respectively. The total number of neighbor points is fixed at 32 for all experiments for a fair comparison. As demonstrated in Table 4, introducing our feature-induced correlation in the conventional Euclidean distance-based approaches can boost performance. However, the proposed feature-induced correlation must work with the Euclidean distance-based correlation. It is because the feature-induced correlation can capture semantically similar points from other instances located far away. Additionally applying the Euclidean distance-based correlation can introduce a proper constraint on the range. + +Analysis of different BGRU configurations. To verify the contributions of the proposed components in the BGRU, we incrementally adopted the IBFA, hybrid correlation, and GRU based on a baseline model. Note that, the baseline model replaces IBFA and the hybrid correlation with BFP [4] and the distance-based correlation, respectively, and removes GRU. As shown in Table 5, IBFA, hybrid correlation and GRU all contribute considerably to the effective estimation. In particular, IBFA improves the accuracy by 0.5 mm on KITTI. Furthermore, using the hybrid correlation and GRU mechanism further reduces the estimation error by $0.7\mathrm{mm}$ and $0.3\mathrm{mm}$ on KITTI, respectively. However, Table 5 also reveals that the hybrid correlation and GRU must cooperate with IBFA to get convincing improvement. + +# 4.6. Runtime + +We compare the running time of our proposed methods to other state-of-the-art iterative approaches [34, 15, 9] in Table 6. All methods are measured on a single NVIDIA Titan RTX GPU. Table 6 and 1 show that our proposed method outperforms by a large margin in terms of running time while achieving superior accuracy and generality. Even under $K_{in} = 2$ , our method also presents outperformed accuracy with faster speed compared to the existing iterative approaches. + +# 5. Conclusion + +This paper presented MSBRN, a novel recurrent bidirectional architecture that is capable of iteratively estimating progressively accurate multi-scale 3D scene flows from two consecutive point cloud frames. Our proposed network also utilized the hybrid correlation for improved flow estimation performance. Experimental results showed that our network significantly outperforms previous state-of-the-art methods on two challenging benchmarks. The proposed method also showed superior efficiency compared to existing iterative state-of-the-art. Extensive experiments also demonstrated the excellent effectiveness of the novel components proposed in this work. + +# Acknowledgement + +This work was supported by the Ministry of Science and ICT (MSIT) of Korea under the National Research Foundation (NRF) grant (2022R1A4A3032913) and the Institute of Information and Communication Technology Planning Evaluation (IITP) grants (IITP-2019-0-00421, IITP-2023-2020-0-01821, IITP-2021-0-02052, IITP-2021-0-02068), and by the Technology Innovation Program (RS-2023-00235718) funded by the Ministry of Trade, Industry & Energy (1415187474). Wencan Cheng was partly supported by the China Scholarship Council (CSC). + +# References + +[1] Paul J Besl and Neil D McKay. Method for registration of 3-d shapes. 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In this paper, we propose a novel multi-scale bidirectional recurrent architecture that iteratively optimizes the coarse-to-fine scene flow estimation. In each resolution scale of estimation, a novel bidirectional gated recurrent unit is proposed to bidirectionally and iteratively augment point features and produce progressively optimized scene flow. The optimization of each iteration is integrated with the hybrid correlation that captures not only local correlation but also semantic correlation for more accurate estimation. Experimental results indicate that our proposed architecture significantly outperforms the existing state-of-the-art approaches on both FlyingThings3D and KITTI benchmarks while maintaining superior time efficiency. Codes and pre-trained models are publicly available at https://github.com/cwc1260/MSBRN." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 512, + 128, + 525 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 512, + 128, + 525 + ], + "spans": [ + { + "bbox": [ + 47, + 512, + 128, + 525 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 533, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 287, + 605 + ], + "type": "text", + "content": "Scene flow estimation is a fundamental task that estimates the dense 3D motion field of points from two consecutive frames [32, 19]. As it provides the basic motion understanding of a dynamic environment, it is meaningful in a variety of high-level applications such as autonomous driving, augmented reality, and robotics [15]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 605, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 714 + ], + "type": "text", + "content": "Early scene flow estimation approaches rely on 2D representations such as RGB images [14, 11, 13, 28, 12]. They basically estimate optical flow and disparity map separately in the 2D space instead of directly estimating scene flow vectors in the 3D space. Recently, with the advances in LiDAR sensors and point cloud-based learning technologies, learning scene flow directly from point clouds has been extensively studied. The pioneering work known as FlowNet3D [19] is the first to introduce hierarchical Point-" + } + ] + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 319, + 245, + 538, + 355 + ], + "blocks": [ + { + "bbox": [ + 319, + 245, + 538, + 355 + ], + "lines": [ + { + "bbox": [ + 319, + 245, + 538, + 355 + ], + "spans": [ + { + "bbox": [ + 319, + 245, + 538, + 355 + ], + "type": "image", + "image_path": "820978a1b7801a6eeb9540813f9ba603965a8cfe472872e245fae135ff5f4c87.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 359, + 547, + 460 + ], + "lines": [ + { + "bbox": [ + 305, + 359, + 547, + 460 + ], + "spans": [ + { + "bbox": [ + 305, + 359, + 547, + 460 + ], + "type": "text", + "content": "Figure 1. Illustration of the multi-scale bidirectional recurrent network for scene flow estimation. The multi-scale features extracted from each input frame are fed into novel bidirectional gated recurrent units (BGRUs) that respectively iterates " + }, + { + "bbox": [ + 305, + 359, + 547, + 460 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 305, + 359, + 547, + 460 + ], + "type": "text", + "content": " times for optimizing scene flows on each scale. Introducing hybrid correlation (HC) further improves the performance by searching correspondence in both the Euclidean and latent feature space. The estimated scene flows are warped with the source frame for a clear comparison with the target frame." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 483, + 547, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 483, + 547, + 533 + ], + "spans": [ + { + "bbox": [ + 305, + 483, + 547, + 533 + ], + "type": "inline_equation", + "content": "\\mathrm{Net}++" + }, + { + "bbox": [ + 305, + 483, + 547, + 533 + ], + "type": "text", + "content": " [26] to directly predict the 3D scene flow based on the point cloud. Following this work, a diverse variety of architectures [33, 36, 9, 32, 15] have been proposed and significantly enhanced performance." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 534, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 547, + 715 + ], + "type": "text", + "content": "Recently, there is a rising trend of iteratively optimizing estimated scene flow by utilizing the recurrent scheme [15, 9, 31] to progressively improve the estimation accuracy. However, they only focus on optimizing single resolution scale which causes large computation latency. On the other hand, another series of works [28, 4] presented their superior efficiency by estimating multi-scale scene flow in a coarse-to-fine manner. However, their single-shot estimation on each scale restricts their performance. To achieve high estimation accuracy while holding high efficiency, we propose an effective and efficient architecture, Multi-Scale Bidirectional Recurrent Network (MSBRN), that iteratively optimizes coarse-to-fine scene flow. Moreover, in our view, the optimization phases of scene flow can be regarded as temporal sequences, which can benefit from the bidirectional" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 317, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 758 + ], + "type": "text", + "content": "10041" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 71, + 285, + 168 + ], + "blocks": [ + { + "bbox": [ + 48, + 71, + 285, + 168 + ], + "lines": [ + { + "bbox": [ + 48, + 71, + 285, + 168 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 285, + 168 + ], + "type": "image", + "image_path": "98f0da9118b1948bde152eedbbef2668155b5a6b2b9b3efcb8c9a5ab0393b79b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 173, + 287, + 218 + ], + "lines": [ + { + "bbox": [ + 46, + 173, + 287, + 218 + ], + "spans": [ + { + "bbox": [ + 46, + 173, + 287, + 218 + ], + "type": "text", + "content": "Figure 2. Examples of two variants of correlation extraction. The bold red and green points are the grouped correlated points of the bold blue source point through the feature-induced correlation and Euclidean distance-based correlation, respectively." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 242, + 286, + 301 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 242, + 286, + 301 + ], + "spans": [ + { + "bbox": [ + 46, + 242, + 286, + 301 + ], + "type": "text", + "content": "tional recurrent architecture [27, 8, 5, 16]. In each specific resolution scale, thus, we apply a novel bidirectional gated recurrent unit (BGRU) to bidirectionally and iteratively augment point features and produce progressively optimized scene flow." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 304, + 286, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 286, + 518 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 286, + 518 + ], + "type": "text", + "content": "Moreover, we also noticed a common limitation of current point cloud-based flow estimation approaches. They aggregate the grouped neighboring points in the Euclidean space when generating the correspondence features between two point frames. The correspondence grouping used in these methods generally exploits " + }, + { + "bbox": [ + 46, + 304, + 286, + 518 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 304, + 286, + 518 + ], + "type": "text", + "content": "-nearest-neighbor (kNN) that only focuses on a specific local region. Thus, these methods may be harmed by nearby non-correlated points in Euclidean space, as shown in Figure 2. To resolve these issues, we first proposed a feature-induced correlation that collects the nearest neighbor points in the latent feature space. Thus, the grouped points from the feature space are semantically related regardless of their distances in Euclidean space. Afterwards, we combined the proposed correlation with the conventional Euclidean distance-based correlation forming the hybrid correlation. Therefore, the network is able to capture distance-insensitive correspondences as well as local correlations." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 522, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 522, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 522, + 286, + 712 + ], + "type": "text", + "content": "We evaluated MSBRN on two challenging benchmarks, the synthetic dataset FlyingThings3D [22] and the real-world LiDAR scan dataset KITTI [23], under both occluded and non-occluded settings. Following the evaluation settings of previous studies, the proposed model is trained only on the FlyingThings3D dataset and evaluated on both datasets to confirm the accuracy and generalization performance. The experimental results show that MSBRN outperforms all other approaches on the FlyingThings3D dataset with " + }, + { + "bbox": [ + 46, + 522, + 286, + 712 + ], + "type": "inline_equation", + "content": "46\\%" + }, + { + "bbox": [ + 46, + 522, + 286, + 712 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 522, + 286, + 712 + ], + "type": "inline_equation", + "content": "27\\%" + }, + { + "bbox": [ + 46, + 522, + 286, + 712 + ], + "type": "text", + "content": " lower errors under the occluded and non-occluded conditions, respectively. Moreover, MSBRN achieves improved generality on the real-world KITTI dataset with " + }, + { + "bbox": [ + 46, + 522, + 286, + 712 + ], + "type": "inline_equation", + "content": "66\\%" + }, + { + "bbox": [ + 46, + 522, + 286, + 712 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 522, + 286, + 712 + ], + "type": "inline_equation", + "content": "32\\%" + }, + { + "bbox": [ + 46, + 522, + 286, + 712 + ], + "type": "text", + "content": " lower errors under the occluded and non-occluded conditions, respectively. Our MSBRN also shows better time efficiency while maintaining higher accuracy compared to other iterative state-of-the-arts." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 72, + 545, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 545, + 95 + ], + "type": "text", + "content": "The key contributions of this paper are summarized as follows:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 317, + 105, + 545, + 300 + ], + "type": "list", + "angle": 0, + "index": 9, + "blocks": [ + { + "bbox": [ + 317, + 105, + 545, + 189 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 105, + 545, + 189 + ], + "spans": [ + { + "bbox": [ + 317, + 105, + 545, + 189 + ], + "type": "text", + "content": "- We propose a novel multi-scale bidirectional recurrent architecture used for a 3D scene flow estimation task based on point cloud. The model can iteratively and bidirectionally enhance features and scene flow estimations in a coarse-to-fine manner in order to significantly improve the performance while maintaining high efficiency." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 317, + 198, + 545, + 245 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 198, + 545, + 245 + ], + "spans": [ + { + "bbox": [ + 317, + 198, + 545, + 245 + ], + "type": "text", + "content": "- We propose a hybrid correspondence grouping that collects corresponding points from the other point frame in both the latent feature space and Euclidean space." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 254, + 545, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 254, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 317, + 254, + 545, + 300 + ], + "type": "text", + "content": "- The proposed model achieves state-of-the-art performance and generality on the synthetic FlyingThings3D and real-world KITTI benchmarks under both occluded and non-occluded conditions." + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 313, + 392, + 325 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 313, + 392, + 325 + ], + "spans": [ + { + "bbox": [ + 306, + 313, + 392, + 325 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 333, + 512, + 344 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 333, + 512, + 344 + ], + "spans": [ + { + "bbox": [ + 306, + 333, + 512, + 344 + ], + "type": "text", + "content": "2.1. Scene Flow Estimation on Point Clouds" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 351, + 545, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 351, + 545, + 589 + ], + "spans": [ + { + "bbox": [ + 304, + 351, + 545, + 589 + ], + "type": "text", + "content": "The first study in solving flow estimation on raw point clouds with learning-based methods was FlowNet3D [19]. FlowNet3D exploited hierarchical PointNet++ [26] and a local correlation learning layer to estimate the scene flow from two raw point cloud frames. Following this scheme, FlowNet3D++ [33] and HCRF-Flow [18] were proposed to further refine the final estimation by introducing auxiliary geometric constraints and high-order CRFs, respectively. However, the performance of these FlowNet3D-based models was restricted by the single-scale flow correlation. To address this flaw, HPLFlownet [10] was proposed in order to capture multi-scale correlations. PointPWC-Net [36] further suggested a coarse-to-fine architecture to regress multi-scale scene flow by applying local correlation extraction hierarchically. Based on the coarse-to-fine design, OGSFNet [24] additionally estimated occlusion masks with an occlusion-aware correlation layer. Furthermore, Bi-PointFlowNet [4] introduced a bidirectional mechanism to bidirectionally propagate point features for informative correlation extraction." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 590, + 545, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 590, + 545, + 662 + ], + "spans": [ + { + "bbox": [ + 304, + 590, + 545, + 662 + ], + "type": "text", + "content": "Nevertheless, the above-mentioned approaches all rely on the local correlation, which has a limit on estimation accuracy when corresponding points are out of the local region. However, the hybrid correlation proposed in this work can alleviate this limitation by considering both local correlation and semantic correlation." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 670, + 509, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 670, + 509, + 682 + ], + "spans": [ + { + "bbox": [ + 306, + 670, + 509, + 682 + ], + "type": "text", + "content": "2.2. Recurrent Models for Flow Estimation" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "Many recent studies have demonstrated a reasonable performance by employing a recurrent architecture to itera-" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10042" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 75, + 548, + 198 + ], + "blocks": [ + { + "bbox": [ + 50, + 75, + 548, + 198 + ], + "lines": [ + { + "bbox": [ + 50, + 75, + 548, + 198 + ], + "spans": [ + { + "bbox": [ + 50, + 75, + 548, + 198 + ], + "type": "image", + "image_path": "4af0d04d3e60bec9789e420426df78fd6d0ab5047520a645e732ecf911f33906.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 202, + 547, + 248 + ], + "lines": [ + { + "bbox": [ + 46, + 202, + 547, + 248 + ], + "spans": [ + { + "bbox": [ + 46, + 202, + 547, + 248 + ], + "type": "text", + "content": "Figure 3. Architecture of MSBRN for scene flow estimation. First, the two consecutive input point frames are fed into the shared hierarchical feature extraction module for multi-level features. At each level, a novel BGRU bidirectionally augments point features and iteratively optimizes correlations and flow predictions. The upsampling layers are adopted between adjacent levels for propagating features and flows from high levels to low levels. The figure is best viewed in color." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 266, + 289, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 266, + 289, + 613 + ], + "spans": [ + { + "bbox": [ + 47, + 266, + 289, + 613 + ], + "type": "text", + "content": "tively refine the estimations [13, 21, 30, 31, 34, 15]. Inspired by the previous iterative refinement models [14, 28, 11, 9, 6], IRR [13] reused its whole architecture as a recurrent unit to iteratively optimize the optical flow. Lv et. al. proposed a approach that iterates a learning-based Inverse Compositional algorithm to optimize dense 3D rigid motion. To further improve the efficiency and convergence, RAFT [30] developed a 4D all-to-all correlation volume with the use of a gated recurrent unit (GRU). Based on RAFT, RAFT-3D [31] promoted the recurrent scheme into scene flow estimation by iteratively estimating a dense field of per-pixel SE(3) motion. Afterward, PV-RAFT [34] was proposed to iteratively capture the point-voxel correlation for scene flow estimation from the point cloud inputs. Different from the RAFT-series methods, FlowStep3D [15] and RCP [9] iteratively optimized the correlation that gradually aligns point clouds based on the iterative closest point (ICP) algorithm [3, 1]. FlowStep3D [15] deployed a gated recurrent unit and the source frame warping for iterative updates correlation at a single dense resolution. Similarly, RCP [9] performed iterative point-wise optimization and subsequently introduced the GRU for regularization. Dong et al. [6] introduced direct multi-body rigidity constraints to a GRU-based recurrent neural network for robust iterative optimization of scene flow estimation. There are several other approaches [25, 17] that treated scene flow estimation as solving an optimal transport problem. They typically required point-wise features to iteratively optimize the all-to-all correlation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "type": "text", + "content": "Nevertheless, the existing iterative methods proceed with the optimization only at a single resolution. To achieve acceptable accuracy, they typically optimize dense resolution, which severely restricts the estimation efficiency. Therefore, we introduce a multi-scale iterative optimization to achieve high accuracy while maintaining high efficiency." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 305, + 266, + 432, + 277 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 266, + 432, + 277 + ], + "spans": [ + { + "bbox": [ + 305, + 266, + 432, + 277 + ], + "type": "text", + "content": "3. MSBRN Architecture" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "spans": [ + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "text", + "content": "The goal of the scene flow estimation task is to estimate 3D point-wise motion vectors representing the non-rigid transformation from two consecutive point frames sampled from a dynamic scene. To solve this task, we propose MSBRN, a coarse-to-fine bidirectional recurrent architecture with the feature-induced correlation, as shown in Figure 3. MSBRN accepts as input the consecutive source and target frames that are represented by only 3D coordinates, " + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "inline_equation", + "content": "S = \\{s_i \\in \\mathbb{R}^3\\}_{i=1}^N" + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "inline_equation", + "content": "T = \\{t_j \\in \\mathbb{R}^3\\}_{j=1}^M" + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "text", + "content": " denote the number of points in the source and target frame, respectively. Note that, " + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "text", + "content": " are not necessarily to be equal because of the sparsity and occlusion in a point cloud. The expected output of MSBRN are 3D scene flow vectors " + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "inline_equation", + "content": "V = \\{v_i \\in \\mathbb{R}^3\\}_{i=1}^N" + }, + { + "bbox": [ + 304, + 287, + 545, + 478 + ], + "type": "text", + "content": " that describe the 3D displacement for every point in the source frame aligning with the target frame." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 479, + 546, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 479, + 546, + 598 + ], + "spans": [ + { + "bbox": [ + 304, + 479, + 546, + 598 + ], + "type": "text", + "content": "Similar to the previous studies [36, 4], MSBRN is implemented as a coarse-to-fine architecture (Sec. 3.3) with the assistance of two existing modules: a multi-scale feature extraction module that extracts multi-scale point features and an upsampling layer that propagates features from higher scales to lower scales. At each upsampled scale, we deploy a novel BGRU (Sec. 3.1) to iteratively augment correlations and optimize scene flows. BGRU also applies a novel hybrid correlation (Sec. 3.2) in order to enhance the quality of the captured correlations." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 610, + 495, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 610, + 495, + 621 + ], + "spans": [ + { + "bbox": [ + 306, + 610, + 495, + 621 + ], + "type": "text", + "content": "3.1. Bidirectional Gated Recurrent Unit" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "We propose a novel BGRU that not only optimizes correlations but also augments point features of both frames bidirectionally and iteratively in various scales, as shown in Figure 4. In contrast, the previous methods [15, 9] that only apply conventional recurrent units to iteratively optimize only correlations for flow estimation in only one single scale. For each specific scale " + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": ", the BGRU accepts source" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10043" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 69, + 547, + 245 + ], + "blocks": [ + { + "bbox": [ + 53, + 69, + 547, + 245 + ], + "lines": [ + { + "bbox": [ + 53, + 69, + 547, + 245 + ], + "spans": [ + { + "bbox": [ + 53, + 69, + 547, + 245 + ], + "type": "image", + "image_path": "d319ee33d0987d0f1b98f95fa61c49617eeec2197fa0080c97b41c081e4c3bea.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 251, + 547, + 298 + ], + "lines": [ + { + "bbox": [ + 46, + 251, + 547, + 298 + ], + "spans": [ + { + "bbox": [ + 46, + 251, + 547, + 298 + ], + "type": "text", + "content": "Figure 4. Structure of the bidirectional gated recurrent unit (BGRU). The proposed BGRU accepts source/target point features, flow estimations and correlations from the previous scale as input and hidden states. The source/target point features are first bidirectionally updated and fed to the proposed hybrid correlation for the candidate correlation generation. Subsequent GRU utilizes the candidate correlations for iteratively updating the correlation states." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "spans": [ + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "text", + "content": "point coordinates and features " + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "inline_equation", + "content": "S^{l,0} = \\{(s^l,f^{(l,0)})\\}" + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "text", + "content": ", target point coordinates and features " + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "inline_equation", + "content": "T^{l,0} = \\{(t^l,g^{(l,0)})\\}" + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "text", + "content": ", correlations " + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "inline_equation", + "content": "E^{l,0}" + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "text", + "content": " and flow " + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "inline_equation", + "content": "V^{l,0}" + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "text", + "content": " as input as well as hidden state variables that will be iteratively updated. After " + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "text", + "content": " iterations, updated " + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "inline_equation", + "content": "P^{l,K}, Q^{l,K}, E^{l,K}" + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "inline_equation", + "content": "V^{l,K}" + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "text", + "content": " are sent to the subsequent scale. In this section, we focus on one specific scale and omit the notation " + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 46, + 314, + 287, + 399 + ], + "type": "text", + "content": " for clarity." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 400, + 287, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 400, + 287, + 483 + ], + "spans": [ + { + "bbox": [ + 46, + 400, + 287, + 483 + ], + "type": "text", + "content": "Warping: Warping enables the source points to progressively approach the target frame. The estimated scene flows of upsampling layers (for the first iteration only) or previous iterations are immediately accumulated to the source frame, i.e. " + }, + { + "bbox": [ + 46, + 400, + 287, + 483 + ], + "type": "inline_equation", + "content": "s = v^{k - 1} + s" + }, + { + "bbox": [ + 46, + 400, + 287, + 483 + ], + "type": "text", + "content": ". The warped source points are further fed to the subsequent feature augmentation for more accurate correlation extraction." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 483, + 287, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 483, + 287, + 567 + ], + "spans": [ + { + "bbox": [ + 46, + 483, + 287, + 567 + ], + "type": "text", + "content": "Iterative Bidirectional Feature Augmentation (IBFA): IBFA accepts as input two frames of point coordinates and corresponding features from the previous " + }, + { + "bbox": [ + 46, + 483, + 287, + 567 + ], + "type": "inline_equation", + "content": "(k - 1)" + }, + { + "bbox": [ + 46, + 483, + 287, + 567 + ], + "type": "text", + "content": "-th iteration, " + }, + { + "bbox": [ + 46, + 483, + 287, + 567 + ], + "type": "inline_equation", + "content": "S^{k - 1} = \\{(s,f^{k - 1})\\}" + }, + { + "bbox": [ + 46, + 483, + 287, + 567 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 483, + 287, + 567 + ], + "type": "inline_equation", + "content": "T^{k - 1} = \\{(t,g^{k - 1})\\}" + }, + { + "bbox": [ + 46, + 483, + 287, + 567 + ], + "type": "text", + "content": ". For each point in both frames, the features are augmented bidirectionally for the current " + }, + { + "bbox": [ + 46, + 483, + 287, + 567 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 483, + 287, + 567 + ], + "type": "text", + "content": "-th iteration by aggregating features from the other frame as follows:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 53, + 575, + 287, + 600 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 575, + 287, + 600 + ], + "spans": [ + { + "bbox": [ + 53, + 575, + 287, + 600 + ], + "type": "interline_equation", + "content": "f ^ {k} = \\underset {\\left(t _ {i}, g _ {i} ^ {k - 1}\\right) \\in \\mathcal {N} _ {T} ^ {k - 1} \\left\\{\\left(s, f ^ {k - 1}\\right) \\right\\}} {\\operatorname {S e t C o n v}} \\left(\\left[ t _ {i} - s, g _ {i} ^ {k - 1}, f ^ {k - 1} \\right]\\right), \\tag {1}", + "image_path": "d0ba5b98f3cad615834d3ce0ad45055586558c6fd302ceba9bcc12dc1da96dbb.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 53, + 620, + 287, + 644 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 620, + 287, + 644 + ], + "spans": [ + { + "bbox": [ + 53, + 620, + 287, + 644 + ], + "type": "interline_equation", + "content": "g ^ {k} = \\underset {\\left(s _ {j}, f _ {j} ^ {k - 1}\\right) \\in \\mathcal {N} _ {S} ^ {k - 1} \\{(t, g ^ {k - 1}) \\}} {\\operatorname {S e t C o n v}} \\left(\\left[ s _ {j} - t, f _ {j} ^ {k - 1}, g ^ {k - 1} \\right]\\right), \\tag {2}", + "image_path": "e1c458da9f8a22959524593e1e8d11dc6013b21c7a15afff1fab5b5312ef7dbc.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "text", + "content": "where SetConv [19] is composed of a shared multi-layer perceptron and a maxpooling layer, " + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{N}_T\\{(s,\\cdot)\\}" + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "text", + "content": " denotes the nearest neighbor points of " + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "text", + "content": ", subscript " + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "inline_equation", + "content": "i,j" + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "text", + "content": " indicate the indices of points in the neighbor group " + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{N}" + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "inline_equation", + "content": "[\\cdot ,\\cdot ]" + }, + { + "bbox": [ + 46, + 653, + 288, + 714 + ], + "type": "text", + "content": " denotes the channel concatenation operator. Note that, the" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 316, + 545, + 351 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 316, + 545, + 351 + ], + "spans": [ + { + "bbox": [ + 304, + 316, + 545, + 351 + ], + "type": "text", + "content": "SetConv in Equation (1) and (2) share the equivalent parameters. The output are buffered as hidden states for the subsequent iteration or scale." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 351, + 546, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 351, + 546, + 434 + ], + "spans": [ + { + "bbox": [ + 304, + 351, + 546, + 434 + ], + "type": "text", + "content": "Iterative Correlation Update: The bidirectionally-augmented features are fed to the hybrid correlation extraction module (Sec. 3.2) to generate candidate correlation features. The candidate correlations serve as the input to a GRU in order to update the state correlation features from the previous iteration. Formally, the correlation features updated by the current iteration is denoted as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 318, + 441, + 545, + 467 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 441, + 545, + 467 + ], + "spans": [ + { + "bbox": [ + 318, + 441, + 545, + 467 + ], + "type": "interline_equation", + "content": "z = \\sigma \\left(\\underset {\\left(s _ {i}, \\tilde {e} _ {i} ^ {k}\\right) \\in \\mathcal {N} _ {\\tilde {S}} ^ {k - 1} \\{(s, e ^ {k - 1}) \\}} {\\operatorname {S e t C o n v} _ {z}} \\left([ s _ {i} - s, e ^ {k - 1}, \\tilde {e} _ {i} ^ {k} ]\\right)\\right), \\tag {3}", + "image_path": "2f95c32782e324cfb335f71d5736b6abef1672c41a9c7f4127a068758dff4430.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 353, + 478, + 545, + 493 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 353, + 478, + 545, + 493 + ], + "spans": [ + { + "bbox": [ + 353, + 478, + 545, + 493 + ], + "type": "interline_equation", + "content": "r _ {i} = \\sigma (M L P _ {r} ([ s _ {i} - s, e ^ {k - 1}, \\widetilde {e} _ {i} ^ {k} ])), \\qquad (4)", + "image_path": "1f2d858472072be0843bfbb744b9bda0a31ba68f7e2fc16a7838e7f6c09b807a.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 515, + 545, + 551 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 515, + 545, + 551 + ], + "spans": [ + { + "bbox": [ + 306, + 515, + 545, + 551 + ], + "type": "interline_equation", + "content": "\\hat {e} ^ {k} = \\tanh \\left(\\underset {\\left(s _ {i}, \\tilde {e} _ {i} ^ {k}\\right) \\in \\mathcal {N} _ {\\tilde {S}} ^ {k - 1} \\left\\{\\left(s, e ^ {k - 1}\\right) \\right\\}} {\\operatorname {S e t C o n v} _ {h}} \\left(\\left[ s _ {i} - s, e ^ {k - 1} \\odot r _ {i}, \\tilde {e} _ {i} ^ {k}\\right)\\right), \\right. \\tag {5}", + "image_path": "7074b518d7a2c3a72cdfdb7b583ca5d5fdfb2ac37cd14100035ce5648911a2de.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 361, + 562, + 545, + 576 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 361, + 562, + 545, + 576 + ], + "spans": [ + { + "bbox": [ + 361, + 562, + 545, + 576 + ], + "type": "interline_equation", + "content": "e ^ {k} = (1 - z) \\odot e ^ {k - 1} + z \\odot \\hat {e} ^ {k}, \\tag {6}", + "image_path": "2d93b0a1092d1dd6543571b29f35d941357ff54ea9ea9a2881c6a40b6f851abe.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 580, + 471, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 580, + 471, + 592 + ], + "spans": [ + { + "bbox": [ + 306, + 580, + 471, + 592 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 306, + 580, + 471, + 592 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 306, + 580, + 471, + 592 + ], + "type": "text", + "content": " denotes the Hadamard product." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 592, + 545, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 592, + 545, + 663 + ], + "spans": [ + { + "bbox": [ + 304, + 592, + 545, + 663 + ], + "type": "text", + "content": "Scene Flow Estimation: Given the updated correlation feature of each point, an MLP is followed to transform the correlation into a flow vector. Additionally, we introduce a residual mechanism by estimating the flow vector refinement " + }, + { + "bbox": [ + 304, + 592, + 545, + 663 + ], + "type": "inline_equation", + "content": "\\Delta V_{k}" + }, + { + "bbox": [ + 304, + 592, + 545, + 663 + ], + "type": "text", + "content": ". The final flow estimation is then accumulated as " + }, + { + "bbox": [ + 304, + 592, + 545, + 663 + ], + "type": "inline_equation", + "content": "V^{k} = V^{k - 1} + \\Delta V^{k}" + }, + { + "bbox": [ + 304, + 592, + 545, + 663 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 671, + 421, + 684 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 671, + 421, + 684 + ], + "spans": [ + { + "bbox": [ + 306, + 671, + 421, + 684 + ], + "type": "text", + "content": "3.2. Hybrid Correlation" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 545, + 714 + ], + "type": "text", + "content": "Feature-induced Correlation: Instead of capturing neighbor points in the conventional Euclidean space, we fetch" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "10044" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": "neighbor points from the latent feature space in order to acquire semantically correlative points. For instance, Figure 2 shows that the proposed correlation can capture semantically similar points (front windscreen) even if they are far away. Thus, the proposed correlation is different from the Euclidean-based correlation that may capture semantically unrelated points (bumper). Formally, given two point sets consisted of 3-dimensional coordinates and " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": "-dimensional features " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "S = \\{(s,f)|s\\in \\mathbb{R}^3,f\\in \\mathbb{R}^C\\}" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "T = \\{(t,g)|t\\in \\mathbb{R}^3,g\\in \\mathbb{R}^C\\}" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": ", for each point " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "(s,f)\\in S" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": ", its collected neighbor points " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "\\mathcal{N}_T\\{(s,f)\\}" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " satisfy " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "\\delta (f,g_i) < \\delta (f,g_j)" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": ", when " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "\\forall (t_i,g_i)\\subset \\mathcal{N}_T\\{(s,f)\\}" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "(t_j,g_j)\\subset Q\\backslash \\mathcal{N}_T\\{(p,f)\\}" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": ". Note that, " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "|\\mathcal{N}_T\\{(s,f)\\}| = K" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " is the hyperparameter that defines the amount of the top-K neighbor points, and " + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "inline_equation", + "content": "\\delta (\\cdot ,\\cdot)" + }, + { + "bbox": [ + 46, + 72, + 289, + 251 + ], + "type": "text", + "content": " is the cosine similarity measure." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 252, + 288, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 252, + 288, + 300 + ], + "spans": [ + { + "bbox": [ + 46, + 252, + 288, + 300 + ], + "type": "text", + "content": "After the corresponding points are collected, the features of the collected points are further aggregated by a learnable symmetric function. Hence, the correlation feature for each point " + }, + { + "bbox": [ + 46, + 252, + 288, + 300 + ], + "type": "inline_equation", + "content": "(p,f)\\in P" + }, + { + "bbox": [ + 46, + 252, + 288, + 300 + ], + "type": "text", + "content": " is formally denoted as:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 91, + 309, + 287, + 330 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 91, + 309, + 287, + 330 + ], + "spans": [ + { + "bbox": [ + 91, + 309, + 287, + 330 + ], + "type": "interline_equation", + "content": "\\widetilde {e} = \\underset {\\left(t _ {i}, g _ {i}\\right) \\in \\mathcal {N} _ {T} \\left\\{\\left(s, f\\right) \\right\\}} {\\operatorname {S e t C o n v}} \\left(\\left[ t _ {i} - s, g _ {i}, f \\right]\\right). \\tag {7}", + "image_path": "b00a75bfd3aada5a3ba684656ea3aea8e7c5e6defcbd7a2d3fb33eda0617afba.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 338, + 289, + 448 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 338, + 289, + 448 + ], + "spans": [ + { + "bbox": [ + 46, + 338, + 289, + 448 + ], + "type": "text", + "content": "Hybrid Correlation: Considering that the conventional grouping can capture fine-grained local motion and the proposed feature-induced grouping can capture correspondence regardless of distances, we integrate the two techniques to take advantage of both correlation extraction strategies. Thus, we fuse the collected points with the feature-induced grouping and conventional grouping as a hybrid neighbor set " + }, + { + "bbox": [ + 46, + 338, + 289, + 448 + ], + "type": "inline_equation", + "content": "\\mathcal{N}_T\\{(s,f)\\}" + }, + { + "bbox": [ + 46, + 338, + 289, + 448 + ], + "type": "text", + "content": " in Equation (7) for the subsequent correlation aggregation." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 455, + 203, + 467 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 455, + 203, + 467 + ], + "spans": [ + { + "bbox": [ + 47, + 455, + 203, + 467 + ], + "type": "text", + "content": "3.3. Coarse-to-Fine Architecture" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 473, + 287, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 473, + 287, + 510 + ], + "spans": [ + { + "bbox": [ + 46, + 473, + 287, + 510 + ], + "type": "text", + "content": "In this section, we thus introduce two existing layers [36] to construct a coarse-to-fine network for multi-scale feature generation and propagation." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 510, + 289, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 289, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 289, + 676 + ], + "type": "text", + "content": "Multi-scale Feature Extraction: The multi-scale feature extraction follows the design that is commonly used in point cloud processing [26, 35]. The feature extraction generates " + }, + { + "bbox": [ + 46, + 510, + 289, + 676 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 510, + 289, + 676 + ], + "type": "text", + "content": "-level pyramid of point features, where the top level is the input point clouds. At each level " + }, + { + "bbox": [ + 46, + 510, + 289, + 676 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 46, + 510, + 289, + 676 + ], + "type": "text", + "content": ", dense input points and their corresponding features are first subsampled through the furthest point sampling, which forms a sparse point set. Then, for each subsampled sparse point, the " + }, + { + "bbox": [ + 46, + 510, + 289, + 676 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 510, + 289, + 676 + ], + "type": "text", + "content": "-nearest neighbor groups dense points locally forming a local region for the feature extraction. Afterwards, a Pointconv [35] layer is applied to aggregate the features from the grouped local points through dynamic weights learned on their local coordinates, and produced the local feature for each sparse point." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 677, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 289, + 715 + ], + "type": "text", + "content": "Upsampling Layer: Since each level produces scene flows and iteratively augmented bidirectional features and correlations, we introduced the upsampling layer to propagate" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": "these features to the following level for a denser optimization. Following the previous works [36, 4], the upsampling layer adopts the 3D interpolation that aggregates " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": " nearest neighbors with their inverse distances as weights. Specifically, in the case of upsampling correlations from the " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": "-th level to the " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "(l - 1)" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": "-th level, the input to the upsampling layer are " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": "-th level's sparse coordinates " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "\\{x_j^l\\}_{j = 1}^{N^l}" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": "-th level's correlations " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "\\{e_j^l\\}_{j = 1}^{N^l}" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "(l - 1)" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": "-th level's dense coordinates " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "\\{x_i^{l - 1}\\}_{i = 1}^{N^{l - 1}}" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "N^{l - 1}" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "N^l" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": " are the number of points and " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "N^{l - 1} > N^l" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": ". The interpolated feature for each point " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "x_{i}^{l}" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": " in the dense " + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "inline_equation", + "content": "(l - 1)" + }, + { + "bbox": [ + 304, + 72, + 547, + 213 + ], + "type": "text", + "content": "-th level is defined as:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 363, + 220, + 545, + 255 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 363, + 220, + 545, + 255 + ], + "spans": [ + { + "bbox": [ + 363, + 220, + 545, + 255 + ], + "type": "interline_equation", + "content": "e _ {i} ^ {l - 1} = \\frac {\\sum_ {j = 1} ^ {k} w \\left(x _ {j} ^ {l} , x _ {i} ^ {l - 1}\\right) e _ {j} ^ {l}}{\\sum_ {j = 1} ^ {k} w \\left(x _ {j} ^ {l} , x _ {i} ^ {l - 1}\\right)}, \\tag {8}", + "image_path": "0fd864ea8915f1d471233b0de9581ccb9ac16b4efa9cd0bb550731260fe29db1.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 256, + 547, + 282 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 256, + 547, + 282 + ], + "spans": [ + { + "bbox": [ + 304, + 256, + 547, + 282 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 256, + 547, + 282 + ], + "type": "inline_equation", + "content": "w(x_{j}^{l},x_{i}^{l - 1}) = 1 / ||x_{j}^{l} - x_{i}^{l - 1}||_{2}" + }, + { + "bbox": [ + 304, + 256, + 547, + 282 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 256, + 547, + 282 + ], + "type": "inline_equation", + "content": "k = 3" + }, + { + "bbox": [ + 304, + 256, + 547, + 282 + ], + "type": "text", + "content": " as suggested by the previous studies [4, 36]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 288, + 395, + 300 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 288, + 395, + 300 + ], + "spans": [ + { + "bbox": [ + 305, + 288, + 395, + 300 + ], + "type": "text", + "content": "3.4. Loss Function" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "spans": [ + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "type": "text", + "content": "Following the previous studies for optical flow estimation [7, 29] and scene flow estimation [32, 36, 4], we train the proposed model in the multi-scale supervision manner. Furthermore, we also supervise the estimations of all intermediate iterations at each scale. All the estimated flows are supervised by the ground truth with the L2 measure. Let " + }, + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "type": "inline_equation", + "content": "\\{v_i^{l,k}\\}_{i=1}^N" + }, + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "type": "text", + "content": " denote the scene flow vectors estimated from the " + }, + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "type": "text", + "content": "-th iteration at the " + }, + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "type": "text", + "content": "-th level and " + }, + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "type": "inline_equation", + "content": "\\{\\hat{v}_i^l\\}_{i=1}^N" + }, + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "type": "text", + "content": " denote the ground truth scene flow vectors of the " + }, + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 306, + 547, + 429 + ], + "type": "text", + "content": "-th scale. The training loss is defined as:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 357, + 434, + 545, + 468 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 357, + 434, + 545, + 468 + ], + "spans": [ + { + "bbox": [ + 357, + 434, + 545, + 468 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\sum_ {l = 0} ^ {L - 1} \\alpha^ {l} \\sum_ {k = 1} ^ {K} \\sum_ {i = 1} ^ {N ^ {l}} \\| \\hat {v} _ {i} ^ {l} - v _ {i} ^ {l, k} \\| _ {2}, \\tag {9}", + "image_path": "bfe07b95621466df16e01fa004ebfdc4748d0bdf8cf9aac988e9ce1ea39d6cb0.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 474, + 547, + 499 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 547, + 499 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 547, + 499 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 474, + 547, + 499 + ], + "type": "inline_equation", + "content": "\\alpha^l" + }, + { + "bbox": [ + 304, + 474, + 547, + 499 + ], + "type": "text", + "content": " is the weight for scale " + }, + { + "bbox": [ + 304, + 474, + 547, + 499 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 474, + 547, + 499 + ], + "type": "text", + "content": ". The weights are " + }, + { + "bbox": [ + 304, + 474, + 547, + 499 + ], + "type": "inline_equation", + "content": "\\alpha^0 = 0.16, \\alpha^1 = 0.08, \\alpha^2 = 0.04, \\alpha^3 = 0.02" + }, + { + "bbox": [ + 304, + 474, + 547, + 499 + ], + "type": "text", + "content": " by default." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 508, + 388, + 521 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 508, + 388, + 521 + ], + "spans": [ + { + "bbox": [ + 305, + 508, + 388, + 521 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 527, + 433, + 540 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 527, + 433, + 540 + ], + "spans": [ + { + "bbox": [ + 305, + 527, + 433, + 540 + ], + "type": "text", + "content": "4.1. Experimental Settings" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "text", + "content": "As shown in Fig. 3, we implemented a hierarchical model with " + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "inline_equation", + "content": "L = 4" + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "text", + "content": " scales. We used " + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "inline_equation", + "content": "N = M = 8" + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "text", + "content": ", 192 points as inputs. The point numbers of each scale are defined as " + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "inline_equation", + "content": "N^1 = 2" + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "text", + "content": ", 048, " + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "inline_equation", + "content": "N^2 = 512" + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "inline_equation", + "content": "N^3 = 256" + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "inline_equation", + "content": "N^4 = 64" + }, + { + "bbox": [ + 304, + 545, + 547, + 714 + ], + "type": "text", + "content": ". We adopted the synthetic FlyingThings3D [22] dataset and the real-world KITTI Scene Flow 2015 [23] dataset to evaluate our model. As in the previous methods, we trained networks only on the synthetic FlyingThings3D dataset and validated the performance on the FlyingThings3D dataset (Sec. 4.3). Finally, we directly evaluated the model trained on FlyingThings3D without any fine-tuning to validate the generalization ability on the real-world KITTI dataset (Sec. 4.4). The experiments are conducted on an NVIDIA Titan RTX GPU with PyTorch." + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "10045" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 63, + 70, + 533, + 312 + ], + "blocks": [ + { + "bbox": [ + 63, + 70, + 533, + 312 + ], + "lines": [ + { + "bbox": [ + 63, + 70, + 533, + 312 + ], + "spans": [ + { + "bbox": [ + 63, + 70, + 533, + 312 + ], + "type": "table", + "html": "
DatasetMethodEPE3D (m) ↓ACC3DS ↑ACC3DR ↑Outliers3D ↓EPE2D (px) ↓ACC2D ↑
FT3DsFlowNet3D [19]0.1130.4120.7710.6025.9740.569
HPLFlowNet [10]0.0800.6140.8550.4294.6720.676
PointPWC [36]0.0590.7380.9280.3423.2390.799
FLOT [25]0.0520.7320.9270.357--
HCRF-Flow [18]0.0480.8350.9500.2612.5650.870
PV-RAFT [34]0.0460.8160.9570.292--
FlowStep3D [15]0.0450.8160.9610.216--
RCP [9]0.0400.8560.9630.197--
Bi-PointFlowNet [4]0.0280.9180.9780.1431.5820.929
Ours0.0150.9730.9920.0560.8330.970
KITTsFlowNet3D [19]0.1770.3740.6680.5277.2140.509
HPLFlowNet [10]0.1170.4780.7780.4104.8050.593
PointPWC [36]0.0690.7280.8880.2651.9020.866
FLOT [25]0.0560.7550.9080.242--
HCRF-Flow [18]0.0530.8630.9440.1792.0700.865
PV-RAFT [34]0.0560.8220.9370.216--
FlowStep3D [15]0.0540.8050.9250.149--
RCP [9]0.0480.8490.9440.122--
Bi-PointFlowNet [4]0.0300.9200.9600.1411.0560.949
Ours0.0110.9710.9890.0850.4430.985
", + "image_path": "37702c74032a6605c68594c260219ae15630c3e56520208ce808d9f650cc2385.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 319, + 547, + 343 + ], + "lines": [ + { + "bbox": [ + 46, + 319, + 547, + 343 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 547, + 343 + ], + "type": "text", + "content": "Table 1. Comparison of the proposed method with previous state-of-the-art methods on the non-occluded FT3D " + }, + { + "bbox": [ + 46, + 319, + 547, + 343 + ], + "type": "inline_equation", + "content": "{}_{s}" + }, + { + "bbox": [ + 46, + 319, + 547, + 343 + ], + "type": "text", + "content": " and KITTI " + }, + { + "bbox": [ + 46, + 319, + 547, + 343 + ], + "type": "inline_equation", + "content": "{}_{s}" + }, + { + "bbox": [ + 46, + 319, + 547, + 343 + ], + "type": "text", + "content": " datasets. All methods are trained only on the FT3D " + }, + { + "bbox": [ + 46, + 319, + 547, + 343 + ], + "type": "inline_equation", + "content": "{}_{s}" + }, + { + "bbox": [ + 46, + 319, + 547, + 343 + ], + "type": "text", + "content": " dataset." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 361, + 170, + 373 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 361, + 170, + 373 + ], + "spans": [ + { + "bbox": [ + 47, + 361, + 170, + 373 + ], + "type": "text", + "content": "4.2. Evaluation Measures" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 380, + 287, + 416 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 380, + 287, + 416 + ], + "spans": [ + { + "bbox": [ + 47, + 380, + 287, + 416 + ], + "type": "text", + "content": "For a fair comparison, we adopted the same evaluation measures that are used in the related works [10, 36, 25, 15, 18, 4]." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 417, + 287, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 417, + 287, + 453 + ], + "spans": [ + { + "bbox": [ + 47, + 417, + 287, + 453 + ], + "type": "text", + "content": "EPE3D, EPE3Dfull (m): the main evaluation measure measuring 3D end-point-error " + }, + { + "bbox": [ + 47, + 417, + 287, + 453 + ], + "type": "inline_equation", + "content": "\\| \\hat{v}_i^l - v_i^l\\|_2" + }, + { + "bbox": [ + 47, + 417, + 287, + 453 + ], + "type": "text", + "content": " averaged over non-occluded points and all points, respectively." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 453, + 287, + 476 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 453, + 287, + 476 + ], + "spans": [ + { + "bbox": [ + 47, + 453, + 287, + 476 + ], + "type": "text", + "content": "ACC3DS: the percentage of points that satisfy EPE3D " + }, + { + "bbox": [ + 47, + 453, + 287, + 476 + ], + "type": "inline_equation", + "content": "< 0.05\\mathrm{m}" + }, + { + "bbox": [ + 47, + 453, + 287, + 476 + ], + "type": "text", + "content": " or relative error " + }, + { + "bbox": [ + 47, + 453, + 287, + 476 + ], + "type": "inline_equation", + "content": "< 5\\%" + }, + { + "bbox": [ + 47, + 453, + 287, + 476 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 478, + 287, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 478, + 287, + 502 + ], + "spans": [ + { + "bbox": [ + 47, + 478, + 287, + 502 + ], + "type": "text", + "content": "ACC3DR: the percentage of points that satisfy EPE3D " + }, + { + "bbox": [ + 47, + 478, + 287, + 502 + ], + "type": "inline_equation", + "content": "< 0.1\\mathrm{m}" + }, + { + "bbox": [ + 47, + 478, + 287, + 502 + ], + "type": "text", + "content": " or relative error " + }, + { + "bbox": [ + 47, + 478, + 287, + 502 + ], + "type": "inline_equation", + "content": "< 10\\%" + }, + { + "bbox": [ + 47, + 478, + 287, + 502 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 503, + 287, + 526 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 503, + 287, + 526 + ], + "spans": [ + { + "bbox": [ + 47, + 503, + 287, + 526 + ], + "type": "text", + "content": "Outliers3D: the percentage of points that satisfy EPE3D " + }, + { + "bbox": [ + 47, + 503, + 287, + 526 + ], + "type": "inline_equation", + "content": ">0.3\\mathrm{m}" + }, + { + "bbox": [ + 47, + 503, + 287, + 526 + ], + "type": "text", + "content": " or relative error " + }, + { + "bbox": [ + 47, + 503, + 287, + 526 + ], + "type": "inline_equation", + "content": ">10\\%" + }, + { + "bbox": [ + 47, + 503, + 287, + 526 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 528, + 287, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 528, + 287, + 563 + ], + "spans": [ + { + "bbox": [ + 47, + 528, + 287, + 563 + ], + "type": "text", + "content": "EPE2D (px): 2D end-point-error measured by projecting points back to the 2D image plane, which is a common measure for optical flow evaluation." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 564, + 287, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 564, + 287, + 588 + ], + "spans": [ + { + "bbox": [ + 47, + 564, + 287, + 588 + ], + "type": "text", + "content": "ACC2D: the percentage of points that satisfy EPE2D " + }, + { + "bbox": [ + 47, + 564, + 287, + 588 + ], + "type": "inline_equation", + "content": "< 3\\mathrm{px}" + }, + { + "bbox": [ + 47, + 564, + 287, + 588 + ], + "type": "text", + "content": " or relative error " + }, + { + "bbox": [ + 47, + 564, + 287, + 588 + ], + "type": "inline_equation", + "content": "< 5\\%" + }, + { + "bbox": [ + 47, + 564, + 287, + 588 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 597, + 278, + 612 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 597, + 278, + 612 + ], + "spans": [ + { + "bbox": [ + 47, + 597, + 278, + 612 + ], + "type": "text", + "content": "4.3. Training and Evaluation on FlyingThings3D" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 288, + 715 + ], + "type": "text", + "content": "Due to the challenge with labeling for dense point cloud scenes, recent models [10, 36, 25, 15, 18, 4] only utilized the synthetic FlyingThing3D dataset for training. The FlyingThing3D [22] dataset provides 19,640 pairs of frames for training and 3,824 pairs of frames for testing. Each frame contains synthetic stereo and RGB-D images rendered from virtual scenes with multiple moving objects sampled from the ShapeNet [2] dataset. We follow the same preprocessing" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 361, + 545, + 421 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 361, + 545, + 421 + ], + "spans": [ + { + "bbox": [ + 304, + 361, + 545, + 421 + ], + "type": "text", + "content": "that generates two subsets: " + }, + { + "bbox": [ + 304, + 361, + 545, + 421 + ], + "type": "inline_equation", + "content": "\\mathrm{FT3D}_o" + }, + { + "bbox": [ + 304, + 361, + 545, + 421 + ], + "type": "text", + "content": " that includes occluded points and " + }, + { + "bbox": [ + 304, + 361, + 545, + 421 + ], + "type": "inline_equation", + "content": "\\mathrm{FT3D}_s" + }, + { + "bbox": [ + 304, + 361, + 545, + 421 + ], + "type": "text", + "content": " that excludes the occluded points, as suggested in [10, 36, 25, 4]. The consecutive input frames are formed by randomly sampling " + }, + { + "bbox": [ + 304, + 361, + 545, + 421 + ], + "type": "inline_equation", + "content": "N = 8" + }, + { + "bbox": [ + 304, + 361, + 545, + 421 + ], + "type": "text", + "content": ", 192 of points from the dataset with non-correspondence." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 422, + 545, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 422, + 545, + 494 + ], + "spans": [ + { + "bbox": [ + 304, + 422, + 545, + 494 + ], + "type": "text", + "content": "For training, we used the AdamW optimizer [20] with beta1 = 0.9, beta2 = 0.999. The learning rate is initially set as " + }, + { + "bbox": [ + 304, + 422, + 545, + 494 + ], + "type": "inline_equation", + "content": "\\alpha = 0.0001" + }, + { + "bbox": [ + 304, + 422, + 545, + 494 + ], + "type": "text", + "content": " and reduced by half every 80 epochs. We trained the model for a total of 560 epochs. The numbers of iterations for all BGRUs are set to " + }, + { + "bbox": [ + 304, + 422, + 545, + 494 + ], + "type": "inline_equation", + "content": "K_{tr} = 4" + }, + { + "bbox": [ + 304, + 422, + 545, + 494 + ], + "type": "text", + "content": " during training and " + }, + { + "bbox": [ + 304, + 422, + 545, + 494 + ], + "type": "inline_equation", + "content": "K_{in} = 4" + }, + { + "bbox": [ + 304, + 422, + 545, + 494 + ], + "type": "text", + "content": " during testing." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 494, + 545, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 494, + 545, + 590 + ], + "spans": [ + { + "bbox": [ + 304, + 494, + 545, + 590 + ], + "type": "text", + "content": "Results. We compared the performance of the proposed model with other state-of-the-art approaches based on point cloud [19, 10, 36, 25, 15, 24, 9, 4]. As presented in Table 1, the proposed method significantly outperforms all recent state-of-the-art methods with more than " + }, + { + "bbox": [ + 304, + 494, + 545, + 590 + ], + "type": "inline_equation", + "content": "46\\%" + }, + { + "bbox": [ + 304, + 494, + 545, + 590 + ], + "type": "text", + "content": " reduction of estimation error under the non-occluded condition. When compared to the related iterative methods FlowStep3D [15] and RCP [9], our model achieves an error reduction of " + }, + { + "bbox": [ + 304, + 494, + 545, + 590 + ], + "type": "inline_equation", + "content": "62\\%" + }, + { + "bbox": [ + 304, + 494, + 545, + 590 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 598, + 448, + 610 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 598, + 448, + 610 + ], + "spans": [ + { + "bbox": [ + 305, + 598, + 448, + 610 + ], + "type": "text", + "content": "4.4. Generalization on KITTI" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 617, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 715 + ], + "type": "text", + "content": "Following the same evaluation strategy as in the recent studies [19, 10, 36, 25, 15, 24, 4], we evaluated the generalization ability of MSBRN on the real-world KITTI [23] dataset with the model that was only trained on the synthetic dataset. The KITTI dataset provides 200 scenes for training and 200 scenes for testing. However, the disparities were missing in the testing scene and parts of the training scenes. Thus, 142 non-occluded scenes (KITTI" + }, + { + "bbox": [ + 304, + 617, + 545, + 715 + ], + "type": "inline_equation", + "content": "_s" + }, + { + "bbox": [ + 304, + 617, + 545, + 715 + ], + "type": "text", + "content": ", re" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "10046" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 82, + 71, + 513, + 246 + ], + "blocks": [ + { + "bbox": [ + 82, + 71, + 513, + 246 + ], + "lines": [ + { + "bbox": [ + 82, + 71, + 513, + 246 + ], + "spans": [ + { + "bbox": [ + 82, + 71, + 513, + 246 + ], + "type": "table", + "html": "
DatasetMethodEPE3Dfull (m) ↓EPE3D (m) ↓ACC3DS ↑ACC3DR ↑Outliers3D ↓
FT3DoFlowNet3D [19]0.2110.1570.2280.5820.804
HPLFlowNet [10]0.2010.1680.2620.5740.812
FLOT [25]0.2500.1530.3960.6600.662
PointPWC [36]0.1950.1550.4160.6990.638
OGSFNet [24]0.1630.1210.5510.7760.518
Bi-PointFlowNet [4]0.1020.0730.7910.8960.274
Ours0.0800.0530.8360.9260.231
KITTIoFlowNet3D [19]0.183-0.0980.3940.799
HPLFlowNet [10]0.343-0.1030.3860.814
FLOT [25]0.130-0.2780.6670.529
PointPWC [36]0.118-0.4030.7570.496
OGSFNet [24]0.075-0.7060.8690.327
Bi-PointFlowNet [4]0.065-0.7690.9060.264
Ours0.044-0.8730.9500.208
", + "image_path": "0c05347bf3441d8ae389ecefedf538612881cde64cb12eb05c83f9d8ebd198f9.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 254, + 546, + 277 + ], + "lines": [ + { + "bbox": [ + 46, + 254, + 546, + 277 + ], + "spans": [ + { + "bbox": [ + 46, + 254, + 546, + 277 + ], + "type": "text", + "content": "Table 2. Comparison of the proposed method with previous state-of-the-art methods on the occluded FT3DO and KITTIO datasets. All methods are trained only on the FT3DO dataset." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 55, + 285, + 544, + 462 + ], + "blocks": [ + { + "bbox": [ + 55, + 285, + 544, + 462 + ], + "lines": [ + { + "bbox": [ + 55, + 285, + 544, + 462 + ], + "spans": [ + { + "bbox": [ + 55, + 285, + 544, + 462 + ], + "type": "image", + "image_path": "fff2732f2eabc30e696b353368435ff79df34285d8218c14033e602128e60a0e.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 466, + 546, + 489 + ], + "lines": [ + { + "bbox": [ + 46, + 466, + 546, + 489 + ], + "spans": [ + { + "bbox": [ + 46, + 466, + 546, + 489 + ], + "type": "text", + "content": "Figure 5. Qualitative results of MSBRN on the non-occluded KITTI dataset. Points are colored to indicate points as from source frame, target frame or as MSBRN estimated points (source frame + scene flow)." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 508, + 287, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 508, + 287, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 508, + 287, + 568 + ], + "type": "text", + "content": "moving occluded points) and 150 occluded scenes (KITTI" + }, + { + "bbox": [ + 46, + 508, + 287, + 568 + ], + "type": "inline_equation", + "content": "_o" + }, + { + "bbox": [ + 46, + 508, + 287, + 568 + ], + "type": "text", + "content": ", remaining occluded points) were available for evaluation with raw point clouds. We removed ground points by height " + }, + { + "bbox": [ + 46, + 508, + 287, + 568 + ], + "type": "inline_equation", + "content": "< 0.3" + }, + { + "bbox": [ + 46, + 508, + 287, + 568 + ], + "type": "text", + "content": " m as suggested by the previous approaches [19, 10, 36, 25, 15, 24] for a fair comparison." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 570, + 289, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 289, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 289, + 713 + ], + "type": "text", + "content": "Results. We compared the generalization ability of MSBRN with the existing state-of-the-art methods based on point cloud [19, 10, 36, 25, 15, 24, 9, 4]. As shown in Table 1 and 2, our proposed method represented the state-of-the-art generality when the model is trained on the synthetic datasets and tested on and real-world KITTI dataset. Our method significantly outperforms other methods by a large margin. Focusing on the main EPE3D measure, our method outperforms the recent state-of-the-art with " + }, + { + "bbox": [ + 46, + 570, + 289, + 713 + ], + "type": "inline_equation", + "content": "63\\%" + }, + { + "bbox": [ + 46, + 570, + 289, + 713 + ], + "type": "text", + "content": " of error reduction on the non-occluded scenes. Compared to the similar iterative methods FlowStep3D [15] and RCP [9], our method shows over " + }, + { + "bbox": [ + 46, + 570, + 289, + 713 + ], + "type": "inline_equation", + "content": "77\\%" + }, + { + "bbox": [ + 46, + 570, + 289, + 713 + ], + "type": "text", + "content": " of error reduction. Moreover, our" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 508, + 545, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 508, + 545, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 508, + 545, + 545 + ], + "type": "text", + "content": "model shows the superior generality on the occluded scenes, as shown in Table 2. Our model shows an over " + }, + { + "bbox": [ + 304, + 508, + 545, + 545 + ], + "type": "inline_equation", + "content": "32\\%" + }, + { + "bbox": [ + 304, + 508, + 545, + 545 + ], + "type": "text", + "content": " reduction of " + }, + { + "bbox": [ + 304, + 508, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\mathrm{EPE3D_{full}}" + }, + { + "bbox": [ + 304, + 508, + 545, + 545 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 552, + 400, + 564 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 552, + 400, + 564 + ], + "spans": [ + { + "bbox": [ + 306, + 552, + 400, + 564 + ], + "type": "text", + "content": "4.5. Ablation Study" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 570, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 713 + ], + "type": "text", + "content": "Number of Iterations. The iteration number of the BGRU is a significant factor that affects the estimation accuracy. It is worth noting that the iteration configuration can be different between the training stage " + }, + { + "bbox": [ + 304, + 570, + 547, + 713 + ], + "type": "inline_equation", + "content": "(K_{tr})" + }, + { + "bbox": [ + 304, + 570, + 547, + 713 + ], + "type": "text", + "content": " and the evaluation stage " + }, + { + "bbox": [ + 304, + 570, + 547, + 713 + ], + "type": "inline_equation", + "content": "(K_{in})" + }, + { + "bbox": [ + 304, + 570, + 547, + 713 + ], + "type": "text", + "content": ". Therefore, we trained and evaluated our method with the different iteration numbers. Note that, all levels proceed with the same iteration number as configured. Table 3 reports the performance comparison between models with the different numbers of BGRU iterations. The result shows that iteratively adopting the proposed BGRU effectively reduces the estimation error on both the synthetic dataset and the real-world dataset. The model delivers" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "10047" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 71, + 282, + 211 + ], + "blocks": [ + { + "bbox": [ + 53, + 71, + 282, + 211 + ], + "lines": [ + { + "bbox": [ + 53, + 71, + 282, + 211 + ], + "spans": [ + { + "bbox": [ + 53, + 71, + 282, + 211 + ], + "type": "table", + "html": "
\\(K_{tr}\\)EPE3D (m) @ \\(K_{in}\\)
123456
FT3\\(d_s\\)10.0260.0710.1010.1490.2040.281
20.0330.0210.0300.0370.0460.049
30.0380.0200.0160.0160.0160.018
40.0400.0240.0170.0150.0150.015
50.0490.0270.0190.0150.0140.014
KITTLs10.0380.1290.1120.1460.1720.230
20.0390.0220.0400.0690.0570.076
30.0390.0210.0150.0140.0130.013
40.0400.0220.0150.0110.0100.009
50.0570.0310.0210.0170.0130.012
", + "image_path": "23d81f3297cf692f2c88e29da83c26d1ca6bb79f67363d7bfd585adc096af737.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 53, + 273, + 282, + 327 + ], + "blocks": [ + { + "bbox": [ + 47, + 220, + 287, + 264 + ], + "lines": [ + { + "bbox": [ + 47, + 220, + 287, + 264 + ], + "spans": [ + { + "bbox": [ + 47, + 220, + 287, + 264 + ], + "type": "text", + "content": "Table 3. Comparison on the EPE2D metric between different training/inference iteration configurations. The model is first trained under a specific " + }, + { + "bbox": [ + 47, + 220, + 287, + 264 + ], + "type": "inline_equation", + "content": "K_{tr}" + }, + { + "bbox": [ + 47, + 220, + 287, + 264 + ], + "type": "text", + "content": " on the FT3Ds dataset and then evaluated with various " + }, + { + "bbox": [ + 47, + 220, + 287, + 264 + ], + "type": "inline_equation", + "content": "K_{ins}" + }, + { + "bbox": [ + 47, + 220, + 287, + 264 + ], + "type": "text", + "content": " on both FT3Ds and KITTIs dataset." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 53, + 273, + 282, + 327 + ], + "lines": [ + { + "bbox": [ + 53, + 273, + 282, + 327 + ], + "spans": [ + { + "bbox": [ + 53, + 273, + 282, + 327 + ], + "type": "table", + "html": "
Correlation type\n# neighbor (dist:feat)Euclidean\n(32:0)Hybrid\n(16:16)Feature\n(0:32)
EPE3D (m)FT3Ds0.0190.0160.022
KITTs0.0180.0150.036
", + "image_path": "5ab590e89fea91b3eba73b9dccd22375cf94ee462a45b035881b26c0d47e776b.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 74, + 389, + 261, + 496 + ], + "blocks": [ + { + "bbox": [ + 47, + 335, + 287, + 380 + ], + "lines": [ + { + "bbox": [ + 47, + 335, + 287, + 380 + ], + "spans": [ + { + "bbox": [ + 47, + 335, + 287, + 380 + ], + "type": "text", + "content": "Table 4. Comparison between different numbers of the neighbor points for the correlation extraction. 'Dist' and 'feat' indicate the Euclidean distance-based neighbor points and the feature-induced neighbor points, respectively." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 74, + 389, + 261, + 496 + ], + "lines": [ + { + "bbox": [ + 74, + 389, + 261, + 496 + ], + "spans": [ + { + "bbox": [ + 74, + 389, + 261, + 496 + ], + "type": "table", + "html": "
IBFAHCGRUFT3Ds EPE3D (m)KITTIs EPE3D (m)
×××0.0290.030
✓××0.0250.025
×✓×0.0290.038
✓×✓0.0190.018
✓✓×0.0210.018
×✓✓0.0270.033
✓✓✓0.0160.015
", + "image_path": "7e8642563e41286706b963a1728a2b09fd2b18133973d6008273685cc65b28fa.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "type": "text", + "content": "the optimal estimation performance when " + }, + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "type": "inline_equation", + "content": "K_{tr} = 4" + }, + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "type": "text", + "content": ". Moreover, the model also demonstrated that the performance is saturated at " + }, + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "type": "inline_equation", + "content": "K_{tr} = 5" + }, + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "type": "text", + "content": ". On the other hand, we observe that the model keeps improving for a few more iterations even though the inference " + }, + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "type": "inline_equation", + "content": "K_{in}" + }, + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "type": "text", + "content": " is larger than the training when the training " + }, + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "type": "inline_equation", + "content": "K_{tr} \\geq 3" + }, + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "type": "text", + "content": ". However, the improvement is negligible thus we stop evaluating at " + }, + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "type": "inline_equation", + "content": "K_{in} = K_{tr}" + }, + { + "bbox": [ + 46, + 581, + 286, + 665 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "content": "Hybrid Correlation. As mentioned in Section 3.2, the hybrid correlation consists of the Euclidean distance-based correlation and the proposed feature-induced correlation, thus can benefit from both of their advantages. To val" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 310, + 71, + 541, + 124 + ], + "blocks": [ + { + "bbox": [ + 47, + 506, + 287, + 562 + ], + "lines": [ + { + "bbox": [ + 47, + 506, + 287, + 562 + ], + "spans": [ + { + "bbox": [ + 47, + 506, + 287, + 562 + ], + "type": "text", + "content": "Table 5. Ablations of different components. IBFA, HC and GRU represent whether the iterative bidirectional feature augmentation, hybrid correlation and GRU are deployed in the model, respectively. The iterative models are trained and evaluated with " + }, + { + "bbox": [ + 47, + 506, + 287, + 562 + ], + "type": "inline_equation", + "content": "K_{tr} = K_{in} = 3" + }, + { + "bbox": [ + 47, + 506, + 287, + 562 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 310, + 71, + 541, + 124 + ], + "lines": [ + { + "bbox": [ + 310, + 71, + 541, + 124 + ], + "spans": [ + { + "bbox": [ + 310, + 71, + 541, + 124 + ], + "type": "table", + "html": "
MethodRuntimeMethodRuntime
PV-RAFT [34]781.1msOurs (Kin=2)209.6ms
FlowStep3D [15]972.7msOurs (Kin=3)287.6ms
RCP [9]2854.6msOurs (Kin=4)365.8ms
", + "image_path": "caefe2dfd99b2026e4644dd92a5cc4a01646334f66ce9c6ba234f14ff26cf8e2.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 132, + 545, + 176 + ], + "lines": [ + { + "bbox": [ + 305, + 132, + 545, + 176 + ], + "spans": [ + { + "bbox": [ + 305, + 132, + 545, + 176 + ], + "type": "text", + "content": "Table 6. Runtime comparison of iterative methods. The results are evaluated on a single TITAN RTX GPU. PV-RAFT, FlowStep3D and RCP are evaluated with their optimal iteration configurations which are 32, 4 and 14, respectively." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 199, + 545, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 199, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 304, + 199, + 545, + 403 + ], + "type": "text", + "content": "idate the effectiveness of the hybrid correlation (16:16), we implemented two ablation experiments: a model with only the Euclidean distance-based correlation (32:0) and a model with only the proposed feature-induced correlation (0:32). Note that, the numbers in brackets indicate the number of Euclidean neighbor points and the number of feature-induced neighbor points, respectively. The total number of neighbor points is fixed at 32 for all experiments for a fair comparison. As demonstrated in Table 4, introducing our feature-induced correlation in the conventional Euclidean distance-based approaches can boost performance. However, the proposed feature-induced correlation must work with the Euclidean distance-based correlation. It is because the feature-induced correlation can capture semantically similar points from other instances located far away. Additionally applying the Euclidean distance-based correlation can introduce a proper constraint on the range." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 404, + 545, + 573 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 404, + 545, + 573 + ], + "spans": [ + { + "bbox": [ + 304, + 404, + 545, + 573 + ], + "type": "text", + "content": "Analysis of different BGRU configurations. To verify the contributions of the proposed components in the BGRU, we incrementally adopted the IBFA, hybrid correlation, and GRU based on a baseline model. Note that, the baseline model replaces IBFA and the hybrid correlation with BFP [4] and the distance-based correlation, respectively, and removes GRU. As shown in Table 5, IBFA, hybrid correlation and GRU all contribute considerably to the effective estimation. In particular, IBFA improves the accuracy by 0.5 mm on KITTI. Furthermore, using the hybrid correlation and GRU mechanism further reduces the estimation error by " + }, + { + "bbox": [ + 304, + 404, + 545, + 573 + ], + "type": "inline_equation", + "content": "0.7\\mathrm{mm}" + }, + { + "bbox": [ + 304, + 404, + 545, + 573 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 404, + 545, + 573 + ], + "type": "inline_equation", + "content": "0.3\\mathrm{mm}" + }, + { + "bbox": [ + 304, + 404, + 545, + 573 + ], + "type": "text", + "content": " on KITTI, respectively. However, Table 5 also reveals that the hybrid correlation and GRU must cooperate with IBFA to get convincing improvement." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 585, + 369, + 597 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 585, + 369, + 597 + ], + "spans": [ + { + "bbox": [ + 306, + 585, + 369, + 597 + ], + "type": "text", + "content": "4.6. Runtime" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "We compare the running time of our proposed methods to other state-of-the-art iterative approaches [34, 15, 9] in Table 6. All methods are measured on a single NVIDIA Titan RTX GPU. Table 6 and 1 show that our proposed method outperforms by a large margin in terms of running time while achieving superior accuracy and generality. Even under " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "K_{in} = 2" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ", our method also presents outperformed accuracy with faster speed compared to the existing iterative approaches." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10048" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 119, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 119, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 119, + 83 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "text", + "content": "This paper presented MSBRN, a novel recurrent bidirectional architecture that is capable of iteratively estimating progressively accurate multi-scale 3D scene flows from two consecutive point cloud frames. Our proposed network also utilized the hybrid correlation for improved flow estimation performance. Experimental results showed that our network significantly outperforms previous state-of-the-art methods on two challenging benchmarks. The proposed method also showed superior efficiency compared to existing iterative state-of-the-art. Extensive experiments also demonstrated the excellent effectiveness of the novel components proposed in this work." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 244, + 145, + 258 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 244, + 145, + 258 + ], + "spans": [ + { + "bbox": [ + 47, + 244, + 145, + 258 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 264, + 289, + 385 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 264, + 289, + 385 + ], + "spans": [ + { + "bbox": [ + 46, + 264, + 289, + 385 + ], + "type": "text", + "content": "This work was supported by the Ministry of Science and ICT (MSIT) of Korea under the National Research Foundation (NRF) grant (2022R1A4A3032913) and the Institute of Information and Communication Technology Planning Evaluation (IITP) grants (IITP-2019-0-00421, IITP-2023-2020-0-01821, IITP-2021-0-02052, IITP-2021-0-02068), and by the Technology Innovation Program (RS-2023-00235718) funded by the Ministry of Trade, Industry & Energy (1415187474). Wencan Cheng was partly supported by the China Scholarship Council (CSC)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 394, + 107, + 407 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 394, + 107, + 407 + ], + "spans": [ + { + "bbox": [ + 47, + 394, + 107, + 407 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 53, + 414, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 12, + "blocks": [ + { + "bbox": [ + 53, + 414, + 287, + 458 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 414, + 287, + 458 + ], + "spans": [ + { + "bbox": [ + 53, + 414, + 287, + 458 + ], + "type": "text", + "content": "[1] Paul J Besl and Neil D McKay. Method for registration of 3-d shapes. In Sensor fusion IV: control paradigms and data structures, volume 1611, pages 586-606. 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Springer, 2020. 1, 2, 3, 5, 6, 7" + } + ] + } + ], + "index": 19 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10050" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/5c2653f2-ab7f-4799-9150-1c49cbf5bd6d_content_list.json b/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/5c2653f2-ab7f-4799-9150-1c49cbf5bd6d_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..843357ecf43f67297b2d354758944ee6cb99a1f3 --- /dev/null +++ b/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/5c2653f2-ab7f-4799-9150-1c49cbf5bd6d_content_list.json @@ -0,0 +1,1950 @@ +[ + { + "type": "text", + "text": "Multi-scale Residual Low-Pass Filter Network for Image Deblurring", + "text_level": 1, + "bbox": [ + 140, + 130, + 828, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Jiangxin Dong Jinshan Pan* Zhongbao Yang Jinhui Tang Nanjing University of Science and Technology", + "bbox": [ + 225, + 180, + 743, + 218 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 251, + 313, + 268 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We present a simple and effective Multi-scale Residual Low-Pass Filter Network (MRLPFNet) that jointly explores the image details and main structures for image deblurring. Our work is motivated by an observation that the difference between the blurry image and the clear one not only contains high-frequency contents but also includes low-frequency information due to the influence of blur, while using the standard residual learning is less effective for modeling the main structure distorted by the blur. Considering that the low-frequency contents usually correspond to main global structures that are spatially variant, we first propose a learnable low-pass filter based on a self-attention mechanism to adaptively explore the global contexts for better modeling the low-frequency information. Then we embed it into a Residual Low-Pass Filter (RLPF) module, which involves an additional fully convolutional neural network with the standard residual learning to model the high-frequency information. We formulate the RLPF module into an end-to-end trainable network based on an encoder and decoder architecture and develop a wavelet-based feature fusion to fuse the multi-scale features. Experimental results show that our method performs favorably against state-of-the-art ones on commonly-used benchmarks.", + "bbox": [ + 75, + 282, + 472, + 630 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 660, + 209, + 676 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The camera shake and object motion are usually inevitable when taking photos with hand-held devices, which lead to significant motion blur effects. Restoring clear photos from blurry ones has attracted lots of attention from both research and industry communities [40]. However, motion deblurring is quite challenging as only the blurred images are available while the blur and latent images are unknown.", + "bbox": [ + 75, + 686, + 468, + 792 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Significant progress has been made in image restoration due to the development of deep neural networks that directly learn the mapping from the degraded observation to", + "bbox": [ + 75, + 794, + 468, + 839 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "the clear image. It is well known that the residual learning strategy [7] has been widely used to ease the training of networks, where a latent clear image $I$ can be restored by the summation of the degraded input $B$ and the output $\\mathcal{N}(B)$ of a residual learning network $\\mathcal{N}$ . This strategy has been proven to be effective in lots of image restoration tasks, e.g., image super-resolution, as the degraded image $B$ shares the same main structures as the clear one $I$ , and the residual between $B$ and $I$ mainly contains image details.", + "bbox": [ + 500, + 252, + 890, + 388 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "However, we note that the difference between a blurry input and its corresponding clear one not only contains image details but also involves some structures. Taking Figure 1 as an example, the main structures in the clear image (e.g., the pillars enclosed in the red boxes of Figure 1(f)) disappear due to the influence of the motion blur effect. Thus, in addition to the details smoothed by the blur, some main structures also exist in the residual between the blurry image and the clear one (see the part enclosed in the red box of Figure 1(b)). As demonstrated in [22], the standard residual learning method [7] is effective for modeling the high-frequency information but less effective to restore the low-frequency contents. Figure 1(c) also shows that using the standard residual learning method may not estimate the main structures of the residual image well, which thus affects the final image restoration (Figure 1(h)). Therefore, it is important for image deblurring to effectively model the main structures distorted by the motion blur.", + "bbox": [ + 496, + 388, + 892, + 660 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To alleviate the above-mentioned problem, the recent methods [15, 34] introduce a frequency branch based on the Fast Fourier Transform (FFT) in the residual network, which achieves good performance. However, as such a frequency branch is achieved by applying $\\mathrm{Conv}1 + \\mathrm{ReLU} + \\mathrm{Conv}1^2$ to the concatenation of the real and imaginary parts of the residual image, it may not effectively model the spatially-variant property of the global main structures in the residual image (Figure 1(d)), resulting in fake structures caused by the blur in the final deblurred image (Figure 1(i)).", + "bbox": [ + 496, + 662, + 893, + 813 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we propose a Multi-scale Residual LowPass Filter Network (MRLPFNet) for high-quality image deblurring. Our goal is to effectively model both the low-", + "bbox": [ + 496, + 814, + 893, + 861 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author", + "bbox": [ + 94, + 849, + 222, + 863 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "1Note that the high-frequency contents in an image correspond to the image details, while the low-frequency ones denote the main structures of an image.", + "bbox": [ + 76, + 863, + 468, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "$^{2}\\mathrm{Conv1} + \\mathrm{ReLU} + \\mathrm{Conv1}$ denotes two $1\\times 1$ convolutional layers with the usual ReLU activation in between.", + "bbox": [ + 500, + 875, + 890, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "12345", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b6581055534c2449b4a4e0f3216c10aee340740d8d6c46966353d086b10c4b54.jpg", + "image_caption": [ + "(a) Blurry input" + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 240, + 183 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/d890def7c410f8ee2710b6a6864d005fa2f34da52bc243c7498f22319f59e694.jpg", + "image_caption": [ + "(b) Difference of (a) & (f)" + ], + "image_footnote": [], + "bbox": [ + 243, + 88, + 401, + 183 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/b4fcf9eafd674f307bb7a97e792e6d159d22645faa4d0ea8d4d1971cf8671d7f.jpg", + "image_caption": [ + "(c) Residual by [37]" + ], + "image_footnote": [], + "bbox": [ + 405, + 88, + 565, + 183 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/62067ed912ba4c674e7408d1d8c95886496b2cb6ff9a0bef0d757b544d212a92.jpg", + "image_caption": [ + "(d) Residual by [15]" + ], + "image_footnote": [], + "bbox": [ + 566, + 88, + 725, + 183 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/30caddc53c4fb065ec0c712383094e3a21e952467851033e66902e6ed492cc27.jpg", + "image_caption": [ + "(e) Residual by MRLPFNet" + ], + "image_footnote": [], + "bbox": [ + 728, + 88, + 890, + 183 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/6e06899f7e041270afb66dc232af5c6198f0b99131befe82a2188c3dbedc69de.jpg", + "image_caption": [ + "(f) Ground truth" + ], + "image_footnote": [], + "bbox": [ + 80, + 196, + 240, + 292 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/1914c8e9e70f904808850776ad18a1569c40a1eb2b60d50cbcc1675f6e6d7848.jpg", + "image_caption": [ + "(g) Restomer [36]" + ], + "image_footnote": [], + "bbox": [ + 243, + 196, + 401, + 292 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/a2ddb9903f8874849d1d4cacd710936bd2350be8d47a4a1934a465ac961d9a3f.jpg", + "image_caption": [ + "(h) MPRNet [37]", + "Figure 1. Visual comparison with state-of-the-art image deblurring methods on a challenging example. Our work is motivated by an observation that the difference between the blurry image and its corresponding clear one not only contains high-frequency contents but also includes low-frequency information due to the influence of the blur as shown in (b). We thus develop a simple yet effective MRLPFNet to learn both image details and spatially-variant structures (see (e)), which thus leads to better-deblurred results as shown in (j)." + ], + "image_footnote": [], + "bbox": [ + 405, + 196, + 563, + 292 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/ac1b2b17d78618d7aee0d9bf8f9988bdd737b5f611d938a95b96eac77fe3984c.jpg", + "image_caption": [ + "(i) DeepRFT [15]" + ], + "image_footnote": [], + "bbox": [ + 566, + 196, + 725, + 292 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/7fd613423c08eb83f42b9334bee12fc7a4e4243346648affdf445fc363b61e7f.jpg", + "image_caption": [ + "(j) MRLPFNet (Ours)" + ], + "image_footnote": [], + "bbox": [ + 728, + 196, + 890, + 292 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "frequency and high-frequency parts of the residual image between the blurry input and its corresponding clear output within the residual learning framework. To better explore the low-frequency information, we propose to intuitively apply a low-pass filter on the residual image to concentrate on the low-frequency part. In addition, as the low-frequency contents in an image correspond to the global main structures, one of whose properties is that they are usually spatially variant, we exploit a learnable low-pass filter module based on a self-attention mechanism (as a basic module) to adaptively explore the global contexts so that the main structures can be better restored for image deblurring. Then we incorporate it in the proposed Residual Low-Pass Filter (RLPF) module with an additional residual learning branch based on a fully convolutional neural network (CNN) for modeling the high-frequency information.", + "bbox": [ + 75, + 383, + 468, + 626 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Furthermore, the multi-scale strategy is widely used in image deblurring. As features from various scales have different spatial resolutions, resizing operations are usually used to fuse these features. However, simply using resizing operations based on downsampling or upsampling will lead to information loss. To this end, we develop a simple yet effective feature fusion module based on the wavelet transform to fuse the features with different spatial resolutions. Finally, we embed the proposed RLPF module and the wavelet-based feature fusion (WFF) module into an end-to-end trainable network within a coarse-to-fine framework. The proposed approach achieves favorable performance on widely-used benchmarks.", + "bbox": [ + 75, + 627, + 468, + 823 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The main contributions are summarized as follows.", + "bbox": [ + 96, + 824, + 434, + 838 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "- We propose an effective RLPF module to model both the high-frequency and low-frequency information of the difference between the network input and output for image deblurring. Specifically, a learnable low", + "bbox": [ + 94, + 839, + 468, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "pass filter is developed based on a self-attention mechanism to adaptively explore the spatially-variant property of the global contexts to effectively reconstruct the low-frequency structures and a fully CNN with the residual learning is adopted to model the high-frequency information.", + "bbox": [ + 529, + 383, + 890, + 474 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We develop a simple yet effective feature fusion module based on the wavelet transform to fuse the features of different scales for better image deblurring.", + "- By training the proposed MRLPFNet in an end-to-end manner, we show that it performs favorably against state-of-the-art methods." + ], + "bbox": [ + 517, + 474, + 890, + 564 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 580, + 640, + 597 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Hand-crafted prior-based methods. As image deblurring is ill-posed, conventional methods usually develop kinds of effective priors to constrain the solution space, e.g., sparsity priors on the image gradient [11, 35] or intensity [19], internal patch recurrence [16], sparsity of dark channel prior [21], etc. These hand-crafted priors can help the blur removal. However, they do not fully exploit the characteristics of the clear image data and usually lead to complicated optimization problems.", + "bbox": [ + 496, + 606, + 890, + 743 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Deep learning-based methods. Instead of manually designing image priors, lots of methods develop kinds of deep CNNs to solve image deblurring. Early approaches employ deep CNN models to estimate blur kernels and then use existing prior-based restoration methods to estimate the clear images [27, 6, 1, 24]. While inaccurate blur kernels will lead to deblurred results with severe artifacts as the blur kernels and latent clear images are estimated independently.", + "bbox": [ + 496, + 750, + 890, + 869 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Instead of estimating blur kernels, numerous methods [17, 39, 28, 5, 38, 26, 37, 3, 18, 12] directly estimate", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "12346", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "clear images from blurry ones. In [17], Nah et al. develop a multi-scale deep CNN, where the restored images from coarse scales are resized to help the estimation of finer scales. To better explore the multi-scale information, Tao et al. [28] develop an effective scale recurrent neural network. In [5], Gao et al. propose a parameter selective sharing and nested skip connection method to improve [17]. Although the methods based on a multi-scale strategy achieve decent performance, simply increasing the model depth with more scales cannot further improve the quality of deblurring. To overcome this problem, methods based on multi-patches have been developed. Zhang et al. [38] develop an effective deep hierarchical multi-patch network, where the features from the previous stage are concatenated to facilitate the estimation of the following stages. Zamir et al. [37] propose a multi-stage progressive method to better explore the features from multi-stages by a cross-scale feature fusion module. In addition, an effective supervised attention module is developed to better guide the estimations of the following stages. As both the multi-scale and multi-patch methods need to perform the network at each scale or stage recurrently, which leads to high computational costs, Cho et al. [3] develop a multi-input and multi-output U-net based on a multi-scale strategy to solve image deblurring.", + "bbox": [ + 76, + 90, + 472, + 454 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "These above-mentioned methods achieve significant performance, most of which adopt the residual learning in the network design. As demonstrated in [20], the residual learning is able to model the image details (i.e., high-frequency information), but is less effective for exploring the main structures (i.e., low-frequency information). To overcome this problem, Mao et al. [15] improve the residual learning network by introducing an additional branch performed in the frequency domain. However, as the main structures involve the spatially-variant global contexts, simply using the local operations (e.g., $1 \\times 1$ convolution in [15]) may not model the main structures well.", + "bbox": [ + 76, + 457, + 472, + 640 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Transformer-based methods. As Transformer is effective for global context exploration and shows great potential in many vision tasks, several methods apply it to image deblurring. Zamir et al. [36] propose an efficient Transformer model by estimating self-attention along the channel dimension. This method is further simplified by [2]. Tsai et al. [29] develop a Transformer-based model by constructing intra- and inter-strip tokens to reweight image features in the horizontal and vertical directions. In [30], Tu et al. develop an effective multi-axis MLP-based architecture. Wang et al. [31] develop a general U-shaped Transformer to solve image deblurring. These Transformer-based approaches achieve decent results. However, as our analysis in Section 3 shows, self-attention has the same effect as the low-pass filter. Simply using Transformers may lead to over-smoothed results.", + "bbox": [ + 76, + 657, + 472, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Low-Pass Filter and Self-Attention", + "text_level": 1, + "bbox": [ + 498, + 89, + 816, + 107 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To better motivate our work, we first describe the relations between the low-pass filter and self-attention.", + "bbox": [ + 498, + 114, + 890, + 143 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given an image $I$ and a low-pass filter $\\mathcal{F}$ , we can obtain a filtered image $f$ by:", + "bbox": [ + 498, + 145, + 890, + 175 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nf (\\mathrm {x}) = \\mathcal {F} (I (\\mathrm {x})) = \\sum_ {\\mathrm {y}} \\mathbf {W} _ {\\mathrm {x y}} I (\\mathrm {y}), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 578, + 185, + 890, + 218 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $x$ and $y$ denote image pixels; $\\mathbf{W}_{\\mathrm{xy}}$ denotes the filter weight for $\\mathcal{F}$ , satisfying $\\mathbf{W}_{\\mathrm{xy}} \\geq 0$ and $\\sum_{y} \\mathbf{W}_{\\mathrm{xy}} = 1$ . The role of a low-pass filter is to do a weighted average in an area with the same size as the filter, thus filtering out the high-frequency information and retaining the low-frequency one. One common type of filter is the linear translation-invariant filter, e.g., the Gaussian filter, which adopts the spatially-invariant filter weight and cannot effectively describe the variant properties of image structures in different spatial areas. Another type of filter is the nonlinear filter, e.g., the bilateral filter, whose weights depend on both the spatial closeness and the intensity difference. Such weights can adaptively model the spatially-variant contexts (e.g., global edges), thus preserving more useful low-frequency information in the filtered image.", + "bbox": [ + 496, + 220, + 892, + 446 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Recently, the attention-based approaches, e.g., self-attention, compute the weighted value as", + "bbox": [ + 498, + 446, + 890, + 477 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Z} = \\mathbf {S} \\circledast \\mathbf {V} = \\operatorname {s o f t m a x} \\left(\\frac {\\mathcal {Q} (F) \\mathcal {K} (F) ^ {\\top}}{\\sqrt {d _ {k}}}\\right) \\mathcal {V} (F), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 522, + 486, + 890, + 522 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $F$ denotes the deep feature extracted from the input image $I$ ; $\\ast$ indicates the matrix multiplication; $\\mathcal{Q}(\\cdot), \\mathcal{K}(\\cdot)$ , and $\\mathcal{V}(\\cdot)$ denote the operations that extract the matrices for the query, key, and value; $d_k$ is the dimension of the keys. A softmax normalized operation is applied to each row of $\\mathbf{S}$ to ensure $\\mathbf{S}_{ij} \\geq 0$ and $\\sum_{j} \\mathbf{S}_{ij} = 1$ , where $i$ and $j$ denote the index of the row and column in $\\mathbf{S}$ . Thus, each row of $\\mathbf{S}$ can be regarded as a low-pass filter. Compared to the bilateral filter whose weight measures the spatial and color similarity based on the exponential Euclidean distance, the attention value measures the similarity of query and key based on the correlation metric. Therefore, it is spatially variant and can model the main structures more adaptively.", + "bbox": [ + 496, + 529, + 893, + 726 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Considering the self-attention (2) is learnable and more flexible, we propose to straightforwardly embed it into the network to better model the low-frequency information for image deblurring.", + "bbox": [ + 496, + 726, + 893, + 787 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. MRLPFNet", + "text_level": 1, + "bbox": [ + 498, + 799, + 624, + 815 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our goal is to develop an effective MRLPFNet for high-quality image deblurring, which can better restore both the image details and main structures. Specifically, we first propose a learnable low-pass filter based on the self-attention method to model the low-frequency information. We then", + "bbox": [ + 496, + 824, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "12347", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/8650aa55cc075fa1195eb00fcb19806bfdf2367403d8d96d7ea3a7ba2373a6f2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 83, + 88, + 607, + 244 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/b321282ffb04b23800025ad00cebeadc84afaba3e5bcbbeb13521bf4014a0b18.jpg", + "image_caption": [ + "Figure 2. Multi-scale residual low-pass filter network. To restore high-quality images with clearer structures, we propose an effective RLPF module that involves a learnable low-pass filter (based on the self-attention) to explore the low-frequency information (through Eqs. (3), (4), and (5)). A wavelet-based feature fusion (WFF) module is developed to fuse the features of various scales for better image deblurring." + ], + "image_footnote": [], + "bbox": [ + 84, + 250, + 607, + 265 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/502accac8d3b6c346e987c32b1bf946104900353fcb996e8ee4b3c5d4dac898d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 614, + 90, + 880, + 266 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "incorporate it in our proposed RLPF module with an additional residual learning branch for high-frequency information exploration. Furthermore, we formulate it into an end-to-end trainable network based on a coarse-to-fine framework and propose a feature fusion module based on the wavelet transform to better utilize the multi-scale features. In the following, we present the details of the proposed method.", + "bbox": [ + 75, + 329, + 470, + 449 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Residual Low-Pass Filter", + "text_level": 1, + "bbox": [ + 76, + 458, + 305, + 472 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As the standard residual learning is adept at exploring the high-frequency information [9, 20] while less effective for the low-frequency information modeling, the method [15] improves the standard residual block by introducing an additional branch that applies Conv1 + ReLU + Conv1 to the features (generated by the FFT) in the frequency domain. Although decent performance has been achieved, the $1 \\times 1$ convolution is spatially invariant, which does not effectively model the spatially-variant structures. To overcome this problem, we propose to further improve it by applying a learnable low-pass filter to concentrate on the global main structures, which is able to model the spatially-variant property of the low-frequency information.", + "bbox": [ + 75, + 481, + 468, + 678 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Specifically, we first generate the feature $\\mathbf{Y}$ from a blurry input $I$ by a shallow feature extraction network (the details are included in the supplemental material). Then the proposed RLPF module explores the properties of residual learning in both the spatial and frequency domains according to [15]:", + "bbox": [ + 75, + 678, + 468, + 768 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {F} = \\mathbf {Y} + \\mathcal {R} (\\mathbf {Y}) + \\mathcal {F} (\\mathbf {Y}), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 181, + 779, + 468, + 796 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{R}(\\cdot)$ denotes a plain network that applies Conv3 + ReLU + Conv3 in the spatial domain and $\\mathcal{F}(\\cdot)$ denotes a network [15] with Conv1 + ReLU + Conv1 employed in the frequency domain.", + "bbox": [ + 76, + 805, + 468, + 866 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As Eq. (3) is based on the locally spatially-invariant convolution operations, it does not effectively model the spatially-variant main structures (see Figure 1(d)). To this end, we develop a learnable low-pass filter, which is proposed based on Eq. (1) and achieved by:", + "bbox": [ + 498, + 329, + 890, + 405 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {h} _ {i} = \\sum_ {j} \\mathbf {S} _ {i j} \\mathbf {f} _ {j}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 640, + 412, + 890, + 446 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbf{f}_j$ is the $j$ -th feature map of $\\mathbf{F}$ . Based on the discussions in Section 3, the self-attention can be regarded as a spatially-variant low-pass filter, which can better model the global low-frequency contents. Then we use the standard scaled dot-production attention in the Transformer according to [36] to estimate the filter weight matrix $\\mathbf{S}$ . Finally, we obtain the filtered feature $\\mathbf{E}$ by:", + "bbox": [ + 498, + 455, + 892, + 561 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {E} = \\mathbf {F} + \\mathcal {D} (\\mathbf {H}), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 637, + 571, + 890, + 587 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbf{H} = \\{\\mathbf{h}_i\\}$ is the low-frequency feature by Eq. (4) and $\\mathcal{D}$ denotes a $3\\times 3$ depth-wise convolution layer.", + "bbox": [ + 498, + 595, + 890, + 626 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We refer to the module achieved by Eqs. (3), (4), and (5) as the proposed RLPF module, which is then embedded into an encoder-decoder architecture as shown in Figure 2(a).", + "bbox": [ + 498, + 627, + 890, + 672 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. Wavelet-based Feature Fusion", + "text_level": 1, + "bbox": [ + 500, + 681, + 767, + 695 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To efficiently ease and improve the deblurring process, the recent methods [3, 15] utilize the multi-scale features generated by different encoder blocks to prompt the learning of various decoder blocks. As the spatial resolutions of the features from different scales are not the same, they are usually resized by downsampling or upsampling operations to the same spatial resolution for feature fusion. However, these resizing operations may lose some important structural details, thus affecting the final image restoration. As the wavelet transform [8] can model the image scale information and is insertable, we develop a wavelet-based feature fusion method to better fuse the features of various scales for image deblurring.", + "bbox": [ + 496, + 704, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "$^3$ Conv3 + ReLU + Conv3 denotes two $3 \\times 3$ convolutional layers with the usual ReLU activation in between.", + "bbox": [ + 76, + 875, + 468, + 898 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "12348", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Specifically, considering two features $\\mathbf{E}_s$ and $\\mathbf{E}_{s + 1}$ generated by Eq. (5) for the finer image scale $s$ and coarser image scale $s + 1$ , we first apply the Haar transform $\\mathcal{H}$ [32, 14, 33] to $\\mathbf{E}_s$ and obtain", + "bbox": [ + 76, + 90, + 468, + 151 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{\\mathbf {E} _ {s} ^ {L L}; \\mathbf {E} _ {s} ^ {L R}; \\mathbf {E} _ {s} ^ {R L}; \\mathbf {E} _ {s} ^ {R R} \\right\\} = \\mathcal {H} (\\mathbf {E} _ {s}), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 160, + 468, + 180 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{E}_s^{LL}$ denotes the low-frequency part and $\\mathbf{E}_s^{LR},\\mathbf{E}_s^{RL}$ , and $\\mathbf{E}_s^{RR}$ correspond to three high-frequency parts. Thus, the resolutions of $\\{\\mathbf{E}_s^{LL};\\mathbf{E}_s^{LR};\\mathbf{E}_s^{RL};\\mathbf{E}_s^{RR}\\}$ are the same as that of $\\mathbf{E}_{s + 1}$ . To make use of both $\\mathbf{E}_s$ and $\\mathbf{E}_{s + 1}$ for the decoder block in the finer image scale $s$ , the wavelet-based feature fusion generates the fused feature $\\hat{\\mathbf{E}}_s$ by:", + "bbox": [ + 76, + 186, + 468, + 280 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {E}} _ {s} = \\mathcal {H} ^ {- 1} \\left(\\mathcal {N} _ {s} ^ {L} \\left(\\mathcal {C} \\left(\\mathbf {E} _ {s} ^ {L L}, \\mathbf {E} _ {s + 1}\\right)\\right), \\mathcal {N} _ {s} ^ {H} \\left(\\mathcal {C} \\left(\\mathbf {E} _ {s} ^ {L R}, \\mathbf {E} _ {s} ^ {R L}, \\mathbf {E} _ {s} ^ {R R}\\right)\\right)\\right), \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 287, + 493, + 319 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathcal{H}^{-1}$ is the inverse Haar transform; $\\mathcal{C}(\\cdot)$ indicates the concatenation along the channel dimension; $\\mathcal{N}_s^L$ is a network consisting of two $3\\times 3$ convolutional layers with the PReLU activation in between and $\\mathcal{N}_s^H$ contains one $1\\times 1$ convolutional layer followed by the PReLU activation and one $3\\times 3$ convolutional layer. When fusing $\\mathbf{E}_s$ and $\\mathbf{E}_{s + 1}$ to facilitate the decoder block in the coarser image scale $s + 1$ , we obtain the fused feature $\\hat{\\mathbf{E}}_{s + 1}$ by", + "bbox": [ + 75, + 320, + 468, + 441 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {E}} _ {s + 1} = \\mathcal {N} _ {s + 1} ^ {L} \\left(\\mathcal {C} \\left(\\mathbf {E} _ {s + 1}, \\mathbf {E} _ {s} ^ {L L}, \\mathcal {N} _ {s + 1} ^ {H} \\left(\\mathcal {C} \\left(\\mathbf {E} _ {s} ^ {L R}, \\mathbf {E} _ {s} ^ {R L}, \\mathbf {E} _ {s} ^ {R R}\\right)\\right)\\right)\\right), \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 449, + 486, + 481 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathcal{N}_{s + 1}^{L}$ and $\\mathcal{N}_{s + 1}^{H}$ have the same network architecture as $\\mathcal{N}_s^L$ and $\\mathcal{N}_s^H$ , respectively (Note that the network parameters are not shared across scales). We take the fused features $\\hat{\\mathbf{E}}_s$ and $\\hat{\\mathbf{E}}_{s + 1}$ instead of $\\mathbf{E}_s$ and $\\mathbf{E}_{s + 1}$ as the input for the following decoder blocks. Figure 2(b) shows the details of the proposed wavelet-based feature fusion module.", + "bbox": [ + 75, + 481, + 468, + 571 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "When fusing features from more scales, we can recurrently use Eqs. (7) and (8). As the wavelet transform is invertible, all the information can be better preserved during the transformation. We show the effectiveness of the wavelet-based feature fusion in Section 6.2.", + "bbox": [ + 75, + 573, + 468, + 648 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5. Experimental Results", + "text_level": 1, + "bbox": [ + 76, + 661, + 282, + 678 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We first describe the implementation details of the proposed MRLPFNet. Then we evaluate our approach on the commonly used benchmarks and compare it against the state-of-the-art methods. Due to the page limit, we include more results in the supplemental material. The PyTorch code and trained models are available at our Project page.", + "bbox": [ + 75, + 686, + 468, + 777 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.1. Implementation details", + "text_level": 1, + "bbox": [ + 76, + 786, + 290, + 801 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We embed the proposed RLPF module into an encoder-decoder network [3], which contains three encoder blocks and three decoder blocks. For each encoder/decoder block, we adopt a stack of 8 RLPF modules (i.e., $N = 8$ in Figure 2(a)). We then use the wavelet-based feature fusion module to fuse the features generated by the encoder blocks of", + "bbox": [ + 75, + 809, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/667ed06557c67f6dbc30233e89046db2b0d965e0980670c3db73a341915e92fe.jpg", + "table_caption": [ + "Table 1. Quantitative evaluations of the proposed approach against state-of-the-art methods on the GoPro dataset [17]. \"MRLPFNet-L\" denotes the proposed method using 20 RLPF modules in each encoder and decoder block (i.e., $N = 20$ in Figure 2(a))." + ], + "table_footnote": [], + "table_body": "
MethodPSNR (dB)SSIM
SRN [28]30.260.9342
SSN [5]30.920.9421
DMPHN [38]31.200.9453
SAPHNet [26]31.850.9480
MPRNet [37]32.660.9589
MPRNet-Local [4]33.310.9637
MIMO-UNet [3]31.730.9510
DeepRFT [15]32.820.9600
Uformer [31]33.060.9670
Restormer [36]32.920.9611
Restormer-Local [4]33.570.9656
MAXIM [30]32.860.9616
NAFNet [2]33.710.9668
Stripformer [29]33.080.9624
MRLPFNet33.500.9650
MRLPFNet-L34.010.9682
", + "bbox": [ + 503, + 143, + 890, + 364 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3 different image scales. We implement our method based on the PyTorch framework and train it from scratch using a machine with two NVIDIA GeForce RTX 3090 GPUs. The proposed network is trained using the Adam optimizer [10] with default parameters. The batch size is set to be 8. The size of each image patch is $256 \\times 256$ pixels. The learning rate is initialized to be $2 \\times 10^{-4}$ and is updated by the Cosine Annealing scheme. The loss function [37] is adopted to constrain the network training.", + "bbox": [ + 496, + 392, + 890, + 527 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.2. Comparisons with the state of the art", + "text_level": 1, + "bbox": [ + 498, + 541, + 820, + 556 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluations on the GoPro dataset. We first quantitatively evaluate the proposed method on the GoPro dataset [17], which contains 2,103 images for training and 1,111 images for the test. We compare the proposed method against several state-of-the-art methods including CNN-based methods (SRN [28], SSN [5], DMPHN [38], SAPHNet [26], MPR-Net [37], MIMO-UNet [3], DeepRFT [15], NAFNet [2]), Transformer-based methods (Restormer [36], Uformer [31], Stripformer [29]), and MLP-based methods (MAXIM [30]). For fair comparisons, we fine-tune or retrain the deep learning-based methods that are not trained on the GoPro dataset. We use the PSNR and SSIM as metrics to evaluate the quality of restored images.", + "bbox": [ + 496, + 565, + 890, + 762 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1 shows the quantitative results. The proposed method generates higher-quality images with higher PSNR and SSIM values than the competing approaches.", + "bbox": [ + 496, + 763, + 890, + 808 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Figure 3 shows a visual comparison. Most of the CNN-based methods, e.g., [37, 3, 2], employ the commonly used residual learning in the network designs, which is less effective for the estimation of the main structures, as demonstrated in Section 1. Thus, these methods [37, 3, 2] do not effectively remove the blur as shown in Figure 3(c), (d), and", + "bbox": [ + 496, + 809, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "12349", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/8f92bd178be9d27d5f6c27a36e1648c057f57f6e8801dce59e59a4c3c3a89b22.jpg", + "image_caption": [ + "(a) Blurry input" + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 240, + 203 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c4b7904d6b1db49b0a416b17187bfcaa3cf89d21ccee0854a788a26300f2a020.jpg", + "image_caption": [ + "(b) Ground truth" + ], + "image_footnote": [], + "bbox": [ + 243, + 88, + 401, + 203 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/ff0ad8ff87bc9c6ceaf2ed56f85ebc88e4820aabeefff810e17440370560c011.jpg", + "image_caption": [ + "(c) MPRNet [37]" + ], + "image_footnote": [], + "bbox": [ + 405, + 89, + 563, + 203 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/095062c2624b6f64e96fd170191c1cfebf72e604dddb8661660ea2caa3bf2753.jpg", + "image_caption": [ + "(d) MIMO-UNet [3]" + ], + "image_footnote": [], + "bbox": [ + 566, + 89, + 725, + 203 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1be4550cc0238fcef0fc919b59ca6a924486d333fec435df1c35bf5e89bb114f.jpg", + "image_caption": [ + "(e) DeepRFT [15]" + ], + "image_footnote": [], + "bbox": [ + 730, + 89, + 888, + 203 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/61646512cc530ba90b0b1e85bd0b08e389dfec53f5df0cc84b7554649d17bbf5.jpg", + "image_caption": [ + "(f) NAFNet [2]" + ], + "image_footnote": [], + "bbox": [ + 80, + 217, + 238, + 330 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/dcb8e754f091f88c22db4f952322f03ad666b00fca542786c3f0026f6dcb02bf.jpg", + "image_caption": [ + "(g) Restomer [36]" + ], + "image_footnote": [], + "bbox": [ + 243, + 217, + 401, + 330 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/762a2f8372a8f47358815f7dd5d03620275a87f458b0dd55141d29e9dab5a5bd.jpg", + "image_caption": [ + "(h) Restormer-Local [4]", + "Figure 3. Example from the GoPro dataset [17]. Compared to the evaluated methods in (c)-(i), the proposed approach generates a better deblurred image with clearer characters in (j)." + ], + "image_footnote": [], + "bbox": [ + 405, + 217, + 563, + 330 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/2c9466c1e4782c04683de9d4cdf04844bb8ab033726566447121e68fc1a5dd94.jpg", + "image_caption": [ + "(i) Stripformer [29]" + ], + "image_footnote": [], + "bbox": [ + 566, + 217, + 725, + 330 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/fd75f4ec1c343dfe9d426adf10d4f39ce3b6b2815b91486723b9e96e7c7e8fac.jpg", + "image_caption": [ + "(j) MRLPFNet" + ], + "image_footnote": [], + "bbox": [ + 730, + 217, + 888, + 330 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "(f). The method [15] improves the residual learning by introducing an additional branch operating in the frequency domain. However, as the main structures are usually spatially variant, simply using localized convolution operations does not effectively model such global properties. The deblurred result in Figure 3(e) still contains the blur effect.", + "bbox": [ + 75, + 398, + 468, + 489 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The recent methods [36, 29] develop Transformers to solve image deblurring. As analyzed in Section 3, Transformers can be regarded as low-pass filters. These methods are able to explore the low-frequency contents but less effective for modeling the high-frequency information, thus leading to over-smoothed deblurred results as shown in Figure 3(g) and (i). In contrast to the above-mentioned methods, the proposed MRLPFNet is able to explore both high- and low-frequency information, generating a better image with clearer details and structures than the competed methods (e.g., the restored numbers in Figure 3(j) are clearer).", + "bbox": [ + 75, + 491, + 468, + 657 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluations on the RealBlur dataset. The RealBlur dataset [23] contains 3,758 image pairs for training and 980 image pairs for the test. Based on the protocols of [23], our approach is compared with the state-of-the-art methods for fair comparisons. Table 2 shows that the proposed method generates the deblurred results with higher PSNR and SSIM values, where the PSNR values of our method are at least 1.08dB and 0.71dB higher than the evaluated methods on the \"RealBlur-R\" and \"RealBlur-J\" datasets, respectively.", + "bbox": [ + 75, + 672, + 468, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Figure 4 shows some visual comparisons of the evaluated methods. The methods [28, 13, 3] based on the standard residual learning do not effectively remove the blur effects as shown in Figure 4(c)-(e). The method [15] improves the standard residual learning, but the restored images are oversmoothed, e.g., the strokes in Figure 4(f). The Transformer", + "bbox": [ + 75, + 810, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/f8264fb011c61c83f009b730df38fa7213fe9acb0ea5198e5eb88b4e5b68ef1d.jpg", + "table_caption": [ + "Table 2. Quantitative evaluations of the proposed approach against state-of-the-art methods on the RealBlur dataset [23]. All the comparison results are generated using the publicly available codes and the models trained on the same training datasets." + ], + "table_footnote": [], + "table_body": "
RealBlur-RRealBlur-J
PSNR (dB)SSIMPSNR (dB)SSIM
SRN [28]38.650.965231.380.9091
DeblurGAN [12]36.440.934729.690.8703
MIMO-UNet+ [3]--31.920.9190
DeepRFT+ [15]39.840.972132.190.9305
Stripformer [29]39.840.973732.480.9290
MRLPFNet40.920.975333.190.9361
", + "bbox": [ + 501, + 453, + 890, + 571 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/c413aa463d13c8a5ec821d2b6926a97443ff48b2d874431def11f8b965d6bd37.jpg", + "table_caption": [ + "Table 3. Quantitative evaluations of the proposed approach against state-of-the-art methods on the HIDE dataset [25]. All the comparison results are generated by the same models trained on the GoPro dataset [17] as in Table 1." + ], + "table_footnote": [], + "table_body": "
MethodPSNR (dB)SSIM
SRN [28]28.360.9040
SAPHNet [26]29.980.9300
MPRNet [37]30.960.9394
MPRNet-Local [4]31.190.9418
MIMO-UNet [3]29.280.9206
MIMO-UNet+ [3]29.990.9304
DeepRFT [15]30.990.9407
DeepRFT+ [15]31.420.9442
Restormer [36]31.220.9423
Restormer-Local [4]31.490.9447
Stripformer [29]31.030.9395
MRLPFNet31.630.9465
", + "bbox": [ + 503, + 641, + 890, + 813 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "based method [29] tends to generate over-smoothed results and does not effectively remove the blur as shown in Figure 4(g). In contrast, our method generates clearer images than the evaluated methods (Figure 4(h)).", + "bbox": [ + 498, + 839, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "12350", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/d3199ca2147d0862ed0e3928716caa501ff800ecca32518316a41ace56020cca.jpg", + "image_caption": [ + "(a) Blurry input" + ], + "image_footnote": [], + "bbox": [ + 81, + 89, + 279, + 265 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e64b748c104a03b6094dcb09077c5f346b8d634bd8e9b139473c682c5a6f8067.jpg", + "image_caption": [ + "(b) Ground truth" + ], + "image_footnote": [], + "bbox": [ + 282, + 90, + 482, + 265 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/c3e86dfe3452a3031759268d4f4469b849a312427795a25696620ef22bcff952.jpg", + "image_caption": [ + "(c) SRN [28]" + ], + "image_footnote": [], + "bbox": [ + 486, + 90, + 684, + 263 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9d04394ec46fade466d265b7703338937f6e42fb391823a701f653958e77eb80.jpg", + "image_caption": [ + "(d) DeblurGAN-V2 [13]" + ], + "image_footnote": [], + "bbox": [ + 689, + 90, + 887, + 265 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/5f6332d4ae5cdf73b8a3b3399d7efce64032af10644a06c55be6fbd3338487a3.jpg", + "image_caption": [ + "(e) MIMO-UNet [3]" + ], + "image_footnote": [], + "bbox": [ + 80, + 281, + 279, + 455 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/52560ac310d7f7554045564df6345b9c19915bdf923712dabcad24b206041281.jpg", + "image_caption": [ + "(f) DeepRFT+ [15]" + ], + "image_footnote": [], + "bbox": [ + 282, + 281, + 482, + 455 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/67c74301564910ec80b93e8b1e1db37ea80bb6878e4e220208a93c4459871c73.jpg", + "image_caption": [ + "(g) Stripformer [29]" + ], + "image_footnote": [], + "bbox": [ + 486, + 281, + 684, + 455 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/29ece7ad1151b45924c9d53085650793f70136e3bac6ecee60137378b3a5d4e5.jpg", + "image_caption": [ + "(h) MRLPFNet", + "Figure 4. Example from the RealBlur dataset [23]. Compared with the deblurred results in (c)-(g), the proposed method recovers a high-quality image with clearer structural details." + ], + "image_footnote": [], + "bbox": [ + 689, + 281, + 888, + 455 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/cd93951443b559230b725e353656f4135f7f18bd65d96ac70578b244d6657462.jpg", + "table_caption": [ + "Table 4. Effectiveness of the proposed low-pass filter and wavelet-based feature fusion for image deblurring. All baseline methods are trained using the same settings as the proposed method for fair comparisons." + ], + "table_footnote": [], + "table_body": "
Low-pass filter (LPF)Feature fusion (FF)GoPro
Bilinear-based (BFF)Wavelet-based (WFF)PSNR (dB)/SSIM
MRLPFNetw/o LPF&FFXXX32.8/0.9606
MRLPFNetw/o LPF&w/BFFX✓X32.9/0.9611
MRLPFNetw/o LPF&w/WFFXX✓33.0/0.9616
MRLPFNetw/ LPF&w/FF✓XX33.4/0.9641
MRLPFNet✓X✓33.5/0.9650
", + "bbox": [ + 81, + 541, + 887, + 643 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "**Evaluations on the **HIDE** dataset.** We further evaluate our method on the **HIDE** dataset [25] by using the model trained on the GoPro dataset. Table 3 shows that the proposed approach generates the deblurred results with the highest PSNR and SSIM values.", + "bbox": [ + 75, + 667, + 468, + 742 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6. Analysis and Discussions", + "text_level": 1, + "bbox": [ + 76, + 760, + 308, + 776 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.1. Effect of the learnable low-pass filter", + "text_level": 1, + "bbox": [ + 76, + 785, + 393, + 801 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The learnable low-pass filter is proposed to explore the spatially-variant low-frequency information so that the global structural contents can be better restored for image deblurring. To demonstrate the effectiveness of the proposed learnable low-pass filter, we first compare our method with a baseline that removes the learnable low-pass fil", + "bbox": [ + 75, + 810, + 468, + 898 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ter (MRLPFNet $_{\\mathrm{w/o LPF\\& w/WFF}}$ for short) and train this baseline using the same settings as ours. We use the GoPro dataset [17] as described in Section 5.2 for evaluation. Table 4 shows the quantitative results, where the PSNR of the proposed MRLPFNet is $0.5\\mathrm{dB}$ higher than the baseline without the learnable low-pass filter. To focus on the effect of the low-pass filter, we further disable the feature fusion module and compare the baselines with and without the learnable low-pass filter (MRLPFNet $_{\\mathrm{w/o LPF\\& FF}}$ and MRLPFNet $_{\\mathrm{w/ LPF\\& w/O FF}}$ for short). The comparisons in Table 4 illustrate the significance of using the learnable low-pass filter, which is able to concentrate on the low-frequency information modeling and effectively recover the spatially-variant image structures for image deblurring.", + "bbox": [ + 496, + 667, + 890, + 880 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Figure 5 shows a visual comparison. The main structures", + "bbox": [ + 517, + 885, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "12351", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/fea7471daf2d2e01b177827ece1e69489a49be8dc442bcb4d0f1a0c898e4877c.jpg", + "image_caption": [ + "(a) Blur input" + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 205, + 180 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c8e595a1c20aed54db82b62ace8e89556c75328c7ded4f4b31a33c79d1e28dec.jpg", + "image_caption": [ + "(b) MRLPFNetw/o LPF&w/ WFF" + ], + "image_footnote": [], + "bbox": [ + 210, + 88, + 338, + 180 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/6af14ea7f7624de23ba0538aef9b78eb8c7aafbe3dec770113b6a420ed091d58.jpg", + "image_caption": [ + "(c) MRLPFNet" + ], + "image_footnote": [], + "bbox": [ + 343, + 88, + 470, + 179 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3dd6df872b10a1aafd391f4915f40abc6e098161a891611cae766b7aa74e4d5e.jpg", + "image_caption": [ + "(d)" + ], + "image_footnote": [], + "bbox": [ + 80, + 193, + 205, + 285 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/66f9e6107fdd5845c53ef46452ee31a31e3d4704df1e853eb07751753d878d15.jpg", + "image_caption": [ + "(e)" + ], + "image_footnote": [], + "bbox": [ + 210, + 193, + 338, + 285 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/736e56dfb4a707c1fce059433a9f1794aae53bfd66215786e874a9a07883fc21.jpg", + "image_caption": [ + "(f)", + "Figure 5. Effect of the proposed learnable low-pass filter. (d) is the residual image between the blurry image and Ground truth. (e) and (f) are the residual images estimated by MRLPFNetw/o LPF&w/ WFF and MRLPFNet, respectively." + ], + "image_footnote": [], + "bbox": [ + 343, + 193, + 470, + 285 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "in the residual image estimated by MRLPFNet $_{\\mathrm{w/o LPF\\& w/ WFF}}$ are not well recovered, e.g., the license plate numbers in Figure 5(e), resulting in the deblurred image with a blur effect (Figure 5(b)). In contrast, the residual image estimated by the proposed MRLPFNet is better restored, as using the learnable low-pass filter is able to model the spatially-variant image structures. Thus, our approach is more effective at yielding a clear image with distinct structures (e.g., the license plate numbers in Figure 5(f)).", + "bbox": [ + 75, + 381, + 467, + 517 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6.2. Effect of the wavelet-based feature fusion", + "text_level": 1, + "bbox": [ + 76, + 527, + 428, + 541 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To demonstrate the effectiveness of the wavelet-based feature fusion on fusing the features with different spatial resolutions, we first disable the learnable low-pass filter in our implementation (MRLPFNetw/o LPF&w/WFF for short). Then we compare with the baseline that replaces the wavelet-based feature fusion with the bilinear interpolation (MRLPFNetw/o LPF&w/BFF for short). The results in Table 4 show that using the bilinear interpolation as the feature fusion does not perform well as our method with the wavelet-based one, since the wavelet transform is invertible and can preserve more accurate information during the transform process. The qualitative comparisons in Figure 6 further show that using the wavelet-based feature fusion is able to improve the quality of the restored image (Figure 6(c)). We also compare our complete network with the baseline that removes the feature fusion module (MRLPFNetw/LPF&w/0FF for short). The comparisons in Figure 6 show the same tendency that using the wavelet-based feature fusion improves the final deblurring performance.", + "bbox": [ + 75, + 550, + 467, + 835 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6.3. Model complexity", + "text_level": 1, + "bbox": [ + 76, + 847, + 250, + 863 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We examine the model complexity of the proposed approach and the state-of-the-art methods in terms of model", + "bbox": [ + 76, + 869, + 467, + 898 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/387d1aa3e62cfc113f4669b6e5e75770c60dcd8156766b68ee1a57e510e048b2.jpg", + "image_caption": [ + "(a) Blurry input" + ], + "image_footnote": [], + "bbox": [ + 504, + 89, + 596, + 148 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/feb5defff863c4d846d44057fb7d8c57019ba343de882c1b12beed3b0764b59b.jpg", + "image_caption": [ + "(b)", + "Figure 6. Effect of the proposed wavelet-based feature fusion. (b) and (c) are the results obtained by the baselines using the Bilinear-based (MRLPFNetw/o LPF&w/BFF in Table 4) and the wavelet-based (MRLPFNetw/o LPF&w/WFF in Table 4) feature fusion, respectively." + ], + "image_footnote": [], + "bbox": [ + 599, + 89, + 694, + 148 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/cae9d2c41dc7cf868b89b37b3419ce3a991f8b52cb87a4517355d7b45faf3e4f.jpg", + "image_caption": [ + "(c)" + ], + "image_footnote": [], + "bbox": [ + 697, + 89, + 792, + 148 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/51f2aa5b2c2332809fc62ef06f04921d76bcf1c6b5ae5c5e5e200b4bed975227.jpg", + "image_caption": [ + "(d) Ground truth" + ], + "image_footnote": [], + "bbox": [ + 794, + 89, + 890, + 148 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/6151cf18dd14ebf8f560fa4a59d7d66ac065715eddb6836420f1dfa8a1491288.jpg", + "table_caption": [ + "Table 5. Model complexity of the top-performance methods on the above-mentioned datasets. The FLOPs are evaluated on image patches with the size of $256 \\times 256$ pixels based on the protocols of existing methods. The running time is evaluated on images with the size of $1280 \\times 720$ pixels. All the results are obtained on a machine with an NVIDIA GeForce RTX 3090 GPU." + ], + "table_footnote": [], + "table_body": "
MethodsModel parameters (M)FLOPs (G)Running time (/s)
MPRNet [37]20.17600.9806
MIMO-UNet+ [3]16.11510.2827
DeepRFT+ [15]23.01830.5518
Restormer [36]26.11550.9798
Stripformer [29]19.71700.6580
MRLPFNetw/o LPF11.4820.2613
MRLPFNet20.61290.8633
", + "bbox": [ + 501, + 314, + 890, + 411 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "parameters, running time, and FLOPs. Table 5 shows that our method has the lowest FLOPs value and also achieves competitive performance against the competed ones in terms of running time.", + "bbox": [ + 498, + 434, + 890, + 494 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitations. As the proposed learnable low-pass filter is based on the self-attention to estimate the filter weights, it moderately increases the running time as shown in Table 5 (see the comparisons of \"MRLPFNetw/o LPF\" and \"MRLPFNet\"). Future work will develop efficient and learnable low-pass filters for better image deblurring.", + "bbox": [ + 498, + 503, + 890, + 594 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "7. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 607, + 617, + 622 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We present an effective MRLPFNet to reconstruct both the low-frequency and high-frequency information for image deblurring. To better explore the spatially-variant structures, we develop a learnable low-pass filter based on the self-attention mechanism. Furthermore, we propose a wavelet-based feature fusion method to effectively fuse the features with different spatial resolutions. By formulating the proposed method into an end-to-end trainable network, we show that it performs favorably against state-of-the-art methods on benchmarks.", + "bbox": [ + 498, + 633, + 890, + 782 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgement. This work was supported in part by the National Key Research and Development Program of China under Grant 2022ZD0118801, the National Natural Science Foundation of China under Grants 62272233, 61922043, 61925204, and U22B2049, and the Fundamental Research Funds for the Central Universities under Grant 30922010910 and 30920041109.", + "bbox": [ + 498, + 795, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "12352", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Ayan Chakrabarti. A neural approach to blind motion deblurring. In ECCV, pages 221-235, 2016. 2", + "[2] Liangyu Chen, Xiaojie Chu, Xiangyu Zhang, and Jian Sun. Simple baselines for image restoration. 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IJCV, 130(9):2103-2130, 2022. 1" + ], + "bbox": [ + 78, + 90, + 468, + 414 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "12354", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/5c2653f2-ab7f-4799-9150-1c49cbf5bd6d_model.json b/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/5c2653f2-ab7f-4799-9150-1c49cbf5bd6d_model.json new file mode 100644 index 0000000000000000000000000000000000000000..fc0008be90ce90d536fb5f7eab2386039bccca40 --- /dev/null +++ b/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/5c2653f2-ab7f-4799-9150-1c49cbf5bd6d_model.json @@ -0,0 +1,2717 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.141, + 0.131, + 0.83, + 0.154 + ], + "angle": 0, + "content": "Multi-scale Residual Low-Pass Filter Network for Image Deblurring" + }, + { + "type": "text", + "bbox": [ + 0.227, + 0.181, + 0.744, + 0.219 + ], + "angle": 0, + "content": "Jiangxin Dong Jinshan Pan* Zhongbao Yang Jinhui Tang Nanjing University of Science and Technology" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.252, + 0.314, + 0.269 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.284, + 0.473, + 0.631 + ], + "angle": 0, + "content": "We present a simple and effective Multi-scale Residual Low-Pass Filter Network (MRLPFNet) that jointly explores the image details and main structures for image deblurring. Our work is motivated by an observation that the difference between the blurry image and the clear one not only contains high-frequency contents but also includes low-frequency information due to the influence of blur, while using the standard residual learning is less effective for modeling the main structure distorted by the blur. Considering that the low-frequency contents usually correspond to main global structures that are spatially variant, we first propose a learnable low-pass filter based on a self-attention mechanism to adaptively explore the global contexts for better modeling the low-frequency information. Then we embed it into a Residual Low-Pass Filter (RLPF) module, which involves an additional fully convolutional neural network with the standard residual learning to model the high-frequency information. We formulate the RLPF module into an end-to-end trainable network based on an encoder and decoder architecture and develop a wavelet-based feature fusion to fuse the multi-scale features. Experimental results show that our method performs favorably against state-of-the-art ones on commonly-used benchmarks." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.661, + 0.21, + 0.677 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.688, + 0.47, + 0.794 + ], + "angle": 0, + "content": "The camera shake and object motion are usually inevitable when taking photos with hand-held devices, which lead to significant motion blur effects. Restoring clear photos from blurry ones has attracted lots of attention from both research and industry communities [40]. However, motion deblurring is quite challenging as only the blurred images are available while the blur and latent images are unknown." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.47, + 0.84 + ], + "angle": 0, + "content": "Significant progress has been made in image restoration due to the development of deep neural networks that directly learn the mapping from the degraded observation to" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.253, + 0.892, + 0.389 + ], + "angle": 0, + "content": "the clear image. It is well known that the residual learning strategy [7] has been widely used to ease the training of networks, where a latent clear image \\( I \\) can be restored by the summation of the degraded input \\( B \\) and the output \\( \\mathcal{N}(B) \\) of a residual learning network \\( \\mathcal{N} \\). This strategy has been proven to be effective in lots of image restoration tasks, e.g., image super-resolution, as the degraded image \\( B \\) shares the same main structures as the clear one \\( I \\), and the residual between \\( B \\) and \\( I \\) mainly contains image details." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.39, + 0.893, + 0.661 + ], + "angle": 0, + "content": "However, we note that the difference between a blurry input and its corresponding clear one not only contains image details but also involves some structures. Taking Figure 1 as an example, the main structures in the clear image (e.g., the pillars enclosed in the red boxes of Figure 1(f)) disappear due to the influence of the motion blur effect. Thus, in addition to the details smoothed by the blur, some main structures also exist in the residual between the blurry image and the clear one (see the part enclosed in the red box of Figure 1(b)). As demonstrated in [22], the standard residual learning method [7] is effective for modeling the high-frequency information but less effective to restore the low-frequency contents. Figure 1(c) also shows that using the standard residual learning method may not estimate the main structures of the residual image well, which thus affects the final image restoration (Figure 1(h)). Therefore, it is important for image deblurring to effectively model the main structures distorted by the motion blur." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.663, + 0.895, + 0.814 + ], + "angle": 0, + "content": "To alleviate the above-mentioned problem, the recent methods [15, 34] introduce a frequency branch based on the Fast Fourier Transform (FFT) in the residual network, which achieves good performance. However, as such a frequency branch is achieved by applying \\(\\mathrm{Conv}1 + \\mathrm{ReLU} + \\mathrm{Conv}1^2\\) to the concatenation of the real and imaginary parts of the residual image, it may not effectively model the spatially-variant property of the global main structures in the residual image (Figure 1(d)), resulting in fake structures caused by the blur in the final deblurred image (Figure 1(i))." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.815, + 0.895, + 0.862 + ], + "angle": 0, + "content": "In this paper, we propose a Multi-scale Residual LowPass Filter Network (MRLPFNet) for high-quality image deblurring. Our goal is to effectively model both the low-" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.851, + 0.223, + 0.864 + ], + "angle": 0, + "content": "*Corresponding author" + }, + { + "type": "page_footnote", + "bbox": [ + 0.078, + 0.864, + 0.47, + 0.901 + ], + "angle": 0, + "content": "1Note that the high-frequency contents in an image correspond to the image details, while the low-frequency ones denote the main structures of an image." + }, + { + "type": "list", + "bbox": [ + 0.078, + 0.851, + 0.47, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.892, + 0.9 + ], + "angle": 0, + "content": "\\(^{2}\\mathrm{Conv1} + \\mathrm{ReLU} + \\mathrm{Conv1}\\) denotes two \\(1\\times 1\\) convolutional layers with the usual ReLU activation in between." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12345" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.241, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.124, + 0.185, + 0.198, + 0.196 + ], + "angle": 0, + "content": "(a) Blurry input" + }, + { + "type": "image", + "bbox": [ + 0.244, + 0.089, + 0.403, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.264, + 0.185, + 0.383, + 0.196 + ], + "angle": 0, + "content": "(b) Difference of (a) & (f)" + }, + { + "type": "image", + "bbox": [ + 0.406, + 0.089, + 0.566, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.439, + 0.185, + 0.533, + 0.196 + ], + "angle": 0, + "content": "(c) Residual by [37]" + }, + { + "type": "image", + "bbox": [ + 0.568, + 0.089, + 0.727, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.602, + 0.185, + 0.695, + 0.196 + ], + "angle": 0, + "content": "(d) Residual by [15]" + }, + { + "type": "image", + "bbox": [ + 0.73, + 0.089, + 0.891, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.746, + 0.185, + 0.875, + 0.196 + ], + "angle": 0, + "content": "(e) Residual by MRLPFNet" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.198, + 0.241, + 0.294 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.123, + 0.295, + 0.199, + 0.305 + ], + "angle": 0, + "content": "(f) Ground truth" + }, + { + "type": "image", + "bbox": [ + 0.244, + 0.198, + 0.403, + 0.294 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.279, + 0.295, + 0.367, + 0.306 + ], + "angle": 0, + "content": "(g) Restomer [36]" + }, + { + "type": "image", + "bbox": [ + 0.406, + 0.198, + 0.565, + 0.294 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.445, + 0.295, + 0.526, + 0.306 + ], + "angle": 0, + "content": "(h) MPRNet [37]" + }, + { + "type": "image", + "bbox": [ + 0.568, + 0.198, + 0.727, + 0.294 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.607, + 0.295, + 0.689, + 0.306 + ], + "angle": 0, + "content": "(i) DeepRFT [15]" + }, + { + "type": "image", + "bbox": [ + 0.73, + 0.198, + 0.891, + 0.294 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.759, + 0.295, + 0.862, + 0.306 + ], + "angle": 0, + "content": "(j) MRLPFNet (Ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.308, + 0.894, + 0.365 + ], + "angle": 0, + "content": "Figure 1. Visual comparison with state-of-the-art image deblurring methods on a challenging example. Our work is motivated by an observation that the difference between the blurry image and its corresponding clear one not only contains high-frequency contents but also includes low-frequency information due to the influence of the blur as shown in (b). We thus develop a simple yet effective MRLPFNet to learn both image details and spatially-variant structures (see (e)), which thus leads to better-deblurred results as shown in (j)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.385, + 0.47, + 0.627 + ], + "angle": 0, + "content": "frequency and high-frequency parts of the residual image between the blurry input and its corresponding clear output within the residual learning framework. To better explore the low-frequency information, we propose to intuitively apply a low-pass filter on the residual image to concentrate on the low-frequency part. In addition, as the low-frequency contents in an image correspond to the global main structures, one of whose properties is that they are usually spatially variant, we exploit a learnable low-pass filter module based on a self-attention mechanism (as a basic module) to adaptively explore the global contexts so that the main structures can be better restored for image deblurring. Then we incorporate it in the proposed Residual Low-Pass Filter (RLPF) module with an additional residual learning branch based on a fully convolutional neural network (CNN) for modeling the high-frequency information." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.628, + 0.47, + 0.824 + ], + "angle": 0, + "content": "Furthermore, the multi-scale strategy is widely used in image deblurring. As features from various scales have different spatial resolutions, resizing operations are usually used to fuse these features. However, simply using resizing operations based on downsampling or upsampling will lead to information loss. To this end, we develop a simple yet effective feature fusion module based on the wavelet transform to fuse the features with different spatial resolutions. Finally, we embed the proposed RLPF module and the wavelet-based feature fusion (WFF) module into an end-to-end trainable network within a coarse-to-fine framework. The proposed approach achieves favorable performance on widely-used benchmarks." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.825, + 0.435, + 0.839 + ], + "angle": 0, + "content": "The main contributions are summarized as follows." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.84, + 0.47, + 0.902 + ], + "angle": 0, + "content": "- We propose an effective RLPF module to model both the high-frequency and low-frequency information of the difference between the network input and output for image deblurring. Specifically, a learnable low" + }, + { + "type": "text", + "bbox": [ + 0.53, + 0.385, + 0.892, + 0.476 + ], + "angle": 0, + "content": "pass filter is developed based on a self-attention mechanism to adaptively explore the spatially-variant property of the global contexts to effectively reconstruct the low-frequency structures and a fully CNN with the residual learning is adopted to model the high-frequency information." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.476, + 0.891, + 0.521 + ], + "angle": 0, + "content": "- We develop a simple yet effective feature fusion module based on the wavelet transform to fuse the features of different scales for better image deblurring." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.521, + 0.892, + 0.565 + ], + "angle": 0, + "content": "- By training the proposed MRLPFNet in an end-to-end manner, we show that it performs favorably against state-of-the-art methods." + }, + { + "type": "list", + "bbox": [ + 0.519, + 0.476, + 0.892, + 0.565 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.581, + 0.642, + 0.598 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.607, + 0.892, + 0.744 + ], + "angle": 0, + "content": "Hand-crafted prior-based methods. As image deblurring is ill-posed, conventional methods usually develop kinds of effective priors to constrain the solution space, e.g., sparsity priors on the image gradient [11, 35] or intensity [19], internal patch recurrence [16], sparsity of dark channel prior [21], etc. These hand-crafted priors can help the blur removal. However, they do not fully exploit the characteristics of the clear image data and usually lead to complicated optimization problems." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.87 + ], + "angle": 0, + "content": "Deep learning-based methods. Instead of manually designing image priors, lots of methods develop kinds of deep CNNs to solve image deblurring. Early approaches employ deep CNN models to estimate blur kernels and then use existing prior-based restoration methods to estimate the clear images [27, 6, 1, 24]. While inaccurate blur kernels will lead to deblurred results with severe artifacts as the blur kernels and latent clear images are estimated independently." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Instead of estimating blur kernels, numerous methods [17, 39, 28, 5, 38, 26, 37, 3, 18, 12] directly estimate" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "12346" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.455 + ], + "angle": 0, + "content": "clear images from blurry ones. In [17], Nah et al. develop a multi-scale deep CNN, where the restored images from coarse scales are resized to help the estimation of finer scales. To better explore the multi-scale information, Tao et al. [28] develop an effective scale recurrent neural network. In [5], Gao et al. propose a parameter selective sharing and nested skip connection method to improve [17]. Although the methods based on a multi-scale strategy achieve decent performance, simply increasing the model depth with more scales cannot further improve the quality of deblurring. To overcome this problem, methods based on multi-patches have been developed. Zhang et al. [38] develop an effective deep hierarchical multi-patch network, where the features from the previous stage are concatenated to facilitate the estimation of the following stages. Zamir et al. [37] propose a multi-stage progressive method to better explore the features from multi-stages by a cross-scale feature fusion module. In addition, an effective supervised attention module is developed to better guide the estimations of the following stages. As both the multi-scale and multi-patch methods need to perform the network at each scale or stage recurrently, which leads to high computational costs, Cho et al. [3] develop a multi-input and multi-output U-net based on a multi-scale strategy to solve image deblurring." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.458, + 0.473, + 0.641 + ], + "angle": 0, + "content": "These above-mentioned methods achieve significant performance, most of which adopt the residual learning in the network design. As demonstrated in [20], the residual learning is able to model the image details (i.e., high-frequency information), but is less effective for exploring the main structures (i.e., low-frequency information). To overcome this problem, Mao et al. [15] improve the residual learning network by introducing an additional branch performed in the frequency domain. However, as the main structures involve the spatially-variant global contexts, simply using the local operations (e.g., \\( 1 \\times 1 \\) convolution in [15]) may not model the main structures well." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.659, + 0.473, + 0.901 + ], + "angle": 0, + "content": "Transformer-based methods. As Transformer is effective for global context exploration and shows great potential in many vision tasks, several methods apply it to image deblurring. Zamir et al. [36] propose an efficient Transformer model by estimating self-attention along the channel dimension. This method is further simplified by [2]. Tsai et al. [29] develop a Transformer-based model by constructing intra- and inter-strip tokens to reweight image features in the horizontal and vertical directions. In [30], Tu et al. develop an effective multi-axis MLP-based architecture. Wang et al. [31] develop a general U-shaped Transformer to solve image deblurring. These Transformer-based approaches achieve decent results. However, as our analysis in Section 3 shows, self-attention has the same effect as the low-pass filter. Simply using Transformers may lead to over-smoothed results." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.09, + 0.818, + 0.108 + ], + "angle": 0, + "content": "3. Low-Pass Filter and Self-Attention" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.115, + 0.892, + 0.145 + ], + "angle": 0, + "content": "To better motivate our work, we first describe the relations between the low-pass filter and self-attention." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.146, + 0.892, + 0.176 + ], + "angle": 0, + "content": "Given an image \\(I\\) and a low-pass filter \\(\\mathcal{F}\\), we can obtain a filtered image \\(f\\) by:" + }, + { + "type": "equation", + "bbox": [ + 0.58, + 0.186, + 0.892, + 0.219 + ], + "angle": 0, + "content": "\\[\nf (\\mathrm {x}) = \\mathcal {F} (I (\\mathrm {x})) = \\sum_ {\\mathrm {y}} \\mathbf {W} _ {\\mathrm {x y}} I (\\mathrm {y}), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.221, + 0.893, + 0.447 + ], + "angle": 0, + "content": "where \\( x \\) and \\( y \\) denote image pixels; \\( \\mathbf{W}_{\\mathrm{xy}} \\) denotes the filter weight for \\( \\mathcal{F} \\), satisfying \\( \\mathbf{W}_{\\mathrm{xy}} \\geq 0 \\) and \\( \\sum_{y} \\mathbf{W}_{\\mathrm{xy}} = 1 \\). The role of a low-pass filter is to do a weighted average in an area with the same size as the filter, thus filtering out the high-frequency information and retaining the low-frequency one. One common type of filter is the linear translation-invariant filter, e.g., the Gaussian filter, which adopts the spatially-invariant filter weight and cannot effectively describe the variant properties of image structures in different spatial areas. Another type of filter is the nonlinear filter, e.g., the bilateral filter, whose weights depend on both the spatial closeness and the intensity difference. Such weights can adaptively model the spatially-variant contexts (e.g., global edges), thus preserving more useful low-frequency information in the filtered image." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.448, + 0.892, + 0.478 + ], + "angle": 0, + "content": "Recently, the attention-based approaches, e.g., self-attention, compute the weighted value as" + }, + { + "type": "equation", + "bbox": [ + 0.523, + 0.487, + 0.892, + 0.523 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Z} = \\mathbf {S} \\circledast \\mathbf {V} = \\operatorname {s o f t m a x} \\left(\\frac {\\mathcal {Q} (F) \\mathcal {K} (F) ^ {\\top}}{\\sqrt {d _ {k}}}\\right) \\mathcal {V} (F), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.53, + 0.895, + 0.727 + ], + "angle": 0, + "content": "where \\(F\\) denotes the deep feature extracted from the input image \\(I\\); \\(\\ast\\) indicates the matrix multiplication; \\(\\mathcal{Q}(\\cdot), \\mathcal{K}(\\cdot)\\), and \\(\\mathcal{V}(\\cdot)\\) denote the operations that extract the matrices for the query, key, and value; \\(d_k\\) is the dimension of the keys. A softmax normalized operation is applied to each row of \\(\\mathbf{S}\\) to ensure \\(\\mathbf{S}_{ij} \\geq 0\\) and \\(\\sum_{j} \\mathbf{S}_{ij} = 1\\), where \\(i\\) and \\(j\\) denote the index of the row and column in \\(\\mathbf{S}\\). Thus, each row of \\(\\mathbf{S}\\) can be regarded as a low-pass filter. Compared to the bilateral filter whose weight measures the spatial and color similarity based on the exponential Euclidean distance, the attention value measures the similarity of query and key based on the correlation metric. Therefore, it is spatially variant and can model the main structures more adaptively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.727, + 0.895, + 0.788 + ], + "angle": 0, + "content": "Considering the self-attention (2) is learnable and more flexible, we propose to straightforwardly embed it into the network to better model the low-frequency information for image deblurring." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.8, + 0.625, + 0.816 + ], + "angle": 0, + "content": "4. MRLPFNet" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Our goal is to develop an effective MRLPFNet for high-quality image deblurring, which can better restore both the image details and main structures. Specifically, we first propose a learnable low-pass filter based on the self-attention method to model the low-frequency information. We then" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "12347" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.089, + 0.608, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.085, + 0.25, + 0.608, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.615, + 0.091, + 0.882, + 0.267 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.273, + 0.893, + 0.318 + ], + "angle": 0, + "content": "Figure 2. Multi-scale residual low-pass filter network. To restore high-quality images with clearer structures, we propose an effective RLPF module that involves a learnable low-pass filter (based on the self-attention) to explore the low-frequency information (through Eqs. (3), (4), and (5)). A wavelet-based feature fusion (WFF) module is developed to fuse the features of various scales for better image deblurring." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.33, + 0.471, + 0.45 + ], + "angle": 0, + "content": "incorporate it in our proposed RLPF module with an additional residual learning branch for high-frequency information exploration. Furthermore, we formulate it into an end-to-end trainable network based on a coarse-to-fine framework and propose a feature fusion module based on the wavelet transform to better utilize the multi-scale features. In the following, we present the details of the proposed method." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.459, + 0.307, + 0.473 + ], + "angle": 0, + "content": "4.1. Residual Low-Pass Filter" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.482, + 0.47, + 0.679 + ], + "angle": 0, + "content": "As the standard residual learning is adept at exploring the high-frequency information [9, 20] while less effective for the low-frequency information modeling, the method [15] improves the standard residual block by introducing an additional branch that applies Conv1 + ReLU + Conv1 to the features (generated by the FFT) in the frequency domain. Although decent performance has been achieved, the \\(1 \\times 1\\) convolution is spatially invariant, which does not effectively model the spatially-variant structures. To overcome this problem, we propose to further improve it by applying a learnable low-pass filter to concentrate on the global main structures, which is able to model the spatially-variant property of the low-frequency information." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.679, + 0.47, + 0.77 + ], + "angle": 0, + "content": "Specifically, we first generate the feature \\(\\mathbf{Y}\\) from a blurry input \\(I\\) by a shallow feature extraction network (the details are included in the supplemental material). Then the proposed RLPF module explores the properties of residual learning in both the spatial and frequency domains according to [15]:" + }, + { + "type": "equation", + "bbox": [ + 0.182, + 0.78, + 0.469, + 0.797 + ], + "angle": 0, + "content": "\\[\n\\mathbf {F} = \\mathbf {Y} + \\mathcal {R} (\\mathbf {Y}) + \\mathcal {F} (\\mathbf {Y}), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.806, + 0.469, + 0.867 + ], + "angle": 0, + "content": "where \\(\\mathcal{R}(\\cdot)\\) denotes a plain network that applies Conv3 + ReLU + Conv3 in the spatial domain and \\(\\mathcal{F}(\\cdot)\\) denotes a network [15] with Conv1 + ReLU + Conv1 employed in the frequency domain." + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.875, + 0.469, + 0.9 + ], + "angle": 0, + "content": "\\(^3\\)Conv3 + ReLU + Conv3 denotes two \\(3 \\times 3\\) convolutional layers with the usual ReLU activation in between." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.33, + 0.892, + 0.406 + ], + "angle": 0, + "content": "As Eq. (3) is based on the locally spatially-invariant convolution operations, it does not effectively model the spatially-variant main structures (see Figure 1(d)). To this end, we develop a learnable low-pass filter, which is proposed based on Eq. (1) and achieved by:" + }, + { + "type": "equation", + "bbox": [ + 0.641, + 0.414, + 0.892, + 0.448 + ], + "angle": 0, + "content": "\\[\n\\mathbf {h} _ {i} = \\sum_ {j} \\mathbf {S} _ {i j} \\mathbf {f} _ {j}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.456, + 0.893, + 0.562 + ], + "angle": 0, + "content": "where \\(\\mathbf{f}_j\\) is the \\(j\\)-th feature map of \\(\\mathbf{F}\\). Based on the discussions in Section 3, the self-attention can be regarded as a spatially-variant low-pass filter, which can better model the global low-frequency contents. Then we use the standard scaled dot-production attention in the Transformer according to [36] to estimate the filter weight matrix \\(\\mathbf{S}\\). Finally, we obtain the filtered feature \\(\\mathbf{E}\\) by:" + }, + { + "type": "equation", + "bbox": [ + 0.638, + 0.572, + 0.891, + 0.588 + ], + "angle": 0, + "content": "\\[\n\\mathbf {E} = \\mathbf {F} + \\mathcal {D} (\\mathbf {H}), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.597, + 0.891, + 0.627 + ], + "angle": 0, + "content": "where \\(\\mathbf{H} = \\{\\mathbf{h}_i\\}\\) is the low-frequency feature by Eq. (4) and \\(\\mathcal{D}\\) denotes a \\(3\\times 3\\) depth-wise convolution layer." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.628, + 0.892, + 0.673 + ], + "angle": 0, + "content": "We refer to the module achieved by Eqs. (3), (4), and (5) as the proposed RLPF module, which is then embedded into an encoder-decoder architecture as shown in Figure 2(a)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.682, + 0.768, + 0.696 + ], + "angle": 0, + "content": "4.2. Wavelet-based Feature Fusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.892, + 0.901 + ], + "angle": 0, + "content": "To efficiently ease and improve the deblurring process, the recent methods [3, 15] utilize the multi-scale features generated by different encoder blocks to prompt the learning of various decoder blocks. As the spatial resolutions of the features from different scales are not the same, they are usually resized by downsampling or upsampling operations to the same spatial resolution for feature fusion. However, these resizing operations may lose some important structural details, thus affecting the final image restoration. As the wavelet transform [8] can model the image scale information and is insertable, we develop a wavelet-based feature fusion method to better fuse the features of various scales for image deblurring." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12348" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "Specifically, considering two features \\(\\mathbf{E}_s\\) and \\(\\mathbf{E}_{s + 1}\\) generated by Eq. (5) for the finer image scale \\(s\\) and coarser image scale \\(s + 1\\), we first apply the Haar transform \\(\\mathcal{H}\\) [32, 14, 33] to \\(\\mathbf{E}_s\\) and obtain" + }, + { + "type": "equation", + "bbox": [ + 0.153, + 0.161, + 0.469, + 0.181 + ], + "angle": 0, + "content": "\\[\n\\left\\{\\mathbf {E} _ {s} ^ {L L}; \\mathbf {E} _ {s} ^ {L R}; \\mathbf {E} _ {s} ^ {R L}; \\mathbf {E} _ {s} ^ {R R} \\right\\} = \\mathcal {H} (\\mathbf {E} _ {s}), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.188, + 0.469, + 0.281 + ], + "angle": 0, + "content": "where \\(\\mathbf{E}_s^{LL}\\) denotes the low-frequency part and \\(\\mathbf{E}_s^{LR},\\mathbf{E}_s^{RL}\\), and \\(\\mathbf{E}_s^{RR}\\) correspond to three high-frequency parts. Thus, the resolutions of \\(\\{\\mathbf{E}_s^{LL};\\mathbf{E}_s^{LR};\\mathbf{E}_s^{RL};\\mathbf{E}_s^{RR}\\}\\) are the same as that of \\(\\mathbf{E}_{s + 1}\\). To make use of both \\(\\mathbf{E}_s\\) and \\(\\mathbf{E}_{s + 1}\\) for the decoder block in the finer image scale \\(s\\), the wavelet-based feature fusion generates the fused feature \\(\\hat{\\mathbf{E}}_s\\) by:" + }, + { + "type": "equation", + "bbox": [ + 0.077, + 0.288, + 0.495, + 0.32 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {E}} _ {s} = \\mathcal {H} ^ {- 1} \\left(\\mathcal {N} _ {s} ^ {L} \\left(\\mathcal {C} \\left(\\mathbf {E} _ {s} ^ {L L}, \\mathbf {E} _ {s + 1}\\right)\\right), \\mathcal {N} _ {s} ^ {H} \\left(\\mathcal {C} \\left(\\mathbf {E} _ {s} ^ {L R}, \\mathbf {E} _ {s} ^ {R L}, \\mathbf {E} _ {s} ^ {R R}\\right)\\right)\\right), \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.321, + 0.469, + 0.442 + ], + "angle": 0, + "content": "where \\(\\mathcal{H}^{-1}\\) is the inverse Haar transform; \\(\\mathcal{C}(\\cdot)\\) indicates the concatenation along the channel dimension; \\(\\mathcal{N}_s^L\\) is a network consisting of two \\(3\\times 3\\) convolutional layers with the PReLU activation in between and \\(\\mathcal{N}_s^H\\) contains one \\(1\\times 1\\) convolutional layer followed by the PReLU activation and one \\(3\\times 3\\) convolutional layer. When fusing \\(\\mathbf{E}_s\\) and \\(\\mathbf{E}_{s + 1}\\) to facilitate the decoder block in the coarser image scale \\(s + 1\\), we obtain the fused feature \\(\\hat{\\mathbf{E}}_{s + 1}\\) by" + }, + { + "type": "equation", + "bbox": [ + 0.077, + 0.45, + 0.487, + 0.482 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {E}} _ {s + 1} = \\mathcal {N} _ {s + 1} ^ {L} \\left(\\mathcal {C} \\left(\\mathbf {E} _ {s + 1}, \\mathbf {E} _ {s} ^ {L L}, \\mathcal {N} _ {s + 1} ^ {H} \\left(\\mathcal {C} \\left(\\mathbf {E} _ {s} ^ {L R}, \\mathbf {E} _ {s} ^ {R L}, \\mathbf {E} _ {s} ^ {R R}\\right)\\right)\\right)\\right), \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.482, + 0.469, + 0.573 + ], + "angle": 0, + "content": "where \\(\\mathcal{N}_{s + 1}^{L}\\) and \\(\\mathcal{N}_{s + 1}^{H}\\) have the same network architecture as \\(\\mathcal{N}_s^L\\) and \\(\\mathcal{N}_s^H\\), respectively (Note that the network parameters are not shared across scales). We take the fused features \\(\\hat{\\mathbf{E}}_s\\) and \\(\\hat{\\mathbf{E}}_{s + 1}\\) instead of \\(\\mathbf{E}_s\\) and \\(\\mathbf{E}_{s + 1}\\) as the input for the following decoder blocks. Figure 2(b) shows the details of the proposed wavelet-based feature fusion module." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.574, + 0.469, + 0.649 + ], + "angle": 0, + "content": "When fusing features from more scales, we can recurrently use Eqs. (7) and (8). As the wavelet transform is invertible, all the information can be better preserved during the transformation. We show the effectiveness of the wavelet-based feature fusion in Section 6.2." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.662, + 0.283, + 0.679 + ], + "angle": 0, + "content": "5. Experimental Results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.688, + 0.469, + 0.779 + ], + "angle": 0, + "content": "We first describe the implementation details of the proposed MRLPFNet. Then we evaluate our approach on the commonly used benchmarks and compare it against the state-of-the-art methods. Due to the page limit, we include more results in the supplemental material. The PyTorch code and trained models are available at our Project page." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.291, + 0.803 + ], + "angle": 0, + "content": "5.1. Implementation details" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.469, + 0.901 + ], + "angle": 0, + "content": "We embed the proposed RLPF module into an encoder-decoder network [3], which contains three encoder blocks and three decoder blocks. For each encoder/decoder block, we adopt a stack of 8 RLPF modules (i.e., \\(N = 8\\) in Figure 2(a)). We then use the wavelet-based feature fusion module to fuse the features generated by the encoder blocks of" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.088, + 0.892, + 0.143 + ], + "angle": 0, + "content": "Table 1. Quantitative evaluations of the proposed approach against state-of-the-art methods on the GoPro dataset [17]. \"MRLPFNet-L\" denotes the proposed method using 20 RLPF modules in each encoder and decoder block (i.e., \\(N = 20\\) in Figure 2(a))." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.145, + 0.892, + 0.366 + ], + "angle": 0, + "content": "
MethodPSNR (dB)SSIM
SRN [28]30.260.9342
SSN [5]30.920.9421
DMPHN [38]31.200.9453
SAPHNet [26]31.850.9480
MPRNet [37]32.660.9589
MPRNet-Local [4]33.310.9637
MIMO-UNet [3]31.730.9510
DeepRFT [15]32.820.9600
Uformer [31]33.060.9670
Restormer [36]32.920.9611
Restormer-Local [4]33.570.9656
MAXIM [30]32.860.9616
NAFNet [2]33.710.9668
Stripformer [29]33.080.9624
MRLPFNet33.500.9650
MRLPFNet-L34.010.9682
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.393, + 0.892, + 0.528 + ], + "angle": 0, + "content": "3 different image scales. We implement our method based on the PyTorch framework and train it from scratch using a machine with two NVIDIA GeForce RTX 3090 GPUs. The proposed network is trained using the Adam optimizer [10] with default parameters. The batch size is set to be 8. The size of each image patch is \\(256 \\times 256\\) pixels. The learning rate is initialized to be \\(2 \\times 10^{-4}\\) and is updated by the Cosine Annealing scheme. The loss function [37] is adopted to constrain the network training." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.542, + 0.821, + 0.558 + ], + "angle": 0, + "content": "5.2. Comparisons with the state of the art" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.566, + 0.892, + 0.763 + ], + "angle": 0, + "content": "Evaluations on the GoPro dataset. We first quantitatively evaluate the proposed method on the GoPro dataset [17], which contains 2,103 images for training and 1,111 images for the test. We compare the proposed method against several state-of-the-art methods including CNN-based methods (SRN [28], SSN [5], DMPHN [38], SAPHNet [26], MPR-Net [37], MIMO-UNet [3], DeepRFT [15], NAFNet [2]), Transformer-based methods (Restormer [36], Uformer [31], Stripformer [29]), and MLP-based methods (MAXIM [30]). For fair comparisons, we fine-tune or retrain the deep learning-based methods that are not trained on the GoPro dataset. We use the PSNR and SSIM as metrics to evaluate the quality of restored images." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.764, + 0.892, + 0.809 + ], + "angle": 0, + "content": "Table 1 shows the quantitative results. The proposed method generates higher-quality images with higher PSNR and SSIM values than the competing approaches." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Figure 3 shows a visual comparison. Most of the CNN-based methods, e.g., [37, 3, 2], employ the commonly used residual learning in the network designs, which is less effective for the estimation of the main structures, as demonstrated in Section 1. Thus, these methods [37, 3, 2] do not effectively remove the blur as shown in Figure 3(c), (d), and" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12349" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.241, + 0.204 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.124, + 0.206, + 0.198, + 0.216 + ], + "angle": 0, + "content": "(a) Blurry input" + }, + { + "type": "image", + "bbox": [ + 0.244, + 0.089, + 0.403, + 0.204 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.285, + 0.206, + 0.362, + 0.215 + ], + "angle": 0, + "content": "(b) Ground truth" + }, + { + "type": "image", + "bbox": [ + 0.406, + 0.09, + 0.565, + 0.204 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.445, + 0.205, + 0.526, + 0.216 + ], + "angle": 0, + "content": "(c) MPRNet [37]" + }, + { + "type": "image", + "bbox": [ + 0.568, + 0.09, + 0.727, + 0.204 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.601, + 0.205, + 0.696, + 0.216 + ], + "angle": 0, + "content": "(d) MIMO-UNet [3]" + }, + { + "type": "image", + "bbox": [ + 0.731, + 0.09, + 0.89, + 0.204 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.768, + 0.205, + 0.853, + 0.216 + ], + "angle": 0, + "content": "(e) DeepRFT [15]" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.218, + 0.24, + 0.332 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.125, + 0.334, + 0.197, + 0.345 + ], + "angle": 0, + "content": "(f) NAFNet [2]" + }, + { + "type": "image", + "bbox": [ + 0.244, + 0.218, + 0.403, + 0.332 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.279, + 0.334, + 0.367, + 0.345 + ], + "angle": 0, + "content": "(g) Restomer [36]" + }, + { + "type": "image", + "bbox": [ + 0.406, + 0.218, + 0.565, + 0.332 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.429, + 0.334, + 0.542, + 0.345 + ], + "angle": 0, + "content": "(h) Restormer-Local [4]" + }, + { + "type": "image", + "bbox": [ + 0.568, + 0.218, + 0.727, + 0.332 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.602, + 0.334, + 0.694, + 0.345 + ], + "angle": 0, + "content": "(i) Stripformer [29]" + }, + { + "type": "image", + "bbox": [ + 0.731, + 0.218, + 0.89, + 0.332 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.776, + 0.334, + 0.846, + 0.345 + ], + "angle": 0, + "content": "(j) MRLPFNet" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.348, + 0.892, + 0.376 + ], + "angle": 0, + "content": "Figure 3. Example from the GoPro dataset [17]. Compared to the evaluated methods in (c)-(i), the proposed approach generates a better deblurred image with clearer characters in (j)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.4, + 0.469, + 0.491 + ], + "angle": 0, + "content": "(f). The method [15] improves the residual learning by introducing an additional branch operating in the frequency domain. However, as the main structures are usually spatially variant, simply using localized convolution operations does not effectively model such global properties. The deblurred result in Figure 3(e) still contains the blur effect." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.492, + 0.469, + 0.659 + ], + "angle": 0, + "content": "The recent methods [36, 29] develop Transformers to solve image deblurring. As analyzed in Section 3, Transformers can be regarded as low-pass filters. These methods are able to explore the low-frequency contents but less effective for modeling the high-frequency information, thus leading to over-smoothed deblurred results as shown in Figure 3(g) and (i). In contrast to the above-mentioned methods, the proposed MRLPFNet is able to explore both high- and low-frequency information, generating a better image with clearer details and structures than the competed methods (e.g., the restored numbers in Figure 3(j) are clearer)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.673, + 0.469, + 0.809 + ], + "angle": 0, + "content": "Evaluations on the RealBlur dataset. The RealBlur dataset [23] contains 3,758 image pairs for training and 980 image pairs for the test. Based on the protocols of [23], our approach is compared with the state-of-the-art methods for fair comparisons. Table 2 shows that the proposed method generates the deblurred results with higher PSNR and SSIM values, where the PSNR values of our method are at least 1.08dB and 0.71dB higher than the evaluated methods on the \"RealBlur-R\" and \"RealBlur-J\" datasets, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Figure 4 shows some visual comparisons of the evaluated methods. The methods [28, 13, 3] based on the standard residual learning do not effectively remove the blur effects as shown in Figure 4(c)-(e). The method [15] improves the standard residual learning, but the restored images are oversmoothed, e.g., the strokes in Figure 4(f). The Transformer" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.396, + 0.892, + 0.452 + ], + "angle": 0, + "content": "Table 2. Quantitative evaluations of the proposed approach against state-of-the-art methods on the RealBlur dataset [23]. All the comparison results are generated using the publicly available codes and the models trained on the same training datasets." + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.454, + 0.892, + 0.572 + ], + "angle": 0, + "content": "
RealBlur-RRealBlur-J
PSNR (dB)SSIMPSNR (dB)SSIM
SRN [28]38.650.965231.380.9091
DeblurGAN [12]36.440.934729.690.8703
MIMO-UNet+ [3]--31.920.9190
DeepRFT+ [15]39.840.972132.190.9305
Stripformer [29]39.840.973732.480.9290
MRLPFNet40.920.975333.190.9361
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.585, + 0.892, + 0.64 + ], + "angle": 0, + "content": "Table 3. Quantitative evaluations of the proposed approach against state-of-the-art methods on the HIDE dataset [25]. All the comparison results are generated by the same models trained on the GoPro dataset [17] as in Table 1." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.642, + 0.892, + 0.814 + ], + "angle": 0, + "content": "
MethodPSNR (dB)SSIM
SRN [28]28.360.9040
SAPHNet [26]29.980.9300
MPRNet [37]30.960.9394
MPRNet-Local [4]31.190.9418
MIMO-UNet [3]29.280.9206
MIMO-UNet+ [3]29.990.9304
DeepRFT [15]30.990.9407
DeepRFT+ [15]31.420.9442
Restormer [36]31.220.9423
Restormer-Local [4]31.490.9447
Stripformer [29]31.030.9395
MRLPFNet31.630.9465
" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "based method [29] tends to generate over-smoothed results and does not effectively remove the blur as shown in Figure 4(g). In contrast, our method generates clearer images than the evaluated methods (Figure 4(h))." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12350" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.09, + 0.28, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.144, + 0.268, + 0.219, + 0.278 + ], + "angle": 0, + "content": "(a) Blurry input" + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.091, + 0.483, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.345, + 0.268, + 0.423, + 0.278 + ], + "angle": 0, + "content": "(b) Ground truth" + }, + { + "type": "image", + "bbox": [ + 0.488, + 0.091, + 0.686, + 0.265 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.556, + 0.267, + 0.617, + 0.278 + ], + "angle": 0, + "content": "(c) SRN [28]" + }, + { + "type": "image", + "bbox": [ + 0.69, + 0.091, + 0.888, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.733, + 0.268, + 0.846, + 0.278 + ], + "angle": 0, + "content": "(d) DeblurGAN-V2 [13]" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.282, + 0.28, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.134, + 0.459, + 0.229, + 0.47 + ], + "angle": 0, + "content": "(e) MIMO-UNet [3]" + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.282, + 0.483, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.339, + 0.459, + 0.429, + 0.47 + ], + "angle": 0, + "content": "(f) DeepRFT+ [15]" + }, + { + "type": "image", + "bbox": [ + 0.488, + 0.282, + 0.686, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.54, + 0.459, + 0.634, + 0.47 + ], + "angle": 0, + "content": "(g) Stripformer [29]" + }, + { + "type": "image", + "bbox": [ + 0.69, + 0.282, + 0.889, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.753, + 0.459, + 0.826, + 0.469 + ], + "angle": 0, + "content": "(h) MRLPFNet" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.473, + 0.89, + 0.501 + ], + "angle": 0, + "content": "Figure 4. Example from the RealBlur dataset [23]. Compared with the deblurred results in (c)-(g), the proposed method recovers a high-quality image with clearer structural details." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.511, + 0.89, + 0.54 + ], + "angle": 0, + "content": "Table 4. Effectiveness of the proposed low-pass filter and wavelet-based feature fusion for image deblurring. All baseline methods are trained using the same settings as the proposed method for fair comparisons." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.542, + 0.888, + 0.644 + ], + "angle": 0, + "content": "
Low-pass filter (LPF)Feature fusion (FF)GoPro
Bilinear-based (BFF)Wavelet-based (WFF)PSNR (dB)/SSIM
MRLPFNetw/o LPF&FFXXX32.8/0.9606
MRLPFNetw/o LPF&w/BFFX✓X32.9/0.9611
MRLPFNetw/o LPF&w/WFFXX✓33.0/0.9616
MRLPFNetw/ LPF&w/FF✓XX33.4/0.9641
MRLPFNet✓X✓33.5/0.9650
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.669, + 0.469, + 0.743 + ], + "angle": 0, + "content": "**Evaluations on the **HIDE** dataset.** We further evaluate our method on the **HIDE** dataset [25] by using the model trained on the GoPro dataset. Table 3 shows that the proposed approach generates the deblurred results with the highest PSNR and SSIM values." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.761, + 0.31, + 0.777 + ], + "angle": 0, + "content": "6. Analysis and Discussions" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.786, + 0.395, + 0.803 + ], + "angle": 0, + "content": "6.1. Effect of the learnable low-pass filter" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.469, + 0.9 + ], + "angle": 0, + "content": "The learnable low-pass filter is proposed to explore the spatially-variant low-frequency information so that the global structural contents can be better restored for image deblurring. To demonstrate the effectiveness of the proposed learnable low-pass filter, we first compare our method with a baseline that removes the learnable low-pass fil" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.669, + 0.892, + 0.881 + ], + "angle": 0, + "content": "ter (MRLPFNet\\(_{\\mathrm{w/o LPF\\& w/WFF}}\\) for short) and train this baseline using the same settings as ours. We use the GoPro dataset [17] as described in Section 5.2 for evaluation. Table 4 shows the quantitative results, where the PSNR of the proposed MRLPFNet is \\(0.5\\mathrm{dB}\\) higher than the baseline without the learnable low-pass filter. To focus on the effect of the low-pass filter, we further disable the feature fusion module and compare the baselines with and without the learnable low-pass filter (MRLPFNet\\(_{\\mathrm{w/o LPF\\& FF}}\\) and MRLPFNet\\(_{\\mathrm{w/ LPF\\& w/O FF}}\\) for short). The comparisons in Table 4 illustrate the significance of using the learnable low-pass filter, which is able to concentrate on the low-frequency information modeling and effectively recover the spatially-variant image structures for image deblurring." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.886, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Figure 5 shows a visual comparison. The main structures" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "12351" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.207, + 0.181 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.106, + 0.182, + 0.18, + 0.192 + ], + "angle": 0, + "content": "(a) Blur input" + }, + { + "type": "image", + "bbox": [ + 0.212, + 0.089, + 0.339, + 0.181 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.208, + 0.182, + 0.341, + 0.192 + ], + "angle": 0, + "content": "(b) MRLPFNetw/o LPF&w/ WFF" + }, + { + "type": "image", + "bbox": [ + 0.344, + 0.089, + 0.471, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.373, + 0.182, + 0.443, + 0.191 + ], + "angle": 0, + "content": "(c) MRLPFNet" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.194, + 0.206, + 0.286 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.136, + 0.288, + 0.15, + 0.297 + ], + "angle": 0, + "content": "(d)" + }, + { + "type": "image", + "bbox": [ + 0.212, + 0.194, + 0.339, + 0.286 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.269, + 0.288, + 0.283, + 0.297 + ], + "angle": 0, + "content": "(e)" + }, + { + "type": "image", + "bbox": [ + 0.344, + 0.194, + 0.471, + 0.286 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.402, + 0.288, + 0.415, + 0.297 + ], + "angle": 0, + "content": "(f)" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.301, + 0.468, + 0.357 + ], + "angle": 0, + "content": "Figure 5. Effect of the proposed learnable low-pass filter. (d) is the residual image between the blurry image and Ground truth. (e) and (f) are the residual images estimated by MRLPFNetw/o LPF&w/ WFF and MRLPFNet, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.382, + 0.468, + 0.518 + ], + "angle": 0, + "content": "in the residual image estimated by MRLPFNet\\(_{\\mathrm{w/o LPF\\& w/ WFF}}\\) are not well recovered, e.g., the license plate numbers in Figure 5(e), resulting in the deblurred image with a blur effect (Figure 5(b)). In contrast, the residual image estimated by the proposed MRLPFNet is better restored, as using the learnable low-pass filter is able to model the spatially-variant image structures. Thus, our approach is more effective at yielding a clear image with distinct structures (e.g., the license plate numbers in Figure 5(f))." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.528, + 0.429, + 0.542 + ], + "angle": 0, + "content": "6.2. Effect of the wavelet-based feature fusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.551, + 0.468, + 0.837 + ], + "angle": 0, + "content": "To demonstrate the effectiveness of the wavelet-based feature fusion on fusing the features with different spatial resolutions, we first disable the learnable low-pass filter in our implementation (MRLPFNetw/o LPF&w/WFF for short). Then we compare with the baseline that replaces the wavelet-based feature fusion with the bilinear interpolation (MRLPFNetw/o LPF&w/BFF for short). The results in Table 4 show that using the bilinear interpolation as the feature fusion does not perform well as our method with the wavelet-based one, since the wavelet transform is invertible and can preserve more accurate information during the transform process. The qualitative comparisons in Figure 6 further show that using the wavelet-based feature fusion is able to improve the quality of the restored image (Figure 6(c)). We also compare our complete network with the baseline that removes the feature fusion module (MRLPFNetw/LPF&w/0FF for short). The comparisons in Figure 6 show the same tendency that using the wavelet-based feature fusion improves the final deblurring performance." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.848, + 0.25, + 0.864 + ], + "angle": 0, + "content": "6.3. Model complexity" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.468, + 0.9 + ], + "angle": 0, + "content": "We examine the model complexity of the proposed approach and the state-of-the-art methods in terms of model" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.09, + 0.598, + 0.15 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.514, + 0.152, + 0.588, + 0.163 + ], + "angle": 0, + "content": "(a) Blurry input" + }, + { + "type": "image", + "bbox": [ + 0.6, + 0.09, + 0.695, + 0.15 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.641, + 0.152, + 0.656, + 0.162 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image", + "bbox": [ + 0.698, + 0.09, + 0.793, + 0.15 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.739, + 0.152, + 0.753, + 0.162 + ], + "angle": 0, + "content": "(c)" + }, + { + "type": "image", + "bbox": [ + 0.795, + 0.09, + 0.891, + 0.15 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.805, + 0.152, + 0.882, + 0.162 + ], + "angle": 0, + "content": "(d) Ground truth" + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.165, + 0.892, + 0.221 + ], + "angle": 0, + "content": "Figure 6. Effect of the proposed wavelet-based feature fusion. (b) and (c) are the results obtained by the baselines using the Bilinear-based (MRLPFNetw/o LPF&w/BFF in Table 4) and the wavelet-based (MRLPFNetw/o LPF&w/WFF in Table 4) feature fusion, respectively." + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.231, + 0.892, + 0.313 + ], + "angle": 0, + "content": "Table 5. Model complexity of the top-performance methods on the above-mentioned datasets. The FLOPs are evaluated on image patches with the size of \\(256 \\times 256\\) pixels based on the protocols of existing methods. The running time is evaluated on images with the size of \\(1280 \\times 720\\) pixels. All the results are obtained on a machine with an NVIDIA GeForce RTX 3090 GPU." + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.315, + 0.891, + 0.412 + ], + "angle": 0, + "content": "
MethodsModel parameters (M)FLOPs (G)Running time (/s)
MPRNet [37]20.17600.9806
MIMO-UNet+ [3]16.11510.2827
DeepRFT+ [15]23.01830.5518
Restormer [36]26.11550.9798
Stripformer [29]19.71700.6580
MRLPFNetw/o LPF11.4820.2613
MRLPFNet20.61290.8633
" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.435, + 0.891, + 0.496 + ], + "angle": 0, + "content": "parameters, running time, and FLOPs. Table 5 shows that our method has the lowest FLOPs value and also achieves competitive performance against the competed ones in terms of running time." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.504, + 0.892, + 0.595 + ], + "angle": 0, + "content": "Limitations. As the proposed learnable low-pass filter is based on the self-attention to estimate the filter weights, it moderately increases the running time as shown in Table 5 (see the comparisons of \"MRLPFNetw/o LPF\" and \"MRLPFNet\"). Future work will develop efficient and learnable low-pass filters for better image deblurring." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.608, + 0.618, + 0.623 + ], + "angle": 0, + "content": "7. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.634, + 0.892, + 0.783 + ], + "angle": 0, + "content": "We present an effective MRLPFNet to reconstruct both the low-frequency and high-frequency information for image deblurring. To better explore the spatially-variant structures, we develop a learnable low-pass filter based on the self-attention mechanism. Furthermore, we propose a wavelet-based feature fusion method to effectively fuse the features with different spatial resolutions. By formulating the proposed method into an end-to-end trainable network, we show that it performs favorably against state-of-the-art methods on benchmarks." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.796, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Acknowledgement. This work was supported in part by the National Key Research and Development Program of China under Grant 2022ZD0118801, the National Natural Science Foundation of China under Grants 62272233, 61922043, 61925204, and U22B2049, and the Fundamental Research Funds for the Central Universities under Grant 30922010910 and 30920041109." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12352" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.117, + 0.468, + 0.143 + ], + "angle": 0, + "content": "[1] Ayan Chakrabarti. A neural approach to blind motion deblurring. In ECCV, pages 221-235, 2016. 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.147, + 0.468, + 0.186 + ], + "angle": 0, + "content": "[2] Liangyu Chen, Xiaojie Chu, Xiangyu Zhang, and Jian Sun. 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IJCV, 130(9):2103-2130, 2022. 1" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.47, + 0.415 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "12354" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/5c2653f2-ab7f-4799-9150-1c49cbf5bd6d_origin.pdf b/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/5c2653f2-ab7f-4799-9150-1c49cbf5bd6d_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..fa08be782a7d4c5aaeeecc6834765ca5b36b5e53 --- /dev/null +++ b/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/5c2653f2-ab7f-4799-9150-1c49cbf5bd6d_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:2553c8a592f13245f398c889835ed2b7670a9c1ce8556c5d23ca608982f6c127 +size 5078407 diff --git a/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/full.md b/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/full.md new file mode 100644 index 0000000000000000000000000000000000000000..ae3ed81e4aae2fee4696318784576d4109e4ede1 --- /dev/null +++ b/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/full.md @@ -0,0 +1,381 @@ +# Multi-scale Residual Low-Pass Filter Network for Image Deblurring + +Jiangxin Dong Jinshan Pan* Zhongbao Yang Jinhui Tang Nanjing University of Science and Technology + +# Abstract + +We present a simple and effective Multi-scale Residual Low-Pass Filter Network (MRLPFNet) that jointly explores the image details and main structures for image deblurring. Our work is motivated by an observation that the difference between the blurry image and the clear one not only contains high-frequency contents but also includes low-frequency information due to the influence of blur, while using the standard residual learning is less effective for modeling the main structure distorted by the blur. Considering that the low-frequency contents usually correspond to main global structures that are spatially variant, we first propose a learnable low-pass filter based on a self-attention mechanism to adaptively explore the global contexts for better modeling the low-frequency information. Then we embed it into a Residual Low-Pass Filter (RLPF) module, which involves an additional fully convolutional neural network with the standard residual learning to model the high-frequency information. We formulate the RLPF module into an end-to-end trainable network based on an encoder and decoder architecture and develop a wavelet-based feature fusion to fuse the multi-scale features. Experimental results show that our method performs favorably against state-of-the-art ones on commonly-used benchmarks. + +# 1. Introduction + +The camera shake and object motion are usually inevitable when taking photos with hand-held devices, which lead to significant motion blur effects. Restoring clear photos from blurry ones has attracted lots of attention from both research and industry communities [40]. However, motion deblurring is quite challenging as only the blurred images are available while the blur and latent images are unknown. + +Significant progress has been made in image restoration due to the development of deep neural networks that directly learn the mapping from the degraded observation to + +the clear image. It is well known that the residual learning strategy [7] has been widely used to ease the training of networks, where a latent clear image $I$ can be restored by the summation of the degraded input $B$ and the output $\mathcal{N}(B)$ of a residual learning network $\mathcal{N}$ . This strategy has been proven to be effective in lots of image restoration tasks, e.g., image super-resolution, as the degraded image $B$ shares the same main structures as the clear one $I$ , and the residual between $B$ and $I$ mainly contains image details. + +However, we note that the difference between a blurry input and its corresponding clear one not only contains image details but also involves some structures. Taking Figure 1 as an example, the main structures in the clear image (e.g., the pillars enclosed in the red boxes of Figure 1(f)) disappear due to the influence of the motion blur effect. Thus, in addition to the details smoothed by the blur, some main structures also exist in the residual between the blurry image and the clear one (see the part enclosed in the red box of Figure 1(b)). As demonstrated in [22], the standard residual learning method [7] is effective for modeling the high-frequency information but less effective to restore the low-frequency contents. Figure 1(c) also shows that using the standard residual learning method may not estimate the main structures of the residual image well, which thus affects the final image restoration (Figure 1(h)). Therefore, it is important for image deblurring to effectively model the main structures distorted by the motion blur. + +To alleviate the above-mentioned problem, the recent methods [15, 34] introduce a frequency branch based on the Fast Fourier Transform (FFT) in the residual network, which achieves good performance. However, as such a frequency branch is achieved by applying $\mathrm{Conv}1 + \mathrm{ReLU} + \mathrm{Conv}1^2$ to the concatenation of the real and imaginary parts of the residual image, it may not effectively model the spatially-variant property of the global main structures in the residual image (Figure 1(d)), resulting in fake structures caused by the blur in the final deblurred image (Figure 1(i)). + +In this paper, we propose a Multi-scale Residual LowPass Filter Network (MRLPFNet) for high-quality image deblurring. Our goal is to effectively model both the low- + +![](images/b6581055534c2449b4a4e0f3216c10aee340740d8d6c46966353d086b10c4b54.jpg) +(a) Blurry input + +![](images/d890def7c410f8ee2710b6a6864d005fa2f34da52bc243c7498f22319f59e694.jpg) +(b) Difference of (a) & (f) + +![](images/b4fcf9eafd674f307bb7a97e792e6d159d22645faa4d0ea8d4d1971cf8671d7f.jpg) +(c) Residual by [37] + +![](images/62067ed912ba4c674e7408d1d8c95886496b2cb6ff9a0bef0d757b544d212a92.jpg) +(d) Residual by [15] + +![](images/30caddc53c4fb065ec0c712383094e3a21e952467851033e66902e6ed492cc27.jpg) +(e) Residual by MRLPFNet + +![](images/6e06899f7e041270afb66dc232af5c6198f0b99131befe82a2188c3dbedc69de.jpg) +(f) Ground truth + +![](images/1914c8e9e70f904808850776ad18a1569c40a1eb2b60d50cbcc1675f6e6d7848.jpg) +(g) Restomer [36] + +![](images/a2ddb9903f8874849d1d4cacd710936bd2350be8d47a4a1934a465ac961d9a3f.jpg) +(h) MPRNet [37] +Figure 1. Visual comparison with state-of-the-art image deblurring methods on a challenging example. Our work is motivated by an observation that the difference between the blurry image and its corresponding clear one not only contains high-frequency contents but also includes low-frequency information due to the influence of the blur as shown in (b). We thus develop a simple yet effective MRLPFNet to learn both image details and spatially-variant structures (see (e)), which thus leads to better-deblurred results as shown in (j). + +![](images/ac1b2b17d78618d7aee0d9bf8f9988bdd737b5f611d938a95b96eac77fe3984c.jpg) +(i) DeepRFT [15] + +![](images/7fd613423c08eb83f42b9334bee12fc7a4e4243346648affdf445fc363b61e7f.jpg) +(j) MRLPFNet (Ours) + +frequency and high-frequency parts of the residual image between the blurry input and its corresponding clear output within the residual learning framework. To better explore the low-frequency information, we propose to intuitively apply a low-pass filter on the residual image to concentrate on the low-frequency part. In addition, as the low-frequency contents in an image correspond to the global main structures, one of whose properties is that they are usually spatially variant, we exploit a learnable low-pass filter module based on a self-attention mechanism (as a basic module) to adaptively explore the global contexts so that the main structures can be better restored for image deblurring. Then we incorporate it in the proposed Residual Low-Pass Filter (RLPF) module with an additional residual learning branch based on a fully convolutional neural network (CNN) for modeling the high-frequency information. + +Furthermore, the multi-scale strategy is widely used in image deblurring. As features from various scales have different spatial resolutions, resizing operations are usually used to fuse these features. However, simply using resizing operations based on downsampling or upsampling will lead to information loss. To this end, we develop a simple yet effective feature fusion module based on the wavelet transform to fuse the features with different spatial resolutions. Finally, we embed the proposed RLPF module and the wavelet-based feature fusion (WFF) module into an end-to-end trainable network within a coarse-to-fine framework. The proposed approach achieves favorable performance on widely-used benchmarks. + +The main contributions are summarized as follows. + +- We propose an effective RLPF module to model both the high-frequency and low-frequency information of the difference between the network input and output for image deblurring. Specifically, a learnable low + +pass filter is developed based on a self-attention mechanism to adaptively explore the spatially-variant property of the global contexts to effectively reconstruct the low-frequency structures and a fully CNN with the residual learning is adopted to model the high-frequency information. + +- We develop a simple yet effective feature fusion module based on the wavelet transform to fuse the features of different scales for better image deblurring. +- By training the proposed MRLPFNet in an end-to-end manner, we show that it performs favorably against state-of-the-art methods. + +# 2. Related Work + +Hand-crafted prior-based methods. As image deblurring is ill-posed, conventional methods usually develop kinds of effective priors to constrain the solution space, e.g., sparsity priors on the image gradient [11, 35] or intensity [19], internal patch recurrence [16], sparsity of dark channel prior [21], etc. These hand-crafted priors can help the blur removal. However, they do not fully exploit the characteristics of the clear image data and usually lead to complicated optimization problems. + +Deep learning-based methods. Instead of manually designing image priors, lots of methods develop kinds of deep CNNs to solve image deblurring. Early approaches employ deep CNN models to estimate blur kernels and then use existing prior-based restoration methods to estimate the clear images [27, 6, 1, 24]. While inaccurate blur kernels will lead to deblurred results with severe artifacts as the blur kernels and latent clear images are estimated independently. + +Instead of estimating blur kernels, numerous methods [17, 39, 28, 5, 38, 26, 37, 3, 18, 12] directly estimate + +clear images from blurry ones. In [17], Nah et al. develop a multi-scale deep CNN, where the restored images from coarse scales are resized to help the estimation of finer scales. To better explore the multi-scale information, Tao et al. [28] develop an effective scale recurrent neural network. In [5], Gao et al. propose a parameter selective sharing and nested skip connection method to improve [17]. Although the methods based on a multi-scale strategy achieve decent performance, simply increasing the model depth with more scales cannot further improve the quality of deblurring. To overcome this problem, methods based on multi-patches have been developed. Zhang et al. [38] develop an effective deep hierarchical multi-patch network, where the features from the previous stage are concatenated to facilitate the estimation of the following stages. Zamir et al. [37] propose a multi-stage progressive method to better explore the features from multi-stages by a cross-scale feature fusion module. In addition, an effective supervised attention module is developed to better guide the estimations of the following stages. As both the multi-scale and multi-patch methods need to perform the network at each scale or stage recurrently, which leads to high computational costs, Cho et al. [3] develop a multi-input and multi-output U-net based on a multi-scale strategy to solve image deblurring. + +These above-mentioned methods achieve significant performance, most of which adopt the residual learning in the network design. As demonstrated in [20], the residual learning is able to model the image details (i.e., high-frequency information), but is less effective for exploring the main structures (i.e., low-frequency information). To overcome this problem, Mao et al. [15] improve the residual learning network by introducing an additional branch performed in the frequency domain. However, as the main structures involve the spatially-variant global contexts, simply using the local operations (e.g., $1 \times 1$ convolution in [15]) may not model the main structures well. + +Transformer-based methods. As Transformer is effective for global context exploration and shows great potential in many vision tasks, several methods apply it to image deblurring. Zamir et al. [36] propose an efficient Transformer model by estimating self-attention along the channel dimension. This method is further simplified by [2]. Tsai et al. [29] develop a Transformer-based model by constructing intra- and inter-strip tokens to reweight image features in the horizontal and vertical directions. In [30], Tu et al. develop an effective multi-axis MLP-based architecture. Wang et al. [31] develop a general U-shaped Transformer to solve image deblurring. These Transformer-based approaches achieve decent results. However, as our analysis in Section 3 shows, self-attention has the same effect as the low-pass filter. Simply using Transformers may lead to over-smoothed results. + +# 3. Low-Pass Filter and Self-Attention + +To better motivate our work, we first describe the relations between the low-pass filter and self-attention. + +Given an image $I$ and a low-pass filter $\mathcal{F}$ , we can obtain a filtered image $f$ by: + +$$ +f (\mathrm {x}) = \mathcal {F} (I (\mathrm {x})) = \sum_ {\mathrm {y}} \mathbf {W} _ {\mathrm {x y}} I (\mathrm {y}), \tag {1} +$$ + +where $x$ and $y$ denote image pixels; $\mathbf{W}_{\mathrm{xy}}$ denotes the filter weight for $\mathcal{F}$ , satisfying $\mathbf{W}_{\mathrm{xy}} \geq 0$ and $\sum_{y} \mathbf{W}_{\mathrm{xy}} = 1$ . The role of a low-pass filter is to do a weighted average in an area with the same size as the filter, thus filtering out the high-frequency information and retaining the low-frequency one. One common type of filter is the linear translation-invariant filter, e.g., the Gaussian filter, which adopts the spatially-invariant filter weight and cannot effectively describe the variant properties of image structures in different spatial areas. Another type of filter is the nonlinear filter, e.g., the bilateral filter, whose weights depend on both the spatial closeness and the intensity difference. Such weights can adaptively model the spatially-variant contexts (e.g., global edges), thus preserving more useful low-frequency information in the filtered image. + +Recently, the attention-based approaches, e.g., self-attention, compute the weighted value as + +$$ +\mathbf {Z} = \mathbf {S} \circledast \mathbf {V} = \operatorname {s o f t m a x} \left(\frac {\mathcal {Q} (F) \mathcal {K} (F) ^ {\top}}{\sqrt {d _ {k}}}\right) \mathcal {V} (F), \tag {2} +$$ + +where $F$ denotes the deep feature extracted from the input image $I$ ; $\ast$ indicates the matrix multiplication; $\mathcal{Q}(\cdot), \mathcal{K}(\cdot)$ , and $\mathcal{V}(\cdot)$ denote the operations that extract the matrices for the query, key, and value; $d_k$ is the dimension of the keys. A softmax normalized operation is applied to each row of $\mathbf{S}$ to ensure $\mathbf{S}_{ij} \geq 0$ and $\sum_{j} \mathbf{S}_{ij} = 1$ , where $i$ and $j$ denote the index of the row and column in $\mathbf{S}$ . Thus, each row of $\mathbf{S}$ can be regarded as a low-pass filter. Compared to the bilateral filter whose weight measures the spatial and color similarity based on the exponential Euclidean distance, the attention value measures the similarity of query and key based on the correlation metric. Therefore, it is spatially variant and can model the main structures more adaptively. + +Considering the self-attention (2) is learnable and more flexible, we propose to straightforwardly embed it into the network to better model the low-frequency information for image deblurring. + +# 4. MRLPFNet + +Our goal is to develop an effective MRLPFNet for high-quality image deblurring, which can better restore both the image details and main structures. Specifically, we first propose a learnable low-pass filter based on the self-attention method to model the low-frequency information. We then + +![](images/8650aa55cc075fa1195eb00fcb19806bfdf2367403d8d96d7ea3a7ba2373a6f2.jpg) + +![](images/b321282ffb04b23800025ad00cebeadc84afaba3e5bcbbeb13521bf4014a0b18.jpg) +Figure 2. Multi-scale residual low-pass filter network. To restore high-quality images with clearer structures, we propose an effective RLPF module that involves a learnable low-pass filter (based on the self-attention) to explore the low-frequency information (through Eqs. (3), (4), and (5)). A wavelet-based feature fusion (WFF) module is developed to fuse the features of various scales for better image deblurring. + +![](images/502accac8d3b6c346e987c32b1bf946104900353fcb996e8ee4b3c5d4dac898d.jpg) + +incorporate it in our proposed RLPF module with an additional residual learning branch for high-frequency information exploration. Furthermore, we formulate it into an end-to-end trainable network based on a coarse-to-fine framework and propose a feature fusion module based on the wavelet transform to better utilize the multi-scale features. In the following, we present the details of the proposed method. + +# 4.1. Residual Low-Pass Filter + +As the standard residual learning is adept at exploring the high-frequency information [9, 20] while less effective for the low-frequency information modeling, the method [15] improves the standard residual block by introducing an additional branch that applies Conv1 + ReLU + Conv1 to the features (generated by the FFT) in the frequency domain. Although decent performance has been achieved, the $1 \times 1$ convolution is spatially invariant, which does not effectively model the spatially-variant structures. To overcome this problem, we propose to further improve it by applying a learnable low-pass filter to concentrate on the global main structures, which is able to model the spatially-variant property of the low-frequency information. + +Specifically, we first generate the feature $\mathbf{Y}$ from a blurry input $I$ by a shallow feature extraction network (the details are included in the supplemental material). Then the proposed RLPF module explores the properties of residual learning in both the spatial and frequency domains according to [15]: + +$$ +\mathbf {F} = \mathbf {Y} + \mathcal {R} (\mathbf {Y}) + \mathcal {F} (\mathbf {Y}), \tag {3} +$$ + +where $\mathcal{R}(\cdot)$ denotes a plain network that applies Conv3 + ReLU + Conv3 in the spatial domain and $\mathcal{F}(\cdot)$ denotes a network [15] with Conv1 + ReLU + Conv1 employed in the frequency domain. + +As Eq. (3) is based on the locally spatially-invariant convolution operations, it does not effectively model the spatially-variant main structures (see Figure 1(d)). To this end, we develop a learnable low-pass filter, which is proposed based on Eq. (1) and achieved by: + +$$ +\mathbf {h} _ {i} = \sum_ {j} \mathbf {S} _ {i j} \mathbf {f} _ {j}, \tag {4} +$$ + +where $\mathbf{f}_j$ is the $j$ -th feature map of $\mathbf{F}$ . Based on the discussions in Section 3, the self-attention can be regarded as a spatially-variant low-pass filter, which can better model the global low-frequency contents. Then we use the standard scaled dot-production attention in the Transformer according to [36] to estimate the filter weight matrix $\mathbf{S}$ . Finally, we obtain the filtered feature $\mathbf{E}$ by: + +$$ +\mathbf {E} = \mathbf {F} + \mathcal {D} (\mathbf {H}), \tag {5} +$$ + +where $\mathbf{H} = \{\mathbf{h}_i\}$ is the low-frequency feature by Eq. (4) and $\mathcal{D}$ denotes a $3\times 3$ depth-wise convolution layer. + +We refer to the module achieved by Eqs. (3), (4), and (5) as the proposed RLPF module, which is then embedded into an encoder-decoder architecture as shown in Figure 2(a). + +# 4.2. Wavelet-based Feature Fusion + +To efficiently ease and improve the deblurring process, the recent methods [3, 15] utilize the multi-scale features generated by different encoder blocks to prompt the learning of various decoder blocks. As the spatial resolutions of the features from different scales are not the same, they are usually resized by downsampling or upsampling operations to the same spatial resolution for feature fusion. However, these resizing operations may lose some important structural details, thus affecting the final image restoration. As the wavelet transform [8] can model the image scale information and is insertable, we develop a wavelet-based feature fusion method to better fuse the features of various scales for image deblurring. + +Specifically, considering two features $\mathbf{E}_s$ and $\mathbf{E}_{s + 1}$ generated by Eq. (5) for the finer image scale $s$ and coarser image scale $s + 1$ , we first apply the Haar transform $\mathcal{H}$ [32, 14, 33] to $\mathbf{E}_s$ and obtain + +$$ +\left\{\mathbf {E} _ {s} ^ {L L}; \mathbf {E} _ {s} ^ {L R}; \mathbf {E} _ {s} ^ {R L}; \mathbf {E} _ {s} ^ {R R} \right\} = \mathcal {H} (\mathbf {E} _ {s}), \tag {6} +$$ + +where $\mathbf{E}_s^{LL}$ denotes the low-frequency part and $\mathbf{E}_s^{LR},\mathbf{E}_s^{RL}$ , and $\mathbf{E}_s^{RR}$ correspond to three high-frequency parts. Thus, the resolutions of $\{\mathbf{E}_s^{LL};\mathbf{E}_s^{LR};\mathbf{E}_s^{RL};\mathbf{E}_s^{RR}\}$ are the same as that of $\mathbf{E}_{s + 1}$ . To make use of both $\mathbf{E}_s$ and $\mathbf{E}_{s + 1}$ for the decoder block in the finer image scale $s$ , the wavelet-based feature fusion generates the fused feature $\hat{\mathbf{E}}_s$ by: + +$$ +\hat {\mathbf {E}} _ {s} = \mathcal {H} ^ {- 1} \left(\mathcal {N} _ {s} ^ {L} \left(\mathcal {C} \left(\mathbf {E} _ {s} ^ {L L}, \mathbf {E} _ {s + 1}\right)\right), \mathcal {N} _ {s} ^ {H} \left(\mathcal {C} \left(\mathbf {E} _ {s} ^ {L R}, \mathbf {E} _ {s} ^ {R L}, \mathbf {E} _ {s} ^ {R R}\right)\right)\right), \tag {7} +$$ + +where $\mathcal{H}^{-1}$ is the inverse Haar transform; $\mathcal{C}(\cdot)$ indicates the concatenation along the channel dimension; $\mathcal{N}_s^L$ is a network consisting of two $3\times 3$ convolutional layers with the PReLU activation in between and $\mathcal{N}_s^H$ contains one $1\times 1$ convolutional layer followed by the PReLU activation and one $3\times 3$ convolutional layer. When fusing $\mathbf{E}_s$ and $\mathbf{E}_{s + 1}$ to facilitate the decoder block in the coarser image scale $s + 1$ , we obtain the fused feature $\hat{\mathbf{E}}_{s + 1}$ by + +$$ +\hat {\mathbf {E}} _ {s + 1} = \mathcal {N} _ {s + 1} ^ {L} \left(\mathcal {C} \left(\mathbf {E} _ {s + 1}, \mathbf {E} _ {s} ^ {L L}, \mathcal {N} _ {s + 1} ^ {H} \left(\mathcal {C} \left(\mathbf {E} _ {s} ^ {L R}, \mathbf {E} _ {s} ^ {R L}, \mathbf {E} _ {s} ^ {R R}\right)\right)\right)\right), \tag {8} +$$ + +where $\mathcal{N}_{s + 1}^{L}$ and $\mathcal{N}_{s + 1}^{H}$ have the same network architecture as $\mathcal{N}_s^L$ and $\mathcal{N}_s^H$ , respectively (Note that the network parameters are not shared across scales). We take the fused features $\hat{\mathbf{E}}_s$ and $\hat{\mathbf{E}}_{s + 1}$ instead of $\mathbf{E}_s$ and $\mathbf{E}_{s + 1}$ as the input for the following decoder blocks. Figure 2(b) shows the details of the proposed wavelet-based feature fusion module. + +When fusing features from more scales, we can recurrently use Eqs. (7) and (8). As the wavelet transform is invertible, all the information can be better preserved during the transformation. We show the effectiveness of the wavelet-based feature fusion in Section 6.2. + +# 5. Experimental Results + +We first describe the implementation details of the proposed MRLPFNet. Then we evaluate our approach on the commonly used benchmarks and compare it against the state-of-the-art methods. Due to the page limit, we include more results in the supplemental material. The PyTorch code and trained models are available at our Project page. + +# 5.1. Implementation details + +We embed the proposed RLPF module into an encoder-decoder network [3], which contains three encoder blocks and three decoder blocks. For each encoder/decoder block, we adopt a stack of 8 RLPF modules (i.e., $N = 8$ in Figure 2(a)). We then use the wavelet-based feature fusion module to fuse the features generated by the encoder blocks of + +Table 1. Quantitative evaluations of the proposed approach against state-of-the-art methods on the GoPro dataset [17]. "MRLPFNet-L" denotes the proposed method using 20 RLPF modules in each encoder and decoder block (i.e., $N = 20$ in Figure 2(a)). + +
MethodPSNR (dB)SSIM
SRN [28]30.260.9342
SSN [5]30.920.9421
DMPHN [38]31.200.9453
SAPHNet [26]31.850.9480
MPRNet [37]32.660.9589
MPRNet-Local [4]33.310.9637
MIMO-UNet [3]31.730.9510
DeepRFT [15]32.820.9600
Uformer [31]33.060.9670
Restormer [36]32.920.9611
Restormer-Local [4]33.570.9656
MAXIM [30]32.860.9616
NAFNet [2]33.710.9668
Stripformer [29]33.080.9624
MRLPFNet33.500.9650
MRLPFNet-L34.010.9682
+ +3 different image scales. We implement our method based on the PyTorch framework and train it from scratch using a machine with two NVIDIA GeForce RTX 3090 GPUs. The proposed network is trained using the Adam optimizer [10] with default parameters. The batch size is set to be 8. The size of each image patch is $256 \times 256$ pixels. The learning rate is initialized to be $2 \times 10^{-4}$ and is updated by the Cosine Annealing scheme. The loss function [37] is adopted to constrain the network training. + +# 5.2. Comparisons with the state of the art + +Evaluations on the GoPro dataset. We first quantitatively evaluate the proposed method on the GoPro dataset [17], which contains 2,103 images for training and 1,111 images for the test. We compare the proposed method against several state-of-the-art methods including CNN-based methods (SRN [28], SSN [5], DMPHN [38], SAPHNet [26], MPR-Net [37], MIMO-UNet [3], DeepRFT [15], NAFNet [2]), Transformer-based methods (Restormer [36], Uformer [31], Stripformer [29]), and MLP-based methods (MAXIM [30]). For fair comparisons, we fine-tune or retrain the deep learning-based methods that are not trained on the GoPro dataset. We use the PSNR and SSIM as metrics to evaluate the quality of restored images. + +Table 1 shows the quantitative results. The proposed method generates higher-quality images with higher PSNR and SSIM values than the competing approaches. + +Figure 3 shows a visual comparison. Most of the CNN-based methods, e.g., [37, 3, 2], employ the commonly used residual learning in the network designs, which is less effective for the estimation of the main structures, as demonstrated in Section 1. Thus, these methods [37, 3, 2] do not effectively remove the blur as shown in Figure 3(c), (d), and + +![](images/8f92bd178be9d27d5f6c27a36e1648c057f57f6e8801dce59e59a4c3c3a89b22.jpg) +(a) Blurry input + +![](images/c4b7904d6b1db49b0a416b17187bfcaa3cf89d21ccee0854a788a26300f2a020.jpg) +(b) Ground truth + +![](images/ff0ad8ff87bc9c6ceaf2ed56f85ebc88e4820aabeefff810e17440370560c011.jpg) +(c) MPRNet [37] + +![](images/095062c2624b6f64e96fd170191c1cfebf72e604dddb8661660ea2caa3bf2753.jpg) +(d) MIMO-UNet [3] + +![](images/1be4550cc0238fcef0fc919b59ca6a924486d333fec435df1c35bf5e89bb114f.jpg) +(e) DeepRFT [15] + +![](images/61646512cc530ba90b0b1e85bd0b08e389dfec53f5df0cc84b7554649d17bbf5.jpg) +(f) NAFNet [2] + +![](images/dcb8e754f091f88c22db4f952322f03ad666b00fca542786c3f0026f6dcb02bf.jpg) +(g) Restomer [36] + +![](images/762a2f8372a8f47358815f7dd5d03620275a87f458b0dd55141d29e9dab5a5bd.jpg) +(h) Restormer-Local [4] +Figure 3. Example from the GoPro dataset [17]. Compared to the evaluated methods in (c)-(i), the proposed approach generates a better deblurred image with clearer characters in (j). + +![](images/2c9466c1e4782c04683de9d4cdf04844bb8ab033726566447121e68fc1a5dd94.jpg) +(i) Stripformer [29] + +![](images/fd75f4ec1c343dfe9d426adf10d4f39ce3b6b2815b91486723b9e96e7c7e8fac.jpg) +(j) MRLPFNet + +(f). The method [15] improves the residual learning by introducing an additional branch operating in the frequency domain. However, as the main structures are usually spatially variant, simply using localized convolution operations does not effectively model such global properties. The deblurred result in Figure 3(e) still contains the blur effect. + +The recent methods [36, 29] develop Transformers to solve image deblurring. As analyzed in Section 3, Transformers can be regarded as low-pass filters. These methods are able to explore the low-frequency contents but less effective for modeling the high-frequency information, thus leading to over-smoothed deblurred results as shown in Figure 3(g) and (i). In contrast to the above-mentioned methods, the proposed MRLPFNet is able to explore both high- and low-frequency information, generating a better image with clearer details and structures than the competed methods (e.g., the restored numbers in Figure 3(j) are clearer). + +Evaluations on the RealBlur dataset. The RealBlur dataset [23] contains 3,758 image pairs for training and 980 image pairs for the test. Based on the protocols of [23], our approach is compared with the state-of-the-art methods for fair comparisons. Table 2 shows that the proposed method generates the deblurred results with higher PSNR and SSIM values, where the PSNR values of our method are at least 1.08dB and 0.71dB higher than the evaluated methods on the "RealBlur-R" and "RealBlur-J" datasets, respectively. + +Figure 4 shows some visual comparisons of the evaluated methods. The methods [28, 13, 3] based on the standard residual learning do not effectively remove the blur effects as shown in Figure 4(c)-(e). The method [15] improves the standard residual learning, but the restored images are oversmoothed, e.g., the strokes in Figure 4(f). The Transformer + +Table 2. Quantitative evaluations of the proposed approach against state-of-the-art methods on the RealBlur dataset [23]. All the comparison results are generated using the publicly available codes and the models trained on the same training datasets. + +
RealBlur-RRealBlur-J
PSNR (dB)SSIMPSNR (dB)SSIM
SRN [28]38.650.965231.380.9091
DeblurGAN [12]36.440.934729.690.8703
MIMO-UNet+ [3]--31.920.9190
DeepRFT+ [15]39.840.972132.190.9305
Stripformer [29]39.840.973732.480.9290
MRLPFNet40.920.975333.190.9361
+ +Table 3. Quantitative evaluations of the proposed approach against state-of-the-art methods on the HIDE dataset [25]. All the comparison results are generated by the same models trained on the GoPro dataset [17] as in Table 1. + +
MethodPSNR (dB)SSIM
SRN [28]28.360.9040
SAPHNet [26]29.980.9300
MPRNet [37]30.960.9394
MPRNet-Local [4]31.190.9418
MIMO-UNet [3]29.280.9206
MIMO-UNet+ [3]29.990.9304
DeepRFT [15]30.990.9407
DeepRFT+ [15]31.420.9442
Restormer [36]31.220.9423
Restormer-Local [4]31.490.9447
Stripformer [29]31.030.9395
MRLPFNet31.630.9465
+ +based method [29] tends to generate over-smoothed results and does not effectively remove the blur as shown in Figure 4(g). In contrast, our method generates clearer images than the evaluated methods (Figure 4(h)). + +![](images/d3199ca2147d0862ed0e3928716caa501ff800ecca32518316a41ace56020cca.jpg) +(a) Blurry input + +![](images/e64b748c104a03b6094dcb09077c5f346b8d634bd8e9b139473c682c5a6f8067.jpg) +(b) Ground truth + +![](images/c3e86dfe3452a3031759268d4f4469b849a312427795a25696620ef22bcff952.jpg) +(c) SRN [28] + +![](images/9d04394ec46fade466d265b7703338937f6e42fb391823a701f653958e77eb80.jpg) +(d) DeblurGAN-V2 [13] + +![](images/5f6332d4ae5cdf73b8a3b3399d7efce64032af10644a06c55be6fbd3338487a3.jpg) +(e) MIMO-UNet [3] + +![](images/52560ac310d7f7554045564df6345b9c19915bdf923712dabcad24b206041281.jpg) +(f) DeepRFT+ [15] + +![](images/67c74301564910ec80b93e8b1e1db37ea80bb6878e4e220208a93c4459871c73.jpg) +(g) Stripformer [29] + +![](images/29ece7ad1151b45924c9d53085650793f70136e3bac6ecee60137378b3a5d4e5.jpg) +(h) MRLPFNet +Figure 4. Example from the RealBlur dataset [23]. Compared with the deblurred results in (c)-(g), the proposed method recovers a high-quality image with clearer structural details. + +Table 4. Effectiveness of the proposed low-pass filter and wavelet-based feature fusion for image deblurring. All baseline methods are trained using the same settings as the proposed method for fair comparisons. + +
Low-pass filter (LPF)Feature fusion (FF)GoPro
Bilinear-based (BFF)Wavelet-based (WFF)PSNR (dB)/SSIM
MRLPFNetw/o LPF&FFXXX32.8/0.9606
MRLPFNetw/o LPF&w/BFFX✓X32.9/0.9611
MRLPFNetw/o LPF&w/WFFXX✓33.0/0.9616
MRLPFNetw/ LPF&w/FF✓XX33.4/0.9641
MRLPFNet✓X✓33.5/0.9650
+ +**Evaluations on the **HIDE** dataset.** We further evaluate our method on the **HIDE** dataset [25] by using the model trained on the GoPro dataset. Table 3 shows that the proposed approach generates the deblurred results with the highest PSNR and SSIM values. + +# 6. Analysis and Discussions + +# 6.1. Effect of the learnable low-pass filter + +The learnable low-pass filter is proposed to explore the spatially-variant low-frequency information so that the global structural contents can be better restored for image deblurring. To demonstrate the effectiveness of the proposed learnable low-pass filter, we first compare our method with a baseline that removes the learnable low-pass fil + +ter (MRLPFNet $_{\mathrm{w/o LPF\& w/WFF}}$ for short) and train this baseline using the same settings as ours. We use the GoPro dataset [17] as described in Section 5.2 for evaluation. Table 4 shows the quantitative results, where the PSNR of the proposed MRLPFNet is $0.5\mathrm{dB}$ higher than the baseline without the learnable low-pass filter. To focus on the effect of the low-pass filter, we further disable the feature fusion module and compare the baselines with and without the learnable low-pass filter (MRLPFNet $_{\mathrm{w/o LPF\& FF}}$ and MRLPFNet $_{\mathrm{w/ LPF\& w/O FF}}$ for short). The comparisons in Table 4 illustrate the significance of using the learnable low-pass filter, which is able to concentrate on the low-frequency information modeling and effectively recover the spatially-variant image structures for image deblurring. + +Figure 5 shows a visual comparison. The main structures + +![](images/fea7471daf2d2e01b177827ece1e69489a49be8dc442bcb4d0f1a0c898e4877c.jpg) +(a) Blur input + +![](images/c8e595a1c20aed54db82b62ace8e89556c75328c7ded4f4b31a33c79d1e28dec.jpg) +(b) MRLPFNetw/o LPF&w/ WFF + +![](images/6af14ea7f7624de23ba0538aef9b78eb8c7aafbe3dec770113b6a420ed091d58.jpg) +(c) MRLPFNet + +![](images/3dd6df872b10a1aafd391f4915f40abc6e098161a891611cae766b7aa74e4d5e.jpg) +(d) + +![](images/66f9e6107fdd5845c53ef46452ee31a31e3d4704df1e853eb07751753d878d15.jpg) +(e) + +![](images/736e56dfb4a707c1fce059433a9f1794aae53bfd66215786e874a9a07883fc21.jpg) +(f) +Figure 5. Effect of the proposed learnable low-pass filter. (d) is the residual image between the blurry image and Ground truth. (e) and (f) are the residual images estimated by MRLPFNetw/o LPF&w/ WFF and MRLPFNet, respectively. + +in the residual image estimated by MRLPFNet $_{\mathrm{w/o LPF\& w/ WFF}}$ are not well recovered, e.g., the license plate numbers in Figure 5(e), resulting in the deblurred image with a blur effect (Figure 5(b)). In contrast, the residual image estimated by the proposed MRLPFNet is better restored, as using the learnable low-pass filter is able to model the spatially-variant image structures. Thus, our approach is more effective at yielding a clear image with distinct structures (e.g., the license plate numbers in Figure 5(f)). + +# 6.2. Effect of the wavelet-based feature fusion + +To demonstrate the effectiveness of the wavelet-based feature fusion on fusing the features with different spatial resolutions, we first disable the learnable low-pass filter in our implementation (MRLPFNetw/o LPF&w/WFF for short). Then we compare with the baseline that replaces the wavelet-based feature fusion with the bilinear interpolation (MRLPFNetw/o LPF&w/BFF for short). The results in Table 4 show that using the bilinear interpolation as the feature fusion does not perform well as our method with the wavelet-based one, since the wavelet transform is invertible and can preserve more accurate information during the transform process. The qualitative comparisons in Figure 6 further show that using the wavelet-based feature fusion is able to improve the quality of the restored image (Figure 6(c)). We also compare our complete network with the baseline that removes the feature fusion module (MRLPFNetw/LPF&w/0FF for short). The comparisons in Figure 6 show the same tendency that using the wavelet-based feature fusion improves the final deblurring performance. + +# 6.3. Model complexity + +We examine the model complexity of the proposed approach and the state-of-the-art methods in terms of model + +![](images/387d1aa3e62cfc113f4669b6e5e75770c60dcd8156766b68ee1a57e510e048b2.jpg) +(a) Blurry input + +![](images/feb5defff863c4d846d44057fb7d8c57019ba343de882c1b12beed3b0764b59b.jpg) +(b) +Figure 6. Effect of the proposed wavelet-based feature fusion. (b) and (c) are the results obtained by the baselines using the Bilinear-based (MRLPFNetw/o LPF&w/BFF in Table 4) and the wavelet-based (MRLPFNetw/o LPF&w/WFF in Table 4) feature fusion, respectively. + +![](images/cae9d2c41dc7cf868b89b37b3419ce3a991f8b52cb87a4517355d7b45faf3e4f.jpg) +(c) + +![](images/51f2aa5b2c2332809fc62ef06f04921d76bcf1c6b5ae5c5e5e200b4bed975227.jpg) +(d) Ground truth + +Table 5. Model complexity of the top-performance methods on the above-mentioned datasets. The FLOPs are evaluated on image patches with the size of $256 \times 256$ pixels based on the protocols of existing methods. The running time is evaluated on images with the size of $1280 \times 720$ pixels. All the results are obtained on a machine with an NVIDIA GeForce RTX 3090 GPU. + +
MethodsModel parameters (M)FLOPs (G)Running time (/s)
MPRNet [37]20.17600.9806
MIMO-UNet+ [3]16.11510.2827
DeepRFT+ [15]23.01830.5518
Restormer [36]26.11550.9798
Stripformer [29]19.71700.6580
MRLPFNetw/o LPF11.4820.2613
MRLPFNet20.61290.8633
+ +parameters, running time, and FLOPs. Table 5 shows that our method has the lowest FLOPs value and also achieves competitive performance against the competed ones in terms of running time. + +Limitations. As the proposed learnable low-pass filter is based on the self-attention to estimate the filter weights, it moderately increases the running time as shown in Table 5 (see the comparisons of "MRLPFNetw/o LPF" and "MRLPFNet"). Future work will develop efficient and learnable low-pass filters for better image deblurring. + +# 7. Conclusion + +We present an effective MRLPFNet to reconstruct both the low-frequency and high-frequency information for image deblurring. To better explore the spatially-variant structures, we develop a learnable low-pass filter based on the self-attention mechanism. Furthermore, we propose a wavelet-based feature fusion method to effectively fuse the features with different spatial resolutions. By formulating the proposed method into an end-to-end trainable network, we show that it performs favorably against state-of-the-art methods on benchmarks. + +Acknowledgement. This work was supported in part by the National Key Research and Development Program of China under Grant 2022ZD0118801, the National Natural Science Foundation of China under Grants 62272233, 61922043, 61925204, and U22B2049, and the Fundamental Research Funds for the Central Universities under Grant 30922010910 and 30920041109. + +# References + +[1] Ayan Chakrabarti. A neural approach to blind motion deblurring. In ECCV, pages 221-235, 2016. 2 +[2] Liangyu Chen, Xiaojie Chu, Xiangyu Zhang, and Jian Sun. Simple baselines for image restoration. In ECCV, 2022. 3, 5, 6 +[3] Sung-Jin Cho, Seo-Won Ji, Jun-Pyo Hong, Seung-Won Jung, and Sung-Jea Ko. Rethinking coarse-to-fine approach in single image deblurring. 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IJCV, 130(9):2103-2130, 2022. 1 \ No newline at end of file diff --git a/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/images.zip b/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..3f2a407a1e1eab8b28222718df3767055cbcf7c6 --- /dev/null +++ b/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:d9b5334400f9565639538566c0da501b59fb85f1e675a1fb48cfe0b51191185e +size 676957 diff --git a/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/layout.json b/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..9a8ac8845a8abbd2bc0c0fadbf581a3ae1c6d06a --- /dev/null +++ b/2023/Multi-Scale Residual Low-Pass Filter Network for Image Deblurring/layout.json @@ -0,0 +1,10517 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 86, + 103, + 507, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 86, + 103, + 507, + 121 + ], + "spans": [ + { + "bbox": [ + 86, + 103, + 507, + 121 + ], + "type": "text", + "content": "Multi-scale Residual Low-Pass Filter Network for Image Deblurring" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 138, + 143, + 455, + 173 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 138, + 143, + 455, + 173 + ], + "spans": [ + { + "bbox": [ + 138, + 143, + 455, + 173 + ], + "type": "text", + "content": "Jiangxin Dong Jinshan Pan* Zhongbao Yang Jinhui Tang Nanjing University of Science and Technology" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 199, + 192, + 213 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 199, + 192, + 213 + ], + "spans": [ + { + "bbox": [ + 143, + 199, + 192, + 213 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 224, + 289, + 499 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 224, + 289, + 499 + ], + "spans": [ + { + "bbox": [ + 46, + 224, + 289, + 499 + ], + "type": "text", + "content": "We present a simple and effective Multi-scale Residual Low-Pass Filter Network (MRLPFNet) that jointly explores the image details and main structures for image deblurring. Our work is motivated by an observation that the difference between the blurry image and the clear one not only contains high-frequency contents but also includes low-frequency information due to the influence of blur, while using the standard residual learning is less effective for modeling the main structure distorted by the blur. Considering that the low-frequency contents usually correspond to main global structures that are spatially variant, we first propose a learnable low-pass filter based on a self-attention mechanism to adaptively explore the global contexts for better modeling the low-frequency information. Then we embed it into a Residual Low-Pass Filter (RLPF) module, which involves an additional fully convolutional neural network with the standard residual learning to model the high-frequency information. We formulate the RLPF module into an end-to-end trainable network based on an encoder and decoder architecture and develop a wavelet-based feature fusion to fuse the multi-scale features. Experimental results show that our method performs favorably against state-of-the-art ones on commonly-used benchmarks." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 523, + 128, + 536 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 523, + 128, + 536 + ], + "spans": [ + { + "bbox": [ + 47, + 523, + 128, + 536 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 544, + 287, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 544, + 287, + 628 + ], + "spans": [ + { + "bbox": [ + 46, + 544, + 287, + 628 + ], + "type": "text", + "content": "The camera shake and object motion are usually inevitable when taking photos with hand-held devices, which lead to significant motion blur effects. Restoring clear photos from blurry ones has attracted lots of attention from both research and industry communities [40]. However, motion deblurring is quite challenging as only the blurred images are available while the blur and latent images are unknown." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 629, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 665 + ], + "type": "text", + "content": "Significant progress has been made in image restoration due to the development of deep neural networks that directly learn the mapping from the degraded observation to" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "spans": [ + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "text", + "content": "the clear image. It is well known that the residual learning strategy [7] has been widely used to ease the training of networks, where a latent clear image " + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "text", + "content": " can be restored by the summation of the degraded input " + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "text", + "content": " and the output " + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "inline_equation", + "content": "\\mathcal{N}(B)" + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "text", + "content": " of a residual learning network " + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "inline_equation", + "content": "\\mathcal{N}" + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "text", + "content": ". This strategy has been proven to be effective in lots of image restoration tasks, e.g., image super-resolution, as the degraded image " + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "text", + "content": " shares the same main structures as the clear one " + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "text", + "content": ", and the residual between " + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 306, + 200, + 545, + 308 + ], + "type": "text", + "content": " mainly contains image details." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 308, + 546, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 308, + 546, + 523 + ], + "spans": [ + { + "bbox": [ + 304, + 308, + 546, + 523 + ], + "type": "text", + "content": "However, we note that the difference between a blurry input and its corresponding clear one not only contains image details but also involves some structures. Taking Figure 1 as an example, the main structures in the clear image (e.g., the pillars enclosed in the red boxes of Figure 1(f)) disappear due to the influence of the motion blur effect. Thus, in addition to the details smoothed by the blur, some main structures also exist in the residual between the blurry image and the clear one (see the part enclosed in the red box of Figure 1(b)). As demonstrated in [22], the standard residual learning method [7] is effective for modeling the high-frequency information but less effective to restore the low-frequency contents. Figure 1(c) also shows that using the standard residual learning method may not estimate the main structures of the residual image well, which thus affects the final image restoration (Figure 1(h)). Therefore, it is important for image deblurring to effectively model the main structures distorted by the motion blur." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 525, + 547, + 644 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 525, + 547, + 644 + ], + "spans": [ + { + "bbox": [ + 304, + 525, + 547, + 644 + ], + "type": "text", + "content": "To alleviate the above-mentioned problem, the recent methods [15, 34] introduce a frequency branch based on the Fast Fourier Transform (FFT) in the residual network, which achieves good performance. However, as such a frequency branch is achieved by applying " + }, + { + "bbox": [ + 304, + 525, + 547, + 644 + ], + "type": "inline_equation", + "content": "\\mathrm{Conv}1 + \\mathrm{ReLU} + \\mathrm{Conv}1^2" + }, + { + "bbox": [ + 304, + 525, + 547, + 644 + ], + "type": "text", + "content": " to the concatenation of the real and imaginary parts of the residual image, it may not effectively model the spatially-variant property of the global main structures in the residual image (Figure 1(d)), resulting in fake structures caused by the blur in the final deblurred image (Figure 1(i))." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 645, + 547, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 645, + 547, + 682 + ], + "spans": [ + { + "bbox": [ + 304, + 645, + 547, + 682 + ], + "type": "text", + "content": "In this paper, we propose a Multi-scale Residual LowPass Filter Network (MRLPFNet) for high-quality image deblurring. Our goal is to effectively model both the low-" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 673, + 136, + 684 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 673, + 136, + 684 + ], + "spans": [ + { + "bbox": [ + 58, + 673, + 136, + 684 + ], + "type": "text", + "content": "*Corresponding author" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 684, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 684, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 684, + 287, + 713 + ], + "type": "text", + "content": "1Note that the high-frequency contents in an image correspond to the image details, while the low-frequency ones denote the main structures of an image." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 693, + 545, + 712 + ], + "type": "page_footnote", + "angle": 0, + 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Visual comparison with state-of-the-art image deblurring methods on a challenging example. Our work is motivated by an observation that the difference between the blurry image and its corresponding clear one not only contains high-frequency contents but also includes low-frequency information due to the influence of the blur as shown in (b). We thus develop a simple yet effective MRLPFNet to learn both image details and spatially-variant structures (see (e)), which thus leads to better-deblurred results as shown in (j)." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 347, + 156, + 444, + 232 + ], + "blocks": [ + { + "bbox": [ + 347, + 156, + 444, + 232 + ], + "lines": [ + { + "bbox": [ + 347, + 156, + 444, + 232 + ], + "spans": [ + { + "bbox": [ + 347, + 156, + 444, + 232 + ], + "type": "image", + "image_path": "ac1b2b17d78618d7aee0d9bf8f9988bdd737b5f611d938a95b96eac77fe3984c.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 371, + 233, + 421, + 242 + ], + "lines": [ + { + "bbox": [ + 371, + 233, + 421, + 242 + ], + "spans": [ + { + "bbox": [ + 371, + 233, + 421, + 242 + ], + "type": "text", + "content": "(i) DeepRFT [15]" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 446, + 156, + 545, + 232 + ], + "blocks": [ + { + "bbox": [ + 446, + 156, + 545, + 232 + ], + "lines": [ + { + "bbox": [ + 446, + 156, + 545, + 232 + ], + "spans": [ + { + "bbox": [ + 446, + 156, + 545, + 232 + ], + "type": "image", + "image_path": "7fd613423c08eb83f42b9334bee12fc7a4e4243346648affdf445fc363b61e7f.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 464, + 233, + 527, + 242 + ], + "lines": [ + { + "bbox": [ + 464, + 233, + 527, + 242 + ], + "spans": [ + { + "bbox": [ + 464, + 233, + 527, + 242 + ], + "type": "text", + "content": "(j) MRLPFNet (Ours)" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "bbox": [ + 46, + 304, + 287, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 287, + 496 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 287, + 496 + ], + "type": "text", + "content": "frequency and high-frequency parts of the residual image between the blurry input and its corresponding clear output within the residual learning framework. To better explore the low-frequency information, we propose to intuitively apply a low-pass filter on the residual image to concentrate on the low-frequency part. In addition, as the low-frequency contents in an image correspond to the global main structures, one of whose properties is that they are usually spatially variant, we exploit a learnable low-pass filter module based on a self-attention mechanism (as a basic module) to adaptively explore the global contexts so that the main structures can be better restored for image deblurring. Then we incorporate it in the proposed Residual Low-Pass Filter (RLPF) module with an additional residual learning branch based on a fully convolutional neural network (CNN) for modeling the high-frequency information." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 46, + 497, + 287, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 497, + 287, + 652 + ], + "spans": [ + { + "bbox": [ + 46, + 497, + 287, + 652 + ], + "type": "text", + "content": "Furthermore, the multi-scale strategy is widely used in image deblurring. As features from various scales have different spatial resolutions, resizing operations are usually used to fuse these features. However, simply using resizing operations based on downsampling or upsampling will lead to information loss. To this end, we develop a simple yet effective feature fusion module based on the wavelet transform to fuse the features with different spatial resolutions. Finally, we embed the proposed RLPF module and the wavelet-based feature fusion (WFF) module into an end-to-end trainable network within a coarse-to-fine framework. The proposed approach achieves favorable performance on widely-used benchmarks." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 59, + 653, + 266, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 653, + 266, + 664 + ], + "spans": [ + { + "bbox": [ + 59, + 653, + 266, + 664 + ], + "type": "text", + "content": "The main contributions are summarized as follows." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 58, + 665, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 665, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 58, + 665, + 287, + 714 + ], + "type": "text", + "content": "- We propose an effective RLPF module to model both the high-frequency and low-frequency information of the difference between the network input and output for image deblurring. Specifically, a learnable low" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 324, + 304, + 545, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 324, + 304, + 545, + 376 + ], + "spans": [ + { + "bbox": [ + 324, + 304, + 545, + 376 + ], + "type": "text", + "content": "pass filter is developed based on a self-attention mechanism to adaptively explore the spatially-variant property of the global contexts to effectively reconstruct the low-frequency structures and a fully CNN with the residual learning is adopted to model the high-frequency information." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 317, + 376, + 545, + 447 + ], + "type": "list", + "angle": 0, + "index": 28, + "blocks": [ + { + "bbox": [ + 317, + 376, + 545, + 412 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 376, + 545, + 412 + ], + "spans": [ + { + "bbox": [ + 317, + 376, + 545, + 412 + ], + "type": "text", + "content": "- We develop a simple yet effective feature fusion module based on the wavelet transform to fuse the features of different scales for better image deblurring." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 317, + 412, + 545, + 447 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 412, + 545, + 447 + ], + "spans": [ + { + "bbox": [ + 317, + 412, + 545, + 447 + ], + "type": "text", + "content": "- By training the proposed MRLPFNet in an end-to-end manner, we show that it performs favorably against state-of-the-art methods." + } + ] + } + ], + "index": 27 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 460, + 392, + 473 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 460, + 392, + 473 + ], + "spans": [ + { + "bbox": [ + 306, + 460, + 392, + 473 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 304, + 480, + 545, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 480, + 545, + 589 + ], + "spans": [ + { + "bbox": [ + 304, + 480, + 545, + 589 + ], + "type": "text", + "content": "Hand-crafted prior-based methods. As image deblurring is ill-posed, conventional methods usually develop kinds of effective priors to constrain the solution space, e.g., sparsity priors on the image gradient [11, 35] or intensity [19], internal patch recurrence [16], sparsity of dark channel prior [21], etc. These hand-crafted priors can help the blur removal. However, they do not fully exploit the characteristics of the clear image data and usually lead to complicated optimization problems." + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 304, + 594, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 689 + ], + "type": "text", + "content": "Deep learning-based methods. Instead of manually designing image priors, lots of methods develop kinds of deep CNNs to solve image deblurring. Early approaches employ deep CNN models to estimate blur kernels and then use existing prior-based restoration methods to estimate the clear images [27, 6, 1, 24]. While inaccurate blur kernels will lead to deblurred results with severe artifacts as the blur kernels and latent clear images are estimated independently." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "Instead of estimating blur kernels, numerous methods [17, 39, 28, 5, 38, 26, 37, 3, 18, 12] directly estimate" + } + ] + } + ], + "index": 32 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "12346" + } + ] + } + ], + "index": 33 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 360 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 360 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 360 + ], + "type": "text", + "content": "clear images from blurry ones. In [17], Nah et al. develop a multi-scale deep CNN, where the restored images from coarse scales are resized to help the estimation of finer scales. To better explore the multi-scale information, Tao et al. [28] develop an effective scale recurrent neural network. In [5], Gao et al. propose a parameter selective sharing and nested skip connection method to improve [17]. Although the methods based on a multi-scale strategy achieve decent performance, simply increasing the model depth with more scales cannot further improve the quality of deblurring. To overcome this problem, methods based on multi-patches have been developed. Zhang et al. [38] develop an effective deep hierarchical multi-patch network, where the features from the previous stage are concatenated to facilitate the estimation of the following stages. Zamir et al. [37] propose a multi-stage progressive method to better explore the features from multi-stages by a cross-scale feature fusion module. In addition, an effective supervised attention module is developed to better guide the estimations of the following stages. As both the multi-scale and multi-patch methods need to perform the network at each scale or stage recurrently, which leads to high computational costs, Cho et al. [3] develop a multi-input and multi-output U-net based on a multi-scale strategy to solve image deblurring." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 362, + 289, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 362, + 289, + 507 + ], + "spans": [ + { + "bbox": [ + 47, + 362, + 289, + 507 + ], + "type": "text", + "content": "These above-mentioned methods achieve significant performance, most of which adopt the residual learning in the network design. As demonstrated in [20], the residual learning is able to model the image details (i.e., high-frequency information), but is less effective for exploring the main structures (i.e., low-frequency information). To overcome this problem, Mao et al. [15] improve the residual learning network by introducing an additional branch performed in the frequency domain. However, as the main structures involve the spatially-variant global contexts, simply using the local operations (e.g., " + }, + { + "bbox": [ + 47, + 362, + 289, + 507 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 47, + 362, + 289, + 507 + ], + "type": "text", + "content": " convolution in [15]) may not model the main structures well." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 521, + 289, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 521, + 289, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 521, + 289, + 713 + ], + "type": "text", + "content": "Transformer-based methods. As Transformer is effective for global context exploration and shows great potential in many vision tasks, several methods apply it to image deblurring. Zamir et al. [36] propose an efficient Transformer model by estimating self-attention along the channel dimension. This method is further simplified by [2]. Tsai et al. [29] develop a Transformer-based model by constructing intra- and inter-strip tokens to reweight image features in the horizontal and vertical directions. In [30], Tu et al. develop an effective multi-axis MLP-based architecture. Wang et al. [31] develop a general U-shaped Transformer to solve image deblurring. These Transformer-based approaches achieve decent results. However, as our analysis in Section 3 shows, self-attention has the same effect as the low-pass filter. Simply using Transformers may lead to over-smoothed results." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 305, + 71, + 500, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 71, + 500, + 85 + ], + "spans": [ + { + "bbox": [ + 305, + 71, + 500, + 85 + ], + "type": "text", + "content": "3. Low-Pass Filter and Self-Attention" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 305, + 91, + 545, + 114 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 91, + 545, + 114 + ], + "spans": [ + { + "bbox": [ + 305, + 91, + 545, + 114 + ], + "type": "text", + "content": "To better motivate our work, we first describe the relations between the low-pass filter and self-attention." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 115, + 545, + 139 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 115, + 545, + 139 + ], + "spans": [ + { + "bbox": [ + 305, + 115, + 545, + 139 + ], + "type": "text", + "content": "Given an image " + }, + { + "bbox": [ + 305, + 115, + 545, + 139 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 305, + 115, + 545, + 139 + ], + "type": "text", + "content": " and a low-pass filter " + }, + { + "bbox": [ + 305, + 115, + 545, + 139 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 305, + 115, + 545, + 139 + ], + "type": "text", + "content": ", we can obtain a filtered image " + }, + { + "bbox": [ + 305, + 115, + 545, + 139 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 305, + 115, + 545, + 139 + ], + "type": "text", + "content": " by:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 354, + 147, + 545, + 173 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 354, + 147, + 545, + 173 + ], + "spans": [ + { + "bbox": [ + 354, + 147, + 545, + 173 + ], + "type": "interline_equation", + "content": "f (\\mathrm {x}) = \\mathcal {F} (I (\\mathrm {x})) = \\sum_ {\\mathrm {y}} \\mathbf {W} _ {\\mathrm {x y}} I (\\mathrm {y}), \\tag {1}", + "image_path": "4683be1beb3cb8e444d9029d1e55766ba3130c09a913fdec420bbecddad3341a.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "spans": [ + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "text", + "content": " denote image pixels; " + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\mathrm{xy}}" + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "text", + "content": " denotes the filter weight for " + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "text", + "content": ", satisfying " + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\mathrm{xy}} \\geq 0" + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "inline_equation", + "content": "\\sum_{y} \\mathbf{W}_{\\mathrm{xy}} = 1" + }, + { + "bbox": [ + 304, + 175, + 546, + 354 + ], + "type": "text", + "content": ". The role of a low-pass filter is to do a weighted average in an area with the same size as the filter, thus filtering out the high-frequency information and retaining the low-frequency one. One common type of filter is the linear translation-invariant filter, e.g., the Gaussian filter, which adopts the spatially-invariant filter weight and cannot effectively describe the variant properties of image structures in different spatial areas. Another type of filter is the nonlinear filter, e.g., the bilateral filter, whose weights depend on both the spatial closeness and the intensity difference. Such weights can adaptively model the spatially-variant contexts (e.g., global edges), thus preserving more useful low-frequency information in the filtered image." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 354, + 545, + 378 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 354, + 545, + 378 + ], + "spans": [ + { + "bbox": [ + 305, + 354, + 545, + 378 + ], + "type": "text", + "content": "Recently, the attention-based approaches, e.g., self-attention, compute the weighted value as" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 320, + 385, + 545, + 414 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 320, + 385, + 545, + 414 + ], + "spans": [ + { + "bbox": [ + 320, + 385, + 545, + 414 + ], + "type": "interline_equation", + "content": "\\mathbf {Z} = \\mathbf {S} \\circledast \\mathbf {V} = \\operatorname {s o f t m a x} \\left(\\frac {\\mathcal {Q} (F) \\mathcal {K} (F) ^ {\\top}}{\\sqrt {d _ {k}}}\\right) \\mathcal {V} (F), \\tag {2}", + "image_path": "0c0eb0abaa3471ea293ba415d8edd4d479e631e7102db4c319b475eff84ca46e.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "spans": [ + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": " denotes the deep feature extracted from the input image " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": "; " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "\\ast" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": " indicates the matrix multiplication; " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "\\mathcal{Q}(\\cdot), \\mathcal{K}(\\cdot)" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "\\mathcal{V}(\\cdot)" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": " denote the operations that extract the matrices for the query, key, and value; " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "d_k" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": " is the dimension of the keys. A softmax normalized operation is applied to each row of " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "\\mathbf{S}" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": " to ensure " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "\\mathbf{S}_{ij} \\geq 0" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "\\sum_{j} \\mathbf{S}_{ij} = 1" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": " denote the index of the row and column in " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "\\mathbf{S}" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": ". Thus, each row of " + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "inline_equation", + "content": "\\mathbf{S}" + }, + { + "bbox": [ + 304, + 419, + 547, + 575 + ], + "type": "text", + "content": " can be regarded as a low-pass filter. Compared to the bilateral filter whose weight measures the spatial and color similarity based on the exponential Euclidean distance, the attention value measures the similarity of query and key based on the correlation metric. Therefore, it is spatially variant and can model the main structures more adaptively." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 575, + 547, + 624 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 575, + 547, + 624 + ], + "spans": [ + { + "bbox": [ + 304, + 575, + 547, + 624 + ], + "type": "text", + "content": "Considering the self-attention (2) is learnable and more flexible, we propose to straightforwardly embed it into the network to better model the low-frequency information for image deblurring." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 633, + 382, + 646 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 633, + 382, + 646 + ], + "spans": [ + { + "bbox": [ + 305, + 633, + 382, + 646 + ], + "type": "text", + "content": "4. MRLPFNet" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "content": "Our goal is to develop an effective MRLPFNet for high-quality image deblurring, which can better restore both the image details and main structures. Specifically, we first propose a learnable low-pass filter based on the self-attention method to model the low-frequency information. We then" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "12347" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 70, + 372, + 194 + ], + "blocks": [ + { + "bbox": [ + 51, + 70, + 372, + 194 + ], + "lines": [ + { + "bbox": [ + 51, + 70, + 372, + 194 + ], + "spans": [ + { + "bbox": [ + 51, + 70, + 372, + 194 + ], + "type": "image", + "image_path": "8650aa55cc075fa1195eb00fcb19806bfdf2367403d8d96d7ea3a7ba2373a6f2.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 52, + 198, + 372, + 210 + ], + "blocks": [ + { + "bbox": [ + 52, + 198, + 372, + 210 + ], + "lines": [ + { + "bbox": [ + 52, + 198, + 372, + 210 + ], + "spans": [ + { + "bbox": [ + 52, + 198, + 372, + 210 + ], + "type": "image", + "image_path": "b321282ffb04b23800025ad00cebeadc84afaba3e5bcbbeb13521bf4014a0b18.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 216, + 546, + 251 + ], + "lines": [ + { + "bbox": [ + 46, + 216, + 546, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 216, + 546, + 251 + ], + "type": "text", + "content": "Figure 2. Multi-scale residual low-pass filter network. To restore high-quality images with clearer structures, we propose an effective RLPF module that involves a learnable low-pass filter (based on the self-attention) to explore the low-frequency information (through Eqs. (3), (4), and (5)). A wavelet-based feature fusion (WFF) module is developed to fuse the features of various scales for better image deblurring." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 376, + 72, + 539, + 211 + ], + "blocks": [ + { + "bbox": [ + 376, + 72, + 539, + 211 + ], + "lines": [ + { + "bbox": [ + 376, + 72, + 539, + 211 + ], + "spans": [ + { + "bbox": [ + 376, + 72, + 539, + 211 + ], + "type": "image", + "image_path": "502accac8d3b6c346e987c32b1bf946104900353fcb996e8ee4b3c5d4dac898d.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 261, + 288, + 356 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 261, + 288, + 356 + ], + "spans": [ + { + "bbox": [ + 46, + 261, + 288, + 356 + ], + "type": "text", + "content": "incorporate it in our proposed RLPF module with an additional residual learning branch for high-frequency information exploration. Furthermore, we formulate it into an end-to-end trainable network based on a coarse-to-fine framework and propose a feature fusion module based on the wavelet transform to better utilize the multi-scale features. In the following, we present the details of the proposed method." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 363, + 187, + 374 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 363, + 187, + 374 + ], + "spans": [ + { + "bbox": [ + 47, + 363, + 187, + 374 + ], + "type": "text", + "content": "4.1. Residual Low-Pass Filter" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 381, + 287, + 537 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 381, + 287, + 537 + ], + "spans": [ + { + "bbox": [ + 46, + 381, + 287, + 537 + ], + "type": "text", + "content": "As the standard residual learning is adept at exploring the high-frequency information [9, 20] while less effective for the low-frequency information modeling, the method [15] improves the standard residual block by introducing an additional branch that applies Conv1 + ReLU + Conv1 to the features (generated by the FFT) in the frequency domain. Although decent performance has been achieved, the " + }, + { + "bbox": [ + 46, + 381, + 287, + 537 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 381, + 287, + 537 + ], + "type": "text", + "content": " convolution is spatially invariant, which does not effectively model the spatially-variant structures. To overcome this problem, we propose to further improve it by applying a learnable low-pass filter to concentrate on the global main structures, which is able to model the spatially-variant property of the low-frequency information." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 537, + 287, + 609 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 537, + 287, + 609 + ], + "spans": [ + { + "bbox": [ + 46, + 537, + 287, + 609 + ], + "type": "text", + "content": "Specifically, we first generate the feature " + }, + { + "bbox": [ + 46, + 537, + 287, + 609 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}" + }, + { + "bbox": [ + 46, + 537, + 287, + 609 + ], + "type": "text", + "content": " from a blurry input " + }, + { + "bbox": [ + 46, + 537, + 287, + 609 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 46, + 537, + 287, + 609 + ], + "type": "text", + "content": " by a shallow feature extraction network (the details are included in the supplemental material). Then the proposed RLPF module explores the properties of residual learning in both the spatial and frequency domains according to [15]:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 111, + 617, + 287, + 631 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 617, + 287, + 631 + ], + "spans": [ + { + "bbox": [ + 111, + 617, + 287, + 631 + ], + "type": "interline_equation", + "content": "\\mathbf {F} = \\mathbf {Y} + \\mathcal {R} (\\mathbf {Y}) + \\mathcal {F} (\\mathbf {Y}), \\tag {3}", + "image_path": "21b7f2080ddb0441ba7ca9441466dd357898a497e2827e1fe9d6eba10c2e323c.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 638, + 287, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 638, + 287, + 686 + ], + "spans": [ + { + "bbox": [ + 47, + 638, + 287, + 686 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 638, + 287, + 686 + ], + "type": "inline_equation", + "content": "\\mathcal{R}(\\cdot)" + }, + { + "bbox": [ + 47, + 638, + 287, + 686 + ], + "type": "text", + "content": " denotes a plain network that applies Conv3 + ReLU + Conv3 in the spatial domain and " + }, + { + "bbox": [ + 47, + 638, + 287, + 686 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 47, + 638, + 287, + 686 + ], + "type": "text", + "content": " denotes a network [15] with Conv1 + ReLU + Conv1 employed in the frequency domain." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 261, + 545, + 321 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 261, + 545, + 321 + ], + "spans": [ + { + "bbox": [ + 305, + 261, + 545, + 321 + ], + "type": "text", + "content": "As Eq. (3) is based on the locally spatially-invariant convolution operations, it does not effectively model the spatially-variant main structures (see Figure 1(d)). To this end, we develop a learnable low-pass filter, which is proposed based on Eq. (1) and achieved by:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 392, + 327, + 545, + 354 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 392, + 327, + 545, + 354 + ], + "spans": [ + { + "bbox": [ + 392, + 327, + 545, + 354 + ], + "type": "interline_equation", + "content": "\\mathbf {h} _ {i} = \\sum_ {j} \\mathbf {S} _ {i j} \\mathbf {f} _ {j}, \\tag {4}", + "image_path": "8ab77e2518d164a95b3a76f5b500f793dd304c718ed26915a0424e363d77d919.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "spans": [ + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "type": "inline_equation", + "content": "\\mathbf{f}_j" + }, + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "type": "text", + "content": "-th feature map of " + }, + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "type": "inline_equation", + "content": "\\mathbf{F}" + }, + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "type": "text", + "content": ". Based on the discussions in Section 3, the self-attention can be regarded as a spatially-variant low-pass filter, which can better model the global low-frequency contents. Then we use the standard scaled dot-production attention in the Transformer according to [36] to estimate the filter weight matrix " + }, + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "type": "inline_equation", + "content": "\\mathbf{S}" + }, + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "type": "text", + "content": ". Finally, we obtain the filtered feature " + }, + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "type": "inline_equation", + "content": "\\mathbf{E}" + }, + { + "bbox": [ + 305, + 361, + 546, + 445 + ], + "type": "text", + "content": " by:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 390, + 453, + 545, + 465 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 390, + 453, + 545, + 465 + ], + "spans": [ + { + "bbox": [ + 390, + 453, + 545, + 465 + ], + "type": "interline_equation", + "content": "\\mathbf {E} = \\mathbf {F} + \\mathcal {D} (\\mathbf {H}), \\tag {5}", + "image_path": "8148373ff55a02d62f29bda1ac67136f4b4113b02a8721758a9f97928b33c63a.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 472, + 545, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 472, + 545, + 496 + ], + "spans": [ + { + "bbox": [ + 305, + 472, + 545, + 496 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 472, + 545, + 496 + ], + "type": "inline_equation", + "content": "\\mathbf{H} = \\{\\mathbf{h}_i\\}" + }, + { + "bbox": [ + 305, + 472, + 545, + 496 + ], + "type": "text", + "content": " is the low-frequency feature by Eq. (4) and " + }, + { + "bbox": [ + 305, + 472, + 545, + 496 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 305, + 472, + 545, + 496 + ], + "type": "text", + "content": " denotes a " + }, + { + "bbox": [ + 305, + 472, + 545, + 496 + ], + "type": "inline_equation", + "content": "3\\times 3" + }, + { + "bbox": [ + 305, + 472, + 545, + 496 + ], + "type": "text", + "content": " depth-wise convolution layer." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 497, + 545, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 497, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 305, + 497, + 545, + 533 + ], + "type": "text", + "content": "We refer to the module achieved by Eqs. (3), (4), and (5) as the proposed RLPF module, which is then embedded into an encoder-decoder architecture as shown in Figure 2(a)." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 540, + 470, + 551 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 540, + 470, + 551 + ], + "spans": [ + { + "bbox": [ + 306, + 540, + 470, + 551 + ], + "type": "text", + "content": "4.2. Wavelet-based Feature Fusion" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 545, + 713 + ], + "type": "text", + "content": "To efficiently ease and improve the deblurring process, the recent methods [3, 15] utilize the multi-scale features generated by different encoder blocks to prompt the learning of various decoder blocks. As the spatial resolutions of the features from different scales are not the same, they are usually resized by downsampling or upsampling operations to the same spatial resolution for feature fusion. However, these resizing operations may lose some important structural details, thus affecting the final image restoration. As the wavelet transform [8] can model the image scale information and is insertable, we develop a wavelet-based feature fusion method to better fuse the features of various scales for image deblurring." + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "type": "inline_equation", + "content": "^3" + }, + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "type": "text", + "content": "Conv3 + ReLU + Conv3 denotes two " + }, + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "type": "inline_equation", + "content": "3 \\times 3" + }, + { + "bbox": [ + 47, + 693, + 287, + 712 + ], + "type": "text", + "content": " convolutional layers with the usual ReLU activation in between." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12348" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": "Specifically, considering two features " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_s" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_{s + 1}" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " generated by Eq. (5) for the finer image scale " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " and coarser image scale " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "s + 1" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": ", we first apply the Haar transform " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "\\mathcal{H}" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " [32, 14, 33] to " + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_s" + }, + { + "bbox": [ + 47, + 72, + 287, + 120 + ], + "type": "text", + "content": " and obtain" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 93, + 127, + 287, + 143 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 127, + 287, + 143 + ], + "spans": [ + { + "bbox": [ + 93, + 127, + 287, + 143 + ], + "type": "interline_equation", + "content": "\\left\\{\\mathbf {E} _ {s} ^ {L L}; \\mathbf {E} _ {s} ^ {L R}; \\mathbf {E} _ {s} ^ {R L}; \\mathbf {E} _ {s} ^ {R R} \\right\\} = \\mathcal {H} (\\mathbf {E} _ {s}), \\tag {6}", + "image_path": "573cc5386859786df7f0b81f57ef5be23eab14a78c1a4927120ac095db3833bb.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "spans": [ + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_s^{LL}" + }, + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "type": "text", + "content": " denotes the low-frequency part and " + }, + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_s^{LR},\\mathbf{E}_s^{RL}" + }, + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_s^{RR}" + }, + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "type": "text", + "content": " correspond to three high-frequency parts. Thus, the resolutions of " + }, + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{E}_s^{LL};\\mathbf{E}_s^{LR};\\mathbf{E}_s^{RL};\\mathbf{E}_s^{RR}\\}" + }, + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "type": "text", + "content": " are the same as that of " + }, + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_{s + 1}" + }, + { + "bbox": [ + 47, + 148, + 287, + 222 + ], + "type": "text", + "content": ". 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When fusing " + }, + { + "bbox": [ + 46, + 254, + 287, + 350 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_s" + }, + { + "bbox": [ + 46, + 254, + 287, + 350 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 254, + 287, + 350 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_{s + 1}" + }, + { + "bbox": [ + 46, + 254, + 287, + 350 + ], + "type": "text", + "content": " to facilitate the decoder block in the coarser image scale " + }, + { + "bbox": [ + 46, + 254, + 287, + 350 + ], + "type": "inline_equation", + "content": "s + 1" + }, + { + "bbox": [ + 46, + 254, + 287, + 350 + ], + "type": "text", + "content": ", we obtain the fused feature " + }, + { + "bbox": [ + 46, + 254, + 287, + 350 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{E}}_{s + 1}" + }, + { + "bbox": [ + 46, + 254, + 287, + 350 + ], + "type": "text", + "content": " by" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 356, + 298, + 381 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 356, + 298, + 381 + ], + "spans": [ + { + "bbox": [ + 47, + 356, + 298, + 381 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {E}} _ {s + 1} = \\mathcal {N} _ {s + 1} ^ {L} \\left(\\mathcal {C} \\left(\\mathbf {E} _ {s + 1}, \\mathbf {E} _ {s} ^ {L L}, \\mathcal {N} _ {s + 1} ^ {H} \\left(\\mathcal {C} \\left(\\mathbf {E} _ {s} ^ {L R}, \\mathbf {E} _ {s} ^ {R L}, \\mathbf {E} _ {s} ^ {R R}\\right)\\right)\\right)\\right), \\tag {8}", + "image_path": "aabf57230a76bd2d3194cf3e00b384253fa4412e2f503516dbf57b688346749f.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "spans": [ + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "inline_equation", + "content": "\\mathcal{N}_{s + 1}^{L}" + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "inline_equation", + "content": "\\mathcal{N}_{s + 1}^{H}" + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "text", + "content": " have the same network architecture as " + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "inline_equation", + "content": "\\mathcal{N}_s^L" + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "inline_equation", + "content": "\\mathcal{N}_s^H" + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "text", + "content": ", respectively (Note that the network parameters are not shared across scales). We take the fused features " + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{E}}_s" + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{E}}_{s + 1}" + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "text", + "content": " instead of " + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_s" + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_{s + 1}" + }, + { + "bbox": [ + 46, + 381, + 287, + 453 + ], + "type": "text", + "content": " as the input for the following decoder blocks. Figure 2(b) shows the details of the proposed wavelet-based feature fusion module." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 454, + 287, + 514 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 454, + 287, + 514 + ], + "spans": [ + { + "bbox": [ + 46, + 454, + 287, + 514 + ], + "type": "text", + "content": "When fusing features from more scales, we can recurrently use Eqs. (7) and (8). As the wavelet transform is invertible, all the information can be better preserved during the transformation. We show the effectiveness of the wavelet-based feature fusion in Section 6.2." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 524, + 173, + 537 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 524, + 173, + 537 + ], + "spans": [ + { + "bbox": [ + 47, + 524, + 173, + 537 + ], + "type": "text", + "content": "5. Experimental Results" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 544, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 544, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 544, + 287, + 616 + ], + "type": "text", + "content": "We first describe the implementation details of the proposed MRLPFNet. Then we evaluate our approach on the commonly used benchmarks and compare it against the state-of-the-art methods. Due to the page limit, we include more results in the supplemental material. The PyTorch code and trained models are available at our Project page." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 623, + 178, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 178, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 178, + 635 + ], + "type": "text", + "content": "5.1. Implementation details" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": "We embed the proposed RLPF module into an encoder-decoder network [3], which contains three encoder blocks and three decoder blocks. For each encoder/decoder block, we adopt a stack of 8 RLPF modules (i.e., " + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "inline_equation", + "content": "N = 8" + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": " in Figure 2(a)). We then use the wavelet-based feature fusion module to fuse the features generated by the encoder blocks of" + } + ] + } + ], + "index": 11 + }, + { + "type": "table", + "bbox": [ + 308, + 114, + 545, + 289 + ], + "blocks": [ + { + "bbox": [ + 305, + 69, + 545, + 113 + ], + "lines": [ + { + "bbox": [ + 305, + 69, + 545, + 113 + ], + "spans": [ + { + "bbox": [ + 305, + 69, + 545, + 113 + ], + "type": "text", + "content": "Table 1. Quantitative evaluations of the proposed approach against state-of-the-art methods on the GoPro dataset [17]. \"MRLPFNet-L\" denotes the proposed method using 20 RLPF modules in each encoder and decoder block (i.e., " + }, + { + "bbox": [ + 305, + 69, + 545, + 113 + ], + "type": "inline_equation", + "content": "N = 20" + }, + { + "bbox": [ + 305, + 69, + 545, + 113 + ], + "type": "text", + "content": " in Figure 2(a))." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 114, + 545, + 289 + ], + "lines": [ + { + "bbox": [ + 308, + 114, + 545, + 289 + ], + "spans": [ + { + "bbox": [ + 308, + 114, + 545, + 289 + ], + "type": "table", + "html": "
MethodPSNR (dB)SSIM
SRN [28]30.260.9342
SSN [5]30.920.9421
DMPHN [38]31.200.9453
SAPHNet [26]31.850.9480
MPRNet [37]32.660.9589
MPRNet-Local [4]33.310.9637
MIMO-UNet [3]31.730.9510
DeepRFT [15]32.820.9600
Uformer [31]33.060.9670
Restormer [36]32.920.9611
Restormer-Local [4]33.570.9656
MAXIM [30]32.860.9616
NAFNet [2]33.710.9668
Stripformer [29]33.080.9624
MRLPFNet33.500.9650
MRLPFNet-L34.010.9682
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The learning rate is initialized to be " + }, + { + "bbox": [ + 304, + 311, + 545, + 418 + ], + "type": "inline_equation", + "content": "2 \\times 10^{-4}" + }, + { + "bbox": [ + 304, + 311, + 545, + 418 + ], + "type": "text", + "content": " and is updated by the Cosine Annealing scheme. The loss function [37] is adopted to constrain the network training." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 429, + 502, + 441 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 429, + 502, + 441 + ], + "spans": [ + { + "bbox": [ + 305, + 429, + 502, + 441 + ], + "type": "text", + "content": "5.2. Comparisons with the state of the art" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 545, + 604 + ], + "type": "text", + "content": "Evaluations on the GoPro dataset. We first quantitatively evaluate the proposed method on the GoPro dataset [17], which contains 2,103 images for training and 1,111 images for the test. We compare the proposed method against several state-of-the-art methods including CNN-based methods (SRN [28], SSN [5], DMPHN [38], SAPHNet [26], MPR-Net [37], MIMO-UNet [3], DeepRFT [15], NAFNet [2]), Transformer-based methods (Restormer [36], Uformer [31], Stripformer [29]), and MLP-based methods (MAXIM [30]). For fair comparisons, we fine-tune or retrain the deep learning-based methods that are not trained on the GoPro dataset. We use the PSNR and SSIM as metrics to evaluate the quality of restored images." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 605, + 545, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 640 + ], + "type": "text", + "content": "Table 1 shows the quantitative results. The proposed method generates higher-quality images with higher PSNR and SSIM values than the competing approaches." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": "Figure 3 shows a visual comparison. Most of the CNN-based methods, e.g., [37, 3, 2], employ the commonly used residual learning in the network designs, which is less effective for the estimation of the main structures, as demonstrated in Section 1. 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Example from the GoPro dataset [17]. Compared to the evaluated methods in (c)-(i), the proposed approach generates a better deblurred image with clearer characters in (j)." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 347, + 172, + 444, + 262 + ], + "blocks": [ + { + "bbox": [ + 347, + 172, + 444, + 262 + ], + "lines": [ + { + "bbox": [ + 347, + 172, + 444, + 262 + ], + "spans": [ + { + "bbox": [ + 347, + 172, + 444, + 262 + ], + "type": "image", + "image_path": "2c9466c1e4782c04683de9d4cdf04844bb8ab033726566447121e68fc1a5dd94.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 368, + 264, + 424, + 273 + ], + "lines": [ + { + "bbox": [ + 368, + 264, + 424, + 273 + ], + "spans": [ + { + "bbox": [ + 368, + 264, + 424, + 273 + ], + "type": "text", + "content": "(i) Stripformer [29]" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 447, + 172, + 544, + 262 + ], + "blocks": [ + { + "bbox": [ + 447, + 172, + 544, + 262 + ], + "lines": [ + { + "bbox": [ + 447, + 172, + 544, + 262 + ], + "spans": [ + { + "bbox": [ + 447, + 172, + 544, + 262 + ], + "type": "image", + "image_path": "fd75f4ec1c343dfe9d426adf10d4f39ce3b6b2815b91486723b9e96e7c7e8fac.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 474, + 264, + 517, + 273 + ], + "lines": [ + { + "bbox": [ + 474, + 264, + 517, + 273 + ], + "spans": [ + { + "bbox": [ + 474, + 264, + 517, + 273 + ], + "type": "text", + "content": "(j) MRLPFNet" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "bbox": [ + 46, + 316, + 287, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 316, + 287, + 388 + ], + "spans": [ + { + "bbox": [ + 46, + 316, + 287, + 388 + ], + "type": "text", + "content": "(f). The method [15] improves the residual learning by introducing an additional branch operating in the frequency domain. However, as the main structures are usually spatially variant, simply using localized convolution operations does not effectively model such global properties. The deblurred result in Figure 3(e) still contains the blur effect." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 46, + 389, + 287, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 389, + 287, + 521 + ], + "spans": [ + { + "bbox": [ + 46, + 389, + 287, + 521 + ], + "type": "text", + "content": "The recent methods [36, 29] develop Transformers to solve image deblurring. As analyzed in Section 3, Transformers can be regarded as low-pass filters. These methods are able to explore the low-frequency contents but less effective for modeling the high-frequency information, thus leading to over-smoothed deblurred results as shown in Figure 3(g) and (i). In contrast to the above-mentioned methods, the proposed MRLPFNet is able to explore both high- and low-frequency information, generating a better image with clearer details and structures than the competed methods (e.g., the restored numbers in Figure 3(j) are clearer)." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 46, + 533, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 287, + 640 + ], + "type": "text", + "content": "Evaluations on the RealBlur dataset. The RealBlur dataset [23] contains 3,758 image pairs for training and 980 image pairs for the test. Based on the protocols of [23], our approach is compared with the state-of-the-art methods for fair comparisons. Table 2 shows that the proposed method generates the deblurred results with higher PSNR and SSIM values, where the PSNR values of our method are at least 1.08dB and 0.71dB higher than the evaluated methods on the \"RealBlur-R\" and \"RealBlur-J\" datasets, respectively." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": "Figure 4 shows some visual comparisons of the evaluated methods. The methods [28, 13, 3] based on the standard residual learning do not effectively remove the blur effects as shown in Figure 4(c)-(e). The method [15] improves the standard residual learning, but the restored images are oversmoothed, e.g., the strokes in Figure 4(f). The Transformer" + } + ] + } + ], + "index": 24 + }, + { + "type": "table", + "bbox": [ + 307, + 359, + 545, + 453 + ], + "blocks": [ + { + "bbox": [ + 305, + 313, + 545, + 357 + ], + "lines": [ + { + "bbox": [ + 305, + 313, + 545, + 357 + ], + "spans": [ + { + "bbox": [ + 305, + 313, + 545, + 357 + ], + "type": "text", + "content": "Table 2. Quantitative evaluations of the proposed approach against state-of-the-art methods on the RealBlur dataset [23]. All the comparison results are generated using the publicly available codes and the models trained on the same training datasets." + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 359, + 545, + 453 + ], + "lines": [ + { + "bbox": [ + 307, + 359, + 545, + 453 + ], + "spans": [ + { + "bbox": [ + 307, + 359, + 545, + 453 + ], + "type": "table", + "html": "
RealBlur-RRealBlur-J
PSNR (dB)SSIMPSNR (dB)SSIM
SRN [28]38.650.965231.380.9091
DeblurGAN [12]36.440.934729.690.8703
MIMO-UNet+ [3]--31.920.9190
DeepRFT+ [15]39.840.972132.190.9305
Stripformer [29]39.840.973732.480.9290
MRLPFNet40.920.975333.190.9361
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MethodPSNR (dB)SSIM
SRN [28]28.360.9040
SAPHNet [26]29.980.9300
MPRNet [37]30.960.9394
MPRNet-Local [4]31.190.9418
MIMO-UNet [3]29.280.9206
MIMO-UNet+ [3]29.990.9304
DeepRFT [15]30.990.9407
DeepRFT+ [15]31.420.9442
Restormer [36]31.220.9423
Restormer-Local [4]31.490.9447
Stripformer [29]31.030.9395
MRLPFNet31.630.9465
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Example from the RealBlur dataset [23]. Compared with the deblurred results in (c)-(g), the proposed method recovers a high-quality image with clearer structural details." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "table", + "bbox": [ + 50, + 429, + 543, + 510 + ], + "blocks": [ + { + "bbox": [ + 46, + 404, + 544, + 427 + ], + "lines": [ + { + "bbox": [ + 46, + 404, + 544, + 427 + ], + "spans": [ + { + "bbox": [ + 46, + 404, + 544, + 427 + ], + "type": "text", + "content": "Table 4. Effectiveness of the proposed low-pass filter and wavelet-based feature fusion for image deblurring. All baseline methods are trained using the same settings as the proposed method for fair comparisons." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 429, + 543, + 510 + ], + "lines": [ + { + "bbox": [ + 50, + 429, + 543, + 510 + ], + "spans": [ + { + "bbox": [ + 50, + 429, + 543, + 510 + ], + "type": "table", + "html": "
Low-pass filter (LPF)Feature fusion (FF)GoPro
Bilinear-based (BFF)Wavelet-based (WFF)PSNR (dB)/SSIM
MRLPFNetw/o LPF&FFXXX32.8/0.9606
MRLPFNetw/o LPF&w/BFFX✓X32.9/0.9611
MRLPFNetw/o LPF&w/WFFXX✓33.0/0.9616
MRLPFNetw/ LPF&w/FF✓XX33.4/0.9641
MRLPFNet✓X✓33.5/0.9650
", + "image_path": "cd93951443b559230b725e353656f4135f7f18bd65d96ac70578b244d6657462.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "table_body" + } + ], + "index": 18 + }, + { + "bbox": [ + 46, + 529, + 287, + 588 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 529, + 287, + 588 + ], + "spans": [ + { + "bbox": [ + 46, + 529, + 287, + 588 + ], + "type": "text", + "content": "**Evaluations on the **HIDE** dataset.** We further evaluate our method on the **HIDE** dataset [25] by using the model trained on the GoPro dataset. Table 3 shows that the proposed approach generates the deblurred results with the highest PSNR and SSIM values." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 47, + 602, + 189, + 615 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 602, + 189, + 615 + ], + "spans": [ + { + "bbox": [ + 47, + 602, + 189, + 615 + ], + "type": "text", + "content": "6. Analysis and Discussions" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 47, + 622, + 241, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 622, + 241, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 622, + 241, + 635 + ], + "type": "text", + "content": "6.1. Effect of the learnable low-pass filter" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 46, + 642, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 712 + ], + "type": "text", + "content": "The learnable low-pass filter is proposed to explore the spatially-variant low-frequency information so that the global structural contents can be better restored for image deblurring. To demonstrate the effectiveness of the proposed learnable low-pass filter, we first compare our method with a baseline that removes the learnable low-pass fil" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 529, + 545, + 697 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 529, + 545, + 697 + ], + "spans": [ + { + "bbox": [ + 304, + 529, + 545, + 697 + ], + "type": "text", + "content": "ter (MRLPFNet" + }, + { + "bbox": [ + 304, + 529, + 545, + 697 + ], + "type": "inline_equation", + "content": "_{\\mathrm{w/o LPF\\& w/WFF}}" + }, + { + "bbox": [ + 304, + 529, + 545, + 697 + ], + "type": "text", + "content": " for short) and train this baseline using the same settings as ours. We use the GoPro dataset [17] as described in Section 5.2 for evaluation. Table 4 shows the quantitative results, where the PSNR of the proposed MRLPFNet is " + }, + { + "bbox": [ + 304, + 529, + 545, + 697 + ], + "type": "inline_equation", + "content": "0.5\\mathrm{dB}" + }, + { + "bbox": [ + 304, + 529, + 545, + 697 + ], + "type": "text", + "content": " higher than the baseline without the learnable low-pass filter. To focus on the effect of the low-pass filter, we further disable the feature fusion module and compare the baselines with and without the learnable low-pass filter (MRLPFNet" + }, + { + "bbox": [ + 304, + 529, + 545, + 697 + ], + "type": "inline_equation", + "content": "_{\\mathrm{w/o LPF\\& FF}}" + }, + { + "bbox": [ + 304, + 529, + 545, + 697 + ], + "type": "text", + "content": " and MRLPFNet" + }, + { + "bbox": [ + 304, + 529, + 545, + 697 + ], + "type": "inline_equation", + "content": "_{\\mathrm{w/ LPF\\& w/O FF}}" + }, + { + "bbox": [ + 304, + 529, + 545, + 697 + ], + "type": "text", + "content": " for short). The comparisons in Table 4 illustrate the significance of using the learnable low-pass filter, which is able to concentrate on the low-frequency information modeling and effectively recover the spatially-variant image structures for image deblurring." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 317, + 701, + 545, + 713 + ], + "type": "text", + "content": "Figure 5 shows a visual comparison. 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Effect of the proposed learnable low-pass filter. (d) is the residual image between the blurry image and Ground truth. (e) and (f) are the residual images estimated by MRLPFNetw/o LPF&w/ WFF and MRLPFNet, respectively." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 302, + 286, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 302, + 286, + 410 + ], + "spans": [ + { + "bbox": [ + 46, + 302, + 286, + 410 + ], + "type": "text", + "content": "in the residual image estimated by MRLPFNet" + }, + { + "bbox": [ + 46, + 302, + 286, + 410 + ], + "type": "inline_equation", + "content": "_{\\mathrm{w/o LPF\\& w/ WFF}}" + }, + { + "bbox": [ + 46, + 302, + 286, + 410 + ], + "type": "text", + "content": " are not well recovered, e.g., the license plate numbers in Figure 5(e), resulting in the deblurred image with a blur effect (Figure 5(b)). In contrast, the residual image estimated by the proposed MRLPFNet is better restored, as using the learnable low-pass filter is able to model the spatially-variant image structures. Thus, our approach is more effective at yielding a clear image with distinct structures (e.g., the license plate numbers in Figure 5(f))." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 418, + 262, + 429 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 418, + 262, + 429 + ], + "spans": [ + { + "bbox": [ + 47, + 418, + 262, + 429 + ], + "type": "text", + "content": "6.2. Effect of the wavelet-based feature fusion" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 436, + 286, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 436, + 286, + 662 + ], + "spans": [ + { + "bbox": [ + 46, + 436, + 286, + 662 + ], + "type": "text", + "content": "To demonstrate the effectiveness of the wavelet-based feature fusion on fusing the features with different spatial resolutions, we first disable the learnable low-pass filter in our implementation (MRLPFNetw/o LPF&w/WFF for short). Then we compare with the baseline that replaces the wavelet-based feature fusion with the bilinear interpolation (MRLPFNetw/o LPF&w/BFF for short). The results in Table 4 show that using the bilinear interpolation as the feature fusion does not perform well as our method with the wavelet-based one, since the wavelet transform is invertible and can preserve more accurate information during the transform process. The qualitative comparisons in Figure 6 further show that using the wavelet-based feature fusion is able to improve the quality of the restored image (Figure 6(c)). We also compare our complete network with the baseline that removes the feature fusion module (MRLPFNetw/LPF&w/0FF for short). The comparisons in Figure 6 show the same tendency that using the wavelet-based feature fusion improves the final deblurring performance." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 47, + 671, + 153, + 684 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 153, + 684 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 153, + 684 + ], + "type": "text", + "content": "6.3. Model complexity" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 47, + 689, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 286, + 712 + ], + "type": "text", + "content": "We examine the model complexity of the proposed approach and the state-of-the-art methods in terms of model" + } + ] + } + ], + "index": 17 + }, + { + "type": "image", + "bbox": [ + 309, + 71, + 365, + 118 + ], + "blocks": [ + { + "bbox": [ + 309, + 71, + 365, + 118 + ], + "lines": [ + { + "bbox": [ + 309, + 71, + 365, + 118 + ], + "spans": [ + { + "bbox": [ + 309, + 71, + 365, + 118 + ], + "type": "image", + "image_path": "387d1aa3e62cfc113f4669b6e5e75770c60dcd8156766b68ee1a57e510e048b2.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 314, + 120, + 359, + 129 + ], + "lines": [ + { + "bbox": [ + 314, + 120, + 359, + 129 + ], + "spans": [ + { + "bbox": [ + 314, + 120, + 359, + 129 + ], + "type": "text", + "content": "(a) Blurry input" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "type": "image", + "bbox": [ + 367, + 71, + 425, + 118 + ], + "blocks": [ + { + "bbox": [ + 367, + 71, + 425, + 118 + ], + "lines": [ + { + "bbox": [ + 367, + 71, + 425, + 118 + ], + "spans": [ + { + "bbox": [ + 367, + 71, + 425, + 118 + ], + "type": "image", + "image_path": "feb5defff863c4d846d44057fb7d8c57019ba343de882c1b12beed3b0764b59b.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 392, + 120, + 401, + 128 + ], + "lines": [ + { + "bbox": [ + 392, + 120, + 401, + 128 + ], + "spans": [ + { + "bbox": [ + 392, + 120, + 401, + 128 + ], + "type": "text", + "content": "(b)" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 306, + 130, + 545, + 175 + ], + "lines": [ + { + "bbox": [ + 306, + 130, + 545, + 175 + ], + "spans": [ + { + "bbox": [ + 306, + 130, + 545, + 175 + ], + "type": "text", + "content": "Figure 6. Effect of the proposed wavelet-based feature fusion. (b) and (c) are the results obtained by the baselines using the Bilinear-based (MRLPFNetw/o LPF&w/BFF in Table 4) and the wavelet-based (MRLPFNetw/o LPF&w/WFF in Table 4) feature fusion, respectively." + } + ] + } + ], + "index": 26, + "angle": 0, + "type": "image_caption" + } + ], + "index": 20 + }, + { + "type": "image", + "bbox": [ + 427, + 71, + 485, + 118 + ], + "blocks": [ + { + "bbox": [ + 427, + 71, + 485, + 118 + ], + "lines": [ + { + "bbox": [ + 427, + 71, + 485, + 118 + ], + "spans": [ + { + "bbox": [ + 427, + 71, + 485, + 118 + ], + "type": "image", + "image_path": "cae9d2c41dc7cf868b89b37b3419ce3a991f8b52cb87a4517355d7b45faf3e4f.jpg" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 452, + 120, + 460, + 128 + ], + "lines": [ + { + "bbox": [ + 452, + 120, + 460, + 128 + ], + "spans": [ + { + "bbox": [ + 452, + 120, + 460, + 128 + ], + "type": "text", + "content": "(c)" + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_caption" + } + ], + "index": 22 + }, + { + "type": "image", + "bbox": [ + 486, + 71, + 545, + 118 + ], + "blocks": [ + { + "bbox": [ + 486, + 71, + 545, + 118 + ], + "lines": [ + { + "bbox": [ + 486, + 71, + 545, + 118 + ], + "spans": [ + { + "bbox": [ + 486, + 71, + 545, + 118 + ], + "type": "image", + "image_path": "51f2aa5b2c2332809fc62ef06f04921d76bcf1c6b5ae5c5e5e200b4bed975227.jpg" + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 492, + 120, + 539, + 128 + ], + "lines": [ + { + "bbox": [ + 492, + 120, + 539, + 128 + ], + "spans": [ + { + "bbox": [ + 492, + 120, + 539, + 128 + ], + "type": "text", + "content": "(d) Ground truth" + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_caption" + } + ], + "index": 24 + }, + { + "type": "table", + "bbox": [ + 307, + 249, + 545, + 326 + ], + "blocks": [ + { + "bbox": [ + 306, + 182, + 545, + 247 + ], + "lines": [ + { + "bbox": [ + 306, + 182, + 545, + 247 + ], + "spans": [ + { + "bbox": [ + 306, + 182, + 545, + 247 + ], + "type": "text", + "content": "Table 5. Model complexity of the top-performance methods on the above-mentioned datasets. The FLOPs are evaluated on image patches with the size of " + }, + { + "bbox": [ + 306, + 182, + 545, + 247 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 306, + 182, + 545, + 247 + ], + "type": "text", + "content": " pixels based on the protocols of existing methods. The running time is evaluated on images with the size of " + }, + { + "bbox": [ + 306, + 182, + 545, + 247 + ], + "type": "inline_equation", + "content": "1280 \\times 720" + }, + { + "bbox": [ + 306, + 182, + 545, + 247 + ], + "type": "text", + "content": " pixels. All the results are obtained on a machine with an NVIDIA GeForce RTX 3090 GPU." + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 249, + 545, + 326 + ], + "lines": [ + { + "bbox": [ + 307, + 249, + 545, + 326 + ], + "spans": [ + { + "bbox": [ + 307, + 249, + 545, + 326 + ], + "type": "table", + "html": "
MethodsModel parameters (M)FLOPs (G)Running time (/s)
MPRNet [37]20.17600.9806
MIMO-UNet+ [3]16.11510.2827
DeepRFT+ [15]23.01830.5518
Restormer [36]26.11550.9798
Stripformer [29]19.71700.6580
MRLPFNetw/o LPF11.4820.2613
MRLPFNet20.61290.8633
", + "image_path": "6151cf18dd14ebf8f560fa4a59d7d66ac065715eddb6836420f1dfa8a1491288.jpg" + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "table_body" + } + ], + "index": 28 + }, + { + "bbox": [ + 305, + 344, + 545, + 392 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 344, + 545, + 392 + ], + "spans": [ + { + "bbox": [ + 305, + 344, + 545, + 392 + ], + "type": "text", + "content": "parameters, running time, and FLOPs. Table 5 shows that our method has the lowest FLOPs value and also achieves competitive performance against the competed ones in terms of running time." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 305, + 399, + 545, + 471 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 399, + 545, + 471 + ], + "spans": [ + { + "bbox": [ + 305, + 399, + 545, + 471 + ], + "type": "text", + "content": "Limitations. As the proposed learnable low-pass filter is based on the self-attention to estimate the filter weights, it moderately increases the running time as shown in Table 5 (see the comparisons of \"MRLPFNetw/o LPF\" and \"MRLPFNet\"). Future work will develop efficient and learnable low-pass filters for better image deblurring." + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 306, + 481, + 378, + 493 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 481, + 378, + 493 + ], + "spans": [ + { + "bbox": [ + 306, + 481, + 378, + 493 + ], + "type": "text", + "content": "7. Conclusion" + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 305, + 502, + 545, + 620 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 502, + 545, + 620 + ], + "spans": [ + { + "bbox": [ + 305, + 502, + 545, + 620 + ], + "type": "text", + "content": "We present an effective MRLPFNet to reconstruct both the low-frequency and high-frequency information for image deblurring. To better explore the spatially-variant structures, we develop a learnable low-pass filter based on the self-attention mechanism. Furthermore, we propose a wavelet-based feature fusion method to effectively fuse the features with different spatial resolutions. By formulating the proposed method into an end-to-end trainable network, we show that it performs favorably against state-of-the-art methods on benchmarks." + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 305, + 630, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 630, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 305, + 630, + 545, + 712 + ], + "type": "text", + "content": "Acknowledgement. This work was supported in part by the National Key Research and Development Program of China under Grant 2022ZD0118801, the National Natural Science Foundation of China under Grants 62272233, 61922043, 61925204, and U22B2049, and the Fundamental Research Funds for the Central Universities under Grant 30922010910 and 30920041109." + } + ] + } + ], + "index": 33 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12352" + } + ] + } + ], + "index": 34 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 92, + 286, + 712 + ], + "type": "list", + "angle": 0, + "index": 18, + "blocks": [ + { + "bbox": [ + 53, + 92, + 286, + 113 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 92, + 286, + 113 + ], + "spans": [ + { + "bbox": [ + 53, + 92, + 286, + 113 + ], + "type": "text", + "content": "[1] Ayan Chakrabarti. 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IJCV, 130(9):2103-2130, 2022. 1" + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "12354" + } + ] + } + ], + "index": 7 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-Task Learning with Knowledge Distillation for Dense Prediction/333e6685-b40e-48b9-a0cd-db1868afbfa7_content_list.json b/2023/Multi-Task Learning with Knowledge Distillation for Dense Prediction/333e6685-b40e-48b9-a0cd-db1868afbfa7_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..131ee564a1f63282ec1b635b6b38b36ba301e2f7 --- /dev/null +++ b/2023/Multi-Task Learning with Knowledge Distillation for Dense Prediction/333e6685-b40e-48b9-a0cd-db1868afbfa7_content_list.json @@ -0,0 +1,1401 @@ +[ + { + "type": "text", + "text": "Multi-Task Learning with Knowledge Distillation for Dense Prediction", + "text_level": 1, + "bbox": [ + 129, + 161, + 838, + 181 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yangyang $\\mathbf{X}\\mathbf{u}^{\\mathrm{l}}$", + "bbox": [ + 253, + 206, + 373, + 224 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yibo Yang3", + "bbox": [ + 438, + 207, + 531, + 224 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Lefei Zhang $^{1,2*}$", + "bbox": [ + 594, + 207, + 719, + 224 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ Institute of Artificial Intelligence and School of Computer Science, Wuhan University, Wuhan, China \n $^{2}$ Hubei Luojia Laboratory, Wuhan, China", + "bbox": [ + 87, + 230, + 895, + 262 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "3 King Abdullah University of Science and Technology, Jeddah, Saudi Arabia", + "bbox": [ + 193, + 263, + 806, + 279 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "yangyangxu@whu.edu.cn, yibo.yang@kaust.edu.sa, zhanglefei@whu.edu.cn", + "bbox": [ + 189, + 282, + 793, + 295 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 327, + 312, + 342 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "While multi-task learning (MTL) has become an attractive topic, its training usually poses more difficulties than the single-task case. How to successfully apply knowledge distillation into MTL to improve training efficiency and model performance is still a challenging problem. In this paper, we introduce a new knowledge distillation procedure with an alternative match for MTL of dense prediction based on two simple design principles. First, for memory and training efficiency, we use a single strong multitask model as a teacher during training instead of multiple teachers, as widely adopted in existing studies. Second, we employ a less sensitive Cauchy-Schwarz (CS) divergence instead of the Kullback-Leibler (KL) divergence and propose a CS distillation loss accordingly. With the less sensitive divergence, our knowledge distillation with an alternative match is applied for capturing inter-task and intratask information between the teacher model and the student model of each task, thereby learning more \"dark knowledge\" for effective distillation. We conducted extensive experiments on dense prediction datasets, including NYUD-v2 and PASCAL-Context, for multiple vision tasks, such as semantic segmentation, human parts segmentation, depth estimation, surface normal estimation, and boundary detection. The results show that our proposed method decidedly improves model performance and the practical inference efficiency.", + "bbox": [ + 75, + 356, + 472, + 717 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 77, + 739, + 208, + 754 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Multi-task learning (MTL) has become an increasingly popular approach in the field of computer vision, where the objective is to train a single model to perform multiple tasks simultaneously. MTL can provide several advantages over traditional single-task learning, including improved efficiency and generalization. First, the shared feature repre", + "bbox": [ + 75, + 763, + 468, + 847 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "sentations can be learned more efficiently than task-specific representations, reducing the overall training time compared to training multiple models independently. Second, the shared feature representations learned across tasks can capture more generalizable information in the data, leading to improved performance on all tasks. For those reasons, the MTL approach has been used extensively in various machine learning problems, such as natural language processing [11], computer vision [3] and speech recognition [4]. Specifically, in this paper, we focus on dense (pixel-wise) prediction vision tasks [49, 15, 23, 41, 20, 21, 29, 48], such as semantic segmentation, instance segmentation, depth estimation, surface normal estimation, saliency estimation, object detection and boundary detection from images.", + "bbox": [ + 499, + 328, + 894, + 522 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "A march of works [32, 46, 9, 3, 52, 2, 56, 53] aims to develop novel MTL architectures and construct efficient shared representation in the multi-taskdense prediction field, which leverages the encoder-decoder architecture. In these frameworks, an encoder is considered to generate a shared feature and then use a decoder to perform multi-task of dense predictions. In the pursuit of better performance, current MTL models are often designed to be deeper and wider, resulting in increasingly larger models. [3, 56] and [53, 24] demonstrate that better performance can be obtained by utilizing a larger backbone network. However, such a heavy model can be more demanding for computation and storage. It has been challenging to design an effective MTL framework that can learn these tasks efficiently. In this paper, we pose and study the question, how can the knowledge from a large size MTL model be transferred to a small MTL model without increasing its size?", + "bbox": [ + 497, + 528, + 894, + 764 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recently, knowledge distillation (KD) [13] has been explored as a method to improve the MTL of dense prediction tasks, such as semantic segmentation, depth estimation, and surface normal prediction. Some studies [30, 12, 16, 1] leverage the unique logit of each task to provide task-specific information to the student model during knowledge transfer. The essence of knowledge distillation lies", + "bbox": [ + 497, + 769, + 894, + 866 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 127, + 49, + 200, + 85 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 253, + 48, + 789, + 86 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author.", + "bbox": [ + 95, + 853, + 223, + 866 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "21550", + "bbox": [ + 463, + 885, + 505, + 897 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "in translating knowledge from the teacher model (large model) to the student model (small model) by mimicking the teacher model's outputs. Typically, knowledge distillation methods use the logits matching by Kullback-Leibler (KL) divergence [13] between the probability distributions of the teacher and the probability distributions of the student. In this way, during training, the student model can be guided by more valuable information signals from the teacher model, therefore, is expected to have a more promising performance than training alone. This approach has shown promising results in improving model performance and generalization and speeding up convergence in MTL. For instance, We found that some works [22, 35, 12, 30, 17] attempt to use knowledge distillation to transfer the knowledge from teacher to student for multiple vision tasks in MTL. We, in particular, identify two technical challenges. 1) Most previous approaches [22, 35, 17] must train a task-specific model for each task, then load the trained task-specific models. 2) Exact logit matching of teacher and student predictions with KL divergence can interfere with the training of the student model and is sensitive to outliers, leading to less effective knowledge distillation.", + "bbox": [ + 75, + 125, + 472, + 429 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address these challenges, we explore knowledge distillation in multi-task learning of dense prediction tasks. We present a novel framework that leverages task-specific guidance to enable effective knowledge transfer. In Figure 1, we show the difference between the existing and our methods. Since using multiple single-task models as teacher models would require an inordinate amount of memory, we only load a single multi-task model as a teacher model instead of loading multiple teacher models. We opt for one strong teacher model to reduce computational and memory costs instead of using multiple teacher models that perform a load of each task separately.", + "bbox": [ + 75, + 433, + 468, + 600 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We take inspiration from mathematical statistics methods from other domains to reduce the uncertainty in students' prediction when using KL divergence (see Figure 1). We propose a novel knowledge distillation with Cauchy-Schwarz (CS) divergence to replace the KL divergence. In addition, during the logit matching, inter-task and intra-task information are transferred from teacher to student. Specifically, we gather the corresponding predicted probabilities in a batch for all tasks, then transfer the inter-task information from teacher to student. For each task, we gather the corresponding predicted probabilities of all classes in a batch, then transfer the intra-task information from teacher to student. Our proposed knowledge distillation with the alternative match is less sensitive to small probabilities and can account for uncertainty in the student model predictions. To further close the computational and memory cost gap, we only use one multi-task teacher model during training. This MTL knowledge distillation procedure provides multiple training settings.", + "bbox": [ + 75, + 603, + 472, + 866 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/4b285195a32208689a9740c062c7a136913f94aae87087d9a6b1821aade41f6b.jpg", + "image_caption": [ + "Figure 1: Difference between existing KD methods and our KD method. $\\mathcal{F}_{st}^{T}$ means the single-task $(st)$ teacher $(T)$ model output. $\\mathcal{F}_{mt}^{T}$ means the multi-task $(mt)$ teacher model output. $\\mathcal{F}_{mt}^{S}$ means the multi-task $(mt)$ student $(S)$ model output. $n$ denotes the number of tasks." + ], + "image_footnote": [], + "bbox": [ + 502, + 125, + 910, + 315 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Through extensive experiments on several publicly available dense prediction datasets (i.e., NYUD-v2 and PASCAL-Context), we compare our results with state-of-the-art methods to demonstrate the effectiveness of our framework.", + "bbox": [ + 497, + 410, + 890, + 479 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, our work makes the following contributions:", + "bbox": [ + 499, + 480, + 890, + 508 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We introduce a new procedure based on knowledge distillation with an alternative match named KDAM, which leverages inter-task and intra-task information. It is less sensitive to small probabilities and can account for uncertainty in the student model predictions.", + "- Our new distillation procedure aims at reproducing computational and memory costs by loading a strong multi-task model as a teacher to guide student learning.", + "- We conduct experiments using our KDAM on two MTL of dense prediction datasets, showing the superiority under different experiment settings." + ], + "bbox": [ + 517, + 515, + 890, + 686 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 499, + 704, + 640, + 719 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-task Learning of Dense Prediction. Multi-task learning for dense prediction [37, 50, 58, 31, 10, 9, 3, 52, 56, 53, 33, 28, 25, 57, 26, 27] has been an active research area in the computer vision community, with many studies exploring various aspects of joint learning for tasks such as semantic segmentation, depth estimation, surface normal estimation, saliency estimation and boundary detection. A survey work [45] shows that MTL is mainly divided into two categories: encoder-based and decoder-based architectures. The encoder-based methods, such as [19, 44, 54], use a", + "bbox": [ + 497, + 726, + 892, + 866 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "21551", + "bbox": [ + 463, + 885, + 504, + 897 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "shared representation from an encoder to input task-specific heads and perform multiple task predictions. NDDR-CNN Network [10] is an encoder-focused MTL model which enables automatic feature fusing at every layer from different tasks and reduces channel dimension by processing the features with a $1 \\times 1$ convolutional layer before feeding the result to the next layer. Their success heavily depends on the encoder (i.e., backbone network) to learn a strong shared representation [47, 59]. However, the encoder-based methods lack task interaction information, failing to capture commonalities and differences among tasks. The decoder-based methods, such as [50, 31, 3, 56, 2], focus on improving each task by repeatedly refining the predictions through cross-task interaction and improving each task's performance. Unlike encoder-based, decoder-based architectures also exchange information during the decoding. MTFormal [51] performs cross-task reasoning and designs the cross-task attention mechanism to achieve effective feature propagation among tasks, resulting in performance improvement in MTL. [52, 56] introduces new techniques for training deeper and wider via Transformers in MTL, allowing for more efficient and accurate MTL performance. Their success depends on a strong backbone network and all relevant task interactions from different dimensions. In addition, [40] introduces a controllable dynamic multi-task architecture for dynamically adjusting the weighting of loss of each task, which allows matching the desired task preference as well as the resource constraints. We propose an KDAM, which uses a strong multi-task model as a teacher to guide the student's multi-task model learning.", + "bbox": [ + 75, + 125, + 472, + 541 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Knowledge Distillation. The objective of the Knowledge distillation [13, 1] is mainly to distill the logits from certain outputs of a teacher to a student by minimizing the KL divergence [13], where the temperature $\\mathcal{T}$ factor is applied to soften the output logits. Knowledge distillation is also introduced into vision tasks, such as image classification [30, 6, 5, 18], segmentation [39, 14, 38] and detection [55, 36, 48]. Knowledge distillation has emerged as an effective technique for improving multi-task learning of dense prediction tasks. Several recent studies [22, 35, 12, 17] have explored various aspects of knowledge distillation in the context of multi-task learning, with a focus on improving model performance and efficiency. The work [8] is to distill representation from a full image to the representation predicted from a masked image to perform multiple tasks. [17] designs the selective training layers for each task using an adaptive feature distillation loss with an online task weighting scheme. This task-based feature distillation allows MTL networks to be trained in a similar manner to single-task networks. Their success depends on multiple strong teacher models to guide student model training, which can get more information from the teacher model during training. However, these distillation MTL", + "bbox": [ + 75, + 548, + 472, + 866 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "models' exact logits matching of teacher and student predictions with KL divergence can interfere with student model training and become more sensitive to outliers, leading to poor knowledge distillation. In this paper, we develop an efficient distillation procedure specific to MTL of dense prediction. We use an alternative knowledge distillation strategy that leverages inter-task and intra-task information. It provides less sensitivity to small probabilities and can account for uncertainty in the student model predictions.", + "bbox": [ + 497, + 125, + 894, + 251 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 499, + 262, + 591, + 277 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Notations", + "text_level": 1, + "bbox": [ + 499, + 285, + 611, + 298 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The input image $x_{i} \\in \\mathbb{R}^{H \\times W \\times C}$ , where $H, W,$ and $C$ are the height, width, and channel of the image feature, respectively. We use $n$ to denote the task number, with $n \\in \\{1, 2, \\dots, N\\}$ , $st$ to denote the single-task and $mt$ to denote the multi-task. Define $\\mathcal{F}_{mt}^{T}$ as the multi-task teacher model and $\\mathcal{F}_{st}^{T}$ as the single-task teacher model.", + "bbox": [ + 497, + 304, + 894, + 390 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Formulation", + "text_level": 1, + "bbox": [ + 499, + 397, + 633, + 410 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The clustering regularizer loss is defined as the Kullback-Leibler (KL) [13] divergence between soft assignment $y_{\\mathrm{pred}}$ and auxiliary target distribution $y_{\\mathrm{true}}$ :", + "bbox": [ + 497, + 418, + 892, + 461 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {L} _ {\\mathrm {K L - d i v}} := K L \\left(y _ {\\text {p r e d}}, y _ {\\text {t r u e}}\\right) = y _ {\\text {t r u e}} \\cdot \\log \\frac {y _ {\\text {t r u e}}}{y _ {\\text {p r e d}}} \\tag {1} \\\\ = y _ {\\text {t r u e}} \\cdot (\\log y _ {\\text {t r u e}} - \\log y _ {\\text {p r e d}}), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 532, + 471, + 890, + 502 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $y_{\\mathrm{pred}}$ is the output of the model and $y_{\\mathrm{true}}$ is the observation labels in the dataset. KL divergence is leveraged in plain KD to transform knowledge from the strong teacher model to the student model, where $y_{\\mathrm{pred}}$ and $y_{\\mathrm{true}}$ are the outputs of the student model and the teacher model. The plain KD loss is represented as:", + "bbox": [ + 497, + 511, + 892, + 595 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {p l a i n} K D} = \\mathcal {T} ^ {2} \\cdot \\mathcal {L} _ {\\mathrm {K L - d i v}} \\left(P _ {S}, P _ {T}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 604, + 890, + 619 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathcal{T}$ is the distillation temperature factor to control the softness of logits of the softmax output. $P_{S}$ is the softmax output of student model. $P_{T}$ is the softmax output of the teacher model. The student and teacher generate the logits $\\mathcal{F}^S$ and $\\mathcal{F}^T$ , respectively.", + "bbox": [ + 497, + 630, + 890, + 700 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nP _ {S} = \\operatorname {s o f t m a x} \\left(\\mathcal {F} ^ {S} / \\mathcal {T}\\right), \\quad P _ {T} = \\operatorname {s o f t m a x} \\left(\\mathcal {F} ^ {T} / \\mathcal {T}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 517, + 707, + 890, + 725 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. KD Alternative Match (KDAM)", + "text_level": 1, + "bbox": [ + 499, + 733, + 781, + 749 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "KL divergence is a distance metric that measures the difference between the teacher's and student's probability distributions. However, it is sensitive to outliers in the data, which can result in unstable training and poor generalization.", + "bbox": [ + 497, + 755, + 890, + 823 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "There are two challenges using KL divergence in plain KD. First, one issue with KL divergence in knowledge distillation is that it can be unstable and lead to vanishing", + "bbox": [ + 497, + 825, + 890, + 866 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "21552", + "bbox": [ + 463, + 885, + 505, + 897 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/15c56f5d5796e6dcc2d53381910089762a57892f3958db9533b1dc53001fff56.jpg", + "image_caption": [ + "Figure 2: Illustration of our knowledge distillation framework in MTL. Inter-task information: transmitted knowledge between the predicted probabilistic distributions on all tasks' channels of teacher and student. Intra-task information: transmitted knowledge of the probabilities of all the instances on each task. For simple purposes, We set two tasks in this figure. $N$ denotes the task number. $\\mathcal{F}_{mt}^{T}$ and $\\mathcal{F}_{mt}^{S}$ means the multi-task $(mt)$ teacher and student model output, respectively." + ], + "image_footnote": [], + "bbox": [ + 122, + 127, + 848, + 324 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "gradients during training. This is because KL divergence involves taking the logarithm of probabilities, which can cause numerical instability when dealing with small or zero probabilities. It can make optimizing models that use KL divergence in knowledge distillation difficult. Second, KL divergence does not consider the uncertainty in the student predictions, which can lead to overconfidence and poor generalization in certain cases. This is particularly relevant in scenarios where the student model is less complex than the teacher model, as the student may not have the capacity to capture all of the information contained in the teacher's soft targets.", + "bbox": [ + 75, + 416, + 468, + 584 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "To address these issues, alternative divergence measures have been proposed, named Cauchy-Schwarz (CS) divergence, which is less sensitive to small probabilities and can account for uncertainty in the student model predictions. In this way, the alternative KD tries to save more task-specific information between the teacher and student on the probabilistic distribution.", + "bbox": [ + 75, + 585, + 468, + 681 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In knowledge distillation, let $\\mathcal{DS} = (x_i,y_i)$ denote the training dataset of the student network, where $x_{i}$ and $y_{i}$ are the input and the corresponding ground truth label, respectively. Let $\\mathcal{DT} = (x_i,P_{T_i})$ denote the training dataset of the teacher network, where $P_{T_i}$ is the predicted probability distribution over the class labels by the teacher network for the input $x_{i}$ . Let $\\mathcal{FS}: \\mathcal{X} \\to \\mathcal{Y}$ and $\\mathcal{FT}: \\mathcal{X} \\to \\Delta^{C - 1}$ denote the student and teacher networks, respectively, where $\\Delta^{C - 1}$ is the $C$ -dimensional probability simplex.", + "bbox": [ + 75, + 684, + 468, + 809 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Knowledge distillation aims to train the student network $\\mathcal{F}^S$ to match the predictions of the teacher network $\\mathcal{F}^T$ for the same input data. To achieve this, we minimize the CS divergence between the soft labels predicted by the teacher", + "bbox": [ + 75, + 811, + 470, + 866 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "network and those predicted by the student network. The CS divergence between the soft label distributions $P_{T_i}$ and $P_{S_i}$ predicted by the teacher and student models, respectively, for the input $x_i$ is defined as:", + "bbox": [ + 497, + 416, + 890, + 473 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {C S} := D _ {C S} \\left(P _ {S}, P _ {T}\\right) = - \\ln \\frac {\\int P _ {T _ {i}} (x) P _ {S _ {i}} (x) d x}{\\sqrt {\\int P _ {T _ {i}} (x) d x \\int P _ {S _ {i}} (x) d x}}. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 499, + 497, + 892, + 547 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Note that $D_{CS} = 0$ only for $P_S = P_T$ . Eq. 4 can improve numerical stability and the ability to account for uncertainty in student predictions.", + "bbox": [ + 497, + 548, + 890, + 589 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The inter-task information for each task. We develop an alternative inter-task comparison strategy in which the distribution of teacher and student of all tasks. The intertask information between teacher and student is defined as:", + "bbox": [ + 497, + 591, + 890, + 646 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {i n t e r} = \\frac {1}{B} \\sum_ {i = 1} ^ {B} D _ {C S} \\left(P _ {S i,:}, P _ {T _ {i,:}}\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 661, + 890, + 699 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where the $B$ denotes batch size.", + "bbox": [ + 499, + 707, + 712, + 719 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The intra-task information for each task. For intraclass information, we discuss why naive hard example mining cannot handle noise/outliers and propose a simple and effective balancing strategy for fast and robust hard example mining. As shown in Figure 2, the intra-task is defined as:", + "bbox": [ + 497, + 722, + 890, + 802 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {i n t r a}} = \\frac {1}{C} \\sum_ {j = 1} ^ {C} D _ {C S} \\left(P _ {S: j}, P _ {T: j}\\right), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 574, + 805, + 890, + 844 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $C$ denotes the channel.", + "bbox": [ + 499, + 851, + 697, + 864 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "21553", + "bbox": [ + 463, + 885, + 504, + 897 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Finally, we wrap task-independent knowledge distillation strategies into MTL. It can be formulated as follows:", + "bbox": [ + 77, + 125, + 468, + 153 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {C S K D} = \\sum_ {n = 1} ^ {N} \\left(\\mathcal {L} _ {\\text {i n t e r}} + \\mathcal {L} _ {\\text {i n t r a}}\\right), \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 159, + 163, + 468, + 201 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the $N$ is the task number. We sum up the $\\mathcal{L}_{inter}$ and $\\mathcal{L}_{intra}$ to improve the distillation performance for MTL.", + "bbox": [ + 77, + 209, + 468, + 238 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Training objective", + "text_level": 1, + "bbox": [ + 77, + 245, + 253, + 260 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As depicted in Figure 2, our method consists of a teacher MT model, a student MT model, and a new strategy of KD. Concretely, we first train a strong MT model as a teacher model. Then we introduce a trained teacher model for the student MT model training. The plain multi-task loss function is given as:", + "bbox": [ + 75, + 266, + 468, + 350 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {m t} := \\mathcal {L} \\left(y _ {\\text {t r u e}}, P _ {S}\\right) = \\sum_ {n = 1} ^ {N} \\lambda_ {n} \\mathcal {L} _ {n}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 157, + 359, + 468, + 397 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\lambda_{n}$ is a hyperparameter factor of the task number $n$ .", + "bbox": [ + 77, + 406, + 460, + 419 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In the multi-task knowledge distillation setting, there are a trained multi-task teacher model (i.e., $T^{mt}$ ) and a student model (i.e., $S^{mt}$ ). As a result, the KDAM overall training loss function is typically a weighted sum of the MTL loss $(\\mathcal{L}_{mt})$ and the knowledge distillation loss.", + "bbox": [ + 75, + 420, + 468, + 489 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {t o t a l}} = \\alpha \\cdot \\mathcal {L} _ {m t} + \\beta \\cdot \\mathcal {L} _ {C S K D} \\left(P _ {S ^ {m t}}, P _ {T ^ {m t}}\\right), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 109, + 500, + 468, + 514 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\alpha$ and $\\beta$ are the scale factor for balancing the losses. In this way, via the $\\mathcal{L}_{CSKD}$ loss, the student to match the strong teacher network's output.", + "bbox": [ + 75, + 524, + 468, + 566 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 77, + 578, + 208, + 593 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We validate the superiority of our KDAM framework under two representative datasets: NYUD-v2 [42] and PASCAL-Context [7]. In Section 4.1, we provide the experimental setup and evaluation details we used for experiments. Section 4.2 presents the main qualitative and quantitative MTL results. Finally, in Section 4.3, we perform ablation studies to verify the effect of components and efficiencies of our method.", + "bbox": [ + 75, + 600, + 468, + 711 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experiment setup", + "text_level": 1, + "bbox": [ + 77, + 720, + 248, + 735 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "NYUD-v2 dataset and metrics. NYUD-v2 comprises RGB and Depth frames 795 images are used for training and 654 images for testing. NYUD-v2 is adopted for semantic segmentation (SemSeg), depth estimation (Depth), surface normal estimation (Normal) and boundary detection (Bound) tasks by providing dense labels. The semantic segmentation labels classify each pixel in the RGB images into one of 40 object categories. Four evaluation metrics are available to evaluate the MTL model performance, which", + "bbox": [ + 75, + 741, + 468, + 865 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "includes mean Intersection over Union (mIoU) for the SemSeg task, root mean square error (rmse) for the Depth task, mean Error (mErr) for the Normal task, and optimal dataset scale F-measure (odsF) for the Bound task.", + "bbox": [ + 497, + 125, + 890, + 179 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "PASCAL-Context dataset and metrics. PASCAL-Context consists of 10,103 images with complex scenes, covering 400 object categories and 59 background regions. PASCAL-Context is adopted for semantic segmentation (SemSeg), human parts segmentation (PartSeg), saliency estimation (Sal), surface normal estimation (Normal), and boundary detection (Bound) tasks by pixel-level semantic labels for each image. Five evaluation metrics are available to evaluate the MTL model performance, which includes mean Intersection over Union (mIoU) for the SemSeg and PartSeg tasks, mean Error (mErr) for the Normal task, optimal dataset scale F-measure (odsF) for the Bound task, and maximum F-measure (maxF) for the Sal task. The average per-task performance drop $(\\Delta_{mt})$ is used to quantify multi-task performance. $\\Delta_{mt} = \\frac{1}{N}\\sum_{i = 1}^{N}(F_{mt,n} - F_{st,n}) / F_{st,n}\\times$ $100\\%$ , where mt, st and $N$ mean multi-task model, single-task baseline and task numbers. $\\Delta_{mt}$ : higher is the better.", + "bbox": [ + 497, + 181, + 890, + 416 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Setting. To be universal, we perform experiments on the NYUD-v2 [42] and PASCAL-Context [7] datasets using different teacher-student pairs. The \"Plain KD vs. DIST vs. Our KDAM\" experiment is conducted using Swin-L [34] as a teacher model, Swin-T [34] and Swin-S [34] as student models on the NYUD-v2. On PASCAL-Context, we adopt Swin-L [34] and Swin-B [34] as teacher models, HRNet18 [43], Swin-T [34] and Swin-S [34] as student models.", + "bbox": [ + 497, + 416, + 890, + 527 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Loss weights. In our experiments, we use the algorithm in [3] to learn weights for each task over the course of training. For a fair comparison, we search the optimal hyperparameters (i.e., the loss ratio $\\alpha$ , $\\beta$ and the temperature $\\mathcal{T}$ ) for each teacher-student pair. On NYUD-v2 and PASCAL-Context, we set $\\alpha = 1.0$ , $\\beta = 1.0$ in Eq. 9 using our TKD method. For plain KD [13], we set $\\alpha = 1.0$ , $\\beta = 1.0$ in Eq. 9 and use a default temperature $\\mathcal{T} = 3$ in Eq. 2. In addition, For a fair comparison, we search the optimal hyperparameters i.e., $\\beta$ and $\\mathcal{T}$ . We choose a temperature set $\\mathcal{T} \\in [0.1, 0.5, 1, 3, 4, 8, 16]$ for an ablation study on NYUD-v2 dataset (see Table 5a & 5b).", + "bbox": [ + 497, + 528, + 890, + 693 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Baselines. Multi-task baseline uses a shared backbone network in conjunction with task-specific heads to perform the predictions for every task. We can choose different networks as backbones, such as HRNet [43] and Swin Transformer [34]. Single-task baseline uses a backbone network with a task head to conduct the predictions for a task.", + "bbox": [ + 497, + 695, + 890, + 777 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Results", + "text_level": 1, + "bbox": [ + 499, + 788, + 591, + 802 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "NYUD-v2 dataset. We investigate the effectiveness of our KDAM on NYUD-v2 dataset. We first train a multi-task baseline model of Swin-L for our knowledge distillation procedure. Then we load the well trained Swin-L model", + "bbox": [ + 497, + 809, + 890, + 866 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "21554", + "bbox": [ + 463, + 885, + 504, + 897 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/111a78aeb09b6fb40a6e55324dbd64176628aeea9e73661acdb6846df420abb1.jpg", + "table_caption": [ + "Table 1: We report the comparison of the MTL models with the state-of-the-art on NYUD-v2 dataset. $\\downarrow$ : lower is better. ’↑’: higher is better. ${\\Delta }_{mt}$ denotes the average per-task performance drop. Swin-◇ indicates that the specific Swin model is uncertain. Gray blocks mean the multi-task baseline using our knowledge distillation method." + ], + "table_footnote": [], + "table_body": "
ModelBackboneParams (M)GFLOPs (G)SemSeg (mIoU)↑Depth (rmse)↓Normal (mErr)↓Bound (odsF)↑Δmt[%]↑
single-task (ST) baselineHRNet1816.0940.9338.020.610420.9476.220.00
multi-task (MT) baselineHRNet184.5217.5936.350.628421.0276.36-1.89
MT+KDAM (Ours)HRNet184.5217.5936.850.625021.0476.10-0.73
Cross-Stitch[37]HRNet184.5217.5936.340.629020.8876.38-1.75
Pad-Net[50]HRNet185.0225.1836.700.626420.8576.50-1.33
PAP[58]HRNet184.5453.0436.720.617820.8276.42-0.95
PSD[31]HRNet184.7121.1036.690.624620.8776.42-1.30
NDDR-CNN[10]HRNet184.5918.6836.720.628820.8976.32-1.51
MTI-Net[46]HRNet1812.5619.1436.610.627020.8576.38-1.44
ATRC[3]HRNet185.0625.7638.900.601020.4876.341.56
ATRC+KDAM (Ours)HRNet185.0625.7639.300.591920.7276.912.05
single-task (ST) baselineSwin-T115.08161.2542.920.610420.9476.220.00
multi-task (MT) baselineSwin-T32.5096.2938.780.631221.0575.60-3.74
MT+KDAM (Ours)Swin-T32.5096.2944.340.60121.0376.41.1
single-task (ST) baselineSwin-S200.33242.6348.920.580420.9477.200.00
multi-task (MT) baselineSwin-S53.82116.6347.900.605321.1776.90-1.96
MTFormer[51]Swin-◇64.03117.7350.560.4830--4.12
MT+KDAM (Ours)Swin-S53.82116.6349.410.56420.6077.31.38
", + "bbox": [ + 90, + 172, + 878, + 457 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/8c0a196c73f6f7c07f8c57dfc8ec364e12b02e129f6e6ddccebc4351b1784632.jpg", + "table_caption": [ + "Table 2: Comparison results of DeMT and InvPT MTL model with our KDAM method. ${}^{\\prime } +$ ’ means performance increase." + ], + "table_footnote": [], + "table_body": "
Network structureAccuracy multi-task student modelsAccuracy of our KDAM
TeacherStudentSemSeg↑Depth↓Normal↓Bound↑SemSeg↑Depth↓Normal↓Bound↑
Swin-LInvPT-T [56]44.270.558920.4676.1044.93 (+ 0.66)0.5577 (+ 0.0012)20.27 (+ 0.19)76.2 (+ 0.1)
Swin-LDeMT-T[53]46.360.587120.6576.9047.07 (+ 0.71)0.5855 (+ 0.0016)20.62 (+ 0.03)76.9 (+ 0.0)
Swin-LDeMT-S[53]51.500.547420.0278.1051.91 (+ 0.41)0.5512 (- 0.0038)20.01 (+ 0.01)78.1 (+ 0.0)
", + "bbox": [ + 80, + 491, + 890, + 570 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "as a teacher model for student model training. In Table 1, ours surpasses the HRNet18, Swin-T and Swin-S multi-task baselines by more than $1.16\\%$ , $4.84\\%$ and $3.34\\%$ (average per-task performance drop $\\Delta_{mt}$ ), respectively. The baseline model coupled with the improvement in $\\Delta_{mt}$ metric by our distillation method demonstrates the effectiveness of distillation. Note that These results are only conducted on the outputs of the multi-task baseline model and have a similar computational cost as the baseline model. Nevertheless, it even achieves better performance compared to those carefully designed methods. As shown in Table 1, although ATRC achieves better performance, it brings much more parameters and computation compared to the MT baseline. By contrast, our method based on distillation is cost-free. We also conduct experiments based on DeMT [53] and InvPT [56] and compare using our KD strategy with the DeMT-T, DeMT-S and InvPT-T. As shown in Table 2, our KDAM is outperformed by DeMT-T +0.71 mIoU and DeMT-S by +0.41 mIoU on SemSeg task. Applying our", + "bbox": [ + 75, + 602, + 472, + 866 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "distillation recipe in combination with the DeMT configuration to prove our method is effective. We can see that all the added KDAM, regardless of DeMT or InvPT, improves the performance. We observe that our distillation with an alternative match leads the state-of-the-art performance.", + "bbox": [ + 497, + 602, + 890, + 672 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "PASCAL-Context. We also use the multi-task baseline model of Swin-L as a teacher model. We further investigate the effectiveness of our KDAM for dense predictions on PASCAL-Context dataset. We train HRNet18, Swin-T and Swin-S baseline with our distillation method. As shown in Table 3, our KDAM outperforms all the previous MTL methods on five dense predictions and the average per-task performance drops $\\Delta_{mt}$ . It is worth mentioning that using a strong Swin-L teacher fails to give HRNet18 baseline an intuitive performance increase. We find that the performance of SemSeg task tends to get better as the student's backbone increases, which shows the effectiveness of our approach in segmentation tasks. Results suggest that our method can learn more semantic features for dense predictions.", + "bbox": [ + 497, + 672, + 892, + 866 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "21555", + "bbox": [ + 463, + 885, + 504, + 897 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/70ee09c94a2faf37d10fac63a60cee71d63fbd4e89435fba6d1fbd7d97283c2c.jpg", + "table_caption": [ + "Table 3: We report a comparison of the MTL models with the state-of-the-art on PASCAL-Context dataset. $\\downarrow$ : lower is better. $\\uparrow$ : higher is better. ${\\Delta }_{m}$ denotes the average per-task performance drop (higher is better). Gray blocks mean the multi-task baseline using our knowledge distillation method." + ], + "table_footnote": [], + "table_body": "
ModelBackboneSemSeg (mIoU)↑PartSeg (mIoU)↑Sal (maxF)↑Normal (mErr)↓Bound (odsF)↑Δmt [%]↑
single-task (ST) baselineHRNet1862.2361.6685.0813.6973.060.00
multi-task (MT) baselineHRNet1851.4857.2383.4314.1069.76-6.77
MT+KDAM (Ours)HRNet1851.9157.6383.9213.9070.1-5.06
PAD-Net [50]HRNet1853.6059.6065.8015.372.50-4.41
ATRC [3]HRNet1857.8957.3383.7713.9969.74-4.45
MQTransformer[52]HRNet1858.9157.4383.7814.1769.80-4.20
ATRC+KDAM (Ours)HRNet1858.9257.5183.8713.9769.75-3.94
single-task (ST) baselineSwin-T67.8156.3282.1814.8170.900.00
multi-task (MT) baselineSwin-T64.7453.2576.8815.8669.00-3.23
MT+KDAM (Ours)Swin-T64.8153.8081.7215.0669.5-2.3
single-task (ST) baselineSwin-S70.8359.7182.6415.1371.200.00
multi-task (MT) baselineSwin-S68.1056.2080.6416.0970.20-3.97
MT+KDAM (Ours)Swin-S68.8056.6281.9115.6170.4-2.54
", + "bbox": [ + 89, + 176, + 884, + 375 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/c05e934d1c0cef2656fb38356c3cd0be9b66ccc70311fb1e887c99abb51d87ed.jpg", + "table_caption": [ + "Table 4: We report a comparison of the multi-task (MT) baseline models using different KD strategies on NYUD-v2 dataset. MT and ST denote multi-task and single-task respectively. Gray blocks mean the MT baseline using our method." + ], + "table_footnote": [], + "table_body": "
Teacher (Student)MetricsAccuracy ST modelsAccuracy MT modelsPlain KDDIST KDOur KDAM
TeacherStudentTeacherStudentStudent (MT)Student (MT)Student(MT)
Swin-L (Swin-T)SemSeg↑56.4642.9254.5338.7844.4843.2744.54
Depth↓0.5080.6100.5320.6310.6040.5990.601
Normal↓19.3820.9419.5121.0521.0321.0221.03
Bound↑78.876.2278.375.6076.8076.5076.40
Δmt[%]↑---2.36-3.741.080.581.10
Swin-L (Swin-S)SemSeg↑56.4648.9254.5347.9049.2049.3949.41
Depth↓0.5080.5800.5320.6050.5710.5600.564
Normal↓19.3820.9419.5121.1720.5820.5120.60
Bound↑78.877.2078.376.9077.2077.277.3
Δmt[%]↑---2.36-1.960.971.61.38
Swin-B (Swin-T)SemSeg↑53.0142.9251.4438.7843.8444.0644.52
Depth↓0.5520.6100.5810.6310.6030.5960.592
Normal↓19.3420.9420.4421.0521.1921.0821.09
Bound↑78.0076.2277.8075.6076.6076.7076.6
Δmt[%]↑---3.2-3.740.491.071.47
", + "bbox": [ + 87, + 425, + 884, + 655 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Studies", + "text_level": 1, + "bbox": [ + 77, + 676, + 240, + 690 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Distillation with alternative match helps minimize the performance gap between teacher and student. In Table 4, we first conduct experiments to compare our KDAM with plain KD [13] and DIST KD [16] at different student and teacher model sizes. We compare three types of teacher-student pairs: Swin-L: Swin-T, Swin-L: Swin-S and Swin-B: Swin-T. As shown in Table 4 (Swin-T (Swin-L) and Swin-T (Swin-B) rows), when the teacher goes larger, the Swin-T students MTL performance $\\Delta_{mt}$ perform even worse than that with a medium-sized Swin-B teacher. We observe that it is not the fact that a larger teacher model leads to better performance. The plain KD using KL di", + "bbox": [ + 75, + 700, + 470, + 866 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "vergence loss can help minimize the performance gap between strong teachers and students. In addition, our KDAM showed an increasing trend with strong teachers and a more significant improvement compared to the other KD strategies, suggesting that our KDAM better handles the differences between student and strong teacher performance. Our KDAM can significantly outperform existing knowledge distillation methods on MTL of dense predictions. The results in Table 4 highlight that our KDAM is applied for capturing inter-task and intra-task information between the teacher model and the student model of each task, and thus learns more \"dark knowledge\" for effective distillation.", + "bbox": [ + 497, + 676, + 890, + 843 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Ablation on hyperparameters $\\mathcal{T}\\& \\beta$ . We compare the ef-", + "bbox": [ + 499, + 852, + 890, + 866 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "21556", + "bbox": [ + 463, + 885, + 505, + 897 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/1220c71f3f613a8ce5ec10b9ec3723c43f059c607ef797e43603c13559dadd2d.jpg", + "table_caption": [ + "Table 5: Ablation experiments of the optimal hyperparameters temperature factor $\\mathcal{T}$ and the loss scale factor $\\beta$ of the plain KD (Eq. 2) using a Swin-L as teacher model and Swin-T as student model on NYUD-v2 dataset.", + "(a) Ablation on $\\beta$ in Eq. 9 using $\\mathcal{T} = 3$ and $\\alpha = 1$ ." + ], + "table_footnote": [], + "table_body": "
KD styleβAccuracy multi-task student models
SemSeg↑Depth↓Normal↓Bound↑
Plain KD0.144.420.600121.1676.2
0.544.900.601521.0976.3
144.470.604421.0376.2
244.610.597521.0076.2
444.090.601721.0676.1
844.420.601821.0776.2
1643.530.610421.3476.3
", + "bbox": [ + 84, + 179, + 453, + 302 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/652b6d78b2b360bece35c76da3f7ba576bf9fbe781f10e13ed9920bb4b6155b1.jpg", + "table_caption": [ + "Table 6: Ablation on part of the loss. The student and teacher models are Swin-T and Swin-L, respectively. \"w/\" indicates \"with\"." + ], + "table_footnote": [], + "table_body": "
MethodAccuracy multi-task student model
SemSeg↑Depth↓Normal↓Bound↑
MT baseline38.780.631221.0575.60
Ours w/ intra43.310.606821.4776.00
Ours w/ inter44.060.596421.0876.50
Ours w/ inter&intra44.340.601221.0376.70
", + "bbox": [ + 80, + 374, + 468, + 461 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "fect of the number of temperature factor $\\mathcal{T}$ and the distillation loss scale factor $\\beta$ in Table 5a & 5b. We find that having a larger temperature of plain KD improves the performance slightly, whereas increasing the number of distillation loss scale factors does not improve the performance.", + "bbox": [ + 75, + 501, + 468, + 571 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Ablation on part of the loss. We compare three different methods named \"Ours w/ inter,\" \"Ours w/ intra\" and \"Ours w/ inter & intra\" in Table 6. To validate the effectiveness of each loss, we conduct experiments to train students with these methods separately. For all tasks, the intrinsic inter-task and intra-task variance of the semantic similarities is actually also informative. We can see that our KDAM can achieve a performance improvement, which proves the effectiveness of the inter-task and intra-task. Our knowledge distillation with an alternative match is applied to capture inter-task and intra-task information between the teacher and the student. The results show our distillation method can learn more \"dark knowledge\" for effective distillation.", + "bbox": [ + 75, + 573, + 468, + 752 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Ablation on training epochs. The default setting for the number of training epochs for teachers and students is 400. We independently train teacher models and pick them up at epoch $200^{th}$ and $400^{th}$ . In Table 7, we conduct ablation experiments of the training epochs using trained Swin-L as a teacher on NYUD-v2 dataset. The teacher model is trained at the $400^{th}$ epoch. The student model of Swin-T are selected at the $50^{th}, 100^{th}, 200^{th}, 300^{th}, 400^{th}, 500^{th}$", + "bbox": [ + 75, + 755, + 468, + 865 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/f2e4cdf12230e96fd9e3010ee19cf3be04c6275bb6119ea55363d8240d522723.jpg", + "table_caption": [ + "(b) Ablation on temperatures $\\mathcal{T}$ in Eq. 2 using $\\alpha = 1$ and $\\beta = 1$ ." + ], + "table_footnote": [], + "table_body": "
KD styleTAccuracy multi-task student models
SemSeg↑Depth↓Normal↓Bound↑
Plain KD0.144.270.607621.1576.1
0.544.520.605421.1676.2
144.830.596921.1076.3
344.470.604421.0376.2
444.210.601421.0576.1
845.350.601221.0476.5
1644.690.605021.0876.1
", + "bbox": [ + 515, + 179, + 887, + 306 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/9f09b3c806033bdc64fc3a11ba14880a17084021f6448d8644c4c8a6b2b1c016.jpg", + "table_caption": [ + "Table 7: Ablation on the training epochs. The student and teacher models are Swin-T and Swin-L, respectively." + ], + "table_footnote": [], + "table_body": "
ModelepochAccuracy multi-task student model
SemSeg↑Depth↓Normal↓Bound↑
KDAM10034.130.671523.2675.3
20042.330.628521.8676.0
30044.140.615621.2876.2
40044.340.601021.0376.2
60045.000.595520.6976.4
", + "bbox": [ + 504, + 359, + 890, + 464 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "and $600^{th}$ epochs. Our multi-task student model reaches 45.00 (mIoU, Semseg) and 0.5955 (rms, Depth) after 600 epochs. We observe that the multi-task student's accuracy increases monotonically with the increase of training epoch. Noticeably, the trained strong teacher model is used for improving student efficiency, while when the student model is not trained still enough leads to poor performance.", + "bbox": [ + 497, + 497, + 890, + 595 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 499, + 606, + 616, + 622 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This paper introduces a new knowledge distillation procedure with an alternative match (KDAM) for MTL of dense prediction based on two simple design principles. For memory and training efficiency, we use a single strong multi-task model as a teacher during training instead of multiple teachers, as widely adopted in existing studies. Furthermore, we employ a less sensitive CS divergence instead of the KL divergence and propose a CS distillation loss accordingly. This technique can significantly improve the MTL model's distillation performance and reduce the training cost. The Extensive experiment results show that our proposed method significantly improves the model performance and the practical inference efficiency.", + "bbox": [ + 497, + 631, + 890, + 809 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgements. This work was supported by the National Natural Science Foundation of China under Grant 62122060 and the Special Fund of Hubei Luojia Laboratory under Grant 220100014.", + "bbox": [ + 497, + 811, + 890, + 865 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "21557", + "bbox": [ + 463, + 885, + 504, + 897 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 124, + 173, + 138 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Lucas Beyer, Xiaohua Zhai, Amélie Royer, Larisa Markeeva, Rohan Anil, and Alexander Kolesnikov. Knowledge distillation: A good teacher is patient and consistent. In CVPR, pages 10925-10934, 2022. 1, 3", + "[2] Deblina Bhattacharjee, Tong Zhang, Sabine Süssrunk, and Mathieu Salzmann. Mult: An end-to-end multitask learning transformer. 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Decoupled multi-task learning with cyclical self-regulation for face parsing. In CVPR, pages 4156-4165, 2022. 3" + ], + "bbox": [ + 502, + 125, + 890, + 758 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "21559", + "bbox": [ + 463, + 885, + 504, + 897 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Multi-Task Learning with Knowledge Distillation for Dense Prediction/333e6685-b40e-48b9-a0cd-db1868afbfa7_model.json b/2023/Multi-Task Learning with Knowledge Distillation for Dense Prediction/333e6685-b40e-48b9-a0cd-db1868afbfa7_model.json new file mode 100644 index 0000000000000000000000000000000000000000..2045794e4fcaec6801000fca39734a03aaeeedb7 --- /dev/null +++ b/2023/Multi-Task Learning with Knowledge Distillation for Dense Prediction/333e6685-b40e-48b9-a0cd-db1868afbfa7_model.json @@ -0,0 +1,2079 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.129, + 0.051, + 0.201, + 0.086 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.254, + 0.049, + 0.79, + 0.087 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.13, + 0.162, + 0.84, + 0.182 + ], + "angle": 0, + "content": "Multi-Task Learning with Knowledge Distillation for Dense Prediction" + }, + { + "type": "text", + "bbox": [ + 0.255, + 0.207, + 0.374, + 0.225 + ], + "angle": 0, + "content": "Yangyang \\(\\mathbf{X}\\mathbf{u}^{\\mathrm{l}}\\)" + }, + { + "type": "text", + "bbox": [ + 0.439, + 0.208, + 0.532, + 0.225 + ], + "angle": 0, + "content": "Yibo Yang3" + }, + { + "type": "text", + "bbox": [ + 0.596, + 0.208, + 0.721, + 0.225 + ], + "angle": 0, + "content": "Lefei Zhang\\(^{1,2*}\\)" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.231, + 0.897, + 0.263 + ], + "angle": 0, + "content": "\\(^{1}\\) Institute of Artificial Intelligence and School of Computer Science, Wuhan University, Wuhan, China \n\\(^{2}\\) Hubei Luojia Laboratory, Wuhan, China" + }, + { + "type": "text", + "bbox": [ + 0.194, + 0.264, + 0.808, + 0.28 + ], + "angle": 0, + "content": "3 King Abdullah University of Science and Technology, Jeddah, Saudi Arabia" + }, + { + "type": "text", + "bbox": [ + 0.19, + 0.283, + 0.794, + 0.296 + ], + "angle": 0, + "content": "yangyangxu@whu.edu.cn, yibo.yang@kaust.edu.sa, zhanglefei@whu.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.328, + 0.313, + 0.343 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.357, + 0.473, + 0.718 + ], + "angle": 0, + "content": "While multi-task learning (MTL) has become an attractive topic, its training usually poses more difficulties than the single-task case. How to successfully apply knowledge distillation into MTL to improve training efficiency and model performance is still a challenging problem. In this paper, we introduce a new knowledge distillation procedure with an alternative match for MTL of dense prediction based on two simple design principles. First, for memory and training efficiency, we use a single strong multitask model as a teacher during training instead of multiple teachers, as widely adopted in existing studies. Second, we employ a less sensitive Cauchy-Schwarz (CS) divergence instead of the Kullback-Leibler (KL) divergence and propose a CS distillation loss accordingly. With the less sensitive divergence, our knowledge distillation with an alternative match is applied for capturing inter-task and intratask information between the teacher model and the student model of each task, thereby learning more \"dark knowledge\" for effective distillation. We conducted extensive experiments on dense prediction datasets, including NYUD-v2 and PASCAL-Context, for multiple vision tasks, such as semantic segmentation, human parts segmentation, depth estimation, surface normal estimation, and boundary detection. The results show that our proposed method decidedly improves model performance and the practical inference efficiency." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.741, + 0.21, + 0.755 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.764, + 0.47, + 0.849 + ], + "angle": 0, + "content": "Multi-task learning (MTL) has become an increasingly popular approach in the field of computer vision, where the objective is to train a single model to perform multiple tasks simultaneously. MTL can provide several advantages over traditional single-task learning, including improved efficiency and generalization. First, the shared feature repre" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.329, + 0.895, + 0.523 + ], + "angle": 0, + "content": "sentations can be learned more efficiently than task-specific representations, reducing the overall training time compared to training multiple models independently. Second, the shared feature representations learned across tasks can capture more generalizable information in the data, leading to improved performance on all tasks. For those reasons, the MTL approach has been used extensively in various machine learning problems, such as natural language processing [11], computer vision [3] and speech recognition [4]. Specifically, in this paper, we focus on dense (pixel-wise) prediction vision tasks [49, 15, 23, 41, 20, 21, 29, 48], such as semantic segmentation, instance segmentation, depth estimation, surface normal estimation, saliency estimation, object detection and boundary detection from images." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.529, + 0.895, + 0.765 + ], + "angle": 0, + "content": "A march of works [32, 46, 9, 3, 52, 2, 56, 53] aims to develop novel MTL architectures and construct efficient shared representation in the multi-taskdense prediction field, which leverages the encoder-decoder architecture. In these frameworks, an encoder is considered to generate a shared feature and then use a decoder to perform multi-task of dense predictions. In the pursuit of better performance, current MTL models are often designed to be deeper and wider, resulting in increasingly larger models. [3, 56] and [53, 24] demonstrate that better performance can be obtained by utilizing a larger backbone network. However, such a heavy model can be more demanding for computation and storage. It has been challenging to design an effective MTL framework that can learn these tasks efficiently. In this paper, we pose and study the question, how can the knowledge from a large size MTL model be transferred to a small MTL model without increasing its size?" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.77, + 0.895, + 0.868 + ], + "angle": 0, + "content": "Recently, knowledge distillation (KD) [13] has been explored as a method to improve the MTL of dense prediction tasks, such as semantic segmentation, depth estimation, and surface normal prediction. Some studies [30, 12, 16, 1] leverage the unique logit of each task to provide task-specific information to the student model during knowledge transfer. The essence of knowledge distillation lies" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.854, + 0.224, + 0.867 + ], + "angle": 0, + "content": "*Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "21550" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.126, + 0.473, + 0.431 + ], + "angle": 0, + "content": "in translating knowledge from the teacher model (large model) to the student model (small model) by mimicking the teacher model's outputs. Typically, knowledge distillation methods use the logits matching by Kullback-Leibler (KL) divergence [13] between the probability distributions of the teacher and the probability distributions of the student. In this way, during training, the student model can be guided by more valuable information signals from the teacher model, therefore, is expected to have a more promising performance than training alone. This approach has shown promising results in improving model performance and generalization and speeding up convergence in MTL. For instance, We found that some works [22, 35, 12, 30, 17] attempt to use knowledge distillation to transfer the knowledge from teacher to student for multiple vision tasks in MTL. We, in particular, identify two technical challenges. 1) Most previous approaches [22, 35, 17] must train a task-specific model for each task, then load the trained task-specific models. 2) Exact logit matching of teacher and student predictions with KL divergence can interfere with the training of the student model and is sensitive to outliers, leading to less effective knowledge distillation." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.434, + 0.47, + 0.601 + ], + "angle": 0, + "content": "To address these challenges, we explore knowledge distillation in multi-task learning of dense prediction tasks. We present a novel framework that leverages task-specific guidance to enable effective knowledge transfer. In Figure 1, we show the difference between the existing and our methods. Since using multiple single-task models as teacher models would require an inordinate amount of memory, we only load a single multi-task model as a teacher model instead of loading multiple teacher models. We opt for one strong teacher model to reduce computational and memory costs instead of using multiple teacher models that perform a load of each task separately." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.604, + 0.473, + 0.868 + ], + "angle": 0, + "content": "We take inspiration from mathematical statistics methods from other domains to reduce the uncertainty in students' prediction when using KL divergence (see Figure 1). We propose a novel knowledge distillation with Cauchy-Schwarz (CS) divergence to replace the KL divergence. In addition, during the logit matching, inter-task and intra-task information are transferred from teacher to student. Specifically, we gather the corresponding predicted probabilities in a batch for all tasks, then transfer the inter-task information from teacher to student. For each task, we gather the corresponding predicted probabilities of all classes in a batch, then transfer the intra-task information from teacher to student. Our proposed knowledge distillation with the alternative match is less sensitive to small probabilities and can account for uncertainty in the student model predictions. To further close the computational and memory cost gap, we only use one multi-task teacher model during training. This MTL knowledge distillation procedure provides multiple training settings." + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.127, + 0.912, + 0.316 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.325, + 0.895, + 0.388 + ], + "angle": 0, + "content": "Figure 1: Difference between existing KD methods and our KD method. \\(\\mathcal{F}_{st}^{T}\\) means the single-task \\((st)\\) teacher \\((T)\\) model output. \\(\\mathcal{F}_{mt}^{T}\\) means the multi-task \\((mt)\\) teacher model output. \\(\\mathcal{F}_{mt}^{S}\\) means the multi-task \\((mt)\\) student \\((S)\\) model output. \\(n\\) denotes the number of tasks." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.412, + 0.892, + 0.48 + ], + "angle": 0, + "content": "Through extensive experiments on several publicly available dense prediction datasets (i.e., NYUD-v2 and PASCAL-Context), we compare our results with state-of-the-art methods to demonstrate the effectiveness of our framework." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.481, + 0.892, + 0.509 + ], + "angle": 0, + "content": "In summary, our work makes the following contributions:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.516, + 0.892, + 0.587 + ], + "angle": 0, + "content": "- We introduce a new procedure based on knowledge distillation with an alternative match named KDAM, which leverages inter-task and intra-task information. It is less sensitive to small probabilities and can account for uncertainty in the student model predictions." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.594, + 0.892, + 0.637 + ], + "angle": 0, + "content": "- Our new distillation procedure aims at reproducing computational and memory costs by loading a strong multi-task model as a teacher to guide student learning." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.644, + 0.892, + 0.687 + ], + "angle": 0, + "content": "- We conduct experiments using our KDAM on two MTL of dense prediction datasets, showing the superiority under different experiment settings." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.516, + 0.892, + 0.687 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.705, + 0.642, + 0.72 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.728, + 0.894, + 0.868 + ], + "angle": 0, + "content": "Multi-task Learning of Dense Prediction. Multi-task learning for dense prediction [37, 50, 58, 31, 10, 9, 3, 52, 56, 53, 33, 28, 25, 57, 26, 27] has been an active research area in the computer vision community, with many studies exploring various aspects of joint learning for tasks such as semantic segmentation, depth estimation, surface normal estimation, saliency estimation and boundary detection. A survey work [45] shows that MTL is mainly divided into two categories: encoder-based and decoder-based architectures. The encoder-based methods, such as [19, 44, 54], use a" + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "21551" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.126, + 0.473, + 0.542 + ], + "angle": 0, + "content": "shared representation from an encoder to input task-specific heads and perform multiple task predictions. NDDR-CNN Network [10] is an encoder-focused MTL model which enables automatic feature fusing at every layer from different tasks and reduces channel dimension by processing the features with a \\( 1 \\times 1 \\) convolutional layer before feeding the result to the next layer. Their success heavily depends on the encoder (i.e., backbone network) to learn a strong shared representation [47, 59]. However, the encoder-based methods lack task interaction information, failing to capture commonalities and differences among tasks. The decoder-based methods, such as [50, 31, 3, 56, 2], focus on improving each task by repeatedly refining the predictions through cross-task interaction and improving each task's performance. Unlike encoder-based, decoder-based architectures also exchange information during the decoding. MTFormal [51] performs cross-task reasoning and designs the cross-task attention mechanism to achieve effective feature propagation among tasks, resulting in performance improvement in MTL. [52, 56] introduces new techniques for training deeper and wider via Transformers in MTL, allowing for more efficient and accurate MTL performance. Their success depends on a strong backbone network and all relevant task interactions from different dimensions. In addition, [40] introduces a controllable dynamic multi-task architecture for dynamically adjusting the weighting of loss of each task, which allows matching the desired task preference as well as the resource constraints. We propose an KDAM, which uses a strong multi-task model as a teacher to guide the student's multi-task model learning." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.549, + 0.473, + 0.868 + ], + "angle": 0, + "content": "Knowledge Distillation. The objective of the Knowledge distillation [13, 1] is mainly to distill the logits from certain outputs of a teacher to a student by minimizing the KL divergence [13], where the temperature \\(\\mathcal{T}\\) factor is applied to soften the output logits. Knowledge distillation is also introduced into vision tasks, such as image classification [30, 6, 5, 18], segmentation [39, 14, 38] and detection [55, 36, 48]. Knowledge distillation has emerged as an effective technique for improving multi-task learning of dense prediction tasks. Several recent studies [22, 35, 12, 17] have explored various aspects of knowledge distillation in the context of multi-task learning, with a focus on improving model performance and efficiency. The work [8] is to distill representation from a full image to the representation predicted from a masked image to perform multiple tasks. [17] designs the selective training layers for each task using an adaptive feature distillation loss with an online task weighting scheme. This task-based feature distillation allows MTL networks to be trained in a similar manner to single-task networks. Their success depends on multiple strong teacher models to guide student model training, which can get more information from the teacher model during training. However, these distillation MTL" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.126, + 0.895, + 0.252 + ], + "angle": 0, + "content": "models' exact logits matching of teacher and student predictions with KL divergence can interfere with student model training and become more sensitive to outliers, leading to poor knowledge distillation. In this paper, we develop an efficient distillation procedure specific to MTL of dense prediction. We use an alternative knowledge distillation strategy that leverages inter-task and intra-task information. It provides less sensitivity to small probabilities and can account for uncertainty in the student model predictions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.263, + 0.593, + 0.278 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.286, + 0.612, + 0.299 + ], + "angle": 0, + "content": "3.1. Notations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.305, + 0.895, + 0.391 + ], + "angle": 0, + "content": "The input image \\( x_{i} \\in \\mathbb{R}^{H \\times W \\times C} \\), where \\( H, W, \\) and \\( C \\) are the height, width, and channel of the image feature, respectively. We use \\( n \\) to denote the task number, with \\( n \\in \\{1, 2, \\dots, N\\} \\), \\( st \\) to denote the single-task and \\( mt \\) to denote the multi-task. Define \\( \\mathcal{F}_{mt}^{T} \\) as the multi-task teacher model and \\( \\mathcal{F}_{st}^{T} \\) as the single-task teacher model." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.398, + 0.634, + 0.412 + ], + "angle": 0, + "content": "3.2. Formulation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.419, + 0.893, + 0.462 + ], + "angle": 0, + "content": "The clustering regularizer loss is defined as the Kullback-Leibler (KL) [13] divergence between soft assignment \\( y_{\\mathrm{pred}} \\) and auxiliary target distribution \\( y_{\\mathrm{true}} \\):" + }, + { + "type": "equation", + "bbox": [ + 0.534, + 0.472, + 0.891, + 0.503 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {L} _ {\\mathrm {K L - d i v}} := K L \\left(y _ {\\text {p r e d}}, y _ {\\text {t r u e}}\\right) = y _ {\\text {t r u e}} \\cdot \\log \\frac {y _ {\\text {t r u e}}}{y _ {\\text {p r e d}}} \\tag {1} \\\\ = y _ {\\text {t r u e}} \\cdot (\\log y _ {\\text {t r u e}} - \\log y _ {\\text {p r e d}}), \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.513, + 0.893, + 0.596 + ], + "angle": 0, + "content": "where \\( y_{\\mathrm{pred}} \\) is the output of the model and \\( y_{\\mathrm{true}} \\) is the observation labels in the dataset. KL divergence is leveraged in plain KD to transform knowledge from the strong teacher model to the student model, where \\( y_{\\mathrm{pred}} \\) and \\( y_{\\mathrm{true}} \\) are the outputs of the student model and the teacher model. The plain KD loss is represented as:" + }, + { + "type": "equation", + "bbox": [ + 0.578, + 0.605, + 0.891, + 0.621 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {p l a i n} K D} = \\mathcal {T} ^ {2} \\cdot \\mathcal {L} _ {\\mathrm {K L - d i v}} \\left(P _ {S}, P _ {T}\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.631, + 0.892, + 0.701 + ], + "angle": 0, + "content": "where \\(\\mathcal{T}\\) is the distillation temperature factor to control the softness of logits of the softmax output. \\(P_{S}\\) is the softmax output of student model. \\(P_{T}\\) is the softmax output of the teacher model. The student and teacher generate the logits \\(\\mathcal{F}^S\\) and \\(\\mathcal{F}^T\\), respectively." + }, + { + "type": "equation", + "bbox": [ + 0.518, + 0.709, + 0.891, + 0.726 + ], + "angle": 0, + "content": "\\[\nP _ {S} = \\operatorname {s o f t m a x} \\left(\\mathcal {F} ^ {S} / \\mathcal {T}\\right), \\quad P _ {T} = \\operatorname {s o f t m a x} \\left(\\mathcal {F} ^ {T} / \\mathcal {T}\\right), \\tag {3}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.735, + 0.783, + 0.75 + ], + "angle": 0, + "content": "3.3. KD Alternative Match (KDAM)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.756, + 0.892, + 0.824 + ], + "angle": 0, + "content": "KL divergence is a distance metric that measures the difference between the teacher's and student's probability distributions. However, it is sensitive to outliers in the data, which can result in unstable training and poor generalization." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.867 + ], + "angle": 0, + "content": "There are two challenges using KL divergence in plain KD. First, one issue with KL divergence in knowledge distillation is that it can be unstable and lead to vanishing" + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "21552" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.123, + 0.128, + 0.849, + 0.325 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.338, + 0.892, + 0.396 + ], + "angle": 0, + "content": "Figure 2: Illustration of our knowledge distillation framework in MTL. Inter-task information: transmitted knowledge between the predicted probabilistic distributions on all tasks' channels of teacher and student. Intra-task information: transmitted knowledge of the probabilities of all the instances on each task. For simple purposes, We set two tasks in this figure. \\(N\\) denotes the task number. \\(\\mathcal{F}_{mt}^{T}\\) and \\(\\mathcal{F}_{mt}^{S}\\) means the multi-task \\((mt)\\) teacher and student model output, respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.418, + 0.47, + 0.585 + ], + "angle": 0, + "content": "gradients during training. This is because KL divergence involves taking the logarithm of probabilities, which can cause numerical instability when dealing with small or zero probabilities. It can make optimizing models that use KL divergence in knowledge distillation difficult. Second, KL divergence does not consider the uncertainty in the student predictions, which can lead to overconfidence and poor generalization in certain cases. This is particularly relevant in scenarios where the student model is less complex than the teacher model, as the student may not have the capacity to capture all of the information contained in the teacher's soft targets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.586, + 0.47, + 0.682 + ], + "angle": 0, + "content": "To address these issues, alternative divergence measures have been proposed, named Cauchy-Schwarz (CS) divergence, which is less sensitive to small probabilities and can account for uncertainty in the student model predictions. In this way, the alternative KD tries to save more task-specific information between the teacher and student on the probabilistic distribution." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.685, + 0.47, + 0.81 + ], + "angle": 0, + "content": "In knowledge distillation, let \\( \\mathcal{DS} = (x_i,y_i) \\) denote the training dataset of the student network, where \\( x_{i} \\) and \\( y_{i} \\) are the input and the corresponding ground truth label, respectively. Let \\( \\mathcal{DT} = (x_i,P_{T_i}) \\) denote the training dataset of the teacher network, where \\( P_{T_i} \\) is the predicted probability distribution over the class labels by the teacher network for the input \\( x_{i} \\). Let \\( \\mathcal{FS}: \\mathcal{X} \\to \\mathcal{Y} \\) and \\( \\mathcal{FT}: \\mathcal{X} \\to \\Delta^{C - 1} \\) denote the student and teacher networks, respectively, where \\( \\Delta^{C - 1} \\) is the \\( C \\)-dimensional probability simplex." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.812, + 0.471, + 0.867 + ], + "angle": 0, + "content": "Knowledge distillation aims to train the student network \\(\\mathcal{F}^S\\) to match the predictions of the teacher network \\(\\mathcal{F}^T\\) for the same input data. To achieve this, we minimize the CS divergence between the soft labels predicted by the teacher" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.418, + 0.892, + 0.474 + ], + "angle": 0, + "content": "network and those predicted by the student network. The CS divergence between the soft label distributions \\( P_{T_i} \\) and \\( P_{S_i} \\) predicted by the teacher and student models, respectively, for the input \\( x_i \\) is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.5, + 0.498, + 0.894, + 0.548 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {C S} := D _ {C S} \\left(P _ {S}, P _ {T}\\right) = - \\ln \\frac {\\int P _ {T _ {i}} (x) P _ {S _ {i}} (x) d x}{\\sqrt {\\int P _ {T _ {i}} (x) d x \\int P _ {S _ {i}} (x) d x}}. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.549, + 0.892, + 0.59 + ], + "angle": 0, + "content": "Note that \\( D_{CS} = 0 \\) only for \\( P_S = P_T \\). Eq. 4 can improve numerical stability and the ability to account for uncertainty in student predictions." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.592, + 0.892, + 0.647 + ], + "angle": 0, + "content": "The inter-task information for each task. We develop an alternative inter-task comparison strategy in which the distribution of teacher and student of all tasks. The intertask information between teacher and student is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.577, + 0.662, + 0.892, + 0.7 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {i n t e r} = \\frac {1}{B} \\sum_ {i = 1} ^ {B} D _ {C S} \\left(P _ {S i,:}, P _ {T _ {i,:}}\\right), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.708, + 0.714, + 0.72 + ], + "angle": 0, + "content": "where the \\(B\\) denotes batch size." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.723, + 0.892, + 0.803 + ], + "angle": 0, + "content": "The intra-task information for each task. For intraclass information, we discuss why naive hard example mining cannot handle noise/outliers and propose a simple and effective balancing strategy for fast and robust hard example mining. As shown in Figure 2, the intra-task is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.576, + 0.806, + 0.892, + 0.845 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {i n t r a}} = \\frac {1}{C} \\sum_ {j = 1} ^ {C} D _ {C S} \\left(P _ {S: j}, P _ {T: j}\\right), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.852, + 0.698, + 0.865 + ], + "angle": 0, + "content": "where \\(C\\) denotes the channel." + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "21553" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.078, + 0.126, + 0.47, + 0.154 + ], + "angle": 0, + "content": "Finally, we wrap task-independent knowledge distillation strategies into MTL. It can be formulated as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.164, + 0.469, + 0.202 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {C S K D} = \\sum_ {n = 1} ^ {N} \\left(\\mathcal {L} _ {\\text {i n t e r}} + \\mathcal {L} _ {\\text {i n t r a}}\\right), \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.21, + 0.47, + 0.239 + ], + "angle": 0, + "content": "where the \\(N\\) is the task number. We sum up the \\(\\mathcal{L}_{inter}\\) and \\(\\mathcal{L}_{intra}\\) to improve the distillation performance for MTL." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.246, + 0.254, + 0.261 + ], + "angle": 0, + "content": "3.4. Training objective" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.267, + 0.469, + 0.351 + ], + "angle": 0, + "content": "As depicted in Figure 2, our method consists of a teacher MT model, a student MT model, and a new strategy of KD. Concretely, we first train a strong MT model as a teacher model. Then we introduce a trained teacher model for the student MT model training. The plain multi-task loss function is given as:" + }, + { + "type": "equation", + "bbox": [ + 0.158, + 0.36, + 0.469, + 0.398 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {m t} := \\mathcal {L} \\left(y _ {\\text {t r u e}}, P _ {S}\\right) = \\sum_ {n = 1} ^ {N} \\lambda_ {n} \\mathcal {L} _ {n}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.407, + 0.462, + 0.42 + ], + "angle": 0, + "content": "where \\(\\lambda_{n}\\) is a hyperparameter factor of the task number \\(n\\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.421, + 0.469, + 0.49 + ], + "angle": 0, + "content": "In the multi-task knowledge distillation setting, there are a trained multi-task teacher model (i.e., \\( T^{mt} \\)) and a student model (i.e., \\( S^{mt} \\)). As a result, the KDAM overall training loss function is typically a weighted sum of the MTL loss \\( (\\mathcal{L}_{mt}) \\) and the knowledge distillation loss." + }, + { + "type": "equation", + "bbox": [ + 0.11, + 0.5, + 0.469, + 0.515 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {t o t a l}} = \\alpha \\cdot \\mathcal {L} _ {m t} + \\beta \\cdot \\mathcal {L} _ {C S K D} \\left(P _ {S ^ {m t}}, P _ {T ^ {m t}}\\right), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.525, + 0.469, + 0.567 + ], + "angle": 0, + "content": "where \\(\\alpha\\) and \\(\\beta\\) are the scale factor for balancing the losses. In this way, via the \\(\\mathcal{L}_{CSKD}\\) loss, the student to match the strong teacher network's output." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.579, + 0.21, + 0.594 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.602, + 0.469, + 0.712 + ], + "angle": 0, + "content": "We validate the superiority of our KDAM framework under two representative datasets: NYUD-v2 [42] and PASCAL-Context [7]. In Section 4.1, we provide the experimental setup and evaluation details we used for experiments. Section 4.2 presents the main qualitative and quantitative MTL results. Finally, in Section 4.3, we perform ablation studies to verify the effect of components and efficiencies of our method." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.721, + 0.25, + 0.736 + ], + "angle": 0, + "content": "4.1. Experiment setup" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.742, + 0.469, + 0.866 + ], + "angle": 0, + "content": "NYUD-v2 dataset and metrics. NYUD-v2 comprises RGB and Depth frames 795 images are used for training and 654 images for testing. NYUD-v2 is adopted for semantic segmentation (SemSeg), depth estimation (Depth), surface normal estimation (Normal) and boundary detection (Bound) tasks by providing dense labels. The semantic segmentation labels classify each pixel in the RGB images into one of 40 object categories. Four evaluation metrics are available to evaluate the MTL model performance, which" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.126, + 0.892, + 0.18 + ], + "angle": 0, + "content": "includes mean Intersection over Union (mIoU) for the SemSeg task, root mean square error (rmse) for the Depth task, mean Error (mErr) for the Normal task, and optimal dataset scale F-measure (odsF) for the Bound task." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.182, + 0.892, + 0.417 + ], + "angle": 0, + "content": "PASCAL-Context dataset and metrics. PASCAL-Context consists of 10,103 images with complex scenes, covering 400 object categories and 59 background regions. PASCAL-Context is adopted for semantic segmentation (SemSeg), human parts segmentation (PartSeg), saliency estimation (Sal), surface normal estimation (Normal), and boundary detection (Bound) tasks by pixel-level semantic labels for each image. Five evaluation metrics are available to evaluate the MTL model performance, which includes mean Intersection over Union (mIoU) for the SemSeg and PartSeg tasks, mean Error (mErr) for the Normal task, optimal dataset scale F-measure (odsF) for the Bound task, and maximum F-measure (maxF) for the Sal task. The average per-task performance drop \\((\\Delta_{mt})\\) is used to quantify multi-task performance. \\(\\Delta_{mt} = \\frac{1}{N}\\sum_{i = 1}^{N}(F_{mt,n} - F_{st,n}) / F_{st,n}\\times\\) \\(100\\%\\) , where mt, st and \\(N\\) mean multi-task model, single-task baseline and task numbers. \\(\\Delta_{mt}\\) : higher is the better." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.418, + 0.892, + 0.528 + ], + "angle": 0, + "content": "Setting. To be universal, we perform experiments on the NYUD-v2 [42] and PASCAL-Context [7] datasets using different teacher-student pairs. The \"Plain KD vs. DIST vs. Our KDAM\" experiment is conducted using Swin-L [34] as a teacher model, Swin-T [34] and Swin-S [34] as student models on the NYUD-v2. On PASCAL-Context, we adopt Swin-L [34] and Swin-B [34] as teacher models, HRNet18 [43], Swin-T [34] and Swin-S [34] as student models." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.529, + 0.892, + 0.694 + ], + "angle": 0, + "content": "Loss weights. In our experiments, we use the algorithm in [3] to learn weights for each task over the course of training. For a fair comparison, we search the optimal hyperparameters (i.e., the loss ratio \\(\\alpha\\), \\(\\beta\\) and the temperature \\(\\mathcal{T}\\)) for each teacher-student pair. On NYUD-v2 and PASCAL-Context, we set \\(\\alpha = 1.0\\), \\(\\beta = 1.0\\) in Eq. 9 using our TKD method. For plain KD [13], we set \\(\\alpha = 1.0\\), \\(\\beta = 1.0\\) in Eq. 9 and use a default temperature \\(\\mathcal{T} = 3\\) in Eq. 2. In addition, For a fair comparison, we search the optimal hyperparameters i.e., \\(\\beta\\) and \\(\\mathcal{T}\\). We choose a temperature set \\(\\mathcal{T} \\in [0.1, 0.5, 1, 3, 4, 8, 16]\\) for an ablation study on NYUD-v2 dataset (see Table 5a & 5b)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.696, + 0.892, + 0.779 + ], + "angle": 0, + "content": "Baselines. Multi-task baseline uses a shared backbone network in conjunction with task-specific heads to perform the predictions for every task. We can choose different networks as backbones, such as HRNet [43] and Swin Transformer [34]. Single-task baseline uses a backbone network with a task head to conduct the predictions for a task." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.789, + 0.593, + 0.803 + ], + "angle": 0, + "content": "4.2. Results" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.811, + 0.892, + 0.867 + ], + "angle": 0, + "content": "NYUD-v2 dataset. We investigate the effectiveness of our KDAM on NYUD-v2 dataset. We first train a multi-task baseline model of Swin-L for our knowledge distillation procedure. Then we load the well trained Swin-L model" + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "21554" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.124, + 0.894, + 0.166 + ], + "angle": 0, + "content": "Table 1: We report the comparison of the MTL models with the state-of-the-art on NYUD-v2 dataset. \\( \\downarrow \\) : lower is better. ’↑’: higher is better. \\( {\\Delta }_{mt} \\) denotes the average per-task performance drop. Swin-◇ indicates that the specific Swin model is uncertain. Gray blocks mean the multi-task baseline using our knowledge distillation method." + }, + { + "type": "table", + "bbox": [ + 0.091, + 0.173, + 0.88, + 0.458 + ], + "angle": 0, + "content": "
ModelBackboneParams (M)GFLOPs (G)SemSeg (mIoU)↑Depth (rmse)↓Normal (mErr)↓Bound (odsF)↑Δmt[%]↑
single-task (ST) baselineHRNet1816.0940.9338.020.610420.9476.220.00
multi-task (MT) baselineHRNet184.5217.5936.350.628421.0276.36-1.89
MT+KDAM (Ours)HRNet184.5217.5936.850.625021.0476.10-0.73
Cross-Stitch[37]HRNet184.5217.5936.340.629020.8876.38-1.75
Pad-Net[50]HRNet185.0225.1836.700.626420.8576.50-1.33
PAP[58]HRNet184.5453.0436.720.617820.8276.42-0.95
PSD[31]HRNet184.7121.1036.690.624620.8776.42-1.30
NDDR-CNN[10]HRNet184.5918.6836.720.628820.8976.32-1.51
MTI-Net[46]HRNet1812.5619.1436.610.627020.8576.38-1.44
ATRC[3]HRNet185.0625.7638.900.601020.4876.341.56
ATRC+KDAM (Ours)HRNet185.0625.7639.300.591920.7276.912.05
single-task (ST) baselineSwin-T115.08161.2542.920.610420.9476.220.00
multi-task (MT) baselineSwin-T32.5096.2938.780.631221.0575.60-3.74
MT+KDAM (Ours)Swin-T32.5096.2944.340.60121.0376.41.1
single-task (ST) baselineSwin-S200.33242.6348.920.580420.9477.200.00
multi-task (MT) baselineSwin-S53.82116.6347.900.605321.1776.90-1.96
MTFormer[51]Swin-◇64.03117.7350.560.4830--4.12
MT+KDAM (Ours)Swin-S53.82116.6349.410.56420.6077.31.38
" + }, + { + "type": "table_caption", + "bbox": [ + 0.084, + 0.469, + 0.884, + 0.485 + ], + "angle": 0, + "content": "Table 2: Comparison results of DeMT and InvPT MTL model with our KDAM method. \\( {}^{\\prime } + \\) ’ means performance increase." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.492, + 0.892, + 0.571 + ], + "angle": 0, + "content": "
Network structureAccuracy multi-task student modelsAccuracy of our KDAM
TeacherStudentSemSeg↑Depth↓Normal↓Bound↑SemSeg↑Depth↓Normal↓Bound↑
Swin-LInvPT-T [56]44.270.558920.4676.1044.93 (+ 0.66)0.5577 (+ 0.0012)20.27 (+ 0.19)76.2 (+ 0.1)
Swin-LDeMT-T[53]46.360.587120.6576.9047.07 (+ 0.71)0.5855 (+ 0.0016)20.62 (+ 0.03)76.9 (+ 0.0)
Swin-LDeMT-S[53]51.500.547420.0278.1051.91 (+ 0.41)0.5512 (- 0.0038)20.01 (+ 0.01)78.1 (+ 0.0)
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.603, + 0.473, + 0.868 + ], + "angle": 0, + "content": "as a teacher model for student model training. In Table 1, ours surpasses the HRNet18, Swin-T and Swin-S multi-task baselines by more than \\(1.16\\%\\), \\(4.84\\%\\) and \\(3.34\\%\\) (average per-task performance drop \\(\\Delta_{mt}\\)), respectively. The baseline model coupled with the improvement in \\(\\Delta_{mt}\\) metric by our distillation method demonstrates the effectiveness of distillation. Note that These results are only conducted on the outputs of the multi-task baseline model and have a similar computational cost as the baseline model. Nevertheless, it even achieves better performance compared to those carefully designed methods. As shown in Table 1, although ATRC achieves better performance, it brings much more parameters and computation compared to the MT baseline. By contrast, our method based on distillation is cost-free. We also conduct experiments based on DeMT [53] and InvPT [56] and compare using our KD strategy with the DeMT-T, DeMT-S and InvPT-T. As shown in Table 2, our KDAM is outperformed by DeMT-T +0.71 mIoU and DeMT-S by +0.41 mIoU on SemSeg task. Applying our" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.603, + 0.892, + 0.673 + ], + "angle": 0, + "content": "distillation recipe in combination with the DeMT configuration to prove our method is effective. We can see that all the added KDAM, regardless of DeMT or InvPT, improves the performance. We observe that our distillation with an alternative match leads the state-of-the-art performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.673, + 0.893, + 0.868 + ], + "angle": 0, + "content": "PASCAL-Context. We also use the multi-task baseline model of Swin-L as a teacher model. We further investigate the effectiveness of our KDAM for dense predictions on PASCAL-Context dataset. We train HRNet18, Swin-T and Swin-S baseline with our distillation method. As shown in Table 3, our KDAM outperforms all the previous MTL methods on five dense predictions and the average per-task performance drops \\(\\Delta_{mt}\\). It is worth mentioning that using a strong Swin-L teacher fails to give HRNet18 baseline an intuitive performance increase. We find that the performance of SemSeg task tends to get better as the student's backbone increases, which shows the effectiveness of our approach in segmentation tasks. Results suggest that our method can learn more semantic features for dense predictions." + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "21555" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.124, + 0.894, + 0.166 + ], + "angle": 0, + "content": "Table 3: We report a comparison of the MTL models with the state-of-the-art on PASCAL-Context dataset. \\( \\downarrow \\) : lower is better. \\( \\uparrow \\) : higher is better. \\( {\\Delta }_{m} \\) denotes the average per-task performance drop (higher is better). Gray blocks mean the multi-task baseline using our knowledge distillation method." + }, + { + "type": "table", + "bbox": [ + 0.09, + 0.177, + 0.885, + 0.376 + ], + "angle": 0, + "content": "
ModelBackboneSemSeg (mIoU)↑PartSeg (mIoU)↑Sal (maxF)↑Normal (mErr)↓Bound (odsF)↑Δmt [%]↑
single-task (ST) baselineHRNet1862.2361.6685.0813.6973.060.00
multi-task (MT) baselineHRNet1851.4857.2383.4314.1069.76-6.77
MT+KDAM (Ours)HRNet1851.9157.6383.9213.9070.1-5.06
PAD-Net [50]HRNet1853.6059.6065.8015.372.50-4.41
ATRC [3]HRNet1857.8957.3383.7713.9969.74-4.45
MQTransformer[52]HRNet1858.9157.4383.7814.1769.80-4.20
ATRC+KDAM (Ours)HRNet1858.9257.5183.8713.9769.75-3.94
single-task (ST) baselineSwin-T67.8156.3282.1814.8170.900.00
multi-task (MT) baselineSwin-T64.7453.2576.8815.8669.00-3.23
MT+KDAM (Ours)Swin-T64.8153.8081.7215.0669.5-2.3
single-task (ST) baselineSwin-S70.8359.7182.6415.1371.200.00
multi-task (MT) baselineSwin-S68.1056.2080.6416.0970.20-3.97
MT+KDAM (Ours)Swin-S68.8056.6281.9115.6170.4-2.54
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.387, + 0.893, + 0.416 + ], + "angle": 0, + "content": "Table 4: We report a comparison of the multi-task (MT) baseline models using different KD strategies on NYUD-v2 dataset. MT and ST denote multi-task and single-task respectively. Gray blocks mean the MT baseline using our method." + }, + { + "type": "table", + "bbox": [ + 0.088, + 0.426, + 0.885, + 0.656 + ], + "angle": 0, + "content": "
Teacher (Student)MetricsAccuracy ST modelsAccuracy MT modelsPlain KDDIST KDOur KDAM
TeacherStudentTeacherStudentStudent (MT)Student (MT)Student(MT)
Swin-L (Swin-T)SemSeg↑56.4642.9254.5338.7844.4843.2744.54
Depth↓0.5080.6100.5320.6310.6040.5990.601
Normal↓19.3820.9419.5121.0521.0321.0221.03
Bound↑78.876.2278.375.6076.8076.5076.40
Δmt[%]↑---2.36-3.741.080.581.10
Swin-L (Swin-S)SemSeg↑56.4648.9254.5347.9049.2049.3949.41
Depth↓0.5080.5800.5320.6050.5710.5600.564
Normal↓19.3820.9419.5121.1720.5820.5120.60
Bound↑78.877.2078.376.9077.2077.277.3
Δmt[%]↑---2.36-1.960.971.61.38
Swin-B (Swin-T)SemSeg↑53.0142.9251.4438.7843.8444.0644.52
Depth↓0.5520.6100.5810.6310.6030.5960.592
Normal↓19.3420.9420.4421.0521.1921.0821.09
Bound↑78.0076.2277.8075.6076.6076.7076.6
Δmt[%]↑---3.2-3.740.491.071.47
" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.677, + 0.242, + 0.691 + ], + "angle": 0, + "content": "4.3. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.701, + 0.471, + 0.867 + ], + "angle": 0, + "content": "Distillation with alternative match helps minimize the performance gap between teacher and student. In Table 4, we first conduct experiments to compare our KDAM with plain KD [13] and DIST KD [16] at different student and teacher model sizes. We compare three types of teacher-student pairs: Swin-L: Swin-T, Swin-L: Swin-S and Swin-B: Swin-T. As shown in Table 4 (Swin-T (Swin-L) and Swin-T (Swin-B) rows), when the teacher goes larger, the Swin-T students MTL performance \\(\\Delta_{mt}\\) perform even worse than that with a medium-sized Swin-B teacher. We observe that it is not the fact that a larger teacher model leads to better performance. The plain KD using KL di" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.678, + 0.892, + 0.844 + ], + "angle": 0, + "content": "vergence loss can help minimize the performance gap between strong teachers and students. In addition, our KDAM showed an increasing trend with strong teachers and a more significant improvement compared to the other KD strategies, suggesting that our KDAM better handles the differences between student and strong teacher performance. Our KDAM can significantly outperform existing knowledge distillation methods on MTL of dense predictions. The results in Table 4 highlight that our KDAM is applied for capturing inter-task and intra-task information between the teacher model and the student model of each task, and thus learns more \"dark knowledge\" for effective distillation." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.853, + 0.892, + 0.867 + ], + "angle": 0, + "content": "Ablation on hyperparameters \\(\\mathcal{T}\\& \\beta\\). We compare the ef-" + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.506, + 0.898 + ], + "angle": 0, + "content": "21556" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.124, + 0.892, + 0.152 + ], + "angle": 0, + "content": "Table 5: Ablation experiments of the optimal hyperparameters temperature factor \\( \\mathcal{T} \\) and the loss scale factor \\( \\beta \\) of the plain KD (Eq. 2) using a Swin-L as teacher model and Swin-T as student model on NYUD-v2 dataset." + }, + { + "type": "table_caption", + "bbox": [ + 0.13, + 0.163, + 0.408, + 0.176 + ], + "angle": 0, + "content": "(a) Ablation on \\(\\beta\\) in Eq. 9 using \\(\\mathcal{T} = 3\\) and \\(\\alpha = 1\\)." + }, + { + "type": "table", + "bbox": [ + 0.085, + 0.18, + 0.455, + 0.304 + ], + "angle": 0, + "content": "
KD styleβAccuracy multi-task student models
SemSeg↑Depth↓Normal↓Bound↑
Plain KD0.144.420.600121.1676.2
0.544.900.601521.0976.3
144.470.604421.0376.2
244.610.597521.0076.2
444.090.601721.0676.1
844.420.601821.0776.2
1643.530.610421.3476.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.322, + 0.47, + 0.362 + ], + "angle": 0, + "content": "Table 6: Ablation on part of the loss. The student and teacher models are Swin-T and Swin-L, respectively. \"w/\" indicates \"with\"." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.375, + 0.469, + 0.463 + ], + "angle": 0, + "content": "
MethodAccuracy multi-task student model
SemSeg↑Depth↓Normal↓Bound↑
MT baseline38.780.631221.0575.60
Ours w/ intra43.310.606821.4776.00
Ours w/ inter44.060.596421.0876.50
Ours w/ inter&intra44.340.601221.0376.70
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.502, + 0.469, + 0.572 + ], + "angle": 0, + "content": "fect of the number of temperature factor \\(\\mathcal{T}\\) and the distillation loss scale factor \\(\\beta\\) in Table 5a & 5b. We find that having a larger temperature of plain KD improves the performance slightly, whereas increasing the number of distillation loss scale factors does not improve the performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.574, + 0.469, + 0.753 + ], + "angle": 0, + "content": "Ablation on part of the loss. We compare three different methods named \"Ours w/ inter,\" \"Ours w/ intra\" and \"Ours w/ inter & intra\" in Table 6. To validate the effectiveness of each loss, we conduct experiments to train students with these methods separately. For all tasks, the intrinsic inter-task and intra-task variance of the semantic similarities is actually also informative. We can see that our KDAM can achieve a performance improvement, which proves the effectiveness of the inter-task and intra-task. Our knowledge distillation with an alternative match is applied to capture inter-task and intra-task information between the teacher and the student. The results show our distillation method can learn more \"dark knowledge\" for effective distillation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.756, + 0.469, + 0.866 + ], + "angle": 0, + "content": "Ablation on training epochs. The default setting for the number of training epochs for teachers and students is 400. We independently train teacher models and pick them up at epoch \\(200^{th}\\) and \\(400^{th}\\). In Table 7, we conduct ablation experiments of the training epochs using trained Swin-L as a teacher on NYUD-v2 dataset. The teacher model is trained at the \\(400^{th}\\) epoch. The student model of Swin-T are selected at the \\(50^{th}, 100^{th}, 200^{th}, 300^{th}, 400^{th}, 500^{th}\\)" + }, + { + "type": "table_caption", + "bbox": [ + 0.52, + 0.163, + 0.88, + 0.176 + ], + "angle": 0, + "content": "(b) Ablation on temperatures \\(\\mathcal{T}\\) in Eq. 2 using \\(\\alpha = 1\\) and \\(\\beta = 1\\)." + }, + { + "type": "table", + "bbox": [ + 0.517, + 0.18, + 0.889, + 0.307 + ], + "angle": 0, + "content": "
KD styleTAccuracy multi-task student models
SemSeg↑Depth↓Normal↓Bound↑
Plain KD0.144.270.607621.1576.1
0.544.520.605421.1676.2
144.830.596921.1076.3
344.470.604421.0376.2
444.210.601421.0576.1
845.350.601221.0476.5
1644.690.605021.0876.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.322, + 0.892, + 0.351 + ], + "angle": 0, + "content": "Table 7: Ablation on the training epochs. The student and teacher models are Swin-T and Swin-L, respectively." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.361, + 0.892, + 0.465 + ], + "angle": 0, + "content": "
ModelepochAccuracy multi-task student model
SemSeg↑Depth↓Normal↓Bound↑
KDAM10034.130.671523.2675.3
20042.330.628521.8676.0
30044.140.615621.2876.2
40044.340.601021.0376.2
60045.000.595520.6976.4
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.498, + 0.892, + 0.596 + ], + "angle": 0, + "content": "and \\(600^{th}\\) epochs. Our multi-task student model reaches 45.00 (mIoU, Semseg) and 0.5955 (rms, Depth) after 600 epochs. We observe that the multi-task student's accuracy increases monotonically with the increase of training epoch. Noticeably, the trained strong teacher model is used for improving student efficiency, while when the student model is not trained still enough leads to poor performance." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.608, + 0.618, + 0.623 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.632, + 0.892, + 0.811 + ], + "angle": 0, + "content": "This paper introduces a new knowledge distillation procedure with an alternative match (KDAM) for MTL of dense prediction based on two simple design principles. For memory and training efficiency, we use a single strong multi-task model as a teacher during training instead of multiple teachers, as widely adopted in existing studies. Furthermore, we employ a less sensitive CS divergence instead of the KL divergence and propose a CS distillation loss accordingly. This technique can significantly improve the MTL model's distillation performance and reduce the training cost. The Extensive experiment results show that our proposed method significantly improves the model performance and the practical inference efficiency." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.812, + 0.892, + 0.866 + ], + "angle": 0, + "content": "Acknowledgements. This work was supported by the National Natural Science Foundation of China under Grant 62122060 and the Special Fund of Hubei Luojia Laboratory under Grant 220100014." + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "21557" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.125, + 0.174, + 0.139 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.148, + 0.47, + 0.198 + ], + "angle": 0, + "content": "[1] Lucas Beyer, Xiaohua Zhai, Amélie Royer, Larisa Markeeva, Rohan Anil, and Alexander Kolesnikov. Knowledge distillation: A good teacher is patient and consistent. In CVPR, pages 10925-10934, 2022. 1, 3" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.2, + 0.47, + 0.237 + ], + "angle": 0, + "content": "[2] Deblina Bhattacharjee, Tong Zhang, Sabine Süssrunk, and Mathieu Salzmann. Mult: An end-to-end multitask learning transformer. 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In CVPR, pages 4156-4165, 2022. 3" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.127, + 0.892, + 0.76 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.465, + 0.887, + 0.505, + 0.898 + ], + "angle": 0, + "content": "21559" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-Task Learning with Knowledge Distillation for Dense Prediction/333e6685-b40e-48b9-a0cd-db1868afbfa7_origin.pdf b/2023/Multi-Task Learning with Knowledge Distillation for Dense Prediction/333e6685-b40e-48b9-a0cd-db1868afbfa7_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..34a2a6b5607c90938747653b4d893ca140e3aa42 --- /dev/null +++ b/2023/Multi-Task Learning with Knowledge Distillation for Dense Prediction/333e6685-b40e-48b9-a0cd-db1868afbfa7_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:daba0245655d819f11a66a0700bc3d9747f695a5ad3aec24ad48e1132208919c +size 361043 diff --git a/2023/Multi-Task Learning with Knowledge Distillation for Dense Prediction/full.md b/2023/Multi-Task Learning with Knowledge Distillation for Dense Prediction/full.md new file mode 100644 index 0000000000000000000000000000000000000000..ac505348ac331d75440560e5e9bb7ec8ba2693e7 --- /dev/null +++ b/2023/Multi-Task Learning with Knowledge Distillation for Dense Prediction/full.md @@ -0,0 +1,296 @@ +# Multi-Task Learning with Knowledge Distillation for Dense Prediction + +Yangyang $\mathbf{X}\mathbf{u}^{\mathrm{l}}$ + +Yibo Yang3 + +Lefei Zhang $^{1,2*}$ + +$^{1}$ Institute of Artificial Intelligence and School of Computer Science, Wuhan University, Wuhan, China + $^{2}$ Hubei Luojia Laboratory, Wuhan, China + +3 King Abdullah University of Science and Technology, Jeddah, Saudi Arabia + +yangyangxu@whu.edu.cn, yibo.yang@kaust.edu.sa, zhanglefei@whu.edu.cn + +# Abstract + +While multi-task learning (MTL) has become an attractive topic, its training usually poses more difficulties than the single-task case. How to successfully apply knowledge distillation into MTL to improve training efficiency and model performance is still a challenging problem. In this paper, we introduce a new knowledge distillation procedure with an alternative match for MTL of dense prediction based on two simple design principles. First, for memory and training efficiency, we use a single strong multitask model as a teacher during training instead of multiple teachers, as widely adopted in existing studies. Second, we employ a less sensitive Cauchy-Schwarz (CS) divergence instead of the Kullback-Leibler (KL) divergence and propose a CS distillation loss accordingly. With the less sensitive divergence, our knowledge distillation with an alternative match is applied for capturing inter-task and intratask information between the teacher model and the student model of each task, thereby learning more "dark knowledge" for effective distillation. We conducted extensive experiments on dense prediction datasets, including NYUD-v2 and PASCAL-Context, for multiple vision tasks, such as semantic segmentation, human parts segmentation, depth estimation, surface normal estimation, and boundary detection. The results show that our proposed method decidedly improves model performance and the practical inference efficiency. + +# 1. Introduction + +Multi-task learning (MTL) has become an increasingly popular approach in the field of computer vision, where the objective is to train a single model to perform multiple tasks simultaneously. MTL can provide several advantages over traditional single-task learning, including improved efficiency and generalization. First, the shared feature repre + +sentations can be learned more efficiently than task-specific representations, reducing the overall training time compared to training multiple models independently. Second, the shared feature representations learned across tasks can capture more generalizable information in the data, leading to improved performance on all tasks. For those reasons, the MTL approach has been used extensively in various machine learning problems, such as natural language processing [11], computer vision [3] and speech recognition [4]. Specifically, in this paper, we focus on dense (pixel-wise) prediction vision tasks [49, 15, 23, 41, 20, 21, 29, 48], such as semantic segmentation, instance segmentation, depth estimation, surface normal estimation, saliency estimation, object detection and boundary detection from images. + +A march of works [32, 46, 9, 3, 52, 2, 56, 53] aims to develop novel MTL architectures and construct efficient shared representation in the multi-taskdense prediction field, which leverages the encoder-decoder architecture. In these frameworks, an encoder is considered to generate a shared feature and then use a decoder to perform multi-task of dense predictions. In the pursuit of better performance, current MTL models are often designed to be deeper and wider, resulting in increasingly larger models. [3, 56] and [53, 24] demonstrate that better performance can be obtained by utilizing a larger backbone network. However, such a heavy model can be more demanding for computation and storage. It has been challenging to design an effective MTL framework that can learn these tasks efficiently. In this paper, we pose and study the question, how can the knowledge from a large size MTL model be transferred to a small MTL model without increasing its size? + +Recently, knowledge distillation (KD) [13] has been explored as a method to improve the MTL of dense prediction tasks, such as semantic segmentation, depth estimation, and surface normal prediction. Some studies [30, 12, 16, 1] leverage the unique logit of each task to provide task-specific information to the student model during knowledge transfer. The essence of knowledge distillation lies + +in translating knowledge from the teacher model (large model) to the student model (small model) by mimicking the teacher model's outputs. Typically, knowledge distillation methods use the logits matching by Kullback-Leibler (KL) divergence [13] between the probability distributions of the teacher and the probability distributions of the student. In this way, during training, the student model can be guided by more valuable information signals from the teacher model, therefore, is expected to have a more promising performance than training alone. This approach has shown promising results in improving model performance and generalization and speeding up convergence in MTL. For instance, We found that some works [22, 35, 12, 30, 17] attempt to use knowledge distillation to transfer the knowledge from teacher to student for multiple vision tasks in MTL. We, in particular, identify two technical challenges. 1) Most previous approaches [22, 35, 17] must train a task-specific model for each task, then load the trained task-specific models. 2) Exact logit matching of teacher and student predictions with KL divergence can interfere with the training of the student model and is sensitive to outliers, leading to less effective knowledge distillation. + +To address these challenges, we explore knowledge distillation in multi-task learning of dense prediction tasks. We present a novel framework that leverages task-specific guidance to enable effective knowledge transfer. In Figure 1, we show the difference between the existing and our methods. Since using multiple single-task models as teacher models would require an inordinate amount of memory, we only load a single multi-task model as a teacher model instead of loading multiple teacher models. We opt for one strong teacher model to reduce computational and memory costs instead of using multiple teacher models that perform a load of each task separately. + +We take inspiration from mathematical statistics methods from other domains to reduce the uncertainty in students' prediction when using KL divergence (see Figure 1). We propose a novel knowledge distillation with Cauchy-Schwarz (CS) divergence to replace the KL divergence. In addition, during the logit matching, inter-task and intra-task information are transferred from teacher to student. Specifically, we gather the corresponding predicted probabilities in a batch for all tasks, then transfer the inter-task information from teacher to student. For each task, we gather the corresponding predicted probabilities of all classes in a batch, then transfer the intra-task information from teacher to student. Our proposed knowledge distillation with the alternative match is less sensitive to small probabilities and can account for uncertainty in the student model predictions. To further close the computational and memory cost gap, we only use one multi-task teacher model during training. This MTL knowledge distillation procedure provides multiple training settings. + +![](images/4b285195a32208689a9740c062c7a136913f94aae87087d9a6b1821aade41f6b.jpg) +Figure 1: Difference between existing KD methods and our KD method. $\mathcal{F}_{st}^{T}$ means the single-task $(st)$ teacher $(T)$ model output. $\mathcal{F}_{mt}^{T}$ means the multi-task $(mt)$ teacher model output. $\mathcal{F}_{mt}^{S}$ means the multi-task $(mt)$ student $(S)$ model output. $n$ denotes the number of tasks. + +Through extensive experiments on several publicly available dense prediction datasets (i.e., NYUD-v2 and PASCAL-Context), we compare our results with state-of-the-art methods to demonstrate the effectiveness of our framework. + +In summary, our work makes the following contributions: + +- We introduce a new procedure based on knowledge distillation with an alternative match named KDAM, which leverages inter-task and intra-task information. It is less sensitive to small probabilities and can account for uncertainty in the student model predictions. +- Our new distillation procedure aims at reproducing computational and memory costs by loading a strong multi-task model as a teacher to guide student learning. +- We conduct experiments using our KDAM on two MTL of dense prediction datasets, showing the superiority under different experiment settings. + +# 2. Related Work + +Multi-task Learning of Dense Prediction. Multi-task learning for dense prediction [37, 50, 58, 31, 10, 9, 3, 52, 56, 53, 33, 28, 25, 57, 26, 27] has been an active research area in the computer vision community, with many studies exploring various aspects of joint learning for tasks such as semantic segmentation, depth estimation, surface normal estimation, saliency estimation and boundary detection. A survey work [45] shows that MTL is mainly divided into two categories: encoder-based and decoder-based architectures. The encoder-based methods, such as [19, 44, 54], use a + +shared representation from an encoder to input task-specific heads and perform multiple task predictions. NDDR-CNN Network [10] is an encoder-focused MTL model which enables automatic feature fusing at every layer from different tasks and reduces channel dimension by processing the features with a $1 \times 1$ convolutional layer before feeding the result to the next layer. Their success heavily depends on the encoder (i.e., backbone network) to learn a strong shared representation [47, 59]. However, the encoder-based methods lack task interaction information, failing to capture commonalities and differences among tasks. The decoder-based methods, such as [50, 31, 3, 56, 2], focus on improving each task by repeatedly refining the predictions through cross-task interaction and improving each task's performance. Unlike encoder-based, decoder-based architectures also exchange information during the decoding. MTFormal [51] performs cross-task reasoning and designs the cross-task attention mechanism to achieve effective feature propagation among tasks, resulting in performance improvement in MTL. [52, 56] introduces new techniques for training deeper and wider via Transformers in MTL, allowing for more efficient and accurate MTL performance. Their success depends on a strong backbone network and all relevant task interactions from different dimensions. In addition, [40] introduces a controllable dynamic multi-task architecture for dynamically adjusting the weighting of loss of each task, which allows matching the desired task preference as well as the resource constraints. We propose an KDAM, which uses a strong multi-task model as a teacher to guide the student's multi-task model learning. + +Knowledge Distillation. The objective of the Knowledge distillation [13, 1] is mainly to distill the logits from certain outputs of a teacher to a student by minimizing the KL divergence [13], where the temperature $\mathcal{T}$ factor is applied to soften the output logits. Knowledge distillation is also introduced into vision tasks, such as image classification [30, 6, 5, 18], segmentation [39, 14, 38] and detection [55, 36, 48]. Knowledge distillation has emerged as an effective technique for improving multi-task learning of dense prediction tasks. Several recent studies [22, 35, 12, 17] have explored various aspects of knowledge distillation in the context of multi-task learning, with a focus on improving model performance and efficiency. The work [8] is to distill representation from a full image to the representation predicted from a masked image to perform multiple tasks. [17] designs the selective training layers for each task using an adaptive feature distillation loss with an online task weighting scheme. This task-based feature distillation allows MTL networks to be trained in a similar manner to single-task networks. Their success depends on multiple strong teacher models to guide student model training, which can get more information from the teacher model during training. However, these distillation MTL + +models' exact logits matching of teacher and student predictions with KL divergence can interfere with student model training and become more sensitive to outliers, leading to poor knowledge distillation. In this paper, we develop an efficient distillation procedure specific to MTL of dense prediction. We use an alternative knowledge distillation strategy that leverages inter-task and intra-task information. It provides less sensitivity to small probabilities and can account for uncertainty in the student model predictions. + +# 3. Method + +# 3.1. Notations + +The input image $x_{i} \in \mathbb{R}^{H \times W \times C}$ , where $H, W,$ and $C$ are the height, width, and channel of the image feature, respectively. We use $n$ to denote the task number, with $n \in \{1, 2, \dots, N\}$ , $st$ to denote the single-task and $mt$ to denote the multi-task. Define $\mathcal{F}_{mt}^{T}$ as the multi-task teacher model and $\mathcal{F}_{st}^{T}$ as the single-task teacher model. + +# 3.2. Formulation + +The clustering regularizer loss is defined as the Kullback-Leibler (KL) [13] divergence between soft assignment $y_{\mathrm{pred}}$ and auxiliary target distribution $y_{\mathrm{true}}$ : + +$$ +\begin{array}{l} \mathcal {L} _ {\mathrm {K L - d i v}} := K L \left(y _ {\text {p r e d}}, y _ {\text {t r u e}}\right) = y _ {\text {t r u e}} \cdot \log \frac {y _ {\text {t r u e}}}{y _ {\text {p r e d}}} \tag {1} \\ = y _ {\text {t r u e}} \cdot (\log y _ {\text {t r u e}} - \log y _ {\text {p r e d}}), \\ \end{array} +$$ + +where $y_{\mathrm{pred}}$ is the output of the model and $y_{\mathrm{true}}$ is the observation labels in the dataset. KL divergence is leveraged in plain KD to transform knowledge from the strong teacher model to the student model, where $y_{\mathrm{pred}}$ and $y_{\mathrm{true}}$ are the outputs of the student model and the teacher model. The plain KD loss is represented as: + +$$ +\mathcal {L} _ {\text {p l a i n} K D} = \mathcal {T} ^ {2} \cdot \mathcal {L} _ {\mathrm {K L - d i v}} \left(P _ {S}, P _ {T}\right), \tag {2} +$$ + +where $\mathcal{T}$ is the distillation temperature factor to control the softness of logits of the softmax output. $P_{S}$ is the softmax output of student model. $P_{T}$ is the softmax output of the teacher model. The student and teacher generate the logits $\mathcal{F}^S$ and $\mathcal{F}^T$ , respectively. + +$$ +P _ {S} = \operatorname {s o f t m a x} \left(\mathcal {F} ^ {S} / \mathcal {T}\right), \quad P _ {T} = \operatorname {s o f t m a x} \left(\mathcal {F} ^ {T} / \mathcal {T}\right), \tag {3} +$$ + +# 3.3. KD Alternative Match (KDAM) + +KL divergence is a distance metric that measures the difference between the teacher's and student's probability distributions. However, it is sensitive to outliers in the data, which can result in unstable training and poor generalization. + +There are two challenges using KL divergence in plain KD. First, one issue with KL divergence in knowledge distillation is that it can be unstable and lead to vanishing + +![](images/15c56f5d5796e6dcc2d53381910089762a57892f3958db9533b1dc53001fff56.jpg) +Figure 2: Illustration of our knowledge distillation framework in MTL. Inter-task information: transmitted knowledge between the predicted probabilistic distributions on all tasks' channels of teacher and student. Intra-task information: transmitted knowledge of the probabilities of all the instances on each task. For simple purposes, We set two tasks in this figure. $N$ denotes the task number. $\mathcal{F}_{mt}^{T}$ and $\mathcal{F}_{mt}^{S}$ means the multi-task $(mt)$ teacher and student model output, respectively. + +gradients during training. This is because KL divergence involves taking the logarithm of probabilities, which can cause numerical instability when dealing with small or zero probabilities. It can make optimizing models that use KL divergence in knowledge distillation difficult. Second, KL divergence does not consider the uncertainty in the student predictions, which can lead to overconfidence and poor generalization in certain cases. This is particularly relevant in scenarios where the student model is less complex than the teacher model, as the student may not have the capacity to capture all of the information contained in the teacher's soft targets. + +To address these issues, alternative divergence measures have been proposed, named Cauchy-Schwarz (CS) divergence, which is less sensitive to small probabilities and can account for uncertainty in the student model predictions. In this way, the alternative KD tries to save more task-specific information between the teacher and student on the probabilistic distribution. + +In knowledge distillation, let $\mathcal{DS} = (x_i,y_i)$ denote the training dataset of the student network, where $x_{i}$ and $y_{i}$ are the input and the corresponding ground truth label, respectively. Let $\mathcal{DT} = (x_i,P_{T_i})$ denote the training dataset of the teacher network, where $P_{T_i}$ is the predicted probability distribution over the class labels by the teacher network for the input $x_{i}$ . Let $\mathcal{FS}: \mathcal{X} \to \mathcal{Y}$ and $\mathcal{FT}: \mathcal{X} \to \Delta^{C - 1}$ denote the student and teacher networks, respectively, where $\Delta^{C - 1}$ is the $C$ -dimensional probability simplex. + +Knowledge distillation aims to train the student network $\mathcal{F}^S$ to match the predictions of the teacher network $\mathcal{F}^T$ for the same input data. To achieve this, we minimize the CS divergence between the soft labels predicted by the teacher + +network and those predicted by the student network. The CS divergence between the soft label distributions $P_{T_i}$ and $P_{S_i}$ predicted by the teacher and student models, respectively, for the input $x_i$ is defined as: + +$$ +\mathcal {L} _ {C S} := D _ {C S} \left(P _ {S}, P _ {T}\right) = - \ln \frac {\int P _ {T _ {i}} (x) P _ {S _ {i}} (x) d x}{\sqrt {\int P _ {T _ {i}} (x) d x \int P _ {S _ {i}} (x) d x}}. \tag {4} +$$ + +Note that $D_{CS} = 0$ only for $P_S = P_T$ . Eq. 4 can improve numerical stability and the ability to account for uncertainty in student predictions. + +The inter-task information for each task. We develop an alternative inter-task comparison strategy in which the distribution of teacher and student of all tasks. The intertask information between teacher and student is defined as: + +$$ +\mathcal {L} _ {i n t e r} = \frac {1}{B} \sum_ {i = 1} ^ {B} D _ {C S} \left(P _ {S i,:}, P _ {T _ {i,:}}\right), \tag {5} +$$ + +where the $B$ denotes batch size. + +The intra-task information for each task. For intraclass information, we discuss why naive hard example mining cannot handle noise/outliers and propose a simple and effective balancing strategy for fast and robust hard example mining. As shown in Figure 2, the intra-task is defined as: + +$$ +\mathcal {L} _ {\text {i n t r a}} = \frac {1}{C} \sum_ {j = 1} ^ {C} D _ {C S} \left(P _ {S: j}, P _ {T: j}\right), \tag {6} +$$ + +where $C$ denotes the channel. + +Finally, we wrap task-independent knowledge distillation strategies into MTL. It can be formulated as follows: + +$$ +\mathcal {L} _ {C S K D} = \sum_ {n = 1} ^ {N} \left(\mathcal {L} _ {\text {i n t e r}} + \mathcal {L} _ {\text {i n t r a}}\right), \tag {7} +$$ + +where the $N$ is the task number. We sum up the $\mathcal{L}_{inter}$ and $\mathcal{L}_{intra}$ to improve the distillation performance for MTL. + +# 3.4. Training objective + +As depicted in Figure 2, our method consists of a teacher MT model, a student MT model, and a new strategy of KD. Concretely, we first train a strong MT model as a teacher model. Then we introduce a trained teacher model for the student MT model training. The plain multi-task loss function is given as: + +$$ +\mathcal {L} _ {m t} := \mathcal {L} \left(y _ {\text {t r u e}}, P _ {S}\right) = \sum_ {n = 1} ^ {N} \lambda_ {n} \mathcal {L} _ {n}, \tag {8} +$$ + +where $\lambda_{n}$ is a hyperparameter factor of the task number $n$ . + +In the multi-task knowledge distillation setting, there are a trained multi-task teacher model (i.e., $T^{mt}$ ) and a student model (i.e., $S^{mt}$ ). As a result, the KDAM overall training loss function is typically a weighted sum of the MTL loss $(\mathcal{L}_{mt})$ and the knowledge distillation loss. + +$$ +\mathcal {L} _ {\text {t o t a l}} = \alpha \cdot \mathcal {L} _ {m t} + \beta \cdot \mathcal {L} _ {C S K D} \left(P _ {S ^ {m t}}, P _ {T ^ {m t}}\right), \tag {9} +$$ + +where $\alpha$ and $\beta$ are the scale factor for balancing the losses. In this way, via the $\mathcal{L}_{CSKD}$ loss, the student to match the strong teacher network's output. + +# 4. Experiments + +We validate the superiority of our KDAM framework under two representative datasets: NYUD-v2 [42] and PASCAL-Context [7]. In Section 4.1, we provide the experimental setup and evaluation details we used for experiments. Section 4.2 presents the main qualitative and quantitative MTL results. Finally, in Section 4.3, we perform ablation studies to verify the effect of components and efficiencies of our method. + +# 4.1. Experiment setup + +NYUD-v2 dataset and metrics. NYUD-v2 comprises RGB and Depth frames 795 images are used for training and 654 images for testing. NYUD-v2 is adopted for semantic segmentation (SemSeg), depth estimation (Depth), surface normal estimation (Normal) and boundary detection (Bound) tasks by providing dense labels. The semantic segmentation labels classify each pixel in the RGB images into one of 40 object categories. Four evaluation metrics are available to evaluate the MTL model performance, which + +includes mean Intersection over Union (mIoU) for the SemSeg task, root mean square error (rmse) for the Depth task, mean Error (mErr) for the Normal task, and optimal dataset scale F-measure (odsF) for the Bound task. + +PASCAL-Context dataset and metrics. PASCAL-Context consists of 10,103 images with complex scenes, covering 400 object categories and 59 background regions. PASCAL-Context is adopted for semantic segmentation (SemSeg), human parts segmentation (PartSeg), saliency estimation (Sal), surface normal estimation (Normal), and boundary detection (Bound) tasks by pixel-level semantic labels for each image. Five evaluation metrics are available to evaluate the MTL model performance, which includes mean Intersection over Union (mIoU) for the SemSeg and PartSeg tasks, mean Error (mErr) for the Normal task, optimal dataset scale F-measure (odsF) for the Bound task, and maximum F-measure (maxF) for the Sal task. The average per-task performance drop $(\Delta_{mt})$ is used to quantify multi-task performance. $\Delta_{mt} = \frac{1}{N}\sum_{i = 1}^{N}(F_{mt,n} - F_{st,n}) / F_{st,n}\times$ $100\%$ , where mt, st and $N$ mean multi-task model, single-task baseline and task numbers. $\Delta_{mt}$ : higher is the better. + +Setting. To be universal, we perform experiments on the NYUD-v2 [42] and PASCAL-Context [7] datasets using different teacher-student pairs. The "Plain KD vs. DIST vs. Our KDAM" experiment is conducted using Swin-L [34] as a teacher model, Swin-T [34] and Swin-S [34] as student models on the NYUD-v2. On PASCAL-Context, we adopt Swin-L [34] and Swin-B [34] as teacher models, HRNet18 [43], Swin-T [34] and Swin-S [34] as student models. + +Loss weights. In our experiments, we use the algorithm in [3] to learn weights for each task over the course of training. For a fair comparison, we search the optimal hyperparameters (i.e., the loss ratio $\alpha$ , $\beta$ and the temperature $\mathcal{T}$ ) for each teacher-student pair. On NYUD-v2 and PASCAL-Context, we set $\alpha = 1.0$ , $\beta = 1.0$ in Eq. 9 using our TKD method. For plain KD [13], we set $\alpha = 1.0$ , $\beta = 1.0$ in Eq. 9 and use a default temperature $\mathcal{T} = 3$ in Eq. 2. In addition, For a fair comparison, we search the optimal hyperparameters i.e., $\beta$ and $\mathcal{T}$ . We choose a temperature set $\mathcal{T} \in [0.1, 0.5, 1, 3, 4, 8, 16]$ for an ablation study on NYUD-v2 dataset (see Table 5a & 5b). + +Baselines. Multi-task baseline uses a shared backbone network in conjunction with task-specific heads to perform the predictions for every task. We can choose different networks as backbones, such as HRNet [43] and Swin Transformer [34]. Single-task baseline uses a backbone network with a task head to conduct the predictions for a task. + +# 4.2. Results + +NYUD-v2 dataset. We investigate the effectiveness of our KDAM on NYUD-v2 dataset. We first train a multi-task baseline model of Swin-L for our knowledge distillation procedure. Then we load the well trained Swin-L model + +Table 1: We report the comparison of the MTL models with the state-of-the-art on NYUD-v2 dataset. $\downarrow$ : lower is better. ’↑’: higher is better. ${\Delta }_{mt}$ denotes the average per-task performance drop. Swin-◇ indicates that the specific Swin model is uncertain. Gray blocks mean the multi-task baseline using our knowledge distillation method. + +
ModelBackboneParams (M)GFLOPs (G)SemSeg (mIoU)↑Depth (rmse)↓Normal (mErr)↓Bound (odsF)↑Δmt[%]↑
single-task (ST) baselineHRNet1816.0940.9338.020.610420.9476.220.00
multi-task (MT) baselineHRNet184.5217.5936.350.628421.0276.36-1.89
MT+KDAM (Ours)HRNet184.5217.5936.850.625021.0476.10-0.73
Cross-Stitch[37]HRNet184.5217.5936.340.629020.8876.38-1.75
Pad-Net[50]HRNet185.0225.1836.700.626420.8576.50-1.33
PAP[58]HRNet184.5453.0436.720.617820.8276.42-0.95
PSD[31]HRNet184.7121.1036.690.624620.8776.42-1.30
NDDR-CNN[10]HRNet184.5918.6836.720.628820.8976.32-1.51
MTI-Net[46]HRNet1812.5619.1436.610.627020.8576.38-1.44
ATRC[3]HRNet185.0625.7638.900.601020.4876.341.56
ATRC+KDAM (Ours)HRNet185.0625.7639.300.591920.7276.912.05
single-task (ST) baselineSwin-T115.08161.2542.920.610420.9476.220.00
multi-task (MT) baselineSwin-T32.5096.2938.780.631221.0575.60-3.74
MT+KDAM (Ours)Swin-T32.5096.2944.340.60121.0376.41.1
single-task (ST) baselineSwin-S200.33242.6348.920.580420.9477.200.00
multi-task (MT) baselineSwin-S53.82116.6347.900.605321.1776.90-1.96
MTFormer[51]Swin-◇64.03117.7350.560.4830--4.12
MT+KDAM (Ours)Swin-S53.82116.6349.410.56420.6077.31.38
+ +Table 2: Comparison results of DeMT and InvPT MTL model with our KDAM method. ${}^{\prime } +$ ’ means performance increase. + +
Network structureAccuracy multi-task student modelsAccuracy of our KDAM
TeacherStudentSemSeg↑Depth↓Normal↓Bound↑SemSeg↑Depth↓Normal↓Bound↑
Swin-LInvPT-T [56]44.270.558920.4676.1044.93 (+ 0.66)0.5577 (+ 0.0012)20.27 (+ 0.19)76.2 (+ 0.1)
Swin-LDeMT-T[53]46.360.587120.6576.9047.07 (+ 0.71)0.5855 (+ 0.0016)20.62 (+ 0.03)76.9 (+ 0.0)
Swin-LDeMT-S[53]51.500.547420.0278.1051.91 (+ 0.41)0.5512 (- 0.0038)20.01 (+ 0.01)78.1 (+ 0.0)
+ +as a teacher model for student model training. In Table 1, ours surpasses the HRNet18, Swin-T and Swin-S multi-task baselines by more than $1.16\%$ , $4.84\%$ and $3.34\%$ (average per-task performance drop $\Delta_{mt}$ ), respectively. The baseline model coupled with the improvement in $\Delta_{mt}$ metric by our distillation method demonstrates the effectiveness of distillation. Note that These results are only conducted on the outputs of the multi-task baseline model and have a similar computational cost as the baseline model. Nevertheless, it even achieves better performance compared to those carefully designed methods. As shown in Table 1, although ATRC achieves better performance, it brings much more parameters and computation compared to the MT baseline. By contrast, our method based on distillation is cost-free. We also conduct experiments based on DeMT [53] and InvPT [56] and compare using our KD strategy with the DeMT-T, DeMT-S and InvPT-T. As shown in Table 2, our KDAM is outperformed by DeMT-T +0.71 mIoU and DeMT-S by +0.41 mIoU on SemSeg task. Applying our + +distillation recipe in combination with the DeMT configuration to prove our method is effective. We can see that all the added KDAM, regardless of DeMT or InvPT, improves the performance. We observe that our distillation with an alternative match leads the state-of-the-art performance. + +PASCAL-Context. We also use the multi-task baseline model of Swin-L as a teacher model. We further investigate the effectiveness of our KDAM for dense predictions on PASCAL-Context dataset. We train HRNet18, Swin-T and Swin-S baseline with our distillation method. As shown in Table 3, our KDAM outperforms all the previous MTL methods on five dense predictions and the average per-task performance drops $\Delta_{mt}$ . It is worth mentioning that using a strong Swin-L teacher fails to give HRNet18 baseline an intuitive performance increase. We find that the performance of SemSeg task tends to get better as the student's backbone increases, which shows the effectiveness of our approach in segmentation tasks. Results suggest that our method can learn more semantic features for dense predictions. + +Table 3: We report a comparison of the MTL models with the state-of-the-art on PASCAL-Context dataset. $\downarrow$ : lower is better. $\uparrow$ : higher is better. ${\Delta }_{m}$ denotes the average per-task performance drop (higher is better). Gray blocks mean the multi-task baseline using our knowledge distillation method. + +
ModelBackboneSemSeg (mIoU)↑PartSeg (mIoU)↑Sal (maxF)↑Normal (mErr)↓Bound (odsF)↑Δmt [%]↑
single-task (ST) baselineHRNet1862.2361.6685.0813.6973.060.00
multi-task (MT) baselineHRNet1851.4857.2383.4314.1069.76-6.77
MT+KDAM (Ours)HRNet1851.9157.6383.9213.9070.1-5.06
PAD-Net [50]HRNet1853.6059.6065.8015.372.50-4.41
ATRC [3]HRNet1857.8957.3383.7713.9969.74-4.45
MQTransformer[52]HRNet1858.9157.4383.7814.1769.80-4.20
ATRC+KDAM (Ours)HRNet1858.9257.5183.8713.9769.75-3.94
single-task (ST) baselineSwin-T67.8156.3282.1814.8170.900.00
multi-task (MT) baselineSwin-T64.7453.2576.8815.8669.00-3.23
MT+KDAM (Ours)Swin-T64.8153.8081.7215.0669.5-2.3
single-task (ST) baselineSwin-S70.8359.7182.6415.1371.200.00
multi-task (MT) baselineSwin-S68.1056.2080.6416.0970.20-3.97
MT+KDAM (Ours)Swin-S68.8056.6281.9115.6170.4-2.54
+ +Table 4: We report a comparison of the multi-task (MT) baseline models using different KD strategies on NYUD-v2 dataset. MT and ST denote multi-task and single-task respectively. Gray blocks mean the MT baseline using our method. + +
Teacher (Student)MetricsAccuracy ST modelsAccuracy MT modelsPlain KDDIST KDOur KDAM
TeacherStudentTeacherStudentStudent (MT)Student (MT)Student(MT)
Swin-L (Swin-T)SemSeg↑56.4642.9254.5338.7844.4843.2744.54
Depth↓0.5080.6100.5320.6310.6040.5990.601
Normal↓19.3820.9419.5121.0521.0321.0221.03
Bound↑78.876.2278.375.6076.8076.5076.40
Δmt[%]↑---2.36-3.741.080.581.10
Swin-L (Swin-S)SemSeg↑56.4648.9254.5347.9049.2049.3949.41
Depth↓0.5080.5800.5320.6050.5710.5600.564
Normal↓19.3820.9419.5121.1720.5820.5120.60
Bound↑78.877.2078.376.9077.2077.277.3
Δmt[%]↑---2.36-1.960.971.61.38
Swin-B (Swin-T)SemSeg↑53.0142.9251.4438.7843.8444.0644.52
Depth↓0.5520.6100.5810.6310.6030.5960.592
Normal↓19.3420.9420.4421.0521.1921.0821.09
Bound↑78.0076.2277.8075.6076.6076.7076.6
Δmt[%]↑---3.2-3.740.491.071.47
+ +# 4.3. Ablation Studies + +Distillation with alternative match helps minimize the performance gap between teacher and student. In Table 4, we first conduct experiments to compare our KDAM with plain KD [13] and DIST KD [16] at different student and teacher model sizes. We compare three types of teacher-student pairs: Swin-L: Swin-T, Swin-L: Swin-S and Swin-B: Swin-T. As shown in Table 4 (Swin-T (Swin-L) and Swin-T (Swin-B) rows), when the teacher goes larger, the Swin-T students MTL performance $\Delta_{mt}$ perform even worse than that with a medium-sized Swin-B teacher. We observe that it is not the fact that a larger teacher model leads to better performance. The plain KD using KL di + +vergence loss can help minimize the performance gap between strong teachers and students. In addition, our KDAM showed an increasing trend with strong teachers and a more significant improvement compared to the other KD strategies, suggesting that our KDAM better handles the differences between student and strong teacher performance. Our KDAM can significantly outperform existing knowledge distillation methods on MTL of dense predictions. The results in Table 4 highlight that our KDAM is applied for capturing inter-task and intra-task information between the teacher model and the student model of each task, and thus learns more "dark knowledge" for effective distillation. + +Ablation on hyperparameters $\mathcal{T}\& \beta$ . We compare the ef- + +Table 5: Ablation experiments of the optimal hyperparameters temperature factor $\mathcal{T}$ and the loss scale factor $\beta$ of the plain KD (Eq. 2) using a Swin-L as teacher model and Swin-T as student model on NYUD-v2 dataset. +(a) Ablation on $\beta$ in Eq. 9 using $\mathcal{T} = 3$ and $\alpha = 1$ . + +
KD styleβAccuracy multi-task student models
SemSeg↑Depth↓Normal↓Bound↑
Plain KD0.144.420.600121.1676.2
0.544.900.601521.0976.3
144.470.604421.0376.2
244.610.597521.0076.2
444.090.601721.0676.1
844.420.601821.0776.2
1643.530.610421.3476.3
+ +Table 6: Ablation on part of the loss. The student and teacher models are Swin-T and Swin-L, respectively. "w/" indicates "with". + +
MethodAccuracy multi-task student model
SemSeg↑Depth↓Normal↓Bound↑
MT baseline38.780.631221.0575.60
Ours w/ intra43.310.606821.4776.00
Ours w/ inter44.060.596421.0876.50
Ours w/ inter&intra44.340.601221.0376.70
+ +fect of the number of temperature factor $\mathcal{T}$ and the distillation loss scale factor $\beta$ in Table 5a & 5b. We find that having a larger temperature of plain KD improves the performance slightly, whereas increasing the number of distillation loss scale factors does not improve the performance. + +Ablation on part of the loss. We compare three different methods named "Ours w/ inter," "Ours w/ intra" and "Ours w/ inter & intra" in Table 6. To validate the effectiveness of each loss, we conduct experiments to train students with these methods separately. For all tasks, the intrinsic inter-task and intra-task variance of the semantic similarities is actually also informative. We can see that our KDAM can achieve a performance improvement, which proves the effectiveness of the inter-task and intra-task. Our knowledge distillation with an alternative match is applied to capture inter-task and intra-task information between the teacher and the student. The results show our distillation method can learn more "dark knowledge" for effective distillation. + +Ablation on training epochs. The default setting for the number of training epochs for teachers and students is 400. We independently train teacher models and pick them up at epoch $200^{th}$ and $400^{th}$ . In Table 7, we conduct ablation experiments of the training epochs using trained Swin-L as a teacher on NYUD-v2 dataset. The teacher model is trained at the $400^{th}$ epoch. The student model of Swin-T are selected at the $50^{th}, 100^{th}, 200^{th}, 300^{th}, 400^{th}, 500^{th}$ + +(b) Ablation on temperatures $\mathcal{T}$ in Eq. 2 using $\alpha = 1$ and $\beta = 1$ . + +
KD styleTAccuracy multi-task student models
SemSeg↑Depth↓Normal↓Bound↑
Plain KD0.144.270.607621.1576.1
0.544.520.605421.1676.2
144.830.596921.1076.3
344.470.604421.0376.2
444.210.601421.0576.1
845.350.601221.0476.5
1644.690.605021.0876.1
+ +Table 7: Ablation on the training epochs. The student and teacher models are Swin-T and Swin-L, respectively. + +
ModelepochAccuracy multi-task student model
SemSeg↑Depth↓Normal↓Bound↑
KDAM10034.130.671523.2675.3
20042.330.628521.8676.0
30044.140.615621.2876.2
40044.340.601021.0376.2
60045.000.595520.6976.4
+ +and $600^{th}$ epochs. Our multi-task student model reaches 45.00 (mIoU, Semseg) and 0.5955 (rms, Depth) after 600 epochs. We observe that the multi-task student's accuracy increases monotonically with the increase of training epoch. Noticeably, the trained strong teacher model is used for improving student efficiency, while when the student model is not trained still enough leads to poor performance. + +# 5. Conclusion + +This paper introduces a new knowledge distillation procedure with an alternative match (KDAM) for MTL of dense prediction based on two simple design principles. For memory and training efficiency, we use a single strong multi-task model as a teacher during training instead of multiple teachers, as widely adopted in existing studies. Furthermore, we employ a less sensitive CS divergence instead of the KL divergence and propose a CS distillation loss accordingly. 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How to successfully apply knowledge distillation into MTL to improve training efficiency and model performance is still a challenging problem. In this paper, we introduce a new knowledge distillation procedure with an alternative match for MTL of dense prediction based on two simple design principles. First, for memory and training efficiency, we use a single strong multitask model as a teacher during training instead of multiple teachers, as widely adopted in existing studies. Second, we employ a less sensitive Cauchy-Schwarz (CS) divergence instead of the Kullback-Leibler (KL) divergence and propose a CS distillation loss accordingly. With the less sensitive divergence, our knowledge distillation with an alternative match is applied for capturing inter-task and intratask information between the teacher model and the student model of each task, thereby learning more \"dark knowledge\" for effective distillation. We conducted extensive experiments on dense prediction datasets, including NYUD-v2 and PASCAL-Context, for multiple vision tasks, such as semantic segmentation, human parts segmentation, depth estimation, surface normal estimation, and boundary detection. The results show that our proposed method decidedly improves model performance and the practical inference efficiency." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 623, + 124, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 623, + 124, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 623, + 124, + 635 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 45, + 643, + 279, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 643, + 279, + 714 + ], + "spans": [ + { + "bbox": [ + 45, + 643, + 279, + 714 + ], + "type": "text", + "content": "Multi-task learning (MTL) has become an increasingly popular approach in the field of computer vision, where the objective is to train a single model to perform multiple tasks simultaneously. MTL can provide several advantages over traditional single-task learning, including improved efficiency and generalization. First, the shared feature repre" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 297, + 277, + 532, + 440 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 277, + 532, + 440 + ], + "spans": [ + { + "bbox": [ + 297, + 277, + 532, + 440 + ], + "type": "text", + "content": "sentations can be learned more efficiently than task-specific representations, reducing the overall training time compared to training multiple models independently. Second, the shared feature representations learned across tasks can capture more generalizable information in the data, leading to improved performance on all tasks. For those reasons, the MTL approach has been used extensively in various machine learning problems, such as natural language processing [11], computer vision [3] and speech recognition [4]. Specifically, in this paper, we focus on dense (pixel-wise) prediction vision tasks [49, 15, 23, 41, 20, 21, 29, 48], such as semantic segmentation, instance segmentation, depth estimation, surface normal estimation, saliency estimation, object detection and boundary detection from images." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 296, + 445, + 532, + 644 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 445, + 532, + 644 + ], + "spans": [ + { + "bbox": [ + 296, + 445, + 532, + 644 + ], + "type": "text", + "content": "A march of works [32, 46, 9, 3, 52, 2, 56, 53] aims to develop novel MTL architectures and construct efficient shared representation in the multi-taskdense prediction field, which leverages the encoder-decoder architecture. In these frameworks, an encoder is considered to generate a shared feature and then use a decoder to perform multi-task of dense predictions. In the pursuit of better performance, current MTL models are often designed to be deeper and wider, resulting in increasingly larger models. [3, 56] and [53, 24] demonstrate that better performance can be obtained by utilizing a larger backbone network. However, such a heavy model can be more demanding for computation and storage. It has been challenging to design an effective MTL framework that can learn these tasks efficiently. In this paper, we pose and study the question, how can the knowledge from a large size MTL model be transferred to a small MTL model without increasing its size?" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 296, + 648, + 532, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 648, + 532, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 648, + 532, + 730 + ], + "type": "text", + "content": "Recently, knowledge distillation (KD) [13] has been explored as a method to improve the MTL of dense prediction tasks, such as semantic segmentation, depth estimation, and surface normal prediction. Some studies [30, 12, 16, 1] leverage the unique logit of each task to provide task-specific information to the student model during knowledge transfer. The essence of knowledge distillation lies" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 76, + 42, + 119, + 72 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 76, + 42, + 119, + 72 + ], + "spans": [ + { + "bbox": [ + 76, + 42, + 119, + 72 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 151, + 41, + 470, + 73 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 151, + 41, + 470, + 73 + ], + "spans": [ + { + "bbox": [ + 151, + 41, + 470, + 73 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 57, + 719, + 133, + 730 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 57, + 719, + 133, + 730 + ], + "spans": [ + { + "bbox": [ + 57, + 719, + 133, + 730 + ], + "type": "text", + "content": "*Corresponding author." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 276, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 301, + 756 + ], + "type": "text", + "content": "21550" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 281, + 362 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 281, + 362 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 281, + 362 + ], + "type": "text", + "content": "in translating knowledge from the teacher model (large model) to the student model (small model) by mimicking the teacher model's outputs. Typically, knowledge distillation methods use the logits matching by Kullback-Leibler (KL) divergence [13] between the probability distributions of the teacher and the probability distributions of the student. In this way, during training, the student model can be guided by more valuable information signals from the teacher model, therefore, is expected to have a more promising performance than training alone. This approach has shown promising results in improving model performance and generalization and speeding up convergence in MTL. For instance, We found that some works [22, 35, 12, 30, 17] attempt to use knowledge distillation to transfer the knowledge from teacher to student for multiple vision tasks in MTL. We, in particular, identify two technical challenges. 1) Most previous approaches [22, 35, 17] must train a task-specific model for each task, then load the trained task-specific models. 2) Exact logit matching of teacher and student predictions with KL divergence can interfere with the training of the student model and is sensitive to outliers, leading to less effective knowledge distillation." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 365, + 279, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 365, + 279, + 506 + ], + "spans": [ + { + "bbox": [ + 45, + 365, + 279, + 506 + ], + "type": "text", + "content": "To address these challenges, we explore knowledge distillation in multi-task learning of dense prediction tasks. We present a novel framework that leverages task-specific guidance to enable effective knowledge transfer. In Figure 1, we show the difference between the existing and our methods. Since using multiple single-task models as teacher models would require an inordinate amount of memory, we only load a single multi-task model as a teacher model instead of loading multiple teacher models. We opt for one strong teacher model to reduce computational and memory costs instead of using multiple teacher models that perform a load of each task separately." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 508, + 281, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 508, + 281, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 508, + 281, + 730 + ], + "type": "text", + "content": "We take inspiration from mathematical statistics methods from other domains to reduce the uncertainty in students' prediction when using KL divergence (see Figure 1). We propose a novel knowledge distillation with Cauchy-Schwarz (CS) divergence to replace the KL divergence. In addition, during the logit matching, inter-task and intra-task information are transferred from teacher to student. Specifically, we gather the corresponding predicted probabilities in a batch for all tasks, then transfer the inter-task information from teacher to student. For each task, we gather the corresponding predicted probabilities of all classes in a batch, then transfer the intra-task information from teacher to student. Our proposed knowledge distillation with the alternative match is less sensitive to small probabilities and can account for uncertainty in the student model predictions. To further close the computational and memory cost gap, we only use one multi-task teacher model during training. This MTL knowledge distillation procedure provides multiple training settings." + } + ] + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 299, + 106, + 542, + 266 + ], + "blocks": [ + { + "bbox": [ + 299, + 106, + 542, + 266 + ], + "lines": [ + { + "bbox": [ + 299, + 106, + 542, + 266 + ], + "spans": [ + { + "bbox": [ + 299, + 106, + 542, + 266 + ], + "type": "image", + "image_path": "4b285195a32208689a9740c062c7a136913f94aae87087d9a6b1821aade41f6b.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "lines": [ + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "spans": [ + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "text", + "content": "Figure 1: Difference between existing KD methods and our KD method. " + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{st}^{T}" + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "text", + "content": " means the single-task " + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "inline_equation", + "content": "(st)" + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "text", + "content": " teacher " + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "inline_equation", + "content": "(T)" + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "text", + "content": " model output. " + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{mt}^{T}" + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "text", + "content": " means the multi-task " + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "inline_equation", + "content": "(mt)" + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "text", + "content": " teacher model output. " + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{mt}^{S}" + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "text", + "content": " means the multi-task " + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "inline_equation", + "content": "(mt)" + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "text", + "content": " student " + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "inline_equation", + "content": "(S)" + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "text", + "content": " model output. " + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 296, + 273, + 532, + 326 + ], + "type": "text", + "content": " denotes the number of tasks." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "spans": [ + { + "bbox": [ + 296, + 346, + 530, + 404 + ], + "type": "text", + "content": "Through extensive experiments on several publicly available dense prediction datasets (i.e., NYUD-v2 and PASCAL-Context), we compare our results with state-of-the-art methods to demonstrate the effectiveness of our framework." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 297, + 405, + 530, + 428 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 405, + 530, + 428 + ], + "spans": [ + { + "bbox": [ + 297, + 405, + 530, + 428 + ], + "type": "text", + "content": "In summary, our work makes the following contributions:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 308, + 434, + 530, + 578 + ], + "type": "list", + "angle": 0, + "index": 10, + "blocks": [ + { + "bbox": [ + 308, + 434, + 530, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 434, + 530, + 494 + ], + "spans": [ + { + "bbox": [ + 308, + 434, + 530, + 494 + ], + "type": "text", + "content": "- We introduce a new procedure based on knowledge distillation with an alternative match named KDAM, which leverages inter-task and intra-task information. It is less sensitive to small probabilities and can account for uncertainty in the student model predictions." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 308, + 500, + 530, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 500, + 530, + 536 + ], + "spans": [ + { + "bbox": [ + 308, + 500, + 530, + 536 + ], + "type": "text", + "content": "- Our new distillation procedure aims at reproducing computational and memory costs by loading a strong multi-task model as a teacher to guide student learning." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 308, + 542, + 530, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 542, + 530, + 578 + ], + "spans": [ + { + "bbox": [ + 308, + 542, + 530, + 578 + ], + "type": "text", + "content": "- We conduct experiments using our KDAM on two MTL of dense prediction datasets, showing the superiority under different experiment settings." + } + ] + } + ], + "index": 9 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 297, + 593, + 381, + 606 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 593, + 381, + 606 + ], + "spans": [ + { + "bbox": [ + 297, + 593, + 381, + 606 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 612, + 531, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 612, + 531, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 612, + 531, + 730 + ], + "type": "text", + "content": "Multi-task Learning of Dense Prediction. Multi-task learning for dense prediction [37, 50, 58, 31, 10, 9, 3, 52, 56, 53, 33, 28, 25, 57, 26, 27] has been an active research area in the computer vision community, with many studies exploring various aspects of joint learning for tasks such as semantic segmentation, depth estimation, surface normal estimation, saliency estimation and boundary detection. A survey work [45] shows that MTL is mainly divided into two categories: encoder-based and decoder-based architectures. The encoder-based methods, such as [19, 44, 54], use a" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "text", + "content": "21551" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 45, + 106, + 281, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 106, + 281, + 456 + ], + "spans": [ + { + "bbox": [ + 45, + 106, + 281, + 456 + ], + "type": "text", + "content": "shared representation from an encoder to input task-specific heads and perform multiple task predictions. NDDR-CNN Network [10] is an encoder-focused MTL model which enables automatic feature fusing at every layer from different tasks and reduces channel dimension by processing the features with a " + }, + { + "bbox": [ + 45, + 106, + 281, + 456 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 45, + 106, + 281, + 456 + ], + "type": "text", + "content": " convolutional layer before feeding the result to the next layer. Their success heavily depends on the encoder (i.e., backbone network) to learn a strong shared representation [47, 59]. However, the encoder-based methods lack task interaction information, failing to capture commonalities and differences among tasks. The decoder-based methods, such as [50, 31, 3, 56, 2], focus on improving each task by repeatedly refining the predictions through cross-task interaction and improving each task's performance. Unlike encoder-based, decoder-based architectures also exchange information during the decoding. MTFormal [51] performs cross-task reasoning and designs the cross-task attention mechanism to achieve effective feature propagation among tasks, resulting in performance improvement in MTL. [52, 56] introduces new techniques for training deeper and wider via Transformers in MTL, allowing for more efficient and accurate MTL performance. Their success depends on a strong backbone network and all relevant task interactions from different dimensions. In addition, [40] introduces a controllable dynamic multi-task architecture for dynamically adjusting the weighting of loss of each task, which allows matching the desired task preference as well as the resource constraints. We propose an KDAM, which uses a strong multi-task model as a teacher to guide the student's multi-task model learning." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 462, + 281, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 462, + 281, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 462, + 281, + 730 + ], + "type": "text", + "content": "Knowledge Distillation. The objective of the Knowledge distillation [13, 1] is mainly to distill the logits from certain outputs of a teacher to a student by minimizing the KL divergence [13], where the temperature " + }, + { + "bbox": [ + 45, + 462, + 281, + 730 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 45, + 462, + 281, + 730 + ], + "type": "text", + "content": " factor is applied to soften the output logits. Knowledge distillation is also introduced into vision tasks, such as image classification [30, 6, 5, 18], segmentation [39, 14, 38] and detection [55, 36, 48]. Knowledge distillation has emerged as an effective technique for improving multi-task learning of dense prediction tasks. Several recent studies [22, 35, 12, 17] have explored various aspects of knowledge distillation in the context of multi-task learning, with a focus on improving model performance and efficiency. The work [8] is to distill representation from a full image to the representation predicted from a masked image to perform multiple tasks. [17] designs the selective training layers for each task using an adaptive feature distillation loss with an online task weighting scheme. This task-based feature distillation allows MTL networks to be trained in a similar manner to single-task networks. Their success depends on multiple strong teacher models to guide student model training, which can get more information from the teacher model during training. However, these distillation MTL" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 296, + 106, + 532, + 212 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 106, + 532, + 212 + ], + "spans": [ + { + "bbox": [ + 296, + 106, + 532, + 212 + ], + "type": "text", + "content": "models' exact logits matching of teacher and student predictions with KL divergence can interfere with student model training and become more sensitive to outliers, leading to poor knowledge distillation. In this paper, we develop an efficient distillation procedure specific to MTL of dense prediction. We use an alternative knowledge distillation strategy that leverages inter-task and intra-task information. It provides less sensitivity to small probabilities and can account for uncertainty in the student model predictions." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 297, + 221, + 352, + 234 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 221, + 352, + 234 + ], + "spans": [ + { + "bbox": [ + 297, + 221, + 352, + 234 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 297, + 240, + 364, + 251 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 240, + 364, + 251 + ], + "spans": [ + { + "bbox": [ + 297, + 240, + 364, + 251 + ], + "type": "text", + "content": "3.1. Notations" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "spans": [ + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "text", + "content": "The input image " + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "inline_equation", + "content": "x_{i} \\in \\mathbb{R}^{H \\times W \\times C}" + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "inline_equation", + "content": "H, W," + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "text", + "content": " are the height, width, and channel of the image feature, respectively. We use " + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "text", + "content": " to denote the task number, with " + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "inline_equation", + "content": "n \\in \\{1, 2, \\dots, N\\}" + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "inline_equation", + "content": "st" + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "text", + "content": " to denote the single-task and " + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "inline_equation", + "content": "mt" + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "text", + "content": " to denote the multi-task. Define " + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{mt}^{T}" + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "text", + "content": " as the multi-task teacher model and " + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{st}^{T}" + }, + { + "bbox": [ + 296, + 256, + 532, + 329 + ], + "type": "text", + "content": " as the single-task teacher model." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 297, + 335, + 377, + 346 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 335, + 377, + 346 + ], + "spans": [ + { + "bbox": [ + 297, + 335, + 377, + 346 + ], + "type": "text", + "content": "3.2. Formulation" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 296, + 352, + 531, + 389 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 352, + 531, + 389 + ], + "spans": [ + { + "bbox": [ + 296, + 352, + 531, + 389 + ], + "type": "text", + "content": "The clustering regularizer loss is defined as the Kullback-Leibler (KL) [13] divergence between soft assignment " + }, + { + "bbox": [ + 296, + 352, + 531, + 389 + ], + "type": "inline_equation", + "content": "y_{\\mathrm{pred}}" + }, + { + "bbox": [ + 296, + 352, + 531, + 389 + ], + "type": "text", + "content": " and auxiliary target distribution " + }, + { + "bbox": [ + 296, + 352, + 531, + 389 + ], + "type": "inline_equation", + "content": "y_{\\mathrm{true}}" + }, + { + "bbox": [ + 296, + 352, + 531, + 389 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 317, + 397, + 530, + 423 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 397, + 530, + 423 + ], + "spans": [ + { + "bbox": [ + 317, + 397, + 530, + 423 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {L} _ {\\mathrm {K L - d i v}} := K L \\left(y _ {\\text {p r e d}}, y _ {\\text {t r u e}}\\right) = y _ {\\text {t r u e}} \\cdot \\log \\frac {y _ {\\text {t r u e}}}{y _ {\\text {p r e d}}} \\tag {1} \\\\ = y _ {\\text {t r u e}} \\cdot (\\log y _ {\\text {t r u e}} - \\log y _ {\\text {p r e d}}), \\\\ \\end{array}", + "image_path": "2815591410f9d87343c764181ff9c1f9d8d8585301f4007582fb129e4ff066c8.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 296, + 431, + 531, + 501 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 431, + 531, + 501 + ], + "spans": [ + { + "bbox": [ + 296, + 431, + 531, + 501 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 296, + 431, + 531, + 501 + ], + "type": "inline_equation", + "content": "y_{\\mathrm{pred}}" + }, + { + "bbox": [ + 296, + 431, + 531, + 501 + ], + "type": "text", + "content": " is the output of the model and " + }, + { + "bbox": [ + 296, + 431, + 531, + 501 + ], + "type": "inline_equation", + "content": "y_{\\mathrm{true}}" + }, + { + "bbox": [ + 296, + 431, + 531, + 501 + ], + "type": "text", + "content": " is the observation labels in the dataset. KL divergence is leveraged in plain KD to transform knowledge from the strong teacher model to the student model, where " + }, + { + "bbox": [ + 296, + 431, + 531, + 501 + ], + "type": "inline_equation", + "content": "y_{\\mathrm{pred}}" + }, + { + "bbox": [ + 296, + 431, + 531, + 501 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 431, + 531, + 501 + ], + "type": "inline_equation", + "content": "y_{\\mathrm{true}}" + }, + { + "bbox": [ + 296, + 431, + 531, + 501 + ], + "type": "text", + "content": " are the outputs of the student model and the teacher model. The plain KD loss is represented as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 343, + 509, + 530, + 522 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 509, + 530, + 522 + ], + "spans": [ + { + "bbox": [ + 343, + 509, + 530, + 522 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {p l a i n} K D} = \\mathcal {T} ^ {2} \\cdot \\mathcal {L} _ {\\mathrm {K L - d i v}} \\left(P _ {S}, P _ {T}\\right), \\tag {2}", + "image_path": "babf826b3bb666826c8a79097fc2a76e7cf21f9dba7029f2bcffb7b1ae0ee2c0.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "spans": [ + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "type": "text", + "content": " is the distillation temperature factor to control the softness of logits of the softmax output. " + }, + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "type": "inline_equation", + "content": "P_{S}" + }, + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "type": "text", + "content": " is the softmax output of student model. " + }, + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "type": "inline_equation", + "content": "P_{T}" + }, + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "type": "text", + "content": " is the softmax output of the teacher model. The student and teacher generate the logits " + }, + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "type": "inline_equation", + "content": "\\mathcal{F}^S" + }, + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "type": "inline_equation", + "content": "\\mathcal{F}^T" + }, + { + "bbox": [ + 296, + 531, + 530, + 590 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 308, + 596, + 530, + 611 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 596, + 530, + 611 + ], + "spans": [ + { + "bbox": [ + 308, + 596, + 530, + 611 + ], + "type": "interline_equation", + "content": "P _ {S} = \\operatorname {s o f t m a x} \\left(\\mathcal {F} ^ {S} / \\mathcal {T}\\right), \\quad P _ {T} = \\operatorname {s o f t m a x} \\left(\\mathcal {F} ^ {T} / \\mathcal {T}\\right), \\tag {3}", + "image_path": "f662e4f49cd90da6d6e5e3c837352c2cddb85a5f70eeab9d6e2466d2c97e598e.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 297, + 618, + 465, + 631 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 618, + 465, + 631 + ], + "spans": [ + { + "bbox": [ + 297, + 618, + 465, + 631 + ], + "type": "text", + "content": "3.3. KD Alternative Match (KDAM)" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 296, + 636, + 530, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 636, + 530, + 693 + ], + "spans": [ + { + "bbox": [ + 296, + 636, + 530, + 693 + ], + "type": "text", + "content": "KL divergence is a distance metric that measures the difference between the teacher's and student's probability distributions. However, it is sensitive to outliers in the data, which can result in unstable training and poor generalization." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 296, + 695, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 695, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 695, + 530, + 730 + ], + "type": "text", + "content": "There are two challenges using KL divergence in plain KD. First, one issue with KL divergence in knowledge distillation is that it can be unstable and lead to vanishing" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 301, + 756 + ], + "type": "text", + "content": "21552" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 73, + 107, + 505, + 273 + ], + "blocks": [ + { + "bbox": [ + 73, + 107, + 505, + 273 + ], + "lines": [ + { + "bbox": [ + 73, + 107, + 505, + 273 + ], + "spans": [ + { + "bbox": [ + 73, + 107, + 505, + 273 + ], + "type": "image", + "image_path": "15c56f5d5796e6dcc2d53381910089762a57892f3958db9533b1dc53001fff56.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 284, + 530, + 333 + ], + "lines": [ + { + "bbox": [ + 45, + 284, + 530, + 333 + ], + "spans": [ + { + "bbox": [ + 45, + 284, + 530, + 333 + ], + "type": "text", + "content": "Figure 2: Illustration of our knowledge distillation framework in MTL. Inter-task information: transmitted knowledge between the predicted probabilistic distributions on all tasks' channels of teacher and student. Intra-task information: transmitted knowledge of the probabilities of all the instances on each task. For simple purposes, We set two tasks in this figure. " + }, + { + "bbox": [ + 45, + 284, + 530, + 333 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 45, + 284, + 530, + 333 + ], + "type": "text", + "content": " denotes the task number. " + }, + { + "bbox": [ + 45, + 284, + 530, + 333 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{mt}^{T}" + }, + { + "bbox": [ + 45, + 284, + 530, + 333 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 284, + 530, + 333 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{mt}^{S}" + }, + { + "bbox": [ + 45, + 284, + 530, + 333 + ], + "type": "text", + "content": " means the multi-task " + }, + { + "bbox": [ + 45, + 284, + 530, + 333 + ], + "type": "inline_equation", + "content": "(mt)" + }, + { + "bbox": [ + 45, + 284, + 530, + 333 + ], + "type": "text", + "content": " teacher and student model output, respectively." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 45, + 351, + 279, + 492 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 351, + 279, + 492 + ], + "spans": [ + { + "bbox": [ + 45, + 351, + 279, + 492 + ], + "type": "text", + "content": "gradients during training. This is because KL divergence involves taking the logarithm of probabilities, which can cause numerical instability when dealing with small or zero probabilities. It can make optimizing models that use KL divergence in knowledge distillation difficult. Second, KL divergence does not consider the uncertainty in the student predictions, which can lead to overconfidence and poor generalization in certain cases. This is particularly relevant in scenarios where the student model is less complex than the teacher model, as the student may not have the capacity to capture all of the information contained in the teacher's soft targets." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 493, + 279, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 493, + 279, + 574 + ], + "spans": [ + { + "bbox": [ + 45, + 493, + 279, + 574 + ], + "type": "text", + "content": "To address these issues, alternative divergence measures have been proposed, named Cauchy-Schwarz (CS) divergence, which is less sensitive to small probabilities and can account for uncertainty in the student model predictions. In this way, the alternative KD tries to save more task-specific information between the teacher and student on the probabilistic distribution." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "spans": [ + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "text", + "content": "In knowledge distillation, let " + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "inline_equation", + "content": "\\mathcal{DS} = (x_i,y_i)" + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "text", + "content": " denote the training dataset of the student network, where " + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "inline_equation", + "content": "x_{i}" + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "inline_equation", + "content": "y_{i}" + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "text", + "content": " are the input and the corresponding ground truth label, respectively. Let " + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "inline_equation", + "content": "\\mathcal{DT} = (x_i,P_{T_i})" + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "text", + "content": " denote the training dataset of the teacher network, where " + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "inline_equation", + "content": "P_{T_i}" + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "text", + "content": " is the predicted probability distribution over the class labels by the teacher network for the input " + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "inline_equation", + "content": "x_{i}" + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "text", + "content": ". Let " + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "inline_equation", + "content": "\\mathcal{FS}: \\mathcal{X} \\to \\mathcal{Y}" + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "inline_equation", + "content": "\\mathcal{FT}: \\mathcal{X} \\to \\Delta^{C - 1}" + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "text", + "content": " denote the student and teacher networks, respectively, where " + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "inline_equation", + "content": "\\Delta^{C - 1}" + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 45, + 576, + 279, + 682 + ], + "type": "text", + "content": "-dimensional probability simplex." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 683, + 280, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 683, + 280, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 683, + 280, + 730 + ], + "type": "text", + "content": "Knowledge distillation aims to train the student network " + }, + { + "bbox": [ + 45, + 683, + 280, + 730 + ], + "type": "inline_equation", + "content": "\\mathcal{F}^S" + }, + { + "bbox": [ + 45, + 683, + 280, + 730 + ], + "type": "text", + "content": " to match the predictions of the teacher network " + }, + { + "bbox": [ + 45, + 683, + 280, + 730 + ], + "type": "inline_equation", + "content": "\\mathcal{F}^T" + }, + { + "bbox": [ + 45, + 683, + 280, + 730 + ], + "type": "text", + "content": " for the same input data. To achieve this, we minimize the CS divergence between the soft labels predicted by the teacher" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 296, + 351, + 530, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 351, + 530, + 399 + ], + "spans": [ + { + "bbox": [ + 296, + 351, + 530, + 399 + ], + "type": "text", + "content": "network and those predicted by the student network. The CS divergence between the soft label distributions " + }, + { + "bbox": [ + 296, + 351, + 530, + 399 + ], + "type": "inline_equation", + "content": "P_{T_i}" + }, + { + "bbox": [ + 296, + 351, + 530, + 399 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 351, + 530, + 399 + ], + "type": "inline_equation", + "content": "P_{S_i}" + }, + { + "bbox": [ + 296, + 351, + 530, + 399 + ], + "type": "text", + "content": " predicted by the teacher and student models, respectively, for the input " + }, + { + "bbox": [ + 296, + 351, + 530, + 399 + ], + "type": "inline_equation", + "content": "x_i" + }, + { + "bbox": [ + 296, + 351, + 530, + 399 + ], + "type": "text", + "content": " is defined as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 297, + 419, + 531, + 461 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 419, + 531, + 461 + ], + "spans": [ + { + "bbox": [ + 297, + 419, + 531, + 461 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {C S} := D _ {C S} \\left(P _ {S}, P _ {T}\\right) = - \\ln \\frac {\\int P _ {T _ {i}} (x) P _ {S _ {i}} (x) d x}{\\sqrt {\\int P _ {T _ {i}} (x) d x \\int P _ {S _ {i}} (x) d x}}. \\tag {4}", + "image_path": "8062f9a1ae84a3b694f9f521f53672737bc0d805dda0ffb76d82d45f8c95b504.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 296, + 462, + 530, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 462, + 530, + 496 + ], + "spans": [ + { + "bbox": [ + 296, + 462, + 530, + 496 + ], + "type": "text", + "content": "Note that " + }, + { + "bbox": [ + 296, + 462, + 530, + 496 + ], + "type": "inline_equation", + "content": "D_{CS} = 0" + }, + { + "bbox": [ + 296, + 462, + 530, + 496 + ], + "type": "text", + "content": " only for " + }, + { + "bbox": [ + 296, + 462, + 530, + 496 + ], + "type": "inline_equation", + "content": "P_S = P_T" + }, + { + "bbox": [ + 296, + 462, + 530, + 496 + ], + "type": "text", + "content": ". Eq. 4 can improve numerical stability and the ability to account for uncertainty in student predictions." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 296, + 498, + 530, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 498, + 530, + 544 + ], + "spans": [ + { + "bbox": [ + 296, + 498, + 530, + 544 + ], + "type": "text", + "content": "The inter-task information for each task. We develop an alternative inter-task comparison strategy in which the distribution of teacher and student of all tasks. The intertask information between teacher and student is defined as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 343, + 557, + 530, + 589 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 557, + 530, + 589 + ], + "spans": [ + { + "bbox": [ + 343, + 557, + 530, + 589 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {i n t e r} = \\frac {1}{B} \\sum_ {i = 1} ^ {B} D _ {C S} \\left(P _ {S i,:}, P _ {T _ {i,:}}\\right), \\tag {5}", + "image_path": "f04bb3db3e15bd91eee213cd73118331a66d07f479a007faeb1258a74c2c7192.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 297, + 596, + 424, + 606 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 596, + 424, + 606 + ], + "spans": [ + { + "bbox": [ + 297, + 596, + 424, + 606 + ], + "type": "text", + "content": "where the " + }, + { + "bbox": [ + 297, + 596, + 424, + 606 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 297, + 596, + 424, + 606 + ], + "type": "text", + "content": " denotes batch size." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 608, + 530, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 608, + 530, + 676 + ], + "spans": [ + { + "bbox": [ + 296, + 608, + 530, + 676 + ], + "type": "text", + "content": "The intra-task information for each task. For intraclass information, we discuss why naive hard example mining cannot handle noise/outliers and propose a simple and effective balancing strategy for fast and robust hard example mining. As shown in Figure 2, the intra-task is defined as:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 342, + 678, + 530, + 711 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 342, + 678, + 530, + 711 + ], + "spans": [ + { + "bbox": [ + 342, + 678, + 530, + 711 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {i n t r a}} = \\frac {1}{C} \\sum_ {j = 1} ^ {C} D _ {C S} \\left(P _ {S: j}, P _ {T: j}\\right), \\tag {6}", + "image_path": "8fb7ef629cb4f94453c026c0f8ad18d0e1fbf01f640052c504cd58b81fe45a72.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 297, + 717, + 415, + 728 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 717, + 415, + 728 + ], + "spans": [ + { + "bbox": [ + 297, + 717, + 415, + 728 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 297, + 717, + 415, + 728 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 297, + 717, + 415, + 728 + ], + "type": "text", + "content": " denotes the channel." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "text", + "content": "21553" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 106, + 279, + 129 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 106, + 279, + 129 + ], + "spans": [ + { + "bbox": [ + 46, + 106, + 279, + 129 + ], + "type": "text", + "content": "Finally, we wrap task-independent knowledge distillation strategies into MTL. It can be formulated as follows:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 95, + 138, + 279, + 170 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 95, + 138, + 279, + 170 + ], + "spans": [ + { + "bbox": [ + 95, + 138, + 279, + 170 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {C S K D} = \\sum_ {n = 1} ^ {N} \\left(\\mathcal {L} _ {\\text {i n t e r}} + \\mathcal {L} _ {\\text {i n t r a}}\\right), \\tag {7}", + "image_path": "4d30d475d11f0b929601a917f9259e86b5cb2ea3f9d5a7822b659fa3d4c5f4ab.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 176, + 279, + 201 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 176, + 279, + 201 + ], + "spans": [ + { + "bbox": [ + 46, + 176, + 279, + 201 + ], + "type": "text", + "content": "where the " + }, + { + "bbox": [ + 46, + 176, + 279, + 201 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 176, + 279, + 201 + ], + "type": "text", + "content": " is the task number. We sum up the " + }, + { + "bbox": [ + 46, + 176, + 279, + 201 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{inter}" + }, + { + "bbox": [ + 46, + 176, + 279, + 201 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 176, + 279, + 201 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{intra}" + }, + { + "bbox": [ + 46, + 176, + 279, + 201 + ], + "type": "text", + "content": " to improve the distillation performance for MTL." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 207, + 151, + 219 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 207, + 151, + 219 + ], + "spans": [ + { + "bbox": [ + 46, + 207, + 151, + 219 + ], + "type": "text", + "content": "3.4. Training objective" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 224, + 279, + 295 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 224, + 279, + 295 + ], + "spans": [ + { + "bbox": [ + 45, + 224, + 279, + 295 + ], + "type": "text", + "content": "As depicted in Figure 2, our method consists of a teacher MT model, a student MT model, and a new strategy of KD. Concretely, we first train a strong MT model as a teacher model. Then we introduce a trained teacher model for the student MT model training. The plain multi-task loss function is given as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 94, + 303, + 279, + 335 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 94, + 303, + 279, + 335 + ], + "spans": [ + { + "bbox": [ + 94, + 303, + 279, + 335 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {m t} := \\mathcal {L} \\left(y _ {\\text {t r u e}}, P _ {S}\\right) = \\sum_ {n = 1} ^ {N} \\lambda_ {n} \\mathcal {L} _ {n}, \\tag {8}", + "image_path": "80b3a74f154d1e6c6781dfeb9b9cbf76c6958594b836b895ec13e8c1acc0b529.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 342, + 274, + 353 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 342, + 274, + 353 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 274, + 353 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 342, + 274, + 353 + ], + "type": "inline_equation", + "content": "\\lambda_{n}" + }, + { + "bbox": [ + 46, + 342, + 274, + 353 + ], + "type": "text", + "content": " is a hyperparameter factor of the task number " + }, + { + "bbox": [ + 46, + 342, + 274, + 353 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 342, + 274, + 353 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 354, + 279, + 412 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 354, + 279, + 412 + ], + "spans": [ + { + "bbox": [ + 45, + 354, + 279, + 412 + ], + "type": "text", + "content": "In the multi-task knowledge distillation setting, there are a trained multi-task teacher model (i.e., " + }, + { + "bbox": [ + 45, + 354, + 279, + 412 + ], + "type": "inline_equation", + "content": "T^{mt}" + }, + { + "bbox": [ + 45, + 354, + 279, + 412 + ], + "type": "text", + "content": ") and a student model (i.e., " + }, + { + "bbox": [ + 45, + 354, + 279, + 412 + ], + "type": "inline_equation", + "content": "S^{mt}" + }, + { + "bbox": [ + 45, + 354, + 279, + 412 + ], + "type": "text", + "content": "). As a result, the KDAM overall training loss function is typically a weighted sum of the MTL loss " + }, + { + "bbox": [ + 45, + 354, + 279, + 412 + ], + "type": "inline_equation", + "content": "(\\mathcal{L}_{mt})" + }, + { + "bbox": [ + 45, + 354, + 279, + 412 + ], + "type": "text", + "content": " and the knowledge distillation loss." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 65, + 421, + 279, + 433 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 421, + 279, + 433 + ], + "spans": [ + { + "bbox": [ + 65, + 421, + 279, + 433 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {t o t a l}} = \\alpha \\cdot \\mathcal {L} _ {m t} + \\beta \\cdot \\mathcal {L} _ {C S K D} \\left(P _ {S ^ {m t}}, P _ {T ^ {m t}}\\right), \\tag {9}", + "image_path": "c8a087c09be1a2062a091ab948ed280fc175c6c2c232681524353d7dc485cb9c.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 45, + 442, + 279, + 477 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 442, + 279, + 477 + ], + "spans": [ + { + "bbox": [ + 45, + 442, + 279, + 477 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 45, + 442, + 279, + 477 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 45, + 442, + 279, + 477 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 442, + 279, + 477 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 45, + 442, + 279, + 477 + ], + "type": "text", + "content": " are the scale factor for balancing the losses. In this way, via the " + }, + { + "bbox": [ + 45, + 442, + 279, + 477 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{CSKD}" + }, + { + "bbox": [ + 45, + 442, + 279, + 477 + ], + "type": "text", + "content": " loss, the student to match the strong teacher network's output." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 487, + 124, + 500 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 487, + 124, + 500 + ], + "spans": [ + { + "bbox": [ + 46, + 487, + 124, + 500 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 45, + 506, + 279, + 599 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 506, + 279, + 599 + ], + "spans": [ + { + "bbox": [ + 45, + 506, + 279, + 599 + ], + "type": "text", + "content": "We validate the superiority of our KDAM framework under two representative datasets: NYUD-v2 [42] and PASCAL-Context [7]. In Section 4.1, we provide the experimental setup and evaluation details we used for experiments. Section 4.2 presents the main qualitative and quantitative MTL results. Finally, in Section 4.3, we perform ablation studies to verify the effect of components and efficiencies of our method." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 607, + 148, + 619 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 607, + 148, + 619 + ], + "spans": [ + { + "bbox": [ + 46, + 607, + 148, + 619 + ], + "type": "text", + "content": "4.1. Experiment setup" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 45, + 624, + 279, + 729 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 624, + 279, + 729 + ], + "spans": [ + { + "bbox": [ + 45, + 624, + 279, + 729 + ], + "type": "text", + "content": "NYUD-v2 dataset and metrics. NYUD-v2 comprises RGB and Depth frames 795 images are used for training and 654 images for testing. NYUD-v2 is adopted for semantic segmentation (SemSeg), depth estimation (Depth), surface normal estimation (Normal) and boundary detection (Bound) tasks by providing dense labels. The semantic segmentation labels classify each pixel in the RGB images into one of 40 object categories. Four evaluation metrics are available to evaluate the MTL model performance, which" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 296, + 106, + 530, + 151 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 106, + 530, + 151 + ], + "spans": [ + { + "bbox": [ + 296, + 106, + 530, + 151 + ], + "type": "text", + "content": "includes mean Intersection over Union (mIoU) for the SemSeg task, root mean square error (rmse) for the Depth task, mean Error (mErr) for the Normal task, and optimal dataset scale F-measure (odsF) for the Bound task." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 296, + 153, + 530, + 351 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 153, + 530, + 351 + ], + "spans": [ + { + "bbox": [ + 296, + 153, + 530, + 351 + ], + "type": "text", + "content": "PASCAL-Context dataset and metrics. PASCAL-Context consists of 10,103 images with complex scenes, covering 400 object categories and 59 background regions. PASCAL-Context is adopted for semantic segmentation (SemSeg), human parts segmentation (PartSeg), saliency estimation (Sal), surface normal estimation (Normal), and boundary detection (Bound) tasks by pixel-level semantic labels for each image. Five evaluation metrics are available to evaluate the MTL model performance, which includes mean Intersection over Union (mIoU) for the SemSeg and PartSeg tasks, mean Error (mErr) for the Normal task, optimal dataset scale F-measure (odsF) for the Bound task, and maximum F-measure (maxF) for the Sal task. The average per-task performance drop " + }, + { + "bbox": [ + 296, + 153, + 530, + 351 + ], + "type": "inline_equation", + "content": "(\\Delta_{mt})" + }, + { + "bbox": [ + 296, + 153, + 530, + 351 + ], + "type": "text", + "content": " is used to quantify multi-task performance. " + }, + { + "bbox": [ + 296, + 153, + 530, + 351 + ], + "type": "inline_equation", + "content": "\\Delta_{mt} = \\frac{1}{N}\\sum_{i = 1}^{N}(F_{mt,n} - F_{st,n}) / F_{st,n}\\times" + }, + { + "bbox": [ + 296, + 153, + 530, + 351 + ], + "type": "inline_equation", + "content": "100\\%" + }, + { + "bbox": [ + 296, + 153, + 530, + 351 + ], + "type": "text", + "content": " , where mt, st and " + }, + { + "bbox": [ + 296, + 153, + 530, + 351 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 296, + 153, + 530, + 351 + ], + "type": "text", + "content": " mean multi-task model, single-task baseline and task numbers. " + }, + { + "bbox": [ + 296, + 153, + 530, + 351 + ], + "type": "inline_equation", + "content": "\\Delta_{mt}" + }, + { + "bbox": [ + 296, + 153, + 530, + 351 + ], + "type": "text", + "content": " : higher is the better." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 296, + 351, + 530, + 444 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 351, + 530, + 444 + ], + "spans": [ + { + "bbox": [ + 296, + 351, + 530, + 444 + ], + "type": "text", + "content": "Setting. To be universal, we perform experiments on the NYUD-v2 [42] and PASCAL-Context [7] datasets using different teacher-student pairs. The \"Plain KD vs. DIST vs. Our KDAM\" experiment is conducted using Swin-L [34] as a teacher model, Swin-T [34] and Swin-S [34] as student models on the NYUD-v2. On PASCAL-Context, we adopt Swin-L [34] and Swin-B [34] as teacher models, HRNet18 [43], Swin-T [34] and Swin-S [34] as student models." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "spans": [ + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "content": "Loss weights. In our experiments, we use the algorithm in [3] to learn weights for each task over the course of training. For a fair comparison, we search the optimal hyperparameters (i.e., the loss ratio " + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "content": " and the temperature " + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "content": ") for each teacher-student pair. On NYUD-v2 and PASCAL-Context, we set " + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "inline_equation", + "content": "\\alpha = 1.0" + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "inline_equation", + "content": "\\beta = 1.0" + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "content": " in Eq. 9 using our TKD method. For plain KD [13], we set " + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "inline_equation", + "content": "\\alpha = 1.0" + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "inline_equation", + "content": "\\beta = 1.0" + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "content": " in Eq. 9 and use a default temperature " + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "inline_equation", + "content": "\\mathcal{T} = 3" + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "content": " in Eq. 2. In addition, For a fair comparison, we search the optimal hyperparameters i.e., " + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "content": ". We choose a temperature set " + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "inline_equation", + "content": "\\mathcal{T} \\in [0.1, 0.5, 1, 3, 4, 8, 16]" + }, + { + "bbox": [ + 296, + 445, + 530, + 584 + ], + "type": "text", + "content": " for an ablation study on NYUD-v2 dataset (see Table 5a & 5b)." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 296, + 586, + 530, + 655 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 586, + 530, + 655 + ], + "spans": [ + { + "bbox": [ + 296, + 586, + 530, + 655 + ], + "type": "text", + "content": "Baselines. Multi-task baseline uses a shared backbone network in conjunction with task-specific heads to perform the predictions for every task. We can choose different networks as backbones, such as HRNet [43] and Swin Transformer [34]. Single-task baseline uses a backbone network with a task head to conduct the predictions for a task." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 297, + 664, + 352, + 676 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 664, + 352, + 676 + ], + "spans": [ + { + "bbox": [ + 297, + 664, + 352, + 676 + ], + "type": "text", + "content": "4.2. Results" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 296, + 682, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 682, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 682, + 530, + 730 + ], + "type": "text", + "content": "NYUD-v2 dataset. We investigate the effectiveness of our KDAM on NYUD-v2 dataset. We first train a multi-task baseline model of Swin-L for our knowledge distillation procedure. Then we load the well trained Swin-L model" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "text", + "content": "21554" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 54, + 145, + 523, + 385 + ], + "blocks": [ + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "lines": [ + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "spans": [ + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "type": "text", + "content": "Table 1: We report the comparison of the MTL models with the state-of-the-art on NYUD-v2 dataset. " + }, + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "type": "inline_equation", + "content": "\\downarrow" + }, + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "type": "text", + "content": " : lower is better. ’↑’: higher is better. " + }, + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "type": "inline_equation", + "content": "{\\Delta }_{mt}" + }, + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "type": "text", + "content": " denotes the average per-task performance drop. Swin-◇ indicates that the specific Swin model is uncertain. Gray blocks mean the multi-task baseline using our knowledge distillation method." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 54, + 145, + 523, + 385 + ], + "lines": [ + { + "bbox": [ + 54, + 145, + 523, + 385 + ], + "spans": [ + { + "bbox": [ + 54, + 145, + 523, + 385 + ], + "type": "table", + "html": "
ModelBackboneParams (M)GFLOPs (G)SemSeg (mIoU)↑Depth (rmse)↓Normal (mErr)↓Bound (odsF)↑Δmt[%]↑
single-task (ST) baselineHRNet1816.0940.9338.020.610420.9476.220.00
multi-task (MT) baselineHRNet184.5217.5936.350.628421.0276.36-1.89
MT+KDAM (Ours)HRNet184.5217.5936.850.625021.0476.10-0.73
Cross-Stitch[37]HRNet184.5217.5936.340.629020.8876.38-1.75
Pad-Net[50]HRNet185.0225.1836.700.626420.8576.50-1.33
PAP[58]HRNet184.5453.0436.720.617820.8276.42-0.95
PSD[31]HRNet184.7121.1036.690.624620.8776.42-1.30
NDDR-CNN[10]HRNet184.5918.6836.720.628820.8976.32-1.51
MTI-Net[46]HRNet1812.5619.1436.610.627020.8576.38-1.44
ATRC[3]HRNet185.0625.7638.900.601020.4876.341.56
ATRC+KDAM (Ours)HRNet185.0625.7639.300.591920.7276.912.05
single-task (ST) baselineSwin-T115.08161.2542.920.610420.9476.220.00
multi-task (MT) baselineSwin-T32.5096.2938.780.631221.0575.60-3.74
MT+KDAM (Ours)Swin-T32.5096.2944.340.60121.0376.41.1
single-task (ST) baselineSwin-S200.33242.6348.920.580420.9477.200.00
multi-task (MT) baselineSwin-S53.82116.6347.900.605321.1776.90-1.96
MTFormer[51]Swin-◇64.03117.7350.560.4830--4.12
MT+KDAM (Ours)Swin-S53.82116.6349.410.56420.6077.31.38
", + "image_path": "111a78aeb09b6fb40a6e55324dbd64176628aeea9e73661acdb6846df420abb1.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 48, + 414, + 530, + 480 + ], + "blocks": [ + { + "bbox": [ + 49, + 394, + 525, + 408 + ], + "lines": [ + { + "bbox": [ + 49, + 394, + 525, + 408 + ], + "spans": [ + { + "bbox": [ + 49, + 394, + 525, + 408 + ], + "type": "text", + "content": "Table 2: Comparison results of DeMT and InvPT MTL model with our KDAM method. " + }, + { + "bbox": [ + 49, + 394, + 525, + 408 + ], + "type": "inline_equation", + "content": "{}^{\\prime } +" + }, + { + "bbox": [ + 49, + 394, + 525, + 408 + ], + "type": "text", + "content": " ’ means performance increase." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 414, + 530, + 480 + ], + "lines": [ + { + "bbox": [ + 48, + 414, + 530, + 480 + ], + "spans": [ + { + "bbox": [ + 48, + 414, + 530, + 480 + ], + "type": "table", + "html": "
Network structureAccuracy multi-task student modelsAccuracy of our KDAM
TeacherStudentSemSeg↑Depth↓Normal↓Bound↑SemSeg↑Depth↓Normal↓Bound↑
Swin-LInvPT-T [56]44.270.558920.4676.1044.93 (+ 0.66)0.5577 (+ 0.0012)20.27 (+ 0.19)76.2 (+ 0.1)
Swin-LDeMT-T[53]46.360.587120.6576.9047.07 (+ 0.71)0.5855 (+ 0.0016)20.62 (+ 0.03)76.9 (+ 0.0)
Swin-LDeMT-S[53]51.500.547420.0278.1051.91 (+ 0.41)0.5512 (- 0.0038)20.01 (+ 0.01)78.1 (+ 0.0)
", + "image_path": "8c0a196c73f6f7c07f8c57dfc8ec364e12b02e129f6e6ddccebc4351b1784632.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "type": "text", + "content": "as a teacher model for student model training. In Table 1, ours surpasses the HRNet18, Swin-T and Swin-S multi-task baselines by more than " + }, + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "type": "inline_equation", + "content": "1.16\\%" + }, + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "type": "inline_equation", + "content": "4.84\\%" + }, + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "type": "inline_equation", + "content": "3.34\\%" + }, + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "type": "text", + "content": " (average per-task performance drop " + }, + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "type": "inline_equation", + "content": "\\Delta_{mt}" + }, + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "type": "text", + "content": "), respectively. The baseline model coupled with the improvement in " + }, + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "type": "inline_equation", + "content": "\\Delta_{mt}" + }, + { + "bbox": [ + 45, + 507, + 281, + 730 + ], + "type": "text", + "content": " metric by our distillation method demonstrates the effectiveness of distillation. Note that These results are only conducted on the outputs of the multi-task baseline model and have a similar computational cost as the baseline model. Nevertheless, it even achieves better performance compared to those carefully designed methods. As shown in Table 1, although ATRC achieves better performance, it brings much more parameters and computation compared to the MT baseline. By contrast, our method based on distillation is cost-free. We also conduct experiments based on DeMT [53] and InvPT [56] and compare using our KD strategy with the DeMT-T, DeMT-S and InvPT-T. As shown in Table 2, our KDAM is outperformed by DeMT-T +0.71 mIoU and DeMT-S by +0.41 mIoU on SemSeg task. Applying our" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 296, + 507, + 530, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 507, + 530, + 566 + ], + "spans": [ + { + "bbox": [ + 296, + 507, + 530, + 566 + ], + "type": "text", + "content": "distillation recipe in combination with the DeMT configuration to prove our method is effective. We can see that all the added KDAM, regardless of DeMT or InvPT, improves the performance. We observe that our distillation with an alternative match leads the state-of-the-art performance." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 296, + 566, + 531, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 566, + 531, + 730 + ], + "spans": [ + { + "bbox": [ + 296, + 566, + 531, + 730 + ], + "type": "text", + "content": "PASCAL-Context. We also use the multi-task baseline model of Swin-L as a teacher model. We further investigate the effectiveness of our KDAM for dense predictions on PASCAL-Context dataset. We train HRNet18, Swin-T and Swin-S baseline with our distillation method. As shown in Table 3, our KDAM outperforms all the previous MTL methods on five dense predictions and the average per-task performance drops " + }, + { + "bbox": [ + 296, + 566, + 531, + 730 + ], + "type": "inline_equation", + "content": "\\Delta_{mt}" + }, + { + "bbox": [ + 296, + 566, + 531, + 730 + ], + "type": "text", + "content": ". It is worth mentioning that using a strong Swin-L teacher fails to give HRNet18 baseline an intuitive performance increase. We find that the performance of SemSeg task tends to get better as the student's backbone increases, which shows the effectiveness of our approach in segmentation tasks. Results suggest that our method can learn more semantic features for dense predictions." + } + ] + } + ], + "index": 6 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "text", + "content": "21555" + } + ] + } + ], + "index": 7 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 149, + 526, + 316 + ], + "blocks": [ + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "lines": [ + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "spans": [ + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "type": "text", + "content": "Table 3: We report a comparison of the MTL models with the state-of-the-art on PASCAL-Context dataset. " + }, + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "type": "inline_equation", + "content": "\\downarrow" + }, + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "type": "text", + "content": " : lower is better. " + }, + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "type": "inline_equation", + "content": "\\uparrow" + }, + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "type": "text", + "content": " : higher is better. " + }, + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "type": "inline_equation", + "content": "{\\Delta }_{m}" + }, + { + "bbox": [ + 45, + 104, + 531, + 139 + ], + "type": "text", + "content": " denotes the average per-task performance drop (higher is better). Gray blocks mean the multi-task baseline using our knowledge distillation method." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 53, + 149, + 526, + 316 + ], + "lines": [ + { + "bbox": [ + 53, + 149, + 526, + 316 + ], + "spans": [ + { + "bbox": [ + 53, + 149, + 526, + 316 + ], + "type": "table", + "html": "
ModelBackboneSemSeg (mIoU)↑PartSeg (mIoU)↑Sal (maxF)↑Normal (mErr)↓Bound (odsF)↑Δmt [%]↑
single-task (ST) baselineHRNet1862.2361.6685.0813.6973.060.00
multi-task (MT) baselineHRNet1851.4857.2383.4314.1069.76-6.77
MT+KDAM (Ours)HRNet1851.9157.6383.9213.9070.1-5.06
PAD-Net [50]HRNet1853.6059.6065.8015.372.50-4.41
ATRC [3]HRNet1857.8957.3383.7713.9969.74-4.45
MQTransformer[52]HRNet1858.9157.4383.7814.1769.80-4.20
ATRC+KDAM (Ours)HRNet1858.9257.5183.8713.9769.75-3.94
single-task (ST) baselineSwin-T67.8156.3282.1814.8170.900.00
multi-task (MT) baselineSwin-T64.7453.2576.8815.8669.00-3.23
MT+KDAM (Ours)Swin-T64.8153.8081.7215.0669.5-2.3
single-task (ST) baselineSwin-S70.8359.7182.6415.1371.200.00
multi-task (MT) baselineSwin-S68.1056.2080.6416.0970.20-3.97
MT+KDAM (Ours)Swin-S68.8056.6281.9115.6170.4-2.54
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Teacher (Student)MetricsAccuracy ST modelsAccuracy MT modelsPlain KDDIST KDOur KDAM
TeacherStudentTeacherStudentStudent (MT)Student (MT)Student(MT)
Swin-L (Swin-T)SemSeg↑56.4642.9254.5338.7844.4843.2744.54
Depth↓0.5080.6100.5320.6310.6040.5990.601
Normal↓19.3820.9419.5121.0521.0321.0221.03
Bound↑78.876.2278.375.6076.8076.5076.40
Δmt[%]↑---2.36-3.741.080.581.10
Swin-L (Swin-S)SemSeg↑56.4648.9254.5347.9049.2049.3949.41
Depth↓0.5080.5800.5320.6050.5710.5600.564
Normal↓19.3820.9419.5121.1720.5820.5120.60
Bound↑78.877.2078.376.9077.2077.277.3
Δmt[%]↑---2.36-1.960.971.61.38
Swin-B (Swin-T)SemSeg↑53.0142.9251.4438.7843.8444.0644.52
Depth↓0.5520.6100.5810.6310.6030.5960.592
Normal↓19.3420.9420.4421.0521.1921.0821.09
Bound↑78.0076.2277.8075.6076.6076.7076.6
Δmt[%]↑---3.2-3.740.491.071.47
", + "image_path": "c05e934d1c0cef2656fb38356c3cd0be9b66ccc70311fb1e887c99abb51d87ed.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 570, + 143, + 581 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 143, + 581 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 143, + 581 + ], + "type": "text", + "content": "4.3. Ablation Studies" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 590, + 280, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 590, + 280, + 730 + ], + "spans": [ + { + "bbox": [ + 45, + 590, + 280, + 730 + ], + "type": "text", + "content": "Distillation with alternative match helps minimize the performance gap between teacher and student. In Table 4, we first conduct experiments to compare our KDAM with plain KD [13] and DIST KD [16] at different student and teacher model sizes. We compare three types of teacher-student pairs: Swin-L: Swin-T, Swin-L: Swin-S and Swin-B: Swin-T. As shown in Table 4 (Swin-T (Swin-L) and Swin-T (Swin-B) rows), when the teacher goes larger, the Swin-T students MTL performance " + }, + { + "bbox": [ + 45, + 590, + 280, + 730 + ], + "type": "inline_equation", + "content": "\\Delta_{mt}" + }, + { + "bbox": [ + 45, + 590, + 280, + 730 + ], + "type": "text", + "content": " perform even worse than that with a medium-sized Swin-B teacher. We observe that it is not the fact that a larger teacher model leads to better performance. The plain KD using KL di" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 296, + 570, + 530, + 710 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 570, + 530, + 710 + ], + "spans": [ + { + "bbox": [ + 296, + 570, + 530, + 710 + ], + "type": "text", + "content": "vergence loss can help minimize the performance gap between strong teachers and students. In addition, our KDAM showed an increasing trend with strong teachers and a more significant improvement compared to the other KD strategies, suggesting that our KDAM better handles the differences between student and strong teacher performance. Our KDAM can significantly outperform existing knowledge distillation methods on MTL of dense predictions. The results in Table 4 highlight that our KDAM is applied for capturing inter-task and intra-task information between the teacher model and the student model of each task, and thus learns more \"dark knowledge\" for effective distillation." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 297, + 718, + 530, + 730 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 718, + 530, + 730 + ], + "spans": [ + { + "bbox": [ + 297, + 718, + 530, + 730 + ], + "type": "text", + "content": "Ablation on hyperparameters " + }, + { + "bbox": [ + 297, + 718, + 530, + 730 + ], + "type": "inline_equation", + "content": "\\mathcal{T}\\& \\beta" + }, + { + "bbox": [ + 297, + 718, + 530, + 730 + ], + "type": "text", + "content": ". We compare the ef-" + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 746, + 301, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 301, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 301, + 756 + ], + "type": "text", + "content": "21556" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 151, + 270, + 255 + ], + "blocks": [ + { + "bbox": [ + 45, + 104, + 530, + 127 + ], + "lines": [ + { + "bbox": [ + 45, + 104, + 530, + 127 + ], + "spans": [ + { + "bbox": [ + 45, + 104, + 530, + 127 + ], + "type": "text", + "content": "Table 5: Ablation experiments of the optimal hyperparameters temperature factor " + }, + { + "bbox": [ + 45, + 104, + 530, + 127 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 45, + 104, + 530, + 127 + ], + "type": "text", + "content": " and the loss scale factor " + }, + { + "bbox": [ + 45, + 104, + 530, + 127 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 45, + 104, + 530, + 127 + ], + "type": "text", + "content": " of the plain KD (Eq. 2) using a Swin-L as teacher model and Swin-T as student model on NYUD-v2 dataset." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 77, + 137, + 242, + 148 + ], + "lines": [ + { + "bbox": [ + 77, + 137, + 242, + 148 + ], + "spans": [ + { + "bbox": [ + 77, + 137, + 242, + 148 + ], + "type": "text", + "content": "(a) Ablation on " + }, + { + "bbox": [ + 77, + 137, + 242, + 148 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 77, + 137, + 242, + 148 + ], + "type": "text", + "content": " in Eq. 9 using " + }, + { + "bbox": [ + 77, + 137, + 242, + 148 + ], + "type": "inline_equation", + "content": "\\mathcal{T} = 3" + }, + { + "bbox": [ + 77, + 137, + 242, + 148 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 77, + 137, + 242, + 148 + ], + "type": "inline_equation", + "content": "\\alpha = 1" + }, + { + "bbox": [ + 77, + 137, + 242, + 148 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 151, + 270, + 255 + ], + "lines": [ + { + "bbox": [ + 50, + 151, + 270, + 255 + ], + "spans": [ + { + "bbox": [ + 50, + 151, + 270, + 255 + ], + "type": "table", + "html": "
KD styleβAccuracy multi-task student models
SemSeg↑Depth↓Normal↓Bound↑
Plain KD0.144.420.600121.1676.2
0.544.900.601521.0976.3
144.470.604421.0376.2
244.610.597521.0076.2
444.090.601721.0676.1
844.420.601821.0776.2
1643.530.610421.3476.3
", + "image_path": "1220c71f3f613a8ce5ec10b9ec3723c43f059c607ef797e43603c13559dadd2d.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 48, + 315, + 279, + 389 + ], + "blocks": [ + { + "bbox": [ + 45, + 271, + 279, + 304 + ], + "lines": [ + { + "bbox": [ + 45, + 271, + 279, + 304 + ], + "spans": [ + { + "bbox": [ + 45, + 271, + 279, + 304 + ], + "type": "text", + "content": "Table 6: Ablation on part of the loss. The student and teacher models are Swin-T and Swin-L, respectively. \"w/\" indicates \"with\"." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 315, + 279, + 389 + ], + "lines": [ + { + "bbox": [ + 48, + 315, + 279, + 389 + ], + "spans": [ + { + "bbox": [ + 48, + 315, + 279, + 389 + ], + "type": "table", + "html": "
MethodAccuracy multi-task student model
SemSeg↑Depth↓Normal↓Bound↑
MT baseline38.780.631221.0575.60
Ours w/ intra43.310.606821.4776.00
Ours w/ inter44.060.596421.0876.50
Ours w/ inter&intra44.340.601221.0376.70
", + "image_path": "652b6d78b2b360bece35c76da3f7ba576bf9fbe781f10e13ed9920bb4b6155b1.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 45, + 422, + 279, + 481 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 422, + 279, + 481 + ], + "spans": [ + { + "bbox": [ + 45, + 422, + 279, + 481 + ], + "type": "text", + "content": "fect of the number of temperature factor " + }, + { + "bbox": [ + 45, + 422, + 279, + 481 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 45, + 422, + 279, + 481 + ], + "type": "text", + "content": " and the distillation loss scale factor " + }, + { + "bbox": [ + 45, + 422, + 279, + 481 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 45, + 422, + 279, + 481 + ], + "type": "text", + "content": " in Table 5a & 5b. We find that having a larger temperature of plain KD improves the performance slightly, whereas increasing the number of distillation loss scale factors does not improve the performance." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 483, + 279, + 634 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 483, + 279, + 634 + ], + "spans": [ + { + "bbox": [ + 45, + 483, + 279, + 634 + ], + "type": "text", + "content": "Ablation on part of the loss. We compare three different methods named \"Ours w/ inter,\" \"Ours w/ intra\" and \"Ours w/ inter & intra\" in Table 6. To validate the effectiveness of each loss, we conduct experiments to train students with these methods separately. For all tasks, the intrinsic inter-task and intra-task variance of the semantic similarities is actually also informative. We can see that our KDAM can achieve a performance improvement, which proves the effectiveness of the inter-task and intra-task. Our knowledge distillation with an alternative match is applied to capture inter-task and intra-task information between the teacher and the student. The results show our distillation method can learn more \"dark knowledge\" for effective distillation." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 45, + 636, + 279, + 729 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 636, + 279, + 729 + ], + "spans": [ + { + "bbox": [ + 45, + 636, + 279, + 729 + ], + "type": "text", + "content": "Ablation on training epochs. The default setting for the number of training epochs for teachers and students is 400. We independently train teacher models and pick them up at epoch " + }, + { + "bbox": [ + 45, + 636, + 279, + 729 + ], + "type": "inline_equation", + "content": "200^{th}" + }, + { + "bbox": [ + 45, + 636, + 279, + 729 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 45, + 636, + 279, + 729 + ], + "type": "inline_equation", + "content": "400^{th}" + }, + { + "bbox": [ + 45, + 636, + 279, + 729 + ], + "type": "text", + "content": ". In Table 7, we conduct ablation experiments of the training epochs using trained Swin-L as a teacher on NYUD-v2 dataset. The teacher model is trained at the " + }, + { + "bbox": [ + 45, + 636, + 279, + 729 + ], + "type": "inline_equation", + "content": "400^{th}" + }, + { + "bbox": [ + 45, + 636, + 279, + 729 + ], + "type": "text", + "content": " epoch. The student model of Swin-T are selected at the " + }, + { + "bbox": [ + 45, + 636, + 279, + 729 + ], + "type": "inline_equation", + "content": "50^{th}, 100^{th}, 200^{th}, 300^{th}, 400^{th}, 500^{th}" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 307, + 151, + 528, + 258 + ], + "blocks": [ + { + "bbox": [ + 309, + 137, + 523, + 148 + ], + "lines": [ + { + "bbox": [ + 309, + 137, + 523, + 148 + ], + "spans": [ + { + "bbox": [ + 309, + 137, + 523, + 148 + ], + "type": "text", + "content": "(b) Ablation on temperatures " + }, + { + "bbox": [ + 309, + 137, + 523, + 148 + ], + "type": "inline_equation", + "content": "\\mathcal{T}" + }, + { + "bbox": [ + 309, + 137, + 523, + 148 + ], + "type": "text", + "content": " in Eq. 2 using " + }, + { + "bbox": [ + 309, + 137, + 523, + 148 + ], + "type": "inline_equation", + "content": "\\alpha = 1" + }, + { + "bbox": [ + 309, + 137, + 523, + 148 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 309, + 137, + 523, + 148 + ], + "type": "inline_equation", + "content": "\\beta = 1" + }, + { + "bbox": [ + 309, + 137, + 523, + 148 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 151, + 528, + 258 + ], + "lines": [ + { + "bbox": [ + 307, + 151, + 528, + 258 + ], + "spans": [ + { + "bbox": [ + 307, + 151, + 528, + 258 + ], + "type": "table", + "html": "
KD styleTAccuracy multi-task student models
SemSeg↑Depth↓Normal↓Bound↑
Plain KD0.144.270.607621.1576.1
0.544.520.605421.1676.2
144.830.596921.1076.3
344.470.604421.0376.2
444.210.601421.0576.1
845.350.601221.0476.5
1644.690.605021.0876.1
", + "image_path": "f2e4cdf12230e96fd9e3010ee19cf3be04c6275bb6119ea55363d8240d522723.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 300, + 303, + 530, + 391 + ], + "blocks": [ + { + "bbox": [ + 297, + 271, + 530, + 295 + ], + "lines": [ + { + "bbox": [ + 297, + 271, + 530, + 295 + ], + "spans": [ + { + "bbox": [ + 297, + 271, + 530, + 295 + ], + "type": "text", + "content": "Table 7: Ablation on the training epochs. The student and teacher models are Swin-T and Swin-L, respectively." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 300, + 303, + 530, + 391 + ], + "lines": [ + { + "bbox": [ + 300, + 303, + 530, + 391 + ], + "spans": [ + { + "bbox": [ + 300, + 303, + 530, + 391 + ], + "type": "table", + "html": "
ModelepochAccuracy multi-task student model
SemSeg↑Depth↓Normal↓Bound↑
KDAM10034.130.671523.2675.3
20042.330.628521.8676.0
30044.140.615621.2876.2
40044.340.601021.0376.2
60045.000.595520.6976.4
", + "image_path": "9f09b3c806033bdc64fc3a11ba14880a17084021f6448d8644c4c8a6b2b1c016.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 296, + 419, + 530, + 501 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 419, + 530, + 501 + ], + "spans": [ + { + "bbox": [ + 296, + 419, + 530, + 501 + ], + "type": "text", + "content": "and " + }, + { + "bbox": [ + 296, + 419, + 530, + 501 + ], + "type": "inline_equation", + "content": "600^{th}" + }, + { + "bbox": [ + 296, + 419, + 530, + 501 + ], + "type": "text", + "content": " epochs. Our multi-task student model reaches 45.00 (mIoU, Semseg) and 0.5955 (rms, Depth) after 600 epochs. We observe that the multi-task student's accuracy increases monotonically with the increase of training epoch. Noticeably, the trained strong teacher model is used for improving student efficiency, while when the student model is not trained still enough leads to poor performance." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 297, + 511, + 367, + 524 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 511, + 367, + 524 + ], + "spans": [ + { + "bbox": [ + 297, + 511, + 367, + 524 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 296, + 532, + 530, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 532, + 530, + 682 + ], + "spans": [ + { + "bbox": [ + 296, + 532, + 530, + 682 + ], + "type": "text", + "content": "This paper introduces a new knowledge distillation procedure with an alternative match (KDAM) for MTL of dense prediction based on two simple design principles. For memory and training efficiency, we use a single strong multi-task model as a teacher during training instead of multiple teachers, as widely adopted in existing studies. Furthermore, we employ a less sensitive CS divergence instead of the KL divergence and propose a CS distillation loss accordingly. This technique can significantly improve the MTL model's distillation performance and reduce the training cost. The Extensive experiment results show that our proposed method significantly improves the model performance and the practical inference efficiency." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 296, + 683, + 530, + 729 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 683, + 530, + 729 + ], + "spans": [ + { + "bbox": [ + 296, + 683, + 530, + 729 + ], + "type": "text", + "content": "Acknowledgements. This work was supported by the National Natural Science Foundation of China under Grant 62122060 and the Special Fund of Hubei Luojia Laboratory under Grant 220100014." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "text", + "content": "21557" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 105, + 103, + 117 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 105, + 103, + 117 + ], + "spans": [ + { + "bbox": [ + 47, + 105, + 103, + 117 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 124, + 279, + 729 + ], + "type": "list", + "angle": 0, + "index": 16, + "blocks": [ + { + "bbox": [ + 51, + 124, + 279, + 166 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 51, + 124, + 279, + 166 + ], + "spans": [ + { + "bbox": [ + 51, + 124, + 279, + 166 + ], + "type": "text", + "content": "[1] Lucas Beyer, Xiaohua Zhai, Amélie Royer, Larisa Markeeva, Rohan Anil, and Alexander Kolesnikov. 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In CVPR, pages 4156-4165, 2022. 3" + } + ] + } + ], + "index": 28 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "spans": [ + { + "bbox": [ + 276, + 746, + 300, + 756 + ], + "type": "text", + "content": "21559" + } + ] + } + ], + "index": 30 + } + ], + "page_size": [ + 595, + 842 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-View Active Fine-Grained Visual Recognition/ee209e69-47ab-4c40-9356-cb8b45ac9b6d_content_list.json b/2023/Multi-View Active Fine-Grained Visual Recognition/ee209e69-47ab-4c40-9356-cb8b45ac9b6d_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..7839ec1988ac432dae2ca431db7259456116113d --- /dev/null +++ b/2023/Multi-View Active Fine-Grained Visual Recognition/ee209e69-47ab-4c40-9356-cb8b45ac9b6d_content_list.json @@ -0,0 +1,1620 @@ +[ + { + "type": "text", + "text": "Multi-View Active Fine-Grained Visual Recognition", + "text_level": 1, + "bbox": [ + 222, + 130, + 746, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Ruoyi Du $^{1}$ , Wenqing Yu $^{1}$ , Heqing Wang $^{1}$ , Ting-En Lin $^{2}$ , Dongliang Chang $^{1*}$ , Zhanyu Ma $^{1}$ $^{1}$ Beijing University of Posts and Telecommunications, China", + "bbox": [ + 130, + 179, + 834, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ {duruoyi, yuwenqing, wangheqing, changdongliang, mazhanyu}@bupt.edu.cn,", + "bbox": [ + 169, + 217, + 799, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "2 sss950123@gmail.com", + "bbox": [ + 395, + 233, + 573, + 250 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 313, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Despite the remarkable progress of Fine-grained visual classification (FGVC) with years of history, it is still limited to recognizing 2D images. Recognizing objects in the physical world (i.e., 3D environment) poses a unique challenge - discriminative information is not only present in visible local regions but also in other unseen views. Therefore, in addition to finding the distinguishable part from the current view, efficient and accurate recognition requires inferring the critical perspective with minimal glances. E.g., a person might recognize a \"Ford sedan\" with a glance at its side and then know that looking at the front can help tell which model it is. In this paper, towards FGVC in the real physical world, we put forward the problem of multi-view active fine-grained visual recognition (MAFR) and complete this study in three steps: (i) a multi-view, fine-grained vehicle dataset is collected as the testbed, (ii) a pilot experiment is designed to validate the need and research value of MAFR, (iii) a policy-gradient-based framework along with a dynamic exiting strategy is proposed to achieve efficient recognition with active view selection. Our comprehensive experiments demonstrate that the proposed method outperforms previous multi-view recognition works and can extend existing state-of-the-art FGVC methods and advanced neural networks to become \"FGVC experts\" in the 3D environment. Our code is available at https://github.com/PRIS-CV/MAFR.", + "bbox": [ + 76, + 318, + 473, + 710 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 742, + 209, + 758 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In the past two decades, fine-grained visual classification (FGVC) has made significant progress in recognizing sub-categories of objects belonging to the same class. This progress has been demonstrated in various domains, such as recognizing cars [32, 57], aircraft [36], birds [50, 48], and foods [39], with extensive outstanding works surpassing human experts in many application scenarios [34, 56,", + "bbox": [ + 75, + 768, + 468, + 876 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d9de0cf15851038211e08ebd798c92337ca1c08180548baa761f3af57fe46ea2.jpg", + "image_caption": [ + "Figure 1. Conventional FGVC versus Multi-view Active FGVC. Conventional FGVC takes a single static image for inference, which may omit the discriminative information. In contrast, Multiview FGVC takes a step further by predicting the potential discriminative view and fusing a sequence of visual information for the final decision." + ], + "image_footnote": [], + "bbox": [ + 503, + 285, + 651, + 450 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/f5c774148ce6f967c61620be94dcceb8a11a769868ce360c15c40997c9604247.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 651, + 285, + 888, + 450 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "19, 53, 13, 4, 5, 16, 14]. However, the previous efforts on FGVC have remained mainly limited to a single-view-based paradigm, where only the visual content within a single static image is considered. This paradigm may be sufficient for coarse-grained classification where inter-class differences are easily captured, such as distinguishing a coupe from other vehicles by its streamlined body, seductive engine, or headlamps. However, fine-grained classification presents a different challenge where discriminative clues are rare and often found in subtle structural differences that are not easily captured by a single static view. For instance, to distinguish between different Ford sedans, one can only rely on subtle differences in the design of car headlights. Predictably, for single-view-based approaches, an image/view without discriminative clues is completely indistinguishable at the fine-grained level, fundamentally limiting the model's theoretical performance.", + "bbox": [ + 496, + 565, + 892, + 821 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Factually, visual recognition is never limited to observing 2D environments and processing static images. Vision algorithms equipped by portal devices (e.g., smartphone, smart glasses, etc.) or embodied AI agents [18] (e.g., intelligent robots) play the core roles during machine-", + "bbox": [ + 496, + 824, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*indicates the corresponding author.", + "bbox": [ + 94, + 887, + 287, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "1568", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "environment interaction and have become one of the focuses of computer vision research. Therefore, to embrace the new trend, a natural extension of ordinary FGVC follows – in addition to locating discriminative parts within an image, we aim to infer the unseen distinguishable perspective within the physical world (i.e., 3D environment). Figure 1 shows an example where, with a single glance from the front, the algorithm may be uncertain about the model of the Ford sedan, but can infer that looking at its front will help to resolve the ambiguity.", + "bbox": [ + 75, + 90, + 472, + 243 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Specifically, we re-propose the concept of active vision [1] in the context of FGVC termed multi-view active fine-grained visual recognition (MAFR). MAFR is based on two essential hypotheses. Firstly, we hypothesize that discriminative information for different fine-grained categories is distributed across various object views, making discriminative perspective inference a non-trivial and worth studying. Secondly, we hypothesize that even views that appear indistinguishable at first glance can contain visual clues that can help infer the discriminative perspective, making the problem solvable.", + "bbox": [ + 75, + 244, + 472, + 411 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To start with, due to the absence of qualified datasets, we first collect a fine-grained, multi-view vehicle dataset named Multi-view Cars (MvCars) as the testbed. MvCars comprises 233 car models from 35 brands, covering 5 different car types. Each car in the dataset has 8 aligned views, and the dataset contains more than 26,000 images. In Section 3.2, we conducted a simple pilot experiment and verified our first hypothesis, which suggests that MvCars is well-suited for the problem at hand.", + "bbox": [ + 75, + 414, + 472, + 549 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Secondly, our next contribution is an efficient multi-view fine-grained recognition framework building upon active next-view selection and dynamic exiting. In particular, following the general idea of view-based 3D object understanding [47], an extraction-aggregation architecture is designed as the feature encoder, where a convolutional neural network (e.g., ResNet50 [25]) is first applied to extract single-view features independently. Then a recurrent neural network (e.g., GRU [11]) is adopted to aggregate multi-view features and form global descriptions. Afterwards, we formulate the next-view selection as a sequential decision process, where the model is demanded to decide the next discriminative view (action) according to previously observed views (state). Therefore, we implement a proximal policy optimization (PPO) [46] based multi-stage training strategy. In addition, considering that the difficulty of recognizing different samples varies and the resulting number of perspectives required differs, we design a dynamic exit inference strategy for better effort allocation - inspired by the idea of budgeted batch classification, a series of exciting confidence thresholds are estimated under a given effort expectation. Note that the proposed framework does not rely on specific neural network architectures. It can extend any", + "bbox": [ + 75, + 553, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "visual recognition network to an FGVC experts in the 3D environment.", + "bbox": [ + 496, + 90, + 890, + 119 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Finally, several carefully designed baselines are reproduced on MvCars as benchmark results, including previous multi-view recognition works, advanced neural networks, and popular FGVC methods. The experimental results demonstrate that the proposed method delivers a better performance-efficient trade-off than all competitors. After that, analysis of the upper bound and the selected trajectories reveals the inherent characteristics of MAFR. In addition, comprehensive ablation studies are carried out to verify the necessities of each model component.", + "bbox": [ + 496, + 121, + 893, + 272 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 287, + 640, + 304 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Fine-Grained Visual Classification", + "text_level": 1, + "bbox": [ + 500, + 313, + 799, + 329 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Due to the inherent subtle inter-class variance and the relatively large intra-class variance, fine-grained visual classification is much more challenging than ordinary coarse-grained classification. With vigorous efforts made by researchers, great progress has been made in many directions. Localization-based approaches [61, 31, 56, 19, 53, 6] that explicitly locate discriminative parts for feature extraction to alleviate the intra-class variance. High-order encoding methods [34, 20, 19, 59, 62, 21] that adopt high-order feature interactions for better representation ability that can capture the subtle differences. Chen et al. [9] and Du et al. [13] train the model with jigsaw patches to implicitly encourage knowledge mining from local regions. Recently, Chang et al. [5] leverage the underlying hierarchical structure of fine-grained categories to achieve user-friendly outputs and better performance.", + "bbox": [ + 496, + 335, + 893, + 578 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Except for good performances being brought, these works above also reveal that FGVC is never just a more challenging classification problem but a stand-alone field that requires well-directed research. In this paper, to further broaden the horizon of FGVC, we propose the multi-view active fine-grained visual recognition (MAFR) task aiming at effectively recognizing fine-grained categories in the 3D environment along with a targeted dataset. It is worth noting that the CompCars [57] dataset also provides a car dataset with view annotations. However, its multi-view images are taken from different samples, making it less suitable for the raised problem.", + "bbox": [ + 496, + 579, + 893, + 760 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Multi-View Recognition", + "text_level": 1, + "bbox": [ + 500, + 771, + 720, + 787 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Elsewhere for common object recognition problems, particular progress has been made to recognizing 3D objects with three trends that can be summarized [7]: point-based methods [42, 44, 2, 41], volume-based methods [37, 55, 43, 38], and view-based methods [10, 47, 29, 30, 60, 58]. Among them, point-based and volume-based approaches demand to perceive the 3D structure of objects via lidar,", + "bbox": [ + 496, + 795, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "1569", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/2575bed094a218698872e0d696ac96dab573a4fa32d7e99fed9796b145a06fcc.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 76, + 88, + 400, + 203 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/0bd51c589ad8875d6f3937018bb8a950bc827c2f705126fed1c71cb82ec33155.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 410, + 88, + 890, + 200 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/acb350d73b01b5e63f9a6c6b056ba03b94a894576a1bf8d1c5be6355a70e1914.jpg", + "image_caption": [ + "Figure 2. Illustration of samples from MvCars and some data statistics: (a) The number of samples per category. (b) The number of samples per type. (c) The number of samples per brand. (d) Results of our pilot experiment. The broken lines show model accuracy based on 8 individual views. Moreover, the bars represent the differences between each category's maximum and minimum accuracy." + ], + "image_footnote": [], + "bbox": [ + 76, + 203, + 401, + 311 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/ce6d3ebb3a27950a258b0c6f2dcc807f29543391afdc28ba71d1fdca22bc28a1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 403, + 204, + 890, + 311 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "depth sensor or something else, which makes them less practicable in daily applications, e.g., recognizing an unfamiliar car for detailed information simply with a mobile phone. On the contrary, view-based methods that leverage multiple surrounding 2D views as descriptors for 3D objects tend to be an optimal choice.", + "bbox": [ + 75, + 382, + 468, + 473 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Specifically, view-based methods share the core idea of encoding single-view features through a vision neural network and then aggregating multi-view features. Su et al. [47] first approaches the multi-view recognition problem with CNN for feature extraction and sum-pooling for aggregation. Then, Johns et al. [29] decomposes image sequences into image pair sets and then aggregates the pair-based classification in a weighted manner. After that, feature concatenation [51], hierarchical attention [22], and weighted fusion [17] are also adopted for better aggregating sequence features. In addition, sequences models (e.g., LSTM [26], GRU [11], Transformer blocks [49], etc) are also widely considered [28, 23, 7] and demonstrate their effectiveness.", + "bbox": [ + 75, + 474, + 468, + 686 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this paper, specifically towards the multi-view active fine-grained visual recognition (MAFR) task, traditional multi-view recognition dataset (e.g., RGB-D [33], ModelNet10, ModelNet40 [55]) is not sufficient any more. Thus, we first collect a fine-grained, multi-view car dataset named MvCars as a suitable testbed. Then, an active fine-grained recognition framework is built upon the general extraction-aggregation scheme. Note that, similar to ours, some approaches also take recognition efficiency into consideration [28, 29] by actively controlling the agent motion within a viewing sphere. However, a strict viewing sphere is not readily available in daily applications, especially for recognition with portable devices. We, therefore, consider the view selection as a discrete decision problem.", + "bbox": [ + 75, + 688, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Dataset", + "text_level": 1, + "bbox": [ + 500, + 380, + 589, + 396 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this work, we first contribute a testbed for MAFR by collecting a multi-view fine-grained car recognition dataset named Multi-view Cars (MvCars). Considering that car recognition is challenging and close to daily life [57], a vehicle dataset can demonstrate well how the MAFR model performs in real applications.", + "bbox": [ + 496, + 412, + 893, + 505 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Data Statistic", + "text_level": 1, + "bbox": [ + 500, + 532, + 640, + 547 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "MvCars consists of 233 models of cars from 35 brands (e.g., Ford, Volvo, Escort, etc.) that cover 5 types (e.g., sedan, SUV, MPV, sports car, and pickup). For each car, we collect and annotate 8 aligned perspectives – front, front-left, front-right, left, right, rear, rear-left, rear-right (as shown in Figure 2), and samples with missing perspectives are discarded. In total, there are 26,552 images collected from 3319 cars and are then split into 15,960/3,000/7,592 (at a ratio of $60\\% /10\\% /30\\%$ ) for train/val/test set, respectively.", + "bbox": [ + 496, + 561, + 893, + 712 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In addition to multi-view and fine-grained, MvCars is also a hierarchical and long-tail dataset. We can easily build the brand-type-model label hierarchies for categories in MvCars, e.g., \"Ford car\"-\"Ford sedan\"-\"Ford Mondeo\", which may benefit directions like hierarchical structure-based FGVC [15] and human-friendly FGVC [5]. The numbers of samples per category are shown in Figure 2 (a), where a significant long-tail distribution can be observed. Such a long-tail dataset is also closer to realistic application and provides a new scenario to related topic [3]. The sample sizes per type and brand are shown in Figure 2 (b) and (c), respectively, and similar data distributions exist.", + "bbox": [ + 496, + 719, + 893, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "1570", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/dd8ef5cf6bd811e232b12b23039424370f9bbf5bbc15ed3ca5d4187b3fcb2f29.jpg", + "image_caption": [ + "Figure 3. Illustration of the proposed MAFR framework where three training stages are included: Stage I for training a multi-view recognition model with smooth predictions, Stage II for optimizing the next-view selection component based on the behavior of the classifier, and Stage III for fine-tuning the recognition model along with the trajectory decided by the actor. Here we use three training steps for brief illustration." + ], + "image_footnote": [], + "bbox": [ + 83, + 89, + 885, + 333 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Pilot Experiment", + "text_level": 1, + "bbox": [ + 76, + 421, + 245, + 436 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "With the collected MvCars, here we first experimentally validate our first hypothesis mentioned in Section 1 – the discriminative information hides in various object views for different fine-grained categories. Factually, it is two-fold: (i) different perspectives contribute differently to FGVC; otherwise, actively selecting object view is meaningless, and (ii) different categories own different discriminative perspectives; otherwise, there is a trivial solution existing – consistently seeking the fixed distinguishable view.", + "bbox": [ + 75, + 445, + 468, + 580 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In particular, for each perspective, we train a ResNet50 [25] for classification and obtain its accuracy in each category. Therefore, we can tell which perspective is more distinguishable for any specific category by comparing the performances of 8 models based on different views. We show the results of 30 classes in Figure 2 (d). Bars in the graph indicate the differences between the maximum and minimum accuracy of each category, and the average difference of all 233 classes is about $36.40\\%$ . It powerfully proves that different perspectives contribute differently in the context of FGVC. On the other hand, broken lines in the graph represent the single-view accuracy changes along with different categories. The interaction of lines indicates that the ranking of view discrimination is inconsistent, demonstrating that different categories have different discriminative perspectives.", + "bbox": [ + 75, + 582, + 468, + 824 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In a word, in MvCars, different perspectives provide significantly various meanings for FGVC, which is also hard to pre-defined via prior knowledge. Thus, an active fine-grained recognition method is called for, and the collected MvCars dataset can serve as an eligible testbed.", + "bbox": [ + 75, + 825, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Methodology", + "text_level": 1, + "bbox": [ + 500, + 420, + 633, + 436 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Overview", + "text_level": 1, + "bbox": [ + 500, + 446, + 609, + 460 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Here we first give an overview of the data flow of MAFR during inference and introduce the model components needed.", + "bbox": [ + 498, + 472, + 892, + 516 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Data structure. For MAFR, a dataset $D$ consists of $N$ samples can be expressed as $D = \\{X_{i},y_{i}\\}_{i = 1}^{N}$ , where $X_{i} = \\{x_{i}^{1},\\ldots ,x_{i}^{v},\\ldots ,x_{i}^{V}\\}$ is a sequence of images depict a specific sample from $V$ perspectives and $y_{i}$ is their common ground-truth label. Note that, the annotations of views $\\{1,\\dots ,V\\}$ are aligned, i.e., for arbitrary two samples $X_{i}$ and $X_{j}$ , $x_{i}^{v}$ and $x_{j}^{v}$ are taken from the same perspective.", + "bbox": [ + 498, + 518, + 892, + 626 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Inference process. For sample $X_{i}$ , the model will take an image $x_{i}^{v_{1}}$ from arbitrary view $v_{1}$ as the initial visual input, which simulates the situation that the model may start recognition while facing any views of the target object. After that, the recognition process will carry on step-by-step. In particular, at step $t$ with input $x_{i}^{v_{t}}$ from view $v_{t}$ , the model will utilize all currently perceived information $\\{x_{i}^{v_{1}},\\ldots ,x_{i}^{v_{t - 1}},x_{i}^{v_{t}}\\}$ to deliver the category prediction $\\hat{y}_i^t$ and the next-view proposal $v_{t + 1}$ . Then, an inference cycle is closed, and the process can continue with $x_{i}^{v_{t + 1}}$ as the next input. Generally, $t\\in [1,T]$ , and $T$ can be set to a maximum $V$ .", + "bbox": [ + 496, + 627, + 893, + 806 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Framework component. An extraction-aggregation structure tends to be an intuitive choice to process a sequence of correlated visual inputs. Similar structures are also developed by previous multi-recognition arts [8]. Specifically, for any image $x_{i}^{v_{t}}$ input the system, a CNN-based feature extractor $\\mathcal{F}(\\cdot)$ is first applied to extract single-", + "bbox": [ + 496, + 810, + 893, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "1571", + "bbox": [ + 483, + 944, + 513, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "view feature as $f_{i}^{v_{t}} = \\mathcal{F}(x_{i}^{v_{t}})$ . It is worth noting that the feature extractors for different views share their weights, and this design will not lead to additional parameters. After that, an ideal model should consider all previously acquired information. Thus, a recurrent neural network is introduced as the aggregator $\\mathcal{R}(\\cdot)$ that aggregates features from all seen perspectives. In particular, we adopt two aggregators with the same structure but individual weights. $\\mathcal{R}_{e}(\\cdot)$ and $\\mathcal{R}_s(\\cdot)$ that, $\\mathcal{R}_e(\\cdot)$ form global embeddings $e_i^t = \\mathcal{R}_e(f_i^{v_1},\\dots ,f_i^{v_t})$ for category prediction, while $\\mathcal{R}_s(\\cdot)$ depicts the current states $s_i^t = \\mathcal{R}_s(f_i^{v_1},\\dots ,f_i^{v_t})$ for next-view selection. Finally, a classifier $\\mathcal{P}(\\cdot)$ and an actor $\\mathcal{A}(\\cdot)$ are equipped in parallel with outputs $\\hat{y}_i^t = \\mathcal{P}(e_i^t)$ and $v_{t + 1} = \\mathcal{A}(s_i^t)$ , respectively.", + "bbox": [ + 75, + 90, + 472, + 303 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Model Training", + "text_level": 1, + "bbox": [ + 76, + 314, + 235, + 330 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "According to the aforementioned inference process, we can tell that the recognition component and the next-view selection component work separately but not independently. The mission of the recognition component is quite straightforward – conducting category prediction based on acquired information as well as possible. While the optimization goal of the next-view selection component largely depends on the behaviour of recognition – basically, the actor should try to select the next-view that can maximize the prediction probability of the target category. Therefore, a three stages training framework is intuitively designed: Stage I aims to train a good recognition model (including $\\mathcal{F}(\\cdot),\\mathcal{R}_e(\\cdot)$ ,and $\\mathcal{P}(\\cdot))$ that can handle sequence input, Stage II aims to optimize the next-view selection module (where $\\mathcal{R}_s(\\cdot)$ and $\\mathcal{A}(\\cdot)$ participate) according to the behaviour of the trained recognition model, and Stages III aims to refine the recognition model under the trajectories decided by the actor.", + "bbox": [ + 75, + 339, + 472, + 595 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Note that the inductive bias behind training the recognition component in the first place is that its behaviour can reveal view discrimination - a more discriminative view will greatly reduce the entropy of category prediction. However, a well-convergent classification model often delivers high-confidence predictions, especially for the small-scale datasets in the FGVC scenario, which will cause little changes in prediction probabilities and limit the information being revealed. For this, we take a very intuitive yet effective solution that splitting the training set $D_{T}$ into two non-overlapping sub-sets for the first two stages respectively - specifically, a rehearsal set $D_{R}$ is used for training the recognition components in Stage I, and a evaluation set $D_{E}$ is used for providing authentic rewards while training the next-view selection module in Stage II. We have $D_{R} \\cup D_{E} = D_{T}$ and $D_{R} \\cap D_{E} = \\emptyset$ . In Stage III, the model will be trained with the whole training set $D_{T}$ .", + "bbox": [ + 75, + 595, + 472, + 852 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The whole framework is illustrated in Figure 3, and introductions about the three stages are as follows.", + "bbox": [ + 75, + 853, + 470, + 883 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Stage I. To train a recognition model that can handle a se", + "bbox": [ + 76, + 885, + 470, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "quence of inputs with dynamic length, each training iteration is divided into $T$ steps with input sequence lengths from 1 to $T$ . As the next-view planning module is not able for now, when $t \\geq 2$ , a new image $x_{i}^{v_{t}}$ is randomly selected from unseen views and appended to the input sequence at the $(t - 1)$ -th step. Here we set $T = V$ to ensure the maximum no-duplicated sequence can be sampled. With cross-entropy for optimization, the loss function for a batch of $B$ samples can be formulated as:", + "bbox": [ + 496, + 90, + 893, + 227 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {C E} (\\hat {y} _ {i} ^ {t}, y _ {i}) = \\frac {- 1}{B T C} \\sum_ {i = 1} ^ {B} \\sum_ {t = 1} ^ {T} \\sum_ {c = 1} ^ {C} y _ {i} \\times \\log (\\hat {y} _ {i, c} ^ {t}), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 522, + 238, + 893, + 280 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $C$ is the total category number, i.e., the channel number of the last layer.", + "bbox": [ + 498, + 291, + 890, + 320 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Additionally, we also introduce a entropy maximization penalty as", + "bbox": [ + 498, + 321, + 890, + 352 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL _ {E M} \\left(\\hat {y} _ {i} ^ {t}\\right) = \\frac {1}{B T C} \\sum_ {i = 1} ^ {B} \\sum_ {t = 1} ^ {T} \\sum_ {c = 1} ^ {C} \\hat {y} _ {i, c} ^ {t} \\times \\log \\left(\\hat {y} _ {i, c} ^ {t}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 526, + 363, + 890, + 405 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "to encourage smooth predictions that can better reveal the priority between views. The total loss can be expressed as $L_{Stage1} = L_{CE}(\\hat{y}_i^t, y_i) + \\alpha \\times L_{EM}(\\hat{y}_i^t)$ , and the degree of entropy maximization constrain can be control by the hyperparameter $\\alpha$ .", + "bbox": [ + 496, + 416, + 893, + 491 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Stage II. Here, the recognition components $(\\mathcal{F}(\\cdot),\\mathcal{R}_e(\\cdot)$ and $\\mathcal{P}(\\cdot))$ are frozen, and we only optimize $\\mathcal{R}_s(\\cdot)$ and $\\mathcal{A}(\\cdot)$ for next-view selection. As a non-differentiable sequential decision problem, we adopt the policy gradient method for optimization instead of directly optimizing with the classification loss. At the $t$ -th $(t\\geq 2)$ training step, the model will receive the input $x_{i}^{v_{t}}$ with the perspective $v_{t}$ decided by the actor at the $(t - 1)$ -th step. Then the view selection components can be updated according to the change of the target category's prediction probability, i.e., the rewards are set as $r_i^t = \\hat{y}_{iy_i}^t -\\hat{y}_{iy_i}^{t - 1}$ . And the $t$ -th $(t\\geq 2)$ step's loss function of Stage II can be simply expressed as: $L_{Stage2} = L_{PG}(v_t,\\hat{y}_i^{t - 1},\\hat{y}_i^t)$ . Detailed expansion of the loss function can be found in Section 4.3", + "bbox": [ + 496, + 491, + 893, + 703 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Notably, for popular policy gradient algorithms [45, 46], the total reward for the current step's optimization is a (weighted) sum of all feature rewards from now on. This is because these methods are designed for scenarios where an agent should achieve an ultimate goal through a series of actions. However, on the contrary, MAFR aims to use as few steps as possible to achieve as high accuracy as possible, i.e., we care more about achieving the best performance at the current step rather than in the future. Therefore, we slightly modify the policy gradient algorithm by utilizing only $r_i^t$ for the $t$ -th step's optimization.", + "bbox": [ + 496, + 703, + 893, + 869 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Stage III. There is nothing new in this stage - all settings are the same as Stage I except for (i) the selected view $v_{t}$", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "1572", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "when $t \\geq 2$ is given by the actor, (ii) the whole training set $D_{T}$ is used. The model is refined under standard classification supervision (i.e., $L_{Stage3} = L_{CE}(\\hat{y}_i^t, y_i)$ ) to especially adjust the trajectories decided by the actor and utilizing all the training data.", + "bbox": [ + 76, + 90, + 468, + 167 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Design Details", + "text_level": 1, + "bbox": [ + 76, + 174, + 223, + 189 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Feature extractor $\\mathcal{F}(\\cdot)$ . The feature extractor can be any backbone network for vision tasks, including various CNN architectures and Transformers (e.g., ResNet50 [25], ViT [12], etc.). Besides, by replacing $\\mathcal{F}(\\cdot)$ with other FGVC models, the proposed method can also extend them to work in 3D environments.", + "bbox": [ + 75, + 196, + 468, + 286 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Feature aggregator $\\mathcal{R}_e(\\cdot)$ and $\\mathcal{R}_s(\\cdot)$ . The two feature aggregators should be able to aggregate information from sequences with variable lengths. Here we adopt GRU [11] for best performance. There are alternatives like LSTM [26], self-attention block [49], etc..", + "bbox": [ + 75, + 287, + 468, + 362 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Classifier $\\mathcal{P}(\\cdot)$ and actor $\\mathcal{A}(\\cdot)$ . Both the classifier and the actor are formed by one fully connected layer. For the cases that equip the proposed framework with other FGVC approaches, the structure of the classifier can be modified accordingly.", + "bbox": [ + 75, + 363, + 468, + 438 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Policy gradient algorithm. For training the actor $\\mathcal{A}(\\cdot)$ (the next-view selection module) at Stgae II, we adopt the proximal policy optimization (PPO) algorithm [46] with a slight modification. Specifically, given a series of inputs $x_{i}^{v_{1}},\\ldots ,x_{i}^{v_{t}}$ at the $t$ -th step, the extractor $\\mathcal{F}(\\cdot)$ and the aggregator $\\mathcal{R}_s(\\cdot)$ are first applied to form the current state:", + "bbox": [ + 75, + 439, + 468, + 529 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\ns _ {i} ^ {t} = \\mathcal {R} _ {s} \\left(\\mathcal {F} \\left(x _ {i} ^ {v _ {1}}\\right), \\dots , \\mathcal {F} \\left(x _ {i} ^ {v _ {t}}\\right)\\right). \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 536, + 468, + 553 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "And then, the actor takes the state $s_i^t$ as input and decides the next view proposal $v_{t + 1}$ as the action (i.e., $v_{t + 1} = \\mathcal{A}(s_i^t)$ ). For the general PPO algorithm with the reward $r_i^t$ for $t$ -th step, the advantage estimator $\\hat{A}_i^t$ can be expressed as:", + "bbox": [ + 75, + 560, + 468, + 622 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {A} _ {t} = - V \\left(s _ {i} ^ {t}\\right) + r _ {i} ^ {t} + \\gamma r _ {i} ^ {t + 1} + \\dots + \\gamma^ {T - t} r _ {i} ^ {T}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 119, + 628, + 468, + 647 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $V(s_i^t)$ is the learned state-value function, $\\gamma \\in (0,1)$ is a pre-defined discount factor, $T$ is the maximum length of the input sequence. The principle behind it is straightforward - the current action should not only benefit the next step but also contribute to the overall goal. However, in this work, aiming at achieving reliable prediction with the least number of steps, we only focus on the profit at the very next step, i.e., we set $\\gamma = 0$ . The advantage estimator we use can be formulated by $\\hat{A}_i^t = -V(s_i^t) + r_i^t$ .", + "bbox": [ + 75, + 652, + 468, + 789 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "After that, we denote the prediction probability of $v_{t}$ by $\\mathcal{A}(v_t|s_i^t)$ . Then the clipped surrogate objective is:", + "bbox": [ + 76, + 789, + 468, + 820 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} L _ {C L I P} = \\frac {1}{B} \\sum_ {i = 1} ^ {B} \\sum_ {t = 2} ^ {T} \\min \\left\\{\\frac {\\mathcal {A} \\left(v _ {t} \\mid s _ {i} ^ {t}\\right)}{\\mathcal {A} _ {o l d} \\left(v _ {t} \\mid s _ {i} ^ {t}\\right)} \\hat {A} _ {i} ^ {t} \\right. \\tag {5} \\\\ c l i p (\\frac {\\mathcal {A} (v _ {t} | s _ {i} ^ {t})}{\\mathcal {A} _ {o l d} (v _ {t} | s _ {i} ^ {t})}, 1 - \\epsilon , 1 + \\epsilon) \\hat {A} _ {i} ^ {t} \\}, \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 130, + 825, + 468, + 904 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathcal{A}_{old}(\\cdot)$ stands for the actor before update, and $\\epsilon \\in (0,1)$ is a hyper-parameter. Note that $t$ starts from $t = 2$ since the first view is randomly selected. Finally, the overall objective of Stage II can be expressed as:", + "bbox": [ + 498, + 90, + 890, + 151 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {S t a g e 2} = L _ {P G} \\left(v _ {t}, \\hat {y} _ {i} ^ {t - 1}\\right) = L _ {C L I P} - c _ {1} L _ {V F} + c _ {2} L _ {E}, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 164, + 890, + 196 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $L_{VF} = \\frac{1}{B}\\sum_{i=1}^{B}\\sum_{t=2}^{T}(V(s_i^t) - V^{target}(s_i^t))^2$ is the squared-error loss suggested by [45], and $L_E = \\frac{1}{B}\\sum_{i=1}^{B}\\sum_{t=2}^{T}S_A(s_i^t)$ is the entropy bonus following [54, 40]. $c_1$ and $c_2$ are hyper-parameters to balance the three loss components.", + "bbox": [ + 498, + 196, + 890, + 272 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Dynamic Exiting", + "text_level": 1, + "bbox": [ + 500, + 285, + 666, + 301 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For the proposed method, we can achieve the accuracy-efficiency trade-off by setting the maximum number of steps. However, simply assigning the same maximum step number to all samples may be too arbitrary since difficult samples may require information from more views than simple samples do. For that, inspired by previous sequential prediction work [52], we introduce the concept of budget batch classification [27] for dynamic exiting. Specifically, defining the exit probability of a certain step to be $p$ , the probability of model exiting at the $t$ -th step is $p_t = \\alpha (1 - p)^{t - 1}p$ , where $\\alpha$ is a scaling factor that ensures $\\sum_{t = 1}^{T_{max}}p_t = 1$ . The value of $p$ can be found by solving the function $C = \\sum_{t = 1}^{T_{max}}t\\times p_t$ , where $C$ is the expectation of average prediction steps. Then, we can estimate the exiting threshold $\\mu_t$ for each step on the validation set. Such a strategy can further reveal the model potential under given step expectations by enabling better resource allocation among all test data.", + "bbox": [ + 498, + 309, + 890, + 583 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiment", + "text_level": 1, + "bbox": [ + 500, + 602, + 622, + 619 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation. The feature extractor $\\mathcal{F}(\\cdot)$ is initialized with ImageNet pre-trained weights, while other model components are randomly initialized. During Stage I and Stage III, we use SGD optimizer with a momentum of 0.9 and the cosine learning rate schedule [35] for optimization. The start learning rate is set to be 0.01 for the feature extractor and 0.1 for the rest. The input images are resize to $256 \\times 256$ and then random-cropped to $224 \\times 224$ . The hyper-parameter $\\alpha$ is set to be 0.01. During Stage II, we use the Adam optimizer with $\\beta_{1} = 0.9$ , $\\beta_{2} = 0.999$ , and the cosine learning rate schedule [35] for optimization. The start learning rate of the actor $\\mathcal{A}(\\cdot)$ is set to be 0.005. The input images are resize to $256 \\times 256$ and then center-cropped to $224 \\times 224$ . The hyper-parameters $\\epsilon$ , $c_{1}$ , and $c_{2}$ are set to be 0.2, 0.5, and 0.01, respectively. The model is trained for 15 epochs for each stage. During inference, the input images are resize to $256 \\times 256$ and then center-cropped to $224 \\times 224$ .", + "bbox": [ + 498, + 628, + 890, + 898 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "1573", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/d220e43dd101661ef42eccaf5b346ca4a1c16700fe03e03a9526a24f08779d98.jpg", + "table_caption": [], + "table_footnote": [ + "Table 1. Results of the proposed method with different backbones. The best results of each section are marked in bold." + ], + "table_body": "
MethodmAcc. (%)w-mAcc. (%)Step2-Acc. (%)
ResNet50RotationNet [30]79.53 ± 0.479.32 ± 0.778.72 ± 0.8
VERAM [8]79.42 ± 0.580.50 ± 1.380.19 ± 1.4
Baseline†78.21 ± 0.378.04 ± 0.576.74 ± 0.3
Baseline‡79.60 ± 0.779.75 ± 1.278.28 ± 0.8
Ours80.84 ± 0.482.20 ± 0.781.45 ± 0.9
Ours*81.33 ± 0.583.25 ± 0.982.86 ± 1.1
ViT-B.16Baseline†80.05 ± 0.480.32 ± 1.378.82 ± 0.4
Baseline‡80.47 ± 0.780.79 ± 1.479.93 ± 1.3
Ours81.35 ± 1.182.60 ± 0.681.53 ± 0.8
Ours*82.13 ± 1.283.58 ± 1.382.50 ± 1.4
PMGBaseline†80.26 ± 0.980.51 ± 1.479.92 ± 0.9
Baseline‡80.65 ± 0.980.98 ± 0.680.21 ± 0.4
Ours82.69 ± 1.183.47 ± 1.482.77 ± 1.3
Ours*82.99 ± 0.384.46 ± 0.583.79 ± 0.6
TransFGBaseline†81.26 ± 1.581.33 ± 0.980.76 ± 0.6
Baseline‡81.78 ± 1.282.15 ± 1.481.52 ± 0.6
Ours83.76 ± 1.384.72 ± 0.584.35 ± 1.0
Ours*84.89 ± 0.385.77 ± 1.385.57 ± 0.6
", + "bbox": [ + 78, + 88, + 472, + 347 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Baseline models. For extensive evaluation, three groups of approaches were considered for comparison: I. previous multi-view recognition methods, including RotationNet [30] and VERAM [8], II. state-of-the-art FGVC methods, including PMG [13] and TransFG [24], and III. advanced vision neural networks, including ResNet [25] and ViT [12]. Specifically, for group I, we re-implemented them with ResNet50 as the backbone model for a fair comparison. And for group II and III, as they are designed for single-view recognition, two baseline frameworks, which may be intuitive choices for most people, are designed to adapt them to the MAFR task: (i) Baseline†: a naive model ensemble scheme, i.e., predictions are independently delivered according to each view, and at the $t$ -th step, the average of $t$ inputs' predictions is adopted as the current result, and (ii) Baseline‡: due to their conciseness, these models can directly serve as the feature extractor of the proposed method, therefore, a strong sequential prediction baseline can be implemented by replacing our feature extractors with these approaches and training under the setting of Stage III.", + "bbox": [ + 75, + 398, + 472, + 700 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Evaluation Metrics. For quantitative evaluation, results based on 3 metrics are reported: (i) Mean Accuracy (mAcc) that takes the mean value of all $T$ steps' accuracy, which can be regarded as the area under the accuracy-step line that represents the general performances of models, (ii) Weighted Mean Accuracy (w-mAcc) that weights different steps with exponentially decreased weights, since the performance of the first few steps should be more important in the consideration of efficiency1, and (iii) Step2 Accuracy", + "bbox": [ + 75, + 702, + 472, + 839 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/7b5a9a57fa67146aa36f206c17e2781d5d9398c3e28cf61b788dc7b63831c691.jpg", + "image_caption": [ + "Figure 4. Illustration of model performance per-step and the performance upper bound from the perspective of trajectory decision." + ], + "image_footnote": [], + "bbox": [ + 504, + 89, + 890, + 304 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "(Step2-Acc) that takes the 2-nd step's accuracy to highlight the profit of the first view selection2.", + "bbox": [ + 500, + 367, + 890, + 398 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.1. Main Results", + "text_level": 1, + "bbox": [ + 500, + 417, + 638, + 431 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The results of the proposed method against all mentioned baselines are reported in Table 5. The table is organized into 4 sections according to different backbone networks. For ResNet50 [25] as the base model, we can observe that Baselined already achieves impressive performance and delivers quite competitive results to previous multi-view recognition models. On the contrary, the proposed method outperforms it by $\\sim 1.2\\%$ $\\sim 2.5\\%$ $\\sim 3.2\\%$ for mAcc, w-mAcc, and Step2-Acc, respectively. The larger margins on w-mAcc and Step2-Acc also demonstrate its superiority in efficiency that benefits from the active next-view selection scheme. In addition, while applying the dynamic exiting strategy, we also calculate these three metrics by obtaining the accuracy when the step expectations equal 1-8, and there is no doubt that it further boosts model performance via a better efforts allocation. An interesting finding is that for models with the next-view selection mechanism, we can generally observe that mAcc $<$ Step2-Acc, while mAcc $>$ Step2-Acc for other models, which indicates a significant performance boosting caused by the active view selection at step 2. In addition, for other baselines implemented with the more advanced network (i.e., ViT [12]) and FGVC models (i.e., PMG [13] and TransFG [24]), the proposed framework can also boost their performance via active view selection and dynamic exiting, which indicates most of the recognition models can be extended to be an FGVC experts in the real physical world.", + "bbox": [ + 496, + 444, + 893, + 853 + ], + "page_idx": 6 + }, + { + "type": "page_footnote", + "text": "1Here we take [0, 0.5039, 0.2520, 0.1260, 0.0630, 0.0315, 0.0157, 0.0079] for w-mAcc when $T = 8$ . The accuracy of the first step is weighted by 0.0 because it is randomly selected and does not relate to the performance of active selection.", + "bbox": [ + 75, + 849, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_footnote", + "text": "2Step2-Acc can be regarded as w-mAcc with weight set $[0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]$ .", + "bbox": [ + 500, + 875, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "1574", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/913a985f046db1415f7e209dfc587c369a992527294a3551455bc7590c3a3f32.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodmAcc. (%)w-mAcc. (%)Step2-Acc. (%)
Random Selection80.15 ± 0.579.86 ± 0.878.28 ± 0.6
Selecting the Farthest80.50 ± 0.481.49 ± 0.680.68 ± 0.9
Selecting w/ Prior80.43 ± 0.681.32 ± 0.980.55 ± 0.7
w/ Duplicate View80.22 ± 0.981.38 ± 0.881.18 ± 1.1
w/o Data Split80.19 ± 0.979.98 ± 1.178.53 ± 0.9
w/o LEM80.24 ± 0.481.57 ± 0.780.96 ± 1.0
w/ Future Rewards80.56 ± 0.681.44 ± 0.880.53 ± 0.8
Ours80.84 ± 0.482.20 ± 0.781.45 ± 0.9
Ours*81.33 ± 0.583.25 ± 0.982.86 ± 1.1
", + "bbox": [ + 78, + 88, + 470, + 229 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 2. Results of ablation studies. The best ones are marked in bold.", + "bbox": [ + 76, + 229, + 468, + 258 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.2. Upper Bound Analysis", + "text_level": 1, + "bbox": [ + 76, + 281, + 290, + 297 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To better illustrate the change of model accuracy over inference steps, we show the accuracy-step lines of all models with ResNet50 [25] as the backbone in Figure 4. At this point, the audiences may question why these models' performances do not consistently increase. With the same question, we study the upper bound of our model. Due to the finite total view numbers, we are able to visit all possible trajectories for each sample. Therefore, a performance upper bound can be obtained from the perspective of trajectory decision - an arbitrary sample will be considered correctly classified when any trajectory allows this sample to be classified correctly. According to Figure 4, the degradation in the last few steps is also observed on the performance upper bound. A similar phenomenon is also observed in previous multi-view recognition works (e.g., [30]). In this work, we also attribute this to the inherent feature of fine-grained recognition in the 3D environment - the discriminative clues only hide in a few views, and the noises caused by intra-class variance will be more likely to be introduced when full visual information (i.e., all views) is included. This echoes the essential insight in the 2D fine-grained recognition where subtle differences of local regions are discriminative, and the global structures are more likely disturbed.", + "bbox": [ + 75, + 305, + 472, + 667 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.3. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 679, + 230, + 695 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this section, we evaluate several variants of the proposed method based on ResNet50 to demonstrate the necessities of our designs. First, to verify the effectiveness of the active next-view selection mechanism, we study our model with no-duplicate inputs of random order and the order decided by the priority found in our pilot experiment. Fortunately, the proposed method passes the test with significant w-mAcc margins of $\\sim 2.3\\%$ and $\\sim 0.9\\%$ , respectively.", + "bbox": [ + 75, + 718, + 468, + 839 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In addition, The farthest viewpoint sampling is also an important baseline - specifically, we implement it by selecting the farthest and unselected view from the second step. In cases where there are two equally distant views, we ran", + "bbox": [ + 75, + 839, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/826dc0dd6afe8f18da8cfe43c1d2415ade88d4a31fa9bb6544fc89f258bfcbe0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 506, + 88, + 689, + 229 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2ec73597dbf687003cb585e772a7b26c7c81aa121c4c9784551803eeb3007350.jpg", + "image_caption": [ + "View-2" + ], + "image_footnote": [], + "bbox": [ + 514, + 233, + 607, + 290 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/6802b837f030fa4de5842fbb077da625a493893cd9702a0d37e9e4f83203a70d.jpg", + "image_caption": [ + "View-4", + "Figure 5. Predicted trajectories of \"Haval H6\" with \"View-2\" and \"View-5\" as the initial views. The darker the colour, the more times the trajectory has been selected. The most selected trajectory is highlighted with blue circles." + ], + "image_footnote": [], + "bbox": [ + 609, + 233, + 699, + 290 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f80e86a52fcc1590d22f12f68e9c3768ea5dbbbac99f9fb82bcdf6e41460c044.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 697, + 88, + 888, + 229 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/08fb35f353fcb3c485f6fefdbd605ae8b170f21f2237e9af17a9ea6a17743be7.jpg", + "image_caption": [ + "View-3" + ], + "image_footnote": [], + "bbox": [ + 700, + 233, + 792, + 290 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2226997a4824da6145de324f7d90ab564beeb44ff7997885fb1d566842a9c1fb.jpg", + "image_caption": [ + "View-5" + ], + "image_footnote": [], + "bbox": [ + 794, + 233, + 885, + 290 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "domly choose one of them. However, the proposed method consistently outperforms it with a significant margin. This is because the most complementary view may not be the farthest one, as we further illustrate on the right in the next Section (see Figure 5).", + "bbox": [ + 496, + 395, + 892, + 470 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Besides, an artificial restriction is added for all evaluations to ensure that new views selected are no-duplicate. It is intuitive since unseen views can offer complementary information, and the information about which views have been selected is easily acquired. Here we also evaluate by allowing duplicate views, and the model performance degrades with no surprise.", + "bbox": [ + 496, + 470, + 890, + 577 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "After that, our designs for model training are also demonstrated to be effective. Splitting the training data into two non-overlapped subsets and encouraging entropy maximization both significantly boost model performance. It is worth noting that when we include the future rewards for policy optimization, mAcc is not significantly affected ( with a slight degradation of $0.28\\%$ ), but w-mAcc and Step2- Acc decrease by $\\sim 0.8\\%$ and $\\sim 0.9\\%$ . This indicates that future rewards may be meaningful for traditional sequential decision problems but not for MAFR, where efficiency is highly required.", + "bbox": [ + 496, + 578, + 893, + 743 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.4. Trajectory Analysis", + "text_level": 1, + "bbox": [ + 500, + 755, + 687, + 771 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "For an in-depth analysis of the characteristics of the MAFR task, we further analyze the view-selection trajectory decided by our model. Specifically, with ResNet50 [25] as the feature extractor, we visualize the predicted trajectories of \"Haval H6\" in Figure 5. The two subplots show the results with \"View-2\" and \"View-5\" as the initial views, respectively, and the darker the colour, the more times the trajectory has been selected. The most se", + "bbox": [ + 496, + 779, + 893, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "1575", + "bbox": [ + 483, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "lected trajectory is highlighted with blue circles. According to the visualization, we can first conclude that there is some certainty in the best trajectory of a particular category – a significant broken line can be observed. However, the optimal trajectory is associated with the complementarity between different views – when we enter View-2, the next best choice is View-4; and when we enter View-5, the next best choice is View-3. Therefore, solving MAFR is not simply a ranking of the discriminative power of perspective information, echoing the results in Section 5.3 that view selecting with prior knowledge does not yield comparative performance. Factually, the optimal trajectory may even vary for different samples, as there is not just a single trajectory in each subplot. However, this may also be caused by the fact that our model still has room for improvement, so we do not discuss it further here.", + "bbox": [ + 75, + 90, + 472, + 330 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 344, + 194, + 359 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This paper extends the fine-grained visual classification to 3D environments and proposes the multi-view active fine-grained visual recognition (MAFR) problem. We first collect a multi-view fine-grained car dataset (MvCars) as a qualified benchmark. Then we re-implement several multiview recognition methods, FGVC approaches, and vision neural networks as baseline methods. A policy-gradient-based framework with a dynamic exiting strategy is proposed for the problem raised and yields the best performance. We also discuss the upper bound and predicted trajectories of the proposed method.", + "bbox": [ + 75, + 369, + 472, + 537 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgment", + "text_level": 1, + "bbox": [ + 76, + 547, + 228, + 565 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was supported in part by National Natural Science Foundation of China (NSFC) No. U19B2036, 62106022, 62225601, in part by Beijing Natural Science Foundation Project No. Z200002, in part by scholarships from China Scholarship Council (CSC) under Grant CSC No. 202206470055, in part by BUPT Excellent Ph.D. Students Foundation No. CX2022152, in part by the Program for Youth Innovative Research Team of BUPT No. 2023QNTD02, and in part by the Supported by High-performance Computing Platform of BUPT.", + "bbox": [ + 75, + 573, + 468, + 724 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 736, + 173, + 750 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] John Aloimonos, Isaac Weiss, and Amit Bandyopadhyay. 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In NeurIPS, 2019. 2" + ], + "bbox": [ + 78, + 90, + 470, + 446 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "1578", + "bbox": [ + 483, + 945, + 514, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multi-View Active Fine-Grained Visual Recognition/ee209e69-47ab-4c40-9356-cb8b45ac9b6d_model.json b/2023/Multi-View Active Fine-Grained Visual Recognition/ee209e69-47ab-4c40-9356-cb8b45ac9b6d_model.json new file mode 100644 index 0000000000000000000000000000000000000000..b3ee438f3e8e45f8d990179138a8396d9d9ff144 --- /dev/null +++ b/2023/Multi-View Active Fine-Grained Visual Recognition/ee209e69-47ab-4c40-9356-cb8b45ac9b6d_model.json @@ -0,0 +1,2301 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.223, + 0.131, + 0.748, + 0.154 + ], + "angle": 0, + "content": "Multi-View Active Fine-Grained Visual Recognition" + }, + { + "type": "text", + "bbox": [ + 0.132, + 0.18, + 0.836, + 0.217 + ], + "angle": 0, + "content": "Ruoyi Du\\(^{1}\\), Wenqing Yu\\(^{1}\\), Heqing Wang\\(^{1}\\), Ting-En Lin\\(^{2}\\), Dongliang Chang\\(^{1*}\\), Zhanyu Ma\\(^{1}\\) \n\\(^{1}\\)Beijing University of Posts and Telecommunications, China" + }, + { + "type": "text", + "bbox": [ + 0.17, + 0.218, + 0.8, + 0.234 + ], + "angle": 0, + "content": "\\(^{1}\\) {duruoyi, yuwenqing, wangheqing, changdongliang, mazhanyu}@bupt.edu.cn," + }, + { + "type": "text", + "bbox": [ + 0.397, + 0.234, + 0.575, + 0.251 + ], + "angle": 0, + "content": "2 sss950123@gmail.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.319, + 0.474, + 0.712 + ], + "angle": 0, + "content": "Despite the remarkable progress of Fine-grained visual classification (FGVC) with years of history, it is still limited to recognizing 2D images. Recognizing objects in the physical world (i.e., 3D environment) poses a unique challenge - discriminative information is not only present in visible local regions but also in other unseen views. Therefore, in addition to finding the distinguishable part from the current view, efficient and accurate recognition requires inferring the critical perspective with minimal glances. E.g., a person might recognize a \"Ford sedan\" with a glance at its side and then know that looking at the front can help tell which model it is. In this paper, towards FGVC in the real physical world, we put forward the problem of multi-view active fine-grained visual recognition (MAFR) and complete this study in three steps: (i) a multi-view, fine-grained vehicle dataset is collected as the testbed, (ii) a pilot experiment is designed to validate the need and research value of MAFR, (iii) a policy-gradient-based framework along with a dynamic exiting strategy is proposed to achieve efficient recognition with active view selection. Our comprehensive experiments demonstrate that the proposed method outperforms previous multi-view recognition works and can extend existing state-of-the-art FGVC methods and advanced neural networks to become \"FGVC experts\" in the 3D environment. Our code is available at https://github.com/PRIS-CV/MAFR." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.743, + 0.21, + 0.759 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.77, + 0.47, + 0.877 + ], + "angle": 0, + "content": "In the past two decades, fine-grained visual classification (FGVC) has made significant progress in recognizing sub-categories of objects belonging to the same class. This progress has been demonstrated in various domains, such as recognizing cars [32, 57], aircraft [36], birds [50, 48], and foods [39], with extensive outstanding works surpassing human experts in many application scenarios [34, 56," + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.286, + 0.653, + 0.452 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.653, + 0.286, + 0.89, + 0.452 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.455, + 0.894, + 0.538 + ], + "angle": 0, + "content": "Figure 1. Conventional FGVC versus Multi-view Active FGVC. Conventional FGVC takes a single static image for inference, which may omit the discriminative information. In contrast, Multiview FGVC takes a step further by predicting the potential discriminative view and fusing a sequence of visual information for the final decision." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.566, + 0.893, + 0.822 + ], + "angle": 0, + "content": "19, 53, 13, 4, 5, 16, 14]. However, the previous efforts on FGVC have remained mainly limited to a single-view-based paradigm, where only the visual content within a single static image is considered. This paradigm may be sufficient for coarse-grained classification where inter-class differences are easily captured, such as distinguishing a coupe from other vehicles by its streamlined body, seductive engine, or headlamps. However, fine-grained classification presents a different challenge where discriminative clues are rare and often found in subtle structural differences that are not easily captured by a single static view. For instance, to distinguish between different Ford sedans, one can only rely on subtle differences in the design of car headlights. Predictably, for single-view-based approaches, an image/view without discriminative clues is completely indistinguishable at the fine-grained level, fundamentally limiting the model's theoretical performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Factually, visual recognition is never limited to observing 2D environments and processing static images. Vision algorithms equipped by portal devices (e.g., smartphone, smart glasses, etc.) or embodied AI agents [18] (e.g., intelligent robots) play the core roles during machine-" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.888, + 0.289, + 0.901 + ], + "angle": 0, + "content": "*indicates the corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1568" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.244 + ], + "angle": 0, + "content": "environment interaction and have become one of the focuses of computer vision research. Therefore, to embrace the new trend, a natural extension of ordinary FGVC follows – in addition to locating discriminative parts within an image, we aim to infer the unseen distinguishable perspective within the physical world (i.e., 3D environment). Figure 1 shows an example where, with a single glance from the front, the algorithm may be uncertain about the model of the Ford sedan, but can infer that looking at its front will help to resolve the ambiguity." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.246, + 0.473, + 0.412 + ], + "angle": 0, + "content": "Specifically, we re-propose the concept of active vision [1] in the context of FGVC termed multi-view active fine-grained visual recognition (MAFR). MAFR is based on two essential hypotheses. Firstly, we hypothesize that discriminative information for different fine-grained categories is distributed across various object views, making discriminative perspective inference a non-trivial and worth studying. Secondly, we hypothesize that even views that appear indistinguishable at first glance can contain visual clues that can help infer the discriminative perspective, making the problem solvable." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.415, + 0.473, + 0.55 + ], + "angle": 0, + "content": "To start with, due to the absence of qualified datasets, we first collect a fine-grained, multi-view vehicle dataset named Multi-view Cars (MvCars) as the testbed. MvCars comprises 233 car models from 35 brands, covering 5 different car types. Each car in the dataset has 8 aligned views, and the dataset contains more than 26,000 images. In Section 3.2, we conducted a simple pilot experiment and verified our first hypothesis, which suggests that MvCars is well-suited for the problem at hand." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.554, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Secondly, our next contribution is an efficient multi-view fine-grained recognition framework building upon active next-view selection and dynamic exiting. In particular, following the general idea of view-based 3D object understanding [47], an extraction-aggregation architecture is designed as the feature encoder, where a convolutional neural network (e.g., ResNet50 [25]) is first applied to extract single-view features independently. Then a recurrent neural network (e.g., GRU [11]) is adopted to aggregate multi-view features and form global descriptions. Afterwards, we formulate the next-view selection as a sequential decision process, where the model is demanded to decide the next discriminative view (action) according to previously observed views (state). Therefore, we implement a proximal policy optimization (PPO) [46] based multi-stage training strategy. In addition, considering that the difficulty of recognizing different samples varies and the resulting number of perspectives required differs, we design a dynamic exit inference strategy for better effort allocation - inspired by the idea of budgeted batch classification, a series of exciting confidence thresholds are estimated under a given effort expectation. Note that the proposed framework does not rely on specific neural network architectures. It can extend any" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.121 + ], + "angle": 0, + "content": "visual recognition network to an FGVC experts in the 3D environment." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.122, + 0.894, + 0.273 + ], + "angle": 0, + "content": "Finally, several carefully designed baselines are reproduced on MvCars as benchmark results, including previous multi-view recognition works, advanced neural networks, and popular FGVC methods. The experimental results demonstrate that the proposed method delivers a better performance-efficient trade-off than all competitors. After that, analysis of the upper bound and the selected trajectories reveals the inherent characteristics of MAFR. In addition, comprehensive ablation studies are carried out to verify the necessities of each model component." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.289, + 0.642, + 0.305 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.314, + 0.8, + 0.33 + ], + "angle": 0, + "content": "2.1. Fine-Grained Visual Classification" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.337, + 0.895, + 0.579 + ], + "angle": 0, + "content": "Due to the inherent subtle inter-class variance and the relatively large intra-class variance, fine-grained visual classification is much more challenging than ordinary coarse-grained classification. With vigorous efforts made by researchers, great progress has been made in many directions. Localization-based approaches [61, 31, 56, 19, 53, 6] that explicitly locate discriminative parts for feature extraction to alleviate the intra-class variance. High-order encoding methods [34, 20, 19, 59, 62, 21] that adopt high-order feature interactions for better representation ability that can capture the subtle differences. Chen et al. [9] and Du et al. [13] train the model with jigsaw patches to implicitly encourage knowledge mining from local regions. Recently, Chang et al. [5] leverage the underlying hierarchical structure of fine-grained categories to achieve user-friendly outputs and better performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.58, + 0.895, + 0.761 + ], + "angle": 0, + "content": "Except for good performances being brought, these works above also reveal that FGVC is never just a more challenging classification problem but a stand-alone field that requires well-directed research. In this paper, to further broaden the horizon of FGVC, we propose the multi-view active fine-grained visual recognition (MAFR) task aiming at effectively recognizing fine-grained categories in the 3D environment along with a targeted dataset. It is worth noting that the CompCars [57] dataset also provides a car dataset with view annotations. However, its multi-view images are taken from different samples, making it less suitable for the raised problem." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.772, + 0.722, + 0.788 + ], + "angle": 0, + "content": "2.2. Multi-View Recognition" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.894, + 0.903 + ], + "angle": 0, + "content": "Elsewhere for common object recognition problems, particular progress has been made to recognizing 3D objects with three trends that can be summarized [7]: point-based methods [42, 44, 2, 41], volume-based methods [37, 55, 43, 38], and view-based methods [10, 47, 29, 30, 60, 58]. Among them, point-based and volume-based approaches demand to perceive the 3D structure of objects via lidar," + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1569" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.089, + 0.401, + 0.204 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.411, + 0.089, + 0.892, + 0.202 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.077, + 0.204, + 0.402, + 0.313 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.405, + 0.205, + 0.891, + 0.313 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.316, + 0.895, + 0.36 + ], + "angle": 0, + "content": "Figure 2. Illustration of samples from MvCars and some data statistics: (a) The number of samples per category. (b) The number of samples per type. (c) The number of samples per brand. (d) Results of our pilot experiment. The broken lines show model accuracy based on 8 individual views. Moreover, the bars represent the differences between each category's maximum and minimum accuracy." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.383, + 0.47, + 0.474 + ], + "angle": 0, + "content": "depth sensor or something else, which makes them less practicable in daily applications, e.g., recognizing an unfamiliar car for detailed information simply with a mobile phone. On the contrary, view-based methods that leverage multiple surrounding 2D views as descriptors for 3D objects tend to be an optimal choice." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.476, + 0.47, + 0.687 + ], + "angle": 0, + "content": "Specifically, view-based methods share the core idea of encoding single-view features through a vision neural network and then aggregating multi-view features. Su et al. [47] first approaches the multi-view recognition problem with CNN for feature extraction and sum-pooling for aggregation. Then, Johns et al. [29] decomposes image sequences into image pair sets and then aggregates the pair-based classification in a weighted manner. After that, feature concatenation [51], hierarchical attention [22], and weighted fusion [17] are also adopted for better aggregating sequence features. In addition, sequences models (e.g., LSTM [26], GRU [11], Transformer blocks [49], etc) are also widely considered [28, 23, 7] and demonstrate their effectiveness." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.903 + ], + "angle": 0, + "content": "In this paper, specifically towards the multi-view active fine-grained visual recognition (MAFR) task, traditional multi-view recognition dataset (e.g., RGB-D [33], ModelNet10, ModelNet40 [55]) is not sufficient any more. Thus, we first collect a fine-grained, multi-view car dataset named MvCars as a suitable testbed. Then, an active fine-grained recognition framework is built upon the general extraction-aggregation scheme. Note that, similar to ours, some approaches also take recognition efficiency into consideration [28, 29] by actively controlling the agent motion within a viewing sphere. However, a strict viewing sphere is not readily available in daily applications, especially for recognition with portable devices. We, therefore, consider the view selection as a discrete decision problem." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.381, + 0.59, + 0.397 + ], + "angle": 0, + "content": "3. Dataset" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.413, + 0.895, + 0.506 + ], + "angle": 0, + "content": "In this work, we first contribute a testbed for MAFR by collecting a multi-view fine-grained car recognition dataset named Multi-view Cars (MvCars). Considering that car recognition is challenging and close to daily life [57], a vehicle dataset can demonstrate well how the MAFR model performs in real applications." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.533, + 0.642, + 0.548 + ], + "angle": 0, + "content": "3.1. Data Statistic" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.562, + 0.894, + 0.713 + ], + "angle": 0, + "content": "MvCars consists of 233 models of cars from 35 brands (e.g., Ford, Volvo, Escort, etc.) that cover 5 types (e.g., sedan, SUV, MPV, sports car, and pickup). For each car, we collect and annotate 8 aligned perspectives – front, front-left, front-right, left, right, rear, rear-left, rear-right (as shown in Figure 2), and samples with missing perspectives are discarded. In total, there are 26,552 images collected from 3319 cars and are then split into 15,960/3,000/7,592 (at a ratio of \\(60\\% /10\\% /30\\%\\)) for train/val/test set, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.902 + ], + "angle": 0, + "content": "In addition to multi-view and fine-grained, MvCars is also a hierarchical and long-tail dataset. We can easily build the brand-type-model label hierarchies for categories in MvCars, e.g., \"Ford car\"-\"Ford sedan\"-\"Ford Mondeo\", which may benefit directions like hierarchical structure-based FGVC [15] and human-friendly FGVC [5]. The numbers of samples per category are shown in Figure 2 (a), where a significant long-tail distribution can be observed. Such a long-tail dataset is also closer to realistic application and provides a new scenario to related topic [3]. The sample sizes per type and brand are shown in Figure 2 (b) and (c), respectively, and similar data distributions exist." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1570" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.09, + 0.887, + 0.334 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.341, + 0.896, + 0.397 + ], + "angle": 0, + "content": "Figure 3. Illustration of the proposed MAFR framework where three training stages are included: Stage I for training a multi-view recognition model with smooth predictions, Stage II for optimizing the next-view selection component based on the behavior of the classifier, and Stage III for fine-tuning the recognition model along with the trajectory decided by the actor. Here we use three training steps for brief illustration." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.422, + 0.246, + 0.437 + ], + "angle": 0, + "content": "3.2. Pilot Experiment" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.446, + 0.47, + 0.581 + ], + "angle": 0, + "content": "With the collected MvCars, here we first experimentally validate our first hypothesis mentioned in Section 1 – the discriminative information hides in various object views for different fine-grained categories. Factually, it is two-fold: (i) different perspectives contribute differently to FGVC; otherwise, actively selecting object view is meaningless, and (ii) different categories own different discriminative perspectives; otherwise, there is a trivial solution existing – consistently seeking the fixed distinguishable view." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.583, + 0.47, + 0.825 + ], + "angle": 0, + "content": "In particular, for each perspective, we train a ResNet50 [25] for classification and obtain its accuracy in each category. Therefore, we can tell which perspective is more distinguishable for any specific category by comparing the performances of 8 models based on different views. We show the results of 30 classes in Figure 2 (d). Bars in the graph indicate the differences between the maximum and minimum accuracy of each category, and the average difference of all 233 classes is about \\(36.40\\%\\). It powerfully proves that different perspectives contribute differently in the context of FGVC. On the other hand, broken lines in the graph represent the single-view accuracy changes along with different categories. The interaction of lines indicates that the ranking of view discrimination is inconsistent, demonstrating that different categories have different discriminative perspectives." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.47, + 0.902 + ], + "angle": 0, + "content": "In a word, in MvCars, different perspectives provide significantly various meanings for FGVC, which is also hard to pre-defined via prior knowledge. Thus, an active fine-grained recognition method is called for, and the collected MvCars dataset can serve as an eligible testbed." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.421, + 0.635, + 0.438 + ], + "angle": 0, + "content": "4. Methodology" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.447, + 0.611, + 0.462 + ], + "angle": 0, + "content": "4.1. Overview" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.473, + 0.893, + 0.517 + ], + "angle": 0, + "content": "Here we first give an overview of the data flow of MAFR during inference and introduce the model components needed." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.52, + 0.893, + 0.627 + ], + "angle": 0, + "content": "Data structure. For MAFR, a dataset \\(D\\) consists of \\(N\\) samples can be expressed as \\(D = \\{X_{i},y_{i}\\}_{i = 1}^{N}\\), where \\(X_{i} = \\{x_{i}^{1},\\ldots ,x_{i}^{v},\\ldots ,x_{i}^{V}\\}\\) is a sequence of images depict a specific sample from \\(V\\) perspectives and \\(y_{i}\\) is their common ground-truth label. Note that, the annotations of views \\(\\{1,\\dots ,V\\}\\) are aligned, i.e., for arbitrary two samples \\(X_{i}\\) and \\(X_{j}\\), \\(x_{i}^{v}\\) and \\(x_{j}^{v}\\) are taken from the same perspective." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.628, + 0.894, + 0.808 + ], + "angle": 0, + "content": "Inference process. For sample \\( X_{i} \\), the model will take an image \\( x_{i}^{v_{1}} \\) from arbitrary view \\( v_{1} \\) as the initial visual input, which simulates the situation that the model may start recognition while facing any views of the target object. After that, the recognition process will carry on step-by-step. In particular, at step \\( t \\) with input \\( x_{i}^{v_{t}} \\) from view \\( v_{t} \\), the model will utilize all currently perceived information \\( \\{x_{i}^{v_{1}},\\ldots ,x_{i}^{v_{t - 1}},x_{i}^{v_{t}}\\} \\) to deliver the category prediction \\( \\hat{y}_i^t \\) and the next-view proposal \\( v_{t + 1} \\). Then, an inference cycle is closed, and the process can continue with \\( x_{i}^{v_{t + 1}} \\) as the next input. Generally, \\( t\\in [1,T] \\), and \\( T \\) can be set to a maximum \\( V \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.894, + 0.902 + ], + "angle": 0, + "content": "Framework component. An extraction-aggregation structure tends to be an intuitive choice to process a sequence of correlated visual inputs. Similar structures are also developed by previous multi-recognition arts [8]. Specifically, for any image \\( x_{i}^{v_{t}} \\) input the system, a CNN-based feature extractor \\( \\mathcal{F}(\\cdot) \\) is first applied to extract single-" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "1571" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.304 + ], + "angle": 0, + "content": "view feature as \\( f_{i}^{v_{t}} = \\mathcal{F}(x_{i}^{v_{t}}) \\). It is worth noting that the feature extractors for different views share their weights, and this design will not lead to additional parameters. After that, an ideal model should consider all previously acquired information. Thus, a recurrent neural network is introduced as the aggregator \\( \\mathcal{R}(\\cdot) \\) that aggregates features from all seen perspectives. In particular, we adopt two aggregators with the same structure but individual weights. \\( \\mathcal{R}_{e}(\\cdot) \\) and \\( \\mathcal{R}_s(\\cdot) \\) that, \\( \\mathcal{R}_e(\\cdot) \\) form global embeddings \\( e_i^t = \\mathcal{R}_e(f_i^{v_1},\\dots ,f_i^{v_t}) \\) for category prediction, while \\( \\mathcal{R}_s(\\cdot) \\) depicts the current states \\( s_i^t = \\mathcal{R}_s(f_i^{v_1},\\dots ,f_i^{v_t}) \\) for next-view selection. Finally, a classifier \\( \\mathcal{P}(\\cdot) \\) and an actor \\( \\mathcal{A}(\\cdot) \\) are equipped in parallel with outputs \\( \\hat{y}_i^t = \\mathcal{P}(e_i^t) \\) and \\( v_{t + 1} = \\mathcal{A}(s_i^t) \\), respectively." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.315, + 0.236, + 0.332 + ], + "angle": 0, + "content": "4.2. Model Training" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.34, + 0.473, + 0.596 + ], + "angle": 0, + "content": "According to the aforementioned inference process, we can tell that the recognition component and the next-view selection component work separately but not independently. The mission of the recognition component is quite straightforward – conducting category prediction based on acquired information as well as possible. While the optimization goal of the next-view selection component largely depends on the behaviour of recognition – basically, the actor should try to select the next-view that can maximize the prediction probability of the target category. Therefore, a three stages training framework is intuitively designed: Stage I aims to train a good recognition model (including \\(\\mathcal{F}(\\cdot),\\mathcal{R}_e(\\cdot)\\) ,and \\(\\mathcal{P}(\\cdot))\\) that can handle sequence input, Stage II aims to optimize the next-view selection module (where \\(\\mathcal{R}_s(\\cdot)\\) and \\(\\mathcal{A}(\\cdot)\\) participate) according to the behaviour of the trained recognition model, and Stages III aims to refine the recognition model under the trajectories decided by the actor." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.597, + 0.473, + 0.853 + ], + "angle": 0, + "content": "Note that the inductive bias behind training the recognition component in the first place is that its behaviour can reveal view discrimination - a more discriminative view will greatly reduce the entropy of category prediction. However, a well-convergent classification model often delivers high-confidence predictions, especially for the small-scale datasets in the FGVC scenario, which will cause little changes in prediction probabilities and limit the information being revealed. For this, we take a very intuitive yet effective solution that splitting the training set \\( D_{T} \\) into two non-overlapping sub-sets for the first two stages respectively - specifically, a rehearsal set \\( D_{R} \\) is used for training the recognition components in Stage I, and a evaluation set \\( D_{E} \\) is used for providing authentic rewards while training the next-view selection module in Stage II. We have \\( D_{R} \\cup D_{E} = D_{T} \\) and \\( D_{R} \\cap D_{E} = \\emptyset \\). In Stage III, the model will be trained with the whole training set \\( D_{T} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.854, + 0.472, + 0.884 + ], + "angle": 0, + "content": "The whole framework is illustrated in Figure 3, and introductions about the three stages are as follows." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.886, + 0.472, + 0.902 + ], + "angle": 0, + "content": "Stage I. To train a recognition model that can handle a se" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.228 + ], + "angle": 0, + "content": "quence of inputs with dynamic length, each training iteration is divided into \\( T \\) steps with input sequence lengths from 1 to \\( T \\). As the next-view planning module is not able for now, when \\( t \\geq 2 \\), a new image \\( x_{i}^{v_{t}} \\) is randomly selected from unseen views and appended to the input sequence at the \\( (t - 1) \\)-th step. Here we set \\( T = V \\) to ensure the maximum no-duplicated sequence can be sampled. With cross-entropy for optimization, the loss function for a batch of \\( B \\) samples can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.524, + 0.239, + 0.895, + 0.281 + ], + "angle": 0, + "content": "\\[\nL _ {C E} (\\hat {y} _ {i} ^ {t}, y _ {i}) = \\frac {- 1}{B T C} \\sum_ {i = 1} ^ {B} \\sum_ {t = 1} ^ {T} \\sum_ {c = 1} ^ {C} y _ {i} \\times \\log (\\hat {y} _ {i, c} ^ {t}), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.292, + 0.892, + 0.321 + ], + "angle": 0, + "content": "where \\(C\\) is the total category number, i.e., the channel number of the last layer." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.322, + 0.892, + 0.353 + ], + "angle": 0, + "content": "Additionally, we also introduce a entropy maximization penalty as" + }, + { + "type": "equation", + "bbox": [ + 0.527, + 0.364, + 0.892, + 0.406 + ], + "angle": 0, + "content": "\\[\nL _ {E M} \\left(\\hat {y} _ {i} ^ {t}\\right) = \\frac {1}{B T C} \\sum_ {i = 1} ^ {B} \\sum_ {t = 1} ^ {T} \\sum_ {c = 1} ^ {C} \\hat {y} _ {i, c} ^ {t} \\times \\log \\left(\\hat {y} _ {i, c} ^ {t}\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.417, + 0.895, + 0.492 + ], + "angle": 0, + "content": "to encourage smooth predictions that can better reveal the priority between views. The total loss can be expressed as \\( L_{Stage1} = L_{CE}(\\hat{y}_i^t, y_i) + \\alpha \\times L_{EM}(\\hat{y}_i^t) \\), and the degree of entropy maximization constrain can be control by the hyperparameter \\( \\alpha \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.492, + 0.895, + 0.704 + ], + "angle": 0, + "content": "Stage II. Here, the recognition components \\((\\mathcal{F}(\\cdot),\\mathcal{R}_e(\\cdot)\\) and \\(\\mathcal{P}(\\cdot))\\) are frozen, and we only optimize \\(\\mathcal{R}_s(\\cdot)\\) and \\(\\mathcal{A}(\\cdot)\\) for next-view selection. As a non-differentiable sequential decision problem, we adopt the policy gradient method for optimization instead of directly optimizing with the classification loss. At the \\(t\\)-th \\((t\\geq 2)\\) training step, the model will receive the input \\(x_{i}^{v_{t}}\\) with the perspective \\(v_{t}\\) decided by the actor at the \\((t - 1)\\)-th step. Then the view selection components can be updated according to the change of the target category's prediction probability, i.e., the rewards are set as \\(r_i^t = \\hat{y}_{iy_i}^t -\\hat{y}_{iy_i}^{t - 1}\\). And the \\(t\\)-th \\((t\\geq 2)\\) step's loss function of Stage II can be simply expressed as: \\(L_{Stage2} = L_{PG}(v_t,\\hat{y}_i^{t - 1},\\hat{y}_i^t)\\). Detailed expansion of the loss function can be found in Section 4.3" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.704, + 0.895, + 0.87 + ], + "angle": 0, + "content": "Notably, for popular policy gradient algorithms [45, 46], the total reward for the current step's optimization is a (weighted) sum of all feature rewards from now on. This is because these methods are designed for scenarios where an agent should achieve an ultimate goal through a series of actions. However, on the contrary, MAFR aims to use as few steps as possible to achieve as high accuracy as possible, i.e., we care more about achieving the best performance at the current step rather than in the future. Therefore, we slightly modify the policy gradient algorithm by utilizing only \\( r_i^t \\) for the \\( t \\)-th step's optimization." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Stage III. There is nothing new in this stage - all settings are the same as Stage I except for (i) the selected view \\( v_{t} \\)" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1572" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.168 + ], + "angle": 0, + "content": "when \\( t \\geq 2 \\) is given by the actor, (ii) the whole training set \\( D_{T} \\) is used. The model is refined under standard classification supervision (i.e., \\( L_{Stage3} = L_{CE}(\\hat{y}_i^t, y_i) \\)) to especially adjust the trajectories decided by the actor and utilizing all the training data." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.175, + 0.224, + 0.19 + ], + "angle": 0, + "content": "4.3. Design Details" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.197, + 0.469, + 0.287 + ], + "angle": 0, + "content": "Feature extractor \\(\\mathcal{F}(\\cdot)\\). The feature extractor can be any backbone network for vision tasks, including various CNN architectures and Transformers (e.g., ResNet50 [25], ViT [12], etc.). Besides, by replacing \\(\\mathcal{F}(\\cdot)\\) with other FGVC models, the proposed method can also extend them to work in 3D environments." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.288, + 0.469, + 0.363 + ], + "angle": 0, + "content": "Feature aggregator \\(\\mathcal{R}_e(\\cdot)\\) and \\(\\mathcal{R}_s(\\cdot)\\). The two feature aggregators should be able to aggregate information from sequences with variable lengths. Here we adopt GRU [11] for best performance. There are alternatives like LSTM [26], self-attention block [49], etc.." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.364, + 0.469, + 0.439 + ], + "angle": 0, + "content": "Classifier \\(\\mathcal{P}(\\cdot)\\) and actor \\(\\mathcal{A}(\\cdot)\\). Both the classifier and the actor are formed by one fully connected layer. For the cases that equip the proposed framework with other FGVC approaches, the structure of the classifier can be modified accordingly." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.44, + 0.469, + 0.53 + ], + "angle": 0, + "content": "Policy gradient algorithm. For training the actor \\(\\mathcal{A}(\\cdot)\\) (the next-view selection module) at Stgae II, we adopt the proximal policy optimization (PPO) algorithm [46] with a slight modification. Specifically, given a series of inputs \\(x_{i}^{v_{1}},\\ldots ,x_{i}^{v_{t}}\\) at the \\(t\\) -th step, the extractor \\(\\mathcal{F}(\\cdot)\\) and the aggregator \\(\\mathcal{R}_s(\\cdot)\\) are first applied to form the current state:" + }, + { + "type": "equation", + "bbox": [ + 0.167, + 0.537, + 0.469, + 0.554 + ], + "angle": 0, + "content": "\\[\ns _ {i} ^ {t} = \\mathcal {R} _ {s} \\left(\\mathcal {F} \\left(x _ {i} ^ {v _ {1}}\\right), \\dots , \\mathcal {F} \\left(x _ {i} ^ {v _ {t}}\\right)\\right). \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.561, + 0.469, + 0.623 + ], + "angle": 0, + "content": "And then, the actor takes the state \\( s_i^t \\) as input and decides the next view proposal \\( v_{t + 1} \\) as the action (i.e., \\( v_{t + 1} = \\mathcal{A}(s_i^t) \\)). For the general PPO algorithm with the reward \\( r_i^t \\) for \\( t \\)-th step, the advantage estimator \\( \\hat{A}_i^t \\) can be expressed as:" + }, + { + "type": "equation", + "bbox": [ + 0.12, + 0.629, + 0.469, + 0.648 + ], + "angle": 0, + "content": "\\[\n\\hat {A} _ {t} = - V \\left(s _ {i} ^ {t}\\right) + r _ {i} ^ {t} + \\gamma r _ {i} ^ {t + 1} + \\dots + \\gamma^ {T - t} r _ {i} ^ {T}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.654, + 0.469, + 0.79 + ], + "angle": 0, + "content": "where \\( V(s_i^t) \\) is the learned state-value function, \\( \\gamma \\in (0,1) \\) is a pre-defined discount factor, \\( T \\) is the maximum length of the input sequence. The principle behind it is straightforward - the current action should not only benefit the next step but also contribute to the overall goal. However, in this work, aiming at achieving reliable prediction with the least number of steps, we only focus on the profit at the very next step, i.e., we set \\( \\gamma = 0 \\). The advantage estimator we use can be formulated by \\( \\hat{A}_i^t = -V(s_i^t) + r_i^t \\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.79, + 0.469, + 0.821 + ], + "angle": 0, + "content": "After that, we denote the prediction probability of \\( v_{t} \\) by \\( \\mathcal{A}(v_t|s_i^t) \\). Then the clipped surrogate objective is:" + }, + { + "type": "equation", + "bbox": [ + 0.131, + 0.827, + 0.469, + 0.905 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} L _ {C L I P} = \\frac {1}{B} \\sum_ {i = 1} ^ {B} \\sum_ {t = 2} ^ {T} \\min \\left\\{\\frac {\\mathcal {A} \\left(v _ {t} \\mid s _ {i} ^ {t}\\right)}{\\mathcal {A} _ {o l d} \\left(v _ {t} \\mid s _ {i} ^ {t}\\right)} \\hat {A} _ {i} ^ {t} \\right. \\tag {5} \\\\ c l i p (\\frac {\\mathcal {A} (v _ {t} | s _ {i} ^ {t})}{\\mathcal {A} _ {o l d} (v _ {t} | s _ {i} ^ {t})}, 1 - \\epsilon , 1 + \\epsilon) \\hat {A} _ {i} ^ {t} \\}, \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "where \\(\\mathcal{A}_{old}(\\cdot)\\) stands for the actor before update, and \\(\\epsilon \\in (0,1)\\) is a hyper-parameter. Note that \\(t\\) starts from \\(t = 2\\) since the first view is randomly selected. Finally, the overall objective of Stage II can be expressed as:" + }, + { + "type": "equation", + "bbox": [ + 0.51, + 0.165, + 0.892, + 0.197 + ], + "angle": 0, + "content": "\\[\nL _ {S t a g e 2} = L _ {P G} \\left(v _ {t}, \\hat {y} _ {i} ^ {t - 1}\\right) = L _ {C L I P} - c _ {1} L _ {V F} + c _ {2} L _ {E}, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.197, + 0.892, + 0.273 + ], + "angle": 0, + "content": "where \\( L_{VF} = \\frac{1}{B}\\sum_{i=1}^{B}\\sum_{t=2}^{T}(V(s_i^t) - V^{target}(s_i^t))^2 \\) is the squared-error loss suggested by [45], and \\( L_E = \\frac{1}{B}\\sum_{i=1}^{B}\\sum_{t=2}^{T}S_A(s_i^t) \\) is the entropy bonus following [54, 40]. \\( c_1 \\) and \\( c_2 \\) are hyper-parameters to balance the three loss components." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.286, + 0.667, + 0.302 + ], + "angle": 0, + "content": "4.4. Dynamic Exiting" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.31, + 0.892, + 0.584 + ], + "angle": 0, + "content": "For the proposed method, we can achieve the accuracy-efficiency trade-off by setting the maximum number of steps. However, simply assigning the same maximum step number to all samples may be too arbitrary since difficult samples may require information from more views than simple samples do. For that, inspired by previous sequential prediction work [52], we introduce the concept of budget batch classification [27] for dynamic exiting. Specifically, defining the exit probability of a certain step to be \\( p \\), the probability of model exiting at the \\( t \\)-th step is \\( p_t = \\alpha (1 - p)^{t - 1}p \\), where \\( \\alpha \\) is a scaling factor that ensures \\( \\sum_{t = 1}^{T_{max}}p_t = 1 \\). The value of \\( p \\) can be found by solving the function \\( C = \\sum_{t = 1}^{T_{max}}t\\times p_t \\), where \\( C \\) is the expectation of average prediction steps. Then, we can estimate the exiting threshold \\( \\mu_t \\) for each step on the validation set. Such a strategy can further reveal the model potential under given step expectations by enabling better resource allocation among all test data." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.603, + 0.624, + 0.62 + ], + "angle": 0, + "content": "5. Experiment" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.629, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Implementation. The feature extractor \\(\\mathcal{F}(\\cdot)\\) is initialized with ImageNet pre-trained weights, while other model components are randomly initialized. During Stage I and Stage III, we use SGD optimizer with a momentum of 0.9 and the cosine learning rate schedule [35] for optimization. The start learning rate is set to be 0.01 for the feature extractor and 0.1 for the rest. The input images are resize to \\(256 \\times 256\\) and then random-cropped to \\(224 \\times 224\\). The hyper-parameter \\(\\alpha\\) is set to be 0.01. During Stage II, we use the Adam optimizer with \\(\\beta_{1} = 0.9\\), \\(\\beta_{2} = 0.999\\), and the cosine learning rate schedule [35] for optimization. The start learning rate of the actor \\(\\mathcal{A}(\\cdot)\\) is set to be 0.005. The input images are resize to \\(256 \\times 256\\) and then center-cropped to \\(224 \\times 224\\). The hyper-parameters \\(\\epsilon\\), \\(c_{1}\\), and \\(c_{2}\\) are set to be 0.2, 0.5, and 0.01, respectively. The model is trained for 15 epochs for each stage. During inference, the input images are resize to \\(256 \\times 256\\) and then center-cropped to \\(224 \\times 224\\)." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1573" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.079, + 0.089, + 0.473, + 0.348 + ], + "angle": 0, + "content": "
MethodmAcc. (%)w-mAcc. (%)Step2-Acc. (%)
ResNet50RotationNet [30]79.53 ± 0.479.32 ± 0.778.72 ± 0.8
VERAM [8]79.42 ± 0.580.50 ± 1.380.19 ± 1.4
Baseline†78.21 ± 0.378.04 ± 0.576.74 ± 0.3
Baseline‡79.60 ± 0.779.75 ± 1.278.28 ± 0.8
Ours80.84 ± 0.482.20 ± 0.781.45 ± 0.9
Ours*81.33 ± 0.583.25 ± 0.982.86 ± 1.1
ViT-B.16Baseline†80.05 ± 0.480.32 ± 1.378.82 ± 0.4
Baseline‡80.47 ± 0.780.79 ± 1.479.93 ± 1.3
Ours81.35 ± 1.182.60 ± 0.681.53 ± 0.8
Ours*82.13 ± 1.283.58 ± 1.382.50 ± 1.4
PMGBaseline†80.26 ± 0.980.51 ± 1.479.92 ± 0.9
Baseline‡80.65 ± 0.980.98 ± 0.680.21 ± 0.4
Ours82.69 ± 1.183.47 ± 1.482.77 ± 1.3
Ours*82.99 ± 0.384.46 ± 0.583.79 ± 0.6
TransFGBaseline†81.26 ± 1.581.33 ± 0.980.76 ± 0.6
Baseline‡81.78 ± 1.282.15 ± 1.481.52 ± 0.6
Ours83.76 ± 1.384.72 ± 0.584.35 ± 1.0
Ours*84.89 ± 0.385.77 ± 1.385.57 ± 0.6
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.077, + 0.348, + 0.47, + 0.376 + ], + "angle": 0, + "content": "Table 1. Results of the proposed method with different backbones. The best results of each section are marked in bold." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.4, + 0.473, + 0.702 + ], + "angle": 0, + "content": "Baseline models. For extensive evaluation, three groups of approaches were considered for comparison: I. previous multi-view recognition methods, including RotationNet [30] and VERAM [8], II. state-of-the-art FGVC methods, including PMG [13] and TransFG [24], and III. advanced vision neural networks, including ResNet [25] and ViT [12]. Specifically, for group I, we re-implemented them with ResNet50 as the backbone model for a fair comparison. And for group II and III, as they are designed for single-view recognition, two baseline frameworks, which may be intuitive choices for most people, are designed to adapt them to the MAFR task: (i) Baseline†: a naive model ensemble scheme, i.e., predictions are independently delivered according to each view, and at the \\(t\\)-th step, the average of \\(t\\) inputs' predictions is adopted as the current result, and (ii) Baseline‡: due to their conciseness, these models can directly serve as the feature extractor of the proposed method, therefore, a strong sequential prediction baseline can be implemented by replacing our feature extractors with these approaches and training under the setting of Stage III." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.703, + 0.473, + 0.84 + ], + "angle": 0, + "content": "Evaluation Metrics. For quantitative evaluation, results based on 3 metrics are reported: (i) Mean Accuracy (mAcc) that takes the mean value of all \\( T \\) steps' accuracy, which can be regarded as the area under the accuracy-step line that represents the general performances of models, (ii) Weighted Mean Accuracy (w-mAcc) that weights different steps with exponentially decreased weights, since the performance of the first few steps should be more important in the consideration of efficiency1, and (iii) Step2 Accuracy" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.09, + 0.891, + 0.305 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.308, + 0.893, + 0.337 + ], + "angle": 0, + "content": "Figure 4. Illustration of model performance per-step and the performance upper bound from the perspective of trajectory decision." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.368, + 0.892, + 0.399 + ], + "angle": 0, + "content": "(Step2-Acc) that takes the 2-nd step's accuracy to highlight the profit of the first view selection2." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.418, + 0.64, + 0.433 + ], + "angle": 0, + "content": "5.1. Main Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.445, + 0.895, + 0.854 + ], + "angle": 0, + "content": "The results of the proposed method against all mentioned baselines are reported in Table 5. The table is organized into 4 sections according to different backbone networks. For ResNet50 [25] as the base model, we can observe that Baselined already achieves impressive performance and delivers quite competitive results to previous multi-view recognition models. On the contrary, the proposed method outperforms it by \\(\\sim 1.2\\%\\) \\(\\sim 2.5\\%\\) \\(\\sim 3.2\\%\\) for mAcc, w-mAcc, and Step2-Acc, respectively. The larger margins on w-mAcc and Step2-Acc also demonstrate its superiority in efficiency that benefits from the active next-view selection scheme. In addition, while applying the dynamic exiting strategy, we also calculate these three metrics by obtaining the accuracy when the step expectations equal 1-8, and there is no doubt that it further boosts model performance via a better efforts allocation. An interesting finding is that for models with the next-view selection mechanism, we can generally observe that mAcc \\(<\\) Step2-Acc, while mAcc \\(>\\) Step2-Acc for other models, which indicates a significant performance boosting caused by the active view selection at step 2. In addition, for other baselines implemented with the more advanced network (i.e., ViT [12]) and FGVC models (i.e., PMG [13] and TransFG [24]), the proposed framework can also boost their performance via active view selection and dynamic exiting, which indicates most of the recognition models can be extended to be an FGVC experts in the real physical world." + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.85, + 0.47, + 0.901 + ], + "angle": 0, + "content": "1Here we take [0, 0.5039, 0.2520, 0.1260, 0.0630, 0.0315, 0.0157, 0.0079] for w-mAcc when \\( T = 8 \\). The accuracy of the first step is weighted by 0.0 because it is randomly selected and does not relate to the performance of active selection." + }, + { + "type": "page_footnote", + "bbox": [ + 0.501, + 0.875, + 0.892, + 0.901 + ], + "angle": 0, + "content": "2Step2-Acc can be regarded as w-mAcc with weight set \\([0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]\\)." + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1574" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.08, + 0.089, + 0.472, + 0.23 + ], + "angle": 0, + "content": "
MethodmAcc. (%)w-mAcc. (%)Step2-Acc. (%)
Random Selection80.15 ± 0.579.86 ± 0.878.28 ± 0.6
Selecting the Farthest80.50 ± 0.481.49 ± 0.680.68 ± 0.9
Selecting w/ Prior80.43 ± 0.681.32 ± 0.980.55 ± 0.7
w/ Duplicate View80.22 ± 0.981.38 ± 0.881.18 ± 1.1
w/o Data Split80.19 ± 0.979.98 ± 1.178.53 ± 0.9
w/o LEM80.24 ± 0.481.57 ± 0.780.96 ± 1.0
w/ Future Rewards80.56 ± 0.681.44 ± 0.880.53 ± 0.8
Ours80.84 ± 0.482.20 ± 0.781.45 ± 0.9
Ours*81.33 ± 0.583.25 ± 0.982.86 ± 1.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.231, + 0.47, + 0.259 + ], + "angle": 0, + "content": "Table 2. Results of ablation studies. The best ones are marked in bold." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.282, + 0.291, + 0.299 + ], + "angle": 0, + "content": "5.2. Upper Bound Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.306, + 0.473, + 0.668 + ], + "angle": 0, + "content": "To better illustrate the change of model accuracy over inference steps, we show the accuracy-step lines of all models with ResNet50 [25] as the backbone in Figure 4. At this point, the audiences may question why these models' performances do not consistently increase. With the same question, we study the upper bound of our model. Due to the finite total view numbers, we are able to visit all possible trajectories for each sample. Therefore, a performance upper bound can be obtained from the perspective of trajectory decision - an arbitrary sample will be considered correctly classified when any trajectory allows this sample to be classified correctly. According to Figure 4, the degradation in the last few steps is also observed on the performance upper bound. A similar phenomenon is also observed in previous multi-view recognition works (e.g., [30]). In this work, we also attribute this to the inherent feature of fine-grained recognition in the 3D environment - the discriminative clues only hide in a few views, and the noises caused by intra-class variance will be more likely to be introduced when full visual information (i.e., all views) is included. This echoes the essential insight in the 2D fine-grained recognition where subtle differences of local regions are discriminative, and the global structures are more likely disturbed." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.68, + 0.231, + 0.696 + ], + "angle": 0, + "content": "5.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.719, + 0.47, + 0.84 + ], + "angle": 0, + "content": "In this section, we evaluate several variants of the proposed method based on ResNet50 to demonstrate the necessities of our designs. First, to verify the effectiveness of the active next-view selection mechanism, we study our model with no-duplicate inputs of random order and the order decided by the priority found in our pilot experiment. Fortunately, the proposed method passes the test with significant w-mAcc margins of \\(\\sim 2.3\\%\\) and \\(\\sim 0.9\\%\\), respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.902 + ], + "angle": 0, + "content": "In addition, The farthest viewpoint sampling is also an important baseline - specifically, we implement it by selecting the farthest and unselected view from the second step. In cases where there are two equally distant views, we ran" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.089, + 0.691, + 0.231 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.515, + 0.234, + 0.609, + 0.291 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.541, + 0.294, + 0.584, + 0.305 + ], + "angle": 0, + "content": "View-2" + }, + { + "type": "image", + "bbox": [ + 0.61, + 0.234, + 0.7, + 0.291 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.634, + 0.294, + 0.676, + 0.305 + ], + "angle": 0, + "content": "View-4" + }, + { + "type": "image", + "bbox": [ + 0.699, + 0.089, + 0.89, + 0.231 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.701, + 0.234, + 0.793, + 0.291 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.726, + 0.294, + 0.77, + 0.305 + ], + "angle": 0, + "content": "View-3" + }, + { + "type": "image", + "bbox": [ + 0.795, + 0.234, + 0.887, + 0.291 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.819, + 0.294, + 0.862, + 0.305 + ], + "angle": 0, + "content": "View-5" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.313, + 0.895, + 0.37 + ], + "angle": 0, + "content": "Figure 5. Predicted trajectories of \"Haval H6\" with \"View-2\" and \"View-5\" as the initial views. The darker the colour, the more times the trajectory has been selected. The most selected trajectory is highlighted with blue circles." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.396, + 0.893, + 0.472 + ], + "angle": 0, + "content": "domly choose one of them. However, the proposed method consistently outperforms it with a significant margin. This is because the most complementary view may not be the farthest one, as we further illustrate on the right in the next Section (see Figure 5)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.472, + 0.892, + 0.578 + ], + "angle": 0, + "content": "Besides, an artificial restriction is added for all evaluations to ensure that new views selected are no-duplicate. It is intuitive since unseen views can offer complementary information, and the information about which views have been selected is easily acquired. Here we also evaluate by allowing duplicate views, and the model performance degrades with no surprise." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.579, + 0.895, + 0.744 + ], + "angle": 0, + "content": "After that, our designs for model training are also demonstrated to be effective. Splitting the training data into two non-overlapped subsets and encouraging entropy maximization both significantly boost model performance. It is worth noting that when we include the future rewards for policy optimization, mAcc is not significantly affected ( with a slight degradation of \\(0.28\\%\\) ), but w-mAcc and Step2- Acc decrease by \\(\\sim 0.8\\%\\) and \\(\\sim 0.9\\%\\). This indicates that future rewards may be meaningful for traditional sequential decision problems but not for MAFR, where efficiency is highly required." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.756, + 0.688, + 0.772 + ], + "angle": 0, + "content": "5.4. Trajectory Analysis" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.901 + ], + "angle": 0, + "content": "For an in-depth analysis of the characteristics of the MAFR task, we further analyze the view-selection trajectory decided by our model. Specifically, with ResNet50 [25] as the feature extractor, we visualize the predicted trajectories of \"Haval H6\" in Figure 5. The two subplots show the results with \"View-2\" and \"View-5\" as the initial views, respectively, and the darker the colour, the more times the trajectory has been selected. The most se" + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "1575" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.332 + ], + "angle": 0, + "content": "lected trajectory is highlighted with blue circles. According to the visualization, we can first conclude that there is some certainty in the best trajectory of a particular category – a significant broken line can be observed. However, the optimal trajectory is associated with the complementarity between different views – when we enter View-2, the next best choice is View-4; and when we enter View-5, the next best choice is View-3. Therefore, solving MAFR is not simply a ranking of the discriminative power of perspective information, echoing the results in Section 5.3 that view selecting with prior knowledge does not yield comparative performance. Factually, the optimal trajectory may even vary for different samples, as there is not just a single trajectory in each subplot. However, this may also be caused by the fact that our model still has room for improvement, so we do not discuss it further here." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.345, + 0.196, + 0.361 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.371, + 0.473, + 0.538 + ], + "angle": 0, + "content": "This paper extends the fine-grained visual classification to 3D environments and proposes the multi-view active fine-grained visual recognition (MAFR) problem. We first collect a multi-view fine-grained car dataset (MvCars) as a qualified benchmark. Then we re-implement several multiview recognition methods, FGVC approaches, and vision neural networks as baseline methods. A policy-gradient-based framework with a dynamic exiting strategy is proposed for the problem raised and yields the best performance. We also discuss the upper bound and predicted trajectories of the proposed method." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.549, + 0.229, + 0.566 + ], + "angle": 0, + "content": "Acknowledgment" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.574, + 0.47, + 0.726 + ], + "angle": 0, + "content": "This work was supported in part by National Natural Science Foundation of China (NSFC) No. U19B2036, 62106022, 62225601, in part by Beijing Natural Science Foundation Project No. Z200002, in part by scholarships from China Scholarship Council (CSC) under Grant CSC No. 202206470055, in part by BUPT Excellent Ph.D. Students Foundation No. CX2022152, in part by the Program for Youth Innovative Research Team of BUPT No. 2023QNTD02, and in part by the Supported by High-performance Computing Platform of BUPT." + }, + { + "type": "title", + "bbox": [ + 0.08, + 0.737, + 0.174, + 0.751 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.085, + 0.761, + 0.47, + 0.801 + ], + "angle": 0, + "content": "[1] John Aloimonos, Isaac Weiss, and Amit Bandyopadhyay. 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In NeurIPS, 2019. 2" + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.471, + 0.448 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.484, + 0.946, + 0.516, + 0.956 + ], + "angle": 0, + "content": "1578" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-View Active Fine-Grained Visual Recognition/ee209e69-47ab-4c40-9356-cb8b45ac9b6d_origin.pdf b/2023/Multi-View Active Fine-Grained Visual Recognition/ee209e69-47ab-4c40-9356-cb8b45ac9b6d_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..f1aa488e398fbe488ecc01333b519ea4ae4c0102 --- /dev/null +++ b/2023/Multi-View Active Fine-Grained Visual Recognition/ee209e69-47ab-4c40-9356-cb8b45ac9b6d_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:9ef523054a719b8df9b236c3a3ff3bb92dd678d9adfcfe8491d2eb676b9609c5 +size 7737884 diff --git a/2023/Multi-View Active Fine-Grained Visual Recognition/full.md b/2023/Multi-View Active Fine-Grained Visual Recognition/full.md new file mode 100644 index 0000000000000000000000000000000000000000..74df1d290ab67c602fc7b4d5475c183c29652401 --- /dev/null +++ b/2023/Multi-View Active Fine-Grained Visual Recognition/full.md @@ -0,0 +1,315 @@ +# Multi-View Active Fine-Grained Visual Recognition + +Ruoyi Du $^{1}$ , Wenqing Yu $^{1}$ , Heqing Wang $^{1}$ , Ting-En Lin $^{2}$ , Dongliang Chang $^{1*}$ , Zhanyu Ma $^{1}$ $^{1}$ Beijing University of Posts and Telecommunications, China + +$^{1}$ {duruoyi, yuwenqing, wangheqing, changdongliang, mazhanyu}@bupt.edu.cn, + +2 sss950123@gmail.com + +# Abstract + +Despite the remarkable progress of Fine-grained visual classification (FGVC) with years of history, it is still limited to recognizing 2D images. Recognizing objects in the physical world (i.e., 3D environment) poses a unique challenge - discriminative information is not only present in visible local regions but also in other unseen views. Therefore, in addition to finding the distinguishable part from the current view, efficient and accurate recognition requires inferring the critical perspective with minimal glances. E.g., a person might recognize a "Ford sedan" with a glance at its side and then know that looking at the front can help tell which model it is. In this paper, towards FGVC in the real physical world, we put forward the problem of multi-view active fine-grained visual recognition (MAFR) and complete this study in three steps: (i) a multi-view, fine-grained vehicle dataset is collected as the testbed, (ii) a pilot experiment is designed to validate the need and research value of MAFR, (iii) a policy-gradient-based framework along with a dynamic exiting strategy is proposed to achieve efficient recognition with active view selection. Our comprehensive experiments demonstrate that the proposed method outperforms previous multi-view recognition works and can extend existing state-of-the-art FGVC methods and advanced neural networks to become "FGVC experts" in the 3D environment. Our code is available at https://github.com/PRIS-CV/MAFR. + +# 1. Introduction + +In the past two decades, fine-grained visual classification (FGVC) has made significant progress in recognizing sub-categories of objects belonging to the same class. This progress has been demonstrated in various domains, such as recognizing cars [32, 57], aircraft [36], birds [50, 48], and foods [39], with extensive outstanding works surpassing human experts in many application scenarios [34, 56, + +![](images/d9de0cf15851038211e08ebd798c92337ca1c08180548baa761f3af57fe46ea2.jpg) +Figure 1. Conventional FGVC versus Multi-view Active FGVC. Conventional FGVC takes a single static image for inference, which may omit the discriminative information. In contrast, Multiview FGVC takes a step further by predicting the potential discriminative view and fusing a sequence of visual information for the final decision. + +![](images/f5c774148ce6f967c61620be94dcceb8a11a769868ce360c15c40997c9604247.jpg) + +19, 53, 13, 4, 5, 16, 14]. However, the previous efforts on FGVC have remained mainly limited to a single-view-based paradigm, where only the visual content within a single static image is considered. This paradigm may be sufficient for coarse-grained classification where inter-class differences are easily captured, such as distinguishing a coupe from other vehicles by its streamlined body, seductive engine, or headlamps. However, fine-grained classification presents a different challenge where discriminative clues are rare and often found in subtle structural differences that are not easily captured by a single static view. For instance, to distinguish between different Ford sedans, one can only rely on subtle differences in the design of car headlights. Predictably, for single-view-based approaches, an image/view without discriminative clues is completely indistinguishable at the fine-grained level, fundamentally limiting the model's theoretical performance. + +Factually, visual recognition is never limited to observing 2D environments and processing static images. Vision algorithms equipped by portal devices (e.g., smartphone, smart glasses, etc.) or embodied AI agents [18] (e.g., intelligent robots) play the core roles during machine- + +environment interaction and have become one of the focuses of computer vision research. Therefore, to embrace the new trend, a natural extension of ordinary FGVC follows – in addition to locating discriminative parts within an image, we aim to infer the unseen distinguishable perspective within the physical world (i.e., 3D environment). Figure 1 shows an example where, with a single glance from the front, the algorithm may be uncertain about the model of the Ford sedan, but can infer that looking at its front will help to resolve the ambiguity. + +Specifically, we re-propose the concept of active vision [1] in the context of FGVC termed multi-view active fine-grained visual recognition (MAFR). MAFR is based on two essential hypotheses. Firstly, we hypothesize that discriminative information for different fine-grained categories is distributed across various object views, making discriminative perspective inference a non-trivial and worth studying. Secondly, we hypothesize that even views that appear indistinguishable at first glance can contain visual clues that can help infer the discriminative perspective, making the problem solvable. + +To start with, due to the absence of qualified datasets, we first collect a fine-grained, multi-view vehicle dataset named Multi-view Cars (MvCars) as the testbed. MvCars comprises 233 car models from 35 brands, covering 5 different car types. Each car in the dataset has 8 aligned views, and the dataset contains more than 26,000 images. In Section 3.2, we conducted a simple pilot experiment and verified our first hypothesis, which suggests that MvCars is well-suited for the problem at hand. + +Secondly, our next contribution is an efficient multi-view fine-grained recognition framework building upon active next-view selection and dynamic exiting. In particular, following the general idea of view-based 3D object understanding [47], an extraction-aggregation architecture is designed as the feature encoder, where a convolutional neural network (e.g., ResNet50 [25]) is first applied to extract single-view features independently. Then a recurrent neural network (e.g., GRU [11]) is adopted to aggregate multi-view features and form global descriptions. Afterwards, we formulate the next-view selection as a sequential decision process, where the model is demanded to decide the next discriminative view (action) according to previously observed views (state). Therefore, we implement a proximal policy optimization (PPO) [46] based multi-stage training strategy. In addition, considering that the difficulty of recognizing different samples varies and the resulting number of perspectives required differs, we design a dynamic exit inference strategy for better effort allocation - inspired by the idea of budgeted batch classification, a series of exciting confidence thresholds are estimated under a given effort expectation. Note that the proposed framework does not rely on specific neural network architectures. It can extend any + +visual recognition network to an FGVC experts in the 3D environment. + +Finally, several carefully designed baselines are reproduced on MvCars as benchmark results, including previous multi-view recognition works, advanced neural networks, and popular FGVC methods. The experimental results demonstrate that the proposed method delivers a better performance-efficient trade-off than all competitors. After that, analysis of the upper bound and the selected trajectories reveals the inherent characteristics of MAFR. In addition, comprehensive ablation studies are carried out to verify the necessities of each model component. + +# 2. Related Work + +# 2.1. Fine-Grained Visual Classification + +Due to the inherent subtle inter-class variance and the relatively large intra-class variance, fine-grained visual classification is much more challenging than ordinary coarse-grained classification. With vigorous efforts made by researchers, great progress has been made in many directions. Localization-based approaches [61, 31, 56, 19, 53, 6] that explicitly locate discriminative parts for feature extraction to alleviate the intra-class variance. High-order encoding methods [34, 20, 19, 59, 62, 21] that adopt high-order feature interactions for better representation ability that can capture the subtle differences. Chen et al. [9] and Du et al. [13] train the model with jigsaw patches to implicitly encourage knowledge mining from local regions. Recently, Chang et al. [5] leverage the underlying hierarchical structure of fine-grained categories to achieve user-friendly outputs and better performance. + +Except for good performances being brought, these works above also reveal that FGVC is never just a more challenging classification problem but a stand-alone field that requires well-directed research. In this paper, to further broaden the horizon of FGVC, we propose the multi-view active fine-grained visual recognition (MAFR) task aiming at effectively recognizing fine-grained categories in the 3D environment along with a targeted dataset. It is worth noting that the CompCars [57] dataset also provides a car dataset with view annotations. However, its multi-view images are taken from different samples, making it less suitable for the raised problem. + +# 2.2. Multi-View Recognition + +Elsewhere for common object recognition problems, particular progress has been made to recognizing 3D objects with three trends that can be summarized [7]: point-based methods [42, 44, 2, 41], volume-based methods [37, 55, 43, 38], and view-based methods [10, 47, 29, 30, 60, 58]. Among them, point-based and volume-based approaches demand to perceive the 3D structure of objects via lidar, + +![](images/2575bed094a218698872e0d696ac96dab573a4fa32d7e99fed9796b145a06fcc.jpg) + +![](images/0bd51c589ad8875d6f3937018bb8a950bc827c2f705126fed1c71cb82ec33155.jpg) + +![](images/acb350d73b01b5e63f9a6c6b056ba03b94a894576a1bf8d1c5be6355a70e1914.jpg) +Figure 2. Illustration of samples from MvCars and some data statistics: (a) The number of samples per category. (b) The number of samples per type. (c) The number of samples per brand. (d) Results of our pilot experiment. The broken lines show model accuracy based on 8 individual views. Moreover, the bars represent the differences between each category's maximum and minimum accuracy. + +![](images/ce6d3ebb3a27950a258b0c6f2dcc807f29543391afdc28ba71d1fdca22bc28a1.jpg) + +depth sensor or something else, which makes them less practicable in daily applications, e.g., recognizing an unfamiliar car for detailed information simply with a mobile phone. On the contrary, view-based methods that leverage multiple surrounding 2D views as descriptors for 3D objects tend to be an optimal choice. + +Specifically, view-based methods share the core idea of encoding single-view features through a vision neural network and then aggregating multi-view features. Su et al. [47] first approaches the multi-view recognition problem with CNN for feature extraction and sum-pooling for aggregation. Then, Johns et al. [29] decomposes image sequences into image pair sets and then aggregates the pair-based classification in a weighted manner. After that, feature concatenation [51], hierarchical attention [22], and weighted fusion [17] are also adopted for better aggregating sequence features. In addition, sequences models (e.g., LSTM [26], GRU [11], Transformer blocks [49], etc) are also widely considered [28, 23, 7] and demonstrate their effectiveness. + +In this paper, specifically towards the multi-view active fine-grained visual recognition (MAFR) task, traditional multi-view recognition dataset (e.g., RGB-D [33], ModelNet10, ModelNet40 [55]) is not sufficient any more. Thus, we first collect a fine-grained, multi-view car dataset named MvCars as a suitable testbed. Then, an active fine-grained recognition framework is built upon the general extraction-aggregation scheme. Note that, similar to ours, some approaches also take recognition efficiency into consideration [28, 29] by actively controlling the agent motion within a viewing sphere. However, a strict viewing sphere is not readily available in daily applications, especially for recognition with portable devices. We, therefore, consider the view selection as a discrete decision problem. + +# 3. Dataset + +In this work, we first contribute a testbed for MAFR by collecting a multi-view fine-grained car recognition dataset named Multi-view Cars (MvCars). Considering that car recognition is challenging and close to daily life [57], a vehicle dataset can demonstrate well how the MAFR model performs in real applications. + +# 3.1. Data Statistic + +MvCars consists of 233 models of cars from 35 brands (e.g., Ford, Volvo, Escort, etc.) that cover 5 types (e.g., sedan, SUV, MPV, sports car, and pickup). For each car, we collect and annotate 8 aligned perspectives – front, front-left, front-right, left, right, rear, rear-left, rear-right (as shown in Figure 2), and samples with missing perspectives are discarded. In total, there are 26,552 images collected from 3319 cars and are then split into 15,960/3,000/7,592 (at a ratio of $60\% /10\% /30\%$ ) for train/val/test set, respectively. + +In addition to multi-view and fine-grained, MvCars is also a hierarchical and long-tail dataset. We can easily build the brand-type-model label hierarchies for categories in MvCars, e.g., "Ford car"-"Ford sedan"-"Ford Mondeo", which may benefit directions like hierarchical structure-based FGVC [15] and human-friendly FGVC [5]. The numbers of samples per category are shown in Figure 2 (a), where a significant long-tail distribution can be observed. Such a long-tail dataset is also closer to realistic application and provides a new scenario to related topic [3]. The sample sizes per type and brand are shown in Figure 2 (b) and (c), respectively, and similar data distributions exist. + +![](images/dd8ef5cf6bd811e232b12b23039424370f9bbf5bbc15ed3ca5d4187b3fcb2f29.jpg) +Figure 3. Illustration of the proposed MAFR framework where three training stages are included: Stage I for training a multi-view recognition model with smooth predictions, Stage II for optimizing the next-view selection component based on the behavior of the classifier, and Stage III for fine-tuning the recognition model along with the trajectory decided by the actor. Here we use three training steps for brief illustration. + +# 3.2. Pilot Experiment + +With the collected MvCars, here we first experimentally validate our first hypothesis mentioned in Section 1 – the discriminative information hides in various object views for different fine-grained categories. Factually, it is two-fold: (i) different perspectives contribute differently to FGVC; otherwise, actively selecting object view is meaningless, and (ii) different categories own different discriminative perspectives; otherwise, there is a trivial solution existing – consistently seeking the fixed distinguishable view. + +In particular, for each perspective, we train a ResNet50 [25] for classification and obtain its accuracy in each category. Therefore, we can tell which perspective is more distinguishable for any specific category by comparing the performances of 8 models based on different views. We show the results of 30 classes in Figure 2 (d). Bars in the graph indicate the differences between the maximum and minimum accuracy of each category, and the average difference of all 233 classes is about $36.40\%$ . It powerfully proves that different perspectives contribute differently in the context of FGVC. On the other hand, broken lines in the graph represent the single-view accuracy changes along with different categories. The interaction of lines indicates that the ranking of view discrimination is inconsistent, demonstrating that different categories have different discriminative perspectives. + +In a word, in MvCars, different perspectives provide significantly various meanings for FGVC, which is also hard to pre-defined via prior knowledge. Thus, an active fine-grained recognition method is called for, and the collected MvCars dataset can serve as an eligible testbed. + +# 4. Methodology + +# 4.1. Overview + +Here we first give an overview of the data flow of MAFR during inference and introduce the model components needed. + +Data structure. For MAFR, a dataset $D$ consists of $N$ samples can be expressed as $D = \{X_{i},y_{i}\}_{i = 1}^{N}$ , where $X_{i} = \{x_{i}^{1},\ldots ,x_{i}^{v},\ldots ,x_{i}^{V}\}$ is a sequence of images depict a specific sample from $V$ perspectives and $y_{i}$ is their common ground-truth label. Note that, the annotations of views $\{1,\dots ,V\}$ are aligned, i.e., for arbitrary two samples $X_{i}$ and $X_{j}$ , $x_{i}^{v}$ and $x_{j}^{v}$ are taken from the same perspective. + +Inference process. For sample $X_{i}$ , the model will take an image $x_{i}^{v_{1}}$ from arbitrary view $v_{1}$ as the initial visual input, which simulates the situation that the model may start recognition while facing any views of the target object. After that, the recognition process will carry on step-by-step. In particular, at step $t$ with input $x_{i}^{v_{t}}$ from view $v_{t}$ , the model will utilize all currently perceived information $\{x_{i}^{v_{1}},\ldots ,x_{i}^{v_{t - 1}},x_{i}^{v_{t}}\}$ to deliver the category prediction $\hat{y}_i^t$ and the next-view proposal $v_{t + 1}$ . Then, an inference cycle is closed, and the process can continue with $x_{i}^{v_{t + 1}}$ as the next input. Generally, $t\in [1,T]$ , and $T$ can be set to a maximum $V$ . + +Framework component. An extraction-aggregation structure tends to be an intuitive choice to process a sequence of correlated visual inputs. Similar structures are also developed by previous multi-recognition arts [8]. Specifically, for any image $x_{i}^{v_{t}}$ input the system, a CNN-based feature extractor $\mathcal{F}(\cdot)$ is first applied to extract single- + +view feature as $f_{i}^{v_{t}} = \mathcal{F}(x_{i}^{v_{t}})$ . It is worth noting that the feature extractors for different views share their weights, and this design will not lead to additional parameters. After that, an ideal model should consider all previously acquired information. Thus, a recurrent neural network is introduced as the aggregator $\mathcal{R}(\cdot)$ that aggregates features from all seen perspectives. In particular, we adopt two aggregators with the same structure but individual weights. $\mathcal{R}_{e}(\cdot)$ and $\mathcal{R}_s(\cdot)$ that, $\mathcal{R}_e(\cdot)$ form global embeddings $e_i^t = \mathcal{R}_e(f_i^{v_1},\dots ,f_i^{v_t})$ for category prediction, while $\mathcal{R}_s(\cdot)$ depicts the current states $s_i^t = \mathcal{R}_s(f_i^{v_1},\dots ,f_i^{v_t})$ for next-view selection. Finally, a classifier $\mathcal{P}(\cdot)$ and an actor $\mathcal{A}(\cdot)$ are equipped in parallel with outputs $\hat{y}_i^t = \mathcal{P}(e_i^t)$ and $v_{t + 1} = \mathcal{A}(s_i^t)$ , respectively. + +# 4.2. Model Training + +According to the aforementioned inference process, we can tell that the recognition component and the next-view selection component work separately but not independently. The mission of the recognition component is quite straightforward – conducting category prediction based on acquired information as well as possible. While the optimization goal of the next-view selection component largely depends on the behaviour of recognition – basically, the actor should try to select the next-view that can maximize the prediction probability of the target category. Therefore, a three stages training framework is intuitively designed: Stage I aims to train a good recognition model (including $\mathcal{F}(\cdot),\mathcal{R}_e(\cdot)$ ,and $\mathcal{P}(\cdot))$ that can handle sequence input, Stage II aims to optimize the next-view selection module (where $\mathcal{R}_s(\cdot)$ and $\mathcal{A}(\cdot)$ participate) according to the behaviour of the trained recognition model, and Stages III aims to refine the recognition model under the trajectories decided by the actor. + +Note that the inductive bias behind training the recognition component in the first place is that its behaviour can reveal view discrimination - a more discriminative view will greatly reduce the entropy of category prediction. However, a well-convergent classification model often delivers high-confidence predictions, especially for the small-scale datasets in the FGVC scenario, which will cause little changes in prediction probabilities and limit the information being revealed. For this, we take a very intuitive yet effective solution that splitting the training set $D_{T}$ into two non-overlapping sub-sets for the first two stages respectively - specifically, a rehearsal set $D_{R}$ is used for training the recognition components in Stage I, and a evaluation set $D_{E}$ is used for providing authentic rewards while training the next-view selection module in Stage II. We have $D_{R} \cup D_{E} = D_{T}$ and $D_{R} \cap D_{E} = \emptyset$ . In Stage III, the model will be trained with the whole training set $D_{T}$ . + +The whole framework is illustrated in Figure 3, and introductions about the three stages are as follows. + +Stage I. To train a recognition model that can handle a se + +quence of inputs with dynamic length, each training iteration is divided into $T$ steps with input sequence lengths from 1 to $T$ . As the next-view planning module is not able for now, when $t \geq 2$ , a new image $x_{i}^{v_{t}}$ is randomly selected from unseen views and appended to the input sequence at the $(t - 1)$ -th step. Here we set $T = V$ to ensure the maximum no-duplicated sequence can be sampled. With cross-entropy for optimization, the loss function for a batch of $B$ samples can be formulated as: + +$$ +L _ {C E} (\hat {y} _ {i} ^ {t}, y _ {i}) = \frac {- 1}{B T C} \sum_ {i = 1} ^ {B} \sum_ {t = 1} ^ {T} \sum_ {c = 1} ^ {C} y _ {i} \times \log (\hat {y} _ {i, c} ^ {t}), \tag {1} +$$ + +where $C$ is the total category number, i.e., the channel number of the last layer. + +Additionally, we also introduce a entropy maximization penalty as + +$$ +L _ {E M} \left(\hat {y} _ {i} ^ {t}\right) = \frac {1}{B T C} \sum_ {i = 1} ^ {B} \sum_ {t = 1} ^ {T} \sum_ {c = 1} ^ {C} \hat {y} _ {i, c} ^ {t} \times \log \left(\hat {y} _ {i, c} ^ {t}\right), \tag {2} +$$ + +to encourage smooth predictions that can better reveal the priority between views. The total loss can be expressed as $L_{Stage1} = L_{CE}(\hat{y}_i^t, y_i) + \alpha \times L_{EM}(\hat{y}_i^t)$ , and the degree of entropy maximization constrain can be control by the hyperparameter $\alpha$ . + +Stage II. Here, the recognition components $(\mathcal{F}(\cdot),\mathcal{R}_e(\cdot)$ and $\mathcal{P}(\cdot))$ are frozen, and we only optimize $\mathcal{R}_s(\cdot)$ and $\mathcal{A}(\cdot)$ for next-view selection. As a non-differentiable sequential decision problem, we adopt the policy gradient method for optimization instead of directly optimizing with the classification loss. At the $t$ -th $(t\geq 2)$ training step, the model will receive the input $x_{i}^{v_{t}}$ with the perspective $v_{t}$ decided by the actor at the $(t - 1)$ -th step. Then the view selection components can be updated according to the change of the target category's prediction probability, i.e., the rewards are set as $r_i^t = \hat{y}_{iy_i}^t -\hat{y}_{iy_i}^{t - 1}$ . And the $t$ -th $(t\geq 2)$ step's loss function of Stage II can be simply expressed as: $L_{Stage2} = L_{PG}(v_t,\hat{y}_i^{t - 1},\hat{y}_i^t)$ . Detailed expansion of the loss function can be found in Section 4.3 + +Notably, for popular policy gradient algorithms [45, 46], the total reward for the current step's optimization is a (weighted) sum of all feature rewards from now on. This is because these methods are designed for scenarios where an agent should achieve an ultimate goal through a series of actions. However, on the contrary, MAFR aims to use as few steps as possible to achieve as high accuracy as possible, i.e., we care more about achieving the best performance at the current step rather than in the future. Therefore, we slightly modify the policy gradient algorithm by utilizing only $r_i^t$ for the $t$ -th step's optimization. + +Stage III. There is nothing new in this stage - all settings are the same as Stage I except for (i) the selected view $v_{t}$ + +when $t \geq 2$ is given by the actor, (ii) the whole training set $D_{T}$ is used. The model is refined under standard classification supervision (i.e., $L_{Stage3} = L_{CE}(\hat{y}_i^t, y_i)$ ) to especially adjust the trajectories decided by the actor and utilizing all the training data. + +# 4.3. Design Details + +Feature extractor $\mathcal{F}(\cdot)$ . The feature extractor can be any backbone network for vision tasks, including various CNN architectures and Transformers (e.g., ResNet50 [25], ViT [12], etc.). Besides, by replacing $\mathcal{F}(\cdot)$ with other FGVC models, the proposed method can also extend them to work in 3D environments. + +Feature aggregator $\mathcal{R}_e(\cdot)$ and $\mathcal{R}_s(\cdot)$ . The two feature aggregators should be able to aggregate information from sequences with variable lengths. Here we adopt GRU [11] for best performance. There are alternatives like LSTM [26], self-attention block [49], etc.. + +Classifier $\mathcal{P}(\cdot)$ and actor $\mathcal{A}(\cdot)$ . Both the classifier and the actor are formed by one fully connected layer. For the cases that equip the proposed framework with other FGVC approaches, the structure of the classifier can be modified accordingly. + +Policy gradient algorithm. For training the actor $\mathcal{A}(\cdot)$ (the next-view selection module) at Stgae II, we adopt the proximal policy optimization (PPO) algorithm [46] with a slight modification. Specifically, given a series of inputs $x_{i}^{v_{1}},\ldots ,x_{i}^{v_{t}}$ at the $t$ -th step, the extractor $\mathcal{F}(\cdot)$ and the aggregator $\mathcal{R}_s(\cdot)$ are first applied to form the current state: + +$$ +s _ {i} ^ {t} = \mathcal {R} _ {s} \left(\mathcal {F} \left(x _ {i} ^ {v _ {1}}\right), \dots , \mathcal {F} \left(x _ {i} ^ {v _ {t}}\right)\right). \tag {3} +$$ + +And then, the actor takes the state $s_i^t$ as input and decides the next view proposal $v_{t + 1}$ as the action (i.e., $v_{t + 1} = \mathcal{A}(s_i^t)$ ). For the general PPO algorithm with the reward $r_i^t$ for $t$ -th step, the advantage estimator $\hat{A}_i^t$ can be expressed as: + +$$ +\hat {A} _ {t} = - V \left(s _ {i} ^ {t}\right) + r _ {i} ^ {t} + \gamma r _ {i} ^ {t + 1} + \dots + \gamma^ {T - t} r _ {i} ^ {T}, \tag {4} +$$ + +where $V(s_i^t)$ is the learned state-value function, $\gamma \in (0,1)$ is a pre-defined discount factor, $T$ is the maximum length of the input sequence. The principle behind it is straightforward - the current action should not only benefit the next step but also contribute to the overall goal. However, in this work, aiming at achieving reliable prediction with the least number of steps, we only focus on the profit at the very next step, i.e., we set $\gamma = 0$ . The advantage estimator we use can be formulated by $\hat{A}_i^t = -V(s_i^t) + r_i^t$ . + +After that, we denote the prediction probability of $v_{t}$ by $\mathcal{A}(v_t|s_i^t)$ . Then the clipped surrogate objective is: + +$$ +\begin{array}{l} L _ {C L I P} = \frac {1}{B} \sum_ {i = 1} ^ {B} \sum_ {t = 2} ^ {T} \min \left\{\frac {\mathcal {A} \left(v _ {t} \mid s _ {i} ^ {t}\right)}{\mathcal {A} _ {o l d} \left(v _ {t} \mid s _ {i} ^ {t}\right)} \hat {A} _ {i} ^ {t} \right. \tag {5} \\ c l i p (\frac {\mathcal {A} (v _ {t} | s _ {i} ^ {t})}{\mathcal {A} _ {o l d} (v _ {t} | s _ {i} ^ {t})}, 1 - \epsilon , 1 + \epsilon) \hat {A} _ {i} ^ {t} \}, \\ \end{array} +$$ + +where $\mathcal{A}_{old}(\cdot)$ stands for the actor before update, and $\epsilon \in (0,1)$ is a hyper-parameter. Note that $t$ starts from $t = 2$ since the first view is randomly selected. Finally, the overall objective of Stage II can be expressed as: + +$$ +L _ {S t a g e 2} = L _ {P G} \left(v _ {t}, \hat {y} _ {i} ^ {t - 1}\right) = L _ {C L I P} - c _ {1} L _ {V F} + c _ {2} L _ {E}, \tag {6} +$$ + +where $L_{VF} = \frac{1}{B}\sum_{i=1}^{B}\sum_{t=2}^{T}(V(s_i^t) - V^{target}(s_i^t))^2$ is the squared-error loss suggested by [45], and $L_E = \frac{1}{B}\sum_{i=1}^{B}\sum_{t=2}^{T}S_A(s_i^t)$ is the entropy bonus following [54, 40]. $c_1$ and $c_2$ are hyper-parameters to balance the three loss components. + +# 4.4. Dynamic Exiting + +For the proposed method, we can achieve the accuracy-efficiency trade-off by setting the maximum number of steps. However, simply assigning the same maximum step number to all samples may be too arbitrary since difficult samples may require information from more views than simple samples do. For that, inspired by previous sequential prediction work [52], we introduce the concept of budget batch classification [27] for dynamic exiting. Specifically, defining the exit probability of a certain step to be $p$ , the probability of model exiting at the $t$ -th step is $p_t = \alpha (1 - p)^{t - 1}p$ , where $\alpha$ is a scaling factor that ensures $\sum_{t = 1}^{T_{max}}p_t = 1$ . The value of $p$ can be found by solving the function $C = \sum_{t = 1}^{T_{max}}t\times p_t$ , where $C$ is the expectation of average prediction steps. Then, we can estimate the exiting threshold $\mu_t$ for each step on the validation set. Such a strategy can further reveal the model potential under given step expectations by enabling better resource allocation among all test data. + +# 5. Experiment + +Implementation. The feature extractor $\mathcal{F}(\cdot)$ is initialized with ImageNet pre-trained weights, while other model components are randomly initialized. During Stage I and Stage III, we use SGD optimizer with a momentum of 0.9 and the cosine learning rate schedule [35] for optimization. The start learning rate is set to be 0.01 for the feature extractor and 0.1 for the rest. The input images are resize to $256 \times 256$ and then random-cropped to $224 \times 224$ . The hyper-parameter $\alpha$ is set to be 0.01. During Stage II, we use the Adam optimizer with $\beta_{1} = 0.9$ , $\beta_{2} = 0.999$ , and the cosine learning rate schedule [35] for optimization. The start learning rate of the actor $\mathcal{A}(\cdot)$ is set to be 0.005. The input images are resize to $256 \times 256$ and then center-cropped to $224 \times 224$ . The hyper-parameters $\epsilon$ , $c_{1}$ , and $c_{2}$ are set to be 0.2, 0.5, and 0.01, respectively. The model is trained for 15 epochs for each stage. During inference, the input images are resize to $256 \times 256$ and then center-cropped to $224 \times 224$ . + +
MethodmAcc. (%)w-mAcc. (%)Step2-Acc. (%)
ResNet50RotationNet [30]79.53 ± 0.479.32 ± 0.778.72 ± 0.8
VERAM [8]79.42 ± 0.580.50 ± 1.380.19 ± 1.4
Baseline†78.21 ± 0.378.04 ± 0.576.74 ± 0.3
Baseline‡79.60 ± 0.779.75 ± 1.278.28 ± 0.8
Ours80.84 ± 0.482.20 ± 0.781.45 ± 0.9
Ours*81.33 ± 0.583.25 ± 0.982.86 ± 1.1
ViT-B.16Baseline†80.05 ± 0.480.32 ± 1.378.82 ± 0.4
Baseline‡80.47 ± 0.780.79 ± 1.479.93 ± 1.3
Ours81.35 ± 1.182.60 ± 0.681.53 ± 0.8
Ours*82.13 ± 1.283.58 ± 1.382.50 ± 1.4
PMGBaseline†80.26 ± 0.980.51 ± 1.479.92 ± 0.9
Baseline‡80.65 ± 0.980.98 ± 0.680.21 ± 0.4
Ours82.69 ± 1.183.47 ± 1.482.77 ± 1.3
Ours*82.99 ± 0.384.46 ± 0.583.79 ± 0.6
TransFGBaseline†81.26 ± 1.581.33 ± 0.980.76 ± 0.6
Baseline‡81.78 ± 1.282.15 ± 1.481.52 ± 0.6
Ours83.76 ± 1.384.72 ± 0.584.35 ± 1.0
Ours*84.89 ± 0.385.77 ± 1.385.57 ± 0.6
+ +Table 1. Results of the proposed method with different backbones. The best results of each section are marked in bold. + +Baseline models. For extensive evaluation, three groups of approaches were considered for comparison: I. previous multi-view recognition methods, including RotationNet [30] and VERAM [8], II. state-of-the-art FGVC methods, including PMG [13] and TransFG [24], and III. advanced vision neural networks, including ResNet [25] and ViT [12]. Specifically, for group I, we re-implemented them with ResNet50 as the backbone model for a fair comparison. And for group II and III, as they are designed for single-view recognition, two baseline frameworks, which may be intuitive choices for most people, are designed to adapt them to the MAFR task: (i) Baseline†: a naive model ensemble scheme, i.e., predictions are independently delivered according to each view, and at the $t$ -th step, the average of $t$ inputs' predictions is adopted as the current result, and (ii) Baseline‡: due to their conciseness, these models can directly serve as the feature extractor of the proposed method, therefore, a strong sequential prediction baseline can be implemented by replacing our feature extractors with these approaches and training under the setting of Stage III. + +Evaluation Metrics. For quantitative evaluation, results based on 3 metrics are reported: (i) Mean Accuracy (mAcc) that takes the mean value of all $T$ steps' accuracy, which can be regarded as the area under the accuracy-step line that represents the general performances of models, (ii) Weighted Mean Accuracy (w-mAcc) that weights different steps with exponentially decreased weights, since the performance of the first few steps should be more important in the consideration of efficiency1, and (iii) Step2 Accuracy + +![](images/7b5a9a57fa67146aa36f206c17e2781d5d9398c3e28cf61b788dc7b63831c691.jpg) +Figure 4. Illustration of model performance per-step and the performance upper bound from the perspective of trajectory decision. + +(Step2-Acc) that takes the 2-nd step's accuracy to highlight the profit of the first view selection2. + +# 5.1. Main Results + +The results of the proposed method against all mentioned baselines are reported in Table 5. The table is organized into 4 sections according to different backbone networks. For ResNet50 [25] as the base model, we can observe that Baselined already achieves impressive performance and delivers quite competitive results to previous multi-view recognition models. On the contrary, the proposed method outperforms it by $\sim 1.2\%$ $\sim 2.5\%$ $\sim 3.2\%$ for mAcc, w-mAcc, and Step2-Acc, respectively. The larger margins on w-mAcc and Step2-Acc also demonstrate its superiority in efficiency that benefits from the active next-view selection scheme. In addition, while applying the dynamic exiting strategy, we also calculate these three metrics by obtaining the accuracy when the step expectations equal 1-8, and there is no doubt that it further boosts model performance via a better efforts allocation. An interesting finding is that for models with the next-view selection mechanism, we can generally observe that mAcc $<$ Step2-Acc, while mAcc $>$ Step2-Acc for other models, which indicates a significant performance boosting caused by the active view selection at step 2. In addition, for other baselines implemented with the more advanced network (i.e., ViT [12]) and FGVC models (i.e., PMG [13] and TransFG [24]), the proposed framework can also boost their performance via active view selection and dynamic exiting, which indicates most of the recognition models can be extended to be an FGVC experts in the real physical world. + +
MethodmAcc. (%)w-mAcc. (%)Step2-Acc. (%)
Random Selection80.15 ± 0.579.86 ± 0.878.28 ± 0.6
Selecting the Farthest80.50 ± 0.481.49 ± 0.680.68 ± 0.9
Selecting w/ Prior80.43 ± 0.681.32 ± 0.980.55 ± 0.7
w/ Duplicate View80.22 ± 0.981.38 ± 0.881.18 ± 1.1
w/o Data Split80.19 ± 0.979.98 ± 1.178.53 ± 0.9
w/o LEM80.24 ± 0.481.57 ± 0.780.96 ± 1.0
w/ Future Rewards80.56 ± 0.681.44 ± 0.880.53 ± 0.8
Ours80.84 ± 0.482.20 ± 0.781.45 ± 0.9
Ours*81.33 ± 0.583.25 ± 0.982.86 ± 1.1
+ +Table 2. Results of ablation studies. The best ones are marked in bold. + +# 5.2. Upper Bound Analysis + +To better illustrate the change of model accuracy over inference steps, we show the accuracy-step lines of all models with ResNet50 [25] as the backbone in Figure 4. At this point, the audiences may question why these models' performances do not consistently increase. With the same question, we study the upper bound of our model. Due to the finite total view numbers, we are able to visit all possible trajectories for each sample. Therefore, a performance upper bound can be obtained from the perspective of trajectory decision - an arbitrary sample will be considered correctly classified when any trajectory allows this sample to be classified correctly. According to Figure 4, the degradation in the last few steps is also observed on the performance upper bound. A similar phenomenon is also observed in previous multi-view recognition works (e.g., [30]). In this work, we also attribute this to the inherent feature of fine-grained recognition in the 3D environment - the discriminative clues only hide in a few views, and the noises caused by intra-class variance will be more likely to be introduced when full visual information (i.e., all views) is included. This echoes the essential insight in the 2D fine-grained recognition where subtle differences of local regions are discriminative, and the global structures are more likely disturbed. + +# 5.3. Ablation Study + +In this section, we evaluate several variants of the proposed method based on ResNet50 to demonstrate the necessities of our designs. First, to verify the effectiveness of the active next-view selection mechanism, we study our model with no-duplicate inputs of random order and the order decided by the priority found in our pilot experiment. Fortunately, the proposed method passes the test with significant w-mAcc margins of $\sim 2.3\%$ and $\sim 0.9\%$ , respectively. + +In addition, The farthest viewpoint sampling is also an important baseline - specifically, we implement it by selecting the farthest and unselected view from the second step. In cases where there are two equally distant views, we ran + +![](images/826dc0dd6afe8f18da8cfe43c1d2415ade88d4a31fa9bb6544fc89f258bfcbe0.jpg) + +![](images/2ec73597dbf687003cb585e772a7b26c7c81aa121c4c9784551803eeb3007350.jpg) +View-2 + +![](images/6802b837f030fa4de5842fbb077da625a493893cd9702a0d37e9e4f83203a70d.jpg) +View-4 +Figure 5. Predicted trajectories of "Haval H6" with "View-2" and "View-5" as the initial views. The darker the colour, the more times the trajectory has been selected. The most selected trajectory is highlighted with blue circles. + +![](images/f80e86a52fcc1590d22f12f68e9c3768ea5dbbbac99f9fb82bcdf6e41460c044.jpg) + +![](images/08fb35f353fcb3c485f6fefdbd605ae8b170f21f2237e9af17a9ea6a17743be7.jpg) +View-3 + +![](images/2226997a4824da6145de324f7d90ab564beeb44ff7997885fb1d566842a9c1fb.jpg) +View-5 + +domly choose one of them. However, the proposed method consistently outperforms it with a significant margin. This is because the most complementary view may not be the farthest one, as we further illustrate on the right in the next Section (see Figure 5). + +Besides, an artificial restriction is added for all evaluations to ensure that new views selected are no-duplicate. It is intuitive since unseen views can offer complementary information, and the information about which views have been selected is easily acquired. Here we also evaluate by allowing duplicate views, and the model performance degrades with no surprise. + +After that, our designs for model training are also demonstrated to be effective. Splitting the training data into two non-overlapped subsets and encouraging entropy maximization both significantly boost model performance. It is worth noting that when we include the future rewards for policy optimization, mAcc is not significantly affected ( with a slight degradation of $0.28\%$ ), but w-mAcc and Step2- Acc decrease by $\sim 0.8\%$ and $\sim 0.9\%$ . This indicates that future rewards may be meaningful for traditional sequential decision problems but not for MAFR, where efficiency is highly required. + +# 5.4. Trajectory Analysis + +For an in-depth analysis of the characteristics of the MAFR task, we further analyze the view-selection trajectory decided by our model. Specifically, with ResNet50 [25] as the feature extractor, we visualize the predicted trajectories of "Haval H6" in Figure 5. The two subplots show the results with "View-2" and "View-5" as the initial views, respectively, and the darker the colour, the more times the trajectory has been selected. The most se + +lected trajectory is highlighted with blue circles. According to the visualization, we can first conclude that there is some certainty in the best trajectory of a particular category – a significant broken line can be observed. However, the optimal trajectory is associated with the complementarity between different views – when we enter View-2, the next best choice is View-4; and when we enter View-5, the next best choice is View-3. Therefore, solving MAFR is not simply a ranking of the discriminative power of perspective information, echoing the results in Section 5.3 that view selecting with prior knowledge does not yield comparative performance. Factually, the optimal trajectory may even vary for different samples, as there is not just a single trajectory in each subplot. However, this may also be caused by the fact that our model still has room for improvement, so we do not discuss it further here. + +# 6. Conclusion + +This paper extends the fine-grained visual classification to 3D environments and proposes the multi-view active fine-grained visual recognition (MAFR) problem. We first collect a multi-view fine-grained car dataset (MvCars) as a qualified benchmark. Then we re-implement several multiview recognition methods, FGVC approaches, and vision neural networks as baseline methods. A policy-gradient-based framework with a dynamic exiting strategy is proposed for the problem raised and yields the best performance. We also discuss the upper bound and predicted trajectories of the proposed method. + +# Acknowledgment + +This work was supported in part by National Natural Science Foundation of China (NSFC) No. U19B2036, 62106022, 62225601, in part by Beijing Natural Science Foundation Project No. Z200002, in part by scholarships from China Scholarship Council (CSC) under Grant CSC No. 202206470055, in part by BUPT Excellent Ph.D. Students Foundation No. CX2022152, in part by the Program for Youth Innovative Research Team of BUPT No. 2023QNTD02, and in part by the Supported by High-performance Computing Platform of BUPT. + +# References + +[1] John Aloimonos, Isaac Weiss, and Amit Bandyopadhyay. Active vision. International Journal of Computer Vision, 1988. 2 +[2] Yasuhiro Aoki, Hunter Goforth, Rangaprasad Arun Srivatsan, and Simon Lucey. Pointnetlk: Robust & efficient point cloud registration using pointnet. In CVPR, 2019. 2 +[3] Samy Bengio. 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Recognizing objects in the physical world (i.e., 3D environment) poses a unique challenge - discriminative information is not only present in visible local regions but also in other unseen views. Therefore, in addition to finding the distinguishable part from the current view, efficient and accurate recognition requires inferring the critical perspective with minimal glances. E.g., a person might recognize a \"Ford sedan\" with a glance at its side and then know that looking at the front can help tell which model it is. In this paper, towards FGVC in the real physical world, we put forward the problem of multi-view active fine-grained visual recognition (MAFR) and complete this study in three steps: (i) a multi-view, fine-grained vehicle dataset is collected as the testbed, (ii) a pilot experiment is designed to validate the need and research value of MAFR, (iii) a policy-gradient-based framework along with a dynamic exiting strategy is proposed to achieve efficient recognition with active view selection. Our comprehensive experiments demonstrate that the proposed method outperforms previous multi-view recognition works and can extend existing state-of-the-art FGVC methods and advanced neural networks to become \"FGVC experts\" in the 3D environment. Our code is available at https://github.com/PRIS-CV/MAFR." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 588, + 128, + 601 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 588, + 128, + 601 + ], + "spans": [ + { + "bbox": [ + 47, + 588, + 128, + 601 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 609, + 287, + 694 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 609, + 287, + 694 + ], + "spans": [ + { + "bbox": [ + 46, + 609, + 287, + 694 + ], + "type": "text", + "content": "In the past two decades, fine-grained visual classification (FGVC) has made significant progress in recognizing sub-categories of objects belonging to the same class. This progress has been demonstrated in various domains, such as recognizing cars [32, 57], aircraft [36], birds [50, 48], and foods [39], with extensive outstanding works surpassing human experts in many application scenarios [34, 56," + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 308, + 226, + 399, + 357 + ], + "blocks": [ + { + "bbox": [ + 308, + 226, + 399, + 357 + ], + "lines": [ + { + "bbox": [ + 308, + 226, + 399, + 357 + ], + "spans": [ + { + "bbox": [ + 308, + 226, + 399, + 357 + ], + "type": "image", + "image_path": "d9de0cf15851038211e08ebd798c92337ca1c08180548baa761f3af57fe46ea2.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 360, + 547, + 426 + ], + "lines": [ + { + "bbox": [ + 305, + 360, + 547, + 426 + ], + "spans": [ + { + "bbox": [ + 305, + 360, + 547, + 426 + ], + "type": "text", + "content": "Figure 1. Conventional FGVC versus Multi-view Active FGVC. Conventional FGVC takes a single static image for inference, which may omit the discriminative information. In contrast, Multiview FGVC takes a step further by predicting the potential discriminative view and fusing a sequence of visual information for the final decision." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 399, + 226, + 544, + 357 + ], + "blocks": [ + { + "bbox": [ + 399, + 226, + 544, + 357 + ], + "lines": [ + { + "bbox": [ + 399, + 226, + 544, + 357 + ], + "spans": [ + { + "bbox": [ + 399, + 226, + 544, + 357 + ], + "type": "image", + "image_path": "f5c774148ce6f967c61620be94dcceb8a11a769868ce360c15c40997c9604247.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 448, + 546, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 448, + 546, + 651 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 546, + 651 + ], + "type": "text", + "content": "19, 53, 13, 4, 5, 16, 14]. However, the previous efforts on FGVC have remained mainly limited to a single-view-based paradigm, where only the visual content within a single static image is considered. This paradigm may be sufficient for coarse-grained classification where inter-class differences are easily captured, such as distinguishing a coupe from other vehicles by its streamlined body, seductive engine, or headlamps. However, fine-grained classification presents a different challenge where discriminative clues are rare and often found in subtle structural differences that are not easily captured by a single static view. For instance, to distinguish between different Ford sedans, one can only rely on subtle differences in the design of car headlights. Predictably, for single-view-based approaches, an image/view without discriminative clues is completely indistinguishable at the fine-grained level, fundamentally limiting the model's theoretical performance." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "content": "Factually, visual recognition is never limited to observing 2D environments and processing static images. Vision algorithms equipped by portal devices (e.g., smartphone, smart glasses, etc.) or embodied AI agents [18] (e.g., intelligent robots) play the core roles during machine-" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 703, + 176, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 703, + 176, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 703, + 176, + 713 + ], + "type": "text", + "content": "*indicates the corresponding author." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1568" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 193 + ], + "type": "text", + "content": "environment interaction and have become one of the focuses of computer vision research. Therefore, to embrace the new trend, a natural extension of ordinary FGVC follows – in addition to locating discriminative parts within an image, we aim to infer the unseen distinguishable perspective within the physical world (i.e., 3D environment). Figure 1 shows an example where, with a single glance from the front, the algorithm may be uncertain about the model of the Ford sedan, but can infer that looking at its front will help to resolve the ambiguity." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 194, + 289, + 326 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 194, + 289, + 326 + ], + "spans": [ + { + "bbox": [ + 46, + 194, + 289, + 326 + ], + "type": "text", + "content": "Specifically, we re-propose the concept of active vision [1] in the context of FGVC termed multi-view active fine-grained visual recognition (MAFR). MAFR is based on two essential hypotheses. Firstly, we hypothesize that discriminative information for different fine-grained categories is distributed across various object views, making discriminative perspective inference a non-trivial and worth studying. Secondly, we hypothesize that even views that appear indistinguishable at first glance can contain visual clues that can help infer the discriminative perspective, making the problem solvable." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 328, + 289, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 328, + 289, + 435 + ], + "spans": [ + { + "bbox": [ + 46, + 328, + 289, + 435 + ], + "type": "text", + "content": "To start with, due to the absence of qualified datasets, we first collect a fine-grained, multi-view vehicle dataset named Multi-view Cars (MvCars) as the testbed. MvCars comprises 233 car models from 35 brands, covering 5 different car types. Each car in the dataset has 8 aligned views, and the dataset contains more than 26,000 images. In Section 3.2, we conducted a simple pilot experiment and verified our first hypothesis, which suggests that MvCars is well-suited for the problem at hand." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 438, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 438, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 438, + 289, + 715 + ], + "type": "text", + "content": "Secondly, our next contribution is an efficient multi-view fine-grained recognition framework building upon active next-view selection and dynamic exiting. In particular, following the general idea of view-based 3D object understanding [47], an extraction-aggregation architecture is designed as the feature encoder, where a convolutional neural network (e.g., ResNet50 [25]) is first applied to extract single-view features independently. Then a recurrent neural network (e.g., GRU [11]) is adopted to aggregate multi-view features and form global descriptions. Afterwards, we formulate the next-view selection as a sequential decision process, where the model is demanded to decide the next discriminative view (action) according to previously observed views (state). Therefore, we implement a proximal policy optimization (PPO) [46] based multi-stage training strategy. In addition, considering that the difficulty of recognizing different samples varies and the resulting number of perspectives required differs, we design a dynamic exit inference strategy for better effort allocation - inspired by the idea of budgeted batch classification, a series of exciting confidence thresholds are estimated under a given effort expectation. Note that the proposed framework does not rely on specific neural network architectures. It can extend any" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 545, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 95 + ], + "type": "text", + "content": "visual recognition network to an FGVC experts in the 3D environment." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 96, + 547, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 96, + 547, + 216 + ], + "spans": [ + { + "bbox": [ + 304, + 96, + 547, + 216 + ], + "type": "text", + "content": "Finally, several carefully designed baselines are reproduced on MvCars as benchmark results, including previous multi-view recognition works, advanced neural networks, and popular FGVC methods. The experimental results demonstrate that the proposed method delivers a better performance-efficient trade-off than all competitors. After that, analysis of the upper bound and the selected trajectories reveals the inherent characteristics of MAFR. In addition, comprehensive ablation studies are carried out to verify the necessities of each model component." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 228, + 392, + 241 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 228, + 392, + 241 + ], + "spans": [ + { + "bbox": [ + 306, + 228, + 392, + 241 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 248, + 489, + 261 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 248, + 489, + 261 + ], + "spans": [ + { + "bbox": [ + 306, + 248, + 489, + 261 + ], + "type": "text", + "content": "2.1. Fine-Grained Visual Classification" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 266, + 547, + 458 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 266, + 547, + 458 + ], + "spans": [ + { + "bbox": [ + 304, + 266, + 547, + 458 + ], + "type": "text", + "content": "Due to the inherent subtle inter-class variance and the relatively large intra-class variance, fine-grained visual classification is much more challenging than ordinary coarse-grained classification. With vigorous efforts made by researchers, great progress has been made in many directions. Localization-based approaches [61, 31, 56, 19, 53, 6] that explicitly locate discriminative parts for feature extraction to alleviate the intra-class variance. High-order encoding methods [34, 20, 19, 59, 62, 21] that adopt high-order feature interactions for better representation ability that can capture the subtle differences. Chen et al. [9] and Du et al. [13] train the model with jigsaw patches to implicitly encourage knowledge mining from local regions. Recently, Chang et al. [5] leverage the underlying hierarchical structure of fine-grained categories to achieve user-friendly outputs and better performance." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 459, + 547, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 459, + 547, + 602 + ], + "spans": [ + { + "bbox": [ + 304, + 459, + 547, + 602 + ], + "type": "text", + "content": "Except for good performances being brought, these works above also reveal that FGVC is never just a more challenging classification problem but a stand-alone field that requires well-directed research. In this paper, to further broaden the horizon of FGVC, we propose the multi-view active fine-grained visual recognition (MAFR) task aiming at effectively recognizing fine-grained categories in the 3D environment along with a targeted dataset. It is worth noting that the CompCars [57] dataset also provides a car dataset with view annotations. However, its multi-view images are taken from different samples, making it less suitable for the raised problem." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 611, + 441, + 624 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 611, + 441, + 624 + ], + "spans": [ + { + "bbox": [ + 306, + 611, + 441, + 624 + ], + "type": "text", + "content": "2.2. Multi-View Recognition" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "content": "Elsewhere for common object recognition problems, particular progress has been made to recognizing 3D objects with three trends that can be summarized [7]: point-based methods [42, 44, 2, 41], volume-based methods [37, 55, 43, 38], and view-based methods [10, 47, 29, 30, 60, 58]. Among them, point-based and volume-based approaches demand to perceive the 3D structure of objects via lidar," + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1569" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 70, + 245, + 161 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 245, + 161 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 245, + 161 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 245, + 161 + ], + "type": "image", + "image_path": "2575bed094a218698872e0d696ac96dab573a4fa32d7e99fed9796b145a06fcc.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 251, + 70, + 545, + 159 + ], + "blocks": [ + { + "bbox": [ + 251, + 70, + 545, + 159 + ], + "lines": [ + { + "bbox": [ + 251, + 70, + 545, + 159 + ], + "spans": [ + { + "bbox": [ + 251, + 70, + 545, + 159 + ], + "type": "image", + "image_path": "0bd51c589ad8875d6f3937018bb8a950bc827c2f705126fed1c71cb82ec33155.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 47, + 161, + 246, + 247 + ], + "blocks": [ + { + "bbox": [ + 47, + 161, + 246, + 247 + ], + "lines": [ + { + "bbox": [ + 47, + 161, + 246, + 247 + ], + "spans": [ + { + "bbox": [ + 47, + 161, + 246, + 247 + ], + "type": "image", + "image_path": "acb350d73b01b5e63f9a6c6b056ba03b94a894576a1bf8d1c5be6355a70e1914.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 250, + 547, + 285 + ], + "lines": [ + { + "bbox": [ + 46, + 250, + 547, + 285 + ], + "spans": [ + { + "bbox": [ + 46, + 250, + 547, + 285 + ], + "type": "text", + "content": "Figure 2. Illustration of samples from MvCars and some data statistics: (a) The number of samples per category. (b) The number of samples per type. (c) The number of samples per brand. (d) Results of our pilot experiment. The broken lines show model accuracy based on 8 individual views. Moreover, the bars represent the differences between each category's maximum and minimum accuracy." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 247, + 162, + 545, + 247 + ], + "blocks": [ + { + "bbox": [ + 247, + 162, + 545, + 247 + ], + "lines": [ + { + "bbox": [ + 247, + 162, + 545, + 247 + ], + "spans": [ + { + "bbox": [ + 247, + 162, + 545, + 247 + ], + "type": "image", + "image_path": "ce6d3ebb3a27950a258b0c6f2dcc807f29543391afdc28ba71d1fdca22bc28a1.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 303, + 287, + 375 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 303, + 287, + 375 + ], + "spans": [ + { + "bbox": [ + 46, + 303, + 287, + 375 + ], + "type": "text", + "content": "depth sensor or something else, which makes them less practicable in daily applications, e.g., recognizing an unfamiliar car for detailed information simply with a mobile phone. On the contrary, view-based methods that leverage multiple surrounding 2D views as descriptors for 3D objects tend to be an optimal choice." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 376, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 376, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 376, + 287, + 544 + ], + "type": "text", + "content": "Specifically, view-based methods share the core idea of encoding single-view features through a vision neural network and then aggregating multi-view features. Su et al. [47] first approaches the multi-view recognition problem with CNN for feature extraction and sum-pooling for aggregation. Then, Johns et al. [29] decomposes image sequences into image pair sets and then aggregates the pair-based classification in a weighted manner. After that, feature concatenation [51], hierarchical attention [22], and weighted fusion [17] are also adopted for better aggregating sequence features. In addition, sequences models (e.g., LSTM [26], GRU [11], Transformer blocks [49], etc) are also widely considered [28, 23, 7] and demonstrate their effectiveness." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 545, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 715 + ], + "type": "text", + "content": "In this paper, specifically towards the multi-view active fine-grained visual recognition (MAFR) task, traditional multi-view recognition dataset (e.g., RGB-D [33], ModelNet10, ModelNet40 [55]) is not sufficient any more. Thus, we first collect a fine-grained, multi-view car dataset named MvCars as a suitable testbed. Then, an active fine-grained recognition framework is built upon the general extraction-aggregation scheme. Note that, similar to ours, some approaches also take recognition efficiency into consideration [28, 29] by actively controlling the agent motion within a viewing sphere. However, a strict viewing sphere is not readily available in daily applications, especially for recognition with portable devices. We, therefore, consider the view selection as a discrete decision problem." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 301, + 361, + 314 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 301, + 361, + 314 + ], + "spans": [ + { + "bbox": [ + 306, + 301, + 361, + 314 + ], + "type": "text", + "content": "3. Dataset" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 327, + 547, + 400 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 327, + 547, + 400 + ], + "spans": [ + { + "bbox": [ + 304, + 327, + 547, + 400 + ], + "type": "text", + "content": "In this work, we first contribute a testbed for MAFR by collecting a multi-view fine-grained car recognition dataset named Multi-view Cars (MvCars). Considering that car recognition is challenging and close to daily life [57], a vehicle dataset can demonstrate well how the MAFR model performs in real applications." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 422, + 392, + 434 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 422, + 392, + 434 + ], + "spans": [ + { + "bbox": [ + 306, + 422, + 392, + 434 + ], + "type": "text", + "content": "3.1. Data Statistic" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 445, + 547, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 445, + 547, + 564 + ], + "spans": [ + { + "bbox": [ + 304, + 445, + 547, + 564 + ], + "type": "text", + "content": "MvCars consists of 233 models of cars from 35 brands (e.g., Ford, Volvo, Escort, etc.) that cover 5 types (e.g., sedan, SUV, MPV, sports car, and pickup). For each car, we collect and annotate 8 aligned perspectives – front, front-left, front-right, left, right, rear, rear-left, rear-right (as shown in Figure 2), and samples with missing perspectives are discarded. In total, there are 26,552 images collected from 3319 cars and are then split into 15,960/3,000/7,592 (at a ratio of " + }, + { + "bbox": [ + 304, + 445, + 547, + 564 + ], + "type": "inline_equation", + "content": "60\\% /10\\% /30\\%" + }, + { + "bbox": [ + 304, + 445, + 547, + 564 + ], + "type": "text", + "content": ") for train/val/test set, respectively." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": "In addition to multi-view and fine-grained, MvCars is also a hierarchical and long-tail dataset. We can easily build the brand-type-model label hierarchies for categories in MvCars, e.g., \"Ford car\"-\"Ford sedan\"-\"Ford Mondeo\", which may benefit directions like hierarchical structure-based FGVC [15] and human-friendly FGVC [5]. The numbers of samples per category are shown in Figure 2 (a), where a significant long-tail distribution can be observed. Such a long-tail dataset is also closer to realistic application and provides a new scenario to related topic [3]. The sample sizes per type and brand are shown in Figure 2 (b) and (c), respectively, and similar data distributions exist." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1570" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 71, + 542, + 264 + ], + "blocks": [ + { + "bbox": [ + 51, + 71, + 542, + 264 + ], + "lines": [ + { + "bbox": [ + 51, + 71, + 542, + 264 + ], + "spans": [ + { + "bbox": [ + 51, + 71, + 542, + 264 + ], + "type": "image", + "image_path": "dd8ef5cf6bd811e232b12b23039424370f9bbf5bbc15ed3ca5d4187b3fcb2f29.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 270, + 548, + 314 + ], + "lines": [ + { + "bbox": [ + 46, + 270, + 548, + 314 + ], + "spans": [ + { + "bbox": [ + 46, + 270, + 548, + 314 + ], + "type": "text", + "content": "Figure 3. Illustration of the proposed MAFR framework where three training stages are included: Stage I for training a multi-view recognition model with smooth predictions, Stage II for optimizing the next-view selection component based on the behavior of the classifier, and Stage III for fine-tuning the recognition model along with the trajectory decided by the actor. Here we use three training steps for brief illustration." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 334, + 150, + 346 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 334, + 150, + 346 + ], + "spans": [ + { + "bbox": [ + 47, + 334, + 150, + 346 + ], + "type": "text", + "content": "3.2. Pilot Experiment" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 353, + 287, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 353, + 287, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 353, + 287, + 460 + ], + "type": "text", + "content": "With the collected MvCars, here we first experimentally validate our first hypothesis mentioned in Section 1 – the discriminative information hides in various object views for different fine-grained categories. Factually, it is two-fold: (i) different perspectives contribute differently to FGVC; otherwise, actively selecting object view is meaningless, and (ii) different categories own different discriminative perspectives; otherwise, there is a trivial solution existing – consistently seeking the fixed distinguishable view." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 461, + 287, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 461, + 287, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 461, + 287, + 653 + ], + "type": "text", + "content": "In particular, for each perspective, we train a ResNet50 [25] for classification and obtain its accuracy in each category. Therefore, we can tell which perspective is more distinguishable for any specific category by comparing the performances of 8 models based on different views. We show the results of 30 classes in Figure 2 (d). Bars in the graph indicate the differences between the maximum and minimum accuracy of each category, and the average difference of all 233 classes is about " + }, + { + "bbox": [ + 46, + 461, + 287, + 653 + ], + "type": "inline_equation", + "content": "36.40\\%" + }, + { + "bbox": [ + 46, + 461, + 287, + 653 + ], + "type": "text", + "content": ". It powerfully proves that different perspectives contribute differently in the context of FGVC. On the other hand, broken lines in the graph represent the single-view accuracy changes along with different categories. The interaction of lines indicates that the ranking of view discrimination is inconsistent, demonstrating that different categories have different discriminative perspectives." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 654, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 287, + 714 + ], + "type": "text", + "content": "In a word, in MvCars, different perspectives provide significantly various meanings for FGVC, which is also hard to pre-defined via prior knowledge. Thus, an active fine-grained recognition method is called for, and the collected MvCars dataset can serve as an eligible testbed." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 333, + 388, + 346 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 333, + 388, + 346 + ], + "spans": [ + { + "bbox": [ + 306, + 333, + 388, + 346 + ], + "type": "text", + "content": "4. Methodology" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 354, + 373, + 365 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 354, + 373, + 365 + ], + "spans": [ + { + "bbox": [ + 306, + 354, + 373, + 365 + ], + "type": "text", + "content": "4.1. Overview" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 374, + 546, + 409 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 374, + 546, + 409 + ], + "spans": [ + { + "bbox": [ + 305, + 374, + 546, + 409 + ], + "type": "text", + "content": "Here we first give an overview of the data flow of MAFR during inference and introduce the model components needed." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "spans": [ + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "content": "Data structure. For MAFR, a dataset " + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "content": " consists of " + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "content": " samples can be expressed as " + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "inline_equation", + "content": "D = \\{X_{i},y_{i}\\}_{i = 1}^{N}" + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "inline_equation", + "content": "X_{i} = \\{x_{i}^{1},\\ldots ,x_{i}^{v},\\ldots ,x_{i}^{V}\\}" + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "content": " is a sequence of images depict a specific sample from " + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "content": " perspectives and " + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "inline_equation", + "content": "y_{i}" + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "content": " is their common ground-truth label. Note that, the annotations of views " + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "inline_equation", + "content": "\\{1,\\dots ,V\\}" + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "content": " are aligned, i.e., for arbitrary two samples " + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "inline_equation", + "content": "X_{i}" + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "inline_equation", + "content": "X_{j}" + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "inline_equation", + "content": "x_{i}^{v}" + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "inline_equation", + "content": "x_{j}^{v}" + }, + { + "bbox": [ + 305, + 411, + 546, + 496 + ], + "type": "text", + "content": " are taken from the same perspective." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "spans": [ + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": "Inference process. For sample " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "X_{i}" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": ", the model will take an image " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "x_{i}^{v_{1}}" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": " from arbitrary view " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "v_{1}" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": " as the initial visual input, which simulates the situation that the model may start recognition while facing any views of the target object. After that, the recognition process will carry on step-by-step. In particular, at step " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": " with input " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "x_{i}^{v_{t}}" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": " from view " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "v_{t}" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": ", the model will utilize all currently perceived information " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\{x_{i}^{v_{1}},\\ldots ,x_{i}^{v_{t - 1}},x_{i}^{v_{t}}\\}" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": " to deliver the category prediction " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "\\hat{y}_i^t" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": " and the next-view proposal " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "v_{t + 1}" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": ". Then, an inference cycle is closed, and the process can continue with " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "x_{i}^{v_{t + 1}}" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": " as the next input. Generally, " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "t\\in [1,T]" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": " can be set to a maximum " + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 304, + 497, + 547, + 639 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 642, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 547, + 714 + ], + "type": "text", + "content": "Framework component. An extraction-aggregation structure tends to be an intuitive choice to process a sequence of correlated visual inputs. Similar structures are also developed by previous multi-recognition arts [8]. Specifically, for any image " + }, + { + "bbox": [ + 304, + 642, + 547, + 714 + ], + "type": "inline_equation", + "content": "x_{i}^{v_{t}}" + }, + { + "bbox": [ + 304, + 642, + 547, + 714 + ], + "type": "text", + "content": " input the system, a CNN-based feature extractor " + }, + { + "bbox": [ + 304, + 642, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 304, + 642, + 547, + 714 + ], + "type": "text", + "content": " is first applied to extract single-" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 314, + 757 + ], + "type": "text", + "content": "1571" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": "view feature as " + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "inline_equation", + "content": "f_{i}^{v_{t}} = \\mathcal{F}(x_{i}^{v_{t}})" + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": ". It is worth noting that the feature extractors for different views share their weights, and this design will not lead to additional parameters. After that, an ideal model should consider all previously acquired information. Thus, a recurrent neural network is introduced as the aggregator " + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{R}(\\cdot)" + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": " that aggregates features from all seen perspectives. In particular, we adopt two aggregators with the same structure but individual weights. " + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_{e}(\\cdot)" + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_s(\\cdot)" + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": " that, " + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_e(\\cdot)" + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": " form global embeddings " + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "inline_equation", + "content": "e_i^t = \\mathcal{R}_e(f_i^{v_1},\\dots ,f_i^{v_t})" + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": " for category prediction, while " + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_s(\\cdot)" + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": " depicts the current states " + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "inline_equation", + "content": "s_i^t = \\mathcal{R}_s(f_i^{v_1},\\dots ,f_i^{v_t})" + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": " for next-view selection. Finally, a classifier " + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{P}(\\cdot)" + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": " and an actor " + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "inline_equation", + "content": "\\mathcal{A}(\\cdot)" + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": " are equipped in parallel with outputs " + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "inline_equation", + "content": "\\hat{y}_i^t = \\mathcal{P}(e_i^t)" + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "inline_equation", + "content": "v_{t + 1} = \\mathcal{A}(s_i^t)" + }, + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 249, + 144, + 262 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 249, + 144, + 262 + ], + "spans": [ + { + "bbox": [ + 47, + 249, + 144, + 262 + ], + "type": "text", + "content": "4.2. Model Training" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 269, + 289, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 269, + 289, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 269, + 289, + 472 + ], + "type": "text", + "content": "According to the aforementioned inference process, we can tell that the recognition component and the next-view selection component work separately but not independently. The mission of the recognition component is quite straightforward – conducting category prediction based on acquired information as well as possible. While the optimization goal of the next-view selection component largely depends on the behaviour of recognition – basically, the actor should try to select the next-view that can maximize the prediction probability of the target category. Therefore, a three stages training framework is intuitively designed: Stage I aims to train a good recognition model (including " + }, + { + "bbox": [ + 46, + 269, + 289, + 472 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot),\\mathcal{R}_e(\\cdot)" + }, + { + "bbox": [ + 46, + 269, + 289, + 472 + ], + "type": "text", + "content": " ,and " + }, + { + "bbox": [ + 46, + 269, + 289, + 472 + ], + "type": "inline_equation", + "content": "\\mathcal{P}(\\cdot))" + }, + { + "bbox": [ + 46, + 269, + 289, + 472 + ], + "type": "text", + "content": " that can handle sequence input, Stage II aims to optimize the next-view selection module (where " + }, + { + "bbox": [ + 46, + 269, + 289, + 472 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_s(\\cdot)" + }, + { + "bbox": [ + 46, + 269, + 289, + 472 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 269, + 289, + 472 + ], + "type": "inline_equation", + "content": "\\mathcal{A}(\\cdot)" + }, + { + "bbox": [ + 46, + 269, + 289, + 472 + ], + "type": "text", + "content": " participate) according to the behaviour of the trained recognition model, and Stages III aims to refine the recognition model under the trajectories decided by the actor." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "spans": [ + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "text", + "content": "Note that the inductive bias behind training the recognition component in the first place is that its behaviour can reveal view discrimination - a more discriminative view will greatly reduce the entropy of category prediction. However, a well-convergent classification model often delivers high-confidence predictions, especially for the small-scale datasets in the FGVC scenario, which will cause little changes in prediction probabilities and limit the information being revealed. For this, we take a very intuitive yet effective solution that splitting the training set " + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "inline_equation", + "content": "D_{T}" + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "text", + "content": " into two non-overlapping sub-sets for the first two stages respectively - specifically, a rehearsal set " + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "inline_equation", + "content": "D_{R}" + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "text", + "content": " is used for training the recognition components in Stage I, and a evaluation set " + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "inline_equation", + "content": "D_{E}" + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "text", + "content": " is used for providing authentic rewards while training the next-view selection module in Stage II. We have " + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "inline_equation", + "content": "D_{R} \\cup D_{E} = D_{T}" + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "inline_equation", + "content": "D_{R} \\cap D_{E} = \\emptyset" + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "text", + "content": ". In Stage III, the model will be trained with the whole training set " + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "inline_equation", + "content": "D_{T}" + }, + { + "bbox": [ + 46, + 472, + 289, + 675 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 676, + 288, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 676, + 288, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 676, + 288, + 700 + ], + "type": "text", + "content": "The whole framework is illustrated in Figure 3, and introductions about the three stages are as follows." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 701, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 701, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 701, + 288, + 714 + ], + "type": "text", + "content": "Stage I. To train a recognition model that can handle a se" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "text", + "content": "quence of inputs with dynamic length, each training iteration is divided into " + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "text", + "content": " steps with input sequence lengths from 1 to " + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "text", + "content": ". As the next-view planning module is not able for now, when " + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "inline_equation", + "content": "t \\geq 2" + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "text", + "content": ", a new image " + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "inline_equation", + "content": "x_{i}^{v_{t}}" + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "text", + "content": " is randomly selected from unseen views and appended to the input sequence at the " + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "inline_equation", + "content": "(t - 1)" + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "text", + "content": "-th step. Here we set " + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "inline_equation", + "content": "T = V" + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "text", + "content": " to ensure the maximum no-duplicated sequence can be sampled. With cross-entropy for optimization, the loss function for a batch of " + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 304, + 72, + 547, + 180 + ], + "type": "text", + "content": " samples can be formulated as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 320, + 189, + 547, + 222 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 320, + 189, + 547, + 222 + ], + "spans": [ + { + "bbox": [ + 320, + 189, + 547, + 222 + ], + "type": "interline_equation", + "content": "L _ {C E} (\\hat {y} _ {i} ^ {t}, y _ {i}) = \\frac {- 1}{B T C} \\sum_ {i = 1} ^ {B} \\sum_ {t = 1} ^ {T} \\sum_ {c = 1} ^ {C} y _ {i} \\times \\log (\\hat {y} _ {i, c} ^ {t}), \\tag {1}", + "image_path": "603fe439981664635e8f592d8d7cfb052708283b50a63628b126a81dde466e6e.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 231, + 545, + 254 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 231, + 545, + 254 + ], + "spans": [ + { + "bbox": [ + 305, + 231, + 545, + 254 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 231, + 545, + 254 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 305, + 231, + 545, + 254 + ], + "type": "text", + "content": " is the total category number, i.e., the channel number of the last layer." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 255, + 545, + 279 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 255, + 545, + 279 + ], + "spans": [ + { + "bbox": [ + 305, + 255, + 545, + 279 + ], + "type": "text", + "content": "Additionally, we also introduce a entropy maximization penalty as" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 322, + 288, + 545, + 321 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 322, + 288, + 545, + 321 + ], + "spans": [ + { + "bbox": [ + 322, + 288, + 545, + 321 + ], + "type": "interline_equation", + "content": "L _ {E M} \\left(\\hat {y} _ {i} ^ {t}\\right) = \\frac {1}{B T C} \\sum_ {i = 1} ^ {B} \\sum_ {t = 1} ^ {T} \\sum_ {c = 1} ^ {C} \\hat {y} _ {i, c} ^ {t} \\times \\log \\left(\\hat {y} _ {i, c} ^ {t}\\right), \\tag {2}", + "image_path": "842cfdff679cac35fda3c61e7572d87ca8b9131c58b0417aa15d2bec30eda054.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 330, + 547, + 389 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 330, + 547, + 389 + ], + "spans": [ + { + "bbox": [ + 304, + 330, + 547, + 389 + ], + "type": "text", + "content": "to encourage smooth predictions that can better reveal the priority between views. The total loss can be expressed as " + }, + { + "bbox": [ + 304, + 330, + 547, + 389 + ], + "type": "inline_equation", + "content": "L_{Stage1} = L_{CE}(\\hat{y}_i^t, y_i) + \\alpha \\times L_{EM}(\\hat{y}_i^t)" + }, + { + "bbox": [ + 304, + 330, + 547, + 389 + ], + "type": "text", + "content": ", and the degree of entropy maximization constrain can be control by the hyperparameter " + }, + { + "bbox": [ + 304, + 330, + 547, + 389 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 330, + 547, + 389 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "spans": [ + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": "Stage II. Here, the recognition components " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "(\\mathcal{F}(\\cdot),\\mathcal{R}_e(\\cdot)" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "\\mathcal{P}(\\cdot))" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": " are frozen, and we only optimize " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_s(\\cdot)" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "\\mathcal{A}(\\cdot)" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": " for next-view selection. As a non-differentiable sequential decision problem, we adopt the policy gradient method for optimization instead of directly optimizing with the classification loss. At the " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": "-th " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "(t\\geq 2)" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": " training step, the model will receive the input " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "x_{i}^{v_{t}}" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": " with the perspective " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "v_{t}" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": " decided by the actor at the " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "(t - 1)" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": "-th step. Then the view selection components can be updated according to the change of the target category's prediction probability, i.e., the rewards are set as " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "r_i^t = \\hat{y}_{iy_i}^t -\\hat{y}_{iy_i}^{t - 1}" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": ". And the " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": "-th " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "(t\\geq 2)" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": " step's loss function of Stage II can be simply expressed as: " + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "inline_equation", + "content": "L_{Stage2} = L_{PG}(v_t,\\hat{y}_i^{t - 1},\\hat{y}_i^t)" + }, + { + "bbox": [ + 304, + 389, + 547, + 557 + ], + "type": "text", + "content": ". Detailed expansion of the loss function can be found in Section 4.3" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 557, + 547, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 557, + 547, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 557, + 547, + 689 + ], + "type": "text", + "content": "Notably, for popular policy gradient algorithms [45, 46], the total reward for the current step's optimization is a (weighted) sum of all feature rewards from now on. This is because these methods are designed for scenarios where an agent should achieve an ultimate goal through a series of actions. However, on the contrary, MAFR aims to use as few steps as possible to achieve as high accuracy as possible, i.e., we care more about achieving the best performance at the current step rather than in the future. Therefore, we slightly modify the policy gradient algorithm by utilizing only " + }, + { + "bbox": [ + 304, + 557, + 547, + 689 + ], + "type": "inline_equation", + "content": "r_i^t" + }, + { + "bbox": [ + 304, + 557, + 547, + 689 + ], + "type": "text", + "content": " for the " + }, + { + "bbox": [ + 304, + 557, + 547, + 689 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 557, + 547, + 689 + ], + "type": "text", + "content": "-th step's optimization." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "Stage III. There is nothing new in this stage - all settings are the same as Stage I except for (i) the selected view " + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "inline_equation", + "content": "v_{t}" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1572" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 133 + ], + "type": "text", + "content": "when " + }, + { + "bbox": [ + 47, + 72, + 287, + 133 + ], + "type": "inline_equation", + "content": "t \\geq 2" + }, + { + "bbox": [ + 47, + 72, + 287, + 133 + ], + "type": "text", + "content": " is given by the actor, (ii) the whole training set " + }, + { + "bbox": [ + 47, + 72, + 287, + 133 + ], + "type": "inline_equation", + "content": "D_{T}" + }, + { + "bbox": [ + 47, + 72, + 287, + 133 + ], + "type": "text", + "content": " is used. The model is refined under standard classification supervision (i.e., " + }, + { + "bbox": [ + 47, + 72, + 287, + 133 + ], + "type": "inline_equation", + "content": "L_{Stage3} = L_{CE}(\\hat{y}_i^t, y_i)" + }, + { + "bbox": [ + 47, + 72, + 287, + 133 + ], + "type": "text", + "content": ") to especially adjust the trajectories decided by the actor and utilizing all the training data." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 138, + 137, + 150 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 138, + 137, + 150 + ], + "spans": [ + { + "bbox": [ + 47, + 138, + 137, + 150 + ], + "type": "text", + "content": "4.3. Design Details" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 156, + 287, + 227 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 156, + 287, + 227 + ], + "spans": [ + { + "bbox": [ + 46, + 156, + 287, + 227 + ], + "type": "text", + "content": "Feature extractor " + }, + { + "bbox": [ + 46, + 156, + 287, + 227 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 46, + 156, + 287, + 227 + ], + "type": "text", + "content": ". The feature extractor can be any backbone network for vision tasks, including various CNN architectures and Transformers (e.g., ResNet50 [25], ViT [12], etc.). Besides, by replacing " + }, + { + "bbox": [ + 46, + 156, + 287, + 227 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 46, + 156, + 287, + 227 + ], + "type": "text", + "content": " with other FGVC models, the proposed method can also extend them to work in 3D environments." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 228, + 287, + 287 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 228, + 287, + 287 + ], + "spans": [ + { + "bbox": [ + 46, + 228, + 287, + 287 + ], + "type": "text", + "content": "Feature aggregator " + }, + { + "bbox": [ + 46, + 228, + 287, + 287 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_e(\\cdot)" + }, + { + "bbox": [ + 46, + 228, + 287, + 287 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 228, + 287, + 287 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_s(\\cdot)" + }, + { + "bbox": [ + 46, + 228, + 287, + 287 + ], + "type": "text", + "content": ". The two feature aggregators should be able to aggregate information from sequences with variable lengths. Here we adopt GRU [11] for best performance. There are alternatives like LSTM [26], self-attention block [49], etc.." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 288, + 287, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 288, + 287, + 347 + ], + "spans": [ + { + "bbox": [ + 46, + 288, + 287, + 347 + ], + "type": "text", + "content": "Classifier " + }, + { + "bbox": [ + 46, + 288, + 287, + 347 + ], + "type": "inline_equation", + "content": "\\mathcal{P}(\\cdot)" + }, + { + "bbox": [ + 46, + 288, + 287, + 347 + ], + "type": "text", + "content": " and actor " + }, + { + "bbox": [ + 46, + 288, + 287, + 347 + ], + "type": "inline_equation", + "content": "\\mathcal{A}(\\cdot)" + }, + { + "bbox": [ + 46, + 288, + 287, + 347 + ], + "type": "text", + "content": ". Both the classifier and the actor are formed by one fully connected layer. For the cases that equip the proposed framework with other FGVC approaches, the structure of the classifier can be modified accordingly." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "spans": [ + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "type": "text", + "content": "Policy gradient algorithm. For training the actor " + }, + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "type": "inline_equation", + "content": "\\mathcal{A}(\\cdot)" + }, + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "type": "text", + "content": " (the next-view selection module) at Stgae II, we adopt the proximal policy optimization (PPO) algorithm [46] with a slight modification. Specifically, given a series of inputs " + }, + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "type": "inline_equation", + "content": "x_{i}^{v_{1}},\\ldots ,x_{i}^{v_{t}}" + }, + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "type": "text", + "content": " at the " + }, + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "type": "text", + "content": " -th step, the extractor " + }, + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "type": "text", + "content": " and the aggregator " + }, + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_s(\\cdot)" + }, + { + "bbox": [ + 46, + 348, + 287, + 419 + ], + "type": "text", + "content": " are first applied to form the current state:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 102, + 425, + 287, + 438 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 425, + 287, + 438 + ], + "spans": [ + { + "bbox": [ + 102, + 425, + 287, + 438 + ], + "type": "interline_equation", + "content": "s _ {i} ^ {t} = \\mathcal {R} _ {s} \\left(\\mathcal {F} \\left(x _ {i} ^ {v _ {1}}\\right), \\dots , \\mathcal {F} \\left(x _ {i} ^ {v _ {t}}\\right)\\right). \\tag {3}", + "image_path": "1afa2b399ba510c2a1bcbb118c5c7095359b224e4e6482d639acf55032988d1d.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "spans": [ + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "text", + "content": "And then, the actor takes the state " + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "inline_equation", + "content": "s_i^t" + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "text", + "content": " as input and decides the next view proposal " + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "inline_equation", + "content": "v_{t + 1}" + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "text", + "content": " as the action (i.e., " + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "inline_equation", + "content": "v_{t + 1} = \\mathcal{A}(s_i^t)" + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "text", + "content": "). For the general PPO algorithm with the reward " + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "inline_equation", + "content": "r_i^t" + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "text", + "content": "-th step, the advantage estimator " + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "inline_equation", + "content": "\\hat{A}_i^t" + }, + { + "bbox": [ + 46, + 444, + 287, + 493 + ], + "type": "text", + "content": " can be expressed as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 73, + 498, + 287, + 513 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 73, + 498, + 287, + 513 + ], + "spans": [ + { + "bbox": [ + 73, + 498, + 287, + 513 + ], + "type": "interline_equation", + "content": "\\hat {A} _ {t} = - V \\left(s _ {i} ^ {t}\\right) + r _ {i} ^ {t} + \\gamma r _ {i} ^ {t + 1} + \\dots + \\gamma^ {T - t} r _ {i} ^ {T}, \\tag {4}", + "image_path": "1fe896f82d9230f4753e73da0ba9d3dd0990aff1cff076f5845be37e67c3d7a1.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "spans": [ + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "type": "inline_equation", + "content": "V(s_i^t)" + }, + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "type": "text", + "content": " is the learned state-value function, " + }, + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "type": "inline_equation", + "content": "\\gamma \\in (0,1)" + }, + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "type": "text", + "content": " is a pre-defined discount factor, " + }, + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "type": "text", + "content": " is the maximum length of the input sequence. The principle behind it is straightforward - the current action should not only benefit the next step but also contribute to the overall goal. However, in this work, aiming at achieving reliable prediction with the least number of steps, we only focus on the profit at the very next step, i.e., we set " + }, + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "type": "inline_equation", + "content": "\\gamma = 0" + }, + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "type": "text", + "content": ". The advantage estimator we use can be formulated by " + }, + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "type": "inline_equation", + "content": "\\hat{A}_i^t = -V(s_i^t) + r_i^t" + }, + { + "bbox": [ + 46, + 517, + 287, + 625 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 625, + 287, + 650 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 625, + 287, + 650 + ], + "spans": [ + { + "bbox": [ + 47, + 625, + 287, + 650 + ], + "type": "text", + "content": "After that, we denote the prediction probability of " + }, + { + "bbox": [ + 47, + 625, + 287, + 650 + ], + "type": "inline_equation", + "content": "v_{t}" + }, + { + "bbox": [ + 47, + 625, + 287, + 650 + ], + "type": "text", + "content": " by " + }, + { + "bbox": [ + 47, + 625, + 287, + 650 + ], + "type": "inline_equation", + "content": "\\mathcal{A}(v_t|s_i^t)" + }, + { + "bbox": [ + 47, + 625, + 287, + 650 + ], + "type": "text", + "content": ". Then the clipped surrogate objective is:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 80, + 654, + 287, + 716 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 654, + 287, + 716 + ], + "spans": [ + { + "bbox": [ + 80, + 654, + 287, + 716 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} L _ {C L I P} = \\frac {1}{B} \\sum_ {i = 1} ^ {B} \\sum_ {t = 2} ^ {T} \\min \\left\\{\\frac {\\mathcal {A} \\left(v _ {t} \\mid s _ {i} ^ {t}\\right)}{\\mathcal {A} _ {o l d} \\left(v _ {t} \\mid s _ {i} ^ {t}\\right)} \\hat {A} _ {i} ^ {t} \\right. \\tag {5} \\\\ c l i p (\\frac {\\mathcal {A} (v _ {t} | s _ {i} ^ {t})}{\\mathcal {A} _ {o l d} (v _ {t} | s _ {i} ^ {t})}, 1 - \\epsilon , 1 + \\epsilon) \\hat {A} _ {i} ^ {t} \\}, \\\\ \\end{array}", + "image_path": "8aaa70d1bc98da3a4bbb6729a7f3a877ea4632080d76837b8f0d2dfa119a3c68.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "\\mathcal{A}_{old}(\\cdot)" + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": " stands for the actor before update, and " + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "\\epsilon \\in (0,1)" + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": " is a hyper-parameter. Note that " + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": " starts from " + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "t = 2" + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": " since the first view is randomly selected. Finally, the overall objective of Stage II can be expressed as:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 312, + 130, + 545, + 156 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 130, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 312, + 130, + 545, + 156 + ], + "type": "interline_equation", + "content": "L _ {S t a g e 2} = L _ {P G} \\left(v _ {t}, \\hat {y} _ {i} ^ {t - 1}\\right) = L _ {C L I P} - c _ {1} L _ {V F} + c _ {2} L _ {E}, \\tag {6}", + "image_path": "118852e585856a4ecdf653bf86204504882a73671e20d0aef2097946e2af6087.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 156, + 545, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 156, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 305, + 156, + 545, + 216 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 156, + 545, + 216 + ], + "type": "inline_equation", + "content": "L_{VF} = \\frac{1}{B}\\sum_{i=1}^{B}\\sum_{t=2}^{T}(V(s_i^t) - V^{target}(s_i^t))^2" + }, + { + "bbox": [ + 305, + 156, + 545, + 216 + ], + "type": "text", + "content": " is the squared-error loss suggested by [45], and " + }, + { + "bbox": [ + 305, + 156, + 545, + 216 + ], + "type": "inline_equation", + "content": "L_E = \\frac{1}{B}\\sum_{i=1}^{B}\\sum_{t=2}^{T}S_A(s_i^t)" + }, + { + "bbox": [ + 305, + 156, + 545, + 216 + ], + "type": "text", + "content": " is the entropy bonus following [54, 40]. " + }, + { + "bbox": [ + 305, + 156, + 545, + 216 + ], + "type": "inline_equation", + "content": "c_1" + }, + { + "bbox": [ + 305, + 156, + 545, + 216 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 156, + 545, + 216 + ], + "type": "inline_equation", + "content": "c_2" + }, + { + "bbox": [ + 305, + 156, + 545, + 216 + ], + "type": "text", + "content": " are hyper-parameters to balance the three loss components." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 226, + 408, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 226, + 408, + 239 + ], + "spans": [ + { + "bbox": [ + 306, + 226, + 408, + 239 + ], + "type": "text", + "content": "4.4. Dynamic Exiting" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "spans": [ + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "text", + "content": "For the proposed method, we can achieve the accuracy-efficiency trade-off by setting the maximum number of steps. However, simply assigning the same maximum step number to all samples may be too arbitrary since difficult samples may require information from more views than simple samples do. For that, inspired by previous sequential prediction work [52], we introduce the concept of budget batch classification [27] for dynamic exiting. Specifically, defining the exit probability of a certain step to be " + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "text", + "content": ", the probability of model exiting at the " + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "text", + "content": "-th step is " + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "inline_equation", + "content": "p_t = \\alpha (1 - p)^{t - 1}p" + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "text", + "content": " is a scaling factor that ensures " + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "inline_equation", + "content": "\\sum_{t = 1}^{T_{max}}p_t = 1" + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "text", + "content": ". The value of " + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "text", + "content": " can be found by solving the function " + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "inline_equation", + "content": "C = \\sum_{t = 1}^{T_{max}}t\\times p_t" + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "text", + "content": " is the expectation of average prediction steps. Then, we can estimate the exiting threshold " + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "inline_equation", + "content": "\\mu_t" + }, + { + "bbox": [ + 305, + 245, + 545, + 462 + ], + "type": "text", + "content": " for each step on the validation set. Such a strategy can further reveal the model potential under given step expectations by enabling better resource allocation among all test data." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 477, + 381, + 491 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 477, + 381, + 491 + ], + "spans": [ + { + "bbox": [ + 306, + 477, + 381, + 491 + ], + "type": "text", + "content": "5. Experiment" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": "Implementation. The feature extractor " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": " is initialized with ImageNet pre-trained weights, while other model components are randomly initialized. During Stage I and Stage III, we use SGD optimizer with a momentum of 0.9 and the cosine learning rate schedule [35] for optimization. The start learning rate is set to be 0.01 for the feature extractor and 0.1 for the rest. The input images are resize to " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": " and then random-cropped to " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": ". The hyper-parameter " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": " is set to be 0.01. During Stage II, we use the Adam optimizer with " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "\\beta_{1} = 0.9" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "\\beta_{2} = 0.999" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": ", and the cosine learning rate schedule [35] for optimization. The start learning rate of the actor " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "\\mathcal{A}(\\cdot)" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": " is set to be 0.005. The input images are resize to " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": " and then center-cropped to " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": ". The hyper-parameters " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "c_{1}" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "c_{2}" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": " are set to be 0.2, 0.5, and 0.01, respectively. The model is trained for 15 epochs for each stage. During inference, the input images are resize to " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": " and then center-cropped to " + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 305, + 498, + 545, + 712 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1573" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 70, + 289, + 275 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 289, + 275 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 289, + 275 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 289, + 275 + ], + "type": "table", + "html": "
MethodmAcc. (%)w-mAcc. (%)Step2-Acc. (%)
ResNet50RotationNet [30]79.53 ± 0.479.32 ± 0.778.72 ± 0.8
VERAM [8]79.42 ± 0.580.50 ± 1.380.19 ± 1.4
Baseline†78.21 ± 0.378.04 ± 0.576.74 ± 0.3
Baseline‡79.60 ± 0.779.75 ± 1.278.28 ± 0.8
Ours80.84 ± 0.482.20 ± 0.781.45 ± 0.9
Ours*81.33 ± 0.583.25 ± 0.982.86 ± 1.1
ViT-B.16Baseline†80.05 ± 0.480.32 ± 1.378.82 ± 0.4
Baseline‡80.47 ± 0.780.79 ± 1.479.93 ± 1.3
Ours81.35 ± 1.182.60 ± 0.681.53 ± 0.8
Ours*82.13 ± 1.283.58 ± 1.382.50 ± 1.4
PMGBaseline†80.26 ± 0.980.51 ± 1.479.92 ± 0.9
Baseline‡80.65 ± 0.980.98 ± 0.680.21 ± 0.4
Ours82.69 ± 1.183.47 ± 1.482.77 ± 1.3
Ours*82.99 ± 0.384.46 ± 0.583.79 ± 0.6
TransFGBaseline†81.26 ± 1.581.33 ± 0.980.76 ± 0.6
Baseline‡81.78 ± 1.282.15 ± 1.481.52 ± 0.6
Ours83.76 ± 1.384.72 ± 0.584.35 ± 1.0
Ours*84.89 ± 0.385.77 ± 1.385.57 ± 0.6
", + "image_path": "d220e43dd101661ef42eccaf5b346ca4a1c16700fe03e03a9526a24f08779d98.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 47, + 275, + 287, + 297 + ], + "lines": [ + { + "bbox": [ + 47, + 275, + 287, + 297 + ], + "spans": [ + { + "bbox": [ + 47, + 275, + 287, + 297 + ], + "type": "text", + "content": "Table 1. Results of the proposed method with different backbones. The best results of each section are marked in bold." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 316, + 289, + 555 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 316, + 289, + 555 + ], + "spans": [ + { + "bbox": [ + 46, + 316, + 289, + 555 + ], + "type": "text", + "content": "Baseline models. For extensive evaluation, three groups of approaches were considered for comparison: I. previous multi-view recognition methods, including RotationNet [30] and VERAM [8], II. state-of-the-art FGVC methods, including PMG [13] and TransFG [24], and III. advanced vision neural networks, including ResNet [25] and ViT [12]. Specifically, for group I, we re-implemented them with ResNet50 as the backbone model for a fair comparison. And for group II and III, as they are designed for single-view recognition, two baseline frameworks, which may be intuitive choices for most people, are designed to adapt them to the MAFR task: (i) Baseline†: a naive model ensemble scheme, i.e., predictions are independently delivered according to each view, and at the " + }, + { + "bbox": [ + 46, + 316, + 289, + 555 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 316, + 289, + 555 + ], + "type": "text", + "content": "-th step, the average of " + }, + { + "bbox": [ + 46, + 316, + 289, + 555 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 316, + 289, + 555 + ], + "type": "text", + "content": " inputs' predictions is adopted as the current result, and (ii) Baseline‡: due to their conciseness, these models can directly serve as the feature extractor of the proposed method, therefore, a strong sequential prediction baseline can be implemented by replacing our feature extractors with these approaches and training under the setting of Stage III." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 556, + 289, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 556, + 289, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 556, + 289, + 665 + ], + "type": "text", + "content": "Evaluation Metrics. For quantitative evaluation, results based on 3 metrics are reported: (i) Mean Accuracy (mAcc) that takes the mean value of all " + }, + { + "bbox": [ + 46, + 556, + 289, + 665 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 556, + 289, + 665 + ], + "type": "text", + "content": " steps' accuracy, which can be regarded as the area under the accuracy-step line that represents the general performances of models, (ii) Weighted Mean Accuracy (w-mAcc) that weights different steps with exponentially decreased weights, since the performance of the first few steps should be more important in the consideration of efficiency1, and (iii) Step2 Accuracy" + } + ] + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 309, + 71, + 545, + 241 + ], + "blocks": [ + { + "bbox": [ + 309, + 71, + 545, + 241 + ], + "lines": [ + { + "bbox": [ + 309, + 71, + 545, + 241 + ], + "spans": [ + { + "bbox": [ + 309, + 71, + 545, + 241 + ], + "type": "image", + "image_path": "7b5a9a57fa67146aa36f206c17e2781d5d9398c3e28cf61b788dc7b63831c691.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 243, + 546, + 266 + ], + "lines": [ + { + "bbox": [ + 306, + 243, + 546, + 266 + ], + "spans": [ + { + "bbox": [ + 306, + 243, + 546, + 266 + ], + "type": "text", + "content": "Figure 4. Illustration of model performance per-step and the performance upper bound from the perspective of trajectory decision." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 291, + 545, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 291, + 545, + 316 + ], + "spans": [ + { + "bbox": [ + 306, + 291, + 545, + 316 + ], + "type": "text", + "content": "(Step2-Acc) that takes the 2-nd step's accuracy to highlight the profit of the first view selection2." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 331, + 391, + 342 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 331, + 391, + 342 + ], + "spans": [ + { + "bbox": [ + 306, + 331, + 391, + 342 + ], + "type": "text", + "content": "5.1. Main Results" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 352, + 547, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 352, + 547, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 352, + 547, + 676 + ], + "type": "text", + "content": "The results of the proposed method against all mentioned baselines are reported in Table 5. The table is organized into 4 sections according to different backbone networks. For ResNet50 [25] as the base model, we can observe that Baselined already achieves impressive performance and delivers quite competitive results to previous multi-view recognition models. On the contrary, the proposed method outperforms it by " + }, + { + "bbox": [ + 304, + 352, + 547, + 676 + ], + "type": "inline_equation", + "content": "\\sim 1.2\\%" + }, + { + "bbox": [ + 304, + 352, + 547, + 676 + ], + "type": "inline_equation", + "content": "\\sim 2.5\\%" + }, + { + "bbox": [ + 304, + 352, + 547, + 676 + ], + "type": "inline_equation", + "content": "\\sim 3.2\\%" + }, + { + "bbox": [ + 304, + 352, + 547, + 676 + ], + "type": "text", + "content": " for mAcc, w-mAcc, and Step2-Acc, respectively. The larger margins on w-mAcc and Step2-Acc also demonstrate its superiority in efficiency that benefits from the active next-view selection scheme. In addition, while applying the dynamic exiting strategy, we also calculate these three metrics by obtaining the accuracy when the step expectations equal 1-8, and there is no doubt that it further boosts model performance via a better efforts allocation. An interesting finding is that for models with the next-view selection mechanism, we can generally observe that mAcc " + }, + { + "bbox": [ + 304, + 352, + 547, + 676 + ], + "type": "inline_equation", + "content": "<" + }, + { + "bbox": [ + 304, + 352, + 547, + 676 + ], + "type": "text", + "content": " Step2-Acc, while mAcc " + }, + { + "bbox": [ + 304, + 352, + 547, + 676 + ], + "type": "inline_equation", + "content": ">" + }, + { + "bbox": [ + 304, + 352, + 547, + 676 + ], + "type": "text", + "content": " Step2-Acc for other models, which indicates a significant performance boosting caused by the active view selection at step 2. In addition, for other baselines implemented with the more advanced network (i.e., ViT [12]) and FGVC models (i.e., PMG [13] and TransFG [24]), the proposed framework can also boost their performance via active view selection and dynamic exiting, which indicates most of the recognition models can be extended to be an FGVC experts in the real physical world." + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 46, + 673, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 673, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 673, + 287, + 713 + ], + "type": "text", + "content": "1Here we take [0, 0.5039, 0.2520, 0.1260, 0.0630, 0.0315, 0.0157, 0.0079] for w-mAcc when " + }, + { + "bbox": [ + 46, + 673, + 287, + 713 + ], + "type": "inline_equation", + "content": "T = 8" + }, + { + "bbox": [ + 46, + 673, + 287, + 713 + ], + "type": "text", + "content": ". The accuracy of the first step is weighted by 0.0 because it is randomly selected and does not relate to the performance of active selection." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": "2Step2-Acc can be regarded as w-mAcc with weight set " + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "inline_equation", + "content": "[0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]" + }, + { + "bbox": [ + 306, + 693, + 545, + 713 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1574" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 70, + 288, + 182 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 288, + 182 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 288, + 182 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 288, + 182 + ], + "type": "table", + "html": "
MethodmAcc. (%)w-mAcc. (%)Step2-Acc. (%)
Random Selection80.15 ± 0.579.86 ± 0.878.28 ± 0.6
Selecting the Farthest80.50 ± 0.481.49 ± 0.680.68 ± 0.9
Selecting w/ Prior80.43 ± 0.681.32 ± 0.980.55 ± 0.7
w/ Duplicate View80.22 ± 0.981.38 ± 0.881.18 ± 1.1
w/o Data Split80.19 ± 0.979.98 ± 1.178.53 ± 0.9
w/o LEM80.24 ± 0.481.57 ± 0.780.96 ± 1.0
w/ Future Rewards80.56 ± 0.681.44 ± 0.880.53 ± 0.8
Ours80.84 ± 0.482.20 ± 0.781.45 ± 0.9
Ours*81.33 ± 0.583.25 ± 0.982.86 ± 1.1
", + "image_path": "913a985f046db1415f7e209dfc587c369a992527294a3551455bc7590c3a3f32.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 182, + 287, + 205 + ], + "lines": [ + { + "bbox": [ + 47, + 182, + 287, + 205 + ], + "spans": [ + { + "bbox": [ + 47, + 182, + 287, + 205 + ], + "type": "text", + "content": "Table 2. Results of ablation studies. The best ones are marked in bold." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 223, + 178, + 236 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 223, + 178, + 236 + ], + "spans": [ + { + "bbox": [ + 47, + 223, + 178, + 236 + ], + "type": "text", + "content": "5.2. Upper Bound Analysis" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 242, + 289, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 242, + 289, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 242, + 289, + 529 + ], + "type": "text", + "content": "To better illustrate the change of model accuracy over inference steps, we show the accuracy-step lines of all models with ResNet50 [25] as the backbone in Figure 4. At this point, the audiences may question why these models' performances do not consistently increase. With the same question, we study the upper bound of our model. Due to the finite total view numbers, we are able to visit all possible trajectories for each sample. Therefore, a performance upper bound can be obtained from the perspective of trajectory decision - an arbitrary sample will be considered correctly classified when any trajectory allows this sample to be classified correctly. According to Figure 4, the degradation in the last few steps is also observed on the performance upper bound. A similar phenomenon is also observed in previous multi-view recognition works (e.g., [30]). In this work, we also attribute this to the inherent feature of fine-grained recognition in the 3D environment - the discriminative clues only hide in a few views, and the noises caused by intra-class variance will be more likely to be introduced when full visual information (i.e., all views) is included. This echoes the essential insight in the 2D fine-grained recognition where subtle differences of local regions are discriminative, and the global structures are more likely disturbed." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 538, + 141, + 551 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 538, + 141, + 551 + ], + "spans": [ + { + "bbox": [ + 47, + 538, + 141, + 551 + ], + "type": "text", + "content": "5.3. Ablation Study" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 569, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 569, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 569, + 287, + 665 + ], + "type": "text", + "content": "In this section, we evaluate several variants of the proposed method based on ResNet50 to demonstrate the necessities of our designs. First, to verify the effectiveness of the active next-view selection mechanism, we study our model with no-duplicate inputs of random order and the order decided by the priority found in our pilot experiment. Fortunately, the proposed method passes the test with significant w-mAcc margins of " + }, + { + "bbox": [ + 46, + 569, + 287, + 665 + ], + "type": "inline_equation", + "content": "\\sim 2.3\\%" + }, + { + "bbox": [ + 46, + 569, + 287, + 665 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 569, + 287, + 665 + ], + "type": "inline_equation", + "content": "\\sim 0.9\\%" + }, + { + "bbox": [ + 46, + 569, + 287, + 665 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "content": "In addition, The farthest viewpoint sampling is also an important baseline - specifically, we implement it by selecting the farthest and unselected view from the second step. In cases where there are two equally distant views, we ran" + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 310, + 70, + 422, + 182 + ], + "blocks": [ + { + "bbox": [ + 310, + 70, + 422, + 182 + ], + "lines": [ + { + "bbox": [ + 310, + 70, + 422, + 182 + ], + "spans": [ + { + "bbox": [ + 310, + 70, + 422, + 182 + ], + "type": "image", + "image_path": "826dc0dd6afe8f18da8cfe43c1d2415ade88d4a31fa9bb6544fc89f258bfcbe0.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 315, + 185, + 372, + 230 + ], + "blocks": [ + { + "bbox": [ + 315, + 185, + 372, + 230 + ], + "lines": [ + { + "bbox": [ + 315, + 185, + 372, + 230 + ], + "spans": [ + { + "bbox": [ + 315, + 185, + 372, + 230 + ], + "type": "image", + "image_path": "2ec73597dbf687003cb585e772a7b26c7c81aa121c4c9784551803eeb3007350.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 331, + 232, + 357, + 241 + ], + "lines": [ + { + "bbox": [ + 331, + 232, + 357, + 241 + ], + "spans": [ + { + "bbox": [ + 331, + 232, + 357, + 241 + ], + "type": "text", + "content": "View-2" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 373, + 185, + 428, + 230 + ], + "blocks": [ + { + "bbox": [ + 373, + 185, + 428, + 230 + ], + "lines": [ + { + "bbox": [ + 373, + 185, + 428, + 230 + ], + "spans": [ + { + "bbox": [ + 373, + 185, + 428, + 230 + ], + "type": "image", + "image_path": "6802b837f030fa4de5842fbb077da625a493893cd9702a0d37e9e4f83203a70d.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 388, + 232, + 413, + 241 + ], + "lines": [ + { + "bbox": [ + 388, + 232, + 413, + 241 + ], + "spans": [ + { + "bbox": [ + 388, + 232, + 413, + 241 + ], + "type": "text", + "content": "View-4" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 247, + 547, + 293 + ], + "lines": [ + { + "bbox": [ + 305, + 247, + 547, + 293 + ], + "spans": [ + { + "bbox": [ + 305, + 247, + 547, + 293 + ], + "type": "text", + "content": "Figure 5. Predicted trajectories of \"Haval H6\" with \"View-2\" and \"View-5\" as the initial views. The darker the colour, the more times the trajectory has been selected. The most selected trajectory is highlighted with blue circles." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 427, + 70, + 544, + 182 + ], + "blocks": [ + { + "bbox": [ + 427, + 70, + 544, + 182 + ], + "lines": [ + { + "bbox": [ + 427, + 70, + 544, + 182 + ], + "spans": [ + { + "bbox": [ + 427, + 70, + 544, + 182 + ], + "type": "image", + "image_path": "f80e86a52fcc1590d22f12f68e9c3768ea5dbbbac99f9fb82bcdf6e41460c044.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 429, + 185, + 485, + 230 + ], + "blocks": [ + { + "bbox": [ + 429, + 185, + 485, + 230 + ], + "lines": [ + { + "bbox": [ + 429, + 185, + 485, + 230 + ], + "spans": [ + { + "bbox": [ + 429, + 185, + 485, + 230 + ], + "type": "image", + "image_path": "08fb35f353fcb3c485f6fefdbd605ae8b170f21f2237e9af17a9ea6a17743be7.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 444, + 232, + 471, + 241 + ], + "lines": [ + { + "bbox": [ + 444, + 232, + 471, + 241 + ], + "spans": [ + { + "bbox": [ + 444, + 232, + 471, + 241 + ], + "type": "text", + "content": "View-3" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 486, + 185, + 542, + 230 + ], + "blocks": [ + { + "bbox": [ + 486, + 185, + 542, + 230 + ], + "lines": [ + { + "bbox": [ + 486, + 185, + 542, + 230 + ], + "spans": [ + { + "bbox": [ + 486, + 185, + 542, + 230 + ], + "type": "image", + "image_path": "2226997a4824da6145de324f7d90ab564beeb44ff7997885fb1d566842a9c1fb.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 501, + 232, + 527, + 241 + ], + "lines": [ + { + "bbox": [ + 501, + 232, + 527, + 241 + ], + "spans": [ + { + "bbox": [ + 501, + 232, + 527, + 241 + ], + "type": "text", + "content": "View-5" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 313, + 546, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 313, + 546, + 373 + ], + "spans": [ + { + "bbox": [ + 304, + 313, + 546, + 373 + ], + "type": "text", + "content": "domly choose one of them. However, the proposed method consistently outperforms it with a significant margin. This is because the most complementary view may not be the farthest one, as we further illustrate on the right in the next Section (see Figure 5)." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 373, + 545, + 457 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 373, + 545, + 457 + ], + "spans": [ + { + "bbox": [ + 304, + 373, + 545, + 457 + ], + "type": "text", + "content": "Besides, an artificial restriction is added for all evaluations to ensure that new views selected are no-duplicate. It is intuitive since unseen views can offer complementary information, and the information about which views have been selected is easily acquired. Here we also evaluate by allowing duplicate views, and the model performance degrades with no surprise." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 458, + 547, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 458, + 547, + 589 + ], + "spans": [ + { + "bbox": [ + 304, + 458, + 547, + 589 + ], + "type": "text", + "content": "After that, our designs for model training are also demonstrated to be effective. Splitting the training data into two non-overlapped subsets and encouraging entropy maximization both significantly boost model performance. It is worth noting that when we include the future rewards for policy optimization, mAcc is not significantly affected ( with a slight degradation of " + }, + { + "bbox": [ + 304, + 458, + 547, + 589 + ], + "type": "inline_equation", + "content": "0.28\\%" + }, + { + "bbox": [ + 304, + 458, + 547, + 589 + ], + "type": "text", + "content": " ), but w-mAcc and Step2- Acc decrease by " + }, + { + "bbox": [ + 304, + 458, + 547, + 589 + ], + "type": "inline_equation", + "content": "\\sim 0.8\\%" + }, + { + "bbox": [ + 304, + 458, + 547, + 589 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 458, + 547, + 589 + ], + "type": "inline_equation", + "content": "\\sim 0.9\\%" + }, + { + "bbox": [ + 304, + 458, + 547, + 589 + ], + "type": "text", + "content": ". This indicates that future rewards may be meaningful for traditional sequential decision problems but not for MAFR, where efficiency is highly required." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 598, + 421, + 611 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 598, + 421, + 611 + ], + "spans": [ + { + "bbox": [ + 306, + 598, + 421, + 611 + ], + "type": "text", + "content": "5.4. Trajectory Analysis" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": "For an in-depth analysis of the characteristics of the MAFR task, we further analyze the view-selection trajectory decided by our model. Specifically, with ResNet50 [25] as the feature extractor, we visualize the predicted trajectories of \"Haval H6\" in Figure 5. The two subplots show the results with \"View-2\" and \"View-5\" as the initial views, respectively, and the darker the colour, the more times the trajectory has been selected. The most se" + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 748, + 315, + 757 + ], + "type": "text", + "content": "1575" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 262 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 262 + ], + "type": "text", + "content": "lected trajectory is highlighted with blue circles. According to the visualization, we can first conclude that there is some certainty in the best trajectory of a particular category – a significant broken line can be observed. However, the optimal trajectory is associated with the complementarity between different views – when we enter View-2, the next best choice is View-4; and when we enter View-5, the next best choice is View-3. Therefore, solving MAFR is not simply a ranking of the discriminative power of perspective information, echoing the results in Section 5.3 that view selecting with prior knowledge does not yield comparative performance. Factually, the optimal trajectory may even vary for different samples, as there is not just a single trajectory in each subplot. However, this may also be caused by the fact that our model still has room for improvement, so we do not discuss it further here." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 273, + 119, + 285 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 273, + 119, + 285 + ], + "spans": [ + { + "bbox": [ + 47, + 273, + 119, + 285 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 293, + 289, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 293, + 289, + 426 + ], + "spans": [ + { + "bbox": [ + 46, + 293, + 289, + 426 + ], + "type": "text", + "content": "This paper extends the fine-grained visual classification to 3D environments and proposes the multi-view active fine-grained visual recognition (MAFR) problem. We first collect a multi-view fine-grained car dataset (MvCars) as a qualified benchmark. Then we re-implement several multiview recognition methods, FGVC approaches, and vision neural networks as baseline methods. A policy-gradient-based framework with a dynamic exiting strategy is proposed for the problem raised and yields the best performance. We also discuss the upper bound and predicted trajectories of the proposed method." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 434, + 140, + 448 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 434, + 140, + 448 + ], + "spans": [ + { + "bbox": [ + 47, + 434, + 140, + 448 + ], + "type": "text", + "content": "Acknowledgment" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 454, + 287, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 454, + 287, + 574 + ], + "spans": [ + { + "bbox": [ + 46, + 454, + 287, + 574 + ], + "type": "text", + "content": "This work was supported in part by National Natural Science Foundation of China (NSFC) No. U19B2036, 62106022, 62225601, in part by Beijing Natural Science Foundation Project No. Z200002, in part by scholarships from China Scholarship Council (CSC) under Grant CSC No. 202206470055, in part by BUPT Excellent Ph.D. Students Foundation No. CX2022152, in part by the Program for Youth Innovative Research Team of BUPT No. 2023QNTD02, and in part by the Supported by High-performance Computing Platform of BUPT." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 48, + 583, + 106, + 594 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 583, + 106, + 594 + ], + "spans": [ + { + "bbox": [ + 48, + 583, + 106, + 594 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 52, + 602, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 10, + "blocks": [ + { + "bbox": [ + 52, + 602, + 287, + 634 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 602, + 287, + 634 + ], + "spans": [ + { + "bbox": [ + 52, + 602, + 287, + 634 + ], + "type": "text", + "content": "[1] John Aloimonos, Isaac Weiss, and Amit Bandyopadhyay. 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In NeurIPS, 2019. 2" + } + ] + } + ], + "index": 7 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 296, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 296, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 296, + 749, + 315, + 757 + ], + "type": "text", + "content": "1578" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-body Depth and Camera Pose Estimation from Multiple Views/92fd5224-0cb4-4518-837c-e6d30b98ac63_content_list.json b/2023/Multi-body Depth and Camera Pose Estimation from Multiple Views/92fd5224-0cb4-4518-837c-e6d30b98ac63_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..335f37abfc0a4b245a7861d182984329b061214e --- /dev/null +++ b/2023/Multi-body Depth and Camera Pose Estimation from Multiple Views/92fd5224-0cb4-4518-837c-e6d30b98ac63_content_list.json @@ -0,0 +1,1933 @@ +[ + { + "type": "text", + "text": "Multi-body Depth and Camera Pose Estimation from Multiple Views", + "text_level": 1, + "bbox": [ + 137, + 130, + 833, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Andrea Porfiri Dal Cin \nPolitecnico di Milano", + "bbox": [ + 148, + 181, + 333, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "andrea.porfiridalcin@polimi.it", + "bbox": [ + 106, + 219, + 372, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Giacomo Boracchi Politecnico di Milano", + "bbox": [ + 441, + 181, + 616, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "giacomo.boracchi@polimi.it", + "bbox": [ + 411, + 219, + 645, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Luca Magri\nPolitecnico di Milano", + "bbox": [ + 684, + 181, + 859, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "luca MAGRI@polimi.it", + "bbox": [ + 684, + 219, + 862, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Traditional and deep Structure-from-Motion (SfM) methods typically operate under the assumption that the scene is rigid, i.e., the environment is static or consists of a single moving object. Few multi-body SfM approaches address the reconstruction of multiple rigid bodies in a scene but suffer from the inherent scale ambiguity of SfM, such that objects are reconstructed at inconsistent scales. We propose a depth and camera pose estimation framework to resolve the scale ambiguity in multi-body scenes. Specifically, starting from disorganized images, we present a novel multi-view scale estimator that resolves the camera pose ambiguity and a multi-body plane sweep network that generalizes depth estimation to dynamic scenes. Experiments demonstrate the advantages of our method over state-of-the-art SfM frameworks in multi-body scenes and show that it achieves comparable results in static scenes. The code and dataset are available at https://github.com/andreadalcin/MultiBodySfM.", + "bbox": [ + 76, + 300, + 473, + 571 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 588, + 209, + 604 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Real-world environments often contain independently moving objects, and their reconstruction is fundamental for safe robot navigation and augmented reality in complex dynamic environments. Unfortunately, traditional and deep learning Structure-from-Motion (SfM) algorithms assume that the scene is static and treat moving objects as outliers, missing important information and producing suboptimal results when the scene is dynamic. In Fig. 1-left, the depth reconstructed by the state-of-the-art DeepSfM [36] shows artifacts in the image region of a moving object (in red).", + "bbox": [ + 75, + 613, + 468, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this work, we go one step further and enable consistent 3D reconstruction (Fig. 1-right) of a scene with multiple rigidly moving objects. This task, also known as Multi-Body Structure-from-Motion (MBSfM), is still open and far from being solved in practice. Traditional MBSfM attempts [1, 26] segment rigid motions to obtain partial reconstructions of individually moving objects in the scene. However, these methods are hampered by the relative scale problem, namely that the 3D structure of each independ-", + "bbox": [ + 75, + 765, + 470, + 902 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Two frames of a dynamic scene with a moving object", + "bbox": [ + 537, + 267, + 875, + 281 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/178cddfc24e17c5f7f7a4edcf14ada7006f3edf48bc067e74dce2af874556780.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 506, + 284, + 702, + 401 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/1a7472eb087d1a77ebf8e80aa446ec098980169bccbfe7a0dae150262fba0ea6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 707, + 285, + 906, + 402 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/c3ae3da1e778c66969979dd534e56e4beed8ee6d123d494229c957633b978419.jpg", + "image_caption": [ + "Reconstructed Depth Maps of the second frame", + "DeepSFM", + "Figure 1: Two-views of a multi-body scene (top-row). Depth estimation networks (e.g. [36]) yield inconsistent depths (bottom-left) for moving objects. Our method explicitly accounts for moving objects to produce geometrically consistent depths (bottom-right)." + ], + "image_footnote": [], + "bbox": [ + 504, + 425, + 704, + 542 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/5ad940e9bcf992d3c8e9ab4e90a7b4246bc98fc40d98db1894a4fbbd751dcb60.jpg", + "image_caption": [ + "Ours" + ], + "image_footnote": [], + "bbox": [ + 707, + 425, + 906, + 542 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "dently moving object is estimated up to a similarity, so that each object is reconstructed in its own scale. Therefore, a unified reconstruction of all objects up to a common global scale factor is impossible without additional information. Similarly, deep methods for SfM that leverage explicit multi-view constraints [34, 36, 13, 29, 4] are affected by the relative scale problem and cannot regress a unified depth map of a multi-body scene since their underlying architecture cannot handle multiple motions.", + "bbox": [ + 496, + 642, + 892, + 777 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recent monocular depth estimators [9, 2] use learned priors to regress dense depth maps from images without exploiting multi-view constraints. Thus, monocular methods implicitly avoid the relative scale problem by regressing consistent depth maps across the entire image. However, monocular depth estimation is inherently ill-posed and these models do not provide the same generalization capabilities of multi-view methods when scenes are static. Fur", + "bbox": [ + 496, + 779, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "17804", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "thermore, the 3D structures inferred from different images of the same scene are not guaranteed to be consistent. Thus, this inconsistency eventually manifests in alignment problems that are not trivial to solve.", + "bbox": [ + 75, + 90, + 468, + 150 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we present a novel deep learning framework for depth and camera pose estimation designed specifically for multi-body scenes. Following consolidated MBSfM pipelines, we perform motion segmentation to recover a set of relative camera poses up to a scale factor and the corresponding sparse 3D reconstructions of each moving object. Then, we depart from existing MBSfM approaches by directly solving the relative scale problem and regressing geometrically consistent depth maps and refined poses.", + "bbox": [ + 75, + 151, + 467, + 286 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Specifically, our main contributions are twofold:", + "bbox": [ + 96, + 287, + 416, + 301 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "(1) a robust scale estimation to fix the scale ambiguity,", + "(2) a multi-body plane sweep network to regress refined camera poses and depth maps in multi-body scenes." + ], + "bbox": [ + 81, + 303, + 467, + 347 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our scale estimator uses monocular depth maps to unify the 3D structures and camera poses under a global scale factor. This is based on a robust voting scheme that mitigates the impact of inaccuracies in monocular depth estimates.", + "bbox": [ + 75, + 348, + 467, + 407 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We adopt a deep neural network for multi-body depth estimation and pose refinement. The network adopts our novel multi-body plane sweep algorithm, which uses all the rigid motions in the scene, now devoid of scale ambiguity, to compute dense depth maps and refined camera poses. Notably, the estimated depth maps are geometrically consistent even in image regions covered by moving objects. Plane sweep has never been extended to support multiple rigid motions to the best of our knowledge. Our network also includes a pose estimation module that refines camera poses based on current depth estimates.", + "bbox": [ + 75, + 409, + 467, + 574 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We demonstrate the effectiveness of our approach on both static and multi-body scenes. On static scenes, our method performs on par with traditional and deep SfM methods. On multi-body scenes, it significantly outperforms SOTA deep learning SfM methods in the depth estimation task and achieves comparable camera pose results.", + "bbox": [ + 75, + 575, + 467, + 664 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Problem Formulation", + "text_level": 1, + "bbox": [ + 76, + 679, + 282, + 695 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-body depth and camera pose estimation is framed as follows. The input is a set of $n$ unstructured images $\\{\\mathbf{I}_i\\}_{i=1}^n$ captured by a moving camera and depicting a multi-body scene in which $\\mu$ objects $\\mathcal{B} = \\{\\beta_i\\}_{i=1}^\\mu$ independently move according to their rigid motions. Without loss of generality, we consider the object $\\beta_1$ to be static w.r.t. to the camera motion. Our goal is to estimate depth maps $\\{\\mathbf{D}_i\\}_{i=1}^n$ for each image $\\mathbf{I}_i$ and the absolute camera poses $\\{\\mathbf{R}_i, \\mathbf{t}_i\\}_{i=1}^n$ in the reference frame of $\\beta_1$ . We assume that: i) an upper bound $M$ on the maximum number $\\mu$ of moving objects in the scene is given, ii) the camera is perspective and its intrinsic parameters $\\mathbf{K}$ are known.", + "bbox": [ + 75, + 703, + 467, + 883 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Consider that our problem is different from non-rigid", + "bbox": [ + 94, + 885, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "SfM [16, 14]. Non-rigid SfM handles a wider class of object deformations but does not assume unstructured input images, typically exploiting dense temporal information, and is restricted to orthographic cameras.", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Related Work", + "text_level": 1, + "bbox": [ + 498, + 162, + 640, + 179 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Depth and camera pose estimation from unstructured images of multi-body scenes is largely unexplored, and most SfM methods either consider static scenes only ( $\\mu = 1$ ) or treat moving objects as outliers. This section focuses on the few SfM methods that address the multi-body scenario ( $\\mu > 1$ ) from unstructured images acquired by perspective cameras. Also, we discuss monocular depth estimation, a component of our solution, and relevant deep multi-view static SfM methods.", + "bbox": [ + 496, + 188, + 890, + 323 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3.1. Multi-body Structure-from-Motion (MBSfM)", + "text_level": 1, + "bbox": [ + 498, + 332, + 883, + 348 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "A few works have addressed MBSfM from unstructured images $\\{\\mathbf{I}_i\\}_{i = 1}^n$ as a generalization of traditional SfM to multi-body scenes. We identify two main research directions. First, early factorization methods [32, 6] segment rigidly moving objects $\\mathcal{B}$ and perform sparse 3D reconstruction in a single step. However, factorization methods rely on restrictive assumptions on camera models and require complete feature tracks, which are seldom available in practice. Due to its lack of robustness, factorization has yet to see practical applications beyond short, unrealistic sequences.", + "bbox": [ + 496, + 354, + 890, + 506 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The second, more recent, research direction separates motion segmentation of objects $\\mathcal{B}$ and their 3D reconstruction. [1, 26] cluster sparse correspondences based on their rigid motion and then recover the 3D structure of each object independently using a SfM pipeline [27]. As discussed in [23, 24, 17], the relative scale problem affects these methods because each object is reconstructed in its own scale. In SLAM, the relative scale problem has been addressed under specific assumptions: [23] assumes objects move in a one-parameter family of motions, and [17] works only with video input and continuous object motion. Our method also decouples motion segmentation and reconstruction. However, we explicitly address the relative scale problem using a learning-based approach without further assumptions on the input images or the motions in the scene.", + "bbox": [ + 496, + 508, + 890, + 733 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3.2. Monocular Depth Estimation", + "text_level": 1, + "bbox": [ + 498, + 741, + 759, + 757 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Recent works [9, 2] recover a dense depth map $\\mathbf{D}_1$ from a single image $\\mathbf{I}_1$ . These methods learn priors to regress depth maps, allowing consistent scale reconstruction of moving objects $\\mathcal{B}$ without scale ambiguity. However, due to the ill-posed nature of monocular depth estimation, generalization is limited and multi-view approaches remain the benchmark for SfM in deep learning.", + "bbox": [ + 496, + 763, + 890, + 869 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In [20, 38], monocular depth maps are estimated from video frames, and then a network is fine-tuned on the entire", + "bbox": [ + 500, + 869, + 890, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "17805", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/99bf2b6261462b2a67043da592310cfbfa4df27273c256d5e0c2072f6070f454.jpg", + "image_caption": [ + "Figure 2: The three main steps of our method: i) motion segmentation: produces a set of essential matrices describing the rigid motion of objects between view pairs. ii) robust scale estimation: uses monocular depth cues to fix the scale ambiguity of each moving object. iii) multi-body plane-sweep network based on our novel multi-body plane-sweep regress refined depth maps and camera poses." + ], + "image_footnote": [], + "bbox": [ + 101, + 87, + 867, + 263 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "video sequence. These methods do not assume unstructured images and require many frames for depth and pose tracking and fine-tuning. In addition, depth estimation for moving objects still relies solely on depth priors, which can lead to inaccuracies as in standard monocular depth estimation.", + "bbox": [ + 75, + 335, + 470, + 412 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.3. Deep Learning for SfM", + "text_level": 1, + "bbox": [ + 76, + 424, + 292, + 440 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Deep learning methods for SfM from unstructured images regress camera poses and dense depth maps using multi-view stereo matching. DeMoN [33] works on image pairs using stacked encoder-decoder networks but lacks explicit multi-view constraints and has limited accuracy. More recent architectures [29, 4, 36, 34, 13, 31] replace the generic encoder-decoder architecture with layers that explicitly enforce multi-view constraints. Other works achieve better results by taking inspiration from traditional Bundle Adjustment: DeepSfM [36] introduces depth and pose cost volumes for iterative refinement, and [29] uses a BA-layer for regression from basis depth maps. Wang et al. [34] propose a scale-invariant network for depth and pose estimation for view pairs. Specifically, camera poses are estimated from essential matrices robustly fitted on fine-tuned optical flow matches, thus treating all moving objects as outliers. Then, depth maps are regressed end-to-end using a CNN similar to DeepSfM. Finally, [4] optimizes non-linear cost functions in SfM using recurring neural networks.", + "bbox": [ + 75, + 449, + 468, + 734 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As the above deep methods embed explicit multi-view geometric constraints in their optimization layers, they are affected by the scale ambiguity of traditional MBSfM and cannot generalize to multi-body scenes, as shown in Fig. 1.", + "bbox": [ + 75, + 737, + 468, + 797 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4. Method", + "text_level": 1, + "bbox": [ + 76, + 814, + 166, + 829 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our method, illustrated in Fig. 2, is structured in three steps. First, given the unstructured images $\\{\\mathbf{I}_i\\}_{i=1}^n$ , we perform motion segmentation from image pairs $\\alpha$ to estimate essential matrices $\\{\\mathbf{E}_k^\\alpha\\}_{j=1}^\\mu$ that encode the $\\mu$ rigid mo", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "tions in the scene. Second, we fix the scale ambiguity of each $\\mathbf{E}_k^\\alpha$ by exploiting cues provided by monocular depth maps $\\{\\mathbf{M}_i\\}_{i=1}^n$ in a robust scale estimation module. Finally, a multi-view depth and camera pose estimation network leverages our novel multi-body plane sweep algorithm to regress geometrically-consistent depth maps $\\{\\mathbf{D}_i\\}_{i=1}^n$ and camera poses $\\{\\mathbf{R}_i, \\mathbf{t}_i\\}_{i=1}^n$ by considering all the $\\mu$ motions.", + "bbox": [ + 496, + 335, + 890, + 444 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "4.1. Motion segmentation", + "text_level": 1, + "bbox": [ + 500, + 452, + 697, + 468 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The goal of motion segmentation is to recover the essential matrices $\\{\\mathbf{E}_k^\\alpha\\}_{k=1}^\\mu$ that encode all rigid motions in the scene in any image pair $\\alpha = (\\mathbf{I}_i, \\mathbf{I}_j)$ . To this end, we combine traditional sparse motion segmentation, based on SIFT [19], with dense deep optical flow matches.", + "bbox": [ + 496, + 476, + 890, + 551 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For each image $\\mathbf{I}_i$ , we extract $\\{x_{i,u}\\}_{u = 1}^{p_i}$ SIFT keypoints and match them across image pairs. Then, for each pair $\\alpha$ , we fit $\\mu$ essential matrices $\\{\\mathbf{E}_k^\\alpha J_{k = 1}^\\mu\\}$ to the matches using RPA [21], a multi-model fitting algorithm. RPA provides a labeling $\\ell^{\\alpha}$ that assigns a matched keypoint to the motion it belongs to. Labels assigned to different image pairs may be inconsistent, thus we use permutation synchronization [1] to enforce a global labelling $\\ell$ that assigns to keypoints belonging to the same motion the same label in all views.", + "bbox": [ + 496, + 551, + 890, + 686 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In multi-body scenes, moving objects can be supported by only a few keypoints. Therefore, to refine the essential matrices, we augment the set of sparse matches with dense ones computed from the optical flow. Similarly to [34], we consider the dense matches at keypoint locations and, thus, avoid the typical inaccuracies of the optical flow caused by illumination changes and texture-less regions. In particular, given an image pair $\\alpha = (\\mathbf{I}_i,\\mathbf{I}_j)$ , for each object $\\beta_{k}\\in \\mathcal{B}$ we consider $U_{k}^{i} = \\{x_{i,u}:\\ell (x_{i,u}) = k\\}$ the sparse keypoints in $\\mathbf{I}_i$ labelled as $k$ . Around each keypoint $x\\in U_k^i$ we consider a squared neighborhood $N(x)$ of $3\\times 3$ pixels. The union of neighborhoods $S_{k}^{i} = \\bigcup_{x\\in U_{k}^{i}}N(x)$ defines a mask in $\\mathbf{I}_i$ as illustrated in Fig. 2. We refine $\\mathbf{E}_k^\\alpha$ by RANSAC equipped with the 5-point algorithm [22, 18] on the set of all", + "bbox": [ + 496, + 688, + 892, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "17806", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/ca029ad142b03b154915006723fecf7efe28d4be8da23070a80a49d8e047fa47.jpg", + "image_caption": [ + "Figure 3: (left) In a multi-body scene, the scale of triangulated structures (orange) differs from the true object scale (cyan), leading to inconsistent relative object scales, i.e., cube bigger than pyramid. The tentative scale factor $\\lambda_{i,u}^{1}$ of $X_{u}^{1} \\in \\beta_{1}$ is the ratio of the monocular depth $m_{i,u}^{1}$ and its triangulated depth $d_{i,u}^{1}$ . (right) Traditional plane sweep [5] vs. our novel multi-body plane sweep." + ], + "image_footnote": [], + "bbox": [ + 81, + 90, + 321, + 253 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/6dc5dd46bef3093738ccaf81dcdef7bc2a36d9517f8070fe80f25268ba922cf9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 421, + 90, + 620, + 243 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/106bd788b20efe4c9aab564588b1343350ea1c550223c3768a24eff46ca0a387.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 643, + 90, + 875, + 244 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "the dense matches corresponding to the mask $S_{k}^{i}$ . The optical flow is computed using the DICL-Flow network [35].", + "bbox": [ + 75, + 324, + 468, + 356 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. Robust Scale Estimation", + "text_level": 1, + "bbox": [ + 76, + 362, + 302, + 376 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We factorize each essential matrix $\\mathbf{E}_k^\\alpha = [\\tilde{\\mathbf{t}}_k^\\alpha ]_\\times \\tilde{\\mathbf{R}}_k^\\alpha$ to obtain the relative camera pose as a rotation $\\tilde{\\mathbf{R}}_k^\\alpha$ and translation $\\tilde{\\mathbf{t}}_k^\\alpha$ . Since each $\\tilde{\\mathbf{t}}_k^\\alpha$ is recovered only up to an unknown scale-factor $\\lambda_{k}$ , each moving object in a multi-body scene is reconstructed in its own arbitrary scale $\\lambda_{k}$ . Specifically, given an image pair $\\alpha$ , we can triangulate from matched image points a set of 3D points $\\{X_u^k\\}_{u = 1}^{p_k}$ belonging to object $\\beta_{k}$ from the up-to-scale camera pose $\\{\\tilde{\\mathbf{R}}_k^\\alpha ,\\tilde{\\mathbf{t}}_k^\\alpha \\}$ . However, these 3D points are expressed in the scale $\\lambda_{k}$ of $\\tilde{\\mathbf{t}}_k^\\alpha$ , meaning that different objects refer to inconsistent scales. Fig. 3-left depicts a multi-body scene where the scale ambiguity manifests as an inconsistent relative scale between objects $\\lambda_{1}\\beta_{1}$ and $\\lambda_{2}\\beta_{2}$ in the triangulated scene (orange) w.r.t. the actual 3D scene (cyan). Thus, the cube $\\lambda_{1}\\beta_{1}$ appears larger than the pyramid $\\lambda_{2}\\beta_{2}$ in the reconstruction.", + "bbox": [ + 75, + 383, + 468, + 613 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We estimate the unknown scale factor $\\lambda_{k}$ for each object $\\beta_{k}$ by first regressing a monocular depth map $\\mathbf{M}_i$ from each image $\\mathbf{I}_i$ using AdaBins [2]. This network processes each $\\mathbf{I}_i$ individually and, thus, is not affected by the multi-view scale ambiguity. We denote by $d_{i,u}^{k}$ and by $m_{i,u}^{k}$ the triangulated and monocular depths respectively of the $u$ -th 3D point $X_{u}^{k}$ w.r.t. $\\mathbf{I}_i$ . Then, for each object $\\beta_{k}$ and image $\\mathbf{I}_i$ , we compute the point-wise scale factor $\\lambda_{i,u}^{k} = d_{i,u}^{k} / m_{i,u}^{k}$ that approximates the real $\\lambda_{k}$ according to the triangulated and monocular depths of $X_{u}^{k}$ .", + "bbox": [ + 75, + 614, + 468, + 765 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As monocular depth maps generally lack in accuracy, we devise a voting scheme to robustly aggregate the scale factors from all images $\\{\\mathbf{I}_i\\}_{i = 1}^n$ and unify all the $\\mu$ camera poses under a global scale factor $\\lambda$ . First, we partition the point-wise scale factors computed from all the images into $\\mu$ sets $\\Lambda_{k} = \\{\\lambda_{i,u}^{k}\\}_{i = 1,u = 1}^{n,p_{k}}$ according to their object $\\beta_{k}$ . Then, to promote robustness, we adopt a Kernel Density Estimator and derive a probability density function $\\phi_{k}$ from each $\\Lambda_{k}$ . We use a Gaussian Kernel $\\mathcal{K}$ with bandwidth $h$ set", + "bbox": [ + 75, + 765, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "at $5\\%$ of the median of the elements in $\\Lambda_{k}$ and define the kernel $\\phi_{k}$ as follows:", + "bbox": [ + 496, + 324, + 890, + 354 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\phi_ {k} (x) = \\sum_ {\\lambda_ {i, u} ^ {k} \\in \\Lambda_ {k}} \\frac {\\mathcal {K} \\left(\\lambda_ {i , u} ^ {k} - x\\right)}{h}. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 598, + 363, + 890, + 404 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The highest peak of $\\phi_{k}$ is denoted by $\\hat{\\lambda}_{k}$ and represents the estimate of the $k$ -th object scale factor $\\lambda_{k}$ . The estimated $\\{\\hat{\\lambda}_k\\}_{k = 1}^\\mu$ are used to scale the pairwise relative camera poses $[\\tilde{\\mathbf{R}}_k^\\alpha ,\\hat{\\lambda}_k^{-1}\\tilde{\\mathbf{t}}_k^\\alpha ]$ by multiplying the translation component. Now, camera poses are aligned to a global scale factor $\\lambda$ . As depths $\\mathbf{M}_i$ are regressed in real-world unit of measurement, $\\lambda \\approx 1$ , i.e., camera poses should be approximately in their real-world scale. We denote the correctly scaled camera poses as $[\\hat{\\mathbf{R}}_k^\\alpha ,\\hat{\\mathbf{t}}_k^\\alpha ]$ and use this unified camera configuration as the initialization for the next step.", + "bbox": [ + 496, + 415, + 892, + 570 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.3. Multi-body Plane Sweep Network", + "text_level": 1, + "bbox": [ + 498, + 579, + 795, + 595 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Although the poses $\\{\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha\\}$ are now aligned to a single scale factor, the depths are only estimated from monocular maps $\\mathbf{M}_i$ which ignore the multi-view constraints. In principle, it could be possible to use camera poses to initialize a multi-view iterative scheme where depths and poses are refined, as in [36], but this would regress inconsistent depths in regions corresponding to moving objects. Thus, we design a novel multi-body depth and pose estimation network that takes the unordered images $\\{\\mathbf{I}_i\\}_{i=1}^n$ and the scale-consistent poses $\\{\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha\\}$ to jointly estimates geometrically consistent depth maps $\\{\\mathbf{D}_i\\}_{i=1}^n$ and refined poses $\\{\\mathbf{R}_i, \\mathbf{t}_i\\}_{i=1}^n$ in the reference frame of object $\\beta_1$ . As shown in Fig. 4, we include two separate branches for depth and pose estimation, which are used alternatively in an iterative scheme using the output of the other branch as input.", + "bbox": [ + 496, + 601, + 890, + 829 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.3.1. Multi-body Depth Estimation Branch", + "text_level": 1, + "bbox": [ + 498, + 835, + 807, + 851 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As depicted in Fig. 4, our depth estimation branch is based on our novel multi-body plane sweep and concatenates the following modules.", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "17807", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/f952cf292e0706cb42a8a330f4798125d97621971a2e9637d9a94fbc23a77049.jpg", + "image_caption": [ + "Figure 4: Multi-body Plane Sweep network. We extract CNN features from input images and build a cost volume using our multi-body plane sweep algorithm. Depth and camera poses are regressed from separate cost volumes with a series of 3D CNN and refinement layers." + ], + "image_footnote": [], + "bbox": [ + 125, + 88, + 851, + 267 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Feature Extraction. A multi-scale CNN with spatial pyramid pooling [12] extracts features $\\{\\mathbf{F}_i\\}_{i=1}^n$ from images $\\{\\mathbf{I}_i\\}_{i=1}^n$ . Each $\\mathbf{F}_i$ has dimension $\\mathbf{C} \\times \\mathbf{W} \\times \\mathbf{H}$ , where $\\mathbf{C}$ , $\\mathbf{W}$ , $\\mathbf{H}$ are feature channels, width and height respectively.", + "bbox": [ + 76, + 325, + 470, + 388 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Multi-body Plane Sweep for Cost Volume Construction. Let us briefly recall how the traditional plane sweep works before describing our contributions. The traditional plane sweep algorithm [5] takes as input an image pair $\\alpha$ of a source $\\mathbf{I}_i$ and target $\\mathbf{I}_j$ and their relative pose $[\\mathbf{R}^\\alpha, \\mathbf{t}^\\alpha]$ . The algorithm samples a set of virtual planes parallel to $\\mathbf{I}_j$ at fixed depths $\\{d_l\\}_{l=1}^L$ . Then, for each depth $d_l$ , the source $\\mathbf{I}_i$ is warped onto the target $\\mathbf{I}_j$ through the homography induced by the plane at $d_l$ and the relative camera pose $[\\mathbf{R}^\\alpha, \\mathbf{t}^\\alpha]$ , as in Fig. 3-right. A dense depth map is obtained by selecting, for each pixel, the depth $d_l$ that minimizes a pixel-wise photometric dissimilarity between the target $\\mathbf{I}_j$ and the warped source $\\mathbf{I}_i$ . Deep methods [13, 36, 34] revisited this framework, but measure feature metric consistency between latent features $\\{\\mathbf{F}_i\\}_{i=1}^n$ instead of photometric dissimilarity. To this end, warped source and target features are aggregated in a single depth cost volume from which depths are regressed through convolutional layers. Unfortunately, both traditional and deep plane sweep methods assume static scenes with a single relative camera pose $[\\mathbf{R}^\\alpha, \\mathbf{t}^\\alpha]$ between the pair $\\alpha$ . As a result, any point belonging to a moving object has an inconsistent depth.", + "bbox": [ + 75, + 398, + 468, + 731 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We propose instead a multi-body plane sweep that considers all the $\\mu$ relative poses $\\{\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha\\}_{k=1}^\\mu$ to warp a source feature $\\mathbf{F}_i$ onto a target $\\mathbf{F}_j$ and construct the depth cost volume. Given a source-target pair $\\alpha = (\\mathbf{I}_i, \\mathbf{I}_j)$ , we uniformly sample $L$ 3D virtual planes at depths $\\{d_l\\}_{l=1}^L$ parallel to the source $\\mathbf{I}_i$ . Then, we sequentially assign each depth plane to one of the $\\mu$ relative camera poses by cycling through the $\\{\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha\\}_{k=1}^\\mu$ . Thus, the individual features $\\mathbf{F}_i$ of the object $\\beta_k$ are warped onto $\\mathbf{F}_j$ in a geometrically consistent manner when considering any depth plane assigned to the camera pose $[\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha]$ relative to $\\beta_k$ . This is depicted in", + "bbox": [ + 75, + 734, + 470, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Fig. 3-right, utilizing color to illustrate the cyclic assignment of the $k$ -th and $h$ -th rigid motions to planes at $d_{l}$ and $d_{l+1}$ , respectively, and to subsequent planes. Finally, each point $u$ in the source feature $\\mathbf{F}_{i}$ is first back-projected onto the virtual planes at $d_{l}$ and then re-projected as $\\tilde{u}_{lk}$ on the target $\\mathbf{F}_{j}$ as follows:", + "bbox": [ + 496, + 325, + 893, + 417 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {\\mathbf {F}} _ {i l} ^ {k} (u) = \\mathbf {F} _ {i} (\\tilde {u} _ {l k}), \\tilde {u} _ {l k} \\sim \\mathbf {K} \\left[ \\hat {\\mathbf {R}} _ {k} ^ {\\alpha} | \\hat {\\mathbf {t}} _ {k} ^ {\\alpha} \\right] \\left[ \\begin{array}{c} (\\mathbf {K} ^ {- 1} u) d _ {l} \\\\ 1 \\end{array} \\right], \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 522, + 426, + 890, + 458 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\tilde{\\mathbf{F}}_{il}^{k}$ is the warped source feature through the homography induced by the plane at $d_{l}$ and the motion $[\\hat{\\mathbf{R}}_k^\\alpha ,\\hat{\\mathbf{t}}_k^\\alpha ]$", + "bbox": [ + 496, + 465, + 890, + 501 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Cost volume Construction. Given the set of virtual depth planes $\\{d_l\\}_{l = 1}^L$ , for each $d_{l}$ , we obtain a warped source feature $\\tilde{\\mathbf{F}}_{il}^{k}$ using Eq. 2 and concatenate it to the target feature $\\mathbf{F}_j$ . This yields a set of $L$ feature blocks, each sized $2\\mathrm{C} \\times \\mathrm{W} \\times \\mathrm{H}$ , that we arrange into a 4D depth cost volume sized $2\\mathrm{C} \\times L \\times \\mathrm{W} \\times \\mathrm{H}$ , as illustrated in Fig. 5. Since the number of virtual planes is significantly higher than the number of motions, all the $\\mu$ motions are assigned to some virtual planes. Thus, our cost volume jointly incorporates all the motions in the scene, unlike traditional plane-sweep methods that assume a single motion.", + "bbox": [ + 496, + 503, + 892, + 671 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Cost volume Regularization. Regularizing the cost volume is fundamental to cope with imperfect latent feature matching, which is especially common in image regions corresponding to texture-less objects or uniform pixel intensity. To this end, we use a sequence of 3D convolutional layers consisting of $L / 2$ filters of size $3\\times 3\\times 3$ with stride 1, and residual connections. Then, we apply a 3D convolution with a single $3\\times 3\\times 3$ filter to obtain a 3D cost volume of size $L\\times \\mathrm{W}\\times \\mathrm{H}$ . Since the order of the stacked features in the cost volume follows the correct virtual plane sequence, 3D convolutional layers can capture the 3D dependencies in the scene to enable consistent depth map estimation. Finally, we apply edge-preserving filtering to the resulting cost volume as in [13, 11]. In the case of multiple source-target image pairs, the final 3D cost volume is obtained by aver", + "bbox": [ + 496, + 674, + 893, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "17808", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "aging the 3D cost volumes from each pair. Further details on the cost volume can be found in the supplementary.", + "bbox": [ + 75, + 90, + 468, + 121 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Depth Regression. We denote as $c_{l}$ each slice of the aggregated cost volume, which corresponds to a plane at $d_{l}$ . Then, we convert the aggregated cost volume to a probability volume as in [15] and use the softmax operation $\\sigma$ to normalize the probability volume across the depth dimension. We estimate the depth map $\\mathbf{D}_i$ for a view $\\mathbf{I}_i$ as follows:", + "bbox": [ + 75, + 125, + 467, + 214 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {D} _ {i} = \\frac {L \\times d _ {\\operatorname* {m i n}}}{\\tilde {l}}, \\tilde {l} = \\sum_ {l = 1} ^ {L} l \\times \\sigma \\left(c _ {l}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 160, + 222, + 468, + 258 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\tilde{l}$ is the map corresponding to the average of virtual plane depths $l\\in \\{1,\\dots ,L\\}$ , weighted by the probabilities $\\sigma (c_l)$ . In (3), $d_{\\mathrm{min}}$ denotes the depth of the closest plane to the source image.", + "bbox": [ + 75, + 267, + 468, + 330 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3.2. Pose Estimation Branch", + "text_level": 1, + "bbox": [ + 76, + 335, + 290, + 348 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We describe our pose estimation branch, which optimizes current camera pose estimates through feature-metric consistency. To this purpose, we use a network architecture akin to the one in [36]. The network receives a pair $\\alpha = (\\mathbf{I}_i,\\mathbf{I}_j)$ , the depth map $\\mathbf{D}_i$ of $\\mathbf{I}_i$ and $[\\hat{\\mathbf{R}}_1^\\alpha ,\\hat{\\mathbf{t}}_1^\\alpha ]$ , the current camera pose estimate in the reference frame of $\\beta_{1}$ , to regress a refined $[\\mathbf{R}_1^\\alpha ,\\mathbf{t}_1^\\alpha ]$ . We uniformly sample $P$ tentative camera poses $\\{\\hat{\\mathbf{R}}_{1p}^{\\alpha},\\hat{\\mathbf{t}}_{1p}^{\\alpha}\\}_{p = 1}^{P}$ by perturbing the rotation and the translation of the initial poses $[\\hat{\\mathbf{R}}_1^\\alpha ,\\hat{\\mathbf{t}}_1^\\alpha ]$ . The $P$ poses are used to construct a pose cost volume by warping each point $u$ in the source feature $\\mathbf{F}_i$ to a point $\\tilde{u}_p$ on the target feature $\\mathbf{F}_j$ as follows:", + "bbox": [ + 75, + 353, + 468, + 537 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {u} _ {p} \\sim \\mathbf {K} \\left[ \\hat {\\mathbf {R}} _ {1 p} ^ {\\alpha} \\mid \\hat {\\mathbf {t}} _ {1 p} ^ {\\alpha} \\right] \\left[ \\begin{array}{c} \\left(\\mathbf {K} ^ {- 1} u\\right) \\mathbf {D} _ {i} (u) \\\\ 1 \\end{array} \\right]. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 547, + 468, + 578 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Finally, a sequence of 3D convolutional layers is applied to the pose cost volume to regress the camera pose $\\left[\\mathbf{R}_1^\\alpha ,\\mathbf{t}_1^\\alpha \\right]$ .", + "bbox": [ + 75, + 580, + 468, + 612 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/65f30614b2fa0778b2be90f2efe26ad89de0e65d696cd261a377683944aa6a02.jpg", + "image_caption": [ + "Figure 5: Cost volume construction by multi-body plane sweep. For each virtual depth plane at $d_{l} \\in \\{d_{l}\\}_{l=1}^{L}$ , we generate a $2\\mathbf{C} \\times \\mathbf{W} \\times \\mathbf{H}$ feature map by concatenating the target feature $\\mathbf{F}_j$ (gray) to the warped source feature $\\tilde{\\mathbf{F}}_{il}^{\\gamma}$ (in color) at depth $d_{l}$ using motion $[\\hat{\\mathbf{R}}_{\\gamma}^{\\alpha}, \\hat{\\mathbf{t}}_{\\gamma}^{\\alpha}]$ . The 4D cost volume is constructed through concatenation of these $L$ feature blocks. $\\tilde{\\mathbf{F}}_{il}^{k}$ (in blue) indicates a source feature $\\mathbf{F}_i$ warped onto $\\mathbf{F}_j$ through the homography induced by the generic plane at $d_{l}$ and its relative camera motion $[\\hat{\\mathbf{R}}_k^{\\alpha}, \\hat{\\mathbf{t}}_k^{\\alpha}]$ . Instead, $\\tilde{\\mathbf{F}}_{il}^{h}$ is induced by the motion $[\\hat{\\mathbf{R}}_h^{\\alpha}, \\hat{\\mathbf{t}}_h^{\\alpha}]$ (in pink)." + ], + "image_footnote": [], + "bbox": [ + 84, + 630, + 468, + 765 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/e2f80f44f669b12f8eda5b9d9990dbc457ee582660f683058f4d51dbe8f74b3f.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
viewMethodlower is better ↓higher is better ↑
Abs RelSq RelRMSERMSElogδ1δ2δ3
Eigen SM (s)svDORN [9]0.0670.2952.9290.1080.9490.9880.995
AdaBins [2]0.0540.1822.3410.0870.9660.9950.999
mvDeepV2D [31]0.0500.2122.4830.0890.9730.9920.997
Wang et al. [34]0.0340.1031.9190.0570.9890.9980.999
Ours0.0440.1482.1250.0680.9740.9960.999
Eigen (s & m)svDORN [9]0.0720.3072.7270.1200.9320.9840.994
AdaBins [2]0.0580.1902.3600.0880.9640.9950.999
mvSfMLearner [39]0.2081.7686.8560.2830.6780.8850.975
CCNet [25]0.1401.0705.3260.2170.8260.9410.975
BANet [29]0.083-3.6400.134---
DeepV2D [31]0.0640.3502.9460.1200.9460.9820.991
Wang et al. [34]0.0550.2242.2730.0910.9560.9840.993
Ours0.0540.1862.2690.0860.9660.9910.996
Eigen MB (m)svDORN [9]0.0720.3072.7270.1200.9320.9840.994
AdaBins [2]0.0620.2012.3720.0920.9590.9940.999
mvDeepV2D [31]0.0890.4013.2780.1520.9310.9650.989
Wang et al. [34]0.0630.2422.3470.1090.9480.9710.991
Ours0.0570.1972.3010.0900.9620.9910.994
", + "bbox": [ + 501, + 89, + 906, + 308 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1: Depth evaluation on KITTI Depth. Results from single-view (sv) and multi-view (mv) depth estimation methods evaluated under two-view SfM setting. Best results in bold.", + "bbox": [ + 498, + 320, + 890, + 362 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3.3. Training and Inference", + "text_level": 1, + "bbox": [ + 500, + 387, + 707, + 402 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We train the feature extractor, 3D convolutions and regression layers in a end-to-end supervised manner. We denote as $\\mathbf{D}$ the depth regressed from the refined cost volume, and as $\\mathbf{D}_{\\mathrm{gt}}$ the ground-truth depth. To improve the learning process, we also regress a depth map $\\tilde{\\mathbf{D}}$ from the cost volume before applying edge-preserving filtering. The loss function is defined as $\\mathcal{L}_{\\mathrm{depth}} = \\sum_{i}\\lambda H(\\tilde{\\mathbf{D}},\\mathbf{D}_{\\mathrm{gt}}) + H(\\mathbf{D},\\mathbf{D}_{\\mathrm{gt}})$ , where $\\lambda = 0.7$ is a weight and $H(\\cdot)$ is the Huber loss. The pose losses $\\mathcal{L}_{\\mathrm{rot}}$ and $\\mathcal{L}_{\\mathrm{trans}}$ are defined as the $\\ell_1$ distance between the predicted and ground-truth absolute poses. Our final loss is then: $\\mathcal{L} = \\lambda_r\\mathcal{L}_{\\mathrm{rot}} + \\lambda_t\\mathcal{L}_{\\mathrm{trans}} + \\lambda_d\\mathcal{L}_{\\mathrm{depth}}$ . All the weights are specified in the supplementary.", + "bbox": [ + 496, + 405, + 890, + 588 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The multi-body plane sweep component of the network has no learnable parameters and is not trained. Our network does not require any form of motion annotation for depth estimation, even in multi-body scenes. For this reason, we train our model on static frames from KITTI [10] and DeMoN [33]. The training and inference are performed in an iterative fashion in four steps, where the regressed depth maps and camera poses are fed to the next iteration.", + "bbox": [ + 496, + 588, + 890, + 709 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 500, + 722, + 632, + 739 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We evaluate our method on static (s) and multi-body (m) datasets for depth and pose estimation against state-of-the-art single-view (sv) and multi-view (mv) methods. In Sec. 5.4 we discuss the limitations of our method and possible countermeasures. Additional experiments and implementation details are provided in the supplementary.", + "bbox": [ + 496, + 747, + 890, + 839 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Datasets, Competitors and Metrics", + "text_level": 1, + "bbox": [ + 500, + 847, + 802, + 863 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "KITTI Depth (s & m) [10] is designed for depth evaluation in autonomous driving and contains several image se", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "17809", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/d8cd6d34c49eb9fafc251a11fe0b23a7b2b2bebeb556df11a195544de7d52502.jpg", + "image_caption": [ + "Figure 6: Multi-body Unstructured Extract. Three view pairs extracted from our proposed dataset for illustration purposes. The dataset contains indoor sequences that depict varied scenarios in which objects of several different sizes move in the scene." + ], + "image_footnote": [], + "bbox": [ + 78, + 88, + 349, + 167 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/15dd3fed94c621f86d5edc96b54f2ae56a90b0af432dccd333f4ab0f910360ac.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 351, + 88, + 620, + 167 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/f635c5d702c084bed50b68d42556fe612894ee4ec25e12405ddf67a7019e65e8.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 622, + 89, + 890, + 167 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/c23b553048674c26ee2805b5da63058f84bee8cb172dee2045db9a59210f023f.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodMVSScenes11SUN3D
DepthPoseDepthPoseDepthPose
L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)
AdaBins [2]0.0480.2360.291--0.0200.3820.270--0.0210.1270.161--
DeMoN [33]0.0470.2020.3055.15614.4470.0190.3150.2480.8098.9180.0190.1140.1721.80118.811
LS-Net [4]0.0510.2210.3114.65311.1220.0100.4100.2104.6538.2100.0150.1890.6501.52114.347
BA-Net [29]0.0300.1500.0803.49911.2380.0800.2100.1303.49910.3700.0150.1100.0601.72913.260
DeepSfM [36]0.0210.1290.0792.8249.8810.0070.1120.0640.4035.8280.0130.0930.0721.70413.107
Wang et al. [34]0.0150.1020.0682.4173.8780.0050.0970.0580.2762.0410.0100.0810.0571.39110.757
Ours (M=1)0.0160.1070.0682.5384.5380.0050.0990.0580.3213.6490.0110.0840.0611.47012.018
Ours (M=2)0.0190.1210.0732.6817.3400.0070.1020.0690.4014.6190.0130.0920.0711.62513.402
Ours (M=3)0.0250.1320.0752.8929.5300.0090.1240.0780.5425.7820.0140.0950.0791.76915.231
Ours (M=4)0.0260.1340.0762.9319.7410.0090.1280.0810.5715.8030.0160.1070.0841.83015.904
", + "bbox": [ + 78, + 213, + 890, + 397 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2: Depth and pose evaluation on MVS, Scenes 11, SUN3D. (s). For all metrics lower is better. Best results are in bold.", + "bbox": [ + 106, + 398, + 859, + 414 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "quences where objects move rigidly. We consider the Eigen [7] split (697 frames) and the Eigen SfM split [34] (256 frames), a subset of the Eigen split without moving objects. In addition, we introduce the Eigen MB split, a subset of the Eigen split that includes 90 frames in which dynamic objects appear and camera motions are well-conditioned.", + "bbox": [ + 75, + 428, + 468, + 518 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "MVS, Scenes11, SUN3D. (s) MVS [33] includes outdoor sequences with large baselines. Scenes11 [33] contains fairly realistic frames from rendered scenes with accurate ground truth depth and camera poses. SUN3D [37] is an indoor dataset with sometimes inaccurate ground truth depth and camera poses. For SUN3D, we consider the split by [33] to exclude frames with high photoconsistency errors.", + "bbox": [ + 75, + 518, + 468, + 625 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ETH3D SLAM. (m) [28] contains SLAM sequences with ground truth depth and camera poses. We consider the dynamic sequences motion1-2-3-4 and, specifically, a 32 frames split where camera motions are well-conditioned.", + "bbox": [ + 75, + 625, + 468, + 684 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Multi-body Unstructured. (m) We capture multi-body indoor sequences using a Kinect with ground truth depth. The dataset is meant for evaluation in varied conditions, for instance, when image sets are unstructured or when both large and big objects move in the scene. We use RGB-D SLAM [8] to fuse visual information and data from the Kinect IMU and annotate accurate camera poses. The dataset includes 42 frames with either one or two moving objects. Samples scenes are reported in Fig.6 and additional details are provided in the supplementary.", + "bbox": [ + 75, + 685, + 468, + 837 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Competitors. We compare against state-of-the-art single-view methods (sv) DORN [9] and AdaBins [2], and multiview methods (mv) DeMoN [33], LS-Net [3], CCNet [25], BANet [29], DeepV2D [31] and Wang et al. [34]. De", + "bbox": [ + 75, + 839, + 468, + 901 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "MoN estimates depth and poses from image pairs, CCNet and SfMLearner mask moving objects before depth and pose estimation, LS-Net, BANet and DeepV2D optimize multi-view differentiable cost functions to minimize photo- or feature-metric errors, and Wang et al. [34] proposes a deep, scale-invariant estimator for depth and camera poses that robustly identify the dominant background motion $\\beta_{1}$ .", + "bbox": [ + 496, + 428, + 890, + 535 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Metrics. To evaluate the quality of depth maps in KITTI Depth, we adopt the metrics in [7], i.e., the depth absolute (Abs Rel) and squared (Sq Rel) relative difference, the RMSE, the $\\mathrm{RMSE}_{\\log}$ , and the thresholds $\\{\\delta_i\\}_{i=1}^3$ . For other datasets, we adopt the metrics in [33], i.e., scale-invariant depth error (sc-inv), relative error to ground truth depth (L1-rel), relative error w.r.t. inverse depth (L1-inv). The definitions of these metrics are in the supplementary. As for pose estimation, we report the angle (in deg) between predicted and ground truth translations $(t_{\\mathrm{err}})$ and rotations $(\\mathbf{R}_{\\mathrm{err}})$ of the cameras with respect to the background motions $\\beta_1$ .", + "bbox": [ + 496, + 542, + 892, + 710 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Implementation Details. We fine-tune the optical flow network on KITTI Depth for a fair comparison to [34]. Otherwise, we train the optical flow on synthetic scenes, as in [35], and let the proposed framework refine initial camera poses. We implement our framework using PyTorch. The batch size is set to 32. The learning rate is set to $1 \\times 10^{-4}$ and is halved after 2 epochs. For KITTI Depth, the feature extractor is initialized with pre-trained weights, which are frozen for the first epoch. For other datasets, we train the network from randomly initialized weights. Training takes approximately 3 days on 2 NVIDIA RTX A6000 GPUs. Further details are reported in the supplementary.", + "bbox": [ + 496, + 719, + 893, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "17810", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/5b55cf973b5a54e27f4878659743b79cbaf37ba986258ab76f727a0ec9053706.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 163, + 88, + 338, + 179 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/295af6aa0eac1fafa1c55dfee975d4907e0d360ee0b07f7cadeb3c3a7a22e19c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 163, + 179, + 338, + 270 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f579030b41183ce8742c01f5d1bfd105521fcda654419ae3858644f85bd03e5b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 163, + 270, + 338, + 361 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1cdf7dbbc8bce09b72a0cd0e2919433667dd4e1f5ebad9bc9ec3edd6dfd7a748.jpg", + "image_caption": [ + "Reference images" + ], + "image_footnote": [], + "bbox": [ + 161, + 361, + 338, + 450 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/db469caba8d10e2a8891200250dd6905ac8fb87fbcc325bd1873ccd3ba6d3650.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 341, + 88, + 495, + 176 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/bb624a27c1be6acdec16cd6dd82b81f1bcaea31c5e80badaf2014716d5b49028.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 341, + 179, + 495, + 270 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/129cd53d864530fa9dc2cd6605235c1a094a1f7ca910238ef6204c93984af434.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 341, + 270, + 495, + 361 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2228f801dbbacd056be4165bc86f27a3a6372c66123a33e44eacd7fdffa5aea2.jpg", + "image_caption": [ + "Ground-truth" + ], + "image_footnote": [], + "bbox": [ + 341, + 361, + 495, + 450 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e6292db839f03c75756a353fd21a743044ead249761f4e8a77b871b7105ae283.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 501, + 89, + 653, + 179 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/90520681561b5094d7b1c1af521575e9acf271d721d3232ac3c1884df01e97b9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 501, + 179, + 653, + 270 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/90b5decd8276bcb2c99ca25e835a493a13ab1504fbcdc52a980822c6a604bae2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 501, + 270, + 653, + 361 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c208eab3af923fd46ec93a827391877fe798cfb203e1d4ee068f7943ef4cf0e9.jpg", + "image_caption": [ + "DeepSfM", + "Figure 7: Qualitative comparisons on ETH3D and Multi-body Unstructured. (m) The yellow boxes highlight moving objects reconstructed by our method but not by DeepSfM [36]." + ], + "image_footnote": [], + "bbox": [ + 501, + 361, + 653, + 450 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f9f856427c97101989ee11d5c48c05d6bbc1ab080f8e80a76d0f14190f6e4ab3.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 656, + 89, + 810, + 179 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2e4e42a3baf8172b8884d487d06a9621ea154db84317e7ff6ad19ce601310aad.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 656, + 179, + 810, + 270 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3fa7e07828de964815fcad1237a36db4db8fb5f641710969b833420156e2ac34.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 656, + 270, + 810, + 361 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2df2c4d5e497a34186dfff6a4946b639aa9902f5e83c397bea0588a44efbc3e4.jpg", + "image_caption": [ + "Ours" + ], + "image_footnote": [], + "bbox": [ + 656, + 361, + 810, + 450 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.2. Static evaluation (s)", + "text_level": 1, + "bbox": [ + 76, + 527, + 266, + 542 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "KITTI Depth. The Eigen SfM block of Tab. 1 reports quantitative results for static depth estimation. Our method beats the single-view methods [9, 2] and also the multi-view DeepV2D [31] in all metrics and with a clear margin. Yet Wang et al. [34] achieves better performance on this static scenes, although it recovers only up-to-scale depth maps.", + "bbox": [ + 75, + 551, + 468, + 643 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "MVS, Scenes11, SUN3D. Quantitative results are shown in Tab. 2. Our method beats the single-view [9, 2] and multiview [33, 4, 29] in most metrics, but achieves results that are on par or slightly worse compared to DeepSfM [36], since we rely on monocular depth cues that are less accurate than the DeMoN depths used in DeepSfM. The best results are achieved by [34]. In the supplementary, we show that our method beats geometric SfM baselines. By setting $M = 1$ and leveraging the static scene assumption, we outperform [36] and are similar to [34]. However, when the scene is static and $M \\geq 2$ motions are considered, our method produces outlying essential matrices that may negatively impact depth estimation. Nonetheless, we achieve good results for $M \\geq 2$ and even outperform [36] in the multi-body configuration $M = 2$ . For $M \\geq 2$ , the performance drop is limited, indicating that $M$ can be larger without affecting depth accuracy substantially.", + "bbox": [ + 75, + 643, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.3. Multi-body evaluation (m)", + "text_level": 1, + "bbox": [ + 500, + 527, + 732, + 544 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "KITTI Depth. The Eigen MB and Eigen blocks of Tab. 1 report quantitative results for depth estimation in the multi-body setting. As opposed to the static case, our method beats its multi-view competitors in both the considered splits. Specifically, we observe the most significant margin in the Eigen MB split, in which dynamic objects negatively affect the quality of static multi-view depth estimators [30, 34]. This is evident in the highlighted portion of Fig. 8, where our method accurately reconstructs the moving vehicle, whereas the state-of-the-art Wang et al. [34] exhibits significant artifacts. As in the static evaluation, our framework beats monocular approaches [2, 9] in most metrics, showing it effectively leverage multi-view constraints for improved depth estimation accuracy. Less strict thresholds $\\delta_{2}$ , $\\delta_{3}$ generally see better results for single-view methods compared to multi-view due to better handling of occlusions and image regions with uniform pixel intensity. However, monocular methods perform worse on the most strict threshold $\\delta_{1}$ and the other accuracy-oriented metrics.", + "bbox": [ + 496, + 551, + 892, + 839 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "ETH3D and Multi-Body Unstructured. Results on these multi-body datasets are reported in Tab. 3. Our method produces more accurate depth and camera pose estimates than its competitors in all metrics. Specifically, our method out", + "bbox": [ + 496, + 839, + 893, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "17811", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f7440bd1a5b7b51da9d3b215bfac406556f97d4169fa0001faa916090a072787.jpg", + "image_caption": [ + "Figure 8: Qualitative results on KITTI (m). The yellow box highlights a moving vehicle that is captured more accurately by our method." + ], + "image_footnote": [], + "bbox": [ + 78, + 89, + 893, + 154 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/6b7d761a7ab5e744807c5d65f7841137aae04a17b24aab577ceded8818e5a442.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodETH3DMulti-body Unstructured
DepthPoseDepthPose
L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)
DeMoN[33]0.380.410.335.6312.040.520.710.414.909.26
AdaBins[2]0.350.390.27--0.480.630.38--
DeepSIM[36]0.120.140.102.809.640.220.220.182.385.03
Wang et al.[34]0.210.190.173.269.040.270.220.192.797.67
Ours (M=1)0.110.140.102.989.580.210.220.182.215.01
Ours (M=2)0.090.120.082.918.530.190.200.171.994.91
Ours (M=3)0.080.110.082.948.280.170.190.161.944.72
Ours (M=4)0.090.110.092.948.230.170.200.171.944.70
", + "bbox": [ + 78, + 176, + 467, + 292 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Table 3: Depth and pose evaluation on multi-body datasets (m). For all metrics, lower is better. Best results are in bold.", + "bbox": [ + 76, + 295, + 467, + 321 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "performs DeMoN [33] by a significant margin and, when compared to DeepSfM [36], attains better results in depth estimation in both datasets. This is shown by the qualitative results of Fig. 7, where depth maps from DeepSfM exhibit noticeable break-ups in the areas corresponding to the moving objects. Our pose estimation is also more accurate, except for the $\\mathbf{R}_{\\mathrm{err}}$ over the ETH3D dataset [28]. Overall, we attribute this difference to: i) DeepSfM suffers from poor initialization from DeMoN, which is not accurate in multi-body scenes and hinders the overall quality of the reconstruction, ii) the plane sweep algorithm adopted by DeepSfM constructs cost volumes that do not satisfy the geometric constraints for the moving objects. Our method also beats Wang et al. [34] in all metrics by a clear margin. As expected, the performance of Wang et al. suffers significantly in multi-body scenes. The moving objects are treated as outliers and negatively impact the accuracy of the estimated camera poses, which, in turn, undermine the quality of depth estimation. By segmenting the rigid motions in the scene before computing camera poses, our method exploits and is robust to the moving objects and achieves state-of-the-art performance in multi-body depth estimation. The effectiveness of multi-body plane sweep (PS) is evidenced by the uplift in performance for $M \\geq 2$ in Tab. 3. Note that for $M = 1$ , a single motion is considered and MBPS specializes to traditional PS, with similar results to [36].", + "bbox": [ + 76, + 330, + 468, + 724 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5.4. Discussion and Limitations", + "text_level": 1, + "bbox": [ + 76, + 733, + 320, + 748 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Our method inherits some known limitations of the multi-view approaches. In this section we discuss their possible mitigations.", + "bbox": [ + 76, + 756, + 468, + 801 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Small camera motions may hinder initial pose estimates. Our pose refinement network mitigates poor initializations, but it may not recover in particularly challenging cases.", + "bbox": [ + 76, + 806, + 467, + 851 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Occlusions are mitigated, as in [13, 36], by aggregating cost volumes from multiple image pairs, if available. However, with only two images, occlusions result in noisy depth maps", + "bbox": [ + 76, + 854, + 468, + 900 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "in the region of the occluded objects, as seen in the second sequence of Fig. 7.", + "bbox": [ + 498, + 179, + 890, + 209 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Monocular depth inaccuracies may hinder the estimation of object scale factors. However, we observed our KDE voting scheme can isolate outlying measurements and return accurate results when enough ( $\\sim 10$ ) factors are computed.", + "bbox": [ + 498, + 218, + 890, + 279 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Non-rigid scenes. Our method is not designed for non-rigid scenes, for which different assumptions are used, e.g. temporal coherence or complete reliance on monocular depth for moving objects. Nevertheless, as shown in the supplementary, our method can reconstruct articulated motions, provided that a sufficient number of motions is considered.", + "bbox": [ + 498, + 287, + 890, + 377 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Virtual depth planes. Our multi-body plane sweep assigns $L / M$ depth planes to each motion, meaning that the more motions considered, the fewer depth planes are assigned to each motion. As stated in the supplementary, we consider up to four motions in our evaluation, as increasing the number of depth planes worsens training and inference times.", + "bbox": [ + 498, + 386, + 890, + 477 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Inference times are on average $\\sim 20\\%$ higher in KITTI Depth with respect to [34] due to the required motion segmentation step, as discussed in the supplementary.", + "bbox": [ + 498, + 486, + 890, + 532 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 553, + 617, + 568 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this paper, we have addressed the problem of multi-body depth and camera pose estimation. We overcome the scale-ambiguity problem typical of all the MBSfM approaches by introducing a learning-based robust voting scheme to unify the scales of all independently moving objects in the scene. In addition, we overcome the static-scene assumption of deep SfM approaches thanks to a novel multi-body plane sweep network that explicitly supports the additional multi-view geometric constraints derived from the multiple bodies. Extensive experiments on multi-body datasets show that our method outperforms state-of-the-art deep learning methods qualitatively and quantitatively.", + "bbox": [ + 496, + 580, + 890, + 763 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements. This paper is supported by FAIR (Future Artificial Intelligence Research) project, funded by the NextGenerationEU program within the PNRR-PE-AI scheme (M4C2, Investment 1.3, Line on Artificial Intelligence). We also gratefully acknowledge NVIDIA Corporation for the GPUs donated within the Academic and Applied Research Program to Giacomo Boracchi and Luca Magri", + "bbox": [ + 496, + 794, + 890, + 900 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "17812", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Federica Arrigoni, Elisa Ricci, and Tomas Pajdla. Multi-frame motion segmentation by combining two-frame results. International Journal of Computer Vision, 130(3):696-728, 2022. 1, 2, 3", + "[2] Shariq Farooq Bhat, Ibrahim Alhashim, and Peter Wonka. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 1851-1858, 2017. 6" + ], + "bbox": [ + 78, + 90, + 468, + 726 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "17814", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multi-body Depth and Camera Pose Estimation from Multiple Views/92fd5224-0cb4-4518-837c-e6d30b98ac63_model.json b/2023/Multi-body Depth and Camera Pose Estimation from Multiple Views/92fd5224-0cb4-4518-837c-e6d30b98ac63_model.json new file mode 100644 index 0000000000000000000000000000000000000000..e2be4e7624af1c2c11a0dbe1ffa85e3831c93384 --- /dev/null +++ b/2023/Multi-body Depth and Camera Pose Estimation from Multiple Views/92fd5224-0cb4-4518-837c-e6d30b98ac63_model.json @@ -0,0 +1,2400 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.138, + 0.131, + 0.834, + 0.154 + ], + "angle": 0, + "content": "Multi-body Depth and Camera Pose Estimation from Multiple Views" + }, + { + "type": "text", + "bbox": [ + 0.15, + 0.182, + 0.334, + 0.216 + ], + "angle": 0, + "content": "Andrea Porfiri Dal Cin \nPolitecnico di Milano" + }, + { + "type": "text", + "bbox": [ + 0.107, + 0.22, + 0.374, + 0.234 + ], + "angle": 0, + "content": "andrea.porfiridalcin@polimi.it" + }, + { + "type": "text", + "bbox": [ + 0.442, + 0.182, + 0.617, + 0.216 + ], + "angle": 0, + "content": "Giacomo Boracchi Politecnico di Milano" + }, + { + "type": "text", + "bbox": [ + 0.413, + 0.22, + 0.647, + 0.234 + ], + "angle": 0, + "content": "giacomo.boracchi@polimi.it" + }, + { + "type": "text", + "bbox": [ + 0.686, + 0.182, + 0.861, + 0.216 + ], + "angle": 0, + "content": "Luca Magri\nPolitecnico di Milano" + }, + { + "type": "text", + "bbox": [ + 0.685, + 0.22, + 0.863, + 0.234 + ], + "angle": 0, + "content": "luca MAGRI@polimi.it" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.301, + 0.474, + 0.573 + ], + "angle": 0, + "content": "Traditional and deep Structure-from-Motion (SfM) methods typically operate under the assumption that the scene is rigid, i.e., the environment is static or consists of a single moving object. Few multi-body SfM approaches address the reconstruction of multiple rigid bodies in a scene but suffer from the inherent scale ambiguity of SfM, such that objects are reconstructed at inconsistent scales. We propose a depth and camera pose estimation framework to resolve the scale ambiguity in multi-body scenes. Specifically, starting from disorganized images, we present a novel multi-view scale estimator that resolves the camera pose ambiguity and a multi-body plane sweep network that generalizes depth estimation to dynamic scenes. Experiments demonstrate the advantages of our method over state-of-the-art SfM frameworks in multi-body scenes and show that it achieves comparable results in static scenes. The code and dataset are available at https://github.com/andreadalcin/MultiBodySfM." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.589, + 0.21, + 0.605 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.614, + 0.47, + 0.765 + ], + "angle": 0, + "content": "Real-world environments often contain independently moving objects, and their reconstruction is fundamental for safe robot navigation and augmented reality in complex dynamic environments. Unfortunately, traditional and deep learning Structure-from-Motion (SfM) algorithms assume that the scene is static and treat moving objects as outliers, missing important information and producing suboptimal results when the scene is dynamic. In Fig. 1-left, the depth reconstructed by the state-of-the-art DeepSfM [36] shows artifacts in the image region of a moving object (in red)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.766, + 0.471, + 0.903 + ], + "angle": 0, + "content": "In this work, we go one step further and enable consistent 3D reconstruction (Fig. 1-right) of a scene with multiple rigidly moving objects. This task, also known as Multi-Body Structure-from-Motion (MBSfM), is still open and far from being solved in practice. Traditional MBSfM attempts [1, 26] segment rigid motions to obtain partial reconstructions of individually moving objects in the scene. However, these methods are hampered by the relative scale problem, namely that the 3D structure of each independ-" + }, + { + "type": "text", + "bbox": [ + 0.539, + 0.268, + 0.876, + 0.282 + ], + "angle": 0, + "content": "Two frames of a dynamic scene with a moving object" + }, + { + "type": "image", + "bbox": [ + 0.508, + 0.285, + 0.704, + 0.402 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.708, + 0.286, + 0.907, + 0.403 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.557, + 0.41, + 0.852, + 0.424 + ], + "angle": 0, + "content": "Reconstructed Depth Maps of the second frame" + }, + { + "type": "image", + "bbox": [ + 0.506, + 0.426, + 0.705, + 0.543 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.571, + 0.545, + 0.638, + 0.559 + ], + "angle": 0, + "content": "DeepSFM" + }, + { + "type": "image", + "bbox": [ + 0.708, + 0.426, + 0.907, + 0.543 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.783, + 0.545, + 0.816, + 0.557 + ], + "angle": 0, + "content": "Ours" + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.564, + 0.893, + 0.621 + ], + "angle": 0, + "content": "Figure 1: Two-views of a multi-body scene (top-row). Depth estimation networks (e.g. [36]) yield inconsistent depths (bottom-left) for moving objects. Our method explicitly accounts for moving objects to produce geometrically consistent depths (bottom-right)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.643, + 0.893, + 0.779 + ], + "angle": 0, + "content": "dently moving object is estimated up to a similarity, so that each object is reconstructed in its own scale. Therefore, a unified reconstruction of all objects up to a common global scale factor is impossible without additional information. Similarly, deep methods for SfM that leverage explicit multi-view constraints [34, 36, 13, 29, 4] are affected by the relative scale problem and cannot regress a unified depth map of a multi-body scene since their underlying architecture cannot handle multiple motions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Recent monocular depth estimators [9, 2] use learned priors to regress dense depth maps from images without exploiting multi-view constraints. Thus, monocular methods implicitly avoid the relative scale problem by regressing consistent depth maps across the entire image. However, monocular depth estimation is inherently ill-posed and these models do not provide the same generalization capabilities of multi-view methods when scenes are static. Fur" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "17804" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.151 + ], + "angle": 0, + "content": "thermore, the 3D structures inferred from different images of the same scene are not guaranteed to be consistent. Thus, this inconsistency eventually manifests in alignment problems that are not trivial to solve." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.152, + 0.468, + 0.287 + ], + "angle": 0, + "content": "In this work, we present a novel deep learning framework for depth and camera pose estimation designed specifically for multi-body scenes. Following consolidated MBSfM pipelines, we perform motion segmentation to recover a set of relative camera poses up to a scale factor and the corresponding sparse 3D reconstructions of each moving object. Then, we depart from existing MBSfM approaches by directly solving the relative scale problem and regressing geometrically consistent depth maps and refined poses." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.289, + 0.418, + 0.303 + ], + "angle": 0, + "content": "Specifically, our main contributions are twofold:" + }, + { + "type": "text", + "bbox": [ + 0.082, + 0.304, + 0.449, + 0.318 + ], + "angle": 0, + "content": "(1) a robust scale estimation to fix the scale ambiguity," + }, + { + "type": "text", + "bbox": [ + 0.082, + 0.319, + 0.468, + 0.348 + ], + "angle": 0, + "content": "(2) a multi-body plane sweep network to regress refined camera poses and depth maps in multi-body scenes." + }, + { + "type": "list", + "bbox": [ + 0.082, + 0.304, + 0.468, + 0.348 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.349, + 0.468, + 0.408 + ], + "angle": 0, + "content": "Our scale estimator uses monocular depth maps to unify the 3D structures and camera poses under a global scale factor. This is based on a robust voting scheme that mitigates the impact of inaccuracies in monocular depth estimates." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.41, + 0.468, + 0.575 + ], + "angle": 0, + "content": "We adopt a deep neural network for multi-body depth estimation and pose refinement. The network adopts our novel multi-body plane sweep algorithm, which uses all the rigid motions in the scene, now devoid of scale ambiguity, to compute dense depth maps and refined camera poses. Notably, the estimated depth maps are geometrically consistent even in image regions covered by moving objects. Plane sweep has never been extended to support multiple rigid motions to the best of our knowledge. Our network also includes a pose estimation module that refines camera poses based on current depth estimates." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.576, + 0.468, + 0.665 + ], + "angle": 0, + "content": "We demonstrate the effectiveness of our approach on both static and multi-body scenes. On static scenes, our method performs on par with traditional and deep SfM methods. On multi-body scenes, it significantly outperforms SOTA deep learning SfM methods in the depth estimation task and achieves comparable camera pose results." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.68, + 0.283, + 0.696 + ], + "angle": 0, + "content": "2. Problem Formulation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.468, + 0.885 + ], + "angle": 0, + "content": "Multi-body depth and camera pose estimation is framed as follows. The input is a set of \\(n\\) unstructured images \\(\\{\\mathbf{I}_i\\}_{i=1}^n\\) captured by a moving camera and depicting a multi-body scene in which \\(\\mu\\) objects \\(\\mathcal{B} = \\{\\beta_i\\}_{i=1}^\\mu\\) independently move according to their rigid motions. Without loss of generality, we consider the object \\(\\beta_1\\) to be static w.r.t. to the camera motion. Our goal is to estimate depth maps \\(\\{\\mathbf{D}_i\\}_{i=1}^n\\) for each image \\(\\mathbf{I}_i\\) and the absolute camera poses \\(\\{\\mathbf{R}_i, \\mathbf{t}_i\\}_{i=1}^n\\) in the reference frame of \\(\\beta_1\\). We assume that: i) an upper bound \\(M\\) on the maximum number \\(\\mu\\) of moving objects in the scene is given, ii) the camera is perspective and its intrinsic parameters \\(\\mathbf{K}\\) are known." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.886, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Consider that our problem is different from non-rigid" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "SfM [16, 14]. Non-rigid SfM handles a wider class of object deformations but does not assume unstructured input images, typically exploiting dense temporal information, and is restricted to orthographic cameras." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.164, + 0.642, + 0.18 + ], + "angle": 0, + "content": "3. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.189, + 0.892, + 0.324 + ], + "angle": 0, + "content": "Depth and camera pose estimation from unstructured images of multi-body scenes is largely unexplored, and most SfM methods either consider static scenes only (\\(\\mu = 1\\)) or treat moving objects as outliers. This section focuses on the few SfM methods that address the multi-body scenario (\\(\\mu > 1\\)) from unstructured images acquired by perspective cameras. Also, we discuss monocular depth estimation, a component of our solution, and relevant deep multi-view static SfM methods." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.333, + 0.885, + 0.349 + ], + "angle": 0, + "content": "3.1. Multi-body Structure-from-Motion (MBSfM)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.356, + 0.892, + 0.507 + ], + "angle": 0, + "content": "A few works have addressed MBSfM from unstructured images \\(\\{\\mathbf{I}_i\\}_{i = 1}^n\\) as a generalization of traditional SfM to multi-body scenes. We identify two main research directions. First, early factorization methods [32, 6] segment rigidly moving objects \\(\\mathcal{B}\\) and perform sparse 3D reconstruction in a single step. However, factorization methods rely on restrictive assumptions on camera models and require complete feature tracks, which are seldom available in practice. Due to its lack of robustness, factorization has yet to see practical applications beyond short, unrealistic sequences." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.509, + 0.892, + 0.734 + ], + "angle": 0, + "content": "The second, more recent, research direction separates motion segmentation of objects \\(\\mathcal{B}\\) and their 3D reconstruction. [1, 26] cluster sparse correspondences based on their rigid motion and then recover the 3D structure of each object independently using a SfM pipeline [27]. As discussed in [23, 24, 17], the relative scale problem affects these methods because each object is reconstructed in its own scale. In SLAM, the relative scale problem has been addressed under specific assumptions: [23] assumes objects move in a one-parameter family of motions, and [17] works only with video input and continuous object motion. Our method also decouples motion segmentation and reconstruction. However, we explicitly address the relative scale problem using a learning-based approach without further assumptions on the input images or the motions in the scene." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.742, + 0.761, + 0.758 + ], + "angle": 0, + "content": "3.2. Monocular Depth Estimation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.87 + ], + "angle": 0, + "content": "Recent works [9, 2] recover a dense depth map \\(\\mathbf{D}_1\\) from a single image \\(\\mathbf{I}_1\\). These methods learn priors to regress depth maps, allowing consistent scale reconstruction of moving objects \\(\\mathcal{B}\\) without scale ambiguity. However, due to the ill-posed nature of monocular depth estimation, generalization is limited and multi-view approaches remain the benchmark for SfM in deep learning." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.9 + ], + "angle": 0, + "content": "In [20, 38], monocular depth maps are estimated from video frames, and then a network is fine-tuned on the entire" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.956 + ], + "angle": 0, + "content": "17805" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.102, + 0.088, + 0.868, + 0.264 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.269, + 0.895, + 0.312 + ], + "angle": 0, + "content": "Figure 2: The three main steps of our method: i) motion segmentation: produces a set of essential matrices describing the rigid motion of objects between view pairs. ii) robust scale estimation: uses monocular depth cues to fix the scale ambiguity of each moving object. iii) multi-body plane-sweep network based on our novel multi-body plane-sweep regress refined depth maps and camera poses." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.337, + 0.471, + 0.414 + ], + "angle": 0, + "content": "video sequence. These methods do not assume unstructured images and require many frames for depth and pose tracking and fine-tuning. In addition, depth estimation for moving objects still relies solely on depth priors, which can lead to inaccuracies as in standard monocular depth estimation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.425, + 0.293, + 0.441 + ], + "angle": 0, + "content": "3.3. Deep Learning for SfM" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.45, + 0.47, + 0.736 + ], + "angle": 0, + "content": "Deep learning methods for SfM from unstructured images regress camera poses and dense depth maps using multi-view stereo matching. DeMoN [33] works on image pairs using stacked encoder-decoder networks but lacks explicit multi-view constraints and has limited accuracy. More recent architectures [29, 4, 36, 34, 13, 31] replace the generic encoder-decoder architecture with layers that explicitly enforce multi-view constraints. Other works achieve better results by taking inspiration from traditional Bundle Adjustment: DeepSfM [36] introduces depth and pose cost volumes for iterative refinement, and [29] uses a BA-layer for regression from basis depth maps. Wang et al. [34] propose a scale-invariant network for depth and pose estimation for view pairs. Specifically, camera poses are estimated from essential matrices robustly fitted on fine-tuned optical flow matches, thus treating all moving objects as outliers. Then, depth maps are regressed end-to-end using a CNN similar to DeepSfM. Finally, [4] optimizes non-linear cost functions in SfM using recurring neural networks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.738, + 0.47, + 0.799 + ], + "angle": 0, + "content": "As the above deep methods embed explicit multi-view geometric constraints in their optimization layers, they are affected by the scale ambiguity of traditional MBSfM and cannot generalize to multi-body scenes, as shown in Fig. 1." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.815, + 0.168, + 0.83 + ], + "angle": 0, + "content": "4. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.904 + ], + "angle": 0, + "content": "Our method, illustrated in Fig. 2, is structured in three steps. First, given the unstructured images \\(\\{\\mathbf{I}_i\\}_{i=1}^n\\), we perform motion segmentation from image pairs \\(\\alpha\\) to estimate essential matrices \\(\\{\\mathbf{E}_k^\\alpha\\}_{j=1}^\\mu\\) that encode the \\(\\mu\\) rigid mo" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.337, + 0.892, + 0.445 + ], + "angle": 0, + "content": "tions in the scene. Second, we fix the scale ambiguity of each \\(\\mathbf{E}_k^\\alpha\\) by exploiting cues provided by monocular depth maps \\(\\{\\mathbf{M}_i\\}_{i=1}^n\\) in a robust scale estimation module. Finally, a multi-view depth and camera pose estimation network leverages our novel multi-body plane sweep algorithm to regress geometrically-consistent depth maps \\(\\{\\mathbf{D}_i\\}_{i=1}^n\\) and camera poses \\(\\{\\mathbf{R}_i, \\mathbf{t}_i\\}_{i=1}^n\\) by considering all the \\(\\mu\\) motions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.453, + 0.699, + 0.469 + ], + "angle": 0, + "content": "4.1. Motion segmentation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.477, + 0.892, + 0.552 + ], + "angle": 0, + "content": "The goal of motion segmentation is to recover the essential matrices \\(\\{\\mathbf{E}_k^\\alpha\\}_{k=1}^\\mu\\) that encode all rigid motions in the scene in any image pair \\(\\alpha = (\\mathbf{I}_i, \\mathbf{I}_j)\\). To this end, we combine traditional sparse motion segmentation, based on SIFT [19], with dense deep optical flow matches." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.552, + 0.892, + 0.688 + ], + "angle": 0, + "content": "For each image \\(\\mathbf{I}_i\\), we extract \\(\\{x_{i,u}\\}_{u = 1}^{p_i}\\) SIFT keypoints and match them across image pairs. Then, for each pair \\(\\alpha\\), we fit \\(\\mu\\) essential matrices \\(\\{\\mathbf{E}_k^\\alpha J_{k = 1}^\\mu\\}\\) to the matches using RPA [21], a multi-model fitting algorithm. RPA provides a labeling \\(\\ell^{\\alpha}\\) that assigns a matched keypoint to the motion it belongs to. Labels assigned to different image pairs may be inconsistent, thus we use permutation synchronization [1] to enforce a global labelling \\(\\ell\\) that assigns to keypoints belonging to the same motion the same label in all views." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.893, + 0.901 + ], + "angle": 0, + "content": "In multi-body scenes, moving objects can be supported by only a few keypoints. Therefore, to refine the essential matrices, we augment the set of sparse matches with dense ones computed from the optical flow. Similarly to [34], we consider the dense matches at keypoint locations and, thus, avoid the typical inaccuracies of the optical flow caused by illumination changes and texture-less regions. In particular, given an image pair \\(\\alpha = (\\mathbf{I}_i,\\mathbf{I}_j)\\), for each object \\(\\beta_{k}\\in \\mathcal{B}\\) we consider \\(U_{k}^{i} = \\{x_{i,u}:\\ell (x_{i,u}) = k\\}\\) the sparse keypoints in \\(\\mathbf{I}_i\\) labelled as \\(k\\). Around each keypoint \\(x\\in U_k^i\\) we consider a squared neighborhood \\(N(x)\\) of \\(3\\times 3\\) pixels. The union of neighborhoods \\(S_{k}^{i} = \\bigcup_{x\\in U_{k}^{i}}N(x)\\) defines a mask in \\(\\mathbf{I}_i\\) as illustrated in Fig. 2. We refine \\(\\mathbf{E}_k^\\alpha\\) by RANSAC equipped with the 5-point algorithm [22, 18] on the set of all" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17806" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.092, + 0.322, + 0.254 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.422, + 0.092, + 0.621, + 0.244 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.645, + 0.092, + 0.876, + 0.245 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.257, + 0.895, + 0.3 + ], + "angle": 0, + "content": "Figure 3: (left) In a multi-body scene, the scale of triangulated structures (orange) differs from the true object scale (cyan), leading to inconsistent relative object scales, i.e., cube bigger than pyramid. The tentative scale factor \\(\\lambda_{i,u}^{1}\\) of \\(X_{u}^{1} \\in \\beta_{1}\\) is the ratio of the monocular depth \\(m_{i,u}^{1}\\) and its triangulated depth \\(d_{i,u}^{1}\\). (right) Traditional plane sweep [5] vs. our novel multi-body plane sweep." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.325, + 0.47, + 0.357 + ], + "angle": 0, + "content": "the dense matches corresponding to the mask \\( S_{k}^{i} \\). The optical flow is computed using the DICL-Flow network [35]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.363, + 0.303, + 0.377 + ], + "angle": 0, + "content": "4.2. Robust Scale Estimation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.385, + 0.47, + 0.614 + ], + "angle": 0, + "content": "We factorize each essential matrix \\(\\mathbf{E}_k^\\alpha = [\\tilde{\\mathbf{t}}_k^\\alpha ]_\\times \\tilde{\\mathbf{R}}_k^\\alpha\\) to obtain the relative camera pose as a rotation \\(\\tilde{\\mathbf{R}}_k^\\alpha\\) and translation \\(\\tilde{\\mathbf{t}}_k^\\alpha\\). Since each \\(\\tilde{\\mathbf{t}}_k^\\alpha\\) is recovered only up to an unknown scale-factor \\(\\lambda_{k}\\), each moving object in a multi-body scene is reconstructed in its own arbitrary scale \\(\\lambda_{k}\\). Specifically, given an image pair \\(\\alpha\\), we can triangulate from matched image points a set of 3D points \\(\\{X_u^k\\}_{u = 1}^{p_k}\\) belonging to object \\(\\beta_{k}\\) from the up-to-scale camera pose \\(\\{\\tilde{\\mathbf{R}}_k^\\alpha ,\\tilde{\\mathbf{t}}_k^\\alpha \\}\\). However, these 3D points are expressed in the scale \\(\\lambda_{k}\\) of \\(\\tilde{\\mathbf{t}}_k^\\alpha\\), meaning that different objects refer to inconsistent scales. Fig. 3-left depicts a multi-body scene where the scale ambiguity manifests as an inconsistent relative scale between objects \\(\\lambda_{1}\\beta_{1}\\) and \\(\\lambda_{2}\\beta_{2}\\) in the triangulated scene (orange) w.r.t. the actual 3D scene (cyan). Thus, the cube \\(\\lambda_{1}\\beta_{1}\\) appears larger than the pyramid \\(\\lambda_{2}\\beta_{2}\\) in the reconstruction." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.615, + 0.47, + 0.766 + ], + "angle": 0, + "content": "We estimate the unknown scale factor \\(\\lambda_{k}\\) for each object \\(\\beta_{k}\\) by first regressing a monocular depth map \\(\\mathbf{M}_i\\) from each image \\(\\mathbf{I}_i\\) using AdaBins [2]. This network processes each \\(\\mathbf{I}_i\\) individually and, thus, is not affected by the multi-view scale ambiguity. We denote by \\(d_{i,u}^{k}\\) and by \\(m_{i,u}^{k}\\) the triangulated and monocular depths respectively of the \\(u\\)-th 3D point \\(X_{u}^{k}\\) w.r.t. \\(\\mathbf{I}_i\\). Then, for each object \\(\\beta_{k}\\) and image \\(\\mathbf{I}_i\\), we compute the point-wise scale factor \\(\\lambda_{i,u}^{k} = d_{i,u}^{k} / m_{i,u}^{k}\\) that approximates the real \\(\\lambda_{k}\\) according to the triangulated and monocular depths of \\(X_{u}^{k}\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.766, + 0.471, + 0.902 + ], + "angle": 0, + "content": "As monocular depth maps generally lack in accuracy, we devise a voting scheme to robustly aggregate the scale factors from all images \\(\\{\\mathbf{I}_i\\}_{i = 1}^n\\) and unify all the \\(\\mu\\) camera poses under a global scale factor \\(\\lambda\\). First, we partition the point-wise scale factors computed from all the images into \\(\\mu\\) sets \\(\\Lambda_{k} = \\{\\lambda_{i,u}^{k}\\}_{i = 1,u = 1}^{n,p_{k}}\\) according to their object \\(\\beta_{k}\\). Then, to promote robustness, we adopt a Kernel Density Estimator and derive a probability density function \\(\\phi_{k}\\) from each \\(\\Lambda_{k}\\). We use a Gaussian Kernel \\(\\mathcal{K}\\) with bandwidth \\(h\\) set" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.325, + 0.892, + 0.355 + ], + "angle": 0, + "content": "at \\(5\\%\\) of the median of the elements in \\(\\Lambda_{k}\\) and define the kernel \\(\\phi_{k}\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.599, + 0.364, + 0.892, + 0.405 + ], + "angle": 0, + "content": "\\[\n\\phi_ {k} (x) = \\sum_ {\\lambda_ {i, u} ^ {k} \\in \\Lambda_ {k}} \\frac {\\mathcal {K} \\left(\\lambda_ {i , u} ^ {k} - x\\right)}{h}. \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.416, + 0.893, + 0.571 + ], + "angle": 0, + "content": "The highest peak of \\(\\phi_{k}\\) is denoted by \\(\\hat{\\lambda}_{k}\\) and represents the estimate of the \\(k\\)-th object scale factor \\(\\lambda_{k}\\). The estimated \\(\\{\\hat{\\lambda}_k\\}_{k = 1}^\\mu\\) are used to scale the pairwise relative camera poses \\([\\tilde{\\mathbf{R}}_k^\\alpha ,\\hat{\\lambda}_k^{-1}\\tilde{\\mathbf{t}}_k^\\alpha ]\\) by multiplying the translation component. Now, camera poses are aligned to a global scale factor \\(\\lambda\\). As depths \\(\\mathbf{M}_i\\) are regressed in real-world unit of measurement, \\(\\lambda \\approx 1\\), i.e., camera poses should be approximately in their real-world scale. We denote the correctly scaled camera poses as \\([\\hat{\\mathbf{R}}_k^\\alpha ,\\hat{\\mathbf{t}}_k^\\alpha ]\\) and use this unified camera configuration as the initialization for the next step." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.58, + 0.796, + 0.596 + ], + "angle": 0, + "content": "4.3. Multi-body Plane Sweep Network" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.602, + 0.892, + 0.83 + ], + "angle": 0, + "content": "Although the poses \\(\\{\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha\\}\\) are now aligned to a single scale factor, the depths are only estimated from monocular maps \\(\\mathbf{M}_i\\) which ignore the multi-view constraints. In principle, it could be possible to use camera poses to initialize a multi-view iterative scheme where depths and poses are refined, as in [36], but this would regress inconsistent depths in regions corresponding to moving objects. Thus, we design a novel multi-body depth and pose estimation network that takes the unordered images \\(\\{\\mathbf{I}_i\\}_{i=1}^n\\) and the scale-consistent poses \\(\\{\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha\\}\\) to jointly estimates geometrically consistent depth maps \\(\\{\\mathbf{D}_i\\}_{i=1}^n\\) and refined poses \\(\\{\\mathbf{R}_i, \\mathbf{t}_i\\}_{i=1}^n\\) in the reference frame of object \\(\\beta_1\\). As shown in Fig. 4, we include two separate branches for depth and pose estimation, which are used alternatively in an iterative scheme using the output of the other branch as input." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.837, + 0.808, + 0.852 + ], + "angle": 0, + "content": "4.3.1. Multi-body Depth Estimation Branch" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "As depicted in Fig. 4, our depth estimation branch is based on our novel multi-body plane sweep and concatenates the following modules." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17807" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.127, + 0.089, + 0.852, + 0.268 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.272, + 0.894, + 0.302 + ], + "angle": 0, + "content": "Figure 4: Multi-body Plane Sweep network. We extract CNN features from input images and build a cost volume using our multi-body plane sweep algorithm. Depth and camera poses are regressed from separate cost volumes with a series of 3D CNN and refinement layers." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.327, + 0.471, + 0.389 + ], + "angle": 0, + "content": "Feature Extraction. A multi-scale CNN with spatial pyramid pooling [12] extracts features \\(\\{\\mathbf{F}_i\\}_{i=1}^n\\) from images \\(\\{\\mathbf{I}_i\\}_{i=1}^n\\). Each \\(\\mathbf{F}_i\\) has dimension \\(\\mathbf{C} \\times \\mathbf{W} \\times \\mathbf{H}\\), where \\(\\mathbf{C}\\), \\(\\mathbf{W}\\), \\(\\mathbf{H}\\) are feature channels, width and height respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.399, + 0.47, + 0.732 + ], + "angle": 0, + "content": "Multi-body Plane Sweep for Cost Volume Construction. Let us briefly recall how the traditional plane sweep works before describing our contributions. The traditional plane sweep algorithm [5] takes as input an image pair \\(\\alpha\\) of a source \\(\\mathbf{I}_i\\) and target \\(\\mathbf{I}_j\\) and their relative pose \\([\\mathbf{R}^\\alpha, \\mathbf{t}^\\alpha]\\). The algorithm samples a set of virtual planes parallel to \\(\\mathbf{I}_j\\) at fixed depths \\(\\{d_l\\}_{l=1}^L\\). Then, for each depth \\(d_l\\), the source \\(\\mathbf{I}_i\\) is warped onto the target \\(\\mathbf{I}_j\\) through the homography induced by the plane at \\(d_l\\) and the relative camera pose \\([\\mathbf{R}^\\alpha, \\mathbf{t}^\\alpha]\\), as in Fig. 3-right. A dense depth map is obtained by selecting, for each pixel, the depth \\(d_l\\) that minimizes a pixel-wise photometric dissimilarity between the target \\(\\mathbf{I}_j\\) and the warped source \\(\\mathbf{I}_i\\). Deep methods [13, 36, 34] revisited this framework, but measure feature metric consistency between latent features \\(\\{\\mathbf{F}_i\\}_{i=1}^n\\) instead of photometric dissimilarity. To this end, warped source and target features are aggregated in a single depth cost volume from which depths are regressed through convolutional layers. Unfortunately, both traditional and deep plane sweep methods assume static scenes with a single relative camera pose \\([\\mathbf{R}^\\alpha, \\mathbf{t}^\\alpha]\\) between the pair \\(\\alpha\\). As a result, any point belonging to a moving object has an inconsistent depth." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.471, + 0.903 + ], + "angle": 0, + "content": "We propose instead a multi-body plane sweep that considers all the \\(\\mu\\) relative poses \\(\\{\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha\\}_{k=1}^\\mu\\) to warp a source feature \\(\\mathbf{F}_i\\) onto a target \\(\\mathbf{F}_j\\) and construct the depth cost volume. Given a source-target pair \\(\\alpha = (\\mathbf{I}_i, \\mathbf{I}_j)\\), we uniformly sample \\(L\\) 3D virtual planes at depths \\(\\{d_l\\}_{l=1}^L\\) parallel to the source \\(\\mathbf{I}_i\\). Then, we sequentially assign each depth plane to one of the \\(\\mu\\) relative camera poses by cycling through the \\(\\{\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha\\}_{k=1}^\\mu\\). Thus, the individual features \\(\\mathbf{F}_i\\) of the object \\(\\beta_k\\) are warped onto \\(\\mathbf{F}_j\\) in a geometrically consistent manner when considering any depth plane assigned to the camera pose \\([\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha]\\) relative to \\(\\beta_k\\). This is depicted in" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.327, + 0.895, + 0.419 + ], + "angle": 0, + "content": "Fig. 3-right, utilizing color to illustrate the cyclic assignment of the \\(k\\)-th and \\(h\\)-th rigid motions to planes at \\(d_{l}\\) and \\(d_{l+1}\\), respectively, and to subsequent planes. Finally, each point \\(u\\) in the source feature \\(\\mathbf{F}_{i}\\) is first back-projected onto the virtual planes at \\(d_{l}\\) and then re-projected as \\(\\tilde{u}_{lk}\\) on the target \\(\\mathbf{F}_{j}\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.523, + 0.427, + 0.892, + 0.459 + ], + "angle": 0, + "content": "\\[\n\\tilde {\\mathbf {F}} _ {i l} ^ {k} (u) = \\mathbf {F} _ {i} (\\tilde {u} _ {l k}), \\tilde {u} _ {l k} \\sim \\mathbf {K} \\left[ \\hat {\\mathbf {R}} _ {k} ^ {\\alpha} | \\hat {\\mathbf {t}} _ {k} ^ {\\alpha} \\right] \\left[ \\begin{array}{c} (\\mathbf {K} ^ {- 1} u) d _ {l} \\\\ 1 \\end{array} \\right], \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.467, + 0.892, + 0.502 + ], + "angle": 0, + "content": "where \\(\\tilde{\\mathbf{F}}_{il}^{k}\\) is the warped source feature through the homography induced by the plane at \\(d_{l}\\) and the motion \\([\\hat{\\mathbf{R}}_k^\\alpha ,\\hat{\\mathbf{t}}_k^\\alpha ]\\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.504, + 0.893, + 0.672 + ], + "angle": 0, + "content": "Cost volume Construction. Given the set of virtual depth planes \\(\\{d_l\\}_{l = 1}^L\\), for each \\(d_{l}\\), we obtain a warped source feature \\(\\tilde{\\mathbf{F}}_{il}^{k}\\) using Eq. 2 and concatenate it to the target feature \\(\\mathbf{F}_j\\). This yields a set of \\(L\\) feature blocks, each sized \\(2\\mathrm{C} \\times \\mathrm{W} \\times \\mathrm{H}\\), that we arrange into a 4D depth cost volume sized \\(2\\mathrm{C} \\times L \\times \\mathrm{W} \\times \\mathrm{H}\\), as illustrated in Fig. 5. Since the number of virtual planes is significantly higher than the number of motions, all the \\(\\mu\\) motions are assigned to some virtual planes. Thus, our cost volume jointly incorporates all the motions in the scene, unlike traditional plane-sweep methods that assume a single motion." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.895, + 0.902 + ], + "angle": 0, + "content": "Cost volume Regularization. Regularizing the cost volume is fundamental to cope with imperfect latent feature matching, which is especially common in image regions corresponding to texture-less objects or uniform pixel intensity. To this end, we use a sequence of 3D convolutional layers consisting of \\( L / 2 \\) filters of size \\( 3\\times 3\\times 3 \\) with stride 1, and residual connections. Then, we apply a 3D convolution with a single \\( 3\\times 3\\times 3 \\) filter to obtain a 3D cost volume of size \\( L\\times \\mathrm{W}\\times \\mathrm{H} \\). Since the order of the stacked features in the cost volume follows the correct virtual plane sequence, 3D convolutional layers can capture the 3D dependencies in the scene to enable consistent depth map estimation. Finally, we apply edge-preserving filtering to the resulting cost volume as in [13, 11]. In the case of multiple source-target image pairs, the final 3D cost volume is obtained by aver" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17808" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.122 + ], + "angle": 0, + "content": "aging the 3D cost volumes from each pair. Further details on the cost volume can be found in the supplementary." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.125, + 0.468, + 0.215 + ], + "angle": 0, + "content": "Depth Regression. We denote as \\( c_{l} \\) each slice of the aggregated cost volume, which corresponds to a plane at \\( d_{l} \\). Then, we convert the aggregated cost volume to a probability volume as in [15] and use the softmax operation \\( \\sigma \\) to normalize the probability volume across the depth dimension. We estimate the depth map \\( \\mathbf{D}_i \\) for a view \\( \\mathbf{I}_i \\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.161, + 0.223, + 0.469, + 0.26 + ], + "angle": 0, + "content": "\\[\n\\mathbf {D} _ {i} = \\frac {L \\times d _ {\\operatorname* {m i n}}}{\\tilde {l}}, \\tilde {l} = \\sum_ {l = 1} ^ {L} l \\times \\sigma \\left(c _ {l}\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.268, + 0.469, + 0.331 + ], + "angle": 0, + "content": "where \\(\\tilde{l}\\) is the map corresponding to the average of virtual plane depths \\(l\\in \\{1,\\dots ,L\\}\\), weighted by the probabilities \\(\\sigma (c_l)\\). In (3), \\(d_{\\mathrm{min}}\\) denotes the depth of the closest plane to the source image." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.336, + 0.292, + 0.349 + ], + "angle": 0, + "content": "4.3.2. Pose Estimation Branch" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.354, + 0.47, + 0.539 + ], + "angle": 0, + "content": "We describe our pose estimation branch, which optimizes current camera pose estimates through feature-metric consistency. To this purpose, we use a network architecture akin to the one in [36]. The network receives a pair \\(\\alpha = (\\mathbf{I}_i,\\mathbf{I}_j)\\), the depth map \\(\\mathbf{D}_i\\) of \\(\\mathbf{I}_i\\) and \\([\\hat{\\mathbf{R}}_1^\\alpha ,\\hat{\\mathbf{t}}_1^\\alpha ]\\), the current camera pose estimate in the reference frame of \\(\\beta_{1}\\), to regress a refined \\([\\mathbf{R}_1^\\alpha ,\\mathbf{t}_1^\\alpha ]\\). We uniformly sample \\(P\\) tentative camera poses \\(\\{\\hat{\\mathbf{R}}_{1p}^{\\alpha},\\hat{\\mathbf{t}}_{1p}^{\\alpha}\\}_{p = 1}^{P}\\) by perturbing the rotation and the translation of the initial poses \\([\\hat{\\mathbf{R}}_1^\\alpha ,\\hat{\\mathbf{t}}_1^\\alpha ]\\). The \\(P\\) poses are used to construct a pose cost volume by warping each point \\(u\\) in the source feature \\(\\mathbf{F}_i\\) to a point \\(\\tilde{u}_p\\) on the target feature \\(\\mathbf{F}_j\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.152, + 0.548, + 0.469, + 0.579 + ], + "angle": 0, + "content": "\\[\n\\tilde {u} _ {p} \\sim \\mathbf {K} \\left[ \\hat {\\mathbf {R}} _ {1 p} ^ {\\alpha} \\mid \\hat {\\mathbf {t}} _ {1 p} ^ {\\alpha} \\right] \\left[ \\begin{array}{c} \\left(\\mathbf {K} ^ {- 1} u\\right) \\mathbf {D} _ {i} (u) \\\\ 1 \\end{array} \\right]. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.469, + 0.613 + ], + "angle": 0, + "content": "Finally, a sequence of 3D convolutional layers is applied to the pose cost volume to regress the camera pose \\(\\left[\\mathbf{R}_1^\\alpha ,\\mathbf{t}_1^\\alpha \\right]\\)." + }, + { + "type": "image", + "bbox": [ + 0.085, + 0.631, + 0.47, + 0.766 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.769, + 0.469, + 0.897 + ], + "angle": 0, + "content": "Figure 5: Cost volume construction by multi-body plane sweep. For each virtual depth plane at \\(d_{l} \\in \\{d_{l}\\}_{l=1}^{L}\\), we generate a \\(2\\mathbf{C} \\times \\mathbf{W} \\times \\mathbf{H}\\) feature map by concatenating the target feature \\(\\mathbf{F}_j\\) (gray) to the warped source feature \\(\\tilde{\\mathbf{F}}_{il}^{\\gamma}\\) (in color) at depth \\(d_{l}\\) using motion \\([\\hat{\\mathbf{R}}_{\\gamma}^{\\alpha}, \\hat{\\mathbf{t}}_{\\gamma}^{\\alpha}]\\). The 4D cost volume is constructed through concatenation of these \\(L\\) feature blocks. \\(\\tilde{\\mathbf{F}}_{il}^{k}\\) (in blue) indicates a source feature \\(\\mathbf{F}_i\\) warped onto \\(\\mathbf{F}_j\\) through the homography induced by the generic plane at \\(d_{l}\\) and its relative camera motion \\([\\hat{\\mathbf{R}}_k^{\\alpha}, \\hat{\\mathbf{t}}_k^{\\alpha}]\\). Instead, \\(\\tilde{\\mathbf{F}}_{il}^{h}\\) is induced by the motion \\([\\hat{\\mathbf{R}}_h^{\\alpha}, \\hat{\\mathbf{t}}_h^{\\alpha}]\\) (in pink)." + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.09, + 0.908, + 0.309 + ], + "angle": 0, + "content": "
viewMethodlower is better ↓higher is better ↑
Abs RelSq RelRMSERMSElogδ1δ2δ3
Eigen SM (s)svDORN [9]0.0670.2952.9290.1080.9490.9880.995
AdaBins [2]0.0540.1822.3410.0870.9660.9950.999
mvDeepV2D [31]0.0500.2122.4830.0890.9730.9920.997
Wang et al. [34]0.0340.1031.9190.0570.9890.9980.999
Ours0.0440.1482.1250.0680.9740.9960.999
Eigen (s & m)svDORN [9]0.0720.3072.7270.1200.9320.9840.994
AdaBins [2]0.0580.1902.3600.0880.9640.9950.999
mvSfMLearner [39]0.2081.7686.8560.2830.6780.8850.975
CCNet [25]0.1401.0705.3260.2170.8260.9410.975
BANet [29]0.083-3.6400.134---
DeepV2D [31]0.0640.3502.9460.1200.9460.9820.991
Wang et al. [34]0.0550.2242.2730.0910.9560.9840.993
Ours0.0540.1862.2690.0860.9660.9910.996
Eigen MB (m)svDORN [9]0.0720.3072.7270.1200.9320.9840.994
AdaBins [2]0.0620.2012.3720.0920.9590.9940.999
mvDeepV2D [31]0.0890.4013.2780.1520.9310.9650.989
Wang et al. [34]0.0630.2422.3470.1090.9480.9710.991
Ours0.0570.1972.3010.0900.9620.9910.994
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.321, + 0.892, + 0.363 + ], + "angle": 0, + "content": "Table 1: Depth evaluation on KITTI Depth. Results from single-view (sv) and multi-view (mv) depth estimation methods evaluated under two-view SfM setting. Best results in bold." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.388, + 0.708, + 0.403 + ], + "angle": 0, + "content": "4.3.3. Training and Inference" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.406, + 0.892, + 0.589 + ], + "angle": 0, + "content": "We train the feature extractor, 3D convolutions and regression layers in a end-to-end supervised manner. We denote as \\(\\mathbf{D}\\) the depth regressed from the refined cost volume, and as \\(\\mathbf{D}_{\\mathrm{gt}}\\) the ground-truth depth. To improve the learning process, we also regress a depth map \\(\\tilde{\\mathbf{D}}\\) from the cost volume before applying edge-preserving filtering. The loss function is defined as \\(\\mathcal{L}_{\\mathrm{depth}} = \\sum_{i}\\lambda H(\\tilde{\\mathbf{D}},\\mathbf{D}_{\\mathrm{gt}}) + H(\\mathbf{D},\\mathbf{D}_{\\mathrm{gt}})\\), where \\(\\lambda = 0.7\\) is a weight and \\(H(\\cdot)\\) is the Huber loss. The pose losses \\(\\mathcal{L}_{\\mathrm{rot}}\\) and \\(\\mathcal{L}_{\\mathrm{trans}}\\) are defined as the \\(\\ell_1\\) distance between the predicted and ground-truth absolute poses. Our final loss is then: \\(\\mathcal{L} = \\lambda_r\\mathcal{L}_{\\mathrm{rot}} + \\lambda_t\\mathcal{L}_{\\mathrm{trans}} + \\lambda_d\\mathcal{L}_{\\mathrm{depth}}\\). All the weights are specified in the supplementary." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.589, + 0.892, + 0.71 + ], + "angle": 0, + "content": "The multi-body plane sweep component of the network has no learnable parameters and is not trained. Our network does not require any form of motion annotation for depth estimation, even in multi-body scenes. For this reason, we train our model on static frames from KITTI [10] and DeMoN [33]. The training and inference are performed in an iterative fashion in four steps, where the regressed depth maps and camera poses are fed to the next iteration." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.723, + 0.633, + 0.74 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.748, + 0.892, + 0.84 + ], + "angle": 0, + "content": "We evaluate our method on static (s) and multi-body (m) datasets for depth and pose estimation against state-of-the-art single-view (sv) and multi-view (mv) methods. In Sec. 5.4 we discuss the limitations of our method and possible countermeasures. Additional experiments and implementation details are provided in the supplementary." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.848, + 0.803, + 0.864 + ], + "angle": 0, + "content": "5.1. Datasets, Competitors and Metrics" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "KITTI Depth (s & m) [10] is designed for depth evaluation in autonomous driving and contains several image se" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17809" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.089, + 0.35, + 0.169 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.352, + 0.089, + 0.621, + 0.169 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.623, + 0.09, + 0.892, + 0.169 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.173, + 0.894, + 0.201 + ], + "angle": 0, + "content": "Figure 6: Multi-body Unstructured Extract. Three view pairs extracted from our proposed dataset for illustration purposes. The dataset contains indoor sequences that depict varied scenarios in which objects of several different sizes move in the scene." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.214, + 0.892, + 0.398 + ], + "angle": 0, + "content": "
MethodMVSScenes11SUN3D
DepthPoseDepthPoseDepthPose
L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)
AdaBins [2]0.0480.2360.291--0.0200.3820.270--0.0210.1270.161--
DeMoN [33]0.0470.2020.3055.15614.4470.0190.3150.2480.8098.9180.0190.1140.1721.80118.811
LS-Net [4]0.0510.2210.3114.65311.1220.0100.4100.2104.6538.2100.0150.1890.6501.52114.347
BA-Net [29]0.0300.1500.0803.49911.2380.0800.2100.1303.49910.3700.0150.1100.0601.72913.260
DeepSfM [36]0.0210.1290.0792.8249.8810.0070.1120.0640.4035.8280.0130.0930.0721.70413.107
Wang et al. [34]0.0150.1020.0682.4173.8780.0050.0970.0580.2762.0410.0100.0810.0571.39110.757
Ours (M=1)0.0160.1070.0682.5384.5380.0050.0990.0580.3213.6490.0110.0840.0611.47012.018
Ours (M=2)0.0190.1210.0732.6817.3400.0070.1020.0690.4014.6190.0130.0920.0711.62513.402
Ours (M=3)0.0250.1320.0752.8929.5300.0090.1240.0780.5425.7820.0140.0950.0791.76915.231
Ours (M=4)0.0260.1340.0762.9319.7410.0090.1280.0810.5715.8030.0160.1070.0841.83015.904
" + }, + { + "type": "table_caption", + "bbox": [ + 0.107, + 0.4, + 0.86, + 0.415 + ], + "angle": 0, + "content": "Table 2: Depth and pose evaluation on MVS, Scenes 11, SUN3D. (s). For all metrics lower is better. Best results are in bold." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.429, + 0.47, + 0.519 + ], + "angle": 0, + "content": "quences where objects move rigidly. We consider the Eigen [7] split (697 frames) and the Eigen SfM split [34] (256 frames), a subset of the Eigen split without moving objects. In addition, we introduce the Eigen MB split, a subset of the Eigen split that includes 90 frames in which dynamic objects appear and camera motions are well-conditioned." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.52, + 0.47, + 0.626 + ], + "angle": 0, + "content": "MVS, Scenes11, SUN3D. (s) MVS [33] includes outdoor sequences with large baselines. Scenes11 [33] contains fairly realistic frames from rendered scenes with accurate ground truth depth and camera poses. SUN3D [37] is an indoor dataset with sometimes inaccurate ground truth depth and camera poses. For SUN3D, we consider the split by [33] to exclude frames with high photoconsistency errors." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.626, + 0.47, + 0.685 + ], + "angle": 0, + "content": "ETH3D SLAM. (m) [28] contains SLAM sequences with ground truth depth and camera poses. We consider the dynamic sequences motion1-2-3-4 and, specifically, a 32 frames split where camera motions are well-conditioned." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.686, + 0.47, + 0.838 + ], + "angle": 0, + "content": "Multi-body Unstructured. (m) We capture multi-body indoor sequences using a Kinect with ground truth depth. The dataset is meant for evaluation in varied conditions, for instance, when image sets are unstructured or when both large and big objects move in the scene. We use RGB-D SLAM [8] to fuse visual information and data from the Kinect IMU and annotate accurate camera poses. The dataset includes 42 frames with either one or two moving objects. Samples scenes are reported in Fig.6 and additional details are provided in the supplementary." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Competitors. We compare against state-of-the-art single-view methods (sv) DORN [9] and AdaBins [2], and multiview methods (mv) DeMoN [33], LS-Net [3], CCNet [25], BANet [29], DeepV2D [31] and Wang et al. [34]. De" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.429, + 0.892, + 0.536 + ], + "angle": 0, + "content": "MoN estimates depth and poses from image pairs, CCNet and SfMLearner mask moving objects before depth and pose estimation, LS-Net, BANet and DeepV2D optimize multi-view differentiable cost functions to minimize photo- or feature-metric errors, and Wang et al. [34] proposes a deep, scale-invariant estimator for depth and camera poses that robustly identify the dominant background motion \\(\\beta_{1}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.543, + 0.893, + 0.711 + ], + "angle": 0, + "content": "Metrics. To evaluate the quality of depth maps in KITTI Depth, we adopt the metrics in [7], i.e., the depth absolute (Abs Rel) and squared (Sq Rel) relative difference, the RMSE, the \\(\\mathrm{RMSE}_{\\log}\\), and the thresholds \\(\\{\\delta_i\\}_{i=1}^3\\). For other datasets, we adopt the metrics in [33], i.e., scale-invariant depth error (sc-inv), relative error to ground truth depth (L1-rel), relative error w.r.t. inverse depth (L1-inv). The definitions of these metrics are in the supplementary. As for pose estimation, we report the angle (in deg) between predicted and ground truth translations \\((t_{\\mathrm{err}})\\) and rotations \\((\\mathbf{R}_{\\mathrm{err}})\\) of the cameras with respect to the background motions \\(\\beta_1\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.902 + ], + "angle": 0, + "content": "Implementation Details. We fine-tune the optical flow network on KITTI Depth for a fair comparison to [34]. Otherwise, we train the optical flow on synthetic scenes, as in [35], and let the proposed framework refine initial camera poses. We implement our framework using PyTorch. The batch size is set to 32. The learning rate is set to \\(1 \\times 10^{-4}\\) and is halved after 2 epochs. For KITTI Depth, the feature extractor is initialized with pre-trained weights, which are frozen for the first epoch. For other datasets, we train the network from randomly initialized weights. Training takes approximately 3 days on 2 NVIDIA RTX A6000 GPUs. Further details are reported in the supplementary." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "17810" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.164, + 0.089, + 0.339, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.164, + 0.18, + 0.339, + 0.271 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.164, + 0.271, + 0.339, + 0.362 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.163, + 0.362, + 0.339, + 0.451 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.199, + 0.455, + 0.328, + 0.47 + ], + "angle": 0, + "content": "Reference images" + }, + { + "type": "image", + "bbox": [ + 0.342, + 0.089, + 0.496, + 0.177 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.342, + 0.18, + 0.496, + 0.271 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.342, + 0.271, + 0.496, + 0.362 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.342, + 0.362, + 0.496, + 0.451 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.375, + 0.455, + 0.466, + 0.469 + ], + "angle": 0, + "content": "Ground-truth" + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.09, + 0.655, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.18, + 0.655, + 0.271 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.271, + 0.655, + 0.362 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.362, + 0.655, + 0.451 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.544, + 0.455, + 0.612, + 0.47 + ], + "angle": 0, + "content": "DeepSfM" + }, + { + "type": "image", + "bbox": [ + 0.658, + 0.09, + 0.811, + 0.18 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.658, + 0.18, + 0.811, + 0.271 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.658, + 0.271, + 0.811, + 0.362 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.658, + 0.362, + 0.811, + 0.452 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.718, + 0.455, + 0.754, + 0.469 + ], + "angle": 0, + "content": "Ours" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.474, + 0.893, + 0.503 + ], + "angle": 0, + "content": "Figure 7: Qualitative comparisons on ETH3D and Multi-body Unstructured. (m) The yellow boxes highlight moving objects reconstructed by our method but not by DeepSfM [36]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.528, + 0.267, + 0.544 + ], + "angle": 0, + "content": "5.2. Static evaluation (s)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.552, + 0.47, + 0.644 + ], + "angle": 0, + "content": "KITTI Depth. The Eigen SfM block of Tab. 1 reports quantitative results for static depth estimation. Our method beats the single-view methods [9, 2] and also the multi-view DeepV2D [31] in all metrics and with a clear margin. Yet Wang et al. [34] achieves better performance on this static scenes, although it recovers only up-to-scale depth maps." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.471, + 0.902 + ], + "angle": 0, + "content": "MVS, Scenes11, SUN3D. Quantitative results are shown in Tab. 2. Our method beats the single-view [9, 2] and multiview [33, 4, 29] in most metrics, but achieves results that are on par or slightly worse compared to DeepSfM [36], since we rely on monocular depth cues that are less accurate than the DeMoN depths used in DeepSfM. The best results are achieved by [34]. In the supplementary, we show that our method beats geometric SfM baselines. By setting \\( M = 1 \\) and leveraging the static scene assumption, we outperform [36] and are similar to [34]. However, when the scene is static and \\( M \\geq 2 \\) motions are considered, our method produces outlying essential matrices that may negatively impact depth estimation. Nonetheless, we achieve good results for \\( M \\geq 2 \\) and even outperform [36] in the multi-body configuration \\( M = 2 \\). For \\( M \\geq 2 \\), the performance drop is limited, indicating that \\( M \\) can be larger without affecting depth accuracy substantially." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.528, + 0.733, + 0.545 + ], + "angle": 0, + "content": "5.3. Multi-body evaluation (m)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.552, + 0.893, + 0.84 + ], + "angle": 0, + "content": "KITTI Depth. The Eigen MB and Eigen blocks of Tab. 1 report quantitative results for depth estimation in the multi-body setting. As opposed to the static case, our method beats its multi-view competitors in both the considered splits. Specifically, we observe the most significant margin in the Eigen MB split, in which dynamic objects negatively affect the quality of static multi-view depth estimators [30, 34]. This is evident in the highlighted portion of Fig. 8, where our method accurately reconstructs the moving vehicle, whereas the state-of-the-art Wang et al. [34] exhibits significant artifacts. As in the static evaluation, our framework beats monocular approaches [2, 9] in most metrics, showing it effectively leverage multi-view constraints for improved depth estimation accuracy. Less strict thresholds \\(\\delta_{2}\\), \\(\\delta_{3}\\) generally see better results for single-view methods compared to multi-view due to better handling of occlusions and image regions with uniform pixel intensity. However, monocular methods perform worse on the most strict threshold \\(\\delta_{1}\\) and the other accuracy-oriented metrics." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.894, + 0.901 + ], + "angle": 0, + "content": "ETH3D and Multi-Body Unstructured. Results on these multi-body datasets are reported in Tab. 3. Our method produces more accurate depth and camera pose estimates than its competitors in all metrics. Specifically, our method out" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "17811" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.079, + 0.09, + 0.895, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.078, + 0.157, + 0.891, + 0.173 + ], + "angle": 0, + "content": "Figure 8: Qualitative results on KITTI (m). The yellow box highlights a moving vehicle that is captured more accurately by our method." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.177, + 0.468, + 0.293 + ], + "angle": 0, + "content": "
MethodETH3DMulti-body Unstructured
DepthPoseDepthPose
L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)
DeMoN[33]0.380.410.335.6312.040.520.710.414.909.26
AdaBins[2]0.350.390.27--0.480.630.38--
DeepSIM[36]0.120.140.102.809.640.220.220.182.385.03
Wang et al.[34]0.210.190.173.269.040.270.220.192.797.67
Ours (M=1)0.110.140.102.989.580.210.220.182.215.01
Ours (M=2)0.090.120.082.918.530.190.200.171.994.91
Ours (M=3)0.080.110.082.948.280.170.190.161.944.72
Ours (M=4)0.090.110.092.948.230.170.200.171.944.70
" + }, + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.296, + 0.468, + 0.323 + ], + "angle": 0, + "content": "Table 3: Depth and pose evaluation on multi-body datasets (m). For all metrics, lower is better. Best results are in bold." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.332, + 0.47, + 0.725 + ], + "angle": 0, + "content": "performs DeMoN [33] by a significant margin and, when compared to DeepSfM [36], attains better results in depth estimation in both datasets. This is shown by the qualitative results of Fig. 7, where depth maps from DeepSfM exhibit noticeable break-ups in the areas corresponding to the moving objects. Our pose estimation is also more accurate, except for the \\(\\mathbf{R}_{\\mathrm{err}}\\) over the ETH3D dataset [28]. Overall, we attribute this difference to: i) DeepSfM suffers from poor initialization from DeMoN, which is not accurate in multi-body scenes and hinders the overall quality of the reconstruction, ii) the plane sweep algorithm adopted by DeepSfM constructs cost volumes that do not satisfy the geometric constraints for the moving objects. Our method also beats Wang et al. [34] in all metrics by a clear margin. As expected, the performance of Wang et al. suffers significantly in multi-body scenes. The moving objects are treated as outliers and negatively impact the accuracy of the estimated camera poses, which, in turn, undermine the quality of depth estimation. By segmenting the rigid motions in the scene before computing camera poses, our method exploits and is robust to the moving objects and achieves state-of-the-art performance in multi-body depth estimation. The effectiveness of multi-body plane sweep (PS) is evidenced by the uplift in performance for \\(M \\geq 2\\) in Tab. 3. Note that for \\(M = 1\\), a single motion is considered and MBPS specializes to traditional PS, with similar results to [36]." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.734, + 0.321, + 0.749 + ], + "angle": 0, + "content": "5.4. Discussion and Limitations" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.757, + 0.469, + 0.802 + ], + "angle": 0, + "content": "Our method inherits some known limitations of the multi-view approaches. In this section we discuss their possible mitigations." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.807, + 0.468, + 0.852 + ], + "angle": 0, + "content": "Small camera motions may hinder initial pose estimates. Our pose refinement network mitigates poor initializations, but it may not recover in particularly challenging cases." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Occlusions are mitigated, as in [13, 36], by aggregating cost volumes from multiple image pairs, if available. However, with only two images, occlusions result in noisy depth maps" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.18, + 0.891, + 0.21 + ], + "angle": 0, + "content": "in the region of the occluded objects, as seen in the second sequence of Fig. 7." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.219, + 0.891, + 0.28 + ], + "angle": 0, + "content": "Monocular depth inaccuracies may hinder the estimation of object scale factors. However, we observed our KDE voting scheme can isolate outlying measurements and return accurate results when enough (\\(\\sim 10\\)) factors are computed." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.288, + 0.891, + 0.378 + ], + "angle": 0, + "content": "Non-rigid scenes. Our method is not designed for non-rigid scenes, for which different assumptions are used, e.g. temporal coherence or complete reliance on monocular depth for moving objects. Nevertheless, as shown in the supplementary, our method can reconstruct articulated motions, provided that a sufficient number of motions is considered." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.387, + 0.891, + 0.478 + ], + "angle": 0, + "content": "Virtual depth planes. Our multi-body plane sweep assigns \\( L / M \\) depth planes to each motion, meaning that the more motions considered, the fewer depth planes are assigned to each motion. As stated in the supplementary, we consider up to four motions in our evaluation, as increasing the number of depth planes worsens training and inference times." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.487, + 0.891, + 0.533 + ], + "angle": 0, + "content": "Inference times are on average \\(\\sim 20\\%\\) higher in KITTI Depth with respect to [34] due to the required motion segmentation step, as discussed in the supplementary." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.554, + 0.619, + 0.569 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.892, + 0.764 + ], + "angle": 0, + "content": "In this paper, we have addressed the problem of multi-body depth and camera pose estimation. We overcome the scale-ambiguity problem typical of all the MBSfM approaches by introducing a learning-based robust voting scheme to unify the scales of all independently moving objects in the scene. In addition, we overcome the static-scene assumption of deep SfM approaches thanks to a novel multi-body plane sweep network that explicitly supports the additional multi-view geometric constraints derived from the multiple bodies. Extensive experiments on multi-body datasets show that our method outperforms state-of-the-art deep learning methods qualitatively and quantitatively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Acknowledgements. This paper is supported by FAIR (Future Artificial Intelligence Research) project, funded by the NextGenerationEU program within the PNRR-PE-AI scheme (M4C2, Investment 1.3, Line on Artificial Intelligence). We also gratefully acknowledge NVIDIA Corporation for the GPUs donated within the Academic and Applied Research Program to Giacomo Boracchi and Luca Magri" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "17812" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.17 + ], + "angle": 0, + "content": "[1] Federica Arrigoni, Elisa Ricci, and Tomas Pajdla. Multi-frame motion segmentation by combining two-frame results. International Journal of Computer Vision, 130(3):696-728, 2022. 1, 2, 3" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.171, + 0.472, + 0.24 + ], + "angle": 0, + "content": "[2] Shariq Farooq Bhat, Ibrahim Alhashim, and Peter Wonka. Adabins: Depth estimation using adaptive bins. 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Few multi-body SfM approaches address the reconstruction of multiple rigid bodies in a scene but suffer from the inherent scale ambiguity of SfM, such that objects are reconstructed at inconsistent scales. We propose a depth and camera pose estimation framework to resolve the scale ambiguity in multi-body scenes. Specifically, starting from disorganized images, we present a novel multi-view scale estimator that resolves the camera pose ambiguity and a multi-body plane sweep network that generalizes depth estimation to dynamic scenes. Experiments demonstrate the advantages of our method over state-of-the-art SfM frameworks in multi-body scenes and show that it achieves comparable results in static scenes. The code and dataset are available at https://github.com/andreadalcin/MultiBodySfM. + +# 1. Introduction + +Real-world environments often contain independently moving objects, and their reconstruction is fundamental for safe robot navigation and augmented reality in complex dynamic environments. Unfortunately, traditional and deep learning Structure-from-Motion (SfM) algorithms assume that the scene is static and treat moving objects as outliers, missing important information and producing suboptimal results when the scene is dynamic. In Fig. 1-left, the depth reconstructed by the state-of-the-art DeepSfM [36] shows artifacts in the image region of a moving object (in red). + +In this work, we go one step further and enable consistent 3D reconstruction (Fig. 1-right) of a scene with multiple rigidly moving objects. This task, also known as Multi-Body Structure-from-Motion (MBSfM), is still open and far from being solved in practice. Traditional MBSfM attempts [1, 26] segment rigid motions to obtain partial reconstructions of individually moving objects in the scene. However, these methods are hampered by the relative scale problem, namely that the 3D structure of each independ- + +Two frames of a dynamic scene with a moving object + +![](images/178cddfc24e17c5f7f7a4edcf14ada7006f3edf48bc067e74dce2af874556780.jpg) + +![](images/1a7472eb087d1a77ebf8e80aa446ec098980169bccbfe7a0dae150262fba0ea6.jpg) + +![](images/c3ae3da1e778c66969979dd534e56e4beed8ee6d123d494229c957633b978419.jpg) +Reconstructed Depth Maps of the second frame +DeepSFM +Figure 1: Two-views of a multi-body scene (top-row). Depth estimation networks (e.g. [36]) yield inconsistent depths (bottom-left) for moving objects. Our method explicitly accounts for moving objects to produce geometrically consistent depths (bottom-right). + +![](images/5ad940e9bcf992d3c8e9ab4e90a7b4246bc98fc40d98db1894a4fbbd751dcb60.jpg) +Ours + +dently moving object is estimated up to a similarity, so that each object is reconstructed in its own scale. Therefore, a unified reconstruction of all objects up to a common global scale factor is impossible without additional information. Similarly, deep methods for SfM that leverage explicit multi-view constraints [34, 36, 13, 29, 4] are affected by the relative scale problem and cannot regress a unified depth map of a multi-body scene since their underlying architecture cannot handle multiple motions. + +Recent monocular depth estimators [9, 2] use learned priors to regress dense depth maps from images without exploiting multi-view constraints. Thus, monocular methods implicitly avoid the relative scale problem by regressing consistent depth maps across the entire image. However, monocular depth estimation is inherently ill-posed and these models do not provide the same generalization capabilities of multi-view methods when scenes are static. Fur + +thermore, the 3D structures inferred from different images of the same scene are not guaranteed to be consistent. Thus, this inconsistency eventually manifests in alignment problems that are not trivial to solve. + +In this work, we present a novel deep learning framework for depth and camera pose estimation designed specifically for multi-body scenes. Following consolidated MBSfM pipelines, we perform motion segmentation to recover a set of relative camera poses up to a scale factor and the corresponding sparse 3D reconstructions of each moving object. Then, we depart from existing MBSfM approaches by directly solving the relative scale problem and regressing geometrically consistent depth maps and refined poses. + +Specifically, our main contributions are twofold: + +(1) a robust scale estimation to fix the scale ambiguity, +(2) a multi-body plane sweep network to regress refined camera poses and depth maps in multi-body scenes. + +Our scale estimator uses monocular depth maps to unify the 3D structures and camera poses under a global scale factor. This is based on a robust voting scheme that mitigates the impact of inaccuracies in monocular depth estimates. + +We adopt a deep neural network for multi-body depth estimation and pose refinement. The network adopts our novel multi-body plane sweep algorithm, which uses all the rigid motions in the scene, now devoid of scale ambiguity, to compute dense depth maps and refined camera poses. Notably, the estimated depth maps are geometrically consistent even in image regions covered by moving objects. Plane sweep has never been extended to support multiple rigid motions to the best of our knowledge. Our network also includes a pose estimation module that refines camera poses based on current depth estimates. + +We demonstrate the effectiveness of our approach on both static and multi-body scenes. On static scenes, our method performs on par with traditional and deep SfM methods. On multi-body scenes, it significantly outperforms SOTA deep learning SfM methods in the depth estimation task and achieves comparable camera pose results. + +# 2. Problem Formulation + +Multi-body depth and camera pose estimation is framed as follows. The input is a set of $n$ unstructured images $\{\mathbf{I}_i\}_{i=1}^n$ captured by a moving camera and depicting a multi-body scene in which $\mu$ objects $\mathcal{B} = \{\beta_i\}_{i=1}^\mu$ independently move according to their rigid motions. Without loss of generality, we consider the object $\beta_1$ to be static w.r.t. to the camera motion. Our goal is to estimate depth maps $\{\mathbf{D}_i\}_{i=1}^n$ for each image $\mathbf{I}_i$ and the absolute camera poses $\{\mathbf{R}_i, \mathbf{t}_i\}_{i=1}^n$ in the reference frame of $\beta_1$ . We assume that: i) an upper bound $M$ on the maximum number $\mu$ of moving objects in the scene is given, ii) the camera is perspective and its intrinsic parameters $\mathbf{K}$ are known. + +Consider that our problem is different from non-rigid + +SfM [16, 14]. Non-rigid SfM handles a wider class of object deformations but does not assume unstructured input images, typically exploiting dense temporal information, and is restricted to orthographic cameras. + +# 3. Related Work + +Depth and camera pose estimation from unstructured images of multi-body scenes is largely unexplored, and most SfM methods either consider static scenes only ( $\mu = 1$ ) or treat moving objects as outliers. This section focuses on the few SfM methods that address the multi-body scenario ( $\mu > 1$ ) from unstructured images acquired by perspective cameras. Also, we discuss monocular depth estimation, a component of our solution, and relevant deep multi-view static SfM methods. + +# 3.1. Multi-body Structure-from-Motion (MBSfM) + +A few works have addressed MBSfM from unstructured images $\{\mathbf{I}_i\}_{i = 1}^n$ as a generalization of traditional SfM to multi-body scenes. We identify two main research directions. First, early factorization methods [32, 6] segment rigidly moving objects $\mathcal{B}$ and perform sparse 3D reconstruction in a single step. However, factorization methods rely on restrictive assumptions on camera models and require complete feature tracks, which are seldom available in practice. Due to its lack of robustness, factorization has yet to see practical applications beyond short, unrealistic sequences. + +The second, more recent, research direction separates motion segmentation of objects $\mathcal{B}$ and their 3D reconstruction. [1, 26] cluster sparse correspondences based on their rigid motion and then recover the 3D structure of each object independently using a SfM pipeline [27]. As discussed in [23, 24, 17], the relative scale problem affects these methods because each object is reconstructed in its own scale. In SLAM, the relative scale problem has been addressed under specific assumptions: [23] assumes objects move in a one-parameter family of motions, and [17] works only with video input and continuous object motion. Our method also decouples motion segmentation and reconstruction. However, we explicitly address the relative scale problem using a learning-based approach without further assumptions on the input images or the motions in the scene. + +# 3.2. Monocular Depth Estimation + +Recent works [9, 2] recover a dense depth map $\mathbf{D}_1$ from a single image $\mathbf{I}_1$ . These methods learn priors to regress depth maps, allowing consistent scale reconstruction of moving objects $\mathcal{B}$ without scale ambiguity. However, due to the ill-posed nature of monocular depth estimation, generalization is limited and multi-view approaches remain the benchmark for SfM in deep learning. + +In [20, 38], monocular depth maps are estimated from video frames, and then a network is fine-tuned on the entire + +![](images/99bf2b6261462b2a67043da592310cfbfa4df27273c256d5e0c2072f6070f454.jpg) +Figure 2: The three main steps of our method: i) motion segmentation: produces a set of essential matrices describing the rigid motion of objects between view pairs. ii) robust scale estimation: uses monocular depth cues to fix the scale ambiguity of each moving object. iii) multi-body plane-sweep network based on our novel multi-body plane-sweep regress refined depth maps and camera poses. + +video sequence. These methods do not assume unstructured images and require many frames for depth and pose tracking and fine-tuning. In addition, depth estimation for moving objects still relies solely on depth priors, which can lead to inaccuracies as in standard monocular depth estimation. + +# 3.3. Deep Learning for SfM + +Deep learning methods for SfM from unstructured images regress camera poses and dense depth maps using multi-view stereo matching. DeMoN [33] works on image pairs using stacked encoder-decoder networks but lacks explicit multi-view constraints and has limited accuracy. More recent architectures [29, 4, 36, 34, 13, 31] replace the generic encoder-decoder architecture with layers that explicitly enforce multi-view constraints. Other works achieve better results by taking inspiration from traditional Bundle Adjustment: DeepSfM [36] introduces depth and pose cost volumes for iterative refinement, and [29] uses a BA-layer for regression from basis depth maps. Wang et al. [34] propose a scale-invariant network for depth and pose estimation for view pairs. Specifically, camera poses are estimated from essential matrices robustly fitted on fine-tuned optical flow matches, thus treating all moving objects as outliers. Then, depth maps are regressed end-to-end using a CNN similar to DeepSfM. Finally, [4] optimizes non-linear cost functions in SfM using recurring neural networks. + +As the above deep methods embed explicit multi-view geometric constraints in their optimization layers, they are affected by the scale ambiguity of traditional MBSfM and cannot generalize to multi-body scenes, as shown in Fig. 1. + +# 4. Method + +Our method, illustrated in Fig. 2, is structured in three steps. First, given the unstructured images $\{\mathbf{I}_i\}_{i=1}^n$ , we perform motion segmentation from image pairs $\alpha$ to estimate essential matrices $\{\mathbf{E}_k^\alpha\}_{j=1}^\mu$ that encode the $\mu$ rigid mo + +tions in the scene. Second, we fix the scale ambiguity of each $\mathbf{E}_k^\alpha$ by exploiting cues provided by monocular depth maps $\{\mathbf{M}_i\}_{i=1}^n$ in a robust scale estimation module. Finally, a multi-view depth and camera pose estimation network leverages our novel multi-body plane sweep algorithm to regress geometrically-consistent depth maps $\{\mathbf{D}_i\}_{i=1}^n$ and camera poses $\{\mathbf{R}_i, \mathbf{t}_i\}_{i=1}^n$ by considering all the $\mu$ motions. + +# 4.1. Motion segmentation + +The goal of motion segmentation is to recover the essential matrices $\{\mathbf{E}_k^\alpha\}_{k=1}^\mu$ that encode all rigid motions in the scene in any image pair $\alpha = (\mathbf{I}_i, \mathbf{I}_j)$ . To this end, we combine traditional sparse motion segmentation, based on SIFT [19], with dense deep optical flow matches. + +For each image $\mathbf{I}_i$ , we extract $\{x_{i,u}\}_{u = 1}^{p_i}$ SIFT keypoints and match them across image pairs. Then, for each pair $\alpha$ , we fit $\mu$ essential matrices $\{\mathbf{E}_k^\alpha J_{k = 1}^\mu\}$ to the matches using RPA [21], a multi-model fitting algorithm. RPA provides a labeling $\ell^{\alpha}$ that assigns a matched keypoint to the motion it belongs to. Labels assigned to different image pairs may be inconsistent, thus we use permutation synchronization [1] to enforce a global labelling $\ell$ that assigns to keypoints belonging to the same motion the same label in all views. + +In multi-body scenes, moving objects can be supported by only a few keypoints. Therefore, to refine the essential matrices, we augment the set of sparse matches with dense ones computed from the optical flow. Similarly to [34], we consider the dense matches at keypoint locations and, thus, avoid the typical inaccuracies of the optical flow caused by illumination changes and texture-less regions. In particular, given an image pair $\alpha = (\mathbf{I}_i,\mathbf{I}_j)$ , for each object $\beta_{k}\in \mathcal{B}$ we consider $U_{k}^{i} = \{x_{i,u}:\ell (x_{i,u}) = k\}$ the sparse keypoints in $\mathbf{I}_i$ labelled as $k$ . Around each keypoint $x\in U_k^i$ we consider a squared neighborhood $N(x)$ of $3\times 3$ pixels. The union of neighborhoods $S_{k}^{i} = \bigcup_{x\in U_{k}^{i}}N(x)$ defines a mask in $\mathbf{I}_i$ as illustrated in Fig. 2. We refine $\mathbf{E}_k^\alpha$ by RANSAC equipped with the 5-point algorithm [22, 18] on the set of all + +![](images/ca029ad142b03b154915006723fecf7efe28d4be8da23070a80a49d8e047fa47.jpg) +Figure 3: (left) In a multi-body scene, the scale of triangulated structures (orange) differs from the true object scale (cyan), leading to inconsistent relative object scales, i.e., cube bigger than pyramid. The tentative scale factor $\lambda_{i,u}^{1}$ of $X_{u}^{1} \in \beta_{1}$ is the ratio of the monocular depth $m_{i,u}^{1}$ and its triangulated depth $d_{i,u}^{1}$ . (right) Traditional plane sweep [5] vs. our novel multi-body plane sweep. + +![](images/6dc5dd46bef3093738ccaf81dcdef7bc2a36d9517f8070fe80f25268ba922cf9.jpg) + +![](images/106bd788b20efe4c9aab564588b1343350ea1c550223c3768a24eff46ca0a387.jpg) + +the dense matches corresponding to the mask $S_{k}^{i}$ . The optical flow is computed using the DICL-Flow network [35]. + +# 4.2. Robust Scale Estimation + +We factorize each essential matrix $\mathbf{E}_k^\alpha = [\tilde{\mathbf{t}}_k^\alpha ]_\times \tilde{\mathbf{R}}_k^\alpha$ to obtain the relative camera pose as a rotation $\tilde{\mathbf{R}}_k^\alpha$ and translation $\tilde{\mathbf{t}}_k^\alpha$ . Since each $\tilde{\mathbf{t}}_k^\alpha$ is recovered only up to an unknown scale-factor $\lambda_{k}$ , each moving object in a multi-body scene is reconstructed in its own arbitrary scale $\lambda_{k}$ . Specifically, given an image pair $\alpha$ , we can triangulate from matched image points a set of 3D points $\{X_u^k\}_{u = 1}^{p_k}$ belonging to object $\beta_{k}$ from the up-to-scale camera pose $\{\tilde{\mathbf{R}}_k^\alpha ,\tilde{\mathbf{t}}_k^\alpha \}$ . However, these 3D points are expressed in the scale $\lambda_{k}$ of $\tilde{\mathbf{t}}_k^\alpha$ , meaning that different objects refer to inconsistent scales. Fig. 3-left depicts a multi-body scene where the scale ambiguity manifests as an inconsistent relative scale between objects $\lambda_{1}\beta_{1}$ and $\lambda_{2}\beta_{2}$ in the triangulated scene (orange) w.r.t. the actual 3D scene (cyan). Thus, the cube $\lambda_{1}\beta_{1}$ appears larger than the pyramid $\lambda_{2}\beta_{2}$ in the reconstruction. + +We estimate the unknown scale factor $\lambda_{k}$ for each object $\beta_{k}$ by first regressing a monocular depth map $\mathbf{M}_i$ from each image $\mathbf{I}_i$ using AdaBins [2]. This network processes each $\mathbf{I}_i$ individually and, thus, is not affected by the multi-view scale ambiguity. We denote by $d_{i,u}^{k}$ and by $m_{i,u}^{k}$ the triangulated and monocular depths respectively of the $u$ -th 3D point $X_{u}^{k}$ w.r.t. $\mathbf{I}_i$ . Then, for each object $\beta_{k}$ and image $\mathbf{I}_i$ , we compute the point-wise scale factor $\lambda_{i,u}^{k} = d_{i,u}^{k} / m_{i,u}^{k}$ that approximates the real $\lambda_{k}$ according to the triangulated and monocular depths of $X_{u}^{k}$ . + +As monocular depth maps generally lack in accuracy, we devise a voting scheme to robustly aggregate the scale factors from all images $\{\mathbf{I}_i\}_{i = 1}^n$ and unify all the $\mu$ camera poses under a global scale factor $\lambda$ . First, we partition the point-wise scale factors computed from all the images into $\mu$ sets $\Lambda_{k} = \{\lambda_{i,u}^{k}\}_{i = 1,u = 1}^{n,p_{k}}$ according to their object $\beta_{k}$ . Then, to promote robustness, we adopt a Kernel Density Estimator and derive a probability density function $\phi_{k}$ from each $\Lambda_{k}$ . We use a Gaussian Kernel $\mathcal{K}$ with bandwidth $h$ set + +at $5\%$ of the median of the elements in $\Lambda_{k}$ and define the kernel $\phi_{k}$ as follows: + +$$ +\phi_ {k} (x) = \sum_ {\lambda_ {i, u} ^ {k} \in \Lambda_ {k}} \frac {\mathcal {K} \left(\lambda_ {i , u} ^ {k} - x\right)}{h}. \tag {1} +$$ + +The highest peak of $\phi_{k}$ is denoted by $\hat{\lambda}_{k}$ and represents the estimate of the $k$ -th object scale factor $\lambda_{k}$ . The estimated $\{\hat{\lambda}_k\}_{k = 1}^\mu$ are used to scale the pairwise relative camera poses $[\tilde{\mathbf{R}}_k^\alpha ,\hat{\lambda}_k^{-1}\tilde{\mathbf{t}}_k^\alpha ]$ by multiplying the translation component. Now, camera poses are aligned to a global scale factor $\lambda$ . As depths $\mathbf{M}_i$ are regressed in real-world unit of measurement, $\lambda \approx 1$ , i.e., camera poses should be approximately in their real-world scale. We denote the correctly scaled camera poses as $[\hat{\mathbf{R}}_k^\alpha ,\hat{\mathbf{t}}_k^\alpha ]$ and use this unified camera configuration as the initialization for the next step. + +# 4.3. Multi-body Plane Sweep Network + +Although the poses $\{\hat{\mathbf{R}}_k^\alpha, \hat{\mathbf{t}}_k^\alpha\}$ are now aligned to a single scale factor, the depths are only estimated from monocular maps $\mathbf{M}_i$ which ignore the multi-view constraints. In principle, it could be possible to use camera poses to initialize a multi-view iterative scheme where depths and poses are refined, as in [36], but this would regress inconsistent depths in regions corresponding to moving objects. Thus, we design a novel multi-body depth and pose estimation network that takes the unordered images $\{\mathbf{I}_i\}_{i=1}^n$ and the scale-consistent poses $\{\hat{\mathbf{R}}_k^\alpha, \hat{\mathbf{t}}_k^\alpha\}$ to jointly estimates geometrically consistent depth maps $\{\mathbf{D}_i\}_{i=1}^n$ and refined poses $\{\mathbf{R}_i, \mathbf{t}_i\}_{i=1}^n$ in the reference frame of object $\beta_1$ . As shown in Fig. 4, we include two separate branches for depth and pose estimation, which are used alternatively in an iterative scheme using the output of the other branch as input. + +# 4.3.1. Multi-body Depth Estimation Branch + +As depicted in Fig. 4, our depth estimation branch is based on our novel multi-body plane sweep and concatenates the following modules. + +![](images/f952cf292e0706cb42a8a330f4798125d97621971a2e9637d9a94fbc23a77049.jpg) +Figure 4: Multi-body Plane Sweep network. We extract CNN features from input images and build a cost volume using our multi-body plane sweep algorithm. Depth and camera poses are regressed from separate cost volumes with a series of 3D CNN and refinement layers. + +Feature Extraction. A multi-scale CNN with spatial pyramid pooling [12] extracts features $\{\mathbf{F}_i\}_{i=1}^n$ from images $\{\mathbf{I}_i\}_{i=1}^n$ . Each $\mathbf{F}_i$ has dimension $\mathbf{C} \times \mathbf{W} \times \mathbf{H}$ , where $\mathbf{C}$ , $\mathbf{W}$ , $\mathbf{H}$ are feature channels, width and height respectively. + +Multi-body Plane Sweep for Cost Volume Construction. Let us briefly recall how the traditional plane sweep works before describing our contributions. The traditional plane sweep algorithm [5] takes as input an image pair $\alpha$ of a source $\mathbf{I}_i$ and target $\mathbf{I}_j$ and their relative pose $[\mathbf{R}^\alpha, \mathbf{t}^\alpha]$ . The algorithm samples a set of virtual planes parallel to $\mathbf{I}_j$ at fixed depths $\{d_l\}_{l=1}^L$ . Then, for each depth $d_l$ , the source $\mathbf{I}_i$ is warped onto the target $\mathbf{I}_j$ through the homography induced by the plane at $d_l$ and the relative camera pose $[\mathbf{R}^\alpha, \mathbf{t}^\alpha]$ , as in Fig. 3-right. A dense depth map is obtained by selecting, for each pixel, the depth $d_l$ that minimizes a pixel-wise photometric dissimilarity between the target $\mathbf{I}_j$ and the warped source $\mathbf{I}_i$ . Deep methods [13, 36, 34] revisited this framework, but measure feature metric consistency between latent features $\{\mathbf{F}_i\}_{i=1}^n$ instead of photometric dissimilarity. To this end, warped source and target features are aggregated in a single depth cost volume from which depths are regressed through convolutional layers. Unfortunately, both traditional and deep plane sweep methods assume static scenes with a single relative camera pose $[\mathbf{R}^\alpha, \mathbf{t}^\alpha]$ between the pair $\alpha$ . As a result, any point belonging to a moving object has an inconsistent depth. + +We propose instead a multi-body plane sweep that considers all the $\mu$ relative poses $\{\hat{\mathbf{R}}_k^\alpha, \hat{\mathbf{t}}_k^\alpha\}_{k=1}^\mu$ to warp a source feature $\mathbf{F}_i$ onto a target $\mathbf{F}_j$ and construct the depth cost volume. Given a source-target pair $\alpha = (\mathbf{I}_i, \mathbf{I}_j)$ , we uniformly sample $L$ 3D virtual planes at depths $\{d_l\}_{l=1}^L$ parallel to the source $\mathbf{I}_i$ . Then, we sequentially assign each depth plane to one of the $\mu$ relative camera poses by cycling through the $\{\hat{\mathbf{R}}_k^\alpha, \hat{\mathbf{t}}_k^\alpha\}_{k=1}^\mu$ . Thus, the individual features $\mathbf{F}_i$ of the object $\beta_k$ are warped onto $\mathbf{F}_j$ in a geometrically consistent manner when considering any depth plane assigned to the camera pose $[\hat{\mathbf{R}}_k^\alpha, \hat{\mathbf{t}}_k^\alpha]$ relative to $\beta_k$ . This is depicted in + +Fig. 3-right, utilizing color to illustrate the cyclic assignment of the $k$ -th and $h$ -th rigid motions to planes at $d_{l}$ and $d_{l+1}$ , respectively, and to subsequent planes. Finally, each point $u$ in the source feature $\mathbf{F}_{i}$ is first back-projected onto the virtual planes at $d_{l}$ and then re-projected as $\tilde{u}_{lk}$ on the target $\mathbf{F}_{j}$ as follows: + +$$ +\tilde {\mathbf {F}} _ {i l} ^ {k} (u) = \mathbf {F} _ {i} (\tilde {u} _ {l k}), \tilde {u} _ {l k} \sim \mathbf {K} \left[ \hat {\mathbf {R}} _ {k} ^ {\alpha} | \hat {\mathbf {t}} _ {k} ^ {\alpha} \right] \left[ \begin{array}{c} (\mathbf {K} ^ {- 1} u) d _ {l} \\ 1 \end{array} \right], \tag {2} +$$ + +where $\tilde{\mathbf{F}}_{il}^{k}$ is the warped source feature through the homography induced by the plane at $d_{l}$ and the motion $[\hat{\mathbf{R}}_k^\alpha ,\hat{\mathbf{t}}_k^\alpha ]$ + +Cost volume Construction. Given the set of virtual depth planes $\{d_l\}_{l = 1}^L$ , for each $d_{l}$ , we obtain a warped source feature $\tilde{\mathbf{F}}_{il}^{k}$ using Eq. 2 and concatenate it to the target feature $\mathbf{F}_j$ . This yields a set of $L$ feature blocks, each sized $2\mathrm{C} \times \mathrm{W} \times \mathrm{H}$ , that we arrange into a 4D depth cost volume sized $2\mathrm{C} \times L \times \mathrm{W} \times \mathrm{H}$ , as illustrated in Fig. 5. Since the number of virtual planes is significantly higher than the number of motions, all the $\mu$ motions are assigned to some virtual planes. Thus, our cost volume jointly incorporates all the motions in the scene, unlike traditional plane-sweep methods that assume a single motion. + +Cost volume Regularization. Regularizing the cost volume is fundamental to cope with imperfect latent feature matching, which is especially common in image regions corresponding to texture-less objects or uniform pixel intensity. To this end, we use a sequence of 3D convolutional layers consisting of $L / 2$ filters of size $3\times 3\times 3$ with stride 1, and residual connections. Then, we apply a 3D convolution with a single $3\times 3\times 3$ filter to obtain a 3D cost volume of size $L\times \mathrm{W}\times \mathrm{H}$ . Since the order of the stacked features in the cost volume follows the correct virtual plane sequence, 3D convolutional layers can capture the 3D dependencies in the scene to enable consistent depth map estimation. Finally, we apply edge-preserving filtering to the resulting cost volume as in [13, 11]. In the case of multiple source-target image pairs, the final 3D cost volume is obtained by aver + +aging the 3D cost volumes from each pair. Further details on the cost volume can be found in the supplementary. + +Depth Regression. We denote as $c_{l}$ each slice of the aggregated cost volume, which corresponds to a plane at $d_{l}$ . Then, we convert the aggregated cost volume to a probability volume as in [15] and use the softmax operation $\sigma$ to normalize the probability volume across the depth dimension. We estimate the depth map $\mathbf{D}_i$ for a view $\mathbf{I}_i$ as follows: + +$$ +\mathbf {D} _ {i} = \frac {L \times d _ {\operatorname* {m i n}}}{\tilde {l}}, \tilde {l} = \sum_ {l = 1} ^ {L} l \times \sigma \left(c _ {l}\right), \tag {3} +$$ + +where $\tilde{l}$ is the map corresponding to the average of virtual plane depths $l\in \{1,\dots ,L\}$ , weighted by the probabilities $\sigma (c_l)$ . In (3), $d_{\mathrm{min}}$ denotes the depth of the closest plane to the source image. + +# 4.3.2. Pose Estimation Branch + +We describe our pose estimation branch, which optimizes current camera pose estimates through feature-metric consistency. To this purpose, we use a network architecture akin to the one in [36]. The network receives a pair $\alpha = (\mathbf{I}_i,\mathbf{I}_j)$ , the depth map $\mathbf{D}_i$ of $\mathbf{I}_i$ and $[\hat{\mathbf{R}}_1^\alpha ,\hat{\mathbf{t}}_1^\alpha ]$ , the current camera pose estimate in the reference frame of $\beta_{1}$ , to regress a refined $[\mathbf{R}_1^\alpha ,\mathbf{t}_1^\alpha ]$ . We uniformly sample $P$ tentative camera poses $\{\hat{\mathbf{R}}_{1p}^{\alpha},\hat{\mathbf{t}}_{1p}^{\alpha}\}_{p = 1}^{P}$ by perturbing the rotation and the translation of the initial poses $[\hat{\mathbf{R}}_1^\alpha ,\hat{\mathbf{t}}_1^\alpha ]$ . The $P$ poses are used to construct a pose cost volume by warping each point $u$ in the source feature $\mathbf{F}_i$ to a point $\tilde{u}_p$ on the target feature $\mathbf{F}_j$ as follows: + +$$ +\tilde {u} _ {p} \sim \mathbf {K} \left[ \hat {\mathbf {R}} _ {1 p} ^ {\alpha} \mid \hat {\mathbf {t}} _ {1 p} ^ {\alpha} \right] \left[ \begin{array}{c} \left(\mathbf {K} ^ {- 1} u\right) \mathbf {D} _ {i} (u) \\ 1 \end{array} \right]. \tag {4} +$$ + +Finally, a sequence of 3D convolutional layers is applied to the pose cost volume to regress the camera pose $\left[\mathbf{R}_1^\alpha ,\mathbf{t}_1^\alpha \right]$ . + +![](images/65f30614b2fa0778b2be90f2efe26ad89de0e65d696cd261a377683944aa6a02.jpg) +Figure 5: Cost volume construction by multi-body plane sweep. For each virtual depth plane at $d_{l} \in \{d_{l}\}_{l=1}^{L}$ , we generate a $2\mathbf{C} \times \mathbf{W} \times \mathbf{H}$ feature map by concatenating the target feature $\mathbf{F}_j$ (gray) to the warped source feature $\tilde{\mathbf{F}}_{il}^{\gamma}$ (in color) at depth $d_{l}$ using motion $[\hat{\mathbf{R}}_{\gamma}^{\alpha}, \hat{\mathbf{t}}_{\gamma}^{\alpha}]$ . The 4D cost volume is constructed through concatenation of these $L$ feature blocks. $\tilde{\mathbf{F}}_{il}^{k}$ (in blue) indicates a source feature $\mathbf{F}_i$ warped onto $\mathbf{F}_j$ through the homography induced by the generic plane at $d_{l}$ and its relative camera motion $[\hat{\mathbf{R}}_k^{\alpha}, \hat{\mathbf{t}}_k^{\alpha}]$ . Instead, $\tilde{\mathbf{F}}_{il}^{h}$ is induced by the motion $[\hat{\mathbf{R}}_h^{\alpha}, \hat{\mathbf{t}}_h^{\alpha}]$ (in pink). + +
viewMethodlower is better ↓higher is better ↑
Abs RelSq RelRMSERMSElogδ1δ2δ3
Eigen SM (s)svDORN [9]0.0670.2952.9290.1080.9490.9880.995
AdaBins [2]0.0540.1822.3410.0870.9660.9950.999
mvDeepV2D [31]0.0500.2122.4830.0890.9730.9920.997
Wang et al. [34]0.0340.1031.9190.0570.9890.9980.999
Ours0.0440.1482.1250.0680.9740.9960.999
Eigen (s & m)svDORN [9]0.0720.3072.7270.1200.9320.9840.994
AdaBins [2]0.0580.1902.3600.0880.9640.9950.999
mvSfMLearner [39]0.2081.7686.8560.2830.6780.8850.975
CCNet [25]0.1401.0705.3260.2170.8260.9410.975
BANet [29]0.083-3.6400.134---
DeepV2D [31]0.0640.3502.9460.1200.9460.9820.991
Wang et al. [34]0.0550.2242.2730.0910.9560.9840.993
Ours0.0540.1862.2690.0860.9660.9910.996
Eigen MB (m)svDORN [9]0.0720.3072.7270.1200.9320.9840.994
AdaBins [2]0.0620.2012.3720.0920.9590.9940.999
mvDeepV2D [31]0.0890.4013.2780.1520.9310.9650.989
Wang et al. [34]0.0630.2422.3470.1090.9480.9710.991
Ours0.0570.1972.3010.0900.9620.9910.994
+ +Table 1: Depth evaluation on KITTI Depth. Results from single-view (sv) and multi-view (mv) depth estimation methods evaluated under two-view SfM setting. Best results in bold. + +# 4.3.3. Training and Inference + +We train the feature extractor, 3D convolutions and regression layers in a end-to-end supervised manner. We denote as $\mathbf{D}$ the depth regressed from the refined cost volume, and as $\mathbf{D}_{\mathrm{gt}}$ the ground-truth depth. To improve the learning process, we also regress a depth map $\tilde{\mathbf{D}}$ from the cost volume before applying edge-preserving filtering. The loss function is defined as $\mathcal{L}_{\mathrm{depth}} = \sum_{i}\lambda H(\tilde{\mathbf{D}},\mathbf{D}_{\mathrm{gt}}) + H(\mathbf{D},\mathbf{D}_{\mathrm{gt}})$ , where $\lambda = 0.7$ is a weight and $H(\cdot)$ is the Huber loss. The pose losses $\mathcal{L}_{\mathrm{rot}}$ and $\mathcal{L}_{\mathrm{trans}}$ are defined as the $\ell_1$ distance between the predicted and ground-truth absolute poses. Our final loss is then: $\mathcal{L} = \lambda_r\mathcal{L}_{\mathrm{rot}} + \lambda_t\mathcal{L}_{\mathrm{trans}} + \lambda_d\mathcal{L}_{\mathrm{depth}}$ . All the weights are specified in the supplementary. + +The multi-body plane sweep component of the network has no learnable parameters and is not trained. Our network does not require any form of motion annotation for depth estimation, even in multi-body scenes. For this reason, we train our model on static frames from KITTI [10] and DeMoN [33]. The training and inference are performed in an iterative fashion in four steps, where the regressed depth maps and camera poses are fed to the next iteration. + +# 5. Experiments + +We evaluate our method on static (s) and multi-body (m) datasets for depth and pose estimation against state-of-the-art single-view (sv) and multi-view (mv) methods. In Sec. 5.4 we discuss the limitations of our method and possible countermeasures. Additional experiments and implementation details are provided in the supplementary. + +# 5.1. Datasets, Competitors and Metrics + +KITTI Depth (s & m) [10] is designed for depth evaluation in autonomous driving and contains several image se + +![](images/d8cd6d34c49eb9fafc251a11fe0b23a7b2b2bebeb556df11a195544de7d52502.jpg) +Figure 6: Multi-body Unstructured Extract. Three view pairs extracted from our proposed dataset for illustration purposes. The dataset contains indoor sequences that depict varied scenarios in which objects of several different sizes move in the scene. + +![](images/15dd3fed94c621f86d5edc96b54f2ae56a90b0af432dccd333f4ab0f910360ac.jpg) + +![](images/f635c5d702c084bed50b68d42556fe612894ee4ec25e12405ddf67a7019e65e8.jpg) + +
MethodMVSScenes11SUN3D
DepthPoseDepthPoseDepthPose
L1-invSc-invL1-rel\( R_{err} \)\( t_{err} \)L1-invSc-invL1-rel\( R_{err} \)\( t_{err} \)L1-invSc-invL1-rel\( R_{err} \)\( t_{err} \)
AdaBins [2]0.0480.2360.291--0.0200.3820.270--0.0210.1270.161--
DeMoN [33]0.0470.2020.3055.15614.4470.0190.3150.2480.8098.9180.0190.1140.1721.80118.811
LS-Net [4]0.0510.2210.3114.65311.1220.0100.4100.2104.6538.2100.0150.1890.6501.52114.347
BA-Net [29]0.0300.1500.0803.49911.2380.0800.2100.1303.49910.3700.0150.1100.0601.72913.260
DeepSfM [36]0.0210.1290.0792.8249.8810.0070.1120.0640.4035.8280.0130.0930.0721.70413.107
Wang et al. [34]0.0150.1020.0682.4173.8780.0050.0970.0580.2762.0410.0100.0810.0571.39110.757
Ours (M=1)0.0160.1070.0682.5384.5380.0050.0990.0580.3213.6490.0110.0840.0611.47012.018
Ours (M=2)0.0190.1210.0732.6817.3400.0070.1020.0690.4014.6190.0130.0920.0711.62513.402
Ours (M=3)0.0250.1320.0752.8929.5300.0090.1240.0780.5425.7820.0140.0950.0791.76915.231
Ours (M=4)0.0260.1340.0762.9319.7410.0090.1280.0810.5715.8030.0160.1070.0841.83015.904
+ +Table 2: Depth and pose evaluation on MVS, Scenes 11, SUN3D. (s). For all metrics lower is better. Best results are in bold. + +quences where objects move rigidly. We consider the Eigen [7] split (697 frames) and the Eigen SfM split [34] (256 frames), a subset of the Eigen split without moving objects. In addition, we introduce the Eigen MB split, a subset of the Eigen split that includes 90 frames in which dynamic objects appear and camera motions are well-conditioned. + +MVS, Scenes11, SUN3D. (s) MVS [33] includes outdoor sequences with large baselines. Scenes11 [33] contains fairly realistic frames from rendered scenes with accurate ground truth depth and camera poses. SUN3D [37] is an indoor dataset with sometimes inaccurate ground truth depth and camera poses. For SUN3D, we consider the split by [33] to exclude frames with high photoconsistency errors. + +ETH3D SLAM. (m) [28] contains SLAM sequences with ground truth depth and camera poses. We consider the dynamic sequences motion1-2-3-4 and, specifically, a 32 frames split where camera motions are well-conditioned. + +Multi-body Unstructured. (m) We capture multi-body indoor sequences using a Kinect with ground truth depth. The dataset is meant for evaluation in varied conditions, for instance, when image sets are unstructured or when both large and big objects move in the scene. We use RGB-D SLAM [8] to fuse visual information and data from the Kinect IMU and annotate accurate camera poses. The dataset includes 42 frames with either one or two moving objects. Samples scenes are reported in Fig.6 and additional details are provided in the supplementary. + +Competitors. We compare against state-of-the-art single-view methods (sv) DORN [9] and AdaBins [2], and multiview methods (mv) DeMoN [33], LS-Net [3], CCNet [25], BANet [29], DeepV2D [31] and Wang et al. [34]. De + +MoN estimates depth and poses from image pairs, CCNet and SfMLearner mask moving objects before depth and pose estimation, LS-Net, BANet and DeepV2D optimize multi-view differentiable cost functions to minimize photo- or feature-metric errors, and Wang et al. [34] proposes a deep, scale-invariant estimator for depth and camera poses that robustly identify the dominant background motion $\beta_{1}$ . + +Metrics. To evaluate the quality of depth maps in KITTI Depth, we adopt the metrics in [7], i.e., the depth absolute (Abs Rel) and squared (Sq Rel) relative difference, the RMSE, the $\mathrm{RMSE}_{\log}$ , and the thresholds $\{\delta_i\}_{i=1}^3$ . For other datasets, we adopt the metrics in [33], i.e., scale-invariant depth error (sc-inv), relative error to ground truth depth (L1-rel), relative error w.r.t. inverse depth (L1-inv). The definitions of these metrics are in the supplementary. As for pose estimation, we report the angle (in deg) between predicted and ground truth translations $(t_{\mathrm{err}})$ and rotations $(\mathbf{R}_{\mathrm{err}})$ of the cameras with respect to the background motions $\beta_1$ . + +Implementation Details. We fine-tune the optical flow network on KITTI Depth for a fair comparison to [34]. Otherwise, we train the optical flow on synthetic scenes, as in [35], and let the proposed framework refine initial camera poses. We implement our framework using PyTorch. The batch size is set to 32. The learning rate is set to $1 \times 10^{-4}$ and is halved after 2 epochs. For KITTI Depth, the feature extractor is initialized with pre-trained weights, which are frozen for the first epoch. For other datasets, we train the network from randomly initialized weights. Training takes approximately 3 days on 2 NVIDIA RTX A6000 GPUs. Further details are reported in the supplementary. + +![](images/5b55cf973b5a54e27f4878659743b79cbaf37ba986258ab76f727a0ec9053706.jpg) + +![](images/295af6aa0eac1fafa1c55dfee975d4907e0d360ee0b07f7cadeb3c3a7a22e19c.jpg) + +![](images/f579030b41183ce8742c01f5d1bfd105521fcda654419ae3858644f85bd03e5b.jpg) + +![](images/1cdf7dbbc8bce09b72a0cd0e2919433667dd4e1f5ebad9bc9ec3edd6dfd7a748.jpg) +Reference images + +![](images/db469caba8d10e2a8891200250dd6905ac8fb87fbcc325bd1873ccd3ba6d3650.jpg) + +![](images/bb624a27c1be6acdec16cd6dd82b81f1bcaea31c5e80badaf2014716d5b49028.jpg) + +![](images/129cd53d864530fa9dc2cd6605235c1a094a1f7ca910238ef6204c93984af434.jpg) + +![](images/2228f801dbbacd056be4165bc86f27a3a6372c66123a33e44eacd7fdffa5aea2.jpg) +Ground-truth + +![](images/e6292db839f03c75756a353fd21a743044ead249761f4e8a77b871b7105ae283.jpg) + +![](images/90520681561b5094d7b1c1af521575e9acf271d721d3232ac3c1884df01e97b9.jpg) + +![](images/90b5decd8276bcb2c99ca25e835a493a13ab1504fbcdc52a980822c6a604bae2.jpg) + +![](images/c208eab3af923fd46ec93a827391877fe798cfb203e1d4ee068f7943ef4cf0e9.jpg) +DeepSfM +Figure 7: Qualitative comparisons on ETH3D and Multi-body Unstructured. (m) The yellow boxes highlight moving objects reconstructed by our method but not by DeepSfM [36]. + +![](images/f9f856427c97101989ee11d5c48c05d6bbc1ab080f8e80a76d0f14190f6e4ab3.jpg) + +![](images/2e4e42a3baf8172b8884d487d06a9621ea154db84317e7ff6ad19ce601310aad.jpg) + +![](images/3fa7e07828de964815fcad1237a36db4db8fb5f641710969b833420156e2ac34.jpg) + +![](images/2df2c4d5e497a34186dfff6a4946b639aa9902f5e83c397bea0588a44efbc3e4.jpg) +Ours + +# 5.2. Static evaluation (s) + +KITTI Depth. The Eigen SfM block of Tab. 1 reports quantitative results for static depth estimation. Our method beats the single-view methods [9, 2] and also the multi-view DeepV2D [31] in all metrics and with a clear margin. Yet Wang et al. [34] achieves better performance on this static scenes, although it recovers only up-to-scale depth maps. + +MVS, Scenes11, SUN3D. Quantitative results are shown in Tab. 2. Our method beats the single-view [9, 2] and multiview [33, 4, 29] in most metrics, but achieves results that are on par or slightly worse compared to DeepSfM [36], since we rely on monocular depth cues that are less accurate than the DeMoN depths used in DeepSfM. The best results are achieved by [34]. In the supplementary, we show that our method beats geometric SfM baselines. By setting $M = 1$ and leveraging the static scene assumption, we outperform [36] and are similar to [34]. However, when the scene is static and $M \geq 2$ motions are considered, our method produces outlying essential matrices that may negatively impact depth estimation. Nonetheless, we achieve good results for $M \geq 2$ and even outperform [36] in the multi-body configuration $M = 2$ . For $M \geq 2$ , the performance drop is limited, indicating that $M$ can be larger without affecting depth accuracy substantially. + +# 5.3. Multi-body evaluation (m) + +KITTI Depth. The Eigen MB and Eigen blocks of Tab. 1 report quantitative results for depth estimation in the multi-body setting. As opposed to the static case, our method beats its multi-view competitors in both the considered splits. Specifically, we observe the most significant margin in the Eigen MB split, in which dynamic objects negatively affect the quality of static multi-view depth estimators [30, 34]. This is evident in the highlighted portion of Fig. 8, where our method accurately reconstructs the moving vehicle, whereas the state-of-the-art Wang et al. [34] exhibits significant artifacts. As in the static evaluation, our framework beats monocular approaches [2, 9] in most metrics, showing it effectively leverage multi-view constraints for improved depth estimation accuracy. Less strict thresholds $\delta_{2}$ , $\delta_{3}$ generally see better results for single-view methods compared to multi-view due to better handling of occlusions and image regions with uniform pixel intensity. However, monocular methods perform worse on the most strict threshold $\delta_{1}$ and the other accuracy-oriented metrics. + +ETH3D and Multi-Body Unstructured. Results on these multi-body datasets are reported in Tab. 3. Our method produces more accurate depth and camera pose estimates than its competitors in all metrics. Specifically, our method out + +![](images/f7440bd1a5b7b51da9d3b215bfac406556f97d4169fa0001faa916090a072787.jpg) +Figure 8: Qualitative results on KITTI (m). The yellow box highlights a moving vehicle that is captured more accurately by our method. + +
MethodETH3DMulti-body Unstructured
DepthPoseDepthPose
L1-invSc-invL1-rel\( R_{err} \)\( t_{err} \)L1-invSc-invL1-rel\( R_{err} \)\( t_{err} \)
DeMoN[33]0.380.410.335.6312.040.520.710.414.909.26
AdaBins[2]0.350.390.27--0.480.630.38--
DeepSIM[36]0.120.140.102.809.640.220.220.182.385.03
Wang et al.[34]0.210.190.173.269.040.270.220.192.797.67
Ours (M=1)0.110.140.102.989.580.210.220.182.215.01
Ours (M=2)0.090.120.082.918.530.190.200.171.994.91
Ours (M=3)0.080.110.082.948.280.170.190.161.944.72
Ours (M=4)0.090.110.092.948.230.170.200.171.944.70
+ +Table 3: Depth and pose evaluation on multi-body datasets (m). For all metrics, lower is better. Best results are in bold. + +performs DeMoN [33] by a significant margin and, when compared to DeepSfM [36], attains better results in depth estimation in both datasets. This is shown by the qualitative results of Fig. 7, where depth maps from DeepSfM exhibit noticeable break-ups in the areas corresponding to the moving objects. Our pose estimation is also more accurate, except for the $\mathbf{R}_{\mathrm{err}}$ over the ETH3D dataset [28]. Overall, we attribute this difference to: i) DeepSfM suffers from poor initialization from DeMoN, which is not accurate in multi-body scenes and hinders the overall quality of the reconstruction, ii) the plane sweep algorithm adopted by DeepSfM constructs cost volumes that do not satisfy the geometric constraints for the moving objects. Our method also beats Wang et al. [34] in all metrics by a clear margin. As expected, the performance of Wang et al. suffers significantly in multi-body scenes. The moving objects are treated as outliers and negatively impact the accuracy of the estimated camera poses, which, in turn, undermine the quality of depth estimation. By segmenting the rigid motions in the scene before computing camera poses, our method exploits and is robust to the moving objects and achieves state-of-the-art performance in multi-body depth estimation. The effectiveness of multi-body plane sweep (PS) is evidenced by the uplift in performance for $M \geq 2$ in Tab. 3. Note that for $M = 1$ , a single motion is considered and MBPS specializes to traditional PS, with similar results to [36]. + +# 5.4. Discussion and Limitations + +Our method inherits some known limitations of the multi-view approaches. In this section we discuss their possible mitigations. + +Small camera motions may hinder initial pose estimates. Our pose refinement network mitigates poor initializations, but it may not recover in particularly challenging cases. + +Occlusions are mitigated, as in [13, 36], by aggregating cost volumes from multiple image pairs, if available. However, with only two images, occlusions result in noisy depth maps + +in the region of the occluded objects, as seen in the second sequence of Fig. 7. + +Monocular depth inaccuracies may hinder the estimation of object scale factors. However, we observed our KDE voting scheme can isolate outlying measurements and return accurate results when enough ( $\sim 10$ ) factors are computed. + +Non-rigid scenes. Our method is not designed for non-rigid scenes, for which different assumptions are used, e.g. temporal coherence or complete reliance on monocular depth for moving objects. Nevertheless, as shown in the supplementary, our method can reconstruct articulated motions, provided that a sufficient number of motions is considered. + +Virtual depth planes. Our multi-body plane sweep assigns $L / M$ depth planes to each motion, meaning that the more motions considered, the fewer depth planes are assigned to each motion. As stated in the supplementary, we consider up to four motions in our evaluation, as increasing the number of depth planes worsens training and inference times. + +Inference times are on average $\sim 20\%$ higher in KITTI Depth with respect to [34] due to the required motion segmentation step, as discussed in the supplementary. + +# 6. Conclusion + +In this paper, we have addressed the problem of multi-body depth and camera pose estimation. We overcome the scale-ambiguity problem typical of all the MBSfM approaches by introducing a learning-based robust voting scheme to unify the scales of all independently moving objects in the scene. In addition, we overcome the static-scene assumption of deep SfM approaches thanks to a novel multi-body plane sweep network that explicitly supports the additional multi-view geometric constraints derived from the multiple bodies. Extensive experiments on multi-body datasets show that our method outperforms state-of-the-art deep learning methods qualitatively and quantitatively. + +Acknowledgements. This paper is supported by FAIR (Future Artificial Intelligence Research) project, funded by the NextGenerationEU program within the PNRR-PE-AI scheme (M4C2, Investment 1.3, Line on Artificial Intelligence). We also gratefully acknowledge NVIDIA Corporation for the GPUs donated within the Academic and Applied Research Program to Giacomo Boracchi and Luca Magri + +# References + +[1] Federica Arrigoni, Elisa Ricci, and Tomas Pajdla. Multi-frame motion segmentation by combining two-frame results. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 1851-1858, 2017. 6 \ No newline at end of file diff --git a/2023/Multi-body Depth and Camera Pose Estimation from Multiple Views/images.zip b/2023/Multi-body Depth and Camera Pose Estimation from Multiple Views/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..2c5f1ed5a1d06ac99448df614a4f327b3a7a4b95 --- /dev/null +++ b/2023/Multi-body Depth and Camera Pose Estimation from Multiple Views/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:80f3791e549b354acd809bf9f6d45ecad8c087800d0f4de9cb2cbc67cc128595 +size 667212 diff --git a/2023/Multi-body Depth and Camera Pose Estimation from Multiple Views/layout.json b/2023/Multi-body Depth and Camera Pose Estimation from Multiple Views/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..829aa40b23a9ca8a546b5d0ed664ee4f6248142d --- /dev/null +++ b/2023/Multi-body Depth and Camera Pose Estimation from Multiple Views/layout.json @@ -0,0 +1,12532 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 84, + 103, + 510, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 84, + 103, + 510, + 121 + ], + "spans": [ + { + "bbox": [ + 84, + 103, + 510, + 121 + ], + "type": "text", + "content": "Multi-body Depth and Camera Pose Estimation from Multiple Views" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 91, + 144, + 204, + 171 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 91, + 144, + 204, + 171 + ], + "spans": [ + { + "bbox": [ + 91, + 144, + 204, + 171 + ], + "type": "text", + "content": "Andrea Porfiri Dal Cin \nPolitecnico di Milano" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 65, + 174, + 228, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 174, + 228, + 185 + ], + "spans": [ + { + "bbox": [ + 65, + 174, + 228, + 185 + ], + "type": "text", + "content": "andrea.porfiridalcin@polimi.it" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 270, + 144, + 377, + 171 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 270, + 144, + 377, + 171 + ], + "spans": [ + { + "bbox": [ + 270, + 144, + 377, + 171 + ], + "type": "text", + "content": "Giacomo Boracchi Politecnico di Milano" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 252, + 174, + 395, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 252, + 174, + 395, + 185 + ], + "spans": [ + { + "bbox": [ + 252, + 174, + 395, + 185 + ], + "type": "text", + "content": "giacomo.boracchi@polimi.it" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 419, + 144, + 526, + 171 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 419, + 144, + 526, + 171 + ], + "spans": [ + { + "bbox": [ + 419, + 144, + 526, + 171 + ], + "type": "text", + "content": "Luca Magri\nPolitecnico di Milano" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 419, + 174, + 528, + 185 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 419, + 174, + 528, + 185 + ], + "spans": [ + { + "bbox": [ + 419, + 174, + 528, + 185 + ], + "type": "text", + "content": "luca MAGRI@polimi.it" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "spans": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 238, + 290, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 238, + 290, + 453 + ], + "spans": [ + { + "bbox": [ + 47, + 238, + 290, + 453 + ], + "type": "text", + "content": "Traditional and deep Structure-from-Motion (SfM) methods typically operate under the assumption that the scene is rigid, i.e., the environment is static or consists of a single moving object. 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The code and dataset are available at https://github.com/andreadalcin/MultiBodySfM." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 466, + 128, + 479 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 466, + 128, + 479 + ], + "spans": [ + { + "bbox": [ + 47, + 466, + 128, + 479 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 486, + 287, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 486, + 287, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 486, + 287, + 605 + ], + "type": "text", + "content": "Real-world environments often contain independently moving objects, and their reconstruction is fundamental for safe robot navigation and augmented reality in complex dynamic environments. Unfortunately, traditional and deep learning Structure-from-Motion (SfM) algorithms assume that the scene is static and treat moving objects as outliers, missing important information and producing suboptimal results when the scene is dynamic. In Fig. 1-left, the depth reconstructed by the state-of-the-art DeepSfM [36] shows artifacts in the image region of a moving object (in red)." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 606, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 606, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 606, + 288, + 715 + ], + "type": "text", + "content": "In this work, we go one step further and enable consistent 3D reconstruction (Fig. 1-right) of a scene with multiple rigidly moving objects. This task, also known as Multi-Body Structure-from-Motion (MBSfM), is still open and far from being solved in practice. 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Depth estimation networks (e.g. [36]) yield inconsistent depths (bottom-left) for moving objects. 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Therefore, a unified reconstruction of all objects up to a common global scale factor is impossible without additional information. Similarly, deep methods for SfM that leverage explicit multi-view constraints [34, 36, 13, 29, 4] are affected by the relative scale problem and cannot regress a unified depth map of a multi-body scene since their underlying architecture cannot handle multiple motions." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 713 + ], + "type": "text", + "content": "Recent monocular depth estimators [9, 2] use learned priors to regress dense depth maps from images without exploiting multi-view constraints. Thus, monocular methods implicitly avoid the relative scale problem by regressing consistent depth maps across the entire image. However, monocular depth estimation is inherently ill-posed and these models do not provide the same generalization capabilities of multi-view methods when scenes are static. Fur" + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "17804" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 119 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 119 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 119 + ], + "type": "text", + "content": "thermore, the 3D structures inferred from different images of the same scene are not guaranteed to be consistent. Thus, this inconsistency eventually manifests in alignment problems that are not trivial to solve." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 120, + 286, + 227 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 120, + 286, + 227 + ], + "spans": [ + { + "bbox": [ + 46, + 120, + 286, + 227 + ], + "type": "text", + "content": "In this work, we present a novel deep learning framework for depth and camera pose estimation designed specifically for multi-body scenes. Following consolidated MBSfM pipelines, we perform motion segmentation to recover a set of relative camera poses up to a scale factor and the corresponding sparse 3D reconstructions of each moving object. Then, we depart from existing MBSfM approaches by directly solving the relative scale problem and regressing geometrically consistent depth maps and refined poses." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 228, + 255, + 239 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 228, + 255, + 239 + ], + "spans": [ + { + "bbox": [ + 59, + 228, + 255, + 239 + ], + "type": "text", + "content": "Specifically, our main contributions are twofold:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 50, + 240, + 286, + 275 + ], + "type": "list", + "angle": 0, + "index": 5, + "blocks": [ + { + "bbox": [ + 50, + 240, + 274, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 50, + 240, + 274, + 251 + ], + "spans": [ + { + "bbox": [ + 50, + 240, + 274, + 251 + ], + "type": "text", + "content": "(1) a robust scale estimation to fix the scale ambiguity," + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 50, + 252, + 286, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 50, + 252, + 286, + 275 + ], + "spans": [ + { + "bbox": [ + 50, + 252, + 286, + 275 + ], + "type": "text", + "content": "(2) a multi-body plane sweep network to regress refined camera poses and depth maps in multi-body scenes." + } + ] + } + ], + "index": 4 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 276, + 286, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 276, + 286, + 323 + ], + "spans": [ + { + "bbox": [ + 46, + 276, + 286, + 323 + ], + "type": "text", + "content": "Our scale estimator uses monocular depth maps to unify the 3D structures and camera poses under a global scale factor. This is based on a robust voting scheme that mitigates the impact of inaccuracies in monocular depth estimates." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 324, + 286, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 324, + 286, + 455 + ], + "spans": [ + { + "bbox": [ + 46, + 324, + 286, + 455 + ], + "type": "text", + "content": "We adopt a deep neural network for multi-body depth estimation and pose refinement. The network adopts our novel multi-body plane sweep algorithm, which uses all the rigid motions in the scene, now devoid of scale ambiguity, to compute dense depth maps and refined camera poses. Notably, the estimated depth maps are geometrically consistent even in image regions covered by moving objects. Plane sweep has never been extended to support multiple rigid motions to the best of our knowledge. Our network also includes a pose estimation module that refines camera poses based on current depth estimates." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 456, + 286, + 526 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 456, + 286, + 526 + ], + "spans": [ + { + "bbox": [ + 46, + 456, + 286, + 526 + ], + "type": "text", + "content": "We demonstrate the effectiveness of our approach on both static and multi-body scenes. On static scenes, our method performs on par with traditional and deep SfM methods. On multi-body scenes, it significantly outperforms SOTA deep learning SfM methods in the depth estimation task and achieves comparable camera pose results." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 538, + 173, + 551 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 538, + 173, + 551 + ], + "spans": [ + { + "bbox": [ + 47, + 538, + 173, + 551 + ], + "type": "text", + "content": "2. Problem Formulation" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": "Multi-body depth and camera pose estimation is framed as follows. The input is a set of " + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": " unstructured images " + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{I}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": " captured by a moving camera and depicting a multi-body scene in which " + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": " objects " + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "inline_equation", + "content": "\\mathcal{B} = \\{\\beta_i\\}_{i=1}^\\mu" + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": " independently move according to their rigid motions. Without loss of generality, we consider the object " + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "inline_equation", + "content": "\\beta_1" + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": " to be static w.r.t. to the camera motion. Our goal is to estimate depth maps " + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{D}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": " for each image " + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": " and the absolute camera poses " + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{R}_i, \\mathbf{t}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": " in the reference frame of " + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "inline_equation", + "content": "\\beta_1" + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": ". We assume that: i) an upper bound " + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": " on the maximum number " + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": " of moving objects in the scene is given, ii) the camera is perspective and its intrinsic parameters " + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "inline_equation", + "content": "\\mathbf{K}" + }, + { + "bbox": [ + 46, + 557, + 286, + 700 + ], + "type": "text", + "content": " are known." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 58, + 701, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 701, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 701, + 286, + 713 + ], + "type": "text", + "content": "Consider that our problem is different from non-rigid" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "SfM [16, 14]. Non-rigid SfM handles a wider class of object deformations but does not assume unstructured input images, typically exploiting dense temporal information, and is restricted to orthographic cameras." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 129, + 392, + 142 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 129, + 392, + 142 + ], + "spans": [ + { + "bbox": [ + 305, + 129, + 392, + 142 + ], + "type": "text", + "content": "3. Related Work" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 149, + 545, + 256 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 149, + 545, + 256 + ], + "spans": [ + { + "bbox": [ + 304, + 149, + 545, + 256 + ], + "type": "text", + "content": "Depth and camera pose estimation from unstructured images of multi-body scenes is largely unexplored, and most SfM methods either consider static scenes only (" + }, + { + "bbox": [ + 304, + 149, + 545, + 256 + ], + "type": "inline_equation", + "content": "\\mu = 1" + }, + { + "bbox": [ + 304, + 149, + 545, + 256 + ], + "type": "text", + "content": ") or treat moving objects as outliers. This section focuses on the few SfM methods that address the multi-body scenario (" + }, + { + "bbox": [ + 304, + 149, + 545, + 256 + ], + "type": "inline_equation", + "content": "\\mu > 1" + }, + { + "bbox": [ + 304, + 149, + 545, + 256 + ], + "type": "text", + "content": ") from unstructured images acquired by perspective cameras. Also, we discuss monocular depth estimation, a component of our solution, and relevant deep multi-view static SfM methods." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 263, + 541, + 276 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 263, + 541, + 276 + ], + "spans": [ + { + "bbox": [ + 305, + 263, + 541, + 276 + ], + "type": "text", + "content": "3.1. Multi-body Structure-from-Motion (MBSfM)" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 281, + 545, + 401 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 281, + 545, + 401 + ], + "spans": [ + { + "bbox": [ + 304, + 281, + 545, + 401 + ], + "type": "text", + "content": "A few works have addressed MBSfM from unstructured images " + }, + { + "bbox": [ + 304, + 281, + 545, + 401 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{I}_i\\}_{i = 1}^n" + }, + { + "bbox": [ + 304, + 281, + 545, + 401 + ], + "type": "text", + "content": " as a generalization of traditional SfM to multi-body scenes. We identify two main research directions. First, early factorization methods [32, 6] segment rigidly moving objects " + }, + { + "bbox": [ + 304, + 281, + 545, + 401 + ], + "type": "inline_equation", + "content": "\\mathcal{B}" + }, + { + "bbox": [ + 304, + 281, + 545, + 401 + ], + "type": "text", + "content": " and perform sparse 3D reconstruction in a single step. However, factorization methods rely on restrictive assumptions on camera models and require complete feature tracks, which are seldom available in practice. Due to its lack of robustness, factorization has yet to see practical applications beyond short, unrealistic sequences." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 403, + 545, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 545, + 581 + ], + "type": "text", + "content": "The second, more recent, research direction separates motion segmentation of objects " + }, + { + "bbox": [ + 304, + 403, + 545, + 581 + ], + "type": "inline_equation", + "content": "\\mathcal{B}" + }, + { + "bbox": [ + 304, + 403, + 545, + 581 + ], + "type": "text", + "content": " and their 3D reconstruction. [1, 26] cluster sparse correspondences based on their rigid motion and then recover the 3D structure of each object independently using a SfM pipeline [27]. As discussed in [23, 24, 17], the relative scale problem affects these methods because each object is reconstructed in its own scale. In SLAM, the relative scale problem has been addressed under specific assumptions: [23] assumes objects move in a one-parameter family of motions, and [17] works only with video input and continuous object motion. Our method also decouples motion segmentation and reconstruction. However, we explicitly address the relative scale problem using a learning-based approach without further assumptions on the input images or the motions in the scene." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 587, + 465, + 600 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 587, + 465, + 600 + ], + "spans": [ + { + "bbox": [ + 305, + 587, + 465, + 600 + ], + "type": "text", + "content": "3.2. Monocular Depth Estimation" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 605, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 689 + ], + "type": "text", + "content": "Recent works [9, 2] recover a dense depth map " + }, + { + "bbox": [ + 304, + 605, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{D}_1" + }, + { + "bbox": [ + 304, + 605, + 545, + 689 + ], + "type": "text", + "content": " from a single image " + }, + { + "bbox": [ + 304, + 605, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_1" + }, + { + "bbox": [ + 304, + 605, + 545, + 689 + ], + "type": "text", + "content": ". These methods learn priors to regress depth maps, allowing consistent scale reconstruction of moving objects " + }, + { + "bbox": [ + 304, + 605, + 545, + 689 + ], + "type": "inline_equation", + "content": "\\mathcal{B}" + }, + { + "bbox": [ + 304, + 605, + 545, + 689 + ], + "type": "text", + "content": " without scale ambiguity. However, due to the ill-posed nature of monocular depth estimation, generalization is limited and multi-view approaches remain the benchmark for SfM in deep learning." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 689, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 712 + ], + "type": "text", + "content": "In [20, 38], monocular depth maps are estimated from video frames, and then a network is fine-tuned on the entire" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17805" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 62, + 69, + 531, + 209 + ], + "blocks": [ + { + "bbox": [ + 62, + 69, + 531, + 209 + ], + "lines": [ + { + "bbox": [ + 62, + 69, + 531, + 209 + ], + "spans": [ + { + "bbox": [ + 62, + 69, + 531, + 209 + ], + "type": "image", + "image_path": "99bf2b6261462b2a67043da592310cfbfa4df27273c256d5e0c2072f6070f454.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 213, + 547, + 247 + ], + "lines": [ + { + "bbox": [ + 46, + 213, + 547, + 247 + ], + "spans": [ + { + "bbox": [ + 46, + 213, + 547, + 247 + ], + "type": "text", + "content": "Figure 2: The three main steps of our method: i) motion segmentation: produces a set of essential matrices describing the rigid motion of objects between view pairs. ii) robust scale estimation: uses monocular depth cues to fix the scale ambiguity of each moving object. iii) multi-body plane-sweep network based on our novel multi-body plane-sweep regress refined depth maps and camera poses." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 266, + 288, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 266, + 288, + 327 + ], + "spans": [ + { + "bbox": [ + 46, + 266, + 288, + 327 + ], + "type": "text", + "content": "video sequence. These methods do not assume unstructured images and require many frames for depth and pose tracking and fine-tuning. In addition, depth estimation for moving objects still relies solely on depth priors, which can lead to inaccuracies as in standard monocular depth estimation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 336, + 179, + 349 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 336, + 179, + 349 + ], + "spans": [ + { + "bbox": [ + 47, + 336, + 179, + 349 + ], + "type": "text", + "content": "3.3. Deep Learning for SfM" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 356, + 287, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 356, + 287, + 582 + ], + "spans": [ + { + "bbox": [ + 46, + 356, + 287, + 582 + ], + "type": "text", + "content": "Deep learning methods for SfM from unstructured images regress camera poses and dense depth maps using multi-view stereo matching. DeMoN [33] works on image pairs using stacked encoder-decoder networks but lacks explicit multi-view constraints and has limited accuracy. More recent architectures [29, 4, 36, 34, 13, 31] replace the generic encoder-decoder architecture with layers that explicitly enforce multi-view constraints. Other works achieve better results by taking inspiration from traditional Bundle Adjustment: DeepSfM [36] introduces depth and pose cost volumes for iterative refinement, and [29] uses a BA-layer for regression from basis depth maps. Wang et al. [34] propose a scale-invariant network for depth and pose estimation for view pairs. Specifically, camera poses are estimated from essential matrices robustly fitted on fine-tuned optical flow matches, thus treating all moving objects as outliers. Then, depth maps are regressed end-to-end using a CNN similar to DeepSfM. Finally, [4] optimizes non-linear cost functions in SfM using recurring neural networks." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 584, + 287, + 632 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 584, + 287, + 632 + ], + "spans": [ + { + "bbox": [ + 46, + 584, + 287, + 632 + ], + "type": "text", + "content": "As the above deep methods embed explicit multi-view geometric constraints in their optimization layers, they are affected by the scale ambiguity of traditional MBSfM and cannot generalize to multi-body scenes, as shown in Fig. 1." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 645, + 102, + 657 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 645, + 102, + 657 + ], + "spans": [ + { + "bbox": [ + 47, + 645, + 102, + 657 + ], + "type": "text", + "content": "4. Method" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": "Our method, illustrated in Fig. 2, is structured in three steps. First, given the unstructured images " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{I}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": ", we perform motion segmentation from image pairs " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " to estimate essential matrices " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{E}_k^\\alpha\\}_{j=1}^\\mu" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " that encode the " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " rigid mo" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "spans": [ + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "type": "text", + "content": "tions in the scene. Second, we fix the scale ambiguity of each " + }, + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_k^\\alpha" + }, + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "type": "text", + "content": " by exploiting cues provided by monocular depth maps " + }, + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{M}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "type": "text", + "content": " in a robust scale estimation module. Finally, a multi-view depth and camera pose estimation network leverages our novel multi-body plane sweep algorithm to regress geometrically-consistent depth maps " + }, + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{D}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "type": "text", + "content": " and camera poses " + }, + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{R}_i, \\mathbf{t}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "type": "text", + "content": " by considering all the " + }, + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 304, + 266, + 545, + 352 + ], + "type": "text", + "content": " motions." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 358, + 427, + 371 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 358, + 427, + 371 + ], + "spans": [ + { + "bbox": [ + 306, + 358, + 427, + 371 + ], + "type": "text", + "content": "4.1. Motion segmentation" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 377, + 545, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 377, + 545, + 437 + ], + "spans": [ + { + "bbox": [ + 304, + 377, + 545, + 437 + ], + "type": "text", + "content": "The goal of motion segmentation is to recover the essential matrices " + }, + { + "bbox": [ + 304, + 377, + 545, + 437 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{E}_k^\\alpha\\}_{k=1}^\\mu" + }, + { + "bbox": [ + 304, + 377, + 545, + 437 + ], + "type": "text", + "content": " that encode all rigid motions in the scene in any image pair " + }, + { + "bbox": [ + 304, + 377, + 545, + 437 + ], + "type": "inline_equation", + "content": "\\alpha = (\\mathbf{I}_i, \\mathbf{I}_j)" + }, + { + "bbox": [ + 304, + 377, + 545, + 437 + ], + "type": "text", + "content": ". To this end, we combine traditional sparse motion segmentation, based on SIFT [19], with dense deep optical flow matches." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "text", + "content": "For each image " + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "text", + "content": ", we extract " + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\{x_{i,u}\\}_{u = 1}^{p_i}" + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "text", + "content": " SIFT keypoints and match them across image pairs. Then, for each pair " + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "text", + "content": ", we fit " + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "text", + "content": " essential matrices " + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{E}_k^\\alpha J_{k = 1}^\\mu\\}" + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "text", + "content": " to the matches using RPA [21], a multi-model fitting algorithm. RPA provides a labeling " + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\ell^{\\alpha}" + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "text", + "content": " that assigns a matched keypoint to the motion it belongs to. Labels assigned to different image pairs may be inconsistent, thus we use permutation synchronization [1] to enforce a global labelling " + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\ell" + }, + { + "bbox": [ + 304, + 437, + 545, + 544 + ], + "type": "text", + "content": " that assigns to keypoints belonging to the same motion the same label in all views." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": "In multi-body scenes, moving objects can be supported by only a few keypoints. Therefore, to refine the essential matrices, we augment the set of sparse matches with dense ones computed from the optical flow. Similarly to [34], we consider the dense matches at keypoint locations and, thus, avoid the typical inaccuracies of the optical flow caused by illumination changes and texture-less regions. In particular, given an image pair " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\alpha = (\\mathbf{I}_i,\\mathbf{I}_j)" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": ", for each object " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\beta_{k}\\in \\mathcal{B}" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " we consider " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "U_{k}^{i} = \\{x_{i,u}:\\ell (x_{i,u}) = k\\}" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " the sparse keypoints in " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " labelled as " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": ". Around each keypoint " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "x\\in U_k^i" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " we consider a squared neighborhood " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "N(x)" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "3\\times 3" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " pixels. The union of neighborhoods " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "S_{k}^{i} = \\bigcup_{x\\in U_{k}^{i}}N(x)" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " defines a mask in " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " as illustrated in Fig. 2. We refine " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_k^\\alpha" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " by RANSAC equipped with the 5-point algorithm [22, 18] on the set of all" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17806" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 72, + 197, + 201 + ], + "blocks": [ + { + "bbox": [ + 50, + 72, + 197, + 201 + ], + "lines": [ + { + "bbox": [ + 50, + 72, + 197, + 201 + ], + "spans": [ + { + "bbox": [ + 50, + 72, + 197, + 201 + ], + "type": "image", + "image_path": "ca029ad142b03b154915006723fecf7efe28d4be8da23070a80a49d8e047fa47.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 203, + 547, + 237 + ], + "lines": [ + { + "bbox": [ + 46, + 203, + 547, + 237 + ], + "spans": [ + { + "bbox": [ + 46, + 203, + 547, + 237 + ], + "type": "text", + "content": "Figure 3: (left) In a multi-body scene, the scale of triangulated structures (orange) differs from the true object scale (cyan), leading to inconsistent relative object scales, i.e., cube bigger than pyramid. The tentative scale factor " + }, + { + "bbox": [ + 46, + 203, + 547, + 237 + ], + "type": "inline_equation", + "content": "\\lambda_{i,u}^{1}" + }, + { + "bbox": [ + 46, + 203, + 547, + 237 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 46, + 203, + 547, + 237 + ], + "type": "inline_equation", + "content": "X_{u}^{1} \\in \\beta_{1}" + }, + { + "bbox": [ + 46, + 203, + 547, + 237 + ], + "type": "text", + "content": " is the ratio of the monocular depth " + }, + { + "bbox": [ + 46, + 203, + 547, + 237 + ], + "type": "inline_equation", + "content": "m_{i,u}^{1}" + }, + { + "bbox": [ + 46, + 203, + 547, + 237 + ], + "type": "text", + "content": " and its triangulated depth " + }, + { + "bbox": [ + 46, + 203, + 547, + 237 + ], + "type": "inline_equation", + "content": "d_{i,u}^{1}" + }, + { + "bbox": [ + 46, + 203, + 547, + 237 + ], + "type": "text", + "content": ". (right) Traditional plane sweep [5] vs. our novel multi-body plane sweep." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 258, + 72, + 380, + 193 + ], + "blocks": [ + { + "bbox": [ + 258, + 72, + 380, + 193 + ], + "lines": [ + { + "bbox": [ + 258, + 72, + 380, + 193 + ], + "spans": [ + { + "bbox": [ + 258, + 72, + 380, + 193 + ], + "type": "image", + "image_path": "6dc5dd46bef3093738ccaf81dcdef7bc2a36d9517f8070fe80f25268ba922cf9.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 394, + 72, + 536, + 194 + ], + "blocks": [ + { + "bbox": [ + 394, + 72, + 536, + 194 + ], + "lines": [ + { + "bbox": [ + 394, + 72, + 536, + 194 + ], + "spans": [ + { + "bbox": [ + 394, + 72, + 536, + 194 + ], + "type": "image", + "image_path": "106bd788b20efe4c9aab564588b1343350ea1c550223c3768a24eff46ca0a387.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 257, + 287, + 282 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 257, + 287, + 282 + ], + "spans": [ + { + "bbox": [ + 46, + 257, + 287, + 282 + ], + "type": "text", + "content": "the dense matches corresponding to the mask " + }, + { + "bbox": [ + 46, + 257, + 287, + 282 + ], + "type": "inline_equation", + "content": "S_{k}^{i}" + }, + { + "bbox": [ + 46, + 257, + 287, + 282 + ], + "type": "text", + "content": ". The optical flow is computed using the DICL-Flow network [35]." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 287, + 185, + 298 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 287, + 185, + 298 + ], + "spans": [ + { + "bbox": [ + 47, + 287, + 185, + 298 + ], + "type": "text", + "content": "4.2. Robust Scale Estimation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "spans": [ + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": "We factorize each essential matrix " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\mathbf{E}_k^\\alpha = [\\tilde{\\mathbf{t}}_k^\\alpha ]_\\times \\tilde{\\mathbf{R}}_k^\\alpha" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": " to obtain the relative camera pose as a rotation " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{R}}_k^\\alpha" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": " and translation " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{t}}_k^\\alpha" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": ". Since each " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{t}}_k^\\alpha" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": " is recovered only up to an unknown scale-factor " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\lambda_{k}" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": ", each moving object in a multi-body scene is reconstructed in its own arbitrary scale " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\lambda_{k}" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": ". Specifically, given an image pair " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": ", we can triangulate from matched image points a set of 3D points " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\{X_u^k\\}_{u = 1}^{p_k}" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": " belonging to object " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\beta_{k}" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": " from the up-to-scale camera pose " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\{\\tilde{\\mathbf{R}}_k^\\alpha ,\\tilde{\\mathbf{t}}_k^\\alpha \\}" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": ". However, these 3D points are expressed in the scale " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\lambda_{k}" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{t}}_k^\\alpha" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": ", meaning that different objects refer to inconsistent scales. Fig. 3-left depicts a multi-body scene where the scale ambiguity manifests as an inconsistent relative scale between objects " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\lambda_{1}\\beta_{1}" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\lambda_{2}\\beta_{2}" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": " in the triangulated scene (orange) w.r.t. the actual 3D scene (cyan). Thus, the cube " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\lambda_{1}\\beta_{1}" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": " appears larger than the pyramid " + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "inline_equation", + "content": "\\lambda_{2}\\beta_{2}" + }, + { + "bbox": [ + 46, + 304, + 287, + 486 + ], + "type": "text", + "content": " in the reconstruction." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "spans": [ + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": "We estimate the unknown scale factor " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "\\lambda_{k}" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": " for each object " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "\\beta_{k}" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": " by first regressing a monocular depth map " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": " from each image " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": " using AdaBins [2]. This network processes each " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": " individually and, thus, is not affected by the multi-view scale ambiguity. We denote by " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "d_{i,u}^{k}" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": " and by " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "m_{i,u}^{k}" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": " the triangulated and monocular depths respectively of the " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "u" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": "-th 3D point " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "X_{u}^{k}" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": " w.r.t. " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": ". Then, for each object " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "\\beta_{k}" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": " and image " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": ", we compute the point-wise scale factor " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "\\lambda_{i,u}^{k} = d_{i,u}^{k} / m_{i,u}^{k}" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": " that approximates the real " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "\\lambda_{k}" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": " according to the triangulated and monocular depths of " + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "inline_equation", + "content": "X_{u}^{k}" + }, + { + "bbox": [ + 46, + 487, + 287, + 606 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "text", + "content": "As monocular depth maps generally lack in accuracy, we devise a voting scheme to robustly aggregate the scale factors from all images " + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{I}_i\\}_{i = 1}^n" + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "text", + "content": " and unify all the " + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "text", + "content": " camera poses under a global scale factor " + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "text", + "content": ". First, we partition the point-wise scale factors computed from all the images into " + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "text", + "content": " sets " + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\Lambda_{k} = \\{\\lambda_{i,u}^{k}\\}_{i = 1,u = 1}^{n,p_{k}}" + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "text", + "content": " according to their object " + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\beta_{k}" + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "text", + "content": ". Then, to promote robustness, we adopt a Kernel Density Estimator and derive a probability density function " + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\phi_{k}" + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "text", + "content": " from each " + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\Lambda_{k}" + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "text", + "content": ". We use a Gaussian Kernel " + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{K}" + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "text", + "content": " with bandwidth " + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 46, + 606, + 288, + 714 + ], + "type": "text", + "content": " set" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 257, + 545, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 257, + 545, + 281 + ], + "spans": [ + { + "bbox": [ + 304, + 257, + 545, + 281 + ], + "type": "text", + "content": "at " + }, + { + "bbox": [ + 304, + 257, + 545, + 281 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 304, + 257, + 545, + 281 + ], + "type": "text", + "content": " of the median of the elements in " + }, + { + "bbox": [ + 304, + 257, + 545, + 281 + ], + "type": "inline_equation", + "content": "\\Lambda_{k}" + }, + { + "bbox": [ + 304, + 257, + 545, + 281 + ], + "type": "text", + "content": " and define the kernel " + }, + { + "bbox": [ + 304, + 257, + 545, + 281 + ], + "type": "inline_equation", + "content": "\\phi_{k}" + }, + { + "bbox": [ + 304, + 257, + 545, + 281 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 366, + 288, + 545, + 320 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 366, + 288, + 545, + 320 + ], + "spans": [ + { + "bbox": [ + 366, + 288, + 545, + 320 + ], + "type": "interline_equation", + "content": "\\phi_ {k} (x) = \\sum_ {\\lambda_ {i, u} ^ {k} \\in \\Lambda_ {k}} \\frac {\\mathcal {K} \\left(\\lambda_ {i , u} ^ {k} - x\\right)}{h}. \\tag {1}", + "image_path": "983f4b994f24c20a8074626804798b5ea6b4c436b36951519cb347c94c5ecf51.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "spans": [ + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "text", + "content": "The highest peak of " + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "inline_equation", + "content": "\\phi_{k}" + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "text", + "content": " is denoted by " + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "inline_equation", + "content": "\\hat{\\lambda}_{k}" + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "text", + "content": " and represents the estimate of the " + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "text", + "content": "-th object scale factor " + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "inline_equation", + "content": "\\lambda_{k}" + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "text", + "content": ". The estimated " + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "inline_equation", + "content": "\\{\\hat{\\lambda}_k\\}_{k = 1}^\\mu" + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "text", + "content": " are used to scale the pairwise relative camera poses " + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "inline_equation", + "content": "[\\tilde{\\mathbf{R}}_k^\\alpha ,\\hat{\\lambda}_k^{-1}\\tilde{\\mathbf{t}}_k^\\alpha ]" + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "text", + "content": " by multiplying the translation component. Now, camera poses are aligned to a global scale factor " + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "text", + "content": ". As depths " + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i" + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "text", + "content": " are regressed in real-world unit of measurement, " + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "inline_equation", + "content": "\\lambda \\approx 1" + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "text", + "content": ", i.e., camera poses should be approximately in their real-world scale. We denote the correctly scaled camera poses as " + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "inline_equation", + "content": "[\\hat{\\mathbf{R}}_k^\\alpha ,\\hat{\\mathbf{t}}_k^\\alpha ]" + }, + { + "bbox": [ + 304, + 329, + 546, + 452 + ], + "type": "text", + "content": " and use this unified camera configuration as the initialization for the next step." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 459, + 487, + 472 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 459, + 487, + 472 + ], + "spans": [ + { + "bbox": [ + 305, + 459, + 487, + 472 + ], + "type": "text", + "content": "4.3. Multi-body Plane Sweep Network" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "spans": [ + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "text", + "content": "Although the poses " + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "inline_equation", + "content": "\\{\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha\\}" + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "text", + "content": " are now aligned to a single scale factor, the depths are only estimated from monocular maps " + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_i" + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "text", + "content": " which ignore the multi-view constraints. In principle, it could be possible to use camera poses to initialize a multi-view iterative scheme where depths and poses are refined, as in [36], but this would regress inconsistent depths in regions corresponding to moving objects. Thus, we design a novel multi-body depth and pose estimation network that takes the unordered images " + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{I}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "text", + "content": " and the scale-consistent poses " + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "inline_equation", + "content": "\\{\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha\\}" + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "text", + "content": " to jointly estimates geometrically consistent depth maps " + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{D}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "text", + "content": " and refined poses " + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{R}_i, \\mathbf{t}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "text", + "content": " in the reference frame of object " + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "inline_equation", + "content": "\\beta_1" + }, + { + "bbox": [ + 304, + 476, + 545, + 657 + ], + "type": "text", + "content": ". As shown in Fig. 4, we include two separate branches for depth and pose estimation, which are used alternatively in an iterative scheme using the output of the other branch as input." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 662, + 494, + 674 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 662, + 494, + 674 + ], + "spans": [ + { + "bbox": [ + 305, + 662, + 494, + 674 + ], + "type": "text", + "content": "4.3.1. Multi-body Depth Estimation Branch" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "As depicted in Fig. 4, our depth estimation branch is based on our novel multi-body plane sweep and concatenates the following modules." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17807" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 77, + 70, + 521, + 212 + ], + "blocks": [ + { + "bbox": [ + 77, + 70, + 521, + 212 + ], + "lines": [ + { + "bbox": [ + 77, + 70, + 521, + 212 + ], + "spans": [ + { + "bbox": [ + 77, + 70, + 521, + 212 + ], + "type": "image", + "image_path": "f952cf292e0706cb42a8a330f4798125d97621971a2e9637d9a94fbc23a77049.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 215, + 547, + 239 + ], + "lines": [ + { + "bbox": [ + 46, + 215, + 547, + 239 + ], + "spans": [ + { + "bbox": [ + 46, + 215, + 547, + 239 + ], + "type": "text", + "content": "Figure 4: Multi-body Plane Sweep network. We extract CNN features from input images and build a cost volume using our multi-body plane sweep algorithm. Depth and camera poses are regressed from separate cost volumes with a series of 3D CNN and refinement layers." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "spans": [ + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "text", + "content": "Feature Extraction. A multi-scale CNN with spatial pyramid pooling [12] extracts features " + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{F}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "text", + "content": " from images " + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{I}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "text", + "content": ". Each " + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_i" + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "text", + "content": " has dimension " + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "inline_equation", + "content": "\\mathbf{C} \\times \\mathbf{W} \\times \\mathbf{H}" + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "inline_equation", + "content": "\\mathbf{C}" + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "inline_equation", + "content": "\\mathbf{W}" + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "inline_equation", + "content": "\\mathbf{H}" + }, + { + "bbox": [ + 47, + 258, + 288, + 308 + ], + "type": "text", + "content": " are feature channels, width and height respectively." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "spans": [ + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": "Multi-body Plane Sweep for Cost Volume Construction. Let us briefly recall how the traditional plane sweep works before describing our contributions. The traditional plane sweep algorithm [5] takes as input an image pair " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": " of a source " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": " and target " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_j" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": " and their relative pose " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "[\\mathbf{R}^\\alpha, \\mathbf{t}^\\alpha]" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": ". The algorithm samples a set of virtual planes parallel to " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_j" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": " at fixed depths " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\{d_l\\}_{l=1}^L" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": ". Then, for each depth " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "d_l" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": ", the source " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": " is warped onto the target " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_j" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": " through the homography induced by the plane at " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "d_l" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": " and the relative camera pose " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "[\\mathbf{R}^\\alpha, \\mathbf{t}^\\alpha]" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": ", as in Fig. 3-right. A dense depth map is obtained by selecting, for each pixel, the depth " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "d_l" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": " that minimizes a pixel-wise photometric dissimilarity between the target " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_j" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": " and the warped source " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": ". Deep methods [13, 36, 34] revisited this framework, but measure feature metric consistency between latent features " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{F}_i\\}_{i=1}^n" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": " instead of photometric dissimilarity. To this end, warped source and target features are aggregated in a single depth cost volume from which depths are regressed through convolutional layers. Unfortunately, both traditional and deep plane sweep methods assume static scenes with a single relative camera pose " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "[\\mathbf{R}^\\alpha, \\mathbf{t}^\\alpha]" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": " between the pair " + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 316, + 287, + 579 + ], + "type": "text", + "content": ". As a result, any point belonging to a moving object has an inconsistent depth." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": "We propose instead a multi-body plane sweep that considers all the " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " relative poses " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\{\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha\\}_{k=1}^\\mu" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " to warp a source feature " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_i" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " onto a target " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_j" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " and construct the depth cost volume. Given a source-target pair " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\alpha = (\\mathbf{I}_i, \\mathbf{I}_j)" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": ", we uniformly sample " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " 3D virtual planes at depths " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\{d_l\\}_{l=1}^L" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " parallel to the source " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": ". Then, we sequentially assign each depth plane to one of the " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " relative camera poses by cycling through the " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\{\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha\\}_{k=1}^\\mu" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": ". Thus, the individual features " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_i" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " of the object " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\beta_k" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " are warped onto " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_j" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " in a geometrically consistent manner when considering any depth plane assigned to the camera pose " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "[\\hat{\\mathbf{R}}_k^\\alpha, \\hat{\\mathbf{t}}_k^\\alpha]" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": " relative to " + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\beta_k" + }, + { + "bbox": [ + 46, + 582, + 288, + 715 + ], + "type": "text", + "content": ". This is depicted in" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "spans": [ + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "text", + "content": "Fig. 3-right, utilizing color to illustrate the cyclic assignment of the " + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "text", + "content": "-th and " + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "text", + "content": "-th rigid motions to planes at " + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "inline_equation", + "content": "d_{l}" + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "inline_equation", + "content": "d_{l+1}" + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "text", + "content": ", respectively, and to subsequent planes. Finally, each point " + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "inline_equation", + "content": "u" + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "text", + "content": " in the source feature " + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{i}" + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "text", + "content": " is first back-projected onto the virtual planes at " + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "inline_equation", + "content": "d_{l}" + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "text", + "content": " and then re-projected as " + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "inline_equation", + "content": "\\tilde{u}_{lk}" + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "text", + "content": " on the target " + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{j}" + }, + { + "bbox": [ + 304, + 258, + 547, + 331 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 320, + 338, + 545, + 363 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 320, + 338, + 545, + 363 + ], + "spans": [ + { + "bbox": [ + 320, + 338, + 545, + 363 + ], + "type": "interline_equation", + "content": "\\tilde {\\mathbf {F}} _ {i l} ^ {k} (u) = \\mathbf {F} _ {i} (\\tilde {u} _ {l k}), \\tilde {u} _ {l k} \\sim \\mathbf {K} \\left[ \\hat {\\mathbf {R}} _ {k} ^ {\\alpha} | \\hat {\\mathbf {t}} _ {k} ^ {\\alpha} \\right] \\left[ \\begin{array}{c} (\\mathbf {K} ^ {- 1} u) d _ {l} \\\\ 1 \\end{array} \\right], \\tag {2}", + "image_path": "fb54ec730b1b581c29d1e99c8c75859304a1de3ccb50fe3008ed062ebae1bbd1.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 369, + 545, + 397 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 369, + 545, + 397 + ], + "spans": [ + { + "bbox": [ + 304, + 369, + 545, + 397 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 369, + 545, + 397 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{F}}_{il}^{k}" + }, + { + "bbox": [ + 304, + 369, + 545, + 397 + ], + "type": "text", + "content": " is the warped source feature through the homography induced by the plane at " + }, + { + "bbox": [ + 304, + 369, + 545, + 397 + ], + "type": "inline_equation", + "content": "d_{l}" + }, + { + "bbox": [ + 304, + 369, + 545, + 397 + ], + "type": "text", + "content": " and the motion " + }, + { + "bbox": [ + 304, + 369, + 545, + 397 + ], + "type": "inline_equation", + "content": "[\\hat{\\mathbf{R}}_k^\\alpha ,\\hat{\\mathbf{t}}_k^\\alpha ]" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "spans": [ + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "text", + "content": "Cost volume Construction. Given the set of virtual depth planes " + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "inline_equation", + "content": "\\{d_l\\}_{l = 1}^L" + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "text", + "content": ", for each " + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "inline_equation", + "content": "d_{l}" + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "text", + "content": ", we obtain a warped source feature " + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{F}}_{il}^{k}" + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "text", + "content": " using Eq. 2 and concatenate it to the target feature " + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_j" + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "text", + "content": ". This yields a set of " + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "text", + "content": " feature blocks, each sized " + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "inline_equation", + "content": "2\\mathrm{C} \\times \\mathrm{W} \\times \\mathrm{H}" + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "text", + "content": ", that we arrange into a 4D depth cost volume sized " + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "inline_equation", + "content": "2\\mathrm{C} \\times L \\times \\mathrm{W} \\times \\mathrm{H}" + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "text", + "content": ", as illustrated in Fig. 5. Since the number of virtual planes is significantly higher than the number of motions, all the " + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 304, + 399, + 546, + 532 + ], + "type": "text", + "content": " motions are assigned to some virtual planes. Thus, our cost volume jointly incorporates all the motions in the scene, unlike traditional plane-sweep methods that assume a single motion." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 534, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 547, + 714 + ], + "type": "text", + "content": "Cost volume Regularization. Regularizing the cost volume is fundamental to cope with imperfect latent feature matching, which is especially common in image regions corresponding to texture-less objects or uniform pixel intensity. To this end, we use a sequence of 3D convolutional layers consisting of " + }, + { + "bbox": [ + 304, + 534, + 547, + 714 + ], + "type": "inline_equation", + "content": "L / 2" + }, + { + "bbox": [ + 304, + 534, + 547, + 714 + ], + "type": "text", + "content": " filters of size " + }, + { + "bbox": [ + 304, + 534, + 547, + 714 + ], + "type": "inline_equation", + "content": "3\\times 3\\times 3" + }, + { + "bbox": [ + 304, + 534, + 547, + 714 + ], + "type": "text", + "content": " with stride 1, and residual connections. Then, we apply a 3D convolution with a single " + }, + { + "bbox": [ + 304, + 534, + 547, + 714 + ], + "type": "inline_equation", + "content": "3\\times 3\\times 3" + }, + { + "bbox": [ + 304, + 534, + 547, + 714 + ], + "type": "text", + "content": " filter to obtain a 3D cost volume of size " + }, + { + "bbox": [ + 304, + 534, + 547, + 714 + ], + "type": "inline_equation", + "content": "L\\times \\mathrm{W}\\times \\mathrm{H}" + }, + { + "bbox": [ + 304, + 534, + 547, + 714 + ], + "type": "text", + "content": ". Since the order of the stacked features in the cost volume follows the correct virtual plane sequence, 3D convolutional layers can capture the 3D dependencies in the scene to enable consistent depth map estimation. Finally, we apply edge-preserving filtering to the resulting cost volume as in [13, 11]. In the case of multiple source-target image pairs, the final 3D cost volume is obtained by aver" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17808" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "type": "text", + "content": "aging the 3D cost volumes from each pair. Further details on the cost volume can be found in the supplementary." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "spans": [ + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "type": "text", + "content": "Depth Regression. We denote as " + }, + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "type": "inline_equation", + "content": "c_{l}" + }, + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "type": "text", + "content": " each slice of the aggregated cost volume, which corresponds to a plane at " + }, + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "type": "inline_equation", + "content": "d_{l}" + }, + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "type": "text", + "content": ". Then, we convert the aggregated cost volume to a probability volume as in [15] and use the softmax operation " + }, + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "type": "text", + "content": " to normalize the probability volume across the depth dimension. We estimate the depth map " + }, + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "type": "inline_equation", + "content": "\\mathbf{D}_i" + }, + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "type": "text", + "content": " for a view " + }, + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 46, + 99, + 286, + 170 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 98, + 176, + 287, + 205 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 98, + 176, + 287, + 205 + ], + "spans": [ + { + "bbox": [ + 98, + 176, + 287, + 205 + ], + "type": "interline_equation", + "content": "\\mathbf {D} _ {i} = \\frac {L \\times d _ {\\operatorname* {m i n}}}{\\tilde {l}}, \\tilde {l} = \\sum_ {l = 1} ^ {L} l \\times \\sigma \\left(c _ {l}\\right), \\tag {3}", + "image_path": "96bfd70ba4e51fc5e82a909d61f57943cd10f2d1247f73fa3e4cb6dd29eb84a2.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 212, + 287, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 212, + 287, + 262 + ], + "spans": [ + { + "bbox": [ + 46, + 212, + 287, + 262 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 212, + 287, + 262 + ], + "type": "inline_equation", + "content": "\\tilde{l}" + }, + { + "bbox": [ + 46, + 212, + 287, + 262 + ], + "type": "text", + "content": " is the map corresponding to the average of virtual plane depths " + }, + { + "bbox": [ + 46, + 212, + 287, + 262 + ], + "type": "inline_equation", + "content": "l\\in \\{1,\\dots ,L\\}" + }, + { + "bbox": [ + 46, + 212, + 287, + 262 + ], + "type": "text", + "content": ", weighted by the probabilities " + }, + { + "bbox": [ + 46, + 212, + 287, + 262 + ], + "type": "inline_equation", + "content": "\\sigma (c_l)" + }, + { + "bbox": [ + 46, + 212, + 287, + 262 + ], + "type": "text", + "content": ". In (3), " + }, + { + "bbox": [ + 46, + 212, + 287, + 262 + ], + "type": "inline_equation", + "content": "d_{\\mathrm{min}}" + }, + { + "bbox": [ + 46, + 212, + 287, + 262 + ], + "type": "text", + "content": " denotes the depth of the closest plane to the source image." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 266, + 178, + 276 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 266, + 178, + 276 + ], + "spans": [ + { + "bbox": [ + 47, + 266, + 178, + 276 + ], + "type": "text", + "content": "4.3.2. Pose Estimation Branch" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "spans": [ + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": "We describe our pose estimation branch, which optimizes current camera pose estimates through feature-metric consistency. To this purpose, we use a network architecture akin to the one in [36]. The network receives a pair " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "\\alpha = (\\mathbf{I}_i,\\mathbf{I}_j)" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": ", the depth map " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{D}_i" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{I}_i" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "[\\hat{\\mathbf{R}}_1^\\alpha ,\\hat{\\mathbf{t}}_1^\\alpha ]" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": ", the current camera pose estimate in the reference frame of " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "\\beta_{1}" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": ", to regress a refined " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "[\\mathbf{R}_1^\\alpha ,\\mathbf{t}_1^\\alpha ]" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": ". We uniformly sample " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": " tentative camera poses " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "\\{\\hat{\\mathbf{R}}_{1p}^{\\alpha},\\hat{\\mathbf{t}}_{1p}^{\\alpha}\\}_{p = 1}^{P}" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": " by perturbing the rotation and the translation of the initial poses " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "[\\hat{\\mathbf{R}}_1^\\alpha ,\\hat{\\mathbf{t}}_1^\\alpha ]" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": ". The " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": " poses are used to construct a pose cost volume by warping each point " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "u" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": " in the source feature " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_i" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": " to a point " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "\\tilde{u}_p" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": " on the target feature " + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_j" + }, + { + "bbox": [ + 46, + 280, + 287, + 426 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 93, + 434, + 287, + 458 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 434, + 287, + 458 + ], + "spans": [ + { + "bbox": [ + 93, + 434, + 287, + 458 + ], + "type": "interline_equation", + "content": "\\tilde {u} _ {p} \\sim \\mathbf {K} \\left[ \\hat {\\mathbf {R}} _ {1 p} ^ {\\alpha} \\mid \\hat {\\mathbf {t}} _ {1 p} ^ {\\alpha} \\right] \\left[ \\begin{array}{c} \\left(\\mathbf {K} ^ {- 1} u\\right) \\mathbf {D} _ {i} (u) \\\\ 1 \\end{array} \\right]. \\tag {4}", + "image_path": "c13947f8232235f2078e3810fad66a15db7936b570f1f7a1893c0ad52de99434.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 460, + 287, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 287, + 485 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 287, + 485 + ], + "type": "text", + "content": "Finally, a sequence of 3D convolutional layers is applied to the pose cost volume to regress the camera pose " + }, + { + "bbox": [ + 46, + 460, + 287, + 485 + ], + "type": "inline_equation", + "content": "\\left[\\mathbf{R}_1^\\alpha ,\\mathbf{t}_1^\\alpha \\right]" + }, + { + "bbox": [ + 46, + 460, + 287, + 485 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 52, + 499, + 287, + 606 + ], + "blocks": [ + { + "bbox": [ + 52, + 499, + 287, + 606 + ], + "lines": [ + { + "bbox": [ + 52, + 499, + 287, + 606 + ], + "spans": [ + { + "bbox": [ + 52, + 499, + 287, + 606 + ], + "type": "image", + "image_path": "65f30614b2fa0778b2be90f2efe26ad89de0e65d696cd261a377683944aa6a02.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "lines": [ + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "spans": [ + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": "Figure 5: Cost volume construction by multi-body plane sweep. For each virtual depth plane at " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "d_{l} \\in \\{d_{l}\\}_{l=1}^{L}" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": ", we generate a " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "2\\mathbf{C} \\times \\mathbf{W} \\times \\mathbf{H}" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": " feature map by concatenating the target feature " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_j" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": " (gray) to the warped source feature " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{F}}_{il}^{\\gamma}" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": " (in color) at depth " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "d_{l}" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": " using motion " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "[\\hat{\\mathbf{R}}_{\\gamma}^{\\alpha}, \\hat{\\mathbf{t}}_{\\gamma}^{\\alpha}]" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": ". The 4D cost volume is constructed through concatenation of these " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": " feature blocks. " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{F}}_{il}^{k}" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": " (in blue) indicates a source feature " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_i" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": " warped onto " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_j" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": " through the homography induced by the generic plane at " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "d_{l}" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": " and its relative camera motion " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "[\\hat{\\mathbf{R}}_k^{\\alpha}, \\hat{\\mathbf{t}}_k^{\\alpha}]" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": ". Instead, " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{F}}_{il}^{h}" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": " is induced by the motion " + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "inline_equation", + "content": "[\\hat{\\mathbf{R}}_h^{\\alpha}, \\hat{\\mathbf{t}}_h^{\\alpha}]" + }, + { + "bbox": [ + 46, + 609, + 287, + 710 + ], + "type": "text", + "content": " (in pink)." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 307, + 71, + 555, + 244 + ], + "blocks": [ + { + "bbox": [ + 307, + 71, + 555, + 244 + ], + "lines": [ + { + "bbox": [ + 307, + 71, + 555, + 244 + ], + "spans": [ + { + "bbox": [ + 307, + 71, + 555, + 244 + ], + "type": "table", + "html": "
viewMethodlower is better ↓higher is better ↑
Abs RelSq RelRMSERMSElogδ1δ2δ3
Eigen SM (s)svDORN [9]0.0670.2952.9290.1080.9490.9880.995
AdaBins [2]0.0540.1822.3410.0870.9660.9950.999
mvDeepV2D [31]0.0500.2122.4830.0890.9730.9920.997
Wang et al. [34]0.0340.1031.9190.0570.9890.9980.999
Ours0.0440.1482.1250.0680.9740.9960.999
Eigen (s & m)svDORN [9]0.0720.3072.7270.1200.9320.9840.994
AdaBins [2]0.0580.1902.3600.0880.9640.9950.999
mvSfMLearner [39]0.2081.7686.8560.2830.6780.8850.975
CCNet [25]0.1401.0705.3260.2170.8260.9410.975
BANet [29]0.083-3.6400.134---
DeepV2D [31]0.0640.3502.9460.1200.9460.9820.991
Wang et al. [34]0.0550.2242.2730.0910.9560.9840.993
Ours0.0540.1862.2690.0860.9660.9910.996
Eigen MB (m)svDORN [9]0.0720.3072.7270.1200.9320.9840.994
AdaBins [2]0.0620.2012.3720.0920.9590.9940.999
mvDeepV2D [31]0.0890.4013.2780.1520.9310.9650.989
Wang et al. [34]0.0630.2422.3470.1090.9480.9710.991
Ours0.0570.1972.3010.0900.9620.9910.994
", + "image_path": "e2f80f44f669b12f8eda5b9d9990dbc457ee582660f683058f4d51dbe8f74b3f.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 254, + 545, + 287 + ], + "lines": [ + { + "bbox": [ + 305, + 254, + 545, + 287 + ], + "spans": [ + { + "bbox": [ + 305, + 254, + 545, + 287 + ], + "type": "text", + "content": "Table 1: Depth evaluation on KITTI Depth. Results from single-view (sv) and multi-view (mv) depth estimation methods evaluated under two-view SfM setting. Best results in bold." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 307, + 433, + 319 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 307, + 433, + 319 + ], + "spans": [ + { + "bbox": [ + 306, + 307, + 433, + 319 + ], + "type": "text", + "content": "4.3.3. Training and Inference" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "spans": [ + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "text", + "content": "We train the feature extractor, 3D convolutions and regression layers in a end-to-end supervised manner. We denote as " + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "inline_equation", + "content": "\\mathbf{D}" + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "text", + "content": " the depth regressed from the refined cost volume, and as " + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "inline_equation", + "content": "\\mathbf{D}_{\\mathrm{gt}}" + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "text", + "content": " the ground-truth depth. To improve the learning process, we also regress a depth map " + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{D}}" + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "text", + "content": " from the cost volume before applying edge-preserving filtering. The loss function is defined as " + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{depth}} = \\sum_{i}\\lambda H(\\tilde{\\mathbf{D}},\\mathbf{D}_{\\mathrm{gt}}) + H(\\mathbf{D},\\mathbf{D}_{\\mathrm{gt}})" + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "inline_equation", + "content": "\\lambda = 0.7" + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "text", + "content": " is a weight and " + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "inline_equation", + "content": "H(\\cdot)" + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "text", + "content": " is the Huber loss. The pose losses " + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{rot}}" + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{trans}}" + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "text", + "content": " are defined as the " + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "inline_equation", + "content": "\\ell_1" + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "text", + "content": " distance between the predicted and ground-truth absolute poses. Our final loss is then: " + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "inline_equation", + "content": "\\mathcal{L} = \\lambda_r\\mathcal{L}_{\\mathrm{rot}} + \\lambda_t\\mathcal{L}_{\\mathrm{trans}} + \\lambda_d\\mathcal{L}_{\\mathrm{depth}}" + }, + { + "bbox": [ + 304, + 321, + 545, + 466 + ], + "type": "text", + "content": ". All the weights are specified in the supplementary." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 466, + 545, + 562 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 466, + 545, + 562 + ], + "spans": [ + { + "bbox": [ + 304, + 466, + 545, + 562 + ], + "type": "text", + "content": "The multi-body plane sweep component of the network has no learnable parameters and is not trained. Our network does not require any form of motion annotation for depth estimation, even in multi-body scenes. For this reason, we train our model on static frames from KITTI [10] and DeMoN [33]. The training and inference are performed in an iterative fashion in four steps, where the regressed depth maps and camera poses are fed to the next iteration." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 572, + 387, + 586 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 572, + 387, + 586 + ], + "spans": [ + { + "bbox": [ + 306, + 572, + 387, + 586 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 592, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 592, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 592, + 545, + 665 + ], + "type": "text", + "content": "We evaluate our method on static (s) and multi-body (m) datasets for depth and pose estimation against state-of-the-art single-view (sv) and multi-view (mv) methods. In Sec. 5.4 we discuss the limitations of our method and possible countermeasures. Additional experiments and implementation details are provided in the supplementary." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 671, + 491, + 684 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 671, + 491, + 684 + ], + "spans": [ + { + "bbox": [ + 306, + 671, + 491, + 684 + ], + "type": "text", + "content": "5.1. Datasets, Competitors and Metrics" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "KITTI Depth (s & m) [10] is designed for depth evaluation in autonomous driving and contains several image se" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17809" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 70, + 214, + 133 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 214, + 133 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 214, + 133 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 214, + 133 + ], + "type": "image", + "image_path": "d8cd6d34c49eb9fafc251a11fe0b23a7b2b2bebeb556df11a195544de7d52502.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 137, + 547, + 159 + ], + "lines": [ + { + "bbox": [ + 47, + 137, + 547, + 159 + ], + "spans": [ + { + "bbox": [ + 47, + 137, + 547, + 159 + ], + "type": "text", + "content": "Figure 6: Multi-body Unstructured Extract. Three view pairs extracted from our proposed dataset for illustration purposes. The dataset contains indoor sequences that depict varied scenarios in which objects of several different sizes move in the scene." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 215, + 70, + 380, + 133 + ], + "blocks": [ + { + "bbox": [ + 215, + 70, + 380, + 133 + ], + "lines": [ + { + "bbox": [ + 215, + 70, + 380, + 133 + ], + "spans": [ + { + "bbox": [ + 215, + 70, + 380, + 133 + ], + "type": "image", + "image_path": "15dd3fed94c621f86d5edc96b54f2ae56a90b0af432dccd333f4ab0f910360ac.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 381, + 71, + 545, + 133 + ], + "blocks": [ + { + "bbox": [ + 381, + 71, + 545, + 133 + ], + "lines": [ + { + "bbox": [ + 381, + 71, + 545, + 133 + ], + "spans": [ + { + "bbox": [ + 381, + 71, + 545, + 133 + ], + "type": "image", + "image_path": "f635c5d702c084bed50b68d42556fe612894ee4ec25e12405ddf67a7019e65e8.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 48, + 169, + 545, + 315 + ], + "blocks": [ + { + "bbox": [ + 48, + 169, + 545, + 315 + ], + "lines": [ + { + "bbox": [ + 48, + 169, + 545, + 315 + ], + "spans": [ + { + "bbox": [ + 48, + 169, + 545, + 315 + ], + "type": "table", + "html": "
MethodMVSScenes11SUN3D
DepthPoseDepthPoseDepthPose
L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)
AdaBins [2]0.0480.2360.291--0.0200.3820.270--0.0210.1270.161--
DeMoN [33]0.0470.2020.3055.15614.4470.0190.3150.2480.8098.9180.0190.1140.1721.80118.811
LS-Net [4]0.0510.2210.3114.65311.1220.0100.4100.2104.6538.2100.0150.1890.6501.52114.347
BA-Net [29]0.0300.1500.0803.49911.2380.0800.2100.1303.49910.3700.0150.1100.0601.72913.260
DeepSfM [36]0.0210.1290.0792.8249.8810.0070.1120.0640.4035.8280.0130.0930.0721.70413.107
Wang et al. [34]0.0150.1020.0682.4173.8780.0050.0970.0580.2762.0410.0100.0810.0571.39110.757
Ours (M=1)0.0160.1070.0682.5384.5380.0050.0990.0580.3213.6490.0110.0840.0611.47012.018
Ours (M=2)0.0190.1210.0732.6817.3400.0070.1020.0690.4014.6190.0130.0920.0711.62513.402
Ours (M=3)0.0250.1320.0752.8929.5300.0090.1240.0780.5425.7820.0140.0950.0791.76915.231
Ours (M=4)0.0260.1340.0762.9319.7410.0090.1280.0810.5715.8030.0160.1070.0841.83015.904
", + "image_path": "c23b553048674c26ee2805b5da63058f84bee8cb172dee2045db9a59210f023f.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 65, + 316, + 526, + 328 + ], + "lines": [ + { + "bbox": [ + 65, + 316, + 526, + 328 + ], + "spans": [ + { + "bbox": [ + 65, + 316, + 526, + 328 + ], + "type": "text", + "content": "Table 2: Depth and pose evaluation on MVS, Scenes 11, SUN3D. (s). For all metrics lower is better. Best results are in bold." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 339, + 287, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 339, + 287, + 411 + ], + "spans": [ + { + "bbox": [ + 46, + 339, + 287, + 411 + ], + "type": "text", + "content": "quences where objects move rigidly. We consider the Eigen [7] split (697 frames) and the Eigen SfM split [34] (256 frames), a subset of the Eigen split without moving objects. In addition, we introduce the Eigen MB split, a subset of the Eigen split that includes 90 frames in which dynamic objects appear and camera motions are well-conditioned." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 411, + 287, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 411, + 287, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 287, + 495 + ], + "type": "text", + "content": "MVS, Scenes11, SUN3D. (s) MVS [33] includes outdoor sequences with large baselines. Scenes11 [33] contains fairly realistic frames from rendered scenes with accurate ground truth depth and camera poses. SUN3D [37] is an indoor dataset with sometimes inaccurate ground truth depth and camera poses. For SUN3D, we consider the split by [33] to exclude frames with high photoconsistency errors." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 495, + 287, + 542 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 495, + 287, + 542 + ], + "spans": [ + { + "bbox": [ + 46, + 495, + 287, + 542 + ], + "type": "text", + "content": "ETH3D SLAM. (m) [28] contains SLAM sequences with ground truth depth and camera poses. We consider the dynamic sequences motion1-2-3-4 and, specifically, a 32 frames split where camera motions are well-conditioned." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 543, + 287, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 543, + 287, + 663 + ], + "spans": [ + { + "bbox": [ + 46, + 543, + 287, + 663 + ], + "type": "text", + "content": "Multi-body Unstructured. (m) We capture multi-body indoor sequences using a Kinect with ground truth depth. The dataset is meant for evaluation in varied conditions, for instance, when image sets are unstructured or when both large and big objects move in the scene. We use RGB-D SLAM [8] to fuse visual information and data from the Kinect IMU and annotate accurate camera poses. The dataset includes 42 frames with either one or two moving objects. Samples scenes are reported in Fig.6 and additional details are provided in the supplementary." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": "Competitors. We compare against state-of-the-art single-view methods (sv) DORN [9] and AdaBins [2], and multiview methods (mv) DeMoN [33], LS-Net [3], CCNet [25], BANet [29], DeepV2D [31] and Wang et al. [34]. De" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 339, + 545, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 339, + 545, + 424 + ], + "spans": [ + { + "bbox": [ + 304, + 339, + 545, + 424 + ], + "type": "text", + "content": "MoN estimates depth and poses from image pairs, CCNet and SfMLearner mask moving objects before depth and pose estimation, LS-Net, BANet and DeepV2D optimize multi-view differentiable cost functions to minimize photo- or feature-metric errors, and Wang et al. [34] proposes a deep, scale-invariant estimator for depth and camera poses that robustly identify the dominant background motion " + }, + { + "bbox": [ + 304, + 339, + 545, + 424 + ], + "type": "inline_equation", + "content": "\\beta_{1}" + }, + { + "bbox": [ + 304, + 339, + 545, + 424 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "spans": [ + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "type": "text", + "content": "Metrics. To evaluate the quality of depth maps in KITTI Depth, we adopt the metrics in [7], i.e., the depth absolute (Abs Rel) and squared (Sq Rel) relative difference, the RMSE, the " + }, + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "type": "inline_equation", + "content": "\\mathrm{RMSE}_{\\log}" + }, + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "type": "text", + "content": ", and the thresholds " + }, + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "type": "inline_equation", + "content": "\\{\\delta_i\\}_{i=1}^3" + }, + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "type": "text", + "content": ". For other datasets, we adopt the metrics in [33], i.e., scale-invariant depth error (sc-inv), relative error to ground truth depth (L1-rel), relative error w.r.t. inverse depth (L1-inv). The definitions of these metrics are in the supplementary. As for pose estimation, we report the angle (in deg) between predicted and ground truth translations " + }, + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "type": "inline_equation", + "content": "(t_{\\mathrm{err}})" + }, + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "type": "text", + "content": " and rotations " + }, + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "type": "inline_equation", + "content": "(\\mathbf{R}_{\\mathrm{err}})" + }, + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "type": "text", + "content": " of the cameras with respect to the background motions " + }, + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "type": "inline_equation", + "content": "\\beta_1" + }, + { + "bbox": [ + 304, + 430, + 546, + 563 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": "Implementation Details. We fine-tune the optical flow network on KITTI Depth for a fair comparison to [34]. Otherwise, we train the optical flow on synthetic scenes, as in [35], and let the proposed framework refine initial camera poses. We implement our framework using PyTorch. The batch size is set to 32. The learning rate is set to " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "1 \\times 10^{-4}" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": " and is halved after 2 epochs. For KITTI Depth, the feature extractor is initialized with pre-trained weights, which are frozen for the first epoch. For other datasets, we train the network from randomly initialized weights. Training takes approximately 3 days on 2 NVIDIA RTX A6000 GPUs. 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(m) The yellow boxes highlight moving objects reconstructed by our method but not by DeepSfM [36]." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 402, + 71, + 496, + 142 + ], + "blocks": [ + { + "bbox": [ + 402, + 71, + 496, + 142 + ], + "lines": [ + { + "bbox": [ + 402, + 71, + 496, + 142 + ], + "spans": [ + { + "bbox": [ + 402, + 71, + 496, + 142 + ], + "type": "image", + "image_path": "f9f856427c97101989ee11d5c48c05d6bbc1ab080f8e80a76d0f14190f6e4ab3.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + } + ], + "index": 15 + }, + { + "type": "image", + "bbox": [ + 402, + 142, + 496, + 214 + ], + "blocks": [ + { + "bbox": [ + 402, + 142, + 496, + 214 + ], + "lines": [ + { + "bbox": [ + 402, + 142, + 496, + 214 + ], + "spans": [ + { + "bbox": [ + 402, + 142, + 496, + 214 + ], + "type": "image", + "image_path": "2e4e42a3baf8172b8884d487d06a9621ea154db84317e7ff6ad19ce601310aad.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 402, + 214, + 496, + 286 + ], + "blocks": [ + { + "bbox": [ + 402, + 214, + 496, + 286 + ], + "lines": [ + { + "bbox": [ + 402, + 214, + 496, + 286 + ], + "spans": [ + { + "bbox": [ + 402, + 214, + 496, + 286 + ], + "type": "image", + "image_path": "3fa7e07828de964815fcad1237a36db4db8fb5f641710969b833420156e2ac34.jpg" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_body" + } + ], + "index": 17 + }, + { + "type": "image", + "bbox": [ + 402, + 286, + 496, + 357 + ], + "blocks": [ + { + "bbox": [ + 402, + 286, + 496, + 357 + ], + "lines": [ + { + "bbox": [ + 402, + 286, + 496, + 357 + ], + "spans": [ + { + "bbox": [ + 402, + 286, + 496, + 357 + ], + "type": "image", + "image_path": "2df2c4d5e497a34186dfff6a4946b639aa9902f5e83c397bea0588a44efbc3e4.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 439, + 360, + 461, + 371 + ], + "lines": [ + { + "bbox": [ + 439, + 360, + 461, + 371 + ], + "spans": [ + { + "bbox": [ + 439, + 360, + 461, + 371 + ], + "type": "text", + "content": "Ours" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "bbox": [ + 47, + 418, + 163, + 430 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 418, + 163, + 430 + ], + "spans": [ + { + "bbox": [ + 47, + 418, + 163, + 430 + ], + "type": "text", + "content": "5.2. Static evaluation (s)" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 46, + 437, + 287, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 510 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 510 + ], + "type": "text", + "content": "KITTI Depth. The Eigen SfM block of Tab. 1 reports quantitative results for static depth estimation. Our method beats the single-view methods [9, 2] and also the multi-view DeepV2D [31] in all metrics and with a clear margin. Yet Wang et al. [34] achieves better performance on this static scenes, although it recovers only up-to-scale depth maps." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "text", + "content": "MVS, Scenes11, SUN3D. Quantitative results are shown in Tab. 2. Our method beats the single-view [9, 2] and multiview [33, 4, 29] in most metrics, but achieves results that are on par or slightly worse compared to DeepSfM [36], since we rely on monocular depth cues that are less accurate than the DeMoN depths used in DeepSfM. The best results are achieved by [34]. In the supplementary, we show that our method beats geometric SfM baselines. By setting " + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "inline_equation", + "content": "M = 1" + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "text", + "content": " and leveraging the static scene assumption, we outperform [36] and are similar to [34]. However, when the scene is static and " + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "inline_equation", + "content": "M \\geq 2" + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "text", + "content": " motions are considered, our method produces outlying essential matrices that may negatively impact depth estimation. Nonetheless, we achieve good results for " + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "inline_equation", + "content": "M \\geq 2" + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "text", + "content": " and even outperform [36] in the multi-body configuration " + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "inline_equation", + "content": "M = 2" + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "text", + "content": ". For " + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "inline_equation", + "content": "M \\geq 2" + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "text", + "content": ", the performance drop is limited, indicating that " + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 510, + 288, + 714 + ], + "type": "text", + "content": " can be larger without affecting depth accuracy substantially." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 306, + 418, + 448, + 431 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 418, + 448, + 431 + ], + "spans": [ + { + "bbox": [ + 306, + 418, + 448, + 431 + ], + "type": "text", + "content": "5.3. Multi-body evaluation (m)" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 437, + 546, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 546, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 546, + 665 + ], + "type": "text", + "content": "KITTI Depth. The Eigen MB and Eigen blocks of Tab. 1 report quantitative results for depth estimation in the multi-body setting. As opposed to the static case, our method beats its multi-view competitors in both the considered splits. Specifically, we observe the most significant margin in the Eigen MB split, in which dynamic objects negatively affect the quality of static multi-view depth estimators [30, 34]. This is evident in the highlighted portion of Fig. 8, where our method accurately reconstructs the moving vehicle, whereas the state-of-the-art Wang et al. [34] exhibits significant artifacts. As in the static evaluation, our framework beats monocular approaches [2, 9] in most metrics, showing it effectively leverage multi-view constraints for improved depth estimation accuracy. Less strict thresholds " + }, + { + "bbox": [ + 304, + 437, + 546, + 665 + ], + "type": "inline_equation", + "content": "\\delta_{2}" + }, + { + "bbox": [ + 304, + 437, + 546, + 665 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 437, + 546, + 665 + ], + "type": "inline_equation", + "content": "\\delta_{3}" + }, + { + "bbox": [ + 304, + 437, + 546, + 665 + ], + "type": "text", + "content": " generally see better results for single-view methods compared to multi-view due to better handling of occlusions and image regions with uniform pixel intensity. However, monocular methods perform worse on the most strict threshold " + }, + { + "bbox": [ + 304, + 437, + 546, + 665 + ], + "type": "inline_equation", + "content": "\\delta_{1}" + }, + { + "bbox": [ + 304, + 437, + 546, + 665 + ], + "type": "text", + "content": " and the other accuracy-oriented metrics." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 547, + 713 + ], + "type": "text", + "content": "ETH3D and Multi-Body Unstructured. Results on these multi-body datasets are reported in Tab. 3. Our method produces more accurate depth and camera pose estimates than its competitors in all metrics. Specifically, our method out" + } + ] + } + ], + "index": 26 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17811" + } + ] + } + ], + "index": 27 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 71, + 547, + 122 + ], + "blocks": [ + { + "bbox": [ + 48, + 71, + 547, + 122 + ], + "lines": [ + { + "bbox": [ + 48, + 71, + 547, + 122 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 547, + 122 + ], + "type": "image", + "image_path": "f7440bd1a5b7b51da9d3b215bfac406556f97d4169fa0001faa916090a072787.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 124, + 545, + 137 + ], + "lines": [ + { + "bbox": [ + 47, + 124, + 545, + 137 + ], + "spans": [ + { + "bbox": [ + 47, + 124, + 545, + 137 + ], + "type": "text", + "content": "Figure 8: Qualitative results on KITTI (m). The yellow box highlights a moving vehicle that is captured more accurately by our method." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 140, + 286, + 232 + ], + "blocks": [ + { + "bbox": [ + 48, + 140, + 286, + 232 + ], + "lines": [ + { + "bbox": [ + 48, + 140, + 286, + 232 + ], + "spans": [ + { + "bbox": [ + 48, + 140, + 286, + 232 + ], + "type": "table", + "html": "
MethodETH3DMulti-body Unstructured
DepthPoseDepthPose
L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)L1-invSc-invL1-rel\\( R_{err} \\)\\( t_{err} \\)
DeMoN[33]0.380.410.335.6312.040.520.710.414.909.26
AdaBins[2]0.350.390.27--0.480.630.38--
DeepSIM[36]0.120.140.102.809.640.220.220.182.385.03
Wang et al.[34]0.210.190.173.269.040.270.220.192.797.67
Ours (M=1)0.110.140.102.989.580.210.220.182.215.01
Ours (M=2)0.090.120.082.918.530.190.200.171.994.91
Ours (M=3)0.080.110.082.948.280.170.190.161.944.72
Ours (M=4)0.090.110.092.948.230.170.200.171.944.70
", + "image_path": "6b7d761a7ab5e744807c5d65f7841137aae04a17b24aab577ceded8818e5a442.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 234, + 286, + 255 + ], + "lines": [ + { + "bbox": [ + 47, + 234, + 286, + 255 + ], + "spans": [ + { + "bbox": [ + 47, + 234, + 286, + 255 + ], + "type": "text", + "content": "Table 3: Depth and pose evaluation on multi-body datasets (m). For all metrics, lower is better. Best results are in bold." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 262, + 287, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 262, + 287, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 262, + 287, + 574 + ], + "type": "text", + "content": "performs DeMoN [33] by a significant margin and, when compared to DeepSfM [36], attains better results in depth estimation in both datasets. This is shown by the qualitative results of Fig. 7, where depth maps from DeepSfM exhibit noticeable break-ups in the areas corresponding to the moving objects. Our pose estimation is also more accurate, except for the " + }, + { + "bbox": [ + 47, + 262, + 287, + 574 + ], + "type": "inline_equation", + "content": "\\mathbf{R}_{\\mathrm{err}}" + }, + { + "bbox": [ + 47, + 262, + 287, + 574 + ], + "type": "text", + "content": " over the ETH3D dataset [28]. Overall, we attribute this difference to: i) DeepSfM suffers from poor initialization from DeMoN, which is not accurate in multi-body scenes and hinders the overall quality of the reconstruction, ii) the plane sweep algorithm adopted by DeepSfM constructs cost volumes that do not satisfy the geometric constraints for the moving objects. Our method also beats Wang et al. [34] in all metrics by a clear margin. As expected, the performance of Wang et al. suffers significantly in multi-body scenes. The moving objects are treated as outliers and negatively impact the accuracy of the estimated camera poses, which, in turn, undermine the quality of depth estimation. By segmenting the rigid motions in the scene before computing camera poses, our method exploits and is robust to the moving objects and achieves state-of-the-art performance in multi-body depth estimation. The effectiveness of multi-body plane sweep (PS) is evidenced by the uplift in performance for " + }, + { + "bbox": [ + 47, + 262, + 287, + 574 + ], + "type": "inline_equation", + "content": "M \\geq 2" + }, + { + "bbox": [ + 47, + 262, + 287, + 574 + ], + "type": "text", + "content": " in Tab. 3. Note that for " + }, + { + "bbox": [ + 47, + 262, + 287, + 574 + ], + "type": "inline_equation", + "content": "M = 1" + }, + { + "bbox": [ + 47, + 262, + 287, + 574 + ], + "type": "text", + "content": ", a single motion is considered and MBPS specializes to traditional PS, with similar results to [36]." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 581, + 196, + 593 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 581, + 196, + 593 + ], + "spans": [ + { + "bbox": [ + 47, + 581, + 196, + 593 + ], + "type": "text", + "content": "5.4. Discussion and Limitations" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 599, + 287, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 599, + 287, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 599, + 287, + 635 + ], + "type": "text", + "content": "Our method inherits some known limitations of the multi-view approaches. In this section we discuss their possible mitigations." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 639, + 286, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 639, + 286, + 674 + ], + "spans": [ + { + "bbox": [ + 47, + 639, + 286, + 674 + ], + "type": "text", + "content": "Small camera motions may hinder initial pose estimates. Our pose refinement network mitigates poor initializations, but it may not recover in particularly challenging cases." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": "Occlusions are mitigated, as in [13, 36], by aggregating cost volumes from multiple image pairs, if available. However, with only two images, occlusions result in noisy depth maps" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 142, + 545, + 166 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 142, + 545, + 166 + ], + "spans": [ + { + "bbox": [ + 305, + 142, + 545, + 166 + ], + "type": "text", + "content": "in the region of the occluded objects, as seen in the second sequence of Fig. 7." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 173, + 545, + 221 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 173, + 545, + 221 + ], + "spans": [ + { + "bbox": [ + 305, + 173, + 545, + 221 + ], + "type": "text", + "content": "Monocular depth inaccuracies may hinder the estimation of object scale factors. However, we observed our KDE voting scheme can isolate outlying measurements and return accurate results when enough (" + }, + { + "bbox": [ + 305, + 173, + 545, + 221 + ], + "type": "inline_equation", + "content": "\\sim 10" + }, + { + "bbox": [ + 305, + 173, + 545, + 221 + ], + "type": "text", + "content": ") factors are computed." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 228, + 545, + 299 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 228, + 545, + 299 + ], + "spans": [ + { + "bbox": [ + 305, + 228, + 545, + 299 + ], + "type": "text", + "content": "Non-rigid scenes. Our method is not designed for non-rigid scenes, for which different assumptions are used, e.g. temporal coherence or complete reliance on monocular depth for moving objects. Nevertheless, as shown in the supplementary, our method can reconstruct articulated motions, provided that a sufficient number of motions is considered." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 306, + 545, + 378 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 306, + 545, + 378 + ], + "spans": [ + { + "bbox": [ + 305, + 306, + 545, + 378 + ], + "type": "text", + "content": "Virtual depth planes. Our multi-body plane sweep assigns " + }, + { + "bbox": [ + 305, + 306, + 545, + 378 + ], + "type": "inline_equation", + "content": "L / M" + }, + { + "bbox": [ + 305, + 306, + 545, + 378 + ], + "type": "text", + "content": " depth planes to each motion, meaning that the more motions considered, the fewer depth planes are assigned to each motion. As stated in the supplementary, we consider up to four motions in our evaluation, as increasing the number of depth planes worsens training and inference times." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 385, + 545, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 385, + 545, + 422 + ], + "spans": [ + { + "bbox": [ + 305, + 385, + 545, + 422 + ], + "type": "text", + "content": "Inference times are on average " + }, + { + "bbox": [ + 305, + 385, + 545, + 422 + ], + "type": "inline_equation", + "content": "\\sim 20\\%" + }, + { + "bbox": [ + 305, + 385, + 545, + 422 + ], + "type": "text", + "content": " higher in KITTI Depth with respect to [34] due to the required motion segmentation step, as discussed in the supplementary." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 438, + 378, + 450 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 438, + 378, + 450 + ], + "spans": [ + { + "bbox": [ + 306, + 438, + 378, + 450 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 460, + 545, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 545, + 605 + ], + "type": "text", + "content": "In this paper, we have addressed the problem of multi-body depth and camera pose estimation. We overcome the scale-ambiguity problem typical of all the MBSfM approaches by introducing a learning-based robust voting scheme to unify the scales of all independently moving objects in the scene. In addition, we overcome the static-scene assumption of deep SfM approaches thanks to a novel multi-body plane sweep network that explicitly supports the additional multi-view geometric constraints derived from the multiple bodies. Extensive experiments on multi-body datasets show that our method outperforms state-of-the-art deep learning methods qualitatively and quantitatively." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": "Acknowledgements. This paper is supported by FAIR (Future Artificial Intelligence Research) project, funded by the NextGenerationEU program within the PNRR-PE-AI scheme (M4C2, Investment 1.3, Line on Artificial Intelligence). We also gratefully acknowledge NVIDIA Corporation for the GPUs donated within the Academic and Applied Research Program to Giacomo Boracchi and Luca Magri" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "17812" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 134 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 134 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 134 + ], + "type": "text", + "content": "[1] Federica Arrigoni, Elisa Ricci, and Tomas Pajdla. 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In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 1851-1858, 2017. 6" + } + ] + } + ], + "index": 9 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "17814" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation/6d6e86b4-be03-4421-80b1-27dd9a45c2b4_content_list.json b/2023/Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation/6d6e86b4-be03-4421-80b1-27dd9a45c2b4_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..944f38436eedcfc4a77e2dadd55ec60f80c44652 --- /dev/null +++ b/2023/Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation/6d6e86b4-be03-4421-80b1-27dd9a45c2b4_content_list.json @@ -0,0 +1,1983 @@ +[ + { + "type": "text", + "text": "Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation", + "text_level": 1, + "bbox": [ + 125, + 128, + 844, + 174 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Nian Liu $^{1}$ Kepan Nan $^{2}$ Wangbo Zhao $^{3}$ Yuanwei Liu $^{2}$ Xiwen Yao $^{2\\dagger}$", + "bbox": [ + 218, + 202, + 767, + 220 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Salman Khan $^{1,4}$ Hisham Cholakkal $^{1}$ Rao Muhammad Anwer $^{1}$ Junwei Han $^{2}$ Fahad Shahbaz Khan $^{1,5}$", + "bbox": [ + 88, + 220, + 890, + 238 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1 Mohamed bin Zayed University of Artificial Intelligence 2 Northwestern Polytechnical University 3 National University of Singapore", + "bbox": [ + 89, + 238, + 879, + 273 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{4}$ Australian National University $^{5}$ CVL, Linköping University", + "bbox": [ + 248, + 273, + 733, + 292 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 325, + 312, + 342 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Few-Shot Video Object Segmentation (FSVOS) aims to segment objects in a query video with the same category defined by a few annotated support images. However, this task was seldom explored. In this work, based on IPMT, a state-of-the-art few-shot image segmentation method that combines external support guidance information with adaptive query guidance cues, we propose to leverage multi-grained temporal guidance information for handling the temporal correlation nature of video data. We decompose the query video information into a clip prototype and a memory prototype for capturing local and long-term internal temporal guidance, respectively. Frame prototypes are further used for each frame independently to handle fine-grained adaptive guidance and enable bidirectional clip-frame prototype communication. To reduce the influence of noisy memory, we propose to leverage the structural similarity relation among different predicted regions and the support for selecting reliable memory frames. Furthermore, a new segmentation loss is also proposed to enhance the category discriminability of the learned prototypes. Experimental results demonstrate that our proposed video IPMT model significantly outperforms previous models on two benchmark datasets. Code is available at https://github.com/nankepan/VIPMT.", + "bbox": [ + 75, + 358, + 473, + 705 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 733, + 207, + 748 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To mitigate the data-hungry issue of modern deep semantic segmentation models [18, 2, 4], few-shot semantic segmentation emerges by only requiring a few support samples with annotated masks for segmenting the objects of the same class in new images. Many recent works [25, 32, 13, 16] have shown very promising results on image data using the meta-learning scheme. They simulate the inference process and partition the training set into numerous episodes, in each", + "bbox": [ + 75, + 757, + 470, + 878 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/1c2fd512074ba0e8b90112e47317e93c140d8eb071c96f9050fa016b39598ec2.jpg", + "image_caption": [ + "Figure 1. Given a few annotated support frames, FSVOS aims to segment the objects with the same category from a query video (a). Simply considering single-frame information leads to inconsecutive segmentation results (b), while our method generates accurate results by using multi-grained temporal prototypes (c)." + ], + "image_footnote": [], + "bbox": [ + 501, + 325, + 573, + 474 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/09d31fb0d3deb2639947235aef7873bd60984f577935aa88d799710613f91ead.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 584, + 335, + 890, + 383 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/79d08fb30710adeb622507f7dcf014110f4114f1b187d3d9fdb403f0e46f8900.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 584, + 390, + 890, + 425 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/736a516b91f587a10ea0f92e80b0f1d8fffbfb23ebee61bfdbc8f106214d1281.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 584, + 433, + 890, + 468 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "of which, the model samples a few support images and learns to guide the segmentation on the query images.", + "bbox": [ + 496, + 566, + 890, + 597 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Inspired by the classic Few-Shot Image Semantic Segmentation (FSISS) task, the Few-Shot Video Object Segmentation (FSVOS) task was introduced by [1, 24]. For FSISS, many works adopt the prototype-based methods, in which a prototype vector is extracted from the support to encode the category guidance information, and then a segmentation head learns to match the prototype with the feature at each query pixel for performing query segmentation. However, the intra-class diversity can cause the matching gap between the support-induced prototype guidance and the query features. The IPMT model [16] solved this problem by learning an intermediate prototype that integrates both support-induced external category guidance knowledge and query-induced adaptive guidance information. As for FSVOS, video data additionally show temporal correlation, from which we can also induce internal temporal guidance. If we ignore this prior knowledge and simply consider single-frame information, the learned prototypes may vary significantly among different frames, leading to inconsecutive segmentation results, as shown in Figure 1 (b).", + "bbox": [ + 496, + 598, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "†Corresponding author: yaoxiwen517@gmail.com.", + "bbox": [ + 94, + 886, + 367, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "18862", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this work, we extend the IPMT model [16] for video data by tackling the temporal correlation nature. Based on the intermediate prototype mechanism of IPMT, we propose to decompose the query video information into the clip-level, frame-level, and memory-level prototypes, consisting of a multi-grained temporal structure, which was NEVER explored by existing models [1, 24]. Among them, the clip prototype encodes local temporal object guidance information in each consecutive clip, while the memory prototype introduces long-term historical guidance cues. Combining them can effectively handle the temporal correlation problem. However, such a design may ignore fine-grained per-frame adaptive guidance information, hence may fail to handle large scene changes and object transformation. To this end, we further learn an adaptive frame prototype by independently encoding per-frame object features. Additionally, we enable bidirectional clip-frame prototype communication by making the clip-level and frame-level prototypes initialize each other, hence promoting intra-clip temporal correlation.", + "bbox": [ + 76, + 90, + 472, + 380 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To better leverage the historical memory guidance, we also follow a Video Object Segmentation (VOS) method [17] and train an IoU regression network to select reliable memory frames for reducing the negative influence brought by noisy memory. However, different from [17], we explicitly consider the nature of the FSVOS task and propose to leverage the structural similarity relation among different predicted regions and the support information for predicting more accurate IoU scores. To make the learned prototype more category discriminative, we also propose a Cross-Category Discriminative Segmentation (CCDS) loss by leveraging negative batch samples. Extensive experimental results have verified the effectiveness of our proposed Video IPMT (VIPMT) model and showed its significant performance improvement over state-of-the-art models.", + "bbox": [ + 76, + 385, + 472, + 612 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In conclusion, our contributions can be summarized as follows:", + "bbox": [ + 76, + 618, + 468, + 648 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- For the very first time, we propose to learn multi-grained temporal prototypes for FSVOS, by extending the IPMT [16] model. Clip and memory prototypes are learned for internal temporal guidance. Frame prototypes are used for fine-grained adaptive guidance and also enable prototype communication.", + "- We propose to leverage the structural similarity relation among different predicted regions and the support for selecting reliable memory information. We also present a CCDS loss using the negative samples within each batch for promoting category discriminability of the learned prototypes.", + "- Experimental results have demonstrated the significant effectiveness of our proposed model, which improves state-of-the-art results by more than $4\\%$ and $3\\%$ , on two benchmark datasets, respectively." + ], + "bbox": [ + 94, + 656, + 468, + 898 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 89, + 640, + 106 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Few-Shot Image Semantic Segmentation", + "text_level": 1, + "bbox": [ + 500, + 114, + 846, + 132 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Most previous FSISS works adopted meta-learning-based methods [27], especially prototype-based models. Specifically, Dong and Xing [9] aggregated a prototype vector on the support images to encode the representative category knowledge first, and then evaluated its similarity with each query pixel in a matching network as the segmentation result. Following this idea, Yang et al. [29] constructed multiple prototypes from limited support images to represent diverse image regions. In [25], Tian et al. used high-level features to generate a prior mask as a supplement to the support prototype for refining the query feature. Liu et al. [15] leveraged non-target prototypes to eliminate distracting regions. BAM [13] used the prototypes of base classes to explicitly suppress corresponding regions. In IPMT [16], Liu et al. proposed to generate an intermediate prototype which encodes the category guidance information from both support and query. However, all these methods only focused on image data and the challenge of video data remains seldom explored.", + "bbox": [ + 496, + 138, + 893, + 412 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Video Object Segmentation", + "text_level": 1, + "bbox": [ + 500, + 422, + 746, + 439 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Another closely related domain is VOS, especially the semi-supervised VOS, in which the mask label of an object in the first frame is given and the model is required to segment the same object in other frames. Some methods [22, 7, 28] tried to leverage optical flow to help segment target objects. Noticing the successful application of memory networks [8, 31] in computer vision, STM [21] proposed a memory mechanism to leverage information from previous frames for segmenting the current frame. Lu et al. [19] followed this idea and improve the memory mechanism with a graph model. For a comprehensive survey please refer to [33].", + "bbox": [ + 496, + 446, + 893, + 613 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Different from semi-supervised VOS, we tackle the FSVOS task with two differences. First, semi-supervised VOS aims to segment the same object indicated in the annotation of the first frame while FSVOS requires to segment the objects of the same class with the annotated support set. Second, the support set in FSVOS can be composed of any images or frames of any videos that contain the target class. Hence, FSVOS is more generalized and faces much larger intra-class diversity between the support set and the query video. In this work, we propose multi-grained temporal prototype learning and bidirectional clip-frame prototype communication for FSVOS, which is different from existing VOS methods.", + "bbox": [ + 496, + 613, + 893, + 808 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Our idea of using the IoU network to select memory frames with high segmentation quality is inspired by [17]. However, in [17], the authors directly regress the IoU score by only taking the image and the mask as the network input. In this work, we further consider the nature of FSVOS and propose to compute several structural similarity maps", + "bbox": [ + 496, + 809, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "18863", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "which explicitly encode the quality assessment prior of the relations among the predicted foreground, background, and the support areas.", + "bbox": [ + 75, + 90, + 468, + 137 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Few-shot Video Object Segmentation", + "text_level": 1, + "bbox": [ + 76, + 146, + 397, + 162 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For the FSVOS task, currently, only a few works have targeted this topic. Chen et al. [1] proposed the first FSVOS dataset and model. They proposed a Domain Agent Network (DAN) to alleviate the large computational cost of the many-to-many attention between the support images and the query video frames, which only considered clip-level temporal information. Siam et al. [24] proposed a temporal transductive inference model, which uses both global and local temporal constraints to obtain per-frame model weights and locally consistent predictions. Compared with them, we optimize multi-grained temporal prototypes while they optimized per-frame model weights. Furthermore, we explicitly use historical memory while they did not.", + "bbox": [ + 75, + 169, + 472, + 367 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Preliminaries", + "text_level": 1, + "bbox": [ + 76, + 380, + 215, + 396 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Problem Definition", + "text_level": 1, + "bbox": [ + 76, + 405, + 259, + 420 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For FSVOS, a whole video object segmentation dataset $\\mathcal{D}$ with multiple object categories $\\mathcal{C}$ is divided into a training subset $\\mathcal{D}_{base}$ and a testing subset $\\mathcal{D}_{novel}$ , whose categories are $\\mathcal{C}_{base}$ and $\\mathcal{C}_{novel}$ , respectively, and satisfy $\\mathcal{C}_{base} \\cap \\mathcal{C}_{novel} = \\emptyset$ and $\\mathcal{C}_{base} \\cup \\mathcal{C}_{novel} = \\mathcal{C}$ . Under the standard few-shot setting and the episodic training scheme, both $\\mathcal{D}_{base}$ and $\\mathcal{D}_{novel}$ are randomly partitioned into a lot of episodes. In each episode, a support set $S$ provides $K$ frames $\\mathbf{I}^{\\mathrm{s}}$ with labeled segmentation masks $\\mathbf{O}^{\\mathrm{s}}$ of a specific object category (we follow [1, 24] to focus on one-way segmentation here), i.e., $S = \\left\\{\\left(\\mathbf{I}^{\\mathrm{s}_i}, \\mathbf{O}^{\\mathrm{s}_i}\\right)\\right\\}_{i=1}^{K}$ , as the meta knowledge of the target class. Then, given a query video $\\mathcal{Q} = \\{\\mathbf{I}^{\\mathrm{q}_i}\\}_{i=1}^{N}$ with $N$ frames, an FSVOS model is used to predict the segmentation masks $\\{\\tilde{\\mathbf{O}}^{\\mathrm{q}_i}\\}_{i=1}^{N}$ of the same category for each frame. The model can be trained on the episodes sampled from $\\mathcal{D}_{base}$ with the given ground truth query masks $\\{\\mathbf{O}^{\\mathrm{q}_i}\\}_{i=1}^{N}$ , learning how to transfer the guidance knowledge from the support to the query. Finally, the FSVOS model is expected to make accurate predictions for unseen categories on $\\mathcal{D}_{novel}$ .", + "bbox": [ + 75, + 428, + 472, + 731 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Review of IPMT", + "text_level": 1, + "bbox": [ + 76, + 739, + 238, + 755 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The IPMT model [16] adopts a transformer-based architecture for the FSISS task. Specifically, FSISS can be modeled by learning an intermediate prototype $\\mathbf{G} \\in \\mathbb{R}^{1 \\times C}$ and pixel-wise feature maps $\\mathbf{F^s}$ and $\\mathbf{F^q}$ for the support and query, respectively, and then conduct iterative mutual optimization between $\\mathbf{G}$ and $\\mathbf{F^q}$ within multiple IPMT layers. Under the $K$ -shot setting, the support features $\\mathbf{F^s} \\in \\mathbb{R}^{Khw \\times C}$ and the flattened masks $\\mathbf{O^s} \\in \\mathbb{R}^{Khw \\times 1}$ , where $h, w, C$ are the height, width, and channel number, respectively.", + "bbox": [ + 75, + 763, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the $l$ -th IPMT layer, given the previous query feature $\\mathbf{F}_{l-1}^{\\mathbf{q}} \\in \\mathbb{R}^{hw \\times C}$ and the flattened binarized mask prediction $\\tilde{\\mathbf{O}}_{l-1}^{\\mathbf{q}} \\in \\mathbb{R}^{hw \\times 1}$ , the intermediate prototype $\\mathbf{G}$ is updated by", + "bbox": [ + 498, + 90, + 890, + 140 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathbf {G} _ {l} = \\mathbf {I P M} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} ^ {\\mathbf {s}}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}, \\mathbf {O} ^ {\\mathbf {s}}, \\tilde {\\mathbf {O}} _ {l - 1} ^ {\\mathbf {q}}\\right) \\tag {1} \\\\ = \\mathbf {M L P} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {s}} + \\mathbf {G} _ {l} ^ {\\mathbf {q}} + \\mathbf {G} _ {l - 1}\\right), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 148, + 890, + 188 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where MLP denotes a multi-layer perception. The $\\mathbf{G}_l^{\\mathrm{s}}$ can be seen as the support prototype which encodes the deterministic guidance knowledge from the support and the $\\mathbf{G}_l^{\\mathbf{q}}$ can be regarded as the query prototype that learns adaptive guidance information from the query. They can be obtained by", + "bbox": [ + 496, + 193, + 893, + 284 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {G} _ {l} ^ {\\mathbf {s}} = \\mathbf {M A t t} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} ^ {\\mathbf {s}}, \\mathbf {O} ^ {\\mathbf {s}}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 294, + 890, + 311 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {G} _ {l} ^ {\\mathbf {q}} = \\mathbf {M A t t} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}, \\tilde {\\mathbf {O}} _ {l - 1} ^ {\\mathbf {q}}\\right). \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 313, + 890, + 330 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Here, MAtt means the masked attention operation [3]:", + "bbox": [ + 500, + 340, + 867, + 356 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {M} \\mathbf {A} \\mathbf {t} \\mathbf {t} (\\mathbf {G}, \\mathbf {F}, \\mathbf {O}) = \\delta \\left(f _ {Q} (\\mathbf {G}) f _ {K} (\\mathbf {F}) ^ {\\top} + \\Delta\\right) f _ {V} (\\mathbf {F}), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 513, + 366, + 890, + 383 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\delta$ means the softmax normalization, $f_{Q}(\\cdot), f_{K}(\\cdot), f_{V}(\\cdot)$ are three linear transformations following [26], and $\\Delta = (1 - \\mathbf{O}^{\\top}) \\cdot (-\\infty)$ is used to modulate the attention matrix, making background attention weights become zeros after softmax.", + "bbox": [ + 496, + 393, + 890, + 468 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Then, the updated $\\mathbf{G}_l$ is used to generate mask predictions for both support and query via a mask generation (MG) process:", + "bbox": [ + 496, + 469, + 890, + 515 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {\\mathbf {O}} _ {l} ^ {\\mathbf {s}} = \\mathbf {M G} \\left(\\mathbf {G} _ {l}, \\mathbf {F} ^ {\\mathbf {s}}\\right), \\tilde {\\mathbf {O}} _ {l} ^ {\\mathbf {q}} = \\mathbf {M G} \\left(\\mathbf {G} _ {l}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 545, + 523, + 890, + 542 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {M G} (\\mathbf {G}, \\mathbf {F}) = \\operatorname {S i g m o i d} \\left(f _ {G} (\\mathbf {G}) \\mathbf {F} ^ {\\top}\\right), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 568, + 566, + 890, + 584 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $f_{G}(\\cdot)$ is another linear transformation. At the same time, the generated prototype $\\mathbf{G}_l$ is also used to update the query feature maps via query activation (QA):", + "bbox": [ + 496, + 590, + 890, + 636 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {F} _ {l} ^ {\\mathbf {q}} = \\mathbf {Q} \\mathbf {A} \\left(\\mathbf {G} _ {l}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}\\right) = \\mathcal {F} _ {\\text {a c t v}} \\left(\\mathbf {G} _ {l} \\odot \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}\\right), \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 545, + 645, + 890, + 664 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\odot$ means concatenation and $\\mathcal{F}_{\\text{actv}}$ is an activation network with two convolution layers.", + "bbox": [ + 496, + 672, + 890, + 703 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In the original implementation, IPMT first feeds the input images into a froze backbone encoder (e.g. ResNet-50 [11]), obtaining multi-scale features $\\{\\mathbf{X}_1,\\mathbf{X}_2,\\mathbf{X}_3,\\mathbf{X}_4\\}$ from the last four convolution blocks, with the scale of 1/4, 1/8, 1/8, and 1/8, respectively. Then, $\\mathbf{X}_1$ and $\\mathbf{X}_2$ are fused to obtain the backbone features for both support and query. Next, a prototype activation (PA) module generates the support features $\\mathbf{F}^{\\mathrm{s}}$ , the initial query feature $\\mathbf{F}_0^{\\mathrm{q}}$ , and the initial query mask $\\tilde{\\mathbf{O}}_0^{\\mathrm{q}}$ . The initial prototype $\\mathbf{G}_0$ is randomly initialized at the beginning and then optimized during training. Afterward, by iteratively operating (1) to (7) in five layers, both prototype and features can be optimized step by step. For more details please refer to [16].", + "bbox": [ + 496, + 704, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "18864", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/61c0b8800fcdb502d13718612e8eeb34cee70e3a543177f5a4701aac3ebbc52b.jpg", + "image_caption": [ + "Figure 2. Main architecture of the proposed VIPMT model for FSVOS. \"RMS\" means our proposed reliable memory selection (Section 4.3), \"MAtt\" means masked attention (4), \"MG\" means mask generation (6), and \"QA\" means query activation (7). In each VIPMT iteration, the input intermediate prototype $\\mathbf{G}_{l-1}$ first generates the support prototype $\\mathbf{G}_l^{\\mathrm{s}}$ (2), the clip prototype $\\mathbf{G}_l^{\\mathrm{c}}$ (8), and the memory prototype $\\mathbf{G}_l^{\\mathrm{m}}$ (13), and combine them to obtain the clip-level intermediate prototype $\\mathbf{G}_l^{\\mathrm{ci}}$ (14). Afterwords, a frame level prototype $\\mathbf{G}_l^{\\mathrm{f}_i}$ is obtained for each frame via (10) and then updates the frame mask $\\tilde{\\mathbf{O}}_l^{\\mathrm{f}_i}$ and frame feature $\\mathbf{F}_l^{\\mathrm{c}_i}$ via (12). Finally, all $\\mathbf{G}_l^{\\mathrm{f}_i}$ are averaged to obtain $\\mathbf{G}_l$ (11), which is input into the next iteration with $\\tilde{\\mathbf{O}}_l^{\\mathrm{f}}$ and $\\mathbf{F}_l^{\\mathrm{c}}$ ." + ], + "image_footnote": [], + "bbox": [ + 83, + 85, + 893, + 300 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Video IPMT", + "text_level": 1, + "bbox": [ + 76, + 410, + 207, + 425 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As shown in Figure 2, we take the original IPMT model as the baseline and combine it with our proposed multi-grained prototype learning scheme for performing the FSVOS task. We elaborate on the design of our clip-level, frame-level, and memory-level prototypes first. Finally, we present the training loss, including the newly proposed CCDS loss.", + "bbox": [ + 75, + 436, + 470, + 527 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Clip Prototype Learning", + "text_level": 1, + "bbox": [ + 76, + 537, + 302, + 553 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Since a video is composed of several consecutive frames, a straightforward way is to directly apply the IPMT model on each query frame. However, such a naive method does not consider any video temporal information and also lacks efficiency. Hence, we propose to take video clips as query units for both training and inference. Given a query video clip $\\mathcal{C} = \\{\\mathbf{I}^{\\mathbf{c}_i}\\}_{i=1}^{T_c}$ with $T_c$ frames, we perform the masked attention with clip-level query features to generate the clip prototype:", + "bbox": [ + 75, + 560, + 468, + 696 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {G} _ {l} ^ {\\mathbf {c}} = \\mathbf {M A t t} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {c}}, \\tilde {\\mathbf {O}} _ {l - 1} ^ {\\mathbf {f}}\\right), \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 156, + 707, + 468, + 724 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbf{F}_{l - 1}^{\\mathbf{c}}\\in \\mathbb{R}^{T_chw\\times C}$ , $\\tilde{\\mathbf{O}}_{l - 1}^{\\mathbf{f}}\\in \\mathbb{R}^{T_chw\\times 1}$ is the previous predicted masks and will be explained later. Then, we obtain the clip-level intermediate prototype:", + "bbox": [ + 75, + 737, + 468, + 784 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {G} _ {l} ^ {\\mathbf {c i}} = \\mathbf {M L P} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {s}} + \\mathbf {G} _ {l} ^ {\\mathbf {c}} + \\mathbf {G} _ {l - 1}\\right), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 156, + 795, + 468, + 813 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "which encodes local guidance information within the whole query clip. Next, we can use (6) to segment the target objects in the whole clip and obtain clip predictions $\\tilde{\\mathbf{O}}_l^{\\mathbf{c}}\\in \\mathbb{R}^{T_chw\\times 1} = \\mathbf{M}\\mathbf{G}(\\mathbf{G}_l^{\\mathbf{ci}},\\mathbf{F}_{l - 1}^{\\mathbf{c}})$ , which preserves temporal coherence within the $T_{c}$ frames.", + "bbox": [ + 75, + 824, + 470, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. Frame Prototype Learning", + "text_level": 1, + "bbox": [ + 500, + 411, + 741, + 428 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The clip-level intermediate prototype $\\mathbf{G}_l^{\\mathrm{ci}}$ uses one prototype to represent the whole clip and encodes the clip consensus object information, however, may ignore frame-level fine-grained cues. This problem may cause a performance drop when the object appearance changes significantly within the clip. To mitigate this problem, we propose to further generate frame-level query prototypes $\\{\\mathbf{G}_{l}\\}_{i = 1}^{T_{c}}$ by updating $\\mathbf{G}_l^{\\mathrm{ci}}$ with related fine-grained object cues in each frame:", + "bbox": [ + 496, + 435, + 893, + 556 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {G} _ {l} ^ {\\mathbf {f} _ {i}} = \\operatorname {M L P} \\left(\\mathbf {M A t t} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {c i}}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {c} _ {i}}, \\tilde {\\mathbf {O}} _ {l} ^ {\\mathbf {c} _ {i}}\\right) + \\mathbf {G} _ {l} ^ {\\mathbf {c i}}\\right). \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 524, + 568, + 890, + 587 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this process, we use $\\mathbf{G}_l^{\\mathbf{ci}}$ as a good initialization to learn each $\\mathbf{G}_l^{\\mathbf{f}_i}$ and subsequently aggregate the frame-level query prototypes as the initialization for the next iteration:", + "bbox": [ + 496, + 599, + 890, + 648 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {G} _ {l} = \\frac {1}{T _ {c}} \\sum_ {i = 1} ^ {T _ {c}} \\mathbf {G} _ {l} ^ {\\mathbf {f} _ {i}}. \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 632, + 660, + 890, + 702 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As such, we enable bidirectional clip-frame prototype communication, which promotes the intra-clip temporal correlation. On the contrary, directly using the clip-level intermediate prototype $\\mathbf{G}_l^{\\mathrm{ci}}$ as the initialization for the next iteration only enables one-way communication from the clip information to the frame-level.", + "bbox": [ + 496, + 713, + 893, + 803 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "At the same time, we use each frame prototype $\\mathbf{G}_l^{\\mathbf{f}_i}$ to generate the frame-level segmentation mask and update the query feature for each frame independently:", + "bbox": [ + 496, + 804, + 890, + 849 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\tilde {\\mathbf {O}} _ {l} ^ {\\mathbf {f} _ {i}} = \\mathbf {M G} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {f} _ {i}}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {c} _ {i}}\\right), \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 611, + 861, + 890, + 888 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {F} _ {l} ^ {\\mathbf {c} _ {i}} = \\mathbf {Q A} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {f} _ {i}}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {c} _ {i}}\\right).\n$$\n", + "text_format": "latex", + "bbox": [ + 617, + 885, + 777, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "18865", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/8f78487e95e2bd67801f1f8efafc6045502f45bc54e2f09917bf334718be8464.jpg", + "image_caption": [ + "Figure 3. Illustration of the generation process of the four structural similarity maps. Red and blue regions indicate objects of two categories, respectively. Here we only show two support frames for concision." + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 472, + 309 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Next, $\\tilde{\\mathbf{O}}_l^{\\mathbf{f}} = \\{\\tilde{\\mathbf{O}}_l^{\\mathbf{f}_i}\\}_{i = 1}^{T_c},\\mathbf{F}_l^{\\mathbf{c}} = \\{\\mathbf{F}_l^{\\mathbf{c}_i}\\}_{i = 1}^{T_c}$ , and $\\mathbf{G}_l$ are input to (8) again for the next iteration.", + "bbox": [ + 75, + 378, + 468, + 412 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Memory Prototype Learning", + "text_level": 1, + "bbox": [ + 76, + 421, + 334, + 436 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Since a whole video usually contains numerous frames, only considering the information within a local clip is suboptimal as long-term historical temporal information is ignored. Many VOS works have also demonstrated that leveraging history memory is crucial for video data to enhance the temporal correlation. To this end, we propose to learn a memory prototype for providing historical guidance information. For each clip except the first one, we can use $T_{m}$ previous frames as the memory set $\\mathcal{M} = \\{\\mathbf{I}^{\\mathbf{m}_i}\\}_{i=1}^{T_m}$ , which also has predicted masks $\\tilde{\\mathbf{O}}^{\\mathbf{m}} \\in \\mathbb{R}^{T_mhw \\times 1}$ . Then, we use masked attention on memory features to generate the memory prototype:", + "bbox": [ + 75, + 444, + 472, + 612 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {G} _ {l} ^ {\\mathbf {m}} = \\mathbf {M A t t} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} ^ {\\mathbf {m}}, \\tilde {\\mathbf {O}} ^ {\\mathbf {m}}\\right), \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 161, + 621, + 468, + 640 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{F}^{\\mathbf{m}}\\in \\mathbb{R}^{T_mhw\\times C}$ and $\\tilde{\\mathbf{O}}^{\\mathbf{m}}\\in \\mathbb{R}^{T_mhw\\times 1}$ . Then, the update of the clip-level intermediate prototype $\\mathbf{G}_l^{\\mathbf{ci}}$ in (9) can be rewritten as", + "bbox": [ + 75, + 646, + 468, + 694 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {G} _ {l} ^ {\\mathrm {c i}} = \\mathbf {M L P} \\left(\\mathbf {G} _ {l} ^ {\\mathrm {s}} + \\mathbf {G} _ {l} ^ {\\mathrm {c}} + \\mathbf {G} _ {l} ^ {\\mathrm {m}} + \\mathbf {G} _ {l - 1}\\right). \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 132, + 703, + 468, + 722 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We do not consider using memory prototype at the frame level since $\\mathbf{G}_l^{\\mathbf{ci}}$ is designed to combine comprehensive guidance information at the clip-level, simultaneously from support, clip, and memory. In contrast, $\\mathbf{G}_l^{\\mathbf{f}_i}$ encodes pure frame adaptive cues and uses $\\mathbf{G}_l^{\\mathbf{ci}}$ as the initialization.", + "bbox": [ + 75, + 729, + 470, + 806 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Reliable Memory Selection. During the training stage, we can use the ground truth memory masks $\\mathbf{O}^{\\mathrm{m}}$ to replace the predicted masks for training an accurate model. However, during the inference stage, we can only use the predicted masks $\\tilde{\\mathbf{O}}^{\\mathrm{m}}$ , which may be very noisy and hence heavily contaminate the learned prototype. To mitigate this problem,", + "bbox": [ + 75, + 810, + 470, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "we follow [17] and train an IoU regression network (IoUNet) to select reliable memory frames which have higher segmentation quality. Different from [17], we explicitly consider the nature of the FSVOS task and propose to leverage the structural similarity among the predicted foreground region, background region, and object region in support images for predicting more accurate IoU scores.", + "bbox": [ + 496, + 90, + 893, + 196 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Specifically, as shown in Figure 3, given the backbone features of an memory frame $\\mathbf{X}_4\\in \\mathbb{R}^{hw\\times C}$ and the support set $\\mathbf{X}_4^{\\mathbf{s}}\\in \\mathbb{R}^{Khw\\times C}$ , the predicted memory mask $\\tilde{\\mathbf{O}}\\in \\mathbb{R}^{hw\\times 1}$ (here we omit the superscript $\\mathbf{m}$ for conciseness), and the ground truth support masks $\\mathbf{O}^{\\mathrm{s}}\\in \\mathbb{R}^{Khw\\times 1}$ , we first obtain the background mask for the memory $\\tilde{\\mathbf{B}} = 1 - \\tilde{\\mathbf{O}}$ . Then, we can evaluate the segmentation quality of the memory frame using a simple and intuitive idea: once it is well segmented, its foreground region $\\tilde{\\mathbf{O}}$ should be dissimilar to the background $\\tilde{\\mathbf{B}}$ and similar to the support foreground $\\mathbf{O}^{\\mathrm{s}}$ , while the background $\\tilde{\\mathbf{B}}$ should be dissimilar to both $\\tilde{\\mathbf{O}}$ and $\\mathbf{O}^{\\mathrm{s}}$ . To this end, we compute the structural similarity map of the foreground area of the memory w.r.t. the background area:", + "bbox": [ + 496, + 196, + 893, + 393 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {S} ^ {f b} = \\operatorname {N o r m} \\left(\\operatorname {M a x} \\left(\\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {O}}\\right) \\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {B}}\\right) ^ {\\top}, 1\\right)\\right), \\tag {15}\n$$\n", + "text_format": "latex", + "bbox": [ + 517, + 401, + 890, + 420 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\odot$ means element-wise multiplication, $\\mathbf{Max}(*,1)$ means obtaining the maximum value along each row, and Norm denotes the min-max normalization to scale the data to the range of [0, 1]. Then, the output map $\\mathbf{S}^{fb}\\in \\mathbb{R}^{hw\\times 1}$ exactly represents how similar each foreground pixel is w.r.t. the background area, as shown in Figure 3.", + "bbox": [ + 496, + 429, + 893, + 518 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Likewise, we can obtain a similarity map $\\mathbf{S}^{bf}$ of the background area w.r.t. the foreground, similarity map $\\mathbf{S}^{fs}$ of the foreground area of the memory w.r.t. the foreground of the support, and similarity map $\\mathbf{S}^{bs}$ of the background area of the memory w.r.t. the foreground of the support:", + "bbox": [ + 496, + 518, + 893, + 595 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {S} ^ {b f} = \\operatorname {N o r m} \\left(\\operatorname {M a x} \\left(\\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {B}}\\right) \\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {O}}\\right) ^ {\\top}, 1\\right)\\right),\n$$\n", + "text_format": "latex", + "bbox": [ + 513, + 604, + 841, + 622 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {S} ^ {f s} = \\operatorname {N o r m} \\left(\\operatorname {M a x} \\left(\\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {O}}\\right) \\left(\\mathbf {X} _ {4} ^ {\\mathbf {s}} \\odot \\mathbf {O} ^ {\\mathbf {s}}\\right) ^ {\\top}, 1\\right)\\right), \\tag {16}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 625, + 890, + 643 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {S} ^ {b s} = \\operatorname {N o r m} (\\operatorname {M a x} ((\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {B}}) (\\mathbf {X} _ {4} ^ {\\mathbf {s}} \\odot \\mathbf {O} ^ {\\mathbf {s}}) ^ {\\top}, 1)).\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 647, + 846, + 666 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Once obtain the four structural similarity maps, we combine them with multi-scale memory features and the original predicted mask $\\tilde{\\mathbf{O}}$ to regress the IoU score of the memory frame. Concretely, we first downsample $\\mathbf{X}_1$ to the 1/8 scale with stride convolution and then fuse it with $\\mathbf{X}_2, \\mathbf{X}_3, \\mathbf{X}_4$ into a combined feature with 256 channels. Then, we concatenate the feature with the four structural similarity maps and $\\tilde{\\mathbf{O}}$ and input them into four convolution layers and two fully connected layers for predicting the IoU score.", + "bbox": [ + 496, + 674, + 893, + 809 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "During training, we design three ways to train the IoUNet. First, we can jointly train it with the FSVOS model, in which case real predicted masks can be used for training the IoUNet. Second, we can train it independently using synthesized video data. Specifically, we randomly add noises to the ground truth masks in the training set and use the synthesized", + "bbox": [ + 496, + 810, + 893, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "18866", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "masks to mimic good and bad predictions. In the third way, we train the IoUNet using synthesized image data with the same noisy mask strategy. We compute the ground truth IoU score for each training mask and use a $L_{1}$ loss as supervision. During testing, we simply select reliable memory frames whose predicted IoU scores are larger than a threshold.", + "bbox": [ + 75, + 90, + 470, + 181 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Training Loss", + "text_level": 1, + "bbox": [ + 76, + 190, + 220, + 207 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We follow IPMT [16] and use the final query feature $\\mathbf{F}_5^{\\mathrm{c}}$ to predict the final segmentation masks via two convolution layers, where Dice loss and IoU loss are both used for optimization. To ease the network training, in each iteration we use binary cross entropy (BCE) loss on the predicted support masks $\\tilde{\\mathbf{O}}_l^{\\mathrm{s}}$ , clip masks $\\tilde{\\mathbf{O}}_l^{\\mathrm{c}}$ , and frame masks $\\tilde{\\mathbf{O}}_l^{\\mathrm{f}}$ . As for memory frames, we generate predictions for them at each iteration using $\\mathbf{MG}(\\mathbf{G}_l^{\\mathrm{ci}}, \\mathbf{F}^{\\mathrm{m}})$ , and then adopt the BCE loss computed with their ground truth masks as supervision.", + "bbox": [ + 75, + 213, + 468, + 349 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Cross Category Discriminative Segmentation Loss. To make the learned clip-level intermediate prototypes $\\mathbf{G}^{\\mathrm{ci}}$ more category discriminative, we furthermore propose a CCDS loss and adopt it within each batch. Suppose our batchsize is set to $B > 1$ , we select $B$ video clips with different object categories to form each batch. Then, during training, we use the prototypes of each video to perform segmentation on other videos and let the predicted masks be all zeros. The idea behind is intuitive: if the prototypes are well optimized for a specific category, they should not activate any region on other videos with different categories. However, since a video may contain multiple object categories and we only have the ground truth of one class under the one-way few-shot learning setting, we propose to use the ground truth masks to filter out the regions for loss calculation:", + "bbox": [ + 75, + 353, + 470, + 580 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {c c d s} = \\frac {1}{(B - 1) B} \\sum_ {b = 1} ^ {B} \\sum_ {j \\neq b} \\frac {1}{\\sum \\mathbf {O} _ {j}} L _ {b, j}, \\tag {17}\n$$\n", + "text_format": "latex", + "bbox": [ + 112, + 590, + 468, + 632 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {b, j} = \\sum_ {l = 1} ^ {5} B C E \\left(\\mathbf {M G} \\left(\\mathbf {G} _ {l, b} ^ {\\mathbf {c i}}, \\mathbf {F} _ {j}\\right) \\odot \\mathbf {O} _ {j}, \\mathbf {Z}\\right), \\tag {18}\n$$\n", + "text_format": "latex", + "bbox": [ + 120, + 638, + 468, + 676 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathbf{G}_{l,b}^{\\mathrm{ci}}$ is the clip-level intermediate prototype in the $l$ -th iteration of the $b$ -th video, $\\mathbf{O}_j$ and $\\mathbf{F}_j$ are the ground truth masks and the backbone features of the $j$ -th video. $\\mathbf{Z}$ is an all zero matrix.", + "bbox": [ + 75, + 688, + 468, + 748 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 76, + 762, + 207, + 777 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Datasets and Evaluation Setting", + "text_level": 1, + "bbox": [ + 76, + 786, + 357, + 801 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Datasets. Following [1, 24], our experiments are conducted on the training set of YouTube-VIS [30] dataset, which has 40 categories and contains 2238 videos with 3774 instances. The dataset is divided into four folds, following the same slit with [1, 24]. In each fold, we use 30 categories for training and the rest 10 categories for testing. Following [1, 24], we", + "bbox": [ + 75, + 809, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "set our experiments on the 5-shot setting and randomly select five images from different videos of the same category as the support set. We also follow [24] and adopt the MiniVSPW [24] dataset to evaluate the generalizability of FSVOS methods. It includes 20 categories and provides longer video sequences than YouTube-VIS, since being more challenging.", + "bbox": [ + 496, + 90, + 893, + 181 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation Setting. As the prior work [1] and VOS methods, we adopt the region similarity $\\mathcal{J}$ and contour similarity $\\mathcal{F}$ for performance evaluation. Apart from this, we also follow [24] and consider the video consistency metric $\\mathrm{VC}_7$ , which captures temporal prediction consistency among long-range adjacent frames over a temporal window of 7. We adopt the average score on four folds, i.e. $\\mathrm{mVC}_7$ , to evaluate the overall performance. We also follow [1, 24] and run the evaluation process five times and report the average results.", + "bbox": [ + 496, + 188, + 892, + 325 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Furthermore, there are two different evaluation protocols proposed in [1] and [24] for sampling episodes during testing. Protocol I fixes the sampled support set for all query videos belonging to the same class in each run, while protocol II randomly samples a support set for every query video, which ensures a more stable performance evaluation. Hence, in this paper we adopt protocol II for evaluation.", + "bbox": [ + 496, + 328, + 893, + 434 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation Details. We adopt ResNet-50 [11] pretrained on ImageNet [23] as our encoder backbone. Following IPMT [16], we freeze the parameters of the backbone during training and do not adopt online finetuning as [1, 24] did. The iteration step is set to 5 as IPMT. We set the clip length $T_{c}$ and the memory length $T_{m}$ to 5 without further tuning. The IoU threshold for selecting reliable memory frames is set to 0.8. When the reliable memory has more frames, we simply randomly select five frames from them. During training, we randomly select three clips from a video as a sample, where the first clip is trained without using memory, the second clip uses the first clip as memory, and the third clip randomly selects five frames from the first two as the memory. We also share the MAtt operation for support and memory since we found this leads to better performance.", + "bbox": [ + 496, + 441, + 893, + 667 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We use Adam as our optimizer. The batchsize is set to $B = 4$ and the learning rate is set to 5e-4. We train our model 100 epochs in total. All experiments are conducted on a NVIDIA Tesla A100 GPU. We adopt random horizontal flip, random crop and random resize to augment the training data. During training and testing, all video frames are downsampled to the resolution of (240,424) as the inputs.", + "bbox": [ + 496, + 671, + 893, + 777 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. Comparison with State-of-the-art Methods", + "text_level": 1, + "bbox": [ + 500, + 797, + 862, + 813 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In Table 1, we compare our VIPMT with four recently published FSISS methods and two FSVOS methods, on the YouTuebe-VIS [30] dataset. We find that our VIPMT largely improves all metrics, i.e. $4\\%$ $\\mathcal{I}$ mean score, near $6\\%$ $\\mathcal{F}$ mean score, and near $5\\%$ $\\mathrm{mVC}_7$ score, although previous", + "bbox": [ + 496, + 824, + 892, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "18867", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/d952802ddd5003528b8d4ed4afd846323c9bb66c29420fb451f04c4d51fb41ff.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodsNameJFmVC7
Fold-1Fold-2Fold-3Fold-4MeanFold-1Fold-2Fold-3Fold-4Mean
FSISSNTRENet [15]39.066.461.761.257.141.163.060.159.455.955.7
SSP [10]46.764.359.354.556.234.853.046.046.745.149.6
VAT [12]42.662.857.056.754.841.656.450.853.050.554.9
IPMT [16]43.865.861.060.757.842.559.557.855.953.957.7
FSVOSDAN [1]43.964.561.162.157.942.462.060.060.056.141.5
TTI [24]47.268.861.463.560.2-----60.8
VIPMT(Ours)50.670.968.866.564.251.366.965.264.462.065.7
", + "bbox": [ + 81, + 88, + 898, + 232 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/70ac45994d6cf506a53e39ef93dbe79bc49cbd90b0a679ad91623c8baa832731.jpg", + "table_caption": [ + "Table 1. Comparison with state-of-the-art methods on YouTube-VIS [30]. Bold means the best performance." + ], + "table_footnote": [], + "table_body": "
MethodsNameJFmVC7
Fold-1Fold-2Fold-3Fold-4MeanFold-1Fold-2Fold-3Fold-4Mean
FSVOSTTI [24]25.237.125.029.629.2-----24.4
VIPMT(Ours)26.242.231.629.432.430.645.736.334.236.742.1
", + "bbox": [ + 81, + 251, + 898, + 321 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/cf0c175c5a240e67f78d12e81be66889bb65f2034db1356af26f81209221a2de.jpg", + "table_caption": [ + "Table 2. Comparison with TTI [24] on MiniVSPW [24]." + ], + "table_footnote": [], + "table_body": "
DatasetsMethodsJ-MeanF-MeanmVC7
YouTube-VISIPMT+STCN [6]58.956.561.7
IPMT+XMem [5]59.256.862.2
IPMT+RDE-VOS [14]59.358.063.3
VIPMT(Ours)64.262.065.7
MiniVSPWIPMT+STCN [6]27.731.139.3
IPMT+XMem [5]27.731.741.1
IPMT+RDE-VOS [14]28.833.540.1
VIPMT(Ours)32.436.742.1
", + "bbox": [ + 86, + 344, + 457, + 462 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "works [1, 24] used on-line learning while we didn't.", + "bbox": [ + 76, + 489, + 419, + 503 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To verify the generalization ability of our method, we compare our method with TTI [24] on MiniVSPW. Table 2 shows our method obtains a significant improvement of more than $3\\%$ on $\\mathcal{I}$ and more than $17\\%$ on $\\mathrm{mVC}_7$ , which verifies that our method works well in more challenging scenarios.", + "bbox": [ + 75, + 505, + 467, + 579 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In Figure 4, we give some visual comparison cases. Compared with TTI [24], our VIMPT is less distracted by other objects and achieves more precise segmentation, even in highly occluded scenes (bottom row).", + "bbox": [ + 75, + 580, + 468, + 640 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We also include three state-of-the-art semi-supervised VOS methods for comparison, i.e. STCN [6], XMem [5], and RDE-VOS [14]. Specifically, we use IPMT for segmenting the first frame and then use VOS methods for propagating the segmentation to the full video. Table 3 demonstrates that such an ad-hoc combination of FSISS and VOS methods can not achieve as good results as our model does.", + "bbox": [ + 75, + 641, + 468, + 747 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 755, + 230, + 771 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In this section, we report ablation study results on the YouTube-VIS dataset. For $\\mathcal{J}$ and $\\mathcal{F}$ we use their average on four folds, i.e. $\\mathcal{J}$ -Mean and $\\mathcal{F}$ -Mean.", + "bbox": [ + 75, + 777, + 468, + 824 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Effectiveness of Each Component. In Table 4, we first", + "bbox": [ + 76, + 827, + 468, + 843 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/364ed69379b87231c6b7d6ffbc1727b2f02962e6cade5f3793fe0a148731b66a.jpg", + "table_caption": [ + "Table 3. Comparison with state-of-the-art VOS methods." + ], + "table_footnote": [], + "table_body": "
NameSettingsJ-MeanF-MeanmVC7
ClipFrameMemoryCCDS
Baseline57.853.957.8
+C✓61.858.860.7
+C+F✓✓62.560.362.1
+C+F+M✓✓✓63.561.962.8
VIPMT✓✓✓✓64.262.065.7
", + "bbox": [ + 501, + 345, + 890, + 430 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4. Ablation study on the effectiveness of each model component. Baseline means IPMT [16].", + "bbox": [ + 500, + 431, + 893, + 458 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "adopt IPMT [16] as the baseline, which processes each video frame independently. Then, we adopt our clip prototype learning, denoted as “+C”. Results show that “+C” surpasses the baseline by a large margin on all metrics, which verifies the effectiveness of using local temporal guidance with our clip prototype learning. After that, we further add the frame prototype learning to “+C”, resulting in “+C+F”. Benefiting from the frame-level fine-grained cues, “+C+F” achieves large performance improvement for $\\mathcal{F}$ -Mean and $\\mathrm{mVC}_7$ . Moreover, we adopt “+C+F+M” to represent adding the memory prototype learning on “+C+F”. It largely improves the performance for both $\\mathcal{J}$ -Mean and $\\mathcal{F}$ -Mean, which shows the importance of long-term temporal information brought by the memory prototype learning. Based on this, we further add the CCDS loss to obtain our final model VIPMT. It also brings obvious improvements, especially on $\\mathrm{mVC}_7$ , from 62.8 to 65.7. This proves the effectiveness of increasing category discrimination for FSVOS.", + "bbox": [ + 496, + 472, + 893, + 744 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In Figure 5, we visualize the predicted masks from the different models mentioned above. We can find that progressive improvements can be brought by using multi-grained temporal prototypes and the CCDS loss.", + "bbox": [ + 496, + 744, + 893, + 806 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Clip-frame Communication. As mentioned in Section 4.2, we use the mean of the frame prototypes ((11)) to initialize the intermediate prototype for the next iteration, which enables bidirectional clip-frame communication. On the contrary, directly using the clip-level intermediate prototype $\\mathbf{G}_l^{\\mathrm{ci}}$ as the initialization only enables one-way communica", + "bbox": [ + 496, + 809, + 895, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_footnote", + "text": "*Please note that here we re-tested the performance of DAN [1] using protocol II. Hence, its scores are different from the original paper. For TTI [24], since the authors did not provide the scores for $\\mathcal{F}$ , we leave them blank. We retrained all FSISS methods on YouTube-VIS for a fair comparison.", + "bbox": [ + 75, + 851, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "18868", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/fb031399959c79851a8afb662da3fe7ccaf71ae543ce411f0336ce66760d5de7.jpg", + "image_caption": [ + "(a)" + ], + "image_footnote": [], + "bbox": [ + 81, + 90, + 196, + 209 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0f3602d911c1af2f2fd064587db89f8cdfd3a6478d56a9d708cfb02789982d18.jpg", + "image_caption": [ + "(b)" + ], + "image_footnote": [], + "bbox": [ + 197, + 90, + 393, + 209 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/458c9a285a992d27530f5cb68bf3dbb6384800c167b43ebea674da4312c56ebf.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 393, + 90, + 540, + 209 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/7855a58614e7e309b38e51c3153edb495a598e3b26c4ce277d05676480fe14f8.jpg", + "image_caption": [ + "(c)" + ], + "image_footnote": [], + "bbox": [ + 545, + 90, + 888, + 209 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/6a8b2661d2ee98532f0f79d1260157e715e20a504632d760899a8ce6bb1817a5.jpg", + "image_caption": [ + "Figure 4. Visualization of comparison cases. (a) Support sets. (b) Predicted masks of our VIMPT. (c) Predicted masks from TTI [24].", + "Support", + "Figure 5. Visualization of the comparison of different ablation study models. We can see progressive improvements brought by the multi-grained temporal prototypes and the CCDS loss." + ], + "image_footnote": [], + "bbox": [ + 80, + 253, + 194, + 372 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4f2b3b3c9be5e35db60b1d6b6ed371ee65a301fd04f6eb75ea1595bfb510fe02.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 194, + 253, + 310, + 314 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/eaaeafcd0bc8209b6ebcdedb801113feae37cff9e7cb0657c57bc3328801b244.jpg", + "image_caption": [ + "Baseline" + ], + "image_footnote": [], + "bbox": [ + 196, + 315, + 310, + 371 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4fbd4e33bf8dc35f113e1098a39db7e0759cf704ea08f395babffbd390626198.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 312, + 253, + 424, + 314 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8c930f7ff89f12a09a529077e9ec9be4bf2b86cd8b3349d930a28eb2edb2e54b.jpg", + "image_caption": [ + "+C" + ], + "image_footnote": [], + "bbox": [ + 312, + 315, + 424, + 371 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/5a7cb1baf074c20e762e4962375492f01bfa38c3e760e85482909d07283991aa.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 426, + 253, + 542, + 314 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/670c99d11fbb10ab9e22ffee0829852a0649b914c45ff8606ffa2031e6d936eb.jpg", + "image_caption": [ + "+C+F" + ], + "image_footnote": [], + "bbox": [ + 426, + 315, + 540, + 371 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c56aa0c8cf82e0663bfb4715e58c5991b0c71e266b5f17f1b27e9c239ee4b78a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 542, + 253, + 656, + 314 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c7bf08493adf4b11244373f7410584eccabbb8c0482adff7b5e9937704bdce49.jpg", + "image_caption": [ + "$+\\mathrm{C} + \\mathrm{F} + \\mathrm{M}$" + ], + "image_footnote": [], + "bbox": [ + 542, + 315, + 656, + 371 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/05684a726804e371f5a4ae7f9f8b4081972b4080e74b78b09d463d0465a315e0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 656, + 253, + 772, + 314 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/fb888146b34842e155489ee92d56f9e6704ace4443939af67695c89be9448117.jpg", + "image_caption": [ + "VIPMT" + ], + "image_footnote": [], + "bbox": [ + 658, + 315, + 772, + 371 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c59217b250fc4cee60b111b92b44ac6d68e42b8de0cda6ba7c1f7bbcb5779eee.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 772, + 253, + 888, + 314 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9a1b65534902c9735561fb06021713e633cdb3b11793b3508b6e19ca6ee83f38.jpg", + "image_caption": [ + "GT" + ], + "image_footnote": [], + "bbox": [ + 772, + 315, + 888, + 371 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/d367fc577eefadd71e96be91fe2ffd2903d60eefdb66b5febcc6a11681102033.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Clip-frame CommunicationJ-MeanF-MeanmVC7
One-way61.459.160.1
Bidirectional62.560.362.1
", + "bbox": [ + 78, + 428, + 467, + 484 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "tion. Here we compare the effectiveness of the two schemes. Results in Table 5 demonstrate that our design of using bidirectional clip-frame communication surpasses the one-way scheme by a large margin on all metrics.", + "bbox": [ + 75, + 512, + 468, + 571 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Different Training Strategies of IoUNet. As mentioned in Section 4.3, we can use three ways to train the IoUNet, i.e. using real predicted masks (\"Real\"), synthesized video data (\"Video\"), and synthesized image data (\"Image\"), respectively. For \"Image\", we use an FSISS dataset COCO-20 $^i$ [20] and remove the classes overlapped with our video data for IoUNet training. We compare their performance in Table 6. We also compare the performance of using our proposed structural similarity maps or not (\"w/ SSM\" and \"w/o SSM\"). The results are reported under the IoU threshold of 0.5. The table demonstrates that using synthesized image data results in the best performance in both \"w/ SSM\" and \"w/o SSM\" settings and using the structural similarity maps always leads to better performance. Another benefit of using image data is that we can train a unified IoUNet for all folds instead of training an IoUNet for each fold. Hence, finally, we use synthesized image data for IoUNet training.", + "bbox": [ + 73, + 578, + 470, + 835 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "IoU Threshold. Finally, we investigate the best IoU threshold for memory selection. Table 7 indicates that 0.8 is the best threshold and using the proposed structural similarity maps always leads to better performance.", + "bbox": [ + 75, + 839, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/b6526ec1841e319e96ae9b575fd8efcfc4fc433c5a46a13c16151eb09b0c9792.jpg", + "table_caption": [ + "Table 5. Comparison of two clip-frame communication schemes." + ], + "table_footnote": [], + "table_body": "
Dataw/o SSMw/ SSM
J-MeanF-MeanmVC7J-MeanF-MeanmVC7
Real62.861.562.663.261.662.8
Video62.961.662.663.261.662.8
Image63.061.762.763.361.763.0
", + "bbox": [ + 503, + 428, + 890, + 500 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/d34395ea07cd434adc287d9fff911d934a9f5fd0d44ee9ca79ed90994c276b8d.jpg", + "table_caption": [ + "Table 6. Different training strategies of IoUNet. SSM means the proposed structural similarity maps." + ], + "table_footnote": [], + "table_body": "
Thresholdw/o SSMw/ SSM
J-MeanF-MeanmVC7J-MeanF-MeanmVC7
0.563.061.762.763.361.763.0
0.663.161.762.963.361.762.7
0.763.161.862.963.461.862.6
0.863.161.862.563.561.962.8
0.963.061.862.363.561.962.5
", + "bbox": [ + 503, + 542, + 890, + 633 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 7. Experimental results of using different IoU thresholds.", + "bbox": [ + 500, + 633, + 893, + 646 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 661, + 617, + 676 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We explored learning multi-grained temporal prototypes to tackle the FSVOS task. Based on the IPMT model, the query video information was decomposed into a clip prototype, a memory prototype, and frame prototypes. We also improved an IoU regression method for selecting reliable memory for FSVOS by leveraging the task prior knowledge and proposed a new loss to enhance the category discriminability of the prototypes. The effectiveness of our proposed VIPMT has been verified on two benchmark datasets.", + "bbox": [ + 496, + 688, + 893, + 823 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments: This work was supported in part by the National Natural Science Foundation of China under Grants 62071388, 62136007, U20B2065 and 62036005, and the Fundamental Research Funds for the Central Universities under Grant D5000230057.", + "bbox": [ + 496, + 830, + 893, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "18869", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 174, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Haoxin Chen, Hanjie Wu, Nanxuan Zhao, Sucheng Ren, and Shengfeng He. Delving deep into many-to-many attention for few-shot video object segmentation. 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IEEE TPAMI, 2022. 2", + "bbox": [ + 78, + 90, + 470, + 133 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "18871", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation/6d6e86b4-be03-4421-80b1-27dd9a45c2b4_model.json b/2023/Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation/6d6e86b4-be03-4421-80b1-27dd9a45c2b4_model.json new file mode 100644 index 0000000000000000000000000000000000000000..2ecedde949f2cc0a18dc0400e2115782783a7e14 --- /dev/null +++ b/2023/Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation/6d6e86b4-be03-4421-80b1-27dd9a45c2b4_model.json @@ -0,0 +1,2420 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.126, + 0.13, + 0.846, + 0.175 + ], + "angle": 0, + "content": "Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.22, + 0.203, + 0.768, + 0.221 + ], + "angle": 0, + "content": "Nian Liu\\(^{1}\\) Kepan Nan\\(^{2}\\) Wangbo Zhao\\(^{3}\\) Yuanwei Liu\\(^{2}\\) Xiwen Yao\\(^{2\\dagger}\\)" + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.221, + 0.892, + 0.239 + ], + "angle": 0, + "content": "Salman Khan\\(^{1,4}\\) Hisham Cholakkal\\(^{1}\\) Rao Muhammad Anwer\\(^{1}\\) Junwei Han\\(^{2}\\) Fahad Shahbaz Khan\\(^{1,5}\\)" + }, + { + "type": "text", + "bbox": [ + 0.09, + 0.239, + 0.88, + 0.275 + ], + "angle": 0, + "content": "1 Mohamed bin Zayed University of Artificial Intelligence 2 Northwestern Polytechnical University 3 National University of Singapore" + }, + { + "type": "text", + "bbox": [ + 0.249, + 0.275, + 0.734, + 0.293 + ], + "angle": 0, + "content": "\\(^{4}\\)Australian National University \\(^{5}\\)CVL, Linköping University" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.327, + 0.313, + 0.343 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.359, + 0.474, + 0.707 + ], + "angle": 0, + "content": "Few-Shot Video Object Segmentation (FSVOS) aims to segment objects in a query video with the same category defined by a few annotated support images. However, this task was seldom explored. In this work, based on IPMT, a state-of-the-art few-shot image segmentation method that combines external support guidance information with adaptive query guidance cues, we propose to leverage multi-grained temporal guidance information for handling the temporal correlation nature of video data. We decompose the query video information into a clip prototype and a memory prototype for capturing local and long-term internal temporal guidance, respectively. Frame prototypes are further used for each frame independently to handle fine-grained adaptive guidance and enable bidirectional clip-frame prototype communication. To reduce the influence of noisy memory, we propose to leverage the structural similarity relation among different predicted regions and the support for selecting reliable memory frames. Furthermore, a new segmentation loss is also proposed to enhance the category discriminability of the learned prototypes. Experimental results demonstrate that our proposed video IPMT model significantly outperforms previous models on two benchmark datasets. Code is available at https://github.com/nankepan/VIPMT." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.734, + 0.208, + 0.749 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.758, + 0.471, + 0.88 + ], + "angle": 0, + "content": "To mitigate the data-hungry issue of modern deep semantic segmentation models [18, 2, 4], few-shot semantic segmentation emerges by only requiring a few support samples with annotated masks for segmenting the objects of the same class in new images. Many recent works [25, 32, 13, 16] have shown very promising results on image data using the meta-learning scheme. They simulate the inference process and partition the training set into numerous episodes, in each" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.326, + 0.574, + 0.476 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.585, + 0.337, + 0.891, + 0.384 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.585, + 0.391, + 0.891, + 0.426 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.586, + 0.434, + 0.891, + 0.469 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.48, + 0.895, + 0.551 + ], + "angle": 0, + "content": "Figure 1. Given a few annotated support frames, FSVOS aims to segment the objects with the same category from a query video (a). Simply considering single-frame information leads to inconsecutive segmentation results (b), while our method generates accurate results by using multi-grained temporal prototypes (c)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.567, + 0.891, + 0.598 + ], + "angle": 0, + "content": "of which, the model samples a few support images and learns to guide the segmentation on the query images." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.599, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Inspired by the classic Few-Shot Image Semantic Segmentation (FSISS) task, the Few-Shot Video Object Segmentation (FSVOS) task was introduced by [1, 24]. For FSISS, many works adopt the prototype-based methods, in which a prototype vector is extracted from the support to encode the category guidance information, and then a segmentation head learns to match the prototype with the feature at each query pixel for performing query segmentation. However, the intra-class diversity can cause the matching gap between the support-induced prototype guidance and the query features. The IPMT model [16] solved this problem by learning an intermediate prototype that integrates both support-induced external category guidance knowledge and query-induced adaptive guidance information. As for FSVOS, video data additionally show temporal correlation, from which we can also induce internal temporal guidance. If we ignore this prior knowledge and simply consider single-frame information, the learned prototypes may vary significantly among different frames, leading to inconsecutive segmentation results, as shown in Figure 1 (b)." + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.368, + 0.901 + ], + "angle": 0, + "content": "†Corresponding author: yaoxiwen517@gmail.com." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18862" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.381 + ], + "angle": 0, + "content": "In this work, we extend the IPMT model [16] for video data by tackling the temporal correlation nature. Based on the intermediate prototype mechanism of IPMT, we propose to decompose the query video information into the clip-level, frame-level, and memory-level prototypes, consisting of a multi-grained temporal structure, which was NEVER explored by existing models [1, 24]. Among them, the clip prototype encodes local temporal object guidance information in each consecutive clip, while the memory prototype introduces long-term historical guidance cues. Combining them can effectively handle the temporal correlation problem. However, such a design may ignore fine-grained per-frame adaptive guidance information, hence may fail to handle large scene changes and object transformation. To this end, we further learn an adaptive frame prototype by independently encoding per-frame object features. Additionally, we enable bidirectional clip-frame prototype communication by making the clip-level and frame-level prototypes initialize each other, hence promoting intra-clip temporal correlation." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.386, + 0.473, + 0.613 + ], + "angle": 0, + "content": "To better leverage the historical memory guidance, we also follow a Video Object Segmentation (VOS) method [17] and train an IoU regression network to select reliable memory frames for reducing the negative influence brought by noisy memory. However, different from [17], we explicitly consider the nature of the FSVOS task and propose to leverage the structural similarity relation among different predicted regions and the support information for predicting more accurate IoU scores. To make the learned prototype more category discriminative, we also propose a Cross-Category Discriminative Segmentation (CCDS) loss by leveraging negative batch samples. Extensive experimental results have verified the effectiveness of our proposed Video IPMT (VIPMT) model and showed its significant performance improvement over state-of-the-art models." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.619, + 0.47, + 0.649 + ], + "angle": 0, + "content": "In conclusion, our contributions can be summarized as follows:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.657, + 0.47, + 0.747 + ], + "angle": 0, + "content": "- For the very first time, we propose to learn multi-grained temporal prototypes for FSVOS, by extending the IPMT [16] model. Clip and memory prototypes are learned for internal temporal guidance. Frame prototypes are used for fine-grained adaptive guidance and also enable prototype communication." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.748, + 0.47, + 0.838 + ], + "angle": 0, + "content": "- We propose to leverage the structural similarity relation among different predicted regions and the support for selecting reliable memory information. We also present a CCDS loss using the negative samples within each batch for promoting category discriminability of the learned prototypes." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.838, + 0.47, + 0.899 + ], + "angle": 0, + "content": "- Experimental results have demonstrated the significant effectiveness of our proposed model, which improves state-of-the-art results by more than \\(4\\%\\) and \\(3\\%\\), on two benchmark datasets, respectively." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.657, + 0.47, + 0.899 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.09, + 0.642, + 0.107 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.115, + 0.847, + 0.133 + ], + "angle": 0, + "content": "2.1. Few-Shot Image Semantic Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.139, + 0.895, + 0.413 + ], + "angle": 0, + "content": "Most previous FSISS works adopted meta-learning-based methods [27], especially prototype-based models. Specifically, Dong and Xing [9] aggregated a prototype vector on the support images to encode the representative category knowledge first, and then evaluated its similarity with each query pixel in a matching network as the segmentation result. Following this idea, Yang et al. [29] constructed multiple prototypes from limited support images to represent diverse image regions. In [25], Tian et al. used high-level features to generate a prior mask as a supplement to the support prototype for refining the query feature. Liu et al. [15] leveraged non-target prototypes to eliminate distracting regions. BAM [13] used the prototypes of base classes to explicitly suppress corresponding regions. In IPMT [16], Liu et al. proposed to generate an intermediate prototype which encodes the category guidance information from both support and query. However, all these methods only focused on image data and the challenge of video data remains seldom explored." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.423, + 0.747, + 0.44 + ], + "angle": 0, + "content": "2.2. Video Object Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.447, + 0.895, + 0.614 + ], + "angle": 0, + "content": "Another closely related domain is VOS, especially the semi-supervised VOS, in which the mask label of an object in the first frame is given and the model is required to segment the same object in other frames. Some methods [22, 7, 28] tried to leverage optical flow to help segment target objects. Noticing the successful application of memory networks [8, 31] in computer vision, STM [21] proposed a memory mechanism to leverage information from previous frames for segmenting the current frame. Lu et al. [19] followed this idea and improve the memory mechanism with a graph model. For a comprehensive survey please refer to [33]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.895, + 0.809 + ], + "angle": 0, + "content": "Different from semi-supervised VOS, we tackle the FSVOS task with two differences. First, semi-supervised VOS aims to segment the same object indicated in the annotation of the first frame while FSVOS requires to segment the objects of the same class with the annotated support set. Second, the support set in FSVOS can be composed of any images or frames of any videos that contain the target class. Hence, FSVOS is more generalized and faces much larger intra-class diversity between the support set and the query video. In this work, we propose multi-grained temporal prototype learning and bidirectional clip-frame prototype communication for FSVOS, which is different from existing VOS methods." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Our idea of using the IoU network to select memory frames with high segmentation quality is inspired by [17]. However, in [17], the authors directly regress the IoU score by only taking the image and the mask as the network input. In this work, we further consider the nature of FSVOS and propose to compute several structural similarity maps" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "18863" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.138 + ], + "angle": 0, + "content": "which explicitly encode the quality assessment prior of the relations among the predicted foreground, background, and the support areas." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.147, + 0.398, + 0.163 + ], + "angle": 0, + "content": "2.3. Few-shot Video Object Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.17, + 0.473, + 0.368 + ], + "angle": 0, + "content": "For the FSVOS task, currently, only a few works have targeted this topic. Chen et al. [1] proposed the first FSVOS dataset and model. They proposed a Domain Agent Network (DAN) to alleviate the large computational cost of the many-to-many attention between the support images and the query video frames, which only considered clip-level temporal information. Siam et al. [24] proposed a temporal transductive inference model, which uses both global and local temporal constraints to obtain per-frame model weights and locally consistent predictions. Compared with them, we optimize multi-grained temporal prototypes while they optimized per-frame model weights. Furthermore, we explicitly use historical memory while they did not." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.381, + 0.216, + 0.397 + ], + "angle": 0, + "content": "3. Preliminaries" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.406, + 0.26, + 0.421 + ], + "angle": 0, + "content": "3.1. Problem Definition" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.429, + 0.473, + 0.732 + ], + "angle": 0, + "content": "For FSVOS, a whole video object segmentation dataset \\(\\mathcal{D}\\) with multiple object categories \\(\\mathcal{C}\\) is divided into a training subset \\(\\mathcal{D}_{base}\\) and a testing subset \\(\\mathcal{D}_{novel}\\), whose categories are \\(\\mathcal{C}_{base}\\) and \\(\\mathcal{C}_{novel}\\), respectively, and satisfy \\(\\mathcal{C}_{base} \\cap \\mathcal{C}_{novel} = \\emptyset\\) and \\(\\mathcal{C}_{base} \\cup \\mathcal{C}_{novel} = \\mathcal{C}\\). Under the standard few-shot setting and the episodic training scheme, both \\(\\mathcal{D}_{base}\\) and \\(\\mathcal{D}_{novel}\\) are randomly partitioned into a lot of episodes. In each episode, a support set \\(S\\) provides \\(K\\) frames \\(\\mathbf{I}^{\\mathrm{s}}\\) with labeled segmentation masks \\(\\mathbf{O}^{\\mathrm{s}}\\) of a specific object category (we follow [1, 24] to focus on one-way segmentation here), i.e., \\(S = \\left\\{\\left(\\mathbf{I}^{\\mathrm{s}_i}, \\mathbf{O}^{\\mathrm{s}_i}\\right)\\right\\}_{i=1}^{K}\\), as the meta knowledge of the target class. Then, given a query video \\(\\mathcal{Q} = \\{\\mathbf{I}^{\\mathrm{q}_i}\\}_{i=1}^{N}\\) with \\(N\\) frames, an FSVOS model is used to predict the segmentation masks \\(\\{\\tilde{\\mathbf{O}}^{\\mathrm{q}_i}\\}_{i=1}^{N}\\) of the same category for each frame. The model can be trained on the episodes sampled from \\(\\mathcal{D}_{base}\\) with the given ground truth query masks \\(\\{\\mathbf{O}^{\\mathrm{q}_i}\\}_{i=1}^{N}\\), learning how to transfer the guidance knowledge from the support to the query. Finally, the FSVOS model is expected to make accurate predictions for unseen categories on \\(\\mathcal{D}_{novel}\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.741, + 0.24, + 0.756 + ], + "angle": 0, + "content": "3.2. Review of IPMT" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.473, + 0.903 + ], + "angle": 0, + "content": "The IPMT model [16] adopts a transformer-based architecture for the FSISS task. Specifically, FSISS can be modeled by learning an intermediate prototype \\(\\mathbf{G} \\in \\mathbb{R}^{1 \\times C}\\) and pixel-wise feature maps \\(\\mathbf{F^s}\\) and \\(\\mathbf{F^q}\\) for the support and query, respectively, and then conduct iterative mutual optimization between \\(\\mathbf{G}\\) and \\(\\mathbf{F^q}\\) within multiple IPMT layers. Under the \\(K\\)-shot setting, the support features \\(\\mathbf{F^s} \\in \\mathbb{R}^{Khw \\times C}\\) and the flattened masks \\(\\mathbf{O^s} \\in \\mathbb{R}^{Khw \\times 1}\\), where \\(h, w, C\\) are the height, width, and channel number, respectively." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.141 + ], + "angle": 0, + "content": "In the \\(l\\)-th IPMT layer, given the previous query feature \\(\\mathbf{F}_{l-1}^{\\mathbf{q}} \\in \\mathbb{R}^{hw \\times C}\\) and the flattened binarized mask prediction \\(\\tilde{\\mathbf{O}}_{l-1}^{\\mathbf{q}} \\in \\mathbb{R}^{hw \\times 1}\\), the intermediate prototype \\(\\mathbf{G}\\) is updated by" + }, + { + "type": "equation", + "bbox": [ + 0.561, + 0.15, + 0.892, + 0.189 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathbf {G} _ {l} = \\mathbf {I P M} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} ^ {\\mathbf {s}}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}, \\mathbf {O} ^ {\\mathbf {s}}, \\tilde {\\mathbf {O}} _ {l - 1} ^ {\\mathbf {q}}\\right) \\tag {1} \\\\ = \\mathbf {M L P} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {s}} + \\mathbf {G} _ {l} ^ {\\mathbf {q}} + \\mathbf {G} _ {l - 1}\\right), \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.194, + 0.895, + 0.285 + ], + "angle": 0, + "content": "where MLP denotes a multi-layer perception. The \\(\\mathbf{G}_l^{\\mathrm{s}}\\) can be seen as the support prototype which encodes the deterministic guidance knowledge from the support and the \\(\\mathbf{G}_l^{\\mathbf{q}}\\) can be regarded as the query prototype that learns adaptive guidance information from the query. They can be obtained by" + }, + { + "type": "equation", + "bbox": [ + 0.568, + 0.295, + 0.892, + 0.312 + ], + "angle": 0, + "content": "\\[\n\\mathbf {G} _ {l} ^ {\\mathbf {s}} = \\mathbf {M A t t} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} ^ {\\mathbf {s}}, \\mathbf {O} ^ {\\mathbf {s}}\\right), \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.568, + 0.314, + 0.892, + 0.332 + ], + "angle": 0, + "content": "\\[\n\\mathbf {G} _ {l} ^ {\\mathbf {q}} = \\mathbf {M A t t} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}, \\tilde {\\mathbf {O}} _ {l - 1} ^ {\\mathbf {q}}\\right). \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.342, + 0.868, + 0.357 + ], + "angle": 0, + "content": "Here, MAtt means the masked attention operation [3]:" + }, + { + "type": "equation", + "bbox": [ + 0.514, + 0.367, + 0.892, + 0.385 + ], + "angle": 0, + "content": "\\[\n\\mathbf {M} \\mathbf {A} \\mathbf {t} \\mathbf {t} (\\mathbf {G}, \\mathbf {F}, \\mathbf {O}) = \\delta \\left(f _ {Q} (\\mathbf {G}) f _ {K} (\\mathbf {F}) ^ {\\top} + \\Delta\\right) f _ {V} (\\mathbf {F}), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.395, + 0.892, + 0.469 + ], + "angle": 0, + "content": "where \\(\\delta\\) means the softmax normalization, \\(f_{Q}(\\cdot), f_{K}(\\cdot), f_{V}(\\cdot)\\) are three linear transformations following [26], and \\(\\Delta = (1 - \\mathbf{O}^{\\top}) \\cdot (-\\infty)\\) is used to modulate the attention matrix, making background attention weights become zeros after softmax." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.47, + 0.892, + 0.516 + ], + "angle": 0, + "content": "Then, the updated \\(\\mathbf{G}_l\\) is used to generate mask predictions for both support and query via a mask generation (MG) process:" + }, + { + "type": "equation", + "bbox": [ + 0.546, + 0.525, + 0.892, + 0.544 + ], + "angle": 0, + "content": "\\[\n\\tilde {\\mathbf {O}} _ {l} ^ {\\mathbf {s}} = \\mathbf {M G} \\left(\\mathbf {G} _ {l}, \\mathbf {F} ^ {\\mathbf {s}}\\right), \\tilde {\\mathbf {O}} _ {l} ^ {\\mathbf {q}} = \\mathbf {M G} \\left(\\mathbf {G} _ {l}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}\\right), \\tag {5}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.569, + 0.568, + 0.892, + 0.585 + ], + "angle": 0, + "content": "\\[\n\\mathbf {M G} (\\mathbf {G}, \\mathbf {F}) = \\operatorname {S i g m o i d} \\left(f _ {G} (\\mathbf {G}) \\mathbf {F} ^ {\\top}\\right), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.591, + 0.892, + 0.637 + ], + "angle": 0, + "content": "where \\(f_{G}(\\cdot)\\) is another linear transformation. At the same time, the generated prototype \\(\\mathbf{G}_l\\) is also used to update the query feature maps via query activation (QA):" + }, + { + "type": "equation", + "bbox": [ + 0.547, + 0.646, + 0.892, + 0.665 + ], + "angle": 0, + "content": "\\[\n\\mathbf {F} _ {l} ^ {\\mathbf {q}} = \\mathbf {Q} \\mathbf {A} \\left(\\mathbf {G} _ {l}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}\\right) = \\mathcal {F} _ {\\text {a c t v}} \\left(\\mathbf {G} _ {l} \\odot \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}\\right), \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.674, + 0.891, + 0.704 + ], + "angle": 0, + "content": "where \\(\\odot\\) means concatenation and \\(\\mathcal{F}_{\\text{actv}}\\) is an activation network with two convolution layers." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.895, + 0.901 + ], + "angle": 0, + "content": "In the original implementation, IPMT first feeds the input images into a froze backbone encoder (e.g. ResNet-50 [11]), obtaining multi-scale features \\(\\{\\mathbf{X}_1,\\mathbf{X}_2,\\mathbf{X}_3,\\mathbf{X}_4\\}\\) from the last four convolution blocks, with the scale of 1/4, 1/8, 1/8, and 1/8, respectively. Then, \\(\\mathbf{X}_1\\) and \\(\\mathbf{X}_2\\) are fused to obtain the backbone features for both support and query. Next, a prototype activation (PA) module generates the support features \\(\\mathbf{F}^{\\mathrm{s}}\\), the initial query feature \\(\\mathbf{F}_0^{\\mathrm{q}}\\), and the initial query mask \\(\\tilde{\\mathbf{O}}_0^{\\mathrm{q}}\\). The initial prototype \\(\\mathbf{G}_0\\) is randomly initialized at the beginning and then optimized during training. Afterward, by iteratively operating (1) to (7) in five layers, both prototype and features can be optimized step by step. For more details please refer to [16]." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18864" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.087, + 0.895, + 0.301 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.313, + 0.895, + 0.4 + ], + "angle": 0, + "content": "Figure 2. Main architecture of the proposed VIPMT model for FSVOS. \"RMS\" means our proposed reliable memory selection (Section 4.3), \"MAtt\" means masked attention (4), \"MG\" means mask generation (6), and \"QA\" means query activation (7). In each VIPMT iteration, the input intermediate prototype \\(\\mathbf{G}_{l-1}\\) first generates the support prototype \\(\\mathbf{G}_l^{\\mathrm{s}}\\) (2), the clip prototype \\(\\mathbf{G}_l^{\\mathrm{c}}\\) (8), and the memory prototype \\(\\mathbf{G}_l^{\\mathrm{m}}\\) (13), and combine them to obtain the clip-level intermediate prototype \\(\\mathbf{G}_l^{\\mathrm{ci}}\\) (14). Afterwords, a frame level prototype \\(\\mathbf{G}_l^{\\mathrm{f}_i}\\) is obtained for each frame via (10) and then updates the frame mask \\(\\tilde{\\mathbf{O}}_l^{\\mathrm{f}_i}\\) and frame feature \\(\\mathbf{F}_l^{\\mathrm{c}_i}\\) via (12). Finally, all \\(\\mathbf{G}_l^{\\mathrm{f}_i}\\) are averaged to obtain \\(\\mathbf{G}_l\\) (11), which is input into the next iteration with \\(\\tilde{\\mathbf{O}}_l^{\\mathrm{f}}\\) and \\(\\mathbf{F}_l^{\\mathrm{c}}\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.411, + 0.208, + 0.426 + ], + "angle": 0, + "content": "4. Video IPMT" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.437, + 0.471, + 0.528 + ], + "angle": 0, + "content": "As shown in Figure 2, we take the original IPMT model as the baseline and combine it with our proposed multi-grained prototype learning scheme for performing the FSVOS task. We elaborate on the design of our clip-level, frame-level, and memory-level prototypes first. Finally, we present the training loss, including the newly proposed CCDS loss." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.538, + 0.303, + 0.554 + ], + "angle": 0, + "content": "4.1. Clip Prototype Learning" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.561, + 0.47, + 0.697 + ], + "angle": 0, + "content": "Since a video is composed of several consecutive frames, a straightforward way is to directly apply the IPMT model on each query frame. However, such a naive method does not consider any video temporal information and also lacks efficiency. Hence, we propose to take video clips as query units for both training and inference. Given a query video clip \\(\\mathcal{C} = \\{\\mathbf{I}^{\\mathbf{c}_i}\\}_{i=1}^{T_c}\\) with \\(T_c\\) frames, we perform the masked attention with clip-level query features to generate the clip prototype:" + }, + { + "type": "equation", + "bbox": [ + 0.157, + 0.708, + 0.47, + 0.726 + ], + "angle": 0, + "content": "\\[\n\\mathbf {G} _ {l} ^ {\\mathbf {c}} = \\mathbf {M A t t} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {c}}, \\tilde {\\mathbf {O}} _ {l - 1} ^ {\\mathbf {f}}\\right), \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.738, + 0.469, + 0.785 + ], + "angle": 0, + "content": "where \\(\\mathbf{F}_{l - 1}^{\\mathbf{c}}\\in \\mathbb{R}^{T_chw\\times C}\\), \\(\\tilde{\\mathbf{O}}_{l - 1}^{\\mathbf{f}}\\in \\mathbb{R}^{T_chw\\times 1}\\) is the previous predicted masks and will be explained later. Then, we obtain the clip-level intermediate prototype:" + }, + { + "type": "equation", + "bbox": [ + 0.157, + 0.796, + 0.47, + 0.814 + ], + "angle": 0, + "content": "\\[\n\\mathbf {G} _ {l} ^ {\\mathbf {c i}} = \\mathbf {M L P} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {s}} + \\mathbf {G} _ {l} ^ {\\mathbf {c}} + \\mathbf {G} _ {l - 1}\\right), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.471, + 0.901 + ], + "angle": 0, + "content": "which encodes local guidance information within the whole query clip. Next, we can use (6) to segment the target objects in the whole clip and obtain clip predictions \\(\\tilde{\\mathbf{O}}_l^{\\mathbf{c}}\\in \\mathbb{R}^{T_chw\\times 1} = \\mathbf{M}\\mathbf{G}(\\mathbf{G}_l^{\\mathbf{ci}},\\mathbf{F}_{l - 1}^{\\mathbf{c}})\\), which preserves temporal coherence within the \\(T_{c}\\) frames." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.412, + 0.743, + 0.429 + ], + "angle": 0, + "content": "4.2. Frame Prototype Learning" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.436, + 0.895, + 0.557 + ], + "angle": 0, + "content": "The clip-level intermediate prototype \\(\\mathbf{G}_l^{\\mathrm{ci}}\\) uses one prototype to represent the whole clip and encodes the clip consensus object information, however, may ignore frame-level fine-grained cues. This problem may cause a performance drop when the object appearance changes significantly within the clip. To mitigate this problem, we propose to further generate frame-level query prototypes \\(\\{\\mathbf{G}_{l}\\}_{i = 1}^{T_{c}}\\) by updating \\(\\mathbf{G}_l^{\\mathrm{ci}}\\) with related fine-grained object cues in each frame:" + }, + { + "type": "equation", + "bbox": [ + 0.525, + 0.569, + 0.892, + 0.588 + ], + "angle": 0, + "content": "\\[\n\\mathbf {G} _ {l} ^ {\\mathbf {f} _ {i}} = \\operatorname {M L P} \\left(\\mathbf {M A t t} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {c i}}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {c} _ {i}}, \\tilde {\\mathbf {O}} _ {l} ^ {\\mathbf {c} _ {i}}\\right) + \\mathbf {G} _ {l} ^ {\\mathbf {c i}}\\right). \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.601, + 0.892, + 0.649 + ], + "angle": 0, + "content": "In this process, we use \\(\\mathbf{G}_l^{\\mathbf{ci}}\\) as a good initialization to learn each \\(\\mathbf{G}_l^{\\mathbf{f}_i}\\) and subsequently aggregate the frame-level query prototypes as the initialization for the next iteration:" + }, + { + "type": "equation", + "bbox": [ + 0.633, + 0.661, + 0.892, + 0.703 + ], + "angle": 0, + "content": "\\[\n\\mathbf {G} _ {l} = \\frac {1}{T _ {c}} \\sum_ {i = 1} ^ {T _ {c}} \\mathbf {G} _ {l} ^ {\\mathbf {f} _ {i}}. \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.714, + 0.894, + 0.804 + ], + "angle": 0, + "content": "As such, we enable bidirectional clip-frame prototype communication, which promotes the intra-clip temporal correlation. On the contrary, directly using the clip-level intermediate prototype \\(\\mathbf{G}_l^{\\mathrm{ci}}\\) as the initialization for the next iteration only enables one-way communication from the clip information to the frame-level." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.805, + 0.892, + 0.851 + ], + "angle": 0, + "content": "At the same time, we use each frame prototype \\(\\mathbf{G}_l^{\\mathbf{f}_i}\\) to generate the frame-level segmentation mask and update the query feature for each frame independently:" + }, + { + "type": "equation", + "bbox": [ + 0.612, + 0.862, + 0.892, + 0.89 + ], + "angle": 0, + "content": "\\[\n\\tilde {\\mathbf {O}} _ {l} ^ {\\mathbf {f} _ {i}} = \\mathbf {M G} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {f} _ {i}}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {c} _ {i}}\\right), \\tag {12}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.619, + 0.886, + 0.779, + 0.904 + ], + "angle": 0, + "content": "\\[\n\\mathbf {F} _ {l} ^ {\\mathbf {c} _ {i}} = \\mathbf {Q A} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {f} _ {i}}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {c} _ {i}}\\right).\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.956 + ], + "angle": 0, + "content": "18865" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.473, + 0.31 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.313, + 0.473, + 0.368 + ], + "angle": 0, + "content": "Figure 3. Illustration of the generation process of the four structural similarity maps. Red and blue regions indicate objects of two categories, respectively. Here we only show two support frames for concision." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.38, + 0.47, + 0.414 + ], + "angle": 0, + "content": "Next, \\(\\tilde{\\mathbf{O}}_l^{\\mathbf{f}} = \\{\\tilde{\\mathbf{O}}_l^{\\mathbf{f}_i}\\}_{i = 1}^{T_c},\\mathbf{F}_l^{\\mathbf{c}} = \\{\\mathbf{F}_l^{\\mathbf{c}_i}\\}_{i = 1}^{T_c}\\), and \\(\\mathbf{G}_l\\) are input to (8) again for the next iteration." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.422, + 0.336, + 0.438 + ], + "angle": 0, + "content": "4.3. Memory Prototype Learning" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.445, + 0.473, + 0.613 + ], + "angle": 0, + "content": "Since a whole video usually contains numerous frames, only considering the information within a local clip is suboptimal as long-term historical temporal information is ignored. Many VOS works have also demonstrated that leveraging history memory is crucial for video data to enhance the temporal correlation. To this end, we propose to learn a memory prototype for providing historical guidance information. For each clip except the first one, we can use \\( T_{m} \\) previous frames as the memory set \\( \\mathcal{M} = \\{\\mathbf{I}^{\\mathbf{m}_i}\\}_{i=1}^{T_m} \\), which also has predicted masks \\( \\tilde{\\mathbf{O}}^{\\mathbf{m}} \\in \\mathbb{R}^{T_mhw \\times 1} \\). Then, we use masked attention on memory features to generate the memory prototype:" + }, + { + "type": "equation", + "bbox": [ + 0.162, + 0.622, + 0.47, + 0.641 + ], + "angle": 0, + "content": "\\[\n\\mathbf {G} _ {l} ^ {\\mathbf {m}} = \\mathbf {M A t t} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} ^ {\\mathbf {m}}, \\tilde {\\mathbf {O}} ^ {\\mathbf {m}}\\right), \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.647, + 0.47, + 0.695 + ], + "angle": 0, + "content": "where \\(\\mathbf{F}^{\\mathbf{m}}\\in \\mathbb{R}^{T_mhw\\times C}\\) and \\(\\tilde{\\mathbf{O}}^{\\mathbf{m}}\\in \\mathbb{R}^{T_mhw\\times 1}\\). Then, the update of the clip-level intermediate prototype \\(\\mathbf{G}_l^{\\mathbf{ci}}\\) in (9) can be rewritten as" + }, + { + "type": "equation", + "bbox": [ + 0.133, + 0.704, + 0.47, + 0.723 + ], + "angle": 0, + "content": "\\[\n\\mathbf {G} _ {l} ^ {\\mathrm {c i}} = \\mathbf {M L P} \\left(\\mathbf {G} _ {l} ^ {\\mathrm {s}} + \\mathbf {G} _ {l} ^ {\\mathrm {c}} + \\mathbf {G} _ {l} ^ {\\mathrm {m}} + \\mathbf {G} _ {l - 1}\\right). \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.731, + 0.471, + 0.807 + ], + "angle": 0, + "content": "We do not consider using memory prototype at the frame level since \\(\\mathbf{G}_l^{\\mathbf{ci}}\\) is designed to combine comprehensive guidance information at the clip-level, simultaneously from support, clip, and memory. In contrast, \\(\\mathbf{G}_l^{\\mathbf{f}_i}\\) encodes pure frame adaptive cues and uses \\(\\mathbf{G}_l^{\\mathbf{ci}}\\) as the initialization." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Reliable Memory Selection. During the training stage, we can use the ground truth memory masks \\(\\mathbf{O}^{\\mathrm{m}}\\) to replace the predicted masks for training an accurate model. However, during the inference stage, we can only use the predicted masks \\(\\tilde{\\mathbf{O}}^{\\mathrm{m}}\\), which may be very noisy and hence heavily contaminate the learned prototype. To mitigate this problem," + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.197 + ], + "angle": 0, + "content": "we follow [17] and train an IoU regression network (IoUNet) to select reliable memory frames which have higher segmentation quality. Different from [17], we explicitly consider the nature of the FSVOS task and propose to leverage the structural similarity among the predicted foreground region, background region, and object region in support images for predicting more accurate IoU scores." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.198, + 0.895, + 0.395 + ], + "angle": 0, + "content": "Specifically, as shown in Figure 3, given the backbone features of an memory frame \\(\\mathbf{X}_4\\in \\mathbb{R}^{hw\\times C}\\) and the support set \\(\\mathbf{X}_4^{\\mathbf{s}}\\in \\mathbb{R}^{Khw\\times C}\\), the predicted memory mask \\(\\tilde{\\mathbf{O}}\\in \\mathbb{R}^{hw\\times 1}\\) (here we omit the superscript \\(\\mathbf{m}\\) for conciseness), and the ground truth support masks \\(\\mathbf{O}^{\\mathrm{s}}\\in \\mathbb{R}^{Khw\\times 1}\\), we first obtain the background mask for the memory \\(\\tilde{\\mathbf{B}} = 1 - \\tilde{\\mathbf{O}}\\). Then, we can evaluate the segmentation quality of the memory frame using a simple and intuitive idea: once it is well segmented, its foreground region \\(\\tilde{\\mathbf{O}}\\) should be dissimilar to the background \\(\\tilde{\\mathbf{B}}\\) and similar to the support foreground \\(\\mathbf{O}^{\\mathrm{s}}\\), while the background \\(\\tilde{\\mathbf{B}}\\) should be dissimilar to both \\(\\tilde{\\mathbf{O}}\\) and \\(\\mathbf{O}^{\\mathrm{s}}\\). To this end, we compute the structural similarity map of the foreground area of the memory w.r.t. the background area:" + }, + { + "type": "equation", + "bbox": [ + 0.518, + 0.402, + 0.892, + 0.421 + ], + "angle": 0, + "content": "\\[\n\\mathbf {S} ^ {f b} = \\operatorname {N o r m} \\left(\\operatorname {M a x} \\left(\\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {O}}\\right) \\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {B}}\\right) ^ {\\top}, 1\\right)\\right), \\tag {15}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.43, + 0.894, + 0.52 + ], + "angle": 0, + "content": "where \\(\\odot\\) means element-wise multiplication, \\(\\mathbf{Max}(*,1)\\) means obtaining the maximum value along each row, and Norm denotes the min-max normalization to scale the data to the range of [0, 1]. Then, the output map \\(\\mathbf{S}^{fb}\\in \\mathbb{R}^{hw\\times 1}\\) exactly represents how similar each foreground pixel is w.r.t. the background area, as shown in Figure 3." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.52, + 0.894, + 0.597 + ], + "angle": 0, + "content": "Likewise, we can obtain a similarity map \\(\\mathbf{S}^{bf}\\) of the background area w.r.t. the foreground, similarity map \\(\\mathbf{S}^{fs}\\) of the foreground area of the memory w.r.t. the foreground of the support, and similarity map \\(\\mathbf{S}^{bs}\\) of the background area of the memory w.r.t. the foreground of the support:" + }, + { + "type": "equation", + "bbox": [ + 0.514, + 0.605, + 0.843, + 0.623 + ], + "angle": 0, + "content": "\\[\n\\mathbf {S} ^ {b f} = \\operatorname {N o r m} \\left(\\operatorname {M a x} \\left(\\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {B}}\\right) \\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {O}}\\right) ^ {\\top}, 1\\right)\\right),\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.516, + 0.626, + 0.892, + 0.645 + ], + "angle": 0, + "content": "\\[\n\\mathbf {S} ^ {f s} = \\operatorname {N o r m} \\left(\\operatorname {M a x} \\left(\\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {O}}\\right) \\left(\\mathbf {X} _ {4} ^ {\\mathbf {s}} \\odot \\mathbf {O} ^ {\\mathbf {s}}\\right) ^ {\\top}, 1\\right)\\right), \\tag {16}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.516, + 0.648, + 0.847, + 0.667 + ], + "angle": 0, + "content": "\\[\n\\mathbf {S} ^ {b s} = \\operatorname {N o r m} (\\operatorname {M a x} ((\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {B}}) (\\mathbf {X} _ {4} ^ {\\mathbf {s}} \\odot \\mathbf {O} ^ {\\mathbf {s}}) ^ {\\top}, 1)).\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.895, + 0.81 + ], + "angle": 0, + "content": "Once obtain the four structural similarity maps, we combine them with multi-scale memory features and the original predicted mask \\(\\tilde{\\mathbf{O}}\\) to regress the IoU score of the memory frame. Concretely, we first downsample \\(\\mathbf{X}_1\\) to the 1/8 scale with stride convolution and then fuse it with \\(\\mathbf{X}_2, \\mathbf{X}_3, \\mathbf{X}_4\\) into a combined feature with 256 channels. Then, we concatenate the feature with the four structural similarity maps and \\(\\tilde{\\mathbf{O}}\\) and input them into four convolution layers and two fully connected layers for predicting the IoU score." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.894, + 0.901 + ], + "angle": 0, + "content": "During training, we design three ways to train the IoUNet. First, we can jointly train it with the FSVOS model, in which case real predicted masks can be used for training the IoUNet. Second, we can train it independently using synthesized video data. Specifically, we randomly add noises to the ground truth masks in the training set and use the synthesized" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18866" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.182 + ], + "angle": 0, + "content": "masks to mimic good and bad predictions. In the third way, we train the IoUNet using synthesized image data with the same noisy mask strategy. We compute the ground truth IoU score for each training mask and use a \\( L_{1} \\) loss as supervision. During testing, we simply select reliable memory frames whose predicted IoU scores are larger than a threshold." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.191, + 0.221, + 0.208 + ], + "angle": 0, + "content": "4.4. Training Loss" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.214, + 0.47, + 0.35 + ], + "angle": 0, + "content": "We follow IPMT [16] and use the final query feature \\(\\mathbf{F}_5^{\\mathrm{c}}\\) to predict the final segmentation masks via two convolution layers, where Dice loss and IoU loss are both used for optimization. To ease the network training, in each iteration we use binary cross entropy (BCE) loss on the predicted support masks \\(\\tilde{\\mathbf{O}}_l^{\\mathrm{s}}\\), clip masks \\(\\tilde{\\mathbf{O}}_l^{\\mathrm{c}}\\), and frame masks \\(\\tilde{\\mathbf{O}}_l^{\\mathrm{f}}\\). As for memory frames, we generate predictions for them at each iteration using \\(\\mathbf{MG}(\\mathbf{G}_l^{\\mathrm{ci}}, \\mathbf{F}^{\\mathrm{m}})\\), and then adopt the BCE loss computed with their ground truth masks as supervision." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.354, + 0.471, + 0.581 + ], + "angle": 0, + "content": "Cross Category Discriminative Segmentation Loss. To make the learned clip-level intermediate prototypes \\(\\mathbf{G}^{\\mathrm{ci}}\\) more category discriminative, we furthermore propose a CCDS loss and adopt it within each batch. Suppose our batchsize is set to \\(B > 1\\), we select \\(B\\) video clips with different object categories to form each batch. Then, during training, we use the prototypes of each video to perform segmentation on other videos and let the predicted masks be all zeros. The idea behind is intuitive: if the prototypes are well optimized for a specific category, they should not activate any region on other videos with different categories. However, since a video may contain multiple object categories and we only have the ground truth of one class under the one-way few-shot learning setting, we propose to use the ground truth masks to filter out the regions for loss calculation:" + }, + { + "type": "equation", + "bbox": [ + 0.113, + 0.592, + 0.47, + 0.633 + ], + "angle": 0, + "content": "\\[\nL _ {c c d s} = \\frac {1}{(B - 1) B} \\sum_ {b = 1} ^ {B} \\sum_ {j \\neq b} \\frac {1}{\\sum \\mathbf {O} _ {j}} L _ {b, j}, \\tag {17}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.121, + 0.639, + 0.47, + 0.678 + ], + "angle": 0, + "content": "\\[\nL _ {b, j} = \\sum_ {l = 1} ^ {5} B C E \\left(\\mathbf {M G} \\left(\\mathbf {G} _ {l, b} ^ {\\mathbf {c i}}, \\mathbf {F} _ {j}\\right) \\odot \\mathbf {O} _ {j}, \\mathbf {Z}\\right), \\tag {18}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.469, + 0.749 + ], + "angle": 0, + "content": "where \\(\\mathbf{G}_{l,b}^{\\mathrm{ci}}\\) is the clip-level intermediate prototype in the \\(l\\)-th iteration of the \\(b\\)-th video, \\(\\mathbf{O}_j\\) and \\(\\mathbf{F}_j\\) are the ground truth masks and the backbone features of the \\(j\\)-th video. \\(\\mathbf{Z}\\) is an all zero matrix." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.763, + 0.208, + 0.779 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.358, + 0.803 + ], + "angle": 0, + "content": "5.1. Datasets and Evaluation Setting" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Datasets. Following [1, 24], our experiments are conducted on the training set of YouTube-VIS [30] dataset, which has 40 categories and contains 2238 videos with 3774 instances. The dataset is divided into four folds, following the same slit with [1, 24]. In each fold, we use 30 categories for training and the rest 10 categories for testing. Following [1, 24], we" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.894, + 0.183 + ], + "angle": 0, + "content": "set our experiments on the 5-shot setting and randomly select five images from different videos of the same category as the support set. We also follow [24] and adopt the MiniVSPW [24] dataset to evaluate the generalizability of FSVOS methods. It includes 20 categories and provides longer video sequences than YouTube-VIS, since being more challenging." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.189, + 0.893, + 0.326 + ], + "angle": 0, + "content": "Evaluation Setting. As the prior work [1] and VOS methods, we adopt the region similarity \\(\\mathcal{J}\\) and contour similarity \\(\\mathcal{F}\\) for performance evaluation. Apart from this, we also follow [24] and consider the video consistency metric \\(\\mathrm{VC}_7\\), which captures temporal prediction consistency among long-range adjacent frames over a temporal window of 7. We adopt the average score on four folds, i.e. \\(\\mathrm{mVC}_7\\), to evaluate the overall performance. We also follow [1, 24] and run the evaluation process five times and report the average results." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.329, + 0.894, + 0.435 + ], + "angle": 0, + "content": "Furthermore, there are two different evaluation protocols proposed in [1] and [24] for sampling episodes during testing. Protocol I fixes the sampled support set for all query videos belonging to the same class in each run, while protocol II randomly samples a support set for every query video, which ensures a more stable performance evaluation. Hence, in this paper we adopt protocol II for evaluation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.442, + 0.895, + 0.669 + ], + "angle": 0, + "content": "Implementation Details. We adopt ResNet-50 [11] pretrained on ImageNet [23] as our encoder backbone. Following IPMT [16], we freeze the parameters of the backbone during training and do not adopt online finetuning as [1, 24] did. The iteration step is set to 5 as IPMT. We set the clip length \\( T_{c} \\) and the memory length \\( T_{m} \\) to 5 without further tuning. The IoU threshold for selecting reliable memory frames is set to 0.8. When the reliable memory has more frames, we simply randomly select five frames from them. During training, we randomly select three clips from a video as a sample, where the first clip is trained without using memory, the second clip uses the first clip as memory, and the third clip randomly selects five frames from the first two as the memory. We also share the MAtt operation for support and memory since we found this leads to better performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.672, + 0.894, + 0.779 + ], + "angle": 0, + "content": "We use Adam as our optimizer. The batchsize is set to \\( B = 4 \\) and the learning rate is set to 5e-4. We train our model 100 epochs in total. All experiments are conducted on a NVIDIA Tesla A100 GPU. We adopt random horizontal flip, random crop and random resize to augment the training data. During training and testing, all video frames are downsampled to the resolution of (240,424) as the inputs." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.799, + 0.864, + 0.814 + ], + "angle": 0, + "content": "5.2. Comparison with State-of-the-art Methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.893, + 0.901 + ], + "angle": 0, + "content": "In Table 1, we compare our VIPMT with four recently published FSISS methods and two FSVOS methods, on the YouTuebe-VIS [30] dataset. We find that our VIPMT largely improves all metrics, i.e. \\(4\\%\\) \\(\\mathcal{I}\\) mean score, near \\(6\\%\\) \\(\\mathcal{F}\\) mean score, and near \\(5\\%\\) \\(\\mathrm{mVC}_7\\) score, although previous" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18867" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.9, + 0.233 + ], + "angle": 0, + "content": "
MethodsNameJFmVC7
Fold-1Fold-2Fold-3Fold-4MeanFold-1Fold-2Fold-3Fold-4Mean
FSISSNTRENet [15]39.066.461.761.257.141.163.060.159.455.955.7
SSP [10]46.764.359.354.556.234.853.046.046.745.149.6
VAT [12]42.662.857.056.754.841.656.450.853.050.554.9
IPMT [16]43.865.861.060.757.842.559.557.855.953.957.7
FSVOSDAN [1]43.964.561.162.157.942.462.060.060.056.141.5
TTI [24]47.268.861.463.560.2-----60.8
VIPMT(Ours)50.670.968.866.564.251.366.965.264.462.065.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.15, + 0.234, + 0.819, + 0.247 + ], + "angle": 0, + "content": "Table 1. Comparison with state-of-the-art methods on YouTube-VIS [30]. Bold means the best performance." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.252, + 0.9, + 0.322 + ], + "angle": 0, + "content": "
MethodsNameJFmVC7
Fold-1Fold-2Fold-3Fold-4MeanFold-1Fold-2Fold-3Fold-4Mean
FSVOSTTI [24]25.237.125.029.629.2-----24.4
VIPMT(Ours)26.242.231.629.432.430.645.736.334.236.742.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.31, + 0.321, + 0.658, + 0.334 + ], + "angle": 0, + "content": "Table 2. Comparison with TTI [24] on MiniVSPW [24]." + }, + { + "type": "table", + "bbox": [ + 0.088, + 0.345, + 0.458, + 0.463 + ], + "angle": 0, + "content": "
DatasetsMethodsJ-MeanF-MeanmVC7
YouTube-VISIPMT+STCN [6]58.956.561.7
IPMT+XMem [5]59.256.862.2
IPMT+RDE-VOS [14]59.358.063.3
VIPMT(Ours)64.262.065.7
MiniVSPWIPMT+STCN [6]27.731.139.3
IPMT+XMem [5]27.731.741.1
IPMT+RDE-VOS [14]28.833.540.1
VIPMT(Ours)32.436.742.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.463, + 0.433, + 0.475 + ], + "angle": 0, + "content": "Table 3. Comparison with state-of-the-art VOS methods." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.49, + 0.42, + 0.505 + ], + "angle": 0, + "content": "works [1, 24] used on-line learning while we didn't." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.506, + 0.468, + 0.58 + ], + "angle": 0, + "content": "To verify the generalization ability of our method, we compare our method with TTI [24] on MiniVSPW. Table 2 shows our method obtains a significant improvement of more than \\(3\\%\\) on \\(\\mathcal{I}\\) and more than \\(17\\%\\) on \\(\\mathrm{mVC}_7\\), which verifies that our method works well in more challenging scenarios." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.47, + 0.641 + ], + "angle": 0, + "content": "In Figure 4, we give some visual comparison cases. Compared with TTI [24], our VIMPT is less distracted by other objects and achieves more precise segmentation, even in highly occluded scenes (bottom row)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.642, + 0.47, + 0.748 + ], + "angle": 0, + "content": "We also include three state-of-the-art semi-supervised VOS methods for comparison, i.e. STCN [6], XMem [5], and RDE-VOS [14]. Specifically, we use IPMT for segmenting the first frame and then use VOS methods for propagating the segmentation to the full video. Table 3 demonstrates that such an ad-hoc combination of FSISS and VOS methods can not achieve as good results as our model does." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.756, + 0.231, + 0.772 + ], + "angle": 0, + "content": "5.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.779, + 0.469, + 0.825 + ], + "angle": 0, + "content": "In this section, we report ablation study results on the YouTube-VIS dataset. For \\(\\mathcal{J}\\) and \\(\\mathcal{F}\\) we use their average on four folds, i.e. \\(\\mathcal{J}\\)-Mean and \\(\\mathcal{F}\\)-Mean." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.828, + 0.469, + 0.844 + ], + "angle": 0, + "content": "Effectiveness of Each Component. In Table 4, we first" + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.346, + 0.892, + 0.431 + ], + "angle": 0, + "content": "
NameSettingsJ-MeanF-MeanmVC7
ClipFrameMemoryCCDS
Baseline57.853.957.8
+C✓61.858.860.7
+C+F✓✓62.560.362.1
+C+F+M✓✓✓63.561.962.8
VIPMT✓✓✓✓64.262.065.7
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.432, + 0.894, + 0.459 + ], + "angle": 0, + "content": "Table 4. Ablation study on the effectiveness of each model component. Baseline means IPMT [16]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.473, + 0.895, + 0.746 + ], + "angle": 0, + "content": "adopt IPMT [16] as the baseline, which processes each video frame independently. Then, we adopt our clip prototype learning, denoted as “+C”. Results show that “+C” surpasses the baseline by a large margin on all metrics, which verifies the effectiveness of using local temporal guidance with our clip prototype learning. After that, we further add the frame prototype learning to “+C”, resulting in “+C+F”. Benefiting from the frame-level fine-grained cues, “+C+F” achieves large performance improvement for \\(\\mathcal{F}\\)-Mean and \\(\\mathrm{mVC}_7\\). Moreover, we adopt “+C+F+M” to represent adding the memory prototype learning on “+C+F”. It largely improves the performance for both \\(\\mathcal{J}\\)-Mean and \\(\\mathcal{F}\\)-Mean, which shows the importance of long-term temporal information brought by the memory prototype learning. Based on this, we further add the CCDS loss to obtain our final model VIPMT. It also brings obvious improvements, especially on \\(\\mathrm{mVC}_7\\), from 62.8 to 65.7. This proves the effectiveness of increasing category discrimination for FSVOS." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.746, + 0.895, + 0.807 + ], + "angle": 0, + "content": "In Figure 5, we visualize the predicted masks from the different models mentioned above. We can find that progressive improvements can be brought by using multi-grained temporal prototypes and the CCDS loss." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.897, + 0.902 + ], + "angle": 0, + "content": "Clip-frame Communication. As mentioned in Section 4.2, we use the mean of the frame prototypes ((11)) to initialize the intermediate prototype for the next iteration, which enables bidirectional clip-frame communication. On the contrary, directly using the clip-level intermediate prototype \\(\\mathbf{G}_l^{\\mathrm{ci}}\\) as the initialization only enables one-way communica" + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.852, + 0.47, + 0.901 + ], + "angle": 0, + "content": "*Please note that here we re-tested the performance of DAN [1] using protocol II. Hence, its scores are different from the original paper. For TTI [24], since the authors did not provide the scores for \\(\\mathcal{F}\\), we leave them blank. We retrained all FSISS methods on YouTube-VIS for a fair comparison." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.956 + ], + "angle": 0, + "content": "18868" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.091, + 0.197, + 0.21 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.128, + 0.211, + 0.145, + 0.221 + ], + "angle": 0, + "content": "(a)" + }, + { + "type": "image", + "bbox": [ + 0.199, + 0.091, + 0.394, + 0.21 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.357, + 0.211, + 0.377, + 0.222 + ], + "angle": 0, + "content": "(b)" + }, + { + "type": "image", + "bbox": [ + 0.394, + 0.091, + 0.542, + 0.21 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.546, + 0.091, + 0.89, + 0.21 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.707, + 0.211, + 0.725, + 0.222 + ], + "angle": 0, + "content": "(c)" + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.226, + 0.873, + 0.24 + ], + "angle": 0, + "content": "Figure 4. Visualization of comparison cases. (a) Support sets. (b) Predicted masks of our VIMPT. (c) Predicted masks from TTI [24]." + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.254, + 0.195, + 0.373 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.108, + 0.372, + 0.153, + 0.383 + ], + "angle": 0, + "content": "Support" + }, + { + "type": "image", + "bbox": [ + 0.196, + 0.254, + 0.312, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.197, + 0.316, + 0.312, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.218, + 0.372, + 0.266, + 0.382 + ], + "angle": 0, + "content": "Baseline" + }, + { + "type": "image", + "bbox": [ + 0.313, + 0.254, + 0.426, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.313, + 0.316, + 0.426, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.355, + 0.373, + 0.372, + 0.382 + ], + "angle": 0, + "content": "+C" + }, + { + "type": "image", + "bbox": [ + 0.427, + 0.254, + 0.543, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.428, + 0.316, + 0.542, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.463, + 0.372, + 0.496, + 0.382 + ], + "angle": 0, + "content": "+C+F" + }, + { + "type": "image", + "bbox": [ + 0.543, + 0.254, + 0.657, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.543, + 0.316, + 0.657, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.562, + 0.372, + 0.613, + 0.382 + ], + "angle": 0, + "content": "\\(+\\mathrm{C} + \\mathrm{F} + \\mathrm{M}\\)" + }, + { + "type": "image", + "bbox": [ + 0.658, + 0.254, + 0.773, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.659, + 0.316, + 0.774, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.688, + 0.372, + 0.731, + 0.382 + ], + "angle": 0, + "content": "VIPMT" + }, + { + "type": "image", + "bbox": [ + 0.774, + 0.254, + 0.89, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.774, + 0.316, + 0.889, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.82, + 0.372, + 0.839, + 0.382 + ], + "angle": 0, + "content": "GT" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.385, + 0.89, + 0.414 + ], + "angle": 0, + "content": "Figure 5. Visualization of the comparison of different ablation study models. We can see progressive improvements brought by the multi-grained temporal prototypes and the CCDS loss." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.429, + 0.468, + 0.485 + ], + "angle": 0, + "content": "
Clip-frame CommunicationJ-MeanF-MeanmVC7
One-way61.459.160.1
Bidirectional62.560.362.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.485, + 0.471, + 0.499 + ], + "angle": 0, + "content": "Table 5. Comparison of two clip-frame communication schemes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.513, + 0.47, + 0.573 + ], + "angle": 0, + "content": "tion. Here we compare the effectiveness of the two schemes. Results in Table 5 demonstrate that our design of using bidirectional clip-frame communication surpasses the one-way scheme by a large margin on all metrics." + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.579, + 0.471, + 0.836 + ], + "angle": 0, + "content": "Different Training Strategies of IoUNet. As mentioned in Section 4.3, we can use three ways to train the IoUNet, i.e. using real predicted masks (\"Real\"), synthesized video data (\"Video\"), and synthesized image data (\"Image\"), respectively. For \"Image\", we use an FSISS dataset COCO-20\\(^i\\) [20] and remove the classes overlapped with our video data for IoUNet training. We compare their performance in Table 6. We also compare the performance of using our proposed structural similarity maps or not (\"w/ SSM\" and \"w/o SSM\"). The results are reported under the IoU threshold of 0.5. The table demonstrates that using synthesized image data results in the best performance in both \"w/ SSM\" and \"w/o SSM\" settings and using the structural similarity maps always leads to better performance. Another benefit of using image data is that we can train a unified IoUNet for all folds instead of training an IoUNet for each fold. Hence, finally, we use synthesized image data for IoUNet training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.902 + ], + "angle": 0, + "content": "IoU Threshold. Finally, we investigate the best IoU threshold for memory selection. Table 7 indicates that 0.8 is the best threshold and using the proposed structural similarity maps always leads to better performance." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.429, + 0.892, + 0.5 + ], + "angle": 0, + "content": "
Dataw/o SSMw/ SSM
J-MeanF-MeanmVC7J-MeanF-MeanmVC7
Real62.861.562.663.261.662.8
Video62.961.662.663.261.662.8
Image63.061.762.763.361.763.0
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.502, + 0.892, + 0.53 + ], + "angle": 0, + "content": "Table 6. Different training strategies of IoUNet. SSM means the proposed structural similarity maps." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.544, + 0.892, + 0.634 + ], + "angle": 0, + "content": "
Thresholdw/o SSMw/ SSM
J-MeanF-MeanmVC7J-MeanF-MeanmVC7
0.563.061.762.763.361.763.0
0.663.161.762.963.361.762.7
0.763.161.862.963.461.862.6
0.863.161.862.563.561.962.8
0.963.061.862.363.561.962.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.634, + 0.894, + 0.647 + ], + "angle": 0, + "content": "Table 7. Experimental results of using different IoU thresholds." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.662, + 0.619, + 0.678 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.894, + 0.824 + ], + "angle": 0, + "content": "We explored learning multi-grained temporal prototypes to tackle the FSVOS task. Based on the IPMT model, the query video information was decomposed into a clip prototype, a memory prototype, and frame prototypes. We also improved an IoU regression method for selecting reliable memory for FSVOS by leveraging the task prior knowledge and proposed a new loss to enhance the category discriminability of the prototypes. The effectiveness of our proposed VIPMT has been verified on two benchmark datasets." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.831, + 0.894, + 0.9 + ], + "angle": 0, + "content": "Acknowledgments: This work was supported in part by the National Natural Science Foundation of China under Grants 62071388, 62136007, U20B2065 and 62036005, and the Fundamental Research Funds for the Central Universities under Grant D5000230057." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "18869" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.175, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.171 + ], + "angle": 0, + "content": "[1] Haoxin Chen, Hanjie Wu, Nanxuan Zhao, Sucheng Ren, and Shengfeng He. Delving deep into many-to-many attention for few-shot video object segmentation. 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IEEE TPAMI, 2022. 2" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.518, + 0.956 + ], + "angle": 0, + "content": "18871" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation/6d6e86b4-be03-4421-80b1-27dd9a45c2b4_origin.pdf b/2023/Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation/6d6e86b4-be03-4421-80b1-27dd9a45c2b4_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..3a8e519b083fc42c93e54a812232665cd43a85dd --- /dev/null +++ b/2023/Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation/6d6e86b4-be03-4421-80b1-27dd9a45c2b4_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:8c87bd2488f99e54e0a463c910ac3746dbf721db3deb6b950805fc9876eeac87 +size 2820600 diff --git a/2023/Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation/full.md b/2023/Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation/full.md new file mode 100644 index 0000000000000000000000000000000000000000..37a07a43ff95ef99e3d7214e8846f8e75b807d10 --- /dev/null +++ b/2023/Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation/full.md @@ -0,0 +1,396 @@ +# Multi-grained Temporal Prototype Learning for Few-shot Video Object Segmentation + +Nian Liu $^{1}$ Kepan Nan $^{2}$ Wangbo Zhao $^{3}$ Yuanwei Liu $^{2}$ Xiwen Yao $^{2\dagger}$ + +Salman Khan $^{1,4}$ Hisham Cholakkal $^{1}$ Rao Muhammad Anwer $^{1}$ Junwei Han $^{2}$ Fahad Shahbaz Khan $^{1,5}$ + +1 Mohamed bin Zayed University of Artificial Intelligence 2 Northwestern Polytechnical University 3 National University of Singapore + +$^{4}$ Australian National University $^{5}$ CVL, Linköping University + +# Abstract + +Few-Shot Video Object Segmentation (FSVOS) aims to segment objects in a query video with the same category defined by a few annotated support images. However, this task was seldom explored. In this work, based on IPMT, a state-of-the-art few-shot image segmentation method that combines external support guidance information with adaptive query guidance cues, we propose to leverage multi-grained temporal guidance information for handling the temporal correlation nature of video data. We decompose the query video information into a clip prototype and a memory prototype for capturing local and long-term internal temporal guidance, respectively. Frame prototypes are further used for each frame independently to handle fine-grained adaptive guidance and enable bidirectional clip-frame prototype communication. To reduce the influence of noisy memory, we propose to leverage the structural similarity relation among different predicted regions and the support for selecting reliable memory frames. Furthermore, a new segmentation loss is also proposed to enhance the category discriminability of the learned prototypes. Experimental results demonstrate that our proposed video IPMT model significantly outperforms previous models on two benchmark datasets. Code is available at https://github.com/nankepan/VIPMT. + +# 1. Introduction + +To mitigate the data-hungry issue of modern deep semantic segmentation models [18, 2, 4], few-shot semantic segmentation emerges by only requiring a few support samples with annotated masks for segmenting the objects of the same class in new images. Many recent works [25, 32, 13, 16] have shown very promising results on image data using the meta-learning scheme. They simulate the inference process and partition the training set into numerous episodes, in each + +![](images/1c2fd512074ba0e8b90112e47317e93c140d8eb071c96f9050fa016b39598ec2.jpg) +Figure 1. Given a few annotated support frames, FSVOS aims to segment the objects with the same category from a query video (a). Simply considering single-frame information leads to inconsecutive segmentation results (b), while our method generates accurate results by using multi-grained temporal prototypes (c). + +![](images/09d31fb0d3deb2639947235aef7873bd60984f577935aa88d799710613f91ead.jpg) + +![](images/79d08fb30710adeb622507f7dcf014110f4114f1b187d3d9fdb403f0e46f8900.jpg) + +![](images/736a516b91f587a10ea0f92e80b0f1d8fffbfb23ebee61bfdbc8f106214d1281.jpg) + +of which, the model samples a few support images and learns to guide the segmentation on the query images. + +Inspired by the classic Few-Shot Image Semantic Segmentation (FSISS) task, the Few-Shot Video Object Segmentation (FSVOS) task was introduced by [1, 24]. For FSISS, many works adopt the prototype-based methods, in which a prototype vector is extracted from the support to encode the category guidance information, and then a segmentation head learns to match the prototype with the feature at each query pixel for performing query segmentation. However, the intra-class diversity can cause the matching gap between the support-induced prototype guidance and the query features. The IPMT model [16] solved this problem by learning an intermediate prototype that integrates both support-induced external category guidance knowledge and query-induced adaptive guidance information. As for FSVOS, video data additionally show temporal correlation, from which we can also induce internal temporal guidance. If we ignore this prior knowledge and simply consider single-frame information, the learned prototypes may vary significantly among different frames, leading to inconsecutive segmentation results, as shown in Figure 1 (b). + +In this work, we extend the IPMT model [16] for video data by tackling the temporal correlation nature. Based on the intermediate prototype mechanism of IPMT, we propose to decompose the query video information into the clip-level, frame-level, and memory-level prototypes, consisting of a multi-grained temporal structure, which was NEVER explored by existing models [1, 24]. Among them, the clip prototype encodes local temporal object guidance information in each consecutive clip, while the memory prototype introduces long-term historical guidance cues. Combining them can effectively handle the temporal correlation problem. However, such a design may ignore fine-grained per-frame adaptive guidance information, hence may fail to handle large scene changes and object transformation. To this end, we further learn an adaptive frame prototype by independently encoding per-frame object features. Additionally, we enable bidirectional clip-frame prototype communication by making the clip-level and frame-level prototypes initialize each other, hence promoting intra-clip temporal correlation. + +To better leverage the historical memory guidance, we also follow a Video Object Segmentation (VOS) method [17] and train an IoU regression network to select reliable memory frames for reducing the negative influence brought by noisy memory. However, different from [17], we explicitly consider the nature of the FSVOS task and propose to leverage the structural similarity relation among different predicted regions and the support information for predicting more accurate IoU scores. To make the learned prototype more category discriminative, we also propose a Cross-Category Discriminative Segmentation (CCDS) loss by leveraging negative batch samples. Extensive experimental results have verified the effectiveness of our proposed Video IPMT (VIPMT) model and showed its significant performance improvement over state-of-the-art models. + +In conclusion, our contributions can be summarized as follows: + +- For the very first time, we propose to learn multi-grained temporal prototypes for FSVOS, by extending the IPMT [16] model. Clip and memory prototypes are learned for internal temporal guidance. Frame prototypes are used for fine-grained adaptive guidance and also enable prototype communication. +- We propose to leverage the structural similarity relation among different predicted regions and the support for selecting reliable memory information. We also present a CCDS loss using the negative samples within each batch for promoting category discriminability of the learned prototypes. +- Experimental results have demonstrated the significant effectiveness of our proposed model, which improves state-of-the-art results by more than $4\%$ and $3\%$ , on two benchmark datasets, respectively. + +# 2. Related Work + +# 2.1. Few-Shot Image Semantic Segmentation + +Most previous FSISS works adopted meta-learning-based methods [27], especially prototype-based models. Specifically, Dong and Xing [9] aggregated a prototype vector on the support images to encode the representative category knowledge first, and then evaluated its similarity with each query pixel in a matching network as the segmentation result. Following this idea, Yang et al. [29] constructed multiple prototypes from limited support images to represent diverse image regions. In [25], Tian et al. used high-level features to generate a prior mask as a supplement to the support prototype for refining the query feature. Liu et al. [15] leveraged non-target prototypes to eliminate distracting regions. BAM [13] used the prototypes of base classes to explicitly suppress corresponding regions. In IPMT [16], Liu et al. proposed to generate an intermediate prototype which encodes the category guidance information from both support and query. However, all these methods only focused on image data and the challenge of video data remains seldom explored. + +# 2.2. Video Object Segmentation + +Another closely related domain is VOS, especially the semi-supervised VOS, in which the mask label of an object in the first frame is given and the model is required to segment the same object in other frames. Some methods [22, 7, 28] tried to leverage optical flow to help segment target objects. Noticing the successful application of memory networks [8, 31] in computer vision, STM [21] proposed a memory mechanism to leverage information from previous frames for segmenting the current frame. Lu et al. [19] followed this idea and improve the memory mechanism with a graph model. For a comprehensive survey please refer to [33]. + +Different from semi-supervised VOS, we tackle the FSVOS task with two differences. First, semi-supervised VOS aims to segment the same object indicated in the annotation of the first frame while FSVOS requires to segment the objects of the same class with the annotated support set. Second, the support set in FSVOS can be composed of any images or frames of any videos that contain the target class. Hence, FSVOS is more generalized and faces much larger intra-class diversity between the support set and the query video. In this work, we propose multi-grained temporal prototype learning and bidirectional clip-frame prototype communication for FSVOS, which is different from existing VOS methods. + +Our idea of using the IoU network to select memory frames with high segmentation quality is inspired by [17]. However, in [17], the authors directly regress the IoU score by only taking the image and the mask as the network input. In this work, we further consider the nature of FSVOS and propose to compute several structural similarity maps + +which explicitly encode the quality assessment prior of the relations among the predicted foreground, background, and the support areas. + +# 2.3. Few-shot Video Object Segmentation + +For the FSVOS task, currently, only a few works have targeted this topic. Chen et al. [1] proposed the first FSVOS dataset and model. They proposed a Domain Agent Network (DAN) to alleviate the large computational cost of the many-to-many attention between the support images and the query video frames, which only considered clip-level temporal information. Siam et al. [24] proposed a temporal transductive inference model, which uses both global and local temporal constraints to obtain per-frame model weights and locally consistent predictions. Compared with them, we optimize multi-grained temporal prototypes while they optimized per-frame model weights. Furthermore, we explicitly use historical memory while they did not. + +# 3. Preliminaries + +# 3.1. Problem Definition + +For FSVOS, a whole video object segmentation dataset $\mathcal{D}$ with multiple object categories $\mathcal{C}$ is divided into a training subset $\mathcal{D}_{base}$ and a testing subset $\mathcal{D}_{novel}$ , whose categories are $\mathcal{C}_{base}$ and $\mathcal{C}_{novel}$ , respectively, and satisfy $\mathcal{C}_{base} \cap \mathcal{C}_{novel} = \emptyset$ and $\mathcal{C}_{base} \cup \mathcal{C}_{novel} = \mathcal{C}$ . Under the standard few-shot setting and the episodic training scheme, both $\mathcal{D}_{base}$ and $\mathcal{D}_{novel}$ are randomly partitioned into a lot of episodes. In each episode, a support set $S$ provides $K$ frames $\mathbf{I}^{\mathrm{s}}$ with labeled segmentation masks $\mathbf{O}^{\mathrm{s}}$ of a specific object category (we follow [1, 24] to focus on one-way segmentation here), i.e., $S = \left\{\left(\mathbf{I}^{\mathrm{s}_i}, \mathbf{O}^{\mathrm{s}_i}\right)\right\}_{i=1}^{K}$ , as the meta knowledge of the target class. Then, given a query video $\mathcal{Q} = \{\mathbf{I}^{\mathrm{q}_i}\}_{i=1}^{N}$ with $N$ frames, an FSVOS model is used to predict the segmentation masks $\{\tilde{\mathbf{O}}^{\mathrm{q}_i}\}_{i=1}^{N}$ of the same category for each frame. The model can be trained on the episodes sampled from $\mathcal{D}_{base}$ with the given ground truth query masks $\{\mathbf{O}^{\mathrm{q}_i}\}_{i=1}^{N}$ , learning how to transfer the guidance knowledge from the support to the query. Finally, the FSVOS model is expected to make accurate predictions for unseen categories on $\mathcal{D}_{novel}$ . + +# 3.2. Review of IPMT + +The IPMT model [16] adopts a transformer-based architecture for the FSISS task. Specifically, FSISS can be modeled by learning an intermediate prototype $\mathbf{G} \in \mathbb{R}^{1 \times C}$ and pixel-wise feature maps $\mathbf{F^s}$ and $\mathbf{F^q}$ for the support and query, respectively, and then conduct iterative mutual optimization between $\mathbf{G}$ and $\mathbf{F^q}$ within multiple IPMT layers. Under the $K$ -shot setting, the support features $\mathbf{F^s} \in \mathbb{R}^{Khw \times C}$ and the flattened masks $\mathbf{O^s} \in \mathbb{R}^{Khw \times 1}$ , where $h, w, C$ are the height, width, and channel number, respectively. + +In the $l$ -th IPMT layer, given the previous query feature $\mathbf{F}_{l-1}^{\mathbf{q}} \in \mathbb{R}^{hw \times C}$ and the flattened binarized mask prediction $\tilde{\mathbf{O}}_{l-1}^{\mathbf{q}} \in \mathbb{R}^{hw \times 1}$ , the intermediate prototype $\mathbf{G}$ is updated by + +$$ +\begin{array}{l} \mathbf {G} _ {l} = \mathbf {I P M} \left(\mathbf {G} _ {l - 1}, \mathbf {F} ^ {\mathbf {s}}, \mathbf {F} _ {l - 1} ^ {\mathbf {q}}, \mathbf {O} ^ {\mathbf {s}}, \tilde {\mathbf {O}} _ {l - 1} ^ {\mathbf {q}}\right) \tag {1} \\ = \mathbf {M L P} \left(\mathbf {G} _ {l} ^ {\mathbf {s}} + \mathbf {G} _ {l} ^ {\mathbf {q}} + \mathbf {G} _ {l - 1}\right), \\ \end{array} +$$ + +where MLP denotes a multi-layer perception. The $\mathbf{G}_l^{\mathrm{s}}$ can be seen as the support prototype which encodes the deterministic guidance knowledge from the support and the $\mathbf{G}_l^{\mathbf{q}}$ can be regarded as the query prototype that learns adaptive guidance information from the query. They can be obtained by + +$$ +\mathbf {G} _ {l} ^ {\mathbf {s}} = \mathbf {M A t t} \left(\mathbf {G} _ {l - 1}, \mathbf {F} ^ {\mathbf {s}}, \mathbf {O} ^ {\mathbf {s}}\right), \tag {2} +$$ + +$$ +\mathbf {G} _ {l} ^ {\mathbf {q}} = \mathbf {M A t t} \left(\mathbf {G} _ {l - 1}, \mathbf {F} _ {l - 1} ^ {\mathbf {q}}, \tilde {\mathbf {O}} _ {l - 1} ^ {\mathbf {q}}\right). \tag {3} +$$ + +Here, MAtt means the masked attention operation [3]: + +$$ +\mathbf {M} \mathbf {A} \mathbf {t} \mathbf {t} (\mathbf {G}, \mathbf {F}, \mathbf {O}) = \delta \left(f _ {Q} (\mathbf {G}) f _ {K} (\mathbf {F}) ^ {\top} + \Delta\right) f _ {V} (\mathbf {F}), \tag {4} +$$ + +where $\delta$ means the softmax normalization, $f_{Q}(\cdot), f_{K}(\cdot), f_{V}(\cdot)$ are three linear transformations following [26], and $\Delta = (1 - \mathbf{O}^{\top}) \cdot (-\infty)$ is used to modulate the attention matrix, making background attention weights become zeros after softmax. + +Then, the updated $\mathbf{G}_l$ is used to generate mask predictions for both support and query via a mask generation (MG) process: + +$$ +\tilde {\mathbf {O}} _ {l} ^ {\mathbf {s}} = \mathbf {M G} \left(\mathbf {G} _ {l}, \mathbf {F} ^ {\mathbf {s}}\right), \tilde {\mathbf {O}} _ {l} ^ {\mathbf {q}} = \mathbf {M G} \left(\mathbf {G} _ {l}, \mathbf {F} _ {l - 1} ^ {\mathbf {q}}\right), \tag {5} +$$ + +$$ +\mathbf {M G} (\mathbf {G}, \mathbf {F}) = \operatorname {S i g m o i d} \left(f _ {G} (\mathbf {G}) \mathbf {F} ^ {\top}\right), \tag {6} +$$ + +where $f_{G}(\cdot)$ is another linear transformation. At the same time, the generated prototype $\mathbf{G}_l$ is also used to update the query feature maps via query activation (QA): + +$$ +\mathbf {F} _ {l} ^ {\mathbf {q}} = \mathbf {Q} \mathbf {A} \left(\mathbf {G} _ {l}, \mathbf {F} _ {l - 1} ^ {\mathbf {q}}\right) = \mathcal {F} _ {\text {a c t v}} \left(\mathbf {G} _ {l} \odot \mathbf {F} _ {l - 1} ^ {\mathbf {q}}\right), \tag {7} +$$ + +where $\odot$ means concatenation and $\mathcal{F}_{\text{actv}}$ is an activation network with two convolution layers. + +In the original implementation, IPMT first feeds the input images into a froze backbone encoder (e.g. ResNet-50 [11]), obtaining multi-scale features $\{\mathbf{X}_1,\mathbf{X}_2,\mathbf{X}_3,\mathbf{X}_4\}$ from the last four convolution blocks, with the scale of 1/4, 1/8, 1/8, and 1/8, respectively. Then, $\mathbf{X}_1$ and $\mathbf{X}_2$ are fused to obtain the backbone features for both support and query. Next, a prototype activation (PA) module generates the support features $\mathbf{F}^{\mathrm{s}}$ , the initial query feature $\mathbf{F}_0^{\mathrm{q}}$ , and the initial query mask $\tilde{\mathbf{O}}_0^{\mathrm{q}}$ . The initial prototype $\mathbf{G}_0$ is randomly initialized at the beginning and then optimized during training. Afterward, by iteratively operating (1) to (7) in five layers, both prototype and features can be optimized step by step. For more details please refer to [16]. + +![](images/61c0b8800fcdb502d13718612e8eeb34cee70e3a543177f5a4701aac3ebbc52b.jpg) +Figure 2. Main architecture of the proposed VIPMT model for FSVOS. "RMS" means our proposed reliable memory selection (Section 4.3), "MAtt" means masked attention (4), "MG" means mask generation (6), and "QA" means query activation (7). In each VIPMT iteration, the input intermediate prototype $\mathbf{G}_{l-1}$ first generates the support prototype $\mathbf{G}_l^{\mathrm{s}}$ (2), the clip prototype $\mathbf{G}_l^{\mathrm{c}}$ (8), and the memory prototype $\mathbf{G}_l^{\mathrm{m}}$ (13), and combine them to obtain the clip-level intermediate prototype $\mathbf{G}_l^{\mathrm{ci}}$ (14). Afterwords, a frame level prototype $\mathbf{G}_l^{\mathrm{f}_i}$ is obtained for each frame via (10) and then updates the frame mask $\tilde{\mathbf{O}}_l^{\mathrm{f}_i}$ and frame feature $\mathbf{F}_l^{\mathrm{c}_i}$ via (12). Finally, all $\mathbf{G}_l^{\mathrm{f}_i}$ are averaged to obtain $\mathbf{G}_l$ (11), which is input into the next iteration with $\tilde{\mathbf{O}}_l^{\mathrm{f}}$ and $\mathbf{F}_l^{\mathrm{c}}$ . + +# 4. Video IPMT + +As shown in Figure 2, we take the original IPMT model as the baseline and combine it with our proposed multi-grained prototype learning scheme for performing the FSVOS task. We elaborate on the design of our clip-level, frame-level, and memory-level prototypes first. Finally, we present the training loss, including the newly proposed CCDS loss. + +# 4.1. Clip Prototype Learning + +Since a video is composed of several consecutive frames, a straightforward way is to directly apply the IPMT model on each query frame. However, such a naive method does not consider any video temporal information and also lacks efficiency. Hence, we propose to take video clips as query units for both training and inference. Given a query video clip $\mathcal{C} = \{\mathbf{I}^{\mathbf{c}_i}\}_{i=1}^{T_c}$ with $T_c$ frames, we perform the masked attention with clip-level query features to generate the clip prototype: + +$$ +\mathbf {G} _ {l} ^ {\mathbf {c}} = \mathbf {M A t t} \left(\mathbf {G} _ {l - 1}, \mathbf {F} _ {l - 1} ^ {\mathbf {c}}, \tilde {\mathbf {O}} _ {l - 1} ^ {\mathbf {f}}\right), \tag {8} +$$ + +where $\mathbf{F}_{l - 1}^{\mathbf{c}}\in \mathbb{R}^{T_chw\times C}$ , $\tilde{\mathbf{O}}_{l - 1}^{\mathbf{f}}\in \mathbb{R}^{T_chw\times 1}$ is the previous predicted masks and will be explained later. Then, we obtain the clip-level intermediate prototype: + +$$ +\mathbf {G} _ {l} ^ {\mathbf {c i}} = \mathbf {M L P} \left(\mathbf {G} _ {l} ^ {\mathbf {s}} + \mathbf {G} _ {l} ^ {\mathbf {c}} + \mathbf {G} _ {l - 1}\right), \tag {9} +$$ + +which encodes local guidance information within the whole query clip. Next, we can use (6) to segment the target objects in the whole clip and obtain clip predictions $\tilde{\mathbf{O}}_l^{\mathbf{c}}\in \mathbb{R}^{T_chw\times 1} = \mathbf{M}\mathbf{G}(\mathbf{G}_l^{\mathbf{ci}},\mathbf{F}_{l - 1}^{\mathbf{c}})$ , which preserves temporal coherence within the $T_{c}$ frames. + +# 4.2. Frame Prototype Learning + +The clip-level intermediate prototype $\mathbf{G}_l^{\mathrm{ci}}$ uses one prototype to represent the whole clip and encodes the clip consensus object information, however, may ignore frame-level fine-grained cues. This problem may cause a performance drop when the object appearance changes significantly within the clip. To mitigate this problem, we propose to further generate frame-level query prototypes $\{\mathbf{G}_{l}\}_{i = 1}^{T_{c}}$ by updating $\mathbf{G}_l^{\mathrm{ci}}$ with related fine-grained object cues in each frame: + +$$ +\mathbf {G} _ {l} ^ {\mathbf {f} _ {i}} = \operatorname {M L P} \left(\mathbf {M A t t} \left(\mathbf {G} _ {l} ^ {\mathbf {c i}}, \mathbf {F} _ {l - 1} ^ {\mathbf {c} _ {i}}, \tilde {\mathbf {O}} _ {l} ^ {\mathbf {c} _ {i}}\right) + \mathbf {G} _ {l} ^ {\mathbf {c i}}\right). \tag {10} +$$ + +In this process, we use $\mathbf{G}_l^{\mathbf{ci}}$ as a good initialization to learn each $\mathbf{G}_l^{\mathbf{f}_i}$ and subsequently aggregate the frame-level query prototypes as the initialization for the next iteration: + +$$ +\mathbf {G} _ {l} = \frac {1}{T _ {c}} \sum_ {i = 1} ^ {T _ {c}} \mathbf {G} _ {l} ^ {\mathbf {f} _ {i}}. \tag {11} +$$ + +As such, we enable bidirectional clip-frame prototype communication, which promotes the intra-clip temporal correlation. On the contrary, directly using the clip-level intermediate prototype $\mathbf{G}_l^{\mathrm{ci}}$ as the initialization for the next iteration only enables one-way communication from the clip information to the frame-level. + +At the same time, we use each frame prototype $\mathbf{G}_l^{\mathbf{f}_i}$ to generate the frame-level segmentation mask and update the query feature for each frame independently: + +$$ +\tilde {\mathbf {O}} _ {l} ^ {\mathbf {f} _ {i}} = \mathbf {M G} \left(\mathbf {G} _ {l} ^ {\mathbf {f} _ {i}}, \mathbf {F} _ {l - 1} ^ {\mathbf {c} _ {i}}\right), \tag {12} +$$ + +$$ +\mathbf {F} _ {l} ^ {\mathbf {c} _ {i}} = \mathbf {Q A} \left(\mathbf {G} _ {l} ^ {\mathbf {f} _ {i}}, \mathbf {F} _ {l - 1} ^ {\mathbf {c} _ {i}}\right). +$$ + +![](images/8f78487e95e2bd67801f1f8efafc6045502f45bc54e2f09917bf334718be8464.jpg) +Figure 3. Illustration of the generation process of the four structural similarity maps. Red and blue regions indicate objects of two categories, respectively. Here we only show two support frames for concision. + +Next, $\tilde{\mathbf{O}}_l^{\mathbf{f}} = \{\tilde{\mathbf{O}}_l^{\mathbf{f}_i}\}_{i = 1}^{T_c},\mathbf{F}_l^{\mathbf{c}} = \{\mathbf{F}_l^{\mathbf{c}_i}\}_{i = 1}^{T_c}$ , and $\mathbf{G}_l$ are input to (8) again for the next iteration. + +# 4.3. Memory Prototype Learning + +Since a whole video usually contains numerous frames, only considering the information within a local clip is suboptimal as long-term historical temporal information is ignored. Many VOS works have also demonstrated that leveraging history memory is crucial for video data to enhance the temporal correlation. To this end, we propose to learn a memory prototype for providing historical guidance information. For each clip except the first one, we can use $T_{m}$ previous frames as the memory set $\mathcal{M} = \{\mathbf{I}^{\mathbf{m}_i}\}_{i=1}^{T_m}$ , which also has predicted masks $\tilde{\mathbf{O}}^{\mathbf{m}} \in \mathbb{R}^{T_mhw \times 1}$ . Then, we use masked attention on memory features to generate the memory prototype: + +$$ +\mathbf {G} _ {l} ^ {\mathbf {m}} = \mathbf {M A t t} \left(\mathbf {G} _ {l - 1}, \mathbf {F} ^ {\mathbf {m}}, \tilde {\mathbf {O}} ^ {\mathbf {m}}\right), \tag {13} +$$ + +where $\mathbf{F}^{\mathbf{m}}\in \mathbb{R}^{T_mhw\times C}$ and $\tilde{\mathbf{O}}^{\mathbf{m}}\in \mathbb{R}^{T_mhw\times 1}$ . Then, the update of the clip-level intermediate prototype $\mathbf{G}_l^{\mathbf{ci}}$ in (9) can be rewritten as + +$$ +\mathbf {G} _ {l} ^ {\mathrm {c i}} = \mathbf {M L P} \left(\mathbf {G} _ {l} ^ {\mathrm {s}} + \mathbf {G} _ {l} ^ {\mathrm {c}} + \mathbf {G} _ {l} ^ {\mathrm {m}} + \mathbf {G} _ {l - 1}\right). \tag {14} +$$ + +We do not consider using memory prototype at the frame level since $\mathbf{G}_l^{\mathbf{ci}}$ is designed to combine comprehensive guidance information at the clip-level, simultaneously from support, clip, and memory. In contrast, $\mathbf{G}_l^{\mathbf{f}_i}$ encodes pure frame adaptive cues and uses $\mathbf{G}_l^{\mathbf{ci}}$ as the initialization. + +Reliable Memory Selection. During the training stage, we can use the ground truth memory masks $\mathbf{O}^{\mathrm{m}}$ to replace the predicted masks for training an accurate model. However, during the inference stage, we can only use the predicted masks $\tilde{\mathbf{O}}^{\mathrm{m}}$ , which may be very noisy and hence heavily contaminate the learned prototype. To mitigate this problem, + +we follow [17] and train an IoU regression network (IoUNet) to select reliable memory frames which have higher segmentation quality. Different from [17], we explicitly consider the nature of the FSVOS task and propose to leverage the structural similarity among the predicted foreground region, background region, and object region in support images for predicting more accurate IoU scores. + +Specifically, as shown in Figure 3, given the backbone features of an memory frame $\mathbf{X}_4\in \mathbb{R}^{hw\times C}$ and the support set $\mathbf{X}_4^{\mathbf{s}}\in \mathbb{R}^{Khw\times C}$ , the predicted memory mask $\tilde{\mathbf{O}}\in \mathbb{R}^{hw\times 1}$ (here we omit the superscript $\mathbf{m}$ for conciseness), and the ground truth support masks $\mathbf{O}^{\mathrm{s}}\in \mathbb{R}^{Khw\times 1}$ , we first obtain the background mask for the memory $\tilde{\mathbf{B}} = 1 - \tilde{\mathbf{O}}$ . Then, we can evaluate the segmentation quality of the memory frame using a simple and intuitive idea: once it is well segmented, its foreground region $\tilde{\mathbf{O}}$ should be dissimilar to the background $\tilde{\mathbf{B}}$ and similar to the support foreground $\mathbf{O}^{\mathrm{s}}$ , while the background $\tilde{\mathbf{B}}$ should be dissimilar to both $\tilde{\mathbf{O}}$ and $\mathbf{O}^{\mathrm{s}}$ . To this end, we compute the structural similarity map of the foreground area of the memory w.r.t. the background area: + +$$ +\mathbf {S} ^ {f b} = \operatorname {N o r m} \left(\operatorname {M a x} \left(\left(\mathbf {X} _ {4} \odot \tilde {\mathbf {O}}\right) \left(\mathbf {X} _ {4} \odot \tilde {\mathbf {B}}\right) ^ {\top}, 1\right)\right), \tag {15} +$$ + +where $\odot$ means element-wise multiplication, $\mathbf{Max}(*,1)$ means obtaining the maximum value along each row, and Norm denotes the min-max normalization to scale the data to the range of [0, 1]. Then, the output map $\mathbf{S}^{fb}\in \mathbb{R}^{hw\times 1}$ exactly represents how similar each foreground pixel is w.r.t. the background area, as shown in Figure 3. + +Likewise, we can obtain a similarity map $\mathbf{S}^{bf}$ of the background area w.r.t. the foreground, similarity map $\mathbf{S}^{fs}$ of the foreground area of the memory w.r.t. the foreground of the support, and similarity map $\mathbf{S}^{bs}$ of the background area of the memory w.r.t. the foreground of the support: + +$$ +\mathbf {S} ^ {b f} = \operatorname {N o r m} \left(\operatorname {M a x} \left(\left(\mathbf {X} _ {4} \odot \tilde {\mathbf {B}}\right) \left(\mathbf {X} _ {4} \odot \tilde {\mathbf {O}}\right) ^ {\top}, 1\right)\right), +$$ + +$$ +\mathbf {S} ^ {f s} = \operatorname {N o r m} \left(\operatorname {M a x} \left(\left(\mathbf {X} _ {4} \odot \tilde {\mathbf {O}}\right) \left(\mathbf {X} _ {4} ^ {\mathbf {s}} \odot \mathbf {O} ^ {\mathbf {s}}\right) ^ {\top}, 1\right)\right), \tag {16} +$$ + +$$ +\mathbf {S} ^ {b s} = \operatorname {N o r m} (\operatorname {M a x} ((\mathbf {X} _ {4} \odot \tilde {\mathbf {B}}) (\mathbf {X} _ {4} ^ {\mathbf {s}} \odot \mathbf {O} ^ {\mathbf {s}}) ^ {\top}, 1)). +$$ + +Once obtain the four structural similarity maps, we combine them with multi-scale memory features and the original predicted mask $\tilde{\mathbf{O}}$ to regress the IoU score of the memory frame. Concretely, we first downsample $\mathbf{X}_1$ to the 1/8 scale with stride convolution and then fuse it with $\mathbf{X}_2, \mathbf{X}_3, \mathbf{X}_4$ into a combined feature with 256 channels. Then, we concatenate the feature with the four structural similarity maps and $\tilde{\mathbf{O}}$ and input them into four convolution layers and two fully connected layers for predicting the IoU score. + +During training, we design three ways to train the IoUNet. First, we can jointly train it with the FSVOS model, in which case real predicted masks can be used for training the IoUNet. Second, we can train it independently using synthesized video data. Specifically, we randomly add noises to the ground truth masks in the training set and use the synthesized + +masks to mimic good and bad predictions. In the third way, we train the IoUNet using synthesized image data with the same noisy mask strategy. We compute the ground truth IoU score for each training mask and use a $L_{1}$ loss as supervision. During testing, we simply select reliable memory frames whose predicted IoU scores are larger than a threshold. + +# 4.4. Training Loss + +We follow IPMT [16] and use the final query feature $\mathbf{F}_5^{\mathrm{c}}$ to predict the final segmentation masks via two convolution layers, where Dice loss and IoU loss are both used for optimization. To ease the network training, in each iteration we use binary cross entropy (BCE) loss on the predicted support masks $\tilde{\mathbf{O}}_l^{\mathrm{s}}$ , clip masks $\tilde{\mathbf{O}}_l^{\mathrm{c}}$ , and frame masks $\tilde{\mathbf{O}}_l^{\mathrm{f}}$ . As for memory frames, we generate predictions for them at each iteration using $\mathbf{MG}(\mathbf{G}_l^{\mathrm{ci}}, \mathbf{F}^{\mathrm{m}})$ , and then adopt the BCE loss computed with their ground truth masks as supervision. + +Cross Category Discriminative Segmentation Loss. To make the learned clip-level intermediate prototypes $\mathbf{G}^{\mathrm{ci}}$ more category discriminative, we furthermore propose a CCDS loss and adopt it within each batch. Suppose our batchsize is set to $B > 1$ , we select $B$ video clips with different object categories to form each batch. Then, during training, we use the prototypes of each video to perform segmentation on other videos and let the predicted masks be all zeros. The idea behind is intuitive: if the prototypes are well optimized for a specific category, they should not activate any region on other videos with different categories. However, since a video may contain multiple object categories and we only have the ground truth of one class under the one-way few-shot learning setting, we propose to use the ground truth masks to filter out the regions for loss calculation: + +$$ +L _ {c c d s} = \frac {1}{(B - 1) B} \sum_ {b = 1} ^ {B} \sum_ {j \neq b} \frac {1}{\sum \mathbf {O} _ {j}} L _ {b, j}, \tag {17} +$$ + +$$ +L _ {b, j} = \sum_ {l = 1} ^ {5} B C E \left(\mathbf {M G} \left(\mathbf {G} _ {l, b} ^ {\mathbf {c i}}, \mathbf {F} _ {j}\right) \odot \mathbf {O} _ {j}, \mathbf {Z}\right), \tag {18} +$$ + +where $\mathbf{G}_{l,b}^{\mathrm{ci}}$ is the clip-level intermediate prototype in the $l$ -th iteration of the $b$ -th video, $\mathbf{O}_j$ and $\mathbf{F}_j$ are the ground truth masks and the backbone features of the $j$ -th video. $\mathbf{Z}$ is an all zero matrix. + +# 5. Experiments + +# 5.1. Datasets and Evaluation Setting + +Datasets. Following [1, 24], our experiments are conducted on the training set of YouTube-VIS [30] dataset, which has 40 categories and contains 2238 videos with 3774 instances. The dataset is divided into four folds, following the same slit with [1, 24]. In each fold, we use 30 categories for training and the rest 10 categories for testing. Following [1, 24], we + +set our experiments on the 5-shot setting and randomly select five images from different videos of the same category as the support set. We also follow [24] and adopt the MiniVSPW [24] dataset to evaluate the generalizability of FSVOS methods. It includes 20 categories and provides longer video sequences than YouTube-VIS, since being more challenging. + +Evaluation Setting. As the prior work [1] and VOS methods, we adopt the region similarity $\mathcal{J}$ and contour similarity $\mathcal{F}$ for performance evaluation. Apart from this, we also follow [24] and consider the video consistency metric $\mathrm{VC}_7$ , which captures temporal prediction consistency among long-range adjacent frames over a temporal window of 7. We adopt the average score on four folds, i.e. $\mathrm{mVC}_7$ , to evaluate the overall performance. We also follow [1, 24] and run the evaluation process five times and report the average results. + +Furthermore, there are two different evaluation protocols proposed in [1] and [24] for sampling episodes during testing. Protocol I fixes the sampled support set for all query videos belonging to the same class in each run, while protocol II randomly samples a support set for every query video, which ensures a more stable performance evaluation. Hence, in this paper we adopt protocol II for evaluation. + +Implementation Details. We adopt ResNet-50 [11] pretrained on ImageNet [23] as our encoder backbone. Following IPMT [16], we freeze the parameters of the backbone during training and do not adopt online finetuning as [1, 24] did. The iteration step is set to 5 as IPMT. We set the clip length $T_{c}$ and the memory length $T_{m}$ to 5 without further tuning. The IoU threshold for selecting reliable memory frames is set to 0.8. When the reliable memory has more frames, we simply randomly select five frames from them. During training, we randomly select three clips from a video as a sample, where the first clip is trained without using memory, the second clip uses the first clip as memory, and the third clip randomly selects five frames from the first two as the memory. We also share the MAtt operation for support and memory since we found this leads to better performance. + +We use Adam as our optimizer. The batchsize is set to $B = 4$ and the learning rate is set to 5e-4. We train our model 100 epochs in total. All experiments are conducted on a NVIDIA Tesla A100 GPU. We adopt random horizontal flip, random crop and random resize to augment the training data. During training and testing, all video frames are downsampled to the resolution of (240,424) as the inputs. + +# 5.2. Comparison with State-of-the-art Methods + +In Table 1, we compare our VIPMT with four recently published FSISS methods and two FSVOS methods, on the YouTuebe-VIS [30] dataset. We find that our VIPMT largely improves all metrics, i.e. $4\%$ $\mathcal{I}$ mean score, near $6\%$ $\mathcal{F}$ mean score, and near $5\%$ $\mathrm{mVC}_7$ score, although previous + +
MethodsNameJFmVC7
Fold-1Fold-2Fold-3Fold-4MeanFold-1Fold-2Fold-3Fold-4Mean
FSISSNTRENet [15]39.066.461.761.257.141.163.060.159.455.955.7
SSP [10]46.764.359.354.556.234.853.046.046.745.149.6
VAT [12]42.662.857.056.754.841.656.450.853.050.554.9
IPMT [16]43.865.861.060.757.842.559.557.855.953.957.7
FSVOSDAN [1]43.964.561.162.157.942.462.060.060.056.141.5
TTI [24]47.268.861.463.560.2-----60.8
VIPMT(Ours)50.670.968.866.564.251.366.965.264.462.065.7
+ +Table 1. Comparison with state-of-the-art methods on YouTube-VIS [30]. Bold means the best performance. + +
MethodsNameJFmVC7
Fold-1Fold-2Fold-3Fold-4MeanFold-1Fold-2Fold-3Fold-4Mean
FSVOSTTI [24]25.237.125.029.629.2-----24.4
VIPMT(Ours)26.242.231.629.432.430.645.736.334.236.742.1
+ +Table 2. Comparison with TTI [24] on MiniVSPW [24]. + +
DatasetsMethodsJ-MeanF-MeanmVC7
YouTube-VISIPMT+STCN [6]58.956.561.7
IPMT+XMem [5]59.256.862.2
IPMT+RDE-VOS [14]59.358.063.3
VIPMT(Ours)64.262.065.7
MiniVSPWIPMT+STCN [6]27.731.139.3
IPMT+XMem [5]27.731.741.1
IPMT+RDE-VOS [14]28.833.540.1
VIPMT(Ours)32.436.742.1
+ +works [1, 24] used on-line learning while we didn't. + +To verify the generalization ability of our method, we compare our method with TTI [24] on MiniVSPW. Table 2 shows our method obtains a significant improvement of more than $3\%$ on $\mathcal{I}$ and more than $17\%$ on $\mathrm{mVC}_7$ , which verifies that our method works well in more challenging scenarios. + +In Figure 4, we give some visual comparison cases. Compared with TTI [24], our VIMPT is less distracted by other objects and achieves more precise segmentation, even in highly occluded scenes (bottom row). + +We also include three state-of-the-art semi-supervised VOS methods for comparison, i.e. STCN [6], XMem [5], and RDE-VOS [14]. Specifically, we use IPMT for segmenting the first frame and then use VOS methods for propagating the segmentation to the full video. Table 3 demonstrates that such an ad-hoc combination of FSISS and VOS methods can not achieve as good results as our model does. + +# 5.3. Ablation Study + +In this section, we report ablation study results on the YouTube-VIS dataset. For $\mathcal{J}$ and $\mathcal{F}$ we use their average on four folds, i.e. $\mathcal{J}$ -Mean and $\mathcal{F}$ -Mean. + +Effectiveness of Each Component. In Table 4, we first + +Table 3. Comparison with state-of-the-art VOS methods. + +
NameSettingsJ-MeanF-MeanmVC7
ClipFrameMemoryCCDS
Baseline57.853.957.8
+C✓61.858.860.7
+C+F✓✓62.560.362.1
+C+F+M✓✓✓63.561.962.8
VIPMT✓✓✓✓64.262.065.7
+ +Table 4. Ablation study on the effectiveness of each model component. Baseline means IPMT [16]. + +adopt IPMT [16] as the baseline, which processes each video frame independently. Then, we adopt our clip prototype learning, denoted as “+C”. Results show that “+C” surpasses the baseline by a large margin on all metrics, which verifies the effectiveness of using local temporal guidance with our clip prototype learning. After that, we further add the frame prototype learning to “+C”, resulting in “+C+F”. Benefiting from the frame-level fine-grained cues, “+C+F” achieves large performance improvement for $\mathcal{F}$ -Mean and $\mathrm{mVC}_7$ . Moreover, we adopt “+C+F+M” to represent adding the memory prototype learning on “+C+F”. It largely improves the performance for both $\mathcal{J}$ -Mean and $\mathcal{F}$ -Mean, which shows the importance of long-term temporal information brought by the memory prototype learning. Based on this, we further add the CCDS loss to obtain our final model VIPMT. It also brings obvious improvements, especially on $\mathrm{mVC}_7$ , from 62.8 to 65.7. This proves the effectiveness of increasing category discrimination for FSVOS. + +In Figure 5, we visualize the predicted masks from the different models mentioned above. We can find that progressive improvements can be brought by using multi-grained temporal prototypes and the CCDS loss. + +Clip-frame Communication. As mentioned in Section 4.2, we use the mean of the frame prototypes ((11)) to initialize the intermediate prototype for the next iteration, which enables bidirectional clip-frame communication. On the contrary, directly using the clip-level intermediate prototype $\mathbf{G}_l^{\mathrm{ci}}$ as the initialization only enables one-way communica + +![](images/fb031399959c79851a8afb662da3fe7ccaf71ae543ce411f0336ce66760d5de7.jpg) +(a) + +![](images/0f3602d911c1af2f2fd064587db89f8cdfd3a6478d56a9d708cfb02789982d18.jpg) +(b) + +![](images/458c9a285a992d27530f5cb68bf3dbb6384800c167b43ebea674da4312c56ebf.jpg) + +![](images/7855a58614e7e309b38e51c3153edb495a598e3b26c4ce277d05676480fe14f8.jpg) +(c) + +![](images/6a8b2661d2ee98532f0f79d1260157e715e20a504632d760899a8ce6bb1817a5.jpg) +Figure 4. Visualization of comparison cases. (a) Support sets. (b) Predicted masks of our VIMPT. (c) Predicted masks from TTI [24]. +Support +Figure 5. Visualization of the comparison of different ablation study models. We can see progressive improvements brought by the multi-grained temporal prototypes and the CCDS loss. + +![](images/4f2b3b3c9be5e35db60b1d6b6ed371ee65a301fd04f6eb75ea1595bfb510fe02.jpg) + +![](images/eaaeafcd0bc8209b6ebcdedb801113feae37cff9e7cb0657c57bc3328801b244.jpg) +Baseline + +![](images/4fbd4e33bf8dc35f113e1098a39db7e0759cf704ea08f395babffbd390626198.jpg) + +![](images/8c930f7ff89f12a09a529077e9ec9be4bf2b86cd8b3349d930a28eb2edb2e54b.jpg) ++C + +![](images/5a7cb1baf074c20e762e4962375492f01bfa38c3e760e85482909d07283991aa.jpg) + +![](images/670c99d11fbb10ab9e22ffee0829852a0649b914c45ff8606ffa2031e6d936eb.jpg) ++C+F + +![](images/c56aa0c8cf82e0663bfb4715e58c5991b0c71e266b5f17f1b27e9c239ee4b78a.jpg) + +![](images/c7bf08493adf4b11244373f7410584eccabbb8c0482adff7b5e9937704bdce49.jpg) +$+\mathrm{C} + \mathrm{F} + \mathrm{M}$ + +![](images/05684a726804e371f5a4ae7f9f8b4081972b4080e74b78b09d463d0465a315e0.jpg) + +![](images/fb888146b34842e155489ee92d56f9e6704ace4443939af67695c89be9448117.jpg) +VIPMT + +![](images/c59217b250fc4cee60b111b92b44ac6d68e42b8de0cda6ba7c1f7bbcb5779eee.jpg) + +![](images/9a1b65534902c9735561fb06021713e633cdb3b11793b3508b6e19ca6ee83f38.jpg) +GT + +
Clip-frame CommunicationJ-MeanF-MeanmVC7
One-way61.459.160.1
Bidirectional62.560.362.1
+ +tion. Here we compare the effectiveness of the two schemes. Results in Table 5 demonstrate that our design of using bidirectional clip-frame communication surpasses the one-way scheme by a large margin on all metrics. + +Different Training Strategies of IoUNet. As mentioned in Section 4.3, we can use three ways to train the IoUNet, i.e. using real predicted masks ("Real"), synthesized video data ("Video"), and synthesized image data ("Image"), respectively. For "Image", we use an FSISS dataset COCO-20 $^i$ [20] and remove the classes overlapped with our video data for IoUNet training. We compare their performance in Table 6. We also compare the performance of using our proposed structural similarity maps or not ("w/ SSM" and "w/o SSM"). The results are reported under the IoU threshold of 0.5. The table demonstrates that using synthesized image data results in the best performance in both "w/ SSM" and "w/o SSM" settings and using the structural similarity maps always leads to better performance. Another benefit of using image data is that we can train a unified IoUNet for all folds instead of training an IoUNet for each fold. Hence, finally, we use synthesized image data for IoUNet training. + +IoU Threshold. Finally, we investigate the best IoU threshold for memory selection. Table 7 indicates that 0.8 is the best threshold and using the proposed structural similarity maps always leads to better performance. + +Table 5. Comparison of two clip-frame communication schemes. + +
Dataw/o SSMw/ SSM
J-MeanF-MeanmVC7J-MeanF-MeanmVC7
Real62.861.562.663.261.662.8
Video62.961.662.663.261.662.8
Image63.061.762.763.361.763.0
+ +Table 6. Different training strategies of IoUNet. SSM means the proposed structural similarity maps. + +
Thresholdw/o SSMw/ SSM
J-MeanF-MeanmVC7J-MeanF-MeanmVC7
0.563.061.762.763.361.763.0
0.663.161.762.963.361.762.7
0.763.161.862.963.461.862.6
0.863.161.862.563.561.962.8
0.963.061.862.363.561.962.5
+ +Table 7. Experimental results of using different IoU thresholds. + +# 6. Conclusion + +We explored learning multi-grained temporal prototypes to tackle the FSVOS task. Based on the IPMT model, the query video information was decomposed into a clip prototype, a memory prototype, and frame prototypes. We also improved an IoU regression method for selecting reliable memory for FSVOS by leveraging the task prior knowledge and proposed a new loss to enhance the category discriminability of the prototypes. The effectiveness of our proposed VIPMT has been verified on two benchmark datasets. + +Acknowledgments: This work was supported in part by the National Natural Science Foundation of China under Grants 62071388, 62136007, U20B2065 and 62036005, and the Fundamental Research Funds for the Central Universities under Grant D5000230057. + +# References + +[1] Haoxin Chen, Hanjie Wu, Nanxuan Zhao, Sucheng Ren, and Shengfeng He. 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In NeurIPS, volume 29, 2016. 2 +[28] Huaxin Xiao, Jiashi Feng, Guosheng Lin, Yu Liu, and Maojun Zhang. Monet: Deep motion exploitation for video object segmentation. In CVPR, pages 1140-1148, 2018. 2 +[29] Boyu Yang, Chang Liu, Bohao Li, Jianbin Jiao, and Qixiang Ye. Prototype mixture models for few-shot semantic segmentation. In ECCV, pages 763-778. Springer, 2020. 2 +[30] Linjie Yang, Yuchen Fan, and Ning Xu. Video instance segmentation. In ICCV, pages 5188-5197, 2019. 6, 7 +[31] Tianyu Yang and Antoni B Chan. Learning dynamic memory networks for object tracking. In ECCV, pages 152-167, 2018. 2 +[32] Gengwei Zhang, Guoliang Kang, Yi Yang, and Yunchao Wei. Few-shot segmentation via cycle-consistent transformer. NeurIPS, 34:21984-21996, 2021. 1 + +[33] Tianfei Zhou, Fatih Porikli, David J Crandall, Luc Van Gool, and Wenguan Wang. A survey on deep learning technique for video segmentation. 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However, this task was seldom explored. In this work, based on IPMT, a state-of-the-art few-shot image segmentation method that combines external support guidance information with adaptive query guidance cues, we propose to leverage multi-grained temporal guidance information for handling the temporal correlation nature of video data. We decompose the query video information into a clip prototype and a memory prototype for capturing local and long-term internal temporal guidance, respectively. Frame prototypes are further used for each frame independently to handle fine-grained adaptive guidance and enable bidirectional clip-frame prototype communication. To reduce the influence of noisy memory, we propose to leverage the structural similarity relation among different predicted regions and the support for selecting reliable memory frames. Furthermore, a new segmentation loss is also proposed to enhance the category discriminability of the learned prototypes. 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Many recent works [25, 32, 13, 16] have shown very promising results on image data using the meta-learning scheme. They simulate the inference process and partition the training set into numerous episodes, in each" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 307, + 258, + 351, + 376 + ], + "blocks": [ + { + "bbox": [ + 307, + 258, + 351, + 376 + ], + "lines": [ + { + "bbox": [ + 307, + 258, + 351, + 376 + ], + "spans": [ + { + "bbox": [ + 307, + 258, + 351, + 376 + ], + "type": "image", + "image_path": "1c2fd512074ba0e8b90112e47317e93c140d8eb071c96f9050fa016b39598ec2.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 380, + 547, + 436 + ], + "lines": [ + { + "bbox": [ + 306, + 380, + 547, + 436 + ], + "spans": [ + { + "bbox": [ + 306, + 380, + 547, + 436 + ], + "type": "text", + "content": "Figure 1. Given a few annotated support frames, FSVOS aims to segment the objects with the same category from a query video (a). Simply considering single-frame information leads to inconsecutive segmentation results (b), while our method generates accurate results by using multi-grained temporal prototypes (c)." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 358, + 266, + 545, + 304 + ], + "blocks": [ + { + "bbox": [ + 358, + 266, + 545, + 304 + ], + "lines": [ + { + "bbox": [ + 358, + 266, + 545, + 304 + ], + "spans": [ + { + "bbox": [ + 358, + 266, + 545, + 304 + ], + "type": "image", + "image_path": "09d31fb0d3deb2639947235aef7873bd60984f577935aa88d799710613f91ead.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 358, + 309, + 545, + 337 + ], + "blocks": [ + { + "bbox": [ + 358, + 309, + 545, + 337 + ], + "lines": [ + { + "bbox": [ + 358, + 309, + 545, + 337 + ], + "spans": [ + { + "bbox": [ + 358, + 309, + 545, + 337 + ], + "type": "image", + "image_path": "79d08fb30710adeb622507f7dcf014110f4114f1b187d3d9fdb403f0e46f8900.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 358, + 343, + 545, + 371 + ], + "blocks": [ + { + "bbox": [ + 358, + 343, + 545, + 371 + ], + "lines": [ + { + "bbox": [ + 358, + 343, + 545, + 371 + ], + "spans": [ + { + "bbox": [ + 358, + 343, + 545, + 371 + ], + "type": "image", + "image_path": "736a516b91f587a10ea0f92e80b0f1d8fffbfb23ebee61bfdbc8f106214d1281.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 449, + 545, + 473 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 449, + 545, + 473 + ], + "spans": [ + { + "bbox": [ + 304, + 449, + 545, + 473 + ], + "type": "text", + "content": "of which, the model samples a few support images and learns to guide the segmentation on the query images." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 474, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 474, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 474, + 547, + 713 + ], + "type": "text", + "content": "Inspired by the classic Few-Shot Image Semantic Segmentation (FSISS) task, the Few-Shot Video Object Segmentation (FSVOS) task was introduced by [1, 24]. For FSISS, many works adopt the prototype-based methods, in which a prototype vector is extracted from the support to encode the category guidance information, and then a segmentation head learns to match the prototype with the feature at each query pixel for performing query segmentation. However, the intra-class diversity can cause the matching gap between the support-induced prototype guidance and the query features. The IPMT model [16] solved this problem by learning an intermediate prototype that integrates both support-induced external category guidance knowledge and query-induced adaptive guidance information. As for FSVOS, video data additionally show temporal correlation, from which we can also induce internal temporal guidance. If we ignore this prior knowledge and simply consider single-frame information, the learned prototypes may vary significantly among different frames, leading to inconsecutive segmentation results, as shown in Figure 1 (b)." + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 225, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 225, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 225, + 713 + ], + "type": "text", + "content": "†Corresponding author: yaoxiwen517@gmail.com." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18862" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 301 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 301 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 301 + ], + "type": "text", + "content": "In this work, we extend the IPMT model [16] for video data by tackling the temporal correlation nature. Based on the intermediate prototype mechanism of IPMT, we propose to decompose the query video information into the clip-level, frame-level, and memory-level prototypes, consisting of a multi-grained temporal structure, which was NEVER explored by existing models [1, 24]. Among them, the clip prototype encodes local temporal object guidance information in each consecutive clip, while the memory prototype introduces long-term historical guidance cues. Combining them can effectively handle the temporal correlation problem. However, such a design may ignore fine-grained per-frame adaptive guidance information, hence may fail to handle large scene changes and object transformation. To this end, we further learn an adaptive frame prototype by independently encoding per-frame object features. Additionally, we enable bidirectional clip-frame prototype communication by making the clip-level and frame-level prototypes initialize each other, hence promoting intra-clip temporal correlation." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 305, + 289, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 305, + 289, + 485 + ], + "spans": [ + { + "bbox": [ + 47, + 305, + 289, + 485 + ], + "type": "text", + "content": "To better leverage the historical memory guidance, we also follow a Video Object Segmentation (VOS) method [17] and train an IoU regression network to select reliable memory frames for reducing the negative influence brought by noisy memory. However, different from [17], we explicitly consider the nature of the FSVOS task and propose to leverage the structural similarity relation among different predicted regions and the support information for predicting more accurate IoU scores. To make the learned prototype more category discriminative, we also propose a Cross-Category Discriminative Segmentation (CCDS) loss by leveraging negative batch samples. Extensive experimental results have verified the effectiveness of our proposed Video IPMT (VIPMT) model and showed its significant performance improvement over state-of-the-art models." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 490, + 287, + 514 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 490, + 287, + 514 + ], + "spans": [ + { + "bbox": [ + 47, + 490, + 287, + 514 + ], + "type": "text", + "content": "In conclusion, our contributions can be summarized as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 520, + 287, + 712 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 58, + 520, + 287, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 520, + 287, + 591 + ], + "spans": [ + { + "bbox": [ + 58, + 520, + 287, + 591 + ], + "type": "text", + "content": "- For the very first time, we propose to learn multi-grained temporal prototypes for FSVOS, by extending the IPMT [16] model. Clip and memory prototypes are learned for internal temporal guidance. Frame prototypes are used for fine-grained adaptive guidance and also enable prototype communication." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 592, + 287, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 592, + 287, + 663 + ], + "spans": [ + { + "bbox": [ + 58, + 592, + 287, + 663 + ], + "type": "text", + "content": "- We propose to leverage the structural similarity relation among different predicted regions and the support for selecting reliable memory information. We also present a CCDS loss using the negative samples within each batch for promoting category discriminability of the learned prototypes." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 663, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 663, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 663, + 287, + 712 + ], + "type": "text", + "content": "- Experimental results have demonstrated the significant effectiveness of our proposed model, which improves state-of-the-art results by more than " + }, + { + "bbox": [ + 58, + 663, + 287, + 712 + ], + "type": "inline_equation", + "content": "4\\%" + }, + { + "bbox": [ + 58, + 663, + 287, + 712 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 58, + 663, + 287, + 712 + ], + "type": "inline_equation", + "content": "3\\%" + }, + { + "bbox": [ + 58, + 663, + 287, + 712 + ], + "type": "text", + "content": ", on two benchmark datasets, respectively." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 71, + 392, + 84 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 71, + 392, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 392, + 84 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 91, + 518, + 105 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 91, + 518, + 105 + ], + "spans": [ + { + "bbox": [ + 306, + 91, + 518, + 105 + ], + "type": "text", + "content": "2.1. Few-Shot Image Semantic Segmentation" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 110, + 547, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 110, + 547, + 327 + ], + "spans": [ + { + "bbox": [ + 304, + 110, + 547, + 327 + ], + "type": "text", + "content": "Most previous FSISS works adopted meta-learning-based methods [27], especially prototype-based models. Specifically, Dong and Xing [9] aggregated a prototype vector on the support images to encode the representative category knowledge first, and then evaluated its similarity with each query pixel in a matching network as the segmentation result. Following this idea, Yang et al. [29] constructed multiple prototypes from limited support images to represent diverse image regions. In [25], Tian et al. used high-level features to generate a prior mask as a supplement to the support prototype for refining the query feature. Liu et al. [15] leveraged non-target prototypes to eliminate distracting regions. BAM [13] used the prototypes of base classes to explicitly suppress corresponding regions. In IPMT [16], Liu et al. proposed to generate an intermediate prototype which encodes the category guidance information from both support and query. However, all these methods only focused on image data and the challenge of video data remains seldom explored." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 335, + 457, + 348 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 335, + 457, + 348 + ], + "spans": [ + { + "bbox": [ + 306, + 335, + 457, + 348 + ], + "type": "text", + "content": "2.2. Video Object Segmentation" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 354, + 547, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 354, + 547, + 486 + ], + "spans": [ + { + "bbox": [ + 304, + 354, + 547, + 486 + ], + "type": "text", + "content": "Another closely related domain is VOS, especially the semi-supervised VOS, in which the mask label of an object in the first frame is given and the model is required to segment the same object in other frames. Some methods [22, 7, 28] tried to leverage optical flow to help segment target objects. Noticing the successful application of memory networks [8, 31] in computer vision, STM [21] proposed a memory mechanism to leverage information from previous frames for segmenting the current frame. Lu et al. [19] followed this idea and improve the memory mechanism with a graph model. For a comprehensive survey please refer to [33]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 486, + 547, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 547, + 640 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 547, + 640 + ], + "type": "text", + "content": "Different from semi-supervised VOS, we tackle the FSVOS task with two differences. First, semi-supervised VOS aims to segment the same object indicated in the annotation of the first frame while FSVOS requires to segment the objects of the same class with the annotated support set. Second, the support set in FSVOS can be composed of any images or frames of any videos that contain the target class. Hence, FSVOS is more generalized and faces much larger intra-class diversity between the support set and the query video. In this work, we propose multi-grained temporal prototype learning and bidirectional clip-frame prototype communication for FSVOS, which is different from existing VOS methods." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "type": "text", + "content": "Our idea of using the IoU network to select memory frames with high segmentation quality is inspired by [17]. However, in [17], the authors directly regress the IoU score by only taking the image and the mask as the network input. In this work, we further consider the nature of FSVOS and propose to compute several structural similarity maps" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "18863" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 109 + ], + "type": "text", + "content": "which explicitly encode the quality assessment prior of the relations among the predicted foreground, background, and the support areas." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 116, + 243, + 129 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 116, + 243, + 129 + ], + "spans": [ + { + "bbox": [ + 47, + 116, + 243, + 129 + ], + "type": "text", + "content": "2.3. Few-shot Video Object Segmentation" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 134, + 289, + 291 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 134, + 289, + 291 + ], + "spans": [ + { + "bbox": [ + 46, + 134, + 289, + 291 + ], + "type": "text", + "content": "For the FSVOS task, currently, only a few works have targeted this topic. Chen et al. [1] proposed the first FSVOS dataset and model. They proposed a Domain Agent Network (DAN) to alleviate the large computational cost of the many-to-many attention between the support images and the query video frames, which only considered clip-level temporal information. Siam et al. [24] proposed a temporal transductive inference model, which uses both global and local temporal constraints to obtain per-frame model weights and locally consistent predictions. Compared with them, we optimize multi-grained temporal prototypes while they optimized per-frame model weights. Furthermore, we explicitly use historical memory while they did not." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 301, + 132, + 314 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 301, + 132, + 314 + ], + "spans": [ + { + "bbox": [ + 47, + 301, + 132, + 314 + ], + "type": "text", + "content": "3. Preliminaries" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 321, + 159, + 333 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 321, + 159, + 333 + ], + "spans": [ + { + "bbox": [ + 47, + 321, + 159, + 333 + ], + "type": "text", + "content": "3.1. Problem Definition" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "spans": [ + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": "For FSVOS, a whole video object segmentation dataset " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " with multiple object categories " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{C}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " is divided into a training subset " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_{base}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " and a testing subset " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_{novel}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": ", whose categories are " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_{base}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_{novel}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": ", respectively, and satisfy " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_{base} \\cap \\mathcal{C}_{novel} = \\emptyset" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_{base} \\cup \\mathcal{C}_{novel} = \\mathcal{C}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": ". Under the standard few-shot setting and the episodic training scheme, both " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_{base}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_{novel}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " are randomly partitioned into a lot of episodes. In each episode, a support set " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " provides " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " frames " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{I}^{\\mathrm{s}}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " with labeled segmentation masks " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathbf{O}^{\\mathrm{s}}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " of a specific object category (we follow [1, 24] to focus on one-way segmentation here), i.e., " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "S = \\left\\{\\left(\\mathbf{I}^{\\mathrm{s}_i}, \\mathbf{O}^{\\mathrm{s}_i}\\right)\\right\\}_{i=1}^{K}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": ", as the meta knowledge of the target class. Then, given a query video " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{Q} = \\{\\mathbf{I}^{\\mathrm{q}_i}\\}_{i=1}^{N}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " frames, an FSVOS model is used to predict the segmentation masks " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\{\\tilde{\\mathbf{O}}^{\\mathrm{q}_i}\\}_{i=1}^{N}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " of the same category for each frame. The model can be trained on the episodes sampled from " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_{base}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": " with the given ground truth query masks " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{O}^{\\mathrm{q}_i}\\}_{i=1}^{N}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": ", learning how to transfer the guidance knowledge from the support to the query. Finally, the FSVOS model is expected to make accurate predictions for unseen categories on " + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "inline_equation", + "content": "\\mathcal{D}_{novel}" + }, + { + "bbox": [ + 46, + 339, + 289, + 579 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 586, + 146, + 598 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 146, + 598 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 146, + 598 + ], + "type": "text", + "content": "3.2. Review of IPMT" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": "The IPMT model [16] adopts a transformer-based architecture for the FSISS task. Specifically, FSISS can be modeled by learning an intermediate prototype " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{G} \\in \\mathbb{R}^{1 \\times C}" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": " and pixel-wise feature maps " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{F^s}" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{F^q}" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": " for the support and query, respectively, and then conduct iterative mutual optimization between " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{G}" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{F^q}" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": " within multiple IPMT layers. Under the " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": "-shot setting, the support features " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{F^s} \\in \\mathbb{R}^{Khw \\times C}" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": " and the flattened masks " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{O^s} \\in \\mathbb{R}^{Khw \\times 1}" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "inline_equation", + "content": "h, w, C" + }, + { + "bbox": [ + 46, + 605, + 289, + 715 + ], + "type": "text", + "content": " are the height, width, and channel number, respectively." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "text", + "content": "In the " + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "text", + "content": "-th IPMT layer, given the previous query feature " + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{l-1}^{\\mathbf{q}} \\in \\mathbb{R}^{hw \\times C}" + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "text", + "content": " and the flattened binarized mask prediction " + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}_{l-1}^{\\mathbf{q}} \\in \\mathbb{R}^{hw \\times 1}" + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "text", + "content": ", the intermediate prototype " + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "inline_equation", + "content": "\\mathbf{G}" + }, + { + "bbox": [ + 305, + 72, + 545, + 111 + ], + "type": "text", + "content": " is updated by" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 343, + 118, + 545, + 149 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 118, + 545, + 149 + ], + "spans": [ + { + "bbox": [ + 343, + 118, + 545, + 149 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathbf {G} _ {l} = \\mathbf {I P M} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} ^ {\\mathbf {s}}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}, \\mathbf {O} ^ {\\mathbf {s}}, \\tilde {\\mathbf {O}} _ {l - 1} ^ {\\mathbf {q}}\\right) \\tag {1} \\\\ = \\mathbf {M L P} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {s}} + \\mathbf {G} _ {l} ^ {\\mathbf {q}} + \\mathbf {G} _ {l - 1}\\right), \\\\ \\end{array}", + "image_path": "cfb44a5f7bc7c7dfc676056effbdee1dd944dd478e64bfe03e74d01528439ee1.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 153, + 547, + 225 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 153, + 547, + 225 + ], + "spans": [ + { + "bbox": [ + 304, + 153, + 547, + 225 + ], + "type": "text", + "content": "where MLP denotes a multi-layer perception. The " + }, + { + "bbox": [ + 304, + 153, + 547, + 225 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathrm{s}}" + }, + { + "bbox": [ + 304, + 153, + 547, + 225 + ], + "type": "text", + "content": " can be seen as the support prototype which encodes the deterministic guidance knowledge from the support and the " + }, + { + "bbox": [ + 304, + 153, + 547, + 225 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathbf{q}}" + }, + { + "bbox": [ + 304, + 153, + 547, + 225 + ], + "type": "text", + "content": " can be regarded as the query prototype that learns adaptive guidance information from the query. They can be obtained by" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 347, + 233, + 545, + 247 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 233, + 545, + 247 + ], + "spans": [ + { + "bbox": [ + 347, + 233, + 545, + 247 + ], + "type": "interline_equation", + "content": "\\mathbf {G} _ {l} ^ {\\mathbf {s}} = \\mathbf {M A t t} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} ^ {\\mathbf {s}}, \\mathbf {O} ^ {\\mathbf {s}}\\right), \\tag {2}", + "image_path": "15d6c501c29781adbd65ca088b902ff8033da8ea42287f4056d2d0b39bc6b1f8.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 347, + 248, + 545, + 262 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 248, + 545, + 262 + ], + "spans": [ + { + "bbox": [ + 347, + 248, + 545, + 262 + ], + "type": "interline_equation", + "content": "\\mathbf {G} _ {l} ^ {\\mathbf {q}} = \\mathbf {M A t t} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}, \\tilde {\\mathbf {O}} _ {l - 1} ^ {\\mathbf {q}}\\right). \\tag {3}", + "image_path": "6fd49f730ffb0c194a1a88410d2ff6ec82dc3a057af3de9e42a2d159cfa5d980.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 270, + 531, + 282 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 270, + 531, + 282 + ], + "spans": [ + { + "bbox": [ + 306, + 270, + 531, + 282 + ], + "type": "text", + "content": "Here, MAtt means the masked attention operation [3]:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 314, + 290, + 545, + 304 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 314, + 290, + 545, + 304 + ], + "spans": [ + { + "bbox": [ + 314, + 290, + 545, + 304 + ], + "type": "interline_equation", + "content": "\\mathbf {M} \\mathbf {A} \\mathbf {t} \\mathbf {t} (\\mathbf {G}, \\mathbf {F}, \\mathbf {O}) = \\delta \\left(f _ {Q} (\\mathbf {G}) f _ {K} (\\mathbf {F}) ^ {\\top} + \\Delta\\right) f _ {V} (\\mathbf {F}), \\tag {4}", + "image_path": "08108bd7f6147b3ff857e54ad11ef56260e5bc7953f0aee709d9a16e340ea5a2.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 312, + 545, + 371 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 545, + 371 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 545, + 371 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 312, + 545, + 371 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 304, + 312, + 545, + 371 + ], + "type": "text", + "content": " means the softmax normalization, " + }, + { + "bbox": [ + 304, + 312, + 545, + 371 + ], + "type": "inline_equation", + "content": "f_{Q}(\\cdot), f_{K}(\\cdot), f_{V}(\\cdot)" + }, + { + "bbox": [ + 304, + 312, + 545, + 371 + ], + "type": "text", + "content": " are three linear transformations following [26], and " + }, + { + "bbox": [ + 304, + 312, + 545, + 371 + ], + "type": "inline_equation", + "content": "\\Delta = (1 - \\mathbf{O}^{\\top}) \\cdot (-\\infty)" + }, + { + "bbox": [ + 304, + 312, + 545, + 371 + ], + "type": "text", + "content": " is used to modulate the attention matrix, making background attention weights become zeros after softmax." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 372, + 545, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 372, + 545, + 408 + ], + "spans": [ + { + "bbox": [ + 304, + 372, + 545, + 408 + ], + "type": "text", + "content": "Then, the updated " + }, + { + "bbox": [ + 304, + 372, + 545, + 408 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l" + }, + { + "bbox": [ + 304, + 372, + 545, + 408 + ], + "type": "text", + "content": " is used to generate mask predictions for both support and query via a mask generation (MG) process:" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 334, + 415, + 545, + 430 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 334, + 415, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 334, + 415, + 545, + 430 + ], + "type": "interline_equation", + "content": "\\tilde {\\mathbf {O}} _ {l} ^ {\\mathbf {s}} = \\mathbf {M G} \\left(\\mathbf {G} _ {l}, \\mathbf {F} ^ {\\mathbf {s}}\\right), \\tilde {\\mathbf {O}} _ {l} ^ {\\mathbf {q}} = \\mathbf {M G} \\left(\\mathbf {G} _ {l}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}\\right), \\tag {5}", + "image_path": "8a0d1a11975b884c96ac09fe33d945b2566593b564801f49d743c3f2d7074044.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 348, + 449, + 545, + 463 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 348, + 449, + 545, + 463 + ], + "spans": [ + { + "bbox": [ + 348, + 449, + 545, + 463 + ], + "type": "interline_equation", + "content": "\\mathbf {M G} (\\mathbf {G}, \\mathbf {F}) = \\operatorname {S i g m o i d} \\left(f _ {G} (\\mathbf {G}) \\mathbf {F} ^ {\\top}\\right), \\tag {6}", + "image_path": "5cbecd176a94445fb6d83145c5fb03c8fa42d291e54e10df06cc964e0004a349.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 468, + 545, + 504 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 468, + 545, + 504 + ], + "spans": [ + { + "bbox": [ + 304, + 468, + 545, + 504 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 468, + 545, + 504 + ], + "type": "inline_equation", + "content": "f_{G}(\\cdot)" + }, + { + "bbox": [ + 304, + 468, + 545, + 504 + ], + "type": "text", + "content": " is another linear transformation. At the same time, the generated prototype " + }, + { + "bbox": [ + 304, + 468, + 545, + 504 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l" + }, + { + "bbox": [ + 304, + 468, + 545, + 504 + ], + "type": "text", + "content": " is also used to update the query feature maps via query activation (QA):" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 334, + 511, + 545, + 526 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 334, + 511, + 545, + 526 + ], + "spans": [ + { + "bbox": [ + 334, + 511, + 545, + 526 + ], + "type": "interline_equation", + "content": "\\mathbf {F} _ {l} ^ {\\mathbf {q}} = \\mathbf {Q} \\mathbf {A} \\left(\\mathbf {G} _ {l}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}\\right) = \\mathcal {F} _ {\\text {a c t v}} \\left(\\mathbf {G} _ {l} \\odot \\mathbf {F} _ {l - 1} ^ {\\mathbf {q}}\\right), \\tag {7}", + "image_path": "c6b0db3211c441741593c6f6bfd7ff604c318b70e9c6c28c5ecbeab8ae7f9be6.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 533, + 545, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 533, + 545, + 557 + ], + "spans": [ + { + "bbox": [ + 304, + 533, + 545, + 557 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 533, + 545, + 557 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 304, + 533, + 545, + 557 + ], + "type": "text", + "content": " means concatenation and " + }, + { + "bbox": [ + 304, + 533, + 545, + 557 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\text{actv}}" + }, + { + "bbox": [ + 304, + 533, + 545, + 557 + ], + "type": "text", + "content": " is an activation network with two convolution layers." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "content": "In the original implementation, IPMT first feeds the input images into a froze backbone encoder (e.g. ResNet-50 [11]), obtaining multi-scale features " + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{X}_1,\\mathbf{X}_2,\\mathbf{X}_3,\\mathbf{X}_4\\}" + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "content": " from the last four convolution blocks, with the scale of 1/4, 1/8, 1/8, and 1/8, respectively. Then, " + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_1" + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_2" + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "content": " are fused to obtain the backbone features for both support and query. Next, a prototype activation (PA) module generates the support features " + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^{\\mathrm{s}}" + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "content": ", the initial query feature " + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_0^{\\mathrm{q}}" + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "content": ", and the initial query mask " + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}_0^{\\mathrm{q}}" + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "content": ". The initial prototype " + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_0" + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "content": " is randomly initialized at the beginning and then optimized during training. Afterward, by iteratively operating (1) to (7) in five layers, both prototype and features can be optimized step by step. For more details please refer to [16]." + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18864" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 68, + 547, + 238 + ], + "blocks": [ + { + "bbox": [ + 51, + 68, + 547, + 238 + ], + "lines": [ + { + "bbox": [ + 51, + 68, + 547, + 238 + ], + "spans": [ + { + "bbox": [ + 51, + 68, + 547, + 238 + ], + "type": "image", + "image_path": "61c0b8800fcdb502d13718612e8eeb34cee70e3a543177f5a4701aac3ebbc52b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "lines": [ + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "spans": [ + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": "Figure 2. Main architecture of the proposed VIPMT model for FSVOS. \"RMS\" means our proposed reliable memory selection (Section 4.3), \"MAtt\" means masked attention (4), \"MG\" means mask generation (6), and \"QA\" means query activation (7). In each VIPMT iteration, the input intermediate prototype " + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_{l-1}" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": " first generates the support prototype " + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathrm{s}}" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": " (2), the clip prototype " + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathrm{c}}" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": " (8), and the memory prototype " + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathrm{m}}" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": " (13), and combine them to obtain the clip-level intermediate prototype " + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathrm{ci}}" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": " (14). Afterwords, a frame level prototype " + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathrm{f}_i}" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": " is obtained for each frame via (10) and then updates the frame mask " + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}_l^{\\mathrm{f}_i}" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": " and frame feature " + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_l^{\\mathrm{c}_i}" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": " via (12). Finally, all " + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathrm{f}_i}" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": " are averaged to obtain " + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": " (11), which is input into the next iteration with " + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}_l^{\\mathrm{f}}" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_l^{\\mathrm{c}}" + }, + { + "bbox": [ + 46, + 247, + 547, + 316 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 325, + 127, + 337 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 325, + 127, + 337 + ], + "spans": [ + { + "bbox": [ + 47, + 325, + 127, + 337 + ], + "type": "text", + "content": "4. Video IPMT" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 346, + 288, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 346, + 288, + 418 + ], + "spans": [ + { + "bbox": [ + 46, + 346, + 288, + 418 + ], + "type": "text", + "content": "As shown in Figure 2, we take the original IPMT model as the baseline and combine it with our proposed multi-grained prototype learning scheme for performing the FSVOS task. We elaborate on the design of our clip-level, frame-level, and memory-level prototypes first. Finally, we present the training loss, including the newly proposed CCDS loss." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 426, + 185, + 438 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 426, + 185, + 438 + ], + "spans": [ + { + "bbox": [ + 47, + 426, + 185, + 438 + ], + "type": "text", + "content": "4.1. Clip Prototype Learning" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 444, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 444, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 444, + 287, + 552 + ], + "type": "text", + "content": "Since a video is composed of several consecutive frames, a straightforward way is to directly apply the IPMT model on each query frame. However, such a naive method does not consider any video temporal information and also lacks efficiency. Hence, we propose to take video clips as query units for both training and inference. Given a query video clip " + }, + { + "bbox": [ + 46, + 444, + 287, + 552 + ], + "type": "inline_equation", + "content": "\\mathcal{C} = \\{\\mathbf{I}^{\\mathbf{c}_i}\\}_{i=1}^{T_c}" + }, + { + "bbox": [ + 46, + 444, + 287, + 552 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 444, + 287, + 552 + ], + "type": "inline_equation", + "content": "T_c" + }, + { + "bbox": [ + 46, + 444, + 287, + 552 + ], + "type": "text", + "content": " frames, we perform the masked attention with clip-level query features to generate the clip prototype:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 96, + 560, + 287, + 574 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 96, + 560, + 287, + 574 + ], + "spans": [ + { + "bbox": [ + 96, + 560, + 287, + 574 + ], + "type": "interline_equation", + "content": "\\mathbf {G} _ {l} ^ {\\mathbf {c}} = \\mathbf {M A t t} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {c}}, \\tilde {\\mathbf {O}} _ {l - 1} ^ {\\mathbf {f}}\\right), \\tag {8}", + "image_path": "d2193ffc3851e8129e5e4bf9dd44e0f95d3eae2e0bbfeeb0de33ab6b1332bcae.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 584, + 287, + 621 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 584, + 287, + 621 + ], + "spans": [ + { + "bbox": [ + 46, + 584, + 287, + 621 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 584, + 287, + 621 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{l - 1}^{\\mathbf{c}}\\in \\mathbb{R}^{T_chw\\times C}" + }, + { + "bbox": [ + 46, + 584, + 287, + 621 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 584, + 287, + 621 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}_{l - 1}^{\\mathbf{f}}\\in \\mathbb{R}^{T_chw\\times 1}" + }, + { + "bbox": [ + 46, + 584, + 287, + 621 + ], + "type": "text", + "content": " is the previous predicted masks and will be explained later. Then, we obtain the clip-level intermediate prototype:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 96, + 630, + 287, + 644 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 96, + 630, + 287, + 644 + ], + "spans": [ + { + "bbox": [ + 96, + 630, + 287, + 644 + ], + "type": "interline_equation", + "content": "\\mathbf {G} _ {l} ^ {\\mathbf {c i}} = \\mathbf {M L P} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {s}} + \\mathbf {G} _ {l} ^ {\\mathbf {c}} + \\mathbf {G} _ {l - 1}\\right), \\tag {9}", + "image_path": "5d89adc97606b7bd306684d7fda7cf9f39349257f72a3b7c3fd104a9c8c9e425.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 653, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 288, + 713 + ], + "type": "text", + "content": "which encodes local guidance information within the whole query clip. Next, we can use (6) to segment the target objects in the whole clip and obtain clip predictions " + }, + { + "bbox": [ + 46, + 653, + 288, + 713 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}_l^{\\mathbf{c}}\\in \\mathbb{R}^{T_chw\\times 1} = \\mathbf{M}\\mathbf{G}(\\mathbf{G}_l^{\\mathbf{ci}},\\mathbf{F}_{l - 1}^{\\mathbf{c}})" + }, + { + "bbox": [ + 46, + 653, + 288, + 713 + ], + "type": "text", + "content": ", which preserves temporal coherence within the " + }, + { + "bbox": [ + 46, + 653, + 288, + 713 + ], + "type": "inline_equation", + "content": "T_{c}" + }, + { + "bbox": [ + 46, + 653, + 288, + 713 + ], + "type": "text", + "content": " frames." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 326, + 454, + 339 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 326, + 454, + 339 + ], + "spans": [ + { + "bbox": [ + 306, + 326, + 454, + 339 + ], + "type": "text", + "content": "4.2. Frame Prototype Learning" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 345, + 547, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 345, + 547, + 441 + ], + "spans": [ + { + "bbox": [ + 304, + 345, + 547, + 441 + ], + "type": "text", + "content": "The clip-level intermediate prototype " + }, + { + "bbox": [ + 304, + 345, + 547, + 441 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathrm{ci}}" + }, + { + "bbox": [ + 304, + 345, + 547, + 441 + ], + "type": "text", + "content": " uses one prototype to represent the whole clip and encodes the clip consensus object information, however, may ignore frame-level fine-grained cues. This problem may cause a performance drop when the object appearance changes significantly within the clip. To mitigate this problem, we propose to further generate frame-level query prototypes " + }, + { + "bbox": [ + 304, + 345, + 547, + 441 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{G}_{l}\\}_{i = 1}^{T_{c}}" + }, + { + "bbox": [ + 304, + 345, + 547, + 441 + ], + "type": "text", + "content": " by updating " + }, + { + "bbox": [ + 304, + 345, + 547, + 441 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathrm{ci}}" + }, + { + "bbox": [ + 304, + 345, + 547, + 441 + ], + "type": "text", + "content": " with related fine-grained object cues in each frame:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 321, + 450, + 545, + 465 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 450, + 545, + 465 + ], + "spans": [ + { + "bbox": [ + 321, + 450, + 545, + 465 + ], + "type": "interline_equation", + "content": "\\mathbf {G} _ {l} ^ {\\mathbf {f} _ {i}} = \\operatorname {M L P} \\left(\\mathbf {M A t t} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {c i}}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {c} _ {i}}, \\tilde {\\mathbf {O}} _ {l} ^ {\\mathbf {c} _ {i}}\\right) + \\mathbf {G} _ {l} ^ {\\mathbf {c i}}\\right). \\tag {10}", + "image_path": "b3fcb2a6468d97f4ce06add97aeee89e0802299216eed992ea349f5191afff6e.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 475, + 545, + 514 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 475, + 545, + 514 + ], + "spans": [ + { + "bbox": [ + 304, + 475, + 545, + 514 + ], + "type": "text", + "content": "In this process, we use " + }, + { + "bbox": [ + 304, + 475, + 545, + 514 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathbf{ci}}" + }, + { + "bbox": [ + 304, + 475, + 545, + 514 + ], + "type": "text", + "content": " as a good initialization to learn each " + }, + { + "bbox": [ + 304, + 475, + 545, + 514 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathbf{f}_i}" + }, + { + "bbox": [ + 304, + 475, + 545, + 514 + ], + "type": "text", + "content": " and subsequently aggregate the frame-level query prototypes as the initialization for the next iteration:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 387, + 523, + 545, + 556 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 387, + 523, + 545, + 556 + ], + "spans": [ + { + "bbox": [ + 387, + 523, + 545, + 556 + ], + "type": "interline_equation", + "content": "\\mathbf {G} _ {l} = \\frac {1}{T _ {c}} \\sum_ {i = 1} ^ {T _ {c}} \\mathbf {G} _ {l} ^ {\\mathbf {f} _ {i}}. \\tag {11}", + "image_path": "df197cac3c38910b5f10d85a95579f0063cfe08ae831ebae2b5181779203ed83.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 565, + 547, + 636 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 565, + 547, + 636 + ], + "spans": [ + { + "bbox": [ + 304, + 565, + 547, + 636 + ], + "type": "text", + "content": "As such, we enable bidirectional clip-frame prototype communication, which promotes the intra-clip temporal correlation. On the contrary, directly using the clip-level intermediate prototype " + }, + { + "bbox": [ + 304, + 565, + 547, + 636 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathrm{ci}}" + }, + { + "bbox": [ + 304, + 565, + 547, + 636 + ], + "type": "text", + "content": " as the initialization for the next iteration only enables one-way communication from the clip information to the frame-level." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 637, + 545, + 673 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 637, + 545, + 673 + ], + "spans": [ + { + "bbox": [ + 304, + 637, + 545, + 673 + ], + "type": "text", + "content": "At the same time, we use each frame prototype " + }, + { + "bbox": [ + 304, + 637, + 545, + 673 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathbf{f}_i}" + }, + { + "bbox": [ + 304, + 637, + 545, + 673 + ], + "type": "text", + "content": " to generate the frame-level segmentation mask and update the query feature for each frame independently:" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 374, + 682, + 545, + 704 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 374, + 682, + 545, + 704 + ], + "spans": [ + { + "bbox": [ + 374, + 682, + 545, + 704 + ], + "type": "interline_equation", + "content": "\\tilde {\\mathbf {O}} _ {l} ^ {\\mathbf {f} _ {i}} = \\mathbf {M G} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {f} _ {i}}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {c} _ {i}}\\right), \\tag {12}", + "image_path": "725254c6a6a988138ef57a275c8a353e9851a1d964c9f845e7e200e2a387412c.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 378, + 701, + 476, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 378, + 701, + 476, + 715 + ], + "spans": [ + { + "bbox": [ + 378, + 701, + 476, + 715 + ], + "type": "interline_equation", + "content": "\\mathbf {F} _ {l} ^ {\\mathbf {c} _ {i}} = \\mathbf {Q A} \\left(\\mathbf {G} _ {l} ^ {\\mathbf {f} _ {i}}, \\mathbf {F} _ {l - 1} ^ {\\mathbf {c} _ {i}}\\right).", + "image_path": "e0aa2a712c2a5e0b57fd7cafc19bfa4b6bd7d35f74e5e78e8e32f34d9a189861.jpg" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18865" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 70, + 289, + 245 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 289, + 245 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 289, + 245 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 289, + 245 + ], + "type": "image", + "image_path": "8f78487e95e2bd67801f1f8efafc6045502f45bc54e2f09917bf334718be8464.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 247, + 289, + 291 + ], + "lines": [ + { + "bbox": [ + 46, + 247, + 289, + 291 + ], + "spans": [ + { + "bbox": [ + 46, + 247, + 289, + 291 + ], + "type": "text", + "content": "Figure 3. Illustration of the generation process of the four structural similarity maps. Red and blue regions indicate objects of two categories, respectively. Here we only show two support frames for concision." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 300, + 287, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 300, + 287, + 327 + ], + "spans": [ + { + "bbox": [ + 46, + 300, + 287, + 327 + ], + "type": "text", + "content": "Next, " + }, + { + "bbox": [ + 46, + 300, + 287, + 327 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}_l^{\\mathbf{f}} = \\{\\tilde{\\mathbf{O}}_l^{\\mathbf{f}_i}\\}_{i = 1}^{T_c},\\mathbf{F}_l^{\\mathbf{c}} = \\{\\mathbf{F}_l^{\\mathbf{c}_i}\\}_{i = 1}^{T_c}" + }, + { + "bbox": [ + 46, + 300, + 287, + 327 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 300, + 287, + 327 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l" + }, + { + "bbox": [ + 46, + 300, + 287, + 327 + ], + "type": "text", + "content": " are input to (8) again for the next iteration." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 334, + 205, + 346 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 334, + 205, + 346 + ], + "spans": [ + { + "bbox": [ + 47, + 334, + 205, + 346 + ], + "type": "text", + "content": "4.3. Memory Prototype Learning" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 352, + 289, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 352, + 289, + 485 + ], + "spans": [ + { + "bbox": [ + 46, + 352, + 289, + 485 + ], + "type": "text", + "content": "Since a whole video usually contains numerous frames, only considering the information within a local clip is suboptimal as long-term historical temporal information is ignored. Many VOS works have also demonstrated that leveraging history memory is crucial for video data to enhance the temporal correlation. To this end, we propose to learn a memory prototype for providing historical guidance information. For each clip except the first one, we can use " + }, + { + "bbox": [ + 46, + 352, + 289, + 485 + ], + "type": "inline_equation", + "content": "T_{m}" + }, + { + "bbox": [ + 46, + 352, + 289, + 485 + ], + "type": "text", + "content": " previous frames as the memory set " + }, + { + "bbox": [ + 46, + 352, + 289, + 485 + ], + "type": "inline_equation", + "content": "\\mathcal{M} = \\{\\mathbf{I}^{\\mathbf{m}_i}\\}_{i=1}^{T_m}" + }, + { + "bbox": [ + 46, + 352, + 289, + 485 + ], + "type": "text", + "content": ", which also has predicted masks " + }, + { + "bbox": [ + 46, + 352, + 289, + 485 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}^{\\mathbf{m}} \\in \\mathbb{R}^{T_mhw \\times 1}" + }, + { + "bbox": [ + 46, + 352, + 289, + 485 + ], + "type": "text", + "content": ". Then, we use masked attention on memory features to generate the memory prototype:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 99, + 492, + 287, + 507 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 99, + 492, + 287, + 507 + ], + "spans": [ + { + "bbox": [ + 99, + 492, + 287, + 507 + ], + "type": "interline_equation", + "content": "\\mathbf {G} _ {l} ^ {\\mathbf {m}} = \\mathbf {M A t t} \\left(\\mathbf {G} _ {l - 1}, \\mathbf {F} ^ {\\mathbf {m}}, \\tilde {\\mathbf {O}} ^ {\\mathbf {m}}\\right), \\tag {13}", + "image_path": "601c69f8f538896010ee7079b3947a376e968ebb92585937128dfff4b3f3eaac.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 512, + 287, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 512, + 287, + 550 + ], + "spans": [ + { + "bbox": [ + 46, + 512, + 287, + 550 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 512, + 287, + 550 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^{\\mathbf{m}}\\in \\mathbb{R}^{T_mhw\\times C}" + }, + { + "bbox": [ + 46, + 512, + 287, + 550 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 512, + 287, + 550 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}^{\\mathbf{m}}\\in \\mathbb{R}^{T_mhw\\times 1}" + }, + { + "bbox": [ + 46, + 512, + 287, + 550 + ], + "type": "text", + "content": ". Then, the update of the clip-level intermediate prototype " + }, + { + "bbox": [ + 46, + 512, + 287, + 550 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathbf{ci}}" + }, + { + "bbox": [ + 46, + 512, + 287, + 550 + ], + "type": "text", + "content": " in (9) can be rewritten as" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 81, + 557, + 287, + 572 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 81, + 557, + 287, + 572 + ], + "spans": [ + { + "bbox": [ + 81, + 557, + 287, + 572 + ], + "type": "interline_equation", + "content": "\\mathbf {G} _ {l} ^ {\\mathrm {c i}} = \\mathbf {M L P} \\left(\\mathbf {G} _ {l} ^ {\\mathrm {s}} + \\mathbf {G} _ {l} ^ {\\mathrm {c}} + \\mathbf {G} _ {l} ^ {\\mathrm {m}} + \\mathbf {G} _ {l - 1}\\right). \\tag {14}", + "image_path": "f04361e604674790eb1584caa5f423955834b9c087fc2ded40f040fbba791b08.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 578, + 288, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 578, + 288, + 639 + ], + "spans": [ + { + "bbox": [ + 46, + 578, + 288, + 639 + ], + "type": "text", + "content": "We do not consider using memory prototype at the frame level since " + }, + { + "bbox": [ + 46, + 578, + 288, + 639 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathbf{ci}}" + }, + { + "bbox": [ + 46, + 578, + 288, + 639 + ], + "type": "text", + "content": " is designed to combine comprehensive guidance information at the clip-level, simultaneously from support, clip, and memory. In contrast, " + }, + { + "bbox": [ + 46, + 578, + 288, + 639 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathbf{f}_i}" + }, + { + "bbox": [ + 46, + 578, + 288, + 639 + ], + "type": "text", + "content": " encodes pure frame adaptive cues and uses " + }, + { + "bbox": [ + 46, + 578, + 288, + 639 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathbf{ci}}" + }, + { + "bbox": [ + 46, + 578, + 288, + 639 + ], + "type": "text", + "content": " as the initialization." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": "Reliable Memory Selection. During the training stage, we can use the ground truth memory masks " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{O}^{\\mathrm{m}}" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": " to replace the predicted masks for training an accurate model. However, during the inference stage, we can only use the predicted masks " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}^{\\mathrm{m}}" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": ", which may be very noisy and hence heavily contaminate the learned prototype. To mitigate this problem," + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 156 + ], + "type": "text", + "content": "we follow [17] and train an IoU regression network (IoUNet) to select reliable memory frames which have higher segmentation quality. Different from [17], we explicitly consider the nature of the FSVOS task and propose to leverage the structural similarity among the predicted foreground region, background region, and object region in support images for predicting more accurate IoU scores." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "spans": [ + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": "Specifically, as shown in Figure 3, given the backbone features of an memory frame " + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_4\\in \\mathbb{R}^{hw\\times C}" + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": " and the support set " + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_4^{\\mathbf{s}}\\in \\mathbb{R}^{Khw\\times C}" + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": ", the predicted memory mask " + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}\\in \\mathbb{R}^{hw\\times 1}" + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": " (here we omit the superscript " + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{m}" + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": " for conciseness), and the ground truth support masks " + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{O}^{\\mathrm{s}}\\in \\mathbb{R}^{Khw\\times 1}" + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": ", we first obtain the background mask for the memory " + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{B}} = 1 - \\tilde{\\mathbf{O}}" + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": ". Then, we can evaluate the segmentation quality of the memory frame using a simple and intuitive idea: once it is well segmented, its foreground region " + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}" + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": " should be dissimilar to the background " + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{B}}" + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": " and similar to the support foreground " + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{O}^{\\mathrm{s}}" + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": ", while the background " + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{B}}" + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": " should be dissimilar to both " + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}" + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "inline_equation", + "content": "\\mathbf{O}^{\\mathrm{s}}" + }, + { + "bbox": [ + 304, + 156, + 547, + 312 + ], + "type": "text", + "content": ". To this end, we compute the structural similarity map of the foreground area of the memory w.r.t. the background area:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 317, + 318, + 545, + 333 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 318, + 545, + 333 + ], + "spans": [ + { + "bbox": [ + 317, + 318, + 545, + 333 + ], + "type": "interline_equation", + "content": "\\mathbf {S} ^ {f b} = \\operatorname {N o r m} \\left(\\operatorname {M a x} \\left(\\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {O}}\\right) \\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {B}}\\right) ^ {\\top}, 1\\right)\\right), \\tag {15}", + "image_path": "55186bb3834791a02fc1b188c3ebf2050fd414eb987ffb68494eb3c5f2fb1c22.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 340, + 547, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 340, + 547, + 411 + ], + "spans": [ + { + "bbox": [ + 304, + 340, + 547, + 411 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 340, + 547, + 411 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 304, + 340, + 547, + 411 + ], + "type": "text", + "content": " means element-wise multiplication, " + }, + { + "bbox": [ + 304, + 340, + 547, + 411 + ], + "type": "inline_equation", + "content": "\\mathbf{Max}(*,1)" + }, + { + "bbox": [ + 304, + 340, + 547, + 411 + ], + "type": "text", + "content": " means obtaining the maximum value along each row, and Norm denotes the min-max normalization to scale the data to the range of [0, 1]. Then, the output map " + }, + { + "bbox": [ + 304, + 340, + 547, + 411 + ], + "type": "inline_equation", + "content": "\\mathbf{S}^{fb}\\in \\mathbb{R}^{hw\\times 1}" + }, + { + "bbox": [ + 304, + 340, + 547, + 411 + ], + "type": "text", + "content": " exactly represents how similar each foreground pixel is w.r.t. the background area, as shown in Figure 3." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 411, + 547, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 411, + 547, + 472 + ], + "spans": [ + { + "bbox": [ + 304, + 411, + 547, + 472 + ], + "type": "text", + "content": "Likewise, we can obtain a similarity map " + }, + { + "bbox": [ + 304, + 411, + 547, + 472 + ], + "type": "inline_equation", + "content": "\\mathbf{S}^{bf}" + }, + { + "bbox": [ + 304, + 411, + 547, + 472 + ], + "type": "text", + "content": " of the background area w.r.t. the foreground, similarity map " + }, + { + "bbox": [ + 304, + 411, + 547, + 472 + ], + "type": "inline_equation", + "content": "\\mathbf{S}^{fs}" + }, + { + "bbox": [ + 304, + 411, + 547, + 472 + ], + "type": "text", + "content": " of the foreground area of the memory w.r.t. the foreground of the support, and similarity map " + }, + { + "bbox": [ + 304, + 411, + 547, + 472 + ], + "type": "inline_equation", + "content": "\\mathbf{S}^{bs}" + }, + { + "bbox": [ + 304, + 411, + 547, + 472 + ], + "type": "text", + "content": " of the background area of the memory w.r.t. the foreground of the support:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 314, + 479, + 515, + 493 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 314, + 479, + 515, + 493 + ], + "spans": [ + { + "bbox": [ + 314, + 479, + 515, + 493 + ], + "type": "interline_equation", + "content": "\\mathbf {S} ^ {b f} = \\operatorname {N o r m} \\left(\\operatorname {M a x} \\left(\\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {B}}\\right) \\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {O}}\\right) ^ {\\top}, 1\\right)\\right),", + "image_path": "4cdf4b7e134b2efa9497d82acb2c9ed8c3e622262701132644c80f551f4be41b.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 315, + 495, + 545, + 510 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 495, + 545, + 510 + ], + "spans": [ + { + "bbox": [ + 315, + 495, + 545, + 510 + ], + "type": "interline_equation", + "content": "\\mathbf {S} ^ {f s} = \\operatorname {N o r m} \\left(\\operatorname {M a x} \\left(\\left(\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {O}}\\right) \\left(\\mathbf {X} _ {4} ^ {\\mathbf {s}} \\odot \\mathbf {O} ^ {\\mathbf {s}}\\right) ^ {\\top}, 1\\right)\\right), \\tag {16}", + "image_path": "a852c6cc7e4ff4d201b904a4950fe87eaf08f4cda3ad67abdbb8c24730272bba.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 315, + 513, + 518, + 528 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 513, + 518, + 528 + ], + "spans": [ + { + "bbox": [ + 315, + 513, + 518, + 528 + ], + "type": "interline_equation", + "content": "\\mathbf {S} ^ {b s} = \\operatorname {N o r m} (\\operatorname {M a x} ((\\mathbf {X} _ {4} \\odot \\tilde {\\mathbf {B}}) (\\mathbf {X} _ {4} ^ {\\mathbf {s}} \\odot \\mathbf {O} ^ {\\mathbf {s}}) ^ {\\top}, 1)).", + "image_path": "030406b167bf3b25efe554d9400987b72643650b5e059ffa3c30e16db49106ee.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 534, + 547, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 547, + 641 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 547, + 641 + ], + "type": "text", + "content": "Once obtain the four structural similarity maps, we combine them with multi-scale memory features and the original predicted mask " + }, + { + "bbox": [ + 304, + 534, + 547, + 641 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}" + }, + { + "bbox": [ + 304, + 534, + 547, + 641 + ], + "type": "text", + "content": " to regress the IoU score of the memory frame. Concretely, we first downsample " + }, + { + "bbox": [ + 304, + 534, + 547, + 641 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_1" + }, + { + "bbox": [ + 304, + 534, + 547, + 641 + ], + "type": "text", + "content": " to the 1/8 scale with stride convolution and then fuse it with " + }, + { + "bbox": [ + 304, + 534, + 547, + 641 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_2, \\mathbf{X}_3, \\mathbf{X}_4" + }, + { + "bbox": [ + 304, + 534, + 547, + 641 + ], + "type": "text", + "content": " into a combined feature with 256 channels. Then, we concatenate the feature with the four structural similarity maps and " + }, + { + "bbox": [ + 304, + 534, + 547, + 641 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}" + }, + { + "bbox": [ + 304, + 534, + 547, + 641 + ], + "type": "text", + "content": " and input them into four convolution layers and two fully connected layers for predicting the IoU score." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 547, + 713 + ], + "type": "text", + "content": "During training, we design three ways to train the IoUNet. First, we can jointly train it with the FSVOS model, in which case real predicted masks can be used for training the IoUNet. Second, we can train it independently using synthesized video data. Specifically, we randomly add noises to the ground truth masks in the training set and use the synthesized" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18866" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "content": "masks to mimic good and bad predictions. In the third way, we train the IoUNet using synthesized image data with the same noisy mask strategy. We compute the ground truth IoU score for each training mask and use a " + }, + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "content": " loss as supervision. During testing, we simply select reliable memory frames whose predicted IoU scores are larger than a threshold." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 151, + 135, + 164 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 151, + 135, + 164 + ], + "spans": [ + { + "bbox": [ + 47, + 151, + 135, + 164 + ], + "type": "text", + "content": "4.4. Training Loss" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "spans": [ + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "type": "text", + "content": "We follow IPMT [16] and use the final query feature " + }, + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_5^{\\mathrm{c}}" + }, + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "type": "text", + "content": " to predict the final segmentation masks via two convolution layers, where Dice loss and IoU loss are both used for optimization. To ease the network training, in each iteration we use binary cross entropy (BCE) loss on the predicted support masks " + }, + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}_l^{\\mathrm{s}}" + }, + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "type": "text", + "content": ", clip masks " + }, + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}_l^{\\mathrm{c}}" + }, + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "type": "text", + "content": ", and frame masks " + }, + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{O}}_l^{\\mathrm{f}}" + }, + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "type": "text", + "content": ". As for memory frames, we generate predictions for them at each iteration using " + }, + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "type": "inline_equation", + "content": "\\mathbf{MG}(\\mathbf{G}_l^{\\mathrm{ci}}, \\mathbf{F}^{\\mathrm{m}})" + }, + { + "bbox": [ + 46, + 169, + 287, + 277 + ], + "type": "text", + "content": ", and then adopt the BCE loss computed with their ground truth masks as supervision." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 280, + 288, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 280, + 288, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 280, + 288, + 460 + ], + "type": "text", + "content": "Cross Category Discriminative Segmentation Loss. To make the learned clip-level intermediate prototypes " + }, + { + "bbox": [ + 46, + 280, + 288, + 460 + ], + "type": "inline_equation", + "content": "\\mathbf{G}^{\\mathrm{ci}}" + }, + { + "bbox": [ + 46, + 280, + 288, + 460 + ], + "type": "text", + "content": " more category discriminative, we furthermore propose a CCDS loss and adopt it within each batch. Suppose our batchsize is set to " + }, + { + "bbox": [ + 46, + 280, + 288, + 460 + ], + "type": "inline_equation", + "content": "B > 1" + }, + { + "bbox": [ + 46, + 280, + 288, + 460 + ], + "type": "text", + "content": ", we select " + }, + { + "bbox": [ + 46, + 280, + 288, + 460 + ], + "type": "inline_equation", + "content": "B" + }, + { + "bbox": [ + 46, + 280, + 288, + 460 + ], + "type": "text", + "content": " video clips with different object categories to form each batch. Then, during training, we use the prototypes of each video to perform segmentation on other videos and let the predicted masks be all zeros. The idea behind is intuitive: if the prototypes are well optimized for a specific category, they should not activate any region on other videos with different categories. However, since a video may contain multiple object categories and we only have the ground truth of one class under the one-way few-shot learning setting, we propose to use the ground truth masks to filter out the regions for loss calculation:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 69, + 468, + 287, + 501 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 69, + 468, + 287, + 501 + ], + "spans": [ + { + "bbox": [ + 69, + 468, + 287, + 501 + ], + "type": "interline_equation", + "content": "L _ {c c d s} = \\frac {1}{(B - 1) B} \\sum_ {b = 1} ^ {B} \\sum_ {j \\neq b} \\frac {1}{\\sum \\mathbf {O} _ {j}} L _ {b, j}, \\tag {17}", + "image_path": "19b1ee8509954f7ad6407dec502767e467813c1615ef4838cef990b9e17425ff.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 74, + 506, + 287, + 536 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 74, + 506, + 287, + 536 + ], + "spans": [ + { + "bbox": [ + 74, + 506, + 287, + 536 + ], + "type": "interline_equation", + "content": "L _ {b, j} = \\sum_ {l = 1} ^ {5} B C E \\left(\\mathbf {M G} \\left(\\mathbf {G} _ {l, b} ^ {\\mathbf {c i}}, \\mathbf {F} _ {j}\\right) \\odot \\mathbf {O} _ {j}, \\mathbf {Z}\\right), \\tag {18}", + "image_path": "ab18852102965187efb580ee74935143584a047bc332ac02de94694e375b49b4.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_{l,b}^{\\mathrm{ci}}" + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "text", + "content": " is the clip-level intermediate prototype in the " + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "text", + "content": "-th iteration of the " + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "text", + "content": "-th video, " + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "inline_equation", + "content": "\\mathbf{O}_j" + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_j" + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "text", + "content": " are the ground truth masks and the backbone features of the " + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "text", + "content": "-th video. " + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "inline_equation", + "content": "\\mathbf{Z}" + }, + { + "bbox": [ + 46, + 545, + 287, + 593 + ], + "type": "text", + "content": " is an all zero matrix." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 604, + 127, + 616 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 604, + 127, + 616 + ], + "spans": [ + { + "bbox": [ + 47, + 604, + 127, + 616 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 623, + 219, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 219, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 219, + 635 + ], + "type": "text", + "content": "5.1. Datasets and Evaluation Setting" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 641, + 287, + 713 + ], + "type": "text", + "content": "Datasets. Following [1, 24], our experiments are conducted on the training set of YouTube-VIS [30] dataset, which has 40 categories and contains 2238 videos with 3774 instances. The dataset is divided into four folds, following the same slit with [1, 24]. In each fold, we use 30 categories for training and the rest 10 categories for testing. Following [1, 24], we" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 144 + ], + "type": "text", + "content": "set our experiments on the 5-shot setting and randomly select five images from different videos of the same category as the support set. We also follow [24] and adopt the MiniVSPW [24] dataset to evaluate the generalizability of FSVOS methods. It includes 20 categories and provides longer video sequences than YouTube-VIS, since being more challenging." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 149, + 546, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 149, + 546, + 258 + ], + "spans": [ + { + "bbox": [ + 304, + 149, + 546, + 258 + ], + "type": "text", + "content": "Evaluation Setting. As the prior work [1] and VOS methods, we adopt the region similarity " + }, + { + "bbox": [ + 304, + 149, + 546, + 258 + ], + "type": "inline_equation", + "content": "\\mathcal{J}" + }, + { + "bbox": [ + 304, + 149, + 546, + 258 + ], + "type": "text", + "content": " and contour similarity " + }, + { + "bbox": [ + 304, + 149, + 546, + 258 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 304, + 149, + 546, + 258 + ], + "type": "text", + "content": " for performance evaluation. Apart from this, we also follow [24] and consider the video consistency metric " + }, + { + "bbox": [ + 304, + 149, + 546, + 258 + ], + "type": "inline_equation", + "content": "\\mathrm{VC}_7" + }, + { + "bbox": [ + 304, + 149, + 546, + 258 + ], + "type": "text", + "content": ", which captures temporal prediction consistency among long-range adjacent frames over a temporal window of 7. We adopt the average score on four folds, i.e. " + }, + { + "bbox": [ + 304, + 149, + 546, + 258 + ], + "type": "inline_equation", + "content": "\\mathrm{mVC}_7" + }, + { + "bbox": [ + 304, + 149, + 546, + 258 + ], + "type": "text", + "content": ", to evaluate the overall performance. We also follow [1, 24] and run the evaluation process five times and report the average results." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 260, + 547, + 344 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 260, + 547, + 344 + ], + "spans": [ + { + "bbox": [ + 304, + 260, + 547, + 344 + ], + "type": "text", + "content": "Furthermore, there are two different evaluation protocols proposed in [1] and [24] for sampling episodes during testing. Protocol I fixes the sampled support set for all query videos belonging to the same class in each run, while protocol II randomly samples a support set for every query video, which ensures a more stable performance evaluation. Hence, in this paper we adopt protocol II for evaluation." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 350, + 547, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 350, + 547, + 529 + ], + "spans": [ + { + "bbox": [ + 304, + 350, + 547, + 529 + ], + "type": "text", + "content": "Implementation Details. We adopt ResNet-50 [11] pretrained on ImageNet [23] as our encoder backbone. Following IPMT [16], we freeze the parameters of the backbone during training and do not adopt online finetuning as [1, 24] did. The iteration step is set to 5 as IPMT. We set the clip length " + }, + { + "bbox": [ + 304, + 350, + 547, + 529 + ], + "type": "inline_equation", + "content": "T_{c}" + }, + { + "bbox": [ + 304, + 350, + 547, + 529 + ], + "type": "text", + "content": " and the memory length " + }, + { + "bbox": [ + 304, + 350, + 547, + 529 + ], + "type": "inline_equation", + "content": "T_{m}" + }, + { + "bbox": [ + 304, + 350, + 547, + 529 + ], + "type": "text", + "content": " to 5 without further tuning. The IoU threshold for selecting reliable memory frames is set to 0.8. When the reliable memory has more frames, we simply randomly select five frames from them. During training, we randomly select three clips from a video as a sample, where the first clip is trained without using memory, the second clip uses the first clip as memory, and the third clip randomly selects five frames from the first two as the memory. We also share the MAtt operation for support and memory since we found this leads to better performance." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 532, + 547, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 532, + 547, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 532, + 547, + 616 + ], + "type": "text", + "content": "We use Adam as our optimizer. The batchsize is set to " + }, + { + "bbox": [ + 304, + 532, + 547, + 616 + ], + "type": "inline_equation", + "content": "B = 4" + }, + { + "bbox": [ + 304, + 532, + 547, + 616 + ], + "type": "text", + "content": " and the learning rate is set to 5e-4. We train our model 100 epochs in total. All experiments are conducted on a NVIDIA Tesla A100 GPU. We adopt random horizontal flip, random crop and random resize to augment the training data. During training and testing, all video frames are downsampled to the resolution of (240,424) as the inputs." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 632, + 528, + 644 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 632, + 528, + 644 + ], + "spans": [ + { + "bbox": [ + 306, + 632, + 528, + 644 + ], + "type": "text", + "content": "5.2. Comparison with State-of-the-art Methods" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "text", + "content": "In Table 1, we compare our VIPMT with four recently published FSISS methods and two FSVOS methods, on the YouTuebe-VIS [30] dataset. We find that our VIPMT largely improves all metrics, i.e. " + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "inline_equation", + "content": "4\\%" + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{I}" + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "text", + "content": " mean score, near " + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "inline_equation", + "content": "6\\%" + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "text", + "content": " mean score, and near " + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathrm{mVC}_7" + }, + { + "bbox": [ + 304, + 653, + 546, + 713 + ], + "type": "text", + "content": " score, although previous" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18867" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 550, + 184 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 550, + 184 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 550, + 184 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 550, + 184 + ], + "type": "table", + "html": "
MethodsNameJFmVC7
Fold-1Fold-2Fold-3Fold-4MeanFold-1Fold-2Fold-3Fold-4Mean
FSISSNTRENet [15]39.066.461.761.257.141.163.060.159.455.955.7
SSP [10]46.764.359.354.556.234.853.046.046.745.149.6
VAT [12]42.662.857.056.754.841.656.450.853.050.554.9
IPMT [16]43.865.861.060.757.842.559.557.855.953.957.7
FSVOSDAN [1]43.964.561.162.157.942.462.060.060.056.141.5
TTI [24]47.268.861.463.560.2-----60.8
VIPMT(Ours)50.670.968.866.564.251.366.965.264.462.065.7
", + "image_path": "d952802ddd5003528b8d4ed4afd846323c9bb66c29420fb451f04c4d51fb41ff.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 199, + 550, + 255 + ], + "blocks": [ + { + "bbox": [ + 91, + 185, + 501, + 195 + ], + "lines": [ + { + "bbox": [ + 91, + 185, + 501, + 195 + ], + "spans": [ + { + "bbox": [ + 91, + 185, + 501, + 195 + ], + "type": "text", + "content": "Table 1. Comparison with state-of-the-art methods on YouTube-VIS [30]. Bold means the best performance." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 199, + 550, + 255 + ], + "lines": [ + { + "bbox": [ + 50, + 199, + 550, + 255 + ], + "spans": [ + { + "bbox": [ + 50, + 199, + 550, + 255 + ], + "type": "table", + "html": "
MethodsNameJFmVC7
Fold-1Fold-2Fold-3Fold-4MeanFold-1Fold-2Fold-3Fold-4Mean
FSVOSTTI [24]25.237.125.029.629.2-----24.4
VIPMT(Ours)26.242.231.629.432.430.645.736.334.236.742.1
", + "image_path": "70ac45994d6cf506a53e39ef93dbe79bc49cbd90b0a679ad91623c8baa832731.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 53, + 273, + 280, + 366 + ], + "blocks": [ + { + "bbox": [ + 189, + 254, + 402, + 264 + ], + "lines": [ + { + "bbox": [ + 189, + 254, + 402, + 264 + ], + "spans": [ + { + "bbox": [ + 189, + 254, + 402, + 264 + ], + "type": "text", + "content": "Table 2. Comparison with TTI [24] on MiniVSPW [24]." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 53, + 273, + 280, + 366 + ], + "lines": [ + { + "bbox": [ + 53, + 273, + 280, + 366 + ], + "spans": [ + { + "bbox": [ + 53, + 273, + 280, + 366 + ], + "type": "table", + "html": "
DatasetsMethodsJ-MeanF-MeanmVC7
YouTube-VISIPMT+STCN [6]58.956.561.7
IPMT+XMem [5]59.256.862.2
IPMT+RDE-VOS [14]59.358.063.3
VIPMT(Ours)64.262.065.7
MiniVSPWIPMT+STCN [6]27.731.139.3
IPMT+XMem [5]27.731.741.1
IPMT+RDE-VOS [14]28.833.540.1
VIPMT(Ours)32.436.742.1
", + "image_path": "cf0c175c5a240e67f78d12e81be66889bb65f2034db1356af26f81209221a2de.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 388, + 257, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 388, + 257, + 399 + ], + "spans": [ + { + "bbox": [ + 47, + 388, + 257, + 399 + ], + "type": "text", + "content": "works [1, 24] used on-line learning while we didn't." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 400, + 286, + 459 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 400, + 286, + 459 + ], + "spans": [ + { + "bbox": [ + 46, + 400, + 286, + 459 + ], + "type": "text", + "content": "To verify the generalization ability of our method, we compare our method with TTI [24] on MiniVSPW. Table 2 shows our method obtains a significant improvement of more than " + }, + { + "bbox": [ + 46, + 400, + 286, + 459 + ], + "type": "inline_equation", + "content": "3\\%" + }, + { + "bbox": [ + 46, + 400, + 286, + 459 + ], + "type": "text", + "content": " on " + }, + { + "bbox": [ + 46, + 400, + 286, + 459 + ], + "type": "inline_equation", + "content": "\\mathcal{I}" + }, + { + "bbox": [ + 46, + 400, + 286, + 459 + ], + "type": "text", + "content": " and more than " + }, + { + "bbox": [ + 46, + 400, + 286, + 459 + ], + "type": "inline_equation", + "content": "17\\%" + }, + { + "bbox": [ + 46, + 400, + 286, + 459 + ], + "type": "text", + "content": " on " + }, + { + "bbox": [ + 46, + 400, + 286, + 459 + ], + "type": "inline_equation", + "content": "\\mathrm{mVC}_7" + }, + { + "bbox": [ + 46, + 400, + 286, + 459 + ], + "type": "text", + "content": ", which verifies that our method works well in more challenging scenarios." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 460, + 287, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 287, + 507 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 287, + 507 + ], + "type": "text", + "content": "In Figure 4, we give some visual comparison cases. Compared with TTI [24], our VIMPT is less distracted by other objects and achieves more precise segmentation, even in highly occluded scenes (bottom row)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 508, + 287, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 508, + 287, + 592 + ], + "spans": [ + { + "bbox": [ + 46, + 508, + 287, + 592 + ], + "type": "text", + "content": "We also include three state-of-the-art semi-supervised VOS methods for comparison, i.e. STCN [6], XMem [5], and RDE-VOS [14]. Specifically, we use IPMT for segmenting the first frame and then use VOS methods for propagating the segmentation to the full video. Table 3 demonstrates that such an ad-hoc combination of FSISS and VOS methods can not achieve as good results as our model does." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 598, + 141, + 611 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 598, + 141, + 611 + ], + "spans": [ + { + "bbox": [ + 47, + 598, + 141, + 611 + ], + "type": "text", + "content": "5.3. Ablation Study" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 616, + 287, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 616, + 287, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 616, + 287, + 653 + ], + "type": "text", + "content": "In this section, we report ablation study results on the YouTube-VIS dataset. For " + }, + { + "bbox": [ + 46, + 616, + 287, + 653 + ], + "type": "inline_equation", + "content": "\\mathcal{J}" + }, + { + "bbox": [ + 46, + 616, + 287, + 653 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 616, + 287, + 653 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 46, + 616, + 287, + 653 + ], + "type": "text", + "content": " we use their average on four folds, i.e. " + }, + { + "bbox": [ + 46, + 616, + 287, + 653 + ], + "type": "inline_equation", + "content": "\\mathcal{J}" + }, + { + "bbox": [ + 46, + 616, + 287, + 653 + ], + "type": "text", + "content": "-Mean and " + }, + { + "bbox": [ + 46, + 616, + 287, + 653 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 46, + 616, + 287, + 653 + ], + "type": "text", + "content": "-Mean." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 655, + 287, + 668 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 655, + 287, + 668 + ], + "spans": [ + { + "bbox": [ + 47, + 655, + 287, + 668 + ], + "type": "text", + "content": "Effectiveness of Each Component. In Table 4, we first" + } + ] + } + ], + "index": 12 + }, + { + "type": "table", + "bbox": [ + 307, + 274, + 545, + 341 + ], + "blocks": [ + { + "bbox": [ + 47, + 366, + 264, + 376 + ], + "lines": [ + { + "bbox": [ + 47, + 366, + 264, + 376 + ], + "spans": [ + { + "bbox": [ + 47, + 366, + 264, + 376 + ], + "type": "text", + "content": "Table 3. Comparison with state-of-the-art VOS methods." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 274, + 545, + 341 + ], + "lines": [ + { + "bbox": [ + 307, + 274, + 545, + 341 + ], + "spans": [ + { + "bbox": [ + 307, + 274, + 545, + 341 + ], + "type": "table", + "html": "
NameSettingsJ-MeanF-MeanmVC7
ClipFrameMemoryCCDS
Baseline57.853.957.8
+C✓61.858.860.7
+C+F✓✓62.560.362.1
+C+F+M✓✓✓63.561.962.8
VIPMT✓✓✓✓64.262.065.7
", + "image_path": "364ed69379b87231c6b7d6ffbc1727b2f02962e6cade5f3793fe0a148731b66a.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "table_body" + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 342, + 547, + 363 + ], + "lines": [ + { + "bbox": [ + 306, + 342, + 547, + 363 + ], + "spans": [ + { + "bbox": [ + 306, + 342, + 547, + 363 + ], + "type": "text", + "content": "Table 4. Ablation study on the effectiveness of each model component. Baseline means IPMT [16]." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "spans": [ + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "type": "text", + "content": "adopt IPMT [16] as the baseline, which processes each video frame independently. Then, we adopt our clip prototype learning, denoted as “+C”. Results show that “+C” surpasses the baseline by a large margin on all metrics, which verifies the effectiveness of using local temporal guidance with our clip prototype learning. After that, we further add the frame prototype learning to “+C”, resulting in “+C+F”. Benefiting from the frame-level fine-grained cues, “+C+F” achieves large performance improvement for " + }, + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "type": "text", + "content": "-Mean and " + }, + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "type": "inline_equation", + "content": "\\mathrm{mVC}_7" + }, + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "type": "text", + "content": ". Moreover, we adopt “+C+F+M” to represent adding the memory prototype learning on “+C+F”. It largely improves the performance for both " + }, + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "type": "inline_equation", + "content": "\\mathcal{J}" + }, + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "type": "text", + "content": "-Mean and " + }, + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "type": "text", + "content": "-Mean, which shows the importance of long-term temporal information brought by the memory prototype learning. Based on this, we further add the CCDS loss to obtain our final model VIPMT. It also brings obvious improvements, especially on " + }, + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "type": "inline_equation", + "content": "\\mathrm{mVC}_7" + }, + { + "bbox": [ + 304, + 374, + 547, + 590 + ], + "type": "text", + "content": ", from 62.8 to 65.7. This proves the effectiveness of increasing category discrimination for FSVOS." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 590, + 547, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 590, + 547, + 639 + ], + "spans": [ + { + "bbox": [ + 304, + 590, + 547, + 639 + ], + "type": "text", + "content": "In Figure 5, we visualize the predicted masks from the different models mentioned above. We can find that progressive improvements can be brought by using multi-grained temporal prototypes and the CCDS loss." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 641, + 548, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 548, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 548, + 714 + ], + "type": "text", + "content": "Clip-frame Communication. As mentioned in Section 4.2, we use the mean of the frame prototypes ((11)) to initialize the intermediate prototype for the next iteration, which enables bidirectional clip-frame communication. On the contrary, directly using the clip-level intermediate prototype " + }, + { + "bbox": [ + 304, + 641, + 548, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_l^{\\mathrm{ci}}" + }, + { + "bbox": [ + 304, + 641, + 548, + 714 + ], + "type": "text", + "content": " as the initialization only enables one-way communica" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 46, + 674, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 674, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 674, + 287, + 713 + ], + "type": "text", + "content": "*Please note that here we re-tested the performance of DAN [1] using protocol II. Hence, its scores are different from the original paper. For TTI [24], since the authors did not provide the scores for " + }, + { + "bbox": [ + 46, + 674, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{F}" + }, + { + "bbox": [ + 46, + 674, + 287, + 713 + ], + "type": "text", + "content": ", we leave them blank. 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Clip-frame CommunicationJ-MeanF-MeanmVC7
One-way61.459.160.1
Bidirectional62.560.362.1
", + "image_path": "d367fc577eefadd71e96be91fe2ffd2903d60eefdb66b5febcc6a11681102033.jpg" + } + ] + } + ], + "index": 29, + "angle": 0, + "type": "table_body" + } + ], + "index": 29 + }, + { + "bbox": [ + 46, + 406, + 287, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 406, + 287, + 453 + ], + "spans": [ + { + "bbox": [ + 46, + 406, + 287, + 453 + ], + "type": "text", + "content": "tion. Here we compare the effectiveness of the two schemes. Results in Table 5 demonstrate that our design of using bidirectional clip-frame communication surpasses the one-way scheme by a large margin on all metrics." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 45, + 458, + 288, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 458, + 288, + 662 + ], + "spans": [ + { + "bbox": [ + 45, + 458, + 288, + 662 + ], + "type": "text", + "content": "Different Training Strategies of IoUNet. As mentioned in Section 4.3, we can use three ways to train the IoUNet, i.e. using real predicted masks (\"Real\"), synthesized video data (\"Video\"), and synthesized image data (\"Image\"), respectively. For \"Image\", we use an FSISS dataset COCO-20" + }, + { + "bbox": [ + 45, + 458, + 288, + 662 + ], + "type": "inline_equation", + "content": "^i" + }, + { + "bbox": [ + 45, + 458, + 288, + 662 + ], + "type": "text", + "content": " [20] and remove the classes overlapped with our video data for IoUNet training. We compare their performance in Table 6. We also compare the performance of using our proposed structural similarity maps or not (\"w/ SSM\" and \"w/o SSM\"). The results are reported under the IoU threshold of 0.5. The table demonstrates that using synthesized image data results in the best performance in both \"w/ SSM\" and \"w/o SSM\" settings and using the structural similarity maps always leads to better performance. Another benefit of using image data is that we can train a unified IoUNet for all folds instead of training an IoUNet for each fold. Hence, finally, we use synthesized image data for IoUNet training." + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 714 + ], + "type": "text", + "content": "IoU Threshold. Finally, we investigate the best IoU threshold for memory selection. Table 7 indicates that 0.8 is the best threshold and using the proposed structural similarity maps always leads to better performance." + } + ] + } + ], + "index": 33 + }, + { + "type": "table", + "bbox": [ + 308, + 339, + 545, + 396 + ], + "blocks": [ + { + "bbox": [ + 47, + 384, + 288, + 395 + ], + "lines": [ + { + "bbox": [ + 47, + 384, + 288, + 395 + ], + "spans": [ + { + "bbox": [ + 47, + 384, + 288, + 395 + ], + "type": "text", + "content": "Table 5. Comparison of two clip-frame communication schemes." + } + ] + } + ], + "index": 30, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 339, + 545, + 396 + ], + "lines": [ + { + "bbox": [ + 308, + 339, + 545, + 396 + ], + "spans": [ + { + "bbox": [ + 308, + 339, + 545, + 396 + ], + "type": "table", + "html": "
Dataw/o SSMw/ SSM
J-MeanF-MeanmVC7J-MeanF-MeanmVC7
Real62.861.562.663.261.662.8
Video62.961.662.663.261.662.8
Image63.061.762.763.361.763.0
", + "image_path": "b6526ec1841e319e96ae9b575fd8efcfc4fc433c5a46a13c16151eb09b0c9792.jpg" + } + ] + } + ], + "index": 34, + "angle": 0, + "type": "table_body" + } + ], + "index": 34 + }, + { + "type": "table", + "bbox": [ + 308, + 430, + 545, + 502 + ], + "blocks": [ + { + "bbox": [ + 306, + 397, + 545, + 419 + ], + "lines": [ + { + "bbox": [ + 306, + 397, + 545, + 419 + ], + "spans": [ + { + "bbox": [ + 306, + 397, + 545, + 419 + ], + "type": "text", + "content": "Table 6. Different training strategies of IoUNet. SSM means the proposed structural similarity maps." + } + ] + } + ], + "index": 35, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 430, + 545, + 502 + ], + "lines": [ + { + "bbox": [ + 308, + 430, + 545, + 502 + ], + "spans": [ + { + "bbox": [ + 308, + 430, + 545, + 502 + ], + "type": "table", + "html": "
Thresholdw/o SSMw/ SSM
J-MeanF-MeanmVC7J-MeanF-MeanmVC7
0.563.061.762.763.361.763.0
0.663.161.762.963.361.762.7
0.763.161.862.963.461.862.6
0.863.161.862.563.561.962.8
0.963.061.862.363.561.962.5
", + "image_path": "d34395ea07cd434adc287d9fff911d934a9f5fd0d44ee9ca79ed90994c276b8d.jpg" + } + ] + } + ], + "index": 36, + "angle": 0, + "type": "table_body" + } + ], + "index": 36 + }, + { + "bbox": [ + 306, + 502, + 547, + 512 + ], + "lines": [ + { + "bbox": [ + 306, + 502, + 547, + 512 + ], + "spans": [ + { + "bbox": [ + 306, + 502, + 547, + 512 + ], + "type": "text", + "content": "Table 7. Experimental results of using different IoU thresholds." + } + ] + } + ], + "index": 37, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 306, + 524, + 378, + 536 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 524, + 378, + 536 + ], + "spans": [ + { + "bbox": [ + 306, + 524, + 378, + 536 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 38 + }, + { + "bbox": [ + 304, + 545, + 547, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 547, + 652 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 547, + 652 + ], + "type": "text", + "content": "We explored learning multi-grained temporal prototypes to tackle the FSVOS task. Based on the IPMT model, the query video information was decomposed into a clip prototype, a memory prototype, and frame prototypes. We also improved an IoU regression method for selecting reliable memory for FSVOS by leveraging the task prior knowledge and proposed a new loss to enhance the category discriminability of the prototypes. The effectiveness of our proposed VIPMT has been verified on two benchmark datasets." + } + ] + } + ], + "index": 39 + }, + { + "bbox": [ + 304, + 658, + 547, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 658, + 547, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 658, + 547, + 712 + ], + "type": "text", + "content": "Acknowledgments: This work was supported in part by the National Natural Science Foundation of China under Grants 62071388, 62136007, U20B2065 and 62036005, and the Fundamental Research Funds for the Central Universities under Grant D5000230057." + } + ] + } + ], + "index": 40 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "18869" + } + ] + } + ], + "index": 41 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 107, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 16, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 135 + ], + "type": "text", + "content": "[1] Haoxin Chen, Hanjie Wu, Nanxuan Zhao, Sucheng Ren, and Shengfeng He. 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IEEE TPAMI, 2022. 2" + } + ] + } + ], + "index": 0 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "18871" + } + ] + } + ], + "index": 1 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-granularity Interaction Simulation for Unsupervised Interactive Segmentation/860ca3f9-f21c-4c96-a4c1-8228c6546c93_content_list.json b/2023/Multi-granularity Interaction Simulation for Unsupervised Interactive Segmentation/860ca3f9-f21c-4c96-a4c1-8228c6546c93_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..a44a8841a910cccf60ace4b8f187d5263a9225a3 --- /dev/null +++ b/2023/Multi-granularity Interaction Simulation for Unsupervised Interactive Segmentation/860ca3f9-f21c-4c96-a4c1-8228c6546c93_content_list.json @@ -0,0 +1,1900 @@ +[ + { + "type": "text", + "text": "Multi-granularity Interaction Simulation for Unsupervised Interactive Segmentation", + "text_level": 1, + "bbox": [ + 199, + 130, + 794, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Kehan Li $^{1,3}$ Yian Zhao $^{1,3}$ Zhennan Wang $^{2}$ Zesen Cheng $^{1,3}$ Peng Jin $^{1,3}$ Xiangyang Ji $^{4}$ Li Yuan $^{1,2,3}$ Chang Liu $^{4*}$ Jie Chen $^{1,2,3*}$", + "bbox": [ + 181, + 202, + 810, + 239 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{1}$ School of Electronic and Computer Engineering, Peking University, Shenzhen, China \n $^{2}$ Peng Cheng Laboratory, Shenzhen, China", + "bbox": [ + 153, + 244, + 839, + 281 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "$^{3}$ AI for Science (AI4S)-Preferred Program, Peking University, Shenzhen, China \n $^{4}$ Department of Automation and BNRist, Tsinghua University, Beijing, China", + "bbox": [ + 179, + 282, + 813, + 316 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "liuchang2022@tsinghua.edu.cn jiechen2019@pku.edu.cn", + "bbox": [ + 261, + 319, + 730, + 334 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 245, + 369, + 325, + 386 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Interactive segmentation enables users to segment as needed by providing cues of objects, which introduces human-computer interaction for many fields, such as image editing and medical image analysis. Typically, massive and expansive pixel-level annotations are spent to train deep models by object-oriented interactions with manually labeled object masks. In this work, we reveal that informative interactions can be made by simulation with semantic-consistent yet diverse region exploration in an unsupervised paradigm. Concretely, we introduce a Multi-granularity Interaction Simulation (MIS) approach to open up a promising direction for unsupervised interactive segmentation. Drawing on the high-quality dense features produced by recent self-supervised models, we propose to gradually merge patches or regions with similar features to form more extensive regions and thus, every merged region serves as a semantic-meaningful multi-granularity proposal. By randomly sampling these proposals and simulating possible interactions based on them, we provide meaningful interaction at multiple granularities to teach the model to understand interactions. Our MIS significantly outperforms non-deep learning unsupervised methods and is even comparable with some previous deep-supervised methods without any annotation.", + "bbox": [ + 86, + 401, + 483, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 89, + 792, + 220, + 806 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Interactive segmentation aims at obtaining high-quality object masks with limited user interaction, allowing users to segment objects as needed. During the development of interactive segmentation, various interactive forms like", + "bbox": [ + 86, + 816, + 480, + 878 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/cc2cde48b7c72dbc6201c482075e442b96bbe46225e40293309a3362537d2fd7.jpg", + "image_caption": [ + "Figure 1. Top: To tackle the reliance on object annotations of previous interactive segmentation methods caused by interaction simulation, we propose Multi-granularity Interaction Simulation (MIS) that simulates interaction by meaningful regions at multiple granularities. Down: The model learns from MIS to successfully understand interactions and produce acceptable segmentation." + ], + "image_footnote": [], + "bbox": [ + 514, + 367, + 903, + 589 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "bounding boxes [20, 32, 43], scribbles [2, 11, 22], and clicks [44, 17, 25, 35, 8, 36, 24, 9] have been explored. Among them, the click-based interaction becomes the mainstream due to its simplicity and well-established training and evaluation protocols.", + "bbox": [ + 509, + 703, + 903, + 779 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "State-of-the-art methods for click-based interactive segmentation are based on deep learning, following the basic paradigm proposed by Xu et al. [44]. Specifically, these methods encode clicks to a distance map and adapt a semantic segmentation model (e.g., FCN [28]) to take the encoded click map as input, and then train the model with interaction-segmentation pairs. Since it is impractical to collect interaction sequences from real users, previous", + "bbox": [ + 509, + 780, + 906, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author. Project page: https://lkhl.github.io/MIS", + "bbox": [ + 107, + 886, + 442, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "666", + "bbox": [ + 486, + 945, + 511, + 955 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d82aa3c18385ca5ce1ef95e0aed1e9bbf43be75b4c89638ff749c1b456d0073b.jpg", + "image_caption": [ + "Figure 2. Illustration of the multi-granularity region proposal generation. For an input image, We first introduce a self-supervised ViT to produce semantic features for each patch of an image. We then gradually merge two similar patches or regions with similar features to perform a new region. All newly generated regions in the merging process constitute meaningful proposals at multiple granularities." + ], + "image_footnote": [], + "bbox": [ + 89, + 85, + 903, + 193 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "methods adopt an interaction simulation strategy [44, 36] that randomly samples clicks based on object segmentation annotations. By training with the simulated clicks and corresponding object masks, the model is able to correctly understand user needs and segment objects with a few clicks, significantly outperforming non-deep learning methods. However, the requirement for a large number of expensive pixel-level annotations behind the powerful performance has been ignored by previous methods, which is derived from the object-level interaction simulation.", + "bbox": [ + 86, + 261, + 480, + 412 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we aim at exploring an annotation-free alternation for interaction simulation to eliminate the reliance on object annotations in interactive segmentation, namely unsupervised interactive segmentation. To achieve it, as shown in the top half of Figure 1, our basic idea is to switch previous object-oriented interaction simulation to some semantic-consistent regions, which can be discovered unsupervisedly. In this case, the model requires diverse examples to understand changeable interactions due to the lack of precise information about objects.", + "bbox": [ + 86, + 414, + 480, + 566 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Therefore, we propose Multi-granularity Interaction Simulation (MIS) to achieve diversity. To ensure the semantic consistency of a region, we first parse the semantic of patches in an image by a Vision Transformer (ViT) [10] pre-trained unsupervisedly with DINO [7]. As shown in Figure 2, we then gradually merge two patches or regions with similar features to form a more extensive region for an image, until only one region remains. In this process, the newly generated region in every step makes up semantic-meaningful multi-granularity proposals. The MIS is finally achieved by randomly sampling these proposals and simulating possible interactions based on them when training the model. Moreover, in order to help the model fight against the unsmoothness on the boundary of proposals caused by the feature extractor, we design a smoothness constraint that considers the low-level feature of pixels. With the meaningful interaction simulated at multiple granularities and the smoothness constraint, the model learns to understand clicks by related regions and produce an acceptable segmentation with several user interactions when inference, while completely discarding object annotations, as shown in the bottom half of Figure 1.", + "bbox": [ + 86, + 568, + 482, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We take the standard protocol [44] to evaluate our method on commonly used datasets including GrabCut [32], Berkeley [29], SBD [15], and DAVIS [31]. Benefiting from the rich interaction examples from our MIS, the trained model achieves inspiring performance. Specifically, it significantly outperforms non-deep learning methods under the premise of unsupervised setting, and even surpasses some early deep supervised methods. In addition, it can also perform as an unsupervised pre-training to improve the performance when only limited annotations are available. The surprising results support that the interactive segmentation task can be solved in a more label-efficient way. Moreover, we believe the proposed method can reduce the labeling costs in segmentation tasks by training an interactive segmentation model unsupervisedly and using it to efficiently make task-specific annotations as needed.", + "bbox": [ + 509, + 261, + 903, + 503 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works", + "text_level": 1, + "bbox": [ + 511, + 520, + 661, + 535 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Non-deep Learning Interactive Image Segmentation. Interactive segmentation has been an active field for over two decades due to its wide applications. Before the era of deep learning, the solutions are based on low-level features and optimization. One of the best-known methods is proposed by Boykov and Jolly [6], who define a graph to describe user-provided hard constraints and pixel relationship, then solve interactive segmentation by graph cut with max-flow algorithm [5]. After that, Rother et al. [32] augment graph cut by more powerful color data modeling and an iterative strategy. Other improved algorithms include random walk [11], geodesic distance [3], and star-convexity [12]. As early unsupervised interactive segmentation methods, these algorithms stuck when processing complex images due to the dependence on low-level features. Unlike their iterative optimization algorithms for input images, we distill user interactions, which are simulated from offline datasets with our method, into a deep neural network. By leveraging the large capabilities of the neural network, our method achieves significantly better performance than them.", + "bbox": [ + 509, + 547, + 903, + 849 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Deep Interactive Image Segmentation. Xu et al. [44] are the first to introduce deep learning on this task by extending FCN [28] with click map and click sampling strategies.", + "bbox": [ + 509, + 854, + 903, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "667", + "bbox": [ + 486, + 945, + 509, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/00e7329cb0e8a191709e26c8811b3e674aceed08c67805672ec1c21f4dd9d451.jpg", + "image_caption": [ + "Figure 3. Illustration of our unsupervised framework to train an interactive segmentation model. For implementation, the MIS is composed of two stages. In the first pre-processing stage, we first parse the semantic of each patch in the image using a pre-trained ViT and take a gradual merging strategy to produce semantic-consistent region proposals at multiple granularities and save them efficiently with a tree structure. In the training stage, given an image, we randomly select proposals from the corresponding merging tree in a top-down manner and further simulate possible clicks based on them, thus providing the model informative interactions." + ], + "image_footnote": [], + "bbox": [ + 89, + 85, + 390, + 261 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/44dcacbf7990d200a701e36df03affd96d68190905fed33ba0eac8ab83407877.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 405, + 85, + 905, + 261 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Based on this pipeline, the researchers gradually increase the performance ceiling of deep learning methods by emphasizing the first click [25], online optimization [17, 35], diffusing prediction [8], edge-guided flow [14], iterative click sampling [36], powerful feature extractor [26], and Gaussian process posterior [45]. On the other hand, some works [24, 9] focus on efficiency and propose to segment on local crops to accelerate inference. Although the deep learning approaches achieve uplifting performance and efficiency, they require large-scale pixel-level annotations to train, which are expensive and laborious to obtain. Unlike previous works, we focus on the dependency on annotations and show that a fully unsupervised framework can also handle interactive segmentation task well.", + "bbox": [ + 86, + 359, + 483, + 570 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Unsupervised Image Segmentation. With the development of self-supervised and unsupervised learning, unsupervised methods for image segmentation task start to emerge. This work is also related to some unsupervised image segmentation methods based on the idea that extracting segments from a pre-trained high-quality dense feature extractor, (e.g., DenseCL [40], DINO [7]). For instance, Simeoni et al. [34] proposed a series of hand-made rules to choose pixels belonging to the same object according to their feature similarity. Wang et al. [41] introduce normalized cuts [33] on the affinity graph constructed by pixel-level representations from DINO to divide the foreground and background of an image. Hamilton et al. [13] train a segmentation head by distilling the feature correspondences from DINO. Melas et al. [30] adopt spectral decomposition on the affinity graph to discover meaningful parts in an image. For instance segmentation, FreeSOLO [39] design pseudo instance mask generation based on multi-scale feature correspondences from densely pre-trained models and train an instance segmentation model with these pseudo masks. Although the masks produced by these methods can", + "bbox": [ + 86, + 583, + 483, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "serve as pseudo labels to train an interactive segmentation model unsupervisedly, only ordinary results are observed through our experiments in Section 4.1, which demonstrate that these task-specific designs is not apposite for interactive segmentation task. In contrast, we propose a novel strategy to discover semantic-consistent yet diverse regions to fit the interactive segmentation task.", + "bbox": [ + 509, + 359, + 906, + 465 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 511, + 481, + 602, + 496 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we introduce the overall framework to solve unsupervised interactive segmentation in detail. Macroscopically, we simulate informative interactions from the proposed Multi-granularity Interaction Simulation (MIS) to train an interactive segmentation model. For implementation, the MIS is composed of two stages, as shown in Figure 3. In the first pre-processing stage, we first parse the semantic of each patch in the image using a ViT [10] trained self-supervisedly with DINO [7], which has been proven to produce high-quality dense semantic features [34, 13, 30]. With these features, we take a gradual merging strategy to produce semantic-consistent region proposals at multiple granularities and save them efficiently with a tree structure. In the training stage, given an image, we randomly select proposals from the corresponding merging tree in a top-down manner and further simulate possible clicks based on them, thus providing the model informative interactions for learning to understand interactions during the training process.", + "bbox": [ + 509, + 507, + 906, + 794 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For training, the model is optimized by the provided interactions, which include meaningful regions and clicks. Specifically, it takes the image and clicks as input and is optimized to produce similar segmentation as the region. Moreover, we design a smoothness constraint when optimizing, for the purpose of mitigating the misleading brought by the inaccurate boundary of the region, which", + "bbox": [ + 509, + 795, + 908, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "668", + "bbox": [ + 486, + 945, + 511, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/c287f084a63be29948a920dfcf1c57a4387eabf374e1f3d26383739522a0a695.jpg", + "image_caption": [ + "Figure 4. Illustration of the cost of merging. The points represent patch features and the circles denote regions that consist of the patches surrounded by it. Merging two regions into one leads to a more divergent cluster and the total SSE increases, thus the cost of merging can be measured as this increment." + ], + "image_footnote": [], + "bbox": [ + 91, + 85, + 480, + 188 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "is caused by the down-sampling in the ViT. The details of MIS and the training objective are described as follows.", + "bbox": [ + 88, + 287, + 482, + 319 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Multi-granularity Interaction Simulation", + "text_level": 1, + "bbox": [ + 88, + 330, + 441, + 348 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Bottom-up Merging. At the core of our MIS is to discover semantic-consistent yet diverse regions, which is achieved efficiently by gradually merging. In the beginning, we produce high-quality semantic features from a ViT [10] trained in a self-supervised manner with DINO [7] to measure the semantic similarity and ensure the semantic-consistency of generated region proposals. In the ViT, an image $\\boldsymbol{I} \\in \\mathbb{R}^{h \\times w \\times 3}$ is divided to non-overlapping $n = \\frac{h}{s} \\times \\frac{w}{s}$ patches with stride $s$ , which are then processed by some Transformer [38] encoder layers. The patch features $\\boldsymbol{F} \\in \\mathbb{R}^{n \\times c}$ are obtained from the last layer of the ViT, where $c$ is the feature dimension. With the patch features, we implement the hierarchical merging process by Algorithm 1 and finally get a tree $T$ which records every merge process.", + "bbox": [ + 86, + 356, + 482, + 568 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Initially, $n$ patches form as $n$ leaf nodes of the tree, and a set $\\mathbb{S}$ is maintained for saving unmerged nodes, which initially contains all the leaf nodes. In each iteration, the two unmerged nodes with the least cost according to their features will be merged to form a new node, until only one unmerged node remains. Thus, there should be totally $n - 1$ iterations, and the index of the newly generated node in $k$ -th iteration is $n + k$ . Moreover, considering the prior that parts belonging to the same object are usually adjacent, we add connectivity constraints when merging to greatly accelerate the search space for finding the minimum cost. Specifically, each patch is only connected to its four adjacent patches and two regions are connected only if at least a pair of patches from them respectively are connected.", + "bbox": [ + 86, + 569, + 482, + 780 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We follow Ward's method [42] to measure the cost of merging, which minimizes the increment in the total within-cluster sum of squared error (SSE) after merging, as shown in Figure 4. Regarding a region $A$ as a cluster that contains some patches, the SSE is defined as", + "bbox": [ + 86, + 781, + 482, + 857 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\ne _ {A} = \\sum_ {i \\in A} \\left\\| \\boldsymbol {F} _ {i} - \\boldsymbol {\\mu} _ {A} \\right\\| ^ {2}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 202, + 869, + 480, + 904 + ], + "page_idx": 3 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [ + "Algorithm 1: Bottom-up Merging" + ], + "code_body": "Input: Patch features $\\pmb{F} \\in \\mathbb{R}^{n \\times c}$ \nOutput: Merge tree $\\pmb{T} \\in \\mathbb{Z}^{(n-1) \\times 2}$ \n1 Initialization: $\\mathbb{S} \\gets \\{1, 2, \\dots, n\\}$ \n2 for $k \\gets 1$ to $n-1$ do \n3 $\\begin{array}{c} i,j \\gets \\operatorname{arg min} \\operatorname{Cost}(i,j,\\pmb{F}) \\text{s.t. Connect}(i,j); \\\\ T_{k,:} \\gets (i,j); \\\\ \\mathbb{S} \\gets \\complement_{\\mathbb{S}}\\{i,j\\} \\cup \\{n+k\\}; \\end{array}$ \n4 \n5 \n6 end", + "bbox": [ + 516, + 111, + 903, + 250 + ], + "page_idx": 3 + }, + { + "type": "code", + "sub_type": "algorithm", + "code_caption": [ + "Algorithm 2: Top-down Sampling" + ], + "code_body": "Input : Merge tree $T$ , decay coefficient $\\alpha$ Output: Node index $k$ \n1 Initialization: $p\\gets 1.0$ $k\\gets n - 1$ \n2 while Rand() $< p$ and $k > 0$ do \n3 if Rand() $< 0.5$ then \n4 $\\mid k\\gets T_{k,0} - n;$ \n5 else \n6 $\\mid k\\gets T_{k,1} - n;$ \n7 end \n8 $p\\gets \\alpha \\cdot p$ \n9 end \n10 $k\\gets k + n$", + "bbox": [ + 513, + 289, + 903, + 479 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\pmb{\\mu}_A\\in \\mathbb{R}^c$ is the center, which can be computed as", + "bbox": [ + 511, + 506, + 883, + 522 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {\\mu} _ {A} = \\frac {1}{s _ {A}} \\sum_ {i \\in A} \\boldsymbol {F} _ {i}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 645, + 530, + 901, + 566 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $s_A$ is the number of patches within $A$ . When merging two regions, the new center is", + "bbox": [ + 509, + 575, + 903, + 607 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {\\mu} _ {A \\cup B} = \\frac {s _ {A} \\boldsymbol {\\mu} _ {A} + s _ {B} \\boldsymbol {\\mu} _ {B}}{s _ {A} + s _ {B}}. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 617, + 617, + 901, + 647 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Then the cost of merging is defined as the difference of SSE before and after merging. Since the SSE of all clusters except the clusters being merged are unchanged, it can be formulated as", + "bbox": [ + 509, + 655, + 903, + 715 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\operatorname {C o s t} (A, B) = e _ {A \\cup B} - \\left(e _ {A} + e _ {B}\\right) \\\\ = \\frac {s _ {A} \\cdot s _ {B}}{s _ {A} + s _ {B}} \\left\\| \\boldsymbol {\\mu} _ {A} - \\boldsymbol {\\mu} _ {B} \\right\\| ^ {2}. \\tag {4} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 575, + 723, + 901, + 771 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Detailed derivation is shown in the appendix.", + "bbox": [ + 509, + 780, + 810, + 795 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "During the merging process, the center $\\mu$ and the size $s$ of each region are recorded. Initially, the size is set to 1 for each patch and the center is its feature. The detailed calculation after each merging is as follows: (1) Computing the center of the newly generated region according to Equation (3). (2) Computing the size of the newly generated region as $s_{A\\cup B} = s_A + s_B$ . (3) Computing the cost of", + "bbox": [ + 509, + 795, + 903, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "669", + "bbox": [ + 486, + 945, + 511, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/d58aa97a31a6adb77281774482694519d0806ecd7a68ea3ed3ab7e618cdd44f2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 89, + 87, + 205, + 154 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/6c761617d25866dae47a11451197e241a0fe143d19986f6c11f9417b0dc2c459.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 210, + 88, + 323, + 154 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/b07cef998e238ac0960e4c8d8ea2b0f8552b3f9627fee677ecf2daa6e1010bc5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 325, + 88, + 437, + 154 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/666d1914842c61e9d6bddcb9bd3a584a0bfdf40ed156b0efaa7abc3e9c21075d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 441, + 88, + 553, + 154 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/ad30728a39a67ef55f56411111fb5b52503af652337a9dd7582ce561912bffc4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 558, + 88, + 671, + 154 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/68b616ea8673792b4b65c6f261d026da5bd084b445eafed05f826c98b742c0e7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 674, + 88, + 787, + 154 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/d4e866a6af1c21edecc2897c202fa043b67cedafde5e31aed6bafbf51939d88a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 789, + 88, + 903, + 154 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/77ab836dc197f6945425062c9a9ce7531e96416d46563246e90f616f77672cca.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 89, + 159, + 204, + 227 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/4fa9b51daeee02580531e6ddb1732880020f68f84327e0695ab88e2611d23bd5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 209, + 159, + 321, + 226 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/a7605f75e08c8a501250c2945fe7f27236baa2a89ccdd60e8b77a6c53d1c4b2c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 325, + 159, + 437, + 226 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/000a610ad15c7a08bf0f74a7f9f22ae525ca7c7c157f2f0fe3a51ee297f3ce0a.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 441, + 159, + 553, + 226 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/b004500b4d88f43e9fc102a145430a9da78b534da1f46f08f85b38c63138a28b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 558, + 159, + 671, + 226 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/eafda1f81865be089345cb1af5669e5f2d0f17706a3c4096eb2d91029727f741.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 674, + 159, + 787, + 226 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/dc0fc2631fa28a21971faabd7e6adf081f3800cc3b919c0a1495177a7108f925.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 789, + 159, + 903, + 226 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/b7e22fb3fdd4a0bed717821b4dd83a63092a6df312f244d44361f2a1c1db6fee.jpg", + "image_caption": [ + "Image" + ], + "image_footnote": [], + "bbox": [ + 89, + 232, + 202, + 299 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/af7dfcad6411d754e30838283f780456b378bdb7e96b816f402f9d617d6f31c2.jpg", + "image_caption": [ + "TokenCut" + ], + "image_footnote": [], + "bbox": [ + 209, + 232, + 323, + 299 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/f6c5e07b9648280eab342d3b77d7b63cddae51ec466b01077e9f3574394730bb.jpg", + "image_caption": [ + "FreeMask", + "Figure 5. Qualitative results of discovered regions for the baselines and our MIS. While the baselines only focus on some salient regions in a fixed granularity, our MIS produces semantic-consistent regions at multiple granularities thus catching more objects and parts." + ], + "image_footnote": [], + "bbox": [ + 325, + 232, + 437, + 299 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/912b848861a0ad7caa4d05968fa3b4b37e95a5c00c1029ed61d721288957ee1a.jpg", + "image_caption": [ + "DSM" + ], + "image_footnote": [], + "bbox": [ + 439, + 232, + 553, + 299 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/dab54f4ebe0eb13d030b24b0db8968bfa9e9a3f12fc7629f9988258307574ec0.jpg", + "image_caption": [ + "Our multi-granularity proposals" + ], + "image_footnote": [], + "bbox": [ + 558, + 232, + 671, + 299 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/e59ad0e75ac1e135f9a6ebf879adf69efda595cd8e7530c2a9a3d244f1b809a0.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 674, + 232, + 787, + 299 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/06ca923ff11ac4ee1c8e5fa7394c8cbc646b1d68a438f0c52b09baa3c70fd495.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 790, + 232, + 903, + 299 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "merging newly generated regions with other regions according to Equation (4). Since the other regions are not changed, the cost between them remains the same.", + "bbox": [ + 86, + 369, + 480, + 414 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "After $n - 1$ iterations, we get a tree structure that is stored by a matrix $T \\in \\mathbb{Z}^{(n - 1)\\times 2}$ , where the $i$ -th row is the indices of the two children of the $i + n$ node. In the tree, each node represents a merge and also represents a region proposal which consists of all patches within the subtree rooted at this node. Hence, with this hierarchical relationship, we obtain $n - 1$ region proposals at multiple granularities for each image, which help the interactive segmentation model to learn various interactions. For storage, there is no need to store all the $n - 1$ masks but only the tree structure, that is, the matrix $T$ , which makes it more space-efficient.", + "bbox": [ + 86, + 420, + 482, + 585 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Top-down Sampling. When training, the MIS is worked based on the stored merging tree. Specifically, when sampling an image for training, we select a mask proposal from its corresponding merging tree for simulating an interaction. In the merging tree, shallow nodes correspond to relatively complete parts or their combinations and deeper nodes are more relevant to finely divided parts. Intuitively, we prefer the complete one while maintaining diversity. Therefore, we design a sampling strategy in a top-down manner and gradually decrease the probability to go deeper, as shown in Algorithm 2. Concretely, we start at the root node (i.e., the node with an index of $2n - 1$ ) and the probability $p = 1.0$ . Then in each iteration, we choose to go deeper or stop with probability $p$ , and decrease $p$ with a coefficient $\\alpha$ . The loop will terminate when choosing to stop or reach a leaf node (i.e., nodes whose index is less than or equal to $n$ ). If it is decided to go deeper, we randomly move the current node to one of its children. Finally, we get the index of a node $k$ corresponding to a region proposal, where the patches in the sub-tree rooted at $k$ are annotated as foreground.", + "bbox": [ + 86, + 598, + 482, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Click Sampling. With the sampled region, the last step is to simulate possible clicks according to the region. Drawing on the experience of previous methods, we use a combination of random and iterative click simulation strategies to produce a click map following RITM [36]. Specifically, some positive and negative clicks are first generated in parallel according to the foreground and background defined by the region. Then some additional clicks are appended by checking the erroneous region of the prediction which is produced by previous clicks. Finally, the MIS generates complete interactions which consist of a segmentation target and corresponding clicks.", + "bbox": [ + 509, + 369, + 903, + 551 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2. Training", + "text_level": 1, + "bbox": [ + 511, + 563, + 616, + 580 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Interactive Segmentation Model. Typical interactive segmentation models are built based on semantic segmentation models (e.g., FCN [28]) by taking an additional click map as input, which is transformed from the coordinate of clicks. Formulically, given an image $\\pmb{I} \\in \\mathbb{R}^{h \\times w \\times 3}$ , a click map $D \\in \\mathbb{R}^{h \\times w \\times 2}$ which presents positive and negative clicks respectively, and previous prediction $B \\in \\{0,1\\}^{h \\times w}$ , the model $\\mathcal{F}(\\cdot)$ outputs the probability of being foreground for each pixel", + "bbox": [ + 509, + 588, + 906, + 724 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\boldsymbol {Q} = \\mathcal {F} (\\operatorname {F u s i o n} (\\boldsymbol {I}, \\boldsymbol {D}, \\boldsymbol {B})) \\text {,} \\boldsymbol {Q} \\in [ 0, 1 ] ^ {h \\times w}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 737, + 903, + 756 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathrm{Fusion}(\\cdot)$ is some kind of fusion operation such as concatenate. Through training, the model learns to map the image and the user clicks to foreground and background segmentation thus can be used interactively when inference.", + "bbox": [ + 509, + 768, + 903, + 829 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Training with Proposals. Under our unsupervised setting, the model learns this mapping by the simulated interactions from the MIS. The model is first learned by the supervision from the multi-granularity region proposals $M$ by optimiz", + "bbox": [ + 509, + 839, + 903, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "670", + "bbox": [ + 486, + 945, + 511, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/5b53ad661ffb3d97f334a68d06b77a3f2062fef4aad2fe46cd3025f8539e9234.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodBackboneGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Deep Supervised Methods
DIOS w/o GC [44] CVPR16FCN8.0212.59--14.3016.7912.5217.11
DIOS w/ GC [44] CVPR16FCN5.086.08--9.2212.809.0312.58
LD [23] CVPR18VGG-193.204.79--7.4110.785.059.57
BRS [17] CVPR19DenseNet2.603.60-5.086.599.785.588.24
f-BRS [35] CVPR20ResNet-1012.302.72-4.574.817.735.047.41
FCA-Net [25] CVPR20ResNet-101-2.08-3.92---7.57
IA+SA [19] ECCV20ConvNet-3.07-4.94--5.16-
CDNet [8] ICCV21ResNet-341.862.181.953.275.187.895.006.89
RITM [36] ICIP22HRNet-181.762.041.873.223.395.434.946.71
FocalClick [9] CVPR22MiT-B01.661.90-3.144.346.515.027.06
FocusCut [24] CVPR22ResNet-1011.461.641.813.013.405.314.856.22
PseudoClick [27] ECCV22HRNet-32-1.84-2.98-5.614.746.16
SimpleClick [26] arXiv22ViT-B1.401.541.442.463.285.244.105.48
Non-deep Learning Methods
GraphCut [6] ICCV01N/A7.9810.00-14.2213.6015.9615.1317.41
Random Walk [11] TPAMI06N/A11.3613.77-14.0212.2215.0416.7118.31
Geodesic Matting [3] IJCV09N/A13.3214.57-15.9615.3617.6018.5919.50
GSC [12] CVPR10N/A7.109.12-12.5712.6915.3115.3517.52
ESC [12] CVPR10N/A7.249.20-12.1112.2114.8615.4117.70
Deep Unsupervised Methods
TokenCut* [41] CVPR22ViT-B3.045.746.309.9710.8213.1610.5615.01
FreeMask* [39] CVPR22ViT-B4.066.105.559.028.6112.018.2613.05
DSM* [30] CVPR22ViT-B3.644.645.497.758.5911.577.0810.11
MIS w/o Lsmooth (Ours)ViT-B2.082.563.405.517.389.926.7810.08
MIS (Ours)ViT-B1.942.323.094.586.919.516.338.44
", + "bbox": [ + 89, + 88, + 903, + 500 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. Comparison with previous methods and baselines on four interactive segmentation benchmarks. $\\star$ denotes baselines that we introduce from other unsupervised tasks. From top to bottom we show the previous deep supervised method, unsupervised non-deep learning method, and our newly proposed deep unsupervised method. All models listed here are trained on SBD dataset. Our MIS achieves superior performance within unsupervised methods and baselines and even exceeds early deep supervised methods (denoted by underline).", + "bbox": [ + 86, + 503, + 903, + 561 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "ing the objective", + "bbox": [ + 88, + 585, + 202, + 599 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {p s e u d o}} = \\operatorname {B C E} (M, Q), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 197, + 613, + 480, + 628 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathrm{BCE}(\\cdot)$ denotes the binary cross entropy loss. Although the region proposals generated by the MIS contains semantics, the possible inaccuracy of the self-supervised feature extractor and the patching process in the ViT will bring some inaccurate part. Fortunately, as discovered by previous research [1] that the model tends to learn effect patterns rather than memorize the noise, we find that the model can learn to correctly map clicks to segmentation after training with these simulated interactions.", + "bbox": [ + 86, + 640, + 482, + 776 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Smoothness Constraint. In order to help the model correct the error caused by patching, we propose a smoothness constraint. We first introduce the bilateral affinity matrix [37, 4] $W$ which presents the affinity of pixels based on their low-level feature and the item $W_{i,j}$ is", + "bbox": [ + 86, + 779, + 480, + 856 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\ne x p (- \\frac {| | \\pmb {a} _ {i} ^ {x y} - \\pmb {a} _ {j} ^ {x y} | | ^ {2}}{2 \\sigma_ {x y} ^ {2}} - \\frac {(a _ {i} ^ {l} - a _ {j} ^ {l}) ^ {2}}{2 \\sigma_ {l} ^ {2}} - \\frac {| | \\pmb {a} _ {i} ^ {u v} - \\pmb {a} _ {j} ^ {u v} | | ^ {2}}{2 \\sigma_ {u v} ^ {2}}),\n$$\n", + "text_format": "latex", + "bbox": [ + 96, + 864, + 472, + 905 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\pmb{a}_i$ is a pixel with a spatial position $(p_i^x, p_i^y)$ and color $(p_i^l, p_i^u, p_i^v)$ and $\\sigma_{xy}, \\sigma_l, \\sigma_{uv}$ control the extent of the spatial, luma, and chroma support of the filter. Motivated by the bilateral solver [4], the smooth constraint is implemented by restricting the model to produce consistent predictions on pixels with high bilateral affinity, which is formulated as", + "bbox": [ + 509, + 585, + 903, + 676 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {s m o o t h}} = \\sum_ {i} \\frac {1}{| \\mathcal {N} _ {i} |} \\sum_ {j \\in \\mathcal {N} _ {i}} \\boldsymbol {W} _ {i j} \\cdot \\left(\\boldsymbol {Q} _ {i} - \\boldsymbol {Q} _ {j}\\right) ^ {2}. \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 555, + 698, + 903, + 736 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "As we mainly concern with the predictions on the boundary, we only perform the loss locally for fast computation and memory efficiency, i.e., for pixel $i$ the loss is calculated in its $5 \\times 5$ neighborhoods $\\mathcal{N}_i$ . Finally, the overall training objective is", + "bbox": [ + 509, + 753, + 903, + 829 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\mathcal {L} _ {\\text {p s e u d o}} + \\lambda \\cdot \\mathcal {L} _ {\\text {s m o o t h}}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 611, + 849, + 901, + 867 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\lambda$ controls the strength of the smoothness constraint.", + "bbox": [ + 511, + 885, + 901, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "671", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/afcc4c36e10e3019e8e81d4c4b53d40cc462d4e2bbc34ceccfde3085f4109f0a.jpg", + "image_caption": [ + "Figure 6. Comparison of IoU-NoC curve. The two dotted lines indicate the performance of supervised approaches. The proposed method achieves surprising performance that significantly exceeds traditional methods and is close to supervised method when the NoC increases." + ], + "image_footnote": [], + "bbox": [ + 94, + 89, + 898, + 224 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/ed31a87045e1a20de0363afd5a242efd5afb8887ef360a67e3e500ed78bcb1ac.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Data RatioInitializationGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
1%Default (MAE [16])2.322.522.364.448.0110.435.818.28
MIS (Ours)1.54 (↓0.78)1.90 (↓0.62)1.95 (↓0.41)3.73 (↓0.71)5.57 (↓2.44)8.15 (↓2.28)5.36 (↓0.45)7.40 (↓0.88)
5%Default (MAE [16])1.682.221.973.645.488.135.147.23
(Ours)1.62 (↓0.06)1.88 (↓0.34)1.95 (↓0.02)3.32 (↓0.32)5.21 (↓0.27)7.49 (↓0.64)4.54 (↓0.60)6.11 (↓1.12)
10%Default (MAE [16])1.641.841.883.215.337.894.886.77
MIS (Ours)1.40 (↓0.24)1.50 (↓0.34)1.64 (↓0.24)2.73 (↓0.48)4.61 (↓0.72)6.95 (↓0.94)4.25 (↓0.63)5.94 (↓0.83)
", + "bbox": [ + 89, + 268, + 903, + 393 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2. Performance with limited annotations. When training the model in a supervised manner with a limited number of annotations (1%, 5%, 10%), the performance can be significantly improved by unsupervised pre-training using the proposed method.", + "bbox": [ + 86, + 398, + 903, + 428 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 88, + 450, + 220, + 467 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Implementation Details. We follow SimpleClick [26] to build the interactive segmentation model, which consists of two patch embedding modules for image and click map respectively, a ViT [10] backbone initialized with MAE [16], a simple feature pyramid [21], and an MLP segmentation head. For training, we optimize the model for 55 epochs using the Adam [18] optimizer with a learning rate of 5e-5, which decays by a factor of 10 at 50 epochs. The decay coefficient $\\alpha$ in Algorithm 2 and the weight $\\lambda$ in Equation (8) are 0.9 and 10.0, respectively. In addition, we set a threshold of 0.05 to filter small proposals. That is to say, we ignore the proposals whose areas are less than 0.05 times the image area. For inference, we set the threshold of binarizing the prediction to 0.5 as normal binary segmentation and use the same pre-processing as [26]. To ensure the fully unsupervised setting, we employ a self-supervisedly pre-trained model as the feature extractor. Specifically, a Vision Transformer (ViT) [10] trained with DINO [7] is adopted since the property of representing patch-level semantics [7, 13, 34]. We use ViT-Small [34] with a patch size of 8. The results with other models are included in the appendix. Before feeding an image into the ViT, we resize the image to make its height and width divisible by the patch size (i.e., the target height is $(h + p - h \\mod p)$ when the original height $h$ is not divisible by the patch size $p$ ), and the position embedding is interpolated to fit the image size using bilinear interpolation. We finally use all output tokens of the last block except the $cls$ token as the patch features.", + "bbox": [ + 86, + 477, + 480, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Evaluation. The evaluation is done under the standard evaluation protocol of click-based interactive segmentation. Specifically, we adopt the same click simulator as previous work [44, 17, 25, 35, 8, 36, 24, 9] to sample clicks when evaluation. Roughly, the next click will be placed at the center of the largest error region by comparing the ground-truth and prediction. We adopt the Number of Click (NoC) as the evaluation metric, which counts the average number of clicks needed to achieve a fixed Intersection over Union (IoU), the smaller the better. We use two commonly used target intersection-over-union (IoU) thresholds $85\\%$ and $90\\%$ , denoted as NoC@85 and NoC@90 respectively. Additionally, the IoU-NoC curves are also adopted to represent the convergence trend of IoU when the NoC increases, as well as compare the IoU metric under the same NoC.", + "bbox": [ + 509, + 452, + 903, + 678 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Dataset. We evaluate the performance of our MIS on the following four benchmarks. (1) GradCut [32]: The dataset contains 50 relatively easy images whose background and foreground have a clear difference. (2) Berkeley [29]: The dataset contains 96 images with 100 instances and some of them are more challenging than GrabCut. (3) SBD [15]: The dataset contains 2,857 images with 6,671 challenging instances, which does not overlap with our training set. (4) DAVIS [31]: We follow previous works [24, 9, 27, 36, 26] and use the same 345 frames for evaluation.", + "bbox": [ + 509, + 683, + 906, + 834 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.1. Quantitative Results", + "text_level": 1, + "bbox": [ + 509, + 845, + 705, + 861 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Baselines. Since the fully unsupervised interactive segmentation has not been explored by previous research, we in-", + "bbox": [ + 509, + 869, + 903, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "672", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/151d0ce19bdf328f8bcbe29d95d0aea2b7e1f9d2f996be0ce8d6df160bfce76c.jpg", + "image_caption": [ + "Ground-truth" + ], + "image_footnote": [], + "bbox": [ + 91, + 88, + 248, + 169 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/53a0bc4461a1326b12f94dbbfad2f22e9ce3611c3d1730d296545e6518c37899.jpg", + "image_caption": [ + "1 click, IoU=0.83" + ], + "image_footnote": [], + "bbox": [ + 254, + 88, + 411, + 169 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a72d786a0e6da17859accde6904019a366ba607a0d96ba84b7cb7adac6dbea49.jpg", + "image_caption": [ + "2 clicks, IoU=0.85" + ], + "image_footnote": [], + "bbox": [ + 416, + 88, + 575, + 169 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/365fff7e0b717e475b17f33153d4864efa100f4eef69200fd18efed96983e0f6.jpg", + "image_caption": [ + "3 click, IoU=0.87" + ], + "image_footnote": [], + "bbox": [ + 581, + 88, + 738, + 169 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/54c64de39febb0fc61cde1a7075c5a7b2b7fd4ef44e19e342c425ac7c5ce5090.jpg", + "image_caption": [ + "4 click, IoU=0.90" + ], + "image_footnote": [], + "bbox": [ + 745, + 88, + 903, + 169 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f758256761b814df8eb4e61b4aea538143b4966183dcff2e0bcfe8a522fc206a.jpg", + "image_caption": [ + "Ground-truth" + ], + "image_footnote": [], + "bbox": [ + 91, + 183, + 248, + 265 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b40a6af71d52d90bde379dfcc23142247a98737bb5cca66ef71f131e549fd4f2.jpg", + "image_caption": [ + "1 click, IoU=0.64" + ], + "image_footnote": [], + "bbox": [ + 254, + 183, + 411, + 265 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2aa631a08745fe12d66def7cefbf81b2155baa8224195a7d8cca871ec5247744.jpg", + "image_caption": [ + "2 clicks, IoU=0.94" + ], + "image_footnote": [], + "bbox": [ + 416, + 183, + 575, + 265 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/49d19041bead7b98109287ef00d93e0ac24202647d3854390ce0f9321ce40232.jpg", + "image_caption": [ + "3 click, IoU=0.97" + ], + "image_footnote": [], + "bbox": [ + 581, + 183, + 738, + 265 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2c7fa2cc2bc66f9846b5694b2f64e398604b29d9697f34dce09bb32714399c2c.jpg", + "image_caption": [ + "5 click, IoU=0.98" + ], + "image_footnote": [], + "bbox": [ + 745, + 183, + 903, + 265 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/617ad7e204ec840a9d2618e0029e1c17b44662412e373f75c7a143acad3d772c.jpg", + "image_caption": [ + "Ground-truth" + ], + "image_footnote": [], + "bbox": [ + 91, + 277, + 248, + 359 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8bc934f23f5f3ea842727c9af4e301a287b4c8fa96a7c932613ce9cd245d20f6.jpg", + "image_caption": [ + "1 click, IoU=0.66" + ], + "image_footnote": [], + "bbox": [ + 254, + 277, + 411, + 359 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a23eaa68dc5757a318837d15b17a82a5243d140fae1768da91bb456945d1b618.jpg", + "image_caption": [ + "2 clicks, IoU=0.87", + "Figure 7. Visualization of the interaction and segmentation. The green and red points indicate positive and negative clicks respectively." + ], + "image_footnote": [], + "bbox": [ + 416, + 277, + 575, + 359 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f92a724ce218f0e879a83796296f8e864401f6e41cd391cabfc08920dba4f38f.jpg", + "image_caption": [ + "3 click, IoU=0.94" + ], + "image_footnote": [], + "bbox": [ + 581, + 277, + 738, + 359 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/31ff22557bd0763e8421a50981ad379bbbdb7c89519a3357d0a480a07eee5733.jpg", + "image_caption": [ + "5 click, IoU=0.96" + ], + "image_footnote": [], + "bbox": [ + 745, + 277, + 903, + 359 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/580e9c46a558097e4aad478e16c350aba323938b65cd501f7e02bb8874e7a143.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ValueGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Strength of the Smoothness Constraint λ
0.02.082.563.405.517.389.926.7810.08
3.02.02 (↓0.06)2.50 (↓0.06)3.07 (↓0.33)5.04 (↓0.47)6.84 (↓0.54)9.33 (↓0.59)6.32 (↓0.46)8.78 (↓1.30)
5.01.94 (↓0.14)2.34 (↓0.22)3.01 (↓0.39)4.71 (↓0.80)6.79 (↓0.59)9.39 (↓0.53)6.39 (↓0.39)8.55 (↓1.53)
10.01.94 (↓0.14)2.32 (↓0.24)3.09 (↓0.31)4.58 (↓0.93)6.91 (↓0.47)9.51 (↓0.41)6.33 (↓0.45)8.44 (↓1.64)
15.02.12 (↑0.04)2.50 (↓0.06)3.25 (↓0.15)5.13 (↓0.38)7.12 (↓0.26)9.85 (↓0.07)6.71 (↓0.07)9.10 (↓0.98)
", + "bbox": [ + 89, + 401, + 903, + 522 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 3. Ablation on the smoothness constraint. The results demonstrate its effectiveness and robustness.", + "bbox": [ + 173, + 527, + 812, + 541 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "produce some baselines which are originally designed for unsupervised salient detection (TokenCut [41]), instance segmentation (FreeMask [39]), and semantic segmentation (DSM [30]) to demonstrate the effectiveness of our method. We follow the official implementation of these baselines to extract mask proposals and use them to train the same model as ours. We denote these baselines by “ $\\star$ ” in Table 1.", + "bbox": [ + 86, + 558, + 482, + 666 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Comparison with Previous Work. For comparison, we present experimental results of previous supervised deep learning methods, non-deep learning methods, baselines, and the proposed MIS on four aforementioned datasets. Under the unsupervised setting, our method significantly outperforms all other methods as shown in the second part of Table 1. It is also worth mentioning that the proposed MIS achieves inspiring performance that is even comparable with some previous supervised approaches. This support that the interactive segmentation task can be solved in a more label-efficient way. Moreover, we show the IoU-NoC curve of previous interactive segmentation methods and MIS in Figure 6, where the dotted lines indicate the upper and lower performance of previous supervised methods. It can be found that our method reaches obviously higher", + "bbox": [ + 86, + 674, + 482, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "IoU compared to the non-deep learning methods, especially in the first few clicks, and gradually converge to the supervised counterpart when NoC increases.", + "bbox": [ + 509, + 558, + 903, + 603 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Comparison with Baselines. MIS also gets advanced results compared to the baselines which only focus on the specific granularity such as the most salient object or fixed number of objects, demonstrating the effectiveness of diverse interactions under the unsupervised setting.", + "bbox": [ + 509, + 607, + 903, + 683 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Supervised Fine-tuning. Besides the fully unsupervised setting, we further fine-tune our model in a supervised manner with only a limited number of annotations (1%, 5%, 10%). As shown in Table 2, the model initialized with MIS pre-training the MAE [16] counterpart especially on the relatively hard dataset (i.e., SBD and DAVIS). These results demonstrate that MIS can serve as a strong unsupervised pre-training method for interactive segmentation when the available annotations are rare.", + "bbox": [ + 509, + 686, + 905, + 821 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.2. Qualitative Results", + "text_level": 1, + "bbox": [ + 509, + 832, + 694, + 848 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Multi-granularity Region Proposal. In Figure 5 we show the qualitative results of the region proposals generated by the baselines and our MIS, where different colors mean dif", + "bbox": [ + 509, + 854, + 903, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "673", + "bbox": [ + 485, + 945, + 511, + 955 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/a9570a21f249d9ba5c4ed5b240c495291c2a876753a7829e646bb12e952d180e.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ValueGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Decay coefficient α
0.02.122.483.895.528.7110.877.849.92
0.81.94 (↓0.18)2.40 (↓0.08)3.08 (↓0.81)4.99 (↓0.53)7.03 (↓1.68)9.62 (↓1.25)6.36 (↓1.48)8.57 (↓1.35)
0.91.94 (↓0.18)2.32 (↓0.16)3.09 (↓0.80)4.58 (↓0.94)6.91 (↓1.80)9.51 (↓1.36)6.33 (↓1.51)8.44 (↓1.48)
0.952.22 (↑0.10)2.62 (↑0.14)3.19 (↓0.70)4.89 (↓0.63)6.91 (↓1.80)9.52 (↓1.35)6.09 (↓1.75)8.54 (↓1.38)
", + "bbox": [ + 89, + 88, + 903, + 195 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/a27abcc4e4bc895d4d86a392b59d0f47a41482c1d6868cfbd43a219d1159d554.jpg", + "table_caption": [ + "Table 4. Ablation on top-down sampling. In the case of $\\alpha = 0$ , only the two children of the root node are sampled and thus multi-granularity is not allowed. The results show the effectiveness of multi-granularity and the robustness of $\\alpha$ ." + ], + "table_footnote": [], + "table_body": "
SamplingGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Uniform3.844.324.426.207.119.957.7110.10
Top-down1.94 (↓1.90)2.32 (↓2.00)3.09 (↓1.33)4.58 (↓1.62)6.91 (↓0.20)9.51 (↓0.44)6.33 (↓1.38)8.44 (↓1.66)
", + "bbox": [ + 89, + 239, + 903, + 303 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Table 5. Ablation on sampling strategy. The proposed top-down sampling strategy is effective because it reasonably assigns different weights to fragmented and complete components, so as to sample complete objects as much as possible while maintaining diversity.", + "bbox": [ + 86, + 306, + 903, + 338 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "ferent mask proposals and our mask proposals. Compared with them, our multi-granularity proposals capture more informative regions and are more diverse. Through the top-down random sampling strategy, our proposals provide the model with rich interactions, which makes the model learn a better mapping from clicks to segmentation under the unsupervised setting.", + "bbox": [ + 86, + 359, + 480, + 465 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Interactive Segmentation. Figure 7 show some interactive segmentation examples of our method. The trained interactive segmentation model is able to capture the outline of the needed object by the first one or two clicks and achieves high IoU with a few clicks, which demonstrates the feasibility of our newly proposed unsupervised setting and the effectiveness of the MIS. For some simple objects, our model can produce satisfactory predictions within the first few clicks. It can also handle complex scenes such as partially occluded objects and adjacent instances.", + "bbox": [ + 86, + 470, + 482, + 623 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 86, + 631, + 243, + 647 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Smoothness Constraint. For the smoothness constraint, we switch the weight $\\lambda$ in Equation (8) to show its effectiveness. The experimental results in Table 3 demonstrate that the smoothness constraint is helpful for improving the performance through the principle that helps the model correct the boundary errors in the proposals. The effectiveness is robust when $\\lambda$ is within a reason range.", + "bbox": [ + 86, + 654, + 482, + 760 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Top-down Sampling. The top-down sampling (Algorithm 2) is the core part of our MIS to achieve diversity. We evaluate its effectiveness by comparing with a fixed-granularity strategy, and a fully random strategy that randomly sample nodes on the merging tree from a uniform distribution. In Table 4, we take $\\alpha = 0.0$ as the baseline. In this case, we always use one of the two children of the root node in the merging tree, thus multi-granularity is not allowed. Comparing the results with $\\alpha = 0.8, 0.9, 0.95$ we", + "bbox": [ + 86, + 763, + 482, + 902 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "can find that the introduction of multi-granularity brings noticeable improvement, especially in the hard dataset. It is also obvious that this hyper-parameter is relatively robust. In addition, the results compared to the fully random sampling strategy in Table 5 also show clear advantages of our top-down sampling strategy. When sampling uniformly, the finely divided object components are more likely to be selected due to the large number, resulting in local perception and thus requiring more clicks to localize objects. In contrast, our top-down sampling strategy reasonably assigns different weights to fragmented and complete components, so as to sample complete objects as much as possible while maintaining diversity.", + "bbox": [ + 509, + 359, + 906, + 556 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 509, + 568, + 632, + 584 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this work, we open up a promising direction for deep interactive segmentation that completely discards the dependence on manual annotations. While previous methods learn the interaction through object-oriented simulation with pixel-level annotations, we propose MIS and demonstrate the feasibility to simulate informative interaction with semantic-consistent regions discovered in an unsupervised manner. Inspiring experimental results show the effectiveness of our method and the potential to reduce the labor of creating annotation without cost via training an interactive segmentation model unsupervisedly. Our experiment also supports that the interactive segmentation task can be solved in a more label-efficient way to trade off the performance and annotations. We hope our exploration can promote the attendance of label efficiency on interactive segmentation.", + "bbox": [ + 509, + 594, + 906, + 820 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements. This work was supported by the National Key R&D Program of China (2022ZD0118101) and the Natural Science Foundation of China (No. 61972217, 32071459, 62176249, 62006133, 62271465, 62202014). Li Yuan is sponsored by CCF Tencent Open Research Fund.", + "bbox": [ + 509, + 825, + 903, + 902 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "674", + "bbox": [ + 485, + 944, + 511, + 957 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 89, + 90, + 184, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Devansh Arpit, Stanislaw Jastrzebski, Nicolas Ballas, David Krueger, Emmanuel Bengio, Maxinder S Kanwal, Tegan Maharaj, Asja Fischer, Aaron Courville, Yoshua Bengio, et al. A closer look at memorization in deep networks. In International Conference on Machine Learning, pages 233-242. PMLR, 2017. 6", + "[2] Junjie Bai and Xiaodong Wu. Error-tolerant scribbles based interactive image segmentation. In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, pages 392-399, 2014. 1", + "[3] Xue Bai and Guillermo Sapiro. 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In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 5297-5306, 2019. 3" + ], + "bbox": [ + 514, + 92, + 903, + 570 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "676", + "bbox": [ + 486, + 945, + 511, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multi-granularity Interaction Simulation for Unsupervised Interactive Segmentation/860ca3f9-f21c-4c96-a4c1-8228c6546c93_model.json b/2023/Multi-granularity Interaction Simulation for Unsupervised Interactive Segmentation/860ca3f9-f21c-4c96-a4c1-8228c6546c93_model.json new file mode 100644 index 0000000000000000000000000000000000000000..161ed5c636b34670fe4c4d68b716b2a6e790031a --- /dev/null +++ b/2023/Multi-granularity Interaction Simulation for Unsupervised Interactive Segmentation/860ca3f9-f21c-4c96-a4c1-8228c6546c93_model.json @@ -0,0 +1,2521 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.2, + 0.131, + 0.795, + 0.177 + ], + "angle": 0, + "content": "Multi-granularity Interaction Simulation for Unsupervised Interactive Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.183, + 0.203, + 0.812, + 0.24 + ], + "angle": 0, + "content": "Kehan Li\\(^{1,3}\\) Yian Zhao\\(^{1,3}\\) Zhennan Wang\\(^{2}\\) Zesen Cheng\\(^{1,3}\\) Peng Jin\\(^{1,3}\\) Xiangyang Ji\\(^{4}\\) Li Yuan\\(^{1,2,3}\\) Chang Liu\\(^{4*}\\) Jie Chen\\(^{1,2,3*}\\)" + }, + { + "type": "text", + "bbox": [ + 0.154, + 0.246, + 0.841, + 0.282 + ], + "angle": 0, + "content": "\\(^{1}\\) School of Electronic and Computer Engineering, Peking University, Shenzhen, China \n\\(^{2}\\) Peng Cheng Laboratory, Shenzhen, China" + }, + { + "type": "text", + "bbox": [ + 0.18, + 0.283, + 0.815, + 0.318 + ], + "angle": 0, + "content": "\\(^{3}\\) AI for Science (AI4S)-Preferred Program, Peking University, Shenzhen, China \n\\(^{4}\\) Department of Automation and BNRist, Tsinghua University, Beijing, China" + }, + { + "type": "text", + "bbox": [ + 0.263, + 0.32, + 0.731, + 0.335 + ], + "angle": 0, + "content": "liuchang2022@tsinghua.edu.cn jiechen2019@pku.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.246, + 0.37, + 0.326, + 0.387 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.402, + 0.484, + 0.765 + ], + "angle": 0, + "content": "Interactive segmentation enables users to segment as needed by providing cues of objects, which introduces human-computer interaction for many fields, such as image editing and medical image analysis. Typically, massive and expansive pixel-level annotations are spent to train deep models by object-oriented interactions with manually labeled object masks. In this work, we reveal that informative interactions can be made by simulation with semantic-consistent yet diverse region exploration in an unsupervised paradigm. Concretely, we introduce a Multi-granularity Interaction Simulation (MIS) approach to open up a promising direction for unsupervised interactive segmentation. Drawing on the high-quality dense features produced by recent self-supervised models, we propose to gradually merge patches or regions with similar features to form more extensive regions and thus, every merged region serves as a semantic-meaningful multi-granularity proposal. By randomly sampling these proposals and simulating possible interactions based on them, we provide meaningful interaction at multiple granularities to teach the model to understand interactions. Our MIS significantly outperforms non-deep learning unsupervised methods and is even comparable with some previous deep-supervised methods without any annotation." + }, + { + "type": "title", + "bbox": [ + 0.09, + 0.793, + 0.221, + 0.808 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.818, + 0.482, + 0.879 + ], + "angle": 0, + "content": "Interactive segmentation aims at obtaining high-quality object masks with limited user interaction, allowing users to segment objects as needed. During the development of interactive segmentation, various interactive forms like" + }, + { + "type": "image", + "bbox": [ + 0.516, + 0.368, + 0.905, + 0.59 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.51, + 0.594, + 0.907, + 0.678 + ], + "angle": 0, + "content": "Figure 1. Top: To tackle the reliance on object annotations of previous interactive segmentation methods caused by interaction simulation, we propose Multi-granularity Interaction Simulation (MIS) that simulates interaction by meaningful regions at multiple granularities. Down: The model learns from MIS to successfully understand interactions and produce acceptable segmentation." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.704, + 0.905, + 0.78 + ], + "angle": 0, + "content": "bounding boxes [20, 32, 43], scribbles [2, 11, 22], and clicks [44, 17, 25, 35, 8, 36, 24, 9] have been explored. Among them, the click-based interaction becomes the mainstream due to its simplicity and well-established training and evaluation protocols." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.781, + 0.907, + 0.903 + ], + "angle": 0, + "content": "State-of-the-art methods for click-based interactive segmentation are based on deep learning, following the basic paradigm proposed by Xu et al. [44]. Specifically, these methods encode clicks to a distance map and adapt a semantic segmentation model (e.g., FCN [28]) to take the encoded click map as input, and then train the model with interaction-segmentation pairs. Since it is impractical to collect interaction sequences from real users, previous" + }, + { + "type": "page_footnote", + "bbox": [ + 0.108, + 0.887, + 0.444, + 0.901 + ], + "angle": 0, + "content": "*Corresponding author. Project page: https://lkhl.github.io/MIS" + }, + { + "type": "page_number", + "bbox": [ + 0.487, + 0.946, + 0.512, + 0.957 + ], + "angle": 0, + "content": "666" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.09, + 0.087, + 0.905, + 0.194 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.088, + 0.196, + 0.905, + 0.239 + ], + "angle": 0, + "content": "Figure 2. Illustration of the multi-granularity region proposal generation. For an input image, We first introduce a self-supervised ViT to produce semantic features for each patch of an image. We then gradually merge two similar patches or regions with similar features to perform a new region. All newly generated regions in the merging process constitute meaningful proposals at multiple granularities." + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.262, + 0.482, + 0.413 + ], + "angle": 0, + "content": "methods adopt an interaction simulation strategy [44, 36] that randomly samples clicks based on object segmentation annotations. By training with the simulated clicks and corresponding object masks, the model is able to correctly understand user needs and segment objects with a few clicks, significantly outperforming non-deep learning methods. However, the requirement for a large number of expensive pixel-level annotations behind the powerful performance has been ignored by previous methods, which is derived from the object-level interaction simulation." + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.415, + 0.481, + 0.567 + ], + "angle": 0, + "content": "In this work, we aim at exploring an annotation-free alternation for interaction simulation to eliminate the reliance on object annotations in interactive segmentation, namely unsupervised interactive segmentation. To achieve it, as shown in the top half of Figure 1, our basic idea is to switch previous object-oriented interaction simulation to some semantic-consistent regions, which can be discovered unsupervisedly. In this case, the model requires diverse examples to understand changeable interactions due to the lack of precise information about objects." + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.569, + 0.483, + 0.902 + ], + "angle": 0, + "content": "Therefore, we propose Multi-granularity Interaction Simulation (MIS) to achieve diversity. To ensure the semantic consistency of a region, we first parse the semantic of patches in an image by a Vision Transformer (ViT) [10] pre-trained unsupervisedly with DINO [7]. As shown in Figure 2, we then gradually merge two patches or regions with similar features to form a more extensive region for an image, until only one region remains. In this process, the newly generated region in every step makes up semantic-meaningful multi-granularity proposals. The MIS is finally achieved by randomly sampling these proposals and simulating possible interactions based on them when training the model. Moreover, in order to help the model fight against the unsmoothness on the boundary of proposals caused by the feature extractor, we design a smoothness constraint that considers the low-level feature of pixels. With the meaningful interaction simulated at multiple granularities and the smoothness constraint, the model learns to understand clicks by related regions and produce an acceptable segmentation with several user interactions when inference, while completely discarding object annotations, as shown in the bottom half of Figure 1." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.262, + 0.905, + 0.504 + ], + "angle": 0, + "content": "We take the standard protocol [44] to evaluate our method on commonly used datasets including GrabCut [32], Berkeley [29], SBD [15], and DAVIS [31]. Benefiting from the rich interaction examples from our MIS, the trained model achieves inspiring performance. Specifically, it significantly outperforms non-deep learning methods under the premise of unsupervised setting, and even surpasses some early deep supervised methods. In addition, it can also perform as an unsupervised pre-training to improve the performance when only limited annotations are available. The surprising results support that the interactive segmentation task can be solved in a more label-efficient way. Moreover, we believe the proposed method can reduce the labeling costs in segmentation tasks by training an interactive segmentation model unsupervisedly and using it to efficiently make task-specific annotations as needed." + }, + { + "type": "title", + "bbox": [ + 0.512, + 0.521, + 0.662, + 0.536 + ], + "angle": 0, + "content": "2. Related Works" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.548, + 0.905, + 0.851 + ], + "angle": 0, + "content": "Non-deep Learning Interactive Image Segmentation. Interactive segmentation has been an active field for over two decades due to its wide applications. Before the era of deep learning, the solutions are based on low-level features and optimization. One of the best-known methods is proposed by Boykov and Jolly [6], who define a graph to describe user-provided hard constraints and pixel relationship, then solve interactive segmentation by graph cut with max-flow algorithm [5]. After that, Rother et al. [32] augment graph cut by more powerful color data modeling and an iterative strategy. Other improved algorithms include random walk [11], geodesic distance [3], and star-convexity [12]. As early unsupervised interactive segmentation methods, these algorithms stuck when processing complex images due to the dependence on low-level features. Unlike their iterative optimization algorithms for input images, we distill user interactions, which are simulated from offline datasets with our method, into a deep neural network. By leveraging the large capabilities of the neural network, our method achieves significantly better performance than them." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.856, + 0.905, + 0.903 + ], + "angle": 0, + "content": "Deep Interactive Image Segmentation. Xu et al. [44] are the first to introduce deep learning on this task by extending FCN [28] with click map and click sampling strategies." + }, + { + "type": "page_number", + "bbox": [ + 0.487, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "667" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.09, + 0.087, + 0.391, + 0.262 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.406, + 0.087, + 0.906, + 0.262 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.088, + 0.265, + 0.906, + 0.337 + ], + "angle": 0, + "content": "Figure 3. Illustration of our unsupervised framework to train an interactive segmentation model. For implementation, the MIS is composed of two stages. In the first pre-processing stage, we first parse the semantic of each patch in the image using a pre-trained ViT and take a gradual merging strategy to produce semantic-consistent region proposals at multiple granularities and save them efficiently with a tree structure. In the training stage, given an image, we randomly select proposals from the corresponding merging tree in a top-down manner and further simulate possible clicks based on them, thus providing the model informative interactions." + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.36, + 0.484, + 0.571 + ], + "angle": 0, + "content": "Based on this pipeline, the researchers gradually increase the performance ceiling of deep learning methods by emphasizing the first click [25], online optimization [17, 35], diffusing prediction [8], edge-guided flow [14], iterative click sampling [36], powerful feature extractor [26], and Gaussian process posterior [45]. On the other hand, some works [24, 9] focus on efficiency and propose to segment on local crops to accelerate inference. Although the deep learning approaches achieve uplifting performance and efficiency, they require large-scale pixel-level annotations to train, which are expensive and laborious to obtain. Unlike previous works, we focus on the dependency on annotations and show that a fully unsupervised framework can also handle interactive segmentation task well." + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.584, + 0.484, + 0.903 + ], + "angle": 0, + "content": "Unsupervised Image Segmentation. With the development of self-supervised and unsupervised learning, unsupervised methods for image segmentation task start to emerge. This work is also related to some unsupervised image segmentation methods based on the idea that extracting segments from a pre-trained high-quality dense feature extractor, (e.g., DenseCL [40], DINO [7]). For instance, Simeoni et al. [34] proposed a series of hand-made rules to choose pixels belonging to the same object according to their feature similarity. Wang et al. [41] introduce normalized cuts [33] on the affinity graph constructed by pixel-level representations from DINO to divide the foreground and background of an image. Hamilton et al. [13] train a segmentation head by distilling the feature correspondences from DINO. Melas et al. [30] adopt spectral decomposition on the affinity graph to discover meaningful parts in an image. For instance segmentation, FreeSOLO [39] design pseudo instance mask generation based on multi-scale feature correspondences from densely pre-trained models and train an instance segmentation model with these pseudo masks. Although the masks produced by these methods can" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.36, + 0.907, + 0.466 + ], + "angle": 0, + "content": "serve as pseudo labels to train an interactive segmentation model unsupervisedly, only ordinary results are observed through our experiments in Section 4.1, which demonstrate that these task-specific designs is not apposite for interactive segmentation task. In contrast, we propose a novel strategy to discover semantic-consistent yet diverse regions to fit the interactive segmentation task." + }, + { + "type": "title", + "bbox": [ + 0.512, + 0.482, + 0.603, + 0.497 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.508, + 0.907, + 0.795 + ], + "angle": 0, + "content": "In this section, we introduce the overall framework to solve unsupervised interactive segmentation in detail. Macroscopically, we simulate informative interactions from the proposed Multi-granularity Interaction Simulation (MIS) to train an interactive segmentation model. For implementation, the MIS is composed of two stages, as shown in Figure 3. In the first pre-processing stage, we first parse the semantic of each patch in the image using a ViT [10] trained self-supervisedly with DINO [7], which has been proven to produce high-quality dense semantic features [34, 13, 30]. With these features, we take a gradual merging strategy to produce semantic-consistent region proposals at multiple granularities and save them efficiently with a tree structure. In the training stage, given an image, we randomly select proposals from the corresponding merging tree in a top-down manner and further simulate possible clicks based on them, thus providing the model informative interactions for learning to understand interactions during the training process." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.796, + 0.909, + 0.903 + ], + "angle": 0, + "content": "For training, the model is optimized by the provided interactions, which include meaningful regions and clicks. Specifically, it takes the image and clicks as input and is optimized to produce similar segmentation as the region. Moreover, we design a smoothness constraint when optimizing, for the purpose of mitigating the misleading brought by the inaccurate boundary of the region, which" + }, + { + "type": "page_number", + "bbox": [ + 0.487, + 0.946, + 0.513, + 0.957 + ], + "angle": 0, + "content": "668" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.092, + 0.087, + 0.482, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.089, + 0.191, + 0.483, + 0.262 + ], + "angle": 0, + "content": "Figure 4. Illustration of the cost of merging. The points represent patch features and the circles denote regions that consist of the patches surrounded by it. Merging two regions into one leads to a more divergent cluster and the total SSE increases, thus the cost of merging can be measured as this increment." + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.288, + 0.483, + 0.32 + ], + "angle": 0, + "content": "is caused by the down-sampling in the ViT. The details of MIS and the training objective are described as follows." + }, + { + "type": "title", + "bbox": [ + 0.089, + 0.332, + 0.442, + 0.349 + ], + "angle": 0, + "content": "3.1. Multi-granularity Interaction Simulation" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.357, + 0.483, + 0.569 + ], + "angle": 0, + "content": "Bottom-up Merging. At the core of our MIS is to discover semantic-consistent yet diverse regions, which is achieved efficiently by gradually merging. In the beginning, we produce high-quality semantic features from a ViT [10] trained in a self-supervised manner with DINO [7] to measure the semantic similarity and ensure the semantic-consistency of generated region proposals. In the ViT, an image \\( \\boldsymbol{I} \\in \\mathbb{R}^{h \\times w \\times 3} \\) is divided to non-overlapping \\( n = \\frac{h}{s} \\times \\frac{w}{s} \\) patches with stride \\( s \\), which are then processed by some Transformer [38] encoder layers. The patch features \\( \\boldsymbol{F} \\in \\mathbb{R}^{n \\times c} \\) are obtained from the last layer of the ViT, where \\( c \\) is the feature dimension. With the patch features, we implement the hierarchical merging process by Algorithm 1 and finally get a tree \\( T \\) which records every merge process." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.57, + 0.483, + 0.781 + ], + "angle": 0, + "content": "Initially, \\( n \\) patches form as \\( n \\) leaf nodes of the tree, and a set \\( \\mathbb{S} \\) is maintained for saving unmerged nodes, which initially contains all the leaf nodes. In each iteration, the two unmerged nodes with the least cost according to their features will be merged to form a new node, until only one unmerged node remains. Thus, there should be totally \\( n - 1 \\) iterations, and the index of the newly generated node in \\( k \\)-th iteration is \\( n + k \\). Moreover, considering the prior that parts belonging to the same object are usually adjacent, we add connectivity constraints when merging to greatly accelerate the search space for finding the minimum cost. Specifically, each patch is only connected to its four adjacent patches and two regions are connected only if at least a pair of patches from them respectively are connected." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.782, + 0.483, + 0.858 + ], + "angle": 0, + "content": "We follow Ward's method [42] to measure the cost of merging, which minimizes the increment in the total within-cluster sum of squared error (SSE) after merging, as shown in Figure 4. Regarding a region \\( A \\) as a cluster that contains some patches, the SSE is defined as" + }, + { + "type": "equation", + "bbox": [ + 0.204, + 0.871, + 0.482, + 0.905 + ], + "angle": 0, + "content": "\\[\ne _ {A} = \\sum_ {i \\in A} \\left\\| \\boldsymbol {F} _ {i} - \\boldsymbol {\\mu} _ {A} \\right\\| ^ {2}, \\tag {1}\n\\]" + }, + { + "type": "code_caption", + "bbox": [ + 0.523, + 0.095, + 0.753, + 0.111 + ], + "angle": 0, + "content": "Algorithm 1: Bottom-up Merging" + }, + { + "type": "algorithm", + "bbox": [ + 0.517, + 0.112, + 0.905, + 0.251 + ], + "angle": 0, + "content": "Input: Patch features \\(\\pmb{F} \\in \\mathbb{R}^{n \\times c}\\) \nOutput: Merge tree \\(\\pmb{T} \\in \\mathbb{Z}^{(n-1) \\times 2}\\) \n1 Initialization: \\(\\mathbb{S} \\gets \\{1, 2, \\dots, n\\}\\) \n2 for \\(k \\gets 1\\) to \\(n-1\\) do \n3 \\(\\begin{array}{c} i,j \\gets \\operatorname{arg min} \\operatorname{Cost}(i,j,\\pmb{F}) \\text{s.t. Connect}(i,j); \\\\ T_{k,:} \\gets (i,j); \\\\ \\mathbb{S} \\gets \\complement_{\\mathbb{S}}\\{i,j\\} \\cup \\{n+k\\}; \\end{array}\\) \n4 \n5 \n6 end" + }, + { + "type": "code_caption", + "bbox": [ + 0.523, + 0.274, + 0.755, + 0.289 + ], + "angle": 0, + "content": "Algorithm 2: Top-down Sampling" + }, + { + "type": "algorithm", + "bbox": [ + 0.514, + 0.29, + 0.905, + 0.48 + ], + "angle": 0, + "content": "Input : Merge tree \\(T\\) , decay coefficient \\(\\alpha\\) Output: Node index \\(k\\) \n1 Initialization: \\(p\\gets 1.0\\) \\(k\\gets n - 1\\) \n2 while Rand() \\(< p\\) and \\(k > 0\\) do \n3 if Rand() \\(< 0.5\\) then \n4 \\(\\mid k\\gets T_{k,0} - n;\\) \n5 else \n6 \\(\\mid k\\gets T_{k,1} - n;\\) \n7 end \n8 \\(p\\gets \\alpha \\cdot p\\) \n9 end \n10 \\(k\\gets k + n\\)" + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.507, + 0.885, + 0.523 + ], + "angle": 0, + "content": "where \\(\\pmb{\\mu}_A\\in \\mathbb{R}^c\\) is the center, which can be computed as" + }, + { + "type": "equation", + "bbox": [ + 0.647, + 0.531, + 0.903, + 0.568 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {\\mu} _ {A} = \\frac {1}{s _ {A}} \\sum_ {i \\in A} \\boldsymbol {F} _ {i}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.577, + 0.905, + 0.608 + ], + "angle": 0, + "content": "where \\( s_A \\) is the number of patches within \\( A \\). When merging two regions, the new center is" + }, + { + "type": "equation", + "bbox": [ + 0.618, + 0.618, + 0.903, + 0.648 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {\\mu} _ {A \\cup B} = \\frac {s _ {A} \\boldsymbol {\\mu} _ {A} + s _ {B} \\boldsymbol {\\mu} _ {B}}{s _ {A} + s _ {B}}. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.656, + 0.905, + 0.716 + ], + "angle": 0, + "content": "Then the cost of merging is defined as the difference of SSE before and after merging. Since the SSE of all clusters except the clusters being merged are unchanged, it can be formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.576, + 0.724, + 0.903, + 0.772 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\operatorname {C o s t} (A, B) = e _ {A \\cup B} - \\left(e _ {A} + e _ {B}\\right) \\\\ = \\frac {s _ {A} \\cdot s _ {B}}{s _ {A} + s _ {B}} \\left\\| \\boldsymbol {\\mu} _ {A} - \\boldsymbol {\\mu} _ {B} \\right\\| ^ {2}. \\tag {4} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.511, + 0.781, + 0.812, + 0.796 + ], + "angle": 0, + "content": "Detailed derivation is shown in the appendix." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.796, + 0.905, + 0.902 + ], + "angle": 0, + "content": "During the merging process, the center \\(\\mu\\) and the size \\(s\\) of each region are recorded. Initially, the size is set to 1 for each patch and the center is its feature. The detailed calculation after each merging is as follows: (1) Computing the center of the newly generated region according to Equation (3). (2) Computing the size of the newly generated region as \\(s_{A\\cup B} = s_A + s_B\\). (3) Computing the cost of" + }, + { + "type": "page_number", + "bbox": [ + 0.487, + 0.946, + 0.512, + 0.957 + ], + "angle": 0, + "content": "669" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.091, + 0.088, + 0.206, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.211, + 0.089, + 0.324, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.326, + 0.089, + 0.439, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.442, + 0.089, + 0.554, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.56, + 0.089, + 0.673, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.675, + 0.089, + 0.788, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.79, + 0.089, + 0.904, + 0.155 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.091, + 0.16, + 0.205, + 0.228 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.21, + 0.16, + 0.323, + 0.227 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.326, + 0.16, + 0.439, + 0.227 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.442, + 0.16, + 0.554, + 0.227 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.56, + 0.16, + 0.673, + 0.227 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.675, + 0.16, + 0.788, + 0.227 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.79, + 0.16, + 0.904, + 0.227 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.091, + 0.233, + 0.204, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.129, + 0.302, + 0.167, + 0.313 + ], + "angle": 0, + "content": "Image" + }, + { + "type": "image", + "bbox": [ + 0.21, + 0.233, + 0.324, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.238, + 0.302, + 0.297, + 0.313 + ], + "angle": 0, + "content": "TokenCut" + }, + { + "type": "image", + "bbox": [ + 0.326, + 0.233, + 0.439, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.352, + 0.302, + 0.412, + 0.313 + ], + "angle": 0, + "content": "FreeMask" + }, + { + "type": "image", + "bbox": [ + 0.441, + 0.233, + 0.554, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.481, + 0.302, + 0.513, + 0.313 + ], + "angle": 0, + "content": "DSM" + }, + { + "type": "image", + "bbox": [ + 0.56, + 0.233, + 0.673, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.639, + 0.302, + 0.825, + 0.315 + ], + "angle": 0, + "content": "Our multi-granularity proposals" + }, + { + "type": "image", + "bbox": [ + 0.675, + 0.233, + 0.788, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.791, + 0.233, + 0.904, + 0.3 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.088, + 0.318, + 0.905, + 0.347 + ], + "angle": 0, + "content": "Figure 5. Qualitative results of discovered regions for the baselines and our MIS. While the baselines only focus on some salient regions in a fixed granularity, our MIS produces semantic-consistent regions at multiple granularities thus catching more objects and parts." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.371, + 0.482, + 0.415 + ], + "angle": 0, + "content": "merging newly generated regions with other regions according to Equation (4). Since the other regions are not changed, the cost between them remains the same." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.421, + 0.483, + 0.587 + ], + "angle": 0, + "content": "After \\( n - 1 \\) iterations, we get a tree structure that is stored by a matrix \\( T \\in \\mathbb{Z}^{(n - 1)\\times 2} \\), where the \\( i \\)-th row is the indices of the two children of the \\( i + n \\) node. In the tree, each node represents a merge and also represents a region proposal which consists of all patches within the subtree rooted at this node. Hence, with this hierarchical relationship, we obtain \\( n - 1 \\) region proposals at multiple granularities for each image, which help the interactive segmentation model to learn various interactions. For storage, there is no need to store all the \\( n - 1 \\) masks but only the tree structure, that is, the matrix \\( T \\), which makes it more space-efficient." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.599, + 0.483, + 0.902 + ], + "angle": 0, + "content": "Top-down Sampling. When training, the MIS is worked based on the stored merging tree. Specifically, when sampling an image for training, we select a mask proposal from its corresponding merging tree for simulating an interaction. In the merging tree, shallow nodes correspond to relatively complete parts or their combinations and deeper nodes are more relevant to finely divided parts. Intuitively, we prefer the complete one while maintaining diversity. Therefore, we design a sampling strategy in a top-down manner and gradually decrease the probability to go deeper, as shown in Algorithm 2. Concretely, we start at the root node (i.e., the node with an index of \\(2n - 1\\)) and the probability \\(p = 1.0\\). Then in each iteration, we choose to go deeper or stop with probability \\(p\\), and decrease \\(p\\) with a coefficient \\(\\alpha\\). The loop will terminate when choosing to stop or reach a leaf node (i.e., nodes whose index is less than or equal to \\(n\\)). If it is decided to go deeper, we randomly move the current node to one of its children. Finally, we get the index of a node \\(k\\) corresponding to a region proposal, where the patches in the sub-tree rooted at \\(k\\) are annotated as foreground." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.371, + 0.905, + 0.552 + ], + "angle": 0, + "content": "Click Sampling. With the sampled region, the last step is to simulate possible clicks according to the region. Drawing on the experience of previous methods, we use a combination of random and iterative click simulation strategies to produce a click map following RITM [36]. Specifically, some positive and negative clicks are first generated in parallel according to the foreground and background defined by the region. Then some additional clicks are appended by checking the erroneous region of the prediction which is produced by previous clicks. Finally, the MIS generates complete interactions which consist of a segmentation target and corresponding clicks." + }, + { + "type": "title", + "bbox": [ + 0.512, + 0.564, + 0.617, + 0.581 + ], + "angle": 0, + "content": "3.2. Training" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.589, + 0.907, + 0.726 + ], + "angle": 0, + "content": "Interactive Segmentation Model. Typical interactive segmentation models are built based on semantic segmentation models (e.g., FCN [28]) by taking an additional click map as input, which is transformed from the coordinate of clicks. Formulically, given an image \\( \\pmb{I} \\in \\mathbb{R}^{h \\times w \\times 3} \\), a click map \\( D \\in \\mathbb{R}^{h \\times w \\times 2} \\) which presents positive and negative clicks respectively, and previous prediction \\( B \\in \\{0,1\\}^{h \\times w} \\), the model \\( \\mathcal{F}(\\cdot) \\) outputs the probability of being foreground for each pixel" + }, + { + "type": "equation", + "bbox": [ + 0.561, + 0.738, + 0.905, + 0.757 + ], + "angle": 0, + "content": "\\[\n\\boldsymbol {Q} = \\mathcal {F} (\\operatorname {F u s i o n} (\\boldsymbol {I}, \\boldsymbol {D}, \\boldsymbol {B})) \\text {,} \\boldsymbol {Q} \\in [ 0, 1 ] ^ {h \\times w}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.77, + 0.905, + 0.83 + ], + "angle": 0, + "content": "where \\( \\mathrm{Fusion}(\\cdot) \\) is some kind of fusion operation such as concatenate. Through training, the model learns to map the image and the user clicks to foreground and background segmentation thus can be used interactively when inference." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.84, + 0.905, + 0.902 + ], + "angle": 0, + "content": "Training with Proposals. Under our unsupervised setting, the model learns this mapping by the simulated interactions from the MIS. The model is first learned by the supervision from the multi-granularity region proposals \\(M\\) by optimiz" + }, + { + "type": "page_number", + "bbox": [ + 0.487, + 0.946, + 0.512, + 0.957 + ], + "angle": 0, + "content": "670" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.09, + 0.089, + 0.905, + 0.5 + ], + "angle": 0, + "content": "
MethodBackboneGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Deep Supervised Methods
DIOS w/o GC [44] CVPR16FCN8.0212.59--14.3016.7912.5217.11
DIOS w/ GC [44] CVPR16FCN5.086.08--9.2212.809.0312.58
LD [23] CVPR18VGG-193.204.79--7.4110.785.059.57
BRS [17] CVPR19DenseNet2.603.60-5.086.599.785.588.24
f-BRS [35] CVPR20ResNet-1012.302.72-4.574.817.735.047.41
FCA-Net [25] CVPR20ResNet-101-2.08-3.92---7.57
IA+SA [19] ECCV20ConvNet-3.07-4.94--5.16-
CDNet [8] ICCV21ResNet-341.862.181.953.275.187.895.006.89
RITM [36] ICIP22HRNet-181.762.041.873.223.395.434.946.71
FocalClick [9] CVPR22MiT-B01.661.90-3.144.346.515.027.06
FocusCut [24] CVPR22ResNet-1011.461.641.813.013.405.314.856.22
PseudoClick [27] ECCV22HRNet-32-1.84-2.98-5.614.746.16
SimpleClick [26] arXiv22ViT-B1.401.541.442.463.285.244.105.48
Non-deep Learning Methods
GraphCut [6] ICCV01N/A7.9810.00-14.2213.6015.9615.1317.41
Random Walk [11] TPAMI06N/A11.3613.77-14.0212.2215.0416.7118.31
Geodesic Matting [3] IJCV09N/A13.3214.57-15.9615.3617.6018.5919.50
GSC [12] CVPR10N/A7.109.12-12.5712.6915.3115.3517.52
ESC [12] CVPR10N/A7.249.20-12.1112.2114.8615.4117.70
Deep Unsupervised Methods
TokenCut* [41] CVPR22ViT-B3.045.746.309.9710.8213.1610.5615.01
FreeMask* [39] CVPR22ViT-B4.066.105.559.028.6112.018.2613.05
DSM* [30] CVPR22ViT-B3.644.645.497.758.5911.577.0810.11
MIS w/o Lsmooth (Ours)ViT-B2.082.563.405.517.389.926.7810.08
MIS (Ours)ViT-B1.942.323.094.586.919.516.338.44
" + }, + { + "type": "table_caption", + "bbox": [ + 0.088, + 0.505, + 0.905, + 0.562 + ], + "angle": 0, + "content": "Table 1. Comparison with previous methods and baselines on four interactive segmentation benchmarks. \\(\\star\\) denotes baselines that we introduce from other unsupervised tasks. From top to bottom we show the previous deep supervised method, unsupervised non-deep learning method, and our newly proposed deep unsupervised method. All models listed here are trained on SBD dataset. Our MIS achieves superior performance within unsupervised methods and baselines and even exceeds early deep supervised methods (denoted by underline)." + }, + { + "type": "text", + "bbox": [ + 0.089, + 0.587, + 0.204, + 0.601 + ], + "angle": 0, + "content": "ing the objective" + }, + { + "type": "equation", + "bbox": [ + 0.199, + 0.614, + 0.481, + 0.63 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {p s e u d o}} = \\operatorname {B C E} (M, Q), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.641, + 0.483, + 0.777 + ], + "angle": 0, + "content": "where \\(\\mathrm{BCE}(\\cdot)\\) denotes the binary cross entropy loss. Although the region proposals generated by the MIS contains semantics, the possible inaccuracy of the self-supervised feature extractor and the patching process in the ViT will bring some inaccurate part. Fortunately, as discovered by previous research [1] that the model tends to learn effect patterns rather than memorize the noise, we find that the model can learn to correctly map clicks to segmentation after training with these simulated interactions." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.78, + 0.482, + 0.857 + ], + "angle": 0, + "content": "Smoothness Constraint. In order to help the model correct the error caused by patching, we propose a smoothness constraint. We first introduce the bilateral affinity matrix [37, 4] \\(W\\) which presents the affinity of pixels based on their low-level feature and the item \\(W_{i,j}\\) is" + }, + { + "type": "equation", + "bbox": [ + 0.097, + 0.866, + 0.473, + 0.906 + ], + "angle": 0, + "content": "\\[\ne x p (- \\frac {| | \\pmb {a} _ {i} ^ {x y} - \\pmb {a} _ {j} ^ {x y} | | ^ {2}}{2 \\sigma_ {x y} ^ {2}} - \\frac {(a _ {i} ^ {l} - a _ {j} ^ {l}) ^ {2}}{2 \\sigma_ {l} ^ {2}} - \\frac {| | \\pmb {a} _ {i} ^ {u v} - \\pmb {a} _ {j} ^ {u v} | | ^ {2}}{2 \\sigma_ {u v} ^ {2}}),\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.586, + 0.905, + 0.678 + ], + "angle": 0, + "content": "where \\(\\pmb{a}_i\\) is a pixel with a spatial position \\((p_i^x, p_i^y)\\) and color \\((p_i^l, p_i^u, p_i^v)\\) and \\(\\sigma_{xy}, \\sigma_l, \\sigma_{uv}\\) control the extent of the spatial, luma, and chroma support of the filter. Motivated by the bilateral solver [4], the smooth constraint is implemented by restricting the model to produce consistent predictions on pixels with high bilateral affinity, which is formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.556, + 0.699, + 0.905, + 0.737 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {s m o o t h}} = \\sum_ {i} \\frac {1}{| \\mathcal {N} _ {i} |} \\sum_ {j \\in \\mathcal {N} _ {i}} \\boldsymbol {W} _ {i j} \\cdot \\left(\\boldsymbol {Q} _ {i} - \\boldsymbol {Q} _ {j}\\right) ^ {2}. \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.754, + 0.905, + 0.83 + ], + "angle": 0, + "content": "As we mainly concern with the predictions on the boundary, we only perform the loss locally for fast computation and memory efficiency, i.e., for pixel \\(i\\) the loss is calculated in its \\(5 \\times 5\\) neighborhoods \\(\\mathcal{N}_i\\). Finally, the overall training objective is" + }, + { + "type": "equation", + "bbox": [ + 0.612, + 0.85, + 0.903, + 0.868 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\mathcal {L} _ {\\text {p s e u d o}} + \\lambda \\cdot \\mathcal {L} _ {\\text {s m o o t h}}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.886, + 0.902, + 0.902 + ], + "angle": 0, + "content": "where \\(\\lambda\\) controls the strength of the smoothness constraint." + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "671" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.095, + 0.09, + 0.899, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.088, + 0.229, + 0.904, + 0.259 + ], + "angle": 0, + "content": "Figure 6. Comparison of IoU-NoC curve. The two dotted lines indicate the performance of supervised approaches. The proposed method achieves surprising performance that significantly exceeds traditional methods and is close to supervised method when the NoC increases." + }, + { + "type": "table", + "bbox": [ + 0.091, + 0.27, + 0.905, + 0.395 + ], + "angle": 0, + "content": "
Data RatioInitializationGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
1%Default (MAE [16])2.322.522.364.448.0110.435.818.28
MIS (Ours)1.54 (↓0.78)1.90 (↓0.62)1.95 (↓0.41)3.73 (↓0.71)5.57 (↓2.44)8.15 (↓2.28)5.36 (↓0.45)7.40 (↓0.88)
5%Default (MAE [16])1.682.221.973.645.488.135.147.23
(Ours)1.62 (↓0.06)1.88 (↓0.34)1.95 (↓0.02)3.32 (↓0.32)5.21 (↓0.27)7.49 (↓0.64)4.54 (↓0.60)6.11 (↓1.12)
10%Default (MAE [16])1.641.841.883.215.337.894.886.77
MIS (Ours)1.40 (↓0.24)1.50 (↓0.34)1.64 (↓0.24)2.73 (↓0.48)4.61 (↓0.72)6.95 (↓0.94)4.25 (↓0.63)5.94 (↓0.83)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.088, + 0.399, + 0.904, + 0.429 + ], + "angle": 0, + "content": "Table 2. Performance with limited annotations. When training the model in a supervised manner with a limited number of annotations (1%, 5%, 10%), the performance can be significantly improved by unsupervised pre-training using the proposed method." + }, + { + "type": "title", + "bbox": [ + 0.089, + 0.451, + 0.221, + 0.468 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.478, + 0.482, + 0.901 + ], + "angle": 0, + "content": "Implementation Details. We follow SimpleClick [26] to build the interactive segmentation model, which consists of two patch embedding modules for image and click map respectively, a ViT [10] backbone initialized with MAE [16], a simple feature pyramid [21], and an MLP segmentation head. For training, we optimize the model for 55 epochs using the Adam [18] optimizer with a learning rate of 5e-5, which decays by a factor of 10 at 50 epochs. The decay coefficient \\(\\alpha\\) in Algorithm 2 and the weight \\(\\lambda\\) in Equation (8) are 0.9 and 10.0, respectively. In addition, we set a threshold of 0.05 to filter small proposals. That is to say, we ignore the proposals whose areas are less than 0.05 times the image area. For inference, we set the threshold of binarizing the prediction to 0.5 as normal binary segmentation and use the same pre-processing as [26]. To ensure the fully unsupervised setting, we employ a self-supervisedly pre-trained model as the feature extractor. Specifically, a Vision Transformer (ViT) [10] trained with DINO [7] is adopted since the property of representing patch-level semantics [7, 13, 34]. We use ViT-Small [34] with a patch size of 8. The results with other models are included in the appendix. Before feeding an image into the ViT, we resize the image to make its height and width divisible by the patch size (i.e., the target height is \\((h + p - h \\mod p)\\) when the original height \\(h\\) is not divisible by the patch size \\(p\\)), and the position embedding is interpolated to fit the image size using bilinear interpolation. We finally use all output tokens of the last block except the \\(cls\\) token as the patch features." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.453, + 0.905, + 0.679 + ], + "angle": 0, + "content": "Evaluation. The evaluation is done under the standard evaluation protocol of click-based interactive segmentation. Specifically, we adopt the same click simulator as previous work [44, 17, 25, 35, 8, 36, 24, 9] to sample clicks when evaluation. Roughly, the next click will be placed at the center of the largest error region by comparing the ground-truth and prediction. We adopt the Number of Click (NoC) as the evaluation metric, which counts the average number of clicks needed to achieve a fixed Intersection over Union (IoU), the smaller the better. We use two commonly used target intersection-over-union (IoU) thresholds \\(85\\%\\) and \\(90\\%\\), denoted as NoC@85 and NoC@90 respectively. Additionally, the IoU-NoC curves are also adopted to represent the convergence trend of IoU when the NoC increases, as well as compare the IoU metric under the same NoC." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.684, + 0.907, + 0.835 + ], + "angle": 0, + "content": "Dataset. We evaluate the performance of our MIS on the following four benchmarks. (1) GradCut [32]: The dataset contains 50 relatively easy images whose background and foreground have a clear difference. (2) Berkeley [29]: The dataset contains 96 images with 100 instances and some of them are more challenging than GrabCut. (3) SBD [15]: The dataset contains 2,857 images with 6,671 challenging instances, which does not overlap with our training set. (4) DAVIS [31]: We follow previous works [24, 9, 27, 36, 26] and use the same 345 frames for evaluation." + }, + { + "type": "title", + "bbox": [ + 0.511, + 0.847, + 0.707, + 0.862 + ], + "angle": 0, + "content": "4.1. Quantitative Results" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.871, + 0.905, + 0.901 + ], + "angle": 0, + "content": "Baselines. Since the fully unsupervised interactive segmentation has not been explored by previous research, we in-" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "672" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.092, + 0.089, + 0.249, + 0.17 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.129, + 0.171, + 0.212, + 0.181 + ], + "angle": 0, + "content": "Ground-truth" + }, + { + "type": "image", + "bbox": [ + 0.255, + 0.089, + 0.413, + 0.17 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.285, + 0.171, + 0.384, + 0.181 + ], + "angle": 0, + "content": "1 click, IoU=0.83" + }, + { + "type": "image", + "bbox": [ + 0.418, + 0.089, + 0.576, + 0.17 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.444, + 0.171, + 0.551, + 0.181 + ], + "angle": 0, + "content": "2 clicks, IoU=0.85" + }, + { + "type": "image", + "bbox": [ + 0.582, + 0.089, + 0.74, + 0.17 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.61, + 0.171, + 0.712, + 0.182 + ], + "angle": 0, + "content": "3 click, IoU=0.87" + }, + { + "type": "image", + "bbox": [ + 0.746, + 0.089, + 0.904, + 0.17 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.774, + 0.171, + 0.875, + 0.182 + ], + "angle": 0, + "content": "4 click, IoU=0.90" + }, + { + "type": "image", + "bbox": [ + 0.092, + 0.184, + 0.249, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.129, + 0.267, + 0.212, + 0.277 + ], + "angle": 0, + "content": "Ground-truth" + }, + { + "type": "image", + "bbox": [ + 0.255, + 0.184, + 0.413, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.284, + 0.267, + 0.384, + 0.277 + ], + "angle": 0, + "content": "1 click, IoU=0.64" + }, + { + "type": "image", + "bbox": [ + 0.418, + 0.184, + 0.576, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.444, + 0.267, + 0.551, + 0.277 + ], + "angle": 0, + "content": "2 clicks, IoU=0.94" + }, + { + "type": "image", + "bbox": [ + 0.582, + 0.184, + 0.74, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.61, + 0.267, + 0.712, + 0.277 + ], + "angle": 0, + "content": "3 click, IoU=0.97" + }, + { + "type": "image", + "bbox": [ + 0.746, + 0.184, + 0.904, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.774, + 0.267, + 0.875, + 0.277 + ], + "angle": 0, + "content": "5 click, IoU=0.98" + }, + { + "type": "image", + "bbox": [ + 0.092, + 0.279, + 0.249, + 0.361 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.129, + 0.362, + 0.212, + 0.372 + ], + "angle": 0, + "content": "Ground-truth" + }, + { + "type": "image", + "bbox": [ + 0.255, + 0.279, + 0.413, + 0.361 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.283, + 0.362, + 0.385, + 0.372 + ], + "angle": 0, + "content": "1 click, IoU=0.66" + }, + { + "type": "image", + "bbox": [ + 0.418, + 0.279, + 0.576, + 0.361 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.444, + 0.362, + 0.551, + 0.372 + ], + "angle": 0, + "content": "2 clicks, IoU=0.87" + }, + { + "type": "image", + "bbox": [ + 0.582, + 0.279, + 0.74, + 0.361 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.61, + 0.362, + 0.712, + 0.372 + ], + "angle": 0, + "content": "3 click, IoU=0.94" + }, + { + "type": "image", + "bbox": [ + 0.746, + 0.279, + 0.904, + 0.361 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.774, + 0.362, + 0.875, + 0.372 + ], + "angle": 0, + "content": "5 click, IoU=0.96" + }, + { + "type": "image_caption", + "bbox": [ + 0.089, + 0.376, + 0.903, + 0.39 + ], + "angle": 0, + "content": "Figure 7. Visualization of the interaction and segmentation. The green and red points indicate positive and negative clicks respectively." + }, + { + "type": "table", + "bbox": [ + 0.091, + 0.402, + 0.905, + 0.523 + ], + "angle": 0, + "content": "
ValueGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Strength of the Smoothness Constraint λ
0.02.082.563.405.517.389.926.7810.08
3.02.02 (↓0.06)2.50 (↓0.06)3.07 (↓0.33)5.04 (↓0.47)6.84 (↓0.54)9.33 (↓0.59)6.32 (↓0.46)8.78 (↓1.30)
5.01.94 (↓0.14)2.34 (↓0.22)3.01 (↓0.39)4.71 (↓0.80)6.79 (↓0.59)9.39 (↓0.53)6.39 (↓0.39)8.55 (↓1.53)
10.01.94 (↓0.14)2.32 (↓0.24)3.09 (↓0.31)4.58 (↓0.93)6.91 (↓0.47)9.51 (↓0.41)6.33 (↓0.45)8.44 (↓1.64)
15.02.12 (↑0.04)2.50 (↓0.06)3.25 (↓0.15)5.13 (↓0.38)7.12 (↓0.26)9.85 (↓0.07)6.71 (↓0.07)9.10 (↓0.98)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.174, + 0.529, + 0.813, + 0.542 + ], + "angle": 0, + "content": "Table 3. Ablation on the smoothness constraint. The results demonstrate its effectiveness and robustness." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.559, + 0.483, + 0.667 + ], + "angle": 0, + "content": "produce some baselines which are originally designed for unsupervised salient detection (TokenCut [41]), instance segmentation (FreeMask [39]), and semantic segmentation (DSM [30]) to demonstrate the effectiveness of our method. We follow the official implementation of these baselines to extract mask proposals and use them to train the same model as ours. We denote these baselines by “\\(\\star\\)” in Table 1." + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.675, + 0.483, + 0.902 + ], + "angle": 0, + "content": "Comparison with Previous Work. For comparison, we present experimental results of previous supervised deep learning methods, non-deep learning methods, baselines, and the proposed MIS on four aforementioned datasets. Under the unsupervised setting, our method significantly outperforms all other methods as shown in the second part of Table 1. It is also worth mentioning that the proposed MIS achieves inspiring performance that is even comparable with some previous supervised approaches. This support that the interactive segmentation task can be solved in a more label-efficient way. Moreover, we show the IoU-NoC curve of previous interactive segmentation methods and MIS in Figure 6, where the dotted lines indicate the upper and lower performance of previous supervised methods. It can be found that our method reaches obviously higher" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.559, + 0.905, + 0.604 + ], + "angle": 0, + "content": "IoU compared to the non-deep learning methods, especially in the first few clicks, and gradually converge to the supervised counterpart when NoC increases." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.608, + 0.905, + 0.684 + ], + "angle": 0, + "content": "Comparison with Baselines. MIS also gets advanced results compared to the baselines which only focus on the specific granularity such as the most salient object or fixed number of objects, demonstrating the effectiveness of diverse interactions under the unsupervised setting." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.687, + 0.906, + 0.822 + ], + "angle": 0, + "content": "Supervised Fine-tuning. Besides the fully unsupervised setting, we further fine-tune our model in a supervised manner with only a limited number of annotations (1%, 5%, 10%). As shown in Table 2, the model initialized with MIS pre-training the MAE [16] counterpart especially on the relatively hard dataset (i.e., SBD and DAVIS). These results demonstrate that MIS can serve as a strong unsupervised pre-training method for interactive segmentation when the available annotations are rare." + }, + { + "type": "title", + "bbox": [ + 0.511, + 0.833, + 0.695, + 0.849 + ], + "angle": 0, + "content": "4.2. Qualitative Results" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.856, + 0.905, + 0.901 + ], + "angle": 0, + "content": "Multi-granularity Region Proposal. In Figure 5 we show the qualitative results of the region proposals generated by the baselines and our MIS, where different colors mean dif" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.512, + 0.957 + ], + "angle": 0, + "content": "673" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.09, + 0.089, + 0.905, + 0.196 + ], + "angle": 0, + "content": "
ValueGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Decay coefficient α
0.02.122.483.895.528.7110.877.849.92
0.81.94 (↓0.18)2.40 (↓0.08)3.08 (↓0.81)4.99 (↓0.53)7.03 (↓1.68)9.62 (↓1.25)6.36 (↓1.48)8.57 (↓1.35)
0.91.94 (↓0.18)2.32 (↓0.16)3.09 (↓0.80)4.58 (↓0.94)6.91 (↓1.80)9.51 (↓1.36)6.33 (↓1.51)8.44 (↓1.48)
0.952.22 (↑0.10)2.62 (↑0.14)3.19 (↓0.70)4.89 (↓0.63)6.91 (↓1.80)9.52 (↓1.35)6.09 (↓1.75)8.54 (↓1.38)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.088, + 0.199, + 0.905, + 0.229 + ], + "angle": 0, + "content": "Table 4. Ablation on top-down sampling. In the case of \\( \\alpha = 0 \\), only the two children of the root node are sampled and thus multi-granularity is not allowed. The results show the effectiveness of multi-granularity and the robustness of \\( \\alpha \\)." + }, + { + "type": "table", + "bbox": [ + 0.09, + 0.24, + 0.905, + 0.304 + ], + "angle": 0, + "content": "
SamplingGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Uniform3.844.324.426.207.119.957.7110.10
Top-down1.94 (↓1.90)2.32 (↓2.00)3.09 (↓1.33)4.58 (↓1.62)6.91 (↓0.20)9.51 (↓0.44)6.33 (↓1.38)8.44 (↓1.66)
" + }, + { + "type": "table_caption", + "bbox": [ + 0.088, + 0.307, + 0.905, + 0.339 + ], + "angle": 0, + "content": "Table 5. Ablation on sampling strategy. The proposed top-down sampling strategy is effective because it reasonably assigns different weights to fragmented and complete components, so as to sample complete objects as much as possible while maintaining diversity." + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.361, + 0.482, + 0.466 + ], + "angle": 0, + "content": "ferent mask proposals and our mask proposals. Compared with them, our multi-granularity proposals capture more informative regions and are more diverse. Through the top-down random sampling strategy, our proposals provide the model with rich interactions, which makes the model learn a better mapping from clicks to segmentation under the unsupervised setting." + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.471, + 0.483, + 0.624 + ], + "angle": 0, + "content": "Interactive Segmentation. Figure 7 show some interactive segmentation examples of our method. The trained interactive segmentation model is able to capture the outline of the needed object by the first one or two clicks and achieves high IoU with a few clicks, which demonstrates the feasibility of our newly proposed unsupervised setting and the effectiveness of the MIS. For some simple objects, our model can produce satisfactory predictions within the first few clicks. It can also handle complex scenes such as partially occluded objects and adjacent instances." + }, + { + "type": "title", + "bbox": [ + 0.088, + 0.632, + 0.245, + 0.648 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.655, + 0.483, + 0.761 + ], + "angle": 0, + "content": "Smoothness Constraint. For the smoothness constraint, we switch the weight \\(\\lambda\\) in Equation (8) to show its effectiveness. The experimental results in Table 3 demonstrate that the smoothness constraint is helpful for improving the performance through the principle that helps the model correct the boundary errors in the proposals. The effectiveness is robust when \\(\\lambda\\) is within a reason range." + }, + { + "type": "text", + "bbox": [ + 0.087, + 0.765, + 0.483, + 0.903 + ], + "angle": 0, + "content": "Top-down Sampling. The top-down sampling (Algorithm 2) is the core part of our MIS to achieve diversity. We evaluate its effectiveness by comparing with a fixed-granularity strategy, and a fully random strategy that randomly sample nodes on the merging tree from a uniform distribution. In Table 4, we take \\(\\alpha = 0.0\\) as the baseline. In this case, we always use one of the two children of the root node in the merging tree, thus multi-granularity is not allowed. Comparing the results with \\(\\alpha = 0.8, 0.9, 0.95\\) we" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.361, + 0.907, + 0.558 + ], + "angle": 0, + "content": "can find that the introduction of multi-granularity brings noticeable improvement, especially in the hard dataset. It is also obvious that this hyper-parameter is relatively robust. In addition, the results compared to the fully random sampling strategy in Table 5 also show clear advantages of our top-down sampling strategy. When sampling uniformly, the finely divided object components are more likely to be selected due to the large number, resulting in local perception and thus requiring more clicks to localize objects. In contrast, our top-down sampling strategy reasonably assigns different weights to fragmented and complete components, so as to sample complete objects as much as possible while maintaining diversity." + }, + { + "type": "title", + "bbox": [ + 0.511, + 0.569, + 0.633, + 0.585 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.595, + 0.907, + 0.821 + ], + "angle": 0, + "content": "In this work, we open up a promising direction for deep interactive segmentation that completely discards the dependence on manual annotations. While previous methods learn the interaction through object-oriented simulation with pixel-level annotations, we propose MIS and demonstrate the feasibility to simulate informative interaction with semantic-consistent regions discovered in an unsupervised manner. Inspiring experimental results show the effectiveness of our method and the potential to reduce the labor of creating annotation without cost via training an interactive segmentation model unsupervisedly. Our experiment also supports that the interactive segmentation task can be solved in a more label-efficient way to trade off the performance and annotations. We hope our exploration can promote the attendance of label efficiency on interactive segmentation." + }, + { + "type": "text", + "bbox": [ + 0.51, + 0.826, + 0.905, + 0.903 + ], + "angle": 0, + "content": "Acknowledgements. This work was supported by the National Key R&D Program of China (2022ZD0118101) and the Natural Science Foundation of China (No. 61972217, 32071459, 62176249, 62006133, 62271465, 62202014). Li Yuan is sponsored by CCF Tencent Open Research Fund." + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.945, + 0.513, + 0.958 + ], + "angle": 0, + "content": "674" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.091, + 0.091, + 0.186, + 0.105 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.099, + 0.116, + 0.482, + 0.198 + ], + "angle": 0, + "content": "[1] Devansh Arpit, Stanislaw Jastrzebski, Nicolas Ballas, David Krueger, Emmanuel Bengio, Maxinder S Kanwal, Tegan Maharaj, Asja Fischer, Aaron Courville, Yoshua Bengio, et al. A closer look at memorization in deep networks. In International Conference on Machine Learning, pages 233-242. PMLR, 2017. 6" + }, + { + "type": "ref_text", + "bbox": [ + 0.099, + 0.201, + 0.482, + 0.257 + ], + "angle": 0, + "content": "[2] Junjie Bai and Xiaodong Wu. Error-tolerant scribbles based interactive image segmentation. 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Typically, massive and expansive pixel-level annotations are spent to train deep models by object-oriented interactions with manually labeled object masks. In this work, we reveal that informative interactions can be made by simulation with semantic-consistent yet diverse region exploration in an unsupervised paradigm. Concretely, we introduce a Multi-granularity Interaction Simulation (MIS) approach to open up a promising direction for unsupervised interactive segmentation. Drawing on the high-quality dense features produced by recent self-supervised models, we propose to gradually merge patches or regions with similar features to form more extensive regions and thus, every merged region serves as a semantic-meaningful multi-granularity proposal. By randomly sampling these proposals and simulating possible interactions based on them, we provide meaningful interaction at multiple granularities to teach the model to understand interactions. Our MIS significantly outperforms non-deep learning unsupervised methods and is even comparable with some previous deep-supervised methods without any annotation. + +# 1. Introduction + +Interactive segmentation aims at obtaining high-quality object masks with limited user interaction, allowing users to segment objects as needed. During the development of interactive segmentation, various interactive forms like + +![](images/cc2cde48b7c72dbc6201c482075e442b96bbe46225e40293309a3362537d2fd7.jpg) +Figure 1. Top: To tackle the reliance on object annotations of previous interactive segmentation methods caused by interaction simulation, we propose Multi-granularity Interaction Simulation (MIS) that simulates interaction by meaningful regions at multiple granularities. Down: The model learns from MIS to successfully understand interactions and produce acceptable segmentation. + +bounding boxes [20, 32, 43], scribbles [2, 11, 22], and clicks [44, 17, 25, 35, 8, 36, 24, 9] have been explored. Among them, the click-based interaction becomes the mainstream due to its simplicity and well-established training and evaluation protocols. + +State-of-the-art methods for click-based interactive segmentation are based on deep learning, following the basic paradigm proposed by Xu et al. [44]. Specifically, these methods encode clicks to a distance map and adapt a semantic segmentation model (e.g., FCN [28]) to take the encoded click map as input, and then train the model with interaction-segmentation pairs. Since it is impractical to collect interaction sequences from real users, previous + +![](images/d82aa3c18385ca5ce1ef95e0aed1e9bbf43be75b4c89638ff749c1b456d0073b.jpg) +Figure 2. Illustration of the multi-granularity region proposal generation. For an input image, We first introduce a self-supervised ViT to produce semantic features for each patch of an image. We then gradually merge two similar patches or regions with similar features to perform a new region. All newly generated regions in the merging process constitute meaningful proposals at multiple granularities. + +methods adopt an interaction simulation strategy [44, 36] that randomly samples clicks based on object segmentation annotations. By training with the simulated clicks and corresponding object masks, the model is able to correctly understand user needs and segment objects with a few clicks, significantly outperforming non-deep learning methods. However, the requirement for a large number of expensive pixel-level annotations behind the powerful performance has been ignored by previous methods, which is derived from the object-level interaction simulation. + +In this work, we aim at exploring an annotation-free alternation for interaction simulation to eliminate the reliance on object annotations in interactive segmentation, namely unsupervised interactive segmentation. To achieve it, as shown in the top half of Figure 1, our basic idea is to switch previous object-oriented interaction simulation to some semantic-consistent regions, which can be discovered unsupervisedly. In this case, the model requires diverse examples to understand changeable interactions due to the lack of precise information about objects. + +Therefore, we propose Multi-granularity Interaction Simulation (MIS) to achieve diversity. To ensure the semantic consistency of a region, we first parse the semantic of patches in an image by a Vision Transformer (ViT) [10] pre-trained unsupervisedly with DINO [7]. As shown in Figure 2, we then gradually merge two patches or regions with similar features to form a more extensive region for an image, until only one region remains. In this process, the newly generated region in every step makes up semantic-meaningful multi-granularity proposals. The MIS is finally achieved by randomly sampling these proposals and simulating possible interactions based on them when training the model. Moreover, in order to help the model fight against the unsmoothness on the boundary of proposals caused by the feature extractor, we design a smoothness constraint that considers the low-level feature of pixels. With the meaningful interaction simulated at multiple granularities and the smoothness constraint, the model learns to understand clicks by related regions and produce an acceptable segmentation with several user interactions when inference, while completely discarding object annotations, as shown in the bottom half of Figure 1. + +We take the standard protocol [44] to evaluate our method on commonly used datasets including GrabCut [32], Berkeley [29], SBD [15], and DAVIS [31]. Benefiting from the rich interaction examples from our MIS, the trained model achieves inspiring performance. Specifically, it significantly outperforms non-deep learning methods under the premise of unsupervised setting, and even surpasses some early deep supervised methods. In addition, it can also perform as an unsupervised pre-training to improve the performance when only limited annotations are available. The surprising results support that the interactive segmentation task can be solved in a more label-efficient way. Moreover, we believe the proposed method can reduce the labeling costs in segmentation tasks by training an interactive segmentation model unsupervisedly and using it to efficiently make task-specific annotations as needed. + +# 2. Related Works + +Non-deep Learning Interactive Image Segmentation. Interactive segmentation has been an active field for over two decades due to its wide applications. Before the era of deep learning, the solutions are based on low-level features and optimization. One of the best-known methods is proposed by Boykov and Jolly [6], who define a graph to describe user-provided hard constraints and pixel relationship, then solve interactive segmentation by graph cut with max-flow algorithm [5]. After that, Rother et al. [32] augment graph cut by more powerful color data modeling and an iterative strategy. Other improved algorithms include random walk [11], geodesic distance [3], and star-convexity [12]. As early unsupervised interactive segmentation methods, these algorithms stuck when processing complex images due to the dependence on low-level features. Unlike their iterative optimization algorithms for input images, we distill user interactions, which are simulated from offline datasets with our method, into a deep neural network. By leveraging the large capabilities of the neural network, our method achieves significantly better performance than them. + +Deep Interactive Image Segmentation. Xu et al. [44] are the first to introduce deep learning on this task by extending FCN [28] with click map and click sampling strategies. + +![](images/00e7329cb0e8a191709e26c8811b3e674aceed08c67805672ec1c21f4dd9d451.jpg) +Figure 3. Illustration of our unsupervised framework to train an interactive segmentation model. For implementation, the MIS is composed of two stages. In the first pre-processing stage, we first parse the semantic of each patch in the image using a pre-trained ViT and take a gradual merging strategy to produce semantic-consistent region proposals at multiple granularities and save them efficiently with a tree structure. In the training stage, given an image, we randomly select proposals from the corresponding merging tree in a top-down manner and further simulate possible clicks based on them, thus providing the model informative interactions. + +![](images/44dcacbf7990d200a701e36df03affd96d68190905fed33ba0eac8ab83407877.jpg) + +Based on this pipeline, the researchers gradually increase the performance ceiling of deep learning methods by emphasizing the first click [25], online optimization [17, 35], diffusing prediction [8], edge-guided flow [14], iterative click sampling [36], powerful feature extractor [26], and Gaussian process posterior [45]. On the other hand, some works [24, 9] focus on efficiency and propose to segment on local crops to accelerate inference. Although the deep learning approaches achieve uplifting performance and efficiency, they require large-scale pixel-level annotations to train, which are expensive and laborious to obtain. Unlike previous works, we focus on the dependency on annotations and show that a fully unsupervised framework can also handle interactive segmentation task well. + +Unsupervised Image Segmentation. With the development of self-supervised and unsupervised learning, unsupervised methods for image segmentation task start to emerge. This work is also related to some unsupervised image segmentation methods based on the idea that extracting segments from a pre-trained high-quality dense feature extractor, (e.g., DenseCL [40], DINO [7]). For instance, Simeoni et al. [34] proposed a series of hand-made rules to choose pixels belonging to the same object according to their feature similarity. Wang et al. [41] introduce normalized cuts [33] on the affinity graph constructed by pixel-level representations from DINO to divide the foreground and background of an image. Hamilton et al. [13] train a segmentation head by distilling the feature correspondences from DINO. Melas et al. [30] adopt spectral decomposition on the affinity graph to discover meaningful parts in an image. For instance segmentation, FreeSOLO [39] design pseudo instance mask generation based on multi-scale feature correspondences from densely pre-trained models and train an instance segmentation model with these pseudo masks. Although the masks produced by these methods can + +serve as pseudo labels to train an interactive segmentation model unsupervisedly, only ordinary results are observed through our experiments in Section 4.1, which demonstrate that these task-specific designs is not apposite for interactive segmentation task. In contrast, we propose a novel strategy to discover semantic-consistent yet diverse regions to fit the interactive segmentation task. + +# 3. Method + +In this section, we introduce the overall framework to solve unsupervised interactive segmentation in detail. Macroscopically, we simulate informative interactions from the proposed Multi-granularity Interaction Simulation (MIS) to train an interactive segmentation model. For implementation, the MIS is composed of two stages, as shown in Figure 3. In the first pre-processing stage, we first parse the semantic of each patch in the image using a ViT [10] trained self-supervisedly with DINO [7], which has been proven to produce high-quality dense semantic features [34, 13, 30]. With these features, we take a gradual merging strategy to produce semantic-consistent region proposals at multiple granularities and save them efficiently with a tree structure. In the training stage, given an image, we randomly select proposals from the corresponding merging tree in a top-down manner and further simulate possible clicks based on them, thus providing the model informative interactions for learning to understand interactions during the training process. + +For training, the model is optimized by the provided interactions, which include meaningful regions and clicks. Specifically, it takes the image and clicks as input and is optimized to produce similar segmentation as the region. Moreover, we design a smoothness constraint when optimizing, for the purpose of mitigating the misleading brought by the inaccurate boundary of the region, which + +![](images/c287f084a63be29948a920dfcf1c57a4387eabf374e1f3d26383739522a0a695.jpg) +Figure 4. Illustration of the cost of merging. The points represent patch features and the circles denote regions that consist of the patches surrounded by it. Merging two regions into one leads to a more divergent cluster and the total SSE increases, thus the cost of merging can be measured as this increment. + +is caused by the down-sampling in the ViT. The details of MIS and the training objective are described as follows. + +# 3.1. Multi-granularity Interaction Simulation + +Bottom-up Merging. At the core of our MIS is to discover semantic-consistent yet diverse regions, which is achieved efficiently by gradually merging. In the beginning, we produce high-quality semantic features from a ViT [10] trained in a self-supervised manner with DINO [7] to measure the semantic similarity and ensure the semantic-consistency of generated region proposals. In the ViT, an image $\boldsymbol{I} \in \mathbb{R}^{h \times w \times 3}$ is divided to non-overlapping $n = \frac{h}{s} \times \frac{w}{s}$ patches with stride $s$ , which are then processed by some Transformer [38] encoder layers. The patch features $\boldsymbol{F} \in \mathbb{R}^{n \times c}$ are obtained from the last layer of the ViT, where $c$ is the feature dimension. With the patch features, we implement the hierarchical merging process by Algorithm 1 and finally get a tree $T$ which records every merge process. + +Initially, $n$ patches form as $n$ leaf nodes of the tree, and a set $\mathbb{S}$ is maintained for saving unmerged nodes, which initially contains all the leaf nodes. In each iteration, the two unmerged nodes with the least cost according to their features will be merged to form a new node, until only one unmerged node remains. Thus, there should be totally $n - 1$ iterations, and the index of the newly generated node in $k$ -th iteration is $n + k$ . Moreover, considering the prior that parts belonging to the same object are usually adjacent, we add connectivity constraints when merging to greatly accelerate the search space for finding the minimum cost. Specifically, each patch is only connected to its four adjacent patches and two regions are connected only if at least a pair of patches from them respectively are connected. + +We follow Ward's method [42] to measure the cost of merging, which minimizes the increment in the total within-cluster sum of squared error (SSE) after merging, as shown in Figure 4. Regarding a region $A$ as a cluster that contains some patches, the SSE is defined as + +$$ +e _ {A} = \sum_ {i \in A} \left\| \boldsymbol {F} _ {i} - \boldsymbol {\mu} _ {A} \right\| ^ {2}, \tag {1} +$$ + +Algorithm 1: Bottom-up Merging +Input: Patch features $\pmb{F} \in \mathbb{R}^{n \times c}$ +Output: Merge tree $\pmb{T} \in \mathbb{Z}^{(n-1) \times 2}$ +1 Initialization: $\mathbb{S} \gets \{1, 2, \dots, n\}$ +2 for $k \gets 1$ to $n-1$ do +3 $\begin{array}{c} i,j \gets \operatorname{arg min} \operatorname{Cost}(i,j,\pmb{F}) \text{s.t. Connect}(i,j); \\ T_{k,:} \gets (i,j); \\ \mathbb{S} \gets \complement_{\mathbb{S}}\{i,j\} \cup \{n+k\}; \end{array}$ +4 +5 +6 end + +Algorithm 2: Top-down Sampling +Input : Merge tree $T$ , decay coefficient $\alpha$ Output: Node index $k$ +1 Initialization: $p\gets 1.0$ $k\gets n - 1$ +2 while Rand() $< p$ and $k > 0$ do +3 if Rand() $< 0.5$ then +4 $\mid k\gets T_{k,0} - n;$ +5 else +6 $\mid k\gets T_{k,1} - n;$ +7 end +8 $p\gets \alpha \cdot p$ +9 end +10 $k\gets k + n$ + +where $\pmb{\mu}_A\in \mathbb{R}^c$ is the center, which can be computed as + +$$ +\boldsymbol {\mu} _ {A} = \frac {1}{s _ {A}} \sum_ {i \in A} \boldsymbol {F} _ {i}, \tag {2} +$$ + +where $s_A$ is the number of patches within $A$ . When merging two regions, the new center is + +$$ +\boldsymbol {\mu} _ {A \cup B} = \frac {s _ {A} \boldsymbol {\mu} _ {A} + s _ {B} \boldsymbol {\mu} _ {B}}{s _ {A} + s _ {B}}. \tag {3} +$$ + +Then the cost of merging is defined as the difference of SSE before and after merging. Since the SSE of all clusters except the clusters being merged are unchanged, it can be formulated as + +$$ +\begin{array}{l} \operatorname {C o s t} (A, B) = e _ {A \cup B} - \left(e _ {A} + e _ {B}\right) \\ = \frac {s _ {A} \cdot s _ {B}}{s _ {A} + s _ {B}} \left\| \boldsymbol {\mu} _ {A} - \boldsymbol {\mu} _ {B} \right\| ^ {2}. \tag {4} \\ \end{array} +$$ + +Detailed derivation is shown in the appendix. + +During the merging process, the center $\mu$ and the size $s$ of each region are recorded. Initially, the size is set to 1 for each patch and the center is its feature. The detailed calculation after each merging is as follows: (1) Computing the center of the newly generated region according to Equation (3). (2) Computing the size of the newly generated region as $s_{A\cup B} = s_A + s_B$ . (3) Computing the cost of + +![](images/d58aa97a31a6adb77281774482694519d0806ecd7a68ea3ed3ab7e618cdd44f2.jpg) + +![](images/6c761617d25866dae47a11451197e241a0fe143d19986f6c11f9417b0dc2c459.jpg) + +![](images/b07cef998e238ac0960e4c8d8ea2b0f8552b3f9627fee677ecf2daa6e1010bc5.jpg) + +![](images/666d1914842c61e9d6bddcb9bd3a584a0bfdf40ed156b0efaa7abc3e9c21075d.jpg) + +![](images/ad30728a39a67ef55f56411111fb5b52503af652337a9dd7582ce561912bffc4.jpg) + +![](images/68b616ea8673792b4b65c6f261d026da5bd084b445eafed05f826c98b742c0e7.jpg) + +![](images/d4e866a6af1c21edecc2897c202fa043b67cedafde5e31aed6bafbf51939d88a.jpg) + +![](images/77ab836dc197f6945425062c9a9ce7531e96416d46563246e90f616f77672cca.jpg) + +![](images/4fa9b51daeee02580531e6ddb1732880020f68f84327e0695ab88e2611d23bd5.jpg) + +![](images/a7605f75e08c8a501250c2945fe7f27236baa2a89ccdd60e8b77a6c53d1c4b2c.jpg) + +![](images/000a610ad15c7a08bf0f74a7f9f22ae525ca7c7c157f2f0fe3a51ee297f3ce0a.jpg) + +![](images/b004500b4d88f43e9fc102a145430a9da78b534da1f46f08f85b38c63138a28b.jpg) + +![](images/eafda1f81865be089345cb1af5669e5f2d0f17706a3c4096eb2d91029727f741.jpg) + +![](images/dc0fc2631fa28a21971faabd7e6adf081f3800cc3b919c0a1495177a7108f925.jpg) + +![](images/b7e22fb3fdd4a0bed717821b4dd83a63092a6df312f244d44361f2a1c1db6fee.jpg) +Image + +![](images/af7dfcad6411d754e30838283f780456b378bdb7e96b816f402f9d617d6f31c2.jpg) +TokenCut + +![](images/f6c5e07b9648280eab342d3b77d7b63cddae51ec466b01077e9f3574394730bb.jpg) +FreeMask +Figure 5. Qualitative results of discovered regions for the baselines and our MIS. While the baselines only focus on some salient regions in a fixed granularity, our MIS produces semantic-consistent regions at multiple granularities thus catching more objects and parts. + +![](images/912b848861a0ad7caa4d05968fa3b4b37e95a5c00c1029ed61d721288957ee1a.jpg) +DSM + +![](images/dab54f4ebe0eb13d030b24b0db8968bfa9e9a3f12fc7629f9988258307574ec0.jpg) +Our multi-granularity proposals + +![](images/e59ad0e75ac1e135f9a6ebf879adf69efda595cd8e7530c2a9a3d244f1b809a0.jpg) + +![](images/06ca923ff11ac4ee1c8e5fa7394c8cbc646b1d68a438f0c52b09baa3c70fd495.jpg) + +merging newly generated regions with other regions according to Equation (4). Since the other regions are not changed, the cost between them remains the same. + +After $n - 1$ iterations, we get a tree structure that is stored by a matrix $T \in \mathbb{Z}^{(n - 1)\times 2}$ , where the $i$ -th row is the indices of the two children of the $i + n$ node. In the tree, each node represents a merge and also represents a region proposal which consists of all patches within the subtree rooted at this node. Hence, with this hierarchical relationship, we obtain $n - 1$ region proposals at multiple granularities for each image, which help the interactive segmentation model to learn various interactions. For storage, there is no need to store all the $n - 1$ masks but only the tree structure, that is, the matrix $T$ , which makes it more space-efficient. + +Top-down Sampling. When training, the MIS is worked based on the stored merging tree. Specifically, when sampling an image for training, we select a mask proposal from its corresponding merging tree for simulating an interaction. In the merging tree, shallow nodes correspond to relatively complete parts or their combinations and deeper nodes are more relevant to finely divided parts. Intuitively, we prefer the complete one while maintaining diversity. Therefore, we design a sampling strategy in a top-down manner and gradually decrease the probability to go deeper, as shown in Algorithm 2. Concretely, we start at the root node (i.e., the node with an index of $2n - 1$ ) and the probability $p = 1.0$ . Then in each iteration, we choose to go deeper or stop with probability $p$ , and decrease $p$ with a coefficient $\alpha$ . The loop will terminate when choosing to stop or reach a leaf node (i.e., nodes whose index is less than or equal to $n$ ). If it is decided to go deeper, we randomly move the current node to one of its children. Finally, we get the index of a node $k$ corresponding to a region proposal, where the patches in the sub-tree rooted at $k$ are annotated as foreground. + +Click Sampling. With the sampled region, the last step is to simulate possible clicks according to the region. Drawing on the experience of previous methods, we use a combination of random and iterative click simulation strategies to produce a click map following RITM [36]. Specifically, some positive and negative clicks are first generated in parallel according to the foreground and background defined by the region. Then some additional clicks are appended by checking the erroneous region of the prediction which is produced by previous clicks. Finally, the MIS generates complete interactions which consist of a segmentation target and corresponding clicks. + +# 3.2. Training + +Interactive Segmentation Model. Typical interactive segmentation models are built based on semantic segmentation models (e.g., FCN [28]) by taking an additional click map as input, which is transformed from the coordinate of clicks. Formulically, given an image $\pmb{I} \in \mathbb{R}^{h \times w \times 3}$ , a click map $D \in \mathbb{R}^{h \times w \times 2}$ which presents positive and negative clicks respectively, and previous prediction $B \in \{0,1\}^{h \times w}$ , the model $\mathcal{F}(\cdot)$ outputs the probability of being foreground for each pixel + +$$ +\boldsymbol {Q} = \mathcal {F} (\operatorname {F u s i o n} (\boldsymbol {I}, \boldsymbol {D}, \boldsymbol {B})) \text {,} \boldsymbol {Q} \in [ 0, 1 ] ^ {h \times w}, \tag {5} +$$ + +where $\mathrm{Fusion}(\cdot)$ is some kind of fusion operation such as concatenate. Through training, the model learns to map the image and the user clicks to foreground and background segmentation thus can be used interactively when inference. + +Training with Proposals. Under our unsupervised setting, the model learns this mapping by the simulated interactions from the MIS. The model is first learned by the supervision from the multi-granularity region proposals $M$ by optimiz + +
MethodBackboneGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Deep Supervised Methods
DIOS w/o GC [44] CVPR16FCN8.0212.59--14.3016.7912.5217.11
DIOS w/ GC [44] CVPR16FCN5.086.08--9.2212.809.0312.58
LD [23] CVPR18VGG-193.204.79--7.4110.785.059.57
BRS [17] CVPR19DenseNet2.603.60-5.086.599.785.588.24
f-BRS [35] CVPR20ResNet-1012.302.72-4.574.817.735.047.41
FCA-Net [25] CVPR20ResNet-101-2.08-3.92---7.57
IA+SA [19] ECCV20ConvNet-3.07-4.94--5.16-
CDNet [8] ICCV21ResNet-341.862.181.953.275.187.895.006.89
RITM [36] ICIP22HRNet-181.762.041.873.223.395.434.946.71
FocalClick [9] CVPR22MiT-B01.661.90-3.144.346.515.027.06
FocusCut [24] CVPR22ResNet-1011.461.641.813.013.405.314.856.22
PseudoClick [27] ECCV22HRNet-32-1.84-2.98-5.614.746.16
SimpleClick [26] arXiv22ViT-B1.401.541.442.463.285.244.105.48
Non-deep Learning Methods
GraphCut [6] ICCV01N/A7.9810.00-14.2213.6015.9615.1317.41
Random Walk [11] TPAMI06N/A11.3613.77-14.0212.2215.0416.7118.31
Geodesic Matting [3] IJCV09N/A13.3214.57-15.9615.3617.6018.5919.50
GSC [12] CVPR10N/A7.109.12-12.5712.6915.3115.3517.52
ESC [12] CVPR10N/A7.249.20-12.1112.2114.8615.4117.70
Deep Unsupervised Methods
TokenCut* [41] CVPR22ViT-B3.045.746.309.9710.8213.1610.5615.01
FreeMask* [39] CVPR22ViT-B4.066.105.559.028.6112.018.2613.05
DSM* [30] CVPR22ViT-B3.644.645.497.758.5911.577.0810.11
MIS w/o Lsmooth (Ours)ViT-B2.082.563.405.517.389.926.7810.08
MIS (Ours)ViT-B1.942.323.094.586.919.516.338.44
+ +Table 1. Comparison with previous methods and baselines on four interactive segmentation benchmarks. $\star$ denotes baselines that we introduce from other unsupervised tasks. From top to bottom we show the previous deep supervised method, unsupervised non-deep learning method, and our newly proposed deep unsupervised method. All models listed here are trained on SBD dataset. Our MIS achieves superior performance within unsupervised methods and baselines and even exceeds early deep supervised methods (denoted by underline). + +ing the objective + +$$ +\mathcal {L} _ {\text {p s e u d o}} = \operatorname {B C E} (M, Q), \tag {6} +$$ + +where $\mathrm{BCE}(\cdot)$ denotes the binary cross entropy loss. Although the region proposals generated by the MIS contains semantics, the possible inaccuracy of the self-supervised feature extractor and the patching process in the ViT will bring some inaccurate part. Fortunately, as discovered by previous research [1] that the model tends to learn effect patterns rather than memorize the noise, we find that the model can learn to correctly map clicks to segmentation after training with these simulated interactions. + +Smoothness Constraint. In order to help the model correct the error caused by patching, we propose a smoothness constraint. We first introduce the bilateral affinity matrix [37, 4] $W$ which presents the affinity of pixels based on their low-level feature and the item $W_{i,j}$ is + +$$ +e x p (- \frac {| | \pmb {a} _ {i} ^ {x y} - \pmb {a} _ {j} ^ {x y} | | ^ {2}}{2 \sigma_ {x y} ^ {2}} - \frac {(a _ {i} ^ {l} - a _ {j} ^ {l}) ^ {2}}{2 \sigma_ {l} ^ {2}} - \frac {| | \pmb {a} _ {i} ^ {u v} - \pmb {a} _ {j} ^ {u v} | | ^ {2}}{2 \sigma_ {u v} ^ {2}}), +$$ + +where $\pmb{a}_i$ is a pixel with a spatial position $(p_i^x, p_i^y)$ and color $(p_i^l, p_i^u, p_i^v)$ and $\sigma_{xy}, \sigma_l, \sigma_{uv}$ control the extent of the spatial, luma, and chroma support of the filter. Motivated by the bilateral solver [4], the smooth constraint is implemented by restricting the model to produce consistent predictions on pixels with high bilateral affinity, which is formulated as + +$$ +\mathcal {L} _ {\text {s m o o t h}} = \sum_ {i} \frac {1}{| \mathcal {N} _ {i} |} \sum_ {j \in \mathcal {N} _ {i}} \boldsymbol {W} _ {i j} \cdot \left(\boldsymbol {Q} _ {i} - \boldsymbol {Q} _ {j}\right) ^ {2}. \tag {7} +$$ + +As we mainly concern with the predictions on the boundary, we only perform the loss locally for fast computation and memory efficiency, i.e., for pixel $i$ the loss is calculated in its $5 \times 5$ neighborhoods $\mathcal{N}_i$ . Finally, the overall training objective is + +$$ +\mathcal {L} = \mathcal {L} _ {\text {p s e u d o}} + \lambda \cdot \mathcal {L} _ {\text {s m o o t h}}, \tag {8} +$$ + +where $\lambda$ controls the strength of the smoothness constraint. + +![](images/afcc4c36e10e3019e8e81d4c4b53d40cc462d4e2bbc34ceccfde3085f4109f0a.jpg) +Figure 6. Comparison of IoU-NoC curve. The two dotted lines indicate the performance of supervised approaches. The proposed method achieves surprising performance that significantly exceeds traditional methods and is close to supervised method when the NoC increases. + +
Data RatioInitializationGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
1%Default (MAE [16])2.322.522.364.448.0110.435.818.28
MIS (Ours)1.54 (↓0.78)1.90 (↓0.62)1.95 (↓0.41)3.73 (↓0.71)5.57 (↓2.44)8.15 (↓2.28)5.36 (↓0.45)7.40 (↓0.88)
5%Default (MAE [16])1.682.221.973.645.488.135.147.23
(Ours)1.62 (↓0.06)1.88 (↓0.34)1.95 (↓0.02)3.32 (↓0.32)5.21 (↓0.27)7.49 (↓0.64)4.54 (↓0.60)6.11 (↓1.12)
10%Default (MAE [16])1.641.841.883.215.337.894.886.77
MIS (Ours)1.40 (↓0.24)1.50 (↓0.34)1.64 (↓0.24)2.73 (↓0.48)4.61 (↓0.72)6.95 (↓0.94)4.25 (↓0.63)5.94 (↓0.83)
+ +Table 2. Performance with limited annotations. When training the model in a supervised manner with a limited number of annotations (1%, 5%, 10%), the performance can be significantly improved by unsupervised pre-training using the proposed method. + +# 4. Experiments + +Implementation Details. We follow SimpleClick [26] to build the interactive segmentation model, which consists of two patch embedding modules for image and click map respectively, a ViT [10] backbone initialized with MAE [16], a simple feature pyramid [21], and an MLP segmentation head. For training, we optimize the model for 55 epochs using the Adam [18] optimizer with a learning rate of 5e-5, which decays by a factor of 10 at 50 epochs. The decay coefficient $\alpha$ in Algorithm 2 and the weight $\lambda$ in Equation (8) are 0.9 and 10.0, respectively. In addition, we set a threshold of 0.05 to filter small proposals. That is to say, we ignore the proposals whose areas are less than 0.05 times the image area. For inference, we set the threshold of binarizing the prediction to 0.5 as normal binary segmentation and use the same pre-processing as [26]. To ensure the fully unsupervised setting, we employ a self-supervisedly pre-trained model as the feature extractor. Specifically, a Vision Transformer (ViT) [10] trained with DINO [7] is adopted since the property of representing patch-level semantics [7, 13, 34]. We use ViT-Small [34] with a patch size of 8. The results with other models are included in the appendix. Before feeding an image into the ViT, we resize the image to make its height and width divisible by the patch size (i.e., the target height is $(h + p - h \mod p)$ when the original height $h$ is not divisible by the patch size $p$ ), and the position embedding is interpolated to fit the image size using bilinear interpolation. We finally use all output tokens of the last block except the $cls$ token as the patch features. + +Evaluation. The evaluation is done under the standard evaluation protocol of click-based interactive segmentation. Specifically, we adopt the same click simulator as previous work [44, 17, 25, 35, 8, 36, 24, 9] to sample clicks when evaluation. Roughly, the next click will be placed at the center of the largest error region by comparing the ground-truth and prediction. We adopt the Number of Click (NoC) as the evaluation metric, which counts the average number of clicks needed to achieve a fixed Intersection over Union (IoU), the smaller the better. We use two commonly used target intersection-over-union (IoU) thresholds $85\%$ and $90\%$ , denoted as NoC@85 and NoC@90 respectively. Additionally, the IoU-NoC curves are also adopted to represent the convergence trend of IoU when the NoC increases, as well as compare the IoU metric under the same NoC. + +Dataset. We evaluate the performance of our MIS on the following four benchmarks. (1) GradCut [32]: The dataset contains 50 relatively easy images whose background and foreground have a clear difference. (2) Berkeley [29]: The dataset contains 96 images with 100 instances and some of them are more challenging than GrabCut. (3) SBD [15]: The dataset contains 2,857 images with 6,671 challenging instances, which does not overlap with our training set. (4) DAVIS [31]: We follow previous works [24, 9, 27, 36, 26] and use the same 345 frames for evaluation. + +# 4.1. Quantitative Results + +Baselines. Since the fully unsupervised interactive segmentation has not been explored by previous research, we in- + +![](images/151d0ce19bdf328f8bcbe29d95d0aea2b7e1f9d2f996be0ce8d6df160bfce76c.jpg) +Ground-truth + +![](images/53a0bc4461a1326b12f94dbbfad2f22e9ce3611c3d1730d296545e6518c37899.jpg) +1 click, IoU=0.83 + +![](images/a72d786a0e6da17859accde6904019a366ba607a0d96ba84b7cb7adac6dbea49.jpg) +2 clicks, IoU=0.85 + +![](images/365fff7e0b717e475b17f33153d4864efa100f4eef69200fd18efed96983e0f6.jpg) +3 click, IoU=0.87 + +![](images/54c64de39febb0fc61cde1a7075c5a7b2b7fd4ef44e19e342c425ac7c5ce5090.jpg) +4 click, IoU=0.90 + +![](images/f758256761b814df8eb4e61b4aea538143b4966183dcff2e0bcfe8a522fc206a.jpg) +Ground-truth + +![](images/b40a6af71d52d90bde379dfcc23142247a98737bb5cca66ef71f131e549fd4f2.jpg) +1 click, IoU=0.64 + +![](images/2aa631a08745fe12d66def7cefbf81b2155baa8224195a7d8cca871ec5247744.jpg) +2 clicks, IoU=0.94 + +![](images/49d19041bead7b98109287ef00d93e0ac24202647d3854390ce0f9321ce40232.jpg) +3 click, IoU=0.97 + +![](images/2c7fa2cc2bc66f9846b5694b2f64e398604b29d9697f34dce09bb32714399c2c.jpg) +5 click, IoU=0.98 + +![](images/617ad7e204ec840a9d2618e0029e1c17b44662412e373f75c7a143acad3d772c.jpg) +Ground-truth + +![](images/8bc934f23f5f3ea842727c9af4e301a287b4c8fa96a7c932613ce9cd245d20f6.jpg) +1 click, IoU=0.66 + +![](images/a23eaa68dc5757a318837d15b17a82a5243d140fae1768da91bb456945d1b618.jpg) +2 clicks, IoU=0.87 +Figure 7. Visualization of the interaction and segmentation. The green and red points indicate positive and negative clicks respectively. + +![](images/f92a724ce218f0e879a83796296f8e864401f6e41cd391cabfc08920dba4f38f.jpg) +3 click, IoU=0.94 + +![](images/31ff22557bd0763e8421a50981ad379bbbdb7c89519a3357d0a480a07eee5733.jpg) +5 click, IoU=0.96 + +
ValueGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Strength of the Smoothness Constraint λ
0.02.082.563.405.517.389.926.7810.08
3.02.02 (↓0.06)2.50 (↓0.06)3.07 (↓0.33)5.04 (↓0.47)6.84 (↓0.54)9.33 (↓0.59)6.32 (↓0.46)8.78 (↓1.30)
5.01.94 (↓0.14)2.34 (↓0.22)3.01 (↓0.39)4.71 (↓0.80)6.79 (↓0.59)9.39 (↓0.53)6.39 (↓0.39)8.55 (↓1.53)
10.01.94 (↓0.14)2.32 (↓0.24)3.09 (↓0.31)4.58 (↓0.93)6.91 (↓0.47)9.51 (↓0.41)6.33 (↓0.45)8.44 (↓1.64)
15.02.12 (↑0.04)2.50 (↓0.06)3.25 (↓0.15)5.13 (↓0.38)7.12 (↓0.26)9.85 (↓0.07)6.71 (↓0.07)9.10 (↓0.98)
+ +Table 3. Ablation on the smoothness constraint. The results demonstrate its effectiveness and robustness. + +produce some baselines which are originally designed for unsupervised salient detection (TokenCut [41]), instance segmentation (FreeMask [39]), and semantic segmentation (DSM [30]) to demonstrate the effectiveness of our method. We follow the official implementation of these baselines to extract mask proposals and use them to train the same model as ours. We denote these baselines by “ $\star$ ” in Table 1. + +Comparison with Previous Work. For comparison, we present experimental results of previous supervised deep learning methods, non-deep learning methods, baselines, and the proposed MIS on four aforementioned datasets. Under the unsupervised setting, our method significantly outperforms all other methods as shown in the second part of Table 1. It is also worth mentioning that the proposed MIS achieves inspiring performance that is even comparable with some previous supervised approaches. This support that the interactive segmentation task can be solved in a more label-efficient way. Moreover, we show the IoU-NoC curve of previous interactive segmentation methods and MIS in Figure 6, where the dotted lines indicate the upper and lower performance of previous supervised methods. It can be found that our method reaches obviously higher + +IoU compared to the non-deep learning methods, especially in the first few clicks, and gradually converge to the supervised counterpart when NoC increases. + +Comparison with Baselines. MIS also gets advanced results compared to the baselines which only focus on the specific granularity such as the most salient object or fixed number of objects, demonstrating the effectiveness of diverse interactions under the unsupervised setting. + +Supervised Fine-tuning. Besides the fully unsupervised setting, we further fine-tune our model in a supervised manner with only a limited number of annotations (1%, 5%, 10%). As shown in Table 2, the model initialized with MIS pre-training the MAE [16] counterpart especially on the relatively hard dataset (i.e., SBD and DAVIS). These results demonstrate that MIS can serve as a strong unsupervised pre-training method for interactive segmentation when the available annotations are rare. + +# 4.2. Qualitative Results + +Multi-granularity Region Proposal. In Figure 5 we show the qualitative results of the region proposals generated by the baselines and our MIS, where different colors mean dif + +
ValueGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Decay coefficient α
0.02.122.483.895.528.7110.877.849.92
0.81.94 (↓0.18)2.40 (↓0.08)3.08 (↓0.81)4.99 (↓0.53)7.03 (↓1.68)9.62 (↓1.25)6.36 (↓1.48)8.57 (↓1.35)
0.91.94 (↓0.18)2.32 (↓0.16)3.09 (↓0.80)4.58 (↓0.94)6.91 (↓1.80)9.51 (↓1.36)6.33 (↓1.51)8.44 (↓1.48)
0.952.22 (↑0.10)2.62 (↑0.14)3.19 (↓0.70)4.89 (↓0.63)6.91 (↓1.80)9.52 (↓1.35)6.09 (↓1.75)8.54 (↓1.38)
+ +Table 4. Ablation on top-down sampling. In the case of $\alpha = 0$ , only the two children of the root node are sampled and thus multi-granularity is not allowed. The results show the effectiveness of multi-granularity and the robustness of $\alpha$ . + +
SamplingGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Uniform3.844.324.426.207.119.957.7110.10
Top-down1.94 (↓1.90)2.32 (↓2.00)3.09 (↓1.33)4.58 (↓1.62)6.91 (↓0.20)9.51 (↓0.44)6.33 (↓1.38)8.44 (↓1.66)
+ +Table 5. Ablation on sampling strategy. The proposed top-down sampling strategy is effective because it reasonably assigns different weights to fragmented and complete components, so as to sample complete objects as much as possible while maintaining diversity. + +ferent mask proposals and our mask proposals. Compared with them, our multi-granularity proposals capture more informative regions and are more diverse. Through the top-down random sampling strategy, our proposals provide the model with rich interactions, which makes the model learn a better mapping from clicks to segmentation under the unsupervised setting. + +Interactive Segmentation. Figure 7 show some interactive segmentation examples of our method. The trained interactive segmentation model is able to capture the outline of the needed object by the first one or two clicks and achieves high IoU with a few clicks, which demonstrates the feasibility of our newly proposed unsupervised setting and the effectiveness of the MIS. For some simple objects, our model can produce satisfactory predictions within the first few clicks. It can also handle complex scenes such as partially occluded objects and adjacent instances. + +# 4.3. Ablation Study + +Smoothness Constraint. For the smoothness constraint, we switch the weight $\lambda$ in Equation (8) to show its effectiveness. The experimental results in Table 3 demonstrate that the smoothness constraint is helpful for improving the performance through the principle that helps the model correct the boundary errors in the proposals. The effectiveness is robust when $\lambda$ is within a reason range. + +Top-down Sampling. The top-down sampling (Algorithm 2) is the core part of our MIS to achieve diversity. We evaluate its effectiveness by comparing with a fixed-granularity strategy, and a fully random strategy that randomly sample nodes on the merging tree from a uniform distribution. In Table 4, we take $\alpha = 0.0$ as the baseline. In this case, we always use one of the two children of the root node in the merging tree, thus multi-granularity is not allowed. Comparing the results with $\alpha = 0.8, 0.9, 0.95$ we + +can find that the introduction of multi-granularity brings noticeable improvement, especially in the hard dataset. It is also obvious that this hyper-parameter is relatively robust. In addition, the results compared to the fully random sampling strategy in Table 5 also show clear advantages of our top-down sampling strategy. When sampling uniformly, the finely divided object components are more likely to be selected due to the large number, resulting in local perception and thus requiring more clicks to localize objects. In contrast, our top-down sampling strategy reasonably assigns different weights to fragmented and complete components, so as to sample complete objects as much as possible while maintaining diversity. + +# 5. Conclusion + +In this work, we open up a promising direction for deep interactive segmentation that completely discards the dependence on manual annotations. While previous methods learn the interaction through object-oriented simulation with pixel-level annotations, we propose MIS and demonstrate the feasibility to simulate informative interaction with semantic-consistent regions discovered in an unsupervised manner. Inspiring experimental results show the effectiveness of our method and the potential to reduce the labor of creating annotation without cost via training an interactive segmentation model unsupervisedly. Our experiment also supports that the interactive segmentation task can be solved in a more label-efficient way to trade off the performance and annotations. We hope our exploration can promote the attendance of label efficiency on interactive segmentation. + +Acknowledgements. This work was supported by the National Key R&D Program of China (2022ZD0118101) and the Natural Science Foundation of China (No. 61972217, 32071459, 62176249, 62006133, 62271465, 62202014). Li Yuan is sponsored by CCF Tencent Open Research Fund. + +# References + +[1] Devansh Arpit, Stanislaw Jastrzebski, Nicolas Ballas, David Krueger, Emmanuel Bengio, Maxinder S Kanwal, Tegan Maharaj, Asja Fischer, Aaron Courville, Yoshua Bengio, et al. A closer look at memorization in deep networks. 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such as image editing and medical image analysis. Typically, massive and expansive pixel-level annotations are spent to train deep models by object-oriented interactions with manually labeled object masks. In this work, we reveal that informative interactions can be made by simulation with semantic-consistent yet diverse region exploration in an unsupervised paradigm. Concretely, we introduce a Multi-granularity Interaction Simulation (MIS) approach to open up a promising direction for unsupervised interactive segmentation. Drawing on the high-quality dense features produced by recent self-supervised models, we propose to gradually merge patches or regions with similar features to form more extensive regions and thus, every merged region serves as a semantic-meaningful multi-granularity proposal. By randomly sampling these proposals and simulating possible interactions based on them, we provide meaningful interaction at multiple granularities to teach the model to understand interactions. Our MIS significantly outperforms non-deep learning unsupervised methods and is even comparable with some previous deep-supervised methods without any annotation." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 55, + 628, + 135, + 639 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 628, + 135, + 639 + ], + "spans": [ + { + "bbox": [ + 55, + 628, + 135, + 639 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 53, + 647, + 294, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 647, + 294, + 696 + ], + "spans": [ + { + "bbox": [ + 53, + 647, + 294, + 696 + ], + "type": "text", + "content": "Interactive segmentation aims at obtaining high-quality object masks with limited user interaction, allowing users to segment objects as needed. During the development of interactive segmentation, various interactive forms like" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 315, + 291, + 553, + 467 + ], + "blocks": [ + { + "bbox": [ + 315, + 291, + 553, + 467 + ], + "lines": [ + { + "bbox": [ + 315, + 291, + 553, + 467 + ], + "spans": [ + { + "bbox": [ + 315, + 291, + 553, + 467 + ], + "type": "image", + "image_path": "cc2cde48b7c72dbc6201c482075e442b96bbe46225e40293309a3362537d2fd7.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 312, + 470, + 555, + 536 + ], + "lines": [ + { + "bbox": [ + 312, + 470, + 555, + 536 + ], + "spans": [ + { + "bbox": [ + 312, + 470, + 555, + 536 + ], + "type": "text", + "content": "Figure 1. Top: To tackle the reliance on object annotations of previous interactive segmentation methods caused by interaction simulation, we propose Multi-granularity Interaction Simulation (MIS) that simulates interaction by meaningful regions at multiple granularities. Down: The model learns from MIS to successfully understand interactions and produce acceptable segmentation." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 312, + 557, + 553, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 557, + 553, + 617 + ], + "spans": [ + { + "bbox": [ + 312, + 557, + 553, + 617 + ], + "type": "text", + "content": "bounding boxes [20, 32, 43], scribbles [2, 11, 22], and clicks [44, 17, 25, 35, 8, 36, 24, 9] have been explored. Among them, the click-based interaction becomes the mainstream due to its simplicity and well-established training and evaluation protocols." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 312, + 618, + 555, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 618, + 555, + 715 + ], + "spans": [ + { + "bbox": [ + 312, + 618, + 555, + 715 + ], + "type": "text", + "content": "State-of-the-art methods for click-based interactive segmentation are based on deep learning, following the basic paradigm proposed by Xu et al. [44]. Specifically, these methods encode clicks to a distance map and adapt a semantic segmentation model (e.g., FCN [28]) to take the encoded click map as input, and then train the model with interaction-segmentation pairs. Since it is impractical to collect interaction sequences from real users, previous" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 66, + 702, + 271, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 702, + 271, + 713 + ], + "spans": [ + { + "bbox": [ + 66, + 702, + 271, + 713 + ], + "type": "text", + "content": "*Corresponding author. Project page: https://lkhl.github.io/MIS" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 298, + 749, + 313, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 749, + 313, + 757 + ], + "spans": [ + { + "bbox": [ + 298, + 749, + 313, + 757 + ], + "type": "text", + "content": "666" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 68, + 553, + 153 + ], + "blocks": [ + { + "bbox": [ + 55, + 68, + 553, + 153 + ], + "lines": [ + { + "bbox": [ + 55, + 68, + 553, + 153 + ], + "spans": [ + { + "bbox": [ + 55, + 68, + 553, + 153 + ], + "type": "image", + "image_path": "d82aa3c18385ca5ce1ef95e0aed1e9bbf43be75b4c89638ff749c1b456d0073b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 53, + 155, + 553, + 189 + ], + "lines": [ + { + "bbox": [ + 53, + 155, + 553, + 189 + ], + "spans": [ + { + "bbox": [ + 53, + 155, + 553, + 189 + ], + "type": "text", + "content": "Figure 2. Illustration of the multi-granularity region proposal generation. For an input image, We first introduce a self-supervised ViT to produce semantic features for each patch of an image. We then gradually merge two similar patches or regions with similar features to perform a new region. All newly generated regions in the merging process constitute meaningful proposals at multiple granularities." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 53, + 207, + 294, + 327 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 207, + 294, + 327 + ], + "spans": [ + { + "bbox": [ + 53, + 207, + 294, + 327 + ], + "type": "text", + "content": "methods adopt an interaction simulation strategy [44, 36] that randomly samples clicks based on object segmentation annotations. By training with the simulated clicks and corresponding object masks, the model is able to correctly understand user needs and segment objects with a few clicks, significantly outperforming non-deep learning methods. However, the requirement for a large number of expensive pixel-level annotations behind the powerful performance has been ignored by previous methods, which is derived from the object-level interaction simulation." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 53, + 328, + 294, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 328, + 294, + 449 + ], + "spans": [ + { + "bbox": [ + 53, + 328, + 294, + 449 + ], + "type": "text", + "content": "In this work, we aim at exploring an annotation-free alternation for interaction simulation to eliminate the reliance on object annotations in interactive segmentation, namely unsupervised interactive segmentation. To achieve it, as shown in the top half of Figure 1, our basic idea is to switch previous object-oriented interaction simulation to some semantic-consistent regions, which can be discovered unsupervisedly. In this case, the model requires diverse examples to understand changeable interactions due to the lack of precise information about objects." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 450, + 295, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 450, + 295, + 714 + ], + "spans": [ + { + "bbox": [ + 53, + 450, + 295, + 714 + ], + "type": "text", + "content": "Therefore, we propose Multi-granularity Interaction Simulation (MIS) to achieve diversity. To ensure the semantic consistency of a region, we first parse the semantic of patches in an image by a Vision Transformer (ViT) [10] pre-trained unsupervisedly with DINO [7]. As shown in Figure 2, we then gradually merge two patches or regions with similar features to form a more extensive region for an image, until only one region remains. In this process, the newly generated region in every step makes up semantic-meaningful multi-granularity proposals. The MIS is finally achieved by randomly sampling these proposals and simulating possible interactions based on them when training the model. Moreover, in order to help the model fight against the unsmoothness on the boundary of proposals caused by the feature extractor, we design a smoothness constraint that considers the low-level feature of pixels. With the meaningful interaction simulated at multiple granularities and the smoothness constraint, the model learns to understand clicks by related regions and produce an acceptable segmentation with several user interactions when inference, while completely discarding object annotations, as shown in the bottom half of Figure 1." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 312, + 207, + 553, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 207, + 553, + 399 + ], + "spans": [ + { + "bbox": [ + 312, + 207, + 553, + 399 + ], + "type": "text", + "content": "We take the standard protocol [44] to evaluate our method on commonly used datasets including GrabCut [32], Berkeley [29], SBD [15], and DAVIS [31]. Benefiting from the rich interaction examples from our MIS, the trained model achieves inspiring performance. Specifically, it significantly outperforms non-deep learning methods under the premise of unsupervised setting, and even surpasses some early deep supervised methods. In addition, it can also perform as an unsupervised pre-training to improve the performance when only limited annotations are available. The surprising results support that the interactive segmentation task can be solved in a more label-efficient way. Moreover, we believe the proposed method can reduce the labeling costs in segmentation tasks by training an interactive segmentation model unsupervisedly and using it to efficiently make task-specific annotations as needed." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 313, + 412, + 405, + 424 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 412, + 405, + 424 + ], + "spans": [ + { + "bbox": [ + 313, + 412, + 405, + 424 + ], + "type": "text", + "content": "2. Related Works" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 312, + 434, + 553, + 673 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 434, + 553, + 673 + ], + "spans": [ + { + "bbox": [ + 312, + 434, + 553, + 673 + ], + "type": "text", + "content": "Non-deep Learning Interactive Image Segmentation. Interactive segmentation has been an active field for over two decades due to its wide applications. Before the era of deep learning, the solutions are based on low-level features and optimization. One of the best-known methods is proposed by Boykov and Jolly [6], who define a graph to describe user-provided hard constraints and pixel relationship, then solve interactive segmentation by graph cut with max-flow algorithm [5]. After that, Rother et al. [32] augment graph cut by more powerful color data modeling and an iterative strategy. Other improved algorithms include random walk [11], geodesic distance [3], and star-convexity [12]. As early unsupervised interactive segmentation methods, these algorithms stuck when processing complex images due to the dependence on low-level features. Unlike their iterative optimization algorithms for input images, we distill user interactions, which are simulated from offline datasets with our method, into a deep neural network. By leveraging the large capabilities of the neural network, our method achieves significantly better performance than them." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 312, + 677, + 553, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 677, + 553, + 715 + ], + "spans": [ + { + "bbox": [ + 312, + 677, + 553, + 715 + ], + "type": "text", + "content": "Deep Interactive Image Segmentation. Xu et al. [44] are the first to introduce deep learning on this task by extending FCN [28] with click map and click sampling strategies." + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 298, + 749, + 312, + 757 + ], + "type": "text", + "content": "667" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 68, + 239, + 207 + ], + "blocks": [ + { + "bbox": [ + 55, + 68, + 239, + 207 + ], + "lines": [ + { + "bbox": [ + 55, + 68, + 239, + 207 + ], + "spans": [ + { + "bbox": [ + 55, + 68, + 239, + 207 + ], + "type": "image", + "image_path": "00e7329cb0e8a191709e26c8811b3e674aceed08c67805672ec1c21f4dd9d451.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 53, + 209, + 554, + 266 + ], + "lines": [ + { + "bbox": [ + 53, + 209, + 554, + 266 + ], + "spans": [ + { + "bbox": [ + 53, + 209, + 554, + 266 + ], + "type": "text", + "content": "Figure 3. Illustration of our unsupervised framework to train an interactive segmentation model. For implementation, the MIS is composed of two stages. In the first pre-processing stage, we first parse the semantic of each patch in the image using a pre-trained ViT and take a gradual merging strategy to produce semantic-consistent region proposals at multiple granularities and save them efficiently with a tree structure. In the training stage, given an image, we randomly select proposals from the corresponding merging tree in a top-down manner and further simulate possible clicks based on them, thus providing the model informative interactions." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 248, + 68, + 554, + 207 + ], + "blocks": [ + { + "bbox": [ + 248, + 68, + 554, + 207 + ], + "lines": [ + { + "bbox": [ + 248, + 68, + 554, + 207 + ], + "spans": [ + { + "bbox": [ + 248, + 68, + 554, + 207 + ], + "type": "image", + "image_path": "44dcacbf7990d200a701e36df03affd96d68190905fed33ba0eac8ab83407877.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 53, + 285, + 296, + 452 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 285, + 296, + 452 + ], + "spans": [ + { + "bbox": [ + 53, + 285, + 296, + 452 + ], + "type": "text", + "content": "Based on this pipeline, the researchers gradually increase the performance ceiling of deep learning methods by emphasizing the first click [25], online optimization [17, 35], diffusing prediction [8], edge-guided flow [14], iterative click sampling [36], powerful feature extractor [26], and Gaussian process posterior [45]. On the other hand, some works [24, 9] focus on efficiency and propose to segment on local crops to accelerate inference. Although the deep learning approaches achieve uplifting performance and efficiency, they require large-scale pixel-level annotations to train, which are expensive and laborious to obtain. Unlike previous works, we focus on the dependency on annotations and show that a fully unsupervised framework can also handle interactive segmentation task well." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 462, + 296, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 462, + 296, + 715 + ], + "spans": [ + { + "bbox": [ + 53, + 462, + 296, + 715 + ], + "type": "text", + "content": "Unsupervised Image Segmentation. With the development of self-supervised and unsupervised learning, unsupervised methods for image segmentation task start to emerge. This work is also related to some unsupervised image segmentation methods based on the idea that extracting segments from a pre-trained high-quality dense feature extractor, (e.g., DenseCL [40], DINO [7]). For instance, Simeoni et al. [34] proposed a series of hand-made rules to choose pixels belonging to the same object according to their feature similarity. Wang et al. [41] introduce normalized cuts [33] on the affinity graph constructed by pixel-level representations from DINO to divide the foreground and background of an image. Hamilton et al. [13] train a segmentation head by distilling the feature correspondences from DINO. Melas et al. [30] adopt spectral decomposition on the affinity graph to discover meaningful parts in an image. For instance segmentation, FreeSOLO [39] design pseudo instance mask generation based on multi-scale feature correspondences from densely pre-trained models and train an instance segmentation model with these pseudo masks. Although the masks produced by these methods can" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 312, + 285, + 555, + 369 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 285, + 555, + 369 + ], + "spans": [ + { + "bbox": [ + 312, + 285, + 555, + 369 + ], + "type": "text", + "content": "serve as pseudo labels to train an interactive segmentation model unsupervisedly, only ordinary results are observed through our experiments in Section 4.1, which demonstrate that these task-specific designs is not apposite for interactive segmentation task. In contrast, we propose a novel strategy to discover semantic-consistent yet diverse regions to fit the interactive segmentation task." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 313, + 381, + 369, + 393 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 381, + 369, + 393 + ], + "spans": [ + { + "bbox": [ + 313, + 381, + 369, + 393 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 312, + 402, + 555, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 402, + 555, + 629 + ], + "spans": [ + { + "bbox": [ + 312, + 402, + 555, + 629 + ], + "type": "text", + "content": "In this section, we introduce the overall framework to solve unsupervised interactive segmentation in detail. Macroscopically, we simulate informative interactions from the proposed Multi-granularity Interaction Simulation (MIS) to train an interactive segmentation model. For implementation, the MIS is composed of two stages, as shown in Figure 3. In the first pre-processing stage, we first parse the semantic of each patch in the image using a ViT [10] trained self-supervisedly with DINO [7], which has been proven to produce high-quality dense semantic features [34, 13, 30]. With these features, we take a gradual merging strategy to produce semantic-consistent region proposals at multiple granularities and save them efficiently with a tree structure. In the training stage, given an image, we randomly select proposals from the corresponding merging tree in a top-down manner and further simulate possible clicks based on them, thus providing the model informative interactions for learning to understand interactions during the training process." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 312, + 630, + 556, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 630, + 556, + 715 + ], + "spans": [ + { + "bbox": [ + 312, + 630, + 556, + 715 + ], + "type": "text", + "content": "For training, the model is optimized by the provided interactions, which include meaningful regions and clicks. Specifically, it takes the image and clicks as input and is optimized to produce similar segmentation as the region. Moreover, we design a smoothness constraint when optimizing, for the purpose of mitigating the misleading brought by the inaccurate boundary of the region, which" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 298, + 749, + 313, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 749, + 313, + 757 + ], + "spans": [ + { + "bbox": [ + 298, + 749, + 313, + 757 + ], + "type": "text", + "content": "668" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 56, + 68, + 294, + 149 + ], + "blocks": [ + { + "bbox": [ + 56, + 68, + 294, + 149 + ], + "lines": [ + { + "bbox": [ + 56, + 68, + 294, + 149 + ], + "spans": [ + { + "bbox": [ + 56, + 68, + 294, + 149 + ], + "type": "image", + "image_path": "c287f084a63be29948a920dfcf1c57a4387eabf374e1f3d26383739522a0a695.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 54, + 151, + 295, + 207 + ], + "lines": [ + { + "bbox": [ + 54, + 151, + 295, + 207 + ], + "spans": [ + { + "bbox": [ + 54, + 151, + 295, + 207 + ], + "type": "text", + "content": "Figure 4. Illustration of the cost of merging. The points represent patch features and the circles denote regions that consist of the patches surrounded by it. Merging two regions into one leads to a more divergent cluster and the total SSE increases, thus the cost of merging can be measured as this increment." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 54, + 228, + 295, + 253 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 228, + 295, + 253 + ], + "spans": [ + { + "bbox": [ + 54, + 228, + 295, + 253 + ], + "type": "text", + "content": "is caused by the down-sampling in the ViT. The details of MIS and the training objective are described as follows." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 54, + 262, + 270, + 276 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 262, + 270, + 276 + ], + "spans": [ + { + "bbox": [ + 54, + 262, + 270, + 276 + ], + "type": "text", + "content": "3.1. Multi-granularity Interaction Simulation" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "spans": [ + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "text", + "content": "Bottom-up Merging. At the core of our MIS is to discover semantic-consistent yet diverse regions, which is achieved efficiently by gradually merging. In the beginning, we produce high-quality semantic features from a ViT [10] trained in a self-supervised manner with DINO [7] to measure the semantic similarity and ensure the semantic-consistency of generated region proposals. In the ViT, an image " + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "inline_equation", + "content": "\\boldsymbol{I} \\in \\mathbb{R}^{h \\times w \\times 3}" + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "text", + "content": " is divided to non-overlapping " + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "inline_equation", + "content": "n = \\frac{h}{s} \\times \\frac{w}{s}" + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "text", + "content": " patches with stride " + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "text", + "content": ", which are then processed by some Transformer [38] encoder layers. The patch features " + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "inline_equation", + "content": "\\boldsymbol{F} \\in \\mathbb{R}^{n \\times c}" + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "text", + "content": " are obtained from the last layer of the ViT, where " + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "text", + "content": " is the feature dimension. With the patch features, we implement the hierarchical merging process by Algorithm 1 and finally get a tree " + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 53, + 282, + 295, + 450 + ], + "type": "text", + "content": " which records every merge process." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "spans": [ + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "text", + "content": "Initially, " + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "text", + "content": " patches form as " + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "text", + "content": " leaf nodes of the tree, and a set " + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "inline_equation", + "content": "\\mathbb{S}" + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "text", + "content": " is maintained for saving unmerged nodes, which initially contains all the leaf nodes. In each iteration, the two unmerged nodes with the least cost according to their features will be merged to form a new node, until only one unmerged node remains. Thus, there should be totally " + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "inline_equation", + "content": "n - 1" + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "text", + "content": " iterations, and the index of the newly generated node in " + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "text", + "content": "-th iteration is " + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "inline_equation", + "content": "n + k" + }, + { + "bbox": [ + 53, + 451, + 295, + 618 + ], + "type": "text", + "content": ". Moreover, considering the prior that parts belonging to the same object are usually adjacent, we add connectivity constraints when merging to greatly accelerate the search space for finding the minimum cost. Specifically, each patch is only connected to its four adjacent patches and two regions are connected only if at least a pair of patches from them respectively are connected." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 53, + 619, + 295, + 679 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 619, + 295, + 679 + ], + "spans": [ + { + "bbox": [ + 53, + 619, + 295, + 679 + ], + "type": "text", + "content": "We follow Ward's method [42] to measure the cost of merging, which minimizes the increment in the total within-cluster sum of squared error (SSE) after merging, as shown in Figure 4. Regarding a region " + }, + { + "bbox": [ + 53, + 619, + 295, + 679 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 53, + 619, + 295, + 679 + ], + "type": "text", + "content": " as a cluster that contains some patches, the SSE is defined as" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 124, + 689, + 294, + 716 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 124, + 689, + 294, + 716 + ], + "spans": [ + { + "bbox": [ + 124, + 689, + 294, + 716 + ], + "type": "interline_equation", + "content": "e _ {A} = \\sum_ {i \\in A} \\left\\| \\boldsymbol {F} _ {i} - \\boldsymbol {\\mu} _ {A} \\right\\| ^ {2}, \\tag {1}", + "image_path": "248df459cc7f717abe48651f046482366cb1a1597d749ae05b16e2ec1277de12.jpg" + } + ] + } + ], + "index": 7 + }, + { + "type": "code", + "bbox": [ + 316, + 88, + 553, + 198 + ], + "blocks": [ + { + "bbox": [ + 320, + 75, + 460, + 87 + ], + "lines": [ + { + "bbox": [ + 320, + 75, + 460, + 87 + ], + "spans": [ + { + "bbox": [ + 320, + 75, + 460, + 87 + ], + "type": "text", + "content": "Algorithm 1: Bottom-up Merging" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "lines": [ + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "spans": [ + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "text", + "content": "Input: Patch features " + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "inline_equation", + "content": "\\pmb{F} \\in \\mathbb{R}^{n \\times c}" + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "text", + "content": " \nOutput: Merge tree " + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "inline_equation", + "content": "\\pmb{T} \\in \\mathbb{Z}^{(n-1) \\times 2}" + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "text", + "content": " \n1 Initialization: " + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "inline_equation", + "content": "\\mathbb{S} \\gets \\{1, 2, \\dots, n\\}" + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "text", + "content": " \n2 for " + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "inline_equation", + "content": "k \\gets 1" + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "inline_equation", + "content": "n-1" + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "text", + "content": " do \n3 " + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "inline_equation", + "content": "\\begin{array}{c} i,j \\gets \\operatorname{arg min} \\operatorname{Cost}(i,j,\\pmb{F}) \\text{s.t. Connect}(i,j); \\\\ T_{k,:} \\gets (i,j); \\\\ \\mathbb{S} \\gets \\complement_{\\mathbb{S}}\\{i,j\\} \\cup \\{n+k\\}; \\end{array}" + }, + { + "bbox": [ + 316, + 88, + 553, + 198 + ], + "type": "text", + "content": " \n4 \n5 \n6 end" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "code_body" + } + ], + "index": 9, + "sub_type": "algorithm" + }, + { + "type": "code", + "bbox": [ + 314, + 229, + 553, + 380 + ], + "blocks": [ + { + "bbox": [ + 320, + 217, + 462, + 228 + ], + "lines": [ + { + "bbox": [ + 320, + 217, + 462, + 228 + ], + "spans": [ + { + "bbox": [ + 320, + 217, + 462, + 228 + ], + "type": "text", + "content": "Algorithm 2: Top-down Sampling" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "code_caption" + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "lines": [ + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "spans": [ + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "text", + "content": "Input : Merge tree " + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "text", + "content": " , decay coefficient " + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "text", + "content": " Output: Node index " + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "text", + "content": " \n1 Initialization: " + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "inline_equation", + "content": "p\\gets 1.0" + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "inline_equation", + "content": "k\\gets n - 1" + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "text", + "content": " \n2 while Rand() " + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "inline_equation", + "content": "< p" + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "inline_equation", + "content": "k > 0" + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "text", + "content": " do \n3 if Rand() " + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "inline_equation", + "content": "< 0.5" + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "text", + "content": " then \n4 " + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "inline_equation", + "content": "\\mid k\\gets T_{k,0} - n;" + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "text", + "content": " \n5 else \n6 " + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "inline_equation", + "content": "\\mid k\\gets T_{k,1} - n;" + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "text", + "content": " \n7 end \n8 " + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "inline_equation", + "content": "p\\gets \\alpha \\cdot p" + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "text", + "content": " \n9 end \n10 " + }, + { + "bbox": [ + 314, + 229, + 553, + 380 + ], + "type": "inline_equation", + "content": "k\\gets k + n" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "code_body" + } + ], + "index": 11, + "sub_type": "algorithm" + }, + { + "bbox": [ + 313, + 401, + 541, + 414 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 401, + 541, + 414 + ], + "spans": [ + { + "bbox": [ + 313, + 401, + 541, + 414 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 313, + 401, + 541, + 414 + ], + "type": "inline_equation", + "content": "\\pmb{\\mu}_A\\in \\mathbb{R}^c" + }, + { + "bbox": [ + 313, + 401, + 541, + 414 + ], + "type": "text", + "content": " is the center, which can be computed as" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 395, + 420, + 552, + 449 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 395, + 420, + 552, + 449 + ], + "spans": [ + { + "bbox": [ + 395, + 420, + 552, + 449 + ], + "type": "interline_equation", + "content": "\\boldsymbol {\\mu} _ {A} = \\frac {1}{s _ {A}} \\sum_ {i \\in A} \\boldsymbol {F} _ {i}, \\tag {2}", + "image_path": "6010c64513bc732cbf8fa6cdb35397f41733f1ce0b459e87d75cd3657651bc85.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 312, + 456, + 553, + 481 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 456, + 553, + 481 + ], + "spans": [ + { + "bbox": [ + 312, + 456, + 553, + 481 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 312, + 456, + 553, + 481 + ], + "type": "inline_equation", + "content": "s_A" + }, + { + "bbox": [ + 312, + 456, + 553, + 481 + ], + "type": "text", + "content": " is the number of patches within " + }, + { + "bbox": [ + 312, + 456, + 553, + 481 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 312, + 456, + 553, + 481 + ], + "type": "text", + "content": ". When merging two regions, the new center is" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 378, + 489, + 552, + 513 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 378, + 489, + 552, + 513 + ], + "spans": [ + { + "bbox": [ + 378, + 489, + 552, + 513 + ], + "type": "interline_equation", + "content": "\\boldsymbol {\\mu} _ {A \\cup B} = \\frac {s _ {A} \\boldsymbol {\\mu} _ {A} + s _ {B} \\boldsymbol {\\mu} _ {B}}{s _ {A} + s _ {B}}. \\tag {3}", + "image_path": "32b9922cd716595ab54318b56c54def1bbe22d5f4136538747080475fe245b9d.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 312, + 519, + 553, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 519, + 553, + 567 + ], + "spans": [ + { + "bbox": [ + 312, + 519, + 553, + 567 + ], + "type": "text", + "content": "Then the cost of merging is defined as the difference of SSE before and after merging. Since the SSE of all clusters except the clusters being merged are unchanged, it can be formulated as" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 352, + 573, + 552, + 611 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 352, + 573, + 552, + 611 + ], + "spans": [ + { + "bbox": [ + 352, + 573, + 552, + 611 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\operatorname {C o s t} (A, B) = e _ {A \\cup B} - \\left(e _ {A} + e _ {B}\\right) \\\\ = \\frac {s _ {A} \\cdot s _ {B}}{s _ {A} + s _ {B}} \\left\\| \\boldsymbol {\\mu} _ {A} - \\boldsymbol {\\mu} _ {B} \\right\\| ^ {2}. \\tag {4} \\\\ \\end{array}", + "image_path": "11eef8bc6f5d2682729f35073bcb3ef26074d602d1b97d3783526d4af0215899.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 312, + 618, + 496, + 630 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 618, + 496, + 630 + ], + "spans": [ + { + "bbox": [ + 312, + 618, + 496, + 630 + ], + "type": "text", + "content": "Detailed derivation is shown in the appendix." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 312, + 630, + 553, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 630, + 553, + 714 + ], + "spans": [ + { + "bbox": [ + 312, + 630, + 553, + 714 + ], + "type": "text", + "content": "During the merging process, the center " + }, + { + "bbox": [ + 312, + 630, + 553, + 714 + ], + "type": "inline_equation", + "content": "\\mu" + }, + { + "bbox": [ + 312, + 630, + 553, + 714 + ], + "type": "text", + "content": " and the size " + }, + { + "bbox": [ + 312, + 630, + 553, + 714 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 312, + 630, + 553, + 714 + ], + "type": "text", + "content": " of each region are recorded. Initially, the size is set to 1 for each patch and the center is its feature. The detailed calculation after each merging is as follows: (1) Computing the center of the newly generated region according to Equation (3). (2) Computing the size of the newly generated region as " + }, + { + "bbox": [ + 312, + 630, + 553, + 714 + ], + "type": "inline_equation", + "content": "s_{A\\cup B} = s_A + s_B" + }, + { + "bbox": [ + 312, + 630, + 553, + 714 + ], + "type": "text", + "content": ". 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Qualitative results of discovered regions for the baselines and our MIS. While the baselines only focus on some salient regions in a fixed granularity, our MIS produces semantic-consistent regions at multiple granularities thus catching more objects and parts." + } + ] + } + ], + "index": 26, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "type": "image", + "bbox": [ + 269, + 184, + 339, + 237 + ], + "blocks": [ + { + "bbox": [ + 269, + 184, + 339, + 237 + ], + "lines": [ + { + "bbox": [ + 269, + 184, + 339, + 237 + ], + "spans": [ + { + "bbox": [ + 269, + 184, + 339, + 237 + ], + "type": "image", + "image_path": "912b848861a0ad7caa4d05968fa3b4b37e95a5c00c1029ed61d721288957ee1a.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 294, + 239, + 313, + 247 + ], + "lines": [ + { + "bbox": [ + 294, + 239, + 313, + 247 + ], + "spans": [ + { + "bbox": [ + 294, + 239, + 313, + 247 + ], + "type": "text", + "content": "DSM" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_caption" + } + ], + "index": 20 + }, + { + "type": "image", + "bbox": [ + 342, + 184, + 411, + 237 + ], + "blocks": [ + { + "bbox": [ + 342, + 184, + 411, + 237 + ], + "lines": [ + { + "bbox": [ + 342, + 184, + 411, + 237 + ], + "spans": [ + { + "bbox": [ + 342, + 184, + 411, + 237 + ], + "type": "image", + "image_path": "dab54f4ebe0eb13d030b24b0db8968bfa9e9a3f12fc7629f9988258307574ec0.jpg" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 391, + 239, + 504, + 249 + ], + "lines": [ + { + "bbox": [ + 391, + 239, + 504, + 249 + ], + "spans": [ + { + "bbox": [ + 391, + 239, + 504, + 249 + ], + "type": "text", + "content": "Our multi-granularity proposals" + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_caption" + } + ], + "index": 22 + }, + { + "type": "image", + "bbox": [ + 413, + 184, + 482, + 237 + ], + "blocks": [ + { + "bbox": [ + 413, + 184, + 482, + 237 + ], + "lines": [ + { + "bbox": [ + 413, + 184, + 482, + 237 + ], + "spans": [ + { + "bbox": [ + 413, + 184, + 482, + 237 + ], + "type": "image", + "image_path": "e59ad0e75ac1e135f9a6ebf879adf69efda595cd8e7530c2a9a3d244f1b809a0.jpg" + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_body" + } + ], + "index": 24 + }, + { + "type": "image", + "bbox": [ + 484, + 184, + 553, + 237 + ], + "blocks": [ + { + "bbox": [ + 484, + 184, + 553, + 237 + ], + "lines": [ + { + "bbox": [ + 484, + 184, + 553, + 237 + ], + "spans": [ + { + "bbox": [ + 484, + 184, + 553, + 237 + ], + "type": "image", + "image_path": "06ca923ff11ac4ee1c8e5fa7394c8cbc646b1d68a438f0c52b09baa3c70fd495.jpg" + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_body" + } + ], + "index": 25 + }, + { + "bbox": [ + 53, + 293, + 294, + 328 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 293, + 294, + 328 + ], + "spans": [ + { + "bbox": [ + 53, + 293, + 294, + 328 + ], + "type": "text", + "content": "merging newly generated regions with other regions according to Equation (4). Since the other regions are not changed, the cost between them remains the same." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "spans": [ + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "text", + "content": "After " + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "inline_equation", + "content": "n - 1" + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "text", + "content": " iterations, we get a tree structure that is stored by a matrix " + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "inline_equation", + "content": "T \\in \\mathbb{Z}^{(n - 1)\\times 2}" + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "text", + "content": ", where the " + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "text", + "content": "-th row is the indices of the two children of the " + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "inline_equation", + "content": "i + n" + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "text", + "content": " node. In the tree, each node represents a merge and also represents a region proposal which consists of all patches within the subtree rooted at this node. Hence, with this hierarchical relationship, we obtain " + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "inline_equation", + "content": "n - 1" + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "text", + "content": " region proposals at multiple granularities for each image, which help the interactive segmentation model to learn various interactions. For storage, there is no need to store all the " + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "inline_equation", + "content": "n - 1" + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "text", + "content": " masks but only the tree structure, that is, the matrix " + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 53, + 333, + 295, + 464 + ], + "type": "text", + "content": ", which makes it more space-efficient." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "spans": [ + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "text", + "content": "Top-down Sampling. When training, the MIS is worked based on the stored merging tree. Specifically, when sampling an image for training, we select a mask proposal from its corresponding merging tree for simulating an interaction. In the merging tree, shallow nodes correspond to relatively complete parts or their combinations and deeper nodes are more relevant to finely divided parts. Intuitively, we prefer the complete one while maintaining diversity. Therefore, we design a sampling strategy in a top-down manner and gradually decrease the probability to go deeper, as shown in Algorithm 2. Concretely, we start at the root node (i.e., the node with an index of " + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "inline_equation", + "content": "2n - 1" + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "text", + "content": ") and the probability " + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "inline_equation", + "content": "p = 1.0" + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "text", + "content": ". Then in each iteration, we choose to go deeper or stop with probability " + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "text", + "content": ", and decrease " + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "text", + "content": " with a coefficient " + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "text", + "content": ". The loop will terminate when choosing to stop or reach a leaf node (i.e., nodes whose index is less than or equal to " + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "text", + "content": "). If it is decided to go deeper, we randomly move the current node to one of its children. Finally, we get the index of a node " + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "text", + "content": " corresponding to a region proposal, where the patches in the sub-tree rooted at " + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 53, + 474, + 295, + 714 + ], + "type": "text", + "content": " are annotated as foreground." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 312, + 293, + 553, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 293, + 553, + 437 + ], + "spans": [ + { + "bbox": [ + 312, + 293, + 553, + 437 + ], + "type": "text", + "content": "Click Sampling. With the sampled region, the last step is to simulate possible clicks according to the region. Drawing on the experience of previous methods, we use a combination of random and iterative click simulation strategies to produce a click map following RITM [36]. Specifically, some positive and negative clicks are first generated in parallel according to the foreground and background defined by the region. Then some additional clicks are appended by checking the erroneous region of the prediction which is produced by previous clicks. Finally, the MIS generates complete interactions which consist of a segmentation target and corresponding clicks." + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 313, + 446, + 377, + 460 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 446, + 377, + 460 + ], + "spans": [ + { + "bbox": [ + 313, + 446, + 377, + 460 + ], + "type": "text", + "content": "3.2. Training" + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 312, + 466, + 555, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 466, + 555, + 574 + ], + "spans": [ + { + "bbox": [ + 312, + 466, + 555, + 574 + ], + "type": "text", + "content": "Interactive Segmentation Model. Typical interactive segmentation models are built based on semantic segmentation models (e.g., FCN [28]) by taking an additional click map as input, which is transformed from the coordinate of clicks. Formulically, given an image " + }, + { + "bbox": [ + 312, + 466, + 555, + 574 + ], + "type": "inline_equation", + "content": "\\pmb{I} \\in \\mathbb{R}^{h \\times w \\times 3}" + }, + { + "bbox": [ + 312, + 466, + 555, + 574 + ], + "type": "text", + "content": ", a click map " + }, + { + "bbox": [ + 312, + 466, + 555, + 574 + ], + "type": "inline_equation", + "content": "D \\in \\mathbb{R}^{h \\times w \\times 2}" + }, + { + "bbox": [ + 312, + 466, + 555, + 574 + ], + "type": "text", + "content": " which presents positive and negative clicks respectively, and previous prediction " + }, + { + "bbox": [ + 312, + 466, + 555, + 574 + ], + "type": "inline_equation", + "content": "B \\in \\{0,1\\}^{h \\times w}" + }, + { + "bbox": [ + 312, + 466, + 555, + 574 + ], + "type": "text", + "content": ", the model " + }, + { + "bbox": [ + 312, + 466, + 555, + 574 + ], + "type": "inline_equation", + "content": "\\mathcal{F}(\\cdot)" + }, + { + "bbox": [ + 312, + 466, + 555, + 574 + ], + "type": "text", + "content": " outputs the probability of being foreground for each pixel" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 343, + 584, + 553, + 599 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 584, + 553, + 599 + ], + "spans": [ + { + "bbox": [ + 343, + 584, + 553, + 599 + ], + "type": "interline_equation", + "content": "\\boldsymbol {Q} = \\mathcal {F} (\\operatorname {F u s i o n} (\\boldsymbol {I}, \\boldsymbol {D}, \\boldsymbol {B})) \\text {,} \\boldsymbol {Q} \\in [ 0, 1 ] ^ {h \\times w}, \\tag {5}", + "image_path": "bc0e422ec9c297b7325b1038ac19f7129445fa840dbf25f947dc9fb614c5e4a4.jpg" + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 312, + 609, + 553, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 609, + 553, + 657 + ], + "spans": [ + { + "bbox": [ + 312, + 609, + 553, + 657 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 312, + 609, + 553, + 657 + ], + "type": "inline_equation", + "content": "\\mathrm{Fusion}(\\cdot)" + }, + { + "bbox": [ + 312, + 609, + 553, + 657 + ], + "type": "text", + "content": " is some kind of fusion operation such as concatenate. Through training, the model learns to map the image and the user clicks to foreground and background segmentation thus can be used interactively when inference." + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 312, + 665, + 553, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 665, + 553, + 714 + ], + "spans": [ + { + "bbox": [ + 312, + 665, + 553, + 714 + ], + "type": "text", + "content": "Training with Proposals. Under our unsupervised setting, the model learns this mapping by the simulated interactions from the MIS. The model is first learned by the supervision from the multi-granularity region proposals " + }, + { + "bbox": [ + 312, + 665, + 553, + 714 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 312, + 665, + 553, + 714 + ], + "type": "text", + "content": " by optimiz" + } + ] + } + ], + "index": 35 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 298, + 749, + 313, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 298, + 749, + 313, + 757 + ], + "spans": [ + { + "bbox": [ + 298, + 749, + 313, + 757 + ], + "type": "text", + "content": "670" + } + ] + } + ], + "index": 36 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 55, + 70, + 553, + 396 + ], + "blocks": [ + { + "bbox": [ + 55, + 70, + 553, + 396 + ], + "lines": [ + { + "bbox": [ + 55, + 70, + 553, + 396 + ], + "spans": [ + { + "bbox": [ + 55, + 70, + 553, + 396 + ], + "type": "table", + "html": "
MethodBackboneGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Deep Supervised Methods
DIOS w/o GC [44] CVPR16FCN8.0212.59--14.3016.7912.5217.11
DIOS w/ GC [44] CVPR16FCN5.086.08--9.2212.809.0312.58
LD [23] CVPR18VGG-193.204.79--7.4110.785.059.57
BRS [17] CVPR19DenseNet2.603.60-5.086.599.785.588.24
f-BRS [35] CVPR20ResNet-1012.302.72-4.574.817.735.047.41
FCA-Net [25] CVPR20ResNet-101-2.08-3.92---7.57
IA+SA [19] ECCV20ConvNet-3.07-4.94--5.16-
CDNet [8] ICCV21ResNet-341.862.181.953.275.187.895.006.89
RITM [36] ICIP22HRNet-181.762.041.873.223.395.434.946.71
FocalClick [9] CVPR22MiT-B01.661.90-3.144.346.515.027.06
FocusCut [24] CVPR22ResNet-1011.461.641.813.013.405.314.856.22
PseudoClick [27] ECCV22HRNet-32-1.84-2.98-5.614.746.16
SimpleClick [26] arXiv22ViT-B1.401.541.442.463.285.244.105.48
Non-deep Learning Methods
GraphCut [6] ICCV01N/A7.9810.00-14.2213.6015.9615.1317.41
Random Walk [11] TPAMI06N/A11.3613.77-14.0212.2215.0416.7118.31
Geodesic Matting [3] IJCV09N/A13.3214.57-15.9615.3617.6018.5919.50
GSC [12] CVPR10N/A7.109.12-12.5712.6915.3115.3517.52
ESC [12] CVPR10N/A7.249.20-12.1112.2114.8615.4117.70
Deep Unsupervised Methods
TokenCut* [41] CVPR22ViT-B3.045.746.309.9710.8213.1610.5615.01
FreeMask* [39] CVPR22ViT-B4.066.105.559.028.6112.018.2613.05
DSM* [30] CVPR22ViT-B3.644.645.497.758.5911.577.0810.11
MIS w/o Lsmooth (Ours)ViT-B2.082.563.405.517.389.926.7810.08
MIS (Ours)ViT-B1.942.323.094.586.919.516.338.44
", + "image_path": "5b53ad661ffb3d97f334a68d06b77a3f2062fef4aad2fe46cd3025f8539e9234.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 53, + 399, + 553, + 445 + ], + "lines": [ + { + "bbox": [ + 53, + 399, + 553, + 445 + ], + "spans": [ + { + "bbox": [ + 53, + 399, + 553, + 445 + ], + "type": "text", + "content": "Table 1. Comparison with previous methods and baselines on four interactive segmentation benchmarks. " + }, + { + "bbox": [ + 53, + 399, + 553, + 445 + ], + "type": "inline_equation", + "content": "\\star" + }, + { + "bbox": [ + 53, + 399, + 553, + 445 + ], + "type": "text", + "content": " denotes baselines that we introduce from other unsupervised tasks. From top to bottom we show the previous deep supervised method, unsupervised non-deep learning method, and our newly proposed deep unsupervised method. All models listed here are trained on SBD dataset. Our MIS achieves superior performance within unsupervised methods and baselines and even exceeds early deep supervised methods (denoted by underline)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 54, + 464, + 124, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 464, + 124, + 475 + ], + "spans": [ + { + "bbox": [ + 54, + 464, + 124, + 475 + ], + "type": "text", + "content": "ing the objective" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 121, + 486, + 294, + 498 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 121, + 486, + 294, + 498 + ], + "spans": [ + { + "bbox": [ + 121, + 486, + 294, + 498 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {p s e u d o}} = \\operatorname {B C E} (M, Q), \\tag {6}", + "image_path": "f4cbcbe2c774bb8d4fa1b30ddfd0eca6609ed3172b8fa64aa55c02d8b7ce1f72.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 507, + 295, + 615 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 507, + 295, + 615 + ], + "spans": [ + { + "bbox": [ + 53, + 507, + 295, + 615 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 53, + 507, + 295, + 615 + ], + "type": "inline_equation", + "content": "\\mathrm{BCE}(\\cdot)" + }, + { + "bbox": [ + 53, + 507, + 295, + 615 + ], + "type": "text", + "content": " denotes the binary cross entropy loss. Although the region proposals generated by the MIS contains semantics, the possible inaccuracy of the self-supervised feature extractor and the patching process in the ViT will bring some inaccurate part. Fortunately, as discovered by previous research [1] that the model tends to learn effect patterns rather than memorize the noise, we find that the model can learn to correctly map clicks to segmentation after training with these simulated interactions." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 53, + 617, + 294, + 678 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 617, + 294, + 678 + ], + "spans": [ + { + "bbox": [ + 53, + 617, + 294, + 678 + ], + "type": "text", + "content": "Smoothness Constraint. In order to help the model correct the error caused by patching, we propose a smoothness constraint. We first introduce the bilateral affinity matrix [37, 4] " + }, + { + "bbox": [ + 53, + 617, + 294, + 678 + ], + "type": "inline_equation", + "content": "W" + }, + { + "bbox": [ + 53, + 617, + 294, + 678 + ], + "type": "text", + "content": " which presents the affinity of pixels based on their low-level feature and the item " + }, + { + "bbox": [ + 53, + 617, + 294, + 678 + ], + "type": "inline_equation", + "content": "W_{i,j}" + }, + { + "bbox": [ + 53, + 617, + 294, + 678 + ], + "type": "text", + "content": " is" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 59, + 685, + 289, + 717 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 685, + 289, + 717 + ], + "spans": [ + { + "bbox": [ + 59, + 685, + 289, + 717 + ], + "type": "interline_equation", + "content": "e x p (- \\frac {| | \\pmb {a} _ {i} ^ {x y} - \\pmb {a} _ {j} ^ {x y} | | ^ {2}}{2 \\sigma_ {x y} ^ {2}} - \\frac {(a _ {i} ^ {l} - a _ {j} ^ {l}) ^ {2}}{2 \\sigma_ {l} ^ {2}} - \\frac {| | \\pmb {a} _ {i} ^ {u v} - \\pmb {a} _ {j} ^ {u v} | | ^ {2}}{2 \\sigma_ {u v} ^ {2}}),", + "image_path": "97fb7ed9d9d900e44c0c91eda263b76aacbc717c38cb05f1f5d61bfafa86d5cb.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 312, + 464, + 553, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 464, + 553, + 536 + ], + "spans": [ + { + "bbox": [ + 312, + 464, + 553, + 536 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 312, + 464, + 553, + 536 + ], + "type": "inline_equation", + "content": "\\pmb{a}_i" + }, + { + "bbox": [ + 312, + 464, + 553, + 536 + ], + "type": "text", + "content": " is a pixel with a spatial position " + }, + { + "bbox": [ + 312, + 464, + 553, + 536 + ], + "type": "inline_equation", + "content": "(p_i^x, p_i^y)" + }, + { + "bbox": [ + 312, + 464, + 553, + 536 + ], + "type": "text", + "content": " and color " + }, + { + "bbox": [ + 312, + 464, + 553, + 536 + ], + "type": "inline_equation", + "content": "(p_i^l, p_i^u, p_i^v)" + }, + { + "bbox": [ + 312, + 464, + 553, + 536 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 312, + 464, + 553, + 536 + ], + "type": "inline_equation", + "content": "\\sigma_{xy}, \\sigma_l, \\sigma_{uv}" + }, + { + "bbox": [ + 312, + 464, + 553, + 536 + ], + "type": "text", + "content": " control the extent of the spatial, luma, and chroma support of the filter. Motivated by the bilateral solver [4], the smooth constraint is implemented by restricting the model to produce consistent predictions on pixels with high bilateral affinity, which is formulated as" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 340, + 553, + 553, + 583 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 340, + 553, + 553, + 583 + ], + "spans": [ + { + "bbox": [ + 340, + 553, + 553, + 583 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {s m o o t h}} = \\sum_ {i} \\frac {1}{| \\mathcal {N} _ {i} |} \\sum_ {j \\in \\mathcal {N} _ {i}} \\boldsymbol {W} _ {i j} \\cdot \\left(\\boldsymbol {Q} _ {i} - \\boldsymbol {Q} _ {j}\\right) ^ {2}. \\tag {7}", + "image_path": "5775f0dcd55c156e8adf0a13afe54d7ae2aef6c5b2530e18d9156eb36f594717.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 312, + 597, + 553, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 597, + 553, + 657 + ], + "spans": [ + { + "bbox": [ + 312, + 597, + 553, + 657 + ], + "type": "text", + "content": "As we mainly concern with the predictions on the boundary, we only perform the loss locally for fast computation and memory efficiency, i.e., for pixel " + }, + { + "bbox": [ + 312, + 597, + 553, + 657 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 312, + 597, + 553, + 657 + ], + "type": "text", + "content": " the loss is calculated in its " + }, + { + "bbox": [ + 312, + 597, + 553, + 657 + ], + "type": "inline_equation", + "content": "5 \\times 5" + }, + { + "bbox": [ + 312, + 597, + 553, + 657 + ], + "type": "text", + "content": " neighborhoods " + }, + { + "bbox": [ + 312, + 597, + 553, + 657 + ], + "type": "inline_equation", + "content": "\\mathcal{N}_i" + }, + { + "bbox": [ + 312, + 597, + 553, + 657 + ], + "type": "text", + "content": ". Finally, the overall training objective is" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 374, + 673, + 552, + 687 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 374, + 673, + 552, + 687 + ], + "spans": [ + { + "bbox": [ + 374, + 673, + 552, + 687 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\mathcal {L} _ {\\text {p s e u d o}} + \\lambda \\cdot \\mathcal {L} _ {\\text {s m o o t h}}, \\tag {8}", + "image_path": "c10c2d8fdeeb33507682ef020c6e77bc35a24e56111a67328d4d40ca08c31bda.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 313, + 701, + 552, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 701, + 552, + 714 + ], + "spans": [ + { + "bbox": [ + 313, + 701, + 552, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 313, + 701, + 552, + 714 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 313, + 701, + 552, + 714 + ], + "type": "text", + "content": " controls the strength of the smoothness constraint." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "671" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 58, + 71, + 550, + 178 + ], + "blocks": [ + { + "bbox": [ + 58, + 71, + 550, + 178 + ], + "lines": [ + { + "bbox": [ + 58, + 71, + 550, + 178 + ], + "spans": [ + { + "bbox": [ + 58, + 71, + 550, + 178 + ], + "type": "image", + "image_path": "afcc4c36e10e3019e8e81d4c4b53d40cc462d4e2bbc34ceccfde3085f4109f0a.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 53, + 181, + 553, + 205 + ], + "lines": [ + { + "bbox": [ + 53, + 181, + 553, + 205 + ], + "spans": [ + { + "bbox": [ + 53, + 181, + 553, + 205 + ], + "type": "text", + "content": "Figure 6. Comparison of IoU-NoC curve. The two dotted lines indicate the performance of supervised approaches. The proposed method achieves surprising performance that significantly exceeds traditional methods and is close to supervised method when the NoC increases." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 55, + 213, + 553, + 312 + ], + "blocks": [ + { + "bbox": [ + 55, + 213, + 553, + 312 + ], + "lines": [ + { + "bbox": [ + 55, + 213, + 553, + 312 + ], + "spans": [ + { + "bbox": [ + 55, + 213, + 553, + 312 + ], + "type": "table", + "html": "
Data RatioInitializationGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
1%Default (MAE [16])2.322.522.364.448.0110.435.818.28
MIS (Ours)1.54 (↓0.78)1.90 (↓0.62)1.95 (↓0.41)3.73 (↓0.71)5.57 (↓2.44)8.15 (↓2.28)5.36 (↓0.45)7.40 (↓0.88)
5%Default (MAE [16])1.682.221.973.645.488.135.147.23
(Ours)1.62 (↓0.06)1.88 (↓0.34)1.95 (↓0.02)3.32 (↓0.32)5.21 (↓0.27)7.49 (↓0.64)4.54 (↓0.60)6.11 (↓1.12)
10%Default (MAE [16])1.641.841.883.215.337.894.886.77
MIS (Ours)1.40 (↓0.24)1.50 (↓0.34)1.64 (↓0.24)2.73 (↓0.48)4.61 (↓0.72)6.95 (↓0.94)4.25 (↓0.63)5.94 (↓0.83)
", + "image_path": "ed31a87045e1a20de0363afd5a242efd5afb8887ef360a67e3e500ed78bcb1ac.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 53, + 316, + 553, + 339 + ], + "lines": [ + { + "bbox": [ + 53, + 316, + 553, + 339 + ], + "spans": [ + { + "bbox": [ + 53, + 316, + 553, + 339 + ], + "type": "text", + "content": "Table 2. Performance with limited annotations. When training the model in a supervised manner with a limited number of annotations (1%, 5%, 10%), the performance can be significantly improved by unsupervised pre-training using the proposed method." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 54, + 357, + 135, + 370 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 357, + 135, + 370 + ], + "spans": [ + { + "bbox": [ + 54, + 357, + 135, + 370 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "spans": [ + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "text", + "content": "Implementation Details. We follow SimpleClick [26] to build the interactive segmentation model, which consists of two patch embedding modules for image and click map respectively, a ViT [10] backbone initialized with MAE [16], a simple feature pyramid [21], and an MLP segmentation head. For training, we optimize the model for 55 epochs using the Adam [18] optimizer with a learning rate of 5e-5, which decays by a factor of 10 at 50 epochs. The decay coefficient " + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "text", + "content": " in Algorithm 2 and the weight " + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "text", + "content": " in Equation (8) are 0.9 and 10.0, respectively. In addition, we set a threshold of 0.05 to filter small proposals. That is to say, we ignore the proposals whose areas are less than 0.05 times the image area. For inference, we set the threshold of binarizing the prediction to 0.5 as normal binary segmentation and use the same pre-processing as [26]. To ensure the fully unsupervised setting, we employ a self-supervisedly pre-trained model as the feature extractor. Specifically, a Vision Transformer (ViT) [10] trained with DINO [7] is adopted since the property of representing patch-level semantics [7, 13, 34]. We use ViT-Small [34] with a patch size of 8. The results with other models are included in the appendix. Before feeding an image into the ViT, we resize the image to make its height and width divisible by the patch size (i.e., the target height is " + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "inline_equation", + "content": "(h + p - h \\mod p)" + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "text", + "content": " when the original height " + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "text", + "content": " is not divisible by the patch size " + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "text", + "content": "), and the position embedding is interpolated to fit the image size using bilinear interpolation. We finally use all output tokens of the last block except the " + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "inline_equation", + "content": "cls" + }, + { + "bbox": [ + 53, + 378, + 294, + 713 + ], + "type": "text", + "content": " token as the patch features." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 312, + 358, + 553, + 537 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 358, + 553, + 537 + ], + "spans": [ + { + "bbox": [ + 312, + 358, + 553, + 537 + ], + "type": "text", + "content": "Evaluation. The evaluation is done under the standard evaluation protocol of click-based interactive segmentation. Specifically, we adopt the same click simulator as previous work [44, 17, 25, 35, 8, 36, 24, 9] to sample clicks when evaluation. Roughly, the next click will be placed at the center of the largest error region by comparing the ground-truth and prediction. We adopt the Number of Click (NoC) as the evaluation metric, which counts the average number of clicks needed to achieve a fixed Intersection over Union (IoU), the smaller the better. We use two commonly used target intersection-over-union (IoU) thresholds " + }, + { + "bbox": [ + 312, + 358, + 553, + 537 + ], + "type": "inline_equation", + "content": "85\\%" + }, + { + "bbox": [ + 312, + 358, + 553, + 537 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 312, + 358, + 553, + 537 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 312, + 358, + 553, + 537 + ], + "type": "text", + "content": ", denoted as NoC@85 and NoC@90 respectively. Additionally, the IoU-NoC curves are also adopted to represent the convergence trend of IoU when the NoC increases, as well as compare the IoU metric under the same NoC." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 312, + 541, + 555, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 541, + 555, + 661 + ], + "spans": [ + { + "bbox": [ + 312, + 541, + 555, + 661 + ], + "type": "text", + "content": "Dataset. We evaluate the performance of our MIS on the following four benchmarks. (1) GradCut [32]: The dataset contains 50 relatively easy images whose background and foreground have a clear difference. (2) Berkeley [29]: The dataset contains 96 images with 100 instances and some of them are more challenging than GrabCut. (3) SBD [15]: The dataset contains 2,857 images with 6,671 challenging instances, which does not overlap with our training set. (4) DAVIS [31]: We follow previous works [24, 9, 27, 36, 26] and use the same 345 frames for evaluation." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 312, + 670, + 432, + 682 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 670, + 432, + 682 + ], + "spans": [ + { + "bbox": [ + 312, + 670, + 432, + 682 + ], + "type": "text", + "content": "4.1. Quantitative Results" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 312, + 689, + 553, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 689, + 553, + 713 + ], + "spans": [ + { + "bbox": [ + 312, + 689, + 553, + 713 + ], + "type": "text", + "content": "Baselines. Since the fully unsupervised interactive segmentation has not been explored by previous research, we in-" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "672" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 56, + 70, + 152, + 134 + ], + "blocks": [ + { + "bbox": [ + 56, + 70, + 152, + 134 + ], + "lines": [ + { + "bbox": [ + 56, + 70, + 152, + 134 + ], + "spans": [ + { + "bbox": [ + 56, + 70, + 152, + 134 + ], + "type": "image", + "image_path": "151d0ce19bdf328f8bcbe29d95d0aea2b7e1f9d2f996be0ce8d6df160bfce76c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 78, + 135, + 129, + 143 + 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ValueGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Strength of the Smoothness Constraint λ
0.02.082.563.405.517.389.926.7810.08
3.02.02 (↓0.06)2.50 (↓0.06)3.07 (↓0.33)5.04 (↓0.47)6.84 (↓0.54)9.33 (↓0.59)6.32 (↓0.46)8.78 (↓1.30)
5.01.94 (↓0.14)2.34 (↓0.22)3.01 (↓0.39)4.71 (↓0.80)6.79 (↓0.59)9.39 (↓0.53)6.39 (↓0.39)8.55 (↓1.53)
10.01.94 (↓0.14)2.32 (↓0.24)3.09 (↓0.31)4.58 (↓0.93)6.91 (↓0.47)9.51 (↓0.41)6.33 (↓0.45)8.44 (↓1.64)
15.02.12 (↑0.04)2.50 (↓0.06)3.25 (↓0.15)5.13 (↓0.38)7.12 (↓0.26)9.85 (↓0.07)6.71 (↓0.07)9.10 (↓0.98)
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The results demonstrate its effectiveness and robustness." + } + ] + } + ], + "index": 32, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 53, + 442, + 295, + 528 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 442, + 295, + 528 + ], + "spans": [ + { + "bbox": [ + 53, + 442, + 295, + 528 + ], + "type": "text", + "content": "produce some baselines which are originally designed for unsupervised salient detection (TokenCut [41]), instance segmentation (FreeMask [39]), and semantic segmentation (DSM [30]) to demonstrate the effectiveness of our method. We follow the official implementation of these baselines to extract mask proposals and use them to train the same model as ours. We denote these baselines by “" + }, + { + "bbox": [ + 53, + 442, + 295, + 528 + ], + "type": "inline_equation", + "content": "\\star" + }, + { + "bbox": [ + 53, + 442, + 295, + 528 + ], + "type": "text", + "content": "” in Table 1." + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 53, + 534, + 295, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 534, + 295, + 714 + ], + "spans": [ + { + "bbox": [ + 53, + 534, + 295, + 714 + ], + "type": "text", + "content": "Comparison with Previous Work. For comparison, we present experimental results of previous supervised deep learning methods, non-deep learning methods, baselines, and the proposed MIS on four aforementioned datasets. Under the unsupervised setting, our method significantly outperforms all other methods as shown in the second part of Table 1. It is also worth mentioning that the proposed MIS achieves inspiring performance that is even comparable with some previous supervised approaches. This support that the interactive segmentation task can be solved in a more label-efficient way. Moreover, we show the IoU-NoC curve of previous interactive segmentation methods and MIS in Figure 6, where the dotted lines indicate the upper and lower performance of previous supervised methods. It can be found that our method reaches obviously higher" + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 312, + 442, + 553, + 478 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 442, + 553, + 478 + ], + "spans": [ + { + "bbox": [ + 312, + 442, + 553, + 478 + ], + "type": "text", + "content": "IoU compared to the non-deep learning methods, especially in the first few clicks, and gradually converge to the supervised counterpart when NoC increases." + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 312, + 481, + 553, + 541 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 481, + 553, + 541 + ], + "spans": [ + { + "bbox": [ + 312, + 481, + 553, + 541 + ], + "type": "text", + "content": "Comparison with Baselines. MIS also gets advanced results compared to the baselines which only focus on the specific granularity such as the most salient object or fixed number of objects, demonstrating the effectiveness of diverse interactions under the unsupervised setting." + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 312, + 544, + 554, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 544, + 554, + 651 + ], + "spans": [ + { + "bbox": [ + 312, + 544, + 554, + 651 + ], + "type": "text", + "content": "Supervised Fine-tuning. Besides the fully unsupervised setting, we further fine-tune our model in a supervised manner with only a limited number of annotations (1%, 5%, 10%). As shown in Table 2, the model initialized with MIS pre-training the MAE [16] counterpart especially on the relatively hard dataset (i.e., SBD and DAVIS). These results demonstrate that MIS can serve as a strong unsupervised pre-training method for interactive segmentation when the available annotations are rare." + } + ] + } + ], + "index": 37 + }, + { + "bbox": [ + 312, + 659, + 425, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 659, + 425, + 672 + ], + "spans": [ + { + "bbox": [ + 312, + 659, + 425, + 672 + ], + "type": "text", + "content": "4.2. Qualitative Results" + } + ] + } + ], + "index": 38 + }, + { + "bbox": [ + 312, + 677, + 553, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 677, + 553, + 713 + ], + "spans": [ + { + "bbox": [ + 312, + 677, + 553, + 713 + ], + "type": "text", + "content": "Multi-granularity Region Proposal. In Figure 5 we show the qualitative results of the region proposals generated by the baselines and our MIS, where different colors mean dif" + } + ] + } + ], + "index": 39 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "type": "text", + "content": "673" + } + ] + } + ], + "index": 40 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 55, + 70, + 553, + 155 + ], + "blocks": [ + { + "bbox": [ + 55, + 70, + 553, + 155 + ], + "lines": [ + { + "bbox": [ + 55, + 70, + 553, + 155 + ], + "spans": [ + { + "bbox": [ + 55, + 70, + 553, + 155 + ], + "type": "table", + "html": "
ValueGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Decay coefficient α
0.02.122.483.895.528.7110.877.849.92
0.81.94 (↓0.18)2.40 (↓0.08)3.08 (↓0.81)4.99 (↓0.53)7.03 (↓1.68)9.62 (↓1.25)6.36 (↓1.48)8.57 (↓1.35)
0.91.94 (↓0.18)2.32 (↓0.16)3.09 (↓0.80)4.58 (↓0.94)6.91 (↓1.80)9.51 (↓1.36)6.33 (↓1.51)8.44 (↓1.48)
0.952.22 (↑0.10)2.62 (↑0.14)3.19 (↓0.70)4.89 (↓0.63)6.91 (↓1.80)9.52 (↓1.35)6.09 (↓1.75)8.54 (↓1.38)
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SamplingGrabCutBerkeleySBDDAVIS
NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓NoC@85 ↓NoC@90 ↓
Uniform3.844.324.426.207.119.957.7110.10
Top-down1.94 (↓1.90)2.32 (↓2.00)3.09 (↓1.33)4.58 (↓1.62)6.91 (↓0.20)9.51 (↓0.44)6.33 (↓1.38)8.44 (↓1.66)
", + "image_path": "a27abcc4e4bc895d4d86a392b59d0f47a41482c1d6868cfbd43a219d1159d554.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 53, + 243, + 553, + 268 + ], + "lines": [ + { + "bbox": [ + 53, + 243, + 553, + 268 + ], + "spans": [ + { + "bbox": [ + 53, + 243, + 553, + 268 + ], + "type": "text", + "content": "Table 5. Ablation on sampling strategy. The proposed top-down sampling strategy is effective because it reasonably assigns different weights to fragmented and complete components, so as to sample complete objects as much as possible while maintaining diversity." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 53, + 285, + 294, + 369 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 285, + 294, + 369 + ], + "spans": [ + { + "bbox": [ + 53, + 285, + 294, + 369 + ], + "type": "text", + "content": "ferent mask proposals and our mask proposals. Compared with them, our multi-granularity proposals capture more informative regions and are more diverse. Through the top-down random sampling strategy, our proposals provide the model with rich interactions, which makes the model learn a better mapping from clicks to segmentation under the unsupervised setting." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 53, + 373, + 295, + 494 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 373, + 295, + 494 + ], + "spans": [ + { + "bbox": [ + 53, + 373, + 295, + 494 + ], + "type": "text", + "content": "Interactive Segmentation. Figure 7 show some interactive segmentation examples of our method. The trained interactive segmentation model is able to capture the outline of the needed object by the first one or two clicks and achieves high IoU with a few clicks, which demonstrates the feasibility of our newly proposed unsupervised setting and the effectiveness of the MIS. For some simple objects, our model can produce satisfactory predictions within the first few clicks. It can also handle complex scenes such as partially occluded objects and adjacent instances." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 53, + 500, + 149, + 513 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 500, + 149, + 513 + ], + "spans": [ + { + "bbox": [ + 53, + 500, + 149, + 513 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 53, + 518, + 295, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 518, + 295, + 602 + ], + "spans": [ + { + "bbox": [ + 53, + 518, + 295, + 602 + ], + "type": "text", + "content": "Smoothness Constraint. For the smoothness constraint, we switch the weight " + }, + { + "bbox": [ + 53, + 518, + 295, + 602 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 53, + 518, + 295, + 602 + ], + "type": "text", + "content": " in Equation (8) to show its effectiveness. The experimental results in Table 3 demonstrate that the smoothness constraint is helpful for improving the performance through the principle that helps the model correct the boundary errors in the proposals. The effectiveness is robust when " + }, + { + "bbox": [ + 53, + 518, + 295, + 602 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 53, + 518, + 295, + 602 + ], + "type": "text", + "content": " is within a reason range." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 53, + 605, + 295, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 605, + 295, + 715 + ], + "spans": [ + { + "bbox": [ + 53, + 605, + 295, + 715 + ], + "type": "text", + "content": "Top-down Sampling. The top-down sampling (Algorithm 2) is the core part of our MIS to achieve diversity. We evaluate its effectiveness by comparing with a fixed-granularity strategy, and a fully random strategy that randomly sample nodes on the merging tree from a uniform distribution. In Table 4, we take " + }, + { + "bbox": [ + 53, + 605, + 295, + 715 + ], + "type": "inline_equation", + "content": "\\alpha = 0.0" + }, + { + "bbox": [ + 53, + 605, + 295, + 715 + ], + "type": "text", + "content": " as the baseline. In this case, we always use one of the two children of the root node in the merging tree, thus multi-granularity is not allowed. Comparing the results with " + }, + { + "bbox": [ + 53, + 605, + 295, + 715 + ], + "type": "inline_equation", + "content": "\\alpha = 0.8, 0.9, 0.95" + }, + { + "bbox": [ + 53, + 605, + 295, + 715 + ], + "type": "text", + "content": " we" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 312, + 285, + 555, + 441 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 285, + 555, + 441 + ], + "spans": [ + { + "bbox": [ + 312, + 285, + 555, + 441 + ], + "type": "text", + "content": "can find that the introduction of multi-granularity brings noticeable improvement, especially in the hard dataset. It is also obvious that this hyper-parameter is relatively robust. In addition, the results compared to the fully random sampling strategy in Table 5 also show clear advantages of our top-down sampling strategy. When sampling uniformly, the finely divided object components are more likely to be selected due to the large number, resulting in local perception and thus requiring more clicks to localize objects. In contrast, our top-down sampling strategy reasonably assigns different weights to fragmented and complete components, so as to sample complete objects as much as possible while maintaining diversity." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 312, + 450, + 387, + 463 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 450, + 387, + 463 + ], + "spans": [ + { + "bbox": [ + 312, + 450, + 387, + 463 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 312, + 471, + 555, + 650 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 471, + 555, + 650 + ], + "spans": [ + { + "bbox": [ + 312, + 471, + 555, + 650 + ], + "type": "text", + "content": "In this work, we open up a promising direction for deep interactive segmentation that completely discards the dependence on manual annotations. While previous methods learn the interaction through object-oriented simulation with pixel-level annotations, we propose MIS and demonstrate the feasibility to simulate informative interaction with semantic-consistent regions discovered in an unsupervised manner. Inspiring experimental results show the effectiveness of our method and the potential to reduce the labor of creating annotation without cost via training an interactive segmentation model unsupervisedly. Our experiment also supports that the interactive segmentation task can be solved in a more label-efficient way to trade off the performance and annotations. We hope our exploration can promote the attendance of label efficiency on interactive segmentation." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 312, + 654, + 553, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 654, + 553, + 715 + ], + "spans": [ + { + "bbox": [ + 312, + 654, + 553, + 715 + ], + "type": "text", + "content": "Acknowledgements. This work was supported by the National Key R&D Program of China (2022ZD0118101) and the Natural Science Foundation of China (No. 61972217, 32071459, 62176249, 62006133, 62271465, 62202014). 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Its branches display part of the well registered targets, which are extraordinarily affluent and manifold. The zoomed-in regions on the right show the segmentation comparison in cyan circles and fusion comparison in orange circles. It is obvious that the proposed method is superior to SOTA methods on both visual effects and mIoU." + ], + "image_footnote": [], + "bbox": [ + 81, + 338, + 467, + 501 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/c8e8dcc745e8f90cc38f7fcddc6619cd3562934cba89961178ac7846a908f03b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 467, + 337, + 607, + 501 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/5152074a6387b181f96d8150372cd023b4aac5ae0613fac95c0d9c2aac59b4b6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 609, + 337, + 746, + 500 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/99baaa803bd6eb1c457bd23e65e09b8b060503ab9273b94d6410e29a2a5f0fc2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 748, + 338, + 888, + 500 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 585, + 313, + 601 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Multi-modality image fusion and segmentation play a vital role in autonomous driving and robotic operation. Early efforts focus on boosting the performance for only one task, e.g., fusion or segmentation, making it hard to reach 'Best of Both Worlds'. To overcome this issue, in this paper, we propose a Multi-interactive Feature learning architecture for image fusion and Segmentation, namely SegMiF, and exploit dual-task correlation to promote the performance of both tasks. The SegMiF is of a cascade structure, containing a fusion sub-network and a commonly used segmentation sub-network. By slickly bridging intermediate features between two components, the knowledge learned from the segmentation task can effectively assist the fusion task. Also, the benefited fusion network supports the segmentation one to perform more pretentionally. Besides, a hierarchical interactive attention block is established to ensure fine-grained mapping of all the vital information between two tasks, so that the modality/semantic features can be fully mutual-interactive. In addition, a dy", + "bbox": [ + 73, + 613, + 473, + 902 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "namic weight factor is introduced to automatically adjust the corresponding weights of each task, which can balance the interactive feature correspondence and break through the limitation of laborious tuning. Furthermore, we construct a smart multi-wave binocular imaging system and collect a full-time multi-modality benchmark with 15 annotated pixel-level categories for image fusion and segmentation. Extensive experiments on several public datasets and our benchmark demonstrate that the proposed method outputs visually appealing fused images and perform averagely $7.66\\%$ higher segmentation mIoU in the real-world scene than the state-of-the-art approaches. The source code and benchmark are available at https://github.com/JinyuanLiu-CV/SegMiF.", + "bbox": [ + 496, + 587, + 895, + 800 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 500, + 829, + 632, + 844 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Accurate and robust scene parsing[1, 2] is a fundamental technology for autonomous driving. However, in complex environments, e.g., inclement weather, only using visi", + "bbox": [ + 496, + 854, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "8115", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "ble sensors may fail to accurately recognize targets. On the contrary, infrared sensors are free from the aforementioned issues but limited in low spatial resolution. Consequently, fusing the infrared and visible image [3, 4, 5, 6, 7] has become a mainstream solution for better scene understanding.", + "bbox": [ + 75, + 90, + 467, + 166 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-modality fusion for scene parsing needs to provide: (i). robust visual appealing image: they require continually generating high-quality images in dynamic scenes. (ii). accurate semantic segmentation: they demand to assign category labels to each pixel. Towards these goals, jointly solving multi-modality image fusion and segmentation becomes an urgent issue.", + "bbox": [ + 75, + 167, + 467, + 271 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Numerous learning-based multi-modality image fusion methods have been fast development [8, 9, 10, 11, 12]. However, most of them concentrate on developing various networks for generating visual-appealing images rather than considering the follow-up high-level vision tasks, posing an obstacle to better scene parsing. Recently, few studies[13, 14, 15, 16] have attempted to design multi-task learning-based loss functions by cascading the fusion network and high-level tasks. Unfortunately, seeking unified appropriate features for either task simultaneously is still a tough issue.", + "bbox": [ + 75, + 272, + 467, + 436 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Moreover, exploring multi-modality fusion and segmentation demands a comprehensive collection of well-alignment image pairs with pixel-level annotated labels. Also, as for one image, the annotated needs to cover a wide range of pixels. Unfortunately, existing multi-modality data collections either focus on image fusion or lack whole image annotated segmentation labels, placing an obstacle to exploring the correlation of the fusion and segmentation.", + "bbox": [ + 75, + 438, + 467, + 558 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "This paper proposes a multi-interactive feature learning architecture for the joint problem of multi-modality fusion and segmentation, namely SegMiF. SegMiF is constructed by a fusion network and a segmentation network, in which the intrinsic features of either one interact via a new proposed hierarchical interactive attention (HIA). HIA fully integrates semantic-/modality-oriented features by fine-grained mapping. We also derive a dynamic weighting factor and seamless it in the interactive training scheme, to automatically learn the optimal parameters for either task. Figure 1 demonstrates that our SegMiF assigns the category to each pixel from the visual-friendly fused result more accurately than the state-of-the-arts (SOTAs). Our contributions can be distilled into four main aspects as follows:", + "bbox": [ + 75, + 559, + 467, + 770 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We formulate both image fusion and segmentation in a joint manner, in which the semantic and pixel-based features can mutually interact. To this end, two tasks can achieve the 'Best of Both Worlds', generating visual-appealing fused images along with accurate scene parsing.", + "- A hierarchical interactive attention is introduced to bridge the feature gap between the fusion network" + ], + "bbox": [ + 94, + 777, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "and the segmentation one. Establishing the semantic/modality multi-head attention mechanism in HIA simultaneously preserves intrinsic modality features and brings more attention to semantic features.", + "bbox": [ + 529, + 90, + 890, + 151 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- An interactive feature training scheme is proposed to overcome the shortcoming of insufficient feature interaction between fusion and segmentation. Seamlessly integrating a dynamic weighting factor allows the exploration of the optimal parameters of each task in an automatic manner.", + "- We construct a smart multi-wave binocular imaging system, and introduce a full-time multi-modality benchmark, namely FMB, to promote the research of both image fusion and segmentation. FMB contains 1500 well-registered infrared and visible image pairs with 15 annotated pixel-level categories (see the left part of Figure 1). Also, it covers a wide range of pixel variations and various severe environments, e.g., dense fog, heavy rain, and low-light condition." + ], + "bbox": [ + 517, + 170, + 890, + 414 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Works", + "text_level": 1, + "bbox": [ + 500, + 441, + 648, + 458 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-modality image fusion In recent years, deep learning based multi-modality image fusion approaches achieved significant progress[11, 12, 17, 18, 19]. Early efforts [8, 9, 10, 20, 21] tend to achieve excellent fusion effects by adjusting the network structure or loss functions. However, a minority pay attention to whether the downstream tasks can be well adapted to fusion. DIDFuse [10] was the first to apply deep decomposition for high and low-frequency features, while AUIF [22] proposed a decomposition and fusion framework based on algorithm unfolding from an optimization perspective. Subsequently, CDDFuse [6] upgraded the decomposition network to a Transformer-CNN dual-stream structure. DDFM [7], for the first time, utilized denoising diffusion models for image fusion tasks. Recently, some methods [23, 13, 24] cascaded fusion and downstream tasks, focusing on improving task performance by achieving oriented fusion. Nevertheless, this kind of native gradient back propagation hinders the fusion network to adapt to subsequent tasks heuristically from the feature level.", + "bbox": [ + 496, + 472, + 890, + 758 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-modality Segmentation Recently, two-stream-based feature fusion models are proposed to perform the segmentation directly. Most of existing methods mostly develop various simple fusion strategies, such as the weighted average [25, 26, 27], summation [28, 29] and concatenation [30, 31]. Nonetheless, direct feature fusion lacks explicit fusion principle to preserve the typical modality feature and pay no attention to the pixel-level visual effects.", + "bbox": [ + 496, + 763, + 890, + 885 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "8116", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/5ebdbf194e48f440514ca0c6cdf03b86ee1d17a2db2579fc4caefad69738ab06.jpg", + "image_caption": [ + "Figure 2: Workflow of our proposed SegMiF. The left part depicts the latent interactive relationship between image fusion and segmentation. The middle part plots the concrete architecture of the SegMiF. The right part details the components of proposed hierarchical interactive attention." + ], + "image_footnote": [], + "bbox": [ + 83, + 88, + 344, + 239 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/436cb10c9073e70c336f00cb3b5835b7706c8d2bf707ff7d0d92aa933799370c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 344, + 88, + 640, + 239 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/67be32218d741da2972828f251e2f875d343fcdf120d003f33d6dcfe23da76e4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 640, + 88, + 883, + 239 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. The Proposed Method", + "text_level": 1, + "bbox": [ + 76, + 324, + 287, + 340 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Problem formulation", + "text_level": 1, + "bbox": [ + 76, + 349, + 274, + 364 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As for image fusion or segmentation tasks, one of the most commonly used ways is to design a neural network, and fully utilize it to find a set of optimal parameters. For this purpose, we suppose that the visible, infrared, and fused image are all gray-scale with the size of $m \\times n$ , denoted as column vectors $\\mathbf{x}$ , $\\mathbf{y}$ , and $\\mathbf{u} \\in \\mathbb{R}^{mn \\times 1}$ , respectively. The optimization model is formulated as:", + "bbox": [ + 75, + 372, + 470, + 478 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\boldsymbol {\\omega} _ {k}} f \\left(\\mathbf {k}, \\mathcal {N} (\\mathbf {x}, \\mathbf {y}; \\boldsymbol {\\omega} _ {k})\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 197, + 489, + 468, + 513 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{k}$ denotes the output of the task-related network $\\mathcal{N}$ with the learnable parameters $\\omega_{\\mathrm{k}}$ . $f(\\cdot)$ is a fidelity term.", + "bbox": [ + 75, + 523, + 468, + 554 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Previous approaches solely design image fusion or segmentation networks, which only can achieve outstanding results for one task. To generate visualappealing fused images along with accurate scene segmentation results, we jointly formulate the two tasks into one goal [32, 33, 34], which can be rewritten as:", + "bbox": [ + 75, + 554, + 468, + 643 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\min _ {\\boldsymbol {\\omega} _ {\\mathrm {u}}, \\boldsymbol {\\omega} _ {\\mathrm {s}}} f _ {\\mathrm {u}} \\left(\\mathbf {u}, \\Phi (\\mathbf {x}, \\mathbf {y}; \\boldsymbol {\\omega} _ {\\mathrm {u}})\\right) + f _ {\\mathrm {s}} \\left(\\mathbf {s}, \\Psi (\\mathbf {x}, \\mathbf {y}; \\boldsymbol {\\omega} _ {\\mathrm {s}})\\right) + g \\left(\\boldsymbol {\\omega} ^ {\\star}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 98, + 669, + 468, + 691 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\omega^{\\star} = [\\omega_{\\mathrm{u}},\\omega_{\\mathrm{s}}]$ . $\\mathbf{u}$ and $\\mathbf{s}$ denote the fused image and segmentation map, which are produced by the fusion network $\\Phi$ and segmentation network $\\Psi$ with the learnable parameters $\\omega_{\\mathrm{u}}$ and $\\omega_{\\mathrm{s}}$ . $g(\\cdot)$ is a constrained term to joint optimize the two tasks. In this paper, we regard the $g(\\cdot)$ as a feature learning constrained manner, and achieve this goal by designing a hierarchical attention along with the interactive training scheme. The visualized illustration is plotted in the left part of Figure 2.", + "bbox": [ + 75, + 700, + 468, + 838 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Feature interaction architecture", + "text_level": 1, + "bbox": [ + 76, + 847, + 359, + 862 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Overview of the whole network. Our proposed SegMiF is designed with cascade principle, composited by image", + "bbox": [ + 76, + 869, + 470, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "fusion and segmentation sub-network. Details of the whole architecture is shown at Figure 2. In specific, we utilize two parallel dilated residual dense blocks (DRDB) [35, 36] to extract features from visual and infrared images. SegFormer [37] is leveraged as the baseline segmentation network to provide semantic parsing. Two scales of semantic features from the backbone, interpolated with original resolutions are embedded into fusion network. In order to sufficiently realize the semantic information sharing, we propose the hierarchical interactive attention (HIA) to transfer high-level knowledge.", + "bbox": [ + 496, + 325, + 890, + 492 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Hierarchical interactive attention. After obtaining modality feature $\\mathbf{F}_{ir},\\mathbf{F}_{vis}$ from fusion network and segmentation feature $\\mathbf{F}_{seg}$ , we build the HIA to construct the fine-grained mapping of these features and strengthen the mutually beneficial representation. Features including $\\mathbf{F}_{ir},\\mathbf{F}_{vis}$ and $\\mathbf{F}_{seg}$ as inputs, two attention mechanisms are leveraged to globally exchange intermediate features. Concatenating features from attentions, fresh modality features are generated based on a residual connection.", + "bbox": [ + 496, + 493, + 890, + 630 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In detail, channel embedding is utilized to decompose modality/semantic features. We can denote the outputs from the linear embedding as $\\{\\mathbf{F}_x^s,\\mathbf{F}_x^m\\}$ with size $\\mathbb{R}^{mn\\times C}$ , where $x\\in \\{ir,vis,seg\\}$ is under a vector formulation. Instead of utilizing the original self-attention mechanisms directly, we bridge these features with complementary interaction from different representation subspaces by MoAM and SoAM.", + "bbox": [ + 496, + 631, + 890, + 737 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/e8464b0d0627836ae85a3385200cbc3862cd89a10da2bade51a2c04432216ffb.jpg", + "image_caption": [ + "Figure 3: Detailed architectures of SoAM and MoAM." + ], + "image_footnote": [], + "bbox": [ + 501, + 750, + 893, + 839 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Both multi-head attention modules are plotted in Fig-", + "bbox": [ + 519, + 885, + 890, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "8117", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ure 3. Semantic-oriented attention module targets to provide more semantic attention for the modality feature. SoAM utilizes the token $\\mathbf{F}_{seg}^{s}$ to generate the Query $Q_{s}$ , which represents the inhere semantic information that needs to be enhanced. The global context representation of each can be calculated by as $K_{ir}^{T}V_{ir}$ and $K_{vis}^{T}V_{vis}$ , where the corresponding Key and Value of each head are from the modality tokens $\\{\\mathbf{F}_{ir}^{m},\\mathbf{F}_{vis}^{m}\\}$ . Denoted the modality context representation as $\\mathbf{G}_{ir}$ , $\\mathbf{G}_{vis}$ , we can calculate the attention as $S_{ir} = Q_s\\mathbf{G}_{ir}$ and $S_{vis} = Q_s\\mathbf{G}_{vis}$ . On the other hand, MoAM is with the complementary principle to investigate the significant feature from semantic contexts. Specifically, MoAM is to introduce two modality queries $Q_{ir},Q_{vis}$ to represent the intrinsic modality feature (e.g., targets and details) from $\\{\\mathbf{F}_{ir}^{m},\\mathbf{F}_{vis}^{m}\\}$ . Similarly, we can obtain the global context of segmentation $\\mathbf{G}_s$ by $K_{s}^{T}V_{s}$ . The cross attention can be formulated as $M_{vis} = Q_s\\mathbf{G}_{vis}$ and $M_{vis} = Q_s\\mathbf{G}_{vis}$ . By concatenating the groups $\\{S_{vis},M_{vis}\\}$ and $\\{S_{ir},M_{ir}\\}$ , we can obtain the comprehensive features with two parallel MLPs with residual connection to aggregate features from SoAM and MoAM.", + "bbox": [ + 76, + 90, + 472, + 409 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Loss function", + "text_level": 1, + "bbox": [ + 76, + 421, + 218, + 434 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The total loss function is combined of an image fusion loss function $\\mathcal{L}_{\\mathrm{f}}$ and segmentation loss $\\mathcal{L}_{\\mathrm{s}}$ . $\\mathcal{L}_{\\mathrm{f}}$ consists of three types of losses, i.e., structure loss $\\mathcal{L}_{\\mathrm{SSIM}}$ , pixel loss $\\mathcal{L}_{\\mathrm{MSE}}$ and gradient loss $\\mathcal{L}_{\\mathrm{grad}}$ . For one fused image, it should preserve overall structures from source images. To this end, the structural similarity index (SSIM) [38, 39, 40, 41] is introduced in function:", + "bbox": [ + 76, + 445, + 468, + 551 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {S S I M}} = \\left(1 - \\mathrm {S S I M} _ {\\mathbf {u}, \\mathbf {x}}\\right) / 2 + \\left(1 - \\mathrm {S S I M} _ {\\mathbf {u}, \\mathbf {y}}\\right) / 2, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 116, + 558, + 468, + 575 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathcal{L}_{\\mathrm{SSIM}}$ denotes structure similarity loss. To maintain the vital intensity in the fused image, we employ the saliency-based pixel loss, it formulated as:", + "bbox": [ + 76, + 589, + 468, + 633 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {M S E}} = \\left\\| \\mathbf {u} - m _ {1} \\mathbf {x} \\right\\| _ {2} ^ {2} + \\left\\| \\mathbf {u} - m _ {2} \\mathbf {y} \\right\\| _ {2} ^ {2}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 143, + 647, + 468, + 666 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $m_{1}$ and $m_{2}$ are saliency weight maps calculated by VSM [42]. Besides, gradient information of images always characterizes texture details, thus, we used $\\mathcal{L}_{\\mathrm{grad}}$ to constrain these textual factors to a multi-scale manner:", + "bbox": [ + 76, + 678, + 468, + 739 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {g r a d}} = \\sum_ {k = 3, 5, 7} \\| \\nabla^ {k} \\mathbf {u} - \\max (\\nabla^ {k} \\mathbf {x}, \\nabla^ {k} \\mathbf {y}) \\| _ {2} ^ {2} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 122, + 751, + 468, + 782 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\nabla$ denotes gradient operators that calculate by $\\nabla = \\mathbf{u} - \\mathcal{G}(\\mathbf{u})$ with combination of different Gauss $(\\mathcal{G})$ kernel size $k$ . Totally, we obtained $\\mathcal{L}_{\\mathrm{f}} = \\mathcal{L}_{\\mathrm{SSIM}} + \\mathcal{L}_{\\mathrm{MSE}} + \\eta \\mathcal{L}_{\\mathrm{grad}}$ .", + "bbox": [ + 76, + 796, + 468, + 843 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Common to previous works, $\\mathcal{L}_{\\mathrm{s}}$ is defined as:", + "bbox": [ + 96, + 843, + 398, + 858 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {s}} \\left(\\mathbf {s}, \\mathbf {s} ^ {*}\\right) = - \\sum_ {\\text {c l a s s}} \\mathbf {s} ^ {*} \\log (\\mathbf {s}), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 173, + 872, + 468, + 904 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbf{s}^*$ represents the segmentation label. We adopt the effective semantic segmentation method SegFormer network $\\Psi$ [37]. The total loss function is:", + "bbox": [ + 498, + 90, + 890, + 136 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {t o t a l}} = \\lambda_ {1} \\mathcal {L} _ {\\mathrm {f}} + \\lambda_ {2} \\mathcal {L} _ {\\mathrm {s}}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 614, + 148, + 890, + 165 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\lambda_{1}$ and $\\lambda_{2}$ are dynamic weighting factor which will be discussed below.", + "bbox": [ + 498, + 176, + 890, + 205 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Dynamic factor for interactive learning", + "text_level": 1, + "bbox": [ + 500, + 217, + 836, + 233 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "By exploiting an alternatively recurrent iterations, we can progressively introduce the task-preferred features into the framework optimization. As mentioned above, at the phase of image fusion, we introduce the dynamic weighting factors $\\lambda_{1}$ and $\\lambda_{2}$ to rapidly measure the importance of task-related losses. We observe that the task-specific balance can be derived from the convergent rate. The intuition is that if the value of losses cannot be further descended, the network may obtain the corresponding optimal weights. If the convergent rate descends fast, we should pay more attention to this task. Learning from the dynamic weight average [43], we further present the factor of task preference $\\eta$ to emphasize the primary goal. Denoted $r_i$ as the convergent rate of $i$ -th task with loss $\\mathcal{L}_i$ , we can compute the rate as:", + "bbox": [ + 498, + 241, + 890, + 452 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nr _ {1} (n - 1) = \\frac {\\mathcal {L} _ {i} (n - 1)}{\\mathcal {L} _ {i} (n - 2)}. \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 611, + 463, + 890, + 496 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Then the procedure of dynamic weight factor of $i$ -th task is formulated as:", + "bbox": [ + 500, + 506, + 890, + 535 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\lambda_ {\\mathrm {i}} (n) = \\frac {\\eta_ {\\mathrm {i}} \\exp \\left(r _ {\\mathrm {i}} (n - 1) / T\\right)}{\\sum_ {k} \\exp \\left(r _ {\\mathrm {k}} (n - 1) / T\\right)}, \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 584, + 545, + 890, + 579 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $T$ is a temperature to control the sensitiveness of two tasks. Different from widely sued GDN [44], this dynamic strategy can actually avoid the complicated computation of various task gradients.", + "bbox": [ + 498, + 589, + 890, + 648 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Then based on the fusion image generated with semantic feature, we can train the segmentation network end-to-end, using the gradient descending $\\omega_{s} \\gets \\omega_{s} - \\nabla_{\\omega_{s}} \\mathcal{L}_{\\mathbb{S}}(\\mathbf{u}; \\omega_{s})$ . The two learning processes are trained alternately until full convergence. Noting that, this training strategy is actually task-agnostic, we also can introduce other different high-level vision tasks into the unified consideration, rather than designing for segmentation unilaterally.", + "bbox": [ + 498, + 648, + 890, + 771 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Full-time Multi-modality Benchmark", + "text_level": 1, + "bbox": [ + 500, + 784, + 836, + 801 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Existing two multi-modality segmentation datasets suffer from few label categories, sparse annotation and monotonous scene, as shown in Figure 6. The proposed FMB dataset aims to overcome these difficulties and promote the development of whole field. A glimpse of FMB is given in Figure 4.", + "bbox": [ + 498, + 810, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "8118", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/8aa6f083139321b291dc3c4021fee41d106d54783255573cb0d7fb81f5b0d660.jpg", + "image_caption": [ + "Figure 4: Visualization of visible/infrared/segmentation images in the proposed FMB dataset. The dataset contains a wide range of real driving scenes under different lighting conditions, and also includes special scenarios with rain, fog, strong light, and even Tyndall Effect." + ], + "image_footnote": [], + "bbox": [ + 99, + 88, + 872, + 212 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/29021975e4f31c1fd2d15f3dc07b2905c700b87c17e1a52c5fc872738e7eca3c.jpg", + "image_caption": [ + "Figure 5: Illustration of the binocular imaging system." + ], + "image_footnote": [], + "bbox": [ + 88, + 275, + 460, + 402 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We built a binocular imaging system that can be placed on the car roof, including a visible camera and an infrared sensor with a wavelength range of $8 - 14\\mu m$ (as shown in the Figure 5). We finally obtained 1500 aligned image pairs with a resolution of $800\\times 600$ . In details, two sensors are individually calibrated using their respected calibration board to obtain internal parameters, and their relative pose relationship is obtained through joint calibration. We calculate the homography matrix $H$ by employing RANSAC1. The infrared images are projected onto visible coordinates using $H$ and cropped, ultimately resulting in pixel-level registered image pairs with a size of $800\\times 600$ .", + "bbox": [ + 75, + 460, + 468, + 640 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The FMB dataset includes rich scenes under different illumination conditions, so that it enables fusion/segmentation model to improve the generalization ability greatly. We labeled $98.16\\%$ of all pixels into 14 different categories including Road, Sidewalk, Building, Traffic Light, Traffic Sign, Vegetation, Sky, Person, Car, Truck, Bus, Motorcycle, Bicycle and Pole, which often appear in real-world automatic driving and semantic understanding tasks.", + "bbox": [ + 75, + 641, + 468, + 762 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 76, + 776, + 209, + 792 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Two representative datasets including MFNet and proposed FMB are utilized for the training and evaluation. The details of these datasets are reported in the above section. Several data augmentation techniques are utilized for the whole training procedure: random resizing with a ratio of", + "bbox": [ + 75, + 801, + 470, + 878 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/d5aea48cfd0c67ab07fadcbc288fdcbd353abfe6f0ee4d56aac183c181ffafdc.jpg", + "image_caption": [ + "Figure 6: Comparison of FMB with existing multi-modality segmentation datasets (i.e., PST900 [31] and MFNet [30])." + ], + "image_footnote": [], + "bbox": [ + 509, + 277, + 883, + 369 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "0.5-2.0, random cropping to $360 \\times 360$ , brightness distortion and normalization. The Adam optimizer with poly learning rate adjustment is utilized to optimize both networks. As for the fusion, the initial learning rate is $1e^{-4}$ and decayed to $1e^{-8}$ progressively. As for segmentation, we first utilized $1e^{-6}$ to warm start the training with 3k iterations, then we conducted the training with intilial learning rate $8e^{-5}$ . With batch size of 8, we trained the framework for 8 rounds. For each round, we set 10k iterations for training segmentation and 5k iterations for fusion. Noting that, a similar configuration of segmentation is also utilized for the training of fusion-based methods. All experiments are performed on an NVIDIA Tesla V100 GPU with PyTorch framework.", + "bbox": [ + 496, + 443, + 893, + 640 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5.1. Results of multi-modality image fusion", + "text_level": 1, + "bbox": [ + 500, + 650, + 831, + 666 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We demonstrate our fusion quality based on qualitative and quantitative analyses with six state-of-the-art competitors, including DIDFuse [10], DenseFuse [45], ReCoNet[11], UMFusion[12], TarDAL[13] and U2Fusion [9].", + "bbox": [ + 496, + 674, + 890, + 750 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Qualitative Comparisons. The qualitative results on MFNet and FMB datasets are depicted in Figure 7, in which we can clearly observe two remarkable advantages of our method. First, the significant characteristics of infrared images can be effectively highlighted. For instance, as shown on the green rectangle of the first group, DIDFuse, ReCoNet and TarDAL are susceptible to strong illumination. In contrast, our method can remarkably preserve this information from infrared images, e.g., the structure of cars and pedestrians. Furthermore, benefiting from the guidance of semantic", + "bbox": [ + 496, + 750, + 892, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "Efficient RANSAC for point-cloud shape detection", + "bbox": [ + 94, + 886, + 370, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "8119", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/7bc7ed056c578188e6ef11ccdd33f6a62dff868071e0937228434bb5b51de164.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 83, + 87, + 183, + 159 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/0e9c59857c4699f1a5bce16363196e2e8e1b19054f4d723f343824dee99a0905.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 183, + 88, + 284, + 159 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/1f49c27e4511c207edd11c82d9d379ee6299c9fa12aed5a1c4b8d13cba6ba306.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 284, + 88, + 383, + 159 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c02894caef09b119339293fe21797b7e166a5855cbc032625b33eb026b0d3ac5.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 383, + 88, + 483, + 159 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/3466209485ff5724f07bf593070392abfa0246a86446881ccbf1904820ac5158.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 483, + 88, + 584, + 159 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/cba7e7924ae660369d527fb818b0312a4200cf7fe4baa614ae567ed598258663.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 584, + 88, + 684, + 159 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/3db9e4f6796c7b47fac6e9c3a790ae07d9a532904f6cb89b23c06118c600836d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 684, + 88, + 784, + 159 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/4b354bfe11ef5e5a014529077d610473af3aa4363e73644a882e0c8ba3a6c51b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 784, + 88, + 885, + 159 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/64951e02302574588ef07b9627c03e32bb36a1e88864c32eb1c20624d6dbfe8f.jpg", + "image_caption": [ + "Source images" + ], + "image_footnote": [], + "bbox": [ + 83, + 161, + 183, + 232 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/7cd3646bfc2de238c9db228e92dcd1c21f30515ae6b8b12b795b565ac8000cf7.jpg", + "image_caption": [ + "DIDFuse" + ], + "image_footnote": [], + "bbox": [ + 184, + 161, + 284, + 232 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/b118f509c459bd9881413aa9866a19cc2d2704709cfd326e6a565d65a6b7b932.jpg", + "image_caption": [ + "DenseFuse" + ], + "image_footnote": [], + "bbox": [ + 284, + 161, + 383, + 232 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/3587ff26ecf05572f57f0b5fde2cdd334ef6dd99f3a83f277ea0752d9ba73d98.jpg", + "image_caption": [ + "ReCoNet" + ], + "image_footnote": [], + "bbox": [ + 385, + 161, + 483, + 232 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/73ed946d90a49ffd38851af674e40ec2f96d01e5f9a25c521dd6c7c0cff8755d.jpg", + "image_caption": [ + "UMFusion" + ], + "image_footnote": [], + "bbox": [ + 483, + 161, + 584, + 232 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/9a471e9a0fabaf4d8f8bbb8c2edebbf3587c7e1bbf42e1f431393c1474e634e4.jpg", + "image_caption": [ + "TarDAL" + ], + "image_footnote": [], + "bbox": [ + 584, + 161, + 684, + 232 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/fef0fdba71ff40da1e1bf23d57565fa22ac9d5597ffaab670e51d5c468807151.jpg", + "image_caption": [ + "U2Fusion" + ], + "image_footnote": [], + "bbox": [ + 684, + 161, + 784, + 232 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/96eb2b77cb4d0f0c78d3a61728b3011d3ac89dc7e51926a9be663311f67d7c29.jpg", + "image_caption": [ + "Ours" + ], + "image_footnote": [], + "bbox": [ + 785, + 161, + 885, + 232 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/f33b089ccbaabdd2147a67809d8cfc85fb160c3e5aa017272eabf9d44982c878.jpg", + "image_caption": [ + "Figure 7: Visual comparison of different fusion approaches on the MFNet and FMB dataset, respectively." + ], + "image_footnote": [], + "bbox": [ + 81, + 292, + 483, + 393 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/f8a90e4a0b8c3259c2725fdf262a4c9b8f7710419354dd1b65be8bf04a9f7b61.jpg", + "image_caption": [ + "Figure 8: Quantitative comparisons of image fusion with six SOTA methods on two datasets. Violin plots illustrating the distribution of the four metrics, in which the white triangles and the black lines indicate mean values and medium values." + ], + "image_footnote": [], + "bbox": [ + 488, + 292, + 880, + 393 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/4f7a4082b6d8810e6e059e23e611e2616ee4050c25ca059e7a7758fbfb785a6c.jpg", + "image_caption": [ + "Figure 9: Qualitative demonstrations of different approaches on the MFNet dataset." + ], + "image_footnote": [], + "bbox": [ + 86, + 444, + 483, + 575 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/f692700d3d45d2320904936768432094442584b6bea2c935667134dca403ade8.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 485, + 444, + 883, + 575 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "information, our method can enhance the texture details of the given scene from either dataset. Compared with other competitors in the second row of Figure 7, our results exhibit a sharper appearance.", + "bbox": [ + 75, + 628, + 468, + 689 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Quantitative Comparisons. We also plot the numerical results with other six fusion competitors on 50 pairs from MFNet and 50 pairs from FMB in Figure 8. Four objective metrics are leveraged for the comparison, including entropy (EN)[46], standard deviation (SD)[47], spatial frequency (SF)[48] and the sum of the correlations of differences (SCD)[49]. Note that our results achieve consistent superiority in terms of these statistical metrics. Specifically, the highest EN and SCD indicate that our method can significantly preserve the largest amount of considerable information transferred from source images. Moreover, the immense average value on SD reflects the high pixel contrast for visual observations. Furthermore, higher SF reflects our", + "bbox": [ + 75, + 703, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "method has rich texture details and contrasts. In summary, our method enhances the texture details for precise observation and stably preserves abundant typical information to support semantic parsing tasks.", + "bbox": [ + 496, + 628, + 890, + 690 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. Results of multi-modality segmentation", + "text_level": 1, + "bbox": [ + 500, + 700, + 836, + 715 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We provide another comprehensive analysis for image segmentation. Besides comparing with the newest fusion-based methods, we also conduct the evaluations with competitive dual-stream methods: GMNet [50], FEANet [51], EGFNet [52], ABMDRNet [53] and LASNet [54].2", + "bbox": [ + 496, + 723, + 890, + 799 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Qualitative Comparisons. Visualized results of segmentation on MFNet are depicted in Figure 9. We also compare various competitive methods in Figure 10 under the newly proposed dataset, which is more challenging with rich categories, complex imaging conditions and complicated scene", + "bbox": [ + 496, + 800, + 890, + 876 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "2We also retrained dual-stream methods on the FMB dataset.", + "bbox": [ + 514, + 886, + 839, + 898 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "8120", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/3dff34908fcab5b78025d33b90e6111b0248f7d0b2ee7ae74f55e897d1a7999f.jpg", + "image_caption": [ + "Figure 10: Qualitative demonstrations for the different methods in daytime and nighttime scenarios on FMB benchmark." + ], + "image_footnote": [], + "bbox": [ + 86, + 87, + 483, + 220 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e4075c859a3a420085bdf1994a2b53aa5d0d8731b66007310e0dec70e47b03c7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 486, + 88, + 883, + 220 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/db9f9a269288721392be6618569ac117234c6f8b52e7b8794e275cc59cc3f6a6.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodsUnlabelCarPersonBikeCurveCar StopConeBumpmAccmIoU
AccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoU
Visible98.297.594.682.281.754.771.261.054.921.661.916.682.143.777.330.869.745.9
Infrared98.697.490.381.885.367.371.654.851.337.353.824.364.733.470.248.065.649.9
LASNet99.297.494.984.281.767.182.156.970.741.156.839.658.148.877.240.175.454.9
EGFNet99.397.795.887.689.069.880.658.871.542.848.733.865.348.371.147.172.754.8
FEANet99.197.893.987.882.771.176.761.165.546.526.622.166.655.377.348.973.255.3
ABMDR99.398.494.384.890.069.675.760.364.045.144.133.161.747.466.250.069.554.8
DIDFuse98.097.395.079.179.564.080.258.544.119.964.023.377.537.869.020.467.544.5
ReCoNet98.197.395.880.488.960.065.055.447.020.769.025.877.839.846.617.465.944.5
U2Fusion98.397.795.282.885.464.877.761.062.732.366.720.975.545.282.350.271.950.8
TarDAL98.397.693.580.786.267.176.560.153.834.955.310.588.638.790.645.571.748.6
Ours98.798.196.387.889.671.481.263.263.547.566.731.185.348.984.850.374.856.1
", + "bbox": [ + 86, + 258, + 879, + 436 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 1: Quantitative semantic segmentation results of different methods on the MFNet dataset.", + "bbox": [ + 169, + 446, + 797, + 462 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "details. As discussed above, existing fusion methods cannot highlight the dimness of infrared targets, and the distant pedestrian can not be recognized. As for dual-stream methods, which utilize the modality feature directly, they are easy to introduce conflicts and weaken the accuracy without a clear feature fusion principle. The results, such as the car occluded by barriers (the first column of Figure 9) and the shape of the human (the second column of Figure 10) can not be precisely classified. It is worth mentioning that interaction feature learning from segmentation can drastically transfer the complementary characteristics for image fusion and further improve the segmentation performance. Thus, our method can continuously classify the objects of diverse scenes with high accuracy.", + "bbox": [ + 75, + 496, + 472, + 709 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Quantitative Comparisons. Table 1 and Table 2 reported the qualitative results among different categories of competitors on MFNet and FMB datasets. These results illustrate our method is ahead of other state-of-the-art methods by a large margin on both segmentation datasets. Noting that our numerical results outperform other methods concerning mIOU and rank second in terms of mACC. Compared with the second one, our method improves $7.66\\%$ and $1.45\\%$ of mIOU on FMB and MFNet respectively. More specifically, the classification of Car and Person is important for the current intelligent perception system. The top two results in these two categories indicate the high perfor", + "bbox": [ + 75, + 719, + 472, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "mance of our method to employ for real-world perception. On the other hand, for thermal-insensitive categories, such as traffic sign, building, bump, due to the effective visual quality preservation and enhancement, our method achieves significant superiority.", + "bbox": [ + 496, + 496, + 890, + 571 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Ablation studies", + "text_level": 1, + "bbox": [ + 498, + 588, + 661, + 603 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Study on HIA. HIA plays a key role in preserving intrinsic modality features from the semantic feature guidance. Firstly, we visualized the representative feature to discuss the effectiveness of HIA in Figure 11. Clearly, HIA can remarkably preserve the salient infrared features with abundant semantic information, avoiding the interference of harsh weather and strong light. Then we plot different variants of HIA to illustrate the inner mechanisms of HIA. As shown in Figure 12. Obviously, the version w/o SoAM loses the classify ability to distinguish confused objectives, e.g., the orange circle in the second row. Meanwhile, \"w/o MoAM\" cannot protect the details at nighttime with color distortion, e.g., the building in the distance. It is worth pointing out that our full model not only provides clear visual observation but also has high sensitiveness to segmentation. Similarly, the quantitative results reported in Table 3 also demonstrate the effectiveness of full HIA for both segmentation benchmarks compared with direct aggregation and other model variants. In brief, HIA is capable enough to", + "bbox": [ + 496, + 613, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "8121", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d7568f1da684dfe8102ad43fae60771dd39e8ef1177fc74698914b1bbfeb200a.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodsCarPersonTruckT-LampT-SignBuildingVegetationPolemAccmIoU
AccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoU
Visible84.578.378.146.673.243.482.523.783.664.089.077.888.582.171.641.873.550.5
Infrared75.669.189.963.366.612.663.124.780.552.987.478.083.775.562.123.069.643.9
GMNet87.679.377.360.149.022.254.121.678.569.089.179.188.983.859.739.864.449.2
LASNet81.372.676.448.629.614.820.72.979.359.086.975.487.681.656.636.756.942.5
EGFNet83.677.479.563.033.517.158.625.282.666.688.577.289.383.563.841.563.047.3
FEANet82.373.978.860.744.732.353.613.573.355.687.679.489.081.266.236.864.546.8
DIDFuse86.377.787.464.466.328.875.929.281.164.487.178.489.582.479.241.873.050.6
ReCoNet83.775.987.765.834.714.983.334.785.666.689.079.288.281.373.344.971.450.9
U2Fusion85.076.687.761.984.614.475.128.381.368.989.578.892.582.274.542.270.147.9
TarDAL81.874.293.356.066.318.875.029.681.266.588.179.187.981.765.941.974.848.1
Ours85.378.378.365.474.447.386.443.186.174.890.082.091.685.072.549.874.554.8
", + "bbox": [ + 89, + 88, + 880, + 265 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "bridge the fusion and segmentation tasks.", + "bbox": [ + 76, + 325, + 349, + 339 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e6c8c91f72d021e4cbb8a3dda4ca322f5605d5082ae786f2844dc208a184ddae.jpg", + "image_caption": [ + "Figure 11: Feature visualization of different stages. From left to right: visible image, infrared image, their features, w/o HIA, and w/ HIA." + ], + "image_footnote": [], + "bbox": [ + 86, + 351, + 460, + 444 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/f181e4419d276f3be1282f06dda582343fad04fb41fae41e45158d1628107473.jpg", + "table_caption": [ + "Table 2: Quantitative semantic segmentation results of different methods on the FMB dataset." + ], + "table_footnote": [], + "table_body": "
ModelHIAMF DatasetFMB Dataset
SoAMMoAMmAccmIoUmAccmIoU
“Concatenate”XX72.652.772.351.3
“Summation”XX71.552.673.752.1
“Average”XX72.952.172.450.7
M1XX67.251.972.450.5
M2X✓73.655.072.752.3
M3✓X72.053.473.154.1
M4✓✓74.856.174.554.8
", + "bbox": [ + 84, + 520, + 460, + 676 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 3: Numerical results about the effectiveness of HIA. The first three are the results of direct feature aggregation. Latter are the results of model variants with HIA.", + "bbox": [ + 75, + 686, + 467, + 733 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Analyzing the dynamic factor. We discussed the impact of the proposed dynamic factor for interactive learning compared with existing multi-task optimization methods, as shown in Figure 13. Manual adjustment requires plenty of prior knowledge and labor consumption. But concurrently, it achieves decent segmentation results. The other five training strategies hardly coordinate the relationship between the two tasks and fail to achieve good visualization and segmentation performance. The dynamic factor enables to better introduce task preferences into optimization, thus achieving", + "bbox": [ + 75, + 750, + 472, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "excellent results on both tasks.", + "bbox": [ + 500, + 325, + 702, + 339 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b0cb6b19667bb91dfcdb20db8176da490bc5ef1a9f06891925aa73c416264758.jpg", + "image_caption": [ + "Figure 12: Visual comparisons of different models." + ], + "image_footnote": [], + "bbox": [ + 501, + 345, + 906, + 484 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e0df24652b3b51ed948a8e09b42dfb71da3152770abc4faf83664234a74acbb7.jpg", + "image_caption": [ + "Figure 13: Comparisons of different strategies of adjusting dynamic factors." + ], + "image_footnote": [], + "bbox": [ + 503, + 521, + 893, + 635 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 699, + 617, + 714 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, a multi-interactive architecture was proposed to formulate fusion and segmentation in a harmonious manner. We introduced a hierarchical interactive attention with dynamic factors, which bridges gaps of cross-task features from architecture and learning perspectives. In addition, we proposed a comprehensive full-time multimodality benchmark, with well-registered targets, abundant scenes and affluent labels.", + "bbox": [ + 496, + 724, + 890, + 843 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Acknowledgments. This work is partially supported by the National Key R&D Program of China (No. 2022YFA1004101), the National Natural Science Foundation of China (No. U22B2052, 62027826).", + "bbox": [ + 496, + 844, + 890, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "8122", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Hengshuang Zhao, Jianping Shi, Xiaojuan Qi, Xiaogang Wang, and Jiaya Jia. Pyramid scene parsing network. In IEEE/CVF CVPR, pages 2881-2890, 2017.", + "[2] Bolei Zhou, Hang Zhao, Xavier Puig, Sanja Fidler, Adela Barriuso, and Antonio Torralba. Scene parsing through ade20k dataset. In IEEE/CVF CVPR, pages 633-641, 2017.", + "[3] Wujie Zhou, Xinyang Lin, Jingsheng Lei, Lu Yu, and Jenq-Neng Hwang. 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In IEEE/CVF CVPR, pages 7482-7491, 2018." + ], + "bbox": [ + 501, + 92, + 890, + 842 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "8124", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Multi-interactive Feature Learning and a Full-time Multi-modality Benchmark for Image Fusion and Segmentation/bd1a1af4-3a04-4546-9ec1-7f24749110ac_model.json b/2023/Multi-interactive Feature Learning and a Full-time Multi-modality Benchmark for Image Fusion and Segmentation/bd1a1af4-3a04-4546-9ec1-7f24749110ac_model.json new file mode 100644 index 0000000000000000000000000000000000000000..a198ed6377ea29ab1633cca5cd097c5451dbe19f --- /dev/null +++ b/2023/Multi-interactive Feature Learning and a Full-time Multi-modality Benchmark for Image Fusion and Segmentation/bd1a1af4-3a04-4546-9ec1-7f24749110ac_model.json @@ -0,0 +1,2475 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.087, + 0.131, + 0.885, + 0.177 + ], + "angle": 0, + "content": "Multi-interactive Feature Learning and a Full-time Multi-modality Benchmark for Image Fusion and Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.086, + 0.203, + 0.933, + 0.294 + ], + "angle": 0, + "content": "Jinyuan Liu†, Zhu Liu‡, Guanyao Wu‡, Long Ma‡, Risheng Liu‡§, Wei Zhong‡, Zhongxuan Luo‡, Xin Fan‡* †School of Mechanical Engineering, Dalian University of Technology ‡International School of Information Science Engineering, Dalian University of Technology §Peng Cheng Laboratory atlantis918@hotmail.com, liuzhu@mail.dlut.edu.cn, xin.fan@dlut.edu.cn" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.339, + 0.468, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.468, + 0.338, + 0.609, + 0.502 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.61, + 0.338, + 0.747, + 0.501 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.749, + 0.339, + 0.889, + 0.501 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.513, + 0.895, + 0.575 + ], + "angle": 0, + "content": "Figure 1: The chord diagram on the left shows the association and relative number of various labels in the proposed FMB dataset. Its branches display part of the well registered targets, which are extraordinarily affluent and manifold. The zoomed-in regions on the right show the segmentation comparison in cyan circles and fusion comparison in orange circles. It is obvious that the proposed method is superior to SOTA methods on both visual effects and mIoU." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.587, + 0.314, + 0.602 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.614, + 0.474, + 0.903 + ], + "angle": 0, + "content": "Multi-modality image fusion and segmentation play a vital role in autonomous driving and robotic operation. Early efforts focus on boosting the performance for only one task, e.g., fusion or segmentation, making it hard to reach 'Best of Both Worlds'. To overcome this issue, in this paper, we propose a Multi-interactive Feature learning architecture for image fusion and Segmentation, namely SegMiF, and exploit dual-task correlation to promote the performance of both tasks. The SegMiF is of a cascade structure, containing a fusion sub-network and a commonly used segmentation sub-network. By slickly bridging intermediate features between two components, the knowledge learned from the segmentation task can effectively assist the fusion task. Also, the benefited fusion network supports the segmentation one to perform more pretentionally. Besides, a hierarchical interactive attention block is established to ensure fine-grained mapping of all the vital information between two tasks, so that the modality/semantic features can be fully mutual-interactive. In addition, a dy" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.588, + 0.896, + 0.801 + ], + "angle": 0, + "content": "namic weight factor is introduced to automatically adjust the corresponding weights of each task, which can balance the interactive feature correspondence and break through the limitation of laborious tuning. Furthermore, we construct a smart multi-wave binocular imaging system and collect a full-time multi-modality benchmark with 15 annotated pixel-level categories for image fusion and segmentation. Extensive experiments on several public datasets and our benchmark demonstrate that the proposed method outputs visually appealing fused images and perform averagely \\(7.66\\%\\) higher segmentation mIoU in the real-world scene than the state-of-the-art approaches. The source code and benchmark are available at https://github.com/JinyuanLiu-CV/SegMiF." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.83, + 0.633, + 0.845 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Accurate and robust scene parsing[1, 2] is a fundamental technology for autonomous driving. However, in complex environments, e.g., inclement weather, only using visi" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8115" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.468, + 0.167 + ], + "angle": 0, + "content": "ble sensors may fail to accurately recognize targets. On the contrary, infrared sensors are free from the aforementioned issues but limited in low spatial resolution. Consequently, fusing the infrared and visible image [3, 4, 5, 6, 7] has become a mainstream solution for better scene understanding." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.168, + 0.468, + 0.272 + ], + "angle": 0, + "content": "Multi-modality fusion for scene parsing needs to provide: (i). robust visual appealing image: they require continually generating high-quality images in dynamic scenes. (ii). accurate semantic segmentation: they demand to assign category labels to each pixel. Towards these goals, jointly solving multi-modality image fusion and segmentation becomes an urgent issue." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.273, + 0.468, + 0.437 + ], + "angle": 0, + "content": "Numerous learning-based multi-modality image fusion methods have been fast development [8, 9, 10, 11, 12]. However, most of them concentrate on developing various networks for generating visual-appealing images rather than considering the follow-up high-level vision tasks, posing an obstacle to better scene parsing. Recently, few studies[13, 14, 15, 16] have attempted to design multi-task learning-based loss functions by cascading the fusion network and high-level tasks. Unfortunately, seeking unified appropriate features for either task simultaneously is still a tough issue." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.439, + 0.468, + 0.559 + ], + "angle": 0, + "content": "Moreover, exploring multi-modality fusion and segmentation demands a comprehensive collection of well-alignment image pairs with pixel-level annotated labels. Also, as for one image, the annotated needs to cover a wide range of pixels. Unfortunately, existing multi-modality data collections either focus on image fusion or lack whole image annotated segmentation labels, placing an obstacle to exploring the correlation of the fusion and segmentation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.56, + 0.468, + 0.771 + ], + "angle": 0, + "content": "This paper proposes a multi-interactive feature learning architecture for the joint problem of multi-modality fusion and segmentation, namely SegMiF. SegMiF is constructed by a fusion network and a segmentation network, in which the intrinsic features of either one interact via a new proposed hierarchical interactive attention (HIA). HIA fully integrates semantic-/modality-oriented features by fine-grained mapping. We also derive a dynamic weighting factor and seamless it in the interactive training scheme, to automatically learn the optimal parameters for either task. Figure 1 demonstrates that our SegMiF assigns the category to each pixel from the visual-friendly fused result more accurately than the state-of-the-arts (SOTAs). Our contributions can be distilled into four main aspects as follows:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.779, + 0.468, + 0.869 + ], + "angle": 0, + "content": "- We formulate both image fusion and segmentation in a joint manner, in which the semantic and pixel-based features can mutually interact. To this end, two tasks can achieve the 'Best of Both Worlds', generating visual-appealing fused images along with accurate scene parsing." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.871, + 0.468, + 0.901 + ], + "angle": 0, + "content": "- A hierarchical interactive attention is introduced to bridge the feature gap between the fusion network" + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.779, + 0.468, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.531, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "and the segmentation one. Establishing the semantic/modality multi-head attention mechanism in HIA simultaneously preserves intrinsic modality features and brings more attention to semantic features." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.171, + 0.892, + 0.26 + ], + "angle": 0, + "content": "- An interactive feature training scheme is proposed to overcome the shortcoming of insufficient feature interaction between fusion and segmentation. Seamlessly integrating a dynamic weighting factor allows the exploration of the optimal parameters of each task in an automatic manner." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.28, + 0.892, + 0.415 + ], + "angle": 0, + "content": "- We construct a smart multi-wave binocular imaging system, and introduce a full-time multi-modality benchmark, namely FMB, to promote the research of both image fusion and segmentation. FMB contains 1500 well-registered infrared and visible image pairs with 15 annotated pixel-level categories (see the left part of Figure 1). Also, it covers a wide range of pixel variations and various severe environments, e.g., dense fog, heavy rain, and low-light condition." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.171, + 0.892, + 0.415 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.443, + 0.65, + 0.459 + ], + "angle": 0, + "content": "2. Related Works" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.473, + 0.892, + 0.76 + ], + "angle": 0, + "content": "Multi-modality image fusion In recent years, deep learning based multi-modality image fusion approaches achieved significant progress[11, 12, 17, 18, 19]. Early efforts [8, 9, 10, 20, 21] tend to achieve excellent fusion effects by adjusting the network structure or loss functions. However, a minority pay attention to whether the downstream tasks can be well adapted to fusion. DIDFuse [10] was the first to apply deep decomposition for high and low-frequency features, while AUIF [22] proposed a decomposition and fusion framework based on algorithm unfolding from an optimization perspective. Subsequently, CDDFuse [6] upgraded the decomposition network to a Transformer-CNN dual-stream structure. DDFM [7], for the first time, utilized denoising diffusion models for image fusion tasks. Recently, some methods [23, 13, 24] cascaded fusion and downstream tasks, focusing on improving task performance by achieving oriented fusion. Nevertheless, this kind of native gradient back propagation hinders the fusion network to adapt to subsequent tasks heuristically from the feature level." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.886 + ], + "angle": 0, + "content": "Multi-modality Segmentation Recently, two-stream-based feature fusion models are proposed to perform the segmentation directly. Most of existing methods mostly develop various simple fusion strategies, such as the weighted average [25, 26, 27], summation [28, 29] and concatenation [30, 31]. Nonetheless, direct feature fusion lacks explicit fusion principle to preserve the typical modality feature and pay no attention to the pixel-level visual effects." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "8116" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.089, + 0.346, + 0.241 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.346, + 0.089, + 0.642, + 0.241 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.642, + 0.089, + 0.885, + 0.241 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.254, + 0.895, + 0.3 + ], + "angle": 0, + "content": "Figure 2: Workflow of our proposed SegMiF. The left part depicts the latent interactive relationship between image fusion and segmentation. The middle part plots the concrete architecture of the SegMiF. The right part details the components of proposed hierarchical interactive attention." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.325, + 0.289, + 0.342 + ], + "angle": 0, + "content": "3. The Proposed Method" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.35, + 0.276, + 0.365 + ], + "angle": 0, + "content": "3.1. Problem formulation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.373, + 0.471, + 0.479 + ], + "angle": 0, + "content": "As for image fusion or segmentation tasks, one of the most commonly used ways is to design a neural network, and fully utilize it to find a set of optimal parameters. For this purpose, we suppose that the visible, infrared, and fused image are all gray-scale with the size of \\(m \\times n\\), denoted as column vectors \\(\\mathbf{x}\\), \\(\\mathbf{y}\\), and \\(\\mathbf{u} \\in \\mathbb{R}^{mn \\times 1}\\), respectively. The optimization model is formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.199, + 0.49, + 0.47, + 0.515 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\boldsymbol {\\omega} _ {k}} f \\left(\\mathbf {k}, \\mathcal {N} (\\mathbf {x}, \\mathbf {y}; \\boldsymbol {\\omega} _ {k})\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.524, + 0.47, + 0.555 + ], + "angle": 0, + "content": "where \\(\\mathbf{k}\\) denotes the output of the task-related network \\(\\mathcal{N}\\) with the learnable parameters \\(\\omega_{\\mathrm{k}}\\). \\(f(\\cdot)\\) is a fidelity term." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.555, + 0.47, + 0.645 + ], + "angle": 0, + "content": "Previous approaches solely design image fusion or segmentation networks, which only can achieve outstanding results for one task. To generate visualappealing fused images along with accurate scene segmentation results, we jointly formulate the two tasks into one goal [32, 33, 34], which can be rewritten as:" + }, + { + "type": "equation", + "bbox": [ + 0.099, + 0.67, + 0.47, + 0.692 + ], + "angle": 0, + "content": "\\[\n\\min _ {\\boldsymbol {\\omega} _ {\\mathrm {u}}, \\boldsymbol {\\omega} _ {\\mathrm {s}}} f _ {\\mathrm {u}} \\left(\\mathbf {u}, \\Phi (\\mathbf {x}, \\mathbf {y}; \\boldsymbol {\\omega} _ {\\mathrm {u}})\\right) + f _ {\\mathrm {s}} \\left(\\mathbf {s}, \\Psi (\\mathbf {x}, \\mathbf {y}; \\boldsymbol {\\omega} _ {\\mathrm {s}})\\right) + g \\left(\\boldsymbol {\\omega} ^ {\\star}\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.702, + 0.47, + 0.839 + ], + "angle": 0, + "content": "where \\(\\omega^{\\star} = [\\omega_{\\mathrm{u}},\\omega_{\\mathrm{s}}]\\). \\(\\mathbf{u}\\) and \\(\\mathbf{s}\\) denote the fused image and segmentation map, which are produced by the fusion network \\(\\Phi\\) and segmentation network \\(\\Psi\\) with the learnable parameters \\(\\omega_{\\mathrm{u}}\\) and \\(\\omega_{\\mathrm{s}}\\). \\(g(\\cdot)\\) is a constrained term to joint optimize the two tasks. In this paper, we regard the \\(g(\\cdot)\\) as a feature learning constrained manner, and achieve this goal by designing a hierarchical attention along with the interactive training scheme. The visualized illustration is plotted in the left part of Figure 2." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.848, + 0.36, + 0.863 + ], + "angle": 0, + "content": "3.2. Feature interaction architecture" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Overview of the whole network. Our proposed SegMiF is designed with cascade principle, composited by image" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.326, + 0.892, + 0.493 + ], + "angle": 0, + "content": "fusion and segmentation sub-network. Details of the whole architecture is shown at Figure 2. In specific, we utilize two parallel dilated residual dense blocks (DRDB) [35, 36] to extract features from visual and infrared images. SegFormer [37] is leveraged as the baseline segmentation network to provide semantic parsing. Two scales of semantic features from the backbone, interpolated with original resolutions are embedded into fusion network. In order to sufficiently realize the semantic information sharing, we propose the hierarchical interactive attention (HIA) to transfer high-level knowledge." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.494, + 0.892, + 0.631 + ], + "angle": 0, + "content": "Hierarchical interactive attention. After obtaining modality feature \\(\\mathbf{F}_{ir},\\mathbf{F}_{vis}\\) from fusion network and segmentation feature \\(\\mathbf{F}_{seg}\\), we build the HIA to construct the fine-grained mapping of these features and strengthen the mutually beneficial representation. Features including \\(\\mathbf{F}_{ir},\\mathbf{F}_{vis}\\) and \\(\\mathbf{F}_{seg}\\) as inputs, two attention mechanisms are leveraged to globally exchange intermediate features. Concatenating features from attentions, fresh modality features are generated based on a residual connection." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.632, + 0.892, + 0.738 + ], + "angle": 0, + "content": "In detail, channel embedding is utilized to decompose modality/semantic features. We can denote the outputs from the linear embedding as \\(\\{\\mathbf{F}_x^s,\\mathbf{F}_x^m\\}\\) with size \\(\\mathbb{R}^{mn\\times C}\\), where \\(x\\in \\{ir,vis,seg\\}\\) is under a vector formulation. Instead of utilizing the original self-attention mechanisms directly, we bridge these features with complementary interaction from different representation subspaces by MoAM and SoAM." + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.751, + 0.895, + 0.84 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.515, + 0.851, + 0.877, + 0.867 + ], + "angle": 0, + "content": "Figure 3: Detailed architectures of SoAM and MoAM." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.886, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Both multi-head attention modules are plotted in Fig-" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8117" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.41 + ], + "angle": 0, + "content": "ure 3. Semantic-oriented attention module targets to provide more semantic attention for the modality feature. SoAM utilizes the token \\(\\mathbf{F}_{seg}^{s}\\) to generate the Query \\(Q_{s}\\), which represents the inhere semantic information that needs to be enhanced. The global context representation of each can be calculated by as \\(K_{ir}^{T}V_{ir}\\) and \\(K_{vis}^{T}V_{vis}\\), where the corresponding Key and Value of each head are from the modality tokens \\(\\{\\mathbf{F}_{ir}^{m},\\mathbf{F}_{vis}^{m}\\}\\). Denoted the modality context representation as \\(\\mathbf{G}_{ir}\\), \\(\\mathbf{G}_{vis}\\), we can calculate the attention as \\(S_{ir} = Q_s\\mathbf{G}_{ir}\\) and \\(S_{vis} = Q_s\\mathbf{G}_{vis}\\). On the other hand, MoAM is with the complementary principle to investigate the significant feature from semantic contexts. Specifically, MoAM is to introduce two modality queries \\(Q_{ir},Q_{vis}\\) to represent the intrinsic modality feature (e.g., targets and details) from \\(\\{\\mathbf{F}_{ir}^{m},\\mathbf{F}_{vis}^{m}\\}\\). Similarly, we can obtain the global context of segmentation \\(\\mathbf{G}_s\\) by \\(K_{s}^{T}V_{s}\\). The cross attention can be formulated as \\(M_{vis} = Q_s\\mathbf{G}_{vis}\\) and \\(M_{vis} = Q_s\\mathbf{G}_{vis}\\). By concatenating the groups \\(\\{S_{vis},M_{vis}\\}\\) and \\(\\{S_{ir},M_{ir}\\}\\), we can obtain the comprehensive features with two parallel MLPs with residual connection to aggregate features from SoAM and MoAM." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.422, + 0.219, + 0.435 + ], + "angle": 0, + "content": "3.3. Loss function" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.446, + 0.47, + 0.552 + ], + "angle": 0, + "content": "The total loss function is combined of an image fusion loss function \\(\\mathcal{L}_{\\mathrm{f}}\\) and segmentation loss \\(\\mathcal{L}_{\\mathrm{s}}\\). \\(\\mathcal{L}_{\\mathrm{f}}\\) consists of three types of losses, i.e., structure loss \\(\\mathcal{L}_{\\mathrm{SSIM}}\\), pixel loss \\(\\mathcal{L}_{\\mathrm{MSE}}\\) and gradient loss \\(\\mathcal{L}_{\\mathrm{grad}}\\). For one fused image, it should preserve overall structures from source images. To this end, the structural similarity index (SSIM) [38, 39, 40, 41] is introduced in function:" + }, + { + "type": "equation", + "bbox": [ + 0.117, + 0.559, + 0.47, + 0.577 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {S S I M}} = \\left(1 - \\mathrm {S S I M} _ {\\mathbf {u}, \\mathbf {x}}\\right) / 2 + \\left(1 - \\mathrm {S S I M} _ {\\mathbf {u}, \\mathbf {y}}\\right) / 2, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.59, + 0.47, + 0.635 + ], + "angle": 0, + "content": "where \\(\\mathcal{L}_{\\mathrm{SSIM}}\\) denotes structure similarity loss. To maintain the vital intensity in the fused image, we employ the saliency-based pixel loss, it formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.144, + 0.648, + 0.469, + 0.667 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {M S E}} = \\left\\| \\mathbf {u} - m _ {1} \\mathbf {x} \\right\\| _ {2} ^ {2} + \\left\\| \\mathbf {u} - m _ {2} \\mathbf {y} \\right\\| _ {2} ^ {2}, \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.679, + 0.47, + 0.74 + ], + "angle": 0, + "content": "where \\( m_{1} \\) and \\( m_{2} \\) are saliency weight maps calculated by VSM [42]. Besides, gradient information of images always characterizes texture details, thus, we used \\( \\mathcal{L}_{\\mathrm{grad}} \\) to constrain these textual factors to a multi-scale manner:" + }, + { + "type": "equation", + "bbox": [ + 0.123, + 0.752, + 0.469, + 0.784 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {g r a d}} = \\sum_ {k = 3, 5, 7} \\| \\nabla^ {k} \\mathbf {u} - \\max (\\nabla^ {k} \\mathbf {x}, \\nabla^ {k} \\mathbf {y}) \\| _ {2} ^ {2} \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.797, + 0.469, + 0.844 + ], + "angle": 0, + "content": "where \\(\\nabla\\) denotes gradient operators that calculate by \\(\\nabla = \\mathbf{u} - \\mathcal{G}(\\mathbf{u})\\) with combination of different Gauss \\((\\mathcal{G})\\) kernel size \\(k\\). Totally, we obtained \\(\\mathcal{L}_{\\mathrm{f}} = \\mathcal{L}_{\\mathrm{SSIM}} + \\mathcal{L}_{\\mathrm{MSE}} + \\eta \\mathcal{L}_{\\mathrm{grad}}\\)." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.844, + 0.399, + 0.859 + ], + "angle": 0, + "content": "Common to previous works, \\(\\mathcal{L}_{\\mathrm{s}}\\) is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.174, + 0.873, + 0.469, + 0.905 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {s}} \\left(\\mathbf {s}, \\mathbf {s} ^ {*}\\right) = - \\sum_ {\\text {c l a s s}} \\mathbf {s} ^ {*} \\log (\\mathbf {s}), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.137 + ], + "angle": 0, + "content": "where \\(\\mathbf{s}^*\\) represents the segmentation label. We adopt the effective semantic segmentation method SegFormer network \\(\\Psi\\) [37]. The total loss function is:" + }, + { + "type": "equation", + "bbox": [ + 0.615, + 0.15, + 0.892, + 0.166 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {t o t a l}} = \\lambda_ {1} \\mathcal {L} _ {\\mathrm {f}} + \\lambda_ {2} \\mathcal {L} _ {\\mathrm {s}}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.178, + 0.892, + 0.207 + ], + "angle": 0, + "content": "where \\(\\lambda_{1}\\) and \\(\\lambda_{2}\\) are dynamic weighting factor which will be discussed below." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.218, + 0.837, + 0.234 + ], + "angle": 0, + "content": "3.4. Dynamic factor for interactive learning" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.242, + 0.892, + 0.453 + ], + "angle": 0, + "content": "By exploiting an alternatively recurrent iterations, we can progressively introduce the task-preferred features into the framework optimization. As mentioned above, at the phase of image fusion, we introduce the dynamic weighting factors \\(\\lambda_{1}\\) and \\(\\lambda_{2}\\) to rapidly measure the importance of task-related losses. We observe that the task-specific balance can be derived from the convergent rate. The intuition is that if the value of losses cannot be further descended, the network may obtain the corresponding optimal weights. If the convergent rate descends fast, we should pay more attention to this task. Learning from the dynamic weight average [43], we further present the factor of task preference \\(\\eta\\) to emphasize the primary goal. Denoted \\(r_i\\) as the convergent rate of \\(i\\)-th task with loss \\(\\mathcal{L}_i\\), we can compute the rate as:" + }, + { + "type": "equation", + "bbox": [ + 0.612, + 0.464, + 0.892, + 0.497 + ], + "angle": 0, + "content": "\\[\nr _ {1} (n - 1) = \\frac {\\mathcal {L} _ {i} (n - 1)}{\\mathcal {L} _ {i} (n - 2)}. \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.507, + 0.892, + 0.536 + ], + "angle": 0, + "content": "Then the procedure of dynamic weight factor of \\(i\\)-th task is formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.585, + 0.546, + 0.892, + 0.58 + ], + "angle": 0, + "content": "\\[\n\\lambda_ {\\mathrm {i}} (n) = \\frac {\\eta_ {\\mathrm {i}} \\exp \\left(r _ {\\mathrm {i}} (n - 1) / T\\right)}{\\sum_ {k} \\exp \\left(r _ {\\mathrm {k}} (n - 1) / T\\right)}, \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.59, + 0.892, + 0.65 + ], + "angle": 0, + "content": "where \\( T \\) is a temperature to control the sensitiveness of two tasks. Different from widely sued GDN [44], this dynamic strategy can actually avoid the complicated computation of various task gradients." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.65, + 0.892, + 0.772 + ], + "angle": 0, + "content": "Then based on the fusion image generated with semantic feature, we can train the segmentation network end-to-end, using the gradient descending \\(\\omega_{s} \\gets \\omega_{s} - \\nabla_{\\omega_{s}} \\mathcal{L}_{\\mathbb{S}}(\\mathbf{u}; \\omega_{s})\\). The two learning processes are trained alternately until full convergence. Noting that, this training strategy is actually task-agnostic, we also can introduce other different high-level vision tasks into the unified consideration, rather than designing for segmentation unilaterally." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.785, + 0.837, + 0.802 + ], + "angle": 0, + "content": "4. Full-time Multi-modality Benchmark" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.811, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Existing two multi-modality segmentation datasets suffer from few label categories, sparse annotation and monotonous scene, as shown in Figure 6. The proposed FMB dataset aims to overcome these difficulties and promote the development of whole field. A glimpse of FMB is given in Figure 4." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8118" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.101, + 0.089, + 0.873, + 0.213 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.223, + 0.895, + 0.27 + ], + "angle": 0, + "content": "Figure 4: Visualization of visible/infrared/segmentation images in the proposed FMB dataset. The dataset contains a wide range of real driving scenes under different lighting conditions, and also includes special scenarios with rain, fog, strong light, and even Tyndall Effect." + }, + { + "type": "image", + "bbox": [ + 0.089, + 0.276, + 0.462, + 0.404 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.093, + 0.418, + 0.454, + 0.435 + ], + "angle": 0, + "content": "Figure 5: Illustration of the binocular imaging system." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.461, + 0.47, + 0.641 + ], + "angle": 0, + "content": "We built a binocular imaging system that can be placed on the car roof, including a visible camera and an infrared sensor with a wavelength range of \\(8 - 14\\mu m\\) (as shown in the Figure 5). We finally obtained 1500 aligned image pairs with a resolution of \\(800\\times 600\\). In details, two sensors are individually calibrated using their respected calibration board to obtain internal parameters, and their relative pose relationship is obtained through joint calibration. We calculate the homography matrix \\(H\\) by employing RANSAC1. The infrared images are projected onto visible coordinates using \\(H\\) and cropped, ultimately resulting in pixel-level registered image pairs with a size of \\(800\\times 600\\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.642, + 0.47, + 0.763 + ], + "angle": 0, + "content": "The FMB dataset includes rich scenes under different illumination conditions, so that it enables fusion/segmentation model to improve the generalization ability greatly. We labeled \\(98.16\\%\\) of all pixels into 14 different categories including Road, Sidewalk, Building, Traffic Light, Traffic Sign, Vegetation, Sky, Person, Car, Truck, Bus, Motorcycle, Bicycle and Pole, which often appear in real-world automatic driving and semantic understanding tasks." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.777, + 0.21, + 0.794 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.802, + 0.471, + 0.879 + ], + "angle": 0, + "content": "Two representative datasets including MFNet and proposed FMB are utilized for the training and evaluation. The details of these datasets are reported in the above section. Several data augmentation techniques are utilized for the whole training procedure: random resizing with a ratio of" + }, + { + "type": "image", + "bbox": [ + 0.511, + 0.278, + 0.885, + 0.371 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.387, + 0.892, + 0.418 + ], + "angle": 0, + "content": "Figure 6: Comparison of FMB with existing multi-modality segmentation datasets (i.e., PST900 [31] and MFNet [30])." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.444, + 0.895, + 0.641 + ], + "angle": 0, + "content": "0.5-2.0, random cropping to \\(360 \\times 360\\), brightness distortion and normalization. The Adam optimizer with poly learning rate adjustment is utilized to optimize both networks. As for the fusion, the initial learning rate is \\(1e^{-4}\\) and decayed to \\(1e^{-8}\\) progressively. As for segmentation, we first utilized \\(1e^{-6}\\) to warm start the training with 3k iterations, then we conducted the training with intilial learning rate \\(8e^{-5}\\). With batch size of 8, we trained the framework for 8 rounds. For each round, we set 10k iterations for training segmentation and 5k iterations for fusion. Noting that, a similar configuration of segmentation is also utilized for the training of fusion-based methods. All experiments are performed on an NVIDIA Tesla V100 GPU with PyTorch framework." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.651, + 0.833, + 0.667 + ], + "angle": 0, + "content": "5.1. Results of multi-modality image fusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.892, + 0.75 + ], + "angle": 0, + "content": "We demonstrate our fusion quality based on qualitative and quantitative analyses with six state-of-the-art competitors, including DIDFuse [10], DenseFuse [45], ReCoNet[11], UMFusion[12], TarDAL[13] and U2Fusion [9]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Qualitative Comparisons. The qualitative results on MFNet and FMB datasets are depicted in Figure 7, in which we can clearly observe two remarkable advantages of our method. First, the significant characteristics of infrared images can be effectively highlighted. For instance, as shown on the green rectangle of the first group, DIDFuse, ReCoNet and TarDAL are susceptible to strong illumination. In contrast, our method can remarkably preserve this information from infrared images, e.g., the structure of cars and pedestrians. Furthermore, benefiting from the guidance of semantic" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.372, + 0.9 + ], + "angle": 0, + "content": "Efficient RANSAC for point-cloud shape detection" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8119" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.084, + 0.088, + 0.184, + 0.16 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.184, + 0.089, + 0.285, + 0.16 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.285, + 0.089, + 0.385, + 0.16 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.385, + 0.089, + 0.484, + 0.16 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.484, + 0.089, + 0.585, + 0.16 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.585, + 0.089, + 0.685, + 0.16 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.685, + 0.089, + 0.785, + 0.16 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.785, + 0.089, + 0.887, + 0.16 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.162, + 0.184, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.085, + 0.236, + 0.184, + 0.251 + ], + "angle": 0, + "content": "Source images" + }, + { + "type": "image", + "bbox": [ + 0.185, + 0.162, + 0.285, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.204, + 0.237, + 0.266, + 0.25 + ], + "angle": 0, + "content": "DIDFuse" + }, + { + "type": "image", + "bbox": [ + 0.285, + 0.162, + 0.385, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.298, + 0.237, + 0.372, + 0.25 + ], + "angle": 0, + "content": "DenseFuse" + }, + { + "type": "image", + "bbox": [ + 0.386, + 0.162, + 0.484, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.404, + 0.237, + 0.467, + 0.25 + ], + "angle": 0, + "content": "ReCoNet" + }, + { + "type": "image", + "bbox": [ + 0.485, + 0.162, + 0.585, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.237, + 0.572, + 0.25 + ], + "angle": 0, + "content": "UMFusion" + }, + { + "type": "image", + "bbox": [ + 0.586, + 0.162, + 0.685, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.607, + 0.237, + 0.664, + 0.25 + ], + "angle": 0, + "content": "TarDAL" + }, + { + "type": "image", + "bbox": [ + 0.686, + 0.162, + 0.785, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.703, + 0.237, + 0.769, + 0.25 + ], + "angle": 0, + "content": "U2Fusion" + }, + { + "type": "image", + "bbox": [ + 0.786, + 0.162, + 0.887, + 0.233 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.819, + 0.237, + 0.854, + 0.25 + ], + "angle": 0, + "content": "Ours" + }, + { + "type": "image_caption", + "bbox": [ + 0.138, + 0.263, + 0.83, + 0.28 + ], + "angle": 0, + "content": "Figure 7: Visual comparison of different fusion approaches on the MFNet and FMB dataset, respectively." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.293, + 0.484, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.489, + 0.293, + 0.882, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.4, + 0.893, + 0.431 + ], + "angle": 0, + "content": "Figure 8: Quantitative comparisons of image fusion with six SOTA methods on two datasets. Violin plots illustrating the distribution of the four metrics, in which the white triangles and the black lines indicate mean values and medium values." + }, + { + "type": "image", + "bbox": [ + 0.087, + 0.445, + 0.484, + 0.577 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.486, + 0.445, + 0.884, + 0.577 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.209, + 0.587, + 0.759, + 0.603 + ], + "angle": 0, + "content": "Figure 9: Qualitative demonstrations of different approaches on the MFNet dataset." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.629, + 0.47, + 0.69 + ], + "angle": 0, + "content": "information, our method can enhance the texture details of the given scene from either dataset. Compared with other competitors in the second row of Figure 7, our results exhibit a sharper appearance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Quantitative Comparisons. We also plot the numerical results with other six fusion competitors on 50 pairs from MFNet and 50 pairs from FMB in Figure 8. Four objective metrics are leveraged for the comparison, including entropy (EN)[46], standard deviation (SD)[47], spatial frequency (SF)[48] and the sum of the correlations of differences (SCD)[49]. Note that our results achieve consistent superiority in terms of these statistical metrics. Specifically, the highest EN and SCD indicate that our method can significantly preserve the largest amount of considerable information transferred from source images. Moreover, the immense average value on SD reflects the high pixel contrast for visual observations. Furthermore, higher SF reflects our" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.892, + 0.691 + ], + "angle": 0, + "content": "method has rich texture details and contrasts. In summary, our method enhances the texture details for precise observation and stably preserves abundant typical information to support semantic parsing tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.701, + 0.838, + 0.717 + ], + "angle": 0, + "content": "5.2. Results of multi-modality segmentation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.724, + 0.892, + 0.8 + ], + "angle": 0, + "content": "We provide another comprehensive analysis for image segmentation. Besides comparing with the newest fusion-based methods, we also conduct the evaluations with competitive dual-stream methods: GMNet [50], FEANet [51], EGFNet [52], ABMDRNet [53] and LASNet [54].2" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.801, + 0.892, + 0.877 + ], + "angle": 0, + "content": "Qualitative Comparisons. Visualized results of segmentation on MFNet are depicted in Figure 9. We also compare various competitive methods in Figure 10 under the newly proposed dataset, which is more challenging with rich categories, complex imaging conditions and complicated scene" + }, + { + "type": "page_footnote", + "bbox": [ + 0.516, + 0.887, + 0.841, + 0.9 + ], + "angle": 0, + "content": "2We also retrained dual-stream methods on the FMB dataset." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8120" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.087, + 0.088, + 0.484, + 0.221 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.487, + 0.089, + 0.885, + 0.221 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.089, + 0.231, + 0.88, + 0.247 + ], + "angle": 0, + "content": "Figure 10: Qualitative demonstrations for the different methods in daytime and nighttime scenarios on FMB benchmark." + }, + { + "type": "table", + "bbox": [ + 0.088, + 0.26, + 0.88, + 0.438 + ], + "angle": 0, + "content": "
MethodsUnlabelCarPersonBikeCurveCar StopConeBumpmAccmIoU
AccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoU
Visible98.297.594.682.281.754.771.261.054.921.661.916.682.143.777.330.869.745.9
Infrared98.697.490.381.885.367.371.654.851.337.353.824.364.733.470.248.065.649.9
LASNet99.297.494.984.281.767.182.156.970.741.156.839.658.148.877.240.175.454.9
EGFNet99.397.795.887.689.069.880.658.871.542.848.733.865.348.371.147.172.754.8
FEANet99.197.893.987.882.771.176.761.165.546.526.622.166.655.377.348.973.255.3
ABMDR99.398.494.384.890.069.675.760.364.045.144.133.161.747.466.250.069.554.8
DIDFuse98.097.395.079.179.564.080.258.544.119.964.023.377.537.869.020.467.544.5
ReCoNet98.197.395.880.488.960.065.055.447.020.769.025.877.839.846.617.465.944.5
U2Fusion98.397.795.282.885.464.877.761.062.732.366.720.975.545.282.350.271.950.8
TarDAL98.397.693.580.786.267.176.560.153.834.955.310.588.638.790.645.571.748.6
Ours98.798.196.387.889.671.481.263.263.547.566.731.185.348.984.850.374.856.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.17, + 0.447, + 0.798, + 0.463 + ], + "angle": 0, + "content": "Table 1: Quantitative semantic segmentation results of different methods on the MFNet dataset." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.497, + 0.473, + 0.71 + ], + "angle": 0, + "content": "details. As discussed above, existing fusion methods cannot highlight the dimness of infrared targets, and the distant pedestrian can not be recognized. As for dual-stream methods, which utilize the modality feature directly, they are easy to introduce conflicts and weaken the accuracy without a clear feature fusion principle. The results, such as the car occluded by barriers (the first column of Figure 9) and the shape of the human (the second column of Figure 10) can not be precisely classified. It is worth mentioning that interaction feature learning from segmentation can drastically transfer the complementary characteristics for image fusion and further improve the segmentation performance. Thus, our method can continuously classify the objects of diverse scenes with high accuracy." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Quantitative Comparisons. Table 1 and Table 2 reported the qualitative results among different categories of competitors on MFNet and FMB datasets. These results illustrate our method is ahead of other state-of-the-art methods by a large margin on both segmentation datasets. Noting that our numerical results outperform other methods concerning mIOU and rank second in terms of mACC. Compared with the second one, our method improves \\(7.66\\%\\) and \\(1.45\\%\\) of mIOU on FMB and MFNet respectively. More specifically, the classification of Car and Person is important for the current intelligent perception system. The top two results in these two categories indicate the high perfor" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.497, + 0.892, + 0.573 + ], + "angle": 0, + "content": "mance of our method to employ for real-world perception. On the other hand, for thermal-insensitive categories, such as traffic sign, building, bump, due to the effective visual quality preservation and enhancement, our method achieves significant superiority." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.589, + 0.663, + 0.604 + ], + "angle": 0, + "content": "5.3. Ablation studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.614, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Study on HIA. HIA plays a key role in preserving intrinsic modality features from the semantic feature guidance. Firstly, we visualized the representative feature to discuss the effectiveness of HIA in Figure 11. Clearly, HIA can remarkably preserve the salient infrared features with abundant semantic information, avoiding the interference of harsh weather and strong light. Then we plot different variants of HIA to illustrate the inner mechanisms of HIA. As shown in Figure 12. Obviously, the version w/o SoAM loses the classify ability to distinguish confused objectives, e.g., the orange circle in the second row. Meanwhile, \"w/o MoAM\" cannot protect the details at nighttime with color distortion, e.g., the building in the distance. It is worth pointing out that our full model not only provides clear visual observation but also has high sensitiveness to segmentation. Similarly, the quantitative results reported in Table 3 also demonstrate the effectiveness of full HIA for both segmentation benchmarks compared with direct aggregation and other model variants. In brief, HIA is capable enough to" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "8121" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.09, + 0.089, + 0.881, + 0.266 + ], + "angle": 0, + "content": "
MethodsCarPersonTruckT-LampT-SignBuildingVegetationPolemAccmIoU
AccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoU
Visible84.578.378.146.673.243.482.523.783.664.089.077.888.582.171.641.873.550.5
Infrared75.669.189.963.366.612.663.124.780.552.987.478.083.775.562.123.069.643.9
GMNet87.679.377.360.149.022.254.121.678.569.089.179.188.983.859.739.864.449.2
LASNet81.372.676.448.629.614.820.72.979.359.086.975.487.681.656.636.756.942.5
EGFNet83.677.479.563.033.517.158.625.282.666.688.577.289.383.563.841.563.047.3
FEANet82.373.978.860.744.732.353.613.573.355.687.679.489.081.266.236.864.546.8
DIDFuse86.377.787.464.466.328.875.929.281.164.487.178.489.582.479.241.873.050.6
ReCoNet83.775.987.765.834.714.983.334.785.666.689.079.288.281.373.344.971.450.9
U2Fusion85.076.687.761.984.614.475.128.381.368.989.578.892.582.274.542.270.147.9
TarDAL81.874.293.356.066.318.875.029.681.266.588.179.187.981.765.941.974.848.1
Ours85.378.378.365.474.447.386.443.186.174.890.082.091.685.072.549.874.554.8
" + }, + { + "type": "table_caption", + "bbox": [ + 0.177, + 0.276, + 0.793, + 0.29 + ], + "angle": 0, + "content": "Table 2: Quantitative semantic segmentation results of different methods on the FMB dataset." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.326, + 0.351, + 0.34 + ], + "angle": 0, + "content": "bridge the fusion and segmentation tasks." + }, + { + "type": "image", + "bbox": [ + 0.087, + 0.352, + 0.462, + 0.445 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.454, + 0.47, + 0.499 + ], + "angle": 0, + "content": "Figure 11: Feature visualization of different stages. From left to right: visible image, infrared image, their features, w/o HIA, and w/ HIA." + }, + { + "type": "table", + "bbox": [ + 0.086, + 0.521, + 0.462, + 0.678 + ], + "angle": 0, + "content": "
ModelHIAMF DatasetFMB Dataset
SoAMMoAMmAccmIoUmAccmIoU
“Concatenate”XX72.652.772.351.3
“Summation”XX71.552.673.752.1
“Average”XX72.952.172.450.7
M1XX67.251.972.450.5
M2X✓73.655.072.752.3
M3✓X72.053.473.154.1
M4✓✓74.856.174.554.8
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.688, + 0.468, + 0.734 + ], + "angle": 0, + "content": "Table 3: Numerical results about the effectiveness of HIA. The first three are the results of direct feature aggregation. Latter are the results of model variants with HIA." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Analyzing the dynamic factor. We discussed the impact of the proposed dynamic factor for interactive learning compared with existing multi-task optimization methods, as shown in Figure 13. Manual adjustment requires plenty of prior knowledge and labor consumption. But concurrently, it achieves decent segmentation results. The other five training strategies hardly coordinate the relationship between the two tasks and fail to achieve good visualization and segmentation performance. The dynamic factor enables to better introduce task preferences into optimization, thus achieving" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.326, + 0.704, + 0.34 + ], + "angle": 0, + "content": "excellent results on both tasks." + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.346, + 0.907, + 0.485 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.527, + 0.489, + 0.866, + 0.505 + ], + "angle": 0, + "content": "Figure 12: Visual comparisons of different models." + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.522, + 0.895, + 0.636 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.641, + 0.892, + 0.672 + ], + "angle": 0, + "content": "Figure 13: Comparisons of different strategies of adjusting dynamic factors." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.7, + 0.619, + 0.715 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.725, + 0.892, + 0.844 + ], + "angle": 0, + "content": "In this paper, a multi-interactive architecture was proposed to formulate fusion and segmentation in a harmonious manner. We introduced a hierarchical interactive attention with dynamic factors, which bridges gaps of cross-task features from architecture and learning perspectives. In addition, we proposed a comprehensive full-time multimodality benchmark, with well-registered targets, abundant scenes and affluent labels." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.845, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Acknowledgments. This work is partially supported by the National Key R&D Program of China (No. 2022YFA1004101), the National Natural Science Foundation of China (No. U22B2052, 62027826)." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "8122" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.469, + 0.157 + ], + "angle": 0, + "content": "[1] Hengshuang Zhao, Jianping Shi, Xiaojuan Qi, Xiaogang Wang, and Jiaya Jia. Pyramid scene parsing network. In IEEE/CVF CVPR, pages 2881-2890, 2017." + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.16, + 0.469, + 0.202 + ], + "angle": 0, + "content": "[2] Bolei Zhou, Hang Zhao, Xavier Puig, Sanja Fidler, Adela Barriuso, and Antonio Torralba. Scene parsing through ade20k dataset. 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Its branches display part of the well registered targets, which are extraordinarily affluent and manifold. The zoomed-in regions on the right show the segmentation comparison in cyan circles and fusion comparison in orange circles. It is obvious that the proposed method is superior to SOTA methods on both visual effects and mIoU. + +![](images/c8e8dcc745e8f90cc38f7fcddc6619cd3562934cba89961178ac7846a908f03b.jpg) + +![](images/5152074a6387b181f96d8150372cd023b4aac5ae0613fac95c0d9c2aac59b4b6.jpg) + +![](images/99baaa803bd6eb1c457bd23e65e09b8b060503ab9273b94d6410e29a2a5f0fc2.jpg) + +# Abstract + +Multi-modality image fusion and segmentation play a vital role in autonomous driving and robotic operation. Early efforts focus on boosting the performance for only one task, e.g., fusion or segmentation, making it hard to reach 'Best of Both Worlds'. To overcome this issue, in this paper, we propose a Multi-interactive Feature learning architecture for image fusion and Segmentation, namely SegMiF, and exploit dual-task correlation to promote the performance of both tasks. The SegMiF is of a cascade structure, containing a fusion sub-network and a commonly used segmentation sub-network. By slickly bridging intermediate features between two components, the knowledge learned from the segmentation task can effectively assist the fusion task. Also, the benefited fusion network supports the segmentation one to perform more pretentionally. Besides, a hierarchical interactive attention block is established to ensure fine-grained mapping of all the vital information between two tasks, so that the modality/semantic features can be fully mutual-interactive. In addition, a dy + +namic weight factor is introduced to automatically adjust the corresponding weights of each task, which can balance the interactive feature correspondence and break through the limitation of laborious tuning. Furthermore, we construct a smart multi-wave binocular imaging system and collect a full-time multi-modality benchmark with 15 annotated pixel-level categories for image fusion and segmentation. Extensive experiments on several public datasets and our benchmark demonstrate that the proposed method outputs visually appealing fused images and perform averagely $7.66\%$ higher segmentation mIoU in the real-world scene than the state-of-the-art approaches. The source code and benchmark are available at https://github.com/JinyuanLiu-CV/SegMiF. + +# 1. Introduction + +Accurate and robust scene parsing[1, 2] is a fundamental technology for autonomous driving. However, in complex environments, e.g., inclement weather, only using visi + +ble sensors may fail to accurately recognize targets. On the contrary, infrared sensors are free from the aforementioned issues but limited in low spatial resolution. Consequently, fusing the infrared and visible image [3, 4, 5, 6, 7] has become a mainstream solution for better scene understanding. + +Multi-modality fusion for scene parsing needs to provide: (i). robust visual appealing image: they require continually generating high-quality images in dynamic scenes. (ii). accurate semantic segmentation: they demand to assign category labels to each pixel. Towards these goals, jointly solving multi-modality image fusion and segmentation becomes an urgent issue. + +Numerous learning-based multi-modality image fusion methods have been fast development [8, 9, 10, 11, 12]. However, most of them concentrate on developing various networks for generating visual-appealing images rather than considering the follow-up high-level vision tasks, posing an obstacle to better scene parsing. Recently, few studies[13, 14, 15, 16] have attempted to design multi-task learning-based loss functions by cascading the fusion network and high-level tasks. Unfortunately, seeking unified appropriate features for either task simultaneously is still a tough issue. + +Moreover, exploring multi-modality fusion and segmentation demands a comprehensive collection of well-alignment image pairs with pixel-level annotated labels. Also, as for one image, the annotated needs to cover a wide range of pixels. Unfortunately, existing multi-modality data collections either focus on image fusion or lack whole image annotated segmentation labels, placing an obstacle to exploring the correlation of the fusion and segmentation. + +This paper proposes a multi-interactive feature learning architecture for the joint problem of multi-modality fusion and segmentation, namely SegMiF. SegMiF is constructed by a fusion network and a segmentation network, in which the intrinsic features of either one interact via a new proposed hierarchical interactive attention (HIA). HIA fully integrates semantic-/modality-oriented features by fine-grained mapping. We also derive a dynamic weighting factor and seamless it in the interactive training scheme, to automatically learn the optimal parameters for either task. Figure 1 demonstrates that our SegMiF assigns the category to each pixel from the visual-friendly fused result more accurately than the state-of-the-arts (SOTAs). Our contributions can be distilled into four main aspects as follows: + +- We formulate both image fusion and segmentation in a joint manner, in which the semantic and pixel-based features can mutually interact. To this end, two tasks can achieve the 'Best of Both Worlds', generating visual-appealing fused images along with accurate scene parsing. +- A hierarchical interactive attention is introduced to bridge the feature gap between the fusion network + +and the segmentation one. Establishing the semantic/modality multi-head attention mechanism in HIA simultaneously preserves intrinsic modality features and brings more attention to semantic features. + +- An interactive feature training scheme is proposed to overcome the shortcoming of insufficient feature interaction between fusion and segmentation. Seamlessly integrating a dynamic weighting factor allows the exploration of the optimal parameters of each task in an automatic manner. +- We construct a smart multi-wave binocular imaging system, and introduce a full-time multi-modality benchmark, namely FMB, to promote the research of both image fusion and segmentation. FMB contains 1500 well-registered infrared and visible image pairs with 15 annotated pixel-level categories (see the left part of Figure 1). Also, it covers a wide range of pixel variations and various severe environments, e.g., dense fog, heavy rain, and low-light condition. + +# 2. Related Works + +Multi-modality image fusion In recent years, deep learning based multi-modality image fusion approaches achieved significant progress[11, 12, 17, 18, 19]. Early efforts [8, 9, 10, 20, 21] tend to achieve excellent fusion effects by adjusting the network structure or loss functions. However, a minority pay attention to whether the downstream tasks can be well adapted to fusion. DIDFuse [10] was the first to apply deep decomposition for high and low-frequency features, while AUIF [22] proposed a decomposition and fusion framework based on algorithm unfolding from an optimization perspective. Subsequently, CDDFuse [6] upgraded the decomposition network to a Transformer-CNN dual-stream structure. DDFM [7], for the first time, utilized denoising diffusion models for image fusion tasks. Recently, some methods [23, 13, 24] cascaded fusion and downstream tasks, focusing on improving task performance by achieving oriented fusion. Nevertheless, this kind of native gradient back propagation hinders the fusion network to adapt to subsequent tasks heuristically from the feature level. + +Multi-modality Segmentation Recently, two-stream-based feature fusion models are proposed to perform the segmentation directly. Most of existing methods mostly develop various simple fusion strategies, such as the weighted average [25, 26, 27], summation [28, 29] and concatenation [30, 31]. Nonetheless, direct feature fusion lacks explicit fusion principle to preserve the typical modality feature and pay no attention to the pixel-level visual effects. + +![](images/5ebdbf194e48f440514ca0c6cdf03b86ee1d17a2db2579fc4caefad69738ab06.jpg) +Figure 2: Workflow of our proposed SegMiF. The left part depicts the latent interactive relationship between image fusion and segmentation. The middle part plots the concrete architecture of the SegMiF. The right part details the components of proposed hierarchical interactive attention. + +![](images/436cb10c9073e70c336f00cb3b5835b7706c8d2bf707ff7d0d92aa933799370c.jpg) + +![](images/67be32218d741da2972828f251e2f875d343fcdf120d003f33d6dcfe23da76e4.jpg) + +# 3. The Proposed Method + +# 3.1. Problem formulation + +As for image fusion or segmentation tasks, one of the most commonly used ways is to design a neural network, and fully utilize it to find a set of optimal parameters. For this purpose, we suppose that the visible, infrared, and fused image are all gray-scale with the size of $m \times n$ , denoted as column vectors $\mathbf{x}$ , $\mathbf{y}$ , and $\mathbf{u} \in \mathbb{R}^{mn \times 1}$ , respectively. The optimization model is formulated as: + +$$ +\min _ {\boldsymbol {\omega} _ {k}} f \left(\mathbf {k}, \mathcal {N} (\mathbf {x}, \mathbf {y}; \boldsymbol {\omega} _ {k})\right), \tag {1} +$$ + +where $\mathbf{k}$ denotes the output of the task-related network $\mathcal{N}$ with the learnable parameters $\omega_{\mathrm{k}}$ . $f(\cdot)$ is a fidelity term. + +Previous approaches solely design image fusion or segmentation networks, which only can achieve outstanding results for one task. To generate visualappealing fused images along with accurate scene segmentation results, we jointly formulate the two tasks into one goal [32, 33, 34], which can be rewritten as: + +$$ +\min _ {\boldsymbol {\omega} _ {\mathrm {u}}, \boldsymbol {\omega} _ {\mathrm {s}}} f _ {\mathrm {u}} \left(\mathbf {u}, \Phi (\mathbf {x}, \mathbf {y}; \boldsymbol {\omega} _ {\mathrm {u}})\right) + f _ {\mathrm {s}} \left(\mathbf {s}, \Psi (\mathbf {x}, \mathbf {y}; \boldsymbol {\omega} _ {\mathrm {s}})\right) + g \left(\boldsymbol {\omega} ^ {\star}\right), \tag {2} +$$ + +where $\omega^{\star} = [\omega_{\mathrm{u}},\omega_{\mathrm{s}}]$ . $\mathbf{u}$ and $\mathbf{s}$ denote the fused image and segmentation map, which are produced by the fusion network $\Phi$ and segmentation network $\Psi$ with the learnable parameters $\omega_{\mathrm{u}}$ and $\omega_{\mathrm{s}}$ . $g(\cdot)$ is a constrained term to joint optimize the two tasks. In this paper, we regard the $g(\cdot)$ as a feature learning constrained manner, and achieve this goal by designing a hierarchical attention along with the interactive training scheme. The visualized illustration is plotted in the left part of Figure 2. + +# 3.2. Feature interaction architecture + +Overview of the whole network. Our proposed SegMiF is designed with cascade principle, composited by image + +fusion and segmentation sub-network. Details of the whole architecture is shown at Figure 2. In specific, we utilize two parallel dilated residual dense blocks (DRDB) [35, 36] to extract features from visual and infrared images. SegFormer [37] is leveraged as the baseline segmentation network to provide semantic parsing. Two scales of semantic features from the backbone, interpolated with original resolutions are embedded into fusion network. In order to sufficiently realize the semantic information sharing, we propose the hierarchical interactive attention (HIA) to transfer high-level knowledge. + +Hierarchical interactive attention. After obtaining modality feature $\mathbf{F}_{ir},\mathbf{F}_{vis}$ from fusion network and segmentation feature $\mathbf{F}_{seg}$ , we build the HIA to construct the fine-grained mapping of these features and strengthen the mutually beneficial representation. Features including $\mathbf{F}_{ir},\mathbf{F}_{vis}$ and $\mathbf{F}_{seg}$ as inputs, two attention mechanisms are leveraged to globally exchange intermediate features. Concatenating features from attentions, fresh modality features are generated based on a residual connection. + +In detail, channel embedding is utilized to decompose modality/semantic features. We can denote the outputs from the linear embedding as $\{\mathbf{F}_x^s,\mathbf{F}_x^m\}$ with size $\mathbb{R}^{mn\times C}$ , where $x\in \{ir,vis,seg\}$ is under a vector formulation. Instead of utilizing the original self-attention mechanisms directly, we bridge these features with complementary interaction from different representation subspaces by MoAM and SoAM. + +![](images/e8464b0d0627836ae85a3385200cbc3862cd89a10da2bade51a2c04432216ffb.jpg) +Figure 3: Detailed architectures of SoAM and MoAM. + +Both multi-head attention modules are plotted in Fig- + +ure 3. Semantic-oriented attention module targets to provide more semantic attention for the modality feature. SoAM utilizes the token $\mathbf{F}_{seg}^{s}$ to generate the Query $Q_{s}$ , which represents the inhere semantic information that needs to be enhanced. The global context representation of each can be calculated by as $K_{ir}^{T}V_{ir}$ and $K_{vis}^{T}V_{vis}$ , where the corresponding Key and Value of each head are from the modality tokens $\{\mathbf{F}_{ir}^{m},\mathbf{F}_{vis}^{m}\}$ . Denoted the modality context representation as $\mathbf{G}_{ir}$ , $\mathbf{G}_{vis}$ , we can calculate the attention as $S_{ir} = Q_s\mathbf{G}_{ir}$ and $S_{vis} = Q_s\mathbf{G}_{vis}$ . On the other hand, MoAM is with the complementary principle to investigate the significant feature from semantic contexts. Specifically, MoAM is to introduce two modality queries $Q_{ir},Q_{vis}$ to represent the intrinsic modality feature (e.g., targets and details) from $\{\mathbf{F}_{ir}^{m},\mathbf{F}_{vis}^{m}\}$ . Similarly, we can obtain the global context of segmentation $\mathbf{G}_s$ by $K_{s}^{T}V_{s}$ . The cross attention can be formulated as $M_{vis} = Q_s\mathbf{G}_{vis}$ and $M_{vis} = Q_s\mathbf{G}_{vis}$ . By concatenating the groups $\{S_{vis},M_{vis}\}$ and $\{S_{ir},M_{ir}\}$ , we can obtain the comprehensive features with two parallel MLPs with residual connection to aggregate features from SoAM and MoAM. + +# 3.3. Loss function + +The total loss function is combined of an image fusion loss function $\mathcal{L}_{\mathrm{f}}$ and segmentation loss $\mathcal{L}_{\mathrm{s}}$ . $\mathcal{L}_{\mathrm{f}}$ consists of three types of losses, i.e., structure loss $\mathcal{L}_{\mathrm{SSIM}}$ , pixel loss $\mathcal{L}_{\mathrm{MSE}}$ and gradient loss $\mathcal{L}_{\mathrm{grad}}$ . For one fused image, it should preserve overall structures from source images. To this end, the structural similarity index (SSIM) [38, 39, 40, 41] is introduced in function: + +$$ +\mathcal {L} _ {\mathrm {S S I M}} = \left(1 - \mathrm {S S I M} _ {\mathbf {u}, \mathbf {x}}\right) / 2 + \left(1 - \mathrm {S S I M} _ {\mathbf {u}, \mathbf {y}}\right) / 2, \tag {3} +$$ + +where $\mathcal{L}_{\mathrm{SSIM}}$ denotes structure similarity loss. To maintain the vital intensity in the fused image, we employ the saliency-based pixel loss, it formulated as: + +$$ +\mathcal {L} _ {\mathrm {M S E}} = \left\| \mathbf {u} - m _ {1} \mathbf {x} \right\| _ {2} ^ {2} + \left\| \mathbf {u} - m _ {2} \mathbf {y} \right\| _ {2} ^ {2}, \tag {4} +$$ + +where $m_{1}$ and $m_{2}$ are saliency weight maps calculated by VSM [42]. Besides, gradient information of images always characterizes texture details, thus, we used $\mathcal{L}_{\mathrm{grad}}$ to constrain these textual factors to a multi-scale manner: + +$$ +\mathcal {L} _ {\mathrm {g r a d}} = \sum_ {k = 3, 5, 7} \| \nabla^ {k} \mathbf {u} - \max (\nabla^ {k} \mathbf {x}, \nabla^ {k} \mathbf {y}) \| _ {2} ^ {2} \tag {5} +$$ + +where $\nabla$ denotes gradient operators that calculate by $\nabla = \mathbf{u} - \mathcal{G}(\mathbf{u})$ with combination of different Gauss $(\mathcal{G})$ kernel size $k$ . Totally, we obtained $\mathcal{L}_{\mathrm{f}} = \mathcal{L}_{\mathrm{SSIM}} + \mathcal{L}_{\mathrm{MSE}} + \eta \mathcal{L}_{\mathrm{grad}}$ . + +Common to previous works, $\mathcal{L}_{\mathrm{s}}$ is defined as: + +$$ +\mathcal {L} _ {\mathrm {s}} \left(\mathbf {s}, \mathbf {s} ^ {*}\right) = - \sum_ {\text {c l a s s}} \mathbf {s} ^ {*} \log (\mathbf {s}), \tag {6} +$$ + +where $\mathbf{s}^*$ represents the segmentation label. We adopt the effective semantic segmentation method SegFormer network $\Psi$ [37]. The total loss function is: + +$$ +\mathcal {L} _ {\text {t o t a l}} = \lambda_ {1} \mathcal {L} _ {\mathrm {f}} + \lambda_ {2} \mathcal {L} _ {\mathrm {s}}, \tag {7} +$$ + +where $\lambda_{1}$ and $\lambda_{2}$ are dynamic weighting factor which will be discussed below. + +# 3.4. Dynamic factor for interactive learning + +By exploiting an alternatively recurrent iterations, we can progressively introduce the task-preferred features into the framework optimization. As mentioned above, at the phase of image fusion, we introduce the dynamic weighting factors $\lambda_{1}$ and $\lambda_{2}$ to rapidly measure the importance of task-related losses. We observe that the task-specific balance can be derived from the convergent rate. The intuition is that if the value of losses cannot be further descended, the network may obtain the corresponding optimal weights. If the convergent rate descends fast, we should pay more attention to this task. Learning from the dynamic weight average [43], we further present the factor of task preference $\eta$ to emphasize the primary goal. Denoted $r_i$ as the convergent rate of $i$ -th task with loss $\mathcal{L}_i$ , we can compute the rate as: + +$$ +r _ {1} (n - 1) = \frac {\mathcal {L} _ {i} (n - 1)}{\mathcal {L} _ {i} (n - 2)}. \tag {8} +$$ + +Then the procedure of dynamic weight factor of $i$ -th task is formulated as: + +$$ +\lambda_ {\mathrm {i}} (n) = \frac {\eta_ {\mathrm {i}} \exp \left(r _ {\mathrm {i}} (n - 1) / T\right)}{\sum_ {k} \exp \left(r _ {\mathrm {k}} (n - 1) / T\right)}, \tag {9} +$$ + +where $T$ is a temperature to control the sensitiveness of two tasks. Different from widely sued GDN [44], this dynamic strategy can actually avoid the complicated computation of various task gradients. + +Then based on the fusion image generated with semantic feature, we can train the segmentation network end-to-end, using the gradient descending $\omega_{s} \gets \omega_{s} - \nabla_{\omega_{s}} \mathcal{L}_{\mathbb{S}}(\mathbf{u}; \omega_{s})$ . The two learning processes are trained alternately until full convergence. Noting that, this training strategy is actually task-agnostic, we also can introduce other different high-level vision tasks into the unified consideration, rather than designing for segmentation unilaterally. + +# 4. Full-time Multi-modality Benchmark + +Existing two multi-modality segmentation datasets suffer from few label categories, sparse annotation and monotonous scene, as shown in Figure 6. The proposed FMB dataset aims to overcome these difficulties and promote the development of whole field. A glimpse of FMB is given in Figure 4. + +![](images/8aa6f083139321b291dc3c4021fee41d106d54783255573cb0d7fb81f5b0d660.jpg) +Figure 4: Visualization of visible/infrared/segmentation images in the proposed FMB dataset. The dataset contains a wide range of real driving scenes under different lighting conditions, and also includes special scenarios with rain, fog, strong light, and even Tyndall Effect. + +![](images/29021975e4f31c1fd2d15f3dc07b2905c700b87c17e1a52c5fc872738e7eca3c.jpg) +Figure 5: Illustration of the binocular imaging system. + +We built a binocular imaging system that can be placed on the car roof, including a visible camera and an infrared sensor with a wavelength range of $8 - 14\mu m$ (as shown in the Figure 5). We finally obtained 1500 aligned image pairs with a resolution of $800\times 600$ . In details, two sensors are individually calibrated using their respected calibration board to obtain internal parameters, and their relative pose relationship is obtained through joint calibration. We calculate the homography matrix $H$ by employing RANSAC1. The infrared images are projected onto visible coordinates using $H$ and cropped, ultimately resulting in pixel-level registered image pairs with a size of $800\times 600$ . + +The FMB dataset includes rich scenes under different illumination conditions, so that it enables fusion/segmentation model to improve the generalization ability greatly. We labeled $98.16\%$ of all pixels into 14 different categories including Road, Sidewalk, Building, Traffic Light, Traffic Sign, Vegetation, Sky, Person, Car, Truck, Bus, Motorcycle, Bicycle and Pole, which often appear in real-world automatic driving and semantic understanding tasks. + +# 5. Experiments + +Two representative datasets including MFNet and proposed FMB are utilized for the training and evaluation. The details of these datasets are reported in the above section. Several data augmentation techniques are utilized for the whole training procedure: random resizing with a ratio of + +![](images/d5aea48cfd0c67ab07fadcbc288fdcbd353abfe6f0ee4d56aac183c181ffafdc.jpg) +Figure 6: Comparison of FMB with existing multi-modality segmentation datasets (i.e., PST900 [31] and MFNet [30]). + +0.5-2.0, random cropping to $360 \times 360$ , brightness distortion and normalization. The Adam optimizer with poly learning rate adjustment is utilized to optimize both networks. As for the fusion, the initial learning rate is $1e^{-4}$ and decayed to $1e^{-8}$ progressively. As for segmentation, we first utilized $1e^{-6}$ to warm start the training with 3k iterations, then we conducted the training with intilial learning rate $8e^{-5}$ . With batch size of 8, we trained the framework for 8 rounds. For each round, we set 10k iterations for training segmentation and 5k iterations for fusion. Noting that, a similar configuration of segmentation is also utilized for the training of fusion-based methods. All experiments are performed on an NVIDIA Tesla V100 GPU with PyTorch framework. + +# 5.1. Results of multi-modality image fusion + +We demonstrate our fusion quality based on qualitative and quantitative analyses with six state-of-the-art competitors, including DIDFuse [10], DenseFuse [45], ReCoNet[11], UMFusion[12], TarDAL[13] and U2Fusion [9]. + +Qualitative Comparisons. The qualitative results on MFNet and FMB datasets are depicted in Figure 7, in which we can clearly observe two remarkable advantages of our method. First, the significant characteristics of infrared images can be effectively highlighted. For instance, as shown on the green rectangle of the first group, DIDFuse, ReCoNet and TarDAL are susceptible to strong illumination. In contrast, our method can remarkably preserve this information from infrared images, e.g., the structure of cars and pedestrians. Furthermore, benefiting from the guidance of semantic + +![](images/7bc7ed056c578188e6ef11ccdd33f6a62dff868071e0937228434bb5b51de164.jpg) + +![](images/0e9c59857c4699f1a5bce16363196e2e8e1b19054f4d723f343824dee99a0905.jpg) + +![](images/1f49c27e4511c207edd11c82d9d379ee6299c9fa12aed5a1c4b8d13cba6ba306.jpg) + +![](images/c02894caef09b119339293fe21797b7e166a5855cbc032625b33eb026b0d3ac5.jpg) + +![](images/3466209485ff5724f07bf593070392abfa0246a86446881ccbf1904820ac5158.jpg) + +![](images/cba7e7924ae660369d527fb818b0312a4200cf7fe4baa614ae567ed598258663.jpg) + +![](images/3db9e4f6796c7b47fac6e9c3a790ae07d9a532904f6cb89b23c06118c600836d.jpg) + +![](images/4b354bfe11ef5e5a014529077d610473af3aa4363e73644a882e0c8ba3a6c51b.jpg) + +![](images/64951e02302574588ef07b9627c03e32bb36a1e88864c32eb1c20624d6dbfe8f.jpg) +Source images + +![](images/7cd3646bfc2de238c9db228e92dcd1c21f30515ae6b8b12b795b565ac8000cf7.jpg) +DIDFuse + +![](images/b118f509c459bd9881413aa9866a19cc2d2704709cfd326e6a565d65a6b7b932.jpg) +DenseFuse + +![](images/3587ff26ecf05572f57f0b5fde2cdd334ef6dd99f3a83f277ea0752d9ba73d98.jpg) +ReCoNet + +![](images/73ed946d90a49ffd38851af674e40ec2f96d01e5f9a25c521dd6c7c0cff8755d.jpg) +UMFusion + +![](images/9a471e9a0fabaf4d8f8bbb8c2edebbf3587c7e1bbf42e1f431393c1474e634e4.jpg) +TarDAL + +![](images/fef0fdba71ff40da1e1bf23d57565fa22ac9d5597ffaab670e51d5c468807151.jpg) +U2Fusion + +![](images/96eb2b77cb4d0f0c78d3a61728b3011d3ac89dc7e51926a9be663311f67d7c29.jpg) +Ours + +![](images/f33b089ccbaabdd2147a67809d8cfc85fb160c3e5aa017272eabf9d44982c878.jpg) +Figure 7: Visual comparison of different fusion approaches on the MFNet and FMB dataset, respectively. + +![](images/f8a90e4a0b8c3259c2725fdf262a4c9b8f7710419354dd1b65be8bf04a9f7b61.jpg) +Figure 8: Quantitative comparisons of image fusion with six SOTA methods on two datasets. Violin plots illustrating the distribution of the four metrics, in which the white triangles and the black lines indicate mean values and medium values. + +![](images/4f7a4082b6d8810e6e059e23e611e2616ee4050c25ca059e7a7758fbfb785a6c.jpg) +Figure 9: Qualitative demonstrations of different approaches on the MFNet dataset. + +![](images/f692700d3d45d2320904936768432094442584b6bea2c935667134dca403ade8.jpg) + +information, our method can enhance the texture details of the given scene from either dataset. Compared with other competitors in the second row of Figure 7, our results exhibit a sharper appearance. + +Quantitative Comparisons. We also plot the numerical results with other six fusion competitors on 50 pairs from MFNet and 50 pairs from FMB in Figure 8. Four objective metrics are leveraged for the comparison, including entropy (EN)[46], standard deviation (SD)[47], spatial frequency (SF)[48] and the sum of the correlations of differences (SCD)[49]. Note that our results achieve consistent superiority in terms of these statistical metrics. Specifically, the highest EN and SCD indicate that our method can significantly preserve the largest amount of considerable information transferred from source images. Moreover, the immense average value on SD reflects the high pixel contrast for visual observations. Furthermore, higher SF reflects our + +method has rich texture details and contrasts. In summary, our method enhances the texture details for precise observation and stably preserves abundant typical information to support semantic parsing tasks. + +# 5.2. Results of multi-modality segmentation + +We provide another comprehensive analysis for image segmentation. Besides comparing with the newest fusion-based methods, we also conduct the evaluations with competitive dual-stream methods: GMNet [50], FEANet [51], EGFNet [52], ABMDRNet [53] and LASNet [54].2 + +Qualitative Comparisons. Visualized results of segmentation on MFNet are depicted in Figure 9. We also compare various competitive methods in Figure 10 under the newly proposed dataset, which is more challenging with rich categories, complex imaging conditions and complicated scene + +![](images/3dff34908fcab5b78025d33b90e6111b0248f7d0b2ee7ae74f55e897d1a7999f.jpg) +Figure 10: Qualitative demonstrations for the different methods in daytime and nighttime scenarios on FMB benchmark. + +![](images/e4075c859a3a420085bdf1994a2b53aa5d0d8731b66007310e0dec70e47b03c7.jpg) + +
MethodsUnlabelCarPersonBikeCurveCar StopConeBumpmAccmIoU
AccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoU
Visible98.297.594.682.281.754.771.261.054.921.661.916.682.143.777.330.869.745.9
Infrared98.697.490.381.885.367.371.654.851.337.353.824.364.733.470.248.065.649.9
LASNet99.297.494.984.281.767.182.156.970.741.156.839.658.148.877.240.175.454.9
EGFNet99.397.795.887.689.069.880.658.871.542.848.733.865.348.371.147.172.754.8
FEANet99.197.893.987.882.771.176.761.165.546.526.622.166.655.377.348.973.255.3
ABMDR99.398.494.384.890.069.675.760.364.045.144.133.161.747.466.250.069.554.8
DIDFuse98.097.395.079.179.564.080.258.544.119.964.023.377.537.869.020.467.544.5
ReCoNet98.197.395.880.488.960.065.055.447.020.769.025.877.839.846.617.465.944.5
U2Fusion98.397.795.282.885.464.877.761.062.732.366.720.975.545.282.350.271.950.8
TarDAL98.397.693.580.786.267.176.560.153.834.955.310.588.638.790.645.571.748.6
Ours98.798.196.387.889.671.481.263.263.547.566.731.185.348.984.850.374.856.1
+ +Table 1: Quantitative semantic segmentation results of different methods on the MFNet dataset. + +details. As discussed above, existing fusion methods cannot highlight the dimness of infrared targets, and the distant pedestrian can not be recognized. As for dual-stream methods, which utilize the modality feature directly, they are easy to introduce conflicts and weaken the accuracy without a clear feature fusion principle. The results, such as the car occluded by barriers (the first column of Figure 9) and the shape of the human (the second column of Figure 10) can not be precisely classified. It is worth mentioning that interaction feature learning from segmentation can drastically transfer the complementary characteristics for image fusion and further improve the segmentation performance. Thus, our method can continuously classify the objects of diverse scenes with high accuracy. + +Quantitative Comparisons. Table 1 and Table 2 reported the qualitative results among different categories of competitors on MFNet and FMB datasets. These results illustrate our method is ahead of other state-of-the-art methods by a large margin on both segmentation datasets. Noting that our numerical results outperform other methods concerning mIOU and rank second in terms of mACC. Compared with the second one, our method improves $7.66\%$ and $1.45\%$ of mIOU on FMB and MFNet respectively. More specifically, the classification of Car and Person is important for the current intelligent perception system. The top two results in these two categories indicate the high perfor + +mance of our method to employ for real-world perception. On the other hand, for thermal-insensitive categories, such as traffic sign, building, bump, due to the effective visual quality preservation and enhancement, our method achieves significant superiority. + +# 5.3. Ablation studies + +Study on HIA. HIA plays a key role in preserving intrinsic modality features from the semantic feature guidance. Firstly, we visualized the representative feature to discuss the effectiveness of HIA in Figure 11. Clearly, HIA can remarkably preserve the salient infrared features with abundant semantic information, avoiding the interference of harsh weather and strong light. Then we plot different variants of HIA to illustrate the inner mechanisms of HIA. As shown in Figure 12. Obviously, the version w/o SoAM loses the classify ability to distinguish confused objectives, e.g., the orange circle in the second row. Meanwhile, "w/o MoAM" cannot protect the details at nighttime with color distortion, e.g., the building in the distance. It is worth pointing out that our full model not only provides clear visual observation but also has high sensitiveness to segmentation. Similarly, the quantitative results reported in Table 3 also demonstrate the effectiveness of full HIA for both segmentation benchmarks compared with direct aggregation and other model variants. In brief, HIA is capable enough to + +
MethodsCarPersonTruckT-LampT-SignBuildingVegetationPolemAccmIoU
AccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoU
Visible84.578.378.146.673.243.482.523.783.664.089.077.888.582.171.641.873.550.5
Infrared75.669.189.963.366.612.663.124.780.552.987.478.083.775.562.123.069.643.9
GMNet87.679.377.360.149.022.254.121.678.569.089.179.188.983.859.739.864.449.2
LASNet81.372.676.448.629.614.820.72.979.359.086.975.487.681.656.636.756.942.5
EGFNet83.677.479.563.033.517.158.625.282.666.688.577.289.383.563.841.563.047.3
FEANet82.373.978.860.744.732.353.613.573.355.687.679.489.081.266.236.864.546.8
DIDFuse86.377.787.464.466.328.875.929.281.164.487.178.489.582.479.241.873.050.6
ReCoNet83.775.987.765.834.714.983.334.785.666.689.079.288.281.373.344.971.450.9
U2Fusion85.076.687.761.984.614.475.128.381.368.989.578.892.582.274.542.270.147.9
TarDAL81.874.293.356.066.318.875.029.681.266.588.179.187.981.765.941.974.848.1
Ours85.378.378.365.474.447.386.443.186.174.890.082.091.685.072.549.874.554.8
+ +bridge the fusion and segmentation tasks. + +![](images/e6c8c91f72d021e4cbb8a3dda4ca322f5605d5082ae786f2844dc208a184ddae.jpg) +Figure 11: Feature visualization of different stages. From left to right: visible image, infrared image, their features, w/o HIA, and w/ HIA. + +Table 2: Quantitative semantic segmentation results of different methods on the FMB dataset. + +
ModelHIAMF DatasetFMB Dataset
SoAMMoAMmAccmIoUmAccmIoU
“Concatenate”XX72.652.772.351.3
“Summation”XX71.552.673.752.1
“Average”XX72.952.172.450.7
M1XX67.251.972.450.5
M2X✓73.655.072.752.3
M3✓X72.053.473.154.1
M4✓✓74.856.174.554.8
+ +Table 3: Numerical results about the effectiveness of HIA. The first three are the results of direct feature aggregation. Latter are the results of model variants with HIA. + +Analyzing the dynamic factor. We discussed the impact of the proposed dynamic factor for interactive learning compared with existing multi-task optimization methods, as shown in Figure 13. Manual adjustment requires plenty of prior knowledge and labor consumption. But concurrently, it achieves decent segmentation results. The other five training strategies hardly coordinate the relationship between the two tasks and fail to achieve good visualization and segmentation performance. The dynamic factor enables to better introduce task preferences into optimization, thus achieving + +excellent results on both tasks. + +![](images/b0cb6b19667bb91dfcdb20db8176da490bc5ef1a9f06891925aa73c416264758.jpg) +Figure 12: Visual comparisons of different models. + +![](images/e0df24652b3b51ed948a8e09b42dfb71da3152770abc4faf83664234a74acbb7.jpg) +Figure 13: Comparisons of different strategies of adjusting dynamic factors. + +# 6. Conclusion + +In this paper, a multi-interactive architecture was proposed to formulate fusion and segmentation in a harmonious manner. We introduced a hierarchical interactive attention with dynamic factors, which bridges gaps of cross-task features from architecture and learning perspectives. In addition, we proposed a comprehensive full-time multimodality benchmark, with well-registered targets, abundant scenes and affluent labels. + +Acknowledgments. This work is partially supported by the National Key R&D Program of China (No. 2022YFA1004101), the National Natural Science Foundation of China (No. U22B2052, 62027826). + +# References + +[1] Hengshuang Zhao, Jianping Shi, Xiaojuan Qi, Xiaogang Wang, and Jiaya Jia. Pyramid scene parsing network. In IEEE/CVF CVPR, pages 2881-2890, 2017. +[2] Bolei Zhou, Hang Zhao, Xavier Puig, Sanja Fidler, Adela Barriuso, and Antonio Torralba. Scene parsing through ade20k dataset. In IEEE/CVF CVPR, pages 633-641, 2017. +[3] Wujie Zhou, Xinyang Lin, Jingsheng Lei, Lu Yu, and Jenq-Neng Hwang. Mffenet: Multiscale feature fusion and enhancement network for rgb-thermal urban road scene parsing. IEEE TMM, 24:2526-2538, 2021. +[4] Wujie Zhou, Shaohua Dong, Caie Xu, and Yaguan Qian. Edge-aware guidance fusion network forrgb-thermal scene parsing. In AAAI, volume 36, pages 3571-3579, 2022. +[5] Zhiying Jiang, Zengxi Zhang, Xin Fan, and Risheng Liu. 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Its branches display part of the well registered targets, which are extraordinarily affluent and manifold. The zoomed-in regions on the right show the segmentation comparison in cyan circles and fusion comparison in orange circles. 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Early efforts focus on boosting the performance for only one task, e.g., fusion or segmentation, making it hard to reach 'Best of Both Worlds'. To overcome this issue, in this paper, we propose a Multi-interactive Feature learning architecture for image fusion and Segmentation, namely SegMiF, and exploit dual-task correlation to promote the performance of both tasks. The SegMiF is of a cascade structure, containing a fusion sub-network and a commonly used segmentation sub-network. By slickly bridging intermediate features between two components, the knowledge learned from the segmentation task can effectively assist the fusion task. Also, the benefited fusion network supports the segmentation one to perform more pretentionally. Besides, a hierarchical interactive attention block is established to ensure fine-grained mapping of all the vital information between two tasks, so that the modality/semantic features can be fully mutual-interactive. In addition, a dy" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 465, + 548, + 634 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 465, + 548, + 634 + ], + "spans": [ + { + "bbox": [ + 304, + 465, + 548, + 634 + ], + "type": "text", + "content": "namic weight factor is introduced to automatically adjust the corresponding weights of each task, which can balance the interactive feature correspondence and break through the limitation of laborious tuning. Furthermore, we construct a smart multi-wave binocular imaging system and collect a full-time multi-modality benchmark with 15 annotated pixel-level categories for image fusion and segmentation. Extensive experiments on several public datasets and our benchmark demonstrate that the proposed method outputs visually appealing fused images and perform averagely " + }, + { + "bbox": [ + 304, + 465, + 548, + 634 + ], + "type": "inline_equation", + "content": "7.66\\%" + }, + { + "bbox": [ + 304, + 465, + 548, + 634 + ], + "type": "text", + "content": " higher segmentation mIoU in the real-world scene than the state-of-the-art approaches. The source code and benchmark are available at https://github.com/JinyuanLiu-CV/SegMiF." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 657, + 387, + 669 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 657, + 387, + 669 + ], + "spans": [ + { + "bbox": [ + 306, + 657, + 387, + 669 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 547, + 715 + ], + "type": "text", + "content": "Accurate and robust scene parsing[1, 2] is a fundamental technology for autonomous driving. However, in complex environments, e.g., inclement weather, only using visi" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8115" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 286, + 132 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 286, + 132 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 286, + 132 + ], + "type": "text", + "content": "ble sensors may fail to accurately recognize targets. On the contrary, infrared sensors are free from the aforementioned issues but limited in low spatial resolution. Consequently, fusing the infrared and visible image [3, 4, 5, 6, 7] has become a mainstream solution for better scene understanding." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 133, + 286, + 215 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 133, + 286, + 215 + ], + "spans": [ + { + "bbox": [ + 46, + 133, + 286, + 215 + ], + "type": "text", + "content": "Multi-modality fusion for scene parsing needs to provide: (i). robust visual appealing image: they require continually generating high-quality images in dynamic scenes. (ii). accurate semantic segmentation: they demand to assign category labels to each pixel. Towards these goals, jointly solving multi-modality image fusion and segmentation becomes an urgent issue." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 216, + 286, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 216, + 286, + 346 + ], + "spans": [ + { + "bbox": [ + 46, + 216, + 286, + 346 + ], + "type": "text", + "content": "Numerous learning-based multi-modality image fusion methods have been fast development [8, 9, 10, 11, 12]. However, most of them concentrate on developing various networks for generating visual-appealing images rather than considering the follow-up high-level vision tasks, posing an obstacle to better scene parsing. Recently, few studies[13, 14, 15, 16] have attempted to design multi-task learning-based loss functions by cascading the fusion network and high-level tasks. Unfortunately, seeking unified appropriate features for either task simultaneously is still a tough issue." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 347, + 286, + 442 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 347, + 286, + 442 + ], + "spans": [ + { + "bbox": [ + 46, + 347, + 286, + 442 + ], + "type": "text", + "content": "Moreover, exploring multi-modality fusion and segmentation demands a comprehensive collection of well-alignment image pairs with pixel-level annotated labels. Also, as for one image, the annotated needs to cover a wide range of pixels. Unfortunately, existing multi-modality data collections either focus on image fusion or lack whole image annotated segmentation labels, placing an obstacle to exploring the correlation of the fusion and segmentation." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 443, + 286, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 443, + 286, + 610 + ], + "spans": [ + { + "bbox": [ + 46, + 443, + 286, + 610 + ], + "type": "text", + "content": "This paper proposes a multi-interactive feature learning architecture for the joint problem of multi-modality fusion and segmentation, namely SegMiF. SegMiF is constructed by a fusion network and a segmentation network, in which the intrinsic features of either one interact via a new proposed hierarchical interactive attention (HIA). HIA fully integrates semantic-/modality-oriented features by fine-grained mapping. We also derive a dynamic weighting factor and seamless it in the interactive training scheme, to automatically learn the optimal parameters for either task. Figure 1 demonstrates that our SegMiF assigns the category to each pixel from the visual-friendly fused result more accurately than the state-of-the-arts (SOTAs). Our contributions can be distilled into four main aspects as follows:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 616, + 286, + 713 + ], + "type": "list", + "angle": 0, + "index": 7, + "blocks": [ + { + "bbox": [ + 58, + 616, + 286, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 616, + 286, + 688 + ], + "spans": [ + { + "bbox": [ + 58, + 616, + 286, + 688 + ], + "type": "text", + "content": "- We formulate both image fusion and segmentation in a joint manner, in which the semantic and pixel-based features can mutually interact. To this end, two tasks can achieve the 'Best of Both Worlds', generating visual-appealing fused images along with accurate scene parsing." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 58, + 689, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 689, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 689, + 286, + 713 + ], + "type": "text", + "content": "- A hierarchical interactive attention is introduced to bridge the feature gap between the fusion network" + } + ] + } + ], + "index": 6 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 324, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 324, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 324, + 72, + 545, + 120 + ], + "type": "text", + "content": "and the segmentation one. Establishing the semantic/modality multi-head attention mechanism in HIA simultaneously preserves intrinsic modality features and brings more attention to semantic features." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 317, + 135, + 545, + 328 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 317, + 135, + 545, + 205 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 135, + 545, + 205 + ], + "spans": [ + { + "bbox": [ + 317, + 135, + 545, + 205 + ], + "type": "text", + "content": "- An interactive feature training scheme is proposed to overcome the shortcoming of insufficient feature interaction between fusion and segmentation. Seamlessly integrating a dynamic weighting factor allows the exploration of the optimal parameters of each task in an automatic manner." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 221, + 545, + 328 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 221, + 545, + 328 + ], + "spans": [ + { + "bbox": [ + 317, + 221, + 545, + 328 + ], + "type": "text", + "content": "- We construct a smart multi-wave binocular imaging system, and introduce a full-time multi-modality benchmark, namely FMB, to promote the research of both image fusion and segmentation. FMB contains 1500 well-registered infrared and visible image pairs with 15 annotated pixel-level categories (see the left part of Figure 1). Also, it covers a wide range of pixel variations and various severe environments, e.g., dense fog, heavy rain, and low-light condition." + } + ] + } + ], + "index": 10 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 350, + 397, + 363 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 350, + 397, + 363 + ], + "spans": [ + { + "bbox": [ + 306, + 350, + 397, + 363 + ], + "type": "text", + "content": "2. Related Works" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 374, + 545, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 374, + 545, + 601 + ], + "spans": [ + { + "bbox": [ + 304, + 374, + 545, + 601 + ], + "type": "text", + "content": "Multi-modality image fusion In recent years, deep learning based multi-modality image fusion approaches achieved significant progress[11, 12, 17, 18, 19]. Early efforts [8, 9, 10, 20, 21] tend to achieve excellent fusion effects by adjusting the network structure or loss functions. However, a minority pay attention to whether the downstream tasks can be well adapted to fusion. DIDFuse [10] was the first to apply deep decomposition for high and low-frequency features, while AUIF [22] proposed a decomposition and fusion framework based on algorithm unfolding from an optimization perspective. Subsequently, CDDFuse [6] upgraded the decomposition network to a Transformer-CNN dual-stream structure. DDFM [7], for the first time, utilized denoising diffusion models for image fusion tasks. Recently, some methods [23, 13, 24] cascaded fusion and downstream tasks, focusing on improving task performance by achieving oriented fusion. Nevertheless, this kind of native gradient back propagation hinders the fusion network to adapt to subsequent tasks heuristically from the feature level." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 605, + 545, + 701 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 701 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 701 + ], + "type": "text", + "content": "Multi-modality Segmentation Recently, two-stream-based feature fusion models are proposed to perform the segmentation directly. Most of existing methods mostly develop various simple fusion strategies, such as the weighted average [25, 26, 27], summation [28, 29] and concatenation [30, 31]. Nonetheless, direct feature fusion lacks explicit fusion principle to preserve the typical modality feature and pay no attention to the pixel-level visual effects." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8116" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 51, + 70, + 211, + 190 + ], + "blocks": [ + { + "bbox": [ + 51, + 70, + 211, + 190 + ], + "lines": [ + { + "bbox": [ + 51, + 70, + 211, + 190 + ], + "spans": [ + { + "bbox": [ + 51, + 70, + 211, + 190 + ], + "type": "image", + "image_path": "5ebdbf194e48f440514ca0c6cdf03b86ee1d17a2db2579fc4caefad69738ab06.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 201, + 547, + 237 + ], + "lines": [ + { + "bbox": [ + 46, + 201, + 547, + 237 + ], + "spans": [ + { + "bbox": [ + 46, + 201, + 547, + 237 + ], + "type": "text", + "content": "Figure 2: Workflow of our proposed SegMiF. The left part depicts the latent interactive relationship between image fusion and segmentation. The middle part plots the concrete architecture of the SegMiF. The right part details the components of proposed hierarchical interactive attention." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 211, + 70, + 392, + 190 + ], + "blocks": [ + { + "bbox": [ + 211, + 70, + 392, + 190 + ], + "lines": [ + { + "bbox": [ + 211, + 70, + 392, + 190 + ], + "spans": [ + { + "bbox": [ + 211, + 70, + 392, + 190 + ], + "type": "image", + "image_path": "436cb10c9073e70c336f00cb3b5835b7706c8d2bf707ff7d0d92aa933799370c.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 392, + 70, + 541, + 190 + ], + "blocks": [ + { + "bbox": [ + 392, + 70, + 541, + 190 + ], + "lines": [ + { + "bbox": [ + 392, + 70, + 541, + 190 + ], + "spans": [ + { + "bbox": [ + 392, + 70, + 541, + 190 + ], + "type": "image", + "image_path": "67be32218d741da2972828f251e2f875d343fcdf120d003f33d6dcfe23da76e4.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 257, + 176, + 270 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 257, + 176, + 270 + ], + "spans": [ + { + "bbox": [ + 47, + 257, + 176, + 270 + ], + "type": "text", + "content": "3. The Proposed Method" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 277, + 168, + 289 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 277, + 168, + 289 + ], + "spans": [ + { + "bbox": [ + 47, + 277, + 168, + 289 + ], + "type": "text", + "content": "3.1. Problem formulation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 295, + 288, + 379 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 295, + 288, + 379 + ], + "spans": [ + { + "bbox": [ + 46, + 295, + 288, + 379 + ], + "type": "text", + "content": "As for image fusion or segmentation tasks, one of the most commonly used ways is to design a neural network, and fully utilize it to find a set of optimal parameters. For this purpose, we suppose that the visible, infrared, and fused image are all gray-scale with the size of " + }, + { + "bbox": [ + 46, + 295, + 288, + 379 + ], + "type": "inline_equation", + "content": "m \\times n" + }, + { + "bbox": [ + 46, + 295, + 288, + 379 + ], + "type": "text", + "content": ", denoted as column vectors " + }, + { + "bbox": [ + 46, + 295, + 288, + 379 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 46, + 295, + 288, + 379 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 295, + 288, + 379 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 46, + 295, + 288, + 379 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 295, + 288, + 379 + ], + "type": "inline_equation", + "content": "\\mathbf{u} \\in \\mathbb{R}^{mn \\times 1}" + }, + { + "bbox": [ + 46, + 295, + 288, + 379 + ], + "type": "text", + "content": ", respectively. The optimization model is formulated as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 121, + 388, + 287, + 407 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 121, + 388, + 287, + 407 + ], + "spans": [ + { + "bbox": [ + 121, + 388, + 287, + 407 + ], + "type": "interline_equation", + "content": "\\min _ {\\boldsymbol {\\omega} _ {k}} f \\left(\\mathbf {k}, \\mathcal {N} (\\mathbf {x}, \\mathbf {y}; \\boldsymbol {\\omega} _ {k})\\right), \\tag {1}", + "image_path": "5c54dd368e10b6060f09a5d18d176362a57cdc6f2f7cc7d8b699b495185a9174.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 415, + 287, + 439 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 415, + 287, + 439 + ], + "spans": [ + { + "bbox": [ + 46, + 415, + 287, + 439 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 415, + 287, + 439 + ], + "type": "inline_equation", + "content": "\\mathbf{k}" + }, + { + "bbox": [ + 46, + 415, + 287, + 439 + ], + "type": "text", + "content": " denotes the output of the task-related network " + }, + { + "bbox": [ + 46, + 415, + 287, + 439 + ], + "type": "inline_equation", + "content": "\\mathcal{N}" + }, + { + "bbox": [ + 46, + 415, + 287, + 439 + ], + "type": "text", + "content": " with the learnable parameters " + }, + { + "bbox": [ + 46, + 415, + 287, + 439 + ], + "type": "inline_equation", + "content": "\\omega_{\\mathrm{k}}" + }, + { + "bbox": [ + 46, + 415, + 287, + 439 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 415, + 287, + 439 + ], + "type": "inline_equation", + "content": "f(\\cdot)" + }, + { + "bbox": [ + 46, + 415, + 287, + 439 + ], + "type": "text", + "content": " is a fidelity term." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 439, + 287, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 439, + 287, + 510 + ], + "spans": [ + { + "bbox": [ + 46, + 439, + 287, + 510 + ], + "type": "text", + "content": "Previous approaches solely design image fusion or segmentation networks, which only can achieve outstanding results for one task. To generate visualappealing fused images along with accurate scene segmentation results, we jointly formulate the two tasks into one goal [32, 33, 34], which can be rewritten as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 60, + 530, + 287, + 548 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 60, + 530, + 287, + 548 + ], + "spans": [ + { + "bbox": [ + 60, + 530, + 287, + 548 + ], + "type": "interline_equation", + "content": "\\min _ {\\boldsymbol {\\omega} _ {\\mathrm {u}}, \\boldsymbol {\\omega} _ {\\mathrm {s}}} f _ {\\mathrm {u}} \\left(\\mathbf {u}, \\Phi (\\mathbf {x}, \\mathbf {y}; \\boldsymbol {\\omega} _ {\\mathrm {u}})\\right) + f _ {\\mathrm {s}} \\left(\\mathbf {s}, \\Psi (\\mathbf {x}, \\mathbf {y}; \\boldsymbol {\\omega} _ {\\mathrm {s}})\\right) + g \\left(\\boldsymbol {\\omega} ^ {\\star}\\right), \\tag {2}", + "image_path": "1cdc9ef716528db612c1921a05a60973411bbecf2bc26e810e2ccb012bd3f584.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "inline_equation", + "content": "\\omega^{\\star} = [\\omega_{\\mathrm{u}},\\omega_{\\mathrm{s}}]" + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "inline_equation", + "content": "\\mathbf{u}" + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "inline_equation", + "content": "\\mathbf{s}" + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "text", + "content": " denote the fused image and segmentation map, which are produced by the fusion network " + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "inline_equation", + "content": "\\Phi" + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "text", + "content": " and segmentation network " + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "inline_equation", + "content": "\\Psi" + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "text", + "content": " with the learnable parameters " + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "inline_equation", + "content": "\\omega_{\\mathrm{u}}" + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "inline_equation", + "content": "\\omega_{\\mathrm{s}}" + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "inline_equation", + "content": "g(\\cdot)" + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "text", + "content": " is a constrained term to joint optimize the two tasks. In this paper, we regard the " + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "inline_equation", + "content": "g(\\cdot)" + }, + { + "bbox": [ + 46, + 555, + 287, + 664 + ], + "type": "text", + "content": " as a feature learning constrained manner, and achieve this goal by designing a hierarchical attention along with the interactive training scheme. The visualized illustration is plotted in the left part of Figure 2." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 671, + 220, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 220, + 683 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 220, + 683 + ], + "type": "text", + "content": "3.2. Feature interaction architecture" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 714 + ], + "type": "text", + "content": "Overview of the whole network. Our proposed SegMiF is designed with cascade principle, composited by image" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 258, + 545, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 258, + 545, + 390 + ], + "spans": [ + { + "bbox": [ + 304, + 258, + 545, + 390 + ], + "type": "text", + "content": "fusion and segmentation sub-network. Details of the whole architecture is shown at Figure 2. In specific, we utilize two parallel dilated residual dense blocks (DRDB) [35, 36] to extract features from visual and infrared images. SegFormer [37] is leveraged as the baseline segmentation network to provide semantic parsing. Two scales of semantic features from the backbone, interpolated with original resolutions are embedded into fusion network. In order to sufficiently realize the semantic information sharing, we propose the hierarchical interactive attention (HIA) to transfer high-level knowledge." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 391, + 545, + 499 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 391, + 545, + 499 + ], + "spans": [ + { + "bbox": [ + 304, + 391, + 545, + 499 + ], + "type": "text", + "content": "Hierarchical interactive attention. After obtaining modality feature " + }, + { + "bbox": [ + 304, + 391, + 545, + 499 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{ir},\\mathbf{F}_{vis}" + }, + { + "bbox": [ + 304, + 391, + 545, + 499 + ], + "type": "text", + "content": " from fusion network and segmentation feature " + }, + { + "bbox": [ + 304, + 391, + 545, + 499 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{seg}" + }, + { + "bbox": [ + 304, + 391, + 545, + 499 + ], + "type": "text", + "content": ", we build the HIA to construct the fine-grained mapping of these features and strengthen the mutually beneficial representation. Features including " + }, + { + "bbox": [ + 304, + 391, + 545, + 499 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{ir},\\mathbf{F}_{vis}" + }, + { + "bbox": [ + 304, + 391, + 545, + 499 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 391, + 545, + 499 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{seg}" + }, + { + "bbox": [ + 304, + 391, + 545, + 499 + ], + "type": "text", + "content": " as inputs, two attention mechanisms are leveraged to globally exchange intermediate features. Concatenating features from attentions, fresh modality features are generated based on a residual connection." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 500, + 545, + 584 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 500, + 545, + 584 + ], + "spans": [ + { + "bbox": [ + 304, + 500, + 545, + 584 + ], + "type": "text", + "content": "In detail, channel embedding is utilized to decompose modality/semantic features. We can denote the outputs from the linear embedding as " + }, + { + "bbox": [ + 304, + 500, + 545, + 584 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{F}_x^s,\\mathbf{F}_x^m\\}" + }, + { + "bbox": [ + 304, + 500, + 545, + 584 + ], + "type": "text", + "content": " with size " + }, + { + "bbox": [ + 304, + 500, + 545, + 584 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{mn\\times C}" + }, + { + "bbox": [ + 304, + 500, + 545, + 584 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 500, + 545, + 584 + ], + "type": "inline_equation", + "content": "x\\in \\{ir,vis,seg\\}" + }, + { + "bbox": [ + 304, + 500, + 545, + 584 + ], + "type": "text", + "content": " is under a vector formulation. Instead of utilizing the original self-attention mechanisms directly, we bridge these features with complementary interaction from different representation subspaces by MoAM and SoAM." + } + ] + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 307, + 594, + 547, + 665 + ], + "blocks": [ + { + "bbox": [ + 307, + 594, + 547, + 665 + ], + "lines": [ + { + "bbox": [ + 307, + 594, + 547, + 665 + ], + "spans": [ + { + "bbox": [ + 307, + 594, + 547, + 665 + ], + "type": "image", + "image_path": "e8464b0d0627836ae85a3385200cbc3862cd89a10da2bade51a2c04432216ffb.jpg" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 315, + 673, + 536, + 686 + ], + "lines": [ + { + "bbox": [ + 315, + 673, + 536, + 686 + ], + "spans": [ + { + "bbox": [ + 315, + 673, + 536, + 686 + ], + "type": "text", + "content": "Figure 3: Detailed architectures of SoAM and MoAM." + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_caption" + } + ], + "index": 17 + }, + { + "bbox": [ + 318, + 701, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 701, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 318, + 701, + 545, + 714 + ], + "type": "text", + "content": "Both multi-head attention modules are plotted in Fig-" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8117" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": "ure 3. Semantic-oriented attention module targets to provide more semantic attention for the modality feature. SoAM utilizes the token " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "\\mathbf{F}_{seg}^{s}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": " to generate the Query " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "Q_{s}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": ", which represents the inhere semantic information that needs to be enhanced. The global context representation of each can be calculated by as " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "K_{ir}^{T}V_{ir}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "K_{vis}^{T}V_{vis}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": ", where the corresponding Key and Value of each head are from the modality tokens " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{F}_{ir}^{m},\\mathbf{F}_{vis}^{m}\\}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": ". Denoted the modality context representation as " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_{ir}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_{vis}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": ", we can calculate the attention as " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "S_{ir} = Q_s\\mathbf{G}_{ir}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "S_{vis} = Q_s\\mathbf{G}_{vis}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": ". On the other hand, MoAM is with the complementary principle to investigate the significant feature from semantic contexts. Specifically, MoAM is to introduce two modality queries " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "Q_{ir},Q_{vis}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": " to represent the intrinsic modality feature (e.g., targets and details) from " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{F}_{ir}^{m},\\mathbf{F}_{vis}^{m}\\}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": ". Similarly, we can obtain the global context of segmentation " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "\\mathbf{G}_s" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": " by " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "K_{s}^{T}V_{s}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": ". The cross attention can be formulated as " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "M_{vis} = Q_s\\mathbf{G}_{vis}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "M_{vis} = Q_s\\mathbf{G}_{vis}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": ". By concatenating the groups " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "\\{S_{vis},M_{vis}\\}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "inline_equation", + "content": "\\{S_{ir},M_{ir}\\}" + }, + { + "bbox": [ + 47, + 72, + 289, + 324 + ], + "type": "text", + "content": ", we can obtain the comprehensive features with two parallel MLPs with residual connection to aggregate features from SoAM and MoAM." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 334, + 134, + 344 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 334, + 134, + 344 + ], + "spans": [ + { + "bbox": [ + 47, + 334, + 134, + 344 + ], + "type": "text", + "content": "3.3. Loss function" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "spans": [ + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "text", + "content": "The total loss function is combined of an image fusion loss function " + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{f}}" + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "text", + "content": " and segmentation loss " + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{s}}" + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{f}}" + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "text", + "content": " consists of three types of losses, i.e., structure loss " + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{SSIM}}" + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "text", + "content": ", pixel loss " + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{MSE}}" + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "text", + "content": " and gradient loss " + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{grad}}" + }, + { + "bbox": [ + 47, + 353, + 287, + 437 + ], + "type": "text", + "content": ". For one fused image, it should preserve overall structures from source images. To this end, the structural similarity index (SSIM) [38, 39, 40, 41] is introduced in function:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 71, + 442, + 287, + 456 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 71, + 442, + 287, + 456 + ], + "spans": [ + { + "bbox": [ + 71, + 442, + 287, + 456 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {S S I M}} = \\left(1 - \\mathrm {S S I M} _ {\\mathbf {u}, \\mathbf {x}}\\right) / 2 + \\left(1 - \\mathrm {S S I M} _ {\\mathbf {u}, \\mathbf {y}}\\right) / 2, \\tag {3}", + "image_path": "42dbdec4504789a9ff252acf5fccf1b3b7ba60d8c4813d99d55ccaabaecac277.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 467, + 287, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 467, + 287, + 502 + ], + "spans": [ + { + "bbox": [ + 47, + 467, + 287, + 502 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 467, + 287, + 502 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{SSIM}}" + }, + { + "bbox": [ + 47, + 467, + 287, + 502 + ], + "type": "text", + "content": " denotes structure similarity loss. To maintain the vital intensity in the fused image, we employ the saliency-based pixel loss, it formulated as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 88, + 513, + 287, + 528 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 88, + 513, + 287, + 528 + ], + "spans": [ + { + "bbox": [ + 88, + 513, + 287, + 528 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {M S E}} = \\left\\| \\mathbf {u} - m _ {1} \\mathbf {x} \\right\\| _ {2} ^ {2} + \\left\\| \\mathbf {u} - m _ {2} \\mathbf {y} \\right\\| _ {2} ^ {2}, \\tag {4}", + "image_path": "167f781f5e852e9d9a91e5f895286bc64cdb1a7daedd0303a4f6a02b55a3ef94.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 537, + 287, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 537, + 287, + 586 + ], + "spans": [ + { + "bbox": [ + 47, + 537, + 287, + 586 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 537, + 287, + 586 + ], + "type": "inline_equation", + "content": "m_{1}" + }, + { + "bbox": [ + 47, + 537, + 287, + 586 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 537, + 287, + 586 + ], + "type": "inline_equation", + "content": "m_{2}" + }, + { + "bbox": [ + 47, + 537, + 287, + 586 + ], + "type": "text", + "content": " are saliency weight maps calculated by VSM [42]. Besides, gradient information of images always characterizes texture details, thus, we used " + }, + { + "bbox": [ + 47, + 537, + 287, + 586 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{grad}}" + }, + { + "bbox": [ + 47, + 537, + 287, + 586 + ], + "type": "text", + "content": " to constrain these textual factors to a multi-scale manner:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 75, + 595, + 287, + 620 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 75, + 595, + 287, + 620 + ], + "spans": [ + { + "bbox": [ + 75, + 595, + 287, + 620 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {g r a d}} = \\sum_ {k = 3, 5, 7} \\| \\nabla^ {k} \\mathbf {u} - \\max (\\nabla^ {k} \\mathbf {x}, \\nabla^ {k} \\mathbf {y}) \\| _ {2} ^ {2} \\tag {5}", + "image_path": "43ad99f8ee4cc97bbb812e240bac765a154ce2a20957063f9ec52067fed99c15.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "spans": [ + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "type": "inline_equation", + "content": "\\nabla" + }, + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "type": "text", + "content": " denotes gradient operators that calculate by " + }, + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "type": "inline_equation", + "content": "\\nabla = \\mathbf{u} - \\mathcal{G}(\\mathbf{u})" + }, + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "type": "text", + "content": " with combination of different Gauss " + }, + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "type": "inline_equation", + "content": "(\\mathcal{G})" + }, + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "type": "text", + "content": " kernel size " + }, + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "type": "text", + "content": ". Totally, we obtained " + }, + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{f}} = \\mathcal{L}_{\\mathrm{SSIM}} + \\mathcal{L}_{\\mathrm{MSE}} + \\eta \\mathcal{L}_{\\mathrm{grad}}" + }, + { + "bbox": [ + 47, + 631, + 287, + 668 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 59, + 668, + 244, + 680 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 668, + 244, + 680 + ], + "spans": [ + { + "bbox": [ + 59, + 668, + 244, + 680 + ], + "type": "text", + "content": "Common to previous works, " + }, + { + "bbox": [ + 59, + 668, + 244, + 680 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{s}}" + }, + { + "bbox": [ + 59, + 668, + 244, + 680 + ], + "type": "text", + "content": " is defined as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 106, + 691, + 287, + 716 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 106, + 691, + 287, + 716 + ], + "spans": [ + { + "bbox": [ + 106, + 691, + 287, + 716 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {s}} \\left(\\mathbf {s}, \\mathbf {s} ^ {*}\\right) = - \\sum_ {\\text {c l a s s}} \\mathbf {s} ^ {*} \\log (\\mathbf {s}), \\tag {6}", + "image_path": "c32b7821d0f4afeb56154127763e51573694b01d0de527ef0aa14a3fb59333fe.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 72, + 545, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 108 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 108 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "\\mathbf{s}^*" + }, + { + "bbox": [ + 305, + 72, + 545, + 108 + ], + "type": "text", + "content": " represents the segmentation label. We adopt the effective semantic segmentation method SegFormer network " + }, + { + "bbox": [ + 305, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "\\Psi" + }, + { + "bbox": [ + 305, + 72, + 545, + 108 + ], + "type": "text", + "content": " [37]. The total loss function is:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 376, + 118, + 545, + 131 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 376, + 118, + 545, + 131 + ], + "spans": [ + { + "bbox": [ + 376, + 118, + 545, + 131 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {t o t a l}} = \\lambda_ {1} \\mathcal {L} _ {\\mathrm {f}} + \\lambda_ {2} \\mathcal {L} _ {\\mathrm {s}}, \\tag {7}", + "image_path": "c30012c727eaa3a5a39a0bbd64c004b3fd7f4eb04e2c3c5151478f3517d235c3.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 140, + 545, + 163 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 140, + 545, + 163 + ], + "spans": [ + { + "bbox": [ + 305, + 140, + 545, + 163 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 140, + 545, + 163 + ], + "type": "inline_equation", + "content": "\\lambda_{1}" + }, + { + "bbox": [ + 305, + 140, + 545, + 163 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 140, + 545, + 163 + ], + "type": "inline_equation", + "content": "\\lambda_{2}" + }, + { + "bbox": [ + 305, + 140, + 545, + 163 + ], + "type": "text", + "content": " are dynamic weighting factor which will be discussed below." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 172, + 512, + 185 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 172, + 512, + 185 + ], + "spans": [ + { + "bbox": [ + 306, + 172, + 512, + 185 + ], + "type": "text", + "content": "3.4. Dynamic factor for interactive learning" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "spans": [ + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "text", + "content": "By exploiting an alternatively recurrent iterations, we can progressively introduce the task-preferred features into the framework optimization. As mentioned above, at the phase of image fusion, we introduce the dynamic weighting factors " + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "inline_equation", + "content": "\\lambda_{1}" + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "inline_equation", + "content": "\\lambda_{2}" + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "text", + "content": " to rapidly measure the importance of task-related losses. We observe that the task-specific balance can be derived from the convergent rate. The intuition is that if the value of losses cannot be further descended, the network may obtain the corresponding optimal weights. If the convergent rate descends fast, we should pay more attention to this task. Learning from the dynamic weight average [43], we further present the factor of task preference " + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "inline_equation", + "content": "\\eta" + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "text", + "content": " to emphasize the primary goal. Denoted " + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "inline_equation", + "content": "r_i" + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "text", + "content": " as the convergent rate of " + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "text", + "content": "-th task with loss " + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_i" + }, + { + "bbox": [ + 305, + 191, + 545, + 358 + ], + "type": "text", + "content": ", we can compute the rate as:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 374, + 367, + 545, + 393 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 374, + 367, + 545, + 393 + ], + "spans": [ + { + "bbox": [ + 374, + 367, + 545, + 393 + ], + "type": "interline_equation", + "content": "r _ {1} (n - 1) = \\frac {\\mathcal {L} _ {i} (n - 1)}{\\mathcal {L} _ {i} (n - 2)}. \\tag {8}", + "image_path": "74325088ea4bc473f2c91ec3792f18cb97fcc0d2761365280d443831da6b0928.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 401, + 545, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 401, + 545, + 424 + ], + "spans": [ + { + "bbox": [ + 306, + 401, + 545, + 424 + ], + "type": "text", + "content": "Then the procedure of dynamic weight factor of " + }, + { + "bbox": [ + 306, + 401, + 545, + 424 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 306, + 401, + 545, + 424 + ], + "type": "text", + "content": "-th task is formulated as:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 358, + 432, + 545, + 459 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 358, + 432, + 545, + 459 + ], + "spans": [ + { + "bbox": [ + 358, + 432, + 545, + 459 + ], + "type": "interline_equation", + "content": "\\lambda_ {\\mathrm {i}} (n) = \\frac {\\eta_ {\\mathrm {i}} \\exp \\left(r _ {\\mathrm {i}} (n - 1) / T\\right)}{\\sum_ {k} \\exp \\left(r _ {\\mathrm {k}} (n - 1) / T\\right)}, \\tag {9}", + "image_path": "228546686abf039fb5f27d08c68056cbe75b495e5a47bbf419bac0ee7c055fed.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 467, + 545, + 514 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 467, + 545, + 514 + ], + "spans": [ + { + "bbox": [ + 305, + 467, + 545, + 514 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 467, + 545, + 514 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 305, + 467, + 545, + 514 + ], + "type": "text", + "content": " is a temperature to control the sensitiveness of two tasks. Different from widely sued GDN [44], this dynamic strategy can actually avoid the complicated computation of various task gradients." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 514, + 545, + 611 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 514, + 545, + 611 + ], + "spans": [ + { + "bbox": [ + 305, + 514, + 545, + 611 + ], + "type": "text", + "content": "Then based on the fusion image generated with semantic feature, we can train the segmentation network end-to-end, using the gradient descending " + }, + { + "bbox": [ + 305, + 514, + 545, + 611 + ], + "type": "inline_equation", + "content": "\\omega_{s} \\gets \\omega_{s} - \\nabla_{\\omega_{s}} \\mathcal{L}_{\\mathbb{S}}(\\mathbf{u}; \\omega_{s})" + }, + { + "bbox": [ + 305, + 514, + 545, + 611 + ], + "type": "text", + "content": ". The two learning processes are trained alternately until full convergence. Noting that, this training strategy is actually task-agnostic, we also can introduce other different high-level vision tasks into the unified consideration, rather than designing for segmentation unilaterally." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 621, + 512, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 621, + 512, + 635 + ], + "spans": [ + { + "bbox": [ + 306, + 621, + 512, + 635 + ], + "type": "text", + "content": "4. Full-time Multi-modality Benchmark" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 642, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 642, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 642, + 545, + 713 + ], + "type": "text", + "content": "Existing two multi-modality segmentation datasets suffer from few label categories, sparse annotation and monotonous scene, as shown in Figure 6. The proposed FMB dataset aims to overcome these difficulties and promote the development of whole field. A glimpse of FMB is given in Figure 4." + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "8118" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 61, + 70, + 534, + 168 + ], + "blocks": [ + { + "bbox": [ + 61, + 70, + 534, + 168 + ], + "lines": [ + { + "bbox": [ + 61, + 70, + 534, + 168 + ], + "spans": [ + { + "bbox": [ + 61, + 70, + 534, + 168 + ], + "type": "image", + "image_path": "8aa6f083139321b291dc3c4021fee41d106d54783255573cb0d7fb81f5b0d660.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 176, + 547, + 213 + ], + "lines": [ + { + "bbox": [ + 46, + 176, + 547, + 213 + ], + "spans": [ + { + "bbox": [ + 46, + 176, + 547, + 213 + ], + "type": "text", + "content": "Figure 4: Visualization of visible/infrared/segmentation images in the proposed FMB dataset. The dataset contains a wide range of real driving scenes under different lighting conditions, and also includes special scenarios with rain, fog, strong light, and even Tyndall Effect." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 54, + 218, + 282, + 319 + ], + "blocks": [ + { + "bbox": [ + 54, + 218, + 282, + 319 + ], + "lines": [ + { + "bbox": [ + 54, + 218, + 282, + 319 + ], + "spans": [ + { + "bbox": [ + 54, + 218, + 282, + 319 + ], + "type": "image", + "image_path": "29021975e4f31c1fd2d15f3dc07b2905c700b87c17e1a52c5fc872738e7eca3c.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 56, + 331, + 277, + 344 + ], + "lines": [ + { + "bbox": [ + 56, + 331, + 277, + 344 + ], + "spans": [ + { + "bbox": [ + 56, + 331, + 277, + 344 + ], + "type": "text", + "content": "Figure 5: Illustration of the binocular imaging system." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "type": "text", + "content": "We built a binocular imaging system that can be placed on the car roof, including a visible camera and an infrared sensor with a wavelength range of " + }, + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "type": "inline_equation", + "content": "8 - 14\\mu m" + }, + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "type": "text", + "content": " (as shown in the Figure 5). We finally obtained 1500 aligned image pairs with a resolution of " + }, + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "type": "inline_equation", + "content": "800\\times 600" + }, + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "type": "text", + "content": ". In details, two sensors are individually calibrated using their respected calibration board to obtain internal parameters, and their relative pose relationship is obtained through joint calibration. We calculate the homography matrix " + }, + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "type": "text", + "content": " by employing RANSAC1. The infrared images are projected onto visible coordinates using " + }, + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "type": "text", + "content": " and cropped, ultimately resulting in pixel-level registered image pairs with a size of " + }, + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "type": "inline_equation", + "content": "800\\times 600" + }, + { + "bbox": [ + 46, + 365, + 287, + 507 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 508, + 287, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 508, + 287, + 604 + ], + "spans": [ + { + "bbox": [ + 46, + 508, + 287, + 604 + ], + "type": "text", + "content": "The FMB dataset includes rich scenes under different illumination conditions, so that it enables fusion/segmentation model to improve the generalization ability greatly. We labeled " + }, + { + "bbox": [ + 46, + 508, + 287, + 604 + ], + "type": "inline_equation", + "content": "98.16\\%" + }, + { + "bbox": [ + 46, + 508, + 287, + 604 + ], + "type": "text", + "content": " of all pixels into 14 different categories including Road, Sidewalk, Building, Traffic Light, Traffic Sign, Vegetation, Sky, Person, Car, Truck, Bus, Motorcycle, Bicycle and Pole, which often appear in real-world automatic driving and semantic understanding tasks." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 615, + 128, + 628 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 615, + 128, + 628 + ], + "spans": [ + { + "bbox": [ + 47, + 615, + 128, + 628 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 635, + 288, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 635, + 288, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 635, + 288, + 696 + ], + "type": "text", + "content": "Two representative datasets including MFNet and proposed FMB are utilized for the training and evaluation. The details of these datasets are reported in the above section. Several data augmentation techniques are utilized for the whole training procedure: random resizing with a ratio of" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 312, + 220, + 541, + 293 + ], + "blocks": [ + { + "bbox": [ + 312, + 220, + 541, + 293 + ], + "lines": [ + { + "bbox": [ + 312, + 220, + 541, + 293 + ], + "spans": [ + { + "bbox": [ + 312, + 220, + 541, + 293 + ], + "type": "image", + "image_path": "d5aea48cfd0c67ab07fadcbc288fdcbd353abfe6f0ee4d56aac183c181ffafdc.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 306, + 545, + 331 + ], + "lines": [ + { + "bbox": [ + 306, + 306, + 545, + 331 + ], + "spans": [ + { + "bbox": [ + 306, + 306, + 545, + 331 + ], + "type": "text", + "content": "Figure 6: Comparison of FMB with existing multi-modality segmentation datasets (i.e., PST900 [31] and MFNet [30])." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "spans": [ + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "type": "text", + "content": "0.5-2.0, random cropping to " + }, + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "type": "inline_equation", + "content": "360 \\times 360" + }, + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "type": "text", + "content": ", brightness distortion and normalization. The Adam optimizer with poly learning rate adjustment is utilized to optimize both networks. As for the fusion, the initial learning rate is " + }, + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "type": "inline_equation", + "content": "1e^{-4}" + }, + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "type": "text", + "content": " and decayed to " + }, + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "type": "inline_equation", + "content": "1e^{-8}" + }, + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "type": "text", + "content": " progressively. As for segmentation, we first utilized " + }, + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "type": "inline_equation", + "content": "1e^{-6}" + }, + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "type": "text", + "content": " to warm start the training with 3k iterations, then we conducted the training with intilial learning rate " + }, + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "type": "inline_equation", + "content": "8e^{-5}" + }, + { + "bbox": [ + 304, + 351, + 547, + 507 + ], + "type": "text", + "content": ". With batch size of 8, we trained the framework for 8 rounds. For each round, we set 10k iterations for training segmentation and 5k iterations for fusion. Noting that, a similar configuration of segmentation is also utilized for the training of fusion-based methods. All experiments are performed on an NVIDIA Tesla V100 GPU with PyTorch framework." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 515, + 509, + 528 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 515, + 509, + 528 + ], + "spans": [ + { + "bbox": [ + 306, + 515, + 509, + 528 + ], + "type": "text", + "content": "5.1. Results of multi-modality image fusion" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 534, + 545, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 545, + 594 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 545, + 594 + ], + "type": "text", + "content": "We demonstrate our fusion quality based on qualitative and quantitative analyses with six state-of-the-art competitors, including DIDFuse [10], DenseFuse [45], ReCoNet[11], UMFusion[12], TarDAL[13] and U2Fusion [9]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "text", + "content": "Qualitative Comparisons. The qualitative results on MFNet and FMB datasets are depicted in Figure 7, in which we can clearly observe two remarkable advantages of our method. First, the significant characteristics of infrared images can be effectively highlighted. For instance, as shown on the green rectangle of the first group, DIDFuse, ReCoNet and TarDAL are susceptible to strong illumination. In contrast, our method can remarkably preserve this information from infrared images, e.g., the structure of cars and pedestrians. 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Violin plots illustrating the distribution of the four metrics, in which the white triangles and the black lines indicate mean values and medium values." + } + ] + } + ], + "index": 27, + "angle": 0, + "type": "image_caption" + } + ], + "index": 26 + }, + { + "type": "image", + "bbox": [ + 53, + 352, + 296, + 456 + ], + "blocks": [ + { + "bbox": [ + 53, + 352, + 296, + 456 + ], + "lines": [ + { + "bbox": [ + 53, + 352, + 296, + 456 + ], + "spans": [ + { + "bbox": [ + 53, + 352, + 296, + 456 + ], + "type": "image", + "image_path": "4f7a4082b6d8810e6e059e23e611e2616ee4050c25ca059e7a7758fbfb785a6c.jpg" + } + ] + } + ], + "index": 28, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 127, + 464, + 464, + 477 + ], + "lines": [ + { + "bbox": [ + 127, + 464, + 464, + 477 + ], + "spans": [ + { + "bbox": [ + 127, + 464, + 464, + 477 + ], + "type": "text", + "content": "Figure 9: Qualitative demonstrations of different approaches on the MFNet dataset." + } + ] + } + ], + "index": 30, + "angle": 0, + "type": "image_caption" + } + ], + "index": 28 + }, + { + "type": "image", + "bbox": [ + 297, + 352, + 541, + 456 + ], + "blocks": [ + { + "bbox": [ + 297, + 352, + 541, + 456 + ], + "lines": [ + { + "bbox": [ + 297, + 352, + 541, + 456 + ], + "spans": [ + { + "bbox": [ + 297, + 352, + 541, + 456 + ], + "type": "image", + "image_path": "f692700d3d45d2320904936768432094442584b6bea2c935667134dca403ade8.jpg" + } + ] + } + ], + "index": 29, + "angle": 0, + "type": "image_body" + } + ], + "index": 29 + }, + { + "bbox": [ + 46, + 498, + 287, + 546 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 498, + 287, + 546 + ], + "spans": [ + { + "bbox": [ + 46, + 498, + 287, + 546 + ], + "type": "text", + "content": "information, our method can enhance the texture details of the given scene from either dataset. Compared with other competitors in the second row of Figure 7, our results exhibit a sharper appearance." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 46, + 557, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 288, + 713 + ], + "type": "text", + "content": "Quantitative Comparisons. We also plot the numerical results with other six fusion competitors on 50 pairs from MFNet and 50 pairs from FMB in Figure 8. Four objective metrics are leveraged for the comparison, including entropy (EN)[46], standard deviation (SD)[47], spatial frequency (SF)[48] and the sum of the correlations of differences (SCD)[49]. Note that our results achieve consistent superiority in terms of these statistical metrics. Specifically, the highest EN and SCD indicate that our method can significantly preserve the largest amount of considerable information transferred from source images. Moreover, the immense average value on SD reflects the high pixel contrast for visual observations. Furthermore, higher SF reflects our" + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 304, + 498, + 545, + 547 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 545, + 547 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 545, + 547 + ], + "type": "text", + "content": "method has rich texture details and contrasts. In summary, our method enhances the texture details for precise observation and stably preserves abundant typical information to support semantic parsing tasks." + } + ] + } + ], + "index": 33 + }, + { + "bbox": [ + 306, + 555, + 512, + 567 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 555, + 512, + 567 + ], + "spans": [ + { + "bbox": [ + 306, + 555, + 512, + 567 + ], + "type": "text", + "content": "5.2. Results of multi-modality segmentation" + } + ] + } + ], + "index": 34 + }, + { + "bbox": [ + 304, + 573, + 545, + 633 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 573, + 545, + 633 + ], + "spans": [ + { + "bbox": [ + 304, + 573, + 545, + 633 + ], + "type": "text", + "content": "We provide another comprehensive analysis for image segmentation. Besides comparing with the newest fusion-based methods, we also conduct the evaluations with competitive dual-stream methods: GMNet [50], FEANet [51], EGFNet [52], ABMDRNet [53] and LASNet [54].2" + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 304, + 634, + 545, + 694 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 634, + 545, + 694 + ], + "spans": [ + { + "bbox": [ + 304, + 634, + 545, + 694 + ], + "type": "text", + "content": "Qualitative Comparisons. Visualized results of segmentation on MFNet are depicted in Figure 9. We also compare various competitive methods in Figure 10 under the newly proposed dataset, which is more challenging with rich categories, complex imaging conditions and complicated scene" + } + ] + } + ], + "index": 36 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 315, + 702, + 514, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 702, + 514, + 712 + ], + "spans": [ + { + "bbox": [ + 315, + 702, + 514, + 712 + ], + "type": "text", + "content": "2We also retrained dual-stream methods on the FMB dataset." + } + ] + } + ], + "index": 37 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8120" + } + ] + } + ], + "index": 38 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 69, + 296, + 175 + ], + "blocks": [ + { + "bbox": [ + 53, + 69, + 296, + 175 + ], + "lines": [ + { + "bbox": [ + 53, + 69, + 296, + 175 + ], + "spans": [ + { + "bbox": [ + 53, + 69, + 296, + 175 + ], + "type": "image", + "image_path": "3dff34908fcab5b78025d33b90e6111b0248f7d0b2ee7ae74f55e897d1a7999f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 54, + 182, + 538, + 195 + ], + "lines": [ + { + "bbox": [ + 54, + 182, + 538, + 195 + ], + "spans": [ + { + "bbox": [ + 54, + 182, + 538, + 195 + ], + "type": "text", + "content": "Figure 10: Qualitative demonstrations for the different methods in daytime and nighttime scenarios on FMB benchmark." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 298, + 70, + 541, + 175 + ], + "blocks": [ + { + "bbox": [ + 298, + 70, + 541, + 175 + ], + "lines": [ + { + "bbox": [ + 298, + 70, + 541, + 175 + ], + "spans": [ + { + "bbox": [ + 298, + 70, + 541, + 175 + ], + "type": "image", + "image_path": "e4075c859a3a420085bdf1994a2b53aa5d0d8731b66007310e0dec70e47b03c7.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 53, + 205, + 538, + 346 + ], + "blocks": [ + { + "bbox": [ + 53, + 205, + 538, + 346 + ], + "lines": [ + { + "bbox": [ + 53, + 205, + 538, + 346 + ], + "spans": [ + { + "bbox": [ + 53, + 205, + 538, + 346 + ], + "type": "table", + "html": "
MethodsUnlabelCarPersonBikeCurveCar StopConeBumpmAccmIoU
AccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoU
Visible98.297.594.682.281.754.771.261.054.921.661.916.682.143.777.330.869.745.9
Infrared98.697.490.381.885.367.371.654.851.337.353.824.364.733.470.248.065.649.9
LASNet99.297.494.984.281.767.182.156.970.741.156.839.658.148.877.240.175.454.9
EGFNet99.397.795.887.689.069.880.658.871.542.848.733.865.348.371.147.172.754.8
FEANet99.197.893.987.882.771.176.761.165.546.526.622.166.655.377.348.973.255.3
ABMDR99.398.494.384.890.069.675.760.364.045.144.133.161.747.466.250.069.554.8
DIDFuse98.097.395.079.179.564.080.258.544.119.964.023.377.537.869.020.467.544.5
ReCoNet98.197.395.880.488.960.065.055.447.020.769.025.877.839.846.617.465.944.5
U2Fusion98.397.795.282.885.464.877.761.062.732.366.720.975.545.282.350.271.950.8
TarDAL98.397.693.580.786.267.176.560.153.834.955.310.588.638.790.645.571.748.6
Ours98.798.196.387.889.671.481.263.263.547.566.731.185.348.984.850.374.856.1
", + "image_path": "db9f9a269288721392be6618569ac117234c6f8b52e7b8794e275cc59cc3f6a6.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 104, + 354, + 488, + 366 + ], + "lines": [ + { + "bbox": [ + 104, + 354, + 488, + 366 + ], + "spans": [ + { + "bbox": [ + 104, + 354, + 488, + 366 + ], + "type": "text", + "content": "Table 1: Quantitative semantic segmentation results of different methods on the MFNet dataset." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 393, + 289, + 562 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 393, + 289, + 562 + ], + "spans": [ + { + "bbox": [ + 46, + 393, + 289, + 562 + ], + "type": "text", + "content": "details. As discussed above, existing fusion methods cannot highlight the dimness of infrared targets, and the distant pedestrian can not be recognized. As for dual-stream methods, which utilize the modality feature directly, they are easy to introduce conflicts and weaken the accuracy without a clear feature fusion principle. The results, such as the car occluded by barriers (the first column of Figure 9) and the shape of the human (the second column of Figure 10) can not be precisely classified. It is worth mentioning that interaction feature learning from segmentation can drastically transfer the complementary characteristics for image fusion and further improve the segmentation performance. Thus, our method can continuously classify the objects of diverse scenes with high accuracy." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 570, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 289, + 715 + ], + "type": "text", + "content": "Quantitative Comparisons. Table 1 and Table 2 reported the qualitative results among different categories of competitors on MFNet and FMB datasets. These results illustrate our method is ahead of other state-of-the-art methods by a large margin on both segmentation datasets. Noting that our numerical results outperform other methods concerning mIOU and rank second in terms of mACC. Compared with the second one, our method improves " + }, + { + "bbox": [ + 46, + 570, + 289, + 715 + ], + "type": "inline_equation", + "content": "7.66\\%" + }, + { + "bbox": [ + 46, + 570, + 289, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 570, + 289, + 715 + ], + "type": "inline_equation", + "content": "1.45\\%" + }, + { + "bbox": [ + 46, + 570, + 289, + 715 + ], + "type": "text", + "content": " of mIOU on FMB and MFNet respectively. More specifically, the classification of Car and Person is important for the current intelligent perception system. The top two results in these two categories indicate the high perfor" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 393, + 545, + 453 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 393, + 545, + 453 + ], + "spans": [ + { + "bbox": [ + 304, + 393, + 545, + 453 + ], + "type": "text", + "content": "mance of our method to employ for real-world perception. On the other hand, for thermal-insensitive categories, such as traffic sign, building, bump, due to the effective visual quality preservation and enhancement, our method achieves significant superiority." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 466, + 405, + 478 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 466, + 405, + 478 + ], + "spans": [ + { + "bbox": [ + 305, + 466, + 405, + 478 + ], + "type": "text", + "content": "5.3. Ablation studies" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 486, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 486, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 545, + 713 + ], + "type": "text", + "content": "Study on HIA. HIA plays a key role in preserving intrinsic modality features from the semantic feature guidance. Firstly, we visualized the representative feature to discuss the effectiveness of HIA in Figure 11. Clearly, HIA can remarkably preserve the salient infrared features with abundant semantic information, avoiding the interference of harsh weather and strong light. Then we plot different variants of HIA to illustrate the inner mechanisms of HIA. As shown in Figure 12. Obviously, the version w/o SoAM loses the classify ability to distinguish confused objectives, e.g., the orange circle in the second row. Meanwhile, \"w/o MoAM\" cannot protect the details at nighttime with color distortion, e.g., the building in the distance. It is worth pointing out that our full model not only provides clear visual observation but also has high sensitiveness to segmentation. Similarly, the quantitative results reported in Table 3 also demonstrate the effectiveness of full HIA for both segmentation benchmarks compared with direct aggregation and other model variants. In brief, HIA is capable enough to" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "8121" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 55, + 70, + 539, + 210 + ], + "blocks": [ + { + "bbox": [ + 55, + 70, + 539, + 210 + ], + "lines": [ + { + "bbox": [ + 55, + 70, + 539, + 210 + ], + "spans": [ + { + "bbox": [ + 55, + 70, + 539, + 210 + ], + "type": "table", + "html": "
MethodsCarPersonTruckT-LampT-SignBuildingVegetationPolemAccmIoU
AccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoUAccIoU
Visible84.578.378.146.673.243.482.523.783.664.089.077.888.582.171.641.873.550.5
Infrared75.669.189.963.366.612.663.124.780.552.987.478.083.775.562.123.069.643.9
GMNet87.679.377.360.149.022.254.121.678.569.089.179.188.983.859.739.864.449.2
LASNet81.372.676.448.629.614.820.72.979.359.086.975.487.681.656.636.756.942.5
EGFNet83.677.479.563.033.517.158.625.282.666.688.577.289.383.563.841.563.047.3
FEANet82.373.978.860.744.732.353.613.573.355.687.679.489.081.266.236.864.546.8
DIDFuse86.377.787.464.466.328.875.929.281.164.487.178.489.582.479.241.873.050.6
ReCoNet83.775.987.765.834.714.983.334.785.666.689.079.288.281.373.344.971.450.9
U2Fusion85.076.687.761.984.614.475.128.381.368.989.578.892.582.274.542.270.147.9
TarDAL81.874.293.356.066.318.875.029.681.266.588.179.187.981.765.941.974.848.1
Ours85.378.378.365.474.447.386.443.186.174.890.082.091.685.072.549.874.554.8
", + "image_path": "d7568f1da684dfe8102ad43fae60771dd39e8ef1177fc74698914b1bbfeb200a.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 258, + 214, + 269 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 258, + 214, + 269 + ], + "spans": [ + { + "bbox": [ + 47, + 258, + 214, + 269 + ], + "type": "text", + "content": "bridge the fusion and segmentation tasks." + } + ] + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 53, + 278, + 282, + 352 + ], + "blocks": [ + { + "bbox": [ + 53, + 278, + 282, + 352 + ], + "lines": [ + { + "bbox": [ + 53, + 278, + 282, + 352 + ], + "spans": [ + { + "bbox": [ + 53, + 278, + 282, + 352 + ], + "type": "image", + "image_path": "e6c8c91f72d021e4cbb8a3dda4ca322f5605d5082ae786f2844dc208a184ddae.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 359, + 287, + 395 + ], + "lines": [ + { + "bbox": [ + 46, + 359, + 287, + 395 + ], + "spans": [ + { + "bbox": [ + 46, + 359, + 287, + 395 + ], + "type": "text", + "content": "Figure 11: Feature visualization of different stages. From left to right: visible image, infrared image, their features, w/o HIA, and w/ HIA." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 52, + 412, + 282, + 536 + ], + "blocks": [ + { + "bbox": [ + 108, + 218, + 485, + 229 + ], + "lines": [ + { + "bbox": [ + 108, + 218, + 485, + 229 + ], + "spans": [ + { + "bbox": [ + 108, + 218, + 485, + 229 + ], + "type": "text", + "content": "Table 2: Quantitative semantic segmentation results of different methods on the FMB dataset." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 412, + 282, + 536 + ], + "lines": [ + { + "bbox": [ + 52, + 412, + 282, + 536 + ], + "spans": [ + { + "bbox": [ + 52, + 412, + 282, + 536 + ], + "type": "table", + "html": "
ModelHIAMF DatasetFMB Dataset
SoAMMoAMmAccmIoUmAccmIoU
“Concatenate”XX72.652.772.351.3
“Summation”XX71.552.673.752.1
“Average”XX72.952.172.450.7
M1XX67.251.972.450.5
M2X✓73.655.072.752.3
M3✓X72.053.473.154.1
M4✓✓74.856.174.554.8
", + "image_path": "f181e4419d276f3be1282f06dda582343fad04fb41fae41e45158d1628107473.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 544, + 286, + 581 + ], + "lines": [ + { + "bbox": [ + 46, + 544, + 286, + 581 + ], + "spans": [ + { + "bbox": [ + 46, + 544, + 286, + 581 + ], + "type": "text", + "content": "Table 3: Numerical results about the effectiveness of HIA. The first three are the results of direct feature aggregation. Latter are the results of model variants with HIA." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 289, + 715 + ], + "type": "text", + "content": "Analyzing the dynamic factor. We discussed the impact of the proposed dynamic factor for interactive learning compared with existing multi-task optimization methods, as shown in Figure 13. Manual adjustment requires plenty of prior knowledge and labor consumption. But concurrently, it achieves decent segmentation results. The other five training strategies hardly coordinate the relationship between the two tasks and fail to achieve good visualization and segmentation performance. The dynamic factor enables to better introduce task preferences into optimization, thus achieving" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 258, + 430, + 269 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 258, + 430, + 269 + ], + "spans": [ + { + "bbox": [ + 306, + 258, + 430, + 269 + ], + "type": "text", + "content": "excellent results on both tasks." + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 307, + 274, + 555, + 384 + ], + "blocks": [ + { + "bbox": [ + 307, + 274, + 555, + 384 + ], + "lines": [ + { + "bbox": [ + 307, + 274, + 555, + 384 + ], + "spans": [ + { + "bbox": [ + 307, + 274, + 555, + 384 + ], + "type": "image", + "image_path": "b0cb6b19667bb91dfcdb20db8176da490bc5ef1a9f06891925aa73c416264758.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 322, + 387, + 529, + 399 + ], + "lines": [ + { + "bbox": [ + 322, + 387, + 529, + 399 + ], + "spans": [ + { + "bbox": [ + 322, + 387, + 529, + 399 + ], + "type": "text", + "content": "Figure 12: Visual comparisons of different models." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 308, + 413, + 547, + 503 + ], + "blocks": [ + { + "bbox": [ + 308, + 413, + 547, + 503 + ], + "lines": [ + { + "bbox": [ + 308, + 413, + 547, + 503 + ], + "spans": [ + { + "bbox": [ + 308, + 413, + 547, + 503 + ], + "type": "image", + "image_path": "e0df24652b3b51ed948a8e09b42dfb71da3152770abc4faf83664234a74acbb7.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 507, + 545, + 532 + ], + "lines": [ + { + "bbox": [ + 306, + 507, + 545, + 532 + ], + "spans": [ + { + "bbox": [ + 306, + 507, + 545, + 532 + ], + "type": "text", + "content": "Figure 13: Comparisons of different strategies of adjusting dynamic factors." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 554, + 378, + 566 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 554, + 378, + 566 + ], + "spans": [ + { + "bbox": [ + 306, + 554, + 378, + 566 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 574, + 545, + 668 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 574, + 545, + 668 + ], + "spans": [ + { + "bbox": [ + 304, + 574, + 545, + 668 + ], + "type": "text", + "content": "In this paper, a multi-interactive architecture was proposed to formulate fusion and segmentation in a harmonious manner. We introduced a hierarchical interactive attention with dynamic factors, which bridges gaps of cross-task features from architecture and learning perspectives. In addition, we proposed a comprehensive full-time multimodality benchmark, with well-registered targets, abundant scenes and affluent labels." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 669, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 669, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 669, + 545, + 712 + ], + "type": "text", + "content": "Acknowledgments. This work is partially supported by the National Key R&D Program of China (No. 2022YFA1004101), the National Natural Science Foundation of China (No. U22B2052, 62027826)." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "8122" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 287, + 712 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 124 + ], + "type": "text", + "content": "[1] Hengshuang Zhao, Jianping Shi, Xiaojuan Qi, Xiaogang Wang, and Jiaya Jia. 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In IEEE/CVF CVPR, pages 7482-7491, 2018." + } + ] + } + ], + "index": 28 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "8124" + } + ] + } + ], + "index": 30 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-label Affordance Mapping from Egocentric Vision/52183b21-9cd5-4c04-8bd7-3d9da9442890_content_list.json b/2023/Multi-label Affordance Mapping from Egocentric Vision/52183b21-9cd5-4c04-8bd7-3d9da9442890_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..7b3a8f9c3d9d15c1e154d130d2ccbe70fd427ced --- /dev/null +++ b/2023/Multi-label Affordance Mapping from Egocentric Vision/52183b21-9cd5-4c04-8bd7-3d9da9442890_content_list.json @@ -0,0 +1,1674 @@ +[ + { + "type": "text", + "text": "Multi-label affordance mapping from egocentric vision", + "text_level": 1, + "bbox": [ + 207, + 130, + 759, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Lorenzo Mur-Labadia Jose J. Guerrero Ruben Martinez-Cantin I3A - Universidad de Zaragoza", + "bbox": [ + 194, + 181, + 772, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "lmur, jguerrer, rmcantin@unizar.es", + "bbox": [ + 333, + 219, + 635, + 233 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 284 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Accurate affordance detection and segmentation with pixel precision is an important piece in many complex systems based on interactions, such as robots and assistive devices. We present a new approach to affordance perception which enables accurate multi-label segmentation. Our approach can be used to automatically extract grounded affordances from first person videos of interactions using a 3D map of the environment providing pixel level precision for the affordance location. We use this method to build the largest and most complete dataset on affordances based on the EPIC-Kitchen dataset, EPIC-Aff, which provides interaction-grounded, multi-label, metric and spatial affordance annotations. Then, we propose a new approach to affordance segmentation based on multi-label detection which enables multiple affordances to co-exists in the same space, for example if they are associated with the same object. We present several strategies of multi-label detection using several segmentation architectures. The experimental results highlight the importance of the multi-label detection. Finally, we show how our metric representation can be exploited for build a map of interaction hotspots in spatial action-centric zones and use that representation to perform a task-oriented navigation.", + "bbox": [ + 75, + 301, + 473, + 650 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 678, + 209, + 694 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "When humans repeatedly interact in a close environment, we associate a set of affordable actions with a certain distribution of objects in a physical space. For example, we associate a pan on a stove with cooking, but the same pan on the sink with washing. A joined spatial-semantic understanding contains powerful insights to understand human behaviour. This requires a close combination of perception, mapping and navigation algorithms; with potential applications in augmented reality systems [60, 61], but also guiding a robot [19, 36] or assistive devices [68]. In the last years, the ability of deep learning models to extract high-level representations has improved the perception of autonomous agents, while egocentric vision offers a pow", + "bbox": [ + 75, + 704, + 470, + 902 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d13ed53fd446066df79aff82af6ae9201dbf55cbde8988341704efef8a72dae7.jpg", + "image_caption": [ + "Figure 1. From a sequence of egocentric observations, our agent creates a spatial-metric multi-label representation of the affordances, enabling a task-oriented navigation." + ], + "image_footnote": [], + "bbox": [ + 513, + 268, + 879, + 481 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "erful viewpoint for modelling human-object interaction understanding. Recent advances include anticipating future actions [23, 26, 1], model the hands-object manipulation [22, 77, 27, 16], detect the change in an object state [2], identify interaction hotspots [20, 54] or create topological maps [55]. Despite the fast movements of a headset camera, egocentric perception has also contributed to the mapping and planning phases: localising the agent in a known 3D map [43], performing visual navigation [56, 62] or building third-person (allocentric) maps [7, 47].", + "bbox": [ + 496, + 551, + 892, + 703 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Gibson's perception theory presents affordances as the potential actions that the environment offers to the agent based on its motor capabilities [25]. For example, the person can afford taking a glass, but the affordances of a soup in a pan can be mixing, emptying, scooping and pouring simultaneously. This multiplicity models better complex dynamic environments and opens the door to multi-agent collaboration with task synchronization. Although some authors have focused on more complex affordance models [50, 75], affordance perception is typically defined as a classification problem. Some authors have focused instead on grounded affordances [20], which provide a more flexible setup and are truly associated with motor capabilities, show", + "bbox": [ + 496, + 704, + 893, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "5238", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "ing improvements in action anticipation [46]. However, most learning approaches in affordance perception consider the problem ungrounded to the agent interaction with the object, requiring previous annotations of each affordance occurrence [53, 58, 48, 19, 8, 57]. While ungrounded methods have the advantage of providing pixel-wise precision, which we call metric understanding of the scene, many grounded approaches rely on full image classification losing any metric meaning. In this paper, we propose a grounded approach with pixel-wise precision, which enables detailed metric understanding while maintaining the flexibility of grounded methods and that can be used as prior information for more complex affordance models [75]. Close to our proposal is the work of Nagarajan et al. [54], which presented a grounded approach for extracting interaction hotspots by directly observing videos. Similar to other previous works, the hotspots are modelled as a single available affordance. Instead, we propose to consider the multiplicity of affordances for a single object or spatial zone through multi-label pixel-wise predictions.", + "bbox": [ + 76, + 90, + 472, + 393 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We build a pipeline to automatically collect multi-label pixel-wise annotations from real-world interactions using a temporal, spatial and semantic representation of the environment. We use this method with the EPIC Kitchens videos [15] to build a dataset of grounded affordances (EPIC-Aff), which to the author's knowledge, constitute the largest dataset in affordance segmentation up to date. We then adapt several segmentation architectures to the multi-label paradigm to extract more diverse information from the scene based on the assumption that the same object may have multiple affordances available. Using a mapping approach we extract the multi-label affordance segmentation to build a map that spatially links activity-centric zones as shows Figure 1, allowing a metric representation of the environmental affordances and goal-directed navigation tasks. Finally, we perform a quantitative evaluation of the extension from common architectures to the multi-label paradigm and we show mapping and planning applications of our approach, that can be used for assistive devices or in robotic scenarios.", + "bbox": [ + 76, + 393, + 472, + 696 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related works", + "text_level": 1, + "bbox": [ + 76, + 714, + 222, + 729 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Learning Visual Affordances", + "text_level": 1, + "bbox": [ + 76, + 739, + 333, + 755 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Ungrounded approaches [53, 58, 48, 19, 8, 57] for affordance perception are fully supervised by manually labelled masks. Due to their similarity with semantic segmentation or object detection tasks, these works use common architectures such as an encoder-decoder [57], proposal-based detectors [19, 58, 48, 8] or Bayesian instance segmentation [52]. Concerning grounded works, Fang et al. [20] extracted a latent representation from demonstration videos or Luo et al. [46] transferred the learning from exocentric", + "bbox": [ + 76, + 763, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "images to the egocentric perspective using only the semantic label as supervision. Nagarajan et al. [54] extracted the interaction hotspots by deriving the gradient-weighted attention maps obtained at training an action classifier on videos. Then Ego-Topo [55] built a topological graph of the scene to perform affordance classification from egocentric videos, grouping each node visually and temporally coherent frames with similar object and action distributions. This allows them to discover activity-centric zones based on their visual content and represent semantically the traversed paths with the edges of the graph.", + "bbox": [ + 496, + 90, + 893, + 258 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Multi-label perception", + "text_level": 1, + "bbox": [ + 500, + 266, + 709, + 282 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In the multi-label segmentation task, we assign two or more categories to a single pixel. A particular case is an amodal segmentation where the relevance of occluded parts depends on the depth order [78, 49]. The most common applications of multi-label segmentation are biomedical works, where there are multiple overlapped non-exclusive levels of tissues. Existing architectures extend a U-Net with minor changes such as a dynamic segmentation head [18], shuffle-attention mechanisms in the skip-connections [39], a combination of appearance and pose features [5] and split-attention modules [38]. The closest approach to multi-label segmentation is multi-label image recognition, where the label imbalance between positives and negatives in each binary classifier and the extraction of features from multiple objects make this task more complex [45]. Class distribution aware losses [73] such as the asymmetric loss [66], the focal loss [42] or the Multi-Label Softmax loss [24] correct the over-suppression of negative samples. On the other hand, Graph Neural Networks such as [74] deal with the feature extraction from multiple objects by creating a dynamic graph for each image that leverages the content-aware category representations. Finally, the transformer architecture extracts multiple attention maps in the different regions of interest [13, 37], guiding the multi-label classification [45] or ranking the class of the pixels considering only the categories selected by the classifier [30].", + "bbox": [ + 496, + 287, + 893, + 681 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Grounded Affordance Labelling", + "text_level": 1, + "bbox": [ + 500, + 694, + 794, + 710 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We extract automatic, interaction-grounded, multi-label pixel-wise and spatial affordance annotations from a sequence of real-world images in complex and cluttered environments, as shows Figure 2. Our multi-label segmentation approach learns all the potential options and does not reduce the perception to a single action. For example, a potato on a chopping board offers cutting, putting, peeling, removing and taking simultaneously. Current affordance segmentation works [19, 53, 58, 46, 52] assume a single-label affordance per object and lose a valuable amount of information. Although other affordance models allow for multiple predictions, these works ignore the segmentation of the inter-", + "bbox": [ + 496, + 719, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "5239", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "table", + "img_path": "images/70be61fdd27bf5d36a8241a46defcc5c378504f19b46df6b4818d429bbac47b3.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DatasetYearIGPixMLCP#Obj.#Aff.#Images.
UMD [53]2017X✓XX17730,000
IIT-Aff [58]2017X✓✓X1098,835
ADE-Aff [14]2018X✓✓X150310,000
OPRA [20]2018✓✓XX-720,774
Grounded I.H [54]2018✓✓XX31201,800*
Ego-Topo [55]2020✓X✓X30475-1201,020-1,115*
PAD v2 [76]2021X✓XX723130,000
AGD20k [46]2022X✓XX503623,816
EPIC-Aff2023✓✓✓✓30420-4338,876
", + "bbox": [ + 81, + 89, + 467, + 191 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Table 1. Visual affordance datasets statistics. I.G: Interaction Grounded. Pix: pixel-wise annotations. ML: multi-label. CP: camera poses #Obj: Number of objects. #Aff: Number of affordances. #Img: total number of images. * The affordance labels are only for evaluation, the model is trained supervised only by action labels provided by [15]", + "bbox": [ + 75, + 200, + 468, + 286 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "action hotspot in the image and lose the pixel-level accuracy of the segmentation models. For example, topological maps extract multiple affordances from an image [55], or action anticipation models predict a probability distribution of the different possibilities [23, 26]. Our methodology gets the best of two worlds producing multi-label metric masks, resulting in a full distribution of affordances. It enables a deeper understanding of the manipulation task such as the grasping points of the tool [3] or the evolution of the manipulation process over time[44]. Similar to previous unsupervised or weakly supervised methods [50], we extract affordance labels from weak VISOR and EPIC Kitchens annotations grounded on actual interactions.", + "bbox": [ + 75, + 321, + 468, + 517 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We join the affordances with their 3D spatial location by extracting the camera poses. The spatial approach to affordance perception is not new for the community. Rhinehart et al. [64] associate the functionality of regions with specific spatial locations, showing that that defining an affordance based solely on semantics is insufficient due to the significant influence of the physical context. For example, a frying pan is only cookable when it is on the hob or a plate is washable when the agent is next to the dishwasher. However, their method results in smooth 2D maps, which can be problematic for the fine-grained affordances in 3D space in our EPIC-Aff dataset. Instead, our method is able to scale up to large environments while maintaining the detail by using neural networks. Other previous works [28, 65] also use SLAM for action prediction but with addressing different problems. In those works, the action is set on the human, while the image provides context; while in our case the action/affordance is set on the environment and the user provides context. In our work, we use COLMAP to extract the relative pose between sparse frames with a filter of the dynamic objects, registering up to $93\\%$ of the frames compared with the $44\\%$ of the frames registered by ORBSLAM [51] on EPIC Kitchens [55]. Recently, EPIC Fields [72] registered the camera pose of the dense videos in EPIC Kitchens using neural rendering techniques.", + "bbox": [ + 75, + 523, + 470, + 901 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/2b71e2d4329d2d0c542c1ca02db5fb8d058a66763b00c4642022028f60060ffe.jpg", + "image_caption": [ + "Take Put Open Close Wash Cut Mix Pour Throw Move Remove Dry Turn-on Turn Shake Turn-off Peel Adjust Empty Scoop" + ], + "image_footnote": [], + "bbox": [ + 504, + 107, + 630, + 176 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/0563947d71e92e29f68898e4bd01fb718a1b83bd81108d7ac549dc0a69ab6331.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 504, + 176, + 630, + 239 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/630b91cd8895561040e5a5760404a3134b63fbaec82bf68285444eebbdbc7794.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 504, + 241, + 630, + 305 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/c5f3cc14ff1ece5b72eb33172dfca9d5a7639554753889f2d1d737d7ee752f5f.jpg", + "image_caption": [ + "Figure 2. Ground truth examples. For visualization purposes, we show a single label of the affordable action on its location, although these are overlapped for the same sample. The food in the bowl affords taking or mixing, while the cutting board on the left affords putting, cutting, moving and peeling." + ], + "image_footnote": [], + "bbox": [ + 504, + 305, + 630, + 369 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/d8bbe056cd7fbd87a68fb10d1bfbdb453f3305c1a4fe50f0c13d3eee92b8810e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 632, + 109, + 759, + 176 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/5bffa2bf744b75b1d4ef81b853fbc6edd32e21a7d3f1a643f9c4ca7813d5affa.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 632, + 176, + 759, + 241 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/efbf17f15c561d671f1ea3c0c87c4fad92d3a17a4fdea81bbf8dea99ae6f97c4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 632, + 241, + 759, + 306 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/333df629d9556865f9831cd1eb20bc2cbc1c9befa460c18c73f8a5b67d812689.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 632, + 306, + 759, + 369 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/63ab3a6104dc2c6138696d952a8e1888a3b4a5f4243535e39e0e34a37e71b505.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 761, + 109, + 887, + 176 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/e58f56ecea4a9ef86031ac652507688f6adb6bd71bb4f67309b7be09d26dc638.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 761, + 176, + 887, + 241 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/827f4cec3f7e365dd8ca79ba609420c2c20cfffd856dba78c1c816b3af35ac04.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 761, + 241, + 887, + 306 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/e2010cf343f1d5a3e12ee1a40839d58780a6bc0f48c6b2c59c9851c3571dc2cd.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 761, + 306, + 887, + 369 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Affordance datasets", + "text_level": 1, + "bbox": [ + 500, + 468, + 687, + 482 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Following our motivation, we conduct a study along the visual affordance datasets shown in Table 1. The ungrounded datasets are subjected to the annotator's consideration and required to draw pixel-wise semantic mask to each object part [58, 53, 14, 76, 46] or additional sensors [35, 9], decreasing the object variability and limiting the scalability due to the annotation costs. The UMD dataset contains a semantic affordance map for objects in isolated conditions and with low variability, which prevents generalisation [53]. The IIT-Aff dataset [58] provides the most comprehensive annotations designed for use in robotics, including multiple objects in a single image. The ADE-Aff dataset [14], built on top of ADE20K scenes, examines the social acceptability of actions about context but is limited to only three affordance classes. The AGD20k [46] dataset includes the largest number of categories and actions by transferring from an exocentric to an egocentric viewpoint perspective. On the other hand, grounded works learn from observing interactions on the EPIC-Kitchens sequences [15], internet demonstration videos [20] or with gaze point with eyetracking devices [21]. The annotations provided are only used for evaluation since they do not require strong supervision. However, these approaches ignore the pixel-wise precision [55] or the multi-label modality of our approach[54].", + "bbox": [ + 496, + 492, + 890, + 853 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Based on the mentioned limitations, our novel dataset EPIC-Aff provides multi-label pixel-wise affordance annotations with the camera pose. It contributes to a diverse and", + "bbox": [ + 498, + 854, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "5240", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "comprehensive affordance database with the largest number of images up to date. This better captures the complexity, dynamics, multiplicity and variability of real-world environments, such as preparing a recipe in a kitchen. Finally, as our labels are automatically extracted, we enable the application of our method to other egocentric datasets.", + "bbox": [ + 75, + 90, + 472, + 183 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. EPIC-Aff dataset", + "text_level": 1, + "bbox": [ + 76, + 191, + 246, + 207 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We detail the procedure shown in Figure 3 for our grounded affordance labelling. EPIC-Aff1 is composed of 38,876 images with up to 43 different affordable actions $\\mathcal{K}$ . We choose the EPIC-Kitchens as the base dataset because of its sequential and repetitive nature, which allows us to extract the 3D geometry, and because the kitchen is a scenario with multi-step and structured activities very rich in semantics. We cover all the object categories present in the EPIC-100 annotations, which constitute a wide, large and diverse knowledge base.", + "bbox": [ + 75, + 215, + 468, + 366 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "From a sequence of video, we join the EPIC-100 narrations [15] and the VISOR Kitchen annotations [17] to obtain a sparse sequence of frames $S_{\\mathcal{M}} = (f_1,\\dots,f_N)$ with the localization of the interactions on the image, as shows Figure 4. The EPIC-100 labels [15] contains narrations formed by an action verb $\\nu$ with an associated object $\\mathcal{O}$ , i.e.: \"add steak\", for more than 100 hours of video. VISOR Kitchens [17] interpolates from sparse annotations to generate semantic masks $\\mathcal{M}$ and bounding boxes $\\mathcal{B}$ on the active objects. We set the centre of the interaction $x_i = \\{u_i,v_i\\}$ in the middle of the intersection between the hand $\\mathcal{B}_h$ and the interacted object $\\mathcal{B}_O$ bounding-boxes given by the narration $\\nu + \\mathcal{O}$ .", + "bbox": [ + 75, + 366, + 470, + 561 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Then, we apply COLMAP, a Structure-from-Motion (SfM) algorithm [69] to obtain the camera poses $T_w^c$ and a point cloud of the environment $\\{X_p\\}$ . In the EPIC-Kitchens [15], each kitchen is composed of multiple videos, thus, we join all the sparse frames with interactions $S_K = \\{S_1 \\ldots S_M\\}$ to relate frames from different videos in a common 3D reference. Furthermore, we use the VISOR semantic masks to avoid including dynamic objects in the point cloud.", + "bbox": [ + 75, + 561, + 468, + 698 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Next, we employ a robust depth estimator based on a neural network $d_{NN} = f_d(\\cdot)$ [63] to predict the depth of interaction points $d_{NN}(x_i)$ . Because the neural network computes the depth up-to-scale, we compute a scale correction factor per image to fit the network scale to the SfM scale: $\\text{scale} = \\frac{\\text{median}(d^{SfM}(X_p) / \\text{median}(d^{NN}(X_p))}{34}$ , where $d^{SfM}(X_p)$ is the depth of all the points $\\{X_p\\}$ visible from the current image and $d^{NN}(X_p)$ is the depth of the same points given by the network estimator.", + "bbox": [ + 75, + 699, + 468, + 834 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Using the predicted depth and the scale projection, we can project the interaction point $x_{i}$ in 3D space $X_{i}$ and", + "bbox": [ + 75, + 835, + 468, + 866 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "use the camera pose to project into the global coordinates $X_{i}^{w} = T_{w}^{c}\\cdot X_{i}^{c}$ . At this point, as shown in Figure 5 we obtain in a common reference a history of all the interactions that occurred in the kitchen $\\mathcal{I}_k = \\{X_1^w,X_2^w,\\ldots ,X_k^w\\}$ , crossgeneralizing for the different sequences. This constitutes our knowledge base that follows our hypothesis that the distribution of affordances is spatially linked to pre-determined physical spaces (i.e you only wash in the dishwasher), not only to the semantic context of a topological graph [55].", + "bbox": [ + 500, + 90, + 890, + 226 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Then, once we store all the past interactions $\\mathcal{I}_k$ with their $\\mathcal{V}_k$ and $\\mathcal{O}_k$ labels, we reproject them back to the new camera reference system $X_i^c = T_c^w \\cdot X_i^w$ . Instead of considering all the object semantic masks as the affordance region, we centre a Gaussian distribution over each affordance-reprojected point $X_i^c$ and build an additive heatmap. Then, the affordance masks $\\mathcal{M}_i^{aff}$ are defined as the regions where the heatmap is greater than 0.25. This is grounded in how humans interact with objects [54] and allows us to consider the different affordability of the object parts (a knife is only graspable with the handle). In order to generate the affordance labels $\\mathcal{A} = \\{(\\mathcal{V}_1, \\mathcal{O}_1, \\mathcal{M}_1^{aff}), \\dots, (\\mathcal{V}_j, \\mathcal{O}_j)\\}$ , we select only those verbs whose associated object $\\mathcal{O}_i$ was present in the VISOR annotations $\\{\\mathcal{M}, \\mathcal{B}\\}$ . With this procedure, we are grounding our dataset in the past interactions in that environment and associating multiple affordances to a single object. We show qualitative samples of the EPIC-Aff in Figure 2.", + "bbox": [ + 498, + 227, + 892, + 500 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We provide two different versions of the dataset: the easy EPIC-Aff and the complex-EPIC Aff, with 20 and 43 affordance classes respectively. There is a challenging class imbalance, as shown the Figure 6 with a significant frequency gap between the most common class (open, with a $16.0\\%$ ) and the less represented (dry, with a $0.3\\%$ ). In Fig. 7 we show the pixel ratio, which reflects that semantically similar or opposite actions are associated with the same space (i.e., turn-on, turn-off, adjust or cut and peel) and the importance of the multi-level approach. This shows that activity-centric zones are physical spaces where there occur multiple common activities, both synonyms or antonyms. For example, in the hob controls region we likely find (i.e., turn-on, turn-off, adjust), while on the dishwasher zone, we will encounter wash and dry.", + "bbox": [ + 498, + 500, + 890, + 727 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Multi-label segmentation and mapping", + "text_level": 1, + "bbox": [ + 500, + 738, + 849, + 757 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this section, we explain our inference procedure. First, we describe the modifications needed to obtain a multi-label segmentation model. We then show how our approach can be applied to mapping and planning tasks.", + "bbox": [ + 498, + 763, + 890, + 825 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Multi-label segmentation", + "text_level": 1, + "bbox": [ + 500, + 832, + 728, + 848 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In this section we describe how we transform classical semantic segmentation models to a multi-label version. While there exists lots of single-label segmentation", + "bbox": [ + 498, + 854, + 890, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "1https://github.com/lmur98/epic_kitchens_ affordances", + "bbox": [ + 76, + 875, + 419, + 898 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "5241", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/ac3b2f0bc50b31f507c173e665cf8f3a9f684bbff4d2d265a898abea0aa7c024.jpg", + "image_caption": [ + "Training: grounded affordance labelling" + ], + "image_footnote": [], + "bbox": [ + 86, + 112, + 467, + 262 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/b8f06551c3fed339c5435b832e7281f28c63254a108cfb0ec368a8c8c93a6c5c.jpg", + "image_caption": [ + "Inference: multi-label segmentation and mapping", + "Figure 3. Left: Pipeline with the automatic extraction of the pixel-wise labels on the EPIC-Aff dataset. We combine the EPIC-100 narration with the VISOR masks annotations to extract the interaction point. Then, using the camera pose extracted from COLMAP, we project all the interactions in a common 3D global reference. Finally, we reproject all the past interactions to each frame, and filter the affordance annotation by the objects present at the image. Right: the multi-label masks predictions from our model are leveraged to a 3D map" + ], + "image_footnote": [], + "bbox": [ + 488, + 112, + 890, + 262 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/c50acae228507d93c513db530669b6c50c5f30f369274a15912b6449150a40bf.jpg", + "image_caption": [ + "Figure 4. Using the masks provided by VISOR Kitchens, we define the intersection between the object and the hand bounding boxes as the center of the interaction. We show in yellow the bounding box of the non-interacting objects, in green the bounding box of the hands and in blue the bounding box of the interacting object." + ], + "image_footnote": [], + "bbox": [ + 80, + 349, + 272, + 435 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/581b699380150b779087f14727b89c641fbbd51a0ae57da613c5be9a31f1751f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 272, + 349, + 467, + 435 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/74cbb3fde0323f9327aa288dd465fa8e5ec45fc433d444d6406cf9bb0deda30e.jpg", + "image_caption": [ + "Figure 5. Historical with all the past interaction frames in that environment, where the blue dots represent the camera poses of the sparse frames from all the sequences" + ], + "image_footnote": [], + "bbox": [ + 81, + 517, + 259, + 618 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/d9efb3b7d88781622cb660d2ef56d4bc0a648b827cc5d17724612d905b83d50e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 279, + 517, + 460, + 618 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/ed42c5f56e5f6183b95c0ef5026e90484623ea38f942f4f2340a930129668857.jpg", + "image_caption": [ + "Figure 6. Distribution of the 20 classes in the easy-EPIC Aff dataset, showing a significant class imbalance." + ], + "image_footnote": [], + "bbox": [ + 78, + 680, + 465, + 825 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/c7c190c980ca71a66a11df2d7c112085e42034d4cb67362607a79a69d6892349.jpg", + "image_caption": [ + "Figure 7. Pixel ratio of the 20 classes in the easy-EPIC Aff dataset, where blue represents high correlation between the two classes and yellow that they do not used to concur in the same pixel." + ], + "image_footnote": [], + "bbox": [ + 558, + 349, + 834, + 551 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "[11, 40, 4, 31, 30, 10] and multi-label image classification works [73, 24, 12, 45], the multi-label segmentation is a more unexplored task restricted to small domains like biomedical images [39, 5].", + "bbox": [ + 496, + 626, + 890, + 686 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Given an input image $\\mathbf{X}$ , the multi-label segmentation goal is to predict a group of categories for each pixel. Therefore, we assume that each pixel could represent multiple affordances (takeable, cuttable, washable, ..., etc.) or not belong to any category. For a total number of $\\kappa$ classes we define the label $y$ for each pixel of the image as $y = [y_{1},\\dots,y_{k}]$ , where $y_{k} = 1$ if the pixel contains the $\\kappa$ -category label, otherwise $y_{k} = 0$ . In order to predict multi-label segmentation masks, we have evaluated two different approaches. First, we use a standard multiclass segmentation networks and evaluate three different heuristics to select multiple labels per pixel. Then, we modify the segmentation networks to output multiple binary classifiers which enable multiple labels to be active.", + "bbox": [ + 496, + 688, + 892, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "5242", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/601ac932e39454861c72bff39e3e3df46b7161ed7021d701ba2e4883cf4f963f.jpg", + "image_caption": [ + "Figure 8. Heuristics to select multiple labels from a probability vector" + ], + "image_footnote": [], + "bbox": [ + 86, + 87, + 459, + 162 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For the multiclass scenario, we assume that the network output is a categorical distribution for all the classes and use the standard supervision loss, the cross-entropy. Then, we transform the probability vector $p = [p_1,\\dots,p_k], \\sum_{k=1}^k p_k = 1$ with three heuristics to choose the multiple winning-classes, as shows Figure 8. On the first method, we select the top- $k$ classes with the largest probability value $p_k$ . Note that we do not consider predictions with a $s_k < 1/k$ , as it occurs to $k_1, k_5$ on Figure 8. The second alternative is max- $\\theta$ , which consists in selecting all the possible classes whose $p_k$ is greater than a threshold $\\theta$ . Finally, the last heuristic is a dynamic $\\theta_d$ threshold. We select the classes whose difference with the next class is larger than a $\\theta_d$ .", + "bbox": [ + 75, + 219, + 468, + 431 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "On the multi-label scenario, the model outputs $\\mathcal{K}$ independent Bernoulli distributions, generating binary probabilities $p = [p_1,\\dots,p_k]$ , where we assume a detection if $p_k > 0.5$ . Then, we substitute the cost function by a class-weighting Binary Cross Entropy (BCE) loss, obtaining $\\mathcal{K}$ binary classifiers. One disadvantage of having independent binary classifiers is that the performance is more sensitive to the class imbalance in the dataset. To alleviate that, we use the Asymmetric (Asym) loss $\\mathcal{L}_{asym}$ [66] shown in Equation 1. It combines the focal loss [71] with the margin loss [70] to reduce the contribution of easy negative samples and rejects unlabeled samples with a continuous gradient.", + "bbox": [ + 75, + 431, + 472, + 613 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nA S L _ {k} = \\left\\{ \\begin{array}{l l} \\log \\left(p _ {k}\\right) \\left(1 - p _ {k}\\right) ^ {\\gamma +}, & y _ {k} = 1 \\\\ \\log \\left(1 - p _ {k}\\right) \\left(p _ {k}\\right) ^ {\\gamma -}, & y _ {k} = 0 \\\\ N & \\kappa \\end{array} \\right. \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 116, + 638, + 468, + 684 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {a s y m} = \\frac {1}{N} \\sum_ {k = 1} ^ {N} \\frac {w _ {k}}{\\mathcal {K}} \\sum_ {k = 1} ^ {\\mathcal {K}} A S L _ {k}\n$$\n", + "text_format": "latex", + "bbox": [ + 117, + 674, + 331, + 715 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For each training image, $\\mathbf{X}$ with $N$ total pixels, $\\mathcal{L}_{\\text{asym}}$ computes a different term depending on if the $y_{k}$ binary label indicating that the class $k$ is present or not in the pixel. We apply a weighting average $w_{c}$ depending on the ratio between positive and negative samples for class $k$ to avoid the class imbalance. Following the original paper [66], we set $\\gamma^{+} = 4$ and $\\gamma^{-} = 1$ .", + "bbox": [ + 75, + 729, + 468, + 834 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Example applications", + "text_level": 1, + "bbox": [ + 76, + 845, + 277, + 862 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Given that our system provides metric information of the affordance location, has information of the camera poses", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "and has multi-label affordance detection, we can apply it to common spatial tasks such as mapping and navigation.", + "bbox": [ + 498, + 90, + 890, + 121 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Mapping of activity-centric zones We take the video sequence and sample unseen frames $\\{f_1, \\dots, f_t\\}$ during training. Following the same procedure as in the extraction of labels, we reproject the inferred semantic masks on the pixels $i, j$ to its respective 3D location $x, y, z$ using the camera intrinsic $K_{int}$ , COLMAP pose $R_w^c$ , $t_w^c$ and the scaled depth $d_{i,j}$ .", + "bbox": [ + 496, + 140, + 890, + 247 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\left[ \\begin{array}{l} x \\\\ y \\\\ z \\end{array} \\right] = d _ {i, j} \\left(R _ {w} ^ {c}\\right) ^ {- 1} K _ {i n t} ^ {- 1} \\left[ \\begin{array}{l} i \\\\ j \\\\ 1 \\end{array} \\right] - t _ {w} ^ {c} \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 580, + 257, + 890, + 306 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We accumulate in a global map the COLMAP key-points to represent the geometry and the segmented affordances regions. We do not perform any fusion on voxels or octrees, since our multi-label approach assumes that a zone can represent several predicted classes. Note that the map representation is common for all the sequences of the same environment, with the potential of linking zones across multiple episodes and learning from past interactions.", + "bbox": [ + 496, + 311, + 890, + 434 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Task-oriented navigation Finally, we introduce a task-oriented navigation experiment to show the relevance of the map representation. We use the COLMAP key-points to build an occupancy grid with the available free space. Then, the agent is initialized in a random localization and asked to navigate to perform a certain action. Once it selects the location from the semantic-metric representation, the agent decides the path planning using a $\\mathbf{A}^*$ search with the Euclidean distance on the free space. We use the point cloud from COLMAP to create an occupancy grid.", + "bbox": [ + 496, + 453, + 890, + 604 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 500, + 619, + 633, + 635 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Models and metrics", + "text_level": 1, + "bbox": [ + 500, + 643, + 687, + 657 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In our experiments, we modify three popular semantic segmentation architectures [33, 67, 10] and compare them with a instance segmentation model [31] plus an interaction hotspots model [54].", + "bbox": [ + 496, + 667, + 890, + 728 + ], + "page_idx": 5 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- Grounded Interaction Hotspots (GIH) [54]: We use the weights on its EPIC-Kitchen trained version to extract predictions from our images. To reduce the gap, we crop our scenes to represent a single object and compare for the same number of affordable actions $\\mathcal{K}$ in the easy-EPIC Aff dataset.", + "- Mask-RCNN [31]: we assume an overlapping in the bounding boxes between two different instances. We do not consider the amodal Mask-RCNN versions [59, 49] which treat differently visible and occlusion" + ], + "bbox": [ + 517, + 738, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "5243", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/8f1b9f74c4f2a8c8786909659a18456e97ca19786879d698e148005d2a64c118.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
TakePutOpenCloseWashCutMixPourThrowMoveRemoveDryTurn-onTurnShakeTurn-offPeelAdjustEmptyScoopmIoU
GIH [54]22.121.913.810.816.325.821.223.714.016.917.212.810.320.516.610.826.19.513.925.817.5
Mask R-CNN [31]37.736.947.143.951.541.446.438.143.642.938.413.152.543.730.850.935.347.133.626.040.1
U-Net dyn-θ[67](ours) U-Net BCE0.10.75.411.922.417.122.217.311.315.921.04.514.821.116.318.412.920.60.59.613.2
(ours) U-Net Asym22.322.530.924.030.223.721.117.717.123.418.58.727.322.413.223.816.222.219.013.120.9
FPN dyn-θ [33](ours) FPN BCE14.313.713.814.721.317.918.318.732.515.715.616.615.218.922.219.519.524.35.715.717.7
(ours) FPN Asym2.42.45.610.221.713.217.717.011.513.620.04.613.822.612.515.514.417.30.89.712.9
Deep-Lab v3 dyn-θ [10](ours) Deep-Lab v3 BCE25.725.933.326.733.222.421.815.418.523.921.47.43.820.813.328.413.624.523.511.622.2
(ours) Deep-Lab v3 Asym36.334.746.142.046.842.742.237.543.341.739.621.347.443.734.345.033.846.338.033.239.8
", + "bbox": [ + 78, + 88, + 893, + 241 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/fa390db8aa6c07f45f738f7a448e5af24afcad2922e5b6214e8dc721da16e6f0.jpg", + "table_caption": [ + "Table 2. Class-wise IoU scores on easy-EPIC Aff test set. All scores are in [%]." + ], + "table_footnote": [ + "Table 3. Affordance multi-label segmentation on easy-EPIC Aff test set (20 classes). Note that except the mIoU and the F1-Score, the rest of the metrics are common for the three versions of the multi-class segmentation models." + ], + "table_body": "
KLD ↓SIM ↑AUC-J ↑mIoU ↑F1-Score ↑mAP ↑AP50 ↑
GIH [54]2.3810.1160.51117.529.414.215.5
Mask-RCNN [31]1.3650.1500.84140.156.559.362.6
U-Net [67] top-K2.5320.3410.8309.517.422.030.5
U-Net [67] max-θ2.5320.3410.83013.223.622.030.5
U-Net [67] dyn-θ2.5320.3410.83013.223.722.030.5
(ours) U-Net + BCE2.7180.3040.94920.934.248.244.7
(ours) U-Net + Asym0.7830.6650.85717.729.915.632.3
FPN [33] top-K2.2290.3620.8128.915.618.924.7
FPN [33] max-θ2.2290.3620.81212.421.818.924.7
FPN [33] dyn-θ2.2290.3620.81212.923.618.924.7
(ours) FPN + BCE1.6130.3650.95522.235.748.744.5
(ours) FPN + Asym0.7890.5460.95639.856.844.159.3
DeepLab-v3 [10] top-K4.9470.1920.91118.931.935.040.9
DeepLab-v3 [10] max-θ4.9470.1920.91119.232.335.040.9
DeepLab-v3 [10] dyn-θ4.9470.1920.91119.532.735.040.9
(ours) DeepLab-v3 + BCE1.2760.1790.96431.347.258.656.2
(ours) DeepLab-v3 + Asym0.6030.6680.96542.360.143.658.5
", + "bbox": [ + 78, + 276, + 468, + 438 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/3369e8640b9f1eef073ef366415847fa729314583df3be9bf27fb789f66af3b4.jpg", + "table_caption": [], + "table_footnote": [ + "Table 4. Affordance multi-label segmentation on complex-EPIC Aff test set (43 classes)." + ], + "table_body": "
KLD ↓SIM ↑AUC-J ↑mIoU ↑F1-Score ↑mAP ↑AP50 ↑
Mask-RCNN2.2870.2110.75617.127.340.146.7
(ours) U-Net Asym1.1040.3200.65712.924.811.217.9
(ours) FPN Asym0.5300.6730.92128.142.924.843.4
(ours) DeepLab-v3 Asym0.5200.6700.93131.146.527.443.9
", + "bbox": [ + 78, + 506, + 468, + 551 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "masks, since our affordance classes $\\mathcal{K}$ are not ranked in order.", + "bbox": [ + 107, + 604, + 468, + 633 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "- Semantic segmentation architectures. We compare the performance of UNet [67], Feature Pyramid Networks (FPN) [33, 41] and DeepLab v-3 [10].", + "bbox": [ + 96, + 647, + 468, + 691 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We train the segmentation models with an input resolution of $232 \\times 348$ for $100k$ iterations using Adam as optimizer with weight decay of $10^{-4}$ , batch size of 8 and a initial learning rate of $10^{-4}$ , using a polynomial decay up to $10^{-6}$ . We apply random crop, color jitter, resize and flipping as data augmentation. In the same way, we train Mask-RCNN SGD and $10^{-2}$ as initial learning rate. We use a Resnet-50 backbone pre-trained onImagenet for all the models in order to perform a fair comparative.", + "bbox": [ + 75, + 703, + 468, + 839 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Following the evaluation of Nagarajan et al, [54], we report the Kullback-Leibler Divergence (KLD) [20], the Similarity metric (SIM) and the Area Under the Curve (AUC-J) [6, 32] which provide different metrics for the mismatch of", + "bbox": [ + 75, + 839, + 468, + 901 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/279b9a8746f7b73c7868e49a1be15052ea28ef7f354e32144d8a2d6fa192f5b3.jpg", + "image_caption": [ + "Figure 9. Evolution of the mIoU for different heuristics to select multiple winning classes from a multi-class probability vector. Left: top- $\\mathcal{K}$ . Center: max- $\\theta$ . Right: dyn- $\\theta$ ." + ], + "image_footnote": [], + "bbox": [ + 500, + 277, + 630, + 369 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/3d4a93d8676e517ebb70f9228c22953c4a9043ae98d9ee2aa9a301fb68b72c65.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 630, + 277, + 758, + 371 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e1afd1898679a5a0ffa484bef9790197456c88b58b3757fa9ad0e6c3053175a1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 759, + 277, + 887, + 371 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "the distribution of heatmaps or affordance regions considering the predictive probability. We also report metrics from segmentation literature, such as the mean Intersection over the Union (mIoU) and the F1-Score to measure the performance of the semantic segmentation, and the Average Precision (AP) AP-50 and mAP to report the performance of the detection metrics.", + "bbox": [ + 496, + 441, + 892, + 547 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Quantitative results", + "text_level": 1, + "bbox": [ + 500, + 559, + 689, + 575 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We compare the performance of different popular architectures on the multi-label affordance segmentation task in Table 3 on the easy-EPIC Aff dataset. DeepLab-v3 trained with the Asymmetric loss obtains the best performance on the segmentation and saliency metrics (42.3 % mIoU 60.1 % F-1 score, 0.603 KLD, 0.668 SIM, 0.965 AUC-J). Since the backbone of the three semantic segmentation models is the same (Resnet-50), the different results are due to the configuration of the different decoders. In the dataset, since the labels represent interaction hotspots, they are not aligned with the borders of the objects and represent a more high-level zone. Thus, the atrous convolution of DeepLab enables to enlarge of the filter's field of view and better captures these regions. We show the per-class segmentation performance in terms of the IoU in Table 2. Comparing with the apparition frequency of the classes in the dataset shown in Figure 6, Mask R-CNN fails at the low-represented classes since it is not trained with the Asymmetric loss. However, it is the best architecture on the detection metrics (59.3 % mAP, 62.6 % AP50). Compared with previous works, the pre-trained version of [54] achieves inter", + "bbox": [ + 496, + 583, + 892, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "5244", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/b845c5ce9377392279756524b551e649c209e6a18bb566b11d4846fc09a70fc7.jpg", + "image_caption": [ + "Figure 10. Spatial distribution of the detected multi-label affordances for multiple time-steps" + ], + "image_footnote": [], + "bbox": [ + 96, + 89, + 877, + 236 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/23479c1f9d74ef7cc74b3ac63ddd69ffb2410cbba660f5615f76ce0136153287.jpg", + "image_caption": [ + "Figure 11. Goal oriented path-planning. In the example, at $t = 36$ we indicate the user the trajectory from the sink to the place where it used to dry the crockery. The blue points represent the steps of the path planning" + ], + "image_footnote": [], + "bbox": [ + 81, + 273, + 467, + 421 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "mediate results on the segmentation metrics (17.5% mIoU, 29.4% F-1 score) but low on the AP scores.", + "bbox": [ + 75, + 505, + 468, + 535 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The results in Figure 9 show the impact of the hyperparameters when adapting the multi-class models. The top- $\\mathcal{K} = 1$ represents the classical multi-label case. The results show how its performance is far from the multi-label versions, supporting the need for specific architectural changes for this scenario. In Figure 9 left, when we increase the number of winning classes, the performance decreases by introducing too many false positives. The other two heuristics achieve better performance since they better reject these outliers. For example, the dyn- $\\theta$ adapts dynamically to the probability distribution shape, obtaining higher mIoU and F-1 in the three cases (see Table 3). Finally, we appreciate similar results on the complex-EPIC Aff, shown in Table 4. In this case, the overall performance decreases due to the higher number of classes and its imbalance.", + "bbox": [ + 75, + 536, + 468, + 762 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.3. Mapping: metric distribution of affordances", + "text_level": 1, + "bbox": [ + 76, + 771, + 454, + 787 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We show on Figure 10 qualitative results of the multi-label interaction hotspots from affordances predicted by the DeepLab-v3 Asym model. Our perception model is consistent from different view-points. For example, the microwave of the left-map in Figure 10 is detected as turn-on both at $t = 0,25,52$ . The qualitative results clearly motivate our multi-label approach: the milkshake on the right", + "bbox": [ + 75, + 794, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "map affords mixing, pouring and taking, or the sink in the center map affords drying and washing. The metric conception of our approach is also relevant, since it reflects the interactions hotspots rather than highlight the complete object (for example grasping a pan only with the handle).", + "bbox": [ + 496, + 277, + 890, + 354 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.4. Task-oriented navigation", + "text_level": 1, + "bbox": [ + 498, + 362, + 728, + 378 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Finally, we use the spatial localization of the affordances to show a proof-of-concept \"task-oriented\" navigation. As we illustrate on Figure 11, we guide the agent according to the action possibilities that the environment offers to him. Therefore, we can ask our system to perform certain action, meaning to go to where the object and affordance are available. The $\\mathrm{A}^*$ indicates to the agent the shortest path from its current location to the position where it took the action in the past. For example, this could guide a visually impaired person with an assistant device [29].", + "bbox": [ + 496, + 385, + 892, + 537 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Limitations", + "text_level": 1, + "bbox": [ + 498, + 550, + 624, + 566 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Our current approach presents several limitations. At the dataset extraction, we assume that the interaction occurs in the intersection between the object and the hand bounding-boxes, thus it depends on the bounding-box aligned to the actual object. This could be mitigated with a detection model for grasping points, but we wanted a simpler version for our prototype as a more convoluted approach might introduce further biases, difficult to detect. Also, the camera poses from COLMAP can be distorted by noisy-frames or dynamic objects non-suppressed by the mask. Furthermore, a real-time mapping system would require a SLAM system such as ORB-SLAM [51] which might reduce the accuracy of COLMAP. Similarly, our dataset is fully based on Kitchen sequences and it does not incorporate another environments introducing important dataset bias in the trained models. However, our automatic labeling pipeline could be easily used to extend the dataset in other scenarios.", + "bbox": [ + 496, + 575, + 892, + 832 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "7. Conclusions", + "text_level": 1, + "bbox": [ + 500, + 844, + 627, + 859 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We introduced a novel multi-label, metric and spatial-oriented perception of affordances. First, we present a", + "bbox": [ + 498, + 869, + 892, + 901 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "5245", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "method for extracting grounded affordances labels based on egocentric interaction videos through a common metric representation of all the past interactions in a common reference. We use this pipeline to build the most complete affordance dataset based on the classic EPIC-Kitchen dataset. This constitutes EPIC-Aff, the largest semantic segmentation dataset of affordances grounded on the human interactions. We also motivate a method for grounded affordance detection with pixel precission using multi-label predictors, which enhances the perception and the representation of the environment. Furthermore, we show that the metric representation obtained can be used to build detailed affordance maps and to guide the user to perform task-oriented navigation tasks.", + "bbox": [ + 75, + 90, + 472, + 303 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements", + "text_level": 1, + "bbox": [ + 76, + 318, + 243, + 335 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was supported by the Spanish Government (PID2021-125209OB-I00, TED2021-129410B-I00 and TED2021-131150B-I00) and the Aragon Government (DGA-T45_23R).", + "bbox": [ + 76, + 344, + 468, + 404 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 420, + 171, + 435 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Yazan Abu Farha, Alexander Richard, and Juergen Gall. When will you do what?-anticipating temporal occurrences of activities. 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In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, pages 1464-1472, 2017." + ], + "bbox": [ + 78, + 90, + 468, + 614 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "5249", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/Multi-label Affordance Mapping from Egocentric Vision/52183b21-9cd5-4c04-8bd7-3d9da9442890_model.json b/2023/Multi-label Affordance Mapping from Egocentric Vision/52183b21-9cd5-4c04-8bd7-3d9da9442890_model.json new file mode 100644 index 0000000000000000000000000000000000000000..79acdc5309415c4f6cc9f6699032cb9eb9f3e2f7 --- /dev/null +++ b/2023/Multi-label Affordance Mapping from Egocentric Vision/52183b21-9cd5-4c04-8bd7-3d9da9442890_model.json @@ -0,0 +1,2556 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.209, + 0.131, + 0.761, + 0.153 + ], + "angle": 0, + "content": "Multi-label affordance mapping from egocentric vision" + }, + { + "type": "text", + "bbox": [ + 0.196, + 0.182, + 0.773, + 0.217 + ], + "angle": 0, + "content": "Lorenzo Mur-Labadia Jose J. Guerrero Ruben Martinez-Cantin I3A - Universidad de Zaragoza" + }, + { + "type": "text", + "bbox": [ + 0.334, + 0.22, + 0.637, + 0.234 + ], + "angle": 0, + "content": "lmur, jguerrer, rmcantin@unizar.es" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.302, + 0.474, + 0.651 + ], + "angle": 0, + "content": "Accurate affordance detection and segmentation with pixel precision is an important piece in many complex systems based on interactions, such as robots and assistive devices. We present a new approach to affordance perception which enables accurate multi-label segmentation. Our approach can be used to automatically extract grounded affordances from first person videos of interactions using a 3D map of the environment providing pixel level precision for the affordance location. We use this method to build the largest and most complete dataset on affordances based on the EPIC-Kitchen dataset, EPIC-Aff, which provides interaction-grounded, multi-label, metric and spatial affordance annotations. Then, we propose a new approach to affordance segmentation based on multi-label detection which enables multiple affordances to co-exists in the same space, for example if they are associated with the same object. We present several strategies of multi-label detection using several segmentation architectures. The experimental results highlight the importance of the multi-label detection. Finally, we show how our metric representation can be exploited for build a map of interaction hotspots in spatial action-centric zones and use that representation to perform a task-oriented navigation." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.679, + 0.21, + 0.695 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.471, + 0.903 + ], + "angle": 0, + "content": "When humans repeatedly interact in a close environment, we associate a set of affordable actions with a certain distribution of objects in a physical space. For example, we associate a pan on a stove with cooking, but the same pan on the sink with washing. A joined spatial-semantic understanding contains powerful insights to understand human behaviour. This requires a close combination of perception, mapping and navigation algorithms; with potential applications in augmented reality systems [60, 61], but also guiding a robot [19, 36] or assistive devices [68]. In the last years, the ability of deep learning models to extract high-level representations has improved the perception of autonomous agents, while egocentric vision offers a pow" + }, + { + "type": "image", + "bbox": [ + 0.514, + 0.269, + 0.88, + 0.482 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.487, + 0.892, + 0.529 + ], + "angle": 0, + "content": "Figure 1. From a sequence of egocentric observations, our agent creates a spatial-metric multi-label representation of the affordances, enabling a task-oriented navigation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.893, + 0.704 + ], + "angle": 0, + "content": "erful viewpoint for modelling human-object interaction understanding. Recent advances include anticipating future actions [23, 26, 1], model the hands-object manipulation [22, 77, 27, 16], detect the change in an object state [2], identify interaction hotspots [20, 54] or create topological maps [55]. Despite the fast movements of a headset camera, egocentric perception has also contributed to the mapping and planning phases: localising the agent in a known 3D map [43], performing visual navigation [56, 62] or building third-person (allocentric) maps [7, 47]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.895, + 0.902 + ], + "angle": 0, + "content": "Gibson's perception theory presents affordances as the potential actions that the environment offers to the agent based on its motor capabilities [25]. For example, the person can afford taking a glass, but the affordances of a soup in a pan can be mixing, emptying, scooping and pouring simultaneously. This multiplicity models better complex dynamic environments and opens the door to multi-agent collaboration with task synchronization. Although some authors have focused on more complex affordance models [50, 75], affordance perception is typically defined as a classification problem. Some authors have focused instead on grounded affordances [20], which provide a more flexible setup and are truly associated with motor capabilities, show" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5238" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.394 + ], + "angle": 0, + "content": "ing improvements in action anticipation [46]. However, most learning approaches in affordance perception consider the problem ungrounded to the agent interaction with the object, requiring previous annotations of each affordance occurrence [53, 58, 48, 19, 8, 57]. While ungrounded methods have the advantage of providing pixel-wise precision, which we call metric understanding of the scene, many grounded approaches rely on full image classification losing any metric meaning. In this paper, we propose a grounded approach with pixel-wise precision, which enables detailed metric understanding while maintaining the flexibility of grounded methods and that can be used as prior information for more complex affordance models [75]. Close to our proposal is the work of Nagarajan et al. [54], which presented a grounded approach for extracting interaction hotspots by directly observing videos. Similar to other previous works, the hotspots are modelled as a single available affordance. Instead, we propose to consider the multiplicity of affordances for a single object or spatial zone through multi-label pixel-wise predictions." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.395, + 0.473, + 0.698 + ], + "angle": 0, + "content": "We build a pipeline to automatically collect multi-label pixel-wise annotations from real-world interactions using a temporal, spatial and semantic representation of the environment. We use this method with the EPIC Kitchens videos [15] to build a dataset of grounded affordances (EPIC-Aff), which to the author's knowledge, constitute the largest dataset in affordance segmentation up to date. We then adapt several segmentation architectures to the multi-label paradigm to extract more diverse information from the scene based on the assumption that the same object may have multiple affordances available. Using a mapping approach we extract the multi-label affordance segmentation to build a map that spatially links activity-centric zones as shows Figure 1, allowing a metric representation of the environmental affordances and goal-directed navigation tasks. Finally, we perform a quantitative evaluation of the extension from common architectures to the multi-label paradigm and we show mapping and planning applications of our approach, that can be used for assistive devices or in robotic scenarios." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.715, + 0.223, + 0.73 + ], + "angle": 0, + "content": "2. Related works" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.741, + 0.334, + 0.756 + ], + "angle": 0, + "content": "2.1. Learning Visual Affordances" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.765, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Ungrounded approaches [53, 58, 48, 19, 8, 57] for affordance perception are fully supervised by manually labelled masks. Due to their similarity with semantic segmentation or object detection tasks, these works use common architectures such as an encoder-decoder [57], proposal-based detectors [19, 58, 48, 8] or Bayesian instance segmentation [52]. Concerning grounded works, Fang et al. [20] extracted a latent representation from demonstration videos or Luo et al. [46] transferred the learning from exocentric" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.26 + ], + "angle": 0, + "content": "images to the egocentric perspective using only the semantic label as supervision. Nagarajan et al. [54] extracted the interaction hotspots by deriving the gradient-weighted attention maps obtained at training an action classifier on videos. Then Ego-Topo [55] built a topological graph of the scene to perform affordance classification from egocentric videos, grouping each node visually and temporally coherent frames with similar object and action distributions. This allows them to discover activity-centric zones based on their visual content and represent semantically the traversed paths with the edges of the graph." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.267, + 0.71, + 0.283 + ], + "angle": 0, + "content": "2.2. Multi-label perception" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.289, + 0.895, + 0.683 + ], + "angle": 0, + "content": "In the multi-label segmentation task, we assign two or more categories to a single pixel. A particular case is an amodal segmentation where the relevance of occluded parts depends on the depth order [78, 49]. The most common applications of multi-label segmentation are biomedical works, where there are multiple overlapped non-exclusive levels of tissues. Existing architectures extend a U-Net with minor changes such as a dynamic segmentation head [18], shuffle-attention mechanisms in the skip-connections [39], a combination of appearance and pose features [5] and split-attention modules [38]. The closest approach to multi-label segmentation is multi-label image recognition, where the label imbalance between positives and negatives in each binary classifier and the extraction of features from multiple objects make this task more complex [45]. Class distribution aware losses [73] such as the asymmetric loss [66], the focal loss [42] or the Multi-Label Softmax loss [24] correct the over-suppression of negative samples. On the other hand, Graph Neural Networks such as [74] deal with the feature extraction from multiple objects by creating a dynamic graph for each image that leverages the content-aware category representations. Finally, the transformer architecture extracts multiple attention maps in the different regions of interest [13, 37], guiding the multi-label classification [45] or ranking the class of the pixels considering only the categories selected by the classifier [30]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.695, + 0.795, + 0.712 + ], + "angle": 0, + "content": "3. Grounded Affordance Labelling" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.903 + ], + "angle": 0, + "content": "We extract automatic, interaction-grounded, multi-label pixel-wise and spatial affordance annotations from a sequence of real-world images in complex and cluttered environments, as shows Figure 2. Our multi-label segmentation approach learns all the potential options and does not reduce the perception to a single action. For example, a potato on a chopping board offers cutting, putting, peeling, removing and taking simultaneously. Current affordance segmentation works [19, 53, 58, 46, 52] assume a single-label affordance per object and lose a valuable amount of information. Although other affordance models allow for multiple predictions, these works ignore the segmentation of the inter-" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5239" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.09, + 0.468, + 0.193 + ], + "angle": 0, + "content": "
DatasetYearIGPixMLCP#Obj.#Aff.#Images.
UMD [53]2017X✓XX17730,000
IIT-Aff [58]2017X✓✓X1098,835
ADE-Aff [14]2018X✓✓X150310,000
OPRA [20]2018✓✓XX-720,774
Grounded I.H [54]2018✓✓XX31201,800*
Ego-Topo [55]2020✓X✓X30475-1201,020-1,115*
PAD v2 [76]2021X✓XX723130,000
AGD20k [46]2022X✓XX503623,816
EPIC-Aff2023✓✓✓✓30420-4338,876
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.202, + 0.47, + 0.287 + ], + "angle": 0, + "content": "Table 1. Visual affordance datasets statistics. I.G: Interaction Grounded. Pix: pixel-wise annotations. ML: multi-label. CP: camera poses #Obj: Number of objects. #Aff: Number of affordances. #Img: total number of images. * The affordance labels are only for evaluation, the model is trained supervised only by action labels provided by [15]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.322, + 0.47, + 0.518 + ], + "angle": 0, + "content": "action hotspot in the image and lose the pixel-level accuracy of the segmentation models. For example, topological maps extract multiple affordances from an image [55], or action anticipation models predict a probability distribution of the different possibilities [23, 26]. Our methodology gets the best of two worlds producing multi-label metric masks, resulting in a full distribution of affordances. It enables a deeper understanding of the manipulation task such as the grasping points of the tool [3] or the evolution of the manipulation process over time[44]. Similar to previous unsupervised or weakly supervised methods [50], we extract affordance labels from weak VISOR and EPIC Kitchens annotations grounded on actual interactions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.524, + 0.471, + 0.902 + ], + "angle": 0, + "content": "We join the affordances with their 3D spatial location by extracting the camera poses. The spatial approach to affordance perception is not new for the community. Rhinehart et al. [64] associate the functionality of regions with specific spatial locations, showing that that defining an affordance based solely on semantics is insufficient due to the significant influence of the physical context. For example, a frying pan is only cookable when it is on the hob or a plate is washable when the agent is next to the dishwasher. However, their method results in smooth 2D maps, which can be problematic for the fine-grained affordances in 3D space in our EPIC-Aff dataset. Instead, our method is able to scale up to large environments while maintaining the detail by using neural networks. Other previous works [28, 65] also use SLAM for action prediction but with addressing different problems. In those works, the action is set on the human, while the image provides context; while in our case the action/affordance is set on the environment and the user provides context. In our work, we use COLMAP to extract the relative pose between sparse frames with a filter of the dynamic objects, registering up to \\(93\\%\\) of the frames compared with the \\(44\\%\\) of the frames registered by ORBSLAM [51] on EPIC Kitchens [55]. Recently, EPIC Fields [72] registered the camera pose of the dense videos in EPIC Kitchens using neural rendering techniques." + }, + { + "type": "image_caption", + "bbox": [ + 0.505, + 0.089, + 0.889, + 0.108 + ], + "angle": 0, + "content": "Take Put Open Close Wash Cut Mix Pour Throw Move Remove Dry Turn-on Turn Shake Turn-off Peel Adjust Empty Scoop" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.108, + 0.631, + 0.178 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.506, + 0.178, + 0.631, + 0.241 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.506, + 0.242, + 0.631, + 0.306 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.506, + 0.306, + 0.631, + 0.371 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.633, + 0.11, + 0.76, + 0.178 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.633, + 0.178, + 0.76, + 0.242 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.633, + 0.242, + 0.76, + 0.307 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.633, + 0.307, + 0.76, + 0.371 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.762, + 0.11, + 0.888, + 0.178 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.762, + 0.178, + 0.888, + 0.242 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.762, + 0.242, + 0.888, + 0.307 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.762, + 0.307, + 0.888, + 0.371 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.373, + 0.892, + 0.443 + ], + "angle": 0, + "content": "Figure 2. Ground truth examples. For visualization purposes, we show a single label of the affordable action on its location, although these are overlapped for the same sample. The food in the bowl affords taking or mixing, while the cutting board on the left affords putting, cutting, moving and peeling." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.469, + 0.689, + 0.483 + ], + "angle": 0, + "content": "3.1. Affordance datasets" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.493, + 0.892, + 0.854 + ], + "angle": 0, + "content": "Following our motivation, we conduct a study along the visual affordance datasets shown in Table 1. The ungrounded datasets are subjected to the annotator's consideration and required to draw pixel-wise semantic mask to each object part [58, 53, 14, 76, 46] or additional sensors [35, 9], decreasing the object variability and limiting the scalability due to the annotation costs. The UMD dataset contains a semantic affordance map for objects in isolated conditions and with low variability, which prevents generalisation [53]. The IIT-Aff dataset [58] provides the most comprehensive annotations designed for use in robotics, including multiple objects in a single image. The ADE-Aff dataset [14], built on top of ADE20K scenes, examines the social acceptability of actions about context but is limited to only three affordance classes. The AGD20k [46] dataset includes the largest number of categories and actions by transferring from an exocentric to an egocentric viewpoint perspective. On the other hand, grounded works learn from observing interactions on the EPIC-Kitchens sequences [15], internet demonstration videos [20] or with gaze point with eyetracking devices [21]. The annotations provided are only used for evaluation since they do not require strong supervision. However, these approaches ignore the pixel-wise precision [55] or the multi-label modality of our approach[54]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Based on the mentioned limitations, our novel dataset EPIC-Aff provides multi-label pixel-wise affordance annotations with the camera pose. It contributes to a diverse and" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5240" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.184 + ], + "angle": 0, + "content": "comprehensive affordance database with the largest number of images up to date. This better captures the complexity, dynamics, multiplicity and variability of real-world environments, such as preparing a recipe in a kitchen. Finally, as our labels are automatically extracted, we enable the application of our method to other egocentric datasets." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.192, + 0.248, + 0.208 + ], + "angle": 0, + "content": "3.2. EPIC-Aff dataset" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.216, + 0.47, + 0.367 + ], + "angle": 0, + "content": "We detail the procedure shown in Figure 3 for our grounded affordance labelling. EPIC-Aff1 is composed of 38,876 images with up to 43 different affordable actions \\(\\mathcal{K}\\). We choose the EPIC-Kitchens as the base dataset because of its sequential and repetitive nature, which allows us to extract the 3D geometry, and because the kitchen is a scenario with multi-step and structured activities very rich in semantics. We cover all the object categories present in the EPIC-100 annotations, which constitute a wide, large and diverse knowledge base." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.367, + 0.471, + 0.562 + ], + "angle": 0, + "content": "From a sequence of video, we join the EPIC-100 narrations [15] and the VISOR Kitchen annotations [17] to obtain a sparse sequence of frames \\( S_{\\mathcal{M}} = (f_1,\\dots,f_N) \\) with the localization of the interactions on the image, as shows Figure 4. The EPIC-100 labels [15] contains narrations formed by an action verb \\( \\nu \\) with an associated object \\( \\mathcal{O} \\), i.e.: \"add steak\", for more than 100 hours of video. VISOR Kitchens [17] interpolates from sparse annotations to generate semantic masks \\( \\mathcal{M} \\) and bounding boxes \\( \\mathcal{B} \\) on the active objects. We set the centre of the interaction \\( x_i = \\{u_i,v_i\\} \\) in the middle of the intersection between the hand \\( \\mathcal{B}_h \\) and the interacted object \\( \\mathcal{B}_O \\) bounding-boxes given by the narration \\( \\nu + \\mathcal{O} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.563, + 0.47, + 0.699 + ], + "angle": 0, + "content": "Then, we apply COLMAP, a Structure-from-Motion (SfM) algorithm [69] to obtain the camera poses \\( T_w^c \\) and a point cloud of the environment \\( \\{X_p\\} \\). In the EPIC-Kitchens [15], each kitchen is composed of multiple videos, thus, we join all the sparse frames with interactions \\( S_K = \\{S_1 \\ldots S_M\\} \\) to relate frames from different videos in a common 3D reference. Furthermore, we use the VISOR semantic masks to avoid including dynamic objects in the point cloud." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.7, + 0.47, + 0.835 + ], + "angle": 0, + "content": "Next, we employ a robust depth estimator based on a neural network \\( d_{NN} = f_d(\\cdot) \\) [63] to predict the depth of interaction points \\( d_{NN}(x_i) \\). Because the neural network computes the depth up-to-scale, we compute a scale correction factor per image to fit the network scale to the SfM scale: \\( \\text{scale} = \\frac{\\text{median}(d^{SfM}(X_p) / \\text{median}(d^{NN}(X_p))}{34} \\), where \\( d^{SfM}(X_p) \\) is the depth of all the points \\( \\{X_p\\} \\) visible from the current image and \\( d^{NN}(X_p) \\) is the depth of the same points given by the network estimator." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.836, + 0.47, + 0.867 + ], + "angle": 0, + "content": "Using the predicted depth and the scale projection, we can project the interaction point \\( x_{i} \\) in 3D space \\( X_{i} \\) and" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.892, + 0.227 + ], + "angle": 0, + "content": "use the camera pose to project into the global coordinates \\( X_{i}^{w} = T_{w}^{c}\\cdot X_{i}^{c} \\). At this point, as shown in Figure 5 we obtain in a common reference a history of all the interactions that occurred in the kitchen \\( \\mathcal{I}_k = \\{X_1^w,X_2^w,\\ldots ,X_k^w\\} \\), crossgeneralizing for the different sequences. This constitutes our knowledge base that follows our hypothesis that the distribution of affordances is spatially linked to pre-determined physical spaces (i.e you only wash in the dishwasher), not only to the semantic context of a topological graph [55]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.228, + 0.893, + 0.501 + ], + "angle": 0, + "content": "Then, once we store all the past interactions \\(\\mathcal{I}_k\\) with their \\(\\mathcal{V}_k\\) and \\(\\mathcal{O}_k\\) labels, we reproject them back to the new camera reference system \\(X_i^c = T_c^w \\cdot X_i^w\\). Instead of considering all the object semantic masks as the affordance region, we centre a Gaussian distribution over each affordance-reprojected point \\(X_i^c\\) and build an additive heatmap. Then, the affordance masks \\(\\mathcal{M}_i^{aff}\\) are defined as the regions where the heatmap is greater than 0.25. This is grounded in how humans interact with objects [54] and allows us to consider the different affordability of the object parts (a knife is only graspable with the handle). In order to generate the affordance labels \\(\\mathcal{A} = \\{(\\mathcal{V}_1, \\mathcal{O}_1, \\mathcal{M}_1^{aff}), \\dots, (\\mathcal{V}_j, \\mathcal{O}_j)\\}\\), we select only those verbs whose associated object \\(\\mathcal{O}_i\\) was present in the VISOR annotations \\(\\{\\mathcal{M}, \\mathcal{B}\\}\\). With this procedure, we are grounding our dataset in the past interactions in that environment and associating multiple affordances to a single object. We show qualitative samples of the EPIC-Aff in Figure 2." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.501, + 0.892, + 0.728 + ], + "angle": 0, + "content": "We provide two different versions of the dataset: the easy EPIC-Aff and the complex-EPIC Aff, with 20 and 43 affordance classes respectively. There is a challenging class imbalance, as shown the Figure 6 with a significant frequency gap between the most common class (open, with a \\(16.0\\%\\) ) and the less represented (dry, with a \\(0.3\\%\\)). In Fig. 7 we show the pixel ratio, which reflects that semantically similar or opposite actions are associated with the same space (i.e., turn-on, turn-off, adjust or cut and peel) and the importance of the multi-level approach. This shows that activity-centric zones are physical spaces where there occur multiple common activities, both synonyms or antonyms. For example, in the hob controls region we likely find (i.e., turn-on, turn-off, adjust), while on the dishwasher zone, we will encounter wash and dry." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.739, + 0.851, + 0.758 + ], + "angle": 0, + "content": "4. Multi-label segmentation and mapping" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.765, + 0.892, + 0.826 + ], + "angle": 0, + "content": "In this section, we explain our inference procedure. First, we describe the modifications needed to obtain a multi-label segmentation model. We then show how our approach can be applied to mapping and planning tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.833, + 0.729, + 0.849 + ], + "angle": 0, + "content": "4.1. Multi-label segmentation" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.892, + 0.902 + ], + "angle": 0, + "content": "In this section we describe how we transform classical semantic segmentation models to a multi-label version. While there exists lots of single-label segmentation" + }, + { + "type": "page_footnote", + "bbox": [ + 0.078, + 0.875, + 0.421, + 0.9 + ], + "angle": 0, + "content": "1https://github.com/lmur98/epic_kitchens_ affordances" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "5241" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.091, + 0.096, + 0.322, + 0.11 + ], + "angle": 0, + "content": "Training: grounded affordance labelling" + }, + { + "type": "image", + "bbox": [ + 0.088, + 0.113, + 0.468, + 0.263 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.492, + 0.096, + 0.78, + 0.11 + ], + "angle": 0, + "content": "Inference: multi-label segmentation and mapping" + }, + { + "type": "image", + "bbox": [ + 0.489, + 0.113, + 0.891, + 0.263 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.271, + 0.894, + 0.329 + ], + "angle": 0, + "content": "Figure 3. Left: Pipeline with the automatic extraction of the pixel-wise labels on the EPIC-Aff dataset. We combine the EPIC-100 narration with the VISOR masks annotations to extract the interaction point. Then, using the camera pose extracted from COLMAP, we project all the interactions in a common 3D global reference. Finally, we reproject all the past interactions to each frame, and filter the affordance annotation by the objects present at the image. Right: the multi-label masks predictions from our model are leveraged to a 3D map" + }, + { + "type": "image", + "bbox": [ + 0.081, + 0.35, + 0.273, + 0.436 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.274, + 0.35, + 0.468, + 0.436 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.438, + 0.47, + 0.507 + ], + "angle": 0, + "content": "Figure 4. Using the masks provided by VISOR Kitchens, we define the intersection between the object and the hand bounding boxes as the center of the interaction. We show in yellow the bounding box of the non-interacting objects, in green the bounding box of the hands and in blue the bounding box of the interacting object." + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.518, + 0.26, + 0.619 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.28, + 0.518, + 0.462, + 0.619 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.626, + 0.47, + 0.669 + ], + "angle": 0, + "content": "Figure 5. Historical with all the past interaction frames in that environment, where the blue dots represent the camera poses of the sparse frames from all the sequences" + }, + { + "type": "image", + "bbox": [ + 0.08, + 0.681, + 0.466, + 0.827 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.832, + 0.47, + 0.86 + ], + "angle": 0, + "content": "Figure 6. Distribution of the 20 classes in the easy-EPIC Aff dataset, showing a significant class imbalance." + }, + { + "type": "image", + "bbox": [ + 0.559, + 0.351, + 0.836, + 0.553 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.556, + 0.892, + 0.599 + ], + "angle": 0, + "content": "Figure 7. Pixel ratio of the 20 classes in the easy-EPIC Aff dataset, where blue represents high correlation between the two classes and yellow that they do not used to concur in the same pixel." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.627, + 0.892, + 0.688 + ], + "angle": 0, + "content": "[11, 40, 4, 31, 30, 10] and multi-label image classification works [73, 24, 12, 45], the multi-label segmentation is a more unexplored task restricted to small domains like biomedical images [39, 5]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Given an input image \\(\\mathbf{X}\\), the multi-label segmentation goal is to predict a group of categories for each pixel. Therefore, we assume that each pixel could represent multiple affordances (takeable, cuttable, washable, ..., etc.) or not belong to any category. For a total number of \\(\\kappa\\) classes we define the label \\(y\\) for each pixel of the image as \\(y = [y_{1},\\dots,y_{k}]\\), where \\(y_{k} = 1\\) if the pixel contains the \\(\\kappa\\)-category label, otherwise \\(y_{k} = 0\\). In order to predict multi-label segmentation masks, we have evaluated two different approaches. First, we use a standard multiclass segmentation networks and evaluate three different heuristics to select multiple labels per pixel. Then, we modify the segmentation networks to output multiple binary classifiers which enable multiple labels to be active." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5242" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.087, + 0.088, + 0.46, + 0.164 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.167, + 0.468, + 0.194 + ], + "angle": 0, + "content": "Figure 8. Heuristics to select multiple labels from a probability vector" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.22, + 0.47, + 0.432 + ], + "angle": 0, + "content": "For the multiclass scenario, we assume that the network output is a categorical distribution for all the classes and use the standard supervision loss, the cross-entropy. Then, we transform the probability vector \\( p = [p_1,\\dots,p_k], \\sum_{k=1}^k p_k = 1 \\) with three heuristics to choose the multiple winning-classes, as shows Figure 8. On the first method, we select the top-\\( k \\) classes with the largest probability value \\( p_k \\). Note that we do not consider predictions with a \\( s_k < 1/k \\), as it occurs to \\( k_1, k_5 \\) on Figure 8. The second alternative is max-\\( \\theta \\), which consists in selecting all the possible classes whose \\( p_k \\) is greater than a threshold \\( \\theta \\). Finally, the last heuristic is a dynamic \\( \\theta_d \\) threshold. We select the classes whose difference with the next class is larger than a \\( \\theta_d \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.433, + 0.473, + 0.614 + ], + "angle": 0, + "content": "On the multi-label scenario, the model outputs \\(\\mathcal{K}\\) independent Bernoulli distributions, generating binary probabilities \\(p = [p_1,\\dots,p_k]\\), where we assume a detection if \\(p_k > 0.5\\). Then, we substitute the cost function by a class-weighting Binary Cross Entropy (BCE) loss, obtaining \\(\\mathcal{K}\\) binary classifiers. One disadvantage of having independent binary classifiers is that the performance is more sensitive to the class imbalance in the dataset. To alleviate that, we use the Asymmetric (Asym) loss \\(\\mathcal{L}_{asym}\\) [66] shown in Equation 1. It combines the focal loss [71] with the margin loss [70] to reduce the contribution of easy negative samples and rejects unlabeled samples with a continuous gradient." + }, + { + "type": "equation", + "bbox": [ + 0.117, + 0.64, + 0.47, + 0.685 + ], + "angle": 0, + "content": "\\[\nA S L _ {k} = \\left\\{ \\begin{array}{l l} \\log \\left(p _ {k}\\right) \\left(1 - p _ {k}\\right) ^ {\\gamma +}, & y _ {k} = 1 \\\\ \\log \\left(1 - p _ {k}\\right) \\left(p _ {k}\\right) ^ {\\gamma -}, & y _ {k} = 0 \\\\ N & \\kappa \\end{array} \\right. \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.118, + 0.675, + 0.332, + 0.717 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {a s y m} = \\frac {1}{N} \\sum_ {k = 1} ^ {N} \\frac {w _ {k}}{\\mathcal {K}} \\sum_ {k = 1} ^ {\\mathcal {K}} A S L _ {k}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.73, + 0.47, + 0.835 + ], + "angle": 0, + "content": "For each training image, \\(\\mathbf{X}\\) with \\(N\\) total pixels, \\(\\mathcal{L}_{\\text{asym}}\\) computes a different term depending on if the \\(y_{k}\\) binary label indicating that the class \\(k\\) is present or not in the pixel. We apply a weighting average \\(w_{c}\\) depending on the ratio between positive and negative samples for class \\(k\\) to avoid the class imbalance. Following the original paper [66], we set \\(\\gamma^{+} = 4\\) and \\(\\gamma^{-} = 1\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.847, + 0.279, + 0.863 + ], + "angle": 0, + "content": "4.2. Example applications" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Given that our system provides metric information of the affordance location, has information of the camera poses" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "and has multi-label affordance detection, we can apply it to common spatial tasks such as mapping and navigation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.141, + 0.892, + 0.248 + ], + "angle": 0, + "content": "Mapping of activity-centric zones We take the video sequence and sample unseen frames \\(\\{f_1, \\dots, f_t\\}\\) during training. Following the same procedure as in the extraction of labels, we reproject the inferred semantic masks on the pixels \\(i, j\\) to its respective 3D location \\(x, y, z\\) using the camera intrinsic \\(K_{int}\\), COLMAP pose \\(R_w^c\\), \\(t_w^c\\) and the scaled depth \\(d_{i,j}\\)." + }, + { + "type": "equation", + "bbox": [ + 0.581, + 0.258, + 0.892, + 0.308 + ], + "angle": 0, + "content": "\\[\n\\left[ \\begin{array}{l} x \\\\ y \\\\ z \\end{array} \\right] = d _ {i, j} \\left(R _ {w} ^ {c}\\right) ^ {- 1} K _ {i n t} ^ {- 1} \\left[ \\begin{array}{l} i \\\\ j \\\\ 1 \\end{array} \\right] - t _ {w} ^ {c} \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.313, + 0.892, + 0.435 + ], + "angle": 0, + "content": "We accumulate in a global map the COLMAP key-points to represent the geometry and the segmented affordances regions. We do not perform any fusion on voxels or octrees, since our multi-label approach assumes that a zone can represent several predicted classes. Note that the map representation is common for all the sequences of the same environment, with the potential of linking zones across multiple episodes and learning from past interactions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.454, + 0.892, + 0.606 + ], + "angle": 0, + "content": "Task-oriented navigation Finally, we introduce a task-oriented navigation experiment to show the relevance of the map representation. We use the COLMAP key-points to build an occupancy grid with the available free space. Then, the agent is initialized in a random localization and asked to navigate to perform a certain action. Once it selects the location from the semantic-metric representation, the agent decides the path planning using a \\(\\mathbf{A}^*\\) search with the Euclidean distance on the free space. We use the point cloud from COLMAP to create an occupancy grid." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.62, + 0.634, + 0.636 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.644, + 0.688, + 0.659 + ], + "angle": 0, + "content": "5.1. Models and metrics" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.668, + 0.892, + 0.729 + ], + "angle": 0, + "content": "In our experiments, we modify three popular semantic segmentation architectures [33, 67, 10] and compare them with a instance segmentation model [31] plus an interaction hotspots model [54]." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.739, + 0.892, + 0.83 + ], + "angle": 0, + "content": "- Grounded Interaction Hotspots (GIH) [54]: We use the weights on its EPIC-Kitchen trained version to extract predictions from our images. To reduce the gap, we crop our scenes to represent a single object and compare for the same number of affordable actions \\(\\mathcal{K}\\) in the easy-EPIC Aff dataset." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "- Mask-RCNN [31]: we assume an overlapping in the bounding boxes between two different instances. We do not consider the amodal Mask-RCNN versions [59, 49] which treat differently visible and occlusion" + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.739, + 0.892, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5243" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.079, + 0.089, + 0.894, + 0.242 + ], + "angle": 0, + "content": "
TakePutOpenCloseWashCutMixPourThrowMoveRemoveDryTurn-onTurnShakeTurn-offPeelAdjustEmptyScoopmIoU
GIH [54]22.121.913.810.816.325.821.223.714.016.917.212.810.320.516.610.826.19.513.925.817.5
Mask R-CNN [31]37.736.947.143.951.541.446.438.143.642.938.413.152.543.730.850.935.347.133.626.040.1
U-Net dyn-θ[67](ours) U-Net BCE0.10.75.411.922.417.122.217.311.315.921.04.514.821.116.318.412.920.60.59.613.2
(ours) U-Net Asym22.322.530.924.030.223.721.117.717.123.418.58.727.322.413.223.816.222.219.013.120.9
FPN dyn-θ [33](ours) FPN BCE14.313.713.814.721.317.918.318.732.515.715.616.615.218.922.219.519.524.35.715.717.7
(ours) FPN Asym2.42.45.610.221.713.217.717.011.513.620.04.613.822.612.515.514.417.30.89.712.9
Deep-Lab v3 dyn-θ [10](ours) Deep-Lab v3 BCE25.725.933.326.733.222.421.815.418.523.921.47.43.820.813.328.413.624.523.511.622.2
(ours) Deep-Lab v3 Asym36.334.746.142.046.842.742.237.543.341.739.621.347.443.734.345.033.846.338.033.239.8
" + }, + { + "type": "table_caption", + "bbox": [ + 0.248, + 0.242, + 0.721, + 0.255 + ], + "angle": 0, + "content": "Table 2. Class-wise IoU scores on easy-EPIC Aff test set. All scores are in [%]." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.277, + 0.469, + 0.439 + ], + "angle": 0, + "content": "
KLD ↓SIM ↑AUC-J ↑mIoU ↑F1-Score ↑mAP ↑AP50 ↑
GIH [54]2.3810.1160.51117.529.414.215.5
Mask-RCNN [31]1.3650.1500.84140.156.559.362.6
U-Net [67] top-K2.5320.3410.8309.517.422.030.5
U-Net [67] max-θ2.5320.3410.83013.223.622.030.5
U-Net [67] dyn-θ2.5320.3410.83013.223.722.030.5
(ours) U-Net + BCE2.7180.3040.94920.934.248.244.7
(ours) U-Net + Asym0.7830.6650.85717.729.915.632.3
FPN [33] top-K2.2290.3620.8128.915.618.924.7
FPN [33] max-θ2.2290.3620.81212.421.818.924.7
FPN [33] dyn-θ2.2290.3620.81212.923.618.924.7
(ours) FPN + BCE1.6130.3650.95522.235.748.744.5
(ours) FPN + Asym0.7890.5460.95639.856.844.159.3
DeepLab-v3 [10] top-K4.9470.1920.91118.931.935.040.9
DeepLab-v3 [10] max-θ4.9470.1920.91119.232.335.040.9
DeepLab-v3 [10] dyn-θ4.9470.1920.91119.532.735.040.9
(ours) DeepLab-v3 + BCE1.2760.1790.96431.347.258.656.2
(ours) DeepLab-v3 + Asym0.6030.6680.96542.360.143.658.5
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.077, + 0.439, + 0.47, + 0.495 + ], + "angle": 0, + "content": "Table 3. Affordance multi-label segmentation on easy-EPIC Aff test set (20 classes). Note that except the mIoU and the F1-Score, the rest of the metrics are common for the three versions of the multi-class segmentation models." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.507, + 0.469, + 0.553 + ], + "angle": 0, + "content": "
KLD ↓SIM ↑AUC-J ↑mIoU ↑F1-Score ↑mAP ↑AP50 ↑
Mask-RCNN2.2870.2110.75617.127.340.146.7
(ours) U-Net Asym1.1040.3200.65712.924.811.217.9
(ours) FPN Asym0.5300.6730.92128.142.924.843.4
(ours) DeepLab-v3 Asym0.5200.6700.93131.146.527.443.9
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.077, + 0.552, + 0.469, + 0.579 + ], + "angle": 0, + "content": "Table 4. Affordance multi-label segmentation on complex-EPIC Aff test set (43 classes)." + }, + { + "type": "text", + "bbox": [ + 0.108, + 0.605, + 0.47, + 0.634 + ], + "angle": 0, + "content": "masks, since our affordance classes \\(\\mathcal{K}\\) are not ranked in order." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.648, + 0.47, + 0.693 + ], + "angle": 0, + "content": "- Semantic segmentation architectures. We compare the performance of UNet [67], Feature Pyramid Networks (FPN) [33, 41] and DeepLab v-3 [10]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.469, + 0.84 + ], + "angle": 0, + "content": "We train the segmentation models with an input resolution of \\(232 \\times 348\\) for \\(100k\\) iterations using Adam as optimizer with weight decay of \\(10^{-4}\\), batch size of 8 and a initial learning rate of \\(10^{-4}\\), using a polynomial decay up to \\(10^{-6}\\). We apply random crop, color jitter, resize and flipping as data augmentation. In the same way, we train Mask-RCNN SGD and \\(10^{-2}\\) as initial learning rate. We use a Resnet-50 backbone pre-trained onImagenet for all the models in order to perform a fair comparative." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Following the evaluation of Nagarajan et al, [54], we report the Kullback-Leibler Divergence (KLD) [20], the Similarity metric (SIM) and the Area Under the Curve (AUC-J) [6, 32] which provide different metrics for the mismatch of" + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.278, + 0.631, + 0.371 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.631, + 0.278, + 0.759, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.76, + 0.278, + 0.888, + 0.372 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.376, + 0.892, + 0.418 + ], + "angle": 0, + "content": "Figure 9. Evolution of the mIoU for different heuristics to select multiple winning classes from a multi-class probability vector. Left: top- \\(\\mathcal{K}\\). Center: max-\\(\\theta\\). Right: dyn-\\(\\theta\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.443, + 0.893, + 0.549 + ], + "angle": 0, + "content": "the distribution of heatmaps or affordance regions considering the predictive probability. We also report metrics from segmentation literature, such as the mean Intersection over the Union (mIoU) and the F1-Score to measure the performance of the semantic segmentation, and the Average Precision (AP) AP-50 and mAP to report the performance of the detection metrics." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.56, + 0.691, + 0.577 + ], + "angle": 0, + "content": "5.2. Quantitative results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.584, + 0.893, + 0.901 + ], + "angle": 0, + "content": "We compare the performance of different popular architectures on the multi-label affordance segmentation task in Table 3 on the easy-EPIC Aff dataset. DeepLab-v3 trained with the Asymmetric loss obtains the best performance on the segmentation and saliency metrics (42.3 % mIoU 60.1 % F-1 score, 0.603 KLD, 0.668 SIM, 0.965 AUC-J). Since the backbone of the three semantic segmentation models is the same (Resnet-50), the different results are due to the configuration of the different decoders. In the dataset, since the labels represent interaction hotspots, they are not aligned with the borders of the objects and represent a more high-level zone. Thus, the atrous convolution of DeepLab enables to enlarge of the filter's field of view and better captures these regions. We show the per-class segmentation performance in terms of the IoU in Table 2. Comparing with the apparition frequency of the classes in the dataset shown in Figure 6, Mask R-CNN fails at the low-represented classes since it is not trained with the Asymmetric loss. However, it is the best architecture on the detection metrics (59.3 % mAP, 62.6 % AP50). Compared with previous works, the pre-trained version of [54] achieves inter" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5244" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.098, + 0.09, + 0.878, + 0.237 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.21, + 0.239, + 0.761, + 0.255 + ], + "angle": 0, + "content": "Figure 10. Spatial distribution of the detected multi-label affordances for multiple time-steps" + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.275, + 0.468, + 0.422 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.425, + 0.471, + 0.482 + ], + "angle": 0, + "content": "Figure 11. Goal oriented path-planning. In the example, at \\( t = 36 \\) we indicate the user the trajectory from the sink to the place where it used to dry the crockery. The blue points represent the steps of the path planning" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.506, + 0.469, + 0.536 + ], + "angle": 0, + "content": "mediate results on the segmentation metrics (17.5% mIoU, 29.4% F-1 score) but low on the AP scores." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.537, + 0.47, + 0.763 + ], + "angle": 0, + "content": "The results in Figure 9 show the impact of the hyperparameters when adapting the multi-class models. The top-\\(\\mathcal{K} = 1\\) represents the classical multi-label case. The results show how its performance is far from the multi-label versions, supporting the need for specific architectural changes for this scenario. In Figure 9 left, when we increase the number of winning classes, the performance decreases by introducing too many false positives. The other two heuristics achieve better performance since they better reject these outliers. For example, the dyn-\\(\\theta\\) adapts dynamically to the probability distribution shape, obtaining higher mIoU and F-1 in the three cases (see Table 3). Finally, we appreciate similar results on the complex-EPIC Aff, shown in Table 4. In this case, the overall performance decreases due to the higher number of classes and its imbalance." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.772, + 0.455, + 0.789 + ], + "angle": 0, + "content": "5.3. Mapping: metric distribution of affordances" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.471, + 0.903 + ], + "angle": 0, + "content": "We show on Figure 10 qualitative results of the multi-label interaction hotspots from affordances predicted by the DeepLab-v3 Asym model. Our perception model is consistent from different view-points. For example, the microwave of the left-map in Figure 10 is detected as turn-on both at \\( t = 0,25,52 \\). The qualitative results clearly motivate our multi-label approach: the milkshake on the right" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.279, + 0.892, + 0.355 + ], + "angle": 0, + "content": "map affords mixing, pouring and taking, or the sink in the center map affords drying and washing. The metric conception of our approach is also relevant, since it reflects the interactions hotspots rather than highlight the complete object (for example grasping a pan only with the handle)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.363, + 0.729, + 0.379 + ], + "angle": 0, + "content": "5.4. Task-oriented navigation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.386, + 0.893, + 0.538 + ], + "angle": 0, + "content": "Finally, we use the spatial localization of the affordances to show a proof-of-concept \"task-oriented\" navigation. As we illustrate on Figure 11, we guide the agent according to the action possibilities that the environment offers to him. Therefore, we can ask our system to perform certain action, meaning to go to where the object and affordance are available. The \\(\\mathrm{A}^*\\) indicates to the agent the shortest path from its current location to the position where it took the action in the past. For example, this could guide a visually impaired person with an assistant device [29]." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.551, + 0.625, + 0.567 + ], + "angle": 0, + "content": "6. Limitations" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.576, + 0.893, + 0.833 + ], + "angle": 0, + "content": "Our current approach presents several limitations. At the dataset extraction, we assume that the interaction occurs in the intersection between the object and the hand bounding-boxes, thus it depends on the bounding-box aligned to the actual object. This could be mitigated with a detection model for grasping points, but we wanted a simpler version for our prototype as a more convoluted approach might introduce further biases, difficult to detect. Also, the camera poses from COLMAP can be distorted by noisy-frames or dynamic objects non-suppressed by the mask. Furthermore, a real-time mapping system would require a SLAM system such as ORB-SLAM [51] which might reduce the accuracy of COLMAP. Similarly, our dataset is fully based on Kitchen sequences and it does not incorporate another environments introducing important dataset bias in the trained models. However, our automatic labeling pipeline could be easily used to extend the dataset in other scenarios." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.845, + 0.628, + 0.861 + ], + "angle": 0, + "content": "7. Conclusions" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.893, + 0.902 + ], + "angle": 0, + "content": "We introduced a novel multi-label, metric and spatial-oriented perception of affordances. First, we present a" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5245" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.304 + ], + "angle": 0, + "content": "method for extracting grounded affordances labels based on egocentric interaction videos through a common metric representation of all the past interactions in a common reference. We use this pipeline to build the most complete affordance dataset based on the classic EPIC-Kitchen dataset. This constitutes EPIC-Aff, the largest semantic segmentation dataset of affordances grounded on the human interactions. We also motivate a method for grounded affordance detection with pixel precission using multi-label predictors, which enhances the perception and the representation of the environment. Furthermore, we show that the metric representation obtained can be used to build detailed affordance maps and to guide the user to perform task-oriented navigation tasks." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.319, + 0.245, + 0.336 + ], + "angle": 0, + "content": "Acknowledgements" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.345, + 0.47, + 0.405 + ], + "angle": 0, + "content": "This work was supported by the Spanish Government (PID2021-125209OB-I00, TED2021-129410B-I00 and TED2021-131150B-I00) and the Aragon Government (DGA-T45_23R)." + }, + { + "type": "title", + "bbox": [ + 0.079, + 0.421, + 0.173, + 0.436 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.446, + 0.47, + 0.516 + ], + "angle": 0, + "content": "[1] Yazan Abu Farha, Alexander Richard, and Juergen Gall. When will you do what?-anticipating temporal occurrences of activities. 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Guerrero Ruben Martinez-Cantin I3A - Universidad de Zaragoza + +lmur, jguerrer, rmcantin@unizar.es + +# Abstract + +Accurate affordance detection and segmentation with pixel precision is an important piece in many complex systems based on interactions, such as robots and assistive devices. We present a new approach to affordance perception which enables accurate multi-label segmentation. Our approach can be used to automatically extract grounded affordances from first person videos of interactions using a 3D map of the environment providing pixel level precision for the affordance location. We use this method to build the largest and most complete dataset on affordances based on the EPIC-Kitchen dataset, EPIC-Aff, which provides interaction-grounded, multi-label, metric and spatial affordance annotations. Then, we propose a new approach to affordance segmentation based on multi-label detection which enables multiple affordances to co-exists in the same space, for example if they are associated with the same object. We present several strategies of multi-label detection using several segmentation architectures. The experimental results highlight the importance of the multi-label detection. Finally, we show how our metric representation can be exploited for build a map of interaction hotspots in spatial action-centric zones and use that representation to perform a task-oriented navigation. + +# 1. Introduction + +When humans repeatedly interact in a close environment, we associate a set of affordable actions with a certain distribution of objects in a physical space. For example, we associate a pan on a stove with cooking, but the same pan on the sink with washing. A joined spatial-semantic understanding contains powerful insights to understand human behaviour. This requires a close combination of perception, mapping and navigation algorithms; with potential applications in augmented reality systems [60, 61], but also guiding a robot [19, 36] or assistive devices [68]. In the last years, the ability of deep learning models to extract high-level representations has improved the perception of autonomous agents, while egocentric vision offers a pow + +![](images/d13ed53fd446066df79aff82af6ae9201dbf55cbde8988341704efef8a72dae7.jpg) +Figure 1. From a sequence of egocentric observations, our agent creates a spatial-metric multi-label representation of the affordances, enabling a task-oriented navigation. + +erful viewpoint for modelling human-object interaction understanding. Recent advances include anticipating future actions [23, 26, 1], model the hands-object manipulation [22, 77, 27, 16], detect the change in an object state [2], identify interaction hotspots [20, 54] or create topological maps [55]. Despite the fast movements of a headset camera, egocentric perception has also contributed to the mapping and planning phases: localising the agent in a known 3D map [43], performing visual navigation [56, 62] or building third-person (allocentric) maps [7, 47]. + +Gibson's perception theory presents affordances as the potential actions that the environment offers to the agent based on its motor capabilities [25]. For example, the person can afford taking a glass, but the affordances of a soup in a pan can be mixing, emptying, scooping and pouring simultaneously. This multiplicity models better complex dynamic environments and opens the door to multi-agent collaboration with task synchronization. Although some authors have focused on more complex affordance models [50, 75], affordance perception is typically defined as a classification problem. Some authors have focused instead on grounded affordances [20], which provide a more flexible setup and are truly associated with motor capabilities, show + +ing improvements in action anticipation [46]. However, most learning approaches in affordance perception consider the problem ungrounded to the agent interaction with the object, requiring previous annotations of each affordance occurrence [53, 58, 48, 19, 8, 57]. While ungrounded methods have the advantage of providing pixel-wise precision, which we call metric understanding of the scene, many grounded approaches rely on full image classification losing any metric meaning. In this paper, we propose a grounded approach with pixel-wise precision, which enables detailed metric understanding while maintaining the flexibility of grounded methods and that can be used as prior information for more complex affordance models [75]. Close to our proposal is the work of Nagarajan et al. [54], which presented a grounded approach for extracting interaction hotspots by directly observing videos. Similar to other previous works, the hotspots are modelled as a single available affordance. Instead, we propose to consider the multiplicity of affordances for a single object or spatial zone through multi-label pixel-wise predictions. + +We build a pipeline to automatically collect multi-label pixel-wise annotations from real-world interactions using a temporal, spatial and semantic representation of the environment. We use this method with the EPIC Kitchens videos [15] to build a dataset of grounded affordances (EPIC-Aff), which to the author's knowledge, constitute the largest dataset in affordance segmentation up to date. We then adapt several segmentation architectures to the multi-label paradigm to extract more diverse information from the scene based on the assumption that the same object may have multiple affordances available. Using a mapping approach we extract the multi-label affordance segmentation to build a map that spatially links activity-centric zones as shows Figure 1, allowing a metric representation of the environmental affordances and goal-directed navigation tasks. Finally, we perform a quantitative evaluation of the extension from common architectures to the multi-label paradigm and we show mapping and planning applications of our approach, that can be used for assistive devices or in robotic scenarios. + +# 2. Related works + +# 2.1. Learning Visual Affordances + +Ungrounded approaches [53, 58, 48, 19, 8, 57] for affordance perception are fully supervised by manually labelled masks. Due to their similarity with semantic segmentation or object detection tasks, these works use common architectures such as an encoder-decoder [57], proposal-based detectors [19, 58, 48, 8] or Bayesian instance segmentation [52]. Concerning grounded works, Fang et al. [20] extracted a latent representation from demonstration videos or Luo et al. [46] transferred the learning from exocentric + +images to the egocentric perspective using only the semantic label as supervision. Nagarajan et al. [54] extracted the interaction hotspots by deriving the gradient-weighted attention maps obtained at training an action classifier on videos. Then Ego-Topo [55] built a topological graph of the scene to perform affordance classification from egocentric videos, grouping each node visually and temporally coherent frames with similar object and action distributions. This allows them to discover activity-centric zones based on their visual content and represent semantically the traversed paths with the edges of the graph. + +# 2.2. Multi-label perception + +In the multi-label segmentation task, we assign two or more categories to a single pixel. A particular case is an amodal segmentation where the relevance of occluded parts depends on the depth order [78, 49]. The most common applications of multi-label segmentation are biomedical works, where there are multiple overlapped non-exclusive levels of tissues. Existing architectures extend a U-Net with minor changes such as a dynamic segmentation head [18], shuffle-attention mechanisms in the skip-connections [39], a combination of appearance and pose features [5] and split-attention modules [38]. The closest approach to multi-label segmentation is multi-label image recognition, where the label imbalance between positives and negatives in each binary classifier and the extraction of features from multiple objects make this task more complex [45]. Class distribution aware losses [73] such as the asymmetric loss [66], the focal loss [42] or the Multi-Label Softmax loss [24] correct the over-suppression of negative samples. On the other hand, Graph Neural Networks such as [74] deal with the feature extraction from multiple objects by creating a dynamic graph for each image that leverages the content-aware category representations. Finally, the transformer architecture extracts multiple attention maps in the different regions of interest [13, 37], guiding the multi-label classification [45] or ranking the class of the pixels considering only the categories selected by the classifier [30]. + +# 3. Grounded Affordance Labelling + +We extract automatic, interaction-grounded, multi-label pixel-wise and spatial affordance annotations from a sequence of real-world images in complex and cluttered environments, as shows Figure 2. Our multi-label segmentation approach learns all the potential options and does not reduce the perception to a single action. For example, a potato on a chopping board offers cutting, putting, peeling, removing and taking simultaneously. Current affordance segmentation works [19, 53, 58, 46, 52] assume a single-label affordance per object and lose a valuable amount of information. Although other affordance models allow for multiple predictions, these works ignore the segmentation of the inter- + +
DatasetYearIGPixMLCP#Obj.#Aff.#Images.
UMD [53]2017X✓XX17730,000
IIT-Aff [58]2017X✓✓X1098,835
ADE-Aff [14]2018X✓✓X150310,000
OPRA [20]2018✓✓XX-720,774
Grounded I.H [54]2018✓✓XX31201,800*
Ego-Topo [55]2020✓X✓X30475-1201,020-1,115*
PAD v2 [76]2021X✓XX723130,000
AGD20k [46]2022X✓XX503623,816
EPIC-Aff2023✓✓✓✓30420-4338,876
+ +Table 1. Visual affordance datasets statistics. I.G: Interaction Grounded. Pix: pixel-wise annotations. ML: multi-label. CP: camera poses #Obj: Number of objects. #Aff: Number of affordances. #Img: total number of images. * The affordance labels are only for evaluation, the model is trained supervised only by action labels provided by [15] + +action hotspot in the image and lose the pixel-level accuracy of the segmentation models. For example, topological maps extract multiple affordances from an image [55], or action anticipation models predict a probability distribution of the different possibilities [23, 26]. Our methodology gets the best of two worlds producing multi-label metric masks, resulting in a full distribution of affordances. It enables a deeper understanding of the manipulation task such as the grasping points of the tool [3] or the evolution of the manipulation process over time[44]. Similar to previous unsupervised or weakly supervised methods [50], we extract affordance labels from weak VISOR and EPIC Kitchens annotations grounded on actual interactions. + +We join the affordances with their 3D spatial location by extracting the camera poses. The spatial approach to affordance perception is not new for the community. Rhinehart et al. [64] associate the functionality of regions with specific spatial locations, showing that that defining an affordance based solely on semantics is insufficient due to the significant influence of the physical context. For example, a frying pan is only cookable when it is on the hob or a plate is washable when the agent is next to the dishwasher. However, their method results in smooth 2D maps, which can be problematic for the fine-grained affordances in 3D space in our EPIC-Aff dataset. Instead, our method is able to scale up to large environments while maintaining the detail by using neural networks. Other previous works [28, 65] also use SLAM for action prediction but with addressing different problems. In those works, the action is set on the human, while the image provides context; while in our case the action/affordance is set on the environment and the user provides context. In our work, we use COLMAP to extract the relative pose between sparse frames with a filter of the dynamic objects, registering up to $93\%$ of the frames compared with the $44\%$ of the frames registered by ORBSLAM [51] on EPIC Kitchens [55]. Recently, EPIC Fields [72] registered the camera pose of the dense videos in EPIC Kitchens using neural rendering techniques. + +![](images/2b71e2d4329d2d0c542c1ca02db5fb8d058a66763b00c4642022028f60060ffe.jpg) +Take Put Open Close Wash Cut Mix Pour Throw Move Remove Dry Turn-on Turn Shake Turn-off Peel Adjust Empty Scoop + +![](images/0563947d71e92e29f68898e4bd01fb718a1b83bd81108d7ac549dc0a69ab6331.jpg) + +![](images/630b91cd8895561040e5a5760404a3134b63fbaec82bf68285444eebbdbc7794.jpg) + +![](images/c5f3cc14ff1ece5b72eb33172dfca9d5a7639554753889f2d1d737d7ee752f5f.jpg) +Figure 2. Ground truth examples. For visualization purposes, we show a single label of the affordable action on its location, although these are overlapped for the same sample. The food in the bowl affords taking or mixing, while the cutting board on the left affords putting, cutting, moving and peeling. + +![](images/d8bbe056cd7fbd87a68fb10d1bfbdb453f3305c1a4fe50f0c13d3eee92b8810e.jpg) + +![](images/5bffa2bf744b75b1d4ef81b853fbc6edd32e21a7d3f1a643f9c4ca7813d5affa.jpg) + +![](images/efbf17f15c561d671f1ea3c0c87c4fad92d3a17a4fdea81bbf8dea99ae6f97c4.jpg) + +![](images/333df629d9556865f9831cd1eb20bc2cbc1c9befa460c18c73f8a5b67d812689.jpg) + +![](images/63ab3a6104dc2c6138696d952a8e1888a3b4a5f4243535e39e0e34a37e71b505.jpg) + +![](images/e58f56ecea4a9ef86031ac652507688f6adb6bd71bb4f67309b7be09d26dc638.jpg) + +![](images/827f4cec3f7e365dd8ca79ba609420c2c20cfffd856dba78c1c816b3af35ac04.jpg) + +![](images/e2010cf343f1d5a3e12ee1a40839d58780a6bc0f48c6b2c59c9851c3571dc2cd.jpg) + +# 3.1. Affordance datasets + +Following our motivation, we conduct a study along the visual affordance datasets shown in Table 1. The ungrounded datasets are subjected to the annotator's consideration and required to draw pixel-wise semantic mask to each object part [58, 53, 14, 76, 46] or additional sensors [35, 9], decreasing the object variability and limiting the scalability due to the annotation costs. The UMD dataset contains a semantic affordance map for objects in isolated conditions and with low variability, which prevents generalisation [53]. The IIT-Aff dataset [58] provides the most comprehensive annotations designed for use in robotics, including multiple objects in a single image. The ADE-Aff dataset [14], built on top of ADE20K scenes, examines the social acceptability of actions about context but is limited to only three affordance classes. The AGD20k [46] dataset includes the largest number of categories and actions by transferring from an exocentric to an egocentric viewpoint perspective. On the other hand, grounded works learn from observing interactions on the EPIC-Kitchens sequences [15], internet demonstration videos [20] or with gaze point with eyetracking devices [21]. The annotations provided are only used for evaluation since they do not require strong supervision. However, these approaches ignore the pixel-wise precision [55] or the multi-label modality of our approach[54]. + +Based on the mentioned limitations, our novel dataset EPIC-Aff provides multi-label pixel-wise affordance annotations with the camera pose. It contributes to a diverse and + +comprehensive affordance database with the largest number of images up to date. This better captures the complexity, dynamics, multiplicity and variability of real-world environments, such as preparing a recipe in a kitchen. Finally, as our labels are automatically extracted, we enable the application of our method to other egocentric datasets. + +# 3.2. EPIC-Aff dataset + +We detail the procedure shown in Figure 3 for our grounded affordance labelling. EPIC-Aff1 is composed of 38,876 images with up to 43 different affordable actions $\mathcal{K}$ . We choose the EPIC-Kitchens as the base dataset because of its sequential and repetitive nature, which allows us to extract the 3D geometry, and because the kitchen is a scenario with multi-step and structured activities very rich in semantics. We cover all the object categories present in the EPIC-100 annotations, which constitute a wide, large and diverse knowledge base. + +From a sequence of video, we join the EPIC-100 narrations [15] and the VISOR Kitchen annotations [17] to obtain a sparse sequence of frames $S_{\mathcal{M}} = (f_1,\dots,f_N)$ with the localization of the interactions on the image, as shows Figure 4. The EPIC-100 labels [15] contains narrations formed by an action verb $\nu$ with an associated object $\mathcal{O}$ , i.e.: "add steak", for more than 100 hours of video. VISOR Kitchens [17] interpolates from sparse annotations to generate semantic masks $\mathcal{M}$ and bounding boxes $\mathcal{B}$ on the active objects. We set the centre of the interaction $x_i = \{u_i,v_i\}$ in the middle of the intersection between the hand $\mathcal{B}_h$ and the interacted object $\mathcal{B}_O$ bounding-boxes given by the narration $\nu + \mathcal{O}$ . + +Then, we apply COLMAP, a Structure-from-Motion (SfM) algorithm [69] to obtain the camera poses $T_w^c$ and a point cloud of the environment $\{X_p\}$ . In the EPIC-Kitchens [15], each kitchen is composed of multiple videos, thus, we join all the sparse frames with interactions $S_K = \{S_1 \ldots S_M\}$ to relate frames from different videos in a common 3D reference. Furthermore, we use the VISOR semantic masks to avoid including dynamic objects in the point cloud. + +Next, we employ a robust depth estimator based on a neural network $d_{NN} = f_d(\cdot)$ [63] to predict the depth of interaction points $d_{NN}(x_i)$ . Because the neural network computes the depth up-to-scale, we compute a scale correction factor per image to fit the network scale to the SfM scale: $\text{scale} = \frac{\text{median}(d^{SfM}(X_p) / \text{median}(d^{NN}(X_p))}{34}$ , where $d^{SfM}(X_p)$ is the depth of all the points $\{X_p\}$ visible from the current image and $d^{NN}(X_p)$ is the depth of the same points given by the network estimator. + +Using the predicted depth and the scale projection, we can project the interaction point $x_{i}$ in 3D space $X_{i}$ and + +use the camera pose to project into the global coordinates $X_{i}^{w} = T_{w}^{c}\cdot X_{i}^{c}$ . At this point, as shown in Figure 5 we obtain in a common reference a history of all the interactions that occurred in the kitchen $\mathcal{I}_k = \{X_1^w,X_2^w,\ldots ,X_k^w\}$ , crossgeneralizing for the different sequences. This constitutes our knowledge base that follows our hypothesis that the distribution of affordances is spatially linked to pre-determined physical spaces (i.e you only wash in the dishwasher), not only to the semantic context of a topological graph [55]. + +Then, once we store all the past interactions $\mathcal{I}_k$ with their $\mathcal{V}_k$ and $\mathcal{O}_k$ labels, we reproject them back to the new camera reference system $X_i^c = T_c^w \cdot X_i^w$ . Instead of considering all the object semantic masks as the affordance region, we centre a Gaussian distribution over each affordance-reprojected point $X_i^c$ and build an additive heatmap. Then, the affordance masks $\mathcal{M}_i^{aff}$ are defined as the regions where the heatmap is greater than 0.25. This is grounded in how humans interact with objects [54] and allows us to consider the different affordability of the object parts (a knife is only graspable with the handle). In order to generate the affordance labels $\mathcal{A} = \{(\mathcal{V}_1, \mathcal{O}_1, \mathcal{M}_1^{aff}), \dots, (\mathcal{V}_j, \mathcal{O}_j)\}$ , we select only those verbs whose associated object $\mathcal{O}_i$ was present in the VISOR annotations $\{\mathcal{M}, \mathcal{B}\}$ . With this procedure, we are grounding our dataset in the past interactions in that environment and associating multiple affordances to a single object. We show qualitative samples of the EPIC-Aff in Figure 2. + +We provide two different versions of the dataset: the easy EPIC-Aff and the complex-EPIC Aff, with 20 and 43 affordance classes respectively. There is a challenging class imbalance, as shown the Figure 6 with a significant frequency gap between the most common class (open, with a $16.0\%$ ) and the less represented (dry, with a $0.3\%$ ). In Fig. 7 we show the pixel ratio, which reflects that semantically similar or opposite actions are associated with the same space (i.e., turn-on, turn-off, adjust or cut and peel) and the importance of the multi-level approach. This shows that activity-centric zones are physical spaces where there occur multiple common activities, both synonyms or antonyms. For example, in the hob controls region we likely find (i.e., turn-on, turn-off, adjust), while on the dishwasher zone, we will encounter wash and dry. + +# 4. Multi-label segmentation and mapping + +In this section, we explain our inference procedure. First, we describe the modifications needed to obtain a multi-label segmentation model. We then show how our approach can be applied to mapping and planning tasks. + +# 4.1. Multi-label segmentation + +In this section we describe how we transform classical semantic segmentation models to a multi-label version. While there exists lots of single-label segmentation + +![](images/ac3b2f0bc50b31f507c173e665cf8f3a9f684bbff4d2d265a898abea0aa7c024.jpg) +Training: grounded affordance labelling + +![](images/b8f06551c3fed339c5435b832e7281f28c63254a108cfb0ec368a8c8c93a6c5c.jpg) +Inference: multi-label segmentation and mapping +Figure 3. Left: Pipeline with the automatic extraction of the pixel-wise labels on the EPIC-Aff dataset. We combine the EPIC-100 narration with the VISOR masks annotations to extract the interaction point. Then, using the camera pose extracted from COLMAP, we project all the interactions in a common 3D global reference. Finally, we reproject all the past interactions to each frame, and filter the affordance annotation by the objects present at the image. Right: the multi-label masks predictions from our model are leveraged to a 3D map + +![](images/c50acae228507d93c513db530669b6c50c5f30f369274a15912b6449150a40bf.jpg) +Figure 4. Using the masks provided by VISOR Kitchens, we define the intersection between the object and the hand bounding boxes as the center of the interaction. We show in yellow the bounding box of the non-interacting objects, in green the bounding box of the hands and in blue the bounding box of the interacting object. + +![](images/581b699380150b779087f14727b89c641fbbd51a0ae57da613c5be9a31f1751f.jpg) + +![](images/74cbb3fde0323f9327aa288dd465fa8e5ec45fc433d444d6406cf9bb0deda30e.jpg) +Figure 5. Historical with all the past interaction frames in that environment, where the blue dots represent the camera poses of the sparse frames from all the sequences + +![](images/d9efb3b7d88781622cb660d2ef56d4bc0a648b827cc5d17724612d905b83d50e.jpg) + +![](images/ed42c5f56e5f6183b95c0ef5026e90484623ea38f942f4f2340a930129668857.jpg) +Figure 6. Distribution of the 20 classes in the easy-EPIC Aff dataset, showing a significant class imbalance. + +![](images/c7c190c980ca71a66a11df2d7c112085e42034d4cb67362607a79a69d6892349.jpg) +Figure 7. Pixel ratio of the 20 classes in the easy-EPIC Aff dataset, where blue represents high correlation between the two classes and yellow that they do not used to concur in the same pixel. + +[11, 40, 4, 31, 30, 10] and multi-label image classification works [73, 24, 12, 45], the multi-label segmentation is a more unexplored task restricted to small domains like biomedical images [39, 5]. + +Given an input image $\mathbf{X}$ , the multi-label segmentation goal is to predict a group of categories for each pixel. Therefore, we assume that each pixel could represent multiple affordances (takeable, cuttable, washable, ..., etc.) or not belong to any category. For a total number of $\kappa$ classes we define the label $y$ for each pixel of the image as $y = [y_{1},\dots,y_{k}]$ , where $y_{k} = 1$ if the pixel contains the $\kappa$ -category label, otherwise $y_{k} = 0$ . In order to predict multi-label segmentation masks, we have evaluated two different approaches. First, we use a standard multiclass segmentation networks and evaluate three different heuristics to select multiple labels per pixel. Then, we modify the segmentation networks to output multiple binary classifiers which enable multiple labels to be active. + +![](images/601ac932e39454861c72bff39e3e3df46b7161ed7021d701ba2e4883cf4f963f.jpg) +Figure 8. Heuristics to select multiple labels from a probability vector + +For the multiclass scenario, we assume that the network output is a categorical distribution for all the classes and use the standard supervision loss, the cross-entropy. Then, we transform the probability vector $p = [p_1,\dots,p_k], \sum_{k=1}^k p_k = 1$ with three heuristics to choose the multiple winning-classes, as shows Figure 8. On the first method, we select the top- $k$ classes with the largest probability value $p_k$ . Note that we do not consider predictions with a $s_k < 1/k$ , as it occurs to $k_1, k_5$ on Figure 8. The second alternative is max- $\theta$ , which consists in selecting all the possible classes whose $p_k$ is greater than a threshold $\theta$ . Finally, the last heuristic is a dynamic $\theta_d$ threshold. We select the classes whose difference with the next class is larger than a $\theta_d$ . + +On the multi-label scenario, the model outputs $\mathcal{K}$ independent Bernoulli distributions, generating binary probabilities $p = [p_1,\dots,p_k]$ , where we assume a detection if $p_k > 0.5$ . Then, we substitute the cost function by a class-weighting Binary Cross Entropy (BCE) loss, obtaining $\mathcal{K}$ binary classifiers. One disadvantage of having independent binary classifiers is that the performance is more sensitive to the class imbalance in the dataset. To alleviate that, we use the Asymmetric (Asym) loss $\mathcal{L}_{asym}$ [66] shown in Equation 1. It combines the focal loss [71] with the margin loss [70] to reduce the contribution of easy negative samples and rejects unlabeled samples with a continuous gradient. + +$$ +A S L _ {k} = \left\{ \begin{array}{l l} \log \left(p _ {k}\right) \left(1 - p _ {k}\right) ^ {\gamma +}, & y _ {k} = 1 \\ \log \left(1 - p _ {k}\right) \left(p _ {k}\right) ^ {\gamma -}, & y _ {k} = 0 \\ N & \kappa \end{array} \right. \tag {1} +$$ + +$$ +\mathcal {L} _ {a s y m} = \frac {1}{N} \sum_ {k = 1} ^ {N} \frac {w _ {k}}{\mathcal {K}} \sum_ {k = 1} ^ {\mathcal {K}} A S L _ {k} +$$ + +For each training image, $\mathbf{X}$ with $N$ total pixels, $\mathcal{L}_{\text{asym}}$ computes a different term depending on if the $y_{k}$ binary label indicating that the class $k$ is present or not in the pixel. We apply a weighting average $w_{c}$ depending on the ratio between positive and negative samples for class $k$ to avoid the class imbalance. Following the original paper [66], we set $\gamma^{+} = 4$ and $\gamma^{-} = 1$ . + +# 4.2. Example applications + +Given that our system provides metric information of the affordance location, has information of the camera poses + +and has multi-label affordance detection, we can apply it to common spatial tasks such as mapping and navigation. + +Mapping of activity-centric zones We take the video sequence and sample unseen frames $\{f_1, \dots, f_t\}$ during training. Following the same procedure as in the extraction of labels, we reproject the inferred semantic masks on the pixels $i, j$ to its respective 3D location $x, y, z$ using the camera intrinsic $K_{int}$ , COLMAP pose $R_w^c$ , $t_w^c$ and the scaled depth $d_{i,j}$ . + +$$ +\left[ \begin{array}{l} x \\ y \\ z \end{array} \right] = d _ {i, j} \left(R _ {w} ^ {c}\right) ^ {- 1} K _ {i n t} ^ {- 1} \left[ \begin{array}{l} i \\ j \\ 1 \end{array} \right] - t _ {w} ^ {c} \tag {2} +$$ + +We accumulate in a global map the COLMAP key-points to represent the geometry and the segmented affordances regions. We do not perform any fusion on voxels or octrees, since our multi-label approach assumes that a zone can represent several predicted classes. Note that the map representation is common for all the sequences of the same environment, with the potential of linking zones across multiple episodes and learning from past interactions. + +Task-oriented navigation Finally, we introduce a task-oriented navigation experiment to show the relevance of the map representation. We use the COLMAP key-points to build an occupancy grid with the available free space. Then, the agent is initialized in a random localization and asked to navigate to perform a certain action. Once it selects the location from the semantic-metric representation, the agent decides the path planning using a $\mathbf{A}^*$ search with the Euclidean distance on the free space. We use the point cloud from COLMAP to create an occupancy grid. + +# 5. Experiments + +# 5.1. Models and metrics + +In our experiments, we modify three popular semantic segmentation architectures [33, 67, 10] and compare them with a instance segmentation model [31] plus an interaction hotspots model [54]. + +- Grounded Interaction Hotspots (GIH) [54]: We use the weights on its EPIC-Kitchen trained version to extract predictions from our images. To reduce the gap, we crop our scenes to represent a single object and compare for the same number of affordable actions $\mathcal{K}$ in the easy-EPIC Aff dataset. +- Mask-RCNN [31]: we assume an overlapping in the bounding boxes between two different instances. We do not consider the amodal Mask-RCNN versions [59, 49] which treat differently visible and occlusion + +
TakePutOpenCloseWashCutMixPourThrowMoveRemoveDryTurn-onTurnShakeTurn-offPeelAdjustEmptyScoopmIoU
GIH [54]22.121.913.810.816.325.821.223.714.016.917.212.810.320.516.610.826.19.513.925.817.5
Mask R-CNN [31]37.736.947.143.951.541.446.438.143.642.938.413.152.543.730.850.935.347.133.626.040.1
U-Net dyn-θ[67](ours) U-Net BCE0.10.75.411.922.417.122.217.311.315.921.04.514.821.116.318.412.920.60.59.613.2
(ours) U-Net Asym22.322.530.924.030.223.721.117.717.123.418.58.727.322.413.223.816.222.219.013.120.9
FPN dyn-θ [33](ours) FPN BCE14.313.713.814.721.317.918.318.732.515.715.616.615.218.922.219.519.524.35.715.717.7
(ours) FPN Asym2.42.45.610.221.713.217.717.011.513.620.04.613.822.612.515.514.417.30.89.712.9
Deep-Lab v3 dyn-θ [10](ours) Deep-Lab v3 BCE25.725.933.326.733.222.421.815.418.523.921.47.43.820.813.328.413.624.523.511.622.2
(ours) Deep-Lab v3 Asym36.334.746.142.046.842.742.237.543.341.739.621.347.443.734.345.033.846.338.033.239.8
+ +Table 2. Class-wise IoU scores on easy-EPIC Aff test set. All scores are in [%]. + +
KLD ↓SIM ↑AUC-J ↑mIoU ↑F1-Score ↑mAP ↑AP50 ↑
GIH [54]2.3810.1160.51117.529.414.215.5
Mask-RCNN [31]1.3650.1500.84140.156.559.362.6
U-Net [67] top-K2.5320.3410.8309.517.422.030.5
U-Net [67] max-θ2.5320.3410.83013.223.622.030.5
U-Net [67] dyn-θ2.5320.3410.83013.223.722.030.5
(ours) U-Net + BCE2.7180.3040.94920.934.248.244.7
(ours) U-Net + Asym0.7830.6650.85717.729.915.632.3
FPN [33] top-K2.2290.3620.8128.915.618.924.7
FPN [33] max-θ2.2290.3620.81212.421.818.924.7
FPN [33] dyn-θ2.2290.3620.81212.923.618.924.7
(ours) FPN + BCE1.6130.3650.95522.235.748.744.5
(ours) FPN + Asym0.7890.5460.95639.856.844.159.3
DeepLab-v3 [10] top-K4.9470.1920.91118.931.935.040.9
DeepLab-v3 [10] max-θ4.9470.1920.91119.232.335.040.9
DeepLab-v3 [10] dyn-θ4.9470.1920.91119.532.735.040.9
(ours) DeepLab-v3 + BCE1.2760.1790.96431.347.258.656.2
(ours) DeepLab-v3 + Asym0.6030.6680.96542.360.143.658.5
+ +Table 3. Affordance multi-label segmentation on easy-EPIC Aff test set (20 classes). Note that except the mIoU and the F1-Score, the rest of the metrics are common for the three versions of the multi-class segmentation models. + +
KLD ↓SIM ↑AUC-J ↑mIoU ↑F1-Score ↑mAP ↑AP50 ↑
Mask-RCNN2.2870.2110.75617.127.340.146.7
(ours) U-Net Asym1.1040.3200.65712.924.811.217.9
(ours) FPN Asym0.5300.6730.92128.142.924.843.4
(ours) DeepLab-v3 Asym0.5200.6700.93131.146.527.443.9
+ +Table 4. Affordance multi-label segmentation on complex-EPIC Aff test set (43 classes). + +masks, since our affordance classes $\mathcal{K}$ are not ranked in order. + +- Semantic segmentation architectures. We compare the performance of UNet [67], Feature Pyramid Networks (FPN) [33, 41] and DeepLab v-3 [10]. + +We train the segmentation models with an input resolution of $232 \times 348$ for $100k$ iterations using Adam as optimizer with weight decay of $10^{-4}$ , batch size of 8 and a initial learning rate of $10^{-4}$ , using a polynomial decay up to $10^{-6}$ . We apply random crop, color jitter, resize and flipping as data augmentation. In the same way, we train Mask-RCNN SGD and $10^{-2}$ as initial learning rate. We use a Resnet-50 backbone pre-trained onImagenet for all the models in order to perform a fair comparative. + +Following the evaluation of Nagarajan et al, [54], we report the Kullback-Leibler Divergence (KLD) [20], the Similarity metric (SIM) and the Area Under the Curve (AUC-J) [6, 32] which provide different metrics for the mismatch of + +![](images/279b9a8746f7b73c7868e49a1be15052ea28ef7f354e32144d8a2d6fa192f5b3.jpg) +Figure 9. Evolution of the mIoU for different heuristics to select multiple winning classes from a multi-class probability vector. Left: top- $\mathcal{K}$ . Center: max- $\theta$ . Right: dyn- $\theta$ . + +![](images/3d4a93d8676e517ebb70f9228c22953c4a9043ae98d9ee2aa9a301fb68b72c65.jpg) + +![](images/e1afd1898679a5a0ffa484bef9790197456c88b58b3757fa9ad0e6c3053175a1.jpg) + +the distribution of heatmaps or affordance regions considering the predictive probability. We also report metrics from segmentation literature, such as the mean Intersection over the Union (mIoU) and the F1-Score to measure the performance of the semantic segmentation, and the Average Precision (AP) AP-50 and mAP to report the performance of the detection metrics. + +# 5.2. Quantitative results + +We compare the performance of different popular architectures on the multi-label affordance segmentation task in Table 3 on the easy-EPIC Aff dataset. DeepLab-v3 trained with the Asymmetric loss obtains the best performance on the segmentation and saliency metrics (42.3 % mIoU 60.1 % F-1 score, 0.603 KLD, 0.668 SIM, 0.965 AUC-J). Since the backbone of the three semantic segmentation models is the same (Resnet-50), the different results are due to the configuration of the different decoders. In the dataset, since the labels represent interaction hotspots, they are not aligned with the borders of the objects and represent a more high-level zone. Thus, the atrous convolution of DeepLab enables to enlarge of the filter's field of view and better captures these regions. We show the per-class segmentation performance in terms of the IoU in Table 2. Comparing with the apparition frequency of the classes in the dataset shown in Figure 6, Mask R-CNN fails at the low-represented classes since it is not trained with the Asymmetric loss. However, it is the best architecture on the detection metrics (59.3 % mAP, 62.6 % AP50). Compared with previous works, the pre-trained version of [54] achieves inter + +![](images/b845c5ce9377392279756524b551e649c209e6a18bb566b11d4846fc09a70fc7.jpg) +Figure 10. Spatial distribution of the detected multi-label affordances for multiple time-steps + +![](images/23479c1f9d74ef7cc74b3ac63ddd69ffb2410cbba660f5615f76ce0136153287.jpg) +Figure 11. Goal oriented path-planning. In the example, at $t = 36$ we indicate the user the trajectory from the sink to the place where it used to dry the crockery. The blue points represent the steps of the path planning + +mediate results on the segmentation metrics (17.5% mIoU, 29.4% F-1 score) but low on the AP scores. + +The results in Figure 9 show the impact of the hyperparameters when adapting the multi-class models. The top- $\mathcal{K} = 1$ represents the classical multi-label case. The results show how its performance is far from the multi-label versions, supporting the need for specific architectural changes for this scenario. In Figure 9 left, when we increase the number of winning classes, the performance decreases by introducing too many false positives. The other two heuristics achieve better performance since they better reject these outliers. For example, the dyn- $\theta$ adapts dynamically to the probability distribution shape, obtaining higher mIoU and F-1 in the three cases (see Table 3). Finally, we appreciate similar results on the complex-EPIC Aff, shown in Table 4. In this case, the overall performance decreases due to the higher number of classes and its imbalance. + +# 5.3. Mapping: metric distribution of affordances + +We show on Figure 10 qualitative results of the multi-label interaction hotspots from affordances predicted by the DeepLab-v3 Asym model. Our perception model is consistent from different view-points. For example, the microwave of the left-map in Figure 10 is detected as turn-on both at $t = 0,25,52$ . The qualitative results clearly motivate our multi-label approach: the milkshake on the right + +map affords mixing, pouring and taking, or the sink in the center map affords drying and washing. The metric conception of our approach is also relevant, since it reflects the interactions hotspots rather than highlight the complete object (for example grasping a pan only with the handle). + +# 5.4. Task-oriented navigation + +Finally, we use the spatial localization of the affordances to show a proof-of-concept "task-oriented" navigation. As we illustrate on Figure 11, we guide the agent according to the action possibilities that the environment offers to him. Therefore, we can ask our system to perform certain action, meaning to go to where the object and affordance are available. The $\mathrm{A}^*$ indicates to the agent the shortest path from its current location to the position where it took the action in the past. For example, this could guide a visually impaired person with an assistant device [29]. + +# 6. Limitations + +Our current approach presents several limitations. At the dataset extraction, we assume that the interaction occurs in the intersection between the object and the hand bounding-boxes, thus it depends on the bounding-box aligned to the actual object. This could be mitigated with a detection model for grasping points, but we wanted a simpler version for our prototype as a more convoluted approach might introduce further biases, difficult to detect. Also, the camera poses from COLMAP can be distorted by noisy-frames or dynamic objects non-suppressed by the mask. Furthermore, a real-time mapping system would require a SLAM system such as ORB-SLAM [51] which might reduce the accuracy of COLMAP. Similarly, our dataset is fully based on Kitchen sequences and it does not incorporate another environments introducing important dataset bias in the trained models. However, our automatic labeling pipeline could be easily used to extend the dataset in other scenarios. + +# 7. Conclusions + +We introduced a novel multi-label, metric and spatial-oriented perception of affordances. First, we present a + +method for extracting grounded affordances labels based on egocentric interaction videos through a common metric representation of all the past interactions in a common reference. We use this pipeline to build the most complete affordance dataset based on the classic EPIC-Kitchen dataset. This constitutes EPIC-Aff, the largest semantic segmentation dataset of affordances grounded on the human interactions. We also motivate a method for grounded affordance detection with pixel precission using multi-label predictors, which enhances the perception and the representation of the environment. Furthermore, we show that the metric representation obtained can be used to build detailed affordance maps and to guide the user to perform task-oriented navigation tasks. + +# Acknowledgements + +This work was supported by the Spanish Government (PID2021-125209OB-I00, TED2021-129410B-I00 and TED2021-131150B-I00) and the Aragon Government (DGA-T45_23R). + +# References + +[1] Yazan Abu Farha, Alexander Richard, and Juergen Gall. When will you do what?-anticipating temporal occurrences of activities. In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, pages 5343-5352, 2018. +[2] Jean-Baptiste Alayrac, Ivan Laptev, Josef Sivic, and Simon Lacoste-Julien. Joint discovery of object states and manipulation actions. In Proceedings of the IEEE International Conference on Computer Vision, pages 2127-2136, 2017. +[3] Paola Ardón, Éric Pairet, Ronald PA Petrick, Subramanian Ramamoorthy, and Katrin S Lohan. 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We present a new approach to affordance perception which enables accurate multi-label segmentation. Our approach can be used to automatically extract grounded affordances from first person videos of interactions using a 3D map of the environment providing pixel level precision for the affordance location. We use this method to build the largest and most complete dataset on affordances based on the EPIC-Kitchen dataset, EPIC-Aff, which provides interaction-grounded, multi-label, metric and spatial affordance annotations. Then, we propose a new approach to affordance segmentation based on multi-label detection which enables multiple affordances to co-exists in the same space, for example if they are associated with the same object. We present several strategies of multi-label detection using several segmentation architectures. The experimental results highlight the importance of the multi-label detection. Finally, we show how our metric representation can be exploited for build a map of interaction hotspots in spatial action-centric zones and use that representation to perform a task-oriented navigation." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 537, + 128, + 550 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 537, + 128, + 550 + ], + "spans": [ + { + "bbox": [ + 47, + 537, + 128, + 550 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 288, + 715 + ], + "type": "text", + "content": "When humans repeatedly interact in a close environment, we associate a set of affordable actions with a certain distribution of objects in a physical space. For example, we associate a pan on a stove with cooking, but the same pan on the sink with washing. A joined spatial-semantic understanding contains powerful insights to understand human behaviour. This requires a close combination of perception, mapping and navigation algorithms; with potential applications in augmented reality systems [60, 61], but also guiding a robot [19, 36] or assistive devices [68]. In the last years, the ability of deep learning models to extract high-level representations has improved the perception of autonomous agents, while egocentric vision offers a pow" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 314, + 213, + 538, + 381 + ], + "blocks": [ + { + "bbox": [ + 314, + 213, + 538, + 381 + ], + "lines": [ + { + "bbox": [ + 314, + 213, + 538, + 381 + ], + "spans": [ + { + "bbox": [ + 314, + 213, + 538, + 381 + ], + "type": "image", + "image_path": "d13ed53fd446066df79aff82af6ae9201dbf55cbde8988341704efef8a72dae7.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 385, + 545, + 418 + ], + "lines": [ + { + "bbox": [ + 305, + 385, + 545, + 418 + ], + "spans": [ + { + "bbox": [ + 305, + 385, + 545, + 418 + ], + "type": "text", + "content": "Figure 1. From a sequence of egocentric observations, our agent creates a spatial-metric multi-label representation of the affordances, enabling a task-oriented navigation." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 437, + 546, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 546, + 557 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 546, + 557 + ], + "type": "text", + "content": "erful viewpoint for modelling human-object interaction understanding. Recent advances include anticipating future actions [23, 26, 1], model the hands-object manipulation [22, 77, 27, 16], detect the change in an object state [2], identify interaction hotspots [20, 54] or create topological maps [55]. Despite the fast movements of a headset camera, egocentric perception has also contributed to the mapping and planning phases: localising the agent in a known 3D map [43], performing visual navigation [56, 62] or building third-person (allocentric) maps [7, 47]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 558, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 547, + 714 + ], + "type": "text", + "content": "Gibson's perception theory presents affordances as the potential actions that the environment offers to the agent based on its motor capabilities [25]. For example, the person can afford taking a glass, but the affordances of a soup in a pan can be mixing, emptying, scooping and pouring simultaneously. This multiplicity models better complex dynamic environments and opens the door to multi-agent collaboration with task synchronization. Although some authors have focused on more complex affordance models [50, 75], affordance perception is typically defined as a classification problem. Some authors have focused instead on grounded affordances [20], which provide a more flexible setup and are truly associated with motor capabilities, show" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5238" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 312 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 312 + ], + "type": "text", + "content": "ing improvements in action anticipation [46]. However, most learning approaches in affordance perception consider the problem ungrounded to the agent interaction with the object, requiring previous annotations of each affordance occurrence [53, 58, 48, 19, 8, 57]. While ungrounded methods have the advantage of providing pixel-wise precision, which we call metric understanding of the scene, many grounded approaches rely on full image classification losing any metric meaning. In this paper, we propose a grounded approach with pixel-wise precision, which enables detailed metric understanding while maintaining the flexibility of grounded methods and that can be used as prior information for more complex affordance models [75]. Close to our proposal is the work of Nagarajan et al. [54], which presented a grounded approach for extracting interaction hotspots by directly observing videos. Similar to other previous works, the hotspots are modelled as a single available affordance. Instead, we propose to consider the multiplicity of affordances for a single object or spatial zone through multi-label pixel-wise predictions." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 312, + 289, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 312, + 289, + 552 + ], + "spans": [ + { + "bbox": [ + 47, + 312, + 289, + 552 + ], + "type": "text", + "content": "We build a pipeline to automatically collect multi-label pixel-wise annotations from real-world interactions using a temporal, spatial and semantic representation of the environment. We use this method with the EPIC Kitchens videos [15] to build a dataset of grounded affordances (EPIC-Aff), which to the author's knowledge, constitute the largest dataset in affordance segmentation up to date. We then adapt several segmentation architectures to the multi-label paradigm to extract more diverse information from the scene based on the assumption that the same object may have multiple affordances available. Using a mapping approach we extract the multi-label affordance segmentation to build a map that spatially links activity-centric zones as shows Figure 1, allowing a metric representation of the environmental affordances and goal-directed navigation tasks. Finally, we perform a quantitative evaluation of the extension from common architectures to the multi-label paradigm and we show mapping and planning applications of our approach, that can be used for assistive devices or in robotic scenarios." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 566, + 136, + 578 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 566, + 136, + 578 + ], + "spans": [ + { + "bbox": [ + 47, + 566, + 136, + 578 + ], + "type": "text", + "content": "2. Related works" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 586, + 204, + 598 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 204, + 598 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 204, + 598 + ], + "type": "text", + "content": "2.1. Learning Visual Affordances" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 605, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 605, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 605, + 287, + 715 + ], + "type": "text", + "content": "Ungrounded approaches [53, 58, 48, 19, 8, 57] for affordance perception are fully supervised by manually labelled masks. Due to their similarity with semantic segmentation or object detection tasks, these works use common architectures such as an encoder-decoder [57], proposal-based detectors [19, 58, 48, 8] or Bayesian instance segmentation [52]. Concerning grounded works, Fang et al. [20] extracted a latent representation from demonstration videos or Luo et al. [46] transferred the learning from exocentric" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 547, + 205 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 205 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 205 + ], + "type": "text", + "content": "images to the egocentric perspective using only the semantic label as supervision. Nagarajan et al. [54] extracted the interaction hotspots by deriving the gradient-weighted attention maps obtained at training an action classifier on videos. Then Ego-Topo [55] built a topological graph of the scene to perform affordance classification from egocentric videos, grouping each node visually and temporally coherent frames with similar object and action distributions. This allows them to discover activity-centric zones based on their visual content and represent semantically the traversed paths with the edges of the graph." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 211, + 434, + 224 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 211, + 434, + 224 + ], + "spans": [ + { + "bbox": [ + 306, + 211, + 434, + 224 + ], + "type": "text", + "content": "2.2. Multi-label perception" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 228, + 547, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 228, + 547, + 540 + ], + "spans": [ + { + "bbox": [ + 304, + 228, + 547, + 540 + ], + "type": "text", + "content": "In the multi-label segmentation task, we assign two or more categories to a single pixel. A particular case is an amodal segmentation where the relevance of occluded parts depends on the depth order [78, 49]. The most common applications of multi-label segmentation are biomedical works, where there are multiple overlapped non-exclusive levels of tissues. Existing architectures extend a U-Net with minor changes such as a dynamic segmentation head [18], shuffle-attention mechanisms in the skip-connections [39], a combination of appearance and pose features [5] and split-attention modules [38]. The closest approach to multi-label segmentation is multi-label image recognition, where the label imbalance between positives and negatives in each binary classifier and the extraction of features from multiple objects make this task more complex [45]. Class distribution aware losses [73] such as the asymmetric loss [66], the focal loss [42] or the Multi-Label Softmax loss [24] correct the over-suppression of negative samples. On the other hand, Graph Neural Networks such as [74] deal with the feature extraction from multiple objects by creating a dynamic graph for each image that leverages the content-aware category representations. Finally, the transformer architecture extracts multiple attention maps in the different regions of interest [13, 37], guiding the multi-label classification [45] or ranking the class of the pixels considering only the categories selected by the classifier [30]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 550, + 486, + 563 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 550, + 486, + 563 + ], + "spans": [ + { + "bbox": [ + 306, + 550, + 486, + 563 + ], + "type": "text", + "content": "3. Grounded Affordance Labelling" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 715 + ], + "type": "text", + "content": "We extract automatic, interaction-grounded, multi-label pixel-wise and spatial affordance annotations from a sequence of real-world images in complex and cluttered environments, as shows Figure 2. Our multi-label segmentation approach learns all the potential options and does not reduce the perception to a single action. For example, a potato on a chopping board offers cutting, putting, peeling, removing and taking simultaneously. Current affordance segmentation works [19, 53, 58, 46, 52] assume a single-label affordance per object and lose a valuable amount of information. Although other affordance models allow for multiple predictions, these works ignore the segmentation of the inter-" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5239" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 71, + 286, + 152 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 286, + 152 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 286, + 152 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 286, + 152 + ], + "type": "table", + "html": "
DatasetYearIGPixMLCP#Obj.#Aff.#Images.
UMD [53]2017X✓XX17730,000
IIT-Aff [58]2017X✓✓X1098,835
ADE-Aff [14]2018X✓✓X150310,000
OPRA [20]2018✓✓XX-720,774
Grounded I.H [54]2018✓✓XX31201,800*
Ego-Topo [55]2020✓X✓X30475-1201,020-1,115*
PAD v2 [76]2021X✓XX723130,000
AGD20k [46]2022X✓XX503623,816
EPIC-Aff2023✓✓✓✓30420-4338,876
", + "image_path": "70be61fdd27bf5d36a8241a46defcc5c378504f19b46df6b4818d429bbac47b3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 159, + 287, + 227 + ], + "lines": [ + { + "bbox": [ + 46, + 159, + 287, + 227 + ], + "spans": [ + { + "bbox": [ + 46, + 159, + 287, + 227 + ], + "type": "text", + "content": "Table 1. Visual affordance datasets statistics. I.G: Interaction Grounded. Pix: pixel-wise annotations. ML: multi-label. CP: camera poses #Obj: Number of objects. #Aff: Number of affordances. #Img: total number of images. * The affordance labels are only for evaluation, the model is trained supervised only by action labels provided by [15]" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 255, + 287, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 255, + 287, + 410 + ], + "spans": [ + { + "bbox": [ + 46, + 255, + 287, + 410 + ], + "type": "text", + "content": "action hotspot in the image and lose the pixel-level accuracy of the segmentation models. For example, topological maps extract multiple affordances from an image [55], or action anticipation models predict a probability distribution of the different possibilities [23, 26]. Our methodology gets the best of two worlds producing multi-label metric masks, resulting in a full distribution of affordances. It enables a deeper understanding of the manipulation task such as the grasping points of the tool [3] or the evolution of the manipulation process over time[44]. Similar to previous unsupervised or weakly supervised methods [50], we extract affordance labels from weak VISOR and EPIC Kitchens annotations grounded on actual interactions." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 415, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 415, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 415, + 288, + 714 + ], + "type": "text", + "content": "We join the affordances with their 3D spatial location by extracting the camera poses. The spatial approach to affordance perception is not new for the community. Rhinehart et al. [64] associate the functionality of regions with specific spatial locations, showing that that defining an affordance based solely on semantics is insufficient due to the significant influence of the physical context. For example, a frying pan is only cookable when it is on the hob or a plate is washable when the agent is next to the dishwasher. However, their method results in smooth 2D maps, which can be problematic for the fine-grained affordances in 3D space in our EPIC-Aff dataset. Instead, our method is able to scale up to large environments while maintaining the detail by using neural networks. Other previous works [28, 65] also use SLAM for action prediction but with addressing different problems. In those works, the action is set on the human, while the image provides context; while in our case the action/affordance is set on the environment and the user provides context. In our work, we use COLMAP to extract the relative pose between sparse frames with a filter of the dynamic objects, registering up to " + }, + { + "bbox": [ + 46, + 415, + 288, + 714 + ], + "type": "inline_equation", + "content": "93\\%" + }, + { + "bbox": [ + 46, + 415, + 288, + 714 + ], + "type": "text", + "content": " of the frames compared with the " + }, + { + "bbox": [ + 46, + 415, + 288, + 714 + ], + "type": "inline_equation", + "content": "44\\%" + }, + { + "bbox": [ + 46, + 415, + 288, + 714 + ], + "type": "text", + "content": " of the frames registered by ORBSLAM [51] on EPIC Kitchens [55]. Recently, EPIC Fields [72] registered the camera pose of the dense videos in EPIC Kitchens using neural rendering techniques." + } + ] + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 309, + 85, + 386, + 140 + ], + "blocks": [ + { + "bbox": [ + 309, + 70, + 544, + 85 + ], + "lines": [ + { + "bbox": [ + 309, + 70, + 544, + 85 + ], + "spans": [ + { + "bbox": [ + 309, + 70, + 544, + 85 + ], + "type": "text", + "content": "Take Put Open Close Wash Cut Mix Pour Throw Move Remove Dry Turn-on Turn Shake Turn-off Peel Adjust Empty Scoop" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 309, + 85, + 386, + 140 + ], + "lines": [ + { + "bbox": [ + 309, + 85, + 386, + 140 + ], + "spans": [ + { + "bbox": [ + 309, + 85, + 386, + 140 + ], + "type": "image", + "image_path": "2b71e2d4329d2d0c542c1ca02db5fb8d058a66763b00c4642022028f60060ffe.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 309, + 140, + 386, + 190 + ], + "blocks": [ + { + "bbox": [ + 309, + 140, + 386, + 190 + ], + "lines": [ + { + "bbox": [ + 309, + 140, + 386, + 190 + ], + "spans": [ + { + "bbox": [ + 309, + 140, + 386, + 190 + ], + "type": "image", + "image_path": "0563947d71e92e29f68898e4bd01fb718a1b83bd81108d7ac549dc0a69ab6331.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 309, + 191, + 386, + 242 + ], + "blocks": [ + { + "bbox": [ + 309, + 191, + 386, + 242 + ], + "lines": [ + { + "bbox": [ + 309, + 191, + 386, + 242 + ], + "spans": [ + { + "bbox": [ + 309, + 191, + 386, + 242 + ], + "type": "image", + "image_path": "630b91cd8895561040e5a5760404a3134b63fbaec82bf68285444eebbdbc7794.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 309, + 242, + 386, + 293 + ], + "blocks": [ + { + "bbox": [ + 309, + 242, + 386, + 293 + ], + "lines": [ + { + "bbox": [ + 309, + 242, + 386, + 293 + ], + "spans": [ + { + "bbox": [ + 309, + 242, + 386, + 293 + ], + "type": "image", + "image_path": "c5f3cc14ff1ece5b72eb33172dfca9d5a7639554753889f2d1d737d7ee752f5f.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 295, + 545, + 350 + ], + "lines": [ + { + "bbox": [ + 305, + 295, + 545, + 350 + ], + "spans": [ + { + "bbox": [ + 305, + 295, + 545, + 350 + ], + "type": "text", + "content": "Figure 2. Ground truth examples. For visualization purposes, we show a single label of the affordable action on its location, although these are overlapped for the same sample. The food in the bowl affords taking or mixing, while the cutting board on the left affords putting, cutting, moving and peeling." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 387, + 87, + 465, + 140 + ], + "blocks": [ + { + "bbox": [ + 387, + 87, + 465, + 140 + ], + "lines": [ + { + "bbox": [ + 387, + 87, + 465, + 140 + ], + "spans": [ + { + "bbox": [ + 387, + 87, + 465, + 140 + ], + "type": "image", + "image_path": "d8bbe056cd7fbd87a68fb10d1bfbdb453f3305c1a4fe50f0c13d3eee92b8810e.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 387, + 140, + 465, + 191 + ], + "blocks": [ + { + "bbox": [ + 387, + 140, + 465, + 191 + ], + "lines": [ + { + "bbox": [ + 387, + 140, + 465, + 191 + ], + "spans": [ + { + "bbox": [ + 387, + 140, + 465, + 191 + ], + "type": "image", + "image_path": "5bffa2bf744b75b1d4ef81b853fbc6edd32e21a7d3f1a643f9c4ca7813d5affa.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 387, + 191, + 465, + 243 + ], + "blocks": [ + { + "bbox": [ + 387, + 191, + 465, + 243 + ], + "lines": [ + { + "bbox": [ + 387, + 191, + 465, + 243 + ], + "spans": [ + { + "bbox": [ + 387, + 191, + 465, + 243 + ], + "type": "image", + "image_path": "efbf17f15c561d671f1ea3c0c87c4fad92d3a17a4fdea81bbf8dea99ae6f97c4.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 387, + 243, + 465, + 293 + ], + "blocks": [ + { + "bbox": [ + 387, + 243, + 465, + 293 + ], + "lines": [ + { + "bbox": [ + 387, + 243, + 465, + 293 + ], + "spans": [ + { + "bbox": [ + 387, + 243, + 465, + 293 + ], + "type": "image", + "image_path": "333df629d9556865f9831cd1eb20bc2cbc1c9befa460c18c73f8a5b67d812689.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 466, + 87, + 543, + 140 + ], + "blocks": [ + { + "bbox": [ + 466, + 87, + 543, + 140 + ], + "lines": [ + { + "bbox": [ + 466, + 87, + 543, + 140 + ], + "spans": [ + { + "bbox": [ + 466, + 87, + 543, + 140 + ], + "type": "image", + "image_path": "63ab3a6104dc2c6138696d952a8e1888a3b4a5f4243535e39e0e34a37e71b505.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 466, + 140, + 543, + 191 + ], + "blocks": [ + { + "bbox": [ + 466, + 140, + 543, + 191 + ], + "lines": [ + { + "bbox": [ + 466, + 140, + 543, + 191 + ], + "spans": [ + { + "bbox": [ + 466, + 140, + 543, + 191 + ], + "type": "image", + "image_path": "e58f56ecea4a9ef86031ac652507688f6adb6bd71bb4f67309b7be09d26dc638.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 466, + 191, + 543, + 243 + ], + "blocks": [ + { + "bbox": [ + 466, + 191, + 543, + 243 + ], + "lines": [ + { + "bbox": [ + 466, + 191, + 543, + 243 + ], + "spans": [ + { + "bbox": [ + 466, + 191, + 543, + 243 + ], + "type": "image", + "image_path": "827f4cec3f7e365dd8ca79ba609420c2c20cfffd856dba78c1c816b3af35ac04.jpg" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_body" + } + ], + "index": 15 + }, + { + "type": "image", + "bbox": [ + 466, + 243, + 543, + 293 + ], + "blocks": [ + { + "bbox": [ + 466, + 243, + 543, + 293 + ], + "lines": [ + { + "bbox": [ + 466, + 243, + 543, + 293 + ], + "spans": [ + { + "bbox": [ + 466, + 243, + 543, + 293 + ], + "type": "image", + "image_path": "e2010cf343f1d5a3e12ee1a40839d58780a6bc0f48c6b2c59c9851c3571dc2cd.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 371, + 421, + 382 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 371, + 421, + 382 + ], + "spans": [ + { + "bbox": [ + 306, + 371, + 421, + 382 + ], + "type": "text", + "content": "3.1. Affordance datasets" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 390, + 545, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 390, + 545, + 676 + ], + "spans": [ + { + "bbox": [ + 304, + 390, + 545, + 676 + ], + "type": "text", + "content": "Following our motivation, we conduct a study along the visual affordance datasets shown in Table 1. The ungrounded datasets are subjected to the annotator's consideration and required to draw pixel-wise semantic mask to each object part [58, 53, 14, 76, 46] or additional sensors [35, 9], decreasing the object variability and limiting the scalability due to the annotation costs. The UMD dataset contains a semantic affordance map for objects in isolated conditions and with low variability, which prevents generalisation [53]. The IIT-Aff dataset [58] provides the most comprehensive annotations designed for use in robotics, including multiple objects in a single image. The ADE-Aff dataset [14], built on top of ADE20K scenes, examines the social acceptability of actions about context but is limited to only three affordance classes. The AGD20k [46] dataset includes the largest number of categories and actions by transferring from an exocentric to an egocentric viewpoint perspective. On the other hand, grounded works learn from observing interactions on the EPIC-Kitchens sequences [15], internet demonstration videos [20] or with gaze point with eyetracking devices [21]. The annotations provided are only used for evaluation since they do not require strong supervision. However, these approaches ignore the pixel-wise precision [55] or the multi-label modality of our approach[54]." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 713 + ], + "type": "text", + "content": "Based on the mentioned limitations, our novel dataset EPIC-Aff provides multi-label pixel-wise affordance annotations with the camera pose. It contributes to a diverse and" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5240" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": "comprehensive affordance database with the largest number of images up to date. This better captures the complexity, dynamics, multiplicity and variability of real-world environments, such as preparing a recipe in a kitchen. Finally, as our labels are automatically extracted, we enable the application of our method to other egocentric datasets." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 152, + 151, + 164 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 152, + 151, + 164 + ], + "spans": [ + { + "bbox": [ + 47, + 152, + 151, + 164 + ], + "type": "text", + "content": "3.2. EPIC-Aff dataset" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 171, + 287, + 290 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 171, + 287, + 290 + ], + "spans": [ + { + "bbox": [ + 46, + 171, + 287, + 290 + ], + "type": "text", + "content": "We detail the procedure shown in Figure 3 for our grounded affordance labelling. EPIC-Aff1 is composed of 38,876 images with up to 43 different affordable actions " + }, + { + "bbox": [ + 46, + 171, + 287, + 290 + ], + "type": "inline_equation", + "content": "\\mathcal{K}" + }, + { + "bbox": [ + 46, + 171, + 287, + 290 + ], + "type": "text", + "content": ". We choose the EPIC-Kitchens as the base dataset because of its sequential and repetitive nature, which allows us to extract the 3D geometry, and because the kitchen is a scenario with multi-step and structured activities very rich in semantics. We cover all the object categories present in the EPIC-100 annotations, which constitute a wide, large and diverse knowledge base." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "spans": [ + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "text", + "content": "From a sequence of video, we join the EPIC-100 narrations [15] and the VISOR Kitchen annotations [17] to obtain a sparse sequence of frames " + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "inline_equation", + "content": "S_{\\mathcal{M}} = (f_1,\\dots,f_N)" + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "text", + "content": " with the localization of the interactions on the image, as shows Figure 4. The EPIC-100 labels [15] contains narrations formed by an action verb " + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "inline_equation", + "content": "\\nu" + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "text", + "content": " with an associated object " + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{O}" + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "text", + "content": ", i.e.: \"add steak\", for more than 100 hours of video. VISOR Kitchens [17] interpolates from sparse annotations to generate semantic masks " + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{M}" + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "text", + "content": " and bounding boxes " + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{B}" + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "text", + "content": " on the active objects. We set the centre of the interaction " + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "inline_equation", + "content": "x_i = \\{u_i,v_i\\}" + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "text", + "content": " in the middle of the intersection between the hand " + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{B}_h" + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "text", + "content": " and the interacted object " + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "inline_equation", + "content": "\\mathcal{B}_O" + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "text", + "content": " bounding-boxes given by the narration " + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "inline_equation", + "content": "\\nu + \\mathcal{O}" + }, + { + "bbox": [ + 46, + 290, + 288, + 445 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 445, + 287, + 553 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 445, + 287, + 553 + ], + "spans": [ + { + "bbox": [ + 46, + 445, + 287, + 553 + ], + "type": "text", + "content": "Then, we apply COLMAP, a Structure-from-Motion (SfM) algorithm [69] to obtain the camera poses " + }, + { + "bbox": [ + 46, + 445, + 287, + 553 + ], + "type": "inline_equation", + "content": "T_w^c" + }, + { + "bbox": [ + 46, + 445, + 287, + 553 + ], + "type": "text", + "content": " and a point cloud of the environment " + }, + { + "bbox": [ + 46, + 445, + 287, + 553 + ], + "type": "inline_equation", + "content": "\\{X_p\\}" + }, + { + "bbox": [ + 46, + 445, + 287, + 553 + ], + "type": "text", + "content": ". In the EPIC-Kitchens [15], each kitchen is composed of multiple videos, thus, we join all the sparse frames with interactions " + }, + { + "bbox": [ + 46, + 445, + 287, + 553 + ], + "type": "inline_equation", + "content": "S_K = \\{S_1 \\ldots S_M\\}" + }, + { + "bbox": [ + 46, + 445, + 287, + 553 + ], + "type": "text", + "content": " to relate frames from different videos in a common 3D reference. Furthermore, we use the VISOR semantic masks to avoid including dynamic objects in the point cloud." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "spans": [ + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "text", + "content": "Next, we employ a robust depth estimator based on a neural network " + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "inline_equation", + "content": "d_{NN} = f_d(\\cdot)" + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "text", + "content": " [63] to predict the depth of interaction points " + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "inline_equation", + "content": "d_{NN}(x_i)" + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "text", + "content": ". Because the neural network computes the depth up-to-scale, we compute a scale correction factor per image to fit the network scale to the SfM scale: " + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "inline_equation", + "content": "\\text{scale} = \\frac{\\text{median}(d^{SfM}(X_p) / \\text{median}(d^{NN}(X_p))}{34}" + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "inline_equation", + "content": "d^{SfM}(X_p)" + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "text", + "content": " is the depth of all the points " + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "inline_equation", + "content": "\\{X_p\\}" + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "text", + "content": " visible from the current image and " + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "inline_equation", + "content": "d^{NN}(X_p)" + }, + { + "bbox": [ + 46, + 554, + 287, + 661 + ], + "type": "text", + "content": " is the depth of the same points given by the network estimator." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 662, + 287, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 662, + 287, + 686 + ], + "spans": [ + { + "bbox": [ + 46, + 662, + 287, + 686 + ], + "type": "text", + "content": "Using the predicted depth and the scale projection, we can project the interaction point " + }, + { + "bbox": [ + 46, + 662, + 287, + 686 + ], + "type": "inline_equation", + "content": "x_{i}" + }, + { + "bbox": [ + 46, + 662, + 287, + 686 + ], + "type": "text", + "content": " in 3D space " + }, + { + "bbox": [ + 46, + 662, + 287, + 686 + ], + "type": "inline_equation", + "content": "X_{i}" + }, + { + "bbox": [ + 46, + 662, + 287, + 686 + ], + "type": "text", + "content": " and" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 72, + 545, + 179 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 545, + 179 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 545, + 179 + ], + "type": "text", + "content": "use the camera pose to project into the global coordinates " + }, + { + "bbox": [ + 306, + 72, + 545, + 179 + ], + "type": "inline_equation", + "content": "X_{i}^{w} = T_{w}^{c}\\cdot X_{i}^{c}" + }, + { + "bbox": [ + 306, + 72, + 545, + 179 + ], + "type": "text", + "content": ". At this point, as shown in Figure 5 we obtain in a common reference a history of all the interactions that occurred in the kitchen " + }, + { + "bbox": [ + 306, + 72, + 545, + 179 + ], + "type": "inline_equation", + "content": "\\mathcal{I}_k = \\{X_1^w,X_2^w,\\ldots ,X_k^w\\}" + }, + { + "bbox": [ + 306, + 72, + 545, + 179 + ], + "type": "text", + "content": ", crossgeneralizing for the different sequences. This constitutes our knowledge base that follows our hypothesis that the distribution of affordances is spatially linked to pre-determined physical spaces (i.e you only wash in the dishwasher), not only to the semantic context of a topological graph [55]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "spans": [ + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "text", + "content": "Then, once we store all the past interactions " + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "inline_equation", + "content": "\\mathcal{I}_k" + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "text", + "content": " with their " + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "inline_equation", + "content": "\\mathcal{V}_k" + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "inline_equation", + "content": "\\mathcal{O}_k" + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "text", + "content": " labels, we reproject them back to the new camera reference system " + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "inline_equation", + "content": "X_i^c = T_c^w \\cdot X_i^w" + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "text", + "content": ". Instead of considering all the object semantic masks as the affordance region, we centre a Gaussian distribution over each affordance-reprojected point " + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "inline_equation", + "content": "X_i^c" + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "text", + "content": " and build an additive heatmap. Then, the affordance masks " + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "inline_equation", + "content": "\\mathcal{M}_i^{aff}" + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "text", + "content": " are defined as the regions where the heatmap is greater than 0.25. This is grounded in how humans interact with objects [54] and allows us to consider the different affordability of the object parts (a knife is only graspable with the handle). In order to generate the affordance labels " + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "inline_equation", + "content": "\\mathcal{A} = \\{(\\mathcal{V}_1, \\mathcal{O}_1, \\mathcal{M}_1^{aff}), \\dots, (\\mathcal{V}_j, \\mathcal{O}_j)\\}" + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "text", + "content": ", we select only those verbs whose associated object " + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "inline_equation", + "content": "\\mathcal{O}_i" + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "text", + "content": " was present in the VISOR annotations " + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{M}, \\mathcal{B}\\}" + }, + { + "bbox": [ + 305, + 180, + 546, + 396 + ], + "type": "text", + "content": ". With this procedure, we are grounding our dataset in the past interactions in that environment and associating multiple affordances to a single object. We show qualitative samples of the EPIC-Aff in Figure 2." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 396, + 545, + 576 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 396, + 545, + 576 + ], + "spans": [ + { + "bbox": [ + 305, + 396, + 545, + 576 + ], + "type": "text", + "content": "We provide two different versions of the dataset: the easy EPIC-Aff and the complex-EPIC Aff, with 20 and 43 affordance classes respectively. There is a challenging class imbalance, as shown the Figure 6 with a significant frequency gap between the most common class (open, with a " + }, + { + "bbox": [ + 305, + 396, + 545, + 576 + ], + "type": "inline_equation", + "content": "16.0\\%" + }, + { + "bbox": [ + 305, + 396, + 545, + 576 + ], + "type": "text", + "content": " ) and the less represented (dry, with a " + }, + { + "bbox": [ + 305, + 396, + 545, + 576 + ], + "type": "inline_equation", + "content": "0.3\\%" + }, + { + "bbox": [ + 305, + 396, + 545, + 576 + ], + "type": "text", + "content": "). In Fig. 7 we show the pixel ratio, which reflects that semantically similar or opposite actions are associated with the same space (i.e., turn-on, turn-off, adjust or cut and peel) and the importance of the multi-level approach. This shows that activity-centric zones are physical spaces where there occur multiple common activities, both synonyms or antonyms. For example, in the hob controls region we likely find (i.e., turn-on, turn-off, adjust), while on the dishwasher zone, we will encounter wash and dry." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 585, + 520, + 600 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 585, + 520, + 600 + ], + "spans": [ + { + "bbox": [ + 306, + 585, + 520, + 600 + ], + "type": "text", + "content": "4. Multi-label segmentation and mapping" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 605, + 545, + 654 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 605, + 545, + 654 + ], + "spans": [ + { + "bbox": [ + 305, + 605, + 545, + 654 + ], + "type": "text", + "content": "In this section, we explain our inference procedure. First, we describe the modifications needed to obtain a multi-label segmentation model. We then show how our approach can be applied to mapping and planning tasks." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 659, + 446, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 659, + 446, + 672 + ], + "spans": [ + { + "bbox": [ + 306, + 659, + 446, + 672 + ], + "type": "text", + "content": "4.1. Multi-label segmentation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 545, + 714 + ], + "type": "text", + "content": "In this section we describe how we transform classical semantic segmentation models to a multi-label version. While there exists lots of single-label segmentation" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 693, + 257, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 257, + 712 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 257, + 712 + ], + "type": "text", + "content": "1https://github.com/lmur98/epic_kitchens_ affordances" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "5241" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 89, + 286, + 208 + ], + "blocks": [ + { + "bbox": [ + 55, + 76, + 197, + 87 + ], + "lines": [ + { + "bbox": [ + 55, + 76, + 197, + 87 + ], + "spans": [ + { + "bbox": [ + 55, + 76, + 197, + 87 + ], + "type": "text", + "content": "Training: grounded affordance labelling" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 53, + 89, + 286, + 208 + ], + "lines": [ + { + "bbox": [ + 53, + 89, + 286, + 208 + ], + "spans": [ + { + "bbox": [ + 53, + 89, + 286, + 208 + ], + "type": "image", + "image_path": "ac3b2f0bc50b31f507c173e665cf8f3a9f684bbff4d2d265a898abea0aa7c024.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 299, + 89, + 545, + 208 + ], + "blocks": [ + { + "bbox": [ + 301, + 76, + 477, + 87 + ], + "lines": [ + { + "bbox": [ + 301, + 76, + 477, + 87 + ], + "spans": [ + { + "bbox": [ + 301, + 76, + 477, + 87 + ], + "type": "text", + "content": "Inference: multi-label segmentation and mapping" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 299, + 89, + 545, + 208 + ], + "lines": [ + { + "bbox": [ + 299, + 89, + 545, + 208 + ], + "spans": [ + { + "bbox": [ + 299, + 89, + 545, + 208 + ], + "type": "image", + "image_path": "b8f06551c3fed339c5435b832e7281f28c63254a108cfb0ec368a8c8c93a6c5c.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 214, + 547, + 260 + ], + "lines": [ + { + "bbox": [ + 46, + 214, + 547, + 260 + ], + "spans": [ + { + "bbox": [ + 46, + 214, + 547, + 260 + ], + "type": "text", + "content": "Figure 3. Left: Pipeline with the automatic extraction of the pixel-wise labels on the EPIC-Aff dataset. We combine the EPIC-100 narration with the VISOR masks annotations to extract the interaction point. Then, using the camera pose extracted from COLMAP, we project all the interactions in a common 3D global reference. Finally, we reproject all the past interactions to each frame, and filter the affordance annotation by the objects present at the image. Right: the multi-label masks predictions from our model are leveraged to a 3D map" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 49, + 277, + 167, + 345 + ], + "blocks": [ + { + "bbox": [ + 49, + 277, + 167, + 345 + ], + "lines": [ + { + "bbox": [ + 49, + 277, + 167, + 345 + ], + "spans": [ + { + "bbox": [ + 49, + 277, + 167, + 345 + ], + "type": "image", + "image_path": "c50acae228507d93c513db530669b6c50c5f30f369274a15912b6449150a40bf.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 346, + 287, + 401 + ], + "lines": [ + { + "bbox": [ + 46, + 346, + 287, + 401 + ], + "spans": [ + { + "bbox": [ + 46, + 346, + 287, + 401 + ], + "type": "text", + "content": "Figure 4. Using the masks provided by VISOR Kitchens, we define the intersection between the object and the hand bounding boxes as the center of the interaction. We show in yellow the bounding box of the non-interacting objects, in green the bounding box of the hands and in blue the bounding box of the interacting object." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 167, + 277, + 286, + 345 + ], + "blocks": [ + { + "bbox": [ + 167, + 277, + 286, + 345 + ], + "lines": [ + { + "bbox": [ + 167, + 277, + 286, + 345 + ], + "spans": [ + { + "bbox": [ + 167, + 277, + 286, + 345 + ], + "type": "image", + "image_path": "581b699380150b779087f14727b89c641fbbd51a0ae57da613c5be9a31f1751f.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 50, + 410, + 159, + 490 + ], + "blocks": [ + { + "bbox": [ + 50, + 410, + 159, + 490 + ], + "lines": [ + { + "bbox": [ + 50, + 410, + 159, + 490 + ], + "spans": [ + { + "bbox": [ + 50, + 410, + 159, + 490 + ], + "type": "image", + "image_path": "74cbb3fde0323f9327aa288dd465fa8e5ec45fc433d444d6406cf9bb0deda30e.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 495, + 287, + 529 + ], + "lines": [ + { + "bbox": [ + 46, + 495, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 495, + 287, + 529 + ], + "type": "text", + "content": "Figure 5. Historical with all the past interaction frames in that environment, where the blue dots represent the camera poses of the sparse frames from all the sequences" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 171, + 410, + 282, + 490 + ], + "blocks": [ + { + "bbox": [ + 171, + 410, + 282, + 490 + ], + "lines": [ + { + "bbox": [ + 171, + 410, + 282, + 490 + ], + "spans": [ + { + "bbox": [ + 171, + 410, + 282, + 490 + ], + "type": "image", + "image_path": "d9efb3b7d88781622cb660d2ef56d4bc0a648b827cc5d17724612d905b83d50e.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 48, + 539, + 285, + 654 + ], + "blocks": [ + { + "bbox": [ + 48, + 539, + 285, + 654 + ], + "lines": [ + { + "bbox": [ + 48, + 539, + 285, + 654 + ], + "spans": [ + { + "bbox": [ + 48, + 539, + 285, + 654 + ], + "type": "image", + "image_path": "ed42c5f56e5f6183b95c0ef5026e90484623ea38f942f4f2340a930129668857.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 658, + 287, + 681 + ], + "lines": [ + { + "bbox": [ + 46, + 658, + 287, + 681 + ], + "spans": [ + { + "bbox": [ + 46, + 658, + 287, + 681 + ], + "type": "text", + "content": "Figure 6. Distribution of the 20 classes in the easy-EPIC Aff dataset, showing a significant class imbalance." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 342, + 277, + 511, + 437 + ], + "blocks": [ + { + "bbox": [ + 342, + 277, + 511, + 437 + ], + "lines": [ + { + "bbox": [ + 342, + 277, + 511, + 437 + ], + "spans": [ + { + "bbox": [ + 342, + 277, + 511, + 437 + ], + "type": "image", + "image_path": "c7c190c980ca71a66a11df2d7c112085e42034d4cb67362607a79a69d6892349.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 440, + 545, + 474 + ], + "lines": [ + { + "bbox": [ + 304, + 440, + 545, + 474 + ], + "spans": [ + { + "bbox": [ + 304, + 440, + 545, + 474 + ], + "type": "text", + "content": "Figure 7. Pixel ratio of the 20 classes in the easy-EPIC Aff dataset, where blue represents high correlation between the two classes and yellow that they do not used to concur in the same pixel." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 496, + 545, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 496, + 545, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 496, + 545, + 544 + ], + "type": "text", + "content": "[11, 40, 4, 31, 30, 10] and multi-label image classification works [73, 24, 12, 45], the multi-label segmentation is a more unexplored task restricted to small domains like biomedical images [39, 5]." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": "Given an input image " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{X}" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": ", the multi-label segmentation goal is to predict a group of categories for each pixel. Therefore, we assume that each pixel could represent multiple affordances (takeable, cuttable, washable, ..., etc.) or not belong to any category. For a total number of " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " classes we define the label " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " for each pixel of the image as " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "y = [y_{1},\\dots,y_{k}]" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "y_{k} = 1" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " if the pixel contains the " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": "-category label, otherwise " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "y_{k} = 0" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": ". In order to predict multi-label segmentation masks, we have evaluated two different approaches. First, we use a standard multiclass segmentation networks and evaluate three different heuristics to select multiple labels per pixel. Then, we modify the segmentation networks to output multiple binary classifiers which enable multiple labels to be active." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5242" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 69, + 281, + 129 + ], + "blocks": [ + { + "bbox": [ + 53, + 69, + 281, + 129 + ], + "lines": [ + { + "bbox": [ + 53, + 69, + 281, + 129 + ], + "spans": [ + { + "bbox": [ + 53, + 69, + 281, + 129 + ], + "type": "image", + "image_path": "601ac932e39454861c72bff39e3e3df46b7161ed7021d701ba2e4883cf4f963f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 132, + 286, + 153 + ], + "lines": [ + { + "bbox": [ + 47, + 132, + 286, + 153 + ], + "spans": [ + { + "bbox": [ + 47, + 132, + 286, + 153 + ], + "type": "text", + "content": "Figure 8. Heuristics to select multiple labels from a probability vector" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "spans": [ + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "text", + "content": "For the multiclass scenario, we assume that the network output is a categorical distribution for all the classes and use the standard supervision loss, the cross-entropy. Then, we transform the probability vector " + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "inline_equation", + "content": "p = [p_1,\\dots,p_k], \\sum_{k=1}^k p_k = 1" + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "text", + "content": " with three heuristics to choose the multiple winning-classes, as shows Figure 8. On the first method, we select the top-" + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "text", + "content": " classes with the largest probability value " + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "inline_equation", + "content": "p_k" + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "text", + "content": ". Note that we do not consider predictions with a " + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "inline_equation", + "content": "s_k < 1/k" + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "text", + "content": ", as it occurs to " + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "inline_equation", + "content": "k_1, k_5" + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "text", + "content": " on Figure 8. The second alternative is max-" + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "text", + "content": ", which consists in selecting all the possible classes whose " + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "inline_equation", + "content": "p_k" + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "text", + "content": " is greater than a threshold " + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "text", + "content": ". Finally, the last heuristic is a dynamic " + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "inline_equation", + "content": "\\theta_d" + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "text", + "content": " threshold. We select the classes whose difference with the next class is larger than a " + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "inline_equation", + "content": "\\theta_d" + }, + { + "bbox": [ + 46, + 174, + 287, + 342 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "text", + "content": "On the multi-label scenario, the model outputs " + }, + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "inline_equation", + "content": "\\mathcal{K}" + }, + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "text", + "content": " independent Bernoulli distributions, generating binary probabilities " + }, + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "inline_equation", + "content": "p = [p_1,\\dots,p_k]" + }, + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "text", + "content": ", where we assume a detection if " + }, + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "inline_equation", + "content": "p_k > 0.5" + }, + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "text", + "content": ". Then, we substitute the cost function by a class-weighting Binary Cross Entropy (BCE) loss, obtaining " + }, + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "inline_equation", + "content": "\\mathcal{K}" + }, + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "text", + "content": " binary classifiers. One disadvantage of having independent binary classifiers is that the performance is more sensitive to the class imbalance in the dataset. To alleviate that, we use the Asymmetric (Asym) loss " + }, + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{asym}" + }, + { + "bbox": [ + 46, + 342, + 289, + 486 + ], + "type": "text", + "content": " [66] shown in Equation 1. It combines the focal loss [71] with the margin loss [70] to reduce the contribution of easy negative samples and rejects unlabeled samples with a continuous gradient." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 71, + 506, + 287, + 542 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 71, + 506, + 287, + 542 + ], + "spans": [ + { + "bbox": [ + 71, + 506, + 287, + 542 + ], + "type": "interline_equation", + "content": "A S L _ {k} = \\left\\{ \\begin{array}{l l} \\log \\left(p _ {k}\\right) \\left(1 - p _ {k}\\right) ^ {\\gamma +}, & y _ {k} = 1 \\\\ \\log \\left(1 - p _ {k}\\right) \\left(p _ {k}\\right) ^ {\\gamma -}, & y _ {k} = 0 \\\\ N & \\kappa \\end{array} \\right. \\tag {1}", + "image_path": "e1fef9745dec6f47bd25dba8902a369ba8cc86f260fe97feeca479d35f360d6e.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 72, + 534, + 203, + 567 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 72, + 534, + 203, + 567 + ], + "spans": [ + { + "bbox": [ + 72, + 534, + 203, + 567 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {a s y m} = \\frac {1}{N} \\sum_ {k = 1} ^ {N} \\frac {w _ {k}}{\\mathcal {K}} \\sum_ {k = 1} ^ {\\mathcal {K}} A S L _ {k}", + "image_path": "3e00cfd2f73b541b5c8447e82968742d46d8b70423e003101e363d541ffab7ef.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "spans": [ + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": "For each training image, " + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "inline_equation", + "content": "\\mathbf{X}" + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": " total pixels, " + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\text{asym}}" + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": " computes a different term depending on if the " + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "inline_equation", + "content": "y_{k}" + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": " binary label indicating that the class " + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": " is present or not in the pixel. We apply a weighting average " + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "inline_equation", + "content": "w_{c}" + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": " depending on the ratio between positive and negative samples for class " + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": " to avoid the class imbalance. Following the original paper [66], we set " + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "inline_equation", + "content": "\\gamma^{+} = 4" + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "inline_equation", + "content": "\\gamma^{-} = 1" + }, + { + "bbox": [ + 46, + 578, + 287, + 661 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 670, + 170, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 670, + 170, + 683 + ], + "spans": [ + { + "bbox": [ + 47, + 670, + 170, + 683 + ], + "type": "text", + "content": "4.2. Example applications" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "Given that our system provides metric information of the affordance location, has information of the camera poses" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": "and has multi-label affordance detection, we can apply it to common spatial tasks such as mapping and navigation." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "spans": [ + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "text", + "content": "Mapping of activity-centric zones We take the video sequence and sample unseen frames " + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "inline_equation", + "content": "\\{f_1, \\dots, f_t\\}" + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "text", + "content": " during training. Following the same procedure as in the extraction of labels, we reproject the inferred semantic masks on the pixels " + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "inline_equation", + "content": "i, j" + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "text", + "content": " to its respective 3D location " + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "inline_equation", + "content": "x, y, z" + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "text", + "content": " using the camera intrinsic " + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "inline_equation", + "content": "K_{int}" + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "text", + "content": ", COLMAP pose " + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "inline_equation", + "content": "R_w^c" + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "inline_equation", + "content": "t_w^c" + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "text", + "content": " and the scaled depth " + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "inline_equation", + "content": "d_{i,j}" + }, + { + "bbox": [ + 304, + 111, + 545, + 196 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 355, + 204, + 545, + 243 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 355, + 204, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 355, + 204, + 545, + 243 + ], + "type": "interline_equation", + "content": "\\left[ \\begin{array}{l} x \\\\ y \\\\ z \\end{array} \\right] = d _ {i, j} \\left(R _ {w} ^ {c}\\right) ^ {- 1} K _ {i n t} ^ {- 1} \\left[ \\begin{array}{l} i \\\\ j \\\\ 1 \\end{array} \\right] - t _ {w} ^ {c} \\tag {2}", + "image_path": "27229135dcf718c4fb7101cccdf61e7a67667417fe3063653dd6ac2972ce1621.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 247, + 545, + 344 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 247, + 545, + 344 + ], + "spans": [ + { + "bbox": [ + 304, + 247, + 545, + 344 + ], + "type": "text", + "content": "We accumulate in a global map the COLMAP key-points to represent the geometry and the segmented affordances regions. We do not perform any fusion on voxels or octrees, since our multi-label approach assumes that a zone can represent several predicted classes. Note that the map representation is common for all the sequences of the same environment, with the potential of linking zones across multiple episodes and learning from past interactions." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 359, + 545, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 359, + 545, + 479 + ], + "spans": [ + { + "bbox": [ + 304, + 359, + 545, + 479 + ], + "type": "text", + "content": "Task-oriented navigation Finally, we introduce a task-oriented navigation experiment to show the relevance of the map representation. We use the COLMAP key-points to build an occupancy grid with the available free space. Then, the agent is initialized in a random localization and asked to navigate to perform a certain action. Once it selects the location from the semantic-metric representation, the agent decides the path planning using a " + }, + { + "bbox": [ + 304, + 359, + 545, + 479 + ], + "type": "inline_equation", + "content": "\\mathbf{A}^*" + }, + { + "bbox": [ + 304, + 359, + 545, + 479 + ], + "type": "text", + "content": " search with the Euclidean distance on the free space. We use the point cloud from COLMAP to create an occupancy grid." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 491, + 388, + 503 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 491, + 388, + 503 + ], + "spans": [ + { + "bbox": [ + 306, + 491, + 388, + 503 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 510, + 421, + 521 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 510, + 421, + 521 + ], + "spans": [ + { + "bbox": [ + 306, + 510, + 421, + 521 + ], + "type": "text", + "content": "5.1. Models and metrics" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 529, + 545, + 577 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 529, + 545, + 577 + ], + "spans": [ + { + "bbox": [ + 304, + 529, + 545, + 577 + ], + "type": "text", + "content": "In our experiments, we modify three popular semantic segmentation architectures [33, 67, 10] and compare them with a instance segmentation model [31] plus an interaction hotspots model [54]." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 317, + 585, + 545, + 713 + ], + "type": "list", + "angle": 0, + "index": 19, + "blocks": [ + { + "bbox": [ + 317, + 585, + 545, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 585, + 545, + 657 + ], + "spans": [ + { + "bbox": [ + 317, + 585, + 545, + 657 + ], + "type": "text", + "content": "- Grounded Interaction Hotspots (GIH) [54]: We use the weights on its EPIC-Kitchen trained version to extract predictions from our images. To reduce the gap, we crop our scenes to represent a single object and compare for the same number of affordable actions " + }, + { + "bbox": [ + 317, + 585, + 545, + 657 + ], + "type": "inline_equation", + "content": "\\mathcal{K}" + }, + { + "bbox": [ + 317, + 585, + 545, + 657 + ], + "type": "text", + "content": " in the easy-EPIC Aff dataset." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 317, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 317, + 665, + 545, + 713 + ], + "type": "text", + "content": "- Mask-RCNN [31]: we assume an overlapping in the bounding boxes between two different instances. We do not consider the amodal Mask-RCNN versions [59, 49] which treat differently visible and occlusion" + } + ] + } + ], + "index": 18 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5243" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 48, + 70, + 547, + 191 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 547, + 191 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 547, + 191 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 547, + 191 + ], + "type": "table", + "html": "
TakePutOpenCloseWashCutMixPourThrowMoveRemoveDryTurn-onTurnShakeTurn-offPeelAdjustEmptyScoopmIoU
GIH [54]22.121.913.810.816.325.821.223.714.016.917.212.810.320.516.610.826.19.513.925.817.5
Mask R-CNN [31]37.736.947.143.951.541.446.438.143.642.938.413.152.543.730.850.935.347.133.626.040.1
U-Net dyn-θ[67](ours) U-Net BCE0.10.75.411.922.417.122.217.311.315.921.04.514.821.116.318.412.920.60.59.613.2
(ours) U-Net Asym22.322.530.924.030.223.721.117.717.123.418.58.727.322.413.223.816.222.219.013.120.9
FPN dyn-θ [33](ours) FPN BCE14.313.713.814.721.317.918.318.732.515.715.616.615.218.922.219.519.524.35.715.717.7
(ours) FPN Asym2.42.45.610.221.713.217.717.011.513.620.04.613.822.612.515.514.417.30.89.712.9
Deep-Lab v3 dyn-θ [10](ours) Deep-Lab v3 BCE25.725.933.326.733.222.421.815.418.523.921.47.43.820.813.328.413.624.523.511.622.2
(ours) Deep-Lab v3 Asym36.334.746.142.046.842.742.237.543.341.739.621.347.443.734.345.033.846.338.033.239.8
", + "image_path": "8f1b9f74c4f2a8c8786909659a18456e97ca19786879d698e148005d2a64c118.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 219, + 287, + 347 + ], + "blocks": [ + { + "bbox": [ + 151, + 191, + 441, + 201 + ], + "lines": [ + { + "bbox": [ + 151, + 191, + 441, + 201 + ], + "spans": [ + { + "bbox": [ + 151, + 191, + 441, + 201 + ], + "type": "text", + "content": "Table 2. Class-wise IoU scores on easy-EPIC Aff test set. All scores are in [%]." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 219, + 287, + 347 + ], + "lines": [ + { + "bbox": [ + 48, + 219, + 287, + 347 + ], + "spans": [ + { + "bbox": [ + 48, + 219, + 287, + 347 + ], + "type": "table", + "html": "
KLD ↓SIM ↑AUC-J ↑mIoU ↑F1-Score ↑mAP ↑AP50 ↑
GIH [54]2.3810.1160.51117.529.414.215.5
Mask-RCNN [31]1.3650.1500.84140.156.559.362.6
U-Net [67] top-K2.5320.3410.8309.517.422.030.5
U-Net [67] max-θ2.5320.3410.83013.223.622.030.5
U-Net [67] dyn-θ2.5320.3410.83013.223.722.030.5
(ours) U-Net + BCE2.7180.3040.94920.934.248.244.7
(ours) U-Net + Asym0.7830.6650.85717.729.915.632.3
FPN [33] top-K2.2290.3620.8128.915.618.924.7
FPN [33] max-θ2.2290.3620.81212.421.818.924.7
FPN [33] dyn-θ2.2290.3620.81212.923.618.924.7
(ours) FPN + BCE1.6130.3650.95522.235.748.744.5
(ours) FPN + Asym0.7890.5460.95639.856.844.159.3
DeepLab-v3 [10] top-K4.9470.1920.91118.931.935.040.9
DeepLab-v3 [10] max-θ4.9470.1920.91119.232.335.040.9
DeepLab-v3 [10] dyn-θ4.9470.1920.91119.532.735.040.9
(ours) DeepLab-v3 + BCE1.2760.1790.96431.347.258.656.2
(ours) DeepLab-v3 + Asym0.6030.6680.96542.360.143.658.5
", + "image_path": "fa390db8aa6c07f45f738f7a448e5af24afcad2922e5b6214e8dc721da16e6f0.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 47, + 347, + 287, + 392 + ], + "lines": [ + { + "bbox": [ + 47, + 347, + 287, + 392 + ], + "spans": [ + { + "bbox": [ + 47, + 347, + 287, + 392 + ], + "type": "text", + "content": "Table 3. Affordance multi-label segmentation on easy-EPIC Aff test set (20 classes). Note that except the mIoU and the F1-Score, the rest of the metrics are common for the three versions of the multi-class segmentation models." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 48, + 401, + 287, + 437 + ], + "blocks": [ + { + "bbox": [ + 48, + 401, + 287, + 437 + ], + "lines": [ + { + "bbox": [ + 48, + 401, + 287, + 437 + ], + "spans": [ + { + "bbox": [ + 48, + 401, + 287, + 437 + ], + "type": "table", + "html": "
KLD ↓SIM ↑AUC-J ↑mIoU ↑F1-Score ↑mAP ↑AP50 ↑
Mask-RCNN2.2870.2110.75617.127.340.146.7
(ours) U-Net Asym1.1040.3200.65712.924.811.217.9
(ours) FPN Asym0.5300.6730.92128.142.924.843.4
(ours) DeepLab-v3 Asym0.5200.6700.93131.146.527.443.9
", + "image_path": "3369e8640b9f1eef073ef366415847fa729314583df3be9bf27fb789f66af3b4.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 47, + 437, + 287, + 458 + ], + "lines": [ + { + "bbox": [ + 47, + 437, + 287, + 458 + ], + "spans": [ + { + "bbox": [ + 47, + 437, + 287, + 458 + ], + "type": "text", + "content": "Table 4. Affordance multi-label segmentation on complex-EPIC Aff test set (43 classes)." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 4 + }, + { + "bbox": [ + 66, + 479, + 287, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 66, + 479, + 287, + 502 + ], + "spans": [ + { + "bbox": [ + 66, + 479, + 287, + 502 + ], + "type": "text", + "content": "masks, since our affordance classes " + }, + { + "bbox": [ + 66, + 479, + 287, + 502 + ], + "type": "inline_equation", + "content": "\\mathcal{K}" + }, + { + "bbox": [ + 66, + 479, + 287, + 502 + ], + "type": "text", + "content": " are not ranked in order." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 59, + 513, + 287, + 548 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 513, + 287, + 548 + ], + "spans": [ + { + "bbox": [ + 59, + 513, + 287, + 548 + ], + "type": "text", + "content": "- Semantic segmentation architectures. We compare the performance of UNet [67], Feature Pyramid Networks (FPN) [33, 41] and DeepLab v-3 [10]." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "text", + "content": "We train the segmentation models with an input resolution of " + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "inline_equation", + "content": "232 \\times 348" + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "inline_equation", + "content": "100k" + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "text", + "content": " iterations using Adam as optimizer with weight decay of " + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "text", + "content": ", batch size of 8 and a initial learning rate of " + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "inline_equation", + "content": "10^{-4}" + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "text", + "content": ", using a polynomial decay up to " + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "inline_equation", + "content": "10^{-6}" + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "text", + "content": ". We apply random crop, color jitter, resize and flipping as data augmentation. In the same way, we train Mask-RCNN SGD and " + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "inline_equation", + "content": "10^{-2}" + }, + { + "bbox": [ + 46, + 557, + 287, + 665 + ], + "type": "text", + "content": " as initial learning rate. We use a Resnet-50 backbone pre-trained onImagenet for all the models in order to perform a fair comparative." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": "Following the evaluation of Nagarajan et al, [54], we report the Kullback-Leibler Divergence (KLD) [20], the Similarity metric (SIM) and the Area Under the Curve (AUC-J) [6, 32] which provide different metrics for the mismatch of" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 306, + 220, + 386, + 293 + ], + "blocks": [ + { + "bbox": [ + 306, + 220, + 386, + 293 + ], + "lines": [ + { + "bbox": [ + 306, + 220, + 386, + 293 + ], + "spans": [ + { + "bbox": [ + 306, + 220, + 386, + 293 + ], + "type": "image", + "image_path": "279b9a8746f7b73c7868e49a1be15052ea28ef7f354e32144d8a2d6fa192f5b3.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 297, + 545, + 331 + ], + "lines": [ + { + "bbox": [ + 305, + 297, + 545, + 331 + ], + "spans": [ + { + "bbox": [ + 305, + 297, + 545, + 331 + ], + "type": "text", + "content": "Figure 9. Evolution of the mIoU for different heuristics to select multiple winning classes from a multi-class probability vector. Left: top- " + }, + { + "bbox": [ + 305, + 297, + 545, + 331 + ], + "type": "inline_equation", + "content": "\\mathcal{K}" + }, + { + "bbox": [ + 305, + 297, + 545, + 331 + ], + "type": "text", + "content": ". Center: max-" + }, + { + "bbox": [ + 305, + 297, + 545, + 331 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 305, + 297, + 545, + 331 + ], + "type": "text", + "content": ". Right: dyn-" + }, + { + "bbox": [ + 305, + 297, + 545, + 331 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 305, + 297, + 545, + 331 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 386, + 220, + 464, + 294 + ], + "blocks": [ + { + "bbox": [ + 386, + 220, + 464, + 294 + ], + "lines": [ + { + "bbox": [ + 386, + 220, + 464, + 294 + ], + "spans": [ + { + "bbox": [ + 386, + 220, + 464, + 294 + ], + "type": "image", + "image_path": "3d4a93d8676e517ebb70f9228c22953c4a9043ae98d9ee2aa9a301fb68b72c65.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 465, + 220, + 543, + 294 + ], + "blocks": [ + { + "bbox": [ + 465, + 220, + 543, + 294 + ], + "lines": [ + { + "bbox": [ + 465, + 220, + 543, + 294 + ], + "spans": [ + { + "bbox": [ + 465, + 220, + 543, + 294 + ], + "type": "image", + "image_path": "e1afd1898679a5a0ffa484bef9790197456c88b58b3757fa9ad0e6c3053175a1.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 350, + 546, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 350, + 546, + 434 + ], + "spans": [ + { + "bbox": [ + 304, + 350, + 546, + 434 + ], + "type": "text", + "content": "the distribution of heatmaps or affordance regions considering the predictive probability. We also report metrics from segmentation literature, such as the mean Intersection over the Union (mIoU) and the F1-Score to measure the performance of the semantic segmentation, and the Average Precision (AP) AP-50 and mAP to report the performance of the detection metrics." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 443, + 422, + 456 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 443, + 422, + 456 + ], + "spans": [ + { + "bbox": [ + 306, + 443, + 422, + 456 + ], + "type": "text", + "content": "5.2. Quantitative results" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 462, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 462, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 462, + 546, + 713 + ], + "type": "text", + "content": "We compare the performance of different popular architectures on the multi-label affordance segmentation task in Table 3 on the easy-EPIC Aff dataset. DeepLab-v3 trained with the Asymmetric loss obtains the best performance on the segmentation and saliency metrics (42.3 % mIoU 60.1 % F-1 score, 0.603 KLD, 0.668 SIM, 0.965 AUC-J). Since the backbone of the three semantic segmentation models is the same (Resnet-50), the different results are due to the configuration of the different decoders. In the dataset, since the labels represent interaction hotspots, they are not aligned with the borders of the objects and represent a more high-level zone. Thus, the atrous convolution of DeepLab enables to enlarge of the filter's field of view and better captures these regions. We show the per-class segmentation performance in terms of the IoU in Table 2. Comparing with the apparition frequency of the classes in the dataset shown in Figure 6, Mask R-CNN fails at the low-represented classes since it is not trained with the Asymmetric loss. However, it is the best architecture on the detection metrics (59.3 % mAP, 62.6 % AP50). Compared with previous works, the pre-trained version of [54] achieves inter" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5244" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 59, + 71, + 537, + 187 + ], + "blocks": [ + { + "bbox": [ + 59, + 71, + 537, + 187 + ], + "lines": [ + { + "bbox": [ + 59, + 71, + 537, + 187 + ], + "spans": [ + { + "bbox": [ + 59, + 71, + 537, + 187 + ], + "type": "image", + "image_path": "b845c5ce9377392279756524b551e649c209e6a18bb566b11d4846fc09a70fc7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 128, + 189, + 465, + 201 + ], + "lines": [ + { + "bbox": [ + 128, + 189, + 465, + 201 + ], + "spans": [ + { + "bbox": [ + 128, + 189, + 465, + 201 + ], + "type": "text", + "content": "Figure 10. Spatial distribution of the detected multi-label affordances for multiple time-steps" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 50, + 217, + 286, + 334 + ], + "blocks": [ + { + "bbox": [ + 50, + 217, + 286, + 334 + ], + "lines": [ + { + "bbox": [ + 50, + 217, + 286, + 334 + ], + "spans": [ + { + "bbox": [ + 50, + 217, + 286, + 334 + ], + "type": "image", + "image_path": "23479c1f9d74ef7cc74b3ac63ddd69ffb2410cbba660f5615f76ce0136153287.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 336, + 288, + 381 + ], + "lines": [ + { + "bbox": [ + 46, + 336, + 288, + 381 + ], + "spans": [ + { + "bbox": [ + 46, + 336, + 288, + 381 + ], + "type": "text", + "content": "Figure 11. Goal oriented path-planning. In the example, at " + }, + { + "bbox": [ + 46, + 336, + 288, + 381 + ], + "type": "inline_equation", + "content": "t = 36" + }, + { + "bbox": [ + 46, + 336, + 288, + 381 + ], + "type": "text", + "content": " we indicate the user the trajectory from the sink to the place where it used to dry the crockery. The blue points represent the steps of the path planning" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 400, + 287, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 400, + 287, + 424 + ], + "spans": [ + { + "bbox": [ + 46, + 400, + 287, + 424 + ], + "type": "text", + "content": "mediate results on the segmentation metrics (17.5% mIoU, 29.4% F-1 score) but low on the AP scores." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 425, + 287, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 425, + 287, + 604 + ], + "spans": [ + { + "bbox": [ + 46, + 425, + 287, + 604 + ], + "type": "text", + "content": "The results in Figure 9 show the impact of the hyperparameters when adapting the multi-class models. The top-" + }, + { + "bbox": [ + 46, + 425, + 287, + 604 + ], + "type": "inline_equation", + "content": "\\mathcal{K} = 1" + }, + { + "bbox": [ + 46, + 425, + 287, + 604 + ], + "type": "text", + "content": " represents the classical multi-label case. The results show how its performance is far from the multi-label versions, supporting the need for specific architectural changes for this scenario. In Figure 9 left, when we increase the number of winning classes, the performance decreases by introducing too many false positives. The other two heuristics achieve better performance since they better reject these outliers. For example, the dyn-" + }, + { + "bbox": [ + 46, + 425, + 287, + 604 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 425, + 287, + 604 + ], + "type": "text", + "content": " adapts dynamically to the probability distribution shape, obtaining higher mIoU and F-1 in the three cases (see Table 3). Finally, we appreciate similar results on the complex-EPIC Aff, shown in Table 4. In this case, the overall performance decreases due to the higher number of classes and its imbalance." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 611, + 278, + 624 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 611, + 278, + 624 + ], + "spans": [ + { + "bbox": [ + 47, + 611, + 278, + 624 + ], + "type": "text", + "content": "5.3. Mapping: metric distribution of affordances" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": "We show on Figure 10 qualitative results of the multi-label interaction hotspots from affordances predicted by the DeepLab-v3 Asym model. Our perception model is consistent from different view-points. For example, the microwave of the left-map in Figure 10 is detected as turn-on both at " + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "inline_equation", + "content": "t = 0,25,52" + }, + { + "bbox": [ + 46, + 629, + 288, + 715 + ], + "type": "text", + "content": ". The qualitative results clearly motivate our multi-label approach: the milkshake on the right" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 220, + 545, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 220, + 545, + 281 + ], + "spans": [ + { + "bbox": [ + 304, + 220, + 545, + 281 + ], + "type": "text", + "content": "map affords mixing, pouring and taking, or the sink in the center map affords drying and washing. The metric conception of our approach is also relevant, since it reflects the interactions hotspots rather than highlight the complete object (for example grasping a pan only with the handle)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 287, + 446, + 300 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 287, + 446, + 300 + ], + "spans": [ + { + "bbox": [ + 305, + 287, + 446, + 300 + ], + "type": "text", + "content": "5.4. Task-oriented navigation" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 305, + 546, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 305, + 546, + 426 + ], + "spans": [ + { + "bbox": [ + 304, + 305, + 546, + 426 + ], + "type": "text", + "content": "Finally, we use the spatial localization of the affordances to show a proof-of-concept \"task-oriented\" navigation. As we illustrate on Figure 11, we guide the agent according to the action possibilities that the environment offers to him. Therefore, we can ask our system to perform certain action, meaning to go to where the object and affordance are available. The " + }, + { + "bbox": [ + 304, + 305, + 546, + 426 + ], + "type": "inline_equation", + "content": "\\mathrm{A}^*" + }, + { + "bbox": [ + 304, + 305, + 546, + 426 + ], + "type": "text", + "content": " indicates to the agent the shortest path from its current location to the position where it took the action in the past. For example, this could guide a visually impaired person with an assistant device [29]." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 436, + 382, + 449 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 436, + 382, + 449 + ], + "spans": [ + { + "bbox": [ + 305, + 436, + 382, + 449 + ], + "type": "text", + "content": "6. Limitations" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 456, + 546, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 456, + 546, + 659 + ], + "spans": [ + { + "bbox": [ + 304, + 456, + 546, + 659 + ], + "type": "text", + "content": "Our current approach presents several limitations. At the dataset extraction, we assume that the interaction occurs in the intersection between the object and the hand bounding-boxes, thus it depends on the bounding-box aligned to the actual object. This could be mitigated with a detection model for grasping points, but we wanted a simpler version for our prototype as a more convoluted approach might introduce further biases, difficult to detect. Also, the camera poses from COLMAP can be distorted by noisy-frames or dynamic objects non-suppressed by the mask. Furthermore, a real-time mapping system would require a SLAM system such as ORB-SLAM [51] which might reduce the accuracy of COLMAP. Similarly, our dataset is fully based on Kitchen sequences and it does not incorporate another environments introducing important dataset bias in the trained models. However, our automatic labeling pipeline could be easily used to extend the dataset in other scenarios." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 669, + 384, + 681 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 669, + 384, + 681 + ], + "spans": [ + { + "bbox": [ + 306, + 669, + 384, + 681 + ], + "type": "text", + "content": "7. Conclusions" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 689, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 546, + 714 + ], + "type": "text", + "content": "We introduced a novel multi-label, metric and spatial-oriented perception of affordances. First, we present a" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5245" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": "method for extracting grounded affordances labels based on egocentric interaction videos through a common metric representation of all the past interactions in a common reference. We use this pipeline to build the most complete affordance dataset based on the classic EPIC-Kitchen dataset. This constitutes EPIC-Aff, the largest semantic segmentation dataset of affordances grounded on the human interactions. We also motivate a method for grounded affordance detection with pixel precission using multi-label predictors, which enhances the perception and the representation of the environment. Furthermore, we show that the metric representation obtained can be used to build detailed affordance maps and to guide the user to perform task-oriented navigation tasks." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 252, + 149, + 266 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 252, + 149, + 266 + ], + "spans": [ + { + "bbox": [ + 47, + 252, + 149, + 266 + ], + "type": "text", + "content": "Acknowledgements" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 273, + 287, + 320 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 273, + 287, + 320 + ], + "spans": [ + { + "bbox": [ + 47, + 273, + 287, + 320 + ], + "type": "text", + "content": "This work was supported by the Spanish Government (PID2021-125209OB-I00, TED2021-129410B-I00 and TED2021-131150B-I00) and the Aragon Government (DGA-T45_23R)." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 48, + 333, + 105, + 345 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 333, + 105, + 345 + ], + "spans": [ + { + "bbox": [ + 48, + 333, + 105, + 345 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 353, + 288, + 712 + ], + "type": "list", + "angle": 0, + "index": 11, + "blocks": [ + { + "bbox": [ + 53, + 353, + 287, + 408 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 353, + 287, + 408 + ], + "spans": [ + { + "bbox": [ + 53, + 353, + 287, + 408 + ], + "type": "text", + "content": "[1] Yazan Abu Farha, Alexander Richard, and Juergen Gall. 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Current research, however, predominantly concentrates on the multi-task dense prediction setting, which overlooks the intrinsic 3D world and its multi-view consistent structures, and lacks the capability for versatile imagination. In response to these limitations, we present a novel problem setting - multi-task view synthesis (MTVS), which reinterprets multi-task prediction as a set of novel-view synthesis tasks for multiple scene properties, including RGB. To tackle the MTVS problem, we propose MuvieNeRF, a framework that incorporates both multi-task and cross-view knowledge to simultaneously synthesize multiple scene properties. MuvieNeRF integrates two key modules, the Cross-Task Attention (CTA) and Cross-View Attention (CVA) modules, enabling the efficient use of information across multiple views and tasks. Extensive evaluation on both synthetic and realistic benchmarks demonstrates that MuvieNeRF is capable of simultaneously synthesizing different scene properties with promising visual quality, even outperforming conventional discriminative models in various settings. Notably, we show that MuvieNeRF exhibits universal applicability across a range of NeRF backbones. Our code is available at https://github.com/zsh2000/MuvieNeRF.", + "bbox": [ + 76, + 301, + 473, + 662 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 696, + 209, + 710 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "When observing a given scene, human minds exhibit a remarkable capability to mentally simulate the objects within it from a novel viewpoint in a versatile manner [40]. It not only includes imagination of the colors of objects, but also extends to numerous associated scene properties such as surface orientation, semantic segmentation, and edge patterns. Prompted by this, a burgeoning interest has emerged, seeking to equip modern robotic systems with similar capabilities for handling multiple tasks. Nevertheless, contemporary research [33, 65, 66] has primarily centered on", + "bbox": [ + 75, + 722, + 468, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/2b6fb237f2ab4e594ef8cc37c31a5363d923c71275131fafe1610fb5460aa50d.jpg", + "image_caption": [ + "(a) Conventional multi-task learning setting" + ], + "image_footnote": [], + "bbox": [ + 506, + 270, + 890, + 381 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/eeb807a01b013e2da067a51a9e488a96ab6b4db5dae14c29dd4ce4918db2b20a.jpg", + "image_caption": [ + "(b) Our multi-task view synthesis pipeline", + "Figure 1. Comparison between (a) the conventional multi-task learning scheme and (b) our multi-task view synthesis setting. The conventional \"discriminative\" multi-task learning makes predictions for single images while multi-task view synthesis aims to render visualizations for multiple scene properties at novel views." + ], + "image_footnote": [], + "bbox": [ + 511, + 417, + 864, + 494 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "the multi-task dense prediction setting, which employs a conventional discriminative model to simultaneously predict multiple pixel-level scene properties using given RGB images (refer to Figure 1(a)). Yet, the methodologies arising from this context often demonstrate practical limitations, primarily due to their tendency to treat each image as a separate entity, without constructing an explicit 3D model that adheres to the principle of multi-view consistency. Even more critically, they lack the ability to \"imagine\" – they are incapable of inferring scene properties from an unseen viewpoint, as these models invariably require RGB images.", + "bbox": [ + 496, + 627, + 892, + 792 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To circumvent these constraints, we propose a novel approach that revisits multi-task learning (MTL) [5] from a synthesis perspective. This leads to a more flexible problem setting that reinterprets multi-task visual learning as a collection of novel-view synthesis problems, which we refer to as multi-task view synthesis (MTVS) (refer to Figure 1(b)). As an illustration, the task of predicting surface", + "bbox": [ + 496, + 795, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Equal contribution", + "bbox": [ + 94, + 887, + 202, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "21538", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "normals for a given image could be reframed as visualizing a three-channel \"image\" with the given pose and camera parameters. With the achievements of Neural Radiance Fields (NeRF) [32], the implicit scene representation offers an effective solution to synthesize scene properties beyond RGB [68]. Importantly, this scene representation takes multi-view geometry into account, which consequently enhances the performance of all tasks.", + "bbox": [ + 75, + 90, + 468, + 210 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Extending from [68], we make the exploration that mining multi-task knowledge can simultaneously enhance the learning of different tasks, extending beyond discriminative models [45, 66] to include synthesis models as well. Furthermore, we argue that the alignment of features across multiple reference views and the target view can reinforce cross-view consistency, thereby bolstering the implicit scene representation learning. Informed by this insight, we propose MuvieNeRF, a unified framework for the MTVS task, which incorporates Multi-task and cross-view knowledge, thus enabling the simultaneous synthesis of multiple scene properties through a shared implicit scene representation. MuvieNeRF can be applied to an arbitrary conditional NeRF architecture and features a unified decoder with two key modules: Cross-Task Attention (CTA) module, which investigates relationships among different scene properties, and Cross-View Attention (CVA) module, which aligns features across multiple views. The integration of these two modules within MuvieNeRF facilitates the efficient utilization of information from multiple views and tasks, leading to better performance across all tasks.", + "bbox": [ + 75, + 214, + 470, + 532 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To demonstrate the effectiveness of our approach, we first instantiate our MuvieNeRF with GeoNeRF [22], a state-of-the-art conditional NeRF model, and conduct comprehensive evaluations on both synthetic and real-world benchmarks. The results illustrate that MuvieNeRF is capable of solving multi-task learning in a synthesis manner, even outperforming several competitive discriminative models in different settings. Moreover, we ablate the choice of conditional NeRF backbones to illustrate the broad applicability of our framework. We further validate the individual contributions of the CVA and CTA modules by building and comparing different variants of MuvieNeRF. Finally, we demonstrate the broader applications and analysis of MuvieNeRF, such as generalization on out-of-distribution datasets.", + "bbox": [ + 75, + 535, + 468, + 761 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, our contributions are three-fold: (1) We pioneer a novel problem definition, multi-task view synthesis (MTVS), which reconsiders multi-task visual learning as a set of view synthesis tasks. The introduction of MTVS paves the way for robots to emulate human-like mental simulation capabilities by utilizing the implicit scene representation offered by Neural Radiance Fields (NeRF). (2) We present MuvieNeRF, a unified framework that employs Cross-Task Attention (CTA) and Cross-View Atten", + "bbox": [ + 75, + 763, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "tion (CVA) modules to leverage cross-view and cross-task information for the MTVS problem. (3) Comprehensive experimental evaluations demonstrate that MuvieNeRF shows promising results for MTVS, and greatly outperforms conventional discriminative models across diverse settings.", + "bbox": [ + 496, + 90, + 890, + 167 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 184, + 640, + 199 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we propose the MuvieNeRF model which leverages both multi-task and cross-view information for multi-task view synthesis. We review the most relevant work in the areas below.", + "bbox": [ + 496, + 210, + 890, + 270 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "View Synthesis aims to generate a target image with an arbitrary camera pose by referring to source images [50]. Numerous existing methods have delivered promising results in this area [2, 34, 44, 57, 63]. However, unlike these conventional approaches, MTVS endeavors to synthesize multiple scene properties, including RGB, from novel viewpoints. In pursuit of a similar goal, another group of methods seeks to render multiple annotations for novel views, following a first-reconstruct-then-render strategy [12, 13, 19, 26]. These methods typically collect or construct a 3D scene representation (e.g., mesh or point cloud) and subsequently render multiple scene properties using 3D-to-2D projection. In contrast, our work constructs an implicit 3D scene representation using a NeRF-style model based on 2D data. This approach is more computationally efficient and, importantly, our implicit representation provides an opportunity to further model task relationships, an advantage the aforementioned methods do not possess.", + "bbox": [ + 496, + 273, + 892, + 546 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Neural Radiance Fields are originally designed for synthesizing novel-view images with ray tracing and volume rendering technologies [32]. Follow-up work [3, 10, 14, 18, 27, 29, 35, 36, 38, 39, 41, 49, 56, 58] further improves the image quality, optimization, and compositionality. In addition, several approaches [6, 22, 48, 64], namely conditional NeRFs, encode the scene information to enable the conditional generalization to novel scenes, which are more aligned with our setting. Our MuvieNeRF takes the encoders from these conditional NeRFs as backbones. Some work has also paid attention to synthesizing other properties of scenes [11, 37, 53, 60, 68, 69]. Among them, SemanticNeRF [69] extends NeRF from synthesizing RGB images to additionally synthesizing semantic labels. SS-NeRF [68] further generalizes the NeRF architecture to simultaneously render RGB and different scene properties with a shared scene representation. Panoptic 3D volumetric representation [43] is introduced to jointly synthesize RGB and panoptic segmentation for in-the-wild images. Different from them, we tackle the novel MTVS task and leverage both cross-view and cross-task information.", + "bbox": [ + 496, + 549, + 892, + 867 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multi-task Learning aims to leverage shared knowledge across different tasks to achieve optimal performance on", + "bbox": [ + 500, + 869, + 890, + 901 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "21539", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "all the tasks. Recent work improves multi-task learning performance by focusing on better optimization strategies [1, 7, 8, 15, 20, 21, 28] and exploring more efficient multi-task architectures [4, 23, 47, 54].", + "bbox": [ + 75, + 90, + 468, + 151 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Cross-task Relationship is an interesting topic in multi-task learning, which aims to explore the underlying task relationships among different visual tasks [24]. Taking the task relationship into consideration, cross-stitch networks [33] adopt a learnable parameter-sharing strategy for multi-task learning. Taskonomy and its follow-up work [45, 65, 66] systematically study the internal task relationships and design the optimal multi-task learning schemes accordingly to obtain the best performance. Inspired by them, we also investigate how to better model multi-task learning but in a synthesis framework with our model-agnostic MuvieNeRF.", + "bbox": [ + 75, + 154, + 470, + 335 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 76, + 347, + 168, + 363 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we first describe our novel multi-task view synthesis problem in Section 3.1. Next, we briefly review conditional neural radiance fields (NeRFs) and volume rendering in Section 3.2. In Section 3.3, we explain the proposed MuvieNeRF (as shown in Figure 2) in detail. Finally, we discuss how we handle a more challenging setting without access to source-view annotations at test time in Section 3.4.", + "bbox": [ + 75, + 372, + 468, + 492 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Multi-task View Synthesis Problem", + "text_level": 1, + "bbox": [ + 76, + 501, + 382, + 517 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Different from conventional multi-task learning settings, our goal is to jointly synthesize multiple scene properties including RGB images from novel views. Therefore, we aim to learn a model $\\Phi$ which takes a set of $V$ source-view task annotations with camera poses as reference, and predicts the task annotations for a novel view given camera pose (Inference Setting I):", + "bbox": [ + 75, + 525, + 468, + 632 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Y} _ {T} = \\Phi \\left(\\left\\{\\left(\\mathbf {Y} _ {i}, \\mathbf {P} _ {i}\\right) \\right\\} _ {i = 1} ^ {V}, \\mathbf {P} _ {T}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 161, + 638, + 468, + 664 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\mathbf{Y}_i = [\\mathbf{x}_i, \\mathbf{y}_i^1, \\dots, \\mathbf{y}_i^K]$ denotes RGB images $\\mathbf{x}_i$ and $K$ other multi-task annotations $\\{\\mathbf{y}_i^j\\}_{j=1}^K$ in the $i^{\\text{th}}$ source view. $\\mathbf{P}_i$ is the $i^{\\text{th}}$ source camera pose, and $\\mathbf{P}_T$ is the target camera pose. During evaluation, $\\Phi$ is supposed to be generalized to novel scenes that are not seen during training.", + "bbox": [ + 76, + 672, + 468, + 753 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For the evaluation of those novel scenes, we also provide a more challenging setting lacking source-view annotations during the inference time with the assumption that the model may not get access to additional annotations other than RGB during inference (Inference Setting II):", + "bbox": [ + 75, + 753, + 468, + 829 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Y} _ {T} = \\Phi \\left(\\left\\{\\left(\\mathbf {x} _ {i}, \\mathbf {P} _ {i}\\right) \\right\\} _ {i = 1} ^ {V}, \\mathbf {P} _ {T}\\right). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 837, + 468, + 863 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "With the above two settings, Inference Setting I allows us to better evaluate the task relationships in our synthesis", + "bbox": [ + 76, + 869, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "framework in a cleaner manner, so it is the focused setting in our paper; Inference Setting II is more aligned with real practice, for which we also propose a solution which is discussed in Sections 3.4 and 4.5.", + "bbox": [ + 496, + 90, + 890, + 150 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Preliminary: Conditional Neural Radiance Fields and Volume Rendering", + "text_level": 1, + "bbox": [ + 498, + 162, + 890, + 194 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Neural radiance fields (NeRFs) [32] propose a powerful solution for implicit scene representation, and are widely used in novel view image synthesis. Given the 3D position of a point $\\mathbf{q} = (x,y,z)$ in the scene and the 2D viewing direction $\\mathbf{d} = (\\theta ,\\phi)$ , NeRFs learn a mapping function $(\\mathbf{c},\\sigma) = F(\\mathbf{q},\\mathbf{d})$ , which maps the 5D input $(\\mathbf{q},\\mathbf{d})$ to RGB color $\\mathbf{c} = (r,g,b)$ and density $\\sigma$ .", + "bbox": [ + 496, + 200, + 890, + 306 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To enhance the generalizability of NeRFs, conditional NeRFs [6, 22, 48, 64] learn a scene representation across multiple scenes. They first extract a feature volume $\\mathbf{W} = E(\\mathbf{x})$ for each input image $\\mathbf{x}$ of a scene. Next, for an arbitrary point $\\mathbf{q}$ on a camera ray with direction $\\mathbf{d}$ , they are able to retrieve the corresponding image feature on $\\mathbf{W}$ by projecting $\\mathbf{q}$ onto the image plane with known pose $\\mathbf{P}$ . We treat the above part as the conditional NeRF encoder, which returns:", + "bbox": [ + 496, + 308, + 890, + 440 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nf _ {\\text {s c e n e}} = F _ {\\text {e n c}} \\left(\\left\\{\\mathbf {x} _ {i}, \\mathbf {P} _ {i} \\right\\} _ {i = 1} ^ {V}, \\mathbf {q}\\right). \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 589, + 441, + 890, + 462 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We have $f_{\\mathrm{scene}} \\in \\mathbb{R}^{V \\times d_{\\mathrm{scene}}}$ , which contains the scene representation from $V$ views. Next, the conditional NeRFs further learn a decoder $(\\mathbf{c}, \\sigma) = F_{\\mathrm{dec}}(\\mathbf{q}, \\mathbf{d}, f_{\\mathrm{scene}})$ to predict the color and density.", + "bbox": [ + 496, + 468, + 890, + 530 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given the color and density of 3D points, NeRFs render the 2D images by running volume rendering for each pixel with ray tracing. Every time when rendering a pixel in a certain view, a ray $\\mathbf{r}(t) = \\mathbf{o} + t\\mathbf{d}$ which origins from the center $\\mathbf{o}$ of the camera plane in the direction $\\mathbf{d}$ is traced. NeRFs randomly sample $M$ points $\\{t_m\\}_{m=1}^M$ with color $\\mathbf{c}(t_m)$ and density $\\sigma(t_m)$ between the near boundary $t_n$ and far boundary $t_f$ . The RGB value of the pixel is given by:", + "bbox": [ + 496, + 531, + 890, + 652 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {C}} (\\mathbf {r}) = \\sum_ {m = 1} ^ {M} \\hat {T} (t _ {m}) \\alpha \\left(\\delta_ {m} \\sigma \\left(t _ {m}\\right)\\right) \\mathbf {c} \\left(t _ {m}\\right), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 563, + 664, + 890, + 705 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\delta_{m}$ is the distance between two consecutive sampled points $(\\delta_{m} = \\| t_{m + 1} - t_{m}\\|),\\alpha (d) = 1 - \\exp (-d)$ , and", + "bbox": [ + 496, + 717, + 890, + 750 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {T} \\left(t _ {m}\\right) = \\exp \\left(- \\sum_ {j = 1} ^ {m - 1} \\delta_ {j} \\sigma \\left(t _ {j}\\right)\\right) \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 584, + 760, + 890, + 809 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "denotes the accumulated transmittance. The same technique can be used to render an arbitrary scene property $\\mathbf{y}^j$ by:", + "bbox": [ + 496, + 820, + 890, + 849 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {Y}} ^ {j} (\\mathbf {r}) = \\sum_ {m = 1} ^ {M} \\hat {T} (t _ {m}) \\alpha \\left(\\delta_ {m} \\sigma \\left(t _ {m}\\right)\\right) \\mathbf {y} ^ {j} \\left(t _ {m}\\right). \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 555, + 862, + 890, + 904 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "21540", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/c51b74901fa9f0fdb0ba8ac351a778c51df743ed2767db8cb25f8b673f7c4277.jpg", + "image_caption": [ + "Figure 2. Model architecture. MuvieNeRF is a unified framework for multi-task view synthesis equipped with Cross-View Attention (CVA) and Cross-Task Attention (CTA) modules. It predicts multiple scene properties for arbitrary 3D coordinates with source-view annotations." + ], + "image_footnote": [], + "bbox": [ + 122, + 93, + 861, + 373 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. MuvieNeRF", + "text_level": 1, + "bbox": [ + 76, + 417, + 207, + 431 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As illustrated in Figure 2, MuvieNeRF first fetches the scene representation $f_{\\mathrm{scene}}$ from the conditional NeRF encoder, then predicts multiple scene properties $[\\mathbf{x}(\\mathbf{q}), \\mathbf{y}^{1}(\\mathbf{q}), \\dots, \\mathbf{y}^{K}(\\mathbf{q})]$ for arbitrary 3D coordinate $\\mathbf{q}$ . The final annotations are rendered by Equation 6. We explain how to predict multiple scene properties with $f_{\\mathrm{scene}}$ and source annotations $[(\\mathbf{Y}_1, \\mathbf{P}_1), \\dots, (\\mathbf{Y}_V, \\mathbf{P}_V)]$ as follows. The full detailed architecture is included in the supplementary.", + "bbox": [ + 75, + 441, + 470, + 580 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3.1 Cross-view Attention Module", + "text_level": 1, + "bbox": [ + 76, + 601, + 334, + 616 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The cross-view attention (CVA) module (Figure 2 bottom left) leverages the multi-view information for MuvieNeRF. To start, we first concatenate $f_{\\mathrm{scene}}$ with a positional embedding derived from the target ray and the source-view image plane: $f_{\\mathrm{scene}}^{\\mathrm{pos}} = [f_{\\mathrm{scene}}; \\gamma(\\theta_{n,v})]$ , where $\\gamma(\\cdot)$ is the positional encoding proposed in [32], and $\\theta_{n,v}$ is the angle between the novel camera ray $\\mathbf{r}$ and the line that connects the camera center of view $v$ and the point $\\mathbf{q}_n$ in the queried ray, which measures the similarity between the source view $v$ and the target view.", + "bbox": [ + 75, + 627, + 468, + 777 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Next, $\\alpha$ CVA modules are used to leverage the cross-view information. Concretely, in each module, we have one self-attention union followed by a multi-layer perceptron (MLP): $f_{\\mathrm{CVA}} = \\mathrm{MLP}_{\\mathrm{CVA}}(f_{\\mathrm{scene}}^{\\mathrm{pos}} + \\mathrm{MHA}(f_{\\mathrm{scene}}^{\\mathrm{pos}}, f_{\\mathrm{scene}}^{\\mathrm{pos}}))$ , where $\\mathrm{MHA}(a, b)$ denotes multi-head attention [52] with $a$ as query and $b$ as key and value.", + "bbox": [ + 75, + 779, + 468, + 869 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "After these processes, we apply $(K + 1)$ different MLPs (corresponding to $K$ vision tasks in multi-task view syn", + "bbox": [ + 75, + 869, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "thesis plus the RGB synthesis task) to broadcast the shared feature, leading to the $(K + 1)$ -branch feature $f_{\\mathrm{task}} \\in \\mathbb{R}^{(K + 1) \\times V \\times d_{\\mathrm{task}}}$ .", + "bbox": [ + 498, + 419, + 892, + 463 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3.2 Cross-task Attention Module", + "text_level": 1, + "bbox": [ + 500, + 488, + 756, + 502 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In order to simultaneously benefit all the downstream tasks, we propose a novel cross-task attention (CTA) module (Figure 2 bottom right) to facilitate knowledge sharing and information flow among all the tasks. The CTA module has two attention components with shared learnable task prompts [62], $p_t \\in \\mathbb{R}^{(K + 1) \\times d_t}$ , where $d_t$ is the dimension of task prompts. The first attention component applies cross-attention between features from each branch and the task prompts $f_{\\mathrm{stage1}} = f_{\\mathrm{task}} + \\mathrm{MHA}(f_{\\mathrm{task}}, p_t)$ . In this stage, we run $K$ MHA individually for each task branch with the shared task prompts. After the cross-attention, we further concatenate $f_{\\mathrm{stage1}}^j$ for task $T_j$ and the corresponding task prompt $p_t^j$ to obtain $f_{\\mathrm{stage1'}}$ .", + "bbox": [ + 496, + 513, + 890, + 714 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Next, we apply the second component to use $\\beta$ self-attention modules for all the branches jointly to leverage the cross-task features. The final feature representation is obtained by: $f_{\\mathrm{stage2}} = \\mathrm{MLP}_{\\mathrm{CTA}}(f_{\\mathrm{stage1'}} + \\mathrm{MHA}(f_{\\mathrm{stage1}}, f_{\\mathrm{stage1'}}))$ .", + "bbox": [ + 496, + 714, + 890, + 791 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Finally, to predict the task annotations of the target view, we adopt the formulation of GeoNeRF [22]. The prediction $\\hat{\\mathbf{y}}^j$ of task $T_{j}$ on the target view is the weighted sum of the source views:", + "bbox": [ + 496, + 791, + 890, + 849 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {y}} ^ {j} = \\sum_ {i = 1} ^ {V} \\mathbf {w} [ j, i ] \\cdot \\mathbf {y} [ j, i ], \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 609, + 862, + 890, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "21541", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/0138ef30853d13474e4a2f89dc323027d2f317ff88d0b792d236ba16df739424.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Evaluation TypeTraining scene evaluationTesting scene evaluation
TaskRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)RGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
ReplicaHeuristic29.600.02720.04820.02140.00490.932520.860.03950.05150.04710.00970.8543
Semantic-NeRF33.600.02110.04030.01280.00370.950727.080.02210.04180.02120.00550.9417
SS-NeRF33.760.02120.03830.01160.00350.953327.220.02240.04050.01960.00530.9483
MuvieNeRF34.920.01930.03450.01000.00340.958228.550.02010.04080.01620.00510.9563
SceneNet RGB-DHeuristic22.660.0496-0.05210.00930.868722.020.0394-0.05250.01240.8917
Semantic-NeRF28.290.0248-0.02120.00500.915228.850.0186-0.01980.00510.9417
SS-NeRF28.930.0244-0.02160.00500.917529.180.0182-0.01970.00520.9510
MuvieNeRF29.290.0237-0.02070.00490.919029.560.0173-0.01890.00500.9556
", + "bbox": [ + 81, + 88, + 890, + 213 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1. Averaged performance of MuvieNeRF on Replica [46] and SceneNet RGB-D [30] datasets on both training scenes and testing scenes. Full results with multiple runs are provided in the supplementary, our model consistently outperforms both the single-task Semantic-NeRF baseline and multi-task SS-NeRF baseline, owing to the proposed CVA and CTA modules.", + "bbox": [ + 75, + 218, + 892, + 261 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the matrix $\\mathbf{y}$ is made of input view annotations $\\{\\mathbf{Y}_i\\}_{i=1}^V$ and $\\mathbf{w}$ is obtained by an additional MLP layer which processes $f_{\\mathrm{stage2}}$ .", + "bbox": [ + 76, + 286, + 468, + 333 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3.3 Optimization", + "text_level": 1, + "bbox": [ + 76, + 354, + 223, + 369 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For the set of $K$ tasks $\\mathcal{T} = \\{T_1, T_2, \\dots, T_K\\}$ including the RGB colors, we apply their objectives individually and the final objective is formulated as", + "bbox": [ + 75, + 378, + 468, + 425 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {M T}} = \\sum_ {T _ {j} \\in \\mathcal {T}} \\lambda_ {T _ {j}} \\mathcal {L} _ {T _ {j}}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 197, + 438, + 468, + 472 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\lambda_{T_j}$ is the weight for the corresponding task $T_{j}$ . For each task, $\\mathcal{L}_{T_j}$ is formulated as:", + "bbox": [ + 75, + 484, + 468, + 517 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {T _ {j}} = \\sum_ {\\mathbf {r} \\in \\mathcal {R}} \\mathcal {L} _ {j} \\left(\\hat {\\mathbf {y}} ^ {j} (\\mathbf {r}), \\mathbf {y} ^ {j} (\\mathbf {r})\\right), \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 171, + 530, + 468, + 561 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{y}^j (\\mathbf{r}),\\hat{\\mathbf{y}}^j (\\mathbf{r})$ are the ground-truth and prediction for a single pixel regarding task $T_{j}$ . $\\mathcal{R}$ is the set of rays $\\mathbf{r}$ for all training views. $\\mathcal{L}_j$ is chosen from $L_{1}$ loss, $L_{2}$ loss, and cross-entropy loss according to the characteristics of the tasks.", + "bbox": [ + 75, + 575, + 468, + 651 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Tackling without Source-view Annotations", + "text_level": 1, + "bbox": [ + 76, + 664, + 437, + 680 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The proposed model is based on the assumption that source-view task annotations are available during inference time. The assumption rules out the influence from inaccurate source-view task information, which sets a cleaner environment to excavate multi-task synergy in a synthesis framework for the MTVS problem. However, from the real application perspective, traditional discriminative models only take RGB images as input without any task annotations. To demonstrate that our model is able to be applied in real scenarios, we introduce the more challenging Inference Setting II formulated by Equation 2 and provide a solution by incorporating a U-Net [42] shaped module $F_{\\mathrm{UNet}}$ into our MuvieNeRF architecture. The detailed architecture of $F_{\\mathrm{UNet}}$ is shown in the supplementary.", + "bbox": [ + 75, + 688, + 470, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Conceptually, $F_{\\mathrm{UNet}}$ takes RGB images from the $V$ source views $\\{\\mathbf{x}_i\\}_{i=1}^V$ as input and produces the corresponding multi-task annotations $\\{\\tilde{\\mathbf{Y}}_i\\}_{i=1}^V$ , where $\\tilde{\\mathbf{Y}}_i = [\\tilde{\\mathbf{y}}_i^1, \\dots, \\tilde{\\mathbf{y}}_i^K]$ . Next, similar to the conditional NeRF encoder, we retrieve the corresponding multi-task annotations $\\{\\tilde{\\mathbf{Y}}_i(\\mathbf{q})\\}_{i=1}^V$ for an arbitrary point $\\mathbf{q}$ by projection.", + "bbox": [ + 498, + 286, + 890, + 377 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "During training time, $F_{\\mathrm{UNet}}$ is trained with pixel-wise task-specific losses. Concretely, for task $T_{j}$ , we have:", + "bbox": [ + 498, + 377, + 890, + 407 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {U _ {j}} = \\sum_ {\\mathbf {r} \\in \\mathcal {R}} \\sum_ {i = 1} ^ {V} \\mathcal {L} _ {j} \\left(\\tilde {\\mathbf {y}} _ {i} ^ {j} (\\mathbf {r}), \\mathbf {y} _ {i} ^ {j} (\\mathbf {r})\\right). \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 417, + 890, + 460 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The final loss becomes $\\mathcal{L}_{\\mathrm{final}} = \\sum_{T_j\\in \\mathcal{T}}\\lambda_{T_j}(\\mathcal{L}_{T_j} + \\mathcal{L}_{U_j})$ for which we take the ground-truth multi-task annotations to learn the weights during training. However, we instead use the predictions produced by $F_{\\mathrm{UNet}}$ for inference:", + "bbox": [ + 498, + 470, + 890, + 532 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {y}} ^ {j} = \\sum_ {i = 1} ^ {V} \\mathbf {w} [ j, i ] \\cdot \\tilde {\\mathbf {y}} [ j, i ]. \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 609, + 542, + 890, + 584 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experimental Evaluation", + "text_level": 1, + "bbox": [ + 500, + 595, + 735, + 613 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In this section, we start with main evaluation from Sections 4.1 to 4.3, including experimental setting, quantitative and qualitative results, and comparison with conventional discriminative multi-task models. Next, we make further investigations in Sections 4.4 and 4.5, including ablation studies and additional explorations. Finally, we discuss the limitations and future work in Section 4.6.", + "bbox": [ + 498, + 621, + 890, + 726 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental Setting", + "text_level": 1, + "bbox": [ + 500, + 736, + 700, + 752 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Model Instantiation: As illustrated in Section 3, our model can build upon arbitrary conditional NeRF encoders. For the main evaluation, we instantiate our model with state-of-the-art GeoNeRF [22]. We use $\\alpha = 4$ and $\\beta = 2$ for the number of self-attention unions in the CVA and CTA modules, respectively. We additionally show the performance with other NeRF encoders in the ablation study.", + "bbox": [ + 498, + 761, + 890, + 867 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Benchmarks: We take two benchmarks for our main evaluation. Replica [46] is a commonly-used indoor scene", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "21542", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/098551de41f3b1bca4a99d98cbbb6f85317533011f2005bd865bd13cfd052336.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
MuvieNeRFw/o SH28.260.0204-0.01710.00510.9557
MuvieNeRFw/o KP27.960.02120.04230.0181-0.9519
MuvieNeRF28.550.02010.04080.01620.00510.9563
", + "bbox": [ + 81, + 88, + 467, + 133 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2. Additional test scene evaluation for our variants without SH (MuvieNeRFw/o SH) and KP (MuvieNeRFw/o KP) tasks on the Replica dataset. These two tasks work as a role of auxiliary tasks.", + "bbox": [ + 76, + 143, + 468, + 199 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "dataset containing high-quality photo-realistic 3D modelling of 18 scenes. Following the data acquisition method as [69], we collect 22 sequences from the scenes, each containing 50 frames at a resolution of $640 \\times 480$ . SceneNet RGB-D [30] is a large-scale photorealistic indoor scene dataset expanding from SceneNet [16]. We include 32 scenes with 40 frames of each at a resolution of $320 \\times 240$ in our evaluation. In addition to the above two datasets, we further evaluate zero-shot adaptation on four out-of-distribution datasets: LLFF [31], TartanAir [55], ScanNet [9], and BlendedMVS [59].", + "bbox": [ + 75, + 223, + 468, + 388 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Task Selection: We select six representative tasks to evaluate our method following previous multi-task learning pipelines [45, 68]. The tasks are Surface Normal Prediction (SN), Shading Estimation (SH), Edges Detection (ED), Keypoints Detection (KP), and Semantic Labeling (SL), together with RGB synthesis. For the SceneNet RGB-D dataset, we drop the SH task due to missing annotations.", + "bbox": [ + 75, + 392, + 468, + 500 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation Setup: For the Replica dataset, we divide the 22 scenes into 18, 1, and 3 for training, validation, and testing, respectively. For SceneNet RGB-D, we split 26 scenes for training, 2 for validation, and 4 for testing. For each scene, we hold out every 8 frames as testing views.", + "bbox": [ + 75, + 501, + 468, + 575 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "For these held-out views, we provide two types of evaluation: Training scene evaluation is conducted on novel views from the training scenes; Testing scene evaluation runs on novel scenes and is used to evaluate the generalization capability of the compared models.", + "bbox": [ + 75, + 577, + 468, + 654 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation Metrics: For RGB synthesis, we measure Peak Signal-to-Noise Ratio (PSNR) for evaluation. For semantic segmentation, we take mean Intersection-over-Union (mIoU). For the other tasks, we evaluate the $L_{1}$ error.", + "bbox": [ + 75, + 655, + 468, + 715 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Baselines: We consider synthesis baselines for the main evaluation. Semantic-NeRF [69] extends NeRF for the semantic segmentation task. We further extend this model in the same way for other tasks, which only considers single-task learning in a NeRF style. SS-NeRF [68] considers multi-task learning in a NeRF style, but ignores the cross-view and cross-task information. We equip both models with the same GeoNeRF backbone as our model. Following [68], we also include a Heuristic baseline which estimates the annotations of the test view by projecting the source labels from the nearest training view to the target view.", + "bbox": [ + 75, + 719, + 468, + 898 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation Details: We set the weights for the six chosen tasks as $\\lambda_{\\mathrm{RGB}} = 1$ , $\\lambda_{\\mathrm{SN}} = 1$ , $\\lambda_{\\mathrm{SL}} = 0.04$ , $\\lambda_{\\mathrm{SH}} = 0.1$ , $\\lambda_{\\mathrm{KP}} = 2$ , and $\\lambda_{\\mathrm{ED}} = 0.4$ based on empirical observations. We use the Adam [25] optimizer with an initial learning rate of $5 \\times 10^{-4}$ and set $\\beta_{1} = 0.9$ , $\\beta_{2} = 0.999$ . During training, each iteration contains a batch size of 1,024 rays randomly sampled from all training scenes.", + "bbox": [ + 496, + 90, + 890, + 196 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "More details about our encoder architectures, dataset processing, out-of-distribution analysis, and implementation are included in the supplementary.", + "bbox": [ + 496, + 196, + 890, + 242 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. MuvieNeRF Is Capable of Solving MTVS", + "text_level": 1, + "bbox": [ + 498, + 251, + 854, + 268 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In Table 1, we present the average results derived from the held-out views across both the training and testing scenes. The key observations are, firstly, it is clear that our problem statement is non-trivial as evidenced by the notably inferior performance exhibited by the simple heuristic baseline when compared to the other models. Secondly, SS-NeRF surpasses Semantic-NeRF on average, indicating the contribution of multi-task learning. Lastly, our model consistently outperforms all the baselines, reaffirming that cross-view and cross-task information are invariably beneficial within our framework.", + "bbox": [ + 496, + 275, + 890, + 440 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Interestingly, we note that MuvieNeRF exhibits a performance closely comparable to the two NeRF baselines on novel scenes for the KP and SH tasks. To decipher the underlying reason, we carry out an additional evaluation on two variants of our model without the two tasks, $\\mathrm{MuvieNEF_{w / oKP}}$ and $\\mathrm{MuvieNEF_{w / oSH}}$ , on the test scenes of Replica in Table 2. Our findings indicate that the KP and SH tasks indeed enhance the learning of other tasks, serving as effective auxiliary tasks. This conclusion aligns with previous studies on traditional multi-task learning models as reported by [45].", + "bbox": [ + 496, + 441, + 890, + 608 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Figure 3 showcases a comparative analysis of the qualitative results. It is evident that our predictions supersede those of other baselines in terms of precision and clarity. This superior performance can be attributed to the additional information provided by shared cross-view and cross-task knowledge, which proves beneficial for the target tasks.", + "bbox": [ + 496, + 608, + 890, + 699 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. MuvieNeRF Beats Discriminative Models", + "text_level": 1, + "bbox": [ + 498, + 708, + 852, + 723 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Although conventional discriminative models fall short in addressing the proposed MTVS problem, we have explored several hybrid settings to facilitate a comparison between our MuvieNeRF and these discriminative models.", + "bbox": [ + 496, + 731, + 890, + 792 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Hybrid Setup: We provide additional RGB images from novel views to the discriminative models under three settings with different choices of RGB images. (1) We train on ground truth (GT) pairs and evaluate on novel view RGB images generated by a NeRF (NeRF's Images (No Tuned)); (2) We additionally fine-tune the discriminative models with paired NeRF's images and corresponding GT (NeRF's Im", + "bbox": [ + 496, + 794, + 890, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "21543", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/e63b5f3657e4ae3faded5cd2249b5480dc20be7420771d8e7f977618e48b3f05.jpg", + "image_caption": [ + "Figure 3. Visual comparisons of our model and baselines on a test scene of Replica dataset [46]. Our predictions are sharper and more accurate compared with other baselines. The underlying reason is that shared cross-view and cross-task knowledge can provide additional information for the target tasks." + ], + "image_footnote": [], + "bbox": [ + 119, + 95, + 844, + 421 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/3472a97de3d75b719760504aee9b60c18eddda59fe20671ba008dc70bb8d5388.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelNeRF's Images (No Tuned)NeRF's Images (Tuned)GT Images (Upper Bound)
SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
Taskgrouping0.05680.07070.04080.00890.53610.05300.06770.04230.00900.55900.04960.06070.02980.00600.6191
MTI-Net0.05600.06360.04180.00780.54400.04860.05490.03890.00780.67530.04220.04980.02810.00500.7196
InvPT0.04790.06180.04000.00910.71390.04740.05870.03280.00740.70840.04090.04840.02820.00550.8158
Ours0.02010.04080.01620.00510.9563----------
", + "bbox": [ + 78, + 476, + 890, + 550 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/f447f07d2baf52d1ae0b699b2ed947c31f38d037a6f6105d66e1cffdb2eb441f.jpg", + "table_caption": [ + "Table 3. Comparison to the discriminative models for the test scenes on Replica [46] dataset. MuvieNeRF clearly beats all the discriminative models in all three settings, indicating that our model is more capable of both performance and generalizability." + ], + "table_footnote": [], + "table_body": "
ModelRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
MuvieNeRFw/o CTA27.550.02140.04240.01980.00560.9501
MuvieNeRFw/o CVA28.250.02060.04070.01700.00520.9557
MuvieNeRF28.550.02010.04080.01620.00510.9563
", + "bbox": [ + 81, + 603, + 467, + 650 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ages (Tuned)); (3) We evaluate on GT images from novel views as the performance upper bound (GT Images (Upper Bound)). For all the settings, we train the discriminative models on both training and testing scenes (training views only) to make sure that they get access to the same number of data as MuvieNeRF.", + "bbox": [ + 75, + 757, + 470, + 848 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Discriminative Baselines: We select three representative baselines of different architectures. Taskgrouping [45] leverages an encoder-decoder architecture with a shared", + "bbox": [ + 75, + 854, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/63a13d170ae74cfe8384bd11079163acf6a4bcff0d644e82c90d4fe5c164c38a.jpg", + "table_caption": [ + "Table 4. Ablation study with CTA and CVA modules on Replica [46] dataset. MuvieNeRF $_{\\mathrm{w/o}}$ CTA is the variant without CTA module; MuvieNeRF $_{\\mathrm{w/o}}$ CVA is the variant without CVA module. The CTA module is more crucial compared to the CVA module while combining them leads to the best performance." + ], + "table_footnote": [], + "table_body": "
BackboneRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
PixelNeRF + SS-NeRF23.210.03280.04570.03760.00740.8620
PixelNeRF + Ours24.140.03020.04200.03420.00680.8961
GNT + SS-NeRF21.510.04050.04970.04200.00960.8302
GNT + Ours22.670.03330.04550.03840.00760.8686
MVSNeRF + SS-NeRF25.270.02610.04190.02480.00610.9294
MVSNeRF + Ours25.730.02480.04080.02270.00560.9303
GeoNeRF + SS-NeRF27.220.02240.04050.01960.00530.9483
GeoNeRF + Ours28.550.02010.04080.01620.00510.9563
", + "bbox": [ + 503, + 603, + 888, + 698 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/f3eb1a948299fc8521dba79ab026adbd0c6014ba147d2f29e18d39d22851a162.jpg", + "table_caption": [ + "Table 5. Ablation study with different choices of conditional NeRF encoders. The proposed MuvieNeRF is universally beneficial to different encoders, owing to the proposed CTA and CVA modules." + ], + "table_footnote": [], + "table_body": "
ModelSN (↓)ED (↓)KP (↓)
Discriminative0.07780.03550.0086
MuvieNeRFD0.06050.02300.0074
", + "bbox": [ + 580, + 763, + 807, + 800 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 6. Results for the setting with unknown nearby-view annotations. MuvieNeRF $_D$ still outperforms the hybrid discriminative model with a similar backbone.", + "bbox": [ + 496, + 800, + 893, + 842 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "representation. MTI-Net [51] adopts a convolutional neural network backbone and enables multi-scale task interactions.", + "bbox": [ + 496, + 869, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "21544", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/edbafa83294c35aee9eddf3ecda8bba7abf80208b33b70186c7b9af2b771b289.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Evaluation TypeTraining scene evaluationTesting scene evaluation
TasksRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)RGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
ReplicaSS-NeRF33.760.02120.03830.01160.00350.953327.220.02240.04050.01960.00530.9483
MuvieNeRF34.920.01930.03450.01000.00340.958228.550.02010.04080.01620.00510.9563
SS-NeRF (Enlarged)34.200.02100.03880.01070.00350.955727.370.02260.04050.01860.00530.9498
SceneNet RGB-DSS-NeRF28.930.0244-0.02160.00500.917529.180.0182-0.01970.00520.9510
MuvieNeRF29.290.0237-0.02070.00490.919029.560.0173-0.01890.00500.9556
SS-NeRF (Enlarged)29.030.0244-0.02150.00490.918629.460.0182-0.01910.00500.9520
", + "bbox": [ + 81, + 88, + 890, + 186 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/131345b33ddb9d8458504b98ad1671f0efb3c9e943ad62c031beed9bfa9e2f28.jpg", + "table_caption": [ + "Table 7. Comparison between MuvieNeRF and an enlarged version of SS-NeRF. our model still significantly outperforms SS-NeRF (Enlarged), indicating that the good performance of MuvieNeRF is not simply achieved by a heavier decoder, and demonstrating the effectiveness of our module designs." + ], + "table_footnote": [], + "table_body": "
ModelRuntime (Per Training Iter.)Num. of Params.FLOPs
SS-NeRF1×1.21M4.57 × 1011
MuvieNeRF1.22×1.30M5.84 × 1011
", + "bbox": [ + 89, + 250, + 452, + 281 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 8. Computational cost for SS-NeRF and MuvieNeRF on Replica dataset. Our CTA and CVA modules are light-weight designs.", + "bbox": [ + 76, + 282, + 467, + 325 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "InvPT [61] takes a transformer-based architecture that encourages long-range and global context to benefit multi-task learning.", + "bbox": [ + 75, + 345, + 467, + 390 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 3 details the averaged results and Figure 3 offers a visual comparison. It is discernible that our MuvieNeRF outstrips all the discriminative models, illustrating that these models struggle to effectively tackle the MTVS problem, despite fine-tuning or utilizing GT images. We surmise that this shortcoming is rooted in the evaluation of novel scenes, wherein the generalization capability of our model noticeably outperforms that of discriminative ones.", + "bbox": [ + 75, + 391, + 467, + 512 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 522, + 228, + 537 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We consider the test scene evaluation on the Replica dataset for the following ablation and exploration sections.", + "bbox": [ + 75, + 545, + 467, + 575 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Contributions of CTA and CVA: We dissect the individual contributions of the proposed CTA and CVA modules in Table 4. An examination of the results reveals a more significant impact from the CTA module, when compared with the CVA module. We postulate that this occurs because the NeRF encoder and volume rendering have already mastered an implicit 3D representation, albeit falling short in modeling task relationships. Nevertheless, the integration of both modules yields further enhancement.", + "bbox": [ + 75, + 577, + 467, + 712 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Choice of Condition NeRF: We also ablate the conditional NeRF encoders with PixelNeRF [64], MVSNeRF [6], GNT [48], and GeoNeRF [22] in Table 5. Note that we only adopt the encoder part defined in Section 3, causing a variation in performance from the full model. Each variant under our design surpasses its respective SS-NeRF baseline, affirming the universal advantage of our proposed CTA and CVA modules across different conditional NeRF encoders.", + "bbox": [ + 75, + 715, + 467, + 835 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Effectiveness of CTA and CVA Modules: By integrating CVA and CTA modules, we concurrently increase the number of trainable parameters. To truly assess the advancements brought by the proposed CVA and CTA modules, we", + "bbox": [ + 75, + 839, + 467, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/55b7c0fcc4a495b0121d6606fd66ba53ba503cfa3ed4c87a12d663f52c192fd2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 526, + 253, + 687, + 356 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/80f6134d1a7ce8d6acc90a3db9f630d795f9a345ee436aab0dca0bdb6f07f3f1.jpg", + "image_caption": [ + "RGB" + ], + "image_footnote": [], + "bbox": [ + 524, + 357, + 687, + 458 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/05b890a09177a557c78cccaf01e88066f1f63222ca81a3bf39e75b09b92e42e7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 689, + 253, + 862, + 321 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/40122bf2468ce72e348b018a6ab7997a6426e4f24b9fd59b368b9834ae21b61b.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 689, + 321, + 862, + 354 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/b66dbefe2abb7286d05039ac8d031f7aebc7f4022e4619f000167990e102ee76.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 689, + 356, + 862, + 388 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/bea2a06bf0cd3508c765cfff5edad7db9d7e0cccc17c6a90942020af1dda942d.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 689, + 390, + 862, + 422 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/bea6f9799c883c94134f021b93efe8e2045cf32a50688c2bc5f30f2b01b4688e.jpg", + "image_caption": [ + "Discriminative MuvieNeRF ${}_{D}$ Ground Truth", + "Figure 4. Visualizations for the setting without nearby-view annotations. our MuvieNeRF $D$ markedly surpasses the discriminative baseline model [45] and can generate results closely paralleling the ground truth, indicating MuvieNeRF $D$ is capable of tackling the more challenging settings." + ], + "image_footnote": [], + "bbox": [ + 689, + 424, + 862, + 458 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "introduce an expanded version of SS-NeRF, designated as SS-NeRF (Enlarged). This variant features a doubled latent dimension, comprising 2.09M parameters and $6.18 \\times 10^{11}$ FLOPs. The outcomes, as illustrated in Table 7, confirm that MuvieNeRF's excellent performance is not simply the result of a more complex decoder, thereby highlighting the effectiveness of our module designs. Moreover, we further list the computational cost for our model and SS-NeRF in Table 8 to show that our CTA and CVA modules are indeed lightweight, but effective designs.", + "bbox": [ + 496, + 565, + 890, + 717 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Additional Explorations", + "text_level": 1, + "bbox": [ + 500, + 729, + 720, + 744 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5.1 Tackling Unknown Source-view Labels", + "text_level": 1, + "bbox": [ + 500, + 753, + 823, + 768 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this section, we apply the variant discussed in Section 3.4 to tackle the more challenging problem setting with unknown nearby-view annotations. In Table 6, we show the quantitative comparisons for this variant, MuvieNeRF $_D$ , and a hybrid baseline, Discriminative [45], which shares almost the same architecture as our discriminative module. We use pre-trained weights from Taskonomy [66] to initialize weights for both models. Limited by the computational", + "bbox": [ + 496, + 779, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "21545", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/40d2deba80684f7c3a1809aa478fd2cd11989310ad76e6db6811193a3e1f112d.jpg", + "image_caption": [ + "GeoNeRF" + ], + "image_footnote": [], + "bbox": [ + 99, + 90, + 210, + 222 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/a20cbb13c7d65fcab97d2e0fa1a187b1a4b178c06d279f94460c5de2bcdbc41d.jpg", + "image_caption": [ + "MuvieNeRF (Ours)" + ], + "image_footnote": [], + "bbox": [ + 215, + 90, + 326, + 222 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/091e080b8419f1378e0f895ab4f76ff0ed35d832aa42bd5c1de2ae7f72cdaa0d.jpg", + "image_caption": [ + "Ground Truth", + "Figure 5. An out-of-distribution comparison on BlendedMVS dataset [59] for GeoNeRF and our MuvieNeRF. Our model offers superior visual quality and preserves sharp contours. More visualizations about other OOD benchmarks are included in the supplementary." + ], + "image_footnote": [], + "bbox": [ + 331, + 90, + 444, + 222 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "constraint, we select three tasks, SN, ED, and KP with the closest relationships [45] for demonstration in this setting.", + "bbox": [ + 75, + 319, + 468, + 349 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In conjunction with the visualizations illustrated in Figure 4, it is clear that our MuvieNeRF $_D$ markedly surpasses the discriminative baseline model [45] and can generate results closely paralleling the ground truth. This observation indicates that our model is capable of tackling more challenging settings. We conjecture the reason is that the weighted sum format (Equation 11) enhances the fault tolerance of the predictions.", + "bbox": [ + 75, + 351, + 468, + 470 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "4.5.2 Out-of-distribution Generalization", + "text_level": 1, + "bbox": [ + 76, + 491, + 372, + 505 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We demonstrate how the multi-task information learned from one dataset can effectively be utilized to benefit other datasets, by performing a zero-shot adaptation on out-of-distribution datasets with our MuvieNeRF trained on Replica. This takes a step further from investigating the generalization ability of unseen testing scenes in previous sections. We consider four datasets in total: LLFF [31], TartanAir [55], ScanNet [9], and BlendedMVS [59] containing indoor, outdoor, and even object-centric scenes.", + "bbox": [ + 75, + 515, + 468, + 651 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "As an illustrative example, we showcase the comparison between the conditional NeRF backbone, GeoNeRF [22], and our MuvieNeRF for the novel-view RGB synthesis task in Table 9 and Figure 5. Evidently, our model surpasses GeoNeRF by a significant margin, offering superior visual quality and retaining sharp contours, likely a result of the edge and surface normal information absorbed during the multi-task training. These outcomes substantiate that augmenting the model with more tasks, as part of our multitask learning strategy, dramatically bolsters the generalization capability, thereby showcasing its immense potential for real-world applications.", + "bbox": [ + 75, + 652, + 468, + 833 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "4.6. Limitations and Future work", + "text_level": 1, + "bbox": [ + 76, + 844, + 336, + 859 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Limitations: One major limitation of this work is the reliance on data. MuvieNeRF requires images from dense", + "bbox": [ + 75, + 869, + 468, + 900 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/4015dc2572cc71e2effd713dbd623e86863c97f5b3c363104cad7d0f0fedad36.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelScanNetTartanAirLLFFBlendedMVS
GeoNeRF31.7126.5120.6816.27
MuvieNeRF32.7630.2122.9120.97
", + "bbox": [ + 522, + 88, + 867, + 127 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Table 9. Averaged PSNR of out-of-distribution RGB synthesis task. Our model surpasses the GeoNeRF baseline by a large margin, affirming that the inclusion of additional tasks, as part of our approach, contributes to a substantial enhancement in the model's generalization capacity.", + "bbox": [ + 498, + 130, + 890, + 200 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "views, a requirement not fulfilled by most multi-task benchmarks. To circumvent this limitation, techniques that allow NeRF to learn from sparse views [35, 67] could be adopted.", + "bbox": [ + 498, + 226, + 890, + 272 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Task Relationships: As elaborated in Section 4.2, SH and KP function as auxiliary tasks within the system. A deeper exploration into the relationships between tasks and the corresponding geometric underpinnings within our synthesis framework offers intriguing avenues for future research.", + "bbox": [ + 498, + 277, + 890, + 353 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Extension to Other Synthesis Models: We have demonstrated that incorporating cross-view geometry and cross-task knowledge can enhance multi-task learning for synthesis models. We anticipate that similar strategies could be extended to 3D synthesis models other than NeRF, such as point clouds [57] and meshes [17, 26].", + "bbox": [ + 498, + 358, + 890, + 449 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 470, + 617, + 486 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This paper introduces the novel concept of Multi-Task View Synthesis (MTVS), recasting multi-task learning as a set of view synthesis problems. Informed by this new perspective, we devise MuvieNeRF, a unified synthesis framework enriched with novel Cross-View Attention and Cross-Task Attention modules. MuvieNeRF enables the simultaneous synthesis of multiple scene properties from novel viewpoints. Through extensive experimental evaluations, we establish MuvieNeRF's proficiency in addressing the MTVS task, with performance exceeding that of discriminative models across various settings. Our model also demonstrates broad applicability, extending to a variety of conditional NeRF backbones.", + "bbox": [ + 498, + 500, + 890, + 695 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 500, + 718, + 658, + 734 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We thank Kangle Deng, Derek Hoiem, Ziqi Pang, Deva Ramanan, Manolis Savva, Shen Zheng, Yuanyi Zhong, JunYan Zhu, and Zhen Zhu for their valuable comments.", + "bbox": [ + 498, + 746, + 890, + 791 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was supported in part by NSF Grant 2106825, Toyota Research Institute, NIFA Award 2020-67021-32799, the Jump ARCHES endowment, the NCSA Fellows program, the Illinois-Inspers Partnership, and the Amazon Research Award. 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Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.207, + 0.131, + 0.766, + 0.154 + ], + "angle": 0, + "content": "Multi-task View Synthesis with Neural Radiance Fields" + }, + { + "type": "text", + "bbox": [ + 0.183, + 0.18, + 0.788, + 0.219 + ], + "angle": 0, + "content": "Shuhong Zheng\\(^{1,*}\\) Zhipeng Bao\\(^{2,*}\\) Martial Hebert\\(^{2}\\) Yu-Xiong Wang\\(^{1}\\) \n\\(^{1}\\)University of Illinois Urbana-Champaign \n\\(^{2}\\)Carnegie Mellon University" + }, + { + "type": "text", + "bbox": [ + 0.229, + 0.22, + 0.733, + 0.235 + ], + "angle": 0, + "content": "{szheng36,yxw}@illinois.edu {zbao,hebert}@cs.cmu.edu" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.302, + 0.474, + 0.664 + ], + "angle": 0, + "content": "Multi-task visual learning is a critical aspect of computer vision. Current research, however, predominantly concentrates on the multi-task dense prediction setting, which overlooks the intrinsic 3D world and its multi-view consistent structures, and lacks the capability for versatile imagination. In response to these limitations, we present a novel problem setting - multi-task view synthesis (MTVS), which reinterprets multi-task prediction as a set of novel-view synthesis tasks for multiple scene properties, including RGB. To tackle the MTVS problem, we propose MuvieNeRF, a framework that incorporates both multi-task and cross-view knowledge to simultaneously synthesize multiple scene properties. MuvieNeRF integrates two key modules, the Cross-Task Attention (CTA) and Cross-View Attention (CVA) modules, enabling the efficient use of information across multiple views and tasks. Extensive evaluation on both synthetic and realistic benchmarks demonstrates that MuvieNeRF is capable of simultaneously synthesizing different scene properties with promising visual quality, even outperforming conventional discriminative models in various settings. Notably, we show that MuvieNeRF exhibits universal applicability across a range of NeRF backbones. Our code is available at https://github.com/zsh2000/MuvieNeRF." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.697, + 0.21, + 0.712 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.723, + 0.47, + 0.875 + ], + "angle": 0, + "content": "When observing a given scene, human minds exhibit a remarkable capability to mentally simulate the objects within it from a novel viewpoint in a versatile manner [40]. It not only includes imagination of the colors of objects, but also extends to numerous associated scene properties such as surface orientation, semantic segmentation, and edge patterns. Prompted by this, a burgeoning interest has emerged, seeking to equip modern robotic systems with similar capabilities for handling multiple tasks. Nevertheless, contemporary research [33, 65, 66] has primarily centered on" + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.271, + 0.891, + 0.382 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.573, + 0.385, + 0.828, + 0.4 + ], + "angle": 0, + "content": "(a) Conventional multi-task learning setting" + }, + { + "type": "image", + "bbox": [ + 0.512, + 0.418, + 0.866, + 0.496 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.576, + 0.502, + 0.822, + 0.516 + ], + "angle": 0, + "content": "(b) Our multi-task view synthesis pipeline" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.531, + 0.894, + 0.603 + ], + "angle": 0, + "content": "Figure 1. Comparison between (a) the conventional multi-task learning scheme and (b) our multi-task view synthesis setting. The conventional \"discriminative\" multi-task learning makes predictions for single images while multi-task view synthesis aims to render visualizations for multiple scene properties at novel views." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.628, + 0.893, + 0.794 + ], + "angle": 0, + "content": "the multi-task dense prediction setting, which employs a conventional discriminative model to simultaneously predict multiple pixel-level scene properties using given RGB images (refer to Figure 1(a)). Yet, the methodologies arising from this context often demonstrate practical limitations, primarily due to their tendency to treat each image as a separate entity, without constructing an explicit 3D model that adheres to the principle of multi-view consistency. Even more critically, they lack the ability to \"imagine\" – they are incapable of inferring scene properties from an unseen viewpoint, as these models invariably require RGB images." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.895, + 0.903 + ], + "angle": 0, + "content": "To circumvent these constraints, we propose a novel approach that revisits multi-task learning (MTL) [5] from a synthesis perspective. This leads to a more flexible problem setting that reinterprets multi-task visual learning as a collection of novel-view synthesis problems, which we refer to as multi-task view synthesis (MTVS) (refer to Figure 1(b)). As an illustration, the task of predicting surface" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.888, + 0.204, + 0.9 + ], + "angle": 0, + "content": "*Equal contribution" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "21538" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.212 + ], + "angle": 0, + "content": "normals for a given image could be reframed as visualizing a three-channel \"image\" with the given pose and camera parameters. With the achievements of Neural Radiance Fields (NeRF) [32], the implicit scene representation offers an effective solution to synthesize scene properties beyond RGB [68]. Importantly, this scene representation takes multi-view geometry into account, which consequently enhances the performance of all tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.215, + 0.471, + 0.533 + ], + "angle": 0, + "content": "Extending from [68], we make the exploration that mining multi-task knowledge can simultaneously enhance the learning of different tasks, extending beyond discriminative models [45, 66] to include synthesis models as well. Furthermore, we argue that the alignment of features across multiple reference views and the target view can reinforce cross-view consistency, thereby bolstering the implicit scene representation learning. Informed by this insight, we propose MuvieNeRF, a unified framework for the MTVS task, which incorporates Multi-task and cross-view knowledge, thus enabling the simultaneous synthesis of multiple scene properties through a shared implicit scene representation. MuvieNeRF can be applied to an arbitrary conditional NeRF architecture and features a unified decoder with two key modules: Cross-Task Attention (CTA) module, which investigates relationships among different scene properties, and Cross-View Attention (CVA) module, which aligns features across multiple views. The integration of these two modules within MuvieNeRF facilitates the efficient utilization of information from multiple views and tasks, leading to better performance across all tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.536, + 0.47, + 0.762 + ], + "angle": 0, + "content": "To demonstrate the effectiveness of our approach, we first instantiate our MuvieNeRF with GeoNeRF [22], a state-of-the-art conditional NeRF model, and conduct comprehensive evaluations on both synthetic and real-world benchmarks. The results illustrate that MuvieNeRF is capable of solving multi-task learning in a synthesis manner, even outperforming several competitive discriminative models in different settings. Moreover, we ablate the choice of conditional NeRF backbones to illustrate the broad applicability of our framework. We further validate the individual contributions of the CVA and CTA modules by building and comparing different variants of MuvieNeRF. Finally, we demonstrate the broader applications and analysis of MuvieNeRF, such as generalization on out-of-distribution datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.903 + ], + "angle": 0, + "content": "In summary, our contributions are three-fold: (1) We pioneer a novel problem definition, multi-task view synthesis (MTVS), which reconsiders multi-task visual learning as a set of view synthesis tasks. The introduction of MTVS paves the way for robots to emulate human-like mental simulation capabilities by utilizing the implicit scene representation offered by Neural Radiance Fields (NeRF). (2) We present MuvieNeRF, a unified framework that employs Cross-Task Attention (CTA) and Cross-View Atten" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.168 + ], + "angle": 0, + "content": "tion (CVA) modules to leverage cross-view and cross-task information for the MTVS problem. (3) Comprehensive experimental evaluations demonstrate that MuvieNeRF shows promising results for MTVS, and greatly outperforms conventional discriminative models across diverse settings." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.185, + 0.642, + 0.2 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.211, + 0.892, + 0.271 + ], + "angle": 0, + "content": "In this work, we propose the MuvieNeRF model which leverages both multi-task and cross-view information for multi-task view synthesis. We review the most relevant work in the areas below." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.275, + 0.893, + 0.547 + ], + "angle": 0, + "content": "View Synthesis aims to generate a target image with an arbitrary camera pose by referring to source images [50]. Numerous existing methods have delivered promising results in this area [2, 34, 44, 57, 63]. However, unlike these conventional approaches, MTVS endeavors to synthesize multiple scene properties, including RGB, from novel viewpoints. In pursuit of a similar goal, another group of methods seeks to render multiple annotations for novel views, following a first-reconstruct-then-render strategy [12, 13, 19, 26]. These methods typically collect or construct a 3D scene representation (e.g., mesh or point cloud) and subsequently render multiple scene properties using 3D-to-2D projection. In contrast, our work constructs an implicit 3D scene representation using a NeRF-style model based on 2D data. This approach is more computationally efficient and, importantly, our implicit representation provides an opportunity to further model task relationships, an advantage the aforementioned methods do not possess." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.55, + 0.893, + 0.868 + ], + "angle": 0, + "content": "Neural Radiance Fields are originally designed for synthesizing novel-view images with ray tracing and volume rendering technologies [32]. Follow-up work [3, 10, 14, 18, 27, 29, 35, 36, 38, 39, 41, 49, 56, 58] further improves the image quality, optimization, and compositionality. In addition, several approaches [6, 22, 48, 64], namely conditional NeRFs, encode the scene information to enable the conditional generalization to novel scenes, which are more aligned with our setting. Our MuvieNeRF takes the encoders from these conditional NeRFs as backbones. Some work has also paid attention to synthesizing other properties of scenes [11, 37, 53, 60, 68, 69]. Among them, SemanticNeRF [69] extends NeRF from synthesizing RGB images to additionally synthesizing semantic labels. SS-NeRF [68] further generalizes the NeRF architecture to simultaneously render RGB and different scene properties with a shared scene representation. Panoptic 3D volumetric representation [43] is introduced to jointly synthesize RGB and panoptic segmentation for in-the-wild images. Different from them, we tackle the novel MTVS task and leverage both cross-view and cross-task information." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Multi-task Learning aims to leverage shared knowledge across different tasks to achieve optimal performance on" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "21539" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "all the tasks. Recent work improves multi-task learning performance by focusing on better optimization strategies [1, 7, 8, 15, 20, 21, 28] and exploring more efficient multi-task architectures [4, 23, 47, 54]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.155, + 0.471, + 0.336 + ], + "angle": 0, + "content": "Cross-task Relationship is an interesting topic in multi-task learning, which aims to explore the underlying task relationships among different visual tasks [24]. Taking the task relationship into consideration, cross-stitch networks [33] adopt a learnable parameter-sharing strategy for multi-task learning. Taskonomy and its follow-up work [45, 65, 66] systematically study the internal task relationships and design the optimal multi-task learning schemes accordingly to obtain the best performance. Inspired by them, we also investigate how to better model multi-task learning but in a synthesis framework with our model-agnostic MuvieNeRF." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.348, + 0.169, + 0.364 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.373, + 0.47, + 0.493 + ], + "angle": 0, + "content": "In this section, we first describe our novel multi-task view synthesis problem in Section 3.1. Next, we briefly review conditional neural radiance fields (NeRFs) and volume rendering in Section 3.2. In Section 3.3, we explain the proposed MuvieNeRF (as shown in Figure 2) in detail. Finally, we discuss how we handle a more challenging setting without access to source-view annotations at test time in Section 3.4." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.502, + 0.383, + 0.518 + ], + "angle": 0, + "content": "3.1. Multi-task View Synthesis Problem" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.526, + 0.469, + 0.633 + ], + "angle": 0, + "content": "Different from conventional multi-task learning settings, our goal is to jointly synthesize multiple scene properties including RGB images from novel views. Therefore, we aim to learn a model \\(\\Phi\\) which takes a set of \\(V\\) source-view task annotations with camera poses as reference, and predicts the task annotations for a novel view given camera pose (Inference Setting I):" + }, + { + "type": "equation", + "bbox": [ + 0.162, + 0.64, + 0.469, + 0.665 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Y} _ {T} = \\Phi \\left(\\left\\{\\left(\\mathbf {Y} _ {i}, \\mathbf {P} _ {i}\\right) \\right\\} _ {i = 1} ^ {V}, \\mathbf {P} _ {T}\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.673, + 0.469, + 0.754 + ], + "angle": 0, + "content": "where \\(\\mathbf{Y}_i = [\\mathbf{x}_i, \\mathbf{y}_i^1, \\dots, \\mathbf{y}_i^K]\\) denotes RGB images \\(\\mathbf{x}_i\\) and \\(K\\) other multi-task annotations \\(\\{\\mathbf{y}_i^j\\}_{j=1}^K\\) in the \\(i^{\\text{th}}\\) source view. \\(\\mathbf{P}_i\\) is the \\(i^{\\text{th}}\\) source camera pose, and \\(\\mathbf{P}_T\\) is the target camera pose. During evaluation, \\(\\Phi\\) is supposed to be generalized to novel scenes that are not seen during training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.755, + 0.469, + 0.83 + ], + "angle": 0, + "content": "For the evaluation of those novel scenes, we also provide a more challenging setting lacking source-view annotations during the inference time with the assumption that the model may not get access to additional annotations other than RGB during inference (Inference Setting II):" + }, + { + "type": "equation", + "bbox": [ + 0.164, + 0.838, + 0.469, + 0.864 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Y} _ {T} = \\Phi \\left(\\left\\{\\left(\\mathbf {x} _ {i}, \\mathbf {P} _ {i}\\right) \\right\\} _ {i = 1} ^ {V}, \\mathbf {P} _ {T}\\right). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.902 + ], + "angle": 0, + "content": "With the above two settings, Inference Setting I allows us to better evaluate the task relationships in our synthesis" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.151 + ], + "angle": 0, + "content": "framework in a cleaner manner, so it is the focused setting in our paper; Inference Setting II is more aligned with real practice, for which we also propose a solution which is discussed in Sections 3.4 and 4.5." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.163, + 0.892, + 0.195 + ], + "angle": 0, + "content": "3.2. Preliminary: Conditional Neural Radiance Fields and Volume Rendering" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.202, + 0.892, + 0.307 + ], + "angle": 0, + "content": "Neural radiance fields (NeRFs) [32] propose a powerful solution for implicit scene representation, and are widely used in novel view image synthesis. Given the 3D position of a point \\(\\mathbf{q} = (x,y,z)\\) in the scene and the 2D viewing direction \\(\\mathbf{d} = (\\theta ,\\phi)\\), NeRFs learn a mapping function \\((\\mathbf{c},\\sigma) = F(\\mathbf{q},\\mathbf{d})\\), which maps the 5D input \\((\\mathbf{q},\\mathbf{d})\\) to RGB color \\(\\mathbf{c} = (r,g,b)\\) and density \\(\\sigma\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.309, + 0.892, + 0.441 + ], + "angle": 0, + "content": "To enhance the generalizability of NeRFs, conditional NeRFs [6, 22, 48, 64] learn a scene representation across multiple scenes. They first extract a feature volume \\(\\mathbf{W} = E(\\mathbf{x})\\) for each input image \\(\\mathbf{x}\\) of a scene. Next, for an arbitrary point \\(\\mathbf{q}\\) on a camera ray with direction \\(\\mathbf{d}\\), they are able to retrieve the corresponding image feature on \\(\\mathbf{W}\\) by projecting \\(\\mathbf{q}\\) onto the image plane with known pose \\(\\mathbf{P}\\). We treat the above part as the conditional NeRF encoder, which returns:" + }, + { + "type": "equation", + "bbox": [ + 0.59, + 0.443, + 0.891, + 0.463 + ], + "angle": 0, + "content": "\\[\nf _ {\\text {s c e n e}} = F _ {\\text {e n c}} \\left(\\left\\{\\mathbf {x} _ {i}, \\mathbf {P} _ {i} \\right\\} _ {i = 1} ^ {V}, \\mathbf {q}\\right). \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.469, + 0.892, + 0.531 + ], + "angle": 0, + "content": "We have \\( f_{\\mathrm{scene}} \\in \\mathbb{R}^{V \\times d_{\\mathrm{scene}}} \\), which contains the scene representation from \\( V \\) views. Next, the conditional NeRFs further learn a decoder \\( (\\mathbf{c}, \\sigma) = F_{\\mathrm{dec}}(\\mathbf{q}, \\mathbf{d}, f_{\\mathrm{scene}}) \\) to predict the color and density." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.532, + 0.892, + 0.653 + ], + "angle": 0, + "content": "Given the color and density of 3D points, NeRFs render the 2D images by running volume rendering for each pixel with ray tracing. Every time when rendering a pixel in a certain view, a ray \\(\\mathbf{r}(t) = \\mathbf{o} + t\\mathbf{d}\\) which origins from the center \\(\\mathbf{o}\\) of the camera plane in the direction \\(\\mathbf{d}\\) is traced. NeRFs randomly sample \\(M\\) points \\(\\{t_m\\}_{m=1}^M\\) with color \\(\\mathbf{c}(t_m)\\) and density \\(\\sigma(t_m)\\) between the near boundary \\(t_n\\) and far boundary \\(t_f\\). The RGB value of the pixel is given by:" + }, + { + "type": "equation", + "bbox": [ + 0.565, + 0.665, + 0.891, + 0.707 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {C}} (\\mathbf {r}) = \\sum_ {m = 1} ^ {M} \\hat {T} (t _ {m}) \\alpha \\left(\\delta_ {m} \\sigma \\left(t _ {m}\\right)\\right) \\mathbf {c} \\left(t _ {m}\\right), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.718, + 0.892, + 0.751 + ], + "angle": 0, + "content": "where \\(\\delta_{m}\\) is the distance between two consecutive sampled points \\((\\delta_{m} = \\| t_{m + 1} - t_{m}\\|),\\alpha (d) = 1 - \\exp (-d)\\) , and" + }, + { + "type": "equation", + "bbox": [ + 0.585, + 0.761, + 0.891, + 0.81 + ], + "angle": 0, + "content": "\\[\n\\hat {T} \\left(t _ {m}\\right) = \\exp \\left(- \\sum_ {j = 1} ^ {m - 1} \\delta_ {j} \\sigma \\left(t _ {j}\\right)\\right) \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.821, + 0.892, + 0.851 + ], + "angle": 0, + "content": "denotes the accumulated transmittance. The same technique can be used to render an arbitrary scene property \\(\\mathbf{y}^j\\) by:" + }, + { + "type": "equation", + "bbox": [ + 0.557, + 0.863, + 0.891, + 0.905 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {Y}} ^ {j} (\\mathbf {r}) = \\sum_ {m = 1} ^ {M} \\hat {T} (t _ {m}) \\alpha \\left(\\delta_ {m} \\sigma \\left(t _ {m}\\right)\\right) \\mathbf {y} ^ {j} \\left(t _ {m}\\right). \\tag {6}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "21540" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.123, + 0.094, + 0.862, + 0.374 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.379, + 0.893, + 0.409 + ], + "angle": 0, + "content": "Figure 2. Model architecture. MuvieNeRF is a unified framework for multi-task view synthesis equipped with Cross-View Attention (CVA) and Cross-Task Attention (CTA) modules. It predicts multiple scene properties for arbitrary 3D coordinates with source-view annotations." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.419, + 0.208, + 0.433 + ], + "angle": 0, + "content": "3.3. MuvieNeRF" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.443, + 0.471, + 0.581 + ], + "angle": 0, + "content": "As illustrated in Figure 2, MuvieNeRF first fetches the scene representation \\( f_{\\mathrm{scene}} \\) from the conditional NeRF encoder, then predicts multiple scene properties \\( [\\mathbf{x}(\\mathbf{q}), \\mathbf{y}^{1}(\\mathbf{q}), \\dots, \\mathbf{y}^{K}(\\mathbf{q})] \\) for arbitrary 3D coordinate \\( \\mathbf{q} \\). The final annotations are rendered by Equation 6. We explain how to predict multiple scene properties with \\( f_{\\mathrm{scene}} \\) and source annotations \\( [(\\mathbf{Y}_1, \\mathbf{P}_1), \\dots, (\\mathbf{Y}_V, \\mathbf{P}_V)] \\) as follows. The full detailed architecture is included in the supplementary." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.602, + 0.336, + 0.617 + ], + "angle": 0, + "content": "3.3.1 Cross-view Attention Module" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.628, + 0.47, + 0.779 + ], + "angle": 0, + "content": "The cross-view attention (CVA) module (Figure 2 bottom left) leverages the multi-view information for MuvieNeRF. To start, we first concatenate \\( f_{\\mathrm{scene}} \\) with a positional embedding derived from the target ray and the source-view image plane: \\( f_{\\mathrm{scene}}^{\\mathrm{pos}} = [f_{\\mathrm{scene}}; \\gamma(\\theta_{n,v})] \\), where \\( \\gamma(\\cdot) \\) is the positional encoding proposed in [32], and \\( \\theta_{n,v} \\) is the angle between the novel camera ray \\( \\mathbf{r} \\) and the line that connects the camera center of view \\( v \\) and the point \\( \\mathbf{q}_n \\) in the queried ray, which measures the similarity between the source view \\( v \\) and the target view." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.469, + 0.87 + ], + "angle": 0, + "content": "Next, \\(\\alpha\\) CVA modules are used to leverage the cross-view information. Concretely, in each module, we have one self-attention union followed by a multi-layer perceptron (MLP): \\(f_{\\mathrm{CVA}} = \\mathrm{MLP}_{\\mathrm{CVA}}(f_{\\mathrm{scene}}^{\\mathrm{pos}} + \\mathrm{MHA}(f_{\\mathrm{scene}}^{\\mathrm{pos}}, f_{\\mathrm{scene}}^{\\mathrm{pos}}))\\), where \\(\\mathrm{MHA}(a, b)\\) denotes multi-head attention [52] with \\(a\\) as query and \\(b\\) as key and value." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.47, + 0.902 + ], + "angle": 0, + "content": "After these processes, we apply \\((K + 1)\\) different MLPs (corresponding to \\(K\\) vision tasks in multi-task view syn" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.42, + 0.893, + 0.464 + ], + "angle": 0, + "content": "thesis plus the RGB synthesis task) to broadcast the shared feature, leading to the \\((K + 1)\\)-branch feature \\(f_{\\mathrm{task}} \\in \\mathbb{R}^{(K + 1) \\times V \\times d_{\\mathrm{task}}}\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.489, + 0.757, + 0.503 + ], + "angle": 0, + "content": "3.3.2 Cross-task Attention Module" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.515, + 0.892, + 0.715 + ], + "angle": 0, + "content": "In order to simultaneously benefit all the downstream tasks, we propose a novel cross-task attention (CTA) module (Figure 2 bottom right) to facilitate knowledge sharing and information flow among all the tasks. The CTA module has two attention components with shared learnable task prompts [62], \\( p_t \\in \\mathbb{R}^{(K + 1) \\times d_t} \\), where \\( d_t \\) is the dimension of task prompts. The first attention component applies cross-attention between features from each branch and the task prompts \\( f_{\\mathrm{stage1}} = f_{\\mathrm{task}} + \\mathrm{MHA}(f_{\\mathrm{task}}, p_t) \\). In this stage, we run \\( K \\) MHA individually for each task branch with the shared task prompts. After the cross-attention, we further concatenate \\( f_{\\mathrm{stage1}}^j \\) for task \\( T_j \\) and the corresponding task prompt \\( p_t^j \\) to obtain \\( f_{\\mathrm{stage1'}} \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.715, + 0.892, + 0.792 + ], + "angle": 0, + "content": "Next, we apply the second component to use \\(\\beta\\) self-attention modules for all the branches jointly to leverage the cross-task features. The final feature representation is obtained by: \\(f_{\\mathrm{stage2}} = \\mathrm{MLP}_{\\mathrm{CTA}}(f_{\\mathrm{stage1'}} + \\mathrm{MHA}(f_{\\mathrm{stage1}}, f_{\\mathrm{stage1'}}))\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.792, + 0.892, + 0.85 + ], + "angle": 0, + "content": "Finally, to predict the task annotations of the target view, we adopt the formulation of GeoNeRF [22]. The prediction \\(\\hat{\\mathbf{y}}^j\\) of task \\(T_{j}\\) on the target view is the weighted sum of the source views:" + }, + { + "type": "equation", + "bbox": [ + 0.611, + 0.863, + 0.892, + 0.904 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {y}} ^ {j} = \\sum_ {i = 1} ^ {V} \\mathbf {w} [ j, i ] \\cdot \\mathbf {y} [ j, i ], \\tag {7}\n\\]" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "21541" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.891, + 0.214 + ], + "angle": 0, + "content": "
Evaluation TypeTraining scene evaluationTesting scene evaluation
TaskRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)RGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
ReplicaHeuristic29.600.02720.04820.02140.00490.932520.860.03950.05150.04710.00970.8543
Semantic-NeRF33.600.02110.04030.01280.00370.950727.080.02210.04180.02120.00550.9417
SS-NeRF33.760.02120.03830.01160.00350.953327.220.02240.04050.01960.00530.9483
MuvieNeRF34.920.01930.03450.01000.00340.958228.550.02010.04080.01620.00510.9563
SceneNet RGB-DHeuristic22.660.0496-0.05210.00930.868722.020.0394-0.05250.01240.8917
Semantic-NeRF28.290.0248-0.02120.00500.915228.850.0186-0.01980.00510.9417
SS-NeRF28.930.0244-0.02160.00500.917529.180.0182-0.01970.00520.9510
MuvieNeRF29.290.0237-0.02070.00490.919029.560.0173-0.01890.00500.9556
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.219, + 0.893, + 0.262 + ], + "angle": 0, + "content": "Table 1. Averaged performance of MuvieNeRF on Replica [46] and SceneNet RGB-D [30] datasets on both training scenes and testing scenes. Full results with multiple runs are provided in the supplementary, our model consistently outperforms both the single-task Semantic-NeRF baseline and multi-task SS-NeRF baseline, owing to the proposed CVA and CTA modules." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.287, + 0.47, + 0.334 + ], + "angle": 0, + "content": "where the matrix \\(\\mathbf{y}\\) is made of input view annotations \\(\\{\\mathbf{Y}_i\\}_{i=1}^V\\) and \\(\\mathbf{w}\\) is obtained by an additional MLP layer which processes \\(f_{\\mathrm{stage2}}\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.355, + 0.224, + 0.37 + ], + "angle": 0, + "content": "3.3.3 Optimization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.38, + 0.47, + 0.426 + ], + "angle": 0, + "content": "For the set of \\(K\\) tasks \\(\\mathcal{T} = \\{T_1, T_2, \\dots, T_K\\}\\) including the RGB colors, we apply their objectives individually and the final objective is formulated as" + }, + { + "type": "equation", + "bbox": [ + 0.198, + 0.439, + 0.469, + 0.473 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {M T}} = \\sum_ {T _ {j} \\in \\mathcal {T}} \\lambda_ {T _ {j}} \\mathcal {L} _ {T _ {j}}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.486, + 0.47, + 0.518 + ], + "angle": 0, + "content": "where \\(\\lambda_{T_j}\\) is the weight for the corresponding task \\(T_{j}\\). For each task, \\(\\mathcal{L}_{T_j}\\) is formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.173, + 0.531, + 0.469, + 0.563 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {T _ {j}} = \\sum_ {\\mathbf {r} \\in \\mathcal {R}} \\mathcal {L} _ {j} \\left(\\hat {\\mathbf {y}} ^ {j} (\\mathbf {r}), \\mathbf {y} ^ {j} (\\mathbf {r})\\right), \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.577, + 0.47, + 0.652 + ], + "angle": 0, + "content": "where \\(\\mathbf{y}^j (\\mathbf{r}),\\hat{\\mathbf{y}}^j (\\mathbf{r})\\) are the ground-truth and prediction for a single pixel regarding task \\(T_{j}\\). \\(\\mathcal{R}\\) is the set of rays \\(\\mathbf{r}\\) for all training views. \\(\\mathcal{L}_j\\) is chosen from \\(L_{1}\\) loss, \\(L_{2}\\) loss, and cross-entropy loss according to the characteristics of the tasks." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.665, + 0.439, + 0.681 + ], + "angle": 0, + "content": "3.4. Tackling without Source-view Annotations" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.902 + ], + "angle": 0, + "content": "The proposed model is based on the assumption that source-view task annotations are available during inference time. The assumption rules out the influence from inaccurate source-view task information, which sets a cleaner environment to excavate multi-task synergy in a synthesis framework for the MTVS problem. However, from the real application perspective, traditional discriminative models only take RGB images as input without any task annotations. To demonstrate that our model is able to be applied in real scenarios, we introduce the more challenging Inference Setting II formulated by Equation 2 and provide a solution by incorporating a U-Net [42] shaped module \\( F_{\\mathrm{UNet}} \\) into our MuvieNeRF architecture. The detailed architecture of \\( F_{\\mathrm{UNet}} \\) is shown in the supplementary." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.287, + 0.892, + 0.378 + ], + "angle": 0, + "content": "Conceptually, \\( F_{\\mathrm{UNet}} \\) takes RGB images from the \\( V \\) source views \\( \\{\\mathbf{x}_i\\}_{i=1}^V \\) as input and produces the corresponding multi-task annotations \\( \\{\\tilde{\\mathbf{Y}}_i\\}_{i=1}^V \\), where \\( \\tilde{\\mathbf{Y}}_i = [\\tilde{\\mathbf{y}}_i^1, \\dots, \\tilde{\\mathbf{y}}_i^K] \\). Next, similar to the conditional NeRF encoder, we retrieve the corresponding multi-task annotations \\( \\{\\tilde{\\mathbf{Y}}_i(\\mathbf{q})\\}_{i=1}^V \\) for an arbitrary point \\( \\mathbf{q} \\) by projection." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.378, + 0.892, + 0.408 + ], + "angle": 0, + "content": "During training time, \\( F_{\\mathrm{UNet}} \\) is trained with pixel-wise task-specific losses. Concretely, for task \\( T_{j} \\), we have:" + }, + { + "type": "equation", + "bbox": [ + 0.582, + 0.419, + 0.892, + 0.462 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {U _ {j}} = \\sum_ {\\mathbf {r} \\in \\mathcal {R}} \\sum_ {i = 1} ^ {V} \\mathcal {L} _ {j} \\left(\\tilde {\\mathbf {y}} _ {i} ^ {j} (\\mathbf {r}), \\mathbf {y} _ {i} ^ {j} (\\mathbf {r})\\right). \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.472, + 0.892, + 0.533 + ], + "angle": 0, + "content": "The final loss becomes \\(\\mathcal{L}_{\\mathrm{final}} = \\sum_{T_j\\in \\mathcal{T}}\\lambda_{T_j}(\\mathcal{L}_{T_j} + \\mathcal{L}_{U_j})\\) for which we take the ground-truth multi-task annotations to learn the weights during training. However, we instead use the predictions produced by \\(F_{\\mathrm{UNet}}\\) for inference:" + }, + { + "type": "equation", + "bbox": [ + 0.611, + 0.544, + 0.891, + 0.585 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {y}} ^ {j} = \\sum_ {i = 1} ^ {V} \\mathbf {w} [ j, i ] \\cdot \\tilde {\\mathbf {y}} [ j, i ]. \\tag {11}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.596, + 0.736, + 0.614 + ], + "angle": 0, + "content": "4. Experimental Evaluation" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.622, + 0.892, + 0.727 + ], + "angle": 0, + "content": "In this section, we start with main evaluation from Sections 4.1 to 4.3, including experimental setting, quantitative and qualitative results, and comparison with conventional discriminative multi-task models. Next, we make further investigations in Sections 4.4 and 4.5, including ablation studies and additional explorations. Finally, we discuss the limitations and future work in Section 4.6." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.737, + 0.702, + 0.753 + ], + "angle": 0, + "content": "4.1. Experimental Setting" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.762, + 0.892, + 0.868 + ], + "angle": 0, + "content": "Model Instantiation: As illustrated in Section 3, our model can build upon arbitrary conditional NeRF encoders. For the main evaluation, we instantiate our model with state-of-the-art GeoNeRF [22]. We use \\(\\alpha = 4\\) and \\(\\beta = 2\\) for the number of self-attention unions in the CVA and CTA modules, respectively. We additionally show the performance with other NeRF encoders in the ablation study." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Benchmarks: We take two benchmarks for our main evaluation. Replica [46] is a commonly-used indoor scene" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "21542" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.468, + 0.134 + ], + "angle": 0, + "content": "
ModelRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
MuvieNeRFw/o SH28.260.0204-0.01710.00510.9557
MuvieNeRFw/o KP27.960.02120.04230.0181-0.9519
MuvieNeRF28.550.02010.04080.01620.00510.9563
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.144, + 0.47, + 0.2 + ], + "angle": 0, + "content": "Table 2. Additional test scene evaluation for our variants without SH (MuvieNeRFw/o SH) and KP (MuvieNeRFw/o KP) tasks on the Replica dataset. These two tasks work as a role of auxiliary tasks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.224, + 0.47, + 0.39 + ], + "angle": 0, + "content": "dataset containing high-quality photo-realistic 3D modelling of 18 scenes. Following the data acquisition method as [69], we collect 22 sequences from the scenes, each containing 50 frames at a resolution of \\(640 \\times 480\\). SceneNet RGB-D [30] is a large-scale photorealistic indoor scene dataset expanding from SceneNet [16]. We include 32 scenes with 40 frames of each at a resolution of \\(320 \\times 240\\) in our evaluation. In addition to the above two datasets, we further evaluate zero-shot adaptation on four out-of-distribution datasets: LLFF [31], TartanAir [55], ScanNet [9], and BlendedMVS [59]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.393, + 0.47, + 0.5 + ], + "angle": 0, + "content": "Task Selection: We select six representative tasks to evaluate our method following previous multi-task learning pipelines [45, 68]. The tasks are Surface Normal Prediction (SN), Shading Estimation (SH), Edges Detection (ED), Keypoints Detection (KP), and Semantic Labeling (SL), together with RGB synthesis. For the SceneNet RGB-D dataset, we drop the SH task due to missing annotations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.502, + 0.47, + 0.577 + ], + "angle": 0, + "content": "Evaluation Setup: For the Replica dataset, we divide the 22 scenes into 18, 1, and 3 for training, validation, and testing, respectively. For SceneNet RGB-D, we split 26 scenes for training, 2 for validation, and 4 for testing. For each scene, we hold out every 8 frames as testing views." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.578, + 0.47, + 0.655 + ], + "angle": 0, + "content": "For these held-out views, we provide two types of evaluation: Training scene evaluation is conducted on novel views from the training scenes; Testing scene evaluation runs on novel scenes and is used to evaluate the generalization capability of the compared models." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.656, + 0.47, + 0.717 + ], + "angle": 0, + "content": "Evaluation Metrics: For RGB synthesis, we measure Peak Signal-to-Noise Ratio (PSNR) for evaluation. For semantic segmentation, we take mean Intersection-over-Union (mIoU). For the other tasks, we evaluate the \\(L_{1}\\) error." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.47, + 0.9 + ], + "angle": 0, + "content": "Baselines: We consider synthesis baselines for the main evaluation. Semantic-NeRF [69] extends NeRF for the semantic segmentation task. We further extend this model in the same way for other tasks, which only considers single-task learning in a NeRF style. SS-NeRF [68] considers multi-task learning in a NeRF style, but ignores the cross-view and cross-task information. We equip both models with the same GeoNeRF backbone as our model. Following [68], we also include a Heuristic baseline which estimates the annotations of the test view by projecting the source labels from the nearest training view to the target view." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.198 + ], + "angle": 0, + "content": "Implementation Details: We set the weights for the six chosen tasks as \\(\\lambda_{\\mathrm{RGB}} = 1\\), \\(\\lambda_{\\mathrm{SN}} = 1\\), \\(\\lambda_{\\mathrm{SL}} = 0.04\\), \\(\\lambda_{\\mathrm{SH}} = 0.1\\), \\(\\lambda_{\\mathrm{KP}} = 2\\), and \\(\\lambda_{\\mathrm{ED}} = 0.4\\) based on empirical observations. We use the Adam [25] optimizer with an initial learning rate of \\(5 \\times 10^{-4}\\) and set \\(\\beta_{1} = 0.9\\), \\(\\beta_{2} = 0.999\\). During training, each iteration contains a batch size of 1,024 rays randomly sampled from all training scenes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.198, + 0.892, + 0.243 + ], + "angle": 0, + "content": "More details about our encoder architectures, dataset processing, out-of-distribution analysis, and implementation are included in the supplementary." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.252, + 0.855, + 0.269 + ], + "angle": 0, + "content": "4.2. MuvieNeRF Is Capable of Solving MTVS" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.276, + 0.892, + 0.441 + ], + "angle": 0, + "content": "In Table 1, we present the average results derived from the held-out views across both the training and testing scenes. The key observations are, firstly, it is clear that our problem statement is non-trivial as evidenced by the notably inferior performance exhibited by the simple heuristic baseline when compared to the other models. Secondly, SS-NeRF surpasses Semantic-NeRF on average, indicating the contribution of multi-task learning. Lastly, our model consistently outperforms all the baselines, reaffirming that cross-view and cross-task information are invariably beneficial within our framework." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.442, + 0.892, + 0.609 + ], + "angle": 0, + "content": "Interestingly, we note that MuvieNeRF exhibits a performance closely comparable to the two NeRF baselines on novel scenes for the KP and SH tasks. To decipher the underlying reason, we carry out an additional evaluation on two variants of our model without the two tasks, \\(\\mathrm{MuvieNEF_{w / oKP}}\\) and \\(\\mathrm{MuvieNEF_{w / oSH}}\\), on the test scenes of Replica in Table 2. Our findings indicate that the KP and SH tasks indeed enhance the learning of other tasks, serving as effective auxiliary tasks. This conclusion aligns with previous studies on traditional multi-task learning models as reported by [45]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.609, + 0.892, + 0.7 + ], + "angle": 0, + "content": "Figure 3 showcases a comparative analysis of the qualitative results. It is evident that our predictions supersede those of other baselines in terms of precision and clarity. This superior performance can be attributed to the additional information provided by shared cross-view and cross-task knowledge, which proves beneficial for the target tasks." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.709, + 0.854, + 0.724 + ], + "angle": 0, + "content": "4.3. MuvieNeRF Beats Discriminative Models" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.732, + 0.892, + 0.793 + ], + "angle": 0, + "content": "Although conventional discriminative models fall short in addressing the proposed MTVS problem, we have explored several hybrid settings to facilitate a comparison between our MuvieNeRF and these discriminative models." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Hybrid Setup: We provide additional RGB images from novel views to the discriminative models under three settings with different choices of RGB images. (1) We train on ground truth (GT) pairs and evaluate on novel view RGB images generated by a NeRF (NeRF's Images (No Tuned)); (2) We additionally fine-tune the discriminative models with paired NeRF's images and corresponding GT (NeRF's Im" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.957 + ], + "angle": 0, + "content": "21543" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.12, + 0.096, + 0.845, + 0.422 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.424, + 0.895, + 0.467 + ], + "angle": 0, + "content": "Figure 3. Visual comparisons of our model and baselines on a test scene of Replica dataset [46]. Our predictions are sharper and more accurate compared with other baselines. The underlying reason is that shared cross-view and cross-task knowledge can provide additional information for the target tasks." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.477, + 0.891, + 0.551 + ], + "angle": 0, + "content": "
ModelNeRF's Images (No Tuned)NeRF's Images (Tuned)GT Images (Upper Bound)
SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
Taskgrouping0.05680.07070.04080.00890.53610.05300.06770.04230.00900.55900.04960.06070.02980.00600.6191
MTI-Net0.05600.06360.04180.00780.54400.04860.05490.03890.00780.67530.04220.04980.02810.00500.7196
InvPT0.04790.06180.04000.00910.71390.04740.05870.03280.00740.70840.04090.04840.02820.00550.8158
Ours0.02010.04080.01620.00510.9563----------
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.554, + 0.893, + 0.583 + ], + "angle": 0, + "content": "Table 3. Comparison to the discriminative models for the test scenes on Replica [46] dataset. MuvieNeRF clearly beats all the discriminative models in all three settings, indicating that our model is more capable of both performance and generalizability." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.604, + 0.468, + 0.651 + ], + "angle": 0, + "content": "
ModelRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
MuvieNeRFw/o CTA27.550.02140.04240.01980.00560.9501
MuvieNeRFw/o CVA28.250.02060.04070.01700.00520.9557
MuvieNeRF28.550.02010.04080.01620.00510.9563
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.656, + 0.471, + 0.727 + ], + "angle": 0, + "content": "Table 4. Ablation study with CTA and CVA modules on Replica [46] dataset. MuvieNeRF\\(_{\\mathrm{w/o}}\\) CTA is the variant without CTA module; MuvieNeRF\\(_{\\mathrm{w/o}}\\) CVA is the variant without CVA module. The CTA module is more crucial compared to the CVA module while combining them leads to the best performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.758, + 0.471, + 0.849 + ], + "angle": 0, + "content": "ages (Tuned)); (3) We evaluate on GT images from novel views as the performance upper bound (GT Images (Upper Bound)). For all the settings, we train the discriminative models on both training and testing scenes (training views only) to make sure that they get access to the same number of data as MuvieNeRF." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Discriminative Baselines: We select three representative baselines of different architectures. Taskgrouping [45] leverages an encoder-decoder architecture with a shared" + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.604, + 0.89, + 0.699 + ], + "angle": 0, + "content": "
BackboneRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
PixelNeRF + SS-NeRF23.210.03280.04570.03760.00740.8620
PixelNeRF + Ours24.140.03020.04200.03420.00680.8961
GNT + SS-NeRF21.510.04050.04970.04200.00960.8302
GNT + Ours22.670.03330.04550.03840.00760.8686
MVSNeRF + SS-NeRF25.270.02610.04190.02480.00610.9294
MVSNeRF + Ours25.730.02480.04080.02270.00560.9303
GeoNeRF + SS-NeRF27.220.02240.04050.01960.00530.9483
GeoNeRF + Ours28.550.02010.04080.01620.00510.9563
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.706, + 0.895, + 0.749 + ], + "angle": 0, + "content": "Table 5. Ablation study with different choices of conditional NeRF encoders. The proposed MuvieNeRF is universally beneficial to different encoders, owing to the proposed CTA and CVA modules." + }, + { + "type": "table", + "bbox": [ + 0.581, + 0.765, + 0.808, + 0.801 + ], + "angle": 0, + "content": "
ModelSN (↓)ED (↓)KP (↓)
Discriminative0.07780.03550.0086
MuvieNeRFD0.06050.02300.0074
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.801, + 0.895, + 0.843 + ], + "angle": 0, + "content": "Table 6. Results for the setting with unknown nearby-view annotations. MuvieNeRF\\(_D\\) still outperforms the hybrid discriminative model with a similar backbone." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.895, + 0.903 + ], + "angle": 0, + "content": "representation. MTI-Net [51] adopts a convolutional neural network backbone and enables multi-scale task interactions." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "21544" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.891, + 0.187 + ], + "angle": 0, + "content": "
Evaluation TypeTraining scene evaluationTesting scene evaluation
TasksRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)RGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
ReplicaSS-NeRF33.760.02120.03830.01160.00350.953327.220.02240.04050.01960.00530.9483
MuvieNeRF34.920.01930.03450.01000.00340.958228.550.02010.04080.01620.00510.9563
SS-NeRF (Enlarged)34.200.02100.03880.01070.00350.955727.370.02260.04050.01860.00530.9498
SceneNet RGB-DSS-NeRF28.930.0244-0.02160.00500.917529.180.0182-0.01970.00520.9510
MuvieNeRF29.290.0237-0.02070.00490.919029.560.0173-0.01890.00500.9556
SS-NeRF (Enlarged)29.030.0244-0.02150.00490.918629.460.0182-0.01910.00500.9520
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.193, + 0.893, + 0.234 + ], + "angle": 0, + "content": "Table 7. Comparison between MuvieNeRF and an enlarged version of SS-NeRF. our model still significantly outperforms SS-NeRF (Enlarged), indicating that the good performance of MuvieNeRF is not simply achieved by a heavier decoder, and demonstrating the effectiveness of our module designs." + }, + { + "type": "table", + "bbox": [ + 0.09, + 0.25, + 0.454, + 0.282 + ], + "angle": 0, + "content": "
ModelRuntime (Per Training Iter.)Num. of Params.FLOPs
SS-NeRF1×1.21M4.57 × 1011
MuvieNeRF1.22×1.30M5.84 × 1011
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.284, + 0.468, + 0.326 + ], + "angle": 0, + "content": "Table 8. Computational cost for SS-NeRF and MuvieNeRF on Replica dataset. Our CTA and CVA modules are light-weight designs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.346, + 0.468, + 0.391 + ], + "angle": 0, + "content": "InvPT [61] takes a transformer-based architecture that encourages long-range and global context to benefit multi-task learning." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.392, + 0.468, + 0.513 + ], + "angle": 0, + "content": "Table 3 details the averaged results and Figure 3 offers a visual comparison. It is discernible that our MuvieNeRF outstrips all the discriminative models, illustrating that these models struggle to effectively tackle the MTVS problem, despite fine-tuning or utilizing GT images. We surmise that this shortcoming is rooted in the evaluation of novel scenes, wherein the generalization capability of our model noticeably outperforms that of discriminative ones." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.523, + 0.23, + 0.539 + ], + "angle": 0, + "content": "4.4. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.546, + 0.468, + 0.576 + ], + "angle": 0, + "content": "We consider the test scene evaluation on the Replica dataset for the following ablation and exploration sections." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.578, + 0.468, + 0.713 + ], + "angle": 0, + "content": "Contributions of CTA and CVA: We dissect the individual contributions of the proposed CTA and CVA modules in Table 4. An examination of the results reveals a more significant impact from the CTA module, when compared with the CVA module. We postulate that this occurs because the NeRF encoder and volume rendering have already mastered an implicit 3D representation, albeit falling short in modeling task relationships. Nevertheless, the integration of both modules yields further enhancement." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.717, + 0.468, + 0.837 + ], + "angle": 0, + "content": "Choice of Condition NeRF: We also ablate the conditional NeRF encoders with PixelNeRF [64], MVSNeRF [6], GNT [48], and GeoNeRF [22] in Table 5. Note that we only adopt the encoder part defined in Section 3, causing a variation in performance from the full model. Each variant under our design surpasses its respective SS-NeRF baseline, affirming the universal advantage of our proposed CTA and CVA modules across different conditional NeRF encoders." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Effectiveness of CTA and CVA Modules: By integrating CVA and CTA modules, we concurrently increase the number of trainable parameters. To truly assess the advancements brought by the proposed CVA and CTA modules, we" + }, + { + "type": "image", + "bbox": [ + 0.527, + 0.255, + 0.688, + 0.357 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.526, + 0.358, + 0.688, + 0.459 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.596, + 0.46, + 0.617, + 0.468 + ], + "angle": 0, + "content": "RGB" + }, + { + "type": "image", + "bbox": [ + 0.69, + 0.255, + 0.864, + 0.322 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.691, + 0.323, + 0.863, + 0.356 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.691, + 0.357, + 0.864, + 0.39 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.691, + 0.391, + 0.864, + 0.424 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.691, + 0.425, + 0.864, + 0.459 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.691, + 0.46, + 0.863, + 0.47 + ], + "angle": 0, + "content": "Discriminative MuvieNeRF \\( {}_{D} \\) Ground Truth" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.47, + 0.892, + 0.54 + ], + "angle": 0, + "content": "Figure 4. Visualizations for the setting without nearby-view annotations. our MuvieNeRF \\(D\\) markedly surpasses the discriminative baseline model [45] and can generate results closely paralleling the ground truth, indicating MuvieNeRF \\(D\\) is capable of tackling the more challenging settings." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.566, + 0.892, + 0.718 + ], + "angle": 0, + "content": "introduce an expanded version of SS-NeRF, designated as SS-NeRF (Enlarged). This variant features a doubled latent dimension, comprising 2.09M parameters and \\(6.18 \\times 10^{11}\\) FLOPs. The outcomes, as illustrated in Table 7, confirm that MuvieNeRF's excellent performance is not simply the result of a more complex decoder, thereby highlighting the effectiveness of our module designs. Moreover, we further list the computational cost for our model and SS-NeRF in Table 8 to show that our CTA and CVA modules are indeed lightweight, but effective designs." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.73, + 0.722, + 0.746 + ], + "angle": 0, + "content": "4.5. Additional Explorations" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.755, + 0.825, + 0.769 + ], + "angle": 0, + "content": "4.5.1 Tackling Unknown Source-view Labels" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this section, we apply the variant discussed in Section 3.4 to tackle the more challenging problem setting with unknown nearby-view annotations. In Table 6, we show the quantitative comparisons for this variant, MuvieNeRF\\(_D\\), and a hybrid baseline, Discriminative [45], which shares almost the same architecture as our discriminative module. We use pre-trained weights from Taskonomy [66] to initialize weights for both models. Limited by the computational" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "21545" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.1, + 0.091, + 0.211, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.13, + 0.224, + 0.181, + 0.234 + ], + "angle": 0, + "content": "GeoNeRF" + }, + { + "type": "image", + "bbox": [ + 0.216, + 0.091, + 0.328, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.224, + 0.224, + 0.319, + 0.235 + ], + "angle": 0, + "content": "MuvieNeRF (Ours)" + }, + { + "type": "image", + "bbox": [ + 0.332, + 0.091, + 0.445, + 0.223 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.354, + 0.224, + 0.422, + 0.234 + ], + "angle": 0, + "content": "Ground Truth" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.237, + 0.47, + 0.307 + ], + "angle": 0, + "content": "Figure 5. An out-of-distribution comparison on BlendedMVS dataset [59] for GeoNeRF and our MuvieNeRF. Our model offers superior visual quality and preserves sharp contours. More visualizations about other OOD benchmarks are included in the supplementary." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.32, + 0.469, + 0.351 + ], + "angle": 0, + "content": "constraint, we select three tasks, SN, ED, and KP with the closest relationships [45] for demonstration in this setting." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.352, + 0.469, + 0.471 + ], + "angle": 0, + "content": "In conjunction with the visualizations illustrated in Figure 4, it is clear that our MuvieNeRF\\(_D\\) markedly surpasses the discriminative baseline model [45] and can generate results closely paralleling the ground truth. This observation indicates that our model is capable of tackling more challenging settings. We conjecture the reason is that the weighted sum format (Equation 11) enhances the fault tolerance of the predictions." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.492, + 0.373, + 0.506 + ], + "angle": 0, + "content": "4.5.2 Out-of-distribution Generalization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.516, + 0.469, + 0.652 + ], + "angle": 0, + "content": "We demonstrate how the multi-task information learned from one dataset can effectively be utilized to benefit other datasets, by performing a zero-shot adaptation on out-of-distribution datasets with our MuvieNeRF trained on Replica. This takes a step further from investigating the generalization ability of unseen testing scenes in previous sections. We consider four datasets in total: LLFF [31], TartanAir [55], ScanNet [9], and BlendedMVS [59] containing indoor, outdoor, and even object-centric scenes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.653, + 0.469, + 0.834 + ], + "angle": 0, + "content": "As an illustrative example, we showcase the comparison between the conditional NeRF backbone, GeoNeRF [22], and our MuvieNeRF for the novel-view RGB synthesis task in Table 9 and Figure 5. Evidently, our model surpasses GeoNeRF by a significant margin, offering superior visual quality and retaining sharp contours, likely a result of the edge and surface normal information absorbed during the multi-task training. These outcomes substantiate that augmenting the model with more tasks, as part of our multitask learning strategy, dramatically bolsters the generalization capability, thereby showcasing its immense potential for real-world applications." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.845, + 0.337, + 0.86 + ], + "angle": 0, + "content": "4.6. Limitations and Future work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Limitations: One major limitation of this work is the reliance on data. MuvieNeRF requires images from dense" + }, + { + "type": "table", + "bbox": [ + 0.523, + 0.089, + 0.868, + 0.128 + ], + "angle": 0, + "content": "
ModelScanNetTartanAirLLFFBlendedMVS
GeoNeRF31.7126.5120.6816.27
MuvieNeRF32.7630.2122.9120.97
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.131, + 0.892, + 0.201 + ], + "angle": 0, + "content": "Table 9. Averaged PSNR of out-of-distribution RGB synthesis task. Our model surpasses the GeoNeRF baseline by a large margin, affirming that the inclusion of additional tasks, as part of our approach, contributes to a substantial enhancement in the model's generalization capacity." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.227, + 0.892, + 0.273 + ], + "angle": 0, + "content": "views, a requirement not fulfilled by most multi-task benchmarks. To circumvent this limitation, techniques that allow NeRF to learn from sparse views [35, 67] could be adopted." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.278, + 0.892, + 0.354 + ], + "angle": 0, + "content": "Task Relationships: As elaborated in Section 4.2, SH and KP function as auxiliary tasks within the system. A deeper exploration into the relationships between tasks and the corresponding geometric underpinnings within our synthesis framework offers intriguing avenues for future research." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.359, + 0.892, + 0.45 + ], + "angle": 0, + "content": "Extension to Other Synthesis Models: We have demonstrated that incorporating cross-view geometry and cross-task knowledge can enhance multi-task learning for synthesis models. We anticipate that similar strategies could be extended to 3D synthesis models other than NeRF, such as point clouds [57] and meshes [17, 26]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.472, + 0.619, + 0.487 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.501, + 0.892, + 0.696 + ], + "angle": 0, + "content": "This paper introduces the novel concept of Multi-Task View Synthesis (MTVS), recasting multi-task learning as a set of view synthesis problems. Informed by this new perspective, we devise MuvieNeRF, a unified synthesis framework enriched with novel Cross-View Attention and Cross-Task Attention modules. MuvieNeRF enables the simultaneous synthesis of multiple scene properties from novel viewpoints. Through extensive experimental evaluations, we establish MuvieNeRF's proficiency in addressing the MTVS task, with performance exceeding that of discriminative models across various settings. Our model also demonstrates broad applicability, extending to a variety of conditional NeRF backbones." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.719, + 0.66, + 0.736 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.747, + 0.892, + 0.792 + ], + "angle": 0, + "content": "We thank Kangle Deng, Derek Hoiem, Ziqi Pang, Deva Ramanan, Manolis Savva, Shen Zheng, Yuanyi Zhong, JunYan Zhu, and Zhen Zhu for their valuable comments." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.795, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This work was supported in part by NSF Grant 2106825, Toyota Research Institute, NIFA Award 2020-67021-32799, the Jump ARCHES endowment, the NCSA Fellows program, the Illinois-Inspers Partnership, and the Amazon Research Award. 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Current research, however, predominantly concentrates on the multi-task dense prediction setting, which overlooks the intrinsic 3D world and its multi-view consistent structures, and lacks the capability for versatile imagination. In response to these limitations, we present a novel problem setting - multi-task view synthesis (MTVS), which reinterprets multi-task prediction as a set of novel-view synthesis tasks for multiple scene properties, including RGB. To tackle the MTVS problem, we propose MuvieNeRF, a framework that incorporates both multi-task and cross-view knowledge to simultaneously synthesize multiple scene properties. MuvieNeRF integrates two key modules, the Cross-Task Attention (CTA) and Cross-View Attention (CVA) modules, enabling the efficient use of information across multiple views and tasks. Extensive evaluation on both synthetic and realistic benchmarks demonstrates that MuvieNeRF is capable of simultaneously synthesizing different scene properties with promising visual quality, even outperforming conventional discriminative models in various settings. Notably, we show that MuvieNeRF exhibits universal applicability across a range of NeRF backbones. Our code is available at https://github.com/zsh2000/MuvieNeRF. + +# 1. Introduction + +When observing a given scene, human minds exhibit a remarkable capability to mentally simulate the objects within it from a novel viewpoint in a versatile manner [40]. It not only includes imagination of the colors of objects, but also extends to numerous associated scene properties such as surface orientation, semantic segmentation, and edge patterns. Prompted by this, a burgeoning interest has emerged, seeking to equip modern robotic systems with similar capabilities for handling multiple tasks. Nevertheless, contemporary research [33, 65, 66] has primarily centered on + +![](images/2b6fb237f2ab4e594ef8cc37c31a5363d923c71275131fafe1610fb5460aa50d.jpg) +(a) Conventional multi-task learning setting + +![](images/eeb807a01b013e2da067a51a9e488a96ab6b4db5dae14c29dd4ce4918db2b20a.jpg) +(b) Our multi-task view synthesis pipeline +Figure 1. Comparison between (a) the conventional multi-task learning scheme and (b) our multi-task view synthesis setting. The conventional "discriminative" multi-task learning makes predictions for single images while multi-task view synthesis aims to render visualizations for multiple scene properties at novel views. + +the multi-task dense prediction setting, which employs a conventional discriminative model to simultaneously predict multiple pixel-level scene properties using given RGB images (refer to Figure 1(a)). Yet, the methodologies arising from this context often demonstrate practical limitations, primarily due to their tendency to treat each image as a separate entity, without constructing an explicit 3D model that adheres to the principle of multi-view consistency. Even more critically, they lack the ability to "imagine" – they are incapable of inferring scene properties from an unseen viewpoint, as these models invariably require RGB images. + +To circumvent these constraints, we propose a novel approach that revisits multi-task learning (MTL) [5] from a synthesis perspective. This leads to a more flexible problem setting that reinterprets multi-task visual learning as a collection of novel-view synthesis problems, which we refer to as multi-task view synthesis (MTVS) (refer to Figure 1(b)). As an illustration, the task of predicting surface + +normals for a given image could be reframed as visualizing a three-channel "image" with the given pose and camera parameters. With the achievements of Neural Radiance Fields (NeRF) [32], the implicit scene representation offers an effective solution to synthesize scene properties beyond RGB [68]. Importantly, this scene representation takes multi-view geometry into account, which consequently enhances the performance of all tasks. + +Extending from [68], we make the exploration that mining multi-task knowledge can simultaneously enhance the learning of different tasks, extending beyond discriminative models [45, 66] to include synthesis models as well. Furthermore, we argue that the alignment of features across multiple reference views and the target view can reinforce cross-view consistency, thereby bolstering the implicit scene representation learning. Informed by this insight, we propose MuvieNeRF, a unified framework for the MTVS task, which incorporates Multi-task and cross-view knowledge, thus enabling the simultaneous synthesis of multiple scene properties through a shared implicit scene representation. MuvieNeRF can be applied to an arbitrary conditional NeRF architecture and features a unified decoder with two key modules: Cross-Task Attention (CTA) module, which investigates relationships among different scene properties, and Cross-View Attention (CVA) module, which aligns features across multiple views. The integration of these two modules within MuvieNeRF facilitates the efficient utilization of information from multiple views and tasks, leading to better performance across all tasks. + +To demonstrate the effectiveness of our approach, we first instantiate our MuvieNeRF with GeoNeRF [22], a state-of-the-art conditional NeRF model, and conduct comprehensive evaluations on both synthetic and real-world benchmarks. The results illustrate that MuvieNeRF is capable of solving multi-task learning in a synthesis manner, even outperforming several competitive discriminative models in different settings. Moreover, we ablate the choice of conditional NeRF backbones to illustrate the broad applicability of our framework. We further validate the individual contributions of the CVA and CTA modules by building and comparing different variants of MuvieNeRF. Finally, we demonstrate the broader applications and analysis of MuvieNeRF, such as generalization on out-of-distribution datasets. + +In summary, our contributions are three-fold: (1) We pioneer a novel problem definition, multi-task view synthesis (MTVS), which reconsiders multi-task visual learning as a set of view synthesis tasks. The introduction of MTVS paves the way for robots to emulate human-like mental simulation capabilities by utilizing the implicit scene representation offered by Neural Radiance Fields (NeRF). (2) We present MuvieNeRF, a unified framework that employs Cross-Task Attention (CTA) and Cross-View Atten + +tion (CVA) modules to leverage cross-view and cross-task information for the MTVS problem. (3) Comprehensive experimental evaluations demonstrate that MuvieNeRF shows promising results for MTVS, and greatly outperforms conventional discriminative models across diverse settings. + +# 2. Related Work + +In this work, we propose the MuvieNeRF model which leverages both multi-task and cross-view information for multi-task view synthesis. We review the most relevant work in the areas below. + +View Synthesis aims to generate a target image with an arbitrary camera pose by referring to source images [50]. Numerous existing methods have delivered promising results in this area [2, 34, 44, 57, 63]. However, unlike these conventional approaches, MTVS endeavors to synthesize multiple scene properties, including RGB, from novel viewpoints. In pursuit of a similar goal, another group of methods seeks to render multiple annotations for novel views, following a first-reconstruct-then-render strategy [12, 13, 19, 26]. These methods typically collect or construct a 3D scene representation (e.g., mesh or point cloud) and subsequently render multiple scene properties using 3D-to-2D projection. In contrast, our work constructs an implicit 3D scene representation using a NeRF-style model based on 2D data. This approach is more computationally efficient and, importantly, our implicit representation provides an opportunity to further model task relationships, an advantage the aforementioned methods do not possess. + +Neural Radiance Fields are originally designed for synthesizing novel-view images with ray tracing and volume rendering technologies [32]. Follow-up work [3, 10, 14, 18, 27, 29, 35, 36, 38, 39, 41, 49, 56, 58] further improves the image quality, optimization, and compositionality. In addition, several approaches [6, 22, 48, 64], namely conditional NeRFs, encode the scene information to enable the conditional generalization to novel scenes, which are more aligned with our setting. Our MuvieNeRF takes the encoders from these conditional NeRFs as backbones. Some work has also paid attention to synthesizing other properties of scenes [11, 37, 53, 60, 68, 69]. Among them, SemanticNeRF [69] extends NeRF from synthesizing RGB images to additionally synthesizing semantic labels. SS-NeRF [68] further generalizes the NeRF architecture to simultaneously render RGB and different scene properties with a shared scene representation. Panoptic 3D volumetric representation [43] is introduced to jointly synthesize RGB and panoptic segmentation for in-the-wild images. Different from them, we tackle the novel MTVS task and leverage both cross-view and cross-task information. + +Multi-task Learning aims to leverage shared knowledge across different tasks to achieve optimal performance on + +all the tasks. Recent work improves multi-task learning performance by focusing on better optimization strategies [1, 7, 8, 15, 20, 21, 28] and exploring more efficient multi-task architectures [4, 23, 47, 54]. + +Cross-task Relationship is an interesting topic in multi-task learning, which aims to explore the underlying task relationships among different visual tasks [24]. Taking the task relationship into consideration, cross-stitch networks [33] adopt a learnable parameter-sharing strategy for multi-task learning. Taskonomy and its follow-up work [45, 65, 66] systematically study the internal task relationships and design the optimal multi-task learning schemes accordingly to obtain the best performance. Inspired by them, we also investigate how to better model multi-task learning but in a synthesis framework with our model-agnostic MuvieNeRF. + +# 3. Method + +In this section, we first describe our novel multi-task view synthesis problem in Section 3.1. Next, we briefly review conditional neural radiance fields (NeRFs) and volume rendering in Section 3.2. In Section 3.3, we explain the proposed MuvieNeRF (as shown in Figure 2) in detail. Finally, we discuss how we handle a more challenging setting without access to source-view annotations at test time in Section 3.4. + +# 3.1. Multi-task View Synthesis Problem + +Different from conventional multi-task learning settings, our goal is to jointly synthesize multiple scene properties including RGB images from novel views. Therefore, we aim to learn a model $\Phi$ which takes a set of $V$ source-view task annotations with camera poses as reference, and predicts the task annotations for a novel view given camera pose (Inference Setting I): + +$$ +\mathbf {Y} _ {T} = \Phi \left(\left\{\left(\mathbf {Y} _ {i}, \mathbf {P} _ {i}\right) \right\} _ {i = 1} ^ {V}, \mathbf {P} _ {T}\right), \tag {1} +$$ + +where $\mathbf{Y}_i = [\mathbf{x}_i, \mathbf{y}_i^1, \dots, \mathbf{y}_i^K]$ denotes RGB images $\mathbf{x}_i$ and $K$ other multi-task annotations $\{\mathbf{y}_i^j\}_{j=1}^K$ in the $i^{\text{th}}$ source view. $\mathbf{P}_i$ is the $i^{\text{th}}$ source camera pose, and $\mathbf{P}_T$ is the target camera pose. During evaluation, $\Phi$ is supposed to be generalized to novel scenes that are not seen during training. + +For the evaluation of those novel scenes, we also provide a more challenging setting lacking source-view annotations during the inference time with the assumption that the model may not get access to additional annotations other than RGB during inference (Inference Setting II): + +$$ +\mathbf {Y} _ {T} = \Phi \left(\left\{\left(\mathbf {x} _ {i}, \mathbf {P} _ {i}\right) \right\} _ {i = 1} ^ {V}, \mathbf {P} _ {T}\right). \tag {2} +$$ + +With the above two settings, Inference Setting I allows us to better evaluate the task relationships in our synthesis + +framework in a cleaner manner, so it is the focused setting in our paper; Inference Setting II is more aligned with real practice, for which we also propose a solution which is discussed in Sections 3.4 and 4.5. + +# 3.2. Preliminary: Conditional Neural Radiance Fields and Volume Rendering + +Neural radiance fields (NeRFs) [32] propose a powerful solution for implicit scene representation, and are widely used in novel view image synthesis. Given the 3D position of a point $\mathbf{q} = (x,y,z)$ in the scene and the 2D viewing direction $\mathbf{d} = (\theta ,\phi)$ , NeRFs learn a mapping function $(\mathbf{c},\sigma) = F(\mathbf{q},\mathbf{d})$ , which maps the 5D input $(\mathbf{q},\mathbf{d})$ to RGB color $\mathbf{c} = (r,g,b)$ and density $\sigma$ . + +To enhance the generalizability of NeRFs, conditional NeRFs [6, 22, 48, 64] learn a scene representation across multiple scenes. They first extract a feature volume $\mathbf{W} = E(\mathbf{x})$ for each input image $\mathbf{x}$ of a scene. Next, for an arbitrary point $\mathbf{q}$ on a camera ray with direction $\mathbf{d}$ , they are able to retrieve the corresponding image feature on $\mathbf{W}$ by projecting $\mathbf{q}$ onto the image plane with known pose $\mathbf{P}$ . We treat the above part as the conditional NeRF encoder, which returns: + +$$ +f _ {\text {s c e n e}} = F _ {\text {e n c}} \left(\left\{\mathbf {x} _ {i}, \mathbf {P} _ {i} \right\} _ {i = 1} ^ {V}, \mathbf {q}\right). \tag {3} +$$ + +We have $f_{\mathrm{scene}} \in \mathbb{R}^{V \times d_{\mathrm{scene}}}$ , which contains the scene representation from $V$ views. Next, the conditional NeRFs further learn a decoder $(\mathbf{c}, \sigma) = F_{\mathrm{dec}}(\mathbf{q}, \mathbf{d}, f_{\mathrm{scene}})$ to predict the color and density. + +Given the color and density of 3D points, NeRFs render the 2D images by running volume rendering for each pixel with ray tracing. Every time when rendering a pixel in a certain view, a ray $\mathbf{r}(t) = \mathbf{o} + t\mathbf{d}$ which origins from the center $\mathbf{o}$ of the camera plane in the direction $\mathbf{d}$ is traced. NeRFs randomly sample $M$ points $\{t_m\}_{m=1}^M$ with color $\mathbf{c}(t_m)$ and density $\sigma(t_m)$ between the near boundary $t_n$ and far boundary $t_f$ . The RGB value of the pixel is given by: + +$$ +\hat {\mathbf {C}} (\mathbf {r}) = \sum_ {m = 1} ^ {M} \hat {T} (t _ {m}) \alpha \left(\delta_ {m} \sigma \left(t _ {m}\right)\right) \mathbf {c} \left(t _ {m}\right), \tag {4} +$$ + +where $\delta_{m}$ is the distance between two consecutive sampled points $(\delta_{m} = \| t_{m + 1} - t_{m}\|),\alpha (d) = 1 - \exp (-d)$ , and + +$$ +\hat {T} \left(t _ {m}\right) = \exp \left(- \sum_ {j = 1} ^ {m - 1} \delta_ {j} \sigma \left(t _ {j}\right)\right) \tag {5} +$$ + +denotes the accumulated transmittance. The same technique can be used to render an arbitrary scene property $\mathbf{y}^j$ by: + +$$ +\hat {\mathbf {Y}} ^ {j} (\mathbf {r}) = \sum_ {m = 1} ^ {M} \hat {T} (t _ {m}) \alpha \left(\delta_ {m} \sigma \left(t _ {m}\right)\right) \mathbf {y} ^ {j} \left(t _ {m}\right). \tag {6} +$$ + +![](images/c51b74901fa9f0fdb0ba8ac351a778c51df743ed2767db8cb25f8b673f7c4277.jpg) +Figure 2. Model architecture. MuvieNeRF is a unified framework for multi-task view synthesis equipped with Cross-View Attention (CVA) and Cross-Task Attention (CTA) modules. It predicts multiple scene properties for arbitrary 3D coordinates with source-view annotations. + +# 3.3. MuvieNeRF + +As illustrated in Figure 2, MuvieNeRF first fetches the scene representation $f_{\mathrm{scene}}$ from the conditional NeRF encoder, then predicts multiple scene properties $[\mathbf{x}(\mathbf{q}), \mathbf{y}^{1}(\mathbf{q}), \dots, \mathbf{y}^{K}(\mathbf{q})]$ for arbitrary 3D coordinate $\mathbf{q}$ . The final annotations are rendered by Equation 6. We explain how to predict multiple scene properties with $f_{\mathrm{scene}}$ and source annotations $[(\mathbf{Y}_1, \mathbf{P}_1), \dots, (\mathbf{Y}_V, \mathbf{P}_V)]$ as follows. The full detailed architecture is included in the supplementary. + +# 3.3.1 Cross-view Attention Module + +The cross-view attention (CVA) module (Figure 2 bottom left) leverages the multi-view information for MuvieNeRF. To start, we first concatenate $f_{\mathrm{scene}}$ with a positional embedding derived from the target ray and the source-view image plane: $f_{\mathrm{scene}}^{\mathrm{pos}} = [f_{\mathrm{scene}}; \gamma(\theta_{n,v})]$ , where $\gamma(\cdot)$ is the positional encoding proposed in [32], and $\theta_{n,v}$ is the angle between the novel camera ray $\mathbf{r}$ and the line that connects the camera center of view $v$ and the point $\mathbf{q}_n$ in the queried ray, which measures the similarity between the source view $v$ and the target view. + +Next, $\alpha$ CVA modules are used to leverage the cross-view information. Concretely, in each module, we have one self-attention union followed by a multi-layer perceptron (MLP): $f_{\mathrm{CVA}} = \mathrm{MLP}_{\mathrm{CVA}}(f_{\mathrm{scene}}^{\mathrm{pos}} + \mathrm{MHA}(f_{\mathrm{scene}}^{\mathrm{pos}}, f_{\mathrm{scene}}^{\mathrm{pos}}))$ , where $\mathrm{MHA}(a, b)$ denotes multi-head attention [52] with $a$ as query and $b$ as key and value. + +After these processes, we apply $(K + 1)$ different MLPs (corresponding to $K$ vision tasks in multi-task view syn + +thesis plus the RGB synthesis task) to broadcast the shared feature, leading to the $(K + 1)$ -branch feature $f_{\mathrm{task}} \in \mathbb{R}^{(K + 1) \times V \times d_{\mathrm{task}}}$ . + +# 3.3.2 Cross-task Attention Module + +In order to simultaneously benefit all the downstream tasks, we propose a novel cross-task attention (CTA) module (Figure 2 bottom right) to facilitate knowledge sharing and information flow among all the tasks. The CTA module has two attention components with shared learnable task prompts [62], $p_t \in \mathbb{R}^{(K + 1) \times d_t}$ , where $d_t$ is the dimension of task prompts. The first attention component applies cross-attention between features from each branch and the task prompts $f_{\mathrm{stage1}} = f_{\mathrm{task}} + \mathrm{MHA}(f_{\mathrm{task}}, p_t)$ . In this stage, we run $K$ MHA individually for each task branch with the shared task prompts. After the cross-attention, we further concatenate $f_{\mathrm{stage1}}^j$ for task $T_j$ and the corresponding task prompt $p_t^j$ to obtain $f_{\mathrm{stage1'}}$ . + +Next, we apply the second component to use $\beta$ self-attention modules for all the branches jointly to leverage the cross-task features. The final feature representation is obtained by: $f_{\mathrm{stage2}} = \mathrm{MLP}_{\mathrm{CTA}}(f_{\mathrm{stage1'}} + \mathrm{MHA}(f_{\mathrm{stage1}}, f_{\mathrm{stage1'}}))$ . + +Finally, to predict the task annotations of the target view, we adopt the formulation of GeoNeRF [22]. The prediction $\hat{\mathbf{y}}^j$ of task $T_{j}$ on the target view is the weighted sum of the source views: + +$$ +\hat {\mathbf {y}} ^ {j} = \sum_ {i = 1} ^ {V} \mathbf {w} [ j, i ] \cdot \mathbf {y} [ j, i ], \tag {7} +$$ + +
Evaluation TypeTraining scene evaluationTesting scene evaluation
TaskRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)RGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
ReplicaHeuristic29.600.02720.04820.02140.00490.932520.860.03950.05150.04710.00970.8543
Semantic-NeRF33.600.02110.04030.01280.00370.950727.080.02210.04180.02120.00550.9417
SS-NeRF33.760.02120.03830.01160.00350.953327.220.02240.04050.01960.00530.9483
MuvieNeRF34.920.01930.03450.01000.00340.958228.550.02010.04080.01620.00510.9563
SceneNet RGB-DHeuristic22.660.0496-0.05210.00930.868722.020.0394-0.05250.01240.8917
Semantic-NeRF28.290.0248-0.02120.00500.915228.850.0186-0.01980.00510.9417
SS-NeRF28.930.0244-0.02160.00500.917529.180.0182-0.01970.00520.9510
MuvieNeRF29.290.0237-0.02070.00490.919029.560.0173-0.01890.00500.9556
+ +Table 1. Averaged performance of MuvieNeRF on Replica [46] and SceneNet RGB-D [30] datasets on both training scenes and testing scenes. Full results with multiple runs are provided in the supplementary, our model consistently outperforms both the single-task Semantic-NeRF baseline and multi-task SS-NeRF baseline, owing to the proposed CVA and CTA modules. + +where the matrix $\mathbf{y}$ is made of input view annotations $\{\mathbf{Y}_i\}_{i=1}^V$ and $\mathbf{w}$ is obtained by an additional MLP layer which processes $f_{\mathrm{stage2}}$ . + +# 3.3.3 Optimization + +For the set of $K$ tasks $\mathcal{T} = \{T_1, T_2, \dots, T_K\}$ including the RGB colors, we apply their objectives individually and the final objective is formulated as + +$$ +\mathcal {L} _ {\mathrm {M T}} = \sum_ {T _ {j} \in \mathcal {T}} \lambda_ {T _ {j}} \mathcal {L} _ {T _ {j}}, \tag {8} +$$ + +where $\lambda_{T_j}$ is the weight for the corresponding task $T_{j}$ . For each task, $\mathcal{L}_{T_j}$ is formulated as: + +$$ +\mathcal {L} _ {T _ {j}} = \sum_ {\mathbf {r} \in \mathcal {R}} \mathcal {L} _ {j} \left(\hat {\mathbf {y}} ^ {j} (\mathbf {r}), \mathbf {y} ^ {j} (\mathbf {r})\right), \tag {9} +$$ + +where $\mathbf{y}^j (\mathbf{r}),\hat{\mathbf{y}}^j (\mathbf{r})$ are the ground-truth and prediction for a single pixel regarding task $T_{j}$ . $\mathcal{R}$ is the set of rays $\mathbf{r}$ for all training views. $\mathcal{L}_j$ is chosen from $L_{1}$ loss, $L_{2}$ loss, and cross-entropy loss according to the characteristics of the tasks. + +# 3.4. Tackling without Source-view Annotations + +The proposed model is based on the assumption that source-view task annotations are available during inference time. The assumption rules out the influence from inaccurate source-view task information, which sets a cleaner environment to excavate multi-task synergy in a synthesis framework for the MTVS problem. However, from the real application perspective, traditional discriminative models only take RGB images as input without any task annotations. To demonstrate that our model is able to be applied in real scenarios, we introduce the more challenging Inference Setting II formulated by Equation 2 and provide a solution by incorporating a U-Net [42] shaped module $F_{\mathrm{UNet}}$ into our MuvieNeRF architecture. The detailed architecture of $F_{\mathrm{UNet}}$ is shown in the supplementary. + +Conceptually, $F_{\mathrm{UNet}}$ takes RGB images from the $V$ source views $\{\mathbf{x}_i\}_{i=1}^V$ as input and produces the corresponding multi-task annotations $\{\tilde{\mathbf{Y}}_i\}_{i=1}^V$ , where $\tilde{\mathbf{Y}}_i = [\tilde{\mathbf{y}}_i^1, \dots, \tilde{\mathbf{y}}_i^K]$ . Next, similar to the conditional NeRF encoder, we retrieve the corresponding multi-task annotations $\{\tilde{\mathbf{Y}}_i(\mathbf{q})\}_{i=1}^V$ for an arbitrary point $\mathbf{q}$ by projection. + +During training time, $F_{\mathrm{UNet}}$ is trained with pixel-wise task-specific losses. Concretely, for task $T_{j}$ , we have: + +$$ +\mathcal {L} _ {U _ {j}} = \sum_ {\mathbf {r} \in \mathcal {R}} \sum_ {i = 1} ^ {V} \mathcal {L} _ {j} \left(\tilde {\mathbf {y}} _ {i} ^ {j} (\mathbf {r}), \mathbf {y} _ {i} ^ {j} (\mathbf {r})\right). \tag {10} +$$ + +The final loss becomes $\mathcal{L}_{\mathrm{final}} = \sum_{T_j\in \mathcal{T}}\lambda_{T_j}(\mathcal{L}_{T_j} + \mathcal{L}_{U_j})$ for which we take the ground-truth multi-task annotations to learn the weights during training. However, we instead use the predictions produced by $F_{\mathrm{UNet}}$ for inference: + +$$ +\hat {\mathbf {y}} ^ {j} = \sum_ {i = 1} ^ {V} \mathbf {w} [ j, i ] \cdot \tilde {\mathbf {y}} [ j, i ]. \tag {11} +$$ + +# 4. Experimental Evaluation + +In this section, we start with main evaluation from Sections 4.1 to 4.3, including experimental setting, quantitative and qualitative results, and comparison with conventional discriminative multi-task models. Next, we make further investigations in Sections 4.4 and 4.5, including ablation studies and additional explorations. Finally, we discuss the limitations and future work in Section 4.6. + +# 4.1. Experimental Setting + +Model Instantiation: As illustrated in Section 3, our model can build upon arbitrary conditional NeRF encoders. For the main evaluation, we instantiate our model with state-of-the-art GeoNeRF [22]. We use $\alpha = 4$ and $\beta = 2$ for the number of self-attention unions in the CVA and CTA modules, respectively. We additionally show the performance with other NeRF encoders in the ablation study. + +Benchmarks: We take two benchmarks for our main evaluation. Replica [46] is a commonly-used indoor scene + +
ModelRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
MuvieNeRFw/o SH28.260.0204-0.01710.00510.9557
MuvieNeRFw/o KP27.960.02120.04230.0181-0.9519
MuvieNeRF28.550.02010.04080.01620.00510.9563
+ +Table 2. Additional test scene evaluation for our variants without SH (MuvieNeRFw/o SH) and KP (MuvieNeRFw/o KP) tasks on the Replica dataset. These two tasks work as a role of auxiliary tasks. + +dataset containing high-quality photo-realistic 3D modelling of 18 scenes. Following the data acquisition method as [69], we collect 22 sequences from the scenes, each containing 50 frames at a resolution of $640 \times 480$ . SceneNet RGB-D [30] is a large-scale photorealistic indoor scene dataset expanding from SceneNet [16]. We include 32 scenes with 40 frames of each at a resolution of $320 \times 240$ in our evaluation. In addition to the above two datasets, we further evaluate zero-shot adaptation on four out-of-distribution datasets: LLFF [31], TartanAir [55], ScanNet [9], and BlendedMVS [59]. + +Task Selection: We select six representative tasks to evaluate our method following previous multi-task learning pipelines [45, 68]. The tasks are Surface Normal Prediction (SN), Shading Estimation (SH), Edges Detection (ED), Keypoints Detection (KP), and Semantic Labeling (SL), together with RGB synthesis. For the SceneNet RGB-D dataset, we drop the SH task due to missing annotations. + +Evaluation Setup: For the Replica dataset, we divide the 22 scenes into 18, 1, and 3 for training, validation, and testing, respectively. For SceneNet RGB-D, we split 26 scenes for training, 2 for validation, and 4 for testing. For each scene, we hold out every 8 frames as testing views. + +For these held-out views, we provide two types of evaluation: Training scene evaluation is conducted on novel views from the training scenes; Testing scene evaluation runs on novel scenes and is used to evaluate the generalization capability of the compared models. + +Evaluation Metrics: For RGB synthesis, we measure Peak Signal-to-Noise Ratio (PSNR) for evaluation. For semantic segmentation, we take mean Intersection-over-Union (mIoU). For the other tasks, we evaluate the $L_{1}$ error. + +Baselines: We consider synthesis baselines for the main evaluation. Semantic-NeRF [69] extends NeRF for the semantic segmentation task. We further extend this model in the same way for other tasks, which only considers single-task learning in a NeRF style. SS-NeRF [68] considers multi-task learning in a NeRF style, but ignores the cross-view and cross-task information. We equip both models with the same GeoNeRF backbone as our model. Following [68], we also include a Heuristic baseline which estimates the annotations of the test view by projecting the source labels from the nearest training view to the target view. + +Implementation Details: We set the weights for the six chosen tasks as $\lambda_{\mathrm{RGB}} = 1$ , $\lambda_{\mathrm{SN}} = 1$ , $\lambda_{\mathrm{SL}} = 0.04$ , $\lambda_{\mathrm{SH}} = 0.1$ , $\lambda_{\mathrm{KP}} = 2$ , and $\lambda_{\mathrm{ED}} = 0.4$ based on empirical observations. We use the Adam [25] optimizer with an initial learning rate of $5 \times 10^{-4}$ and set $\beta_{1} = 0.9$ , $\beta_{2} = 0.999$ . During training, each iteration contains a batch size of 1,024 rays randomly sampled from all training scenes. + +More details about our encoder architectures, dataset processing, out-of-distribution analysis, and implementation are included in the supplementary. + +# 4.2. MuvieNeRF Is Capable of Solving MTVS + +In Table 1, we present the average results derived from the held-out views across both the training and testing scenes. The key observations are, firstly, it is clear that our problem statement is non-trivial as evidenced by the notably inferior performance exhibited by the simple heuristic baseline when compared to the other models. Secondly, SS-NeRF surpasses Semantic-NeRF on average, indicating the contribution of multi-task learning. Lastly, our model consistently outperforms all the baselines, reaffirming that cross-view and cross-task information are invariably beneficial within our framework. + +Interestingly, we note that MuvieNeRF exhibits a performance closely comparable to the two NeRF baselines on novel scenes for the KP and SH tasks. To decipher the underlying reason, we carry out an additional evaluation on two variants of our model without the two tasks, $\mathrm{MuvieNEF_{w / oKP}}$ and $\mathrm{MuvieNEF_{w / oSH}}$ , on the test scenes of Replica in Table 2. Our findings indicate that the KP and SH tasks indeed enhance the learning of other tasks, serving as effective auxiliary tasks. This conclusion aligns with previous studies on traditional multi-task learning models as reported by [45]. + +Figure 3 showcases a comparative analysis of the qualitative results. It is evident that our predictions supersede those of other baselines in terms of precision and clarity. This superior performance can be attributed to the additional information provided by shared cross-view and cross-task knowledge, which proves beneficial for the target tasks. + +# 4.3. MuvieNeRF Beats Discriminative Models + +Although conventional discriminative models fall short in addressing the proposed MTVS problem, we have explored several hybrid settings to facilitate a comparison between our MuvieNeRF and these discriminative models. + +Hybrid Setup: We provide additional RGB images from novel views to the discriminative models under three settings with different choices of RGB images. (1) We train on ground truth (GT) pairs and evaluate on novel view RGB images generated by a NeRF (NeRF's Images (No Tuned)); (2) We additionally fine-tune the discriminative models with paired NeRF's images and corresponding GT (NeRF's Im + +![](images/e63b5f3657e4ae3faded5cd2249b5480dc20be7420771d8e7f977618e48b3f05.jpg) +Figure 3. Visual comparisons of our model and baselines on a test scene of Replica dataset [46]. Our predictions are sharper and more accurate compared with other baselines. The underlying reason is that shared cross-view and cross-task knowledge can provide additional information for the target tasks. + +
ModelNeRF's Images (No Tuned)NeRF's Images (Tuned)GT Images (Upper Bound)
SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
Taskgrouping0.05680.07070.04080.00890.53610.05300.06770.04230.00900.55900.04960.06070.02980.00600.6191
MTI-Net0.05600.06360.04180.00780.54400.04860.05490.03890.00780.67530.04220.04980.02810.00500.7196
InvPT0.04790.06180.04000.00910.71390.04740.05870.03280.00740.70840.04090.04840.02820.00550.8158
Ours0.02010.04080.01620.00510.9563----------
+ +Table 3. Comparison to the discriminative models for the test scenes on Replica [46] dataset. MuvieNeRF clearly beats all the discriminative models in all three settings, indicating that our model is more capable of both performance and generalizability. + +
ModelRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
MuvieNeRFw/o CTA27.550.02140.04240.01980.00560.9501
MuvieNeRFw/o CVA28.250.02060.04070.01700.00520.9557
MuvieNeRF28.550.02010.04080.01620.00510.9563
+ +ages (Tuned)); (3) We evaluate on GT images from novel views as the performance upper bound (GT Images (Upper Bound)). For all the settings, we train the discriminative models on both training and testing scenes (training views only) to make sure that they get access to the same number of data as MuvieNeRF. + +Discriminative Baselines: We select three representative baselines of different architectures. Taskgrouping [45] leverages an encoder-decoder architecture with a shared + +Table 4. Ablation study with CTA and CVA modules on Replica [46] dataset. MuvieNeRF $_{\mathrm{w/o}}$ CTA is the variant without CTA module; MuvieNeRF $_{\mathrm{w/o}}$ CVA is the variant without CVA module. The CTA module is more crucial compared to the CVA module while combining them leads to the best performance. + +
BackboneRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
PixelNeRF + SS-NeRF23.210.03280.04570.03760.00740.8620
PixelNeRF + Ours24.140.03020.04200.03420.00680.8961
GNT + SS-NeRF21.510.04050.04970.04200.00960.8302
GNT + Ours22.670.03330.04550.03840.00760.8686
MVSNeRF + SS-NeRF25.270.02610.04190.02480.00610.9294
MVSNeRF + Ours25.730.02480.04080.02270.00560.9303
GeoNeRF + SS-NeRF27.220.02240.04050.01960.00530.9483
GeoNeRF + Ours28.550.02010.04080.01620.00510.9563
+ +Table 5. Ablation study with different choices of conditional NeRF encoders. The proposed MuvieNeRF is universally beneficial to different encoders, owing to the proposed CTA and CVA modules. + +
ModelSN (↓)ED (↓)KP (↓)
Discriminative0.07780.03550.0086
MuvieNeRFD0.06050.02300.0074
+ +Table 6. Results for the setting with unknown nearby-view annotations. MuvieNeRF $_D$ still outperforms the hybrid discriminative model with a similar backbone. + +representation. MTI-Net [51] adopts a convolutional neural network backbone and enables multi-scale task interactions. + +
Evaluation TypeTraining scene evaluationTesting scene evaluation
TasksRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)RGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
ReplicaSS-NeRF33.760.02120.03830.01160.00350.953327.220.02240.04050.01960.00530.9483
MuvieNeRF34.920.01930.03450.01000.00340.958228.550.02010.04080.01620.00510.9563
SS-NeRF (Enlarged)34.200.02100.03880.01070.00350.955727.370.02260.04050.01860.00530.9498
SceneNet RGB-DSS-NeRF28.930.0244-0.02160.00500.917529.180.0182-0.01970.00520.9510
MuvieNeRF29.290.0237-0.02070.00490.919029.560.0173-0.01890.00500.9556
SS-NeRF (Enlarged)29.030.0244-0.02150.00490.918629.460.0182-0.01910.00500.9520
+ +Table 7. Comparison between MuvieNeRF and an enlarged version of SS-NeRF. our model still significantly outperforms SS-NeRF (Enlarged), indicating that the good performance of MuvieNeRF is not simply achieved by a heavier decoder, and demonstrating the effectiveness of our module designs. + +
ModelRuntime (Per Training Iter.)Num. of Params.FLOPs
SS-NeRF1×1.21M4.57 × 1011
MuvieNeRF1.22×1.30M5.84 × 1011
+ +Table 8. Computational cost for SS-NeRF and MuvieNeRF on Replica dataset. Our CTA and CVA modules are light-weight designs. + +InvPT [61] takes a transformer-based architecture that encourages long-range and global context to benefit multi-task learning. + +Table 3 details the averaged results and Figure 3 offers a visual comparison. It is discernible that our MuvieNeRF outstrips all the discriminative models, illustrating that these models struggle to effectively tackle the MTVS problem, despite fine-tuning or utilizing GT images. We surmise that this shortcoming is rooted in the evaluation of novel scenes, wherein the generalization capability of our model noticeably outperforms that of discriminative ones. + +# 4.4. Ablation Study + +We consider the test scene evaluation on the Replica dataset for the following ablation and exploration sections. + +Contributions of CTA and CVA: We dissect the individual contributions of the proposed CTA and CVA modules in Table 4. An examination of the results reveals a more significant impact from the CTA module, when compared with the CVA module. We postulate that this occurs because the NeRF encoder and volume rendering have already mastered an implicit 3D representation, albeit falling short in modeling task relationships. Nevertheless, the integration of both modules yields further enhancement. + +Choice of Condition NeRF: We also ablate the conditional NeRF encoders with PixelNeRF [64], MVSNeRF [6], GNT [48], and GeoNeRF [22] in Table 5. Note that we only adopt the encoder part defined in Section 3, causing a variation in performance from the full model. Each variant under our design surpasses its respective SS-NeRF baseline, affirming the universal advantage of our proposed CTA and CVA modules across different conditional NeRF encoders. + +Effectiveness of CTA and CVA Modules: By integrating CVA and CTA modules, we concurrently increase the number of trainable parameters. To truly assess the advancements brought by the proposed CVA and CTA modules, we + +![](images/55b7c0fcc4a495b0121d6606fd66ba53ba503cfa3ed4c87a12d663f52c192fd2.jpg) + +![](images/80f6134d1a7ce8d6acc90a3db9f630d795f9a345ee436aab0dca0bdb6f07f3f1.jpg) +RGB + +![](images/05b890a09177a557c78cccaf01e88066f1f63222ca81a3bf39e75b09b92e42e7.jpg) + +![](images/40122bf2468ce72e348b018a6ab7997a6426e4f24b9fd59b368b9834ae21b61b.jpg) + +![](images/b66dbefe2abb7286d05039ac8d031f7aebc7f4022e4619f000167990e102ee76.jpg) + +![](images/bea2a06bf0cd3508c765cfff5edad7db9d7e0cccc17c6a90942020af1dda942d.jpg) + +![](images/bea6f9799c883c94134f021b93efe8e2045cf32a50688c2bc5f30f2b01b4688e.jpg) +Discriminative MuvieNeRF ${}_{D}$ Ground Truth +Figure 4. Visualizations for the setting without nearby-view annotations. our MuvieNeRF $D$ markedly surpasses the discriminative baseline model [45] and can generate results closely paralleling the ground truth, indicating MuvieNeRF $D$ is capable of tackling the more challenging settings. + +introduce an expanded version of SS-NeRF, designated as SS-NeRF (Enlarged). This variant features a doubled latent dimension, comprising 2.09M parameters and $6.18 \times 10^{11}$ FLOPs. The outcomes, as illustrated in Table 7, confirm that MuvieNeRF's excellent performance is not simply the result of a more complex decoder, thereby highlighting the effectiveness of our module designs. Moreover, we further list the computational cost for our model and SS-NeRF in Table 8 to show that our CTA and CVA modules are indeed lightweight, but effective designs. + +# 4.5. Additional Explorations + +# 4.5.1 Tackling Unknown Source-view Labels + +In this section, we apply the variant discussed in Section 3.4 to tackle the more challenging problem setting with unknown nearby-view annotations. In Table 6, we show the quantitative comparisons for this variant, MuvieNeRF $_D$ , and a hybrid baseline, Discriminative [45], which shares almost the same architecture as our discriminative module. We use pre-trained weights from Taskonomy [66] to initialize weights for both models. Limited by the computational + +![](images/40d2deba80684f7c3a1809aa478fd2cd11989310ad76e6db6811193a3e1f112d.jpg) +GeoNeRF + +![](images/a20cbb13c7d65fcab97d2e0fa1a187b1a4b178c06d279f94460c5de2bcdbc41d.jpg) +MuvieNeRF (Ours) + +![](images/091e080b8419f1378e0f895ab4f76ff0ed35d832aa42bd5c1de2ae7f72cdaa0d.jpg) +Ground Truth +Figure 5. An out-of-distribution comparison on BlendedMVS dataset [59] for GeoNeRF and our MuvieNeRF. Our model offers superior visual quality and preserves sharp contours. More visualizations about other OOD benchmarks are included in the supplementary. + +constraint, we select three tasks, SN, ED, and KP with the closest relationships [45] for demonstration in this setting. + +In conjunction with the visualizations illustrated in Figure 4, it is clear that our MuvieNeRF $_D$ markedly surpasses the discriminative baseline model [45] and can generate results closely paralleling the ground truth. This observation indicates that our model is capable of tackling more challenging settings. We conjecture the reason is that the weighted sum format (Equation 11) enhances the fault tolerance of the predictions. + +# 4.5.2 Out-of-distribution Generalization + +We demonstrate how the multi-task information learned from one dataset can effectively be utilized to benefit other datasets, by performing a zero-shot adaptation on out-of-distribution datasets with our MuvieNeRF trained on Replica. This takes a step further from investigating the generalization ability of unseen testing scenes in previous sections. We consider four datasets in total: LLFF [31], TartanAir [55], ScanNet [9], and BlendedMVS [59] containing indoor, outdoor, and even object-centric scenes. + +As an illustrative example, we showcase the comparison between the conditional NeRF backbone, GeoNeRF [22], and our MuvieNeRF for the novel-view RGB synthesis task in Table 9 and Figure 5. Evidently, our model surpasses GeoNeRF by a significant margin, offering superior visual quality and retaining sharp contours, likely a result of the edge and surface normal information absorbed during the multi-task training. These outcomes substantiate that augmenting the model with more tasks, as part of our multitask learning strategy, dramatically bolsters the generalization capability, thereby showcasing its immense potential for real-world applications. + +# 4.6. Limitations and Future work + +Limitations: One major limitation of this work is the reliance on data. MuvieNeRF requires images from dense + +
ModelScanNetTartanAirLLFFBlendedMVS
GeoNeRF31.7126.5120.6816.27
MuvieNeRF32.7630.2122.9120.97
+ +Table 9. Averaged PSNR of out-of-distribution RGB synthesis task. Our model surpasses the GeoNeRF baseline by a large margin, affirming that the inclusion of additional tasks, as part of our approach, contributes to a substantial enhancement in the model's generalization capacity. + +views, a requirement not fulfilled by most multi-task benchmarks. To circumvent this limitation, techniques that allow NeRF to learn from sparse views [35, 67] could be adopted. + +Task Relationships: As elaborated in Section 4.2, SH and KP function as auxiliary tasks within the system. A deeper exploration into the relationships between tasks and the corresponding geometric underpinnings within our synthesis framework offers intriguing avenues for future research. + +Extension to Other Synthesis Models: We have demonstrated that incorporating cross-view geometry and cross-task knowledge can enhance multi-task learning for synthesis models. We anticipate that similar strategies could be extended to 3D synthesis models other than NeRF, such as point clouds [57] and meshes [17, 26]. + +# 5. Conclusion + +This paper introduces the novel concept of Multi-Task View Synthesis (MTVS), recasting multi-task learning as a set of view synthesis problems. Informed by this new perspective, we devise MuvieNeRF, a unified synthesis framework enriched with novel Cross-View Attention and Cross-Task Attention modules. MuvieNeRF enables the simultaneous synthesis of multiple scene properties from novel viewpoints. Through extensive experimental evaluations, we establish MuvieNeRF's proficiency in addressing the MTVS task, with performance exceeding that of discriminative models across various settings. Our model also demonstrates broad applicability, extending to a variety of conditional NeRF backbones. + +# Acknowledgement + +We thank Kangle Deng, Derek Hoiem, Ziqi Pang, Deva Ramanan, Manolis Savva, Shen Zheng, Yuanyi Zhong, JunYan Zhu, and Zhen Zhu for their valuable comments. + +This work was supported in part by NSF Grant 2106825, Toyota Research Institute, NIFA Award 2020-67021-32799, the Jump ARCHES endowment, the NCSA Fellows program, the Illinois-Inspers Partnership, and the Amazon Research Award. This work used NVIDIA GPUs at NCSA Delta through allocations CIS220014 and CIS230012 from the ACCESS program. + +# References + +[1] Zhipeng Bao, Martial Hebert, and Yu-Xiong Wang. Generative modeling for multi-task visual learning. In ICML, 2022. 3 +[2] Zhipeng Bao, Yu-Xiong Wang, and Martial Hebert. Bowtie networks: Generative modeling for joint few-shot recognition and novel-view synthesis. In ICLR, 2021. 2 +[3] Jonathan T. 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Current research, however, predominantly concentrates on the multi-task dense prediction setting, which overlooks the intrinsic 3D world and its multi-view consistent structures, and lacks the capability for versatile imagination. In response to these limitations, we present a novel problem setting - multi-task view synthesis (MTVS), which reinterprets multi-task prediction as a set of novel-view synthesis tasks for multiple scene properties, including RGB. To tackle the MTVS problem, we propose MuvieNeRF, a framework that incorporates both multi-task and cross-view knowledge to simultaneously synthesize multiple scene properties. MuvieNeRF integrates two key modules, the Cross-Task Attention (CTA) and Cross-View Attention (CVA) modules, enabling the efficient use of information across multiple views and tasks. Extensive evaluation on both synthetic and realistic benchmarks demonstrates that MuvieNeRF is capable of simultaneously synthesizing different scene properties with promising visual quality, even outperforming conventional discriminative models in various settings. Notably, we show that MuvieNeRF exhibits universal applicability across a range of NeRF backbones. Our code is available at https://github.com/zsh2000/MuvieNeRF." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 552, + 128, + 563 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 552, + 128, + 563 + ], + "spans": [ + { + "bbox": [ + 47, + 552, + 128, + 563 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 572, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 572, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 572, + 287, + 693 + ], + "type": "text", + "content": "When observing a given scene, human minds exhibit a remarkable capability to mentally simulate the objects within it from a novel viewpoint in a versatile manner [40]. It not only includes imagination of the colors of objects, but also extends to numerous associated scene properties such as surface orientation, semantic segmentation, and edge patterns. Prompted by this, a burgeoning interest has emerged, seeking to equip modern robotic systems with similar capabilities for handling multiple tasks. Nevertheless, contemporary research [33, 65, 66] has primarily centered on" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 310, + 214, + 545, + 302 + ], + "blocks": [ + { + "bbox": [ + 310, + 214, + 545, + 302 + ], + "lines": [ + { + "bbox": [ + 310, + 214, + 545, + 302 + ], + "spans": [ + { + "bbox": [ + 310, + 214, + 545, + 302 + ], + "type": "image", + "image_path": "2b6fb237f2ab4e594ef8cc37c31a5363d923c71275131fafe1610fb5460aa50d.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 350, + 304, + 506, + 316 + ], + "lines": [ + { + "bbox": [ + 350, + 304, + 506, + 316 + ], + "spans": [ + { + "bbox": [ + 350, + 304, + 506, + 316 + ], + "type": "text", + "content": "(a) Conventional multi-task learning setting" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 313, + 331, + 529, + 392 + ], + "blocks": [ + { + "bbox": [ + 313, + 331, + 529, + 392 + ], + "lines": [ + { + "bbox": [ + 313, + 331, + 529, + 392 + ], + "spans": [ + { + "bbox": [ + 313, + 331, + 529, + 392 + ], + "type": "image", + "image_path": "eeb807a01b013e2da067a51a9e488a96ab6b4db5dae14c29dd4ce4918db2b20a.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 352, + 397, + 503, + 408 + ], + "lines": [ + { + "bbox": [ + 352, + 397, + 503, + 408 + ], + "spans": [ + { + "bbox": [ + 352, + 397, + 503, + 408 + ], + "type": "text", + "content": "(b) Our multi-task view synthesis pipeline" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 420, + 547, + 477 + ], + "lines": [ + { + "bbox": [ + 304, + 420, + 547, + 477 + ], + "spans": [ + { + "bbox": [ + 304, + 420, + 547, + 477 + ], + "type": "text", + "content": "Figure 1. Comparison between (a) the conventional multi-task learning scheme and (b) our multi-task view synthesis setting. The conventional \"discriminative\" multi-task learning makes predictions for single images while multi-task view synthesis aims to render visualizations for multiple scene properties at novel views." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 497, + 546, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 497, + 546, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 497, + 546, + 628 + ], + "type": "text", + "content": "the multi-task dense prediction setting, which employs a conventional discriminative model to simultaneously predict multiple pixel-level scene properties using given RGB images (refer to Figure 1(a)). Yet, the methodologies arising from this context often demonstrate practical limitations, primarily due to their tendency to treat each image as a separate entity, without constructing an explicit 3D model that adheres to the principle of multi-view consistency. Even more critically, they lack the ability to \"imagine\" – they are incapable of inferring scene properties from an unseen viewpoint, as these models invariably require RGB images." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 547, + 715 + ], + "type": "text", + "content": "To circumvent these constraints, we propose a novel approach that revisits multi-task learning (MTL) [5] from a synthesis perspective. This leads to a more flexible problem setting that reinterprets multi-task visual learning as a collection of novel-view synthesis problems, which we refer to as multi-task view synthesis (MTVS) (refer to Figure 1(b)). As an illustration, the task of predicting surface" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 703, + 124, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 703, + 124, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 703, + 124, + 712 + ], + "type": "text", + "content": "*Equal contribution" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "21538" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 167 + ], + "type": "text", + "content": "normals for a given image could be reframed as visualizing a three-channel \"image\" with the given pose and camera parameters. With the achievements of Neural Radiance Fields (NeRF) [32], the implicit scene representation offers an effective solution to synthesize scene properties beyond RGB [68]. Importantly, this scene representation takes multi-view geometry into account, which consequently enhances the performance of all tasks." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 170, + 288, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 170, + 288, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 170, + 288, + 422 + ], + "type": "text", + "content": "Extending from [68], we make the exploration that mining multi-task knowledge can simultaneously enhance the learning of different tasks, extending beyond discriminative models [45, 66] to include synthesis models as well. Furthermore, we argue that the alignment of features across multiple reference views and the target view can reinforce cross-view consistency, thereby bolstering the implicit scene representation learning. Informed by this insight, we propose MuvieNeRF, a unified framework for the MTVS task, which incorporates Multi-task and cross-view knowledge, thus enabling the simultaneous synthesis of multiple scene properties through a shared implicit scene representation. MuvieNeRF can be applied to an arbitrary conditional NeRF architecture and features a unified decoder with two key modules: Cross-Task Attention (CTA) module, which investigates relationships among different scene properties, and Cross-View Attention (CVA) module, which aligns features across multiple views. The integration of these two modules within MuvieNeRF facilitates the efficient utilization of information from multiple views and tasks, leading to better performance across all tasks." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 424, + 287, + 603 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 424, + 287, + 603 + ], + "spans": [ + { + "bbox": [ + 46, + 424, + 287, + 603 + ], + "type": "text", + "content": "To demonstrate the effectiveness of our approach, we first instantiate our MuvieNeRF with GeoNeRF [22], a state-of-the-art conditional NeRF model, and conduct comprehensive evaluations on both synthetic and real-world benchmarks. The results illustrate that MuvieNeRF is capable of solving multi-task learning in a synthesis manner, even outperforming several competitive discriminative models in different settings. Moreover, we ablate the choice of conditional NeRF backbones to illustrate the broad applicability of our framework. We further validate the individual contributions of the CVA and CTA modules by building and comparing different variants of MuvieNeRF. Finally, we demonstrate the broader applications and analysis of MuvieNeRF, such as generalization on out-of-distribution datasets." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 715 + ], + "type": "text", + "content": "In summary, our contributions are three-fold: (1) We pioneer a novel problem definition, multi-task view synthesis (MTVS), which reconsiders multi-task visual learning as a set of view synthesis tasks. The introduction of MTVS paves the way for robots to emulate human-like mental simulation capabilities by utilizing the implicit scene representation offered by Neural Radiance Fields (NeRF). (2) We present MuvieNeRF, a unified framework that employs Cross-Task Attention (CTA) and Cross-View Atten" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "text", + "content": "tion (CVA) modules to leverage cross-view and cross-task information for the MTVS problem. (3) Comprehensive experimental evaluations demonstrate that MuvieNeRF shows promising results for MTVS, and greatly outperforms conventional discriminative models across diverse settings." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 146, + 392, + 158 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 146, + 392, + 158 + ], + "spans": [ + { + "bbox": [ + 306, + 146, + 392, + 158 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 167, + 545, + 214 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 167, + 545, + 214 + ], + "spans": [ + { + "bbox": [ + 304, + 167, + 545, + 214 + ], + "type": "text", + "content": "In this work, we propose the MuvieNeRF model which leverages both multi-task and cross-view information for multi-task view synthesis. We review the most relevant work in the areas below." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 217, + 546, + 433 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 217, + 546, + 433 + ], + "spans": [ + { + "bbox": [ + 304, + 217, + 546, + 433 + ], + "type": "text", + "content": "View Synthesis aims to generate a target image with an arbitrary camera pose by referring to source images [50]. Numerous existing methods have delivered promising results in this area [2, 34, 44, 57, 63]. However, unlike these conventional approaches, MTVS endeavors to synthesize multiple scene properties, including RGB, from novel viewpoints. In pursuit of a similar goal, another group of methods seeks to render multiple annotations for novel views, following a first-reconstruct-then-render strategy [12, 13, 19, 26]. These methods typically collect or construct a 3D scene representation (e.g., mesh or point cloud) and subsequently render multiple scene properties using 3D-to-2D projection. In contrast, our work constructs an implicit 3D scene representation using a NeRF-style model based on 2D data. This approach is more computationally efficient and, importantly, our implicit representation provides an opportunity to further model task relationships, an advantage the aforementioned methods do not possess." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 435, + 546, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 435, + 546, + 687 + ], + "spans": [ + { + "bbox": [ + 304, + 435, + 546, + 687 + ], + "type": "text", + "content": "Neural Radiance Fields are originally designed for synthesizing novel-view images with ray tracing and volume rendering technologies [32]. Follow-up work [3, 10, 14, 18, 27, 29, 35, 36, 38, 39, 41, 49, 56, 58] further improves the image quality, optimization, and compositionality. In addition, several approaches [6, 22, 48, 64], namely conditional NeRFs, encode the scene information to enable the conditional generalization to novel scenes, which are more aligned with our setting. Our MuvieNeRF takes the encoders from these conditional NeRFs as backbones. Some work has also paid attention to synthesizing other properties of scenes [11, 37, 53, 60, 68, 69]. Among them, SemanticNeRF [69] extends NeRF from synthesizing RGB images to additionally synthesizing semantic labels. SS-NeRF [68] further generalizes the NeRF architecture to simultaneously render RGB and different scene properties with a shared scene representation. Panoptic 3D volumetric representation [43] is introduced to jointly synthesize RGB and panoptic segmentation for in-the-wild images. Different from them, we tackle the novel MTVS task and leverage both cross-view and cross-task information." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 714 + ], + "type": "text", + "content": "Multi-task Learning aims to leverage shared knowledge across different tasks to achieve optimal performance on" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "21539" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": "all the tasks. Recent work improves multi-task learning performance by focusing on better optimization strategies [1, 7, 8, 15, 20, 21, 28] and exploring more efficient multi-task architectures [4, 23, 47, 54]." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 122, + 288, + 266 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 122, + 288, + 266 + ], + "spans": [ + { + "bbox": [ + 46, + 122, + 288, + 266 + ], + "type": "text", + "content": "Cross-task Relationship is an interesting topic in multi-task learning, which aims to explore the underlying task relationships among different visual tasks [24]. Taking the task relationship into consideration, cross-stitch networks [33] adopt a learnable parameter-sharing strategy for multi-task learning. Taskonomy and its follow-up work [45, 65, 66] systematically study the internal task relationships and design the optimal multi-task learning schemes accordingly to obtain the best performance. Inspired by them, we also investigate how to better model multi-task learning but in a synthesis framework with our model-agnostic MuvieNeRF." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 275, + 103, + 288 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 275, + 103, + 288 + ], + "spans": [ + { + "bbox": [ + 47, + 275, + 103, + 288 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 295, + 287, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 295, + 287, + 390 + ], + "spans": [ + { + "bbox": [ + 46, + 295, + 287, + 390 + ], + "type": "text", + "content": "In this section, we first describe our novel multi-task view synthesis problem in Section 3.1. Next, we briefly review conditional neural radiance fields (NeRFs) and volume rendering in Section 3.2. In Section 3.3, we explain the proposed MuvieNeRF (as shown in Figure 2) in detail. Finally, we discuss how we handle a more challenging setting without access to source-view annotations at test time in Section 3.4." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 397, + 234, + 410 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 397, + 234, + 410 + ], + "spans": [ + { + "bbox": [ + 47, + 397, + 234, + 410 + ], + "type": "text", + "content": "3.1. Multi-task View Synthesis Problem" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 416, + 287, + 501 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 416, + 287, + 501 + ], + "spans": [ + { + "bbox": [ + 46, + 416, + 287, + 501 + ], + "type": "text", + "content": "Different from conventional multi-task learning settings, our goal is to jointly synthesize multiple scene properties including RGB images from novel views. Therefore, we aim to learn a model " + }, + { + "bbox": [ + 46, + 416, + 287, + 501 + ], + "type": "inline_equation", + "content": "\\Phi" + }, + { + "bbox": [ + 46, + 416, + 287, + 501 + ], + "type": "text", + "content": " which takes a set of " + }, + { + "bbox": [ + 46, + 416, + 287, + 501 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 46, + 416, + 287, + 501 + ], + "type": "text", + "content": " source-view task annotations with camera poses as reference, and predicts the task annotations for a novel view given camera pose (Inference Setting I):" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 99, + 506, + 287, + 526 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 99, + 506, + 287, + 526 + ], + "spans": [ + { + "bbox": [ + 99, + 506, + 287, + 526 + ], + "type": "interline_equation", + "content": "\\mathbf {Y} _ {T} = \\Phi \\left(\\left\\{\\left(\\mathbf {Y} _ {i}, \\mathbf {P} _ {i}\\right) \\right\\} _ {i = 1} ^ {V}, \\mathbf {P} _ {T}\\right), \\tag {1}", + "image_path": "27982b1b60f76ec03fbc7198c04e5334ee4bb526c702c53cc1c707986c512509.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "spans": [ + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "inline_equation", + "content": "\\mathbf{Y}_i = [\\mathbf{x}_i, \\mathbf{y}_i^1, \\dots, \\mathbf{y}_i^K]" + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "text", + "content": " denotes RGB images " + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i" + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "text", + "content": " other multi-task annotations " + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{y}_i^j\\}_{j=1}^K" + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "text", + "content": " in the " + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "inline_equation", + "content": "i^{\\text{th}}" + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "text", + "content": " source view. " + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_i" + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "text", + "content": " is the " + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "inline_equation", + "content": "i^{\\text{th}}" + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "text", + "content": " source camera pose, and " + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_T" + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "text", + "content": " is the target camera pose. During evaluation, " + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "inline_equation", + "content": "\\Phi" + }, + { + "bbox": [ + 47, + 533, + 287, + 597 + ], + "type": "text", + "content": " is supposed to be generalized to novel scenes that are not seen during training." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 597, + 287, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 597, + 287, + 657 + ], + "spans": [ + { + "bbox": [ + 46, + 597, + 287, + 657 + ], + "type": "text", + "content": "For the evaluation of those novel scenes, we also provide a more challenging setting lacking source-view annotations during the inference time with the assumption that the model may not get access to additional annotations other than RGB during inference (Inference Setting II):" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 100, + 663, + 287, + 684 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 663, + 287, + 684 + ], + "spans": [ + { + "bbox": [ + 100, + 663, + 287, + 684 + ], + "type": "interline_equation", + "content": "\\mathbf {Y} _ {T} = \\Phi \\left(\\left\\{\\left(\\mathbf {x} _ {i}, \\mathbf {P} _ {i}\\right) \\right\\} _ {i = 1} ^ {V}, \\mathbf {P} _ {T}\\right). \\tag {2}", + "image_path": "7f1463000db5d581b397af046f6e2cacaaead951dc1beb032a631205b75e5cd1.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 714 + ], + "type": "text", + "content": "With the above two settings, Inference Setting I allows us to better evaluate the task relationships in our synthesis" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 119 + ], + "type": "text", + "content": "framework in a cleaner manner, so it is the focused setting in our paper; Inference Setting II is more aligned with real practice, for which we also propose a solution which is discussed in Sections 3.4 and 4.5." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 129, + 545, + 154 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 129, + 545, + 154 + ], + "spans": [ + { + "bbox": [ + 305, + 129, + 545, + 154 + ], + "type": "text", + "content": "3.2. Preliminary: Conditional Neural Radiance Fields and Volume Rendering" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "text", + "content": "Neural radiance fields (NeRFs) [32] propose a powerful solution for implicit scene representation, and are widely used in novel view image synthesis. Given the 3D position of a point " + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\mathbf{q} = (x,y,z)" + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "text", + "content": " in the scene and the 2D viewing direction " + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\mathbf{d} = (\\theta ,\\phi)" + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "text", + "content": ", NeRFs learn a mapping function " + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "inline_equation", + "content": "(\\mathbf{c},\\sigma) = F(\\mathbf{q},\\mathbf{d})" + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "text", + "content": ", which maps the 5D input " + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "inline_equation", + "content": "(\\mathbf{q},\\mathbf{d})" + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "text", + "content": " to RGB color " + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\mathbf{c} = (r,g,b)" + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "text", + "content": " and density " + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 159, + 545, + 243 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "spans": [ + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "text", + "content": "To enhance the generalizability of NeRFs, conditional NeRFs [6, 22, 48, 64] learn a scene representation across multiple scenes. They first extract a feature volume " + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "inline_equation", + "content": "\\mathbf{W} = E(\\mathbf{x})" + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "text", + "content": " for each input image " + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "inline_equation", + "content": "\\mathbf{x}" + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "text", + "content": " of a scene. Next, for an arbitrary point " + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "inline_equation", + "content": "\\mathbf{q}" + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "text", + "content": " on a camera ray with direction " + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "inline_equation", + "content": "\\mathbf{d}" + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "text", + "content": ", they are able to retrieve the corresponding image feature on " + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "inline_equation", + "content": "\\mathbf{W}" + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "text", + "content": " by projecting " + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "inline_equation", + "content": "\\mathbf{q}" + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "text", + "content": " onto the image plane with known pose " + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "inline_equation", + "content": "\\mathbf{P}" + }, + { + "bbox": [ + 304, + 244, + 545, + 349 + ], + "type": "text", + "content": ". We treat the above part as the conditional NeRF encoder, which returns:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 361, + 350, + 545, + 366 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 361, + 350, + 545, + 366 + ], + "spans": [ + { + "bbox": [ + 361, + 350, + 545, + 366 + ], + "type": "interline_equation", + "content": "f _ {\\text {s c e n e}} = F _ {\\text {e n c}} \\left(\\left\\{\\mathbf {x} _ {i}, \\mathbf {P} _ {i} \\right\\} _ {i = 1} ^ {V}, \\mathbf {q}\\right). \\tag {3}", + "image_path": "3f22c893478a64a6b48fd0c7b98d71c71f9fec0559741b5d24260e4ffd82d770.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 371, + 545, + 420 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 371, + 545, + 420 + ], + "spans": [ + { + "bbox": [ + 304, + 371, + 545, + 420 + ], + "type": "text", + "content": "We have " + }, + { + "bbox": [ + 304, + 371, + 545, + 420 + ], + "type": "inline_equation", + "content": "f_{\\mathrm{scene}} \\in \\mathbb{R}^{V \\times d_{\\mathrm{scene}}}" + }, + { + "bbox": [ + 304, + 371, + 545, + 420 + ], + "type": "text", + "content": ", which contains the scene representation from " + }, + { + "bbox": [ + 304, + 371, + 545, + 420 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 304, + 371, + 545, + 420 + ], + "type": "text", + "content": " views. Next, the conditional NeRFs further learn a decoder " + }, + { + "bbox": [ + 304, + 371, + 545, + 420 + ], + "type": "inline_equation", + "content": "(\\mathbf{c}, \\sigma) = F_{\\mathrm{dec}}(\\mathbf{q}, \\mathbf{d}, f_{\\mathrm{scene}})" + }, + { + "bbox": [ + 304, + 371, + 545, + 420 + ], + "type": "text", + "content": " to predict the color and density." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "spans": [ + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "text", + "content": "Given the color and density of 3D points, NeRFs render the 2D images by running volume rendering for each pixel with ray tracing. Every time when rendering a pixel in a certain view, a ray " + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "inline_equation", + "content": "\\mathbf{r}(t) = \\mathbf{o} + t\\mathbf{d}" + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "text", + "content": " which origins from the center " + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "inline_equation", + "content": "\\mathbf{o}" + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "text", + "content": " of the camera plane in the direction " + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "inline_equation", + "content": "\\mathbf{d}" + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "text", + "content": " is traced. NeRFs randomly sample " + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "text", + "content": " points " + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "inline_equation", + "content": "\\{t_m\\}_{m=1}^M" + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "text", + "content": " with color " + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "inline_equation", + "content": "\\mathbf{c}(t_m)" + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "text", + "content": " and density " + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "inline_equation", + "content": "\\sigma(t_m)" + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "text", + "content": " between the near boundary " + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "inline_equation", + "content": "t_n" + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "text", + "content": " and far boundary " + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "inline_equation", + "content": "t_f" + }, + { + "bbox": [ + 304, + 421, + 545, + 517 + ], + "type": "text", + "content": ". The RGB value of the pixel is given by:" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 345, + 526, + 545, + 559 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 345, + 526, + 545, + 559 + ], + "spans": [ + { + "bbox": [ + 345, + 526, + 545, + 559 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {C}} (\\mathbf {r}) = \\sum_ {m = 1} ^ {M} \\hat {T} (t _ {m}) \\alpha \\left(\\delta_ {m} \\sigma \\left(t _ {m}\\right)\\right) \\mathbf {c} \\left(t _ {m}\\right), \\tag {4}", + "image_path": "6fa0fb122240994af324b64e467c545ffc1a20951803608f48f99e789137902b.jpg" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 568, + 545, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 568, + 545, + 594 + ], + "spans": [ + { + "bbox": [ + 304, + 568, + 545, + 594 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 568, + 545, + 594 + ], + "type": "inline_equation", + "content": "\\delta_{m}" + }, + { + "bbox": [ + 304, + 568, + 545, + 594 + ], + "type": "text", + "content": " is the distance between two consecutive sampled points " + }, + { + "bbox": [ + 304, + 568, + 545, + 594 + ], + "type": "inline_equation", + "content": "(\\delta_{m} = \\| t_{m + 1} - t_{m}\\|),\\alpha (d) = 1 - \\exp (-d)" + }, + { + "bbox": [ + 304, + 568, + 545, + 594 + ], + "type": "text", + "content": " , and" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 358, + 602, + 545, + 641 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 358, + 602, + 545, + 641 + ], + "spans": [ + { + "bbox": [ + 358, + 602, + 545, + 641 + ], + "type": "interline_equation", + "content": "\\hat {T} \\left(t _ {m}\\right) = \\exp \\left(- \\sum_ {j = 1} ^ {m - 1} \\delta_ {j} \\sigma \\left(t _ {j}\\right)\\right) \\tag {5}", + "image_path": "93db2700dc9db5aeed6e57d53d809b2f67d423b2006941183e9787639132174b.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 650, + 545, + 673 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 650, + 545, + 673 + ], + "spans": [ + { + "bbox": [ + 304, + 650, + 545, + 673 + ], + "type": "text", + "content": "denotes the accumulated transmittance. The same technique can be used to render an arbitrary scene property " + }, + { + "bbox": [ + 304, + 650, + 545, + 673 + ], + "type": "inline_equation", + "content": "\\mathbf{y}^j" + }, + { + "bbox": [ + 304, + 650, + 545, + 673 + ], + "type": "text", + "content": " by:" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 340, + 683, + 545, + 716 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 340, + 683, + 545, + 716 + ], + "spans": [ + { + "bbox": [ + 340, + 683, + 545, + 716 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {Y}} ^ {j} (\\mathbf {r}) = \\sum_ {m = 1} ^ {M} \\hat {T} (t _ {m}) \\alpha \\left(\\delta_ {m} \\sigma \\left(t _ {m}\\right)\\right) \\mathbf {y} ^ {j} \\left(t _ {m}\\right). \\tag {6}", + "image_path": "ab7d18caaf5584c3822fb1135bc85a21c021c62b09cba74dc38f22fbf4be5804.jpg" + } + ] + } + ], + "index": 22 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "21540" + } + ] + } + ], + "index": 23 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 75, + 74, + 527, + 296 + ], + "blocks": [ + { + "bbox": [ + 75, + 74, + 527, + 296 + ], + "lines": [ + { + "bbox": [ + 75, + 74, + 527, + 296 + ], + "spans": [ + { + "bbox": [ + 75, + 74, + 527, + 296 + ], + "type": "image", + "image_path": "c51b74901fa9f0fdb0ba8ac351a778c51df743ed2767db8cb25f8b673f7c4277.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 300, + 546, + 323 + ], + "lines": [ + { + "bbox": [ + 46, + 300, + 546, + 323 + ], + "spans": [ + { + "bbox": [ + 46, + 300, + 546, + 323 + ], + "type": "text", + "content": "Figure 2. Model architecture. MuvieNeRF is a unified framework for multi-task view synthesis equipped with Cross-View Attention (CVA) and Cross-Task Attention (CTA) modules. It predicts multiple scene properties for arbitrary 3D coordinates with source-view annotations." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 331, + 127, + 342 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 331, + 127, + 342 + ], + "spans": [ + { + "bbox": [ + 47, + 331, + 127, + 342 + ], + "type": "text", + "content": "3.3. MuvieNeRF" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "type": "text", + "content": "As illustrated in Figure 2, MuvieNeRF first fetches the scene representation " + }, + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "type": "inline_equation", + "content": "f_{\\mathrm{scene}}" + }, + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "type": "text", + "content": " from the conditional NeRF encoder, then predicts multiple scene properties " + }, + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "type": "inline_equation", + "content": "[\\mathbf{x}(\\mathbf{q}), \\mathbf{y}^{1}(\\mathbf{q}), \\dots, \\mathbf{y}^{K}(\\mathbf{q})]" + }, + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "type": "text", + "content": " for arbitrary 3D coordinate " + }, + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "type": "inline_equation", + "content": "\\mathbf{q}" + }, + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "type": "text", + "content": ". The final annotations are rendered by Equation 6. We explain how to predict multiple scene properties with " + }, + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "type": "inline_equation", + "content": "f_{\\mathrm{scene}}" + }, + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "type": "text", + "content": " and source annotations " + }, + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "type": "inline_equation", + "content": "[(\\mathbf{Y}_1, \\mathbf{P}_1), \\dots, (\\mathbf{Y}_V, \\mathbf{P}_V)]" + }, + { + "bbox": [ + 46, + 350, + 288, + 460 + ], + "type": "text", + "content": " as follows. The full detailed architecture is included in the supplementary." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 476, + 205, + 488 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 476, + 205, + 488 + ], + "spans": [ + { + "bbox": [ + 47, + 476, + 205, + 488 + ], + "type": "text", + "content": "3.3.1 Cross-view Attention Module" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "text", + "content": "The cross-view attention (CVA) module (Figure 2 bottom left) leverages the multi-view information for MuvieNeRF. To start, we first concatenate " + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "inline_equation", + "content": "f_{\\mathrm{scene}}" + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "text", + "content": " with a positional embedding derived from the target ray and the source-view image plane: " + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "inline_equation", + "content": "f_{\\mathrm{scene}}^{\\mathrm{pos}} = [f_{\\mathrm{scene}}; \\gamma(\\theta_{n,v})]" + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "inline_equation", + "content": "\\gamma(\\cdot)" + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "text", + "content": " is the positional encoding proposed in [32], and " + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "inline_equation", + "content": "\\theta_{n,v}" + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "text", + "content": " is the angle between the novel camera ray " + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "inline_equation", + "content": "\\mathbf{r}" + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "text", + "content": " and the line that connects the camera center of view " + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "text", + "content": " and the point " + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "inline_equation", + "content": "\\mathbf{q}_n" + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "text", + "content": " in the queried ray, which measures the similarity between the source view " + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "inline_equation", + "content": "v" + }, + { + "bbox": [ + 46, + 497, + 287, + 616 + ], + "type": "text", + "content": " and the target view." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "text", + "content": "Next, " + }, + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "text", + "content": " CVA modules are used to leverage the cross-view information. Concretely, in each module, we have one self-attention union followed by a multi-layer perceptron (MLP): " + }, + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "inline_equation", + "content": "f_{\\mathrm{CVA}} = \\mathrm{MLP}_{\\mathrm{CVA}}(f_{\\mathrm{scene}}^{\\mathrm{pos}} + \\mathrm{MHA}(f_{\\mathrm{scene}}^{\\mathrm{pos}}, f_{\\mathrm{scene}}^{\\mathrm{pos}}))" + }, + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "inline_equation", + "content": "\\mathrm{MHA}(a, b)" + }, + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "text", + "content": " denotes multi-head attention [52] with " + }, + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "text", + "content": " as query and " + }, + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "inline_equation", + "content": "b" + }, + { + "bbox": [ + 46, + 617, + 287, + 689 + ], + "type": "text", + "content": " as key and value." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "content": "After these processes, we apply " + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "(K + 1)" + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "content": " different MLPs (corresponding to " + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 689, + 287, + 714 + ], + "type": "text", + "content": " vision tasks in multi-task view syn" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 332, + 546, + 367 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 332, + 546, + 367 + ], + "spans": [ + { + "bbox": [ + 305, + 332, + 546, + 367 + ], + "type": "text", + "content": "thesis plus the RGB synthesis task) to broadcast the shared feature, leading to the " + }, + { + "bbox": [ + 305, + 332, + 546, + 367 + ], + "type": "inline_equation", + "content": "(K + 1)" + }, + { + "bbox": [ + 305, + 332, + 546, + 367 + ], + "type": "text", + "content": "-branch feature " + }, + { + "bbox": [ + 305, + 332, + 546, + 367 + ], + "type": "inline_equation", + "content": "f_{\\mathrm{task}} \\in \\mathbb{R}^{(K + 1) \\times V \\times d_{\\mathrm{task}}}" + }, + { + "bbox": [ + 305, + 332, + 546, + 367 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 387, + 463, + 398 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 387, + 463, + 398 + ], + "spans": [ + { + "bbox": [ + 306, + 387, + 463, + 398 + ], + "type": "text", + "content": "3.3.2 Cross-task Attention Module" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "spans": [ + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "text", + "content": "In order to simultaneously benefit all the downstream tasks, we propose a novel cross-task attention (CTA) module (Figure 2 bottom right) to facilitate knowledge sharing and information flow among all the tasks. The CTA module has two attention components with shared learnable task prompts [62], " + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "inline_equation", + "content": "p_t \\in \\mathbb{R}^{(K + 1) \\times d_t}" + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "inline_equation", + "content": "d_t" + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "text", + "content": " is the dimension of task prompts. The first attention component applies cross-attention between features from each branch and the task prompts " + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "inline_equation", + "content": "f_{\\mathrm{stage1}} = f_{\\mathrm{task}} + \\mathrm{MHA}(f_{\\mathrm{task}}, p_t)" + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "text", + "content": ". In this stage, we run " + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "text", + "content": " MHA individually for each task branch with the shared task prompts. After the cross-attention, we further concatenate " + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "inline_equation", + "content": "f_{\\mathrm{stage1}}^j" + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "text", + "content": " for task " + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "inline_equation", + "content": "T_j" + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "text", + "content": " and the corresponding task prompt " + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "inline_equation", + "content": "p_t^j" + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "text", + "content": " to obtain " + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "inline_equation", + "content": "f_{\\mathrm{stage1'}}" + }, + { + "bbox": [ + 304, + 407, + 545, + 566 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 566, + 545, + 627 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 566, + 545, + 627 + ], + "spans": [ + { + "bbox": [ + 304, + 566, + 545, + 627 + ], + "type": "text", + "content": "Next, we apply the second component to use " + }, + { + "bbox": [ + 304, + 566, + 545, + 627 + ], + "type": "inline_equation", + "content": "\\beta" + }, + { + "bbox": [ + 304, + 566, + 545, + 627 + ], + "type": "text", + "content": " self-attention modules for all the branches jointly to leverage the cross-task features. The final feature representation is obtained by: " + }, + { + "bbox": [ + 304, + 566, + 545, + 627 + ], + "type": "inline_equation", + "content": "f_{\\mathrm{stage2}} = \\mathrm{MLP}_{\\mathrm{CTA}}(f_{\\mathrm{stage1'}} + \\mathrm{MHA}(f_{\\mathrm{stage1}}, f_{\\mathrm{stage1'}}))" + }, + { + "bbox": [ + 304, + 566, + 545, + 627 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 627, + 545, + 673 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 627, + 545, + 673 + ], + "spans": [ + { + "bbox": [ + 304, + 627, + 545, + 673 + ], + "type": "text", + "content": "Finally, to predict the task annotations of the target view, we adopt the formulation of GeoNeRF [22]. The prediction " + }, + { + "bbox": [ + 304, + 627, + 545, + 673 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{y}}^j" + }, + { + "bbox": [ + 304, + 627, + 545, + 673 + ], + "type": "text", + "content": " of task " + }, + { + "bbox": [ + 304, + 627, + 545, + 673 + ], + "type": "inline_equation", + "content": "T_{j}" + }, + { + "bbox": [ + 304, + 627, + 545, + 673 + ], + "type": "text", + "content": " on the target view is the weighted sum of the source views:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 373, + 683, + 545, + 715 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 373, + 683, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 373, + 683, + 545, + 715 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {y}} ^ {j} = \\sum_ {i = 1} ^ {V} \\mathbf {w} [ j, i ] \\cdot \\mathbf {y} [ j, i ], \\tag {7}", + "image_path": "eec3f0438a105ef3c5ce97117157f7cb543a3d467fd639257243bc35be95af91.jpg" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "21541" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 545, + 169 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 545, + 169 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 545, + 169 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 545, + 169 + ], + "type": "table", + "html": "
Evaluation TypeTraining scene evaluationTesting scene evaluation
TaskRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)RGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
ReplicaHeuristic29.600.02720.04820.02140.00490.932520.860.03950.05150.04710.00970.8543
Semantic-NeRF33.600.02110.04030.01280.00370.950727.080.02210.04180.02120.00550.9417
SS-NeRF33.760.02120.03830.01160.00350.953327.220.02240.04050.01960.00530.9483
MuvieNeRF34.920.01930.03450.01000.00340.958228.550.02010.04080.01620.00510.9563
SceneNet RGB-DHeuristic22.660.0496-0.05210.00930.868722.020.0394-0.05250.01240.8917
Semantic-NeRF28.290.0248-0.02120.00500.915228.850.0186-0.01980.00510.9417
SS-NeRF28.930.0244-0.02160.00500.917529.180.0182-0.01970.00520.9510
MuvieNeRF29.290.0237-0.02070.00490.919029.560.0173-0.01890.00500.9556
", + "image_path": "0138ef30853d13474e4a2f89dc323027d2f317ff88d0b792d236ba16df739424.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 173, + 546, + 207 + ], + "lines": [ + { + "bbox": [ + 46, + 173, + 546, + 207 + ], + "spans": [ + { + "bbox": [ + 46, + 173, + 546, + 207 + ], + "type": "text", + "content": "Table 1. Averaged performance of MuvieNeRF on Replica [46] and SceneNet RGB-D [30] datasets on both training scenes and testing scenes. Full results with multiple runs are provided in the supplementary, our model consistently outperforms both the single-task Semantic-NeRF baseline and multi-task SS-NeRF baseline, owing to the proposed CVA and CTA modules." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 227, + 287, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 227, + 287, + 264 + ], + "spans": [ + { + "bbox": [ + 47, + 227, + 287, + 264 + ], + "type": "text", + "content": "where the matrix " + }, + { + "bbox": [ + 47, + 227, + 287, + 264 + ], + "type": "inline_equation", + "content": "\\mathbf{y}" + }, + { + "bbox": [ + 47, + 227, + 287, + 264 + ], + "type": "text", + "content": " is made of input view annotations " + }, + { + "bbox": [ + 47, + 227, + 287, + 264 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{Y}_i\\}_{i=1}^V" + }, + { + "bbox": [ + 47, + 227, + 287, + 264 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 227, + 287, + 264 + ], + "type": "inline_equation", + "content": "\\mathbf{w}" + }, + { + "bbox": [ + 47, + 227, + 287, + 264 + ], + "type": "text", + "content": " is obtained by an additional MLP layer which processes " + }, + { + "bbox": [ + 47, + 227, + 287, + 264 + ], + "type": "inline_equation", + "content": "f_{\\mathrm{stage2}}" + }, + { + "bbox": [ + 47, + 227, + 287, + 264 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 281, + 137, + 293 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 281, + 137, + 293 + ], + "spans": [ + { + "bbox": [ + 47, + 281, + 137, + 293 + ], + "type": "text", + "content": "3.3.3 Optimization" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 300, + 287, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 300, + 287, + 337 + ], + "spans": [ + { + "bbox": [ + 46, + 300, + 287, + 337 + ], + "type": "text", + "content": "For the set of " + }, + { + "bbox": [ + 46, + 300, + 287, + 337 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 300, + 287, + 337 + ], + "type": "text", + "content": " tasks " + }, + { + "bbox": [ + 46, + 300, + 287, + 337 + ], + "type": "inline_equation", + "content": "\\mathcal{T} = \\{T_1, T_2, \\dots, T_K\\}" + }, + { + "bbox": [ + 46, + 300, + 287, + 337 + ], + "type": "text", + "content": " including the RGB colors, we apply their objectives individually and the final objective is formulated as" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 121, + 347, + 287, + 374 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 121, + 347, + 287, + 374 + ], + "spans": [ + { + "bbox": [ + 121, + 347, + 287, + 374 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {M T}} = \\sum_ {T _ {j} \\in \\mathcal {T}} \\lambda_ {T _ {j}} \\mathcal {L} _ {T _ {j}}, \\tag {8}", + "image_path": "d841160784fa61b34beab597a32bc38b6561f8ba998de7de49c3fc47d6a6b84a.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 384, + 287, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 384, + 287, + 410 + ], + "spans": [ + { + "bbox": [ + 46, + 384, + 287, + 410 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 384, + 287, + 410 + ], + "type": "inline_equation", + "content": "\\lambda_{T_j}" + }, + { + "bbox": [ + 46, + 384, + 287, + 410 + ], + "type": "text", + "content": " is the weight for the corresponding task " + }, + { + "bbox": [ + 46, + 384, + 287, + 410 + ], + "type": "inline_equation", + "content": "T_{j}" + }, + { + "bbox": [ + 46, + 384, + 287, + 410 + ], + "type": "text", + "content": ". For each task, " + }, + { + "bbox": [ + 46, + 384, + 287, + 410 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{T_j}" + }, + { + "bbox": [ + 46, + 384, + 287, + 410 + ], + "type": "text", + "content": " is formulated as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 105, + 420, + 287, + 445 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 105, + 420, + 287, + 445 + ], + "spans": [ + { + "bbox": [ + 105, + 420, + 287, + 445 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {T _ {j}} = \\sum_ {\\mathbf {r} \\in \\mathcal {R}} \\mathcal {L} _ {j} \\left(\\hat {\\mathbf {y}} ^ {j} (\\mathbf {r}), \\mathbf {y} ^ {j} (\\mathbf {r})\\right), \\tag {9}", + "image_path": "941177c0ac2c6bfa4ec6769656c9ad3427b6e8a3f2d970fbb2389e08a07d67b2.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "spans": [ + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\mathbf{y}^j (\\mathbf{r}),\\hat{\\mathbf{y}}^j (\\mathbf{r})" + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "text", + "content": " are the ground-truth and prediction for a single pixel regarding task " + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "inline_equation", + "content": "T_{j}" + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\mathcal{R}" + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "text", + "content": " is the set of rays " + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\mathbf{r}" + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "text", + "content": " for all training views. " + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_j" + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "text", + "content": " is chosen from " + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "text", + "content": " loss, " + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "inline_equation", + "content": "L_{2}" + }, + { + "bbox": [ + 46, + 456, + 287, + 516 + ], + "type": "text", + "content": " loss, and cross-entropy loss according to the characteristics of the tasks." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 526, + 268, + 539 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 526, + 268, + 539 + ], + "spans": [ + { + "bbox": [ + 47, + 526, + 268, + 539 + ], + "type": "text", + "content": "3.4. Tackling without Source-view Annotations" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 545, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 714 + ], + "type": "text", + "content": "The proposed model is based on the assumption that source-view task annotations are available during inference time. The assumption rules out the influence from inaccurate source-view task information, which sets a cleaner environment to excavate multi-task synergy in a synthesis framework for the MTVS problem. However, from the real application perspective, traditional discriminative models only take RGB images as input without any task annotations. To demonstrate that our model is able to be applied in real scenarios, we introduce the more challenging Inference Setting II formulated by Equation 2 and provide a solution by incorporating a U-Net [42] shaped module " + }, + { + "bbox": [ + 46, + 545, + 288, + 714 + ], + "type": "inline_equation", + "content": "F_{\\mathrm{UNet}}" + }, + { + "bbox": [ + 46, + 545, + 288, + 714 + ], + "type": "text", + "content": " into our MuvieNeRF architecture. The detailed architecture of " + }, + { + "bbox": [ + 46, + 545, + 288, + 714 + ], + "type": "inline_equation", + "content": "F_{\\mathrm{UNet}}" + }, + { + "bbox": [ + 46, + 545, + 288, + 714 + ], + "type": "text", + "content": " is shown in the supplementary." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "spans": [ + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "text", + "content": "Conceptually, " + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "inline_equation", + "content": "F_{\\mathrm{UNet}}" + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "text", + "content": " takes RGB images from the " + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "inline_equation", + "content": "V" + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "text", + "content": " source views " + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "inline_equation", + "content": "\\{\\mathbf{x}_i\\}_{i=1}^V" + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "text", + "content": " as input and produces the corresponding multi-task annotations " + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "inline_equation", + "content": "\\{\\tilde{\\mathbf{Y}}_i\\}_{i=1}^V" + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "inline_equation", + "content": "\\tilde{\\mathbf{Y}}_i = [\\tilde{\\mathbf{y}}_i^1, \\dots, \\tilde{\\mathbf{y}}_i^K]" + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "text", + "content": ". Next, similar to the conditional NeRF encoder, we retrieve the corresponding multi-task annotations " + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "inline_equation", + "content": "\\{\\tilde{\\mathbf{Y}}_i(\\mathbf{q})\\}_{i=1}^V" + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "text", + "content": " for an arbitrary point " + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "inline_equation", + "content": "\\mathbf{q}" + }, + { + "bbox": [ + 305, + 227, + 545, + 299 + ], + "type": "text", + "content": " by projection." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 299, + 545, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 299, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 305, + 299, + 545, + 323 + ], + "type": "text", + "content": "During training time, " + }, + { + "bbox": [ + 305, + 299, + 545, + 323 + ], + "type": "inline_equation", + "content": "F_{\\mathrm{UNet}}" + }, + { + "bbox": [ + 305, + 299, + 545, + 323 + ], + "type": "text", + "content": " is trained with pixel-wise task-specific losses. Concretely, for task " + }, + { + "bbox": [ + 305, + 299, + 545, + 323 + ], + "type": "inline_equation", + "content": "T_{j}" + }, + { + "bbox": [ + 305, + 299, + 545, + 323 + ], + "type": "text", + "content": ", we have:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 356, + 331, + 545, + 365 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 331, + 545, + 365 + ], + "spans": [ + { + "bbox": [ + 356, + 331, + 545, + 365 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {U _ {j}} = \\sum_ {\\mathbf {r} \\in \\mathcal {R}} \\sum_ {i = 1} ^ {V} \\mathcal {L} _ {j} \\left(\\tilde {\\mathbf {y}} _ {i} ^ {j} (\\mathbf {r}), \\mathbf {y} _ {i} ^ {j} (\\mathbf {r})\\right). \\tag {10}", + "image_path": "fdec725dc3d6017b82af4ca40380e718102ff62c62460b874f6cc2deeeb51b63.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 373, + 545, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 373, + 545, + 422 + ], + "spans": [ + { + "bbox": [ + 305, + 373, + 545, + 422 + ], + "type": "text", + "content": "The final loss becomes " + }, + { + "bbox": [ + 305, + 373, + 545, + 422 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{final}} = \\sum_{T_j\\in \\mathcal{T}}\\lambda_{T_j}(\\mathcal{L}_{T_j} + \\mathcal{L}_{U_j})" + }, + { + "bbox": [ + 305, + 373, + 545, + 422 + ], + "type": "text", + "content": " for which we take the ground-truth multi-task annotations to learn the weights during training. However, we instead use the predictions produced by " + }, + { + "bbox": [ + 305, + 373, + 545, + 422 + ], + "type": "inline_equation", + "content": "F_{\\mathrm{UNet}}" + }, + { + "bbox": [ + 305, + 373, + 545, + 422 + ], + "type": "text", + "content": " for inference:" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 373, + 430, + 545, + 463 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 373, + 430, + 545, + 463 + ], + "spans": [ + { + "bbox": [ + 373, + 430, + 545, + 463 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {y}} ^ {j} = \\sum_ {i = 1} ^ {V} \\mathbf {w} [ j, i ] \\cdot \\tilde {\\mathbf {y}} [ j, i ]. \\tag {11}", + "image_path": "1f0f88af9647c9bece3534f171b224d7f8a1df9f79957ba2abb0aa4df8e59c3d.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 472, + 450, + 486 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 472, + 450, + 486 + ], + "spans": [ + { + "bbox": [ + 306, + 472, + 450, + 486 + ], + "type": "text", + "content": "4. Experimental Evaluation" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 492, + 545, + 575 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 492, + 545, + 575 + ], + "spans": [ + { + "bbox": [ + 305, + 492, + 545, + 575 + ], + "type": "text", + "content": "In this section, we start with main evaluation from Sections 4.1 to 4.3, including experimental setting, quantitative and qualitative results, and comparison with conventional discriminative multi-task models. Next, we make further investigations in Sections 4.4 and 4.5, including ablation studies and additional explorations. Finally, we discuss the limitations and future work in Section 4.6." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 583, + 429, + 596 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 583, + 429, + 596 + ], + "spans": [ + { + "bbox": [ + 306, + 583, + 429, + 596 + ], + "type": "text", + "content": "4.1. Experimental Setting" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 603, + 545, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 603, + 545, + 687 + ], + "spans": [ + { + "bbox": [ + 305, + 603, + 545, + 687 + ], + "type": "text", + "content": "Model Instantiation: As illustrated in Section 3, our model can build upon arbitrary conditional NeRF encoders. For the main evaluation, we instantiate our model with state-of-the-art GeoNeRF [22]. We use " + }, + { + "bbox": [ + 305, + 603, + 545, + 687 + ], + "type": "inline_equation", + "content": "\\alpha = 4" + }, + { + "bbox": [ + 305, + 603, + 545, + 687 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 603, + 545, + 687 + ], + "type": "inline_equation", + "content": "\\beta = 2" + }, + { + "bbox": [ + 305, + 603, + 545, + 687 + ], + "type": "text", + "content": " for the number of self-attention unions in the CVA and CTA modules, respectively. We additionally show the performance with other NeRF encoders in the ablation study." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "Benchmarks: We take two benchmarks for our main evaluation. Replica [46] is a commonly-used indoor scene" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "21542" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 286, + 106 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 286, + 106 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 286, + 106 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 286, + 106 + ], + "type": "table", + "html": "
ModelRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
MuvieNeRFw/o SH28.260.0204-0.01710.00510.9557
MuvieNeRFw/o KP27.960.02120.04230.0181-0.9519
MuvieNeRF28.550.02010.04080.01620.00510.9563
", + "image_path": "098551de41f3b1bca4a99d98cbbb6f85317533011f2005bd865bd13cfd052336.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 114, + 287, + 158 + ], + "lines": [ + { + "bbox": [ + 47, + 114, + 287, + 158 + ], + "spans": [ + { + "bbox": [ + 47, + 114, + 287, + 158 + ], + "type": "text", + "content": "Table 2. Additional test scene evaluation for our variants without SH (MuvieNeRFw/o SH) and KP (MuvieNeRFw/o KP) tasks on the Replica dataset. These two tasks work as a role of auxiliary tasks." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 177, + 287, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 177, + 287, + 308 + ], + "spans": [ + { + "bbox": [ + 46, + 177, + 287, + 308 + ], + "type": "text", + "content": "dataset containing high-quality photo-realistic 3D modelling of 18 scenes. Following the data acquisition method as [69], we collect 22 sequences from the scenes, each containing 50 frames at a resolution of " + }, + { + "bbox": [ + 46, + 177, + 287, + 308 + ], + "type": "inline_equation", + "content": "640 \\times 480" + }, + { + "bbox": [ + 46, + 177, + 287, + 308 + ], + "type": "text", + "content": ". SceneNet RGB-D [30] is a large-scale photorealistic indoor scene dataset expanding from SceneNet [16]. We include 32 scenes with 40 frames of each at a resolution of " + }, + { + "bbox": [ + 46, + 177, + 287, + 308 + ], + "type": "inline_equation", + "content": "320 \\times 240" + }, + { + "bbox": [ + 46, + 177, + 287, + 308 + ], + "type": "text", + "content": " in our evaluation. In addition to the above two datasets, we further evaluate zero-shot adaptation on four out-of-distribution datasets: LLFF [31], TartanAir [55], ScanNet [9], and BlendedMVS [59]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 311, + 287, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 311, + 287, + 396 + ], + "spans": [ + { + "bbox": [ + 46, + 311, + 287, + 396 + ], + "type": "text", + "content": "Task Selection: We select six representative tasks to evaluate our method following previous multi-task learning pipelines [45, 68]. The tasks are Surface Normal Prediction (SN), Shading Estimation (SH), Edges Detection (ED), Keypoints Detection (KP), and Semantic Labeling (SL), together with RGB synthesis. For the SceneNet RGB-D dataset, we drop the SH task due to missing annotations." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 397, + 287, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 397, + 287, + 456 + ], + "spans": [ + { + "bbox": [ + 46, + 397, + 287, + 456 + ], + "type": "text", + "content": "Evaluation Setup: For the Replica dataset, we divide the 22 scenes into 18, 1, and 3 for training, validation, and testing, respectively. For SceneNet RGB-D, we split 26 scenes for training, 2 for validation, and 4 for testing. For each scene, we hold out every 8 frames as testing views." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 457, + 287, + 518 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 457, + 287, + 518 + ], + "spans": [ + { + "bbox": [ + 46, + 457, + 287, + 518 + ], + "type": "text", + "content": "For these held-out views, we provide two types of evaluation: Training scene evaluation is conducted on novel views from the training scenes; Testing scene evaluation runs on novel scenes and is used to evaluate the generalization capability of the compared models." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 519, + 287, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 519, + 287, + 567 + ], + "spans": [ + { + "bbox": [ + 46, + 519, + 287, + 567 + ], + "type": "text", + "content": "Evaluation Metrics: For RGB synthesis, we measure Peak Signal-to-Noise Ratio (PSNR) for evaluation. For semantic segmentation, we take mean Intersection-over-Union (mIoU). For the other tasks, we evaluate the " + }, + { + "bbox": [ + 46, + 519, + 287, + 567 + ], + "type": "inline_equation", + "content": "L_{1}" + }, + { + "bbox": [ + 46, + 519, + 287, + 567 + ], + "type": "text", + "content": " error." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 570, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 712 + ], + "type": "text", + "content": "Baselines: We consider synthesis baselines for the main evaluation. Semantic-NeRF [69] extends NeRF for the semantic segmentation task. We further extend this model in the same way for other tasks, which only considers single-task learning in a NeRF style. SS-NeRF [68] considers multi-task learning in a NeRF style, but ignores the cross-view and cross-task information. We equip both models with the same GeoNeRF backbone as our model. Following [68], we also include a Heuristic baseline which estimates the annotations of the test view by projecting the source labels from the nearest training view to the target view." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": "Implementation Details: We set the weights for the six chosen tasks as " + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{RGB}} = 1" + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{SN}} = 1" + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{SL}} = 0.04" + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{SH}} = 0.1" + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{KP}} = 2" + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "inline_equation", + "content": "\\lambda_{\\mathrm{ED}} = 0.4" + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": " based on empirical observations. We use the Adam [25] optimizer with an initial learning rate of " + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "inline_equation", + "content": "5 \\times 10^{-4}" + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": " and set " + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "inline_equation", + "content": "\\beta_{1} = 0.9" + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "inline_equation", + "content": "\\beta_{2} = 0.999" + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": ". During training, each iteration contains a batch size of 1,024 rays randomly sampled from all training scenes." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 156, + 545, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 156, + 545, + 192 + ], + "spans": [ + { + "bbox": [ + 304, + 156, + 545, + 192 + ], + "type": "text", + "content": "More details about our encoder architectures, dataset processing, out-of-distribution analysis, and implementation are included in the supplementary." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 199, + 523, + 213 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 199, + 523, + 213 + ], + "spans": [ + { + "bbox": [ + 305, + 199, + 523, + 213 + ], + "type": "text", + "content": "4.2. MuvieNeRF Is Capable of Solving MTVS" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 218, + 545, + 349 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 218, + 545, + 349 + ], + "spans": [ + { + "bbox": [ + 304, + 218, + 545, + 349 + ], + "type": "text", + "content": "In Table 1, we present the average results derived from the held-out views across both the training and testing scenes. The key observations are, firstly, it is clear that our problem statement is non-trivial as evidenced by the notably inferior performance exhibited by the simple heuristic baseline when compared to the other models. Secondly, SS-NeRF surpasses Semantic-NeRF on average, indicating the contribution of multi-task learning. Lastly, our model consistently outperforms all the baselines, reaffirming that cross-view and cross-task information are invariably beneficial within our framework." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 350, + 545, + 482 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 350, + 545, + 482 + ], + "spans": [ + { + "bbox": [ + 304, + 350, + 545, + 482 + ], + "type": "text", + "content": "Interestingly, we note that MuvieNeRF exhibits a performance closely comparable to the two NeRF baselines on novel scenes for the KP and SH tasks. To decipher the underlying reason, we carry out an additional evaluation on two variants of our model without the two tasks, " + }, + { + "bbox": [ + 304, + 350, + 545, + 482 + ], + "type": "inline_equation", + "content": "\\mathrm{MuvieNEF_{w / oKP}}" + }, + { + "bbox": [ + 304, + 350, + 545, + 482 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 350, + 545, + 482 + ], + "type": "inline_equation", + "content": "\\mathrm{MuvieNEF_{w / oSH}}" + }, + { + "bbox": [ + 304, + 350, + 545, + 482 + ], + "type": "text", + "content": ", on the test scenes of Replica in Table 2. Our findings indicate that the KP and SH tasks indeed enhance the learning of other tasks, serving as effective auxiliary tasks. This conclusion aligns with previous studies on traditional multi-task learning models as reported by [45]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 482, + 545, + 554 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 482, + 545, + 554 + ], + "spans": [ + { + "bbox": [ + 304, + 482, + 545, + 554 + ], + "type": "text", + "content": "Figure 3 showcases a comparative analysis of the qualitative results. It is evident that our predictions supersede those of other baselines in terms of precision and clarity. This superior performance can be attributed to the additional information provided by shared cross-view and cross-task knowledge, which proves beneficial for the target tasks." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 561, + 522, + 573 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 561, + 522, + 573 + ], + "spans": [ + { + "bbox": [ + 305, + 561, + 522, + 573 + ], + "type": "text", + "content": "4.3. MuvieNeRF Beats Discriminative Models" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 579, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 579, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 579, + 545, + 628 + ], + "type": "text", + "content": "Although conventional discriminative models fall short in addressing the proposed MTVS problem, we have explored several hybrid settings to facilitate a comparison between our MuvieNeRF and these discriminative models." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 714 + ], + "type": "text", + "content": "Hybrid Setup: We provide additional RGB images from novel views to the discriminative models under three settings with different choices of RGB images. (1) We train on ground truth (GT) pairs and evaluate on novel view RGB images generated by a NeRF (NeRF's Images (No Tuned)); (2) We additionally fine-tune the discriminative models with paired NeRF's images and corresponding GT (NeRF's Im" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "21543" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 73, + 76, + 517, + 334 + ], + "blocks": [ + { + "bbox": [ + 73, + 76, + 517, + 334 + ], + "lines": [ + { + "bbox": [ + 73, + 76, + 517, + 334 + ], + "spans": [ + { + "bbox": [ + 73, + 76, + 517, + 334 + ], + "type": "image", + "image_path": "e63b5f3657e4ae3faded5cd2249b5480dc20be7420771d8e7f977618e48b3f05.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 335, + 547, + 369 + ], + "lines": [ + { + "bbox": [ + 46, + 335, + 547, + 369 + ], + "spans": [ + { + "bbox": [ + 46, + 335, + 547, + 369 + ], + "type": "text", + "content": "Figure 3. Visual comparisons of our model and baselines on a test scene of Replica dataset [46]. Our predictions are sharper and more accurate compared with other baselines. The underlying reason is that shared cross-view and cross-task knowledge can provide additional information for the target tasks." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 48, + 377, + 545, + 436 + ], + "blocks": [ + { + "bbox": [ + 48, + 377, + 545, + 436 + ], + "lines": [ + { + "bbox": [ + 48, + 377, + 545, + 436 + ], + "spans": [ + { + "bbox": [ + 48, + 377, + 545, + 436 + ], + "type": "table", + "html": "
ModelNeRF's Images (No Tuned)NeRF's Images (Tuned)GT Images (Upper Bound)
SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
Taskgrouping0.05680.07070.04080.00890.53610.05300.06770.04230.00900.55900.04960.06070.02980.00600.6191
MTI-Net0.05600.06360.04180.00780.54400.04860.05490.03890.00780.67530.04220.04980.02810.00500.7196
InvPT0.04790.06180.04000.00910.71390.04740.05870.03280.00740.70840.04090.04840.02820.00550.8158
Ours0.02010.04080.01620.00510.9563----------
", + "image_path": "3472a97de3d75b719760504aee9b60c18eddda59fe20671ba008dc70bb8d5388.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 50, + 478, + 286, + 515 + ], + "blocks": [ + { + "bbox": [ + 46, + 438, + 546, + 461 + ], + "lines": [ + { + "bbox": [ + 46, + 438, + 546, + 461 + ], + "spans": [ + { + "bbox": [ + 46, + 438, + 546, + 461 + ], + "type": "text", + "content": "Table 3. Comparison to the discriminative models for the test scenes on Replica [46] dataset. MuvieNeRF clearly beats all the discriminative models in all three settings, indicating that our model is more capable of both performance and generalizability." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 478, + 286, + 515 + ], + "lines": [ + { + "bbox": [ + 50, + 478, + 286, + 515 + ], + "spans": [ + { + "bbox": [ + 50, + 478, + 286, + 515 + ], + "type": "table", + "html": "
ModelRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
MuvieNeRFw/o CTA27.550.02140.04240.01980.00560.9501
MuvieNeRFw/o CVA28.250.02060.04070.01700.00520.9557
MuvieNeRF28.550.02010.04080.01620.00510.9563
", + "image_path": "f447f07d2baf52d1ae0b699b2ed947c31f38d037a6f6105d66e1cffdb2eb441f.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 600, + 288, + 672 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 600, + 288, + 672 + ], + "spans": [ + { + "bbox": [ + 46, + 600, + 288, + 672 + ], + "type": "text", + "content": "ages (Tuned)); (3) We evaluate on GT images from novel views as the performance upper bound (GT Images (Upper Bound)). For all the settings, we train the discriminative models on both training and testing scenes (training views only) to make sure that they get access to the same number of data as MuvieNeRF." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 715 + ], + "type": "text", + "content": "Discriminative Baselines: We select three representative baselines of different architectures. Taskgrouping [45] leverages an encoder-decoder architecture with a shared" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 308, + 478, + 544, + 553 + ], + "blocks": [ + { + "bbox": [ + 46, + 519, + 288, + 575 + ], + "lines": [ + { + "bbox": [ + 46, + 519, + 288, + 575 + ], + "spans": [ + { + "bbox": [ + 46, + 519, + 288, + 575 + ], + "type": "text", + "content": "Table 4. Ablation study with CTA and CVA modules on Replica [46] dataset. MuvieNeRF" + }, + { + "bbox": [ + 46, + 519, + 288, + 575 + ], + "type": "inline_equation", + "content": "_{\\mathrm{w/o}}" + }, + { + "bbox": [ + 46, + 519, + 288, + 575 + ], + "type": "text", + "content": " CTA is the variant without CTA module; MuvieNeRF" + }, + { + "bbox": [ + 46, + 519, + 288, + 575 + ], + "type": "inline_equation", + "content": "_{\\mathrm{w/o}}" + }, + { + "bbox": [ + 46, + 519, + 288, + 575 + ], + "type": "text", + "content": " CVA is the variant without CVA module. The CTA module is more crucial compared to the CVA module while combining them leads to the best performance." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 308, + 478, + 544, + 553 + ], + "lines": [ + { + "bbox": [ + 308, + 478, + 544, + 553 + ], + "spans": [ + { + "bbox": [ + 308, + 478, + 544, + 553 + ], + "type": "table", + "html": "
BackboneRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
PixelNeRF + SS-NeRF23.210.03280.04570.03760.00740.8620
PixelNeRF + Ours24.140.03020.04200.03420.00680.8961
GNT + SS-NeRF21.510.04050.04970.04200.00960.8302
GNT + Ours22.670.03330.04550.03840.00760.8686
MVSNeRF + SS-NeRF25.270.02610.04190.02480.00610.9294
MVSNeRF + Ours25.730.02480.04080.02270.00560.9303
GeoNeRF + SS-NeRF27.220.02240.04050.01960.00530.9483
GeoNeRF + Ours28.550.02010.04080.01620.00510.9563
", + "image_path": "63a13d170ae74cfe8384bd11079163acf6a4bcff0d644e82c90d4fe5c164c38a.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 355, + 605, + 494, + 634 + ], + "blocks": [ + { + "bbox": [ + 304, + 559, + 547, + 593 + ], + "lines": [ + { + "bbox": [ + 304, + 559, + 547, + 593 + ], + "spans": [ + { + "bbox": [ + 304, + 559, + 547, + 593 + ], + "type": "text", + "content": "Table 5. Ablation study with different choices of conditional NeRF encoders. The proposed MuvieNeRF is universally beneficial to different encoders, owing to the proposed CTA and CVA modules." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 355, + 605, + 494, + 634 + ], + "lines": [ + { + "bbox": [ + 355, + 605, + 494, + 634 + ], + "spans": [ + { + "bbox": [ + 355, + 605, + 494, + 634 + ], + "type": "table", + "html": "
ModelSN (↓)ED (↓)KP (↓)
Discriminative0.07780.03550.0086
MuvieNeRFD0.06050.02300.0074
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Evaluation TypeTraining scene evaluationTesting scene evaluation
TasksRGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)RGB (↑)SN (↓)SH (↓)ED (↓)KP (↓)SL (↑)
ReplicaSS-NeRF33.760.02120.03830.01160.00350.953327.220.02240.04050.01960.00530.9483
MuvieNeRF34.920.01930.03450.01000.00340.958228.550.02010.04080.01620.00510.9563
SS-NeRF (Enlarged)34.200.02100.03880.01070.00350.955727.370.02260.04050.01860.00530.9498
SceneNet RGB-DSS-NeRF28.930.0244-0.02160.00500.917529.180.0182-0.01970.00520.9510
MuvieNeRF29.290.0237-0.02070.00490.919029.560.0173-0.01890.00500.9556
SS-NeRF (Enlarged)29.030.0244-0.02150.00490.918629.460.0182-0.01910.00500.9520
", + "image_path": "edbafa83294c35aee9eddf3ecda8bba7abf80208b33b70186c7b9af2b771b289.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 55, + 198, + 277, + 223 + ], + "blocks": [ + { + "bbox": [ + 46, + 152, + 546, + 185 + ], + "lines": [ + { + "bbox": [ + 46, + 152, + 546, + 185 + ], + "spans": [ + { + "bbox": [ + 46, + 152, + 546, + 185 + ], + "type": "text", + "content": "Table 7. Comparison between MuvieNeRF and an enlarged version of SS-NeRF. our model still significantly outperforms SS-NeRF (Enlarged), indicating that the good performance of MuvieNeRF is not simply achieved by a heavier decoder, and demonstrating the effectiveness of our module designs." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 55, + 198, + 277, + 223 + ], + "lines": [ + { + "bbox": [ + 55, + 198, + 277, + 223 + ], + "spans": [ + { + "bbox": [ + 55, + 198, + 277, + 223 + ], + "type": "table", + "html": "
ModelRuntime (Per Training Iter.)Num. of Params.FLOPs
SS-NeRF1×1.21M4.57 × 1011
MuvieNeRF1.22×1.30M5.84 × 1011
", + "image_path": "131345b33ddb9d8458504b98ad1671f0efb3c9e943ad62c031beed9bfa9e2f28.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 224, + 286, + 258 + ], + "lines": [ + { + "bbox": [ + 47, + 224, + 286, + 258 + ], + "spans": [ + { + "bbox": [ + 47, + 224, + 286, + 258 + ], + "type": "text", + "content": "Table 8. Computational cost for SS-NeRF and MuvieNeRF on Replica dataset. Our CTA and CVA modules are light-weight designs." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 274, + 286, + 309 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 274, + 286, + 309 + ], + "spans": [ + { + "bbox": [ + 46, + 274, + 286, + 309 + ], + "type": "text", + "content": "InvPT [61] takes a transformer-based architecture that encourages long-range and global context to benefit multi-task learning." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 310, + 286, + 406 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 310, + 286, + 406 + ], + "spans": [ + { + "bbox": [ + 46, + 310, + 286, + 406 + ], + "type": "text", + "content": "Table 3 details the averaged results and Figure 3 offers a visual comparison. It is discernible that our MuvieNeRF outstrips all the discriminative models, illustrating that these models struggle to effectively tackle the MTVS problem, despite fine-tuning or utilizing GT images. We surmise that this shortcoming is rooted in the evaluation of novel scenes, wherein the generalization capability of our model noticeably outperforms that of discriminative ones." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 414, + 140, + 426 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 414, + 140, + 426 + ], + "spans": [ + { + "bbox": [ + 47, + 414, + 140, + 426 + ], + "type": "text", + "content": "4.4. Ablation Study" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 432, + 286, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 432, + 286, + 456 + ], + "spans": [ + { + "bbox": [ + 46, + 432, + 286, + 456 + ], + "type": "text", + "content": "We consider the test scene evaluation on the Replica dataset for the following ablation and exploration sections." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 457, + 286, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 457, + 286, + 564 + ], + "spans": [ + { + "bbox": [ + 46, + 457, + 286, + 564 + ], + "type": "text", + "content": "Contributions of CTA and CVA: We dissect the individual contributions of the proposed CTA and CVA modules in Table 4. An examination of the results reveals a more significant impact from the CTA module, when compared with the CVA module. We postulate that this occurs because the NeRF encoder and volume rendering have already mastered an implicit 3D representation, albeit falling short in modeling task relationships. Nevertheless, the integration of both modules yields further enhancement." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 567, + 286, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 567, + 286, + 662 + ], + "spans": [ + { + "bbox": [ + 46, + 567, + 286, + 662 + ], + "type": "text", + "content": "Choice of Condition NeRF: We also ablate the conditional NeRF encoders with PixelNeRF [64], MVSNeRF [6], GNT [48], and GeoNeRF [22] in Table 5. Note that we only adopt the encoder part defined in Section 3, causing a variation in performance from the full model. Each variant under our design surpasses its respective SS-NeRF baseline, affirming the universal advantage of our proposed CTA and CVA modules across different conditional NeRF encoders." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 286, + 713 + ], + "type": "text", + "content": "Effectiveness of CTA and CVA Modules: By integrating CVA and CTA modules, we concurrently increase the number of trainable parameters. 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Visualizations for the setting without nearby-view annotations. our MuvieNeRF " + }, + { + "bbox": [ + 305, + 372, + 545, + 427 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 305, + 372, + 545, + 427 + ], + "type": "text", + "content": " markedly surpasses the discriminative baseline model [45] and can generate results closely paralleling the ground truth, indicating MuvieNeRF " + }, + { + "bbox": [ + 305, + 372, + 545, + 427 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 305, + 372, + 545, + 427 + ], + "type": "text", + "content": " is capable of tackling the more challenging settings." + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 448, + 545, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 448, + 545, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 545, + 568 + ], + "type": "text", + "content": "introduce an expanded version of SS-NeRF, designated as SS-NeRF (Enlarged). This variant features a doubled latent dimension, comprising 2.09M parameters and " + }, + { + "bbox": [ + 304, + 448, + 545, + 568 + ], + "type": "inline_equation", + "content": "6.18 \\times 10^{11}" + }, + { + "bbox": [ + 304, + 448, + 545, + 568 + ], + "type": "text", + "content": " FLOPs. The outcomes, as illustrated in Table 7, confirm that MuvieNeRF's excellent performance is not simply the result of a more complex decoder, thereby highlighting the effectiveness of our module designs. Moreover, we further list the computational cost for our model and SS-NeRF in Table 8 to show that our CTA and CVA modules are indeed lightweight, but effective designs." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 578, + 441, + 590 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 578, + 441, + 590 + ], + "spans": [ + { + "bbox": [ + 306, + 578, + 441, + 590 + ], + "type": "text", + "content": "4.5. Additional Explorations" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 306, + 597, + 504, + 609 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 597, + 504, + 609 + ], + "spans": [ + { + "bbox": [ + 306, + 597, + 504, + 609 + ], + "type": "text", + "content": "4.5.1 Tackling Unknown Source-view Labels" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": "In this section, we apply the variant discussed in Section 3.4 to tackle the more challenging problem setting with unknown nearby-view annotations. In Table 6, we show the quantitative comparisons for this variant, MuvieNeRF" + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "inline_equation", + "content": "_D" + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": ", and a hybrid baseline, Discriminative [45], which shares almost the same architecture as our discriminative module. We use pre-trained weights from Taskonomy [66] to initialize weights for both models. 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An out-of-distribution comparison on BlendedMVS dataset [59] for GeoNeRF and our MuvieNeRF. Our model offers superior visual quality and preserves sharp contours. More visualizations about other OOD benchmarks are included in the supplementary." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 253, + 287, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 253, + 287, + 277 + ], + "spans": [ + { + "bbox": [ + 46, + 253, + 287, + 277 + ], + "type": "text", + "content": "constraint, we select three tasks, SN, ED, and KP with the closest relationships [45] for demonstration in this setting." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 278, + 287, + 373 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 278, + 287, + 373 + ], + "spans": [ + { + "bbox": [ + 46, + 278, + 287, + 373 + ], + "type": "text", + "content": "In conjunction with the visualizations illustrated in Figure 4, it is clear that our MuvieNeRF" + }, + { + "bbox": [ + 46, + 278, + 287, + 373 + ], + "type": "inline_equation", + "content": "_D" + }, + { + "bbox": [ + 46, + 278, + 287, + 373 + ], + "type": "text", + "content": " markedly surpasses the discriminative baseline model [45] and can generate results closely paralleling the ground truth. This observation indicates that our model is capable of tackling more challenging settings. We conjecture the reason is that the weighted sum format (Equation 11) enhances the fault tolerance of the predictions." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 389, + 228, + 400 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 389, + 228, + 400 + ], + "spans": [ + { + "bbox": [ + 47, + 389, + 228, + 400 + ], + "type": "text", + "content": "4.5.2 Out-of-distribution Generalization" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 408, + 287, + 516 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 408, + 287, + 516 + ], + "spans": [ + { + "bbox": [ + 46, + 408, + 287, + 516 + ], + "type": "text", + "content": "We demonstrate how the multi-task information learned from one dataset can effectively be utilized to benefit other datasets, by performing a zero-shot adaptation on out-of-distribution datasets with our MuvieNeRF trained on Replica. This takes a step further from investigating the generalization ability of unseen testing scenes in previous sections. We consider four datasets in total: LLFF [31], TartanAir [55], ScanNet [9], and BlendedMVS [59] containing indoor, outdoor, and even object-centric scenes." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 517, + 287, + 660 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 517, + 287, + 660 + ], + "spans": [ + { + "bbox": [ + 46, + 517, + 287, + 660 + ], + "type": "text", + "content": "As an illustrative example, we showcase the comparison between the conditional NeRF backbone, GeoNeRF [22], and our MuvieNeRF for the novel-view RGB synthesis task in Table 9 and Figure 5. Evidently, our model surpasses GeoNeRF by a significant margin, offering superior visual quality and retaining sharp contours, likely a result of the edge and surface normal information absorbed during the multi-task training. These outcomes substantiate that augmenting the model with more tasks, as part of our multitask learning strategy, dramatically bolsters the generalization capability, thereby showcasing its immense potential for real-world applications." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 669, + 206, + 681 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 669, + 206, + 681 + ], + "spans": [ + { + "bbox": [ + 47, + 669, + 206, + 681 + ], + "type": "text", + "content": "4.6. Limitations and Future work" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 287, + 713 + ], + "type": "text", + "content": "Limitations: One major limitation of this work is the reliance on data. MuvieNeRF requires images from dense" + } + ] + } + ], + "index": 13 + }, + { + "type": "table", + "bbox": [ + 320, + 70, + 531, + 101 + ], + "blocks": [ + { + "bbox": [ + 320, + 70, + 531, + 101 + ], + "lines": [ + { + "bbox": [ + 320, + 70, + 531, + 101 + ], + "spans": [ + { + "bbox": [ + 320, + 70, + 531, + 101 + ], + "type": "table", + "html": "
ModelScanNetTartanAirLLFFBlendedMVS
GeoNeRF31.7126.5120.6816.27
MuvieNeRF32.7630.2122.9120.97
", + "image_path": "4015dc2572cc71e2effd713dbd623e86863c97f5b3c363104cad7d0f0fedad36.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 103, + 545, + 159 + ], + "lines": [ + { + "bbox": [ + 305, + 103, + 545, + 159 + ], + "spans": [ + { + "bbox": [ + 305, + 103, + 545, + 159 + ], + "type": "text", + "content": "Table 9. Averaged PSNR of out-of-distribution RGB synthesis task. Our model surpasses the GeoNeRF baseline by a large margin, affirming that the inclusion of additional tasks, as part of our approach, contributes to a substantial enhancement in the model's generalization capacity." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 305, + 179, + 545, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 179, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 305, + 179, + 545, + 216 + ], + "type": "text", + "content": "views, a requirement not fulfilled by most multi-task benchmarks. To circumvent this limitation, techniques that allow NeRF to learn from sparse views [35, 67] could be adopted." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 220, + 545, + 280 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 220, + 545, + 280 + ], + "spans": [ + { + "bbox": [ + 305, + 220, + 545, + 280 + ], + "type": "text", + "content": "Task Relationships: As elaborated in Section 4.2, SH and KP function as auxiliary tasks within the system. A deeper exploration into the relationships between tasks and the corresponding geometric underpinnings within our synthesis framework offers intriguing avenues for future research." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 284, + 545, + 356 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 284, + 545, + 356 + ], + "spans": [ + { + "bbox": [ + 305, + 284, + 545, + 356 + ], + "type": "text", + "content": "Extension to Other Synthesis Models: We have demonstrated that incorporating cross-view geometry and cross-task knowledge can enhance multi-task learning for synthesis models. We anticipate that similar strategies could be extended to 3D synthesis models other than NeRF, such as point clouds [57] and meshes [17, 26]." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 373, + 378, + 385 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 373, + 378, + 385 + ], + "spans": [ + { + "bbox": [ + 306, + 373, + 378, + 385 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 396, + 545, + 551 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 396, + 545, + 551 + ], + "spans": [ + { + "bbox": [ + 305, + 396, + 545, + 551 + ], + "type": "text", + "content": "This paper introduces the novel concept of Multi-Task View Synthesis (MTVS), recasting multi-task learning as a set of view synthesis problems. Informed by this new perspective, we devise MuvieNeRF, a unified synthesis framework enriched with novel Cross-View Attention and Cross-Task Attention modules. MuvieNeRF enables the simultaneous synthesis of multiple scene properties from novel viewpoints. Through extensive experimental evaluations, we establish MuvieNeRF's proficiency in addressing the MTVS task, with performance exceeding that of discriminative models across various settings. Our model also demonstrates broad applicability, extending to a variety of conditional NeRF backbones." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 569, + 403, + 582 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 569, + 403, + 582 + ], + "spans": [ + { + "bbox": [ + 306, + 569, + 403, + 582 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 591, + 545, + 627 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 591, + 545, + 627 + ], + "spans": [ + { + "bbox": [ + 305, + 591, + 545, + 627 + ], + "type": "text", + "content": "We thank Kangle Deng, Derek Hoiem, Ziqi Pang, Deva Ramanan, Manolis Savva, Shen Zheng, Yuanyi Zhong, JunYan Zhu, and Zhen Zhu for their valuable comments." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 629, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 629, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 629, + 545, + 713 + ], + "type": "text", + "content": "This work was supported in part by NSF Grant 2106825, Toyota Research Institute, NIFA Award 2020-67021-32799, the Jump ARCHES endowment, the NCSA Fellows program, the Illinois-Inspers Partnership, and the Amazon Research Award. 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While promising performance has been shown on seen noise distributions, existing approaches often suffer from generalisation to unseen noise types or general and real noise. It is understandable as the model is designed to learn paired mapping (e.g. from a noisy image to its clean version). In this paper, we instead propose to learn to disentangle the noisy image, under the intuitive assumption that different corrupted versions of the same clean image share a common latent space. A self-supervised learning framework is proposed to achieve the goal, without looking at the latent clean image. By taking two different corrupted versions of the same image as input, the proposed Multi-view Self-supervised Disentanglement (MeD) approach learns to disentangle the latent clean features from the corruptions and recover the clean image consequently. Extensive experimental analysis on both synthetic and real noise shows the superiority of the proposed method over prior self-supervised approaches, especially on unseen novel noise types. On real noise, the proposed method even outperforms its supervised counterparts by over 3 dB.", + "bbox": [ + 75, + 301, + 473, + 633 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 665, + 209, + 681 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Image restoration is a critical sub-field of computer vision, exploring the reconstruction of image signals from corrupted observations. Examples of such ill-posed low-level image restoration problems include image denoising [16,25,26,29,33,35,38], super-resolution [2,8,19,30,37], and JPEG artefact removal [7, 12, 31], to name a few. Usually, a mapping function dedicated to the training data distribution is learned between the corrupted and clean images to address the problem. While many image restoration systems perform well when evaluated over the same corruption distribution that they have seen, they are often required to be deployed in settings where the environment is unknown and", + "bbox": [ + 75, + 691, + 468, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/ff5442c64c4b77977a480f53fa8931da5918ba53d2ce360ed7cdd3b46fe5d814.jpg", + "image_caption": [ + "(a) Noisy/ Clean" + ], + "image_footnote": [], + "bbox": [ + 517, + 273, + 696, + 455 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b5626a1a442483f90faf4a0f2c9aa17f026b04482ccea7a16a44a7958a169d8a.jpg", + "image_caption": [ + "(b) N2C [21], Supervised" + ], + "image_footnote": [], + "bbox": [ + 702, + 273, + 880, + 455 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/b39275238920d1558ee3498690cb6e3a417210456a9c52dba3c34af67d7b8854.jpg", + "image_caption": [ + "(c) LIR [9], Self-supervised", + "Figure 1. Denoising performance on unseen Speckle Noise with $\\hat{\\pmb{v}} = 50$ . The models were trained with Gaussian noise $\\sigma \\in [5,50]$ . (a) The noisy and clean images, with ground-truth clean patches shown below. (b) Noise-to-Clean (N2C) [21] is trained with clean images. (c) LIR [9] is self-supervised but needs unpaired clean images as training data. (d) Our approach is fully self-supervised, training with only the noisy input data." + ], + "image_footnote": [], + "bbox": [ + 517, + 479, + 697, + 661 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/920463002582708f96ac0f8563b7bf8162d8c7fd37d0fb16a3f8ef3a7025503a.jpg", + "image_caption": [ + "(d) Ours, Self-supervised" + ], + "image_footnote": [], + "bbox": [ + 702, + 479, + 882, + 661 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "off the training distribution. These settings, such as medical imaging, computational lithography, and remote sensing, require image restoration methods that can handle complex and unknown corruptions. Moreover, in many real-world image-denoising tasks, ground truth images are unavailable, introducing additional challenges.", + "bbox": [ + 496, + 809, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Equal contribution.", + "bbox": [ + 101, + 887, + 212, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "12281", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Limitations of existing methods: Current low-level corruption removal tasks aim to address the inquiry of \"what is the clean image provided a corrupted observation?\" However, the ill-posed nature of this problem formulation poses a significant challenge in obtaining a unique resolution [5].", + "bbox": [ + 75, + 90, + 467, + 166 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To mitigate this limitation, researchers often introduce additional information, either explicitly or implicitly. For example, in [15], Laine et al. explicitly use the prior knowledge of noise as complementary input, generating a new invertible image model. Alternatively, Learning Invariant Representation (LIR) [9] implicitly enforces the interpretability in the feature space to guarantee the admissibility of the output. However, these additional forms of information may not always be practical in real-world scenarios or may not result in satisfactory performance.", + "bbox": [ + 75, + 167, + 467, + 316 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Main idea and problem formulation: Our motivation for tackling this ill-posed nature stems from the solution in the 3D reconstruction of utilising multiple views to provide a unique estimation of the real scene [1]. Building on this motivation, we propose a training scheme that is explicitly built on multi-corrupted views and perform Multi-view self-supervised Disentanglement, abbreviated as $MeD$ .", + "bbox": [ + 75, + 335, + 467, + 439 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Under this new multi-view setting, we reformulate the task problem as \"what is the shared latent information across these views?\" instead of the conventional \"what is the clean image?\" By doing so, MeD can effectively leverage the scene coherence of multi-view data and capture underlying common parts without requiring access to the clean image. This makes it more practical and scalable in real-world scenarios. An example of the proposed method with comparison to prior works is shown in Figure 1, indicating its effectiveness over the state-of-the-art.", + "bbox": [ + 75, + 441, + 467, + 590 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Specifically, given any scene image $x^{k} \\sim \\mathcal{X}, k \\in \\mathbb{N}$ sampled uniformly from a clean image set $\\mathcal{X}$ , MeD produces two contaminated views:", + "bbox": [ + 75, + 590, + 467, + 635 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\ny _ {1} ^ {k} \\triangleq \\mathcal {T} _ {1} \\left(x ^ {k}\\right), y _ {2} ^ {k} \\triangleq \\mathcal {T} _ {2} \\left(x ^ {k}\\right), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 176, + 643, + 467, + 664 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "forming two independent corrupted image sets $\\{\\mathcal{Y}_1\\}, \\{\\mathcal{Y}_2\\}$ , where $y_1^k \\in \\mathcal{Y}_1$ , $y_2^k \\in \\mathcal{Y}_2$ . The $\\mathcal{T}_1$ and $\\mathcal{T}_2$ represent two random independent image degradation operations.", + "bbox": [ + 75, + 671, + 467, + 717 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We parameterise our scene feature encoder $G_{\\theta}^{\\mathcal{X}}$ and decoder $D_{\\psi}^{\\mathcal{X}}$ with $\\theta$ and $\\psi$ . Considering the image pair $\\{y_1^k, y_2^k\\}_{k \\in \\mathbb{N}}$ , the core of the presented method can be summarised as:", + "bbox": [ + 76, + 717, + 467, + 779 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\nG _ {\\theta} ^ {\\mathcal {X}} \\left(y _ {1} ^ {k}\\right) \\triangleq z _ {x} ^ {k, i} \\triangleq G _ {\\theta} ^ {\\mathcal {X}} \\left(y _ {2} ^ {k}\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 179, + 787, + 467, + 806 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {x} ^ {k} \\triangleq D _ {\\psi} ^ {\\mathcal {X}} \\left(z _ {x} ^ {k, i}\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 217, + 808, + 467, + 828 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "where $z_{x}^{k,i}$ represents the shared scene latent between $y_{1}^{k}$ and $y_{2}^{k}$ with $i$ referring to the input image index of $y_{i}$ . A clean image estimator $D_{\\psi}^{\\mathcal{X}}$ forms an all-deterministic reverse mapping from $z_{x}^{k,i}$ to reconstruct an estimated clean", + "bbox": [ + 76, + 837, + 467, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "image $\\hat{x}^k$ . Similarly, the noise latent $u_{\\eta}^{k,i}$ is factorised from a corrupted view with a corruption encoder $E_{\\rho}^{\\mathcal{N}}$ . After words, the resulting corruption is reconstructed from $u_{\\eta}^{k,i}$ through the use of a corruption decoder, represented by $F_{\\phi}^{\\mathcal{N}}$ .", + "bbox": [ + 498, + 90, + 890, + 157 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The disentanglement is then performed between $\\{z_{x}^{k,i},u_{\\eta}^{k,j}\\}_{i\\neq j}$ on a cross compose decoder $R_{\\delta}^{\\mathcal{V}}$ with parameter $\\delta$ , which can be formulated as:", + "bbox": [ + 500, + 156, + 890, + 200 + ], + "page_idx": 1 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {y} _ {1} ^ {k} \\triangleq R _ {\\delta} ^ {\\mathcal {Y}} \\left(z _ {x} ^ {k, 2}, u _ {\\eta} ^ {k, 1}\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 620, + 212, + 890, + 232 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "It should be noted that Equation (4) is performed over latent features $u$ and $z$ from different views. When assuming that $z_{x}^{k}$ remains constant across views, the reconstructed view $\\hat{y}_{1}^{k}$ is determined by the $u_{\\eta}^{k,1}$ .", + "bbox": [ + 498, + 242, + 890, + 305 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Contributions. The contributions of our work are summarised as follows:", + "bbox": [ + 498, + 321, + 888, + 349 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- We propose a new problem formulation to address the ill-posed problem of image denoising using only noisy examples, in a different paradigm than prior works.", + "- We introduce a disentangled representation learning framework that leverages multiple corrupted views to learn the shared scene latent, by exploiting the coherence across views of the same scene and separating noise and scene in the latent space.", + "- Extensive experimental analysis validates the effectiveness of the proposed MeD, outperforming existing methods with more robust performance to unknown noise distributions, even better than its supervised counterparts." + ], + "bbox": [ + 517, + 362, + 890, + 578 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 603, + 638, + 618 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Single-view image restoration: In [8], Dong et al. were the first to employ a deep network in super-resolution. Later, a range of single view-based models expanded the idea of supervised deep learning to handle image restoration tasks, such as deblurring [14], JPEG artefacts [12], inpainting [17, 34] and denoising [16, 26, 35]. Recently, it is receiving increasing interest in relaxing the prerequisite of supervised learning with corrupted/ clean image pairs. In the context of image denoising, the \"corrupted/clean\" pair denotes a corrupted input image and its corresponding clean image for calculating the loss. To tackle the issue of the lack of clean data, several methods have been proposed, such as the Noise2Noise (N2N) method [16] and Recorrupted-to-Recorrupted (R2R) [26], which train deep networks on pairs of noisy images. Noise2Void (N2V) [13], Noise2Self (N2S) [4], and the method proposed by Laine et al. [15] are based on the blind-spot strategy that discards some pixels in the input and predicts them using the remaining. In the field", + "bbox": [ + 496, + 628, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "12282", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/f5280f823dd4ee0c6858aa9cf449e00e93f57c914ccb8cfcfea437565f22fdfb.jpg", + "image_caption": [ + "Figure 2. Method Overview. This figure illustrates the main steps of our proposed method, MeD, which first generates scene features (cubes) and distortion features (cuboids). The colour of them indicates their image source. In the right section, the features are rearranged and utilised for the four forward paths, from top to bottom, which are the reconstructions of noise $(\\hat{\\eta}_1^k)$ , scene $(\\hat{x}_2^k)$ , input image $(y_2^k)$ and shared scene $(\\hat{x}^k)$ . It is noteworthy that $\\hat{y}_2^k$ is reconstructed using $z_x^{k,1}$ from $y_1^k$ and $u_{\\eta}^{k,2}$ from $y_2^k$ for feature disentanglement. Additionally, the reconstruction of $\\hat{x}^k$ relies on mixed scene features to facilitate learning of invariant scene latent. Moreover, the reconstruction paths for $(\\hat{\\eta}_2,\\hat{x}_1,$ and $y_{1})$ are not depicted here, as they differ from the given paths only in their sub-indexes." + ], + "image_footnote": [], + "bbox": [ + 78, + 87, + 890, + 362 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "of single-image denoising, some methods such as DIP [29] and S2S [27], have achieved remarkable denoising results using only one noisy image.", + "bbox": [ + 75, + 474, + 468, + 518 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "These methods, however, often inevitably compromise image quality to noise reduction, resulting in over-smoothed output. This trade-off is further exacerbated under domain shifts when dealing with unknown noise distributions.", + "bbox": [ + 75, + 520, + 470, + 580 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Restoration based on multiple views: Existing multiview variants of image restoration methods mainly focus on sequential data such as video or burst images. For example, Tico [28] builds a paradigm that separates the unique and common features within the multi-frame to produce a denoised estimate. Liu et al. [20] models degrading elements as foreground and estimate background using video data. Deep Burst Denoising (DBD) [11] performs multi-view denoising based on burst images. Each image is taken in a short exposure time and serves as a corrupted observation of the clean image.", + "bbox": [ + 75, + 604, + 468, + 770 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Unlike the above-mentioned methods, our $MeD$ aims to use multiple static observations simultaneously to learn the latent representation of a clean scene that is shared by multiple discrete views.", + "bbox": [ + 75, + 771, + 470, + 832 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Self-supervised feature disentanglement: Another notable path of work has attempted to disentangle underlying invariant content from distorted images. For instance, $UID$ -", + "bbox": [ + 75, + 854, + 470, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "GAN [22] utilises unpaired clean/blurred images to disentangle content and blurring effects in the feature space and yield improved deblurring performance. Similarly, $LIR$ [9] used unpaired input to isolate invariant content features through self-supervised inter-domain transformation.", + "bbox": [ + 496, + 474, + 890, + 549 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "However, these methods are limited to synthetic noise and do not extend well in real-world scenarios due to their reliance on clean images. In contrast, our method is purely based on multiple noisy views of the same static scene and aims to disentangle the scene from corruption, without the need for clean image supervision.", + "bbox": [ + 496, + 551, + 890, + 642 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 500, + 660, + 635, + 678 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our primary objective is to identify the commonalities among different views in the denoising process. To achieve this, we aim to discover the shared scene $z_{x}^{k}$ that is degradation-agnostic over various corrupted views $\\{y_{i}^{k}\\}_{k\\in \\mathbb{N}}$ via our proposed training schema, namely Multi-view self-supervised Disentanglement (MeD). A graphic depiction of MeD is shown in Figure 2, composed of the representation learning process in the left panel, and four distinct reconstruction pathways in the right panel.", + "bbox": [ + 496, + 686, + 890, + 823 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The detailed design of the proposed schema will be introduced in the following subsections. Section 3.1 explains the restoration of noise and scene. Section 3.2 details the reconstruction of noisy input using a cross-feature combination. Section 3.3 elaborates on the reconstruction of the", + "bbox": [ + 496, + 825, + 890, + 898 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "12283", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "scene using mixed scene latent.", + "bbox": [ + 76, + 90, + 287, + 104 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We will start our introduction by outlining three essential properties that a multi-view representation disentanglement technique should exhibit.", + "bbox": [ + 76, + 106, + 468, + 151 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Pre-assumed properties: Suppose the scene latent space and corruption latent space are symbolised by $\\mathcal{Z}_x$ and $\\mathcal{U}_{\\eta}$ , respectively.", + "bbox": [ + 76, + 169, + 468, + 214 + ], + "page_idx": 3 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "(1) Independence: For any scene latent $z_{x}^{k} \\in \\mathcal{Z}_{x}$ , it is expected to be independent of any corruption latent $u_{\\eta}^{k,i}, \\in \\mathcal{U}_{\\eta}$ .", + "(2) Consistency: There exists one shared latent code $z_{x}^{k} \\in \\mathcal{Z}_{x}$ that is capable of representing the shared clean component of all instances in the set $\\{y_{i}^{k}\\}$ .", + "(3) Composability: Recovery of the corrupted view $y_{i}^{k}$ can be achieved using the feature pairs $z_{x}^{k}, u_{\\eta}^{k,i}$ , and the index of the recovered view is determined by the index of the corruption latent, which represents the unique component within that particular view." + ], + "bbox": [ + 81, + 220, + 468, + 407 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "A key step of our method is to realise these prerequisites by determining how to implement the latent space assumption. As shown in the left panel of Figure 2, to infer our latent space assumption, MeD is comprised of two encoders and three decoders: A shared content latent encoder $G_{\\theta}^{\\mathcal{X}}$ and its decoder $D_{\\psi}^{\\mathcal{X}}$ , an auxiliary noise latent encoder $E_{\\rho}^{\\mathcal{N}}$ and its decoder $F_{\\phi}^{\\mathcal{N}}$ , and a cross disentangle-ment decoder $R_{\\delta}^{\\mathcal{Y}}$ .", + "bbox": [ + 76, + 416, + 468, + 542 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Main Forward Process", + "text_level": 1, + "bbox": [ + 76, + 550, + 287, + 564 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Given two corrupted views of the same image $x^{k}$ , $y_{1}^{k} \\triangleq \\mathcal{T}_{1}(x^{k})$ and $y_{2}^{k} \\triangleq \\mathcal{T}_{2}(x^{k})$ , the encoder $G_{\\theta}^{\\mathcal{X}}$ mainly perform the scene feature space encoding that can be formulated as:", + "bbox": [ + 76, + 573, + 468, + 619 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nz _ {x} ^ {k, 1} \\triangleq G _ {\\theta} ^ {\\mathcal {X}} \\left(y _ {1} ^ {k}\\right), z _ {x} ^ {k, 2} \\triangleq G _ {\\theta} ^ {\\mathcal {X}} \\left(y _ {2} ^ {k}\\right), \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 631, + 468, + 650 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $z_{x}^{k,1}$ and $z_{x}^{k,2}$ are the estimation of the scene feature corresponding to the inputs $y_{1}^{k}$ and $y_{2}^{k}$ .", + "bbox": [ + 76, + 654, + 468, + 686 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The process of clean image reconstruction is then completed by the $D_{\\psi}^{\\mathcal{X}}$ :", + "bbox": [ + 76, + 686, + 468, + 717 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {x} _ {1} ^ {k} \\triangleq D _ {\\psi} ^ {\\mathcal {X}} \\left(z _ {x} ^ {k, 1}\\right), \\hat {x} _ {2} ^ {k} \\triangleq D _ {\\psi} ^ {\\mathcal {X}} \\left(z _ {x} ^ {k, 2}\\right). \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 156, + 726, + 468, + 746 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Similar to the process of estimating scene features, the estimation of distortion features by $E_{\\rho}^{\\mathcal{N}}$ , followed by the reconstruction of noise with $F_{\\phi}^{\\mathcal{N}}$ , can be described as follows:", + "bbox": [ + 76, + 753, + 468, + 801 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nu _ {n} ^ {k, 1} \\triangleq E _ {\\rho} ^ {\\mathcal {N}} \\left(y _ {1} ^ {k}\\right), u _ {n} ^ {k, 2} \\triangleq E _ {\\rho} ^ {\\mathcal {N}} \\left(y _ {2} ^ {k}\\right), \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 156, + 821, + 468, + 847 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\eta} _ {1} ^ {k} \\triangleq F _ {\\phi} ^ {\\mathcal {N}} \\left(u _ {n} ^ {k, 1}\\right), \\hat {\\eta} _ {2} ^ {k} \\triangleq F _ {\\phi} ^ {\\mathcal {N}} \\left(u _ {n} ^ {k, 2}\\right).\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 843, + 385, + 862 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We adhere to the methodology introduced by N2N [16] to use noisy images as supervisory signals. The objective", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "function of the aforementioned process can be simplified to:", + "bbox": [ + 498, + 90, + 890, + 119 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\underset {\\theta , \\psi} {\\operatorname {a r g m i n}} \\mathcal {L} ^ {\\mathcal {X}} \\triangleq | | \\hat {x} _ {1} ^ {k} - y _ {2} ^ {k} | |, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 580, + 128, + 890, + 162 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\underset {\\rho , \\phi} {\\operatorname {a r g m i n}} \\mathcal {L} ^ {\\mathcal {N}} \\triangleq | | \\left(y _ {1} ^ {k} - \\hat {\\eta} _ {1} ^ {k}\\right) - y _ {2} ^ {k} | |. \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 583, + 151, + 890, + 186 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The objective of $\\hat{x}_2^k$ and $\\hat{\\eta}_2^k$ are the same as above, with only a subscript difference. It should be noted that, although our objective functions are similar to that of N2N, our goal is not simply to find and remove noise, but rather to capture the common features shared across multiple views.", + "bbox": [ + 498, + 198, + 890, + 273 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Cross Disentanglement", + "text_level": 1, + "bbox": [ + 500, + 284, + 712, + 299 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "For general latent codes $z_{x}^{k}$ to sufficiently represent scene information in the image space, it is natural to assume that these codes exhibit a certain degree of freedom, allowing them to intersect with the noise space. Consequently, there is no guarantee of complete isolation between $z_{x}^{k}$ and $u_{\\eta}^{k}$ . To meet the requirements of properties (1) and (3), we use an additional decoder $R_{\\delta}^{y}$ to reconstruct a corrupted view over a cross-feature combination, e.g. $z_{x}^{k,1}$ from $y_{1}$ and $u_{n}^{k,2}$ from $x_{2}$ , which can be represented as:", + "bbox": [ + 498, + 306, + 890, + 441 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {y} _ {1} ^ {k} \\triangleq R _ {\\delta} ^ {\\mathcal {Y}} \\left(z _ {x} ^ {k, 2}, u _ {n} ^ {k, 1}\\right), \\hat {y} _ {2} ^ {k} \\triangleq R _ {\\delta} ^ {\\mathcal {Y}} \\left(z _ {x} ^ {k, 1}, u _ {n} ^ {k, 2}\\right). \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 547, + 454, + 890, + 473 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "This realisation explicitly requires $z_{x}^{k,i}$ to represent the common part and $u_{n}^{k,j}$ to represent the unique part within the corrupted views. We then optimise $\\{\\theta ,\\rho ,\\delta \\}$ from $\\{G_{\\theta}^{\\mathcal{X}},E_{\\rho}^{\\mathcal{N}},R_{\\delta}^{\\mathcal{Y}}\\}$ using the following objective:", + "bbox": [ + 498, + 484, + 890, + 547 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\underset {\\theta , \\rho , \\delta} {\\operatorname {a r g m i n}} \\mathcal {L} ^ {\\mathcal {C}} \\triangleq | | \\hat {y} _ {1} ^ {k} - y _ {1} ^ {k} | | + | | \\hat {y} _ {2} ^ {k} - y _ {2} ^ {k} | |. \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 558, + 890, + 585 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Generally, it is possible for there to be a trivial solution from $u_{n}^{k,i}$ to $y_{i}^{k}$ in Equation (9) such as, when $u_{n}^{k,1}$ is extracted from $y_{1}^{k}$ and used to reconstruct it as well. However, Equation (7) explicitly requires $u_{n}^{k,1}$ to rebuild the noise, which prevents the collapse of $u_{n}^{k,1}$ in expressing $y_{1}^{k}$ .", + "bbox": [ + 498, + 595, + 890, + 672 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Bernoulli Manifold Mixture", + "text_level": 1, + "bbox": [ + 500, + 681, + 750, + 695 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The aforementioned latent constraint might appear to be restricted at first, but in fact, it enables us to capture a large number of degrees of freedom in latent space implementation. For instance, it is possible to have multiple scene features that correspond to a single scene. However, in such cases, the mapping from input to scene features becomes ambiguous. To tackle this issue, we propose the use of the Bernoulli Manifold Mixture (BMM) as a means of leveraging the shared structure within the scene latent.", + "bbox": [ + 498, + 704, + 890, + 839 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Given the assumption of property (2), the acquired scene features $z_{x}^{k,1}$ and $z_{x}^{k,2}$ are expected to be identical and interchangeable with one another, as they both refer to the same scene feature. BMM establishes a new explicit connection", + "bbox": [ + 498, + 840, + 890, + 898 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "12284", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "between the scene features of multi-views, which can be expressed in the equation as:", + "bbox": [ + 75, + 90, + 468, + 121 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {z} _ {x} ^ {k} \\triangleq \\operatorname {M i x} _ {p} \\left(z _ {x} ^ {k, 1}, z _ {x} ^ {k, 2}\\right), \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 192, + 131, + 468, + 150 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the $\\hat{z}_x^k$ is an estimation of the true underlying scene feature. Let $b_{f}$ define a sample instance drawn from a Bernoulli distribution with probability $p\\in (0,1)$ , the function $\\mathrm{Mix}_p(\\cdot)$ described in Equation (11) denotes:", + "bbox": [ + 75, + 160, + 468, + 222 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {M i x} _ {p} (\\boldsymbol {m}, \\boldsymbol {n}) \\triangleq b _ {f} \\odot \\boldsymbol {m} + (1 - b _ {f}) \\odot \\boldsymbol {n}. \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 133, + 233, + 468, + 251 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "By establishing this new connection (Equation 11), we can enhance the interchangeability between $z_{x}^{k,1}$ and $z_{x}^{k,2}$ by optimising the reconstruction performance on $\\hat{z}_{x}^{k}$ .", + "bbox": [ + 75, + 262, + 468, + 306 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Lemma 1. Assuming $z_{x}^{k,i}\\sim N_{\\mathbf{x}}(\\boldsymbol {\\mu},\\boldsymbol {\\Sigma})$ , where $N_{\\mathbf{x}}$ denotes multivariate Gaussian distributions and then $\\pmb{\\mu}$ and $\\pmb{\\Sigma}$ is the mean and the covariance matrix.", + "bbox": [ + 75, + 306, + 468, + 351 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "For a given function $G_{\\theta}^{\\mathcal{X}}(\\cdot)$ , assume $\\forall k, i, m, n \\in \\mathbb{N}$ , the following property holds:", + "bbox": [ + 73, + 351, + 468, + 383 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {E} \\left[ G _ {\\theta} ^ {\\mathcal {X}} \\left(z _ {x} ^ {k, i}\\right) \\right] \\triangleq \\mathbb {E} \\left[ G _ {\\theta} ^ {\\mathcal {X}} \\left(\\operatorname {M i x} _ {p} \\left(z _ {x} ^ {k, m}, z _ {x} ^ {k, n}\\right)\\right) \\right]. \\tag {13}\n$$\n", + "text_format": "latex", + "bbox": [ + 104, + 392, + 468, + 412 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Proof. Assume $z_{x}^{k,m}, z_{x}^{k,n} \\in \\mathbb{R}^{\\dim}$ are i.i.d., we may also factorise $b_{f} \\in \\mathbb{R}^{\\dim}$ . Write", + "bbox": [ + 75, + 421, + 468, + 452 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {z} _ {x} ^ {k} \\triangleq \\operatorname {M i x} _ {p} \\left(z _ {x} ^ {k, m}, z _ {x} ^ {k, n}\\right) \\tag {14}\n$$\n", + "text_format": "latex", + "bbox": [ + 192, + 465, + 468, + 483 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "so that we can have", + "bbox": [ + 76, + 496, + 209, + 508 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\hat {z} _ {x} \\sim N _ {\\mathbf {x}} \\left(\\left(b _ {f} + 1 - b _ {f}\\right) \\boldsymbol {\\mu}, \\left(b _ {f} ^ {2} + \\left(1 - b _ {f}\\right) ^ {2}\\right) \\boldsymbol {\\Sigma}\\right) \\tag {15} \\\\ \\sim N _ {\\mathbf {x}} (\\boldsymbol {\\mu}, \\boldsymbol {\\Sigma}) \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 102, + 518, + 468, + 556 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "with the fact that Bernoulli sample $b_{f}^{2} = b_{f}$ , the mixed feature $\\hat{z}_{x}$ is in the same representation distribution as $z_{x}^{k,i}$ .", + "bbox": [ + 75, + 569, + 468, + 602 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In MeD, we denote $\\hat{z}_x = G_\\theta^\\chi (\\hat{z}_x^k)$ , and the objective for implementing Equation (13) can be formulated as follows:", + "bbox": [ + 75, + 616, + 468, + 646 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\underset {\\theta , \\rho , \\psi} {\\operatorname {a r g m i n}} \\mathcal {L} ^ {\\mathcal {M}} \\triangleq \\lambda | | \\hat {z} _ {x} - \\operatorname {M i x} _ {p} \\left(y _ {1} ^ {k}, y _ {2} ^ {k}\\right) | |, \\tag {16}\n$$\n", + "text_format": "latex", + "bbox": [ + 138, + 657, + 468, + 684 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the $\\lambda$ is the weight parameter. Here, the target is using a mixed version of $y_1^k$ and $y_2^k$ . The choice of this is driven by the intuition that the hybrid version would better align with the aforementioned blended features.", + "bbox": [ + 75, + 695, + 468, + 755 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 76, + 768, + 207, + 786 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To evaluate the effectiveness of our proposed method, we assess our method against several representative self-supervised denoising methods, including Noise2Noise (N2N) [16], Noise2Self (N2S) [4] and Recorrupted2Recorrupted (R2R) [26], and the invariant feature learning method LIR [9]. Moreover, we also evaluate our approach against two supervised baseline", + "bbox": [ + 75, + 794, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "methods (Noise2Clean (N2C) [21] and multi-frame method DBD [11]) to further validate its effectiveness. Comparisons to more methods, including methods using only one noisy image, are presented in the supplementary material.", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We start our experiments by denoising synthetic additive white Gaussian noise (AWGN) in Section 4.2, and then move on to testing unseen noise levels and noise types in Section 4.3 and Section 4.4, respectively. Furthermore, we evaluate the performance in real-world scenarios in Section 4.5. In Section 4.6, we expand our experiments to incorporate more views to study their impact on performance. Finally, in Section 4.7, we apply our method to other tasks, e.g. image super-resolution and inpainting, to demonstrate its generalisation ability.", + "bbox": [ + 496, + 154, + 890, + 305 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental Setups", + "text_level": 1, + "bbox": [ + 498, + 321, + 696, + 338 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Noted that, the nature of feature disentanglement requires no leak from input to output, however, the global residual connection of the original DnCNN [35] cannot satisfy. Thus, we incorporate the Swin-Transformer (Swin-T) [21] instead of the traditionally used DnCNN in our experiments. Nevertheless, as Swin-T is not originally designed for image restoration, we make some modifications to enforce local dependence across the image. Specifically, we add one Convolution Layer each before the patch embedding and after the patch unembedding of Swin-T, as inspired by SwinIR [18]. The resulting modified network backbone is denoted as Swin-Tx.", + "bbox": [ + 496, + 348, + 890, + 527 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To ensure a fair comparison, we use the Swin-Tx backbone for all methods in our study, except for DBD. As DBD did not release the code, we follow the instructions presented in the paper and make our best effort to re-implement it. However, we observe that the two-view DBD could not converge efficiently, which is consistent with the findings in the paper. Therefore, we limit our evaluation to the four-view DBD, denoted as $\\mathrm{DBD}_4$ . Furthermore, we replace the U-Net backbone originally used in the LIR method with Swin-Tx to maintain consistency in our evaluation. This results in an average improvement of approximately 1 dB in PSNR for Gaussian denoising.", + "bbox": [ + 496, + 532, + 890, + 713 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In all experiments, all methods were trained using only DIV2K [3] and the same optimisation parameters, except for LIR and $\\mathrm{DBD}_4$ which used manually selected parameters obtained through experiments. For more training and evaluation details including the choice of parameters, please refer to the supplementary material. Code is available at: https://github.com/chgwer2/Multi-view-Self-supervised-Disentanglement-Denoising.", + "bbox": [ + 496, + 715, + 890, + 837 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Remark: In tables, the best results are highlighted in bold, while the second best is underlined.", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "12285", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/dff297503d973abe73449a6a25ecf1659ff9f40f7015ea5a4048dc1a3aa75c2c.jpg", + "table_caption": [ + "Table 1. Quantitative comparison of different methods on CBSD68 Dataset [23] for Synthetic Gaussian noise. The experiments were conducted on fixed and random variance, respectively. The best results are highlighted in bold, while the second best is underlined." + ], + "table_footnote": [], + "table_body": "
Training SchemaTest \\(\\hat{\\sigma}\\)Noisy/ Clean N2C [21]\\(DBD_4\\) [11]N2N [16]Noisy/ Noisy N2S [4]R2R [26]Invariant Feature
LIR [9]MeD (ours)
Gaussian\\(\\sigma = 25\\)1533.36/0.902033.57/0.909232.64/0.880532.77/0.878029.74/0.786531.06/0.863233.11/0.8880
2530.83/0.849431.31/0.854830.68/0.833430.99/0.840530.45/0.818330.01/0.802430.57/0.8496
5024.76/0.551925.12/0.558324.59/0.538522.13/0.392824.02/0.513321.97/0.357825.67/0.6026
7520.75/0.337621.09/0.341220.60/0.316217.86/0.199819.10/0.264116.23/0.168923.09/0.4320
Gaussian\\(\\sigma \\in [5,50]\\)1533.47/0.902733.12/0.891533.45/0.894531.28/0.818720.76/0.250830.85/0.843133.62/0.9026
2530.87/0.853830.64/0.849130.77/0.842329.65/0.780123.91/0.455228.92/0.806930.91/0.8573
5027.41/0.736127.13/0.729027.15/0.721927.00/0.711426.92/0.691125.13/0.619127.48/0.7530
7525.05/0.622324.97/0.620524.80/0.590824.89/0.602323.83/0.513222.37/0.421225.40/0.6645
", + "bbox": [ + 80, + 114, + 888, + 267 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/fb7436f383ebe17bff03774d1aaca4f5828b08178905a6cdf4b1f80b7b5491b1.jpg", + "table_caption": [ + "Table 2. Quantitative result of generalisation performance experiment on CBSD68 [23]. All methods use Gaussian $\\sigma = 25$ for pre-trained methods and then Gaussian $\\sigma \\in [5, 50]$ for fine-turning. The better result in each method is highlighted in italics." + ], + "table_footnote": [], + "table_body": "
Fine-tuning MethodN2C [21]N2N [16]LIR [9]MeD
Pretraining MethodN2CMeDN2NMeDLIRMeDMeD
Gaussian, δ ∈ [15, 75]29.20/ 0.779729.53/ 0.808129.04/ 0.764229.21/ 0.789026.42/ 0.664027.25/ 0.703629.60/ 0.8101
Local Var Gaussian35.62/ 0.930835.85/ 0.943935.66/ 0.925635.73/ 0.931029.26/ 0.817030.51/ 0.838735.91/ 0.9762
Poisson Noise40.49/ 0.973642.80/ 0.977641.35/ 0.973642.27/ 0.981331.23/ 0.867233.47/ 0.893245.05/ 0.9826
Speckle,帽子 ∈ [25, 50]33.36/ 0.900433.40/ 0.904433.32/ 0.893133.33/ 0.890728.28/ 0.771329.82/ 0.822933.48/ 0.9115
S&P,帽子 ∈ [0.3, 0.5]28.85/ 0.826730.73/ 0.837228.59/ 0.800329.45/ 0.825526.69/ 0.724127.62/ 0.746030.84/ 0.9135
Average33.50/ 0.882234.46/ 0.894233.59/ 0.871434.00/ 0.883528.38/ 0.768729.73/ 0.800934.98/ 0.9188
", + "bbox": [ + 80, + 306, + 888, + 429 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. AWGN Noise Removal", + "text_level": 1, + "bbox": [ + 76, + 452, + 287, + 467 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We first investigate the denoising generalisation of the methods using synthetic zero-mean additive white Gaussian noise (AWGN). The experiments are divided into two parts. The first segment employs fixed variance AWGN, whereas the second segment employs varied variance Gaussian for training in a separate manner. Table 1 summarises the quantitative results evaluated on CBSD68 Dataset [23] at variance levels of 15, 25, 50, and 75.", + "bbox": [ + 75, + 476, + 468, + 595 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Analysis: In the fixed variance setting, MeD performs inferior compared to the other methods on lower noise levels of 15 and 25. However, as the methods face more severe corruption, MeD outperforms all self-supervised and supervised methods, showing our greater advantage of handling severe noise. For instance, at $\\sigma = 75$ , MeD outperforms the second-best method (N2C) by around 2 dB. These results suggest that MeD has a remarkable ability to generalise to a range of unseen noise levels in Gaussian noise.", + "bbox": [ + 75, + 597, + 468, + 731 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In the context of random variance, it has been observed that MeD exhibits superior performance across all four noise levels compared to other methods, including supervised methods. These findings imply that MeD can benefit more from varying training noise than other methods. More experiments and details on AWGN noise removal can be found in the supplementary material.", + "bbox": [ + 75, + 733, + 468, + 838 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.3. Generalisation on Unseen Noise Removal", + "text_level": 1, + "bbox": [ + 76, + 847, + 428, + 862 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In the previous subsection, we demonstrated the remarkable generalisation ability of our model in the case of Gaus", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "sian noise. Here, we aim to extend this investigation to other types of unseen noise and evaluate the denoising generalisation ability of our method. Specifically, we consider Poisson noise, Speckle noise, Local Variance Gaussian noise, and Salt-and-Pepper noise. For a more detailed synthetic process, please refer to the supplementary material.", + "bbox": [ + 496, + 453, + 890, + 544 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "First, we demonstrate qualitative comparisons of denoising unseen noise types using models trained only with Gaussian $\\sigma = 25$ in Figure 3. Next, in order to further verify the denoising generalisation ability of MeD, we employ its scene encoder and decoder as pre-trained models to be compared against other methods. It should be noted that the pre-training and fine-tuning methods employed in this study may differ, as shown in Table 2. The pre-training of all test models was conducted on a Gaussian sigma value of 25, followed by fine-tuning with a Gaussian sigma range of 5 to 50. Since the training schema of N2S, R2R, and DBD $_4$ differs from MeD, we do not include them in this section. However, evaluations of these methods on unseen noise are still presented in Section 4.4 under different settings.", + "bbox": [ + 496, + 547, + 892, + 760 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Analysis: Qualitative results in Figure 3 show that under Gaussian $\\sigma = 25$ training settings, our method surpasses other methods in denoising unseen noise types. Additionally, Table 2 shows that the approaches using pre-trained MeD models outperform their self-transfer models for N2C, N2N, and LIR, with improvements of up to $2\\mathrm{dB}$ in some cases. On average, the MeD pre-trained models show a performance gain of around $0.5\\mathrm{dB}$ across all methods, highlighting the potential of MeD as a powerful pre-training", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "12286", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/4a9364f18bf096a984a5c4830cf35849e87a10d646a1f08aa41fb34fbf6bcee9.jpg", + "image_caption": [ + "Figure 3. Qualitative denoising results on unseen noise types. All the methods are trained with Gaussian $\\sigma = 25$ . The quantitative PSNR/SSIM results are provided underneath the respective images. Best viewed in colour (zoom-in for a better comparison)." + ], + "image_footnote": [], + "bbox": [ + 89, + 88, + 898, + 373 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/fa241e2d6e0d12ab1e1999d02c59bd66e2027ce208f4f6ce07c2591d03967768.jpg", + "table_caption": [ + "Table 3. Analysis of Noise Pool on CBSD68 [23]. All methods were trained using randomly drawn noise from the Noise Pool." + ], + "table_footnote": [], + "table_body": "
Test NoiseNoisy/ CleanNoisy/ NoisyInvariant Feature
N2C [21]DBD4 [11]N2N [16]N2S [4]R2R [26]LIR [9]MeD (ours)
Gaussian, θ ∈ [15, 75]29.24/0.775429.05/0.761629.23/0.763428.58/0.758926.43/0.663926.67/0.686629.61/0.8178
Local Var Gaussian (LVG)36.64/0.944236.18/0.930736.65/0.923533.24/0.885834.70/0.877931.61/0.862737.99/0.9568
Poisson Noise45.72/0.976444.23/0.960645.64/0.979946.31/0.980844.45/0.949143.27/0.929248.10/0.9916
Speckle, v ∈ [25, 50]35.58/0.941735.24/0.938535.34/0.947535.13/0.959634.20/0.907833.98/0.881037.21/0.9715
S&P, r ∈ [0.3, 0.5]38.85/0.916537.10/0.888438.89/0.928938.22/0.933036.17/0.908733.43/0.820242.33/0.9695
Gaussian θ = 25 + Speckle v = 2530.19/0.827929.24/0.815630.32/0.831729.51/0.805028.78/0.774429.20/0.787131.92/0.8726
Gaussian θ = 50 + Speckle v = 2527.30/0.725126.55/0.712627.23/0.733126.91/0.708126.49/0.693526.19/0.694129.68/0.7928
LVG + Poisson31.78/0.908731.10/0.884231.60/0.761730.15/0.808628.52/0.714427.33/0.723434.29/0.9325
Poisson + Speckle v = 2531.39/0.906930.86/0.878231.52/0.893530.58/0.906730.34/0.889729.93/0.855433.04/0.9258
Average34.08/0.880333.28/0.863434.05/0.862633.18/0.860732.23/0.819931.29/0.804436.02/0.9145
", + "bbox": [ + 81, + 430, + 890, + 601 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "method for image denoising. It is noteworthy that the self-transfer MeD model exhibits the best denoising performance across all validation noise types, even outperforming the supervised method, N2C. This is particularly evident in Poisson noise, where MeD surpasses N2C by $\\sim 3$ dB. These results highlight the generalisation ability of our approach in handling unseen noise.", + "bbox": [ + 75, + 627, + 468, + 733 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.4. Experiments on General Noise Pool", + "text_level": 1, + "bbox": [ + 76, + 741, + 383, + 757 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Here we further investigate the generalisation ability of our method by introducing our general Noise Pool. The Noise Pool comprises the five aforementioned types of noise, each with a diverse range of noise levels. During training, we randomly sample from the noise pool to provide the model with noisy images. This novel approach simulates a realistic scenario where noise is unknown and can originate from various sources to some extent.", + "bbox": [ + 75, + 763, + 468, + 883 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Specifically, we evaluated all methods using the random", + "bbox": [ + 96, + 885, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "noise pool approach to train and test on combined or single noise types. The results are summarised in Table 3.", + "bbox": [ + 500, + 628, + 890, + 657 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Analysis: In Table 3, our MeD approach outperforms all other methods significantly on all the test noise types. For example, when a test noise containing a combination of Gaussian noise with $\\hat{\\sigma} = 50$ and Speckle noise with $\\hat{v} = 25$ is used, other methods exhibit an approximate performance of $\\sim 27$ dB. However, MeD achieves significantly better results with a performance of $29.68\\mathrm{dB}$ . And on average, MeD exhibits a performance that is approximately $2\\mathrm{dB}$ better than other methods. Our findings show that utilising a comprehensive noise pool for training purposes can effectively improve the generalisation capability. Furthermore, the remarkable denoising generalisation ability of our MeD approach, in comparison to other methods, is particularly advantageous for real-world applications.", + "bbox": [ + 496, + 688, + 892, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "12287", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/299f035bc59010939b024056417be746ecac205818020c263c2b6282b2a66236.jpg", + "image_caption": [ + "23.68/0.2967" + ], + "image_footnote": [], + "bbox": [ + 98, + 88, + 395, + 258 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/31984eba46abcda06654c2f4af62a408c6e45f7205ab8dcca7ea01208262e6fc.jpg", + "image_caption": [ + "Noisy Image from SIDD [1] (ISO 800)", + "25.33/0.3865", + "Noisy Image from SIDD", + "Figure 4. Real Noise Removal Example of SIDD [1]. All the methods are trained with Noise Pool on the DIV2K [2] dataset. It can be seen that the proposed MeD can remove much real noise even without training with real-noise distribution (zoom in for a better comparison)." + ], + "image_footnote": [], + "bbox": [ + 98, + 292, + 395, + 465 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4208278d4294533f2e701c41092cd0e0a448ffedb407ef11e0f940e44e916669.jpg", + "image_caption": [ + "PSNR/ SSIM" + ], + "image_footnote": [], + "bbox": [ + 397, + 89, + 514, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/368e22ecf92ecabb0e4c6d5989d070dbfc298855a9d2624479434e5cc91aec3c.jpg", + "image_caption": [ + "Ground Truth [1]", + "28.58/0.6081" + ], + "image_footnote": [], + "bbox": [ + 397, + 189, + 514, + 258 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/48f7e84016ff3e3ac40ed96938b62967f5bb93efd68f4ee7378696b4a20ebcc1.jpg", + "image_caption": [ + "N2S [4]", + "PSNR/ SSIM" + ], + "image_footnote": [], + "bbox": [ + 397, + 290, + 514, + 362 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a812d9ecf16f26bc1fd04c3381a436840b4e03f6a2505585be28aa87c3783155.jpg", + "image_caption": [ + "Reference", + "27.58/0.5516", + "N2S [4]" + ], + "image_footnote": [], + "bbox": [ + 397, + 393, + 514, + 465 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/bf46359e66d67194ba2291666827a2db1d03d7f353782c722dd00c55440af375.jpg", + "image_caption": [ + "31.38/0.8912" + ], + "image_footnote": [], + "bbox": [ + 517, + 89, + 635, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/6ac8164e84c0be7417902af9d788371a65cd1b836dca4f759aac0e8d6087e0a8.jpg", + "image_caption": [ + "N2C [21]", + "26.58/0.4257" + ], + "image_footnote": [], + "bbox": [ + 517, + 189, + 635, + 258 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e5f1a76058abb08b195c2d15b5ed3c572ba4f621f91d6732317905f489954f53.jpg", + "image_caption": [ + "R2R [26]", + "28.36/0.5661" + ], + "image_footnote": [], + "bbox": [ + 517, + 290, + 635, + 362 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0224298f373927398c2d536b6b2f126404fd1a9765ba3c1f163a667c2d7e379b.jpg", + "image_caption": [ + "N2C [21]", + "26.77/0.4889", + "R2R [26]" + ], + "image_footnote": [], + "bbox": [ + 517, + 393, + 635, + 465 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/22cd848216bbb1c261cad8c5e2d79457875c2c0edc0293f070ffe52ece4b6557.jpg", + "image_caption": [ + "30.19/0.7449" + ], + "image_footnote": [], + "bbox": [ + 637, + 89, + 754, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/19cd42d46af1dac7e261d109e044bf319ed117649965d2360ac36b4a9b8649d5.jpg", + "image_caption": [ + "$\\mathrm{DBD}_4$ [11]", + "25.91/0.3795" + ], + "image_footnote": [], + "bbox": [ + 637, + 189, + 754, + 258 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/c3da253c319cda95c8cbf681a689612717c95ebc7d8167697cbadf362435c1bf.jpg", + "image_caption": [ + "LIR [9]", + "27.58/0.5406" + ], + "image_footnote": [], + "bbox": [ + 637, + 290, + 754, + 362 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9fd37291b971d5e769d3b23748871b4db2e59a4c8f5e7e17ba62171900eb13eb.jpg", + "image_caption": [ + "$\\mathrm{DBD}_4$ [11]", + "26.45/0.4752", + "LIR [9]" + ], + "image_footnote": [], + "bbox": [ + 637, + 393, + 754, + 465 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/9b3ddeadb5538ea7241678518896fcdc6cd7c1e4a28ee27a15e74a536b4aa62e.jpg", + "image_caption": [ + "29.60/0.7053" + ], + "image_footnote": [], + "bbox": [ + 756, + 89, + 877, + 157 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/522e6dba673ab52deb06310ea6007bc01e9217790a01eae6aff3b36b5d12d312.jpg", + "image_caption": [ + "N2N [16]", + "33.07/0.8849" + ], + "image_footnote": [], + "bbox": [ + 756, + 189, + 877, + 258 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2e12321648df346c62b959357c3b8b23cbe0f7ddba79eccdbd930416f2926fc0.jpg", + "image_caption": [ + "MeD (Ours)", + "27.23/0.49" + ], + "image_footnote": [], + "bbox": [ + 756, + 290, + 877, + 362 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4300d7c2bbd8c192b2338e62e086a374e61126a6c5dfede61dec1ee9a7265f14.jpg", + "image_caption": [ + "N2N [16]", + "30.23/0.6703", + "MeD (Ours)" + ], + "image_footnote": [], + "bbox": [ + 756, + 393, + 877, + 465 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/0e953a78bdb8b19a6960a703f3ac23e84ba5d4518c0fc52b9c7c8f75718ea22c.jpg", + "table_caption": [ + "Table 4. Quantitative result obtained from the application of various methods trained on a general Noise Pool to real noise datasets." + ], + "table_footnote": [], + "table_body": "
MethodPolyU [32]SIDD [1]CC [24]Average
N2C [21]35.89/0.965230.37/0.602837.89/0.940834.72/0.8363
DBD4 [11]35.69/0.957130.23/0.617337.74/0.935734.55/0.8367
N2N [16]36.22/0.967932.82/0.729737.39/0.957035.48/0.8849
N2S [4]36.41/0.972130.98/0.601837.58/0.962234.99/0.8454
R2R [26]34.58/0.889029.64/0.570835.35/0.847833.19/0.7692
LIR [9]34.81/0.727828.76/0.529635.50/0.840333.02/0.6992
MeD (ours)38.65/0.985535.81/0.827840.08/0.974538.18/0.9293
", + "bbox": [ + 80, + 579, + 468, + 681 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.5. Real Noise Removal", + "text_level": 1, + "bbox": [ + 76, + 709, + 266, + 724 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In our previous experiments, we demonstrated the exceptional denoising performance of our MeD approach on synthetic noises. However, real-world noise is often more complex and challenging than synthetic noise. In this subsection, we aim to evaluate the generalisation performance of our approach on real-world noise by testing it on the SIDD [1], CC [24] and PolyU [32] datasets. To assess the denoising performance on real-world noise, we use the same pre-trained models as in Section 4.4. The representative qualitative results on the SIDD dataset in the standard RGB colour space are presented in Figure 4.", + "bbox": [ + 75, + 734, + 468, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Analysis: As shown in Table 4, our approach significantly outperforms all other methods across all three datasets, with a performance improvement of 2-3 dB over the second-best approach, and also consistently outperforms its supervised counterparts (i.e. N2C and $\\mathrm{DBD}_4$ ) by over 3 dB. These results suggest the effectiveness and generalisability of the proposed approach in real-world denoising scenarios.", + "bbox": [ + 496, + 555, + 890, + 661 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Our approach achieves remarkable performance on real-world noise without even being trained on more expensive real-world data. For a more complete study, we also conduct experiments on model training with real-world data (for more details please refer to the supplementary material), showing superior performance and even better generalisation ability to data out of the training data distribution.", + "bbox": [ + 496, + 667, + 890, + 773 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In Figure 4, the presence of noise persists even after applying denoising techniques, yet ours demonstrates the most authentic outcomes compared to others. For instance, while the noise particles remain prominent in the N2C results, they are absent in our results. Overall, the results indicate that the MeD approach is well-suited for real-world denoising tasks, providing a robust and reliable solution for", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "12288", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/794b2efd69f1da9a81ff47dd28c2f802354860cae14c74fd9a7352a0b7430f0f.jpg", + "table_caption": [ + "Table 5. Multiple views ( $\\geq 2$ ) study,with average PSNR/SSIM." + ], + "table_footnote": [], + "table_body": "
#ViewsGaussianLVGPoissonSpeckleS&P
229.61/0.817837.99/0.956848.10/0.991637.21/0.971542.33/0.9695
329.68/0.819738.05/0.957748.23/0.992037.40/0.973342.45/0.9703
429.70/0.820438.08/0.958048.31/0.992137.47/0.974042.49/0.9709
", + "bbox": [ + 80, + 101, + 467, + 148 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/5fe4300a3ea61f811cafd3d0bfccf6dfbb657460b1c876bc22a5e7c65c25dab0.jpg", + "table_caption": [ + "Table 6. Average PSNR/SSIM of super-resolution results on Set5 [6]. Learning-based methods are trained with Corruption Pool." + ], + "table_footnote": [], + "table_body": "
ScaleBicubicRCAN [37]DASR [30]MeD (ours)
×233.63/ 0.928536.12/ 0.933936.98/ 0.947137.12/ 0.9527
×330.37/ 0.865234.15/ 0.928634.11/ 0.918734.92/ 0.9294
×428.35/ 0.808431.94/ 0.887131.54/ 0.873632.50/ 0.8956
", + "bbox": [ + 80, + 189, + 465, + 247 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "improving image quality in challenging environments.", + "bbox": [ + 76, + 273, + 434, + 287 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "4.6. Expand to More Views", + "text_level": 1, + "bbox": [ + 76, + 297, + 289, + 313 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Although we only showcase two views for the experiments above, our method can be easily expanded to multiple views. To investigate the impact of the numbers of views, here we further conduct a study comparing 2, 3, and 4 views, in Table 5.", + "bbox": [ + 75, + 320, + 467, + 395 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "The results indicate that increasing the number of views consistently improves the performance across different noise types. For example, when dealing with Speckle noise, the 4-view model achieves a $0.26\\mathrm{dB}$ higher PSNR than the 2-view model. However, it is worth noting that employing $n$ views requires $n!$ cross-computations within each view pair during training, resulting in a significant increase in computational cost (e.g. from 2-view to 4-view leads to a $10\\times$ training time increase in our experiment).", + "bbox": [ + 75, + 396, + 467, + 532 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "4.7. More Application Exploration", + "text_level": 1, + "bbox": [ + 76, + 541, + 344, + 558 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Here we investigate the potential of the proposed MeD for other more general image restoration tasks, such as image super-resolution and inpainting. In this study, we generalise the previously defined degradation (noise) to a residual image between a clean image and a corrupted image. Moreover, we expand the definition from Noise Pool to a more general one - Corruption Pool that contains not only noise but also general corruption.", + "bbox": [ + 75, + 565, + 467, + 686 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Super resolution. Image super-resolution aims to enlarge the resolution of a low-resolution image. We train our method on the DIV2K dataset [3], where we randomly choose different downscale methods from a Corruption Pool that consists of random Gaussian noise and four types of down-scaling (bicubic, lanczos, bilinear, and hamming). We benchmark our method against the supervised method RCAN [37] that aims for high PSNR and the recent unsupervised methods DASR [30] that are specialised for superresolution. We conduct our evaluation on the Set5 dataset [6] with scaling factors of 2, 3, and 4. The results in Table 6 show the effectiveness of our method over both supervised and unsupervised approaches.", + "bbox": [ + 75, + 704, + 467, + 900 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/7c91730d6cda630aa5cfbb1cf8fe6423527f22f8cd4f59504f1e2656e469549b.jpg", + "table_caption": [ + "Table 7. Average PSNR/SSIM of inpainting results on Set11 [29]. S2S and DIP are trained and tested on the same single image. MeD is trained with Corruption Pool." + ], + "table_footnote": [], + "table_body": "
Dropping RatioDIP [29]S2S [27]MeD (Ours)
50%33.45/ 0.921734.91/ 0.947936.24/ 0.9617
70%28.53/ 0.850130.94/ 0.884531.05/ 0.9161
90%24.39/ 0.736025.97/ 0.793326.01/ 0.8052
", + "bbox": [ + 513, + 133, + 879, + 200 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Inpainting. We also apply our method to the image inpainting task, which fills in missing pixels. We choose two single-image deep learning methods - Self2Self (S2S) [27] and DIP [29], for comparison. Our MeD is trained with Corruption Pool containing noises, down-scaling, and inpainting mask operations altogether. To compare our method (MeD) with other state-of-the-art methods, we conduct experiments on the Set 11 dataset [29] with three different pixel dropping ratios: $50\\%$ , $70\\%$ , and $90\\%$ . The results are shown in Table 7, suggesting the effectiveness of MeD again in the image inpainting task.", + "bbox": [ + 496, + 232, + 890, + 398 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 419, + 617, + 434 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this paper, we have presented a new self-supervised learning method (MeD) for image denoising that disentangles scene and noise features in a constraint feature space. Our approach has demonstrated exceptional denoising performance in both synthetic and real-world noise scenarios, with particularly significant performance on real-world noise. MeD can handle complex noise with better performance than other state-of-the-art methods, as validated by consistent performance gain across various datasets and noise types. Our approach has decent generalisation ability, requiring only noisy images for training and efficiently denoising real-world noise without seeing any clean ground truth data. This opens up new possibilities for training deep models without the need for costly labelled data. Furthermore, our model can be easily adapted to other low-level image restoration tasks. We hope this could provide a new baseline for future research in image disentanglement and the extension to other image processing tasks.", + "bbox": [ + 496, + 446, + 890, + 719 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 500, + 736, + 645, + 752 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "The computations described in this research were performed using the Baskerville Tier 2 HPC service1. Baskerville was funded by the EPSRC and UKRI through the World Class Labs scheme (EP/T022221/1) and the Digital Research Infrastructure programme (EP/W032244/1) and is operated by Advanced Research Computing at the University of Birmingham.", + "bbox": [ + 496, + 761, + 890, + 868 + ], + "page_idx": 8 + }, + { + "type": "page_footnote", + "text": "$^{1}$ https://www.baskerville.ac.uk/", + "bbox": [ + 517, + 886, + 687, + 898 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "12289", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Abdelrahman Abdelhamed, Stephen Lin, and Michael S Brown. A high-quality denoising dataset for smartphone cameras. 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In Proceedings of the AAAI Conference on Artificial Intelligence, volume 34, pages 13074-13081, 2020." + ], + "bbox": [ + 78, + 90, + 470, + 811 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "12291", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/bd73600c-bf62-4573-910c-f059e97c644d_model.json b/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/bd73600c-bf62-4573-910c-f059e97c644d_model.json new file mode 100644 index 0000000000000000000000000000000000000000..bb17f5f6cd7576062a14f7810fd88c3251f7faa5 --- /dev/null +++ b/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/bd73600c-bf62-4573-910c-f059e97c644d_model.json @@ -0,0 +1,3027 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.114, + 0.127, + 0.856, + 0.15 + ], + "angle": 0, + "content": "Multi-view Self-supervised Disentanglement for General Image Denoising" + }, + { + "type": "text", + "bbox": [ + 0.173, + 0.165, + 0.276, + 0.185 + ], + "angle": 0, + "content": "Hao Chen\\*,1" + }, + { + "type": "text", + "bbox": [ + 0.301, + 0.165, + 0.43, + 0.185 + ], + "angle": 0, + "content": "Chenyuan \\(\\mathrm{Qu}^{*,1}\\)" + }, + { + "type": "text", + "bbox": [ + 0.455, + 0.166, + 0.543, + 0.185 + ], + "angle": 0, + "content": "Yu Zhang²" + }, + { + "type": "text", + "bbox": [ + 0.568, + 0.166, + 0.666, + 0.184 + ], + "angle": 0, + "content": "Chen Chen3" + }, + { + "type": "text", + "bbox": [ + 0.691, + 0.166, + 0.79, + 0.184 + ], + "angle": 0, + "content": "Jianbo Jiao" + }, + { + "type": "text", + "bbox": [ + 0.111, + 0.191, + 0.86, + 0.211 + ], + "angle": 0, + "content": "\\(^{1}\\)University of Birmingham \\(^{2}\\)Shanghai Jiao Tong University \\(^{3}\\)University of Central Florida" + }, + { + "type": "text", + "bbox": [ + 0.305, + 0.216, + 0.667, + 0.235 + ], + "angle": 0, + "content": "Project page: https://chqwer2.github.io/MeD/" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.285 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.302, + 0.474, + 0.635 + ], + "angle": 0, + "content": "With its significant performance improvements, the deep learning paradigm has become a standard tool for modern image denoisers. While promising performance has been shown on seen noise distributions, existing approaches often suffer from generalisation to unseen noise types or general and real noise. It is understandable as the model is designed to learn paired mapping (e.g. from a noisy image to its clean version). In this paper, we instead propose to learn to disentangle the noisy image, under the intuitive assumption that different corrupted versions of the same clean image share a common latent space. A self-supervised learning framework is proposed to achieve the goal, without looking at the latent clean image. By taking two different corrupted versions of the same image as input, the proposed Multi-view Self-supervised Disentanglement (MeD) approach learns to disentangle the latent clean features from the corruptions and recover the clean image consequently. Extensive experimental analysis on both synthetic and real noise shows the superiority of the proposed method over prior self-supervised approaches, especially on unseen novel noise types. On real noise, the proposed method even outperforms its supervised counterparts by over 3 dB." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.666, + 0.21, + 0.682 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.692, + 0.47, + 0.875 + ], + "angle": 0, + "content": "Image restoration is a critical sub-field of computer vision, exploring the reconstruction of image signals from corrupted observations. Examples of such ill-posed low-level image restoration problems include image denoising [16,25,26,29,33,35,38], super-resolution [2,8,19,30,37], and JPEG artefact removal [7, 12, 31], to name a few. Usually, a mapping function dedicated to the training data distribution is learned between the corrupted and clean images to address the problem. While many image restoration systems perform well when evaluated over the same corruption distribution that they have seen, they are often required to be deployed in settings where the environment is unknown and" + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.275, + 0.697, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.549, + 0.459, + 0.66, + 0.473 + ], + "angle": 0, + "content": "(a) Noisy/ Clean" + }, + { + "type": "image", + "bbox": [ + 0.704, + 0.275, + 0.882, + 0.457 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.711, + 0.459, + 0.879, + 0.473 + ], + "angle": 0, + "content": "(b) N2C [21], Supervised" + }, + { + "type": "image", + "bbox": [ + 0.519, + 0.48, + 0.698, + 0.662 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.516, + 0.664, + 0.697, + 0.679 + ], + "angle": 0, + "content": "(c) LIR [9], Self-supervised" + }, + { + "type": "image", + "bbox": [ + 0.704, + 0.48, + 0.883, + 0.662 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.712, + 0.664, + 0.877, + 0.679 + ], + "angle": 0, + "content": "(d) Ours, Self-supervised" + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.687, + 0.895, + 0.786 + ], + "angle": 0, + "content": "Figure 1. Denoising performance on unseen Speckle Noise with \\(\\hat{\\pmb{v}} = 50\\). The models were trained with Gaussian noise \\(\\sigma \\in [5,50]\\). (a) The noisy and clean images, with ground-truth clean patches shown below. (b) Noise-to-Clean (N2C) [21] is trained with clean images. (c) LIR [9] is self-supervised but needs unpaired clean images as training data. (d) Our approach is fully self-supervised, training with only the noisy input data." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.895, + 0.903 + ], + "angle": 0, + "content": "off the training distribution. These settings, such as medical imaging, computational lithography, and remote sensing, require image restoration methods that can handle complex and unknown corruptions. Moreover, in many real-world image-denoising tasks, ground truth images are unavailable, introducing additional challenges." + }, + { + "type": "page_footnote", + "bbox": [ + 0.102, + 0.888, + 0.214, + 0.9 + ], + "angle": 0, + "content": "*Equal contribution." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "12281" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.468, + 0.167 + ], + "angle": 0, + "content": "Limitations of existing methods: Current low-level corruption removal tasks aim to address the inquiry of \"what is the clean image provided a corrupted observation?\" However, the ill-posed nature of this problem formulation poses a significant challenge in obtaining a unique resolution [5]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.168, + 0.468, + 0.318 + ], + "angle": 0, + "content": "To mitigate this limitation, researchers often introduce additional information, either explicitly or implicitly. For example, in [15], Laine et al. explicitly use the prior knowledge of noise as complementary input, generating a new invertible image model. Alternatively, Learning Invariant Representation (LIR) [9] implicitly enforces the interpretability in the feature space to guarantee the admissibility of the output. However, these additional forms of information may not always be practical in real-world scenarios or may not result in satisfactory performance." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.336, + 0.468, + 0.44 + ], + "angle": 0, + "content": "Main idea and problem formulation: Our motivation for tackling this ill-posed nature stems from the solution in the 3D reconstruction of utilising multiple views to provide a unique estimation of the real scene [1]. Building on this motivation, we propose a training scheme that is explicitly built on multi-corrupted views and perform Multi-view self-supervised Disentanglement, abbreviated as \\( MeD \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.442, + 0.468, + 0.591 + ], + "angle": 0, + "content": "Under this new multi-view setting, we reformulate the task problem as \"what is the shared latent information across these views?\" instead of the conventional \"what is the clean image?\" By doing so, MeD can effectively leverage the scene coherence of multi-view data and capture underlying common parts without requiring access to the clean image. This makes it more practical and scalable in real-world scenarios. An example of the proposed method with comparison to prior works is shown in Figure 1, indicating its effectiveness over the state-of-the-art." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.592, + 0.468, + 0.636 + ], + "angle": 0, + "content": "Specifically, given any scene image \\( x^{k} \\sim \\mathcal{X}, k \\in \\mathbb{N} \\) sampled uniformly from a clean image set \\( \\mathcal{X} \\), MeD produces two contaminated views:" + }, + { + "type": "equation", + "bbox": [ + 0.178, + 0.645, + 0.468, + 0.665 + ], + "angle": 0, + "content": "\\[\ny _ {1} ^ {k} \\triangleq \\mathcal {T} _ {1} \\left(x ^ {k}\\right), y _ {2} ^ {k} \\triangleq \\mathcal {T} _ {2} \\left(x ^ {k}\\right), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.672, + 0.468, + 0.718 + ], + "angle": 0, + "content": "forming two independent corrupted image sets \\(\\{\\mathcal{Y}_1\\}, \\{\\mathcal{Y}_2\\}\\), where \\(y_1^k \\in \\mathcal{Y}_1\\), \\(y_2^k \\in \\mathcal{Y}_2\\). The \\(\\mathcal{T}_1\\) and \\(\\mathcal{T}_2\\) represent two random independent image degradation operations." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.718, + 0.468, + 0.78 + ], + "angle": 0, + "content": "We parameterise our scene feature encoder \\(G_{\\theta}^{\\mathcal{X}}\\) and decoder \\(D_{\\psi}^{\\mathcal{X}}\\) with \\(\\theta\\) and \\(\\psi\\). Considering the image pair \\(\\{y_1^k, y_2^k\\}_{k \\in \\mathbb{N}}\\), the core of the presented method can be summarised as:" + }, + { + "type": "equation", + "bbox": [ + 0.18, + 0.788, + 0.468, + 0.807 + ], + "angle": 0, + "content": "\\[\nG _ {\\theta} ^ {\\mathcal {X}} \\left(y _ {1} ^ {k}\\right) \\triangleq z _ {x} ^ {k, i} \\triangleq G _ {\\theta} ^ {\\mathcal {X}} \\left(y _ {2} ^ {k}\\right), \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.218, + 0.809, + 0.468, + 0.829 + ], + "angle": 0, + "content": "\\[\n\\hat {x} ^ {k} \\triangleq D _ {\\psi} ^ {\\mathcal {X}} \\left(z _ {x} ^ {k, i}\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.838, + 0.468, + 0.902 + ], + "angle": 0, + "content": "where \\( z_{x}^{k,i} \\) represents the shared scene latent between \\( y_{1}^{k} \\) and \\( y_{2}^{k} \\) with \\( i \\) referring to the input image index of \\( y_{i} \\). A clean image estimator \\( D_{\\psi}^{\\mathcal{X}} \\) forms an all-deterministic reverse mapping from \\( z_{x}^{k,i} \\) to reconstruct an estimated clean" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.091, + 0.891, + 0.158 + ], + "angle": 0, + "content": "image \\(\\hat{x}^k\\). Similarly, the noise latent \\(u_{\\eta}^{k,i}\\) is factorised from a corrupted view with a corruption encoder \\(E_{\\rho}^{\\mathcal{N}}\\). After words, the resulting corruption is reconstructed from \\(u_{\\eta}^{k,i}\\) through the use of a corruption decoder, represented by \\(F_{\\phi}^{\\mathcal{N}}\\)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.157, + 0.891, + 0.202 + ], + "angle": 0, + "content": "The disentanglement is then performed between \\(\\{z_{x}^{k,i},u_{\\eta}^{k,j}\\}_{i\\neq j}\\) on a cross compose decoder \\(R_{\\delta}^{\\mathcal{V}}\\) with parameter \\(\\delta\\), which can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.622, + 0.213, + 0.891, + 0.233 + ], + "angle": 0, + "content": "\\[\n\\hat {y} _ {1} ^ {k} \\triangleq R _ {\\delta} ^ {\\mathcal {Y}} \\left(z _ {x} ^ {k, 2}, u _ {\\eta} ^ {k, 1}\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.243, + 0.891, + 0.306 + ], + "angle": 0, + "content": "It should be noted that Equation (4) is performed over latent features \\( u \\) and \\( z \\) from different views. When assuming that \\( z_{x}^{k} \\) remains constant across views, the reconstructed view \\( \\hat{y}_{1}^{k} \\) is determined by the \\( u_{\\eta}^{k,1} \\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.322, + 0.89, + 0.351 + ], + "angle": 0, + "content": "Contributions. The contributions of our work are summarised as follows:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.363, + 0.891, + 0.408 + ], + "angle": 0, + "content": "- We propose a new problem formulation to address the ill-posed problem of image denoising using only noisy examples, in a different paradigm than prior works." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.418, + 0.891, + 0.493 + ], + "angle": 0, + "content": "- We introduce a disentangled representation learning framework that leverages multiple corrupted views to learn the shared scene latent, by exploiting the coherence across views of the same scene and separating noise and scene in the latent space." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.504, + 0.891, + 0.579 + ], + "angle": 0, + "content": "- Extensive experimental analysis validates the effectiveness of the proposed MeD, outperforming existing methods with more robust performance to unknown noise distributions, even better than its supervised counterparts." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.363, + 0.891, + 0.579 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.604, + 0.64, + 0.619 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Single-view image restoration: In [8], Dong et al. were the first to employ a deep network in super-resolution. Later, a range of single view-based models expanded the idea of supervised deep learning to handle image restoration tasks, such as deblurring [14], JPEG artefacts [12], inpainting [17, 34] and denoising [16, 26, 35]. Recently, it is receiving increasing interest in relaxing the prerequisite of supervised learning with corrupted/ clean image pairs. In the context of image denoising, the \"corrupted/clean\" pair denotes a corrupted input image and its corresponding clean image for calculating the loss. To tackle the issue of the lack of clean data, several methods have been proposed, such as the Noise2Noise (N2N) method [16] and Recorrupted-to-Recorrupted (R2R) [26], which train deep networks on pairs of noisy images. Noise2Void (N2V) [13], Noise2Self (N2S) [4], and the method proposed by Laine et al. [15] are based on the blind-spot strategy that discards some pixels in the input and predicts them using the remaining. In the field" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12282" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.088, + 0.891, + 0.363 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.367, + 0.897, + 0.451 + ], + "angle": 0, + "content": "Figure 2. Method Overview. This figure illustrates the main steps of our proposed method, MeD, which first generates scene features (cubes) and distortion features (cuboids). The colour of them indicates their image source. In the right section, the features are rearranged and utilised for the four forward paths, from top to bottom, which are the reconstructions of noise \\((\\hat{\\eta}_1^k)\\), scene \\((\\hat{x}_2^k)\\), input image \\((y_2^k)\\) and shared scene \\((\\hat{x}^k)\\). It is noteworthy that \\(\\hat{y}_2^k\\) is reconstructed using \\(z_x^{k,1}\\) from \\(y_1^k\\) and \\(u_{\\eta}^{k,2}\\) from \\(y_2^k\\) for feature disentanglement. Additionally, the reconstruction of \\(\\hat{x}^k\\) relies on mixed scene features to facilitate learning of invariant scene latent. Moreover, the reconstruction paths for \\((\\hat{\\eta}_2,\\hat{x}_1,\\) and \\(y_{1})\\) are not depicted here, as they differ from the given paths only in their sub-indexes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.475, + 0.47, + 0.52 + ], + "angle": 0, + "content": "of single-image denoising, some methods such as DIP [29] and S2S [27], have achieved remarkable denoising results using only one noisy image." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.521, + 0.471, + 0.581 + ], + "angle": 0, + "content": "These methods, however, often inevitably compromise image quality to noise reduction, resulting in over-smoothed output. This trade-off is further exacerbated under domain shifts when dealing with unknown noise distributions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.605, + 0.47, + 0.771 + ], + "angle": 0, + "content": "Restoration based on multiple views: Existing multiview variants of image restoration methods mainly focus on sequential data such as video or burst images. For example, Tico [28] builds a paradigm that separates the unique and common features within the multi-frame to produce a denoised estimate. Liu et al. [20] models degrading elements as foreground and estimate background using video data. Deep Burst Denoising (DBD) [11] performs multi-view denoising based on burst images. Each image is taken in a short exposure time and serves as a corrupted observation of the clean image." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.772, + 0.471, + 0.833 + ], + "angle": 0, + "content": "Unlike the above-mentioned methods, our \\( MeD \\) aims to use multiple static observations simultaneously to learn the latent representation of a clean scene that is shared by multiple discrete views." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Self-supervised feature disentanglement: Another notable path of work has attempted to disentangle underlying invariant content from distorted images. For instance, \\(UID\\)-" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.475, + 0.892, + 0.55 + ], + "angle": 0, + "content": "GAN [22] utilises unpaired clean/blurred images to disentangle content and blurring effects in the feature space and yield improved deblurring performance. Similarly, \\(LIR\\) [9] used unpaired input to isolate invariant content features through self-supervised inter-domain transformation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.552, + 0.892, + 0.643 + ], + "angle": 0, + "content": "However, these methods are limited to synthetic noise and do not extend well in real-world scenarios due to their reliance on clean images. In contrast, our method is purely based on multiple noisy views of the same static scene and aims to disentangle the scene from corruption, without the need for clean image supervision." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.661, + 0.637, + 0.679 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.688, + 0.892, + 0.824 + ], + "angle": 0, + "content": "Our primary objective is to identify the commonalities among different views in the denoising process. To achieve this, we aim to discover the shared scene \\( z_{x}^{k} \\) that is degradation-agnostic over various corrupted views \\( \\{y_{i}^{k}\\}_{k\\in \\mathbb{N}} \\) via our proposed training schema, namely Multi-view self-supervised Disentanglement (MeD). A graphic depiction of MeD is shown in Figure 2, composed of the representation learning process in the left panel, and four distinct reconstruction pathways in the right panel." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.826, + 0.892, + 0.9 + ], + "angle": 0, + "content": "The detailed design of the proposed schema will be introduced in the following subsections. Section 3.1 explains the restoration of noise and scene. Section 3.2 details the reconstruction of noisy input using a cross-feature combination. Section 3.3 elaborates on the reconstruction of the" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12283" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.289, + 0.106 + ], + "angle": 0, + "content": "scene using mixed scene latent." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.107, + 0.47, + 0.152 + ], + "angle": 0, + "content": "We will start our introduction by outlining three essential properties that a multi-view representation disentanglement technique should exhibit." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.17, + 0.469, + 0.215 + ], + "angle": 0, + "content": "Pre-assumed properties: Suppose the scene latent space and corruption latent space are symbolised by \\(\\mathcal{Z}_x\\) and \\(\\mathcal{U}_{\\eta}\\), respectively." + }, + { + "type": "text", + "bbox": [ + 0.082, + 0.222, + 0.47, + 0.271 + ], + "angle": 0, + "content": "(1) Independence: For any scene latent \\( z_{x}^{k} \\in \\mathcal{Z}_{x} \\), it is expected to be independent of any corruption latent \\( u_{\\eta}^{k,i}, \\in \\mathcal{U}_{\\eta} \\)." + }, + { + "type": "text", + "bbox": [ + 0.082, + 0.279, + 0.469, + 0.327 + ], + "angle": 0, + "content": "(2) Consistency: There exists one shared latent code \\( z_{x}^{k} \\in \\mathcal{Z}_{x} \\) that is capable of representing the shared clean component of all instances in the set \\( \\{y_{i}^{k}\\} \\)." + }, + { + "type": "text", + "bbox": [ + 0.082, + 0.333, + 0.469, + 0.409 + ], + "angle": 0, + "content": "(3) Composability: Recovery of the corrupted view \\( y_{i}^{k} \\) can be achieved using the feature pairs \\( z_{x}^{k}, u_{\\eta}^{k,i} \\), and the index of the recovered view is determined by the index of the corruption latent, which represents the unique component within that particular view." + }, + { + "type": "list", + "bbox": [ + 0.082, + 0.222, + 0.47, + 0.409 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.417, + 0.47, + 0.543 + ], + "angle": 0, + "content": "A key step of our method is to realise these prerequisites by determining how to implement the latent space assumption. As shown in the left panel of Figure 2, to infer our latent space assumption, MeD is comprised of two encoders and three decoders: A shared content latent encoder \\( G_{\\theta}^{\\mathcal{X}} \\) and its decoder \\( D_{\\psi}^{\\mathcal{X}} \\), an auxiliary noise latent encoder \\( E_{\\rho}^{\\mathcal{N}} \\) and its decoder \\( F_{\\phi}^{\\mathcal{N}} \\), and a cross disentangle-ment decoder \\( R_{\\delta}^{\\mathcal{Y}} \\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.551, + 0.289, + 0.565 + ], + "angle": 0, + "content": "3.1. Main Forward Process" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.574, + 0.469, + 0.62 + ], + "angle": 0, + "content": "Given two corrupted views of the same image \\( x^{k} \\), \\( y_{1}^{k} \\triangleq \\mathcal{T}_{1}(x^{k}) \\) and \\( y_{2}^{k} \\triangleq \\mathcal{T}_{2}(x^{k}) \\), the encoder \\( G_{\\theta}^{\\mathcal{X}} \\) mainly perform the scene feature space encoding that can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.632, + 0.469, + 0.651 + ], + "angle": 0, + "content": "\\[\nz _ {x} ^ {k, 1} \\triangleq G _ {\\theta} ^ {\\mathcal {X}} \\left(y _ {1} ^ {k}\\right), z _ {x} ^ {k, 2} \\triangleq G _ {\\theta} ^ {\\mathcal {X}} \\left(y _ {2} ^ {k}\\right), \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.655, + 0.469, + 0.687 + ], + "angle": 0, + "content": "where \\( z_{x}^{k,1} \\) and \\( z_{x}^{k,2} \\) are the estimation of the scene feature corresponding to the inputs \\( y_{1}^{k} \\) and \\( y_{2}^{k} \\)." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.687, + 0.469, + 0.718 + ], + "angle": 0, + "content": "The process of clean image reconstruction is then completed by the \\(D_{\\psi}^{\\mathcal{X}}\\):" + }, + { + "type": "equation", + "bbox": [ + 0.158, + 0.727, + 0.469, + 0.747 + ], + "angle": 0, + "content": "\\[\n\\hat {x} _ {1} ^ {k} \\triangleq D _ {\\psi} ^ {\\mathcal {X}} \\left(z _ {x} ^ {k, 1}\\right), \\hat {x} _ {2} ^ {k} \\triangleq D _ {\\psi} ^ {\\mathcal {X}} \\left(z _ {x} ^ {k, 2}\\right). \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.755, + 0.469, + 0.803 + ], + "angle": 0, + "content": "Similar to the process of estimating scene features, the estimation of distortion features by \\( E_{\\rho}^{\\mathcal{N}} \\), followed by the reconstruction of noise with \\( F_{\\phi}^{\\mathcal{N}} \\), can be described as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.157, + 0.822, + 0.469, + 0.848 + ], + "angle": 0, + "content": "\\[\nu _ {n} ^ {k, 1} \\triangleq E _ {\\rho} ^ {\\mathcal {N}} \\left(y _ {1} ^ {k}\\right), u _ {n} ^ {k, 2} \\triangleq E _ {\\rho} ^ {\\mathcal {N}} \\left(y _ {2} ^ {k}\\right), \\tag {7}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.159, + 0.844, + 0.387, + 0.863 + ], + "angle": 0, + "content": "\\[\n\\hat {\\eta} _ {1} ^ {k} \\triangleq F _ {\\phi} ^ {\\mathcal {N}} \\left(u _ {n} ^ {k, 1}\\right), \\hat {\\eta} _ {2} ^ {k} \\triangleq F _ {\\phi} ^ {\\mathcal {N}} \\left(u _ {n} ^ {k, 2}\\right).\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "We adhere to the methodology introduced by N2N [16] to use noisy images as supervisory signals. The objective" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.12 + ], + "angle": 0, + "content": "function of the aforementioned process can be simplified to:" + }, + { + "type": "equation", + "bbox": [ + 0.581, + 0.129, + 0.891, + 0.164 + ], + "angle": 0, + "content": "\\[\n\\underset {\\theta , \\psi} {\\operatorname {a r g m i n}} \\mathcal {L} ^ {\\mathcal {X}} \\triangleq | | \\hat {x} _ {1} ^ {k} - y _ {2} ^ {k} | |, \\tag {8}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.584, + 0.152, + 0.891, + 0.187 + ], + "angle": 0, + "content": "\\[\n\\underset {\\rho , \\phi} {\\operatorname {a r g m i n}} \\mathcal {L} ^ {\\mathcal {N}} \\triangleq | | \\left(y _ {1} ^ {k} - \\hat {\\eta} _ {1} ^ {k}\\right) - y _ {2} ^ {k} | |. \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.199, + 0.892, + 0.275 + ], + "angle": 0, + "content": "The objective of \\(\\hat{x}_2^k\\) and \\(\\hat{\\eta}_2^k\\) are the same as above, with only a subscript difference. It should be noted that, although our objective functions are similar to that of N2N, our goal is not simply to find and remove noise, but rather to capture the common features shared across multiple views." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.285, + 0.714, + 0.3 + ], + "angle": 0, + "content": "3.2. Cross Disentanglement" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.307, + 0.892, + 0.443 + ], + "angle": 0, + "content": "For general latent codes \\( z_{x}^{k} \\) to sufficiently represent scene information in the image space, it is natural to assume that these codes exhibit a certain degree of freedom, allowing them to intersect with the noise space. Consequently, there is no guarantee of complete isolation between \\( z_{x}^{k} \\) and \\( u_{\\eta}^{k} \\). To meet the requirements of properties (1) and (3), we use an additional decoder \\( R_{\\delta}^{y} \\) to reconstruct a corrupted view over a cross-feature combination, e.g. \\( z_{x}^{k,1} \\) from \\( y_{1} \\) and \\( u_{n}^{k,2} \\) from \\( x_{2} \\), which can be represented as:" + }, + { + "type": "equation", + "bbox": [ + 0.549, + 0.455, + 0.891, + 0.474 + ], + "angle": 0, + "content": "\\[\n\\hat {y} _ {1} ^ {k} \\triangleq R _ {\\delta} ^ {\\mathcal {Y}} \\left(z _ {x} ^ {k, 2}, u _ {n} ^ {k, 1}\\right), \\hat {y} _ {2} ^ {k} \\triangleq R _ {\\delta} ^ {\\mathcal {Y}} \\left(z _ {x} ^ {k, 1}, u _ {n} ^ {k, 2}\\right). \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.486, + 0.892, + 0.548 + ], + "angle": 0, + "content": "This realisation explicitly requires \\(z_{x}^{k,i}\\) to represent the common part and \\(u_{n}^{k,j}\\) to represent the unique part within the corrupted views. We then optimise \\(\\{\\theta ,\\rho ,\\delta \\}\\) from \\(\\{G_{\\theta}^{\\mathcal{X}},E_{\\rho}^{\\mathcal{N}},R_{\\delta}^{\\mathcal{Y}}\\}\\) using the following objective:" + }, + { + "type": "equation", + "bbox": [ + 0.562, + 0.559, + 0.891, + 0.586 + ], + "angle": 0, + "content": "\\[\n\\underset {\\theta , \\rho , \\delta} {\\operatorname {a r g m i n}} \\mathcal {L} ^ {\\mathcal {C}} \\triangleq | | \\hat {y} _ {1} ^ {k} - y _ {1} ^ {k} | | + | | \\hat {y} _ {2} ^ {k} - y _ {2} ^ {k} | |. \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.597, + 0.892, + 0.674 + ], + "angle": 0, + "content": "Generally, it is possible for there to be a trivial solution from \\( u_{n}^{k,i} \\) to \\( y_{i}^{k} \\) in Equation (9) such as, when \\( u_{n}^{k,1} \\) is extracted from \\( y_{1}^{k} \\) and used to reconstruct it as well. However, Equation (7) explicitly requires \\( u_{n}^{k,1} \\) to rebuild the noise, which prevents the collapse of \\( u_{n}^{k,1} \\) in expressing \\( y_{1}^{k} \\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.682, + 0.75, + 0.696 + ], + "angle": 0, + "content": "3.3. Bernoulli Manifold Mixture" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.705, + 0.892, + 0.84 + ], + "angle": 0, + "content": "The aforementioned latent constraint might appear to be restricted at first, but in fact, it enables us to capture a large number of degrees of freedom in latent space implementation. For instance, it is possible to have multiple scene features that correspond to a single scene. However, in such cases, the mapping from input to scene features becomes ambiguous. To tackle this issue, we propose the use of the Bernoulli Manifold Mixture (BMM) as a means of leveraging the shared structure within the scene latent." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.841, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Given the assumption of property (2), the acquired scene features \\( z_{x}^{k,1} \\) and \\( z_{x}^{k,2} \\) are expected to be identical and interchangeable with one another, as they both refer to the same scene feature. BMM establishes a new explicit connection" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12284" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.122 + ], + "angle": 0, + "content": "between the scene features of multi-views, which can be expressed in the equation as:" + }, + { + "type": "equation", + "bbox": [ + 0.194, + 0.132, + 0.469, + 0.151 + ], + "angle": 0, + "content": "\\[\n\\hat {z} _ {x} ^ {k} \\triangleq \\operatorname {M i x} _ {p} \\left(z _ {x} ^ {k, 1}, z _ {x} ^ {k, 2}\\right), \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.161, + 0.47, + 0.223 + ], + "angle": 0, + "content": "where the \\(\\hat{z}_x^k\\) is an estimation of the true underlying scene feature. Let \\(b_{f}\\) define a sample instance drawn from a Bernoulli distribution with probability \\(p\\in (0,1)\\), the function \\(\\mathrm{Mix}_p(\\cdot)\\) described in Equation (11) denotes:" + }, + { + "type": "equation", + "bbox": [ + 0.135, + 0.234, + 0.469, + 0.252 + ], + "angle": 0, + "content": "\\[\n\\operatorname {M i x} _ {p} (\\boldsymbol {m}, \\boldsymbol {n}) \\triangleq b _ {f} \\odot \\boldsymbol {m} + (1 - b _ {f}) \\odot \\boldsymbol {n}. \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.263, + 0.469, + 0.308 + ], + "angle": 0, + "content": "By establishing this new connection (Equation 11), we can enhance the interchangeability between \\( z_{x}^{k,1} \\) and \\( z_{x}^{k,2} \\) by optimising the reconstruction performance on \\( \\hat{z}_{x}^{k} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.308, + 0.469, + 0.352 + ], + "angle": 0, + "content": "Lemma 1. Assuming \\( z_{x}^{k,i}\\sim N_{\\mathbf{x}}(\\boldsymbol {\\mu},\\boldsymbol {\\Sigma}) \\), where \\( N_{\\mathbf{x}} \\) denotes multivariate Gaussian distributions and then \\( \\pmb{\\mu} \\) and \\( \\pmb{\\Sigma} \\) is the mean and the covariance matrix." + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.352, + 0.469, + 0.384 + ], + "angle": 0, + "content": "For a given function \\(G_{\\theta}^{\\mathcal{X}}(\\cdot)\\), assume \\(\\forall k, i, m, n \\in \\mathbb{N}\\), the following property holds:" + }, + { + "type": "equation", + "bbox": [ + 0.106, + 0.393, + 0.469, + 0.413 + ], + "angle": 0, + "content": "\\[\n\\mathbb {E} \\left[ G _ {\\theta} ^ {\\mathcal {X}} \\left(z _ {x} ^ {k, i}\\right) \\right] \\triangleq \\mathbb {E} \\left[ G _ {\\theta} ^ {\\mathcal {X}} \\left(\\operatorname {M i x} _ {p} \\left(z _ {x} ^ {k, m}, z _ {x} ^ {k, n}\\right)\\right) \\right]. \\tag {13}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.422, + 0.469, + 0.453 + ], + "angle": 0, + "content": "Proof. Assume \\(z_{x}^{k,m}, z_{x}^{k,n} \\in \\mathbb{R}^{\\dim}\\) are i.i.d., we may also factorise \\(b_{f} \\in \\mathbb{R}^{\\dim}\\). Write" + }, + { + "type": "equation", + "bbox": [ + 0.194, + 0.466, + 0.469, + 0.484 + ], + "angle": 0, + "content": "\\[\n\\hat {z} _ {x} ^ {k} \\triangleq \\operatorname {M i x} _ {p} \\left(z _ {x} ^ {k, m}, z _ {x} ^ {k, n}\\right) \\tag {14}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.497, + 0.21, + 0.51 + ], + "angle": 0, + "content": "so that we can have" + }, + { + "type": "equation", + "bbox": [ + 0.103, + 0.519, + 0.469, + 0.557 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\hat {z} _ {x} \\sim N _ {\\mathbf {x}} \\left(\\left(b _ {f} + 1 - b _ {f}\\right) \\boldsymbol {\\mu}, \\left(b _ {f} ^ {2} + \\left(1 - b _ {f}\\right) ^ {2}\\right) \\boldsymbol {\\Sigma}\\right) \\tag {15} \\\\ \\sim N _ {\\mathbf {x}} (\\boldsymbol {\\mu}, \\boldsymbol {\\Sigma}) \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.57, + 0.469, + 0.603 + ], + "angle": 0, + "content": "with the fact that Bernoulli sample \\( b_{f}^{2} = b_{f} \\), the mixed feature \\( \\hat{z}_{x} \\) is in the same representation distribution as \\( z_{x}^{k,i} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.617, + 0.469, + 0.647 + ], + "angle": 0, + "content": "In MeD, we denote \\(\\hat{z}_x = G_\\theta^\\chi (\\hat{z}_x^k)\\), and the objective for implementing Equation (13) can be formulated as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.14, + 0.658, + 0.469, + 0.685 + ], + "angle": 0, + "content": "\\[\n\\underset {\\theta , \\rho , \\psi} {\\operatorname {a r g m i n}} \\mathcal {L} ^ {\\mathcal {M}} \\triangleq \\lambda | | \\hat {z} _ {x} - \\operatorname {M i x} _ {p} \\left(y _ {1} ^ {k}, y _ {2} ^ {k}\\right) | |, \\tag {16}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.696, + 0.469, + 0.756 + ], + "angle": 0, + "content": "where the \\(\\lambda\\) is the weight parameter. Here, the target is using a mixed version of \\(y_1^k\\) and \\(y_2^k\\). The choice of this is driven by the intuition that the hybrid version would better align with the aforementioned blended features." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.77, + 0.208, + 0.787 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.469, + 0.901 + ], + "angle": 0, + "content": "To evaluate the effectiveness of our proposed method, we assess our method against several representative self-supervised denoising methods, including Noise2Noise (N2N) [16], Noise2Self (N2S) [4] and Recorrupted2Recorrupted (R2R) [26], and the invariant feature learning method LIR [9]. Moreover, we also evaluate our approach against two supervised baseline" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "methods (Noise2Clean (N2C) [21] and multi-frame method DBD [11]) to further validate its effectiveness. Comparisons to more methods, including methods using only one noisy image, are presented in the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.155, + 0.892, + 0.306 + ], + "angle": 0, + "content": "We start our experiments by denoising synthetic additive white Gaussian noise (AWGN) in Section 4.2, and then move on to testing unseen noise levels and noise types in Section 4.3 and Section 4.4, respectively. Furthermore, we evaluate the performance in real-world scenarios in Section 4.5. In Section 4.6, we expand our experiments to incorporate more views to study their impact on performance. Finally, in Section 4.7, we apply our method to other tasks, e.g. image super-resolution and inpainting, to demonstrate its generalisation ability." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.323, + 0.697, + 0.339 + ], + "angle": 0, + "content": "4.1. Experimental Setups" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.349, + 0.892, + 0.529 + ], + "angle": 0, + "content": "Noted that, the nature of feature disentanglement requires no leak from input to output, however, the global residual connection of the original DnCNN [35] cannot satisfy. Thus, we incorporate the Swin-Transformer (Swin-T) [21] instead of the traditionally used DnCNN in our experiments. Nevertheless, as Swin-T is not originally designed for image restoration, we make some modifications to enforce local dependence across the image. Specifically, we add one Convolution Layer each before the patch embedding and after the patch unembedding of Swin-T, as inspired by SwinIR [18]. The resulting modified network backbone is denoted as Swin-Tx." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.533, + 0.892, + 0.714 + ], + "angle": 0, + "content": "To ensure a fair comparison, we use the Swin-Tx backbone for all methods in our study, except for DBD. As DBD did not release the code, we follow the instructions presented in the paper and make our best effort to re-implement it. However, we observe that the two-view DBD could not converge efficiently, which is consistent with the findings in the paper. Therefore, we limit our evaluation to the four-view DBD, denoted as \\(\\mathrm{DBD}_4\\). Furthermore, we replace the U-Net backbone originally used in the LIR method with Swin-Tx to maintain consistency in our evaluation. This results in an average improvement of approximately 1 dB in PSNR for Gaussian denoising." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.717, + 0.892, + 0.838 + ], + "angle": 0, + "content": "In all experiments, all methods were trained using only DIV2K [3] and the same optimisation parameters, except for LIR and \\(\\mathrm{DBD}_4\\) which used manually selected parameters obtained through experiments. For more training and evaluation details including the choice of parameters, please refer to the supplementary material. Code is available at: https://github.com/chgwer2/Multi-view-Self-supervised-Disentanglement-Denoising." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Remark: In tables, the best results are highlighted in bold, while the second best is underlined." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "12285" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.088, + 0.892, + 0.114 + ], + "angle": 0, + "content": "Table 1. Quantitative comparison of different methods on CBSD68 Dataset [23] for Synthetic Gaussian noise. The experiments were conducted on fixed and random variance, respectively. The best results are highlighted in bold, while the second best is underlined." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.115, + 0.89, + 0.268 + ], + "angle": 0, + "content": "
Training SchemaTest \\(\\hat{\\sigma}\\)Noisy/ Clean N2C [21]\\(DBD_4\\) [11]N2N [16]Noisy/ Noisy N2S [4]R2R [26]Invariant Feature
LIR [9]MeD (ours)
Gaussian\\(\\sigma = 25\\)1533.36/0.902033.57/0.909232.64/0.880532.77/0.878029.74/0.786531.06/0.863233.11/0.8880
2530.83/0.849431.31/0.854830.68/0.833430.99/0.840530.45/0.818330.01/0.802430.57/0.8496
5024.76/0.551925.12/0.558324.59/0.538522.13/0.392824.02/0.513321.97/0.357825.67/0.6026
7520.75/0.337621.09/0.341220.60/0.316217.86/0.199819.10/0.264116.23/0.168923.09/0.4320
Gaussian\\(\\sigma \\in [5,50]\\)1533.47/0.902733.12/0.891533.45/0.894531.28/0.818720.76/0.250830.85/0.843133.62/0.9026
2530.87/0.853830.64/0.849130.77/0.842329.65/0.780123.91/0.455228.92/0.806930.91/0.8573
5027.41/0.736127.13/0.729027.15/0.721927.00/0.711426.92/0.691125.13/0.619127.48/0.7530
7525.05/0.622324.97/0.620524.80/0.590824.89/0.602323.83/0.513222.37/0.421225.40/0.6645
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.279, + 0.892, + 0.307 + ], + "angle": 0, + "content": "Table 2. Quantitative result of generalisation performance experiment on CBSD68 [23]. All methods use Gaussian \\(\\sigma = 25\\) for pre-trained methods and then Gaussian \\(\\sigma \\in [5, 50]\\) for fine-turning. The better result in each method is highlighted in italics." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.308, + 0.89, + 0.43 + ], + "angle": 0, + "content": "
Fine-tuning MethodN2C [21]N2N [16]LIR [9]MeD
Pretraining MethodN2CMeDN2NMeDLIRMeDMeD
Gaussian, δ ∈ [15, 75]29.20/ 0.779729.53/ 0.808129.04/ 0.764229.21/ 0.789026.42/ 0.664027.25/ 0.703629.60/ 0.8101
Local Var Gaussian35.62/ 0.930835.85/ 0.943935.66/ 0.925635.73/ 0.931029.26/ 0.817030.51/ 0.838735.91/ 0.9762
Poisson Noise40.49/ 0.973642.80/ 0.977641.35/ 0.973642.27/ 0.981331.23/ 0.867233.47/ 0.893245.05/ 0.9826
Speckle,帽子 ∈ [25, 50]33.36/ 0.900433.40/ 0.904433.32/ 0.893133.33/ 0.890728.28/ 0.771329.82/ 0.822933.48/ 0.9115
S&P,帽子 ∈ [0.3, 0.5]28.85/ 0.826730.73/ 0.837228.59/ 0.800329.45/ 0.825526.69/ 0.724127.62/ 0.746030.84/ 0.9135
Average33.50/ 0.882234.46/ 0.894233.59/ 0.871434.00/ 0.883528.38/ 0.768729.73/ 0.800934.98/ 0.9188
" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.453, + 0.289, + 0.468 + ], + "angle": 0, + "content": "4.2. AWGN Noise Removal" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.477, + 0.469, + 0.596 + ], + "angle": 0, + "content": "We first investigate the denoising generalisation of the methods using synthetic zero-mean additive white Gaussian noise (AWGN). The experiments are divided into two parts. The first segment employs fixed variance AWGN, whereas the second segment employs varied variance Gaussian for training in a separate manner. Table 1 summarises the quantitative results evaluated on CBSD68 Dataset [23] at variance levels of 15, 25, 50, and 75." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.598, + 0.469, + 0.732 + ], + "angle": 0, + "content": "Analysis: In the fixed variance setting, MeD performs inferior compared to the other methods on lower noise levels of 15 and 25. However, as the methods face more severe corruption, MeD outperforms all self-supervised and supervised methods, showing our greater advantage of handling severe noise. For instance, at \\(\\sigma = 75\\), MeD outperforms the second-best method (N2C) by around 2 dB. These results suggest that MeD has a remarkable ability to generalise to a range of unseen noise levels in Gaussian noise." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.734, + 0.469, + 0.839 + ], + "angle": 0, + "content": "In the context of random variance, it has been observed that MeD exhibits superior performance across all four noise levels compared to other methods, including supervised methods. These findings imply that MeD can benefit more from varying training noise than other methods. More experiments and details on AWGN noise removal can be found in the supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.848, + 0.429, + 0.863 + ], + "angle": 0, + "content": "4.3. Generalisation on Unseen Noise Removal" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.469, + 0.901 + ], + "angle": 0, + "content": "In the previous subsection, we demonstrated the remarkable generalisation ability of our model in the case of Gaus" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.454, + 0.892, + 0.545 + ], + "angle": 0, + "content": "sian noise. Here, we aim to extend this investigation to other types of unseen noise and evaluate the denoising generalisation ability of our method. Specifically, we consider Poisson noise, Speckle noise, Local Variance Gaussian noise, and Salt-and-Pepper noise. For a more detailed synthetic process, please refer to the supplementary material." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.549, + 0.893, + 0.761 + ], + "angle": 0, + "content": "First, we demonstrate qualitative comparisons of denoising unseen noise types using models trained only with Gaussian \\(\\sigma = 25\\) in Figure 3. Next, in order to further verify the denoising generalisation ability of MeD, we employ its scene encoder and decoder as pre-trained models to be compared against other methods. It should be noted that the pre-training and fine-tuning methods employed in this study may differ, as shown in Table 2. The pre-training of all test models was conducted on a Gaussian sigma value of 25, followed by fine-tuning with a Gaussian sigma range of 5 to 50. Since the training schema of N2S, R2R, and DBD\\(_4\\) differs from MeD, we do not include them in this section. However, evaluations of these methods on unseen noise are still presented in Section 4.4 under different settings." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Analysis: Qualitative results in Figure 3 show that under Gaussian \\(\\sigma = 25\\) training settings, our method surpasses other methods in denoising unseen noise types. Additionally, Table 2 shows that the approaches using pre-trained MeD models outperform their self-transfer models for N2C, N2N, and LIR, with improvements of up to \\(2\\mathrm{dB}\\) in some cases. On average, the MeD pre-trained models show a performance gain of around \\(0.5\\mathrm{dB}\\) across all methods, highlighting the potential of MeD as a powerful pre-training" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12286" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.09, + 0.089, + 0.9, + 0.374 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.378, + 0.893, + 0.407 + ], + "angle": 0, + "content": "Figure 3. Qualitative denoising results on unseen noise types. All the methods are trained with Gaussian \\(\\sigma = 25\\). The quantitative PSNR/SSIM results are provided underneath the respective images. Best viewed in colour (zoom-in for a better comparison)." + }, + { + "type": "table_caption", + "bbox": [ + 0.109, + 0.417, + 0.854, + 0.43 + ], + "angle": 0, + "content": "Table 3. Analysis of Noise Pool on CBSD68 [23]. All methods were trained using randomly drawn noise from the Noise Pool." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.431, + 0.891, + 0.602 + ], + "angle": 0, + "content": "
Test NoiseNoisy/ CleanNoisy/ NoisyInvariant Feature
N2C [21]DBD4 [11]N2N [16]N2S [4]R2R [26]LIR [9]MeD (ours)
Gaussian, θ ∈ [15, 75]29.24/0.775429.05/0.761629.23/0.763428.58/0.758926.43/0.663926.67/0.686629.61/0.8178
Local Var Gaussian (LVG)36.64/0.944236.18/0.930736.65/0.923533.24/0.885834.70/0.877931.61/0.862737.99/0.9568
Poisson Noise45.72/0.976444.23/0.960645.64/0.979946.31/0.980844.45/0.949143.27/0.929248.10/0.9916
Speckle, v ∈ [25, 50]35.58/0.941735.24/0.938535.34/0.947535.13/0.959634.20/0.907833.98/0.881037.21/0.9715
S&P, r ∈ [0.3, 0.5]38.85/0.916537.10/0.888438.89/0.928938.22/0.933036.17/0.908733.43/0.820242.33/0.9695
Gaussian θ = 25 + Speckle v = 2530.19/0.827929.24/0.815630.32/0.831729.51/0.805028.78/0.774429.20/0.787131.92/0.8726
Gaussian θ = 50 + Speckle v = 2527.30/0.725126.55/0.712627.23/0.733126.91/0.708126.49/0.693526.19/0.694129.68/0.7928
LVG + Poisson31.78/0.908731.10/0.884231.60/0.761730.15/0.808628.52/0.714427.33/0.723434.29/0.9325
Poisson + Speckle v = 2531.39/0.906930.86/0.878231.52/0.893530.58/0.906730.34/0.889729.93/0.855433.04/0.9258
Average34.08/0.880333.28/0.863434.05/0.862633.18/0.860732.23/0.819931.29/0.804436.02/0.9145
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.628, + 0.47, + 0.734 + ], + "angle": 0, + "content": "method for image denoising. It is noteworthy that the self-transfer MeD model exhibits the best denoising performance across all validation noise types, even outperforming the supervised method, N2C. This is particularly evident in Poisson noise, where MeD surpasses N2C by \\(\\sim 3\\) dB. These results highlight the generalisation ability of our approach in handling unseen noise." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.742, + 0.385, + 0.758 + ], + "angle": 0, + "content": "4.4. Experiments on General Noise Pool" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.47, + 0.885 + ], + "angle": 0, + "content": "Here we further investigate the generalisation ability of our method by introducing our general Noise Pool. The Noise Pool comprises the five aforementioned types of noise, each with a diverse range of noise levels. During training, we randomly sample from the noise pool to provide the model with noisy images. This novel approach simulates a realistic scenario where noise is unknown and can originate from various sources to some extent." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.886, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Specifically, we evaluated all methods using the random" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.629, + 0.892, + 0.658 + ], + "angle": 0, + "content": "noise pool approach to train and test on combined or single noise types. The results are summarised in Table 3." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Analysis: In Table 3, our MeD approach outperforms all other methods significantly on all the test noise types. For example, when a test noise containing a combination of Gaussian noise with \\(\\hat{\\sigma} = 50\\) and Speckle noise with \\(\\hat{v} = 25\\) is used, other methods exhibit an approximate performance of \\(\\sim 27\\) dB. However, MeD achieves significantly better results with a performance of \\(29.68\\mathrm{dB}\\). And on average, MeD exhibits a performance that is approximately \\(2\\mathrm{dB}\\) better than other methods. Our findings show that utilising a comprehensive noise pool for training purposes can effectively improve the generalisation capability. Furthermore, the remarkable denoising generalisation ability of our MeD approach, in comparison to other methods, is particularly advantageous for real-world applications." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "12287" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.099, + 0.089, + 0.396, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.209, + 0.264, + 0.289, + 0.275 + ], + "angle": 0, + "content": "23.68/0.2967" + }, + { + "type": "image_caption", + "bbox": [ + 0.138, + 0.278, + 0.36, + 0.291 + ], + "angle": 0, + "content": "Noisy Image from SIDD [1] (ISO 800)" + }, + { + "type": "image", + "bbox": [ + 0.099, + 0.293, + 0.397, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.209, + 0.47, + 0.289, + 0.481 + ], + "angle": 0, + "content": "25.33/0.3865" + }, + { + "type": "image_caption", + "bbox": [ + 0.178, + 0.485, + 0.32, + 0.497 + ], + "angle": 0, + "content": "Noisy Image from SIDD" + }, + { + "type": "image", + "bbox": [ + 0.398, + 0.09, + 0.516, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.419, + 0.163, + 0.498, + 0.174 + ], + "angle": 0, + "content": "PSNR/ SSIM" + }, + { + "type": "image_caption", + "bbox": [ + 0.408, + 0.178, + 0.508, + 0.19 + ], + "angle": 0, + "content": "Ground Truth [1]" + }, + { + "type": "image", + "bbox": [ + 0.398, + 0.19, + 0.516, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.418, + 0.264, + 0.497, + 0.275 + ], + "angle": 0, + "content": "28.58/0.6081" + }, + { + "type": "image_caption", + "bbox": [ + 0.435, + 0.279, + 0.482, + 0.29 + ], + "angle": 0, + "content": "N2S [4]" + }, + { + "type": "image", + "bbox": [ + 0.398, + 0.291, + 0.516, + 0.363 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.419, + 0.367, + 0.498, + 0.378 + ], + "angle": 0, + "content": "PSNR/ SSIM" + }, + { + "type": "image_caption", + "bbox": [ + 0.428, + 0.382, + 0.488, + 0.393 + ], + "angle": 0, + "content": "Reference" + }, + { + "type": "image", + "bbox": [ + 0.398, + 0.394, + 0.516, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.418, + 0.47, + 0.499, + 0.481 + ], + "angle": 0, + "content": "27.58/0.5516" + }, + { + "type": "image_caption", + "bbox": [ + 0.435, + 0.485, + 0.482, + 0.497 + ], + "angle": 0, + "content": "N2S [4]" + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.09, + 0.636, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.541, + 0.163, + 0.621, + 0.174 + ], + "angle": 0, + "content": "31.38/0.8912" + }, + { + "type": "image_caption", + "bbox": [ + 0.55, + 0.178, + 0.607, + 0.189 + ], + "angle": 0, + "content": "N2C [21]" + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.19, + 0.636, + 0.259 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.539, + 0.264, + 0.619, + 0.275 + ], + "angle": 0, + "content": "26.58/0.4257" + }, + { + "type": "image_caption", + "bbox": [ + 0.553, + 0.279, + 0.608, + 0.29 + ], + "angle": 0, + "content": "R2R [26]" + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.291, + 0.636, + 0.363 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.541, + 0.367, + 0.619, + 0.378 + ], + "angle": 0, + "content": "28.36/0.5661" + }, + { + "type": "image_caption", + "bbox": [ + 0.551, + 0.382, + 0.607, + 0.394 + ], + "angle": 0, + "content": "N2C [21]" + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.394, + 0.636, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.539, + 0.47, + 0.619, + 0.481 + ], + "angle": 0, + "content": "26.77/0.4889" + }, + { + "type": "image_caption", + "bbox": [ + 0.553, + 0.485, + 0.608, + 0.497 + ], + "angle": 0, + "content": "R2R [26]" + }, + { + "type": "image", + "bbox": [ + 0.638, + 0.09, + 0.756, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.661, + 0.163, + 0.739, + 0.174 + ], + "angle": 0, + "content": "30.19/0.7449" + }, + { + "type": "image_caption", + "bbox": [ + 0.663, + 0.178, + 0.732, + 0.189 + ], + "angle": 0, + "content": "\\(\\mathrm{DBD}_4\\) [11]" + }, + { + "type": "image", + "bbox": [ + 0.638, + 0.19, + 0.756, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.659, + 0.264, + 0.738, + 0.275 + ], + "angle": 0, + "content": "25.91/0.3795" + }, + { + "type": "image_caption", + "bbox": [ + 0.678, + 0.279, + 0.723, + 0.29 + ], + "angle": 0, + "content": "LIR [9]" + }, + { + "type": "image", + "bbox": [ + 0.638, + 0.291, + 0.756, + 0.363 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.659, + 0.367, + 0.739, + 0.378 + ], + "angle": 0, + "content": "27.58/0.5406" + }, + { + "type": "image_caption", + "bbox": [ + 0.666, + 0.382, + 0.732, + 0.394 + ], + "angle": 0, + "content": "\\(\\mathrm{DBD}_4\\) [11]" + }, + { + "type": "image", + "bbox": [ + 0.638, + 0.395, + 0.756, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.653, + 0.469, + 0.742, + 0.481 + ], + "angle": 0, + "content": "26.45/0.4752" + }, + { + "type": "image_caption", + "bbox": [ + 0.678, + 0.484, + 0.723, + 0.497 + ], + "angle": 0, + "content": "LIR [9]" + }, + { + "type": "image", + "bbox": [ + 0.758, + 0.09, + 0.878, + 0.159 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.78, + 0.163, + 0.859, + 0.174 + ], + "angle": 0, + "content": "29.60/0.7053" + }, + { + "type": "image_caption", + "bbox": [ + 0.791, + 0.178, + 0.847, + 0.189 + ], + "angle": 0, + "content": "N2N [16]" + }, + { + "type": "image", + "bbox": [ + 0.758, + 0.19, + 0.878, + 0.26 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.78, + 0.264, + 0.859, + 0.275 + ], + "angle": 0, + "content": "33.07/0.8849" + }, + { + "type": "image_caption", + "bbox": [ + 0.782, + 0.279, + 0.853, + 0.29 + ], + "angle": 0, + "content": "MeD (Ours)" + }, + { + "type": "image", + "bbox": [ + 0.758, + 0.291, + 0.878, + 0.363 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.786, + 0.367, + 0.853, + 0.378 + ], + "angle": 0, + "content": "27.23/0.49" + }, + { + "type": "image_caption", + "bbox": [ + 0.791, + 0.382, + 0.847, + 0.394 + ], + "angle": 0, + "content": "N2N [16]" + }, + { + "type": "image", + "bbox": [ + 0.758, + 0.395, + 0.878, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.78, + 0.47, + 0.859, + 0.481 + ], + "angle": 0, + "content": "30.23/0.6703" + }, + { + "type": "image_caption", + "bbox": [ + 0.787, + 0.485, + 0.858, + 0.497 + ], + "angle": 0, + "content": "MeD (Ours)" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.502, + 0.891, + 0.531 + ], + "angle": 0, + "content": "Figure 4. Real Noise Removal Example of SIDD [1]. All the methods are trained with Noise Pool on the DIV2K [2] dataset. It can be seen that the proposed MeD can remove much real noise even without training with real-noise distribution (zoom in for a better comparison)." + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.552, + 0.468, + 0.579 + ], + "angle": 0, + "content": "Table 4. Quantitative result obtained from the application of various methods trained on a general Noise Pool to real noise datasets." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.58, + 0.47, + 0.682 + ], + "angle": 0, + "content": "
MethodPolyU [32]SIDD [1]CC [24]Average
N2C [21]35.89/0.965230.37/0.602837.89/0.940834.72/0.8363
DBD4 [11]35.69/0.957130.23/0.617337.74/0.935734.55/0.8367
N2N [16]36.22/0.967932.82/0.729737.39/0.957035.48/0.8849
N2S [4]36.41/0.972130.98/0.601837.58/0.962234.99/0.8454
R2R [26]34.58/0.889029.64/0.570835.35/0.847833.19/0.7692
LIR [9]34.81/0.727828.76/0.529635.50/0.840333.02/0.6992
MeD (ours)38.65/0.985535.81/0.827840.08/0.974538.18/0.9293
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.71, + 0.267, + 0.725 + ], + "angle": 0, + "content": "4.5. Real Noise Removal" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.47, + 0.901 + ], + "angle": 0, + "content": "In our previous experiments, we demonstrated the exceptional denoising performance of our MeD approach on synthetic noises. However, real-world noise is often more complex and challenging than synthetic noise. In this subsection, we aim to evaluate the generalisation performance of our approach on real-world noise by testing it on the SIDD [1], CC [24] and PolyU [32] datasets. To assess the denoising performance on real-world noise, we use the same pre-trained models as in Section 4.4. The representative qualitative results on the SIDD dataset in the standard RGB colour space are presented in Figure 4." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.556, + 0.892, + 0.662 + ], + "angle": 0, + "content": "Analysis: As shown in Table 4, our approach significantly outperforms all other methods across all three datasets, with a performance improvement of 2-3 dB over the second-best approach, and also consistently outperforms its supervised counterparts (i.e. N2C and \\(\\mathrm{DBD}_4\\)) by over 3 dB. These results suggest the effectiveness and generalisability of the proposed approach in real-world denoising scenarios." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.668, + 0.892, + 0.774 + ], + "angle": 0, + "content": "Our approach achieves remarkable performance on real-world noise without even being trained on more expensive real-world data. For a more complete study, we also conduct experiments on model training with real-world data (for more details please refer to the supplementary material), showing superior performance and even better generalisation ability to data out of the training data distribution." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In Figure 4, the presence of noise persists even after applying denoising techniques, yet ours demonstrates the most authentic outcomes compared to others. For instance, while the noise particles remain prominent in the N2C results, they are absent in our results. Overall, the results indicate that the MeD approach is well-suited for real-world denoising tasks, providing a robust and reliable solution for" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "12288" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.079, + 0.088, + 0.457, + 0.1 + ], + "angle": 0, + "content": "Table 5. Multiple views ( \\( \\geq 2 \\) ) study,with average PSNR/SSIM." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.102, + 0.468, + 0.149 + ], + "angle": 0, + "content": "
#ViewsGaussianLVGPoissonSpeckleS&P
229.61/0.817837.99/0.956848.10/0.991637.21/0.971542.33/0.9695
329.68/0.819738.05/0.957748.23/0.992037.40/0.973342.45/0.9703
429.70/0.820438.08/0.958048.31/0.992137.47/0.974042.49/0.9709
" + }, + { + "type": "table_caption", + "bbox": [ + 0.079, + 0.162, + 0.468, + 0.189 + ], + "angle": 0, + "content": "Table 6. Average PSNR/SSIM of super-resolution results on Set5 [6]. Learning-based methods are trained with Corruption Pool." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.19, + 0.466, + 0.248 + ], + "angle": 0, + "content": "
ScaleBicubicRCAN [37]DASR [30]MeD (ours)
×233.63/ 0.928536.12/ 0.933936.98/ 0.947137.12/ 0.9527
×330.37/ 0.865234.15/ 0.928634.11/ 0.918734.92/ 0.9294
×428.35/ 0.808431.94/ 0.887131.54/ 0.873632.50/ 0.8956
" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.274, + 0.435, + 0.289 + ], + "angle": 0, + "content": "improving image quality in challenging environments." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.298, + 0.29, + 0.314 + ], + "angle": 0, + "content": "4.6. Expand to More Views" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.321, + 0.468, + 0.396 + ], + "angle": 0, + "content": "Although we only showcase two views for the experiments above, our method can be easily expanded to multiple views. To investigate the impact of the numbers of views, here we further conduct a study comparing 2, 3, and 4 views, in Table 5." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.397, + 0.468, + 0.533 + ], + "angle": 0, + "content": "The results indicate that increasing the number of views consistently improves the performance across different noise types. For example, when dealing with Speckle noise, the 4-view model achieves a \\(0.26\\mathrm{dB}\\) higher PSNR than the 2-view model. However, it is worth noting that employing \\(n\\) views requires \\(n!\\) cross-computations within each view pair during training, resulting in a significant increase in computational cost (e.g. from 2-view to 4-view leads to a \\(10\\times\\) training time increase in our experiment)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.542, + 0.345, + 0.559 + ], + "angle": 0, + "content": "4.7. More Application Exploration" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.566, + 0.468, + 0.687 + ], + "angle": 0, + "content": "Here we investigate the potential of the proposed MeD for other more general image restoration tasks, such as image super-resolution and inpainting. In this study, we generalise the previously defined degradation (noise) to a residual image between a clean image and a corrupted image. Moreover, we expand the definition from Noise Pool to a more general one - Corruption Pool that contains not only noise but also general corruption." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Super resolution. Image super-resolution aims to enlarge the resolution of a low-resolution image. We train our method on the DIV2K dataset [3], where we randomly choose different downscale methods from a Corruption Pool that consists of random Gaussian noise and four types of down-scaling (bicubic, lanczos, bilinear, and hamming). We benchmark our method against the supervised method RCAN [37] that aims for high PSNR and the recent unsupervised methods DASR [30] that are specialised for superresolution. We conduct our evaluation on the Set5 dataset [6] with scaling factors of 2, 3, and 4. The results in Table 6 show the effectiveness of our method over both supervised and unsupervised approaches." + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.087, + 0.892, + 0.13 + ], + "angle": 0, + "content": "Table 7. Average PSNR/SSIM of inpainting results on Set11 [29]. S2S and DIP are trained and tested on the same single image. MeD is trained with Corruption Pool." + }, + { + "type": "table", + "bbox": [ + 0.514, + 0.135, + 0.88, + 0.202 + ], + "angle": 0, + "content": "
Dropping RatioDIP [29]S2S [27]MeD (Ours)
50%33.45/ 0.921734.91/ 0.947936.24/ 0.9617
70%28.53/ 0.850130.94/ 0.884531.05/ 0.9161
90%24.39/ 0.736025.97/ 0.793326.01/ 0.8052
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.233, + 0.892, + 0.4 + ], + "angle": 0, + "content": "Inpainting. We also apply our method to the image inpainting task, which fills in missing pixels. We choose two single-image deep learning methods - Self2Self (S2S) [27] and DIP [29], for comparison. Our MeD is trained with Corruption Pool containing noises, down-scaling, and inpainting mask operations altogether. To compare our method (MeD) with other state-of-the-art methods, we conduct experiments on the Set 11 dataset [29] with three different pixel dropping ratios: \\(50\\%\\), \\(70\\%\\), and \\(90\\%\\). The results are shown in Table 7, suggesting the effectiveness of MeD again in the image inpainting task." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.42, + 0.619, + 0.435 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.448, + 0.892, + 0.72 + ], + "angle": 0, + "content": "In this paper, we have presented a new self-supervised learning method (MeD) for image denoising that disentangles scene and noise features in a constraint feature space. Our approach has demonstrated exceptional denoising performance in both synthetic and real-world noise scenarios, with particularly significant performance on real-world noise. MeD can handle complex noise with better performance than other state-of-the-art methods, as validated by consistent performance gain across various datasets and noise types. Our approach has decent generalisation ability, requiring only noisy images for training and efficiently denoising real-world noise without seeing any clean ground truth data. This opens up new possibilities for training deep models without the need for costly labelled data. Furthermore, our model can be easily adapted to other low-level image restoration tasks. We hope this could provide a new baseline for future research in image disentanglement and the extension to other image processing tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.737, + 0.647, + 0.753 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.762, + 0.892, + 0.869 + ], + "angle": 0, + "content": "The computations described in this research were performed using the Baskerville Tier 2 HPC service1. Baskerville was funded by the EPSRC and UKRI through the World Class Labs scheme (EP/T022221/1) and the Digital Research Infrastructure programme (EP/W032244/1) and is operated by Advanced Research Computing at the University of Birmingham." + }, + { + "type": "page_footnote", + "bbox": [ + 0.518, + 0.887, + 0.688, + 0.9 + ], + "angle": 0, + "content": "\\(^{1}\\)https://www.baskerville.ac.uk/" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "12289" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.184 + ], + "angle": 0, + "content": "[1] Abdelrahman Abdelhamed, Stephen Lin, and Michael S Brown. A high-quality denoising dataset for smartphone cameras. 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In Proceedings of the AAAI Conference on Artificial Intelligence, volume 34, pages 13074-13081, 2020." + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.092, + 0.471, + 0.812 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.518, + 0.957 + ], + "angle": 0, + "content": "12291" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/bd73600c-bf62-4573-910c-f059e97c644d_origin.pdf b/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/bd73600c-bf62-4573-910c-f059e97c644d_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..8692a91f9108cf2dbf3bdd8e314c14867400bb9c --- /dev/null +++ b/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/bd73600c-bf62-4573-910c-f059e97c644d_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:3defdccfd1f069b3c713164ce1300bfea5f7b9cdf95291602796090cbcff71b7 +size 8965636 diff --git a/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/full.md b/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/full.md new file mode 100644 index 0000000000000000000000000000000000000000..f47e79db39c3c881746d4bb2680cfdc957c12127 --- /dev/null +++ b/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/full.md @@ -0,0 +1,457 @@ +# Multi-view Self-supervised Disentanglement for General Image Denoising + +Hao Chen\*,1 + +Chenyuan $\mathrm{Qu}^{*,1}$ + +Yu Zhang² + +Chen Chen3 + +Jianbo Jiao + +$^{1}$ University of Birmingham $^{2}$ Shanghai Jiao Tong University $^{3}$ University of Central Florida + +Project page: https://chqwer2.github.io/MeD/ + +# Abstract + +With its significant performance improvements, the deep learning paradigm has become a standard tool for modern image denoisers. While promising performance has been shown on seen noise distributions, existing approaches often suffer from generalisation to unseen noise types or general and real noise. It is understandable as the model is designed to learn paired mapping (e.g. from a noisy image to its clean version). In this paper, we instead propose to learn to disentangle the noisy image, under the intuitive assumption that different corrupted versions of the same clean image share a common latent space. A self-supervised learning framework is proposed to achieve the goal, without looking at the latent clean image. By taking two different corrupted versions of the same image as input, the proposed Multi-view Self-supervised Disentanglement (MeD) approach learns to disentangle the latent clean features from the corruptions and recover the clean image consequently. Extensive experimental analysis on both synthetic and real noise shows the superiority of the proposed method over prior self-supervised approaches, especially on unseen novel noise types. On real noise, the proposed method even outperforms its supervised counterparts by over 3 dB. + +# 1. Introduction + +Image restoration is a critical sub-field of computer vision, exploring the reconstruction of image signals from corrupted observations. Examples of such ill-posed low-level image restoration problems include image denoising [16,25,26,29,33,35,38], super-resolution [2,8,19,30,37], and JPEG artefact removal [7, 12, 31], to name a few. Usually, a mapping function dedicated to the training data distribution is learned between the corrupted and clean images to address the problem. While many image restoration systems perform well when evaluated over the same corruption distribution that they have seen, they are often required to be deployed in settings where the environment is unknown and + +![](images/ff5442c64c4b77977a480f53fa8931da5918ba53d2ce360ed7cdd3b46fe5d814.jpg) +(a) Noisy/ Clean + +![](images/b5626a1a442483f90faf4a0f2c9aa17f026b04482ccea7a16a44a7958a169d8a.jpg) +(b) N2C [21], Supervised + +![](images/b39275238920d1558ee3498690cb6e3a417210456a9c52dba3c34af67d7b8854.jpg) +(c) LIR [9], Self-supervised +Figure 1. Denoising performance on unseen Speckle Noise with $\hat{\pmb{v}} = 50$ . The models were trained with Gaussian noise $\sigma \in [5,50]$ . (a) The noisy and clean images, with ground-truth clean patches shown below. (b) Noise-to-Clean (N2C) [21] is trained with clean images. (c) LIR [9] is self-supervised but needs unpaired clean images as training data. (d) Our approach is fully self-supervised, training with only the noisy input data. + +![](images/920463002582708f96ac0f8563b7bf8162d8c7fd37d0fb16a3f8ef3a7025503a.jpg) +(d) Ours, Self-supervised + +off the training distribution. These settings, such as medical imaging, computational lithography, and remote sensing, require image restoration methods that can handle complex and unknown corruptions. Moreover, in many real-world image-denoising tasks, ground truth images are unavailable, introducing additional challenges. + +Limitations of existing methods: Current low-level corruption removal tasks aim to address the inquiry of "what is the clean image provided a corrupted observation?" However, the ill-posed nature of this problem formulation poses a significant challenge in obtaining a unique resolution [5]. + +To mitigate this limitation, researchers often introduce additional information, either explicitly or implicitly. For example, in [15], Laine et al. explicitly use the prior knowledge of noise as complementary input, generating a new invertible image model. Alternatively, Learning Invariant Representation (LIR) [9] implicitly enforces the interpretability in the feature space to guarantee the admissibility of the output. However, these additional forms of information may not always be practical in real-world scenarios or may not result in satisfactory performance. + +Main idea and problem formulation: Our motivation for tackling this ill-posed nature stems from the solution in the 3D reconstruction of utilising multiple views to provide a unique estimation of the real scene [1]. Building on this motivation, we propose a training scheme that is explicitly built on multi-corrupted views and perform Multi-view self-supervised Disentanglement, abbreviated as $MeD$ . + +Under this new multi-view setting, we reformulate the task problem as "what is the shared latent information across these views?" instead of the conventional "what is the clean image?" By doing so, MeD can effectively leverage the scene coherence of multi-view data and capture underlying common parts without requiring access to the clean image. This makes it more practical and scalable in real-world scenarios. An example of the proposed method with comparison to prior works is shown in Figure 1, indicating its effectiveness over the state-of-the-art. + +Specifically, given any scene image $x^{k} \sim \mathcal{X}, k \in \mathbb{N}$ sampled uniformly from a clean image set $\mathcal{X}$ , MeD produces two contaminated views: + +$$ +y _ {1} ^ {k} \triangleq \mathcal {T} _ {1} \left(x ^ {k}\right), y _ {2} ^ {k} \triangleq \mathcal {T} _ {2} \left(x ^ {k}\right), \tag {1} +$$ + +forming two independent corrupted image sets $\{\mathcal{Y}_1\}, \{\mathcal{Y}_2\}$ , where $y_1^k \in \mathcal{Y}_1$ , $y_2^k \in \mathcal{Y}_2$ . The $\mathcal{T}_1$ and $\mathcal{T}_2$ represent two random independent image degradation operations. + +We parameterise our scene feature encoder $G_{\theta}^{\mathcal{X}}$ and decoder $D_{\psi}^{\mathcal{X}}$ with $\theta$ and $\psi$ . Considering the image pair $\{y_1^k, y_2^k\}_{k \in \mathbb{N}}$ , the core of the presented method can be summarised as: + +$$ +G _ {\theta} ^ {\mathcal {X}} \left(y _ {1} ^ {k}\right) \triangleq z _ {x} ^ {k, i} \triangleq G _ {\theta} ^ {\mathcal {X}} \left(y _ {2} ^ {k}\right), \tag {2} +$$ + +$$ +\hat {x} ^ {k} \triangleq D _ {\psi} ^ {\mathcal {X}} \left(z _ {x} ^ {k, i}\right), \tag {3} +$$ + +where $z_{x}^{k,i}$ represents the shared scene latent between $y_{1}^{k}$ and $y_{2}^{k}$ with $i$ referring to the input image index of $y_{i}$ . A clean image estimator $D_{\psi}^{\mathcal{X}}$ forms an all-deterministic reverse mapping from $z_{x}^{k,i}$ to reconstruct an estimated clean + +image $\hat{x}^k$ . Similarly, the noise latent $u_{\eta}^{k,i}$ is factorised from a corrupted view with a corruption encoder $E_{\rho}^{\mathcal{N}}$ . After words, the resulting corruption is reconstructed from $u_{\eta}^{k,i}$ through the use of a corruption decoder, represented by $F_{\phi}^{\mathcal{N}}$ . + +The disentanglement is then performed between $\{z_{x}^{k,i},u_{\eta}^{k,j}\}_{i\neq j}$ on a cross compose decoder $R_{\delta}^{\mathcal{V}}$ with parameter $\delta$ , which can be formulated as: + +$$ +\hat {y} _ {1} ^ {k} \triangleq R _ {\delta} ^ {\mathcal {Y}} \left(z _ {x} ^ {k, 2}, u _ {\eta} ^ {k, 1}\right). \tag {4} +$$ + +It should be noted that Equation (4) is performed over latent features $u$ and $z$ from different views. When assuming that $z_{x}^{k}$ remains constant across views, the reconstructed view $\hat{y}_{1}^{k}$ is determined by the $u_{\eta}^{k,1}$ . + +Contributions. The contributions of our work are summarised as follows: + +- We propose a new problem formulation to address the ill-posed problem of image denoising using only noisy examples, in a different paradigm than prior works. +- We introduce a disentangled representation learning framework that leverages multiple corrupted views to learn the shared scene latent, by exploiting the coherence across views of the same scene and separating noise and scene in the latent space. +- Extensive experimental analysis validates the effectiveness of the proposed MeD, outperforming existing methods with more robust performance to unknown noise distributions, even better than its supervised counterparts. + +# 2. Related Work + +Single-view image restoration: In [8], Dong et al. were the first to employ a deep network in super-resolution. Later, a range of single view-based models expanded the idea of supervised deep learning to handle image restoration tasks, such as deblurring [14], JPEG artefacts [12], inpainting [17, 34] and denoising [16, 26, 35]. Recently, it is receiving increasing interest in relaxing the prerequisite of supervised learning with corrupted/ clean image pairs. In the context of image denoising, the "corrupted/clean" pair denotes a corrupted input image and its corresponding clean image for calculating the loss. To tackle the issue of the lack of clean data, several methods have been proposed, such as the Noise2Noise (N2N) method [16] and Recorrupted-to-Recorrupted (R2R) [26], which train deep networks on pairs of noisy images. Noise2Void (N2V) [13], Noise2Self (N2S) [4], and the method proposed by Laine et al. [15] are based on the blind-spot strategy that discards some pixels in the input and predicts them using the remaining. In the field + +![](images/f5280f823dd4ee0c6858aa9cf449e00e93f57c914ccb8cfcfea437565f22fdfb.jpg) +Figure 2. Method Overview. This figure illustrates the main steps of our proposed method, MeD, which first generates scene features (cubes) and distortion features (cuboids). The colour of them indicates their image source. In the right section, the features are rearranged and utilised for the four forward paths, from top to bottom, which are the reconstructions of noise $(\hat{\eta}_1^k)$ , scene $(\hat{x}_2^k)$ , input image $(y_2^k)$ and shared scene $(\hat{x}^k)$ . It is noteworthy that $\hat{y}_2^k$ is reconstructed using $z_x^{k,1}$ from $y_1^k$ and $u_{\eta}^{k,2}$ from $y_2^k$ for feature disentanglement. Additionally, the reconstruction of $\hat{x}^k$ relies on mixed scene features to facilitate learning of invariant scene latent. Moreover, the reconstruction paths for $(\hat{\eta}_2,\hat{x}_1,$ and $y_{1})$ are not depicted here, as they differ from the given paths only in their sub-indexes. + +of single-image denoising, some methods such as DIP [29] and S2S [27], have achieved remarkable denoising results using only one noisy image. + +These methods, however, often inevitably compromise image quality to noise reduction, resulting in over-smoothed output. This trade-off is further exacerbated under domain shifts when dealing with unknown noise distributions. + +Restoration based on multiple views: Existing multiview variants of image restoration methods mainly focus on sequential data such as video or burst images. For example, Tico [28] builds a paradigm that separates the unique and common features within the multi-frame to produce a denoised estimate. Liu et al. [20] models degrading elements as foreground and estimate background using video data. Deep Burst Denoising (DBD) [11] performs multi-view denoising based on burst images. Each image is taken in a short exposure time and serves as a corrupted observation of the clean image. + +Unlike the above-mentioned methods, our $MeD$ aims to use multiple static observations simultaneously to learn the latent representation of a clean scene that is shared by multiple discrete views. + +Self-supervised feature disentanglement: Another notable path of work has attempted to disentangle underlying invariant content from distorted images. For instance, $UID$ - + +GAN [22] utilises unpaired clean/blurred images to disentangle content and blurring effects in the feature space and yield improved deblurring performance. Similarly, $LIR$ [9] used unpaired input to isolate invariant content features through self-supervised inter-domain transformation. + +However, these methods are limited to synthetic noise and do not extend well in real-world scenarios due to their reliance on clean images. In contrast, our method is purely based on multiple noisy views of the same static scene and aims to disentangle the scene from corruption, without the need for clean image supervision. + +# 3. Methodology + +Our primary objective is to identify the commonalities among different views in the denoising process. To achieve this, we aim to discover the shared scene $z_{x}^{k}$ that is degradation-agnostic over various corrupted views $\{y_{i}^{k}\}_{k\in \mathbb{N}}$ via our proposed training schema, namely Multi-view self-supervised Disentanglement (MeD). A graphic depiction of MeD is shown in Figure 2, composed of the representation learning process in the left panel, and four distinct reconstruction pathways in the right panel. + +The detailed design of the proposed schema will be introduced in the following subsections. Section 3.1 explains the restoration of noise and scene. Section 3.2 details the reconstruction of noisy input using a cross-feature combination. Section 3.3 elaborates on the reconstruction of the + +scene using mixed scene latent. + +We will start our introduction by outlining three essential properties that a multi-view representation disentanglement technique should exhibit. + +Pre-assumed properties: Suppose the scene latent space and corruption latent space are symbolised by $\mathcal{Z}_x$ and $\mathcal{U}_{\eta}$ , respectively. + +(1) Independence: For any scene latent $z_{x}^{k} \in \mathcal{Z}_{x}$ , it is expected to be independent of any corruption latent $u_{\eta}^{k,i}, \in \mathcal{U}_{\eta}$ . +(2) Consistency: There exists one shared latent code $z_{x}^{k} \in \mathcal{Z}_{x}$ that is capable of representing the shared clean component of all instances in the set $\{y_{i}^{k}\}$ . +(3) Composability: Recovery of the corrupted view $y_{i}^{k}$ can be achieved using the feature pairs $z_{x}^{k}, u_{\eta}^{k,i}$ , and the index of the recovered view is determined by the index of the corruption latent, which represents the unique component within that particular view. + +A key step of our method is to realise these prerequisites by determining how to implement the latent space assumption. As shown in the left panel of Figure 2, to infer our latent space assumption, MeD is comprised of two encoders and three decoders: A shared content latent encoder $G_{\theta}^{\mathcal{X}}$ and its decoder $D_{\psi}^{\mathcal{X}}$ , an auxiliary noise latent encoder $E_{\rho}^{\mathcal{N}}$ and its decoder $F_{\phi}^{\mathcal{N}}$ , and a cross disentangle-ment decoder $R_{\delta}^{\mathcal{Y}}$ . + +# 3.1. Main Forward Process + +Given two corrupted views of the same image $x^{k}$ , $y_{1}^{k} \triangleq \mathcal{T}_{1}(x^{k})$ and $y_{2}^{k} \triangleq \mathcal{T}_{2}(x^{k})$ , the encoder $G_{\theta}^{\mathcal{X}}$ mainly perform the scene feature space encoding that can be formulated as: + +$$ +z _ {x} ^ {k, 1} \triangleq G _ {\theta} ^ {\mathcal {X}} \left(y _ {1} ^ {k}\right), z _ {x} ^ {k, 2} \triangleq G _ {\theta} ^ {\mathcal {X}} \left(y _ {2} ^ {k}\right), \tag {5} +$$ + +where $z_{x}^{k,1}$ and $z_{x}^{k,2}$ are the estimation of the scene feature corresponding to the inputs $y_{1}^{k}$ and $y_{2}^{k}$ . + +The process of clean image reconstruction is then completed by the $D_{\psi}^{\mathcal{X}}$ : + +$$ +\hat {x} _ {1} ^ {k} \triangleq D _ {\psi} ^ {\mathcal {X}} \left(z _ {x} ^ {k, 1}\right), \hat {x} _ {2} ^ {k} \triangleq D _ {\psi} ^ {\mathcal {X}} \left(z _ {x} ^ {k, 2}\right). \tag {6} +$$ + +Similar to the process of estimating scene features, the estimation of distortion features by $E_{\rho}^{\mathcal{N}}$ , followed by the reconstruction of noise with $F_{\phi}^{\mathcal{N}}$ , can be described as follows: + +$$ +u _ {n} ^ {k, 1} \triangleq E _ {\rho} ^ {\mathcal {N}} \left(y _ {1} ^ {k}\right), u _ {n} ^ {k, 2} \triangleq E _ {\rho} ^ {\mathcal {N}} \left(y _ {2} ^ {k}\right), \tag {7} +$$ + +$$ +\hat {\eta} _ {1} ^ {k} \triangleq F _ {\phi} ^ {\mathcal {N}} \left(u _ {n} ^ {k, 1}\right), \hat {\eta} _ {2} ^ {k} \triangleq F _ {\phi} ^ {\mathcal {N}} \left(u _ {n} ^ {k, 2}\right). +$$ + +We adhere to the methodology introduced by N2N [16] to use noisy images as supervisory signals. The objective + +function of the aforementioned process can be simplified to: + +$$ +\underset {\theta , \psi} {\operatorname {a r g m i n}} \mathcal {L} ^ {\mathcal {X}} \triangleq | | \hat {x} _ {1} ^ {k} - y _ {2} ^ {k} | |, \tag {8} +$$ + +$$ +\underset {\rho , \phi} {\operatorname {a r g m i n}} \mathcal {L} ^ {\mathcal {N}} \triangleq | | \left(y _ {1} ^ {k} - \hat {\eta} _ {1} ^ {k}\right) - y _ {2} ^ {k} | |. \tag {8} +$$ + +The objective of $\hat{x}_2^k$ and $\hat{\eta}_2^k$ are the same as above, with only a subscript difference. It should be noted that, although our objective functions are similar to that of N2N, our goal is not simply to find and remove noise, but rather to capture the common features shared across multiple views. + +# 3.2. Cross Disentanglement + +For general latent codes $z_{x}^{k}$ to sufficiently represent scene information in the image space, it is natural to assume that these codes exhibit a certain degree of freedom, allowing them to intersect with the noise space. Consequently, there is no guarantee of complete isolation between $z_{x}^{k}$ and $u_{\eta}^{k}$ . To meet the requirements of properties (1) and (3), we use an additional decoder $R_{\delta}^{y}$ to reconstruct a corrupted view over a cross-feature combination, e.g. $z_{x}^{k,1}$ from $y_{1}$ and $u_{n}^{k,2}$ from $x_{2}$ , which can be represented as: + +$$ +\hat {y} _ {1} ^ {k} \triangleq R _ {\delta} ^ {\mathcal {Y}} \left(z _ {x} ^ {k, 2}, u _ {n} ^ {k, 1}\right), \hat {y} _ {2} ^ {k} \triangleq R _ {\delta} ^ {\mathcal {Y}} \left(z _ {x} ^ {k, 1}, u _ {n} ^ {k, 2}\right). \tag {9} +$$ + +This realisation explicitly requires $z_{x}^{k,i}$ to represent the common part and $u_{n}^{k,j}$ to represent the unique part within the corrupted views. We then optimise $\{\theta ,\rho ,\delta \}$ from $\{G_{\theta}^{\mathcal{X}},E_{\rho}^{\mathcal{N}},R_{\delta}^{\mathcal{Y}}\}$ using the following objective: + +$$ +\underset {\theta , \rho , \delta} {\operatorname {a r g m i n}} \mathcal {L} ^ {\mathcal {C}} \triangleq | | \hat {y} _ {1} ^ {k} - y _ {1} ^ {k} | | + | | \hat {y} _ {2} ^ {k} - y _ {2} ^ {k} | |. \tag {10} +$$ + +Generally, it is possible for there to be a trivial solution from $u_{n}^{k,i}$ to $y_{i}^{k}$ in Equation (9) such as, when $u_{n}^{k,1}$ is extracted from $y_{1}^{k}$ and used to reconstruct it as well. However, Equation (7) explicitly requires $u_{n}^{k,1}$ to rebuild the noise, which prevents the collapse of $u_{n}^{k,1}$ in expressing $y_{1}^{k}$ . + +# 3.3. Bernoulli Manifold Mixture + +The aforementioned latent constraint might appear to be restricted at first, but in fact, it enables us to capture a large number of degrees of freedom in latent space implementation. For instance, it is possible to have multiple scene features that correspond to a single scene. However, in such cases, the mapping from input to scene features becomes ambiguous. To tackle this issue, we propose the use of the Bernoulli Manifold Mixture (BMM) as a means of leveraging the shared structure within the scene latent. + +Given the assumption of property (2), the acquired scene features $z_{x}^{k,1}$ and $z_{x}^{k,2}$ are expected to be identical and interchangeable with one another, as they both refer to the same scene feature. BMM establishes a new explicit connection + +between the scene features of multi-views, which can be expressed in the equation as: + +$$ +\hat {z} _ {x} ^ {k} \triangleq \operatorname {M i x} _ {p} \left(z _ {x} ^ {k, 1}, z _ {x} ^ {k, 2}\right), \tag {11} +$$ + +where the $\hat{z}_x^k$ is an estimation of the true underlying scene feature. Let $b_{f}$ define a sample instance drawn from a Bernoulli distribution with probability $p\in (0,1)$ , the function $\mathrm{Mix}_p(\cdot)$ described in Equation (11) denotes: + +$$ +\operatorname {M i x} _ {p} (\boldsymbol {m}, \boldsymbol {n}) \triangleq b _ {f} \odot \boldsymbol {m} + (1 - b _ {f}) \odot \boldsymbol {n}. \tag {12} +$$ + +By establishing this new connection (Equation 11), we can enhance the interchangeability between $z_{x}^{k,1}$ and $z_{x}^{k,2}$ by optimising the reconstruction performance on $\hat{z}_{x}^{k}$ . + +Lemma 1. Assuming $z_{x}^{k,i}\sim N_{\mathbf{x}}(\boldsymbol {\mu},\boldsymbol {\Sigma})$ , where $N_{\mathbf{x}}$ denotes multivariate Gaussian distributions and then $\pmb{\mu}$ and $\pmb{\Sigma}$ is the mean and the covariance matrix. + +For a given function $G_{\theta}^{\mathcal{X}}(\cdot)$ , assume $\forall k, i, m, n \in \mathbb{N}$ , the following property holds: + +$$ +\mathbb {E} \left[ G _ {\theta} ^ {\mathcal {X}} \left(z _ {x} ^ {k, i}\right) \right] \triangleq \mathbb {E} \left[ G _ {\theta} ^ {\mathcal {X}} \left(\operatorname {M i x} _ {p} \left(z _ {x} ^ {k, m}, z _ {x} ^ {k, n}\right)\right) \right]. \tag {13} +$$ + +Proof. Assume $z_{x}^{k,m}, z_{x}^{k,n} \in \mathbb{R}^{\dim}$ are i.i.d., we may also factorise $b_{f} \in \mathbb{R}^{\dim}$ . Write + +$$ +\hat {z} _ {x} ^ {k} \triangleq \operatorname {M i x} _ {p} \left(z _ {x} ^ {k, m}, z _ {x} ^ {k, n}\right) \tag {14} +$$ + +so that we can have + +$$ +\begin{array}{l} \hat {z} _ {x} \sim N _ {\mathbf {x}} \left(\left(b _ {f} + 1 - b _ {f}\right) \boldsymbol {\mu}, \left(b _ {f} ^ {2} + \left(1 - b _ {f}\right) ^ {2}\right) \boldsymbol {\Sigma}\right) \tag {15} \\ \sim N _ {\mathbf {x}} (\boldsymbol {\mu}, \boldsymbol {\Sigma}) \\ \end{array} +$$ + +with the fact that Bernoulli sample $b_{f}^{2} = b_{f}$ , the mixed feature $\hat{z}_{x}$ is in the same representation distribution as $z_{x}^{k,i}$ . + +In MeD, we denote $\hat{z}_x = G_\theta^\chi (\hat{z}_x^k)$ , and the objective for implementing Equation (13) can be formulated as follows: + +$$ +\underset {\theta , \rho , \psi} {\operatorname {a r g m i n}} \mathcal {L} ^ {\mathcal {M}} \triangleq \lambda | | \hat {z} _ {x} - \operatorname {M i x} _ {p} \left(y _ {1} ^ {k}, y _ {2} ^ {k}\right) | |, \tag {16} +$$ + +where the $\lambda$ is the weight parameter. Here, the target is using a mixed version of $y_1^k$ and $y_2^k$ . The choice of this is driven by the intuition that the hybrid version would better align with the aforementioned blended features. + +# 4. Experiments + +To evaluate the effectiveness of our proposed method, we assess our method against several representative self-supervised denoising methods, including Noise2Noise (N2N) [16], Noise2Self (N2S) [4] and Recorrupted2Recorrupted (R2R) [26], and the invariant feature learning method LIR [9]. Moreover, we also evaluate our approach against two supervised baseline + +methods (Noise2Clean (N2C) [21] and multi-frame method DBD [11]) to further validate its effectiveness. Comparisons to more methods, including methods using only one noisy image, are presented in the supplementary material. + +We start our experiments by denoising synthetic additive white Gaussian noise (AWGN) in Section 4.2, and then move on to testing unseen noise levels and noise types in Section 4.3 and Section 4.4, respectively. Furthermore, we evaluate the performance in real-world scenarios in Section 4.5. In Section 4.6, we expand our experiments to incorporate more views to study their impact on performance. Finally, in Section 4.7, we apply our method to other tasks, e.g. image super-resolution and inpainting, to demonstrate its generalisation ability. + +# 4.1. Experimental Setups + +Noted that, the nature of feature disentanglement requires no leak from input to output, however, the global residual connection of the original DnCNN [35] cannot satisfy. Thus, we incorporate the Swin-Transformer (Swin-T) [21] instead of the traditionally used DnCNN in our experiments. Nevertheless, as Swin-T is not originally designed for image restoration, we make some modifications to enforce local dependence across the image. Specifically, we add one Convolution Layer each before the patch embedding and after the patch unembedding of Swin-T, as inspired by SwinIR [18]. The resulting modified network backbone is denoted as Swin-Tx. + +To ensure a fair comparison, we use the Swin-Tx backbone for all methods in our study, except for DBD. As DBD did not release the code, we follow the instructions presented in the paper and make our best effort to re-implement it. However, we observe that the two-view DBD could not converge efficiently, which is consistent with the findings in the paper. Therefore, we limit our evaluation to the four-view DBD, denoted as $\mathrm{DBD}_4$ . Furthermore, we replace the U-Net backbone originally used in the LIR method with Swin-Tx to maintain consistency in our evaluation. This results in an average improvement of approximately 1 dB in PSNR for Gaussian denoising. + +In all experiments, all methods were trained using only DIV2K [3] and the same optimisation parameters, except for LIR and $\mathrm{DBD}_4$ which used manually selected parameters obtained through experiments. For more training and evaluation details including the choice of parameters, please refer to the supplementary material. Code is available at: https://github.com/chgwer2/Multi-view-Self-supervised-Disentanglement-Denoising. + +Remark: In tables, the best results are highlighted in bold, while the second best is underlined. + +Table 1. Quantitative comparison of different methods on CBSD68 Dataset [23] for Synthetic Gaussian noise. The experiments were conducted on fixed and random variance, respectively. The best results are highlighted in bold, while the second best is underlined. + +
Training SchemaTest \(\hat{\sigma}\)Noisy/ Clean N2C [21]\(DBD_4\) [11]N2N [16]Noisy/ Noisy N2S [4]R2R [26]Invariant Feature
LIR [9]MeD (ours)
Gaussian\(\sigma = 25\)1533.36/0.902033.57/0.909232.64/0.880532.77/0.878029.74/0.786531.06/0.863233.11/0.8880
2530.83/0.849431.31/0.854830.68/0.833430.99/0.840530.45/0.818330.01/0.802430.57/0.8496
5024.76/0.551925.12/0.558324.59/0.538522.13/0.392824.02/0.513321.97/0.357825.67/0.6026
7520.75/0.337621.09/0.341220.60/0.316217.86/0.199819.10/0.264116.23/0.168923.09/0.4320
Gaussian\(\sigma \in [5,50]\)1533.47/0.902733.12/0.891533.45/0.894531.28/0.818720.76/0.250830.85/0.843133.62/0.9026
2530.87/0.853830.64/0.849130.77/0.842329.65/0.780123.91/0.455228.92/0.806930.91/0.8573
5027.41/0.736127.13/0.729027.15/0.721927.00/0.711426.92/0.691125.13/0.619127.48/0.7530
7525.05/0.622324.97/0.620524.80/0.590824.89/0.602323.83/0.513222.37/0.421225.40/0.6645
+ +Table 2. Quantitative result of generalisation performance experiment on CBSD68 [23]. All methods use Gaussian $\sigma = 25$ for pre-trained methods and then Gaussian $\sigma \in [5, 50]$ for fine-turning. The better result in each method is highlighted in italics. + +
Fine-tuning MethodN2C [21]N2N [16]LIR [9]MeD
Pretraining MethodN2CMeDN2NMeDLIRMeDMeD
Gaussian, δ ∈ [15, 75]29.20/ 0.779729.53/ 0.808129.04/ 0.764229.21/ 0.789026.42/ 0.664027.25/ 0.703629.60/ 0.8101
Local Var Gaussian35.62/ 0.930835.85/ 0.943935.66/ 0.925635.73/ 0.931029.26/ 0.817030.51/ 0.838735.91/ 0.9762
Poisson Noise40.49/ 0.973642.80/ 0.977641.35/ 0.973642.27/ 0.981331.23/ 0.867233.47/ 0.893245.05/ 0.9826
Speckle,帽子 ∈ [25, 50]33.36/ 0.900433.40/ 0.904433.32/ 0.893133.33/ 0.890728.28/ 0.771329.82/ 0.822933.48/ 0.9115
S&P,帽子 ∈ [0.3, 0.5]28.85/ 0.826730.73/ 0.837228.59/ 0.800329.45/ 0.825526.69/ 0.724127.62/ 0.746030.84/ 0.9135
Average33.50/ 0.882234.46/ 0.894233.59/ 0.871434.00/ 0.883528.38/ 0.768729.73/ 0.800934.98/ 0.9188
+ +# 4.2. AWGN Noise Removal + +We first investigate the denoising generalisation of the methods using synthetic zero-mean additive white Gaussian noise (AWGN). The experiments are divided into two parts. The first segment employs fixed variance AWGN, whereas the second segment employs varied variance Gaussian for training in a separate manner. Table 1 summarises the quantitative results evaluated on CBSD68 Dataset [23] at variance levels of 15, 25, 50, and 75. + +Analysis: In the fixed variance setting, MeD performs inferior compared to the other methods on lower noise levels of 15 and 25. However, as the methods face more severe corruption, MeD outperforms all self-supervised and supervised methods, showing our greater advantage of handling severe noise. For instance, at $\sigma = 75$ , MeD outperforms the second-best method (N2C) by around 2 dB. These results suggest that MeD has a remarkable ability to generalise to a range of unseen noise levels in Gaussian noise. + +In the context of random variance, it has been observed that MeD exhibits superior performance across all four noise levels compared to other methods, including supervised methods. These findings imply that MeD can benefit more from varying training noise than other methods. More experiments and details on AWGN noise removal can be found in the supplementary material. + +# 4.3. Generalisation on Unseen Noise Removal + +In the previous subsection, we demonstrated the remarkable generalisation ability of our model in the case of Gaus + +sian noise. Here, we aim to extend this investigation to other types of unseen noise and evaluate the denoising generalisation ability of our method. Specifically, we consider Poisson noise, Speckle noise, Local Variance Gaussian noise, and Salt-and-Pepper noise. For a more detailed synthetic process, please refer to the supplementary material. + +First, we demonstrate qualitative comparisons of denoising unseen noise types using models trained only with Gaussian $\sigma = 25$ in Figure 3. Next, in order to further verify the denoising generalisation ability of MeD, we employ its scene encoder and decoder as pre-trained models to be compared against other methods. It should be noted that the pre-training and fine-tuning methods employed in this study may differ, as shown in Table 2. The pre-training of all test models was conducted on a Gaussian sigma value of 25, followed by fine-tuning with a Gaussian sigma range of 5 to 50. Since the training schema of N2S, R2R, and DBD $_4$ differs from MeD, we do not include them in this section. However, evaluations of these methods on unseen noise are still presented in Section 4.4 under different settings. + +Analysis: Qualitative results in Figure 3 show that under Gaussian $\sigma = 25$ training settings, our method surpasses other methods in denoising unseen noise types. Additionally, Table 2 shows that the approaches using pre-trained MeD models outperform their self-transfer models for N2C, N2N, and LIR, with improvements of up to $2\mathrm{dB}$ in some cases. On average, the MeD pre-trained models show a performance gain of around $0.5\mathrm{dB}$ across all methods, highlighting the potential of MeD as a powerful pre-training + +![](images/4a9364f18bf096a984a5c4830cf35849e87a10d646a1f08aa41fb34fbf6bcee9.jpg) +Figure 3. Qualitative denoising results on unseen noise types. All the methods are trained with Gaussian $\sigma = 25$ . The quantitative PSNR/SSIM results are provided underneath the respective images. Best viewed in colour (zoom-in for a better comparison). + +Table 3. Analysis of Noise Pool on CBSD68 [23]. All methods were trained using randomly drawn noise from the Noise Pool. + +
Test NoiseNoisy/ CleanNoisy/ NoisyInvariant Feature
N2C [21]DBD4 [11]N2N [16]N2S [4]R2R [26]LIR [9]MeD (ours)
Gaussian, θ ∈ [15, 75]29.24/0.775429.05/0.761629.23/0.763428.58/0.758926.43/0.663926.67/0.686629.61/0.8178
Local Var Gaussian (LVG)36.64/0.944236.18/0.930736.65/0.923533.24/0.885834.70/0.877931.61/0.862737.99/0.9568
Poisson Noise45.72/0.976444.23/0.960645.64/0.979946.31/0.980844.45/0.949143.27/0.929248.10/0.9916
Speckle, v ∈ [25, 50]35.58/0.941735.24/0.938535.34/0.947535.13/0.959634.20/0.907833.98/0.881037.21/0.9715
S&P, r ∈ [0.3, 0.5]38.85/0.916537.10/0.888438.89/0.928938.22/0.933036.17/0.908733.43/0.820242.33/0.9695
Gaussian θ = 25 + Speckle v = 2530.19/0.827929.24/0.815630.32/0.831729.51/0.805028.78/0.774429.20/0.787131.92/0.8726
Gaussian θ = 50 + Speckle v = 2527.30/0.725126.55/0.712627.23/0.733126.91/0.708126.49/0.693526.19/0.694129.68/0.7928
LVG + Poisson31.78/0.908731.10/0.884231.60/0.761730.15/0.808628.52/0.714427.33/0.723434.29/0.9325
Poisson + Speckle v = 2531.39/0.906930.86/0.878231.52/0.893530.58/0.906730.34/0.889729.93/0.855433.04/0.9258
Average34.08/0.880333.28/0.863434.05/0.862633.18/0.860732.23/0.819931.29/0.804436.02/0.9145
+ +method for image denoising. It is noteworthy that the self-transfer MeD model exhibits the best denoising performance across all validation noise types, even outperforming the supervised method, N2C. This is particularly evident in Poisson noise, where MeD surpasses N2C by $\sim 3$ dB. These results highlight the generalisation ability of our approach in handling unseen noise. + +# 4.4. Experiments on General Noise Pool + +Here we further investigate the generalisation ability of our method by introducing our general Noise Pool. The Noise Pool comprises the five aforementioned types of noise, each with a diverse range of noise levels. During training, we randomly sample from the noise pool to provide the model with noisy images. This novel approach simulates a realistic scenario where noise is unknown and can originate from various sources to some extent. + +Specifically, we evaluated all methods using the random + +noise pool approach to train and test on combined or single noise types. The results are summarised in Table 3. + +Analysis: In Table 3, our MeD approach outperforms all other methods significantly on all the test noise types. For example, when a test noise containing a combination of Gaussian noise with $\hat{\sigma} = 50$ and Speckle noise with $\hat{v} = 25$ is used, other methods exhibit an approximate performance of $\sim 27$ dB. However, MeD achieves significantly better results with a performance of $29.68\mathrm{dB}$ . And on average, MeD exhibits a performance that is approximately $2\mathrm{dB}$ better than other methods. Our findings show that utilising a comprehensive noise pool for training purposes can effectively improve the generalisation capability. Furthermore, the remarkable denoising generalisation ability of our MeD approach, in comparison to other methods, is particularly advantageous for real-world applications. + +![](images/299f035bc59010939b024056417be746ecac205818020c263c2b6282b2a66236.jpg) +23.68/0.2967 + +![](images/31984eba46abcda06654c2f4af62a408c6e45f7205ab8dcca7ea01208262e6fc.jpg) +Noisy Image from SIDD [1] (ISO 800) +25.33/0.3865 +Noisy Image from SIDD +Figure 4. Real Noise Removal Example of SIDD [1]. All the methods are trained with Noise Pool on the DIV2K [2] dataset. It can be seen that the proposed MeD can remove much real noise even without training with real-noise distribution (zoom in for a better comparison). + +![](images/4208278d4294533f2e701c41092cd0e0a448ffedb407ef11e0f940e44e916669.jpg) +PSNR/ SSIM + +![](images/368e22ecf92ecabb0e4c6d5989d070dbfc298855a9d2624479434e5cc91aec3c.jpg) +Ground Truth [1] +28.58/0.6081 + +![](images/48f7e84016ff3e3ac40ed96938b62967f5bb93efd68f4ee7378696b4a20ebcc1.jpg) +N2S [4] +PSNR/ SSIM + +![](images/a812d9ecf16f26bc1fd04c3381a436840b4e03f6a2505585be28aa87c3783155.jpg) +Reference +27.58/0.5516 +N2S [4] + +![](images/bf46359e66d67194ba2291666827a2db1d03d7f353782c722dd00c55440af375.jpg) +31.38/0.8912 + +![](images/6ac8164e84c0be7417902af9d788371a65cd1b836dca4f759aac0e8d6087e0a8.jpg) +N2C [21] +26.58/0.4257 + +![](images/e5f1a76058abb08b195c2d15b5ed3c572ba4f621f91d6732317905f489954f53.jpg) +R2R [26] +28.36/0.5661 + +![](images/0224298f373927398c2d536b6b2f126404fd1a9765ba3c1f163a667c2d7e379b.jpg) +N2C [21] +26.77/0.4889 +R2R [26] + +![](images/22cd848216bbb1c261cad8c5e2d79457875c2c0edc0293f070ffe52ece4b6557.jpg) +30.19/0.7449 + +![](images/19cd42d46af1dac7e261d109e044bf319ed117649965d2360ac36b4a9b8649d5.jpg) +$\mathrm{DBD}_4$ [11] +25.91/0.3795 + +![](images/c3da253c319cda95c8cbf681a689612717c95ebc7d8167697cbadf362435c1bf.jpg) +LIR [9] +27.58/0.5406 + +![](images/9fd37291b971d5e769d3b23748871b4db2e59a4c8f5e7e17ba62171900eb13eb.jpg) +$\mathrm{DBD}_4$ [11] +26.45/0.4752 +LIR [9] + +![](images/9b3ddeadb5538ea7241678518896fcdc6cd7c1e4a28ee27a15e74a536b4aa62e.jpg) +29.60/0.7053 + +![](images/522e6dba673ab52deb06310ea6007bc01e9217790a01eae6aff3b36b5d12d312.jpg) +N2N [16] +33.07/0.8849 + +![](images/2e12321648df346c62b959357c3b8b23cbe0f7ddba79eccdbd930416f2926fc0.jpg) +MeD (Ours) +27.23/0.49 + +![](images/4300d7c2bbd8c192b2338e62e086a374e61126a6c5dfede61dec1ee9a7265f14.jpg) +N2N [16] +30.23/0.6703 +MeD (Ours) + +Table 4. Quantitative result obtained from the application of various methods trained on a general Noise Pool to real noise datasets. + +
MethodPolyU [32]SIDD [1]CC [24]Average
N2C [21]35.89/0.965230.37/0.602837.89/0.940834.72/0.8363
DBD4 [11]35.69/0.957130.23/0.617337.74/0.935734.55/0.8367
N2N [16]36.22/0.967932.82/0.729737.39/0.957035.48/0.8849
N2S [4]36.41/0.972130.98/0.601837.58/0.962234.99/0.8454
R2R [26]34.58/0.889029.64/0.570835.35/0.847833.19/0.7692
LIR [9]34.81/0.727828.76/0.529635.50/0.840333.02/0.6992
MeD (ours)38.65/0.985535.81/0.827840.08/0.974538.18/0.9293
+ +# 4.5. Real Noise Removal + +In our previous experiments, we demonstrated the exceptional denoising performance of our MeD approach on synthetic noises. However, real-world noise is often more complex and challenging than synthetic noise. In this subsection, we aim to evaluate the generalisation performance of our approach on real-world noise by testing it on the SIDD [1], CC [24] and PolyU [32] datasets. To assess the denoising performance on real-world noise, we use the same pre-trained models as in Section 4.4. The representative qualitative results on the SIDD dataset in the standard RGB colour space are presented in Figure 4. + +Analysis: As shown in Table 4, our approach significantly outperforms all other methods across all three datasets, with a performance improvement of 2-3 dB over the second-best approach, and also consistently outperforms its supervised counterparts (i.e. N2C and $\mathrm{DBD}_4$ ) by over 3 dB. These results suggest the effectiveness and generalisability of the proposed approach in real-world denoising scenarios. + +Our approach achieves remarkable performance on real-world noise without even being trained on more expensive real-world data. For a more complete study, we also conduct experiments on model training with real-world data (for more details please refer to the supplementary material), showing superior performance and even better generalisation ability to data out of the training data distribution. + +In Figure 4, the presence of noise persists even after applying denoising techniques, yet ours demonstrates the most authentic outcomes compared to others. For instance, while the noise particles remain prominent in the N2C results, they are absent in our results. Overall, the results indicate that the MeD approach is well-suited for real-world denoising tasks, providing a robust and reliable solution for + +Table 5. Multiple views ( $\geq 2$ ) study,with average PSNR/SSIM. + +
#ViewsGaussianLVGPoissonSpeckleS&P
229.61/0.817837.99/0.956848.10/0.991637.21/0.971542.33/0.9695
329.68/0.819738.05/0.957748.23/0.992037.40/0.973342.45/0.9703
429.70/0.820438.08/0.958048.31/0.992137.47/0.974042.49/0.9709
+ +Table 6. Average PSNR/SSIM of super-resolution results on Set5 [6]. Learning-based methods are trained with Corruption Pool. + +
ScaleBicubicRCAN [37]DASR [30]MeD (ours)
×233.63/ 0.928536.12/ 0.933936.98/ 0.947137.12/ 0.9527
×330.37/ 0.865234.15/ 0.928634.11/ 0.918734.92/ 0.9294
×428.35/ 0.808431.94/ 0.887131.54/ 0.873632.50/ 0.8956
+ +improving image quality in challenging environments. + +# 4.6. Expand to More Views + +Although we only showcase two views for the experiments above, our method can be easily expanded to multiple views. To investigate the impact of the numbers of views, here we further conduct a study comparing 2, 3, and 4 views, in Table 5. + +The results indicate that increasing the number of views consistently improves the performance across different noise types. For example, when dealing with Speckle noise, the 4-view model achieves a $0.26\mathrm{dB}$ higher PSNR than the 2-view model. However, it is worth noting that employing $n$ views requires $n!$ cross-computations within each view pair during training, resulting in a significant increase in computational cost (e.g. from 2-view to 4-view leads to a $10\times$ training time increase in our experiment). + +# 4.7. More Application Exploration + +Here we investigate the potential of the proposed MeD for other more general image restoration tasks, such as image super-resolution and inpainting. In this study, we generalise the previously defined degradation (noise) to a residual image between a clean image and a corrupted image. Moreover, we expand the definition from Noise Pool to a more general one - Corruption Pool that contains not only noise but also general corruption. + +Super resolution. Image super-resolution aims to enlarge the resolution of a low-resolution image. We train our method on the DIV2K dataset [3], where we randomly choose different downscale methods from a Corruption Pool that consists of random Gaussian noise and four types of down-scaling (bicubic, lanczos, bilinear, and hamming). We benchmark our method against the supervised method RCAN [37] that aims for high PSNR and the recent unsupervised methods DASR [30] that are specialised for superresolution. We conduct our evaluation on the Set5 dataset [6] with scaling factors of 2, 3, and 4. The results in Table 6 show the effectiveness of our method over both supervised and unsupervised approaches. + +Table 7. Average PSNR/SSIM of inpainting results on Set11 [29]. S2S and DIP are trained and tested on the same single image. MeD is trained with Corruption Pool. + +
Dropping RatioDIP [29]S2S [27]MeD (Ours)
50%33.45/ 0.921734.91/ 0.947936.24/ 0.9617
70%28.53/ 0.850130.94/ 0.884531.05/ 0.9161
90%24.39/ 0.736025.97/ 0.793326.01/ 0.8052
+ +Inpainting. We also apply our method to the image inpainting task, which fills in missing pixels. We choose two single-image deep learning methods - Self2Self (S2S) [27] and DIP [29], for comparison. Our MeD is trained with Corruption Pool containing noises, down-scaling, and inpainting mask operations altogether. To compare our method (MeD) with other state-of-the-art methods, we conduct experiments on the Set 11 dataset [29] with three different pixel dropping ratios: $50\%$ , $70\%$ , and $90\%$ . The results are shown in Table 7, suggesting the effectiveness of MeD again in the image inpainting task. + +# 5. Conclusion + +In this paper, we have presented a new self-supervised learning method (MeD) for image denoising that disentangles scene and noise features in a constraint feature space. Our approach has demonstrated exceptional denoising performance in both synthetic and real-world noise scenarios, with particularly significant performance on real-world noise. MeD can handle complex noise with better performance than other state-of-the-art methods, as validated by consistent performance gain across various datasets and noise types. Our approach has decent generalisation ability, requiring only noisy images for training and efficiently denoising real-world noise without seeing any clean ground truth data. This opens up new possibilities for training deep models without the need for costly labelled data. Furthermore, our model can be easily adapted to other low-level image restoration tasks. We hope this could provide a new baseline for future research in image disentanglement and the extension to other image processing tasks. + +# Acknowledgement + +The computations described in this research were performed using the Baskerville Tier 2 HPC service1. 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In Proceedings of the AAAI Conference on Artificial Intelligence, volume 34, pages 13074-13081, 2020. \ No newline at end of file diff --git a/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/images.zip b/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..5109300e0ca8918fd978c07576df45a2cb7e812c --- /dev/null +++ b/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:6023691e813d4717d604e2f6d68f6982025c6359d913a410a3254845f9663168 +size 1072992 diff --git a/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/layout.json b/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..316487508918488ed65730db2706321d84a43287 --- /dev/null +++ b/2023/Multi-view Self-supervised Disentanglement for General Image Denoising/layout.json @@ -0,0 +1,12468 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 69, + 100, + 523, + 118 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 69, + 100, + 523, + 118 + ], + "spans": [ + { + "bbox": [ + 69, + 100, + 523, + 118 + ], + "type": "text", + "content": "Multi-view Self-supervised Disentanglement for General Image Denoising" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 105, + 130, + 168, + 146 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 105, + 130, + 168, + 146 + ], + "spans": [ + { + "bbox": [ + 105, + 130, + 168, + 146 + ], + "type": "text", + "content": "Hao Chen\\*,1" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 184, + 130, + 263, + 146 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 184, + 130, + 263, + 146 + ], + "spans": [ + { + "bbox": [ + 184, + 130, + 263, + 146 + ], + "type": "text", + "content": "Chenyuan " + }, + { + "bbox": [ + 184, + 130, + 263, + 146 + ], + "type": "inline_equation", + "content": "\\mathrm{Qu}^{*,1}" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 278, + 131, + 332, + 146 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 278, + 131, + 332, + 146 + ], + "spans": [ + { + "bbox": [ + 278, + 131, + 332, + 146 + ], + "type": "text", + "content": "Yu Zhang²" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 347, + 131, + 407, + 145 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 131, + 407, + 145 + ], + "spans": [ + { + "bbox": [ + 347, + 131, + 407, + 145 + ], + "type": "text", + "content": "Chen Chen3" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 422, + 131, + 483, + 145 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 422, + 131, + 483, + 145 + ], + "spans": [ + { + "bbox": [ + 422, + 131, + 483, + 145 + ], + "type": "text", + "content": "Jianbo Jiao" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 67, + 151, + 526, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 67, + 151, + 526, + 167 + ], + "spans": [ + { + "bbox": [ + 67, + 151, + 526, + 167 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 67, + 151, + 526, + 167 + ], + "type": "text", + "content": "University of Birmingham " + }, + { + "bbox": [ + 67, + 151, + 526, + 167 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 67, + 151, + 526, + 167 + ], + "type": "text", + "content": "Shanghai Jiao Tong University " + }, + { + "bbox": [ + 67, + 151, + 526, + 167 + ], + "type": "inline_equation", + "content": "^{3}" + }, + { + "bbox": [ + 67, + 151, + 526, + 167 + ], + "type": "text", + "content": "University of Central Florida" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 186, + 171, + 408, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 186, + 171, + 408, + 186 + ], + "spans": [ + { + "bbox": [ + 186, + 171, + 408, + 186 + ], + "type": "text", + "content": "Project page: https://chqwer2.github.io/MeD/" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "spans": [ + { + "bbox": [ + 143, + 213, + 192, + 225 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 239, + 290, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 239, + 290, + 502 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 290, + 502 + ], + "type": "text", + "content": "With its significant performance improvements, the deep learning paradigm has become a standard tool for modern image denoisers. While promising performance has been shown on seen noise distributions, existing approaches often suffer from generalisation to unseen noise types or general and real noise. It is understandable as the model is designed to learn paired mapping (e.g. from a noisy image to its clean version). In this paper, we instead propose to learn to disentangle the noisy image, under the intuitive assumption that different corrupted versions of the same clean image share a common latent space. A self-supervised learning framework is proposed to achieve the goal, without looking at the latent clean image. By taking two different corrupted versions of the same image as input, the proposed Multi-view Self-supervised Disentanglement (MeD) approach learns to disentangle the latent clean features from the corruptions and recover the clean image consequently. Extensive experimental analysis on both synthetic and real noise shows the superiority of the proposed method over prior self-supervised approaches, especially on unseen novel noise types. On real noise, the proposed method even outperforms its supervised counterparts by over 3 dB." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 527, + 128, + 540 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 527, + 128, + 540 + ], + "spans": [ + { + "bbox": [ + 47, + 527, + 128, + 540 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 548, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 548, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 548, + 287, + 693 + ], + "type": "text", + "content": "Image restoration is a critical sub-field of computer vision, exploring the reconstruction of image signals from corrupted observations. Examples of such ill-posed low-level image restoration problems include image denoising [16,25,26,29,33,35,38], super-resolution [2,8,19,30,37], and JPEG artefact removal [7, 12, 31], to name a few. Usually, a mapping function dedicated to the training data distribution is learned between the corrupted and clean images to address the problem. While many image restoration systems perform well when evaluated over the same corruption distribution that they have seen, they are often required to be deployed in settings where the environment is unknown and" + } + ] + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 317, + 217, + 426, + 361 + ], + "blocks": [ + { + "bbox": [ + 317, + 217, + 426, + 361 + ], + "lines": [ + { + "bbox": [ + 317, + 217, + 426, + 361 + ], + "spans": [ + { + "bbox": [ + 317, + 217, + 426, + 361 + ], + "type": "image", + "image_path": "ff5442c64c4b77977a480f53fa8931da5918ba53d2ce360ed7cdd3b46fe5d814.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 335, + 363, + 403, + 374 + ], + "lines": [ + { + "bbox": [ + 335, + 363, + 403, + 374 + ], + "spans": [ + { + "bbox": [ + 335, + 363, + 403, + 374 + ], + "type": "text", + "content": "(a) Noisy/ Clean" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 430, + 217, + 539, + 361 + ], + "blocks": [ + { + "bbox": [ + 430, + 217, + 539, + 361 + ], + "lines": [ + { + "bbox": [ + 430, + 217, + 539, + 361 + ], + "spans": [ + { + "bbox": [ + 430, + 217, + 539, + 361 + ], + "type": "image", + "image_path": "b5626a1a442483f90faf4a0f2c9aa17f026b04482ccea7a16a44a7958a169d8a.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 435, + 363, + 537, + 374 + ], + "lines": [ + { + "bbox": [ + 435, + 363, + 537, + 374 + ], + "spans": [ + { + "bbox": [ + 435, + 363, + 537, + 374 + ], + "type": "text", + "content": "(b) N2C [21], Supervised" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 317, + 380, + 427, + 524 + ], + "blocks": [ + { + "bbox": [ + 317, + 380, + 427, + 524 + ], + "lines": [ + { + "bbox": [ + 317, + 380, + 427, + 524 + ], + "spans": [ + { + "bbox": [ + 317, + 380, + 427, + 524 + ], + "type": "image", + "image_path": "b39275238920d1558ee3498690cb6e3a417210456a9c52dba3c34af67d7b8854.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 315, + 525, + 426, + 537 + ], + "lines": [ + { + "bbox": [ + 315, + 525, + 426, + 537 + ], + "spans": [ + { + "bbox": [ + 315, + 525, + 426, + 537 + ], + "type": "text", + "content": "(c) LIR [9], Self-supervised" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 544, + 547, + 622 + ], + "lines": [ + { + "bbox": [ + 304, + 544, + 547, + 622 + ], + "spans": [ + { + "bbox": [ + 304, + 544, + 547, + 622 + ], + "type": "text", + "content": "Figure 1. Denoising performance on unseen Speckle Noise with " + }, + { + "bbox": [ + 304, + 544, + 547, + 622 + ], + "type": "inline_equation", + "content": "\\hat{\\pmb{v}} = 50" + }, + { + "bbox": [ + 304, + 544, + 547, + 622 + ], + "type": "text", + "content": ". The models were trained with Gaussian noise " + }, + { + "bbox": [ + 304, + 544, + 547, + 622 + ], + "type": "inline_equation", + "content": "\\sigma \\in [5,50]" + }, + { + "bbox": [ + 304, + 544, + 547, + 622 + ], + "type": "text", + "content": ". (a) The noisy and clean images, with ground-truth clean patches shown below. (b) Noise-to-Clean (N2C) [21] is trained with clean images. (c) LIR [9] is self-supervised but needs unpaired clean images as training data. (d) Our approach is fully self-supervised, training with only the noisy input data." + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "type": "image", + "bbox": [ + 430, + 380, + 540, + 524 + ], + "blocks": [ + { + "bbox": [ + 430, + 380, + 540, + 524 + ], + "lines": [ + { + "bbox": [ + 430, + 380, + 540, + 524 + ], + "spans": [ + { + "bbox": [ + 430, + 380, + 540, + 524 + ], + "type": "image", + "image_path": "920463002582708f96ac0f8563b7bf8162d8c7fd37d0fb16a3f8ef3a7025503a.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 435, + 525, + 536, + 537 + ], + "lines": [ + { + "bbox": [ + 435, + 525, + 536, + 537 + ], + "spans": [ + { + "bbox": [ + 435, + 525, + 536, + 537 + ], + "type": "text", + "content": "(d) Ours, Self-supervised" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_caption" + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 547, + 715 + ], + "type": "text", + "content": "off the training distribution. These settings, such as medical imaging, computational lithography, and remote sensing, require image restoration methods that can handle complex and unknown corruptions. Moreover, in many real-world image-denoising tasks, ground truth images are unavailable, introducing additional challenges." + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 62, + 703, + 130, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 62, + 703, + 130, + 712 + ], + "spans": [ + { + "bbox": [ + 62, + 703, + 130, + 712 + ], + "type": "text", + "content": "*Equal contribution." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12281" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 286, + 132 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 286, + 132 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 286, + 132 + ], + "type": "text", + "content": "Limitations of existing methods: Current low-level corruption removal tasks aim to address the inquiry of \"what is the clean image provided a corrupted observation?\" However, the ill-posed nature of this problem formulation poses a significant challenge in obtaining a unique resolution [5]." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 133, + 286, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 133, + 286, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 133, + 286, + 251 + ], + "type": "text", + "content": "To mitigate this limitation, researchers often introduce additional information, either explicitly or implicitly. For example, in [15], Laine et al. explicitly use the prior knowledge of noise as complementary input, generating a new invertible image model. Alternatively, Learning Invariant Representation (LIR) [9] implicitly enforces the interpretability in the feature space to guarantee the admissibility of the output. However, these additional forms of information may not always be practical in real-world scenarios or may not result in satisfactory performance." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 266, + 286, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 266, + 286, + 348 + ], + "spans": [ + { + "bbox": [ + 46, + 266, + 286, + 348 + ], + "type": "text", + "content": "Main idea and problem formulation: Our motivation for tackling this ill-posed nature stems from the solution in the 3D reconstruction of utilising multiple views to provide a unique estimation of the real scene [1]. Building on this motivation, we propose a training scheme that is explicitly built on multi-corrupted views and perform Multi-view self-supervised Disentanglement, abbreviated as " + }, + { + "bbox": [ + 46, + 266, + 286, + 348 + ], + "type": "inline_equation", + "content": "MeD" + }, + { + "bbox": [ + 46, + 266, + 286, + 348 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 350, + 286, + 468 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 350, + 286, + 468 + ], + "spans": [ + { + "bbox": [ + 46, + 350, + 286, + 468 + ], + "type": "text", + "content": "Under this new multi-view setting, we reformulate the task problem as \"what is the shared latent information across these views?\" instead of the conventional \"what is the clean image?\" By doing so, MeD can effectively leverage the scene coherence of multi-view data and capture underlying common parts without requiring access to the clean image. This makes it more practical and scalable in real-world scenarios. An example of the proposed method with comparison to prior works is shown in Figure 1, indicating its effectiveness over the state-of-the-art." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 468, + 286, + 503 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 468, + 286, + 503 + ], + "spans": [ + { + "bbox": [ + 46, + 468, + 286, + 503 + ], + "type": "text", + "content": "Specifically, given any scene image " + }, + { + "bbox": [ + 46, + 468, + 286, + 503 + ], + "type": "inline_equation", + "content": "x^{k} \\sim \\mathcal{X}, k \\in \\mathbb{N}" + }, + { + "bbox": [ + 46, + 468, + 286, + 503 + ], + "type": "text", + "content": " sampled uniformly from a clean image set " + }, + { + "bbox": [ + 46, + 468, + 286, + 503 + ], + "type": "inline_equation", + "content": "\\mathcal{X}" + }, + { + "bbox": [ + 46, + 468, + 286, + 503 + ], + "type": "text", + "content": ", MeD produces two contaminated views:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 108, + 510, + 286, + 526 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 108, + 510, + 286, + 526 + ], + "spans": [ + { + "bbox": [ + 108, + 510, + 286, + 526 + ], + "type": "interline_equation", + "content": "y _ {1} ^ {k} \\triangleq \\mathcal {T} _ {1} \\left(x ^ {k}\\right), y _ {2} ^ {k} \\triangleq \\mathcal {T} _ {2} \\left(x ^ {k}\\right), \\tag {1}", + "image_path": "c2c35906c6ca11aeb920b3ea2a2f2ddca2bb192a5ef1c455a4fe46ca2104a1b7.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "spans": [ + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "type": "text", + "content": "forming two independent corrupted image sets " + }, + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "type": "inline_equation", + "content": "\\{\\mathcal{Y}_1\\}, \\{\\mathcal{Y}_2\\}" + }, + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "type": "inline_equation", + "content": "y_1^k \\in \\mathcal{Y}_1" + }, + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "type": "inline_equation", + "content": "y_2^k \\in \\mathcal{Y}_2" + }, + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "type": "text", + "content": ". The " + }, + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_1" + }, + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_2" + }, + { + "bbox": [ + 46, + 532, + 286, + 568 + ], + "type": "text", + "content": " represent two random independent image degradation operations." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "spans": [ + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "type": "text", + "content": "We parameterise our scene feature encoder " + }, + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "type": "inline_equation", + "content": "G_{\\theta}^{\\mathcal{X}}" + }, + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "type": "text", + "content": " and decoder " + }, + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "type": "inline_equation", + "content": "D_{\\psi}^{\\mathcal{X}}" + }, + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "type": "inline_equation", + "content": "\\psi" + }, + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "type": "text", + "content": ". Considering the image pair " + }, + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "type": "inline_equation", + "content": "\\{y_1^k, y_2^k\\}_{k \\in \\mathbb{N}}" + }, + { + "bbox": [ + 47, + 568, + 286, + 617 + ], + "type": "text", + "content": ", the core of the presented method can be summarised as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 110, + 624, + 286, + 639 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 110, + 624, + 286, + 639 + ], + "spans": [ + { + "bbox": [ + 110, + 624, + 286, + 639 + ], + "type": "interline_equation", + "content": "G _ {\\theta} ^ {\\mathcal {X}} \\left(y _ {1} ^ {k}\\right) \\triangleq z _ {x} ^ {k, i} \\triangleq G _ {\\theta} ^ {\\mathcal {X}} \\left(y _ {2} ^ {k}\\right), \\tag {2}", + "image_path": "99783de702d9957acb9a1a4fb4b61ebe8af8cb97f4fd5446f06ef1d47725918e.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 133, + 640, + 286, + 656 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 133, + 640, + 286, + 656 + ], + "spans": [ + { + "bbox": [ + 133, + 640, + 286, + 656 + ], + "type": "interline_equation", + "content": "\\hat {x} ^ {k} \\triangleq D _ {\\psi} ^ {\\mathcal {X}} \\left(z _ {x} ^ {k, i}\\right), \\tag {3}", + "image_path": "3b130ff9e95b869a75a689d50c04d104b3771ea32a6cb2f940761e1a26ebe56e.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "inline_equation", + "content": "z_{x}^{k,i}" + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "text", + "content": " represents the shared scene latent between " + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "inline_equation", + "content": "y_{1}^{k}" + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "inline_equation", + "content": "y_{2}^{k}" + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "text", + "content": " referring to the input image index of " + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "inline_equation", + "content": "y_{i}" + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "text", + "content": ". A clean image estimator " + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "inline_equation", + "content": "D_{\\psi}^{\\mathcal{X}}" + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "text", + "content": " forms an all-deterministic reverse mapping from " + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "inline_equation", + "content": "z_{x}^{k,i}" + }, + { + "bbox": [ + 47, + 663, + 286, + 714 + ], + "type": "text", + "content": " to reconstruct an estimated clean" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "type": "text", + "content": "image " + }, + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "type": "inline_equation", + "content": "\\hat{x}^k" + }, + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "type": "text", + "content": ". Similarly, the noise latent " + }, + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "type": "inline_equation", + "content": "u_{\\eta}^{k,i}" + }, + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "type": "text", + "content": " is factorised from a corrupted view with a corruption encoder " + }, + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "type": "inline_equation", + "content": "E_{\\rho}^{\\mathcal{N}}" + }, + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "type": "text", + "content": ". After words, the resulting corruption is reconstructed from " + }, + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "type": "inline_equation", + "content": "u_{\\eta}^{k,i}" + }, + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "type": "text", + "content": " through the use of a corruption decoder, represented by " + }, + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "type": "inline_equation", + "content": "F_{\\phi}^{\\mathcal{N}}" + }, + { + "bbox": [ + 305, + 72, + 545, + 125 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 124, + 545, + 159 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 124, + 545, + 159 + ], + "spans": [ + { + "bbox": [ + 306, + 124, + 545, + 159 + ], + "type": "text", + "content": "The disentanglement is then performed between " + }, + { + "bbox": [ + 306, + 124, + 545, + 159 + ], + "type": "inline_equation", + "content": "\\{z_{x}^{k,i},u_{\\eta}^{k,j}\\}_{i\\neq j}" + }, + { + "bbox": [ + 306, + 124, + 545, + 159 + ], + "type": "text", + "content": " on a cross compose decoder " + }, + { + "bbox": [ + 306, + 124, + 545, + 159 + ], + "type": "inline_equation", + "content": "R_{\\delta}^{\\mathcal{V}}" + }, + { + "bbox": [ + 306, + 124, + 545, + 159 + ], + "type": "text", + "content": " with parameter " + }, + { + "bbox": [ + 306, + 124, + 545, + 159 + ], + "type": "inline_equation", + "content": "\\delta" + }, + { + "bbox": [ + 306, + 124, + 545, + 159 + ], + "type": "text", + "content": ", which can be formulated as:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 380, + 168, + 545, + 184 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 380, + 168, + 545, + 184 + ], + "spans": [ + { + "bbox": [ + 380, + 168, + 545, + 184 + ], + "type": "interline_equation", + "content": "\\hat {y} _ {1} ^ {k} \\triangleq R _ {\\delta} ^ {\\mathcal {Y}} \\left(z _ {x} ^ {k, 2}, u _ {\\eta} ^ {k, 1}\\right). \\tag {4}", + "image_path": "43fa6bfa54e90406144be0c8144669ae8989c29b0b05551b9ca2307e9a04d42f.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "spans": [ + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "type": "text", + "content": "It should be noted that Equation (4) is performed over latent features " + }, + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "type": "inline_equation", + "content": "u" + }, + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "type": "text", + "content": " from different views. When assuming that " + }, + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "type": "inline_equation", + "content": "z_{x}^{k}" + }, + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "type": "text", + "content": " remains constant across views, the reconstructed view " + }, + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "type": "inline_equation", + "content": "\\hat{y}_{1}^{k}" + }, + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "type": "text", + "content": " is determined by the " + }, + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "type": "inline_equation", + "content": "u_{\\eta}^{k,1}" + }, + { + "bbox": [ + 305, + 192, + 545, + 242 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 255, + 544, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 255, + 544, + 277 + ], + "spans": [ + { + "bbox": [ + 305, + 255, + 544, + 277 + ], + "type": "text", + "content": "Contributions. The contributions of our work are summarised as follows:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 317, + 287, + 545, + 458 + ], + "type": "list", + "angle": 0, + "index": 19, + "blocks": [ + { + "bbox": [ + 317, + 287, + 545, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 287, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 317, + 287, + 545, + 323 + ], + "type": "text", + "content": "- We propose a new problem formulation to address the ill-posed problem of image denoising using only noisy examples, in a different paradigm than prior works." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 317, + 331, + 545, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 331, + 545, + 390 + ], + "spans": [ + { + "bbox": [ + 317, + 331, + 545, + 390 + ], + "type": "text", + "content": "- We introduce a disentangled representation learning framework that leverages multiple corrupted views to learn the shared scene latent, by exploiting the coherence across views of the same scene and separating noise and scene in the latent space." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 317, + 399, + 545, + 458 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 399, + 545, + 458 + ], + "spans": [ + { + "bbox": [ + 317, + 399, + 545, + 458 + ], + "type": "text", + "content": "- Extensive experimental analysis validates the effectiveness of the proposed MeD, outperforming existing methods with more robust performance to unknown noise distributions, even better than its supervised counterparts." + } + ] + } + ], + "index": 18 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 478, + 391, + 490 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 478, + 391, + 490 + ], + "spans": [ + { + "bbox": [ + 306, + 478, + 391, + 490 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 545, + 713 + ], + "type": "text", + "content": "Single-view image restoration: In [8], Dong et al. were the first to employ a deep network in super-resolution. Later, a range of single view-based models expanded the idea of supervised deep learning to handle image restoration tasks, such as deblurring [14], JPEG artefacts [12], inpainting [17, 34] and denoising [16, 26, 35]. Recently, it is receiving increasing interest in relaxing the prerequisite of supervised learning with corrupted/ clean image pairs. In the context of image denoising, the \"corrupted/clean\" pair denotes a corrupted input image and its corresponding clean image for calculating the loss. To tackle the issue of the lack of clean data, several methods have been proposed, such as the Noise2Noise (N2N) method [16] and Recorrupted-to-Recorrupted (R2R) [26], which train deep networks on pairs of noisy images. Noise2Void (N2V) [13], Noise2Self (N2S) [4], and the method proposed by Laine et al. [15] are based on the blind-spot strategy that discards some pixels in the input and predicts them using the remaining. In the field" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12282" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 69, + 545, + 287 + ], + "blocks": [ + { + "bbox": [ + 48, + 69, + 545, + 287 + ], + "lines": [ + { + "bbox": [ + 48, + 69, + 545, + 287 + ], + "spans": [ + { + "bbox": [ + 48, + 69, + 545, + 287 + ], + "type": "image", + "image_path": "f5280f823dd4ee0c6858aa9cf449e00e93f57c914ccb8cfcfea437565f22fdfb.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "lines": [ + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "spans": [ + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": "Figure 2. Method Overview. This figure illustrates the main steps of our proposed method, MeD, which first generates scene features (cubes) and distortion features (cuboids). The colour of them indicates their image source. In the right section, the features are rearranged and utilised for the four forward paths, from top to bottom, which are the reconstructions of noise " + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "inline_equation", + "content": "(\\hat{\\eta}_1^k)" + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": ", scene " + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "inline_equation", + "content": "(\\hat{x}_2^k)" + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": ", input image " + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "inline_equation", + "content": "(y_2^k)" + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": " and shared scene " + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "inline_equation", + "content": "(\\hat{x}^k)" + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": ". It is noteworthy that " + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "inline_equation", + "content": "\\hat{y}_2^k" + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": " is reconstructed using " + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "inline_equation", + "content": "z_x^{k,1}" + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "inline_equation", + "content": "y_1^k" + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "inline_equation", + "content": "u_{\\eta}^{k,2}" + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "inline_equation", + "content": "y_2^k" + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": " for feature disentanglement. Additionally, the reconstruction of " + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "inline_equation", + "content": "\\hat{x}^k" + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": " relies on mixed scene features to facilitate learning of invariant scene latent. Moreover, the reconstruction paths for " + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "inline_equation", + "content": "(\\hat{\\eta}_2,\\hat{x}_1," + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "inline_equation", + "content": "y_{1})" + }, + { + "bbox": [ + 46, + 290, + 548, + 357 + ], + "type": "text", + "content": " are not depicted here, as they differ from the given paths only in their sub-indexes." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 376, + 287, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 376, + 287, + 411 + ], + "spans": [ + { + "bbox": [ + 46, + 376, + 287, + 411 + ], + "type": "text", + "content": "of single-image denoising, some methods such as DIP [29] and S2S [27], have achieved remarkable denoising results using only one noisy image." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 412, + 288, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 412, + 288, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 412, + 288, + 460 + ], + "type": "text", + "content": "These methods, however, often inevitably compromise image quality to noise reduction, resulting in over-smoothed output. This trade-off is further exacerbated under domain shifts when dealing with unknown noise distributions." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 479, + 287, + 610 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 479, + 287, + 610 + ], + "spans": [ + { + "bbox": [ + 46, + 479, + 287, + 610 + ], + "type": "text", + "content": "Restoration based on multiple views: Existing multiview variants of image restoration methods mainly focus on sequential data such as video or burst images. For example, Tico [28] builds a paradigm that separates the unique and common features within the multi-frame to produce a denoised estimate. Liu et al. [20] models degrading elements as foreground and estimate background using video data. Deep Burst Denoising (DBD) [11] performs multi-view denoising based on burst images. Each image is taken in a short exposure time and serves as a corrupted observation of the clean image." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 611, + 288, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 611, + 288, + 659 + ], + "spans": [ + { + "bbox": [ + 46, + 611, + 288, + 659 + ], + "type": "text", + "content": "Unlike the above-mentioned methods, our " + }, + { + "bbox": [ + 46, + 611, + 288, + 659 + ], + "type": "inline_equation", + "content": "MeD" + }, + { + "bbox": [ + 46, + 611, + 288, + 659 + ], + "type": "text", + "content": " aims to use multiple static observations simultaneously to learn the latent representation of a clean scene that is shared by multiple discrete views." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "content": "Self-supervised feature disentanglement: Another notable path of work has attempted to disentangle underlying invariant content from distorted images. For instance, " + }, + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "inline_equation", + "content": "UID" + }, + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "content": "-" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 376, + 545, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 376, + 545, + 435 + ], + "spans": [ + { + "bbox": [ + 304, + 376, + 545, + 435 + ], + "type": "text", + "content": "GAN [22] utilises unpaired clean/blurred images to disentangle content and blurring effects in the feature space and yield improved deblurring performance. Similarly, " + }, + { + "bbox": [ + 304, + 376, + 545, + 435 + ], + "type": "inline_equation", + "content": "LIR" + }, + { + "bbox": [ + 304, + 376, + 545, + 435 + ], + "type": "text", + "content": " [9] used unpaired input to isolate invariant content features through self-supervised inter-domain transformation." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 437, + 545, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 545, + 509 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 545, + 509 + ], + "type": "text", + "content": "However, these methods are limited to synthetic noise and do not extend well in real-world scenarios due to their reliance on clean images. In contrast, our method is purely based on multiple noisy views of the same static scene and aims to disentangle the scene from corruption, without the need for clean image supervision." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 523, + 389, + 537 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 523, + 389, + 537 + ], + "spans": [ + { + "bbox": [ + 306, + 523, + 389, + 537 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 544, + 545, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 544, + 545, + 652 + ], + "spans": [ + { + "bbox": [ + 304, + 544, + 545, + 652 + ], + "type": "text", + "content": "Our primary objective is to identify the commonalities among different views in the denoising process. To achieve this, we aim to discover the shared scene " + }, + { + "bbox": [ + 304, + 544, + 545, + 652 + ], + "type": "inline_equation", + "content": "z_{x}^{k}" + }, + { + "bbox": [ + 304, + 544, + 545, + 652 + ], + "type": "text", + "content": " that is degradation-agnostic over various corrupted views " + }, + { + "bbox": [ + 304, + 544, + 545, + 652 + ], + "type": "inline_equation", + "content": "\\{y_{i}^{k}\\}_{k\\in \\mathbb{N}}" + }, + { + "bbox": [ + 304, + 544, + 545, + 652 + ], + "type": "text", + "content": " via our proposed training schema, namely Multi-view self-supervised Disentanglement (MeD). A graphic depiction of MeD is shown in Figure 2, composed of the representation learning process in the left panel, and four distinct reconstruction pathways in the right panel." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 654, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 654, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 654, + 545, + 712 + ], + "type": "text", + "content": "The detailed design of the proposed schema will be introduced in the following subsections. Section 3.1 explains the restoration of noise and scene. Section 3.2 details the reconstruction of noisy input using a cross-feature combination. Section 3.3 elaborates on the reconstruction of the" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12283" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 176, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 176, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 176, + 83 + ], + "type": "text", + "content": "scene using mixed scene latent." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 84, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 84, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 47, + 84, + 287, + 120 + ], + "type": "text", + "content": "We will start our introduction by outlining three essential properties that a multi-view representation disentanglement technique should exhibit." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 134, + 287, + 170 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 134, + 287, + 170 + ], + "spans": [ + { + "bbox": [ + 47, + 134, + 287, + 170 + ], + "type": "text", + "content": "Pre-assumed properties: Suppose the scene latent space and corruption latent space are symbolised by " + }, + { + "bbox": [ + 47, + 134, + 287, + 170 + ], + "type": "inline_equation", + "content": "\\mathcal{Z}_x" + }, + { + "bbox": [ + 47, + 134, + 287, + 170 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 134, + 287, + 170 + ], + "type": "inline_equation", + "content": "\\mathcal{U}_{\\eta}" + }, + { + "bbox": [ + 47, + 134, + 287, + 170 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 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view " + }, + { + "bbox": [ + 50, + 263, + 287, + 323 + ], + "type": "inline_equation", + "content": "y_{i}^{k}" + }, + { + "bbox": [ + 50, + 263, + 287, + 323 + ], + "type": "text", + "content": " can be achieved using the feature pairs " + }, + { + "bbox": [ + 50, + 263, + 287, + 323 + ], + "type": "inline_equation", + "content": "z_{x}^{k}, u_{\\eta}^{k,i}" + }, + { + "bbox": [ + 50, + 263, + 287, + 323 + ], + "type": "text", + "content": ", and the index of the recovered view is determined by the index of the corruption latent, which represents the unique component within that particular view." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "spans": [ + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "type": "text", + "content": "A key step of our method is to realise these prerequisites by determining how to implement the latent space assumption. As shown in the left panel of Figure 2, to infer our latent space assumption, MeD is comprised of two encoders and three decoders: A shared content latent encoder " + }, + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "type": "inline_equation", + "content": "G_{\\theta}^{\\mathcal{X}}" + }, + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "type": "text", + "content": " and its decoder " + }, + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "type": "inline_equation", + "content": "D_{\\psi}^{\\mathcal{X}}" + }, + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "type": "text", + "content": ", an auxiliary noise latent encoder " + }, + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "type": "inline_equation", + "content": "E_{\\rho}^{\\mathcal{N}}" + }, + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "type": "text", + "content": " and its decoder " + }, + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "type": "inline_equation", + "content": "F_{\\phi}^{\\mathcal{N}}" + }, + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "type": "text", + "content": ", and a cross disentangle-ment decoder " + }, + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "type": "inline_equation", + "content": "R_{\\delta}^{\\mathcal{Y}}" + }, + { + "bbox": [ + 47, + 330, + 287, + 430 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 436, + 176, + 447 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 436, + 176, + 447 + ], + "spans": [ + { + "bbox": [ + 47, + 436, + 176, + 447 + ], + "type": "text", + "content": "3.1. Main Forward Process" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 454, + 287, + 491 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 454, + 287, + 491 + ], + "spans": [ + { + "bbox": [ + 47, + 454, + 287, + 491 + ], + "type": "text", + "content": "Given two corrupted views of the same image " + }, + { + "bbox": [ + 47, + 454, + 287, + 491 + ], + "type": "inline_equation", + "content": "x^{k}" + }, + { + "bbox": [ + 47, + 454, + 287, + 491 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 454, + 287, + 491 + ], + "type": "inline_equation", + "content": "y_{1}^{k} \\triangleq \\mathcal{T}_{1}(x^{k})" + }, + { + "bbox": [ + 47, + 454, + 287, + 491 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 454, + 287, + 491 + ], + "type": "inline_equation", + "content": "y_{2}^{k} \\triangleq \\mathcal{T}_{2}(x^{k})" + }, + { + "bbox": [ + 47, + 454, + 287, + 491 + ], + "type": "text", + "content": ", the encoder " + }, + { + "bbox": [ + 47, + 454, + 287, + 491 + ], + "type": "inline_equation", + "content": "G_{\\theta}^{\\mathcal{X}}" + }, + { + "bbox": [ + 47, + 454, + 287, + 491 + ], + "type": "text", + "content": " mainly perform the scene feature space encoding that can be formulated as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 97, + 500, + 287, + 515 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 500, + 287, + 515 + ], + "spans": [ + { + "bbox": [ + 97, + 500, + 287, + 515 + ], + "type": "interline_equation", + "content": "z _ {x} ^ {k, 1} \\triangleq G _ {\\theta} ^ {\\mathcal {X}} \\left(y _ {1} ^ {k}\\right), z _ {x} ^ {k, 2} \\triangleq G _ {\\theta} ^ {\\mathcal {X}} \\left(y _ {2} ^ {k}\\right), \\tag {5}", + "image_path": "48a3746c12ae546d32cb677b9e758bc42e06546da3d6751ba6decc75e23b8694.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 518, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ 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+ }, + { + "bbox": [ + 96, + 651, + 287, + 671 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 96, + 651, + 287, + 671 + ], + "spans": [ + { + "bbox": [ + 96, + 651, + 287, + 671 + ], + "type": "interline_equation", + "content": "u _ {n} ^ {k, 1} \\triangleq E _ {\\rho} ^ {\\mathcal {N}} \\left(y _ {1} ^ {k}\\right), u _ {n} ^ {k, 2} \\triangleq E _ {\\rho} ^ {\\mathcal {N}} \\left(y _ {2} ^ {k}\\right), \\tag {7}", + "image_path": "95c85cafb7d2525f1d6fcc6f982654dcd33634693c5fcf15bab30129354f2876.jpg" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 97, + 668, + 236, + 683 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 668, + 236, + 683 + ], + "spans": [ + { + "bbox": [ + 97, + 668, + 236, + 683 + ], + "type": "interline_equation", + "content": "\\hat {\\eta} _ {1} ^ {k} \\triangleq F _ {\\phi} ^ {\\mathcal {N}} \\left(u _ {n} ^ {k, 1}\\right), \\hat {\\eta} _ {2} ^ {k} \\triangleq F _ {\\phi} ^ {\\mathcal {N}} \\left(u _ {n} ^ {k, 2}\\right).", + "image_path": "6460590f7d72b6e2ca756a382c9635621df55ed7e9f21d32d0fa3357f50672e3.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "We adhere to the methodology introduced by N2N [16] to use noisy images as supervisory signals. The objective" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 72, + 545, + 95 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 95 + ], + "type": "text", + "content": "function of the aforementioned process can be simplified to:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 355, + 102, + 545, + 129 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 355, + 102, + 545, + 129 + ], + "spans": [ + { + "bbox": [ + 355, + 102, + 545, + 129 + ], + "type": "interline_equation", + "content": "\\underset {\\theta , \\psi} {\\operatorname {a r g m i n}} \\mathcal {L} ^ {\\mathcal {X}} \\triangleq | | \\hat {x} _ {1} ^ {k} - y _ {2} ^ {k} | |, \\tag {8}", + "image_path": "a2b2308d18d95462a75dbe041122fe7a7825039e9086456f778013fab56e15f7.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 357, + 120, + 545, + 148 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 357, + 120, + 545, + 148 + ], + "spans": [ + { + "bbox": [ + 357, + 120, + 545, + 148 + ], + "type": "interline_equation", + "content": "\\underset {\\rho , \\phi} {\\operatorname {a r g m i n}} \\mathcal {L} ^ {\\mathcal {N}} \\triangleq | | \\left(y _ {1} ^ {k} - \\hat {\\eta} _ {1} ^ {k}\\right) - y _ {2} ^ {k} | |. \\tag {8}", + "image_path": "894c5bbf4a463091aabe45c9a350f6f46cd52ec9cbe9bf26291d1b02a7a7e5d5.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 157, + 545, + 217 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 157, + 545, + 217 + ], + "spans": [ + { + "bbox": [ + 305, + 157, + 545, + 217 + ], + "type": "text", + "content": "The objective of " + }, + { + "bbox": [ + 305, + 157, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\hat{x}_2^k" + }, + { + "bbox": [ + 305, + 157, + 545, + 217 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 157, + 545, + 217 + ], + "type": "inline_equation", + "content": "\\hat{\\eta}_2^k" + }, + { + "bbox": [ + 305, + 157, + 545, + 217 + ], + "type": "text", + "content": " are the same as above, with only a subscript difference. It should be noted that, although our objective functions are similar to that of N2N, our goal is not simply to find and remove noise, but rather to capture the common features shared across multiple views." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 225, + 436, + 237 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 225, + 436, + 237 + ], + "spans": [ + { + "bbox": [ + 306, + 225, + 436, + 237 + ], + "type": "text", + "content": "3.2. Cross Disentanglement" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "spans": [ + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "text", + "content": "For general latent codes " + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "inline_equation", + "content": "z_{x}^{k}" + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "text", + "content": " to sufficiently represent scene information in the image space, it is natural to assume that these codes exhibit a certain degree of freedom, allowing them to intersect with the noise space. Consequently, there is no guarantee of complete isolation between " + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "inline_equation", + "content": "z_{x}^{k}" + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "inline_equation", + "content": "u_{\\eta}^{k}" + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "text", + "content": ". To meet the requirements of properties (1) and (3), we use an additional decoder " + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "inline_equation", + "content": "R_{\\delta}^{y}" + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "text", + "content": " to reconstruct a corrupted view over a cross-feature combination, e.g. " + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "inline_equation", + "content": "z_{x}^{k,1}" + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "inline_equation", + "content": "y_{1}" + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "inline_equation", + "content": "u_{n}^{k,2}" + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "inline_equation", + "content": "x_{2}" + }, + { + "bbox": [ + 305, + 243, + 545, + 350 + ], + "type": "text", + "content": ", which can be represented as:" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 335, + 360, + 545, + 375 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 335, + 360, + 545, + 375 + ], + "spans": [ + { + "bbox": [ + 335, + 360, + 545, + 375 + ], + "type": "interline_equation", + "content": "\\hat {y} _ {1} ^ {k} \\triangleq R _ {\\delta} ^ {\\mathcal {Y}} \\left(z _ {x} ^ {k, 2}, u _ {n} ^ {k, 1}\\right), \\hat {y} _ {2} ^ {k} \\triangleq R _ {\\delta} ^ {\\mathcal {Y}} \\left(z _ {x} ^ {k, 1}, u _ {n} ^ {k, 2}\\right). \\tag {9}", + "image_path": "7c9177ab6acecc0a35e3c4250d6a01f0297326734d13a6b2deea3187162d9a50.jpg" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 305, + 384, + 545, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 384, + 545, + 434 + ], + "spans": [ + { + "bbox": [ + 305, + 384, + 545, + 434 + ], + "type": "text", + "content": "This realisation explicitly requires " + }, + { + "bbox": [ + 305, + 384, + 545, + 434 + ], + "type": "inline_equation", + "content": "z_{x}^{k,i}" + }, + { + "bbox": [ + 305, + 384, + 545, + 434 + ], + "type": "text", + "content": " to represent the common part and " + }, + { + "bbox": [ + 305, + 384, + 545, + 434 + ], + "type": "inline_equation", + "content": "u_{n}^{k,j}" + }, + { + "bbox": [ + 305, + 384, + 545, + 434 + ], + "type": "text", + "content": " to represent the unique part within the corrupted views. We then optimise " + }, + { + "bbox": [ + 305, + 384, + 545, + 434 + ], + "type": "inline_equation", + "content": "\\{\\theta ,\\rho ,\\delta \\}" + }, + { + "bbox": [ + 305, + 384, + 545, + 434 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 305, + 384, + 545, + 434 + ], + "type": "inline_equation", + "content": "\\{G_{\\theta}^{\\mathcal{X}},E_{\\rho}^{\\mathcal{N}},R_{\\delta}^{\\mathcal{Y}}\\}" + }, + { + "bbox": [ + 305, + 384, + 545, + 434 + ], + "type": "text", + "content": " using the following objective:" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 343, + 442, + 545, + 464 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 442, + 545, + 464 + ], + "spans": [ + { + "bbox": [ + 343, + 442, + 545, + 464 + ], + "type": "interline_equation", + "content": "\\underset {\\theta , \\rho , \\delta} {\\operatorname {a r g m i n}} \\mathcal {L} ^ {\\mathcal {C}} \\triangleq | | \\hat {y} _ {1} ^ {k} - y _ {1} ^ {k} | | + | | \\hat {y} _ {2} ^ {k} - y _ {2} ^ {k} | |. \\tag {10}", + "image_path": "d4e491ac597e27c14c2a38a84991b7a9a24573ab9c289f6e1265312e4af20a52.jpg" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "text", + "content": "Generally, it is possible for there to be a trivial solution from " + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "inline_equation", + "content": "u_{n}^{k,i}" + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "inline_equation", + "content": "y_{i}^{k}" + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "text", + "content": " in Equation (9) such as, when " + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "inline_equation", + "content": "u_{n}^{k,1}" + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "text", + "content": " is extracted from " + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "inline_equation", + "content": "y_{1}^{k}" + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "text", + "content": " and used to reconstruct it as well. However, Equation (7) explicitly requires " + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "inline_equation", + "content": "u_{n}^{k,1}" + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "text", + "content": " to rebuild the noise, which prevents the collapse of " + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "inline_equation", + "content": "u_{n}^{k,1}" + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "text", + "content": " in expressing " + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "inline_equation", + "content": "y_{1}^{k}" + }, + { + "bbox": [ + 305, + 472, + 545, + 533 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 306, + 540, + 459, + 551 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 540, + 459, + 551 + ], + "spans": [ + { + "bbox": [ + 306, + 540, + 459, + 551 + ], + "type": "text", + "content": "3.3. Bernoulli Manifold Mixture" + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 305, + 558, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 558, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 305, + 558, + 545, + 665 + ], + "type": "text", + "content": "The aforementioned latent constraint might appear to be restricted at first, but in fact, it enables us to capture a large number of degrees of freedom in latent space implementation. For instance, it is possible to have multiple scene features that correspond to a single scene. However, in such cases, the mapping from input to scene features becomes ambiguous. To tackle this issue, we propose the use of the Bernoulli Manifold Mixture (BMM) as a means of leveraging the shared structure within the scene latent." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 305, + 666, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 666, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 305, + 666, + 545, + 712 + ], + "type": "text", + "content": "Given the assumption of property (2), the acquired scene features " + }, + { + "bbox": [ + 305, + 666, + 545, + 712 + ], + "type": "inline_equation", + "content": "z_{x}^{k,1}" + }, + { + "bbox": [ + 305, + 666, + 545, + 712 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 666, + 545, + 712 + ], + "type": "inline_equation", + "content": "z_{x}^{k,2}" + }, + { + "bbox": [ + 305, + 666, + 545, + 712 + ], + "type": "text", + "content": " are expected to be identical and interchangeable with one another, as they both refer to the same scene feature. BMM establishes a new explicit connection" + } + ] + } + ], + "index": 30 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12284" + } + ] + } + ], + "index": 31 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 96 + ], + "type": "text", + "content": "between the scene features of multi-views, which can be expressed in the equation as:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 118, + 104, + 287, + 119 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 118, + 104, + 287, + 119 + ], + "spans": [ + { + "bbox": [ + 118, + 104, + 287, + 119 + ], + "type": "interline_equation", + "content": "\\hat {z} _ {x} ^ {k} \\triangleq \\operatorname {M i x} _ {p} \\left(z _ {x} ^ {k, 1}, z _ {x} ^ {k, 2}\\right), \\tag {11}", + "image_path": "358877d880b48e7d566e511e2c361378aba35d63bb776962139dc13e838a5ca9.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 127, + 287, + 176 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 127, + 287, + 176 + ], + "spans": [ + { + "bbox": [ + 46, + 127, + 287, + 176 + ], + "type": "text", + "content": "where the " + }, + { + "bbox": [ + 46, + 127, + 287, + 176 + ], + "type": "inline_equation", + "content": "\\hat{z}_x^k" + }, + { + "bbox": [ + 46, + 127, + 287, + 176 + ], + "type": "text", + "content": " is an estimation of the true underlying scene feature. Let " + }, + { + "bbox": [ + 46, + 127, + 287, + 176 + ], + "type": "inline_equation", + "content": "b_{f}" + }, + { + "bbox": [ + 46, + 127, + 287, + 176 + ], + "type": "text", + "content": " define a sample instance drawn from a Bernoulli distribution with probability " + }, + { + "bbox": [ + 46, + 127, + 287, + 176 + ], + "type": "inline_equation", + "content": "p\\in (0,1)" + }, + { + "bbox": [ + 46, + 127, + 287, + 176 + ], + "type": "text", + "content": ", the function " + }, + { + "bbox": [ + 46, + 127, + 287, + 176 + ], + "type": "inline_equation", + "content": "\\mathrm{Mix}_p(\\cdot)" + }, + { + "bbox": [ + 46, + 127, + 287, + 176 + ], + "type": "text", + "content": " described in Equation (11) denotes:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 82, + 185, + 287, + 199 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 82, + 185, + 287, + 199 + ], + "spans": [ + { + "bbox": [ + 82, + 185, + 287, + 199 + ], + "type": "interline_equation", + "content": "\\operatorname {M i x} _ {p} (\\boldsymbol {m}, \\boldsymbol {n}) \\triangleq b _ {f} \\odot \\boldsymbol {m} + (1 - b _ {f}) \\odot \\boldsymbol {n}. \\tag {12}", + "image_path": "e5d94624c18538198d92b2f622196633a1b207db17079261597f5f36dfa6ea9f.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 208, + 287, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 208, + 287, + 243 + ], + "spans": [ + { + "bbox": [ + 46, + 208, + 287, + 243 + ], + "type": "text", + "content": "By establishing this new connection (Equation 11), we can enhance the interchangeability between " + }, + { + "bbox": [ + 46, + 208, + 287, + 243 + ], + "type": "inline_equation", + "content": "z_{x}^{k,1}" + }, + { + "bbox": [ + 46, + 208, + 287, + 243 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 208, + 287, + 243 + ], + "type": "inline_equation", + "content": "z_{x}^{k,2}" + }, + { + "bbox": [ + 46, + 208, + 287, + 243 + ], + "type": "text", + "content": " by optimising the reconstruction performance on " + }, + { + "bbox": [ + 46, + 208, + 287, + 243 + ], + "type": "inline_equation", + "content": "\\hat{z}_{x}^{k}" + }, + { + "bbox": [ + 46, + 208, + 287, + 243 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 243, + 287, + 278 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 243, + 287, + 278 + ], + "spans": [ + { + "bbox": [ + 46, + 243, + 287, + 278 + ], + "type": "text", + "content": "Lemma 1. Assuming " + }, + { + "bbox": [ + 46, + 243, + 287, + 278 + ], + "type": "inline_equation", + "content": "z_{x}^{k,i}\\sim N_{\\mathbf{x}}(\\boldsymbol {\\mu},\\boldsymbol {\\Sigma})" + }, + { + "bbox": [ + 46, + 243, + 287, + 278 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 243, + 287, + 278 + ], + "type": "inline_equation", + "content": "N_{\\mathbf{x}}" + }, + { + "bbox": [ + 46, + 243, + 287, + 278 + ], + "type": "text", + "content": " denotes multivariate Gaussian distributions and then " + }, + { + "bbox": [ + 46, + 243, + 287, + 278 + ], + "type": "inline_equation", + "content": "\\pmb{\\mu}" + }, + { + "bbox": [ + 46, + 243, + 287, + 278 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 243, + 287, + 278 + ], + "type": "inline_equation", + "content": "\\pmb{\\Sigma}" + }, + { + "bbox": [ + 46, + 243, + 287, + 278 + ], + "type": "text", + "content": " is the mean and the covariance matrix." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 45, + 278, + 287, + 304 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 278, + 287, + 304 + ], + "spans": [ + { + "bbox": [ + 45, + 278, + 287, + 304 + ], + "type": "text", + "content": "For a given function " + }, + { + "bbox": [ + 45, + 278, + 287, + 304 + ], + "type": "inline_equation", + "content": "G_{\\theta}^{\\mathcal{X}}(\\cdot)" + }, + { + "bbox": [ + 45, + 278, + 287, + 304 + ], + "type": "text", + "content": ", assume " + }, + { + "bbox": [ + 45, + 278, + 287, + 304 + ], + "type": "inline_equation", + "content": "\\forall k, i, m, n \\in \\mathbb{N}" + }, + { + "bbox": [ + 45, + 278, + 287, + 304 + ], + "type": "text", + "content": ", the following property holds:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 64, + 311, + 287, + 327 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 64, + 311, + 287, + 327 + ], + "spans": [ + { + "bbox": [ + 64, + 311, + 287, + 327 + ], + "type": "interline_equation", + "content": "\\mathbb {E} \\left[ G _ {\\theta} ^ {\\mathcal {X}} \\left(z _ {x} ^ {k, i}\\right) \\right] \\triangleq \\mathbb {E} \\left[ G _ {\\theta} ^ {\\mathcal {X}} \\left(\\operatorname {M i x} _ {p} \\left(z _ {x} ^ {k, m}, z _ {x} ^ {k, n}\\right)\\right) \\right]. \\tag {13}", + "image_path": "527ff6b97929f2ef141dd14a6309f77597e4bbcbf5d801d1375e423f8adc8fa9.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 334, + 287, + 358 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 334, + 287, + 358 + ], + "spans": [ + { + "bbox": [ + 46, + 334, + 287, + 358 + ], + "type": "text", + "content": "Proof. Assume " + }, + { + "bbox": [ + 46, + 334, + 287, + 358 + ], + "type": "inline_equation", + "content": "z_{x}^{k,m}, z_{x}^{k,n} \\in \\mathbb{R}^{\\dim}" + }, + { + "bbox": [ + 46, + 334, + 287, + 358 + ], + "type": "text", + "content": " are i.i.d., we may also factorise " + }, + { + "bbox": [ + 46, + 334, + 287, + 358 + ], + "type": "inline_equation", + "content": "b_{f} \\in \\mathbb{R}^{\\dim}" + }, + { + "bbox": [ + 46, + 334, + 287, + 358 + ], + "type": "text", + "content": ". Write" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 118, + 369, + 287, + 383 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 118, + 369, + 287, + 383 + ], + "spans": [ + { + "bbox": [ + 118, + 369, + 287, + 383 + ], + "type": "interline_equation", + "content": "\\hat {z} _ {x} ^ {k} \\triangleq \\operatorname {M i x} _ {p} \\left(z _ {x} ^ {k, m}, z _ {x} ^ {k, n}\\right) \\tag {14}", + "image_path": "c41e16943172477a18564728b0a4781876a161d9ac98fe366b8b8f0296fc338b.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 393, + 128, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 393, + 128, + 403 + ], + "spans": [ + { + "bbox": [ + 47, + 393, + 128, + 403 + ], + "type": "text", + "content": "so that we can have" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 63, + 411, + 287, + 441 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 63, + 411, + 287, + 441 + ], + "spans": [ + { + "bbox": [ + 63, + 411, + 287, + 441 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\hat {z} _ {x} \\sim N _ {\\mathbf {x}} \\left(\\left(b _ {f} + 1 - b _ {f}\\right) \\boldsymbol {\\mu}, \\left(b _ {f} ^ {2} + \\left(1 - b _ {f}\\right) ^ {2}\\right) \\boldsymbol {\\Sigma}\\right) \\tag {15} \\\\ \\sim N _ {\\mathbf {x}} (\\boldsymbol {\\mu}, \\boldsymbol {\\Sigma}) \\\\ \\end{array}", + "image_path": "30723ddc86af26ce13804be03cc921603a8120996b4553645466b1bb20e27f3a.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 451, + 287, + 477 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 451, + 287, + 477 + ], + "spans": [ + { + "bbox": [ + 46, + 451, + 287, + 477 + ], + "type": "text", + "content": "with the fact that Bernoulli sample " + }, + { + "bbox": [ + 46, + 451, + 287, + 477 + ], + "type": "inline_equation", + "content": "b_{f}^{2} = b_{f}" + }, + { + "bbox": [ + 46, + 451, + 287, + 477 + ], + "type": "text", + "content": ", the mixed feature " + }, + { + "bbox": [ + 46, + 451, + 287, + 477 + ], + "type": "inline_equation", + "content": "\\hat{z}_{x}" + }, + { + "bbox": [ + 46, + 451, + 287, + 477 + ], + "type": "text", + "content": " is in the same representation distribution as " + }, + { + "bbox": [ + 46, + 451, + 287, + 477 + ], + "type": "inline_equation", + "content": "z_{x}^{k,i}" + }, + { + "bbox": [ + 46, + 451, + 287, + 477 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 488, + 287, + 512 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 488, + 287, + 512 + ], + "spans": [ + { + "bbox": [ + 46, + 488, + 287, + 512 + ], + "type": "text", + "content": "In MeD, we denote " + }, + { + "bbox": [ + 46, + 488, + 287, + 512 + ], + "type": "inline_equation", + "content": "\\hat{z}_x = G_\\theta^\\chi (\\hat{z}_x^k)" + }, + { + "bbox": [ + 46, + 488, + 287, + 512 + ], + "type": "text", + "content": ", and the objective for implementing Equation (13) can be formulated as follows:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 85, + 521, + 287, + 542 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 85, + 521, + 287, + 542 + ], + "spans": [ + { + "bbox": [ + 85, + 521, + 287, + 542 + ], + "type": "interline_equation", + "content": "\\underset {\\theta , \\rho , \\psi} {\\operatorname {a r g m i n}} \\mathcal {L} ^ {\\mathcal {M}} \\triangleq \\lambda | | \\hat {z} _ {x} - \\operatorname {M i x} _ {p} \\left(y _ {1} ^ {k}, y _ {2} ^ {k}\\right) | |, \\tag {16}", + "image_path": "fdeb266597826f69d5ac661b29a73f145e13af496e4c3902c95fd9931a6bf399.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 551, + 287, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 551, + 287, + 598 + ], + "spans": [ + { + "bbox": [ + 46, + 551, + 287, + 598 + ], + "type": "text", + "content": "where the " + }, + { + "bbox": [ + 46, + 551, + 287, + 598 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 551, + 287, + 598 + ], + "type": "text", + "content": " is the weight parameter. Here, the target is using a mixed version of " + }, + { + "bbox": [ + 46, + 551, + 287, + 598 + ], + "type": "inline_equation", + "content": "y_1^k" + }, + { + "bbox": [ + 46, + 551, + 287, + 598 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 551, + 287, + 598 + ], + "type": "inline_equation", + "content": "y_2^k" + }, + { + "bbox": [ + 46, + 551, + 287, + 598 + ], + "type": "text", + "content": ". The choice of this is driven by the intuition that the hybrid version would better align with the aforementioned blended features." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 47, + 609, + 127, + 623 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 609, + 127, + 623 + ], + "spans": [ + { + "bbox": [ + 47, + 609, + 127, + 623 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "content": "To evaluate the effectiveness of our proposed method, we assess our method against several representative self-supervised denoising methods, including Noise2Noise (N2N) [16], Noise2Self (N2S) [4] and Recorrupted2Recorrupted (R2R) [26], and the invariant feature learning method LIR [9]. Moreover, we also evaluate our approach against two supervised baseline" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "methods (Noise2Clean (N2C) [21] and multi-frame method DBD [11]) to further validate its effectiveness. Comparisons to more methods, including methods using only one noisy image, are presented in the supplementary material." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 122, + 545, + 242 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 122, + 545, + 242 + ], + "spans": [ + { + "bbox": [ + 304, + 122, + 545, + 242 + ], + "type": "text", + "content": "We start our experiments by denoising synthetic additive white Gaussian noise (AWGN) in Section 4.2, and then move on to testing unseen noise levels and noise types in Section 4.3 and Section 4.4, respectively. Furthermore, we evaluate the performance in real-world scenarios in Section 4.5. In Section 4.6, we expand our experiments to incorporate more views to study their impact on performance. Finally, in Section 4.7, we apply our method to other tasks, e.g. image super-resolution and inpainting, to demonstrate its generalisation ability." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 255, + 426, + 268 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 255, + 426, + 268 + ], + "spans": [ + { + "bbox": [ + 305, + 255, + 426, + 268 + ], + "type": "text", + "content": "4.1. Experimental Setups" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 276, + 545, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 276, + 545, + 418 + ], + "spans": [ + { + "bbox": [ + 304, + 276, + 545, + 418 + ], + "type": "text", + "content": "Noted that, the nature of feature disentanglement requires no leak from input to output, however, the global residual connection of the original DnCNN [35] cannot satisfy. Thus, we incorporate the Swin-Transformer (Swin-T) [21] instead of the traditionally used DnCNN in our experiments. Nevertheless, as Swin-T is not originally designed for image restoration, we make some modifications to enforce local dependence across the image. Specifically, we add one Convolution Layer each before the patch embedding and after the patch unembedding of Swin-T, as inspired by SwinIR [18]. The resulting modified network backbone is denoted as Swin-Tx." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 422, + 545, + 565 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 422, + 545, + 565 + ], + "spans": [ + { + "bbox": [ + 304, + 422, + 545, + 565 + ], + "type": "text", + "content": "To ensure a fair comparison, we use the Swin-Tx backbone for all methods in our study, except for DBD. As DBD did not release the code, we follow the instructions presented in the paper and make our best effort to re-implement it. However, we observe that the two-view DBD could not converge efficiently, which is consistent with the findings in the paper. Therefore, we limit our evaluation to the four-view DBD, denoted as " + }, + { + "bbox": [ + 304, + 422, + 545, + 565 + ], + "type": "inline_equation", + "content": "\\mathrm{DBD}_4" + }, + { + "bbox": [ + 304, + 422, + 545, + 565 + ], + "type": "text", + "content": ". Furthermore, we replace the U-Net backbone originally used in the LIR method with Swin-Tx to maintain consistency in our evaluation. This results in an average improvement of approximately 1 dB in PSNR for Gaussian denoising." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 567, + 545, + 663 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 567, + 545, + 663 + ], + "spans": [ + { + "bbox": [ + 304, + 567, + 545, + 663 + ], + "type": "text", + "content": "In all experiments, all methods were trained using only DIV2K [3] and the same optimisation parameters, except for LIR and " + }, + { + "bbox": [ + 304, + 567, + 545, + 663 + ], + "type": "inline_equation", + "content": "\\mathrm{DBD}_4" + }, + { + "bbox": [ + 304, + 567, + 545, + 663 + ], + "type": "text", + "content": " which used manually selected parameters obtained through experiments. For more training and evaluation details including the choice of parameters, please refer to the supplementary material. Code is available at: https://github.com/chgwer2/Multi-view-Self-supervised-Disentanglement-Denoising." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "Remark: In tables, the best results are highlighted in bold, while the second best is underlined." + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12285" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 91, + 544, + 212 + ], + "blocks": [ + { + "bbox": [ + 47, + 69, + 545, + 90 + ], + "lines": [ + { + "bbox": [ + 47, + 69, + 545, + 90 + ], + "spans": [ + { + "bbox": [ + 47, + 69, + 545, + 90 + ], + "type": "text", + "content": "Table 1. Quantitative comparison of different methods on CBSD68 Dataset [23] for Synthetic Gaussian noise. The experiments were conducted on fixed and random variance, respectively. The best results are highlighted in bold, while the second best is underlined." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 91, + 544, + 212 + ], + "lines": [ + { + "bbox": [ + 49, + 91, + 544, + 212 + ], + "spans": [ + { + "bbox": [ + 49, + 91, + 544, + 212 + ], + "type": "table", + "html": "
Training SchemaTest \\(\\hat{\\sigma}\\)Noisy/ Clean N2C [21]\\(DBD_4\\) [11]N2N [16]Noisy/ Noisy N2S [4]R2R [26]Invariant Feature
LIR [9]MeD (ours)
Gaussian\\(\\sigma = 25\\)1533.36/0.902033.57/0.909232.64/0.880532.77/0.878029.74/0.786531.06/0.863233.11/0.8880
2530.83/0.849431.31/0.854830.68/0.833430.99/0.840530.45/0.818330.01/0.802430.57/0.8496
5024.76/0.551925.12/0.558324.59/0.538522.13/0.392824.02/0.513321.97/0.357825.67/0.6026
7520.75/0.337621.09/0.341220.60/0.316217.86/0.199819.10/0.264116.23/0.168923.09/0.4320
Gaussian\\(\\sigma \\in [5,50]\\)1533.47/0.902733.12/0.891533.45/0.894531.28/0.818720.76/0.250830.85/0.843133.62/0.9026
2530.87/0.853830.64/0.849130.77/0.842329.65/0.780123.91/0.455228.92/0.806930.91/0.8573
5027.41/0.736127.13/0.729027.15/0.721927.00/0.711426.92/0.691125.13/0.619127.48/0.7530
7525.05/0.622324.97/0.620524.80/0.590824.89/0.602323.83/0.513222.37/0.421225.40/0.6645
", + "image_path": "dff297503d973abe73449a6a25ecf1659ff9f40f7015ea5a4048dc1a3aa75c2c.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 49, + 243, + 544, + 340 + ], + "blocks": [ + { + "bbox": [ + 47, + 220, + 545, + 243 + ], + "lines": [ + { + "bbox": [ + 47, + 220, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 47, + 220, + 545, + 243 + ], + "type": "text", + "content": "Table 2. Quantitative result of generalisation performance experiment on CBSD68 [23]. All methods use Gaussian " + }, + { + "bbox": [ + 47, + 220, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\sigma = 25" + }, + { + "bbox": [ + 47, + 220, + 545, + 243 + ], + "type": "text", + "content": " for pre-trained methods and then Gaussian " + }, + { + "bbox": [ + 47, + 220, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\sigma \\in [5, 50]" + }, + { + "bbox": [ + 47, + 220, + 545, + 243 + ], + "type": "text", + "content": " for fine-turning. The better result in each method is highlighted in italics." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 243, + 544, + 340 + ], + "lines": [ + { + "bbox": [ + 49, + 243, + 544, + 340 + ], + "spans": [ + { + "bbox": [ + 49, + 243, + 544, + 340 + ], + "type": "table", + "html": "
Fine-tuning MethodN2C [21]N2N [16]LIR [9]MeD
Pretraining MethodN2CMeDN2NMeDLIRMeDMeD
Gaussian, δ ∈ [15, 75]29.20/ 0.779729.53/ 0.808129.04/ 0.764229.21/ 0.789026.42/ 0.664027.25/ 0.703629.60/ 0.8101
Local Var Gaussian35.62/ 0.930835.85/ 0.943935.66/ 0.925635.73/ 0.931029.26/ 0.817030.51/ 0.838735.91/ 0.9762
Poisson Noise40.49/ 0.973642.80/ 0.977641.35/ 0.973642.27/ 0.981331.23/ 0.867233.47/ 0.893245.05/ 0.9826
Speckle,帽子 ∈ [25, 50]33.36/ 0.900433.40/ 0.904433.32/ 0.893133.33/ 0.890728.28/ 0.771329.82/ 0.822933.48/ 0.9115
S&P,帽子 ∈ [0.3, 0.5]28.85/ 0.826730.73/ 0.837228.59/ 0.800329.45/ 0.825526.69/ 0.724127.62/ 0.746030.84/ 0.9135
Average33.50/ 0.882234.46/ 0.894233.59/ 0.871434.00/ 0.883528.38/ 0.768729.73/ 0.800934.98/ 0.9188
", + "image_path": "fb7436f383ebe17bff03774d1aaca4f5828b08178905a6cdf4b1f80b7b5491b1.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 358, + 176, + 370 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 358, + 176, + 370 + ], + "spans": [ + { + "bbox": [ + 47, + 358, + 176, + 370 + ], + "type": "text", + "content": "4.2. AWGN Noise Removal" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 377, + 287, + 472 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 377, + 287, + 472 + ], + "spans": [ + { + "bbox": [ + 46, + 377, + 287, + 472 + ], + "type": "text", + "content": "We first investigate the denoising generalisation of the methods using synthetic zero-mean additive white Gaussian noise (AWGN). The experiments are divided into two parts. The first segment employs fixed variance AWGN, whereas the second segment employs varied variance Gaussian for training in a separate manner. Table 1 summarises the quantitative results evaluated on CBSD68 Dataset [23] at variance levels of 15, 25, 50, and 75." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 473, + 287, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 473, + 287, + 579 + ], + "spans": [ + { + "bbox": [ + 46, + 473, + 287, + 579 + ], + "type": "text", + "content": "Analysis: In the fixed variance setting, MeD performs inferior compared to the other methods on lower noise levels of 15 and 25. However, as the methods face more severe corruption, MeD outperforms all self-supervised and supervised methods, showing our greater advantage of handling severe noise. For instance, at " + }, + { + "bbox": [ + 46, + 473, + 287, + 579 + ], + "type": "inline_equation", + "content": "\\sigma = 75" + }, + { + "bbox": [ + 46, + 473, + 287, + 579 + ], + "type": "text", + "content": ", MeD outperforms the second-best method (N2C) by around 2 dB. These results suggest that MeD has a remarkable ability to generalise to a range of unseen noise levels in Gaussian noise." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 581, + 287, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 581, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 581, + 287, + 664 + ], + "type": "text", + "content": "In the context of random variance, it has been observed that MeD exhibits superior performance across all four noise levels compared to other methods, including supervised methods. These findings imply that MeD can benefit more from varying training noise than other methods. More experiments and details on AWGN noise removal can be found in the supplementary material." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 671, + 262, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 671, + 262, + 683 + ], + "spans": [ + { + "bbox": [ + 47, + 671, + 262, + 683 + ], + "type": "text", + "content": "4.3. Generalisation on Unseen Noise Removal" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "In the previous subsection, we demonstrated the remarkable generalisation ability of our model in the case of Gaus" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 359, + 545, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 359, + 545, + 431 + ], + "spans": [ + { + "bbox": [ + 304, + 359, + 545, + 431 + ], + "type": "text", + "content": "sian noise. Here, we aim to extend this investigation to other types of unseen noise and evaluate the denoising generalisation ability of our method. Specifically, we consider Poisson noise, Speckle noise, Local Variance Gaussian noise, and Salt-and-Pepper noise. For a more detailed synthetic process, please refer to the supplementary material." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 434, + 546, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 434, + 546, + 602 + ], + "spans": [ + { + "bbox": [ + 304, + 434, + 546, + 602 + ], + "type": "text", + "content": "First, we demonstrate qualitative comparisons of denoising unseen noise types using models trained only with Gaussian " + }, + { + "bbox": [ + 304, + 434, + 546, + 602 + ], + "type": "inline_equation", + "content": "\\sigma = 25" + }, + { + "bbox": [ + 304, + 434, + 546, + 602 + ], + "type": "text", + "content": " in Figure 3. Next, in order to further verify the denoising generalisation ability of MeD, we employ its scene encoder and decoder as pre-trained models to be compared against other methods. It should be noted that the pre-training and fine-tuning methods employed in this study may differ, as shown in Table 2. The pre-training of all test models was conducted on a Gaussian sigma value of 25, followed by fine-tuning with a Gaussian sigma range of 5 to 50. Since the training schema of N2S, R2R, and DBD" + }, + { + "bbox": [ + 304, + 434, + 546, + 602 + ], + "type": "inline_equation", + "content": "_4" + }, + { + "bbox": [ + 304, + 434, + 546, + 602 + ], + "type": "text", + "content": " differs from MeD, we do not include them in this section. However, evaluations of these methods on unseen noise are still presented in Section 4.4 under different settings." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "Analysis: Qualitative results in Figure 3 show that under Gaussian " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\sigma = 25" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " training settings, our method surpasses other methods in denoising unseen noise types. Additionally, Table 2 shows that the approaches using pre-trained MeD models outperform their self-transfer models for N2C, N2N, and LIR, with improvements of up to " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "2\\mathrm{dB}" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " in some cases. On average, the MeD pre-trained models show a performance gain of around " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "0.5\\mathrm{dB}" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " across all methods, highlighting the potential of MeD as a powerful pre-training" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "12286" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 70, + 550, + 296 + ], + "blocks": [ + { + "bbox": [ + 55, + 70, + 550, + 296 + ], + "lines": [ + { + "bbox": [ + 55, + 70, + 550, + 296 + ], + "spans": [ + { + "bbox": [ + 55, + 70, + 550, + 296 + ], + "type": "image", + "image_path": "4a9364f18bf096a984a5c4830cf35849e87a10d646a1f08aa41fb34fbf6bcee9.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 299, + 546, + 322 + ], + "lines": [ + { + "bbox": [ + 46, + 299, + 546, + 322 + ], + "spans": [ + { + "bbox": [ + 46, + 299, + 546, + 322 + ], + "type": "text", + "content": "Figure 3. Qualitative denoising results on unseen noise types. All the methods are trained with Gaussian " + }, + { + "bbox": [ + 46, + 299, + 546, + 322 + ], + "type": "inline_equation", + "content": "\\sigma = 25" + }, + { + "bbox": [ + 46, + 299, + 546, + 322 + ], + "type": "text", + "content": ". The quantitative PSNR/SSIM results are provided underneath the respective images. Best viewed in colour (zoom-in for a better comparison)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 341, + 545, + 476 + ], + "blocks": [ + { + "bbox": [ + 66, + 330, + 522, + 340 + ], + "lines": [ + { + "bbox": [ + 66, + 330, + 522, + 340 + ], + "spans": [ + { + "bbox": [ + 66, + 330, + 522, + 340 + ], + "type": "text", + "content": "Table 3. Analysis of Noise Pool on CBSD68 [23]. All methods were trained using randomly drawn noise from the Noise Pool." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 341, + 545, + 476 + ], + "lines": [ + { + "bbox": [ + 50, + 341, + 545, + 476 + ], + "spans": [ + { + "bbox": [ + 50, + 341, + 545, + 476 + ], + "type": "table", + "html": "
Test NoiseNoisy/ CleanNoisy/ NoisyInvariant Feature
N2C [21]DBD4 [11]N2N [16]N2S [4]R2R [26]LIR [9]MeD (ours)
Gaussian, θ ∈ [15, 75]29.24/0.775429.05/0.761629.23/0.763428.58/0.758926.43/0.663926.67/0.686629.61/0.8178
Local Var Gaussian (LVG)36.64/0.944236.18/0.930736.65/0.923533.24/0.885834.70/0.877931.61/0.862737.99/0.9568
Poisson Noise45.72/0.976444.23/0.960645.64/0.979946.31/0.980844.45/0.949143.27/0.929248.10/0.9916
Speckle, v ∈ [25, 50]35.58/0.941735.24/0.938535.34/0.947535.13/0.959634.20/0.907833.98/0.881037.21/0.9715
S&P, r ∈ [0.3, 0.5]38.85/0.916537.10/0.888438.89/0.928938.22/0.933036.17/0.908733.43/0.820242.33/0.9695
Gaussian θ = 25 + Speckle v = 2530.19/0.827929.24/0.815630.32/0.831729.51/0.805028.78/0.774429.20/0.787131.92/0.8726
Gaussian θ = 50 + Speckle v = 2527.30/0.725126.55/0.712627.23/0.733126.91/0.708126.49/0.693526.19/0.694129.68/0.7928
LVG + Poisson31.78/0.908731.10/0.884231.60/0.761730.15/0.808628.52/0.714427.33/0.723434.29/0.9325
Poisson + Speckle v = 2531.39/0.906930.86/0.878231.52/0.893530.58/0.906730.34/0.889729.93/0.855433.04/0.9258
Average34.08/0.880333.28/0.863434.05/0.862633.18/0.860732.23/0.819931.29/0.804436.02/0.9145
", + "image_path": "fa241e2d6e0d12ab1e1999d02c59bd66e2027ce208f4f6ce07c2591d03967768.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 497, + 287, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 497, + 287, + 581 + ], + "spans": [ + { + "bbox": [ + 46, + 497, + 287, + 581 + ], + "type": "text", + "content": "method for image denoising. It is noteworthy that the self-transfer MeD model exhibits the best denoising performance across all validation noise types, even outperforming the supervised method, N2C. This is particularly evident in Poisson noise, where MeD surpasses N2C by " + }, + { + "bbox": [ + 46, + 497, + 287, + 581 + ], + "type": "inline_equation", + "content": "\\sim 3" + }, + { + "bbox": [ + 46, + 497, + 287, + 581 + ], + "type": "text", + "content": " dB. These results highlight the generalisation ability of our approach in handling unseen noise." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 587, + 235, + 600 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 587, + 235, + 600 + ], + "spans": [ + { + "bbox": [ + 47, + 587, + 235, + 600 + ], + "type": "text", + "content": "4.4. Experiments on General Noise Pool" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 605, + 287, + 700 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 700 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 700 + ], + "type": "text", + "content": "Here we further investigate the generalisation ability of our method by introducing our general Noise Pool. The Noise Pool comprises the five aforementioned types of noise, each with a diverse range of noise levels. During training, we randomly sample from the noise pool to provide the model with noisy images. This novel approach simulates a realistic scenario where noise is unknown and can originate from various sources to some extent." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 59, + 701, + 287, + 713 + ], + "type": "text", + "content": "Specifically, we evaluated all methods using the random" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 498, + 545, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 498, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 306, + 498, + 545, + 521 + ], + "type": "text", + "content": "noise pool approach to train and test on combined or single noise types. The results are summarised in Table 3." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": "Analysis: In Table 3, our MeD approach outperforms all other methods significantly on all the test noise types. For example, when a test noise containing a combination of Gaussian noise with " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\hat{\\sigma} = 50" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " and Speckle noise with " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\hat{v} = 25" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " is used, other methods exhibit an approximate performance of " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "\\sim 27" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " dB. However, MeD achieves significantly better results with a performance of " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "29.68\\mathrm{dB}" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": ". And on average, MeD exhibits a performance that is approximately " + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "inline_equation", + "content": "2\\mathrm{dB}" + }, + { + "bbox": [ + 304, + 545, + 546, + 713 + ], + "type": "text", + "content": " better than other methods. Our findings show that utilising a comprehensive noise pool for training purposes can effectively improve the generalisation capability. Furthermore, the remarkable denoising generalisation ability of our MeD approach, in comparison to other methods, is particularly advantageous for real-world applications." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12287" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 60, + 70, + 242, + 205 + ], + "blocks": [ + { + "bbox": [ + 60, + 70, + 242, + 205 + ], + "lines": [ + { + "bbox": [ + 60, + 70, + 242, + 205 + ], + "spans": [ + { + "bbox": [ + 60, + 70, + 242, + 205 + ], + "type": "image", + "image_path": "299f035bc59010939b024056417be746ecac205818020c263c2b6282b2a66236.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 127, + 209, + 176, + 217 + ], + "lines": [ + { + "bbox": [ + 127, + 209, + 176, + 217 + ], + "spans": [ + { + "bbox": [ + 127, + 209, + 176, + 217 + ], + "type": "text", + "content": "23.68/0.2967" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 60, + 232, + 242, + 369 + ], + "blocks": [ + { + "bbox": [ + 84, + 220, + 220, + 230 + ], + "lines": [ + { + "bbox": [ + 84, + 220, + 220, + 230 + ], + "spans": [ + { + "bbox": [ + 84, + 220, + 220, + 230 + ], + "type": "text", + "content": "Noisy Image from SIDD [1] (ISO 800)" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 60, + 232, + 242, + 369 + ], + "lines": [ + { + "bbox": [ + 60, + 232, + 242, + 369 + ], + "spans": [ + { + "bbox": [ + 60, + 232, + 242, + 369 + ], + "type": "image", + "image_path": "31984eba46abcda06654c2f4af62a408c6e45f7205ab8dcca7ea01208262e6fc.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 127, + 372, + 176, + 380 + ], + "lines": [ + { + "bbox": [ + 127, + 372, + 176, + 380 + ], + "spans": [ + { + "bbox": [ + 127, + 372, + 176, + 380 + ], + "type": "text", + "content": "25.33/0.3865" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 108, + 384, + 195, + 393 + ], + "lines": [ + { + "bbox": [ + 108, + 384, + 195, + 393 + ], + "spans": [ + { + "bbox": [ + 108, + 384, + 195, + 393 + ], + "type": "text", + "content": "Noisy Image from SIDD" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 397, + 545, + 420 + ], + "lines": [ + { + "bbox": [ + 46, + 397, + 545, + 420 + ], + "spans": [ + { + "bbox": [ + 46, + 397, + 545, + 420 + ], + "type": "text", + "content": "Figure 4. Real Noise Removal Example of SIDD [1]. All the methods are trained with Noise Pool on the DIV2K [2] dataset. It can be seen that the proposed MeD can remove much real noise even without training with real-noise distribution (zoom in for a better comparison)." + } + ] + } + ], + "index": 54, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 243, + 71, + 315, + 125 + ], + "blocks": [ + { + "bbox": [ + 243, + 71, + 315, + 125 + ], + "lines": [ + { + "bbox": [ + 243, + 71, + 315, + 125 + ], + "spans": [ + { + "bbox": [ + 243, + 71, + 315, + 125 + ], + "type": "image", + "image_path": "4208278d4294533f2e701c41092cd0e0a448ffedb407ef11e0f940e44e916669.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 256, + 129, + 304, + 137 + ], + "lines": [ + { + "bbox": [ + 256, + 129, + 304, + 137 + ], + "spans": [ + { + "bbox": [ + 256, + 129, + 304, + 137 + ], + "type": "text", + "content": "PSNR/ SSIM" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + 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Quantitative result obtained from the application of various methods trained on a general Noise Pool to real noise datasets." + } + ] + } + ], + "index": 55, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 459, + 287, + 540 + ], + "lines": [ + { + "bbox": [ + 49, + 459, + 287, + 540 + ], + "spans": [ + { + "bbox": [ + 49, + 459, + 287, + 540 + ], + "type": "table", + "html": "
MethodPolyU [32]SIDD [1]CC [24]Average
N2C [21]35.89/0.965230.37/0.602837.89/0.940834.72/0.8363
DBD4 [11]35.69/0.957130.23/0.617337.74/0.935734.55/0.8367
N2N [16]36.22/0.967932.82/0.729737.39/0.957035.48/0.8849
N2S [4]36.41/0.972130.98/0.601837.58/0.962234.99/0.8454
R2R [26]34.58/0.889029.64/0.570835.35/0.847833.19/0.7692
LIR [9]34.81/0.727828.76/0.529635.50/0.840333.02/0.6992
MeD (ours)38.65/0.985535.81/0.827840.08/0.974538.18/0.9293
", + "image_path": "0e953a78bdb8b19a6960a703f3ac23e84ba5d4518c0fc52b9c7c8f75718ea22c.jpg" + } + ] + } + ], + "index": 56, + "angle": 0, + "type": "table_body" + } + ], + "index": 56 + }, + { + "bbox": [ + 47, + 562, + 163, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 562, + 163, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 562, + 163, + 574 + ], + "type": "text", + "content": "4.5. Real Noise Removal" + } + ] + } + ], + "index": 57 + }, + { + "bbox": [ + 46, + 582, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 287, + 713 + ], + "type": "text", + "content": "In our previous experiments, we demonstrated the exceptional denoising performance of our MeD approach on synthetic noises. However, real-world noise is often more complex and challenging than synthetic noise. In this subsection, we aim to evaluate the generalisation performance of our approach on real-world noise by testing it on the SIDD [1], CC [24] and PolyU [32] datasets. To assess the denoising performance on real-world noise, we use the same pre-trained models as in Section 4.4. The representative qualitative results on the SIDD dataset in the standard RGB colour space are presented in Figure 4." + } + ] + } + ], + "index": 58 + }, + { + "bbox": [ + 304, + 440, + 545, + 524 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 440, + 545, + 524 + ], + "spans": [ + { + "bbox": [ + 304, + 440, + 545, + 524 + ], + "type": "text", + "content": "Analysis: As shown in Table 4, our approach significantly outperforms all other methods across all three datasets, with a performance improvement of 2-3 dB over the second-best approach, and also consistently outperforms its supervised counterparts (i.e. N2C and " + }, + { + "bbox": [ + 304, + 440, + 545, + 524 + ], + "type": "inline_equation", + "content": "\\mathrm{DBD}_4" + }, + { + "bbox": [ + 304, + 440, + 545, + 524 + ], + "type": "text", + "content": ") by over 3 dB. These results suggest the effectiveness and generalisability of the proposed approach in real-world denoising scenarios." + } + ] + } + ], + "index": 59 + }, + { + "bbox": [ + 304, + 529, + 545, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 529, + 545, + 613 + ], + "spans": [ + { + "bbox": [ + 304, + 529, + 545, + 613 + ], + "type": "text", + "content": "Our approach achieves remarkable performance on real-world noise without even being trained on more expensive real-world data. For a more complete study, we also conduct experiments on model training with real-world data (for more details please refer to the supplementary material), showing superior performance and even better generalisation ability to data out of the training data distribution." + } + ] + } + ], + "index": 60 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "In Figure 4, the presence of noise persists even after applying denoising techniques, yet ours demonstrates the most authentic outcomes compared to others. For instance, while the noise particles remain prominent in the N2C results, they are absent in our results. Overall, the results indicate that the MeD approach is well-suited for real-world denoising tasks, providing a robust and reliable solution for" + } + ] + } + ], + "index": 61 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12288" + } + ] + } + ], + "index": 62 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 80, + 286, + 118 + ], + "blocks": [ + { + "bbox": [ + 48, + 69, + 279, + 79 + ], + "lines": [ + { + "bbox": [ + 48, + 69, + 279, + 79 + ], + "spans": [ + { + "bbox": [ + 48, + 69, + 279, + 79 + ], + "type": "text", + "content": "Table 5. Multiple views ( " + }, + { + "bbox": [ + 48, + 69, + 279, + 79 + ], + "type": "inline_equation", + "content": "\\geq 2" + }, + { + "bbox": [ + 48, + 69, + 279, + 79 + ], + "type": "text", + "content": " ) study,with average PSNR/SSIM." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 80, + 286, + 118 + ], + "lines": [ + { + "bbox": [ + 49, + 80, + 286, + 118 + ], + "spans": [ + { + "bbox": [ + 49, + 80, + 286, + 118 + ], + "type": "table", + "html": "
#ViewsGaussianLVGPoissonSpeckleS&P
229.61/0.817837.99/0.956848.10/0.991637.21/0.971542.33/0.9695
329.68/0.819738.05/0.957748.23/0.992037.40/0.973342.45/0.9703
429.70/0.820438.08/0.958048.31/0.992137.47/0.974042.49/0.9709
", + "image_path": "794b2efd69f1da9a81ff47dd28c2f802354860cae14c74fd9a7352a0b7430f0f.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 49, + 150, + 285, + 196 + ], + "blocks": [ + { + "bbox": [ + 48, + 128, + 286, + 149 + ], + "lines": [ + { + "bbox": [ + 48, + 128, + 286, + 149 + ], + "spans": [ + { + "bbox": [ + 48, + 128, + 286, + 149 + ], + "type": "text", + "content": "Table 6. Average PSNR/SSIM of super-resolution results on Set5 [6]. Learning-based methods are trained with Corruption Pool." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 150, + 285, + 196 + ], + "lines": [ + { + "bbox": [ + 49, + 150, + 285, + 196 + ], + "spans": [ + { + "bbox": [ + 49, + 150, + 285, + 196 + ], + "type": "table", + "html": "
ScaleBicubicRCAN [37]DASR [30]MeD (ours)
×233.63/ 0.928536.12/ 0.933936.98/ 0.947137.12/ 0.9527
×330.37/ 0.865234.15/ 0.928634.11/ 0.918734.92/ 0.9294
×428.35/ 0.808431.94/ 0.887131.54/ 0.873632.50/ 0.8956
", + "image_path": "5fe4300a3ea61f811cafd3d0bfccf6dfbb657460b1c876bc22a5e7c65c25dab0.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 217, + 266, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 217, + 266, + 228 + ], + "spans": [ + { + "bbox": [ + 47, + 217, + 266, + 228 + ], + "type": "text", + "content": "improving image quality in challenging environments." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 236, + 177, + 248 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 236, + 177, + 248 + ], + "spans": [ + { + "bbox": [ + 47, + 236, + 177, + 248 + ], + "type": "text", + "content": "4.6. Expand to More Views" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 254, + 286, + 313 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 254, + 286, + 313 + ], + "spans": [ + { + "bbox": [ + 46, + 254, + 286, + 313 + ], + "type": "text", + "content": "Although we only showcase two views for the experiments above, our method can be easily expanded to multiple views. To investigate the impact of the numbers of views, here we further conduct a study comparing 2, 3, and 4 views, in Table 5." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 314, + 286, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 314, + 286, + 422 + ], + "spans": [ + { + "bbox": [ + 46, + 314, + 286, + 422 + ], + "type": "text", + "content": "The results indicate that increasing the number of views consistently improves the performance across different noise types. For example, when dealing with Speckle noise, the 4-view model achieves a " + }, + { + "bbox": [ + 46, + 314, + 286, + 422 + ], + "type": "inline_equation", + "content": "0.26\\mathrm{dB}" + }, + { + "bbox": [ + 46, + 314, + 286, + 422 + ], + "type": "text", + "content": " higher PSNR than the 2-view model. However, it is worth noting that employing " + }, + { + "bbox": [ + 46, + 314, + 286, + 422 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 314, + 286, + 422 + ], + "type": "text", + "content": " views requires " + }, + { + "bbox": [ + 46, + 314, + 286, + 422 + ], + "type": "inline_equation", + "content": "n!" + }, + { + "bbox": [ + 46, + 314, + 286, + 422 + ], + "type": "text", + "content": " cross-computations within each view pair during training, resulting in a significant increase in computational cost (e.g. from 2-view to 4-view leads to a " + }, + { + "bbox": [ + 46, + 314, + 286, + 422 + ], + "type": "inline_equation", + "content": "10\\times" + }, + { + "bbox": [ + 46, + 314, + 286, + 422 + ], + "type": "text", + "content": " training time increase in our experiment)." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 429, + 211, + 442 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 429, + 211, + 442 + ], + "spans": [ + { + "bbox": [ + 47, + 429, + 211, + 442 + ], + "type": "text", + "content": "4.7. More Application Exploration" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 448, + 286, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 448, + 286, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 448, + 286, + 544 + ], + "type": "text", + "content": "Here we investigate the potential of the proposed MeD for other more general image restoration tasks, such as image super-resolution and inpainting. In this study, we generalise the previously defined degradation (noise) to a residual image between a clean image and a corrupted image. Moreover, we expand the definition from Noise Pool to a more general one - Corruption Pool that contains not only noise but also general corruption." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 558, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 286, + 713 + ], + "type": "text", + "content": "Super resolution. Image super-resolution aims to enlarge the resolution of a low-resolution image. We train our method on the DIV2K dataset [3], where we randomly choose different downscale methods from a Corruption Pool that consists of random Gaussian noise and four types of down-scaling (bicubic, lanczos, bilinear, and hamming). We benchmark our method against the supervised method RCAN [37] that aims for high PSNR and the recent unsupervised methods DASR [30] that are specialised for superresolution. We conduct our evaluation on the Set5 dataset [6] with scaling factors of 2, 3, and 4. The results in Table 6 show the effectiveness of our method over both supervised and unsupervised approaches." + } + ] + } + ], + "index": 10 + }, + { + "type": "table", + "bbox": [ + 314, + 106, + 538, + 159 + ], + "blocks": [ + { + "bbox": [ + 305, + 68, + 545, + 102 + ], + "lines": [ + { + "bbox": [ + 305, + 68, + 545, + 102 + ], + "spans": [ + { + "bbox": [ + 305, + 68, + 545, + 102 + ], + "type": "text", + "content": "Table 7. Average PSNR/SSIM of inpainting results on Set11 [29]. S2S and DIP are trained and tested on the same single image. MeD is trained with Corruption Pool." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 314, + 106, + 538, + 159 + ], + "lines": [ + { + "bbox": [ + 314, + 106, + 538, + 159 + ], + "spans": [ + { + "bbox": [ + 314, + 106, + 538, + 159 + ], + "type": "table", + "html": "
Dropping RatioDIP [29]S2S [27]MeD (Ours)
50%33.45/ 0.921734.91/ 0.947936.24/ 0.9617
70%28.53/ 0.850130.94/ 0.884531.05/ 0.9161
90%24.39/ 0.736025.97/ 0.793326.01/ 0.8052
", + "image_path": "7c91730d6cda630aa5cfbb1cf8fe6423527f22f8cd4f59504f1e2656e469549b.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_body" + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 184, + 545, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 184, + 545, + 316 + ], + "spans": [ + { + "bbox": [ + 304, + 184, + 545, + 316 + ], + "type": "text", + "content": "Inpainting. We also apply our method to the image inpainting task, which fills in missing pixels. We choose two single-image deep learning methods - Self2Self (S2S) [27] and DIP [29], for comparison. Our MeD is trained with Corruption Pool containing noises, down-scaling, and inpainting mask operations altogether. To compare our method (MeD) with other state-of-the-art methods, we conduct experiments on the Set 11 dataset [29] with three different pixel dropping ratios: " + }, + { + "bbox": [ + 304, + 184, + 545, + 316 + ], + "type": "inline_equation", + "content": "50\\%" + }, + { + "bbox": [ + 304, + 184, + 545, + 316 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 184, + 545, + 316 + ], + "type": "inline_equation", + "content": "70\\%" + }, + { + "bbox": [ + 304, + 184, + 545, + 316 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 184, + 545, + 316 + ], + "type": "inline_equation", + "content": "90\\%" + }, + { + "bbox": [ + 304, + 184, + 545, + 316 + ], + "type": "text", + "content": ". The results are shown in Table 7, suggesting the effectiveness of MeD again in the image inpainting task." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 332, + 378, + 344 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 332, + 378, + 344 + ], + "spans": [ + { + "bbox": [ + 306, + 332, + 378, + 344 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 354, + 545, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 354, + 545, + 570 + ], + "spans": [ + { + "bbox": [ + 304, + 354, + 545, + 570 + ], + "type": "text", + "content": "In this paper, we have presented a new self-supervised learning method (MeD) for image denoising that disentangles scene and noise features in a constraint feature space. Our approach has demonstrated exceptional denoising performance in both synthetic and real-world noise scenarios, with particularly significant performance on real-world noise. MeD can handle complex noise with better performance than other state-of-the-art methods, as validated by consistent performance gain across various datasets and noise types. Our approach has decent generalisation ability, requiring only noisy images for training and efficiently denoising real-world noise without seeing any clean ground truth data. This opens up new possibilities for training deep models without the need for costly labelled data. Furthermore, our model can be easily adapted to other low-level image restoration tasks. We hope this could provide a new baseline for future research in image disentanglement and the extension to other image processing tasks." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 583, + 395, + 596 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 583, + 395, + 596 + ], + "spans": [ + { + "bbox": [ + 306, + 583, + 395, + 596 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 603, + 545, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 603, + 545, + 688 + ], + "spans": [ + { + "bbox": [ + 304, + 603, + 545, + 688 + ], + "type": "text", + "content": "The computations described in this research were performed using the Baskerville Tier 2 HPC service1. Baskerville was funded by the EPSRC and UKRI through the World Class Labs scheme (EP/T022221/1) and the Digital Research Infrastructure programme (EP/W032244/1) and is operated by Advanced Research Computing at the University of Birmingham." + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 317, + 702, + 421, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 702, + 421, + 712 + ], + "spans": [ + { + "bbox": [ + 317, + 702, + 421, + 712 + ], + "type": "inline_equation", + "content": "^{1}" + }, + { + "bbox": [ + 317, + 702, + 421, + 712 + ], + "type": "text", + "content": "https://www.baskerville.ac.uk/" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "12289" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 16, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "text", + "content": "[1] Abdelrahman Abdelhamed, Stephen Lin, and Michael S Brown. 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A comparison of PGVS-Net on 3 selected frames from an RGB-P video sequence from our novel PGV-117 dataset against the method of Kalra et al. [14] and Mei et al. [29]. From left to right: RGB, AoLP, and DoLP input images; glass segmentation results for selected frames compared to the ground truth segmentation; evolution of error over the video sequence. Both prior methods are temporally unstable due to significant temporal changes in DoLP. In contrast, PGVS-Net combines multi-view polarization cues for segmentation propagation, yielding a temporally stable glass segmentation." + ], + "image_footnote": [], + "bbox": [ + 98, + 250, + 186, + 414 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/3f0df20144e61073f3d040f6b96ecc57abda7f0f1a987882202519033bc25e60.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 187, + 250, + 313, + 412 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/fe65343d1967c92816e10569d69d96401ecf06529e215c9da172fa3e6f00f5e2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 316, + 251, + 467, + 412 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/4ac587f36162d38706fae31e2e692179930fa8211c322e1d10369f6e45985c65.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 467, + 251, + 617, + 412 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e146953f12cd463233e284809489f94f4acfef84d3bbb30064eac5176319c0a1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 619, + 258, + 870, + 414 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 521, + 313, + 536 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "In this paper, we present the first polarization-guided video glass segmentation propagation solution (PGVS-Net) that can robustly and coherently propagate glass segmentation in RGB-P video sequences. By leveraging spatiotemporal polarization and color information, our method combines multi-view polarization cues and thus can alleviate the view dependence of single-input intensity variations on glass objects. We demonstrate that our model can outperform glass segmentation on RGB-only video sequences as well as produce more robust segmentation than per-frame RGB-P single-image segmentation methods. To train and validate PGVS-Net, we introduce a novel RGB-P Glass Video dataset (PGV-117) containing 117 video sequences of scenes captured with different types of camera paths, lighting conditions, dynamics, and glass types.", + "bbox": [ + 75, + 551, + 472, + 781 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 806, + 209, + 821 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Transparent objects, such as glass, are common in man-made environments. Despite their prevalence, such objects pose numerous challenges for industrial and academic", + "bbox": [ + 75, + 833, + 470, + 878 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "vision processing algorithms due to their view-dependent appearance, statistical similarity to the background environment, and lack of texture. These challenges are particularly acute for segmentation tasks that underpin autonomous driving, robotics, and aerial drone navigation. Traditional learning-based solutions [8, 30, 50, 51] that rely on RGB textures for feature extraction often fail to adequately model the illumination and view-dependent glass features. Consequently, recent advances have explored richer modalities such as light fields [44] and polarization [14, 18, 21, 29, 46, 49] for more robust segmentation of glass objects. Polarization has proven to be a strong cue for glass segmentation in still images [14, 29]. The availability of commercial off-the-shelf RGB-P cameras (e.g., Flir and Lucid), makes this last category an attractive modality for glass segmentation.", + "bbox": [ + 500, + 522, + 892, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Polarization of reflected light depends on various factors such as surface normals, material types, and illumination and view directions [2]. Due to the polarimetric near-specular behavior, glass materials are particularly challenging; small changes in object orientation and/or view/light direction can induce a rapid change in polarization state. For example, consider the glass areas '1' in Figure 2 that show a glass door in various stages of being closed. In this example, the RGB textures remain almost unchanged, but", + "bbox": [ + 496, + 763, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding authors.", + "bbox": [ + 94, + 887, + 227, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "23218", + "bbox": [ + 478, + 924, + 519, + 936 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/a811fc1ed27b676cb74968e09efb14db1cb6d7d431b772097b6cb59e2f32f698.jpg", + "image_caption": [ + "Figure 2. Representative exemplars from the PGV-117 dataset containing a total of 117 video sequences captured with a variety of camera movement patterns, lighting conditions, scene dynamics, and materials. Glass areas '1' depict a door in various stages of being closed. Glass areas '2' are captured by moving the camera." + ], + "image_footnote": [], + "bbox": [ + 80, + 89, + 470, + 465 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "changes in the surface normal induce a significant decrease in the Angle of Linear Polarization (AoLP) from close to $\\pi$ (red-blue mixture) to less than half $\\pi$ (full blue), and a noticeable reduction in the Degree of Linear Polarization (DoLP) from 0.137 to 0.043. Similarly, moving the camera will induce a similar change in the polarization (e.g., the glass areas '2' in Figure 2). These observations suggest that polarization cues are beneficial for glass segmentation and can provide additional guidance. Furthermore, the DOLP in glass area '1' is unstable across the entire span of the video sequence, with noticeable DoLP reductions at specific angles of incidence ( $\\rho = 0.043$ ). Such types of instabilities can confuse methods [14, 29] that only rely on a single-frame RGB-P as input (Figure 1, right). Moreover, extracting glass features from RGB textures or polarization cues from a single view may also be difficult (e.g., under low light conditions as in Figure 1 left). As a consequence, polarization cues that are robust for static single image segmentation methods, can still yield temporally disjoint and inconsistent segmentation results when applied to", + "bbox": [ + 75, + 598, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "video sequences, especially when object orientation and/or viewpoint changes.", + "bbox": [ + 498, + 90, + 890, + 121 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we introduce a Polarization Video Glass Segmentation network (PGVS-Net) to robustly and coherently propagate an initial glass segmentation mask over an RGB-P video sequence. PGVS-Net perceives multi-view polarimetric features from long-range memory and short-range integration. A variation of the Spatio-Temporal Memory network (STM) [33] is introduced to leverage spectral polarization cues for constructing long-range view dependency. A well-designed Polarization-Guide Integration module (PGI) is responsible for the frame identity and historical polarization matching. Furthermore, a novel Polarization Temporal Forward module (PTF) integrates previous polarization cues to promote short-range spectral consistency during the decoder process. We also leverage cross-modal and cross-temporal attention (CMTA) to integrate multimodal features and temporal representations from different frames. To train and test PGVS-Net, we capture and annotate a large-scale video glass segmentation dataset, PGV-117, which includes 21,485 annotated RGB-P frames and masks. We demonstrate, using this newly created dataset, that our PGVS-Net outperforms competing single-frame RGB-P glass segmentation methods as well as RGB-based video segmentation methods both quantitatively and qualitatively.", + "bbox": [ + 496, + 128, + 892, + 492 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In summary, our contributions are:", + "bbox": [ + 519, + 501, + 750, + 515 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- A novel Polarization Video Glass Segmentation network (PGVS-Net) to robustly provide glass segmentation propagation in RGB-P video sequences;", + "- A series of polarimetric consistency and integration modules to enhance spatio-temporal correlation of spectral polarization cues;", + "- A large-scale video glass segmentation dataset, PGV117, containing 21,485 frames with spectral polarization cues and densely-annotated masks." + ], + "bbox": [ + 519, + 525, + 890, + 659 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Background and Related Work", + "text_level": 1, + "bbox": [ + 500, + 700, + 784, + 717 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Polarization. Light is an electro-magnetic wave, whose polarization state describes the orientation of the transverse electric field, which can be unpolarized (i.e., random), linearly polarized (i.e. biased towards a single direction), or circularly polarized. We focus our discussion on linear polarization as supported by recent commercial polarization-array CMOS sensors, which allows us to record four distinct linear-polarization states per pixel: $I_{0^{\\circ}}$ , $I_{45^{\\circ}}$ , $I_{90^{\\circ}}$ , and $I_{135^{\\circ}}$ , where $I_x$ describes the intensity of linearly-polarized light at an angle $x$ . These four linear polarization measurements allow us to compute the linear-polarization compo", + "bbox": [ + 496, + 734, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "23219", + "bbox": [ + 478, + 924, + 517, + 936 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "nents of the Stokes vector $S = [S_0,S_1,S_2]$", + "bbox": [ + 76, + 90, + 367, + 107 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nS _ {0} = I _ {0 ^ {\\circ}} + I _ {9 0 ^ {\\circ}} = I _ {4 5 ^ {\\circ}} + I _ {1 3 5 ^ {\\circ}},\n$$\n", + "text_format": "latex", + "bbox": [ + 161, + 119, + 383, + 135 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nS _ {1} = I _ {0 ^ {\\circ}} - I _ {9 0 ^ {\\circ}}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 135, + 467, + 150 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nS _ {2} = I _ {4 5 ^ {\\circ}} - I _ {1 3 5 ^ {\\circ}},\n$$\n", + "text_format": "latex", + "bbox": [ + 163, + 151, + 292, + 166 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $S_{0}$ is the total light intensity, $S_{1}$ and $S_{2}$ are the ratio of the $0^{\\circ}$ and $45^{\\circ}$ , respectively, linear polarization intensity over its perpendicular counterpart. Given the linear Stokes vector, the degree of linear polarization (DoLP) and the angle of linear polarization (AoLP) are defined as:", + "bbox": [ + 76, + 178, + 468, + 253 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\mathrm {D o L P} = \\frac {\\sqrt {S _ {1} ^ {2} + S _ {2} ^ {2}}}{S _ {0}}, \\quad \\mathrm {A o L P} = \\frac {1}{2} \\arctan \\left(\\frac {S _ {2}}{S _ {1}}\\right). \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 266, + 468, + 301 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Glass Object Segmentation. RGB texture information has proven to be an effective cue for image detection [41, 42, 43] and segmentation [24, 36, 37]. However, accurately segmenting glass objects in images remains a challenging problem because of the dynamic texture patterns that vary with viewing conditions due to reflection and transmission that share the statistics of the surrounding scene. Prior glass segmentation methods operating exclusively on RGB images have leveraged contextual information [30, 52, 53] or boundary cues [9, 50] to address these challenges. However, the effectiveness of RGB-only appearance cues depends on the lighting conditions, the amount of scene clutter, and the presence of nefarious actors (e.g., print-out-spoofs) [14]. One avenue to improve glass segmentation robustness is to include additional modalities that further differentiate glass objects from others, such as scene depth [28], thermal information [12], and polarization [14, 29]. Our approach falls in this latter category, and we rely on RGB and polarization (RGB-P) to robustly segment glass objects. However, the strength of the polarization cues can vary from frame to frame in a video sequence due to changes in view or lighting conditions yielding inconsistent object segmentation between frames. In this work, we leverage multi-view observations to recover a more complete, less view-dependent, description of the polarization properties of objects in the scene, resulting in a temporally more robust glass segmentation.", + "bbox": [ + 76, + 320, + 468, + 728 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Video Segmentation and Detection. Video sequences can offer additional temporal cues to aid segmentation and detection tasks, but simultaneously also introduce the additional challenge of temporal consistency. Semantic video segmentation methods enhance temporal consistency via a variety of temporal propagating approaches such as optical flow[13, 32, 55], spatially varying convolutions [23], and recurrent network architectures [40]. In the absence of semantic cues, video object segmentation approaches estimate consistent class-agnostic object masks and instance", + "bbox": [ + 76, + 750, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "IDs by exploiting spatial and temporal information to propagate an initial mask [4, 7, 11, 20, 26, 33, 39]. Panoptic segmentation [16] is a popular and successful segmentation approach that unifies semantic and instance segmentation, and which has also been extended to video segmentation [15, 22, 35, 47]. In addition to segmentation, the related problem of object detection has recently also been extended to video sequences in different application domains such as salient object detection [17, 19], camouflaged object detection [5], shadow detection [3, 25], and video action detection [54]. Similar to prior work, we also exploit spatial and temporal cues. In addition, we also leverage the richer embedded cues in RGB-P videos and gather robust polarization cues from multi-view observations to aid in propagating glass segmentation masks in video sequences. To the best of our knowledge, none of the prior segmentation propagation methods can effectively leverage polarization cues that are uncorrelated with RGB features.", + "bbox": [ + 496, + 90, + 890, + 362 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Polarimetric Video Glass Segmentation", + "text_level": 1, + "bbox": [ + 500, + 376, + 852, + 393 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our Polarization Video Glass Segmentation network (PGVS-Net) sequentially processes video frames beginning with the second frame, utilizing the ground truth annotation provided in the initial frame. As the video processing unfolds, preceding frames with object masks—established in the first frame or inferred in subsequent frames—are employed as memory frames. Furthermore, the current frame, excluding the object mask, assumes the role of the query frame. Note that each frame consists of trichromatic intensity $I$ , AoLP $\\varphi$ , and DoLP $\\rho$ information.", + "bbox": [ + 496, + 402, + 890, + 551 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Inspired by the successful Spatial-Temporal Memory (STM) framework [4, 33], we encode each frame into a paired set of key and value maps. Specifically, for a given modality $x$ , we utilize a ResNet50 architecture [10] to encode the modality into three distinct feature maps: $f_{b1}^{x}, f_{b2}^{x}$ , and $f_{b3}^{x}$ , corresponding to the outputs of the first, second, and third blocks, respectively. The key feature map of each frame is derived using our specially devised Polarization-Guided Integration module (PGI; detailed in Section 3.1), based on $f_{b1}^{x}, f_{b2}^{x}$ , and $f_{b3}^{x}$ . Importantly, both memory and query frames employ the same methodology to generate key maps. For memory frames, the value map is generated through the following steps:", + "bbox": [ + 496, + 553, + 890, + 750 + ], + "page_idx": 2 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. Trichromatic $I$ , $\\varphi$ , $\\rho$ , and the glass mask are concatenated along the channel dimension and fed as input to a ResNet18 model [10] to produce a feature map;", + "2. The resulting feature map is concatenated with $f_{b3}^{x}$ and subjected to two residual blocks [10] and a Convolutional Block Attention Module (CBAM) [48] attention block;", + "3. Finally, the memory value maps are produced by aggregating the multimodality maps from step 2." + ], + "bbox": [ + 511, + 750, + 890, + 885 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In essence, relying on the query key and the pairs of mem", + "bbox": [ + 500, + 886, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "23220", + "bbox": [ + 478, + 924, + 517, + 935 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/45fe6e4ad30c875c46000e0eb91ab5841682ec6840775fb2417d7cdc1ef934cb.jpg", + "image_caption": [ + "Figure 3. Overview of PGVS-Net. The RGB-P Memory and PGI fused keys are designed to store long-range multi-view polarization cues. The short-range spectral propagation are implemented by the CMTA and PTF modules." + ], + "image_footnote": [], + "bbox": [ + 78, + 88, + 898, + 428 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ory key and value maps, PGVS-Net endeavors to estimate the value map (discussed in Section 3.2) for a given query frame through multi-view polarimetric propagation (described in Section 3.3) and the extraction of temporal correlations (explained in Section 3.4). The resultant value map of the query frame is then translated into the glass mask of the query frame via a decoder (introduced in Section 3.5). Our PGVS-Net is summarized in Figure 3.", + "bbox": [ + 75, + 494, + 468, + 617 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Polarization-Guided Integration", + "text_level": 1, + "bbox": [ + 76, + 623, + 362, + 641 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Polarization information provides strong cues on the material properties. We therefore leverage these polarization cues as guidance to combine multimodal key feature maps for each frame. To achieve this, we introduce a novel Polarization-Guided Integration (PGI) module. Formally, the PGI is defined as:", + "bbox": [ + 75, + 647, + 468, + 736 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nk _ {x} = \\Psi (f _ {b 3} ^ {x}),\n$$\n", + "text_format": "latex", + "bbox": [ + 137, + 743, + 233, + 760 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {Y} _ {1} = \\gamma_ {1} * \\left\\{\\left[ \\Psi \\left(k _ {I}\\right) * \\Psi \\left(k _ {\\varphi}\\right) \\right] * \\Psi \\left(k _ {I}\\right) \\right\\}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 137, + 762, + 468, + 784 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {Y} _ {2} = \\gamma_ {2} * \\left\\{\\left[ \\Psi \\left(k _ {I}\\right) * \\Psi \\left(k _ {\\rho}\\right) \\right] * \\Psi \\left(k _ {I}\\right) \\right\\}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 137, + 780, + 468, + 797 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nk = \\Psi \\left(\\left[ k _ {I}, \\mathcal {Y} _ {1}, \\mathcal {Y} _ {2} \\right]\\right)\n$$\n", + "text_format": "latex", + "bbox": [ + 147, + 800, + 282, + 816 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $x$ is either $I$ , $\\varphi$ , or $\\rho$ ; $\\gamma_{1}$ and $\\gamma_{2}$ are learnable parameters; $\\Psi(\\cdot)$ represents a convolution layer, followed by a regional pooling operation (output size equals 11) and an additional convolution layer; $\\oplus$ indicates a matrix multiplication. $k_{x} \\in \\mathbb{R}^{BT \\times H \\times W \\times C}$ , where $B, T, H, W, C$ are the", + "bbox": [ + 75, + 824, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "batch size, temporal length, and the height, width, and channel size of a feature map, respectively.", + "bbox": [ + 498, + 494, + 890, + 526 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Query Value Prediction", + "text_level": 1, + "bbox": [ + 500, + 566, + 718, + 584 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In the context of a query frame, we establish a connection between RGB-P information from multiple views by investigating the interplay between the query key and memory keys. This interaction results in corresponding value features grounded in memory affinity. Our model employs an STM variant for RGB-P memory, dynamically amalgamating multimodal inputs and establishing correlations across diverse views over an extensive temporal span.", + "bbox": [ + 496, + 602, + 890, + 724 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Concretely, when provided with a query key $k^Q$ , we anticipate the query value $v^Q$ through the utilization of a softmax-normalized affinity matrix, which is computed from the pairing of $(k^M, k^Q)$ [4]. This computation allows us to extract the most pertinent memory values. The computation of memory affinity adheres to the methodology outlined by Cheng et al. [4] (for a comprehensive explanation, please refer to the supplementary material). Memory values encapsulate historical RGB-P information of a scene, ensuring that the affinity mechanism facilitates the far-reaching propagation of multi-view spectral polarization within $v^Q$ .", + "bbox": [ + 496, + 734, + 892, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "23221", + "bbox": [ + 478, + 924, + 517, + 936 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Cross Modal-Temporal Attention", + "text_level": 1, + "bbox": [ + 76, + 90, + 369, + 107 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To this point, the query value prediction process only utilizes long term memory by leveraging the collective information contained in the memory frames. However, captured trichromatic information also exhibits rapid changes across different modalities, indicating potential target area boundaries over short time-intervals. These changes across diverse modalities are not well captured by a long-term memory framework. To address this shortcoming, we introduce a Cross Modal-Temporal Attention module (CMTA) to model the short-term interactions between the query and its one preceding memory frame.", + "bbox": [ + 75, + 116, + 468, + 282 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Central to our CMTA module is a multi-head self-attention mechanism inspired by the transformer architecture [45]. This mechanism is first applied along the modality dimension and then extended to the temporal dimension. Formally, the CMTA can be defined as follows:", + "bbox": [ + 75, + 284, + 468, + 359 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\chi_ {m} = \\left[ \\mathcal {R} _ {m} \\left(k _ {I}\\right), \\mathcal {R} _ {m} \\left(k _ {\\varphi}\\right), \\mathcal {R} _ {m} \\left(k _ {\\rho}\\right) \\right], \\\\ F _ {m} = \\mathcal {L} \\left[ \\Upsilon \\left(\\mathcal {L} \\left(\\chi_ {m}\\right)\\right) + \\chi_ {m} \\right], (4) \\\\ \\chi_ {t} = \\left[ \\mathcal {R} _ {t} \\left(\\mathcal {C} _ {I} \\left(F _ {m}\\right)\\right), \\mathcal {R} _ {t} \\left(\\mathcal {C} _ {\\varphi} \\left(F _ {m}\\right)\\right), \\mathcal {R} _ {t} \\left(\\mathcal {C} _ {\\rho} \\left(F _ {m}\\right)\\right) \\right], (4) \\\\ F _ {t} = \\mathcal {L} [ \\Upsilon (\\mathcal {L} (\\chi_ {t})) + \\chi_ {t} ], \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 96, + 376, + 468, + 450 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $[\\cdot]$ indicates the concatenation on the first dimension; $\\Upsilon$ indicates a multi-head self-attention block [45]; $\\mathcal{L}$ refers to Layer Normalization [1]. $\\mathcal{R}_m$ is a modality reshape operator, which transfers the shape of $k_{c}$ from $\\mathbb{R}^{B\\times T\\times H\\times W\\times C}$ into $\\mathbb{R}^{BT\\times HW\\times C}$ . $\\mathcal{R}_t$ is a reshape operator in the temporal domain, which reshape a feature map from $\\mathbb{R}^{B\\times T\\times H\\times W\\times C}\\rightarrow \\mathbb{R}^{B\\times THW\\times C}$ . $\\mathcal{C}_x$ is the chunked vector for modality $x$ . Finally, the derived $F_{t}$ is concatenated with the query value acquired through the query value prediction process, and subsequently forwarded as input to the decoder.", + "bbox": [ + 75, + 465, + 468, + 630 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Polarimetric Temporal Forward", + "text_level": 1, + "bbox": [ + 76, + 648, + 361, + 665 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The examples in Figure 2 demonstrate that the polarization cues provide strong temporal continuity cues. The core idea of leveraging polarimetric continuity is that the polarization for the query frame can benefit from the preceding memory frame's polarization cues. To actualize this, the Polarimetric Temporal Forward (PTF) module engages $f_{b1}^{x}$ and $f_{b2}^{x}$ , sourced from the query and the preceding memory frame, as inputs. This module carries out an unfolding operation $(\\mathcal{U})$ on these inputs. In order to distinguish between the features from the query and memory frames, an additional subscript is appended to the feature samples. For instance, $f_{M - b1}^{x}$ and $f_{Q - b2}^{x}$ represent the feature map of block 1 from a memory frame and the feature map of block 2 from a query frame for the modality $x$ , respectively. Formally, given $f_{M - b1}^{x}$ and $f_{Q - b1}^{x}$ , the PTF operation is defined", + "bbox": [ + 75, + 674, + 470, + 902 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "as:", + "bbox": [ + 500, + 94, + 522, + 104 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} U _ {\\varphi} ^ {M}, U _ {\\rho} ^ {M} = \\mathcal {U} \\left(f _ {M - b 1} ^ {\\varphi}\\right), \\mathcal {U} \\left(f _ {M - b 1} ^ {\\rho}\\right), \\\\ F _ {\\varphi} ^ {Q}, F _ {\\rho} ^ {Q} = \\mathcal {R} (f _ {Q - b 1} ^ {\\varphi}), \\mathcal {R} (f _ {\\rho - b 1} ^ {\\varphi}), \\\\ S _ {\\varphi} = \\sigma \\left(\\mathcal {S} \\left(F _ {\\varphi} ^ {Q} \\otimes U _ {\\varphi} ^ {M}\\right)\\right) \\otimes U _ {\\varphi} ^ {M} + f _ {b 1} ^ {\\varphi}, \\tag {5} \\\\ S _ {\\rho} = \\sigma \\left(\\mathcal {S} \\left(F _ {\\rho} ^ {Q} \\otimes U _ {\\rho} ^ {M}\\right)\\right) \\otimes U _ {\\rho} ^ {M} + f _ {b 1} ^ {\\rho}, \\\\ F _ {b 1} ^ {P T F} = S _ {\\varphi} + S _ {\\rho} + f _ {b 1} ^ {I}, \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 545, + 109, + 890, + 213 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathcal{R}$ and $S$ denote the reshape operation and sum operation applied to the first dimension, respectively; $\\otimes$ indicates the element-wise multiplication; $\\sigma$ is the softmax function. $U_{\\varphi}, U_{\\rho} \\in \\mathbb{R}^{C \\times P \\times H \\times W}$ , where $P$ denotes the window size during the unfold convolution, and $f_{b2}^{I}, f_{b2}^{\\varphi}, f_{b2}^{\\rho} \\in \\mathbb{R}^{C \\times 1 \\times H \\times W}$ .", + "bbox": [ + 496, + 219, + 890, + 306 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "PTF further applies the described operations to $f_{b2}^{\\varphi}, f_{b2}^{\\rho}$ and $f_{b2}^{I}$ , yielding the output $F_{b2}^{PTF}$ . In our implementation, we establish the window sizes for unfold convolutions as 7 and 9 for $f_{b2}$ and $f_{b1}$ , respectively. Through this design, PTF enables dynamic incorporation via unfold convolutions, fostering forward propagation among adjacent polarimetric features and thereby achieving inter-frame view dependency.", + "bbox": [ + 496, + 309, + 890, + 431 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.5. Decoder", + "text_level": 1, + "bbox": [ + 500, + 439, + 601, + 454 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We employ a straightforward yet effective decoder to translate the acquired query value into the corresponding glass masks of the query frame. Our decoder encompasses two UNet-like [38] upsampling blocks, tasked with reinstating the resolution of the query value map to $1/4$ of the query frame's dimensions. Subsequently, a prediction convolution transforms the channel configuration of the resultant feature map to a single channel, which is then upsampled to match the resolution of the query frame. In addition to the query value, this decoder taps into the feature maps offered by the PTF module to reinforce temporal coherence. Specifically, $F^{PTF}b1$ and $F^{PTF}b2$ serve as inputs to the first and second upsampling blocks, respectively.", + "bbox": [ + 496, + 460, + 890, + 657 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.6. Implementation Details", + "text_level": 1, + "bbox": [ + 500, + 666, + 718, + 681 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We implement PGVS-Net in PyTorch. For training, input images are randomly cropped to $384 \\times 384$ and augmented by horizontal random flipping, translations, and affine transforms. During training, the sequence takes a group of three frames as the input of the network. The masks of ground truth glass areas in the first frame are provided as input, and we employ a binary cross-entropy (BCE) loss to supervise the output mask of the last two frames. For optimization, we use the Adam optimizer with a weight decay of $1e - 7$ . The learning rate is fixed at $1e - 5$ . Training takes three days to converge on a dual TITAN V100 graphics card setup after 150,000 iterations with a batch size of 4. During inference, we update the memory bank every three frames.", + "bbox": [ + 496, + 688, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "footer", + "text": "23222", + "bbox": [ + 478, + 924, + 519, + 936 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/de384d01d466c80d77ec98d6512f718bdac8622d3362ff6778421987dadc1abb.jpg", + "image_caption": [ + "Figure 4. Summary of camera motions (left) and the PGV-117 dataset characteristics (right). To avoid biasing PGV-117 into certain types of camera motions, we implement different camera motion strategies. The blue areas represent the glass target. The 117 video sequences are captured with different types of camera paths, lighting conditions, dynamics, and materials (dark indicates ground glass)." + ], + "image_footnote": [], + "bbox": [ + 89, + 89, + 455, + 328 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. PGV-117 dataset", + "text_level": 1, + "bbox": [ + 76, + 470, + 243, + 486 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We introduce a novel RGB-P-video-based dataset, PGV-117, to support and stimulate research in video-based glass segmentation. The dataset is collected using a trichromatic (RGB) polarizer-array camera (LUCID PHX050S), equipped with four directional linear-polarizers, i.e., $0^{\\circ}$ , $45^{\\circ}$ , $90^{\\circ}$ and $135^{\\circ}$ . The frame rate is fixed at 30fps, and we vary the exposure time from $3,000\\mu s$ to $39,999\\mu s$ depending on the scene and lighting conditions. Each frame in the PGV-117 dataset includes: an RGB image, four directional polarization images, inferred spectral AoLP and DoLP maps, and the captured RAW camera data. Table 1 summarizes PGV-117 statistics in comparison to prior datasets. Care was taken during creation of PGV-117 to ensure a sufficient variation in lighting conditions, camera paths, and scene dynamics.", + "bbox": [ + 75, + 497, + 468, + 724 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Lighting conditions. PGV-117 is collected in various indoor environments, such as shopping malls, office buildings, and classrooms, as well as in a variety of outdoor environments. For outdoor environments, we capture sequences spanning during the full time-range from daytime to night. As such, PGV-117 offers four types of lighting variations: normal, low-light, saturated light, and high-dynamic-range. Additionally, we also consider diverse glass types in PGV-117, including clear, frosted, and patterned glasses, tinted glass on vehicles, and outdoor and indoor glass walls.", + "bbox": [ + 75, + 750, + 468, + 901 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/0f96a021d5ecd3259ea350b8ad47e29fe363e79a9a0662dd48ff296af916e0fb.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DatasetsTaskFramesADPSeq(tr+v/te)
DAVIS2017 [34]VOS10,459#190/60
DAVSOD [6]VSOD23,938#136/90
MoCA-Mask [5]VCOD22,939#571/16
RGBP-Glass [29]IGS4,511#1✓-
PGV-117VGS21,485#1✓85/32
", + "bbox": [ + 504, + 89, + 888, + 196 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 1. Statistics of PGV-117 compared to representative video datasets and glass datasets. In each column, we list: the primary Task for which the dataset was designed (Video Object Segmentation (VOS), Video Saliency Object Detection (VSOD), Video Camouflaged Object Detection (VCOD), and Image Glass Segmentation (IGS)); $AD$ : the annotation interval in #frames; $P$ : whether the dataset includes polarization; and $Seq(tr + v)/te$ : the number of training and validation exemplars versus test exemplars.", + "bbox": [ + 496, + 207, + 890, + 343 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Camera motion patterns. Polarization cues are angle dependent. To avoid biasing PGV-117 to certain view angles and camera paths, we randomly pick one of five predetermined camera motion patterns: front, inclined, circular, straight-forward, and up-down; see Figure 4 for a visual summary. During acquisition, we also recapture some glass areas back and forth to enrich the robustness and diversity.", + "bbox": [ + 496, + 372, + 890, + 478 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Dynamics. PGV-117 captures both static and dynamic scenes (e.g., doors/windows opening and closing, and pedestrians occluding glass).", + "bbox": [ + 496, + 501, + 890, + 547 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Frame removal. Frames characterized by motion blur and overexposure are excluded due to the inherent ambiguity in their annotations. Typically, we remove 1 to 2 frames per static-camera sequence, and about $20\\%$ frames for a moving-camera sequence.", + "bbox": [ + 496, + 570, + 890, + 647 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiments", + "text_level": 1, + "bbox": [ + 500, + 662, + 633, + 680 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this section, we first compare the performance of PGVS-Net under continuous polarization to demonstrate the robustness of combining multi-view and temporal consistency (subsection 5.1). Next, we validate the efficacy of our model by quantitatively and qualitatively comparing PGVS-Net against polarization-based and SOTA video methods retrained on the PGV-117 dataset. To quantify performance, we adopt four prevalent evaluation metrics: intersection over union (IoU), weighted F-measure $(\\mathrm{F}_{\\beta})$ [27], mean absolute error (MAE), and balance error rate (BER) [31]. Finally, we perform an ablation study to show the impact of the different components that comprise PGVS-Net (subsection 5.3). Please refer to the supplementary materials for additional images and video results.", + "bbox": [ + 496, + 689, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "23223", + "bbox": [ + 478, + 924, + 517, + 936 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c279678244d2dece7e9009c076b1538c2c0937d1926bab80595847d9b5a84788.jpg", + "image_caption": [ + "Figure 5. Error plots comparing PGVS-Net to PM-RCNN and PGSNet for four different sequences. For reference, the DoLP is also included to indicate which frames pose a greater challenge for RGB-P methods." + ], + "image_footnote": [], + "bbox": [ + 89, + 92, + 279, + 220 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/05de1b1275e1bbef5f55391ab4fc71e52b3dbaf93baf73ceb50a041edc2b4d04.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 282, + 92, + 478, + 220 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/afb07196161750ebe915b7b2d10c3f0861ee509d5463005bae812469865d7495.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 478, + 92, + 676, + 220 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/e6dec4091c1cdb305a859519963c8608f18f9f148249de935ecaedd6fdf03039.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 676, + 92, + 880, + 220 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.1. Multi-view Polarimetric Consistency", + "text_level": 1, + "bbox": [ + 76, + 281, + 393, + 297 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Due to their near-specular reflection and refraction behavior, glass materials are more sensitive to changes in view/light conditions. While RGB-P cues have proven to be essential for robust single-image glass segmentation, ignoring the temporal instability can result in inconsistent glass segmentation over time. PGVS-Net is specially designed to leverage and aggregate temporal changes in polarization cues. Figure 5 illustrates the correlation between variations in polarization intensity (DoLP) and the corresponding performance levels (measured by mIoU) in comparison to two image-based polarimetric techniques [14, 29] (applied independently to each frame) across diverse video sequences. The distinct abrupt shifts in the curve within Figure 5 due to the removal frames with motion blur (section 4), which breaks the temporal continuity and may degrade the multiview dependency of PGVS-Net.", + "bbox": [ + 75, + 305, + 468, + 546 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "From the first result in Figure 5, we can observe that when DoLP changes significantly, prior single-frame image-based methods fail to produce a consistent, coherent segmentation. In contrast, our model not only stores and leverages historical polarization information, but also enhances the current frame with the prior polarization information through the CMTA and PTF modules, resulting in good temporal consistency. The second result in Figure 5 shows that our model can still maintain a stable performance when the overall DoLP changes within the sequence cover a relatively large range (between 0.2 and 0.45). The third and fourth result in Figure 5 show that PGVS-Net can achieve better performance in low light and high brightness environments with extremely low overall DoLP over the sequence (less than 0.12).", + "bbox": [ + 75, + 547, + 470, + 773 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Comparison to the State-of-the-art", + "text_level": 1, + "bbox": [ + 76, + 786, + 380, + 801 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We compare PGVS-Net to prior single-frame image-based glass segmentation methods and state-of-the-art video segmentation methods. We retrain all methods on the PGV-117 dataset and evaluate them on the 32 test sequences. We compare against: RGB-input GSD [30] where the input and supervision are replaced with our", + "bbox": [ + 75, + 810, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/289406115e58e144f07438b1e5acf6445384b7f1e76541c9727b1ae8eb874ad7.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodsIoU↑Fβ↑MAE↓BER↓
GSDIS[30]80.290.8280.11512.34
EAFIS[49]41.690.5560.45043.91
PM-RCNNIS[14]76.130.7970.14015.83
PGSIS[29]79.690.8730.11912.31
STICTVU[25]50.680.5770.29932.03
ViShaVS[3]77.420.8050.13613.77
STCNVS[4]80.850.8260.12012.77
RDEVS[20]74.870.7630.16915.95
PGVS-Net (Ours)84.600.8670.09910.02
", + "bbox": [ + 514, + 280, + 879, + 450 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 2. Quantitative comparison of PGVS-Net with prior SOTA methods (method subscripts: IS: Image-based supervised, VS: Video-based supervised, and $VU$ : Video-based without labels). The top and second best results are highlighted in red and blue, respectively.", + "bbox": [ + 498, + 460, + 892, + 536 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "dataset; RGB-P glass segmentation methods EAF [49], PM-RCNN [14] and PGS [29]; STICT [25] (since this is an unsupervised method, we use the polarimetric dataset from [29] as labeled images for training); ViSha [3] is a recent video shadow detection method; STM-based video segmentation methods STCN [4] and RDE [20] (with ground truth masks during training and using the mask from GSD [30] during evaluation). In all our examples, during inference, the initial masks for PGVS-Net are provided by the polarization-aware PGSNet [29]. The quantitative and qualitative results are shown in Table 2 and Figure 6.", + "bbox": [ + 496, + 566, + 890, + 733 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "PGVS-Net outperforms state-of-the-art methods by a significant margin and improves IoU, MAE, and BER by 3.75, 0.016, and 2.29 over the next best method, demonstrating the effectiveness of multi-view polarization propagation for video glass segmentation. PGVS-Net performs slightly less than PGS-Net on the $\\mathrm{F}_{\\beta}$ metric, which again illustrates the robustness of polarization cues for glass segmentation for both still-image and video sequences. Figure 6 further qualitatively illustrates the robustness of PGVS-Net. We refer to the video sequences in the supplementary material to qualitatively evaluate the temporally", + "bbox": [ + 496, + 734, + 892, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "23224", + "bbox": [ + 478, + 924, + 517, + 935 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/47213855b4533228afed374244f4e6b1b6c7c92333fb7084587ba1dbd7229d67.jpg", + "image_caption": [ + "Figure 6. Qualitative comparison of our model against state-of-the-art image-based glass segmentation methods and video detection/segmentation methods. All models are retrained on PGV-117." + ], + "image_footnote": [], + "bbox": [ + 86, + 89, + 903, + 329 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/ac67882c5fed5f43f34280df6e0ea8e4b593c41cc8f578f5c012f360351ef0b1.jpg", + "image_caption": [ + "Figure 7. Qualitative comparison of the different ablation combinations of PGVS-Net." + ], + "image_footnote": [], + "bbox": [ + 86, + 378, + 901, + 503 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/e68223be1a83808abee2b083ecdb7a6658f4680c004f3a7853813697d17db757.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
NetworksIoU↑Fβ↑MAE↓BER↓
RGB78.960.8070.14213.88
RGB-P81.010.8270.13113.16
RGB-P+PGI83.680.8600.10110.43
RGB-P+PTF81.780.8380.12212.38
RGB-P+CMTA83.810.8620.10010.88
RGB-P+PGI+CMTA+PTF(M5)80.760.8260.13412.82
PGVS-Net84.600.8670.09910.02
", + "bbox": [ + 78, + 545, + 468, + 683 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 3. Summary of ablation experiments: Polarization cues (RGB-P) outperform RGB-only cues. The combination of all modules (PGVS-Net) produces the overall best results. 'M5' indicates that the long-range memory is updated every five frames during inference.", + "bbox": [ + 75, + 694, + 470, + 772 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "coherent glass segmentation propagation.", + "bbox": [ + 76, + 801, + 352, + 816 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.3. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 829, + 230, + 845 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We validate the impact of each component in PGVS-Net by disabling one or more components and comparing the performance on the PGV-117 test set (Table 3). The net", + "bbox": [ + 75, + 854, + 470, + 900 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "work named 'RGB' uses only RGB textures to populate and query the memory to predict glass areas without any other modules. The 'RGB-P' network uses RGB-P information to store, read and calculate memory features. All other networks start from the 'RGB-P' baseline with the listed modules enabled. Finally, we indicate with 'M5' that the memory is updated every five frames during the inference stage as opposed to every three frames for PGVS-Net.", + "bbox": [ + 496, + 547, + 890, + 669 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The improved performance of the 'RGB-P' network over 'RGB' shows that polarization provides additional cues for glass segmentation. PGI combines tripartite key features to retrieve affinity from historical views. Its attribute performance gain shows that integrated RGB-P streams can better mine multi-view similarity than single-stream matching. The PTF module further improves the segmentation accuracy (e.g., IoU increases from 81.01 to 81.78). Adding the CMTA module further improves the performance on the four metrics, demonstrating that the cross-modal and cross-temporal integration provides rich short-range references for query frames. Finally, the full PGVS-Net with all modules enabled achieves the best results when combined with a memory update every three frames.", + "bbox": [ + 496, + 689, + 892, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "23225", + "bbox": [ + 478, + 924, + 517, + 936 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/aa204cc6f7bc377688a5ae8731d6da89b222a7873a7d1fcbfaf2742f92a6fe83.jpg", + "image_caption": [ + "Figure 8. Two failure cases with inaccurate glass segmentation highlighted in the red boxes." + ], + "image_footnote": [], + "bbox": [ + 88, + 89, + 460, + 265 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5.4. Failure Cases and Limitations", + "text_level": 1, + "bbox": [ + 76, + 329, + 344, + 345 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Our method propagates a single initial mask, and thus its overall quality is affected by the quality of the initial mask. For glass areas with no initial or historical references, little information can be propagated from multi-view observations. While PGVS-Net can augment glass segmentation in such scenarios by harnessing spatial characteristics across both the RGB and polarization domain, it is possible that the segmentation can result in gaps in the glass segmentation results (two failure cases are shown in Figure 8). An interesting avenue for future research would be to determine the most reliable RGB-P frame for initial mask estimation before propagating it to the rest of the sequence. Furthermore, although PGVS-Net significantly outperforms other video segmentation methods in accuracy, its tripartite-modal integration and temporal consistency strategy of polarization cues require additional inference time. Our unoptimized implementation currently operates at 7fps.", + "bbox": [ + 75, + 354, + 468, + 612 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 631, + 194, + 647 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this paper, we introduced a Polarization Video Glass Segmentation network (PGVS-Net), that exploits historical multi-view spectral polarization cues to segment glass areas, and which outperforms state-of-the-art polarization-related image and video segmentation networks. PGVS-Net leverages RGB-P memory and PGI-fused keys to correlate input frames with view-dependent polarization information from prior spectral cues. We show that the continuous changes in illumination are better captured by polarimetric features, and that long-range affinity helps to better balance single-input instabilities than single image methods. In addition, CMTA and PTF provide short-range polarization cues for low-level polarimetric features, providing rich wavelength details in the decoder phase. We also create a novel video glass segmentation dataset (PGV-117) to train and evaluate PGVS-Net.", + "bbox": [ + 75, + 657, + 468, + 898 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements", + "text_level": 1, + "bbox": [ + 500, + 90, + 668, + 107 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was supported in part by National Key Research and Development Program of China (2022ZD0210 500), the National Natural Science Foundation of China under Grants 61972067/U21A20491, and the Distinguished Young Scholars Funding of Dalian (No. 2022RJ01). Pieter Peers was supported in part by NSF grant IIS-1909028. Felix Heide was supported by an NSF CAREER Award (2047359), a Packard Foundation Fellowship, a Sloan Research Fellowship, a Sony Young Faculty Award, a Project X Innovation Award, and an Amazon Science Research Award. Seung-Hwan Baek acknowledges the support from NRF Korea (RS-2023-00211658, 2022R1A6A1A03052954) and Samsung Electronics.", + "bbox": [ + 496, + 114, + 890, + 311 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 500, + 323, + 596, + 339 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Lei Jimmy Ba, Jamie Ryan Kiros, and Geoffrey E. Hinton. Layer normalization. CoRR, abs/1607.06450, 2016.", + "[2] Seung-Hwan Baek, Tizian Zeltner, Hyunjin Ku, Inseung Hwang, Xin Tong, Wenzel Jakob, and Min H Kim. Image-based acquisition and modeling of polarimetric reflectance. 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In CVPR, 2017." + ], + "bbox": [ + 78, + 92, + 467, + 445 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "23228", + "bbox": [ + 478, + 924, + 517, + 936 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multi-view Spectral Polarization Propagation for Video Glass Segmentation/da43f4ff-b9d6-45ae-8913-a53d60c1040d_model.json b/2023/Multi-view Spectral Polarization Propagation for Video Glass Segmentation/da43f4ff-b9d6-45ae-8913-a53d60c1040d_model.json new file mode 100644 index 0000000000000000000000000000000000000000..c0fd4083187283a2ffb980d27e4fc5c19462e4e7 --- /dev/null +++ b/2023/Multi-view Spectral Polarization Propagation for Video Glass Segmentation/da43f4ff-b9d6-45ae-8913-a53d60c1040d_model.json @@ -0,0 +1,2125 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.104, + 0.13, + 0.868, + 0.154 + ], + "angle": 0, + "content": "Multi-view Spectral Polarization Propagation for Video Glass Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.221, + 0.181, + 0.751, + 0.219 + ], + "angle": 0, + "content": "Yu Qiao, Bo Dong*, Ao Jin, Yu Fu, Seung-Hwan Baek, Felix Heide Pieter Peers, Xiaopeng Wei* Xin Yang*" + }, + { + "type": "image", + "bbox": [ + 0.099, + 0.251, + 0.187, + 0.415 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.189, + 0.251, + 0.315, + 0.414 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.317, + 0.252, + 0.468, + 0.414 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.468, + 0.252, + 0.618, + 0.414 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.62, + 0.259, + 0.871, + 0.415 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.423, + 0.896, + 0.502 + ], + "angle": 0, + "content": "Figure 1. A comparison of PGVS-Net on 3 selected frames from an RGB-P video sequence from our novel PGV-117 dataset against the method of Kalra et al. [14] and Mei et al. [29]. From left to right: RGB, AoLP, and DoLP input images; glass segmentation results for selected frames compared to the ground truth segmentation; evolution of error over the video sequence. Both prior methods are temporally unstable due to significant temporal changes in DoLP. In contrast, PGVS-Net combines multi-view polarization cues for segmentation propagation, yielding a temporally stable glass segmentation." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.522, + 0.314, + 0.537 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.553, + 0.473, + 0.782 + ], + "angle": 0, + "content": "In this paper, we present the first polarization-guided video glass segmentation propagation solution (PGVS-Net) that can robustly and coherently propagate glass segmentation in RGB-P video sequences. By leveraging spatiotemporal polarization and color information, our method combines multi-view polarization cues and thus can alleviate the view dependence of single-input intensity variations on glass objects. We demonstrate that our model can outperform glass segmentation on RGB-only video sequences as well as produce more robust segmentation than per-frame RGB-P single-image segmentation methods. To train and validate PGVS-Net, we introduce a novel RGB-P Glass Video dataset (PGV-117) containing 117 video sequences of scenes captured with different types of camera paths, lighting conditions, dynamics, and glass types." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.808, + 0.21, + 0.823 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.834, + 0.471, + 0.88 + ], + "angle": 0, + "content": "Transparent objects, such as glass, are common in man-made environments. Despite their prevalence, such objects pose numerous challenges for industrial and academic" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.523, + 0.893, + 0.764 + ], + "angle": 0, + "content": "vision processing algorithms due to their view-dependent appearance, statistical similarity to the background environment, and lack of texture. These challenges are particularly acute for segmentation tasks that underpin autonomous driving, robotics, and aerial drone navigation. Traditional learning-based solutions [8, 30, 50, 51] that rely on RGB textures for feature extraction often fail to adequately model the illumination and view-dependent glass features. Consequently, recent advances have explored richer modalities such as light fields [44] and polarization [14, 18, 21, 29, 46, 49] for more robust segmentation of glass objects. Polarization has proven to be a strong cue for glass segmentation in still images [14, 29]. The availability of commercial off-the-shelf RGB-P cameras (e.g., Flir and Lucid), makes this last category an attractive modality for glass segmentation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Polarization of reflected light depends on various factors such as surface normals, material types, and illumination and view directions [2]. Due to the polarimetric near-specular behavior, glass materials are particularly challenging; small changes in object orientation and/or view/light direction can induce a rapid change in polarization state. For example, consider the glass areas '1' in Figure 2 that show a glass door in various stages of being closed. In this example, the RGB textures remain almost unchanged, but" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.888, + 0.228, + 0.9 + ], + "angle": 0, + "content": "*Corresponding authors." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.925, + 0.521, + 0.937 + ], + "angle": 0, + "content": "23218" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.09, + 0.472, + 0.466 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.475, + 0.471, + 0.566 + ], + "angle": 0, + "content": "Figure 2. Representative exemplars from the PGV-117 dataset containing a total of 117 video sequences captured with a variety of camera movement patterns, lighting conditions, scene dynamics, and materials. Glass areas '1' depict a door in various stages of being closed. Glass areas '2' are captured by moving the camera." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.599, + 0.47, + 0.903 + ], + "angle": 0, + "content": "changes in the surface normal induce a significant decrease in the Angle of Linear Polarization (AoLP) from close to \\(\\pi\\) (red-blue mixture) to less than half \\(\\pi\\) (full blue), and a noticeable reduction in the Degree of Linear Polarization (DoLP) from 0.137 to 0.043. Similarly, moving the camera will induce a similar change in the polarization (e.g., the glass areas '2' in Figure 2). These observations suggest that polarization cues are beneficial for glass segmentation and can provide additional guidance. Furthermore, the DOLP in glass area '1' is unstable across the entire span of the video sequence, with noticeable DoLP reductions at specific angles of incidence (\\(\\rho = 0.043\\)). Such types of instabilities can confuse methods [14, 29] that only rely on a single-frame RGB-P as input (Figure 1, right). Moreover, extracting glass features from RGB textures or polarization cues from a single view may also be difficult (e.g., under low light conditions as in Figure 1 left). As a consequence, polarization cues that are robust for static single image segmentation methods, can still yield temporally disjoint and inconsistent segmentation results when applied to" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "video sequences, especially when object orientation and/or viewpoint changes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.13, + 0.893, + 0.493 + ], + "angle": 0, + "content": "In this paper, we introduce a Polarization Video Glass Segmentation network (PGVS-Net) to robustly and coherently propagate an initial glass segmentation mask over an RGB-P video sequence. PGVS-Net perceives multi-view polarimetric features from long-range memory and short-range integration. A variation of the Spatio-Temporal Memory network (STM) [33] is introduced to leverage spectral polarization cues for constructing long-range view dependency. A well-designed Polarization-Guide Integration module (PGI) is responsible for the frame identity and historical polarization matching. Furthermore, a novel Polarization Temporal Forward module (PTF) integrates previous polarization cues to promote short-range spectral consistency during the decoder process. We also leverage cross-modal and cross-temporal attention (CMTA) to integrate multimodal features and temporal representations from different frames. To train and test PGVS-Net, we capture and annotate a large-scale video glass segmentation dataset, PGV-117, which includes 21,485 annotated RGB-P frames and masks. We demonstrate, using this newly created dataset, that our PGVS-Net outperforms competing single-frame RGB-P glass segmentation methods as well as RGB-based video segmentation methods both quantitatively and qualitatively." + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.502, + 0.75, + 0.516 + ], + "angle": 0, + "content": "In summary, our contributions are:" + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.526, + 0.892, + 0.569 + ], + "angle": 0, + "content": "- A novel Polarization Video Glass Segmentation network (PGVS-Net) to robustly provide glass segmentation propagation in RGB-P video sequences;" + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.571, + 0.892, + 0.614 + ], + "angle": 0, + "content": "- A series of polarimetric consistency and integration modules to enhance spatio-temporal correlation of spectral polarization cues;" + }, + { + "type": "text", + "bbox": [ + 0.52, + 0.616, + 0.891, + 0.66 + ], + "angle": 0, + "content": "- A large-scale video glass segmentation dataset, PGV117, containing 21,485 frames with spectral polarization cues and densely-annotated masks." + }, + { + "type": "list", + "bbox": [ + 0.52, + 0.526, + 0.892, + 0.66 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.701, + 0.785, + 0.718 + ], + "angle": 0, + "content": "2. Background and Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Polarization. Light is an electro-magnetic wave, whose polarization state describes the orientation of the transverse electric field, which can be unpolarized (i.e., random), linearly polarized (i.e. biased towards a single direction), or circularly polarized. We focus our discussion on linear polarization as supported by recent commercial polarization-array CMOS sensors, which allows us to record four distinct linear-polarization states per pixel: \\( I_{0^{\\circ}} \\), \\( I_{45^{\\circ}} \\), \\( I_{90^{\\circ}} \\), and \\( I_{135^{\\circ}} \\), where \\( I_x \\) describes the intensity of linearly-polarized light at an angle \\( x \\). These four linear polarization measurements allow us to compute the linear-polarization compo" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.925, + 0.519, + 0.937 + ], + "angle": 0, + "content": "23219" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.091, + 0.368, + 0.108 + ], + "angle": 0, + "content": "nents of the Stokes vector \\(S = [S_0,S_1,S_2]\\)" + }, + { + "type": "equation", + "bbox": [ + 0.162, + 0.12, + 0.384, + 0.136 + ], + "angle": 0, + "content": "\\[\nS _ {0} = I _ {0 ^ {\\circ}} + I _ {9 0 ^ {\\circ}} = I _ {4 5 ^ {\\circ}} + I _ {1 3 5 ^ {\\circ}},\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.165, + 0.136, + 0.468, + 0.151 + ], + "angle": 0, + "content": "\\[\nS _ {1} = I _ {0 ^ {\\circ}} - I _ {9 0 ^ {\\circ}}, \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.165, + 0.152, + 0.293, + 0.167 + ], + "angle": 0, + "content": "\\[\nS _ {2} = I _ {4 5 ^ {\\circ}} - I _ {1 3 5 ^ {\\circ}},\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.179, + 0.469, + 0.255 + ], + "angle": 0, + "content": "where \\( S_{0} \\) is the total light intensity, \\( S_{1} \\) and \\( S_{2} \\) are the ratio of the \\( 0^{\\circ} \\) and \\( 45^{\\circ} \\), respectively, linear polarization intensity over its perpendicular counterpart. Given the linear Stokes vector, the degree of linear polarization (DoLP) and the angle of linear polarization (AoLP) are defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.09, + 0.267, + 0.47, + 0.302 + ], + "angle": 0, + "content": "\\[\n\\mathrm {D o L P} = \\frac {\\sqrt {S _ {1} ^ {2} + S _ {2} ^ {2}}}{S _ {0}}, \\quad \\mathrm {A o L P} = \\frac {1}{2} \\arctan \\left(\\frac {S _ {2}}{S _ {1}}\\right). \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.321, + 0.47, + 0.729 + ], + "angle": 0, + "content": "Glass Object Segmentation. RGB texture information has proven to be an effective cue for image detection [41, 42, 43] and segmentation [24, 36, 37]. However, accurately segmenting glass objects in images remains a challenging problem because of the dynamic texture patterns that vary with viewing conditions due to reflection and transmission that share the statistics of the surrounding scene. Prior glass segmentation methods operating exclusively on RGB images have leveraged contextual information [30, 52, 53] or boundary cues [9, 50] to address these challenges. However, the effectiveness of RGB-only appearance cues depends on the lighting conditions, the amount of scene clutter, and the presence of nefarious actors (e.g., print-out-spoofs) [14]. One avenue to improve glass segmentation robustness is to include additional modalities that further differentiate glass objects from others, such as scene depth [28], thermal information [12], and polarization [14, 29]. Our approach falls in this latter category, and we rely on RGB and polarization (RGB-P) to robustly segment glass objects. However, the strength of the polarization cues can vary from frame to frame in a video sequence due to changes in view or lighting conditions yielding inconsistent object segmentation between frames. In this work, we leverage multi-view observations to recover a more complete, less view-dependent, description of the polarization properties of objects in the scene, resulting in a temporally more robust glass segmentation." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.75, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Video Segmentation and Detection. Video sequences can offer additional temporal cues to aid segmentation and detection tasks, but simultaneously also introduce the additional challenge of temporal consistency. Semantic video segmentation methods enhance temporal consistency via a variety of temporal propagating approaches such as optical flow[13, 32, 55], spatially varying convolutions [23], and recurrent network architectures [40]. In the absence of semantic cues, video object segmentation approaches estimate consistent class-agnostic object masks and instance" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.363 + ], + "angle": 0, + "content": "IDs by exploiting spatial and temporal information to propagate an initial mask [4, 7, 11, 20, 26, 33, 39]. Panoptic segmentation [16] is a popular and successful segmentation approach that unifies semantic and instance segmentation, and which has also been extended to video segmentation [15, 22, 35, 47]. In addition to segmentation, the related problem of object detection has recently also been extended to video sequences in different application domains such as salient object detection [17, 19], camouflaged object detection [5], shadow detection [3, 25], and video action detection [54]. Similar to prior work, we also exploit spatial and temporal cues. In addition, we also leverage the richer embedded cues in RGB-P videos and gather robust polarization cues from multi-view observations to aid in propagating glass segmentation masks in video sequences. To the best of our knowledge, none of the prior segmentation propagation methods can effectively leverage polarization cues that are uncorrelated with RGB features." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.377, + 0.853, + 0.394 + ], + "angle": 0, + "content": "3. Polarimetric Video Glass Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.403, + 0.892, + 0.553 + ], + "angle": 0, + "content": "Our Polarization Video Glass Segmentation network (PGVS-Net) sequentially processes video frames beginning with the second frame, utilizing the ground truth annotation provided in the initial frame. As the video processing unfolds, preceding frames with object masks—established in the first frame or inferred in subsequent frames—are employed as memory frames. Furthermore, the current frame, excluding the object mask, assumes the role of the query frame. Note that each frame consists of trichromatic intensity \\( I \\), AoLP \\( \\varphi \\), and DoLP \\( \\rho \\) information." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.554, + 0.892, + 0.75 + ], + "angle": 0, + "content": "Inspired by the successful Spatial-Temporal Memory (STM) framework [4, 33], we encode each frame into a paired set of key and value maps. Specifically, for a given modality \\( x \\), we utilize a ResNet50 architecture [10] to encode the modality into three distinct feature maps: \\( f_{b1}^{x}, f_{b2}^{x} \\), and \\( f_{b3}^{x} \\), corresponding to the outputs of the first, second, and third blocks, respectively. The key feature map of each frame is derived using our specially devised Polarization-Guided Integration module (PGI; detailed in Section 3.1), based on \\( f_{b1}^{x}, f_{b2}^{x} \\), and \\( f_{b3}^{x} \\). Importantly, both memory and query frames employ the same methodology to generate key maps. For memory frames, the value map is generated through the following steps:" + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.751, + 0.892, + 0.795 + ], + "angle": 0, + "content": "1. Trichromatic \\(I\\), \\(\\varphi\\), \\(\\rho\\), and the glass mask are concatenated along the channel dimension and fed as input to a ResNet18 model [10] to produce a feature map;" + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.796, + 0.892, + 0.854 + ], + "angle": 0, + "content": "2. The resulting feature map is concatenated with \\( f_{b3}^{x} \\) and subjected to two residual blocks [10] and a Convolutional Block Attention Module (CBAM) [48] attention block;" + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.856, + 0.891, + 0.886 + ], + "angle": 0, + "content": "3. Finally, the memory value maps are produced by aggregating the multimodality maps from step 2." + }, + { + "type": "list", + "bbox": [ + 0.512, + 0.751, + 0.892, + 0.886 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.887, + 0.891, + 0.901 + ], + "angle": 0, + "content": "In essence, relying on the query key and the pairs of mem" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.925, + 0.519, + 0.936 + ], + "angle": 0, + "content": "23220" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.089, + 0.899, + 0.429 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.438, + 0.894, + 0.47 + ], + "angle": 0, + "content": "Figure 3. Overview of PGVS-Net. The RGB-P Memory and PGI fused keys are designed to store long-range multi-view polarization cues. The short-range spectral propagation are implemented by the CMTA and PTF modules." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.495, + 0.47, + 0.618 + ], + "angle": 0, + "content": "ory key and value maps, PGVS-Net endeavors to estimate the value map (discussed in Section 3.2) for a given query frame through multi-view polarimetric propagation (described in Section 3.3) and the extraction of temporal correlations (explained in Section 3.4). The resultant value map of the query frame is then translated into the glass mask of the query frame via a decoder (introduced in Section 3.5). Our PGVS-Net is summarized in Figure 3." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.624, + 0.363, + 0.642 + ], + "angle": 0, + "content": "3.1. Polarization-Guided Integration" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.648, + 0.47, + 0.737 + ], + "angle": 0, + "content": "Polarization information provides strong cues on the material properties. We therefore leverage these polarization cues as guidance to combine multimodal key feature maps for each frame. To achieve this, we introduce a novel Polarization-Guided Integration (PGI) module. Formally, the PGI is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.138, + 0.744, + 0.234, + 0.761 + ], + "angle": 0, + "content": "\\[\nk _ {x} = \\Psi (f _ {b 3} ^ {x}),\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.138, + 0.763, + 0.469, + 0.785 + ], + "angle": 0, + "content": "\\[\n\\mathcal {Y} _ {1} = \\gamma_ {1} * \\left\\{\\left[ \\Psi \\left(k _ {I}\\right) * \\Psi \\left(k _ {\\varphi}\\right) \\right] * \\Psi \\left(k _ {I}\\right) \\right\\}, \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.138, + 0.781, + 0.469, + 0.799 + ], + "angle": 0, + "content": "\\[\n\\mathcal {Y} _ {2} = \\gamma_ {2} * \\left\\{\\left[ \\Psi \\left(k _ {I}\\right) * \\Psi \\left(k _ {\\rho}\\right) \\right] * \\Psi \\left(k _ {I}\\right) \\right\\}, \\tag {3}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.148, + 0.801, + 0.283, + 0.818 + ], + "angle": 0, + "content": "\\[\nk = \\Psi \\left(\\left[ k _ {I}, \\mathcal {Y} _ {1}, \\mathcal {Y} _ {2} \\right]\\right)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.901 + ], + "angle": 0, + "content": "where \\(x\\) is either \\(I\\), \\(\\varphi\\), or \\(\\rho\\); \\(\\gamma_{1}\\) and \\(\\gamma_{2}\\) are learnable parameters; \\(\\Psi(\\cdot)\\) represents a convolution layer, followed by a regional pooling operation (output size equals 11) and an additional convolution layer; \\(\\oplus\\) indicates a matrix multiplication. \\(k_{x} \\in \\mathbb{R}^{BT \\times H \\times W \\times C}\\), where \\(B, T, H, W, C\\) are the" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.495, + 0.892, + 0.527 + ], + "angle": 0, + "content": "batch size, temporal length, and the height, width, and channel size of a feature map, respectively." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.568, + 0.719, + 0.585 + ], + "angle": 0, + "content": "3.2. Query Value Prediction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.603, + 0.892, + 0.725 + ], + "angle": 0, + "content": "In the context of a query frame, we establish a connection between RGB-P information from multiple views by investigating the interplay between the query key and memory keys. This interaction results in corresponding value features grounded in memory affinity. Our model employs an STM variant for RGB-P memory, dynamically amalgamating multimodal inputs and establishing correlations across diverse views over an extensive temporal span." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.893, + 0.903 + ], + "angle": 0, + "content": "Concretely, when provided with a query key \\( k^Q \\), we anticipate the query value \\( v^Q \\) through the utilization of a softmax-normalized affinity matrix, which is computed from the pairing of \\( (k^M, k^Q) \\) [4]. This computation allows us to extract the most pertinent memory values. The computation of memory affinity adheres to the methodology outlined by Cheng et al. [4] (for a comprehensive explanation, please refer to the supplementary material). Memory values encapsulate historical RGB-P information of a scene, ensuring that the affinity mechanism facilitates the far-reaching propagation of multi-view spectral polarization within \\( v^Q \\)." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.925, + 0.518, + 0.937 + ], + "angle": 0, + "content": "23221" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.091, + 0.37, + 0.108 + ], + "angle": 0, + "content": "3.3. Cross Modal-Temporal Attention" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.117, + 0.47, + 0.283 + ], + "angle": 0, + "content": "To this point, the query value prediction process only utilizes long term memory by leveraging the collective information contained in the memory frames. However, captured trichromatic information also exhibits rapid changes across different modalities, indicating potential target area boundaries over short time-intervals. These changes across diverse modalities are not well captured by a long-term memory framework. To address this shortcoming, we introduce a Cross Modal-Temporal Attention module (CMTA) to model the short-term interactions between the query and its one preceding memory frame." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.285, + 0.47, + 0.361 + ], + "angle": 0, + "content": "Central to our CMTA module is a multi-head self-attention mechanism inspired by the transformer architecture [45]. This mechanism is first applied along the modality dimension and then extended to the temporal dimension. Formally, the CMTA can be defined as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.098, + 0.377, + 0.469, + 0.451 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\chi_ {m} = \\left[ \\mathcal {R} _ {m} \\left(k _ {I}\\right), \\mathcal {R} _ {m} \\left(k _ {\\varphi}\\right), \\mathcal {R} _ {m} \\left(k _ {\\rho}\\right) \\right], \\\\ F _ {m} = \\mathcal {L} \\left[ \\Upsilon \\left(\\mathcal {L} \\left(\\chi_ {m}\\right)\\right) + \\chi_ {m} \\right], (4) \\\\ \\chi_ {t} = \\left[ \\mathcal {R} _ {t} \\left(\\mathcal {C} _ {I} \\left(F _ {m}\\right)\\right), \\mathcal {R} _ {t} \\left(\\mathcal {C} _ {\\varphi} \\left(F _ {m}\\right)\\right), \\mathcal {R} _ {t} \\left(\\mathcal {C} _ {\\rho} \\left(F _ {m}\\right)\\right) \\right], (4) \\\\ F _ {t} = \\mathcal {L} [ \\Upsilon (\\mathcal {L} (\\chi_ {t})) + \\chi_ {t} ], \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.466, + 0.47, + 0.631 + ], + "angle": 0, + "content": "where \\([\\cdot]\\) indicates the concatenation on the first dimension; \\(\\Upsilon\\) indicates a multi-head self-attention block [45]; \\(\\mathcal{L}\\) refers to Layer Normalization [1]. \\(\\mathcal{R}_m\\) is a modality reshape operator, which transfers the shape of \\(k_{c}\\) from \\(\\mathbb{R}^{B\\times T\\times H\\times W\\times C}\\) into \\(\\mathbb{R}^{BT\\times HW\\times C}\\). \\(\\mathcal{R}_t\\) is a reshape operator in the temporal domain, which reshape a feature map from \\(\\mathbb{R}^{B\\times T\\times H\\times W\\times C}\\rightarrow \\mathbb{R}^{B\\times THW\\times C}\\). \\(\\mathcal{C}_x\\) is the chunked vector for modality \\(x\\). Finally, the derived \\(F_{t}\\) is concatenated with the query value acquired through the query value prediction process, and subsequently forwarded as input to the decoder." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.649, + 0.362, + 0.666 + ], + "angle": 0, + "content": "3.4. Polarimetric Temporal Forward" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.675, + 0.471, + 0.904 + ], + "angle": 0, + "content": "The examples in Figure 2 demonstrate that the polarization cues provide strong temporal continuity cues. The core idea of leveraging polarimetric continuity is that the polarization for the query frame can benefit from the preceding memory frame's polarization cues. To actualize this, the Polarimetric Temporal Forward (PTF) module engages \\( f_{b1}^{x} \\) and \\( f_{b2}^{x} \\), sourced from the query and the preceding memory frame, as inputs. This module carries out an unfolding operation \\( (\\mathcal{U}) \\) on these inputs. In order to distinguish between the features from the query and memory frames, an additional subscript is appended to the feature samples. For instance, \\( f_{M - b1}^{x} \\) and \\( f_{Q - b2}^{x} \\) represent the feature map of block 1 from a memory frame and the feature map of block 2 from a query frame for the modality \\( x \\), respectively. Formally, given \\( f_{M - b1}^{x} \\) and \\( f_{Q - b1}^{x} \\), the PTF operation is defined" + }, + { + "type": "text", + "bbox": [ + 0.501, + 0.095, + 0.523, + 0.105 + ], + "angle": 0, + "content": "as:" + }, + { + "type": "equation", + "bbox": [ + 0.546, + 0.11, + 0.892, + 0.214 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} U _ {\\varphi} ^ {M}, U _ {\\rho} ^ {M} = \\mathcal {U} \\left(f _ {M - b 1} ^ {\\varphi}\\right), \\mathcal {U} \\left(f _ {M - b 1} ^ {\\rho}\\right), \\\\ F _ {\\varphi} ^ {Q}, F _ {\\rho} ^ {Q} = \\mathcal {R} (f _ {Q - b 1} ^ {\\varphi}), \\mathcal {R} (f _ {\\rho - b 1} ^ {\\varphi}), \\\\ S _ {\\varphi} = \\sigma \\left(\\mathcal {S} \\left(F _ {\\varphi} ^ {Q} \\otimes U _ {\\varphi} ^ {M}\\right)\\right) \\otimes U _ {\\varphi} ^ {M} + f _ {b 1} ^ {\\varphi}, \\tag {5} \\\\ S _ {\\rho} = \\sigma \\left(\\mathcal {S} \\left(F _ {\\rho} ^ {Q} \\otimes U _ {\\rho} ^ {M}\\right)\\right) \\otimes U _ {\\rho} ^ {M} + f _ {b 1} ^ {\\rho}, \\\\ F _ {b 1} ^ {P T F} = S _ {\\varphi} + S _ {\\rho} + f _ {b 1} ^ {I}, \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.22, + 0.892, + 0.307 + ], + "angle": 0, + "content": "where \\(\\mathcal{R}\\) and \\(S\\) denote the reshape operation and sum operation applied to the first dimension, respectively; \\(\\otimes\\) indicates the element-wise multiplication; \\(\\sigma\\) is the softmax function. \\(U_{\\varphi}, U_{\\rho} \\in \\mathbb{R}^{C \\times P \\times H \\times W}\\), where \\(P\\) denotes the window size during the unfold convolution, and \\(f_{b2}^{I}, f_{b2}^{\\varphi}, f_{b2}^{\\rho} \\in \\mathbb{R}^{C \\times 1 \\times H \\times W}\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.31, + 0.892, + 0.432 + ], + "angle": 0, + "content": "PTF further applies the described operations to \\( f_{b2}^{\\varphi}, f_{b2}^{\\rho} \\) and \\( f_{b2}^{I} \\), yielding the output \\( F_{b2}^{PTF} \\). In our implementation, we establish the window sizes for unfold convolutions as 7 and 9 for \\( f_{b2} \\) and \\( f_{b1} \\), respectively. Through this design, PTF enables dynamic incorporation via unfold convolutions, fostering forward propagation among adjacent polarimetric features and thereby achieving inter-frame view dependency." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.44, + 0.602, + 0.455 + ], + "angle": 0, + "content": "3.5. Decoder" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.462, + 0.892, + 0.659 + ], + "angle": 0, + "content": "We employ a straightforward yet effective decoder to translate the acquired query value into the corresponding glass masks of the query frame. Our decoder encompasses two UNet-like [38] upsampling blocks, tasked with reinstating the resolution of the query value map to \\(1/4\\) of the query frame's dimensions. Subsequently, a prediction convolution transforms the channel configuration of the resultant feature map to a single channel, which is then upsampled to match the resolution of the query frame. In addition to the query value, this decoder taps into the feature maps offered by the PTF module to reinforce temporal coherence. Specifically, \\(F^{PTF}b1\\) and \\(F^{PTF}b2\\) serve as inputs to the first and second upsampling blocks, respectively." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.667, + 0.719, + 0.683 + ], + "angle": 0, + "content": "3.6. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We implement PGVS-Net in PyTorch. For training, input images are randomly cropped to \\(384 \\times 384\\) and augmented by horizontal random flipping, translations, and affine transforms. During training, the sequence takes a group of three frames as the input of the network. The masks of ground truth glass areas in the first frame are provided as input, and we employ a binary cross-entropy (BCE) loss to supervise the output mask of the last two frames. For optimization, we use the Adam optimizer with a weight decay of \\(1e - 7\\). The learning rate is fixed at \\(1e - 5\\). Training takes three days to converge on a dual TITAN V100 graphics card setup after 150,000 iterations with a batch size of 4. During inference, we update the memory bank every three frames." + }, + { + "type": "footer", + "bbox": [ + 0.479, + 0.925, + 0.521, + 0.937 + ], + "angle": 0, + "content": "23222" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.091, + 0.09, + 0.456, + 0.329 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.338, + 0.47, + 0.445 + ], + "angle": 0, + "content": "Figure 4. Summary of camera motions (left) and the PGV-117 dataset characteristics (right). To avoid biasing PGV-117 into certain types of camera motions, we implement different camera motion strategies. The blue areas represent the glass target. The 117 video sequences are captured with different types of camera paths, lighting conditions, dynamics, and materials (dark indicates ground glass)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.472, + 0.245, + 0.487 + ], + "angle": 0, + "content": "4. PGV-117 dataset" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.498, + 0.47, + 0.726 + ], + "angle": 0, + "content": "We introduce a novel RGB-P-video-based dataset, PGV-117, to support and stimulate research in video-based glass segmentation. The dataset is collected using a trichromatic (RGB) polarizer-array camera (LUCID PHX050S), equipped with four directional linear-polarizers, i.e., \\(0^{\\circ}\\), \\(45^{\\circ}\\), \\(90^{\\circ}\\) and \\(135^{\\circ}\\). The frame rate is fixed at 30fps, and we vary the exposure time from \\(3,000\\mu s\\) to \\(39,999\\mu s\\) depending on the scene and lighting conditions. Each frame in the PGV-117 dataset includes: an RGB image, four directional polarization images, inferred spectral AoLP and DoLP maps, and the captured RAW camera data. Table 1 summarizes PGV-117 statistics in comparison to prior datasets. Care was taken during creation of PGV-117 to ensure a sufficient variation in lighting conditions, camera paths, and scene dynamics." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Lighting conditions. PGV-117 is collected in various indoor environments, such as shopping malls, office buildings, and classrooms, as well as in a variety of outdoor environments. For outdoor environments, we capture sequences spanning during the full time-range from daytime to night. As such, PGV-117 offers four types of lighting variations: normal, low-light, saturated light, and high-dynamic-range. Additionally, we also consider diverse glass types in PGV-117, including clear, frosted, and patterned glasses, tinted glass on vehicles, and outdoor and indoor glass walls." + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.09, + 0.889, + 0.198 + ], + "angle": 0, + "content": "
DatasetsTaskFramesADPSeq(tr+v/te)
DAVIS2017 [34]VOS10,459#190/60
DAVSOD [6]VSOD23,938#136/90
MoCA-Mask [5]VCOD22,939#571/16
RGBP-Glass [29]IGS4,511#1✓-
PGV-117VGS21,485#1✓85/32
" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.208, + 0.892, + 0.344 + ], + "angle": 0, + "content": "Table 1. Statistics of PGV-117 compared to representative video datasets and glass datasets. In each column, we list: the primary Task for which the dataset was designed (Video Object Segmentation (VOS), Video Saliency Object Detection (VSOD), Video Camouflaged Object Detection (VCOD), and Image Glass Segmentation (IGS)); \\(AD\\): the annotation interval in #frames; \\(P\\): whether the dataset includes polarization; and \\(Seq(tr + v)/te\\): the number of training and validation exemplars versus test exemplars." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.373, + 0.892, + 0.479 + ], + "angle": 0, + "content": "Camera motion patterns. Polarization cues are angle dependent. To avoid biasing PGV-117 to certain view angles and camera paths, we randomly pick one of five predetermined camera motion patterns: front, inclined, circular, straight-forward, and up-down; see Figure 4 for a visual summary. During acquisition, we also recapture some glass areas back and forth to enrich the robustness and diversity." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.502, + 0.892, + 0.548 + ], + "angle": 0, + "content": "Dynamics. PGV-117 captures both static and dynamic scenes (e.g., doors/windows opening and closing, and pedestrians occluding glass)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.571, + 0.892, + 0.648 + ], + "angle": 0, + "content": "Frame removal. Frames characterized by motion blur and overexposure are excluded due to the inherent ambiguity in their annotations. Typically, we remove 1 to 2 frames per static-camera sequence, and about \\(20\\%\\) frames for a moving-camera sequence." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.664, + 0.634, + 0.681 + ], + "angle": 0, + "content": "5. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.69, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In this section, we first compare the performance of PGVS-Net under continuous polarization to demonstrate the robustness of combining multi-view and temporal consistency (subsection 5.1). Next, we validate the efficacy of our model by quantitatively and qualitatively comparing PGVS-Net against polarization-based and SOTA video methods retrained on the PGV-117 dataset. To quantify performance, we adopt four prevalent evaluation metrics: intersection over union (IoU), weighted F-measure \\((\\mathrm{F}_{\\beta})\\) [27], mean absolute error (MAE), and balance error rate (BER) [31]. Finally, we perform an ablation study to show the impact of the different components that comprise PGVS-Net (subsection 5.3). Please refer to the supplementary materials for additional images and video results." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.925, + 0.519, + 0.937 + ], + "angle": 0, + "content": "23223" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.09, + 0.093, + 0.28, + 0.222 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.284, + 0.093, + 0.48, + 0.222 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.48, + 0.093, + 0.677, + 0.222 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.677, + 0.093, + 0.882, + 0.222 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.225, + 0.894, + 0.256 + ], + "angle": 0, + "content": "Figure 5. Error plots comparing PGVS-Net to PM-RCNN and PGSNet for four different sequences. For reference, the DoLP is also included to indicate which frames pose a greater challenge for RGB-P methods." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.282, + 0.395, + 0.299 + ], + "angle": 0, + "content": "5.1. Multi-view Polarimetric Consistency" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.306, + 0.47, + 0.547 + ], + "angle": 0, + "content": "Due to their near-specular reflection and refraction behavior, glass materials are more sensitive to changes in view/light conditions. While RGB-P cues have proven to be essential for robust single-image glass segmentation, ignoring the temporal instability can result in inconsistent glass segmentation over time. PGVS-Net is specially designed to leverage and aggregate temporal changes in polarization cues. Figure 5 illustrates the correlation between variations in polarization intensity (DoLP) and the corresponding performance levels (measured by mIoU) in comparison to two image-based polarimetric techniques [14, 29] (applied independently to each frame) across diverse video sequences. The distinct abrupt shifts in the curve within Figure 5 due to the removal frames with motion blur (section 4), which breaks the temporal continuity and may degrade the multiview dependency of PGVS-Net." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.549, + 0.471, + 0.775 + ], + "angle": 0, + "content": "From the first result in Figure 5, we can observe that when DoLP changes significantly, prior single-frame image-based methods fail to produce a consistent, coherent segmentation. In contrast, our model not only stores and leverages historical polarization information, but also enhances the current frame with the prior polarization information through the CMTA and PTF modules, resulting in good temporal consistency. The second result in Figure 5 shows that our model can still maintain a stable performance when the overall DoLP changes within the sequence cover a relatively large range (between 0.2 and 0.45). The third and fourth result in Figure 5 show that PGVS-Net can achieve better performance in low light and high brightness environments with extremely low overall DoLP over the sequence (less than 0.12)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.787, + 0.381, + 0.803 + ], + "angle": 0, + "content": "5.2. Comparison to the State-of-the-art" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.47, + 0.901 + ], + "angle": 0, + "content": "We compare PGVS-Net to prior single-frame image-based glass segmentation methods and state-of-the-art video segmentation methods. We retrain all methods on the PGV-117 dataset and evaluate them on the 32 test sequences. We compare against: RGB-input GSD [30] where the input and supervision are replaced with our" + }, + { + "type": "table", + "bbox": [ + 0.515, + 0.281, + 0.88, + 0.451 + ], + "angle": 0, + "content": "
MethodsIoU↑Fβ↑MAE↓BER↓
GSDIS[30]80.290.8280.11512.34
EAFIS[49]41.690.5560.45043.91
PM-RCNNIS[14]76.130.7970.14015.83
PGSIS[29]79.690.8730.11912.31
STICTVU[25]50.680.5770.29932.03
ViShaVS[3]77.420.8050.13613.77
STCNVS[4]80.850.8260.12012.77
RDEVS[20]74.870.7630.16915.95
PGVS-Net (Ours)84.600.8670.09910.02
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.461, + 0.893, + 0.537 + ], + "angle": 0, + "content": "Table 2. Quantitative comparison of PGVS-Net with prior SOTA methods (method subscripts: IS: Image-based supervised, VS: Video-based supervised, and \\( VU \\): Video-based without labels). The top and second best results are highlighted in red and blue, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.567, + 0.892, + 0.734 + ], + "angle": 0, + "content": "dataset; RGB-P glass segmentation methods EAF [49], PM-RCNN [14] and PGS [29]; STICT [25] (since this is an unsupervised method, we use the polarimetric dataset from [29] as labeled images for training); ViSha [3] is a recent video shadow detection method; STM-based video segmentation methods STCN [4] and RDE [20] (with ground truth masks during training and using the mask from GSD [30] during evaluation). In all our examples, during inference, the initial masks for PGVS-Net are provided by the polarization-aware PGSNet [29]. The quantitative and qualitative results are shown in Table 2 and Figure 6." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.893, + 0.902 + ], + "angle": 0, + "content": "PGVS-Net outperforms state-of-the-art methods by a significant margin and improves IoU, MAE, and BER by 3.75, 0.016, and 2.29 over the next best method, demonstrating the effectiveness of multi-view polarization propagation for video glass segmentation. PGVS-Net performs slightly less than PGS-Net on the \\( \\mathrm{F}_{\\beta} \\) metric, which again illustrates the robustness of polarization cues for glass segmentation for both still-image and video sequences. Figure 6 further qualitatively illustrates the robustness of PGVS-Net. We refer to the video sequences in the supplementary material to qualitatively evaluate the temporally" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.925, + 0.519, + 0.936 + ], + "angle": 0, + "content": "23224" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.09, + 0.904, + 0.33 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.332, + 0.895, + 0.364 + ], + "angle": 0, + "content": "Figure 6. Qualitative comparison of our model against state-of-the-art image-based glass segmentation methods and video detection/segmentation methods. All models are retrained on PGV-117." + }, + { + "type": "image", + "bbox": [ + 0.088, + 0.379, + 0.902, + 0.504 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.2, + 0.507, + 0.768, + 0.523 + ], + "angle": 0, + "content": "Figure 7. Qualitative comparison of the different ablation combinations of PGVS-Net." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.546, + 0.469, + 0.684 + ], + "angle": 0, + "content": "
NetworksIoU↑Fβ↑MAE↓BER↓
RGB78.960.8070.14213.88
RGB-P81.010.8270.13113.16
RGB-P+PGI83.680.8600.10110.43
RGB-P+PTF81.780.8380.12212.38
RGB-P+CMTA83.810.8620.10010.88
RGB-P+PGI+CMTA+PTF(M5)80.760.8260.13412.82
PGVS-Net84.600.8670.09910.02
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.695, + 0.471, + 0.773 + ], + "angle": 0, + "content": "Table 3. Summary of ablation experiments: Polarization cues (RGB-P) outperform RGB-only cues. The combination of all modules (PGVS-Net) produces the overall best results. 'M5' indicates that the long-range memory is updated every five frames during inference." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.802, + 0.353, + 0.817 + ], + "angle": 0, + "content": "coherent glass segmentation propagation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.83, + 0.231, + 0.847 + ], + "angle": 0, + "content": "5.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.471, + 0.901 + ], + "angle": 0, + "content": "We validate the impact of each component in PGVS-Net by disabling one or more components and comparing the performance on the PGV-117 test set (Table 3). The net" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.549, + 0.892, + 0.67 + ], + "angle": 0, + "content": "work named 'RGB' uses only RGB textures to populate and query the memory to predict glass areas without any other modules. The 'RGB-P' network uses RGB-P information to store, read and calculate memory features. All other networks start from the 'RGB-P' baseline with the listed modules enabled. Finally, we indicate with 'M5' that the memory is updated every five frames during the inference stage as opposed to every three frames for PGVS-Net." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.69, + 0.893, + 0.901 + ], + "angle": 0, + "content": "The improved performance of the 'RGB-P' network over 'RGB' shows that polarization provides additional cues for glass segmentation. PGI combines tripartite key features to retrieve affinity from historical views. Its attribute performance gain shows that integrated RGB-P streams can better mine multi-view similarity than single-stream matching. The PTF module further improves the segmentation accuracy (e.g., IoU increases from 81.01 to 81.78). Adding the CMTA module further improves the performance on the four metrics, demonstrating that the cross-modal and cross-temporal integration provides rich short-range references for query frames. Finally, the full PGVS-Net with all modules enabled achieves the best results when combined with a memory update every three frames." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.925, + 0.519, + 0.937 + ], + "angle": 0, + "content": "23225" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.089, + 0.09, + 0.462, + 0.266 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.27, + 0.468, + 0.3 + ], + "angle": 0, + "content": "Figure 8. Two failure cases with inaccurate glass segmentation highlighted in the red boxes." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.33, + 0.345, + 0.346 + ], + "angle": 0, + "content": "5.4. Failure Cases and Limitations" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.356, + 0.47, + 0.613 + ], + "angle": 0, + "content": "Our method propagates a single initial mask, and thus its overall quality is affected by the quality of the initial mask. For glass areas with no initial or historical references, little information can be propagated from multi-view observations. While PGVS-Net can augment glass segmentation in such scenarios by harnessing spatial characteristics across both the RGB and polarization domain, it is possible that the segmentation can result in gaps in the glass segmentation results (two failure cases are shown in Figure 8). An interesting avenue for future research would be to determine the most reliable RGB-P frame for initial mask estimation before propagating it to the rest of the sequence. Furthermore, although PGVS-Net significantly outperforms other video segmentation methods in accuracy, its tripartite-modal integration and temporal consistency strategy of polarization cues require additional inference time. Our unoptimized implementation currently operates at 7fps." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.632, + 0.196, + 0.648 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.47, + 0.9 + ], + "angle": 0, + "content": "In this paper, we introduced a Polarization Video Glass Segmentation network (PGVS-Net), that exploits historical multi-view spectral polarization cues to segment glass areas, and which outperforms state-of-the-art polarization-related image and video segmentation networks. PGVS-Net leverages RGB-P memory and PGI-fused keys to correlate input frames with view-dependent polarization information from prior spectral cues. We show that the continuous changes in illumination are better captured by polarimetric features, and that long-range affinity helps to better balance single-input instabilities than single image methods. In addition, CMTA and PTF provide short-range polarization cues for low-level polarimetric features, providing rich wavelength details in the decoder phase. We also create a novel video glass segmentation dataset (PGV-117) to train and evaluate PGVS-Net." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.091, + 0.669, + 0.108 + ], + "angle": 0, + "content": "Acknowledgements" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.115, + 0.892, + 0.312 + ], + "angle": 0, + "content": "This work was supported in part by National Key Research and Development Program of China (2022ZD0210 500), the National Natural Science Foundation of China under Grants 61972067/U21A20491, and the Distinguished Young Scholars Funding of Dalian (No. 2022RJ01). Pieter Peers was supported in part by NSF grant IIS-1909028. Felix Heide was supported by an NSF CAREER Award (2047359), a Packard Foundation Fellowship, a Sloan Research Fellowship, a Sony Young Faculty Award, a Project X Innovation Award, and an Amazon Science Research Award. Seung-Hwan Baek acknowledges the support from NRF Korea (RS-2023-00211658, 2022R1A6A1A03052954) and Samsung Electronics." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.324, + 0.597, + 0.34 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.508, + 0.348, + 0.891, + 0.378 + ], + "angle": 0, + "content": "[1] Lei Jimmy Ba, Jamie Ryan Kiros, and Geoffrey E. Hinton. Layer normalization. CoRR, abs/1607.06450, 2016." + }, + { + "type": "ref_text", + "bbox": [ + 0.509, + 0.379, + 0.892, + 0.433 + ], + "angle": 0, + "content": "[2] Seung-Hwan Baek, Tizian Zeltner, Hyunjin Ku, Inseung Hwang, Xin Tong, Wenzel Jakob, and Min H Kim. Image-based acquisition and modeling of polarimetric reflectance. ACM TOG, 2020." + }, + { + "type": "ref_text", + "bbox": [ + 0.509, + 0.434, + 0.892, + 0.476 + ], + "angle": 0, + "content": "[3] Zhihao Chen, Liang Wan, Lei Zhu, Jia Shen, Huazhu Fu, Wennan Liu, and Jing Qin. Triple-cooperative video shadow detection. 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In CVPR, 2017." + }, + { + "type": "list", + "bbox": [ + 0.08, + 0.093, + 0.468, + 0.446 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.925, + 0.519, + 0.937 + ], + "angle": 0, + "content": "23228" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-view Spectral Polarization Propagation for Video Glass Segmentation/da43f4ff-b9d6-45ae-8913-a53d60c1040d_origin.pdf b/2023/Multi-view Spectral Polarization Propagation for Video Glass Segmentation/da43f4ff-b9d6-45ae-8913-a53d60c1040d_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..0f6235b6b81d024eb815bfaafd5712f8a791cfbd --- /dev/null +++ b/2023/Multi-view Spectral Polarization Propagation for Video Glass Segmentation/da43f4ff-b9d6-45ae-8913-a53d60c1040d_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:fc3d0966ee7f61c77480abab45ebb690d2514211bcfc39a9ea9be7ff1a79ff74 +size 9885190 diff --git a/2023/Multi-view Spectral Polarization Propagation for Video Glass Segmentation/full.md b/2023/Multi-view Spectral Polarization Propagation for Video Glass Segmentation/full.md new file mode 100644 index 0000000000000000000000000000000000000000..489b632e27d94da8e097d68407e8a57d9087037b --- /dev/null +++ b/2023/Multi-view Spectral Polarization Propagation for Video Glass Segmentation/full.md @@ -0,0 +1,298 @@ +# Multi-view Spectral Polarization Propagation for Video Glass Segmentation + +Yu Qiao, Bo Dong*, Ao Jin, Yu Fu, Seung-Hwan Baek, Felix Heide Pieter Peers, Xiaopeng Wei* Xin Yang* + +![](images/b8a4350c0a9381aede033ef0e75a126d07c9b40a659c0fbf3c77b118dca08d64.jpg) +Figure 1. A comparison of PGVS-Net on 3 selected frames from an RGB-P video sequence from our novel PGV-117 dataset against the method of Kalra et al. [14] and Mei et al. [29]. From left to right: RGB, AoLP, and DoLP input images; glass segmentation results for selected frames compared to the ground truth segmentation; evolution of error over the video sequence. Both prior methods are temporally unstable due to significant temporal changes in DoLP. In contrast, PGVS-Net combines multi-view polarization cues for segmentation propagation, yielding a temporally stable glass segmentation. + +![](images/3f0df20144e61073f3d040f6b96ecc57abda7f0f1a987882202519033bc25e60.jpg) + +![](images/fe65343d1967c92816e10569d69d96401ecf06529e215c9da172fa3e6f00f5e2.jpg) + +![](images/4ac587f36162d38706fae31e2e692179930fa8211c322e1d10369f6e45985c65.jpg) + +![](images/e146953f12cd463233e284809489f94f4acfef84d3bbb30064eac5176319c0a1.jpg) + +# Abstract + +In this paper, we present the first polarization-guided video glass segmentation propagation solution (PGVS-Net) that can robustly and coherently propagate glass segmentation in RGB-P video sequences. By leveraging spatiotemporal polarization and color information, our method combines multi-view polarization cues and thus can alleviate the view dependence of single-input intensity variations on glass objects. We demonstrate that our model can outperform glass segmentation on RGB-only video sequences as well as produce more robust segmentation than per-frame RGB-P single-image segmentation methods. To train and validate PGVS-Net, we introduce a novel RGB-P Glass Video dataset (PGV-117) containing 117 video sequences of scenes captured with different types of camera paths, lighting conditions, dynamics, and glass types. + +# 1. Introduction + +Transparent objects, such as glass, are common in man-made environments. Despite their prevalence, such objects pose numerous challenges for industrial and academic + +vision processing algorithms due to their view-dependent appearance, statistical similarity to the background environment, and lack of texture. These challenges are particularly acute for segmentation tasks that underpin autonomous driving, robotics, and aerial drone navigation. Traditional learning-based solutions [8, 30, 50, 51] that rely on RGB textures for feature extraction often fail to adequately model the illumination and view-dependent glass features. Consequently, recent advances have explored richer modalities such as light fields [44] and polarization [14, 18, 21, 29, 46, 49] for more robust segmentation of glass objects. Polarization has proven to be a strong cue for glass segmentation in still images [14, 29]. The availability of commercial off-the-shelf RGB-P cameras (e.g., Flir and Lucid), makes this last category an attractive modality for glass segmentation. + +Polarization of reflected light depends on various factors such as surface normals, material types, and illumination and view directions [2]. Due to the polarimetric near-specular behavior, glass materials are particularly challenging; small changes in object orientation and/or view/light direction can induce a rapid change in polarization state. For example, consider the glass areas '1' in Figure 2 that show a glass door in various stages of being closed. In this example, the RGB textures remain almost unchanged, but + +![](images/a811fc1ed27b676cb74968e09efb14db1cb6d7d431b772097b6cb59e2f32f698.jpg) +Figure 2. Representative exemplars from the PGV-117 dataset containing a total of 117 video sequences captured with a variety of camera movement patterns, lighting conditions, scene dynamics, and materials. Glass areas '1' depict a door in various stages of being closed. Glass areas '2' are captured by moving the camera. + +changes in the surface normal induce a significant decrease in the Angle of Linear Polarization (AoLP) from close to $\pi$ (red-blue mixture) to less than half $\pi$ (full blue), and a noticeable reduction in the Degree of Linear Polarization (DoLP) from 0.137 to 0.043. Similarly, moving the camera will induce a similar change in the polarization (e.g., the glass areas '2' in Figure 2). These observations suggest that polarization cues are beneficial for glass segmentation and can provide additional guidance. Furthermore, the DOLP in glass area '1' is unstable across the entire span of the video sequence, with noticeable DoLP reductions at specific angles of incidence ( $\rho = 0.043$ ). Such types of instabilities can confuse methods [14, 29] that only rely on a single-frame RGB-P as input (Figure 1, right). Moreover, extracting glass features from RGB textures or polarization cues from a single view may also be difficult (e.g., under low light conditions as in Figure 1 left). As a consequence, polarization cues that are robust for static single image segmentation methods, can still yield temporally disjoint and inconsistent segmentation results when applied to + +video sequences, especially when object orientation and/or viewpoint changes. + +In this paper, we introduce a Polarization Video Glass Segmentation network (PGVS-Net) to robustly and coherently propagate an initial glass segmentation mask over an RGB-P video sequence. PGVS-Net perceives multi-view polarimetric features from long-range memory and short-range integration. A variation of the Spatio-Temporal Memory network (STM) [33] is introduced to leverage spectral polarization cues for constructing long-range view dependency. A well-designed Polarization-Guide Integration module (PGI) is responsible for the frame identity and historical polarization matching. Furthermore, a novel Polarization Temporal Forward module (PTF) integrates previous polarization cues to promote short-range spectral consistency during the decoder process. We also leverage cross-modal and cross-temporal attention (CMTA) to integrate multimodal features and temporal representations from different frames. To train and test PGVS-Net, we capture and annotate a large-scale video glass segmentation dataset, PGV-117, which includes 21,485 annotated RGB-P frames and masks. We demonstrate, using this newly created dataset, that our PGVS-Net outperforms competing single-frame RGB-P glass segmentation methods as well as RGB-based video segmentation methods both quantitatively and qualitatively. + +In summary, our contributions are: + +- A novel Polarization Video Glass Segmentation network (PGVS-Net) to robustly provide glass segmentation propagation in RGB-P video sequences; +- A series of polarimetric consistency and integration modules to enhance spatio-temporal correlation of spectral polarization cues; +- A large-scale video glass segmentation dataset, PGV117, containing 21,485 frames with spectral polarization cues and densely-annotated masks. + +# 2. Background and Related Work + +Polarization. Light is an electro-magnetic wave, whose polarization state describes the orientation of the transverse electric field, which can be unpolarized (i.e., random), linearly polarized (i.e. biased towards a single direction), or circularly polarized. We focus our discussion on linear polarization as supported by recent commercial polarization-array CMOS sensors, which allows us to record four distinct linear-polarization states per pixel: $I_{0^{\circ}}$ , $I_{45^{\circ}}$ , $I_{90^{\circ}}$ , and $I_{135^{\circ}}$ , where $I_x$ describes the intensity of linearly-polarized light at an angle $x$ . These four linear polarization measurements allow us to compute the linear-polarization compo + +nents of the Stokes vector $S = [S_0,S_1,S_2]$ + +$$ +S _ {0} = I _ {0 ^ {\circ}} + I _ {9 0 ^ {\circ}} = I _ {4 5 ^ {\circ}} + I _ {1 3 5 ^ {\circ}}, +$$ + +$$ +S _ {1} = I _ {0 ^ {\circ}} - I _ {9 0 ^ {\circ}}, \tag {1} +$$ + +$$ +S _ {2} = I _ {4 5 ^ {\circ}} - I _ {1 3 5 ^ {\circ}}, +$$ + +where $S_{0}$ is the total light intensity, $S_{1}$ and $S_{2}$ are the ratio of the $0^{\circ}$ and $45^{\circ}$ , respectively, linear polarization intensity over its perpendicular counterpart. Given the linear Stokes vector, the degree of linear polarization (DoLP) and the angle of linear polarization (AoLP) are defined as: + +$$ +\mathrm {D o L P} = \frac {\sqrt {S _ {1} ^ {2} + S _ {2} ^ {2}}}{S _ {0}}, \quad \mathrm {A o L P} = \frac {1}{2} \arctan \left(\frac {S _ {2}}{S _ {1}}\right). \tag {2} +$$ + +Glass Object Segmentation. RGB texture information has proven to be an effective cue for image detection [41, 42, 43] and segmentation [24, 36, 37]. However, accurately segmenting glass objects in images remains a challenging problem because of the dynamic texture patterns that vary with viewing conditions due to reflection and transmission that share the statistics of the surrounding scene. Prior glass segmentation methods operating exclusively on RGB images have leveraged contextual information [30, 52, 53] or boundary cues [9, 50] to address these challenges. However, the effectiveness of RGB-only appearance cues depends on the lighting conditions, the amount of scene clutter, and the presence of nefarious actors (e.g., print-out-spoofs) [14]. One avenue to improve glass segmentation robustness is to include additional modalities that further differentiate glass objects from others, such as scene depth [28], thermal information [12], and polarization [14, 29]. Our approach falls in this latter category, and we rely on RGB and polarization (RGB-P) to robustly segment glass objects. However, the strength of the polarization cues can vary from frame to frame in a video sequence due to changes in view or lighting conditions yielding inconsistent object segmentation between frames. In this work, we leverage multi-view observations to recover a more complete, less view-dependent, description of the polarization properties of objects in the scene, resulting in a temporally more robust glass segmentation. + +Video Segmentation and Detection. Video sequences can offer additional temporal cues to aid segmentation and detection tasks, but simultaneously also introduce the additional challenge of temporal consistency. Semantic video segmentation methods enhance temporal consistency via a variety of temporal propagating approaches such as optical flow[13, 32, 55], spatially varying convolutions [23], and recurrent network architectures [40]. In the absence of semantic cues, video object segmentation approaches estimate consistent class-agnostic object masks and instance + +IDs by exploiting spatial and temporal information to propagate an initial mask [4, 7, 11, 20, 26, 33, 39]. Panoptic segmentation [16] is a popular and successful segmentation approach that unifies semantic and instance segmentation, and which has also been extended to video segmentation [15, 22, 35, 47]. In addition to segmentation, the related problem of object detection has recently also been extended to video sequences in different application domains such as salient object detection [17, 19], camouflaged object detection [5], shadow detection [3, 25], and video action detection [54]. Similar to prior work, we also exploit spatial and temporal cues. In addition, we also leverage the richer embedded cues in RGB-P videos and gather robust polarization cues from multi-view observations to aid in propagating glass segmentation masks in video sequences. To the best of our knowledge, none of the prior segmentation propagation methods can effectively leverage polarization cues that are uncorrelated with RGB features. + +# 3. Polarimetric Video Glass Segmentation + +Our Polarization Video Glass Segmentation network (PGVS-Net) sequentially processes video frames beginning with the second frame, utilizing the ground truth annotation provided in the initial frame. As the video processing unfolds, preceding frames with object masks—established in the first frame or inferred in subsequent frames—are employed as memory frames. Furthermore, the current frame, excluding the object mask, assumes the role of the query frame. Note that each frame consists of trichromatic intensity $I$ , AoLP $\varphi$ , and DoLP $\rho$ information. + +Inspired by the successful Spatial-Temporal Memory (STM) framework [4, 33], we encode each frame into a paired set of key and value maps. Specifically, for a given modality $x$ , we utilize a ResNet50 architecture [10] to encode the modality into three distinct feature maps: $f_{b1}^{x}, f_{b2}^{x}$ , and $f_{b3}^{x}$ , corresponding to the outputs of the first, second, and third blocks, respectively. The key feature map of each frame is derived using our specially devised Polarization-Guided Integration module (PGI; detailed in Section 3.1), based on $f_{b1}^{x}, f_{b2}^{x}$ , and $f_{b3}^{x}$ . Importantly, both memory and query frames employ the same methodology to generate key maps. For memory frames, the value map is generated through the following steps: + +1. Trichromatic $I$ , $\varphi$ , $\rho$ , and the glass mask are concatenated along the channel dimension and fed as input to a ResNet18 model [10] to produce a feature map; +2. The resulting feature map is concatenated with $f_{b3}^{x}$ and subjected to two residual blocks [10] and a Convolutional Block Attention Module (CBAM) [48] attention block; +3. Finally, the memory value maps are produced by aggregating the multimodality maps from step 2. + +In essence, relying on the query key and the pairs of mem + +![](images/45fe6e4ad30c875c46000e0eb91ab5841682ec6840775fb2417d7cdc1ef934cb.jpg) +Figure 3. Overview of PGVS-Net. The RGB-P Memory and PGI fused keys are designed to store long-range multi-view polarization cues. The short-range spectral propagation are implemented by the CMTA and PTF modules. + +ory key and value maps, PGVS-Net endeavors to estimate the value map (discussed in Section 3.2) for a given query frame through multi-view polarimetric propagation (described in Section 3.3) and the extraction of temporal correlations (explained in Section 3.4). The resultant value map of the query frame is then translated into the glass mask of the query frame via a decoder (introduced in Section 3.5). Our PGVS-Net is summarized in Figure 3. + +# 3.1. Polarization-Guided Integration + +Polarization information provides strong cues on the material properties. We therefore leverage these polarization cues as guidance to combine multimodal key feature maps for each frame. To achieve this, we introduce a novel Polarization-Guided Integration (PGI) module. Formally, the PGI is defined as: + +$$ +k _ {x} = \Psi (f _ {b 3} ^ {x}), +$$ + +$$ +\mathcal {Y} _ {1} = \gamma_ {1} * \left\{\left[ \Psi \left(k _ {I}\right) * \Psi \left(k _ {\varphi}\right) \right] * \Psi \left(k _ {I}\right) \right\}, \tag {3} +$$ + +$$ +\mathcal {Y} _ {2} = \gamma_ {2} * \left\{\left[ \Psi \left(k _ {I}\right) * \Psi \left(k _ {\rho}\right) \right] * \Psi \left(k _ {I}\right) \right\}, \tag {3} +$$ + +$$ +k = \Psi \left(\left[ k _ {I}, \mathcal {Y} _ {1}, \mathcal {Y} _ {2} \right]\right) +$$ + +where $x$ is either $I$ , $\varphi$ , or $\rho$ ; $\gamma_{1}$ and $\gamma_{2}$ are learnable parameters; $\Psi(\cdot)$ represents a convolution layer, followed by a regional pooling operation (output size equals 11) and an additional convolution layer; $\oplus$ indicates a matrix multiplication. $k_{x} \in \mathbb{R}^{BT \times H \times W \times C}$ , where $B, T, H, W, C$ are the + +batch size, temporal length, and the height, width, and channel size of a feature map, respectively. + +# 3.2. Query Value Prediction + +In the context of a query frame, we establish a connection between RGB-P information from multiple views by investigating the interplay between the query key and memory keys. This interaction results in corresponding value features grounded in memory affinity. Our model employs an STM variant for RGB-P memory, dynamically amalgamating multimodal inputs and establishing correlations across diverse views over an extensive temporal span. + +Concretely, when provided with a query key $k^Q$ , we anticipate the query value $v^Q$ through the utilization of a softmax-normalized affinity matrix, which is computed from the pairing of $(k^M, k^Q)$ [4]. This computation allows us to extract the most pertinent memory values. The computation of memory affinity adheres to the methodology outlined by Cheng et al. [4] (for a comprehensive explanation, please refer to the supplementary material). Memory values encapsulate historical RGB-P information of a scene, ensuring that the affinity mechanism facilitates the far-reaching propagation of multi-view spectral polarization within $v^Q$ . + +# 3.3. Cross Modal-Temporal Attention + +To this point, the query value prediction process only utilizes long term memory by leveraging the collective information contained in the memory frames. However, captured trichromatic information also exhibits rapid changes across different modalities, indicating potential target area boundaries over short time-intervals. These changes across diverse modalities are not well captured by a long-term memory framework. To address this shortcoming, we introduce a Cross Modal-Temporal Attention module (CMTA) to model the short-term interactions between the query and its one preceding memory frame. + +Central to our CMTA module is a multi-head self-attention mechanism inspired by the transformer architecture [45]. This mechanism is first applied along the modality dimension and then extended to the temporal dimension. Formally, the CMTA can be defined as follows: + +$$ +\begin{array}{l} \chi_ {m} = \left[ \mathcal {R} _ {m} \left(k _ {I}\right), \mathcal {R} _ {m} \left(k _ {\varphi}\right), \mathcal {R} _ {m} \left(k _ {\rho}\right) \right], \\ F _ {m} = \mathcal {L} \left[ \Upsilon \left(\mathcal {L} \left(\chi_ {m}\right)\right) + \chi_ {m} \right], (4) \\ \chi_ {t} = \left[ \mathcal {R} _ {t} \left(\mathcal {C} _ {I} \left(F _ {m}\right)\right), \mathcal {R} _ {t} \left(\mathcal {C} _ {\varphi} \left(F _ {m}\right)\right), \mathcal {R} _ {t} \left(\mathcal {C} _ {\rho} \left(F _ {m}\right)\right) \right], (4) \\ F _ {t} = \mathcal {L} [ \Upsilon (\mathcal {L} (\chi_ {t})) + \chi_ {t} ], \\ \end{array} +$$ + +where $[\cdot]$ indicates the concatenation on the first dimension; $\Upsilon$ indicates a multi-head self-attention block [45]; $\mathcal{L}$ refers to Layer Normalization [1]. $\mathcal{R}_m$ is a modality reshape operator, which transfers the shape of $k_{c}$ from $\mathbb{R}^{B\times T\times H\times W\times C}$ into $\mathbb{R}^{BT\times HW\times C}$ . $\mathcal{R}_t$ is a reshape operator in the temporal domain, which reshape a feature map from $\mathbb{R}^{B\times T\times H\times W\times C}\rightarrow \mathbb{R}^{B\times THW\times C}$ . $\mathcal{C}_x$ is the chunked vector for modality $x$ . Finally, the derived $F_{t}$ is concatenated with the query value acquired through the query value prediction process, and subsequently forwarded as input to the decoder. + +# 3.4. Polarimetric Temporal Forward + +The examples in Figure 2 demonstrate that the polarization cues provide strong temporal continuity cues. The core idea of leveraging polarimetric continuity is that the polarization for the query frame can benefit from the preceding memory frame's polarization cues. To actualize this, the Polarimetric Temporal Forward (PTF) module engages $f_{b1}^{x}$ and $f_{b2}^{x}$ , sourced from the query and the preceding memory frame, as inputs. This module carries out an unfolding operation $(\mathcal{U})$ on these inputs. In order to distinguish between the features from the query and memory frames, an additional subscript is appended to the feature samples. For instance, $f_{M - b1}^{x}$ and $f_{Q - b2}^{x}$ represent the feature map of block 1 from a memory frame and the feature map of block 2 from a query frame for the modality $x$ , respectively. Formally, given $f_{M - b1}^{x}$ and $f_{Q - b1}^{x}$ , the PTF operation is defined + +as: + +$$ +\begin{array}{l} U _ {\varphi} ^ {M}, U _ {\rho} ^ {M} = \mathcal {U} \left(f _ {M - b 1} ^ {\varphi}\right), \mathcal {U} \left(f _ {M - b 1} ^ {\rho}\right), \\ F _ {\varphi} ^ {Q}, F _ {\rho} ^ {Q} = \mathcal {R} (f _ {Q - b 1} ^ {\varphi}), \mathcal {R} (f _ {\rho - b 1} ^ {\varphi}), \\ S _ {\varphi} = \sigma \left(\mathcal {S} \left(F _ {\varphi} ^ {Q} \otimes U _ {\varphi} ^ {M}\right)\right) \otimes U _ {\varphi} ^ {M} + f _ {b 1} ^ {\varphi}, \tag {5} \\ S _ {\rho} = \sigma \left(\mathcal {S} \left(F _ {\rho} ^ {Q} \otimes U _ {\rho} ^ {M}\right)\right) \otimes U _ {\rho} ^ {M} + f _ {b 1} ^ {\rho}, \\ F _ {b 1} ^ {P T F} = S _ {\varphi} + S _ {\rho} + f _ {b 1} ^ {I}, \\ \end{array} +$$ + +where $\mathcal{R}$ and $S$ denote the reshape operation and sum operation applied to the first dimension, respectively; $\otimes$ indicates the element-wise multiplication; $\sigma$ is the softmax function. $U_{\varphi}, U_{\rho} \in \mathbb{R}^{C \times P \times H \times W}$ , where $P$ denotes the window size during the unfold convolution, and $f_{b2}^{I}, f_{b2}^{\varphi}, f_{b2}^{\rho} \in \mathbb{R}^{C \times 1 \times H \times W}$ . + +PTF further applies the described operations to $f_{b2}^{\varphi}, f_{b2}^{\rho}$ and $f_{b2}^{I}$ , yielding the output $F_{b2}^{PTF}$ . In our implementation, we establish the window sizes for unfold convolutions as 7 and 9 for $f_{b2}$ and $f_{b1}$ , respectively. Through this design, PTF enables dynamic incorporation via unfold convolutions, fostering forward propagation among adjacent polarimetric features and thereby achieving inter-frame view dependency. + +# 3.5. Decoder + +We employ a straightforward yet effective decoder to translate the acquired query value into the corresponding glass masks of the query frame. Our decoder encompasses two UNet-like [38] upsampling blocks, tasked with reinstating the resolution of the query value map to $1/4$ of the query frame's dimensions. Subsequently, a prediction convolution transforms the channel configuration of the resultant feature map to a single channel, which is then upsampled to match the resolution of the query frame. In addition to the query value, this decoder taps into the feature maps offered by the PTF module to reinforce temporal coherence. Specifically, $F^{PTF}b1$ and $F^{PTF}b2$ serve as inputs to the first and second upsampling blocks, respectively. + +# 3.6. Implementation Details + +We implement PGVS-Net in PyTorch. For training, input images are randomly cropped to $384 \times 384$ and augmented by horizontal random flipping, translations, and affine transforms. During training, the sequence takes a group of three frames as the input of the network. The masks of ground truth glass areas in the first frame are provided as input, and we employ a binary cross-entropy (BCE) loss to supervise the output mask of the last two frames. For optimization, we use the Adam optimizer with a weight decay of $1e - 7$ . The learning rate is fixed at $1e - 5$ . Training takes three days to converge on a dual TITAN V100 graphics card setup after 150,000 iterations with a batch size of 4. During inference, we update the memory bank every three frames. + +![](images/de384d01d466c80d77ec98d6512f718bdac8622d3362ff6778421987dadc1abb.jpg) +Figure 4. Summary of camera motions (left) and the PGV-117 dataset characteristics (right). To avoid biasing PGV-117 into certain types of camera motions, we implement different camera motion strategies. The blue areas represent the glass target. The 117 video sequences are captured with different types of camera paths, lighting conditions, dynamics, and materials (dark indicates ground glass). + +# 4. PGV-117 dataset + +We introduce a novel RGB-P-video-based dataset, PGV-117, to support and stimulate research in video-based glass segmentation. The dataset is collected using a trichromatic (RGB) polarizer-array camera (LUCID PHX050S), equipped with four directional linear-polarizers, i.e., $0^{\circ}$ , $45^{\circ}$ , $90^{\circ}$ and $135^{\circ}$ . The frame rate is fixed at 30fps, and we vary the exposure time from $3,000\mu s$ to $39,999\mu s$ depending on the scene and lighting conditions. Each frame in the PGV-117 dataset includes: an RGB image, four directional polarization images, inferred spectral AoLP and DoLP maps, and the captured RAW camera data. Table 1 summarizes PGV-117 statistics in comparison to prior datasets. Care was taken during creation of PGV-117 to ensure a sufficient variation in lighting conditions, camera paths, and scene dynamics. + +Lighting conditions. PGV-117 is collected in various indoor environments, such as shopping malls, office buildings, and classrooms, as well as in a variety of outdoor environments. For outdoor environments, we capture sequences spanning during the full time-range from daytime to night. As such, PGV-117 offers four types of lighting variations: normal, low-light, saturated light, and high-dynamic-range. Additionally, we also consider diverse glass types in PGV-117, including clear, frosted, and patterned glasses, tinted glass on vehicles, and outdoor and indoor glass walls. + +
DatasetsTaskFramesADPSeq(tr+v/te)
DAVIS2017 [34]VOS10,459#190/60
DAVSOD [6]VSOD23,938#136/90
MoCA-Mask [5]VCOD22,939#571/16
RGBP-Glass [29]IGS4,511#1✓-
PGV-117VGS21,485#1✓85/32
+ +Table 1. Statistics of PGV-117 compared to representative video datasets and glass datasets. In each column, we list: the primary Task for which the dataset was designed (Video Object Segmentation (VOS), Video Saliency Object Detection (VSOD), Video Camouflaged Object Detection (VCOD), and Image Glass Segmentation (IGS)); $AD$ : the annotation interval in #frames; $P$ : whether the dataset includes polarization; and $Seq(tr + v)/te$ : the number of training and validation exemplars versus test exemplars. + +Camera motion patterns. Polarization cues are angle dependent. To avoid biasing PGV-117 to certain view angles and camera paths, we randomly pick one of five predetermined camera motion patterns: front, inclined, circular, straight-forward, and up-down; see Figure 4 for a visual summary. During acquisition, we also recapture some glass areas back and forth to enrich the robustness and diversity. + +Dynamics. PGV-117 captures both static and dynamic scenes (e.g., doors/windows opening and closing, and pedestrians occluding glass). + +Frame removal. Frames characterized by motion blur and overexposure are excluded due to the inherent ambiguity in their annotations. Typically, we remove 1 to 2 frames per static-camera sequence, and about $20\%$ frames for a moving-camera sequence. + +# 5. Experiments + +In this section, we first compare the performance of PGVS-Net under continuous polarization to demonstrate the robustness of combining multi-view and temporal consistency (subsection 5.1). Next, we validate the efficacy of our model by quantitatively and qualitatively comparing PGVS-Net against polarization-based and SOTA video methods retrained on the PGV-117 dataset. To quantify performance, we adopt four prevalent evaluation metrics: intersection over union (IoU), weighted F-measure $(\mathrm{F}_{\beta})$ [27], mean absolute error (MAE), and balance error rate (BER) [31]. Finally, we perform an ablation study to show the impact of the different components that comprise PGVS-Net (subsection 5.3). Please refer to the supplementary materials for additional images and video results. + +![](images/c279678244d2dece7e9009c076b1538c2c0937d1926bab80595847d9b5a84788.jpg) +Figure 5. Error plots comparing PGVS-Net to PM-RCNN and PGSNet for four different sequences. For reference, the DoLP is also included to indicate which frames pose a greater challenge for RGB-P methods. + +![](images/05de1b1275e1bbef5f55391ab4fc71e52b3dbaf93baf73ceb50a041edc2b4d04.jpg) + +![](images/afb07196161750ebe915b7b2d10c3f0861ee509d5463005bae812469865d7495.jpg) + +![](images/e6dec4091c1cdb305a859519963c8608f18f9f148249de935ecaedd6fdf03039.jpg) + +# 5.1. Multi-view Polarimetric Consistency + +Due to their near-specular reflection and refraction behavior, glass materials are more sensitive to changes in view/light conditions. While RGB-P cues have proven to be essential for robust single-image glass segmentation, ignoring the temporal instability can result in inconsistent glass segmentation over time. PGVS-Net is specially designed to leverage and aggregate temporal changes in polarization cues. Figure 5 illustrates the correlation between variations in polarization intensity (DoLP) and the corresponding performance levels (measured by mIoU) in comparison to two image-based polarimetric techniques [14, 29] (applied independently to each frame) across diverse video sequences. The distinct abrupt shifts in the curve within Figure 5 due to the removal frames with motion blur (section 4), which breaks the temporal continuity and may degrade the multiview dependency of PGVS-Net. + +From the first result in Figure 5, we can observe that when DoLP changes significantly, prior single-frame image-based methods fail to produce a consistent, coherent segmentation. In contrast, our model not only stores and leverages historical polarization information, but also enhances the current frame with the prior polarization information through the CMTA and PTF modules, resulting in good temporal consistency. The second result in Figure 5 shows that our model can still maintain a stable performance when the overall DoLP changes within the sequence cover a relatively large range (between 0.2 and 0.45). The third and fourth result in Figure 5 show that PGVS-Net can achieve better performance in low light and high brightness environments with extremely low overall DoLP over the sequence (less than 0.12). + +# 5.2. Comparison to the State-of-the-art + +We compare PGVS-Net to prior single-frame image-based glass segmentation methods and state-of-the-art video segmentation methods. We retrain all methods on the PGV-117 dataset and evaluate them on the 32 test sequences. We compare against: RGB-input GSD [30] where the input and supervision are replaced with our + +
MethodsIoU↑Fβ↑MAE↓BER↓
GSDIS[30]80.290.8280.11512.34
EAFIS[49]41.690.5560.45043.91
PM-RCNNIS[14]76.130.7970.14015.83
PGSIS[29]79.690.8730.11912.31
STICTVU[25]50.680.5770.29932.03
ViShaVS[3]77.420.8050.13613.77
STCNVS[4]80.850.8260.12012.77
RDEVS[20]74.870.7630.16915.95
PGVS-Net (Ours)84.600.8670.09910.02
+ +Table 2. Quantitative comparison of PGVS-Net with prior SOTA methods (method subscripts: IS: Image-based supervised, VS: Video-based supervised, and $VU$ : Video-based without labels). The top and second best results are highlighted in red and blue, respectively. + +dataset; RGB-P glass segmentation methods EAF [49], PM-RCNN [14] and PGS [29]; STICT [25] (since this is an unsupervised method, we use the polarimetric dataset from [29] as labeled images for training); ViSha [3] is a recent video shadow detection method; STM-based video segmentation methods STCN [4] and RDE [20] (with ground truth masks during training and using the mask from GSD [30] during evaluation). In all our examples, during inference, the initial masks for PGVS-Net are provided by the polarization-aware PGSNet [29]. The quantitative and qualitative results are shown in Table 2 and Figure 6. + +PGVS-Net outperforms state-of-the-art methods by a significant margin and improves IoU, MAE, and BER by 3.75, 0.016, and 2.29 over the next best method, demonstrating the effectiveness of multi-view polarization propagation for video glass segmentation. PGVS-Net performs slightly less than PGS-Net on the $\mathrm{F}_{\beta}$ metric, which again illustrates the robustness of polarization cues for glass segmentation for both still-image and video sequences. Figure 6 further qualitatively illustrates the robustness of PGVS-Net. We refer to the video sequences in the supplementary material to qualitatively evaluate the temporally + +![](images/47213855b4533228afed374244f4e6b1b6c7c92333fb7084587ba1dbd7229d67.jpg) +Figure 6. Qualitative comparison of our model against state-of-the-art image-based glass segmentation methods and video detection/segmentation methods. All models are retrained on PGV-117. + +![](images/ac67882c5fed5f43f34280df6e0ea8e4b593c41cc8f578f5c012f360351ef0b1.jpg) +Figure 7. Qualitative comparison of the different ablation combinations of PGVS-Net. + +
NetworksIoU↑Fβ↑MAE↓BER↓
RGB78.960.8070.14213.88
RGB-P81.010.8270.13113.16
RGB-P+PGI83.680.8600.10110.43
RGB-P+PTF81.780.8380.12212.38
RGB-P+CMTA83.810.8620.10010.88
RGB-P+PGI+CMTA+PTF(M5)80.760.8260.13412.82
PGVS-Net84.600.8670.09910.02
+ +Table 3. Summary of ablation experiments: Polarization cues (RGB-P) outperform RGB-only cues. The combination of all modules (PGVS-Net) produces the overall best results. 'M5' indicates that the long-range memory is updated every five frames during inference. + +coherent glass segmentation propagation. + +# 5.3. Ablation Study + +We validate the impact of each component in PGVS-Net by disabling one or more components and comparing the performance on the PGV-117 test set (Table 3). The net + +work named 'RGB' uses only RGB textures to populate and query the memory to predict glass areas without any other modules. The 'RGB-P' network uses RGB-P information to store, read and calculate memory features. All other networks start from the 'RGB-P' baseline with the listed modules enabled. Finally, we indicate with 'M5' that the memory is updated every five frames during the inference stage as opposed to every three frames for PGVS-Net. + +The improved performance of the 'RGB-P' network over 'RGB' shows that polarization provides additional cues for glass segmentation. PGI combines tripartite key features to retrieve affinity from historical views. Its attribute performance gain shows that integrated RGB-P streams can better mine multi-view similarity than single-stream matching. The PTF module further improves the segmentation accuracy (e.g., IoU increases from 81.01 to 81.78). Adding the CMTA module further improves the performance on the four metrics, demonstrating that the cross-modal and cross-temporal integration provides rich short-range references for query frames. Finally, the full PGVS-Net with all modules enabled achieves the best results when combined with a memory update every three frames. + +![](images/aa204cc6f7bc377688a5ae8731d6da89b222a7873a7d1fcbfaf2742f92a6fe83.jpg) +Figure 8. Two failure cases with inaccurate glass segmentation highlighted in the red boxes. + +# 5.4. Failure Cases and Limitations + +Our method propagates a single initial mask, and thus its overall quality is affected by the quality of the initial mask. For glass areas with no initial or historical references, little information can be propagated from multi-view observations. While PGVS-Net can augment glass segmentation in such scenarios by harnessing spatial characteristics across both the RGB and polarization domain, it is possible that the segmentation can result in gaps in the glass segmentation results (two failure cases are shown in Figure 8). An interesting avenue for future research would be to determine the most reliable RGB-P frame for initial mask estimation before propagating it to the rest of the sequence. Furthermore, although PGVS-Net significantly outperforms other video segmentation methods in accuracy, its tripartite-modal integration and temporal consistency strategy of polarization cues require additional inference time. Our unoptimized implementation currently operates at 7fps. + +# 6. Conclusion + +In this paper, we introduced a Polarization Video Glass Segmentation network (PGVS-Net), that exploits historical multi-view spectral polarization cues to segment glass areas, and which outperforms state-of-the-art polarization-related image and video segmentation networks. PGVS-Net leverages RGB-P memory and PGI-fused keys to correlate input frames with view-dependent polarization information from prior spectral cues. We show that the continuous changes in illumination are better captured by polarimetric features, and that long-range affinity helps to better balance single-input instabilities than single image methods. In addition, CMTA and PTF provide short-range polarization cues for low-level polarimetric features, providing rich wavelength details in the decoder phase. We also create a novel video glass segmentation dataset (PGV-117) to train and evaluate PGVS-Net. + +# Acknowledgements + +This work was supported in part by National Key Research and Development Program of China (2022ZD0210 500), the National Natural Science Foundation of China under Grants 61972067/U21A20491, and the Distinguished Young Scholars Funding of Dalian (No. 2022RJ01). Pieter Peers was supported in part by NSF grant IIS-1909028. Felix Heide was supported by an NSF CAREER Award (2047359), a Packard Foundation Fellowship, a Sloan Research Fellowship, a Sony Young Faculty Award, a Project X Innovation Award, and an Amazon Science Research Award. Seung-Hwan Baek acknowledges the support from NRF Korea (RS-2023-00211658, 2022R1A6A1A03052954) and Samsung Electronics. + +# References + +[1] Lei Jimmy Ba, Jamie Ryan Kiros, and Geoffrey E. Hinton. Layer normalization. CoRR, abs/1607.06450, 2016. +[2] Seung-Hwan Baek, Tizian Zeltner, Hyunjin Ku, Inseung Hwang, Xin Tong, Wenzel Jakob, and Min H Kim. Image-based acquisition and modeling of polarimetric reflectance. ACM TOG, 2020. +[3] Zhihao Chen, Liang Wan, Lei Zhu, Jia Shen, Huazhu Fu, Wennan Liu, and Jing Qin. Triple-cooperative video shadow detection. In CVPR, 2021. +[4] Ho Kei Cheng, Yu-Wing Tai, and Chi-Keung Tang. Rethinking space-time networks with improved memory coverage for efficient video object segmentation. 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A comparison of PGVS-Net on 3 selected frames from an RGB-P video sequence from our novel PGV-117 dataset against the method of Kalra et al. [14] and Mei et al. [29]. From left to right: RGB, AoLP, and DoLP input images; glass segmentation results for selected frames compared to the ground truth segmentation; evolution of error over the video sequence. Both prior methods are temporally unstable due to significant temporal changes in DoLP. In contrast, PGVS-Net combines multi-view polarization cues for segmentation propagation, yielding a temporally stable glass segmentation." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 115, + 198, + 192, + 327 + ], + "blocks": [ + { + "bbox": [ + 115, + 198, + 192, + 327 + ], + "lines": [ + { + "bbox": [ + 115, + 198, + 192, + 327 + ], + "spans": [ + { + "bbox": [ + 115, + 198, + 192, + 327 + ], + "type": "image", + "image_path": "3f0df20144e61073f3d040f6b96ecc57abda7f0f1a987882202519033bc25e60.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_body" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 194, + 199, + 286, + 327 + ], + "blocks": [ + { + "bbox": [ + 194, + 199, + 286, + 327 + ], + "lines": [ + { + "bbox": [ + 194, + 199, + 286, + 327 + ], + "spans": [ + { + "bbox": [ + 194, + 199, + 286, + 327 + ], + "type": "image", + "image_path": "fe65343d1967c92816e10569d69d96401ecf06529e215c9da172fa3e6f00f5e2.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 286, + 199, + 378, + 327 + ], + "blocks": [ + { + "bbox": [ + 286, + 199, + 378, + 327 + ], + "lines": [ + { + "bbox": [ + 286, + 199, + 378, + 327 + ], + "spans": [ + { + "bbox": [ + 286, + 199, + 378, + 327 + ], + "type": "image", + "image_path": "4ac587f36162d38706fae31e2e692179930fa8211c322e1d10369f6e45985c65.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 379, + 205, + 533, + 328 + ], + "blocks": [ + { + "bbox": [ + 379, + 205, + 533, + 328 + ], + "lines": [ + { + "bbox": [ + 379, + 205, + 533, + 328 + ], + "spans": [ + { + "bbox": [ + 379, + 205, + 533, + 328 + ], + "type": "image", + "image_path": "e146953f12cd463233e284809489f94f4acfef84d3bbb30064eac5176319c0a1.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 143, + 413, + 192, + 425 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 413, + 192, + 425 + ], + "spans": [ + { + "bbox": [ + 143, + 413, + 192, + 425 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 437, + 289, + 619 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 289, + 619 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 289, + 619 + ], + "type": "text", + "content": "In this paper, we present the first polarization-guided video glass segmentation propagation solution (PGVS-Net) that can robustly and coherently propagate glass segmentation in RGB-P video sequences. By leveraging spatiotemporal polarization and color information, our method combines multi-view polarization cues and thus can alleviate the view dependence of single-input intensity variations on glass objects. We demonstrate that our model can outperform glass segmentation on RGB-only video sequences as well as produce more robust segmentation than per-frame RGB-P single-image segmentation methods. To train and validate PGVS-Net, we introduce a novel RGB-P Glass Video dataset (PGV-117) containing 117 video sequences of scenes captured with different types of camera paths, lighting conditions, dynamics, and glass types." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 639, + 128, + 651 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 639, + 128, + 651 + ], + "spans": [ + { + "bbox": [ + 47, + 639, + 128, + 651 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 660, + 288, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 660, + 288, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 660, + 288, + 696 + ], + "type": "text", + "content": "Transparent objects, such as glass, are common in man-made environments. Despite their prevalence, such objects pose numerous challenges for industrial and academic" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 414, + 546, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 414, + 546, + 605 + ], + "spans": [ + { + "bbox": [ + 306, + 414, + 546, + 605 + ], + "type": "text", + "content": "vision processing algorithms due to their view-dependent appearance, statistical similarity to the background environment, and lack of texture. These challenges are particularly acute for segmentation tasks that underpin autonomous driving, robotics, and aerial drone navigation. Traditional learning-based solutions [8, 30, 50, 51] that rely on RGB textures for feature extraction often fail to adequately model the illumination and view-dependent glass features. Consequently, recent advances have explored richer modalities such as light fields [44] and polarization [14, 18, 21, 29, 46, 49] for more robust segmentation of glass objects. Polarization has proven to be a strong cue for glass segmentation in still images [14, 29]. The availability of commercial off-the-shelf RGB-P cameras (e.g., Flir and Lucid), makes this last category an attractive modality for glass segmentation." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 547, + 715 + ], + "type": "text", + "content": "Polarization of reflected light depends on various factors such as surface normals, material types, and illumination and view directions [2]. Due to the polarimetric near-specular behavior, glass materials are particularly challenging; small changes in object orientation and/or view/light direction can induce a rapid change in polarization state. For example, consider the glass areas '1' in Figure 2 that show a glass door in various stages of being closed. In this example, the RGB textures remain almost unchanged, but" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 703, + 139, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 703, + 139, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 703, + 139, + 712 + ], + "type": "text", + "content": "*Corresponding authors." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 293, + 732, + 318, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 732, + 318, + 742 + ], + "spans": [ + { + "bbox": [ + 293, + 732, + 318, + 742 + ], + "type": "text", + "content": "23218" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 71, + 288, + 369 + ], + "blocks": [ + { + "bbox": [ + 49, + 71, + 288, + 369 + ], + "lines": [ + { + "bbox": [ + 49, + 71, + 288, + 369 + ], + "spans": [ + { + "bbox": [ + 49, + 71, + 288, + 369 + ], + "type": "image", + "image_path": "a811fc1ed27b676cb74968e09efb14db1cb6d7d431b772097b6cb59e2f32f698.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 376, + 288, + 448 + ], + "lines": [ + { + "bbox": [ + 46, + 376, + 288, + 448 + ], + "spans": [ + { + "bbox": [ + 46, + 376, + 288, + 448 + ], + "type": "text", + "content": "Figure 2. Representative exemplars from the PGV-117 dataset containing a total of 117 video sequences captured with a variety of camera movement patterns, lighting conditions, scene dynamics, and materials. Glass areas '1' depict a door in various stages of being closed. Glass areas '2' are captured by moving the camera." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 474, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 474, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 474, + 287, + 715 + ], + "type": "text", + "content": "changes in the surface normal induce a significant decrease in the Angle of Linear Polarization (AoLP) from close to " + }, + { + "bbox": [ + 46, + 474, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\pi" + }, + { + "bbox": [ + 46, + 474, + 287, + 715 + ], + "type": "text", + "content": " (red-blue mixture) to less than half " + }, + { + "bbox": [ + 46, + 474, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\pi" + }, + { + "bbox": [ + 46, + 474, + 287, + 715 + ], + "type": "text", + "content": " (full blue), and a noticeable reduction in the Degree of Linear Polarization (DoLP) from 0.137 to 0.043. Similarly, moving the camera will induce a similar change in the polarization (e.g., the glass areas '2' in Figure 2). These observations suggest that polarization cues are beneficial for glass segmentation and can provide additional guidance. Furthermore, the DOLP in glass area '1' is unstable across the entire span of the video sequence, with noticeable DoLP reductions at specific angles of incidence (" + }, + { + "bbox": [ + 46, + 474, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\rho = 0.043" + }, + { + "bbox": [ + 46, + 474, + 287, + 715 + ], + "type": "text", + "content": "). Such types of instabilities can confuse methods [14, 29] that only rely on a single-frame RGB-P as input (Figure 1, right). Moreover, extracting glass features from RGB textures or polarization cues from a single view may also be difficult (e.g., under low light conditions as in Figure 1 left). As a consequence, polarization cues that are robust for static single image segmentation methods, can still yield temporally disjoint and inconsistent segmentation results when applied to" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": "video sequences, especially when object orientation and/or viewpoint changes." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 102, + 546, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 102, + 546, + 390 + ], + "spans": [ + { + "bbox": [ + 304, + 102, + 546, + 390 + ], + "type": "text", + "content": "In this paper, we introduce a Polarization Video Glass Segmentation network (PGVS-Net) to robustly and coherently propagate an initial glass segmentation mask over an RGB-P video sequence. PGVS-Net perceives multi-view polarimetric features from long-range memory and short-range integration. A variation of the Spatio-Temporal Memory network (STM) [33] is introduced to leverage spectral polarization cues for constructing long-range view dependency. A well-designed Polarization-Guide Integration module (PGI) is responsible for the frame identity and historical polarization matching. Furthermore, a novel Polarization Temporal Forward module (PTF) integrates previous polarization cues to promote short-range spectral consistency during the decoder process. We also leverage cross-modal and cross-temporal attention (CMTA) to integrate multimodal features and temporal representations from different frames. To train and test PGVS-Net, we capture and annotate a large-scale video glass segmentation dataset, PGV-117, which includes 21,485 annotated RGB-P frames and masks. We demonstrate, using this newly created dataset, that our PGVS-Net outperforms competing single-frame RGB-P glass segmentation methods as well as RGB-based video segmentation methods both quantitatively and qualitatively." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 318, + 397, + 459, + 408 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 397, + 459, + 408 + ], + "spans": [ + { + "bbox": [ + 318, + 397, + 459, + 408 + ], + "type": "text", + "content": "In summary, our contributions are:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 318, + 416, + 545, + 522 + ], + "type": "list", + "angle": 0, + "index": 9, + "blocks": [ + { + "bbox": [ + 318, + 416, + 545, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 416, + 545, + 450 + ], + "spans": [ + { + "bbox": [ + 318, + 416, + 545, + 450 + ], + "type": "text", + "content": "- A novel Polarization Video Glass Segmentation network (PGVS-Net) to robustly provide glass segmentation propagation in RGB-P video sequences;" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 318, + 452, + 545, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 452, + 545, + 486 + ], + "spans": [ + { + "bbox": [ + 318, + 452, + 545, + 486 + ], + "type": "text", + "content": "- A series of polarimetric consistency and integration modules to enhance spatio-temporal correlation of spectral polarization cues;" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 318, + 487, + 545, + 522 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 487, + 545, + 522 + ], + "spans": [ + { + "bbox": [ + 318, + 487, + 545, + 522 + ], + "type": "text", + "content": "- A large-scale video glass segmentation dataset, PGV117, containing 21,485 frames with spectral polarization cues and densely-annotated masks." + } + ] + } + ], + "index": 8 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 555, + 480, + 568 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 555, + 480, + 568 + ], + "spans": [ + { + "bbox": [ + 306, + 555, + 480, + 568 + ], + "type": "text", + "content": "2. Background and Related Work" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": "Polarization. Light is an electro-magnetic wave, whose polarization state describes the orientation of the transverse electric field, which can be unpolarized (i.e., random), linearly polarized (i.e. biased towards a single direction), or circularly polarized. We focus our discussion on linear polarization as supported by recent commercial polarization-array CMOS sensors, which allows us to record four distinct linear-polarization states per pixel: " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "I_{0^{\\circ}}" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "I_{45^{\\circ}}" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "I_{90^{\\circ}}" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "I_{135^{\\circ}}" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "I_x" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": " describes the intensity of linearly-polarized light at an angle " + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 582, + 545, + 713 + ], + "type": "text", + "content": ". These four linear polarization measurements allow us to compute the linear-polarization compo" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "spans": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "type": "text", + "content": "23219" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 225, + 85 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 225, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 225, + 85 + ], + "type": "text", + "content": "nents of the Stokes vector " + }, + { + "bbox": [ + 47, + 72, + 225, + 85 + ], + "type": "inline_equation", + "content": "S = [S_0,S_1,S_2]" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 99, + 95, + 235, + 107 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 99, + 95, + 235, + 107 + ], + "spans": [ + { + "bbox": [ + 99, + 95, + 235, + 107 + ], + "type": "interline_equation", + "content": "S _ {0} = I _ {0 ^ {\\circ}} + I _ {9 0 ^ {\\circ}} = I _ {4 5 ^ {\\circ}} + I _ {1 3 5 ^ {\\circ}},", + "image_path": "7ed82045e4b6ddedaf542257a27e53027fd99d264869595fabf2a307d3db80ad.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 100, + 107, + 286, + 119 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 107, + 286, + 119 + ], + "spans": [ + { + "bbox": [ + 100, + 107, + 286, + 119 + ], + "type": "interline_equation", + "content": "S _ {1} = I _ {0 ^ {\\circ}} - I _ {9 0 ^ {\\circ}}, \\tag {1}", + "image_path": "b278fbf16a47e275cfb0a6976f7fe79978f579125c48c1f2adc939a152729192.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 100, + 120, + 179, + 132 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 100, + 120, + 179, + 132 + ], + "spans": [ + { + "bbox": [ + 100, + 120, + 179, + 132 + ], + "type": "interline_equation", + "content": "S _ {2} = I _ {4 5 ^ {\\circ}} - I _ {1 3 5 ^ {\\circ}},", + "image_path": "0d9d813ff5406e2f9bd4cda311fe00c4d5a004832a58ff1c4b4c2f374e90e1e3.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "spans": [ + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "type": "inline_equation", + "content": "S_{0}" + }, + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "type": "text", + "content": " is the total light intensity, " + }, + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "type": "inline_equation", + "content": "S_{1}" + }, + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "type": "inline_equation", + "content": "S_{2}" + }, + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "type": "text", + "content": " are the ratio of the " + }, + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "type": "inline_equation", + "content": "0^{\\circ}" + }, + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "type": "inline_equation", + "content": "45^{\\circ}" + }, + { + "bbox": [ + 47, + 141, + 287, + 201 + ], + "type": "text", + "content": ", respectively, linear polarization intensity over its perpendicular counterpart. Given the linear Stokes vector, the degree of linear polarization (DoLP) and the angle of linear polarization (AoLP) are defined as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 55, + 211, + 287, + 239 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 211, + 287, + 239 + ], + "spans": [ + { + "bbox": [ + 55, + 211, + 287, + 239 + ], + "type": "interline_equation", + "content": "\\mathrm {D o L P} = \\frac {\\sqrt {S _ {1} ^ {2} + S _ {2} ^ {2}}}{S _ {0}}, \\quad \\mathrm {A o L P} = \\frac {1}{2} \\arctan \\left(\\frac {S _ {2}}{S _ {1}}\\right). \\tag {2}", + "image_path": "36215f856a5b2629c763b0f55b2368c4a796e6e48dc1b1c6378b4c421e7627c3.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 254, + 287, + 577 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 254, + 287, + 577 + ], + "spans": [ + { + "bbox": [ + 47, + 254, + 287, + 577 + ], + "type": "text", + "content": "Glass Object Segmentation. RGB texture information has proven to be an effective cue for image detection [41, 42, 43] and segmentation [24, 36, 37]. However, accurately segmenting glass objects in images remains a challenging problem because of the dynamic texture patterns that vary with viewing conditions due to reflection and transmission that share the statistics of the surrounding scene. Prior glass segmentation methods operating exclusively on RGB images have leveraged contextual information [30, 52, 53] or boundary cues [9, 50] to address these challenges. However, the effectiveness of RGB-only appearance cues depends on the lighting conditions, the amount of scene clutter, and the presence of nefarious actors (e.g., print-out-spoofs) [14]. One avenue to improve glass segmentation robustness is to include additional modalities that further differentiate glass objects from others, such as scene depth [28], thermal information [12], and polarization [14, 29]. Our approach falls in this latter category, and we rely on RGB and polarization (RGB-P) to robustly segment glass objects. However, the strength of the polarization cues can vary from frame to frame in a video sequence due to changes in view or lighting conditions yielding inconsistent object segmentation between frames. In this work, we leverage multi-view observations to recover a more complete, less view-dependent, description of the polarization properties of objects in the scene, resulting in a temporally more robust glass segmentation." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 594, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 594, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 594, + 287, + 713 + ], + "type": "text", + "content": "Video Segmentation and Detection. Video sequences can offer additional temporal cues to aid segmentation and detection tasks, but simultaneously also introduce the additional challenge of temporal consistency. Semantic video segmentation methods enhance temporal consistency via a variety of temporal propagating approaches such as optical flow[13, 32, 55], spatially varying convolutions [23], and recurrent network architectures [40]. In the absence of semantic cues, video object segmentation approaches estimate consistent class-agnostic object masks and instance" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 287 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 287 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 287 + ], + "type": "text", + "content": "IDs by exploiting spatial and temporal information to propagate an initial mask [4, 7, 11, 20, 26, 33, 39]. Panoptic segmentation [16] is a popular and successful segmentation approach that unifies semantic and instance segmentation, and which has also been extended to video segmentation [15, 22, 35, 47]. In addition to segmentation, the related problem of object detection has recently also been extended to video sequences in different application domains such as salient object detection [17, 19], camouflaged object detection [5], shadow detection [3, 25], and video action detection [54]. Similar to prior work, we also exploit spatial and temporal cues. In addition, we also leverage the richer embedded cues in RGB-P videos and gather robust polarization cues from multi-view observations to aid in propagating glass segmentation masks in video sequences. To the best of our knowledge, none of the prior segmentation propagation methods can effectively leverage polarization cues that are uncorrelated with RGB features." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 298, + 522, + 312 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 298, + 522, + 312 + ], + "spans": [ + { + "bbox": [ + 306, + 298, + 522, + 312 + ], + "type": "text", + "content": "3. Polarimetric Video Glass Segmentation" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 319, + 545, + 437 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 319, + 545, + 437 + ], + "spans": [ + { + "bbox": [ + 304, + 319, + 545, + 437 + ], + "type": "text", + "content": "Our Polarization Video Glass Segmentation network (PGVS-Net) sequentially processes video frames beginning with the second frame, utilizing the ground truth annotation provided in the initial frame. As the video processing unfolds, preceding frames with object masks—established in the first frame or inferred in subsequent frames—are employed as memory frames. Furthermore, the current frame, excluding the object mask, assumes the role of the query frame. Note that each frame consists of trichromatic intensity " + }, + { + "bbox": [ + 304, + 319, + 545, + 437 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 319, + 545, + 437 + ], + "type": "text", + "content": ", AoLP " + }, + { + "bbox": [ + 304, + 319, + 545, + 437 + ], + "type": "inline_equation", + "content": "\\varphi" + }, + { + "bbox": [ + 304, + 319, + 545, + 437 + ], + "type": "text", + "content": ", and DoLP " + }, + { + "bbox": [ + 304, + 319, + 545, + 437 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 304, + 319, + 545, + 437 + ], + "type": "text", + "content": " information." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "spans": [ + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "type": "text", + "content": "Inspired by the successful Spatial-Temporal Memory (STM) framework [4, 33], we encode each frame into a paired set of key and value maps. Specifically, for a given modality " + }, + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "type": "text", + "content": ", we utilize a ResNet50 architecture [10] to encode the modality into three distinct feature maps: " + }, + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "type": "inline_equation", + "content": "f_{b1}^{x}, f_{b2}^{x}" + }, + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "type": "inline_equation", + "content": "f_{b3}^{x}" + }, + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "type": "text", + "content": ", corresponding to the outputs of the first, second, and third blocks, respectively. The key feature map of each frame is derived using our specially devised Polarization-Guided Integration module (PGI; detailed in Section 3.1), based on " + }, + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "type": "inline_equation", + "content": "f_{b1}^{x}, f_{b2}^{x}" + }, + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "type": "inline_equation", + "content": "f_{b3}^{x}" + }, + { + "bbox": [ + 304, + 438, + 545, + 594 + ], + "type": "text", + "content": ". Importantly, both memory and query frames employ the same methodology to generate key maps. For memory frames, the value map is generated through the following steps:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 313, + 594, + 545, + 701 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 313, + 594, + 545, + 629 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 594, + 545, + 629 + ], + "spans": [ + { + "bbox": [ + 313, + 594, + 545, + 629 + ], + "type": "text", + "content": "1. Trichromatic " + }, + { + "bbox": [ + 313, + 594, + 545, + 629 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 313, + 594, + 545, + 629 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 313, + 594, + 545, + 629 + ], + "type": "inline_equation", + "content": "\\varphi" + }, + { + "bbox": [ + 313, + 594, + 545, + 629 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 313, + 594, + 545, + 629 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 313, + 594, + 545, + 629 + ], + "type": "text", + "content": ", and the glass mask are concatenated along the channel dimension and fed as input to a ResNet18 model [10] to produce a feature map;" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 313, + 630, + 545, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 630, + 545, + 676 + ], + "spans": [ + { + "bbox": [ + 313, + 630, + 545, + 676 + ], + "type": "text", + "content": "2. The resulting feature map is concatenated with " + }, + { + "bbox": [ + 313, + 630, + 545, + 676 + ], + "type": "inline_equation", + "content": "f_{b3}^{x}" + }, + { + "bbox": [ + 313, + 630, + 545, + 676 + ], + "type": "text", + "content": " and subjected to two residual blocks [10] and a Convolutional Block Attention Module (CBAM) [48] attention block;" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 313, + 677, + 545, + 701 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 677, + 545, + 701 + ], + "spans": [ + { + "bbox": [ + 313, + 677, + 545, + 701 + ], + "type": "text", + "content": "3. Finally, the memory value maps are produced by aggregating the multimodality maps from step 2." + } + ] + } + ], + "index": 14 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 702, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 702, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 702, + 545, + 713 + ], + "type": "text", + "content": "In essence, relying on the query key and the pairs of mem" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 732, + 317, + 741 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 732, + 317, + 741 + ], + "spans": [ + { + "bbox": [ + 293, + 732, + 317, + 741 + ], + "type": "text", + "content": "23220" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 70, + 550, + 339 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 550, + 339 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 550, + 339 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 550, + 339 + ], + "type": "image", + "image_path": "45fe6e4ad30c875c46000e0eb91ab5841682ec6840775fb2417d7cdc1ef934cb.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 346, + 547, + 372 + ], + "lines": [ + { + "bbox": [ + 46, + 346, + 547, + 372 + ], + "spans": [ + { + "bbox": [ + 46, + 346, + 547, + 372 + ], + "type": "text", + "content": "Figure 3. Overview of PGVS-Net. The RGB-P Memory and PGI fused keys are designed to store long-range multi-view polarization cues. The short-range spectral propagation are implemented by the CMTA and PTF modules." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 392, + 287, + 489 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 392, + 287, + 489 + ], + "spans": [ + { + "bbox": [ + 46, + 392, + 287, + 489 + ], + "type": "text", + "content": "ory key and value maps, PGVS-Net endeavors to estimate the value map (discussed in Section 3.2) for a given query frame through multi-view polarimetric propagation (described in Section 3.3) and the extraction of temporal correlations (explained in Section 3.4). The resultant value map of the query frame is then translated into the glass mask of the query frame via a decoder (introduced in Section 3.5). Our PGVS-Net is summarized in Figure 3." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 494, + 222, + 508 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 494, + 222, + 508 + ], + "spans": [ + { + "bbox": [ + 47, + 494, + 222, + 508 + ], + "type": "text", + "content": "3.1. Polarization-Guided Integration" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 513, + 287, + 583 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 513, + 287, + 583 + ], + "spans": [ + { + "bbox": [ + 46, + 513, + 287, + 583 + ], + "type": "text", + "content": "Polarization information provides strong cues on the material properties. We therefore leverage these polarization cues as guidance to combine multimodal key feature maps for each frame. To achieve this, we introduce a novel Polarization-Guided Integration (PGI) module. Formally, the PGI is defined as:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 84, + 589, + 143, + 602 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 84, + 589, + 143, + 602 + ], + "spans": [ + { + "bbox": [ + 84, + 589, + 143, + 602 + ], + "type": "interline_equation", + "content": "k _ {x} = \\Psi (f _ {b 3} ^ {x}),", + "image_path": "18299e0d9081e57fa18fa5427be572a0c8b62fa0cafde6b7819f2d85c85ea51a.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 84, + 604, + 287, + 621 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 84, + 604, + 287, + 621 + ], + "spans": [ + { + "bbox": [ + 84, + 604, + 287, + 621 + ], + "type": "interline_equation", + "content": "\\mathcal {Y} _ {1} = \\gamma_ {1} * \\left\\{\\left[ \\Psi \\left(k _ {I}\\right) * \\Psi \\left(k _ {\\varphi}\\right) \\right] * \\Psi \\left(k _ {I}\\right) \\right\\}, \\tag {3}", + "image_path": "571cf4f1ab39bf7234f57ea230a5822b18dde8bfee71108704555f34981ed3c0.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 84, + 618, + 287, + 632 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 84, + 618, + 287, + 632 + ], + "spans": [ + { + "bbox": [ + 84, + 618, + 287, + 632 + ], + "type": "interline_equation", + "content": "\\mathcal {Y} _ {2} = \\gamma_ {2} * \\left\\{\\left[ \\Psi \\left(k _ {I}\\right) * \\Psi \\left(k _ {\\rho}\\right) \\right] * \\Psi \\left(k _ {I}\\right) \\right\\}, \\tag {3}", + "image_path": "874ed177e9718135e0ad7dab44fe834121da4e81285fbfc6f8f516bfce0c8ad3.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 90, + 634, + 173, + 647 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 90, + 634, + 173, + 647 + ], + "spans": [ + { + "bbox": [ + 90, + 634, + 173, + 647 + ], + "type": "interline_equation", + "content": "k = \\Psi \\left(\\left[ k _ {I}, \\mathcal {Y} _ {1}, \\mathcal {Y} _ {2} \\right]\\right)", + "image_path": "94a3755414d9623652cf6b9dc6c673ed998b5f96d0232c1749950f182a1a0abf.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "content": " is either " + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\varphi" + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "content": ", or " + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\rho" + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "content": "; " + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\gamma_{1}" + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\gamma_{2}" + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "content": " are learnable parameters; " + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\Psi(\\cdot)" + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "content": " represents a convolution layer, followed by a regional pooling operation (output size equals 11) and an additional convolution layer; " + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\oplus" + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "content": " indicates a matrix multiplication. " + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "inline_equation", + "content": "k_{x} \\in \\mathbb{R}^{BT \\times H \\times W \\times C}" + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "inline_equation", + "content": "B, T, H, W, C" + }, + { + "bbox": [ + 46, + 653, + 287, + 713 + ], + "type": "text", + "content": " are the" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 392, + 545, + 417 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 392, + 545, + 417 + ], + "spans": [ + { + "bbox": [ + 305, + 392, + 545, + 417 + ], + "type": "text", + "content": "batch size, temporal length, and the height, width, and channel size of a feature map, respectively." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 449, + 440, + 463 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 449, + 440, + 463 + ], + "spans": [ + { + "bbox": [ + 306, + 449, + 440, + 463 + ], + "type": "text", + "content": "3.2. Query Value Prediction" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 477, + 545, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 477, + 545, + 574 + ], + "spans": [ + { + "bbox": [ + 304, + 477, + 545, + 574 + ], + "type": "text", + "content": "In the context of a query frame, we establish a connection between RGB-P information from multiple views by investigating the interplay between the query key and memory keys. This interaction results in corresponding value features grounded in memory affinity. Our model employs an STM variant for RGB-P memory, dynamically amalgamating multimodal inputs and establishing correlations across diverse views over an extensive temporal span." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 582, + 546, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 546, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 546, + 715 + ], + "type": "text", + "content": "Concretely, when provided with a query key " + }, + { + "bbox": [ + 304, + 582, + 546, + 715 + ], + "type": "inline_equation", + "content": "k^Q" + }, + { + "bbox": [ + 304, + 582, + 546, + 715 + ], + "type": "text", + "content": ", we anticipate the query value " + }, + { + "bbox": [ + 304, + 582, + 546, + 715 + ], + "type": "inline_equation", + "content": "v^Q" + }, + { + "bbox": [ + 304, + 582, + 546, + 715 + ], + "type": "text", + "content": " through the utilization of a softmax-normalized affinity matrix, which is computed from the pairing of " + }, + { + "bbox": [ + 304, + 582, + 546, + 715 + ], + "type": "inline_equation", + "content": "(k^M, k^Q)" + }, + { + "bbox": [ + 304, + 582, + 546, + 715 + ], + "type": "text", + "content": " [4]. This computation allows us to extract the most pertinent memory values. The computation of memory affinity adheres to the methodology outlined by Cheng et al. [4] (for a comprehensive explanation, please refer to the supplementary material). Memory values encapsulate historical RGB-P information of a scene, ensuring that the affinity mechanism facilitates the far-reaching propagation of multi-view spectral polarization within " + }, + { + "bbox": [ + 304, + 582, + 546, + 715 + ], + "type": "inline_equation", + "content": "v^Q" + }, + { + "bbox": [ + 304, + 582, + 546, + 715 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "spans": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "type": "text", + "content": "23221" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 226, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 226, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 226, + 85 + ], + "type": "text", + "content": "3.3. Cross Modal-Temporal Attention" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 92, + 287, + 224 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 92, + 287, + 224 + ], + "spans": [ + { + "bbox": [ + 46, + 92, + 287, + 224 + ], + "type": "text", + "content": "To this point, the query value prediction process only utilizes long term memory by leveraging the collective information contained in the memory frames. However, captured trichromatic information also exhibits rapid changes across different modalities, indicating potential target area boundaries over short time-intervals. These changes across diverse modalities are not well captured by a long-term memory framework. To address this shortcoming, we introduce a Cross Modal-Temporal Attention module (CMTA) to model the short-term interactions between the query and its one preceding memory frame." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 225, + 287, + 285 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 225, + 287, + 285 + ], + "spans": [ + { + "bbox": [ + 46, + 225, + 287, + 285 + ], + "type": "text", + "content": "Central to our CMTA module is a multi-head self-attention mechanism inspired by the transformer architecture [45]. This mechanism is first applied along the modality dimension and then extended to the temporal dimension. Formally, the CMTA can be defined as follows:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 59, + 298, + 287, + 357 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 298, + 287, + 357 + ], + "spans": [ + { + "bbox": [ + 59, + 298, + 287, + 357 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\chi_ {m} = \\left[ \\mathcal {R} _ {m} \\left(k _ {I}\\right), \\mathcal {R} _ {m} \\left(k _ {\\varphi}\\right), \\mathcal {R} _ {m} \\left(k _ {\\rho}\\right) \\right], \\\\ F _ {m} = \\mathcal {L} \\left[ \\Upsilon \\left(\\mathcal {L} \\left(\\chi_ {m}\\right)\\right) + \\chi_ {m} \\right], (4) \\\\ \\chi_ {t} = \\left[ \\mathcal {R} _ {t} \\left(\\mathcal {C} _ {I} \\left(F _ {m}\\right)\\right), \\mathcal {R} _ {t} \\left(\\mathcal {C} _ {\\varphi} \\left(F _ {m}\\right)\\right), \\mathcal {R} _ {t} \\left(\\mathcal {C} _ {\\rho} \\left(F _ {m}\\right)\\right) \\right], (4) \\\\ F _ {t} = \\mathcal {L} [ \\Upsilon (\\mathcal {L} (\\chi_ {t})) + \\chi_ {t} ], \\\\ \\end{array}", + "image_path": "2b0e33728d3a47b4824843f16f8a219cd22ed3ec26ef349e2a9220c84e4193a4.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "spans": [ + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "inline_equation", + "content": "[\\cdot]" + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": " indicates the concatenation on the first dimension; " + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "inline_equation", + "content": "\\Upsilon" + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": " indicates a multi-head self-attention block [45]; " + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "inline_equation", + "content": "\\mathcal{L}" + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": " refers to Layer Normalization [1]. " + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_m" + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": " is a modality reshape operator, which transfers the shape of " + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "inline_equation", + "content": "k_{c}" + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": " from " + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{B\\times T\\times H\\times W\\times C}" + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": " into " + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{BT\\times HW\\times C}" + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "inline_equation", + "content": "\\mathcal{R}_t" + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": " is a reshape operator in the temporal domain, which reshape a feature map from " + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{B\\times T\\times H\\times W\\times C}\\rightarrow \\mathbb{R}^{B\\times THW\\times C}" + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "inline_equation", + "content": "\\mathcal{C}_x" + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": " is the chunked vector for modality " + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": ". Finally, the derived " + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "inline_equation", + "content": "F_{t}" + }, + { + "bbox": [ + 46, + 369, + 287, + 499 + ], + "type": "text", + "content": " is concatenated with the query value acquired through the query value prediction process, and subsequently forwarded as input to the decoder." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 514, + 221, + 527 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 514, + 221, + 527 + ], + "spans": [ + { + "bbox": [ + 47, + 514, + 221, + 527 + ], + "type": "text", + "content": "3.4. Polarimetric Temporal Forward" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "content": "The examples in Figure 2 demonstrate that the polarization cues provide strong temporal continuity cues. The core idea of leveraging polarimetric continuity is that the polarization for the query frame can benefit from the preceding memory frame's polarization cues. To actualize this, the Polarimetric Temporal Forward (PTF) module engages " + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{b1}^{x}" + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{b2}^{x}" + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "content": ", sourced from the query and the preceding memory frame, as inputs. This module carries out an unfolding operation " + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "inline_equation", + "content": "(\\mathcal{U})" + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "content": " on these inputs. In order to distinguish between the features from the query and memory frames, an additional subscript is appended to the feature samples. For instance, " + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{M - b1}^{x}" + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{Q - b2}^{x}" + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "content": " represent the feature map of block 1 from a memory frame and the feature map of block 2 from a query frame for the modality " + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "content": ", respectively. Formally, given " + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{M - b1}^{x}" + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "inline_equation", + "content": "f_{Q - b1}^{x}" + }, + { + "bbox": [ + 46, + 534, + 288, + 715 + ], + "type": "text", + "content": ", the PTF operation is defined" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 75, + 320, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 75, + 320, + 83 + ], + "spans": [ + { + "bbox": [ + 306, + 75, + 320, + 83 + ], + "type": "text", + "content": "as:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 334, + 87, + 545, + 169 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 334, + 87, + 545, + 169 + ], + "spans": [ + { + "bbox": [ + 334, + 87, + 545, + 169 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} U _ {\\varphi} ^ {M}, U _ {\\rho} ^ {M} = \\mathcal {U} \\left(f _ {M - b 1} ^ {\\varphi}\\right), \\mathcal {U} \\left(f _ {M - b 1} ^ {\\rho}\\right), \\\\ F _ {\\varphi} ^ {Q}, F _ {\\rho} ^ {Q} = \\mathcal {R} (f _ {Q - b 1} ^ {\\varphi}), \\mathcal {R} (f _ {\\rho - b 1} ^ {\\varphi}), \\\\ S _ {\\varphi} = \\sigma \\left(\\mathcal {S} \\left(F _ {\\varphi} ^ {Q} \\otimes U _ {\\varphi} ^ {M}\\right)\\right) \\otimes U _ {\\varphi} ^ {M} + f _ {b 1} ^ {\\varphi}, \\tag {5} \\\\ S _ {\\rho} = \\sigma \\left(\\mathcal {S} \\left(F _ {\\rho} ^ {Q} \\otimes U _ {\\rho} ^ {M}\\right)\\right) \\otimes U _ {\\rho} ^ {M} + f _ {b 1} ^ {\\rho}, \\\\ F _ {b 1} ^ {P T F} = S _ {\\varphi} + S _ {\\rho} + f _ {b 1} ^ {I}, \\\\ \\end{array}", + "image_path": "6a9cf21e7bb6a62465008101f10a57031e5207f8cbd9636b7b7e4621bd20801f.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "spans": [ + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\mathcal{R}" + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "text", + "content": " denote the reshape operation and sum operation applied to the first dimension, respectively; " + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\otimes" + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "text", + "content": " indicates the element-wise multiplication; " + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "text", + "content": " is the softmax function. " + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "inline_equation", + "content": "U_{\\varphi}, U_{\\rho} \\in \\mathbb{R}^{C \\times P \\times H \\times W}" + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "text", + "content": " denotes the window size during the unfold convolution, and " + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "inline_equation", + "content": "f_{b2}^{I}, f_{b2}^{\\varphi}, f_{b2}^{\\rho} \\in \\mathbb{R}^{C \\times 1 \\times H \\times W}" + }, + { + "bbox": [ + 304, + 174, + 545, + 243 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "spans": [ + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "type": "text", + "content": "PTF further applies the described operations to " + }, + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "type": "inline_equation", + "content": "f_{b2}^{\\varphi}, f_{b2}^{\\rho}" + }, + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "type": "inline_equation", + "content": "f_{b2}^{I}" + }, + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "type": "text", + "content": ", yielding the output " + }, + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "type": "inline_equation", + "content": "F_{b2}^{PTF}" + }, + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "type": "text", + "content": ". In our implementation, we establish the window sizes for unfold convolutions as 7 and 9 for " + }, + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "type": "inline_equation", + "content": "f_{b2}" + }, + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "type": "inline_equation", + "content": "f_{b1}" + }, + { + "bbox": [ + 304, + 245, + 545, + 342 + ], + "type": "text", + "content": ", respectively. Through this design, PTF enables dynamic incorporation via unfold convolutions, fostering forward propagation among adjacent polarimetric features and thereby achieving inter-frame view dependency." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 348, + 368, + 360 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 348, + 368, + 360 + ], + "spans": [ + { + "bbox": [ + 306, + 348, + 368, + 360 + ], + "type": "text", + "content": "3.5. Decoder" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 365, + 545, + 521 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 365, + 545, + 521 + ], + "spans": [ + { + "bbox": [ + 304, + 365, + 545, + 521 + ], + "type": "text", + "content": "We employ a straightforward yet effective decoder to translate the acquired query value into the corresponding glass masks of the query frame. Our decoder encompasses two UNet-like [38] upsampling blocks, tasked with reinstating the resolution of the query value map to " + }, + { + "bbox": [ + 304, + 365, + 545, + 521 + ], + "type": "inline_equation", + "content": "1/4" + }, + { + "bbox": [ + 304, + 365, + 545, + 521 + ], + "type": "text", + "content": " of the query frame's dimensions. Subsequently, a prediction convolution transforms the channel configuration of the resultant feature map to a single channel, which is then upsampled to match the resolution of the query frame. In addition to the query value, this decoder taps into the feature maps offered by the PTF module to reinforce temporal coherence. Specifically, " + }, + { + "bbox": [ + 304, + 365, + 545, + 521 + ], + "type": "inline_equation", + "content": "F^{PTF}b1" + }, + { + "bbox": [ + 304, + 365, + 545, + 521 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 365, + 545, + 521 + ], + "type": "inline_equation", + "content": "F^{PTF}b2" + }, + { + "bbox": [ + 304, + 365, + 545, + 521 + ], + "type": "text", + "content": " serve as inputs to the first and second upsampling blocks, respectively." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 528, + 440, + 540 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 528, + 440, + 540 + ], + "spans": [ + { + "bbox": [ + 306, + 528, + 440, + 540 + ], + "type": "text", + "content": "3.6. Implementation Details" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "text", + "content": "We implement PGVS-Net in PyTorch. For training, input images are randomly cropped to " + }, + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "inline_equation", + "content": "384 \\times 384" + }, + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "text", + "content": " and augmented by horizontal random flipping, translations, and affine transforms. During training, the sequence takes a group of three frames as the input of the network. The masks of ground truth glass areas in the first frame are provided as input, and we employ a binary cross-entropy (BCE) loss to supervise the output mask of the last two frames. For optimization, we use the Adam optimizer with a weight decay of " + }, + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "inline_equation", + "content": "1e - 7" + }, + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "text", + "content": ". The learning rate is fixed at " + }, + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "inline_equation", + "content": "1e - 5" + }, + { + "bbox": [ + 304, + 545, + 545, + 713 + ], + "type": "text", + "content": ". Training takes three days to converge on a dual TITAN V100 graphics card setup after 150,000 iterations with a batch size of 4. During inference, we update the memory bank every three frames." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 732, + 318, + 742 + ], + "type": "footer", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 732, + 318, + 742 + ], + "spans": [ + { + "bbox": [ + 293, + 732, + 318, + 742 + ], + "type": "text", + "content": "23222" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 71, + 279, + 260 + ], + "blocks": [ + { + "bbox": [ + 55, + 71, + 279, + 260 + ], + "lines": [ + { + "bbox": [ + 55, + 71, + 279, + 260 + ], + "spans": [ + { + "bbox": [ + 55, + 71, + 279, + 260 + ], + "type": "image", + "image_path": "de384d01d466c80d77ec98d6512f718bdac8622d3362ff6778421987dadc1abb.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 267, + 287, + 352 + ], + "lines": [ + { + "bbox": [ + 46, + 267, + 287, + 352 + ], + "spans": [ + { + "bbox": [ + 46, + 267, + 287, + 352 + ], + "type": "text", + "content": "Figure 4. Summary of camera motions (left) and the PGV-117 dataset characteristics (right). To avoid biasing PGV-117 into certain types of camera motions, we implement different camera motion strategies. The blue areas represent the glass target. The 117 video sequences are captured with different types of camera paths, lighting conditions, dynamics, and materials (dark indicates ground glass)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 373, + 149, + 385 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 373, + 149, + 385 + ], + "spans": [ + { + "bbox": [ + 47, + 373, + 149, + 385 + ], + "type": "text", + "content": "4. PGV-117 dataset" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "spans": [ + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "text", + "content": "We introduce a novel RGB-P-video-based dataset, PGV-117, to support and stimulate research in video-based glass segmentation. The dataset is collected using a trichromatic (RGB) polarizer-array camera (LUCID PHX050S), equipped with four directional linear-polarizers, i.e., " + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "inline_equation", + "content": "0^{\\circ}" + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "inline_equation", + "content": "45^{\\circ}" + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "inline_equation", + "content": "90^{\\circ}" + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "inline_equation", + "content": "135^{\\circ}" + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "text", + "content": ". The frame rate is fixed at 30fps, and we vary the exposure time from " + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "inline_equation", + "content": "3,000\\mu s" + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "inline_equation", + "content": "39,999\\mu s" + }, + { + "bbox": [ + 46, + 394, + 287, + 574 + ], + "type": "text", + "content": " depending on the scene and lighting conditions. Each frame in the PGV-117 dataset includes: an RGB image, four directional polarization images, inferred spectral AoLP and DoLP maps, and the captured RAW camera data. Table 1 summarizes PGV-117 statistics in comparison to prior datasets. Care was taken during creation of PGV-117 to ensure a sufficient variation in lighting conditions, camera paths, and scene dynamics." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "type": "text", + "content": "Lighting conditions. PGV-117 is collected in various indoor environments, such as shopping malls, office buildings, and classrooms, as well as in a variety of outdoor environments. For outdoor environments, we capture sequences spanning during the full time-range from daytime to night. As such, PGV-117 offers four types of lighting variations: normal, low-light, saturated light, and high-dynamic-range. Additionally, we also consider diverse glass types in PGV-117, including clear, frosted, and patterned glasses, tinted glass on vehicles, and outdoor and indoor glass walls." + } + ] + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 309, + 71, + 544, + 156 + ], + "blocks": [ + { + "bbox": [ + 309, + 71, + 544, + 156 + ], + "lines": [ + { + "bbox": [ + 309, + 71, + 544, + 156 + ], + "spans": [ + { + "bbox": [ + 309, + 71, + 544, + 156 + ], + "type": "table", + "html": "
DatasetsTaskFramesADPSeq(tr+v/te)
DAVIS2017 [34]VOS10,459#190/60
DAVSOD [6]VSOD23,938#136/90
MoCA-Mask [5]VCOD22,939#571/16
RGBP-Glass [29]IGS4,511#1✓-
PGV-117VGS21,485#1✓85/32
", + "image_path": "0f96a021d5ecd3259ea350b8ad47e29fe363e79a9a0662dd48ff296af916e0fb.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 164, + 545, + 272 + ], + "lines": [ + { + "bbox": [ + 304, + 164, + 545, + 272 + ], + "spans": [ + { + "bbox": [ + 304, + 164, + 545, + 272 + ], + "type": "text", + "content": "Table 1. Statistics of PGV-117 compared to representative video datasets and glass datasets. In each column, we list: the primary Task for which the dataset was designed (Video Object Segmentation (VOS), Video Saliency Object Detection (VSOD), Video Camouflaged Object Detection (VCOD), and Image Glass Segmentation (IGS)); " + }, + { + "bbox": [ + 304, + 164, + 545, + 272 + ], + "type": "inline_equation", + "content": "AD" + }, + { + "bbox": [ + 304, + 164, + 545, + 272 + ], + "type": "text", + "content": ": the annotation interval in #frames; " + }, + { + "bbox": [ + 304, + 164, + 545, + 272 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 304, + 164, + 545, + 272 + ], + "type": "text", + "content": ": whether the dataset includes polarization; and " + }, + { + "bbox": [ + 304, + 164, + 545, + 272 + ], + "type": "inline_equation", + "content": "Seq(tr + v)/te" + }, + { + "bbox": [ + 304, + 164, + 545, + 272 + ], + "type": "text", + "content": ": the number of training and validation exemplars versus test exemplars." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 295, + 545, + 379 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 295, + 545, + 379 + ], + "spans": [ + { + "bbox": [ + 304, + 295, + 545, + 379 + ], + "type": "text", + "content": "Camera motion patterns. Polarization cues are angle dependent. To avoid biasing PGV-117 to certain view angles and camera paths, we randomly pick one of five predetermined camera motion patterns: front, inclined, circular, straight-forward, and up-down; see Figure 4 for a visual summary. During acquisition, we also recapture some glass areas back and forth to enrich the robustness and diversity." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 397, + 545, + 434 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 397, + 545, + 434 + ], + "spans": [ + { + "bbox": [ + 304, + 397, + 545, + 434 + ], + "type": "text", + "content": "Dynamics. PGV-117 captures both static and dynamic scenes (e.g., doors/windows opening and closing, and pedestrians occluding glass)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 452, + 545, + 513 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 452, + 545, + 513 + ], + "spans": [ + { + "bbox": [ + 304, + 452, + 545, + 513 + ], + "type": "text", + "content": "Frame removal. Frames characterized by motion blur and overexposure are excluded due to the inherent ambiguity in their annotations. Typically, we remove 1 to 2 frames per static-camera sequence, and about " + }, + { + "bbox": [ + 304, + 452, + 545, + 513 + ], + "type": "inline_equation", + "content": "20\\%" + }, + { + "bbox": [ + 304, + 452, + 545, + 513 + ], + "type": "text", + "content": " frames for a moving-camera sequence." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 525, + 388, + 539 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 525, + 388, + 539 + ], + "spans": [ + { + "bbox": [ + 306, + 525, + 388, + 539 + ], + "type": "text", + "content": "5. Experiments" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "text", + "content": "In this section, we first compare the performance of PGVS-Net under continuous polarization to demonstrate the robustness of combining multi-view and temporal consistency (subsection 5.1). Next, we validate the efficacy of our model by quantitatively and qualitatively comparing PGVS-Net against polarization-based and SOTA video methods retrained on the PGV-117 dataset. To quantify performance, we adopt four prevalent evaluation metrics: intersection over union (IoU), weighted F-measure " + }, + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "inline_equation", + "content": "(\\mathrm{F}_{\\beta})" + }, + { + "bbox": [ + 304, + 546, + 545, + 713 + ], + "type": "text", + "content": " [27], mean absolute error (MAE), and balance error rate (BER) [31]. Finally, we perform an ablation study to show the impact of the different components that comprise PGVS-Net (subsection 5.3). Please refer to the supplementary materials for additional images and video results." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "spans": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "type": "text", + "content": "23223" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 73, + 171, + 175 + ], + "blocks": [ + { + "bbox": [ + 55, + 73, + 171, + 175 + ], + "lines": [ + { + "bbox": [ + 55, + 73, + 171, + 175 + ], + "spans": [ + { + "bbox": [ + 55, + 73, + 171, + 175 + ], + "type": "image", + "image_path": "c279678244d2dece7e9009c076b1538c2c0937d1926bab80595847d9b5a84788.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 178, + 547, + 202 + ], + "lines": [ + { + "bbox": [ + 46, + 178, + 547, + 202 + ], + "spans": [ + { + "bbox": [ + 46, + 178, + 547, + 202 + ], + "type": "text", + "content": "Figure 5. Error plots comparing PGVS-Net to PM-RCNN and PGSNet for four different sequences. For reference, the DoLP is also included to indicate which frames pose a greater challenge for RGB-P methods." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 173, + 73, + 293, + 175 + ], + "blocks": [ + { + "bbox": [ + 173, + 73, + 293, + 175 + ], + "lines": [ + { + "bbox": [ + 173, + 73, + 293, + 175 + ], + "spans": [ + { + "bbox": [ + 173, + 73, + 293, + 175 + ], + "type": "image", + "image_path": "05de1b1275e1bbef5f55391ab4fc71e52b3dbaf93baf73ceb50a041edc2b4d04.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 293, + 73, + 414, + 175 + ], + "blocks": [ + { + "bbox": [ + 293, + 73, + 414, + 175 + ], + "lines": [ + { + "bbox": [ + 293, + 73, + 414, + 175 + ], + "spans": [ + { + "bbox": [ + 293, + 73, + 414, + 175 + ], + "type": "image", + "image_path": "afb07196161750ebe915b7b2d10c3f0861ee509d5463005bae812469865d7495.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 414, + 73, + 539, + 175 + ], + "blocks": [ + { + "bbox": [ + 414, + 73, + 539, + 175 + ], + "lines": [ + { + "bbox": [ + 414, + 73, + 539, + 175 + ], + "spans": [ + { + "bbox": [ + 414, + 73, + 539, + 175 + ], + "type": "image", + "image_path": "e6dec4091c1cdb305a859519963c8608f18f9f148249de935ecaedd6fdf03039.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 223, + 241, + 236 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 223, + 241, + 236 + ], + "spans": [ + { + "bbox": [ + 47, + 223, + 241, + 236 + ], + "type": "text", + "content": "5.1. Multi-view Polarimetric Consistency" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 242, + 287, + 433 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 242, + 287, + 433 + ], + "spans": [ + { + "bbox": [ + 46, + 242, + 287, + 433 + ], + "type": "text", + "content": "Due to their near-specular reflection and refraction behavior, glass materials are more sensitive to changes in view/light conditions. While RGB-P cues have proven to be essential for robust single-image glass segmentation, ignoring the temporal instability can result in inconsistent glass segmentation over time. PGVS-Net is specially designed to leverage and aggregate temporal changes in polarization cues. Figure 5 illustrates the correlation between variations in polarization intensity (DoLP) and the corresponding performance levels (measured by mIoU) in comparison to two image-based polarimetric techniques [14, 29] (applied independently to each frame) across diverse video sequences. The distinct abrupt shifts in the curve within Figure 5 due to the removal frames with motion blur (section 4), which breaks the temporal continuity and may degrade the multiview dependency of PGVS-Net." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 434, + 288, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 434, + 288, + 613 + ], + "spans": [ + { + "bbox": [ + 46, + 434, + 288, + 613 + ], + "type": "text", + "content": "From the first result in Figure 5, we can observe that when DoLP changes significantly, prior single-frame image-based methods fail to produce a consistent, coherent segmentation. In contrast, our model not only stores and leverages historical polarization information, but also enhances the current frame with the prior polarization information through the CMTA and PTF modules, resulting in good temporal consistency. The second result in Figure 5 shows that our model can still maintain a stable performance when the overall DoLP changes within the sequence cover a relatively large range (between 0.2 and 0.45). The third and fourth result in Figure 5 show that PGVS-Net can achieve better performance in low light and high brightness environments with extremely low overall DoLP over the sequence (less than 0.12)." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 623, + 233, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 623, + 233, + 635 + ], + "spans": [ + { + "bbox": [ + 47, + 623, + 233, + 635 + ], + "type": "text", + "content": "5.2. Comparison to the State-of-the-art" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": "We compare PGVS-Net to prior single-frame image-based glass segmentation methods and state-of-the-art video segmentation methods. We retrain all methods on the PGV-117 dataset and evaluate them on the 32 test sequences. We compare against: RGB-input GSD [30] where the input and supervision are replaced with our" + } + ] + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 315, + 222, + 538, + 357 + ], + "blocks": [ + { + "bbox": [ + 315, + 222, + 538, + 357 + ], + "lines": [ + { + "bbox": [ + 315, + 222, + 538, + 357 + ], + "spans": [ + { + "bbox": [ + 315, + 222, + 538, + 357 + ], + "type": "table", + "html": "
MethodsIoU↑Fβ↑MAE↓BER↓
GSDIS[30]80.290.8280.11512.34
EAFIS[49]41.690.5560.45043.91
PM-RCNNIS[14]76.130.7970.14015.83
PGSIS[29]79.690.8730.11912.31
STICTVU[25]50.680.5770.29932.03
ViShaVS[3]77.420.8050.13613.77
STCNVS[4]80.850.8260.12012.77
RDEVS[20]74.870.7630.16915.95
PGVS-Net (Ours)84.600.8670.09910.02
", + "image_path": "289406115e58e144f07438b1e5acf6445384b7f1e76541c9727b1ae8eb874ad7.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 365, + 546, + 425 + ], + "lines": [ + { + "bbox": [ + 305, + 365, + 546, + 425 + ], + "spans": [ + { + "bbox": [ + 305, + 365, + 546, + 425 + ], + "type": "text", + "content": "Table 2. Quantitative comparison of PGVS-Net with prior SOTA methods (method subscripts: IS: Image-based supervised, VS: Video-based supervised, and " + }, + { + "bbox": [ + 305, + 365, + 546, + 425 + ], + "type": "inline_equation", + "content": "VU" + }, + { + "bbox": [ + 305, + 365, + 546, + 425 + ], + "type": "text", + "content": ": Video-based without labels). The top and second best results are highlighted in red and blue, respectively." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 449, + 545, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 449, + 545, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 449, + 545, + 581 + ], + "type": "text", + "content": "dataset; RGB-P glass segmentation methods EAF [49], PM-RCNN [14] and PGS [29]; STICT [25] (since this is an unsupervised method, we use the polarimetric dataset from [29] as labeled images for training); ViSha [3] is a recent video shadow detection method; STM-based video segmentation methods STCN [4] and RDE [20] (with ground truth masks during training and using the mask from GSD [30] during evaluation). In all our examples, during inference, the initial masks for PGVS-Net are provided by the polarization-aware PGSNet [29]. The quantitative and qualitative results are shown in Table 2 and Figure 6." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 582, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 546, + 714 + ], + "type": "text", + "content": "PGVS-Net outperforms state-of-the-art methods by a significant margin and improves IoU, MAE, and BER by 3.75, 0.016, and 2.29 over the next best method, demonstrating the effectiveness of multi-view polarization propagation for video glass segmentation. PGVS-Net performs slightly less than PGS-Net on the " + }, + { + "bbox": [ + 304, + 582, + 546, + 714 + ], + "type": "inline_equation", + "content": "\\mathrm{F}_{\\beta}" + }, + { + "bbox": [ + 304, + 582, + 546, + 714 + ], + "type": "text", + "content": " metric, which again illustrates the robustness of polarization cues for glass segmentation for both still-image and video sequences. Figure 6 further qualitatively illustrates the robustness of PGVS-Net. We refer to the video sequences in the supplementary material to qualitatively evaluate the temporally" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 732, + 317, + 741 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 732, + 317, + 741 + ], + "spans": [ + { + "bbox": [ + 293, + 732, + 317, + 741 + ], + "type": "text", + "content": "23224" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 71, + 553, + 261 + ], + "blocks": [ + { + "bbox": [ + 53, + 71, + 553, + 261 + ], + "lines": [ + { + "bbox": [ + 53, + 71, + 553, + 261 + ], + "spans": [ + { + "bbox": [ + 53, + 71, + 553, + 261 + ], + "type": "image", + "image_path": "47213855b4533228afed374244f4e6b1b6c7c92333fb7084587ba1dbd7229d67.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 262, + 547, + 288 + ], + "lines": [ + { + "bbox": [ + 46, + 262, + 547, + 288 + ], + "spans": [ + { + "bbox": [ + 46, + 262, + 547, + 288 + ], + "type": "text", + "content": "Figure 6. Qualitative comparison of our model against state-of-the-art image-based glass segmentation methods and video detection/segmentation methods. All models are retrained on PGV-117." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 53, + 300, + 552, + 399 + ], + "blocks": [ + { + "bbox": [ + 53, + 300, + 552, + 399 + ], + "lines": [ + { + "bbox": [ + 53, + 300, + 552, + 399 + ], + "spans": [ + { + "bbox": [ + 53, + 300, + 552, + 399 + ], + "type": "image", + "image_path": "ac67882c5fed5f43f34280df6e0ea8e4b593c41cc8f578f5c012f360351ef0b1.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 122, + 401, + 470, + 414 + ], + "lines": [ + { + "bbox": [ + 122, + 401, + 470, + 414 + ], + "spans": [ + { + "bbox": [ + 122, + 401, + 470, + 414 + ], + "type": "text", + "content": "Figure 7. Qualitative comparison of the different ablation combinations of PGVS-Net." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 48, + 432, + 287, + 541 + ], + "blocks": [ + { + "bbox": [ + 48, + 432, + 287, + 541 + ], + "lines": [ + { + "bbox": [ + 48, + 432, + 287, + 541 + ], + "spans": [ + { + "bbox": [ + 48, + 432, + 287, + 541 + ], + "type": "table", + "html": "
NetworksIoU↑Fβ↑MAE↓BER↓
RGB78.960.8070.14213.88
RGB-P81.010.8270.13113.16
RGB-P+PGI83.680.8600.10110.43
RGB-P+PTF81.780.8380.12212.38
RGB-P+CMTA83.810.8620.10010.88
RGB-P+PGI+CMTA+PTF(M5)80.760.8260.13412.82
PGVS-Net84.600.8670.09910.02
", + "image_path": "e68223be1a83808abee2b083ecdb7a6658f4680c004f3a7853813697d17db757.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 550, + 288, + 612 + ], + "lines": [ + { + "bbox": [ + 46, + 550, + 288, + 612 + ], + "spans": [ + { + "bbox": [ + 46, + 550, + 288, + 612 + ], + "type": "text", + "content": "Table 3. Summary of ablation experiments: Polarization cues (RGB-P) outperform RGB-only cues. The combination of all modules (PGVS-Net) produces the overall best results. 'M5' indicates that the long-range memory is updated every five frames during inference." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 47, + 635, + 216, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 635, + 216, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 635, + 216, + 647 + ], + "type": "text", + "content": "coherent glass segmentation propagation." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 657, + 141, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 657, + 141, + 670 + ], + "spans": [ + { + "bbox": [ + 47, + 657, + 141, + 670 + ], + "type": "text", + "content": "5.3. Ablation Study" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 288, + 713 + ], + "type": "text", + "content": "We validate the impact of each component in PGVS-Net by disabling one or more components and comparing the performance on the PGV-117 test set (Table 3). The net" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 434, + 545, + 530 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 434, + 545, + 530 + ], + "spans": [ + { + "bbox": [ + 304, + 434, + 545, + 530 + ], + "type": "text", + "content": "work named 'RGB' uses only RGB textures to populate and query the memory to predict glass areas without any other modules. The 'RGB-P' network uses RGB-P information to store, read and calculate memory features. All other networks start from the 'RGB-P' baseline with the listed modules enabled. Finally, we indicate with 'M5' that the memory is updated every five frames during the inference stage as opposed to every three frames for PGVS-Net." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 546, + 546, + 713 + ], + "type": "text", + "content": "The improved performance of the 'RGB-P' network over 'RGB' shows that polarization provides additional cues for glass segmentation. PGI combines tripartite key features to retrieve affinity from historical views. Its attribute performance gain shows that integrated RGB-P streams can better mine multi-view similarity than single-stream matching. The PTF module further improves the segmentation accuracy (e.g., IoU increases from 81.01 to 81.78). Adding the CMTA module further improves the performance on the four metrics, demonstrating that the cross-modal and cross-temporal integration provides rich short-range references for query frames. Finally, the full PGVS-Net with all modules enabled achieves the best results when combined with a memory update every three frames." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "spans": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "type": "text", + "content": "23225" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 54, + 71, + 282, + 210 + ], + "blocks": [ + { + "bbox": [ + 54, + 71, + 282, + 210 + ], + "lines": [ + { + "bbox": [ + 54, + 71, + 282, + 210 + ], + "spans": [ + { + "bbox": [ + 54, + 71, + 282, + 210 + ], + "type": "image", + "image_path": "aa204cc6f7bc377688a5ae8731d6da89b222a7873a7d1fcbfaf2742f92a6fe83.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 213, + 286, + 237 + ], + "lines": [ + { + "bbox": [ + 47, + 213, + 286, + 237 + ], + "spans": [ + { + "bbox": [ + 47, + 213, + 286, + 237 + ], + "type": "text", + "content": "Figure 8. Two failure cases with inaccurate glass segmentation highlighted in the red boxes." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 261, + 211, + 274 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 261, + 211, + 274 + ], + "spans": [ + { + "bbox": [ + 47, + 261, + 211, + 274 + ], + "type": "text", + "content": "5.4. Failure Cases and Limitations" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 281, + 287, + 485 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 281, + 287, + 485 + ], + "spans": [ + { + "bbox": [ + 46, + 281, + 287, + 485 + ], + "type": "text", + "content": "Our method propagates a single initial mask, and thus its overall quality is affected by the quality of the initial mask. For glass areas with no initial or historical references, little information can be propagated from multi-view observations. While PGVS-Net can augment glass segmentation in such scenarios by harnessing spatial characteristics across both the RGB and polarization domain, it is possible that the segmentation can result in gaps in the glass segmentation results (two failure cases are shown in Figure 8). An interesting avenue for future research would be to determine the most reliable RGB-P frame for initial mask estimation before propagating it to the rest of the sequence. Furthermore, although PGVS-Net significantly outperforms other video segmentation methods in accuracy, its tripartite-modal integration and temporal consistency strategy of polarization cues require additional inference time. Our unoptimized implementation currently operates at 7fps." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 500, + 119, + 513 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 500, + 119, + 513 + ], + "spans": [ + { + "bbox": [ + 47, + 500, + 119, + 513 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 521, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 712 + ], + "type": "text", + "content": "In this paper, we introduced a Polarization Video Glass Segmentation network (PGVS-Net), that exploits historical multi-view spectral polarization cues to segment glass areas, and which outperforms state-of-the-art polarization-related image and video segmentation networks. PGVS-Net leverages RGB-P memory and PGI-fused keys to correlate input frames with view-dependent polarization information from prior spectral cues. We show that the continuous changes in illumination are better captured by polarimetric features, and that long-range affinity helps to better balance single-input instabilities than single image methods. In addition, CMTA and PTF provide short-range polarization cues for low-level polarimetric features, providing rich wavelength details in the decoder phase. We also create a novel video glass segmentation dataset (PGV-117) to train and evaluate PGVS-Net." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 72, + 409, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 409, + 85 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 409, + 85 + ], + "type": "text", + "content": "Acknowledgements" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 91, + 545, + 247 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 91, + 545, + 247 + ], + "spans": [ + { + "bbox": [ + 304, + 91, + 545, + 247 + ], + "type": "text", + "content": "This work was supported in part by National Key Research and Development Program of China (2022ZD0210 500), the National Natural Science Foundation of China under Grants 61972067/U21A20491, and the Distinguished Young Scholars Funding of Dalian (No. 2022RJ01). Pieter Peers was supported in part by NSF grant IIS-1909028. Felix Heide was supported by an NSF CAREER Award (2047359), a Packard Foundation Fellowship, a Sloan Research Fellowship, a Sony Young Faculty Award, a Project X Innovation Award, and an Amazon Science Research Award. 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In CVPR, 2017." + } + ] + } + ], + "index": 7 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "spans": [ + { + "bbox": [ + 293, + 732, + 317, + 742 + ], + "type": "text", + "content": "23228" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 10 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi-weather Image Restoration via Domain Translation/582b1bcf-2ccd-4515-9e72-bf5ada976e39_content_list.json b/2023/Multi-weather Image Restoration via Domain Translation/582b1bcf-2ccd-4515-9e72-bf5ada976e39_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..2d023b71a7c0e44fad034fad07f40a1d246120c3 --- /dev/null +++ b/2023/Multi-weather Image Restoration via Domain Translation/582b1bcf-2ccd-4515-9e72-bf5ada976e39_content_list.json @@ -0,0 +1,1579 @@ +[ + { + "type": "text", + "text": "Multi-weather Image Restoration via Domain Translation", + "text_level": 1, + "bbox": [ + 192, + 130, + 777, + 151 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Prashant W. Patil1, Sunil Gupta1, Santu Rana1, Svetha Venkatesh1, and Subrahmanyam Murala2 \n1Deakin University, Geelong Warun Ponds Campus, VIC, Australia, 2 Trinity College Dublin, Ireland", + "bbox": [ + 86, + 180, + 885, + 219 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "prashant.patil@deakin.edu.au", + "bbox": [ + 361, + 219, + 611, + 232 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 268, + 313, + 282 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Weather degraded conditions such as rain, haze, snow, etc. may degrade the performance of most computer vision systems. Therefore, effective restoration of multiweather degraded images is an essential prerequisite for successful functioning of such systems. The current multiweather image restoration approaches utilize a model that is trained on a combined dataset consisting of individual images for rainy, snowy, and hazy weather degradations. These methods may face challenges when dealing with real-world situations where the images may have multiple, more intricate weather conditions. To address this issue, we propose a domain translation-based unified method for multi-weather image restoration. In this approach, the proposed network learns multiple weather degradations simultaneously, making it immune for real-world conditions. Specifically, we first propose an instance-level domain (weather) translation with multi-attentive feature learning approach to get different weather-degraded variants of the same scenario. Next, the original and translated images are used as input to the proposed novel multi-weather restoration network which utilizes a progressive multi-domain deformable alignment (PMDA) with cascaded multi-head attention (CMA). The proposed PMDA facilitates the restoration network to learn weather-invariant clues effectively. Further, PMDA and respective decoder features are merged via proposed CMA module for restoration. Extensive experimental results on synthetic and real-world hazy, rainy, and snowy image databases clearly demonstrate that our model outperforms the state-of-the-art multi-weather image restoration methods. Code is available at https://github.com/pwp1208/DomainTranslation_Multi-weather_Restoration.", + "bbox": [ + 75, + 297, + 473, + 781 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 803, + 209, + 818 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Fog, snow, rain, haze or their combintations often degrade the quality of images recorded for computer vision applications such as surveillance, traffic monitoring, and autonomous driving. These applications routinely involve sub-tasks such as optical flow estimation [36], object detec", + "bbox": [ + 75, + 825, + 468, + 902 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/9f8d80d544a97eeef764719987e64b3c59ace9109548263e65068cc053f4a31a.jpg", + "image_caption": [ + "Figure 1. Upper-part: Thumbnail of the proposed domain translation based multi-weather image restoration approach. Lower-part: Sample restoration results: (a) de-hazing, (b) de-raining with veiling effect, and (c) de-snowing with veiling effect." + ], + "image_footnote": [], + "bbox": [ + 504, + 267, + 887, + 513 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "tion [8], depth estimation [27], etc., which use algorithms or models expecting clean image as their input. Therefore, restoration of images degraded by one or many weather conditions is an important problem.", + "bbox": [ + 496, + 609, + 892, + 670 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Although remarkable success has been achieved in restoration of particular domain such as image de-hazing, image de-raining, and image de-snowing, multi-weather degraded image restoration is still an open problem. Existing works handle multiple weather degradations via separate weather specific encoders [15], or separate training for each weather [1]. To handle multiple degradations with separate training-based models, typically these weather-specific models are put in a cascade, e.g., haze removal followed by rain removal. But, such an approach may produce undesirable results as the erroneous output of any one of the earlier stages affects the overall result in an unpredictable manner. Also, in order to select the appropriate restoration model, prior information about the degradation must be available. To overcome these limitations, researchers intro", + "bbox": [ + 496, + 674, + 893, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "21696", + "bbox": [ + 478, + 945, + 519, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "duced various unified (single trainable parameters) models based on knowledge distillation [4], transformer [33], contrastive degradation guidance [12] and degradation removal with feature corrector [11] for multi-weather image restoration. These models are trained using a combined dataset that contains individual degraded images representing rainy, snowy, and hazy weather, etc. As real-world scenario may have more intricate weather conditions, which limits the performance of [4], [33], [11], [12] methods. Therefore, the restoration architecture should be able to perform significantly for any weather degradation.", + "bbox": [ + 75, + 90, + 472, + 256 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address the above challenges, we propose multiweather image restoration framework where we first create different weather degradations of a degraded image and use them to learn a set of features that jointly represent all the degraded images. Since the common part across diverse weather degraded images is the clean image (i.e., everything except weather degradations), our feature extractor learns to suppress the weather specific information and thus learns weather-invariant features. A practical advantage of this learning scheme is that our feature extractor can be also used for real data even though it is trained using synthetic data. This is because the synthetic and real-world images mainly differ in the weather-degradations, and since our feature extractor learns to suppress it, it can close the domain gap between synthetic and real-world data.", + "bbox": [ + 75, + 257, + 472, + 482 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Following this idea, we propose a domain translation based unified approach for multi-weather image restoration. In order to achieve this, we first used a domain translation approach, where any of the degraded image can be translated to specific domain (e.g., hazy, rain with veil, snow with veil). We then propose a restoration architecture which takes domain translated and original degraded images as input to generate degradation free output. The proposed restoration network comprises of two components: namely a progressive multi-domain deformable alignment (PMDA) and cascaded multi-head attention (CMA) blocks. PMDA module performs inter domain offset feature alignment which facilitates the restoration network to learn weather-invariant representation effectively. Further, the CMA block is proposed to aggregate the respective PMDA and decoder features for effective restoration. Our main contributions are:", + "bbox": [ + 75, + 484, + 472, + 739 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- A novel unified architecture for multi-weather image restoration. It utilizes a single trainable model to restore all weather degradations.", + "- A domain-translation with multi-attentive feature learning to achieve unified model's generalizability.", + "- A progressive multi-domain deformable alignment and cascaded multi-head attention modules for multiweather image restoration." + ], + "bbox": [ + 94, + 742, + 467, + 869 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Extensive experimental analysis on various weather-degraded synthetic and real-world datasets demonstrate that", + "bbox": [ + 75, + 871, + 470, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "the proposed multi-weather restoration framework outperforms the existing state-of-the-art (SOTA) methods. An overview and sample results of the proposed method for real-world images are given in Figure 1.", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 498, + 164, + 640, + 180 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Single Weather Degradation Removal", + "text_level": 1, + "bbox": [ + 498, + 186, + 825, + 202 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "De-hazing: Earlier research on single image de-hazing was directed towards hand-crafted based approaches [6], [32]. The emergence of deep learning networks brought advancements in degradation removal methods, and the researchers proposed various approaches towards the task of haze, rain or snow removal from images. Zhou et al. [40] proposed feedback spatial attention-based architecture with iterative extraction of the high-level information. With iterative process, the improper feature learning at the initial steps may cause an up-stretched error at the last stage and lead to ineffective results. Recently, Liu et al. [17] proposed three-stage visibility enhancement approach with multi-scale attention with multi-feature fusion module. The hazy-image and depth-map-based feature learning with cross-connection and residual channel attention module is proposed in [7] for the de-hazing task. However, getting an accurate depth map for dense hazy images is a challenging task which may produce unrealistic de-hazing results. Density and depth information is integrated with unpaired learning for image de-hazing [37].", + "bbox": [ + 496, + 207, + 890, + 508 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "De-raining: Deng et al. [5] considered rain removal and detail recovery as separate tasks and proposed two parallel sub-networks which make use of dilated convolutions and squeeze-and-excitation networks. Zamir et al. [38], proposed a multi-stage approach which progressively restores a degraded image by injecting supervision at each stage, while processing different scales of the input images.", + "bbox": [ + 496, + 508, + 890, + 614 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "De-snowing: Snow removal from single image is even more challenging task due to the non-transparency property of snow, which results in occluded background region and loss of details. In [39], the authors analyzed the difference between snow streaks and clear background edges, and applied a multi-guided filter to remove snowflakes. A three-stage hierarchical approach is proposed in [34], which combine image decomposition and dictionary learning. Even though these algorithms work effectively for specific weather degradation removal, performance may degrade in the presence of real-world weather degradation. Because along with rain or snow streaks, there is a strong veiling effect present, particularly in heavy rain or snow.", + "bbox": [ + 496, + 614, + 890, + 811 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Multi-weather Degradation Removal", + "text_level": 1, + "bbox": [ + 498, + 819, + 818, + 834 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In 2019, the first attempt was made in [1], to handle single image de-hazing and the de-raining problem with specific weather training. A two-stage approach is proposed [14], in which the first stage estimates the rain streaks, trans", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "21697", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/6e62e5a7287519a99b7aa8f8a83b17ee28d8059f3c4b2c18147612ae0c472e9b.jpg", + "image_caption": [ + "Figure 2. Overview of the proposed multi-weather image restoration algorithm. Initially, the weather degraded image is translated to different domains ( $I_{\\mathbb{D}1}$ : hazy, $I_{\\mathbb{D}2}$ : rain with veil and $I_{\\mathbb{D}3}$ : snow with veil). Next, these translated and input images are processed through separate encoders and aligned using proposed progressive multi-domain feature alignment with cascaded multi-head attention module." + ], + "image_footnote": [], + "bbox": [ + 76, + 85, + 890, + 314 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "mission map, and atmospheric light from the input image. Li et al. [15] proposed a multi-weather image restoration approach where authors leverage neural architecture search for processing the features extracted from the task-specific encoders of rain with veil, rain-drop, and snow. Also, the selection of particular encoder while dealing with real-world weather degraded images is one of the limitation of [15]. Similar to heavy rain, heavy snow will also show a strong veiling effect in the real scene. The first attempt was made by [2] to handle snow and veiling effects simultaneously. They used the modified partial convolution and the differentiable dark channel prior layer. Chen et al. [3] proposed a dual-tree wavelet transform based approach with complex wavelet loss. In [38], authors proposed a multistage architecture that progressively learns restoration functions from degraded images. They handle image de-raining, de-blurring, and de-noising degradations via specific training. Recently, a contrastive-based degraded encoder and degradation-guided restoration network is proposed in [12] to handle image de-nosing, de-raining, and de-hazing tasks. Valanarasu et al. [33] proposed a transformer-based approach for rain with veil, snow and rain-drop removal. They also introduced learnable weather-type embeddings to handle different weather degradation effectively. Chen [4] propsoed two-stage i.e. knowledge collation and knowledge examination with multi-teacher and student architecture for adverse weather removal. Kulkarni et al. [11] proposed dual stream (appearing degradation and veiling effect removal) architecture for multi-weather image restoration. These [4] (28M) [15] (41M), [33] (31M) methods achieved superior performance but at the cost of increased computational complexity.", + "bbox": [ + 75, + 393, + 472, + 878 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Domain Translation", + "text_level": 1, + "bbox": [ + 500, + 392, + 689, + 406 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Since our proposed restoration model is built upon domain translation, we briefly review it in this section. With a recent deep learning advancement, many algorithms are proposed for domain transfer task like structure-guided arbitrary [18], semantic context-aware [16], etc. In [10], authors proposed a memory-guided unsupervised approach to perform diverse translation between two visual domains e.g., Sunny to night, rainy to sunny. They have used separate content and style encoders to learn content and style features from input and target domains. Inspired by this, we have proposed an architecture for instance-level image-to-image translation between original degraded input to required domains. To the best of author's knowledge, this is the first weather-to-weather translation approach for restoration tasks.", + "bbox": [ + 496, + 412, + 893, + 638 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed Framework", + "text_level": 1, + "bbox": [ + 498, + 651, + 705, + 669 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this work, a solution to handle multiple weather degradations is proposed with a unified network without any pretrained weights or domain specific knowledge.", + "bbox": [ + 496, + 674, + 890, + 718 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Overall Pipeline: Overview of the proposed framework is shown in Figure 2. Given a weather degraded image $(I)$ , we first aim to learn a weather invariant representation of the image making the restoration task for multi-weather scenario easier. To learn a weather-invariant representation for $I$ , we first propose the domain translation (DT) of given image $I$ into its different weather variants. For example, we take any weather degraded image $I$ and translate it into a corresponding hazy, rain with veil and snow with veil images. We refer to each weather condition as a domain, denoting them as hazy $(\\mathbb{D}_1)$ , rain with veil $(\\mathbb{D}_2)$ , and snow with veil $(\\mathbb{D}_3)$ , etc. In using domain translation, our main", + "bbox": [ + 496, + 719, + 893, + 901 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "21698", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/5aec34dfe2f791c0a777d2f62d1ccef5910de3ecf483cd8c1d4718d4515004d7.jpg", + "image_caption": [ + "Figure 3. Overview of the proposed domain translation architecture with multi-attentive feature extraction (MFE) module." + ], + "image_footnote": [], + "bbox": [ + 88, + 88, + 467, + 253 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "idea is to create different weather degradations of the same image and use them to train a feature extractor to learn a common set of features that simultaneously represent all the degraded images. Since the common part across diverse weather degraded images is the clean image (everything except weather degradations), our feature extractor learns to suppress the weather specific information and thus learning weather-invariant features. Another practical advantage is that this feature extractor can be used for real data even though it is learnt using synthetic data. This is because only difference between the synthetic generated and real-world images lies in the weather-degradations and since our feature extractor learns to suppress it, the domain gap between synthetic and real-world data is closed.", + "bbox": [ + 75, + 325, + 472, + 537 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We propose a restoration generator $(G_{r})$ where these weather degraded images $(I, I_{\\mathbb{D}1}, I_{\\mathbb{D}2}$ and $I_{\\mathbb{D}3})$ are fed as input. The proposed $G_{r}$ encodes each of the inputs via multi-receptive and multi-scale convolution block based encoders (see in Figure 2) in order to learn to domain-relevant features (see $F_{l}^{\\mathbb{D}_{1}}, F_{l}^{\\mathbb{D}_{2}}, F_{l}^{\\mathbb{D}_{3}}, F_{l \\in (1,3)}^{I}$ in Figure 2). Except first encoder, every encoder down-samples the input features. At last encoder layer, these separately learned features are aggregated and forwarded to the decoder via successive deformable convolutions $(DC_{3})$ for final reconstruction. These extracted features are then processed through successive decoder layers to have final restored image. While reconstruction, the independently learned encoder features processed via proposed progressive multi-domain feature alignment (PMDA) are forwarded to the respective decoder through skip connection. Further, the PMDA features and respective decoder features are merged effectively through proposed cascaded multi-head attention (CMA) to provide the restored image $(I_{g})$ . Summarizing the overall pipeline of the proposed framework as: 1) domain translation (refer Section 3.1), and 2) Multi-weather image restoration (refer Section 3.2). Detailed exposition of each step of the proposed pipeline is provided in following subsections.", + "bbox": [ + 76, + 554, + 472, + 902 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/76fab252493bd39d5fc5761421ab3413d2753229601f943363b6200d866e57f6.jpg", + "image_caption": [ + "Figure 4. Visual results of the proposed DT network." + ], + "image_footnote": [], + "bbox": [ + 501, + 89, + 893, + 157 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Domain-translation Architecture", + "text_level": 1, + "bbox": [ + 500, + 200, + 790, + 215 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The proposed DT approach takes weather degraded image $(I)$ as input and translates it to other weather domains $I_{\\mathbb{D}_i\\in (1,2,3)}$ . We have used U-Net [28] architecture as generator to perform translation of any weather degraded image over the required domain. This architecture mainly comprises of four encoders and four decoders (see DT in Figure 2). The encoder block is defined as: $\\{En_{l\\perp \\times f};[l\\in (1,4),f = 16]\\}$ . Similar to this, the decoder block is defined as: $\\{De_{l\\perp \\times f};[l\\in (4,1),f = 16]\\}$ , where, $l$ and $(l\\times f)$ represent encoder or decoder level and number of filters in encoder or decoder respectively.", + "bbox": [ + 496, + 223, + 890, + 388 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Multi-attentive Feature Extraction: The input image $(I)$ is given to the encoder which will give features $\\left(\\psi_{l\\epsilon (1,4)}\\right)$ . While giving a skip connection from the respective encoder to the decoder, we have processed these features via the proposed multi-attentive feature extraction (MFE) module (see MFE block in DT of 2 for more details). In MFE, the respective $l^{th}$ encoder-level features $(\\psi_l)$ are processed as:", + "bbox": [ + 496, + 388, + 892, + 496 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nx _ {G} ^ {M R} = \\left\\langle C _ {d \\epsilon (1, 2, 3)} ^ {3} (\\psi_ {l}) \\right\\rangle ; x _ {G} ^ {M S} = \\left\\langle C _ {1} ^ {k \\epsilon (1, 3, 5)} (\\psi_ {l}) \\right\\rangle \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 508, + 508, + 890, + 535 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where, $x_{G}^{MR}$ and $x_{G}^{MS}$ are multi-receptive and multi-scale features, $C_d^k$ is convolution with $k \\times k$ kernel and $d$ dilation rate, $\\langle \\cdot \\rangle$ is concatenation followed by convolution with $1 \\times 1$ kernel (refer Figure 3 for more details). Required contextual and spatial information is extracted using dilated and multi-scale convolutions through large receptive fields. Here, we form four different groups by splitting the features into groups of $x_{G_{i\\epsilon(1,4)}}^{MR}$ and $x_{G_{i\\epsilon(1,4)}}^{MS}$ containing equal number of channels in each group and merge respective $x_{G_i}^{MR}$ and $x_{G_i}^{MS}$ to form $x_{i\\epsilon(1,4)}$ . Further, these merged features $x_{i\\epsilon(1,4)}$ are processed via multi-scale attention as: $C_1D_k(x_i) \\odot \\varsigma(C_1D_k(x_i))$ , where $\\varsigma$ is GeLu activation, $\\odot$ is dot product, $k = (2 \\times i) - 1$ (see Figure 3). This splitting and merging of multi-receptive and multi-scale features through multi-scale attention help the network for robust feature representation learning. Sample visual results for domain translation network are shown in Figure 4. From Figure 4, it is clear that the proposed DT network is able to generate three different degradation $(I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3})$ irrespective of input degradation. With this intuition, the three outputs of the DT architecture $(I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3})$ are used along with original weather degraded image $(I)$ as input to the proposed restoration architecture.", + "bbox": [ + 496, + 550, + 893, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "21699", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/28fba42e8694fbb49925d716ac6e298be8c132a87b43af5e0d0d3369eb4eec0d.jpg", + "image_caption": [ + "Figure 5. Overview of the proposed progressive multi-domain deformable alignment module for effective feature aggregation." + ], + "image_footnote": [], + "bbox": [ + 81, + 88, + 472, + 256 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2. Multi-weather Image Restoration Architecture", + "text_level": 1, + "bbox": [ + 76, + 321, + 468, + 338 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The proposed restoration framework is shown in Figure 2 which comprises two major modules: 1) Progressive Multi-domain Deformable Alignment, and 2) Cascaded Multi-head Attention module. Details are given below. Progressive Multi-domain Deformable Alignment: As various weather degradations have different representation (refer $DT$ images of Figure 4), the unified architecture urges alignment of domain (weather) translated features for effective multi-weather restoration. To achieve effective feature alignment, we propose a progressive multi-domain deformable alignment module. The proposed PMDA facilitates the network to learn weather-invariant representation effectively. The independently learned features from all the translated domains i.e. $F_{l}^{\\mathbb{D}_{1}}, F_{l}^{\\mathbb{D}_{2}}, F_{l}^{\\mathbb{D}_{3}}$ and input image $F_{l}^{I}$ of $l^{th}$ encoder layer are forwarded to the proposed PMDA module (refer the Figure 5 for more details). Initially, every domain features are split into four groups i.e. $\\gamma_{i}^{domain}$ , $i \\in (1,4)$ , domain $\\in (\\mathbb{D}_1, \\mathbb{D}_2, \\mathbb{D}_3, I)$ . Further, we process two input domains progressively in proposed inter-domain offset feature alignment (see $\\square$ in Figure 5). Here, in the inter-domain offset feature alignment, inputs from any two domains are used to generate the offsets for actual deformable convolution layer (see DA in Figure 5). Initially, the $\\mathbb{D}_1$ domain features are aligned with input image features. Because, the rainy and snowy degradations are more complex as compared to hazy degradation. All the aligned features of all the respective $i_{th}$ group $\\gamma_{i}^{domain}$ are finally merged to generate $\\gamma_{i}'$ . All the groups are processed in similar way through inter-domain offset feature alignment (see $\\square$ in Figure 5) and concatenation followed by a convolution $\\rightarrow$ Relu layer as:", + "bbox": [ + 73, + 340, + 472, + 811 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\gamma_ {l} = < \\gamma_ {1} ^ {\\prime}, \\gamma_ {2} ^ {\\prime}, \\gamma_ {3} ^ {\\prime}, \\gamma_ {4} ^ {\\prime} > \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 187, + 815, + 468, + 832 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where, $l$ is $l^{th}$ encoder layer, $< \\cdot >$ is concatenation followed by $1 \\times 1$ convolution and ReLu operation. In the progressive inter-domain offset feature alignment for every group $\\gamma_{i}$ , the offset generation and deformable alignment is", + "bbox": [ + 75, + 839, + 470, + 902 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/0df884662892c09e936a837e57aea9d826dde808a0ed2d95a453e44a3a132606.jpg", + "image_caption": [ + "Figure 6. Overview of the proposed cascaded multi-head attention module for feature merging." + ], + "image_footnote": [], + "bbox": [ + 501, + 88, + 887, + 275 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "done with the offset convolution and deformable convolution respectively with different kernel size $k = (2 \\times i) - 1$ i.e. for $i = 4$ the kernel size is $k = 7$ for both offset convolution $(C_k)$ and deformable convolution $(DC_k)$ (see DA in Figure 5). Overall response of progressive inter-domain feature alignment (see in Figure 5) for $i^{th}$ group as:", + "bbox": [ + 498, + 329, + 890, + 420 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\gamma_ {i} ^ {\\prime} = < \\gamma_ {i} ^ {I}, \\chi , \\varphi \\left(\\chi , \\gamma_ {i} ^ {\\mathbb {D} _ {2}}\\right), \\varphi \\left(\\varphi \\left(\\chi , \\gamma_ {i} ^ {\\mathbb {D} _ {2}}\\right), \\gamma_ {i} ^ {\\mathbb {D} _ {3}}\\right) > \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 519, + 422, + 890, + 441 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where, $\\chi = \\varphi (\\gamma_i^I,\\gamma_i^{\\mathbb{D}_1})$ $\\varphi$ is the progressive inter-domain feature alignment. This PMDA module helps for disentanglement of task-relevant data of restoration and taskirrelevant data of various degradation. Therefore, these PMDA features are then forwarded to the respective decoder level via skip connection. Cascaded Multi-head Attention: To effectively merge the decoder features with the respective processed encoder features via PMDA module, we propose a cascaded multi-head attention (CMA). The multi-head attention proposed here consists of deformable convolutions to capture maximum receptive fields. Like transformer layers, the proposed CMA has the structure as attention $\\rightarrow$ layer-norm $\\rightarrow$ feed forward network. So the proposed CMA is able to capture the long term dependencies along-with the high receptive fields due to deformable attention. We use the term cascaded as we are using two successive multi-head attentions (MHA) see in Figure 6) with two inputs from previous decoder $(D_{e(i - 1)})$ and respective PMDA level feature $(\\xi_l)$ .This cascading allows to capture global dependencies effectively. The output of MHA is given as:", + "bbox": [ + 498, + 449, + 892, + 767 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nZ = \\sigma (Q \\cdot K ^ {T}) \\cdot V \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 625, + 770, + 890, + 787 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where, $Q = X$ , $K = DC_{3}(C_{1}(Y))$ , $V = DC_{3}(C_{1}(Y))$ , and $X, Y$ are the inputs to MHA. So the input to first MHA are $D_{e(i-1)}$ and $\\xi_{l}$ and second MHA are $Z_{1}$ and $D_{e(i-1)}$ (see Figure 6). To further process these features, we pass the response of first and second MHA through layer-norm (LN) with respect to $\\xi_{l}$ and $D_{e(i-1)}$ respectively. So the responses of both the LN are given as:", + "bbox": [ + 498, + 794, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "21700", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nL N _ {1} = L N \\left(Z _ {2} + D _ {e (i - 1)}\\right); \\quad L N _ {2} = L N \\left(Z _ {1} + \\xi_ {l}\\right) \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 90, + 467, + 107 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Further, the output of first LN is processed through feed forward network (FFN) followed by a LN. Finally, the output of the CMA $(D_{ei})$ is given as:", + "bbox": [ + 76, + 113, + 467, + 159 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nD _ {e i} = \\left\\langle L N _ {2}, L N \\left(F F N \\left(L N _ {1}\\right) + L N _ {1}\\right) \\right\\rangle \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 133, + 162, + 467, + 179 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where, $< \\cdot >$ is concatenation operation.", + "bbox": [ + 76, + 186, + 346, + 200 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Training Settings", + "text_level": 1, + "bbox": [ + 76, + 209, + 246, + 227 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The proposed restoration network is trained using synthetic data with original and domain translated images as input to get restored image under adversarial settings similar to [9], [23], [22]. To get domain transalted images, domain translation network is trained separately for each required domain like $\\mathbb{D}_1$ : hazy, $\\mathbb{D}_2$ : rain with veil and $\\mathbb{D}_3$ : snow with veil under adversarial settings [9]. The initial learning rate is set to $2 \\times 10^{-4}$ which is reduced by factor of 0.1 as the losses plateau. The networks are trained with PyTorch library on NVIDIA DGX Tesla V100 32 GB GPU. While training the networks, the discriminator is same as in [9].", + "bbox": [ + 75, + 231, + 467, + 398 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Domain Translation Losses", + "text_level": 1, + "bbox": [ + 76, + 402, + 321, + 417 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We train the proposed DT network separately (see $\\phi_1, \\phi_2, \\phi_3$ in Figure 2) for generating each weather degraded image $(I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3})$ . While training of the network to generate particular weather degraded image (e.g., $I_{\\mathbb{D}2}$ ), any of the synthetically degraded images $(I)$ is provided as input. The loss is calculated between the domain translated image (e.g., $I_{\\mathbb{D}2}$ ) and the respective target (e.g., $I_{Rv}$ ). We denote by $I_H, I_{Rv}, I_{Sv}$ are the synthetically degraded target images for $I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3}$ domains respectively. Using these notations, the loss is calculated between the image pairs $(I_{\\mathbb{D}1}, I_H), (I_{\\mathbb{D}2}, I_{Rv})$ , and $(I_{\\mathbb{D}3}, I_{Sv})$ for generation of $I_{\\mathbb{D}1}, I_{\\mathbb{D}2}$ and $I_{\\mathbb{D}3}$ images respectively. The adversarial learning is adopted for DT network training. Along with $\\mathbb{L}_1$ loss, adversarial loss $(\\mathbb{L}_A)$ for DT network is calculated. To guide the network for textural and structural information, the perceptual loss $(\\mathbb{L}_V)$ is calculated between the translated and original target image by passing them through the pre-trained VGG19 model [30]. Further, the contrastive loss $(\\mathbb{L}_c)$ [35] in a common latent feature space is used to maximize and minimize the difference between $(I_{\\mathbb{D}_{i \\in (1,2,3)}, I})$ and $(I_{\\mathbb{D}_{i \\in (1,2,3)}, I_{\\mathbb{T}_{i \\in (H,Rv,Sv)}}})$ respectively. Also, the style loss $(\\mathbb{L}_{S_d})$ with mean and standard deviation are considered. The total loss $(\\mathbb{L}_d)$ is:", + "bbox": [ + 75, + 422, + 467, + 768 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {L} _ {d} \\left(\\mathbb {D} _ {i}, \\mathbb {T} _ {i}\\right) = \\lambda_ {1} \\mathbb {L} _ {1} + \\lambda_ {2} \\mathbb {L} _ {A} + \\lambda_ {3} \\mathbb {L} _ {V} + \\lambda_ {4} \\mathbb {L} _ {c} + \\lambda_ {5} \\mathbb {L} _ {s} \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 773, + 467, + 789 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where, the weights $\\lambda_{k\\epsilon (1,5)}$ for each loss are set empirically.", + "bbox": [ + 76, + 796, + 467, + 813 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Image Restoration Losses", + "text_level": 1, + "bbox": [ + 76, + 820, + 310, + 835 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Along with domain-translated images $(I_{\\mathbb{D}_{i\\epsilon (1,2,3)})}$ , the original degraded image $(I)$ is used as input to get restored image $(I_g)$ . The proposed restoration network is required to generate the restored image similar to the clean image $(I_c)$", + "bbox": [ + 76, + 840, + 467, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "in adversarial manner. The $\\mathbb{L}_1$ loss is used to optimize the network for better reconstruction. The adversarial loss $(\\mathbb{L}_A)$ is the min-max problem between generator and discriminator, respectively. Along with this loss, the perceptual loss $(\\mathbb{L}_V)$ [30] between $(I_g,I_c)$ , contrastive loss $(\\mathbb{L}_c)$ [35] between $(I,I_g,I_c)$ are considered. So, the total loss $(\\mathbb{L}_r)$ is:", + "bbox": [ + 496, + 90, + 890, + 181 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbb {L} _ {r} \\left(I _ {g}, I _ {c}\\right) = \\lambda_ {1} \\mathbb {L} _ {1} + \\lambda_ {2} \\mathbb {L} _ {A} + \\lambda_ {3} \\mathbb {L} _ {V} + \\lambda_ {4} \\mathbb {L} _ {c} \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 544, + 189, + 890, + 205 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where, the weights $\\lambda_{k\\epsilon (1,4)}$ for each loss are set empirically. (loss functions are explained in supplementary material).", + "bbox": [ + 496, + 207, + 890, + 237 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Results and Discussion", + "text_level": 1, + "bbox": [ + 498, + 246, + 714, + 261 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Datasets and Evaluation Metrics", + "text_level": 1, + "bbox": [ + 498, + 267, + 785, + 281 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Synthetic Objective Testing Set (SOTS) [13]: 1000 indoor and outdoor images are provided for testing purpose. From training set, 5000 images are considered for training purpose. We have used outdoor images for result analysis.", + "bbox": [ + 496, + 286, + 890, + 348 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Outdoor-Rain Database (ORD) [14]: This database images are degraded by rain and fog. 9000 and 750 images are provided for training and testing purpose respectively.", + "bbox": [ + 496, + 348, + 890, + 392 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Comprehensive Snow Database (CSD) [3] : 8000 and 2000 images are provided for training and testing purpose respectively with combination of snow and fog degradation.", + "bbox": [ + 496, + 393, + 890, + 436 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Real-world Databases: The image restoration algorithm is said to be domain generalised if it restores the synthetic as well as real-world degraded images efficiently. To scrutinize this, we have used three different real-world degraded image datasets named as Real-world Task-driven Testing Set (RTTS) [13], Snow realistic [19] and Rain In Driving (RID) [31] for experimental analysis.", + "bbox": [ + 496, + 438, + 890, + 542 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We have considered all synthetic databases training sets in combination for training of the proposed restoration network. For testing purpose, the respective testing sets and real-world datasets are used. The reference based evaluation metrics includes average Peak Signal-to-Noise Ratio (PSNR), and Structural Similarity Index Measure (SSIM). Average Naturalness Image Quality Evaluator (NIQE) [21], Entropy and Blind/Referenceless Image Spatial Quality Evaluator (BRISQUE) [20] evaluation metrics are used in case of real-world weather degraded image restoration. We have used the released source code and provided trained models by respective authors to get the results on synthetic and real-world datasets.", + "bbox": [ + 496, + 544, + 890, + 739 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. Real-world Result Evaluation", + "text_level": 1, + "bbox": [ + 498, + 744, + 763, + 758 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The RTTS [13], Snow realistic [19] and RID [31] datasets are considered for real-world experimental analysis. The NIQE $(\\downarrow)$ , entropy $(\\uparrow)$ and BRISQUE $(\\downarrow)$ parameters are used for real-world quantitative analysis as provided in [29] ( $\\downarrow$ : lower is better, $\\uparrow$ : higher is better). The qualitative and quantitative analysis on real-world degraded images are provided in Figure 7 and Table 1 respectively. Proposed method de-hazing results follow the depth criteria. Whereas, UMVR, KD and TW methods are unable to", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "21701", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/c63323b1768d93f3b8c9bf62a5a855aa7fb04816a108eb5ca7b2eca245fe2de2.jpg", + "image_caption": [ + "Figure 7. Qualitative analysis of the proposed and existing methods: UMVR [11], KD [4], TW [33] for multi-weather image restoration." + ], + "image_footnote": [], + "bbox": [ + 84, + 93, + 364, + 467 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/30866fa4b126616a01644fa5e6732b86772d25046d51233808f08680e912c5d1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 370, + 93, + 496, + 467 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/645bb1b0100e68910c1ecaf9d3d6b3c936d4a52a89c041f4f0c221115246dbbb.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 501, + 93, + 627, + 467 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/ca84057d6054e39c59899a38d8e4297df4a117ec2f68ef32d9ef5fb569a499a7.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 635, + 93, + 759, + 467 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6bd469eff47417b5f99c27b26ea073a183d4f1335683439b11ade0bc5b9afb6e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 764, + 93, + 890, + 467 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/7d03edfe47014543efd10b9df1accc40194563a14194d272aea75e4bfbb5b974.jpg", + "table_caption": [ + "Table 1. Subjective results on real-world weather degraded images for de-hazing, de-raining with veil and snow with veil removal." + ], + "table_footnote": [], + "table_body": "
DatabaseMethodsNIQE (↓)Entropy (↑)BRISQUE (↓)
RTTSUMVR [11]5.0097.22128.625
KD [4]4.9967.29726.837
TW [33]5.7037.26329.874
Ours4.8597.50524.761
RIDUMVR [11]6.6047.48624.296
KD [4]6.9437.45924.841
TW [33]7.4967.39324.165
Ours7.6257.49223.931
Snow realisticUMVR [11]4.2967.35423.761
KD [4]6.6437.45924.841
TW [33]5.6287.33125.377
Ours4.1967.57221.884
", + "bbox": [ + 78, + 537, + 486, + 779 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "remove haze in depth (see column 1 and 2 from Figure 7). In presence of heavy rain, the baseline methods are not able to remove the rain effect completely due to strong veiling effect. Whereas, the proposed method can remove the rain with veiling effect significantly (see column 3 and 4 from Figure 7). In case of heavy snow, the effect of veiling ef", + "bbox": [ + 75, + 809, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/b1ab0a9a99fe92e05754503261281aa2b8efb14f9794082dba7c6710e6e0c6e6.jpg", + "table_caption": [ + "Table 2. Quantitative results analysis for de-hazing (SOTS), deraining with veil (ORD) and snow with veil (CSD) removal in terms of average PSNR/SSIM." + ], + "table_footnote": [], + "table_body": "
MethodsSOTSCSDORD
UMVR [11]33.41/0.98028.65/0.90022.99/0.830
KD [4]34.64/0.98531.35/0.95029.05/0.916
TW [33]32.45/0.95529.76/0.94027.96/0.950
Ours36.26/0.98732.95/0.94231.24/0.951
", + "bbox": [ + 501, + 551, + 897, + 647 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "fect is still present in the restored results of existing methods. However, the veiling effect is reduced substantially with the proposed restoration method (see column 5 and 6 from Figure 7). From the visual results, it is observed that the proposed method restores plausible results as compared to existing SOTA methods.", + "bbox": [ + 496, + 664, + 893, + 755 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Synthetic Result Evaluation", + "text_level": 1, + "bbox": [ + 500, + 760, + 750, + 775 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We compared the proposed approach with SOTA unified restoration methods: UMVR [11], KD [4], TW [33] on SOTS-outdoor, CSD and outdoor-rain databases in terms of average PSNR, and SSIM. The quantitative analysis is provided in the Table 2 (see supplementary material for qualitative results). The provided qualitative and quantitative results validate the effectiveness of the proposed method compared to existing unified (UMVR [11], KD [4], TW", + "bbox": [ + 496, + 779, + 893, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "21702", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/2680c8d63f0f4803037f36959e0c7823ac4c4e333fd8e0a42499c3f7608ed450.jpg", + "image_caption": [ + "Figure 8. Visual analysis of the proposed and existing methods: UMVR [11], KD [4], TW [33] for night-time image restoration." + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 155, + 236 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e483082c5930cbb16db0f675b79f987d8259ae98f61ab30154b296486c439a96.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 156, + 88, + 232, + 236 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/442d595cdf593843857fac1c511cced01e9a39d36b517c487ac38f3cf28a9ac2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 233, + 88, + 310, + 236 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/61017a31b333b229e7fddb4e16bd68036323c7c92d927a76820c3dd9be376482.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 310, + 88, + 387, + 236 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/e30bb6a49a85468083150eadd4532941a620a2f7258d70cba47860d2699bee97.jpg", + "image_caption": [ + "Figure 9. Object detection and depth estimation analysis on degraded and restored images by existing UMVR [11], KD [4], TW [33], and proposed multi-weather image restoration method." + ], + "image_footnote": [], + "bbox": [ + 388, + 88, + 464, + 236 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/8229527ac7b036495e0559a00ddb08eec24577f6d941d264fe7b825f10b12e2e.jpg", + "table_caption": [ + "Table 3. Ablation study on the proposed modules with outdoor rain database (IL: Independent Learning, PMDA: Progressive Multidomain Alignment and CMA: Cascaded Multi-head Attention)" + ], + "table_footnote": [], + "table_body": "
ModulePSNRSSIM
Baseline26.490.887
Baseline + IL (Net-1)27.890.905
Baseline + IL + PMDA (Net-2)29.530.942
Baseline + IL + PMDA + CMA31.240.951
", + "bbox": [ + 99, + 324, + 447, + 416 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "[33]) methods on synthetic datasets. Specifically, our unified architecture has $\\sim 11\\mathrm{M}$ parameters (including domain-translation architecture) whereas the existing unified architectures KD [4], and TW [33] have $\\sim 28\\mathrm{M}$ and $\\sim 31\\mathrm{M}$ parameters respectively.", + "bbox": [ + 75, + 435, + 467, + 511 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "As seen from the Table 1 and 2, our method's performance on synthetic data is usually comparable to SOTA that are trained using the respective synthetic datasets. We note that while our method learns from the synthetic data, it does not over-fit on synthetic data. Therefore, it performs well on both synthetic and real-world datasets. This proves that the domain generalization ability of the proposed method is better compared to SOTA unified restoration methods.", + "bbox": [ + 75, + 511, + 467, + 632 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.4. Night-time Multi-weather Restoration", + "text_level": 1, + "bbox": [ + 76, + 640, + 405, + 656 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Weather-degraded image/video restoration is equally important in night conditions as in day conditions [24]. Therefore, we examined the effectiveness of the proposed and existing networks for night-time multi-weather degradation removal. We labeled this analysis as cross-domain. We directly tested the proposed and existing models on real-world night-time multi-weather images downloaded from Internet. Sample results for night-time de-hazing, de-raining and de-snowing are provided in the Figure 8. From the visual results, it is observed that the proposed method performance is significantly better compared to existing methods for night-time multi-weather restoration.", + "bbox": [ + 75, + 660, + 467, + 840 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.5. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 849, + 228, + 864 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We analyse the contributions of individual modules (independent feature learning, PMDA, and CMA) of the pro", + "bbox": [ + 76, + 869, + 467, + 900 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f3bff04379b8342fa5c028bd19bf6cf47a0a55291f01a498c4cc560c8d9ff926.jpg", + "image_caption": [ + "Input Image" + ], + "image_footnote": [], + "bbox": [ + 501, + 88, + 576, + 195 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/328f6d4dba69e3d30f97e7ff94c4034a8e948ec33f4a168efbab4aba95b46522.jpg", + "image_caption": [ + "UMVR" + ], + "image_footnote": [], + "bbox": [ + 578, + 88, + 655, + 195 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a0cab4d48119b451d47c58a9f817f6d7f9d96e927bfea717814414b25df1899a.jpg", + "image_caption": [ + "D" + ], + "image_footnote": [], + "bbox": [ + 656, + 88, + 732, + 195 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4afb46e4519249f07cff463c97b89a44c3651c07438bc7e3b814ba01ca2a2eee.jpg", + "image_caption": [ + "W" + ], + "image_footnote": [], + "bbox": [ + 733, + 88, + 810, + 195 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/88a8578db640409aa017611d5643c7351c11b0013f445f9ec8229f618ae65ffb.jpg", + "image_caption": [ + "Ours" + ], + "image_footnote": [], + "bbox": [ + 810, + 88, + 885, + 195 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "posed architecture in the ablation study conducted on ORD database. We start the ablation with single encoder-decoder architecture and named as \"Baseline\".", + "bbox": [ + 498, + 271, + 890, + 316 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Independent Feature Learning: In the proposed restoration approach, four inputs $(I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3}$ and $I)$ are processed parallelly to learn the features independently. Is this independent feature learning effective for multiweather image restoration? To examine this, these inputs are processed through single (baseline) and parallel Net-1 encoders. From the Table 3 results, it is clear that the proposed independent feature learning is effective for extracting the features from all domains.", + "bbox": [ + 496, + 316, + 890, + 450 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Progressive Multi-domain Deformable Alignment: Along with effective feature extraction, the multi-domain feature alignment has significant importance in restoration. To do this task, we have proposed PMDA module and used at each encoder stage. How does this proposed PMDA module helps the network to integrate the multi-domain features effectively? To scrutinize this, the efficiency of proposed restoration network is examined without (Net-1) and with (Net-2) PMDA. The quantitative analysis is provided in Table 3. From these results, it is evident that the proposed PMDA works effectively for multi-domain feature alignment.", + "bbox": [ + 496, + 452, + 890, + 633 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Cascaded Multi-head Attention: Applying attention on the encoder or decoder features affects differently while restoring the clean image. Therefore, we have applied cascaded multi-head attention on respective PMDA and decoder features. We analysed the network accuracy without (Net-2) and with (baseline+IL+PMDA+CMA) CMA module i.e. final proposed network. The results in Table 3 proves the effectiveness of the proposed CMA module for restoration. The more ablation analysis for SOTS and CSD database is provided in the supplementary material.", + "bbox": [ + 496, + 633, + 890, + 784 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.6. Real-world Applications", + "text_level": 1, + "bbox": [ + 500, + 790, + 722, + 806 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Restoration module can be used as a preprocessing step for down-stream applications like object detection, depth estimation, etc. To this end, we have evaluated the benefits of the proposed and existing restoration methods as a preprocessing step for the object detection [26] and depth estimation task [25]. The visual analysis for object detection", + "bbox": [ + 496, + 810, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "21703", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "and depth predictions is provided in Figure 9. As seen from the Figure 9, depth predictions or confidence in detecting objects of the restored images with proposed approach are more accurate than existing methods and degraded image. Clearly, the proposed domain-translation based restoration approach performs favourably against the SOTA methods for object detection and depth predictions task.", + "bbox": [ + 75, + 90, + 472, + 196 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 208, + 194, + 224 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In this work, we proposed the first weather-invariant representation learning based multi-domain progressive deform-able alignment architecture for multi-weather image restoration. The weather-invariant representation learning helps to learn a representation that is common across diverse weather conditions and also similar across real or synthetic weather degraded images. Further, the proposed progressive multi-domain deform-able alignment module effectively merges the independently learned multi-domain features. This progressive alignment of features helps the network to reduce the degradation in step-by-step manner. Finally, effective restoration is done via CMA to capture long-term dependencies with respective PMDA and decoder features. Results analysis is conducted on real-world and synthetic benchmark hazy, rainy and snowy datasets. Also, the night-time multi-weather restoration results are analysed as cross-domain analysis. Extensive comparisons demonstrate the generalizability of the proposed method over SOTA methods. Further, we have analysed the effectiveness of the proposed and existing methods for object detection and depth estimation tasks for verifying its usefulness in real-world applications.", + "bbox": [ + 75, + 229, + 472, + 564 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 76, + 578, + 174, + 594 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Dongdong Chen, Mingming He, Qingnan Fan, Jing Liao, Liheng Zhang, Dongdong Hou, Lu Yuan, and Gang Hua. Gated context aggregation network for image dehazing and deraining. In 2019 IEEE winter conference on applications of computer vision (WACV), pages 1375-1383. 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IEEE Transactions on Neural Networks and Learning Systems, 2022. 2" + ], + "bbox": [ + 501, + 92, + 890, + 683 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "21705", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Multi-weather Image Restoration via Domain Translation/582b1bcf-2ccd-4515-9e72-bf5ada976e39_model.json b/2023/Multi-weather Image Restoration via Domain Translation/582b1bcf-2ccd-4515-9e72-bf5ada976e39_model.json new file mode 100644 index 0000000000000000000000000000000000000000..f345fc9243c446cddcaeadb9327c7d9891f4c29e --- /dev/null +++ b/2023/Multi-weather Image Restoration via Domain Translation/582b1bcf-2ccd-4515-9e72-bf5ada976e39_model.json @@ -0,0 +1,2101 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.194, + 0.131, + 0.778, + 0.152 + ], + "angle": 0, + "content": "Multi-weather Image Restoration via Domain Translation" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.181, + 0.887, + 0.22 + ], + "angle": 0, + "content": "Prashant W. Patil1, Sunil Gupta1, Santu Rana1, Svetha Venkatesh1, and Subrahmanyam Murala2 \n1Deakin University, Geelong Warun Ponds Campus, VIC, Australia, 2 Trinity College Dublin, Ireland" + }, + { + "type": "text", + "bbox": [ + 0.362, + 0.22, + 0.612, + 0.233 + ], + "angle": 0, + "content": "prashant.patil@deakin.edu.au" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.269, + 0.314, + 0.284 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.298, + 0.474, + 0.782 + ], + "angle": 0, + "content": "Weather degraded conditions such as rain, haze, snow, etc. may degrade the performance of most computer vision systems. Therefore, effective restoration of multiweather degraded images is an essential prerequisite for successful functioning of such systems. The current multiweather image restoration approaches utilize a model that is trained on a combined dataset consisting of individual images for rainy, snowy, and hazy weather degradations. These methods may face challenges when dealing with real-world situations where the images may have multiple, more intricate weather conditions. To address this issue, we propose a domain translation-based unified method for multi-weather image restoration. In this approach, the proposed network learns multiple weather degradations simultaneously, making it immune for real-world conditions. Specifically, we first propose an instance-level domain (weather) translation with multi-attentive feature learning approach to get different weather-degraded variants of the same scenario. Next, the original and translated images are used as input to the proposed novel multi-weather restoration network which utilizes a progressive multi-domain deformable alignment (PMDA) with cascaded multi-head attention (CMA). The proposed PMDA facilitates the restoration network to learn weather-invariant clues effectively. Further, PMDA and respective decoder features are merged via proposed CMA module for restoration. Extensive experimental results on synthetic and real-world hazy, rainy, and snowy image databases clearly demonstrate that our model outperforms the state-of-the-art multi-weather image restoration methods. Code is available at https://github.com/pwp1208/DomainTranslation_Multi-weather_Restoration." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.804, + 0.21, + 0.819 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.826, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Fog, snow, rain, haze or their combintations often degrade the quality of images recorded for computer vision applications such as surveillance, traffic monitoring, and autonomous driving. These applications routinely involve sub-tasks such as optical flow estimation [36], object detec" + }, + { + "type": "image", + "bbox": [ + 0.505, + 0.268, + 0.888, + 0.515 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.528, + 0.895, + 0.585 + ], + "angle": 0, + "content": "Figure 1. Upper-part: Thumbnail of the proposed domain translation based multi-weather image restoration approach. Lower-part: Sample restoration results: (a) de-hazing, (b) de-raining with veiling effect, and (c) de-snowing with veiling effect." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.61, + 0.893, + 0.671 + ], + "angle": 0, + "content": "tion [8], depth estimation [27], etc., which use algorithms or models expecting clean image as their input. Therefore, restoration of images degraded by one or many weather conditions is an important problem." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Although remarkable success has been achieved in restoration of particular domain such as image de-hazing, image de-raining, and image de-snowing, multi-weather degraded image restoration is still an open problem. Existing works handle multiple weather degradations via separate weather specific encoders [15], or separate training for each weather [1]. To handle multiple degradations with separate training-based models, typically these weather-specific models are put in a cascade, e.g., haze removal followed by rain removal. But, such an approach may produce undesirable results as the erroneous output of any one of the earlier stages affects the overall result in an unpredictable manner. Also, in order to select the appropriate restoration model, prior information about the degradation must be available. To overcome these limitations, researchers intro" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.946, + 0.521, + 0.957 + ], + "angle": 0, + "content": "21696" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.257 + ], + "angle": 0, + "content": "duced various unified (single trainable parameters) models based on knowledge distillation [4], transformer [33], contrastive degradation guidance [12] and degradation removal with feature corrector [11] for multi-weather image restoration. These models are trained using a combined dataset that contains individual degraded images representing rainy, snowy, and hazy weather, etc. As real-world scenario may have more intricate weather conditions, which limits the performance of [4], [33], [11], [12] methods. Therefore, the restoration architecture should be able to perform significantly for any weather degradation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.258, + 0.473, + 0.483 + ], + "angle": 0, + "content": "To address the above challenges, we propose multiweather image restoration framework where we first create different weather degradations of a degraded image and use them to learn a set of features that jointly represent all the degraded images. Since the common part across diverse weather degraded images is the clean image (i.e., everything except weather degradations), our feature extractor learns to suppress the weather specific information and thus learns weather-invariant features. A practical advantage of this learning scheme is that our feature extractor can be also used for real data even though it is trained using synthetic data. This is because the synthetic and real-world images mainly differ in the weather-degradations, and since our feature extractor learns to suppress it, it can close the domain gap between synthetic and real-world data." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.485, + 0.473, + 0.74 + ], + "angle": 0, + "content": "Following this idea, we propose a domain translation based unified approach for multi-weather image restoration. In order to achieve this, we first used a domain translation approach, where any of the degraded image can be translated to specific domain (e.g., hazy, rain with veil, snow with veil). We then propose a restoration architecture which takes domain translated and original degraded images as input to generate degradation free output. The proposed restoration network comprises of two components: namely a progressive multi-domain deformable alignment (PMDA) and cascaded multi-head attention (CMA) blocks. PMDA module performs inter domain offset feature alignment which facilitates the restoration network to learn weather-invariant representation effectively. Further, the CMA block is proposed to aggregate the respective PMDA and decoder features for effective restoration. Our main contributions are:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.743, + 0.468, + 0.787 + ], + "angle": 0, + "content": "- A novel unified architecture for multi-weather image restoration. It utilizes a single trainable model to restore all weather degradations." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.792, + 0.468, + 0.822 + ], + "angle": 0, + "content": "- A domain-translation with multi-attentive feature learning to achieve unified model's generalizability." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.827, + 0.468, + 0.871 + ], + "angle": 0, + "content": "- A progressive multi-domain deformable alignment and cascaded multi-head attention modules for multiweather image restoration." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.743, + 0.468, + 0.871 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.872, + 0.472, + 0.901 + ], + "angle": 0, + "content": "Extensive experimental analysis on various weather-degraded synthetic and real-world datasets demonstrate that" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "the proposed multi-weather restoration framework outperforms the existing state-of-the-art (SOTA) methods. An overview and sample results of the proposed method for real-world images are given in Figure 1." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.165, + 0.642, + 0.181 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.187, + 0.826, + 0.203 + ], + "angle": 0, + "content": "2.1. Single Weather Degradation Removal" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.208, + 0.892, + 0.509 + ], + "angle": 0, + "content": "De-hazing: Earlier research on single image de-hazing was directed towards hand-crafted based approaches [6], [32]. The emergence of deep learning networks brought advancements in degradation removal methods, and the researchers proposed various approaches towards the task of haze, rain or snow removal from images. Zhou et al. [40] proposed feedback spatial attention-based architecture with iterative extraction of the high-level information. With iterative process, the improper feature learning at the initial steps may cause an up-stretched error at the last stage and lead to ineffective results. Recently, Liu et al. [17] proposed three-stage visibility enhancement approach with multi-scale attention with multi-feature fusion module. The hazy-image and depth-map-based feature learning with cross-connection and residual channel attention module is proposed in [7] for the de-hazing task. However, getting an accurate depth map for dense hazy images is a challenging task which may produce unrealistic de-hazing results. Density and depth information is integrated with unpaired learning for image de-hazing [37]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.51, + 0.892, + 0.615 + ], + "angle": 0, + "content": "De-raining: Deng et al. [5] considered rain removal and detail recovery as separate tasks and proposed two parallel sub-networks which make use of dilated convolutions and squeeze-and-excitation networks. Zamir et al. [38], proposed a multi-stage approach which progressively restores a degraded image by injecting supervision at each stage, while processing different scales of the input images." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.616, + 0.892, + 0.812 + ], + "angle": 0, + "content": "De-snowing: Snow removal from single image is even more challenging task due to the non-transparency property of snow, which results in occluded background region and loss of details. In [39], the authors analyzed the difference between snow streaks and clear background edges, and applied a multi-guided filter to remove snowflakes. A three-stage hierarchical approach is proposed in [34], which combine image decomposition and dictionary learning. Even though these algorithms work effectively for specific weather degradation removal, performance may degrade in the presence of real-world weather degradation. Because along with rain or snow streaks, there is a strong veiling effect present, particularly in heavy rain or snow." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.82, + 0.82, + 0.835 + ], + "angle": 0, + "content": "2.2. Multi-weather Degradation Removal" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In 2019, the first attempt was made in [1], to handle single image de-hazing and the de-raining problem with specific weather training. A two-stage approach is proposed [14], in which the first stage estimates the rain streaks, trans" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.957 + ], + "angle": 0, + "content": "21697" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.087, + 0.891, + 0.315 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.334, + 0.895, + 0.378 + ], + "angle": 0, + "content": "Figure 2. Overview of the proposed multi-weather image restoration algorithm. Initially, the weather degraded image is translated to different domains (\\(I_{\\mathbb{D}1}\\): hazy, \\(I_{\\mathbb{D}2}\\): rain with veil and \\(I_{\\mathbb{D}3}\\): snow with veil). Next, these translated and input images are processed through separate encoders and aligned using proposed progressive multi-domain feature alignment with cascaded multi-head attention module." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.394, + 0.473, + 0.88 + ], + "angle": 0, + "content": "mission map, and atmospheric light from the input image. Li et al. [15] proposed a multi-weather image restoration approach where authors leverage neural architecture search for processing the features extracted from the task-specific encoders of rain with veil, rain-drop, and snow. Also, the selection of particular encoder while dealing with real-world weather degraded images is one of the limitation of [15]. Similar to heavy rain, heavy snow will also show a strong veiling effect in the real scene. The first attempt was made by [2] to handle snow and veiling effects simultaneously. They used the modified partial convolution and the differentiable dark channel prior layer. Chen et al. [3] proposed a dual-tree wavelet transform based approach with complex wavelet loss. In [38], authors proposed a multistage architecture that progressively learns restoration functions from degraded images. They handle image de-raining, de-blurring, and de-noising degradations via specific training. Recently, a contrastive-based degraded encoder and degradation-guided restoration network is proposed in [12] to handle image de-nosing, de-raining, and de-hazing tasks. Valanarasu et al. [33] proposed a transformer-based approach for rain with veil, snow and rain-drop removal. They also introduced learnable weather-type embeddings to handle different weather degradation effectively. Chen [4] propsoed two-stage i.e. knowledge collation and knowledge examination with multi-teacher and student architecture for adverse weather removal. Kulkarni et al. [11] proposed dual stream (appearing degradation and veiling effect removal) architecture for multi-weather image restoration. These [4] (28M) [15] (41M), [33] (31M) methods achieved superior performance but at the cost of increased computational complexity." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.393, + 0.691, + 0.407 + ], + "angle": 0, + "content": "2.3. Domain Translation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.413, + 0.895, + 0.64 + ], + "angle": 0, + "content": "Since our proposed restoration model is built upon domain translation, we briefly review it in this section. With a recent deep learning advancement, many algorithms are proposed for domain transfer task like structure-guided arbitrary [18], semantic context-aware [16], etc. In [10], authors proposed a memory-guided unsupervised approach to perform diverse translation between two visual domains e.g., Sunny to night, rainy to sunny. They have used separate content and style encoders to learn content and style features from input and target domains. Inspired by this, we have proposed an architecture for instance-level image-to-image translation between original degraded input to required domains. To the best of author's knowledge, this is the first weather-to-weather translation approach for restoration tasks." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.652, + 0.707, + 0.67 + ], + "angle": 0, + "content": "3. Proposed Framework" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.892, + 0.719 + ], + "angle": 0, + "content": "In this work, a solution to handle multiple weather degradations is proposed with a unified network without any pretrained weights or domain specific knowledge." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.895, + 0.902 + ], + "angle": 0, + "content": "Overall Pipeline: Overview of the proposed framework is shown in Figure 2. Given a weather degraded image \\((I)\\), we first aim to learn a weather invariant representation of the image making the restoration task for multi-weather scenario easier. To learn a weather-invariant representation for \\(I\\), we first propose the domain translation (DT) of given image \\(I\\) into its different weather variants. For example, we take any weather degraded image \\(I\\) and translate it into a corresponding hazy, rain with veil and snow with veil images. We refer to each weather condition as a domain, denoting them as hazy \\((\\mathbb{D}_1)\\), rain with veil \\((\\mathbb{D}_2)\\), and snow with veil \\((\\mathbb{D}_3)\\), etc. In using domain translation, our main" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "21698" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.089, + 0.089, + 0.468, + 0.254 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.26, + 0.47, + 0.288 + ], + "angle": 0, + "content": "Figure 3. Overview of the proposed domain translation architecture with multi-attentive feature extraction (MFE) module." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.327, + 0.473, + 0.538 + ], + "angle": 0, + "content": "idea is to create different weather degradations of the same image and use them to train a feature extractor to learn a common set of features that simultaneously represent all the degraded images. Since the common part across diverse weather degraded images is the clean image (everything except weather degradations), our feature extractor learns to suppress the weather specific information and thus learning weather-invariant features. Another practical advantage is that this feature extractor can be used for real data even though it is learnt using synthetic data. This is because only difference between the synthetic generated and real-world images lies in the weather-degradations and since our feature extractor learns to suppress it, the domain gap between synthetic and real-world data is closed." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.555, + 0.473, + 0.904 + ], + "angle": 0, + "content": "We propose a restoration generator \\((G_{r})\\) where these weather degraded images \\((I, I_{\\mathbb{D}1}, I_{\\mathbb{D}2}\\) and \\(I_{\\mathbb{D}3})\\) are fed as input. The proposed \\(G_{r}\\) encodes each of the inputs via multi-receptive and multi-scale convolution block based encoders (see in Figure 2) in order to learn to domain-relevant features (see \\(F_{l}^{\\mathbb{D}_{1}}, F_{l}^{\\mathbb{D}_{2}}, F_{l}^{\\mathbb{D}_{3}}, F_{l \\in (1,3)}^{I}\\) in Figure 2). Except first encoder, every encoder down-samples the input features. At last encoder layer, these separately learned features are aggregated and forwarded to the decoder via successive deformable convolutions \\((DC_{3})\\) for final reconstruction. These extracted features are then processed through successive decoder layers to have final restored image. While reconstruction, the independently learned encoder features processed via proposed progressive multi-domain feature alignment (PMDA) are forwarded to the respective decoder through skip connection. Further, the PMDA features and respective decoder features are merged effectively through proposed cascaded multi-head attention (CMA) to provide the restored image \\((I_{g})\\). Summarizing the overall pipeline of the proposed framework as: 1) domain translation (refer Section 3.1), and 2) Multi-weather image restoration (refer Section 3.2). Detailed exposition of each step of the proposed pipeline is provided in following subsections." + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.09, + 0.895, + 0.158 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.538, + 0.165, + 0.855, + 0.18 + ], + "angle": 0, + "content": "Figure 4. Visual results of the proposed DT network." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.202, + 0.791, + 0.217 + ], + "angle": 0, + "content": "3.1. Domain-translation Architecture" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.224, + 0.892, + 0.39 + ], + "angle": 0, + "content": "The proposed DT approach takes weather degraded image \\((I)\\) as input and translates it to other weather domains \\(I_{\\mathbb{D}_i\\in (1,2,3)}\\). We have used U-Net [28] architecture as generator to perform translation of any weather degraded image over the required domain. This architecture mainly comprises of four encoders and four decoders (see DT in Figure 2). The encoder block is defined as: \\(\\{En_{l\\perp \\times f};[l\\in (1,4),f = 16]\\}\\). Similar to this, the decoder block is defined as: \\(\\{De_{l\\perp \\times f};[l\\in (4,1),f = 16]\\}\\), where, \\(l\\) and \\((l\\times f)\\) represent encoder or decoder level and number of filters in encoder or decoder respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.39, + 0.893, + 0.497 + ], + "angle": 0, + "content": "Multi-attentive Feature Extraction: The input image \\((I)\\) is given to the encoder which will give features \\(\\left(\\psi_{l\\epsilon (1,4)}\\right)\\). While giving a skip connection from the respective encoder to the decoder, we have processed these features via the proposed multi-attentive feature extraction (MFE) module (see MFE block in DT of 2 for more details). In MFE, the respective \\(l^{th}\\) encoder-level features \\((\\psi_l)\\) are processed as:" + }, + { + "type": "equation", + "bbox": [ + 0.509, + 0.509, + 0.892, + 0.536 + ], + "angle": 0, + "content": "\\[\nx _ {G} ^ {M R} = \\left\\langle C _ {d \\epsilon (1, 2, 3)} ^ {3} (\\psi_ {l}) \\right\\rangle ; x _ {G} ^ {M S} = \\left\\langle C _ {1} ^ {k \\epsilon (1, 3, 5)} (\\psi_ {l}) \\right\\rangle \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.551, + 0.895, + 0.902 + ], + "angle": 0, + "content": "where, \\( x_{G}^{MR} \\) and \\( x_{G}^{MS} \\) are multi-receptive and multi-scale features, \\( C_d^k \\) is convolution with \\( k \\times k \\) kernel and \\( d \\) dilation rate, \\( \\langle \\cdot \\rangle \\) is concatenation followed by convolution with \\( 1 \\times 1 \\) kernel (refer Figure 3 for more details). Required contextual and spatial information is extracted using dilated and multi-scale convolutions through large receptive fields. Here, we form four different groups by splitting the features into groups of \\( x_{G_{i\\epsilon(1,4)}}^{MR} \\) and \\( x_{G_{i\\epsilon(1,4)}}^{MS} \\) containing equal number of channels in each group and merge respective \\( x_{G_i}^{MR} \\) and \\( x_{G_i}^{MS} \\) to form \\( x_{i\\epsilon(1,4)} \\). Further, these merged features \\( x_{i\\epsilon(1,4)} \\) are processed via multi-scale attention as: \\( C_1D_k(x_i) \\odot \\varsigma(C_1D_k(x_i)) \\), where \\( \\varsigma \\) is GeLu activation, \\( \\odot \\) is dot product, \\( k = (2 \\times i) - 1 \\) (see Figure 3). This splitting and merging of multi-receptive and multi-scale features through multi-scale attention help the network for robust feature representation learning. Sample visual results for domain translation network are shown in Figure 4. From Figure 4, it is clear that the proposed DT network is able to generate three different degradation \\( (I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3}) \\) irrespective of input degradation. With this intuition, the three outputs of the DT architecture \\( (I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3}) \\) are used along with original weather degraded image \\( (I) \\) as input to the proposed restoration architecture." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "21699" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.082, + 0.089, + 0.473, + 0.257 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.277, + 0.47, + 0.306 + ], + "angle": 0, + "content": "Figure 5. Overview of the proposed progressive multi-domain deformable alignment module for effective feature aggregation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.323, + 0.47, + 0.339 + ], + "angle": 0, + "content": "3.2. Multi-weather Image Restoration Architecture" + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.342, + 0.473, + 0.812 + ], + "angle": 0, + "content": "The proposed restoration framework is shown in Figure 2 which comprises two major modules: 1) Progressive Multi-domain Deformable Alignment, and 2) Cascaded Multi-head Attention module. Details are given below. Progressive Multi-domain Deformable Alignment: As various weather degradations have different representation (refer \\(DT\\) images of Figure 4), the unified architecture urges alignment of domain (weather) translated features for effective multi-weather restoration. To achieve effective feature alignment, we propose a progressive multi-domain deformable alignment module. The proposed PMDA facilitates the network to learn weather-invariant representation effectively. The independently learned features from all the translated domains i.e. \\(F_{l}^{\\mathbb{D}_{1}}, F_{l}^{\\mathbb{D}_{2}}, F_{l}^{\\mathbb{D}_{3}}\\) and input image \\(F_{l}^{I}\\) of \\(l^{th}\\) encoder layer are forwarded to the proposed PMDA module (refer the Figure 5 for more details). Initially, every domain features are split into four groups i.e. \\(\\gamma_{i}^{domain}\\), \\(i \\in (1,4)\\), domain \\(\\in (\\mathbb{D}_1, \\mathbb{D}_2, \\mathbb{D}_3, I)\\). Further, we process two input domains progressively in proposed inter-domain offset feature alignment (see \\(\\square\\) in Figure 5). Here, in the inter-domain offset feature alignment, inputs from any two domains are used to generate the offsets for actual deformable convolution layer (see DA in Figure 5). Initially, the \\(\\mathbb{D}_1\\) domain features are aligned with input image features. Because, the rainy and snowy degradations are more complex as compared to hazy degradation. All the aligned features of all the respective \\(i_{th}\\) group \\(\\gamma_{i}^{domain}\\) are finally merged to generate \\(\\gamma_{i}'\\). All the groups are processed in similar way through inter-domain offset feature alignment (see \\(\\square\\) in Figure 5) and concatenation followed by a convolution \\(\\rightarrow\\) Relu layer as:" + }, + { + "type": "equation", + "bbox": [ + 0.188, + 0.816, + 0.47, + 0.833 + ], + "angle": 0, + "content": "\\[\n\\gamma_ {l} = < \\gamma_ {1} ^ {\\prime}, \\gamma_ {2} ^ {\\prime}, \\gamma_ {3} ^ {\\prime}, \\gamma_ {4} ^ {\\prime} > \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.471, + 0.903 + ], + "angle": 0, + "content": "where, \\( l \\) is \\( l^{th} \\) encoder layer, \\( < \\cdot > \\) is concatenation followed by \\( 1 \\times 1 \\) convolution and ReLu operation. In the progressive inter-domain offset feature alignment for every group \\( \\gamma_{i} \\), the offset generation and deformable alignment is" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.089, + 0.888, + 0.276 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.281, + 0.892, + 0.309 + ], + "angle": 0, + "content": "Figure 6. Overview of the proposed cascaded multi-head attention module for feature merging." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.33, + 0.892, + 0.421 + ], + "angle": 0, + "content": "done with the offset convolution and deformable convolution respectively with different kernel size \\( k = (2 \\times i) - 1 \\) i.e. for \\( i = 4 \\) the kernel size is \\( k = 7 \\) for both offset convolution \\( (C_k) \\) and deformable convolution \\( (DC_k) \\) (see DA in Figure 5). Overall response of progressive inter-domain feature alignment (see in Figure 5) for \\( i^{th} \\) group as:" + }, + { + "type": "equation", + "bbox": [ + 0.52, + 0.423, + 0.892, + 0.443 + ], + "angle": 0, + "content": "\\[\n\\gamma_ {i} ^ {\\prime} = < \\gamma_ {i} ^ {I}, \\chi , \\varphi \\left(\\chi , \\gamma_ {i} ^ {\\mathbb {D} _ {2}}\\right), \\varphi \\left(\\varphi \\left(\\chi , \\gamma_ {i} ^ {\\mathbb {D} _ {2}}\\right), \\gamma_ {i} ^ {\\mathbb {D} _ {3}}\\right) > \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.45, + 0.893, + 0.768 + ], + "angle": 0, + "content": "where, \\(\\chi = \\varphi (\\gamma_i^I,\\gamma_i^{\\mathbb{D}_1})\\) \\(\\varphi\\) is the progressive inter-domain feature alignment. This PMDA module helps for disentanglement of task-relevant data of restoration and taskirrelevant data of various degradation. Therefore, these PMDA features are then forwarded to the respective decoder level via skip connection. Cascaded Multi-head Attention: To effectively merge the decoder features with the respective processed encoder features via PMDA module, we propose a cascaded multi-head attention (CMA). The multi-head attention proposed here consists of deformable convolutions to capture maximum receptive fields. Like transformer layers, the proposed CMA has the structure as attention \\(\\rightarrow\\) layer-norm \\(\\rightarrow\\) feed forward network. So the proposed CMA is able to capture the long term dependencies along-with the high receptive fields due to deformable attention. We use the term cascaded as we are using two successive multi-head attentions (MHA) see in Figure 6) with two inputs from previous decoder \\((D_{e(i - 1)})\\) and respective PMDA level feature \\((\\xi_l)\\) .This cascading allows to capture global dependencies effectively. The output of MHA is given as:" + }, + { + "type": "equation", + "bbox": [ + 0.627, + 0.771, + 0.891, + 0.789 + ], + "angle": 0, + "content": "\\[\nZ = \\sigma (Q \\cdot K ^ {T}) \\cdot V \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.795, + 0.892, + 0.902 + ], + "angle": 0, + "content": "where, \\(Q = X\\), \\(K = DC_{3}(C_{1}(Y))\\), \\(V = DC_{3}(C_{1}(Y))\\), and \\(X, Y\\) are the inputs to MHA. So the input to first MHA are \\(D_{e(i-1)}\\) and \\(\\xi_{l}\\) and second MHA are \\(Z_{1}\\) and \\(D_{e(i-1)}\\) (see Figure 6). To further process these features, we pass the response of first and second MHA through layer-norm (LN) with respect to \\(\\xi_{l}\\) and \\(D_{e(i-1)}\\) respectively. So the responses of both the LN are given as:" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "21700" + } + ], + [ + { + "type": "equation", + "bbox": [ + 0.088, + 0.091, + 0.468, + 0.108 + ], + "angle": 0, + "content": "\\[\nL N _ {1} = L N \\left(Z _ {2} + D _ {e (i - 1)}\\right); \\quad L N _ {2} = L N \\left(Z _ {1} + \\xi_ {l}\\right) \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.114, + 0.468, + 0.16 + ], + "angle": 0, + "content": "Further, the output of first LN is processed through feed forward network (FFN) followed by a LN. Finally, the output of the CMA \\((D_{ei})\\) is given as:" + }, + { + "type": "equation", + "bbox": [ + 0.135, + 0.163, + 0.468, + 0.18 + ], + "angle": 0, + "content": "\\[\nD _ {e i} = \\left\\langle L N _ {2}, L N \\left(F F N \\left(L N _ {1}\\right) + L N _ {1}\\right) \\right\\rangle \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.187, + 0.348, + 0.202 + ], + "angle": 0, + "content": "where, \\(< \\cdot >\\) is concatenation operation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.21, + 0.247, + 0.228 + ], + "angle": 0, + "content": "4. Training Settings" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.232, + 0.468, + 0.399 + ], + "angle": 0, + "content": "The proposed restoration network is trained using synthetic data with original and domain translated images as input to get restored image under adversarial settings similar to [9], [23], [22]. To get domain transalted images, domain translation network is trained separately for each required domain like \\(\\mathbb{D}_1\\): hazy, \\(\\mathbb{D}_2\\): rain with veil and \\(\\mathbb{D}_3\\): snow with veil under adversarial settings [9]. The initial learning rate is set to \\(2 \\times 10^{-4}\\) which is reduced by factor of 0.1 as the losses plateau. The networks are trained with PyTorch library on NVIDIA DGX Tesla V100 32 GB GPU. While training the networks, the discriminator is same as in [9]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.404, + 0.322, + 0.418 + ], + "angle": 0, + "content": "4.1. Domain Translation Losses" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.423, + 0.468, + 0.77 + ], + "angle": 0, + "content": "We train the proposed DT network separately (see \\(\\phi_1, \\phi_2, \\phi_3\\) in Figure 2) for generating each weather degraded image \\((I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3})\\). While training of the network to generate particular weather degraded image (e.g., \\(I_{\\mathbb{D}2}\\)), any of the synthetically degraded images \\((I)\\) is provided as input. The loss is calculated between the domain translated image (e.g., \\(I_{\\mathbb{D}2}\\)) and the respective target (e.g., \\(I_{Rv}\\)). We denote by \\(I_H, I_{Rv}, I_{Sv}\\) are the synthetically degraded target images for \\(I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3}\\) domains respectively. Using these notations, the loss is calculated between the image pairs \\((I_{\\mathbb{D}1}, I_H), (I_{\\mathbb{D}2}, I_{Rv})\\), and \\((I_{\\mathbb{D}3}, I_{Sv})\\) for generation of \\(I_{\\mathbb{D}1}, I_{\\mathbb{D}2}\\) and \\(I_{\\mathbb{D}3}\\) images respectively. The adversarial learning is adopted for DT network training. Along with \\(\\mathbb{L}_1\\) loss, adversarial loss \\((\\mathbb{L}_A)\\) for DT network is calculated. To guide the network for textural and structural information, the perceptual loss \\((\\mathbb{L}_V)\\) is calculated between the translated and original target image by passing them through the pre-trained VGG19 model [30]. Further, the contrastive loss \\((\\mathbb{L}_c)\\) [35] in a common latent feature space is used to maximize and minimize the difference between \\((I_{\\mathbb{D}_{i \\in (1,2,3)}, I})\\) and \\((I_{\\mathbb{D}_{i \\in (1,2,3)}, I_{\\mathbb{T}_{i \\in (H,Rv,Sv)}}})\\) respectively. Also, the style loss \\((\\mathbb{L}_{S_d})\\) with mean and standard deviation are considered. The total loss \\((\\mathbb{L}_d)\\) is:" + }, + { + "type": "equation", + "bbox": [ + 0.085, + 0.774, + 0.468, + 0.79 + ], + "angle": 0, + "content": "\\[\n\\mathbb {L} _ {d} \\left(\\mathbb {D} _ {i}, \\mathbb {T} _ {i}\\right) = \\lambda_ {1} \\mathbb {L} _ {1} + \\lambda_ {2} \\mathbb {L} _ {A} + \\lambda_ {3} \\mathbb {L} _ {V} + \\lambda_ {4} \\mathbb {L} _ {c} + \\lambda_ {5} \\mathbb {L} _ {s} \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.797, + 0.468, + 0.814 + ], + "angle": 0, + "content": "where, the weights \\(\\lambda_{k\\epsilon (1,5)}\\) for each loss are set empirically." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.821, + 0.312, + 0.836 + ], + "angle": 0, + "content": "4.2. Image Restoration Losses" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.841, + 0.468, + 0.902 + ], + "angle": 0, + "content": "Along with domain-translated images \\((I_{\\mathbb{D}_{i\\epsilon (1,2,3)})}\\), the original degraded image \\((I)\\) is used as input to get restored image \\((I_g)\\). The proposed restoration network is required to generate the restored image similar to the clean image \\((I_c)\\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.183 + ], + "angle": 0, + "content": "in adversarial manner. The \\(\\mathbb{L}_1\\) loss is used to optimize the network for better reconstruction. The adversarial loss \\((\\mathbb{L}_A)\\) is the min-max problem between generator and discriminator, respectively. Along with this loss, the perceptual loss \\((\\mathbb{L}_V)\\) [30] between \\((I_g,I_c)\\), contrastive loss \\((\\mathbb{L}_c)\\) [35] between \\((I,I_g,I_c)\\) are considered. So, the total loss \\((\\mathbb{L}_r)\\) is:" + }, + { + "type": "equation", + "bbox": [ + 0.545, + 0.19, + 0.891, + 0.206 + ], + "angle": 0, + "content": "\\[\n\\mathbb {L} _ {r} \\left(I _ {g}, I _ {c}\\right) = \\lambda_ {1} \\mathbb {L} _ {1} + \\lambda_ {2} \\mathbb {L} _ {A} + \\lambda_ {3} \\mathbb {L} _ {V} + \\lambda_ {4} \\mathbb {L} _ {c} \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.208, + 0.891, + 0.238 + ], + "angle": 0, + "content": "where, the weights \\(\\lambda_{k\\epsilon (1,4)}\\) for each loss are set empirically. (loss functions are explained in supplementary material)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.247, + 0.715, + 0.262 + ], + "angle": 0, + "content": "5. Results and Discussion" + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.268, + 0.787, + 0.282 + ], + "angle": 0, + "content": "5.1. Datasets and Evaluation Metrics" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.287, + 0.892, + 0.349 + ], + "angle": 0, + "content": "Synthetic Objective Testing Set (SOTS) [13]: 1000 indoor and outdoor images are provided for testing purpose. From training set, 5000 images are considered for training purpose. We have used outdoor images for result analysis." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.349, + 0.892, + 0.393 + ], + "angle": 0, + "content": "Outdoor-Rain Database (ORD) [14]: This database images are degraded by rain and fog. 9000 and 750 images are provided for training and testing purpose respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.394, + 0.892, + 0.438 + ], + "angle": 0, + "content": "Comprehensive Snow Database (CSD) [3] : 8000 and 2000 images are provided for training and testing purpose respectively with combination of snow and fog degradation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.439, + 0.892, + 0.544 + ], + "angle": 0, + "content": "Real-world Databases: The image restoration algorithm is said to be domain generalised if it restores the synthetic as well as real-world degraded images efficiently. To scrutinize this, we have used three different real-world degraded image datasets named as Real-world Task-driven Testing Set (RTTS) [13], Snow realistic [19] and Rain In Driving (RID) [31] for experimental analysis." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.545, + 0.892, + 0.74 + ], + "angle": 0, + "content": "We have considered all synthetic databases training sets in combination for training of the proposed restoration network. For testing purpose, the respective testing sets and real-world datasets are used. The reference based evaluation metrics includes average Peak Signal-to-Noise Ratio (PSNR), and Structural Similarity Index Measure (SSIM). Average Naturalness Image Quality Evaluator (NIQE) [21], Entropy and Blind/Referenceless Image Spatial Quality Evaluator (BRISQUE) [20] evaluation metrics are used in case of real-world weather degraded image restoration. We have used the released source code and provided trained models by respective authors to get the results on synthetic and real-world datasets." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.746, + 0.764, + 0.76 + ], + "angle": 0, + "content": "5.2. Real-world Result Evaluation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "The RTTS [13], Snow realistic [19] and RID [31] datasets are considered for real-world experimental analysis. The NIQE \\((\\downarrow)\\), entropy \\((\\uparrow)\\) and BRISQUE \\((\\downarrow)\\) parameters are used for real-world quantitative analysis as provided in [29] ( \\( \\downarrow \\): lower is better, \\( \\uparrow \\): higher is better). The qualitative and quantitative analysis on real-world degraded images are provided in Figure 7 and Table 1 respectively. Proposed method de-hazing results follow the depth criteria. Whereas, UMVR, KD and TW methods are unable to" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "21701" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.086, + 0.094, + 0.366, + 0.468 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.371, + 0.094, + 0.498, + 0.468 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.094, + 0.629, + 0.468 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.637, + 0.094, + 0.761, + 0.468 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.765, + 0.094, + 0.892, + 0.468 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.481, + 0.882, + 0.496 + ], + "angle": 0, + "content": "Figure 7. Qualitative analysis of the proposed and existing methods: UMVR [11], KD [4], TW [33] for multi-weather image restoration." + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.509, + 0.471, + 0.537 + ], + "angle": 0, + "content": "Table 1. Subjective results on real-world weather degraded images for de-hazing, de-raining with veil and snow with veil removal." + }, + { + "type": "table", + "bbox": [ + 0.079, + 0.539, + 0.487, + 0.78 + ], + "angle": 0, + "content": "
DatabaseMethodsNIQE (↓)Entropy (↑)BRISQUE (↓)
RTTSUMVR [11]5.0097.22128.625
KD [4]4.9967.29726.837
TW [33]5.7037.26329.874
Ours4.8597.50524.761
RIDUMVR [11]6.6047.48624.296
KD [4]6.9437.45924.841
TW [33]7.4967.39324.165
Ours7.6257.49223.931
Snow realisticUMVR [11]4.2967.35423.761
KD [4]6.6437.45924.841
TW [33]5.6287.33125.377
Ours4.1967.57221.884
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.81, + 0.471, + 0.903 + ], + "angle": 0, + "content": "remove haze in depth (see column 1 and 2 from Figure 7). In presence of heavy rain, the baseline methods are not able to remove the rain effect completely due to strong veiling effect. Whereas, the proposed method can remove the rain with veiling effect significantly (see column 3 and 4 from Figure 7). In case of heavy snow, the effect of veiling ef" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.509, + 0.892, + 0.551 + ], + "angle": 0, + "content": "Table 2. Quantitative results analysis for de-hazing (SOTS), deraining with veil (ORD) and snow with veil (CSD) removal in terms of average PSNR/SSIM." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.553, + 0.898, + 0.648 + ], + "angle": 0, + "content": "
MethodsSOTSCSDORD
UMVR [11]33.41/0.98028.65/0.90022.99/0.830
KD [4]34.64/0.98531.35/0.95029.05/0.916
TW [33]32.45/0.95529.76/0.94027.96/0.950
Ours36.26/0.98732.95/0.94231.24/0.951
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.665, + 0.894, + 0.756 + ], + "angle": 0, + "content": "fect is still present in the restored results of existing methods. However, the veiling effect is reduced substantially with the proposed restoration method (see column 5 and 6 from Figure 7). From the visual results, it is observed that the proposed method restores plausible results as compared to existing SOTA methods." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.761, + 0.75, + 0.776 + ], + "angle": 0, + "content": "5.3. Synthetic Result Evaluation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.903 + ], + "angle": 0, + "content": "We compared the proposed approach with SOTA unified restoration methods: UMVR [11], KD [4], TW [33] on SOTS-outdoor, CSD and outdoor-rain databases in terms of average PSNR, and SSIM. The quantitative analysis is provided in the Table 2 (see supplementary material for qualitative results). The provided qualitative and quantitative results validate the effectiveness of the proposed method compared to existing unified (UMVR [11], KD [4], TW" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "21702" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.156, + 0.237 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.157, + 0.089, + 0.233, + 0.237 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.234, + 0.089, + 0.311, + 0.237 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.312, + 0.089, + 0.388, + 0.237 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.39, + 0.089, + 0.465, + 0.237 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.242, + 0.468, + 0.27 + ], + "angle": 0, + "content": "Figure 8. Visual analysis of the proposed and existing methods: UMVR [11], KD [4], TW [33] for night-time image restoration." + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.278, + 0.469, + 0.32 + ], + "angle": 0, + "content": "Table 3. Ablation study on the proposed modules with outdoor rain database (IL: Independent Learning, PMDA: Progressive Multidomain Alignment and CMA: Cascaded Multi-head Attention)" + }, + { + "type": "table", + "bbox": [ + 0.1, + 0.325, + 0.449, + 0.417 + ], + "angle": 0, + "content": "
ModulePSNRSSIM
Baseline26.490.887
Baseline + IL (Net-1)27.890.905
Baseline + IL + PMDA (Net-2)29.530.942
Baseline + IL + PMDA + CMA31.240.951
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.436, + 0.468, + 0.512 + ], + "angle": 0, + "content": "[33]) methods on synthetic datasets. Specifically, our unified architecture has \\(\\sim 11\\mathrm{M}\\) parameters (including domain-translation architecture) whereas the existing unified architectures KD [4], and TW [33] have \\(\\sim 28\\mathrm{M}\\) and \\(\\sim 31\\mathrm{M}\\) parameters respectively." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.512, + 0.468, + 0.633 + ], + "angle": 0, + "content": "As seen from the Table 1 and 2, our method's performance on synthetic data is usually comparable to SOTA that are trained using the respective synthetic datasets. We note that while our method learns from the synthetic data, it does not over-fit on synthetic data. Therefore, it performs well on both synthetic and real-world datasets. This proves that the domain generalization ability of the proposed method is better compared to SOTA unified restoration methods." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.641, + 0.406, + 0.657 + ], + "angle": 0, + "content": "5.4. Night-time Multi-weather Restoration" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.661, + 0.468, + 0.842 + ], + "angle": 0, + "content": "Weather-degraded image/video restoration is equally important in night conditions as in day conditions [24]. Therefore, we examined the effectiveness of the proposed and existing networks for night-time multi-weather degradation removal. We labeled this analysis as cross-domain. We directly tested the proposed and existing models on real-world night-time multi-weather images downloaded from Internet. Sample results for night-time de-hazing, de-raining and de-snowing are provided in the Figure 8. From the visual results, it is observed that the proposed method performance is significantly better compared to existing methods for night-time multi-weather restoration." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.85, + 0.229, + 0.866 + ], + "angle": 0, + "content": "5.5. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.468, + 0.901 + ], + "angle": 0, + "content": "We analyse the contributions of individual modules (independent feature learning, PMDA, and CMA) of the pro" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.089, + 0.578, + 0.196 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.523, + 0.196, + 0.562, + 0.203 + ], + "angle": 0, + "content": "Input Image" + }, + { + "type": "image", + "bbox": [ + 0.58, + 0.089, + 0.656, + 0.196 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.609, + 0.197, + 0.631, + 0.203 + ], + "angle": 0, + "content": "UMVR" + }, + { + "type": "image", + "bbox": [ + 0.658, + 0.089, + 0.733, + 0.196 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.694, + 0.197, + 0.703, + 0.203 + ], + "angle": 0, + "content": "D" + }, + { + "type": "image", + "bbox": [ + 0.735, + 0.089, + 0.811, + 0.196 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.777, + 0.197, + 0.784, + 0.203 + ], + "angle": 0, + "content": "W" + }, + { + "type": "image", + "bbox": [ + 0.812, + 0.089, + 0.887, + 0.196 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.842, + 0.197, + 0.856, + 0.203 + ], + "angle": 0, + "content": "Ours" + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.213, + 0.892, + 0.255 + ], + "angle": 0, + "content": "Figure 9. Object detection and depth estimation analysis on degraded and restored images by existing UMVR [11], KD [4], TW [33], and proposed multi-weather image restoration method." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.272, + 0.892, + 0.317 + ], + "angle": 0, + "content": "posed architecture in the ablation study conducted on ORD database. We start the ablation with single encoder-decoder architecture and named as \"Baseline\"." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.318, + 0.892, + 0.452 + ], + "angle": 0, + "content": "Independent Feature Learning: In the proposed restoration approach, four inputs \\((I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3}\\) and \\(I)\\) are processed parallelly to learn the features independently. Is this independent feature learning effective for multiweather image restoration? To examine this, these inputs are processed through single (baseline) and parallel Net-1 encoders. From the Table 3 results, it is clear that the proposed independent feature learning is effective for extracting the features from all domains." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.453, + 0.892, + 0.634 + ], + "angle": 0, + "content": "Progressive Multi-domain Deformable Alignment: Along with effective feature extraction, the multi-domain feature alignment has significant importance in restoration. To do this task, we have proposed PMDA module and used at each encoder stage. How does this proposed PMDA module helps the network to integrate the multi-domain features effectively? To scrutinize this, the efficiency of proposed restoration network is examined without (Net-1) and with (Net-2) PMDA. The quantitative analysis is provided in Table 3. From these results, it is evident that the proposed PMDA works effectively for multi-domain feature alignment." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.635, + 0.892, + 0.785 + ], + "angle": 0, + "content": "Cascaded Multi-head Attention: Applying attention on the encoder or decoder features affects differently while restoring the clean image. Therefore, we have applied cascaded multi-head attention on respective PMDA and decoder features. We analysed the network accuracy without (Net-2) and with (baseline+IL+PMDA+CMA) CMA module i.e. final proposed network. The results in Table 3 proves the effectiveness of the proposed CMA module for restoration. The more ablation analysis for SOTS and CSD database is provided in the supplementary material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.791, + 0.723, + 0.807 + ], + "angle": 0, + "content": "5.6. Real-world Applications" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.811, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Restoration module can be used as a preprocessing step for down-stream applications like object detection, depth estimation, etc. To this end, we have evaluated the benefits of the proposed and existing restoration methods as a preprocessing step for the object detection [26] and depth estimation task [25]. The visual analysis for object detection" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "21703" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.198 + ], + "angle": 0, + "content": "and depth predictions is provided in Figure 9. As seen from the Figure 9, depth predictions or confidence in detecting objects of the restored images with proposed approach are more accurate than existing methods and degraded image. Clearly, the proposed domain-translation based restoration approach performs favourably against the SOTA methods for object detection and depth predictions task." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.209, + 0.196, + 0.225 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.231, + 0.473, + 0.565 + ], + "angle": 0, + "content": "In this work, we proposed the first weather-invariant representation learning based multi-domain progressive deform-able alignment architecture for multi-weather image restoration. The weather-invariant representation learning helps to learn a representation that is common across diverse weather conditions and also similar across real or synthetic weather degraded images. Further, the proposed progressive multi-domain deform-able alignment module effectively merges the independently learned multi-domain features. This progressive alignment of features helps the network to reduce the degradation in step-by-step manner. Finally, effective restoration is done via CMA to capture long-term dependencies with respective PMDA and decoder features. Results analysis is conducted on real-world and synthetic benchmark hazy, rainy and snowy datasets. Also, the night-time multi-weather restoration results are analysed as cross-domain analysis. Extensive comparisons demonstrate the generalizability of the proposed method over SOTA methods. Further, we have analysed the effectiveness of the proposed and existing methods for object detection and depth estimation tasks for verifying its usefulness in real-world applications." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.579, + 0.175, + 0.595 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.605, + 0.47, + 0.675 + ], + "angle": 0, + "content": "[1] Dongdong Chen, Mingming He, Qingnan Fan, Jing Liao, Liheng Zhang, Dongdong Hou, Lu Yuan, and Gang Hua. Gated context aggregation network for image dehazing and deraining. In 2019 IEEE winter conference on applications of computer vision (WACV), pages 1375-1383. IEEE, 2019. 1, 2" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.676, + 0.472, + 0.758 + ], + "angle": 0, + "content": "[2] Wei-Ting Chen, Hao-Yu Fang, Jian-Jiun Ding, Cheng-Che Tsai, and Sy-Yen Kuo. 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IEEE Transactions on Neural Networks and Learning Systems, 2022. 2" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.684 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "21705" + } + ] +] \ No newline at end of file diff --git a/2023/Multi-weather Image Restoration via Domain Translation/582b1bcf-2ccd-4515-9e72-bf5ada976e39_origin.pdf b/2023/Multi-weather Image Restoration via Domain Translation/582b1bcf-2ccd-4515-9e72-bf5ada976e39_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..4b642deed1a26d07620706fd20a6b4285597d34e --- /dev/null +++ b/2023/Multi-weather Image Restoration via Domain Translation/582b1bcf-2ccd-4515-9e72-bf5ada976e39_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:5fe79189c3bcca03a9ad8ffcb50d68a95776c8ff2e076c5ca85b36226009664a +size 9443569 diff --git a/2023/Multi-weather Image Restoration via Domain Translation/full.md b/2023/Multi-weather Image Restoration via Domain Translation/full.md new file mode 100644 index 0000000000000000000000000000000000000000..4eb4a481cccacca0b1fea374038c537b86b1ecf2 --- /dev/null +++ b/2023/Multi-weather Image Restoration via Domain Translation/full.md @@ -0,0 +1,307 @@ +# Multi-weather Image Restoration via Domain Translation + +Prashant W. Patil1, Sunil Gupta1, Santu Rana1, Svetha Venkatesh1, and Subrahmanyam Murala2 +1Deakin University, Geelong Warun Ponds Campus, VIC, Australia, 2 Trinity College Dublin, Ireland + +prashant.patil@deakin.edu.au + +# Abstract + +Weather degraded conditions such as rain, haze, snow, etc. may degrade the performance of most computer vision systems. Therefore, effective restoration of multiweather degraded images is an essential prerequisite for successful functioning of such systems. The current multiweather image restoration approaches utilize a model that is trained on a combined dataset consisting of individual images for rainy, snowy, and hazy weather degradations. These methods may face challenges when dealing with real-world situations where the images may have multiple, more intricate weather conditions. To address this issue, we propose a domain translation-based unified method for multi-weather image restoration. In this approach, the proposed network learns multiple weather degradations simultaneously, making it immune for real-world conditions. Specifically, we first propose an instance-level domain (weather) translation with multi-attentive feature learning approach to get different weather-degraded variants of the same scenario. Next, the original and translated images are used as input to the proposed novel multi-weather restoration network which utilizes a progressive multi-domain deformable alignment (PMDA) with cascaded multi-head attention (CMA). The proposed PMDA facilitates the restoration network to learn weather-invariant clues effectively. Further, PMDA and respective decoder features are merged via proposed CMA module for restoration. Extensive experimental results on synthetic and real-world hazy, rainy, and snowy image databases clearly demonstrate that our model outperforms the state-of-the-art multi-weather image restoration methods. Code is available at https://github.com/pwp1208/DomainTranslation_Multi-weather_Restoration. + +# 1. Introduction + +Fog, snow, rain, haze or their combintations often degrade the quality of images recorded for computer vision applications such as surveillance, traffic monitoring, and autonomous driving. These applications routinely involve sub-tasks such as optical flow estimation [36], object detec + +![](images/9f8d80d544a97eeef764719987e64b3c59ace9109548263e65068cc053f4a31a.jpg) +Figure 1. Upper-part: Thumbnail of the proposed domain translation based multi-weather image restoration approach. Lower-part: Sample restoration results: (a) de-hazing, (b) de-raining with veiling effect, and (c) de-snowing with veiling effect. + +tion [8], depth estimation [27], etc., which use algorithms or models expecting clean image as their input. Therefore, restoration of images degraded by one or many weather conditions is an important problem. + +Although remarkable success has been achieved in restoration of particular domain such as image de-hazing, image de-raining, and image de-snowing, multi-weather degraded image restoration is still an open problem. Existing works handle multiple weather degradations via separate weather specific encoders [15], or separate training for each weather [1]. To handle multiple degradations with separate training-based models, typically these weather-specific models are put in a cascade, e.g., haze removal followed by rain removal. But, such an approach may produce undesirable results as the erroneous output of any one of the earlier stages affects the overall result in an unpredictable manner. Also, in order to select the appropriate restoration model, prior information about the degradation must be available. To overcome these limitations, researchers intro + +duced various unified (single trainable parameters) models based on knowledge distillation [4], transformer [33], contrastive degradation guidance [12] and degradation removal with feature corrector [11] for multi-weather image restoration. These models are trained using a combined dataset that contains individual degraded images representing rainy, snowy, and hazy weather, etc. As real-world scenario may have more intricate weather conditions, which limits the performance of [4], [33], [11], [12] methods. Therefore, the restoration architecture should be able to perform significantly for any weather degradation. + +To address the above challenges, we propose multiweather image restoration framework where we first create different weather degradations of a degraded image and use them to learn a set of features that jointly represent all the degraded images. Since the common part across diverse weather degraded images is the clean image (i.e., everything except weather degradations), our feature extractor learns to suppress the weather specific information and thus learns weather-invariant features. A practical advantage of this learning scheme is that our feature extractor can be also used for real data even though it is trained using synthetic data. This is because the synthetic and real-world images mainly differ in the weather-degradations, and since our feature extractor learns to suppress it, it can close the domain gap between synthetic and real-world data. + +Following this idea, we propose a domain translation based unified approach for multi-weather image restoration. In order to achieve this, we first used a domain translation approach, where any of the degraded image can be translated to specific domain (e.g., hazy, rain with veil, snow with veil). We then propose a restoration architecture which takes domain translated and original degraded images as input to generate degradation free output. The proposed restoration network comprises of two components: namely a progressive multi-domain deformable alignment (PMDA) and cascaded multi-head attention (CMA) blocks. PMDA module performs inter domain offset feature alignment which facilitates the restoration network to learn weather-invariant representation effectively. Further, the CMA block is proposed to aggregate the respective PMDA and decoder features for effective restoration. Our main contributions are: + +- A novel unified architecture for multi-weather image restoration. It utilizes a single trainable model to restore all weather degradations. +- A domain-translation with multi-attentive feature learning to achieve unified model's generalizability. +- A progressive multi-domain deformable alignment and cascaded multi-head attention modules for multiweather image restoration. + +Extensive experimental analysis on various weather-degraded synthetic and real-world datasets demonstrate that + +the proposed multi-weather restoration framework outperforms the existing state-of-the-art (SOTA) methods. An overview and sample results of the proposed method for real-world images are given in Figure 1. + +# 2. Related Work + +# 2.1. Single Weather Degradation Removal + +De-hazing: Earlier research on single image de-hazing was directed towards hand-crafted based approaches [6], [32]. The emergence of deep learning networks brought advancements in degradation removal methods, and the researchers proposed various approaches towards the task of haze, rain or snow removal from images. Zhou et al. [40] proposed feedback spatial attention-based architecture with iterative extraction of the high-level information. With iterative process, the improper feature learning at the initial steps may cause an up-stretched error at the last stage and lead to ineffective results. Recently, Liu et al. [17] proposed three-stage visibility enhancement approach with multi-scale attention with multi-feature fusion module. The hazy-image and depth-map-based feature learning with cross-connection and residual channel attention module is proposed in [7] for the de-hazing task. However, getting an accurate depth map for dense hazy images is a challenging task which may produce unrealistic de-hazing results. Density and depth information is integrated with unpaired learning for image de-hazing [37]. + +De-raining: Deng et al. [5] considered rain removal and detail recovery as separate tasks and proposed two parallel sub-networks which make use of dilated convolutions and squeeze-and-excitation networks. Zamir et al. [38], proposed a multi-stage approach which progressively restores a degraded image by injecting supervision at each stage, while processing different scales of the input images. + +De-snowing: Snow removal from single image is even more challenging task due to the non-transparency property of snow, which results in occluded background region and loss of details. In [39], the authors analyzed the difference between snow streaks and clear background edges, and applied a multi-guided filter to remove snowflakes. A three-stage hierarchical approach is proposed in [34], which combine image decomposition and dictionary learning. Even though these algorithms work effectively for specific weather degradation removal, performance may degrade in the presence of real-world weather degradation. Because along with rain or snow streaks, there is a strong veiling effect present, particularly in heavy rain or snow. + +# 2.2. Multi-weather Degradation Removal + +In 2019, the first attempt was made in [1], to handle single image de-hazing and the de-raining problem with specific weather training. A two-stage approach is proposed [14], in which the first stage estimates the rain streaks, trans + +![](images/6e62e5a7287519a99b7aa8f8a83b17ee28d8059f3c4b2c18147612ae0c472e9b.jpg) +Figure 2. Overview of the proposed multi-weather image restoration algorithm. Initially, the weather degraded image is translated to different domains ( $I_{\mathbb{D}1}$ : hazy, $I_{\mathbb{D}2}$ : rain with veil and $I_{\mathbb{D}3}$ : snow with veil). Next, these translated and input images are processed through separate encoders and aligned using proposed progressive multi-domain feature alignment with cascaded multi-head attention module. + +mission map, and atmospheric light from the input image. Li et al. [15] proposed a multi-weather image restoration approach where authors leverage neural architecture search for processing the features extracted from the task-specific encoders of rain with veil, rain-drop, and snow. Also, the selection of particular encoder while dealing with real-world weather degraded images is one of the limitation of [15]. Similar to heavy rain, heavy snow will also show a strong veiling effect in the real scene. The first attempt was made by [2] to handle snow and veiling effects simultaneously. They used the modified partial convolution and the differentiable dark channel prior layer. Chen et al. [3] proposed a dual-tree wavelet transform based approach with complex wavelet loss. In [38], authors proposed a multistage architecture that progressively learns restoration functions from degraded images. They handle image de-raining, de-blurring, and de-noising degradations via specific training. Recently, a contrastive-based degraded encoder and degradation-guided restoration network is proposed in [12] to handle image de-nosing, de-raining, and de-hazing tasks. Valanarasu et al. [33] proposed a transformer-based approach for rain with veil, snow and rain-drop removal. They also introduced learnable weather-type embeddings to handle different weather degradation effectively. Chen [4] propsoed two-stage i.e. knowledge collation and knowledge examination with multi-teacher and student architecture for adverse weather removal. Kulkarni et al. [11] proposed dual stream (appearing degradation and veiling effect removal) architecture for multi-weather image restoration. These [4] (28M) [15] (41M), [33] (31M) methods achieved superior performance but at the cost of increased computational complexity. + +# 2.3. Domain Translation + +Since our proposed restoration model is built upon domain translation, we briefly review it in this section. With a recent deep learning advancement, many algorithms are proposed for domain transfer task like structure-guided arbitrary [18], semantic context-aware [16], etc. In [10], authors proposed a memory-guided unsupervised approach to perform diverse translation between two visual domains e.g., Sunny to night, rainy to sunny. They have used separate content and style encoders to learn content and style features from input and target domains. Inspired by this, we have proposed an architecture for instance-level image-to-image translation between original degraded input to required domains. To the best of author's knowledge, this is the first weather-to-weather translation approach for restoration tasks. + +# 3. Proposed Framework + +In this work, a solution to handle multiple weather degradations is proposed with a unified network without any pretrained weights or domain specific knowledge. + +Overall Pipeline: Overview of the proposed framework is shown in Figure 2. Given a weather degraded image $(I)$ , we first aim to learn a weather invariant representation of the image making the restoration task for multi-weather scenario easier. To learn a weather-invariant representation for $I$ , we first propose the domain translation (DT) of given image $I$ into its different weather variants. For example, we take any weather degraded image $I$ and translate it into a corresponding hazy, rain with veil and snow with veil images. We refer to each weather condition as a domain, denoting them as hazy $(\mathbb{D}_1)$ , rain with veil $(\mathbb{D}_2)$ , and snow with veil $(\mathbb{D}_3)$ , etc. In using domain translation, our main + +![](images/5aec34dfe2f791c0a777d2f62d1ccef5910de3ecf483cd8c1d4718d4515004d7.jpg) +Figure 3. Overview of the proposed domain translation architecture with multi-attentive feature extraction (MFE) module. + +idea is to create different weather degradations of the same image and use them to train a feature extractor to learn a common set of features that simultaneously represent all the degraded images. Since the common part across diverse weather degraded images is the clean image (everything except weather degradations), our feature extractor learns to suppress the weather specific information and thus learning weather-invariant features. Another practical advantage is that this feature extractor can be used for real data even though it is learnt using synthetic data. This is because only difference between the synthetic generated and real-world images lies in the weather-degradations and since our feature extractor learns to suppress it, the domain gap between synthetic and real-world data is closed. + +We propose a restoration generator $(G_{r})$ where these weather degraded images $(I, I_{\mathbb{D}1}, I_{\mathbb{D}2}$ and $I_{\mathbb{D}3})$ are fed as input. The proposed $G_{r}$ encodes each of the inputs via multi-receptive and multi-scale convolution block based encoders (see in Figure 2) in order to learn to domain-relevant features (see $F_{l}^{\mathbb{D}_{1}}, F_{l}^{\mathbb{D}_{2}}, F_{l}^{\mathbb{D}_{3}}, F_{l \in (1,3)}^{I}$ in Figure 2). Except first encoder, every encoder down-samples the input features. At last encoder layer, these separately learned features are aggregated and forwarded to the decoder via successive deformable convolutions $(DC_{3})$ for final reconstruction. These extracted features are then processed through successive decoder layers to have final restored image. While reconstruction, the independently learned encoder features processed via proposed progressive multi-domain feature alignment (PMDA) are forwarded to the respective decoder through skip connection. Further, the PMDA features and respective decoder features are merged effectively through proposed cascaded multi-head attention (CMA) to provide the restored image $(I_{g})$ . Summarizing the overall pipeline of the proposed framework as: 1) domain translation (refer Section 3.1), and 2) Multi-weather image restoration (refer Section 3.2). Detailed exposition of each step of the proposed pipeline is provided in following subsections. + +![](images/76fab252493bd39d5fc5761421ab3413d2753229601f943363b6200d866e57f6.jpg) +Figure 4. Visual results of the proposed DT network. + +# 3.1. Domain-translation Architecture + +The proposed DT approach takes weather degraded image $(I)$ as input and translates it to other weather domains $I_{\mathbb{D}_i\in (1,2,3)}$ . We have used U-Net [28] architecture as generator to perform translation of any weather degraded image over the required domain. This architecture mainly comprises of four encoders and four decoders (see DT in Figure 2). The encoder block is defined as: $\{En_{l\perp \times f};[l\in (1,4),f = 16]\}$ . Similar to this, the decoder block is defined as: $\{De_{l\perp \times f};[l\in (4,1),f = 16]\}$ , where, $l$ and $(l\times f)$ represent encoder or decoder level and number of filters in encoder or decoder respectively. + +Multi-attentive Feature Extraction: The input image $(I)$ is given to the encoder which will give features $\left(\psi_{l\epsilon (1,4)}\right)$ . While giving a skip connection from the respective encoder to the decoder, we have processed these features via the proposed multi-attentive feature extraction (MFE) module (see MFE block in DT of 2 for more details). In MFE, the respective $l^{th}$ encoder-level features $(\psi_l)$ are processed as: + +$$ +x _ {G} ^ {M R} = \left\langle C _ {d \epsilon (1, 2, 3)} ^ {3} (\psi_ {l}) \right\rangle ; x _ {G} ^ {M S} = \left\langle C _ {1} ^ {k \epsilon (1, 3, 5)} (\psi_ {l}) \right\rangle \tag {1} +$$ + +where, $x_{G}^{MR}$ and $x_{G}^{MS}$ are multi-receptive and multi-scale features, $C_d^k$ is convolution with $k \times k$ kernel and $d$ dilation rate, $\langle \cdot \rangle$ is concatenation followed by convolution with $1 \times 1$ kernel (refer Figure 3 for more details). Required contextual and spatial information is extracted using dilated and multi-scale convolutions through large receptive fields. Here, we form four different groups by splitting the features into groups of $x_{G_{i\epsilon(1,4)}}^{MR}$ and $x_{G_{i\epsilon(1,4)}}^{MS}$ containing equal number of channels in each group and merge respective $x_{G_i}^{MR}$ and $x_{G_i}^{MS}$ to form $x_{i\epsilon(1,4)}$ . Further, these merged features $x_{i\epsilon(1,4)}$ are processed via multi-scale attention as: $C_1D_k(x_i) \odot \varsigma(C_1D_k(x_i))$ , where $\varsigma$ is GeLu activation, $\odot$ is dot product, $k = (2 \times i) - 1$ (see Figure 3). This splitting and merging of multi-receptive and multi-scale features through multi-scale attention help the network for robust feature representation learning. Sample visual results for domain translation network are shown in Figure 4. From Figure 4, it is clear that the proposed DT network is able to generate three different degradation $(I_{\mathbb{D}1}, I_{\mathbb{D}2}, I_{\mathbb{D}3})$ irrespective of input degradation. With this intuition, the three outputs of the DT architecture $(I_{\mathbb{D}1}, I_{\mathbb{D}2}, I_{\mathbb{D}3})$ are used along with original weather degraded image $(I)$ as input to the proposed restoration architecture. + +![](images/28fba42e8694fbb49925d716ac6e298be8c132a87b43af5e0d0d3369eb4eec0d.jpg) +Figure 5. Overview of the proposed progressive multi-domain deformable alignment module for effective feature aggregation. + +# 3.2. Multi-weather Image Restoration Architecture + +The proposed restoration framework is shown in Figure 2 which comprises two major modules: 1) Progressive Multi-domain Deformable Alignment, and 2) Cascaded Multi-head Attention module. Details are given below. Progressive Multi-domain Deformable Alignment: As various weather degradations have different representation (refer $DT$ images of Figure 4), the unified architecture urges alignment of domain (weather) translated features for effective multi-weather restoration. To achieve effective feature alignment, we propose a progressive multi-domain deformable alignment module. The proposed PMDA facilitates the network to learn weather-invariant representation effectively. The independently learned features from all the translated domains i.e. $F_{l}^{\mathbb{D}_{1}}, F_{l}^{\mathbb{D}_{2}}, F_{l}^{\mathbb{D}_{3}}$ and input image $F_{l}^{I}$ of $l^{th}$ encoder layer are forwarded to the proposed PMDA module (refer the Figure 5 for more details). Initially, every domain features are split into four groups i.e. $\gamma_{i}^{domain}$ , $i \in (1,4)$ , domain $\in (\mathbb{D}_1, \mathbb{D}_2, \mathbb{D}_3, I)$ . Further, we process two input domains progressively in proposed inter-domain offset feature alignment (see $\square$ in Figure 5). Here, in the inter-domain offset feature alignment, inputs from any two domains are used to generate the offsets for actual deformable convolution layer (see DA in Figure 5). Initially, the $\mathbb{D}_1$ domain features are aligned with input image features. Because, the rainy and snowy degradations are more complex as compared to hazy degradation. All the aligned features of all the respective $i_{th}$ group $\gamma_{i}^{domain}$ are finally merged to generate $\gamma_{i}'$ . All the groups are processed in similar way through inter-domain offset feature alignment (see $\square$ in Figure 5) and concatenation followed by a convolution $\rightarrow$ Relu layer as: + +$$ +\gamma_ {l} = < \gamma_ {1} ^ {\prime}, \gamma_ {2} ^ {\prime}, \gamma_ {3} ^ {\prime}, \gamma_ {4} ^ {\prime} > \tag {2} +$$ + +where, $l$ is $l^{th}$ encoder layer, $< \cdot >$ is concatenation followed by $1 \times 1$ convolution and ReLu operation. In the progressive inter-domain offset feature alignment for every group $\gamma_{i}$ , the offset generation and deformable alignment is + +![](images/0df884662892c09e936a837e57aea9d826dde808a0ed2d95a453e44a3a132606.jpg) +Figure 6. Overview of the proposed cascaded multi-head attention module for feature merging. + +done with the offset convolution and deformable convolution respectively with different kernel size $k = (2 \times i) - 1$ i.e. for $i = 4$ the kernel size is $k = 7$ for both offset convolution $(C_k)$ and deformable convolution $(DC_k)$ (see DA in Figure 5). Overall response of progressive inter-domain feature alignment (see in Figure 5) for $i^{th}$ group as: + +$$ +\gamma_ {i} ^ {\prime} = < \gamma_ {i} ^ {I}, \chi , \varphi \left(\chi , \gamma_ {i} ^ {\mathbb {D} _ {2}}\right), \varphi \left(\varphi \left(\chi , \gamma_ {i} ^ {\mathbb {D} _ {2}}\right), \gamma_ {i} ^ {\mathbb {D} _ {3}}\right) > \tag {3} +$$ + +where, $\chi = \varphi (\gamma_i^I,\gamma_i^{\mathbb{D}_1})$ $\varphi$ is the progressive inter-domain feature alignment. This PMDA module helps for disentanglement of task-relevant data of restoration and taskirrelevant data of various degradation. Therefore, these PMDA features are then forwarded to the respective decoder level via skip connection. Cascaded Multi-head Attention: To effectively merge the decoder features with the respective processed encoder features via PMDA module, we propose a cascaded multi-head attention (CMA). The multi-head attention proposed here consists of deformable convolutions to capture maximum receptive fields. Like transformer layers, the proposed CMA has the structure as attention $\rightarrow$ layer-norm $\rightarrow$ feed forward network. So the proposed CMA is able to capture the long term dependencies along-with the high receptive fields due to deformable attention. We use the term cascaded as we are using two successive multi-head attentions (MHA) see in Figure 6) with two inputs from previous decoder $(D_{e(i - 1)})$ and respective PMDA level feature $(\xi_l)$ .This cascading allows to capture global dependencies effectively. The output of MHA is given as: + +$$ +Z = \sigma (Q \cdot K ^ {T}) \cdot V \tag {4} +$$ + +where, $Q = X$ , $K = DC_{3}(C_{1}(Y))$ , $V = DC_{3}(C_{1}(Y))$ , and $X, Y$ are the inputs to MHA. So the input to first MHA are $D_{e(i-1)}$ and $\xi_{l}$ and second MHA are $Z_{1}$ and $D_{e(i-1)}$ (see Figure 6). To further process these features, we pass the response of first and second MHA through layer-norm (LN) with respect to $\xi_{l}$ and $D_{e(i-1)}$ respectively. So the responses of both the LN are given as: + +$$ +L N _ {1} = L N \left(Z _ {2} + D _ {e (i - 1)}\right); \quad L N _ {2} = L N \left(Z _ {1} + \xi_ {l}\right) \tag {5} +$$ + +Further, the output of first LN is processed through feed forward network (FFN) followed by a LN. Finally, the output of the CMA $(D_{ei})$ is given as: + +$$ +D _ {e i} = \left\langle L N _ {2}, L N \left(F F N \left(L N _ {1}\right) + L N _ {1}\right) \right\rangle \tag {6} +$$ + +where, $< \cdot >$ is concatenation operation. + +# 4. Training Settings + +The proposed restoration network is trained using synthetic data with original and domain translated images as input to get restored image under adversarial settings similar to [9], [23], [22]. To get domain transalted images, domain translation network is trained separately for each required domain like $\mathbb{D}_1$ : hazy, $\mathbb{D}_2$ : rain with veil and $\mathbb{D}_3$ : snow with veil under adversarial settings [9]. The initial learning rate is set to $2 \times 10^{-4}$ which is reduced by factor of 0.1 as the losses plateau. The networks are trained with PyTorch library on NVIDIA DGX Tesla V100 32 GB GPU. While training the networks, the discriminator is same as in [9]. + +# 4.1. Domain Translation Losses + +We train the proposed DT network separately (see $\phi_1, \phi_2, \phi_3$ in Figure 2) for generating each weather degraded image $(I_{\mathbb{D}1}, I_{\mathbb{D}2}, I_{\mathbb{D}3})$ . While training of the network to generate particular weather degraded image (e.g., $I_{\mathbb{D}2}$ ), any of the synthetically degraded images $(I)$ is provided as input. The loss is calculated between the domain translated image (e.g., $I_{\mathbb{D}2}$ ) and the respective target (e.g., $I_{Rv}$ ). We denote by $I_H, I_{Rv}, I_{Sv}$ are the synthetically degraded target images for $I_{\mathbb{D}1}, I_{\mathbb{D}2}, I_{\mathbb{D}3}$ domains respectively. Using these notations, the loss is calculated between the image pairs $(I_{\mathbb{D}1}, I_H), (I_{\mathbb{D}2}, I_{Rv})$ , and $(I_{\mathbb{D}3}, I_{Sv})$ for generation of $I_{\mathbb{D}1}, I_{\mathbb{D}2}$ and $I_{\mathbb{D}3}$ images respectively. The adversarial learning is adopted for DT network training. Along with $\mathbb{L}_1$ loss, adversarial loss $(\mathbb{L}_A)$ for DT network is calculated. To guide the network for textural and structural information, the perceptual loss $(\mathbb{L}_V)$ is calculated between the translated and original target image by passing them through the pre-trained VGG19 model [30]. Further, the contrastive loss $(\mathbb{L}_c)$ [35] in a common latent feature space is used to maximize and minimize the difference between $(I_{\mathbb{D}_{i \in (1,2,3)}, I})$ and $(I_{\mathbb{D}_{i \in (1,2,3)}, I_{\mathbb{T}_{i \in (H,Rv,Sv)}}})$ respectively. Also, the style loss $(\mathbb{L}_{S_d})$ with mean and standard deviation are considered. The total loss $(\mathbb{L}_d)$ is: + +$$ +\mathbb {L} _ {d} \left(\mathbb {D} _ {i}, \mathbb {T} _ {i}\right) = \lambda_ {1} \mathbb {L} _ {1} + \lambda_ {2} \mathbb {L} _ {A} + \lambda_ {3} \mathbb {L} _ {V} + \lambda_ {4} \mathbb {L} _ {c} + \lambda_ {5} \mathbb {L} _ {s} \tag {7} +$$ + +where, the weights $\lambda_{k\epsilon (1,5)}$ for each loss are set empirically. + +# 4.2. Image Restoration Losses + +Along with domain-translated images $(I_{\mathbb{D}_{i\epsilon (1,2,3)})}$ , the original degraded image $(I)$ is used as input to get restored image $(I_g)$ . The proposed restoration network is required to generate the restored image similar to the clean image $(I_c)$ + +in adversarial manner. The $\mathbb{L}_1$ loss is used to optimize the network for better reconstruction. The adversarial loss $(\mathbb{L}_A)$ is the min-max problem between generator and discriminator, respectively. Along with this loss, the perceptual loss $(\mathbb{L}_V)$ [30] between $(I_g,I_c)$ , contrastive loss $(\mathbb{L}_c)$ [35] between $(I,I_g,I_c)$ are considered. So, the total loss $(\mathbb{L}_r)$ is: + +$$ +\mathbb {L} _ {r} \left(I _ {g}, I _ {c}\right) = \lambda_ {1} \mathbb {L} _ {1} + \lambda_ {2} \mathbb {L} _ {A} + \lambda_ {3} \mathbb {L} _ {V} + \lambda_ {4} \mathbb {L} _ {c} \tag {8} +$$ + +where, the weights $\lambda_{k\epsilon (1,4)}$ for each loss are set empirically. (loss functions are explained in supplementary material). + +# 5. Results and Discussion + +# 5.1. Datasets and Evaluation Metrics + +Synthetic Objective Testing Set (SOTS) [13]: 1000 indoor and outdoor images are provided for testing purpose. From training set, 5000 images are considered for training purpose. We have used outdoor images for result analysis. + +Outdoor-Rain Database (ORD) [14]: This database images are degraded by rain and fog. 9000 and 750 images are provided for training and testing purpose respectively. + +Comprehensive Snow Database (CSD) [3] : 8000 and 2000 images are provided for training and testing purpose respectively with combination of snow and fog degradation. + +Real-world Databases: The image restoration algorithm is said to be domain generalised if it restores the synthetic as well as real-world degraded images efficiently. To scrutinize this, we have used three different real-world degraded image datasets named as Real-world Task-driven Testing Set (RTTS) [13], Snow realistic [19] and Rain In Driving (RID) [31] for experimental analysis. + +We have considered all synthetic databases training sets in combination for training of the proposed restoration network. For testing purpose, the respective testing sets and real-world datasets are used. The reference based evaluation metrics includes average Peak Signal-to-Noise Ratio (PSNR), and Structural Similarity Index Measure (SSIM). Average Naturalness Image Quality Evaluator (NIQE) [21], Entropy and Blind/Referenceless Image Spatial Quality Evaluator (BRISQUE) [20] evaluation metrics are used in case of real-world weather degraded image restoration. We have used the released source code and provided trained models by respective authors to get the results on synthetic and real-world datasets. + +# 5.2. Real-world Result Evaluation + +The RTTS [13], Snow realistic [19] and RID [31] datasets are considered for real-world experimental analysis. The NIQE $(\downarrow)$ , entropy $(\uparrow)$ and BRISQUE $(\downarrow)$ parameters are used for real-world quantitative analysis as provided in [29] ( $\downarrow$ : lower is better, $\uparrow$ : higher is better). The qualitative and quantitative analysis on real-world degraded images are provided in Figure 7 and Table 1 respectively. Proposed method de-hazing results follow the depth criteria. Whereas, UMVR, KD and TW methods are unable to + +![](images/c63323b1768d93f3b8c9bf62a5a855aa7fb04816a108eb5ca7b2eca245fe2de2.jpg) +Figure 7. Qualitative analysis of the proposed and existing methods: UMVR [11], KD [4], TW [33] for multi-weather image restoration. + +![](images/30866fa4b126616a01644fa5e6732b86772d25046d51233808f08680e912c5d1.jpg) + +![](images/645bb1b0100e68910c1ecaf9d3d6b3c936d4a52a89c041f4f0c221115246dbbb.jpg) + +![](images/ca84057d6054e39c59899a38d8e4297df4a117ec2f68ef32d9ef5fb569a499a7.jpg) + +![](images/6bd469eff47417b5f99c27b26ea073a183d4f1335683439b11ade0bc5b9afb6e.jpg) + +Table 1. Subjective results on real-world weather degraded images for de-hazing, de-raining with veil and snow with veil removal. + +
DatabaseMethodsNIQE (↓)Entropy (↑)BRISQUE (↓)
RTTSUMVR [11]5.0097.22128.625
KD [4]4.9967.29726.837
TW [33]5.7037.26329.874
Ours4.8597.50524.761
RIDUMVR [11]6.6047.48624.296
KD [4]6.9437.45924.841
TW [33]7.4967.39324.165
Ours7.6257.49223.931
Snow realisticUMVR [11]4.2967.35423.761
KD [4]6.6437.45924.841
TW [33]5.6287.33125.377
Ours4.1967.57221.884
+ +remove haze in depth (see column 1 and 2 from Figure 7). In presence of heavy rain, the baseline methods are not able to remove the rain effect completely due to strong veiling effect. Whereas, the proposed method can remove the rain with veiling effect significantly (see column 3 and 4 from Figure 7). In case of heavy snow, the effect of veiling ef + +Table 2. Quantitative results analysis for de-hazing (SOTS), deraining with veil (ORD) and snow with veil (CSD) removal in terms of average PSNR/SSIM. + +
MethodsSOTSCSDORD
UMVR [11]33.41/0.98028.65/0.90022.99/0.830
KD [4]34.64/0.98531.35/0.95029.05/0.916
TW [33]32.45/0.95529.76/0.94027.96/0.950
Ours36.26/0.98732.95/0.94231.24/0.951
+ +fect is still present in the restored results of existing methods. However, the veiling effect is reduced substantially with the proposed restoration method (see column 5 and 6 from Figure 7). From the visual results, it is observed that the proposed method restores plausible results as compared to existing SOTA methods. + +# 5.3. Synthetic Result Evaluation + +We compared the proposed approach with SOTA unified restoration methods: UMVR [11], KD [4], TW [33] on SOTS-outdoor, CSD and outdoor-rain databases in terms of average PSNR, and SSIM. The quantitative analysis is provided in the Table 2 (see supplementary material for qualitative results). The provided qualitative and quantitative results validate the effectiveness of the proposed method compared to existing unified (UMVR [11], KD [4], TW + +![](images/2680c8d63f0f4803037f36959e0c7823ac4c4e333fd8e0a42499c3f7608ed450.jpg) +Figure 8. Visual analysis of the proposed and existing methods: UMVR [11], KD [4], TW [33] for night-time image restoration. + +![](images/e483082c5930cbb16db0f675b79f987d8259ae98f61ab30154b296486c439a96.jpg) + +![](images/442d595cdf593843857fac1c511cced01e9a39d36b517c487ac38f3cf28a9ac2.jpg) + +![](images/61017a31b333b229e7fddb4e16bd68036323c7c92d927a76820c3dd9be376482.jpg) + +![](images/e30bb6a49a85468083150eadd4532941a620a2f7258d70cba47860d2699bee97.jpg) +Figure 9. Object detection and depth estimation analysis on degraded and restored images by existing UMVR [11], KD [4], TW [33], and proposed multi-weather image restoration method. + +Table 3. Ablation study on the proposed modules with outdoor rain database (IL: Independent Learning, PMDA: Progressive Multidomain Alignment and CMA: Cascaded Multi-head Attention) + +
ModulePSNRSSIM
Baseline26.490.887
Baseline + IL (Net-1)27.890.905
Baseline + IL + PMDA (Net-2)29.530.942
Baseline + IL + PMDA + CMA31.240.951
+ +[33]) methods on synthetic datasets. Specifically, our unified architecture has $\sim 11\mathrm{M}$ parameters (including domain-translation architecture) whereas the existing unified architectures KD [4], and TW [33] have $\sim 28\mathrm{M}$ and $\sim 31\mathrm{M}$ parameters respectively. + +As seen from the Table 1 and 2, our method's performance on synthetic data is usually comparable to SOTA that are trained using the respective synthetic datasets. We note that while our method learns from the synthetic data, it does not over-fit on synthetic data. Therefore, it performs well on both synthetic and real-world datasets. This proves that the domain generalization ability of the proposed method is better compared to SOTA unified restoration methods. + +# 5.4. Night-time Multi-weather Restoration + +Weather-degraded image/video restoration is equally important in night conditions as in day conditions [24]. Therefore, we examined the effectiveness of the proposed and existing networks for night-time multi-weather degradation removal. We labeled this analysis as cross-domain. We directly tested the proposed and existing models on real-world night-time multi-weather images downloaded from Internet. Sample results for night-time de-hazing, de-raining and de-snowing are provided in the Figure 8. From the visual results, it is observed that the proposed method performance is significantly better compared to existing methods for night-time multi-weather restoration. + +# 5.5. Ablation Study + +We analyse the contributions of individual modules (independent feature learning, PMDA, and CMA) of the pro + +![](images/f3bff04379b8342fa5c028bd19bf6cf47a0a55291f01a498c4cc560c8d9ff926.jpg) +Input Image + +![](images/328f6d4dba69e3d30f97e7ff94c4034a8e948ec33f4a168efbab4aba95b46522.jpg) +UMVR + +![](images/a0cab4d48119b451d47c58a9f817f6d7f9d96e927bfea717814414b25df1899a.jpg) +D + +![](images/4afb46e4519249f07cff463c97b89a44c3651c07438bc7e3b814ba01ca2a2eee.jpg) +W + +![](images/88a8578db640409aa017611d5643c7351c11b0013f445f9ec8229f618ae65ffb.jpg) +Ours + +posed architecture in the ablation study conducted on ORD database. We start the ablation with single encoder-decoder architecture and named as "Baseline". + +Independent Feature Learning: In the proposed restoration approach, four inputs $(I_{\mathbb{D}1}, I_{\mathbb{D}2}, I_{\mathbb{D}3}$ and $I)$ are processed parallelly to learn the features independently. Is this independent feature learning effective for multiweather image restoration? To examine this, these inputs are processed through single (baseline) and parallel Net-1 encoders. From the Table 3 results, it is clear that the proposed independent feature learning is effective for extracting the features from all domains. + +Progressive Multi-domain Deformable Alignment: Along with effective feature extraction, the multi-domain feature alignment has significant importance in restoration. To do this task, we have proposed PMDA module and used at each encoder stage. How does this proposed PMDA module helps the network to integrate the multi-domain features effectively? To scrutinize this, the efficiency of proposed restoration network is examined without (Net-1) and with (Net-2) PMDA. The quantitative analysis is provided in Table 3. From these results, it is evident that the proposed PMDA works effectively for multi-domain feature alignment. + +Cascaded Multi-head Attention: Applying attention on the encoder or decoder features affects differently while restoring the clean image. Therefore, we have applied cascaded multi-head attention on respective PMDA and decoder features. We analysed the network accuracy without (Net-2) and with (baseline+IL+PMDA+CMA) CMA module i.e. final proposed network. The results in Table 3 proves the effectiveness of the proposed CMA module for restoration. The more ablation analysis for SOTS and CSD database is provided in the supplementary material. + +# 5.6. Real-world Applications + +Restoration module can be used as a preprocessing step for down-stream applications like object detection, depth estimation, etc. To this end, we have evaluated the benefits of the proposed and existing restoration methods as a preprocessing step for the object detection [26] and depth estimation task [25]. The visual analysis for object detection + +and depth predictions is provided in Figure 9. As seen from the Figure 9, depth predictions or confidence in detecting objects of the restored images with proposed approach are more accurate than existing methods and degraded image. Clearly, the proposed domain-translation based restoration approach performs favourably against the SOTA methods for object detection and depth predictions task. + +# 6. Conclusion + +In this work, we proposed the first weather-invariant representation learning based multi-domain progressive deform-able alignment architecture for multi-weather image restoration. The weather-invariant representation learning helps to learn a representation that is common across diverse weather conditions and also similar across real or synthetic weather degraded images. Further, the proposed progressive multi-domain deform-able alignment module effectively merges the independently learned multi-domain features. This progressive alignment of features helps the network to reduce the degradation in step-by-step manner. Finally, effective restoration is done via CMA to capture long-term dependencies with respective PMDA and decoder features. Results analysis is conducted on real-world and synthetic benchmark hazy, rainy and snowy datasets. Also, the night-time multi-weather restoration results are analysed as cross-domain analysis. Extensive comparisons demonstrate the generalizability of the proposed method over SOTA methods. Further, we have analysed the effectiveness of the proposed and existing methods for object detection and depth estimation tasks for verifying its usefulness in real-world applications. + +# References + +[1] Dongdong Chen, Mingming He, Qingnan Fan, Jing Liao, Liheng Zhang, Dongdong Hou, Lu Yuan, and Gang Hua. Gated context aggregation network for image dehazing and deraining. In 2019 IEEE winter conference on applications of computer vision (WACV), pages 1375-1383. IEEE, 2019. 1, 2 +[2] Wei-Ting Chen, Hao-Yu Fang, Jian-Jiun Ding, Cheng-Che Tsai, and Sy-Yen Kuo. JSTASR: Joint size and transparency-aware snow removal algorithm based on modified partial convolution and veiling effect removal. In European Conference on Computer Vision, pages 754-770. Springer, 2020. 3 +[3] Wei-Ting Chen, Hao-Yu Fang, Cheng-Lin Hsieh, Cheng-Che Tsai, I Chen, Jian-Jiun Ding, Sy-Yen Kuo, et al. 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IEEE Transactions on Neural Networks and Learning Systems, 2022. 2 \ No newline at end of file diff --git a/2023/Multi-weather Image Restoration via Domain Translation/images.zip b/2023/Multi-weather Image Restoration via Domain Translation/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..5aba84f780acd4c0aa7b63c235336dab90a9696d --- /dev/null +++ b/2023/Multi-weather Image Restoration via Domain Translation/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:41b7274fd13667556a78d10f8164ad189357cad1fde9ae7c342515f9764c7f99 +size 826821 diff --git a/2023/Multi-weather Image Restoration via Domain Translation/layout.json b/2023/Multi-weather Image Restoration via Domain Translation/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..f797ac96eace15c34e9c6971d416d2ead5ca6336 --- /dev/null +++ b/2023/Multi-weather Image Restoration via Domain Translation/layout.json @@ -0,0 +1,9277 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 118, + 103, + 476, + 120 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 118, + 103, + 476, + 120 + ], + "spans": [ + { + "bbox": [ + 118, + 103, + 476, + 120 + ], + "type": "text", + "content": "Multi-weather Image Restoration via Domain Translation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 53, + 143, + 542, + 174 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 143, + 542, + 174 + ], + "spans": [ + { + "bbox": [ + 53, + 143, + 542, + 174 + ], + "type": "text", + "content": "Prashant W. Patil1, Sunil Gupta1, Santu Rana1, Svetha Venkatesh1, and Subrahmanyam Murala2 \n1Deakin University, Geelong Warun Ponds Campus, VIC, Australia, 2 Trinity College Dublin, Ireland" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 221, + 174, + 374, + 184 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 221, + 174, + 374, + 184 + ], + "spans": [ + { + "bbox": [ + 221, + 174, + 374, + 184 + ], + "type": "text", + "content": "prashant.patil@deakin.edu.au" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 213, + 192, + 224 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 213, + 192, + 224 + ], + "spans": [ + { + "bbox": [ + 143, + 213, + 192, + 224 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 236, + 290, + 619 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 236, + 290, + 619 + ], + "spans": [ + { + "bbox": [ + 46, + 236, + 290, + 619 + ], + "type": "text", + "content": "Weather degraded conditions such as rain, haze, snow, etc. may degrade the performance of most computer vision systems. Therefore, effective restoration of multiweather degraded images is an essential prerequisite for successful functioning of such systems. The current multiweather image restoration approaches utilize a model that is trained on a combined dataset consisting of individual images for rainy, snowy, and hazy weather degradations. These methods may face challenges when dealing with real-world situations where the images may have multiple, more intricate weather conditions. To address this issue, we propose a domain translation-based unified method for multi-weather image restoration. In this approach, the proposed network learns multiple weather degradations simultaneously, making it immune for real-world conditions. Specifically, we first propose an instance-level domain (weather) translation with multi-attentive feature learning approach to get different weather-degraded variants of the same scenario. Next, the original and translated images are used as input to the proposed novel multi-weather restoration network which utilizes a progressive multi-domain deformable alignment (PMDA) with cascaded multi-head attention (CMA). The proposed PMDA facilitates the restoration network to learn weather-invariant clues effectively. Further, PMDA and respective decoder features are merged via proposed CMA module for restoration. Extensive experimental results on synthetic and real-world hazy, rainy, and snowy image databases clearly demonstrate that our model outperforms the state-of-the-art multi-weather image restoration methods. Code is available at https://github.com/pwp1208/DomainTranslation_Multi-weather_Restoration." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 636, + 128, + 648 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 636, + 128, + 648 + ], + "spans": [ + { + "bbox": [ + 47, + 636, + 128, + 648 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 287, + 715 + ], + "type": "text", + "content": "Fog, snow, rain, haze or their combintations often degrade the quality of images recorded for computer vision applications such as surveillance, traffic monitoring, and autonomous driving. These applications routinely involve sub-tasks such as optical flow estimation [36], object detec" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 309, + 212, + 543, + 407 + ], + "blocks": [ + { + "bbox": [ + 309, + 212, + 543, + 407 + ], + "lines": [ + { + "bbox": [ + 309, + 212, + 543, + 407 + ], + "spans": [ + { + "bbox": [ + 309, + 212, + 543, + 407 + ], + "type": "image", + "image_path": "9f8d80d544a97eeef764719987e64b3c59ace9109548263e65068cc053f4a31a.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 418, + 547, + 463 + ], + "lines": [ + { + "bbox": [ + 305, + 418, + 547, + 463 + ], + "spans": [ + { + "bbox": [ + 305, + 418, + 547, + 463 + ], + "type": "text", + "content": "Figure 1. Upper-part: Thumbnail of the proposed domain translation based multi-weather image restoration approach. Lower-part: Sample restoration results: (a) de-hazing, (b) de-raining with veiling effect, and (c) de-snowing with veiling effect." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 483, + 546, + 531 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 483, + 546, + 531 + ], + "spans": [ + { + "bbox": [ + 304, + 483, + 546, + 531 + ], + "type": "text", + "content": "tion [8], depth estimation [27], etc., which use algorithms or models expecting clean image as their input. Therefore, restoration of images degraded by one or many weather conditions is an important problem." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 534, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 547, + 713 + ], + "type": "text", + "content": "Although remarkable success has been achieved in restoration of particular domain such as image de-hazing, image de-raining, and image de-snowing, multi-weather degraded image restoration is still an open problem. Existing works handle multiple weather degradations via separate weather specific encoders [15], or separate training for each weather [1]. To handle multiple degradations with separate training-based models, typically these weather-specific models are put in a cascade, e.g., haze removal followed by rain removal. But, such an approach may produce undesirable results as the erroneous output of any one of the earlier stages affects the overall result in an unpredictable manner. Also, in order to select the appropriate restoration model, prior information about the degradation must be available. To overcome these limitations, researchers intro" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "type": "text", + "content": "21696" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 203 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 203 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 203 + ], + "type": "text", + "content": "duced various unified (single trainable parameters) models based on knowledge distillation [4], transformer [33], contrastive degradation guidance [12] and degradation removal with feature corrector [11] for multi-weather image restoration. These models are trained using a combined dataset that contains individual degraded images representing rainy, snowy, and hazy weather, etc. As real-world scenario may have more intricate weather conditions, which limits the performance of [4], [33], [11], [12] methods. Therefore, the restoration architecture should be able to perform significantly for any weather degradation." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 204, + 289, + 382 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 204, + 289, + 382 + ], + "spans": [ + { + "bbox": [ + 46, + 204, + 289, + 382 + ], + "type": "text", + "content": "To address the above challenges, we propose multiweather image restoration framework where we first create different weather degradations of a degraded image and use them to learn a set of features that jointly represent all the degraded images. Since the common part across diverse weather degraded images is the clean image (i.e., everything except weather degradations), our feature extractor learns to suppress the weather specific information and thus learns weather-invariant features. A practical advantage of this learning scheme is that our feature extractor can be also used for real data even though it is trained using synthetic data. This is because the synthetic and real-world images mainly differ in the weather-degradations, and since our feature extractor learns to suppress it, it can close the domain gap between synthetic and real-world data." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 384, + 289, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 384, + 289, + 586 + ], + "spans": [ + { + "bbox": [ + 46, + 384, + 289, + 586 + ], + "type": "text", + "content": "Following this idea, we propose a domain translation based unified approach for multi-weather image restoration. In order to achieve this, we first used a domain translation approach, where any of the degraded image can be translated to specific domain (e.g., hazy, rain with veil, snow with veil). We then propose a restoration architecture which takes domain translated and original degraded images as input to generate degradation free output. The proposed restoration network comprises of two components: namely a progressive multi-domain deformable alignment (PMDA) and cascaded multi-head attention (CMA) blocks. PMDA module performs inter domain offset feature alignment which facilitates the restoration network to learn weather-invariant representation effectively. Further, the CMA block is proposed to aggregate the respective PMDA and decoder features for effective restoration. Our main contributions are:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 588, + 286, + 689 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 58, + 588, + 286, + 623 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 588, + 286, + 623 + ], + "spans": [ + { + "bbox": [ + 58, + 588, + 286, + 623 + ], + "type": "text", + "content": "- A novel unified architecture for multi-weather image restoration. It utilizes a single trainable model to restore all weather degradations." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 627, + 286, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 627, + 286, + 651 + ], + "spans": [ + { + "bbox": [ + 58, + 627, + 286, + 651 + ], + "type": "text", + "content": "- A domain-translation with multi-attentive feature learning to achieve unified model's generalizability." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 654, + 286, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 654, + 286, + 689 + ], + "spans": [ + { + "bbox": [ + 58, + 654, + 286, + 689 + ], + "type": "text", + "content": "- A progressive multi-domain deformable alignment and cascaded multi-head attention modules for multiweather image restoration." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 46, + 690, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 690, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 690, + 288, + 713 + ], + "type": "text", + "content": "Extensive experimental analysis on various weather-degraded synthetic and real-world datasets demonstrate that" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "the proposed multi-weather restoration framework outperforms the existing state-of-the-art (SOTA) methods. An overview and sample results of the proposed method for real-world images are given in Figure 1." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 130, + 392, + 143 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 130, + 392, + 143 + ], + "spans": [ + { + "bbox": [ + 305, + 130, + 392, + 143 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 148, + 505, + 160 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 148, + 505, + 160 + ], + "spans": [ + { + "bbox": [ + 305, + 148, + 505, + 160 + ], + "type": "text", + "content": "2.1. Single Weather Degradation Removal" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 164, + 545, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 164, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 304, + 164, + 545, + 403 + ], + "type": "text", + "content": "De-hazing: Earlier research on single image de-hazing was directed towards hand-crafted based approaches [6], [32]. The emergence of deep learning networks brought advancements in degradation removal methods, and the researchers proposed various approaches towards the task of haze, rain or snow removal from images. Zhou et al. [40] proposed feedback spatial attention-based architecture with iterative extraction of the high-level information. With iterative process, the improper feature learning at the initial steps may cause an up-stretched error at the last stage and lead to ineffective results. Recently, Liu et al. [17] proposed three-stage visibility enhancement approach with multi-scale attention with multi-feature fusion module. The hazy-image and depth-map-based feature learning with cross-connection and residual channel attention module is proposed in [7] for the de-hazing task. However, getting an accurate depth map for dense hazy images is a challenging task which may produce unrealistic de-hazing results. Density and depth information is integrated with unpaired learning for image de-hazing [37]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 403, + 545, + 487 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 545, + 487 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 545, + 487 + ], + "type": "text", + "content": "De-raining: Deng et al. [5] considered rain removal and detail recovery as separate tasks and proposed two parallel sub-networks which make use of dilated convolutions and squeeze-and-excitation networks. Zamir et al. [38], proposed a multi-stage approach which progressively restores a degraded image by injecting supervision at each stage, while processing different scales of the input images." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 487, + 545, + 643 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 487, + 545, + 643 + ], + "spans": [ + { + "bbox": [ + 304, + 487, + 545, + 643 + ], + "type": "text", + "content": "De-snowing: Snow removal from single image is even more challenging task due to the non-transparency property of snow, which results in occluded background region and loss of details. In [39], the authors analyzed the difference between snow streaks and clear background edges, and applied a multi-guided filter to remove snowflakes. A three-stage hierarchical approach is proposed in [34], which combine image decomposition and dictionary learning. Even though these algorithms work effectively for specific weather degradation removal, performance may degrade in the presence of real-world weather degradation. Because along with rain or snow streaks, there is a strong veiling effect present, particularly in heavy rain or snow." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 649, + 501, + 661 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 649, + 501, + 661 + ], + "spans": [ + { + "bbox": [ + 305, + 649, + 501, + 661 + ], + "type": "text", + "content": "2.2. Multi-weather Degradation Removal" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "In 2019, the first attempt was made in [1], to handle single image de-hazing and the de-raining problem with specific weather training. A two-stage approach is proposed [14], in which the first stage estimates the rain streaks, trans" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "21697" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 68, + 545, + 249 + ], + "blocks": [ + { + "bbox": [ + 47, + 68, + 545, + 249 + ], + "lines": [ + { + "bbox": [ + 47, + 68, + 545, + 249 + ], + "spans": [ + { + "bbox": [ + 47, + 68, + 545, + 249 + ], + "type": "image", + "image_path": "6e62e5a7287519a99b7aa8f8a83b17ee28d8059f3c4b2c18147612ae0c472e9b.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 264, + 547, + 299 + ], + "lines": [ + { + "bbox": [ + 46, + 264, + 547, + 299 + ], + "spans": [ + { + "bbox": [ + 46, + 264, + 547, + 299 + ], + "type": "text", + "content": "Figure 2. Overview of the proposed multi-weather image restoration algorithm. Initially, the weather degraded image is translated to different domains (" + }, + { + "bbox": [ + 46, + 264, + 547, + 299 + ], + "type": "inline_equation", + "content": "I_{\\mathbb{D}1}" + }, + { + "bbox": [ + 46, + 264, + 547, + 299 + ], + "type": "text", + "content": ": hazy, " + }, + { + "bbox": [ + 46, + 264, + 547, + 299 + ], + "type": "inline_equation", + "content": "I_{\\mathbb{D}2}" + }, + { + "bbox": [ + 46, + 264, + 547, + 299 + ], + "type": "text", + "content": ": rain with veil and " + }, + { + "bbox": [ + 46, + 264, + 547, + 299 + ], + "type": "inline_equation", + "content": "I_{\\mathbb{D}3}" + }, + { + "bbox": [ + 46, + 264, + 547, + 299 + ], + "type": "text", + "content": ": snow with veil). Next, these translated and input images are processed through separate encoders and aligned using proposed progressive multi-domain feature alignment with cascaded multi-head attention module." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 312, + 289, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 312, + 289, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 312, + 289, + 696 + ], + "type": "text", + "content": "mission map, and atmospheric light from the input image. Li et al. [15] proposed a multi-weather image restoration approach where authors leverage neural architecture search for processing the features extracted from the task-specific encoders of rain with veil, rain-drop, and snow. Also, the selection of particular encoder while dealing with real-world weather degraded images is one of the limitation of [15]. Similar to heavy rain, heavy snow will also show a strong veiling effect in the real scene. The first attempt was made by [2] to handle snow and veiling effects simultaneously. They used the modified partial convolution and the differentiable dark channel prior layer. Chen et al. [3] proposed a dual-tree wavelet transform based approach with complex wavelet loss. In [38], authors proposed a multistage architecture that progressively learns restoration functions from degraded images. They handle image de-raining, de-blurring, and de-noising degradations via specific training. Recently, a contrastive-based degraded encoder and degradation-guided restoration network is proposed in [12] to handle image de-nosing, de-raining, and de-hazing tasks. Valanarasu et al. [33] proposed a transformer-based approach for rain with veil, snow and rain-drop removal. They also introduced learnable weather-type embeddings to handle different weather degradation effectively. Chen [4] propsoed two-stage i.e. knowledge collation and knowledge examination with multi-teacher and student architecture for adverse weather removal. Kulkarni et al. [11] proposed dual stream (appearing degradation and veiling effect removal) architecture for multi-weather image restoration. These [4] (28M) [15] (41M), [33] (31M) methods achieved superior performance but at the cost of increased computational complexity." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 306, + 311, + 422, + 322 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 311, + 422, + 322 + ], + "spans": [ + { + "bbox": [ + 306, + 311, + 422, + 322 + ], + "type": "text", + "content": "2.3. Domain Translation" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 327, + 547, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 327, + 547, + 506 + ], + "spans": [ + { + "bbox": [ + 304, + 327, + 547, + 506 + ], + "type": "text", + "content": "Since our proposed restoration model is built upon domain translation, we briefly review it in this section. With a recent deep learning advancement, many algorithms are proposed for domain transfer task like structure-guided arbitrary [18], semantic context-aware [16], etc. In [10], authors proposed a memory-guided unsupervised approach to perform diverse translation between two visual domains e.g., Sunny to night, rainy to sunny. They have used separate content and style encoders to learn content and style features from input and target domains. Inspired by this, we have proposed an architecture for instance-level image-to-image translation between original degraded input to required domains. To the best of author's knowledge, this is the first weather-to-weather translation approach for restoration tasks." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 516, + 432, + 530 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 516, + 432, + 530 + ], + "spans": [ + { + "bbox": [ + 305, + 516, + 432, + 530 + ], + "type": "text", + "content": "3. Proposed Framework" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 534, + 545, + 569 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 545, + 569 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 545, + 569 + ], + "type": "text", + "content": "In this work, a solution to handle multiple weather degradations is proposed with a unified network without any pretrained weights or domain specific knowledge." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": "Overall Pipeline: Overview of the proposed framework is shown in Figure 2. Given a weather degraded image " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "(I)" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": ", we first aim to learn a weather invariant representation of the image making the restoration task for multi-weather scenario easier. To learn a weather-invariant representation for " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": ", we first propose the domain translation (DT) of given image " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": " into its different weather variants. For example, we take any weather degraded image " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": " and translate it into a corresponding hazy, rain with veil and snow with veil images. We refer to each weather condition as a domain, denoting them as hazy " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "(\\mathbb{D}_1)" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": ", rain with veil " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "(\\mathbb{D}_2)" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": ", and snow with veil " + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "inline_equation", + "content": "(\\mathbb{D}_3)" + }, + { + "bbox": [ + 304, + 570, + 547, + 714 + ], + "type": "text", + "content": ", etc. In using domain translation, our main" + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "21698" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 54, + 70, + 286, + 201 + ], + "blocks": [ + { + "bbox": [ + 54, + 70, + 286, + 201 + ], + "lines": [ + { + "bbox": [ + 54, + 70, + 286, + 201 + ], + "spans": [ + { + "bbox": [ + 54, + 70, + 286, + 201 + ], + "type": "image", + "image_path": "5aec34dfe2f791c0a777d2f62d1ccef5910de3ecf483cd8c1d4718d4515004d7.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 205, + 287, + 228 + ], + "lines": [ + { + "bbox": [ + 47, + 205, + 287, + 228 + ], + "spans": [ + { + "bbox": [ + 47, + 205, + 287, + 228 + ], + "type": "text", + "content": "Figure 3. Overview of the proposed domain translation architecture with multi-attentive feature extraction (MFE) module." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 258, + 289, + 426 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 258, + 289, + 426 + ], + "spans": [ + { + "bbox": [ + 46, + 258, + 289, + 426 + ], + "type": "text", + "content": "idea is to create different weather degradations of the same image and use them to train a feature extractor to learn a common set of features that simultaneously represent all the degraded images. Since the common part across diverse weather degraded images is the clean image (everything except weather degradations), our feature extractor learns to suppress the weather specific information and thus learning weather-invariant features. Another practical advantage is that this feature extractor can be used for real data even though it is learnt using synthetic data. This is because only difference between the synthetic generated and real-world images lies in the weather-degradations and since our feature extractor learns to suppress it, the domain gap between synthetic and real-world data is closed." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "text", + "content": "We propose a restoration generator " + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "inline_equation", + "content": "(G_{r})" + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "text", + "content": " where these weather degraded images " + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "inline_equation", + "content": "(I, I_{\\mathbb{D}1}, I_{\\mathbb{D}2}" + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "inline_equation", + "content": "I_{\\mathbb{D}3})" + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "text", + "content": " are fed as input. The proposed " + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "inline_equation", + "content": "G_{r}" + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "text", + "content": " encodes each of the inputs via multi-receptive and multi-scale convolution block based encoders (see in Figure 2) in order to learn to domain-relevant features (see " + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "inline_equation", + "content": "F_{l}^{\\mathbb{D}_{1}}, F_{l}^{\\mathbb{D}_{2}}, F_{l}^{\\mathbb{D}_{3}}, F_{l \\in (1,3)}^{I}" + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "text", + "content": " in Figure 2). Except first encoder, every encoder down-samples the input features. At last encoder layer, these separately learned features are aggregated and forwarded to the decoder via successive deformable convolutions " + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "inline_equation", + "content": "(DC_{3})" + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "text", + "content": " for final reconstruction. These extracted features are then processed through successive decoder layers to have final restored image. While reconstruction, the independently learned encoder features processed via proposed progressive multi-domain feature alignment (PMDA) are forwarded to the respective decoder through skip connection. Further, the PMDA features and respective decoder features are merged effectively through proposed cascaded multi-head attention (CMA) to provide the restored image " + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "inline_equation", + "content": "(I_{g})" + }, + { + "bbox": [ + 47, + 439, + 289, + 715 + ], + "type": "text", + "content": ". Summarizing the overall pipeline of the proposed framework as: 1) domain translation (refer Section 3.1), and 2) Multi-weather image restoration (refer Section 3.2). Detailed exposition of each step of the proposed pipeline is provided in following subsections." + } + ] + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 307, + 71, + 547, + 125 + ], + "blocks": [ + { + "bbox": [ + 307, + 71, + 547, + 125 + ], + "lines": [ + { + "bbox": [ + 307, + 71, + 547, + 125 + ], + "spans": [ + { + "bbox": [ + 307, + 71, + 547, + 125 + ], + "type": "image", + "image_path": "76fab252493bd39d5fc5761421ab3413d2753229601f943363b6200d866e57f6.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 329, + 130, + 523, + 142 + ], + "lines": [ + { + "bbox": [ + 329, + 130, + 523, + 142 + ], + "spans": [ + { + "bbox": [ + 329, + 130, + 523, + 142 + ], + "type": "text", + "content": "Figure 4. Visual results of the proposed DT network." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 159, + 484, + 171 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 159, + 484, + 171 + ], + "spans": [ + { + "bbox": [ + 306, + 159, + 484, + 171 + ], + "type": "text", + "content": "3.1. Domain-translation Architecture" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "spans": [ + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "text", + "content": "The proposed DT approach takes weather degraded image " + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "inline_equation", + "content": "(I)" + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "text", + "content": " as input and translates it to other weather domains " + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "inline_equation", + "content": "I_{\\mathbb{D}_i\\in (1,2,3)}" + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "text", + "content": ". We have used U-Net [28] architecture as generator to perform translation of any weather degraded image over the required domain. This architecture mainly comprises of four encoders and four decoders (see DT in Figure 2). The encoder block is defined as: " + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "inline_equation", + "content": "\\{En_{l\\perp \\times f};[l\\in (1,4),f = 16]\\}" + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "text", + "content": ". Similar to this, the decoder block is defined as: " + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "inline_equation", + "content": "\\{De_{l\\perp \\times f};[l\\in (4,1),f = 16]\\}" + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "text", + "content": ", where, " + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "inline_equation", + "content": "(l\\times f)" + }, + { + "bbox": [ + 304, + 177, + 545, + 308 + ], + "type": "text", + "content": " represent encoder or decoder level and number of filters in encoder or decoder respectively." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 308, + 546, + 393 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 308, + 546, + 393 + ], + "spans": [ + { + "bbox": [ + 304, + 308, + 546, + 393 + ], + "type": "text", + "content": "Multi-attentive Feature Extraction: The input image " + }, + { + "bbox": [ + 304, + 308, + 546, + 393 + ], + "type": "inline_equation", + "content": "(I)" + }, + { + "bbox": [ + 304, + 308, + 546, + 393 + ], + "type": "text", + "content": " is given to the encoder which will give features " + }, + { + "bbox": [ + 304, + 308, + 546, + 393 + ], + "type": "inline_equation", + "content": "\\left(\\psi_{l\\epsilon (1,4)}\\right)" + }, + { + "bbox": [ + 304, + 308, + 546, + 393 + ], + "type": "text", + "content": ". While giving a skip connection from the respective encoder to the decoder, we have processed these features via the proposed multi-attentive feature extraction (MFE) module (see MFE block in DT of 2 for more details). In MFE, the respective " + }, + { + "bbox": [ + 304, + 308, + 546, + 393 + ], + "type": "inline_equation", + "content": "l^{th}" + }, + { + "bbox": [ + 304, + 308, + 546, + 393 + ], + "type": "text", + "content": " encoder-level features " + }, + { + "bbox": [ + 304, + 308, + 546, + 393 + ], + "type": "inline_equation", + "content": "(\\psi_l)" + }, + { + "bbox": [ + 304, + 308, + 546, + 393 + ], + "type": "text", + "content": " are processed as:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 311, + 403, + 545, + 424 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 403, + 545, + 424 + ], + "spans": [ + { + "bbox": [ + 311, + 403, + 545, + 424 + ], + "type": "interline_equation", + "content": "x _ {G} ^ {M R} = \\left\\langle C _ {d \\epsilon (1, 2, 3)} ^ {3} (\\psi_ {l}) \\right\\rangle ; x _ {G} ^ {M S} = \\left\\langle C _ {1} ^ {k \\epsilon (1, 3, 5)} (\\psi_ {l}) \\right\\rangle \\tag {1}", + "image_path": "223a8b75e7901d3b07d3b61311e8725096a7d227d62599734902fd34a3b0265d.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": "where, " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "x_{G}^{MR}" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "x_{G}^{MS}" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " are multi-receptive and multi-scale features, " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "C_d^k" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " is convolution with " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "k \\times k" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " kernel and " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " dilation rate, " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\langle \\cdot \\rangle" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " is concatenation followed by convolution with " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " kernel (refer Figure 3 for more details). Required contextual and spatial information is extracted using dilated and multi-scale convolutions through large receptive fields. Here, we form four different groups by splitting the features into groups of " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "x_{G_{i\\epsilon(1,4)}}^{MR}" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "x_{G_{i\\epsilon(1,4)}}^{MS}" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " containing equal number of channels in each group and merge respective " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "x_{G_i}^{MR}" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "x_{G_i}^{MS}" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " to form " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "x_{i\\epsilon(1,4)}" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": ". Further, these merged features " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "x_{i\\epsilon(1,4)}" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " are processed via multi-scale attention as: " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "C_1D_k(x_i) \\odot \\varsigma(C_1D_k(x_i))" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\varsigma" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " is GeLu activation, " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " is dot product, " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "k = (2 \\times i) - 1" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " (see Figure 3). This splitting and merging of multi-receptive and multi-scale features through multi-scale attention help the network for robust feature representation learning. Sample visual results for domain translation network are shown in Figure 4. From Figure 4, it is clear that the proposed DT network is able to generate three different degradation " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "(I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3})" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " irrespective of input degradation. With this intuition, the three outputs of the DT architecture " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "(I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3})" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " are used along with original weather degraded image " + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "inline_equation", + "content": "(I)" + }, + { + "bbox": [ + 304, + 436, + 547, + 714 + ], + "type": "text", + "content": " as input to the proposed restoration architecture." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "21699" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 50, + 70, + 289, + 203 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 289, + 203 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 289, + 203 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 289, + 203 + ], + "type": "image", + "image_path": "28fba42e8694fbb49925d716ac6e298be8c132a87b43af5e0d0d3369eb4eec0d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 219, + 287, + 242 + ], + "lines": [ + { + "bbox": [ + 46, + 219, + 287, + 242 + ], + "spans": [ + { + "bbox": [ + 46, + 219, + 287, + 242 + ], + "type": "text", + "content": "Figure 5. Overview of the proposed progressive multi-domain deformable alignment module for effective feature aggregation." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 255, + 287, + 268 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 255, + 287, + 268 + ], + "spans": [ + { + "bbox": [ + 47, + 255, + 287, + 268 + ], + "type": "text", + "content": "3.2. Multi-weather Image Restoration Architecture" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "spans": [ + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": "The proposed restoration framework is shown in Figure 2 which comprises two major modules: 1) Progressive Multi-domain Deformable Alignment, and 2) Cascaded Multi-head Attention module. Details are given below. Progressive Multi-domain Deformable Alignment: As various weather degradations have different representation (refer " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "DT" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": " images of Figure 4), the unified architecture urges alignment of domain (weather) translated features for effective multi-weather restoration. To achieve effective feature alignment, we propose a progressive multi-domain deformable alignment module. The proposed PMDA facilitates the network to learn weather-invariant representation effectively. The independently learned features from all the translated domains i.e. " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "F_{l}^{\\mathbb{D}_{1}}, F_{l}^{\\mathbb{D}_{2}}, F_{l}^{\\mathbb{D}_{3}}" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": " and input image " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "F_{l}^{I}" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "l^{th}" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": " encoder layer are forwarded to the proposed PMDA module (refer the Figure 5 for more details). Initially, every domain features are split into four groups i.e. " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "\\gamma_{i}^{domain}" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "i \\in (1,4)" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": ", domain " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "\\in (\\mathbb{D}_1, \\mathbb{D}_2, \\mathbb{D}_3, I)" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": ". Further, we process two input domains progressively in proposed inter-domain offset feature alignment (see " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "\\square" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": " in Figure 5). Here, in the inter-domain offset feature alignment, inputs from any two domains are used to generate the offsets for actual deformable convolution layer (see DA in Figure 5). Initially, the " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "\\mathbb{D}_1" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": " domain features are aligned with input image features. Because, the rainy and snowy degradations are more complex as compared to hazy degradation. All the aligned features of all the respective " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "i_{th}" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": " group " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "\\gamma_{i}^{domain}" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": " are finally merged to generate " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "\\gamma_{i}'" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": ". All the groups are processed in similar way through inter-domain offset feature alignment (see " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "\\square" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": " in Figure 5) and concatenation followed by a convolution " + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 45, + 270, + 289, + 643 + ], + "type": "text", + "content": " Relu layer as:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 115, + 646, + 287, + 659 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 115, + 646, + 287, + 659 + ], + "spans": [ + { + "bbox": [ + 115, + 646, + 287, + 659 + ], + "type": "interline_equation", + "content": "\\gamma_ {l} = < \\gamma_ {1} ^ {\\prime}, \\gamma_ {2} ^ {\\prime}, \\gamma_ {3} ^ {\\prime}, \\gamma_ {4} ^ {\\prime} > \\tag {2}", + "image_path": "e3f3990af5b19c96b8cfbb262d2a0f4ac3ddd45be4539ba4a533d2e28ee3dee4.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": "where, " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "l" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " is " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "l^{th}" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " encoder layer, " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "< \\cdot >" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " is concatenation followed by " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": " convolution and ReLu operation. In the progressive inter-domain offset feature alignment for every group " + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\gamma_{i}" + }, + { + "bbox": [ + 46, + 665, + 288, + 715 + ], + "type": "text", + "content": ", the offset generation and deformable alignment is" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 307, + 70, + 543, + 218 + ], + "blocks": [ + { + "bbox": [ + 307, + 70, + 543, + 218 + ], + "lines": [ + { + "bbox": [ + 307, + 70, + 543, + 218 + ], + "spans": [ + { + "bbox": [ + 307, + 70, + 543, + 218 + ], + "type": "image", + "image_path": "0df884662892c09e936a837e57aea9d826dde808a0ed2d95a453e44a3a132606.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 222, + 545, + 244 + ], + "lines": [ + { + "bbox": [ + 306, + 222, + 545, + 244 + ], + "spans": [ + { + "bbox": [ + 306, + 222, + 545, + 244 + ], + "type": "text", + "content": "Figure 6. Overview of the proposed cascaded multi-head attention module for feature merging." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "spans": [ + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "text", + "content": "done with the offset convolution and deformable convolution respectively with different kernel size " + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "inline_equation", + "content": "k = (2 \\times i) - 1" + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "text", + "content": " i.e. for " + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "inline_equation", + "content": "i = 4" + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "text", + "content": " the kernel size is " + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "inline_equation", + "content": "k = 7" + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "text", + "content": " for both offset convolution " + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "inline_equation", + "content": "(C_k)" + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "text", + "content": " and deformable convolution " + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "inline_equation", + "content": "(DC_k)" + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "text", + "content": " (see DA in Figure 5). Overall response of progressive inter-domain feature alignment (see in Figure 5) for " + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "inline_equation", + "content": "i^{th}" + }, + { + "bbox": [ + 305, + 261, + 545, + 333 + ], + "type": "text", + "content": " group as:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 318, + 335, + 545, + 350 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 318, + 335, + 545, + 350 + ], + "spans": [ + { + "bbox": [ + 318, + 335, + 545, + 350 + ], + "type": "interline_equation", + "content": "\\gamma_ {i} ^ {\\prime} = < \\gamma_ {i} ^ {I}, \\chi , \\varphi \\left(\\chi , \\gamma_ {i} ^ {\\mathbb {D} _ {2}}\\right), \\varphi \\left(\\varphi \\left(\\chi , \\gamma_ {i} ^ {\\mathbb {D} _ {2}}\\right), \\gamma_ {i} ^ {\\mathbb {D} _ {3}}\\right) > \\tag {3}", + "image_path": "04c6c431cca4589fd3e4d6647844bc31b4ba0655c1d2701834923310a6e2f80e.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "spans": [ + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "text", + "content": "where, " + }, + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "inline_equation", + "content": "\\chi = \\varphi (\\gamma_i^I,\\gamma_i^{\\mathbb{D}_1})" + }, + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "inline_equation", + "content": "\\varphi" + }, + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "text", + "content": " is the progressive inter-domain feature alignment. This PMDA module helps for disentanglement of task-relevant data of restoration and taskirrelevant data of various degradation. Therefore, these PMDA features are then forwarded to the respective decoder level via skip connection. Cascaded Multi-head Attention: To effectively merge the decoder features with the respective processed encoder features via PMDA module, we propose a cascaded multi-head attention (CMA). The multi-head attention proposed here consists of deformable convolutions to capture maximum receptive fields. Like transformer layers, the proposed CMA has the structure as attention " + }, + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "text", + "content": " layer-norm " + }, + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "text", + "content": " feed forward network. So the proposed CMA is able to capture the long term dependencies along-with the high receptive fields due to deformable attention. We use the term cascaded as we are using two successive multi-head attentions (MHA) see in Figure 6) with two inputs from previous decoder " + }, + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "inline_equation", + "content": "(D_{e(i - 1)})" + }, + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "text", + "content": " and respective PMDA level feature " + }, + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "inline_equation", + "content": "(\\xi_l)" + }, + { + "bbox": [ + 305, + 356, + 546, + 608 + ], + "type": "text", + "content": " .This cascading allows to capture global dependencies effectively. The output of MHA is given as:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 383, + 610, + 545, + 624 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 383, + 610, + 545, + 624 + ], + "spans": [ + { + "bbox": [ + 383, + 610, + 545, + 624 + ], + "type": "interline_equation", + "content": "Z = \\sigma (Q \\cdot K ^ {T}) \\cdot V \\tag {4}", + "image_path": "1a71b70cb9acf17d8ce490e58a19537e95a4afa2cde5b22743900ae9b25f2761.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "text", + "content": "where, " + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "Q = X" + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "K = DC_{3}(C_{1}(Y))" + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "V = DC_{3}(C_{1}(Y))" + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "X, Y" + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "text", + "content": " are the inputs to MHA. So the input to first MHA are " + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "D_{e(i-1)}" + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\xi_{l}" + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "text", + "content": " and second MHA are " + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "Z_{1}" + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "D_{e(i-1)}" + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "text", + "content": " (see Figure 6). To further process these features, we pass the response of first and second MHA through layer-norm (LN) with respect to " + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\xi_{l}" + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "inline_equation", + "content": "D_{e(i-1)}" + }, + { + "bbox": [ + 305, + 629, + 545, + 714 + ], + "type": "text", + "content": " respectively. So the responses of both the LN are given as:" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "21700" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 53, + 72, + 286, + 85 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 72, + 286, + 85 + ], + "spans": [ + { + "bbox": [ + 53, + 72, + 286, + 85 + ], + "type": "interline_equation", + "content": "L N _ {1} = L N \\left(Z _ {2} + D _ {e (i - 1)}\\right); \\quad L N _ {2} = L N \\left(Z _ {1} + \\xi_ {l}\\right) \\tag {5}", + "image_path": "68542f57766062e17d91530f53696fc02a31b62e048e3e45d1ddd0bc6afff936.jpg" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 90, + 286, + 126 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 90, + 286, + 126 + ], + "spans": [ + { + "bbox": [ + 47, + 90, + 286, + 126 + ], + "type": "text", + "content": "Further, the output of first LN is processed through feed forward network (FFN) followed by a LN. Finally, the output of the CMA " + }, + { + "bbox": [ + 47, + 90, + 286, + 126 + ], + "type": "inline_equation", + "content": "(D_{ei})" + }, + { + "bbox": [ + 47, + 90, + 286, + 126 + ], + "type": "text", + "content": " is given as:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 82, + 129, + 286, + 142 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 82, + 129, + 286, + 142 + ], + "spans": [ + { + "bbox": [ + 82, + 129, + 286, + 142 + ], + "type": "interline_equation", + "content": "D _ {e i} = \\left\\langle L N _ {2}, L N \\left(F F N \\left(L N _ {1}\\right) + L N _ {1}\\right) \\right\\rangle \\tag {6}", + "image_path": "c52b094a36d37424b2066f862a35c9cf3edba4eec6ca673e74eef6be905e5d6c.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 148, + 212, + 159 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 148, + 212, + 159 + ], + "spans": [ + { + "bbox": [ + 47, + 148, + 212, + 159 + ], + "type": "text", + "content": "where, " + }, + { + "bbox": [ + 47, + 148, + 212, + 159 + ], + "type": "inline_equation", + "content": "< \\cdot >" + }, + { + "bbox": [ + 47, + 148, + 212, + 159 + ], + "type": "text", + "content": " is concatenation operation." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 166, + 151, + 180 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 166, + 151, + 180 + ], + "spans": [ + { + "bbox": [ + 47, + 166, + 151, + 180 + ], + "type": "text", + "content": "4. Training Settings" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 183, + 286, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 183, + 286, + 316 + ], + "spans": [ + { + "bbox": [ + 46, + 183, + 286, + 316 + ], + "type": "text", + "content": "The proposed restoration network is trained using synthetic data with original and domain translated images as input to get restored image under adversarial settings similar to [9], [23], [22]. To get domain transalted images, domain translation network is trained separately for each required domain like " + }, + { + "bbox": [ + 46, + 183, + 286, + 316 + ], + "type": "inline_equation", + "content": "\\mathbb{D}_1" + }, + { + "bbox": [ + 46, + 183, + 286, + 316 + ], + "type": "text", + "content": ": hazy, " + }, + { + "bbox": [ + 46, + 183, + 286, + 316 + ], + "type": "inline_equation", + "content": "\\mathbb{D}_2" + }, + { + "bbox": [ + 46, + 183, + 286, + 316 + ], + "type": "text", + "content": ": rain with veil and " + }, + { + "bbox": [ + 46, + 183, + 286, + 316 + ], + "type": "inline_equation", + "content": "\\mathbb{D}_3" + }, + { + "bbox": [ + 46, + 183, + 286, + 316 + ], + "type": "text", + "content": ": snow with veil under adversarial settings [9]. The initial learning rate is set to " + }, + { + "bbox": [ + 46, + 183, + 286, + 316 + ], + "type": "inline_equation", + "content": "2 \\times 10^{-4}" + }, + { + "bbox": [ + 46, + 183, + 286, + 316 + ], + "type": "text", + "content": " which is reduced by factor of 0.1 as the losses plateau. The networks are trained with PyTorch library on NVIDIA DGX Tesla V100 32 GB GPU. While training the networks, the discriminator is same as in [9]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 319, + 197, + 331 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 319, + 197, + 331 + ], + "spans": [ + { + "bbox": [ + 47, + 319, + 197, + 331 + ], + "type": "text", + "content": "4.1. Domain Translation Losses" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "spans": [ + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": "We train the proposed DT network separately (see " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "\\phi_1, \\phi_2, \\phi_3" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " in Figure 2) for generating each weather degraded image " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "(I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3})" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": ". While training of the network to generate particular weather degraded image (e.g., " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "I_{\\mathbb{D}2}" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": "), any of the synthetically degraded images " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "(I)" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " is provided as input. The loss is calculated between the domain translated image (e.g., " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "I_{\\mathbb{D}2}" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": ") and the respective target (e.g., " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "I_{Rv}" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": "). We denote by " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "I_H, I_{Rv}, I_{Sv}" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " are the synthetically degraded target images for " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3}" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " domains respectively. Using these notations, the loss is calculated between the image pairs " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "(I_{\\mathbb{D}1}, I_H), (I_{\\mathbb{D}2}, I_{Rv})" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "(I_{\\mathbb{D}3}, I_{Sv})" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " for generation of " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "I_{\\mathbb{D}1}, I_{\\mathbb{D}2}" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "I_{\\mathbb{D}3}" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " images respectively. The adversarial learning is adopted for DT network training. Along with " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "\\mathbb{L}_1" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " loss, adversarial loss " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "(\\mathbb{L}_A)" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " for DT network is calculated. To guide the network for textural and structural information, the perceptual loss " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "(\\mathbb{L}_V)" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " is calculated between the translated and original target image by passing them through the pre-trained VGG19 model [30]. Further, the contrastive loss " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "(\\mathbb{L}_c)" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " [35] in a common latent feature space is used to maximize and minimize the difference between " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "(I_{\\mathbb{D}_{i \\in (1,2,3)}, I})" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "(I_{\\mathbb{D}_{i \\in (1,2,3)}, I_{\\mathbb{T}_{i \\in (H,Rv,Sv)}}})" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " respectively. Also, the style loss " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "(\\mathbb{L}_{S_d})" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " with mean and standard deviation are considered. The total loss " + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "inline_equation", + "content": "(\\mathbb{L}_d)" + }, + { + "bbox": [ + 46, + 335, + 286, + 609 + ], + "type": "text", + "content": " is:" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 52, + 613, + 286, + 625 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 613, + 286, + 625 + ], + "spans": [ + { + "bbox": [ + 52, + 613, + 286, + 625 + ], + "type": "interline_equation", + "content": "\\mathbb {L} _ {d} \\left(\\mathbb {D} _ {i}, \\mathbb {T} _ {i}\\right) = \\lambda_ {1} \\mathbb {L} _ {1} + \\lambda_ {2} \\mathbb {L} _ {A} + \\lambda_ {3} \\mathbb {L} _ {V} + \\lambda_ {4} \\mathbb {L} _ {c} + \\lambda_ {5} \\mathbb {L} _ {s} \\tag {7}", + "image_path": "d997fc8c510c6bb86e189858bac69d2ca748d90da84eaed8c1f142238fc52b40.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 631, + 286, + 644 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 631, + 286, + 644 + ], + "spans": [ + { + "bbox": [ + 47, + 631, + 286, + 644 + ], + "type": "text", + "content": "where, the weights " + }, + { + "bbox": [ + 47, + 631, + 286, + 644 + ], + "type": "inline_equation", + "content": "\\lambda_{k\\epsilon (1,5)}" + }, + { + "bbox": [ + 47, + 631, + 286, + 644 + ], + "type": "text", + "content": " for each loss are set empirically." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 650, + 190, + 662 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 650, + 190, + 662 + ], + "spans": [ + { + "bbox": [ + 47, + 650, + 190, + 662 + ], + "type": "text", + "content": "4.2. Image Restoration Losses" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 666, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 666, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 666, + 286, + 714 + ], + "type": "text", + "content": "Along with domain-translated images " + }, + { + "bbox": [ + 47, + 666, + 286, + 714 + ], + "type": "inline_equation", + "content": "(I_{\\mathbb{D}_{i\\epsilon (1,2,3)})}" + }, + { + "bbox": [ + 47, + 666, + 286, + 714 + ], + "type": "text", + "content": ", the original degraded image " + }, + { + "bbox": [ + 47, + 666, + 286, + 714 + ], + "type": "inline_equation", + "content": "(I)" + }, + { + "bbox": [ + 47, + 666, + 286, + 714 + ], + "type": "text", + "content": " is used as input to get restored image " + }, + { + "bbox": [ + 47, + 666, + 286, + 714 + ], + "type": "inline_equation", + "content": "(I_g)" + }, + { + "bbox": [ + 47, + 666, + 286, + 714 + ], + "type": "text", + "content": ". The proposed restoration network is required to generate the restored image similar to the clean image " + }, + { + "bbox": [ + 47, + 666, + 286, + 714 + ], + "type": "inline_equation", + "content": "(I_c)" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": "in adversarial manner. The " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "\\mathbb{L}_1" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " loss is used to optimize the network for better reconstruction. The adversarial loss " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "(\\mathbb{L}_A)" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " is the min-max problem between generator and discriminator, respectively. Along with this loss, the perceptual loss " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "(\\mathbb{L}_V)" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " [30] between " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "(I_g,I_c)" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": ", contrastive loss " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "(\\mathbb{L}_c)" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " [35] between " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "(I,I_g,I_c)" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " are considered. So, the total loss " + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "inline_equation", + "content": "(\\mathbb{L}_r)" + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": " is:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 333, + 150, + 545, + 163 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 333, + 150, + 545, + 163 + ], + "spans": [ + { + "bbox": [ + 333, + 150, + 545, + 163 + ], + "type": "interline_equation", + "content": "\\mathbb {L} _ {r} \\left(I _ {g}, I _ {c}\\right) = \\lambda_ {1} \\mathbb {L} _ {1} + \\lambda_ {2} \\mathbb {L} _ {A} + \\lambda_ {3} \\mathbb {L} _ {V} + \\lambda_ {4} \\mathbb {L} _ {c} \\tag {8}", + "image_path": "7e8d0cc16a815df78d59c7907aed366eb8affbcc03abe84a3794605bda16c5bd.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 164, + 545, + 188 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 164, + 545, + 188 + ], + "spans": [ + { + "bbox": [ + 304, + 164, + 545, + 188 + ], + "type": "text", + "content": "where, the weights " + }, + { + "bbox": [ + 304, + 164, + 545, + 188 + ], + "type": "inline_equation", + "content": "\\lambda_{k\\epsilon (1,4)}" + }, + { + "bbox": [ + 304, + 164, + 545, + 188 + ], + "type": "text", + "content": " for each loss are set empirically. (loss functions are explained in supplementary material)." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 195, + 437, + 207 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 195, + 437, + 207 + ], + "spans": [ + { + "bbox": [ + 305, + 195, + 437, + 207 + ], + "type": "text", + "content": "5. Results and Discussion" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 212, + 481, + 223 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 212, + 481, + 223 + ], + "spans": [ + { + "bbox": [ + 305, + 212, + 481, + 223 + ], + "type": "text", + "content": "5.1. Datasets and Evaluation Metrics" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 227, + 545, + 276 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 227, + 545, + 276 + ], + "spans": [ + { + "bbox": [ + 304, + 227, + 545, + 276 + ], + "type": "text", + "content": "Synthetic Objective Testing Set (SOTS) [13]: 1000 indoor and outdoor images are provided for testing purpose. From training set, 5000 images are considered for training purpose. We have used outdoor images for result analysis." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 276, + 545, + 311 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 276, + 545, + 311 + ], + "spans": [ + { + "bbox": [ + 304, + 276, + 545, + 311 + ], + "type": "text", + "content": "Outdoor-Rain Database (ORD) [14]: This database images are degraded by rain and fog. 9000 and 750 images are provided for training and testing purpose respectively." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 312, + 545, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 545, + 346 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 545, + 346 + ], + "type": "text", + "content": "Comprehensive Snow Database (CSD) [3] : 8000 and 2000 images are provided for training and testing purpose respectively with combination of snow and fog degradation." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 347, + 545, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 347, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 304, + 347, + 545, + 430 + ], + "type": "text", + "content": "Real-world Databases: The image restoration algorithm is said to be domain generalised if it restores the synthetic as well as real-world degraded images efficiently. To scrutinize this, we have used three different real-world degraded image datasets named as Real-world Task-driven Testing Set (RTTS) [13], Snow realistic [19] and Rain In Driving (RID) [31] for experimental analysis." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 431, + 545, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 431, + 545, + 586 + ], + "spans": [ + { + "bbox": [ + 304, + 431, + 545, + 586 + ], + "type": "text", + "content": "We have considered all synthetic databases training sets in combination for training of the proposed restoration network. For testing purpose, the respective testing sets and real-world datasets are used. The reference based evaluation metrics includes average Peak Signal-to-Noise Ratio (PSNR), and Structural Similarity Index Measure (SSIM). Average Naturalness Image Quality Evaluator (NIQE) [21], Entropy and Blind/Referenceless Image Spatial Quality Evaluator (BRISQUE) [20] evaluation metrics are used in case of real-world weather degraded image restoration. We have used the released source code and provided trained models by respective authors to get the results on synthetic and real-world datasets." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 305, + 590, + 467, + 601 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 590, + 467, + 601 + ], + "spans": [ + { + "bbox": [ + 305, + 590, + 467, + 601 + ], + "type": "text", + "content": "5.2. Real-world Result Evaluation" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "The RTTS [13], Snow realistic [19] and RID [31] datasets are considered for real-world experimental analysis. The NIQE " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "(\\downarrow)" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ", entropy " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "(\\uparrow)" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " and BRISQUE " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "(\\downarrow)" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": " parameters are used for real-world quantitative analysis as provided in [29] ( " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\downarrow" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ": lower is better, " + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\uparrow" + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": ": higher is better). The qualitative and quantitative analysis on real-world degraded images are provided in Figure 7 and Table 1 respectively. Proposed method de-hazing results follow the depth criteria. Whereas, UMVR, KD and TW methods are unable to" + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "21701" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 52, + 74, + 223, + 370 + ], + "blocks": [ + { + "bbox": [ + 52, + 74, + 223, + 370 + ], + "lines": [ + { + "bbox": [ + 52, + 74, + 223, + 370 + ], + "spans": [ + { + "bbox": [ + 52, + 74, + 223, + 370 + ], + "type": "image", + "image_path": "c63323b1768d93f3b8c9bf62a5a855aa7fb04816a108eb5ca7b2eca245fe2de2.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 380, + 539, + 392 + ], + "lines": [ + { + "bbox": [ + 47, + 380, + 539, + 392 + ], + "spans": [ + { + "bbox": [ + 47, + 380, + 539, + 392 + ], + "type": "text", + "content": "Figure 7. Qualitative analysis of the proposed and existing methods: UMVR [11], KD [4], TW [33] for multi-weather image restoration." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 227, + 74, + 304, + 370 + ], + "blocks": [ + { + "bbox": [ + 227, + 74, + 304, + 370 + ], + "lines": [ + { + "bbox": [ + 227, + 74, + 304, + 370 + ], + "spans": [ + { + "bbox": [ + 227, + 74, + 304, + 370 + ], + "type": "image", + "image_path": "30866fa4b126616a01644fa5e6732b86772d25046d51233808f08680e912c5d1.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 307, + 74, + 384, + 370 + ], + "blocks": [ + { + "bbox": [ + 307, + 74, + 384, + 370 + ], + "lines": [ + { + "bbox": [ + 307, + 74, + 384, + 370 + ], + "spans": [ + { + "bbox": [ + 307, + 74, + 384, + 370 + ], + "type": "image", + "image_path": "645bb1b0100e68910c1ecaf9d3d6b3c936d4a52a89c041f4f0c221115246dbbb.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 389, + 74, + 465, + 370 + ], + "blocks": [ + { + "bbox": [ + 389, + 74, + 465, + 370 + ], + "lines": [ + { + "bbox": [ + 389, + 74, + 465, + 370 + ], + "spans": [ + { + "bbox": [ + 389, + 74, + 465, + 370 + ], + "type": "image", + "image_path": "ca84057d6054e39c59899a38d8e4297df4a117ec2f68ef32d9ef5fb569a499a7.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 468, + 74, + 545, + 370 + ], + "blocks": [ + { + "bbox": [ + 468, + 74, + 545, + 370 + ], + "lines": [ + { + "bbox": [ + 468, + 74, + 545, + 370 + ], + "spans": [ + { + "bbox": [ + 468, + 74, + 545, + 370 + ], + "type": "image", + "image_path": "6bd469eff47417b5f99c27b26ea073a183d4f1335683439b11ade0bc5b9afb6e.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 48, + 426, + 298, + 617 + ], + "blocks": [ + { + "bbox": [ + 47, + 403, + 288, + 425 + ], + "lines": [ + { + "bbox": [ + 47, + 403, + 288, + 425 + ], + "spans": [ + { + "bbox": [ + 47, + 403, + 288, + 425 + ], + "type": "text", + "content": "Table 1. Subjective results on real-world weather degraded images for de-hazing, de-raining with veil and snow with veil removal." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 48, + 426, + 298, + 617 + ], + "lines": [ + { + "bbox": [ + 48, + 426, + 298, + 617 + ], + "spans": [ + { + "bbox": [ + 48, + 426, + 298, + 617 + ], + "type": "table", + "html": "
DatabaseMethodsNIQE (↓)Entropy (↑)BRISQUE (↓)
RTTSUMVR [11]5.0097.22128.625
KD [4]4.9967.29726.837
TW [33]5.7037.26329.874
Ours4.8597.50524.761
RIDUMVR [11]6.6047.48624.296
KD [4]6.9437.45924.841
TW [33]7.4967.39324.165
Ours7.6257.49223.931
Snow realisticUMVR [11]4.2967.35423.761
KD [4]6.6437.45924.841
TW [33]5.6287.33125.377
Ours4.1967.57221.884
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MethodsSOTSCSDORD
UMVR [11]33.41/0.98028.65/0.90022.99/0.830
KD [4]34.64/0.98531.35/0.95029.05/0.916
TW [33]32.45/0.95529.76/0.94027.96/0.950
Ours36.26/0.98732.95/0.94231.24/0.951
", + "image_path": "b1ab0a9a99fe92e05754503261281aa2b8efb14f9794082dba7c6710e6e0c6e6.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_body" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 526, + 547, + 598 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 526, + 547, + 598 + ], + "spans": [ + { + "bbox": [ + 304, + 526, + 547, + 598 + ], + "type": "text", + "content": "fect is still present in the restored results of existing methods. However, the veiling effect is reduced substantially with the proposed restoration method (see column 5 and 6 from Figure 7). From the visual results, it is observed that the proposed method restores plausible results as compared to existing SOTA methods." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 602, + 459, + 614 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 602, + 459, + 614 + ], + "spans": [ + { + "bbox": [ + 306, + 602, + 459, + 614 + ], + "type": "text", + "content": "5.3. Synthetic Result Evaluation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": "We compared the proposed approach with SOTA unified restoration methods: UMVR [11], KD [4], TW [33] on SOTS-outdoor, CSD and outdoor-rain databases in terms of average PSNR, and SSIM. The quantitative analysis is provided in the Table 2 (see supplementary material for qualitative results). The provided qualitative and quantitative results validate the effectiveness of the proposed method compared to existing unified (UMVR [11], KD [4], TW" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "21702" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 70, + 95, + 187 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 95, + 187 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 95, + 187 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 95, + 187 + ], + "type": "image", + "image_path": "2680c8d63f0f4803037f36959e0c7823ac4c4e333fd8e0a42499c3f7608ed450.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 191, + 286, + 213 + ], + "lines": [ + { + "bbox": [ + 47, + 191, + 286, + 213 + ], + "spans": [ + { + "bbox": [ + 47, + 191, + 286, + 213 + ], + "type": "text", + "content": "Figure 8. Visual analysis of the proposed and existing methods: UMVR [11], KD [4], TW [33] for night-time image restoration." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 96, + 70, + 142, + 187 + ], + "blocks": [ + { + "bbox": [ + 96, + 70, + 142, + 187 + ], + "lines": [ + { + "bbox": [ + 96, + 70, + 142, + 187 + ], + "spans": [ + { + "bbox": [ + 96, + 70, + 142, + 187 + ], + "type": "image", + "image_path": "e483082c5930cbb16db0f675b79f987d8259ae98f61ab30154b296486c439a96.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 143, + 70, + 190, + 187 + ], + "blocks": [ + { + "bbox": [ + 143, + 70, + 190, + 187 + ], + "lines": [ + { + "bbox": [ + 143, + 70, + 190, + 187 + ], + "spans": [ + { + "bbox": [ + 143, + 70, + 190, + 187 + ], + "type": "image", + "image_path": "442d595cdf593843857fac1c511cced01e9a39d36b517c487ac38f3cf28a9ac2.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 190, + 70, + 237, + 187 + ], + "blocks": [ + { + "bbox": [ + 190, + 70, + 237, + 187 + ], + "lines": [ + { + "bbox": [ + 190, + 70, + 237, + 187 + ], + "spans": [ + { + "bbox": [ + 190, + 70, + 237, + 187 + ], + "type": "image", + "image_path": "61017a31b333b229e7fddb4e16bd68036323c7c92d927a76820c3dd9be376482.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 238, + 70, + 284, + 187 + ], + "blocks": [ + { + "bbox": [ + 238, + 70, + 284, + 187 + ], + "lines": [ + { + "bbox": [ + 238, + 70, + 284, + 187 + ], + "spans": [ + { + "bbox": [ + 238, + 70, + 284, + 187 + ], + "type": "image", + "image_path": "e30bb6a49a85468083150eadd4532941a620a2f7258d70cba47860d2699bee97.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 168, + 545, + 201 + ], + "lines": [ + { + "bbox": [ + 306, + 168, + 545, + 201 + ], + "spans": [ + { + "bbox": [ + 306, + 168, + 545, + 201 + ], + "type": "text", + "content": "Figure 9. Object detection and depth estimation analysis on degraded and restored images by existing UMVR [11], KD [4], TW [33], and proposed multi-weather image restoration method." + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "type": "table", + "bbox": [ + 61, + 257, + 274, + 330 + ], + "blocks": [ + { + "bbox": [ + 47, + 220, + 287, + 253 + ], + "lines": [ + { + "bbox": [ + 47, + 220, + 287, + 253 + ], + "spans": [ + { + "bbox": [ + 47, + 220, + 287, + 253 + ], + "type": "text", + "content": "Table 3. Ablation study on the proposed modules with outdoor rain database (IL: Independent Learning, PMDA: Progressive Multidomain Alignment and CMA: Cascaded Multi-head Attention)" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 61, + 257, + 274, + 330 + ], + "lines": [ + { + "bbox": [ + 61, + 257, + 274, + 330 + ], + "spans": [ + { + "bbox": [ + 61, + 257, + 274, + 330 + ], + "type": "table", + "html": "
ModulePSNRSSIM
Baseline26.490.887
Baseline + IL (Net-1)27.890.905
Baseline + IL + PMDA (Net-2)29.530.942
Baseline + IL + PMDA + CMA31.240.951
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Specifically, our unified architecture has " + }, + { + "bbox": [ + 46, + 345, + 286, + 405 + ], + "type": "inline_equation", + "content": "\\sim 11\\mathrm{M}" + }, + { + "bbox": [ + 46, + 345, + 286, + 405 + ], + "type": "text", + "content": " parameters (including domain-translation architecture) whereas the existing unified architectures KD [4], and TW [33] have " + }, + { + "bbox": [ + 46, + 345, + 286, + 405 + ], + "type": "inline_equation", + "content": "\\sim 28\\mathrm{M}" + }, + { + "bbox": [ + 46, + 345, + 286, + 405 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 345, + 286, + 405 + ], + "type": "inline_equation", + "content": "\\sim 31\\mathrm{M}" + }, + { + "bbox": [ + 46, + 345, + 286, + 405 + ], + "type": "text", + "content": " parameters respectively." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 405, + 286, + 501 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 405, + 286, + 501 + ], + "spans": [ + { + "bbox": [ + 46, + 405, + 286, + 501 + ], + "type": "text", + "content": "As seen from the Table 1 and 2, our method's performance on synthetic data is usually comparable to SOTA that are trained using the respective synthetic datasets. We note that while our method learns from the synthetic data, it does not over-fit on synthetic data. Therefore, it performs well on both synthetic and real-world datasets. This proves that the domain generalization ability of the proposed method is better compared to SOTA unified restoration methods." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 507, + 248, + 520 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 507, + 248, + 520 + ], + "spans": [ + { + "bbox": [ + 47, + 507, + 248, + 520 + ], + "type": "text", + "content": "5.4. Night-time Multi-weather Restoration" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 523, + 286, + 666 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 523, + 286, + 666 + ], + "spans": [ + { + "bbox": [ + 46, + 523, + 286, + 666 + ], + "type": "text", + "content": "Weather-degraded image/video restoration is equally important in night conditions as in day conditions [24]. Therefore, we examined the effectiveness of the proposed and existing networks for night-time multi-weather degradation removal. We labeled this analysis as cross-domain. We directly tested the proposed and existing models on real-world night-time multi-weather images downloaded from Internet. Sample results for night-time de-hazing, de-raining and de-snowing are provided in the Figure 8. From the visual results, it is observed that the proposed method performance is significantly better compared to existing methods for night-time multi-weather restoration." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 673, + 140, + 685 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 673, + 140, + 685 + ], + "spans": [ + { + "bbox": [ + 47, + 673, + 140, + 685 + ], + "type": "text", + "content": "5.5. Ablation Study" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 47, + 689, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 286, + 713 + ], + "type": "text", + "content": "We analyse the contributions of individual modules (independent feature learning, PMDA, and CMA) of the pro" + } + ] + } + ], + "index": 13 + }, + { + "type": "image", + "bbox": [ + 307, + 70, + 353, + 155 + ], + "blocks": [ + { + "bbox": [ + 307, + 70, + 353, + 155 + ], + "lines": [ + { + "bbox": [ + 307, + 70, + 353, + 155 + ], + "spans": [ + { + "bbox": [ + 307, + 70, + 353, + 155 + ], + "type": "image", + "image_path": "f3bff04379b8342fa5c028bd19bf6cf47a0a55291f01a498c4cc560c8d9ff926.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 320, + 155, + 343, + 160 + ], + "lines": [ + { + "bbox": [ + 320, + 155, + 343, + 160 + ], + "spans": [ + { + "bbox": [ + 320, + 155, + 343, + 160 + ], + "type": "text", + "content": "Input Image" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 14 + }, + { + "type": "image", + "bbox": [ + 354, + 70, + 401, + 155 + ], + "blocks": [ + { + "bbox": [ + 354, + 70, + 401, + 155 + ], + "lines": [ + { + "bbox": [ + 354, + 70, + 401, + 155 + ], + "spans": [ + { + "bbox": [ + 354, + 70, + 401, + 155 + ], + "type": "image", + "image_path": "328f6d4dba69e3d30f97e7ff94c4034a8e948ec33f4a168efbab4aba95b46522.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 372, + 156, + 386, + 160 + ], + "lines": [ + { + "bbox": [ + 372, + 156, + 386, + 160 + ], + "spans": [ + { + "bbox": [ + 372, + 156, + 386, + 160 + ], + "type": "text", + "content": "UMVR" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "type": "image", + "bbox": [ + 402, + 70, + 448, + 155 + ], + "blocks": [ + { + "bbox": [ + 402, + 70, + 448, + 155 + ], + "lines": [ + { + "bbox": [ + 402, + 70, + 448, + 155 + ], + "spans": [ + { + "bbox": [ + 402, + 70, + 448, + 155 + ], + "type": "image", + "image_path": "a0cab4d48119b451d47c58a9f817f6d7f9d96e927bfea717814414b25df1899a.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 424, + 156, + 430, + 160 + ], + "lines": [ + { + "bbox": [ + 424, + 156, + 430, + 160 + ], + "spans": [ + { + "bbox": [ + 424, + 156, + 430, + 160 + ], + "type": "text", + "content": "D" + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 18 + }, + { + "type": "image", + "bbox": [ + 449, + 70, + 496, + 155 + ], + "blocks": [ + { + "bbox": [ + 449, + 70, + 496, + 155 + ], + "lines": [ + { + "bbox": [ + 449, + 70, + 496, + 155 + ], + "spans": [ + { + "bbox": [ + 449, + 70, + 496, + 155 + ], + "type": "image", + "image_path": "4afb46e4519249f07cff463c97b89a44c3651c07438bc7e3b814ba01ca2a2eee.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 475, + 156, + 479, + 160 + ], + "lines": [ + { + "bbox": [ + 475, + 156, + 479, + 160 + ], + "spans": [ + { + "bbox": [ + 475, + 156, + 479, + 160 + ], + "type": "text", + "content": "W" + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "image_caption" + } + ], + "index": 20 + }, + { + "type": "image", + "bbox": [ + 496, + 70, + 542, + 155 + ], + "blocks": [ + { + "bbox": [ + 496, + 70, + 542, + 155 + ], + "lines": [ + { + "bbox": [ + 496, + 70, + 542, + 155 + ], + "spans": [ + { + "bbox": [ + 496, + 70, + 542, + 155 + ], + "type": "image", + "image_path": "88a8578db640409aa017611d5643c7351c11b0013f445f9ec8229f618ae65ffb.jpg" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 515, + 156, + 523, + 160 + ], + "lines": [ + { + "bbox": [ + 515, + 156, + 523, + 160 + ], + "spans": [ + { + "bbox": [ + 515, + 156, + 523, + 160 + ], + "type": "text", + "content": "Ours" + } + ] + } + ], + "index": 23, + "angle": 0, + "type": "image_caption" + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 215, + 545, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 215, + 545, + 251 + ], + "spans": [ + { + "bbox": [ + 305, + 215, + 545, + 251 + ], + "type": "text", + "content": "posed architecture in the ablation study conducted on ORD database. We start the ablation with single encoder-decoder architecture and named as \"Baseline\"." + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 304, + 251, + 545, + 357 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 251, + 545, + 357 + ], + "spans": [ + { + "bbox": [ + 304, + 251, + 545, + 357 + ], + "type": "text", + "content": "Independent Feature Learning: In the proposed restoration approach, four inputs " + }, + { + "bbox": [ + 304, + 251, + 545, + 357 + ], + "type": "inline_equation", + "content": "(I_{\\mathbb{D}1}, I_{\\mathbb{D}2}, I_{\\mathbb{D}3}" + }, + { + "bbox": [ + 304, + 251, + 545, + 357 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 251, + 545, + 357 + ], + "type": "inline_equation", + "content": "I)" + }, + { + "bbox": [ + 304, + 251, + 545, + 357 + ], + "type": "text", + "content": " are processed parallelly to learn the features independently. Is this independent feature learning effective for multiweather image restoration? To examine this, these inputs are processed through single (baseline) and parallel Net-1 encoders. From the Table 3 results, it is clear that the proposed independent feature learning is effective for extracting the features from all domains." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 358, + 545, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 358, + 545, + 502 + ], + "spans": [ + { + "bbox": [ + 304, + 358, + 545, + 502 + ], + "type": "text", + "content": "Progressive Multi-domain Deformable Alignment: Along with effective feature extraction, the multi-domain feature alignment has significant importance in restoration. To do this task, we have proposed PMDA module and used at each encoder stage. How does this proposed PMDA module helps the network to integrate the multi-domain features effectively? To scrutinize this, the efficiency of proposed restoration network is examined without (Net-1) and with (Net-2) PMDA. The quantitative analysis is provided in Table 3. From these results, it is evident that the proposed PMDA works effectively for multi-domain feature alignment." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 304, + 502, + 545, + 621 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 502, + 545, + 621 + ], + "spans": [ + { + "bbox": [ + 304, + 502, + 545, + 621 + ], + "type": "text", + "content": "Cascaded Multi-head Attention: Applying attention on the encoder or decoder features affects differently while restoring the clean image. Therefore, we have applied cascaded multi-head attention on respective PMDA and decoder features. We analysed the network accuracy without (Net-2) and with (baseline+IL+PMDA+CMA) CMA module i.e. final proposed network. The results in Table 3 proves the effectiveness of the proposed CMA module for restoration. The more ablation analysis for SOTS and CSD database is provided in the supplementary material." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 306, + 626, + 442, + 639 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 626, + 442, + 639 + ], + "spans": [ + { + "bbox": [ + 306, + 626, + 442, + 639 + ], + "type": "text", + "content": "5.6. Real-world Applications" + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 642, + 545, + 713 + ], + "type": "text", + "content": "Restoration module can be used as a preprocessing step for down-stream applications like object detection, depth estimation, etc. To this end, we have evaluated the benefits of the proposed and existing restoration methods as a preprocessing step for the object detection [26] and depth estimation task [25]. The visual analysis for object detection" + } + ] + } + ], + "index": 30 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "21703" + } + ] + } + ], + "index": 31 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 156 + ], + "type": "text", + "content": "and depth predictions is provided in Figure 9. As seen from the Figure 9, depth predictions or confidence in detecting objects of the restored images with proposed approach are more accurate than existing methods and degraded image. Clearly, the proposed domain-translation based restoration approach performs favourably against the SOTA methods for object detection and depth predictions task." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 165, + 119, + 178 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 165, + 119, + 178 + ], + "spans": [ + { + "bbox": [ + 47, + 165, + 119, + 178 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 182, + 289, + 447 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 182, + 289, + 447 + ], + "spans": [ + { + "bbox": [ + 46, + 182, + 289, + 447 + ], + "type": "text", + "content": "In this work, we proposed the first weather-invariant representation learning based multi-domain progressive deform-able alignment architecture for multi-weather image restoration. The weather-invariant representation learning helps to learn a representation that is common across diverse weather conditions and also similar across real or synthetic weather degraded images. Further, the proposed progressive multi-domain deform-able alignment module effectively merges the independently learned multi-domain features. This progressive alignment of features helps the network to reduce the degradation in step-by-step manner. Finally, effective restoration is done via CMA to capture long-term dependencies with respective PMDA and decoder features. Results analysis is conducted on real-world and synthetic benchmark hazy, rainy and snowy datasets. Also, the night-time multi-weather restoration results are analysed as cross-domain analysis. Extensive comparisons demonstrate the generalizability of the proposed method over SOTA methods. Further, we have analysed the effectiveness of the proposed and existing methods for object detection and depth estimation tasks for verifying its usefulness in real-world applications." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 458, + 107, + 471 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 458, + 107, + 471 + ], + "spans": [ + { + "bbox": [ + 47, + 458, + 107, + 471 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 479, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 8, + "blocks": [ + { + "bbox": [ + 53, + 479, + 287, + 534 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 479, + 287, + 534 + ], + "spans": [ + { + "bbox": [ + 53, + 479, + 287, + 534 + ], + "type": "text", + "content": "[1] Dongdong Chen, Mingming He, Qingnan Fan, Jing Liao, Liheng Zhang, Dongdong Hou, Lu Yuan, and Gang Hua. 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IEEE Transactions on Neural Networks and Learning Systems, 2022. 2" + } + ] + } + ], + "index": 24 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "21705" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multi3DRefer_ Grounding Text Description to Multiple 3D Objects/5fd3a41b-68c4-4dc5-a721-e608deb32134_content_list.json b/2023/Multi3DRefer_ Grounding Text Description to Multiple 3D Objects/5fd3a41b-68c4-4dc5-a721-e608deb32134_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..fb4dcc1a24c3247b9c90b7083bebe7cbe3e94b2d --- /dev/null +++ b/2023/Multi3DRefer_ Grounding Text Description to Multiple 3D Objects/5fd3a41b-68c4-4dc5-a721-e608deb32134_content_list.json @@ -0,0 +1,1880 @@ +[ + { + "type": "text", + "text": "Multi3DRefer: Grounding Text Description to Multiple 3D Objects", + "text_level": 1, + "bbox": [ + 145, + 130, + 823, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yiming Zhang1 ZeMing Gong1 Angel X. Chang1,2", + "bbox": [ + 264, + 179, + 704, + 198 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Simon Fraser University1 Alberta Machine Intelligence Institute (Amii)2", + "bbox": [ + 191, + 198, + 781, + 217 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "{yza440, zmgong, angelx}@sfu.ca", + "bbox": [ + 346, + 219, + 622, + 234 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "https://3dlg-hcvc.github.io/multi3defer/", + "bbox": [ + 320, + 237, + 645, + 250 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 313, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We introduce the task of localizing a flexible number of objects in real-world 3D scenes using natural language descriptions. Existing 3D visual grounding tasks focus on localizing a unique object given a text description. However, such a strict setting is unnatural as localizing potentially multiple objects is a common need in real-world scenarios and robotic tasks (e.g., visual navigation and object rearrangement). To address this setting we propose Multi3DRefer, generalizing the ScanRefer dataset and task. Our dataset contains 61926 descriptions of 11609 objects, where zero, single or multiple target objects are referenced by each description. We also introduce a new evaluation metric and benchmark methods from prior work to enable further investigation of multi-modal 3D scene understanding. Furthermore, we develop a better baseline leveraging 2D features from CLIP by rendering object proposals online with contrastive learning, which outperforms the state of the art on the ScanRefer benchmark.", + "bbox": [ + 75, + 316, + 473, + 590 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 618, + 209, + 633 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "There is growing interest in multi-modal methods that connect language and vision, tackling tasks such as image captioning, visual question answering, text-to-image retrieval, and generation. One fundamental task is visual grounding where natural language text queries are linked to regions of an image or 3D scene. While the problem of visual grounding has been well studied in 2D images, there are fewer datasets and methods studying the problem in 3D scenes. Being able to indicate the object that the text \"the first of four stools\" references in a 3D scene is useful for applications in robotics, AR/VR, and online 3D environments where we have access to not just a static image, but a 3D scene. Work on 3D datasets for visual grounding [7, 4] has spurred the development of methods for 3D visual grounding [41, 63, 60, 22, 21, 2, 58, 7] and the inverse task of 3D captioning [7], as well as unified methods that tackle both [8, 6, 9].", + "bbox": [ + 75, + 643, + 472, + 902 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e519d0c3e99726b7c6f00cf403a85bc04d9aed31107b17469a2ce17584259c0d.jpg", + "image_caption": [ + "This is a round stool. it is the first of four stools.", + "Figure 1: We introduce Multi3DRefer, a dataset and task where there are potentially multiple target objects for a given description. In ScanRefer [7] (left), the description corresponds to exactly one object (blue box), while in Multi3DRefer (right), there are multiple target objects." + ], + "image_footnote": [], + "bbox": [ + 501, + 286, + 893, + 450 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "However, existing datasets and tasks [7, 4] are designed with the assumption that there is a unique target object when performing visual grounding in a 3D scene. This assumption makes ambiguous descriptions that may refer to multiple objects problematic (see Fig. 1). Furthermore, this explicitly discourages visual grounding methods from demonstrating generalization to similar object instances on the basis of common features of the objects (e.g., similar size, color, texture) and spatial relations between objects (e.g., first in a row left-to-right or right-to-left).", + "bbox": [ + 496, + 582, + 893, + 733 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We address these shortcomings with an enhanced dataset and task that we call Multi3DRefer where a flexible number of target objects (zero, single or multiple) in a 3D scene are localized given language descriptions. We modify and enhance language data from ScanRefer [7] and propose evaluation metrics to benchmark prior work and a CLIP-based method that we propose on the flexible number visual grounding task. In summary, we make the following contributions: 1) generalize 3D visual grounding to a flexible number of target objects given natural language descriptions. 2) create an enhanced dataset based on ScanRefer [7]", + "bbox": [ + 496, + 734, + 895, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "15225", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "with augmentations from ChatGPT $^1$ , consisting of 61926 descriptions in 800 ScanNet V2 [15] scenes. 3) benchmark three prior 3D visual grounding approaches adapted to Multi3DRefer 4) design an end-to-end approach leveraging CLIP [47] embeddings and online rendering of object proposals with contrastive learning.", + "bbox": [ + 75, + 90, + 472, + 183 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related work", + "text_level": 1, + "bbox": [ + 76, + 196, + 215, + 212 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this paper, we focus on description localization where a single description may describe one or more objects in a 3D scene. Below, we review work in grounding in 2D and 3D, as well as recent work leveraging pre-trained vision-language models for 3D scene understanding.", + "bbox": [ + 75, + 220, + 468, + 297 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Visual grounding in 2D. A variety of datasets and methods have been proposed to investigate visual grounding tasks such as referring expressions [30, 42, 20] and phrase localization [44, 45] in 2D images. These datasets have enabled developing various visual-language grounding models [59, 61, 57, 39, 16, 37, 64]. Typically, in these datasets and tasks each phrase refers to exactly one object. A notable exception is the VGPhraseCut [54] dataset, based on Visual Genome [33] using templated phrases where each phrase is grounded to potentially multiple instance segments.", + "bbox": [ + 75, + 299, + 468, + 450 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Recent work in language and vision has started to tackle more flexible grounding. Kim et al. [31] noted that not all queries can be visually grounded (i.e. it is possible to have no targets) and constructed a dataset to study grounding performance when there are unanswerable queries. Kuo et al. [35] proposed a single model for referring expression comprehension, object detection, and phrase localization. While their model can handle multiple objects, the queries for multiple objects are typically short and category-based. Recent work [29, 36] reframed the problem of object detection as phrase grounding by introducing losses to align words to regions. These methods are flexible and have been used to improve both detection and visual grounding. In our work, we construct a dataset for flexible grounding in 3D.", + "bbox": [ + 75, + 450, + 470, + 662 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Visual grounding in 3D. Early work studied selecting the correct 3D shapes based on a text description in reference game setups [3, 53, 32], as well as learning joint language-3D embeddings for 3D text-to-shape retrieval [11, 51]. These works focused on descriptions of single objects in isolation. Moving beyond single 3D objects, researchers also studied grounding of language to objects in 3D scenes. At the scene level, ScanRefer [7] and ReferIt3D [4] introduce two datasets consisting of language descriptions of 3D objects from the real-world dataset ScanNet [15]. In detail, ReferIt3D [4] contains both template-based descriptions generated based on spatial relations between objects (Sr3D) and human-annotated fine-grained descriptions (Nr3D). They also propose two different grounding tasks,", + "bbox": [ + 75, + 665, + 470, + 878 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/5cffbf93247c31c9915521a453a878bcfcbfec75aa369958cbba30b26581f187.jpg", + "image_caption": [ + "Zero Target", + "This is a white cabinet. It is next to a desk.", + "Figure 2: Example description-scene pairs in the Multi3DRefer dataset with zero, single, or multiple target objects. Blue boxes indicate ground truth target objects." + ], + "image_footnote": [], + "bbox": [ + 503, + 103, + 624, + 178 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/d1cc49bf56ccdc696f23a1547e2190863d5d5c68678d6743ec679fd867b75f28.jpg", + "image_caption": [ + "Single Target (ScanRefer)", + "This is a black chair. It is in the middle of two chairs." + ], + "image_footnote": [], + "bbox": [ + 635, + 103, + 756, + 178 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/eeaccc6f83578748aba92c69b547d0779532e2cff97b75828d9e715db02cdb88.jpg", + "image_caption": [ + "Multiple Targets", + "This is a black chair facing the door." + ], + "image_footnote": [], + "bbox": [ + 767, + 104, + 887, + 178 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "both localizing a unique target object referred by a description. ScanRefer [7] requires both object detection and grounding, while ReferIt3D [4] focuses on discriminating a target object from multiple objects of that semantic class given ground-truth object bounding boxes.", + "bbox": [ + 496, + 294, + 890, + 369 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Different approaches [7, 4] have been proposed to tackle the two tasks, with models focusing on graph representations [21, 60, 17], improved handling of relations [63, 12], neurosymbolic reasoning [19], leveraging multi-view images and 2D semantics [58, 24, 22, 5], to unified models that can address both grounding and captioning [6, 8, 23, 9]. Recently, Abdelreheem et al. [1], Wu et al. [55] showed that including training on dense annotations can improve performance. Jain et al. [25] proposed to tackle object detection and visual grounding in a unified way by aligning features for text tokens with object proposals. In this work, we compare the performance of three recent models on our task Multi3DRefer with a new CLIP-based model.", + "bbox": [ + 496, + 369, + 892, + 566 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3D understanding using vision-language models. Large pre-trained text-vision models such as CLIP [47] and ALIGN [27] enabled work leveraging these models for 3D scene understanding. Recent work learn joint embeddings with text-image-3D representations [56, 62], used for disambiguating referring expressions [53] or text-to-shape retrieval [51]. Incorporating pre-trained 2D visual features also enabled expansion of 3D detection and instance segmentation to a larger number of categories [50], as well as tackling open vocabulary 3D detection [40, 52], and building of 3D semantic maps [26]. In our work, we show that we can leverage CLIP for improved visual grounding.", + "bbox": [ + 496, + 570, + 890, + 752 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Multi3DRefer dataset", + "text_level": 1, + "bbox": [ + 500, + 768, + 705, + 784 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To study our task, we build the Multi3DRefer dataset, a superset of the existing ScanRefer dataset [7] with language descriptions of varying granularities. We augment ScanRefer [7] to create a dataset with 3 types of description-scene pairs: a) Zero Target; b) Single Target; and c) Multiple Targets, indicating zero, single, or multiple target objects in the scene match the description (see Fig. 2). In addition, we use", + "bbox": [ + 496, + 794, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_footnote", + "text": "1https://openai.com/blog/chatgpt/", + "bbox": [ + 94, + 886, + 354, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "15226", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "table", + "img_path": "images/388d87955139c2f8aa000cebe0e53dee5313b0f5e242bf972999967ad62808bc.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DatasetZero TargetSingle TargetMultiple TargetsTotal
ScanRefer [7]-51583-51583
Sr3D [4]-83572-83572
Sr3D+ [4]-114532-114532
Nr3D [4]-41503-41503
Multi3DRefer6688420601317861926
", + "bbox": [ + 80, + 89, + 465, + 176 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Table 1: Compared to existing 3D visual grounding datasets, our Multi3DRefer dataset contains text that describes zero, single, or multiple target objects.", + "bbox": [ + 76, + 179, + 467, + 224 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/7bd4ea636cd690f9abf55381d7e590df8dd7871573c4fe57cacc2225d515fc91.jpg", + "image_caption": [ + "Figure 3: Multi3DRefer data construction pipeline showing the generation process of Zero Target (red), Single Target (blue) and Multiple Target (orange) data. We use ChatGPT to add diversity to the description. All scene-description pairs are manually verified and modified if needed." + ], + "image_footnote": [], + "bbox": [ + 94, + 239, + 447, + 566 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ChatGPT to augment the descriptions so they are more natural and diverse (see Fig. 3 for the overall data construction pipeline). To ensure the dataset is of high quality we manually verify all generated samples. We obtain a dataset with 61926 descriptions in total (see Tabs. 1 and 3 for statistics).", + "bbox": [ + 75, + 681, + 467, + 758 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Adapting text for multiple targets", + "text_level": 1, + "bbox": [ + 76, + 770, + 370, + 787 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We start with scene-description pairs from ScanRefer [7] and augment the data to create samples that refer to zero or more targets. For Single Target descriptions (type b), we take the released ScanRefer dataset which consists of description-scene pairs that have been initially verified to refer to unique objects [7]. We double-checked whether these descriptions indeed refer to unique objects and we", + "bbox": [ + 75, + 794, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "found 9324 descriptions that are ambiguous. We use these ambiguous descriptions as an initial set of type (c) descriptions that can refer to multiple objects. For additional type (c) descriptions, we obtain from the ScanRefer authors 7741 ambiguous descriptions that can refer to multiple objects and annotate those descriptions with matching objects. To collect type (a) description (no target object) as well as more type (c) descriptions, we develop an efficient data collection pipeline consisting of two stages: 1) automated description generation; and 2) verification and modification. This pipeline maximizes the use of the existing ScanRefer dataset and reduces manual annotation. Below, we describe how we generate and verify additional data samples.", + "bbox": [ + 496, + 90, + 890, + 287 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Zero Target. To obtain descriptions with no target objects, we establish negative pairs of scenes with existing descriptions selected randomly from other scenes. We then manually verify that descriptions do not match any objects in the new scene. To reduce the number of description-scene pairs that need to be verified, we automatically check whether the semantic class of the target object for the description appears in the scene. Only if the semantic class appears in the scene does it need to be manually verified. Out of 6688 samples, we manually verify 5630 with 1058 automatically checked to have no matching objects. For pairs that need verification, human annotators are shown the description along with an interactive view of the scene to check that there are no matching objects.", + "bbox": [ + 496, + 290, + 890, + 501 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Multiple Targets. To generate descriptions with multiple targets, we start with the original description-scene pairs in the ScanRefer dataset. We then randomly select descriptions and trim the text to the first punctuation to obtain shorter, more ambiguous descriptions (e.g., \"The cabinet is white and in the back of the room. It is the one on the left.\" $\\rightarrow$ \"The cabinet is white and in the back of the room\"). Note that descriptions in which the semantic class of the target object only has a unique object in the scene are skipped. The trimmed text and scene pairs are sent to the annotation interface. This time, annotators are asked to select all eligible objects of a description in a 3D interactive scene mesh. Annotators are also asked to modify trimmed descriptions to fix errors and increase diversity (see Fig. 4 for examples).", + "bbox": [ + 496, + 505, + 890, + 717 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Rephrasing using ChatGPT", + "text_level": 1, + "bbox": [ + 500, + 728, + 750, + 744 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "To increase description diversity we use the ChatGPT model text-davinci-002-render for sentence rephrasing. We provide ChatGPT with the following prompts:", + "bbox": [ + 496, + 752, + 890, + 797 + ], + "page_idx": 2 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "1. I will give you a sentence describing an object, please help me polish it and keep its meaning.", + "2. Help me reword a sentence to a different format but keep its meaning.", + "3. Help me reword a sentence to make it more natural.", + "4. Help me reword a sentence describing an object, you should describe the colors and the spatial information in a different way.", + "5. Help me reword a sentence to an interesting format, you should keep its meaning." + ], + "bbox": [ + 506, + 797, + 890, + 898 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "15227", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/516fd701e8fcbe4b459e037d39b7c29ade03d241603b8ab6122049c2d369b46a.jpg", + "image_caption": [ + "ScanRefer", + "Multi3DRefer", + "T: This is a white kitchen cabinet located to the left of the over and stove unit.", + "M: This is a white kitchen cabinet located near the over and stove unit.", + "ScanRefer" + ], + "image_footnote": [], + "bbox": [ + 107, + 141, + 272, + 247 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/60db7c60ef9de9e51fa2c76a6c257896059a334d7e34f47fab6c397b24fda30f.jpg", + "image_caption": [ + "This is a white kitchen cabinet located to the left of the over and stove unit. It has four drawers with silver handles.", + "R: A white kitchen cabinet is situated near the oven and stove unit." + ], + "image_footnote": [], + "bbox": [ + 277, + 142, + 441, + 247 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/2c8fc41025d993e4afd8985fbd767e082bec7afb92e57f364b8535e53ae69081.jpg", + "image_caption": [ + "There is a rectangular blue pillow with colorful decorations. It is on a larger cushion in front of the window by the side of the room.", + "ScanRefer" + ], + "image_footnote": [], + "bbox": [ + 109, + 301, + 272, + 407 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/8c4a79c3d54a253d64f53f31e1663beb3226491a92007e0d564d07f38b855187.jpg", + "image_caption": [ + "M: There is a rectangular pillow with colorful decorations. It is on a larger cushion in front of the window by the side of the room. R: A rectangular pillow, adorned with colorful decorations, rests upon a larger cushion positioned by the side of the room, right in front of the window.", + "Multi3DRefer" + ], + "image_footnote": [], + "bbox": [ + 277, + 303, + 441, + 407 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/92ce8e4961ea89b06b1511e8e5b17294ca71f7180ce96c3b167db5d5412a5117.jpg", + "image_caption": [ + "This is a green patterned chair. It is at a brown table.", + "Figure 4: Examples of generated revised descriptions of multiple targets for the Multi3DRefer dataset where we trim (T) to create more ambiguous descriptions, modify (M) by human, and reword (R) using ChatGPT. All descriptions are verified by annotators (see bounding boxes for target objects). Note that the reworded (R) descriptions provide more variation in sentence structure." + ], + "image_footnote": [], + "bbox": [ + 109, + 433, + 272, + 539 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/575b7e0d4d7caa47b79ef097cef4f43139aa1fcd8b1a0bbf9e36dcb64df7afe8.jpg", + "image_caption": [ + "R: A green patterned chair sits beside a brown table." + ], + "image_footnote": [], + "bbox": [ + 277, + 433, + 441, + 539 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/7c73cbd9f0340cd5203853baaa7f50dd4fb0fd3cffef53dbd19d81bf245a6db1.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Unique wordsTotal wordsAvg. description length
Original5067101619016.4
Rephrased707793693515.1
", + "bbox": [ + 81, + 672, + 467, + 724 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Tab. 2 shows statistics comparing the descriptions before and after rephrasing. We see a richer vocabulary but shorter descriptions after ChatGPT rephrasing. Below we provide examples of the original (O) and reworded (R) text:", + "bbox": [ + 75, + 825, + 467, + 886 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "O: The table is a round table. It is located between two chairs to the", + "bbox": [ + 84, + 887, + 468, + 898 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/1e119eb23c14532c2e15452686adb9dd9bb14a2460501451b870eb3ddc2923eb.jpg", + "table_caption": [ + "Table 2: Comparison of Multi3DRefer language data before and after ChatGPT rephrasing. We count the number of unique words, total words, and the average description length, excluding punctuation." + ], + "table_footnote": [], + "table_body": "
SpatialColorTextureShapeTotal
ScanRefer [7]511173469258641741651583
Nr3D [4]3971111939526856841503
Sr3D [4]835726254064883572
Sr3D+ [4]11453286660744114532
Multi3DRefer600284130771211969261926
", + "bbox": [ + 504, + 88, + 888, + 186 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Table 3: Breakdown of spatial, color, texture, and shape information in object descriptions from different datasets.", + "bbox": [ + 500, + 196, + 890, + 227 + ], + "page_idx": 3 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "right, and two chairs to the left of it.", + "R: The round table is situated between two chairs to its right and two chairs to its left.", + "O: This is a table on the wall in the room. It is next to the window and a few lined-up chairs.", + "R: A wall-mounted table resides coaxily beside a window in the room, accompanied by a row of orderly chairs.", + "O: A sink on the vanity. It is to the right of the vacuum cleaners.", + "R: The sink is located on the vanity to the right of the vacuum cleaners.", + "O: This is a white kitchen cabinet located near the over and stove unit.", + "R: A white kitchen cabinet is situated near the oven and stove unit" + ], + "bbox": [ + 508, + 266, + 890, + 415 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The rephrased text preserves the original meaning while being more natural. In addition, ChatGPT automatically corrects typos (e.g., over to oven in the last example).", + "bbox": [ + 500, + 421, + 890, + 467 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Verification", + "text_level": 1, + "bbox": [ + 500, + 489, + 624, + 503 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "After we obtain a set of ChatGPT reworded descriptions, we manually verify the descriptions are well-written and that the object(s) matched in the scene are accurate. We create a web interface for verifiers to check whether the description matches the identified target objects (see supplement for details). The web interface shows the description together with an interactive 3D view of the scene and the target objects. The verifiers check if the description matches the target objects and only the target objects, or modify the list of target objects (by selecting appropriate objects), or improve the description to fix typos and ambiguities. The verification was performed by 5 students over a period of one month.", + "bbox": [ + 496, + 517, + 890, + 712 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.4. Dataset statistics", + "text_level": 1, + "bbox": [ + 500, + 737, + 663, + 752 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In total, our dataset consists of 61926 language descriptions, with 51583 directly obtained from ScanRefer [7], of which 6688 descriptions match zero-targets and 13178 match multiple. For Multiple Targets, the scenes are typically offices or meeting rooms with many chairs and tables. See Tab. 1 for a comparison of our final dataset against prior datasets. We also provide annotations for each description as to whether it refers to spatial, color, texture, or shape attributes (see Tab. 3).", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "15228", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/ed990a157b0f5a517fb2c0ca868937d0b078d00fb491f86326e8c470e0b46ca0.jpg", + "image_caption": [ + "Figure 5: Our M3DRef-CLIP end-to-end architecture. Given a scene point cloud and a text description with $L$ tokens (we pad shorter descriptions and truncate longer ones), the detector first predicts $M$ object proposals and their 3D features. Then an online renderer renders $N$ -view images for each proposal and feeds them into the image encoder to get 2D features. A transformer-based module then fuses both language features and $2\\mathrm{D} + 3\\mathrm{D}$ object features and outputs scores indicating the match of each object to the description. We use PointGroup [28] to detect and segment the objects in 3D and select CLIP [47] + MLPs as the language and image encoder. A contrastive loss is applied between sentence features and object features." + ], + "image_footnote": [], + "bbox": [ + 78, + 88, + 890, + 324 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Task", + "text_level": 1, + "bbox": [ + 76, + 452, + 142, + 467 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In the Multi3DRefer task, we are given as input a 3D real-world scene represented as a point cloud $P \\in \\mathbb{R}^{N \\times (3 + C)}$ and a free-form language description with a variable number $M \\in \\mathbb{N}$ of referred objects, where $N, C$ are the number of points and the number of point feature channels, respectively. The goal is to predict axis-aligned bounding boxes for all $M$ objects that match the description. Compared to prior work, the difficulty of our task is that the number of referred objects is flexible, i.e., a description can refer to not only one or multiple target objects but also no objects. Predicting too many or too few target objects are both penalized by our evaluation metrics.", + "bbox": [ + 75, + 484, + 472, + 667 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Evaluation metrics. To evaluate grounding for a flexible number of target objects, we measure the F1 score at the intersection over union (IoU) thresholds of $\\tau_{\\mathrm{eval}} = 0.25$ and 0.5 (F1@0.25 and F1@0.5). To investigate model performance for different scenarios, we consider the following 5 cases: a) zero target w/o distractors of the same semantic class; b) zero target w/ distractors; c) single target w/o distractors; d) single target w/ distractors; and e) multiple targets. Note that c) and d) correspond to the \"unique\" and \"multiple\" cases in ScanRefer [7]. In addition, a) and c) are easier cases where there are zero or a unique target object of its semantic class in a scene, while b) and d) are more difficult cases containing one or multiple target objects of the same semantic class in a scene. We also report the micro-average of the 5 cases as an overall score.", + "bbox": [ + 75, + 672, + 472, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "During evaluations, we first calculate per-pair IoUs between ground truth and predicted bounding boxes in a scene, and then apply the Hungarian algorithm [34] to get an optimal one-to-one matching between predicted and GT bounding boxes. To get the maximum matched IoU, we use the following cost function:", + "bbox": [ + 496, + 453, + 893, + 544 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {C o s t} (i, j) = - \\operatorname {I o U} (i, j) \\text {f o r} i, j \\in \\{1 \\dots N \\}\n$$\n", + "text_format": "latex", + "bbox": [ + 544, + 546, + 846, + 563 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $N = \\max (\\# Predictions, \\# GTs)$ . After obtaining the optimal match, we take pairs with IoUs higher than $\\tau_{\\mathrm{eval}}$ to be True Positives (TP). We treat the Zero Target (ZT) case as a special case where recall is always set to 1, and precision is set to 1 if there is no prediction or 0 otherwise.", + "bbox": [ + 496, + 564, + 893, + 642 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "5. Method", + "text_level": 1, + "bbox": [ + 500, + 654, + 591, + 669 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We propose M3DRef-CLIP, a CLIP-based approach and compare to three recent approaches: 3DVG-Transformer [63], 3DJCG [6] and D3Net [8]. We selected these methods as they were among the top performers on the ScanRefer [7] benchmark with available open-source code. Note that 3DJCG [6] and D3Net [8] are unified models, which can do both grounding and captioning tasks. All four models are two-stage approaches, where a 3D object detector first identifies a set of bounding box candidates, and a disambiguation module then selects the target bounding box. In the original ScanRefer setting, the three compared models are trained using a cross-entropy loss $L_{\\mathrm{ref}}$ where the predicted bounding box has the highest IoU ( $> \\tau_{\\mathrm{train}}$ ) with", + "bbox": [ + 496, + 680, + 893, + 878 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "$^{2}$ kaldir.vc.in.tum.de/scanrefer_benchmark", + "bbox": [ + 514, + 886, + 743, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "15229", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "the GT bounding box as the target bounding box to calculate the loss. For our task, we use a binary cross-entropy loss for $L_{\\mathrm{ref}}$ as our problem is a multi-label task (vs classification).", + "bbox": [ + 76, + 90, + 468, + 137 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. M3DRef-CLIP", + "text_level": 1, + "bbox": [ + 76, + 148, + 230, + 162 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "M3DRef-CLIP follows the two-stage architecture with PointGroup [28] as the detector, CLIP [47] as the text encoder and a transformer-based fusion module (see Fig. 5). We use PointGroup [28] to obtain object proposals along with their 3D features $\\mathbf{F}^{3\\mathrm{d}} \\in R^{32}$ . The output object proposals are fed into an online object renderer, which renders multi-view 2D images for each object proposal. We use CLIP [47] to encode the images and use an MLP to project the average of the output 2D image features to obtain $\\mathbf{F}^{2\\mathrm{d}} \\in \\mathbb{R}^{128}$ . The 2D and 3D features are concatenated to form and passed through a 1D convolution (that projects the combined 160-dim features down to 128-dim) to obtain the final visual features $\\mathbf{F}^{\\mathrm{obj}} \\in \\mathbb{R}^{128}$ for an object proposal:", + "bbox": [ + 75, + 172, + 468, + 369 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {F} ^ {\\mathrm {o b j}} = \\operatorname {c o n v} _ {\\mathrm {l d}} ([ \\mathbf {F} ^ {\\mathrm {3 d}}; \\mathbf {F} ^ {\\mathrm {2 d}} ]), \\quad \\mathbf {F} ^ {\\mathrm {2 d}} = \\frac {\\operatorname {M L P} (\\sum_ {i = 1} ^ {N} \\mathbf {F} _ {i} ^ {\\mathrm {2 d}})}{N}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 371, + 454, + 402 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We use the CLIP text encoder with an MLP to obtain both 128-dim token-level and sentence embeddings. We use a transformer-based fusion module to combine object features and token-level embeddings and output confidence scores for each proposal. To improve the training, we apply a contrastive loss between sentence and object features.", + "bbox": [ + 75, + 402, + 468, + 492 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. Loss function", + "text_level": 1, + "bbox": [ + 76, + 505, + 217, + 518 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We train the network end-to-end with the total loss $L = L_{\\mathrm{det}} + L_c + L_{\\mathrm{ref}}$ consisting of the detection loss $L_{\\mathrm{det}}$ , contrastive loss $L_{\\mathrm{c}}$ , and the reference loss $L_{\\mathrm{ref}}$ . The detection loss $L_{\\mathrm{det}}$ is introduced in PointGroup [28] and consists of four parts: 1) cross-entropy loss for supervising per-point semantic class prediction; 2) $L_1$ loss for supervising perpoint offset vector towards object centers; 3) directional loss formed as a mean of minus cosine similarities for further constraining the direction of per-point offset vectors; 4) binary cross-entropy loss for supervising per-point objectness confidence score. To help learn better multi-modal embeddings, we introduce a symmetric contrastive loss $L_{c}$ [47], which can handle a flexible number of target objects as shown below:", + "bbox": [ + 75, + 530, + 468, + 739 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {\\mathrm {c}} ^ {O \\rightarrow S} = - \\log \\frac {\\exp (\\cos (\\bar {O} _ {i} , S _ {i}) / \\tau)}{\\sum_ {i = 1} ^ {n} \\exp (\\cos (\\bar {O} _ {i} , S _ {j}) / \\tau)}\n$$\n", + "text_format": "latex", + "bbox": [ + 129, + 739, + 413, + 773 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nL _ {\\mathrm {c}} ^ {S \\rightarrow O} = - \\log \\frac {\\exp (\\cos (S _ {i} , \\bar {O} _ {i}) / \\tau)}{\\sum_ {i = 1} ^ {n} \\exp (\\cos (S _ {i} , \\bar {O} _ {j}) / \\tau)}\n$$\n", + "text_format": "latex", + "bbox": [ + 129, + 775, + 413, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $S$ is sentence features, $\\bar{O}$ is the mean of object features of all target objects paired with a description, and $\\tau$ is a temperature parameter. Finally, the reference loss $L_{\\mathrm{ref}}$ supervises the matching module to select objects satisfying the description. We use the multi-class cross-entropy loss as $L_{\\mathrm{ref}}$ for experiments on ScanRefer [7], Nr3D [4] and", + "bbox": [ + 75, + 810, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Multi3DRefer (ST) where each description only refers to a single target object. For experiments on Multi3DRefer, $L_{\\mathrm{ref}}$ is a sum of binary cross-entropy losses over detected objects.", + "bbox": [ + 498, + 90, + 890, + 151 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training. To set up positive (i.e. valid target bounding boxes) and negative instances between the GT bounding boxes and proposed bounding boxes, we use two strategies (see supplement for detailed comparisons):", + "bbox": [ + 498, + 154, + 890, + 215 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "All All predicted bounding boxes with IoU higher than the threshold $\\tau_{\\mathrm{train}}$ with GT bounding boxes are considered target bounding boxes.", + "bbox": [ + 498, + 217, + 890, + 263 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Hungarian We apply the Hungarian algorithm [34] to do bipartite matching, which ensures an optimal solution. We use the same IoU threshold $\\tau_{\\mathrm{train}}$ to filter prediction-GT bounding box pairs.", + "bbox": [ + 498, + 266, + 890, + 325 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Inference. At inference time, we take all bounding boxes with predicted scores above the threshold $\\tau_{\\mathrm{pred}}$ as positives (predicted target bounding boxes for the description). See the supplement for comparisons of different $\\tau_{\\mathrm{pred}}$ .", + "bbox": [ + 498, + 329, + 890, + 391 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "6. Experiments", + "text_level": 1, + "bbox": [ + 500, + 405, + 632, + 421 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We conduct experiments on both ScanRefer [7] and Multi3DRefer datasets and consider two setups: grounding objects with GT and predicted bounding boxes.", + "bbox": [ + 498, + 431, + 890, + 474 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "GT bounding boxes. For M3DRef-CLIP and D3Net [8], we input the complete scene and apply GT point masks for each object to get GT bounding boxes and masked features from the pre-trained detector (PointGroup for both D3Net and our M3DRef-CLIP). For 3DVG-Trans [63] and 3DJCG [6], we use their original GT setting following the method proposed by ReferIt3D [4]. Single input objects are first extracted from the scene using the GT masks and PointNet++ [46] is used for obtaining the object features. For all methods, we disable the $L_{det}$ loss when using GT boxes.", + "bbox": [ + 498, + 478, + 890, + 630 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Predicted bounding boxes. We use the original detector design of each method to predict bounding boxes and extract features.", + "bbox": [ + 498, + 632, + 890, + 676 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "6.1. Implementation details", + "text_level": 1, + "bbox": [ + 500, + 688, + 714, + 704 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We implement M3DRef-CLIP using PyTorch Lightning3 and PyTorch3D [48]. We train the model end-to-end on a single NVIDIA RTX A5000 with a batch size of 4, using the AdamW optimizer [38] with a learning rate of $5e^{-4}$ . We use a re-implementation of PointGroup4 with the Minkowski Engine [14]. Following D3Net [8], we pretrain our PointGroup module on all ScanNet v2 training scans with the 18 ScanRefer categories. We take point coordinates, point normals and per-point multi-view features $P \\in \\mathbb{R}^{N \\times (3 + 3 + 128)}$ as the input. For data augmentation, we randomly apply", + "bbox": [ + 498, + 710, + 890, + 864 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "$^{3}$ www.pytorchlightning.ai", + "bbox": [ + 517, + 875, + 658, + 887 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "4https://github.com/3dlg-hcvc/minsu3d", + "bbox": [ + 517, + 887, + 728, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "15230", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/b44a07a1b5458889a44e8bff9ef8f2732f892b998e186f595a5e8d18f552de73.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ZT w/o DistractorsZT w DistractorsST w/o DistractorsST w/ DistractorsMultiple Targets
TrainValTestTotalTrainValTestTotalTrainValTestTotalTrainValTestTotalTrainValTestTotal
ScanRefer [7]--------85002297120111998281657211420939585----
Multi3DRefer2702528596382621603783242862719820991106104032204053584259316579738275768313178
", + "bbox": [ + 80, + 88, + 890, + 147 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d5f07a5688696cc1a83c06c60cdd18b894b33f51f25cffc7b79045c7e00c909c.jpg", + "table_caption": [ + "Table 4: Breakdown of different datasets in 5 scenarios. ZT and ST denote Zero Target and Single Target, respectively." + ], + "table_footnote": [ + "Table 5: For unified models [8, 6, 9], we report both the grounding-only (G) performance as well as their best performance. We use * to indicate joint grounding and captioning models trained with extra data." + ], + "table_body": "
Acc@0.5 on ValAcc@0.5 on Test
UniqueMultipleAllUniqueMultipleAll
3DVG-Trans+ [63]62.030.336.457.931.037.0
InstanceRefer [60]66.824.832.966.726.935.8
FFL-3DOG [17]67.925.734.0---
SAT [58]50.825.230.1---
3D-SPS [41]66.729.837.0---
MVT [22]66.525.333.3---
BUTD-DETR [25]66.335.139.8---
D3Net (G) [8]70.427.135.665.827.336.0
D3Net* [8]72.030.137.968.430.739.2
3DJCG (G) [6]64.530.336.9---
3DJCG* [6]64.330.837.360.631.237.8
HAM [10]67.934.040.663.733.240.1
UniT3D (G) [9]74.827.636.5---
UniT3D* [9]73.131.139.1---
M3DRef-CLIP77.236.844.770.938.145.5
", + "bbox": [ + 80, + 196, + 465, + 411 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "coordinate jitter, x-axis flipping and rotation around the z-axis. We freeze a pre-trained CLIP with ViT-B/32 and only train additional MLPs. For encoding the text with CLIP, we follow CLIP and tokenizer with a lower-cased BPE, and [SOS] and [EOS] tokens added (the output corresponding to [EOS] is used as the sentence representation).", + "bbox": [ + 76, + 510, + 468, + 599 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Object renderer. For each object proposal, we render 3 views horizontally spaced 120 degrees apart, at a distance of $1\\mathrm{m}$ , with elevation angle of $45^{\\circ}$ . We crop coordinates and colors from the input scene point cloud using predicted bounding boxes and set point radius to $2.5\\mathrm{cm}$ and image size to $224^2$ . We use CUDA to batch index scene point clouds and crop in parallel, and render the batches sparsely to avoid padding overhead. Rendering is implemented with PyTorch3D [48] and executed on the GPU.", + "bbox": [ + 75, + 602, + 468, + 738 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.2. Results", + "text_level": 1, + "bbox": [ + 76, + 748, + 169, + 762 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.2.1 Performance of M3DRef-CLIP", + "text_level": 1, + "bbox": [ + 76, + 771, + 346, + 785 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We first validate the performance of M3DRef-CLIP on ScanRefer (see Tab. 5) and Nr3D [4] (see Tab. 6) datasets and compare it against recent models. On ScanRefer, our method outperforms all prior works including those joint models leveraging extra input data by a large margin on both val set and test set (online benchmarking). In our ablation study, we find that the use of the CLIP text encoder is a key", + "bbox": [ + 75, + 794, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/63ff655e64e37c6213cf585d6cad96891d3ccef33c97d3dfdbe057da1e51660b.jpg", + "table_caption": [], + "table_footnote": [ + "Table 6: Comparison of methods on Nr3D [4] val set with GT boxes." + ], + "table_body": "
EasyHardView-DepView-IndepAll
3DVG-Trans [63]48.534.834.843.740.8
InstanceRefer [60]46.031.834.541.938.8
FFL-3DOG [17]48.235.037.144.741.7
TransRefer3D [18]48.536.036.544.942.1
SAT [58]56.342.446.950.449.2
3D-SPS [41]58.145.148.053.251.5
MVT [22]61.349.154.355.455.4
BUTD-DETR [25]60.748.446.058.054.6
HAM [10]54.341.941.551.448.2
LanguageRefer [49]51.036.641.745.043.9
LAR [5]56.141.846.750.248.9
M3DRef-CLIP55.643.442.352.949.4
", + "bbox": [ + 501, + 196, + 888, + 375 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/f32c944e564e3e7c60c888a32e54b5f649c710b1ca782de4320c1c040c80238b.jpg", + "table_caption": [], + "table_footnote": [ + "Table 7: We compare results of training M3DRef with GT boxes on different datasets' val set. We only use the Single Target (ST) case in Multi3DRefer dataset." + ], + "table_body": "
Training DatasetAcc on ScanReferAcc on Multi3DRefer (ST)
UniqueMultipleAllUniqueMultipleAll
ScanRefer [7]89.349.156.979.548.257.0
Multi3DRefer (ST)88.546.955.086.352.962.3
Multi3DRefer (ST) + ScanRefer90.851.058.788.056.765.5
", + "bbox": [ + 501, + 428, + 888, + 491 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "factor to the strong performance of our model on ScanRefer. Another key factor is the use of a strong 3D object instance segmentation network (PointGroup) as our object detector. For instance, the PointGroup-based methods [8, 9] readily outperform VoteNet-based methods [63, 6] on the unique subset of ScanRefer.", + "bbox": [ + 496, + 575, + 890, + 665 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "For Nr3D [4], we achieve comparable but less competitive results because of our weaker ground-truth box encoder. Note that SAT [58] and MVT [22] also leverage 2D images but render them offline. Overall, using additional 2D image information is helpful for two-stage methods.", + "bbox": [ + 496, + 667, + 890, + 743 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "6.2.2 Multi3DRefer", + "text_level": 1, + "bbox": [ + 500, + 766, + 651, + 780 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We split the Multi3DRefer data into train/val/test by scene following the ScanRefer split, resulting in a rough split ratio of 7:2:1 for the scene-description pairs. See Tab. 4 for statistics, including the number of descriptions with zero, single, or multiple targets.", + "bbox": [ + 496, + 791, + 890, + 867 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Usefulness of Multi3DRefer dataset. To study the usefulness of the Multi3DRefer dataset, we compare the perfor", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "15231", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/baf6c4a364e3b0a40a8dd48aa3c1ac062f69820923f96334c14bdb7d1ab797fb.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
F1 (GT boxes)F1@0.5 (Pred boxes)
ZT w/o DZT w/ DST w/o DST w/ DMTAllZT w/o DZT w/ DST w/o DST w/ DMTAll
3DVG-Trans+ [63]45.314.358.935.254.244.187.145.827.516.726.525.5
D3Net (Grounding) [8]71.620.478.244.461.655.581.632.538.623.335.032.2
3DJCG (Grounding) [6]47.916.459.135.554.244.694.166.926.016.726.226.6
M3DRef-CLIP74.229.484.152.367.262.381.839.447.830.637.938.4
", + "bbox": [ + 80, + 88, + 890, + 185 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/c4e262a8623c9904dcadc59d00c05bfcbeb48beee16eea3b5af8c1b511d8ff17.jpg", + "table_caption": [ + "Table 8: Comparison of different methods on Multi3DRefer. Our M3DRef-CLIP outperforms prior work on most metrics." + ], + "table_footnote": [], + "table_body": "
Eval DatasetAcc (GT boxes)Acc@0.5 (Pred boxes)
UniqueMultipleAllUniqueMultipleAll
Multi3DRefer (ST)86.951.561.567.340.147.7
ScanRefer [7]88.046.154.373.534.341.9
", + "bbox": [ + 80, + 227, + 467, + 291 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 9: M3DRef-CLIP evaluated on Multi3DRefer (ST) and ScanRefer with both GT and predicted bounding boxes.", + "bbox": [ + 76, + 292, + 467, + 323 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "mance of training M3DRef-CLIP with the original ScanRefer data and with our Multi3DRefer data for the Single Target (ST) case. We evaluate on both ScanRefer and Multi3DRefer (ST), using GT bounding boxes. Tab. 7 shows that our reworded data can improve performance on ScanRefer. Prior work has also shown that incorporating additional labeled data can help, but they typically used either a captioning model [8, 9], mixed additional annotated data [58], or used dense annotations [1]. We show that simple rewordings (without accessing the images) also help.", + "bbox": [ + 75, + 362, + 468, + 513 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We also evaluate M3DRef-CLIP trained on Multi3DRefer using ScanRefer's task setting (Tab. 9) of predicted objects. We observe that the model trained on Multi3DRefer data and task achieves similar performance to the model trained on ScanRefer data and task, which illustrates the generalization of Multi3DRefer.", + "bbox": [ + 75, + 518, + 468, + 609 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Evaluation on Multi3DRefer. We compare four models on the Multi3DRefer dataset using both ground-truth and predicted boxes (Tab. 8). In our experiments, we focus on two-stage methods that perform well on ScanRefer. We adapt the code of 3DVG-Trans, 3DJCG and D3Net to our task. For 3DVG-Trans, we use the enhanced version 3DVG-Trans+ provided by the authors. We only train and evaluate the grounding model of 3DJCG and D3Net.", + "bbox": [ + 75, + 619, + 468, + 739 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To analyze the performance of the models, we break down the zero (ZT) and single-target (ST) case to without and with distractors (D) of the same class. Overall, having distractors is more challenging. We note that M3DRef-CLIP outperforms the other methods on Multi3DRefer, and that 3DJCG is better at handling the ZT case with predicted boxes. Fig. 6 shows qualitative results.", + "bbox": [ + 75, + 746, + 468, + 853 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/808753537d6ac0ac1bf469ecfcb5d833fb0090ce602e78c4f4be49158423eb94.jpg", + "image_caption": [ + "Figure 6: Qualitative results of D3Net [8] versus M3DRef-CLIP on Multi3DRefer using predicted boxes. Blue boxes indicate GT, green boxes are true positives with IoU threshold $\\tau_{\\mathrm{pred}} > 0.5$ . Red boxes are false positives." + ], + "image_footnote": [], + "bbox": [ + 506, + 227, + 888, + 527 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6.2.3 Ablation studies", + "text_level": 1, + "bbox": [ + 500, + 625, + 666, + 638 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Does CLIP help? We experiment with just using pure CLIP for both text and image encoding vs combining CLIP and 3D features (see Tab. 10). We also report results using a GRU [13]-based text encoder with GloVE [43] embedding, as used in prior work [7, 63, 8]. Although our GRU and 3D variants are similar at a high level to the grounding model of D3Net (which also used GRU and PointGroup with a transformer-based fusion module), we outperform the D3Net grounding module. Tab. 10 shows that using the CLIP text encoder improves performance, and combining CLIP and 3D features yields the best performance. The CLIP image encoder by itself underperforms the 3D features, showing the usefulness of 3D information.", + "bbox": [ + 496, + 654, + 890, + 851 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Does contrastive learning help? Tab. 11 reports the performance of M3DRef with and without contrastive learning on ScanRefer, Nr3D [4] and Multi3DRefer. We observe the", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_footnote", + "text": "5 github.com/zlcccc/3DVG-Transformer", + "bbox": [ + 94, + 886, + 312, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "15232", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/a458af0a9377d1ba34b60c1037a60c354b82237d353ca1844357601aaf3532b2.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
TextVisionAcc (ScanRefer)F1 (Multi3DRefer)
UniqMultAllZT w/o DZT w/ DST w/o DST w/ DMTAll
GTGRU3D88.843.552.370.127.381.649.363.359.1
CLIPCLIP78.942.149.358.327.874.144.761.054.4
CLIP3D+CLIP89.349.156.974.229.484.152.367.262.3
PredGRU3D72.232.840.478.842.149.428.537.037.4
CLIPCLIP71.231.239.064.436.042.925.733.733.1
CLIP3D+CLIP77.236.844.781.839.447.830.637.938.4
", + "bbox": [ + 119, + 88, + 841, + 237 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/3e6eeead53ed77ec255d35cbd6685de14e30ae306f41ec46c317fb71c3829127.jpg", + "table_caption": [ + "Table 10: Ablations in training M3DRef using different feature embeddings and ground-truth boxes (top rows) and predicted boxes (bottom rows). The combination of CLIP [47] and 3D features achieves the best performance. We use PointGroup [28] for our 3D object detector and feature extractor." + ], + "table_footnote": [], + "table_body": "
ScanReferNr3DMulti3DRefer
UniqueMultipleAllEasyHardView-DepView-IndepAllZT w/o DZT w/ DST w/o DST w/ DMTAll
w/ contrastive89.349.156.955.643.442.352.949.474.229.484.152.367.262.3
w/o contrastive89.647.255.450.935.337.645.642.967.423.883.452.066.561.1
", + "bbox": [ + 80, + 297, + 888, + 362 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/99bc1de63491d686b44e6c73f48230f290a09b29faf1046510038935ed4a057d.jpg", + "table_caption": [ + "Table 11: Ablation of M3DRef-CLIP with and without contrastive loss using GT boxes." + ], + "table_footnote": [], + "table_body": "
TextVisionSpatialColorTextureShape
GRU3D55.867.776.477.8
CLIP3D+CLIP58.871.979.482.5
", + "bbox": [ + 83, + 404, + 459, + 465 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Table 12: Breakdown of M3DRef performance (with GRU vs CLIP) on descriptions with different attributes. We report F1 scores with GT boxes on Multi3DRefer val set.", + "bbox": [ + 78, + 476, + 467, + 521 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "benefit of the contrastive loss for all tasks, especially Nr3D.", + "bbox": [ + 78, + 550, + 465, + 565 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6.3. Analysis of M3DRef-CLIP", + "text_level": 1, + "bbox": [ + 78, + 577, + 315, + 593 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "To better study the Multi3DRefer data and understand how M3DRef-CLIP helps address the task, we break down evaluation of Multi3DRefer based on attributes provided in the description: spatial, color, texture, and shape information. For this analysis, these four splits are mutually exclusive, i.e. we only keep descriptions that describe exactly 1 attribute from the four and discard others. We compare using M3DRef with GRU with 3D PointGroup features vs our full M3DRef-CLIP model (with CLIP image and text encoders). We use the GT boxes setting and report F1 scores in Tab. 12. We observe that adding features from CLIP [47] helps identify all these attributes. We found that descriptions with spatial terms are more challenging than descriptions with texture or shape.", + "bbox": [ + 80, + 601, + 467, + 811 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "7. Conclusion", + "text_level": 1, + "bbox": [ + 80, + 829, + 192, + 844 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We present Multi3DRefer, a more realistic task of grounding a flexible number of objects in real-world 3D scenes using natural language descriptions. We designed", + "bbox": [ + 80, + 854, + 467, + 900 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "a simple and efficient data generation pipeline to create data with less human effort, by leveraging existing language data and ChatGPT. With this pipeline, we created a more diverse dataset consisting of more natural descriptions of varying granularity. We also explored an end-to-end baseline method for solving the new task, which enables the online rendering of proposal objects to generate 2D cues, it also demonstrated the usefulness of CLIP [47] and the multi-modal contrastive loss. We believe Multi3DRefer will bring more challenges and practical value in the direction of bridging 3D vision and language, especially for robotics and embodied AI tasks.", + "bbox": [ + 501, + 407, + 890, + 587 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Future Work. Our current design relies on features from the 3D object detector to capture the global context, and the 2D image encoder to capture per-object attributes. Using positional encoding could improve the ability of the model to handle spatial relations. Investigating whether positional encoding improves the model, and what kind of positional encoding works best is a great avenue for future work.", + "bbox": [ + 503, + 599, + 890, + 704 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements", + "text_level": 1, + "bbox": [ + 503, + 744, + 665, + 762 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was funded in part by a Canada CIFAR AI Chair and NSERC Discovery Grant, and enabled in part by support from the Digital Research Alliance of Canada. We thank Zhenyu (Dave) Chen for providing us with the ambiguous descriptions initially collected for ScanRefer, and Manolis Savva for proofreading and editing suggestions. We also thank Archita Srivastava, Cody Ning, and Austin T. Wang for helping to verify the Multi3DRefer dataset.", + "bbox": [ + 503, + 779, + 890, + 898 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "15233", + "bbox": [ + 480, + 946, + 517, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Ahmed Abdelreheem, Kyle Olszewski, Hsin-Ying Lee, Peter Wonka, and Panos Achlioptas. ScanEnts3D: Exploiting phrase-to-3D-object correspondences for improved visio-linguistic models in 3D scenes. arXiv preprint arXiv:2212.06250, 2022.", + "[2] Ahmed Abdelreheem, Ujjwal Upadhyay, Ivan Skorokhodov, Rawan Al Yahya, Jun Chen, and Mohamed Elhoseiny. 3DRefTransformer: Fine-grained object identification in real-world scenes using natural language. 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Springer, 2022." + ], + "bbox": [ + 501, + 92, + 890, + 188 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "15236", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/Multi3DRefer_ Grounding Text Description to Multiple 3D Objects/5fd3a41b-68c4-4dc5-a721-e608deb32134_model.json b/2023/Multi3DRefer_ Grounding Text Description to Multiple 3D Objects/5fd3a41b-68c4-4dc5-a721-e608deb32134_model.json new file mode 100644 index 0000000000000000000000000000000000000000..edde4362cf877b03725072f4b68aedd4c9df08d9 --- /dev/null +++ b/2023/Multi3DRefer_ Grounding Text Description to Multiple 3D Objects/5fd3a41b-68c4-4dc5-a721-e608deb32134_model.json @@ -0,0 +1,2919 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.147, + 0.131, + 0.825, + 0.154 + ], + "angle": 0, + "content": "Multi3DRefer: Grounding Text Description to Multiple 3D Objects" + }, + { + "type": "text", + "bbox": [ + 0.265, + 0.18, + 0.705, + 0.199 + ], + "angle": 0, + "content": "Yiming Zhang1 ZeMing Gong1 Angel X. Chang1,2" + }, + { + "type": "text", + "bbox": [ + 0.192, + 0.199, + 0.782, + 0.218 + ], + "angle": 0, + "content": "Simon Fraser University1 Alberta Machine Intelligence Institute (Amii)2" + }, + { + "type": "text", + "bbox": [ + 0.348, + 0.22, + 0.623, + 0.235 + ], + "angle": 0, + "content": "{yza440, zmgong, angelx}@sfu.ca" + }, + { + "type": "text", + "bbox": [ + 0.321, + 0.238, + 0.647, + 0.251 + ], + "angle": 0, + "content": "https://3dlg-hcvc.github.io/multi3defer/" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.318, + 0.474, + 0.592 + ], + "angle": 0, + "content": "We introduce the task of localizing a flexible number of objects in real-world 3D scenes using natural language descriptions. Existing 3D visual grounding tasks focus on localizing a unique object given a text description. However, such a strict setting is unnatural as localizing potentially multiple objects is a common need in real-world scenarios and robotic tasks (e.g., visual navigation and object rearrangement). To address this setting we propose Multi3DRefer, generalizing the ScanRefer dataset and task. Our dataset contains 61926 descriptions of 11609 objects, where zero, single or multiple target objects are referenced by each description. We also introduce a new evaluation metric and benchmark methods from prior work to enable further investigation of multi-modal 3D scene understanding. Furthermore, we develop a better baseline leveraging 2D features from CLIP by rendering object proposals online with contrastive learning, which outperforms the state of the art on the ScanRefer benchmark." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.619, + 0.21, + 0.635 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.644, + 0.473, + 0.903 + ], + "angle": 0, + "content": "There is growing interest in multi-modal methods that connect language and vision, tackling tasks such as image captioning, visual question answering, text-to-image retrieval, and generation. One fundamental task is visual grounding where natural language text queries are linked to regions of an image or 3D scene. While the problem of visual grounding has been well studied in 2D images, there are fewer datasets and methods studying the problem in 3D scenes. Being able to indicate the object that the text \"the first of four stools\" references in a 3D scene is useful for applications in robotics, AR/VR, and online 3D environments where we have access to not just a static image, but a 3D scene. Work on 3D datasets for visual grounding [7, 4] has spurred the development of methods for 3D visual grounding [41, 63, 60, 22, 21, 2, 58, 7] and the inverse task of 3D captioning [7], as well as unified methods that tackle both [8, 6, 9]." + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.287, + 0.895, + 0.452 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.559, + 0.458, + 0.837, + 0.471 + ], + "angle": 0, + "content": "This is a round stool. it is the first of four stools." + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.477, + 0.895, + 0.555 + ], + "angle": 0, + "content": "Figure 1: We introduce Multi3DRefer, a dataset and task where there are potentially multiple target objects for a given description. In ScanRefer [7] (left), the description corresponds to exactly one object (blue box), while in Multi3DRefer (right), there are multiple target objects." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.583, + 0.895, + 0.734 + ], + "angle": 0, + "content": "However, existing datasets and tasks [7, 4] are designed with the assumption that there is a unique target object when performing visual grounding in a 3D scene. This assumption makes ambiguous descriptions that may refer to multiple objects problematic (see Fig. 1). Furthermore, this explicitly discourages visual grounding methods from demonstrating generalization to similar object instances on the basis of common features of the objects (e.g., similar size, color, texture) and spatial relations between objects (e.g., first in a row left-to-right or right-to-left)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.896, + 0.903 + ], + "angle": 0, + "content": "We address these shortcomings with an enhanced dataset and task that we call Multi3DRefer where a flexible number of target objects (zero, single or multiple) in a 3D scene are localized given language descriptions. We modify and enhance language data from ScanRefer [7] and propose evaluation metrics to benchmark prior work and a CLIP-based method that we propose on the flexible number visual grounding task. In summary, we make the following contributions: 1) generalize 3D visual grounding to a flexible number of target objects given natural language descriptions. 2) create an enhanced dataset based on ScanRefer [7]" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "15225" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.184 + ], + "angle": 0, + "content": "with augmentations from ChatGPT\\(^1\\), consisting of 61926 descriptions in 800 ScanNet V2 [15] scenes. 3) benchmark three prior 3D visual grounding approaches adapted to Multi3DRefer 4) design an end-to-end approach leveraging CLIP [47] embeddings and online rendering of object proposals with contrastive learning." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.197, + 0.216, + 0.213 + ], + "angle": 0, + "content": "2. Related work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.222, + 0.47, + 0.299 + ], + "angle": 0, + "content": "In this paper, we focus on description localization where a single description may describe one or more objects in a 3D scene. Below, we review work in grounding in 2D and 3D, as well as recent work leveraging pre-trained vision-language models for 3D scene understanding." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.3, + 0.47, + 0.451 + ], + "angle": 0, + "content": "Visual grounding in 2D. A variety of datasets and methods have been proposed to investigate visual grounding tasks such as referring expressions [30, 42, 20] and phrase localization [44, 45] in 2D images. These datasets have enabled developing various visual-language grounding models [59, 61, 57, 39, 16, 37, 64]. Typically, in these datasets and tasks each phrase refers to exactly one object. A notable exception is the VGPhraseCut [54] dataset, based on Visual Genome [33] using templated phrases where each phrase is grounded to potentially multiple instance segments." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.452, + 0.471, + 0.664 + ], + "angle": 0, + "content": "Recent work in language and vision has started to tackle more flexible grounding. Kim et al. [31] noted that not all queries can be visually grounded (i.e. it is possible to have no targets) and constructed a dataset to study grounding performance when there are unanswerable queries. Kuo et al. [35] proposed a single model for referring expression comprehension, object detection, and phrase localization. While their model can handle multiple objects, the queries for multiple objects are typically short and category-based. Recent work [29, 36] reframed the problem of object detection as phrase grounding by introducing losses to align words to regions. These methods are flexible and have been used to improve both detection and visual grounding. In our work, we construct a dataset for flexible grounding in 3D." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.666, + 0.471, + 0.879 + ], + "angle": 0, + "content": "Visual grounding in 3D. Early work studied selecting the correct 3D shapes based on a text description in reference game setups [3, 53, 32], as well as learning joint language-3D embeddings for 3D text-to-shape retrieval [11, 51]. These works focused on descriptions of single objects in isolation. Moving beyond single 3D objects, researchers also studied grounding of language to objects in 3D scenes. At the scene level, ScanRefer [7] and ReferIt3D [4] introduce two datasets consisting of language descriptions of 3D objects from the real-world dataset ScanNet [15]. In detail, ReferIt3D [4] contains both template-based descriptions generated based on spatial relations between objects (Sr3D) and human-annotated fine-grained descriptions (Nr3D). They also propose two different grounding tasks," + }, + { + "type": "image_caption", + "bbox": [ + 0.504, + 0.091, + 0.551, + 0.101 + ], + "angle": 0, + "content": "Zero Target" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.104, + 0.625, + 0.179 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.513, + 0.181, + 0.616, + 0.199 + ], + "angle": 0, + "content": "This is a white cabinet. It is next to a desk." + }, + { + "type": "image_caption", + "bbox": [ + 0.636, + 0.091, + 0.732, + 0.101 + ], + "angle": 0, + "content": "Single Target (ScanRefer)" + }, + { + "type": "image", + "bbox": [ + 0.636, + 0.104, + 0.757, + 0.179 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.638, + 0.181, + 0.753, + 0.199 + ], + "angle": 0, + "content": "This is a black chair. It is in the middle of two chairs." + }, + { + "type": "image_caption", + "bbox": [ + 0.771, + 0.091, + 0.833, + 0.101 + ], + "angle": 0, + "content": "Multiple Targets" + }, + { + "type": "image", + "bbox": [ + 0.768, + 0.105, + 0.888, + 0.179 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.771, + 0.181, + 0.884, + 0.198 + ], + "angle": 0, + "content": "This is a black chair facing the door." + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.22, + 0.892, + 0.267 + ], + "angle": 0, + "content": "Figure 2: Example description-scene pairs in the Multi3DRefer dataset with zero, single, or multiple target objects. Blue boxes indicate ground truth target objects." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.295, + 0.892, + 0.37 + ], + "angle": 0, + "content": "both localizing a unique target object referred by a description. ScanRefer [7] requires both object detection and grounding, while ReferIt3D [4] focuses on discriminating a target object from multiple objects of that semantic class given ground-truth object bounding boxes." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.371, + 0.893, + 0.567 + ], + "angle": 0, + "content": "Different approaches [7, 4] have been proposed to tackle the two tasks, with models focusing on graph representations [21, 60, 17], improved handling of relations [63, 12], neurosymbolic reasoning [19], leveraging multi-view images and 2D semantics [58, 24, 22, 5], to unified models that can address both grounding and captioning [6, 8, 23, 9]. Recently, Abdelreheem et al. [1], Wu et al. [55] showed that including training on dense annotations can improve performance. Jain et al. [25] proposed to tackle object detection and visual grounding in a unified way by aligning features for text tokens with object proposals. In this work, we compare the performance of three recent models on our task Multi3DRefer with a new CLIP-based model." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.571, + 0.892, + 0.753 + ], + "angle": 0, + "content": "3D understanding using vision-language models. Large pre-trained text-vision models such as CLIP [47] and ALIGN [27] enabled work leveraging these models for 3D scene understanding. Recent work learn joint embeddings with text-image-3D representations [56, 62], used for disambiguating referring expressions [53] or text-to-shape retrieval [51]. Incorporating pre-trained 2D visual features also enabled expansion of 3D detection and instance segmentation to a larger number of categories [50], as well as tackling open vocabulary 3D detection [40, 52], and building of 3D semantic maps [26]. In our work, we show that we can leverage CLIP for improved visual grounding." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.769, + 0.707, + 0.785 + ], + "angle": 0, + "content": "3. Multi3DRefer dataset" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.795, + 0.892, + 0.901 + ], + "angle": 0, + "content": "To study our task, we build the Multi3DRefer dataset, a superset of the existing ScanRefer dataset [7] with language descriptions of varying granularities. We augment ScanRefer [7] to create a dataset with 3 types of description-scene pairs: a) Zero Target; b) Single Target; and c) Multiple Targets, indicating zero, single, or multiple target objects in the scene match the description (see Fig. 2). In addition, we use" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.356, + 0.901 + ], + "angle": 0, + "content": "1https://openai.com/blog/chatgpt/" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "15226" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.081, + 0.09, + 0.467, + 0.178 + ], + "angle": 0, + "content": "
DatasetZero TargetSingle TargetMultiple TargetsTotal
ScanRefer [7]-51583-51583
Sr3D [4]-83572-83572
Sr3D+ [4]-114532-114532
Nr3D [4]-41503-41503
Multi3DRefer6688420601317861926
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.18, + 0.468, + 0.225 + ], + "angle": 0, + "content": "Table 1: Compared to existing 3D visual grounding datasets, our Multi3DRefer dataset contains text that describes zero, single, or multiple target objects." + }, + { + "type": "image", + "bbox": [ + 0.096, + 0.24, + 0.449, + 0.568 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.578, + 0.47, + 0.653 + ], + "angle": 0, + "content": "Figure 3: Multi3DRefer data construction pipeline showing the generation process of Zero Target (red), Single Target (blue) and Multiple Target (orange) data. We use ChatGPT to add diversity to the description. All scene-description pairs are manually verified and modified if needed." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.683, + 0.468, + 0.759 + ], + "angle": 0, + "content": "ChatGPT to augment the descriptions so they are more natural and diverse (see Fig. 3 for the overall data construction pipeline). To ensure the dataset is of high quality we manually verify all generated samples. We obtain a dataset with 61926 descriptions in total (see Tabs. 1 and 3 for statistics)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.771, + 0.371, + 0.788 + ], + "angle": 0, + "content": "3.1. Adapting text for multiple targets" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.469, + 0.901 + ], + "angle": 0, + "content": "We start with scene-description pairs from ScanRefer [7] and augment the data to create samples that refer to zero or more targets. For Single Target descriptions (type b), we take the released ScanRefer dataset which consists of description-scene pairs that have been initially verified to refer to unique objects [7]. We double-checked whether these descriptions indeed refer to unique objects and we" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.288 + ], + "angle": 0, + "content": "found 9324 descriptions that are ambiguous. We use these ambiguous descriptions as an initial set of type (c) descriptions that can refer to multiple objects. For additional type (c) descriptions, we obtain from the ScanRefer authors 7741 ambiguous descriptions that can refer to multiple objects and annotate those descriptions with matching objects. To collect type (a) description (no target object) as well as more type (c) descriptions, we develop an efficient data collection pipeline consisting of two stages: 1) automated description generation; and 2) verification and modification. This pipeline maximizes the use of the existing ScanRefer dataset and reduces manual annotation. Below, we describe how we generate and verify additional data samples." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.291, + 0.892, + 0.502 + ], + "angle": 0, + "content": "Zero Target. To obtain descriptions with no target objects, we establish negative pairs of scenes with existing descriptions selected randomly from other scenes. We then manually verify that descriptions do not match any objects in the new scene. To reduce the number of description-scene pairs that need to be verified, we automatically check whether the semantic class of the target object for the description appears in the scene. Only if the semantic class appears in the scene does it need to be manually verified. Out of 6688 samples, we manually verify 5630 with 1058 automatically checked to have no matching objects. For pairs that need verification, human annotators are shown the description along with an interactive view of the scene to check that there are no matching objects." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.506, + 0.892, + 0.718 + ], + "angle": 0, + "content": "Multiple Targets. To generate descriptions with multiple targets, we start with the original description-scene pairs in the ScanRefer dataset. We then randomly select descriptions and trim the text to the first punctuation to obtain shorter, more ambiguous descriptions (e.g., \"The cabinet is white and in the back of the room. It is the one on the left.\" \\(\\rightarrow\\) \"The cabinet is white and in the back of the room\"). Note that descriptions in which the semantic class of the target object only has a unique object in the scene are skipped. The trimmed text and scene pairs are sent to the annotation interface. This time, annotators are asked to select all eligible objects of a description in a 3D interactive scene mesh. Annotators are also asked to modify trimmed descriptions to fix errors and increase diversity (see Fig. 4 for examples)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.729, + 0.75, + 0.745 + ], + "angle": 0, + "content": "3.2. Rephrasing using ChatGPT" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.753, + 0.891, + 0.798 + ], + "angle": 0, + "content": "To increase description diversity we use the ChatGPT model text-davinci-002-render for sentence rephrasing. We provide ChatGPT with the following prompts:" + }, + { + "type": "text", + "bbox": [ + 0.508, + 0.799, + 0.891, + 0.822 + ], + "angle": 0, + "content": "1. I will give you a sentence describing an object, please help me polish it and keep its meaning." + }, + { + "type": "text", + "bbox": [ + 0.508, + 0.823, + 0.89, + 0.834 + ], + "angle": 0, + "content": "2. Help me reword a sentence to a different format but keep its meaning." + }, + { + "type": "text", + "bbox": [ + 0.508, + 0.834, + 0.799, + 0.845 + ], + "angle": 0, + "content": "3. Help me reword a sentence to make it more natural." + }, + { + "type": "text", + "bbox": [ + 0.508, + 0.846, + 0.891, + 0.87 + ], + "angle": 0, + "content": "4. Help me reword a sentence describing an object, you should describe the colors and the spatial information in a different way." + }, + { + "type": "text", + "bbox": [ + 0.508, + 0.873, + 0.891, + 0.9 + ], + "angle": 0, + "content": "5. Help me reword a sentence to an interesting format, you should keep its meaning." + }, + { + "type": "list", + "bbox": [ + 0.508, + 0.799, + 0.891, + 0.9 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "15227" + } + ], + [ + { + "type": "image_caption", + "bbox": [ + 0.109, + 0.103, + 0.153, + 0.11 + ], + "angle": 0, + "content": "ScanRefer" + }, + { + "type": "image_caption", + "bbox": [ + 0.11, + 0.111, + 0.27, + 0.132 + ], + "angle": 0, + "content": "This is a white kitchen cabinet located to the left of the over and stove unit. It has four drawers with silver handles." + }, + { + "type": "image_caption", + "bbox": [ + 0.278, + 0.092, + 0.333, + 0.099 + ], + "angle": 0, + "content": "Multi3DRefer" + }, + { + "type": "image_caption", + "bbox": [ + 0.278, + 0.1, + 0.435, + 0.113 + ], + "angle": 0, + "content": "T: This is a white kitchen cabinet located to the left of the over and stove unit." + }, + { + "type": "image_caption", + "bbox": [ + 0.278, + 0.114, + 0.434, + 0.127 + ], + "angle": 0, + "content": "M: This is a white kitchen cabinet located near the over and stove unit." + }, + { + "type": "image_caption", + "bbox": [ + 0.278, + 0.128, + 0.432, + 0.141 + ], + "angle": 0, + "content": "R: A white kitchen cabinet is situated near the oven and stove unit." + }, + { + "type": "image", + "bbox": [ + 0.109, + 0.142, + 0.273, + 0.248 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.278, + 0.143, + 0.442, + 0.248 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.108, + 0.259, + 0.151, + 0.266 + ], + "angle": 0, + "content": "ScanRefer" + }, + { + "type": "image_caption", + "bbox": [ + 0.108, + 0.267, + 0.263, + 0.288 + ], + "angle": 0, + "content": "There is a rectangular blue pillow with colorful decorations. It is on a larger cushion in front of the window by the side of the room." + }, + { + "type": "image_caption", + "bbox": [ + 0.278, + 0.259, + 0.434, + 0.306 + ], + "angle": 0, + "content": "M: There is a rectangular pillow with colorful decorations. It is on a larger cushion in front of the window by the side of the room. R: A rectangular pillow, adorned with colorful decorations, rests upon a larger cushion positioned by the side of the room, right in front of the window." + }, + { + "type": "image", + "bbox": [ + 0.11, + 0.303, + 0.273, + 0.408 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.278, + 0.304, + 0.442, + 0.408 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.109, + 0.412, + 0.153, + 0.419 + ], + "angle": 0, + "content": "ScanRefer" + }, + { + "type": "image_caption", + "bbox": [ + 0.11, + 0.421, + 0.265, + 0.434 + ], + "angle": 0, + "content": "This is a green patterned chair. It is at a brown table." + }, + { + "type": "image_caption", + "bbox": [ + 0.278, + 0.412, + 0.331, + 0.419 + ], + "angle": 0, + "content": "Multi3DRefer" + }, + { + "type": "image_caption", + "bbox": [ + 0.278, + 0.421, + 0.434, + 0.434 + ], + "angle": 0, + "content": "R: A green patterned chair sits beside a brown table." + }, + { + "type": "image", + "bbox": [ + 0.11, + 0.434, + 0.273, + 0.54 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.278, + 0.434, + 0.442, + 0.54 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.551, + 0.47, + 0.655 + ], + "angle": 0, + "content": "Figure 4: Examples of generated revised descriptions of multiple targets for the Multi3DRefer dataset where we trim (T) to create more ambiguous descriptions, modify (M) by human, and reword (R) using ChatGPT. All descriptions are verified by annotators (see bounding boxes for target objects). Note that the reworded (R) descriptions provide more variation in sentence structure." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.674, + 0.468, + 0.726 + ], + "angle": 0, + "content": "
Unique wordsTotal wordsAvg. description length
Original5067101619016.4
Rephrased707793693515.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.735, + 0.47, + 0.797 + ], + "angle": 0, + "content": "Table 2: Comparison of Multi3DRefer language data before and after ChatGPT rephrasing. We count the number of unique words, total words, and the average description length, excluding punctuation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.827, + 0.468, + 0.887 + ], + "angle": 0, + "content": "Tab. 2 shows statistics comparing the descriptions before and after rephrasing. We see a richer vocabulary but shorter descriptions after ChatGPT rephrasing. Below we provide examples of the original (O) and reworded (R) text:" + }, + { + "type": "text", + "bbox": [ + 0.085, + 0.888, + 0.469, + 0.9 + ], + "angle": 0, + "content": "O: The table is a round table. It is located between two chairs to the" + }, + { + "type": "table", + "bbox": [ + 0.505, + 0.089, + 0.89, + 0.188 + ], + "angle": 0, + "content": "
SpatialColorTextureShapeTotal
ScanRefer [7]511173469258641741651583
Nr3D [4]3971111939526856841503
Sr3D [4]835726254064883572
Sr3D+ [4]11453286660744114532
Multi3DRefer600284130771211969261926
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.198, + 0.892, + 0.228 + ], + "angle": 0, + "content": "Table 3: Breakdown of spatial, color, texture, and shape information in object descriptions from different datasets." + }, + { + "type": "text", + "bbox": [ + 0.526, + 0.267, + 0.718, + 0.279 + ], + "angle": 0, + "content": "right, and two chairs to the left of it." + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.28, + 0.891, + 0.303 + ], + "angle": 0, + "content": "R: The round table is situated between two chairs to its right and two chairs to its left." + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.308, + 0.891, + 0.331 + ], + "angle": 0, + "content": "O: This is a table on the wall in the room. It is next to the window and a few lined-up chairs." + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.332, + 0.89, + 0.356 + ], + "angle": 0, + "content": "R: A wall-mounted table resides coaxily beside a window in the room, accompanied by a row of orderly chairs." + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.361, + 0.847, + 0.372 + ], + "angle": 0, + "content": "O: A sink on the vanity. It is to the right of the vacuum cleaners." + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.374, + 0.884, + 0.385 + ], + "angle": 0, + "content": "R: The sink is located on the vanity to the right of the vacuum cleaners." + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.389, + 0.881, + 0.401 + ], + "angle": 0, + "content": "O: This is a white kitchen cabinet located near the over and stove unit." + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.405, + 0.858, + 0.416 + ], + "angle": 0, + "content": "R: A white kitchen cabinet is situated near the oven and stove unit" + }, + { + "type": "list", + "bbox": [ + 0.509, + 0.267, + 0.891, + 0.416 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.422, + 0.892, + 0.468 + ], + "angle": 0, + "content": "The rephrased text preserves the original meaning while being more natural. In addition, ChatGPT automatically corrects typos (e.g., over to oven in the last example)." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.49, + 0.625, + 0.505 + ], + "angle": 0, + "content": "3.3. Verification" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.518, + 0.892, + 0.713 + ], + "angle": 0, + "content": "After we obtain a set of ChatGPT reworded descriptions, we manually verify the descriptions are well-written and that the object(s) matched in the scene are accurate. We create a web interface for verifiers to check whether the description matches the identified target objects (see supplement for details). The web interface shows the description together with an interactive 3D view of the scene and the target objects. The verifiers check if the description matches the target objects and only the target objects, or modify the list of target objects (by selecting appropriate objects), or improve the description to fix typos and ambiguities. The verification was performed by 5 students over a period of one month." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.738, + 0.665, + 0.753 + ], + "angle": 0, + "content": "3.4. Dataset statistics" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In total, our dataset consists of 61926 language descriptions, with 51583 directly obtained from ScanRefer [7], of which 6688 descriptions match zero-targets and 13178 match multiple. For Multiple Targets, the scenes are typically offices or meeting rooms with many chairs and tables. See Tab. 1 for a comparison of our final dataset against prior datasets. We also provide annotations for each description as to whether it refers to spatial, color, texture, or shape attributes (see Tab. 3)." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15228" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.089, + 0.891, + 0.325 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.336, + 0.895, + 0.43 + ], + "angle": 0, + "content": "Figure 5: Our M3DRef-CLIP end-to-end architecture. Given a scene point cloud and a text description with \\( L \\) tokens (we pad shorter descriptions and truncate longer ones), the detector first predicts \\( M \\) object proposals and their 3D features. Then an online renderer renders \\( N \\)-view images for each proposal and feeds them into the image encoder to get 2D features. A transformer-based module then fuses both language features and \\( 2\\mathrm{D} + 3\\mathrm{D} \\) object features and outputs scores indicating the match of each object to the description. We use PointGroup [28] to detect and segment the objects in 3D and select CLIP [47] + MLPs as the language and image encoder. A contrastive loss is applied between sentence features and object features." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.453, + 0.143, + 0.468 + ], + "angle": 0, + "content": "4. Task" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.485, + 0.473, + 0.668 + ], + "angle": 0, + "content": "In the Multi3DRefer task, we are given as input a 3D real-world scene represented as a point cloud \\( P \\in \\mathbb{R}^{N \\times (3 + C)} \\) and a free-form language description with a variable number \\( M \\in \\mathbb{N} \\) of referred objects, where \\( N, C \\) are the number of points and the number of point feature channels, respectively. The goal is to predict axis-aligned bounding boxes for all \\( M \\) objects that match the description. Compared to prior work, the difficulty of our task is that the number of referred objects is flexible, i.e., a description can refer to not only one or multiple target objects but also no objects. Predicting too many or too few target objects are both penalized by our evaluation metrics." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.674, + 0.473, + 0.902 + ], + "angle": 0, + "content": "Evaluation metrics. To evaluate grounding for a flexible number of target objects, we measure the F1 score at the intersection over union (IoU) thresholds of \\(\\tau_{\\mathrm{eval}} = 0.25\\) and 0.5 (F1@0.25 and F1@0.5). To investigate model performance for different scenarios, we consider the following 5 cases: a) zero target w/o distractors of the same semantic class; b) zero target w/ distractors; c) single target w/o distractors; d) single target w/ distractors; and e) multiple targets. Note that c) and d) correspond to the \"unique\" and \"multiple\" cases in ScanRefer [7]. In addition, a) and c) are easier cases where there are zero or a unique target object of its semantic class in a scene, while b) and d) are more difficult cases containing one or multiple target objects of the same semantic class in a scene. We also report the micro-average of the 5 cases as an overall score." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.454, + 0.895, + 0.545 + ], + "angle": 0, + "content": "During evaluations, we first calculate per-pair IoUs between ground truth and predicted bounding boxes in a scene, and then apply the Hungarian algorithm [34] to get an optimal one-to-one matching between predicted and GT bounding boxes. To get the maximum matched IoU, we use the following cost function:" + }, + { + "type": "equation", + "bbox": [ + 0.545, + 0.547, + 0.847, + 0.564 + ], + "angle": 0, + "content": "\\[\n\\operatorname {C o s t} (i, j) = - \\operatorname {I o U} (i, j) \\text {f o r} i, j \\in \\{1 \\dots N \\}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.565, + 0.895, + 0.643 + ], + "angle": 0, + "content": "where \\(N = \\max (\\# Predictions, \\# GTs)\\). After obtaining the optimal match, we take pairs with IoUs higher than \\(\\tau_{\\mathrm{eval}}\\) to be True Positives (TP). We treat the Zero Target (ZT) case as a special case where recall is always set to 1, and precision is set to 1 if there is no prediction or 0 otherwise." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.655, + 0.593, + 0.67 + ], + "angle": 0, + "content": "5. Method" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.681, + 0.895, + 0.879 + ], + "angle": 0, + "content": "We propose M3DRef-CLIP, a CLIP-based approach and compare to three recent approaches: 3DVG-Transformer [63], 3DJCG [6] and D3Net [8]. We selected these methods as they were among the top performers on the ScanRefer [7] benchmark with available open-source code. Note that 3DJCG [6] and D3Net [8] are unified models, which can do both grounding and captioning tasks. All four models are two-stage approaches, where a 3D object detector first identifies a set of bounding box candidates, and a disambiguation module then selects the target bounding box. In the original ScanRefer setting, the three compared models are trained using a cross-entropy loss \\( L_{\\mathrm{ref}} \\) where the predicted bounding box has the highest IoU (\\( > \\tau_{\\mathrm{train}} \\)) with" + }, + { + "type": "page_footnote", + "bbox": [ + 0.516, + 0.887, + 0.744, + 0.9 + ], + "angle": 0, + "content": "\\(^{2}\\)kaldir.vc.in.tum.de/scanrefer_benchmark" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "15229" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.138 + ], + "angle": 0, + "content": "the GT bounding box as the target bounding box to calculate the loss. For our task, we use a binary cross-entropy loss for \\( L_{\\mathrm{ref}} \\) as our problem is a multi-label task (vs classification)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.149, + 0.231, + 0.163 + ], + "angle": 0, + "content": "5.1. M3DRef-CLIP" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.173, + 0.47, + 0.37 + ], + "angle": 0, + "content": "M3DRef-CLIP follows the two-stage architecture with PointGroup [28] as the detector, CLIP [47] as the text encoder and a transformer-based fusion module (see Fig. 5). We use PointGroup [28] to obtain object proposals along with their 3D features \\(\\mathbf{F}^{3\\mathrm{d}} \\in R^{32}\\). The output object proposals are fed into an online object renderer, which renders multi-view 2D images for each object proposal. We use CLIP [47] to encode the images and use an MLP to project the average of the output 2D image features to obtain \\(\\mathbf{F}^{2\\mathrm{d}} \\in \\mathbb{R}^{128}\\). The 2D and 3D features are concatenated to form and passed through a 1D convolution (that projects the combined 160-dim features down to 128-dim) to obtain the final visual features \\(\\mathbf{F}^{\\mathrm{obj}} \\in \\mathbb{R}^{128}\\) for an object proposal:" + }, + { + "type": "equation", + "bbox": [ + 0.09, + 0.372, + 0.455, + 0.403 + ], + "angle": 0, + "content": "\\[\n\\mathbf {F} ^ {\\mathrm {o b j}} = \\operatorname {c o n v} _ {\\mathrm {l d}} ([ \\mathbf {F} ^ {\\mathrm {3 d}}; \\mathbf {F} ^ {\\mathrm {2 d}} ]), \\quad \\mathbf {F} ^ {\\mathrm {2 d}} = \\frac {\\operatorname {M L P} (\\sum_ {i = 1} ^ {N} \\mathbf {F} _ {i} ^ {\\mathrm {2 d}})}{N}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.403, + 0.469, + 0.493 + ], + "angle": 0, + "content": "We use the CLIP text encoder with an MLP to obtain both 128-dim token-level and sentence embeddings. We use a transformer-based fusion module to combine object features and token-level embeddings and output confidence scores for each proposal. To improve the training, we apply a contrastive loss between sentence and object features." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.506, + 0.218, + 0.52 + ], + "angle": 0, + "content": "5.2. Loss function" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.531, + 0.47, + 0.74 + ], + "angle": 0, + "content": "We train the network end-to-end with the total loss \\( L = L_{\\mathrm{det}} + L_c + L_{\\mathrm{ref}} \\) consisting of the detection loss \\( L_{\\mathrm{det}} \\), contrastive loss \\( L_{\\mathrm{c}} \\), and the reference loss \\( L_{\\mathrm{ref}} \\). The detection loss \\( L_{\\mathrm{det}} \\) is introduced in PointGroup [28] and consists of four parts: 1) cross-entropy loss for supervising per-point semantic class prediction; 2) \\( L_1 \\) loss for supervising perpoint offset vector towards object centers; 3) directional loss formed as a mean of minus cosine similarities for further constraining the direction of per-point offset vectors; 4) binary cross-entropy loss for supervising per-point objectness confidence score. To help learn better multi-modal embeddings, we introduce a symmetric contrastive loss \\( L_{c} \\) [47], which can handle a flexible number of target objects as shown below:" + }, + { + "type": "equation", + "bbox": [ + 0.13, + 0.741, + 0.415, + 0.775 + ], + "angle": 0, + "content": "\\[\nL _ {\\mathrm {c}} ^ {O \\rightarrow S} = - \\log \\frac {\\exp (\\cos (\\bar {O} _ {i} , S _ {i}) / \\tau)}{\\sum_ {i = 1} ^ {n} \\exp (\\cos (\\bar {O} _ {i} , S _ {j}) / \\tau)}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.13, + 0.776, + 0.415, + 0.809 + ], + "angle": 0, + "content": "\\[\nL _ {\\mathrm {c}} ^ {S \\rightarrow O} = - \\log \\frac {\\exp (\\cos (S _ {i} , \\bar {O} _ {i}) / \\tau)}{\\sum_ {i = 1} ^ {n} \\exp (\\cos (S _ {i} , \\bar {O} _ {j}) / \\tau)}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.469, + 0.901 + ], + "angle": 0, + "content": "where \\(S\\) is sentence features, \\(\\bar{O}\\) is the mean of object features of all target objects paired with a description, and \\(\\tau\\) is a temperature parameter. Finally, the reference loss \\(L_{\\mathrm{ref}}\\) supervises the matching module to select objects satisfying the description. We use the multi-class cross-entropy loss as \\(L_{\\mathrm{ref}}\\) for experiments on ScanRefer [7], Nr3D [4] and" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "Multi3DRefer (ST) where each description only refers to a single target object. For experiments on Multi3DRefer, \\( L_{\\mathrm{ref}} \\) is a sum of binary cross-entropy losses over detected objects." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.155, + 0.892, + 0.216 + ], + "angle": 0, + "content": "Training. To set up positive (i.e. valid target bounding boxes) and negative instances between the GT bounding boxes and proposed bounding boxes, we use two strategies (see supplement for detailed comparisons):" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.218, + 0.892, + 0.264 + ], + "angle": 0, + "content": "All All predicted bounding boxes with IoU higher than the threshold \\(\\tau_{\\mathrm{train}}\\) with GT bounding boxes are considered target bounding boxes." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.267, + 0.892, + 0.327 + ], + "angle": 0, + "content": "Hungarian We apply the Hungarian algorithm [34] to do bipartite matching, which ensures an optimal solution. We use the same IoU threshold \\(\\tau_{\\mathrm{train}}\\) to filter prediction-GT bounding box pairs." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.33, + 0.892, + 0.392 + ], + "angle": 0, + "content": "Inference. At inference time, we take all bounding boxes with predicted scores above the threshold \\(\\tau_{\\mathrm{pred}}\\) as positives (predicted target bounding boxes for the description). See the supplement for comparisons of different \\(\\tau_{\\mathrm{pred}}\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.406, + 0.633, + 0.422 + ], + "angle": 0, + "content": "6. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.432, + 0.892, + 0.476 + ], + "angle": 0, + "content": "We conduct experiments on both ScanRefer [7] and Multi3DRefer datasets and consider two setups: grounding objects with GT and predicted bounding boxes." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.479, + 0.892, + 0.631 + ], + "angle": 0, + "content": "GT bounding boxes. For M3DRef-CLIP and D3Net [8], we input the complete scene and apply GT point masks for each object to get GT bounding boxes and masked features from the pre-trained detector (PointGroup for both D3Net and our M3DRef-CLIP). For 3DVG-Trans [63] and 3DJCG [6], we use their original GT setting following the method proposed by ReferIt3D [4]. Single input objects are first extracted from the scene using the GT masks and PointNet++ [46] is used for obtaining the object features. For all methods, we disable the \\(L_{det}\\) loss when using GT boxes." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.633, + 0.892, + 0.678 + ], + "angle": 0, + "content": "Predicted bounding boxes. We use the original detector design of each method to predict bounding boxes and extract features." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.689, + 0.715, + 0.705 + ], + "angle": 0, + "content": "6.1. Implementation details" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.712, + 0.892, + 0.865 + ], + "angle": 0, + "content": "We implement M3DRef-CLIP using PyTorch Lightning3 and PyTorch3D [48]. We train the model end-to-end on a single NVIDIA RTX A5000 with a batch size of 4, using the AdamW optimizer [38] with a learning rate of \\(5e^{-4}\\). We use a re-implementation of PointGroup4 with the Minkowski Engine [14]. Following D3Net [8], we pretrain our PointGroup module on all ScanNet v2 training scans with the 18 ScanRefer categories. We take point coordinates, point normals and per-point multi-view features \\(P \\in \\mathbb{R}^{N \\times (3 + 3 + 128)}\\) as the input. For data augmentation, we randomly apply" + }, + { + "type": "page_footnote", + "bbox": [ + 0.518, + 0.875, + 0.66, + 0.888 + ], + "angle": 0, + "content": "\\(^{3}\\)www.pytorchlightning.ai" + }, + { + "type": "page_footnote", + "bbox": [ + 0.518, + 0.888, + 0.729, + 0.901 + ], + "angle": 0, + "content": "4https://github.com/3dlg-hcvc/minsu3d" + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.875, + 0.729, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15230" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.081, + 0.089, + 0.891, + 0.148 + ], + "angle": 0, + "content": "
ZT w/o DistractorsZT w DistractorsST w/o DistractorsST w/ DistractorsMultiple Targets
TrainValTestTotalTrainValTestTotalTrainValTestTotalTrainValTestTotalTrainValTestTotal
ScanRefer [7]--------85002297120111998281657211420939585----
Multi3DRefer2702528596382621603783242862719820991106104032204053584259316579738275768313178
" + }, + { + "type": "table_caption", + "bbox": [ + 0.095, + 0.159, + 0.872, + 0.174 + ], + "angle": 0, + "content": "Table 4: Breakdown of different datasets in 5 scenarios. ZT and ST denote Zero Target and Single Target, respectively." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.198, + 0.467, + 0.412 + ], + "angle": 0, + "content": "
Acc@0.5 on ValAcc@0.5 on Test
UniqueMultipleAllUniqueMultipleAll
3DVG-Trans+ [63]62.030.336.457.931.037.0
InstanceRefer [60]66.824.832.966.726.935.8
FFL-3DOG [17]67.925.734.0---
SAT [58]50.825.230.1---
3D-SPS [41]66.729.837.0---
MVT [22]66.525.333.3---
BUTD-DETR [25]66.335.139.8---
D3Net (G) [8]70.427.135.665.827.336.0
D3Net* [8]72.030.137.968.430.739.2
3DJCG (G) [6]64.530.336.9---
3DJCG* [6]64.330.837.360.631.237.8
HAM [10]67.934.040.663.733.240.1
UniT3D (G) [9]74.827.636.5---
UniT3D* [9]73.131.139.1---
M3DRef-CLIP77.236.844.770.938.145.5
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.077, + 0.424, + 0.469, + 0.484 + ], + "angle": 0, + "content": "Table 5: For unified models [8, 6, 9], we report both the grounding-only (G) performance as well as their best performance. We use * to indicate joint grounding and captioning models trained with extra data." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.511, + 0.469, + 0.601 + ], + "angle": 0, + "content": "coordinate jitter, x-axis flipping and rotation around the z-axis. We freeze a pre-trained CLIP with ViT-B/32 and only train additional MLPs. For encoding the text with CLIP, we follow CLIP and tokenizer with a lower-cased BPE, and [SOS] and [EOS] tokens added (the output corresponding to [EOS] is used as the sentence representation)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.603, + 0.469, + 0.739 + ], + "angle": 0, + "content": "Object renderer. For each object proposal, we render 3 views horizontally spaced 120 degrees apart, at a distance of \\(1\\mathrm{m}\\), with elevation angle of \\(45^{\\circ}\\). We crop coordinates and colors from the input scene point cloud using predicted bounding boxes and set point radius to \\(2.5\\mathrm{cm}\\) and image size to \\(224^2\\). We use CUDA to batch index scene point clouds and crop in parallel, and render the batches sparsely to avoid padding overhead. Rendering is implemented with PyTorch3D [48] and executed on the GPU." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.749, + 0.17, + 0.763 + ], + "angle": 0, + "content": "6.2. Results" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.772, + 0.347, + 0.786 + ], + "angle": 0, + "content": "6.2.1 Performance of M3DRef-CLIP" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.469, + 0.901 + ], + "angle": 0, + "content": "We first validate the performance of M3DRef-CLIP on ScanRefer (see Tab. 5) and Nr3D [4] (see Tab. 6) datasets and compare it against recent models. On ScanRefer, our method outperforms all prior works including those joint models leveraging extra input data by a large margin on both val set and test set (online benchmarking). In our ablation study, we find that the use of the CLIP text encoder is a key" + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.198, + 0.89, + 0.376 + ], + "angle": 0, + "content": "
EasyHardView-DepView-IndepAll
3DVG-Trans [63]48.534.834.843.740.8
InstanceRefer [60]46.031.834.541.938.8
FFL-3DOG [17]48.235.037.144.741.7
TransRefer3D [18]48.536.036.544.942.1
SAT [58]56.342.446.950.449.2
3D-SPS [41]58.145.148.053.251.5
MVT [22]61.349.154.355.455.4
BUTD-DETR [25]60.748.446.058.054.6
HAM [10]54.341.941.551.448.2
LanguageRefer [49]51.036.641.745.043.9
LAR [5]56.141.846.750.248.9
M3DRef-CLIP55.643.442.352.949.4
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.5, + 0.383, + 0.892, + 0.412 + ], + "angle": 0, + "content": "Table 6: Comparison of methods on Nr3D [4] val set with GT boxes." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.429, + 0.89, + 0.492 + ], + "angle": 0, + "content": "
Training DatasetAcc on ScanReferAcc on Multi3DRefer (ST)
UniqueMultipleAllUniqueMultipleAll
ScanRefer [7]89.349.156.979.548.257.0
Multi3DRefer (ST)88.546.955.086.352.962.3
Multi3DRefer (ST) + ScanRefer90.851.058.788.056.765.5
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.499, + 0.502, + 0.892, + 0.548 + ], + "angle": 0, + "content": "Table 7: We compare results of training M3DRef with GT boxes on different datasets' val set. We only use the Single Target (ST) case in Multi3DRefer dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.577, + 0.892, + 0.666 + ], + "angle": 0, + "content": "factor to the strong performance of our model on ScanRefer. Another key factor is the use of a strong 3D object instance segmentation network (PointGroup) as our object detector. For instance, the PointGroup-based methods [8, 9] readily outperform VoteNet-based methods [63, 6] on the unique subset of ScanRefer." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.668, + 0.892, + 0.744 + ], + "angle": 0, + "content": "For Nr3D [4], we achieve comparable but less competitive results because of our weaker ground-truth box encoder. Note that SAT [58] and MVT [22] also leverage 2D images but render them offline. Overall, using additional 2D image information is helpful for two-stage methods." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.767, + 0.652, + 0.781 + ], + "angle": 0, + "content": "6.2.2 Multi3DRefer" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.792, + 0.892, + 0.868 + ], + "angle": 0, + "content": "We split the Multi3DRefer data into train/val/test by scene following the ScanRefer split, resulting in a rough split ratio of 7:2:1 for the scene-description pairs. See Tab. 4 for statistics, including the number of descriptions with zero, single, or multiple targets." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Usefulness of Multi3DRefer dataset. To study the usefulness of the Multi3DRefer dataset, we compare the perfor" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "15231" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.081, + 0.089, + 0.891, + 0.186 + ], + "angle": 0, + "content": "
F1 (GT boxes)F1@0.5 (Pred boxes)
ZT w/o DZT w/ DST w/o DST w/ DMTAllZT w/o DZT w/ DST w/o DST w/ DMTAll
3DVG-Trans+ [63]45.314.358.935.254.244.187.145.827.516.726.525.5
D3Net (Grounding) [8]71.620.478.244.461.655.581.632.538.623.335.032.2
3DJCG (Grounding) [6]47.916.459.135.554.244.694.166.926.016.726.226.6
M3DRef-CLIP74.229.484.152.367.262.381.839.447.830.637.938.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.083, + 0.189, + 0.885, + 0.205 + ], + "angle": 0, + "content": "Table 8: Comparison of different methods on Multi3DRefer. Our M3DRef-CLIP outperforms prior work on most metrics." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.228, + 0.468, + 0.292 + ], + "angle": 0, + "content": "
Eval DatasetAcc (GT boxes)Acc@0.5 (Pred boxes)
UniqueMultipleAllUniqueMultipleAll
Multi3DRefer (ST)86.951.561.567.340.147.7
ScanRefer [7]88.046.154.373.534.341.9
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.293, + 0.468, + 0.324 + ], + "angle": 0, + "content": "Table 9: M3DRef-CLIP evaluated on Multi3DRefer (ST) and ScanRefer with both GT and predicted bounding boxes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.363, + 0.47, + 0.515 + ], + "angle": 0, + "content": "mance of training M3DRef-CLIP with the original ScanRefer data and with our Multi3DRefer data for the Single Target (ST) case. We evaluate on both ScanRefer and Multi3DRefer (ST), using GT bounding boxes. Tab. 7 shows that our reworded data can improve performance on ScanRefer. Prior work has also shown that incorporating additional labeled data can help, but they typically used either a captioning model [8, 9], mixed additional annotated data [58], or used dense annotations [1]. We show that simple rewordings (without accessing the images) also help." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.52, + 0.47, + 0.611 + ], + "angle": 0, + "content": "We also evaluate M3DRef-CLIP trained on Multi3DRefer using ScanRefer's task setting (Tab. 9) of predicted objects. We observe that the model trained on Multi3DRefer data and task achieves similar performance to the model trained on ScanRefer data and task, which illustrates the generalization of Multi3DRefer." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.62, + 0.47, + 0.741 + ], + "angle": 0, + "content": "Evaluation on Multi3DRefer. We compare four models on the Multi3DRefer dataset using both ground-truth and predicted boxes (Tab. 8). In our experiments, we focus on two-stage methods that perform well on ScanRefer. We adapt the code of 3DVG-Trans, 3DJCG and D3Net to our task. For 3DVG-Trans, we use the enhanced version 3DVG-Trans+ provided by the authors. We only train and evaluate the grounding model of 3DJCG and D3Net." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.747, + 0.47, + 0.854 + ], + "angle": 0, + "content": "To analyze the performance of the models, we break down the zero (ZT) and single-target (ST) case to without and with distractors (D) of the same class. Overall, having distractors is more challenging. We note that M3DRef-CLIP outperforms the other methods on Multi3DRefer, and that 3DJCG is better at handling the ZT case with predicted boxes. Fig. 6 shows qualitative results." + }, + { + "type": "image", + "bbox": [ + 0.507, + 0.228, + 0.889, + 0.529 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.535, + 0.892, + 0.596 + ], + "angle": 0, + "content": "Figure 6: Qualitative results of D3Net [8] versus M3DRef-CLIP on Multi3DRefer using predicted boxes. Blue boxes indicate GT, green boxes are true positives with IoU threshold \\(\\tau_{\\mathrm{pred}} > 0.5\\). Red boxes are false positives." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.625, + 0.667, + 0.64 + ], + "angle": 0, + "content": "6.2.3 Ablation studies" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.655, + 0.892, + 0.852 + ], + "angle": 0, + "content": "Does CLIP help? We experiment with just using pure CLIP for both text and image encoding vs combining CLIP and 3D features (see Tab. 10). We also report results using a GRU [13]-based text encoder with GloVE [43] embedding, as used in prior work [7, 63, 8]. Although our GRU and 3D variants are similar at a high level to the grounding model of D3Net (which also used GRU and PointGroup with a transformer-based fusion module), we outperform the D3Net grounding module. Tab. 10 shows that using the CLIP text encoder improves performance, and combining CLIP and 3D features yields the best performance. The CLIP image encoder by itself underperforms the 3D features, showing the usefulness of 3D information." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Does contrastive learning help? Tab. 11 reports the performance of M3DRef with and without contrastive learning on ScanRefer, Nr3D [4] and Multi3DRefer. We observe the" + }, + { + "type": "page_footnote", + "bbox": [ + 0.095, + 0.887, + 0.313, + 0.9 + ], + "angle": 0, + "content": "5 github.com/zlcccc/3DVG-Transformer" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15232" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.12, + 0.089, + 0.842, + 0.238 + ], + "angle": 0, + "content": "
TextVisionAcc (ScanRefer)F1 (Multi3DRefer)
UniqMultAllZT w/o DZT w/ DST w/o DST w/ DMTAll
GTGRU3D88.843.552.370.127.381.649.363.359.1
CLIPCLIP78.942.149.358.327.874.144.761.054.4
CLIP3D+CLIP89.349.156.974.229.484.152.367.262.3
PredGRU3D72.232.840.478.842.149.428.537.037.4
CLIPCLIP71.231.239.064.436.042.925.733.733.1
CLIP3D+CLIP77.236.844.781.839.447.830.637.938.4
" + }, + { + "type": "table_caption", + "bbox": [ + 0.08, + 0.24, + 0.892, + 0.284 + ], + "angle": 0, + "content": "Table 10: Ablations in training M3DRef using different feature embeddings and ground-truth boxes (top rows) and predicted boxes (bottom rows). The combination of CLIP [47] and 3D features achieves the best performance. We use PointGroup [28] for our 3D object detector and feature extractor." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.298, + 0.89, + 0.363 + ], + "angle": 0, + "content": "
ScanReferNr3DMulti3DRefer
UniqueMultipleAllEasyHardView-DepView-IndepAllZT w/o DZT w/ DST w/o DST w/ DMTAll
w/ contrastive89.349.156.955.643.442.352.949.474.229.484.152.367.262.3
w/o contrastive89.647.255.450.935.337.645.642.967.423.883.452.066.561.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.199, + 0.365, + 0.772, + 0.38 + ], + "angle": 0, + "content": "Table 11: Ablation of M3DRef-CLIP with and without contrastive loss using GT boxes." + }, + { + "type": "table", + "bbox": [ + 0.084, + 0.405, + 0.46, + 0.466 + ], + "angle": 0, + "content": "
TextVisionSpatialColorTextureShape
GRU3D55.867.776.477.8
CLIP3D+CLIP58.871.979.482.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.08, + 0.477, + 0.468, + 0.522 + ], + "angle": 0, + "content": "Table 12: Breakdown of M3DRef performance (with GRU vs CLIP) on descriptions with different attributes. We report F1 scores with GT boxes on Multi3DRefer val set." + }, + { + "type": "text", + "bbox": [ + 0.08, + 0.551, + 0.467, + 0.566 + ], + "angle": 0, + "content": "benefit of the contrastive loss for all tasks, especially Nr3D." + }, + { + "type": "title", + "bbox": [ + 0.08, + 0.578, + 0.316, + 0.594 + ], + "angle": 0, + "content": "6.3. Analysis of M3DRef-CLIP" + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.602, + 0.468, + 0.813 + ], + "angle": 0, + "content": "To better study the Multi3DRefer data and understand how M3DRef-CLIP helps address the task, we break down evaluation of Multi3DRefer based on attributes provided in the description: spatial, color, texture, and shape information. For this analysis, these four splits are mutually exclusive, i.e. we only keep descriptions that describe exactly 1 attribute from the four and discard others. We compare using M3DRef with GRU with 3D PointGroup features vs our full M3DRef-CLIP model (with CLIP image and text encoders). We use the GT boxes setting and report F1 scores in Tab. 12. We observe that adding features from CLIP [47] helps identify all these attributes. We found that descriptions with spatial terms are more challenging than descriptions with texture or shape." + }, + { + "type": "title", + "bbox": [ + 0.081, + 0.83, + 0.194, + 0.845 + ], + "angle": 0, + "content": "7. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.856, + 0.468, + 0.901 + ], + "angle": 0, + "content": "We present Multi3DRefer, a more realistic task of grounding a flexible number of objects in real-world 3D scenes using natural language descriptions. We designed" + }, + { + "type": "text", + "bbox": [ + 0.503, + 0.408, + 0.891, + 0.588 + ], + "angle": 0, + "content": "a simple and efficient data generation pipeline to create data with less human effort, by leveraging existing language data and ChatGPT. With this pipeline, we created a more diverse dataset consisting of more natural descriptions of varying granularity. We also explored an end-to-end baseline method for solving the new task, which enables the online rendering of proposal objects to generate 2D cues, it also demonstrated the usefulness of CLIP [47] and the multi-modal contrastive loss. We believe Multi3DRefer will bring more challenges and practical value in the direction of bridging 3D vision and language, especially for robotics and embodied AI tasks." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.6, + 0.891, + 0.705 + ], + "angle": 0, + "content": "Future Work. Our current design relies on features from the 3D object detector to capture the global context, and the 2D image encoder to capture per-object attributes. Using positional encoding could improve the ability of the model to handle spatial relations. Investigating whether positional encoding improves the model, and what kind of positional encoding works best is a great avenue for future work." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.746, + 0.666, + 0.763 + ], + "angle": 0, + "content": "Acknowledgements" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.78, + 0.891, + 0.9 + ], + "angle": 0, + "content": "This work was funded in part by a Canada CIFAR AI Chair and NSERC Discovery Grant, and enabled in part by support from the Digital Research Alliance of Canada. We thank Zhenyu (Dave) Chen for providing us with the ambiguous descriptions initially collected for ScanRefer, and Manolis Savva for proofreading and editing suggestions. We also thank Archita Srivastava, Cody Ning, and Austin T. Wang for helping to verify the Multi3DRefer dataset." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.947, + 0.518, + 0.957 + ], + "angle": 0, + "content": "15233" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.184 + ], + "angle": 0, + "content": "[1] Ahmed Abdelreheem, Kyle Olszewski, Hsin-Ying Lee, Peter Wonka, and Panos Achlioptas. 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Springer, 2022." + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.189 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "15236" + } + ] +] \ No newline at end of file diff --git a/2023/Multi3DRefer_ Grounding Text Description to Multiple 3D Objects/5fd3a41b-68c4-4dc5-a721-e608deb32134_origin.pdf b/2023/Multi3DRefer_ Grounding Text Description to Multiple 3D Objects/5fd3a41b-68c4-4dc5-a721-e608deb32134_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..a5e01985531c43779517c5ebb30e9c1874d82817 --- /dev/null +++ b/2023/Multi3DRefer_ Grounding Text Description to Multiple 3D Objects/5fd3a41b-68c4-4dc5-a721-e608deb32134_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:5df811c6e72b9420b193b6d83bf58eaf5d9d5c7b0702499154f9636b3f01b235 +size 7239380 diff --git a/2023/Multi3DRefer_ Grounding Text Description to Multiple 3D Objects/full.md b/2023/Multi3DRefer_ Grounding Text Description to Multiple 3D Objects/full.md new file mode 100644 index 0000000000000000000000000000000000000000..ad6349018c5b847811e4435ac09702a40de112ce --- /dev/null +++ b/2023/Multi3DRefer_ Grounding Text Description to Multiple 3D Objects/full.md @@ -0,0 +1,380 @@ +# Multi3DRefer: Grounding Text Description to Multiple 3D Objects + +Yiming Zhang1 ZeMing Gong1 Angel X. Chang1,2 + +Simon Fraser University1 Alberta Machine Intelligence Institute (Amii)2 + +{yza440, zmgong, angelx}@sfu.ca + +https://3dlg-hcvc.github.io/multi3defer/ + +# Abstract + +We introduce the task of localizing a flexible number of objects in real-world 3D scenes using natural language descriptions. Existing 3D visual grounding tasks focus on localizing a unique object given a text description. However, such a strict setting is unnatural as localizing potentially multiple objects is a common need in real-world scenarios and robotic tasks (e.g., visual navigation and object rearrangement). To address this setting we propose Multi3DRefer, generalizing the ScanRefer dataset and task. Our dataset contains 61926 descriptions of 11609 objects, where zero, single or multiple target objects are referenced by each description. We also introduce a new evaluation metric and benchmark methods from prior work to enable further investigation of multi-modal 3D scene understanding. Furthermore, we develop a better baseline leveraging 2D features from CLIP by rendering object proposals online with contrastive learning, which outperforms the state of the art on the ScanRefer benchmark. + +# 1. Introduction + +There is growing interest in multi-modal methods that connect language and vision, tackling tasks such as image captioning, visual question answering, text-to-image retrieval, and generation. One fundamental task is visual grounding where natural language text queries are linked to regions of an image or 3D scene. While the problem of visual grounding has been well studied in 2D images, there are fewer datasets and methods studying the problem in 3D scenes. Being able to indicate the object that the text "the first of four stools" references in a 3D scene is useful for applications in robotics, AR/VR, and online 3D environments where we have access to not just a static image, but a 3D scene. Work on 3D datasets for visual grounding [7, 4] has spurred the development of methods for 3D visual grounding [41, 63, 60, 22, 21, 2, 58, 7] and the inverse task of 3D captioning [7], as well as unified methods that tackle both [8, 6, 9]. + +![](images/e519d0c3e99726b7c6f00cf403a85bc04d9aed31107b17469a2ce17584259c0d.jpg) +This is a round stool. it is the first of four stools. +Figure 1: We introduce Multi3DRefer, a dataset and task where there are potentially multiple target objects for a given description. In ScanRefer [7] (left), the description corresponds to exactly one object (blue box), while in Multi3DRefer (right), there are multiple target objects. + +However, existing datasets and tasks [7, 4] are designed with the assumption that there is a unique target object when performing visual grounding in a 3D scene. This assumption makes ambiguous descriptions that may refer to multiple objects problematic (see Fig. 1). Furthermore, this explicitly discourages visual grounding methods from demonstrating generalization to similar object instances on the basis of common features of the objects (e.g., similar size, color, texture) and spatial relations between objects (e.g., first in a row left-to-right or right-to-left). + +We address these shortcomings with an enhanced dataset and task that we call Multi3DRefer where a flexible number of target objects (zero, single or multiple) in a 3D scene are localized given language descriptions. We modify and enhance language data from ScanRefer [7] and propose evaluation metrics to benchmark prior work and a CLIP-based method that we propose on the flexible number visual grounding task. In summary, we make the following contributions: 1) generalize 3D visual grounding to a flexible number of target objects given natural language descriptions. 2) create an enhanced dataset based on ScanRefer [7] + +with augmentations from ChatGPT $^1$ , consisting of 61926 descriptions in 800 ScanNet V2 [15] scenes. 3) benchmark three prior 3D visual grounding approaches adapted to Multi3DRefer 4) design an end-to-end approach leveraging CLIP [47] embeddings and online rendering of object proposals with contrastive learning. + +# 2. Related work + +In this paper, we focus on description localization where a single description may describe one or more objects in a 3D scene. Below, we review work in grounding in 2D and 3D, as well as recent work leveraging pre-trained vision-language models for 3D scene understanding. + +Visual grounding in 2D. A variety of datasets and methods have been proposed to investigate visual grounding tasks such as referring expressions [30, 42, 20] and phrase localization [44, 45] in 2D images. These datasets have enabled developing various visual-language grounding models [59, 61, 57, 39, 16, 37, 64]. Typically, in these datasets and tasks each phrase refers to exactly one object. A notable exception is the VGPhraseCut [54] dataset, based on Visual Genome [33] using templated phrases where each phrase is grounded to potentially multiple instance segments. + +Recent work in language and vision has started to tackle more flexible grounding. Kim et al. [31] noted that not all queries can be visually grounded (i.e. it is possible to have no targets) and constructed a dataset to study grounding performance when there are unanswerable queries. Kuo et al. [35] proposed a single model for referring expression comprehension, object detection, and phrase localization. While their model can handle multiple objects, the queries for multiple objects are typically short and category-based. Recent work [29, 36] reframed the problem of object detection as phrase grounding by introducing losses to align words to regions. These methods are flexible and have been used to improve both detection and visual grounding. In our work, we construct a dataset for flexible grounding in 3D. + +Visual grounding in 3D. Early work studied selecting the correct 3D shapes based on a text description in reference game setups [3, 53, 32], as well as learning joint language-3D embeddings for 3D text-to-shape retrieval [11, 51]. These works focused on descriptions of single objects in isolation. Moving beyond single 3D objects, researchers also studied grounding of language to objects in 3D scenes. At the scene level, ScanRefer [7] and ReferIt3D [4] introduce two datasets consisting of language descriptions of 3D objects from the real-world dataset ScanNet [15]. In detail, ReferIt3D [4] contains both template-based descriptions generated based on spatial relations between objects (Sr3D) and human-annotated fine-grained descriptions (Nr3D). They also propose two different grounding tasks, + +![](images/5cffbf93247c31c9915521a453a878bcfcbfec75aa369958cbba30b26581f187.jpg) +Zero Target +This is a white cabinet. It is next to a desk. +Figure 2: Example description-scene pairs in the Multi3DRefer dataset with zero, single, or multiple target objects. Blue boxes indicate ground truth target objects. + +![](images/d1cc49bf56ccdc696f23a1547e2190863d5d5c68678d6743ec679fd867b75f28.jpg) +Single Target (ScanRefer) +This is a black chair. It is in the middle of two chairs. + +![](images/eeaccc6f83578748aba92c69b547d0779532e2cff97b75828d9e715db02cdb88.jpg) +Multiple Targets +This is a black chair facing the door. + +both localizing a unique target object referred by a description. ScanRefer [7] requires both object detection and grounding, while ReferIt3D [4] focuses on discriminating a target object from multiple objects of that semantic class given ground-truth object bounding boxes. + +Different approaches [7, 4] have been proposed to tackle the two tasks, with models focusing on graph representations [21, 60, 17], improved handling of relations [63, 12], neurosymbolic reasoning [19], leveraging multi-view images and 2D semantics [58, 24, 22, 5], to unified models that can address both grounding and captioning [6, 8, 23, 9]. Recently, Abdelreheem et al. [1], Wu et al. [55] showed that including training on dense annotations can improve performance. Jain et al. [25] proposed to tackle object detection and visual grounding in a unified way by aligning features for text tokens with object proposals. In this work, we compare the performance of three recent models on our task Multi3DRefer with a new CLIP-based model. + +3D understanding using vision-language models. Large pre-trained text-vision models such as CLIP [47] and ALIGN [27] enabled work leveraging these models for 3D scene understanding. Recent work learn joint embeddings with text-image-3D representations [56, 62], used for disambiguating referring expressions [53] or text-to-shape retrieval [51]. Incorporating pre-trained 2D visual features also enabled expansion of 3D detection and instance segmentation to a larger number of categories [50], as well as tackling open vocabulary 3D detection [40, 52], and building of 3D semantic maps [26]. In our work, we show that we can leverage CLIP for improved visual grounding. + +# 3. Multi3DRefer dataset + +To study our task, we build the Multi3DRefer dataset, a superset of the existing ScanRefer dataset [7] with language descriptions of varying granularities. We augment ScanRefer [7] to create a dataset with 3 types of description-scene pairs: a) Zero Target; b) Single Target; and c) Multiple Targets, indicating zero, single, or multiple target objects in the scene match the description (see Fig. 2). In addition, we use + +
DatasetZero TargetSingle TargetMultiple TargetsTotal
ScanRefer [7]-51583-51583
Sr3D [4]-83572-83572
Sr3D+ [4]-114532-114532
Nr3D [4]-41503-41503
Multi3DRefer6688420601317861926
+ +Table 1: Compared to existing 3D visual grounding datasets, our Multi3DRefer dataset contains text that describes zero, single, or multiple target objects. + +![](images/7bd4ea636cd690f9abf55381d7e590df8dd7871573c4fe57cacc2225d515fc91.jpg) +Figure 3: Multi3DRefer data construction pipeline showing the generation process of Zero Target (red), Single Target (blue) and Multiple Target (orange) data. We use ChatGPT to add diversity to the description. All scene-description pairs are manually verified and modified if needed. + +ChatGPT to augment the descriptions so they are more natural and diverse (see Fig. 3 for the overall data construction pipeline). To ensure the dataset is of high quality we manually verify all generated samples. We obtain a dataset with 61926 descriptions in total (see Tabs. 1 and 3 for statistics). + +# 3.1. Adapting text for multiple targets + +We start with scene-description pairs from ScanRefer [7] and augment the data to create samples that refer to zero or more targets. For Single Target descriptions (type b), we take the released ScanRefer dataset which consists of description-scene pairs that have been initially verified to refer to unique objects [7]. We double-checked whether these descriptions indeed refer to unique objects and we + +found 9324 descriptions that are ambiguous. We use these ambiguous descriptions as an initial set of type (c) descriptions that can refer to multiple objects. For additional type (c) descriptions, we obtain from the ScanRefer authors 7741 ambiguous descriptions that can refer to multiple objects and annotate those descriptions with matching objects. To collect type (a) description (no target object) as well as more type (c) descriptions, we develop an efficient data collection pipeline consisting of two stages: 1) automated description generation; and 2) verification and modification. This pipeline maximizes the use of the existing ScanRefer dataset and reduces manual annotation. Below, we describe how we generate and verify additional data samples. + +Zero Target. To obtain descriptions with no target objects, we establish negative pairs of scenes with existing descriptions selected randomly from other scenes. We then manually verify that descriptions do not match any objects in the new scene. To reduce the number of description-scene pairs that need to be verified, we automatically check whether the semantic class of the target object for the description appears in the scene. Only if the semantic class appears in the scene does it need to be manually verified. Out of 6688 samples, we manually verify 5630 with 1058 automatically checked to have no matching objects. For pairs that need verification, human annotators are shown the description along with an interactive view of the scene to check that there are no matching objects. + +Multiple Targets. To generate descriptions with multiple targets, we start with the original description-scene pairs in the ScanRefer dataset. We then randomly select descriptions and trim the text to the first punctuation to obtain shorter, more ambiguous descriptions (e.g., "The cabinet is white and in the back of the room. It is the one on the left." $\rightarrow$ "The cabinet is white and in the back of the room"). Note that descriptions in which the semantic class of the target object only has a unique object in the scene are skipped. The trimmed text and scene pairs are sent to the annotation interface. This time, annotators are asked to select all eligible objects of a description in a 3D interactive scene mesh. Annotators are also asked to modify trimmed descriptions to fix errors and increase diversity (see Fig. 4 for examples). + +# 3.2. Rephrasing using ChatGPT + +To increase description diversity we use the ChatGPT model text-davinci-002-render for sentence rephrasing. We provide ChatGPT with the following prompts: + +1. I will give you a sentence describing an object, please help me polish it and keep its meaning. +2. Help me reword a sentence to a different format but keep its meaning. +3. Help me reword a sentence to make it more natural. +4. Help me reword a sentence describing an object, you should describe the colors and the spatial information in a different way. +5. Help me reword a sentence to an interesting format, you should keep its meaning. + +![](images/516fd701e8fcbe4b459e037d39b7c29ade03d241603b8ab6122049c2d369b46a.jpg) +ScanRefer +Multi3DRefer +T: This is a white kitchen cabinet located to the left of the over and stove unit. +M: This is a white kitchen cabinet located near the over and stove unit. +ScanRefer + +![](images/60db7c60ef9de9e51fa2c76a6c257896059a334d7e34f47fab6c397b24fda30f.jpg) +This is a white kitchen cabinet located to the left of the over and stove unit. It has four drawers with silver handles. +R: A white kitchen cabinet is situated near the oven and stove unit. + +![](images/2c8fc41025d993e4afd8985fbd767e082bec7afb92e57f364b8535e53ae69081.jpg) +There is a rectangular blue pillow with colorful decorations. It is on a larger cushion in front of the window by the side of the room. +ScanRefer + +![](images/8c4a79c3d54a253d64f53f31e1663beb3226491a92007e0d564d07f38b855187.jpg) +M: There is a rectangular pillow with colorful decorations. It is on a larger cushion in front of the window by the side of the room. R: A rectangular pillow, adorned with colorful decorations, rests upon a larger cushion positioned by the side of the room, right in front of the window. +Multi3DRefer + +![](images/92ce8e4961ea89b06b1511e8e5b17294ca71f7180ce96c3b167db5d5412a5117.jpg) +This is a green patterned chair. It is at a brown table. +Figure 4: Examples of generated revised descriptions of multiple targets for the Multi3DRefer dataset where we trim (T) to create more ambiguous descriptions, modify (M) by human, and reword (R) using ChatGPT. All descriptions are verified by annotators (see bounding boxes for target objects). Note that the reworded (R) descriptions provide more variation in sentence structure. + +![](images/575b7e0d4d7caa47b79ef097cef4f43139aa1fcd8b1a0bbf9e36dcb64df7afe8.jpg) +R: A green patterned chair sits beside a brown table. + +
Unique wordsTotal wordsAvg. description length
Original5067101619016.4
Rephrased707793693515.1
+ +Tab. 2 shows statistics comparing the descriptions before and after rephrasing. We see a richer vocabulary but shorter descriptions after ChatGPT rephrasing. Below we provide examples of the original (O) and reworded (R) text: + +O: The table is a round table. It is located between two chairs to the + +Table 2: Comparison of Multi3DRefer language data before and after ChatGPT rephrasing. We count the number of unique words, total words, and the average description length, excluding punctuation. + +
SpatialColorTextureShapeTotal
ScanRefer [7]511173469258641741651583
Nr3D [4]3971111939526856841503
Sr3D [4]835726254064883572
Sr3D+ [4]11453286660744114532
Multi3DRefer600284130771211969261926
+ +Table 3: Breakdown of spatial, color, texture, and shape information in object descriptions from different datasets. + +right, and two chairs to the left of it. +R: The round table is situated between two chairs to its right and two chairs to its left. +O: This is a table on the wall in the room. It is next to the window and a few lined-up chairs. +R: A wall-mounted table resides coaxily beside a window in the room, accompanied by a row of orderly chairs. +O: A sink on the vanity. It is to the right of the vacuum cleaners. +R: The sink is located on the vanity to the right of the vacuum cleaners. +O: This is a white kitchen cabinet located near the over and stove unit. +R: A white kitchen cabinet is situated near the oven and stove unit + +The rephrased text preserves the original meaning while being more natural. In addition, ChatGPT automatically corrects typos (e.g., over to oven in the last example). + +# 3.3. Verification + +After we obtain a set of ChatGPT reworded descriptions, we manually verify the descriptions are well-written and that the object(s) matched in the scene are accurate. We create a web interface for verifiers to check whether the description matches the identified target objects (see supplement for details). The web interface shows the description together with an interactive 3D view of the scene and the target objects. The verifiers check if the description matches the target objects and only the target objects, or modify the list of target objects (by selecting appropriate objects), or improve the description to fix typos and ambiguities. The verification was performed by 5 students over a period of one month. + +# 3.4. Dataset statistics + +In total, our dataset consists of 61926 language descriptions, with 51583 directly obtained from ScanRefer [7], of which 6688 descriptions match zero-targets and 13178 match multiple. For Multiple Targets, the scenes are typically offices or meeting rooms with many chairs and tables. See Tab. 1 for a comparison of our final dataset against prior datasets. We also provide annotations for each description as to whether it refers to spatial, color, texture, or shape attributes (see Tab. 3). + +![](images/ed990a157b0f5a517fb2c0ca868937d0b078d00fb491f86326e8c470e0b46ca0.jpg) +Figure 5: Our M3DRef-CLIP end-to-end architecture. Given a scene point cloud and a text description with $L$ tokens (we pad shorter descriptions and truncate longer ones), the detector first predicts $M$ object proposals and their 3D features. Then an online renderer renders $N$ -view images for each proposal and feeds them into the image encoder to get 2D features. A transformer-based module then fuses both language features and $2\mathrm{D} + 3\mathrm{D}$ object features and outputs scores indicating the match of each object to the description. We use PointGroup [28] to detect and segment the objects in 3D and select CLIP [47] + MLPs as the language and image encoder. A contrastive loss is applied between sentence features and object features. + +# 4. Task + +In the Multi3DRefer task, we are given as input a 3D real-world scene represented as a point cloud $P \in \mathbb{R}^{N \times (3 + C)}$ and a free-form language description with a variable number $M \in \mathbb{N}$ of referred objects, where $N, C$ are the number of points and the number of point feature channels, respectively. The goal is to predict axis-aligned bounding boxes for all $M$ objects that match the description. Compared to prior work, the difficulty of our task is that the number of referred objects is flexible, i.e., a description can refer to not only one or multiple target objects but also no objects. Predicting too many or too few target objects are both penalized by our evaluation metrics. + +Evaluation metrics. To evaluate grounding for a flexible number of target objects, we measure the F1 score at the intersection over union (IoU) thresholds of $\tau_{\mathrm{eval}} = 0.25$ and 0.5 (F1@0.25 and F1@0.5). To investigate model performance for different scenarios, we consider the following 5 cases: a) zero target w/o distractors of the same semantic class; b) zero target w/ distractors; c) single target w/o distractors; d) single target w/ distractors; and e) multiple targets. Note that c) and d) correspond to the "unique" and "multiple" cases in ScanRefer [7]. In addition, a) and c) are easier cases where there are zero or a unique target object of its semantic class in a scene, while b) and d) are more difficult cases containing one or multiple target objects of the same semantic class in a scene. We also report the micro-average of the 5 cases as an overall score. + +During evaluations, we first calculate per-pair IoUs between ground truth and predicted bounding boxes in a scene, and then apply the Hungarian algorithm [34] to get an optimal one-to-one matching between predicted and GT bounding boxes. To get the maximum matched IoU, we use the following cost function: + +$$ +\operatorname {C o s t} (i, j) = - \operatorname {I o U} (i, j) \text {f o r} i, j \in \{1 \dots N \} +$$ + +where $N = \max (\# Predictions, \# GTs)$ . After obtaining the optimal match, we take pairs with IoUs higher than $\tau_{\mathrm{eval}}$ to be True Positives (TP). We treat the Zero Target (ZT) case as a special case where recall is always set to 1, and precision is set to 1 if there is no prediction or 0 otherwise. + +# 5. Method + +We propose M3DRef-CLIP, a CLIP-based approach and compare to three recent approaches: 3DVG-Transformer [63], 3DJCG [6] and D3Net [8]. We selected these methods as they were among the top performers on the ScanRefer [7] benchmark with available open-source code. Note that 3DJCG [6] and D3Net [8] are unified models, which can do both grounding and captioning tasks. All four models are two-stage approaches, where a 3D object detector first identifies a set of bounding box candidates, and a disambiguation module then selects the target bounding box. In the original ScanRefer setting, the three compared models are trained using a cross-entropy loss $L_{\mathrm{ref}}$ where the predicted bounding box has the highest IoU ( $> \tau_{\mathrm{train}}$ ) with + +the GT bounding box as the target bounding box to calculate the loss. For our task, we use a binary cross-entropy loss for $L_{\mathrm{ref}}$ as our problem is a multi-label task (vs classification). + +# 5.1. M3DRef-CLIP + +M3DRef-CLIP follows the two-stage architecture with PointGroup [28] as the detector, CLIP [47] as the text encoder and a transformer-based fusion module (see Fig. 5). We use PointGroup [28] to obtain object proposals along with their 3D features $\mathbf{F}^{3\mathrm{d}} \in R^{32}$ . The output object proposals are fed into an online object renderer, which renders multi-view 2D images for each object proposal. We use CLIP [47] to encode the images and use an MLP to project the average of the output 2D image features to obtain $\mathbf{F}^{2\mathrm{d}} \in \mathbb{R}^{128}$ . The 2D and 3D features are concatenated to form and passed through a 1D convolution (that projects the combined 160-dim features down to 128-dim) to obtain the final visual features $\mathbf{F}^{\mathrm{obj}} \in \mathbb{R}^{128}$ for an object proposal: + +$$ +\mathbf {F} ^ {\mathrm {o b j}} = \operatorname {c o n v} _ {\mathrm {l d}} ([ \mathbf {F} ^ {\mathrm {3 d}}; \mathbf {F} ^ {\mathrm {2 d}} ]), \quad \mathbf {F} ^ {\mathrm {2 d}} = \frac {\operatorname {M L P} (\sum_ {i = 1} ^ {N} \mathbf {F} _ {i} ^ {\mathrm {2 d}})}{N} +$$ + +We use the CLIP text encoder with an MLP to obtain both 128-dim token-level and sentence embeddings. We use a transformer-based fusion module to combine object features and token-level embeddings and output confidence scores for each proposal. To improve the training, we apply a contrastive loss between sentence and object features. + +# 5.2. Loss function + +We train the network end-to-end with the total loss $L = L_{\mathrm{det}} + L_c + L_{\mathrm{ref}}$ consisting of the detection loss $L_{\mathrm{det}}$ , contrastive loss $L_{\mathrm{c}}$ , and the reference loss $L_{\mathrm{ref}}$ . The detection loss $L_{\mathrm{det}}$ is introduced in PointGroup [28] and consists of four parts: 1) cross-entropy loss for supervising per-point semantic class prediction; 2) $L_1$ loss for supervising perpoint offset vector towards object centers; 3) directional loss formed as a mean of minus cosine similarities for further constraining the direction of per-point offset vectors; 4) binary cross-entropy loss for supervising per-point objectness confidence score. To help learn better multi-modal embeddings, we introduce a symmetric contrastive loss $L_{c}$ [47], which can handle a flexible number of target objects as shown below: + +$$ +L _ {\mathrm {c}} ^ {O \rightarrow S} = - \log \frac {\exp (\cos (\bar {O} _ {i} , S _ {i}) / \tau)}{\sum_ {i = 1} ^ {n} \exp (\cos (\bar {O} _ {i} , S _ {j}) / \tau)} +$$ + +$$ +L _ {\mathrm {c}} ^ {S \rightarrow O} = - \log \frac {\exp (\cos (S _ {i} , \bar {O} _ {i}) / \tau)}{\sum_ {i = 1} ^ {n} \exp (\cos (S _ {i} , \bar {O} _ {j}) / \tau)} +$$ + +where $S$ is sentence features, $\bar{O}$ is the mean of object features of all target objects paired with a description, and $\tau$ is a temperature parameter. Finally, the reference loss $L_{\mathrm{ref}}$ supervises the matching module to select objects satisfying the description. We use the multi-class cross-entropy loss as $L_{\mathrm{ref}}$ for experiments on ScanRefer [7], Nr3D [4] and + +Multi3DRefer (ST) where each description only refers to a single target object. For experiments on Multi3DRefer, $L_{\mathrm{ref}}$ is a sum of binary cross-entropy losses over detected objects. + +Training. To set up positive (i.e. valid target bounding boxes) and negative instances between the GT bounding boxes and proposed bounding boxes, we use two strategies (see supplement for detailed comparisons): + +All All predicted bounding boxes with IoU higher than the threshold $\tau_{\mathrm{train}}$ with GT bounding boxes are considered target bounding boxes. + +Hungarian We apply the Hungarian algorithm [34] to do bipartite matching, which ensures an optimal solution. We use the same IoU threshold $\tau_{\mathrm{train}}$ to filter prediction-GT bounding box pairs. + +Inference. At inference time, we take all bounding boxes with predicted scores above the threshold $\tau_{\mathrm{pred}}$ as positives (predicted target bounding boxes for the description). See the supplement for comparisons of different $\tau_{\mathrm{pred}}$ . + +# 6. Experiments + +We conduct experiments on both ScanRefer [7] and Multi3DRefer datasets and consider two setups: grounding objects with GT and predicted bounding boxes. + +GT bounding boxes. For M3DRef-CLIP and D3Net [8], we input the complete scene and apply GT point masks for each object to get GT bounding boxes and masked features from the pre-trained detector (PointGroup for both D3Net and our M3DRef-CLIP). For 3DVG-Trans [63] and 3DJCG [6], we use their original GT setting following the method proposed by ReferIt3D [4]. Single input objects are first extracted from the scene using the GT masks and PointNet++ [46] is used for obtaining the object features. For all methods, we disable the $L_{det}$ loss when using GT boxes. + +Predicted bounding boxes. We use the original detector design of each method to predict bounding boxes and extract features. + +# 6.1. Implementation details + +We implement M3DRef-CLIP using PyTorch Lightning3 and PyTorch3D [48]. We train the model end-to-end on a single NVIDIA RTX A5000 with a batch size of 4, using the AdamW optimizer [38] with a learning rate of $5e^{-4}$ . We use a re-implementation of PointGroup4 with the Minkowski Engine [14]. Following D3Net [8], we pretrain our PointGroup module on all ScanNet v2 training scans with the 18 ScanRefer categories. We take point coordinates, point normals and per-point multi-view features $P \in \mathbb{R}^{N \times (3 + 3 + 128)}$ as the input. For data augmentation, we randomly apply + +
ZT w/o DistractorsZT w DistractorsST w/o DistractorsST w/ DistractorsMultiple Targets
TrainValTestTotalTrainValTestTotalTrainValTestTotalTrainValTestTotalTrainValTestTotal
ScanRefer [7]--------85002297120111998281657211420939585----
Multi3DRefer2702528596382621603783242862719820991106104032204053584259316579738275768313178
+ +Table 4: Breakdown of different datasets in 5 scenarios. ZT and ST denote Zero Target and Single Target, respectively. + +
Acc@0.5 on ValAcc@0.5 on Test
UniqueMultipleAllUniqueMultipleAll
3DVG-Trans+ [63]62.030.336.457.931.037.0
InstanceRefer [60]66.824.832.966.726.935.8
FFL-3DOG [17]67.925.734.0---
SAT [58]50.825.230.1---
3D-SPS [41]66.729.837.0---
MVT [22]66.525.333.3---
BUTD-DETR [25]66.335.139.8---
D3Net (G) [8]70.427.135.665.827.336.0
D3Net* [8]72.030.137.968.430.739.2
3DJCG (G) [6]64.530.336.9---
3DJCG* [6]64.330.837.360.631.237.8
HAM [10]67.934.040.663.733.240.1
UniT3D (G) [9]74.827.636.5---
UniT3D* [9]73.131.139.1---
M3DRef-CLIP77.236.844.770.938.145.5
+ +Table 5: For unified models [8, 6, 9], we report both the grounding-only (G) performance as well as their best performance. We use * to indicate joint grounding and captioning models trained with extra data. + +coordinate jitter, x-axis flipping and rotation around the z-axis. We freeze a pre-trained CLIP with ViT-B/32 and only train additional MLPs. For encoding the text with CLIP, we follow CLIP and tokenizer with a lower-cased BPE, and [SOS] and [EOS] tokens added (the output corresponding to [EOS] is used as the sentence representation). + +Object renderer. For each object proposal, we render 3 views horizontally spaced 120 degrees apart, at a distance of $1\mathrm{m}$ , with elevation angle of $45^{\circ}$ . We crop coordinates and colors from the input scene point cloud using predicted bounding boxes and set point radius to $2.5\mathrm{cm}$ and image size to $224^2$ . We use CUDA to batch index scene point clouds and crop in parallel, and render the batches sparsely to avoid padding overhead. Rendering is implemented with PyTorch3D [48] and executed on the GPU. + +# 6.2. Results + +# 6.2.1 Performance of M3DRef-CLIP + +We first validate the performance of M3DRef-CLIP on ScanRefer (see Tab. 5) and Nr3D [4] (see Tab. 6) datasets and compare it against recent models. On ScanRefer, our method outperforms all prior works including those joint models leveraging extra input data by a large margin on both val set and test set (online benchmarking). In our ablation study, we find that the use of the CLIP text encoder is a key + +
EasyHardView-DepView-IndepAll
3DVG-Trans [63]48.534.834.843.740.8
InstanceRefer [60]46.031.834.541.938.8
FFL-3DOG [17]48.235.037.144.741.7
TransRefer3D [18]48.536.036.544.942.1
SAT [58]56.342.446.950.449.2
3D-SPS [41]58.145.148.053.251.5
MVT [22]61.349.154.355.455.4
BUTD-DETR [25]60.748.446.058.054.6
HAM [10]54.341.941.551.448.2
LanguageRefer [49]51.036.641.745.043.9
LAR [5]56.141.846.750.248.9
M3DRef-CLIP55.643.442.352.949.4
+ +Table 6: Comparison of methods on Nr3D [4] val set with GT boxes. + +
Training DatasetAcc on ScanReferAcc on Multi3DRefer (ST)
UniqueMultipleAllUniqueMultipleAll
ScanRefer [7]89.349.156.979.548.257.0
Multi3DRefer (ST)88.546.955.086.352.962.3
Multi3DRefer (ST) + ScanRefer90.851.058.788.056.765.5
+ +Table 7: We compare results of training M3DRef with GT boxes on different datasets' val set. We only use the Single Target (ST) case in Multi3DRefer dataset. + +factor to the strong performance of our model on ScanRefer. Another key factor is the use of a strong 3D object instance segmentation network (PointGroup) as our object detector. For instance, the PointGroup-based methods [8, 9] readily outperform VoteNet-based methods [63, 6] on the unique subset of ScanRefer. + +For Nr3D [4], we achieve comparable but less competitive results because of our weaker ground-truth box encoder. Note that SAT [58] and MVT [22] also leverage 2D images but render them offline. Overall, using additional 2D image information is helpful for two-stage methods. + +# 6.2.2 Multi3DRefer + +We split the Multi3DRefer data into train/val/test by scene following the ScanRefer split, resulting in a rough split ratio of 7:2:1 for the scene-description pairs. See Tab. 4 for statistics, including the number of descriptions with zero, single, or multiple targets. + +Usefulness of Multi3DRefer dataset. To study the usefulness of the Multi3DRefer dataset, we compare the perfor + +
F1 (GT boxes)F1@0.5 (Pred boxes)
ZT w/o DZT w/ DST w/o DST w/ DMTAllZT w/o DZT w/ DST w/o DST w/ DMTAll
3DVG-Trans+ [63]45.314.358.935.254.244.187.145.827.516.726.525.5
D3Net (Grounding) [8]71.620.478.244.461.655.581.632.538.623.335.032.2
3DJCG (Grounding) [6]47.916.459.135.554.244.694.166.926.016.726.226.6
M3DRef-CLIP74.229.484.152.367.262.381.839.447.830.637.938.4
+ +Table 8: Comparison of different methods on Multi3DRefer. Our M3DRef-CLIP outperforms prior work on most metrics. + +
Eval DatasetAcc (GT boxes)Acc@0.5 (Pred boxes)
UniqueMultipleAllUniqueMultipleAll
Multi3DRefer (ST)86.951.561.567.340.147.7
ScanRefer [7]88.046.154.373.534.341.9
+ +Table 9: M3DRef-CLIP evaluated on Multi3DRefer (ST) and ScanRefer with both GT and predicted bounding boxes. + +mance of training M3DRef-CLIP with the original ScanRefer data and with our Multi3DRefer data for the Single Target (ST) case. We evaluate on both ScanRefer and Multi3DRefer (ST), using GT bounding boxes. Tab. 7 shows that our reworded data can improve performance on ScanRefer. Prior work has also shown that incorporating additional labeled data can help, but they typically used either a captioning model [8, 9], mixed additional annotated data [58], or used dense annotations [1]. We show that simple rewordings (without accessing the images) also help. + +We also evaluate M3DRef-CLIP trained on Multi3DRefer using ScanRefer's task setting (Tab. 9) of predicted objects. We observe that the model trained on Multi3DRefer data and task achieves similar performance to the model trained on ScanRefer data and task, which illustrates the generalization of Multi3DRefer. + +Evaluation on Multi3DRefer. We compare four models on the Multi3DRefer dataset using both ground-truth and predicted boxes (Tab. 8). In our experiments, we focus on two-stage methods that perform well on ScanRefer. We adapt the code of 3DVG-Trans, 3DJCG and D3Net to our task. For 3DVG-Trans, we use the enhanced version 3DVG-Trans+ provided by the authors. We only train and evaluate the grounding model of 3DJCG and D3Net. + +To analyze the performance of the models, we break down the zero (ZT) and single-target (ST) case to without and with distractors (D) of the same class. Overall, having distractors is more challenging. We note that M3DRef-CLIP outperforms the other methods on Multi3DRefer, and that 3DJCG is better at handling the ZT case with predicted boxes. Fig. 6 shows qualitative results. + +![](images/808753537d6ac0ac1bf469ecfcb5d833fb0090ce602e78c4f4be49158423eb94.jpg) +Figure 6: Qualitative results of D3Net [8] versus M3DRef-CLIP on Multi3DRefer using predicted boxes. Blue boxes indicate GT, green boxes are true positives with IoU threshold $\tau_{\mathrm{pred}} > 0.5$ . Red boxes are false positives. + +# 6.2.3 Ablation studies + +Does CLIP help? We experiment with just using pure CLIP for both text and image encoding vs combining CLIP and 3D features (see Tab. 10). We also report results using a GRU [13]-based text encoder with GloVE [43] embedding, as used in prior work [7, 63, 8]. Although our GRU and 3D variants are similar at a high level to the grounding model of D3Net (which also used GRU and PointGroup with a transformer-based fusion module), we outperform the D3Net grounding module. Tab. 10 shows that using the CLIP text encoder improves performance, and combining CLIP and 3D features yields the best performance. The CLIP image encoder by itself underperforms the 3D features, showing the usefulness of 3D information. + +Does contrastive learning help? Tab. 11 reports the performance of M3DRef with and without contrastive learning on ScanRefer, Nr3D [4] and Multi3DRefer. We observe the + +
TextVisionAcc (ScanRefer)F1 (Multi3DRefer)
UniqMultAllZT w/o DZT w/ DST w/o DST w/ DMTAll
GTGRU3D88.843.552.370.127.381.649.363.359.1
CLIPCLIP78.942.149.358.327.874.144.761.054.4
CLIP3D+CLIP89.349.156.974.229.484.152.367.262.3
PredGRU3D72.232.840.478.842.149.428.537.037.4
CLIPCLIP71.231.239.064.436.042.925.733.733.1
CLIP3D+CLIP77.236.844.781.839.447.830.637.938.4
+ +Table 10: Ablations in training M3DRef using different feature embeddings and ground-truth boxes (top rows) and predicted boxes (bottom rows). The combination of CLIP [47] and 3D features achieves the best performance. We use PointGroup [28] for our 3D object detector and feature extractor. + +
ScanReferNr3DMulti3DRefer
UniqueMultipleAllEasyHardView-DepView-IndepAllZT w/o DZT w/ DST w/o DST w/ DMTAll
w/ contrastive89.349.156.955.643.442.352.949.474.229.484.152.367.262.3
w/o contrastive89.647.255.450.935.337.645.642.967.423.883.452.066.561.1
+ +Table 11: Ablation of M3DRef-CLIP with and without contrastive loss using GT boxes. + +
TextVisionSpatialColorTextureShape
GRU3D55.867.776.477.8
CLIP3D+CLIP58.871.979.482.5
+ +Table 12: Breakdown of M3DRef performance (with GRU vs CLIP) on descriptions with different attributes. We report F1 scores with GT boxes on Multi3DRefer val set. + +benefit of the contrastive loss for all tasks, especially Nr3D. + +# 6.3. Analysis of M3DRef-CLIP + +To better study the Multi3DRefer data and understand how M3DRef-CLIP helps address the task, we break down evaluation of Multi3DRefer based on attributes provided in the description: spatial, color, texture, and shape information. For this analysis, these four splits are mutually exclusive, i.e. we only keep descriptions that describe exactly 1 attribute from the four and discard others. We compare using M3DRef with GRU with 3D PointGroup features vs our full M3DRef-CLIP model (with CLIP image and text encoders). We use the GT boxes setting and report F1 scores in Tab. 12. We observe that adding features from CLIP [47] helps identify all these attributes. We found that descriptions with spatial terms are more challenging than descriptions with texture or shape. + +# 7. Conclusion + +We present Multi3DRefer, a more realistic task of grounding a flexible number of objects in real-world 3D scenes using natural language descriptions. We designed + +a simple and efficient data generation pipeline to create data with less human effort, by leveraging existing language data and ChatGPT. With this pipeline, we created a more diverse dataset consisting of more natural descriptions of varying granularity. We also explored an end-to-end baseline method for solving the new task, which enables the online rendering of proposal objects to generate 2D cues, it also demonstrated the usefulness of CLIP [47] and the multi-modal contrastive loss. We believe Multi3DRefer will bring more challenges and practical value in the direction of bridging 3D vision and language, especially for robotics and embodied AI tasks. + +Future Work. Our current design relies on features from the 3D object detector to capture the global context, and the 2D image encoder to capture per-object attributes. Using positional encoding could improve the ability of the model to handle spatial relations. Investigating whether positional encoding improves the model, and what kind of positional encoding works best is a great avenue for future work. + +# Acknowledgements + +This work was funded in part by a Canada CIFAR AI Chair and NSERC Discovery Grant, and enabled in part by support from the Digital Research Alliance of Canada. We thank Zhenyu (Dave) Chen for providing us with the ambiguous descriptions initially collected for ScanRefer, and Manolis Savva for proofreading and editing suggestions. We also thank Archita Srivastava, Cody Ning, and Austin T. Wang for helping to verify the Multi3DRefer dataset. + +# References + +[1] Ahmed Abdelreheem, Kyle Olszewski, Hsin-Ying Lee, Peter Wonka, and Panos Achlioptas. 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Existing 3D visual grounding tasks focus on localizing a unique object given a text description. However, such a strict setting is unnatural as localizing potentially multiple objects is a common need in real-world scenarios and robotic tasks (e.g., visual navigation and object rearrangement). To address this setting we propose Multi3DRefer, generalizing the ScanRefer dataset and task. Our dataset contains 61926 descriptions of 11609 objects, where zero, single or multiple target objects are referenced by each description. We also introduce a new evaluation metric and benchmark methods from prior work to enable further investigation of multi-modal 3D scene understanding. Furthermore, we develop a better baseline leveraging 2D features from CLIP by rendering object proposals online with contrastive learning, which outperforms the state of the art on the ScanRefer benchmark." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 490, + 128, + 502 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 490, + 128, + 502 + ], + "spans": [ + { + "bbox": [ + 47, + 490, + 128, + 502 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 510, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 289, + 715 + ], + "type": "text", + "content": "There is growing interest in multi-modal methods that connect language and vision, tackling tasks such as image captioning, visual question answering, text-to-image retrieval, and generation. One fundamental task is visual grounding where natural language text queries are linked to regions of an image or 3D scene. While the problem of visual grounding has been well studied in 2D images, there are fewer datasets and methods studying the problem in 3D scenes. Being able to indicate the object that the text \"the first of four stools\" references in a 3D scene is useful for applications in robotics, AR/VR, and online 3D environments where we have access to not just a static image, but a 3D scene. Work on 3D datasets for visual grounding [7, 4] has spurred the development of methods for 3D visual grounding [41, 63, 60, 22, 21, 2, 58, 7] and the inverse task of 3D captioning [7], as well as unified methods that tackle both [8, 6, 9]." + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 307, + 227, + 547, + 357 + ], + "blocks": [ + { + "bbox": [ + 307, + 227, + 547, + 357 + ], + "lines": [ + { + "bbox": [ + 307, + 227, + 547, + 357 + ], + "spans": [ + { + "bbox": [ + 307, + 227, + 547, + 357 + ], + "type": "image", + "image_path": "e519d0c3e99726b7c6f00cf403a85bc04d9aed31107b17469a2ce17584259c0d.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 342, + 362, + 512, + 373 + ], + "lines": [ + { + "bbox": [ + 342, + 362, + 512, + 373 + ], + "spans": [ + { + "bbox": [ + 342, + 362, + 512, + 373 + ], + "type": "text", + "content": "This is a round stool. it is the first of four stools." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 377, + 547, + 439 + ], + "lines": [ + { + "bbox": [ + 305, + 377, + 547, + 439 + ], + "spans": [ + { + "bbox": [ + 305, + 377, + 547, + 439 + ], + "type": "text", + "content": "Figure 1: We introduce Multi3DRefer, a dataset and task where there are potentially multiple target objects for a given description. In ScanRefer [7] (left), the description corresponds to exactly one object (blue box), while in Multi3DRefer (right), there are multiple target objects." + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 461, + 547, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 461, + 547, + 581 + ], + "spans": [ + { + "bbox": [ + 304, + 461, + 547, + 581 + ], + "type": "text", + "content": "However, existing datasets and tasks [7, 4] are designed with the assumption that there is a unique target object when performing visual grounding in a 3D scene. This assumption makes ambiguous descriptions that may refer to multiple objects problematic (see Fig. 1). Furthermore, this explicitly discourages visual grounding methods from demonstrating generalization to similar object instances on the basis of common features of the objects (e.g., similar size, color, texture) and spatial relations between objects (e.g., first in a row left-to-right or right-to-left)." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 548, + 715 + ], + "type": "text", + "content": "We address these shortcomings with an enhanced dataset and task that we call Multi3DRefer where a flexible number of target objects (zero, single or multiple) in a 3D scene are localized given language descriptions. We modify and enhance language data from ScanRefer [7] and propose evaluation metrics to benchmark prior work and a CLIP-based method that we propose on the flexible number visual grounding task. In summary, we make the following contributions: 1) generalize 3D visual grounding to a flexible number of target objects given natural language descriptions. 2) create an enhanced dataset based on ScanRefer [7]" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "15225" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": "with augmentations from ChatGPT" + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "inline_equation", + "content": "^1" + }, + { + "bbox": [ + 46, + 72, + 289, + 145 + ], + "type": "text", + "content": ", consisting of 61926 descriptions in 800 ScanNet V2 [15] scenes. 3) benchmark three prior 3D visual grounding approaches adapted to Multi3DRefer 4) design an end-to-end approach leveraging CLIP [47] embeddings and online rendering of object proposals with contrastive learning." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 156, + 132, + 168 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 156, + 132, + 168 + ], + "spans": [ + { + "bbox": [ + 47, + 156, + 132, + 168 + ], + "type": "text", + "content": "2. Related work" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 175, + 287, + 236 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 175, + 287, + 236 + ], + "spans": [ + { + "bbox": [ + 46, + 175, + 287, + 236 + ], + "type": "text", + "content": "In this paper, we focus on description localization where a single description may describe one or more objects in a 3D scene. Below, we review work in grounding in 2D and 3D, as well as recent work leveraging pre-trained vision-language models for 3D scene understanding." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 237, + 287, + 357 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 237, + 287, + 357 + ], + "spans": [ + { + "bbox": [ + 46, + 237, + 287, + 357 + ], + "type": "text", + "content": "Visual grounding in 2D. A variety of datasets and methods have been proposed to investigate visual grounding tasks such as referring expressions [30, 42, 20] and phrase localization [44, 45] in 2D images. These datasets have enabled developing various visual-language grounding models [59, 61, 57, 39, 16, 37, 64]. Typically, in these datasets and tasks each phrase refers to exactly one object. A notable exception is the VGPhraseCut [54] dataset, based on Visual Genome [33] using templated phrases where each phrase is grounded to potentially multiple instance segments." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 357, + 288, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 357, + 288, + 525 + ], + "spans": [ + { + "bbox": [ + 46, + 357, + 288, + 525 + ], + "type": "text", + "content": "Recent work in language and vision has started to tackle more flexible grounding. Kim et al. [31] noted that not all queries can be visually grounded (i.e. it is possible to have no targets) and constructed a dataset to study grounding performance when there are unanswerable queries. Kuo et al. [35] proposed a single model for referring expression comprehension, object detection, and phrase localization. While their model can handle multiple objects, the queries for multiple objects are typically short and category-based. Recent work [29, 36] reframed the problem of object detection as phrase grounding by introducing losses to align words to regions. These methods are flexible and have been used to improve both detection and visual grounding. In our work, we construct a dataset for flexible grounding in 3D." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 527, + 288, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 527, + 288, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 527, + 288, + 696 + ], + "type": "text", + "content": "Visual grounding in 3D. Early work studied selecting the correct 3D shapes based on a text description in reference game setups [3, 53, 32], as well as learning joint language-3D embeddings for 3D text-to-shape retrieval [11, 51]. These works focused on descriptions of single objects in isolation. Moving beyond single 3D objects, researchers also studied grounding of language to objects in 3D scenes. At the scene level, ScanRefer [7] and ReferIt3D [4] introduce two datasets consisting of language descriptions of 3D objects from the real-world dataset ScanNet [15]. In detail, ReferIt3D [4] contains both template-based descriptions generated based on spatial relations between objects (Sr3D) and human-annotated fine-grained descriptions (Nr3D). They also propose two different grounding tasks," + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 308, + 82, + 382, + 141 + ], + "blocks": [ + { + "bbox": [ + 308, + 72, + 337, + 79 + ], + "lines": [ + { + "bbox": [ + 308, + 72, + 337, + 79 + ], + "spans": [ + { + "bbox": [ + 308, + 72, + 337, + 79 + ], + "type": "text", + "content": "Zero Target" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 308, + 82, + 382, + 141 + ], + "lines": [ + { + "bbox": [ + 308, + 82, + 382, + 141 + ], + "spans": [ + { + "bbox": [ + 308, + 82, + 382, + 141 + ], + "type": "image", + "image_path": "5cffbf93247c31c9915521a453a878bcfcbfec75aa369958cbba30b26581f187.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 313, + 143, + 376, + 157 + ], + "lines": [ + { + "bbox": [ + 313, + 143, + 376, + 157 + ], + "spans": [ + { + "bbox": [ + 313, + 143, + 376, + 157 + ], + "type": "text", + "content": "This is a white cabinet. It is next to a desk." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 304, + 174, + 545, + 211 + ], + "lines": [ + { + "bbox": [ + 304, + 174, + 545, + 211 + ], + "spans": [ + { + "bbox": [ + 304, + 174, + 545, + 211 + ], + "type": "text", + "content": "Figure 2: Example description-scene pairs in the Multi3DRefer dataset with zero, single, or multiple target objects. Blue boxes indicate ground truth target objects." + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 389, + 82, + 463, + 141 + ], + "blocks": [ + { + "bbox": [ + 389, + 72, + 447, + 79 + ], + "lines": [ + { + "bbox": [ + 389, + 72, + 447, + 79 + ], + "spans": [ + { + "bbox": [ + 389, + 72, + 447, + 79 + ], + "type": "text", + "content": "Single Target (ScanRefer)" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 389, + 82, + 463, + 141 + ], + "lines": [ + { + "bbox": [ + 389, + 82, + 463, + 141 + ], + "spans": [ + { + "bbox": [ + 389, + 82, + 463, + 141 + ], + "type": "image", + "image_path": "d1cc49bf56ccdc696f23a1547e2190863d5d5c68678d6743ec679fd867b75f28.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 390, + 143, + 460, + 157 + ], + "lines": [ + { + "bbox": [ + 390, + 143, + 460, + 157 + ], + "spans": [ + { + "bbox": [ + 390, + 143, + 460, + 157 + ], + "type": "text", + "content": "This is a black chair. It is in the middle of two chairs." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 470, + 83, + 543, + 141 + ], + "blocks": [ + { + "bbox": [ + 471, + 72, + 509, + 79 + ], + "lines": [ + { + "bbox": [ + 471, + 72, + 509, + 79 + ], + "spans": [ + { + "bbox": [ + 471, + 72, + 509, + 79 + ], + "type": "text", + "content": "Multiple Targets" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 470, + 83, + 543, + 141 + ], + "lines": [ + { + "bbox": [ + 470, + 83, + 543, + 141 + ], + "spans": [ + { + "bbox": [ + 470, + 83, + 543, + 141 + ], + "type": "image", + "image_path": "eeaccc6f83578748aba92c69b547d0779532e2cff97b75828d9e715db02cdb88.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 471, + 143, + 541, + 156 + ], + "lines": [ + { + "bbox": [ + 471, + 143, + 541, + 156 + ], + "spans": [ + { + "bbox": [ + 471, + 143, + 541, + 156 + ], + "type": "text", + "content": "This is a black chair facing the door." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 233, + 545, + 293 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 233, + 545, + 293 + ], + "spans": [ + { + "bbox": [ + 304, + 233, + 545, + 293 + ], + "type": "text", + "content": "both localizing a unique target object referred by a description. ScanRefer [7] requires both object detection and grounding, while ReferIt3D [4] focuses on discriminating a target object from multiple objects of that semantic class given ground-truth object bounding boxes." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 293, + 546, + 449 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 293, + 546, + 449 + ], + "spans": [ + { + "bbox": [ + 304, + 293, + 546, + 449 + ], + "type": "text", + "content": "Different approaches [7, 4] have been proposed to tackle the two tasks, with models focusing on graph representations [21, 60, 17], improved handling of relations [63, 12], neurosymbolic reasoning [19], leveraging multi-view images and 2D semantics [58, 24, 22, 5], to unified models that can address both grounding and captioning [6, 8, 23, 9]. Recently, Abdelreheem et al. [1], Wu et al. [55] showed that including training on dense annotations can improve performance. Jain et al. [25] proposed to tackle object detection and visual grounding in a unified way by aligning features for text tokens with object proposals. In this work, we compare the performance of three recent models on our task Multi3DRefer with a new CLIP-based model." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 452, + 545, + 596 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 452, + 545, + 596 + ], + "spans": [ + { + "bbox": [ + 304, + 452, + 545, + 596 + ], + "type": "text", + "content": "3D understanding using vision-language models. Large pre-trained text-vision models such as CLIP [47] and ALIGN [27] enabled work leveraging these models for 3D scene understanding. Recent work learn joint embeddings with text-image-3D representations [56, 62], used for disambiguating referring expressions [53] or text-to-shape retrieval [51]. Incorporating pre-trained 2D visual features also enabled expansion of 3D detection and instance segmentation to a larger number of categories [50], as well as tackling open vocabulary 3D detection [40, 52], and building of 3D semantic maps [26]. In our work, we show that we can leverage CLIP for improved visual grounding." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 609, + 432, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 609, + 432, + 621 + ], + "spans": [ + { + "bbox": [ + 306, + 609, + 432, + 621 + ], + "type": "text", + "content": "3. Multi3DRefer dataset" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 629, + 545, + 713 + ], + "type": "text", + "content": "To study our task, we build the Multi3DRefer dataset, a superset of the existing ScanRefer dataset [7] with language descriptions of varying granularities. We augment ScanRefer [7] to create a dataset with 3 types of description-scene pairs: a) Zero Target; b) Single Target; and c) Multiple Targets, indicating zero, single, or multiple target objects in the scene match the description (see Fig. 2). In addition, we use" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 58, + 702, + 217, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 217, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 217, + 713 + ], + "type": "text", + "content": "1https://openai.com/blog/chatgpt/" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "15226" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 71, + 285, + 140 + ], + "blocks": [ + { + "bbox": [ + 49, + 71, + 285, + 140 + ], + "lines": [ + { + "bbox": [ + 49, + 71, + 285, + 140 + ], + "spans": [ + { + "bbox": [ + 49, + 71, + 285, + 140 + ], + "type": "table", + "html": "
DatasetZero TargetSingle TargetMultiple TargetsTotal
ScanRefer [7]-51583-51583
Sr3D [4]-83572-83572
Sr3D+ [4]-114532-114532
Nr3D [4]-41503-41503
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", + "image_path": "388d87955139c2f8aa000cebe0e53dee5313b0f5e242bf972999967ad62808bc.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 142, + 286, + 178 + ], + "lines": [ + { + "bbox": [ + 47, + 142, + 286, + 178 + ], + "spans": [ + { + "bbox": [ + 47, + 142, + 286, + 178 + ], + "type": "text", + "content": "Table 1: Compared to existing 3D visual grounding datasets, our Multi3DRefer dataset contains text that describes zero, single, or multiple target objects." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "text" + }, + { + "type": "image", + "bbox": [ + 58, + 190, + 274, + 449 + ], + "blocks": [ + { + "bbox": [ + 58, + 190, + 274, + 449 + ], + "lines": [ + { + "bbox": [ + 58, + 190, + 274, + 449 + ], + "spans": [ + { + "bbox": [ + 58, + 190, + 274, + 449 + ], + "type": "image", + "image_path": "7bd4ea636cd690f9abf55381d7e590df8dd7871573c4fe57cacc2225d515fc91.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 457, + 287, + 517 + ], + "lines": [ + { + "bbox": [ + 46, + 457, + 287, + 517 + ], + "spans": [ + { + "bbox": [ + 46, + 457, + 287, + 517 + ], + "type": "text", + "content": "Figure 3: Multi3DRefer data construction pipeline showing the generation process of Zero Target (red), Single Target (blue) and Multiple Target (orange) data. We use ChatGPT to add diversity to the description. All scene-description pairs are manually verified and modified if needed." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 540, + 286, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 540, + 286, + 601 + ], + "spans": [ + { + "bbox": [ + 46, + 540, + 286, + 601 + ], + "type": "text", + "content": "ChatGPT to augment the descriptions so they are more natural and diverse (see Fig. 3 for the overall data construction pipeline). To ensure the dataset is of high quality we manually verify all generated samples. We obtain a dataset with 61926 descriptions in total (see Tabs. 1 and 3 for statistics)." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 610, + 227, + 624 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 610, + 227, + 624 + ], + "spans": [ + { + "bbox": [ + 47, + 610, + 227, + 624 + ], + "type": "text", + "content": "3.1. Adapting text for multiple targets" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "content": "We start with scene-description pairs from ScanRefer [7] and augment the data to create samples that refer to zero or more targets. For Single Target descriptions (type b), we take the released ScanRefer dataset which consists of description-scene pairs that have been initially verified to refer to unique objects [7]. We double-checked whether these descriptions indeed refer to unique objects and we" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 228 + ], + "type": "text", + "content": "found 9324 descriptions that are ambiguous. We use these ambiguous descriptions as an initial set of type (c) descriptions that can refer to multiple objects. For additional type (c) descriptions, we obtain from the ScanRefer authors 7741 ambiguous descriptions that can refer to multiple objects and annotate those descriptions with matching objects. To collect type (a) description (no target object) as well as more type (c) descriptions, we develop an efficient data collection pipeline consisting of two stages: 1) automated description generation; and 2) verification and modification. This pipeline maximizes the use of the existing ScanRefer dataset and reduces manual annotation. Below, we describe how we generate and verify additional data samples." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 230, + 545, + 397 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 230, + 545, + 397 + ], + "spans": [ + { + "bbox": [ + 304, + 230, + 545, + 397 + ], + "type": "text", + "content": "Zero Target. To obtain descriptions with no target objects, we establish negative pairs of scenes with existing descriptions selected randomly from other scenes. We then manually verify that descriptions do not match any objects in the new scene. To reduce the number of description-scene pairs that need to be verified, we automatically check whether the semantic class of the target object for the description appears in the scene. Only if the semantic class appears in the scene does it need to be manually verified. Out of 6688 samples, we manually verify 5630 with 1058 automatically checked to have no matching objects. For pairs that need verification, human annotators are shown the description along with an interactive view of the scene to check that there are no matching objects." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 400, + 545, + 568 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 400, + 545, + 568 + ], + "spans": [ + { + "bbox": [ + 304, + 400, + 545, + 568 + ], + "type": "text", + "content": "Multiple Targets. To generate descriptions with multiple targets, we start with the original description-scene pairs in the ScanRefer dataset. We then randomly select descriptions and trim the text to the first punctuation to obtain shorter, more ambiguous descriptions (e.g., \"The cabinet is white and in the back of the room. It is the one on the left.\" " + }, + { + "bbox": [ + 304, + 400, + 545, + 568 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 304, + 400, + 545, + 568 + ], + "type": "text", + "content": " \"The cabinet is white and in the back of the room\"). Note that descriptions in which the semantic class of the target object only has a unique object in the scene are skipped. The trimmed text and scene pairs are sent to the annotation interface. This time, annotators are asked to select all eligible objects of a description in a 3D interactive scene mesh. Annotators are also asked to modify trimmed descriptions to fix errors and increase diversity (see Fig. 4 for examples)." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 577, + 459, + 590 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 577, + 459, + 590 + ], + "spans": [ + { + "bbox": [ + 306, + 577, + 459, + 590 + ], + "type": "text", + "content": "3.2. Rephrasing using ChatGPT" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 596, + 545, + 632 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 596, + 545, + 632 + ], + "spans": [ + { + "bbox": [ + 304, + 596, + 545, + 632 + ], + "type": "text", + "content": "To increase description diversity we use the ChatGPT model text-davinci-002-render for sentence rephrasing. We provide ChatGPT with the following prompts:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 310, + 632, + 545, + 712 + ], + "type": "list", + "angle": 0, + "index": 17, + "blocks": [ + { + "bbox": [ + 310, + 632, + 545, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 632, + 545, + 651 + ], + "spans": [ + { + "bbox": [ + 310, + 632, + 545, + 651 + ], + "type": "text", + "content": "1. I will give you a sentence describing an object, please help me polish it and keep its meaning." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 310, + 651, + 544, + 660 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 651, + 544, + 660 + ], + "spans": [ + { + "bbox": [ + 310, + 651, + 544, + 660 + ], + "type": "text", + "content": "2. Help me reword a sentence to a different format but keep its meaning." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 310, + 660, + 488, + 669 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 660, + 488, + 669 + ], + "spans": [ + { + "bbox": [ + 310, + 660, + 488, + 669 + ], + "type": "text", + "content": "3. Help me reword a sentence to make it more natural." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 310, + 670, + 545, + 689 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 670, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 310, + 670, + 545, + 689 + ], + "type": "text", + "content": "4. Help me reword a sentence describing an object, you should describe the colors and the spatial information in a different way." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 310, + 691, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 691, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 310, + 691, + 545, + 712 + ], + "type": "text", + "content": "5. Help me reword a sentence to an interesting format, you should keep its meaning." + } + ] + } + ], + "index": 16 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15227" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 66, + 112, + 167, + 196 + ], + "blocks": [ + { + "bbox": [ + 66, + 81, + 93, + 87 + ], + "lines": [ + { + "bbox": [ + 66, + 81, + 93, + 87 + ], + "spans": [ + { + "bbox": [ + 66, + 81, + 93, + 87 + ], + "type": "text", + "content": "ScanRefer" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 170, + 72, + 203, + 78 + ], + "lines": [ + { + "bbox": [ + 170, + 72, + 203, + 78 + ], + "spans": [ + { + "bbox": [ + 170, + 72, + 203, + 78 + ], + "type": "text", + "content": "Multi3DRefer" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 170, + 79, + 266, + 89 + ], + "lines": [ + { + "bbox": [ + 170, + 79, + 266, + 89 + ], + "spans": [ + { + "bbox": [ + 170, + 79, + 266, + 89 + ], + "type": "text", + "content": "T: This is a white kitchen cabinet located to the left of the over and stove unit." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 170, + 90, + 265, + 100 + ], + "lines": [ + { + "bbox": [ + 170, + 90, + 265, + 100 + ], + "spans": [ + { + "bbox": [ + 170, + 90, + 265, + 100 + ], + "type": "text", + "content": "M: This is a white kitchen cabinet located near the over and stove unit." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 66, + 112, + 167, + 196 + ], + "lines": [ + { + "bbox": [ + 66, + 112, + 167, + 196 + ], + "spans": [ + { + "bbox": [ + 66, + 112, + 167, + 196 + ], + "type": "image", + "image_path": "516fd701e8fcbe4b459e037d39b7c29ade03d241603b8ab6122049c2d369b46a.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 66, + 205, + 92, + 210 + ], + "lines": [ + { + "bbox": [ + 66, + 205, + 92, + 210 + ], + "spans": [ + { + "bbox": [ + 66, + 205, + 92, + 210 + ], + "type": "text", + "content": "ScanRefer" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 170, + 113, + 270, + 196 + ], + "blocks": [ + { + "bbox": [ + 67, + 87, + 165, + 104 + ], + "lines": [ + { + "bbox": [ + 67, + 87, + 165, + 104 + ], + "spans": [ + { + "bbox": [ + 67, + 87, + 165, + 104 + ], + "type": "text", + "content": "This is a white kitchen cabinet located to the left of the over and stove unit. It has four drawers with silver handles." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 170, + 101, + 264, + 111 + ], + "lines": [ + { + "bbox": [ + 170, + 101, + 264, + 111 + ], + "spans": [ + { + "bbox": [ + 170, + 101, + 264, + 111 + ], + "type": "text", + "content": "R: A white kitchen cabinet is situated near the oven and stove unit." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 170, + 113, + 270, + 196 + ], + "lines": [ + { + "bbox": [ + 170, + 113, + 270, + 196 + ], + "spans": [ + { + "bbox": [ + 170, + 113, + 270, + 196 + ], + "type": "image", + "image_path": "60db7c60ef9de9e51fa2c76a6c257896059a334d7e34f47fab6c397b24fda30f.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 67, + 239, + 167, + 323 + ], + "blocks": [ + { + "bbox": [ + 66, + 211, + 160, + 228 + ], + "lines": [ + { + "bbox": [ + 66, + 211, + 160, + 228 + ], + "spans": [ + { + "bbox": [ + 66, + 211, + 160, + 228 + ], + "type": "text", + "content": "There is a rectangular blue pillow with colorful decorations. It is on a larger cushion in front of the window by the side of the room." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 67, + 239, + 167, + 323 + ], + "lines": [ + { + "bbox": [ + 67, + 239, + 167, + 323 + ], + "spans": [ + { + "bbox": [ + 67, + 239, + 167, + 323 + ], + "type": "image", + "image_path": "2c8fc41025d993e4afd8985fbd767e082bec7afb92e57f364b8535e53ae69081.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 66, + 326, + 93, + 331 + ], + "lines": [ + { + "bbox": [ + 66, + 326, + 93, + 331 + ], + "spans": [ + { + "bbox": [ + 66, + 326, + 93, + 331 + ], + "type": "text", + "content": "ScanRefer" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 170, + 240, + 270, + 323 + ], + "blocks": [ + { + "bbox": [ + 170, + 205, + 265, + 242 + ], + "lines": [ + { + "bbox": [ + 170, + 205, + 265, + 242 + ], + "spans": [ + { + "bbox": [ + 170, + 205, + 265, + 242 + ], + "type": "text", + "content": "M: There is a rectangular pillow with colorful decorations. 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R: A rectangular pillow, adorned with colorful decorations, rests upon a larger cushion positioned by the side of the room, right in front of the window." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 170, + 240, + 270, + 323 + ], + "lines": [ + { + "bbox": [ + 170, + 240, + 270, + 323 + ], + "spans": [ + { + "bbox": [ + 170, + 240, + 270, + 323 + ], + "type": "image", + "image_path": "8c4a79c3d54a253d64f53f31e1663beb3226491a92007e0d564d07f38b855187.jpg" + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 170, + 326, + 202, + 331 + ], + "lines": [ + { + "bbox": [ + 170, + 326, + 202, + 331 + ], + "spans": [ + { + "bbox": [ + 170, + 326, + 202, + 331 + ], + "type": "text", + "content": "Multi3DRefer" + } + ] + } + ], + "index": 15, + "angle": 0, + "type": "image_caption" + } + ], + "index": 12 + }, + { + "type": "image", + "bbox": [ + 67, + 343, + 167, + 427 + ], + "blocks": [ + { + "bbox": [ + 67, + 333, + 162, + 343 + ], + "lines": [ + { + "bbox": [ + 67, + 333, + 162, + 343 + ], + "spans": [ + { + "bbox": [ + 67, + 333, + 162, + 343 + ], + "type": "text", + "content": "This is a green patterned chair. It is at a brown table." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 67, + 343, + 167, + 427 + ], + "lines": [ + { + "bbox": [ + 67, + 343, + 167, + 427 + ], + "spans": [ + { + "bbox": [ + 67, + 343, + 167, + 427 + ], + "type": "image", + "image_path": "92ce8e4961ea89b06b1511e8e5b17294ca71f7180ce96c3b167db5d5412a5117.jpg" + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 436, + 287, + 518 + ], + "lines": [ + { + "bbox": [ + 46, + 436, + 287, + 518 + ], + "spans": [ + { + "bbox": [ + 46, + 436, + 287, + 518 + ], + "type": "text", + "content": "Figure 4: Examples of generated revised descriptions of multiple targets for the Multi3DRefer dataset where we trim (T) to create more ambiguous descriptions, modify (M) by human, and reword (R) using ChatGPT. All descriptions are verified by annotators (see bounding boxes for target objects). Note that the reworded (R) descriptions provide more variation in sentence structure." + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "image_caption" + } + ], + "index": 17 + }, + { + "type": "image", + "bbox": [ + 170, + 343, + 270, + 427 + ], + "blocks": [ + { + "bbox": [ + 170, + 333, + 265, + 343 + ], + "lines": [ + { + "bbox": [ + 170, + 333, + 265, + 343 + ], + "spans": [ + { + "bbox": [ + 170, + 333, + 265, + 343 + ], + "type": "text", + "content": "R: A green patterned chair sits beside a brown table." + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 170, + 343, + 270, + 427 + ], + "lines": [ + { + "bbox": [ + 170, + 343, + 270, + 427 + ], + "spans": [ + { + "bbox": [ + 170, + 343, + 270, + 427 + ], + "type": "image", + "image_path": "575b7e0d4d7caa47b79ef097cef4f43139aa1fcd8b1a0bbf9e36dcb64df7afe8.jpg" + } + ] + } + ], + "index": 18, + "angle": 0, + "type": "image_body" + } + ], + "index": 18 + }, + { + "type": "table", + "bbox": [ + 50, + 533, + 286, + 574 + ], + "blocks": [ + { + "bbox": [ + 50, + 533, + 286, + 574 + ], + "lines": [ + { + "bbox": [ + 50, + 533, + 286, + 574 + ], + "spans": [ + { + "bbox": [ + 50, + 533, + 286, + 574 + ], + "type": "table", + "html": "
Unique wordsTotal wordsAvg. description length
Original5067101619016.4
Rephrased707793693515.1
", + "image_path": "7c73cbd9f0340cd5203853baaa7f50dd4fb0fd3cffef53dbd19d81bf245a6db1.jpg" + } + ] + } + ], + "index": 20, + "angle": 0, + "type": "table_body" + } + ], + "index": 20 + }, + { + "bbox": [ + 46, + 654, + 286, + 702 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 654, + 286, + 702 + ], + "spans": [ + { + "bbox": [ + 46, + 654, + 286, + 702 + ], + "type": "text", + "content": "Tab. 2 shows statistics comparing the descriptions before and after rephrasing. We see a richer vocabulary but shorter descriptions after ChatGPT rephrasing. Below we provide examples of the original (O) and reworded (R) text:" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 52, + 703, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 703, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 52, + 703, + 287, + 712 + ], + "type": "text", + "content": "O: The table is a round table. It is located between two chairs to the" + } + ] + } + ], + "index": 23 + }, + { + "type": "table", + "bbox": [ + 309, + 70, + 544, + 148 + ], + "blocks": [ + { + "bbox": [ + 46, + 582, + 287, + 631 + ], + "lines": [ + { + "bbox": [ + 46, + 582, + 287, + 631 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 287, + 631 + ], + "type": "text", + "content": "Table 2: Comparison of Multi3DRefer language data before and after ChatGPT rephrasing. We count the number of unique words, total words, and the average description length, excluding punctuation." + } + ] + } + ], + "index": 21, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 309, + 70, + 544, + 148 + ], + "lines": [ + { + "bbox": [ + 309, + 70, + 544, + 148 + ], + "spans": [ + { + "bbox": [ + 309, + 70, + 544, + 148 + ], + "type": "table", + "html": "
SpatialColorTextureShapeTotal
ScanRefer [7]511173469258641741651583
Nr3D [4]3971111939526856841503
Sr3D [4]835726254064883572
Sr3D+ [4]11453286660744114532
Multi3DRefer600284130771211969261926
", + "image_path": "1e119eb23c14532c2e15452686adb9dd9bb14a2460501451b870eb3ddc2923eb.jpg" + } + ] + } + ], + "index": 24, + "angle": 0, + "type": "table_body" + } + ], + "index": 24 + }, + { + "bbox": [ + 306, + 156, + 545, + 180 + ], + "lines": [ + { + "bbox": [ + 306, + 156, + 545, + 180 + ], + "spans": [ + { + "bbox": [ + 306, + 156, + 545, + 180 + ], + "type": "text", + "content": "Table 3: Breakdown of spatial, color, texture, and shape information in object descriptions from different datasets." + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 311, + 211, + 545, + 329 + ], + "type": "list", + "angle": 0, + "index": 34, + "blocks": [ + { + "bbox": [ + 321, + 211, + 439, + 220 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 211, + 439, + 220 + ], + "spans": [ + { + "bbox": [ + 321, + 211, + 439, + 220 + ], + "type": "text", + "content": "right, and two chairs to the left of it." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 311, + 221, + 545, + 239 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 221, + 545, + 239 + ], + "spans": [ + { + "bbox": [ + 311, + 221, + 545, + 239 + ], + "type": "text", + "content": "R: The round table is situated between two chairs to its right and two chairs to its left." + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 311, + 243, + 545, + 262 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 243, + 545, + 262 + ], + "spans": [ + { + "bbox": [ + 311, + 243, + 545, + 262 + ], + "type": "text", + "content": "O: This is a table on the wall in the room. It is next to the window and a few lined-up chairs." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 311, + 262, + 544, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 262, + 544, + 281 + ], + "spans": [ + { + "bbox": [ + 311, + 262, + 544, + 281 + ], + "type": "text", + "content": "R: A wall-mounted table resides coaxily beside a window in the room, accompanied by a row of orderly chairs." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 311, + 285, + 518, + 294 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 285, + 518, + 294 + ], + "spans": [ + { + "bbox": [ + 311, + 285, + 518, + 294 + ], + "type": "text", + "content": "O: A sink on the vanity. It is to the right of the vacuum cleaners." + } + ] + } + ], + "index": 30 + }, + { + "bbox": [ + 311, + 296, + 541, + 304 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 296, + 541, + 304 + ], + "spans": [ + { + "bbox": [ + 311, + 296, + 541, + 304 + ], + "type": "text", + "content": "R: The sink is located on the vanity to the right of the vacuum cleaners." + } + ] + } + ], + "index": 31 + }, + { + "bbox": [ + 311, + 308, + 539, + 317 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 308, + 539, + 317 + ], + "spans": [ + { + "bbox": [ + 311, + 308, + 539, + 317 + ], + "type": "text", + "content": "O: This is a white kitchen cabinet located near the over and stove unit." + } + ] + } + ], + "index": 32 + }, + { + "bbox": [ + 311, + 320, + 525, + 329 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 320, + 525, + 329 + ], + "spans": [ + { + "bbox": [ + 311, + 320, + 525, + 329 + ], + "type": "text", + "content": "R: A white kitchen cabinet is situated near the oven and stove unit" + } + ] + } + ], + "index": 33 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 334, + 545, + 370 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 334, + 545, + 370 + ], + "spans": [ + { + "bbox": [ + 306, + 334, + 545, + 370 + ], + "type": "text", + "content": "The rephrased text preserves the original meaning while being more natural. In addition, ChatGPT automatically corrects typos (e.g., over to oven in the last example)." + } + ] + } + ], + "index": 35 + }, + { + "bbox": [ + 306, + 388, + 382, + 399 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 388, + 382, + 399 + ], + "spans": [ + { + "bbox": [ + 306, + 388, + 382, + 399 + ], + "type": "text", + "content": "3.3. Verification" + } + ] + } + ], + "index": 36 + }, + { + "bbox": [ + 304, + 410, + 545, + 564 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 410, + 545, + 564 + ], + "spans": [ + { + "bbox": [ + 304, + 410, + 545, + 564 + ], + "type": "text", + "content": "After we obtain a set of ChatGPT reworded descriptions, we manually verify the descriptions are well-written and that the object(s) matched in the scene are accurate. We create a web interface for verifiers to check whether the description matches the identified target objects (see supplement for details). The web interface shows the description together with an interactive 3D view of the scene and the target objects. The verifiers check if the description matches the target objects and only the target objects, or modify the list of target objects (by selecting appropriate objects), or improve the description to fix typos and ambiguities. The verification was performed by 5 students over a period of one month." + } + ] + } + ], + "index": 37 + }, + { + "bbox": [ + 306, + 584, + 406, + 596 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 584, + 406, + 596 + ], + "spans": [ + { + "bbox": [ + 306, + 584, + 406, + 596 + ], + "type": "text", + "content": "3.4. Dataset statistics" + } + ] + } + ], + "index": 38 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "In total, our dataset consists of 61926 language descriptions, with 51583 directly obtained from ScanRefer [7], of which 6688 descriptions match zero-targets and 13178 match multiple. For Multiple Targets, the scenes are typically offices or meeting rooms with many chairs and tables. See Tab. 1 for a comparison of our final dataset against prior datasets. We also provide annotations for each description as to whether it refers to spatial, color, texture, or shape attributes (see Tab. 3)." + } + ] + } + ], + "index": 39 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15228" + } + ] + } + ], + "index": 40 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 70, + 545, + 257 + ], + "blocks": [ + { + "bbox": [ + 48, + 70, + 545, + 257 + ], + "lines": [ + { + "bbox": [ + 48, + 70, + 545, + 257 + ], + "spans": [ + { + "bbox": [ + 48, + 70, + 545, + 257 + ], + "type": "image", + "image_path": "ed990a157b0f5a517fb2c0ca868937d0b078d00fb491f86326e8c470e0b46ca0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 266, + 547, + 340 + ], + "lines": [ + { + "bbox": [ + 46, + 266, + 547, + 340 + ], + "spans": [ + { + "bbox": [ + 46, + 266, + 547, + 340 + ], + "type": "text", + "content": "Figure 5: Our M3DRef-CLIP end-to-end architecture. Given a scene point cloud and a text description with " + }, + { + "bbox": [ + 46, + 266, + 547, + 340 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 266, + 547, + 340 + ], + "type": "text", + "content": " tokens (we pad shorter descriptions and truncate longer ones), the detector first predicts " + }, + { + "bbox": [ + 46, + 266, + 547, + 340 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 266, + 547, + 340 + ], + "type": "text", + "content": " object proposals and their 3D features. Then an online renderer renders " + }, + { + "bbox": [ + 46, + 266, + 547, + 340 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 266, + 547, + 340 + ], + "type": "text", + "content": "-view images for each proposal and feeds them into the image encoder to get 2D features. A transformer-based module then fuses both language features and " + }, + { + "bbox": [ + 46, + 266, + 547, + 340 + ], + "type": "inline_equation", + "content": "2\\mathrm{D} + 3\\mathrm{D}" + }, + { + "bbox": [ + 46, + 266, + 547, + 340 + ], + "type": "text", + "content": " object features and outputs scores indicating the match of each object to the description. We use PointGroup [28] to detect and segment the objects in 3D and select CLIP [47] + MLPs as the language and image encoder. A contrastive loss is applied between sentence features and object features." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 358, + 87, + 370 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 358, + 87, + 370 + ], + "spans": [ + { + "bbox": [ + 47, + 358, + 87, + 370 + ], + "type": "text", + "content": "4. Task" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 384, + 289, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 384, + 289, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 384, + 289, + 529 + ], + "type": "text", + "content": "In the Multi3DRefer task, we are given as input a 3D real-world scene represented as a point cloud " + }, + { + "bbox": [ + 46, + 384, + 289, + 529 + ], + "type": "inline_equation", + "content": "P \\in \\mathbb{R}^{N \\times (3 + C)}" + }, + { + "bbox": [ + 46, + 384, + 289, + 529 + ], + "type": "text", + "content": " and a free-form language description with a variable number " + }, + { + "bbox": [ + 46, + 384, + 289, + 529 + ], + "type": "inline_equation", + "content": "M \\in \\mathbb{N}" + }, + { + "bbox": [ + 46, + 384, + 289, + 529 + ], + "type": "text", + "content": " of referred objects, where " + }, + { + "bbox": [ + 46, + 384, + 289, + 529 + ], + "type": "inline_equation", + "content": "N, C" + }, + { + "bbox": [ + 46, + 384, + 289, + 529 + ], + "type": "text", + "content": " are the number of points and the number of point feature channels, respectively. The goal is to predict axis-aligned bounding boxes for all " + }, + { + "bbox": [ + 46, + 384, + 289, + 529 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 384, + 289, + 529 + ], + "type": "text", + "content": " objects that match the description. Compared to prior work, the difficulty of our task is that the number of referred objects is flexible, i.e., a description can refer to not only one or multiple target objects but also no objects. Predicting too many or too few target objects are both penalized by our evaluation metrics." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": "Evaluation metrics. To evaluate grounding for a flexible number of target objects, we measure the F1 score at the intersection over union (IoU) thresholds of " + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{eval}} = 0.25" + }, + { + "bbox": [ + 46, + 533, + 289, + 714 + ], + "type": "text", + "content": " and 0.5 (F1@0.25 and F1@0.5). To investigate model performance for different scenarios, we consider the following 5 cases: a) zero target w/o distractors of the same semantic class; b) zero target w/ distractors; c) single target w/o distractors; d) single target w/ distractors; and e) multiple targets. Note that c) and d) correspond to the \"unique\" and \"multiple\" cases in ScanRefer [7]. In addition, a) and c) are easier cases where there are zero or a unique target object of its semantic class in a scene, while b) and d) are more difficult cases containing one or multiple target objects of the same semantic class in a scene. We also report the micro-average of the 5 cases as an overall score." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 359, + 547, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 359, + 547, + 431 + ], + "spans": [ + { + "bbox": [ + 304, + 359, + 547, + 431 + ], + "type": "text", + "content": "During evaluations, we first calculate per-pair IoUs between ground truth and predicted bounding boxes in a scene, and then apply the Hungarian algorithm [34] to get an optimal one-to-one matching between predicted and GT bounding boxes. To get the maximum matched IoU, we use the following cost function:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 333, + 433, + 518, + 446 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 333, + 433, + 518, + 446 + ], + "spans": [ + { + "bbox": [ + 333, + 433, + 518, + 446 + ], + "type": "interline_equation", + "content": "\\operatorname {C o s t} (i, j) = - \\operatorname {I o U} (i, j) \\text {f o r} i, j \\in \\{1 \\dots N \\}", + "image_path": "7f3b5ff158a97b392fbfb6c6d6da79a267eed524c7249d62e8187d183282166e.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 447, + 547, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 447, + 547, + 509 + ], + "spans": [ + { + "bbox": [ + 304, + 447, + 547, + 509 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 447, + 547, + 509 + ], + "type": "inline_equation", + "content": "N = \\max (\\# Predictions, \\# GTs)" + }, + { + "bbox": [ + 304, + 447, + 547, + 509 + ], + "type": "text", + "content": ". After obtaining the optimal match, we take pairs with IoUs higher than " + }, + { + "bbox": [ + 304, + 447, + 547, + 509 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{eval}}" + }, + { + "bbox": [ + 304, + 447, + 547, + 509 + ], + "type": "text", + "content": " to be True Positives (TP). We treat the Zero Target (ZT) case as a special case where recall is always set to 1, and precision is set to 1 if there is no prediction or 0 otherwise." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 518, + 362, + 530 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 518, + 362, + 530 + ], + "spans": [ + { + "bbox": [ + 306, + 518, + 362, + 530 + ], + "type": "text", + "content": "5. Method" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 539, + 547, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 539, + 547, + 696 + ], + "spans": [ + { + "bbox": [ + 304, + 539, + 547, + 696 + ], + "type": "text", + "content": "We propose M3DRef-CLIP, a CLIP-based approach and compare to three recent approaches: 3DVG-Transformer [63], 3DJCG [6] and D3Net [8]. We selected these methods as they were among the top performers on the ScanRefer [7] benchmark with available open-source code. Note that 3DJCG [6] and D3Net [8] are unified models, which can do both grounding and captioning tasks. All four models are two-stage approaches, where a 3D object detector first identifies a set of bounding box candidates, and a disambiguation module then selects the target bounding box. In the original ScanRefer setting, the three compared models are trained using a cross-entropy loss " + }, + { + "bbox": [ + 304, + 539, + 547, + 696 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{ref}}" + }, + { + "bbox": [ + 304, + 539, + 547, + 696 + ], + "type": "text", + "content": " where the predicted bounding box has the highest IoU (" + }, + { + "bbox": [ + 304, + 539, + 547, + 696 + ], + "type": "inline_equation", + "content": "> \\tau_{\\mathrm{train}}" + }, + { + "bbox": [ + 304, + 539, + 547, + 696 + ], + "type": "text", + "content": ") with" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 315, + 702, + 455, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 702, + 455, + 712 + ], + "spans": [ + { + "bbox": [ + 315, + 702, + 455, + 712 + ], + "type": "inline_equation", + "content": "^{2}" + }, + { + "bbox": [ + 315, + 702, + 455, + 712 + ], + "type": "text", + "content": "kaldir.vc.in.tum.de/scanrefer_benchmark" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "15229" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "content": "the GT bounding box as the target bounding box to calculate the loss. For our task, we use a binary cross-entropy loss for " + }, + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{ref}}" + }, + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "content": " as our problem is a multi-label task (vs classification)." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 118, + 141, + 129 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 118, + 141, + 129 + ], + "spans": [ + { + "bbox": [ + 47, + 118, + 141, + 129 + ], + "type": "text", + "content": "5.1. M3DRef-CLIP" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 137, + 287, + 293 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 137, + 287, + 293 + ], + "spans": [ + { + "bbox": [ + 46, + 137, + 287, + 293 + ], + "type": "text", + "content": "M3DRef-CLIP follows the two-stage architecture with PointGroup [28] as the detector, CLIP [47] as the text encoder and a transformer-based fusion module (see Fig. 5). We use PointGroup [28] to obtain object proposals along with their 3D features " + }, + { + "bbox": [ + 46, + 137, + 287, + 293 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^{3\\mathrm{d}} \\in R^{32}" + }, + { + "bbox": [ + 46, + 137, + 287, + 293 + ], + "type": "text", + "content": ". The output object proposals are fed into an online object renderer, which renders multi-view 2D images for each object proposal. We use CLIP [47] to encode the images and use an MLP to project the average of the output 2D image features to obtain " + }, + { + "bbox": [ + 46, + 137, + 287, + 293 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^{2\\mathrm{d}} \\in \\mathbb{R}^{128}" + }, + { + "bbox": [ + 46, + 137, + 287, + 293 + ], + "type": "text", + "content": ". The 2D and 3D features are concatenated to form and passed through a 1D convolution (that projects the combined 160-dim features down to 128-dim) to obtain the final visual features " + }, + { + "bbox": [ + 46, + 137, + 287, + 293 + ], + "type": "inline_equation", + "content": "\\mathbf{F}^{\\mathrm{obj}} \\in \\mathbb{R}^{128}" + }, + { + "bbox": [ + 46, + 137, + 287, + 293 + ], + "type": "text", + "content": " for an object proposal:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 55, + 294, + 278, + 319 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 294, + 278, + 319 + ], + "spans": [ + { + "bbox": [ + 55, + 294, + 278, + 319 + ], + "type": "interline_equation", + "content": "\\mathbf {F} ^ {\\mathrm {o b j}} = \\operatorname {c o n v} _ {\\mathrm {l d}} ([ \\mathbf {F} ^ {\\mathrm {3 d}}; \\mathbf {F} ^ {\\mathrm {2 d}} ]), \\quad \\mathbf {F} ^ {\\mathrm {2 d}} = \\frac {\\operatorname {M L P} (\\sum_ {i = 1} ^ {N} \\mathbf {F} _ {i} ^ {\\mathrm {2 d}})}{N}", + "image_path": "200a68fe71844fd05db00ae1d5c3e38a74a21086d370d50b617b42378e5435df.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 319, + 287, + 390 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 319, + 287, + 390 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 287, + 390 + ], + "type": "text", + "content": "We use the CLIP text encoder with an MLP to obtain both 128-dim token-level and sentence embeddings. We use a transformer-based fusion module to combine object features and token-level embeddings and output confidence scores for each proposal. To improve the training, we apply a contrastive loss between sentence and object features." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 400, + 133, + 411 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 400, + 133, + 411 + ], + "spans": [ + { + "bbox": [ + 47, + 400, + 133, + 411 + ], + "type": "text", + "content": "5.2. Loss function" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "spans": [ + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "text", + "content": "We train the network end-to-end with the total loss " + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "inline_equation", + "content": "L = L_{\\mathrm{det}} + L_c + L_{\\mathrm{ref}}" + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "text", + "content": " consisting of the detection loss " + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{det}}" + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "text", + "content": ", contrastive loss " + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{c}}" + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "text", + "content": ", and the reference loss " + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{ref}}" + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "text", + "content": ". The detection loss " + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{det}}" + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "text", + "content": " is introduced in PointGroup [28] and consists of four parts: 1) cross-entropy loss for supervising per-point semantic class prediction; 2) " + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "inline_equation", + "content": "L_1" + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "text", + "content": " loss for supervising perpoint offset vector towards object centers; 3) directional loss formed as a mean of minus cosine similarities for further constraining the direction of per-point offset vectors; 4) binary cross-entropy loss for supervising per-point objectness confidence score. To help learn better multi-modal embeddings, we introduce a symmetric contrastive loss " + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "inline_equation", + "content": "L_{c}" + }, + { + "bbox": [ + 46, + 420, + 287, + 586 + ], + "type": "text", + "content": " [47], which can handle a flexible number of target objects as shown below:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 79, + 586, + 253, + 613 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 79, + 586, + 253, + 613 + ], + "spans": [ + { + "bbox": [ + 79, + 586, + 253, + 613 + ], + "type": "interline_equation", + "content": "L _ {\\mathrm {c}} ^ {O \\rightarrow S} = - \\log \\frac {\\exp (\\cos (\\bar {O} _ {i} , S _ {i}) / \\tau)}{\\sum_ {i = 1} ^ {n} \\exp (\\cos (\\bar {O} _ {i} , S _ {j}) / \\tau)}", + "image_path": "0531a5acb4fc1c82435b7fceb327a9f6aca99324f42f453bf8b25059dec34f57.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 79, + 614, + 253, + 640 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 79, + 614, + 253, + 640 + ], + "spans": [ + { + "bbox": [ + 79, + 614, + 253, + 640 + ], + "type": "interline_equation", + "content": "L _ {\\mathrm {c}} ^ {S \\rightarrow O} = - \\log \\frac {\\exp (\\cos (S _ {i} , \\bar {O} _ {i}) / \\tau)}{\\sum_ {i = 1} ^ {n} \\exp (\\cos (S _ {i} , \\bar {O} _ {j}) / \\tau)}", + "image_path": "ca314e7cb2c48353812b7cce0e40abfbf8127452d8e6f7e8610baff99c65d559.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": " is sentence features, " + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\bar{O}" + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": " is the mean of object features of all target objects paired with a description, and " + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": " is a temperature parameter. Finally, the reference loss " + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{ref}}" + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": " supervises the matching module to select objects satisfying the description. We use the multi-class cross-entropy loss as " + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{ref}}" + }, + { + "bbox": [ + 46, + 642, + 287, + 713 + ], + "type": "text", + "content": " for experiments on ScanRefer [7], Nr3D [4] and" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": "Multi3DRefer (ST) where each description only refers to a single target object. For experiments on Multi3DRefer, " + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "L_{\\mathrm{ref}}" + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": " is a sum of binary cross-entropy losses over detected objects." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 122, + 545, + 171 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 122, + 545, + 171 + ], + "spans": [ + { + "bbox": [ + 305, + 122, + 545, + 171 + ], + "type": "text", + "content": "Training. To set up positive (i.e. valid target bounding boxes) and negative instances between the GT bounding boxes and proposed bounding boxes, we use two strategies (see supplement for detailed comparisons):" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 172, + 545, + 209 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 172, + 545, + 209 + ], + "spans": [ + { + "bbox": [ + 305, + 172, + 545, + 209 + ], + "type": "text", + "content": "All All predicted bounding boxes with IoU higher than the threshold " + }, + { + "bbox": [ + 305, + 172, + 545, + 209 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{train}}" + }, + { + "bbox": [ + 305, + 172, + 545, + 209 + ], + "type": "text", + "content": " with GT bounding boxes are considered target bounding boxes." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 211, + 545, + 258 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 211, + 545, + 258 + ], + "spans": [ + { + "bbox": [ + 305, + 211, + 545, + 258 + ], + "type": "text", + "content": "Hungarian We apply the Hungarian algorithm [34] to do bipartite matching, which ensures an optimal solution. We use the same IoU threshold " + }, + { + "bbox": [ + 305, + 211, + 545, + 258 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{train}}" + }, + { + "bbox": [ + 305, + 211, + 545, + 258 + ], + "type": "text", + "content": " to filter prediction-GT bounding box pairs." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 261, + 545, + 310 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 261, + 545, + 310 + ], + "spans": [ + { + "bbox": [ + 305, + 261, + 545, + 310 + ], + "type": "text", + "content": "Inference. At inference time, we take all bounding boxes with predicted scores above the threshold " + }, + { + "bbox": [ + 305, + 261, + 545, + 310 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{pred}}" + }, + { + "bbox": [ + 305, + 261, + 545, + 310 + ], + "type": "text", + "content": " as positives (predicted target bounding boxes for the description). See the supplement for comparisons of different " + }, + { + "bbox": [ + 305, + 261, + 545, + 310 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{pred}}" + }, + { + "bbox": [ + 305, + 261, + 545, + 310 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 321, + 387, + 334 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 321, + 387, + 334 + ], + "spans": [ + { + "bbox": [ + 306, + 321, + 387, + 334 + ], + "type": "text", + "content": "6. Experiments" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 342, + 545, + 376 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 342, + 545, + 376 + ], + "spans": [ + { + "bbox": [ + 305, + 342, + 545, + 376 + ], + "type": "text", + "content": "We conduct experiments on both ScanRefer [7] and Multi3DRefer datasets and consider two setups: grounding objects with GT and predicted bounding boxes." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 379, + 545, + 499 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 379, + 545, + 499 + ], + "spans": [ + { + "bbox": [ + 305, + 379, + 545, + 499 + ], + "type": "text", + "content": "GT bounding boxes. For M3DRef-CLIP and D3Net [8], we input the complete scene and apply GT point masks for each object to get GT bounding boxes and masked features from the pre-trained detector (PointGroup for both D3Net and our M3DRef-CLIP). For 3DVG-Trans [63] and 3DJCG [6], we use their original GT setting following the method proposed by ReferIt3D [4]. Single input objects are first extracted from the scene using the GT masks and PointNet++ [46] is used for obtaining the object features. For all methods, we disable the " + }, + { + "bbox": [ + 305, + 379, + 545, + 499 + ], + "type": "inline_equation", + "content": "L_{det}" + }, + { + "bbox": [ + 305, + 379, + 545, + 499 + ], + "type": "text", + "content": " loss when using GT boxes." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 501, + 545, + 536 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 501, + 545, + 536 + ], + "spans": [ + { + "bbox": [ + 305, + 501, + 545, + 536 + ], + "type": "text", + "content": "Predicted bounding boxes. We use the original detector design of each method to predict bounding boxes and extract features." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 545, + 437, + 558 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 545, + 437, + 558 + ], + "spans": [ + { + "bbox": [ + 306, + 545, + 437, + 558 + ], + "type": "text", + "content": "6.1. Implementation details" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 305, + 563, + 545, + 685 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 563, + 545, + 685 + ], + "spans": [ + { + "bbox": [ + 305, + 563, + 545, + 685 + ], + "type": "text", + "content": "We implement M3DRef-CLIP using PyTorch Lightning3 and PyTorch3D [48]. We train the model end-to-end on a single NVIDIA RTX A5000 with a batch size of 4, using the AdamW optimizer [38] with a learning rate of " + }, + { + "bbox": [ + 305, + 563, + 545, + 685 + ], + "type": "inline_equation", + "content": "5e^{-4}" + }, + { + "bbox": [ + 305, + 563, + 545, + 685 + ], + "type": "text", + "content": ". We use a re-implementation of PointGroup4 with the Minkowski Engine [14]. Following D3Net [8], we pretrain our PointGroup module on all ScanNet v2 training scans with the 18 ScanRefer categories. We take point coordinates, point normals and per-point multi-view features " + }, + { + "bbox": [ + 305, + 563, + 545, + 685 + ], + "type": "inline_equation", + "content": "P \\in \\mathbb{R}^{N \\times (3 + 3 + 128)}" + }, + { + "bbox": [ + 305, + 563, + 545, + 685 + ], + "type": "text", + "content": " as the input. For data augmentation, we randomly apply" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 317, + 693, + 403, + 703 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 693, + 403, + 703 + ], + "spans": [ + { + "bbox": [ + 317, + 693, + 403, + 703 + ], + "type": "inline_equation", + "content": "^{3}" + }, + { + "bbox": [ + 317, + 693, + 403, + 703 + ], + "type": "text", + "content": "www.pytorchlightning.ai" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 317, + 703, + 446, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 703, + 446, + 713 + ], + "spans": [ + { + "bbox": [ + 317, + 703, + 446, + 713 + ], + "type": "text", + "content": "4https://github.com/3dlg-hcvc/minsu3d" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15230" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 70, + 545, + 117 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 545, + 117 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 545, + 117 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 545, + 117 + ], + "type": "table", + "html": "
ZT w/o DistractorsZT w DistractorsST w/o DistractorsST w/ DistractorsMultiple Targets
TrainValTestTotalTrainValTestTotalTrainValTestTotalTrainValTestTotalTrainValTestTotal
ScanRefer [7]--------85002297120111998281657211420939585----
Multi3DRefer2702528596382621603783242862719820991106104032204053584259316579738275768313178
", + "image_path": "b44a07a1b5458889a44e8bff9ef8f2732f892b998e186f595a5e8d18f552de73.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 49, + 156, + 285, + 326 + ], + "blocks": [ + { + "bbox": [ + 58, + 125, + 533, + 137 + ], + "lines": [ + { + "bbox": [ + 58, + 125, + 533, + 137 + ], + "spans": [ + { + "bbox": [ + 58, + 125, + 533, + 137 + ], + "type": "text", + "content": "Table 4: Breakdown of different datasets in 5 scenarios. ZT and ST denote Zero Target and Single Target, respectively." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 156, + 285, + 326 + ], + "lines": [ + { + "bbox": [ + 49, + 156, + 285, + 326 + ], + "spans": [ + { + "bbox": [ + 49, + 156, + 285, + 326 + ], + "type": "table", + "html": "
Acc@0.5 on ValAcc@0.5 on Test
UniqueMultipleAllUniqueMultipleAll
3DVG-Trans+ [63]62.030.336.457.931.037.0
InstanceRefer [60]66.824.832.966.726.935.8
FFL-3DOG [17]67.925.734.0---
SAT [58]50.825.230.1---
3D-SPS [41]66.729.837.0---
MVT [22]66.525.333.3---
BUTD-DETR [25]66.335.139.8---
D3Net (G) [8]70.427.135.665.827.336.0
D3Net* [8]72.030.137.968.430.739.2
3DJCG (G) [6]64.530.336.9---
3DJCG* [6]64.330.837.360.631.237.8
HAM [10]67.934.040.663.733.240.1
UniT3D (G) [9]74.827.636.5---
UniT3D* [9]73.131.139.1---
M3DRef-CLIP77.236.844.770.938.145.5
", + "image_path": "d5f07a5688696cc1a83c06c60cdd18b894b33f51f25cffc7b79045c7e00c909c.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 47, + 335, + 287, + 383 + ], + "lines": [ + { + "bbox": [ + 47, + 335, + 287, + 383 + ], + "spans": [ + { + "bbox": [ + 47, + 335, + 287, + 383 + ], + "type": "text", + "content": "Table 5: For unified models [8, 6, 9], we report both the grounding-only (G) performance as well as their best performance. We use * to indicate joint grounding and captioning models trained with extra data." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 404, + 287, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 404, + 287, + 475 + ], + "spans": [ + { + "bbox": [ + 47, + 404, + 287, + 475 + ], + "type": "text", + "content": "coordinate jitter, x-axis flipping and rotation around the z-axis. We freeze a pre-trained CLIP with ViT-B/32 and only train additional MLPs. For encoding the text with CLIP, we follow CLIP and tokenizer with a lower-cased BPE, and [SOS] and [EOS] tokens added (the output corresponding to [EOS] is used as the sentence representation)." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 477, + 287, + 585 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 477, + 287, + 585 + ], + "spans": [ + { + "bbox": [ + 46, + 477, + 287, + 585 + ], + "type": "text", + "content": "Object renderer. For each object proposal, we render 3 views horizontally spaced 120 degrees apart, at a distance of " + }, + { + "bbox": [ + 46, + 477, + 287, + 585 + ], + "type": "inline_equation", + "content": "1\\mathrm{m}" + }, + { + "bbox": [ + 46, + 477, + 287, + 585 + ], + "type": "text", + "content": ", with elevation angle of " + }, + { + "bbox": [ + 46, + 477, + 287, + 585 + ], + "type": "inline_equation", + "content": "45^{\\circ}" + }, + { + "bbox": [ + 46, + 477, + 287, + 585 + ], + "type": "text", + "content": ". We crop coordinates and colors from the input scene point cloud using predicted bounding boxes and set point radius to " + }, + { + "bbox": [ + 46, + 477, + 287, + 585 + ], + "type": "inline_equation", + "content": "2.5\\mathrm{cm}" + }, + { + "bbox": [ + 46, + 477, + 287, + 585 + ], + "type": "text", + "content": " and image size to " + }, + { + "bbox": [ + 46, + 477, + 287, + 585 + ], + "type": "inline_equation", + "content": "224^2" + }, + { + "bbox": [ + 46, + 477, + 287, + 585 + ], + "type": "text", + "content": ". We use CUDA to batch index scene point clouds and crop in parallel, and render the batches sparsely to avoid padding overhead. Rendering is implemented with PyTorch3D [48] and executed on the GPU." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 593, + 104, + 604 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 593, + 104, + 604 + ], + "spans": [ + { + "bbox": [ + 47, + 593, + 104, + 604 + ], + "type": "text", + "content": "6.2. Results" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 611, + 212, + 622 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 611, + 212, + 622 + ], + "spans": [ + { + "bbox": [ + 47, + 611, + 212, + 622 + ], + "type": "text", + "content": "6.2.1 Performance of M3DRef-CLIP" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 713 + ], + "type": "text", + "content": "We first validate the performance of M3DRef-CLIP on ScanRefer (see Tab. 5) and Nr3D [4] (see Tab. 6) datasets and compare it against recent models. On ScanRefer, our method outperforms all prior works including those joint models leveraging extra input data by a large margin on both val set and test set (online benchmarking). In our ablation study, we find that the use of the CLIP text encoder is a key" + } + ] + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 307, + 156, + 544, + 297 + ], + "blocks": [ + { + "bbox": [ + 307, + 156, + 544, + 297 + ], + "lines": [ + { + "bbox": [ + 307, + 156, + 544, + 297 + ], + "spans": [ + { + "bbox": [ + 307, + 156, + 544, + 297 + ], + "type": "table", + "html": "
EasyHardView-DepView-IndepAll
3DVG-Trans [63]48.534.834.843.740.8
InstanceRefer [60]46.031.834.541.938.8
FFL-3DOG [17]48.235.037.144.741.7
TransRefer3D [18]48.536.036.544.942.1
SAT [58]56.342.446.950.449.2
3D-SPS [41]58.145.148.053.251.5
MVT [22]61.349.154.355.455.4
BUTD-DETR [25]60.748.446.058.054.6
HAM [10]54.341.941.551.448.2
LanguageRefer [49]51.036.641.745.043.9
LAR [5]56.141.846.750.248.9
M3DRef-CLIP55.643.442.352.949.4
", + "image_path": "63ff655e64e37c6213cf585d6cad96891d3ccef33c97d3dfdbe057da1e51660b.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 306, + 303, + 545, + 326 + ], + "lines": [ + { + "bbox": [ + 306, + 303, + 545, + 326 + ], + "spans": [ + { + "bbox": [ + 306, + 303, + 545, + 326 + ], + "type": "text", + "content": "Table 6: Comparison of methods on Nr3D [4] val set with GT boxes." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 9 + }, + { + "type": "table", + "bbox": [ + 307, + 339, + 544, + 389 + ], + "blocks": [ + { + "bbox": [ + 307, + 339, + 544, + 389 + ], + "lines": [ + { + "bbox": [ + 307, + 339, + 544, + 389 + ], + "spans": [ + { + "bbox": [ + 307, + 339, + 544, + 389 + ], + "type": "table", + "html": "
Training DatasetAcc on ScanReferAcc on Multi3DRefer (ST)
UniqueMultipleAllUniqueMultipleAll
ScanRefer [7]89.349.156.979.548.257.0
Multi3DRefer (ST)88.546.955.086.352.962.3
Multi3DRefer (ST) + ScanRefer90.851.058.788.056.765.5
", + "image_path": "f32c944e564e3e7c60c888a32e54b5f649c710b1ca782de4320c1c040c80238b.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 305, + 397, + 545, + 434 + ], + "lines": [ + { + "bbox": [ + 305, + 397, + 545, + 434 + ], + "spans": [ + { + "bbox": [ + 305, + 397, + 545, + 434 + ], + "type": "text", + "content": "Table 7: We compare results of training M3DRef with GT boxes on different datasets' val set. We only use the Single Target (ST) case in Multi3DRefer dataset." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 456, + 545, + 527 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 456, + 545, + 527 + ], + "spans": [ + { + "bbox": [ + 304, + 456, + 545, + 527 + ], + "type": "text", + "content": "factor to the strong performance of our model on ScanRefer. Another key factor is the use of a strong 3D object instance segmentation network (PointGroup) as our object detector. For instance, the PointGroup-based methods [8, 9] readily outperform VoteNet-based methods [63, 6] on the unique subset of ScanRefer." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 529, + 545, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 529, + 545, + 589 + ], + "spans": [ + { + "bbox": [ + 304, + 529, + 545, + 589 + ], + "type": "text", + "content": "For Nr3D [4], we achieve comparable but less competitive results because of our weaker ground-truth box encoder. Note that SAT [58] and MVT [22] also leverage 2D images but render them offline. Overall, using additional 2D image information is helpful for two-stage methods." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 607, + 399, + 618 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 607, + 399, + 618 + ], + "spans": [ + { + "bbox": [ + 306, + 607, + 399, + 618 + ], + "type": "text", + "content": "6.2.2 Multi3DRefer" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 627, + 545, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 627, + 545, + 687 + ], + "spans": [ + { + "bbox": [ + 304, + 627, + 545, + 687 + ], + "type": "text", + "content": "We split the Multi3DRefer data into train/val/test by scene following the ScanRefer split, resulting in a rough split ratio of 7:2:1 for the scene-description pairs. See Tab. 4 for statistics, including the number of descriptions with zero, single, or multiple targets." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "Usefulness of Multi3DRefer dataset. To study the usefulness of the Multi3DRefer dataset, we compare the perfor" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15231" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 70, + 545, + 147 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 545, + 147 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 545, + 147 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 545, + 147 + ], + "type": "table", + "html": "
F1 (GT boxes)F1@0.5 (Pred boxes)
ZT w/o DZT w/ DST w/o DST w/ DMTAllZT w/o DZT w/ DST w/o DST w/ DMTAll
3DVG-Trans+ [63]45.314.358.935.254.244.187.145.827.516.726.525.5
D3Net (Grounding) [8]71.620.478.244.461.655.581.632.538.623.335.032.2
3DJCG (Grounding) [6]47.916.459.135.554.244.694.166.926.016.726.226.6
M3DRef-CLIP74.229.484.152.367.262.381.839.447.830.637.938.4
", + "image_path": "baf6c4a364e3b0a40a8dd48aa3c1ac062f69820923f96334c14bdb7d1ab797fb.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 49, + 180, + 286, + 231 + ], + "blocks": [ + { + "bbox": [ + 50, + 149, + 541, + 162 + ], + "lines": [ + { + "bbox": [ + 50, + 149, + 541, + 162 + ], + "spans": [ + { + "bbox": [ + 50, + 149, + 541, + 162 + ], + "type": "text", + "content": "Table 8: Comparison of different methods on Multi3DRefer. Our M3DRef-CLIP outperforms prior work on most metrics." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 180, + 286, + 231 + ], + "lines": [ + { + "bbox": [ + 49, + 180, + 286, + 231 + ], + "spans": [ + { + "bbox": [ + 49, + 180, + 286, + 231 + ], + "type": "table", + "html": "
Eval DatasetAcc (GT boxes)Acc@0.5 (Pred boxes)
UniqueMultipleAllUniqueMultipleAll
Multi3DRefer (ST)86.951.561.567.340.147.7
ScanRefer [7]88.046.154.373.534.341.9
", + "image_path": "c4e262a8623c9904dcadc59d00c05bfcbeb48beee16eea3b5af8c1b511d8ff17.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 232, + 286, + 256 + ], + "lines": [ + { + "bbox": [ + 47, + 232, + 286, + 256 + ], + "spans": [ + { + "bbox": [ + 47, + 232, + 286, + 256 + ], + "type": "text", + "content": "Table 9: M3DRef-CLIP evaluated on Multi3DRefer (ST) and ScanRefer with both GT and predicted bounding boxes." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 287, + 287, + 407 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 287, + 287, + 407 + ], + "spans": [ + { + "bbox": [ + 46, + 287, + 287, + 407 + ], + "type": "text", + "content": "mance of training M3DRef-CLIP with the original ScanRefer data and with our Multi3DRefer data for the Single Target (ST) case. We evaluate on both ScanRefer and Multi3DRefer (ST), using GT bounding boxes. Tab. 7 shows that our reworded data can improve performance on ScanRefer. Prior work has also shown that incorporating additional labeled data can help, but they typically used either a captioning model [8, 9], mixed additional annotated data [58], or used dense annotations [1]. We show that simple rewordings (without accessing the images) also help." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 411, + 287, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 411, + 287, + 483 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 287, + 483 + ], + "type": "text", + "content": "We also evaluate M3DRef-CLIP trained on Multi3DRefer using ScanRefer's task setting (Tab. 9) of predicted objects. We observe that the model trained on Multi3DRefer data and task achieves similar performance to the model trained on ScanRefer data and task, which illustrates the generalization of Multi3DRefer." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 491, + 287, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 491, + 287, + 586 + ], + "spans": [ + { + "bbox": [ + 46, + 491, + 287, + 586 + ], + "type": "text", + "content": "Evaluation on Multi3DRefer. We compare four models on the Multi3DRefer dataset using both ground-truth and predicted boxes (Tab. 8). In our experiments, we focus on two-stage methods that perform well on ScanRefer. We adapt the code of 3DVG-Trans, 3DJCG and D3Net to our task. For 3DVG-Trans, we use the enhanced version 3DVG-Trans+ provided by the authors. We only train and evaluate the grounding model of 3DJCG and D3Net." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 591, + 287, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 591, + 287, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 591, + 287, + 676 + ], + "type": "text", + "content": "To analyze the performance of the models, we break down the zero (ZT) and single-target (ST) case to without and with distractors (D) of the same class. Overall, having distractors is more challenging. We note that M3DRef-CLIP outperforms the other methods on Multi3DRefer, and that 3DJCG is better at handling the ZT case with predicted boxes. Fig. 6 shows qualitative results." + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 310, + 180, + 544, + 418 + ], + "blocks": [ + { + "bbox": [ + 310, + 180, + 544, + 418 + ], + "lines": [ + { + "bbox": [ + 310, + 180, + 544, + 418 + ], + "spans": [ + { + "bbox": [ + 310, + 180, + 544, + 418 + ], + "type": "image", + "image_path": "808753537d6ac0ac1bf469ecfcb5d833fb0090ce602e78c4f4be49158423eb94.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 423, + 545, + 472 + ], + "lines": [ + { + "bbox": [ + 304, + 423, + 545, + 472 + ], + "spans": [ + { + "bbox": [ + 304, + 423, + 545, + 472 + ], + "type": "text", + "content": "Figure 6: Qualitative results of D3Net [8] versus M3DRef-CLIP on Multi3DRefer using predicted boxes. Blue boxes indicate GT, green boxes are true positives with IoU threshold " + }, + { + "bbox": [ + 304, + 423, + 545, + 472 + ], + "type": "inline_equation", + "content": "\\tau_{\\mathrm{pred}} > 0.5" + }, + { + "bbox": [ + 304, + 423, + 545, + 472 + ], + "type": "text", + "content": ". Red boxes are false positives." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 495, + 408, + 506 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 495, + 408, + 506 + ], + "spans": [ + { + "bbox": [ + 306, + 495, + 408, + 506 + ], + "type": "text", + "content": "6.2.3 Ablation studies" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 518, + 545, + 674 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 518, + 545, + 674 + ], + "spans": [ + { + "bbox": [ + 304, + 518, + 545, + 674 + ], + "type": "text", + "content": "Does CLIP help? We experiment with just using pure CLIP for both text and image encoding vs combining CLIP and 3D features (see Tab. 10). We also report results using a GRU [13]-based text encoder with GloVE [43] embedding, as used in prior work [7, 63, 8]. Although our GRU and 3D variants are similar at a high level to the grounding model of D3Net (which also used GRU and PointGroup with a transformer-based fusion module), we outperform the D3Net grounding module. Tab. 10 shows that using the CLIP text encoder improves performance, and combining CLIP and 3D features yields the best performance. The CLIP image encoder by itself underperforms the 3D features, showing the usefulness of 3D information." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "Does contrastive learning help? Tab. 11 reports the performance of M3DRef with and without contrastive learning on ScanRefer, Nr3D [4] and Multi3DRefer. We observe the" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 58, + 702, + 191, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 191, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 191, + 712 + ], + "type": "text", + "content": "5 github.com/zlcccc/3DVG-Transformer" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "15232" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 73, + 70, + 515, + 188 + ], + "blocks": [ + { + "bbox": [ + 73, + 70, + 515, + 188 + ], + "lines": [ + { + "bbox": [ + 73, + 70, + 515, + 188 + ], + "spans": [ + { + "bbox": [ + 73, + 70, + 515, + 188 + ], + "type": "table", + "html": "
TextVisionAcc (ScanRefer)F1 (Multi3DRefer)
UniqMultAllZT w/o DZT w/ DST w/o DST w/ DMTAll
GTGRU3D88.843.552.370.127.381.649.363.359.1
CLIPCLIP78.942.149.358.327.874.144.761.054.4
CLIP3D+CLIP89.349.156.974.229.484.152.367.262.3
PredGRU3D72.232.840.478.842.149.428.537.037.4
CLIPCLIP71.231.239.064.436.042.925.733.733.1
CLIP3D+CLIP77.236.844.781.839.447.830.637.938.4
", + "image_path": "a458af0a9377d1ba34b60c1037a60c354b82237d353ca1844357601aaf3532b2.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 49, + 236, + 544, + 287 + ], + "blocks": [ + { + "bbox": [ + 48, + 190, + 545, + 224 + ], + "lines": [ + { + "bbox": [ + 48, + 190, + 545, + 224 + ], + "spans": [ + { + "bbox": [ + 48, + 190, + 545, + 224 + ], + "type": "text", + "content": "Table 10: Ablations in training M3DRef using different feature embeddings and ground-truth boxes (top rows) and predicted boxes (bottom rows). The combination of CLIP [47] and 3D features achieves the best performance. We use PointGroup [28] for our 3D object detector and feature extractor." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 236, + 544, + 287 + ], + "lines": [ + { + "bbox": [ + 49, + 236, + 544, + 287 + ], + "spans": [ + { + "bbox": [ + 49, + 236, + 544, + 287 + ], + "type": "table", + "html": "
ScanReferNr3DMulti3DRefer
UniqueMultipleAllEasyHardView-DepView-IndepAllZT w/o DZT w/ DST w/o DST w/ DMTAll
w/ contrastive89.349.156.955.643.442.352.949.474.229.484.152.367.262.3
w/o contrastive89.647.255.450.935.337.645.642.967.423.883.452.066.561.1
", + "image_path": "3e6eeead53ed77ec255d35cbd6685de14e30ae306f41ec46c317fb71c3829127.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "type": "table", + "bbox": [ + 51, + 320, + 281, + 369 + ], + "blocks": [ + { + "bbox": [ + 121, + 289, + 472, + 300 + ], + "lines": [ + { + "bbox": [ + 121, + 289, + 472, + 300 + ], + "spans": [ + { + "bbox": [ + 121, + 289, + 472, + 300 + ], + "type": "text", + "content": "Table 11: Ablation of M3DRef-CLIP with and without contrastive loss using GT boxes." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 51, + 320, + 281, + 369 + ], + "lines": [ + { + "bbox": [ + 51, + 320, + 281, + 369 + ], + "spans": [ + { + "bbox": [ + 51, + 320, + 281, + 369 + ], + "type": "table", + "html": "
TextVisionSpatialColorTextureShape
GRU3D55.867.776.477.8
CLIP3D+CLIP58.871.979.482.5
", + "image_path": "99bc1de63491d686b44e6c73f48230f290a09b29faf1046510038935ed4a057d.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 48, + 377, + 286, + 413 + ], + "lines": [ + { + "bbox": [ + 48, + 377, + 286, + 413 + ], + "spans": [ + { + "bbox": [ + 48, + 377, + 286, + 413 + ], + "type": "text", + "content": "Table 12: Breakdown of M3DRef performance (with GRU vs CLIP) on descriptions with different attributes. We report F1 scores with GT boxes on Multi3DRefer val set." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 48, + 436, + 285, + 448 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 436, + 285, + 448 + ], + "spans": [ + { + "bbox": [ + 48, + 436, + 285, + 448 + ], + "type": "text", + "content": "benefit of the contrastive loss for all tasks, especially Nr3D." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 48, + 457, + 193, + 470 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 457, + 193, + 470 + ], + "spans": [ + { + "bbox": [ + 48, + 457, + 193, + 470 + ], + "type": "text", + "content": "6.3. Analysis of M3DRef-CLIP" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 49, + 476, + 286, + 643 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 476, + 286, + 643 + ], + "spans": [ + { + "bbox": [ + 49, + 476, + 286, + 643 + ], + "type": "text", + "content": "To better study the Multi3DRefer data and understand how M3DRef-CLIP helps address the task, we break down evaluation of Multi3DRefer based on attributes provided in the description: spatial, color, texture, and shape information. For this analysis, these four splits are mutually exclusive, i.e. we only keep descriptions that describe exactly 1 attribute from the four and discard others. We compare using M3DRef with GRU with 3D PointGroup features vs our full M3DRef-CLIP model (with CLIP image and text encoders). We use the GT boxes setting and report F1 scores in Tab. 12. We observe that adding features from CLIP [47] helps identify all these attributes. We found that descriptions with spatial terms are more challenging than descriptions with texture or shape." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 49, + 657, + 118, + 669 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 657, + 118, + 669 + ], + "spans": [ + { + "bbox": [ + 49, + 657, + 118, + 669 + ], + "type": "text", + "content": "7. Conclusion" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 49, + 677, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 677, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 49, + 677, + 286, + 713 + ], + "type": "text", + "content": "We present Multi3DRefer, a more realistic task of grounding a flexible number of objects in real-world 3D scenes using natural language descriptions. We designed" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 307, + 323, + 545, + 465 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 323, + 545, + 465 + ], + "spans": [ + { + "bbox": [ + 307, + 323, + 545, + 465 + ], + "type": "text", + "content": "a simple and efficient data generation pipeline to create data with less human effort, by leveraging existing language data and ChatGPT. With this pipeline, we created a more diverse dataset consisting of more natural descriptions of varying granularity. We also explored an end-to-end baseline method for solving the new task, which enables the online rendering of proposal objects to generate 2D cues, it also demonstrated the usefulness of CLIP [47] and the multi-modal contrastive loss. We believe Multi3DRefer will bring more challenges and practical value in the direction of bridging 3D vision and language, especially for robotics and embodied AI tasks." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 308, + 475, + 545, + 558 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 475, + 545, + 558 + ], + "spans": [ + { + "bbox": [ + 308, + 475, + 545, + 558 + ], + "type": "text", + "content": "Future Work. Our current design relies on features from the 3D object detector to capture the global context, and the 2D image encoder to capture per-object attributes. Using positional encoding could improve the ability of the model to handle spatial relations. Investigating whether positional encoding improves the model, and what kind of positional encoding works best is a great avenue for future work." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 308, + 590, + 407, + 604 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 590, + 407, + 604 + ], + "spans": [ + { + "bbox": [ + 308, + 590, + 407, + 604 + ], + "type": "text", + "content": "Acknowledgements" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 308, + 617, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 617, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 308, + 617, + 545, + 712 + ], + "type": "text", + "content": "This work was funded in part by a Canada CIFAR AI Chair and NSERC Discovery Grant, and enabled in part by support from the Digital Research Alliance of Canada. We thank Zhenyu (Dave) Chen for providing us with the ambiguous descriptions initially collected for ScanRefer, and Manolis Savva for proofreading and editing suggestions. We also thank Archita Srivastava, Cody Ning, and Austin T. Wang for helping to verify the Multi3DRefer dataset." + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 750, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 750, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 750, + 317, + 757 + ], + "type": "text", + "content": "15233" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 705 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "text", + "content": "[1] Ahmed Abdelreheem, Kyle Olszewski, Hsin-Ying Lee, Peter Wonka, and Panos Achlioptas. 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Standard models, e.g. CNNs or Vision Transformers, which receive RGB frames as input perform well, however, their performance improves further by employing additional input modalities (e.g. object detections, optical flow, audio, etc.) which provide cues complementary to the RGB modality. The added complexity of the modality-specific modules, on the other hand, makes these models impractical for deployment. The goal of this work is to retain the performance of such a multimodal approach, while using only the RGB frames as input at inference time. We demonstrate that for egocentric action recognition on the Epic-Kitchens and the Something-Something datasets, students which are taught by multimodal teachers tend to be more accurate and better calibrated than architecturally equivalent models trained on ground truth labels in a unimodal or multimodal fashion. We further adopt a principled multimodal knowledge distillation framework, allowing us to deal with issues which occur when applying multimodal knowledge distillation in a naive manner. Lastly, we demonstrate the achieved reduction in computational complexity, and show that our approach maintains higher performance with the reduction of the number of input views. We release our code at: https://github.com/gorjanradevski/multimodal-distillation", + "bbox": [ + 75, + 318, + 473, + 698 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 727, + 209, + 742 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The purpose of egocentric vision is enabling machines to interpret real-world data taken from a human's perspective. Its applications are numerous, ranging from recognizing [63] or anticipating [15] actions, to more complex tasks such as recognizing egocentric object-state changes, localizing action instances of a particular video moment [22], etc. The focal point of egocentric vision is hand-object interactions. Usually, these hand-object interactions take", + "bbox": [ + 75, + 753, + 468, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/8604e921b093e3b2b786c773320fdd312f9c74c36c17b063b5cb4e6bcd14a507.jpg", + "image_caption": [ + "Figure 1: Motivation: The multimodal action recognition model is powerful, but too slow to be used in practice. The distilled student is significantly faster yet achieves competitive performance." + ], + "image_footnote": [], + "bbox": [ + 501, + 287, + 890, + 425 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "place in cluttered environments, where the object of interest is often occluded, or occurs only during a short time period. Furthermore, egocentric vision often suffers from motion blur – due to the movement of the scene objects or the camera itself – and thus, understanding video content from RGB frames alone may be challenging.", + "bbox": [ + 496, + 506, + 892, + 597 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To cope with these challenges, various egocentric action recognition methods [25, 29, 33, 43, 56, 59, 61] demonstrate that explicitly modelling hand-object interactions (usually represented via bounding boxes & object categories) significantly improves the action recognition performance, most notably in a compositional generalization setup [43]. Similarly, other works show that leveraging multiple modalities (optical flow, audio, etc.) at inference time yields improved performance [16, 28, 36, 57]. The assumptions these methods make are (i) that all modalities used during training are also available at inference time, and (ii) the compute budget at inference time would be sufficient to obtain and process the additional modalities. Such assumptions make these methods cumbersome or even impossible to use in practice, e.g. on a limited compute budget such as in the case of embedded devices. Namely, using dedicated models for each additional modality (e.g. object detector, object tracker and a transformer when using bounding boxes & object categories as input [43]), increases both the memory footprint as well as the inference time. Ideally, video understanding", + "bbox": [ + 496, + 599, + 893, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "* Authors contributed equally.", + "bbox": [ + 94, + 887, + 261, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "5213", + "bbox": [ + 482, + 944, + 514, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "models would leverage additional modalities during training, while the resulting model would use only RGB frames at inference time, i.e. when deployed in practice.", + "bbox": [ + 75, + 90, + 468, + 136 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "One way to achieve the aforementioned goal is training omnivorous models, i.e. models trained jointly on multiple modalities, which have been shown to generalize better [20] than unimodal counterparts. In this work, we take a different route and transfer multimodal knowledge to models subsequently used in a unimodal setting. Namely, we distill the knowledge from a multimodal ensemble - exhibiting superior performance, but unviable for deployment - to a standard RGB-based action recognition model [5] (see Fig. 1).", + "bbox": [ + 75, + 136, + 467, + 272 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Contributions. We employ state-of-the-art knowledge distillation practices [6] and ① show that a student [31] taught by a multimodal teacher, is both more accurate and better calibrated than the same model trained from scratch or in an omnivorous fashion (§4.1); ② We provide motivation and establish a simple but reliable multimodal distillation approach, which overcomes the issue of potentially suboptimal modality-specific teachers (§4.2); ③ We demonstrate that the distilled student performs on par with significantly larger models, and maintains performance in computationally cheaper inference setups (§4.3).", + "bbox": [ + 75, + 272, + 467, + 438 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 452, + 217, + 467 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Knowledge distillation. Originally introduced by Hinton et al. [26], knowledge distillation is used to transfer the knowledge from one model, i.e. a teacher, to another model, i.e. a student, by training the student to match the teacher's (intermediate) outputs on a certain dataset. Shown to be useful in a variety of contexts, the primary goal is model compression - transferring the knowledge from a larger, cumbersome teacher model, or from a teacher exhibiting a different inductive bias [9, 52], to a typically lightweight student model [10, 35, 55]. Another line of work [2, 47] proposes to distill from ensembles of large teacher models to lightweight student models, obtaining promising results. Compared to these works, we focus on knowledge distillation from a multimodal teacher ensemble, i.e. a set of models where each is trained on a distinct modality.", + "bbox": [ + 75, + 478, + 467, + 703 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multimodal knowledge distillation has been previously used mainly in a cross-modal fashion, where the teacher and the student receive different modalities as input. In some works, the teacher receives RGB images while the student receives depth or optical flow images [24], while in others, the teacher receives RGB images as input, while the student receives audio as input [3]. In contrast, other works explore a multimodal knowledge expansion scenario, where a multimodal student learns from pseudo-labels of a unimodal teacher [58]. We, on the other hand, focus on scenarios where obtaining additional modalities (optical flow, object detections, audio, etc.) during inference is prohibitive due to a limited compute budget, and therefore multimodal", + "bbox": [ + 75, + 704, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "data is only used during training time. Multimodal knowledge distillation for action recognition has been previously explored in the works of Gracia et al. [17, 18]. They propose to train a model on aligned data from two modalities, where a model which receives data from modality A is trained to imitate the intermediate features of a model which receives training data from modality B. This approach is shown to yield performance improvements compared to an RGB baseline when using RGB and depth data. Moreover, the Mars [11] and D3d [49] methods, similarly to us, leverage RGB frames and optical flow during training to improve test-time performance of a model that performs inference using RGB frames alone. This is achieved by matching the corresponding features or probabilistic outputs of the modality-specific models during training. Compared to these works, we consider a more general knowledge distillation setting [6, 26], with a multimodal teacher ensemble used to provide a better approximation of the true posterior. Lastly, we consider a more diverse and broader set of modalities (RGB frames, optical flow, audio and object detections) compared to the aforementioned works.", + "bbox": [ + 496, + 90, + 890, + 407 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multimodal (egocentric) video understanding. In the context of (egocentric) video understanding, several works have shown that using additional modalities at inference time significantly improves performance [25, 29, 33, 36, 43, 50, 56, 61]. The hypothesis is intuitive - certain actions are more easily understood from specific modalities, e.g. to recognize that a person is \"pushing something from left to right,\" the bounding boxes alone are sufficient [33, 43]. Nevertheless, the assumption these works make is that all modalities used during training are available during inference, and that the compute budget allows for processing additional modalities other than the RGB frames. To that end, multiple works [25, 29, 33, 43, 56, 61] effectively use a Faster R-CNN [44], multiple object tracker (MOT), and object detection-specific models at inference time. In contrast, we posit that for egocentric video understanding, computing additional modalities on the fly may be prohibitive. Therefore, we propose a distillation approach which uses multimodal data only during training, while the resulting model is dependent on RGB frames alone during inference.", + "bbox": [ + 496, + 412, + 890, + 715 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Models robust to missing modalities during inference. A parallel route to our goal - retaining the performance of multimodal approaches, while using only the RGB frames at inference time - is to explicitly train models to be robust to missing modalities during inference [37, 39, 62]; or more recently, to process different modalities altogether interchangeably - Omnivorous models [12, 19, 20]. These models have been shown to generalize better than models trained on unimodal data. In this work, we train an Omnivorous model using the same architecture as our student, and show that the student distilled from a multimodal teacher generalizes better than its Omnivorous variant.", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "5214", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 76, + 89, + 210, + 107 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Egocentric Action Recognition", + "text_level": 1, + "bbox": [ + 76, + 116, + 346, + 132 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We assume we are given an input $\\mathbf{x} \\in \\mathbb{R}^{T \\times D_1 \\times D_2 \\dots \\times D_L}$ , which describes an egocentric action sequence, where $T$ is the number of time-steps, while $D_1 \\times D_2 \\dots \\times D_L$ represent other dimensions of the input data, e.g. the height, width and the number of channels of a video frame. The goal of the model $f$ is to produce a discrete probability distribution over a predefined set of $C$ classes, i.e. $\\hat{\\mathbf{y}} = \\sigma(f(\\mathbf{x})) \\in \\mathbb{R}_+^C$ , where $\\sigma$ is the softmax operator. The classes represent the actions, or alternatively, the nouns and verbs constituting the actions (e.g. the active video object and the activity).", + "bbox": [ + 75, + 140, + 468, + 292 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Given a dataset $\\mathbb{D} = \\{(\\mathbf{x}_1,\\mathbf{y}_1),\\dots ,(\\mathbf{x}_N,\\mathbf{y}_N)\\}$ of $N$ egocentric action sequences $\\mathbf{x}_i$ paired with labels $\\mathbf{y}_i\\in \\mathbb{R}_+^C$ the model is trained by minimizing the standard crossentropy objective $\\mathcal{L}_{\\mathrm{CE}} = -\\frac{1}{N}\\sum_{i = 1}^{N}\\mathbf{y}_i\\cdot \\log \\sigma (f(\\mathbf{x}_i))$ where $\\cdot$ represents the scalar product. In the case of actions characterized by separate nouns and verbs, and accompanied by their respective labels $\\mathbf{y}_i^n$ and $\\mathbf{y}_i^v$ , separate prediction heads produce $f^n (\\mathbf{x}_i)$ and $f^{v}(\\mathbf{x}_{i})$ . Finally, the model is trained by minimizing the sum of the loss terms corresponding to the nouns and verbs, $\\mathcal{L}_{\\mathrm{CE}}^n$ and $\\mathcal{L}_{\\mathrm{CE}}^v$ respectively.", + "bbox": [ + 75, + 294, + 470, + 448 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Multimodal Knowledge Distillation", + "text_level": 1, + "bbox": [ + 76, + 462, + 382, + 478 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In egocentric vision, there often exist more than one input modality that characterize the same actions. The action recognition task may thus be performed via the use of multiple modalities, leveraged only during training [20, 42], or both during training and inference [16,28,36,57] by ensembling [57] models, multimodal-fusion [28, 43], etc. However, in the case of the latter, processing multimodal data may be computationally prohibitive at inference time (e.g. due to a limited compute budget).", + "bbox": [ + 75, + 488, + 468, + 625 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The fundamental concept our method builds on is knowledge distillation [26], featuring a teacher (usually larger model, exhibiting strong performance, but cumbersome to use in practice) and a student (typically a smaller model, trained to mimic the teacher [6]). Focusing on the most accessible data modality - RGB video frames (e.g. obtained using a single monocular video camera) - we opt for distilling the knowledge of a multimodal ensemble to a single model that relies on RGB inputs alone. We make a modification to the standard knowledge distillation approach, by altering the teacher such that (i) it is not a single model, but rather an ensemble of models, and (ii) the constituting models receive different modalities as input.", + "bbox": [ + 75, + 626, + 468, + 821 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Teacher ensemble. Given $M$ datasets $\\mathbb{D}^m = \\left\\{(\\mathbf{x}_1^m,\\mathbf{y}_1),\\dots ,(\\mathbf{x}_N^m,\\mathbf{y}_N)\\right\\}$ of different modalities, we train a separate model $f^{m}$ by minimizing the learning objective $\\mathcal{L}_{\\mathrm{CE}}^m = -\\frac{1}{N}\\sum_{i = 1}^N\\mathbf{y}_i\\cdot \\log \\sigma \\left(f^m (\\mathbf{x}_i^m)\\right)$ for each modality. Finally, the output of the ensemble can be obtained by aver", + "bbox": [ + 76, + 824, + 468, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "aging the outputs of the individual teachers:", + "bbox": [ + 500, + 90, + 790, + 106 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {y}} _ {i} ^ {t} = \\sigma \\left(\\frac {1}{M} \\sum_ {m = 1} ^ {M} f ^ {m} \\left(\\mathbf {x} _ {i} ^ {m}\\right)\\right). \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 594, + 116, + 890, + 159 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Intuitively, under-performing modality-specific models could negatively affect the performance of the ensemble. We thus consider assigning different weights to the output logits of each model in the ensemble, before aggregating their predictions. Ideally, we would want to perform a Bayesian prediction: $p(\\mathbf{y}|\\mathbf{x},\\mathbb{D}) = \\int_{f\\in F}p(\\mathbf{y}|\\mathbf{x},f)p(f|\\mathbb{D})df$ . For a given finite ensemble of $M$ diverse predictors, we replace the integral with a sum over the individual models: $p(\\mathbf{y}|\\mathbf{x},\\mathbb{D}) \\approx \\sum_{m = 1}^{M}p(\\mathbf{y}|\\mathbf{x},f^{m})p(f^{m}|\\mathbb{D})$ . We further approximate $p(f^{m}|\\mathbb{D})$ via its proportionality to the data likelihood $p(\\mathbb{D}|f^{m})$ under the Bayes rule: $p(f^{m}|\\mathbb{D}) \\propto p(\\mathbb{D}|f^{m})$ ; which itself can be expressed in terms of the cross-entropy that the model $f^{m}$ exhibits on the dataset $\\mathbb{D}$ .", + "bbox": [ + 496, + 167, + 890, + 378 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The cross-entropy $e^{m}$ of each modality-specific model in the ensemble can be estimated on a holdout set:", + "bbox": [ + 496, + 380, + 890, + 410 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\ne ^ {m} = - \\frac {1}{Z} \\sum_ {i = 1} ^ {Z} \\mathbf {y} _ {i} \\cdot \\log \\sigma \\left(f ^ {m} \\left(\\mathbf {x} _ {i} ^ {m}\\right)\\right), \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 570, + 421, + 890, + 463 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $Z$ is the number of held-out samples used to estimate the weights. Then, we can obtain the weights for the modality-specific models via softmax normalization of the negative cross-entropy terms:", + "bbox": [ + 496, + 468, + 890, + 529 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nw ^ {m} \\propto \\exp (- e ^ {m} / \\gamma), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 624, + 542, + 890, + 560 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $\\gamma$ is a temperature term which controls the entropy of the model weights, e.g. if $\\gamma \\rightarrow \\infty$ , equal weights would be given to each teacher - resulting in an arithmetic mean.", + "bbox": [ + 496, + 566, + 890, + 611 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We finally compute the weighted average of the predictions of $M$ modality-specific models as the teacher output:", + "bbox": [ + 496, + 611, + 890, + 642 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\mathbf {y}} _ {i} ^ {t} = \\sigma \\left(\\sum_ {m = 1} ^ {M} w ^ {m} f ^ {m} \\left(\\mathbf {x} _ {i} ^ {m}\\right)\\right). \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 593, + 652, + 890, + 694 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Figure 2 presents a high-level overview of our approach. In summary, our student is taught by a multimodal teacher which is itself an ensemble of multiple modality-specific models, trained separately on each modality.", + "bbox": [ + 496, + 698, + 890, + 758 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Training objective. During training, we perform multimodal knowledge distillation, as originally proposed by Hinton et al. [26]. Specifically, we minimize the KL-divergence $\\mathcal{L}_{\\mathrm{KL}}$ between the class probabilities predicted by the teacher $\\hat{\\mathbf{y}}_i^t = [\\hat{y}_{i,1}^t,\\dots ,\\hat{y}_{i,C}^t ]\\in \\mathbb{R}_+^C$ and the class probabilities of the student $\\hat{\\mathbf{y}}_i^s = [\\hat{y}_{i,1}^s,\\dots ,\\hat{y}_{i,C}^s ]\\in \\mathbb{R}_+^C$ as $\\mathcal{L}_{\\mathrm{KL}} = \\frac{1}{N}\\sum_{i = 1}^{N}(-\\hat{\\mathbf{y}}_i^t\\cdot \\log \\hat{\\mathbf{y}}_i^s +\\hat{\\mathbf{y}}_i^t\\cdot \\log \\hat{\\mathbf{y}}_i^t)$", + "bbox": [ + 496, + 758, + 890, + 871 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Additionally, we use a temperature parameter $\\tau$ to control the entropy of the predicted probability scores while", + "bbox": [ + 496, + 871, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "5215", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/9ac8af93b1196f7aea28e027580d21545919a65cd5d46de3a2651cb691f36c21.jpg", + "image_caption": [ + "Figure 2: Overview of the main components of our approach." + ], + "image_footnote": [], + "bbox": [ + 80, + 88, + 467, + 215 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/13582a1cc6701508e3570c60d83285ee99c4574f5a3491007d9cf1c8728734b9.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Epic-Kitchens RegularSomething-Something
MethodNoun Acc.Noun ECEVerb Acc.Verb ECEAction Acc.Action ECE
RGB Baseline52.019.961.717.159.321.2
Teacher (γ = 30.0)52.32.0466.83.466.68.1
Teacher (γ = 1.0)53.98.966.94.266.79.0
Epic-Kitchens Unseen EnvironmentsSomething-Else
MethodNoun Acc.Noun ECEVerb Acc.Verb ECEAction Acc.Action ECE
RGB Baseline38.326.951.724.051.821.4
Teacher (γ = 30.0)42.96.0258.09.963.36.5
Teacher (γ = 1.0)43.89.557.79.763.58.1
", + "bbox": [ + 81, + 255, + 467, + 362 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Table 1: Accuracy & Expected Calibration Error (ECE) of the RGB baseline and Teacher ensemble on Epic-Kitchens and Something-Something (regular & unseen splits). All available modalities for the respective dataset used in the ensemble.", + "bbox": [ + 75, + 373, + 470, + 429 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "preserving their ranking, i.e. $\\hat{y}_j^s\\propto \\exp (\\hat{y}_j^s /\\tau)$ . As per standard practice [26], we use the temperature parameter $\\pmb{\\tau}$ to also rescale the KL-divergence loss, i.e. $\\mathcal{L}_{\\mathrm{KL}} = \\mathcal{L}_{\\mathrm{KL}}\\cdot \\tau^2$ . We further use the standard cross-entropy action recognition loss $\\mathcal{L}_{\\mathrm{CE}}$ , and compute the final loss:", + "bbox": [ + 75, + 458, + 468, + 535 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} = \\lambda \\cdot \\mathcal {L} _ {\\mathrm {K L}} + (1 - \\lambda) \\cdot \\mathcal {L} _ {\\mathrm {C E}}, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 171, + 553, + 468, + 569 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\lambda$ balances the distillation loss $\\mathcal{L}_{\\mathrm{KL}}$ and the action recognition loss $\\mathcal{L}_{\\mathrm{CE}}$ . For example, with $\\lambda = 0.0$ we would effectively be training the modality-specific RGB model, while with $\\lambda = 1.0$ , we would perform solely multimodal knowledge distillation.", + "bbox": [ + 75, + 580, + 468, + 655 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Optimality of a multimodal ensemble teacher. The work of Menon et al. [34] further demonstrates that in the context of distillation, a teacher that predicts the Bayes class-probability distribution over the labels $\\mathbf{p}^{*}(\\mathbf{x}) = [\\mathbb{P}(y|\\mathbf{x})]_{y\\in [C]}$ exhibits the lowest possible variance of the student objective for any convex loss function.", + "bbox": [ + 75, + 657, + 468, + 747 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The student trained to minimize the KL-divergence between its output and the Bayes class-probabilities would thus generalize the best. In a preliminary experiment shown in Table 1, we demonstrate that the multimodal ensemble (both for $\\gamma = 1$ and $\\gamma = 30.0$ ) achieves a significantly higher accuracy and lower calibration error, and thus represents a better approximation of the Bayes class probabilities than a single modality-specific model. This may lead to a lower-variance objective for the student and improved generalization during knowledge distillation [34].", + "bbox": [ + 75, + 750, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Experiments & Discussion", + "text_level": 1, + "bbox": [ + 500, + 89, + 746, + 107 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Datasets. We use the Something-Something (V2) [21] and the Epic-Kitchens (100) [14] datasets. Something-Something contains videos of people performing 174 (object agnostic) unique actions with their hands, e.g. \"pushing [something] left\", \"taking [something] out of [something]\", etc. Epic-Kitchens' videos take place in kitchen environments, where the actions are noun-verb compositions. The 300 unique nouns indicate the active object in the video, while 97 unique verbs indicate the activity, e.g. \"cutting carrot\", \"washing pan\", etc. During evaluation, the action is considered correct if both the noun and the verb are correctly predicted. Additionally, we use the Something-Else [33] dataset and the Epic-Kitchens Unseen split to measure the compositional generalization ability of the models w.r.t. unseen objects and environments.", + "bbox": [ + 496, + 114, + 890, + 340 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Modalities. In addition to the RGB frames (the modality of interest at inference time), in our experiments we consider the following modalities:", + "bbox": [ + 496, + 342, + 890, + 387 + ], + "page_idx": 3 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "(i) Optical flow (OF): First used by I3D [8] for action recognition, it is also used by recent state-of-the-art (egocentric) video understanding methods [57]. We use optical flow obtained using TV-L1 [60].", + "(ii) Object detections (OBJ): Shown to significantly improve the performance of standard (RGB) egocentric video understanding models across datasets [25, 33, 43, 56, 61]. As per [46], we use the object detector trained on object-agnostic annotations, i.e. with \"hands\" and \"objects\" object labels.", + "(iii) Audio (A): For certain datasets [13, 14], several works [28, 57] have shown that using audio improves action recognition performance. The audio is obtained directly from the recorded video." + ], + "bbox": [ + 503, + 398, + 890, + 631 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Moreover, if available, one may include additional modalities, e.g. depth estimates, heat maps, etc. For Something-Something and Something-Else there is no audio available, while we use the object detections provided by [25, 33], and optical flow from [54]. For Epic-Kitchens we use the modalities available and released with the dataset itself [14]: optical flow and audio.", + "bbox": [ + 496, + 643, + 890, + 748 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Models. We use a Swin-Tiny (Swin-T) Transformer [31] to encode RGB frames, optical flow, and audio. Each optical flow frame is represented as a $224 \\times 224 \\times 2$ tensor, where the two values at each spatial location represent the $x$ and $y$ velocity components. In the case of audio, we extract 1.116 second-audio segments (0.558s before its corresponding time-step and 0.558s after it) for each frame. We compute the mel-spectrogram of the audio segment (see details in Supp. B), which is subsequently resized to desired width and height. We thus treat each modality as a sequence of", + "bbox": [ + 496, + 750, + 892, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "5216", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 3 + }, + { + "type": "table", + "img_path": "images/86b31fb386872aac0604f8e6482d65e3d00b07fe40a1eb312d0d2779ed661d62.jpg", + "table_caption": [], + "table_footnote": [ + "(a) Epic-Kitchens [14]: Recognition of the active video object (noun) and the activity (verb)." + ], + "table_body": "
MethodTraining ModalitiesInference ModalitiesNoun@1Verb@1Action@1
BaselineRGBRGB52.061.738.3
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB34.151.952.259.065.365.625.939.539.9+1.6
Modality-specificTeacherStudentA—RGB & AARGB & ARGB22.352.761.546.564.462.4+0.715.139.837.9-0.4
TeacherStudent—RGB & OF & ARGB & OF & ARGB52.351.7-0.366.865.4+3.740.539.3+1.0
", + "bbox": [ + 81, + 88, + 467, + 196 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/9711cabd0843f4ec95b8a50625bb4bef1afcf6cab507fa22430100a774ef2d75.jpg", + "table_caption": [], + "table_footnote": [ + "(b) Something-Something [21]: Object-agnostic action recognition." + ], + "table_body": "
MethodTraining ModalitiesInference ModalitiesAction@1Action@5
BaselineRGBRGB60.386.4
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB49.364.379.088.9
\\( 62.8_{+2.5} \\)\\( 88.9_{+2.5} \\)
Modality-specific TeacherStudentOBJ—RGB & OBJOBJRGB & OBJRGB47.965.376.289.5
\\( 63.2_{+2.9} \\)\\( 88.7_{+2.3} \\)
TeacherStudent—RGB & OF & OBJRGB & OF & OBJRGB66.6\\( 63.0_{+2.7} \\)90.5\\( 88.9_{+2.5} \\)
", + "bbox": [ + 521, + 88, + 870, + 196 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 2: Egocentric action recognition. RGB = Video frames; OF = Optical flow; A = Audio; OBJ = Object detections. Multimodal distillation with $\\lambda = 1.0$ and $\\gamma = 30.0$ . Improvement over RGB frames baseline [31] in red.", + "bbox": [ + 75, + 238, + 892, + 267 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$224 \\times 224$ multi-channel images, which we provide as input to the vision transformer, as per the common practice in recent vision models [19, 20]. To encode the object detections, i.e. bounding boxes and object categories of the scene objects, we use a state-of-the-art model - STLT [43]. In STLT, a spatial and temporal transformer separately encode the spatial and temporal arrangement of the objects occurring in the video. The multimodal teacher we use during knowledge distillation is an ensemble of individual, modality-specific models. Unless noted otherwise, the student is a Swin-T model which receives RGB frames as input, both during training (distillation) and inference. In addition to Swin-T, in §4.3, we also consider ResNet3D [27] (18 and 50 layers deep) light-weight student models which receive video frames of size $112 \\times 112$ as input.", + "bbox": [ + 75, + 292, + 468, + 520 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Metrics. Besides accuracy, we measure Expected Calibration Error (ECE) [23]. As per [23, 45], we sort the predictions based on the per-class confidence scores and group them into $K$ bins $B_{k}$ , each associated with a confidence interval $I_{B_k} = \\left(\\frac{k - 1}{K},\\frac{k}{K}\\right)$ , where $K = 15$ . ECE represents the discrepancy between the average accuracy $acc(B_k)$ and the average confidence $conf(B_k)$ in each bin $B_{k}$ :", + "bbox": [ + 75, + 520, + 468, + 626 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathrm {E C E} = \\sum_ {k = 1} ^ {K} \\frac {\\left| B _ {k} \\right|}{N} \\left| a c c \\left(B _ {k}\\right) - c o n f \\left(B _ {k}\\right) \\right|, \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 133, + 637, + 468, + 679 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $N$ is the number of evaluation samples.", + "bbox": [ + 76, + 689, + 383, + 703 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Implementation details. We train all models for 60 epochs using AdamW [32], with a peak learning rate of $1e - 4$ , linearly increased for the first $5\\%$ of the training and decreased to 0.0 by the end of the specified 60 epochs. We use weight decay with a regularization coefficient of $5e - 2$ , and clip the gradients when their norm exceeds 5.0. For Epic-Kitchens, we sample 32 frames with a fixed stride of 2, and for Something-Something and Something-Else we evenly sample 16 frames to cover the whole video. We use a single spatial and temporal crop, unless stated otherwise. During training, we chose a random start frame, while during inference, we select the start frame such that the sequence covers the central portion of the video. If we", + "bbox": [ + 75, + 704, + 470, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "use multiple temporal crops as test-time augmentation, we chose the start frames such that the video is covered uniformly. During training we apply standard data augmentations - random spatial video crops, color jittering, and horizontal flips (for Epic-Kitchens only). The temperature parameter $\\tau$ is fixed to 10.0 for both the student and the teacher during multimodal knowledge distillation. In §4.2 we ablate the impact of the loss balancing term $\\lambda$ and the Ensemble Teacher Weighting temperature term $\\gamma^1$ .", + "bbox": [ + 496, + 292, + 890, + 430 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "During training we follow the consistent teaching paradigm [6] where the student and teacher strictly receive the same views of the data - we ensure for spatial and temporal consistency, i.e. the models receive the same frame indices, same random crops, and horizontal flips.", + "bbox": [ + 496, + 430, + 890, + 506 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Multimodal Distillation for Egocentric Vision", + "text_level": 1, + "bbox": [ + 498, + 513, + 883, + 530 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We first verify the overall effectiveness of multimodal knowledge distillation on the task of egocentric action recognition for both object-agnostic actions (Something-Something) and actions represented as noun-verb compositions (Epic-Kitchens). Across all experiments, we fix $\\lambda$ to 1.0, i.e. we train solely with multimodal knowledge distillation. Similarly, we set $\\gamma$ to a large value ( $\\gamma = 30.0$ ), where effectively each teacher equally contributes to the ensemble output. Note that in this setting, models trained on modalities such as optical flow and audio may underperform, and thus adversely affect the ensemble teacher performance of recognizing active objects, i.e. nouns.", + "bbox": [ + 496, + 537, + 892, + 719 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1.1 Recognizing Egocentric Actions", + "text_level": 1, + "bbox": [ + 498, + 736, + 774, + 752 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In Table 2, we report performance on Something-Something V2 [21] and Epic-Kitchens 100 [14]. In line with the previous findings reported in the literature [33, 43, 57], we find that employing additional modalities at inference time significantly improves the performance compared to the RGB baseline model, for both the Epic-Kitchens and the Something-Something datasets.", + "bbox": [ + 496, + 760, + 890, + 867 + ], + "page_idx": 4 + }, + { + "type": "page_footnote", + "text": "1As the datasets' test sets either do not exist [33], or have restricted access, we report results using the model after the final training epoch.", + "bbox": [ + 500, + 875, + 892, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "5217", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/0d3c251a14923897eaf8c875aed26461e9c733c66c7c90ff597ad8663d9245b1.jpg", + "table_caption": [], + "table_footnote": [ + "(a) Epic-Kitchens Unseen Environments [14]: Recognition of the active object (noun) and the activity (verb) on participants unseen during training." + ], + "table_body": "
MethodTraining ModalitiesInference ModalitiesNoun@1Verb@1Action@1
BaselineRGBRGB38.351.725.4
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB28.041.042.5+4.253.254.955.9+4.221.628.430.2+4.8
Modality-specificTeacherStudentA—RGB & AARGB & ARGB15.041.941.8+3.541.555.351.8+0.19.128.527.5+2.1
TeacherStudent—RGB & OF & ARGB & OF & ARGB42.943.7+5.458.054.1+3.430.329.6+4.2
", + "bbox": [ + 81, + 88, + 468, + 196 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/888060f4134e99134239eae59ae795cb512febf8bbb83d5940920b97e52bb83c.jpg", + "table_caption": [], + "table_footnote": [ + "(b) Something-Else [33]: Object-agnostic action recognition featuring objects unseen during training." + ], + "table_body": "
MethodTraining ModalitiesInference ModalitiesAction@1Action@5
BaselineRGBRGB51.879.5
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB49.061.058.2+6.477.486.485.1+5.6
Modality-specificTeacherStudentOBJ—RGB & OBJOBJRGB & OBJRGB41.459.457.5+5.767.384.584.1+4.6
TeacherStudent—RGB & OF & OBJRGB & OF & OBJRGB63.659.1+7.387.786.1+6.6
", + "bbox": [ + 521, + 88, + 870, + 196 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/ed11356bc84f8c6e5efd99d893f2e77942e512f628650d1ab3704f1b0fb2d13e.jpg", + "table_caption": [ + "Table 3: Egocentric action recognition with unseen environments and objects. RGB = Video frames; OF = Optical flow; A = Audio; OBJ = Object detections. Multimodal distillation with λ = 1.0 and γ = 30.0. Improvement over RGB frames baseline [31] in red." + ], + "table_footnote": [], + "table_body": "
Epic-Kitchens Regular splitSomething-Something
MethodNoun@1Verb@1Action@1Action@1Action@5
Omnivore [20]47.862.835.958.486.2
Student51.765.439.363.088.9
Epic-Kitchens Unseen ParticipantsSomething-Else
Omnivore [20]38.554.527.958.384.9
Student43.754.129.659.186.1
", + "bbox": [ + 99, + 290, + 447, + 383 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 4: Comparison with Omnivorous models [20]. All models are Swin-T and perform inference using only RGB frames. Multimodal distillation using all modalities with $\\lambda = 1.0$ and $\\gamma = 30.0$ .", + "bbox": [ + 75, + 392, + 468, + 435 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "A novel observation by our work is that multimodal knowledge distillation performs well in the context of egocentric video understanding, with student models often approaching the performance of the multimodal teacher ensemble. For Epic-Kitchens (Table 2a), we observe that when the student is distilled from an RGB & OF, or RGB & OF & A teacher, it is superior to the baseline model, as well as all modality-specific models, for recognizing actions. On the other hand, distilling from an RGB & A teacher yields performance lower than the baseline, due to the low performance of the model trained only on audio data. Specifically, we observe that the audio-specific teacher lowers the noun (active object) recognition performance. In §4.2, we propose a solution for this issue. For Something-Something (Table 2b), the student model is superior to the baseline for each combination of modalities. When distilling from all available modalities (RGB & OF & OBJ), the resulting model outperforms the baseline by $3.7\\%$ in terms of the top-1 accuracy. In terms of the top-5 accuracy on Something-Something, the students achieve performance that is nearly on par with the multimodal teacher ensemble.", + "bbox": [ + 75, + 460, + 470, + 779 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1.2 Generalizing to Unseen Environments & Objects", + "text_level": 1, + "bbox": [ + 75, + 796, + 468, + 811 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We investigate to what extent our findings translate to the compositional generalization setting2, in which the performance of standard video models deteriorates significantly", + "bbox": [ + 75, + 820, + 468, + 866 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/f3f8e2941eb7ba6d3d0c20f2f6dd7014a5b81364f93b60c631eb47e9eb4e7e87.jpg", + "image_caption": [ + "Figure 3: Expected Calibration Error across datasets. The student is Swin-T trained with $\\lambda = 1.0$ and $\\gamma = 30.0$ ." + ], + "image_footnote": [], + "bbox": [ + 501, + 300, + 689, + 393 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/6ee4f632f5e1179c3698c744f4dee1ac8ab517cafad04b606d0709822e1181c6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 692, + 300, + 890, + 393 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "[33]. In the Something-Something dataset, the objects the people interact with might overlap between training and testing, potentially allowing models to pick up undesirable biases w.r.t. object appearance to discriminate between the actions. Therefore, Something-Else proposes a compositional generalization data split, on which the objects at training and testing time do not overlap, such that the models encounter strictly novel objects during testing. Similarly, the rich visual environments featured in the Epic-Kitchen training data may also provide the model with spurious cues for predicting the actions and lead to significant performance drop on new, unobserved environments. The Epic-Kitchens Unseen split consists of a subset of videos in the validation set from participants whose videos were not present in the training dataset, giving insight into how our approach generalizes to new visual environments. We report the performance of our approach Epic-Kitchens Unseen split and the Something-Else [33] split in Table 3. The general observation across datasets and modalities is that the distilled students significantly outperform the RGB baseline model, and are sometimes even competitive with their respective teacher. Notably, on Something-Else, the student distilled from an RGB & OF & OBJ teacher outperforms the baseline by $7.3\\%$ in terms of top-1 accuracy.", + "bbox": [ + 496, + 460, + 890, + 824 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1.3 Comparison with Omnivorous Models", + "text_level": 1, + "bbox": [ + 500, + 845, + 820, + 859 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We explicitly compare multimodal knowledge distillation against Omnivorous models [19, 20], which are trained", + "bbox": [ + 500, + 869, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "2Compositional generalization measures to what extent the model can generalize to novel combinations of concepts observed during training.", + "bbox": [ + 76, + 875, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "5218", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/6974477f9853b80b117d7cc94e022a0a323394e99fc513ebe8e2d3a8718b3875.jpg", + "image_caption": [ + "Figure 4: Per-class improvement of the student over the RGB baseline on the top-20 most frequent actions across datasets." + ], + "image_footnote": [], + "bbox": [ + 76, + 87, + 472, + 258 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "jointly on all modalities featuring non-aligned data, e.g. with RGB frames obtained from one dataset and depth maps from another [20]. These models have been proven to generalize better compared to their unimodal counterparts. We train the Omnivore model using batches comprised of data from the same modality, where we randomly sample the modality for each training batch3. Additionally, we train the Omnivore models for $M \\times$ more epochs ( $M$ is the number of modalities), to account for the random sampling of modalities during training. We represent the object detections modality as bounding boxes with a line thickness of 2px pasted on a white canvas where each category is colored uniquely, e.g. hand in blue and object in red.", + "bbox": [ + 75, + 324, + 468, + 520 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We report results in Table 4. Even though on the Epic-Kitchens Unseen split and the Something-Else dataset the Omnivore model exhibits strong performance ( $\\sim 5.5\\%$ improvement on top of the baseline on Something-Else), the multimodal distillation approach achieves even higher performance. Nevertheless, we conclude that both approaches represent viable options for training multimodal models which leverage unimodal inputs during inference.", + "bbox": [ + 75, + 521, + 468, + 643 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.1.4 Effect on Model Calibration", + "text_level": 1, + "bbox": [ + 76, + 662, + 328, + 676 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Next to the improvements in action recognition performance we observe, we also investigate how the distilled student fares against the baseline in terms of model calibration. That is, whether the probability score of the predicted class reflects the accuracy of predicting the said class [23, 41]. More importantly, we verify whether distilling from additional modalities yields better calibrated students. In Fig. 3, we measure the Expected Calibration error [23] (ECE) on the Epic-Kitchens (regular & unseen), and the Something-Something and Something-Else datasets. We report the ECE for an RGB model trained using the ground truth la", + "bbox": [ + 75, + 686, + 468, + 853 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/3ccadf9d6f6bd68975f58d165cfb35439fd1f62b646c73125cafffa7882b3483.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ObjectiveλγNoun@1Verb@1Action@1
LCE0.0—52.061.738.3
LKL1.030.051.765.439.3
LCE ∧ LKL0.830.052.665.140.4
LCE ∧ LKL0.83.053.066.941.0
LKL1.01.053.165.540.5
LCE ∧ LKL0.81.053.565.441.2
LCE ∧ LKL0.80.3353.664.740.5
", + "bbox": [ + 553, + 89, + 841, + 183 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 5: Ablation study on the Epic-Kitchens dataset. λ: Distillation and Cross-Entropy loss balancing term; γ: Temperature of the Ensemble Teacher Weighting.", + "bbox": [ + 498, + 193, + 893, + 236 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "bels, as well as all distilled students reported in Table 2 and Table 3. The general observation is that across datasets, distillation improves the models' calibration. Furthermore, we find that increasing the number of modalities used in the ensemble improves the model calibration.", + "bbox": [ + 496, + 262, + 893, + 339 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.1.5 Per-Class Performance Breakdown", + "text_level": 1, + "bbox": [ + 498, + 358, + 799, + 372 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In Fig 4, we present the relative change in action recognition accuracy of the student model obtained via multimodal distillation w.r.t. the architecturally equivalent baseline RGB model trained on ground truth labels, computed on the top-20 most frequent classes (actions) on Epic-Kitchens and Something-Something. Overall, we observe that multimodal distillation generally improves performance across different actions, and particularly so on Something-Something, where we achieve improvements in terms of all of the top-20 most frequent action classes.", + "bbox": [ + 496, + 383, + 890, + 534 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Ensemble Teacher Weighting", + "text_level": 1, + "bbox": [ + 498, + 544, + 761, + 561 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In §4.1 we observe that distilling from multimodal teachers yields students which are superior to models trained on the ground truth labels. Nevertheless, if a weak teacher is added in the ensemble, it negatively affects the knowledge distillation and yields a student which is inferior than using the ground truth labels, e.g. adding the audio-specific teacher in the ensemble for Epic-Kitchens. To cope with this, we weigh the logits of the teacher ensemble as discussed in §3.2. Namely, we use the two hyperparameters $(\\lambda$ and $\\gamma)$ for (i) balancing between the ground truth and the distillation loss: $\\lambda$ (Equation 5), and (ii) controlling how the predictions of modality-specific models are combined in the ensemble: $\\gamma$ (Equation 3). We report results for Epic-Kitchens in Table 5, including the values for $\\lambda$ and $\\gamma$ as well as the objective we effectively minimize. We observe that the model trained only on the ground truth labels ( $\\lambda = 0.0$ ), is inferior to all other models. Using a large $\\gamma$ (e.g. 30.0) - effectively assigning equal weights to all models in the ensemble - we observe to perform well despite the simple setup (we use this model in the experiments in §4.1). Additionally, training using the task loss in addition to the distillation loss ( $\\lambda = 0.8$ ) further improves the performance. The", + "bbox": [ + 496, + 568, + 890, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_footnote", + "text": "$^{3}$ Girdhar et al. [20] show that there is no performance difference if the batches contain mixed data from different modalities, however, we found that using homogeneous batches yields better performance.", + "bbox": [ + 75, + 862, + 468, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "5219", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/459215aa9a90da4897f2a18f629d954ad5a2e6198ee719933287292161486487.jpg", + "image_caption": [ + "Figure 5: Top-1 action accuracy of Teacher, Student & Baseline models and their associated computational cost in giga-FLOPs $(10^{9})$ required to update the input and predict the action. Note: Top-left corner is optimal (i.e. faster and most accurate models)." + ], + "image_footnote": [], + "bbox": [ + 89, + 102, + 450, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/5a2ae4b4f8c46cbe1fbc45f032a0c3e3b6e62a1379f3ffb5edcd768f61e859c4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 491, + 102, + 851, + 292 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/4cd7f76a2b38f9000b69aa49cf1738fbe56698f7c0837e770f8480770c102c2f.jpg", + "image_caption": [ + "Figure 6: Performance degradation when reducing the number of inference clips/crops (Epic-Kitchens/Something-Something)." + ], + "image_footnote": [], + "bbox": [ + 81, + 358, + 460, + 571 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "best performing model uses both the task and the distillation loss $(\\lambda = 0.8)$ , and assigns weights to each teacher in the ensemble based on its performance on $Z = 1000$ randomly sampled videos held-out from the training dataset, with a normalization temperature $\\gamma = 1.0$ . Moreover, we find that lowering the normalization temperature $\\gamma$ further $(\\gamma = 0.33)$ - giving higher weight to the best performing model in the ensemble - yields lower performance. Similarly, increasing the normalization temperature to $\\gamma = 3.0$ , thus equalizing the model weights, also negatively affects performance.", + "bbox": [ + 75, + 637, + 468, + 789 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.3. Efficiency Analysis", + "text_level": 1, + "bbox": [ + 76, + 800, + 259, + 816 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Despite the strong performance multimodal action recognition models exhibit, we argue that the high computational complexity makes them cumbersome for deployment, particularly compared to a model which uses only RGB video during inference. The teacher ensemble used for", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Epic-Kitchens uses three modality-specific Swin-T models, where each has 28.22M parameters, and requires 140.33 GFLOPs for processing single-view 32 frame/spectrogram video. Assuming such an ensemble is deployed, the optical flow would have to be computed on-the-fly4. Using RAFT, we measure a total added computation of 163.37 GFLOPs for such a model. We consider the computation required to obtain the spectrograms of 1.116s audio segments to be negligible in comparison. Therefore, when using all three modalities, updating the input sequences for each newly observed frame and performing action recognition would require 584.36 GFLOPs. In contrast, the distilled student is a single RGB model, and in the case of Swin-T requires 140.33 GFLOPs – which represents a reduction of $75.98\\%$ .", + "bbox": [ + 496, + 361, + 890, + 573 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We report results on the Epic-Kitchens dataset in Fig. 5 for: (i) All variations of teacher models (RGB & OF, RGB & A, and RGB & OF & A); (ii) The Swin-T student model, distilled with $\\lambda = 0.8$ and $\\gamma = 1.0$ ; (iii) The Swin-T baseline model, trained with $\\lambda = 0.0$ ; (iv) Two new ResNet3D models [27] (with depth of 50 and 18 layers), exhibiting less parameters and GFLOPs compared to the Swin-T model. The resolution size of the ResNet3D models is $112 \\times 112$ . For each ResNet3D, we report action recognition performance of the baseline with $\\lambda = 0.0$ , and performance of the distilled students with $\\lambda = 0.8$ and $\\gamma = 1.0$ .", + "bbox": [ + 496, + 574, + 890, + 739 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We observe a consistently higher performance of the student models compared to the same model architecture trained on ground truth labels alone. Notably, our best performing student achieves comparable performance to the significantly more expensive RGB & OF & A teacher. Furthermore, the R3D-18 and R3D-50 students outperform", + "bbox": [ + 496, + 742, + 890, + 834 + ], + "page_idx": 7 + }, + { + "type": "page_footnote", + "text": "4The Duality-based TV-L1 [40, 60] can be efficiently computed on a GPU (5-10 FPS) [4]. Deep Learning-based approaches, e.g. RAFT [51], require 163.37 GFLOPs, however, achieve higher FPS of 21.10, measured with 10 refinement iterations and resolution of $256 \\times 456$ .", + "bbox": [ + 496, + 849, + 893, + 898 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "5220", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/28ecc3676b1f443cb379c03d77bbc74d779c304241739bdf452862c0785e44fa.jpg", + "image_caption": [ + "Figure 7: Qualitative example for the Epic Kitchens (Left) & the Something-Something (Right) datasets." + ], + "image_footnote": [], + "bbox": [ + 80, + 89, + 272, + 253 + ], + "page_idx": 8 + }, + { + "type": "image", + "img_path": "images/a4424c354c8de2dad348f85600ceecd7f53e0e65f3d70059259ea18599a85ed1.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 274, + 89, + 467, + 252 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "their counterparts trained on class labels. Finally, we observe that the R3D-18 student matches the performance of the larger, and computationally more expensive R3D-50 trained on ground truth labels.", + "bbox": [ + 75, + 319, + 467, + 378 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "4.3.1 Effect of Test-Time Augmentation", + "text_level": 1, + "bbox": [ + 76, + 398, + 366, + 412 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Lastly, we inspect the relationship between action recognition performance and the number of temporal clips (on Epic-Kitchens) and spatial crops (on Something-Something) sampled from the video during inference. Note that our goal is to reduce the computational complexity while maintaining the performance. Since standard video models [1, 7, 30, 31] use multiple temporal clips and spatial crops as test-time augmentation to obtain further performance improvements, we explore the extent to which the distilled model is dependent on their availability during inference. We report results in Fig. 6, where we observe that the distilled model $(\\lambda = 1.0)$ is much less adversely affected by the reduction of both sampled temporal clips and spatial crops during inference, compared to the same model trained on the ground truth labels $(\\lambda = 0.0)$ .", + "bbox": [ + 75, + 421, + 467, + 648 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "4.4. Qualitative Examples", + "text_level": 1, + "bbox": [ + 76, + 657, + 277, + 672 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "In Fig. 7, we showcase the classes corresponding to the highest scores predicted by the student and the individual modality-specific models in the teacher ensemble, as well as the ground truth label (on Epic-Kitchens and Something-Something datasets). For both examples, we observe that the student picks up on relevant cues from each modality and accurately predicts the action of interest (see Supp. H for additional qualitative examples).", + "bbox": [ + 75, + 680, + 467, + 801 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 814, + 194, + 830 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We demonstrated a simple, yet effective distillation-based approach for leveraging multimodal data only during training in order to improve a model that uses solely RGB frames during inference. Our experiments indicate clear", + "bbox": [ + 75, + 839, + 467, + 898 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "performance improvements over models trained on ground truth labels. We further showed an advantageous tradeoff between the high performance of a cumbersome multimodal ensemble, and low computational complexity of unimodal approaches. Moreover, our approach relies less on expensive test-time augmentations, otherwise widely used in the literature to improve the egocentric action recognition models' performance.", + "bbox": [ + 496, + 90, + 890, + 210 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Limitations & Future work. Notably, in this work we considered only the task of action recognition, while multimodal distillation can be readily applied to other egocentric tasks [22]. Future work may also feature additional modalities such as depth, hand poses, motion captured by inertial sensors (IMU), etc., available in recent large-scale egocentric datasets [22].", + "bbox": [ + 496, + 212, + 890, + 316 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 500, + 330, + 658, + 348 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We acknowledge the funding from the Flemish Government under the Onderzoeksprogramma Artificièle Intelligente (AI) Vlaanderen programme.", + "bbox": [ + 498, + 356, + 890, + 402 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "5221", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Anurag Arnab, Mostafa Dehghani, Georg Heigold, Chen Sun, Mario Lucic, and Cordelia Schmid. 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In Proceedings of the IEEE International Conference on Computer Vision, pages 4498-4506, 2015. 1" + ], + "bbox": [ + 78, + 90, + 468, + 755 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "5224", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/Multimodal Distillation for Egocentric Action Recognition/3b080565-3bdc-4aa7-989c-41508102f95e_model.json b/2023/Multimodal Distillation for Egocentric Action Recognition/3b080565-3bdc-4aa7-989c-41508102f95e_model.json new file mode 100644 index 0000000000000000000000000000000000000000..40ce196fd082db62aeb15ffb7ea0fdb86ef7e72d --- /dev/null +++ b/2023/Multimodal Distillation for Egocentric Action Recognition/3b080565-3bdc-4aa7-989c-41508102f95e_model.json @@ -0,0 +1,2435 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.192, + 0.131, + 0.78, + 0.154 + ], + "angle": 0, + "content": "Multimodal Distillation for Egocentric Action Recognition" + }, + { + "type": "text", + "bbox": [ + 0.153, + 0.181, + 0.768, + 0.254 + ], + "angle": 0, + "content": "Gorjan Radevski* Dusan Grujicic* Matthew Blaschko Marie-Francine Moens Tinne Tuytelaars KU Leuven University, Belgium {firstname}. {lastname}@kuleuven.be" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.319, + 0.474, + 0.699 + ], + "angle": 0, + "content": "The focal point of egocentric video understanding is modelling hand-object interactions. Standard models, e.g. CNNs or Vision Transformers, which receive RGB frames as input perform well, however, their performance improves further by employing additional input modalities (e.g. object detections, optical flow, audio, etc.) which provide cues complementary to the RGB modality. The added complexity of the modality-specific modules, on the other hand, makes these models impractical for deployment. The goal of this work is to retain the performance of such a multimodal approach, while using only the RGB frames as input at inference time. We demonstrate that for egocentric action recognition on the Epic-Kitchens and the Something-Something datasets, students which are taught by multimodal teachers tend to be more accurate and better calibrated than architecturally equivalent models trained on ground truth labels in a unimodal or multimodal fashion. We further adopt a principled multimodal knowledge distillation framework, allowing us to deal with issues which occur when applying multimodal knowledge distillation in a naive manner. Lastly, we demonstrate the achieved reduction in computational complexity, and show that our approach maintains higher performance with the reduction of the number of input views. We release our code at: https://github.com/gorjanradevski/multimodal-distillation" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.728, + 0.21, + 0.743 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.754, + 0.47, + 0.876 + ], + "angle": 0, + "content": "The purpose of egocentric vision is enabling machines to interpret real-world data taken from a human's perspective. Its applications are numerous, ranging from recognizing [63] or anticipating [15] actions, to more complex tasks such as recognizing egocentric object-state changes, localizing action instances of a particular video moment [22], etc. The focal point of egocentric vision is hand-object interactions. Usually, these hand-object interactions take" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.288, + 0.891, + 0.426 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.435, + 0.894, + 0.478 + ], + "angle": 0, + "content": "Figure 1: Motivation: The multimodal action recognition model is powerful, but too slow to be used in practice. The distilled student is significantly faster yet achieves competitive performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.507, + 0.893, + 0.598 + ], + "angle": 0, + "content": "place in cluttered environments, where the object of interest is often occluded, or occurs only during a short time period. Furthermore, egocentric vision often suffers from motion blur – due to the movement of the scene objects or the camera itself – and thus, understanding video content from RGB frames alone may be challenging." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.6, + 0.895, + 0.902 + ], + "angle": 0, + "content": "To cope with these challenges, various egocentric action recognition methods [25, 29, 33, 43, 56, 59, 61] demonstrate that explicitly modelling hand-object interactions (usually represented via bounding boxes & object categories) significantly improves the action recognition performance, most notably in a compositional generalization setup [43]. Similarly, other works show that leveraging multiple modalities (optical flow, audio, etc.) at inference time yields improved performance [16, 28, 36, 57]. The assumptions these methods make are (i) that all modalities used during training are also available at inference time, and (ii) the compute budget at inference time would be sufficient to obtain and process the additional modalities. Such assumptions make these methods cumbersome or even impossible to use in practice, e.g. on a limited compute budget such as in the case of embedded devices. Namely, using dedicated models for each additional modality (e.g. object detector, object tracker and a transformer when using bounding boxes & object categories as input [43]), increases both the memory footprint as well as the inference time. Ideally, video understanding" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.888, + 0.262, + 0.901 + ], + "angle": 0, + "content": "* Authors contributed equally." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.958 + ], + "angle": 0, + "content": "5213" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.137 + ], + "angle": 0, + "content": "models would leverage additional modalities during training, while the resulting model would use only RGB frames at inference time, i.e. when deployed in practice." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.137, + 0.468, + 0.273 + ], + "angle": 0, + "content": "One way to achieve the aforementioned goal is training omnivorous models, i.e. models trained jointly on multiple modalities, which have been shown to generalize better [20] than unimodal counterparts. In this work, we take a different route and transfer multimodal knowledge to models subsequently used in a unimodal setting. Namely, we distill the knowledge from a multimodal ensemble - exhibiting superior performance, but unviable for deployment - to a standard RGB-based action recognition model [5] (see Fig. 1)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.273, + 0.468, + 0.439 + ], + "angle": 0, + "content": "Contributions. We employ state-of-the-art knowledge distillation practices [6] and ① show that a student [31] taught by a multimodal teacher, is both more accurate and better calibrated than the same model trained from scratch or in an omnivorous fashion (§4.1); ② We provide motivation and establish a simple but reliable multimodal distillation approach, which overcomes the issue of potentially suboptimal modality-specific teachers (§4.2); ③ We demonstrate that the distilled student performs on par with significantly larger models, and maintains performance in computationally cheaper inference setups (§4.3)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.453, + 0.218, + 0.468 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.479, + 0.468, + 0.704 + ], + "angle": 0, + "content": "Knowledge distillation. Originally introduced by Hinton et al. [26], knowledge distillation is used to transfer the knowledge from one model, i.e. a teacher, to another model, i.e. a student, by training the student to match the teacher's (intermediate) outputs on a certain dataset. Shown to be useful in a variety of contexts, the primary goal is model compression - transferring the knowledge from a larger, cumbersome teacher model, or from a teacher exhibiting a different inductive bias [9, 52], to a typically lightweight student model [10, 35, 55]. Another line of work [2, 47] proposes to distill from ensembles of large teacher models to lightweight student models, obtaining promising results. Compared to these works, we focus on knowledge distillation from a multimodal teacher ensemble, i.e. a set of models where each is trained on a distinct modality." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Multimodal knowledge distillation has been previously used mainly in a cross-modal fashion, where the teacher and the student receive different modalities as input. In some works, the teacher receives RGB images while the student receives depth or optical flow images [24], while in others, the teacher receives RGB images as input, while the student receives audio as input [3]. In contrast, other works explore a multimodal knowledge expansion scenario, where a multimodal student learns from pseudo-labels of a unimodal teacher [58]. We, on the other hand, focus on scenarios where obtaining additional modalities (optical flow, object detections, audio, etc.) during inference is prohibitive due to a limited compute budget, and therefore multimodal" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.409 + ], + "angle": 0, + "content": "data is only used during training time. Multimodal knowledge distillation for action recognition has been previously explored in the works of Gracia et al. [17, 18]. They propose to train a model on aligned data from two modalities, where a model which receives data from modality A is trained to imitate the intermediate features of a model which receives training data from modality B. This approach is shown to yield performance improvements compared to an RGB baseline when using RGB and depth data. Moreover, the Mars [11] and D3d [49] methods, similarly to us, leverage RGB frames and optical flow during training to improve test-time performance of a model that performs inference using RGB frames alone. This is achieved by matching the corresponding features or probabilistic outputs of the modality-specific models during training. Compared to these works, we consider a more general knowledge distillation setting [6, 26], with a multimodal teacher ensemble used to provide a better approximation of the true posterior. Lastly, we consider a more diverse and broader set of modalities (RGB frames, optical flow, audio and object detections) compared to the aforementioned works." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.413, + 0.892, + 0.716 + ], + "angle": 0, + "content": "Multimodal (egocentric) video understanding. In the context of (egocentric) video understanding, several works have shown that using additional modalities at inference time significantly improves performance [25, 29, 33, 36, 43, 50, 56, 61]. The hypothesis is intuitive - certain actions are more easily understood from specific modalities, e.g. to recognize that a person is \"pushing something from left to right,\" the bounding boxes alone are sufficient [33, 43]. Nevertheless, the assumption these works make is that all modalities used during training are available during inference, and that the compute budget allows for processing additional modalities other than the RGB frames. To that end, multiple works [25, 29, 33, 43, 56, 61] effectively use a Faster R-CNN [44], multiple object tracker (MOT), and object detection-specific models at inference time. In contrast, we posit that for egocentric video understanding, computing additional modalities on the fly may be prohibitive. Therefore, we propose a distillation approach which uses multimodal data only during training, while the resulting model is dependent on RGB frames alone during inference." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Models robust to missing modalities during inference. A parallel route to our goal - retaining the performance of multimodal approaches, while using only the RGB frames at inference time - is to explicitly train models to be robust to missing modalities during inference [37, 39, 62]; or more recently, to process different modalities altogether interchangeably - Omnivorous models [12, 19, 20]. These models have been shown to generalize better than models trained on unimodal data. In this work, we train an Omnivorous model using the same architecture as our student, and show that the student distilled from a multimodal teacher generalizes better than its Omnivorous variant." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5214" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.09, + 0.212, + 0.108 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.117, + 0.348, + 0.133 + ], + "angle": 0, + "content": "3.1. Egocentric Action Recognition" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.141, + 0.47, + 0.294 + ], + "angle": 0, + "content": "We assume we are given an input \\(\\mathbf{x} \\in \\mathbb{R}^{T \\times D_1 \\times D_2 \\dots \\times D_L}\\), which describes an egocentric action sequence, where \\(T\\) is the number of time-steps, while \\(D_1 \\times D_2 \\dots \\times D_L\\) represent other dimensions of the input data, e.g. the height, width and the number of channels of a video frame. The goal of the model \\(f\\) is to produce a discrete probability distribution over a predefined set of \\(C\\) classes, i.e. \\(\\hat{\\mathbf{y}} = \\sigma(f(\\mathbf{x})) \\in \\mathbb{R}_+^C\\), where \\(\\sigma\\) is the softmax operator. The classes represent the actions, or alternatively, the nouns and verbs constituting the actions (e.g. the active video object and the activity)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.295, + 0.471, + 0.449 + ], + "angle": 0, + "content": "Given a dataset \\(\\mathbb{D} = \\{(\\mathbf{x}_1,\\mathbf{y}_1),\\dots ,(\\mathbf{x}_N,\\mathbf{y}_N)\\}\\) of \\(N\\) egocentric action sequences \\(\\mathbf{x}_i\\) paired with labels \\(\\mathbf{y}_i\\in \\mathbb{R}_+^C\\) the model is trained by minimizing the standard crossentropy objective \\(\\mathcal{L}_{\\mathrm{CE}} = -\\frac{1}{N}\\sum_{i = 1}^{N}\\mathbf{y}_i\\cdot \\log \\sigma (f(\\mathbf{x}_i))\\) where \\(\\cdot\\) represents the scalar product. In the case of actions characterized by separate nouns and verbs, and accompanied by their respective labels \\(\\mathbf{y}_i^n\\) and \\(\\mathbf{y}_i^v\\) , separate prediction heads produce \\(f^n (\\mathbf{x}_i)\\) and \\(f^{v}(\\mathbf{x}_{i})\\) . Finally, the model is trained by minimizing the sum of the loss terms corresponding to the nouns and verbs, \\(\\mathcal{L}_{\\mathrm{CE}}^n\\) and \\(\\mathcal{L}_{\\mathrm{CE}}^v\\) respectively." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.463, + 0.383, + 0.479 + ], + "angle": 0, + "content": "3.2. Multimodal Knowledge Distillation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.489, + 0.469, + 0.625 + ], + "angle": 0, + "content": "In egocentric vision, there often exist more than one input modality that characterize the same actions. The action recognition task may thus be performed via the use of multiple modalities, leveraged only during training [20, 42], or both during training and inference [16,28,36,57] by ensembling [57] models, multimodal-fusion [28, 43], etc. However, in the case of the latter, processing multimodal data may be computationally prohibitive at inference time (e.g. due to a limited compute budget)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.627, + 0.469, + 0.822 + ], + "angle": 0, + "content": "The fundamental concept our method builds on is knowledge distillation [26], featuring a teacher (usually larger model, exhibiting strong performance, but cumbersome to use in practice) and a student (typically a smaller model, trained to mimic the teacher [6]). Focusing on the most accessible data modality - RGB video frames (e.g. obtained using a single monocular video camera) - we opt for distilling the knowledge of a multimodal ensemble to a single model that relies on RGB inputs alone. We make a modification to the standard knowledge distillation approach, by altering the teacher such that (i) it is not a single model, but rather an ensemble of models, and (ii) the constituting models receive different modalities as input." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.825, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Teacher ensemble. Given \\(M\\) datasets \\(\\mathbb{D}^m = \\left\\{(\\mathbf{x}_1^m,\\mathbf{y}_1),\\dots ,(\\mathbf{x}_N^m,\\mathbf{y}_N)\\right\\}\\) of different modalities, we train a separate model \\(f^{m}\\) by minimizing the learning objective \\(\\mathcal{L}_{\\mathrm{CE}}^m = -\\frac{1}{N}\\sum_{i = 1}^N\\mathbf{y}_i\\cdot \\log \\sigma \\left(f^m (\\mathbf{x}_i^m)\\right)\\) for each modality. Finally, the output of the ensemble can be obtained by aver" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.792, + 0.107 + ], + "angle": 0, + "content": "aging the outputs of the individual teachers:" + }, + { + "type": "equation", + "bbox": [ + 0.595, + 0.117, + 0.892, + 0.16 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {y}} _ {i} ^ {t} = \\sigma \\left(\\frac {1}{M} \\sum_ {m = 1} ^ {M} f ^ {m} \\left(\\mathbf {x} _ {i} ^ {m}\\right)\\right). \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.168, + 0.892, + 0.38 + ], + "angle": 0, + "content": "Intuitively, under-performing modality-specific models could negatively affect the performance of the ensemble. We thus consider assigning different weights to the output logits of each model in the ensemble, before aggregating their predictions. Ideally, we would want to perform a Bayesian prediction: \\( p(\\mathbf{y}|\\mathbf{x},\\mathbb{D}) = \\int_{f\\in F}p(\\mathbf{y}|\\mathbf{x},f)p(f|\\mathbb{D})df \\). For a given finite ensemble of \\( M \\) diverse predictors, we replace the integral with a sum over the individual models: \\( p(\\mathbf{y}|\\mathbf{x},\\mathbb{D}) \\approx \\sum_{m = 1}^{M}p(\\mathbf{y}|\\mathbf{x},f^{m})p(f^{m}|\\mathbb{D}) \\). We further approximate \\( p(f^{m}|\\mathbb{D}) \\) via its proportionality to the data likelihood \\( p(\\mathbb{D}|f^{m}) \\) under the Bayes rule: \\( p(f^{m}|\\mathbb{D}) \\propto p(\\mathbb{D}|f^{m}) \\); which itself can be expressed in terms of the cross-entropy that the model \\( f^{m} \\) exhibits on the dataset \\( \\mathbb{D} \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.381, + 0.892, + 0.411 + ], + "angle": 0, + "content": "The cross-entropy \\( e^{m} \\) of each modality-specific model in the ensemble can be estimated on a holdout set:" + }, + { + "type": "equation", + "bbox": [ + 0.571, + 0.422, + 0.892, + 0.464 + ], + "angle": 0, + "content": "\\[\ne ^ {m} = - \\frac {1}{Z} \\sum_ {i = 1} ^ {Z} \\mathbf {y} _ {i} \\cdot \\log \\sigma \\left(f ^ {m} \\left(\\mathbf {x} _ {i} ^ {m}\\right)\\right), \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.469, + 0.892, + 0.53 + ], + "angle": 0, + "content": "where \\( Z \\) is the number of held-out samples used to estimate the weights. Then, we can obtain the weights for the modality-specific models via softmax normalization of the negative cross-entropy terms:" + }, + { + "type": "equation", + "bbox": [ + 0.625, + 0.543, + 0.891, + 0.561 + ], + "angle": 0, + "content": "\\[\nw ^ {m} \\propto \\exp (- e ^ {m} / \\gamma), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.567, + 0.891, + 0.612 + ], + "angle": 0, + "content": "where \\(\\gamma\\) is a temperature term which controls the entropy of the model weights, e.g. if \\(\\gamma \\rightarrow \\infty\\), equal weights would be given to each teacher - resulting in an arithmetic mean." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.612, + 0.891, + 0.643 + ], + "angle": 0, + "content": "We finally compute the weighted average of the predictions of \\( M \\) modality-specific models as the teacher output:" + }, + { + "type": "equation", + "bbox": [ + 0.594, + 0.653, + 0.891, + 0.695 + ], + "angle": 0, + "content": "\\[\n\\hat {\\mathbf {y}} _ {i} ^ {t} = \\sigma \\left(\\sum_ {m = 1} ^ {M} w ^ {m} f ^ {m} \\left(\\mathbf {x} _ {i} ^ {m}\\right)\\right). \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.699, + 0.891, + 0.759 + ], + "angle": 0, + "content": "Figure 2 presents a high-level overview of our approach. In summary, our student is taught by a multimodal teacher which is itself an ensemble of multiple modality-specific models, trained separately on each modality." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.76, + 0.892, + 0.872 + ], + "angle": 0, + "content": "Training objective. During training, we perform multimodal knowledge distillation, as originally proposed by Hinton et al. [26]. Specifically, we minimize the KL-divergence \\(\\mathcal{L}_{\\mathrm{KL}}\\) between the class probabilities predicted by the teacher \\(\\hat{\\mathbf{y}}_i^t = [\\hat{y}_{i,1}^t,\\dots ,\\hat{y}_{i,C}^t ]\\in \\mathbb{R}_+^C\\) and the class probabilities of the student \\(\\hat{\\mathbf{y}}_i^s = [\\hat{y}_{i,1}^s,\\dots ,\\hat{y}_{i,C}^s ]\\in \\mathbb{R}_+^C\\) as \\(\\mathcal{L}_{\\mathrm{KL}} = \\frac{1}{N}\\sum_{i = 1}^{N}(-\\hat{\\mathbf{y}}_i^t\\cdot \\log \\hat{\\mathbf{y}}_i^s +\\hat{\\mathbf{y}}_i^t\\cdot \\log \\hat{\\mathbf{y}}_i^t)\\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.872, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Additionally, we use a temperature parameter \\(\\tau\\) to control the entropy of the predicted probability scores while" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5215" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.089, + 0.468, + 0.216 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.09, + 0.225, + 0.455, + 0.24 + ], + "angle": 0, + "content": "Figure 2: Overview of the main components of our approach." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.256, + 0.468, + 0.363 + ], + "angle": 0, + "content": "
Epic-Kitchens RegularSomething-Something
MethodNoun Acc.Noun ECEVerb Acc.Verb ECEAction Acc.Action ECE
RGB Baseline52.019.961.717.159.321.2
Teacher (γ = 30.0)52.32.0466.83.466.68.1
Teacher (γ = 1.0)53.98.966.94.266.79.0
Epic-Kitchens Unseen EnvironmentsSomething-Else
MethodNoun Acc.Noun ECEVerb Acc.Verb ECEAction Acc.Action ECE
RGB Baseline38.326.951.724.051.821.4
Teacher (γ = 30.0)42.96.0258.09.963.36.5
Teacher (γ = 1.0)43.89.557.79.763.58.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.374, + 0.471, + 0.43 + ], + "angle": 0, + "content": "Table 1: Accuracy & Expected Calibration Error (ECE) of the RGB baseline and Teacher ensemble on Epic-Kitchens and Something-Something (regular & unseen splits). All available modalities for the respective dataset used in the ensemble." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.459, + 0.47, + 0.536 + ], + "angle": 0, + "content": "preserving their ranking, i.e. \\(\\hat{y}_j^s\\propto \\exp (\\hat{y}_j^s /\\tau)\\). As per standard practice [26], we use the temperature parameter \\(\\pmb{\\tau}\\) to also rescale the KL-divergence loss, i.e. \\(\\mathcal{L}_{\\mathrm{KL}} = \\mathcal{L}_{\\mathrm{KL}}\\cdot \\tau^2\\). We further use the standard cross-entropy action recognition loss \\(\\mathcal{L}_{\\mathrm{CE}}\\), and compute the final loss:" + }, + { + "type": "equation", + "bbox": [ + 0.173, + 0.554, + 0.469, + 0.57 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} = \\lambda \\cdot \\mathcal {L} _ {\\mathrm {K L}} + (1 - \\lambda) \\cdot \\mathcal {L} _ {\\mathrm {C E}}, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.582, + 0.47, + 0.656 + ], + "angle": 0, + "content": "where \\(\\lambda\\) balances the distillation loss \\(\\mathcal{L}_{\\mathrm{KL}}\\) and the action recognition loss \\(\\mathcal{L}_{\\mathrm{CE}}\\). For example, with \\(\\lambda = 0.0\\) we would effectively be training the modality-specific RGB model, while with \\(\\lambda = 1.0\\), we would perform solely multimodal knowledge distillation." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.658, + 0.469, + 0.748 + ], + "angle": 0, + "content": "Optimality of a multimodal ensemble teacher. The work of Menon et al. [34] further demonstrates that in the context of distillation, a teacher that predicts the Bayes class-probability distribution over the labels \\(\\mathbf{p}^{*}(\\mathbf{x}) = [\\mathbb{P}(y|\\mathbf{x})]_{y\\in [C]}\\) exhibits the lowest possible variance of the student objective for any convex loss function." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.47, + 0.902 + ], + "angle": 0, + "content": "The student trained to minimize the KL-divergence between its output and the Bayes class-probabilities would thus generalize the best. In a preliminary experiment shown in Table 1, we demonstrate that the multimodal ensemble (both for \\(\\gamma = 1\\) and \\(\\gamma = 30.0\\)) achieves a significantly higher accuracy and lower calibration error, and thus represents a better approximation of the Bayes class probabilities than a single modality-specific model. This may lead to a lower-variance objective for the student and improved generalization during knowledge distillation [34]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.09, + 0.747, + 0.108 + ], + "angle": 0, + "content": "4. Experiments & Discussion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.115, + 0.892, + 0.342 + ], + "angle": 0, + "content": "Datasets. We use the Something-Something (V2) [21] and the Epic-Kitchens (100) [14] datasets. Something-Something contains videos of people performing 174 (object agnostic) unique actions with their hands, e.g. \"pushing [something] left\", \"taking [something] out of [something]\", etc. Epic-Kitchens' videos take place in kitchen environments, where the actions are noun-verb compositions. The 300 unique nouns indicate the active object in the video, while 97 unique verbs indicate the activity, e.g. \"cutting carrot\", \"washing pan\", etc. During evaluation, the action is considered correct if both the noun and the verb are correctly predicted. Additionally, we use the Something-Else [33] dataset and the Epic-Kitchens Unseen split to measure the compositional generalization ability of the models w.r.t. unseen objects and environments." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.343, + 0.892, + 0.388 + ], + "angle": 0, + "content": "Modalities. In addition to the RGB frames (the modality of interest at inference time), in our experiments we consider the following modalities:" + }, + { + "type": "text", + "bbox": [ + 0.512, + 0.399, + 0.892, + 0.46 + ], + "angle": 0, + "content": "(i) Optical flow (OF): First used by I3D [8] for action recognition, it is also used by recent state-of-the-art (egocentric) video understanding methods [57]. We use optical flow obtained using TV-L1 [60]." + }, + { + "type": "text", + "bbox": [ + 0.509, + 0.471, + 0.892, + 0.562 + ], + "angle": 0, + "content": "(ii) Object detections (OBJ): Shown to significantly improve the performance of standard (RGB) egocentric video understanding models across datasets [25, 33, 43, 56, 61]. As per [46], we use the object detector trained on object-agnostic annotations, i.e. with \"hands\" and \"objects\" object labels." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.573, + 0.892, + 0.632 + ], + "angle": 0, + "content": "(iii) Audio (A): For certain datasets [13, 14], several works [28, 57] have shown that using audio improves action recognition performance. The audio is obtained directly from the recorded video." + }, + { + "type": "list", + "bbox": [ + 0.504, + 0.399, + 0.892, + 0.632 + ], + "angle": 0, + "content": null + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.892, + 0.749 + ], + "angle": 0, + "content": "Moreover, if available, one may include additional modalities, e.g. depth estimates, heat maps, etc. For Something-Something and Something-Else there is no audio available, while we use the object detections provided by [25, 33], and optical flow from [54]. For Epic-Kitchens we use the modalities available and released with the dataset itself [14]: optical flow and audio." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.893, + 0.901 + ], + "angle": 0, + "content": "Models. We use a Swin-Tiny (Swin-T) Transformer [31] to encode RGB frames, optical flow, and audio. Each optical flow frame is represented as a \\(224 \\times 224 \\times 2\\) tensor, where the two values at each spatial location represent the \\(x\\) and \\(y\\) velocity components. In the case of audio, we extract 1.116 second-audio segments (0.558s before its corresponding time-step and 0.558s after it) for each frame. We compute the mel-spectrogram of the audio segment (see details in Supp. B), which is subsequently resized to desired width and height. We thus treat each modality as a sequence of" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5216" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.468, + 0.198 + ], + "angle": 0, + "content": "
MethodTraining ModalitiesInference ModalitiesNoun@1Verb@1Action@1
BaselineRGBRGB52.061.738.3
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB34.151.952.259.065.365.625.939.539.9+1.6
Modality-specificTeacherStudentA—RGB & AARGB & ARGB22.352.761.546.564.462.4+0.715.139.837.9-0.4
TeacherStudent—RGB & OF & ARGB & OF & ARGB52.351.7-0.366.865.4+3.740.539.3+1.0
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.077, + 0.202, + 0.472, + 0.228 + ], + "angle": 0, + "content": "(a) Epic-Kitchens [14]: Recognition of the active video object (noun) and the activity (verb)." + }, + { + "type": "table", + "bbox": [ + 0.522, + 0.089, + 0.871, + 0.198 + ], + "angle": 0, + "content": "
MethodTraining ModalitiesInference ModalitiesAction@1Action@5
BaselineRGBRGB60.386.4
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB49.364.379.088.9
\\( 62.8_{+2.5} \\)\\( 88.9_{+2.5} \\)
Modality-specific TeacherStudentOBJ—RGB & OBJOBJRGB & OBJRGB47.965.376.289.5
\\( 63.2_{+2.9} \\)\\( 88.7_{+2.3} \\)
TeacherStudent—RGB & OF & OBJRGB & OF & OBJRGB66.6\\( 63.0_{+2.7} \\)90.5\\( 88.9_{+2.5} \\)
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.516, + 0.202, + 0.873, + 0.216 + ], + "angle": 0, + "content": "(b) Something-Something [21]: Object-agnostic action recognition." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.239, + 0.893, + 0.268 + ], + "angle": 0, + "content": "Table 2: Egocentric action recognition. RGB = Video frames; OF = Optical flow; A = Audio; OBJ = Object detections. Multimodal distillation with \\(\\lambda = 1.0\\) and \\(\\gamma = 30.0\\). Improvement over RGB frames baseline [31] in red." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.294, + 0.47, + 0.521 + ], + "angle": 0, + "content": "\\(224 \\times 224\\) multi-channel images, which we provide as input to the vision transformer, as per the common practice in recent vision models [19, 20]. To encode the object detections, i.e. bounding boxes and object categories of the scene objects, we use a state-of-the-art model - STLT [43]. In STLT, a spatial and temporal transformer separately encode the spatial and temporal arrangement of the objects occurring in the video. The multimodal teacher we use during knowledge distillation is an ensemble of individual, modality-specific models. Unless noted otherwise, the student is a Swin-T model which receives RGB frames as input, both during training (distillation) and inference. In addition to Swin-T, in §4.3, we also consider ResNet3D [27] (18 and 50 layers deep) light-weight student models which receive video frames of size \\(112 \\times 112\\) as input." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.521, + 0.47, + 0.627 + ], + "angle": 0, + "content": "Metrics. Besides accuracy, we measure Expected Calibration Error (ECE) [23]. As per [23, 45], we sort the predictions based on the per-class confidence scores and group them into \\( K \\) bins \\( B_{k} \\), each associated with a confidence interval \\( I_{B_k} = \\left(\\frac{k - 1}{K},\\frac{k}{K}\\right) \\), where \\( K = 15 \\). ECE represents the discrepancy between the average accuracy \\( acc(B_k) \\) and the average confidence \\( conf(B_k) \\) in each bin \\( B_{k} \\):" + }, + { + "type": "equation", + "bbox": [ + 0.135, + 0.638, + 0.47, + 0.68 + ], + "angle": 0, + "content": "\\[\n\\mathrm {E C E} = \\sum_ {k = 1} ^ {K} \\frac {\\left| B _ {k} \\right|}{N} \\left| a c c \\left(B _ {k}\\right) - c o n f \\left(B _ {k}\\right) \\right|, \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.69, + 0.384, + 0.704 + ], + "angle": 0, + "content": "where \\(N\\) is the number of evaluation samples." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.705, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Implementation details. We train all models for 60 epochs using AdamW [32], with a peak learning rate of \\(1e - 4\\), linearly increased for the first \\(5\\%\\) of the training and decreased to 0.0 by the end of the specified 60 epochs. We use weight decay with a regularization coefficient of \\(5e - 2\\), and clip the gradients when their norm exceeds 5.0. For Epic-Kitchens, we sample 32 frames with a fixed stride of 2, and for Something-Something and Something-Else we evenly sample 16 frames to cover the whole video. We use a single spatial and temporal crop, unless stated otherwise. During training, we chose a random start frame, while during inference, we select the start frame such that the sequence covers the central portion of the video. If we" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.294, + 0.892, + 0.431 + ], + "angle": 0, + "content": "use multiple temporal crops as test-time augmentation, we chose the start frames such that the video is covered uniformly. During training we apply standard data augmentations - random spatial video crops, color jittering, and horizontal flips (for Epic-Kitchens only). The temperature parameter \\(\\tau\\) is fixed to 10.0 for both the student and the teacher during multimodal knowledge distillation. In §4.2 we ablate the impact of the loss balancing term \\(\\lambda\\) and the Ensemble Teacher Weighting temperature term \\(\\gamma^1\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.431, + 0.892, + 0.507 + ], + "angle": 0, + "content": "During training we follow the consistent teaching paradigm [6] where the student and teacher strictly receive the same views of the data - we ensure for spatial and temporal consistency, i.e. the models receive the same frame indices, same random crops, and horizontal flips." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.515, + 0.884, + 0.531 + ], + "angle": 0, + "content": "4.1. Multimodal Distillation for Egocentric Vision" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.538, + 0.893, + 0.72 + ], + "angle": 0, + "content": "We first verify the overall effectiveness of multimodal knowledge distillation on the task of egocentric action recognition for both object-agnostic actions (Something-Something) and actions represented as noun-verb compositions (Epic-Kitchens). Across all experiments, we fix \\(\\lambda\\) to 1.0, i.e. we train solely with multimodal knowledge distillation. Similarly, we set \\(\\gamma\\) to a large value (\\(\\gamma = 30.0\\)), where effectively each teacher equally contributes to the ensemble output. Note that in this setting, models trained on modalities such as optical flow and audio may underperform, and thus adversely affect the ensemble teacher performance of recognizing active objects, i.e. nouns." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.737, + 0.776, + 0.753 + ], + "angle": 0, + "content": "4.1.1 Recognizing Egocentric Actions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.761, + 0.892, + 0.868 + ], + "angle": 0, + "content": "In Table 2, we report performance on Something-Something V2 [21] and Epic-Kitchens 100 [14]. In line with the previous findings reported in the literature [33, 43, 57], we find that employing additional modalities at inference time significantly improves the performance compared to the RGB baseline model, for both the Epic-Kitchens and the Something-Something datasets." + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.893, + 0.901 + ], + "angle": 0, + "content": "1As the datasets' test sets either do not exist [33], or have restricted access, we report results using the model after the final training epoch." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5217" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.089, + 0.47, + 0.198 + ], + "angle": 0, + "content": "
MethodTraining ModalitiesInference ModalitiesNoun@1Verb@1Action@1
BaselineRGBRGB38.351.725.4
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB28.041.042.5+4.253.254.955.9+4.221.628.430.2+4.8
Modality-specificTeacherStudentA—RGB & AARGB & ARGB15.041.941.8+3.541.555.351.8+0.19.128.527.5+2.1
TeacherStudent—RGB & OF & ARGB & OF & ARGB42.943.7+5.458.054.1+3.430.329.6+4.2
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.077, + 0.202, + 0.472, + 0.228 + ], + "angle": 0, + "content": "(a) Epic-Kitchens Unseen Environments [14]: Recognition of the active object (noun) and the activity (verb) on participants unseen during training." + }, + { + "type": "table", + "bbox": [ + 0.522, + 0.089, + 0.871, + 0.198 + ], + "angle": 0, + "content": "
MethodTraining ModalitiesInference ModalitiesAction@1Action@5
BaselineRGBRGB51.879.5
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB49.061.058.2+6.477.486.485.1+5.6
Modality-specificTeacherStudentOBJ—RGB & OBJOBJRGB & OBJRGB41.459.457.5+5.767.384.584.1+4.6
TeacherStudent—RGB & OF & OBJRGB & OF & OBJRGB63.659.1+7.387.786.1+6.6
" + }, + { + "type": "table_footnote", + "bbox": [ + 0.497, + 0.202, + 0.892, + 0.228 + ], + "angle": 0, + "content": "(b) Something-Else [33]: Object-agnostic action recognition featuring objects unseen during training." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.239, + 0.892, + 0.269 + ], + "angle": 0, + "content": "Table 3: Egocentric action recognition with unseen environments and objects. RGB = Video frames; OF = Optical flow; A = Audio; OBJ = Object detections. Multimodal distillation with λ = 1.0 and γ = 30.0. Improvement over RGB frames baseline [31] in red." + }, + { + "type": "table", + "bbox": [ + 0.101, + 0.291, + 0.449, + 0.384 + ], + "angle": 0, + "content": "
Epic-Kitchens Regular splitSomething-Something
MethodNoun@1Verb@1Action@1Action@1Action@5
Omnivore [20]47.862.835.958.486.2
Student51.765.439.363.088.9
Epic-Kitchens Unseen ParticipantsSomething-Else
Omnivore [20]38.554.527.958.384.9
Student43.754.129.659.186.1
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.393, + 0.47, + 0.436 + ], + "angle": 0, + "content": "Table 4: Comparison with Omnivorous models [20]. All models are Swin-T and perform inference using only RGB frames. Multimodal distillation using all modalities with \\( \\lambda = 1.0 \\) and \\( \\gamma = 30.0 \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.462, + 0.471, + 0.78 + ], + "angle": 0, + "content": "A novel observation by our work is that multimodal knowledge distillation performs well in the context of egocentric video understanding, with student models often approaching the performance of the multimodal teacher ensemble. For Epic-Kitchens (Table 2a), we observe that when the student is distilled from an RGB & OF, or RGB & OF & A teacher, it is superior to the baseline model, as well as all modality-specific models, for recognizing actions. On the other hand, distilling from an RGB & A teacher yields performance lower than the baseline, due to the low performance of the model trained only on audio data. Specifically, we observe that the audio-specific teacher lowers the noun (active object) recognition performance. In §4.2, we propose a solution for this issue. For Something-Something (Table 2b), the student model is superior to the baseline for each combination of modalities. When distilling from all available modalities (RGB & OF & OBJ), the resulting model outperforms the baseline by \\(3.7\\%\\) in terms of the top-1 accuracy. In terms of the top-5 accuracy on Something-Something, the students achieve performance that is nearly on par with the multimodal teacher ensemble." + }, + { + "type": "title", + "bbox": [ + 0.076, + 0.797, + 0.47, + 0.813 + ], + "angle": 0, + "content": "4.1.2 Generalizing to Unseen Environments & Objects" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.821, + 0.469, + 0.867 + ], + "angle": 0, + "content": "We investigate to what extent our findings translate to the compositional generalization setting2, in which the performance of standard video models deteriorates significantly" + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.301, + 0.69, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.693, + 0.301, + 0.892, + 0.395 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.406, + 0.892, + 0.434 + ], + "angle": 0, + "content": "Figure 3: Expected Calibration Error across datasets. The student is Swin-T trained with \\(\\lambda = 1.0\\) and \\(\\gamma = 30.0\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.462, + 0.892, + 0.825 + ], + "angle": 0, + "content": "[33]. In the Something-Something dataset, the objects the people interact with might overlap between training and testing, potentially allowing models to pick up undesirable biases w.r.t. object appearance to discriminate between the actions. Therefore, Something-Else proposes a compositional generalization data split, on which the objects at training and testing time do not overlap, such that the models encounter strictly novel objects during testing. Similarly, the rich visual environments featured in the Epic-Kitchen training data may also provide the model with spurious cues for predicting the actions and lead to significant performance drop on new, unobserved environments. The Epic-Kitchens Unseen split consists of a subset of videos in the validation set from participants whose videos were not present in the training dataset, giving insight into how our approach generalizes to new visual environments. We report the performance of our approach Epic-Kitchens Unseen split and the Something-Else [33] split in Table 3. The general observation across datasets and modalities is that the distilled students significantly outperform the RGB baseline model, and are sometimes even competitive with their respective teacher. Notably, on Something-Else, the student distilled from an RGB & OF & OBJ teacher outperforms the baseline by \\(7.3\\%\\) in terms of top-1 accuracy." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.846, + 0.821, + 0.861 + ], + "angle": 0, + "content": "4.1.3 Comparison with Omnivorous Models" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We explicitly compare multimodal knowledge distillation against Omnivorous models [19, 20], which are trained" + }, + { + "type": "page_footnote", + "bbox": [ + 0.077, + 0.875, + 0.469, + 0.901 + ], + "angle": 0, + "content": "2Compositional generalization measures to what extent the model can generalize to novel combinations of concepts observed during training." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5218" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.088, + 0.473, + 0.259 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.269, + 0.47, + 0.299 + ], + "angle": 0, + "content": "Figure 4: Per-class improvement of the student over the RGB baseline on the top-20 most frequent actions across datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.325, + 0.47, + 0.521 + ], + "angle": 0, + "content": "jointly on all modalities featuring non-aligned data, e.g. with RGB frames obtained from one dataset and depth maps from another [20]. These models have been proven to generalize better compared to their unimodal counterparts. We train the Omnivore model using batches comprised of data from the same modality, where we randomly sample the modality for each training batch3. Additionally, we train the Omnivore models for \\( M \\times \\) more epochs (\\( M \\) is the number of modalities), to account for the random sampling of modalities during training. We represent the object detections modality as bounding boxes with a line thickness of 2px pasted on a white canvas where each category is colored uniquely, e.g. hand in blue and object in red." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.522, + 0.47, + 0.645 + ], + "angle": 0, + "content": "We report results in Table 4. Even though on the Epic-Kitchens Unseen split and the Something-Else dataset the Omnivore model exhibits strong performance (\\(\\sim 5.5\\%\\) improvement on top of the baseline on Something-Else), the multimodal distillation approach achieves even higher performance. Nevertheless, we conclude that both approaches represent viable options for training multimodal models which leverage unimodal inputs during inference." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.663, + 0.33, + 0.677 + ], + "angle": 0, + "content": "4.1.4 Effect on Model Calibration" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.687, + 0.47, + 0.854 + ], + "angle": 0, + "content": "Next to the improvements in action recognition performance we observe, we also investigate how the distilled student fares against the baseline in terms of model calibration. That is, whether the probability score of the predicted class reflects the accuracy of predicting the said class [23, 41]. More importantly, we verify whether distilling from additional modalities yields better calibrated students. In Fig. 3, we measure the Expected Calibration error [23] (ECE) on the Epic-Kitchens (regular & unseen), and the Something-Something and Something-Else datasets. We report the ECE for an RGB model trained using the ground truth la" + }, + { + "type": "table", + "bbox": [ + 0.554, + 0.09, + 0.842, + 0.184 + ], + "angle": 0, + "content": "
ObjectiveλγNoun@1Verb@1Action@1
LCE0.0—52.061.738.3
LKL1.030.051.765.439.3
LCE ∧ LKL0.830.052.665.140.4
LCE ∧ LKL0.83.053.066.941.0
LKL1.01.053.165.540.5
LCE ∧ LKL0.81.053.565.441.2
LCE ∧ LKL0.80.3353.664.740.5
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.194, + 0.895, + 0.237 + ], + "angle": 0, + "content": "Table 5: Ablation study on the Epic-Kitchens dataset. λ: Distillation and Cross-Entropy loss balancing term; γ: Temperature of the Ensemble Teacher Weighting." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.263, + 0.895, + 0.34 + ], + "angle": 0, + "content": "bels, as well as all distilled students reported in Table 2 and Table 3. The general observation is that across datasets, distillation improves the models' calibration. Furthermore, we find that increasing the number of modalities used in the ensemble improves the model calibration." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.359, + 0.8, + 0.373 + ], + "angle": 0, + "content": "4.1.5 Per-Class Performance Breakdown" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.384, + 0.892, + 0.535 + ], + "angle": 0, + "content": "In Fig 4, we present the relative change in action recognition accuracy of the student model obtained via multimodal distillation w.r.t. the architecturally equivalent baseline RGB model trained on ground truth labels, computed on the top-20 most frequent classes (actions) on Epic-Kitchens and Something-Something. Overall, we observe that multimodal distillation generally improves performance across different actions, and particularly so on Something-Something, where we achieve improvements in terms of all of the top-20 most frequent action classes." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.545, + 0.762, + 0.562 + ], + "angle": 0, + "content": "4.2. Ensemble Teacher Weighting" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.569, + 0.892, + 0.903 + ], + "angle": 0, + "content": "In §4.1 we observe that distilling from multimodal teachers yields students which are superior to models trained on the ground truth labels. Nevertheless, if a weak teacher is added in the ensemble, it negatively affects the knowledge distillation and yields a student which is inferior than using the ground truth labels, e.g. adding the audio-specific teacher in the ensemble for Epic-Kitchens. To cope with this, we weigh the logits of the teacher ensemble as discussed in §3.2. Namely, we use the two hyperparameters \\((\\lambda\\) and \\(\\gamma)\\) for (i) balancing between the ground truth and the distillation loss: \\(\\lambda\\) (Equation 5), and (ii) controlling how the predictions of modality-specific models are combined in the ensemble: \\(\\gamma\\) (Equation 3). We report results for Epic-Kitchens in Table 5, including the values for \\(\\lambda\\) and \\(\\gamma\\) as well as the objective we effectively minimize. We observe that the model trained only on the ground truth labels (\\(\\lambda = 0.0\\)), is inferior to all other models. Using a large \\(\\gamma\\) (e.g. 30.0) - effectively assigning equal weights to all models in the ensemble - we observe to perform well despite the simple setup (we use this model in the experiments in §4.1). Additionally, training using the task loss in addition to the distillation loss (\\(\\lambda = 0.8\\)) further improves the performance. The" + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.863, + 0.47, + 0.903 + ], + "angle": 0, + "content": "\\(^{3}\\)Girdhar et al. [20] show that there is no performance difference if the batches contain mixed data from different modalities, however, we found that using homogeneous batches yields better performance." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5219" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.091, + 0.103, + 0.452, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.492, + 0.103, + 0.852, + 0.293 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.307, + 0.894, + 0.337 + ], + "angle": 0, + "content": "Figure 5: Top-1 action accuracy of Teacher, Student & Baseline models and their associated computational cost in giga-FLOPs \\((10^{9})\\) required to update the input and predict the action. Note: Top-left corner is optimal (i.e. faster and most accurate models)." + }, + { + "type": "image", + "bbox": [ + 0.083, + 0.359, + 0.462, + 0.573 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.582, + 0.472, + 0.612 + ], + "angle": 0, + "content": "Figure 6: Performance degradation when reducing the number of inference clips/crops (Epic-Kitchens/Something-Something)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.638, + 0.47, + 0.79 + ], + "angle": 0, + "content": "best performing model uses both the task and the distillation loss \\((\\lambda = 0.8)\\), and assigns weights to each teacher in the ensemble based on its performance on \\(Z = 1000\\) randomly sampled videos held-out from the training dataset, with a normalization temperature \\(\\gamma = 1.0\\). Moreover, we find that lowering the normalization temperature \\(\\gamma\\) further \\((\\gamma = 0.33)\\) - giving higher weight to the best performing model in the ensemble - yields lower performance. Similarly, increasing the normalization temperature to \\(\\gamma = 3.0\\), thus equalizing the model weights, also negatively affects performance." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.801, + 0.26, + 0.818 + ], + "angle": 0, + "content": "4.3. Efficiency Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "Despite the strong performance multimodal action recognition models exhibit, we argue that the high computational complexity makes them cumbersome for deployment, particularly compared to a model which uses only RGB video during inference. The teacher ensemble used for" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.362, + 0.892, + 0.574 + ], + "angle": 0, + "content": "Epic-Kitchens uses three modality-specific Swin-T models, where each has 28.22M parameters, and requires 140.33 GFLOPs for processing single-view 32 frame/spectrogram video. Assuming such an ensemble is deployed, the optical flow would have to be computed on-the-fly4. Using RAFT, we measure a total added computation of 163.37 GFLOPs for such a model. We consider the computation required to obtain the spectrograms of 1.116s audio segments to be negligible in comparison. Therefore, when using all three modalities, updating the input sequences for each newly observed frame and performing action recognition would require 584.36 GFLOPs. In contrast, the distilled student is a single RGB model, and in the case of Swin-T requires 140.33 GFLOPs – which represents a reduction of \\(75.98\\%\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.575, + 0.892, + 0.741 + ], + "angle": 0, + "content": "We report results on the Epic-Kitchens dataset in Fig. 5 for: (i) All variations of teacher models (RGB & OF, RGB & A, and RGB & OF & A); (ii) The Swin-T student model, distilled with \\(\\lambda = 0.8\\) and \\(\\gamma = 1.0\\); (iii) The Swin-T baseline model, trained with \\(\\lambda = 0.0\\); (iv) Two new ResNet3D models [27] (with depth of 50 and 18 layers), exhibiting less parameters and GFLOPs compared to the Swin-T model. The resolution size of the ResNet3D models is \\(112 \\times 112\\). For each ResNet3D, we report action recognition performance of the baseline with \\(\\lambda = 0.0\\), and performance of the distilled students with \\(\\lambda = 0.8\\) and \\(\\gamma = 1.0\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.743, + 0.892, + 0.835 + ], + "angle": 0, + "content": "We observe a consistently higher performance of the student models compared to the same model architecture trained on ground truth labels alone. Notably, our best performing student achieves comparable performance to the significantly more expensive RGB & OF & A teacher. Furthermore, the R3D-18 and R3D-50 students outperform" + }, + { + "type": "page_footnote", + "bbox": [ + 0.498, + 0.851, + 0.894, + 0.9 + ], + "angle": 0, + "content": "4The Duality-based TV-L1 [40, 60] can be efficiently computed on a GPU (5-10 FPS) [4]. Deep Learning-based approaches, e.g. RAFT [51], require 163.37 GFLOPs, however, achieve higher FPS of 21.10, measured with 10 refinement iterations and resolution of \\(256 \\times 456\\)." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "5220" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.09, + 0.273, + 0.255 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.276, + 0.09, + 0.468, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.266, + 0.47, + 0.294 + ], + "angle": 0, + "content": "Figure 7: Qualitative example for the Epic Kitchens (Left) & the Something-Something (Right) datasets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.32, + 0.468, + 0.38 + ], + "angle": 0, + "content": "their counterparts trained on class labels. Finally, we observe that the R3D-18 student matches the performance of the larger, and computationally more expensive R3D-50 trained on ground truth labels." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.399, + 0.367, + 0.414 + ], + "angle": 0, + "content": "4.3.1 Effect of Test-Time Augmentation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.422, + 0.468, + 0.649 + ], + "angle": 0, + "content": "Lastly, we inspect the relationship between action recognition performance and the number of temporal clips (on Epic-Kitchens) and spatial crops (on Something-Something) sampled from the video during inference. Note that our goal is to reduce the computational complexity while maintaining the performance. Since standard video models [1, 7, 30, 31] use multiple temporal clips and spatial crops as test-time augmentation to obtain further performance improvements, we explore the extent to which the distilled model is dependent on their availability during inference. We report results in Fig. 6, where we observe that the distilled model \\((\\lambda = 1.0)\\) is much less adversely affected by the reduction of both sampled temporal clips and spatial crops during inference, compared to the same model trained on the ground truth labels \\((\\lambda = 0.0)\\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.658, + 0.279, + 0.674 + ], + "angle": 0, + "content": "4.4. Qualitative Examples" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.681, + 0.468, + 0.802 + ], + "angle": 0, + "content": "In Fig. 7, we showcase the classes corresponding to the highest scores predicted by the student and the individual modality-specific models in the teacher ensemble, as well as the ground truth label (on Epic-Kitchens and Something-Something datasets). For both examples, we observe that the student picks up on relevant cues from each modality and accurately predicts the action of interest (see Supp. H for additional qualitative examples)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.815, + 0.195, + 0.831 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.468, + 0.9 + ], + "angle": 0, + "content": "We demonstrated a simple, yet effective distillation-based approach for leveraging multimodal data only during training in order to improve a model that uses solely RGB frames during inference. Our experiments indicate clear" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.212 + ], + "angle": 0, + "content": "performance improvements over models trained on ground truth labels. We further showed an advantageous tradeoff between the high performance of a cumbersome multimodal ensemble, and low computational complexity of unimodal approaches. Moreover, our approach relies less on expensive test-time augmentations, otherwise widely used in the literature to improve the egocentric action recognition models' performance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.213, + 0.892, + 0.318 + ], + "angle": 0, + "content": "Limitations & Future work. Notably, in this work we considered only the task of action recognition, while multimodal distillation can be readily applied to other egocentric tasks [22]. Future work may also feature additional modalities such as depth, hand poses, motion captured by inertial sensors (IMU), etc., available in recent large-scale egocentric datasets [22]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.332, + 0.66, + 0.349 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.357, + 0.892, + 0.403 + ], + "angle": 0, + "content": "We acknowledge the funding from the Flemish Government under the Onderzoeksprogramma Artificièle Intelligente (AI) Vlaanderen programme." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "5221" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.116, + 0.47, + 0.184 + ], + "angle": 0, + "content": "[1] Anurag Arnab, Mostafa Dehghani, Georg Heigold, Chen Sun, Mario Lucic, and Cordelia Schmid. 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Standard models, e.g. CNNs or Vision Transformers, which receive RGB frames as input perform well, however, their performance improves further by employing additional input modalities (e.g. object detections, optical flow, audio, etc.) which provide cues complementary to the RGB modality. The added complexity of the modality-specific modules, on the other hand, makes these models impractical for deployment. The goal of this work is to retain the performance of such a multimodal approach, while using only the RGB frames as input at inference time. We demonstrate that for egocentric action recognition on the Epic-Kitchens and the Something-Something datasets, students which are taught by multimodal teachers tend to be more accurate and better calibrated than architecturally equivalent models trained on ground truth labels in a unimodal or multimodal fashion. We further adopt a principled multimodal knowledge distillation framework, allowing us to deal with issues which occur when applying multimodal knowledge distillation in a naive manner. Lastly, we demonstrate the achieved reduction in computational complexity, and show that our approach maintains higher performance with the reduction of the number of input views. We release our code at: https://github.com/gorjanradevski/multimodal-distillation + +# 1. Introduction + +The purpose of egocentric vision is enabling machines to interpret real-world data taken from a human's perspective. Its applications are numerous, ranging from recognizing [63] or anticipating [15] actions, to more complex tasks such as recognizing egocentric object-state changes, localizing action instances of a particular video moment [22], etc. The focal point of egocentric vision is hand-object interactions. Usually, these hand-object interactions take + +![](images/8604e921b093e3b2b786c773320fdd312f9c74c36c17b063b5cb4e6bcd14a507.jpg) +Figure 1: Motivation: The multimodal action recognition model is powerful, but too slow to be used in practice. The distilled student is significantly faster yet achieves competitive performance. + +place in cluttered environments, where the object of interest is often occluded, or occurs only during a short time period. Furthermore, egocentric vision often suffers from motion blur – due to the movement of the scene objects or the camera itself – and thus, understanding video content from RGB frames alone may be challenging. + +To cope with these challenges, various egocentric action recognition methods [25, 29, 33, 43, 56, 59, 61] demonstrate that explicitly modelling hand-object interactions (usually represented via bounding boxes & object categories) significantly improves the action recognition performance, most notably in a compositional generalization setup [43]. Similarly, other works show that leveraging multiple modalities (optical flow, audio, etc.) at inference time yields improved performance [16, 28, 36, 57]. The assumptions these methods make are (i) that all modalities used during training are also available at inference time, and (ii) the compute budget at inference time would be sufficient to obtain and process the additional modalities. Such assumptions make these methods cumbersome or even impossible to use in practice, e.g. on a limited compute budget such as in the case of embedded devices. Namely, using dedicated models for each additional modality (e.g. object detector, object tracker and a transformer when using bounding boxes & object categories as input [43]), increases both the memory footprint as well as the inference time. Ideally, video understanding + +models would leverage additional modalities during training, while the resulting model would use only RGB frames at inference time, i.e. when deployed in practice. + +One way to achieve the aforementioned goal is training omnivorous models, i.e. models trained jointly on multiple modalities, which have been shown to generalize better [20] than unimodal counterparts. In this work, we take a different route and transfer multimodal knowledge to models subsequently used in a unimodal setting. Namely, we distill the knowledge from a multimodal ensemble - exhibiting superior performance, but unviable for deployment - to a standard RGB-based action recognition model [5] (see Fig. 1). + +Contributions. We employ state-of-the-art knowledge distillation practices [6] and ① show that a student [31] taught by a multimodal teacher, is both more accurate and better calibrated than the same model trained from scratch or in an omnivorous fashion (§4.1); ② We provide motivation and establish a simple but reliable multimodal distillation approach, which overcomes the issue of potentially suboptimal modality-specific teachers (§4.2); ③ We demonstrate that the distilled student performs on par with significantly larger models, and maintains performance in computationally cheaper inference setups (§4.3). + +# 2. Related Work + +Knowledge distillation. Originally introduced by Hinton et al. [26], knowledge distillation is used to transfer the knowledge from one model, i.e. a teacher, to another model, i.e. a student, by training the student to match the teacher's (intermediate) outputs on a certain dataset. Shown to be useful in a variety of contexts, the primary goal is model compression - transferring the knowledge from a larger, cumbersome teacher model, or from a teacher exhibiting a different inductive bias [9, 52], to a typically lightweight student model [10, 35, 55]. Another line of work [2, 47] proposes to distill from ensembles of large teacher models to lightweight student models, obtaining promising results. Compared to these works, we focus on knowledge distillation from a multimodal teacher ensemble, i.e. a set of models where each is trained on a distinct modality. + +Multimodal knowledge distillation has been previously used mainly in a cross-modal fashion, where the teacher and the student receive different modalities as input. In some works, the teacher receives RGB images while the student receives depth or optical flow images [24], while in others, the teacher receives RGB images as input, while the student receives audio as input [3]. In contrast, other works explore a multimodal knowledge expansion scenario, where a multimodal student learns from pseudo-labels of a unimodal teacher [58]. We, on the other hand, focus on scenarios where obtaining additional modalities (optical flow, object detections, audio, etc.) during inference is prohibitive due to a limited compute budget, and therefore multimodal + +data is only used during training time. Multimodal knowledge distillation for action recognition has been previously explored in the works of Gracia et al. [17, 18]. They propose to train a model on aligned data from two modalities, where a model which receives data from modality A is trained to imitate the intermediate features of a model which receives training data from modality B. This approach is shown to yield performance improvements compared to an RGB baseline when using RGB and depth data. Moreover, the Mars [11] and D3d [49] methods, similarly to us, leverage RGB frames and optical flow during training to improve test-time performance of a model that performs inference using RGB frames alone. This is achieved by matching the corresponding features or probabilistic outputs of the modality-specific models during training. Compared to these works, we consider a more general knowledge distillation setting [6, 26], with a multimodal teacher ensemble used to provide a better approximation of the true posterior. Lastly, we consider a more diverse and broader set of modalities (RGB frames, optical flow, audio and object detections) compared to the aforementioned works. + +Multimodal (egocentric) video understanding. In the context of (egocentric) video understanding, several works have shown that using additional modalities at inference time significantly improves performance [25, 29, 33, 36, 43, 50, 56, 61]. The hypothesis is intuitive - certain actions are more easily understood from specific modalities, e.g. to recognize that a person is "pushing something from left to right," the bounding boxes alone are sufficient [33, 43]. Nevertheless, the assumption these works make is that all modalities used during training are available during inference, and that the compute budget allows for processing additional modalities other than the RGB frames. To that end, multiple works [25, 29, 33, 43, 56, 61] effectively use a Faster R-CNN [44], multiple object tracker (MOT), and object detection-specific models at inference time. In contrast, we posit that for egocentric video understanding, computing additional modalities on the fly may be prohibitive. Therefore, we propose a distillation approach which uses multimodal data only during training, while the resulting model is dependent on RGB frames alone during inference. + +Models robust to missing modalities during inference. A parallel route to our goal - retaining the performance of multimodal approaches, while using only the RGB frames at inference time - is to explicitly train models to be robust to missing modalities during inference [37, 39, 62]; or more recently, to process different modalities altogether interchangeably - Omnivorous models [12, 19, 20]. These models have been shown to generalize better than models trained on unimodal data. In this work, we train an Omnivorous model using the same architecture as our student, and show that the student distilled from a multimodal teacher generalizes better than its Omnivorous variant. + +# 3. Methodology + +# 3.1. Egocentric Action Recognition + +We assume we are given an input $\mathbf{x} \in \mathbb{R}^{T \times D_1 \times D_2 \dots \times D_L}$ , which describes an egocentric action sequence, where $T$ is the number of time-steps, while $D_1 \times D_2 \dots \times D_L$ represent other dimensions of the input data, e.g. the height, width and the number of channels of a video frame. The goal of the model $f$ is to produce a discrete probability distribution over a predefined set of $C$ classes, i.e. $\hat{\mathbf{y}} = \sigma(f(\mathbf{x})) \in \mathbb{R}_+^C$ , where $\sigma$ is the softmax operator. The classes represent the actions, or alternatively, the nouns and verbs constituting the actions (e.g. the active video object and the activity). + +Given a dataset $\mathbb{D} = \{(\mathbf{x}_1,\mathbf{y}_1),\dots ,(\mathbf{x}_N,\mathbf{y}_N)\}$ of $N$ egocentric action sequences $\mathbf{x}_i$ paired with labels $\mathbf{y}_i\in \mathbb{R}_+^C$ the model is trained by minimizing the standard crossentropy objective $\mathcal{L}_{\mathrm{CE}} = -\frac{1}{N}\sum_{i = 1}^{N}\mathbf{y}_i\cdot \log \sigma (f(\mathbf{x}_i))$ where $\cdot$ represents the scalar product. In the case of actions characterized by separate nouns and verbs, and accompanied by their respective labels $\mathbf{y}_i^n$ and $\mathbf{y}_i^v$ , separate prediction heads produce $f^n (\mathbf{x}_i)$ and $f^{v}(\mathbf{x}_{i})$ . Finally, the model is trained by minimizing the sum of the loss terms corresponding to the nouns and verbs, $\mathcal{L}_{\mathrm{CE}}^n$ and $\mathcal{L}_{\mathrm{CE}}^v$ respectively. + +# 3.2. Multimodal Knowledge Distillation + +In egocentric vision, there often exist more than one input modality that characterize the same actions. The action recognition task may thus be performed via the use of multiple modalities, leveraged only during training [20, 42], or both during training and inference [16,28,36,57] by ensembling [57] models, multimodal-fusion [28, 43], etc. However, in the case of the latter, processing multimodal data may be computationally prohibitive at inference time (e.g. due to a limited compute budget). + +The fundamental concept our method builds on is knowledge distillation [26], featuring a teacher (usually larger model, exhibiting strong performance, but cumbersome to use in practice) and a student (typically a smaller model, trained to mimic the teacher [6]). Focusing on the most accessible data modality - RGB video frames (e.g. obtained using a single monocular video camera) - we opt for distilling the knowledge of a multimodal ensemble to a single model that relies on RGB inputs alone. We make a modification to the standard knowledge distillation approach, by altering the teacher such that (i) it is not a single model, but rather an ensemble of models, and (ii) the constituting models receive different modalities as input. + +Teacher ensemble. Given $M$ datasets $\mathbb{D}^m = \left\{(\mathbf{x}_1^m,\mathbf{y}_1),\dots ,(\mathbf{x}_N^m,\mathbf{y}_N)\right\}$ of different modalities, we train a separate model $f^{m}$ by minimizing the learning objective $\mathcal{L}_{\mathrm{CE}}^m = -\frac{1}{N}\sum_{i = 1}^N\mathbf{y}_i\cdot \log \sigma \left(f^m (\mathbf{x}_i^m)\right)$ for each modality. Finally, the output of the ensemble can be obtained by aver + +aging the outputs of the individual teachers: + +$$ +\hat {\mathbf {y}} _ {i} ^ {t} = \sigma \left(\frac {1}{M} \sum_ {m = 1} ^ {M} f ^ {m} \left(\mathbf {x} _ {i} ^ {m}\right)\right). \tag {1} +$$ + +Intuitively, under-performing modality-specific models could negatively affect the performance of the ensemble. We thus consider assigning different weights to the output logits of each model in the ensemble, before aggregating their predictions. Ideally, we would want to perform a Bayesian prediction: $p(\mathbf{y}|\mathbf{x},\mathbb{D}) = \int_{f\in F}p(\mathbf{y}|\mathbf{x},f)p(f|\mathbb{D})df$ . For a given finite ensemble of $M$ diverse predictors, we replace the integral with a sum over the individual models: $p(\mathbf{y}|\mathbf{x},\mathbb{D}) \approx \sum_{m = 1}^{M}p(\mathbf{y}|\mathbf{x},f^{m})p(f^{m}|\mathbb{D})$ . We further approximate $p(f^{m}|\mathbb{D})$ via its proportionality to the data likelihood $p(\mathbb{D}|f^{m})$ under the Bayes rule: $p(f^{m}|\mathbb{D}) \propto p(\mathbb{D}|f^{m})$ ; which itself can be expressed in terms of the cross-entropy that the model $f^{m}$ exhibits on the dataset $\mathbb{D}$ . + +The cross-entropy $e^{m}$ of each modality-specific model in the ensemble can be estimated on a holdout set: + +$$ +e ^ {m} = - \frac {1}{Z} \sum_ {i = 1} ^ {Z} \mathbf {y} _ {i} \cdot \log \sigma \left(f ^ {m} \left(\mathbf {x} _ {i} ^ {m}\right)\right), \tag {2} +$$ + +where $Z$ is the number of held-out samples used to estimate the weights. Then, we can obtain the weights for the modality-specific models via softmax normalization of the negative cross-entropy terms: + +$$ +w ^ {m} \propto \exp (- e ^ {m} / \gamma), \tag {3} +$$ + +where $\gamma$ is a temperature term which controls the entropy of the model weights, e.g. if $\gamma \rightarrow \infty$ , equal weights would be given to each teacher - resulting in an arithmetic mean. + +We finally compute the weighted average of the predictions of $M$ modality-specific models as the teacher output: + +$$ +\hat {\mathbf {y}} _ {i} ^ {t} = \sigma \left(\sum_ {m = 1} ^ {M} w ^ {m} f ^ {m} \left(\mathbf {x} _ {i} ^ {m}\right)\right). \tag {4} +$$ + +Figure 2 presents a high-level overview of our approach. In summary, our student is taught by a multimodal teacher which is itself an ensemble of multiple modality-specific models, trained separately on each modality. + +Training objective. During training, we perform multimodal knowledge distillation, as originally proposed by Hinton et al. [26]. Specifically, we minimize the KL-divergence $\mathcal{L}_{\mathrm{KL}}$ between the class probabilities predicted by the teacher $\hat{\mathbf{y}}_i^t = [\hat{y}_{i,1}^t,\dots ,\hat{y}_{i,C}^t ]\in \mathbb{R}_+^C$ and the class probabilities of the student $\hat{\mathbf{y}}_i^s = [\hat{y}_{i,1}^s,\dots ,\hat{y}_{i,C}^s ]\in \mathbb{R}_+^C$ as $\mathcal{L}_{\mathrm{KL}} = \frac{1}{N}\sum_{i = 1}^{N}(-\hat{\mathbf{y}}_i^t\cdot \log \hat{\mathbf{y}}_i^s +\hat{\mathbf{y}}_i^t\cdot \log \hat{\mathbf{y}}_i^t)$ + +Additionally, we use a temperature parameter $\tau$ to control the entropy of the predicted probability scores while + +![](images/9ac8af93b1196f7aea28e027580d21545919a65cd5d46de3a2651cb691f36c21.jpg) +Figure 2: Overview of the main components of our approach. + +
Epic-Kitchens RegularSomething-Something
MethodNoun Acc.Noun ECEVerb Acc.Verb ECEAction Acc.Action ECE
RGB Baseline52.019.961.717.159.321.2
Teacher (γ = 30.0)52.32.0466.83.466.68.1
Teacher (γ = 1.0)53.98.966.94.266.79.0
Epic-Kitchens Unseen EnvironmentsSomething-Else
MethodNoun Acc.Noun ECEVerb Acc.Verb ECEAction Acc.Action ECE
RGB Baseline38.326.951.724.051.821.4
Teacher (γ = 30.0)42.96.0258.09.963.36.5
Teacher (γ = 1.0)43.89.557.79.763.58.1
+ +Table 1: Accuracy & Expected Calibration Error (ECE) of the RGB baseline and Teacher ensemble on Epic-Kitchens and Something-Something (regular & unseen splits). All available modalities for the respective dataset used in the ensemble. + +preserving their ranking, i.e. $\hat{y}_j^s\propto \exp (\hat{y}_j^s /\tau)$ . As per standard practice [26], we use the temperature parameter $\pmb{\tau}$ to also rescale the KL-divergence loss, i.e. $\mathcal{L}_{\mathrm{KL}} = \mathcal{L}_{\mathrm{KL}}\cdot \tau^2$ . We further use the standard cross-entropy action recognition loss $\mathcal{L}_{\mathrm{CE}}$ , and compute the final loss: + +$$ +\mathcal {L} = \lambda \cdot \mathcal {L} _ {\mathrm {K L}} + (1 - \lambda) \cdot \mathcal {L} _ {\mathrm {C E}}, \tag {5} +$$ + +where $\lambda$ balances the distillation loss $\mathcal{L}_{\mathrm{KL}}$ and the action recognition loss $\mathcal{L}_{\mathrm{CE}}$ . For example, with $\lambda = 0.0$ we would effectively be training the modality-specific RGB model, while with $\lambda = 1.0$ , we would perform solely multimodal knowledge distillation. + +Optimality of a multimodal ensemble teacher. The work of Menon et al. [34] further demonstrates that in the context of distillation, a teacher that predicts the Bayes class-probability distribution over the labels $\mathbf{p}^{*}(\mathbf{x}) = [\mathbb{P}(y|\mathbf{x})]_{y\in [C]}$ exhibits the lowest possible variance of the student objective for any convex loss function. + +The student trained to minimize the KL-divergence between its output and the Bayes class-probabilities would thus generalize the best. In a preliminary experiment shown in Table 1, we demonstrate that the multimodal ensemble (both for $\gamma = 1$ and $\gamma = 30.0$ ) achieves a significantly higher accuracy and lower calibration error, and thus represents a better approximation of the Bayes class probabilities than a single modality-specific model. This may lead to a lower-variance objective for the student and improved generalization during knowledge distillation [34]. + +# 4. Experiments & Discussion + +Datasets. We use the Something-Something (V2) [21] and the Epic-Kitchens (100) [14] datasets. Something-Something contains videos of people performing 174 (object agnostic) unique actions with their hands, e.g. "pushing [something] left", "taking [something] out of [something]", etc. Epic-Kitchens' videos take place in kitchen environments, where the actions are noun-verb compositions. The 300 unique nouns indicate the active object in the video, while 97 unique verbs indicate the activity, e.g. "cutting carrot", "washing pan", etc. During evaluation, the action is considered correct if both the noun and the verb are correctly predicted. Additionally, we use the Something-Else [33] dataset and the Epic-Kitchens Unseen split to measure the compositional generalization ability of the models w.r.t. unseen objects and environments. + +Modalities. In addition to the RGB frames (the modality of interest at inference time), in our experiments we consider the following modalities: + +(i) Optical flow (OF): First used by I3D [8] for action recognition, it is also used by recent state-of-the-art (egocentric) video understanding methods [57]. We use optical flow obtained using TV-L1 [60]. +(ii) Object detections (OBJ): Shown to significantly improve the performance of standard (RGB) egocentric video understanding models across datasets [25, 33, 43, 56, 61]. As per [46], we use the object detector trained on object-agnostic annotations, i.e. with "hands" and "objects" object labels. +(iii) Audio (A): For certain datasets [13, 14], several works [28, 57] have shown that using audio improves action recognition performance. The audio is obtained directly from the recorded video. + +Moreover, if available, one may include additional modalities, e.g. depth estimates, heat maps, etc. For Something-Something and Something-Else there is no audio available, while we use the object detections provided by [25, 33], and optical flow from [54]. For Epic-Kitchens we use the modalities available and released with the dataset itself [14]: optical flow and audio. + +Models. We use a Swin-Tiny (Swin-T) Transformer [31] to encode RGB frames, optical flow, and audio. Each optical flow frame is represented as a $224 \times 224 \times 2$ tensor, where the two values at each spatial location represent the $x$ and $y$ velocity components. In the case of audio, we extract 1.116 second-audio segments (0.558s before its corresponding time-step and 0.558s after it) for each frame. We compute the mel-spectrogram of the audio segment (see details in Supp. B), which is subsequently resized to desired width and height. We thus treat each modality as a sequence of + +
MethodTraining ModalitiesInference ModalitiesNoun@1Verb@1Action@1
BaselineRGBRGB52.061.738.3
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB34.151.952.259.065.365.625.939.539.9+1.6
Modality-specificTeacherStudentA—RGB & AARGB & ARGB22.352.761.546.564.462.4+0.715.139.837.9-0.4
TeacherStudent—RGB & OF & ARGB & OF & ARGB52.351.7-0.366.865.4+3.740.539.3+1.0
+ +(a) Epic-Kitchens [14]: Recognition of the active video object (noun) and the activity (verb). + +
MethodTraining ModalitiesInference ModalitiesAction@1Action@5
BaselineRGBRGB60.386.4
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB49.364.379.088.9
\( 62.8_{+2.5} \)\( 88.9_{+2.5} \)
Modality-specific TeacherStudentOBJ—RGB & OBJOBJRGB & OBJRGB47.965.376.289.5
\( 63.2_{+2.9} \)\( 88.7_{+2.3} \)
TeacherStudent—RGB & OF & OBJRGB & OF & OBJRGB66.6\( 63.0_{+2.7} \)90.5\( 88.9_{+2.5} \)
+ +(b) Something-Something [21]: Object-agnostic action recognition. + +Table 2: Egocentric action recognition. RGB = Video frames; OF = Optical flow; A = Audio; OBJ = Object detections. Multimodal distillation with $\lambda = 1.0$ and $\gamma = 30.0$ . Improvement over RGB frames baseline [31] in red. + +$224 \times 224$ multi-channel images, which we provide as input to the vision transformer, as per the common practice in recent vision models [19, 20]. To encode the object detections, i.e. bounding boxes and object categories of the scene objects, we use a state-of-the-art model - STLT [43]. In STLT, a spatial and temporal transformer separately encode the spatial and temporal arrangement of the objects occurring in the video. The multimodal teacher we use during knowledge distillation is an ensemble of individual, modality-specific models. Unless noted otherwise, the student is a Swin-T model which receives RGB frames as input, both during training (distillation) and inference. In addition to Swin-T, in §4.3, we also consider ResNet3D [27] (18 and 50 layers deep) light-weight student models which receive video frames of size $112 \times 112$ as input. + +Metrics. Besides accuracy, we measure Expected Calibration Error (ECE) [23]. As per [23, 45], we sort the predictions based on the per-class confidence scores and group them into $K$ bins $B_{k}$ , each associated with a confidence interval $I_{B_k} = \left(\frac{k - 1}{K},\frac{k}{K}\right)$ , where $K = 15$ . ECE represents the discrepancy between the average accuracy $acc(B_k)$ and the average confidence $conf(B_k)$ in each bin $B_{k}$ : + +$$ +\mathrm {E C E} = \sum_ {k = 1} ^ {K} \frac {\left| B _ {k} \right|}{N} \left| a c c \left(B _ {k}\right) - c o n f \left(B _ {k}\right) \right|, \tag {6} +$$ + +where $N$ is the number of evaluation samples. + +Implementation details. We train all models for 60 epochs using AdamW [32], with a peak learning rate of $1e - 4$ , linearly increased for the first $5\%$ of the training and decreased to 0.0 by the end of the specified 60 epochs. We use weight decay with a regularization coefficient of $5e - 2$ , and clip the gradients when their norm exceeds 5.0. For Epic-Kitchens, we sample 32 frames with a fixed stride of 2, and for Something-Something and Something-Else we evenly sample 16 frames to cover the whole video. We use a single spatial and temporal crop, unless stated otherwise. During training, we chose a random start frame, while during inference, we select the start frame such that the sequence covers the central portion of the video. If we + +use multiple temporal crops as test-time augmentation, we chose the start frames such that the video is covered uniformly. During training we apply standard data augmentations - random spatial video crops, color jittering, and horizontal flips (for Epic-Kitchens only). The temperature parameter $\tau$ is fixed to 10.0 for both the student and the teacher during multimodal knowledge distillation. In §4.2 we ablate the impact of the loss balancing term $\lambda$ and the Ensemble Teacher Weighting temperature term $\gamma^1$ . + +During training we follow the consistent teaching paradigm [6] where the student and teacher strictly receive the same views of the data - we ensure for spatial and temporal consistency, i.e. the models receive the same frame indices, same random crops, and horizontal flips. + +# 4.1. Multimodal Distillation for Egocentric Vision + +We first verify the overall effectiveness of multimodal knowledge distillation on the task of egocentric action recognition for both object-agnostic actions (Something-Something) and actions represented as noun-verb compositions (Epic-Kitchens). Across all experiments, we fix $\lambda$ to 1.0, i.e. we train solely with multimodal knowledge distillation. Similarly, we set $\gamma$ to a large value ( $\gamma = 30.0$ ), where effectively each teacher equally contributes to the ensemble output. Note that in this setting, models trained on modalities such as optical flow and audio may underperform, and thus adversely affect the ensemble teacher performance of recognizing active objects, i.e. nouns. + +# 4.1.1 Recognizing Egocentric Actions + +In Table 2, we report performance on Something-Something V2 [21] and Epic-Kitchens 100 [14]. In line with the previous findings reported in the literature [33, 43, 57], we find that employing additional modalities at inference time significantly improves the performance compared to the RGB baseline model, for both the Epic-Kitchens and the Something-Something datasets. + +
MethodTraining ModalitiesInference ModalitiesNoun@1Verb@1Action@1
BaselineRGBRGB38.351.725.4
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB28.041.042.5+4.253.254.955.9+4.221.628.430.2+4.8
Modality-specificTeacherStudentA—RGB & AARGB & ARGB15.041.941.8+3.541.555.351.8+0.19.128.527.5+2.1
TeacherStudent—RGB & OF & ARGB & OF & ARGB42.943.7+5.458.054.1+3.430.329.6+4.2
+ +(a) Epic-Kitchens Unseen Environments [14]: Recognition of the active object (noun) and the activity (verb) on participants unseen during training. + +
MethodTraining ModalitiesInference ModalitiesAction@1Action@5
BaselineRGBRGB51.879.5
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB49.061.058.2+6.477.486.485.1+5.6
Modality-specificTeacherStudentOBJ—RGB & OBJOBJRGB & OBJRGB41.459.457.5+5.767.384.584.1+4.6
TeacherStudent—RGB & OF & OBJRGB & OF & OBJRGB63.659.1+7.387.786.1+6.6
+ +(b) Something-Else [33]: Object-agnostic action recognition featuring objects unseen during training. + +Table 3: Egocentric action recognition with unseen environments and objects. RGB = Video frames; OF = Optical flow; A = Audio; OBJ = Object detections. Multimodal distillation with λ = 1.0 and γ = 30.0. Improvement over RGB frames baseline [31] in red. + +
Epic-Kitchens Regular splitSomething-Something
MethodNoun@1Verb@1Action@1Action@1Action@5
Omnivore [20]47.862.835.958.486.2
Student51.765.439.363.088.9
Epic-Kitchens Unseen ParticipantsSomething-Else
Omnivore [20]38.554.527.958.384.9
Student43.754.129.659.186.1
+ +Table 4: Comparison with Omnivorous models [20]. All models are Swin-T and perform inference using only RGB frames. Multimodal distillation using all modalities with $\lambda = 1.0$ and $\gamma = 30.0$ . + +A novel observation by our work is that multimodal knowledge distillation performs well in the context of egocentric video understanding, with student models often approaching the performance of the multimodal teacher ensemble. For Epic-Kitchens (Table 2a), we observe that when the student is distilled from an RGB & OF, or RGB & OF & A teacher, it is superior to the baseline model, as well as all modality-specific models, for recognizing actions. On the other hand, distilling from an RGB & A teacher yields performance lower than the baseline, due to the low performance of the model trained only on audio data. Specifically, we observe that the audio-specific teacher lowers the noun (active object) recognition performance. In §4.2, we propose a solution for this issue. For Something-Something (Table 2b), the student model is superior to the baseline for each combination of modalities. When distilling from all available modalities (RGB & OF & OBJ), the resulting model outperforms the baseline by $3.7\%$ in terms of the top-1 accuracy. In terms of the top-5 accuracy on Something-Something, the students achieve performance that is nearly on par with the multimodal teacher ensemble. + +# 4.1.2 Generalizing to Unseen Environments & Objects + +We investigate to what extent our findings translate to the compositional generalization setting2, in which the performance of standard video models deteriorates significantly + +![](images/f3f8e2941eb7ba6d3d0c20f2f6dd7014a5b81364f93b60c631eb47e9eb4e7e87.jpg) +Figure 3: Expected Calibration Error across datasets. The student is Swin-T trained with $\lambda = 1.0$ and $\gamma = 30.0$ . + +![](images/6ee4f632f5e1179c3698c744f4dee1ac8ab517cafad04b606d0709822e1181c6.jpg) + +[33]. In the Something-Something dataset, the objects the people interact with might overlap between training and testing, potentially allowing models to pick up undesirable biases w.r.t. object appearance to discriminate between the actions. Therefore, Something-Else proposes a compositional generalization data split, on which the objects at training and testing time do not overlap, such that the models encounter strictly novel objects during testing. Similarly, the rich visual environments featured in the Epic-Kitchen training data may also provide the model with spurious cues for predicting the actions and lead to significant performance drop on new, unobserved environments. The Epic-Kitchens Unseen split consists of a subset of videos in the validation set from participants whose videos were not present in the training dataset, giving insight into how our approach generalizes to new visual environments. We report the performance of our approach Epic-Kitchens Unseen split and the Something-Else [33] split in Table 3. The general observation across datasets and modalities is that the distilled students significantly outperform the RGB baseline model, and are sometimes even competitive with their respective teacher. Notably, on Something-Else, the student distilled from an RGB & OF & OBJ teacher outperforms the baseline by $7.3\%$ in terms of top-1 accuracy. + +# 4.1.3 Comparison with Omnivorous Models + +We explicitly compare multimodal knowledge distillation against Omnivorous models [19, 20], which are trained + +![](images/6974477f9853b80b117d7cc94e022a0a323394e99fc513ebe8e2d3a8718b3875.jpg) +Figure 4: Per-class improvement of the student over the RGB baseline on the top-20 most frequent actions across datasets. + +jointly on all modalities featuring non-aligned data, e.g. with RGB frames obtained from one dataset and depth maps from another [20]. These models have been proven to generalize better compared to their unimodal counterparts. We train the Omnivore model using batches comprised of data from the same modality, where we randomly sample the modality for each training batch3. Additionally, we train the Omnivore models for $M \times$ more epochs ( $M$ is the number of modalities), to account for the random sampling of modalities during training. We represent the object detections modality as bounding boxes with a line thickness of 2px pasted on a white canvas where each category is colored uniquely, e.g. hand in blue and object in red. + +We report results in Table 4. Even though on the Epic-Kitchens Unseen split and the Something-Else dataset the Omnivore model exhibits strong performance ( $\sim 5.5\%$ improvement on top of the baseline on Something-Else), the multimodal distillation approach achieves even higher performance. Nevertheless, we conclude that both approaches represent viable options for training multimodal models which leverage unimodal inputs during inference. + +# 4.1.4 Effect on Model Calibration + +Next to the improvements in action recognition performance we observe, we also investigate how the distilled student fares against the baseline in terms of model calibration. That is, whether the probability score of the predicted class reflects the accuracy of predicting the said class [23, 41]. More importantly, we verify whether distilling from additional modalities yields better calibrated students. In Fig. 3, we measure the Expected Calibration error [23] (ECE) on the Epic-Kitchens (regular & unseen), and the Something-Something and Something-Else datasets. We report the ECE for an RGB model trained using the ground truth la + +
ObjectiveλγNoun@1Verb@1Action@1
LCE0.0—52.061.738.3
LKL1.030.051.765.439.3
LCE ∧ LKL0.830.052.665.140.4
LCE ∧ LKL0.83.053.066.941.0
LKL1.01.053.165.540.5
LCE ∧ LKL0.81.053.565.441.2
LCE ∧ LKL0.80.3353.664.740.5
+ +Table 5: Ablation study on the Epic-Kitchens dataset. λ: Distillation and Cross-Entropy loss balancing term; γ: Temperature of the Ensemble Teacher Weighting. + +bels, as well as all distilled students reported in Table 2 and Table 3. The general observation is that across datasets, distillation improves the models' calibration. Furthermore, we find that increasing the number of modalities used in the ensemble improves the model calibration. + +# 4.1.5 Per-Class Performance Breakdown + +In Fig 4, we present the relative change in action recognition accuracy of the student model obtained via multimodal distillation w.r.t. the architecturally equivalent baseline RGB model trained on ground truth labels, computed on the top-20 most frequent classes (actions) on Epic-Kitchens and Something-Something. Overall, we observe that multimodal distillation generally improves performance across different actions, and particularly so on Something-Something, where we achieve improvements in terms of all of the top-20 most frequent action classes. + +# 4.2. Ensemble Teacher Weighting + +In §4.1 we observe that distilling from multimodal teachers yields students which are superior to models trained on the ground truth labels. Nevertheless, if a weak teacher is added in the ensemble, it negatively affects the knowledge distillation and yields a student which is inferior than using the ground truth labels, e.g. adding the audio-specific teacher in the ensemble for Epic-Kitchens. To cope with this, we weigh the logits of the teacher ensemble as discussed in §3.2. Namely, we use the two hyperparameters $(\lambda$ and $\gamma)$ for (i) balancing between the ground truth and the distillation loss: $\lambda$ (Equation 5), and (ii) controlling how the predictions of modality-specific models are combined in the ensemble: $\gamma$ (Equation 3). We report results for Epic-Kitchens in Table 5, including the values for $\lambda$ and $\gamma$ as well as the objective we effectively minimize. We observe that the model trained only on the ground truth labels ( $\lambda = 0.0$ ), is inferior to all other models. Using a large $\gamma$ (e.g. 30.0) - effectively assigning equal weights to all models in the ensemble - we observe to perform well despite the simple setup (we use this model in the experiments in §4.1). Additionally, training using the task loss in addition to the distillation loss ( $\lambda = 0.8$ ) further improves the performance. The + +![](images/459215aa9a90da4897f2a18f629d954ad5a2e6198ee719933287292161486487.jpg) +Figure 5: Top-1 action accuracy of Teacher, Student & Baseline models and their associated computational cost in giga-FLOPs $(10^{9})$ required to update the input and predict the action. Note: Top-left corner is optimal (i.e. faster and most accurate models). + +![](images/5a2ae4b4f8c46cbe1fbc45f032a0c3e3b6e62a1379f3ffb5edcd768f61e859c4.jpg) + +![](images/4cd7f76a2b38f9000b69aa49cf1738fbe56698f7c0837e770f8480770c102c2f.jpg) +Figure 6: Performance degradation when reducing the number of inference clips/crops (Epic-Kitchens/Something-Something). + +best performing model uses both the task and the distillation loss $(\lambda = 0.8)$ , and assigns weights to each teacher in the ensemble based on its performance on $Z = 1000$ randomly sampled videos held-out from the training dataset, with a normalization temperature $\gamma = 1.0$ . Moreover, we find that lowering the normalization temperature $\gamma$ further $(\gamma = 0.33)$ - giving higher weight to the best performing model in the ensemble - yields lower performance. Similarly, increasing the normalization temperature to $\gamma = 3.0$ , thus equalizing the model weights, also negatively affects performance. + +# 4.3. Efficiency Analysis + +Despite the strong performance multimodal action recognition models exhibit, we argue that the high computational complexity makes them cumbersome for deployment, particularly compared to a model which uses only RGB video during inference. The teacher ensemble used for + +Epic-Kitchens uses three modality-specific Swin-T models, where each has 28.22M parameters, and requires 140.33 GFLOPs for processing single-view 32 frame/spectrogram video. Assuming such an ensemble is deployed, the optical flow would have to be computed on-the-fly4. Using RAFT, we measure a total added computation of 163.37 GFLOPs for such a model. We consider the computation required to obtain the spectrograms of 1.116s audio segments to be negligible in comparison. Therefore, when using all three modalities, updating the input sequences for each newly observed frame and performing action recognition would require 584.36 GFLOPs. In contrast, the distilled student is a single RGB model, and in the case of Swin-T requires 140.33 GFLOPs – which represents a reduction of $75.98\%$ . + +We report results on the Epic-Kitchens dataset in Fig. 5 for: (i) All variations of teacher models (RGB & OF, RGB & A, and RGB & OF & A); (ii) The Swin-T student model, distilled with $\lambda = 0.8$ and $\gamma = 1.0$ ; (iii) The Swin-T baseline model, trained with $\lambda = 0.0$ ; (iv) Two new ResNet3D models [27] (with depth of 50 and 18 layers), exhibiting less parameters and GFLOPs compared to the Swin-T model. The resolution size of the ResNet3D models is $112 \times 112$ . For each ResNet3D, we report action recognition performance of the baseline with $\lambda = 0.0$ , and performance of the distilled students with $\lambda = 0.8$ and $\gamma = 1.0$ . + +We observe a consistently higher performance of the student models compared to the same model architecture trained on ground truth labels alone. Notably, our best performing student achieves comparable performance to the significantly more expensive RGB & OF & A teacher. Furthermore, the R3D-18 and R3D-50 students outperform + +![](images/28ecc3676b1f443cb379c03d77bbc74d779c304241739bdf452862c0785e44fa.jpg) +Figure 7: Qualitative example for the Epic Kitchens (Left) & the Something-Something (Right) datasets. + +![](images/a4424c354c8de2dad348f85600ceecd7f53e0e65f3d70059259ea18599a85ed1.jpg) + +their counterparts trained on class labels. Finally, we observe that the R3D-18 student matches the performance of the larger, and computationally more expensive R3D-50 trained on ground truth labels. + +# 4.3.1 Effect of Test-Time Augmentation + +Lastly, we inspect the relationship between action recognition performance and the number of temporal clips (on Epic-Kitchens) and spatial crops (on Something-Something) sampled from the video during inference. Note that our goal is to reduce the computational complexity while maintaining the performance. Since standard video models [1, 7, 30, 31] use multiple temporal clips and spatial crops as test-time augmentation to obtain further performance improvements, we explore the extent to which the distilled model is dependent on their availability during inference. We report results in Fig. 6, where we observe that the distilled model $(\lambda = 1.0)$ is much less adversely affected by the reduction of both sampled temporal clips and spatial crops during inference, compared to the same model trained on the ground truth labels $(\lambda = 0.0)$ . + +# 4.4. Qualitative Examples + +In Fig. 7, we showcase the classes corresponding to the highest scores predicted by the student and the individual modality-specific models in the teacher ensemble, as well as the ground truth label (on Epic-Kitchens and Something-Something datasets). For both examples, we observe that the student picks up on relevant cues from each modality and accurately predicts the action of interest (see Supp. H for additional qualitative examples). + +# 5. Conclusion + +We demonstrated a simple, yet effective distillation-based approach for leveraging multimodal data only during training in order to improve a model that uses solely RGB frames during inference. Our experiments indicate clear + +performance improvements over models trained on ground truth labels. We further showed an advantageous tradeoff between the high performance of a cumbersome multimodal ensemble, and low computational complexity of unimodal approaches. Moreover, our approach relies less on expensive test-time augmentations, otherwise widely used in the literature to improve the egocentric action recognition models' performance. + +Limitations & Future work. Notably, in this work we considered only the task of action recognition, while multimodal distillation can be readily applied to other egocentric tasks [22]. Future work may also feature additional modalities such as depth, hand poses, motion captured by inertial sensors (IMU), etc., available in recent large-scale egocentric datasets [22]. + +# Acknowledgement + +We acknowledge the funding from the Flemish Government under the Onderzoeksprogramma Artificièle Intelligente (AI) Vlaanderen programme. + +# References + +[1] Anurag Arnab, Mostafa Dehghani, Georg Heigold, Chen Sun, Mario Lucic, and Cordelia Schmid. Vivit: A video vision transformer. In Proceedings of the IEEE/CVF International Conference on Computer Vision, pages 6836-6846, 2021. 9 +[2] Umar Asif, Jianbin Tang, and Stefan Harrer. Ensemble knowledge distillation for learning improved and efficient networks. arXiv preprint arXiv:1909.08097, 2019. 2 +[3] Yusuf Aytar, Carl Vondrick, and Antonio Torralba. Sound-net: Learning sound representations from unlabeled video. 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Standard models, e.g. CNNs or Vision Transformers, which receive RGB frames as input perform well, however, their performance improves further by employing additional input modalities (e.g. object detections, optical flow, audio, etc.) which provide cues complementary to the RGB modality. The added complexity of the modality-specific modules, on the other hand, makes these models impractical for deployment. The goal of this work is to retain the performance of such a multimodal approach, while using only the RGB frames as input at inference time. We demonstrate that for egocentric action recognition on the Epic-Kitchens and the Something-Something datasets, students which are taught by multimodal teachers tend to be more accurate and better calibrated than architecturally equivalent models trained on ground truth labels in a unimodal or multimodal fashion. We further adopt a principled multimodal knowledge distillation framework, allowing us to deal with issues which occur when applying multimodal knowledge distillation in a naive manner. Lastly, we demonstrate the achieved reduction in computational complexity, and show that our approach maintains higher performance with the reduction of the number of input views. We release our code at: https://github.com/gorjanradevski/multimodal-distillation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 576, + 128, + 588 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 576, + 128, + 588 + ], + "spans": [ + { + "bbox": [ + 47, + 576, + 128, + 588 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 597, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 597, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 597, + 287, + 693 + ], + "type": "text", + "content": "The purpose of egocentric vision is enabling machines to interpret real-world data taken from a human's perspective. Its applications are numerous, ranging from recognizing [63] or anticipating [15] actions, to more complex tasks such as recognizing egocentric object-state changes, localizing action instances of a particular video moment [22], etc. The focal point of egocentric vision is hand-object interactions. Usually, these hand-object interactions take" + } + ] + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 307, + 228, + 545, + 337 + ], + "blocks": [ + { + "bbox": [ + 307, + 228, + 545, + 337 + ], + "lines": [ + { + "bbox": [ + 307, + 228, + 545, + 337 + ], + "spans": [ + { + "bbox": [ + 307, + 228, + 545, + 337 + ], + "type": "image", + "image_path": "8604e921b093e3b2b786c773320fdd312f9c74c36c17b063b5cb4e6bcd14a507.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 344, + 547, + 378 + ], + "lines": [ + { + "bbox": [ + 305, + 344, + 547, + 378 + ], + "spans": [ + { + "bbox": [ + 305, + 344, + 547, + 378 + ], + "type": "text", + "content": "Figure 1: Motivation: The multimodal action recognition model is powerful, but too slow to be used in practice. The distilled student is significantly faster yet achieves competitive performance." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 401, + 546, + 473 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 401, + 546, + 473 + ], + "spans": [ + { + "bbox": [ + 304, + 401, + 546, + 473 + ], + "type": "text", + "content": "place in cluttered environments, where the object of interest is often occluded, or occurs only during a short time period. Furthermore, egocentric vision often suffers from motion blur – due to the movement of the scene objects or the camera itself – and thus, understanding video content from RGB frames alone may be challenging." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 475, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 475, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 475, + 547, + 714 + ], + "type": "text", + "content": "To cope with these challenges, various egocentric action recognition methods [25, 29, 33, 43, 56, 59, 61] demonstrate that explicitly modelling hand-object interactions (usually represented via bounding boxes & object categories) significantly improves the action recognition performance, most notably in a compositional generalization setup [43]. Similarly, other works show that leveraging multiple modalities (optical flow, audio, etc.) at inference time yields improved performance [16, 28, 36, 57]. The assumptions these methods make are (i) that all modalities used during training are also available at inference time, and (ii) the compute budget at inference time would be sufficient to obtain and process the additional modalities. Such assumptions make these methods cumbersome or even impossible to use in practice, e.g. on a limited compute budget such as in the case of embedded devices. Namely, using dedicated models for each additional modality (e.g. object detector, object tracker and a transformer when using bounding boxes & object categories as input [43]), increases both the memory footprint as well as the inference time. Ideally, video understanding" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 703, + 160, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 703, + 160, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 703, + 160, + 713 + ], + "type": "text", + "content": "* Authors contributed equally." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 758 + ], + "type": "text", + "content": "5213" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "content": "models would leverage additional modalities during training, while the resulting model would use only RGB frames at inference time, i.e. when deployed in practice." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 108, + 286, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 108, + 286, + 216 + ], + "spans": [ + { + "bbox": [ + 46, + 108, + 286, + 216 + ], + "type": "text", + "content": "One way to achieve the aforementioned goal is training omnivorous models, i.e. models trained jointly on multiple modalities, which have been shown to generalize better [20] than unimodal counterparts. In this work, we take a different route and transfer multimodal knowledge to models subsequently used in a unimodal setting. Namely, we distill the knowledge from a multimodal ensemble - exhibiting superior performance, but unviable for deployment - to a standard RGB-based action recognition model [5] (see Fig. 1)." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 216, + 286, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 216, + 286, + 347 + ], + "spans": [ + { + "bbox": [ + 46, + 216, + 286, + 347 + ], + "type": "text", + "content": "Contributions. We employ state-of-the-art knowledge distillation practices [6] and ① show that a student [31] taught by a multimodal teacher, is both more accurate and better calibrated than the same model trained from scratch or in an omnivorous fashion (§4.1); ② We provide motivation and establish a simple but reliable multimodal distillation approach, which overcomes the issue of potentially suboptimal modality-specific teachers (§4.2); ③ We demonstrate that the distilled student performs on par with significantly larger models, and maintains performance in computationally cheaper inference setups (§4.3)." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 358, + 133, + 370 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 358, + 133, + 370 + ], + "spans": [ + { + "bbox": [ + 47, + 358, + 133, + 370 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 379, + 286, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 379, + 286, + 557 + ], + "spans": [ + { + "bbox": [ + 46, + 379, + 286, + 557 + ], + "type": "text", + "content": "Knowledge distillation. Originally introduced by Hinton et al. [26], knowledge distillation is used to transfer the knowledge from one model, i.e. a teacher, to another model, i.e. a student, by training the student to match the teacher's (intermediate) outputs on a certain dataset. Shown to be useful in a variety of contexts, the primary goal is model compression - transferring the knowledge from a larger, cumbersome teacher model, or from a teacher exhibiting a different inductive bias [9, 52], to a typically lightweight student model [10, 35, 55]. Another line of work [2, 47] proposes to distill from ensembles of large teacher models to lightweight student models, obtaining promising results. Compared to these works, we focus on knowledge distillation from a multimodal teacher ensemble, i.e. a set of models where each is trained on a distinct modality." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 558, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 286, + 713 + ], + "type": "text", + "content": "Multimodal knowledge distillation has been previously used mainly in a cross-modal fashion, where the teacher and the student receive different modalities as input. In some works, the teacher receives RGB images while the student receives depth or optical flow images [24], while in others, the teacher receives RGB images as input, while the student receives audio as input [3]. In contrast, other works explore a multimodal knowledge expansion scenario, where a multimodal student learns from pseudo-labels of a unimodal teacher [58]. We, on the other hand, focus on scenarios where obtaining additional modalities (optical flow, object detections, audio, etc.) during inference is prohibitive due to a limited compute budget, and therefore multimodal" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 72, + 545, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 323 + ], + "type": "text", + "content": "data is only used during training time. Multimodal knowledge distillation for action recognition has been previously explored in the works of Gracia et al. [17, 18]. They propose to train a model on aligned data from two modalities, where a model which receives data from modality A is trained to imitate the intermediate features of a model which receives training data from modality B. This approach is shown to yield performance improvements compared to an RGB baseline when using RGB and depth data. Moreover, the Mars [11] and D3d [49] methods, similarly to us, leverage RGB frames and optical flow during training to improve test-time performance of a model that performs inference using RGB frames alone. This is achieved by matching the corresponding features or probabilistic outputs of the modality-specific models during training. Compared to these works, we consider a more general knowledge distillation setting [6, 26], with a multimodal teacher ensemble used to provide a better approximation of the true posterior. Lastly, we consider a more diverse and broader set of modalities (RGB frames, optical flow, audio and object detections) compared to the aforementioned works." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 327, + 545, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 327, + 545, + 567 + ], + "spans": [ + { + "bbox": [ + 304, + 327, + 545, + 567 + ], + "type": "text", + "content": "Multimodal (egocentric) video understanding. In the context of (egocentric) video understanding, several works have shown that using additional modalities at inference time significantly improves performance [25, 29, 33, 36, 43, 50, 56, 61]. The hypothesis is intuitive - certain actions are more easily understood from specific modalities, e.g. to recognize that a person is \"pushing something from left to right,\" the bounding boxes alone are sufficient [33, 43]. Nevertheless, the assumption these works make is that all modalities used during training are available during inference, and that the compute budget allows for processing additional modalities other than the RGB frames. To that end, multiple works [25, 29, 33, 43, 56, 61] effectively use a Faster R-CNN [44], multiple object tracker (MOT), and object detection-specific models at inference time. In contrast, we posit that for egocentric video understanding, computing additional modalities on the fly may be prohibitive. Therefore, we propose a distillation approach which uses multimodal data only during training, while the resulting model is dependent on RGB frames alone during inference." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "Models robust to missing modalities during inference. A parallel route to our goal - retaining the performance of multimodal approaches, while using only the RGB frames at inference time - is to explicitly train models to be robust to missing modalities during inference [37, 39, 62]; or more recently, to process different modalities altogether interchangeably - Omnivorous models [12, 19, 20]. These models have been shown to generalize better than models trained on unimodal data. In this work, we train an Omnivorous model using the same architecture as our student, and show that the student distilled from a multimodal teacher generalizes better than its Omnivorous variant." + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5214" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 129, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 129, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 129, + 85 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 92, + 212, + 105 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 92, + 212, + 105 + ], + "spans": [ + { + "bbox": [ + 47, + 92, + 212, + 105 + ], + "type": "text", + "content": "3.1. Egocentric Action Recognition" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "spans": [ + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "text", + "content": "We assume we are given an input " + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "inline_equation", + "content": "\\mathbf{x} \\in \\mathbb{R}^{T \\times D_1 \\times D_2 \\dots \\times D_L}" + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "text", + "content": ", which describes an egocentric action sequence, where " + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "text", + "content": " is the number of time-steps, while " + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "inline_equation", + "content": "D_1 \\times D_2 \\dots \\times D_L" + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "text", + "content": " represent other dimensions of the input data, e.g. the height, width and the number of channels of a video frame. The goal of the model " + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "text", + "content": " is to produce a discrete probability distribution over a predefined set of " + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "text", + "content": " classes, i.e. " + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{y}} = \\sigma(f(\\mathbf{x})) \\in \\mathbb{R}_+^C" + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "inline_equation", + "content": "\\sigma" + }, + { + "bbox": [ + 46, + 111, + 287, + 232 + ], + "type": "text", + "content": " is the softmax operator. The classes represent the actions, or alternatively, the nouns and verbs constituting the actions (e.g. the active video object and the activity)." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "spans": [ + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": "Given a dataset " + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "inline_equation", + "content": "\\mathbb{D} = \\{(\\mathbf{x}_1,\\mathbf{y}_1),\\dots ,(\\mathbf{x}_N,\\mathbf{y}_N)\\}" + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": " egocentric action sequences " + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "inline_equation", + "content": "\\mathbf{x}_i" + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": " paired with labels " + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "inline_equation", + "content": "\\mathbf{y}_i\\in \\mathbb{R}_+^C" + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": " the model is trained by minimizing the standard crossentropy objective " + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{CE}} = -\\frac{1}{N}\\sum_{i = 1}^{N}\\mathbf{y}_i\\cdot \\log \\sigma (f(\\mathbf{x}_i))" + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "inline_equation", + "content": "\\cdot" + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": " represents the scalar product. In the case of actions characterized by separate nouns and verbs, and accompanied by their respective labels " + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "inline_equation", + "content": "\\mathbf{y}_i^n" + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "inline_equation", + "content": "\\mathbf{y}_i^v" + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": " , separate prediction heads produce " + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "inline_equation", + "content": "f^n (\\mathbf{x}_i)" + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "inline_equation", + "content": "f^{v}(\\mathbf{x}_{i})" + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": " . Finally, the model is trained by minimizing the sum of the loss terms corresponding to the nouns and verbs, " + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{CE}}^n" + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{CE}}^v" + }, + { + "bbox": [ + 46, + 233, + 288, + 355 + ], + "type": "text", + "content": " respectively." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 366, + 234, + 379 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 366, + 234, + 379 + ], + "spans": [ + { + "bbox": [ + 47, + 366, + 234, + 379 + ], + "type": "text", + "content": "3.2. Multimodal Knowledge Distillation" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 387, + 287, + 495 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 387, + 287, + 495 + ], + "spans": [ + { + "bbox": [ + 46, + 387, + 287, + 495 + ], + "type": "text", + "content": "In egocentric vision, there often exist more than one input modality that characterize the same actions. The action recognition task may thus be performed via the use of multiple modalities, leveraged only during training [20, 42], or both during training and inference [16,28,36,57] by ensembling [57] models, multimodal-fusion [28, 43], etc. However, in the case of the latter, processing multimodal data may be computationally prohibitive at inference time (e.g. due to a limited compute budget)." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 496, + 287, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 496, + 287, + 651 + ], + "spans": [ + { + "bbox": [ + 46, + 496, + 287, + 651 + ], + "type": "text", + "content": "The fundamental concept our method builds on is knowledge distillation [26], featuring a teacher (usually larger model, exhibiting strong performance, but cumbersome to use in practice) and a student (typically a smaller model, trained to mimic the teacher [6]). Focusing on the most accessible data modality - RGB video frames (e.g. obtained using a single monocular video camera) - we opt for distilling the knowledge of a multimodal ensemble to a single model that relies on RGB inputs alone. We make a modification to the standard knowledge distillation approach, by altering the teacher such that (i) it is not a single model, but rather an ensemble of models, and (ii) the constituting models receive different modalities as input." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "content": "Teacher ensemble. Given " + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "content": " datasets " + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathbb{D}^m = \\left\\{(\\mathbf{x}_1^m,\\mathbf{y}_1),\\dots ,(\\mathbf{x}_N^m,\\mathbf{y}_N)\\right\\}" + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "content": " of different modalities, we train a separate model " + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "inline_equation", + "content": "f^{m}" + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "content": " by minimizing the learning objective " + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{CE}}^m = -\\frac{1}{N}\\sum_{i = 1}^N\\mathbf{y}_i\\cdot \\log \\sigma \\left(f^m (\\mathbf{x}_i^m)\\right)" + }, + { + "bbox": [ + 47, + 653, + 287, + 714 + ], + "type": "text", + "content": " for each modality. Finally, the output of the ensemble can be obtained by aver" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 72, + 484, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 484, + 84 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 484, + 84 + ], + "type": "text", + "content": "aging the outputs of the individual teachers:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 364, + 92, + 545, + 126 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 364, + 92, + 545, + 126 + ], + "spans": [ + { + "bbox": [ + 364, + 92, + 545, + 126 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {y}} _ {i} ^ {t} = \\sigma \\left(\\frac {1}{M} \\sum_ {m = 1} ^ {M} f ^ {m} \\left(\\mathbf {x} _ {i} ^ {m}\\right)\\right). \\tag {1}", + "image_path": "0407140d6a245ff444f579db92702ff5443c45a324a8a679fec36d6134f1ef11.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "text", + "content": "Intuitively, under-performing modality-specific models could negatively affect the performance of the ensemble. We thus consider assigning different weights to the output logits of each model in the ensemble, before aggregating their predictions. Ideally, we would want to perform a Bayesian prediction: " + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "inline_equation", + "content": "p(\\mathbf{y}|\\mathbf{x},\\mathbb{D}) = \\int_{f\\in F}p(\\mathbf{y}|\\mathbf{x},f)p(f|\\mathbb{D})df" + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "text", + "content": ". For a given finite ensemble of " + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "text", + "content": " diverse predictors, we replace the integral with a sum over the individual models: " + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "inline_equation", + "content": "p(\\mathbf{y}|\\mathbf{x},\\mathbb{D}) \\approx \\sum_{m = 1}^{M}p(\\mathbf{y}|\\mathbf{x},f^{m})p(f^{m}|\\mathbb{D})" + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "text", + "content": ". We further approximate " + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "inline_equation", + "content": "p(f^{m}|\\mathbb{D})" + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "text", + "content": " via its proportionality to the data likelihood " + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "inline_equation", + "content": "p(\\mathbb{D}|f^{m})" + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "text", + "content": " under the Bayes rule: " + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "inline_equation", + "content": "p(f^{m}|\\mathbb{D}) \\propto p(\\mathbb{D}|f^{m})" + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "text", + "content": "; which itself can be expressed in terms of the cross-entropy that the model " + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "inline_equation", + "content": "f^{m}" + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "text", + "content": " exhibits on the dataset " + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "inline_equation", + "content": "\\mathbb{D}" + }, + { + "bbox": [ + 304, + 133, + 545, + 300 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 301, + 545, + 325 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 301, + 545, + 325 + ], + "spans": [ + { + "bbox": [ + 304, + 301, + 545, + 325 + ], + "type": "text", + "content": "The cross-entropy " + }, + { + "bbox": [ + 304, + 301, + 545, + 325 + ], + "type": "inline_equation", + "content": "e^{m}" + }, + { + "bbox": [ + 304, + 301, + 545, + 325 + ], + "type": "text", + "content": " of each modality-specific model in the ensemble can be estimated on a holdout set:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 349, + 334, + 545, + 367 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 349, + 334, + 545, + 367 + ], + "spans": [ + { + "bbox": [ + 349, + 334, + 545, + 367 + ], + "type": "interline_equation", + "content": "e ^ {m} = - \\frac {1}{Z} \\sum_ {i = 1} ^ {Z} \\mathbf {y} _ {i} \\cdot \\log \\sigma \\left(f ^ {m} \\left(\\mathbf {x} _ {i} ^ {m}\\right)\\right), \\tag {2}", + "image_path": "6f92b450e93045ae5fd338b4a5dcf97a1d28ea06293dc1655de3b441c77d7713.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 371, + 545, + 419 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 371, + 545, + 419 + ], + "spans": [ + { + "bbox": [ + 304, + 371, + 545, + 419 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 371, + 545, + 419 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 304, + 371, + 545, + 419 + ], + "type": "text", + "content": " is the number of held-out samples used to estimate the weights. Then, we can obtain the weights for the modality-specific models via softmax normalization of the negative cross-entropy terms:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 382, + 430, + 545, + 444 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 382, + 430, + 545, + 444 + ], + "spans": [ + { + "bbox": [ + 382, + 430, + 545, + 444 + ], + "type": "interline_equation", + "content": "w ^ {m} \\propto \\exp (- e ^ {m} / \\gamma), \\tag {3}", + "image_path": "d5b036bc765fa78f3e24510ee6e3f19ef9d3b9c4b9fd76ef1494d3764da83397.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 449, + 545, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 449, + 545, + 484 + ], + "spans": [ + { + "bbox": [ + 304, + 449, + 545, + 484 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 449, + 545, + 484 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 449, + 545, + 484 + ], + "type": "text", + "content": " is a temperature term which controls the entropy of the model weights, e.g. if " + }, + { + "bbox": [ + 304, + 449, + 545, + 484 + ], + "type": "inline_equation", + "content": "\\gamma \\rightarrow \\infty" + }, + { + "bbox": [ + 304, + 449, + 545, + 484 + ], + "type": "text", + "content": ", equal weights would be given to each teacher - resulting in an arithmetic mean." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 484, + 545, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 484, + 545, + 509 + ], + "spans": [ + { + "bbox": [ + 304, + 484, + 545, + 509 + ], + "type": "text", + "content": "We finally compute the weighted average of the predictions of " + }, + { + "bbox": [ + 304, + 484, + 545, + 509 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 484, + 545, + 509 + ], + "type": "text", + "content": " modality-specific models as the teacher output:" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 363, + 517, + 545, + 550 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 363, + 517, + 545, + 550 + ], + "spans": [ + { + "bbox": [ + 363, + 517, + 545, + 550 + ], + "type": "interline_equation", + "content": "\\hat {\\mathbf {y}} _ {i} ^ {t} = \\sigma \\left(\\sum_ {m = 1} ^ {M} w ^ {m} f ^ {m} \\left(\\mathbf {x} _ {i} ^ {m}\\right)\\right). \\tag {4}", + "image_path": "acba0d581f0c2320ffd24a8a8c90b619a0a7d85aa40115ab8a68498e219620f0.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 553, + 545, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 553, + 545, + 601 + ], + "spans": [ + { + "bbox": [ + 304, + 553, + 545, + 601 + ], + "type": "text", + "content": "Figure 2 presents a high-level overview of our approach. In summary, our student is taught by a multimodal teacher which is itself an ensemble of multiple modality-specific models, trained separately on each modality." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 601, + 545, + 690 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 601, + 545, + 690 + ], + "spans": [ + { + "bbox": [ + 304, + 601, + 545, + 690 + ], + "type": "text", + "content": "Training objective. During training, we perform multimodal knowledge distillation, as originally proposed by Hinton et al. [26]. Specifically, we minimize the KL-divergence " + }, + { + "bbox": [ + 304, + 601, + 545, + 690 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{KL}}" + }, + { + "bbox": [ + 304, + 601, + 545, + 690 + ], + "type": "text", + "content": " between the class probabilities predicted by the teacher " + }, + { + "bbox": [ + 304, + 601, + 545, + 690 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{y}}_i^t = [\\hat{y}_{i,1}^t,\\dots ,\\hat{y}_{i,C}^t ]\\in \\mathbb{R}_+^C" + }, + { + "bbox": [ + 304, + 601, + 545, + 690 + ], + "type": "text", + "content": " and the class probabilities of the student " + }, + { + "bbox": [ + 304, + 601, + 545, + 690 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{y}}_i^s = [\\hat{y}_{i,1}^s,\\dots ,\\hat{y}_{i,C}^s ]\\in \\mathbb{R}_+^C" + }, + { + "bbox": [ + 304, + 601, + 545, + 690 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 304, + 601, + 545, + 690 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{KL}} = \\frac{1}{N}\\sum_{i = 1}^{N}(-\\hat{\\mathbf{y}}_i^t\\cdot \\log \\hat{\\mathbf{y}}_i^s +\\hat{\\mathbf{y}}_i^t\\cdot \\log \\hat{\\mathbf{y}}_i^t)" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 690, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 690, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 690, + 545, + 713 + ], + "type": "text", + "content": "Additionally, we use a temperature parameter " + }, + { + "bbox": [ + 304, + 690, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 304, + 690, + 545, + 713 + ], + "type": "text", + "content": " to control the entropy of the predicted probability scores while" + } + ] + } + ], + "index": 20 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5215" + } + ] + } + ], + "index": 21 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 70, + 286, + 171 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 286, + 171 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 286, + 171 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 286, + 171 + ], + "type": "image", + "image_path": "9ac8af93b1196f7aea28e027580d21545919a65cd5d46de3a2651cb691f36c21.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 55, + 178, + 278, + 190 + ], + "lines": [ + { + "bbox": [ + 55, + 178, + 278, + 190 + ], + "spans": [ + { + "bbox": [ + 55, + 178, + 278, + 190 + ], + "type": "text", + "content": "Figure 2: Overview of the main components of our approach." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 202, + 286, + 287 + ], + "blocks": [ + { + "bbox": [ + 50, + 202, + 286, + 287 + ], + "lines": [ + { + "bbox": [ + 50, + 202, + 286, + 287 + ], + "spans": [ + { + "bbox": [ + 50, + 202, + 286, + 287 + ], + "type": "table", + "html": "
Epic-Kitchens RegularSomething-Something
MethodNoun Acc.Noun ECEVerb Acc.Verb ECEAction Acc.Action ECE
RGB Baseline52.019.961.717.159.321.2
Teacher (γ = 30.0)52.32.0466.83.466.68.1
Teacher (γ = 1.0)53.98.966.94.266.79.0
Epic-Kitchens Unseen EnvironmentsSomething-Else
MethodNoun Acc.Noun ECEVerb Acc.Verb ECEAction Acc.Action ECE
RGB Baseline38.326.951.724.051.821.4
Teacher (γ = 30.0)42.96.0258.09.963.36.5
Teacher (γ = 1.0)43.89.557.79.763.58.1
", + "image_path": "13582a1cc6701508e3570c60d83285ee99c4574f5a3491007d9cf1c8728734b9.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 296, + 288, + 340 + ], + "lines": [ + { + "bbox": [ + 46, + 296, + 288, + 340 + ], + "spans": [ + { + "bbox": [ + 46, + 296, + 288, + 340 + ], + "type": "text", + "content": "Table 1: Accuracy & Expected Calibration Error (ECE) of the RGB baseline and Teacher ensemble on Epic-Kitchens and Something-Something (regular & unseen splits). All available modalities for the respective dataset used in the ensemble." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 363, + 287, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 363, + 287, + 424 + ], + "spans": [ + { + "bbox": [ + 46, + 363, + 287, + 424 + ], + "type": "text", + "content": "preserving their ranking, i.e. " + }, + { + "bbox": [ + 46, + 363, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\hat{y}_j^s\\propto \\exp (\\hat{y}_j^s /\\tau)" + }, + { + "bbox": [ + 46, + 363, + 287, + 424 + ], + "type": "text", + "content": ". As per standard practice [26], we use the temperature parameter " + }, + { + "bbox": [ + 46, + 363, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\pmb{\\tau}" + }, + { + "bbox": [ + 46, + 363, + 287, + 424 + ], + "type": "text", + "content": " to also rescale the KL-divergence loss, i.e. " + }, + { + "bbox": [ + 46, + 363, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{KL}} = \\mathcal{L}_{\\mathrm{KL}}\\cdot \\tau^2" + }, + { + "bbox": [ + 46, + 363, + 287, + 424 + ], + "type": "text", + "content": ". We further use the standard cross-entropy action recognition loss " + }, + { + "bbox": [ + 46, + 363, + 287, + 424 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{CE}}" + }, + { + "bbox": [ + 46, + 363, + 287, + 424 + ], + "type": "text", + "content": ", and compute the final loss:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 105, + 438, + 287, + 451 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 105, + 438, + 287, + 451 + ], + "spans": [ + { + "bbox": [ + 105, + 438, + 287, + 451 + ], + "type": "interline_equation", + "content": "\\mathcal {L} = \\lambda \\cdot \\mathcal {L} _ {\\mathrm {K L}} + (1 - \\lambda) \\cdot \\mathcal {L} _ {\\mathrm {C E}}, \\tag {5}", + "image_path": "368313c093e9a2a4a731b9067d135878df9a49502105479c857340e3a01e2017.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "text", + "content": " balances the distillation loss " + }, + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{KL}}" + }, + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "text", + "content": " and the action recognition loss " + }, + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{CE}}" + }, + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "text", + "content": ". For example, with " + }, + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "inline_equation", + "content": "\\lambda = 0.0" + }, + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "text", + "content": " we would effectively be training the modality-specific RGB model, while with " + }, + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "inline_equation", + "content": "\\lambda = 1.0" + }, + { + "bbox": [ + 46, + 460, + 287, + 519 + ], + "type": "text", + "content": ", we would perform solely multimodal knowledge distillation." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 521, + 287, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 592 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 592 + ], + "type": "text", + "content": "Optimality of a multimodal ensemble teacher. The work of Menon et al. [34] further demonstrates that in the context of distillation, a teacher that predicts the Bayes class-probability distribution over the labels " + }, + { + "bbox": [ + 46, + 521, + 287, + 592 + ], + "type": "inline_equation", + "content": "\\mathbf{p}^{*}(\\mathbf{x}) = [\\mathbb{P}(y|\\mathbf{x})]_{y\\in [C]}" + }, + { + "bbox": [ + 46, + 521, + 287, + 592 + ], + "type": "text", + "content": " exhibits the lowest possible variance of the student objective for any convex loss function." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "type": "text", + "content": "The student trained to minimize the KL-divergence between its output and the Bayes class-probabilities would thus generalize the best. In a preliminary experiment shown in Table 1, we demonstrate that the multimodal ensemble (both for " + }, + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\gamma = 1" + }, + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\gamma = 30.0" + }, + { + "bbox": [ + 46, + 594, + 287, + 714 + ], + "type": "text", + "content": ") achieves a significantly higher accuracy and lower calibration error, and thus represents a better approximation of the Bayes class probabilities than a single modality-specific model. This may lead to a lower-variance objective for the student and improved generalization during knowledge distillation [34]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 71, + 457, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 71, + 457, + 85 + ], + "spans": [ + { + "bbox": [ + 306, + 71, + 457, + 85 + ], + "type": "text", + "content": "4. Experiments & Discussion" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 91, + 545, + 270 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 91, + 545, + 270 + ], + "spans": [ + { + "bbox": [ + 304, + 91, + 545, + 270 + ], + "type": "text", + "content": "Datasets. We use the Something-Something (V2) [21] and the Epic-Kitchens (100) [14] datasets. Something-Something contains videos of people performing 174 (object agnostic) unique actions with their hands, e.g. \"pushing [something] left\", \"taking [something] out of [something]\", etc. Epic-Kitchens' videos take place in kitchen environments, where the actions are noun-verb compositions. The 300 unique nouns indicate the active object in the video, while 97 unique verbs indicate the activity, e.g. \"cutting carrot\", \"washing pan\", etc. During evaluation, the action is considered correct if both the noun and the verb are correctly predicted. Additionally, we use the Something-Else [33] dataset and the Epic-Kitchens Unseen split to measure the compositional generalization ability of the models w.r.t. unseen objects and environments." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 271, + 545, + 307 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 271, + 545, + 307 + ], + "spans": [ + { + "bbox": [ + 304, + 271, + 545, + 307 + ], + "type": "text", + "content": "Modalities. In addition to the RGB frames (the modality of interest at inference time), in our experiments we consider the following modalities:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 308, + 316, + 545, + 500 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 313, + 316, + 545, + 364 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 316, + 545, + 364 + ], + "spans": [ + { + "bbox": [ + 313, + 316, + 545, + 364 + ], + "type": "text", + "content": "(i) Optical flow (OF): First used by I3D [8] for action recognition, it is also used by recent state-of-the-art (egocentric) video understanding methods [57]. We use optical flow obtained using TV-L1 [60]." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 311, + 373, + 545, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 373, + 545, + 445 + ], + "spans": [ + { + "bbox": [ + 311, + 373, + 545, + 445 + ], + "type": "text", + "content": "(ii) Object detections (OBJ): Shown to significantly improve the performance of standard (RGB) egocentric video understanding models across datasets [25, 33, 43, 56, 61]. As per [46], we use the object detector trained on object-agnostic annotations, i.e. with \"hands\" and \"objects\" object labels." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 308, + 453, + 545, + 500 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 453, + 545, + 500 + ], + "spans": [ + { + "bbox": [ + 308, + 453, + 545, + 500 + ], + "type": "text", + "content": "(iii) Audio (A): For certain datasets [13, 14], several works [28, 57] have shown that using audio improves action recognition performance. The audio is obtained directly from the recorded video." + } + ] + } + ], + "index": 14 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 304, + 510, + 545, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 593 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 593 + ], + "type": "text", + "content": "Moreover, if available, one may include additional modalities, e.g. depth estimates, heat maps, etc. For Something-Something and Something-Else there is no audio available, while we use the object detections provided by [25, 33], and optical flow from [54]. For Epic-Kitchens we use the modalities available and released with the dataset itself [14]: optical flow and audio." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "text", + "content": "Models. We use a Swin-Tiny (Swin-T) Transformer [31] to encode RGB frames, optical flow, and audio. Each optical flow frame is represented as a " + }, + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "inline_equation", + "content": "224 \\times 224 \\times 2" + }, + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "text", + "content": " tensor, where the two values at each spatial location represent the " + }, + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 304, + 594, + 546, + 713 + ], + "type": "text", + "content": " velocity components. In the case of audio, we extract 1.116 second-audio segments (0.558s before its corresponding time-step and 0.558s after it) for each frame. We compute the mel-spectrogram of the audio segment (see details in Supp. B), which is subsequently resized to desired width and height. We thus treat each modality as a sequence of" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5216" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 286, + 156 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 286, + 156 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 286, + 156 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 286, + 156 + ], + "type": "table", + "html": "
MethodTraining ModalitiesInference ModalitiesNoun@1Verb@1Action@1
BaselineRGBRGB52.061.738.3
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB34.151.952.259.065.365.625.939.539.9+1.6
Modality-specificTeacherStudentA—RGB & AARGB & ARGB22.352.761.546.564.462.4+0.715.139.837.9-0.4
TeacherStudent—RGB & OF & ARGB & OF & ARGB52.351.7-0.366.865.4+3.740.539.3+1.0
", + "image_path": "86b31fb386872aac0604f8e6482d65e3d00b07fe40a1eb312d0d2779ed661d62.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 47, + 159, + 288, + 180 + ], + "lines": [ + { + "bbox": [ + 47, + 159, + 288, + 180 + ], + "spans": [ + { + "bbox": [ + 47, + 159, + 288, + 180 + ], + "type": "text", + "content": "(a) Epic-Kitchens [14]: Recognition of the active video object (noun) and the activity (verb)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 319, + 70, + 533, + 156 + ], + "blocks": [ + { + "bbox": [ + 319, + 70, + 533, + 156 + ], + "lines": [ + { + "bbox": [ + 319, + 70, + 533, + 156 + ], + "spans": [ + { + "bbox": [ + 319, + 70, + 533, + 156 + ], + "type": "table", + "html": "
MethodTraining ModalitiesInference ModalitiesAction@1Action@5
BaselineRGBRGB60.386.4
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB49.364.379.088.9
\\( 62.8_{+2.5} \\)\\( 88.9_{+2.5} \\)
Modality-specific TeacherStudentOBJ—RGB & OBJOBJRGB & OBJRGB47.965.376.289.5
\\( 63.2_{+2.9} \\)\\( 88.7_{+2.3} \\)
TeacherStudent—RGB & OF & OBJRGB & OF & OBJRGB66.6\\( 63.0_{+2.7} \\)90.5\\( 88.9_{+2.5} \\)
", + "image_path": "9711cabd0843f4ec95b8a50625bb4bef1afcf6cab507fa22430100a774ef2d75.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 315, + 159, + 534, + 171 + ], + "lines": [ + { + "bbox": [ + 315, + 159, + 534, + 171 + ], + "spans": [ + { + "bbox": [ + 315, + 159, + 534, + 171 + ], + "type": "text", + "content": "(b) Something-Something [21]: Object-agnostic action recognition." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 189, + 546, + 212 + ], + "lines": [ + { + "bbox": [ + 46, + 189, + 546, + 212 + ], + "spans": [ + { + "bbox": [ + 46, + 189, + 546, + 212 + ], + "type": "text", + "content": "Table 2: Egocentric action recognition. RGB = Video frames; OF = Optical flow; A = Audio; OBJ = Object detections. Multimodal distillation with " + }, + { + "bbox": [ + 46, + 189, + 546, + 212 + ], + "type": "inline_equation", + "content": "\\lambda = 1.0" + }, + { + "bbox": [ + 46, + 189, + 546, + 212 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 189, + 546, + 212 + ], + "type": "inline_equation", + "content": "\\gamma = 30.0" + }, + { + "bbox": [ + 46, + 189, + 546, + 212 + ], + "type": "text", + "content": ". Improvement over RGB frames baseline [31] in red." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 232, + 287, + 412 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 232, + 287, + 412 + ], + "spans": [ + { + "bbox": [ + 46, + 232, + 287, + 412 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 46, + 232, + 287, + 412 + ], + "type": "text", + "content": " multi-channel images, which we provide as input to the vision transformer, as per the common practice in recent vision models [19, 20]. To encode the object detections, i.e. bounding boxes and object categories of the scene objects, we use a state-of-the-art model - STLT [43]. In STLT, a spatial and temporal transformer separately encode the spatial and temporal arrangement of the objects occurring in the video. The multimodal teacher we use during knowledge distillation is an ensemble of individual, modality-specific models. Unless noted otherwise, the student is a Swin-T model which receives RGB frames as input, both during training (distillation) and inference. In addition to Swin-T, in §4.3, we also consider ResNet3D [27] (18 and 50 layers deep) light-weight student models which receive video frames of size " + }, + { + "bbox": [ + 46, + 232, + 287, + 412 + ], + "type": "inline_equation", + "content": "112 \\times 112" + }, + { + "bbox": [ + 46, + 232, + 287, + 412 + ], + "type": "text", + "content": " as input." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "spans": [ + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "text", + "content": "Metrics. Besides accuracy, we measure Expected Calibration Error (ECE) [23]. As per [23, 45], we sort the predictions based on the per-class confidence scores and group them into " + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "text", + "content": " bins " + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "inline_equation", + "content": "B_{k}" + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "text", + "content": ", each associated with a confidence interval " + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "inline_equation", + "content": "I_{B_k} = \\left(\\frac{k - 1}{K},\\frac{k}{K}\\right)" + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "inline_equation", + "content": "K = 15" + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "text", + "content": ". ECE represents the discrepancy between the average accuracy " + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "inline_equation", + "content": "acc(B_k)" + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "text", + "content": " and the average confidence " + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "inline_equation", + "content": "conf(B_k)" + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "text", + "content": " in each bin " + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "inline_equation", + "content": "B_{k}" + }, + { + "bbox": [ + 46, + 412, + 287, + 496 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 82, + 505, + 287, + 538 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 82, + 505, + 287, + 538 + ], + "spans": [ + { + "bbox": [ + 82, + 505, + 287, + 538 + ], + "type": "interline_equation", + "content": "\\mathrm {E C E} = \\sum_ {k = 1} ^ {K} \\frac {\\left| B _ {k} \\right|}{N} \\left| a c c \\left(B _ {k}\\right) - c o n f \\left(B _ {k}\\right) \\right|, \\tag {6}", + "image_path": "105bf7304ac02ffa3f95d97aaa56668802d1c25207e9aafcef54bfecf9e4939e.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 546, + 235, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 546, + 235, + 557 + ], + "spans": [ + { + "bbox": [ + 47, + 546, + 235, + 557 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 546, + 235, + 557 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 47, + 546, + 235, + 557 + ], + "type": "text", + "content": " is the number of evaluation samples." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 558, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 558, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 558, + 288, + 713 + ], + "type": "text", + "content": "Implementation details. We train all models for 60 epochs using AdamW [32], with a peak learning rate of " + }, + { + "bbox": [ + 46, + 558, + 288, + 713 + ], + "type": "inline_equation", + "content": "1e - 4" + }, + { + "bbox": [ + 46, + 558, + 288, + 713 + ], + "type": "text", + "content": ", linearly increased for the first " + }, + { + "bbox": [ + 46, + 558, + 288, + 713 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 46, + 558, + 288, + 713 + ], + "type": "text", + "content": " of the training and decreased to 0.0 by the end of the specified 60 epochs. We use weight decay with a regularization coefficient of " + }, + { + "bbox": [ + 46, + 558, + 288, + 713 + ], + "type": "inline_equation", + "content": "5e - 2" + }, + { + "bbox": [ + 46, + 558, + 288, + 713 + ], + "type": "text", + "content": ", and clip the gradients when their norm exceeds 5.0. For Epic-Kitchens, we sample 32 frames with a fixed stride of 2, and for Something-Something and Something-Else we evenly sample 16 frames to cover the whole video. We use a single spatial and temporal crop, unless stated otherwise. During training, we chose a random start frame, while during inference, we select the start frame such that the sequence covers the central portion of the video. If we" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 232, + 545, + 341 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 232, + 545, + 341 + ], + "spans": [ + { + "bbox": [ + 304, + 232, + 545, + 341 + ], + "type": "text", + "content": "use multiple temporal crops as test-time augmentation, we chose the start frames such that the video is covered uniformly. During training we apply standard data augmentations - random spatial video crops, color jittering, and horizontal flips (for Epic-Kitchens only). The temperature parameter " + }, + { + "bbox": [ + 304, + 232, + 545, + 341 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 304, + 232, + 545, + 341 + ], + "type": "text", + "content": " is fixed to 10.0 for both the student and the teacher during multimodal knowledge distillation. In §4.2 we ablate the impact of the loss balancing term " + }, + { + "bbox": [ + 304, + 232, + 545, + 341 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 232, + 545, + 341 + ], + "type": "text", + "content": " and the Ensemble Teacher Weighting temperature term " + }, + { + "bbox": [ + 304, + 232, + 545, + 341 + ], + "type": "inline_equation", + "content": "\\gamma^1" + }, + { + "bbox": [ + 304, + 232, + 545, + 341 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 341, + 545, + 401 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 341, + 545, + 401 + ], + "spans": [ + { + "bbox": [ + 304, + 341, + 545, + 401 + ], + "type": "text", + "content": "During training we follow the consistent teaching paradigm [6] where the student and teacher strictly receive the same views of the data - we ensure for spatial and temporal consistency, i.e. the models receive the same frame indices, same random crops, and horizontal flips." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 407, + 541, + 420 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 407, + 541, + 420 + ], + "spans": [ + { + "bbox": [ + 305, + 407, + 541, + 420 + ], + "type": "text", + "content": "4.1. Multimodal Distillation for Egocentric Vision" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 426, + 546, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 546, + 570 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 546, + 570 + ], + "type": "text", + "content": "We first verify the overall effectiveness of multimodal knowledge distillation on the task of egocentric action recognition for both object-agnostic actions (Something-Something) and actions represented as noun-verb compositions (Epic-Kitchens). Across all experiments, we fix " + }, + { + "bbox": [ + 304, + 426, + 546, + 570 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 426, + 546, + 570 + ], + "type": "text", + "content": " to 1.0, i.e. we train solely with multimodal knowledge distillation. Similarly, we set " + }, + { + "bbox": [ + 304, + 426, + 546, + 570 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 426, + 546, + 570 + ], + "type": "text", + "content": " to a large value (" + }, + { + "bbox": [ + 304, + 426, + 546, + 570 + ], + "type": "inline_equation", + "content": "\\gamma = 30.0" + }, + { + "bbox": [ + 304, + 426, + 546, + 570 + ], + "type": "text", + "content": "), where effectively each teacher equally contributes to the ensemble output. Note that in this setting, models trained on modalities such as optical flow and audio may underperform, and thus adversely affect the ensemble teacher performance of recognizing active objects, i.e. nouns." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 583, + 474, + 596 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 583, + 474, + 596 + ], + "spans": [ + { + "bbox": [ + 305, + 583, + 474, + 596 + ], + "type": "text", + "content": "4.1.1 Recognizing Egocentric Actions" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 602, + 545, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 602, + 545, + 687 + ], + "spans": [ + { + "bbox": [ + 304, + 602, + 545, + 687 + ], + "type": "text", + "content": "In Table 2, we report performance on Something-Something V2 [21] and Epic-Kitchens 100 [14]. In line with the previous findings reported in the literature [33, 43, 57], we find that employing additional modalities at inference time significantly improves the performance compared to the RGB baseline model, for both the Epic-Kitchens and the Something-Something datasets." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 693, + 546, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 546, + 713 + ], + "type": "text", + "content": "1As the datasets' test sets either do not exist [33], or have restricted access, we report results using the model after the final training epoch." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5217" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 70, + 287, + 156 + ], + "blocks": [ + { + "bbox": [ + 50, + 70, + 287, + 156 + ], + "lines": [ + { + "bbox": [ + 50, + 70, + 287, + 156 + ], + "spans": [ + { + "bbox": [ + 50, + 70, + 287, + 156 + ], + "type": "table", + "html": "
MethodTraining ModalitiesInference ModalitiesNoun@1Verb@1Action@1
BaselineRGBRGB38.351.725.4
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB28.041.042.5+4.253.254.955.9+4.221.628.430.2+4.8
Modality-specificTeacherStudentA—RGB & AARGB & ARGB15.041.941.8+3.541.555.351.8+0.19.128.527.5+2.1
TeacherStudent—RGB & OF & ARGB & OF & ARGB42.943.7+5.458.054.1+3.430.329.6+4.2
", + "image_path": "0d3c251a14923897eaf8c875aed26461e9c733c66c7c90ff597ad8663d9245b1.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + }, + { + "bbox": [ + 47, + 159, + 288, + 180 + ], + "lines": [ + { + "bbox": [ + 47, + 159, + 288, + 180 + ], + "spans": [ + { + "bbox": [ + 47, + 159, + 288, + 180 + ], + "type": "text", + "content": "(a) Epic-Kitchens Unseen Environments [14]: Recognition of the active object (noun) and the activity (verb) on participants unseen during training." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_footnote" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 319, + 70, + 533, + 156 + ], + "blocks": [ + { + "bbox": [ + 319, + 70, + 533, + 156 + ], + "lines": [ + { + "bbox": [ + 319, + 70, + 533, + 156 + ], + "spans": [ + { + "bbox": [ + 319, + 70, + 533, + 156 + ], + "type": "table", + "html": "
MethodTraining ModalitiesInference ModalitiesAction@1Action@5
BaselineRGBRGB51.879.5
Modality-specific TeacherStudentOF—RGB & OFOFRGB & OFRGB49.061.058.2+6.477.486.485.1+5.6
Modality-specificTeacherStudentOBJ—RGB & OBJOBJRGB & OBJRGB41.459.457.5+5.767.384.584.1+4.6
TeacherStudent—RGB & OF & OBJRGB & OF & OBJRGB63.659.1+7.387.786.1+6.6
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Epic-Kitchens Regular splitSomething-Something
MethodNoun@1Verb@1Action@1Action@1Action@5
Omnivore [20]47.862.835.958.486.2
Student51.765.439.363.088.9
Epic-Kitchens Unseen ParticipantsSomething-Else
Omnivore [20]38.554.527.958.384.9
Student43.754.129.659.186.1
", + "image_path": "ed11356bc84f8c6e5efd99d893f2e77942e512f628650d1ab3704f1b0fb2d13e.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 311, + 287, + 345 + ], + "lines": [ + { + "bbox": [ + 46, + 311, + 287, + 345 + ], + "spans": [ + { + "bbox": [ + 46, + 311, + 287, + 345 + ], + "type": "text", + "content": "Table 4: Comparison with Omnivorous models [20]. All models are Swin-T and perform inference using only RGB frames. Multimodal distillation using all modalities with " + }, + { + "bbox": [ + 46, + 311, + 287, + 345 + ], + "type": "inline_equation", + "content": "\\lambda = 1.0" + }, + { + "bbox": [ + 46, + 311, + 287, + 345 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 311, + 287, + 345 + ], + "type": "inline_equation", + "content": "\\gamma = 30.0" + }, + { + "bbox": [ + 46, + 311, + 287, + 345 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 365, + 288, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 365, + 288, + 617 + ], + "spans": [ + { + "bbox": [ + 46, + 365, + 288, + 617 + ], + "type": "text", + "content": "A novel observation by our work is that multimodal knowledge distillation performs well in the context of egocentric video understanding, with student models often approaching the performance of the multimodal teacher ensemble. For Epic-Kitchens (Table 2a), we observe that when the student is distilled from an RGB & OF, or RGB & OF & A teacher, it is superior to the baseline model, as well as all modality-specific models, for recognizing actions. On the other hand, distilling from an RGB & A teacher yields performance lower than the baseline, due to the low performance of the model trained only on audio data. Specifically, we observe that the audio-specific teacher lowers the noun (active object) recognition performance. In §4.2, we propose a solution for this issue. For Something-Something (Table 2b), the student model is superior to the baseline for each combination of modalities. When distilling from all available modalities (RGB & OF & OBJ), the resulting model outperforms the baseline by " + }, + { + "bbox": [ + 46, + 365, + 288, + 617 + ], + "type": "inline_equation", + "content": "3.7\\%" + }, + { + "bbox": [ + 46, + 365, + 288, + 617 + ], + "type": "text", + "content": " in terms of the top-1 accuracy. In terms of the top-5 accuracy on Something-Something, the students achieve performance that is nearly on par with the multimodal teacher ensemble." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 631, + 287, + 643 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 631, + 287, + 643 + ], + "spans": [ + { + "bbox": [ + 46, + 631, + 287, + 643 + ], + "type": "text", + "content": "4.1.2 Generalizing to Unseen Environments & Objects" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 650, + 287, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 650, + 287, + 686 + ], + "spans": [ + { + "bbox": [ + 46, + 650, + 287, + 686 + ], + "type": "text", + "content": "We investigate to what extent our findings translate to the compositional generalization setting2, in which the performance of standard video models deteriorates significantly" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 307, + 238, + 422, + 312 + ], + "blocks": [ + { + "bbox": [ + 307, + 238, + 422, + 312 + ], + "lines": [ + { + "bbox": [ + 307, + 238, + 422, + 312 + ], + "spans": [ + { + "bbox": [ + 307, + 238, + 422, + 312 + ], + "type": "image", + "image_path": "f3f8e2941eb7ba6d3d0c20f2f6dd7014a5b81364f93b60c631eb47e9eb4e7e87.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 321, + 545, + 343 + ], + "lines": [ + { + "bbox": [ + 305, + 321, + 545, + 343 + ], + "spans": [ + { + "bbox": [ + 305, + 321, + 545, + 343 + ], + "type": "text", + "content": "Figure 3: Expected Calibration Error across datasets. The student is Swin-T trained with " + }, + { + "bbox": [ + 305, + 321, + 545, + 343 + ], + "type": "inline_equation", + "content": "\\lambda = 1.0" + }, + { + "bbox": [ + 305, + 321, + 545, + 343 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 321, + 545, + 343 + ], + "type": "inline_equation", + "content": "\\gamma = 30.0" + }, + { + "bbox": [ + 305, + 321, + 545, + 343 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 424, + 238, + 545, + 312 + ], + "blocks": [ + { + "bbox": [ + 424, + 238, + 545, + 312 + ], + "lines": [ + { + "bbox": [ + 424, + 238, + 545, + 312 + ], + "spans": [ + { + "bbox": [ + 424, + 238, + 545, + 312 + ], + "type": "image", + "image_path": "6ee4f632f5e1179c3698c744f4dee1ac8ab517cafad04b606d0709822e1181c6.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 365, + 545, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 365, + 545, + 653 + ], + "spans": [ + { + "bbox": [ + 304, + 365, + 545, + 653 + ], + "type": "text", + "content": "[33]. In the Something-Something dataset, the objects the people interact with might overlap between training and testing, potentially allowing models to pick up undesirable biases w.r.t. object appearance to discriminate between the actions. Therefore, Something-Else proposes a compositional generalization data split, on which the objects at training and testing time do not overlap, such that the models encounter strictly novel objects during testing. Similarly, the rich visual environments featured in the Epic-Kitchen training data may also provide the model with spurious cues for predicting the actions and lead to significant performance drop on new, unobserved environments. The Epic-Kitchens Unseen split consists of a subset of videos in the validation set from participants whose videos were not present in the training dataset, giving insight into how our approach generalizes to new visual environments. We report the performance of our approach Epic-Kitchens Unseen split and the Something-Else [33] split in Table 3. The general observation across datasets and modalities is that the distilled students significantly outperform the RGB baseline model, and are sometimes even competitive with their respective teacher. Notably, on Something-Else, the student distilled from an RGB & OF & OBJ teacher outperforms the baseline by " + }, + { + "bbox": [ + 304, + 365, + 545, + 653 + ], + "type": "inline_equation", + "content": "7.3\\%" + }, + { + "bbox": [ + 304, + 365, + 545, + 653 + ], + "type": "text", + "content": " in terms of top-1 accuracy." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 670, + 502, + 681 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 670, + 502, + 681 + ], + "spans": [ + { + "bbox": [ + 306, + 670, + 502, + 681 + ], + "type": "text", + "content": "4.1.3 Comparison with Omnivorous Models" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 713 + ], + "type": "text", + "content": "We explicitly compare multimodal knowledge distillation against Omnivorous models [19, 20], which are trained" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "text", + "content": "2Compositional generalization measures to what extent the model can generalize to novel combinations of concepts observed during training." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5218" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 69, + 289, + 205 + ], + "blocks": [ + { + "bbox": [ + 47, + 69, + 289, + 205 + ], + "lines": [ + { + "bbox": [ + 47, + 69, + 289, + 205 + ], + "spans": [ + { + "bbox": [ + 47, + 69, + 289, + 205 + ], + "type": "image", + "image_path": "6974477f9853b80b117d7cc94e022a0a323394e99fc513ebe8e2d3a8718b3875.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 213, + 287, + 236 + ], + "lines": [ + { + "bbox": [ + 46, + 213, + 287, + 236 + ], + "spans": [ + { + "bbox": [ + 46, + 213, + 287, + 236 + ], + "type": "text", + "content": "Figure 4: Per-class improvement of the student over the RGB baseline on the top-20 most frequent actions across datasets." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 257, + 287, + 412 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 257, + 287, + 412 + ], + "spans": [ + { + "bbox": [ + 46, + 257, + 287, + 412 + ], + "type": "text", + "content": "jointly on all modalities featuring non-aligned data, e.g. with RGB frames obtained from one dataset and depth maps from another [20]. These models have been proven to generalize better compared to their unimodal counterparts. We train the Omnivore model using batches comprised of data from the same modality, where we randomly sample the modality for each training batch3. Additionally, we train the Omnivore models for " + }, + { + "bbox": [ + 46, + 257, + 287, + 412 + ], + "type": "inline_equation", + "content": "M \\times" + }, + { + "bbox": [ + 46, + 257, + 287, + 412 + ], + "type": "text", + "content": " more epochs (" + }, + { + "bbox": [ + 46, + 257, + 287, + 412 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 46, + 257, + 287, + 412 + ], + "type": "text", + "content": " is the number of modalities), to account for the random sampling of modalities during training. We represent the object detections modality as bounding boxes with a line thickness of 2px pasted on a white canvas where each category is colored uniquely, e.g. hand in blue and object in red." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 413, + 287, + 510 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 413, + 287, + 510 + ], + "spans": [ + { + "bbox": [ + 46, + 413, + 287, + 510 + ], + "type": "text", + "content": "We report results in Table 4. Even though on the Epic-Kitchens Unseen split and the Something-Else dataset the Omnivore model exhibits strong performance (" + }, + { + "bbox": [ + 46, + 413, + 287, + 510 + ], + "type": "inline_equation", + "content": "\\sim 5.5\\%" + }, + { + "bbox": [ + 46, + 413, + 287, + 510 + ], + "type": "text", + "content": " improvement on top of the baseline on Something-Else), the multimodal distillation approach achieves even higher performance. Nevertheless, we conclude that both approaches represent viable options for training multimodal models which leverage unimodal inputs during inference." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 525, + 201, + 536 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 525, + 201, + 536 + ], + "spans": [ + { + "bbox": [ + 47, + 525, + 201, + 536 + ], + "type": "text", + "content": "4.1.4 Effect on Model Calibration" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 544, + 287, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 544, + 287, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 544, + 287, + 676 + ], + "type": "text", + "content": "Next to the improvements in action recognition performance we observe, we also investigate how the distilled student fares against the baseline in terms of model calibration. That is, whether the probability score of the predicted class reflects the accuracy of predicting the said class [23, 41]. More importantly, we verify whether distilling from additional modalities yields better calibrated students. In Fig. 3, we measure the Expected Calibration error [23] (ECE) on the Epic-Kitchens (regular & unseen), and the Something-Something and Something-Else datasets. We report the ECE for an RGB model trained using the ground truth la" + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 339, + 71, + 515, + 145 + ], + "blocks": [ + { + "bbox": [ + 339, + 71, + 515, + 145 + ], + "lines": [ + { + "bbox": [ + 339, + 71, + 515, + 145 + ], + "spans": [ + { + "bbox": [ + 339, + 71, + 515, + 145 + ], + "type": "table", + "html": "
ObjectiveλγNoun@1Verb@1Action@1
LCE0.0—52.061.738.3
LKL1.030.051.765.439.3
LCE ∧ LKL0.830.052.665.140.4
LCE ∧ LKL0.83.053.066.941.0
LKL1.01.053.165.540.5
LCE ∧ LKL0.81.053.565.441.2
LCE ∧ LKL0.80.3353.664.740.5
", + "image_path": "3ccadf9d6f6bd68975f58d165cfb35439fd1f62b646c73125cafffa7882b3483.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 153, + 547, + 187 + ], + "lines": [ + { + "bbox": [ + 305, + 153, + 547, + 187 + ], + "spans": [ + { + "bbox": [ + 305, + 153, + 547, + 187 + ], + "type": "text", + "content": "Table 5: Ablation study on the Epic-Kitchens dataset. λ: Distillation and Cross-Entropy loss balancing term; γ: Temperature of the Ensemble Teacher Weighting." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 208, + 547, + 269 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 208, + 547, + 269 + ], + "spans": [ + { + "bbox": [ + 304, + 208, + 547, + 269 + ], + "type": "text", + "content": "bels, as well as all distilled students reported in Table 2 and Table 3. The general observation is that across datasets, distillation improves the models' calibration. Furthermore, we find that increasing the number of modalities used in the ensemble improves the model calibration." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 284, + 489, + 295 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 284, + 489, + 295 + ], + "spans": [ + { + "bbox": [ + 305, + 284, + 489, + 295 + ], + "type": "text", + "content": "4.1.5 Per-Class Performance Breakdown" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 304, + 545, + 423 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 304, + 545, + 423 + ], + "spans": [ + { + "bbox": [ + 304, + 304, + 545, + 423 + ], + "type": "text", + "content": "In Fig 4, we present the relative change in action recognition accuracy of the student model obtained via multimodal distillation w.r.t. the architecturally equivalent baseline RGB model trained on ground truth labels, computed on the top-20 most frequent classes (actions) on Epic-Kitchens and Something-Something. Overall, we observe that multimodal distillation generally improves performance across different actions, and particularly so on Something-Something, where we achieve improvements in terms of all of the top-20 most frequent action classes." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 431, + 466, + 445 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 431, + 466, + 445 + ], + "spans": [ + { + "bbox": [ + 305, + 431, + 466, + 445 + ], + "type": "text", + "content": "4.2. Ensemble Teacher Weighting" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "text", + "content": "In §4.1 we observe that distilling from multimodal teachers yields students which are superior to models trained on the ground truth labels. Nevertheless, if a weak teacher is added in the ensemble, it negatively affects the knowledge distillation and yields a student which is inferior than using the ground truth labels, e.g. adding the audio-specific teacher in the ensemble for Epic-Kitchens. To cope with this, we weigh the logits of the teacher ensemble as discussed in §3.2. Namely, we use the two hyperparameters " + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "inline_equation", + "content": "(\\lambda" + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\gamma)" + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "text", + "content": " for (i) balancing between the ground truth and the distillation loss: " + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "text", + "content": " (Equation 5), and (ii) controlling how the predictions of modality-specific models are combined in the ensemble: " + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "text", + "content": " (Equation 3). We report results for Epic-Kitchens in Table 5, including the values for " + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "text", + "content": " as well as the objective we effectively minimize. We observe that the model trained only on the ground truth labels (" + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\lambda = 0.0" + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "text", + "content": "), is inferior to all other models. Using a large " + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "text", + "content": " (e.g. 30.0) - effectively assigning equal weights to all models in the ensemble - we observe to perform well despite the simple setup (we use this model in the experiments in §4.1). Additionally, training using the task loss in addition to the distillation loss (" + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\lambda = 0.8" + }, + { + "bbox": [ + 304, + 450, + 545, + 715 + ], + "type": "text", + "content": ") further improves the performance. The" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 46, + 683, + 287, + 715 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 683, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 683, + 287, + 715 + ], + "type": "inline_equation", + "content": "^{3}" + }, + { + "bbox": [ + 46, + 683, + 287, + 715 + ], + "type": "text", + "content": "Girdhar et al. [20] show that there is no performance difference if the batches contain mixed data from different modalities, however, we found that using homogeneous batches yields better performance." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5219" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 81, + 276, + 232 + ], + "blocks": [ + { + "bbox": [ + 55, + 81, + 276, + 232 + ], + "lines": [ + { + "bbox": [ + 55, + 81, + 276, + 232 + ], + "spans": [ + { + "bbox": [ + 55, + 81, + 276, + 232 + ], + "type": "image", + "image_path": "459215aa9a90da4897f2a18f629d954ad5a2e6198ee719933287292161486487.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 243, + 547, + 266 + ], + "lines": [ + { + "bbox": [ + 46, + 243, + 547, + 266 + ], + "spans": [ + { + "bbox": [ + 46, + 243, + 547, + 266 + ], + "type": "text", + "content": "Figure 5: Top-1 action accuracy of Teacher, Student & Baseline models and their associated computational cost in giga-FLOPs " + }, + { + "bbox": [ + 46, + 243, + 547, + 266 + ], + "type": "inline_equation", + "content": "(10^{9})" + }, + { + "bbox": [ + 46, + 243, + 547, + 266 + ], + "type": "text", + "content": " required to update the input and predict the action. Note: Top-left corner is optimal (i.e. faster and most accurate models)." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 301, + 81, + 521, + 232 + ], + "blocks": [ + { + "bbox": [ + 301, + 81, + 521, + 232 + ], + "lines": [ + { + "bbox": [ + 301, + 81, + 521, + 232 + ], + "spans": [ + { + "bbox": [ + 301, + 81, + 521, + 232 + ], + "type": "image", + "image_path": "5a2ae4b4f8c46cbe1fbc45f032a0c3e3b6e62a1379f3ffb5edcd768f61e859c4.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 50, + 284, + 282, + 453 + ], + "blocks": [ + { + "bbox": [ + 50, + 284, + 282, + 453 + ], + "lines": [ + { + "bbox": [ + 50, + 284, + 282, + 453 + ], + "spans": [ + { + "bbox": [ + 50, + 284, + 282, + 453 + ], + "type": "image", + "image_path": "4cd7f76a2b38f9000b69aa49cf1738fbe56698f7c0837e770f8480770c102c2f.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 460, + 288, + 484 + ], + "lines": [ + { + "bbox": [ + 47, + 460, + 288, + 484 + ], + "spans": [ + { + "bbox": [ + 47, + 460, + 288, + 484 + ], + "type": "text", + "content": "Figure 6: Performance degradation when reducing the number of inference clips/crops (Epic-Kitchens/Something-Something)." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "spans": [ + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "text", + "content": "best performing model uses both the task and the distillation loss " + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "inline_equation", + "content": "(\\lambda = 0.8)" + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "text", + "content": ", and assigns weights to each teacher in the ensemble based on its performance on " + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "inline_equation", + "content": "Z = 1000" + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "text", + "content": " randomly sampled videos held-out from the training dataset, with a normalization temperature " + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "inline_equation", + "content": "\\gamma = 1.0" + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "text", + "content": ". Moreover, we find that lowering the normalization temperature " + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "text", + "content": " further " + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "inline_equation", + "content": "(\\gamma = 0.33)" + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "text", + "content": " - giving higher weight to the best performing model in the ensemble - yields lower performance. Similarly, increasing the normalization temperature to " + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "inline_equation", + "content": "\\gamma = 3.0" + }, + { + "bbox": [ + 46, + 505, + 287, + 625 + ], + "type": "text", + "content": ", thus equalizing the model weights, also negatively affects performance." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 634, + 159, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 634, + 159, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 634, + 159, + 647 + ], + "type": "text", + "content": "4.3. Efficiency Analysis" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "Despite the strong performance multimodal action recognition models exhibit, we argue that the high computational complexity makes them cumbersome for deployment, particularly compared to a model which uses only RGB video during inference. The teacher ensemble used for" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 286, + 545, + 454 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 286, + 545, + 454 + ], + "spans": [ + { + "bbox": [ + 304, + 286, + 545, + 454 + ], + "type": "text", + "content": "Epic-Kitchens uses three modality-specific Swin-T models, where each has 28.22M parameters, and requires 140.33 GFLOPs for processing single-view 32 frame/spectrogram video. Assuming such an ensemble is deployed, the optical flow would have to be computed on-the-fly4. Using RAFT, we measure a total added computation of 163.37 GFLOPs for such a model. We consider the computation required to obtain the spectrograms of 1.116s audio segments to be negligible in comparison. Therefore, when using all three modalities, updating the input sequences for each newly observed frame and performing action recognition would require 584.36 GFLOPs. In contrast, the distilled student is a single RGB model, and in the case of Swin-T requires 140.33 GFLOPs – which represents a reduction of " + }, + { + "bbox": [ + 304, + 286, + 545, + 454 + ], + "type": "inline_equation", + "content": "75.98\\%" + }, + { + "bbox": [ + 304, + 286, + 545, + 454 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "spans": [ + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "text", + "content": "We report results on the Epic-Kitchens dataset in Fig. 5 for: (i) All variations of teacher models (RGB & OF, RGB & A, and RGB & OF & A); (ii) The Swin-T student model, distilled with " + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "inline_equation", + "content": "\\lambda = 0.8" + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "inline_equation", + "content": "\\gamma = 1.0" + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "text", + "content": "; (iii) The Swin-T baseline model, trained with " + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "inline_equation", + "content": "\\lambda = 0.0" + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "text", + "content": "; (iv) Two new ResNet3D models [27] (with depth of 50 and 18 layers), exhibiting less parameters and GFLOPs compared to the Swin-T model. The resolution size of the ResNet3D models is " + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "inline_equation", + "content": "112 \\times 112" + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "text", + "content": ". For each ResNet3D, we report action recognition performance of the baseline with " + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "inline_equation", + "content": "\\lambda = 0.0" + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "text", + "content": ", and performance of the distilled students with " + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "inline_equation", + "content": "\\lambda = 0.8" + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "inline_equation", + "content": "\\gamma = 1.0" + }, + { + "bbox": [ + 304, + 455, + 545, + 586 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 588, + 545, + 661 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 588, + 545, + 661 + ], + "spans": [ + { + "bbox": [ + 304, + 588, + 545, + 661 + ], + "type": "text", + "content": "We observe a consistently higher performance of the student models compared to the same model architecture trained on ground truth labels alone. Notably, our best performing student achieves comparable performance to the significantly more expensive RGB & OF & A teacher. Furthermore, the R3D-18 and R3D-50 students outperform" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 304, + 673, + 547, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 673, + 547, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 673, + 547, + 712 + ], + "type": "text", + "content": "4The Duality-based TV-L1 [40, 60] can be efficiently computed on a GPU (5-10 FPS) [4]. Deep Learning-based approaches, e.g. RAFT [51], require 163.37 GFLOPs, however, achieve higher FPS of 21.10, measured with 10 refinement iterations and resolution of " + }, + { + "bbox": [ + 304, + 673, + 547, + 712 + ], + "type": "inline_equation", + "content": "256 \\times 456" + }, + { + "bbox": [ + 304, + 673, + 547, + 712 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "5220" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 71, + 167, + 201 + ], + "blocks": [ + { + "bbox": [ + 49, + 71, + 167, + 201 + ], + "lines": [ + { + "bbox": [ + 49, + 71, + 167, + 201 + ], + "spans": [ + { + "bbox": [ + 49, + 71, + 167, + 201 + ], + "type": "image", + "image_path": "28ecc3676b1f443cb379c03d77bbc74d779c304241739bdf452862c0785e44fa.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 210, + 287, + 232 + ], + "lines": [ + { + "bbox": [ + 47, + 210, + 287, + 232 + ], + "spans": [ + { + "bbox": [ + 47, + 210, + 287, + 232 + ], + "type": "text", + "content": "Figure 7: Qualitative example for the Epic Kitchens (Left) & the Something-Something (Right) datasets." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 168, + 71, + 286, + 200 + ], + "blocks": [ + { + "bbox": [ + 168, + 71, + 286, + 200 + ], + "lines": [ + { + "bbox": [ + 168, + 71, + 286, + 200 + ], + "spans": [ + { + "bbox": [ + 168, + 71, + 286, + 200 + ], + "type": "image", + "image_path": "a4424c354c8de2dad348f85600ceecd7f53e0e65f3d70059259ea18599a85ed1.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 253, + 286, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 253, + 286, + 300 + ], + "spans": [ + { + "bbox": [ + 46, + 253, + 286, + 300 + ], + "type": "text", + "content": "their counterparts trained on class labels. Finally, we observe that the R3D-18 student matches the performance of the larger, and computationally more expensive R3D-50 trained on ground truth labels." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 316, + 224, + 327 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 316, + 224, + 327 + ], + "spans": [ + { + "bbox": [ + 47, + 316, + 224, + 327 + ], + "type": "text", + "content": "4.3.1 Effect of Test-Time Augmentation" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 334, + 286, + 514 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 334, + 286, + 514 + ], + "spans": [ + { + "bbox": [ + 46, + 334, + 286, + 514 + ], + "type": "text", + "content": "Lastly, we inspect the relationship between action recognition performance and the number of temporal clips (on Epic-Kitchens) and spatial crops (on Something-Something) sampled from the video during inference. Note that our goal is to reduce the computational complexity while maintaining the performance. Since standard video models [1, 7, 30, 31] use multiple temporal clips and spatial crops as test-time augmentation to obtain further performance improvements, we explore the extent to which the distilled model is dependent on their availability during inference. We report results in Fig. 6, where we observe that the distilled model " + }, + { + "bbox": [ + 46, + 334, + 286, + 514 + ], + "type": "inline_equation", + "content": "(\\lambda = 1.0)" + }, + { + "bbox": [ + 46, + 334, + 286, + 514 + ], + "type": "text", + "content": " is much less adversely affected by the reduction of both sampled temporal clips and spatial crops during inference, compared to the same model trained on the ground truth labels " + }, + { + "bbox": [ + 46, + 334, + 286, + 514 + ], + "type": "inline_equation", + "content": "(\\lambda = 0.0)" + }, + { + "bbox": [ + 46, + 334, + 286, + 514 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 521, + 170, + 533 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 521, + 170, + 533 + ], + "spans": [ + { + "bbox": [ + 47, + 521, + 170, + 533 + ], + "type": "text", + "content": "4.4. Qualitative Examples" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 539, + 286, + 635 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 539, + 286, + 635 + ], + "spans": [ + { + "bbox": [ + 46, + 539, + 286, + 635 + ], + "type": "text", + "content": "In Fig. 7, we showcase the classes corresponding to the highest scores predicted by the student and the individual modality-specific models in the teacher ensemble, as well as the ground truth label (on Epic-Kitchens and Something-Something datasets). For both examples, we observe that the student picks up on relevant cues from each modality and accurately predicts the action of interest (see Supp. H for additional qualitative examples)." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 645, + 119, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 645, + 119, + 658 + ], + "spans": [ + { + "bbox": [ + 47, + 645, + 119, + 658 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 665, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 286, + 712 + ], + "type": "text", + "content": "We demonstrated a simple, yet effective distillation-based approach for leveraging multimodal data only during training in order to improve a model that uses solely RGB frames during inference. Our experiments indicate clear" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": "performance improvements over models trained on ground truth labels. We further showed an advantageous tradeoff between the high performance of a cumbersome multimodal ensemble, and low computational complexity of unimodal approaches. Moreover, our approach relies less on expensive test-time augmentations, otherwise widely used in the literature to improve the egocentric action recognition models' performance." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 168, + 545, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 168, + 545, + 251 + ], + "spans": [ + { + "bbox": [ + 304, + 168, + 545, + 251 + ], + "type": "text", + "content": "Limitations & Future work. Notably, in this work we considered only the task of action recognition, while multimodal distillation can be readily applied to other egocentric tasks [22]. Future work may also feature additional modalities such as depth, hand poses, motion captured by inertial sensors (IMU), etc., available in recent large-scale egocentric datasets [22]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 262, + 403, + 276 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 262, + 403, + 276 + ], + "spans": [ + { + "bbox": [ + 306, + 262, + 403, + 276 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 282, + 545, + 319 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 282, + 545, + 319 + ], + "spans": [ + { + "bbox": [ + 305, + 282, + 545, + 319 + ], + "type": "text", + "content": "We acknowledge the funding from the Flemish Government under the Onderzoeksprogramma Artificièle Intelligente (AI) Vlaanderen programme." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "5221" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 145 + ], + "type": "text", + "content": "[1] Anurag Arnab, Mostafa Dehghani, Georg Heigold, Chen Sun, Mario Lucic, and Cordelia Schmid. 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In this work, we propose a novel multimodal garment designer framework based on latent diffusion models that can generate a novel fashion image conditioned on text, human keypoints, and a garment sketch." + ], + "image_footnote": [], + "bbox": [ + 78, + 305, + 890, + 577 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 622, + 313, + 638 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Fashion illustration is used by designers to communicate their vision and to bring the design idea from conceptualization to realization, showing how clothes interact with the human body. In this context, computer vision can thus be used to improve the fashion design process. Differently from previous works that mainly focused on the virtual try-on of garments, we propose the task of multimodal-conditioned fashion image editing, guiding the generation of human-centric fashion images by following multimodal prompts, such as text, human body poses, and garment sketches. We tackle this problem by proposing a new architecture based on latent diffusion models, an approach that has not been used before in the fashion domain. Given the lack of existing datasets suitable for the task, we also extend two existing fashion datasets, namely Dress Code and VITON-HD, with multimodal annotations collected in a semi-automatic manner. Experimental re", + "bbox": [ + 75, + 643, + 473, + 900 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "sults on these new datasets demonstrate the effectiveness of our proposal, both in terms of realism and coherence with the given multimodal inputs. Source code and collected multimodal annotations are publicly available at: https://github.com/aimagelab/multimodal-garment-designer.", + "bbox": [ + 498, + 619, + 892, + 696 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 500, + 715, + 632, + 732 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Computer Vision research has always paid much attention both to the human person and to fashion-related problems, especially working on the recognition and retrieval of clothing items [11, 22], the recommendation of similar garments [8, 18, 39], and the virtual try-on of clothes and accessories [7, 13, 27, 28, 47, 52]. In the last years, some research efforts have been dedicated to the text-conditioned image editing task where, given a model image and a textual description of a garment, the goal is to generate the", + "bbox": [ + 496, + 742, + 893, + 878 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Equal contribution.", + "bbox": [ + 524, + 887, + 635, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "23393", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "input model wearing a new clothing item corresponding to the given textual description. In this context, only a few works [19,33,56] have been proposed, exclusively employing GAN-based approaches for the generative step.", + "bbox": [ + 75, + 90, + 468, + 151 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Recently, diffusion models [10, 17, 30, 41] have attracted more and more attention due to their outstanding generation capabilities, allowing the improvement of a variety of downstream tasks in several domains, while their applicability to the fashion domain is still unexplored. Many different solutions have been introduced and can roughly be identified based on the denoising conditions used to guide the diffusion process, which can enable greater control of the synthesized output. A particular type of diffusion model has been proposed in [37] that, instead of applying the diffusion process in the pixel space, defines the forward and the reverse processes in the latent space of a pre-trained autoencoder, becoming one of the leading choices thanks to its reduced computational cost. Although this solution can generate highly realistic images, it does not perform well in human-centric generation tasks and can not deal with multiple conditioning signals to guide the generation phase.", + "bbox": [ + 75, + 154, + 470, + 411 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In this work, we address an extended and more general framework and define the new task of multimodal-conditioned fashion image editing, which allows guiding the generative process via multimodal prompts while preserving the identity and body shape of a given person (Fig. 1). To tackle this task, we introduce a new architecture, called Multimodal Garment Designer (MGD), that emulates the process of a designer conceiving a new garment on a model shape, based on preliminary indications provided through a textual sentence or a garment sketch. In particular, starting from Stable Diffusion [37], we propose a denoising network that can be conditioned by multiple modalities and also takes into account the pose consistency between input and generated images, thus improving the effectiveness of human-centric diffusion models.", + "bbox": [ + 75, + 412, + 468, + 638 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address the newly proposed task, we present a semiautomatic framework to extend existing datasets with multimodal data. Specifically, we start from two famous virtual try-on datasets (i.e. Dress Code [28] and VITON-HD [7]) and extend them with textual descriptions and garment sketches. Experimental results on the two proposed multimodal fashion benchmarks show both quantitatively and qualitatively that our proposed architecture generates high-quality images based on the given multimodal inputs and outperforms all considered competitors and baselines, also according to human evaluations.", + "bbox": [ + 75, + 642, + 468, + 808 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To sum up, our contributions are as follows: (1) We propose a novel task of multimodal-conditioned fashion image editing, which entails the use of multimodal data to guide the generation. (2) We introduce a new human-centric generative architecture based on latent diffusion models, capable of following multimodal prompts while preserving the", + "bbox": [ + 75, + 810, + 468, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "model's characteristics. (3) To tackle the new task, we extend two existing fashion datasets with textual sentences and garment sketches devising a semi-automatic annotation framework. (4) Extensive experiments demonstrate that the proposed approach outperforms other competitors in terms of realism and coherence with multimodal inputs.", + "bbox": [ + 496, + 90, + 890, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 193, + 640, + 208 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Text-Guided Image Generation. Creating an image that faithfully reflects the provided textual prompt is the goal of text-to-image synthesis. In this context, early approaches were based on GANs [45, 51, 53, 55], while most recent solutions exploit the effectiveness of diffusion models [31, 35, 37]. In the fashion domain, only a few attempts of text-to-image synthesis have been proposed [19, 33, 56]. Specifically, Zhu et al. [56] presented a GAN-based solution that generates the final image conditioned on both textual descriptions and semantic layouts. A different approach is the one introduced in [33], where a latent code regularization technique is employed to augment the GAN inversion process by exploiting CLIP textual embeddings [34] to guide the image editing process. Instead, Jiang et al. [19] proposed an architecture that synthesizes full-body images by mapping the textual descriptions of clothing items into one-hot vectors, limiting however the expressiveness capability of the conditioning signal.", + "bbox": [ + 496, + 218, + 890, + 489 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multimodal Image Generation with Diffusion Models. A related line of works aims to condition existing diffusion models on different modalities thus enabling greater control over the generation process [5, 6, 25, 29, 48]. For example, Choi et al. [6] proposed to refine the generative process of an unconditional denoising diffusion probabilistic model [30] by matching each latent variable with the given reference image. On a different line, the approach introduced in [25] adds noise to a stroke-based input and applies the reverse stochastic differential equation to synthesize images, without additional training. Wang et al. [48], instead, proposed to learn a highly semantic latent space and perform conditional finetuning for each downstream task to map the guidance signals to the pre-trained space. Other recent works proposed to add sketches as additional conditioning signals, either concatenating them with the model input [5] or training an MLP-based edge predictor to map latent features to spatial maps [46].", + "bbox": [ + 496, + 493, + 890, + 763 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Among contemporary works that aim to condition pretrained latent diffusion models, ControlNet [54] proposes to extend the Stable Diffusion model [37] with an additional conditioning input. This process involves creating two versions of the original model's weights: one that remains fixed and unchanged (locked copy) and another that can be updated during training (trainable copy). The purpose of this is to allow the trainable version to learn the newly introduced condition while the locked version retains the origi", + "bbox": [ + 496, + 765, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "23394", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/35fd084287558bf2793f24e73ada81b2c93658bc4a35b3ccb6a18845922e39c3.jpg", + "image_caption": [ + "Figure 2. Overview of the proposed Multimodal Garment Designer (MGD), a human-centric latent diffusion model conditioned on multiple modalities (i.e. text, human pose, and garment sketch)." + ], + "image_footnote": [], + "bbox": [ + 76, + 85, + 890, + 263 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "nal model knowledge. On the other hand, T2I-Adapter [29] learns modality-specific adapter modules that enable Stable Diffusion conditioning on new modalities.", + "bbox": [ + 75, + 315, + 468, + 359 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In contrast, we focus on the fashion domain and propose a human-centric architecture based on latent diffusion models that directly exploits the conditioning of textual sentences and other modalities such as human body poses and garment sketches.", + "bbox": [ + 75, + 361, + 468, + 436 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed Method", + "text_level": 1, + "bbox": [ + 76, + 450, + 250, + 467 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this section, we propose a novel task to automatically edit a human-centric fashion image conditioned on multiple modalities. Specifically, given the model image $I \\in \\mathbb{R}^{H \\times W \\times 3}$ , its pose map $P \\in \\mathbb{R}^{H \\times W \\times 18}$ where the channels represent the human keypoints, a textual description $Y$ of a garment, and a sketch of the same $S \\in \\mathbb{R}^{H \\times W \\times 1}$ , we want to generate a new image $\\tilde{I} \\in \\mathbb{R}^{H \\times W \\times 3}$ that retains the information of the input model while substituting the target garment according to the multimodal inputs. To tackle the task, we propose a novel latent diffusion approach, called Multimodal Garment Designer (MGD), that can effectively combine multimodal information when generating the new image $\\tilde{I}$ . Our proposed architecture is a general framework that can be easily extended to other modalities such as texture and 3d information. We strongly believe this task can foster research in the field and enhance the design process of new fashion items with greater customization. An overview of our model is shown in Fig. 2.", + "bbox": [ + 75, + 474, + 470, + 748 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Preliminaries", + "text_level": 1, + "bbox": [ + 76, + 756, + 217, + 771 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "While diffusion models [41] are latent variable architectures that work in the same dimensionality of the data (i.e. in the pixel space), latent diffusion models (LDMs) [37] operate in the latent space of a pre-trained autoencoder achieving higher computational efficiency while preserving the generation quality. In our work, we leverage the Stable Diffusion model [37], a text-to-image implementation of LDMs as a starting point to perform multimodal condition-", + "bbox": [ + 75, + 779, + 470, + 901 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "ing for human-centric fashion image editing. Stable Diffusion is composed of an autoencoder with an encoder $\\mathcal{E}$ and a decoder $\\mathcal{D}$ , a text-time-conditional U-Net denoising model $\\epsilon_{\\theta}$ , and a CLIP-based text encoder $T_{E}$ taking as input a text $Y$ . The encoder $\\mathcal{E}$ compresses an image $I$ into a lower-dimensional latent space defined in $\\mathbb{R}^{h\\times w\\times 4}$ , where $h = H / 8$ and $w = W / 8$ . The decoder $\\mathcal{D}$ performs the opposite operation, decoding a latent variable into the pixel space. For the sake of clarity, we define the $\\epsilon_{\\theta}$ convolutional input (i.e. $z_{t}$ in this case) as spatial input $\\gamma$ because of the property of convolutions to preserve the spatial structure and the attention conditioning input as $\\psi$ . The denoising network $\\epsilon_{\\theta}$ is trained according to the following loss:", + "bbox": [ + 496, + 315, + 893, + 512 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nL = \\mathbb {E} _ {\\mathcal {E} (I), Y, \\epsilon \\sim \\mathcal {N} (0, 1), t} \\left[ \\| \\epsilon - \\epsilon_ {\\theta} (\\gamma , \\psi) \\| _ {2} ^ {2} \\right], \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 553, + 521, + 890, + 542 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $t$ is the diffusing time step, $\\gamma = z_{t}$ , $\\psi = [t;T_{E}(Y)]$ , and $\\epsilon \\sim \\mathcal{N}(0,1)$ is the Gaussian noise added to $\\mathcal{E}(I)$ .", + "bbox": [ + 496, + 550, + 890, + 582 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Human-Centric Image Editing", + "text_level": 1, + "bbox": [ + 500, + 590, + 772, + 606 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Our task aims to generate a new image $\\tilde{I}$ , by replacing in the input image $I$ the target garment using multimodal inputs, while preserving the model's identity and physical characteristics. As a natural consequence, this task can be identified as a particular type of inpainting tailored for human body data. Instead of using a standard text-to-image model, we perform inpainting concatenating along the channel dimension of the denoising network input $z_{t}$ an encoded masked image $\\mathcal{E}(I_M)$ and the relative resized binary inpainting mask $m\\in \\{0,1\\}^{h\\times w\\times 1}$ , which is derived from the original inpainting mask $M\\in \\{0,1\\}^{H\\times W\\times 1}$ . Since here, the spatial input of the denoising network is $\\gamma = [z_t;m;\\mathcal{E}(I_M)],\\gamma \\in \\mathbb{R}^{h\\times w\\times 9}$ . Thanks to the fully convolutional nature of the encoder $\\mathcal{E}$ and the decoder $\\mathcal{D}$ , this LDMs-based architecture can preserve the spatial information in the latent space. Exploiting this feature, our method can thus optionally add conditioning constraints to the generation. In particular, we propose to add two generation constraints in addition to the textual information: the", + "bbox": [ + 496, + 612, + 893, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "23395", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "model pose map $P$ to preserve the original human pose of the input model and the garment sketch $S$ to allow the final users to better condition the garment generation process.", + "bbox": [ + 75, + 90, + 468, + 136 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Pose Map Conditioning. In most cases [21, 24, 44], inpainting is performed with the objective of either removing or entirely replacing the content of the masked region. However, in our task, we aim to remove all information regarding the garment worn by the model while preserving the model's body information and identity. Thus, we propose to improve the garment inpainting process by using the bounding box of the segmentation mask along with pose map information representing body keypoints. This approach enables the preservation of the model's physical characteristics in the masked region while allowing the inpainting of garments with different shapes. Differently from conventional inpainting techniques, we focus on selectively retaining and discarding specific information within the masked region to achieve the desired outcome. To enhance the performance of the denoising network with human body keypoints, we modify the first convolution layer of the network by adding 18 additional channels, one for each keypoint. Adding new inputs usually would require retraining the model from scratch, thus consuming time, data, and resources, especially in the case of data-hungry models like the diffusion ones. Therefore, we propose to extend the kernels of the pre-trained input layer of the denoising network with randomly initialized weights sampled from a uniform distribution [14] and retrain the whole network. This consistently reduces the number of training steps and enables training with less data. Our experiments show that such improvement enhances the consistency of the body information between the generated image and the original one.", + "bbox": [ + 75, + 138, + 472, + 578 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Incorporating Sketches. Fully describing a garment using only textual descriptions is a challenging task due to the complexity and ambiguity of natural language. While text can convey specific attributes like style, color, and patterns of a garment, it may not provide sufficient information about its spatial characteristics, such as shape and size. This limitation can hinder the customization of the generated clothing item other than the ability to accurately match the user's intended style. Therefore, we propose to leverage garment sketches to enrich the textual input with additional spatial fine-grained details. We achieve this following the same approach described for pose map conditioning. The final spatial input of our denoising network is $\\gamma = [z_t; m; \\mathcal{E}(I_M); p; s], [p; s] \\in \\mathbb{R}^{h \\times w \\times (18 + 1)}$ , $p$ and $s$ are obtained by resizing $P$ and $S$ to match the latent space dimensions. In the case of sketches, we only condition the early steps of the denoising process as the final steps have little influence on the shapes [2].", + "bbox": [ + 75, + 580, + 468, + 852 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Mask Composition. To preserve the model identity when performing human-centric inpainting, we perform mask composition as the final step of the proposed approach.", + "bbox": [ + 75, + 854, + 468, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Defining $\\hat{I} = \\mathcal{D}(z_0) \\in \\mathbb{R}^{H \\times W \\times 3}$ as the output of the decoder $\\mathcal{D}$ and $M_{\\mathrm{head}} \\in \\{0,1\\}^{H \\times W \\times 1}$ as the model face binary mask of the image $I$ , the final output image $\\tilde{I}$ is obtained as follows: $\\tilde{I} = M_{\\mathrm{head}} \\odot I + (1 - M_{\\mathrm{head}}) \\odot \\hat{I}$ , where $\\odot$ denotes the element-wise multiplication operator.", + "bbox": [ + 496, + 89, + 890, + 167 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Training and Inference", + "text_level": 1, + "bbox": [ + 498, + 175, + 714, + 191 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As in standard latent diffusion models, given an encoded input $z = \\mathcal{E}(I)$ , the proposed denoising network is trained to predict the noise stochastically added to $z$ . The corresponding objective function can be specified as", + "bbox": [ + 496, + 199, + 890, + 260 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nL = \\mathbb {E} _ {\\mathcal {E} (I), Y, \\epsilon \\sim \\mathcal {N} (0, 1), t, \\mathcal {E} (I _ {M}), m, p, s} \\left[ \\| \\epsilon - \\epsilon_ {\\theta} (\\gamma , \\psi) \\| _ {2} ^ {2} \\right], \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 514, + 284, + 890, + 316 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\gamma = [z_{t};m;\\mathcal{E}(I_{M});p;s]$ and $\\psi = [t;T_E(Y)]$", + "bbox": [ + 498, + 316, + 841, + 333 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Classifier-Free Guidance. Classifier-free guidance is an inference technique that requires the denoising network to work both conditioned and unconditioned. This method modifies the unconditional model predicted noise moving it toward the conditioned one. Specifically, the predicted diffusion process at time $t$ , given the generic condition $c$ , is computed as follows:", + "bbox": [ + 496, + 335, + 890, + 441 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\epsilon} _ {\\theta} \\left(z _ {t} | c\\right) = \\epsilon_ {\\theta} \\left(z _ {t} | \\emptyset\\right) + \\alpha \\cdot \\left(\\epsilon_ {\\theta} \\left(z _ {t} | c\\right) - \\epsilon_ {\\theta} \\left(z _ {t} | \\emptyset\\right)\\right), \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 537, + 452, + 890, + 469 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\epsilon_{\\theta}(z_t|c)$ is the predicted noise at time $t$ given the condition $c$ , $\\epsilon_{\\theta}(z_t|\\emptyset)$ is the predicted noise at time $t$ given the null condition, and the guidance scale $\\alpha$ controls the degree of extrapolation towards the condition.", + "bbox": [ + 496, + 479, + 890, + 539 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Since our model deals with three conditions (i.e. text, pose map, and sketch), we use the fast variant multi-condition classifier-free guidance proposed in [1]. Instead of performing the classifier-free guidance according to each condition probability, it computes the direction of the joint probability of all the conditions $\\Delta_{\\mathrm{joint}}^t = \\epsilon_\\theta (z_t|\\{c_i\\}_{i = 1}^{i = N}) - \\epsilon_\\theta (z_t|\\emptyset)$ :", + "bbox": [ + 496, + 541, + 890, + 647 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {\\epsilon} _ {\\theta} \\left(z _ {t} \\mid \\left\\{c _ {i} \\right\\} _ {i = 1} ^ {i = N}\\right) = \\epsilon_ {\\theta} \\left(z _ {t} \\mid \\emptyset\\right) + \\alpha \\cdot \\Delta_ {\\text {j o i n t}} ^ {t}. \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 563, + 656, + 890, + 675 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "This reduces the number of feed-forward executions from $N + 1$ to 2.", + "bbox": [ + 500, + 685, + 890, + 714 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Unconditional Training. Ensuring the ability of the denoising model to work both with and without conditions is achieved by replacing at training time the condition with a null one according to a fixed probability. This approach allows the model to learn from both conditional and unconditional samples, resulting in improved mode coverage and sample fidelity. Moreover, this technique also allows the model to optionally use the control signals at prediction time. Since our approach considers multiple conditions, we propose to extend the input masking to each condition independently. Experiments show that tuning this parameter can effectively affect the quality of the final result.", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "23396", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Collecting Multimodal Fashion Datasets", + "text_level": 1, + "bbox": [ + 76, + 89, + 436, + 107 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Currently available datasets for fashion image generation often contain low-resolution images and lack all the required multimodal information needed to perform the task previously described. For this reason, the collection of new multimodal datasets for the fashion domain plays a crucial role to advance research in the field. To this aim, we start from two recent high-resolution fashion datasets introduced for the virtual try-on task, namely Dress Code [28] and VITON-HD [7], and extend them with textual sentences and garment sketches. Both datasets include image pairs with a resolution of $1024 \\times 768$ , each composed of a garment image and a reference model wearing the given fashion item. In this section, we introduce a framework to semi-automatically annotate fashion images with multimodal information and provide a complete description of how to enrich Dress Code and VITON-HD with garment-related text and sketches. We call our extended versions of these datasets Dress Code Multimodal and VITON-HD Multimodal, respectively. Sample images and multimodal data of the collected datasets can be found in Fig. 3.", + "bbox": [ + 75, + 114, + 472, + 417 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Dataset Collection and Annotation", + "text_level": 1, + "bbox": [ + 76, + 426, + 377, + 441 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Data Preparation. We start the annotation from the Dress Code dataset, which contains more than 53k model-garment pairs of multiple categories. As a first step, we need to associate each garment with a textual description containing fashion-specific and non-generic terms which are sufficiently detailed but not extremely lengthy to be exploited for constraining the generation. Motivated by recent findings in the field showing that humans tend to describe fashion items using only a few words [3], we propose to use noun chunks (i.e. short textual sentences composed of a noun along with its modifiers) that can effectively capture important information while reducing unnecessary words or details. Given that manually annotating all the images would be time-consuming and resource-intensive1, we propose a novel framework to semi-automatically annotate the dataset using noun chunks. Firstly, domain-specific captions are collected from two available fashion datasets, namely FashionIQ [50] and Fashion200k [12], standardizing them with word lemmatization and eventually reducing each word to its root form with the NLTK library2. Then, we extract noun chunks from the captions, filtering the results by removing all textual items that start with or contain special characters. After this pre-processing stage, we obtain more than 60k unique noun chunks, divided into three different categories (i.e. upper-body clothes, lower-body clothes, and dresses).", + "bbox": [ + 75, + 450, + 472, + 829 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "1Since the Dress Code dataset consists of over 53k fashion items and assuming that each annotation requires approximately 5 minutes, a single annotator working 8 hours per day, 5 days a week, and 260 working days per year would take more than 2 years to complete the annotation task.", + "bbox": [ + 75, + 838, + 468, + 887 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "2 https://www.nltk.org/", + "bbox": [ + 96, + 887, + 217, + 898 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/1494a2f1d8b5661e28509a21f1bc94c1438e70f3476478bc3c481902a4c7d5e7.jpg", + "image_caption": [ + "Figure 3. Sample images and multimodal data from our newly collected datasets." + ], + "image_footnote": [], + "bbox": [ + 501, + 87, + 893, + 252 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/1b21f52b47cc8d4e4e6a58955b4e30978c230dac00fc57e05c8e6cd72b7742b5.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
DatasetTextPoseSketch# Images# Products# Unique Texts# Unique Words
VITON-HD [7]X✓X27,35813,679--
Dress Code [28]X✓X107,58453,792--
Be Your Own Prada [56]✓✓X78,979N/A3,972445
DF-Multimodal [19]✓✓X44,096N/A10,25377
VITON-HD Multimodal✓✓✓27,35813,6795,1431,613
Dress Code Multimodal✓✓✓107,58453,79225,5962,995
", + "bbox": [ + 501, + 294, + 890, + 392 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Table 1. Comparison of Dress Code and VITON-HD Multimodal with other fashion datasets with multimodal annotations.", + "bbox": [ + 500, + 401, + 890, + 429 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To determine the most relevant noun chunks for each garment, we employ the CLIP model [34] and its open-source adaptation (i.e. OpenCLIP [49]). We select the VIT-L14@336 and $\\mathrm{RN50\\times 64}$ models for CLIP, and the VIT-L14, ViT-H14, and ViT-g14 models for OpenCLIP. Prompt ensembling is performed to improve the results and, for each image, we select 25 noun chunks based on the top-5 noun chunks per model rated by cosine similarity between image and text embeddings, avoiding repetitions.", + "bbox": [ + 496, + 439, + 890, + 575 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Fine-Grained Textual Annotation. To ensure the accuracy and representativeness of our annotations, we manually annotate a significant portion of Dress Code images. In particular, we select the three most representative noun chunks, among the 25 automatically associated, with each garment image. To minimize the annotation time, we develop a custom annotation tool that constrains the annotation time to an average time of 60 seconds per item and allows the annotator to manually insert noun chunks in the case that none of the automatically extracted ones are suitable for the image. Overall, we manually annotate 26,400 different garments (8,800 for each category) out of the 53,792 products included in the dataset, ensuring to include all fashion items of the original test set [28].", + "bbox": [ + 496, + 579, + 890, + 790 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Coarse-Grained Textual Annotation. To complete the annotation, we first finetune the OpenCLIP ViT-B32 model, pre-trained on the English portion of the LAION5B dataset [40], using the newly annotated image-text pairs. We then use this model and the collected set of noun chunks to automatically tag all the remaining elements of the Dress Code dataset with the three most similar noun chunks, al", + "bbox": [ + 496, + 795, + 890, + 898 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "23397", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "ways determined via cosine similarity between multimodal embeddings. We employ the same strategy also to automatically annotate all garment images of the VITON-HD dataset. In this case, since this dataset only contains upper-body clothes, we limit the table noun chunks to the ones describing upper-body garments.", + "bbox": [ + 75, + 90, + 470, + 181 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Extracting Sketches. The introduction of garment sketches can provide valuable design details that are not easily discernible from text alone. In this way, the dataset can provide a more accurate and comprehensive representation of the garments, leading to improved quality and better control of the generated design details. To extract sketches for both Dress Code and VITON-HD datasets, we employ PiDiNet [43], a pre-trained edge detection network.", + "bbox": [ + 75, + 185, + 468, + 306 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Given that the selected datasets have originally been introduced for virtual try-on, they consist of both paired and unpaired test sets. While for the paired set we can directly use the human parsing mask to extract the garment of interest worn by the model and then feed it to the edge detection network, for the unpaired set we need to first create a warped version of the in-shop garment matching the body pose and shape of the target model. Following virtual try-on methods [47, 52], we train a geometric transformation module that performs a thin-plate spline transformation [36] of the input garment and then refines the warped result using a U-Net model [38]. From each warped garment, we extract the sketch image enabling the use of the proposed solution even in unpaired settings.", + "bbox": [ + 75, + 306, + 470, + 518 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison with Other Datasets", + "text_level": 1, + "bbox": [ + 76, + 527, + 366, + 542 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The only two text-to-image generation datasets available in the fashion domain [19, 56] are both based on images from the DeepFashion dataset [22]. While the dataset introduced in [56] contains short textual descriptions, DeepFashion-Multimodal [19] is annotated with attributes (e.g. category, color, fabric, etc.) that can be composed in longer captions. In Table 1, we summarize the main statistics of the publicly available datasets textual annotations compared with those of our newly extended datasets. As can be seen, our datasets contain more variety in terms of textual items and words, confirming the appropriateness of our annotation procedure and enabling a more personalized control of the generation process. Also, it is worth noting that the other datasets have no in-shop garment images making them difficult to employ in our case.", + "bbox": [ + 75, + 551, + 468, + 777 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experimental Evaluation", + "text_level": 1, + "bbox": [ + 76, + 791, + 310, + 808 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Implementation Details and Competitors", + "text_level": 1, + "bbox": [ + 76, + 816, + 426, + 832 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training and Inference. All models are trained on the original splits of the Dress Code Multimodal and VITON-HD Multimodal datasets on a single NVIDIA A100 GPU for 150k steps, using a batch size of 16, a learning rate", + "bbox": [ + 75, + 839, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "of $10^{-5}$ with a linear warmup for the first 500 iterations, and AdamW [23] as optimizer with weight decay $10^{-2}$ . To speed up training and save memory, we use mixed precision [26]. We set both the fraction of steps conditioned by the sketch and the portion of masked conditions during training to 0.2. During inference, we employ the DDIM [42] with 50 steps as noise scheduler and set the classifier-free guidance parameter $\\alpha$ to 7.5.", + "bbox": [ + 496, + 90, + 890, + 212 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Baselines and Competitors. As first competitor, we use the out-of-the-box implementation of the inpainting Stable Diffusion pipeline3 provided by Huggingface. Moreover, we adapt two existing models, namely FICE [33] and SDEdit [25], to work on our setting. In particular, we retrain all main components of the FICE model on the newly collected datasets. We employ the same resolution used by the authors (i.e. $256 \\times 256$ ), downsampling each image to $256 \\times 192$ and applying padding to match the desired size (which is then removed during evaluation). To compare our model with a different conditioning strategy, we employ the approach proposed in [25] using our model trained only with text and human poses as input modalities and perform the sketch guidance using as starting latent variable the sketch image with added random noise. Following the original paper instructions, we use 0.8 as the strength parameter.", + "bbox": [ + 496, + 215, + 892, + 458 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.2. Evaluation Metrics", + "text_level": 1, + "bbox": [ + 500, + 467, + 683, + 482 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To assess the realism of generated images, we employ the Fréchet Inception Distance (FID) [16] and the Kernel Inception Distance (KID) [4]. For both metrics, we adopt the implementation proposed in [32]. Instead, to evaluate the adherence of the image to the textual conditioning input, we employ the CLIP Score (CLIP-S) [15] provided in the TorchMetrics library [9], using the OpenCLIP ViT-H/14 model as cross-modal architecture. We compute the score on the inpainted region of the generated output pasted on a $224 \\times 224$ white background.", + "bbox": [ + 496, + 491, + 890, + 642 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Pose Distance (PD). We propose a novel pose distance metric that measures the coherence of human body poses between the generated image and the original one estimating the distance between the human keypoints extracted from the original and generated images. Specifically, we employ the OpenPifPaf [20] human pose estimation network and compute the $\\ell_2$ distance between each pair of real-generated corresponding estimated keypoints. We only consider the keypoints involved in the generation (i.e. that falls in the mask $M$ ) and weigh each keypoints distance with the detector confidence to take into account any estimation errors.", + "bbox": [ + 496, + 646, + 890, + 811 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Sketch Distance (SD). To quantify the adherence of the generated image to the sketch constraint, we propose a novel sketch distance metric. To compute the score, we extract the segmentation map of the original and generated", + "bbox": [ + 496, + 816, + 890, + 877 + ], + "page_idx": 5 + }, + { + "type": "page_footnote", + "text": "3https://huggingface.co/runwayml/stable-diffusion-inpainting", + "bbox": [ + 514, + 886, + 843, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "23398", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/cf9d9b28e7f0ad9143ba64f5e9a456f4dcc6d50c7e582a8adf44e3fe4f281195.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModelResolutionModalitiesDress Code MultimodalVITON-HD Multimodal
TextPoseSketchFID ↓KID ↓CLIP-S ↑PD ↓SD ↓FID ↓KID ↓CLIP-S ↑PD ↓SD ↓
Paired setting
Stable Diffusion [37]256×192✓17.059.2828.714.62-15.186.3830.405.04-
FICE [33]256×192✓✓30.6323.5428.726.87-49.4444.7429.266.37-
MGD (ours)256×192✓✓5.571.6731.332.37-10.113.1431.852.90-
Paired setting
Stable Diffusion [37]512×384✓17.439.4829.189.240.46716.286.5630.7010.780.410
SDEdit [25]512×384✓✓✓10.195.0329.215.410.39813.074.6630.586.760.306
MGD (ours)512×384✓✓✓5.742.1131.684.720.37410.603.2632.395.940.253
Unpaired setting
Stable Diffusion [37]256×192✓19.1110.6927.535.07-17.377.5528.405.50-
FICE [33]256×192✓✓34.1426.8626.037.15-52.7448.5825.946.58-
MGD (ours)256×192✓✓7.012.1929.582.96-11.543.1829.953.30-
Unpaired setting
Stable Diffusion [37]512×384✓19.5510.8028.029.890.58218.457.8728.7411.600.561
SDEdit [25]512×384✓✓✓11.385.6927.106.160.50915.125.6728.617.350.406
MGD (ours)512×384✓✓✓7.732.8230.046.790.45812.813.8630.757.220.317
", + "bbox": [ + 81, + 89, + 890, + 343 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d7ae560265dea6f00f89ae23e0b50e84ac478623ac1bcb5b538436a773d6728e.jpg", + "table_caption": [ + "Table 2. Quantitative results on the Dress Code Multimodal and VITON-HD Multimodal datasets for both paired and unpaired settings ." + ], + "table_footnote": [], + "table_body": "
ModelModalitiesDress Code Multimodal
TextPoseSketchFID ↓KID ↓CLIP-S ↑PD ↓SD ↓
MGD (ours)✓6.192.1531.796.160.411
✓✓6.312.3331.675.310.405
✓✓✓5.742.1131.684.720.374
ModelModalitiesVITON-HD Multimodal
TextPoseSketchFID ↓KID ↓CLIP-S ↑PD ↓SD ↓
MGD (ours)✓11.393.5232.167.830.339
✓✓11.073.3632.276.770.318
✓✓✓10.603.2632.395.940.253
", + "bbox": [ + 81, + 378, + 465, + 523 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "garments using an off-the-shelf clothing segmentation network $^{4}$ . We then use the segmented garment area to extract garment sketches using the PIDInet [43] edge detector network. The final score is the mean squared error between these sketches, weighting the per-pixel results on the inverse pixel frequency of the activated pixels. More details about these proposed metrics can be found in the supplementary.", + "bbox": [ + 75, + 574, + 468, + 681 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Experimental Results", + "text_level": 1, + "bbox": [ + 76, + 688, + 279, + 705 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Comparison with Other Methods. We test our proposal for the paired and unpaired settings of the considered datasets. In the former, the conditions (e.g. text, sketch) refers to the garment the model is wearing, while in the latter, the in-shop garment differs from the worn one. In Table 2, we report the quantitative results on Dress Code Multimodal and VITON-HD Multimodal in comparison with the aforementioned competitors. As can be seen, the proposed MGD model consistently outperforms competitors, in terms of realism (i.e. FID and KID) and coherency with input modalities (i.e. CLIP-S, PD, and SD). In particu", + "bbox": [ + 75, + 712, + 468, + 878 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/14e67e88cad2ecb0f7b416781d6509b6c69acf0ef2f5430d3c96f9bf4dbb53ca.jpg", + "table_caption": [ + "Table 3. Performance analysis on the paired setting of both datasets as input modalities vary." + ], + "table_footnote": [], + "table_body": "
ModalitiesRealismMultimodal Coherence
TextPoseSketchStable Diff.FICESDEditStable Diff.FICESDEdit
Dress✓70.82--65.32--
✓✓70.7396.26-65.1584.48-
✓✓✓70.29-52.5465.38-66.23
VITON✓67.03--57.76--
✓✓66.1793.84-73.7383.46-
✓✓✓60.71-53.4469.47-59.34
", + "bbox": [ + 501, + 378, + 890, + 478 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Table 4. User study results on the unpaired setting of both datasets. We report the percentage of times an image from MGD is preferred against a competitor. Comparisons with FICE [33] are performed at $256 \\times 192$ resolution.", + "bbox": [ + 498, + 487, + 890, + 542 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "lar, when considering low-resolution results, we notice that FICE [33] can produce images fairly consistent with the text conditioning, albeit less realistic than other methods. While Stable Diffusion [37] enhances image realism, it fails to preserve the input model's pose due to the lack of pose information in the inputs. It is noteworthy that in this case, we compare the results of our model only using text and pose map as conditioning since both considered competitors are not conditioned on sketches. For this reason, we do not report the results in terms of sketch distance for low-resolution images.", + "bbox": [ + 496, + 563, + 890, + 731 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In the high-resolution setting, we evaluate instead our MGD method using all multimodal conditions (i.e. text, pose map, and sketch) as input. In this case, we compare MGD with Stable Diffusion [37] plus SDEdit [25], where we use our text-pose conditioned denoising network as SDEdit backbone. Our findings indicate that Stable Diffusion performs worse in terms of the pose distance than both SDEdit and MGD, owing to the lack of pose information in the inputs. It is noteworthy that SDEdit performs worse than our model in all metrics. We attribute this behavior to the way sketch conditioning happens. In SDEdit,", + "bbox": [ + 496, + 734, + 890, + 902 + ], + "page_idx": 6 + }, + { + "type": "page_footnote", + "text": "4https://github.com/levindabhi/cloth-segmentation", + "bbox": [ + 94, + 886, + 362, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "23399", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/6ec420afa290eb1e9fbc2f2ba28ad4a9ac7cb30c22fa8b19f5b3e67adb70fcfc.jpg", + "image_caption": [ + "Figure 4. Sample generated images on Dress Code Multimodal and VITON-HD Multimodal (bottom left) using all multimodal inputs." + ], + "image_footnote": [], + "bbox": [ + 76, + 87, + 483, + 380 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/1a62e80663022be32de11fd9b9ce70962ee0b23552e560afc74440dcea6af1f6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 483, + 88, + 890, + 378 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "it occurs only at the beginning by initializing $z_{t}$ using the sketch image with added noise according to the conditioning strength, while our model conditions the denoising process in multiple steps, depending on the sketch conditioning parameter. Qualitative results reported in Fig. 4 highlight how our model better follows the given conditions and generate high-realistic images.", + "bbox": [ + 75, + 419, + 470, + 525 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To validate our results based on human judgment, we conduct a user study that evaluates both the realism of the generation and the adherence to multimodal inputs. Overall we collect about 7k evaluations involving more than 150 users. Additional details are reported in the supplementary. Table 4 shows the user study results. Also in this case our model outperforms the competitors, thus confirming the effectiveness of our proposal.", + "bbox": [ + 75, + 527, + 468, + 650 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Varying Input Modalities. In Table 3, we study the behavior of our MGD model when the input modalities are masked (i.e. where we feed the model with a zero tensor instead of the considered modality). In particular, we focus on the CLIP-S for text adherence and on the newly proposed pose and sketch distances for the pose and sketch coherency, respectively. Notice that the text input anchors the CLIP-S metrics of all experiments and makes them comparable in all cases. Starting from the fully conditioned model (i.e. text, pose, sketch), we mask the sketch. As the decrease of the sketch distance in Table 3 confirms, this input actually influences the generation process of our model in both the considered datasets. Also, this modality slightly affects the pose distance as the sketch implicitly contains information about the model's body pose. We further mask the pose map input and compare the output with previous results. In", + "bbox": [ + 75, + 657, + 470, + 902 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/c9dbe5d4e464705675714775d23fe35b26cb2cd5fbf538b3a9ba0162c416d518.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
Uncond. PortionSketch Cond.Dress Code Multimodal
FID ↓KID ↓CLIP-S ↑PD ↓SD ↓
0.11.09.643.7630.247.660.459
0.21.08.623.2429.067.510.430
0.31.010.934.7828.477.690.432
0.20.88.563.2829.317.320.433
0.20.68.433.2129.517.320.436
0.20.48.113.0029.797.130.440
0.20.27.732.8230.046.790.458
0.20.07.822.8529.936.260.519
", + "bbox": [ + 503, + 417, + 888, + 554 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 5. Ablation analysis of our complete model varying the unconditioning portion during training and the sketch conditioning steps. Results refer to the unpaired setting.", + "bbox": [ + 498, + 563, + 890, + 606 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "this case, we can also notice a consistent difference with the text-only conditioned model, according to all metrics except CLIP-S as expected. These results confirm that our MGD model can effectively deal with the conditions in a disentangled way, making them optional.", + "bbox": [ + 496, + 621, + 890, + 698 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Unconditional Training and Sketch Conditioning. In Table 5, we inquire about the fully conditioned network performance according to the variance of the portion of unconditional training. Additionally, we evaluate the results by varying the fraction of sketch conditioning steps. As can be seen, the best results are achieved by using 0.2 for both parameters. In particular, for unconditional training, we train three different models (i.e. with 0.1, 0.2, and 0.3). When evaluating the sketch conditioning parameter, we test our model with values between 0 and 1 with a stride of 0.2. It is worth noting that the sketch distance consistently decreases as the number of sketch conditioning steps increases, showing the robustness of the approach.", + "bbox": [ + 496, + 704, + 892, + 901 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "23400", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 90, + 194, + 104 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "The Multimodal Garment Designer proposed in this paper is the first latent diffusion model defined for human-centric fashion image editing, conditioned by multimodal inputs such as text, body pose, and sketches. The novel architecture, trained on two new semi-automatically annotated datasets and evaluated with standard and newly proposed metrics, as well as by user studies, is very promising. The result is one of the first successful attempts to mimic the designers' job in the creative process of fashion design and could be a starting point for a capillary adoption of diffusion models in creative industries, oversight by human input.", + "bbox": [ + 75, + 114, + 472, + 282 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgments", + "text_level": 1, + "bbox": [ + 76, + 294, + 235, + 311 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work has partially been supported by the European Commission under the PNRR-M4C2 project \"FAIR - Future Artificial Intelligence Research\" and the European Horizon 2020 Programme (grant number 101004545 - ReInHerit), and by the PRIN project \"CREATIVE: CRoss-modal understanding and gEnerATIon of Visual and tExtual content\" (CUP B87G22000460001), co-funded by the Italian Ministry of University.", + "bbox": [ + 75, + 319, + 472, + 441 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 76, + 453, + 174, + 468 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Omri Avrahami, Thomas Hayes, Oran Gafni, Sonal Gupta, Yaniv Taigman, Devi Parikh, Dani Lischinski, Ohad Fried, and Xi Yin. 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In ICCV, 2017. 2, 5, 6" + ], + "bbox": [ + 501, + 92, + 890, + 895 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "23402", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Multimodal Garment Designer_ Human-Centric Latent Diffusion Models for Fashion Image Editing/aa9f2273-dd32-4864-b87b-f6ed07d1408f_model.json b/2023/Multimodal Garment Designer_ Human-Centric Latent Diffusion Models for Fashion Image Editing/aa9f2273-dd32-4864-b87b-f6ed07d1408f_model.json new file mode 100644 index 0000000000000000000000000000000000000000..f5345e61c0f3d69c59f21abe12db0e594e8812c5 --- /dev/null +++ b/2023/Multimodal Garment Designer_ Human-Centric Latent Diffusion Models for Fashion Image Editing/aa9f2273-dd32-4864-b87b-f6ed07d1408f_model.json @@ -0,0 +1,1991 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.145, + 0.131, + 0.828, + 0.177 + ], + "angle": 0, + "content": "Multimodal Garment Designer: Human-Centric Latent Diffusion Models for Fashion Image Editing" + }, + { + "type": "text", + "bbox": [ + 0.17, + 0.203, + 0.802, + 0.294 + ], + "angle": 0, + "content": "Alberto Baldrati\\(^{1,3,*}\\), Davide Morelli\\(^{2,3,*}\\), Giuseppe Cartella\\(^{2}\\), Marcella Cornia\\(^{2}\\), Marco Bertini\\(^{1}\\), Rita Cucchiara\\(^{2,4}\\) \n\\(^{1}\\)University of Florence, Italy \\(^{2}\\)University of Modena and Reggio Emilia, Italy \\(^{3}\\)University of Pisa, Italy \\(^{4}\\)IIT-CNR, Italy \n\\(^{1}\\{name.surname\\} @unifi.it\\) \\(^{2}\\{name.surname\\} @unimore.it\\)" + }, + { + "type": "image", + "bbox": [ + 0.08, + 0.306, + 0.891, + 0.578 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.582, + 0.893, + 0.61 + ], + "angle": 0, + "content": "Figure 1. In this work, we propose a novel multimodal garment designer framework based on latent diffusion models that can generate a novel fashion image conditioned on text, human keypoints, and a garment sketch." + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.623, + 0.314, + 0.639 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.645, + 0.474, + 0.901 + ], + "angle": 0, + "content": "Fashion illustration is used by designers to communicate their vision and to bring the design idea from conceptualization to realization, showing how clothes interact with the human body. In this context, computer vision can thus be used to improve the fashion design process. Differently from previous works that mainly focused on the virtual try-on of garments, we propose the task of multimodal-conditioned fashion image editing, guiding the generation of human-centric fashion images by following multimodal prompts, such as text, human body poses, and garment sketches. We tackle this problem by proposing a new architecture based on latent diffusion models, an approach that has not been used before in the fashion domain. Given the lack of existing datasets suitable for the task, we also extend two existing fashion datasets, namely Dress Code and VITON-HD, with multimodal annotations collected in a semi-automatic manner. Experimental re" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.621, + 0.893, + 0.698 + ], + "angle": 0, + "content": "sults on these new datasets demonstrate the effectiveness of our proposal, both in terms of realism and coherence with the given multimodal inputs. Source code and collected multimodal annotations are publicly available at: https://github.com/aimagelab/multimodal-garment-designer." + }, + { + "type": "title", + "bbox": [ + 0.501, + 0.717, + 0.633, + 0.733 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.743, + 0.894, + 0.879 + ], + "angle": 0, + "content": "Computer Vision research has always paid much attention both to the human person and to fashion-related problems, especially working on the recognition and retrieval of clothing items [11, 22], the recommendation of similar garments [8, 18, 39], and the virtual try-on of clothes and accessories [7, 13, 27, 28, 47, 52]. In the last years, some research efforts have been dedicated to the text-conditioned image editing task where, given a model image and a textual description of a garment, the goal is to generate the" + }, + { + "type": "page_footnote", + "bbox": [ + 0.525, + 0.888, + 0.637, + 0.9 + ], + "angle": 0, + "content": "*Equal contribution." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23393" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "input model wearing a new clothing item corresponding to the given textual description. In this context, only a few works [19,33,56] have been proposed, exclusively employing GAN-based approaches for the generative step." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.155, + 0.471, + 0.412 + ], + "angle": 0, + "content": "Recently, diffusion models [10, 17, 30, 41] have attracted more and more attention due to their outstanding generation capabilities, allowing the improvement of a variety of downstream tasks in several domains, while their applicability to the fashion domain is still unexplored. Many different solutions have been introduced and can roughly be identified based on the denoising conditions used to guide the diffusion process, which can enable greater control of the synthesized output. A particular type of diffusion model has been proposed in [37] that, instead of applying the diffusion process in the pixel space, defines the forward and the reverse processes in the latent space of a pre-trained autoencoder, becoming one of the leading choices thanks to its reduced computational cost. Although this solution can generate highly realistic images, it does not perform well in human-centric generation tasks and can not deal with multiple conditioning signals to guide the generation phase." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.413, + 0.47, + 0.639 + ], + "angle": 0, + "content": "In this work, we address an extended and more general framework and define the new task of multimodal-conditioned fashion image editing, which allows guiding the generative process via multimodal prompts while preserving the identity and body shape of a given person (Fig. 1). To tackle this task, we introduce a new architecture, called Multimodal Garment Designer (MGD), that emulates the process of a designer conceiving a new garment on a model shape, based on preliminary indications provided through a textual sentence or a garment sketch. In particular, starting from Stable Diffusion [37], we propose a denoising network that can be conditioned by multiple modalities and also takes into account the pose consistency between input and generated images, thus improving the effectiveness of human-centric diffusion models." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.643, + 0.47, + 0.809 + ], + "angle": 0, + "content": "To address the newly proposed task, we present a semiautomatic framework to extend existing datasets with multimodal data. Specifically, we start from two famous virtual try-on datasets (i.e. Dress Code [28] and VITON-HD [7]) and extend them with textual descriptions and garment sketches. Experimental results on the two proposed multimodal fashion benchmarks show both quantitatively and qualitatively that our proposed architecture generates high-quality images based on the given multimodal inputs and outperforms all considered competitors and baselines, also according to human evaluations." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.47, + 0.903 + ], + "angle": 0, + "content": "To sum up, our contributions are as follows: (1) We propose a novel task of multimodal-conditioned fashion image editing, which entails the use of multimodal data to guide the generation. (2) We introduce a new human-centric generative architecture based on latent diffusion models, capable of following multimodal prompts while preserving the" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.183 + ], + "angle": 0, + "content": "model's characteristics. (3) To tackle the new task, we extend two existing fashion datasets with textual sentences and garment sketches devising a semi-automatic annotation framework. (4) Extensive experiments demonstrate that the proposed approach outperforms other competitors in terms of realism and coherence with multimodal inputs." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.194, + 0.642, + 0.209 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.219, + 0.892, + 0.49 + ], + "angle": 0, + "content": "Text-Guided Image Generation. Creating an image that faithfully reflects the provided textual prompt is the goal of text-to-image synthesis. In this context, early approaches were based on GANs [45, 51, 53, 55], while most recent solutions exploit the effectiveness of diffusion models [31, 35, 37]. In the fashion domain, only a few attempts of text-to-image synthesis have been proposed [19, 33, 56]. Specifically, Zhu et al. [56] presented a GAN-based solution that generates the final image conditioned on both textual descriptions and semantic layouts. A different approach is the one introduced in [33], where a latent code regularization technique is employed to augment the GAN inversion process by exploiting CLIP textual embeddings [34] to guide the image editing process. Instead, Jiang et al. [19] proposed an architecture that synthesizes full-body images by mapping the textual descriptions of clothing items into one-hot vectors, limiting however the expressiveness capability of the conditioning signal." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.494, + 0.892, + 0.765 + ], + "angle": 0, + "content": "Multimodal Image Generation with Diffusion Models. A related line of works aims to condition existing diffusion models on different modalities thus enabling greater control over the generation process [5, 6, 25, 29, 48]. For example, Choi et al. [6] proposed to refine the generative process of an unconditional denoising diffusion probabilistic model [30] by matching each latent variable with the given reference image. On a different line, the approach introduced in [25] adds noise to a stroke-based input and applies the reverse stochastic differential equation to synthesize images, without additional training. Wang et al. [48], instead, proposed to learn a highly semantic latent space and perform conditional finetuning for each downstream task to map the guidance signals to the pre-trained space. Other recent works proposed to add sketches as additional conditioning signals, either concatenating them with the model input [5] or training an MLP-based edge predictor to map latent features to spatial maps [46]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.766, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Among contemporary works that aim to condition pretrained latent diffusion models, ControlNet [54] proposes to extend the Stable Diffusion model [37] with an additional conditioning input. This process involves creating two versions of the original model's weights: one that remains fixed and unchanged (locked copy) and another that can be updated during training (trainable copy). The purpose of this is to allow the trainable version to learn the newly introduced condition while the locked version retains the origi" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "23394" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.087, + 0.892, + 0.264 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.274, + 0.893, + 0.304 + ], + "angle": 0, + "content": "Figure 2. Overview of the proposed Multimodal Garment Designer (MGD), a human-centric latent diffusion model conditioned on multiple modalities (i.e. text, human pose, and garment sketch)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.316, + 0.47, + 0.361 + ], + "angle": 0, + "content": "nal model knowledge. On the other hand, T2I-Adapter [29] learns modality-specific adapter modules that enable Stable Diffusion conditioning on new modalities." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.362, + 0.47, + 0.437 + ], + "angle": 0, + "content": "In contrast, we focus on the fashion domain and propose a human-centric architecture based on latent diffusion models that directly exploits the conditioning of textual sentences and other modalities such as human body poses and garment sketches." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.451, + 0.251, + 0.468 + ], + "angle": 0, + "content": "3. Proposed Method" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.476, + 0.471, + 0.749 + ], + "angle": 0, + "content": "In this section, we propose a novel task to automatically edit a human-centric fashion image conditioned on multiple modalities. Specifically, given the model image \\( I \\in \\mathbb{R}^{H \\times W \\times 3} \\), its pose map \\( P \\in \\mathbb{R}^{H \\times W \\times 18} \\) where the channels represent the human keypoints, a textual description \\( Y \\) of a garment, and a sketch of the same \\( S \\in \\mathbb{R}^{H \\times W \\times 1} \\), we want to generate a new image \\( \\tilde{I} \\in \\mathbb{R}^{H \\times W \\times 3} \\) that retains the information of the input model while substituting the target garment according to the multimodal inputs. To tackle the task, we propose a novel latent diffusion approach, called Multimodal Garment Designer (MGD), that can effectively combine multimodal information when generating the new image \\( \\tilde{I} \\). Our proposed architecture is a general framework that can be easily extended to other modalities such as texture and 3d information. We strongly believe this task can foster research in the field and enhance the design process of new fashion items with greater customization. An overview of our model is shown in Fig. 2." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.757, + 0.218, + 0.772 + ], + "angle": 0, + "content": "3.1. Preliminaries" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.78, + 0.471, + 0.902 + ], + "angle": 0, + "content": "While diffusion models [41] are latent variable architectures that work in the same dimensionality of the data (i.e. in the pixel space), latent diffusion models (LDMs) [37] operate in the latent space of a pre-trained autoencoder achieving higher computational efficiency while preserving the generation quality. In our work, we leverage the Stable Diffusion model [37], a text-to-image implementation of LDMs as a starting point to perform multimodal condition-" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.316, + 0.895, + 0.513 + ], + "angle": 0, + "content": "ing for human-centric fashion image editing. Stable Diffusion is composed of an autoencoder with an encoder \\(\\mathcal{E}\\) and a decoder \\(\\mathcal{D}\\), a text-time-conditional U-Net denoising model \\(\\epsilon_{\\theta}\\), and a CLIP-based text encoder \\(T_{E}\\) taking as input a text \\(Y\\). The encoder \\(\\mathcal{E}\\) compresses an image \\(I\\) into a lower-dimensional latent space defined in \\(\\mathbb{R}^{h\\times w\\times 4}\\), where \\(h = H / 8\\) and \\(w = W / 8\\). The decoder \\(\\mathcal{D}\\) performs the opposite operation, decoding a latent variable into the pixel space. For the sake of clarity, we define the \\(\\epsilon_{\\theta}\\) convolutional input (i.e. \\(z_{t}\\) in this case) as spatial input \\(\\gamma\\) because of the property of convolutions to preserve the spatial structure and the attention conditioning input as \\(\\psi\\). The denoising network \\(\\epsilon_{\\theta}\\) is trained according to the following loss:" + }, + { + "type": "equation", + "bbox": [ + 0.554, + 0.522, + 0.892, + 0.543 + ], + "angle": 0, + "content": "\\[\nL = \\mathbb {E} _ {\\mathcal {E} (I), Y, \\epsilon \\sim \\mathcal {N} (0, 1), t} \\left[ \\| \\epsilon - \\epsilon_ {\\theta} (\\gamma , \\psi) \\| _ {2} ^ {2} \\right], \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.551, + 0.892, + 0.583 + ], + "angle": 0, + "content": "where \\(t\\) is the diffusing time step, \\(\\gamma = z_{t}\\), \\(\\psi = [t;T_{E}(Y)]\\), and \\(\\epsilon \\sim \\mathcal{N}(0,1)\\) is the Gaussian noise added to \\(\\mathcal{E}(I)\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.591, + 0.774, + 0.607 + ], + "angle": 0, + "content": "3.2. Human-Centric Image Editing" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.613, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Our task aims to generate a new image \\(\\tilde{I}\\), by replacing in the input image \\(I\\) the target garment using multimodal inputs, while preserving the model's identity and physical characteristics. As a natural consequence, this task can be identified as a particular type of inpainting tailored for human body data. Instead of using a standard text-to-image model, we perform inpainting concatenating along the channel dimension of the denoising network input \\(z_{t}\\) an encoded masked image \\(\\mathcal{E}(I_M)\\) and the relative resized binary inpainting mask \\(m\\in \\{0,1\\}^{h\\times w\\times 1}\\), which is derived from the original inpainting mask \\(M\\in \\{0,1\\}^{H\\times W\\times 1}\\). Since here, the spatial input of the denoising network is \\(\\gamma = [z_t;m;\\mathcal{E}(I_M)],\\gamma \\in \\mathbb{R}^{h\\times w\\times 9}\\). Thanks to the fully convolutional nature of the encoder \\(\\mathcal{E}\\) and the decoder \\(\\mathcal{D}\\), this LDMs-based architecture can preserve the spatial information in the latent space. Exploiting this feature, our method can thus optionally add conditioning constraints to the generation. In particular, we propose to add two generation constraints in addition to the textual information: the" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23395" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.137 + ], + "angle": 0, + "content": "model pose map \\( P \\) to preserve the original human pose of the input model and the garment sketch \\( S \\) to allow the final users to better condition the garment generation process." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.14, + 0.473, + 0.579 + ], + "angle": 0, + "content": "Pose Map Conditioning. In most cases [21, 24, 44], inpainting is performed with the objective of either removing or entirely replacing the content of the masked region. However, in our task, we aim to remove all information regarding the garment worn by the model while preserving the model's body information and identity. Thus, we propose to improve the garment inpainting process by using the bounding box of the segmentation mask along with pose map information representing body keypoints. This approach enables the preservation of the model's physical characteristics in the masked region while allowing the inpainting of garments with different shapes. Differently from conventional inpainting techniques, we focus on selectively retaining and discarding specific information within the masked region to achieve the desired outcome. To enhance the performance of the denoising network with human body keypoints, we modify the first convolution layer of the network by adding 18 additional channels, one for each keypoint. Adding new inputs usually would require retraining the model from scratch, thus consuming time, data, and resources, especially in the case of data-hungry models like the diffusion ones. Therefore, we propose to extend the kernels of the pre-trained input layer of the denoising network with randomly initialized weights sampled from a uniform distribution [14] and retrain the whole network. This consistently reduces the number of training steps and enables training with less data. Our experiments show that such improvement enhances the consistency of the body information between the generated image and the original one." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.581, + 0.47, + 0.853 + ], + "angle": 0, + "content": "Incorporating Sketches. Fully describing a garment using only textual descriptions is a challenging task due to the complexity and ambiguity of natural language. While text can convey specific attributes like style, color, and patterns of a garment, it may not provide sufficient information about its spatial characteristics, such as shape and size. This limitation can hinder the customization of the generated clothing item other than the ability to accurately match the user's intended style. Therefore, we propose to leverage garment sketches to enrich the textual input with additional spatial fine-grained details. We achieve this following the same approach described for pose map conditioning. The final spatial input of our denoising network is \\(\\gamma = [z_t; m; \\mathcal{E}(I_M); p; s], [p; s] \\in \\mathbb{R}^{h \\times w \\times (18 + 1)}\\), \\(p\\) and \\(s\\) are obtained by resizing \\(P\\) and \\(S\\) to match the latent space dimensions. In the case of sketches, we only condition the early steps of the denoising process as the final steps have little influence on the shapes [2]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.902 + ], + "angle": 0, + "content": "Mask Composition. To preserve the model identity when performing human-centric inpainting, we perform mask composition as the final step of the proposed approach." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.09, + 0.892, + 0.168 + ], + "angle": 0, + "content": "Defining \\(\\hat{I} = \\mathcal{D}(z_0) \\in \\mathbb{R}^{H \\times W \\times 3}\\) as the output of the decoder \\(\\mathcal{D}\\) and \\(M_{\\mathrm{head}} \\in \\{0,1\\}^{H \\times W \\times 1}\\) as the model face binary mask of the image \\(I\\), the final output image \\(\\tilde{I}\\) is obtained as follows: \\(\\tilde{I} = M_{\\mathrm{head}} \\odot I + (1 - M_{\\mathrm{head}}) \\odot \\hat{I}\\), where \\(\\odot\\) denotes the element-wise multiplication operator." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.176, + 0.715, + 0.192 + ], + "angle": 0, + "content": "3.3. Training and Inference" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.2, + 0.892, + 0.261 + ], + "angle": 0, + "content": "As in standard latent diffusion models, given an encoded input \\( z = \\mathcal{E}(I) \\), the proposed denoising network is trained to predict the noise stochastically added to \\( z \\). The corresponding objective function can be specified as" + }, + { + "type": "equation", + "bbox": [ + 0.516, + 0.285, + 0.891, + 0.317 + ], + "angle": 0, + "content": "\\[\nL = \\mathbb {E} _ {\\mathcal {E} (I), Y, \\epsilon \\sim \\mathcal {N} (0, 1), t, \\mathcal {E} (I _ {M}), m, p, s} \\left[ \\| \\epsilon - \\epsilon_ {\\theta} (\\gamma , \\psi) \\| _ {2} ^ {2} \\right], \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.317, + 0.843, + 0.334 + ], + "angle": 0, + "content": "where \\(\\gamma = [z_{t};m;\\mathcal{E}(I_{M});p;s]\\) and \\(\\psi = [t;T_E(Y)]\\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.336, + 0.892, + 0.442 + ], + "angle": 0, + "content": "Classifier-Free Guidance. Classifier-free guidance is an inference technique that requires the denoising network to work both conditioned and unconditioned. This method modifies the unconditional model predicted noise moving it toward the conditioned one. Specifically, the predicted diffusion process at time \\( t \\), given the generic condition \\( c \\), is computed as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.538, + 0.453, + 0.892, + 0.47 + ], + "angle": 0, + "content": "\\[\n\\hat {\\epsilon} _ {\\theta} \\left(z _ {t} | c\\right) = \\epsilon_ {\\theta} \\left(z _ {t} | \\emptyset\\right) + \\alpha \\cdot \\left(\\epsilon_ {\\theta} \\left(z _ {t} | c\\right) - \\epsilon_ {\\theta} \\left(z _ {t} | \\emptyset\\right)\\right), \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.481, + 0.891, + 0.54 + ], + "angle": 0, + "content": "where \\(\\epsilon_{\\theta}(z_t|c)\\) is the predicted noise at time \\(t\\) given the condition \\(c\\), \\(\\epsilon_{\\theta}(z_t|\\emptyset)\\) is the predicted noise at time \\(t\\) given the null condition, and the guidance scale \\(\\alpha\\) controls the degree of extrapolation towards the condition." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.542, + 0.892, + 0.648 + ], + "angle": 0, + "content": "Since our model deals with three conditions (i.e. text, pose map, and sketch), we use the fast variant multi-condition classifier-free guidance proposed in [1]. Instead of performing the classifier-free guidance according to each condition probability, it computes the direction of the joint probability of all the conditions \\(\\Delta_{\\mathrm{joint}}^t = \\epsilon_\\theta (z_t|\\{c_i\\}_{i = 1}^{i = N}) - \\epsilon_\\theta (z_t|\\emptyset)\\):" + }, + { + "type": "equation", + "bbox": [ + 0.564, + 0.657, + 0.891, + 0.676 + ], + "angle": 0, + "content": "\\[\n\\hat {\\epsilon} _ {\\theta} \\left(z _ {t} \\mid \\left\\{c _ {i} \\right\\} _ {i = 1} ^ {i = N}\\right) = \\epsilon_ {\\theta} \\left(z _ {t} \\mid \\emptyset\\right) + \\alpha \\cdot \\Delta_ {\\text {j o i n t}} ^ {t}. \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.686, + 0.891, + 0.715 + ], + "angle": 0, + "content": "This reduces the number of feed-forward executions from \\( N + 1 \\) to 2." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Unconditional Training. Ensuring the ability of the denoising model to work both with and without conditions is achieved by replacing at training time the condition with a null one according to a fixed probability. This approach allows the model to learn from both conditional and unconditional samples, resulting in improved mode coverage and sample fidelity. Moreover, this technique also allows the model to optionally use the control signals at prediction time. Since our approach considers multiple conditions, we propose to extend the input masking to each condition independently. Experiments show that tuning this parameter can effectively affect the quality of the final result." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.957 + ], + "angle": 0, + "content": "23396" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.09, + 0.437, + 0.108 + ], + "angle": 0, + "content": "4. Collecting Multimodal Fashion Datasets" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.116, + 0.473, + 0.419 + ], + "angle": 0, + "content": "Currently available datasets for fashion image generation often contain low-resolution images and lack all the required multimodal information needed to perform the task previously described. For this reason, the collection of new multimodal datasets for the fashion domain plays a crucial role to advance research in the field. To this aim, we start from two recent high-resolution fashion datasets introduced for the virtual try-on task, namely Dress Code [28] and VITON-HD [7], and extend them with textual sentences and garment sketches. Both datasets include image pairs with a resolution of \\(1024 \\times 768\\), each composed of a garment image and a reference model wearing the given fashion item. In this section, we introduce a framework to semi-automatically annotate fashion images with multimodal information and provide a complete description of how to enrich Dress Code and VITON-HD with garment-related text and sketches. We call our extended versions of these datasets Dress Code Multimodal and VITON-HD Multimodal, respectively. Sample images and multimodal data of the collected datasets can be found in Fig. 3." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.428, + 0.379, + 0.443 + ], + "angle": 0, + "content": "4.1. Dataset Collection and Annotation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.452, + 0.473, + 0.83 + ], + "angle": 0, + "content": "Data Preparation. We start the annotation from the Dress Code dataset, which contains more than 53k model-garment pairs of multiple categories. As a first step, we need to associate each garment with a textual description containing fashion-specific and non-generic terms which are sufficiently detailed but not extremely lengthy to be exploited for constraining the generation. Motivated by recent findings in the field showing that humans tend to describe fashion items using only a few words [3], we propose to use noun chunks (i.e. short textual sentences composed of a noun along with its modifiers) that can effectively capture important information while reducing unnecessary words or details. Given that manually annotating all the images would be time-consuming and resource-intensive1, we propose a novel framework to semi-automatically annotate the dataset using noun chunks. Firstly, domain-specific captions are collected from two available fashion datasets, namely FashionIQ [50] and Fashion200k [12], standardizing them with word lemmatization and eventually reducing each word to its root form with the NLTK library2. Then, we extract noun chunks from the captions, filtering the results by removing all textual items that start with or contain special characters. After this pre-processing stage, we obtain more than 60k unique noun chunks, divided into three different categories (i.e. upper-body clothes, lower-body clothes, and dresses)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.839, + 0.47, + 0.888 + ], + "angle": 0, + "content": "1Since the Dress Code dataset consists of over 53k fashion items and assuming that each annotation requires approximately 5 minutes, a single annotator working 8 hours per day, 5 days a week, and 260 working days per year would take more than 2 years to complete the annotation task." + }, + { + "type": "text", + "bbox": [ + 0.098, + 0.888, + 0.218, + 0.9 + ], + "angle": 0, + "content": "2 https://www.nltk.org/" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.088, + 0.895, + 0.253 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.5, + 0.263, + 0.892, + 0.289 + ], + "angle": 0, + "content": "Figure 3. Sample images and multimodal data from our newly collected datasets." + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.295, + 0.891, + 0.393 + ], + "angle": 0, + "content": "
DatasetTextPoseSketch# Images# Products# Unique Texts# Unique Words
VITON-HD [7]X✓X27,35813,679--
Dress Code [28]X✓X107,58453,792--
Be Your Own Prada [56]✓✓X78,979N/A3,972445
DF-Multimodal [19]✓✓X44,096N/A10,25377
VITON-HD Multimodal✓✓✓27,35813,6795,1431,613
Dress Code Multimodal✓✓✓107,58453,79225,5962,995
" + }, + { + "type": "table_caption", + "bbox": [ + 0.5, + 0.402, + 0.892, + 0.43 + ], + "angle": 0, + "content": "Table 1. Comparison of Dress Code and VITON-HD Multimodal with other fashion datasets with multimodal annotations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.44, + 0.892, + 0.576 + ], + "angle": 0, + "content": "To determine the most relevant noun chunks for each garment, we employ the CLIP model [34] and its open-source adaptation (i.e. OpenCLIP [49]). We select the VIT-L14@336 and \\(\\mathrm{RN50\\times 64}\\) models for CLIP, and the VIT-L14, ViT-H14, and ViT-g14 models for OpenCLIP. Prompt ensembling is performed to improve the results and, for each image, we select 25 noun chunks based on the top-5 noun chunks per model rated by cosine similarity between image and text embeddings, avoiding repetitions." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.58, + 0.892, + 0.791 + ], + "angle": 0, + "content": "Fine-Grained Textual Annotation. To ensure the accuracy and representativeness of our annotations, we manually annotate a significant portion of Dress Code images. In particular, we select the three most representative noun chunks, among the 25 automatically associated, with each garment image. To minimize the annotation time, we develop a custom annotation tool that constrains the annotation time to an average time of 60 seconds per item and allows the annotator to manually insert noun chunks in the case that none of the automatically extracted ones are suitable for the image. Overall, we manually annotate 26,400 different garments (8,800 for each category) out of the 53,792 products included in the dataset, ensuring to include all fashion items of the original test set [28]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.9 + ], + "angle": 0, + "content": "Coarse-Grained Textual Annotation. To complete the annotation, we first finetune the OpenCLIP ViT-B32 model, pre-trained on the English portion of the LAION5B dataset [40], using the newly annotated image-text pairs. We then use this model and the collected set of noun chunks to automatically tag all the remaining elements of the Dress Code dataset with the three most similar noun chunks, al" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23397" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.182 + ], + "angle": 0, + "content": "ways determined via cosine similarity between multimodal embeddings. We employ the same strategy also to automatically annotate all garment images of the VITON-HD dataset. In this case, since this dataset only contains upper-body clothes, we limit the table noun chunks to the ones describing upper-body garments." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.186, + 0.47, + 0.307 + ], + "angle": 0, + "content": "Extracting Sketches. The introduction of garment sketches can provide valuable design details that are not easily discernible from text alone. In this way, the dataset can provide a more accurate and comprehensive representation of the garments, leading to improved quality and better control of the generated design details. To extract sketches for both Dress Code and VITON-HD datasets, we employ PiDiNet [43], a pre-trained edge detection network." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.308, + 0.471, + 0.519 + ], + "angle": 0, + "content": "Given that the selected datasets have originally been introduced for virtual try-on, they consist of both paired and unpaired test sets. While for the paired set we can directly use the human parsing mask to extract the garment of interest worn by the model and then feed it to the edge detection network, for the unpaired set we need to first create a warped version of the in-shop garment matching the body pose and shape of the target model. Following virtual try-on methods [47, 52], we train a geometric transformation module that performs a thin-plate spline transformation [36] of the input garment and then refines the warped result using a U-Net model [38]. From each warped garment, we extract the sketch image enabling the use of the proposed solution even in unpaired settings." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.529, + 0.367, + 0.543 + ], + "angle": 0, + "content": "4.2. Comparison with Other Datasets" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.552, + 0.47, + 0.779 + ], + "angle": 0, + "content": "The only two text-to-image generation datasets available in the fashion domain [19, 56] are both based on images from the DeepFashion dataset [22]. While the dataset introduced in [56] contains short textual descriptions, DeepFashion-Multimodal [19] is annotated with attributes (e.g. category, color, fabric, etc.) that can be composed in longer captions. In Table 1, we summarize the main statistics of the publicly available datasets textual annotations compared with those of our newly extended datasets. As can be seen, our datasets contain more variety in terms of textual items and words, confirming the appropriateness of our annotation procedure and enabling a more personalized control of the generation process. Also, it is worth noting that the other datasets have no in-shop garment images making them difficult to employ in our case." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.792, + 0.312, + 0.809 + ], + "angle": 0, + "content": "5. Experimental Evaluation" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.817, + 0.427, + 0.833 + ], + "angle": 0, + "content": "5.1. Implementation Details and Competitors" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Training and Inference. All models are trained on the original splits of the Dress Code Multimodal and VITON-HD Multimodal datasets on a single NVIDIA A100 GPU for 150k steps, using a batch size of 16, a learning rate" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.213 + ], + "angle": 0, + "content": "of \\(10^{-5}\\) with a linear warmup for the first 500 iterations, and AdamW [23] as optimizer with weight decay \\(10^{-2}\\). To speed up training and save memory, we use mixed precision [26]. We set both the fraction of steps conditioned by the sketch and the portion of masked conditions during training to 0.2. During inference, we employ the DDIM [42] with 50 steps as noise scheduler and set the classifier-free guidance parameter \\(\\alpha\\) to 7.5." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.217, + 0.893, + 0.459 + ], + "angle": 0, + "content": "Baselines and Competitors. As first competitor, we use the out-of-the-box implementation of the inpainting Stable Diffusion pipeline3 provided by Huggingface. Moreover, we adapt two existing models, namely FICE [33] and SDEdit [25], to work on our setting. In particular, we retrain all main components of the FICE model on the newly collected datasets. We employ the same resolution used by the authors (i.e. \\(256 \\times 256\\)), downsampling each image to \\(256 \\times 192\\) and applying padding to match the desired size (which is then removed during evaluation). To compare our model with a different conditioning strategy, we employ the approach proposed in [25] using our model trained only with text and human poses as input modalities and perform the sketch guidance using as starting latent variable the sketch image with added random noise. Following the original paper instructions, we use 0.8 as the strength parameter." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.468, + 0.684, + 0.483 + ], + "angle": 0, + "content": "5.2. Evaluation Metrics" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.492, + 0.892, + 0.643 + ], + "angle": 0, + "content": "To assess the realism of generated images, we employ the Fréchet Inception Distance (FID) [16] and the Kernel Inception Distance (KID) [4]. For both metrics, we adopt the implementation proposed in [32]. Instead, to evaluate the adherence of the image to the textual conditioning input, we employ the CLIP Score (CLIP-S) [15] provided in the TorchMetrics library [9], using the OpenCLIP ViT-H/14 model as cross-modal architecture. We compute the score on the inpainted region of the generated output pasted on a \\(224 \\times 224\\) white background." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.647, + 0.892, + 0.812 + ], + "angle": 0, + "content": "Pose Distance (PD). We propose a novel pose distance metric that measures the coherence of human body poses between the generated image and the original one estimating the distance between the human keypoints extracted from the original and generated images. Specifically, we employ the OpenPifPaf [20] human pose estimation network and compute the \\(\\ell_2\\) distance between each pair of real-generated corresponding estimated keypoints. We only consider the keypoints involved in the generation (i.e. that falls in the mask \\(M\\)) and weigh each keypoints distance with the detector confidence to take into account any estimation errors." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.817, + 0.892, + 0.878 + ], + "angle": 0, + "content": "Sketch Distance (SD). To quantify the adherence of the generated image to the sketch constraint, we propose a novel sketch distance metric. To compute the score, we extract the segmentation map of the original and generated" + }, + { + "type": "page_footnote", + "bbox": [ + 0.516, + 0.887, + 0.844, + 0.901 + ], + "angle": 0, + "content": "3https://huggingface.co/runwayml/stable-diffusion-inpainting" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23398" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.082, + 0.09, + 0.892, + 0.344 + ], + "angle": 0, + "content": "
ModelResolutionModalitiesDress Code MultimodalVITON-HD Multimodal
TextPoseSketchFID ↓KID ↓CLIP-S ↑PD ↓SD ↓FID ↓KID ↓CLIP-S ↑PD ↓SD ↓
Paired setting
Stable Diffusion [37]256×192✓17.059.2828.714.62-15.186.3830.405.04-
FICE [33]256×192✓✓30.6323.5428.726.87-49.4444.7429.266.37-
MGD (ours)256×192✓✓5.571.6731.332.37-10.113.1431.852.90-
Paired setting
Stable Diffusion [37]512×384✓17.439.4829.189.240.46716.286.5630.7010.780.410
SDEdit [25]512×384✓✓✓10.195.0329.215.410.39813.074.6630.586.760.306
MGD (ours)512×384✓✓✓5.742.1131.684.720.37410.603.2632.395.940.253
Unpaired setting
Stable Diffusion [37]256×192✓19.1110.6927.535.07-17.377.5528.405.50-
FICE [33]256×192✓✓34.1426.8626.037.15-52.7448.5825.946.58-
MGD (ours)256×192✓✓7.012.1929.582.96-11.543.1829.953.30-
Unpaired setting
Stable Diffusion [37]512×384✓19.5510.8028.029.890.58218.457.8728.7411.600.561
SDEdit [25]512×384✓✓✓11.385.6927.106.160.50915.125.6728.617.350.406
MGD (ours)512×384✓✓✓7.732.8230.046.790.45812.813.8630.757.220.317
" + }, + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.351, + 0.88, + 0.368 + ], + "angle": 0, + "content": "Table 2. Quantitative results on the Dress Code Multimodal and VITON-HD Multimodal datasets for both paired and unpaired settings ." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.379, + 0.467, + 0.525 + ], + "angle": 0, + "content": "
ModelModalitiesDress Code Multimodal
TextPoseSketchFID ↓KID ↓CLIP-S ↑PD ↓SD ↓
MGD (ours)✓6.192.1531.796.160.411
✓✓6.312.3331.675.310.405
✓✓✓5.742.1131.684.720.374
ModelModalitiesVITON-HD Multimodal
TextPoseSketchFID ↓KID ↓CLIP-S ↑PD ↓SD ↓
MGD (ours)✓11.393.5232.167.830.339
✓✓11.073.3632.276.770.318
✓✓✓10.603.2632.395.940.253
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.535, + 0.471, + 0.565 + ], + "angle": 0, + "content": "Table 3. Performance analysis on the paired setting of both datasets as input modalities vary." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.575, + 0.47, + 0.682 + ], + "angle": 0, + "content": "garments using an off-the-shelf clothing segmentation network\\(^{4}\\). We then use the segmented garment area to extract garment sketches using the PIDInet [43] edge detector network. The final score is the mean squared error between these sketches, weighting the per-pixel results on the inverse pixel frequency of the activated pixels. More details about these proposed metrics can be found in the supplementary." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.689, + 0.28, + 0.706 + ], + "angle": 0, + "content": "5.3. Experimental Results" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.713, + 0.47, + 0.879 + ], + "angle": 0, + "content": "Comparison with Other Methods. We test our proposal for the paired and unpaired settings of the considered datasets. In the former, the conditions (e.g. text, sketch) refers to the garment the model is wearing, while in the latter, the in-shop garment differs from the worn one. In Table 2, we report the quantitative results on Dress Code Multimodal and VITON-HD Multimodal in comparison with the aforementioned competitors. As can be seen, the proposed MGD model consistently outperforms competitors, in terms of realism (i.e. FID and KID) and coherency with input modalities (i.e. CLIP-S, PD, and SD). In particu" + }, + { + "type": "table", + "bbox": [ + 0.503, + 0.379, + 0.891, + 0.479 + ], + "angle": 0, + "content": "
ModalitiesRealismMultimodal Coherence
TextPoseSketchStable Diff.FICESDEditStable Diff.FICESDEdit
Dress✓70.82--65.32--
✓✓70.7396.26-65.1584.48-
✓✓✓70.29-52.5465.38-66.23
VITON✓67.03--57.76--
✓✓66.1793.84-73.7383.46-
✓✓✓60.71-53.4469.47-59.34
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.488, + 0.892, + 0.543 + ], + "angle": 0, + "content": "Table 4. User study results on the unpaired setting of both datasets. We report the percentage of times an image from MGD is preferred against a competitor. Comparisons with FICE [33] are performed at \\(256 \\times 192\\) resolution." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.564, + 0.892, + 0.732 + ], + "angle": 0, + "content": "lar, when considering low-resolution results, we notice that FICE [33] can produce images fairly consistent with the text conditioning, albeit less realistic than other methods. While Stable Diffusion [37] enhances image realism, it fails to preserve the input model's pose due to the lack of pose information in the inputs. It is noteworthy that in this case, we compare the results of our model only using text and pose map as conditioning since both considered competitors are not conditioned on sketches. For this reason, we do not report the results in terms of sketch distance for low-resolution images." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.735, + 0.892, + 0.903 + ], + "angle": 0, + "content": "In the high-resolution setting, we evaluate instead our MGD method using all multimodal conditions (i.e. text, pose map, and sketch) as input. In this case, we compare MGD with Stable Diffusion [37] plus SDEdit [25], where we use our text-pose conditioned denoising network as SDEdit backbone. Our findings indicate that Stable Diffusion performs worse in terms of the pose distance than both SDEdit and MGD, owing to the lack of pose information in the inputs. It is noteworthy that SDEdit performs worse than our model in all metrics. We attribute this behavior to the way sketch conditioning happens. In SDEdit," + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.363, + 0.901 + ], + "angle": 0, + "content": "4https://github.com/levindabhi/cloth-segmentation" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "23399" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.078, + 0.088, + 0.485, + 0.381 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.484, + 0.089, + 0.892, + 0.38 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.077, + 0.389, + 0.871, + 0.406 + ], + "angle": 0, + "content": "Figure 4. Sample generated images on Dress Code Multimodal and VITON-HD Multimodal (bottom left) using all multimodal inputs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.42, + 0.471, + 0.526 + ], + "angle": 0, + "content": "it occurs only at the beginning by initializing \\( z_{t} \\) using the sketch image with added noise according to the conditioning strength, while our model conditions the denoising process in multiple steps, depending on the sketch conditioning parameter. Qualitative results reported in Fig. 4 highlight how our model better follows the given conditions and generate high-realistic images." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.529, + 0.47, + 0.651 + ], + "angle": 0, + "content": "To validate our results based on human judgment, we conduct a user study that evaluates both the realism of the generation and the adherence to multimodal inputs. Overall we collect about 7k evaluations involving more than 150 users. Additional details are reported in the supplementary. Table 4 shows the user study results. Also in this case our model outperforms the competitors, thus confirming the effectiveness of our proposal." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Varying Input Modalities. In Table 3, we study the behavior of our MGD model when the input modalities are masked (i.e. where we feed the model with a zero tensor instead of the considered modality). In particular, we focus on the CLIP-S for text adherence and on the newly proposed pose and sketch distances for the pose and sketch coherency, respectively. Notice that the text input anchors the CLIP-S metrics of all experiments and makes them comparable in all cases. Starting from the fully conditioned model (i.e. text, pose, sketch), we mask the sketch. As the decrease of the sketch distance in Table 3 confirms, this input actually influences the generation process of our model in both the considered datasets. Also, this modality slightly affects the pose distance as the sketch implicitly contains information about the model's body pose. We further mask the pose map input and compare the output with previous results. In" + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.418, + 0.89, + 0.555 + ], + "angle": 0, + "content": "
Uncond. PortionSketch Cond.Dress Code Multimodal
FID ↓KID ↓CLIP-S ↑PD ↓SD ↓
0.11.09.643.7630.247.660.459
0.21.08.623.2429.067.510.430
0.31.010.934.7828.477.690.432
0.20.88.563.2829.317.320.433
0.20.68.433.2129.517.320.436
0.20.48.113.0029.797.130.440
0.20.27.732.8230.046.790.458
0.20.07.822.8529.936.260.519
" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.564, + 0.892, + 0.607 + ], + "angle": 0, + "content": "Table 5. Ablation analysis of our complete model varying the unconditioning portion during training and the sketch conditioning steps. Results refer to the unpaired setting." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.622, + 0.892, + 0.699 + ], + "angle": 0, + "content": "this case, we can also notice a consistent difference with the text-only conditioned model, according to all metrics except CLIP-S as expected. These results confirm that our MGD model can effectively deal with the conditions in a disentangled way, making them optional." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.893, + 0.902 + ], + "angle": 0, + "content": "Unconditional Training and Sketch Conditioning. In Table 5, we inquire about the fully conditioned network performance according to the variance of the portion of unconditional training. Additionally, we evaluate the results by varying the fraction of sketch conditioning steps. As can be seen, the best results are achieved by using 0.2 for both parameters. In particular, for unconditional training, we train three different models (i.e. with 0.1, 0.2, and 0.3). When evaluating the sketch conditioning parameter, we test our model with values between 0 and 1 with a stride of 0.2. It is worth noting that the sketch distance consistently decreases as the number of sketch conditioning steps increases, showing the robustness of the approach." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "23400" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.078, + 0.091, + 0.196, + 0.106 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.115, + 0.473, + 0.283 + ], + "angle": 0, + "content": "The Multimodal Garment Designer proposed in this paper is the first latent diffusion model defined for human-centric fashion image editing, conditioned by multimodal inputs such as text, body pose, and sketches. The novel architecture, trained on two new semi-automatically annotated datasets and evaluated with standard and newly proposed metrics, as well as by user studies, is very promising. The result is one of the first successful attempts to mimic the designers' job in the creative process of fashion design and could be a starting point for a capillary adoption of diffusion models in creative industries, oversight by human input." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.295, + 0.236, + 0.312 + ], + "angle": 0, + "content": "Acknowledgments" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.32, + 0.473, + 0.442 + ], + "angle": 0, + "content": "This work has partially been supported by the European Commission under the PNRR-M4C2 project \"FAIR - Future Artificial Intelligence Research\" and the European Horizon 2020 Programme (grant number 101004545 - ReInHerit), and by the PRIN project \"CREATIVE: CRoss-modal understanding and gEnerATIon of Visual and tExtual content\" (CUP B87G22000460001), co-funded by the Italian Ministry of University." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.454, + 0.175, + 0.469 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.478, + 0.47, + 0.534 + ], + "angle": 0, + "content": "[1] Omri Avrahami, Thomas Hayes, Oran Gafni, Sonal Gupta, Yaniv Taigman, Devi Parikh, Dani Lischinski, Ohad Fried, and Xi Yin. 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In ICCV, 2017. 2, 5, 6" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.896 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23402" + } + ] +] \ No newline at end of file diff --git a/2023/Multimodal Garment Designer_ Human-Centric Latent Diffusion Models for Fashion Image Editing/aa9f2273-dd32-4864-b87b-f6ed07d1408f_origin.pdf b/2023/Multimodal Garment Designer_ Human-Centric Latent Diffusion Models for Fashion Image Editing/aa9f2273-dd32-4864-b87b-f6ed07d1408f_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..13009332304eaf3c9673739eb99ac2f5b35eec0f --- /dev/null +++ b/2023/Multimodal Garment Designer_ Human-Centric Latent Diffusion Models for Fashion Image Editing/aa9f2273-dd32-4864-b87b-f6ed07d1408f_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:a31822f0569dcdaa5eb6099b5df1020d4e917d7252c1cb3a00eb3bbb871b1076 +size 2605557 diff --git a/2023/Multimodal Garment Designer_ Human-Centric Latent Diffusion Models for Fashion Image Editing/full.md b/2023/Multimodal Garment Designer_ Human-Centric Latent Diffusion Models for Fashion Image Editing/full.md new file mode 100644 index 0000000000000000000000000000000000000000..761fafa4455545f7fff1477db63159ea381a85db --- /dev/null +++ b/2023/Multimodal Garment Designer_ Human-Centric Latent Diffusion Models for Fashion Image Editing/full.md @@ -0,0 +1,269 @@ +# Multimodal Garment Designer: Human-Centric Latent Diffusion Models for Fashion Image Editing + +Alberto Baldrati $^{1,3,*}$ , Davide Morelli $^{2,3,*}$ , Giuseppe Cartella $^{2}$ , Marcella Cornia $^{2}$ , Marco Bertini $^{1}$ , Rita Cucchiara $^{2,4}$ $^{1}$ University of Florence, Italy $^{2}$ University of Modena and Reggio Emilia, Italy $^{3}$ University of Pisa, Italy $^{4}$ IIT-CNR, Italy + $^{1}\{name.surname\} @unifi.it$ $^{2}\{name.surname\} @unimore.it$ + +![](images/de1a89aa7daef0d48b62e7f9012deb1f609e61fcfddba5319c8acb57de13da7c.jpg) +Figure 1. In this work, we propose a novel multimodal garment designer framework based on latent diffusion models that can generate a novel fashion image conditioned on text, human keypoints, and a garment sketch. + +# Abstract + +Fashion illustration is used by designers to communicate their vision and to bring the design idea from conceptualization to realization, showing how clothes interact with the human body. In this context, computer vision can thus be used to improve the fashion design process. Differently from previous works that mainly focused on the virtual try-on of garments, we propose the task of multimodal-conditioned fashion image editing, guiding the generation of human-centric fashion images by following multimodal prompts, such as text, human body poses, and garment sketches. We tackle this problem by proposing a new architecture based on latent diffusion models, an approach that has not been used before in the fashion domain. Given the lack of existing datasets suitable for the task, we also extend two existing fashion datasets, namely Dress Code and VITON-HD, with multimodal annotations collected in a semi-automatic manner. Experimental re + +sults on these new datasets demonstrate the effectiveness of our proposal, both in terms of realism and coherence with the given multimodal inputs. Source code and collected multimodal annotations are publicly available at: https://github.com/aimagelab/multimodal-garment-designer. + +# 1. Introduction + +Computer Vision research has always paid much attention both to the human person and to fashion-related problems, especially working on the recognition and retrieval of clothing items [11, 22], the recommendation of similar garments [8, 18, 39], and the virtual try-on of clothes and accessories [7, 13, 27, 28, 47, 52]. In the last years, some research efforts have been dedicated to the text-conditioned image editing task where, given a model image and a textual description of a garment, the goal is to generate the + +input model wearing a new clothing item corresponding to the given textual description. In this context, only a few works [19,33,56] have been proposed, exclusively employing GAN-based approaches for the generative step. + +Recently, diffusion models [10, 17, 30, 41] have attracted more and more attention due to their outstanding generation capabilities, allowing the improvement of a variety of downstream tasks in several domains, while their applicability to the fashion domain is still unexplored. Many different solutions have been introduced and can roughly be identified based on the denoising conditions used to guide the diffusion process, which can enable greater control of the synthesized output. A particular type of diffusion model has been proposed in [37] that, instead of applying the diffusion process in the pixel space, defines the forward and the reverse processes in the latent space of a pre-trained autoencoder, becoming one of the leading choices thanks to its reduced computational cost. Although this solution can generate highly realistic images, it does not perform well in human-centric generation tasks and can not deal with multiple conditioning signals to guide the generation phase. + +In this work, we address an extended and more general framework and define the new task of multimodal-conditioned fashion image editing, which allows guiding the generative process via multimodal prompts while preserving the identity and body shape of a given person (Fig. 1). To tackle this task, we introduce a new architecture, called Multimodal Garment Designer (MGD), that emulates the process of a designer conceiving a new garment on a model shape, based on preliminary indications provided through a textual sentence or a garment sketch. In particular, starting from Stable Diffusion [37], we propose a denoising network that can be conditioned by multiple modalities and also takes into account the pose consistency between input and generated images, thus improving the effectiveness of human-centric diffusion models. + +To address the newly proposed task, we present a semiautomatic framework to extend existing datasets with multimodal data. Specifically, we start from two famous virtual try-on datasets (i.e. Dress Code [28] and VITON-HD [7]) and extend them with textual descriptions and garment sketches. Experimental results on the two proposed multimodal fashion benchmarks show both quantitatively and qualitatively that our proposed architecture generates high-quality images based on the given multimodal inputs and outperforms all considered competitors and baselines, also according to human evaluations. + +To sum up, our contributions are as follows: (1) We propose a novel task of multimodal-conditioned fashion image editing, which entails the use of multimodal data to guide the generation. (2) We introduce a new human-centric generative architecture based on latent diffusion models, capable of following multimodal prompts while preserving the + +model's characteristics. (3) To tackle the new task, we extend two existing fashion datasets with textual sentences and garment sketches devising a semi-automatic annotation framework. (4) Extensive experiments demonstrate that the proposed approach outperforms other competitors in terms of realism and coherence with multimodal inputs. + +# 2. Related Work + +Text-Guided Image Generation. Creating an image that faithfully reflects the provided textual prompt is the goal of text-to-image synthesis. In this context, early approaches were based on GANs [45, 51, 53, 55], while most recent solutions exploit the effectiveness of diffusion models [31, 35, 37]. In the fashion domain, only a few attempts of text-to-image synthesis have been proposed [19, 33, 56]. Specifically, Zhu et al. [56] presented a GAN-based solution that generates the final image conditioned on both textual descriptions and semantic layouts. A different approach is the one introduced in [33], where a latent code regularization technique is employed to augment the GAN inversion process by exploiting CLIP textual embeddings [34] to guide the image editing process. Instead, Jiang et al. [19] proposed an architecture that synthesizes full-body images by mapping the textual descriptions of clothing items into one-hot vectors, limiting however the expressiveness capability of the conditioning signal. + +Multimodal Image Generation with Diffusion Models. A related line of works aims to condition existing diffusion models on different modalities thus enabling greater control over the generation process [5, 6, 25, 29, 48]. For example, Choi et al. [6] proposed to refine the generative process of an unconditional denoising diffusion probabilistic model [30] by matching each latent variable with the given reference image. On a different line, the approach introduced in [25] adds noise to a stroke-based input and applies the reverse stochastic differential equation to synthesize images, without additional training. Wang et al. [48], instead, proposed to learn a highly semantic latent space and perform conditional finetuning for each downstream task to map the guidance signals to the pre-trained space. Other recent works proposed to add sketches as additional conditioning signals, either concatenating them with the model input [5] or training an MLP-based edge predictor to map latent features to spatial maps [46]. + +Among contemporary works that aim to condition pretrained latent diffusion models, ControlNet [54] proposes to extend the Stable Diffusion model [37] with an additional conditioning input. This process involves creating two versions of the original model's weights: one that remains fixed and unchanged (locked copy) and another that can be updated during training (trainable copy). The purpose of this is to allow the trainable version to learn the newly introduced condition while the locked version retains the origi + +![](images/35fd084287558bf2793f24e73ada81b2c93658bc4a35b3ccb6a18845922e39c3.jpg) +Figure 2. Overview of the proposed Multimodal Garment Designer (MGD), a human-centric latent diffusion model conditioned on multiple modalities (i.e. text, human pose, and garment sketch). + +nal model knowledge. On the other hand, T2I-Adapter [29] learns modality-specific adapter modules that enable Stable Diffusion conditioning on new modalities. + +In contrast, we focus on the fashion domain and propose a human-centric architecture based on latent diffusion models that directly exploits the conditioning of textual sentences and other modalities such as human body poses and garment sketches. + +# 3. Proposed Method + +In this section, we propose a novel task to automatically edit a human-centric fashion image conditioned on multiple modalities. Specifically, given the model image $I \in \mathbb{R}^{H \times W \times 3}$ , its pose map $P \in \mathbb{R}^{H \times W \times 18}$ where the channels represent the human keypoints, a textual description $Y$ of a garment, and a sketch of the same $S \in \mathbb{R}^{H \times W \times 1}$ , we want to generate a new image $\tilde{I} \in \mathbb{R}^{H \times W \times 3}$ that retains the information of the input model while substituting the target garment according to the multimodal inputs. To tackle the task, we propose a novel latent diffusion approach, called Multimodal Garment Designer (MGD), that can effectively combine multimodal information when generating the new image $\tilde{I}$ . Our proposed architecture is a general framework that can be easily extended to other modalities such as texture and 3d information. We strongly believe this task can foster research in the field and enhance the design process of new fashion items with greater customization. An overview of our model is shown in Fig. 2. + +# 3.1. Preliminaries + +While diffusion models [41] are latent variable architectures that work in the same dimensionality of the data (i.e. in the pixel space), latent diffusion models (LDMs) [37] operate in the latent space of a pre-trained autoencoder achieving higher computational efficiency while preserving the generation quality. In our work, we leverage the Stable Diffusion model [37], a text-to-image implementation of LDMs as a starting point to perform multimodal condition- + +ing for human-centric fashion image editing. Stable Diffusion is composed of an autoencoder with an encoder $\mathcal{E}$ and a decoder $\mathcal{D}$ , a text-time-conditional U-Net denoising model $\epsilon_{\theta}$ , and a CLIP-based text encoder $T_{E}$ taking as input a text $Y$ . The encoder $\mathcal{E}$ compresses an image $I$ into a lower-dimensional latent space defined in $\mathbb{R}^{h\times w\times 4}$ , where $h = H / 8$ and $w = W / 8$ . The decoder $\mathcal{D}$ performs the opposite operation, decoding a latent variable into the pixel space. For the sake of clarity, we define the $\epsilon_{\theta}$ convolutional input (i.e. $z_{t}$ in this case) as spatial input $\gamma$ because of the property of convolutions to preserve the spatial structure and the attention conditioning input as $\psi$ . The denoising network $\epsilon_{\theta}$ is trained according to the following loss: + +$$ +L = \mathbb {E} _ {\mathcal {E} (I), Y, \epsilon \sim \mathcal {N} (0, 1), t} \left[ \| \epsilon - \epsilon_ {\theta} (\gamma , \psi) \| _ {2} ^ {2} \right], \tag {1} +$$ + +where $t$ is the diffusing time step, $\gamma = z_{t}$ , $\psi = [t;T_{E}(Y)]$ , and $\epsilon \sim \mathcal{N}(0,1)$ is the Gaussian noise added to $\mathcal{E}(I)$ . + +# 3.2. Human-Centric Image Editing + +Our task aims to generate a new image $\tilde{I}$ , by replacing in the input image $I$ the target garment using multimodal inputs, while preserving the model's identity and physical characteristics. As a natural consequence, this task can be identified as a particular type of inpainting tailored for human body data. Instead of using a standard text-to-image model, we perform inpainting concatenating along the channel dimension of the denoising network input $z_{t}$ an encoded masked image $\mathcal{E}(I_M)$ and the relative resized binary inpainting mask $m\in \{0,1\}^{h\times w\times 1}$ , which is derived from the original inpainting mask $M\in \{0,1\}^{H\times W\times 1}$ . Since here, the spatial input of the denoising network is $\gamma = [z_t;m;\mathcal{E}(I_M)],\gamma \in \mathbb{R}^{h\times w\times 9}$ . Thanks to the fully convolutional nature of the encoder $\mathcal{E}$ and the decoder $\mathcal{D}$ , this LDMs-based architecture can preserve the spatial information in the latent space. Exploiting this feature, our method can thus optionally add conditioning constraints to the generation. In particular, we propose to add two generation constraints in addition to the textual information: the + +model pose map $P$ to preserve the original human pose of the input model and the garment sketch $S$ to allow the final users to better condition the garment generation process. + +Pose Map Conditioning. In most cases [21, 24, 44], inpainting is performed with the objective of either removing or entirely replacing the content of the masked region. However, in our task, we aim to remove all information regarding the garment worn by the model while preserving the model's body information and identity. Thus, we propose to improve the garment inpainting process by using the bounding box of the segmentation mask along with pose map information representing body keypoints. This approach enables the preservation of the model's physical characteristics in the masked region while allowing the inpainting of garments with different shapes. Differently from conventional inpainting techniques, we focus on selectively retaining and discarding specific information within the masked region to achieve the desired outcome. To enhance the performance of the denoising network with human body keypoints, we modify the first convolution layer of the network by adding 18 additional channels, one for each keypoint. Adding new inputs usually would require retraining the model from scratch, thus consuming time, data, and resources, especially in the case of data-hungry models like the diffusion ones. Therefore, we propose to extend the kernels of the pre-trained input layer of the denoising network with randomly initialized weights sampled from a uniform distribution [14] and retrain the whole network. This consistently reduces the number of training steps and enables training with less data. Our experiments show that such improvement enhances the consistency of the body information between the generated image and the original one. + +Incorporating Sketches. Fully describing a garment using only textual descriptions is a challenging task due to the complexity and ambiguity of natural language. While text can convey specific attributes like style, color, and patterns of a garment, it may not provide sufficient information about its spatial characteristics, such as shape and size. This limitation can hinder the customization of the generated clothing item other than the ability to accurately match the user's intended style. Therefore, we propose to leverage garment sketches to enrich the textual input with additional spatial fine-grained details. We achieve this following the same approach described for pose map conditioning. The final spatial input of our denoising network is $\gamma = [z_t; m; \mathcal{E}(I_M); p; s], [p; s] \in \mathbb{R}^{h \times w \times (18 + 1)}$ , $p$ and $s$ are obtained by resizing $P$ and $S$ to match the latent space dimensions. In the case of sketches, we only condition the early steps of the denoising process as the final steps have little influence on the shapes [2]. + +Mask Composition. To preserve the model identity when performing human-centric inpainting, we perform mask composition as the final step of the proposed approach. + +Defining $\hat{I} = \mathcal{D}(z_0) \in \mathbb{R}^{H \times W \times 3}$ as the output of the decoder $\mathcal{D}$ and $M_{\mathrm{head}} \in \{0,1\}^{H \times W \times 1}$ as the model face binary mask of the image $I$ , the final output image $\tilde{I}$ is obtained as follows: $\tilde{I} = M_{\mathrm{head}} \odot I + (1 - M_{\mathrm{head}}) \odot \hat{I}$ , where $\odot$ denotes the element-wise multiplication operator. + +# 3.3. Training and Inference + +As in standard latent diffusion models, given an encoded input $z = \mathcal{E}(I)$ , the proposed denoising network is trained to predict the noise stochastically added to $z$ . The corresponding objective function can be specified as + +$$ +L = \mathbb {E} _ {\mathcal {E} (I), Y, \epsilon \sim \mathcal {N} (0, 1), t, \mathcal {E} (I _ {M}), m, p, s} \left[ \| \epsilon - \epsilon_ {\theta} (\gamma , \psi) \| _ {2} ^ {2} \right], \tag {2} +$$ + +where $\gamma = [z_{t};m;\mathcal{E}(I_{M});p;s]$ and $\psi = [t;T_E(Y)]$ + +Classifier-Free Guidance. Classifier-free guidance is an inference technique that requires the denoising network to work both conditioned and unconditioned. This method modifies the unconditional model predicted noise moving it toward the conditioned one. Specifically, the predicted diffusion process at time $t$ , given the generic condition $c$ , is computed as follows: + +$$ +\hat {\epsilon} _ {\theta} \left(z _ {t} | c\right) = \epsilon_ {\theta} \left(z _ {t} | \emptyset\right) + \alpha \cdot \left(\epsilon_ {\theta} \left(z _ {t} | c\right) - \epsilon_ {\theta} \left(z _ {t} | \emptyset\right)\right), \tag {3} +$$ + +where $\epsilon_{\theta}(z_t|c)$ is the predicted noise at time $t$ given the condition $c$ , $\epsilon_{\theta}(z_t|\emptyset)$ is the predicted noise at time $t$ given the null condition, and the guidance scale $\alpha$ controls the degree of extrapolation towards the condition. + +Since our model deals with three conditions (i.e. text, pose map, and sketch), we use the fast variant multi-condition classifier-free guidance proposed in [1]. Instead of performing the classifier-free guidance according to each condition probability, it computes the direction of the joint probability of all the conditions $\Delta_{\mathrm{joint}}^t = \epsilon_\theta (z_t|\{c_i\}_{i = 1}^{i = N}) - \epsilon_\theta (z_t|\emptyset)$ : + +$$ +\hat {\epsilon} _ {\theta} \left(z _ {t} \mid \left\{c _ {i} \right\} _ {i = 1} ^ {i = N}\right) = \epsilon_ {\theta} \left(z _ {t} \mid \emptyset\right) + \alpha \cdot \Delta_ {\text {j o i n t}} ^ {t}. \tag {4} +$$ + +This reduces the number of feed-forward executions from $N + 1$ to 2. + +Unconditional Training. Ensuring the ability of the denoising model to work both with and without conditions is achieved by replacing at training time the condition with a null one according to a fixed probability. This approach allows the model to learn from both conditional and unconditional samples, resulting in improved mode coverage and sample fidelity. Moreover, this technique also allows the model to optionally use the control signals at prediction time. Since our approach considers multiple conditions, we propose to extend the input masking to each condition independently. Experiments show that tuning this parameter can effectively affect the quality of the final result. + +# 4. Collecting Multimodal Fashion Datasets + +Currently available datasets for fashion image generation often contain low-resolution images and lack all the required multimodal information needed to perform the task previously described. For this reason, the collection of new multimodal datasets for the fashion domain plays a crucial role to advance research in the field. To this aim, we start from two recent high-resolution fashion datasets introduced for the virtual try-on task, namely Dress Code [28] and VITON-HD [7], and extend them with textual sentences and garment sketches. Both datasets include image pairs with a resolution of $1024 \times 768$ , each composed of a garment image and a reference model wearing the given fashion item. In this section, we introduce a framework to semi-automatically annotate fashion images with multimodal information and provide a complete description of how to enrich Dress Code and VITON-HD with garment-related text and sketches. We call our extended versions of these datasets Dress Code Multimodal and VITON-HD Multimodal, respectively. Sample images and multimodal data of the collected datasets can be found in Fig. 3. + +# 4.1. Dataset Collection and Annotation + +Data Preparation. We start the annotation from the Dress Code dataset, which contains more than 53k model-garment pairs of multiple categories. As a first step, we need to associate each garment with a textual description containing fashion-specific and non-generic terms which are sufficiently detailed but not extremely lengthy to be exploited for constraining the generation. Motivated by recent findings in the field showing that humans tend to describe fashion items using only a few words [3], we propose to use noun chunks (i.e. short textual sentences composed of a noun along with its modifiers) that can effectively capture important information while reducing unnecessary words or details. Given that manually annotating all the images would be time-consuming and resource-intensive1, we propose a novel framework to semi-automatically annotate the dataset using noun chunks. Firstly, domain-specific captions are collected from two available fashion datasets, namely FashionIQ [50] and Fashion200k [12], standardizing them with word lemmatization and eventually reducing each word to its root form with the NLTK library2. Then, we extract noun chunks from the captions, filtering the results by removing all textual items that start with or contain special characters. After this pre-processing stage, we obtain more than 60k unique noun chunks, divided into three different categories (i.e. upper-body clothes, lower-body clothes, and dresses). + +1Since the Dress Code dataset consists of over 53k fashion items and assuming that each annotation requires approximately 5 minutes, a single annotator working 8 hours per day, 5 days a week, and 260 working days per year would take more than 2 years to complete the annotation task. + +2 https://www.nltk.org/ + +![](images/1494a2f1d8b5661e28509a21f1bc94c1438e70f3476478bc3c481902a4c7d5e7.jpg) +Figure 3. Sample images and multimodal data from our newly collected datasets. + +
DatasetTextPoseSketch# Images# Products# Unique Texts# Unique Words
VITON-HD [7]X✓X27,35813,679--
Dress Code [28]X✓X107,58453,792--
Be Your Own Prada [56]✓✓X78,979N/A3,972445
DF-Multimodal [19]✓✓X44,096N/A10,25377
VITON-HD Multimodal✓✓✓27,35813,6795,1431,613
Dress Code Multimodal✓✓✓107,58453,79225,5962,995
+ +Table 1. Comparison of Dress Code and VITON-HD Multimodal with other fashion datasets with multimodal annotations. + +To determine the most relevant noun chunks for each garment, we employ the CLIP model [34] and its open-source adaptation (i.e. OpenCLIP [49]). We select the VIT-L14@336 and $\mathrm{RN50\times 64}$ models for CLIP, and the VIT-L14, ViT-H14, and ViT-g14 models for OpenCLIP. Prompt ensembling is performed to improve the results and, for each image, we select 25 noun chunks based on the top-5 noun chunks per model rated by cosine similarity between image and text embeddings, avoiding repetitions. + +Fine-Grained Textual Annotation. To ensure the accuracy and representativeness of our annotations, we manually annotate a significant portion of Dress Code images. In particular, we select the three most representative noun chunks, among the 25 automatically associated, with each garment image. To minimize the annotation time, we develop a custom annotation tool that constrains the annotation time to an average time of 60 seconds per item and allows the annotator to manually insert noun chunks in the case that none of the automatically extracted ones are suitable for the image. Overall, we manually annotate 26,400 different garments (8,800 for each category) out of the 53,792 products included in the dataset, ensuring to include all fashion items of the original test set [28]. + +Coarse-Grained Textual Annotation. To complete the annotation, we first finetune the OpenCLIP ViT-B32 model, pre-trained on the English portion of the LAION5B dataset [40], using the newly annotated image-text pairs. We then use this model and the collected set of noun chunks to automatically tag all the remaining elements of the Dress Code dataset with the three most similar noun chunks, al + +ways determined via cosine similarity between multimodal embeddings. We employ the same strategy also to automatically annotate all garment images of the VITON-HD dataset. In this case, since this dataset only contains upper-body clothes, we limit the table noun chunks to the ones describing upper-body garments. + +Extracting Sketches. The introduction of garment sketches can provide valuable design details that are not easily discernible from text alone. In this way, the dataset can provide a more accurate and comprehensive representation of the garments, leading to improved quality and better control of the generated design details. To extract sketches for both Dress Code and VITON-HD datasets, we employ PiDiNet [43], a pre-trained edge detection network. + +Given that the selected datasets have originally been introduced for virtual try-on, they consist of both paired and unpaired test sets. While for the paired set we can directly use the human parsing mask to extract the garment of interest worn by the model and then feed it to the edge detection network, for the unpaired set we need to first create a warped version of the in-shop garment matching the body pose and shape of the target model. Following virtual try-on methods [47, 52], we train a geometric transformation module that performs a thin-plate spline transformation [36] of the input garment and then refines the warped result using a U-Net model [38]. From each warped garment, we extract the sketch image enabling the use of the proposed solution even in unpaired settings. + +# 4.2. Comparison with Other Datasets + +The only two text-to-image generation datasets available in the fashion domain [19, 56] are both based on images from the DeepFashion dataset [22]. While the dataset introduced in [56] contains short textual descriptions, DeepFashion-Multimodal [19] is annotated with attributes (e.g. category, color, fabric, etc.) that can be composed in longer captions. In Table 1, we summarize the main statistics of the publicly available datasets textual annotations compared with those of our newly extended datasets. As can be seen, our datasets contain more variety in terms of textual items and words, confirming the appropriateness of our annotation procedure and enabling a more personalized control of the generation process. Also, it is worth noting that the other datasets have no in-shop garment images making them difficult to employ in our case. + +# 5. Experimental Evaluation + +# 5.1. Implementation Details and Competitors + +Training and Inference. All models are trained on the original splits of the Dress Code Multimodal and VITON-HD Multimodal datasets on a single NVIDIA A100 GPU for 150k steps, using a batch size of 16, a learning rate + +of $10^{-5}$ with a linear warmup for the first 500 iterations, and AdamW [23] as optimizer with weight decay $10^{-2}$ . To speed up training and save memory, we use mixed precision [26]. We set both the fraction of steps conditioned by the sketch and the portion of masked conditions during training to 0.2. During inference, we employ the DDIM [42] with 50 steps as noise scheduler and set the classifier-free guidance parameter $\alpha$ to 7.5. + +Baselines and Competitors. As first competitor, we use the out-of-the-box implementation of the inpainting Stable Diffusion pipeline3 provided by Huggingface. Moreover, we adapt two existing models, namely FICE [33] and SDEdit [25], to work on our setting. In particular, we retrain all main components of the FICE model on the newly collected datasets. We employ the same resolution used by the authors (i.e. $256 \times 256$ ), downsampling each image to $256 \times 192$ and applying padding to match the desired size (which is then removed during evaluation). To compare our model with a different conditioning strategy, we employ the approach proposed in [25] using our model trained only with text and human poses as input modalities and perform the sketch guidance using as starting latent variable the sketch image with added random noise. Following the original paper instructions, we use 0.8 as the strength parameter. + +# 5.2. Evaluation Metrics + +To assess the realism of generated images, we employ the Fréchet Inception Distance (FID) [16] and the Kernel Inception Distance (KID) [4]. For both metrics, we adopt the implementation proposed in [32]. Instead, to evaluate the adherence of the image to the textual conditioning input, we employ the CLIP Score (CLIP-S) [15] provided in the TorchMetrics library [9], using the OpenCLIP ViT-H/14 model as cross-modal architecture. We compute the score on the inpainted region of the generated output pasted on a $224 \times 224$ white background. + +Pose Distance (PD). We propose a novel pose distance metric that measures the coherence of human body poses between the generated image and the original one estimating the distance between the human keypoints extracted from the original and generated images. Specifically, we employ the OpenPifPaf [20] human pose estimation network and compute the $\ell_2$ distance between each pair of real-generated corresponding estimated keypoints. We only consider the keypoints involved in the generation (i.e. that falls in the mask $M$ ) and weigh each keypoints distance with the detector confidence to take into account any estimation errors. + +Sketch Distance (SD). To quantify the adherence of the generated image to the sketch constraint, we propose a novel sketch distance metric. To compute the score, we extract the segmentation map of the original and generated + +
ModelResolutionModalitiesDress Code MultimodalVITON-HD Multimodal
TextPoseSketchFID ↓KID ↓CLIP-S ↑PD ↓SD ↓FID ↓KID ↓CLIP-S ↑PD ↓SD ↓
Paired setting
Stable Diffusion [37]256×192✓17.059.2828.714.62-15.186.3830.405.04-
FICE [33]256×192✓✓30.6323.5428.726.87-49.4444.7429.266.37-
MGD (ours)256×192✓✓5.571.6731.332.37-10.113.1431.852.90-
Paired setting
Stable Diffusion [37]512×384✓17.439.4829.189.240.46716.286.5630.7010.780.410
SDEdit [25]512×384✓✓✓10.195.0329.215.410.39813.074.6630.586.760.306
MGD (ours)512×384✓✓✓5.742.1131.684.720.37410.603.2632.395.940.253
Unpaired setting
Stable Diffusion [37]256×192✓19.1110.6927.535.07-17.377.5528.405.50-
FICE [33]256×192✓✓34.1426.8626.037.15-52.7448.5825.946.58-
MGD (ours)256×192✓✓7.012.1929.582.96-11.543.1829.953.30-
Unpaired setting
Stable Diffusion [37]512×384✓19.5510.8028.029.890.58218.457.8728.7411.600.561
SDEdit [25]512×384✓✓✓11.385.6927.106.160.50915.125.6728.617.350.406
MGD (ours)512×384✓✓✓7.732.8230.046.790.45812.813.8630.757.220.317
+ +Table 2. Quantitative results on the Dress Code Multimodal and VITON-HD Multimodal datasets for both paired and unpaired settings . + +
ModelModalitiesDress Code Multimodal
TextPoseSketchFID ↓KID ↓CLIP-S ↑PD ↓SD ↓
MGD (ours)✓6.192.1531.796.160.411
✓✓6.312.3331.675.310.405
✓✓✓5.742.1131.684.720.374
ModelModalitiesVITON-HD Multimodal
TextPoseSketchFID ↓KID ↓CLIP-S ↑PD ↓SD ↓
MGD (ours)✓11.393.5232.167.830.339
✓✓11.073.3632.276.770.318
✓✓✓10.603.2632.395.940.253
+ +garments using an off-the-shelf clothing segmentation network $^{4}$ . We then use the segmented garment area to extract garment sketches using the PIDInet [43] edge detector network. The final score is the mean squared error between these sketches, weighting the per-pixel results on the inverse pixel frequency of the activated pixels. More details about these proposed metrics can be found in the supplementary. + +# 5.3. Experimental Results + +Comparison with Other Methods. We test our proposal for the paired and unpaired settings of the considered datasets. In the former, the conditions (e.g. text, sketch) refers to the garment the model is wearing, while in the latter, the in-shop garment differs from the worn one. In Table 2, we report the quantitative results on Dress Code Multimodal and VITON-HD Multimodal in comparison with the aforementioned competitors. As can be seen, the proposed MGD model consistently outperforms competitors, in terms of realism (i.e. FID and KID) and coherency with input modalities (i.e. CLIP-S, PD, and SD). In particu + +Table 3. Performance analysis on the paired setting of both datasets as input modalities vary. + +
ModalitiesRealismMultimodal Coherence
TextPoseSketchStable Diff.FICESDEditStable Diff.FICESDEdit
Dress✓70.82--65.32--
✓✓70.7396.26-65.1584.48-
✓✓✓70.29-52.5465.38-66.23
VITON✓67.03--57.76--
✓✓66.1793.84-73.7383.46-
✓✓✓60.71-53.4469.47-59.34
+ +Table 4. User study results on the unpaired setting of both datasets. We report the percentage of times an image from MGD is preferred against a competitor. Comparisons with FICE [33] are performed at $256 \times 192$ resolution. + +lar, when considering low-resolution results, we notice that FICE [33] can produce images fairly consistent with the text conditioning, albeit less realistic than other methods. While Stable Diffusion [37] enhances image realism, it fails to preserve the input model's pose due to the lack of pose information in the inputs. It is noteworthy that in this case, we compare the results of our model only using text and pose map as conditioning since both considered competitors are not conditioned on sketches. For this reason, we do not report the results in terms of sketch distance for low-resolution images. + +In the high-resolution setting, we evaluate instead our MGD method using all multimodal conditions (i.e. text, pose map, and sketch) as input. In this case, we compare MGD with Stable Diffusion [37] plus SDEdit [25], where we use our text-pose conditioned denoising network as SDEdit backbone. Our findings indicate that Stable Diffusion performs worse in terms of the pose distance than both SDEdit and MGD, owing to the lack of pose information in the inputs. It is noteworthy that SDEdit performs worse than our model in all metrics. We attribute this behavior to the way sketch conditioning happens. In SDEdit, + +![](images/6ec420afa290eb1e9fbc2f2ba28ad4a9ac7cb30c22fa8b19f5b3e67adb70fcfc.jpg) +Figure 4. Sample generated images on Dress Code Multimodal and VITON-HD Multimodal (bottom left) using all multimodal inputs. + +![](images/1a62e80663022be32de11fd9b9ce70962ee0b23552e560afc74440dcea6af1f6.jpg) + +it occurs only at the beginning by initializing $z_{t}$ using the sketch image with added noise according to the conditioning strength, while our model conditions the denoising process in multiple steps, depending on the sketch conditioning parameter. Qualitative results reported in Fig. 4 highlight how our model better follows the given conditions and generate high-realistic images. + +To validate our results based on human judgment, we conduct a user study that evaluates both the realism of the generation and the adherence to multimodal inputs. Overall we collect about 7k evaluations involving more than 150 users. Additional details are reported in the supplementary. Table 4 shows the user study results. Also in this case our model outperforms the competitors, thus confirming the effectiveness of our proposal. + +Varying Input Modalities. In Table 3, we study the behavior of our MGD model when the input modalities are masked (i.e. where we feed the model with a zero tensor instead of the considered modality). In particular, we focus on the CLIP-S for text adherence and on the newly proposed pose and sketch distances for the pose and sketch coherency, respectively. Notice that the text input anchors the CLIP-S metrics of all experiments and makes them comparable in all cases. Starting from the fully conditioned model (i.e. text, pose, sketch), we mask the sketch. As the decrease of the sketch distance in Table 3 confirms, this input actually influences the generation process of our model in both the considered datasets. Also, this modality slightly affects the pose distance as the sketch implicitly contains information about the model's body pose. We further mask the pose map input and compare the output with previous results. In + +
Uncond. PortionSketch Cond.Dress Code Multimodal
FID ↓KID ↓CLIP-S ↑PD ↓SD ↓
0.11.09.643.7630.247.660.459
0.21.08.623.2429.067.510.430
0.31.010.934.7828.477.690.432
0.20.88.563.2829.317.320.433
0.20.68.433.2129.517.320.436
0.20.48.113.0029.797.130.440
0.20.27.732.8230.046.790.458
0.20.07.822.8529.936.260.519
+ +Table 5. Ablation analysis of our complete model varying the unconditioning portion during training and the sketch conditioning steps. Results refer to the unpaired setting. + +this case, we can also notice a consistent difference with the text-only conditioned model, according to all metrics except CLIP-S as expected. These results confirm that our MGD model can effectively deal with the conditions in a disentangled way, making them optional. + +Unconditional Training and Sketch Conditioning. In Table 5, we inquire about the fully conditioned network performance according to the variance of the portion of unconditional training. Additionally, we evaluate the results by varying the fraction of sketch conditioning steps. As can be seen, the best results are achieved by using 0.2 for both parameters. In particular, for unconditional training, we train three different models (i.e. with 0.1, 0.2, and 0.3). When evaluating the sketch conditioning parameter, we test our model with values between 0 and 1 with a stride of 0.2. It is worth noting that the sketch distance consistently decreases as the number of sketch conditioning steps increases, showing the robustness of the approach. + +# 6. Conclusion + +The Multimodal Garment Designer proposed in this paper is the first latent diffusion model defined for human-centric fashion image editing, conditioned by multimodal inputs such as text, body pose, and sketches. The novel architecture, trained on two new semi-automatically annotated datasets and evaluated with standard and newly proposed metrics, as well as by user studies, is very promising. The result is one of the first successful attempts to mimic the designers' job in the creative process of fashion design and could be a starting point for a capillary adoption of diffusion models in creative industries, oversight by human input. + +# Acknowledgments + +This work has partially been supported by the European Commission under the PNRR-M4C2 project "FAIR - Future Artificial Intelligence Research" and the European Horizon 2020 Programme (grant number 101004545 - ReInHerit), and by the PRIN project "CREATIVE: CRoss-modal understanding and gEnerATIon of Visual and tExtual content" (CUP B87G22000460001), co-funded by the Italian Ministry of University. + +# References + +[1] Omri Avrahami, Thomas Hayes, Oran Gafni, Sonal Gupta, Yaniv Taigman, Devi Parikh, Dani Lischinski, Ohad Fried, and Xi Yin. SpaText: Spatio-Textual Representation for Controllable Image Generation. 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In this work, we propose a novel multimodal garment designer framework based on latent diffusion models that can generate a novel fashion image conditioned on text, human keypoints, and a garment sketch." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 143, + 493, + 192, + 506 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 493, + 192, + 506 + ], + "spans": [ + { + "bbox": [ + 143, + 493, + 192, + 506 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 510, + 290, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 510, + 290, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 510, + 290, + 713 + ], + "type": "text", + "content": "Fashion illustration is used by designers to communicate their vision and to bring the design idea from conceptualization to realization, showing how clothes interact with the human body. In this context, computer vision can thus be used to improve the fashion design process. Differently from previous works that mainly focused on the virtual try-on of garments, we propose the task of multimodal-conditioned fashion image editing, guiding the generation of human-centric fashion images by following multimodal prompts, such as text, human body poses, and garment sketches. We tackle this problem by proposing a new architecture based on latent diffusion models, an approach that has not been used before in the fashion domain. Given the lack of existing datasets suitable for the task, we also extend two existing fashion datasets, namely Dress Code and VITON-HD, with multimodal annotations collected in a semi-automatic manner. Experimental re" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 491, + 546, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 491, + 546, + 552 + ], + "spans": [ + { + "bbox": [ + 305, + 491, + 546, + 552 + ], + "type": "text", + "content": "sults on these new datasets demonstrate the effectiveness of our proposal, both in terms of realism and coherence with the given multimodal inputs. Source code and collected multimodal annotations are publicly available at: https://github.com/aimagelab/multimodal-garment-designer." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 567, + 387, + 580 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 567, + 387, + 580 + ], + "spans": [ + { + "bbox": [ + 306, + 567, + 387, + 580 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 588, + 547, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 588, + 547, + 696 + ], + "spans": [ + { + "bbox": [ + 304, + 588, + 547, + 696 + ], + "type": "text", + "content": "Computer Vision research has always paid much attention both to the human person and to fashion-related problems, especially working on the recognition and retrieval of clothing items [11, 22], the recommendation of similar garments [8, 18, 39], and the virtual try-on of clothes and accessories [7, 13, 27, 28, 47, 52]. In the last years, some research efforts have been dedicated to the text-conditioned image editing task where, given a model image and a textual description of a garment, the goal is to generate the" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 321, + 703, + 389, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 321, + 703, + 389, + 712 + ], + "spans": [ + { + "bbox": [ + 321, + 703, + 389, + 712 + ], + "type": "text", + "content": "*Equal contribution." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23393" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": "input model wearing a new clothing item corresponding to the given textual description. In this context, only a few works [19,33,56] have been proposed, exclusively employing GAN-based approaches for the generative step." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 122, + 288, + 326 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 122, + 288, + 326 + ], + "spans": [ + { + "bbox": [ + 46, + 122, + 288, + 326 + ], + "type": "text", + "content": "Recently, diffusion models [10, 17, 30, 41] have attracted more and more attention due to their outstanding generation capabilities, allowing the improvement of a variety of downstream tasks in several domains, while their applicability to the fashion domain is still unexplored. Many different solutions have been introduced and can roughly be identified based on the denoising conditions used to guide the diffusion process, which can enable greater control of the synthesized output. A particular type of diffusion model has been proposed in [37] that, instead of applying the diffusion process in the pixel space, defines the forward and the reverse processes in the latent space of a pre-trained autoencoder, becoming one of the leading choices thanks to its reduced computational cost. Although this solution can generate highly realistic images, it does not perform well in human-centric generation tasks and can not deal with multiple conditioning signals to guide the generation phase." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 327, + 287, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 327, + 287, + 506 + ], + "spans": [ + { + "bbox": [ + 46, + 327, + 287, + 506 + ], + "type": "text", + "content": "In this work, we address an extended and more general framework and define the new task of multimodal-conditioned fashion image editing, which allows guiding the generative process via multimodal prompts while preserving the identity and body shape of a given person (Fig. 1). To tackle this task, we introduce a new architecture, called Multimodal Garment Designer (MGD), that emulates the process of a designer conceiving a new garment on a model shape, based on preliminary indications provided through a textual sentence or a garment sketch. In particular, starting from Stable Diffusion [37], we propose a denoising network that can be conditioned by multiple modalities and also takes into account the pose consistency between input and generated images, thus improving the effectiveness of human-centric diffusion models." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 509, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 509, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 509, + 287, + 640 + ], + "type": "text", + "content": "To address the newly proposed task, we present a semiautomatic framework to extend existing datasets with multimodal data. Specifically, we start from two famous virtual try-on datasets (i.e. Dress Code [28] and VITON-HD [7]) and extend them with textual descriptions and garment sketches. Experimental results on the two proposed multimodal fashion benchmarks show both quantitatively and qualitatively that our proposed architecture generates high-quality images based on the given multimodal inputs and outperforms all considered competitors and baselines, also according to human evaluations." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 715 + ], + "type": "text", + "content": "To sum up, our contributions are as follows: (1) We propose a novel task of multimodal-conditioned fashion image editing, which entails the use of multimodal data to guide the generation. (2) We introduce a new human-centric generative architecture based on latent diffusion models, capable of following multimodal prompts while preserving the" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 144 + ], + "type": "text", + "content": "model's characteristics. (3) To tackle the new task, we extend two existing fashion datasets with textual sentences and garment sketches devising a semi-automatic annotation framework. (4) Extensive experiments demonstrate that the proposed approach outperforms other competitors in terms of realism and coherence with multimodal inputs." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 153, + 392, + 165 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 153, + 392, + 165 + ], + "spans": [ + { + "bbox": [ + 306, + 153, + 392, + 165 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 173, + 545, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 173, + 545, + 388 + ], + "spans": [ + { + "bbox": [ + 304, + 173, + 545, + 388 + ], + "type": "text", + "content": "Text-Guided Image Generation. Creating an image that faithfully reflects the provided textual prompt is the goal of text-to-image synthesis. In this context, early approaches were based on GANs [45, 51, 53, 55], while most recent solutions exploit the effectiveness of diffusion models [31, 35, 37]. In the fashion domain, only a few attempts of text-to-image synthesis have been proposed [19, 33, 56]. Specifically, Zhu et al. [56] presented a GAN-based solution that generates the final image conditioned on both textual descriptions and semantic layouts. A different approach is the one introduced in [33], where a latent code regularization technique is employed to augment the GAN inversion process by exploiting CLIP textual embeddings [34] to guide the image editing process. Instead, Jiang et al. [19] proposed an architecture that synthesizes full-body images by mapping the textual descriptions of clothing items into one-hot vectors, limiting however the expressiveness capability of the conditioning signal." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 391, + 545, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 391, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 391, + 545, + 605 + ], + "type": "text", + "content": "Multimodal Image Generation with Diffusion Models. A related line of works aims to condition existing diffusion models on different modalities thus enabling greater control over the generation process [5, 6, 25, 29, 48]. For example, Choi et al. [6] proposed to refine the generative process of an unconditional denoising diffusion probabilistic model [30] by matching each latent variable with the given reference image. On a different line, the approach introduced in [25] adds noise to a stroke-based input and applies the reverse stochastic differential equation to synthesize images, without additional training. Wang et al. [48], instead, proposed to learn a highly semantic latent space and perform conditional finetuning for each downstream task to map the guidance signals to the pre-trained space. Other recent works proposed to add sketches as additional conditioning signals, either concatenating them with the model input [5] or training an MLP-based edge predictor to map latent features to spatial maps [46]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "text", + "content": "Among contemporary works that aim to condition pretrained latent diffusion models, ControlNet [54] proposes to extend the Stable Diffusion model [37] with an additional conditioning input. This process involves creating two versions of the original model's weights: one that remains fixed and unchanged (locked copy) and another that can be updated during training (trainable copy). The purpose of this is to allow the trainable version to learn the newly introduced condition while the locked version retains the origi" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "23394" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 68, + 545, + 209 + ], + "blocks": [ + { + "bbox": [ + 47, + 68, + 545, + 209 + ], + "lines": [ + { + "bbox": [ + 47, + 68, + 545, + 209 + ], + "spans": [ + { + "bbox": [ + 47, + 68, + 545, + 209 + ], + "type": "image", + "image_path": "35fd084287558bf2793f24e73ada81b2c93658bc4a35b3ccb6a18845922e39c3.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 217, + 546, + 240 + ], + "lines": [ + { + "bbox": [ + 46, + 217, + 546, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 217, + 546, + 240 + ], + "type": "text", + "content": "Figure 2. Overview of the proposed Multimodal Garment Designer (MGD), a human-centric latent diffusion model conditioned on multiple modalities (i.e. text, human pose, and garment sketch)." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 250, + 287, + 285 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 250, + 287, + 285 + ], + "spans": [ + { + "bbox": [ + 46, + 250, + 287, + 285 + ], + "type": "text", + "content": "nal model knowledge. On the other hand, T2I-Adapter [29] learns modality-specific adapter modules that enable Stable Diffusion conditioning on new modalities." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 286, + 287, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 286, + 287, + 346 + ], + "spans": [ + { + "bbox": [ + 46, + 286, + 287, + 346 + ], + "type": "text", + "content": "In contrast, we focus on the fashion domain and propose a human-centric architecture based on latent diffusion models that directly exploits the conditioning of textual sentences and other modalities such as human body poses and garment sketches." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 357, + 153, + 370 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 357, + 153, + 370 + ], + "spans": [ + { + "bbox": [ + 47, + 357, + 153, + 370 + ], + "type": "text", + "content": "3. Proposed Method" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "spans": [ + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "text", + "content": "In this section, we propose a novel task to automatically edit a human-centric fashion image conditioned on multiple modalities. Specifically, given the model image " + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "inline_equation", + "content": "I \\in \\mathbb{R}^{H \\times W \\times 3}" + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "text", + "content": ", its pose map " + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "inline_equation", + "content": "P \\in \\mathbb{R}^{H \\times W \\times 18}" + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "text", + "content": " where the channels represent the human keypoints, a textual description " + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "text", + "content": " of a garment, and a sketch of the same " + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "inline_equation", + "content": "S \\in \\mathbb{R}^{H \\times W \\times 1}" + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "text", + "content": ", we want to generate a new image " + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "inline_equation", + "content": "\\tilde{I} \\in \\mathbb{R}^{H \\times W \\times 3}" + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "text", + "content": " that retains the information of the input model while substituting the target garment according to the multimodal inputs. To tackle the task, we propose a novel latent diffusion approach, called Multimodal Garment Designer (MGD), that can effectively combine multimodal information when generating the new image " + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "inline_equation", + "content": "\\tilde{I}" + }, + { + "bbox": [ + 46, + 376, + 288, + 593 + ], + "type": "text", + "content": ". Our proposed architecture is a general framework that can be easily extended to other modalities such as texture and 3d information. We strongly believe this task can foster research in the field and enhance the design process of new fashion items with greater customization. An overview of our model is shown in Fig. 2." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 599, + 133, + 611 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 599, + 133, + 611 + ], + "spans": [ + { + "bbox": [ + 47, + 599, + 133, + 611 + ], + "type": "text", + "content": "3.1. Preliminaries" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 617, + 288, + 714 + ], + "type": "text", + "content": "While diffusion models [41] are latent variable architectures that work in the same dimensionality of the data (i.e. in the pixel space), latent diffusion models (LDMs) [37] operate in the latent space of a pre-trained autoencoder achieving higher computational efficiency while preserving the generation quality. In our work, we leverage the Stable Diffusion model [37], a text-to-image implementation of LDMs as a starting point to perform multimodal condition-" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "spans": [ + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": "ing for human-centric fashion image editing. Stable Diffusion is composed of an autoencoder with an encoder " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "\\mathcal{E}" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": " and a decoder " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": ", a text-time-conditional U-Net denoising model " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "\\epsilon_{\\theta}" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": ", and a CLIP-based text encoder " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "T_{E}" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": " taking as input a text " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": ". The encoder " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "\\mathcal{E}" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": " compresses an image " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": " into a lower-dimensional latent space defined in " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^{h\\times w\\times 4}" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "h = H / 8" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "w = W / 8" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": ". The decoder " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": " performs the opposite operation, decoding a latent variable into the pixel space. For the sake of clarity, we define the " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "\\epsilon_{\\theta}" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": " convolutional input (i.e. " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "z_{t}" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": " in this case) as spatial input " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": " because of the property of convolutions to preserve the spatial structure and the attention conditioning input as " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "\\psi" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": ". The denoising network " + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "inline_equation", + "content": "\\epsilon_{\\theta}" + }, + { + "bbox": [ + 304, + 250, + 547, + 406 + ], + "type": "text", + "content": " is trained according to the following loss:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 339, + 413, + 545, + 430 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 339, + 413, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 339, + 413, + 545, + 430 + ], + "type": "interline_equation", + "content": "L = \\mathbb {E} _ {\\mathcal {E} (I), Y, \\epsilon \\sim \\mathcal {N} (0, 1), t} \\left[ \\| \\epsilon - \\epsilon_ {\\theta} (\\gamma , \\psi) \\| _ {2} ^ {2} \\right], \\tag {1}", + "image_path": "fa6285987d1a0f1a95682f8493b57715862052d11e666a65aa5a18c3b38636ba.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "spans": [ + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "type": "text", + "content": " is the diffusing time step, " + }, + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "type": "inline_equation", + "content": "\\gamma = z_{t}" + }, + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "type": "inline_equation", + "content": "\\psi = [t;T_{E}(Y)]" + }, + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "type": "inline_equation", + "content": "\\epsilon \\sim \\mathcal{N}(0,1)" + }, + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "type": "text", + "content": " is the Gaussian noise added to " + }, + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "type": "inline_equation", + "content": "\\mathcal{E}(I)" + }, + { + "bbox": [ + 304, + 436, + 545, + 461 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 468, + 473, + 480 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 468, + 473, + 480 + ], + "spans": [ + { + "bbox": [ + 306, + 468, + 473, + 480 + ], + "type": "text", + "content": "3.2. Human-Centric Image Editing" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "text", + "content": "Our task aims to generate a new image " + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\tilde{I}" + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "text", + "content": ", by replacing in the input image " + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "text", + "content": " the target garment using multimodal inputs, while preserving the model's identity and physical characteristics. As a natural consequence, this task can be identified as a particular type of inpainting tailored for human body data. Instead of using a standard text-to-image model, we perform inpainting concatenating along the channel dimension of the denoising network input " + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "inline_equation", + "content": "z_{t}" + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "text", + "content": " an encoded masked image " + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{E}(I_M)" + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "text", + "content": " and the relative resized binary inpainting mask " + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "inline_equation", + "content": "m\\in \\{0,1\\}^{h\\times w\\times 1}" + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "text", + "content": ", which is derived from the original inpainting mask " + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "inline_equation", + "content": "M\\in \\{0,1\\}^{H\\times W\\times 1}" + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "text", + "content": ". Since here, the spatial input of the denoising network is " + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\gamma = [z_t;m;\\mathcal{E}(I_M)],\\gamma \\in \\mathbb{R}^{h\\times w\\times 9}" + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "text", + "content": ". Thanks to the fully convolutional nature of the encoder " + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{E}" + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "text", + "content": " and the decoder " + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 304, + 485, + 547, + 713 + ], + "type": "text", + "content": ", this LDMs-based architecture can preserve the spatial information in the latent space. Exploiting this feature, our method can thus optionally add conditioning constraints to the generation. In particular, we propose to add two generation constraints in addition to the textual information: the" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23395" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "content": "model pose map " + }, + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "content": " to preserve the original human pose of the input model and the garment sketch " + }, + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "content": " to allow the final users to better condition the garment generation process." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 110, + 289, + 458 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 110, + 289, + 458 + ], + "spans": [ + { + "bbox": [ + 46, + 110, + 289, + 458 + ], + "type": "text", + "content": "Pose Map Conditioning. In most cases [21, 24, 44], inpainting is performed with the objective of either removing or entirely replacing the content of the masked region. However, in our task, we aim to remove all information regarding the garment worn by the model while preserving the model's body information and identity. Thus, we propose to improve the garment inpainting process by using the bounding box of the segmentation mask along with pose map information representing body keypoints. This approach enables the preservation of the model's physical characteristics in the masked region while allowing the inpainting of garments with different shapes. Differently from conventional inpainting techniques, we focus on selectively retaining and discarding specific information within the masked region to achieve the desired outcome. To enhance the performance of the denoising network with human body keypoints, we modify the first convolution layer of the network by adding 18 additional channels, one for each keypoint. Adding new inputs usually would require retraining the model from scratch, thus consuming time, data, and resources, especially in the case of data-hungry models like the diffusion ones. Therefore, we propose to extend the kernels of the pre-trained input layer of the denoising network with randomly initialized weights sampled from a uniform distribution [14] and retrain the whole network. This consistently reduces the number of training steps and enables training with less data. Our experiments show that such improvement enhances the consistency of the body information between the generated image and the original one." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "spans": [ + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "type": "text", + "content": "Incorporating Sketches. Fully describing a garment using only textual descriptions is a challenging task due to the complexity and ambiguity of natural language. While text can convey specific attributes like style, color, and patterns of a garment, it may not provide sufficient information about its spatial characteristics, such as shape and size. This limitation can hinder the customization of the generated clothing item other than the ability to accurately match the user's intended style. Therefore, we propose to leverage garment sketches to enrich the textual input with additional spatial fine-grained details. We achieve this following the same approach described for pose map conditioning. The final spatial input of our denoising network is " + }, + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "type": "inline_equation", + "content": "\\gamma = [z_t; m; \\mathcal{E}(I_M); p; s], [p; s] \\in \\mathbb{R}^{h \\times w \\times (18 + 1)}" + }, + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "type": "inline_equation", + "content": "s" + }, + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "type": "text", + "content": " are obtained by resizing " + }, + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "type": "inline_equation", + "content": "P" + }, + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 46, + 460, + 287, + 675 + ], + "type": "text", + "content": " to match the latent space dimensions. In the case of sketches, we only condition the early steps of the denoising process as the final steps have little influence on the shapes [2]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": "Mask Composition. To preserve the model identity when performing human-centric inpainting, we perform mask composition as the final step of the proposed approach." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "spans": [ + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "text", + "content": "Defining " + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\hat{I} = \\mathcal{D}(z_0) \\in \\mathbb{R}^{H \\times W \\times 3}" + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "text", + "content": " as the output of the decoder " + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\mathcal{D}" + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "inline_equation", + "content": "M_{\\mathrm{head}} \\in \\{0,1\\}^{H \\times W \\times 1}" + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "text", + "content": " as the model face binary mask of the image " + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "text", + "content": ", the final output image " + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\tilde{I}" + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "text", + "content": " is obtained as follows: " + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\tilde{I} = M_{\\mathrm{head}} \\odot I + (1 - M_{\\mathrm{head}}) \\odot \\hat{I}" + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 304, + 71, + 545, + 133 + ], + "type": "text", + "content": " denotes the element-wise multiplication operator." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 139, + 437, + 152 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 139, + 437, + 152 + ], + "spans": [ + { + "bbox": [ + 305, + 139, + 437, + 152 + ], + "type": "text", + "content": "3.3. Training and Inference" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 158, + 545, + 206 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 158, + 545, + 206 + ], + "spans": [ + { + "bbox": [ + 304, + 158, + 545, + 206 + ], + "type": "text", + "content": "As in standard latent diffusion models, given an encoded input " + }, + { + "bbox": [ + 304, + 158, + 545, + 206 + ], + "type": "inline_equation", + "content": "z = \\mathcal{E}(I)" + }, + { + "bbox": [ + 304, + 158, + 545, + 206 + ], + "type": "text", + "content": ", the proposed denoising network is trained to predict the noise stochastically added to " + }, + { + "bbox": [ + 304, + 158, + 545, + 206 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 304, + 158, + 545, + 206 + ], + "type": "text", + "content": ". The corresponding objective function can be specified as" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 315, + 225, + 545, + 251 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 225, + 545, + 251 + ], + "spans": [ + { + "bbox": [ + 315, + 225, + 545, + 251 + ], + "type": "interline_equation", + "content": "L = \\mathbb {E} _ {\\mathcal {E} (I), Y, \\epsilon \\sim \\mathcal {N} (0, 1), t, \\mathcal {E} (I _ {M}), m, p, s} \\left[ \\| \\epsilon - \\epsilon_ {\\theta} (\\gamma , \\psi) \\| _ {2} ^ {2} \\right], \\tag {2}", + "image_path": "b2212ad28756e0e9dd52117d41729ab77bf2c90d01784e9b8065d702d42b19f0.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 251, + 515, + 264 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 251, + 515, + 264 + ], + "spans": [ + { + "bbox": [ + 305, + 251, + 515, + 264 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 251, + 515, + 264 + ], + "type": "inline_equation", + "content": "\\gamma = [z_{t};m;\\mathcal{E}(I_{M});p;s]" + }, + { + "bbox": [ + 305, + 251, + 515, + 264 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 251, + 515, + 264 + ], + "type": "inline_equation", + "content": "\\psi = [t;T_E(Y)]" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 266, + 545, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 266, + 545, + 350 + ], + "spans": [ + { + "bbox": [ + 304, + 266, + 545, + 350 + ], + "type": "text", + "content": "Classifier-Free Guidance. Classifier-free guidance is an inference technique that requires the denoising network to work both conditioned and unconditioned. This method modifies the unconditional model predicted noise moving it toward the conditioned one. Specifically, the predicted diffusion process at time " + }, + { + "bbox": [ + 304, + 266, + 545, + 350 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 266, + 545, + 350 + ], + "type": "text", + "content": ", given the generic condition " + }, + { + "bbox": [ + 304, + 266, + 545, + 350 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 266, + 545, + 350 + ], + "type": "text", + "content": ", is computed as follows:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 329, + 358, + 545, + 372 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 329, + 358, + 545, + 372 + ], + "spans": [ + { + "bbox": [ + 329, + 358, + 545, + 372 + ], + "type": "interline_equation", + "content": "\\hat {\\epsilon} _ {\\theta} \\left(z _ {t} | c\\right) = \\epsilon_ {\\theta} \\left(z _ {t} | \\emptyset\\right) + \\alpha \\cdot \\left(\\epsilon_ {\\theta} \\left(z _ {t} | c\\right) - \\epsilon_ {\\theta} \\left(z _ {t} | \\emptyset\\right)\\right), \\tag {3}", + "image_path": "41ebe382a5d95f19294c92749358795f9c3ff4e712748988d668a34b32a7968e.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "spans": [ + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "inline_equation", + "content": "\\epsilon_{\\theta}(z_t|c)" + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "text", + "content": " is the predicted noise at time " + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "text", + "content": " given the condition " + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "inline_equation", + "content": "\\epsilon_{\\theta}(z_t|\\emptyset)" + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "text", + "content": " is the predicted noise at time " + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "text", + "content": " given the null condition, and the guidance scale " + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 380, + 545, + 427 + ], + "type": "text", + "content": " controls the degree of extrapolation towards the condition." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 429, + 545, + 513 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 429, + 545, + 513 + ], + "spans": [ + { + "bbox": [ + 304, + 429, + 545, + 513 + ], + "type": "text", + "content": "Since our model deals with three conditions (i.e. text, pose map, and sketch), we use the fast variant multi-condition classifier-free guidance proposed in [1]. Instead of performing the classifier-free guidance according to each condition probability, it computes the direction of the joint probability of all the conditions " + }, + { + "bbox": [ + 304, + 429, + 545, + 513 + ], + "type": "inline_equation", + "content": "\\Delta_{\\mathrm{joint}}^t = \\epsilon_\\theta (z_t|\\{c_i\\}_{i = 1}^{i = N}) - \\epsilon_\\theta (z_t|\\emptyset)" + }, + { + "bbox": [ + 304, + 429, + 545, + 513 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 345, + 520, + 545, + 535 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 345, + 520, + 545, + 535 + ], + "spans": [ + { + "bbox": [ + 345, + 520, + 545, + 535 + ], + "type": "interline_equation", + "content": "\\hat {\\epsilon} _ {\\theta} \\left(z _ {t} \\mid \\left\\{c _ {i} \\right\\} _ {i = 1} ^ {i = N}\\right) = \\epsilon_ {\\theta} \\left(z _ {t} \\mid \\emptyset\\right) + \\alpha \\cdot \\Delta_ {\\text {j o i n t}} ^ {t}. \\tag {4}", + "image_path": "050bc2739cf5ca5ea90d9b7fc885e67d307c0fc181670de56fecf4031773abf0.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 543, + 545, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 543, + 545, + 566 + ], + "spans": [ + { + "bbox": [ + 306, + 543, + 545, + 566 + ], + "type": "text", + "content": "This reduces the number of feed-forward executions from " + }, + { + "bbox": [ + 306, + 543, + 545, + 566 + ], + "type": "inline_equation", + "content": "N + 1" + }, + { + "bbox": [ + 306, + 543, + 545, + 566 + ], + "type": "text", + "content": " to 2." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "Unconditional Training. Ensuring the ability of the denoising model to work both with and without conditions is achieved by replacing at training time the condition with a null one according to a fixed probability. This approach allows the model to learn from both conditional and unconditional samples, resulting in improved mode coverage and sample fidelity. Moreover, this technique also allows the model to optionally use the control signals at prediction time. Since our approach considers multiple conditions, we propose to extend the input masking to each condition independently. Experiments show that tuning this parameter can effectively affect the quality of the final result." + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "23396" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 71, + 267, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 71, + 267, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 267, + 85 + ], + "type": "text", + "content": "4. Collecting Multimodal Fashion Datasets" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 289, + 331 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 289, + 331 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 289, + 331 + ], + "type": "text", + "content": "Currently available datasets for fashion image generation often contain low-resolution images and lack all the required multimodal information needed to perform the task previously described. For this reason, the collection of new multimodal datasets for the fashion domain plays a crucial role to advance research in the field. To this aim, we start from two recent high-resolution fashion datasets introduced for the virtual try-on task, namely Dress Code [28] and VITON-HD [7], and extend them with textual sentences and garment sketches. Both datasets include image pairs with a resolution of " + }, + { + "bbox": [ + 46, + 91, + 289, + 331 + ], + "type": "inline_equation", + "content": "1024 \\times 768" + }, + { + "bbox": [ + 46, + 91, + 289, + 331 + ], + "type": "text", + "content": ", each composed of a garment image and a reference model wearing the given fashion item. In this section, we introduce a framework to semi-automatically annotate fashion images with multimodal information and provide a complete description of how to enrich Dress Code and VITON-HD with garment-related text and sketches. We call our extended versions of these datasets Dress Code Multimodal and VITON-HD Multimodal, respectively. Sample images and multimodal data of the collected datasets can be found in Fig. 3." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 338, + 231, + 350 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 338, + 231, + 350 + ], + "spans": [ + { + "bbox": [ + 47, + 338, + 231, + 350 + ], + "type": "text", + "content": "4.1. Dataset Collection and Annotation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 357, + 289, + 657 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 357, + 289, + 657 + ], + "spans": [ + { + "bbox": [ + 46, + 357, + 289, + 657 + ], + "type": "text", + "content": "Data Preparation. We start the annotation from the Dress Code dataset, which contains more than 53k model-garment pairs of multiple categories. As a first step, we need to associate each garment with a textual description containing fashion-specific and non-generic terms which are sufficiently detailed but not extremely lengthy to be exploited for constraining the generation. Motivated by recent findings in the field showing that humans tend to describe fashion items using only a few words [3], we propose to use noun chunks (i.e. short textual sentences composed of a noun along with its modifiers) that can effectively capture important information while reducing unnecessary words or details. Given that manually annotating all the images would be time-consuming and resource-intensive1, we propose a novel framework to semi-automatically annotate the dataset using noun chunks. Firstly, domain-specific captions are collected from two available fashion datasets, namely FashionIQ [50] and Fashion200k [12], standardizing them with word lemmatization and eventually reducing each word to its root form with the NLTK library2. Then, we extract noun chunks from the captions, filtering the results by removing all textual items that start with or contain special characters. After this pre-processing stage, we obtain more than 60k unique noun chunks, divided into three different categories (i.e. upper-body clothes, lower-body clothes, and dresses)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 664, + 287, + 703 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 664, + 287, + 703 + ], + "spans": [ + { + "bbox": [ + 46, + 664, + 287, + 703 + ], + "type": "text", + "content": "1Since the Dress Code dataset consists of over 53k fashion items and assuming that each annotation requires approximately 5 minutes, a single annotator working 8 hours per day, 5 days a week, and 260 working days per year would take more than 2 years to complete the annotation task." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 59, + 703, + 133, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 703, + 133, + 712 + ], + "spans": [ + { + "bbox": [ + 59, + 703, + 133, + 712 + ], + "type": "text", + "content": "2 https://www.nltk.org/" + } + ] + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 307, + 69, + 547, + 200 + ], + "blocks": [ + { + "bbox": [ + 307, + 69, + 547, + 200 + ], + "lines": [ + { + "bbox": [ + 307, + 69, + 547, + 200 + ], + "spans": [ + { + "bbox": [ + 307, + 69, + 547, + 200 + ], + "type": "image", + "image_path": "1494a2f1d8b5661e28509a21f1bc94c1438e70f3476478bc3c481902a4c7d5e7.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 306, + 208, + 545, + 228 + ], + "lines": [ + { + "bbox": [ + 306, + 208, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 306, + 208, + 545, + 228 + ], + "type": "text", + "content": "Figure 3. Sample images and multimodal data from our newly collected datasets." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 307, + 233, + 545, + 311 + ], + "blocks": [ + { + "bbox": [ + 307, + 233, + 545, + 311 + ], + "lines": [ + { + "bbox": [ + 307, + 233, + 545, + 311 + ], + "spans": [ + { + "bbox": [ + 307, + 233, + 545, + 311 + ], + "type": "table", + "html": "
DatasetTextPoseSketch# Images# Products# Unique Texts# Unique Words
VITON-HD [7]X✓X27,35813,679--
Dress Code [28]X✓X107,58453,792--
Be Your Own Prada [56]✓✓X78,979N/A3,972445
DF-Multimodal [19]✓✓X44,096N/A10,25377
VITON-HD Multimodal✓✓✓27,35813,6795,1431,613
Dress Code Multimodal✓✓✓107,58453,79225,5962,995
", + "image_path": "1b21f52b47cc8d4e4e6a58955b4e30978c230dac00fc57e05c8e6cd72b7742b5.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 318, + 545, + 340 + ], + "lines": [ + { + "bbox": [ + 306, + 318, + 545, + 340 + ], + "spans": [ + { + "bbox": [ + 306, + 318, + 545, + 340 + ], + "type": "text", + "content": "Table 1. Comparison of Dress Code and VITON-HD Multimodal with other fashion datasets with multimodal annotations." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 348, + 545, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 348, + 545, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 348, + 545, + 456 + ], + "type": "text", + "content": "To determine the most relevant noun chunks for each garment, we employ the CLIP model [34] and its open-source adaptation (i.e. OpenCLIP [49]). We select the VIT-L14@336 and " + }, + { + "bbox": [ + 304, + 348, + 545, + 456 + ], + "type": "inline_equation", + "content": "\\mathrm{RN50\\times 64}" + }, + { + "bbox": [ + 304, + 348, + 545, + 456 + ], + "type": "text", + "content": " models for CLIP, and the VIT-L14, ViT-H14, and ViT-g14 models for OpenCLIP. Prompt ensembling is performed to improve the results and, for each image, we select 25 noun chunks based on the top-5 noun chunks per model rated by cosine similarity between image and text embeddings, avoiding repetitions." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 459, + 545, + 626 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 459, + 545, + 626 + ], + "spans": [ + { + "bbox": [ + 304, + 459, + 545, + 626 + ], + "type": "text", + "content": "Fine-Grained Textual Annotation. To ensure the accuracy and representativeness of our annotations, we manually annotate a significant portion of Dress Code images. In particular, we select the three most representative noun chunks, among the 25 automatically associated, with each garment image. To minimize the annotation time, we develop a custom annotation tool that constrains the annotation time to an average time of 60 seconds per item and allows the annotator to manually insert noun chunks in the case that none of the automatically extracted ones are suitable for the image. Overall, we manually annotate 26,400 different garments (8,800 for each category) out of the 53,792 products included in the dataset, ensuring to include all fashion items of the original test set [28]." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 630, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 712 + ], + "type": "text", + "content": "Coarse-Grained Textual Annotation. To complete the annotation, we first finetune the OpenCLIP ViT-B32 model, pre-trained on the English portion of the LAION5B dataset [40], using the newly annotated image-text pairs. We then use this model and the collected set of noun chunks to automatically tag all the remaining elements of the Dress Code dataset with the three most similar noun chunks, al" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23397" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 144 + ], + "type": "text", + "content": "ways determined via cosine similarity between multimodal embeddings. We employ the same strategy also to automatically annotate all garment images of the VITON-HD dataset. In this case, since this dataset only contains upper-body clothes, we limit the table noun chunks to the ones describing upper-body garments." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 147, + 287, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 147, + 287, + 243 + ], + "spans": [ + { + "bbox": [ + 46, + 147, + 287, + 243 + ], + "type": "text", + "content": "Extracting Sketches. The introduction of garment sketches can provide valuable design details that are not easily discernible from text alone. In this way, the dataset can provide a more accurate and comprehensive representation of the garments, leading to improved quality and better control of the generated design details. To extract sketches for both Dress Code and VITON-HD datasets, we employ PiDiNet [43], a pre-trained edge detection network." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 243, + 288, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 243, + 288, + 411 + ], + "spans": [ + { + "bbox": [ + 46, + 243, + 288, + 411 + ], + "type": "text", + "content": "Given that the selected datasets have originally been introduced for virtual try-on, they consist of both paired and unpaired test sets. While for the paired set we can directly use the human parsing mask to extract the garment of interest worn by the model and then feed it to the edge detection network, for the unpaired set we need to first create a warped version of the in-shop garment matching the body pose and shape of the target model. Following virtual try-on methods [47, 52], we train a geometric transformation module that performs a thin-plate spline transformation [36] of the input garment and then refines the warped result using a U-Net model [38]. From each warped garment, we extract the sketch image enabling the use of the proposed solution even in unpaired settings." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 418, + 224, + 430 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 418, + 224, + 430 + ], + "spans": [ + { + "bbox": [ + 47, + 418, + 224, + 430 + ], + "type": "text", + "content": "4.2. Comparison with Other Datasets" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 437, + 287, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 616 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 616 + ], + "type": "text", + "content": "The only two text-to-image generation datasets available in the fashion domain [19, 56] are both based on images from the DeepFashion dataset [22]. While the dataset introduced in [56] contains short textual descriptions, DeepFashion-Multimodal [19] is annotated with attributes (e.g. category, color, fabric, etc.) that can be composed in longer captions. In Table 1, we summarize the main statistics of the publicly available datasets textual annotations compared with those of our newly extended datasets. As can be seen, our datasets contain more variety in terms of textual items and words, confirming the appropriateness of our annotation procedure and enabling a more personalized control of the generation process. Also, it is worth noting that the other datasets have no in-shop garment images making them difficult to employ in our case." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 627, + 190, + 640 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 627, + 190, + 640 + ], + "spans": [ + { + "bbox": [ + 47, + 627, + 190, + 640 + ], + "type": "text", + "content": "5. Experimental Evaluation" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 647, + 261, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 647, + 261, + 659 + ], + "spans": [ + { + "bbox": [ + 47, + 647, + 261, + 659 + ], + "type": "text", + "content": "5.1. Implementation Details and Competitors" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": "Training and Inference. All models are trained on the original splits of the Dress Code Multimodal and VITON-HD Multimodal datasets on a single NVIDIA A100 GPU for 150k steps, using a batch size of 16, a learning rate" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "content": "of " + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "inline_equation", + "content": "10^{-5}" + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "content": " with a linear warmup for the first 500 iterations, and AdamW [23] as optimizer with weight decay " + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "inline_equation", + "content": "10^{-2}" + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "content": ". To speed up training and save memory, we use mixed precision [26]. We set both the fraction of steps conditioned by the sketch and the portion of masked conditions during training to 0.2. During inference, we employ the DDIM [42] with 50 steps as noise scheduler and set the classifier-free guidance parameter " + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 72, + 545, + 168 + ], + "type": "text", + "content": " to 7.5." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 171, + 546, + 363 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 171, + 546, + 363 + ], + "spans": [ + { + "bbox": [ + 304, + 171, + 546, + 363 + ], + "type": "text", + "content": "Baselines and Competitors. As first competitor, we use the out-of-the-box implementation of the inpainting Stable Diffusion pipeline3 provided by Huggingface. Moreover, we adapt two existing models, namely FICE [33] and SDEdit [25], to work on our setting. In particular, we retrain all main components of the FICE model on the newly collected datasets. We employ the same resolution used by the authors (i.e. " + }, + { + "bbox": [ + 304, + 171, + 546, + 363 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 304, + 171, + 546, + 363 + ], + "type": "text", + "content": "), downsampling each image to " + }, + { + "bbox": [ + 304, + 171, + 546, + 363 + ], + "type": "inline_equation", + "content": "256 \\times 192" + }, + { + "bbox": [ + 304, + 171, + 546, + 363 + ], + "type": "text", + "content": " and applying padding to match the desired size (which is then removed during evaluation). To compare our model with a different conditioning strategy, we employ the approach proposed in [25] using our model trained only with text and human poses as input modalities and perform the sketch guidance using as starting latent variable the sketch image with added random noise. Following the original paper instructions, we use 0.8 as the strength parameter." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 370, + 418, + 382 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 370, + 418, + 382 + ], + "spans": [ + { + "bbox": [ + 306, + 370, + 418, + 382 + ], + "type": "text", + "content": "5.2. Evaluation Metrics" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 389, + 545, + 509 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 389, + 545, + 509 + ], + "spans": [ + { + "bbox": [ + 304, + 389, + 545, + 509 + ], + "type": "text", + "content": "To assess the realism of generated images, we employ the Fréchet Inception Distance (FID) [16] and the Kernel Inception Distance (KID) [4]. For both metrics, we adopt the implementation proposed in [32]. Instead, to evaluate the adherence of the image to the textual conditioning input, we employ the CLIP Score (CLIP-S) [15] provided in the TorchMetrics library [9], using the OpenCLIP ViT-H/14 model as cross-modal architecture. We compute the score on the inpainted region of the generated output pasted on a " + }, + { + "bbox": [ + 304, + 389, + 545, + 509 + ], + "type": "inline_equation", + "content": "224 \\times 224" + }, + { + "bbox": [ + 304, + 389, + 545, + 509 + ], + "type": "text", + "content": " white background." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 512, + 545, + 643 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 512, + 545, + 643 + ], + "spans": [ + { + "bbox": [ + 304, + 512, + 545, + 643 + ], + "type": "text", + "content": "Pose Distance (PD). We propose a novel pose distance metric that measures the coherence of human body poses between the generated image and the original one estimating the distance between the human keypoints extracted from the original and generated images. Specifically, we employ the OpenPifPaf [20] human pose estimation network and compute the " + }, + { + "bbox": [ + 304, + 512, + 545, + 643 + ], + "type": "inline_equation", + "content": "\\ell_2" + }, + { + "bbox": [ + 304, + 512, + 545, + 643 + ], + "type": "text", + "content": " distance between each pair of real-generated corresponding estimated keypoints. We only consider the keypoints involved in the generation (i.e. that falls in the mask " + }, + { + "bbox": [ + 304, + 512, + 545, + 643 + ], + "type": "inline_equation", + "content": "M" + }, + { + "bbox": [ + 304, + 512, + 545, + 643 + ], + "type": "text", + "content": ") and weigh each keypoints distance with the detector confidence to take into account any estimation errors." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 647, + 545, + 695 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 647, + 545, + 695 + ], + "spans": [ + { + "bbox": [ + 304, + 647, + 545, + 695 + ], + "type": "text", + "content": "Sketch Distance (SD). To quantify the adherence of the generated image to the sketch constraint, we propose a novel sketch distance metric. To compute the score, we extract the segmentation map of the original and generated" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 315, + 702, + 516, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 315, + 702, + 516, + 713 + ], + "spans": [ + { + "bbox": [ + 315, + 702, + 516, + 713 + ], + "type": "text", + "content": "3https://huggingface.co/runwayml/stable-diffusion-inpainting" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23398" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 71, + 545, + 272 + ], + "blocks": [ + { + "bbox": [ + 50, + 71, + 545, + 272 + ], + "lines": [ + { + "bbox": [ + 50, + 71, + 545, + 272 + ], + "spans": [ + { + "bbox": [ + 50, + 71, + 545, + 272 + ], + "type": "table", + "html": "
ModelResolutionModalitiesDress Code MultimodalVITON-HD Multimodal
TextPoseSketchFID ↓KID ↓CLIP-S ↑PD ↓SD ↓FID ↓KID ↓CLIP-S ↑PD ↓SD ↓
Paired setting
Stable Diffusion [37]256×192✓17.059.2828.714.62-15.186.3830.405.04-
FICE [33]256×192✓✓30.6323.5428.726.87-49.4444.7429.266.37-
MGD (ours)256×192✓✓5.571.6731.332.37-10.113.1431.852.90-
Paired setting
Stable Diffusion [37]512×384✓17.439.4829.189.240.46716.286.5630.7010.780.410
SDEdit [25]512×384✓✓✓10.195.0329.215.410.39813.074.6630.586.760.306
MGD (ours)512×384✓✓✓5.742.1131.684.720.37410.603.2632.395.940.253
Unpaired setting
Stable Diffusion [37]256×192✓19.1110.6927.535.07-17.377.5528.405.50-
FICE [33]256×192✓✓34.1426.8626.037.15-52.7448.5825.946.58-
MGD (ours)256×192✓✓7.012.1929.582.96-11.543.1829.953.30-
Unpaired setting
Stable Diffusion [37]512×384✓19.5510.8028.029.890.58218.457.8728.7411.600.561
SDEdit [25]512×384✓✓✓11.385.6927.106.160.50915.125.6728.617.350.406
MGD (ours)512×384✓✓✓7.732.8230.046.790.45812.813.8630.757.220.317
", + "image_path": "cf9d9b28e7f0ad9143ba64f5e9a456f4dcc6d50c7e582a8adf44e3fe4f281195.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 50, + 300, + 285, + 415 + ], + "blocks": [ + { + "bbox": [ + 47, + 277, + 538, + 291 + ], + "lines": [ + { + "bbox": [ + 47, + 277, + 538, + 291 + ], + "spans": [ + { + "bbox": [ + 47, + 277, + 538, + 291 + ], + "type": "text", + "content": "Table 2. Quantitative results on the Dress Code Multimodal and VITON-HD Multimodal datasets for both paired and unpaired settings ." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 300, + 285, + 415 + ], + "lines": [ + { + "bbox": [ + 50, + 300, + 285, + 415 + ], + "spans": [ + { + "bbox": [ + 50, + 300, + 285, + 415 + ], + "type": "table", + "html": "
ModelModalitiesDress Code Multimodal
TextPoseSketchFID ↓KID ↓CLIP-S ↑PD ↓SD ↓
MGD (ours)✓6.192.1531.796.160.411
✓✓6.312.3331.675.310.405
✓✓✓5.742.1131.684.720.374
ModelModalitiesVITON-HD Multimodal
TextPoseSketchFID ↓KID ↓CLIP-S ↑PD ↓SD ↓
MGD (ours)✓11.393.5232.167.830.339
✓✓11.073.3632.276.770.318
✓✓✓10.603.2632.395.940.253
", + "image_path": "d7ae560265dea6f00f89ae23e0b50e84ac478623ac1bcb5b538436a773d6728e.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 455, + 287, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 455, + 287, + 540 + ], + "spans": [ + { + "bbox": [ + 46, + 455, + 287, + 540 + ], + "type": "text", + "content": "garments using an off-the-shelf clothing segmentation network" + }, + { + "bbox": [ + 46, + 455, + 287, + 540 + ], + "type": "inline_equation", + "content": "^{4}" + }, + { + "bbox": [ + 46, + 455, + 287, + 540 + ], + "type": "text", + "content": ". We then use the segmented garment area to extract garment sketches using the PIDInet [43] edge detector network. The final score is the mean squared error between these sketches, weighting the per-pixel results on the inverse pixel frequency of the activated pixels. More details about these proposed metrics can be found in the supplementary." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 545, + 171, + 559 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 545, + 171, + 559 + ], + "spans": [ + { + "bbox": [ + 47, + 545, + 171, + 559 + ], + "type": "text", + "content": "5.3. Experimental Results" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 564, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 564, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 46, + 564, + 287, + 696 + ], + "type": "text", + "content": "Comparison with Other Methods. We test our proposal for the paired and unpaired settings of the considered datasets. In the former, the conditions (e.g. text, sketch) refers to the garment the model is wearing, while in the latter, the in-shop garment differs from the worn one. In Table 2, we report the quantitative results on Dress Code Multimodal and VITON-HD Multimodal in comparison with the aforementioned competitors. As can be seen, the proposed MGD model consistently outperforms competitors, in terms of realism (i.e. FID and KID) and coherency with input modalities (i.e. CLIP-S, PD, and SD). In particu" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 307, + 300, + 545, + 379 + ], + "blocks": [ + { + "bbox": [ + 47, + 423, + 288, + 447 + ], + "lines": [ + { + "bbox": [ + 47, + 423, + 288, + 447 + ], + "spans": [ + { + "bbox": [ + 47, + 423, + 288, + 447 + ], + "type": "text", + "content": "Table 3. Performance analysis on the paired setting of both datasets as input modalities vary." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 300, + 545, + 379 + ], + "lines": [ + { + "bbox": [ + 307, + 300, + 545, + 379 + ], + "spans": [ + { + "bbox": [ + 307, + 300, + 545, + 379 + ], + "type": "table", + "html": "
ModalitiesRealismMultimodal Coherence
TextPoseSketchStable Diff.FICESDEditStable Diff.FICESDEdit
Dress✓70.82--65.32--
✓✓70.7396.26-65.1584.48-
✓✓✓70.29-52.5465.38-66.23
VITON✓67.03--57.76--
✓✓66.1793.84-73.7383.46-
✓✓✓60.71-53.4469.47-59.34
", + "image_path": "14e67e88cad2ecb0f7b416781d6509b6c69acf0ef2f5430d3c96f9bf4dbb53ca.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 386, + 545, + 430 + ], + "lines": [ + { + "bbox": [ + 305, + 386, + 545, + 430 + ], + "spans": [ + { + "bbox": [ + 305, + 386, + 545, + 430 + ], + "type": "text", + "content": "Table 4. User study results on the unpaired setting of both datasets. We report the percentage of times an image from MGD is preferred against a competitor. Comparisons with FICE [33] are performed at " + }, + { + "bbox": [ + 305, + 386, + 545, + 430 + ], + "type": "inline_equation", + "content": "256 \\times 192" + }, + { + "bbox": [ + 305, + 386, + 545, + 430 + ], + "type": "text", + "content": " resolution." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 446, + 545, + 579 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 446, + 545, + 579 + ], + "spans": [ + { + "bbox": [ + 304, + 446, + 545, + 579 + ], + "type": "text", + "content": "lar, when considering low-resolution results, we notice that FICE [33] can produce images fairly consistent with the text conditioning, albeit less realistic than other methods. While Stable Diffusion [37] enhances image realism, it fails to preserve the input model's pose due to the lack of pose information in the inputs. It is noteworthy that in this case, we compare the results of our model only using text and pose map as conditioning since both considered competitors are not conditioned on sketches. For this reason, we do not report the results in terms of sketch distance for low-resolution images." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 582, + 545, + 715 + ], + "type": "text", + "content": "In the high-resolution setting, we evaluate instead our MGD method using all multimodal conditions (i.e. text, pose map, and sketch) as input. In this case, we compare MGD with Stable Diffusion [37] plus SDEdit [25], where we use our text-pose conditioned denoising network as SDEdit backbone. Our findings indicate that Stable Diffusion performs worse in terms of the pose distance than both SDEdit and MGD, owing to the lack of pose information in the inputs. It is noteworthy that SDEdit performs worse than our model in all metrics. We attribute this behavior to the way sketch conditioning happens. In SDEdit," + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 58, + 702, + 222, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 222, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 222, + 713 + ], + "type": "text", + "content": "4https://github.com/levindabhi/cloth-segmentation" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "23399" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 47, + 69, + 296, + 301 + ], + "blocks": [ + { + "bbox": [ + 47, + 69, + 296, + 301 + ], + "lines": [ + { + "bbox": [ + 47, + 69, + 296, + 301 + ], + "spans": [ + { + "bbox": [ + 47, + 69, + 296, + 301 + ], + "type": "image", + "image_path": "6ec420afa290eb1e9fbc2f2ba28ad4a9ac7cb30c22fa8b19f5b3e67adb70fcfc.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 47, + 308, + 533, + 321 + ], + "lines": [ + { + "bbox": [ + 47, + 308, + 533, + 321 + ], + "spans": [ + { + "bbox": [ + 47, + 308, + 533, + 321 + ], + "type": "text", + "content": "Figure 4. Sample generated images on Dress Code Multimodal and VITON-HD Multimodal (bottom left) using all multimodal inputs." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 296, + 70, + 545, + 300 + ], + "blocks": [ + { + "bbox": [ + 296, + 70, + 545, + 300 + ], + "lines": [ + { + "bbox": [ + 296, + 70, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 296, + 70, + 545, + 300 + ], + "type": "image", + "image_path": "1a62e80663022be32de11fd9b9ce70962ee0b23552e560afc74440dcea6af1f6.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 332, + 288, + 416 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 332, + 288, + 416 + ], + "spans": [ + { + "bbox": [ + 46, + 332, + 288, + 416 + ], + "type": "text", + "content": "it occurs only at the beginning by initializing " + }, + { + "bbox": [ + 46, + 332, + 288, + 416 + ], + "type": "inline_equation", + "content": "z_{t}" + }, + { + "bbox": [ + 46, + 332, + 288, + 416 + ], + "type": "text", + "content": " using the sketch image with added noise according to the conditioning strength, while our model conditions the denoising process in multiple steps, depending on the sketch conditioning parameter. Qualitative results reported in Fig. 4 highlight how our model better follows the given conditions and generate high-realistic images." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 418, + 287, + 515 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 418, + 287, + 515 + ], + "spans": [ + { + "bbox": [ + 46, + 418, + 287, + 515 + ], + "type": "text", + "content": "To validate our results based on human judgment, we conduct a user study that evaluates both the realism of the generation and the adherence to multimodal inputs. Overall we collect about 7k evaluations involving more than 150 users. Additional details are reported in the supplementary. Table 4 shows the user study results. Also in this case our model outperforms the competitors, thus confirming the effectiveness of our proposal." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 521, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 288, + 715 + ], + "type": "text", + "content": "Varying Input Modalities. In Table 3, we study the behavior of our MGD model when the input modalities are masked (i.e. where we feed the model with a zero tensor instead of the considered modality). In particular, we focus on the CLIP-S for text adherence and on the newly proposed pose and sketch distances for the pose and sketch coherency, respectively. Notice that the text input anchors the CLIP-S metrics of all experiments and makes them comparable in all cases. Starting from the fully conditioned model (i.e. text, pose, sketch), we mask the sketch. As the decrease of the sketch distance in Table 3 confirms, this input actually influences the generation process of our model in both the considered datasets. Also, this modality slightly affects the pose distance as the sketch implicitly contains information about the model's body pose. We further mask the pose map input and compare the output with previous results. In" + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 308, + 331, + 544, + 439 + ], + "blocks": [ + { + "bbox": [ + 308, + 331, + 544, + 439 + ], + "lines": [ + { + "bbox": [ + 308, + 331, + 544, + 439 + ], + "spans": [ + { + "bbox": [ + 308, + 331, + 544, + 439 + ], + "type": "table", + "html": "
Uncond. PortionSketch Cond.Dress Code Multimodal
FID ↓KID ↓CLIP-S ↑PD ↓SD ↓
0.11.09.643.7630.247.660.459
0.21.08.623.2429.067.510.430
0.31.010.934.7828.477.690.432
0.20.88.563.2829.317.320.433
0.20.68.433.2129.517.320.436
0.20.48.113.0029.797.130.440
0.20.27.732.8230.046.790.458
0.20.07.822.8529.936.260.519
", + "image_path": "c9dbe5d4e464705675714775d23fe35b26cb2cd5fbf538b3a9ba0162c416d518.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_body" + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 446, + 545, + 480 + ], + "lines": [ + { + "bbox": [ + 305, + 446, + 545, + 480 + ], + "spans": [ + { + "bbox": [ + 305, + 446, + 545, + 480 + ], + "type": "text", + "content": "Table 5. Ablation analysis of our complete model varying the unconditioning portion during training and the sketch conditioning steps. Results refer to the unpaired setting." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 304, + 492, + 545, + 553 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 492, + 545, + 553 + ], + "spans": [ + { + "bbox": [ + 304, + 492, + 545, + 553 + ], + "type": "text", + "content": "this case, we can also notice a consistent difference with the text-only conditioned model, according to all metrics except CLIP-S as expected. These results confirm that our MGD model can effectively deal with the conditions in a disentangled way, making them optional." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 558, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 546, + 714 + ], + "type": "text", + "content": "Unconditional Training and Sketch Conditioning. In Table 5, we inquire about the fully conditioned network performance according to the variance of the portion of unconditional training. Additionally, we evaluate the results by varying the fraction of sketch conditioning steps. As can be seen, the best results are achieved by using 0.2 for both parameters. In particular, for unconditional training, we train three different models (i.e. with 0.1, 0.2, and 0.3). When evaluating the sketch conditioning parameter, we test our model with values between 0 and 1 with a stride of 0.2. It is worth noting that the sketch distance consistently decreases as the number of sketch conditioning steps increases, showing the robustness of the approach." + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "23400" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 119, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 119, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 119, + 83 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 91, + 289, + 224 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 91, + 289, + 224 + ], + "spans": [ + { + "bbox": [ + 46, + 91, + 289, + 224 + ], + "type": "text", + "content": "The Multimodal Garment Designer proposed in this paper is the first latent diffusion model defined for human-centric fashion image editing, conditioned by multimodal inputs such as text, body pose, and sketches. The novel architecture, trained on two new semi-automatically annotated datasets and evaluated with standard and newly proposed metrics, as well as by user studies, is very promising. The result is one of the first successful attempts to mimic the designers' job in the creative process of fashion design and could be a starting point for a capillary adoption of diffusion models in creative industries, oversight by human input." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 233, + 144, + 247 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 233, + 144, + 247 + ], + "spans": [ + { + "bbox": [ + 47, + 233, + 144, + 247 + ], + "type": "text", + "content": "Acknowledgments" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 253, + 289, + 350 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 253, + 289, + 350 + ], + "spans": [ + { + "bbox": [ + 46, + 253, + 289, + 350 + ], + "type": "text", + "content": "This work has partially been supported by the European Commission under the PNRR-M4C2 project \"FAIR - Future Artificial Intelligence Research\" and the European Horizon 2020 Programme (grant number 101004545 - ReInHerit), and by the PRIN project \"CREATIVE: CRoss-modal understanding and gEnerATIon of Visual and tExtual content\" (CUP B87G22000460001), co-funded by the Italian Ministry of University." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 359, + 107, + 371 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 359, + 107, + 371 + ], + "spans": [ + { + "bbox": [ + 47, + 359, + 107, + 371 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 53, + 378, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 14, + "blocks": [ + { + "bbox": [ + 53, + 378, + 287, + 422 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 378, + 287, + 422 + ], + "spans": [ + { + "bbox": [ + 53, + 378, + 287, + 422 + ], + "type": "text", + "content": "[1] Omri Avrahami, Thomas Hayes, Oran Gafni, Sonal Gupta, Yaniv Taigman, Devi Parikh, Dani Lischinski, Ohad Fried, and Xi Yin. 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Despite significant advancements in this area, this task remains a challenging problem as it requires a comprehensive understanding of multimodal cues and high-level semantics. To tackle this issue, we propose a multimodal high-order relation transformer, which integrates a high-order encoder and an adaptive decoder in a unified framework. By modeling the multimodal cues and exploring similarities between the shots, the encoder is capable of capturing high-order relations between shots and extracting shot features with context semantics. By clustering the shots adaptively, the decoder can discover more universal switch pattern between successive scenes, thus helping scene boundary detection. Extensive experimental results on three standard benchmarks demonstrate that the proposed model performs favorably against state-of-the-art video scene detection methods.", + "bbox": [ + 75, + 335, + 473, + 608 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 633, + 209, + 648 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Cognitive science has discovered that humans usually comprehend a long video by breaking down it into meaningful units and reasoning about their relationships [20]. Therefore, dividing a long video into a series of meaningful story-telling video scenes, i.e. video scene detection, turns out to be a crucial task towards high-level video understanding. In filmmaking and video production, the term 'scene' is a basic unit for story-telling, consisting of a series of semantic cohesive shots, while the term 'shot' is a series of frames captured by the same camera over an uninterrupted period of time [4]. The task of video scene detection has drawn remarkable attention and can be widely adopted to various tough applications, including video caption, content-driven video search, scene classification, human-centric storyline construction and so on [8, 15, 31]. Although significant progress has been achieved in recent years, video scene", + "bbox": [ + 75, + 659, + 470, + 900 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/1f8c70b7ec4ce57c62ec6808d2226888bed38e9d9b80b491c4357d38cbe684be.jpg", + "image_caption": [ + "(a) Two consecutive scenes in movie Blade Runner." + ], + "image_footnote": [], + "bbox": [ + 511, + 303, + 877, + 409 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/7dcecbe38f5a9a964a540de95deec2444d2a3aa64dcbfa3ab614afbb62098433.jpg", + "image_caption": [ + "(b) Histograms of similarities between shots." + ], + "image_footnote": [], + "bbox": [ + 511, + 426, + 875, + 547 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/0d2efe1cccf6c1bd7445ff05b0e14bfb3dd524a1318b62c3387d971f7b34d8e7.jpg", + "image_caption": [ + "(c) Diverse scene boundaries in movie Blade Runner." + ], + "image_footnote": [], + "bbox": [ + 517, + 564, + 874, + 603 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Figure 1: (a) There is minimal visual alteration at the scene boundary, while the audio content undergoes significant changes. (b) Direct similarities between shots near the boundary can all have high scores, while the trend of similarity variation can provide more discriminative signals. (c) Scene boundaries can vary greatly even in the same movie. Therefore, learning shot-level representations alone is insufficient for this class-agnostic task.", + "bbox": [ + 496, + 631, + 890, + 752 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "detection remains challenging due to requiring semantic understanding in a long-term video.", + "bbox": [ + 496, + 763, + 890, + 792 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Recently, researchers have proposed methods like [4, 15, 20, 38] that leverage visual cues in unlabeled videos to model scene boundary. These approaches mainly employ an unsupervised contrastive learning strategy to differentiate shots from distinct scenes. Although these methods have taken a big step forward, they simply use visual appearance cues to generate pseudo labels for contrastive", + "bbox": [ + 496, + 795, + 890, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "22081", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "learning, resulting in the model learning the differences of shots at the visual apparent level rather than semantic level. In order to address above limitations, approaches such as [18, 19, 23, 27] introduce various expert networks to model multimodal signals like visual, audio, cast and place in various video understanding tasks. These methods still struggle to accurately identify scene boundaries in long-term videos, particularly those with complex story-telling structures. This is due to that modeling context of the shots plays a crucial role in identifying boundaries. Furthermore, all previous methods [1, 4, 23, 20, 27, 38] primarily emphasize learning discriminative shot features and overlook that scene boundary detection is a class-agnostic task. Thus they fail to identify more universal switch pattern between different scenes which is less dependent on appearance.", + "bbox": [ + 80, + 90, + 467, + 316 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Based on the above analysis and the characteristics of scene boundary detection, we believe following aspects are important in this task: (1) The multimodal shot representations can provide comprehensive cues to detect scene boundary. (2) The high-order relation provides corrections for the context of shots. (3) The scene-level representations, derived from adaptively aggregation of shots features, can effectively indicate the switch pattern between different scenes. Firstly, as shown in Figure 1a, there is minimal alteration in the visual appearance between Scene A and scene B. However, the audio signal undergoes a significant change, making it easier to discern the transition between scenes. Secondly, as shown in Figure 1b, the shots before and after the scene boundary, such as shot 48 and shot 49, exhibit high similarities, suggesting that the scene switch can occur seamlessly. Neither the environment nor the characters change, only the two men's behavior changes. Under this circumstances, considering only the similarities between shots (first-order relation) can lead to undetectable blurred boundaries. Fortunately, by representing shots 47-49 as 10-dimensional similarity vectors based on their similarities with reference shots 43-52, we can observe a significant change near the scene boundary. This motivates us that the similarities between these similarity vectors, denoted as high-order relation, can correct for the first-order relation. Thirdly, unlike the common video action detection task, video scene detection is a category-agnostic task [5]. As shown in Figure 1c, even within the same movie, the appearances of the 'scene boundary shots' (i.e. shots 48, 52, 63, 80) still vary greatly. It is more important to discover the switch pattern between successive scenes rather than learn shot-level representations. This encourages us to learn more contextual and category-agnostic scene-level representations, which can be adaptively aggregated from shot-level features.", + "bbox": [ + 80, + 321, + 467, + 849 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Take these observations together, we propose the Multimodal High-order Relation Transformer for video scene detection, which can model multimodal cues, high-order", + "bbox": [ + 80, + 856, + 467, + 898 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "relation and scene adaptive clustering in a unified structure. Specifically, we first take multimodal expert networks and clip encoders to extract multimodal clip-level shot embeddings for the input shot sequence. Then our designed multimodal high-order relation transformer, consisting of a high-order encoder and an adaptive decoder, is employed to model the high-order relation for the shots and generate contextual scene-level representation in a unified framework. In detail, the high-order encoder primarily employs the multi-head and self-attention mechanism on the multimodal shot embeddings to produce high-order relationships ('relation in relation'), thereby enhancing the appropriate correlations between shots and suppressing erroneous ones. And the adaptive decoder merges contextual shot embeddings into scene representations with learnable scene prototypes and cross-attention. Finally, we take those contextualized shot embeddings for scene boundary classification and scene embeddings for boundary position regression.", + "bbox": [ + 503, + 90, + 888, + 361 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The major contributions of this work can be summarized as follows: (1) We propose the Multimodal High-order Relation Transformer, which can model multimodal cues, high-order relation and scene adaptive clustering in a unified structure. (2) In our transformer, we design the high-order encoder to enhance the context of shots and rectify noises in the correlation map of shots caused by their imperfect features. We further employ the adaptive decoder to aggregate shot features, which is better at capturing switch pattern between scenes rather than visual appearance. (3) Extensive experimental results on three standard benchmarks including MovieNetSSeg [12], OVSD [27] and BBC planet earth [1] demonstrate that the proposed model can outperform previous works by a large margin, and can be even competitive with those pre-training methods which consume more than 5 times training data.", + "bbox": [ + 503, + 363, + 888, + 603 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 503, + 611, + 638, + 626 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The basic assumption of video scene detection is that one shot can only belong to one scene, thus scene boundaries are a subset of shot boundaries [30]. As a result, the pre-task of scene detection is usually shot detection [14], which divides a video into sequences of time-continuous, non-overlapping shots. Given shot sequences, the video scene segmentation problem can be modeled as shot grouping, which clusters consecutive shots into scenes, or binary classification, which predicts whether a shot is a scene boundary. Many methods have been proposed [1, 4, 27, 20, 38], which can be categorized as unsupervised methods, supervised methods and self-supervised methods.", + "bbox": [ + 503, + 628, + 888, + 808 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Unsupervised Methods. Early works utilize a variety of unsupervised methods. Among them, [24, 29] cluster shots according to spatiotemporal video features or shot color similarities. [27] obtains a consecutive segmentation by dynamic programming. [28] presents a novel normalized cost function for optimally grouping shots into scenes. Other", + "bbox": [ + 503, + 811, + 888, + 898 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "22082", + "bbox": [ + 478, + 946, + 517, + 955 + ], + "page_idx": 1 + }, + { + "type": "image", + "img_path": "images/5d620c58cc8cca4783ec5b768ae62c7b14472d4652f38e61d3a390fad80961db.jpg", + "image_caption": [ + "Figure 2: Our method follows a three-stage pipeline. Firstly, we extract multimodal features with short-term context using multimodal backbones and clip encoders. In the second stage, our high-order encoder models complex multimodal cues and context for each shot, while the decoder adaptively aggregates shots within the same scene. Finally, we employ separate heads for central shot classification and scene boundary position regression. Please refer to the text for more details." + ], + "image_footnote": [], + "bbox": [ + 158, + 89, + 803, + 234 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "works make use of multimodal information [27]. For instance, [30] uses both low-level and high-level audio features, visual features to build scene transition graph and extend the unimodal STG-based temporal segmentation technique to multimodal scene segmentation. However, these methods are trained on small-scale datasets [1, 27], leading to poor generalization. Our method turns to deep learning and is trained with newly proposed large dataset [12], obtaining much better performance and generalization.", + "bbox": [ + 75, + 309, + 470, + 445 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Supervised and Self-Supervised Methods. As more and larger datasets are presented [4, 5, 20, 23, 38, 32, 37, 39], researchers are turning to supervised methods. With large-scale datasets, the deep neural network has a great advantage on extracting semantic features. [22] uses Alexresnet365 to extract scene features, while [13] achieves video scene segmentation using an image captioning model to extract semantic information of shots. [23] proposes a supervised baseline utilizing multimodal features to perform a shot-level binary classification, followed by an iterative optimal grouping. Recently, self-supervised methods achieve the best performance. Among them, [4] proposes a shot contrastive pre-training strategy to learn distinguishable shot representation. [38] achieves scene consistency representation learning using a novel positive sample selection strategy in contrast learning. And [20] mainly focuses on designing boundary-aware self-supervised tasks. However, these methods ignore multimodal information and simply use visual appearance cues to contrast different shots, while scene segmentation relies on semantic context. On the contrary, we can jointly model multimodal cues, high-order relation enhanced context with our proposed high-order encoder. And our proposed decoder can adaptive merge shot features into scene-level features to discover the switch pattern between video scenes.", + "bbox": [ + 75, + 446, + 470, + 824 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Multimodal High-order Relation Transformer", + "text_level": 1, + "bbox": [ + 76, + 837, + 468, + 869 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "As shown in Figure 2, our method deals with the multimodal shot-level video inputs in a pipeline of clip-level shot", + "bbox": [ + 76, + 869, + 470, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "embedding, multimodal high-order context modeling and boundary classification. Given a full-length input video, we first split it into a constituent set of shots with the standard shot detection techniques [30]. We then use the sliding window to get a continuous subsequence of shots $\\{s_0,s_1,\\dots,s_l\\}$ , and extract its multimodal representations (i.e. visual, place and audio) with the various expert networks. And the clip encoder is employed to model each shot's short-term context. Based on these multimodal shot features, we then perform multimodal high-order context modeling to exploit story-telling semantics for each shot. Specifically, the proposed multimodal high-order relation transformer first adopts the high-order encoder to take both multimodal cues and high-order relationships into consideration. Then the followed adaptive decoder is employed to aggregate shots into scenes. Finally, we adopt both shot features with contextual information and dynamically aggregated scene features for scene boundary prediction.", + "bbox": [ + 496, + 309, + 893, + 583 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Clip-level Shot Embedding", + "text_level": 1, + "bbox": [ + 498, + 592, + 743, + 609 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Multimodal Expert Networks. A long-term video is a typical multimodal data containing different high-level semantics [23]. Thus visual features extracted by classical backbones like I3D [2] or TSN [36] are insufficient for the video scene detection task. Instead, the story-telling high semantics can be better described and complemented by multimodal representations. Observing that, in addition to visual contents, a 'scene' is closely related to shots sharing common place, audio elements. Following [23] we adopt visual, place and audio expert networks to extract multimodal shot features.", + "bbox": [ + 496, + 612, + 893, + 777 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Following [1, 20, 23], we first extract the key frame for each shot in the sequence $\\{s_0,s_1,\\dots ,s_l\\}$ . Then we (1) adopt the ViT [7] to get visual features $\\mathbf{R}^{\\mathbf{v}} = \\{r_0^v,r_1^v,\\dots ,r_l^v\\}$ , (2) employ the ResNet50 [10] pretrained on Places dataset [40] to get place features $\\mathbf{R}^{\\mathbf{p}} = \\{r_0^p,r_1^p,\\dots ,r_l^p\\}$ , and (3) take stft [34] followed by the pretrained VGGish [11] to get audio features $\\mathbf{R}^{\\mathbf{a}} = \\{r_0^a,r_1^a,\\dots ,r_l^a\\}$ . The superscript $v,a,p$ denote for the different modality. Noting that all the expert", + "bbox": [ + 496, + 779, + 893, + 902 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "22083", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/8bc8a06e9e1371f11f2adc9c19f31fe3b3799fdbd5c10ca5470de1c06216b680.jpg", + "image_caption": [ + "Figure 3: The proposed Multimodal High-order Relation Transformer is designed to enhance shot features with high-order context and discover the switch pattern between scenes. Specifically, the high-order encoder can fuse multimodal cues and model context for each shot under the guidance of high-order relation extractor. Additionally, the subsequent decoder adaptively aggregate shots in the same scene and captures the switch pattern between scenes. Best viewed with colors." + ], + "image_footnote": [], + "bbox": [ + 119, + 89, + 851, + 330 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "networks are frozen during the training process.", + "bbox": [ + 76, + 410, + 393, + 425 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Aiming to enhancing shot features with high-order context and discovering the switch pattern between scenes, we design a transformer-based architecture. As shown in Figure 3, it consists of a high-order encoder and an adaptive decoder. The encoder is applied to fuse complex multimodal cues and model context for each shot with the help of high-order relation extractor, while the decoder is responsible for adaptively aggregating shots in the same scene.", + "bbox": [ + 75, + 431, + 470, + 553 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Clip Encoder. Following [23], we add a clip encoder on a local window for each shot's representations, aiming to obtain their clip-level representations. Specifically, taking the visual feature $r_i^v$ of shot $i$ for example, we consider the differences $\\mathbf{S}_{\\mathbf{D}}$ and relations $\\mathbf{S}_{\\mathbf{R}}$ of its n-earby shots in a window with length $2w_{s}$ , i.e. $\\mathbf{V}_i = \\left\\{r_{i - (w_s - 1)}^v,\\dots ,r_i^v,\\dots ,r_{i + w_s}^v\\right\\}$ . This process can be performed by temporal convolution layers $\\Psi$ and fully connected layers FC, as shown in Equation (1):", + "bbox": [ + 76, + 559, + 470, + 703 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathbf {S} _ {\\mathbf {D}} \\left(\\mathbf {V} _ {i}\\right) = \\Psi \\left(\\left\\{r _ {i - \\left(w _ {s} - 1\\right)}, \\dots , r _ {i} ^ {v} \\right\\}\\right) \\cdot \\Psi \\left(\\left\\{r _ {i + 1} ^ {v}, \\dots , r _ {i + w _ {s}} ^ {v} \\right\\}\\right), \\\\ \\mathbf {S} _ {\\mathbf {R}} (\\mathbf {V} _ {i}) = \\Psi (\\{r _ {i - (w _ {s} - 1)} ^ {v}, \\dots , r _ {i + w _ {s}} ^ {v} \\}), \\\\ r _ {i} ^ {v ^ {+}} = \\mathbf {F C} (\\operatorname {c o n c a t} \\left(\\mathbf {S} _ {\\mathbf {D}} \\left(\\mathbf {V} _ {i}\\right), \\mathbf {S} _ {\\mathbf {R}} \\left(\\mathbf {V} _ {i}\\right)\\right)), \\tag {1} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 83, + 726, + 470, + 792 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\text{concat}$ denotes the concatenation operation, $\\cdot$ denotes the inner product. Similar operations are performed on the place and audio modality, and the updated shot features can be described by $\\mathbf{R}^{\\mathbf{v}^{+}} = \\{r_{0}^{v^{+}}, r_{1}^{v^{+}}, \\dots, r_{l}^{v^{+}}\\}$ , $\\mathbf{R}^{\\mathbf{p}^{+}} = \\{r_{0}^{p^{+}}, r_{1}^{p^{+}}, \\dots, r_{l}^{p^{+}}\\}$ , $\\mathbf{R}^{\\mathbf{a}^{+}} = \\{r_{0}^{a^{+}}, r_{1}^{a^{+}}, \\dots, r_{l}^{a^{+}}\\}$ . Consequently, these multimodal shot features are enhanced with short-term context.", + "bbox": [ + 75, + 792, + 468, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Multimodal High-order Context Modeling", + "text_level": 1, + "bbox": [ + 500, + 409, + 861, + 425 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Aiming to enhancing shot features with high-order context and discovering the switch pattern between scenes, we design a transformer-based architecture. As shown in Figure 3, it consists of a high-order encoder and an adaptive decoder. The encoder is applied to fuse complex multimodal cues and model context for each shot with the help of high-order relation extractor, while the decoder is responsible for adaptively aggregating shots in the same scene.", + "bbox": [ + 496, + 440, + 890, + 561 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "High-order Relation Extractor. As discussed above, directly adopting the standard transformer encoder [35] over the shot sequence features may introduce noises in the correlation map due to imperfect shot features, and ignore comprehensive 'high-order relation' signal. Thus, we innovatively design the high-order relation extractor to correct first-order relations and fuse the multimodal cues jointly. As shown in the upper part of Figure 3, taking the multimodality shot sequence features $\\mathbf{R}^{\\mathbf{v}^{+}}$ , $\\mathbf{R}^{\\mathbf{p}^{+}}$ , $\\mathbf{R}^{\\mathbf{a}^{+}}$ as inputs, we first calculate the multi-head based temporal similarity matrix for each modality, generating a first-order multimodal relation map $\\mathbf{M} \\in \\mathcal{R}^{(l + 1) \\times (l + 1) \\times 3h}$ , which naturally contains temporal positional signal. Note that $l + 1$ is the length of shot sequence and $h$ is the number of heads. Then a shallow CNN is applied on $\\mathbf{M}$ to fuse multimodal cues and model neighboring first-order relations. And one standard transformer layer followed by linear layers and sigmoid function is adopted to model the global associations of each shot's relation, producing the guidance map $\\mathbf{M}_{\\mathbf{C}}$ .", + "bbox": [ + 496, + 571, + 892, + 861 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "High-order Encoder for Context Modeling. As shown in the bottom left part of Figure 3, we fuse multimodal fea", + "bbox": [ + 498, + 869, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "22084", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "tures with concatenation operation and a simple linear layer:", + "bbox": [ + 76, + 90, + 468, + 106 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nr _ {i} ^ {f} = \\mathbf {F C} \\left(\\operatorname {c o n c a t} \\left(r _ {i} ^ {v ^ {+}}, r _ {i} ^ {p ^ {+}}, r _ {i} ^ {a ^ {+}}\\right)\\right) \\in \\mathcal {R} ^ {d _ {f}}, \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 130, + 113, + 468, + 133 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "producing fused shot sequence features $\\mathbf{R}^f\\in \\mathcal{R}^{(l + 1)\\times d_f}$ where the superscript $f$ denotes for fusion. Then we apply the guidance map $\\mathbf{M_C}$ to enhance context modeling in a conventional transformer encoder. In detail, we first generate transformed queries and key-values pairs by: $\\mathbf{Q} = \\mathbf{R}^{f}\\mathbf{W}^{Q},\\mathbf{K} = \\mathbf{R}^{f}\\mathbf{W}^{K},\\mathbf{V} = \\mathbf{R}^{f}\\mathbf{W}^{V}$ , where $\\mathbf{W}^Q\\in \\mathcal{R}^{d_f\\times d_k},\\mathbf{W}^K\\in \\mathcal{R}^{d_f\\times d_k},\\mathbf{W}^V\\in \\mathcal{R}^{d_f\\times d_v}$ . Noting that we omit the multi-head scripts to simplify the expression here. Then the modified attention process HoAttn(Rf), under the guidance from the high-order multimodal relation cues $\\mathbf{M_C}$ , can be described by:", + "bbox": [ + 76, + 138, + 472, + 306 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {H o A t t n} \\left(\\mathbf {R} ^ {f}\\right) = \\left(\\mathbf {M} _ {C} \\odot \\operatorname {s o f t m a x} \\left(\\frac {\\mathbf {Q K} ^ {T}}{\\sqrt {d _ {k}}}\\right)\\right) \\mathbf {V}, \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 99, + 311, + 468, + 347 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\odot$ denotes Hadamard product, indicating $\\mathbf{M}_C$ works as a rectifier to enhance the appropriate correlations and suppress the erroneous ones. The residual connections, normalization operation and feed-forward layer are concatenated after this attention block, as shown in Figure 3. As a result, the high-order encoder can produce shot representations $\\mathbf{R}^{f^*} = \\{r_0^{f^*}, r_1^{f^*}, \\dots, r_l^{f^*}\\}$ . And $\\mathbf{R}^{f^*}$ contains comprehensive multi-modality contextual information. The above two parts fit together as our High-order Encoder and can serve as a basic block, offering a flexible high-order relation perception function.", + "bbox": [ + 75, + 351, + 468, + 518 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Adaptive Decoder for Shot Clustering. Although the high-order encoder successfully models both multimodal cues and high-order relations into the shot representations, it is still challenging to detect scene boundaries. Because even appearances of 'boundary shots' within the same video can vary dramatically. It is essential to learn the switch pattern between scenes, rather than simple shot features. Consequently, we design an adaptive decoder to dynamically merge shots within the same scene, resulting in aggregated contextual scene features. Our decoder also follows the query-key-value design in the vanilla transformer [35], making the full model unified.", + "bbox": [ + 75, + 518, + 468, + 699 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As shown in the right part of Figure 3, our adaptive decoder consists of a pair of learnable scene prototypes $\\mathbf{P} = \\{p_1, p_2\\}$ and an attention block. In order to reduce the domain gap between scene prototypes and shot features, we first employ the average pooled feature of all shots to modify the scene prototypes. The attention interaction between the shots and scene prototypes can be formulated by:", + "bbox": [ + 75, + 700, + 468, + 806 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {P} ^ {*} = \\mathbf {P} \\odot a v g (\\mathbf {R} ^ {f ^ {*}}),\n$$\n", + "text_format": "latex", + "bbox": [ + 173, + 811, + 328, + 828 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {A} _ {S} = \\left(\\mathbf {P} ^ {*} \\mathbf {W} _ {q}\\right) \\left(\\mathbf {R} ^ {f ^ {*}} \\mathbf {W} _ {k}\\right) ^ {T}, \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 173, + 828, + 468, + 845 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {Z} = \\{z _ {1}, z _ {2} \\} = \\mathbf {A} _ {S} \\mathbf {R} ^ {f ^ {*}},\n$$\n", + "text_format": "latex", + "bbox": [ + 173, + 845, + 346, + 861 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{W}_q\\in \\mathcal{R}^{d_s\\times d_q}$ , $\\mathbf{W}_k\\in \\mathcal{R}^{d_f\\times d_q}$ are learnable parameters. The affinity matrix $\\mathbf{A}_S\\in \\mathcal{R}^{2\\times (l + 1)}$ measures the rel", + "bbox": [ + 76, + 869, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "evance between each prototype and the shots, which directs the aggregation of shots into scenes. And $\\{z_1,z_2\\}$ indicate the dynamically aggregated scene representations, which is used to regress the scene boundary positions.", + "bbox": [ + 496, + 90, + 890, + 151 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Objective Function and Data Augmentation", + "text_level": 1, + "bbox": [ + 498, + 157, + 870, + 172 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Based on above discuss, we learn a set of shot representations $\\mathbf{R}^{f^*} = \\{r_0^{f^*}, r_1^{f^*}, \\dots, r_l^{f^*}\\}$ and two adaptively merged scene features $\\mathbf{Z} = \\{z_1, z_2\\}$ for the input shot sequence $\\{s_0, s_1, \\dots, s_l\\}$ . For each shot sequence, we make prediction on the central shot $r_{[l/2]}^{f^*}$ , i.e. determining whether it's a scene boundary or not. The subscript $[l/2]$ stands for the floor function. The classification loss can be formulated as:", + "bbox": [ + 496, + 176, + 890, + 303 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {L} _ {p r e} = - \\left[ y _ {c} \\log \\left(\\phi \\left(r _ {\\lfloor l / 2 \\rfloor} ^ {f ^ {*}}\\right)\\right) + \\left(1 - y _ {c}\\right) \\log \\left(\\phi \\left(r _ {\\lfloor l / 2 \\rfloor} ^ {f ^ {*}}\\right)\\right) \\right], \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 311, + 890, + 335 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $y_{c}$ is the label for the central shot, deciding whether it's a scene boundary, and $\\phi$ is a binary classification head. Moreover, ordering to learn adaptive scene representations, we adopt the adaptively merged scene features $\\mathbf{Z} = \\{z_1,z_2\\}$ and a regression head $\\gamma$ to regress the position of the boundary in the shot sequence:", + "bbox": [ + 496, + 343, + 893, + 434 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {L} _ {r e g} = \\mathbf {M S E} [ p, \\gamma (\\text {c o n c a t} (z _ {1}, z _ {2})) ], \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 571, + 446, + 890, + 464 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $p$ is the ground-truth position of the scene boundary in the shot sequence, and $p = -1$ or $p = l + 1$ stands for there are no boundaries or multiple boundaries in the sequence. MSE denotes the mean squared error. The overall training loss can be $\\mathbf{L} = \\mathbf{L}_{pre} + \\alpha \\mathbf{L}_{reg}$ , where $\\alpha$ is a hyperparameter.", + "bbox": [ + 496, + 474, + 890, + 565 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Moreover, there is a serious class-imbalance problem in the scene detection task, because boundaries are rare in a long video. Thus, we construct shot sequence samples with positive boundary on the central position by concatenating two distant subsequences in the same video or two subsequences from different videos:", + "bbox": [ + 496, + 565, + 890, + 656 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{s _ {0}, \\dots , s _ {l / 2}, \\dots , s _ {l} \\right\\} _ {\\text {n e w}} = \\left\\{s _ {0}, \\dots , s _ {l / 2} \\right\\} _ {v _ {0}} + \\left\\{s _ {l / 2}, \\dots , s _ {l} \\right\\} _ {v _ {1}}. \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 500, + 667, + 890, + 698 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The ratio of constructed samples to origin samples is adjustable according to the data distribution.", + "bbox": [ + 496, + 699, + 890, + 729 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experimental Results", + "text_level": 1, + "bbox": [ + 498, + 742, + 705, + 758 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Experimental Setup", + "text_level": 1, + "bbox": [ + 500, + 763, + 689, + 779 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Dataset. To demonstrate the effectiveness of our proposed method, we carry out extensive experiments on three public available datasets, including MovieNet-SSeg [12], BBC planet earth [1] and OVSD [27]. MovieNet [12], containing 1,100 videos with 1.6M shots, is the largest dataset for video understanding analysis by far. And the MovieNet-SSeg is a sub-dataset of that, with 190, 64 and 64 videos labeled with scene boundaries for training, validating and", + "bbox": [ + 496, + 780, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "22085", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/36b899171d4c6b6243498423e4f6deb6fbeef523206ae3846b8c7a6410d120d8.jpg", + "table_caption": [ + "Table 1: Results on the MovieNetSSeg dataset. The best results are in bold, and the second best are in bold and underlined. Note that self-supervised methods are pretrained with 1100 videos in MovieNet (MS-1100), and fine-tuned with 190 training videos in MovieSSeg (MS-190). Using less than 1/5 of the training data, our model can achieve competitive results." + ], + "table_footnote": [], + "table_body": "
MethodTraining DataAP (↑)mIoU (↑)AUC-ROC (↑)F1 (↑)
Supervised Learning
Siamese [1]MS-19035.839.6--
MS-LSTM [12]MS-19046.546.2--
LGSS [23]MS-19047.148.8--
OursMS-19054.851.290.346.3
Unsupervised Learning
GraphCut [25]None14.129.7--
SCSA [3]None14.730.5--
DP [9]None15.532.0--
Story Graph [33]None25.135.7--
Grouping [27]None33.637.2--
Self-supervised Learning
ShotCoL [4]MS-110053.4---
SCRL [38]MS-110054.8--51.4
BaSSL [20]MS-110056.349.590.345.7
", + "bbox": [ + 165, + 138, + 802, + 388 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "testing. Besides, we also carry out experiments on BBC planet earth [1] and OVSD [27] dataset. BBC planet earth contains 11 documentaries and OVSD contains 21 various videos. And we just take them as the testing set to verify the generalization of our model, i.e. our model trained on MovieScenes-SSeg is directly tested them, because of their limited scale and unavailable splitting strategy.", + "bbox": [ + 75, + 412, + 468, + 518 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation Metrics. We make comprehensive validations on our model with several metrics: (1) Average Precision(AP), it's the mean of AP of $y_{c} = 1$ for each video. (2) mIoU, the averaged intersection over union (IoU) between detected scene boundary with their closest ground-truth scene boundary. (3) F1 score, the harmonic mean of the precision and recall, taking both recall and precision into consideration. (4) AUC - ROC, short for area under the receiver operating characteristics.", + "bbox": [ + 75, + 518, + 468, + 655 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation Details. The proposed High-Order Relation Aware Multi-modality Network is implemented in PyTorch framework [21] with NVIDIA V100 GPUs.", + "bbox": [ + 75, + 657, + 468, + 702 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To begin with, we set the shot sequence length as 7, which is able to contain enough contextual information while requiring relative low memory resource. In the clip-level shot embedding stage, we only take visual, place and audio modalities mentioned in [23], as they play the most crucial roles in scene boundary detection. In specific, we use ViT-B/16 pretrained on ImageNet [6], ResNet50 pretrained on Place dataset [40], and VGGish pretrained on AVA-ActivaSpeaker [26] to extract multimodal shot features with 768, 2048, 128 dimensions respectively. All of them were frozen during training. The clip encoder employs the 1D-CNN [16] and the FC layer to transform them into 384, 256, 128 dimensional vectors. This indicates the im", + "bbox": [ + 75, + 703, + 470, + 900 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/42d1348a41d799f2f81c83d73be4db35363e8be4e98d38d3d294d4480087662a.jpg", + "table_caption": [ + "Table 2: Results of AP on BBC planet earth and OVSD datasets. Performances are achieved by the model trained on the MovieNetSSeg dataset without any fine-tuning." + ], + "table_footnote": [], + "table_body": "
MethodBBCOVSD
SimCLR实例) [4]32.325.5
SimCLR(temperal) [4]34.224.9
SimCLR(NN) [4]32.925.0
BaSSL(More Training Data) [20]40.028.7
Ours38.727.5
", + "bbox": [ + 501, + 459, + 893, + 555 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "portance of each modality, which will be verified in the ablation studies. In the followed multimodal high-order context modeling stage, the high-order relation extractor first maps the multimodal features as the correlation map $\\mathbf{M}$ with 8 heads. Feeding $\\mathbf{M}$ into the shallow CNN with 4 layers, one transformer encoder layer and the followed linear layer, we get the high-order relation-aware guidance map $\\mathbf{M}_{\\mathbf{C}}$ . We set the corresponding high-order context modeling encoder with 8 heads, 1 layer, and hidden units as 768. Finally, in the Adaptive Decoder, the dimensions of the merged scene features and the shot features remain the same. As a result, the scale of learnable parameters in our model is approximately equivalent to the sum of two layers of transformer encoder, four layers of CNN and several linear layers, which is comparable to that of BaSSL [20] without its' backbone.", + "bbox": [ + 496, + 580, + 890, + 821 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The model is trained for 10 epochs with the Adam optimizer [17]. We start training with a learning rate of 0.0002, and decay the learning rate using a cosine schedule. The batch-size is set to 128 for all experiments. And the hyperparameter $\\alpha$ in loss is set to 0.2. At last, for evaluation on", + "bbox": [ + 496, + 824, + 890, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "22086", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "the testing set, we tackle the over-fitting by choosing the s-napshot of the model based on the validation set. Noting that during inference, for each shot sequence we only make prediction on the central shot. Only if the classification head predicts to be positive, or the regression head outputs the central position, we take it as a positive boundary.", + "bbox": [ + 75, + 90, + 470, + 183 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.2. Performance Comparison", + "text_level": 1, + "bbox": [ + 76, + 186, + 312, + 204 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We compare with several recent state-of-the-art methods on the MovieNet-SSeg [12] in Table 1. And verifying the generation ability of our method by carrying out experiments on BBC planet earth [1] and OVSD [27] datasets in Table 2. We can find that our proposed High-Order Relation Aware Multi-modality Network achieves much better performance compared with the supervised methods, and can be competitive with the self-supervised ones while consuming much less training resources.", + "bbox": [ + 75, + 208, + 468, + 343 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results on MovieNet-SSeg. Table 1 presents the quantitative results on MovieNet-SSeg. We compare our method with various types of methods, including supervised, unsupervised and self-supervised approaches. The results demonstrate that under the same settings, our methods can outperform previous works by a large margin and can be even competitive with those which employ more than 5 times training data. Particularly, our method achieves 54.8 for AP, 51.2 for mIoU, 90.3 for AUC - ROC and 46.3 for F1. Noting that our method can offer a much more convenient way for training and testing compared with BaSSL, ShotCoL and SCRL [20, 4, 38]. For fair comparison, we also conduct experiments using identical multi-modality settings, specifically by the same features generated by expert networks. As shown in Tabel 3, using less external knowledge, our approach can still outperform LGSS by a large margin. Different from previous works which neglect the high-order relations among the shot sequence and only focus on learning shot features, our method jointly models both of them in a unified deep model.", + "bbox": [ + 75, + 345, + 470, + 647 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results on BBC planet earth and OVSD. As shown in Table 2, we further validate performance of our method on BBC planet earth [1] and OVSD [27]. The training and testing splits are not available and the scale of dataset size are quite small (11 for BBC, and 21 for OVSD respectively), in addition, 2 out of 21 videos in OVSD is not available. Consequently, we just directly employ the model trained on MovieNetSSeg without any fine-tune, and take inference on these two datasets. SimCLR(x) corresponds to ShotCoL [4] using different contrastive learning strategies reproduced by [20]. The results demonstrate advanced generalization ability of our methods. It's competitive with shot-level pretraining methods.", + "bbox": [ + 75, + 648, + 468, + 844 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Studies and Analysis", + "text_level": 1, + "bbox": [ + 76, + 849, + 344, + 864 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "To carry out analysis and evaluate the contribution of each component and setting in our method, we conduct a", + "bbox": [ + 76, + 869, + 470, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/59716d9002e413e15786bfc9bd3e7f8f8f522d80630584cef273db2572bddca3.jpg", + "table_caption": [ + "Table 4: Impact of multimodal semantics, where three elements are studied including visual, place, and audio. † denotes that the results are copied from [23]." + ], + "table_footnote": [], + "table_body": "
MethodplaceaudiovisualAP (↑)
Grouping [27]†✓✓✓23.8
StoryGraph [33]†✓✓✓33.2
Siamese [1]†✓✓✓34.1
LGSS [23]✓✓✓47.1
Ours✓50.9
Ours✓16.3
Ours✓52.4
Ours✓✓48.4
Ours✓✓53.4
Ours✓✓53.1
Ours✓✓✓54.8
", + "bbox": [ + 501, + 138, + 883, + 325 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "series of ablation studies. All the following comparative experiments are conducted on the MovieNetSSeg dataset.", + "bbox": [ + 496, + 337, + 890, + 367 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Impact of Multimodal Semantics. First of all, we revisit the impact of each modality in Table 4. We utilize the whole pipeline with clip-level shot embedding and multimodal high-order context modeling to make predictions on the testing set. Experiment starts from the model using only one modality features, and gradually adds different modality cues. Observing the second block of Table 4, we get the conclusion that visual modality plays the most important role in video scene detection. It's hard for single audio features to obtain satisfied results. From the third part of Table 4, we learn that both audio and place modalities can give complementary cues to the visual modality, and improves the final results. In particularly, audio improves 2.7 in terms of AP, place improves 3.5 for AP. Combining three modalities can produce the best result, i.e. 54.8 for AP. Compared with previous works in Table 4, our method gets the best results. Because our approach takes a more comprehensive way to fuse the multimodal features and drive them to complement with each other in a unified model. This can prove the hypothesis we presented above, i.e. multimodal content can complement for each other in the task of scene boundary detection.", + "bbox": [ + 496, + 369, + 892, + 702 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Impact of Different Components. We take experiments to validate the effect of different components in our method, including the clip encoder, the high-order encoder and adaptive decoder in our multimodal high-order relation transformer. Specifically, taking the full model as baseline, we remove the clip encoder which is denoted as 'w/o CE'. Removing the high-order relation extractor can verify the effectiveness of modeling high-order context, and we denote it as 'w/o HR', i.e. without high-order relation guidance. And the model without the full high-order encoder in the multimodal high-order relation transformer is denoted as 'w/o CR' for 'without context relation', as it lacks the context relationship modeling. And the model without the", + "bbox": [ + 496, + 704, + 893, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "22087", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/9c2a1e8173e28c3a97aebe69af67a1798374a4cc901daaf31f9484ee75c3229e.jpg", + "table_caption": [ + "Table 3: Results on the MovieNetSSeg dataset with different multimodal semantics settings, which demonstrate the effectiveness of our approach under fair conditions." + ], + "table_footnote": [], + "table_body": "
MethodLGSS (audio)LGSS (place)LGSS (audio+place)LGSS (audio+place +act+cast)Ours (audio)Ours (place)Ours (audio+place)Ours (audio+place +visual)
AP(↑)17.539.043.447.116.350.948.454.8
", + "bbox": [ + 86, + 125, + 875, + 189 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/ab95f4e91d7d452c8ff44329bc42206ec04e93412ebdc2aedd81cae3430a5a5a.jpg", + "table_caption": [ + "Table 5: Impact of different components. We take the full model as baseline." + ], + "table_footnote": [], + "table_body": "
ModalityAP (↑)mIoU (↑)AUC-ROC (↑)F1 (↑)
w/o CE52.348.390.045.5
w/o HR51.150.388.444.4
w/o CR48.645.988.645.2
w/o Cluster54.350.990.346.2
Full Model54.851.290.346.3
", + "bbox": [ + 78, + 244, + 460, + 340 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/8dea7ba4d3e6e86738fa18eddf012e57c048201c56667761416ac7a0562718d7.jpg", + "image_caption": [ + "Figure 4: Impact of different data augmentation strategies." + ], + "image_footnote": [], + "bbox": [ + 78, + 356, + 271, + 470 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/f864ad00e6773ea5bb9cc1080d8cf36280e53b7776ef2258b7be1cc8ecb7dc11.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 272, + 357, + 467, + 469 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "proposed adaptive decoder is formulated as 'w/o Cluster', which does not need to cluster shots within the same scene. As shown in the first line of Table 5, removing the clip encoder leads to 2.5 drop on AP, and 0.8 on F1. If the model taken out the high-order relation extractor AP drops 3.7. Furthermore, if we remove the high-order encoder, the performance can degrade a lot, i.e. 6.2 on AP, 5.3 on mIoU. This demonstrates that modeling context and high-order relationships among the video shots is of great significance for the video scene detection task. Besides, comparing the last two lines in Table 5 can prove the necessity of clustering shots within the same scene. Lacking the guidance from scene-level representations, the results on AP drops 0.5, and mIoU drops 0.3.", + "bbox": [ + 75, + 507, + 468, + 718 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Impact of Data Augmentation. Figure 4 demonstrates the impact of different data augmentations. We add shot sequence samples from one video to another video with positive boundary on the central position, to make the model to learn robust scene boundary pattern. If the two videos are from the same video, we call this augmentation method as 'Intra'. Otherwise, as 'Inter'. Hyperparameter ratio controls the rate of newly constructed samples. When the ratio equals zero, we only adopt shot sequence samples by sliding window on every training video without any data augmentation. Having appropriate numerical values for ratio is crucial since setting it too low can prevent the model from", + "bbox": [ + 75, + 719, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "acquiring positive samples, while setting it too high can lead to overfitting. Optimal outcome is obtained with a ratio of 0.3 for 'Intra' augmentation and 0.2 for 'Inter' augmentation. Therefore, we incorporate these two hyperparameters in our complete model. Figure 4 shows that both of 'Intra' and 'Inter' can improve the performance, while 'Intra' is better. The reason may be that 'Intra' helps constructing harder samples.", + "bbox": [ + 496, + 213, + 893, + 334 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Qualitative Analysis. In this part, we visualize similarity matrixes of 50 consecutive shot representations from multimodal features, which can intuitively prove the importance of multimodal cues in the task of scene boundary detection. Specifically, the models are trained with different multimodal semantic settings, and output multimodal shot features respectively. Then we visualize the matrix of cosine similarity between them. The ground-truth labels of scenes (i.e. shot clusters) are marked by red rectangles. It is obvious in Figure 5, shots are clearly clustered into scenes by multimodal features, i.e. the similarities between the shots before and after the boundaries are quite small. Besides, we can see that audio features can hardly separate the shots into different scenes, and the similarity matrix of place or visual features can roughly cluster the shots into scenes near the ground-truth. For single audio or place features, the similarities around boundaries are smooth, which may lead to confusing boundary detection results. Thus, we believe that audio, place and visual features can complement with each other to achieve better performance.", + "bbox": [ + 496, + 335, + 893, + 636 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 640, + 619, + 655 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose a unified multimodal framework for video scene boundary detection. And we design a novel Multimodal High-order Relation Transformer, which can model multimodal cues, high-order relation and scene adaptive clustering in a unified structure. We extract multimodal shot representations and model their clip-level context using expert networks and a clip encoder. Then we use a high-order encoder to uncover complex associations among the features and exploit contextual semantics. Then an adaptive decoder in our transformer is proposed to dynamically merge shots in the same scene, which is effective at discovering switch pattern between scenes rather than visual appearance. We have systematically studied the influence of our idea and carried out experiments. The results demonstrate the effectiveness of our model by achieving significant performance.", + "bbox": [ + 496, + 657, + 893, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "22088", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/68bcf80734161ab816517186dd22f51f039b33559d79adf5f3de25a8f7a0329f.jpg", + "image_caption": [ + "Figure 5: Visualization of similarity matrixes between shot representations in randomly sampled 50 consecutive shots. The ground-truth labels of scenes (shot clusters) are marked by red rectangles." + ], + "image_footnote": [], + "bbox": [ + 107, + 95, + 444, + 386 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Acknowledgment", + "text_level": 1, + "bbox": [ + 76, + 477, + 246, + 494 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was partially supported by National Nature Science Foundation of China (Grant 62022078, 62121002) and National Defense Basic Scientific Research Program (2021601B013).", + "bbox": [ + 75, + 502, + 468, + 563 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 76, + 577, + 171, + 592 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Lorenzo Baraldi, Costantino Grana, and Rita Cucchiara. A deep siamese network for scene detection in broadcast videos. 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IEEE transactions on pattern analysis and machine intelligence, 40(6):1452-1464, 2017." + ], + "bbox": [ + 503, + 92, + 890, + 613 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "22090", + "bbox": [ + 478, + 945, + 519, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Multimodal High-order Relation Transformer for Scene Boundary Detection/4648d770-3062-4c5f-b2d3-868636bc79b2_model.json b/2023/Multimodal High-order Relation Transformer for Scene Boundary Detection/4648d770-3062-4c5f-b2d3-868636bc79b2_model.json new file mode 100644 index 0000000000000000000000000000000000000000..942740cfa809a3dc07e7df2999108f4f122cf5bf --- /dev/null +++ b/2023/Multimodal High-order Relation Transformer for Scene Boundary Detection/4648d770-3062-4c5f-b2d3-868636bc79b2_model.json @@ -0,0 +1,1848 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.099, + 0.131, + 0.872, + 0.152 + ], + "angle": 0, + "content": "Multimodal High-order Relation Transformer for Scene Boundary Detection" + }, + { + "type": "text", + "bbox": [ + 0.205, + 0.18, + 0.765, + 0.233 + ], + "angle": 0, + "content": "Xi Wei\\(^{1}\\), Zhangxiang Shi\\(^{1}\\), Tianzhu Zhang\\(^{1,*}\\), Xiaoyuan Yu\\(^{2}\\), Lei Xiao\\(^{2}\\) \n\\(^{1}\\) University of Science and Technology of China \n\\(^{2}\\) Huawei Cloud" + }, + { + "type": "text", + "bbox": [ + 0.233, + 0.237, + 0.725, + 0.27 + ], + "angle": 0, + "content": "{wx33921, szxszx}@mail.ustc.edu.cn, tzzhang@ustc.edu.cn, yuxiaoyuan@huawei.com, xiaolei199311@126.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.305, + 0.313, + 0.32 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.336, + 0.474, + 0.609 + ], + "angle": 0, + "content": "Scene boundary detection breaks down long videos into meaningful story-telling units and plays a crucial role in high-level video understanding. Despite significant advancements in this area, this task remains a challenging problem as it requires a comprehensive understanding of multimodal cues and high-level semantics. To tackle this issue, we propose a multimodal high-order relation transformer, which integrates a high-order encoder and an adaptive decoder in a unified framework. By modeling the multimodal cues and exploring similarities between the shots, the encoder is capable of capturing high-order relations between shots and extracting shot features with context semantics. By clustering the shots adaptively, the decoder can discover more universal switch pattern between successive scenes, thus helping scene boundary detection. Extensive experimental results on three standard benchmarks demonstrate that the proposed model performs favorably against state-of-the-art video scene detection methods." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.634, + 0.21, + 0.649 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.66, + 0.471, + 0.901 + ], + "angle": 0, + "content": "Cognitive science has discovered that humans usually comprehend a long video by breaking down it into meaningful units and reasoning about their relationships [20]. Therefore, dividing a long video into a series of meaningful story-telling video scenes, i.e. video scene detection, turns out to be a crucial task towards high-level video understanding. In filmmaking and video production, the term 'scene' is a basic unit for story-telling, consisting of a series of semantic cohesive shots, while the term 'shot' is a series of frames captured by the same camera over an uninterrupted period of time [4]. The task of video scene detection has drawn remarkable attention and can be widely adopted to various tough applications, including video caption, content-driven video search, scene classification, human-centric storyline construction and so on [8, 15, 31]. Although significant progress has been achieved in recent years, video scene" + }, + { + "type": "image", + "bbox": [ + 0.513, + 0.304, + 0.879, + 0.41 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.561, + 0.413, + 0.834, + 0.425 + ], + "angle": 0, + "content": "(a) Two consecutive scenes in movie Blade Runner." + }, + { + "type": "image", + "bbox": [ + 0.512, + 0.427, + 0.877, + 0.548 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.578, + 0.551, + 0.815, + 0.563 + ], + "angle": 0, + "content": "(b) Histograms of similarities between shots." + }, + { + "type": "image", + "bbox": [ + 0.518, + 0.565, + 0.875, + 0.604 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.555, + 0.607, + 0.838, + 0.62 + ], + "angle": 0, + "content": "(c) Diverse scene boundaries in movie Blade Runner." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.632, + 0.892, + 0.753 + ], + "angle": 0, + "content": "Figure 1: (a) There is minimal visual alteration at the scene boundary, while the audio content undergoes significant changes. (b) Direct similarities between shots near the boundary can all have high scores, while the trend of similarity variation can provide more discriminative signals. (c) Scene boundaries can vary greatly even in the same movie. Therefore, learning shot-level representations alone is insufficient for this class-agnostic task." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.764, + 0.891, + 0.794 + ], + "angle": 0, + "content": "detection remains challenging due to requiring semantic understanding in a long-term video." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.796, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Recently, researchers have proposed methods like [4, 15, 20, 38] that leverage visual cues in unlabeled videos to model scene boundary. These approaches mainly employ an unsupervised contrastive learning strategy to differentiate shots from distinct scenes. Although these methods have taken a big step forward, they simply use visual appearance cues to generate pseudo labels for contrastive" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "22081" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.081, + 0.092, + 0.468, + 0.317 + ], + "angle": 0, + "content": "learning, resulting in the model learning the differences of shots at the visual apparent level rather than semantic level. In order to address above limitations, approaches such as [18, 19, 23, 27] introduce various expert networks to model multimodal signals like visual, audio, cast and place in various video understanding tasks. These methods still struggle to accurately identify scene boundaries in long-term videos, particularly those with complex story-telling structures. This is due to that modeling context of the shots plays a crucial role in identifying boundaries. Furthermore, all previous methods [1, 4, 23, 20, 27, 38] primarily emphasize learning discriminative shot features and overlook that scene boundary detection is a class-agnostic task. Thus they fail to identify more universal switch pattern between different scenes which is less dependent on appearance." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.322, + 0.468, + 0.851 + ], + "angle": 0, + "content": "Based on the above analysis and the characteristics of scene boundary detection, we believe following aspects are important in this task: (1) The multimodal shot representations can provide comprehensive cues to detect scene boundary. (2) The high-order relation provides corrections for the context of shots. (3) The scene-level representations, derived from adaptively aggregation of shots features, can effectively indicate the switch pattern between different scenes. Firstly, as shown in Figure 1a, there is minimal alteration in the visual appearance between Scene A and scene B. However, the audio signal undergoes a significant change, making it easier to discern the transition between scenes. Secondly, as shown in Figure 1b, the shots before and after the scene boundary, such as shot 48 and shot 49, exhibit high similarities, suggesting that the scene switch can occur seamlessly. Neither the environment nor the characters change, only the two men's behavior changes. Under this circumstances, considering only the similarities between shots (first-order relation) can lead to undetectable blurred boundaries. Fortunately, by representing shots 47-49 as 10-dimensional similarity vectors based on their similarities with reference shots 43-52, we can observe a significant change near the scene boundary. This motivates us that the similarities between these similarity vectors, denoted as high-order relation, can correct for the first-order relation. Thirdly, unlike the common video action detection task, video scene detection is a category-agnostic task [5]. As shown in Figure 1c, even within the same movie, the appearances of the 'scene boundary shots' (i.e. shots 48, 52, 63, 80) still vary greatly. It is more important to discover the switch pattern between successive scenes rather than learn shot-level representations. This encourages us to learn more contextual and category-agnostic scene-level representations, which can be adaptively aggregated from shot-level features." + }, + { + "type": "text", + "bbox": [ + 0.081, + 0.857, + 0.468, + 0.899 + ], + "angle": 0, + "content": "Take these observations together, we propose the Multimodal High-order Relation Transformer for video scene detection, which can model multimodal cues, high-order" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.092, + 0.89, + 0.362 + ], + "angle": 0, + "content": "relation and scene adaptive clustering in a unified structure. Specifically, we first take multimodal expert networks and clip encoders to extract multimodal clip-level shot embeddings for the input shot sequence. Then our designed multimodal high-order relation transformer, consisting of a high-order encoder and an adaptive decoder, is employed to model the high-order relation for the shots and generate contextual scene-level representation in a unified framework. In detail, the high-order encoder primarily employs the multi-head and self-attention mechanism on the multimodal shot embeddings to produce high-order relationships ('relation in relation'), thereby enhancing the appropriate correlations between shots and suppressing erroneous ones. And the adaptive decoder merges contextual shot embeddings into scene representations with learnable scene prototypes and cross-attention. Finally, we take those contextualized shot embeddings for scene boundary classification and scene embeddings for boundary position regression." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.364, + 0.89, + 0.604 + ], + "angle": 0, + "content": "The major contributions of this work can be summarized as follows: (1) We propose the Multimodal High-order Relation Transformer, which can model multimodal cues, high-order relation and scene adaptive clustering in a unified structure. (2) In our transformer, we design the high-order encoder to enhance the context of shots and rectify noises in the correlation map of shots caused by their imperfect features. We further employ the adaptive decoder to aggregate shot features, which is better at capturing switch pattern between scenes rather than visual appearance. (3) Extensive experimental results on three standard benchmarks including MovieNetSSeg [12], OVSD [27] and BBC planet earth [1] demonstrate that the proposed model can outperform previous works by a large margin, and can be even competitive with those pre-training methods which consume more than 5 times training data." + }, + { + "type": "title", + "bbox": [ + 0.504, + 0.612, + 0.64, + 0.627 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.63, + 0.89, + 0.809 + ], + "angle": 0, + "content": "The basic assumption of video scene detection is that one shot can only belong to one scene, thus scene boundaries are a subset of shot boundaries [30]. As a result, the pre-task of scene detection is usually shot detection [14], which divides a video into sequences of time-continuous, non-overlapping shots. Given shot sequences, the video scene segmentation problem can be modeled as shot grouping, which clusters consecutive shots into scenes, or binary classification, which predicts whether a shot is a scene boundary. Many methods have been proposed [1, 4, 27, 20, 38], which can be categorized as unsupervised methods, supervised methods and self-supervised methods." + }, + { + "type": "text", + "bbox": [ + 0.504, + 0.812, + 0.89, + 0.899 + ], + "angle": 0, + "content": "Unsupervised Methods. Early works utilize a variety of unsupervised methods. Among them, [24, 29] cluster shots according to spatiotemporal video features or shot color similarities. [27] obtains a consecutive segmentation by dynamic programming. [28] presents a novel normalized cost function for optimally grouping shots into scenes. Other" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.947, + 0.518, + 0.957 + ], + "angle": 0, + "content": "22082" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.159, + 0.09, + 0.805, + 0.235 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.241, + 0.895, + 0.304 + ], + "angle": 0, + "content": "Figure 2: Our method follows a three-stage pipeline. Firstly, we extract multimodal features with short-term context using multimodal backbones and clip encoders. In the second stage, our high-order encoder models complex multimodal cues and context for each shot, while the decoder adaptively aggregates shots within the same scene. Finally, we employ separate heads for central shot classification and scene boundary position regression. Please refer to the text for more details." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.31, + 0.471, + 0.446 + ], + "angle": 0, + "content": "works make use of multimodal information [27]. For instance, [30] uses both low-level and high-level audio features, visual features to build scene transition graph and extend the unimodal STG-based temporal segmentation technique to multimodal scene segmentation. However, these methods are trained on small-scale datasets [1, 27], leading to poor generalization. Our method turns to deep learning and is trained with newly proposed large dataset [12], obtaining much better performance and generalization." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.447, + 0.471, + 0.825 + ], + "angle": 0, + "content": "Supervised and Self-Supervised Methods. As more and larger datasets are presented [4, 5, 20, 23, 38, 32, 37, 39], researchers are turning to supervised methods. With large-scale datasets, the deep neural network has a great advantage on extracting semantic features. [22] uses Alexresnet365 to extract scene features, while [13] achieves video scene segmentation using an image captioning model to extract semantic information of shots. [23] proposes a supervised baseline utilizing multimodal features to perform a shot-level binary classification, followed by an iterative optimal grouping. Recently, self-supervised methods achieve the best performance. Among them, [4] proposes a shot contrastive pre-training strategy to learn distinguishable shot representation. [38] achieves scene consistency representation learning using a novel positive sample selection strategy in contrast learning. And [20] mainly focuses on designing boundary-aware self-supervised tasks. However, these methods ignore multimodal information and simply use visual appearance cues to contrast different shots, while scene segmentation relies on semantic context. On the contrary, we can jointly model multimodal cues, high-order relation enhanced context with our proposed high-order encoder. And our proposed decoder can adaptive merge shot features into scene-level features to discover the switch pattern between video scenes." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.838, + 0.47, + 0.871 + ], + "angle": 0, + "content": "3. Multimodal High-order Relation Transformer" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.903 + ], + "angle": 0, + "content": "As shown in Figure 2, our method deals with the multimodal shot-level video inputs in a pipeline of clip-level shot" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.31, + 0.895, + 0.584 + ], + "angle": 0, + "content": "embedding, multimodal high-order context modeling and boundary classification. Given a full-length input video, we first split it into a constituent set of shots with the standard shot detection techniques [30]. We then use the sliding window to get a continuous subsequence of shots \\(\\{s_0,s_1,\\dots,s_l\\}\\), and extract its multimodal representations (i.e. visual, place and audio) with the various expert networks. And the clip encoder is employed to model each shot's short-term context. Based on these multimodal shot features, we then perform multimodal high-order context modeling to exploit story-telling semantics for each shot. Specifically, the proposed multimodal high-order relation transformer first adopts the high-order encoder to take both multimodal cues and high-order relationships into consideration. Then the followed adaptive decoder is employed to aggregate shots into scenes. Finally, we adopt both shot features with contextual information and dynamically aggregated scene features for scene boundary prediction." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.593, + 0.744, + 0.61 + ], + "angle": 0, + "content": "3.1. Clip-level Shot Embedding" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.613, + 0.894, + 0.779 + ], + "angle": 0, + "content": "Multimodal Expert Networks. A long-term video is a typical multimodal data containing different high-level semantics [23]. Thus visual features extracted by classical backbones like I3D [2] or TSN [36] are insufficient for the video scene detection task. Instead, the story-telling high semantics can be better described and complemented by multimodal representations. Observing that, in addition to visual contents, a 'scene' is closely related to shots sharing common place, audio elements. Following [23] we adopt visual, place and audio expert networks to extract multimodal shot features." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Following [1, 20, 23], we first extract the key frame for each shot in the sequence \\(\\{s_0,s_1,\\dots ,s_l\\}\\). Then we (1) adopt the ViT [7] to get visual features \\(\\mathbf{R}^{\\mathbf{v}} = \\{r_0^v,r_1^v,\\dots ,r_l^v\\}\\), (2) employ the ResNet50 [10] pretrained on Places dataset [40] to get place features \\(\\mathbf{R}^{\\mathbf{p}} = \\{r_0^p,r_1^p,\\dots ,r_l^p\\}\\), and (3) take stft [34] followed by the pretrained VGGish [11] to get audio features \\(\\mathbf{R}^{\\mathbf{a}} = \\{r_0^a,r_1^a,\\dots ,r_l^a\\}\\). The superscript \\(v,a,p\\) denote for the different modality. Noting that all the expert" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22083" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.12, + 0.09, + 0.852, + 0.332 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.341, + 0.895, + 0.404 + ], + "angle": 0, + "content": "Figure 3: The proposed Multimodal High-order Relation Transformer is designed to enhance shot features with high-order context and discover the switch pattern between scenes. Specifically, the high-order encoder can fuse multimodal cues and model context for each shot under the guidance of high-order relation extractor. Additionally, the subsequent decoder adaptively aggregate shots in the same scene and captures the switch pattern between scenes. Best viewed with colors." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.411, + 0.395, + 0.426 + ], + "angle": 0, + "content": "networks are frozen during the training process." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.433, + 0.471, + 0.554 + ], + "angle": 0, + "content": "Aiming to enhancing shot features with high-order context and discovering the switch pattern between scenes, we design a transformer-based architecture. As shown in Figure 3, it consists of a high-order encoder and an adaptive decoder. The encoder is applied to fuse complex multimodal cues and model context for each shot with the help of high-order relation extractor, while the decoder is responsible for adaptively aggregating shots in the same scene." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.56, + 0.471, + 0.704 + ], + "angle": 0, + "content": "Clip Encoder. Following [23], we add a clip encoder on a local window for each shot's representations, aiming to obtain their clip-level representations. Specifically, taking the visual feature \\( r_i^v \\) of shot \\( i \\) for example, we consider the differences \\( \\mathbf{S}_{\\mathbf{D}} \\) and relations \\( \\mathbf{S}_{\\mathbf{R}} \\) of its n-earby shots in a window with length \\( 2w_{s} \\), i.e. \\( \\mathbf{V}_i = \\left\\{r_{i - (w_s - 1)}^v,\\dots ,r_i^v,\\dots ,r_{i + w_s}^v\\right\\} \\). This process can be performed by temporal convolution layers \\( \\Psi \\) and fully connected layers FC, as shown in Equation (1):" + }, + { + "type": "equation", + "bbox": [ + 0.084, + 0.727, + 0.472, + 0.793 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathbf {S} _ {\\mathbf {D}} \\left(\\mathbf {V} _ {i}\\right) = \\Psi \\left(\\left\\{r _ {i - \\left(w _ {s} - 1\\right)}, \\dots , r _ {i} ^ {v} \\right\\}\\right) \\cdot \\Psi \\left(\\left\\{r _ {i + 1} ^ {v}, \\dots , r _ {i + w _ {s}} ^ {v} \\right\\}\\right), \\\\ \\mathbf {S} _ {\\mathbf {R}} (\\mathbf {V} _ {i}) = \\Psi (\\{r _ {i - (w _ {s} - 1)} ^ {v}, \\dots , r _ {i + w _ {s}} ^ {v} \\}), \\\\ r _ {i} ^ {v ^ {+}} = \\mathbf {F C} (\\operatorname {c o n c a t} \\left(\\mathbf {S} _ {\\mathbf {D}} \\left(\\mathbf {V} _ {i}\\right), \\mathbf {S} _ {\\mathbf {R}} \\left(\\mathbf {V} _ {i}\\right)\\right)), \\tag {1} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.794, + 0.47, + 0.904 + ], + "angle": 0, + "content": "where \\( \\text{concat} \\) denotes the concatenation operation, \\( \\cdot \\) denotes the inner product. Similar operations are performed on the place and audio modality, and the updated shot features can be described by \\( \\mathbf{R}^{\\mathbf{v}^{+}} = \\{r_{0}^{v^{+}}, r_{1}^{v^{+}}, \\dots, r_{l}^{v^{+}}\\} \\), \\( \\mathbf{R}^{\\mathbf{p}^{+}} = \\{r_{0}^{p^{+}}, r_{1}^{p^{+}}, \\dots, r_{l}^{p^{+}}\\} \\), \\( \\mathbf{R}^{\\mathbf{a}^{+}} = \\{r_{0}^{a^{+}}, r_{1}^{a^{+}}, \\dots, r_{l}^{a^{+}}\\} \\). Consequently, these multimodal shot features are enhanced with short-term context." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.41, + 0.862, + 0.426 + ], + "angle": 0, + "content": "3.2. Multimodal High-order Context Modeling" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.441, + 0.892, + 0.562 + ], + "angle": 0, + "content": "Aiming to enhancing shot features with high-order context and discovering the switch pattern between scenes, we design a transformer-based architecture. As shown in Figure 3, it consists of a high-order encoder and an adaptive decoder. The encoder is applied to fuse complex multimodal cues and model context for each shot with the help of high-order relation extractor, while the decoder is responsible for adaptively aggregating shots in the same scene." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.572, + 0.893, + 0.862 + ], + "angle": 0, + "content": "High-order Relation Extractor. As discussed above, directly adopting the standard transformer encoder [35] over the shot sequence features may introduce noises in the correlation map due to imperfect shot features, and ignore comprehensive 'high-order relation' signal. Thus, we innovatively design the high-order relation extractor to correct first-order relations and fuse the multimodal cues jointly. As shown in the upper part of Figure 3, taking the multimodality shot sequence features \\(\\mathbf{R}^{\\mathbf{v}^{+}}\\), \\(\\mathbf{R}^{\\mathbf{p}^{+}}\\), \\(\\mathbf{R}^{\\mathbf{a}^{+}}\\) as inputs, we first calculate the multi-head based temporal similarity matrix for each modality, generating a first-order multimodal relation map \\(\\mathbf{M} \\in \\mathcal{R}^{(l + 1) \\times (l + 1) \\times 3h}\\), which naturally contains temporal positional signal. Note that \\(l + 1\\) is the length of shot sequence and \\(h\\) is the number of heads. Then a shallow CNN is applied on \\(\\mathbf{M}\\) to fuse multimodal cues and model neighboring first-order relations. And one standard transformer layer followed by linear layers and sigmoid function is adopted to model the global associations of each shot's relation, producing the guidance map \\(\\mathbf{M}_{\\mathbf{C}}\\)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "High-order Encoder for Context Modeling. As shown in the bottom left part of Figure 3, we fuse multimodal fea" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22084" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.107 + ], + "angle": 0, + "content": "tures with concatenation operation and a simple linear layer:" + }, + { + "type": "equation", + "bbox": [ + 0.132, + 0.114, + 0.47, + 0.134 + ], + "angle": 0, + "content": "\\[\nr _ {i} ^ {f} = \\mathbf {F C} \\left(\\operatorname {c o n c a t} \\left(r _ {i} ^ {v ^ {+}}, r _ {i} ^ {p ^ {+}}, r _ {i} ^ {a ^ {+}}\\right)\\right) \\in \\mathcal {R} ^ {d _ {f}}, \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.139, + 0.473, + 0.307 + ], + "angle": 0, + "content": "producing fused shot sequence features \\(\\mathbf{R}^f\\in \\mathcal{R}^{(l + 1)\\times d_f}\\) where the superscript \\(f\\) denotes for fusion. Then we apply the guidance map \\(\\mathbf{M_C}\\) to enhance context modeling in a conventional transformer encoder. In detail, we first generate transformed queries and key-values pairs by: \\(\\mathbf{Q} = \\mathbf{R}^{f}\\mathbf{W}^{Q},\\mathbf{K} = \\mathbf{R}^{f}\\mathbf{W}^{K},\\mathbf{V} = \\mathbf{R}^{f}\\mathbf{W}^{V}\\), where \\(\\mathbf{W}^Q\\in \\mathcal{R}^{d_f\\times d_k},\\mathbf{W}^K\\in \\mathcal{R}^{d_f\\times d_k},\\mathbf{W}^V\\in \\mathcal{R}^{d_f\\times d_v}\\). Noting that we omit the multi-head scripts to simplify the expression here. Then the modified attention process HoAttn(Rf), under the guidance from the high-order multimodal relation cues \\(\\mathbf{M_C}\\), can be described by:" + }, + { + "type": "equation", + "bbox": [ + 0.101, + 0.313, + 0.47, + 0.348 + ], + "angle": 0, + "content": "\\[\n\\mathbf {H o A t t n} \\left(\\mathbf {R} ^ {f}\\right) = \\left(\\mathbf {M} _ {C} \\odot \\operatorname {s o f t m a x} \\left(\\frac {\\mathbf {Q K} ^ {T}}{\\sqrt {d _ {k}}}\\right)\\right) \\mathbf {V}, \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.352, + 0.47, + 0.519 + ], + "angle": 0, + "content": "where \\(\\odot\\) denotes Hadamard product, indicating \\(\\mathbf{M}_C\\) works as a rectifier to enhance the appropriate correlations and suppress the erroneous ones. The residual connections, normalization operation and feed-forward layer are concatenated after this attention block, as shown in Figure 3. As a result, the high-order encoder can produce shot representations \\(\\mathbf{R}^{f^*} = \\{r_0^{f^*}, r_1^{f^*}, \\dots, r_l^{f^*}\\}\\). And \\(\\mathbf{R}^{f^*}\\) contains comprehensive multi-modality contextual information. The above two parts fit together as our High-order Encoder and can serve as a basic block, offering a flexible high-order relation perception function." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.52, + 0.47, + 0.7 + ], + "angle": 0, + "content": "Adaptive Decoder for Shot Clustering. Although the high-order encoder successfully models both multimodal cues and high-order relations into the shot representations, it is still challenging to detect scene boundaries. Because even appearances of 'boundary shots' within the same video can vary dramatically. It is essential to learn the switch pattern between scenes, rather than simple shot features. Consequently, we design an adaptive decoder to dynamically merge shots within the same scene, resulting in aggregated contextual scene features. Our decoder also follows the query-key-value design in the vanilla transformer [35], making the full model unified." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.701, + 0.47, + 0.807 + ], + "angle": 0, + "content": "As shown in the right part of Figure 3, our adaptive decoder consists of a pair of learnable scene prototypes \\(\\mathbf{P} = \\{p_1, p_2\\}\\) and an attention block. In order to reduce the domain gap between scene prototypes and shot features, we first employ the average pooled feature of all shots to modify the scene prototypes. The attention interaction between the shots and scene prototypes can be formulated by:" + }, + { + "type": "equation", + "bbox": [ + 0.174, + 0.813, + 0.329, + 0.829 + ], + "angle": 0, + "content": "\\[\n\\mathbf {P} ^ {*} = \\mathbf {P} \\odot a v g (\\mathbf {R} ^ {f ^ {*}}),\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.174, + 0.829, + 0.469, + 0.846 + ], + "angle": 0, + "content": "\\[\n\\mathbf {A} _ {S} = \\left(\\mathbf {P} ^ {*} \\mathbf {W} _ {q}\\right) \\left(\\mathbf {R} ^ {f ^ {*}} \\mathbf {W} _ {k}\\right) ^ {T}, \\tag {4}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.174, + 0.846, + 0.348, + 0.862 + ], + "angle": 0, + "content": "\\[\n\\mathbf {Z} = \\{z _ {1}, z _ {2} \\} = \\mathbf {A} _ {S} \\mathbf {R} ^ {f ^ {*}},\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.87, + 0.469, + 0.901 + ], + "angle": 0, + "content": "where \\(\\mathbf{W}_q\\in \\mathcal{R}^{d_s\\times d_q}\\), \\(\\mathbf{W}_k\\in \\mathcal{R}^{d_f\\times d_q}\\) are learnable parameters. The affinity matrix \\(\\mathbf{A}_S\\in \\mathcal{R}^{2\\times (l + 1)}\\) measures the rel" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "evance between each prototype and the shots, which directs the aggregation of shots into scenes. And \\(\\{z_1,z_2\\}\\) indicate the dynamically aggregated scene representations, which is used to regress the scene boundary positions." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.158, + 0.871, + 0.174 + ], + "angle": 0, + "content": "3.3. Objective Function and Data Augmentation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.178, + 0.892, + 0.304 + ], + "angle": 0, + "content": "Based on above discuss, we learn a set of shot representations \\(\\mathbf{R}^{f^*} = \\{r_0^{f^*}, r_1^{f^*}, \\dots, r_l^{f^*}\\}\\) and two adaptively merged scene features \\(\\mathbf{Z} = \\{z_1, z_2\\}\\) for the input shot sequence \\(\\{s_0, s_1, \\dots, s_l\\}\\). For each shot sequence, we make prediction on the central shot \\(r_{[l/2]}^{f^*}\\), i.e. determining whether it's a scene boundary or not. The subscript \\([l/2]\\) stands for the floor function. The classification loss can be formulated as:" + }, + { + "type": "equation", + "bbox": [ + 0.508, + 0.313, + 0.892, + 0.337 + ], + "angle": 0, + "content": "\\[\n\\mathbf {L} _ {p r e} = - \\left[ y _ {c} \\log \\left(\\phi \\left(r _ {\\lfloor l / 2 \\rfloor} ^ {f ^ {*}}\\right)\\right) + \\left(1 - y _ {c}\\right) \\log \\left(\\phi \\left(r _ {\\lfloor l / 2 \\rfloor} ^ {f ^ {*}}\\right)\\right) \\right], \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.344, + 0.894, + 0.435 + ], + "angle": 0, + "content": "where \\( y_{c} \\) is the label for the central shot, deciding whether it's a scene boundary, and \\( \\phi \\) is a binary classification head. Moreover, ordering to learn adaptive scene representations, we adopt the adaptively merged scene features \\( \\mathbf{Z} = \\{z_1,z_2\\} \\) and a regression head \\( \\gamma \\) to regress the position of the boundary in the shot sequence:" + }, + { + "type": "equation", + "bbox": [ + 0.573, + 0.447, + 0.891, + 0.465 + ], + "angle": 0, + "content": "\\[\n\\mathbf {L} _ {r e g} = \\mathbf {M S E} [ p, \\gamma (\\text {c o n c a t} (z _ {1}, z _ {2})) ], \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.476, + 0.892, + 0.566 + ], + "angle": 0, + "content": "where \\( p \\) is the ground-truth position of the scene boundary in the shot sequence, and \\( p = -1 \\) or \\( p = l + 1 \\) stands for there are no boundaries or multiple boundaries in the sequence. MSE denotes the mean squared error. The overall training loss can be \\( \\mathbf{L} = \\mathbf{L}_{pre} + \\alpha \\mathbf{L}_{reg} \\), where \\( \\alpha \\) is a hyperparameter." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.566, + 0.892, + 0.657 + ], + "angle": 0, + "content": "Moreover, there is a serious class-imbalance problem in the scene detection task, because boundaries are rare in a long video. Thus, we construct shot sequence samples with positive boundary on the central position by concatenating two distant subsequences in the same video or two subsequences from different videos:" + }, + { + "type": "equation", + "bbox": [ + 0.501, + 0.669, + 0.891, + 0.699 + ], + "angle": 0, + "content": "\\[\n\\left\\{s _ {0}, \\dots , s _ {l / 2}, \\dots , s _ {l} \\right\\} _ {\\text {n e w}} = \\left\\{s _ {0}, \\dots , s _ {l / 2} \\right\\} _ {v _ {0}} + \\left\\{s _ {l / 2}, \\dots , s _ {l} \\right\\} _ {v _ {1}}. \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.7, + 0.891, + 0.73 + ], + "angle": 0, + "content": "The ratio of constructed samples to origin samples is adjustable according to the data distribution." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.743, + 0.706, + 0.759 + ], + "angle": 0, + "content": "4. Experimental Results" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.764, + 0.691, + 0.78 + ], + "angle": 0, + "content": "4.1. Experimental Setup" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.781, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Dataset. To demonstrate the effectiveness of our proposed method, we carry out extensive experiments on three public available datasets, including MovieNet-SSeg [12], BBC planet earth [1] and OVSD [27]. MovieNet [12], containing 1,100 videos with 1.6M shots, is the largest dataset for video understanding analysis by far. And the MovieNet-SSeg is a sub-dataset of that, with 190, 64 and 64 videos labeled with scene boundaries for training, validating and" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22085" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.089, + 0.892, + 0.135 + ], + "angle": 0, + "content": "Table 1: Results on the MovieNetSSeg dataset. The best results are in bold, and the second best are in bold and underlined. Note that self-supervised methods are pretrained with 1100 videos in MovieNet (MS-1100), and fine-tuned with 190 training videos in MovieSSeg (MS-190). Using less than 1/5 of the training data, our model can achieve competitive results." + }, + { + "type": "table", + "bbox": [ + 0.166, + 0.139, + 0.803, + 0.389 + ], + "angle": 0, + "content": "
MethodTraining DataAP (↑)mIoU (↑)AUC-ROC (↑)F1 (↑)
Supervised Learning
Siamese [1]MS-19035.839.6--
MS-LSTM [12]MS-19046.546.2--
LGSS [23]MS-19047.148.8--
OursMS-19054.851.290.346.3
Unsupervised Learning
GraphCut [25]None14.129.7--
SCSA [3]None14.730.5--
DP [9]None15.532.0--
Story Graph [33]None25.135.7--
Grouping [27]None33.637.2--
Self-supervised Learning
ShotCoL [4]MS-110053.4---
SCRL [38]MS-110054.8--51.4
BaSSL [20]MS-110056.349.590.345.7
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.413, + 0.47, + 0.519 + ], + "angle": 0, + "content": "testing. Besides, we also carry out experiments on BBC planet earth [1] and OVSD [27] dataset. BBC planet earth contains 11 documentaries and OVSD contains 21 various videos. And we just take them as the testing set to verify the generalization of our model, i.e. our model trained on MovieScenes-SSeg is directly tested them, because of their limited scale and unavailable splitting strategy." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.52, + 0.47, + 0.656 + ], + "angle": 0, + "content": "Evaluation Metrics. We make comprehensive validations on our model with several metrics: (1) Average Precision(AP), it's the mean of AP of \\( y_{c} = 1 \\) for each video. (2) mIoU, the averaged intersection over union (IoU) between detected scene boundary with their closest ground-truth scene boundary. (3) F1 score, the harmonic mean of the precision and recall, taking both recall and precision into consideration. (4) AUC - ROC, short for area under the receiver operating characteristics." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.658, + 0.47, + 0.703 + ], + "angle": 0, + "content": "Implementation Details. The proposed High-Order Relation Aware Multi-modality Network is implemented in PyTorch framework [21] with NVIDIA V100 GPUs." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.471, + 0.901 + ], + "angle": 0, + "content": "To begin with, we set the shot sequence length as 7, which is able to contain enough contextual information while requiring relative low memory resource. In the clip-level shot embedding stage, we only take visual, place and audio modalities mentioned in [23], as they play the most crucial roles in scene boundary detection. In specific, we use ViT-B/16 pretrained on ImageNet [6], ResNet50 pretrained on Place dataset [40], and VGGish pretrained on AVA-ActivaSpeaker [26] to extract multimodal shot features with 768, 2048, 128 dimensions respectively. All of them were frozen during training. The clip encoder employs the 1D-CNN [16] and the FC layer to transform them into 384, 256, 128 dimensional vectors. This indicates the im" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.411, + 0.892, + 0.457 + ], + "angle": 0, + "content": "Table 2: Results of AP on BBC planet earth and OVSD datasets. Performances are achieved by the model trained on the MovieNetSSeg dataset without any fine-tuning." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.46, + 0.895, + 0.556 + ], + "angle": 0, + "content": "
MethodBBCOVSD
SimCLR实例) [4]32.325.5
SimCLR(temperal) [4]34.224.9
SimCLR(NN) [4]32.925.0
BaSSL(More Training Data) [20]40.028.7
Ours38.727.5
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.581, + 0.892, + 0.822 + ], + "angle": 0, + "content": "portance of each modality, which will be verified in the ablation studies. In the followed multimodal high-order context modeling stage, the high-order relation extractor first maps the multimodal features as the correlation map \\(\\mathbf{M}\\) with 8 heads. Feeding \\(\\mathbf{M}\\) into the shallow CNN with 4 layers, one transformer encoder layer and the followed linear layer, we get the high-order relation-aware guidance map \\(\\mathbf{M}_{\\mathbf{C}}\\). We set the corresponding high-order context modeling encoder with 8 heads, 1 layer, and hidden units as 768. Finally, in the Adaptive Decoder, the dimensions of the merged scene features and the shot features remain the same. As a result, the scale of learnable parameters in our model is approximately equivalent to the sum of two layers of transformer encoder, four layers of CNN and several linear layers, which is comparable to that of BaSSL [20] without its' backbone." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.892, + 0.903 + ], + "angle": 0, + "content": "The model is trained for 10 epochs with the Adam optimizer [17]. We start training with a learning rate of 0.0002, and decay the learning rate using a cosine schedule. The batch-size is set to 128 for all experiments. And the hyperparameter \\(\\alpha\\) in loss is set to 0.2. At last, for evaluation on" + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22086" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.471, + 0.184 + ], + "angle": 0, + "content": "the testing set, we tackle the over-fitting by choosing the s-napshot of the model based on the validation set. Noting that during inference, for each shot sequence we only make prediction on the central shot. Only if the classification head predicts to be positive, or the regression head outputs the central position, we take it as a positive boundary." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.188, + 0.313, + 0.205 + ], + "angle": 0, + "content": "4.2. Performance Comparison" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.209, + 0.47, + 0.344 + ], + "angle": 0, + "content": "We compare with several recent state-of-the-art methods on the MovieNet-SSeg [12] in Table 1. And verifying the generation ability of our method by carrying out experiments on BBC planet earth [1] and OVSD [27] datasets in Table 2. We can find that our proposed High-Order Relation Aware Multi-modality Network achieves much better performance compared with the supervised methods, and can be competitive with the self-supervised ones while consuming much less training resources." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.346, + 0.471, + 0.648 + ], + "angle": 0, + "content": "Results on MovieNet-SSeg. Table 1 presents the quantitative results on MovieNet-SSeg. We compare our method with various types of methods, including supervised, unsupervised and self-supervised approaches. The results demonstrate that under the same settings, our methods can outperform previous works by a large margin and can be even competitive with those which employ more than 5 times training data. Particularly, our method achieves 54.8 for AP, 51.2 for mIoU, 90.3 for AUC - ROC and 46.3 for F1. Noting that our method can offer a much more convenient way for training and testing compared with BaSSL, ShotCoL and SCRL [20, 4, 38]. For fair comparison, we also conduct experiments using identical multi-modality settings, specifically by the same features generated by expert networks. As shown in Tabel 3, using less external knowledge, our approach can still outperform LGSS by a large margin. Different from previous works which neglect the high-order relations among the shot sequence and only focus on learning shot features, our method jointly models both of them in a unified deep model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.649, + 0.47, + 0.845 + ], + "angle": 0, + "content": "Results on BBC planet earth and OVSD. As shown in Table 2, we further validate performance of our method on BBC planet earth [1] and OVSD [27]. The training and testing splits are not available and the scale of dataset size are quite small (11 for BBC, and 21 for OVSD respectively), in addition, 2 out of 21 videos in OVSD is not available. Consequently, we just directly employ the model trained on MovieNetSSeg without any fine-tune, and take inference on these two datasets. SimCLR(x) corresponds to ShotCoL [4] using different contrastive learning strategies reproduced by [20]. The results demonstrate advanced generalization ability of our methods. It's competitive with shot-level pretraining methods." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.85, + 0.345, + 0.866 + ], + "angle": 0, + "content": "4.3. Ablation Studies and Analysis" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.471, + 0.901 + ], + "angle": 0, + "content": "To carry out analysis and evaluate the contribution of each component and setting in our method, we conduct a" + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.09, + 0.892, + 0.135 + ], + "angle": 0, + "content": "Table 4: Impact of multimodal semantics, where three elements are studied including visual, place, and audio. † denotes that the results are copied from [23]." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.139, + 0.885, + 0.327 + ], + "angle": 0, + "content": "
MethodplaceaudiovisualAP (↑)
Grouping [27]†✓✓✓23.8
StoryGraph [33]†✓✓✓33.2
Siamese [1]†✓✓✓34.1
LGSS [23]✓✓✓47.1
Ours✓50.9
Ours✓16.3
Ours✓52.4
Ours✓✓48.4
Ours✓✓53.4
Ours✓✓53.1
Ours✓✓✓54.8
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.338, + 0.892, + 0.368 + ], + "angle": 0, + "content": "series of ablation studies. All the following comparative experiments are conducted on the MovieNetSSeg dataset." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.37, + 0.893, + 0.703 + ], + "angle": 0, + "content": "Impact of Multimodal Semantics. First of all, we revisit the impact of each modality in Table 4. We utilize the whole pipeline with clip-level shot embedding and multimodal high-order context modeling to make predictions on the testing set. Experiment starts from the model using only one modality features, and gradually adds different modality cues. Observing the second block of Table 4, we get the conclusion that visual modality plays the most important role in video scene detection. It's hard for single audio features to obtain satisfied results. From the third part of Table 4, we learn that both audio and place modalities can give complementary cues to the visual modality, and improves the final results. In particularly, audio improves 2.7 in terms of AP, place improves 3.5 for AP. Combining three modalities can produce the best result, i.e. 54.8 for AP. Compared with previous works in Table 4, our method gets the best results. Because our approach takes a more comprehensive way to fuse the multimodal features and drive them to complement with each other in a unified model. This can prove the hypothesis we presented above, i.e. multimodal content can complement for each other in the task of scene boundary detection." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.894, + 0.901 + ], + "angle": 0, + "content": "Impact of Different Components. We take experiments to validate the effect of different components in our method, including the clip encoder, the high-order encoder and adaptive decoder in our multimodal high-order relation transformer. Specifically, taking the full model as baseline, we remove the clip encoder which is denoted as 'w/o CE'. Removing the high-order relation extractor can verify the effectiveness of modeling high-order context, and we denote it as 'w/o HR', i.e. without high-order relation guidance. And the model without the full high-order encoder in the multimodal high-order relation transformer is denoted as 'w/o CR' for 'without context relation', as it lacks the context relationship modeling. And the model without the" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "22087" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.089, + 0.894, + 0.121 + ], + "angle": 0, + "content": "Table 3: Results on the MovieNetSSeg dataset with different multimodal semantics settings, which demonstrate the effectiveness of our approach under fair conditions." + }, + { + "type": "table", + "bbox": [ + 0.088, + 0.125, + 0.877, + 0.19 + ], + "angle": 0, + "content": "
MethodLGSS (audio)LGSS (place)LGSS (audio+place)LGSS (audio+place +act+cast)Ours (audio)Ours (place)Ours (audio+place)Ours (audio+place +visual)
AP(↑)17.539.043.447.116.350.948.454.8
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.212, + 0.47, + 0.242 + ], + "angle": 0, + "content": "Table 5: Impact of different components. We take the full model as baseline." + }, + { + "type": "table", + "bbox": [ + 0.08, + 0.246, + 0.462, + 0.342 + ], + "angle": 0, + "content": "
ModalityAP (↑)mIoU (↑)AUC-ROC (↑)F1 (↑)
w/o CE52.348.390.045.5
w/o HR51.150.388.444.4
w/o CR48.645.988.645.2
w/o Cluster54.350.990.346.2
Full Model54.851.290.346.3
" + }, + { + "type": "image", + "bbox": [ + 0.08, + 0.357, + 0.272, + 0.471 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.274, + 0.358, + 0.468, + 0.47 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.08, + 0.482, + 0.466, + 0.499 + ], + "angle": 0, + "content": "Figure 4: Impact of different data augmentation strategies." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.508, + 0.47, + 0.719 + ], + "angle": 0, + "content": "proposed adaptive decoder is formulated as 'w/o Cluster', which does not need to cluster shots within the same scene. As shown in the first line of Table 5, removing the clip encoder leads to 2.5 drop on AP, and 0.8 on F1. If the model taken out the high-order relation extractor AP drops 3.7. Furthermore, if we remove the high-order encoder, the performance can degrade a lot, i.e. 6.2 on AP, 5.3 on mIoU. This demonstrates that modeling context and high-order relationships among the video shots is of great significance for the video scene detection task. Besides, comparing the last two lines in Table 5 can prove the necessity of clustering shots within the same scene. Lacking the guidance from scene-level representations, the results on AP drops 0.5, and mIoU drops 0.3." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.471, + 0.902 + ], + "angle": 0, + "content": "Impact of Data Augmentation. Figure 4 demonstrates the impact of different data augmentations. We add shot sequence samples from one video to another video with positive boundary on the central position, to make the model to learn robust scene boundary pattern. If the two videos are from the same video, we call this augmentation method as 'Intra'. Otherwise, as 'Inter'. Hyperparameter ratio controls the rate of newly constructed samples. When the ratio equals zero, we only adopt shot sequence samples by sliding window on every training video without any data augmentation. Having appropriate numerical values for ratio is crucial since setting it too low can prevent the model from" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.214, + 0.895, + 0.335 + ], + "angle": 0, + "content": "acquiring positive samples, while setting it too high can lead to overfitting. Optimal outcome is obtained with a ratio of 0.3 for 'Intra' augmentation and 0.2 for 'Inter' augmentation. Therefore, we incorporate these two hyperparameters in our complete model. Figure 4 shows that both of 'Intra' and 'Inter' can improve the performance, while 'Intra' is better. The reason may be that 'Intra' helps constructing harder samples." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.336, + 0.895, + 0.637 + ], + "angle": 0, + "content": "Qualitative Analysis. In this part, we visualize similarity matrixes of 50 consecutive shot representations from multimodal features, which can intuitively prove the importance of multimodal cues in the task of scene boundary detection. Specifically, the models are trained with different multimodal semantic settings, and output multimodal shot features respectively. Then we visualize the matrix of cosine similarity between them. The ground-truth labels of scenes (i.e. shot clusters) are marked by red rectangles. It is obvious in Figure 5, shots are clearly clustered into scenes by multimodal features, i.e. the similarities between the shots before and after the boundaries are quite small. Besides, we can see that audio features can hardly separate the shots into different scenes, and the similarity matrix of place or visual features can roughly cluster the shots into scenes near the ground-truth. For single audio or place features, the similarities around boundaries are smooth, which may lead to confusing boundary detection results. Thus, we believe that audio, place and visual features can complement with each other to achieve better performance." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.641, + 0.62, + 0.656 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.659, + 0.894, + 0.901 + ], + "angle": 0, + "content": "In this paper, we propose a unified multimodal framework for video scene boundary detection. And we design a novel Multimodal High-order Relation Transformer, which can model multimodal cues, high-order relation and scene adaptive clustering in a unified structure. We extract multimodal shot representations and model their clip-level context using expert networks and a clip encoder. Then we use a high-order encoder to uncover complex associations among the features and exploit contextual semantics. Then an adaptive decoder in our transformer is proposed to dynamically merge shots in the same scene, which is effective at discovering switch pattern between scenes rather than visual appearance. We have systematically studied the influence of our idea and carried out experiments. The results demonstrate the effectiveness of our model by achieving significant performance." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "22088" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.108, + 0.096, + 0.446, + 0.387 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.405, + 0.47, + 0.466 + ], + "angle": 0, + "content": "Figure 5: Visualization of similarity matrixes between shot representations in randomly sampled 50 consecutive shots. The ground-truth labels of scenes (shot clusters) are marked by red rectangles." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.478, + 0.248, + 0.495 + ], + "angle": 0, + "content": "6. Acknowledgment" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.503, + 0.47, + 0.564 + ], + "angle": 0, + "content": "This work was partially supported by National Nature Science Foundation of China (Grant 62022078, 62121002) and National Defense Basic Scientific Research Program (2021601B013)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.578, + 0.173, + 0.593 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.085, + 0.604, + 0.47, + 0.659 + ], + "angle": 0, + "content": "[1] Lorenzo Baraldi, Costantino Grana, and Rita Cucchiara. A deep siamese network for scene detection in broadcast videos. 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Despite significant advancements in this area, this task remains a challenging problem as it requires a comprehensive understanding of multimodal cues and high-level semantics. To tackle this issue, we propose a multimodal high-order relation transformer, which integrates a high-order encoder and an adaptive decoder in a unified framework. By modeling the multimodal cues and exploring similarities between the shots, the encoder is capable of capturing high-order relations between shots and extracting shot features with context semantics. By clustering the shots adaptively, the decoder can discover more universal switch pattern between successive scenes, thus helping scene boundary detection. Extensive experimental results on three standard benchmarks demonstrate that the proposed model performs favorably against state-of-the-art video scene detection methods. + +# 1. Introduction + +Cognitive science has discovered that humans usually comprehend a long video by breaking down it into meaningful units and reasoning about their relationships [20]. Therefore, dividing a long video into a series of meaningful story-telling video scenes, i.e. video scene detection, turns out to be a crucial task towards high-level video understanding. In filmmaking and video production, the term 'scene' is a basic unit for story-telling, consisting of a series of semantic cohesive shots, while the term 'shot' is a series of frames captured by the same camera over an uninterrupted period of time [4]. The task of video scene detection has drawn remarkable attention and can be widely adopted to various tough applications, including video caption, content-driven video search, scene classification, human-centric storyline construction and so on [8, 15, 31]. Although significant progress has been achieved in recent years, video scene + +![](images/1f8c70b7ec4ce57c62ec6808d2226888bed38e9d9b80b491c4357d38cbe684be.jpg) +(a) Two consecutive scenes in movie Blade Runner. + +![](images/7dcecbe38f5a9a964a540de95deec2444d2a3aa64dcbfa3ab614afbb62098433.jpg) +(b) Histograms of similarities between shots. + +![](images/0d2efe1cccf6c1bd7445ff05b0e14bfb3dd524a1318b62c3387d971f7b34d8e7.jpg) +(c) Diverse scene boundaries in movie Blade Runner. + +Figure 1: (a) There is minimal visual alteration at the scene boundary, while the audio content undergoes significant changes. (b) Direct similarities between shots near the boundary can all have high scores, while the trend of similarity variation can provide more discriminative signals. (c) Scene boundaries can vary greatly even in the same movie. Therefore, learning shot-level representations alone is insufficient for this class-agnostic task. + +detection remains challenging due to requiring semantic understanding in a long-term video. + +Recently, researchers have proposed methods like [4, 15, 20, 38] that leverage visual cues in unlabeled videos to model scene boundary. These approaches mainly employ an unsupervised contrastive learning strategy to differentiate shots from distinct scenes. Although these methods have taken a big step forward, they simply use visual appearance cues to generate pseudo labels for contrastive + +learning, resulting in the model learning the differences of shots at the visual apparent level rather than semantic level. In order to address above limitations, approaches such as [18, 19, 23, 27] introduce various expert networks to model multimodal signals like visual, audio, cast and place in various video understanding tasks. These methods still struggle to accurately identify scene boundaries in long-term videos, particularly those with complex story-telling structures. This is due to that modeling context of the shots plays a crucial role in identifying boundaries. Furthermore, all previous methods [1, 4, 23, 20, 27, 38] primarily emphasize learning discriminative shot features and overlook that scene boundary detection is a class-agnostic task. Thus they fail to identify more universal switch pattern between different scenes which is less dependent on appearance. + +Based on the above analysis and the characteristics of scene boundary detection, we believe following aspects are important in this task: (1) The multimodal shot representations can provide comprehensive cues to detect scene boundary. (2) The high-order relation provides corrections for the context of shots. (3) The scene-level representations, derived from adaptively aggregation of shots features, can effectively indicate the switch pattern between different scenes. Firstly, as shown in Figure 1a, there is minimal alteration in the visual appearance between Scene A and scene B. However, the audio signal undergoes a significant change, making it easier to discern the transition between scenes. Secondly, as shown in Figure 1b, the shots before and after the scene boundary, such as shot 48 and shot 49, exhibit high similarities, suggesting that the scene switch can occur seamlessly. Neither the environment nor the characters change, only the two men's behavior changes. Under this circumstances, considering only the similarities between shots (first-order relation) can lead to undetectable blurred boundaries. Fortunately, by representing shots 47-49 as 10-dimensional similarity vectors based on their similarities with reference shots 43-52, we can observe a significant change near the scene boundary. This motivates us that the similarities between these similarity vectors, denoted as high-order relation, can correct for the first-order relation. Thirdly, unlike the common video action detection task, video scene detection is a category-agnostic task [5]. As shown in Figure 1c, even within the same movie, the appearances of the 'scene boundary shots' (i.e. shots 48, 52, 63, 80) still vary greatly. It is more important to discover the switch pattern between successive scenes rather than learn shot-level representations. This encourages us to learn more contextual and category-agnostic scene-level representations, which can be adaptively aggregated from shot-level features. + +Take these observations together, we propose the Multimodal High-order Relation Transformer for video scene detection, which can model multimodal cues, high-order + +relation and scene adaptive clustering in a unified structure. Specifically, we first take multimodal expert networks and clip encoders to extract multimodal clip-level shot embeddings for the input shot sequence. Then our designed multimodal high-order relation transformer, consisting of a high-order encoder and an adaptive decoder, is employed to model the high-order relation for the shots and generate contextual scene-level representation in a unified framework. In detail, the high-order encoder primarily employs the multi-head and self-attention mechanism on the multimodal shot embeddings to produce high-order relationships ('relation in relation'), thereby enhancing the appropriate correlations between shots and suppressing erroneous ones. And the adaptive decoder merges contextual shot embeddings into scene representations with learnable scene prototypes and cross-attention. Finally, we take those contextualized shot embeddings for scene boundary classification and scene embeddings for boundary position regression. + +The major contributions of this work can be summarized as follows: (1) We propose the Multimodal High-order Relation Transformer, which can model multimodal cues, high-order relation and scene adaptive clustering in a unified structure. (2) In our transformer, we design the high-order encoder to enhance the context of shots and rectify noises in the correlation map of shots caused by their imperfect features. We further employ the adaptive decoder to aggregate shot features, which is better at capturing switch pattern between scenes rather than visual appearance. (3) Extensive experimental results on three standard benchmarks including MovieNetSSeg [12], OVSD [27] and BBC planet earth [1] demonstrate that the proposed model can outperform previous works by a large margin, and can be even competitive with those pre-training methods which consume more than 5 times training data. + +# 2. Related Work + +The basic assumption of video scene detection is that one shot can only belong to one scene, thus scene boundaries are a subset of shot boundaries [30]. As a result, the pre-task of scene detection is usually shot detection [14], which divides a video into sequences of time-continuous, non-overlapping shots. Given shot sequences, the video scene segmentation problem can be modeled as shot grouping, which clusters consecutive shots into scenes, or binary classification, which predicts whether a shot is a scene boundary. Many methods have been proposed [1, 4, 27, 20, 38], which can be categorized as unsupervised methods, supervised methods and self-supervised methods. + +Unsupervised Methods. Early works utilize a variety of unsupervised methods. Among them, [24, 29] cluster shots according to spatiotemporal video features or shot color similarities. [27] obtains a consecutive segmentation by dynamic programming. [28] presents a novel normalized cost function for optimally grouping shots into scenes. Other + +![](images/5d620c58cc8cca4783ec5b768ae62c7b14472d4652f38e61d3a390fad80961db.jpg) +Figure 2: Our method follows a three-stage pipeline. Firstly, we extract multimodal features with short-term context using multimodal backbones and clip encoders. In the second stage, our high-order encoder models complex multimodal cues and context for each shot, while the decoder adaptively aggregates shots within the same scene. Finally, we employ separate heads for central shot classification and scene boundary position regression. Please refer to the text for more details. + +works make use of multimodal information [27]. For instance, [30] uses both low-level and high-level audio features, visual features to build scene transition graph and extend the unimodal STG-based temporal segmentation technique to multimodal scene segmentation. However, these methods are trained on small-scale datasets [1, 27], leading to poor generalization. Our method turns to deep learning and is trained with newly proposed large dataset [12], obtaining much better performance and generalization. + +Supervised and Self-Supervised Methods. As more and larger datasets are presented [4, 5, 20, 23, 38, 32, 37, 39], researchers are turning to supervised methods. With large-scale datasets, the deep neural network has a great advantage on extracting semantic features. [22] uses Alexresnet365 to extract scene features, while [13] achieves video scene segmentation using an image captioning model to extract semantic information of shots. [23] proposes a supervised baseline utilizing multimodal features to perform a shot-level binary classification, followed by an iterative optimal grouping. Recently, self-supervised methods achieve the best performance. Among them, [4] proposes a shot contrastive pre-training strategy to learn distinguishable shot representation. [38] achieves scene consistency representation learning using a novel positive sample selection strategy in contrast learning. And [20] mainly focuses on designing boundary-aware self-supervised tasks. However, these methods ignore multimodal information and simply use visual appearance cues to contrast different shots, while scene segmentation relies on semantic context. On the contrary, we can jointly model multimodal cues, high-order relation enhanced context with our proposed high-order encoder. And our proposed decoder can adaptive merge shot features into scene-level features to discover the switch pattern between video scenes. + +# 3. Multimodal High-order Relation Transformer + +As shown in Figure 2, our method deals with the multimodal shot-level video inputs in a pipeline of clip-level shot + +embedding, multimodal high-order context modeling and boundary classification. Given a full-length input video, we first split it into a constituent set of shots with the standard shot detection techniques [30]. We then use the sliding window to get a continuous subsequence of shots $\{s_0,s_1,\dots,s_l\}$ , and extract its multimodal representations (i.e. visual, place and audio) with the various expert networks. And the clip encoder is employed to model each shot's short-term context. Based on these multimodal shot features, we then perform multimodal high-order context modeling to exploit story-telling semantics for each shot. Specifically, the proposed multimodal high-order relation transformer first adopts the high-order encoder to take both multimodal cues and high-order relationships into consideration. Then the followed adaptive decoder is employed to aggregate shots into scenes. Finally, we adopt both shot features with contextual information and dynamically aggregated scene features for scene boundary prediction. + +# 3.1. Clip-level Shot Embedding + +Multimodal Expert Networks. A long-term video is a typical multimodal data containing different high-level semantics [23]. Thus visual features extracted by classical backbones like I3D [2] or TSN [36] are insufficient for the video scene detection task. Instead, the story-telling high semantics can be better described and complemented by multimodal representations. Observing that, in addition to visual contents, a 'scene' is closely related to shots sharing common place, audio elements. Following [23] we adopt visual, place and audio expert networks to extract multimodal shot features. + +Following [1, 20, 23], we first extract the key frame for each shot in the sequence $\{s_0,s_1,\dots ,s_l\}$ . Then we (1) adopt the ViT [7] to get visual features $\mathbf{R}^{\mathbf{v}} = \{r_0^v,r_1^v,\dots ,r_l^v\}$ , (2) employ the ResNet50 [10] pretrained on Places dataset [40] to get place features $\mathbf{R}^{\mathbf{p}} = \{r_0^p,r_1^p,\dots ,r_l^p\}$ , and (3) take stft [34] followed by the pretrained VGGish [11] to get audio features $\mathbf{R}^{\mathbf{a}} = \{r_0^a,r_1^a,\dots ,r_l^a\}$ . The superscript $v,a,p$ denote for the different modality. Noting that all the expert + +![](images/8bc8a06e9e1371f11f2adc9c19f31fe3b3799fdbd5c10ca5470de1c06216b680.jpg) +Figure 3: The proposed Multimodal High-order Relation Transformer is designed to enhance shot features with high-order context and discover the switch pattern between scenes. Specifically, the high-order encoder can fuse multimodal cues and model context for each shot under the guidance of high-order relation extractor. Additionally, the subsequent decoder adaptively aggregate shots in the same scene and captures the switch pattern between scenes. Best viewed with colors. + +networks are frozen during the training process. + +Aiming to enhancing shot features with high-order context and discovering the switch pattern between scenes, we design a transformer-based architecture. As shown in Figure 3, it consists of a high-order encoder and an adaptive decoder. The encoder is applied to fuse complex multimodal cues and model context for each shot with the help of high-order relation extractor, while the decoder is responsible for adaptively aggregating shots in the same scene. + +Clip Encoder. Following [23], we add a clip encoder on a local window for each shot's representations, aiming to obtain their clip-level representations. Specifically, taking the visual feature $r_i^v$ of shot $i$ for example, we consider the differences $\mathbf{S}_{\mathbf{D}}$ and relations $\mathbf{S}_{\mathbf{R}}$ of its n-earby shots in a window with length $2w_{s}$ , i.e. $\mathbf{V}_i = \left\{r_{i - (w_s - 1)}^v,\dots ,r_i^v,\dots ,r_{i + w_s}^v\right\}$ . This process can be performed by temporal convolution layers $\Psi$ and fully connected layers FC, as shown in Equation (1): + +$$ +\begin{array}{l} \mathbf {S} _ {\mathbf {D}} \left(\mathbf {V} _ {i}\right) = \Psi \left(\left\{r _ {i - \left(w _ {s} - 1\right)}, \dots , r _ {i} ^ {v} \right\}\right) \cdot \Psi \left(\left\{r _ {i + 1} ^ {v}, \dots , r _ {i + w _ {s}} ^ {v} \right\}\right), \\ \mathbf {S} _ {\mathbf {R}} (\mathbf {V} _ {i}) = \Psi (\{r _ {i - (w _ {s} - 1)} ^ {v}, \dots , r _ {i + w _ {s}} ^ {v} \}), \\ r _ {i} ^ {v ^ {+}} = \mathbf {F C} (\operatorname {c o n c a t} \left(\mathbf {S} _ {\mathbf {D}} \left(\mathbf {V} _ {i}\right), \mathbf {S} _ {\mathbf {R}} \left(\mathbf {V} _ {i}\right)\right)), \tag {1} \\ \end{array} +$$ + +where $\text{concat}$ denotes the concatenation operation, $\cdot$ denotes the inner product. Similar operations are performed on the place and audio modality, and the updated shot features can be described by $\mathbf{R}^{\mathbf{v}^{+}} = \{r_{0}^{v^{+}}, r_{1}^{v^{+}}, \dots, r_{l}^{v^{+}}\}$ , $\mathbf{R}^{\mathbf{p}^{+}} = \{r_{0}^{p^{+}}, r_{1}^{p^{+}}, \dots, r_{l}^{p^{+}}\}$ , $\mathbf{R}^{\mathbf{a}^{+}} = \{r_{0}^{a^{+}}, r_{1}^{a^{+}}, \dots, r_{l}^{a^{+}}\}$ . Consequently, these multimodal shot features are enhanced with short-term context. + +# 3.2. Multimodal High-order Context Modeling + +Aiming to enhancing shot features with high-order context and discovering the switch pattern between scenes, we design a transformer-based architecture. As shown in Figure 3, it consists of a high-order encoder and an adaptive decoder. The encoder is applied to fuse complex multimodal cues and model context for each shot with the help of high-order relation extractor, while the decoder is responsible for adaptively aggregating shots in the same scene. + +High-order Relation Extractor. As discussed above, directly adopting the standard transformer encoder [35] over the shot sequence features may introduce noises in the correlation map due to imperfect shot features, and ignore comprehensive 'high-order relation' signal. Thus, we innovatively design the high-order relation extractor to correct first-order relations and fuse the multimodal cues jointly. As shown in the upper part of Figure 3, taking the multimodality shot sequence features $\mathbf{R}^{\mathbf{v}^{+}}$ , $\mathbf{R}^{\mathbf{p}^{+}}$ , $\mathbf{R}^{\mathbf{a}^{+}}$ as inputs, we first calculate the multi-head based temporal similarity matrix for each modality, generating a first-order multimodal relation map $\mathbf{M} \in \mathcal{R}^{(l + 1) \times (l + 1) \times 3h}$ , which naturally contains temporal positional signal. Note that $l + 1$ is the length of shot sequence and $h$ is the number of heads. Then a shallow CNN is applied on $\mathbf{M}$ to fuse multimodal cues and model neighboring first-order relations. And one standard transformer layer followed by linear layers and sigmoid function is adopted to model the global associations of each shot's relation, producing the guidance map $\mathbf{M}_{\mathbf{C}}$ . + +High-order Encoder for Context Modeling. As shown in the bottom left part of Figure 3, we fuse multimodal fea + +tures with concatenation operation and a simple linear layer: + +$$ +r _ {i} ^ {f} = \mathbf {F C} \left(\operatorname {c o n c a t} \left(r _ {i} ^ {v ^ {+}}, r _ {i} ^ {p ^ {+}}, r _ {i} ^ {a ^ {+}}\right)\right) \in \mathcal {R} ^ {d _ {f}}, \tag {2} +$$ + +producing fused shot sequence features $\mathbf{R}^f\in \mathcal{R}^{(l + 1)\times d_f}$ where the superscript $f$ denotes for fusion. Then we apply the guidance map $\mathbf{M_C}$ to enhance context modeling in a conventional transformer encoder. In detail, we first generate transformed queries and key-values pairs by: $\mathbf{Q} = \mathbf{R}^{f}\mathbf{W}^{Q},\mathbf{K} = \mathbf{R}^{f}\mathbf{W}^{K},\mathbf{V} = \mathbf{R}^{f}\mathbf{W}^{V}$ , where $\mathbf{W}^Q\in \mathcal{R}^{d_f\times d_k},\mathbf{W}^K\in \mathcal{R}^{d_f\times d_k},\mathbf{W}^V\in \mathcal{R}^{d_f\times d_v}$ . Noting that we omit the multi-head scripts to simplify the expression here. Then the modified attention process HoAttn(Rf), under the guidance from the high-order multimodal relation cues $\mathbf{M_C}$ , can be described by: + +$$ +\mathbf {H o A t t n} \left(\mathbf {R} ^ {f}\right) = \left(\mathbf {M} _ {C} \odot \operatorname {s o f t m a x} \left(\frac {\mathbf {Q K} ^ {T}}{\sqrt {d _ {k}}}\right)\right) \mathbf {V}, \tag {3} +$$ + +where $\odot$ denotes Hadamard product, indicating $\mathbf{M}_C$ works as a rectifier to enhance the appropriate correlations and suppress the erroneous ones. The residual connections, normalization operation and feed-forward layer are concatenated after this attention block, as shown in Figure 3. As a result, the high-order encoder can produce shot representations $\mathbf{R}^{f^*} = \{r_0^{f^*}, r_1^{f^*}, \dots, r_l^{f^*}\}$ . And $\mathbf{R}^{f^*}$ contains comprehensive multi-modality contextual information. The above two parts fit together as our High-order Encoder and can serve as a basic block, offering a flexible high-order relation perception function. + +Adaptive Decoder for Shot Clustering. Although the high-order encoder successfully models both multimodal cues and high-order relations into the shot representations, it is still challenging to detect scene boundaries. Because even appearances of 'boundary shots' within the same video can vary dramatically. It is essential to learn the switch pattern between scenes, rather than simple shot features. Consequently, we design an adaptive decoder to dynamically merge shots within the same scene, resulting in aggregated contextual scene features. Our decoder also follows the query-key-value design in the vanilla transformer [35], making the full model unified. + +As shown in the right part of Figure 3, our adaptive decoder consists of a pair of learnable scene prototypes $\mathbf{P} = \{p_1, p_2\}$ and an attention block. In order to reduce the domain gap between scene prototypes and shot features, we first employ the average pooled feature of all shots to modify the scene prototypes. The attention interaction between the shots and scene prototypes can be formulated by: + +$$ +\mathbf {P} ^ {*} = \mathbf {P} \odot a v g (\mathbf {R} ^ {f ^ {*}}), +$$ + +$$ +\mathbf {A} _ {S} = \left(\mathbf {P} ^ {*} \mathbf {W} _ {q}\right) \left(\mathbf {R} ^ {f ^ {*}} \mathbf {W} _ {k}\right) ^ {T}, \tag {4} +$$ + +$$ +\mathbf {Z} = \{z _ {1}, z _ {2} \} = \mathbf {A} _ {S} \mathbf {R} ^ {f ^ {*}}, +$$ + +where $\mathbf{W}_q\in \mathcal{R}^{d_s\times d_q}$ , $\mathbf{W}_k\in \mathcal{R}^{d_f\times d_q}$ are learnable parameters. The affinity matrix $\mathbf{A}_S\in \mathcal{R}^{2\times (l + 1)}$ measures the rel + +evance between each prototype and the shots, which directs the aggregation of shots into scenes. And $\{z_1,z_2\}$ indicate the dynamically aggregated scene representations, which is used to regress the scene boundary positions. + +# 3.3. Objective Function and Data Augmentation + +Based on above discuss, we learn a set of shot representations $\mathbf{R}^{f^*} = \{r_0^{f^*}, r_1^{f^*}, \dots, r_l^{f^*}\}$ and two adaptively merged scene features $\mathbf{Z} = \{z_1, z_2\}$ for the input shot sequence $\{s_0, s_1, \dots, s_l\}$ . For each shot sequence, we make prediction on the central shot $r_{[l/2]}^{f^*}$ , i.e. determining whether it's a scene boundary or not. The subscript $[l/2]$ stands for the floor function. The classification loss can be formulated as: + +$$ +\mathbf {L} _ {p r e} = - \left[ y _ {c} \log \left(\phi \left(r _ {\lfloor l / 2 \rfloor} ^ {f ^ {*}}\right)\right) + \left(1 - y _ {c}\right) \log \left(\phi \left(r _ {\lfloor l / 2 \rfloor} ^ {f ^ {*}}\right)\right) \right], \tag {5} +$$ + +where $y_{c}$ is the label for the central shot, deciding whether it's a scene boundary, and $\phi$ is a binary classification head. Moreover, ordering to learn adaptive scene representations, we adopt the adaptively merged scene features $\mathbf{Z} = \{z_1,z_2\}$ and a regression head $\gamma$ to regress the position of the boundary in the shot sequence: + +$$ +\mathbf {L} _ {r e g} = \mathbf {M S E} [ p, \gamma (\text {c o n c a t} (z _ {1}, z _ {2})) ], \tag {6} +$$ + +where $p$ is the ground-truth position of the scene boundary in the shot sequence, and $p = -1$ or $p = l + 1$ stands for there are no boundaries or multiple boundaries in the sequence. MSE denotes the mean squared error. The overall training loss can be $\mathbf{L} = \mathbf{L}_{pre} + \alpha \mathbf{L}_{reg}$ , where $\alpha$ is a hyperparameter. + +Moreover, there is a serious class-imbalance problem in the scene detection task, because boundaries are rare in a long video. Thus, we construct shot sequence samples with positive boundary on the central position by concatenating two distant subsequences in the same video or two subsequences from different videos: + +$$ +\left\{s _ {0}, \dots , s _ {l / 2}, \dots , s _ {l} \right\} _ {\text {n e w}} = \left\{s _ {0}, \dots , s _ {l / 2} \right\} _ {v _ {0}} + \left\{s _ {l / 2}, \dots , s _ {l} \right\} _ {v _ {1}}. \tag {7} +$$ + +The ratio of constructed samples to origin samples is adjustable according to the data distribution. + +# 4. Experimental Results + +# 4.1. Experimental Setup + +Dataset. To demonstrate the effectiveness of our proposed method, we carry out extensive experiments on three public available datasets, including MovieNet-SSeg [12], BBC planet earth [1] and OVSD [27]. MovieNet [12], containing 1,100 videos with 1.6M shots, is the largest dataset for video understanding analysis by far. And the MovieNet-SSeg is a sub-dataset of that, with 190, 64 and 64 videos labeled with scene boundaries for training, validating and + +Table 1: Results on the MovieNetSSeg dataset. The best results are in bold, and the second best are in bold and underlined. Note that self-supervised methods are pretrained with 1100 videos in MovieNet (MS-1100), and fine-tuned with 190 training videos in MovieSSeg (MS-190). Using less than 1/5 of the training data, our model can achieve competitive results. + +
MethodTraining DataAP (↑)mIoU (↑)AUC-ROC (↑)F1 (↑)
Supervised Learning
Siamese [1]MS-19035.839.6--
MS-LSTM [12]MS-19046.546.2--
LGSS [23]MS-19047.148.8--
OursMS-19054.851.290.346.3
Unsupervised Learning
GraphCut [25]None14.129.7--
SCSA [3]None14.730.5--
DP [9]None15.532.0--
Story Graph [33]None25.135.7--
Grouping [27]None33.637.2--
Self-supervised Learning
ShotCoL [4]MS-110053.4---
SCRL [38]MS-110054.8--51.4
BaSSL [20]MS-110056.349.590.345.7
+ +testing. Besides, we also carry out experiments on BBC planet earth [1] and OVSD [27] dataset. BBC planet earth contains 11 documentaries and OVSD contains 21 various videos. And we just take them as the testing set to verify the generalization of our model, i.e. our model trained on MovieScenes-SSeg is directly tested them, because of their limited scale and unavailable splitting strategy. + +Evaluation Metrics. We make comprehensive validations on our model with several metrics: (1) Average Precision(AP), it's the mean of AP of $y_{c} = 1$ for each video. (2) mIoU, the averaged intersection over union (IoU) between detected scene boundary with their closest ground-truth scene boundary. (3) F1 score, the harmonic mean of the precision and recall, taking both recall and precision into consideration. (4) AUC - ROC, short for area under the receiver operating characteristics. + +Implementation Details. The proposed High-Order Relation Aware Multi-modality Network is implemented in PyTorch framework [21] with NVIDIA V100 GPUs. + +To begin with, we set the shot sequence length as 7, which is able to contain enough contextual information while requiring relative low memory resource. In the clip-level shot embedding stage, we only take visual, place and audio modalities mentioned in [23], as they play the most crucial roles in scene boundary detection. In specific, we use ViT-B/16 pretrained on ImageNet [6], ResNet50 pretrained on Place dataset [40], and VGGish pretrained on AVA-ActivaSpeaker [26] to extract multimodal shot features with 768, 2048, 128 dimensions respectively. All of them were frozen during training. The clip encoder employs the 1D-CNN [16] and the FC layer to transform them into 384, 256, 128 dimensional vectors. This indicates the im + +Table 2: Results of AP on BBC planet earth and OVSD datasets. Performances are achieved by the model trained on the MovieNetSSeg dataset without any fine-tuning. + +
MethodBBCOVSD
SimCLR实例) [4]32.325.5
SimCLR(temperal) [4]34.224.9
SimCLR(NN) [4]32.925.0
BaSSL(More Training Data) [20]40.028.7
Ours38.727.5
+ +portance of each modality, which will be verified in the ablation studies. In the followed multimodal high-order context modeling stage, the high-order relation extractor first maps the multimodal features as the correlation map $\mathbf{M}$ with 8 heads. Feeding $\mathbf{M}$ into the shallow CNN with 4 layers, one transformer encoder layer and the followed linear layer, we get the high-order relation-aware guidance map $\mathbf{M}_{\mathbf{C}}$ . We set the corresponding high-order context modeling encoder with 8 heads, 1 layer, and hidden units as 768. Finally, in the Adaptive Decoder, the dimensions of the merged scene features and the shot features remain the same. As a result, the scale of learnable parameters in our model is approximately equivalent to the sum of two layers of transformer encoder, four layers of CNN and several linear layers, which is comparable to that of BaSSL [20] without its' backbone. + +The model is trained for 10 epochs with the Adam optimizer [17]. We start training with a learning rate of 0.0002, and decay the learning rate using a cosine schedule. The batch-size is set to 128 for all experiments. And the hyperparameter $\alpha$ in loss is set to 0.2. At last, for evaluation on + +the testing set, we tackle the over-fitting by choosing the s-napshot of the model based on the validation set. Noting that during inference, for each shot sequence we only make prediction on the central shot. Only if the classification head predicts to be positive, or the regression head outputs the central position, we take it as a positive boundary. + +# 4.2. Performance Comparison + +We compare with several recent state-of-the-art methods on the MovieNet-SSeg [12] in Table 1. And verifying the generation ability of our method by carrying out experiments on BBC planet earth [1] and OVSD [27] datasets in Table 2. We can find that our proposed High-Order Relation Aware Multi-modality Network achieves much better performance compared with the supervised methods, and can be competitive with the self-supervised ones while consuming much less training resources. + +Results on MovieNet-SSeg. Table 1 presents the quantitative results on MovieNet-SSeg. We compare our method with various types of methods, including supervised, unsupervised and self-supervised approaches. The results demonstrate that under the same settings, our methods can outperform previous works by a large margin and can be even competitive with those which employ more than 5 times training data. Particularly, our method achieves 54.8 for AP, 51.2 for mIoU, 90.3 for AUC - ROC and 46.3 for F1. Noting that our method can offer a much more convenient way for training and testing compared with BaSSL, ShotCoL and SCRL [20, 4, 38]. For fair comparison, we also conduct experiments using identical multi-modality settings, specifically by the same features generated by expert networks. As shown in Tabel 3, using less external knowledge, our approach can still outperform LGSS by a large margin. Different from previous works which neglect the high-order relations among the shot sequence and only focus on learning shot features, our method jointly models both of them in a unified deep model. + +Results on BBC planet earth and OVSD. As shown in Table 2, we further validate performance of our method on BBC planet earth [1] and OVSD [27]. The training and testing splits are not available and the scale of dataset size are quite small (11 for BBC, and 21 for OVSD respectively), in addition, 2 out of 21 videos in OVSD is not available. Consequently, we just directly employ the model trained on MovieNetSSeg without any fine-tune, and take inference on these two datasets. SimCLR(x) corresponds to ShotCoL [4] using different contrastive learning strategies reproduced by [20]. The results demonstrate advanced generalization ability of our methods. It's competitive with shot-level pretraining methods. + +# 4.3. Ablation Studies and Analysis + +To carry out analysis and evaluate the contribution of each component and setting in our method, we conduct a + +Table 4: Impact of multimodal semantics, where three elements are studied including visual, place, and audio. † denotes that the results are copied from [23]. + +
MethodplaceaudiovisualAP (↑)
Grouping [27]†✓✓✓23.8
StoryGraph [33]†✓✓✓33.2
Siamese [1]†✓✓✓34.1
LGSS [23]✓✓✓47.1
Ours✓50.9
Ours✓16.3
Ours✓52.4
Ours✓✓48.4
Ours✓✓53.4
Ours✓✓53.1
Ours✓✓✓54.8
+ +series of ablation studies. All the following comparative experiments are conducted on the MovieNetSSeg dataset. + +Impact of Multimodal Semantics. First of all, we revisit the impact of each modality in Table 4. We utilize the whole pipeline with clip-level shot embedding and multimodal high-order context modeling to make predictions on the testing set. Experiment starts from the model using only one modality features, and gradually adds different modality cues. Observing the second block of Table 4, we get the conclusion that visual modality plays the most important role in video scene detection. It's hard for single audio features to obtain satisfied results. From the third part of Table 4, we learn that both audio and place modalities can give complementary cues to the visual modality, and improves the final results. In particularly, audio improves 2.7 in terms of AP, place improves 3.5 for AP. Combining three modalities can produce the best result, i.e. 54.8 for AP. Compared with previous works in Table 4, our method gets the best results. Because our approach takes a more comprehensive way to fuse the multimodal features and drive them to complement with each other in a unified model. This can prove the hypothesis we presented above, i.e. multimodal content can complement for each other in the task of scene boundary detection. + +Impact of Different Components. We take experiments to validate the effect of different components in our method, including the clip encoder, the high-order encoder and adaptive decoder in our multimodal high-order relation transformer. Specifically, taking the full model as baseline, we remove the clip encoder which is denoted as 'w/o CE'. Removing the high-order relation extractor can verify the effectiveness of modeling high-order context, and we denote it as 'w/o HR', i.e. without high-order relation guidance. And the model without the full high-order encoder in the multimodal high-order relation transformer is denoted as 'w/o CR' for 'without context relation', as it lacks the context relationship modeling. And the model without the + +Table 3: Results on the MovieNetSSeg dataset with different multimodal semantics settings, which demonstrate the effectiveness of our approach under fair conditions. + +
MethodLGSS (audio)LGSS (place)LGSS (audio+place)LGSS (audio+place +act+cast)Ours (audio)Ours (place)Ours (audio+place)Ours (audio+place +visual)
AP(↑)17.539.043.447.116.350.948.454.8
+ +Table 5: Impact of different components. We take the full model as baseline. + +
ModalityAP (↑)mIoU (↑)AUC-ROC (↑)F1 (↑)
w/o CE52.348.390.045.5
w/o HR51.150.388.444.4
w/o CR48.645.988.645.2
w/o Cluster54.350.990.346.2
Full Model54.851.290.346.3
+ +![](images/8dea7ba4d3e6e86738fa18eddf012e57c048201c56667761416ac7a0562718d7.jpg) +Figure 4: Impact of different data augmentation strategies. + +![](images/f864ad00e6773ea5bb9cc1080d8cf36280e53b7776ef2258b7be1cc8ecb7dc11.jpg) + +proposed adaptive decoder is formulated as 'w/o Cluster', which does not need to cluster shots within the same scene. As shown in the first line of Table 5, removing the clip encoder leads to 2.5 drop on AP, and 0.8 on F1. If the model taken out the high-order relation extractor AP drops 3.7. Furthermore, if we remove the high-order encoder, the performance can degrade a lot, i.e. 6.2 on AP, 5.3 on mIoU. This demonstrates that modeling context and high-order relationships among the video shots is of great significance for the video scene detection task. Besides, comparing the last two lines in Table 5 can prove the necessity of clustering shots within the same scene. Lacking the guidance from scene-level representations, the results on AP drops 0.5, and mIoU drops 0.3. + +Impact of Data Augmentation. Figure 4 demonstrates the impact of different data augmentations. We add shot sequence samples from one video to another video with positive boundary on the central position, to make the model to learn robust scene boundary pattern. If the two videos are from the same video, we call this augmentation method as 'Intra'. Otherwise, as 'Inter'. Hyperparameter ratio controls the rate of newly constructed samples. When the ratio equals zero, we only adopt shot sequence samples by sliding window on every training video without any data augmentation. Having appropriate numerical values for ratio is crucial since setting it too low can prevent the model from + +acquiring positive samples, while setting it too high can lead to overfitting. Optimal outcome is obtained with a ratio of 0.3 for 'Intra' augmentation and 0.2 for 'Inter' augmentation. Therefore, we incorporate these two hyperparameters in our complete model. Figure 4 shows that both of 'Intra' and 'Inter' can improve the performance, while 'Intra' is better. The reason may be that 'Intra' helps constructing harder samples. + +Qualitative Analysis. In this part, we visualize similarity matrixes of 50 consecutive shot representations from multimodal features, which can intuitively prove the importance of multimodal cues in the task of scene boundary detection. Specifically, the models are trained with different multimodal semantic settings, and output multimodal shot features respectively. Then we visualize the matrix of cosine similarity between them. The ground-truth labels of scenes (i.e. shot clusters) are marked by red rectangles. It is obvious in Figure 5, shots are clearly clustered into scenes by multimodal features, i.e. the similarities between the shots before and after the boundaries are quite small. Besides, we can see that audio features can hardly separate the shots into different scenes, and the similarity matrix of place or visual features can roughly cluster the shots into scenes near the ground-truth. For single audio or place features, the similarities around boundaries are smooth, which may lead to confusing boundary detection results. Thus, we believe that audio, place and visual features can complement with each other to achieve better performance. + +# 5. Conclusion + +In this paper, we propose a unified multimodal framework for video scene boundary detection. And we design a novel Multimodal High-order Relation Transformer, which can model multimodal cues, high-order relation and scene adaptive clustering in a unified structure. We extract multimodal shot representations and model their clip-level context using expert networks and a clip encoder. Then we use a high-order encoder to uncover complex associations among the features and exploit contextual semantics. Then an adaptive decoder in our transformer is proposed to dynamically merge shots in the same scene, which is effective at discovering switch pattern between scenes rather than visual appearance. We have systematically studied the influence of our idea and carried out experiments. The results demonstrate the effectiveness of our model by achieving significant performance. + +![](images/68bcf80734161ab816517186dd22f51f039b33559d79adf5f3de25a8f7a0329f.jpg) +Figure 5: Visualization of similarity matrixes between shot representations in randomly sampled 50 consecutive shots. The ground-truth labels of scenes (shot clusters) are marked by red rectangles. + +# 6. Acknowledgment + +This work was partially supported by National Nature Science Foundation of China (Grant 62022078, 62121002) and National Defense Basic Scientific Research Program (2021601B013). + +# References + +[1] Lorenzo Baraldi, Costantino Grana, and Rita Cucchiara. 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Despite significant advancements in this area, this task remains a challenging problem as it requires a comprehensive understanding of multimodal cues and high-level semantics. To tackle this issue, we propose a multimodal high-order relation transformer, which integrates a high-order encoder and an adaptive decoder in a unified framework. By modeling the multimodal cues and exploring similarities between the shots, the encoder is capable of capturing high-order relations between shots and extracting shot features with context semantics. By clustering the shots adaptively, the decoder can discover more universal switch pattern between successive scenes, thus helping scene boundary detection. Extensive experimental results on three standard benchmarks demonstrate that the proposed model performs favorably against state-of-the-art video scene detection methods." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 502, + 128, + 514 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 502, + 128, + 514 + ], + "spans": [ + { + "bbox": [ + 47, + 502, + 128, + 514 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 522, + 288, + 713 + ], + "type": "text", + "content": "Cognitive science has discovered that humans usually comprehend a long video by breaking down it into meaningful units and reasoning about their relationships [20]. Therefore, dividing a long video into a series of meaningful story-telling video scenes, i.e. video scene detection, turns out to be a crucial task towards high-level video understanding. In filmmaking and video production, the term 'scene' is a basic unit for story-telling, consisting of a series of semantic cohesive shots, while the term 'shot' is a series of frames captured by the same camera over an uninterrupted period of time [4]. The task of video scene detection has drawn remarkable attention and can be widely adopted to various tough applications, including video caption, content-driven video search, scene classification, human-centric storyline construction and so on [8, 15, 31]. Although significant progress has been achieved in recent years, video scene" + } + ] + } + ], + "index": 8 + }, + { + "type": "image", + "bbox": [ + 313, + 240, + 537, + 324 + ], + "blocks": [ + { + "bbox": [ + 313, + 240, + 537, + 324 + ], + "lines": [ + { + "bbox": [ + 313, + 240, + 537, + 324 + ], + "spans": [ + { + "bbox": [ + 313, + 240, + 537, + 324 + ], + "type": "image", + "image_path": "1f8c70b7ec4ce57c62ec6808d2226888bed38e9d9b80b491c4357d38cbe684be.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 343, + 327, + 510, + 336 + ], + "lines": [ + { + "bbox": [ + 343, + 327, + 510, + 336 + ], + "spans": [ + { + "bbox": [ + 343, + 327, + 510, + 336 + ], + "type": "text", + "content": "(a) Two consecutive scenes in movie Blade Runner." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 313, + 338, + 536, + 434 + ], + "blocks": [ + { + "bbox": [ + 313, + 338, + 536, + 434 + ], + "lines": [ + { + "bbox": [ + 313, + 338, + 536, + 434 + ], + "spans": [ + { + "bbox": [ + 313, + 338, + 536, + 434 + ], + "type": "image", + "image_path": "7dcecbe38f5a9a964a540de95deec2444d2a3aa64dcbfa3ab614afbb62098433.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 353, + 436, + 498, + 445 + ], + "lines": [ + { + "bbox": [ + 353, + 436, + 498, + 445 + ], + "spans": [ + { + "bbox": [ + 353, + 436, + 498, + 445 + ], + "type": "text", + "content": "(b) Histograms of similarities between shots." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "type": "image", + "bbox": [ + 317, + 447, + 535, + 478 + ], + "blocks": [ + { + "bbox": [ + 317, + 447, + 535, + 478 + ], + "lines": [ + { + "bbox": [ + 317, + 447, + 535, + 478 + ], + "spans": [ + { + "bbox": [ + 317, + 447, + 535, + 478 + ], + "type": "image", + "image_path": "0d2efe1cccf6c1bd7445ff05b0e14bfb3dd524a1318b62c3387d971f7b34d8e7.jpg" + } + ] + } + ], + "index": 13, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 339, + 480, + 512, + 491 + ], + "lines": [ + { + "bbox": [ + 339, + 480, + 512, + 491 + ], + "spans": [ + { + "bbox": [ + 339, + 480, + 512, + 491 + ], + "type": "text", + "content": "(c) Diverse scene boundaries in movie Blade Runner." + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "image_caption" + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 500, + 545, + 596 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 500, + 545, + 596 + ], + "spans": [ + { + "bbox": [ + 304, + 500, + 545, + 596 + ], + "type": "text", + "content": "Figure 1: (a) There is minimal visual alteration at the scene boundary, while the audio content undergoes significant changes. (b) Direct similarities between shots near the boundary can all have high scores, while the trend of similarity variation can provide more discriminative signals. (c) Scene boundaries can vary greatly even in the same movie. Therefore, learning shot-level representations alone is insufficient for this class-agnostic task." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 605, + 545, + 628 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 628 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 628 + ], + "type": "text", + "content": "detection remains challenging due to requiring semantic understanding in a long-term video." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 630, + 545, + 713 + ], + "type": "text", + "content": "Recently, researchers have proposed methods like [4, 15, 20, 38] that leverage visual cues in unlabeled videos to model scene boundary. These approaches mainly employ an unsupervised contrastive learning strategy to differentiate shots from distinct scenes. Although these methods have taken a big step forward, they simply use visual appearance cues to generate pseudo labels for contrastive" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22081" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 49, + 72, + 286, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 72, + 286, + 251 + ], + "spans": [ + { + "bbox": [ + 49, + 72, + 286, + 251 + ], + "type": "text", + "content": "learning, resulting in the model learning the differences of shots at the visual apparent level rather than semantic level. In order to address above limitations, approaches such as [18, 19, 23, 27] introduce various expert networks to model multimodal signals like visual, audio, cast and place in various video understanding tasks. These methods still struggle to accurately identify scene boundaries in long-term videos, particularly those with complex story-telling structures. This is due to that modeling context of the shots plays a crucial role in identifying boundaries. Furthermore, all previous methods [1, 4, 23, 20, 27, 38] primarily emphasize learning discriminative shot features and overlook that scene boundary detection is a class-agnostic task. Thus they fail to identify more universal switch pattern between different scenes which is less dependent on appearance." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 49, + 255, + 286, + 673 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 255, + 286, + 673 + ], + "spans": [ + { + "bbox": [ + 49, + 255, + 286, + 673 + ], + "type": "text", + "content": "Based on the above analysis and the characteristics of scene boundary detection, we believe following aspects are important in this task: (1) The multimodal shot representations can provide comprehensive cues to detect scene boundary. (2) The high-order relation provides corrections for the context of shots. (3) The scene-level representations, derived from adaptively aggregation of shots features, can effectively indicate the switch pattern between different scenes. Firstly, as shown in Figure 1a, there is minimal alteration in the visual appearance between Scene A and scene B. However, the audio signal undergoes a significant change, making it easier to discern the transition between scenes. Secondly, as shown in Figure 1b, the shots before and after the scene boundary, such as shot 48 and shot 49, exhibit high similarities, suggesting that the scene switch can occur seamlessly. Neither the environment nor the characters change, only the two men's behavior changes. Under this circumstances, considering only the similarities between shots (first-order relation) can lead to undetectable blurred boundaries. Fortunately, by representing shots 47-49 as 10-dimensional similarity vectors based on their similarities with reference shots 43-52, we can observe a significant change near the scene boundary. This motivates us that the similarities between these similarity vectors, denoted as high-order relation, can correct for the first-order relation. Thirdly, unlike the common video action detection task, video scene detection is a category-agnostic task [5]. As shown in Figure 1c, even within the same movie, the appearances of the 'scene boundary shots' (i.e. shots 48, 52, 63, 80) still vary greatly. It is more important to discover the switch pattern between successive scenes rather than learn shot-level representations. This encourages us to learn more contextual and category-agnostic scene-level representations, which can be adaptively aggregated from shot-level features." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 49, + 678, + 286, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 49, + 678, + 286, + 712 + ], + "spans": [ + { + "bbox": [ + 49, + 678, + 286, + 712 + ], + "type": "text", + "content": "Take these observations together, we propose the Multimodal High-order Relation Transformer for video scene detection, which can model multimodal cues, high-order" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 308, + 72, + 544, + 286 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 72, + 544, + 286 + ], + "spans": [ + { + "bbox": [ + 308, + 72, + 544, + 286 + ], + "type": "text", + "content": "relation and scene adaptive clustering in a unified structure. Specifically, we first take multimodal expert networks and clip encoders to extract multimodal clip-level shot embeddings for the input shot sequence. Then our designed multimodal high-order relation transformer, consisting of a high-order encoder and an adaptive decoder, is employed to model the high-order relation for the shots and generate contextual scene-level representation in a unified framework. In detail, the high-order encoder primarily employs the multi-head and self-attention mechanism on the multimodal shot embeddings to produce high-order relationships ('relation in relation'), thereby enhancing the appropriate correlations between shots and suppressing erroneous ones. And the adaptive decoder merges contextual shot embeddings into scene representations with learnable scene prototypes and cross-attention. Finally, we take those contextualized shot embeddings for scene boundary classification and scene embeddings for boundary position regression." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 308, + 288, + 544, + 478 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 288, + 544, + 478 + ], + "spans": [ + { + "bbox": [ + 308, + 288, + 544, + 478 + ], + "type": "text", + "content": "The major contributions of this work can be summarized as follows: (1) We propose the Multimodal High-order Relation Transformer, which can model multimodal cues, high-order relation and scene adaptive clustering in a unified structure. (2) In our transformer, we design the high-order encoder to enhance the context of shots and rectify noises in the correlation map of shots caused by their imperfect features. We further employ the adaptive decoder to aggregate shot features, which is better at capturing switch pattern between scenes rather than visual appearance. (3) Extensive experimental results on three standard benchmarks including MovieNetSSeg [12], OVSD [27] and BBC planet earth [1] demonstrate that the proposed model can outperform previous works by a large margin, and can be even competitive with those pre-training methods which consume more than 5 times training data." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 308, + 484, + 391, + 496 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 484, + 391, + 496 + ], + "spans": [ + { + "bbox": [ + 308, + 484, + 391, + 496 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 308, + 498, + 544, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 498, + 544, + 640 + ], + "spans": [ + { + "bbox": [ + 308, + 498, + 544, + 640 + ], + "type": "text", + "content": "The basic assumption of video scene detection is that one shot can only belong to one scene, thus scene boundaries are a subset of shot boundaries [30]. As a result, the pre-task of scene detection is usually shot detection [14], which divides a video into sequences of time-continuous, non-overlapping shots. Given shot sequences, the video scene segmentation problem can be modeled as shot grouping, which clusters consecutive shots into scenes, or binary classification, which predicts whether a shot is a scene boundary. Many methods have been proposed [1, 4, 27, 20, 38], which can be categorized as unsupervised methods, supervised methods and self-supervised methods." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 308, + 643, + 544, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 308, + 643, + 544, + 712 + ], + "spans": [ + { + "bbox": [ + 308, + 643, + 544, + 712 + ], + "type": "text", + "content": "Unsupervised Methods. Early works utilize a variety of unsupervised methods. Among them, [24, 29] cluster shots according to spatiotemporal video features or shot color similarities. [27] obtains a consecutive segmentation by dynamic programming. [28] presents a novel normalized cost function for optimally grouping shots into scenes. Other" + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 750, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 750, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 750, + 317, + 757 + ], + "type": "text", + "content": "22082" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 97, + 71, + 492, + 186 + ], + "blocks": [ + { + "bbox": [ + 97, + 71, + 492, + 186 + ], + "lines": [ + { + "bbox": [ + 97, + 71, + 492, + 186 + ], + "spans": [ + { + "bbox": [ + 97, + 71, + 492, + 186 + ], + "type": "image", + "image_path": "5d620c58cc8cca4783ec5b768ae62c7b14472d4652f38e61d3a390fad80961db.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 190, + 547, + 240 + ], + "lines": [ + { + "bbox": [ + 46, + 190, + 547, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 190, + 547, + 240 + ], + "type": "text", + "content": "Figure 2: Our method follows a three-stage pipeline. Firstly, we extract multimodal features with short-term context using multimodal backbones and clip encoders. In the second stage, our high-order encoder models complex multimodal cues and context for each shot, while the decoder adaptively aggregates shots within the same scene. Finally, we employ separate heads for central shot classification and scene boundary position regression. Please refer to the text for more details." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 245, + 288, + 353 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 245, + 288, + 353 + ], + "spans": [ + { + "bbox": [ + 46, + 245, + 288, + 353 + ], + "type": "text", + "content": "works make use of multimodal information [27]. For instance, [30] uses both low-level and high-level audio features, visual features to build scene transition graph and extend the unimodal STG-based temporal segmentation technique to multimodal scene segmentation. However, these methods are trained on small-scale datasets [1, 27], leading to poor generalization. Our method turns to deep learning and is trained with newly proposed large dataset [12], obtaining much better performance and generalization." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 354, + 288, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 354, + 288, + 653 + ], + "spans": [ + { + "bbox": [ + 46, + 354, + 288, + 653 + ], + "type": "text", + "content": "Supervised and Self-Supervised Methods. As more and larger datasets are presented [4, 5, 20, 23, 38, 32, 37, 39], researchers are turning to supervised methods. With large-scale datasets, the deep neural network has a great advantage on extracting semantic features. [22] uses Alexresnet365 to extract scene features, while [13] achieves video scene segmentation using an image captioning model to extract semantic information of shots. [23] proposes a supervised baseline utilizing multimodal features to perform a shot-level binary classification, followed by an iterative optimal grouping. Recently, self-supervised methods achieve the best performance. Among them, [4] proposes a shot contrastive pre-training strategy to learn distinguishable shot representation. [38] achieves scene consistency representation learning using a novel positive sample selection strategy in contrast learning. And [20] mainly focuses on designing boundary-aware self-supervised tasks. However, these methods ignore multimodal information and simply use visual appearance cues to contrast different shots, while scene segmentation relies on semantic context. On the contrary, we can jointly model multimodal cues, high-order relation enhanced context with our proposed high-order encoder. And our proposed decoder can adaptive merge shot features into scene-level features to discover the switch pattern between video scenes." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 663, + 287, + 689 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 663, + 287, + 689 + ], + "spans": [ + { + "bbox": [ + 47, + 663, + 287, + 689 + ], + "type": "text", + "content": "3. Multimodal High-order Relation Transformer" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 715 + ], + "type": "text", + "content": "As shown in Figure 2, our method deals with the multimodal shot-level video inputs in a pipeline of clip-level shot" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 245, + 547, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 245, + 547, + 462 + ], + "spans": [ + { + "bbox": [ + 304, + 245, + 547, + 462 + ], + "type": "text", + "content": "embedding, multimodal high-order context modeling and boundary classification. Given a full-length input video, we first split it into a constituent set of shots with the standard shot detection techniques [30]. We then use the sliding window to get a continuous subsequence of shots " + }, + { + "bbox": [ + 304, + 245, + 547, + 462 + ], + "type": "inline_equation", + "content": "\\{s_0,s_1,\\dots,s_l\\}" + }, + { + "bbox": [ + 304, + 245, + 547, + 462 + ], + "type": "text", + "content": ", and extract its multimodal representations (i.e. visual, place and audio) with the various expert networks. And the clip encoder is employed to model each shot's short-term context. Based on these multimodal shot features, we then perform multimodal high-order context modeling to exploit story-telling semantics for each shot. Specifically, the proposed multimodal high-order relation transformer first adopts the high-order encoder to take both multimodal cues and high-order relationships into consideration. Then the followed adaptive decoder is employed to aggregate shots into scenes. Finally, we adopt both shot features with contextual information and dynamically aggregated scene features for scene boundary prediction." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 469, + 455, + 483 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 469, + 455, + 483 + ], + "spans": [ + { + "bbox": [ + 305, + 469, + 455, + 483 + ], + "type": "text", + "content": "3.1. Clip-level Shot Embedding" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 485, + 547, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 485, + 547, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 485, + 547, + 616 + ], + "type": "text", + "content": "Multimodal Expert Networks. A long-term video is a typical multimodal data containing different high-level semantics [23]. Thus visual features extracted by classical backbones like I3D [2] or TSN [36] are insufficient for the video scene detection task. Instead, the story-telling high semantics can be better described and complemented by multimodal representations. Observing that, in addition to visual contents, a 'scene' is closely related to shots sharing common place, audio elements. Following [23] we adopt visual, place and audio expert networks to extract multimodal shot features." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": "Following [1, 20, 23], we first extract the key frame for each shot in the sequence " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\{s_0,s_1,\\dots ,s_l\\}" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": ". Then we (1) adopt the ViT [7] to get visual features " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^{\\mathbf{v}} = \\{r_0^v,r_1^v,\\dots ,r_l^v\\}" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": ", (2) employ the ResNet50 [10] pretrained on Places dataset [40] to get place features " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^{\\mathbf{p}} = \\{r_0^p,r_1^p,\\dots ,r_l^p\\}" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": ", and (3) take stft [34] followed by the pretrained VGGish [11] to get audio features " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^{\\mathbf{a}} = \\{r_0^a,r_1^a,\\dots ,r_l^a\\}" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": ". The superscript " + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "inline_equation", + "content": "v,a,p" + }, + { + "bbox": [ + 304, + 617, + 547, + 715 + ], + "type": "text", + "content": " denote for the different modality. Noting that all the expert" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22083" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 73, + 71, + 521, + 262 + ], + "blocks": [ + { + "bbox": [ + 73, + 71, + 521, + 262 + ], + "lines": [ + { + "bbox": [ + 73, + 71, + 521, + 262 + ], + "spans": [ + { + "bbox": [ + 73, + 71, + 521, + 262 + ], + "type": "image", + "image_path": "8bc8a06e9e1371f11f2adc9c19f31fe3b3799fdbd5c10ca5470de1c06216b680.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 270, + 547, + 319 + ], + "lines": [ + { + "bbox": [ + 46, + 270, + 547, + 319 + ], + "spans": [ + { + "bbox": [ + 46, + 270, + 547, + 319 + ], + "type": "text", + "content": "Figure 3: The proposed Multimodal High-order Relation Transformer is designed to enhance shot features with high-order context and discover the switch pattern between scenes. Specifically, the high-order encoder can fuse multimodal cues and model context for each shot under the guidance of high-order relation extractor. Additionally, the subsequent decoder adaptively aggregate shots in the same scene and captures the switch pattern between scenes. Best viewed with colors." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 325, + 241, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 325, + 241, + 337 + ], + "spans": [ + { + "bbox": [ + 47, + 325, + 241, + 337 + ], + "type": "text", + "content": "networks are frozen during the training process." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 342, + 288, + 438 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 342, + 288, + 438 + ], + "spans": [ + { + "bbox": [ + 46, + 342, + 288, + 438 + ], + "type": "text", + "content": "Aiming to enhancing shot features with high-order context and discovering the switch pattern between scenes, we design a transformer-based architecture. As shown in Figure 3, it consists of a high-order encoder and an adaptive decoder. The encoder is applied to fuse complex multimodal cues and model context for each shot with the help of high-order relation extractor, while the decoder is responsible for adaptively aggregating shots in the same scene." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "spans": [ + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "text", + "content": "Clip Encoder. Following [23], we add a clip encoder on a local window for each shot's representations, aiming to obtain their clip-level representations. Specifically, taking the visual feature " + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "inline_equation", + "content": "r_i^v" + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "text", + "content": " of shot " + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "text", + "content": " for example, we consider the differences " + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "inline_equation", + "content": "\\mathbf{S}_{\\mathbf{D}}" + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "text", + "content": " and relations " + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "inline_equation", + "content": "\\mathbf{S}_{\\mathbf{R}}" + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "text", + "content": " of its n-earby shots in a window with length " + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "inline_equation", + "content": "2w_{s}" + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "text", + "content": ", i.e. " + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "inline_equation", + "content": "\\mathbf{V}_i = \\left\\{r_{i - (w_s - 1)}^v,\\dots ,r_i^v,\\dots ,r_{i + w_s}^v\\right\\}" + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "text", + "content": ". This process can be performed by temporal convolution layers " + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "inline_equation", + "content": "\\Psi" + }, + { + "bbox": [ + 47, + 443, + 288, + 557 + ], + "type": "text", + "content": " and fully connected layers FC, as shown in Equation (1):" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 51, + 575, + 288, + 628 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 51, + 575, + 288, + 628 + ], + "spans": [ + { + "bbox": [ + 51, + 575, + 288, + 628 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathbf {S} _ {\\mathbf {D}} \\left(\\mathbf {V} _ {i}\\right) = \\Psi \\left(\\left\\{r _ {i - \\left(w _ {s} - 1\\right)}, \\dots , r _ {i} ^ {v} \\right\\}\\right) \\cdot \\Psi \\left(\\left\\{r _ {i + 1} ^ {v}, \\dots , r _ {i + w _ {s}} ^ {v} \\right\\}\\right), \\\\ \\mathbf {S} _ {\\mathbf {R}} (\\mathbf {V} _ {i}) = \\Psi (\\{r _ {i - (w _ {s} - 1)} ^ {v}, \\dots , r _ {i + w _ {s}} ^ {v} \\}), \\\\ r _ {i} ^ {v ^ {+}} = \\mathbf {F C} (\\operatorname {c o n c a t} \\left(\\mathbf {S} _ {\\mathbf {D}} \\left(\\mathbf {V} _ {i}\\right), \\mathbf {S} _ {\\mathbf {R}} \\left(\\mathbf {V} _ {i}\\right)\\right)), \\tag {1} \\\\ \\end{array}", + "image_path": "83bfdf7f2722afcafdb782f7ed3c0e1b0caac775afa650524c130769cb2e71cc.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\text{concat}" + }, + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "type": "text", + "content": " denotes the concatenation operation, " + }, + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\cdot" + }, + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "type": "text", + "content": " denotes the inner product. Similar operations are performed on the place and audio modality, and the updated shot features can be described by " + }, + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^{\\mathbf{v}^{+}} = \\{r_{0}^{v^{+}}, r_{1}^{v^{+}}, \\dots, r_{l}^{v^{+}}\\}" + }, + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^{\\mathbf{p}^{+}} = \\{r_{0}^{p^{+}}, r_{1}^{p^{+}}, \\dots, r_{l}^{p^{+}}\\}" + }, + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^{\\mathbf{a}^{+}} = \\{r_{0}^{a^{+}}, r_{1}^{a^{+}}, \\dots, r_{l}^{a^{+}}\\}" + }, + { + "bbox": [ + 46, + 628, + 287, + 715 + ], + "type": "text", + "content": ". Consequently, these multimodal shot features are enhanced with short-term context." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 324, + 527, + 337 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 324, + 527, + 337 + ], + "spans": [ + { + "bbox": [ + 306, + 324, + 527, + 337 + ], + "type": "text", + "content": "3.2. Multimodal High-order Context Modeling" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 349, + 545, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 349, + 545, + 445 + ], + "spans": [ + { + "bbox": [ + 304, + 349, + 545, + 445 + ], + "type": "text", + "content": "Aiming to enhancing shot features with high-order context and discovering the switch pattern between scenes, we design a transformer-based architecture. As shown in Figure 3, it consists of a high-order encoder and an adaptive decoder. The encoder is applied to fuse complex multimodal cues and model context for each shot with the help of high-order relation extractor, while the decoder is responsible for adaptively aggregating shots in the same scene." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "spans": [ + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "text", + "content": "High-order Relation Extractor. As discussed above, directly adopting the standard transformer encoder [35] over the shot sequence features may introduce noises in the correlation map due to imperfect shot features, and ignore comprehensive 'high-order relation' signal. Thus, we innovatively design the high-order relation extractor to correct first-order relations and fuse the multimodal cues jointly. As shown in the upper part of Figure 3, taking the multimodality shot sequence features " + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^{\\mathbf{v}^{+}}" + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^{\\mathbf{p}^{+}}" + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^{\\mathbf{a}^{+}}" + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "text", + "content": " as inputs, we first calculate the multi-head based temporal similarity matrix for each modality, generating a first-order multimodal relation map " + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "inline_equation", + "content": "\\mathbf{M} \\in \\mathcal{R}^{(l + 1) \\times (l + 1) \\times 3h}" + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "text", + "content": ", which naturally contains temporal positional signal. Note that " + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "inline_equation", + "content": "l + 1" + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "text", + "content": " is the length of shot sequence and " + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "text", + "content": " is the number of heads. Then a shallow CNN is applied on " + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "inline_equation", + "content": "\\mathbf{M}" + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "text", + "content": " to fuse multimodal cues and model neighboring first-order relations. And one standard transformer layer followed by linear layers and sigmoid function is adopted to model the global associations of each shot's relation, producing the guidance map " + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_{\\mathbf{C}}" + }, + { + "bbox": [ + 304, + 453, + 546, + 682 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 713 + ], + "type": "text", + "content": "High-order Encoder for Context Modeling. As shown in the bottom left part of Figure 3, we fuse multimodal fea" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22084" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 84 + ], + "type": "text", + "content": "tures with concatenation operation and a simple linear layer:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 80, + 90, + 287, + 106 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 80, + 90, + 287, + 106 + ], + "spans": [ + { + "bbox": [ + 80, + 90, + 287, + 106 + ], + "type": "interline_equation", + "content": "r _ {i} ^ {f} = \\mathbf {F C} \\left(\\operatorname {c o n c a t} \\left(r _ {i} ^ {v ^ {+}}, r _ {i} ^ {p ^ {+}}, r _ {i} ^ {a ^ {+}}\\right)\\right) \\in \\mathcal {R} ^ {d _ {f}}, \\tag {2}", + "image_path": "127fb9f35eb4db42d506ef58c3fbee851b71a79c9d03023ffa6e2e74752cce96.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "spans": [ + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "text", + "content": "producing fused shot sequence features " + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^f\\in \\mathcal{R}^{(l + 1)\\times d_f}" + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "text", + "content": " where the superscript " + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "inline_equation", + "content": "f" + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "text", + "content": " denotes for fusion. Then we apply the guidance map " + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "inline_equation", + "content": "\\mathbf{M_C}" + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "text", + "content": " to enhance context modeling in a conventional transformer encoder. In detail, we first generate transformed queries and key-values pairs by: " + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "inline_equation", + "content": "\\mathbf{Q} = \\mathbf{R}^{f}\\mathbf{W}^{Q},\\mathbf{K} = \\mathbf{R}^{f}\\mathbf{W}^{K},\\mathbf{V} = \\mathbf{R}^{f}\\mathbf{W}^{V}" + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "inline_equation", + "content": "\\mathbf{W}^Q\\in \\mathcal{R}^{d_f\\times d_k},\\mathbf{W}^K\\in \\mathcal{R}^{d_f\\times d_k},\\mathbf{W}^V\\in \\mathcal{R}^{d_f\\times d_v}" + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "text", + "content": ". Noting that we omit the multi-head scripts to simplify the expression here. Then the modified attention process HoAttn(Rf), under the guidance from the high-order multimodal relation cues " + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "inline_equation", + "content": "\\mathbf{M_C}" + }, + { + "bbox": [ + 47, + 110, + 289, + 243 + ], + "type": "text", + "content": ", can be described by:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 61, + 247, + 287, + 275 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 247, + 287, + 275 + ], + "spans": [ + { + "bbox": [ + 61, + 247, + 287, + 275 + ], + "type": "interline_equation", + "content": "\\mathbf {H o A t t n} \\left(\\mathbf {R} ^ {f}\\right) = \\left(\\mathbf {M} _ {C} \\odot \\operatorname {s o f t m a x} \\left(\\frac {\\mathbf {Q K} ^ {T}}{\\sqrt {d _ {k}}}\\right)\\right) \\mathbf {V}, \\tag {3}", + "image_path": "244a1946c272ee56e7d6b26cdc2497d2b27f34ac8ba6b4f87a3f64a0ff6fb29d.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 278, + 287, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 278, + 287, + 411 + ], + "spans": [ + { + "bbox": [ + 46, + 278, + 287, + 411 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 278, + 287, + 411 + ], + "type": "inline_equation", + "content": "\\odot" + }, + { + "bbox": [ + 46, + 278, + 287, + 411 + ], + "type": "text", + "content": " denotes Hadamard product, indicating " + }, + { + "bbox": [ + 46, + 278, + 287, + 411 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_C" + }, + { + "bbox": [ + 46, + 278, + 287, + 411 + ], + "type": "text", + "content": " works as a rectifier to enhance the appropriate correlations and suppress the erroneous ones. The residual connections, normalization operation and feed-forward layer are concatenated after this attention block, as shown in Figure 3. As a result, the high-order encoder can produce shot representations " + }, + { + "bbox": [ + 46, + 278, + 287, + 411 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^{f^*} = \\{r_0^{f^*}, r_1^{f^*}, \\dots, r_l^{f^*}\\}" + }, + { + "bbox": [ + 46, + 278, + 287, + 411 + ], + "type": "text", + "content": ". And " + }, + { + "bbox": [ + 46, + 278, + 287, + 411 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^{f^*}" + }, + { + "bbox": [ + 46, + 278, + 287, + 411 + ], + "type": "text", + "content": " contains comprehensive multi-modality contextual information. The above two parts fit together as our High-order Encoder and can serve as a basic block, offering a flexible high-order relation perception function." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 411, + 287, + 554 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 411, + 287, + 554 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 287, + 554 + ], + "type": "text", + "content": "Adaptive Decoder for Shot Clustering. Although the high-order encoder successfully models both multimodal cues and high-order relations into the shot representations, it is still challenging to detect scene boundaries. Because even appearances of 'boundary shots' within the same video can vary dramatically. It is essential to learn the switch pattern between scenes, rather than simple shot features. Consequently, we design an adaptive decoder to dynamically merge shots within the same scene, resulting in aggregated contextual scene features. Our decoder also follows the query-key-value design in the vanilla transformer [35], making the full model unified." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 555, + 287, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 555, + 287, + 639 + ], + "spans": [ + { + "bbox": [ + 46, + 555, + 287, + 639 + ], + "type": "text", + "content": "As shown in the right part of Figure 3, our adaptive decoder consists of a pair of learnable scene prototypes " + }, + { + "bbox": [ + 46, + 555, + 287, + 639 + ], + "type": "inline_equation", + "content": "\\mathbf{P} = \\{p_1, p_2\\}" + }, + { + "bbox": [ + 46, + 555, + 287, + 639 + ], + "type": "text", + "content": " and an attention block. In order to reduce the domain gap between scene prototypes and shot features, we first employ the average pooled feature of all shots to modify the scene prototypes. The attention interaction between the shots and scene prototypes can be formulated by:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 106, + 643, + 201, + 656 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 106, + 643, + 201, + 656 + ], + "spans": [ + { + "bbox": [ + 106, + 643, + 201, + 656 + ], + "type": "interline_equation", + "content": "\\mathbf {P} ^ {*} = \\mathbf {P} \\odot a v g (\\mathbf {R} ^ {f ^ {*}}),", + "image_path": "aa7d8908b064d47bb1c313b72775a36cf70ba45db98fa780834aceb52861e355.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 106, + 656, + 287, + 670 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 106, + 656, + 287, + 670 + ], + "spans": [ + { + "bbox": [ + 106, + 656, + 287, + 670 + ], + "type": "interline_equation", + "content": "\\mathbf {A} _ {S} = \\left(\\mathbf {P} ^ {*} \\mathbf {W} _ {q}\\right) \\left(\\mathbf {R} ^ {f ^ {*}} \\mathbf {W} _ {k}\\right) ^ {T}, \\tag {4}", + "image_path": "352e8a36581879e43c7feb945b995c3a29943428ce83fbf55a3162312c01c4a4.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 106, + 670, + 212, + 682 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 106, + 670, + 212, + 682 + ], + "spans": [ + { + "bbox": [ + 106, + 670, + 212, + 682 + ], + "type": "interline_equation", + "content": "\\mathbf {Z} = \\{z _ {1}, z _ {2} \\} = \\mathbf {A} _ {S} \\mathbf {R} ^ {f ^ {*}},", + "image_path": "09fa9e204762df03dbc578b3b5fd86e2d599d61d88cbd730cd56363b02a92352.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_q\\in \\mathcal{R}^{d_s\\times d_q}" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_k\\in \\mathcal{R}^{d_f\\times d_q}" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " are learnable parameters. The affinity matrix " + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\mathbf{A}_S\\in \\mathcal{R}^{2\\times (l + 1)}" + }, + { + "bbox": [ + 47, + 689, + 287, + 713 + ], + "type": "text", + "content": " measures the rel" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": "evance between each prototype and the shots, which directs the aggregation of shots into scenes. And " + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "\\{z_1,z_2\\}" + }, + { + "bbox": [ + 304, + 72, + 545, + 120 + ], + "type": "text", + "content": " indicate the dynamically aggregated scene representations, which is used to regress the scene boundary positions." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 125, + 533, + 137 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 125, + 533, + 137 + ], + "spans": [ + { + "bbox": [ + 305, + 125, + 533, + 137 + ], + "type": "text", + "content": "3.3. Objective Function and Data Augmentation" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "spans": [ + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "type": "text", + "content": "Based on above discuss, we learn a set of shot representations " + }, + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "type": "inline_equation", + "content": "\\mathbf{R}^{f^*} = \\{r_0^{f^*}, r_1^{f^*}, \\dots, r_l^{f^*}\\}" + }, + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "type": "text", + "content": " and two adaptively merged scene features " + }, + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "type": "inline_equation", + "content": "\\mathbf{Z} = \\{z_1, z_2\\}" + }, + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "type": "text", + "content": " for the input shot sequence " + }, + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "type": "inline_equation", + "content": "\\{s_0, s_1, \\dots, s_l\\}" + }, + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "type": "text", + "content": ". For each shot sequence, we make prediction on the central shot " + }, + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "type": "inline_equation", + "content": "r_{[l/2]}^{f^*}" + }, + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "type": "text", + "content": ", i.e. determining whether it's a scene boundary or not. The subscript " + }, + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "type": "inline_equation", + "content": "[l/2]" + }, + { + "bbox": [ + 304, + 140, + 545, + 240 + ], + "type": "text", + "content": " stands for the floor function. The classification loss can be formulated as:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 310, + 247, + 545, + 266 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 247, + 545, + 266 + ], + "spans": [ + { + "bbox": [ + 310, + 247, + 545, + 266 + ], + "type": "interline_equation", + "content": "\\mathbf {L} _ {p r e} = - \\left[ y _ {c} \\log \\left(\\phi \\left(r _ {\\lfloor l / 2 \\rfloor} ^ {f ^ {*}}\\right)\\right) + \\left(1 - y _ {c}\\right) \\log \\left(\\phi \\left(r _ {\\lfloor l / 2 \\rfloor} ^ {f ^ {*}}\\right)\\right) \\right], \\tag {5}", + "image_path": "9492c79f9b20cedeb2e8d62da9247b979d2fcfb65a6deaaa79faf0ad42f5e794.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 272, + 547, + 344 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 272, + 547, + 344 + ], + "spans": [ + { + "bbox": [ + 304, + 272, + 547, + 344 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 272, + 547, + 344 + ], + "type": "inline_equation", + "content": "y_{c}" + }, + { + "bbox": [ + 304, + 272, + 547, + 344 + ], + "type": "text", + "content": " is the label for the central shot, deciding whether it's a scene boundary, and " + }, + { + "bbox": [ + 304, + 272, + 547, + 344 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 304, + 272, + 547, + 344 + ], + "type": "text", + "content": " is a binary classification head. Moreover, ordering to learn adaptive scene representations, we adopt the adaptively merged scene features " + }, + { + "bbox": [ + 304, + 272, + 547, + 344 + ], + "type": "inline_equation", + "content": "\\mathbf{Z} = \\{z_1,z_2\\}" + }, + { + "bbox": [ + 304, + 272, + 547, + 344 + ], + "type": "text", + "content": " and a regression head " + }, + { + "bbox": [ + 304, + 272, + 547, + 344 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 304, + 272, + 547, + 344 + ], + "type": "text", + "content": " to regress the position of the boundary in the shot sequence:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 350, + 354, + 545, + 368 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 350, + 354, + 545, + 368 + ], + "spans": [ + { + "bbox": [ + 350, + 354, + 545, + 368 + ], + "type": "interline_equation", + "content": "\\mathbf {L} _ {r e g} = \\mathbf {M S E} [ p, \\gamma (\\text {c o n c a t} (z _ {1}, z _ {2})) ], \\tag {6}", + "image_path": "93cb7efcde5df32236889b045247d48ffa40af8812ea6d271cbe096eb5c5cc48.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "spans": [ + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "type": "inline_equation", + "content": "p" + }, + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "type": "text", + "content": " is the ground-truth position of the scene boundary in the shot sequence, and " + }, + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "type": "inline_equation", + "content": "p = -1" + }, + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "type": "text", + "content": " or " + }, + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "type": "inline_equation", + "content": "p = l + 1" + }, + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "type": "text", + "content": " stands for there are no boundaries or multiple boundaries in the sequence. MSE denotes the mean squared error. The overall training loss can be " + }, + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "type": "inline_equation", + "content": "\\mathbf{L} = \\mathbf{L}_{pre} + \\alpha \\mathbf{L}_{reg}" + }, + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 376, + 545, + 448 + ], + "type": "text", + "content": " is a hyperparameter." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 448, + 545, + 520 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 448, + 545, + 520 + ], + "spans": [ + { + "bbox": [ + 304, + 448, + 545, + 520 + ], + "type": "text", + "content": "Moreover, there is a serious class-imbalance problem in the scene detection task, because boundaries are rare in a long video. Thus, we construct shot sequence samples with positive boundary on the central position by concatenating two distant subsequences in the same video or two subsequences from different videos:" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 306, + 529, + 545, + 553 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 529, + 545, + 553 + ], + "spans": [ + { + "bbox": [ + 306, + 529, + 545, + 553 + ], + "type": "interline_equation", + "content": "\\left\\{s _ {0}, \\dots , s _ {l / 2}, \\dots , s _ {l} \\right\\} _ {\\text {n e w}} = \\left\\{s _ {0}, \\dots , s _ {l / 2} \\right\\} _ {v _ {0}} + \\left\\{s _ {l / 2}, \\dots , s _ {l} \\right\\} _ {v _ {1}}. \\tag {7}", + "image_path": "a2099ab37bcddfd0433553dd25dc11dceb8874df6b0b8b6ffe63d2a6b61a9654.jpg" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 554, + 545, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 554, + 545, + 578 + ], + "spans": [ + { + "bbox": [ + 304, + 554, + 545, + 578 + ], + "type": "text", + "content": "The ratio of constructed samples to origin samples is adjustable according to the data distribution." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 305, + 588, + 432, + 601 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 588, + 432, + 601 + ], + "spans": [ + { + "bbox": [ + 305, + 588, + 432, + 601 + ], + "type": "text", + "content": "4. Experimental Results" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 605, + 422, + 617 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 605, + 422, + 617 + ], + "spans": [ + { + "bbox": [ + 306, + 605, + 422, + 617 + ], + "type": "text", + "content": "4.1. Experimental Setup" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 618, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 618, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 618, + 545, + 713 + ], + "type": "text", + "content": "Dataset. To demonstrate the effectiveness of our proposed method, we carry out extensive experiments on three public available datasets, including MovieNet-SSeg [12], BBC planet earth [1] and OVSD [27]. MovieNet [12], containing 1,100 videos with 1.6M shots, is the largest dataset for video understanding analysis by far. And the MovieNet-SSeg is a sub-dataset of that, with 190, 64 and 64 videos labeled with scene boundaries for training, validating and" + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22085" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 101, + 110, + 491, + 308 + ], + "blocks": [ + { + "bbox": [ + 46, + 70, + 545, + 106 + ], + "lines": [ + { + "bbox": [ + 46, + 70, + 545, + 106 + ], + "spans": [ + { + "bbox": [ + 46, + 70, + 545, + 106 + ], + "type": "text", + "content": "Table 1: Results on the MovieNetSSeg dataset. The best results are in bold, and the second best are in bold and underlined. Note that self-supervised methods are pretrained with 1100 videos in MovieNet (MS-1100), and fine-tuned with 190 training videos in MovieSSeg (MS-190). Using less than 1/5 of the training data, our model can achieve competitive results." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 101, + 110, + 491, + 308 + ], + "lines": [ + { + "bbox": [ + 101, + 110, + 491, + 308 + ], + "spans": [ + { + "bbox": [ + 101, + 110, + 491, + 308 + ], + "type": "table", + "html": "
MethodTraining DataAP (↑)mIoU (↑)AUC-ROC (↑)F1 (↑)
Supervised Learning
Siamese [1]MS-19035.839.6--
MS-LSTM [12]MS-19046.546.2--
LGSS [23]MS-19047.148.8--
OursMS-19054.851.290.346.3
Unsupervised Learning
GraphCut [25]None14.129.7--
SCSA [3]None14.730.5--
DP [9]None15.532.0--
Story Graph [33]None25.135.7--
Grouping [27]None33.637.2--
Self-supervised Learning
ShotCoL [4]MS-110053.4---
SCRL [38]MS-110054.8--51.4
BaSSL [20]MS-110056.349.590.345.7
", + "image_path": "36b899171d4c6b6243498423e4f6deb6fbeef523206ae3846b8c7a6410d120d8.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 327, + 287, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 327, + 287, + 411 + ], + "spans": [ + { + "bbox": [ + 46, + 327, + 287, + 411 + ], + "type": "text", + "content": "testing. Besides, we also carry out experiments on BBC planet earth [1] and OVSD [27] dataset. BBC planet earth contains 11 documentaries and OVSD contains 21 various videos. And we just take them as the testing set to verify the generalization of our model, i.e. our model trained on MovieScenes-SSeg is directly tested them, because of their limited scale and unavailable splitting strategy." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 411, + 287, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 411, + 287, + 519 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 287, + 519 + ], + "type": "text", + "content": "Evaluation Metrics. We make comprehensive validations on our model with several metrics: (1) Average Precision(AP), it's the mean of AP of " + }, + { + "bbox": [ + 46, + 411, + 287, + 519 + ], + "type": "inline_equation", + "content": "y_{c} = 1" + }, + { + "bbox": [ + 46, + 411, + 287, + 519 + ], + "type": "text", + "content": " for each video. (2) mIoU, the averaged intersection over union (IoU) between detected scene boundary with their closest ground-truth scene boundary. (3) F1 score, the harmonic mean of the precision and recall, taking both recall and precision into consideration. (4) AUC - ROC, short for area under the receiver operating characteristics." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 521, + 287, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 556 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 556 + ], + "type": "text", + "content": "Implementation Details. The proposed High-Order Relation Aware Multi-modality Network is implemented in PyTorch framework [21] with NVIDIA V100 GPUs." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 557, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 288, + 713 + ], + "type": "text", + "content": "To begin with, we set the shot sequence length as 7, which is able to contain enough contextual information while requiring relative low memory resource. In the clip-level shot embedding stage, we only take visual, place and audio modalities mentioned in [23], as they play the most crucial roles in scene boundary detection. In specific, we use ViT-B/16 pretrained on ImageNet [6], ResNet50 pretrained on Place dataset [40], and VGGish pretrained on AVA-ActivaSpeaker [26] to extract multimodal shot features with 768, 2048, 128 dimensions respectively. All of them were frozen during training. The clip encoder employs the 1D-CNN [16] and the FC layer to transform them into 384, 256, 128 dimensional vectors. This indicates the im" + } + ] + } + ], + "index": 5 + }, + { + "type": "table", + "bbox": [ + 307, + 364, + 547, + 440 + ], + "blocks": [ + { + "bbox": [ + 304, + 325, + 545, + 361 + ], + "lines": [ + { + "bbox": [ + 304, + 325, + 545, + 361 + ], + "spans": [ + { + "bbox": [ + 304, + 325, + 545, + 361 + ], + "type": "text", + "content": "Table 2: Results of AP on BBC planet earth and OVSD datasets. Performances are achieved by the model trained on the MovieNetSSeg dataset without any fine-tuning." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 364, + 547, + 440 + ], + "lines": [ + { + "bbox": [ + 307, + 364, + 547, + 440 + ], + "spans": [ + { + "bbox": [ + 307, + 364, + 547, + 440 + ], + "type": "table", + "html": "
MethodBBCOVSD
SimCLR实例) [4]32.325.5
SimCLR(temperal) [4]34.224.9
SimCLR(NN) [4]32.925.0
BaSSL(More Training Data) [20]40.028.7
Ours38.727.5
", + "image_path": "42d1348a41d799f2f81c83d73be4db35363e8be4e98d38d3d294d4480087662a.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 460, + 545, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 460, + 545, + 651 + ], + "spans": [ + { + "bbox": [ + 304, + 460, + 545, + 651 + ], + "type": "text", + "content": "portance of each modality, which will be verified in the ablation studies. In the followed multimodal high-order context modeling stage, the high-order relation extractor first maps the multimodal features as the correlation map " + }, + { + "bbox": [ + 304, + 460, + 545, + 651 + ], + "type": "inline_equation", + "content": "\\mathbf{M}" + }, + { + "bbox": [ + 304, + 460, + 545, + 651 + ], + "type": "text", + "content": " with 8 heads. Feeding " + }, + { + "bbox": [ + 304, + 460, + 545, + 651 + ], + "type": "inline_equation", + "content": "\\mathbf{M}" + }, + { + "bbox": [ + 304, + 460, + 545, + 651 + ], + "type": "text", + "content": " into the shallow CNN with 4 layers, one transformer encoder layer and the followed linear layer, we get the high-order relation-aware guidance map " + }, + { + "bbox": [ + 304, + 460, + 545, + 651 + ], + "type": "inline_equation", + "content": "\\mathbf{M}_{\\mathbf{C}}" + }, + { + "bbox": [ + 304, + 460, + 545, + 651 + ], + "type": "text", + "content": ". We set the corresponding high-order context modeling encoder with 8 heads, 1 layer, and hidden units as 768. Finally, in the Adaptive Decoder, the dimensions of the merged scene features and the shot features remain the same. As a result, the scale of learnable parameters in our model is approximately equivalent to the sum of two layers of transformer encoder, four layers of CNN and several linear layers, which is comparable to that of BaSSL [20] without its' backbone." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 653, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 545, + 715 + ], + "type": "text", + "content": "The model is trained for 10 epochs with the Adam optimizer [17]. We start training with a learning rate of 0.0002, and decay the learning rate using a cosine schedule. The batch-size is set to 128 for all experiments. And the hyperparameter " + }, + { + "bbox": [ + 304, + 653, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 304, + 653, + 545, + 715 + ], + "type": "text", + "content": " in loss is set to 0.2. At last, for evaluation on" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 317, + 757 + ], + "type": "text", + "content": "22086" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 288, + 145 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 288, + 145 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 288, + 145 + ], + "type": "text", + "content": "the testing set, we tackle the over-fitting by choosing the s-napshot of the model based on the validation set. Noting that during inference, for each shot sequence we only make prediction on the central shot. Only if the classification head predicts to be positive, or the regression head outputs the central position, we take it as a positive boundary." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 148, + 191, + 162 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 148, + 191, + 162 + ], + "spans": [ + { + "bbox": [ + 47, + 148, + 191, + 162 + ], + "type": "text", + "content": "4.2. Performance Comparison" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 165, + 287, + 272 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 165, + 287, + 272 + ], + "spans": [ + { + "bbox": [ + 46, + 165, + 287, + 272 + ], + "type": "text", + "content": "We compare with several recent state-of-the-art methods on the MovieNet-SSeg [12] in Table 1. And verifying the generation ability of our method by carrying out experiments on BBC planet earth [1] and OVSD [27] datasets in Table 2. We can find that our proposed High-Order Relation Aware Multi-modality Network achieves much better performance compared with the supervised methods, and can be competitive with the self-supervised ones while consuming much less training resources." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 274, + 288, + 513 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 274, + 288, + 513 + ], + "spans": [ + { + "bbox": [ + 46, + 274, + 288, + 513 + ], + "type": "text", + "content": "Results on MovieNet-SSeg. Table 1 presents the quantitative results on MovieNet-SSeg. We compare our method with various types of methods, including supervised, unsupervised and self-supervised approaches. The results demonstrate that under the same settings, our methods can outperform previous works by a large margin and can be even competitive with those which employ more than 5 times training data. Particularly, our method achieves 54.8 for AP, 51.2 for mIoU, 90.3 for AUC - ROC and 46.3 for F1. Noting that our method can offer a much more convenient way for training and testing compared with BaSSL, ShotCoL and SCRL [20, 4, 38]. For fair comparison, we also conduct experiments using identical multi-modality settings, specifically by the same features generated by expert networks. As shown in Tabel 3, using less external knowledge, our approach can still outperform LGSS by a large margin. Different from previous works which neglect the high-order relations among the shot sequence and only focus on learning shot features, our method jointly models both of them in a unified deep model." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 514, + 287, + 669 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 514, + 287, + 669 + ], + "spans": [ + { + "bbox": [ + 46, + 514, + 287, + 669 + ], + "type": "text", + "content": "Results on BBC planet earth and OVSD. As shown in Table 2, we further validate performance of our method on BBC planet earth [1] and OVSD [27]. The training and testing splits are not available and the scale of dataset size are quite small (11 for BBC, and 21 for OVSD respectively), in addition, 2 out of 21 videos in OVSD is not available. Consequently, we just directly employ the model trained on MovieNetSSeg without any fine-tune, and take inference on these two datasets. SimCLR(x) corresponds to ShotCoL [4] using different contrastive learning strategies reproduced by [20]. The results demonstrate advanced generalization ability of our methods. It's competitive with shot-level pretraining methods." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 673, + 211, + 685 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 673, + 211, + 685 + ], + "spans": [ + { + "bbox": [ + 47, + 673, + 211, + 685 + ], + "type": "text", + "content": "4.3. Ablation Studies and Analysis" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 689, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 288, + 713 + ], + "type": "text", + "content": "To carry out analysis and evaluate the contribution of each component and setting in our method, we conduct a" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 307, + 110, + 541, + 258 + ], + "blocks": [ + { + "bbox": [ + 304, + 71, + 545, + 106 + ], + "lines": [ + { + "bbox": [ + 304, + 71, + 545, + 106 + ], + "spans": [ + { + "bbox": [ + 304, + 71, + 545, + 106 + ], + "type": "text", + "content": "Table 4: Impact of multimodal semantics, where three elements are studied including visual, place, and audio. † denotes that the results are copied from [23]." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 110, + 541, + 258 + ], + "lines": [ + { + "bbox": [ + 307, + 110, + 541, + 258 + ], + "spans": [ + { + "bbox": [ + 307, + 110, + 541, + 258 + ], + "type": "table", + "html": "
MethodplaceaudiovisualAP (↑)
Grouping [27]†✓✓✓23.8
StoryGraph [33]†✓✓✓33.2
Siamese [1]†✓✓✓34.1
LGSS [23]✓✓✓47.1
Ours✓50.9
Ours✓16.3
Ours✓52.4
Ours✓✓48.4
Ours✓✓53.4
Ours✓✓53.1
Ours✓✓✓54.8
", + "image_path": "59716d9002e413e15786bfc9bd3e7f8f8f522d80630584cef273db2572bddca3.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 267, + 545, + 291 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 267, + 545, + 291 + ], + "spans": [ + { + "bbox": [ + 304, + 267, + 545, + 291 + ], + "type": "text", + "content": "series of ablation studies. All the following comparative experiments are conducted on the MovieNetSSeg dataset." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 293, + 546, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 293, + 546, + 556 + ], + "spans": [ + { + "bbox": [ + 304, + 293, + 546, + 556 + ], + "type": "text", + "content": "Impact of Multimodal Semantics. First of all, we revisit the impact of each modality in Table 4. We utilize the whole pipeline with clip-level shot embedding and multimodal high-order context modeling to make predictions on the testing set. Experiment starts from the model using only one modality features, and gradually adds different modality cues. Observing the second block of Table 4, we get the conclusion that visual modality plays the most important role in video scene detection. It's hard for single audio features to obtain satisfied results. From the third part of Table 4, we learn that both audio and place modalities can give complementary cues to the visual modality, and improves the final results. In particularly, audio improves 2.7 in terms of AP, place improves 3.5 for AP. Combining three modalities can produce the best result, i.e. 54.8 for AP. Compared with previous works in Table 4, our method gets the best results. Because our approach takes a more comprehensive way to fuse the multimodal features and drive them to complement with each other in a unified model. This can prove the hypothesis we presented above, i.e. multimodal content can complement for each other in the task of scene boundary detection." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 547, + 713 + ], + "type": "text", + "content": "Impact of Different Components. We take experiments to validate the effect of different components in our method, including the clip encoder, the high-order encoder and adaptive decoder in our multimodal high-order relation transformer. Specifically, taking the full model as baseline, we remove the clip encoder which is denoted as 'w/o CE'. Removing the high-order relation extractor can verify the effectiveness of modeling high-order context, and we denote it as 'w/o HR', i.e. without high-order relation guidance. And the model without the full high-order encoder in the multimodal high-order relation transformer is denoted as 'w/o CR' for 'without context relation', as it lacks the context relationship modeling. And the model without the" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "22087" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 53, + 99, + 536, + 150 + ], + "blocks": [ + { + "bbox": [ + 46, + 70, + 547, + 95 + ], + "lines": [ + { + "bbox": [ + 46, + 70, + 547, + 95 + ], + "spans": [ + { + "bbox": [ + 46, + 70, + 547, + 95 + ], + "type": "text", + "content": "Table 3: Results on the MovieNetSSeg dataset with different multimodal semantics settings, which demonstrate the effectiveness of our approach under fair conditions." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 53, + 99, + 536, + 150 + ], + "lines": [ + { + "bbox": [ + 53, + 99, + 536, + 150 + ], + "spans": [ + { + "bbox": [ + 53, + 99, + 536, + 150 + ], + "type": "table", + "html": "
MethodLGSS (audio)LGSS (place)LGSS (audio+place)LGSS (audio+place +act+cast)Ours (audio)Ours (place)Ours (audio+place)Ours (audio+place +visual)
AP(↑)17.539.043.447.116.350.948.454.8
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ModalityAP (↑)mIoU (↑)AUC-ROC (↑)F1 (↑)
w/o CE52.348.390.045.5
w/o HR51.150.388.444.4
w/o CR48.645.988.645.2
w/o Cluster54.350.990.346.2
Full Model54.851.290.346.3
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As shown in the first line of Table 5, removing the clip encoder leads to 2.5 drop on AP, and 0.8 on F1. If the model taken out the high-order relation extractor AP drops 3.7. Furthermore, if we remove the high-order encoder, the performance can degrade a lot, i.e. 6.2 on AP, 5.3 on mIoU. This demonstrates that modeling context and high-order relationships among the video shots is of great significance for the video scene detection task. Besides, comparing the last two lines in Table 5 can prove the necessity of clustering shots within the same scene. Lacking the guidance from scene-level representations, the results on AP drops 0.5, and mIoU drops 0.3." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": "Impact of Data Augmentation. Figure 4 demonstrates the impact of different data augmentations. We add shot sequence samples from one video to another video with positive boundary on the central position, to make the model to learn robust scene boundary pattern. If the two videos are from the same video, we call this augmentation method as 'Intra'. Otherwise, as 'Inter'. Hyperparameter ratio controls the rate of newly constructed samples. When the ratio equals zero, we only adopt shot sequence samples by sliding window on every training video without any data augmentation. Having appropriate numerical values for ratio is crucial since setting it too low can prevent the model from" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 169, + 547, + 265 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 169, + 547, + 265 + ], + "spans": [ + { + "bbox": [ + 304, + 169, + 547, + 265 + ], + "type": "text", + "content": "acquiring positive samples, while setting it too high can lead to overfitting. Optimal outcome is obtained with a ratio of 0.3 for 'Intra' augmentation and 0.2 for 'Inter' augmentation. Therefore, we incorporate these two hyperparameters in our complete model. Figure 4 shows that both of 'Intra' and 'Inter' can improve the performance, while 'Intra' is better. The reason may be that 'Intra' helps constructing harder samples." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 266, + 547, + 504 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 266, + 547, + 504 + ], + "spans": [ + { + "bbox": [ + 304, + 266, + 547, + 504 + ], + "type": "text", + "content": "Qualitative Analysis. In this part, we visualize similarity matrixes of 50 consecutive shot representations from multimodal features, which can intuitively prove the importance of multimodal cues in the task of scene boundary detection. Specifically, the models are trained with different multimodal semantic settings, and output multimodal shot features respectively. Then we visualize the matrix of cosine similarity between them. The ground-truth labels of scenes (i.e. shot clusters) are marked by red rectangles. It is obvious in Figure 5, shots are clearly clustered into scenes by multimodal features, i.e. the similarities between the shots before and after the boundaries are quite small. Besides, we can see that audio features can hardly separate the shots into different scenes, and the similarity matrix of place or visual features can roughly cluster the shots into scenes near the ground-truth. For single audio or place features, the similarities around boundaries are smooth, which may lead to confusing boundary detection results. Thus, we believe that audio, place and visual features can complement with each other to achieve better performance." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 507, + 379, + 519 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 507, + 379, + 519 + ], + "spans": [ + { + "bbox": [ + 306, + 507, + 379, + 519 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 521, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 521, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 521, + 547, + 713 + ], + "type": "text", + "content": "In this paper, we propose a unified multimodal framework for video scene boundary detection. And we design a novel Multimodal High-order Relation Transformer, which can model multimodal cues, high-order relation and scene adaptive clustering in a unified structure. We extract multimodal shot representations and model their clip-level context using expert networks and a clip encoder. Then we use a high-order encoder to uncover complex associations among the features and exploit contextual semantics. Then an adaptive decoder in our transformer is proposed to dynamically merge shots in the same scene, which is effective at discovering switch pattern between scenes rather than visual appearance. We have systematically studied the influence of our idea and carried out experiments. The results demonstrate the effectiveness of our model by achieving significant performance." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "22088" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 66, + 76, + 272, + 306 + ], + "blocks": [ + { + "bbox": [ + 66, + 76, + 272, + 306 + ], + "lines": [ + { + "bbox": [ + 66, + 76, + 272, + 306 + ], + "spans": [ + { + "bbox": [ + 66, + 76, + 272, + 306 + ], + "type": "image", + "image_path": "68bcf80734161ab816517186dd22f51f039b33559d79adf5f3de25a8f7a0329f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 320, + 287, + 369 + ], + "lines": [ + { + "bbox": [ + 46, + 320, + 287, + 369 + ], + "spans": [ + { + "bbox": [ + 46, + 320, + 287, + 369 + ], + "type": "text", + "content": "Figure 5: Visualization of similarity matrixes between shot representations in randomly sampled 50 consecutive shots. The ground-truth labels of scenes (shot clusters) are marked by red rectangles." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 378, + 151, + 392 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 378, + 151, + 392 + ], + "spans": [ + { + "bbox": [ + 47, + 378, + 151, + 392 + ], + "type": "text", + "content": "6. Acknowledgment" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 398, + 287, + 446 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 398, + 287, + 446 + ], + "spans": [ + { + "bbox": [ + 46, + 398, + 287, + 446 + ], + "type": "text", + "content": "This work was partially supported by National Nature Science Foundation of China (Grant 62022078, 62121002) and National Defense Basic Scientific Research Program (2021601B013)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 457, + 105, + 469 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 457, + 105, + 469 + ], + "spans": [ + { + "bbox": [ + 47, + 457, + 105, + 469 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 52, + 478, + 287, + 713 + ], + "type": "list", + "angle": 0, + "index": 10, + "blocks": [ + { + "bbox": [ + 52, + 478, + 287, + 521 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 478, + 287, + 521 + ], + "spans": [ + { + "bbox": [ + 52, + 478, + 287, + 521 + ], + "type": "text", + "content": "[1] Lorenzo Baraldi, Costantino Grana, and Rita Cucchiara. 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Leading OCC techniques constrain the latent representations of normal1 motions to limited volumes and detect as abnormal anything outside, which accounts satisfactorily for the openset'ness of anomalies. But normalcy shares the same openset'ness property since humans can perform the same action in several ways, which the leading techniques neglect.", + "bbox": [ + 75, + 377, + 468, + 513 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "We propose a novel generative model for video anomaly detection (VAD), which assumes that both normality and abnormality are multimodal. We consider skeletal representations and leverage state-of-the-art diffusion probabilistic models to generate multimodal future human poses. We contribute a novel conditioning on the past motion of people and exploit the improved mode coverage capabilities of diffusion processes to generate different-but-plausible future motions. Upon the statistical aggregation of future modes, an anomaly is detected when the generated set of motions is not pertinent to the actual future. We validate our model on 4 established benchmarks: UBnormal, HR-UBnormal, HR-STC, and HR-Avenue, with extensive experiments surpassing state-of-the-art results.", + "bbox": [ + 75, + 513, + 470, + 724 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 756, + 209, + 772 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Video Anomaly Detection (VAD) is a crucial task in computer vision and security applications. It enables early detection of unusual or abnormal events in videos, such as accidents, illnesses, or people's behavior which may threaten public safety [41]. However, several aspects make VAD a challenging task. Firstly, the definition of anomaly", + "bbox": [ + 75, + 782, + 468, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/9fc03492ac8e2f9a9a62d7c9619413480442f22f4a2046703b79ee9770b59c05.jpg", + "image_caption": [ + "Figure 1: MoCoDAD detects anomalies by synthesizing and statistically aggregating multi-modal future motions, conditioned on past poses (frames on the left). Red (top) and green (bottom) distributions represent examples of anomaly and normality generations (2d mapped via t-SNE). Within the distribution modes (dashed-contoured), the red dots are the actual true futures corresponding to the conditioning past frames. In the case of normality, the true future lies within a main distribution mode, and the generated predictions are pertinent. In the case of abnormality, the true future lies in the tail of the distribution modes, which yields poorer predictions, highlighting anomalies." + ], + "image_footnote": [], + "bbox": [ + 500, + 340, + 893, + 592 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "is highly subjective and varies depending on the context and application, making it difficult to define it universally. Secondly, anomalies are intrinsically rare. To account for data scarcity, models generally learn from regular samples only (also known as One Class Classification - OCC) or have to", + "bbox": [ + 496, + 824, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Authors contributed equally.", + "bbox": [ + 94, + 886, + 254, + 901 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "10318", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "cope with the data imbalance. Thirdly, anomaly detection is intrinsically an openset problem, and modeling anomalies needs to account for diversity beyond the training set.", + "bbox": [ + 75, + 90, + 468, + 136 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "An \"ideal\" model for anomaly detection should consider that there are infinitely many anomalous and non-anomalous ways of performing an action. Current state-of-the-art OCC techniques [9, 24, 25, 26] fail to address this issue. Indeed, they focus on learning either a single reconstruction or prediction of the input, or deriving a latent representation of normal actions, thereby constraining them to a limited latent volume. This last approach successfully accounts for the openset'ness of anomalies, i.e., anything mapped outside the normality region is considered abnormal. However, forcing normality into constrained volumes may not work for diverse-but-still-normal behaviors, i.e., OCC misclassifies as anomalous those not fitting in the volume.", + "bbox": [ + 75, + 136, + 468, + 345 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We propose Motion Conditioned Diffusion Anomaly Detection - hereafter MoCoDAD - a novel generative model for VAD, which assumes that both normality and abnormality are multimodal2. Given a motion sequence, be it normal or anomalous, the sequence is split and the later (future) frames are corrupted to become random noise. Conditioned on the first (past) clean input frames, MoCoDAD synthesizes multimodal reconstructions of the corrupted frames. MoCoDAD discerns normality from anomaly by comparing the multimodal distributions. In the case of normality, the generated motions are diverse but pertinent, i.e. they are biased towards the true uncorrupted frames. In the case of abnormality, the synthesized motion is also diverse, but it lacks pertinence, as shown in Fig. 1 and discussed in Sec. 5.", + "bbox": [ + 75, + 347, + 470, + 559 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "MoCoDAD is the first diffusion-based technique for video anomaly detection. We are inspired by Denoising Diffusion Probabilistic Models (DDPMs) [40, 14], state-of-the-art, among others, in image synthesis [31, 30, 33], motion synthesis [43, 49], and 3D generation tasks [53]. DDPMs are selected for their improved mode coverage [48], i.e. they generate diverse multimodal motions, which MoCoDAD statistically aggregates (see the respective ablative study in Sec. 5).", + "bbox": [ + 75, + 559, + 468, + 694 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Besides multimodality, a crucial aspect of MoCoDAD is the choice of the conditioning strategy to guide the synthesis. We consider human motion as skeletal representations and propose corrupting the body joint coordinates at each frame by displacing them with random translations. Conditioning refers to the process that provides the model with the uncorrupted first part of the motion sequence (past) to guide the denoising of the corrupted second part (future). In this study, we compare three modeling choices to find the most", + "bbox": [ + 75, + 695, + 468, + 830 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "1To avoid ambiguity, in this work, the term \"normal\" is the contrary of anomalous, not the synonym of \"Gaussian\". Normal refers to \"normality\" (or \"normalcy\"). Anomalous/abnormal refers to abnormality/anomaly.", + "bbox": [ + 75, + 838, + 468, + 875 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2In this work, multimodal refers to distributions with multiple modes, not to mixing modalities (video, audio, text, etc.)", + "bbox": [ + 75, + 875, + 468, + 898 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "suitable conditioning strategy. We experiment with (1) directly feeding the denoising module with the concatenation of the uncorrupted poses with the displaced sequence [35]. For the other two strategies, we get a latent representation of the input (via (2) an encoding module and (3) an autoencoder) and feed the network with this learned representation (cf. Sec. 3.2). The third strategy works best (cf. Sec. 5.3).", + "bbox": [ + 496, + 90, + 890, + 196 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We evaluate MoCoDAD on three challenging benchmarks of human-related anomalies, namely, HR-UBnormal [1, 9], HR-ShanghaiTech Campus [23, 26] (HR-STC), and HR-Avenue [22, 26], and on the most recent VAD dataset UBnormal [1]. MoCoDAD achieves state-of-the-art (SoA) performance on all four datasets, which demonstrates the effectiveness of modeling multimodality for normal and abnormal motions. Notably, by not using appearance, MoCoDAD benefits increased privacy protection (no visual facial nor body features) and better computational efficiency, thanks to the lightweight body kinematic representations. We summarize our contributions as follows:", + "bbox": [ + 496, + 196, + 892, + 391 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- A novel generative VAD model based on comparing the multimodality of normal and abnormal motion generations;", + "- The first probabilistic diffusion-based approach for VAD, which fully exploits the enhanced modecoverage capabilities of diffusive probabilistic models;", + "- A novel motion-based conditioning on the clean input sequence to steer the synthesis towards diverse pertinent motion in the case of normality;", + "A thorough validation on UBnormal, HR-UBnormal, HR-STC, and HR-Avenue benchmarks where we outperform the SoA by $5.1\\%$ , $4.4\\%$ , $5\\%$ , $8\\%$ , respectively." + ], + "bbox": [ + 517, + 393, + 890, + 588 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 602, + 640, + 617 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Previous work relates to ours from two main perspectives: Video Anomaly Detection methods (see Sec. 2.1), and diffusion models for motion synthesis (see Sec. 2.2).", + "bbox": [ + 496, + 627, + 890, + 672 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Video Anomaly Detection Techniques", + "text_level": 1, + "bbox": [ + 498, + 681, + 823, + 696 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Pioneer works analyze the trajectory of the agents in the frames to discriminate those distant from normality [5, 16, 19]. Within recent literature, two major trends can be identified: latent- and reconstruction-based methods. VAD techniques also vary based on the type of input data they use, such as videos or human skeletal pose motions. MoCoDAD, as all the VAD works presented in this section, adheres to the OCC protocol, which simulates the scarcity of anomalies in real-world scenarios [18].", + "bbox": [ + 496, + 704, + 890, + 839 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Latent-based VAD methods identify abnormality according to a score extracted from a learned latent space whereby normality is supposedly mapped into a constrained volume, and anomalies are those latents lying outside, with a larger", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "10319", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "score (see [34, 38, 42, 46] for an overview of latent-based AD). Sabokrou et al. [36] propose a two-staged cascade of deep neural networks. First, they employ a stack of autoencoders that detects points of interest (POIs) while excluding irrelevant patches (e.g., background). Second, they identify anomalies by densely extracting and modeling discriminative patches at POIs. Notice that this work constrains normality to belong to a single mode and anomalies outside, thus, addressing the openset'ness of anomalies, but it hampers the multimodal and diversity [51] aspect of normal motions. Contrarily, our work considers the multimodality of normal and abnormal motions.", + "bbox": [ + 75, + 90, + 472, + 272 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Notably, Nguyen et al. [27] propose an image-based technique exploring multimodal anomaly detection via multi-headed VAEs. However, considering a fixed number of modes for reality amends multimodality only partially, as it misses to unleash its openset'ness. Differently, we adopt diffusion models for their improved mode coverage and generate multiple futures, not being constrained on a fixed number of heads (see Sec. 5).", + "bbox": [ + 75, + 275, + 472, + 397 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Reconstruction-based VAD methods consider the original metric space of the input and leverage reconstruction as the proxy task to derive an anomaly score. These models are trained to encode and reconstruct the input from normal events, producing larger errors on anomalies not seen during training. [7, 13, 52] use sequences of frames and feed them to convolutional autoencoders. Gong et al. [12] \"memorize\" the most representative normal poses to discriminate new input samples. Liu et al. [21] tackle intensity and gradient loss, optical flow, and adversarial training. Luo et al. [23] use stacked RNNs with temporally-coherent sparse coding enforcing similar neighboring frames to be encoded with similar reconstruction coefficients. Barbalau et al. [3] builds upon [10] and integrates the reconstruction of the input frames, via multi-headed attention, into a multitask learning framework. Besides [10, 21], all works rely on a single reconstruction proxy task via non-variational architectures that learn discrete manifolds. However, normality and abnormality are multimodal and diverse, making it hard for these techniques to have an exact match (reconstruction) over the GT. Additionally, GANs used in [21] suffer from mode collapse [44] lacking to represent the multimodality of reality. Similarly to [27], [3] can represent only a fixed number of modalities, which does represent the openset'ness of reality. MoCoDAD is a reconstruction-based approach and leverages diffusion processes [8] to account for the openset'ness of normalcy and anomalies in terms of pertinence to the GT.", + "bbox": [ + 75, + 398, + 472, + 821 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Skeleton-based VAD methods exploit compact spatiotemporal skeletal representations of human motion instead of raw video frames. Morais et al. [26] use two GRU autoencoder branches to account for the global and local decomposition of the skeleton in a particular frame. Luo et", + "bbox": [ + 75, + 824, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "al. [24] exploit stacked layers of ST-GCN [50] to accumulate joint information over the spatio-temporal dimensions of the frame and predict joints in the future. However, [50] uses a fixed adjacency matrix, depicting joint connections, for all ST-GCN layers, which hinders the exploration of intra-frame and intra-joint relationships, two factors that play a crucial role in improving the encoding of spatio-temporal features [39]. Markovitz et al. [25] utilize the encoder of an ST-GCN autoencoder to embed spacetime skeletons into a latent vector. This vector is then fed to an end-to-end trainable deep-embedded clustering procedure which produces $k$ clusters representing the multimodality of normalcy and anomalies. Flaborea et al. [9] propose COSKAD and force the normal instances into the same latent region driving the distances to a common center. MoCoDAD is also a skeleton-based approach that mitigates the choice of $k$ a priori to cover the multimodality of reality.", + "bbox": [ + 496, + 90, + 893, + 349 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Diffusion Models", + "text_level": 1, + "bbox": [ + 500, + 359, + 668, + 376 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Diffusion models have marked a revolution in generative tasks such as image and video synthesis [35, 43, 49], but they have not been employed for VAD. Saadatnejad et al. [35] propose a two-step framework based on temporal cascaded diffusion (TCD). First, they denoise imperfect observation sequences and, then, improve the predictions of the (frozen) model on repaired frames. Tevet et al. [43] use a transformer encoder to learn arbitrary length motions [2, 29] coherent with a particular conditioning signal $c$ . They experiment with constrained synthesis where $c$ is a text prompt (i.e., text-to-motion) or a specific action class (i.e., action-to-motion) and unconstrained synthesis where $c$ is not specified. Chen et al. [49] design a transformer-based VAE [29] to learn a representative latent space for human motion sequences. They apply a diffusion model in this latent space to generate vivid motion sequences while obeying specific conditions similar to [43]. Differently, MoCoDAD is a diffusion-based model that uses conditioning over a portion of the input (e.g., previous frames condition the generation of future ones).", + "bbox": [ + 496, + 385, + 893, + 686 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Wyatt et al. [47] propose AnoDDPM, a diffusion model on images, which does not require the entire Markov chain (noise/denoise) to take place. They use decaying octaves of simplex noising functions to distinguish the corruption rate of low-frequency components from high-frequency ones. However, they add and remove noise without conditioning, identifying anomalies when noise removal diverges from the input. Differently, MoCoDAD is based on generating and comparing multimodal motions against the GT in terms of pertinence. Our proposed model is the first to exploit the multimodal generative and improved mode-coverage capabilities of diffusive techniques, via forecasting tasks, further to being first in adopting them for detecting video anomalies. Hence, to transfer DDPMs from video-based", + "bbox": [ + 496, + 688, + 895, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "10320", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Anomaly Detection to skeleton-based VAD we rely on a U-Net-shaped stack of STS-GCN [39, 37] layers, which includes the spatio-temporal aspects of joints in sequences of human poses.", + "bbox": [ + 75, + 90, + 472, + 151 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3. Methodology", + "text_level": 1, + "bbox": [ + 76, + 165, + 212, + 181 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "MoCoDAD learns to reconstruct the later (future) corrupted poses by conditioning on the first (past) poses. Sec. 3.1 describes the training diffusion denoising process, how it generates multimodal reconstructions, and statistically aggregates them at inference to detect anomalies. Sec. 3.2 details conditioning on past frames, and Sec. 3.3 describes the architecture of MoCoDAD. For the sake of completeness, in Sec. A.1 of the Supplementary, we present preliminary concepts of DDPMs.", + "bbox": [ + 75, + 190, + 472, + 327 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1. Diffusion on Trajectories", + "text_level": 1, + "bbox": [ + 76, + 335, + 305, + 351 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Training We define a diffusion technique that learns to reconstruct corrupted future motion sequences conditioned on clean past ones.", + "bbox": [ + 75, + 358, + 468, + 402 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Let $X_{a} = \\{x_{a}^{1},\\ldots ,x_{a}^{N}\\}$ be a sequence of $N$ timecontiguous poses belonging to a single actor $a$ . Since our model considers one actor at a time, we use $X = \\{x^{1},\\dots,x^{N}\\}$ for notation simplicity. Each pose $x^{i}$ can be seen as a graph $x^{i} = (J,A)$ where $J$ represents the set of joints, and $A$ is the adjacency matrix representing the joint connections. Notice that each joint is attributed with a set of spatial coordinates in $\\mathbb{R}^C$ , hence $x^{i}\\in \\mathbb{R}^{|J|\\times C}$ , and $X\\in \\mathbb{R}^{N\\times |J|\\times C}$ . Here, we use $C = 2$ as the person's pose is extracted from images at each frame.", + "bbox": [ + 75, + 402, + 468, + 554 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We divide $X$ into two parts: the past $X^{1:k}$ and the future sequence of poses $X^{k+1:N}$ with $k \\in \\{1, \\dots, N\\}$ .", + "bbox": [ + 75, + 554, + 468, + 585 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "During the forward process $q$ , we corrupt the coordinates of the joints by adding random translation noise. We sample a random displacement map $\\varepsilon^{k + 1:N} \\in \\mathbb{R}^{(N - k) \\times |J| \\times C}$ from a distribution $\\mathcal{N}(0, \\mathbf{I})$ and add it to $X^{k + 1:N}$ to randomly translate the position of its nodes.", + "bbox": [ + 75, + 585, + 468, + 660 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The magnitude of the added displacement depends on a variance scheduler $\\beta_{t} \\in (0,1)$ and a diffusion timestep $t \\sim \\mathcal{U}_{[1,T]}$ . As a result, $q$ increasingly corrupts the joints $x^{i}$ at each diffusion timestep $t$ (i.e., $x_{t=1}^{i} \\to \\dots \\to x_{t=T}^{i}$ ) making $x_{t=T}^{i}$ indistinguishable from a pose with randomly sampled joints' spatial coordinates.", + "bbox": [ + 75, + 660, + 468, + 751 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "The reverse process $p_{\\theta}$ unrolls the corruption, estimating the spatial displacement map $\\varepsilon^{k + 1:N}$ via a U-Net-like architecture $\\varepsilon_{\\theta}$ (see Sec. 3.3 for more details). To achieve an approximation of $\\varepsilon^{k + 1:N}$ , we train the network conditioned on the diffusion timestep $t$ (embedded through an MLP $\\tau_{\\theta}$ ) and the embedding $h$ of the previous trajectory $X^{1:k}$ .", + "bbox": [ + 75, + 751, + 468, + 843 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "In Eq. 1, similarly to [33], we define the displacement estimation objective4.", + "bbox": [ + 500, + 90, + 893, + 121 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {d i s p}} = \\mathbb {E} _ {t, X, \\varepsilon} \\left[ \\left| \\left| \\varepsilon - \\varepsilon_ {\\theta} \\left(X _ {t}, t, h\\right) \\right| \\right| \\right] \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 570, + 131, + 890, + 165 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Inspired by [11], we smooth $\\mathcal{L}_{disp}$ as follows:", + "bbox": [ + 500, + 170, + 805, + 186 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {s m o o t h}} = \\left\\{ \\begin{array}{l l} 0. 5 \\cdot \\left(\\mathcal {L} _ {\\text {d i s p}}\\right) ^ {2} & \\text {i f} \\left| \\mathcal {L} _ {\\text {d i s p}} \\right| < 1 \\\\ \\left| \\mathcal {L} _ {\\text {d i s p}} \\right| - 0. 5 & \\text {o t h e r w i s e} \\end{array} \\right. \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 547, + 196, + 890, + 239 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Inference At inference time, MoCoDAD generates multimodal future sequences of poses from random displacement maps, conditioned on the past frames, then aggregates them statistically to detect anomalies.", + "bbox": [ + 498, + 253, + 893, + 314 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We sample a random displacement $z \\sim \\mathcal{N}(0, \\mathbf{I})$ and consider it the starting point of the synthesis process that generates a future human motion via Eq. 3.", + "bbox": [ + 498, + 314, + 893, + 359 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nX _ {t - 1} = \\frac {1}{\\sqrt {\\alpha_ {t}}} \\left(X _ {t} - \\frac {1 - \\alpha_ {t}}{\\sqrt {1 - \\alpha_ {t}}} \\varepsilon_ {\\theta} \\left(X _ {t}, t, h\\right)\\right) + z \\sqrt {\\beta_ {t}} \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 506, + 369, + 890, + 405 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Note the motion conditioning $h$ , encoding the past $k$ frames. We generate $m$ diverse future pose trajectories $Z_{1},\\ldots ,Z_{m}$ . For each $Z_{i}$ , we compute the reconstruction error via the smoothed loss $s_i = \\mathcal{L}_{smooth}(|X - Z_i|)$ used in training (cf. Eq. 2).", + "bbox": [ + 498, + 415, + 890, + 489 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We aggregate all the scores from the generations $S = \\{s_1, \\ldots, s_m\\}$ to distill a single anomaly score for that sequence. This score is subsequently assigned to the corresponding frames to assess their level of anomaly. In scenarios where multiple actors occupy the same frames, we assign the average anomaly score to those frames. See the Supplementary for a detailed description. We explore different strategies for distilling the anomaly score from $S$ : (1) the diversity between the normal and anomalous generations and (2) aggregation statistics. To account for diversity, we consider the diversity metric $rF = \\mathrm{mean}(\\mathcal{L}_{smooth}) / \\min (\\mathcal{L}_{smooth})$ introduced by [6, 28]. Diversity stems from testing whether anomalous generations are more diverse than normals, but the diversity score fails to detect anomalies, nearly dropping to random chance. We explain this by normalcy and anomaly having a similar degree of diversity, as we experimentally validate in Sec. 5.1.", + "bbox": [ + 498, + 489, + 892, + 747 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We consider as aggregation statistics the mean, quantile robust statistics including the median, as well as maximum and minimum selectors, in terms of $\\mathcal{L}_{smooth}$ distances between the $m$ generated and the GT future motion. Our analysis highlights that the minimum distance is the best on average. This reinforces the original hypothesis that normality-conditioned generated motions are as diverse as abnormal-conditioned ones but more biased to the actual", + "bbox": [ + 496, + 747, + 893, + 867 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "4For readability purposes, for what follows, we omit the superscript $k + 1:N$ , and assume that we are considering only future motion.", + "bbox": [ + 500, + 875, + 893, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "3In this paper, a displacement map is equivalent to the addition of noise (corruption) to the input, e.g., in [14]. We use this term to emphasize that we move the joints away from their original spatial position. We invite the reader to consider displacing and corrupting as interchangeable here.", + "bbox": [ + 75, + 849, + 468, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "10321", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/67f5d381ca28fc7f2fc1cd2e74788e7f92736d4485e6c7af37128b48eb306901.jpg", + "image_caption": [ + "Figure 2: Overview of the proposed MoCoDAD. A sequence of $N$ skeletal motions ( $N = 6$ in the example) is split into past (top-right $X^{1:k}$ frames, $k = 3$ in the example) and future (top-left $X^{k+1:N}$ frames). During training, the Forward Diffusion block adds noise to the future frames, shifting each joint by a random vector displacement of varying intensity (increasing with the diffusion timestep $t$ ). Then the Reverse Diffusion learns to estimate the noise. A key aspect of MoCoDAD is the conditioning, i.e. how to encode the past clean $k$ frames and guide the synthesis of relevant futures." + ], + "image_footnote": [], + "bbox": [ + 163, + 88, + 810, + 333 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/796f0fb32210b3e8c34b860574485e54b3b67c412ecf16027e2099c95d316b94.jpg", + "image_caption": [ + "Figure 3: Comparison of the three conditioning strategies." + ], + "image_footnote": [], + "bbox": [ + 81, + 454, + 472, + 583 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "motion, thus more likely to generate samples close to it. See Sec. 5.2 for the experimental evaluation.", + "bbox": [ + 75, + 636, + 468, + 667 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2. Motion Conditioning for multimodal Pose Forecasting", + "text_level": 1, + "bbox": [ + 76, + 678, + 468, + 710 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The choice of the conditioning strategy is a crucial factor for diffusion models, as it determines how the conditioning information is fed into the network, and it directly affects the quality of the outputs. In this work, we propose a thorough examination of different strategies for feeding the diffusion models with the conditioning information.", + "bbox": [ + 75, + 718, + 468, + 808 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We identify three different modeling choices for conditioning the diffusion, illustrated in Fig. 3, i.e., input concatenation, $E2E$ -embedding, and $AE$ -embedding. Input concatenation refers to conditioning with a portion of the raw input motion. Here, we keep the past sequence of poses $X^{1:k}$ (the conditioning signal) uncorrupted and pretend it", + "bbox": [ + 75, + 810, + 470, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "to the corrupted future sequence $X_{t}^{k + 1:N}$ . Input concatenation has been explored in previous work for pose forecasting reaching SoA performances in [35].", + "bbox": [ + 496, + 458, + 890, + 503 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Both embedding choices refer to passing the conditioning past frames through an encoder $E$ , then providing them to all latent layers of the denoising model (cf. incoming vertical arrows into the orange layers in Fig. 2). Here, $E$ is a GCN [39] and it encodes sequences of poses $X^{1:k}$ into the representation $h = E(X^{1:k})$ . In the case of $E2E$ -embedding, $E$ is jointly learned with the rest of the architecture, leveraging the training $\\mathcal{L}_{\\text{smooth}}$ loss. The $AE$ -embedding adds an auxiliary reconstruction loss $\\mathcal{L}_{\\text{rec}}$ to support training $E$ , as it tasks a decoding network $D$ to reconstruct the conditioning past frames according to the following loss function:", + "bbox": [ + 496, + 505, + 892, + 686 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {r e c} = \\left| \\left| D (E (X ^ {1: k})) - X ^ {1: k} \\right| \\right| _ {2} ^ {2} \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 581, + 702, + 890, + 739 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "In the case of $AE$ -embedding, the auxiliary is summed to the main loss, resulting in the following total loss:", + "bbox": [ + 498, + 750, + 890, + 779 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {t o t} = \\lambda_ {1} \\mathcal {L} _ {\\text {s m o o t h}} + \\lambda_ {2} \\mathcal {L} _ {\\text {r e c}} \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 598, + 794, + 890, + 811 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\lambda_1, \\lambda_2 \\in [0, 1]$ account for the contribution of each loss function respectively. Lastly, since DDPMs benefit from being conditioned on the timestep $t$ , we add the embedding $\\tau_{\\theta}(t)$ to the latent $h$ and feed the resulting motion-temporal signal to each layer of our network $\\varepsilon_{\\theta}$ [43].", + "bbox": [ + 496, + 824, + 890, + 901 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "10322", + "bbox": [ + 480, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/9317dc120249e6cbab6e80801879f614fb54c9eb2103feb4c9ca064bb46ad7a0.jpg", + "table_caption": [ + "Table 1: Comparison of MoCoDAD against SoA in terms of AUC on the three Human-Related datasets (i.e., HR-STC, HR-Avenue and HR-UBnormal) and UBnormal. OCC skeleton-based techniques are marked with a $*$ ." + ], + "table_footnote": [], + "table_body": "
HR-STCHR-AvenueHR-UBnormalUBnormal
Conv-AE [13]CVPR '1669.884.8--
Pred [21]CVPR '1872.786.2--
MPED-RNN [26] *CVPR '1975.486.361.260.6
GEPC [25] *CVPR '2074.858.155.253.4
Multi-timescale Prediction [32] *WACV '2077.088.3--
Normal Graph [24]Neurocomputing '2176.587.3--
PoseCVAE [15] *ICPR '2175.787.8--
BiPOCO [17] *Arxiv '2274.987.052.350.7
STGCAE-LSTM [20] *Neurocomputing '2277.286.3--
SSMTL++ [3]CVIU '23---62.1
COSKAD [9] *Arxiv '2377.187.865.565.0
MoCoDAD *77.689.068.468.3
", + "bbox": [ + 119, + 130, + 846, + 330 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "The results of evaluation are discussed in Sec. 5.3, whereby applying an AE-embedding conditioning on $X^{1:k}$ emerges with results beyond the SoA.", + "bbox": [ + 76, + 356, + 468, + 402 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "3.3. Architecture Description", + "text_level": 1, + "bbox": [ + 76, + 436, + 303, + 453 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Fig. 2 illustrates the architecture of MoCoDAD. We distinguish two main blocks: a conditioning auto-encoder for the past motion, $X^{1:k}$ , and a denoising model for $X^{k+1:N}$ . The main diffusion model architecture is the neural network, represented with orange blocks, tasked with estimating the corrupting noise in the input motion, thus reconstructing the actual future motion. As done in [47], we rely on a U-Net like architecture. Our skeletal-motion diffusion network progressively contracts and then expands (rebuilds) the spatial dimension of the input sequence of poses. To account for the temporal dimension of the input sequences, we build the U-Net with space-time separable GCN (STSGCN) layers proposed in [39]. The conditioning autoencoder relies on STS-GCN to reconstruct the past motion and embed it into a latent space used to condition the diffusion.", + "bbox": [ + 75, + 468, + 468, + 696 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In detail, the U-Net takes in input $X^{k + 1:N}$ and a motion-temporal conditioning signal $h + \\tau_{\\theta}(t)$ which provides the network with the diffusion timestep and the encoded past-motion information. Furthermore, to align the dimensionality of this conditioning signal with that of the network's layers, the former is fed into an embedding layer projecting it to the correct vector space. This embedded conditioning signal is then fed to each STS-GCN layer. The contracting process of the U-Net progressively aggregates the joints of the poses (i.e., $\\mathbb{R}^J \\to \\mathbb{R}^d$ s.t. $d \\leq J$ ) while the expansion part \"deconvolutes\" the joints' vector space until it reaches the original space $\\mathbb{R}^J$ . Residual connections are present between specular layers.", + "bbox": [ + 75, + 703, + 470, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiments", + "text_level": 1, + "bbox": [ + 500, + 354, + 633, + 372 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Here we compare MoCoDAD with SoA approaches and provide a detailed discussion on the achieved performances. In Sec. D of the Supplementary, we provide the reader with a thorough description of the implementation details.", + "bbox": [ + 498, + 380, + 890, + 439 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "As done in [1, 3, 9, 10, 21, 24, 25, 26], we report the Receiver Operating Characteristic Area Under the Curve (ROC-AUC) to assess the quality of MoCoDAD predictions on UBnormal [1], and the HR filtered [9] versions of STC [23], Avenue [22], and UBnormal.", + "bbox": [ + 498, + 441, + 890, + 516 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Datasets", + "text_level": 1, + "bbox": [ + 500, + 526, + 602, + 541 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We use the UBnormal dataset [1] which contains 29 scenes synthesized from 2D natural images with the Cinema4D software. Each scene appears in 19 clips featuring both normal and abnormal events. The split into train, validation, and test adheres to the open-set policy, providing disjoint sets of types of anomalies for training, validation, and test; in accordance with the OCC setting, we only include normal actions for the training set. We also consider the processed poses and the human-related (HR) filtering of the dataset proposed by [9]. To compare with other state-of-the-art methods, we also experiment on the HR versions of the ShanghaiTech Campus (STC) [23] and the CUHK Avenue [22] datasets introduced by [26]. The former includes 13 scenes recorded with different cameras, for a total of about 300,000 frames, and 101 testing clips with 130 anomalous events. The latter consists of 16 training videos and 21 testing videos with a total of 47 anomalous events.", + "bbox": [ + 496, + 549, + 890, + 806 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison with state-of-the-art", + "text_level": 1, + "bbox": [ + 500, + 816, + 790, + 832 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Leading OCC techniques. We compare against SoA OCC techniques. Among these, MPED-RNN [26] combines the reconstruction and prediction errors of a two-branches-RNN to spot anomalies. Normal Graph [24] uses spatial", + "bbox": [ + 498, + 839, + 890, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "10323", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/48e792fb694210239e75ca27dff76f8ba4e352c4ba145b9400ab4779d8771d15.jpg", + "table_caption": [ + "Table 2: Comparison of MoCoDAD against supervised (†) and weakly supervised (‡) methods introduced in [1] in terms of AUC on the UBnormal dataset." + ], + "table_footnote": [], + "table_body": "
ParamsUBnormal
Sultani et al. [41] †-50.3
AED-SSMTL [10] †>80M61.3
TimeSformer [4] †121M68.5
AED-SSMTL [10] ‡>80M59.3
MoCoDAD142K68.3
", + "bbox": [ + 135, + 145, + 405, + 241 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "temporal GCNs (ST-GCN) to encode skeletal sequences. GEPC [25] encodes the input sequences with an STGCN, and clusters the embeddings in the latent space. Multi-timescale Prediction [32] encodes the observed input sequence and predicts future poses at different time scales through intermediate fully-connected layers. Both PoseCVAE [15] and BiPOCO [17] exploit a Conditioned Variational-Autoencoder to learn a posterior distribution of normal actions and use encoded past and future sequences to reconstruct the future one. The former uses an MLP-based architecture, while the latter is GRU-based. STGCAE-LSTM [20] reconstructs the past pose sequence and predicts the future one by an LSTM-based autoencoder. SSMTL++ [3] extends [10]; it replaces the convolutions with a transformer, changes the object detection backbone, and adds a few auxiliary proxy tasks. COSKAD [9] builds on STS-GCN to map the embeddings of normal poses into a narrow region in the latent space.", + "bbox": [ + 73, + 262, + 468, + 532 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results. In Table 1, we compare MoCoDAD and SoA methods on the three HR datasets and on UBnormal. MoCoDAD achieves the best AUC score of 77.6, 89.0, and 68.4 on HR-STC, HR-Avenue, and HR-UBnormal, respectively. Our proposed method outperforms the current best [9], up to $4.4\\%$ , demonstrating the importance of considering a range of different possible futures for each sample. Additionally, MoCoDAD achieves an AUC of 68.3 on the full UBnormal dataset, surpassing COSKAD by $5.1\\%$ . This can be due to the improved sensitivity that emerges from our proposed model: considering more than a single deterministic future smooths the prediction of MoCoDAD avoiding penalizing excessively hard-still-normal samples which would be considered anomalous based on the reconstruction error of a deterministic model.", + "bbox": [ + 73, + 536, + 468, + 762 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results VS. Supervised and Weakly Supervised methods Table 2 evaluates MoCoDAD with supervised and weakly supervised methods reported in [1]. Notice that, despite the absence of supervision or visual information, MoCoDAD is competitive with methods exploiting a stronger form of supervision. In detail, MoCoDAD (68.3) outperforms the weakly supervised method [10] (59.3) and other fully supervised methods and is competitive with [4] (68.5). Further, our approach only presents a fraction of the parameters of", + "bbox": [ + 75, + 763, + 470, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "its competitors. Notably, MoCoDAD is $\\sim 852\\times$ smaller than the current best [4].", + "bbox": [ + 498, + 90, + 890, + 121 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5. Discussion", + "text_level": 1, + "bbox": [ + 500, + 137, + 612, + 152 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Here, we delve into a detailed discussion about the multimodal future generations (cf Sec. 5.1), the influence of the statistical aggregation of multiple generations and the normal Vs. anomalous conditioning (cf. Sec. 5.2), the effect of different conditioning strategies (cf. Sec. 3.2). Additionally, we discuss forecasting proxy tasks (Sec. 5.4) and analyze MoCoDAD's performances with the diffusion process applied to the latent space. (Sec. 5.5).", + "bbox": [ + 496, + 162, + 890, + 285 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.1. Multimodality", + "text_level": 1, + "bbox": [ + 500, + 295, + 648, + 311 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We question whether MoCoDAD can generate diverse multimodal motions and whether conditioning on normal or abnormal motions affects diversity. We provide an example of generated future motions in Fig. 5 (left), where we project the samples in 2D with t-SNE [45] for better visualization. Notice that both sets of generations have similar variance, showing that MoCoDAD produces diverse samples with both normal and abnormal conditioning sequences. Motions stemming from normal conditioning are biased toward the true future since they are mapped around it. Whereas, in the case of abnormal conditioning, the ground truth motion lies on the edge of the predictions' region, hence being correctly predicted with a lower chance.", + "bbox": [ + 496, + 320, + 890, + 517 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We also measure diversity, employing the $rF$ diversity metric from literature [6, 28]. We visualize the $rF$ trend when increasing the number of generations in Fig. 5 (right). If the generated motion had no diversity, e.g., when generating only once, the $rF$ would be equal to 1. Rather, the diversity ratio monotonically increases with the number of generations for both normal and abnormal cases, i.e., the more generated samples, the larger the empirical mode coverage and the diversity. We note that, following intuition, the diversity for abnormal cases grows slightly larger than for normal cases, but the $rF$ measures remain comparable.", + "bbox": [ + 496, + 517, + 890, + 684 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Statistical aggregations of generated motions", + "text_level": 1, + "bbox": [ + 500, + 695, + 879, + 710 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We evaluate the anomaly detection performance when varying the number of generations $m$ and the aggregation strategy for the anomaly score $S$ (cf. Sec. 3.1). Fig. 4 (right) shows that the AUC positively correlates with the number of generated future motions for quantiles $Q < 0.5$ , while the correlation is negative for the mean estimate and $Q > 0.5$ . Such correlation can be better understood by looking at Fig. 4 (left), which depicts the average reconstruction error probability density function (PDF) for $m = 50$ : when conditioned on normal past motions, MoCoDAD produces generations which are centered around the true future and, thus, is more likely to yield lower error scores than when", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "10324", + "bbox": [ + 480, + 944, + 519, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/24c7754b04072608620527b568febf73daa222135851859bfa85f7374c89a7b0.jpg", + "image_caption": [ + "Figure 4: (left) Histograms of the reconstruction errors for 50 synthesized future motions, computed on the HR-UBnormal test set, for the case of conditioning on normal and abnormal past motions. (right) Correlation between the AUC scores and the number of generations, with each curve corresponding to a different aggregation statistic." + ], + "image_footnote": [], + "bbox": [ + 155, + 104, + 421, + 250 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3800d3f9bcfa80879e6e55aadd7b1ee51324ac9bf14acbaa4257d7e58a7d89b4.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 447, + 108, + 831, + 247 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/0be238cdf2bab952ddc55af1a4b8e651c4f8094c8b94187bccc28bb3fed9fbb5.jpg", + "image_caption": [ + "Figure 5: (left) Distribution of 1000 generated future motions, when conditioning on a normal past motion (top) and on an abnormal one (bottom). 2-dimensional projections are estimated via t-SNE [45]. Note how the true future motion (red dot) lies within a main distribution mode in the case of normality, but it lies in a marginal region for abnormality. (right) Plot of the diversity ratio $rF$ [28], measuring the diversity of the generated future motions for normal and anomalous conditioning pasts. Moving along the $x$ -axis, with more generated motion, the $rF$ measures grow (MoCoDAD generates multimodal diverse motion) but they remain comparable (generating from normal and abnormal is anyhow multimodal)." + ], + "image_footnote": [], + "bbox": [ + 192, + 343, + 439, + 488 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/dcefbd7c4da137c74fda5f6b47dc4796c6f59896fa1e769d4a2f3dad49828667.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 493, + 338, + 761, + 479 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "generating with abnormal conditioning. The performance saturates for $m > 50$ .", + "bbox": [ + 75, + 617, + 468, + 647 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.3. Conditioning", + "text_level": 1, + "bbox": [ + 76, + 662, + 217, + 679 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Here, we provide the reader with the performances of our method with different encoding approaches of the past (i.e., how the past motion is provided to the model) from which the future is generated (see Table 3).", + "bbox": [ + 75, + 686, + 468, + 747 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "As illustrated in Sec. 3.2, Input Concatenation concatenates the clean past frames to the corrupted part of each motion sample and feeds it directly to the denoising module. This strategy surpasses recent baselines (cf. Table 1) with AUC scores of 64.96 and 65.20 on UBnormal and HRUBnormal, respectively. We deem this strategy suboptimal since it does not allow the past motion conditioning to be injected at each layer (as with the embedding strategies), and, thus force the network to \"remember\" this information rather than focusing on the denoising of the future.", + "bbox": [ + 75, + 750, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "The E2E-embedding strategy encodes the motion history in the clean past frames and provides it to the latent layers of the denoising model, but it does not improve performance. We believe this happens because the learned embedding is not supervised, and it may not be representative enough of the original motion.", + "bbox": [ + 496, + 617, + 890, + 708 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "AE-embedding accounts for the best performances. It couples the encoder $E$ with a symmetric decoder $D$ and trains the whole model with an auxiliary loss $\\mathcal{L}_{rec}$ which supervises the reconstruction of the first part of the motion (cf. Sec. 3.2). This past encoding strategy reaches 68.3 and 68.4 on UBnormal and HR-UBnormal, outperforming SoA techniques.", + "bbox": [ + 496, + 709, + 890, + 816 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.4. Proxy Task", + "text_level": 1, + "bbox": [ + 500, + 830, + 624, + 845 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In Table 4 we assess the effectiveness of the forecasting proxy task (cf. Sec. 3.1). To this end, instead of limiting ourselves towards a rigid past-future split of poses, we ex", + "bbox": [ + 496, + 854, + 890, + 901 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "10325", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/c4d42ac3b3805a347e08a9dae22b3c7a081d74b26a4d9f26ad2495a28d9e9051.jpg", + "table_caption": [ + "Table 3: Ablation study on the different methods for integrating conditioning information into the model." + ], + "table_footnote": [], + "table_body": "
HR-UBnormalUBnormal
Input Concatenation65.265.0
E2E-embedding64.464.2
AE-embedding (MoCoDAD)68.468.3
", + "bbox": [ + 81, + 130, + 468, + 200 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/b2f166fe02e812ec781541226568397d0a29d7f422a8f5a4b2d88ebbb3a65622.jpg", + "table_caption": [ + "Table 4: Ablation study on the type of conditioning information to feed into the model to generate the missing frame." + ], + "table_footnote": [], + "table_body": "
HR-UBnormalUBnormal
Random Imputation65.265.1
In-between Imputation65.765.7
Forecasting (MoCoDAD)68.468.3
", + "bbox": [ + 81, + 255, + 467, + 328 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "pllore two additional proxy tasks: i.e., in-between and random imputation. For in-between imputation, we corrupt the central $N - k$ poses and reserve the start and end of the sequence to condition the diffusion. For random imputation, we randomly select $N - k$ poses out of the full motion and corrupt them; the rest of the sequence is used for conditioning. Table 4 shows that random imputation is the worst proxy task (AUC of 65.10 and 65.21 for UBnormal and HR-UBnormal, respectively). Randomly splitting the sequence into two parts introduces inter-pose temporal gaps. Hence, we believe that this makes the reconstruction of noncontiguous motion more cumbersome. In-between imputation reaches an AUC of 65.65 and 65.72, respectively. We think that \"stitching\" the central motion to its endpoints is an easier task leading both normal and abnormal motions to be equally well reconstructed. Finally, forecasting is the best-performing proxy task with an AUC of 68.3 and 68.4 for UBnormal and HR-UBnormal.", + "bbox": [ + 75, + 353, + 468, + 625 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5.5. Latent space", + "text_level": 1, + "bbox": [ + 76, + 635, + 210, + 651 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Diffusion on latent space has been adopted to improve computational efficiency in various domains [33]. MLD [49] is one of the most recent works in motion forecasting that applies the diffusion process directly in the latent space.", + "bbox": [ + 75, + 657, + 467, + 733 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Here, we propose an analysis that assesses the performance of MoCoDAD's diffusion process in the latent space. Thus, we propose two latent variations of MoCoDAD: MoCoDAD+MLD and Latent-MoCoDAD. For MoCoDAD+MLD we use a VAE to produce a latent representation $Z \\in \\mathbb{R}^d$ of the uncorrupted sequence $X^{k + 1:N}$ and we perform the diffusion process on $Z$ with the transformer-based denoising model as described in [49]. For Latent-MoCoDAD we rely on an STS-VAE to learn $Z$ given $X^{k + 1:N}$ and use the diffusion process, proposed in Sec. 3.2, on $Z$ . For both these variants, we feed the cor", + "bbox": [ + 75, + 734, + 467, + 900 + ], + "page_idx": 8 + }, + { + "type": "table", + "img_path": "images/f16e113d2bd1cd9b2e293fd58ef2f817bb408d3fd782403edec3acdad5cee63b.jpg", + "table_caption": [ + "Table 5: AUC-ROC performance of diffusion on latent vs original space." + ], + "table_footnote": [], + "table_body": "
HR-UBnormalUBnormal
MoCoDAD+MLD58.158.1
Latent-MoCoDAD62.662.5
MoCoDAD68.468.3
", + "bbox": [ + 511, + 130, + 879, + 209 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "rupted $Z$ to an MLP with conditioning signal $h + \\tau_{\\theta}(t)$ to reverse the diffusion and leave the conditioning component as is in the original MoCoDAD (i.e., encoding of history poses $X^{1:k}$ ).", + "bbox": [ + 496, + 234, + 890, + 296 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Although the described variants can be trained end-to-end, we achieved the best performances by pre-training the autoencoder and training the diffusion module in the learned latent space keeping the autoencoder module frozen. We set the latent space dimension to $d = 16$ and the MLP blocks to (16,8,16) interleaved with ReLU activations.", + "bbox": [ + 496, + 297, + 890, + 387 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Table 5 illustrates the performances in terms of AUC-ROC of MoCoDAD and its latent variants on UBnormal and HR-UBnormal. Notice that the latent variants underperform w.r.t. the original MoCoDAD. We suspect that diffusion on latent spaces is not effective in skeleton-based VAD due to the lightweight encoding of the skeletons. This adheres with the literature since also MLD [49] shows that applying diffusion in the latent space underperforms w.r.t. the original proposal of the model.", + "bbox": [ + 496, + 388, + 890, + 525 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 542, + 617, + 558 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We have presented a novel approach that models and exploits the diversity of normal and abnormal motions. In the former case, the forecast motions are multi-modal and pertinent to the observed portion of the sequence, as the model understands the underlying action. In the case of abnormal, the forecast motions do not show a bias towards the true future as the model does not expect any obvious outcome. Motivated by the improved mode coverage, this work has been the first to take advantage of probabilistic diffusion models for video anomaly detection, including a thorough analysis of the main design choices. MoCoDAD sets a novel SoA among OCC techniques, and it catches up with supervised techniques while not using anomaly training labels.", + "bbox": [ + 496, + 569, + 890, + 779 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgements", + "text_level": 1, + "bbox": [ + 500, + 797, + 666, + 815 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was carried out while Stefano D'Arrigo was enrolled in the Italian National Doctorate on Artificial Intelligence run by Sapienza University of Rome. We thank DsTech S.r.l. and the PNRR MUR project PE0000013-FAIR for partially funding this study.", + "bbox": [ + 496, + 824, + 890, + 900 + ], + "page_idx": 8 + }, + { + "type": "page_number", + "text": "10326", + "bbox": [ + 480, + 944, + 517, + 955 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 9 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Andra Acsintoae, Andrei Florescu, Mariana-Iuliana Georgescu, Tudor Mare, Paul Sumedrea, Radu Tudor Ionescu, Fahad Shahbaz Khan, and Mubarak Shah. Ubnormal: New benchmark for supervised open-set video anomaly detection. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 20143-20153, 2022.", + "[2] Emre Aksan, Manuel Kaufmann, Peng Cao, and Otmar Hilliges. A spatio-temporal transformer for 3d human motion prediction. 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In Proceedings of the IEEE/CVF International Conference on Computer Vision (ICCV), pages 5826-5835, October 2021." + ], + "bbox": [ + 501, + 90, + 893, + 204 + ], + "page_idx": 11 + }, + { + "type": "page_number", + "text": "10329", + "bbox": [ + 480, + 945, + 517, + 955 + ], + "page_idx": 11 + } +] \ No newline at end of file diff --git a/2023/Multimodal Motion Conditioned Diffusion Model for Skeleton-based Video Anomaly Detection/c4ebdef1-c8e8-46eb-8870-f0578399391a_model.json b/2023/Multimodal Motion Conditioned Diffusion Model for Skeleton-based Video Anomaly Detection/c4ebdef1-c8e8-46eb-8870-f0578399391a_model.json new file mode 100644 index 0000000000000000000000000000000000000000..875d380f7b741aa0c05634bb838f1f49de8b3bed --- /dev/null +++ b/2023/Multimodal Motion Conditioned Diffusion Model for Skeleton-based Video Anomaly Detection/c4ebdef1-c8e8-46eb-8870-f0578399391a_model.json @@ -0,0 +1,2336 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.108, + 0.13, + 0.865, + 0.177 + ], + "angle": 0, + "content": "Multimodal Motion Conditioned Diffusion Model for Skeleton-based Video Anomaly Detection" + }, + { + "type": "text", + "bbox": [ + 0.155, + 0.204, + 0.816, + 0.24 + ], + "angle": 0, + "content": "Alessandro Flaborea* Luca Collorone* Guido Maria D'Amely di Melendugno* Stefano D'Arrigo* Bardh Prenkaj Fabio Galasso" + }, + { + "type": "text", + "bbox": [ + 0.088, + 0.242, + 0.882, + 0.258 + ], + "angle": 0, + "content": "{flaborea,damely,darrigo,prenkaj,galasso}@di.uniromal.it luca.collorone@diag.uniromal.it" + }, + { + "type": "text", + "bbox": [ + 0.33, + 0.275, + 0.642, + 0.311 + ], + "angle": 0, + "content": "Sapienza University of Rome, Italy https://github.com/aleflabo/MoCoDAD" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.345, + 0.314, + 0.361 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.378, + 0.47, + 0.514 + ], + "angle": 0, + "content": "Anomalies are rare and anomaly detection is often therefore framed as One-Class Classification (OCC), i.e. trained solely on normalcy. Leading OCC techniques constrain the latent representations of normal1 motions to limited volumes and detect as abnormal anything outside, which accounts satisfactorily for the openset'ness of anomalies. But normalcy shares the same openset'ness property since humans can perform the same action in several ways, which the leading techniques neglect." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.515, + 0.471, + 0.726 + ], + "angle": 0, + "content": "We propose a novel generative model for video anomaly detection (VAD), which assumes that both normality and abnormality are multimodal. We consider skeletal representations and leverage state-of-the-art diffusion probabilistic models to generate multimodal future human poses. We contribute a novel conditioning on the past motion of people and exploit the improved mode coverage capabilities of diffusion processes to generate different-but-plausible future motions. Upon the statistical aggregation of future modes, an anomaly is detected when the generated set of motions is not pertinent to the actual future. We validate our model on 4 established benchmarks: UBnormal, HR-UBnormal, HR-STC, and HR-Avenue, with extensive experiments surpassing state-of-the-art results." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.757, + 0.21, + 0.773 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.783, + 0.47, + 0.876 + ], + "angle": 0, + "content": "Video Anomaly Detection (VAD) is a crucial task in computer vision and security applications. It enables early detection of unusual or abnormal events in videos, such as accidents, illnesses, or people's behavior which may threaten public safety [41]. However, several aspects make VAD a challenging task. Firstly, the definition of anomaly" + }, + { + "type": "image", + "bbox": [ + 0.501, + 0.342, + 0.895, + 0.593 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.614, + 0.895, + 0.798 + ], + "angle": 0, + "content": "Figure 1: MoCoDAD detects anomalies by synthesizing and statistically aggregating multi-modal future motions, conditioned on past poses (frames on the left). Red (top) and green (bottom) distributions represent examples of anomaly and normality generations (2d mapped via t-SNE). Within the distribution modes (dashed-contoured), the red dots are the actual true futures corresponding to the conditioning past frames. In the case of normality, the true future lies within a main distribution mode, and the generated predictions are pertinent. In the case of abnormality, the true future lies in the tail of the distribution modes, which yields poorer predictions, highlighting anomalies." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.895, + 0.903 + ], + "angle": 0, + "content": "is highly subjective and varies depending on the context and application, making it difficult to define it universally. Secondly, anomalies are intrinsically rare. To account for data scarcity, models generally learn from regular samples only (also known as One Class Classification - OCC) or have to" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.887, + 0.255, + 0.902 + ], + "angle": 0, + "content": "*Authors contributed equally." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "10318" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.137 + ], + "angle": 0, + "content": "cope with the data imbalance. Thirdly, anomaly detection is intrinsically an openset problem, and modeling anomalies needs to account for diversity beyond the training set." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.137, + 0.47, + 0.346 + ], + "angle": 0, + "content": "An \"ideal\" model for anomaly detection should consider that there are infinitely many anomalous and non-anomalous ways of performing an action. Current state-of-the-art OCC techniques [9, 24, 25, 26] fail to address this issue. Indeed, they focus on learning either a single reconstruction or prediction of the input, or deriving a latent representation of normal actions, thereby constraining them to a limited latent volume. This last approach successfully accounts for the openset'ness of anomalies, i.e., anything mapped outside the normality region is considered abnormal. However, forcing normality into constrained volumes may not work for diverse-but-still-normal behaviors, i.e., OCC misclassifies as anomalous those not fitting in the volume." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.348, + 0.471, + 0.56 + ], + "angle": 0, + "content": "We propose Motion Conditioned Diffusion Anomaly Detection - hereafter MoCoDAD - a novel generative model for VAD, which assumes that both normality and abnormality are multimodal2. Given a motion sequence, be it normal or anomalous, the sequence is split and the later (future) frames are corrupted to become random noise. Conditioned on the first (past) clean input frames, MoCoDAD synthesizes multimodal reconstructions of the corrupted frames. MoCoDAD discerns normality from anomaly by comparing the multimodal distributions. In the case of normality, the generated motions are diverse but pertinent, i.e. they are biased towards the true uncorrupted frames. In the case of abnormality, the synthesized motion is also diverse, but it lacks pertinence, as shown in Fig. 1 and discussed in Sec. 5." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.56, + 0.47, + 0.695 + ], + "angle": 0, + "content": "MoCoDAD is the first diffusion-based technique for video anomaly detection. We are inspired by Denoising Diffusion Probabilistic Models (DDPMs) [40, 14], state-of-the-art, among others, in image synthesis [31, 30, 33], motion synthesis [43, 49], and 3D generation tasks [53]. DDPMs are selected for their improved mode coverage [48], i.e. they generate diverse multimodal motions, which MoCoDAD statistically aggregates (see the respective ablative study in Sec. 5)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.696, + 0.47, + 0.831 + ], + "angle": 0, + "content": "Besides multimodality, a crucial aspect of MoCoDAD is the choice of the conditioning strategy to guide the synthesis. We consider human motion as skeletal representations and propose corrupting the body joint coordinates at each frame by displacing them with random translations. Conditioning refers to the process that provides the model with the uncorrupted first part of the motion sequence (past) to guide the denoising of the corrupted second part (future). In this study, we compare three modeling choices to find the most" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.839, + 0.47, + 0.875 + ], + "angle": 0, + "content": "1To avoid ambiguity, in this work, the term \"normal\" is the contrary of anomalous, not the synonym of \"Gaussian\". Normal refers to \"normality\" (or \"normalcy\"). Anomalous/abnormal refers to abnormality/anomaly." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.876, + 0.469, + 0.9 + ], + "angle": 0, + "content": "2In this work, multimodal refers to distributions with multiple modes, not to mixing modalities (video, audio, text, etc.)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.197 + ], + "angle": 0, + "content": "suitable conditioning strategy. We experiment with (1) directly feeding the denoising module with the concatenation of the uncorrupted poses with the displaced sequence [35]. For the other two strategies, we get a latent representation of the input (via (2) an encoding module and (3) an autoencoder) and feed the network with this learned representation (cf. Sec. 3.2). The third strategy works best (cf. Sec. 5.3)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.198, + 0.893, + 0.392 + ], + "angle": 0, + "content": "We evaluate MoCoDAD on three challenging benchmarks of human-related anomalies, namely, HR-UBnormal [1, 9], HR-ShanghaiTech Campus [23, 26] (HR-STC), and HR-Avenue [22, 26], and on the most recent VAD dataset UBnormal [1]. MoCoDAD achieves state-of-the-art (SoA) performance on all four datasets, which demonstrates the effectiveness of modeling multimodality for normal and abnormal motions. Notably, by not using appearance, MoCoDAD benefits increased privacy protection (no visual facial nor body features) and better computational efficiency, thanks to the lightweight body kinematic representations. We summarize our contributions as follows:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.394, + 0.891, + 0.437 + ], + "angle": 0, + "content": "- A novel generative VAD model based on comparing the multimodality of normal and abnormal motion generations;" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.439, + 0.891, + 0.484 + ], + "angle": 0, + "content": "- The first probabilistic diffusion-based approach for VAD, which fully exploits the enhanced modecoverage capabilities of diffusive probabilistic models;" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.484, + 0.891, + 0.529 + ], + "angle": 0, + "content": "- A novel motion-based conditioning on the clean input sequence to steer the synthesis towards diverse pertinent motion in the case of normality;" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.53, + 0.891, + 0.589 + ], + "angle": 0, + "content": "A thorough validation on UBnormal, HR-UBnormal, HR-STC, and HR-Avenue benchmarks where we outperform the SoA by \\(5.1\\%\\), \\(4.4\\%\\), \\(5\\%\\), \\(8\\%\\), respectively." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.394, + 0.891, + 0.589 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.603, + 0.642, + 0.618 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.628, + 0.892, + 0.673 + ], + "angle": 0, + "content": "Previous work relates to ours from two main perspectives: Video Anomaly Detection methods (see Sec. 2.1), and diffusion models for motion synthesis (see Sec. 2.2)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.682, + 0.824, + 0.698 + ], + "angle": 0, + "content": "2.1. Video Anomaly Detection Techniques" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.892, + 0.84 + ], + "angle": 0, + "content": "Pioneer works analyze the trajectory of the agents in the frames to discriminate those distant from normality [5, 16, 19]. Within recent literature, two major trends can be identified: latent- and reconstruction-based methods. VAD techniques also vary based on the type of input data they use, such as videos or human skeletal pose motions. MoCoDAD, as all the VAD works presented in this section, adheres to the OCC protocol, which simulates the scarcity of anomalies in real-world scenarios [18]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Latent-based VAD methods identify abnormality according to a score extracted from a learned latent space whereby normality is supposedly mapped into a constrained volume, and anomalies are those latents lying outside, with a larger" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "10319" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.273 + ], + "angle": 0, + "content": "score (see [34, 38, 42, 46] for an overview of latent-based AD). Sabokrou et al. [36] propose a two-staged cascade of deep neural networks. First, they employ a stack of autoencoders that detects points of interest (POIs) while excluding irrelevant patches (e.g., background). Second, they identify anomalies by densely extracting and modeling discriminative patches at POIs. Notice that this work constrains normality to belong to a single mode and anomalies outside, thus, addressing the openset'ness of anomalies, but it hampers the multimodal and diversity [51] aspect of normal motions. Contrarily, our work considers the multimodality of normal and abnormal motions." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.276, + 0.473, + 0.398 + ], + "angle": 0, + "content": "Notably, Nguyen et al. [27] propose an image-based technique exploring multimodal anomaly detection via multi-headed VAEs. However, considering a fixed number of modes for reality amends multimodality only partially, as it misses to unleash its openset'ness. Differently, we adopt diffusion models for their improved mode coverage and generate multiple futures, not being constrained on a fixed number of heads (see Sec. 5)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.399, + 0.473, + 0.822 + ], + "angle": 0, + "content": "Reconstruction-based VAD methods consider the original metric space of the input and leverage reconstruction as the proxy task to derive an anomaly score. These models are trained to encode and reconstruct the input from normal events, producing larger errors on anomalies not seen during training. [7, 13, 52] use sequences of frames and feed them to convolutional autoencoders. Gong et al. [12] \"memorize\" the most representative normal poses to discriminate new input samples. Liu et al. [21] tackle intensity and gradient loss, optical flow, and adversarial training. Luo et al. [23] use stacked RNNs with temporally-coherent sparse coding enforcing similar neighboring frames to be encoded with similar reconstruction coefficients. Barbalau et al. [3] builds upon [10] and integrates the reconstruction of the input frames, via multi-headed attention, into a multitask learning framework. Besides [10, 21], all works rely on a single reconstruction proxy task via non-variational architectures that learn discrete manifolds. However, normality and abnormality are multimodal and diverse, making it hard for these techniques to have an exact match (reconstruction) over the GT. Additionally, GANs used in [21] suffer from mode collapse [44] lacking to represent the multimodality of reality. Similarly to [27], [3] can represent only a fixed number of modalities, which does represent the openset'ness of reality. MoCoDAD is a reconstruction-based approach and leverages diffusion processes [8] to account for the openset'ness of normalcy and anomalies in terms of pertinence to the GT." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Skeleton-based VAD methods exploit compact spatiotemporal skeletal representations of human motion instead of raw video frames. Morais et al. [26] use two GRU autoencoder branches to account for the global and local decomposition of the skeleton in a particular frame. Luo et" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.895, + 0.351 + ], + "angle": 0, + "content": "al. [24] exploit stacked layers of ST-GCN [50] to accumulate joint information over the spatio-temporal dimensions of the frame and predict joints in the future. However, [50] uses a fixed adjacency matrix, depicting joint connections, for all ST-GCN layers, which hinders the exploration of intra-frame and intra-joint relationships, two factors that play a crucial role in improving the encoding of spatio-temporal features [39]. Markovitz et al. [25] utilize the encoder of an ST-GCN autoencoder to embed spacetime skeletons into a latent vector. This vector is then fed to an end-to-end trainable deep-embedded clustering procedure which produces \\(k\\) clusters representing the multimodality of normalcy and anomalies. Flaborea et al. [9] propose COSKAD and force the normal instances into the same latent region driving the distances to a common center. MoCoDAD is also a skeleton-based approach that mitigates the choice of \\(k\\) a priori to cover the multimodality of reality." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.361, + 0.669, + 0.377 + ], + "angle": 0, + "content": "2.2. Diffusion Models" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.386, + 0.895, + 0.688 + ], + "angle": 0, + "content": "Diffusion models have marked a revolution in generative tasks such as image and video synthesis [35, 43, 49], but they have not been employed for VAD. Saadatnejad et al. [35] propose a two-step framework based on temporal cascaded diffusion (TCD). First, they denoise imperfect observation sequences and, then, improve the predictions of the (frozen) model on repaired frames. Tevet et al. [43] use a transformer encoder to learn arbitrary length motions [2, 29] coherent with a particular conditioning signal \\( c \\). They experiment with constrained synthesis where \\( c \\) is a text prompt (i.e., text-to-motion) or a specific action class (i.e., action-to-motion) and unconstrained synthesis where \\( c \\) is not specified. Chen et al. [49] design a transformer-based VAE [29] to learn a representative latent space for human motion sequences. They apply a diffusion model in this latent space to generate vivid motion sequences while obeying specific conditions similar to [43]. Differently, MoCoDAD is a diffusion-based model that uses conditioning over a portion of the input (e.g., previous frames condition the generation of future ones)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.897, + 0.901 + ], + "angle": 0, + "content": "Wyatt et al. [47] propose AnoDDPM, a diffusion model on images, which does not require the entire Markov chain (noise/denoise) to take place. They use decaying octaves of simplex noising functions to distinguish the corruption rate of low-frequency components from high-frequency ones. However, they add and remove noise without conditioning, identifying anomalies when noise removal diverges from the input. Differently, MoCoDAD is based on generating and comparing multimodal motions against the GT in terms of pertinence. Our proposed model is the first to exploit the multimodal generative and improved mode-coverage capabilities of diffusive techniques, via forecasting tasks, further to being first in adopting them for detecting video anomalies. Hence, to transfer DDPMs from video-based" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "10320" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.152 + ], + "angle": 0, + "content": "Anomaly Detection to skeleton-based VAD we rely on a U-Net-shaped stack of STS-GCN [39, 37] layers, which includes the spatio-temporal aspects of joints in sequences of human poses." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.166, + 0.214, + 0.183 + ], + "angle": 0, + "content": "3. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.191, + 0.473, + 0.328 + ], + "angle": 0, + "content": "MoCoDAD learns to reconstruct the later (future) corrupted poses by conditioning on the first (past) poses. Sec. 3.1 describes the training diffusion denoising process, how it generates multimodal reconstructions, and statistically aggregates them at inference to detect anomalies. Sec. 3.2 details conditioning on past frames, and Sec. 3.3 describes the architecture of MoCoDAD. For the sake of completeness, in Sec. A.1 of the Supplementary, we present preliminary concepts of DDPMs." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.336, + 0.307, + 0.352 + ], + "angle": 0, + "content": "3.1. Diffusion on Trajectories" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.359, + 0.47, + 0.404 + ], + "angle": 0, + "content": "Training We define a diffusion technique that learns to reconstruct corrupted future motion sequences conditioned on clean past ones." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.404, + 0.47, + 0.555 + ], + "angle": 0, + "content": "Let \\( X_{a} = \\{x_{a}^{1},\\ldots ,x_{a}^{N}\\} \\) be a sequence of \\( N \\) timecontiguous poses belonging to a single actor \\( a \\). Since our model considers one actor at a time, we use \\( X = \\{x^{1},\\dots,x^{N}\\} \\) for notation simplicity. Each pose \\( x^{i} \\) can be seen as a graph \\( x^{i} = (J,A) \\) where \\( J \\) represents the set of joints, and \\( A \\) is the adjacency matrix representing the joint connections. Notice that each joint is attributed with a set of spatial coordinates in \\( \\mathbb{R}^C \\), hence \\( x^{i}\\in \\mathbb{R}^{|J|\\times C} \\), and \\( X\\in \\mathbb{R}^{N\\times |J|\\times C} \\). Here, we use \\( C = 2 \\) as the person's pose is extracted from images at each frame." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.555, + 0.47, + 0.586 + ], + "angle": 0, + "content": "We divide \\( X \\) into two parts: the past \\( X^{1:k} \\) and the future sequence of poses \\( X^{k+1:N} \\) with \\( k \\in \\{1, \\dots, N\\} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.586, + 0.47, + 0.661 + ], + "angle": 0, + "content": "During the forward process \\(q\\), we corrupt the coordinates of the joints by adding random translation noise. We sample a random displacement map \\(\\varepsilon^{k + 1:N} \\in \\mathbb{R}^{(N - k) \\times |J| \\times C}\\) from a distribution \\(\\mathcal{N}(0, \\mathbf{I})\\) and add it to \\(X^{k + 1:N}\\) to randomly translate the position of its nodes." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.661, + 0.47, + 0.752 + ], + "angle": 0, + "content": "The magnitude of the added displacement depends on a variance scheduler \\(\\beta_{t} \\in (0,1)\\) and a diffusion timestep \\(t \\sim \\mathcal{U}_{[1,T]}\\). As a result, \\(q\\) increasingly corrupts the joints \\(x^{i}\\) at each diffusion timestep \\(t\\) (i.e., \\(x_{t=1}^{i} \\to \\dots \\to x_{t=T}^{i}\\)) making \\(x_{t=T}^{i}\\) indistinguishable from a pose with randomly sampled joints' spatial coordinates." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.752, + 0.47, + 0.844 + ], + "angle": 0, + "content": "The reverse process \\( p_{\\theta} \\) unrolls the corruption, estimating the spatial displacement map \\( \\varepsilon^{k + 1:N} \\) via a U-Net-like architecture \\( \\varepsilon_{\\theta} \\) (see Sec. 3.3 for more details). To achieve an approximation of \\( \\varepsilon^{k + 1:N} \\), we train the network conditioned on the diffusion timestep \\( t \\) (embedded through an MLP \\( \\tau_{\\theta} \\)) and the embedding \\( h \\) of the previous trajectory \\( X^{1:k} \\)." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.092, + 0.894, + 0.122 + ], + "angle": 0, + "content": "In Eq. 1, similarly to [33], we define the displacement estimation objective4." + }, + { + "type": "equation", + "bbox": [ + 0.571, + 0.132, + 0.892, + 0.166 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {d i s p}} = \\mathbb {E} _ {t, X, \\varepsilon} \\left[ \\left| \\left| \\varepsilon - \\varepsilon_ {\\theta} \\left(X _ {t}, t, h\\right) \\right| \\right| \\right] \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.171, + 0.807, + 0.187 + ], + "angle": 0, + "content": "Inspired by [11], we smooth \\(\\mathcal{L}_{disp}\\) as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.548, + 0.198, + 0.892, + 0.24 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {s m o o t h}} = \\left\\{ \\begin{array}{l l} 0. 5 \\cdot \\left(\\mathcal {L} _ {\\text {d i s p}}\\right) ^ {2} & \\text {i f} \\left| \\mathcal {L} _ {\\text {d i s p}} \\right| < 1 \\\\ \\left| \\mathcal {L} _ {\\text {d i s p}} \\right| - 0. 5 & \\text {o t h e r w i s e} \\end{array} \\right. \\tag {2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.255, + 0.894, + 0.315 + ], + "angle": 0, + "content": "Inference At inference time, MoCoDAD generates multimodal future sequences of poses from random displacement maps, conditioned on the past frames, then aggregates them statistically to detect anomalies." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.315, + 0.894, + 0.361 + ], + "angle": 0, + "content": "We sample a random displacement \\(z \\sim \\mathcal{N}(0, \\mathbf{I})\\) and consider it the starting point of the synthesis process that generates a future human motion via Eq. 3." + }, + { + "type": "equation", + "bbox": [ + 0.508, + 0.371, + 0.892, + 0.406 + ], + "angle": 0, + "content": "\\[\nX _ {t - 1} = \\frac {1}{\\sqrt {\\alpha_ {t}}} \\left(X _ {t} - \\frac {1 - \\alpha_ {t}}{\\sqrt {1 - \\alpha_ {t}}} \\varepsilon_ {\\theta} \\left(X _ {t}, t, h\\right)\\right) + z \\sqrt {\\beta_ {t}} \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.416, + 0.892, + 0.49 + ], + "angle": 0, + "content": "Note the motion conditioning \\( h \\), encoding the past \\( k \\) frames. We generate \\( m \\) diverse future pose trajectories \\( Z_{1},\\ldots ,Z_{m} \\). For each \\( Z_{i} \\), we compute the reconstruction error via the smoothed loss \\( s_i = \\mathcal{L}_{smooth}(|X - Z_i|) \\) used in training (cf. Eq. 2)." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.491, + 0.893, + 0.748 + ], + "angle": 0, + "content": "We aggregate all the scores from the generations \\( S = \\{s_1, \\ldots, s_m\\} \\) to distill a single anomaly score for that sequence. This score is subsequently assigned to the corresponding frames to assess their level of anomaly. In scenarios where multiple actors occupy the same frames, we assign the average anomaly score to those frames. See the Supplementary for a detailed description. We explore different strategies for distilling the anomaly score from \\( S \\): (1) the diversity between the normal and anomalous generations and (2) aggregation statistics. To account for diversity, we consider the diversity metric \\( rF = \\mathrm{mean}(\\mathcal{L}_{smooth}) / \\min (\\mathcal{L}_{smooth}) \\) introduced by [6, 28]. Diversity stems from testing whether anomalous generations are more diverse than normals, but the diversity score fails to detect anomalies, nearly dropping to random chance. We explain this by normalcy and anomaly having a similar degree of diversity, as we experimentally validate in Sec. 5.1." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.748, + 0.894, + 0.868 + ], + "angle": 0, + "content": "We consider as aggregation statistics the mean, quantile robust statistics including the median, as well as maximum and minimum selectors, in terms of \\(\\mathcal{L}_{smooth}\\) distances between the \\(m\\) generated and the GT future motion. Our analysis highlights that the minimum distance is the best on average. This reinforces the original hypothesis that normality-conditioned generated motions are as diverse as abnormal-conditioned ones but more biased to the actual" + }, + { + "type": "page_footnote", + "bbox": [ + 0.5, + 0.875, + 0.894, + 0.901 + ], + "angle": 0, + "content": "4For readability purposes, for what follows, we omit the superscript \\(k + 1:N\\), and assume that we are considering only future motion." + }, + { + "type": "page_footnote", + "bbox": [ + 0.076, + 0.85, + 0.47, + 0.901 + ], + "angle": 0, + "content": "3In this paper, a displacement map is equivalent to the addition of noise (corruption) to the input, e.g., in [14]. We use this term to emphasize that we move the joints away from their original spatial position. We invite the reader to consider displacing and corrupting as interchangeable here." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "10321" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.164, + 0.089, + 0.812, + 0.334 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.344, + 0.895, + 0.422 + ], + "angle": 0, + "content": "Figure 2: Overview of the proposed MoCoDAD. A sequence of \\(N\\) skeletal motions (\\(N = 6\\) in the example) is split into past (top-right \\(X^{1:k}\\) frames, \\(k = 3\\) in the example) and future (top-left \\(X^{k+1:N}\\) frames). During training, the Forward Diffusion block adds noise to the future frames, shifting each joint by a random vector displacement of varying intensity (increasing with the diffusion timestep \\(t\\)). Then the Reverse Diffusion learns to estimate the noise. A key aspect of MoCoDAD is the conditioning, i.e. how to encode the past clean \\(k\\) frames and guide the synthesis of relevant futures." + }, + { + "type": "image", + "bbox": [ + 0.082, + 0.455, + 0.473, + 0.584 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.081, + 0.592, + 0.466, + 0.609 + ], + "angle": 0, + "content": "Figure 3: Comparison of the three conditioning strategies." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.637, + 0.47, + 0.669 + ], + "angle": 0, + "content": "motion, thus more likely to generate samples close to it. See Sec. 5.2 for the experimental evaluation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.679, + 0.47, + 0.711 + ], + "angle": 0, + "content": "3.2. Motion Conditioning for multimodal Pose Forecasting" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.719, + 0.47, + 0.809 + ], + "angle": 0, + "content": "The choice of the conditioning strategy is a crucial factor for diffusion models, as it determines how the conditioning information is fed into the network, and it directly affects the quality of the outputs. In this work, we propose a thorough examination of different strategies for feeding the diffusion models with the conditioning information." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.471, + 0.902 + ], + "angle": 0, + "content": "We identify three different modeling choices for conditioning the diffusion, illustrated in Fig. 3, i.e., input concatenation, \\(E2E\\)-embedding, and \\(AE\\)-embedding. Input concatenation refers to conditioning with a portion of the raw input motion. Here, we keep the past sequence of poses \\(X^{1:k}\\) (the conditioning signal) uncorrupted and pretend it" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.459, + 0.892, + 0.505 + ], + "angle": 0, + "content": "to the corrupted future sequence \\( X_{t}^{k + 1:N} \\). Input concatenation has been explored in previous work for pose forecasting reaching SoA performances in [35]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.506, + 0.893, + 0.687 + ], + "angle": 0, + "content": "Both embedding choices refer to passing the conditioning past frames through an encoder \\( E \\), then providing them to all latent layers of the denoising model (cf. incoming vertical arrows into the orange layers in Fig. 2). Here, \\( E \\) is a GCN [39] and it encodes sequences of poses \\( X^{1:k} \\) into the representation \\( h = E(X^{1:k}) \\). In the case of \\( E2E \\)-embedding, \\( E \\) is jointly learned with the rest of the architecture, leveraging the training \\( \\mathcal{L}_{\\text{smooth}} \\) loss. The \\( AE \\)-embedding adds an auxiliary reconstruction loss \\( \\mathcal{L}_{\\text{rec}} \\) to support training \\( E \\), as it tasks a decoding network \\( D \\) to reconstruct the conditioning past frames according to the following loss function:" + }, + { + "type": "equation", + "bbox": [ + 0.583, + 0.703, + 0.892, + 0.74 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {r e c} = \\left| \\left| D (E (X ^ {1: k})) - X ^ {1: k} \\right| \\right| _ {2} ^ {2} \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.75, + 0.892, + 0.78 + ], + "angle": 0, + "content": "In the case of \\(AE\\)-embedding, the auxiliary is summed to the main loss, resulting in the following total loss:" + }, + { + "type": "equation", + "bbox": [ + 0.599, + 0.795, + 0.892, + 0.812 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {t o t} = \\lambda_ {1} \\mathcal {L} _ {\\text {s m o o t h}} + \\lambda_ {2} \\mathcal {L} _ {\\text {r e c}} \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.892, + 0.902 + ], + "angle": 0, + "content": "where \\(\\lambda_1, \\lambda_2 \\in [0, 1]\\) account for the contribution of each loss function respectively. Lastly, since DDPMs benefit from being conditioned on the timestep \\(t\\), we add the embedding \\(\\tau_{\\theta}(t)\\) to the latent \\(h\\) and feed the resulting motion-temporal signal to each layer of our network \\(\\varepsilon_{\\theta}\\) [43]." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.958 + ], + "angle": 0, + "content": "10322" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.892, + 0.121 + ], + "angle": 0, + "content": "Table 1: Comparison of MoCoDAD against SoA in terms of AUC on the three Human-Related datasets (i.e., HR-STC, HR-Avenue and HR-UBnormal) and UBnormal. OCC skeleton-based techniques are marked with a \\(*\\)." + }, + { + "type": "table", + "bbox": [ + 0.12, + 0.131, + 0.847, + 0.332 + ], + "angle": 0, + "content": "
HR-STCHR-AvenueHR-UBnormalUBnormal
Conv-AE [13]CVPR '1669.884.8--
Pred [21]CVPR '1872.786.2--
MPED-RNN [26] *CVPR '1975.486.361.260.6
GEPC [25] *CVPR '2074.858.155.253.4
Multi-timescale Prediction [32] *WACV '2077.088.3--
Normal Graph [24]Neurocomputing '2176.587.3--
PoseCVAE [15] *ICPR '2175.787.8--
BiPOCO [17] *Arxiv '2274.987.052.350.7
STGCAE-LSTM [20] *Neurocomputing '2277.286.3--
SSMTL++ [3]CVIU '23---62.1
COSKAD [9] *Arxiv '2377.187.865.565.0
MoCoDAD *77.689.068.468.3
" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.357, + 0.47, + 0.403 + ], + "angle": 0, + "content": "The results of evaluation are discussed in Sec. 5.3, whereby applying an AE-embedding conditioning on \\( X^{1:k} \\) emerges with results beyond the SoA." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.438, + 0.304, + 0.454 + ], + "angle": 0, + "content": "3.3. Architecture Description" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.469, + 0.47, + 0.697 + ], + "angle": 0, + "content": "Fig. 2 illustrates the architecture of MoCoDAD. We distinguish two main blocks: a conditioning auto-encoder for the past motion, \\( X^{1:k} \\), and a denoising model for \\( X^{k+1:N} \\). The main diffusion model architecture is the neural network, represented with orange blocks, tasked with estimating the corrupting noise in the input motion, thus reconstructing the actual future motion. As done in [47], we rely on a U-Net like architecture. Our skeletal-motion diffusion network progressively contracts and then expands (rebuilds) the spatial dimension of the input sequence of poses. To account for the temporal dimension of the input sequences, we build the U-Net with space-time separable GCN (STSGCN) layers proposed in [39]. The conditioning autoencoder relies on STS-GCN to reconstruct the past motion and embed it into a latent space used to condition the diffusion." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.704, + 0.471, + 0.902 + ], + "angle": 0, + "content": "In detail, the U-Net takes in input \\( X^{k + 1:N} \\) and a motion-temporal conditioning signal \\( h + \\tau_{\\theta}(t) \\) which provides the network with the diffusion timestep and the encoded past-motion information. Furthermore, to align the dimensionality of this conditioning signal with that of the network's layers, the former is fed into an embedding layer projecting it to the correct vector space. This embedded conditioning signal is then fed to each STS-GCN layer. The contracting process of the U-Net progressively aggregates the joints of the poses (i.e., \\( \\mathbb{R}^J \\to \\mathbb{R}^d \\) s.t. \\( d \\leq J \\)) while the expansion part \"deconvolutes\" the joints' vector space until it reaches the original space \\( \\mathbb{R}^J \\). Residual connections are present between specular layers." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.355, + 0.634, + 0.373 + ], + "angle": 0, + "content": "4. Experiments" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.381, + 0.892, + 0.44 + ], + "angle": 0, + "content": "Here we compare MoCoDAD with SoA approaches and provide a detailed discussion on the achieved performances. In Sec. D of the Supplementary, we provide the reader with a thorough description of the implementation details." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.442, + 0.892, + 0.517 + ], + "angle": 0, + "content": "As done in [1, 3, 9, 10, 21, 24, 25, 26], we report the Receiver Operating Characteristic Area Under the Curve (ROC-AUC) to assess the quality of MoCoDAD predictions on UBnormal [1], and the HR filtered [9] versions of STC [23], Avenue [22], and UBnormal." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.527, + 0.603, + 0.542 + ], + "angle": 0, + "content": "4.1. Datasets" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.55, + 0.892, + 0.807 + ], + "angle": 0, + "content": "We use the UBnormal dataset [1] which contains 29 scenes synthesized from 2D natural images with the Cinema4D software. Each scene appears in 19 clips featuring both normal and abnormal events. The split into train, validation, and test adheres to the open-set policy, providing disjoint sets of types of anomalies for training, validation, and test; in accordance with the OCC setting, we only include normal actions for the training set. We also consider the processed poses and the human-related (HR) filtering of the dataset proposed by [9]. To compare with other state-of-the-art methods, we also experiment on the HR versions of the ShanghaiTech Campus (STC) [23] and the CUHK Avenue [22] datasets introduced by [26]. The former includes 13 scenes recorded with different cameras, for a total of about 300,000 frames, and 101 testing clips with 130 anomalous events. The latter consists of 16 training videos and 21 testing videos with a total of 47 anomalous events." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.817, + 0.791, + 0.833 + ], + "angle": 0, + "content": "4.2. Comparison with state-of-the-art" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.84, + 0.892, + 0.902 + ], + "angle": 0, + "content": "Leading OCC techniques. We compare against SoA OCC techniques. Among these, MPED-RNN [26] combines the reconstruction and prediction errors of a two-branches-RNN to spot anomalies. Normal Graph [24] uses spatial" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "10323" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.089, + 0.472, + 0.135 + ], + "angle": 0, + "content": "Table 2: Comparison of MoCoDAD against supervised (†) and weakly supervised (‡) methods introduced in [1] in terms of AUC on the UBnormal dataset." + }, + { + "type": "table", + "bbox": [ + 0.136, + 0.146, + 0.406, + 0.242 + ], + "angle": 0, + "content": "
ParamsUBnormal
Sultani et al. [41] †-50.3
AED-SSMTL [10] †>80M61.3
TimeSformer [4] †121M68.5
AED-SSMTL [10] ‡>80M59.3
MoCoDAD142K68.3
" + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.263, + 0.47, + 0.534 + ], + "angle": 0, + "content": "temporal GCNs (ST-GCN) to encode skeletal sequences. GEPC [25] encodes the input sequences with an STGCN, and clusters the embeddings in the latent space. Multi-timescale Prediction [32] encodes the observed input sequence and predicts future poses at different time scales through intermediate fully-connected layers. Both PoseCVAE [15] and BiPOCO [17] exploit a Conditioned Variational-Autoencoder to learn a posterior distribution of normal actions and use encoded past and future sequences to reconstruct the future one. The former uses an MLP-based architecture, while the latter is GRU-based. STGCAE-LSTM [20] reconstructs the past pose sequence and predicts the future one by an LSTM-based autoencoder. SSMTL++ [3] extends [10]; it replaces the convolutions with a transformer, changes the object detection backbone, and adds a few auxiliary proxy tasks. COSKAD [9] builds on STS-GCN to map the embeddings of normal poses into a narrow region in the latent space." + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.537, + 0.47, + 0.763 + ], + "angle": 0, + "content": "Results. In Table 1, we compare MoCoDAD and SoA methods on the three HR datasets and on UBnormal. MoCoDAD achieves the best AUC score of 77.6, 89.0, and 68.4 on HR-STC, HR-Avenue, and HR-UBnormal, respectively. Our proposed method outperforms the current best [9], up to \\(4.4\\%\\), demonstrating the importance of considering a range of different possible futures for each sample. Additionally, MoCoDAD achieves an AUC of 68.3 on the full UBnormal dataset, surpassing COSKAD by \\(5.1\\%\\). This can be due to the improved sensitivity that emerges from our proposed model: considering more than a single deterministic future smooths the prediction of MoCoDAD avoiding penalizing excessively hard-still-normal samples which would be considered anomalous based on the reconstruction error of a deterministic model." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.765, + 0.471, + 0.903 + ], + "angle": 0, + "content": "Results VS. Supervised and Weakly Supervised methods Table 2 evaluates MoCoDAD with supervised and weakly supervised methods reported in [1]. Notice that, despite the absence of supervision or visual information, MoCoDAD is competitive with methods exploiting a stronger form of supervision. In detail, MoCoDAD (68.3) outperforms the weakly supervised method [10] (59.3) and other fully supervised methods and is competitive with [4] (68.5). Further, our approach only presents a fraction of the parameters of" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.122 + ], + "angle": 0, + "content": "its competitors. Notably, MoCoDAD is \\(\\sim 852\\times\\) smaller than the current best [4]." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.138, + 0.614, + 0.154 + ], + "angle": 0, + "content": "5. Discussion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.164, + 0.892, + 0.286 + ], + "angle": 0, + "content": "Here, we delve into a detailed discussion about the multimodal future generations (cf Sec. 5.1), the influence of the statistical aggregation of multiple generations and the normal Vs. anomalous conditioning (cf. Sec. 5.2), the effect of different conditioning strategies (cf. Sec. 3.2). Additionally, we discuss forecasting proxy tasks (Sec. 5.4) and analyze MoCoDAD's performances with the diffusion process applied to the latent space. (Sec. 5.5)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.296, + 0.649, + 0.312 + ], + "angle": 0, + "content": "5.1. Multimodality" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.321, + 0.892, + 0.518 + ], + "angle": 0, + "content": "We question whether MoCoDAD can generate diverse multimodal motions and whether conditioning on normal or abnormal motions affects diversity. We provide an example of generated future motions in Fig. 5 (left), where we project the samples in 2D with t-SNE [45] for better visualization. Notice that both sets of generations have similar variance, showing that MoCoDAD produces diverse samples with both normal and abnormal conditioning sequences. Motions stemming from normal conditioning are biased toward the true future since they are mapped around it. Whereas, in the case of abnormal conditioning, the ground truth motion lies on the edge of the predictions' region, hence being correctly predicted with a lower chance." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.518, + 0.892, + 0.685 + ], + "angle": 0, + "content": "We also measure diversity, employing the \\( rF \\) diversity metric from literature [6, 28]. We visualize the \\( rF \\) trend when increasing the number of generations in Fig. 5 (right). If the generated motion had no diversity, e.g., when generating only once, the \\( rF \\) would be equal to 1. Rather, the diversity ratio monotonically increases with the number of generations for both normal and abnormal cases, i.e., the more generated samples, the larger the empirical mode coverage and the diversity. We note that, following intuition, the diversity for abnormal cases grows slightly larger than for normal cases, but the \\( rF \\) measures remain comparable." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.696, + 0.88, + 0.712 + ], + "angle": 0, + "content": "5.2. Statistical aggregations of generated motions" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "We evaluate the anomaly detection performance when varying the number of generations \\( m \\) and the aggregation strategy for the anomaly score \\( S \\) (cf. Sec. 3.1). Fig. 4 (right) shows that the AUC positively correlates with the number of generated future motions for quantiles \\( Q < 0.5 \\), while the correlation is negative for the mean estimate and \\( Q > 0.5 \\). Such correlation can be better understood by looking at Fig. 4 (left), which depicts the average reconstruction error probability density function (PDF) for \\( m = 50 \\): when conditioned on normal past motions, MoCoDAD produces generations which are centered around the true future and, thus, is more likely to yield lower error scores than when" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "10324" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.156, + 0.106, + 0.422, + 0.25 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.449, + 0.109, + 0.832, + 0.248 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.075, + 0.26, + 0.894, + 0.307 + ], + "angle": 0, + "content": "Figure 4: (left) Histograms of the reconstruction errors for 50 synthesized future motions, computed on the HR-UBnormal test set, for the case of conditioning on normal and abnormal past motions. (right) Correlation between the AUC scores and the number of generations, with each curve corresponding to a different aggregation statistic." + }, + { + "type": "image", + "bbox": [ + 0.193, + 0.344, + 0.441, + 0.489 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.495, + 0.339, + 0.763, + 0.48 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.075, + 0.5, + 0.892, + 0.592 + ], + "angle": 0, + "content": "Figure 5: (left) Distribution of 1000 generated future motions, when conditioning on a normal past motion (top) and on an abnormal one (bottom). 2-dimensional projections are estimated via t-SNE [45]. Note how the true future motion (red dot) lies within a main distribution mode in the case of normality, but it lies in a marginal region for abnormality. (right) Plot of the diversity ratio \\( rF \\) [28], measuring the diversity of the generated future motions for normal and anomalous conditioning pasts. Moving along the \\( x \\)-axis, with more generated motion, the \\( rF \\) measures grow (MoCoDAD generates multimodal diverse motion) but they remain comparable (generating from normal and abnormal is anyhow multimodal)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.618, + 0.47, + 0.648 + ], + "angle": 0, + "content": "generating with abnormal conditioning. The performance saturates for \\( m > 50 \\)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.663, + 0.218, + 0.68 + ], + "angle": 0, + "content": "5.3. Conditioning" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.688, + 0.47, + 0.748 + ], + "angle": 0, + "content": "Here, we provide the reader with the performances of our method with different encoding approaches of the past (i.e., how the past motion is provided to the model) from which the future is generated (see Table 3)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.75, + 0.471, + 0.902 + ], + "angle": 0, + "content": "As illustrated in Sec. 3.2, Input Concatenation concatenates the clean past frames to the corrupted part of each motion sample and feeds it directly to the denoising module. This strategy surpasses recent baselines (cf. Table 1) with AUC scores of 64.96 and 65.20 on UBnormal and HRUBnormal, respectively. We deem this strategy suboptimal since it does not allow the past motion conditioning to be injected at each layer (as with the embedding strategies), and, thus force the network to \"remember\" this information rather than focusing on the denoising of the future." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.618, + 0.892, + 0.709 + ], + "angle": 0, + "content": "The E2E-embedding strategy encodes the motion history in the clean past frames and provides it to the latent layers of the denoising model, but it does not improve performance. We believe this happens because the learned embedding is not supervised, and it may not be representative enough of the original motion." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.71, + 0.892, + 0.817 + ], + "angle": 0, + "content": "AE-embedding accounts for the best performances. It couples the encoder \\( E \\) with a symmetric decoder \\( D \\) and trains the whole model with an auxiliary loss \\( \\mathcal{L}_{rec} \\) which supervises the reconstruction of the first part of the motion (cf. Sec. 3.2). This past encoding strategy reaches 68.3 and 68.4 on UBnormal and HR-UBnormal, outperforming SoA techniques." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.831, + 0.625, + 0.847 + ], + "angle": 0, + "content": "5.4. Proxy Task" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.902 + ], + "angle": 0, + "content": "In Table 4 we assess the effectiveness of the forecasting proxy task (cf. Sec. 3.1). To this end, instead of limiting ourselves towards a rigid past-future split of poses, we ex" + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "10325" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.089, + 0.47, + 0.12 + ], + "angle": 0, + "content": "Table 3: Ablation study on the different methods for integrating conditioning information into the model." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.131, + 0.47, + 0.201 + ], + "angle": 0, + "content": "
HR-UBnormalUBnormal
Input Concatenation65.265.0
E2E-embedding64.464.2
AE-embedding (MoCoDAD)68.468.3
" + }, + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.214, + 0.468, + 0.245 + ], + "angle": 0, + "content": "Table 4: Ablation study on the type of conditioning information to feed into the model to generate the missing frame." + }, + { + "type": "table", + "bbox": [ + 0.082, + 0.256, + 0.468, + 0.329 + ], + "angle": 0, + "content": "
HR-UBnormalUBnormal
Random Imputation65.265.1
In-between Imputation65.765.7
Forecasting (MoCoDAD)68.468.3
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.354, + 0.47, + 0.626 + ], + "angle": 0, + "content": "pllore two additional proxy tasks: i.e., in-between and random imputation. For in-between imputation, we corrupt the central \\( N - k \\) poses and reserve the start and end of the sequence to condition the diffusion. For random imputation, we randomly select \\( N - k \\) poses out of the full motion and corrupt them; the rest of the sequence is used for conditioning. Table 4 shows that random imputation is the worst proxy task (AUC of 65.10 and 65.21 for UBnormal and HR-UBnormal, respectively). Randomly splitting the sequence into two parts introduces inter-pose temporal gaps. Hence, we believe that this makes the reconstruction of noncontiguous motion more cumbersome. In-between imputation reaches an AUC of 65.65 and 65.72, respectively. We think that \"stitching\" the central motion to its endpoints is an easier task leading both normal and abnormal motions to be equally well reconstructed. Finally, forecasting is the best-performing proxy task with an AUC of 68.3 and 68.4 for UBnormal and HR-UBnormal." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.636, + 0.212, + 0.652 + ], + "angle": 0, + "content": "5.5. Latent space" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.468, + 0.734 + ], + "angle": 0, + "content": "Diffusion on latent space has been adopted to improve computational efficiency in various domains [33]. MLD [49] is one of the most recent works in motion forecasting that applies the diffusion process directly in the latent space." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Here, we propose an analysis that assesses the performance of MoCoDAD's diffusion process in the latent space. Thus, we propose two latent variations of MoCoDAD: MoCoDAD+MLD and Latent-MoCoDAD. For MoCoDAD+MLD we use a VAE to produce a latent representation \\( Z \\in \\mathbb{R}^d \\) of the uncorrupted sequence \\( X^{k + 1:N} \\) and we perform the diffusion process on \\( Z \\) with the transformer-based denoising model as described in [49]. For Latent-MoCoDAD we rely on an STS-VAE to learn \\( Z \\) given \\( X^{k + 1:N} \\) and use the diffusion process, proposed in Sec. 3.2, on \\( Z \\). For both these variants, we feed the cor" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.089, + 0.892, + 0.121 + ], + "angle": 0, + "content": "Table 5: AUC-ROC performance of diffusion on latent vs original space." + }, + { + "type": "table", + "bbox": [ + 0.513, + 0.131, + 0.88, + 0.21 + ], + "angle": 0, + "content": "
HR-UBnormalUBnormal
MoCoDAD+MLD58.158.1
Latent-MoCoDAD62.662.5
MoCoDAD68.468.3
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.236, + 0.892, + 0.297 + ], + "angle": 0, + "content": "rupted \\( Z \\) to an MLP with conditioning signal \\( h + \\tau_{\\theta}(t) \\) to reverse the diffusion and leave the conditioning component as is in the original MoCoDAD (i.e., encoding of history poses \\( X^{1:k} \\))." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.298, + 0.892, + 0.388 + ], + "angle": 0, + "content": "Although the described variants can be trained end-to-end, we achieved the best performances by pre-training the autoencoder and training the diffusion module in the learned latent space keeping the autoencoder module frozen. We set the latent space dimension to \\( d = 16 \\) and the MLP blocks to (16,8,16) interleaved with ReLU activations." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.39, + 0.892, + 0.526 + ], + "angle": 0, + "content": "Table 5 illustrates the performances in terms of AUC-ROC of MoCoDAD and its latent variants on UBnormal and HR-UBnormal. Notice that the latent variants underperform w.r.t. the original MoCoDAD. We suspect that diffusion on latent spaces is not effective in skeleton-based VAD due to the lightweight encoding of the skeletons. This adheres with the literature since also MLD [49] shows that applying diffusion in the latent space underperforms w.r.t. the original proposal of the model." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.544, + 0.619, + 0.559 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.57, + 0.892, + 0.78 + ], + "angle": 0, + "content": "We have presented a novel approach that models and exploits the diversity of normal and abnormal motions. In the former case, the forecast motions are multi-modal and pertinent to the observed portion of the sequence, as the model understands the underlying action. In the case of abnormal, the forecast motions do not show a bias towards the true future as the model does not expect any obvious outcome. Motivated by the improved mode coverage, this work has been the first to take advantage of probabilistic diffusion models for video anomaly detection, including a thorough analysis of the main design choices. MoCoDAD sets a novel SoA among OCC techniques, and it catches up with supervised techniques while not using anomaly training labels." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.799, + 0.667, + 0.816 + ], + "angle": 0, + "content": "Acknowledgements" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.825, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This work was carried out while Stefano D'Arrigo was enrolled in the Italian National Doctorate on Artificial Intelligence run by Sapienza University of Rome. We thank DsTech S.r.l. and the PNRR MUR project PE0000013-FAIR for partially funding this study." + }, + { + "type": "page_number", + "bbox": [ + 0.481, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "10326" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.115, + 0.47, + 0.212 + ], + "angle": 0, + "content": "[1] Andra Acsintoae, Andrei Florescu, Mariana-Iuliana Georgescu, Tudor Mare, Paul Sumedrea, Radu Tudor Ionescu, Fahad Shahbaz Khan, and Mubarak Shah. Ubnormal: New benchmark for supervised open-set video anomaly detection. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 20143-20153, 2022." + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.213, + 0.471, + 0.268 + ], + "angle": 0, + "content": "[2] Emre Aksan, Manuel Kaufmann, Peng Cao, and Otmar Hilliges. 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Leading OCC techniques constrain the latent representations of normal1 motions to limited volumes and detect as abnormal anything outside, which accounts satisfactorily for the openset'ness of anomalies. But normalcy shares the same openset'ness property since humans can perform the same action in several ways, which the leading techniques neglect. + +We propose a novel generative model for video anomaly detection (VAD), which assumes that both normality and abnormality are multimodal. We consider skeletal representations and leverage state-of-the-art diffusion probabilistic models to generate multimodal future human poses. We contribute a novel conditioning on the past motion of people and exploit the improved mode coverage capabilities of diffusion processes to generate different-but-plausible future motions. Upon the statistical aggregation of future modes, an anomaly is detected when the generated set of motions is not pertinent to the actual future. We validate our model on 4 established benchmarks: UBnormal, HR-UBnormal, HR-STC, and HR-Avenue, with extensive experiments surpassing state-of-the-art results. + +# 1. Introduction + +Video Anomaly Detection (VAD) is a crucial task in computer vision and security applications. It enables early detection of unusual or abnormal events in videos, such as accidents, illnesses, or people's behavior which may threaten public safety [41]. However, several aspects make VAD a challenging task. Firstly, the definition of anomaly + +![](images/9fc03492ac8e2f9a9a62d7c9619413480442f22f4a2046703b79ee9770b59c05.jpg) +Figure 1: MoCoDAD detects anomalies by synthesizing and statistically aggregating multi-modal future motions, conditioned on past poses (frames on the left). Red (top) and green (bottom) distributions represent examples of anomaly and normality generations (2d mapped via t-SNE). Within the distribution modes (dashed-contoured), the red dots are the actual true futures corresponding to the conditioning past frames. In the case of normality, the true future lies within a main distribution mode, and the generated predictions are pertinent. In the case of abnormality, the true future lies in the tail of the distribution modes, which yields poorer predictions, highlighting anomalies. + +is highly subjective and varies depending on the context and application, making it difficult to define it universally. Secondly, anomalies are intrinsically rare. To account for data scarcity, models generally learn from regular samples only (also known as One Class Classification - OCC) or have to + +cope with the data imbalance. Thirdly, anomaly detection is intrinsically an openset problem, and modeling anomalies needs to account for diversity beyond the training set. + +An "ideal" model for anomaly detection should consider that there are infinitely many anomalous and non-anomalous ways of performing an action. Current state-of-the-art OCC techniques [9, 24, 25, 26] fail to address this issue. Indeed, they focus on learning either a single reconstruction or prediction of the input, or deriving a latent representation of normal actions, thereby constraining them to a limited latent volume. This last approach successfully accounts for the openset'ness of anomalies, i.e., anything mapped outside the normality region is considered abnormal. However, forcing normality into constrained volumes may not work for diverse-but-still-normal behaviors, i.e., OCC misclassifies as anomalous those not fitting in the volume. + +We propose Motion Conditioned Diffusion Anomaly Detection - hereafter MoCoDAD - a novel generative model for VAD, which assumes that both normality and abnormality are multimodal2. Given a motion sequence, be it normal or anomalous, the sequence is split and the later (future) frames are corrupted to become random noise. Conditioned on the first (past) clean input frames, MoCoDAD synthesizes multimodal reconstructions of the corrupted frames. MoCoDAD discerns normality from anomaly by comparing the multimodal distributions. In the case of normality, the generated motions are diverse but pertinent, i.e. they are biased towards the true uncorrupted frames. In the case of abnormality, the synthesized motion is also diverse, but it lacks pertinence, as shown in Fig. 1 and discussed in Sec. 5. + +MoCoDAD is the first diffusion-based technique for video anomaly detection. We are inspired by Denoising Diffusion Probabilistic Models (DDPMs) [40, 14], state-of-the-art, among others, in image synthesis [31, 30, 33], motion synthesis [43, 49], and 3D generation tasks [53]. DDPMs are selected for their improved mode coverage [48], i.e. they generate diverse multimodal motions, which MoCoDAD statistically aggregates (see the respective ablative study in Sec. 5). + +Besides multimodality, a crucial aspect of MoCoDAD is the choice of the conditioning strategy to guide the synthesis. We consider human motion as skeletal representations and propose corrupting the body joint coordinates at each frame by displacing them with random translations. Conditioning refers to the process that provides the model with the uncorrupted first part of the motion sequence (past) to guide the denoising of the corrupted second part (future). In this study, we compare three modeling choices to find the most + +1To avoid ambiguity, in this work, the term "normal" is the contrary of anomalous, not the synonym of "Gaussian". Normal refers to "normality" (or "normalcy"). Anomalous/abnormal refers to abnormality/anomaly. + +2In this work, multimodal refers to distributions with multiple modes, not to mixing modalities (video, audio, text, etc.) + +suitable conditioning strategy. We experiment with (1) directly feeding the denoising module with the concatenation of the uncorrupted poses with the displaced sequence [35]. For the other two strategies, we get a latent representation of the input (via (2) an encoding module and (3) an autoencoder) and feed the network with this learned representation (cf. Sec. 3.2). The third strategy works best (cf. Sec. 5.3). + +We evaluate MoCoDAD on three challenging benchmarks of human-related anomalies, namely, HR-UBnormal [1, 9], HR-ShanghaiTech Campus [23, 26] (HR-STC), and HR-Avenue [22, 26], and on the most recent VAD dataset UBnormal [1]. MoCoDAD achieves state-of-the-art (SoA) performance on all four datasets, which demonstrates the effectiveness of modeling multimodality for normal and abnormal motions. Notably, by not using appearance, MoCoDAD benefits increased privacy protection (no visual facial nor body features) and better computational efficiency, thanks to the lightweight body kinematic representations. We summarize our contributions as follows: + +- A novel generative VAD model based on comparing the multimodality of normal and abnormal motion generations; +- The first probabilistic diffusion-based approach for VAD, which fully exploits the enhanced modecoverage capabilities of diffusive probabilistic models; +- A novel motion-based conditioning on the clean input sequence to steer the synthesis towards diverse pertinent motion in the case of normality; +A thorough validation on UBnormal, HR-UBnormal, HR-STC, and HR-Avenue benchmarks where we outperform the SoA by $5.1\%$ , $4.4\%$ , $5\%$ , $8\%$ , respectively. + +# 2. Related Work + +Previous work relates to ours from two main perspectives: Video Anomaly Detection methods (see Sec. 2.1), and diffusion models for motion synthesis (see Sec. 2.2). + +# 2.1. Video Anomaly Detection Techniques + +Pioneer works analyze the trajectory of the agents in the frames to discriminate those distant from normality [5, 16, 19]. Within recent literature, two major trends can be identified: latent- and reconstruction-based methods. VAD techniques also vary based on the type of input data they use, such as videos or human skeletal pose motions. MoCoDAD, as all the VAD works presented in this section, adheres to the OCC protocol, which simulates the scarcity of anomalies in real-world scenarios [18]. + +Latent-based VAD methods identify abnormality according to a score extracted from a learned latent space whereby normality is supposedly mapped into a constrained volume, and anomalies are those latents lying outside, with a larger + +score (see [34, 38, 42, 46] for an overview of latent-based AD). Sabokrou et al. [36] propose a two-staged cascade of deep neural networks. First, they employ a stack of autoencoders that detects points of interest (POIs) while excluding irrelevant patches (e.g., background). Second, they identify anomalies by densely extracting and modeling discriminative patches at POIs. Notice that this work constrains normality to belong to a single mode and anomalies outside, thus, addressing the openset'ness of anomalies, but it hampers the multimodal and diversity [51] aspect of normal motions. Contrarily, our work considers the multimodality of normal and abnormal motions. + +Notably, Nguyen et al. [27] propose an image-based technique exploring multimodal anomaly detection via multi-headed VAEs. However, considering a fixed number of modes for reality amends multimodality only partially, as it misses to unleash its openset'ness. Differently, we adopt diffusion models for their improved mode coverage and generate multiple futures, not being constrained on a fixed number of heads (see Sec. 5). + +Reconstruction-based VAD methods consider the original metric space of the input and leverage reconstruction as the proxy task to derive an anomaly score. These models are trained to encode and reconstruct the input from normal events, producing larger errors on anomalies not seen during training. [7, 13, 52] use sequences of frames and feed them to convolutional autoencoders. Gong et al. [12] "memorize" the most representative normal poses to discriminate new input samples. Liu et al. [21] tackle intensity and gradient loss, optical flow, and adversarial training. Luo et al. [23] use stacked RNNs with temporally-coherent sparse coding enforcing similar neighboring frames to be encoded with similar reconstruction coefficients. Barbalau et al. [3] builds upon [10] and integrates the reconstruction of the input frames, via multi-headed attention, into a multitask learning framework. Besides [10, 21], all works rely on a single reconstruction proxy task via non-variational architectures that learn discrete manifolds. However, normality and abnormality are multimodal and diverse, making it hard for these techniques to have an exact match (reconstruction) over the GT. Additionally, GANs used in [21] suffer from mode collapse [44] lacking to represent the multimodality of reality. Similarly to [27], [3] can represent only a fixed number of modalities, which does represent the openset'ness of reality. MoCoDAD is a reconstruction-based approach and leverages diffusion processes [8] to account for the openset'ness of normalcy and anomalies in terms of pertinence to the GT. + +Skeleton-based VAD methods exploit compact spatiotemporal skeletal representations of human motion instead of raw video frames. Morais et al. [26] use two GRU autoencoder branches to account for the global and local decomposition of the skeleton in a particular frame. Luo et + +al. [24] exploit stacked layers of ST-GCN [50] to accumulate joint information over the spatio-temporal dimensions of the frame and predict joints in the future. However, [50] uses a fixed adjacency matrix, depicting joint connections, for all ST-GCN layers, which hinders the exploration of intra-frame and intra-joint relationships, two factors that play a crucial role in improving the encoding of spatio-temporal features [39]. Markovitz et al. [25] utilize the encoder of an ST-GCN autoencoder to embed spacetime skeletons into a latent vector. This vector is then fed to an end-to-end trainable deep-embedded clustering procedure which produces $k$ clusters representing the multimodality of normalcy and anomalies. Flaborea et al. [9] propose COSKAD and force the normal instances into the same latent region driving the distances to a common center. MoCoDAD is also a skeleton-based approach that mitigates the choice of $k$ a priori to cover the multimodality of reality. + +# 2.2. Diffusion Models + +Diffusion models have marked a revolution in generative tasks such as image and video synthesis [35, 43, 49], but they have not been employed for VAD. Saadatnejad et al. [35] propose a two-step framework based on temporal cascaded diffusion (TCD). First, they denoise imperfect observation sequences and, then, improve the predictions of the (frozen) model on repaired frames. Tevet et al. [43] use a transformer encoder to learn arbitrary length motions [2, 29] coherent with a particular conditioning signal $c$ . They experiment with constrained synthesis where $c$ is a text prompt (i.e., text-to-motion) or a specific action class (i.e., action-to-motion) and unconstrained synthesis where $c$ is not specified. Chen et al. [49] design a transformer-based VAE [29] to learn a representative latent space for human motion sequences. They apply a diffusion model in this latent space to generate vivid motion sequences while obeying specific conditions similar to [43]. Differently, MoCoDAD is a diffusion-based model that uses conditioning over a portion of the input (e.g., previous frames condition the generation of future ones). + +Wyatt et al. [47] propose AnoDDPM, a diffusion model on images, which does not require the entire Markov chain (noise/denoise) to take place. They use decaying octaves of simplex noising functions to distinguish the corruption rate of low-frequency components from high-frequency ones. However, they add and remove noise without conditioning, identifying anomalies when noise removal diverges from the input. Differently, MoCoDAD is based on generating and comparing multimodal motions against the GT in terms of pertinence. Our proposed model is the first to exploit the multimodal generative and improved mode-coverage capabilities of diffusive techniques, via forecasting tasks, further to being first in adopting them for detecting video anomalies. Hence, to transfer DDPMs from video-based + +Anomaly Detection to skeleton-based VAD we rely on a U-Net-shaped stack of STS-GCN [39, 37] layers, which includes the spatio-temporal aspects of joints in sequences of human poses. + +# 3. Methodology + +MoCoDAD learns to reconstruct the later (future) corrupted poses by conditioning on the first (past) poses. Sec. 3.1 describes the training diffusion denoising process, how it generates multimodal reconstructions, and statistically aggregates them at inference to detect anomalies. Sec. 3.2 details conditioning on past frames, and Sec. 3.3 describes the architecture of MoCoDAD. For the sake of completeness, in Sec. A.1 of the Supplementary, we present preliminary concepts of DDPMs. + +# 3.1. Diffusion on Trajectories + +Training We define a diffusion technique that learns to reconstruct corrupted future motion sequences conditioned on clean past ones. + +Let $X_{a} = \{x_{a}^{1},\ldots ,x_{a}^{N}\}$ be a sequence of $N$ timecontiguous poses belonging to a single actor $a$ . Since our model considers one actor at a time, we use $X = \{x^{1},\dots,x^{N}\}$ for notation simplicity. Each pose $x^{i}$ can be seen as a graph $x^{i} = (J,A)$ where $J$ represents the set of joints, and $A$ is the adjacency matrix representing the joint connections. Notice that each joint is attributed with a set of spatial coordinates in $\mathbb{R}^C$ , hence $x^{i}\in \mathbb{R}^{|J|\times C}$ , and $X\in \mathbb{R}^{N\times |J|\times C}$ . Here, we use $C = 2$ as the person's pose is extracted from images at each frame. + +We divide $X$ into two parts: the past $X^{1:k}$ and the future sequence of poses $X^{k+1:N}$ with $k \in \{1, \dots, N\}$ . + +During the forward process $q$ , we corrupt the coordinates of the joints by adding random translation noise. We sample a random displacement map $\varepsilon^{k + 1:N} \in \mathbb{R}^{(N - k) \times |J| \times C}$ from a distribution $\mathcal{N}(0, \mathbf{I})$ and add it to $X^{k + 1:N}$ to randomly translate the position of its nodes. + +The magnitude of the added displacement depends on a variance scheduler $\beta_{t} \in (0,1)$ and a diffusion timestep $t \sim \mathcal{U}_{[1,T]}$ . As a result, $q$ increasingly corrupts the joints $x^{i}$ at each diffusion timestep $t$ (i.e., $x_{t=1}^{i} \to \dots \to x_{t=T}^{i}$ ) making $x_{t=T}^{i}$ indistinguishable from a pose with randomly sampled joints' spatial coordinates. + +The reverse process $p_{\theta}$ unrolls the corruption, estimating the spatial displacement map $\varepsilon^{k + 1:N}$ via a U-Net-like architecture $\varepsilon_{\theta}$ (see Sec. 3.3 for more details). To achieve an approximation of $\varepsilon^{k + 1:N}$ , we train the network conditioned on the diffusion timestep $t$ (embedded through an MLP $\tau_{\theta}$ ) and the embedding $h$ of the previous trajectory $X^{1:k}$ . + +In Eq. 1, similarly to [33], we define the displacement estimation objective4. + +$$ +\mathcal {L} _ {\text {d i s p}} = \mathbb {E} _ {t, X, \varepsilon} \left[ \left| \left| \varepsilon - \varepsilon_ {\theta} \left(X _ {t}, t, h\right) \right| \right| \right] \tag {1} +$$ + +Inspired by [11], we smooth $\mathcal{L}_{disp}$ as follows: + +$$ +\mathcal {L} _ {\text {s m o o t h}} = \left\{ \begin{array}{l l} 0. 5 \cdot \left(\mathcal {L} _ {\text {d i s p}}\right) ^ {2} & \text {i f} \left| \mathcal {L} _ {\text {d i s p}} \right| < 1 \\ \left| \mathcal {L} _ {\text {d i s p}} \right| - 0. 5 & \text {o t h e r w i s e} \end{array} \right. \tag {2} +$$ + +Inference At inference time, MoCoDAD generates multimodal future sequences of poses from random displacement maps, conditioned on the past frames, then aggregates them statistically to detect anomalies. + +We sample a random displacement $z \sim \mathcal{N}(0, \mathbf{I})$ and consider it the starting point of the synthesis process that generates a future human motion via Eq. 3. + +$$ +X _ {t - 1} = \frac {1}{\sqrt {\alpha_ {t}}} \left(X _ {t} - \frac {1 - \alpha_ {t}}{\sqrt {1 - \alpha_ {t}}} \varepsilon_ {\theta} \left(X _ {t}, t, h\right)\right) + z \sqrt {\beta_ {t}} \tag {3} +$$ + +Note the motion conditioning $h$ , encoding the past $k$ frames. We generate $m$ diverse future pose trajectories $Z_{1},\ldots ,Z_{m}$ . For each $Z_{i}$ , we compute the reconstruction error via the smoothed loss $s_i = \mathcal{L}_{smooth}(|X - Z_i|)$ used in training (cf. Eq. 2). + +We aggregate all the scores from the generations $S = \{s_1, \ldots, s_m\}$ to distill a single anomaly score for that sequence. This score is subsequently assigned to the corresponding frames to assess their level of anomaly. In scenarios where multiple actors occupy the same frames, we assign the average anomaly score to those frames. See the Supplementary for a detailed description. We explore different strategies for distilling the anomaly score from $S$ : (1) the diversity between the normal and anomalous generations and (2) aggregation statistics. To account for diversity, we consider the diversity metric $rF = \mathrm{mean}(\mathcal{L}_{smooth}) / \min (\mathcal{L}_{smooth})$ introduced by [6, 28]. Diversity stems from testing whether anomalous generations are more diverse than normals, but the diversity score fails to detect anomalies, nearly dropping to random chance. We explain this by normalcy and anomaly having a similar degree of diversity, as we experimentally validate in Sec. 5.1. + +We consider as aggregation statistics the mean, quantile robust statistics including the median, as well as maximum and minimum selectors, in terms of $\mathcal{L}_{smooth}$ distances between the $m$ generated and the GT future motion. Our analysis highlights that the minimum distance is the best on average. This reinforces the original hypothesis that normality-conditioned generated motions are as diverse as abnormal-conditioned ones but more biased to the actual + +![](images/67f5d381ca28fc7f2fc1cd2e74788e7f92736d4485e6c7af37128b48eb306901.jpg) +Figure 2: Overview of the proposed MoCoDAD. A sequence of $N$ skeletal motions ( $N = 6$ in the example) is split into past (top-right $X^{1:k}$ frames, $k = 3$ in the example) and future (top-left $X^{k+1:N}$ frames). During training, the Forward Diffusion block adds noise to the future frames, shifting each joint by a random vector displacement of varying intensity (increasing with the diffusion timestep $t$ ). Then the Reverse Diffusion learns to estimate the noise. A key aspect of MoCoDAD is the conditioning, i.e. how to encode the past clean $k$ frames and guide the synthesis of relevant futures. + +![](images/796f0fb32210b3e8c34b860574485e54b3b67c412ecf16027e2099c95d316b94.jpg) +Figure 3: Comparison of the three conditioning strategies. + +motion, thus more likely to generate samples close to it. See Sec. 5.2 for the experimental evaluation. + +# 3.2. Motion Conditioning for multimodal Pose Forecasting + +The choice of the conditioning strategy is a crucial factor for diffusion models, as it determines how the conditioning information is fed into the network, and it directly affects the quality of the outputs. In this work, we propose a thorough examination of different strategies for feeding the diffusion models with the conditioning information. + +We identify three different modeling choices for conditioning the diffusion, illustrated in Fig. 3, i.e., input concatenation, $E2E$ -embedding, and $AE$ -embedding. Input concatenation refers to conditioning with a portion of the raw input motion. Here, we keep the past sequence of poses $X^{1:k}$ (the conditioning signal) uncorrupted and pretend it + +to the corrupted future sequence $X_{t}^{k + 1:N}$ . Input concatenation has been explored in previous work for pose forecasting reaching SoA performances in [35]. + +Both embedding choices refer to passing the conditioning past frames through an encoder $E$ , then providing them to all latent layers of the denoising model (cf. incoming vertical arrows into the orange layers in Fig. 2). Here, $E$ is a GCN [39] and it encodes sequences of poses $X^{1:k}$ into the representation $h = E(X^{1:k})$ . In the case of $E2E$ -embedding, $E$ is jointly learned with the rest of the architecture, leveraging the training $\mathcal{L}_{\text{smooth}}$ loss. The $AE$ -embedding adds an auxiliary reconstruction loss $\mathcal{L}_{\text{rec}}$ to support training $E$ , as it tasks a decoding network $D$ to reconstruct the conditioning past frames according to the following loss function: + +$$ +\mathcal {L} _ {r e c} = \left| \left| D (E (X ^ {1: k})) - X ^ {1: k} \right| \right| _ {2} ^ {2} \tag {4} +$$ + +In the case of $AE$ -embedding, the auxiliary is summed to the main loss, resulting in the following total loss: + +$$ +\mathcal {L} _ {t o t} = \lambda_ {1} \mathcal {L} _ {\text {s m o o t h}} + \lambda_ {2} \mathcal {L} _ {\text {r e c}} \tag {5} +$$ + +where $\lambda_1, \lambda_2 \in [0, 1]$ account for the contribution of each loss function respectively. Lastly, since DDPMs benefit from being conditioned on the timestep $t$ , we add the embedding $\tau_{\theta}(t)$ to the latent $h$ and feed the resulting motion-temporal signal to each layer of our network $\varepsilon_{\theta}$ [43]. + +Table 1: Comparison of MoCoDAD against SoA in terms of AUC on the three Human-Related datasets (i.e., HR-STC, HR-Avenue and HR-UBnormal) and UBnormal. OCC skeleton-based techniques are marked with a $*$ . + +
HR-STCHR-AvenueHR-UBnormalUBnormal
Conv-AE [13]CVPR '1669.884.8--
Pred [21]CVPR '1872.786.2--
MPED-RNN [26] *CVPR '1975.486.361.260.6
GEPC [25] *CVPR '2074.858.155.253.4
Multi-timescale Prediction [32] *WACV '2077.088.3--
Normal Graph [24]Neurocomputing '2176.587.3--
PoseCVAE [15] *ICPR '2175.787.8--
BiPOCO [17] *Arxiv '2274.987.052.350.7
STGCAE-LSTM [20] *Neurocomputing '2277.286.3--
SSMTL++ [3]CVIU '23---62.1
COSKAD [9] *Arxiv '2377.187.865.565.0
MoCoDAD *77.689.068.468.3
+ +The results of evaluation are discussed in Sec. 5.3, whereby applying an AE-embedding conditioning on $X^{1:k}$ emerges with results beyond the SoA. + +# 3.3. Architecture Description + +Fig. 2 illustrates the architecture of MoCoDAD. We distinguish two main blocks: a conditioning auto-encoder for the past motion, $X^{1:k}$ , and a denoising model for $X^{k+1:N}$ . The main diffusion model architecture is the neural network, represented with orange blocks, tasked with estimating the corrupting noise in the input motion, thus reconstructing the actual future motion. As done in [47], we rely on a U-Net like architecture. Our skeletal-motion diffusion network progressively contracts and then expands (rebuilds) the spatial dimension of the input sequence of poses. To account for the temporal dimension of the input sequences, we build the U-Net with space-time separable GCN (STSGCN) layers proposed in [39]. The conditioning autoencoder relies on STS-GCN to reconstruct the past motion and embed it into a latent space used to condition the diffusion. + +In detail, the U-Net takes in input $X^{k + 1:N}$ and a motion-temporal conditioning signal $h + \tau_{\theta}(t)$ which provides the network with the diffusion timestep and the encoded past-motion information. Furthermore, to align the dimensionality of this conditioning signal with that of the network's layers, the former is fed into an embedding layer projecting it to the correct vector space. This embedded conditioning signal is then fed to each STS-GCN layer. The contracting process of the U-Net progressively aggregates the joints of the poses (i.e., $\mathbb{R}^J \to \mathbb{R}^d$ s.t. $d \leq J$ ) while the expansion part "deconvolutes" the joints' vector space until it reaches the original space $\mathbb{R}^J$ . Residual connections are present between specular layers. + +# 4. Experiments + +Here we compare MoCoDAD with SoA approaches and provide a detailed discussion on the achieved performances. In Sec. D of the Supplementary, we provide the reader with a thorough description of the implementation details. + +As done in [1, 3, 9, 10, 21, 24, 25, 26], we report the Receiver Operating Characteristic Area Under the Curve (ROC-AUC) to assess the quality of MoCoDAD predictions on UBnormal [1], and the HR filtered [9] versions of STC [23], Avenue [22], and UBnormal. + +# 4.1. Datasets + +We use the UBnormal dataset [1] which contains 29 scenes synthesized from 2D natural images with the Cinema4D software. Each scene appears in 19 clips featuring both normal and abnormal events. The split into train, validation, and test adheres to the open-set policy, providing disjoint sets of types of anomalies for training, validation, and test; in accordance with the OCC setting, we only include normal actions for the training set. We also consider the processed poses and the human-related (HR) filtering of the dataset proposed by [9]. To compare with other state-of-the-art methods, we also experiment on the HR versions of the ShanghaiTech Campus (STC) [23] and the CUHK Avenue [22] datasets introduced by [26]. The former includes 13 scenes recorded with different cameras, for a total of about 300,000 frames, and 101 testing clips with 130 anomalous events. The latter consists of 16 training videos and 21 testing videos with a total of 47 anomalous events. + +# 4.2. Comparison with state-of-the-art + +Leading OCC techniques. We compare against SoA OCC techniques. Among these, MPED-RNN [26] combines the reconstruction and prediction errors of a two-branches-RNN to spot anomalies. Normal Graph [24] uses spatial + +Table 2: Comparison of MoCoDAD against supervised (†) and weakly supervised (‡) methods introduced in [1] in terms of AUC on the UBnormal dataset. + +
ParamsUBnormal
Sultani et al. [41] †-50.3
AED-SSMTL [10] †>80M61.3
TimeSformer [4] †121M68.5
AED-SSMTL [10] ‡>80M59.3
MoCoDAD142K68.3
+ +temporal GCNs (ST-GCN) to encode skeletal sequences. GEPC [25] encodes the input sequences with an STGCN, and clusters the embeddings in the latent space. Multi-timescale Prediction [32] encodes the observed input sequence and predicts future poses at different time scales through intermediate fully-connected layers. Both PoseCVAE [15] and BiPOCO [17] exploit a Conditioned Variational-Autoencoder to learn a posterior distribution of normal actions and use encoded past and future sequences to reconstruct the future one. The former uses an MLP-based architecture, while the latter is GRU-based. STGCAE-LSTM [20] reconstructs the past pose sequence and predicts the future one by an LSTM-based autoencoder. SSMTL++ [3] extends [10]; it replaces the convolutions with a transformer, changes the object detection backbone, and adds a few auxiliary proxy tasks. COSKAD [9] builds on STS-GCN to map the embeddings of normal poses into a narrow region in the latent space. + +Results. In Table 1, we compare MoCoDAD and SoA methods on the three HR datasets and on UBnormal. MoCoDAD achieves the best AUC score of 77.6, 89.0, and 68.4 on HR-STC, HR-Avenue, and HR-UBnormal, respectively. Our proposed method outperforms the current best [9], up to $4.4\%$ , demonstrating the importance of considering a range of different possible futures for each sample. Additionally, MoCoDAD achieves an AUC of 68.3 on the full UBnormal dataset, surpassing COSKAD by $5.1\%$ . This can be due to the improved sensitivity that emerges from our proposed model: considering more than a single deterministic future smooths the prediction of MoCoDAD avoiding penalizing excessively hard-still-normal samples which would be considered anomalous based on the reconstruction error of a deterministic model. + +Results VS. Supervised and Weakly Supervised methods Table 2 evaluates MoCoDAD with supervised and weakly supervised methods reported in [1]. Notice that, despite the absence of supervision or visual information, MoCoDAD is competitive with methods exploiting a stronger form of supervision. In detail, MoCoDAD (68.3) outperforms the weakly supervised method [10] (59.3) and other fully supervised methods and is competitive with [4] (68.5). Further, our approach only presents a fraction of the parameters of + +its competitors. Notably, MoCoDAD is $\sim 852\times$ smaller than the current best [4]. + +# 5. Discussion + +Here, we delve into a detailed discussion about the multimodal future generations (cf Sec. 5.1), the influence of the statistical aggregation of multiple generations and the normal Vs. anomalous conditioning (cf. Sec. 5.2), the effect of different conditioning strategies (cf. Sec. 3.2). Additionally, we discuss forecasting proxy tasks (Sec. 5.4) and analyze MoCoDAD's performances with the diffusion process applied to the latent space. (Sec. 5.5). + +# 5.1. Multimodality + +We question whether MoCoDAD can generate diverse multimodal motions and whether conditioning on normal or abnormal motions affects diversity. We provide an example of generated future motions in Fig. 5 (left), where we project the samples in 2D with t-SNE [45] for better visualization. Notice that both sets of generations have similar variance, showing that MoCoDAD produces diverse samples with both normal and abnormal conditioning sequences. Motions stemming from normal conditioning are biased toward the true future since they are mapped around it. Whereas, in the case of abnormal conditioning, the ground truth motion lies on the edge of the predictions' region, hence being correctly predicted with a lower chance. + +We also measure diversity, employing the $rF$ diversity metric from literature [6, 28]. We visualize the $rF$ trend when increasing the number of generations in Fig. 5 (right). If the generated motion had no diversity, e.g., when generating only once, the $rF$ would be equal to 1. Rather, the diversity ratio monotonically increases with the number of generations for both normal and abnormal cases, i.e., the more generated samples, the larger the empirical mode coverage and the diversity. We note that, following intuition, the diversity for abnormal cases grows slightly larger than for normal cases, but the $rF$ measures remain comparable. + +# 5.2. Statistical aggregations of generated motions + +We evaluate the anomaly detection performance when varying the number of generations $m$ and the aggregation strategy for the anomaly score $S$ (cf. Sec. 3.1). Fig. 4 (right) shows that the AUC positively correlates with the number of generated future motions for quantiles $Q < 0.5$ , while the correlation is negative for the mean estimate and $Q > 0.5$ . Such correlation can be better understood by looking at Fig. 4 (left), which depicts the average reconstruction error probability density function (PDF) for $m = 50$ : when conditioned on normal past motions, MoCoDAD produces generations which are centered around the true future and, thus, is more likely to yield lower error scores than when + +![](images/24c7754b04072608620527b568febf73daa222135851859bfa85f7374c89a7b0.jpg) +Figure 4: (left) Histograms of the reconstruction errors for 50 synthesized future motions, computed on the HR-UBnormal test set, for the case of conditioning on normal and abnormal past motions. (right) Correlation between the AUC scores and the number of generations, with each curve corresponding to a different aggregation statistic. + +![](images/3800d3f9bcfa80879e6e55aadd7b1ee51324ac9bf14acbaa4257d7e58a7d89b4.jpg) + +![](images/0be238cdf2bab952ddc55af1a4b8e651c4f8094c8b94187bccc28bb3fed9fbb5.jpg) +Figure 5: (left) Distribution of 1000 generated future motions, when conditioning on a normal past motion (top) and on an abnormal one (bottom). 2-dimensional projections are estimated via t-SNE [45]. Note how the true future motion (red dot) lies within a main distribution mode in the case of normality, but it lies in a marginal region for abnormality. (right) Plot of the diversity ratio $rF$ [28], measuring the diversity of the generated future motions for normal and anomalous conditioning pasts. Moving along the $x$ -axis, with more generated motion, the $rF$ measures grow (MoCoDAD generates multimodal diverse motion) but they remain comparable (generating from normal and abnormal is anyhow multimodal). + +![](images/dcefbd7c4da137c74fda5f6b47dc4796c6f59896fa1e769d4a2f3dad49828667.jpg) + +generating with abnormal conditioning. The performance saturates for $m > 50$ . + +# 5.3. Conditioning + +Here, we provide the reader with the performances of our method with different encoding approaches of the past (i.e., how the past motion is provided to the model) from which the future is generated (see Table 3). + +As illustrated in Sec. 3.2, Input Concatenation concatenates the clean past frames to the corrupted part of each motion sample and feeds it directly to the denoising module. This strategy surpasses recent baselines (cf. Table 1) with AUC scores of 64.96 and 65.20 on UBnormal and HRUBnormal, respectively. We deem this strategy suboptimal since it does not allow the past motion conditioning to be injected at each layer (as with the embedding strategies), and, thus force the network to "remember" this information rather than focusing on the denoising of the future. + +The E2E-embedding strategy encodes the motion history in the clean past frames and provides it to the latent layers of the denoising model, but it does not improve performance. We believe this happens because the learned embedding is not supervised, and it may not be representative enough of the original motion. + +AE-embedding accounts for the best performances. It couples the encoder $E$ with a symmetric decoder $D$ and trains the whole model with an auxiliary loss $\mathcal{L}_{rec}$ which supervises the reconstruction of the first part of the motion (cf. Sec. 3.2). This past encoding strategy reaches 68.3 and 68.4 on UBnormal and HR-UBnormal, outperforming SoA techniques. + +# 5.4. Proxy Task + +In Table 4 we assess the effectiveness of the forecasting proxy task (cf. Sec. 3.1). To this end, instead of limiting ourselves towards a rigid past-future split of poses, we ex + +Table 3: Ablation study on the different methods for integrating conditioning information into the model. + +
HR-UBnormalUBnormal
Input Concatenation65.265.0
E2E-embedding64.464.2
AE-embedding (MoCoDAD)68.468.3
+ +Table 4: Ablation study on the type of conditioning information to feed into the model to generate the missing frame. + +
HR-UBnormalUBnormal
Random Imputation65.265.1
In-between Imputation65.765.7
Forecasting (MoCoDAD)68.468.3
+ +pllore two additional proxy tasks: i.e., in-between and random imputation. For in-between imputation, we corrupt the central $N - k$ poses and reserve the start and end of the sequence to condition the diffusion. For random imputation, we randomly select $N - k$ poses out of the full motion and corrupt them; the rest of the sequence is used for conditioning. Table 4 shows that random imputation is the worst proxy task (AUC of 65.10 and 65.21 for UBnormal and HR-UBnormal, respectively). Randomly splitting the sequence into two parts introduces inter-pose temporal gaps. Hence, we believe that this makes the reconstruction of noncontiguous motion more cumbersome. In-between imputation reaches an AUC of 65.65 and 65.72, respectively. We think that "stitching" the central motion to its endpoints is an easier task leading both normal and abnormal motions to be equally well reconstructed. Finally, forecasting is the best-performing proxy task with an AUC of 68.3 and 68.4 for UBnormal and HR-UBnormal. + +# 5.5. Latent space + +Diffusion on latent space has been adopted to improve computational efficiency in various domains [33]. MLD [49] is one of the most recent works in motion forecasting that applies the diffusion process directly in the latent space. + +Here, we propose an analysis that assesses the performance of MoCoDAD's diffusion process in the latent space. Thus, we propose two latent variations of MoCoDAD: MoCoDAD+MLD and Latent-MoCoDAD. For MoCoDAD+MLD we use a VAE to produce a latent representation $Z \in \mathbb{R}^d$ of the uncorrupted sequence $X^{k + 1:N}$ and we perform the diffusion process on $Z$ with the transformer-based denoising model as described in [49]. For Latent-MoCoDAD we rely on an STS-VAE to learn $Z$ given $X^{k + 1:N}$ and use the diffusion process, proposed in Sec. 3.2, on $Z$ . For both these variants, we feed the cor + +Table 5: AUC-ROC performance of diffusion on latent vs original space. + +
HR-UBnormalUBnormal
MoCoDAD+MLD58.158.1
Latent-MoCoDAD62.662.5
MoCoDAD68.468.3
+ +rupted $Z$ to an MLP with conditioning signal $h + \tau_{\theta}(t)$ to reverse the diffusion and leave the conditioning component as is in the original MoCoDAD (i.e., encoding of history poses $X^{1:k}$ ). + +Although the described variants can be trained end-to-end, we achieved the best performances by pre-training the autoencoder and training the diffusion module in the learned latent space keeping the autoencoder module frozen. We set the latent space dimension to $d = 16$ and the MLP blocks to (16,8,16) interleaved with ReLU activations. + +Table 5 illustrates the performances in terms of AUC-ROC of MoCoDAD and its latent variants on UBnormal and HR-UBnormal. Notice that the latent variants underperform w.r.t. the original MoCoDAD. We suspect that diffusion on latent spaces is not effective in skeleton-based VAD due to the lightweight encoding of the skeletons. This adheres with the literature since also MLD [49] shows that applying diffusion in the latent space underperforms w.r.t. the original proposal of the model. + +# 6. Conclusion + +We have presented a novel approach that models and exploits the diversity of normal and abnormal motions. In the former case, the forecast motions are multi-modal and pertinent to the observed portion of the sequence, as the model understands the underlying action. In the case of abnormal, the forecast motions do not show a bias towards the true future as the model does not expect any obvious outcome. Motivated by the improved mode coverage, this work has been the first to take advantage of probabilistic diffusion models for video anomaly detection, including a thorough analysis of the main design choices. MoCoDAD sets a novel SoA among OCC techniques, and it catches up with supervised techniques while not using anomaly training labels. + +# Acknowledgements + +This work was carried out while Stefano D'Arrigo was enrolled in the Italian National Doctorate on Artificial Intelligence run by Sapienza University of Rome. We thank DsTech S.r.l. and the PNRR MUR project PE0000013-FAIR for partially funding this study. + +# References + +[1] Andra Acsintoae, Andrei Florescu, Mariana-Iuliana Georgescu, Tudor Mare, Paul Sumedrea, Radu Tudor Ionescu, Fahad Shahbaz Khan, and Mubarak Shah. Ubnormal: New benchmark for supervised open-set video anomaly detection. In Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, pages 20143-20153, 2022. +[2] Emre Aksan, Manuel Kaufmann, Peng Cao, and Otmar Hilliges. A spatio-temporal transformer for 3d human motion prediction. In 2021 International Conference on 3D Vision (3DV), pages 565-574. 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Leading OCC techniques constrain the latent representations of normal1 motions to limited volumes and detect as abnormal anything outside, which accounts satisfactorily for the openset'ness of anomalies. But normalcy shares the same openset'ness property since humans can perform the same action in several ways, which the leading techniques neglect." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 407, + 288, + 574 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 407, + 288, + 574 + ], + "spans": [ + { + "bbox": [ + 46, + 407, + 288, + 574 + ], + "type": "text", + "content": "We propose a novel generative model for video anomaly detection (VAD), which assumes that both normality and abnormality are multimodal. We consider skeletal representations and leverage state-of-the-art diffusion probabilistic models to generate multimodal future human poses. We contribute a novel conditioning on the past motion of people and exploit the improved mode coverage capabilities of diffusion processes to generate different-but-plausible future motions. Upon the statistical aggregation of future modes, an anomaly is detected when the generated set of motions is not pertinent to the actual future. We validate our model on 4 established benchmarks: UBnormal, HR-UBnormal, HR-STC, and HR-Avenue, with extensive experiments surpassing state-of-the-art results." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 599, + 128, + 612 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 599, + 128, + 612 + ], + "spans": [ + { + "bbox": [ + 47, + 599, + 128, + 612 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 620, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 620, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 620, + 287, + 693 + ], + "type": "text", + "content": "Video Anomaly Detection (VAD) is a crucial task in computer vision and security applications. It enables early detection of unusual or abnormal events in videos, such as accidents, illnesses, or people's behavior which may threaten public safety [41]. However, several aspects make VAD a challenging task. Firstly, the definition of anomaly" + } + ] + } + ], + "index": 10 + }, + { + "type": "image", + "bbox": [ + 306, + 270, + 547, + 469 + ], + "blocks": [ + { + "bbox": [ + 306, + 270, + 547, + 469 + ], + "lines": [ + { + "bbox": [ + 306, + 270, + 547, + 469 + ], + "spans": [ + { + "bbox": [ + 306, + 270, + 547, + 469 + ], + "type": "image", + "image_path": "9fc03492ac8e2f9a9a62d7c9619413480442f22f4a2046703b79ee9770b59c05.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 486, + 547, + 632 + ], + "lines": [ + { + "bbox": [ + 304, + 486, + 547, + 632 + ], + "spans": [ + { + "bbox": [ + 304, + 486, + 547, + 632 + ], + "type": "text", + "content": "Figure 1: MoCoDAD detects anomalies by synthesizing and statistically aggregating multi-modal future motions, conditioned on past poses (frames on the left). Red (top) and green (bottom) distributions represent examples of anomaly and normality generations (2d mapped via t-SNE). Within the distribution modes (dashed-contoured), the red dots are the actual true futures corresponding to the conditioning past frames. In the case of normality, the true future lies within a main distribution mode, and the generated predictions are pertinent. In the case of abnormality, the true future lies in the tail of the distribution modes, which yields poorer predictions, highlighting anomalies." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "image_caption" + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 547, + 715 + ], + "type": "text", + "content": "is highly subjective and varies depending on the context and application, making it difficult to define it universally. Secondly, anomalies are intrinsically rare. 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Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 702, + 156, + 714 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 702, + 156, + 714 + ], + "spans": [ + { + "bbox": [ + 58, + 702, + 156, + 714 + ], + "type": "text", + "content": "*Authors contributed equally." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "10318" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 108 + ], + "type": "text", + "content": "cope with the data imbalance. Thirdly, anomaly detection is intrinsically an openset problem, and modeling anomalies needs to account for diversity beyond the training set." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 108, + 287, + 274 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 108, + 287, + 274 + ], + "spans": [ + { + "bbox": [ + 46, + 108, + 287, + 274 + ], + "type": "text", + "content": "An \"ideal\" model for anomaly detection should consider that there are infinitely many anomalous and non-anomalous ways of performing an action. Current state-of-the-art OCC techniques [9, 24, 25, 26] fail to address this issue. Indeed, they focus on learning either a single reconstruction or prediction of the input, or deriving a latent representation of normal actions, thereby constraining them to a limited latent volume. This last approach successfully accounts for the openset'ness of anomalies, i.e., anything mapped outside the normality region is considered abnormal. However, forcing normality into constrained volumes may not work for diverse-but-still-normal behaviors, i.e., OCC misclassifies as anomalous those not fitting in the volume." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 275, + 288, + 443 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 275, + 288, + 443 + ], + "spans": [ + { + "bbox": [ + 46, + 275, + 288, + 443 + ], + "type": "text", + "content": "We propose Motion Conditioned Diffusion Anomaly Detection - hereafter MoCoDAD - a novel generative model for VAD, which assumes that both normality and abnormality are multimodal2. Given a motion sequence, be it normal or anomalous, the sequence is split and the later (future) frames are corrupted to become random noise. Conditioned on the first (past) clean input frames, MoCoDAD synthesizes multimodal reconstructions of the corrupted frames. MoCoDAD discerns normality from anomaly by comparing the multimodal distributions. In the case of normality, the generated motions are diverse but pertinent, i.e. they are biased towards the true uncorrupted frames. In the case of abnormality, the synthesized motion is also diverse, but it lacks pertinence, as shown in Fig. 1 and discussed in Sec. 5." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 443, + 287, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 443, + 287, + 550 + ], + "spans": [ + { + "bbox": [ + 46, + 443, + 287, + 550 + ], + "type": "text", + "content": "MoCoDAD is the first diffusion-based technique for video anomaly detection. We are inspired by Denoising Diffusion Probabilistic Models (DDPMs) [40, 14], state-of-the-art, among others, in image synthesis [31, 30, 33], motion synthesis [43, 49], and 3D generation tasks [53]. DDPMs are selected for their improved mode coverage [48], i.e. they generate diverse multimodal motions, which MoCoDAD statistically aggregates (see the respective ablative study in Sec. 5)." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 551, + 287, + 658 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 551, + 287, + 658 + ], + "spans": [ + { + "bbox": [ + 46, + 551, + 287, + 658 + ], + "type": "text", + "content": "Besides multimodality, a crucial aspect of MoCoDAD is the choice of the conditioning strategy to guide the synthesis. We consider human motion as skeletal representations and propose corrupting the body joint coordinates at each frame by displacing them with random translations. Conditioning refers to the process that provides the model with the uncorrupted first part of the motion sequence (past) to guide the denoising of the corrupted second part (future). In this study, we compare three modeling choices to find the most" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 664, + 287, + 693 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 664, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 46, + 664, + 287, + 693 + ], + "type": "text", + "content": "1To avoid ambiguity, in this work, the term \"normal\" is the contrary of anomalous, not the synonym of \"Gaussian\". Normal refers to \"normality\" (or \"normalcy\"). Anomalous/abnormal refers to abnormality/anomaly." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 693, + 287, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 693, + 287, + 712 + ], + "spans": [ + { + "bbox": [ + 46, + 693, + 287, + 712 + ], + "type": "text", + "content": "2In this work, multimodal refers to distributions with multiple modes, not to mixing modalities (video, audio, text, etc.)" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 156 + ], + "type": "text", + "content": "suitable conditioning strategy. We experiment with (1) directly feeding the denoising module with the concatenation of the uncorrupted poses with the displaced sequence [35]. For the other two strategies, we get a latent representation of the input (via (2) an encoding module and (3) an autoencoder) and feed the network with this learned representation (cf. Sec. 3.2). The third strategy works best (cf. Sec. 5.3)." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 156, + 546, + 310 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 156, + 546, + 310 + ], + "spans": [ + { + "bbox": [ + 304, + 156, + 546, + 310 + ], + "type": "text", + "content": "We evaluate MoCoDAD on three challenging benchmarks of human-related anomalies, namely, HR-UBnormal [1, 9], HR-ShanghaiTech Campus [23, 26] (HR-STC), and HR-Avenue [22, 26], and on the most recent VAD dataset UBnormal [1]. MoCoDAD achieves state-of-the-art (SoA) performance on all four datasets, which demonstrates the effectiveness of modeling multimodality for normal and abnormal motions. Notably, by not using appearance, MoCoDAD benefits increased privacy protection (no visual facial nor body features) and better computational efficiency, thanks to the lightweight body kinematic representations. We summarize our contributions as follows:" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 317, + 312, + 545, + 466 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 317, + 312, + 545, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 312, + 545, + 346 + ], + "spans": [ + { + "bbox": [ + 317, + 312, + 545, + 346 + ], + "type": "text", + "content": "- A novel generative VAD model based on comparing the multimodality of normal and abnormal motion generations;" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 317, + 347, + 545, + 383 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 347, + 545, + 383 + ], + "spans": [ + { + "bbox": [ + 317, + 347, + 545, + 383 + ], + "type": "text", + "content": "- The first probabilistic diffusion-based approach for VAD, which fully exploits the enhanced modecoverage capabilities of diffusive probabilistic models;" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 317, + 383, + 545, + 418 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 383, + 545, + 418 + ], + "spans": [ + { + "bbox": [ + 317, + 383, + 545, + 418 + ], + "type": "text", + "content": "- A novel motion-based conditioning on the clean input sequence to steer the synthesis towards diverse pertinent motion in the case of normality;" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 317, + 419, + 545, + 466 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 419, + 545, + 466 + ], + "spans": [ + { + "bbox": [ + 317, + 419, + 545, + 466 + ], + "type": "text", + "content": "A thorough validation on UBnormal, HR-UBnormal, HR-STC, and HR-Avenue benchmarks where we outperform the SoA by " + }, + { + "bbox": [ + 317, + 419, + 545, + 466 + ], + "type": "inline_equation", + "content": "5.1\\%" + }, + { + "bbox": [ + 317, + 419, + 545, + 466 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 317, + 419, + 545, + 466 + ], + "type": "inline_equation", + "content": "4.4\\%" + }, + { + "bbox": [ + 317, + 419, + 545, + 466 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 317, + 419, + 545, + 466 + ], + "type": "inline_equation", + "content": "5\\%" + }, + { + "bbox": [ + 317, + 419, + 545, + 466 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 317, + 419, + 545, + 466 + ], + "type": "inline_equation", + "content": "8\\%" + }, + { + "bbox": [ + 317, + 419, + 545, + 466 + ], + "type": "text", + "content": ", respectively." + } + ] + } + ], + "index": 12 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 306, + 477, + 392, + 489 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 477, + 392, + 489 + ], + "spans": [ + { + "bbox": [ + 306, + 477, + 392, + 489 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 497, + 545, + 533 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 497, + 545, + 533 + ], + "spans": [ + { + "bbox": [ + 304, + 497, + 545, + 533 + ], + "type": "text", + "content": "Previous work relates to ours from two main perspectives: Video Anomaly Detection methods (see Sec. 2.1), and diffusion models for motion synthesis (see Sec. 2.2)." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 540, + 504, + 552 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 540, + 504, + 552 + ], + "spans": [ + { + "bbox": [ + 305, + 540, + 504, + 552 + ], + "type": "text", + "content": "2.1. Video Anomaly Detection Techniques" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 558, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 545, + 665 + ], + "type": "text", + "content": "Pioneer works analyze the trajectory of the agents in the frames to discriminate those distant from normality [5, 16, 19]. Within recent literature, two major trends can be identified: latent- and reconstruction-based methods. VAD techniques also vary based on the type of input data they use, such as videos or human skeletal pose motions. MoCoDAD, as all the VAD works presented in this section, adheres to the OCC protocol, which simulates the scarcity of anomalies in real-world scenarios [18]." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "Latent-based VAD methods identify abnormality according to a score extracted from a learned latent space whereby normality is supposedly mapped into a constrained volume, and anomalies are those latents lying outside, with a larger" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "10319" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 216 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 216 + ], + "type": "text", + "content": "score (see [34, 38, 42, 46] for an overview of latent-based AD). Sabokrou et al. [36] propose a two-staged cascade of deep neural networks. First, they employ a stack of autoencoders that detects points of interest (POIs) while excluding irrelevant patches (e.g., background). Second, they identify anomalies by densely extracting and modeling discriminative patches at POIs. Notice that this work constrains normality to belong to a single mode and anomalies outside, thus, addressing the openset'ness of anomalies, but it hampers the multimodal and diversity [51] aspect of normal motions. Contrarily, our work considers the multimodality of normal and abnormal motions." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 218, + 289, + 315 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 218, + 289, + 315 + ], + "spans": [ + { + "bbox": [ + 46, + 218, + 289, + 315 + ], + "type": "text", + "content": "Notably, Nguyen et al. [27] propose an image-based technique exploring multimodal anomaly detection via multi-headed VAEs. However, considering a fixed number of modes for reality amends multimodality only partially, as it misses to unleash its openset'ness. Differently, we adopt diffusion models for their improved mode coverage and generate multiple futures, not being constrained on a fixed number of heads (see Sec. 5)." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 316, + 289, + 651 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 316, + 289, + 651 + ], + "spans": [ + { + "bbox": [ + 46, + 316, + 289, + 651 + ], + "type": "text", + "content": "Reconstruction-based VAD methods consider the original metric space of the input and leverage reconstruction as the proxy task to derive an anomaly score. These models are trained to encode and reconstruct the input from normal events, producing larger errors on anomalies not seen during training. [7, 13, 52] use sequences of frames and feed them to convolutional autoencoders. Gong et al. [12] \"memorize\" the most representative normal poses to discriminate new input samples. Liu et al. [21] tackle intensity and gradient loss, optical flow, and adversarial training. Luo et al. [23] use stacked RNNs with temporally-coherent sparse coding enforcing similar neighboring frames to be encoded with similar reconstruction coefficients. Barbalau et al. [3] builds upon [10] and integrates the reconstruction of the input frames, via multi-headed attention, into a multitask learning framework. Besides [10, 21], all works rely on a single reconstruction proxy task via non-variational architectures that learn discrete manifolds. However, normality and abnormality are multimodal and diverse, making it hard for these techniques to have an exact match (reconstruction) over the GT. Additionally, GANs used in [21] suffer from mode collapse [44] lacking to represent the multimodality of reality. Similarly to [27], [3] can represent only a fixed number of modalities, which does represent the openset'ness of reality. MoCoDAD is a reconstruction-based approach and leverages diffusion processes [8] to account for the openset'ness of normalcy and anomalies in terms of pertinence to the GT." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 653, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 289, + 715 + ], + "type": "text", + "content": "Skeleton-based VAD methods exploit compact spatiotemporal skeletal representations of human motion instead of raw video frames. Morais et al. [26] use two GRU autoencoder branches to account for the global and local decomposition of the skeleton in a particular frame. Luo et" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "type": "text", + "content": "al. [24] exploit stacked layers of ST-GCN [50] to accumulate joint information over the spatio-temporal dimensions of the frame and predict joints in the future. However, [50] uses a fixed adjacency matrix, depicting joint connections, for all ST-GCN layers, which hinders the exploration of intra-frame and intra-joint relationships, two factors that play a crucial role in improving the encoding of spatio-temporal features [39]. Markovitz et al. [25] utilize the encoder of an ST-GCN autoencoder to embed spacetime skeletons into a latent vector. This vector is then fed to an end-to-end trainable deep-embedded clustering procedure which produces " + }, + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "type": "text", + "content": " clusters representing the multimodality of normalcy and anomalies. Flaborea et al. [9] propose COSKAD and force the normal instances into the same latent region driving the distances to a common center. MoCoDAD is also a skeleton-based approach that mitigates the choice of " + }, + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 72, + 547, + 277 + ], + "type": "text", + "content": " a priori to cover the multimodality of reality." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 285, + 409, + 298 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 285, + 409, + 298 + ], + "spans": [ + { + "bbox": [ + 306, + 285, + 409, + 298 + ], + "type": "text", + "content": "2.2. Diffusion Models" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 305, + 547, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 305, + 547, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 305, + 547, + 544 + ], + "type": "text", + "content": "Diffusion models have marked a revolution in generative tasks such as image and video synthesis [35, 43, 49], but they have not been employed for VAD. Saadatnejad et al. [35] propose a two-step framework based on temporal cascaded diffusion (TCD). First, they denoise imperfect observation sequences and, then, improve the predictions of the (frozen) model on repaired frames. Tevet et al. [43] use a transformer encoder to learn arbitrary length motions [2, 29] coherent with a particular conditioning signal " + }, + { + "bbox": [ + 304, + 305, + 547, + 544 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 305, + 547, + 544 + ], + "type": "text", + "content": ". They experiment with constrained synthesis where " + }, + { + "bbox": [ + 304, + 305, + 547, + 544 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 305, + 547, + 544 + ], + "type": "text", + "content": " is a text prompt (i.e., text-to-motion) or a specific action class (i.e., action-to-motion) and unconstrained synthesis where " + }, + { + "bbox": [ + 304, + 305, + 547, + 544 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 304, + 305, + 547, + 544 + ], + "type": "text", + "content": " is not specified. Chen et al. [49] design a transformer-based VAE [29] to learn a representative latent space for human motion sequences. They apply a diffusion model in this latent space to generate vivid motion sequences while obeying specific conditions similar to [43]. Differently, MoCoDAD is a diffusion-based model that uses conditioning over a portion of the input (e.g., previous frames condition the generation of future ones)." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 545, + 548, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 548, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 548, + 713 + ], + "type": "text", + "content": "Wyatt et al. [47] propose AnoDDPM, a diffusion model on images, which does not require the entire Markov chain (noise/denoise) to take place. They use decaying octaves of simplex noising functions to distinguish the corruption rate of low-frequency components from high-frequency ones. However, they add and remove noise without conditioning, identifying anomalies when noise removal diverges from the input. Differently, MoCoDAD is based on generating and comparing multimodal motions against the GT in terms of pertinence. Our proposed model is the first to exploit the multimodal generative and improved mode-coverage capabilities of diffusive techniques, via forecasting tasks, further to being first in adopting them for detecting video anomalies. Hence, to transfer DDPMs from video-based" + } + ] + } + ], + "index": 7 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "10320" + } + ] + } + ], + "index": 8 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 120 + ], + "type": "text", + "content": "Anomaly Detection to skeleton-based VAD we rely on a U-Net-shaped stack of STS-GCN [39, 37] layers, which includes the spatio-temporal aspects of joints in sequences of human poses." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 131, + 130, + 144 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 131, + 130, + 144 + ], + "spans": [ + { + "bbox": [ + 47, + 131, + 130, + 144 + ], + "type": "text", + "content": "3. Methodology" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 151, + 289, + 259 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 151, + 289, + 259 + ], + "spans": [ + { + "bbox": [ + 46, + 151, + 289, + 259 + ], + "type": "text", + "content": "MoCoDAD learns to reconstruct the later (future) corrupted poses by conditioning on the first (past) poses. Sec. 3.1 describes the training diffusion denoising process, how it generates multimodal reconstructions, and statistically aggregates them at inference to detect anomalies. Sec. 3.2 details conditioning on past frames, and Sec. 3.3 describes the architecture of MoCoDAD. For the sake of completeness, in Sec. A.1 of the Supplementary, we present preliminary concepts of DDPMs." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 266, + 187, + 278 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 266, + 187, + 278 + ], + "spans": [ + { + "bbox": [ + 47, + 266, + 187, + 278 + ], + "type": "text", + "content": "3.1. Diffusion on Trajectories" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 284, + 287, + 319 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 284, + 287, + 319 + ], + "spans": [ + { + "bbox": [ + 46, + 284, + 287, + 319 + ], + "type": "text", + "content": "Training We define a diffusion technique that learns to reconstruct corrupted future motion sequences conditioned on clean past ones." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "spans": [ + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": "Let " + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "inline_equation", + "content": "X_{a} = \\{x_{a}^{1},\\ldots ,x_{a}^{N}\\}" + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": " be a sequence of " + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": " timecontiguous poses belonging to a single actor " + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "inline_equation", + "content": "a" + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": ". Since our model considers one actor at a time, we use " + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "inline_equation", + "content": "X = \\{x^{1},\\dots,x^{N}\\}" + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": " for notation simplicity. Each pose " + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "inline_equation", + "content": "x^{i}" + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": " can be seen as a graph " + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "inline_equation", + "content": "x^{i} = (J,A)" + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": " where " + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "inline_equation", + "content": "J" + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": " represents the set of joints, and " + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": " is the adjacency matrix representing the joint connections. Notice that each joint is attributed with a set of spatial coordinates in " + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^C" + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": ", hence " + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "inline_equation", + "content": "x^{i}\\in \\mathbb{R}^{|J|\\times C}" + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "inline_equation", + "content": "X\\in \\mathbb{R}^{N\\times |J|\\times C}" + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": ". Here, we use " + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "inline_equation", + "content": "C = 2" + }, + { + "bbox": [ + 46, + 319, + 287, + 439 + ], + "type": "text", + "content": " as the person's pose is extracted from images at each frame." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "type": "text", + "content": "We divide " + }, + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "type": "text", + "content": " into two parts: the past " + }, + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "type": "inline_equation", + "content": "X^{1:k}" + }, + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "type": "text", + "content": " and the future sequence of poses " + }, + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "type": "inline_equation", + "content": "X^{k+1:N}" + }, + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "type": "inline_equation", + "content": "k \\in \\{1, \\dots, N\\}" + }, + { + "bbox": [ + 46, + 439, + 287, + 464 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 464, + 287, + 523 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 464, + 287, + 523 + ], + "spans": [ + { + "bbox": [ + 46, + 464, + 287, + 523 + ], + "type": "text", + "content": "During the forward process " + }, + { + "bbox": [ + 46, + 464, + 287, + 523 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 46, + 464, + 287, + 523 + ], + "type": "text", + "content": ", we corrupt the coordinates of the joints by adding random translation noise. We sample a random displacement map " + }, + { + "bbox": [ + 46, + 464, + 287, + 523 + ], + "type": "inline_equation", + "content": "\\varepsilon^{k + 1:N} \\in \\mathbb{R}^{(N - k) \\times |J| \\times C}" + }, + { + "bbox": [ + 46, + 464, + 287, + 523 + ], + "type": "text", + "content": " from a distribution " + }, + { + "bbox": [ + 46, + 464, + 287, + 523 + ], + "type": "inline_equation", + "content": "\\mathcal{N}(0, \\mathbf{I})" + }, + { + "bbox": [ + 46, + 464, + 287, + 523 + ], + "type": "text", + "content": " and add it to " + }, + { + "bbox": [ + 46, + 464, + 287, + 523 + ], + "type": "inline_equation", + "content": "X^{k + 1:N}" + }, + { + "bbox": [ + 46, + 464, + 287, + 523 + ], + "type": "text", + "content": " to randomly translate the position of its nodes." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "spans": [ + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "text", + "content": "The magnitude of the added displacement depends on a variance scheduler " + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "inline_equation", + "content": "\\beta_{t} \\in (0,1)" + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "text", + "content": " and a diffusion timestep " + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "inline_equation", + "content": "t \\sim \\mathcal{U}_{[1,T]}" + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "text", + "content": ". As a result, " + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "inline_equation", + "content": "q" + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "text", + "content": " increasingly corrupts the joints " + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "inline_equation", + "content": "x^{i}" + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "text", + "content": " at each diffusion timestep " + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "text", + "content": " (i.e., " + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "inline_equation", + "content": "x_{t=1}^{i} \\to \\dots \\to x_{t=T}^{i}" + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "text", + "content": ") making " + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "inline_equation", + "content": "x_{t=T}^{i}" + }, + { + "bbox": [ + 46, + 523, + 287, + 595 + ], + "type": "text", + "content": " indistinguishable from a pose with randomly sampled joints' spatial coordinates." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "spans": [ + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "text", + "content": "The reverse process " + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "inline_equation", + "content": "p_{\\theta}" + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "text", + "content": " unrolls the corruption, estimating the spatial displacement map " + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "inline_equation", + "content": "\\varepsilon^{k + 1:N}" + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "text", + "content": " via a U-Net-like architecture " + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "inline_equation", + "content": "\\varepsilon_{\\theta}" + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "text", + "content": " (see Sec. 3.3 for more details). To achieve an approximation of " + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "inline_equation", + "content": "\\varepsilon^{k + 1:N}" + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "text", + "content": ", we train the network conditioned on the diffusion timestep " + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "text", + "content": " (embedded through an MLP " + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "inline_equation", + "content": "\\tau_{\\theta}" + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "text", + "content": ") and the embedding " + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "text", + "content": " of the previous trajectory " + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "inline_equation", + "content": "X^{1:k}" + }, + { + "bbox": [ + 46, + 595, + 287, + 668 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 72, + 547, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 72, + 547, + 96 + ], + "spans": [ + { + "bbox": [ + 306, + 72, + 547, + 96 + ], + "type": "text", + "content": "In Eq. 1, similarly to [33], we define the displacement estimation objective4." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 349, + 104, + 545, + 131 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 349, + 104, + 545, + 131 + ], + "spans": [ + { + "bbox": [ + 349, + 104, + 545, + 131 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {d i s p}} = \\mathbb {E} _ {t, X, \\varepsilon} \\left[ \\left| \\left| \\varepsilon - \\varepsilon_ {\\theta} \\left(X _ {t}, t, h\\right) \\right| \\right| \\right] \\tag {1}", + "image_path": "54bdc67df28b75594fa4013aa65b89cff58be28100840eba5af0610b6ad769d6.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 135, + 493, + 148 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 135, + 493, + 148 + ], + "spans": [ + { + "bbox": [ + 306, + 135, + 493, + 148 + ], + "type": "text", + "content": "Inspired by [11], we smooth " + }, + { + "bbox": [ + 306, + 135, + 493, + 148 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{disp}" + }, + { + "bbox": [ + 306, + 135, + 493, + 148 + ], + "type": "text", + "content": " as follows:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 335, + 156, + 545, + 190 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 335, + 156, + 545, + 190 + ], + "spans": [ + { + "bbox": [ + 335, + 156, + 545, + 190 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {s m o o t h}} = \\left\\{ \\begin{array}{l l} 0. 5 \\cdot \\left(\\mathcal {L} _ {\\text {d i s p}}\\right) ^ {2} & \\text {i f} \\left| \\mathcal {L} _ {\\text {d i s p}} \\right| < 1 \\\\ \\left| \\mathcal {L} _ {\\text {d i s p}} \\right| - 0. 5 & \\text {o t h e r w i s e} \\end{array} \\right. \\tag {2}", + "image_path": "7cb19262ce51e6bf1fa74b429ec3d2a76e0bcfca94ac0ef70fb8f80a12446c44.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 201, + 547, + 249 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 201, + 547, + 249 + ], + "spans": [ + { + "bbox": [ + 305, + 201, + 547, + 249 + ], + "type": "text", + "content": "Inference At inference time, MoCoDAD generates multimodal future sequences of poses from random displacement maps, conditioned on the past frames, then aggregates them statistically to detect anomalies." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 249, + 547, + 285 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 249, + 547, + 285 + ], + "spans": [ + { + "bbox": [ + 305, + 249, + 547, + 285 + ], + "type": "text", + "content": "We sample a random displacement " + }, + { + "bbox": [ + 305, + 249, + 547, + 285 + ], + "type": "inline_equation", + "content": "z \\sim \\mathcal{N}(0, \\mathbf{I})" + }, + { + "bbox": [ + 305, + 249, + 547, + 285 + ], + "type": "text", + "content": " and consider it the starting point of the synthesis process that generates a future human motion via Eq. 3." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 310, + 293, + 545, + 321 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 293, + 545, + 321 + ], + "spans": [ + { + "bbox": [ + 310, + 293, + 545, + 321 + ], + "type": "interline_equation", + "content": "X _ {t - 1} = \\frac {1}{\\sqrt {\\alpha_ {t}}} \\left(X _ {t} - \\frac {1 - \\alpha_ {t}}{\\sqrt {1 - \\alpha_ {t}}} \\varepsilon_ {\\theta} \\left(X _ {t}, t, h\\right)\\right) + z \\sqrt {\\beta_ {t}} \\tag {3}", + "image_path": "e42454ab833623dc13397deeb04e6a953bc0b49fd99e4b3b80b6d4797374b42e.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "spans": [ + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "text", + "content": "Note the motion conditioning " + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "text", + "content": ", encoding the past " + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "text", + "content": " frames. We generate " + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "text", + "content": " diverse future pose trajectories " + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "inline_equation", + "content": "Z_{1},\\ldots ,Z_{m}" + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "text", + "content": ". For each " + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "inline_equation", + "content": "Z_{i}" + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "text", + "content": ", we compute the reconstruction error via the smoothed loss " + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "inline_equation", + "content": "s_i = \\mathcal{L}_{smooth}(|X - Z_i|)" + }, + { + "bbox": [ + 305, + 329, + 545, + 388 + ], + "type": "text", + "content": " used in training (cf. Eq. 2)." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 388, + 546, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 388, + 546, + 592 + ], + "spans": [ + { + "bbox": [ + 305, + 388, + 546, + 592 + ], + "type": "text", + "content": "We aggregate all the scores from the generations " + }, + { + "bbox": [ + 305, + 388, + 546, + 592 + ], + "type": "inline_equation", + "content": "S = \\{s_1, \\ldots, s_m\\}" + }, + { + "bbox": [ + 305, + 388, + 546, + 592 + ], + "type": "text", + "content": " to distill a single anomaly score for that sequence. This score is subsequently assigned to the corresponding frames to assess their level of anomaly. In scenarios where multiple actors occupy the same frames, we assign the average anomaly score to those frames. See the Supplementary for a detailed description. We explore different strategies for distilling the anomaly score from " + }, + { + "bbox": [ + 305, + 388, + 546, + 592 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 305, + 388, + 546, + 592 + ], + "type": "text", + "content": ": (1) the diversity between the normal and anomalous generations and (2) aggregation statistics. To account for diversity, we consider the diversity metric " + }, + { + "bbox": [ + 305, + 388, + 546, + 592 + ], + "type": "inline_equation", + "content": "rF = \\mathrm{mean}(\\mathcal{L}_{smooth}) / \\min (\\mathcal{L}_{smooth})" + }, + { + "bbox": [ + 305, + 388, + 546, + 592 + ], + "type": "text", + "content": " introduced by [6, 28]. Diversity stems from testing whether anomalous generations are more diverse than normals, but the diversity score fails to detect anomalies, nearly dropping to random chance. We explain this by normalcy and anomaly having a similar degree of diversity, as we experimentally validate in Sec. 5.1." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 592, + 547, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 592, + 547, + 687 + ], + "spans": [ + { + "bbox": [ + 304, + 592, + 547, + 687 + ], + "type": "text", + "content": "We consider as aggregation statistics the mean, quantile robust statistics including the median, as well as maximum and minimum selectors, in terms of " + }, + { + "bbox": [ + 304, + 592, + 547, + 687 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{smooth}" + }, + { + "bbox": [ + 304, + 592, + 547, + 687 + ], + "type": "text", + "content": " distances between the " + }, + { + "bbox": [ + 304, + 592, + 547, + 687 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 592, + 547, + 687 + ], + "type": "text", + "content": " generated and the GT future motion. Our analysis highlights that the minimum distance is the best on average. This reinforces the original hypothesis that normality-conditioned generated motions are as diverse as abnormal-conditioned ones but more biased to the actual" + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 306, + 693, + 547, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 693, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 693, + 547, + 713 + ], + "type": "text", + "content": "4For readability purposes, for what follows, we omit the superscript " + }, + { + "bbox": [ + 306, + 693, + 547, + 713 + ], + "type": "inline_equation", + "content": "k + 1:N" + }, + { + "bbox": [ + 306, + 693, + 547, + 713 + ], + "type": "text", + "content": ", and assume that we are considering only future motion." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 46, + 673, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 673, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 673, + 287, + 713 + ], + "type": "text", + "content": "3In this paper, a displacement map is equivalent to the addition of noise (corruption) to the input, e.g., in [14]. We use this term to emphasize that we move the joints away from their original spatial position. We invite the reader to consider displacing and corrupting as interchangeable here." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10321" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 100, + 70, + 496, + 264 + ], + "blocks": [ + { + "bbox": [ + 100, + 70, + 496, + 264 + ], + "lines": [ + { + "bbox": [ + 100, + 70, + 496, + 264 + ], + "spans": [ + { + "bbox": [ + 100, + 70, + 496, + 264 + ], + "type": "image", + "image_path": "67f5d381ca28fc7f2fc1cd2e74788e7f92736d4485e6c7af37128b48eb306901.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "lines": [ + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "spans": [ + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "text", + "content": "Figure 2: Overview of the proposed MoCoDAD. A sequence of " + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "text", + "content": " skeletal motions (" + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "inline_equation", + "content": "N = 6" + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "text", + "content": " in the example) is split into past (top-right " + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "inline_equation", + "content": "X^{1:k}" + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "text", + "content": " frames, " + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "inline_equation", + "content": "k = 3" + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "text", + "content": " in the example) and future (top-left " + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "inline_equation", + "content": "X^{k+1:N}" + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "text", + "content": " frames). During training, the Forward Diffusion block adds noise to the future frames, shifting each joint by a random vector displacement of varying intensity (increasing with the diffusion timestep " + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "text", + "content": "). Then the Reverse Diffusion learns to estimate the noise. A key aspect of MoCoDAD is the conditioning, i.e. how to encode the past clean " + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 46, + 272, + 547, + 334 + ], + "type": "text", + "content": " frames and guide the synthesis of relevant futures." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 50, + 360, + 289, + 462 + ], + "blocks": [ + { + "bbox": [ + 50, + 360, + 289, + 462 + ], + "lines": [ + { + "bbox": [ + 50, + 360, + 289, + 462 + ], + "spans": [ + { + "bbox": [ + 50, + 360, + 289, + 462 + ], + "type": "image", + "image_path": "796f0fb32210b3e8c34b860574485e54b3b67c412ecf16027e2099c95d316b94.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 49, + 468, + 285, + 482 + ], + "lines": [ + { + "bbox": [ + 49, + 468, + 285, + 482 + ], + "spans": [ + { + "bbox": [ + 49, + 468, + 285, + 482 + ], + "type": "text", + "content": "Figure 3: Comparison of the three conditioning strategies." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 504, + 287, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 504, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 46, + 504, + 287, + 529 + ], + "type": "text", + "content": "motion, thus more likely to generate samples close to it. See Sec. 5.2 for the experimental evaluation." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 537, + 287, + 563 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 537, + 287, + 563 + ], + "spans": [ + { + "bbox": [ + 47, + 537, + 287, + 563 + ], + "type": "text", + "content": "3.2. Motion Conditioning for multimodal Pose Forecasting" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 569, + 287, + 640 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 569, + 287, + 640 + ], + "spans": [ + { + "bbox": [ + 46, + 569, + 287, + 640 + ], + "type": "text", + "content": "The choice of the conditioning strategy is a crucial factor for diffusion models, as it determines how the conditioning information is fed into the network, and it directly affects the quality of the outputs. In this work, we propose a thorough examination of different strategies for feeding the diffusion models with the conditioning information." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": "We identify three different modeling choices for conditioning the diffusion, illustrated in Fig. 3, i.e., input concatenation, " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "E2E" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": "-embedding, and " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "AE" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": "-embedding. Input concatenation refers to conditioning with a portion of the raw input motion. Here, we keep the past sequence of poses " + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "inline_equation", + "content": "X^{1:k}" + }, + { + "bbox": [ + 46, + 642, + 288, + 714 + ], + "type": "text", + "content": " (the conditioning signal) uncorrupted and pretend it" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 363, + 545, + 399 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 363, + 545, + 399 + ], + "spans": [ + { + "bbox": [ + 304, + 363, + 545, + 399 + ], + "type": "text", + "content": "to the corrupted future sequence " + }, + { + "bbox": [ + 304, + 363, + 545, + 399 + ], + "type": "inline_equation", + "content": "X_{t}^{k + 1:N}" + }, + { + "bbox": [ + 304, + 363, + 545, + 399 + ], + "type": "text", + "content": ". Input concatenation has been explored in previous work for pose forecasting reaching SoA performances in [35]." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "content": "Both embedding choices refer to passing the conditioning past frames through an encoder " + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "inline_equation", + "content": "E" + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "content": ", then providing them to all latent layers of the denoising model (cf. incoming vertical arrows into the orange layers in Fig. 2). Here, " + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "inline_equation", + "content": "E" + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "content": " is a GCN [39] and it encodes sequences of poses " + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "inline_equation", + "content": "X^{1:k}" + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "content": " into the representation " + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "inline_equation", + "content": "h = E(X^{1:k})" + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "content": ". In the case of " + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "inline_equation", + "content": "E2E" + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "content": "-embedding, " + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "inline_equation", + "content": "E" + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "content": " is jointly learned with the rest of the architecture, leveraging the training " + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\text{smooth}}" + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "content": " loss. The " + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "inline_equation", + "content": "AE" + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "content": "-embedding adds an auxiliary reconstruction loss " + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\text{rec}}" + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "content": " to support training " + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "inline_equation", + "content": "E" + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "content": ", as it tasks a decoding network " + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 400, + 546, + 544 + ], + "type": "text", + "content": " to reconstruct the conditioning past frames according to the following loss function:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 356, + 556, + 545, + 586 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 356, + 556, + 545, + 586 + ], + "spans": [ + { + "bbox": [ + 356, + 556, + 545, + 586 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {r e c} = \\left| \\left| D (E (X ^ {1: k})) - X ^ {1: k} \\right| \\right| _ {2} ^ {2} \\tag {4}", + "image_path": "3c60c513ed069692602963de72aa44114b3c4ff5702a107a819ad3f0f97c998d.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 594, + 545, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 594, + 545, + 617 + ], + "spans": [ + { + "bbox": [ + 305, + 594, + 545, + 617 + ], + "type": "text", + "content": "In the case of " + }, + { + "bbox": [ + 305, + 594, + 545, + 617 + ], + "type": "inline_equation", + "content": "AE" + }, + { + "bbox": [ + 305, + 594, + 545, + 617 + ], + "type": "text", + "content": "-embedding, the auxiliary is summed to the main loss, resulting in the following total loss:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 366, + 629, + 545, + 643 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 366, + 629, + 545, + 643 + ], + "spans": [ + { + "bbox": [ + 366, + 629, + 545, + 643 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {t o t} = \\lambda_ {1} \\mathcal {L} _ {\\text {s m o o t h}} + \\lambda_ {2} \\mathcal {L} _ {\\text {r e c}} \\tag {5}", + "image_path": "6782125f5214d0f5ae8acbf00a0216056f35afb24566014316c39cc1e80aa335.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\lambda_1, \\lambda_2 \\in [0, 1]" + }, + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "type": "text", + "content": " account for the contribution of each loss function respectively. Lastly, since DDPMs benefit from being conditioned on the timestep " + }, + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "type": "text", + "content": ", we add the embedding " + }, + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\tau_{\\theta}(t)" + }, + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "type": "text", + "content": " to the latent " + }, + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "type": "inline_equation", + "content": "h" + }, + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "type": "text", + "content": " and feed the resulting motion-temporal signal to each layer of our network " + }, + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\varepsilon_{\\theta}" + }, + { + "bbox": [ + 304, + 653, + 545, + 714 + ], + "type": "text", + "content": " [43]." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 758 + ], + "type": "text", + "content": "10322" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 73, + 103, + 518, + 262 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "text", + "content": "Table 1: Comparison of MoCoDAD against SoA in terms of AUC on the three Human-Related datasets (i.e., HR-STC, HR-Avenue and HR-UBnormal) and UBnormal. OCC skeleton-based techniques are marked with a " + }, + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "inline_equation", + "content": "*" + }, + { + "bbox": [ + 47, + 70, + 545, + 95 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 73, + 103, + 518, + 262 + ], + "lines": [ + { + "bbox": [ + 73, + 103, + 518, + 262 + ], + "spans": [ + { + "bbox": [ + 73, + 103, + 518, + 262 + ], + "type": "table", + "html": "
HR-STCHR-AvenueHR-UBnormalUBnormal
Conv-AE [13]CVPR '1669.884.8--
Pred [21]CVPR '1872.786.2--
MPED-RNN [26] *CVPR '1975.486.361.260.6
GEPC [25] *CVPR '2074.858.155.253.4
Multi-timescale Prediction [32] *WACV '2077.088.3--
Normal Graph [24]Neurocomputing '2176.587.3--
PoseCVAE [15] *ICPR '2175.787.8--
BiPOCO [17] *Arxiv '2274.987.052.350.7
STGCAE-LSTM [20] *Neurocomputing '2277.286.3--
SSMTL++ [3]CVIU '23---62.1
COSKAD [9] *Arxiv '2377.187.865.565.0
MoCoDAD *77.689.068.468.3
", + "image_path": "9317dc120249e6cbab6e80801879f614fb54c9eb2103feb4c9ca064bb46ad7a0.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 282, + 287, + 319 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 282, + 287, + 319 + ], + "spans": [ + { + "bbox": [ + 47, + 282, + 287, + 319 + ], + "type": "text", + "content": "The results of evaluation are discussed in Sec. 5.3, whereby applying an AE-embedding conditioning on " + }, + { + "bbox": [ + 47, + 282, + 287, + 319 + ], + "type": "inline_equation", + "content": "X^{1:k}" + }, + { + "bbox": [ + 47, + 282, + 287, + 319 + ], + "type": "text", + "content": " emerges with results beyond the SoA." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 346, + 186, + 359 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 346, + 186, + 359 + ], + "spans": [ + { + "bbox": [ + 47, + 346, + 186, + 359 + ], + "type": "text", + "content": "3.3. Architecture Description" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 371, + 287, + 552 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 371, + 287, + 552 + ], + "spans": [ + { + "bbox": [ + 46, + 371, + 287, + 552 + ], + "type": "text", + "content": "Fig. 2 illustrates the architecture of MoCoDAD. We distinguish two main blocks: a conditioning auto-encoder for the past motion, " + }, + { + "bbox": [ + 46, + 371, + 287, + 552 + ], + "type": "inline_equation", + "content": "X^{1:k}" + }, + { + "bbox": [ + 46, + 371, + 287, + 552 + ], + "type": "text", + "content": ", and a denoising model for " + }, + { + "bbox": [ + 46, + 371, + 287, + 552 + ], + "type": "inline_equation", + "content": "X^{k+1:N}" + }, + { + "bbox": [ + 46, + 371, + 287, + 552 + ], + "type": "text", + "content": ". The main diffusion model architecture is the neural network, represented with orange blocks, tasked with estimating the corrupting noise in the input motion, thus reconstructing the actual future motion. As done in [47], we rely on a U-Net like architecture. Our skeletal-motion diffusion network progressively contracts and then expands (rebuilds) the spatial dimension of the input sequence of poses. To account for the temporal dimension of the input sequences, we build the U-Net with space-time separable GCN (STSGCN) layers proposed in [39]. The conditioning autoencoder relies on STS-GCN to reconstruct the past motion and embed it into a latent space used to condition the diffusion." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "text", + "content": "In detail, the U-Net takes in input " + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "inline_equation", + "content": "X^{k + 1:N}" + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "text", + "content": " and a motion-temporal conditioning signal " + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "inline_equation", + "content": "h + \\tau_{\\theta}(t)" + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "text", + "content": " which provides the network with the diffusion timestep and the encoded past-motion information. Furthermore, to align the dimensionality of this conditioning signal with that of the network's layers, the former is fed into an embedding layer projecting it to the correct vector space. This embedded conditioning signal is then fed to each STS-GCN layer. The contracting process of the U-Net progressively aggregates the joints of the poses (i.e., " + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^J \\to \\mathbb{R}^d" + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "text", + "content": " s.t. " + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "inline_equation", + "content": "d \\leq J" + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "text", + "content": ") while the expansion part \"deconvolutes\" the joints' vector space until it reaches the original space " + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\mathbb{R}^J" + }, + { + "bbox": [ + 46, + 557, + 288, + 714 + ], + "type": "text", + "content": ". Residual connections are present between specular layers." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 281, + 388, + 295 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 281, + 388, + 295 + ], + "spans": [ + { + "bbox": [ + 306, + 281, + 388, + 295 + ], + "type": "text", + "content": "4. Experiments" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 305, + 301, + 545, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 301, + 545, + 348 + ], + "spans": [ + { + "bbox": [ + 305, + 301, + 545, + 348 + ], + "type": "text", + "content": "Here we compare MoCoDAD with SoA approaches and provide a detailed discussion on the achieved performances. In Sec. D of the Supplementary, we provide the reader with a thorough description of the implementation details." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 350, + 545, + 409 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 350, + 545, + 409 + ], + "spans": [ + { + "bbox": [ + 305, + 350, + 545, + 409 + ], + "type": "text", + "content": "As done in [1, 3, 9, 10, 21, 24, 25, 26], we report the Receiver Operating Characteristic Area Under the Curve (ROC-AUC) to assess the quality of MoCoDAD predictions on UBnormal [1], and the HR filtered [9] versions of STC [23], Avenue [22], and UBnormal." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 417, + 369, + 429 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 417, + 369, + 429 + ], + "spans": [ + { + "bbox": [ + 306, + 417, + 369, + 429 + ], + "type": "text", + "content": "4.1. Datasets" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 435, + 545, + 639 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 435, + 545, + 639 + ], + "spans": [ + { + "bbox": [ + 304, + 435, + 545, + 639 + ], + "type": "text", + "content": "We use the UBnormal dataset [1] which contains 29 scenes synthesized from 2D natural images with the Cinema4D software. Each scene appears in 19 clips featuring both normal and abnormal events. The split into train, validation, and test adheres to the open-set policy, providing disjoint sets of types of anomalies for training, validation, and test; in accordance with the OCC setting, we only include normal actions for the training set. We also consider the processed poses and the human-related (HR) filtering of the dataset proposed by [9]. To compare with other state-of-the-art methods, we also experiment on the HR versions of the ShanghaiTech Campus (STC) [23] and the CUHK Avenue [22] datasets introduced by [26]. The former includes 13 scenes recorded with different cameras, for a total of about 300,000 frames, and 101 testing clips with 130 anomalous events. The latter consists of 16 training videos and 21 testing videos with a total of 47 anomalous events." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 647, + 484, + 659 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 647, + 484, + 659 + ], + "spans": [ + { + "bbox": [ + 306, + 647, + 484, + 659 + ], + "type": "text", + "content": "4.2. Comparison with state-of-the-art" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 665, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 665, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 665, + 545, + 714 + ], + "type": "text", + "content": "Leading OCC techniques. We compare against SoA OCC techniques. Among these, MPED-RNN [26] combines the reconstruction and prediction errors of a two-branches-RNN to spot anomalies. Normal Graph [24] uses spatial" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10323" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 83, + 115, + 248, + 191 + ], + "blocks": [ + { + "bbox": [ + 46, + 70, + 288, + 106 + ], + "lines": [ + { + "bbox": [ + 46, + 70, + 288, + 106 + ], + "spans": [ + { + "bbox": [ + 46, + 70, + 288, + 106 + ], + "type": "text", + "content": "Table 2: Comparison of MoCoDAD against supervised (†) and weakly supervised (‡) methods introduced in [1] in terms of AUC on the UBnormal dataset." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 83, + 115, + 248, + 191 + ], + "lines": [ + { + "bbox": [ + 83, + 115, + 248, + 191 + ], + "spans": [ + { + "bbox": [ + 83, + 115, + 248, + 191 + ], + "type": "table", + "html": "
ParamsUBnormal
Sultani et al. [41] †-50.3
AED-SSMTL [10] †>80M61.3
TimeSformer [4] †121M68.5
AED-SSMTL [10] ‡>80M59.3
MoCoDAD142K68.3
", + "image_path": "48e792fb694210239e75ca27dff76f8ba4e352c4ba145b9400ab4779d8771d15.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 45, + 208, + 287, + 422 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 208, + 287, + 422 + ], + "spans": [ + { + "bbox": [ + 45, + 208, + 287, + 422 + ], + "type": "text", + "content": "temporal GCNs (ST-GCN) to encode skeletal sequences. GEPC [25] encodes the input sequences with an STGCN, and clusters the embeddings in the latent space. Multi-timescale Prediction [32] encodes the observed input sequence and predicts future poses at different time scales through intermediate fully-connected layers. Both PoseCVAE [15] and BiPOCO [17] exploit a Conditioned Variational-Autoencoder to learn a posterior distribution of normal actions and use encoded past and future sequences to reconstruct the future one. The former uses an MLP-based architecture, while the latter is GRU-based. STGCAE-LSTM [20] reconstructs the past pose sequence and predicts the future one by an LSTM-based autoencoder. SSMTL++ [3] extends [10]; it replaces the convolutions with a transformer, changes the object detection backbone, and adds a few auxiliary proxy tasks. COSKAD [9] builds on STS-GCN to map the embeddings of normal poses into a narrow region in the latent space." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 45, + 425, + 287, + 604 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 425, + 287, + 604 + ], + "spans": [ + { + "bbox": [ + 45, + 425, + 287, + 604 + ], + "type": "text", + "content": "Results. In Table 1, we compare MoCoDAD and SoA methods on the three HR datasets and on UBnormal. MoCoDAD achieves the best AUC score of 77.6, 89.0, and 68.4 on HR-STC, HR-Avenue, and HR-UBnormal, respectively. Our proposed method outperforms the current best [9], up to " + }, + { + "bbox": [ + 45, + 425, + 287, + 604 + ], + "type": "inline_equation", + "content": "4.4\\%" + }, + { + "bbox": [ + 45, + 425, + 287, + 604 + ], + "type": "text", + "content": ", demonstrating the importance of considering a range of different possible futures for each sample. Additionally, MoCoDAD achieves an AUC of 68.3 on the full UBnormal dataset, surpassing COSKAD by " + }, + { + "bbox": [ + 45, + 425, + 287, + 604 + ], + "type": "inline_equation", + "content": "5.1\\%" + }, + { + "bbox": [ + 45, + 425, + 287, + 604 + ], + "type": "text", + "content": ". This can be due to the improved sensitivity that emerges from our proposed model: considering more than a single deterministic future smooths the prediction of MoCoDAD avoiding penalizing excessively hard-still-normal samples which would be considered anomalous based on the reconstruction error of a deterministic model." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 288, + 715 + ], + "type": "text", + "content": "Results VS. Supervised and Weakly Supervised methods Table 2 evaluates MoCoDAD with supervised and weakly supervised methods reported in [1]. Notice that, despite the absence of supervision or visual information, MoCoDAD is competitive with methods exploiting a stronger form of supervision. In detail, MoCoDAD (68.3) outperforms the weakly supervised method [10] (59.3) and other fully supervised methods and is competitive with [4] (68.5). Further, our approach only presents a fraction of the parameters of" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": "its competitors. Notably, MoCoDAD is " + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "inline_equation", + "content": "\\sim 852\\times" + }, + { + "bbox": [ + 305, + 72, + 545, + 96 + ], + "type": "text", + "content": " smaller than the current best [4]." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 109, + 375, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 109, + 375, + 121 + ], + "spans": [ + { + "bbox": [ + 306, + 109, + 375, + 121 + ], + "type": "text", + "content": "5. Discussion" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 129, + 545, + 226 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 129, + 545, + 226 + ], + "spans": [ + { + "bbox": [ + 304, + 129, + 545, + 226 + ], + "type": "text", + "content": "Here, we delve into a detailed discussion about the multimodal future generations (cf Sec. 5.1), the influence of the statistical aggregation of multiple generations and the normal Vs. anomalous conditioning (cf. Sec. 5.2), the effect of different conditioning strategies (cf. Sec. 3.2). Additionally, we discuss forecasting proxy tasks (Sec. 5.4) and analyze MoCoDAD's performances with the diffusion process applied to the latent space. (Sec. 5.5)." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 234, + 397, + 247 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 234, + 397, + 247 + ], + "spans": [ + { + "bbox": [ + 306, + 234, + 397, + 247 + ], + "type": "text", + "content": "5.1. Multimodality" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 254, + 545, + 410 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 254, + 545, + 410 + ], + "spans": [ + { + "bbox": [ + 304, + 254, + 545, + 410 + ], + "type": "text", + "content": "We question whether MoCoDAD can generate diverse multimodal motions and whether conditioning on normal or abnormal motions affects diversity. We provide an example of generated future motions in Fig. 5 (left), where we project the samples in 2D with t-SNE [45] for better visualization. Notice that both sets of generations have similar variance, showing that MoCoDAD produces diverse samples with both normal and abnormal conditioning sequences. Motions stemming from normal conditioning are biased toward the true future since they are mapped around it. Whereas, in the case of abnormal conditioning, the ground truth motion lies on the edge of the predictions' region, hence being correctly predicted with a lower chance." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 410, + 545, + 542 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 410, + 545, + 542 + ], + "spans": [ + { + "bbox": [ + 304, + 410, + 545, + 542 + ], + "type": "text", + "content": "We also measure diversity, employing the " + }, + { + "bbox": [ + 304, + 410, + 545, + 542 + ], + "type": "inline_equation", + "content": "rF" + }, + { + "bbox": [ + 304, + 410, + 545, + 542 + ], + "type": "text", + "content": " diversity metric from literature [6, 28]. We visualize the " + }, + { + "bbox": [ + 304, + 410, + 545, + 542 + ], + "type": "inline_equation", + "content": "rF" + }, + { + "bbox": [ + 304, + 410, + 545, + 542 + ], + "type": "text", + "content": " trend when increasing the number of generations in Fig. 5 (right). If the generated motion had no diversity, e.g., when generating only once, the " + }, + { + "bbox": [ + 304, + 410, + 545, + 542 + ], + "type": "inline_equation", + "content": "rF" + }, + { + "bbox": [ + 304, + 410, + 545, + 542 + ], + "type": "text", + "content": " would be equal to 1. Rather, the diversity ratio monotonically increases with the number of generations for both normal and abnormal cases, i.e., the more generated samples, the larger the empirical mode coverage and the diversity. We note that, following intuition, the diversity for abnormal cases grows slightly larger than for normal cases, but the " + }, + { + "bbox": [ + 304, + 410, + 545, + 542 + ], + "type": "inline_equation", + "content": "rF" + }, + { + "bbox": [ + 304, + 410, + 545, + 542 + ], + "type": "text", + "content": " measures remain comparable." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 551, + 538, + 563 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 551, + 538, + 563 + ], + "spans": [ + { + "bbox": [ + 306, + 551, + 538, + 563 + ], + "type": "text", + "content": "5.2. Statistical aggregations of generated motions" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "We evaluate the anomaly detection performance when varying the number of generations " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " and the aggregation strategy for the anomaly score " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "S" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": " (cf. Sec. 3.1). Fig. 4 (right) shows that the AUC positively correlates with the number of generated future motions for quantiles " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "Q < 0.5" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": ", while the correlation is negative for the mean estimate and " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "Q > 0.5" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": ". Such correlation can be better understood by looking at Fig. 4 (left), which depicts the average reconstruction error probability density function (PDF) for " + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "inline_equation", + "content": "m = 50" + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": ": when conditioned on normal past motions, MoCoDAD produces generations which are centered around the true future and, thus, is more likely to yield lower error scores than when" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 318, + 757 + ], + "type": "text", + "content": "10324" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 95, + 83, + 258, + 198 + ], + "blocks": [ + { + "bbox": [ + 95, + 83, + 258, + 198 + ], + "lines": [ + { + "bbox": [ + 95, + 83, + 258, + 198 + ], + "spans": [ + { + "bbox": [ + 95, + 83, + 258, + 198 + ], + "type": "image", + "image_path": "24c7754b04072608620527b568febf73daa222135851859bfa85f7374c89a7b0.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 205, + 547, + 243 + ], + "lines": [ + { + "bbox": [ + 45, + 205, + 547, + 243 + ], + "spans": [ + { + "bbox": [ + 45, + 205, + 547, + 243 + ], + "type": "text", + "content": "Figure 4: (left) Histograms of the reconstruction errors for 50 synthesized future motions, computed on the HR-UBnormal test set, for the case of conditioning on normal and abnormal past motions. (right) Correlation between the AUC scores and the number of generations, with each curve corresponding to a different aggregation statistic." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 274, + 86, + 509, + 196 + ], + "blocks": [ + { + "bbox": [ + 274, + 86, + 509, + 196 + ], + "lines": [ + { + "bbox": [ + 274, + 86, + 509, + 196 + ], + "spans": [ + { + "bbox": [ + 274, + 86, + 509, + 196 + ], + "type": "image", + "image_path": "3800d3f9bcfa80879e6e55aadd7b1ee51324ac9bf14acbaa4257d7e58a7d89b4.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "type": "image", + "bbox": [ + 118, + 272, + 269, + 387 + ], + "blocks": [ + { + "bbox": [ + 118, + 272, + 269, + 387 + ], + "lines": [ + { + "bbox": [ + 118, + 272, + 269, + 387 + ], + "spans": [ + { + "bbox": [ + 118, + 272, + 269, + 387 + ], + "type": "image", + "image_path": "0be238cdf2bab952ddc55af1a4b8e651c4f8094c8b94187bccc28bb3fed9fbb5.jpg" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 45, + 396, + 545, + 468 + ], + "lines": [ + { + "bbox": [ + 45, + 396, + 545, + 468 + ], + "spans": [ + { + "bbox": [ + 45, + 396, + 545, + 468 + ], + "type": "text", + "content": "Figure 5: (left) Distribution of 1000 generated future motions, when conditioning on a normal past motion (top) and on an abnormal one (bottom). 2-dimensional projections are estimated via t-SNE [45]. Note how the true future motion (red dot) lies within a main distribution mode in the case of normality, but it lies in a marginal region for abnormality. (right) Plot of the diversity ratio " + }, + { + "bbox": [ + 45, + 396, + 545, + 468 + ], + "type": "inline_equation", + "content": "rF" + }, + { + "bbox": [ + 45, + 396, + 545, + 468 + ], + "type": "text", + "content": " [28], measuring the diversity of the generated future motions for normal and anomalous conditioning pasts. Moving along the " + }, + { + "bbox": [ + 45, + 396, + 545, + 468 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 45, + 396, + 545, + 468 + ], + "type": "text", + "content": "-axis, with more generated motion, the " + }, + { + "bbox": [ + 45, + 396, + 545, + 468 + ], + "type": "inline_equation", + "content": "rF" + }, + { + "bbox": [ + 45, + 396, + 545, + 468 + ], + "type": "text", + "content": " measures grow (MoCoDAD generates multimodal diverse motion) but they remain comparable (generating from normal and abnormal is anyhow multimodal)." + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + } + ], + "index": 3 + }, + { + "type": "image", + "bbox": [ + 302, + 268, + 466, + 380 + ], + "blocks": [ + { + "bbox": [ + 302, + 268, + 466, + 380 + ], + "lines": [ + { + "bbox": [ + 302, + 268, + 466, + 380 + ], + "spans": [ + { + "bbox": [ + 302, + 268, + 466, + 380 + ], + "type": "image", + "image_path": "dcefbd7c4da137c74fda5f6b47dc4796c6f59896fa1e769d4a2f3dad49828667.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 489, + 287, + 513 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 489, + 287, + 513 + ], + "spans": [ + { + "bbox": [ + 46, + 489, + 287, + 513 + ], + "type": "text", + "content": "generating with abnormal conditioning. The performance saturates for " + }, + { + "bbox": [ + 46, + 489, + 287, + 513 + ], + "type": "inline_equation", + "content": "m > 50" + }, + { + "bbox": [ + 46, + 489, + 287, + 513 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 525, + 133, + 538 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 525, + 133, + 538 + ], + "spans": [ + { + "bbox": [ + 47, + 525, + 133, + 538 + ], + "type": "text", + "content": "5.3. Conditioning" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 544, + 287, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 544, + 287, + 592 + ], + "spans": [ + { + "bbox": [ + 46, + 544, + 287, + 592 + ], + "type": "text", + "content": "Here, we provide the reader with the performances of our method with different encoding approaches of the past (i.e., how the past motion is provided to the model) from which the future is generated (see Table 3)." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 594, + 288, + 714 + ], + "type": "text", + "content": "As illustrated in Sec. 3.2, Input Concatenation concatenates the clean past frames to the corrupted part of each motion sample and feeds it directly to the denoising module. This strategy surpasses recent baselines (cf. Table 1) with AUC scores of 64.96 and 65.20 on UBnormal and HRUBnormal, respectively. We deem this strategy suboptimal since it does not allow the past motion conditioning to be injected at each layer (as with the embedding strategies), and, thus force the network to \"remember\" this information rather than focusing on the denoising of the future." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 489, + 545, + 561 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 489, + 545, + 561 + ], + "spans": [ + { + "bbox": [ + 304, + 489, + 545, + 561 + ], + "type": "text", + "content": "The E2E-embedding strategy encodes the motion history in the clean past frames and provides it to the latent layers of the denoising model, but it does not improve performance. We believe this happens because the learned embedding is not supervised, and it may not be representative enough of the original motion." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 562, + 545, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 562, + 545, + 647 + ], + "spans": [ + { + "bbox": [ + 304, + 562, + 545, + 647 + ], + "type": "text", + "content": "AE-embedding accounts for the best performances. It couples the encoder " + }, + { + "bbox": [ + 304, + 562, + 545, + 647 + ], + "type": "inline_equation", + "content": "E" + }, + { + "bbox": [ + 304, + 562, + 545, + 647 + ], + "type": "text", + "content": " with a symmetric decoder " + }, + { + "bbox": [ + 304, + 562, + 545, + 647 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 304, + 562, + 545, + 647 + ], + "type": "text", + "content": " and trains the whole model with an auxiliary loss " + }, + { + "bbox": [ + 304, + 562, + 545, + 647 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{rec}" + }, + { + "bbox": [ + 304, + 562, + 545, + 647 + ], + "type": "text", + "content": " which supervises the reconstruction of the first part of the motion (cf. Sec. 3.2). This past encoding strategy reaches 68.3 and 68.4 on UBnormal and HR-UBnormal, outperforming SoA techniques." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 658, + 382, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 658, + 382, + 670 + ], + "spans": [ + { + "bbox": [ + 306, + 658, + 382, + 670 + ], + "type": "text", + "content": "5.4. Proxy Task" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 714 + ], + "type": "text", + "content": "In Table 4 we assess the effectiveness of the forecasting proxy task (cf. Sec. 3.1). To this end, instead of limiting ourselves towards a rigid past-future split of poses, we ex" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10325" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 50, + 103, + 287, + 159 + ], + "blocks": [ + { + "bbox": [ + 47, + 70, + 287, + 95 + ], + "lines": [ + { + "bbox": [ + 47, + 70, + 287, + 95 + ], + "spans": [ + { + "bbox": [ + 47, + 70, + 287, + 95 + ], + "type": "text", + "content": "Table 3: Ablation study on the different methods for integrating conditioning information into the model." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 103, + 287, + 159 + ], + "lines": [ + { + "bbox": [ + 50, + 103, + 287, + 159 + ], + "spans": [ + { + "bbox": [ + 50, + 103, + 287, + 159 + ], + "type": "table", + "html": "
HR-UBnormalUBnormal
Input Concatenation65.265.0
E2E-embedding64.464.2
AE-embedding (MoCoDAD)68.468.3
", + "image_path": "c4d42ac3b3805a347e08a9dae22b3c7a081d74b26a4d9f26ad2495a28d9e9051.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "type": "table", + "bbox": [ + 50, + 202, + 286, + 260 + ], + "blocks": [ + { + "bbox": [ + 47, + 169, + 286, + 194 + ], + "lines": [ + { + "bbox": [ + 47, + 169, + 286, + 194 + ], + "spans": [ + { + "bbox": [ + 47, + 169, + 286, + 194 + ], + "type": "text", + "content": "Table 4: Ablation study on the type of conditioning information to feed into the model to generate the missing frame." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 50, + 202, + 286, + 260 + ], + "lines": [ + { + "bbox": [ + 50, + 202, + 286, + 260 + ], + "spans": [ + { + "bbox": [ + 50, + 202, + 286, + 260 + ], + "type": "table", + "html": "
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For random imputation, we randomly select " + }, + { + "bbox": [ + 46, + 280, + 287, + 495 + ], + "type": "inline_equation", + "content": "N - k" + }, + { + "bbox": [ + 46, + 280, + 287, + 495 + ], + "type": "text", + "content": " poses out of the full motion and corrupt them; the rest of the sequence is used for conditioning. Table 4 shows that random imputation is the worst proxy task (AUC of 65.10 and 65.21 for UBnormal and HR-UBnormal, respectively). Randomly splitting the sequence into two parts introduces inter-pose temporal gaps. Hence, we believe that this makes the reconstruction of noncontiguous motion more cumbersome. In-between imputation reaches an AUC of 65.65 and 65.72, respectively. We think that \"stitching\" the central motion to its endpoints is an easier task leading both normal and abnormal motions to be equally well reconstructed. Finally, forecasting is the best-performing proxy task with an AUC of 68.3 and 68.4 for UBnormal and HR-UBnormal." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 503, + 129, + 516 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 503, + 129, + 516 + ], + "spans": [ + { + "bbox": [ + 47, + 503, + 129, + 516 + ], + "type": "text", + "content": "5.5. Latent space" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 521, + 286, + 581 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 286, + 581 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 286, + 581 + ], + "type": "text", + "content": "Diffusion on latent space has been adopted to improve computational efficiency in various domains [33]. MLD [49] is one of the most recent works in motion forecasting that applies the diffusion process directly in the latent space." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "content": "Here, we propose an analysis that assesses the performance of MoCoDAD's diffusion process in the latent space. Thus, we propose two latent variations of MoCoDAD: MoCoDAD+MLD and Latent-MoCoDAD. For MoCoDAD+MLD we use a VAE to produce a latent representation " + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "inline_equation", + "content": "Z \\in \\mathbb{R}^d" + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "content": " of the uncorrupted sequence " + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "inline_equation", + "content": "X^{k + 1:N}" + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "content": " and we perform the diffusion process on " + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "content": " with the transformer-based denoising model as described in [49]. For Latent-MoCoDAD we rely on an STS-VAE to learn " + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "content": " given " + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "inline_equation", + "content": "X^{k + 1:N}" + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "content": " and use the diffusion process, proposed in Sec. 3.2, on " + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "inline_equation", + "content": "Z" + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "content": ". For both these variants, we feed the cor" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 313, + 103, + 538, + 166 + ], + "blocks": [ + { + "bbox": [ + 305, + 70, + 545, + 95 + ], + "lines": [ + { + "bbox": [ + 305, + 70, + 545, + 95 + ], + "spans": [ + { + "bbox": [ + 305, + 70, + 545, + 95 + ], + "type": "text", + "content": "Table 5: AUC-ROC performance of diffusion on latent vs original space." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 313, + 103, + 538, + 166 + ], + "lines": [ + { + "bbox": [ + 313, + 103, + 538, + 166 + ], + "spans": [ + { + "bbox": [ + 313, + 103, + 538, + 166 + ], + "type": "table", + "html": "
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We set the latent space dimension to " + }, + { + "bbox": [ + 304, + 236, + 545, + 307 + ], + "type": "inline_equation", + "content": "d = 16" + }, + { + "bbox": [ + 304, + 236, + 545, + 307 + ], + "type": "text", + "content": " and the MLP blocks to (16,8,16) interleaved with ReLU activations." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 308, + 545, + 416 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 308, + 545, + 416 + ], + "spans": [ + { + "bbox": [ + 304, + 308, + 545, + 416 + ], + "type": "text", + "content": "Table 5 illustrates the performances in terms of AUC-ROC of MoCoDAD and its latent variants on UBnormal and HR-UBnormal. Notice that the latent variants underperform w.r.t. the original MoCoDAD. We suspect that diffusion on latent spaces is not effective in skeleton-based VAD due to the lightweight encoding of the skeletons. This adheres with the literature since also MLD [49] shows that applying diffusion in the latent space underperforms w.r.t. the original proposal of the model." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 306, + 430, + 378, + 442 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 430, + 378, + 442 + ], + "spans": [ + { + "bbox": [ + 306, + 430, + 378, + 442 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 451, + 545, + 617 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 451, + 545, + 617 + ], + "spans": [ + { + "bbox": [ + 304, + 451, + 545, + 617 + ], + "type": "text", + "content": "We have presented a novel approach that models and exploits the diversity of normal and abnormal motions. In the former case, the forecast motions are multi-modal and pertinent to the observed portion of the sequence, as the model understands the underlying action. In the case of abnormal, the forecast motions do not show a bias towards the true future as the model does not expect any obvious outcome. Motivated by the improved mode coverage, this work has been the first to take advantage of probabilistic diffusion models for video anomaly detection, including a thorough analysis of the main design choices. MoCoDAD sets a novel SoA among OCC techniques, and it catches up with supervised techniques while not using anomaly training labels." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 632, + 408, + 646 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 632, + 408, + 646 + ], + "spans": [ + { + "bbox": [ + 306, + 632, + 408, + 646 + ], + "type": "text", + "content": "Acknowledgements" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 653, + 545, + 713 + ], + "type": "text", + "content": "This work was carried out while Stefano D'Arrigo was enrolled in the Italian National Doctorate on Artificial Intelligence run by Sapienza University of Rome. We thank DsTech S.r.l. and the PNRR MUR project PE0000013-FAIR for partially funding this study." + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 317, + 757 + ], + "type": "text", + "content": "10326" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 8 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 48, + 91, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 91, + 287, + 167 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 91, + 287, + 167 + ], + "spans": [ + { + "bbox": [ + 53, + 91, + 287, + 167 + ], + "type": "text", + "content": "[1] Andra Acsintoae, Andrei Florescu, Mariana-Iuliana Georgescu, Tudor Mare, Paul Sumedrea, Radu Tudor Ionescu, Fahad Shahbaz Khan, and Mubarak Shah. 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In Proceedings of the IEEE/CVF International Conference on Computer Vision (ICCV), pages 5826-5835, October 2021." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 749, + 317, + 757 + ], + "type": "text", + "content": "10329" + } + ] + } + ], + "index": 7 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 11 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction/5f20046b-2925-4246-b895-fa5914bd8de8_content_list.json b/2023/Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction/5f20046b-2925-4246-b895-fa5914bd8de8_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..199abd601c6423db80861fca5ec6f4925c89f2cd --- /dev/null +++ b/2023/Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction/5f20046b-2925-4246-b895-fa5914bd8de8_content_list.json @@ -0,0 +1,1536 @@ +[ + { + "type": "text", + "text": "Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction", + "text_level": 1, + "bbox": [ + 94, + 128, + 875, + 176 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Yingxue Xu Hao Chen* \nThe Hong Kong University of Science and Technology \n{yxueb, jhc}@cse.ust.hk", + "bbox": [ + 267, + 203, + 700, + 257 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 291, + 313, + 306 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Survival prediction is a complicated ordinal regression task that aims to predict the ranking risk of death, which generally benefits from the integration of histology and genomic data. Despite the progress in joint learning from pathology and genomics, existing methods still suffer from challenging issues: 1) Due to the large size of pathological images, it is difficult to effectively represent the gigapixel whole slide images (WSIs). 2) Interactions within tumor microenvironment (TME) in histology are essential for survival analysis. Although current approaches attempt to model these interactions via co-attention between histology and genomic data, they focus on only dense local similarity across modalities, which fails to capture global consistency between potential structures, i.e. TME-related interactions of histology and co-expression of genomic data. To address these challenges, we propose a Multimodal Optimal Transport-based Co-Attention Transformer framework with global structure consistency, in which optimal transport (OT) is applied to match patches of a WSI and genes embeddings for selecting informative patches to represent the gigapixel WSI. More importantly, OT-based co-attention provides a global awareness to effectively capture structural interactions within TME for survival prediction. To overcome high computational complexity of OT, we propose a robust and efficient implementation over micro-batch of WSI patches by approximating the original OT with unbalanced mini-batch OT. Extensive experiments show the superiority of our method on five benchmark datasets compared to the state-of-the-art methods. The code is released1.", + "bbox": [ + 75, + 323, + 473, + 763 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 792, + 209, + 806 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Survival prediction is a complex ordinal regression task that aims to estimate the relative risk of death in cancer prognosis, which generally integrates the manual as", + "bbox": [ + 75, + 816, + 468, + 864 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/d0532019981f2c01aadc76576d221a7a50d6aafa98cd8f11c1074b0cf0d1354c.jpg", + "image_caption": [ + "Figure 1. Comparison between (a) Co-Attention and (b) OT-based Co-Attention, where (a) learns weights of instances by dense attention, and (b) identifies informative instances by optimal transport matching flow from a global perspective, which enforces considering potential structures of each modality, i.e. interactions within WSIs and co-expression within genomics." + ], + "image_footnote": [], + "bbox": [ + 535, + 292, + 861, + 517 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "sessment of qualitative morphological information from pathology data and quantitative molecular profiles from genomic data in clinical settings [6, 55, 4]. Despite recent advances in multimodal learning for histology and genomics [5, 55, 27, 34], there still exists several open issues. Among others, one daunting challenge is to capture key information from heterogeneous modalities for effective fusion. Particularly, due to the large size of about $500,000 \\times 500,000$ pixels, it is challenging to effectively represent gigapixel whole slide images without losing key information. Furthermore, visual concepts of tumor microenvironment (TME) within pathological images are verified to have significant associations with survival analysis in various cancer types [42, 1, 25], e.g. cellular components including fibroblast cells and various immune cells that can alter cancer cell behaviors [33]. However, the TME-related patches occupy only a tiny proportion of the entire WSI, leading to a fine-grained visual recognition problem [54] that is indiscernible", + "bbox": [ + 496, + 628, + 893, + 902 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding author\n1https://github.com/Innse/MOTCat", + "bbox": [ + 94, + 875, + 346, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "21241", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "by conventional multimodal learning.", + "bbox": [ + 76, + 90, + 326, + 104 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Recently attention-based multiple instance learning (MIL) [19, 26] has provided a typical solution to identify informative instances, in which a WSI is formulated as a bag of patches (instances) and an attention score is assigned for each instance as a weight for selection. In multimodal learning, genomic data has been applied to guide the selection of TME-related instances by co-attention mechanism across modalities [5], as genes expression might correspond to some morphological characteristics revealed in pathological TME [29, 38]. They [5] densely calculate similarity scores for each pair of pathology and genomic instances as weights of selection to capture fine-grained visual information in WSIs, as shown in Fig. 1 (a). However, this type of approaches with a local view may not thoroughly learn information about TME, since they ignore global potential structure [55] within modality, e.g. interactions within TME for histology and co-expression for genomics [31, 51].", + "bbox": [ + 75, + 109, + 468, + 366 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Fruitful works [31, 33, 5] demonstrate that the interactions within TME are important indicators affecting survival outcomes, e.g. co-occurrence of tumor cells with tumor-infiltrating lymphocytes (TILs) of the immune system is a positive prognostic indicator. However, these collaborative components in TME might be spatially dispersed throughout the entire WSI, which indicates long-range structural associations in WSI, as shown in Fig. 1 (b). On the other hand, genes co-expression [49, 55] also suggests a potential structure. There might be intrinsic consistency between these two potential structures [55, 31], as some studies have verified that genomic mutations can alter normal functions and biological processes of TILs within TME [51, 47]. By leveraging the global consistency between their potential structures to match histology and genomic data, it is more likely to identify TME-related patches from WSIs. However, existing co-attention-based multimodal learning focuses on only dense local similarity, neglecting the global coherence of potential structures.", + "bbox": [ + 75, + 368, + 470, + 655 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address these challenges, we propose a Multimodal Optimal Transport-based Co-Attention Transformer (MOTCat) framework with global structure consistency, in which optimal transport-based co-attention is applied to match instances between histology and genomics from a global perspective, as shown in Fig. 1 (b). Optimal transport (OT) [11, 3, 41], as a structural matching approach, is able to generate an optimal matching solution with the overall minimum matching cost, based on local pairwise cost between instances of histology and genomics. As a result, instances of a WSI that have high global structure consistency with genes co-expressions can be identified to represent the WSI. These instances might be more strongly associated with TME that contributes to survival prediction. In this way, the aforementioned two challenges can be addressed by OT-based Co-Attention simultaneously.", + "bbox": [ + 75, + 657, + 468, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Compared with the conventional co-attention mechanism, the advantages of the proposed OT-based co-attention are three-fold. First, optimal transport provides the instances matching process with global awareness. Marginal constraints of total mass equality enforce a trade-off of instances within modality for transporting during optimization, instead of only considering the local similarity of pairwise instances as conventional co-attention does. It enables the modeling of structural interactions of WSIs and co-expressions of genomics, which is beneficial to survival prediction. Second, the learned patch-level attention score is not a rigorous metric for selecting informative instances under weak supervision [48], i.e. slide-level survival time, especially with only a small number of WSI samples. As an alternative, the optimal matching flow is the rigorous closed-form solution to OT problem without accessing any label, achieved by solving the Linear Programming problem. Last, the optimal matching flow provides a transformation between two modalities under preserving the potential structure, which reduces cross-modal heterogeneity gap.", + "bbox": [ + 496, + 90, + 890, + 393 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Nevertheless, due to a massive number of patches from gigapixel WSIs, OT-based co-attention might suffer from high computational complexity, preventing from applying OT to pathology data in practice. To address this, we propose a robust and efficient implementation of OT-based coattention for matching histology and genomics. Specifically, we split all instances of a WSI into a subset termed Micro-Batch and get the averaged result as a proxy to approximate the solution to the original OT problem over all instances by unbalanced optimal transport [13], which can provide a more robust approximation to the subset sampling with the theoretical and experimental guarantee.", + "bbox": [ + 496, + 393, + 892, + 575 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "It is worth noting that the proposed method is a generalized multimodal learning framework that captures potential structure across modalities with global structure consistency. The contributions of this work are summarized as follows: (1) we propose a novel multimodal OT-based Co-Attention Transformer with global structure consistency, where OT-based co-attention is used to identify informative instances by global optimal matching, which allows modeling interactions of histology and co-expression of genomics. (2) We propose a robust and efficient implementation of OT-based co-attention over Micro-Batch. (3) Extensive experiments on five benchmark datasets show significant improvement over state-of-the-art methods.", + "bbox": [ + 496, + 575, + 890, + 772 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 789, + 640, + 806 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Multimodal Learning in Healthcare", + "text_level": 1, + "bbox": [ + 500, + 815, + 810, + 830 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "In clinical settings, the patient state is often characterized by a spectrum of various modalities [30], such as pathology [54, 32], radiology [39, 50], genomics [28, 47, 31], etc. Multimodal learning has shown superiority by leveraging", + "bbox": [ + 496, + 839, + 890, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "21242", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "the complementary information from multimodal data [30], in which the key issue is to overcome data heterogeneity for better feature fusion. Most existing methods can be roughly classified into three categories: early fusion [18, 43], late fusion [20, 4], and intermediate fusion [5, 24]. Early fusion is to aggregate all modalities at the input level. The most straightforward solution is fusion operators such as concatenation [18], Kronecker Product [35], etc. However, it neglects intra-modality dynamics [30]. On the contrary, late fusion [15] integrates the predictions from individually separated models at the decision level for the final decision, which cannot fully explore cross-modal interactions. Recently, intermediate fusion has attracted much interest by capturing cross-modal interconnections at different levels, where the typical one is attention-based multimodal fusion [5]. For example, Zhu et al. [52] proposed a triplet attention to integrate MRI and diffusion tensor imaging (DTI) for epilepsy diagnosis. IMGFN [55] designed a graph attention network for survival prediction. MCAT [5] proposed a co-attention to identify informative instances of gigapixel WSI with genomic features as queries. HFBSurv [27] progressively integrated multimodal information from the low level to the high level for survival analysis. Note that our method MOTCat belongs to one of the intermediate fusion approaches, which explores the global consistency of potential structure by optimal transport.", + "bbox": [ + 76, + 90, + 472, + 484 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Multiple Instance Learning in Pathology", + "text_level": 1, + "bbox": [ + 76, + 497, + 423, + 513 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Since it is difficult to represent WSIs of large size, MIL algorithms have achieved remarkable progress in pathology, in which WSIs are often formulated as a bag of pathology patches. MIL in pathology generally can be divided into two categories: instance-based algorithms [2, 44, 7] and embedding-based algorithms [19, 16, 32]. The former aims to select a small number of instances within each WSI for training an aggregation model. The latter one is to map each instance into a low-dimension fixed-length embedding offline, and then to learn a bag-level representation based on instance-level embeddings. There are several strategies for aggregating instance-level embeddings. One is clustering-based methods [37, 40], where all the instance-level embeddings are clustered to several centroids that are integrated for the final prediction. The most common strategy is attention-based MIL (AB-MIL) [19, 26] that assigns a weight for each instance, in which various approaches are developed differing in the ways to generate the weighting values. For example, one of the first AB-MIL [19] used a side-branch network for generating attention weights, followed by DS-MIL [26] adopted cosine distance to measure the similarity of instances as weights. Recently, transformer-based MIL like TransMIL [36] has leveraged the self-attention mechanism to explore long-range interactions in WSI. Furthermore, DTFD-MIL [48]", + "bbox": [ + 76, + 523, + 472, + 902 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "proposed the double-tier MIL framework for more rigorous instance weights. Unlike AB-MIL, we use optimal match flow generated by OT between pathological and genomic instances to identify instances of WSI that have global potential structure consistency with that of genomics.", + "bbox": [ + 496, + 90, + 890, + 167 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.3. Survival Prediction", + "text_level": 1, + "bbox": [ + 500, + 176, + 686, + 191 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Survival outcome prediction, also known as time-to-event analysis [23], aims to predict the probability of experiencing an event of interest, e.g. death event in the clinical setting, before a specific time under both right-censored and uncensored data. Right-censored data refers to cases where the outcome event cannot be observed within the study period [23]. Before the deep learning era, statistical models dominated survival analysis. The typical one is Cox Proportional Hazards (CoxPH) model [9] that characterizes the hazard function, the risk of death, by an exponential linear model. DeepSurv [12] is the first work incorporating deep learning into survival analysis, which models the risk function by several fully connected layers and feeds it to the CoxPH model for the final hazard function. Furthermore, DeepConvSurv [53] first attempted to use pathological images for a deep survival model. Recent works [27, 6, 34, 4, 5] tend to directly estimate the hazard function by deep learning models without any statistical assumption. Histology and genomics data are often integrated as the gold standard for predicting survival outcomes with promising performance [4, 6, 55]. Similarly, our method incorporates these two modalities for better survival prediction by learning their global structural coherence.", + "bbox": [ + 496, + 200, + 893, + 549 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Method", + "text_level": 1, + "bbox": [ + 500, + 563, + 589, + 578 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Overview and Problem Formulation", + "text_level": 1, + "bbox": [ + 500, + 589, + 815, + 604 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The overall framework of the proposed method is shown in Fig. 2. In this work, we aim to estimate the hazard functions $h_n(t)$ considered as the risk probability of experiencing death event in a small interval after time point $t$ for $n$ -th patient, based on pathology data $\\mathbf{X}_n^p$ and genomic data $\\mathbf{X}_n^g$ .", + "bbox": [ + 496, + 612, + 890, + 688 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "For pathology, we formulate each WSI as a \"bag\" structure in a conventional multiple instance learning (MIL) setting, where a bag consists of a collection of instances that are patched from the tissue-containing image regions of a WSI, and instance-level features are extracted from patch images. Genomic data is also organized as a \"bag\" based on the biological functional impact of genes. For each instance of the genomic bag, we adopt an encoder to extract genes embeddings. The bags formulations for histology and genomics are illustrated in Sec. 3.1.1 and 3.1.2, respectively.", + "bbox": [ + 496, + 688, + 890, + 839 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Then, Optimal Transport-based Co-Attention is applied to match instances of a WSI and the corresponding genomic instances to model pathological interactions and genomic co-expressions, so that the instances with high structure", + "bbox": [ + 496, + 839, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "21243", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/7b6acfca1801614b6ae081eae9790be0bd482f57788bc455b8e94629d402916d.jpg", + "image_caption": [ + "Figure 2. Overview of Multimodal Optimal Transport-based Co-Attention Transformer (MOTCat) architecture, in which both modalities are formulated as bags representations and a micro-batch of the WSI bag is sampled as pathological input. Then OT-based Co-attention is to calculate optimal matching flow for identifying informative instances with global structure consistency. After aggregating selected instances, features from both modalities are concatenated for survival prediction." + ], + "image_footnote": [], + "bbox": [ + 78, + 92, + 890, + 330 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "consistency can be identified to represent the whole modality. This part will be demonstrated in Sec. 3.2.", + "bbox": [ + 75, + 416, + 468, + 446 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "After that, a Transformer encoder will integrate all instances after selection for each modality into a bag-level representation, in which each instance is treated as a token. The bag-level representation will be concatenated into the multimodal features for predicting a hazard function to get the ordinal survival risk. The details will be described in Sec. 3.1.3. Finally, optimization process over Micro-Batch and the corresponding computational complexity analysis will be presented in Sec. 3.3.", + "bbox": [ + 75, + 446, + 470, + 583 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1.1 WSI Bags Formulation", + "text_level": 1, + "bbox": [ + 76, + 601, + 292, + 617 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "We formulate the learning process of pathology images (WSIs) as a weakly-supervised MIL task, in which each WSI $\\mathbf{X}_n^p$ is represented as a bag with access to only bag-level (slide-level) labels. Given a bag $\\mathbf{X}_n^p = \\{\\mathbf{x}_{n,i}^p\\}_{i = 1}^{M_p}$ of $M_{p}$ permutation-invariant instances, the goal is to encode instance-level features of a WSI into a compact bag-level feature embedding and then assign a bag-level label to it. To this end, we apply a CNN encoder $f_{p}(\\cdot)$ for each patch of the WSI to obtain a bag $\\mathbf{B}_n^p$ of instance-level features:", + "bbox": [ + 75, + 625, + 472, + 763 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {B} _ {n} ^ {p} = \\left\\{f _ {p} \\left(\\mathbf {x} _ {n, i} ^ {p}\\right): \\mathbf {x} _ {n, i} ^ {p} \\in \\mathbf {X} _ {n} ^ {p} \\right\\} = \\left\\{\\mathbf {b} _ {n, i} ^ {p} \\right\\} _ {i = 1} ^ {M _ {p}}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 124, + 773, + 468, + 796 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\mathbf{B}_n^p\\in \\mathbb{R}^{M_p\\times d}$ contains $d$ -dimensional instances and $\\mathbf{b}_{n,i}^p = f_p(\\mathbf{x}_{n,i}^p)$ . After identifying informative instances of $\\mathbf{B}_n^p$ by OT-based Co-Attention, we construct a new bag $\\hat{\\mathbf{B}}_n^p\\in \\mathbb{R}^{\\hat{M}_p\\times d}$ of features with $\\hat{M}_p$ instances, which will be illustrated in detail in Section 3.2. Then, a transformer encoder is used as a global aggregation model $\\mathcal{T}_p(\\cdot)$ to obtain", + "bbox": [ + 75, + 806, + 470, + 902 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "the bag-level representation $H_{n}^{p} = \\mathcal{T}_{p}(\\hat{\\mathbf{B}}_{n}^{p})$ for the subsequent features fusion.", + "bbox": [ + 496, + 415, + 890, + 446 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Algorithm 1 The MOTCat Algorithm", + "text_level": 1, + "bbox": [ + 501, + 460, + 754, + 477 + ], + "page_idx": 3 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "Input: A WSI bag as $\\mathbf{X}_n^p = \\{\\mathbf{x}_{n,i}^p\\}_{i = 1}^{M_p}$ ; A genomic bag as $\\mathbf{X}_n^g = \\{\\mathbf{x}_{n,j}^g\\}_{j = 1}^{M_g}$ . $m$ refers to the size for a micro-batch of a WSI.", + "Output: The optimal parameters of model;", + "1: // Sample micro-batch from the WSI bag $X_{n}^{p,m} = \\{\\mathbf{x}_{n,i}^{p}\\}_{i=1}^{m}$ each time.", + "2: for $X_{n}^{p,m}$ in $\\mathbf{X}_n^p$ do", + "3: Fix model parameters $f_{p}, f_{g}, \\mathcal{T}_{p}$ and $\\mathcal{T}_g$ .", + "4: // To extract a bag of instance-level features", + "5: // Eq. 1 over micro-batch of histology", + "6: $B_{n}^{p,m} = \\{f_{p}(\\mathbf{x}_{n,i}^{p}):\\mathbf{x}_{n,i}^{p}\\in X_{n}^{p,m}\\}$", + "7: // Eq. 2 of genomics", + "8: $\\mathbf{B}_n^g = \\{f_g^j (\\mathbf{x}_{n,j}^g):\\mathbf{x}_{n,j}^g\\in \\mathbf{X}_n^g\\}$", + "9: Optimize $\\mathbf{P}_n^m$ via Sinkhorn-Knopp matrix scaling algorithm [8, 14]:", + "10: $\\mathbf{P}_n^m\\gets \\arg \\min_{\\mathbf{P}_n^m}\\mathcal{W}^m (B_n^{p,m},\\mathbf{B}_n^g) / /$ Eq. 5", + "Fix $\\mathbf{P}_n^m$ and select instances from $B_n^{p,m}$ by:", + "12: $\\bar{B}_n^{p,m} = \\mathbf{P}_n^{m|}B_n^{p,m}$", + "13: // To get bag-level representation", + "14: $H_{n}^{p,m} = \\mathcal{T}_{p}\\left(\\hat{B}_{n}^{p,m}\\right) / /$ for histology", + "15: $H_{n}^{g} = \\mathcal{T}_{g}\\left(\\hat{\\mathbf{B}}_{n}^{g}\\right) / /$ for genomics", + "16: $H_{n}^{m} = H_{n}^{p,m} \\bowtie H_{n}^{g} // \\text{Concatenation}$", + "17: Calculate the overall loss function $\\mathcal{L}$ of Eq. 6.", + "18: Update parameters of $f_{g}$ , $\\mathcal{T}_{p}$ , $\\mathcal{T}_{g}$ and the last fully connected layers of $f_{p}$ by Adam.", + "19: end for" + ], + "bbox": [ + 506, + 479, + 890, + 892 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "21244", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.1.2 Genomic Bags Formulation", + "text_level": 1, + "bbox": [ + 76, + 90, + 323, + 107 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Genomic data consists of $1 \\times 1$ attributes, such as mutation status, transcript abundance (RNA-Seq), copy number variation (CNV) and other molecular characterizations. Following the organization of genomic data in the previous work [5, 28] that categories them according to the biological functional impact, the expressive genomic bag can be organized as $\\mathbf{X}_n^g = \\{\\mathbf{x}_{n,j}^g\\}_{j=1}^{M_g} \\in \\mathbb{R}^{M_g \\times d_j}$ with $M_g$ instances of unique functional categories. For $j$ -th category, the corresponding genomic embedding consists of $d_j$ -dimensional attributes encoded by a separated network $f_g^j(\\cdot)$ . Similarly, a bag $\\mathbf{B}_n^g \\in \\mathbb{R}^{M_g \\times d}$ of genomic data with $M_g$ instances can be constructed as follows:", + "bbox": [ + 75, + 114, + 472, + 297 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {B} _ {n} ^ {g} = \\{f _ {g} ^ {j} (\\mathbf {x} _ {n, j} ^ {g}): \\mathbf {x} _ {n, j} ^ {g} \\in \\mathbf {X} _ {n} ^ {g} \\} = \\{\\mathbf {b} _ {n, j} ^ {g} \\} _ {j = 1} ^ {M _ {g}}, \\quad (2)\n$$\n", + "text_format": "latex", + "bbox": [ + 119, + 306, + 468, + 330 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "which is aggregated to the bag-level embedding by a transformer encoder $H_{n}^{g} = \\mathcal{T}_{g}(\\mathbf{B}_{n}^{g})$ as well.", + "bbox": [ + 76, + 337, + 468, + 369 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.1.3 Multimodal Survival Prediction Formulation", + "text_level": 1, + "bbox": [ + 76, + 385, + 444, + 400 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Survival outcome prediction aims to predict the risk probability of an outcome event occurring before a specific time, in which the outcome event is not always observed, leading to a right-censored event. In this task, let $c \\in \\{0,1\\}$ be censor status indicating whether the outcome event is right-censored ( $c = 1$ ) or not ( $c = 0$ ), and $t \\in \\mathbb{R}^+$ refers to the overall survival time (in months). Given a training set of $N$ pathology-genomics pairs $\\mathcal{D} = \\{(\\mathbf{X}_n^p, \\mathbf{X}_n^g), c_n, t^n\\}_{n=1}^N$ , we can acquire the bag-level features $H_n^p$ of WSIs and $H_n^g$ of genomic data for $n$ -th patient data $\\mathbf{X}_n = ((\\mathbf{X}_n^p, \\mathbf{X}_n^g), c_n, t^n)$ , as described in Section 3.1.1 and 3.1.2. After integrating $H_n^p$ and $H_n^g$ into the multimodal features $H_n$ by concatenation, we estimate the hazard function $h_n(t|H_n) = h_n(T = t | T \\geq t, H_n) \\in [0,1]$ which is viewed as the probability of death event occurring at around time point $t$ . Instead of predicting the overall survival time $t^n$ , the survival prediction task is to estimate the ordinal risk of death via the cumulative survival function:", + "bbox": [ + 75, + 409, + 472, + 681 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nS _ {n} (t \\mid H _ {n}) = \\prod_ {z = 1} ^ {t} \\left(1 - h _ {n} (z \\mid H _ {n})\\right) \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 160, + 689, + 468, + 729 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.2. Optimal Transport-based Co-Attention", + "text_level": 1, + "bbox": [ + 76, + 739, + 415, + 756 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "To identify TME-related instances of WSIs, we utilize the global potential structure consistency between TME interactions of pathology and genes co-expressions as the evidence of selecting instances, in which optimal transport is used to learn the optimal matching flow between a WSI feature bag $\\mathbf{B}_n^p\\in \\mathbb{R}^{M_p\\times d}$ and a genomic bag $\\mathbf{B}_n^g\\in \\mathbb{R}^{M_g\\times d}$ . Formally, an optimal transport from the WSI feature bag $\\mathbf{B}_n^p = [\\mathbf{b}_{n,1}^p,\\mathbf{b}_{n,2}^p,\\dots ,\\mathbf{b}_{n,M_p}^p ]$ to the genomic embedding $\\mathrm{bag}\\mathbf{B}_n^g = [\\mathbf{b}_{n,1}^g,\\mathbf{b}_{n,2}^g,\\dots ,\\mathbf{b}_{n,M_g}^g ]$ can be defined by the", + "bbox": [ + 75, + 762, + 472, + 905 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "discrete Kantorovich formulation [21] to search the overall optimal matching flow $\\mathbf{P}_n$ between $\\mathbf{B}_n^p$ and $\\mathbf{B}_n^g$ :", + "bbox": [ + 498, + 90, + 890, + 122 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {W} \\left(\\mathbf {B} _ {n} ^ {p}, \\mathbf {B} _ {n} ^ {g}\\right) = \\min _ {\\mathbf {P} _ {n} \\in \\Pi \\left(\\mu_ {p}, \\mu_ {g}\\right)} < \\mathbf {P} _ {n}, \\mathbf {C} _ {n} > _ {F} \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 550, + 132, + 890, + 159 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\mathbf{C}_n\\geq 0\\in \\mathbb{R}^{M_p\\times M_g}$ is a cost matrix given by $\\mathbf{C}_n^{u,v} = c(\\mathbf{b}_{n,u}^p,\\mathbf{b}_{n,v}^g)$ with a ground distance metric $c(\\cdot)$ such as $l_{2}$ -distance, that measures the distance of local pairwise instances $\\mathbf{b}_{n,u}^p\\in \\mathbf{B}_n^p$ in the WSI bag and the genomic one of a unique functional category $\\mathbf{b}_{n,v}^g\\in \\mathbf{B}_n^g$", + "bbox": [ + 496, + 167, + 890, + 244 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Here $\\Pi (\\mu_p,\\mu_g) = \\{\\mathbf{P}_n\\in \\mathbb{R}_+^{M_p\\times M_g}|\\mathbf{P}_n\\mathbf{1}_{M_g} = \\mu_p,\\mathbf{P}_n^\\top \\mathbf{1}_{M_p} = \\mu_g\\}$ involves the marginal constraints of total mass equality between marginal distributions, $\\mu_{p}$ and $\\mu_{g}$ , for the WSI bag and the genomic bag, and $\\mathbf{1}_k$ is a $k$ -dimensional vector of ones. Specifically, $\\Pi (\\mu_p,\\mu_g)$ refers to the set of joint probabilistic couplings between the two marginal empirical distributions of pathology data and genomic data. Intuitively, it describes how to distribute instances of a WSI bag $\\mathbf{B}_n^p$ to the genomic embedding of a genomic bag $\\mathbf{B}_n^g$ based on the cost matrix $\\mathbf{C}_n$ , under the marginal constraints of total mass equality between distributions $\\mu_{p}$ and $\\mu_{g}$ . Note that $< \\cdot >_{F}$ refers to the Frobenius dot product, and thus Eq. 4 encourages to achieve the overall minimum matching cost by finding optimal matching flow based on local pairwise similarity. In this way, the optimal transport of Eq. 4 is able to enforce a trade-off of instances within modality, which allows the model to capture the potential structure of visual interactions for histology and co-expressions for genomic data.", + "bbox": [ + 496, + 244, + 890, + 535 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Once acquiring the optimal matching flow $\\mathbf{P}_n^*$ , informative instances of a WSI are identified by $\\hat{\\mathbf{B}}_n^p = \\mathbf{P}_n^\\top \\mathbf{B}_n^p$ to represent the WSI, which also aligns pathology distribution to genomics distribution under preserving the potential structure across modalities for alleviating heterogeneity.", + "bbox": [ + 496, + 536, + 890, + 611 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As such, the proposed OT-based Co-Attention simultaneously addresses two issues: not only does it achieve the effective representation for gigapixel WSIs by identifying informative instances via OT matching, but marginal constraints of OT enable the selected instances to have global structure consistency with genomic data.", + "bbox": [ + 496, + 611, + 890, + 702 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Optimization over Micro-Batch", + "text_level": 1, + "bbox": [ + 500, + 710, + 777, + 727 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Due to the large size of the WSI bag, it is difficult to apply optimal transport for matching histology data and genomic data. Recent work [48] has validated that MIL on WSI can benefit from multiple subsets of a bag randomly sampled from the original WSI bag. It provides a way to train the model over Micro-Batch of a WSI, where micro-batch is defined as a subset sampled from a bag of WSI instances. Furthermore, inspired by a variant [13] of OT that offers a solution to approximate the original OT over mini-batches with a theoretical guarantee of convergence, we propose to use the variant UMBOT formulation [13] over micro-batch of WSI instead of the original OT over", + "bbox": [ + 496, + 732, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "21245", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "all instances of a WSI. Then the Eq. 4 becomes:", + "bbox": [ + 76, + 90, + 395, + 106 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {W} ^ {m} \\left(B _ {n} ^ {p, m}, \\mathbf {B} _ {n} ^ {g}\\right) = \\min _ {\\mathbf {P} _ {n} ^ {m} \\in \\Pi \\left(\\mu_ {p} ^ {m}, \\mu_ {g}\\right)} < \\mathbf {P} _ {n} ^ {m}, \\mathbf {C} _ {n} ^ {m} > _ {F} \\\\ + \\epsilon K L \\left(\\mathbf {P} _ {n} ^ {m} \\mid \\mu_ {p} ^ {m} \\otimes \\mu_ {g}\\right) + \\tau \\left(D _ {\\phi} \\left(\\mathbf {P} _ {n, p} ^ {m} \\mid \\mid \\mu_ {p} ^ {m}\\right) + D _ {\\phi} \\left(\\mathbf {P} _ {n, g} ^ {m} \\mid \\mid \\mu_ {g}\\right)\\right) \\tag {5} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 112, + 467, + 169 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $B_{n}^{p,m}$ is micro-batch of size $m$ sampled from $\\mathbf{B}_n^p$ . Similarly, $\\mathbf{C}_n^m \\in \\mathbb{R}^{m \\times M_g}$ is the cost matrix over micro-batch of WSI $B_{n}^{p,m}$ and $\\mathbf{B}_n^g$ , and the optimal matching flow $\\mathbf{P}_n^m \\in \\mathbb{R}^{m \\times M_g}$ is optimized over micro-batch as well. Here $\\mathbf{P}_{n,p}^m$ and $\\mathbf{P}_{n,g}^m$ represent the marginals of $\\mathbf{P}_n^m$ , and $D_{\\phi}$ is Csiszar divergences, $\\tau$ and $\\epsilon \\geq 0$ are the coefficients of marginal penalization and entropic regularization, respectively. $KL$ refers to Kullback-Leibler divergence.", + "bbox": [ + 76, + 169, + 467, + 289 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Computational complexity. With the benefit of UMBOT for approximating the original OT, the computational complexity of optimization is reduced from $\\mathcal{O}(M^3\\log (M))$ to $\\mathcal{O}(\\frac{M}{m}\\times m^2) = \\mathcal{O}(M\\times m)$ , where $M = \\max (M_p,M_g)$ and $m\\ll M$ . The whole optimization procedure of the proposed MOTCat is presented in Alg. 1", + "bbox": [ + 76, + 289, + 467, + 380 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Loss function. Following the previous work [5], the overall loss function is formulated by NLL-loss [46]:", + "bbox": [ + 76, + 380, + 467, + 411 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {L} = - \\frac {m}{M _ {p}} \\sum_ {n = 1} ^ {N} \\sum_ {X _ {n} ^ {p, m} \\in \\mathbf {X} _ {n} ^ {p}} c _ {n} \\cdot \\log \\left(S _ {n} ^ {m} \\left(t _ {n} \\mid H _ {n} ^ {m}\\right)\\right) \\\\ - \\frac {m}{M _ {p}} \\sum_ {n = 1} ^ {N} \\sum_ {X _ {n} ^ {p, m} \\in \\mathbf {X} _ {n} ^ {p}} \\left\\{\\left(1 - c _ {n}\\right) \\cdot \\log \\left(S _ {n} ^ {m} \\left(t _ {n} - 1 \\mid H _ {n} ^ {m}\\right)\\right) \\right. \\\\ \\left. + \\left(1 - c _ {n}\\right) \\cdot \\log \\left(h _ {n} ^ {m} \\left(t _ {n} \\mid H _ {n} ^ {m}\\right)\\right) \\right\\} \\tag {6} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 420, + 468, + 542 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $H_{n}^{m}$ refers to the multimodal features over micro-batch formulated in line 16 of Alg. 1. $h_{n}^{m}$ and $S_{n}^{m}$ are the hazard function and cumulative survival function over micro-batch, respectively.", + "bbox": [ + 76, + 542, + 468, + 604 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experiment", + "text_level": 1, + "bbox": [ + 76, + 616, + 200, + 633 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this section, we first present datasets and settings following previous experimental protocols [5, 6] for fair comparisons. Next, we demonstrate the performance results of the proposed method compared with the state-of-the-art (SOTA) methods, including unimodal and multimodal approaches. After that, we investigate the effectiveness of each component in our method and the effect on the size of micro-batch strategy. Finally, from a statistical point of view, we present Kaplan-Meier survival curves and Logrank test to show the performance of survival analysis. Interpretable visualization for histology data and genomic data are presented in supplementary materials.", + "bbox": [ + 75, + 642, + 468, + 823 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Datasets and Settings", + "text_level": 1, + "bbox": [ + 76, + 832, + 276, + 848 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Datasets. To demonstrate the performance of the proposed method, we conducted various experiments over five public cancer datasets from The Cancer Genome Atlas (TCGA)", + "bbox": [ + 76, + 854, + 468, + 900 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "that contains paired diagnostic WSIs and genomic data with ground-truth survival outcome: Bladder Urothelial Carcinoma (BLCA), Breast Invasive Carcinoma (BRCA), Uterine Corpus Endometrial Carcinoma (UCEC), Glioblastoma & Lower Grade Glioma (GBMLGG), and Lung Adenocarcinoma (LUAD). The number of cases for each cancer type is shown by $N$ in Tab. 1. Note that cases of these cancer datasets used for all compared methods are not less than cases used in the proposed method. For genomic data, the number of unique functional categories $M_g$ is set as 6 following [28, 5], including 1) Tumor Suppression, 2) Oncogenesis, 3) Protein Kinases, 4) Cellular Differentiation, 5) Transcription, and 6) Cytokines and Growth.", + "bbox": [ + 496, + 90, + 890, + 286 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Evaluation. For each cancer dataset, we perform 5-fold cross-validation with a 4:1 ratio of training-validation sets and report the cross-validated concordance index (C-Index) and its standard deviation (std) to quantify the performance of correctly ranking the predicted patient risk scores with respect to overall survival.", + "bbox": [ + 496, + 287, + 890, + 378 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Implementation. For each WSI, we first apply the OTSU's threshold method to segment tissue regions, and then non-overlapping $256 \\times 256$ patches are extracted from the tissue region over $20 \\times$ magnification. Then, we use ImageNet-pretrained [10] ResNet-50 [17] and a 256-d fully-connected layer as the feature encoder $f_{p}$ to extract the 1024-d embedding for each patch, where parameters of ResNet-50 are frozen. For genomic data, we adopt SNN [22] as the feature encoder $f_{g}$ following the setting of [5].", + "bbox": [ + 496, + 378, + 890, + 516 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "During training, we follow the setting of [5] for a fair comparison. Specifically, we adopt Adam optimizer with the initial learning rate of $2 \\times 10^{-4}$ and weight decay of $1 \\times 10^{-5}$ . Due to the large size of WSIs, the batch size for WSIs is 1 with 32 gradient accumulation steps, and all experiments are trained for 20 epochs. The size of MicroBatch $m$ is set as 256. Regarding the hyper-parameters of OT in Eq. 5, the coefficient of marginal penalization $\\tau$ is 0.5 for all cancer datasets, and the coefficient of entropic regularization $\\epsilon$ is 0.05 for BLCA and LUAD, as well as 0.1 for BRCA, UCEC and GBMLGG.", + "bbox": [ + 496, + 515, + 890, + 681 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Results", + "text_level": 1, + "bbox": [ + 500, + 694, + 591, + 708 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "We compare our method against the unimodal baselines and the multimodal SOTA methods as follows:", + "bbox": [ + 496, + 717, + 888, + 747 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Unimodal Baseline. For genomic data, we adopt SNN [22] that has been used previously for survival outcome prediction in the TCGA [4, 5], and SNNTrans [22, 36] which incorporates SNN as the feature extractor and TransMIL [36] as the global aggregation model for MIL. For histology, we compare the SOTA MIL methods AttnMIL [19], DeepAttnMISL [45], CLAM [32], TransMIL [36], and DTFDMIL [48].", + "bbox": [ + 496, + 748, + 890, + 868 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Multimodal SOTA. We compare four SOTA methods for multimodal survival outcome prediction including", + "bbox": [ + 496, + 869, + 890, + 900 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "21246", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/61565ece6a852a6422ffcb54271161230511029b5d39f6a7d83b9fc356bed57b.jpg", + "table_caption": [ + "Table 1. C-Index (mean ± std) performance over five cancer datasets. Patho. and Geno. refer to pathology modality and genomic modality, respectively. The best results and the second-best results are highlighted in bold and in underline, respectively." + ], + "table_footnote": [], + "table_body": "
ModelPatho.Geno.BLCA (N=373)BRCA (N=956)UCEC (N=480)GBMLGG (N=569)LUAD (N=453)
SNN* [22]✓0.618 ± 0.0220.624 ± 0.0600.679 ± 0.0400.834 ± 0.0120.611 ± 0.047
SNNTrans* [22, 36]✓0.659 ± 0.0320.647 ± 0.0630.656 ± 0.0380.839 ± 0.0140.638 ± 0.022
AttnMIL* [19]✓0.599 ± 0.0480.609 ± 0.0650.658 ± 0.0360.818 ± 0.0250.620 ± 0.061
DeepAttnMISL [45]✓0.504 ± 0.0420.524 ± 0.0430.597 ± 0.0590.734 ± 0.0290.548 ± 0.050
CLAM-SB* [32]✓0.559 ± 0.0340.573 ± 0.0440.644 ± 0.0610.779 ± 0.0310.594 ± 0.063
CLAM-MB* [32]✓0.565 ± 0.0270.578 ± 0.0320.609 ± 0.0820.776 ± 0.0340.582 ± 0.072
TransMIL* [36]✓0.575 ± 0.0340.666 ± 0.0290.655 ± 0.0460.798 ± 0.0430.642 ± 0.046
DTFD-MIL* [48]✓0.546 ± 0.0210.609 ± 0.0590.656 ± 0.0450.792 ± 0.0230.585 ± 0.066
Pathomic [4]✓✓0.586 ± 0.062--0.826 ± 0.0090.543 ± 0.065
PONET [34]✓✓0.643 ± 0.037---0.646 ± 0.047
Porpoise* [6]✓✓0.636 ± 0.0240.652 ± 0.0420.695 ± 0.0320.834 ± 0.0170.647 ± 0.031
MCAT* [5]✓✓0.672 ± 0.0320.659 ± 0.0310.649 ± 0.0430.835 ± 0.0240.659 ± 0.027
MOTCat (Ours)✓✓0.683 ± 0.0260.673 ± 0.0060.675 ± 0.0400.849 ± 0.0280.670 ± 0.038
", + "bbox": [ + 93, + 116, + 874, + 351 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "MCAT [5], Pathomic [4], Porpoise [6] and PONET [34].", + "text_level": 1, + "bbox": [ + 76, + 375, + 464, + 391 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Results are shown in Tab. 1, where the methods marked * are re-implemented and the best results are reported, and other results are obtained from their papers. Note that due to varying cancer datasets used in their works, not all results of the five datasets used in this work can be reported, and hence we use ' -' to indicate the results are not reported in their papers.", + "bbox": [ + 75, + 392, + 468, + 496 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Unimodal vs. Multimodal. Compared with all unimodal approaches, the proposed method achieves the highest performance in 4 out of 5 cancer datasets, indicating the effective fusion of multimodal data in our method. Note that the overall performance of genomic data is better than that of histology, which validates the reasonability of using genomic data for guiding the selection of instances in WSIs. In particular, most multimodal methods are inferior to the unimodal model of genomics in UCEC dataset, suggesting the serious challenge in multimodal fusion. Nevertheless, the proposed method can achieve the comparative performance with genomic model on UCEC.", + "bbox": [ + 75, + 498, + 468, + 679 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Multimodal SOTA v.s. MOTCat. In one-versus-all comparisons of multimodal models, the proposed method achieves superior performance on all benchmarks with $1.0\\% - 2.6\\%$ performance gains except UCEC. In comparing the proposed method with the most similar work MCAT in multimodal fusion, our method gets better results on all datasets, indicating the effectiveness of learning the intramodal potential structure consistency from a global perspective between TME-related interactions of histology and genomic co-expression.", + "bbox": [ + 75, + 681, + 468, + 833 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 845, + 230, + 862 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We first investigate the effectiveness of OT-based coattention component (denoted by OT) and the micro-batch", + "bbox": [ + 76, + 869, + 468, + 902 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "strategy (denoted by MB). Furthermore, the effect on the size of micro-batch and the actual computational speed of our method are explored.", + "bbox": [ + 496, + 375, + 890, + 421 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Component validation. As shown in Tab. 2, we observe that multimodal fusion can benefit from micro-batch strategy by comparing (a) and (b), and OT-based co-attention further improves the performance by approximating the original results with the averaged results over micro-batches via UMBOT. As a result, our method achieves the best overall performance. These improvements both demonstrate the effectiveness of each component for the proposed method.", + "bbox": [ + 496, + 422, + 890, + 545 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Additionally, recent work [48] has claimed that MIL on WSIs can benefit from learning over sub-bags in a WSI, which is also validated by performance increases in variant (b). The reason why it can profit from micro-batch might be that it increases the number of bags, so that more features can be used for survival analysis.", + "bbox": [ + 496, + 547, + 890, + 638 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Size of Micro-batch. To show the robustness of approximation to the size of Micro-batch strategy, we compare several variants of the proposed method over the varying sizes of micro-batch, as shown in the quantitative analysis of Fig. 3. The qualitative analysis of the effect on size of Micro-Batch can be found in the supplementary materials, which also achieves the consistent conclusion.", + "bbox": [ + 496, + 640, + 890, + 746 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "For the quantitative analysis in Fig. 3, two variants of the proposed method are compared: 1) UMBOT $\\rightarrow$ EMD: To demonstrate the robustness of different OT variants, we replace UMBOT used in our method with the original OT (i.e. EMD) for comparison, which is equivalent to the Eq. (4) done over Micro-batch. 2) UMBOT $\\rightarrow$ CoAttn: To compare the robustness of the proposed OT-based co-attention and the original co-attention, we replace UMBOT with the co-attention used in MCAT [5] and train the model over Micro-batch for comparison.", + "bbox": [ + 496, + 750, + 890, + 901 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "21247", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/8d42093406d24d4e97e55b55d61e7e810ff4f4e7bd2be49c279154957bfcaf26.jpg", + "table_caption": [ + "Table 2. Ablation study assessing C-Index (mean ± std) performance of MOTCat over five datasets, in which version (c) in bold is the proposed method with full components, and (a) and (b) refer to its variants. The best results are marked in bold." + ], + "table_footnote": [], + "table_body": "
VariantsOTMBBLCABRCAUCECGBMLGGLUAD
(a) MCAT0.672 ± 0.0320.659 ± 0.0310.649 ± 0.0430.835 ± 0.0240.659 ± 0.027
(b) MOTCat w/o OT✓0.663 ± 0.0250.666 ± 0.0170.663 ± 0.0310.845 ± 0.0230.673 ± 0.036
(c) MOTCat✓✓0.683 ± 0.0260.673 ± 0.0060.675 ± 0.0400.849 ± 0.0280.670 ± 0.038
", + "bbox": [ + 76, + 114, + 890, + 191 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a6fb8cf62fd8bce7b4428bc01fb7deddca3626a25ad71f966b3e948b54f5af7c.jpg", + "image_caption": [ + "Effect on Size of Micro-Batch (over 128, 256 and 512)" + ], + "image_footnote": [], + "bbox": [ + 83, + 212, + 343, + 339 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/7a602d1e530f6288ca89eb06e9b4cf7b38e722f3ec0a41375721fca37fd76fec.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 357, + 212, + 614, + 339 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/dfe0d9abe54ca716b76e4404ac2ee138c79b082b5151602b0cc45fb358b2877a.jpg", + "image_caption": [ + "Figure 3. Boxplots of C-Index over various sizes of Micro-batch for our method and two variants on five cancer datasets, in which the green triangle means the averaged results of all sizes and the horizontal line in the box represents the median result." + ], + "image_footnote": [], + "bbox": [ + 357, + 349, + 614, + 474 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/043643c531f79873ed07a1347582545f133da90a28c51ebfe88f64d3ddfae42e.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 625, + 212, + 887, + 339 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/abdf0f9023965c62a40d85a337595bf84ac412b0e50ef9d596993185288765e9.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 630, + 349, + 887, + 474 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "From the results of Fig. 3, we can see that 1) our method achieves the best averaged performance of various sizes compared with the two variants, especially on BRCA with the most samples of 956. 2) Further, on UCEC and LUAD datasets, the proposed method gets the most robust results. 3) Although the second variant UMBOT $\\rightarrow$ CoAttn shows slightly better robustness on BLCA and BRCA, the performance of our method surpasses it by a large margin. In a nutshell, the proposed method achieves a better trade-off between performance and robustness, compared with different OT variants or the co-attention of MCAT.", + "bbox": [ + 75, + 537, + 472, + 704 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Computational Speed. We measure the actual averaged computational speed for 10 WSIs (about 150k patches in total) on one GPU of NVIDIA GeForce RTX 3090. The proposed method is compared with a variant 'org-OT' that replaces UMBOT by the original OT. However, the original OT with the high complexity takes extreme long time for one WSI (about 20k patches), and thus we fail to measure the actual computational time for the original OT in a short time. Here we present the speed of our method, which suggests our method makes it practicable to apply OT to histology and genomics. Specifically, the training speed of the proposed method is $6540~\\mathrm{p / s}$ (p/s refers to the number", + "bbox": [ + 75, + 719, + 470, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "of processing patches per second) and the inference speed is $11885\\mathrm{p / s}$ .", + "bbox": [ + 496, + 537, + 892, + 568 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Statistical Analysis", + "text_level": 1, + "bbox": [ + 498, + 579, + 684, + 595 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To show a statistical difference in patient stratification performance, we visualize the Kaplan-Meier survival curves for different methods, in which patients are separated into two groups of low-risk and high-risk based on predicted risk scores, and then the statistics on ground-truth survival time are presented for each group in Fig. 4. The Logrank test is conducted to measure the statistically significant difference in two groups of patients, where a lower P-value indicates better performance of patient stratification. From the results of Fig. 4, intuitively our method separates patients of low and high risk more clearly on all datasets. In the Logrank test, our method achieves a lower P-value on all datasets in comparison to MCAT, especially on BLCA, BRCA and UCEC with a large margin of magnitude.", + "bbox": [ + 496, + 603, + 893, + 815 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 829, + 619, + 845 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we present a novel Multimodal Optimal Transport-based Co-Attention Transformer with global structure consistency to tackle two important issues in mul", + "bbox": [ + 498, + 854, + 892, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "21248", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/3a6391f8914dbb249aa49e79df36b9b76ef5350d26f6117130b79663c5464b7a.jpg", + "image_caption": [ + "Figure 4. Kaplan-Meier Analysis on five cancer datasets, where patient stratifications of low risk (green) and high risk (red) are presented. Shaded areas refer to the confidence intervals. P-value $< 0.05$ means significant statistical difference in two groups, and lower P-value is better. (Zoom in for better viewing.)" + ], + "image_footnote": [], + "bbox": [ + 86, + 89, + 883, + 297 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "timodal learning of histology and genomics for survival prediction. First, we utilize a new OT-based Co-Attention to match pairwise instances between histology and genomics for selecting informative instances strongly related to tumor microenvironment, which provides a way to effectively represent gigapixel WSIs. Second, optimal transport offers a global awareness for modeling potential structure within modality, i.e. pathological interactions and genomic co-expression. Furthermore, to enable applying OT-based Co-Attention in practice, we propose a robust and efficient implementation over micro-batch of WSI bags, in which the approximation over micro-batch might provide a solution to update the parameters of extractor for patch images in an end-to-end way instead of extracting feature embeddings offline, which will be further explored in the future.", + "bbox": [ + 75, + 367, + 472, + 594 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Acknowledgement", + "text_level": 1, + "bbox": [ + 76, + 609, + 236, + 627 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This work was supported by National Natural Science Foundation of China (No. 62202403), Shenzhen Science and Technology Innovation Committee (Project No. SGDX20210823103201011) and Hong Kong Innovation and Technology Fund (No. PRP/034/22FX).", + "bbox": [ + 75, + 633, + 468, + 719 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 76, + 734, + 174, + 750 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Khalid AbdulJabbar, Shan E Ahmed Raza, Rachel Rosenthal, Mariam Jamal-Hanjani, Selvaraju Veeriah, Ayse Akarca, Tom Lund, David A Moore, Roberto Salgado, Maise Al Bakir, et al. 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IEEE, 2016. 3", + "[54] Xinliang Zhu, Jiawen Yao, Feiyun Zhu, and Junzhou Huang. Wsisa: Making survival prediction from whole slide histopathological images. In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 7234-7242, 2017. 1, 2", + "[55] Yingli Zuo, Yawen Wu, Zixiao Lu, Qi Zhu, Kun Huang, Daoqiang Zhang, and Wei Shao. Identify consistent imaging genomic biomarkers for characterizing the survival-associated interactions between tumor-infiltrating lymphocytes and tumors. In Medical Image Computing and Computer Assisted Intervention-MICCAI 2022: 25th International Conference, Singapore, September 18-22, 2022, Proceedings, Part II, pages 222-231. Springer, 2022. 1, 2, 3" + ], + "bbox": [ + 501, + 92, + 890, + 751 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "21251", + "bbox": [ + 478, + 945, + 517, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction/5f20046b-2925-4246-b895-fa5914bd8de8_model.json b/2023/Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction/5f20046b-2925-4246-b895-fa5914bd8de8_model.json new file mode 100644 index 0000000000000000000000000000000000000000..a2b467ab95b65b13830b531f481817f873d186c2 --- /dev/null +++ b/2023/Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction/5f20046b-2925-4246-b895-fa5914bd8de8_model.json @@ -0,0 +1,2345 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.096, + 0.13, + 0.877, + 0.177 + ], + "angle": 0, + "content": "Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction" + }, + { + "type": "text", + "bbox": [ + 0.268, + 0.204, + 0.701, + 0.258 + ], + "angle": 0, + "content": "Yingxue Xu Hao Chen* \nThe Hong Kong University of Science and Technology \n{yxueb, jhc}@cse.ust.hk" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.292, + 0.314, + 0.308 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.324, + 0.474, + 0.765 + ], + "angle": 0, + "content": "Survival prediction is a complicated ordinal regression task that aims to predict the ranking risk of death, which generally benefits from the integration of histology and genomic data. Despite the progress in joint learning from pathology and genomics, existing methods still suffer from challenging issues: 1) Due to the large size of pathological images, it is difficult to effectively represent the gigapixel whole slide images (WSIs). 2) Interactions within tumor microenvironment (TME) in histology are essential for survival analysis. Although current approaches attempt to model these interactions via co-attention between histology and genomic data, they focus on only dense local similarity across modalities, which fails to capture global consistency between potential structures, i.e. TME-related interactions of histology and co-expression of genomic data. To address these challenges, we propose a Multimodal Optimal Transport-based Co-Attention Transformer framework with global structure consistency, in which optimal transport (OT) is applied to match patches of a WSI and genes embeddings for selecting informative patches to represent the gigapixel WSI. More importantly, OT-based co-attention provides a global awareness to effectively capture structural interactions within TME for survival prediction. To overcome high computational complexity of OT, we propose a robust and efficient implementation over micro-batch of WSI patches by approximating the original OT with unbalanced mini-batch OT. Extensive experiments show the superiority of our method on five benchmark datasets compared to the state-of-the-art methods. The code is released1." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.793, + 0.21, + 0.808 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.818, + 0.47, + 0.865 + ], + "angle": 0, + "content": "Survival prediction is a complex ordinal regression task that aims to estimate the relative risk of death in cancer prognosis, which generally integrates the manual as" + }, + { + "type": "image", + "bbox": [ + 0.536, + 0.294, + 0.862, + 0.518 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.52, + 0.895, + 0.604 + ], + "angle": 0, + "content": "Figure 1. Comparison between (a) Co-Attention and (b) OT-based Co-Attention, where (a) learns weights of instances by dense attention, and (b) identifies informative instances by optimal transport matching flow from a global perspective, which enforces considering potential structures of each modality, i.e. interactions within WSIs and co-expression within genomics." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.629, + 0.895, + 0.903 + ], + "angle": 0, + "content": "sessment of qualitative morphological information from pathology data and quantitative molecular profiles from genomic data in clinical settings [6, 55, 4]. Despite recent advances in multimodal learning for histology and genomics [5, 55, 27, 34], there still exists several open issues. Among others, one daunting challenge is to capture key information from heterogeneous modalities for effective fusion. Particularly, due to the large size of about \\(500,000 \\times 500,000\\) pixels, it is challenging to effectively represent gigapixel whole slide images without losing key information. Furthermore, visual concepts of tumor microenvironment (TME) within pathological images are verified to have significant associations with survival analysis in various cancer types [42, 1, 25], e.g. cellular components including fibroblast cells and various immune cells that can alter cancer cell behaviors [33]. However, the TME-related patches occupy only a tiny proportion of the entire WSI, leading to a fine-grained visual recognition problem [54] that is indiscernible" + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.875, + 0.348, + 0.901 + ], + "angle": 0, + "content": "*Corresponding author\n1https://github.com/Innse/MOTCat" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "21241" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.327, + 0.106 + ], + "angle": 0, + "content": "by conventional multimodal learning." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.11, + 0.47, + 0.367 + ], + "angle": 0, + "content": "Recently attention-based multiple instance learning (MIL) [19, 26] has provided a typical solution to identify informative instances, in which a WSI is formulated as a bag of patches (instances) and an attention score is assigned for each instance as a weight for selection. In multimodal learning, genomic data has been applied to guide the selection of TME-related instances by co-attention mechanism across modalities [5], as genes expression might correspond to some morphological characteristics revealed in pathological TME [29, 38]. They [5] densely calculate similarity scores for each pair of pathology and genomic instances as weights of selection to capture fine-grained visual information in WSIs, as shown in Fig. 1 (a). However, this type of approaches with a local view may not thoroughly learn information about TME, since they ignore global potential structure [55] within modality, e.g. interactions within TME for histology and co-expression for genomics [31, 51]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.369, + 0.471, + 0.656 + ], + "angle": 0, + "content": "Fruitful works [31, 33, 5] demonstrate that the interactions within TME are important indicators affecting survival outcomes, e.g. co-occurrence of tumor cells with tumor-infiltrating lymphocytes (TILs) of the immune system is a positive prognostic indicator. However, these collaborative components in TME might be spatially dispersed throughout the entire WSI, which indicates long-range structural associations in WSI, as shown in Fig. 1 (b). On the other hand, genes co-expression [49, 55] also suggests a potential structure. There might be intrinsic consistency between these two potential structures [55, 31], as some studies have verified that genomic mutations can alter normal functions and biological processes of TILs within TME [51, 47]. By leveraging the global consistency between their potential structures to match histology and genomic data, it is more likely to identify TME-related patches from WSIs. However, existing co-attention-based multimodal learning focuses on only dense local similarity, neglecting the global coherence of potential structures." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.659, + 0.47, + 0.902 + ], + "angle": 0, + "content": "To address these challenges, we propose a Multimodal Optimal Transport-based Co-Attention Transformer (MOTCat) framework with global structure consistency, in which optimal transport-based co-attention is applied to match instances between histology and genomics from a global perspective, as shown in Fig. 1 (b). Optimal transport (OT) [11, 3, 41], as a structural matching approach, is able to generate an optimal matching solution with the overall minimum matching cost, based on local pairwise cost between instances of histology and genomics. As a result, instances of a WSI that have high global structure consistency with genes co-expressions can be identified to represent the WSI. These instances might be more strongly associated with TME that contributes to survival prediction. In this way, the aforementioned two challenges can be addressed by OT-based Co-Attention simultaneously." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.394 + ], + "angle": 0, + "content": "Compared with the conventional co-attention mechanism, the advantages of the proposed OT-based co-attention are three-fold. First, optimal transport provides the instances matching process with global awareness. Marginal constraints of total mass equality enforce a trade-off of instances within modality for transporting during optimization, instead of only considering the local similarity of pairwise instances as conventional co-attention does. It enables the modeling of structural interactions of WSIs and co-expressions of genomics, which is beneficial to survival prediction. Second, the learned patch-level attention score is not a rigorous metric for selecting informative instances under weak supervision [48], i.e. slide-level survival time, especially with only a small number of WSI samples. As an alternative, the optimal matching flow is the rigorous closed-form solution to OT problem without accessing any label, achieved by solving the Linear Programming problem. Last, the optimal matching flow provides a transformation between two modalities under preserving the potential structure, which reduces cross-modal heterogeneity gap." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.395, + 0.893, + 0.576 + ], + "angle": 0, + "content": "Nevertheless, due to a massive number of patches from gigapixel WSIs, OT-based co-attention might suffer from high computational complexity, preventing from applying OT to pathology data in practice. To address this, we propose a robust and efficient implementation of OT-based coattention for matching histology and genomics. Specifically, we split all instances of a WSI into a subset termed Micro-Batch and get the averaged result as a proxy to approximate the solution to the original OT problem over all instances by unbalanced optimal transport [13], which can provide a more robust approximation to the subset sampling with the theoretical and experimental guarantee." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.577, + 0.892, + 0.773 + ], + "angle": 0, + "content": "It is worth noting that the proposed method is a generalized multimodal learning framework that captures potential structure across modalities with global structure consistency. The contributions of this work are summarized as follows: (1) we propose a novel multimodal OT-based Co-Attention Transformer with global structure consistency, where OT-based co-attention is used to identify informative instances by global optimal matching, which allows modeling interactions of histology and co-expression of genomics. (2) We propose a robust and efficient implementation of OT-based co-attention over Micro-Batch. (3) Extensive experiments on five benchmark datasets show significant improvement over state-of-the-art methods." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.79, + 0.642, + 0.807 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.816, + 0.812, + 0.832 + ], + "angle": 0, + "content": "2.1. Multimodal Learning in Healthcare" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.903 + ], + "angle": 0, + "content": "In clinical settings, the patient state is often characterized by a spectrum of various modalities [30], such as pathology [54, 32], radiology [39, 50], genomics [28, 47, 31], etc. Multimodal learning has shown superiority by leveraging" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "21242" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.485 + ], + "angle": 0, + "content": "the complementary information from multimodal data [30], in which the key issue is to overcome data heterogeneity for better feature fusion. Most existing methods can be roughly classified into three categories: early fusion [18, 43], late fusion [20, 4], and intermediate fusion [5, 24]. Early fusion is to aggregate all modalities at the input level. The most straightforward solution is fusion operators such as concatenation [18], Kronecker Product [35], etc. However, it neglects intra-modality dynamics [30]. On the contrary, late fusion [15] integrates the predictions from individually separated models at the decision level for the final decision, which cannot fully explore cross-modal interactions. Recently, intermediate fusion has attracted much interest by capturing cross-modal interconnections at different levels, where the typical one is attention-based multimodal fusion [5]. For example, Zhu et al. [52] proposed a triplet attention to integrate MRI and diffusion tensor imaging (DTI) for epilepsy diagnosis. IMGFN [55] designed a graph attention network for survival prediction. MCAT [5] proposed a co-attention to identify informative instances of gigapixel WSI with genomic features as queries. HFBSurv [27] progressively integrated multimodal information from the low level to the high level for survival analysis. Note that our method MOTCat belongs to one of the intermediate fusion approaches, which explores the global consistency of potential structure by optimal transport." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.498, + 0.424, + 0.515 + ], + "angle": 0, + "content": "2.2. Multiple Instance Learning in Pathology" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.524, + 0.473, + 0.904 + ], + "angle": 0, + "content": "Since it is difficult to represent WSIs of large size, MIL algorithms have achieved remarkable progress in pathology, in which WSIs are often formulated as a bag of pathology patches. MIL in pathology generally can be divided into two categories: instance-based algorithms [2, 44, 7] and embedding-based algorithms [19, 16, 32]. The former aims to select a small number of instances within each WSI for training an aggregation model. The latter one is to map each instance into a low-dimension fixed-length embedding offline, and then to learn a bag-level representation based on instance-level embeddings. There are several strategies for aggregating instance-level embeddings. One is clustering-based methods [37, 40], where all the instance-level embeddings are clustered to several centroids that are integrated for the final prediction. The most common strategy is attention-based MIL (AB-MIL) [19, 26] that assigns a weight for each instance, in which various approaches are developed differing in the ways to generate the weighting values. For example, one of the first AB-MIL [19] used a side-branch network for generating attention weights, followed by DS-MIL [26] adopted cosine distance to measure the similarity of instances as weights. Recently, transformer-based MIL like TransMIL [36] has leveraged the self-attention mechanism to explore long-range interactions in WSI. Furthermore, DTFD-MIL [48]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.168 + ], + "angle": 0, + "content": "proposed the double-tier MIL framework for more rigorous instance weights. Unlike AB-MIL, we use optimal match flow generated by OT between pathological and genomic instances to identify instances of WSI that have global potential structure consistency with that of genomics." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.178, + 0.687, + 0.193 + ], + "angle": 0, + "content": "2.3. Survival Prediction" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.202, + 0.895, + 0.55 + ], + "angle": 0, + "content": "Survival outcome prediction, also known as time-to-event analysis [23], aims to predict the probability of experiencing an event of interest, e.g. death event in the clinical setting, before a specific time under both right-censored and uncensored data. Right-censored data refers to cases where the outcome event cannot be observed within the study period [23]. Before the deep learning era, statistical models dominated survival analysis. The typical one is Cox Proportional Hazards (CoxPH) model [9] that characterizes the hazard function, the risk of death, by an exponential linear model. DeepSurv [12] is the first work incorporating deep learning into survival analysis, which models the risk function by several fully connected layers and feeds it to the CoxPH model for the final hazard function. Furthermore, DeepConvSurv [53] first attempted to use pathological images for a deep survival model. Recent works [27, 6, 34, 4, 5] tend to directly estimate the hazard function by deep learning models without any statistical assumption. Histology and genomics data are often integrated as the gold standard for predicting survival outcomes with promising performance [4, 6, 55]. Similarly, our method incorporates these two modalities for better survival prediction by learning their global structural coherence." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.564, + 0.591, + 0.579 + ], + "angle": 0, + "content": "3. Method" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.59, + 0.816, + 0.605 + ], + "angle": 0, + "content": "3.1. Overview and Problem Formulation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.613, + 0.892, + 0.689 + ], + "angle": 0, + "content": "The overall framework of the proposed method is shown in Fig. 2. In this work, we aim to estimate the hazard functions \\( h_n(t) \\) considered as the risk probability of experiencing death event in a small interval after time point \\( t \\) for \\( n \\)-th patient, based on pathology data \\( \\mathbf{X}_n^p \\) and genomic data \\( \\mathbf{X}_n^g \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.892, + 0.84 + ], + "angle": 0, + "content": "For pathology, we formulate each WSI as a \"bag\" structure in a conventional multiple instance learning (MIL) setting, where a bag consists of a collection of instances that are patched from the tissue-containing image regions of a WSI, and instance-level features are extracted from patch images. Genomic data is also organized as a \"bag\" based on the biological functional impact of genes. For each instance of the genomic bag, we adopt an encoder to extract genes embeddings. The bags formulations for histology and genomics are illustrated in Sec. 3.1.1 and 3.1.2, respectively." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Then, Optimal Transport-based Co-Attention is applied to match instances of a WSI and the corresponding genomic instances to model pathological interactions and genomic co-expressions, so that the instances with high structure" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.957 + ], + "angle": 0, + "content": "21243" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.093, + 0.892, + 0.332 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.335, + 0.894, + 0.395 + ], + "angle": 0, + "content": "Figure 2. Overview of Multimodal Optimal Transport-based Co-Attention Transformer (MOTCat) architecture, in which both modalities are formulated as bags representations and a micro-batch of the WSI bag is sampled as pathological input. Then OT-based Co-attention is to calculate optimal matching flow for identifying informative instances with global structure consistency. After aggregating selected instances, features from both modalities are concatenated for survival prediction." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.417, + 0.469, + 0.447 + ], + "angle": 0, + "content": "consistency can be identified to represent the whole modality. This part will be demonstrated in Sec. 3.2." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.448, + 0.471, + 0.584 + ], + "angle": 0, + "content": "After that, a Transformer encoder will integrate all instances after selection for each modality into a bag-level representation, in which each instance is treated as a token. The bag-level representation will be concatenated into the multimodal features for predicting a hazard function to get the ordinal survival risk. The details will be described in Sec. 3.1.3. Finally, optimization process over Micro-Batch and the corresponding computational complexity analysis will be presented in Sec. 3.3." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.602, + 0.294, + 0.618 + ], + "angle": 0, + "content": "3.1.1 WSI Bags Formulation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.625, + 0.473, + 0.765 + ], + "angle": 0, + "content": "We formulate the learning process of pathology images (WSIs) as a weakly-supervised MIL task, in which each WSI \\(\\mathbf{X}_n^p\\) is represented as a bag with access to only bag-level (slide-level) labels. Given a bag \\(\\mathbf{X}_n^p = \\{\\mathbf{x}_{n,i}^p\\}_{i = 1}^{M_p}\\) of \\(M_{p}\\) permutation-invariant instances, the goal is to encode instance-level features of a WSI into a compact bag-level feature embedding and then assign a bag-level label to it. To this end, we apply a CNN encoder \\(f_{p}(\\cdot)\\) for each patch of the WSI to obtain a bag \\(\\mathbf{B}_n^p\\) of instance-level features:" + }, + { + "type": "equation", + "bbox": [ + 0.125, + 0.775, + 0.47, + 0.797 + ], + "angle": 0, + "content": "\\[\n\\mathbf {B} _ {n} ^ {p} = \\left\\{f _ {p} \\left(\\mathbf {x} _ {n, i} ^ {p}\\right): \\mathbf {x} _ {n, i} ^ {p} \\in \\mathbf {X} _ {n} ^ {p} \\right\\} = \\left\\{\\mathbf {b} _ {n, i} ^ {p} \\right\\} _ {i = 1} ^ {M _ {p}}, \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.807, + 0.471, + 0.903 + ], + "angle": 0, + "content": "where \\(\\mathbf{B}_n^p\\in \\mathbb{R}^{M_p\\times d}\\) contains \\(d\\) -dimensional instances and \\(\\mathbf{b}_{n,i}^p = f_p(\\mathbf{x}_{n,i}^p)\\). After identifying informative instances of \\(\\mathbf{B}_n^p\\) by OT-based Co-Attention, we construct a new bag \\(\\hat{\\mathbf{B}}_n^p\\in \\mathbb{R}^{\\hat{M}_p\\times d}\\) of features with \\(\\hat{M}_p\\) instances, which will be illustrated in detail in Section 3.2. Then, a transformer encoder is used as a global aggregation model \\(\\mathcal{T}_p(\\cdot)\\) to obtain" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.416, + 0.892, + 0.448 + ], + "angle": 0, + "content": "the bag-level representation \\( H_{n}^{p} = \\mathcal{T}_{p}(\\hat{\\mathbf{B}}_{n}^{p}) \\) for the subsequent features fusion." + }, + { + "type": "title", + "bbox": [ + 0.502, + 0.462, + 0.755, + 0.478 + ], + "angle": 0, + "content": "Algorithm 1 The MOTCat Algorithm" + }, + { + "type": "ref_text", + "bbox": [ + 0.501, + 0.481, + 0.892, + 0.532 + ], + "angle": 0, + "content": "Input: A WSI bag as \\(\\mathbf{X}_n^p = \\{\\mathbf{x}_{n,i}^p\\}_{i = 1}^{M_p}\\); A genomic bag as \\(\\mathbf{X}_n^g = \\{\\mathbf{x}_{n,j}^g\\}_{j = 1}^{M_g}\\). \\(m\\) refers to the size for a micro-batch of a WSI." + }, + { + "type": "ref_text", + "bbox": [ + 0.502, + 0.534, + 0.792, + 0.548 + ], + "angle": 0, + "content": "Output: The optimal parameters of model;" + }, + { + "type": "ref_text", + "bbox": [ + 0.509, + 0.549, + 0.892, + 0.579 + ], + "angle": 0, + "content": "1: // Sample micro-batch from the WSI bag \\( X_{n}^{p,m} = \\{\\mathbf{x}_{n,i}^{p}\\}_{i=1}^{m} \\) each time." + }, + { + "type": "ref_text", + "bbox": [ + 0.511, + 0.579, + 0.662, + 0.594 + ], + "angle": 0, + "content": "2: for \\( X_{n}^{p,m} \\) in \\( \\mathbf{X}_n^p \\) do" + }, + { + "type": "ref_text", + "bbox": [ + 0.512, + 0.595, + 0.819, + 0.61 + ], + "angle": 0, + "content": "3: Fix model parameters \\( f_{p}, f_{g}, \\mathcal{T}_{p} \\) and \\( \\mathcal{T}_g \\)." + }, + { + "type": "ref_text", + "bbox": [ + 0.512, + 0.611, + 0.842, + 0.623 + ], + "angle": 0, + "content": "4: // To extract a bag of instance-level features" + }, + { + "type": "ref_text", + "bbox": [ + 0.512, + 0.625, + 0.803, + 0.639 + ], + "angle": 0, + "content": "5: // Eq. 1 over micro-batch of histology" + }, + { + "type": "ref_text", + "bbox": [ + 0.511, + 0.64, + 0.783, + 0.655 + ], + "angle": 0, + "content": "6: \\(B_{n}^{p,m} = \\{f_{p}(\\mathbf{x}_{n,i}^{p}):\\mathbf{x}_{n,i}^{p}\\in X_{n}^{p,m}\\}\\)" + }, + { + "type": "ref_text", + "bbox": [ + 0.512, + 0.656, + 0.69, + 0.669 + ], + "angle": 0, + "content": "7: // Eq. 2 of genomics" + }, + { + "type": "ref_text", + "bbox": [ + 0.512, + 0.67, + 0.759, + 0.686 + ], + "angle": 0, + "content": "8: \\(\\mathbf{B}_n^g = \\{f_g^j (\\mathbf{x}_{n,j}^g):\\mathbf{x}_{n,j}^g\\in \\mathbf{X}_n^g\\}\\)" + }, + { + "type": "ref_text", + "bbox": [ + 0.509, + 0.686, + 0.891, + 0.714 + ], + "angle": 0, + "content": "9: Optimize \\(\\mathbf{P}_n^m\\) via Sinkhorn-Knopp matrix scaling algorithm [8, 14]:" + }, + { + "type": "ref_text", + "bbox": [ + 0.508, + 0.715, + 0.861, + 0.731 + ], + "angle": 0, + "content": "10: \\(\\mathbf{P}_n^m\\gets \\arg \\min_{\\mathbf{P}_n^m}\\mathcal{W}^m (B_n^{p,m},\\mathbf{B}_n^g) / /\\) Eq. 5" + }, + { + "type": "ref_text", + "bbox": [ + 0.507, + 0.731, + 0.842, + 0.745 + ], + "angle": 0, + "content": "Fix \\(\\mathbf{P}_n^m\\) and select instances from \\(B_n^{p,m}\\) by:" + }, + { + "type": "ref_text", + "bbox": [ + 0.508, + 0.745, + 0.702, + 0.76 + ], + "angle": 0, + "content": "12: \\(\\bar{B}_n^{p,m} = \\mathbf{P}_n^{m|}B_n^{p,m}\\)" + }, + { + "type": "ref_text", + "bbox": [ + 0.508, + 0.761, + 0.772, + 0.775 + ], + "angle": 0, + "content": "13: // To get bag-level representation" + }, + { + "type": "ref_text", + "bbox": [ + 0.508, + 0.775, + 0.791, + 0.799 + ], + "angle": 0, + "content": "14: \\(H_{n}^{p,m} = \\mathcal{T}_{p}\\left(\\hat{B}_{n}^{p,m}\\right) / /\\) for histology" + }, + { + "type": "ref_text", + "bbox": [ + 0.508, + 0.799, + 0.765, + 0.821 + ], + "angle": 0, + "content": "15: \\(H_{n}^{g} = \\mathcal{T}_{g}\\left(\\hat{\\mathbf{B}}_{n}^{g}\\right) / /\\) for genomics" + }, + { + "type": "ref_text", + "bbox": [ + 0.507, + 0.822, + 0.8, + 0.836 + ], + "angle": 0, + "content": "16: \\( H_{n}^{m} = H_{n}^{p,m} \\bowtie H_{n}^{g} // \\text{Concatenation} \\)" + }, + { + "type": "ref_text", + "bbox": [ + 0.507, + 0.837, + 0.854, + 0.851 + ], + "angle": 0, + "content": "17: Calculate the overall loss function \\(\\mathcal{L}\\) of Eq. 6." + }, + { + "type": "ref_text", + "bbox": [ + 0.507, + 0.852, + 0.891, + 0.881 + ], + "angle": 0, + "content": "18: Update parameters of \\( f_{g} \\), \\( \\mathcal{T}_{p} \\), \\( \\mathcal{T}_{g} \\) and the last fully connected layers of \\( f_{p} \\) by Adam." + }, + { + "type": "ref_text", + "bbox": [ + 0.508, + 0.882, + 0.583, + 0.893 + ], + "angle": 0, + "content": "19: end for" + }, + { + "type": "list", + "bbox": [ + 0.507, + 0.481, + 0.892, + 0.893 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "21244" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.077, + 0.092, + 0.325, + 0.108 + ], + "angle": 0, + "content": "3.1.2 Genomic Bags Formulation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.115, + 0.473, + 0.299 + ], + "angle": 0, + "content": "Genomic data consists of \\(1 \\times 1\\) attributes, such as mutation status, transcript abundance (RNA-Seq), copy number variation (CNV) and other molecular characterizations. Following the organization of genomic data in the previous work [5, 28] that categories them according to the biological functional impact, the expressive genomic bag can be organized as \\(\\mathbf{X}_n^g = \\{\\mathbf{x}_{n,j}^g\\}_{j=1}^{M_g} \\in \\mathbb{R}^{M_g \\times d_j}\\) with \\(M_g\\) instances of unique functional categories. For \\(j\\)-th category, the corresponding genomic embedding consists of \\(d_j\\)-dimensional attributes encoded by a separated network \\(f_g^j(\\cdot)\\). Similarly, a bag \\(\\mathbf{B}_n^g \\in \\mathbb{R}^{M_g \\times d}\\) of genomic data with \\(M_g\\) instances can be constructed as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.12, + 0.308, + 0.47, + 0.332 + ], + "angle": 0, + "content": "\\[\n\\mathbf {B} _ {n} ^ {g} = \\{f _ {g} ^ {j} (\\mathbf {x} _ {n, j} ^ {g}): \\mathbf {x} _ {n, j} ^ {g} \\in \\mathbf {X} _ {n} ^ {g} \\} = \\{\\mathbf {b} _ {n, j} ^ {g} \\} _ {j = 1} ^ {M _ {g}}, \\quad (2)\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.338, + 0.47, + 0.371 + ], + "angle": 0, + "content": "which is aggregated to the bag-level embedding by a transformer encoder \\( H_{n}^{g} = \\mathcal{T}_{g}(\\mathbf{B}_{n}^{g}) \\) as well." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.386, + 0.445, + 0.401 + ], + "angle": 0, + "content": "3.1.3 Multimodal Survival Prediction Formulation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.41, + 0.473, + 0.683 + ], + "angle": 0, + "content": "Survival outcome prediction aims to predict the risk probability of an outcome event occurring before a specific time, in which the outcome event is not always observed, leading to a right-censored event. In this task, let \\( c \\in \\{0,1\\} \\) be censor status indicating whether the outcome event is right-censored (\\( c = 1 \\)) or not (\\( c = 0 \\)), and \\( t \\in \\mathbb{R}^+ \\) refers to the overall survival time (in months). Given a training set of \\( N \\) pathology-genomics pairs \\( \\mathcal{D} = \\{(\\mathbf{X}_n^p, \\mathbf{X}_n^g), c_n, t^n\\}_{n=1}^N \\), we can acquire the bag-level features \\( H_n^p \\) of WSIs and \\( H_n^g \\) of genomic data for \\( n \\)-th patient data \\( \\mathbf{X}_n = ((\\mathbf{X}_n^p, \\mathbf{X}_n^g), c_n, t^n) \\), as described in Section 3.1.1 and 3.1.2. After integrating \\( H_n^p \\) and \\( H_n^g \\) into the multimodal features \\( H_n \\) by concatenation, we estimate the hazard function \\( h_n(t|H_n) = h_n(T = t | T \\geq t, H_n) \\in [0,1] \\) which is viewed as the probability of death event occurring at around time point \\( t \\). Instead of predicting the overall survival time \\( t^n \\), the survival prediction task is to estimate the ordinal risk of death via the cumulative survival function:" + }, + { + "type": "equation", + "bbox": [ + 0.161, + 0.69, + 0.47, + 0.731 + ], + "angle": 0, + "content": "\\[\nS _ {n} (t \\mid H _ {n}) = \\prod_ {z = 1} ^ {t} \\left(1 - h _ {n} (z \\mid H _ {n})\\right) \\tag {3}\n\\]" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.74, + 0.416, + 0.757 + ], + "angle": 0, + "content": "3.2. Optimal Transport-based Co-Attention" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.763, + 0.473, + 0.906 + ], + "angle": 0, + "content": "To identify TME-related instances of WSIs, we utilize the global potential structure consistency between TME interactions of pathology and genes co-expressions as the evidence of selecting instances, in which optimal transport is used to learn the optimal matching flow between a WSI feature bag \\(\\mathbf{B}_n^p\\in \\mathbb{R}^{M_p\\times d}\\) and a genomic bag \\(\\mathbf{B}_n^g\\in \\mathbb{R}^{M_g\\times d}\\). Formally, an optimal transport from the WSI feature bag \\(\\mathbf{B}_n^p = [\\mathbf{b}_{n,1}^p,\\mathbf{b}_{n,2}^p,\\dots ,\\mathbf{b}_{n,M_p}^p ]\\) to the genomic embedding \\(\\mathrm{bag}\\mathbf{B}_n^g = [\\mathbf{b}_{n,1}^g,\\mathbf{b}_{n,2}^g,\\dots ,\\mathbf{b}_{n,M_g}^g ]\\) can be defined by the" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.123 + ], + "angle": 0, + "content": "discrete Kantorovich formulation [21] to search the overall optimal matching flow \\(\\mathbf{P}_n\\) between \\(\\mathbf{B}_n^p\\) and \\(\\mathbf{B}_n^g\\):" + }, + { + "type": "equation", + "bbox": [ + 0.551, + 0.133, + 0.892, + 0.16 + ], + "angle": 0, + "content": "\\[\n\\mathcal {W} \\left(\\mathbf {B} _ {n} ^ {p}, \\mathbf {B} _ {n} ^ {g}\\right) = \\min _ {\\mathbf {P} _ {n} \\in \\Pi \\left(\\mu_ {p}, \\mu_ {g}\\right)} < \\mathbf {P} _ {n}, \\mathbf {C} _ {n} > _ {F} \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.169, + 0.892, + 0.246 + ], + "angle": 0, + "content": "where \\(\\mathbf{C}_n\\geq 0\\in \\mathbb{R}^{M_p\\times M_g}\\) is a cost matrix given by \\(\\mathbf{C}_n^{u,v} = c(\\mathbf{b}_{n,u}^p,\\mathbf{b}_{n,v}^g)\\) with a ground distance metric \\(c(\\cdot)\\) such as \\(l_{2}\\)-distance, that measures the distance of local pairwise instances \\(\\mathbf{b}_{n,u}^p\\in \\mathbf{B}_n^p\\) in the WSI bag and the genomic one of a unique functional category \\(\\mathbf{b}_{n,v}^g\\in \\mathbf{B}_n^g\\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.246, + 0.892, + 0.536 + ], + "angle": 0, + "content": "Here \\(\\Pi (\\mu_p,\\mu_g) = \\{\\mathbf{P}_n\\in \\mathbb{R}_+^{M_p\\times M_g}|\\mathbf{P}_n\\mathbf{1}_{M_g} = \\mu_p,\\mathbf{P}_n^\\top \\mathbf{1}_{M_p} = \\mu_g\\}\\) involves the marginal constraints of total mass equality between marginal distributions, \\(\\mu_{p}\\) and \\(\\mu_{g}\\), for the WSI bag and the genomic bag, and \\(\\mathbf{1}_k\\) is a \\(k\\)-dimensional vector of ones. Specifically, \\(\\Pi (\\mu_p,\\mu_g)\\) refers to the set of joint probabilistic couplings between the two marginal empirical distributions of pathology data and genomic data. Intuitively, it describes how to distribute instances of a WSI bag \\(\\mathbf{B}_n^p\\) to the genomic embedding of a genomic bag \\(\\mathbf{B}_n^g\\) based on the cost matrix \\(\\mathbf{C}_n\\), under the marginal constraints of total mass equality between distributions \\(\\mu_{p}\\) and \\(\\mu_{g}\\). Note that \\(< \\cdot >_{F}\\) refers to the Frobenius dot product, and thus Eq. 4 encourages to achieve the overall minimum matching cost by finding optimal matching flow based on local pairwise similarity. In this way, the optimal transport of Eq. 4 is able to enforce a trade-off of instances within modality, which allows the model to capture the potential structure of visual interactions for histology and co-expressions for genomic data." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.537, + 0.892, + 0.612 + ], + "angle": 0, + "content": "Once acquiring the optimal matching flow \\(\\mathbf{P}_n^*\\), informative instances of a WSI are identified by \\(\\hat{\\mathbf{B}}_n^p = \\mathbf{P}_n^\\top \\mathbf{B}_n^p\\) to represent the WSI, which also aligns pathology distribution to genomics distribution under preserving the potential structure across modalities for alleviating heterogeneity." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.612, + 0.892, + 0.703 + ], + "angle": 0, + "content": "As such, the proposed OT-based Co-Attention simultaneously addresses two issues: not only does it achieve the effective representation for gigapixel WSIs by identifying informative instances via OT matching, but marginal constraints of OT enable the selected instances to have global structure consistency with genomic data." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.712, + 0.779, + 0.728 + ], + "angle": 0, + "content": "3.3. Optimization over Micro-Batch" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.733, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Due to the large size of the WSI bag, it is difficult to apply optimal transport for matching histology data and genomic data. Recent work [48] has validated that MIL on WSI can benefit from multiple subsets of a bag randomly sampled from the original WSI bag. It provides a way to train the model over Micro-Batch of a WSI, where micro-batch is defined as a subset sampled from a bag of WSI instances. Furthermore, inspired by a variant [13] of OT that offers a solution to approximate the original OT over mini-batches with a theoretical guarantee of convergence, we propose to use the variant UMBOT formulation [13] over micro-batch of WSI instead of the original OT over" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "21245" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.396, + 0.107 + ], + "angle": 0, + "content": "all instances of a WSI. Then the Eq. 4 becomes:" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.113, + 0.468, + 0.17 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {W} ^ {m} \\left(B _ {n} ^ {p, m}, \\mathbf {B} _ {n} ^ {g}\\right) = \\min _ {\\mathbf {P} _ {n} ^ {m} \\in \\Pi \\left(\\mu_ {p} ^ {m}, \\mu_ {g}\\right)} < \\mathbf {P} _ {n} ^ {m}, \\mathbf {C} _ {n} ^ {m} > _ {F} \\\\ + \\epsilon K L \\left(\\mathbf {P} _ {n} ^ {m} \\mid \\mu_ {p} ^ {m} \\otimes \\mu_ {g}\\right) + \\tau \\left(D _ {\\phi} \\left(\\mathbf {P} _ {n, p} ^ {m} \\mid \\mid \\mu_ {p} ^ {m}\\right) + D _ {\\phi} \\left(\\mathbf {P} _ {n, g} ^ {m} \\mid \\mid \\mu_ {g}\\right)\\right) \\tag {5} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.17, + 0.468, + 0.29 + ], + "angle": 0, + "content": "where \\( B_{n}^{p,m} \\) is micro-batch of size \\( m \\) sampled from \\( \\mathbf{B}_n^p \\). Similarly, \\( \\mathbf{C}_n^m \\in \\mathbb{R}^{m \\times M_g} \\) is the cost matrix over micro-batch of WSI \\( B_{n}^{p,m} \\) and \\( \\mathbf{B}_n^g \\), and the optimal matching flow \\( \\mathbf{P}_n^m \\in \\mathbb{R}^{m \\times M_g} \\) is optimized over micro-batch as well. Here \\( \\mathbf{P}_{n,p}^m \\) and \\( \\mathbf{P}_{n,g}^m \\) represent the marginals of \\( \\mathbf{P}_n^m \\), and \\( D_{\\phi} \\) is Csiszar divergences, \\( \\tau \\) and \\( \\epsilon \\geq 0 \\) are the coefficients of marginal penalization and entropic regularization, respectively. \\( KL \\) refers to Kullback-Leibler divergence." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.29, + 0.468, + 0.381 + ], + "angle": 0, + "content": "Computational complexity. With the benefit of UMBOT for approximating the original OT, the computational complexity of optimization is reduced from \\(\\mathcal{O}(M^3\\log (M))\\) to \\(\\mathcal{O}(\\frac{M}{m}\\times m^2) = \\mathcal{O}(M\\times m)\\), where \\(M = \\max (M_p,M_g)\\) and \\(m\\ll M\\). The whole optimization procedure of the proposed MOTCat is presented in Alg. 1" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.381, + 0.468, + 0.412 + ], + "angle": 0, + "content": "Loss function. Following the previous work [5], the overall loss function is formulated by NLL-loss [46]:" + }, + { + "type": "equation", + "bbox": [ + 0.077, + 0.421, + 0.47, + 0.544 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {L} = - \\frac {m}{M _ {p}} \\sum_ {n = 1} ^ {N} \\sum_ {X _ {n} ^ {p, m} \\in \\mathbf {X} _ {n} ^ {p}} c _ {n} \\cdot \\log \\left(S _ {n} ^ {m} \\left(t _ {n} \\mid H _ {n} ^ {m}\\right)\\right) \\\\ - \\frac {m}{M _ {p}} \\sum_ {n = 1} ^ {N} \\sum_ {X _ {n} ^ {p, m} \\in \\mathbf {X} _ {n} ^ {p}} \\left\\{\\left(1 - c _ {n}\\right) \\cdot \\log \\left(S _ {n} ^ {m} \\left(t _ {n} - 1 \\mid H _ {n} ^ {m}\\right)\\right) \\right. \\\\ \\left. + \\left(1 - c _ {n}\\right) \\cdot \\log \\left(h _ {n} ^ {m} \\left(t _ {n} \\mid H _ {n} ^ {m}\\right)\\right) \\right\\} \\tag {6} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.544, + 0.469, + 0.605 + ], + "angle": 0, + "content": "where \\( H_{n}^{m} \\) refers to the multimodal features over micro-batch formulated in line 16 of Alg. 1. \\( h_{n}^{m} \\) and \\( S_{n}^{m} \\) are the hazard function and cumulative survival function over micro-batch, respectively." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.617, + 0.202, + 0.634 + ], + "angle": 0, + "content": "4. Experiment" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.643, + 0.469, + 0.824 + ], + "angle": 0, + "content": "In this section, we first present datasets and settings following previous experimental protocols [5, 6] for fair comparisons. Next, we demonstrate the performance results of the proposed method compared with the state-of-the-art (SOTA) methods, including unimodal and multimodal approaches. After that, we investigate the effectiveness of each component in our method and the effect on the size of micro-batch strategy. Finally, from a statistical point of view, we present Kaplan-Meier survival curves and Logrank test to show the performance of survival analysis. Interpretable visualization for histology data and genomic data are presented in supplementary materials." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.833, + 0.277, + 0.849 + ], + "angle": 0, + "content": "4.1. Datasets and Settings" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.856, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Datasets. To demonstrate the performance of the proposed method, we conducted various experiments over five public cancer datasets from The Cancer Genome Atlas (TCGA)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.287 + ], + "angle": 0, + "content": "that contains paired diagnostic WSIs and genomic data with ground-truth survival outcome: Bladder Urothelial Carcinoma (BLCA), Breast Invasive Carcinoma (BRCA), Uterine Corpus Endometrial Carcinoma (UCEC), Glioblastoma & Lower Grade Glioma (GBMLGG), and Lung Adenocarcinoma (LUAD). The number of cases for each cancer type is shown by \\(N\\) in Tab. 1. Note that cases of these cancer datasets used for all compared methods are not less than cases used in the proposed method. For genomic data, the number of unique functional categories \\(M_g\\) is set as 6 following [28, 5], including 1) Tumor Suppression, 2) Oncogenesis, 3) Protein Kinases, 4) Cellular Differentiation, 5) Transcription, and 6) Cytokines and Growth." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.288, + 0.892, + 0.379 + ], + "angle": 0, + "content": "Evaluation. For each cancer dataset, we perform 5-fold cross-validation with a 4:1 ratio of training-validation sets and report the cross-validated concordance index (C-Index) and its standard deviation (std) to quantify the performance of correctly ranking the predicted patient risk scores with respect to overall survival." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.38, + 0.892, + 0.517 + ], + "angle": 0, + "content": "Implementation. For each WSI, we first apply the OTSU's threshold method to segment tissue regions, and then non-overlapping \\(256 \\times 256\\) patches are extracted from the tissue region over \\(20 \\times\\) magnification. Then, we use ImageNet-pretrained [10] ResNet-50 [17] and a 256-d fully-connected layer as the feature encoder \\(f_{p}\\) to extract the 1024-d embedding for each patch, where parameters of ResNet-50 are frozen. For genomic data, we adopt SNN [22] as the feature encoder \\(f_{g}\\) following the setting of [5]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.516, + 0.892, + 0.682 + ], + "angle": 0, + "content": "During training, we follow the setting of [5] for a fair comparison. Specifically, we adopt Adam optimizer with the initial learning rate of \\(2 \\times 10^{-4}\\) and weight decay of \\(1 \\times 10^{-5}\\). Due to the large size of WSIs, the batch size for WSIs is 1 with 32 gradient accumulation steps, and all experiments are trained for 20 epochs. The size of MicroBatch \\(m\\) is set as 256. Regarding the hyper-parameters of OT in Eq. 5, the coefficient of marginal penalization \\(\\tau\\) is 0.5 for all cancer datasets, and the coefficient of entropic regularization \\(\\epsilon\\) is 0.05 for BLCA and LUAD, as well as 0.1 for BRCA, UCEC and GBMLGG." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.695, + 0.593, + 0.709 + ], + "angle": 0, + "content": "4.2. Results" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.718, + 0.89, + 0.748 + ], + "angle": 0, + "content": "We compare our method against the unimodal baselines and the multimodal SOTA methods as follows:" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.749, + 0.892, + 0.869 + ], + "angle": 0, + "content": "Unimodal Baseline. For genomic data, we adopt SNN [22] that has been used previously for survival outcome prediction in the TCGA [4, 5], and SNNTrans [22, 36] which incorporates SNN as the feature extractor and TransMIL [36] as the global aggregation model for MIL. For histology, we compare the SOTA MIL methods AttnMIL [19], DeepAttnMISL [45], CLAM [32], TransMIL [36], and DTFDMIL [48]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Multimodal SOTA. We compare four SOTA methods for multimodal survival outcome prediction including" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "21246" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.088, + 0.892, + 0.116 + ], + "angle": 0, + "content": "Table 1. C-Index (mean ± std) performance over five cancer datasets. Patho. and Geno. refer to pathology modality and genomic modality, respectively. The best results and the second-best results are highlighted in bold and in underline, respectively." + }, + { + "type": "table", + "bbox": [ + 0.094, + 0.117, + 0.875, + 0.352 + ], + "angle": 0, + "content": "
ModelPatho.Geno.BLCA (N=373)BRCA (N=956)UCEC (N=480)GBMLGG (N=569)LUAD (N=453)
SNN* [22]✓0.618 ± 0.0220.624 ± 0.0600.679 ± 0.0400.834 ± 0.0120.611 ± 0.047
SNNTrans* [22, 36]✓0.659 ± 0.0320.647 ± 0.0630.656 ± 0.0380.839 ± 0.0140.638 ± 0.022
AttnMIL* [19]✓0.599 ± 0.0480.609 ± 0.0650.658 ± 0.0360.818 ± 0.0250.620 ± 0.061
DeepAttnMISL [45]✓0.504 ± 0.0420.524 ± 0.0430.597 ± 0.0590.734 ± 0.0290.548 ± 0.050
CLAM-SB* [32]✓0.559 ± 0.0340.573 ± 0.0440.644 ± 0.0610.779 ± 0.0310.594 ± 0.063
CLAM-MB* [32]✓0.565 ± 0.0270.578 ± 0.0320.609 ± 0.0820.776 ± 0.0340.582 ± 0.072
TransMIL* [36]✓0.575 ± 0.0340.666 ± 0.0290.655 ± 0.0460.798 ± 0.0430.642 ± 0.046
DTFD-MIL* [48]✓0.546 ± 0.0210.609 ± 0.0590.656 ± 0.0450.792 ± 0.0230.585 ± 0.066
Pathomic [4]✓✓0.586 ± 0.062--0.826 ± 0.0090.543 ± 0.065
PONET [34]✓✓0.643 ± 0.037---0.646 ± 0.047
Porpoise* [6]✓✓0.636 ± 0.0240.652 ± 0.0420.695 ± 0.0320.834 ± 0.0170.647 ± 0.031
MCAT* [5]✓✓0.672 ± 0.0320.659 ± 0.0310.649 ± 0.0430.835 ± 0.0240.659 ± 0.027
MOTCat (Ours)✓✓0.683 ± 0.0260.673 ± 0.0060.675 ± 0.0400.849 ± 0.0280.670 ± 0.038
" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.376, + 0.465, + 0.392 + ], + "angle": 0, + "content": "MCAT [5], Pathomic [4], Porpoise [6] and PONET [34]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.393, + 0.47, + 0.497 + ], + "angle": 0, + "content": "Results are shown in Tab. 1, where the methods marked * are re-implemented and the best results are reported, and other results are obtained from their papers. Note that due to varying cancer datasets used in their works, not all results of the five datasets used in this work can be reported, and hence we use ' -' to indicate the results are not reported in their papers." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.499, + 0.47, + 0.68 + ], + "angle": 0, + "content": "Unimodal vs. Multimodal. Compared with all unimodal approaches, the proposed method achieves the highest performance in 4 out of 5 cancer datasets, indicating the effective fusion of multimodal data in our method. Note that the overall performance of genomic data is better than that of histology, which validates the reasonability of using genomic data for guiding the selection of instances in WSIs. In particular, most multimodal methods are inferior to the unimodal model of genomics in UCEC dataset, suggesting the serious challenge in multimodal fusion. Nevertheless, the proposed method can achieve the comparative performance with genomic model on UCEC." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.682, + 0.47, + 0.834 + ], + "angle": 0, + "content": "Multimodal SOTA v.s. MOTCat. In one-versus-all comparisons of multimodal models, the proposed method achieves superior performance on all benchmarks with \\(1.0\\% - 2.6\\%\\) performance gains except UCEC. In comparing the proposed method with the most similar work MCAT in multimodal fusion, our method gets better results on all datasets, indicating the effectiveness of learning the intramodal potential structure consistency from a global perspective between TME-related interactions of histology and genomic co-expression." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.846, + 0.231, + 0.863 + ], + "angle": 0, + "content": "4.3. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.871, + 0.47, + 0.903 + ], + "angle": 0, + "content": "We first investigate the effectiveness of OT-based coattention component (denoted by OT) and the micro-batch" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.376, + 0.892, + 0.422 + ], + "angle": 0, + "content": "strategy (denoted by MB). Furthermore, the effect on the size of micro-batch and the actual computational speed of our method are explored." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.424, + 0.892, + 0.546 + ], + "angle": 0, + "content": "Component validation. As shown in Tab. 2, we observe that multimodal fusion can benefit from micro-batch strategy by comparing (a) and (b), and OT-based co-attention further improves the performance by approximating the original results with the averaged results over micro-batches via UMBOT. As a result, our method achieves the best overall performance. These improvements both demonstrate the effectiveness of each component for the proposed method." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.548, + 0.892, + 0.639 + ], + "angle": 0, + "content": "Additionally, recent work [48] has claimed that MIL on WSIs can benefit from learning over sub-bags in a WSI, which is also validated by performance increases in variant (b). The reason why it can profit from micro-batch might be that it increases the number of bags, so that more features can be used for survival analysis." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.641, + 0.892, + 0.747 + ], + "angle": 0, + "content": "Size of Micro-batch. To show the robustness of approximation to the size of Micro-batch strategy, we compare several variants of the proposed method over the varying sizes of micro-batch, as shown in the quantitative analysis of Fig. 3. The qualitative analysis of the effect on size of Micro-Batch can be found in the supplementary materials, which also achieves the consistent conclusion." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.892, + 0.902 + ], + "angle": 0, + "content": "For the quantitative analysis in Fig. 3, two variants of the proposed method are compared: 1) UMBOT \\(\\rightarrow\\) EMD: To demonstrate the robustness of different OT variants, we replace UMBOT used in our method with the original OT (i.e. EMD) for comparison, which is equivalent to the Eq. (4) done over Micro-batch. 2) UMBOT \\(\\rightarrow\\) CoAttn: To compare the robustness of the proposed OT-based co-attention and the original co-attention, we replace UMBOT with the co-attention used in MCAT [5] and train the model over Micro-batch for comparison." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "21247" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.088, + 0.892, + 0.116 + ], + "angle": 0, + "content": "Table 2. Ablation study assessing C-Index (mean ± std) performance of MOTCat over five datasets, in which version (c) in bold is the proposed method with full components, and (a) and (b) refer to its variants. The best results are marked in bold." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.115, + 0.892, + 0.192 + ], + "angle": 0, + "content": "
VariantsOTMBBLCABRCAUCECGBMLGGLUAD
(a) MCAT0.672 ± 0.0320.659 ± 0.0310.649 ± 0.0430.835 ± 0.0240.659 ± 0.027
(b) MOTCat w/o OT✓0.663 ± 0.0250.666 ± 0.0170.663 ± 0.0310.845 ± 0.0230.673 ± 0.036
(c) MOTCat✓✓0.683 ± 0.0260.673 ± 0.0060.675 ± 0.0400.849 ± 0.0280.670 ± 0.038
" + }, + { + "type": "image", + "bbox": [ + 0.084, + 0.213, + 0.344, + 0.34 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.107, + 0.398, + 0.329, + 0.43 + ], + "angle": 0, + "content": "Effect on Size of Micro-Batch (over 128, 256 and 512)" + }, + { + "type": "image", + "bbox": [ + 0.358, + 0.213, + 0.615, + 0.34 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.358, + 0.351, + 0.615, + 0.476 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.626, + 0.213, + 0.888, + 0.34 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.631, + 0.351, + 0.888, + 0.476 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.485, + 0.893, + 0.515 + ], + "angle": 0, + "content": "Figure 3. Boxplots of C-Index over various sizes of Micro-batch for our method and two variants on five cancer datasets, in which the green triangle means the averaged results of all sizes and the horizontal line in the box represents the median result." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.539, + 0.473, + 0.705 + ], + "angle": 0, + "content": "From the results of Fig. 3, we can see that 1) our method achieves the best averaged performance of various sizes compared with the two variants, especially on BRCA with the most samples of 956. 2) Further, on UCEC and LUAD datasets, the proposed method gets the most robust results. 3) Although the second variant UMBOT \\(\\rightarrow\\) CoAttn shows slightly better robustness on BLCA and BRCA, the performance of our method surpasses it by a large margin. In a nutshell, the proposed method achieves a better trade-off between performance and robustness, compared with different OT variants or the co-attention of MCAT." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.472, + 0.902 + ], + "angle": 0, + "content": "Computational Speed. We measure the actual averaged computational speed for 10 WSIs (about 150k patches in total) on one GPU of NVIDIA GeForce RTX 3090. The proposed method is compared with a variant 'org-OT' that replaces UMBOT by the original OT. However, the original OT with the high complexity takes extreme long time for one WSI (about 20k patches), and thus we fail to measure the actual computational time for the original OT in a short time. Here we present the speed of our method, which suggests our method makes it practicable to apply OT to histology and genomics. Specifically, the training speed of the proposed method is \\(6540~\\mathrm{p / s}\\) (p/s refers to the number" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.539, + 0.893, + 0.569 + ], + "angle": 0, + "content": "of processing patches per second) and the inference speed is \\(11885\\mathrm{p / s}\\)." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.58, + 0.685, + 0.596 + ], + "angle": 0, + "content": "4.4. Statistical Analysis" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.604, + 0.895, + 0.816 + ], + "angle": 0, + "content": "To show a statistical difference in patient stratification performance, we visualize the Kaplan-Meier survival curves for different methods, in which patients are separated into two groups of low-risk and high-risk based on predicted risk scores, and then the statistics on ground-truth survival time are presented for each group in Fig. 4. The Logrank test is conducted to measure the statistically significant difference in two groups of patients, where a lower P-value indicates better performance of patient stratification. From the results of Fig. 4, intuitively our method separates patients of low and high risk more clearly on all datasets. In the Logrank test, our method achieves a lower P-value on all datasets in comparison to MCAT, especially on BLCA, BRCA and UCEC with a large margin of magnitude." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.83, + 0.62, + 0.846 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.856, + 0.893, + 0.901 + ], + "angle": 0, + "content": "In this paper, we present a novel Multimodal Optimal Transport-based Co-Attention Transformer with global structure consistency to tackle two important issues in mul" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.957 + ], + "angle": 0, + "content": "21248" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.088, + 0.09, + 0.885, + 0.299 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.301, + 0.893, + 0.345 + ], + "angle": 0, + "content": "Figure 4. Kaplan-Meier Analysis on five cancer datasets, where patient stratifications of low risk (green) and high risk (red) are presented. Shaded areas refer to the confidence intervals. P-value \\(< 0.05\\) means significant statistical difference in two groups, and lower P-value is better. (Zoom in for better viewing.)" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.368, + 0.473, + 0.595 + ], + "angle": 0, + "content": "timodal learning of histology and genomics for survival prediction. First, we utilize a new OT-based Co-Attention to match pairwise instances between histology and genomics for selecting informative instances strongly related to tumor microenvironment, which provides a way to effectively represent gigapixel WSIs. Second, optimal transport offers a global awareness for modeling potential structure within modality, i.e. pathological interactions and genomic co-expression. Furthermore, to enable applying OT-based Co-Attention in practice, we propose a robust and efficient implementation over micro-batch of WSI bags, in which the approximation over micro-batch might provide a solution to update the parameters of extractor for patch images in an end-to-end way instead of extracting feature embeddings offline, which will be further explored in the future." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.61, + 0.238, + 0.628 + ], + "angle": 0, + "content": "Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.634, + 0.47, + 0.72 + ], + "angle": 0, + "content": "This work was supported by National Natural Science Foundation of China (No. 62202403), Shenzhen Science and Technology Innovation Committee (Project No. SGDX20210823103201011) and Hong Kong Innovation and Technology Fund (No. PRP/034/22FX)." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.735, + 0.175, + 0.751 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.085, + 0.76, + 0.47, + 0.844 + ], + "angle": 0, + "content": "[1] Khalid AbdulJabbar, Shan E Ahmed Raza, Rachel Rosenthal, Mariam Jamal-Hanjani, Selvaraju Veeriah, Ayse Akarca, Tom Lund, David A Moore, Roberto Salgado, Maise Al Bakir, et al. 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Despite the progress in joint learning from pathology and genomics, existing methods still suffer from challenging issues: 1) Due to the large size of pathological images, it is difficult to effectively represent the gigapixel whole slide images (WSIs). 2) Interactions within tumor microenvironment (TME) in histology are essential for survival analysis. Although current approaches attempt to model these interactions via co-attention between histology and genomic data, they focus on only dense local similarity across modalities, which fails to capture global consistency between potential structures, i.e. TME-related interactions of histology and co-expression of genomic data. To address these challenges, we propose a Multimodal Optimal Transport-based Co-Attention Transformer framework with global structure consistency, in which optimal transport (OT) is applied to match patches of a WSI and genes embeddings for selecting informative patches to represent the gigapixel WSI. More importantly, OT-based co-attention provides a global awareness to effectively capture structural interactions within TME for survival prediction. To overcome high computational complexity of OT, we propose a robust and efficient implementation over micro-batch of WSI patches by approximating the original OT with unbalanced mini-batch OT. Extensive experiments show the superiority of our method on five benchmark datasets compared to the state-of-the-art methods. The code is released1. + +# 1. Introduction + +Survival prediction is a complex ordinal regression task that aims to estimate the relative risk of death in cancer prognosis, which generally integrates the manual as + +![](images/d0532019981f2c01aadc76576d221a7a50d6aafa98cd8f11c1074b0cf0d1354c.jpg) +Figure 1. Comparison between (a) Co-Attention and (b) OT-based Co-Attention, where (a) learns weights of instances by dense attention, and (b) identifies informative instances by optimal transport matching flow from a global perspective, which enforces considering potential structures of each modality, i.e. interactions within WSIs and co-expression within genomics. + +sessment of qualitative morphological information from pathology data and quantitative molecular profiles from genomic data in clinical settings [6, 55, 4]. Despite recent advances in multimodal learning for histology and genomics [5, 55, 27, 34], there still exists several open issues. Among others, one daunting challenge is to capture key information from heterogeneous modalities for effective fusion. Particularly, due to the large size of about $500,000 \times 500,000$ pixels, it is challenging to effectively represent gigapixel whole slide images without losing key information. Furthermore, visual concepts of tumor microenvironment (TME) within pathological images are verified to have significant associations with survival analysis in various cancer types [42, 1, 25], e.g. cellular components including fibroblast cells and various immune cells that can alter cancer cell behaviors [33]. However, the TME-related patches occupy only a tiny proportion of the entire WSI, leading to a fine-grained visual recognition problem [54] that is indiscernible + +by conventional multimodal learning. + +Recently attention-based multiple instance learning (MIL) [19, 26] has provided a typical solution to identify informative instances, in which a WSI is formulated as a bag of patches (instances) and an attention score is assigned for each instance as a weight for selection. In multimodal learning, genomic data has been applied to guide the selection of TME-related instances by co-attention mechanism across modalities [5], as genes expression might correspond to some morphological characteristics revealed in pathological TME [29, 38]. They [5] densely calculate similarity scores for each pair of pathology and genomic instances as weights of selection to capture fine-grained visual information in WSIs, as shown in Fig. 1 (a). However, this type of approaches with a local view may not thoroughly learn information about TME, since they ignore global potential structure [55] within modality, e.g. interactions within TME for histology and co-expression for genomics [31, 51]. + +Fruitful works [31, 33, 5] demonstrate that the interactions within TME are important indicators affecting survival outcomes, e.g. co-occurrence of tumor cells with tumor-infiltrating lymphocytes (TILs) of the immune system is a positive prognostic indicator. However, these collaborative components in TME might be spatially dispersed throughout the entire WSI, which indicates long-range structural associations in WSI, as shown in Fig. 1 (b). On the other hand, genes co-expression [49, 55] also suggests a potential structure. There might be intrinsic consistency between these two potential structures [55, 31], as some studies have verified that genomic mutations can alter normal functions and biological processes of TILs within TME [51, 47]. By leveraging the global consistency between their potential structures to match histology and genomic data, it is more likely to identify TME-related patches from WSIs. However, existing co-attention-based multimodal learning focuses on only dense local similarity, neglecting the global coherence of potential structures. + +To address these challenges, we propose a Multimodal Optimal Transport-based Co-Attention Transformer (MOTCat) framework with global structure consistency, in which optimal transport-based co-attention is applied to match instances between histology and genomics from a global perspective, as shown in Fig. 1 (b). Optimal transport (OT) [11, 3, 41], as a structural matching approach, is able to generate an optimal matching solution with the overall minimum matching cost, based on local pairwise cost between instances of histology and genomics. As a result, instances of a WSI that have high global structure consistency with genes co-expressions can be identified to represent the WSI. These instances might be more strongly associated with TME that contributes to survival prediction. In this way, the aforementioned two challenges can be addressed by OT-based Co-Attention simultaneously. + +Compared with the conventional co-attention mechanism, the advantages of the proposed OT-based co-attention are three-fold. First, optimal transport provides the instances matching process with global awareness. Marginal constraints of total mass equality enforce a trade-off of instances within modality for transporting during optimization, instead of only considering the local similarity of pairwise instances as conventional co-attention does. It enables the modeling of structural interactions of WSIs and co-expressions of genomics, which is beneficial to survival prediction. Second, the learned patch-level attention score is not a rigorous metric for selecting informative instances under weak supervision [48], i.e. slide-level survival time, especially with only a small number of WSI samples. As an alternative, the optimal matching flow is the rigorous closed-form solution to OT problem without accessing any label, achieved by solving the Linear Programming problem. Last, the optimal matching flow provides a transformation between two modalities under preserving the potential structure, which reduces cross-modal heterogeneity gap. + +Nevertheless, due to a massive number of patches from gigapixel WSIs, OT-based co-attention might suffer from high computational complexity, preventing from applying OT to pathology data in practice. To address this, we propose a robust and efficient implementation of OT-based coattention for matching histology and genomics. Specifically, we split all instances of a WSI into a subset termed Micro-Batch and get the averaged result as a proxy to approximate the solution to the original OT problem over all instances by unbalanced optimal transport [13], which can provide a more robust approximation to the subset sampling with the theoretical and experimental guarantee. + +It is worth noting that the proposed method is a generalized multimodal learning framework that captures potential structure across modalities with global structure consistency. The contributions of this work are summarized as follows: (1) we propose a novel multimodal OT-based Co-Attention Transformer with global structure consistency, where OT-based co-attention is used to identify informative instances by global optimal matching, which allows modeling interactions of histology and co-expression of genomics. (2) We propose a robust and efficient implementation of OT-based co-attention over Micro-Batch. (3) Extensive experiments on five benchmark datasets show significant improvement over state-of-the-art methods. + +# 2. Related Work + +# 2.1. Multimodal Learning in Healthcare + +In clinical settings, the patient state is often characterized by a spectrum of various modalities [30], such as pathology [54, 32], radiology [39, 50], genomics [28, 47, 31], etc. Multimodal learning has shown superiority by leveraging + +the complementary information from multimodal data [30], in which the key issue is to overcome data heterogeneity for better feature fusion. Most existing methods can be roughly classified into three categories: early fusion [18, 43], late fusion [20, 4], and intermediate fusion [5, 24]. Early fusion is to aggregate all modalities at the input level. The most straightforward solution is fusion operators such as concatenation [18], Kronecker Product [35], etc. However, it neglects intra-modality dynamics [30]. On the contrary, late fusion [15] integrates the predictions from individually separated models at the decision level for the final decision, which cannot fully explore cross-modal interactions. Recently, intermediate fusion has attracted much interest by capturing cross-modal interconnections at different levels, where the typical one is attention-based multimodal fusion [5]. For example, Zhu et al. [52] proposed a triplet attention to integrate MRI and diffusion tensor imaging (DTI) for epilepsy diagnosis. IMGFN [55] designed a graph attention network for survival prediction. MCAT [5] proposed a co-attention to identify informative instances of gigapixel WSI with genomic features as queries. HFBSurv [27] progressively integrated multimodal information from the low level to the high level for survival analysis. Note that our method MOTCat belongs to one of the intermediate fusion approaches, which explores the global consistency of potential structure by optimal transport. + +# 2.2. Multiple Instance Learning in Pathology + +Since it is difficult to represent WSIs of large size, MIL algorithms have achieved remarkable progress in pathology, in which WSIs are often formulated as a bag of pathology patches. MIL in pathology generally can be divided into two categories: instance-based algorithms [2, 44, 7] and embedding-based algorithms [19, 16, 32]. The former aims to select a small number of instances within each WSI for training an aggregation model. The latter one is to map each instance into a low-dimension fixed-length embedding offline, and then to learn a bag-level representation based on instance-level embeddings. There are several strategies for aggregating instance-level embeddings. One is clustering-based methods [37, 40], where all the instance-level embeddings are clustered to several centroids that are integrated for the final prediction. The most common strategy is attention-based MIL (AB-MIL) [19, 26] that assigns a weight for each instance, in which various approaches are developed differing in the ways to generate the weighting values. For example, one of the first AB-MIL [19] used a side-branch network for generating attention weights, followed by DS-MIL [26] adopted cosine distance to measure the similarity of instances as weights. Recently, transformer-based MIL like TransMIL [36] has leveraged the self-attention mechanism to explore long-range interactions in WSI. Furthermore, DTFD-MIL [48] + +proposed the double-tier MIL framework for more rigorous instance weights. Unlike AB-MIL, we use optimal match flow generated by OT between pathological and genomic instances to identify instances of WSI that have global potential structure consistency with that of genomics. + +# 2.3. Survival Prediction + +Survival outcome prediction, also known as time-to-event analysis [23], aims to predict the probability of experiencing an event of interest, e.g. death event in the clinical setting, before a specific time under both right-censored and uncensored data. Right-censored data refers to cases where the outcome event cannot be observed within the study period [23]. Before the deep learning era, statistical models dominated survival analysis. The typical one is Cox Proportional Hazards (CoxPH) model [9] that characterizes the hazard function, the risk of death, by an exponential linear model. DeepSurv [12] is the first work incorporating deep learning into survival analysis, which models the risk function by several fully connected layers and feeds it to the CoxPH model for the final hazard function. Furthermore, DeepConvSurv [53] first attempted to use pathological images for a deep survival model. Recent works [27, 6, 34, 4, 5] tend to directly estimate the hazard function by deep learning models without any statistical assumption. Histology and genomics data are often integrated as the gold standard for predicting survival outcomes with promising performance [4, 6, 55]. Similarly, our method incorporates these two modalities for better survival prediction by learning their global structural coherence. + +# 3. Method + +# 3.1. Overview and Problem Formulation + +The overall framework of the proposed method is shown in Fig. 2. In this work, we aim to estimate the hazard functions $h_n(t)$ considered as the risk probability of experiencing death event in a small interval after time point $t$ for $n$ -th patient, based on pathology data $\mathbf{X}_n^p$ and genomic data $\mathbf{X}_n^g$ . + +For pathology, we formulate each WSI as a "bag" structure in a conventional multiple instance learning (MIL) setting, where a bag consists of a collection of instances that are patched from the tissue-containing image regions of a WSI, and instance-level features are extracted from patch images. Genomic data is also organized as a "bag" based on the biological functional impact of genes. For each instance of the genomic bag, we adopt an encoder to extract genes embeddings. The bags formulations for histology and genomics are illustrated in Sec. 3.1.1 and 3.1.2, respectively. + +Then, Optimal Transport-based Co-Attention is applied to match instances of a WSI and the corresponding genomic instances to model pathological interactions and genomic co-expressions, so that the instances with high structure + +![](images/7b6acfca1801614b6ae081eae9790be0bd482f57788bc455b8e94629d402916d.jpg) +Figure 2. Overview of Multimodal Optimal Transport-based Co-Attention Transformer (MOTCat) architecture, in which both modalities are formulated as bags representations and a micro-batch of the WSI bag is sampled as pathological input. Then OT-based Co-attention is to calculate optimal matching flow for identifying informative instances with global structure consistency. After aggregating selected instances, features from both modalities are concatenated for survival prediction. + +consistency can be identified to represent the whole modality. This part will be demonstrated in Sec. 3.2. + +After that, a Transformer encoder will integrate all instances after selection for each modality into a bag-level representation, in which each instance is treated as a token. The bag-level representation will be concatenated into the multimodal features for predicting a hazard function to get the ordinal survival risk. The details will be described in Sec. 3.1.3. Finally, optimization process over Micro-Batch and the corresponding computational complexity analysis will be presented in Sec. 3.3. + +# 3.1.1 WSI Bags Formulation + +We formulate the learning process of pathology images (WSIs) as a weakly-supervised MIL task, in which each WSI $\mathbf{X}_n^p$ is represented as a bag with access to only bag-level (slide-level) labels. Given a bag $\mathbf{X}_n^p = \{\mathbf{x}_{n,i}^p\}_{i = 1}^{M_p}$ of $M_{p}$ permutation-invariant instances, the goal is to encode instance-level features of a WSI into a compact bag-level feature embedding and then assign a bag-level label to it. To this end, we apply a CNN encoder $f_{p}(\cdot)$ for each patch of the WSI to obtain a bag $\mathbf{B}_n^p$ of instance-level features: + +$$ +\mathbf {B} _ {n} ^ {p} = \left\{f _ {p} \left(\mathbf {x} _ {n, i} ^ {p}\right): \mathbf {x} _ {n, i} ^ {p} \in \mathbf {X} _ {n} ^ {p} \right\} = \left\{\mathbf {b} _ {n, i} ^ {p} \right\} _ {i = 1} ^ {M _ {p}}, \tag {1} +$$ + +where $\mathbf{B}_n^p\in \mathbb{R}^{M_p\times d}$ contains $d$ -dimensional instances and $\mathbf{b}_{n,i}^p = f_p(\mathbf{x}_{n,i}^p)$ . After identifying informative instances of $\mathbf{B}_n^p$ by OT-based Co-Attention, we construct a new bag $\hat{\mathbf{B}}_n^p\in \mathbb{R}^{\hat{M}_p\times d}$ of features with $\hat{M}_p$ instances, which will be illustrated in detail in Section 3.2. Then, a transformer encoder is used as a global aggregation model $\mathcal{T}_p(\cdot)$ to obtain + +the bag-level representation $H_{n}^{p} = \mathcal{T}_{p}(\hat{\mathbf{B}}_{n}^{p})$ for the subsequent features fusion. + +# Algorithm 1 The MOTCat Algorithm + +Input: A WSI bag as $\mathbf{X}_n^p = \{\mathbf{x}_{n,i}^p\}_{i = 1}^{M_p}$ ; A genomic bag as $\mathbf{X}_n^g = \{\mathbf{x}_{n,j}^g\}_{j = 1}^{M_g}$ . $m$ refers to the size for a micro-batch of a WSI. +Output: The optimal parameters of model; +1: // Sample micro-batch from the WSI bag $X_{n}^{p,m} = \{\mathbf{x}_{n,i}^{p}\}_{i=1}^{m}$ each time. +2: for $X_{n}^{p,m}$ in $\mathbf{X}_n^p$ do +3: Fix model parameters $f_{p}, f_{g}, \mathcal{T}_{p}$ and $\mathcal{T}_g$ . +4: // To extract a bag of instance-level features +5: // Eq. 1 over micro-batch of histology +6: $B_{n}^{p,m} = \{f_{p}(\mathbf{x}_{n,i}^{p}):\mathbf{x}_{n,i}^{p}\in X_{n}^{p,m}\}$ +7: // Eq. 2 of genomics +8: $\mathbf{B}_n^g = \{f_g^j (\mathbf{x}_{n,j}^g):\mathbf{x}_{n,j}^g\in \mathbf{X}_n^g\}$ +9: Optimize $\mathbf{P}_n^m$ via Sinkhorn-Knopp matrix scaling algorithm [8, 14]: +10: $\mathbf{P}_n^m\gets \arg \min_{\mathbf{P}_n^m}\mathcal{W}^m (B_n^{p,m},\mathbf{B}_n^g) / /$ Eq. 5 +Fix $\mathbf{P}_n^m$ and select instances from $B_n^{p,m}$ by: +12: $\bar{B}_n^{p,m} = \mathbf{P}_n^{m|}B_n^{p,m}$ +13: // To get bag-level representation +14: $H_{n}^{p,m} = \mathcal{T}_{p}\left(\hat{B}_{n}^{p,m}\right) / /$ for histology +15: $H_{n}^{g} = \mathcal{T}_{g}\left(\hat{\mathbf{B}}_{n}^{g}\right) / /$ for genomics +16: $H_{n}^{m} = H_{n}^{p,m} \bowtie H_{n}^{g} // \text{Concatenation}$ +17: Calculate the overall loss function $\mathcal{L}$ of Eq. 6. +18: Update parameters of $f_{g}$ , $\mathcal{T}_{p}$ , $\mathcal{T}_{g}$ and the last fully connected layers of $f_{p}$ by Adam. +19: end for + +# 3.1.2 Genomic Bags Formulation + +Genomic data consists of $1 \times 1$ attributes, such as mutation status, transcript abundance (RNA-Seq), copy number variation (CNV) and other molecular characterizations. Following the organization of genomic data in the previous work [5, 28] that categories them according to the biological functional impact, the expressive genomic bag can be organized as $\mathbf{X}_n^g = \{\mathbf{x}_{n,j}^g\}_{j=1}^{M_g} \in \mathbb{R}^{M_g \times d_j}$ with $M_g$ instances of unique functional categories. For $j$ -th category, the corresponding genomic embedding consists of $d_j$ -dimensional attributes encoded by a separated network $f_g^j(\cdot)$ . Similarly, a bag $\mathbf{B}_n^g \in \mathbb{R}^{M_g \times d}$ of genomic data with $M_g$ instances can be constructed as follows: + +$$ +\mathbf {B} _ {n} ^ {g} = \{f _ {g} ^ {j} (\mathbf {x} _ {n, j} ^ {g}): \mathbf {x} _ {n, j} ^ {g} \in \mathbf {X} _ {n} ^ {g} \} = \{\mathbf {b} _ {n, j} ^ {g} \} _ {j = 1} ^ {M _ {g}}, \quad (2) +$$ + +which is aggregated to the bag-level embedding by a transformer encoder $H_{n}^{g} = \mathcal{T}_{g}(\mathbf{B}_{n}^{g})$ as well. + +# 3.1.3 Multimodal Survival Prediction Formulation + +Survival outcome prediction aims to predict the risk probability of an outcome event occurring before a specific time, in which the outcome event is not always observed, leading to a right-censored event. In this task, let $c \in \{0,1\}$ be censor status indicating whether the outcome event is right-censored ( $c = 1$ ) or not ( $c = 0$ ), and $t \in \mathbb{R}^+$ refers to the overall survival time (in months). Given a training set of $N$ pathology-genomics pairs $\mathcal{D} = \{(\mathbf{X}_n^p, \mathbf{X}_n^g), c_n, t^n\}_{n=1}^N$ , we can acquire the bag-level features $H_n^p$ of WSIs and $H_n^g$ of genomic data for $n$ -th patient data $\mathbf{X}_n = ((\mathbf{X}_n^p, \mathbf{X}_n^g), c_n, t^n)$ , as described in Section 3.1.1 and 3.1.2. After integrating $H_n^p$ and $H_n^g$ into the multimodal features $H_n$ by concatenation, we estimate the hazard function $h_n(t|H_n) = h_n(T = t | T \geq t, H_n) \in [0,1]$ which is viewed as the probability of death event occurring at around time point $t$ . Instead of predicting the overall survival time $t^n$ , the survival prediction task is to estimate the ordinal risk of death via the cumulative survival function: + +$$ +S _ {n} (t \mid H _ {n}) = \prod_ {z = 1} ^ {t} \left(1 - h _ {n} (z \mid H _ {n})\right) \tag {3} +$$ + +# 3.2. Optimal Transport-based Co-Attention + +To identify TME-related instances of WSIs, we utilize the global potential structure consistency between TME interactions of pathology and genes co-expressions as the evidence of selecting instances, in which optimal transport is used to learn the optimal matching flow between a WSI feature bag $\mathbf{B}_n^p\in \mathbb{R}^{M_p\times d}$ and a genomic bag $\mathbf{B}_n^g\in \mathbb{R}^{M_g\times d}$ . Formally, an optimal transport from the WSI feature bag $\mathbf{B}_n^p = [\mathbf{b}_{n,1}^p,\mathbf{b}_{n,2}^p,\dots ,\mathbf{b}_{n,M_p}^p ]$ to the genomic embedding $\mathrm{bag}\mathbf{B}_n^g = [\mathbf{b}_{n,1}^g,\mathbf{b}_{n,2}^g,\dots ,\mathbf{b}_{n,M_g}^g ]$ can be defined by the + +discrete Kantorovich formulation [21] to search the overall optimal matching flow $\mathbf{P}_n$ between $\mathbf{B}_n^p$ and $\mathbf{B}_n^g$ : + +$$ +\mathcal {W} \left(\mathbf {B} _ {n} ^ {p}, \mathbf {B} _ {n} ^ {g}\right) = \min _ {\mathbf {P} _ {n} \in \Pi \left(\mu_ {p}, \mu_ {g}\right)} < \mathbf {P} _ {n}, \mathbf {C} _ {n} > _ {F} \tag {4} +$$ + +where $\mathbf{C}_n\geq 0\in \mathbb{R}^{M_p\times M_g}$ is a cost matrix given by $\mathbf{C}_n^{u,v} = c(\mathbf{b}_{n,u}^p,\mathbf{b}_{n,v}^g)$ with a ground distance metric $c(\cdot)$ such as $l_{2}$ -distance, that measures the distance of local pairwise instances $\mathbf{b}_{n,u}^p\in \mathbf{B}_n^p$ in the WSI bag and the genomic one of a unique functional category $\mathbf{b}_{n,v}^g\in \mathbf{B}_n^g$ + +Here $\Pi (\mu_p,\mu_g) = \{\mathbf{P}_n\in \mathbb{R}_+^{M_p\times M_g}|\mathbf{P}_n\mathbf{1}_{M_g} = \mu_p,\mathbf{P}_n^\top \mathbf{1}_{M_p} = \mu_g\}$ involves the marginal constraints of total mass equality between marginal distributions, $\mu_{p}$ and $\mu_{g}$ , for the WSI bag and the genomic bag, and $\mathbf{1}_k$ is a $k$ -dimensional vector of ones. Specifically, $\Pi (\mu_p,\mu_g)$ refers to the set of joint probabilistic couplings between the two marginal empirical distributions of pathology data and genomic data. Intuitively, it describes how to distribute instances of a WSI bag $\mathbf{B}_n^p$ to the genomic embedding of a genomic bag $\mathbf{B}_n^g$ based on the cost matrix $\mathbf{C}_n$ , under the marginal constraints of total mass equality between distributions $\mu_{p}$ and $\mu_{g}$ . Note that $< \cdot >_{F}$ refers to the Frobenius dot product, and thus Eq. 4 encourages to achieve the overall minimum matching cost by finding optimal matching flow based on local pairwise similarity. In this way, the optimal transport of Eq. 4 is able to enforce a trade-off of instances within modality, which allows the model to capture the potential structure of visual interactions for histology and co-expressions for genomic data. + +Once acquiring the optimal matching flow $\mathbf{P}_n^*$ , informative instances of a WSI are identified by $\hat{\mathbf{B}}_n^p = \mathbf{P}_n^\top \mathbf{B}_n^p$ to represent the WSI, which also aligns pathology distribution to genomics distribution under preserving the potential structure across modalities for alleviating heterogeneity. + +As such, the proposed OT-based Co-Attention simultaneously addresses two issues: not only does it achieve the effective representation for gigapixel WSIs by identifying informative instances via OT matching, but marginal constraints of OT enable the selected instances to have global structure consistency with genomic data. + +# 3.3. Optimization over Micro-Batch + +Due to the large size of the WSI bag, it is difficult to apply optimal transport for matching histology data and genomic data. Recent work [48] has validated that MIL on WSI can benefit from multiple subsets of a bag randomly sampled from the original WSI bag. It provides a way to train the model over Micro-Batch of a WSI, where micro-batch is defined as a subset sampled from a bag of WSI instances. Furthermore, inspired by a variant [13] of OT that offers a solution to approximate the original OT over mini-batches with a theoretical guarantee of convergence, we propose to use the variant UMBOT formulation [13] over micro-batch of WSI instead of the original OT over + +all instances of a WSI. Then the Eq. 4 becomes: + +$$ +\begin{array}{l} \mathcal {W} ^ {m} \left(B _ {n} ^ {p, m}, \mathbf {B} _ {n} ^ {g}\right) = \min _ {\mathbf {P} _ {n} ^ {m} \in \Pi \left(\mu_ {p} ^ {m}, \mu_ {g}\right)} < \mathbf {P} _ {n} ^ {m}, \mathbf {C} _ {n} ^ {m} > _ {F} \\ + \epsilon K L \left(\mathbf {P} _ {n} ^ {m} \mid \mu_ {p} ^ {m} \otimes \mu_ {g}\right) + \tau \left(D _ {\phi} \left(\mathbf {P} _ {n, p} ^ {m} \mid \mid \mu_ {p} ^ {m}\right) + D _ {\phi} \left(\mathbf {P} _ {n, g} ^ {m} \mid \mid \mu_ {g}\right)\right) \tag {5} \\ \end{array} +$$ + +where $B_{n}^{p,m}$ is micro-batch of size $m$ sampled from $\mathbf{B}_n^p$ . Similarly, $\mathbf{C}_n^m \in \mathbb{R}^{m \times M_g}$ is the cost matrix over micro-batch of WSI $B_{n}^{p,m}$ and $\mathbf{B}_n^g$ , and the optimal matching flow $\mathbf{P}_n^m \in \mathbb{R}^{m \times M_g}$ is optimized over micro-batch as well. Here $\mathbf{P}_{n,p}^m$ and $\mathbf{P}_{n,g}^m$ represent the marginals of $\mathbf{P}_n^m$ , and $D_{\phi}$ is Csiszar divergences, $\tau$ and $\epsilon \geq 0$ are the coefficients of marginal penalization and entropic regularization, respectively. $KL$ refers to Kullback-Leibler divergence. + +Computational complexity. With the benefit of UMBOT for approximating the original OT, the computational complexity of optimization is reduced from $\mathcal{O}(M^3\log (M))$ to $\mathcal{O}(\frac{M}{m}\times m^2) = \mathcal{O}(M\times m)$ , where $M = \max (M_p,M_g)$ and $m\ll M$ . The whole optimization procedure of the proposed MOTCat is presented in Alg. 1 + +Loss function. Following the previous work [5], the overall loss function is formulated by NLL-loss [46]: + +$$ +\begin{array}{l} \mathcal {L} = - \frac {m}{M _ {p}} \sum_ {n = 1} ^ {N} \sum_ {X _ {n} ^ {p, m} \in \mathbf {X} _ {n} ^ {p}} c _ {n} \cdot \log \left(S _ {n} ^ {m} \left(t _ {n} \mid H _ {n} ^ {m}\right)\right) \\ - \frac {m}{M _ {p}} \sum_ {n = 1} ^ {N} \sum_ {X _ {n} ^ {p, m} \in \mathbf {X} _ {n} ^ {p}} \left\{\left(1 - c _ {n}\right) \cdot \log \left(S _ {n} ^ {m} \left(t _ {n} - 1 \mid H _ {n} ^ {m}\right)\right) \right. \\ \left. + \left(1 - c _ {n}\right) \cdot \log \left(h _ {n} ^ {m} \left(t _ {n} \mid H _ {n} ^ {m}\right)\right) \right\} \tag {6} \\ \end{array} +$$ + +where $H_{n}^{m}$ refers to the multimodal features over micro-batch formulated in line 16 of Alg. 1. $h_{n}^{m}$ and $S_{n}^{m}$ are the hazard function and cumulative survival function over micro-batch, respectively. + +# 4. Experiment + +In this section, we first present datasets and settings following previous experimental protocols [5, 6] for fair comparisons. Next, we demonstrate the performance results of the proposed method compared with the state-of-the-art (SOTA) methods, including unimodal and multimodal approaches. After that, we investigate the effectiveness of each component in our method and the effect on the size of micro-batch strategy. Finally, from a statistical point of view, we present Kaplan-Meier survival curves and Logrank test to show the performance of survival analysis. Interpretable visualization for histology data and genomic data are presented in supplementary materials. + +# 4.1. Datasets and Settings + +Datasets. To demonstrate the performance of the proposed method, we conducted various experiments over five public cancer datasets from The Cancer Genome Atlas (TCGA) + +that contains paired diagnostic WSIs and genomic data with ground-truth survival outcome: Bladder Urothelial Carcinoma (BLCA), Breast Invasive Carcinoma (BRCA), Uterine Corpus Endometrial Carcinoma (UCEC), Glioblastoma & Lower Grade Glioma (GBMLGG), and Lung Adenocarcinoma (LUAD). The number of cases for each cancer type is shown by $N$ in Tab. 1. Note that cases of these cancer datasets used for all compared methods are not less than cases used in the proposed method. For genomic data, the number of unique functional categories $M_g$ is set as 6 following [28, 5], including 1) Tumor Suppression, 2) Oncogenesis, 3) Protein Kinases, 4) Cellular Differentiation, 5) Transcription, and 6) Cytokines and Growth. + +Evaluation. For each cancer dataset, we perform 5-fold cross-validation with a 4:1 ratio of training-validation sets and report the cross-validated concordance index (C-Index) and its standard deviation (std) to quantify the performance of correctly ranking the predicted patient risk scores with respect to overall survival. + +Implementation. For each WSI, we first apply the OTSU's threshold method to segment tissue regions, and then non-overlapping $256 \times 256$ patches are extracted from the tissue region over $20 \times$ magnification. Then, we use ImageNet-pretrained [10] ResNet-50 [17] and a 256-d fully-connected layer as the feature encoder $f_{p}$ to extract the 1024-d embedding for each patch, where parameters of ResNet-50 are frozen. For genomic data, we adopt SNN [22] as the feature encoder $f_{g}$ following the setting of [5]. + +During training, we follow the setting of [5] for a fair comparison. Specifically, we adopt Adam optimizer with the initial learning rate of $2 \times 10^{-4}$ and weight decay of $1 \times 10^{-5}$ . Due to the large size of WSIs, the batch size for WSIs is 1 with 32 gradient accumulation steps, and all experiments are trained for 20 epochs. The size of MicroBatch $m$ is set as 256. Regarding the hyper-parameters of OT in Eq. 5, the coefficient of marginal penalization $\tau$ is 0.5 for all cancer datasets, and the coefficient of entropic regularization $\epsilon$ is 0.05 for BLCA and LUAD, as well as 0.1 for BRCA, UCEC and GBMLGG. + +# 4.2. Results + +We compare our method against the unimodal baselines and the multimodal SOTA methods as follows: + +Unimodal Baseline. For genomic data, we adopt SNN [22] that has been used previously for survival outcome prediction in the TCGA [4, 5], and SNNTrans [22, 36] which incorporates SNN as the feature extractor and TransMIL [36] as the global aggregation model for MIL. For histology, we compare the SOTA MIL methods AttnMIL [19], DeepAttnMISL [45], CLAM [32], TransMIL [36], and DTFDMIL [48]. + +Multimodal SOTA. We compare four SOTA methods for multimodal survival outcome prediction including + +Table 1. C-Index (mean ± std) performance over five cancer datasets. Patho. and Geno. refer to pathology modality and genomic modality, respectively. The best results and the second-best results are highlighted in bold and in underline, respectively. + +
ModelPatho.Geno.BLCA (N=373)BRCA (N=956)UCEC (N=480)GBMLGG (N=569)LUAD (N=453)
SNN* [22]✓0.618 ± 0.0220.624 ± 0.0600.679 ± 0.0400.834 ± 0.0120.611 ± 0.047
SNNTrans* [22, 36]✓0.659 ± 0.0320.647 ± 0.0630.656 ± 0.0380.839 ± 0.0140.638 ± 0.022
AttnMIL* [19]✓0.599 ± 0.0480.609 ± 0.0650.658 ± 0.0360.818 ± 0.0250.620 ± 0.061
DeepAttnMISL [45]✓0.504 ± 0.0420.524 ± 0.0430.597 ± 0.0590.734 ± 0.0290.548 ± 0.050
CLAM-SB* [32]✓0.559 ± 0.0340.573 ± 0.0440.644 ± 0.0610.779 ± 0.0310.594 ± 0.063
CLAM-MB* [32]✓0.565 ± 0.0270.578 ± 0.0320.609 ± 0.0820.776 ± 0.0340.582 ± 0.072
TransMIL* [36]✓0.575 ± 0.0340.666 ± 0.0290.655 ± 0.0460.798 ± 0.0430.642 ± 0.046
DTFD-MIL* [48]✓0.546 ± 0.0210.609 ± 0.0590.656 ± 0.0450.792 ± 0.0230.585 ± 0.066
Pathomic [4]✓✓0.586 ± 0.062--0.826 ± 0.0090.543 ± 0.065
PONET [34]✓✓0.643 ± 0.037---0.646 ± 0.047
Porpoise* [6]✓✓0.636 ± 0.0240.652 ± 0.0420.695 ± 0.0320.834 ± 0.0170.647 ± 0.031
MCAT* [5]✓✓0.672 ± 0.0320.659 ± 0.0310.649 ± 0.0430.835 ± 0.0240.659 ± 0.027
MOTCat (Ours)✓✓0.683 ± 0.0260.673 ± 0.0060.675 ± 0.0400.849 ± 0.0280.670 ± 0.038
+ +# MCAT [5], Pathomic [4], Porpoise [6] and PONET [34]. + +Results are shown in Tab. 1, where the methods marked * are re-implemented and the best results are reported, and other results are obtained from their papers. Note that due to varying cancer datasets used in their works, not all results of the five datasets used in this work can be reported, and hence we use ' -' to indicate the results are not reported in their papers. + +Unimodal vs. Multimodal. Compared with all unimodal approaches, the proposed method achieves the highest performance in 4 out of 5 cancer datasets, indicating the effective fusion of multimodal data in our method. Note that the overall performance of genomic data is better than that of histology, which validates the reasonability of using genomic data for guiding the selection of instances in WSIs. In particular, most multimodal methods are inferior to the unimodal model of genomics in UCEC dataset, suggesting the serious challenge in multimodal fusion. Nevertheless, the proposed method can achieve the comparative performance with genomic model on UCEC. + +Multimodal SOTA v.s. MOTCat. In one-versus-all comparisons of multimodal models, the proposed method achieves superior performance on all benchmarks with $1.0\% - 2.6\%$ performance gains except UCEC. In comparing the proposed method with the most similar work MCAT in multimodal fusion, our method gets better results on all datasets, indicating the effectiveness of learning the intramodal potential structure consistency from a global perspective between TME-related interactions of histology and genomic co-expression. + +# 4.3. Ablation Study + +We first investigate the effectiveness of OT-based coattention component (denoted by OT) and the micro-batch + +strategy (denoted by MB). Furthermore, the effect on the size of micro-batch and the actual computational speed of our method are explored. + +Component validation. As shown in Tab. 2, we observe that multimodal fusion can benefit from micro-batch strategy by comparing (a) and (b), and OT-based co-attention further improves the performance by approximating the original results with the averaged results over micro-batches via UMBOT. As a result, our method achieves the best overall performance. These improvements both demonstrate the effectiveness of each component for the proposed method. + +Additionally, recent work [48] has claimed that MIL on WSIs can benefit from learning over sub-bags in a WSI, which is also validated by performance increases in variant (b). The reason why it can profit from micro-batch might be that it increases the number of bags, so that more features can be used for survival analysis. + +Size of Micro-batch. To show the robustness of approximation to the size of Micro-batch strategy, we compare several variants of the proposed method over the varying sizes of micro-batch, as shown in the quantitative analysis of Fig. 3. The qualitative analysis of the effect on size of Micro-Batch can be found in the supplementary materials, which also achieves the consistent conclusion. + +For the quantitative analysis in Fig. 3, two variants of the proposed method are compared: 1) UMBOT $\rightarrow$ EMD: To demonstrate the robustness of different OT variants, we replace UMBOT used in our method with the original OT (i.e. EMD) for comparison, which is equivalent to the Eq. (4) done over Micro-batch. 2) UMBOT $\rightarrow$ CoAttn: To compare the robustness of the proposed OT-based co-attention and the original co-attention, we replace UMBOT with the co-attention used in MCAT [5] and train the model over Micro-batch for comparison. + +Table 2. Ablation study assessing C-Index (mean ± std) performance of MOTCat over five datasets, in which version (c) in bold is the proposed method with full components, and (a) and (b) refer to its variants. The best results are marked in bold. + +
VariantsOTMBBLCABRCAUCECGBMLGGLUAD
(a) MCAT0.672 ± 0.0320.659 ± 0.0310.649 ± 0.0430.835 ± 0.0240.659 ± 0.027
(b) MOTCat w/o OT✓0.663 ± 0.0250.666 ± 0.0170.663 ± 0.0310.845 ± 0.0230.673 ± 0.036
(c) MOTCat✓✓0.683 ± 0.0260.673 ± 0.0060.675 ± 0.0400.849 ± 0.0280.670 ± 0.038
+ +![](images/a6fb8cf62fd8bce7b4428bc01fb7deddca3626a25ad71f966b3e948b54f5af7c.jpg) +Effect on Size of Micro-Batch (over 128, 256 and 512) + +![](images/7a602d1e530f6288ca89eb06e9b4cf7b38e722f3ec0a41375721fca37fd76fec.jpg) + +![](images/dfe0d9abe54ca716b76e4404ac2ee138c79b082b5151602b0cc45fb358b2877a.jpg) +Figure 3. Boxplots of C-Index over various sizes of Micro-batch for our method and two variants on five cancer datasets, in which the green triangle means the averaged results of all sizes and the horizontal line in the box represents the median result. + +![](images/043643c531f79873ed07a1347582545f133da90a28c51ebfe88f64d3ddfae42e.jpg) + +![](images/abdf0f9023965c62a40d85a337595bf84ac412b0e50ef9d596993185288765e9.jpg) + +From the results of Fig. 3, we can see that 1) our method achieves the best averaged performance of various sizes compared with the two variants, especially on BRCA with the most samples of 956. 2) Further, on UCEC and LUAD datasets, the proposed method gets the most robust results. 3) Although the second variant UMBOT $\rightarrow$ CoAttn shows slightly better robustness on BLCA and BRCA, the performance of our method surpasses it by a large margin. In a nutshell, the proposed method achieves a better trade-off between performance and robustness, compared with different OT variants or the co-attention of MCAT. + +Computational Speed. We measure the actual averaged computational speed for 10 WSIs (about 150k patches in total) on one GPU of NVIDIA GeForce RTX 3090. The proposed method is compared with a variant 'org-OT' that replaces UMBOT by the original OT. However, the original OT with the high complexity takes extreme long time for one WSI (about 20k patches), and thus we fail to measure the actual computational time for the original OT in a short time. Here we present the speed of our method, which suggests our method makes it practicable to apply OT to histology and genomics. Specifically, the training speed of the proposed method is $6540~\mathrm{p / s}$ (p/s refers to the number + +of processing patches per second) and the inference speed is $11885\mathrm{p / s}$ . + +# 4.4. Statistical Analysis + +To show a statistical difference in patient stratification performance, we visualize the Kaplan-Meier survival curves for different methods, in which patients are separated into two groups of low-risk and high-risk based on predicted risk scores, and then the statistics on ground-truth survival time are presented for each group in Fig. 4. The Logrank test is conducted to measure the statistically significant difference in two groups of patients, where a lower P-value indicates better performance of patient stratification. From the results of Fig. 4, intuitively our method separates patients of low and high risk more clearly on all datasets. In the Logrank test, our method achieves a lower P-value on all datasets in comparison to MCAT, especially on BLCA, BRCA and UCEC with a large margin of magnitude. + +# 5. Conclusion + +In this paper, we present a novel Multimodal Optimal Transport-based Co-Attention Transformer with global structure consistency to tackle two important issues in mul + +![](images/3a6391f8914dbb249aa49e79df36b9b76ef5350d26f6117130b79663c5464b7a.jpg) +Figure 4. Kaplan-Meier Analysis on five cancer datasets, where patient stratifications of low risk (green) and high risk (red) are presented. Shaded areas refer to the confidence intervals. P-value $< 0.05$ means significant statistical difference in two groups, and lower P-value is better. (Zoom in for better viewing.) + +timodal learning of histology and genomics for survival prediction. First, we utilize a new OT-based Co-Attention to match pairwise instances between histology and genomics for selecting informative instances strongly related to tumor microenvironment, which provides a way to effectively represent gigapixel WSIs. Second, optimal transport offers a global awareness for modeling potential structure within modality, i.e. pathological interactions and genomic co-expression. Furthermore, to enable applying OT-based Co-Attention in practice, we propose a robust and efficient implementation over micro-batch of WSI bags, in which the approximation over micro-batch might provide a solution to update the parameters of extractor for patch images in an end-to-end way instead of extracting feature embeddings offline, which will be further explored in the future. + +# Acknowledgement + +This work was supported by National Natural Science Foundation of China (No. 62202403), Shenzhen Science and Technology Innovation Committee (Project No. SGDX20210823103201011) and Hong Kong Innovation and Technology Fund (No. PRP/034/22FX). + +# References + +[1] Khalid AbdulJabbar, Shan E Ahmed Raza, Rachel Rosenthal, Mariam Jamal-Hanjani, Selvaraju Veeriah, Ayse Akarca, Tom Lund, David A Moore, Roberto Salgado, Maise Al Bakir, et al. Geospatial immune variability illuminates differential evolution of lung adenocarcinoma. 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Springer, 2022. 1, 2, 3 \ No newline at end of file diff --git a/2023/Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction/images.zip b/2023/Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..09afc2e69bbca7c7a74ae489b30dcb33d9fd9694 --- /dev/null +++ b/2023/Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:7fcd7664fc68330c9bbaf0d93ef0d7a605e51eb6f753816a0c76e359dc2da00d +size 545243 diff --git a/2023/Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction/layout.json b/2023/Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..92ebba1f32857d1cdea8d87d14be2fce42946eff --- /dev/null +++ b/2023/Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction/layout.json @@ -0,0 +1,9695 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 58, + 102, + 536, + 140 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 102, + 536, + 140 + ], + "spans": [ + { + "bbox": [ + 58, + 102, + 536, + 140 + ], + "type": "text", + "content": "Multimodal Optimal Transport-based Co-Attention Transformer with Global Structure Consistency for Survival Prediction" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 164, + 161, + 429, + 204 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 164, + 161, + 429, + 204 + ], + "spans": [ + { + "bbox": [ + 164, + 161, + 429, + 204 + ], + "type": "text", + "content": "Yingxue Xu Hao Chen* \nThe Hong Kong University of Science and Technology \n{yxueb, jhc}@cse.ust.hk" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "spans": [ + { + "bbox": [ + 143, + 231, + 192, + 243 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 256, + 290, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 256, + 290, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 256, + 290, + 605 + ], + "type": "text", + "content": "Survival prediction is a complicated ordinal regression task that aims to predict the ranking risk of death, which generally benefits from the integration of histology and genomic data. Despite the progress in joint learning from pathology and genomics, existing methods still suffer from challenging issues: 1) Due to the large size of pathological images, it is difficult to effectively represent the gigapixel whole slide images (WSIs). 2) Interactions within tumor microenvironment (TME) in histology are essential for survival analysis. Although current approaches attempt to model these interactions via co-attention between histology and genomic data, they focus on only dense local similarity across modalities, which fails to capture global consistency between potential structures, i.e. TME-related interactions of histology and co-expression of genomic data. To address these challenges, we propose a Multimodal Optimal Transport-based Co-Attention Transformer framework with global structure consistency, in which optimal transport (OT) is applied to match patches of a WSI and genes embeddings for selecting informative patches to represent the gigapixel WSI. More importantly, OT-based co-attention provides a global awareness to effectively capture structural interactions within TME for survival prediction. To overcome high computational complexity of OT, we propose a robust and efficient implementation over micro-batch of WSI patches by approximating the original OT with unbalanced mini-batch OT. Extensive experiments show the superiority of our method on five benchmark datasets compared to the state-of-the-art methods. The code is released1." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 628, + 128, + 639 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 628, + 128, + 639 + ], + "spans": [ + { + "bbox": [ + 47, + 628, + 128, + 639 + ], + "type": "text", + "content": "1. 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Comparison between (a) Co-Attention and (b) OT-based Co-Attention, where (a) learns weights of instances by dense attention, and (b) identifies informative instances by optimal transport matching flow from a global perspective, which enforces considering potential structures of each modality, i.e. interactions within WSIs and co-expression within genomics." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "text", + "content": "sessment of qualitative morphological information from pathology data and quantitative molecular profiles from genomic data in clinical settings [6, 55, 4]. Despite recent advances in multimodal learning for histology and genomics [5, 55, 27, 34], there still exists several open issues. Among others, one daunting challenge is to capture key information from heterogeneous modalities for effective fusion. Particularly, due to the large size of about " + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "inline_equation", + "content": "500,000 \\times 500,000" + }, + { + "bbox": [ + 304, + 498, + 547, + 715 + ], + "type": "text", + "content": " pixels, it is challenging to effectively represent gigapixel whole slide images without losing key information. Furthermore, visual concepts of tumor microenvironment (TME) within pathological images are verified to have significant associations with survival analysis in various cancer types [42, 1, 25], e.g. cellular components including fibroblast cells and various immune cells that can alter cancer cell behaviors [33]. However, the TME-related patches occupy only a tiny proportion of the entire WSI, leading to a fine-grained visual recognition problem [54] that is indiscernible" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 693, + 212, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 693, + 212, + 713 + ], + "spans": [ + { + "bbox": [ + 58, + 693, + 212, + 713 + ], + "type": "text", + "content": "*Corresponding author\n1https://github.com/Innse/MOTCat" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "21241" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 200, + 83 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 200, + 83 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 200, + 83 + ], + "type": "text", + "content": "by conventional multimodal learning." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 87, + 287, + 290 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 87, + 287, + 290 + ], + "spans": [ + { + "bbox": [ + 46, + 87, + 287, + 290 + ], + "type": "text", + "content": "Recently attention-based multiple instance learning (MIL) [19, 26] has provided a typical solution to identify informative instances, in which a WSI is formulated as a bag of patches (instances) and an attention score is assigned for each instance as a weight for selection. In multimodal learning, genomic data has been applied to guide the selection of TME-related instances by co-attention mechanism across modalities [5], as genes expression might correspond to some morphological characteristics revealed in pathological TME [29, 38]. They [5] densely calculate similarity scores for each pair of pathology and genomic instances as weights of selection to capture fine-grained visual information in WSIs, as shown in Fig. 1 (a). However, this type of approaches with a local view may not thoroughly learn information about TME, since they ignore global potential structure [55] within modality, e.g. interactions within TME for histology and co-expression for genomics [31, 51]." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 292, + 288, + 519 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 292, + 288, + 519 + ], + "spans": [ + { + "bbox": [ + 46, + 292, + 288, + 519 + ], + "type": "text", + "content": "Fruitful works [31, 33, 5] demonstrate that the interactions within TME are important indicators affecting survival outcomes, e.g. co-occurrence of tumor cells with tumor-infiltrating lymphocytes (TILs) of the immune system is a positive prognostic indicator. However, these collaborative components in TME might be spatially dispersed throughout the entire WSI, which indicates long-range structural associations in WSI, as shown in Fig. 1 (b). On the other hand, genes co-expression [49, 55] also suggests a potential structure. There might be intrinsic consistency between these two potential structures [55, 31], as some studies have verified that genomic mutations can alter normal functions and biological processes of TILs within TME [51, 47]. By leveraging the global consistency between their potential structures to match histology and genomic data, it is more likely to identify TME-related patches from WSIs. However, existing co-attention-based multimodal learning focuses on only dense local similarity, neglecting the global coherence of potential structures." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 521, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 521, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 521, + 287, + 714 + ], + "type": "text", + "content": "To address these challenges, we propose a Multimodal Optimal Transport-based Co-Attention Transformer (MOTCat) framework with global structure consistency, in which optimal transport-based co-attention is applied to match instances between histology and genomics from a global perspective, as shown in Fig. 1 (b). Optimal transport (OT) [11, 3, 41], as a structural matching approach, is able to generate an optimal matching solution with the overall minimum matching cost, based on local pairwise cost between instances of histology and genomics. As a result, instances of a WSI that have high global structure consistency with genes co-expressions can be identified to represent the WSI. These instances might be more strongly associated with TME that contributes to survival prediction. In this way, the aforementioned two challenges can be addressed by OT-based Co-Attention simultaneously." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 72, + 545, + 312 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 312 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 312 + ], + "type": "text", + "content": "Compared with the conventional co-attention mechanism, the advantages of the proposed OT-based co-attention are three-fold. First, optimal transport provides the instances matching process with global awareness. Marginal constraints of total mass equality enforce a trade-off of instances within modality for transporting during optimization, instead of only considering the local similarity of pairwise instances as conventional co-attention does. It enables the modeling of structural interactions of WSIs and co-expressions of genomics, which is beneficial to survival prediction. Second, the learned patch-level attention score is not a rigorous metric for selecting informative instances under weak supervision [48], i.e. slide-level survival time, especially with only a small number of WSI samples. As an alternative, the optimal matching flow is the rigorous closed-form solution to OT problem without accessing any label, achieved by solving the Linear Programming problem. Last, the optimal matching flow provides a transformation between two modalities under preserving the potential structure, which reduces cross-modal heterogeneity gap." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 312, + 546, + 456 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 312, + 546, + 456 + ], + "spans": [ + { + "bbox": [ + 304, + 312, + 546, + 456 + ], + "type": "text", + "content": "Nevertheless, due to a massive number of patches from gigapixel WSIs, OT-based co-attention might suffer from high computational complexity, preventing from applying OT to pathology data in practice. To address this, we propose a robust and efficient implementation of OT-based coattention for matching histology and genomics. Specifically, we split all instances of a WSI into a subset termed Micro-Batch and get the averaged result as a proxy to approximate the solution to the original OT problem over all instances by unbalanced optimal transport [13], which can provide a more robust approximation to the subset sampling with the theoretical and experimental guarantee." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 456, + 545, + 612 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 456, + 545, + 612 + ], + "spans": [ + { + "bbox": [ + 304, + 456, + 545, + 612 + ], + "type": "text", + "content": "It is worth noting that the proposed method is a generalized multimodal learning framework that captures potential structure across modalities with global structure consistency. The contributions of this work are summarized as follows: (1) we propose a novel multimodal OT-based Co-Attention Transformer with global structure consistency, where OT-based co-attention is used to identify informative instances by global optimal matching, which allows modeling interactions of histology and co-expression of genomics. (2) We propose a robust and efficient implementation of OT-based co-attention over Micro-Batch. (3) Extensive experiments on five benchmark datasets show significant improvement over state-of-the-art methods." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 625, + 392, + 639 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 625, + 392, + 639 + ], + "spans": [ + { + "bbox": [ + 306, + 625, + 392, + 639 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 646, + 496, + 658 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 646, + 496, + 658 + ], + "spans": [ + { + "bbox": [ + 306, + 646, + 496, + 658 + ], + "type": "text", + "content": "2.1. Multimodal Learning in Healthcare" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 665, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 715 + ], + "type": "text", + "content": "In clinical settings, the patient state is often characterized by a spectrum of various modalities [30], such as pathology [54, 32], radiology [39, 50], genomics [28, 47, 31], etc. Multimodal learning has shown superiority by leveraging" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "21242" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 384 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 384 + ], + "type": "text", + "content": "the complementary information from multimodal data [30], in which the key issue is to overcome data heterogeneity for better feature fusion. Most existing methods can be roughly classified into three categories: early fusion [18, 43], late fusion [20, 4], and intermediate fusion [5, 24]. Early fusion is to aggregate all modalities at the input level. The most straightforward solution is fusion operators such as concatenation [18], Kronecker Product [35], etc. However, it neglects intra-modality dynamics [30]. On the contrary, late fusion [15] integrates the predictions from individually separated models at the decision level for the final decision, which cannot fully explore cross-modal interactions. Recently, intermediate fusion has attracted much interest by capturing cross-modal interconnections at different levels, where the typical one is attention-based multimodal fusion [5]. For example, Zhu et al. [52] proposed a triplet attention to integrate MRI and diffusion tensor imaging (DTI) for epilepsy diagnosis. IMGFN [55] designed a graph attention network for survival prediction. MCAT [5] proposed a co-attention to identify informative instances of gigapixel WSI with genomic features as queries. HFBSurv [27] progressively integrated multimodal information from the low level to the high level for survival analysis. Note that our method MOTCat belongs to one of the intermediate fusion approaches, which explores the global consistency of potential structure by optimal transport." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 394, + 259, + 407 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 394, + 259, + 407 + ], + "spans": [ + { + "bbox": [ + 47, + 394, + 259, + 407 + ], + "type": "text", + "content": "2.2. Multiple Instance Learning in Pathology" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 415, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 415, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 415, + 289, + 715 + ], + "type": "text", + "content": "Since it is difficult to represent WSIs of large size, MIL algorithms have achieved remarkable progress in pathology, in which WSIs are often formulated as a bag of pathology patches. MIL in pathology generally can be divided into two categories: instance-based algorithms [2, 44, 7] and embedding-based algorithms [19, 16, 32]. The former aims to select a small number of instances within each WSI for training an aggregation model. The latter one is to map each instance into a low-dimension fixed-length embedding offline, and then to learn a bag-level representation based on instance-level embeddings. There are several strategies for aggregating instance-level embeddings. One is clustering-based methods [37, 40], where all the instance-level embeddings are clustered to several centroids that are integrated for the final prediction. The most common strategy is attention-based MIL (AB-MIL) [19, 26] that assigns a weight for each instance, in which various approaches are developed differing in the ways to generate the weighting values. For example, one of the first AB-MIL [19] used a side-branch network for generating attention weights, followed by DS-MIL [26] adopted cosine distance to measure the similarity of instances as weights. Recently, transformer-based MIL like TransMIL [36] has leveraged the self-attention mechanism to explore long-range interactions in WSI. Furthermore, DTFD-MIL [48]" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 133 + ], + "type": "text", + "content": "proposed the double-tier MIL framework for more rigorous instance weights. Unlike AB-MIL, we use optimal match flow generated by OT between pathological and genomic instances to identify instances of WSI that have global potential structure consistency with that of genomics." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 306, + 140, + 420, + 152 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 140, + 420, + 152 + ], + "spans": [ + { + "bbox": [ + 306, + 140, + 420, + 152 + ], + "type": "text", + "content": "2.3. Survival Prediction" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 159, + 547, + 435 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 159, + 547, + 435 + ], + "spans": [ + { + "bbox": [ + 304, + 159, + 547, + 435 + ], + "type": "text", + "content": "Survival outcome prediction, also known as time-to-event analysis [23], aims to predict the probability of experiencing an event of interest, e.g. death event in the clinical setting, before a specific time under both right-censored and uncensored data. Right-censored data refers to cases where the outcome event cannot be observed within the study period [23]. Before the deep learning era, statistical models dominated survival analysis. The typical one is Cox Proportional Hazards (CoxPH) model [9] that characterizes the hazard function, the risk of death, by an exponential linear model. DeepSurv [12] is the first work incorporating deep learning into survival analysis, which models the risk function by several fully connected layers and feeds it to the CoxPH model for the final hazard function. Furthermore, DeepConvSurv [53] first attempted to use pathological images for a deep survival model. Recent works [27, 6, 34, 4, 5] tend to directly estimate the hazard function by deep learning models without any statistical assumption. Histology and genomics data are often integrated as the gold standard for predicting survival outcomes with promising performance [4, 6, 55]. Similarly, our method incorporates these two modalities for better survival prediction by learning their global structural coherence." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 446, + 361, + 458 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 446, + 361, + 458 + ], + "spans": [ + { + "bbox": [ + 306, + 446, + 361, + 458 + ], + "type": "text", + "content": "3. Method" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 467, + 499, + 479 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 467, + 499, + 479 + ], + "spans": [ + { + "bbox": [ + 306, + 467, + 499, + 479 + ], + "type": "text", + "content": "3.1. Overview and Problem Formulation" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "type": "text", + "content": "The overall framework of the proposed method is shown in Fig. 2. In this work, we aim to estimate the hazard functions " + }, + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "type": "inline_equation", + "content": "h_n(t)" + }, + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "type": "text", + "content": " considered as the risk probability of experiencing death event in a small interval after time point " + }, + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "type": "text", + "content": "-th patient, based on pathology data " + }, + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_n^p" + }, + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "type": "text", + "content": " and genomic data " + }, + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_n^g" + }, + { + "bbox": [ + 304, + 485, + 545, + 545 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 545, + 545, + 665 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 545, + 665 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 545, + 665 + ], + "type": "text", + "content": "For pathology, we formulate each WSI as a \"bag\" structure in a conventional multiple instance learning (MIL) setting, where a bag consists of a collection of instances that are patched from the tissue-containing image regions of a WSI, and instance-level features are extracted from patch images. Genomic data is also organized as a \"bag\" based on the biological functional impact of genes. For each instance of the genomic bag, we adopt an encoder to extract genes embeddings. The bags formulations for histology and genomics are illustrated in Sec. 3.1.1 and 3.1.2, respectively." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 713 + ], + "type": "text", + "content": "Then, Optimal Transport-based Co-Attention is applied to match instances of a WSI and the corresponding genomic instances to model pathological interactions and genomic co-expressions, so that the instances with high structure" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "21243" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 73, + 545, + 262 + ], + "blocks": [ + { + "bbox": [ + 48, + 73, + 545, + 262 + ], + "lines": [ + { + "bbox": [ + 48, + 73, + 545, + 262 + ], + "spans": [ + { + "bbox": [ + 48, + 73, + 545, + 262 + ], + "type": "image", + "image_path": "7b6acfca1801614b6ae081eae9790be0bd482f57788bc455b8e94629d402916d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 265, + 547, + 312 + ], + "lines": [ + { + "bbox": [ + 46, + 265, + 547, + 312 + ], + "spans": [ + { + "bbox": [ + 46, + 265, + 547, + 312 + ], + "type": "text", + "content": "Figure 2. Overview of Multimodal Optimal Transport-based Co-Attention Transformer (MOTCat) architecture, in which both modalities are formulated as bags representations and a micro-batch of the WSI bag is sampled as pathological input. Then OT-based Co-attention is to calculate optimal matching flow for identifying informative instances with global structure consistency. After aggregating selected instances, features from both modalities are concatenated for survival prediction." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 330, + 287, + 354 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 330, + 287, + 354 + ], + "spans": [ + { + "bbox": [ + 46, + 330, + 287, + 354 + ], + "type": "text", + "content": "consistency can be identified to represent the whole modality. This part will be demonstrated in Sec. 3.2." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 354, + 288, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 354, + 288, + 462 + ], + "spans": [ + { + "bbox": [ + 46, + 354, + 288, + 462 + ], + "type": "text", + "content": "After that, a Transformer encoder will integrate all instances after selection for each modality into a bag-level representation, in which each instance is treated as a token. The bag-level representation will be concatenated into the multimodal features for predicting a hazard function to get the ordinal survival risk. The details will be described in Sec. 3.1.3. Finally, optimization process over Micro-Batch and the corresponding computational complexity analysis will be presented in Sec. 3.3." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 476, + 179, + 489 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 476, + 179, + 489 + ], + "spans": [ + { + "bbox": [ + 47, + 476, + 179, + 489 + ], + "type": "text", + "content": "3.1.1 WSI Bags Formulation" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "spans": [ + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "type": "text", + "content": "We formulate the learning process of pathology images (WSIs) as a weakly-supervised MIL task, in which each WSI " + }, + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_n^p" + }, + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "type": "text", + "content": " is represented as a bag with access to only bag-level (slide-level) labels. Given a bag " + }, + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_n^p = \\{\\mathbf{x}_{n,i}^p\\}_{i = 1}^{M_p}" + }, + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "type": "text", + "content": " of " + }, + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "type": "inline_equation", + "content": "M_{p}" + }, + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "type": "text", + "content": " permutation-invariant instances, the goal is to encode instance-level features of a WSI into a compact bag-level feature embedding and then assign a bag-level label to it. To this end, we apply a CNN encoder " + }, + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "type": "inline_equation", + "content": "f_{p}(\\cdot)" + }, + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "type": "text", + "content": " for each patch of the WSI to obtain a bag " + }, + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^p" + }, + { + "bbox": [ + 46, + 495, + 289, + 605 + ], + "type": "text", + "content": " of instance-level features:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 76, + 613, + 287, + 631 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 76, + 613, + 287, + 631 + ], + "spans": [ + { + "bbox": [ + 76, + 613, + 287, + 631 + ], + "type": "interline_equation", + "content": "\\mathbf {B} _ {n} ^ {p} = \\left\\{f _ {p} \\left(\\mathbf {x} _ {n, i} ^ {p}\\right): \\mathbf {x} _ {n, i} ^ {p} \\in \\mathbf {X} _ {n} ^ {p} \\right\\} = \\left\\{\\mathbf {b} _ {n, i} ^ {p} \\right\\} _ {i = 1} ^ {M _ {p}}, \\tag {1}", + "image_path": "326c3d50d21448851b998b7b4fb9aa29166042942728d94bd861106764821f19.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^p\\in \\mathbb{R}^{M_p\\times d}" + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "text", + "content": " contains " + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "inline_equation", + "content": "d" + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "text", + "content": " -dimensional instances and " + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{b}_{n,i}^p = f_p(\\mathbf{x}_{n,i}^p)" + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "text", + "content": ". After identifying informative instances of " + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^p" + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "text", + "content": " by OT-based Co-Attention, we construct a new bag " + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{B}}_n^p\\in \\mathbb{R}^{\\hat{M}_p\\times d}" + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "text", + "content": " of features with " + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\hat{M}_p" + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "text", + "content": " instances, which will be illustrated in detail in Section 3.2. Then, a transformer encoder is used as a global aggregation model " + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_p(\\cdot)" + }, + { + "bbox": [ + 46, + 639, + 288, + 715 + ], + "type": "text", + "content": " to obtain" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 329, + 545, + 354 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 329, + 545, + 354 + ], + "spans": [ + { + "bbox": [ + 304, + 329, + 545, + 354 + ], + "type": "text", + "content": "the bag-level representation " + }, + { + "bbox": [ + 304, + 329, + 545, + 354 + ], + "type": "inline_equation", + "content": "H_{n}^{p} = \\mathcal{T}_{p}(\\hat{\\mathbf{B}}_{n}^{p})" + }, + { + "bbox": [ + 304, + 329, + 545, + 354 + ], + "type": "text", + "content": " for the subsequent features fusion." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 307, + 365, + 462, + 378 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 365, + 462, + 378 + ], + "spans": [ + { + "bbox": [ + 307, + 365, + 462, + 378 + ], + "type": "text", + "content": "Algorithm 1 The MOTCat Algorithm" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 310, + 380, + 545, + 707 + ], + "type": "list", + "angle": 0, + "index": 31, + "blocks": [ + { + "bbox": [ + 306, + 380, + 545, + 421 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 380, + 545, + 421 + ], + "spans": [ + { + "bbox": [ + 306, + 380, + 545, + 421 + ], + "type": "text", + "content": "Input: A WSI bag as " + }, + { + "bbox": [ + 306, + 380, + 545, + 421 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_n^p = \\{\\mathbf{x}_{n,i}^p\\}_{i = 1}^{M_p}" + }, + { + "bbox": [ + 306, + 380, + 545, + 421 + ], + "type": "text", + "content": "; A genomic bag as " + }, + { + "bbox": [ + 306, + 380, + 545, + 421 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_n^g = \\{\\mathbf{x}_{n,j}^g\\}_{j = 1}^{M_g}" + }, + { + "bbox": [ + 306, + 380, + 545, + 421 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 306, + 380, + 545, + 421 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 306, + 380, + 545, + 421 + ], + "type": "text", + "content": " refers to the size for a micro-batch of a WSI." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 307, + 422, + 484, + 434 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 307, + 422, + 484, + 434 + ], + "spans": [ + { + "bbox": [ + 307, + 422, + 484, + 434 + ], + "type": "text", + "content": "Output: The optimal parameters of model;" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 311, + 434, + 545, + 458 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 434, + 545, + 458 + ], + "spans": [ + { + "bbox": [ + 311, + 434, + 545, + 458 + ], + "type": "text", + "content": "1: // Sample micro-batch from the WSI bag " + }, + { + "bbox": [ + 311, + 434, + 545, + 458 + ], + "type": "inline_equation", + "content": "X_{n}^{p,m} = \\{\\mathbf{x}_{n,i}^{p}\\}_{i=1}^{m}" + }, + { + "bbox": [ + 311, + 434, + 545, + 458 + ], + "type": "text", + "content": " each time." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 312, + 458, + 405, + 470 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 458, + 405, + 470 + ], + "spans": [ + { + "bbox": [ + 312, + 458, + 405, + 470 + ], + "type": "text", + "content": "2: for " + }, + { + "bbox": [ + 312, + 458, + 405, + 470 + ], + "type": "inline_equation", + "content": "X_{n}^{p,m}" + }, + { + "bbox": [ + 312, + 458, + 405, + 470 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 312, + 458, + 405, + 470 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_n^p" + }, + { + "bbox": [ + 312, + 458, + 405, + 470 + ], + "type": "text", + "content": " do" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 313, + 471, + 501, + 483 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 471, + 501, + 483 + ], + "spans": [ + { + "bbox": [ + 313, + 471, + 501, + 483 + ], + "type": "text", + "content": "3: Fix model parameters " + }, + { + "bbox": [ + 313, + 471, + 501, + 483 + ], + "type": "inline_equation", + "content": "f_{p}, f_{g}, \\mathcal{T}_{p}" + }, + { + "bbox": [ + 313, + 471, + 501, + 483 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 313, + 471, + 501, + 483 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_g" + }, + { + "bbox": [ + 313, + 471, + 501, + 483 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 313, + 483, + 515, + 493 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 483, + 515, + 493 + ], + "spans": [ + { + "bbox": [ + 313, + 483, + 515, + 493 + ], + "type": "text", + "content": "4: // To extract a bag of instance-level features" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 313, + 495, + 491, + 506 + ], + "type": "ref_text", + "angle": 0, + "lines": [ 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313, + 530, + 464, + 543 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 313, + 530, + 464, + 543 + ], + "spans": [ + { + "bbox": [ + 313, + 530, + 464, + 543 + ], + "type": "text", + "content": "8: " + }, + { + "bbox": [ + 313, + 530, + 464, + 543 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^g = \\{f_g^j (\\mathbf{x}_{n,j}^g):\\mathbf{x}_{n,j}^g\\in \\mathbf{X}_n^g\\}" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 311, + 543, + 545, + 565 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 311, + 543, + 545, + 565 + ], + "spans": [ + { + "bbox": [ + 311, + 543, + 545, + 565 + ], + "type": "text", + "content": "9: Optimize " + }, + { + "bbox": [ + 311, + 543, + 545, + 565 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_n^m" + }, + { + "bbox": [ + 311, + 543, + 545, + 565 + ], + "type": "text", + "content": " via Sinkhorn-Knopp matrix scaling algorithm [8, 14]:" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 310, + 566, + 526, + 578 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 566, + 526, + 578 + ], + "spans": [ + { + "bbox": [ + 310, + 566, + 526, + 578 + ], + "type": "text", + "content": "10: " + }, + { + "bbox": [ + 310, + 566, + 526, + 578 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_n^m\\gets \\arg \\min_{\\mathbf{P}_n^m}\\mathcal{W}^m (B_n^{p,m},\\mathbf{B}_n^g) / /" + }, + { + "bbox": [ + 310, + 566, + 526, + 578 + ], + "type": "text", + "content": " Eq. 5" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 310, + 578, + 515, + 590 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 578, + 515, + 590 + ], + "spans": [ + { + "bbox": [ + 310, + 578, + 515, + 590 + ], + "type": "text", + "content": "Fix " + }, + { + "bbox": [ + 310, + 578, + 515, + 590 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_n^m" + }, + { + "bbox": [ + 310, + 578, + 515, + 590 + ], + "type": "text", + "content": " and select instances from " + }, + { + "bbox": [ + 310, + 578, + 515, + 590 + ], + "type": "inline_equation", + "content": "B_n^{p,m}" + }, + { + "bbox": [ + 310, + 578, + 515, + 590 + ], + "type": "text", + "content": " by:" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 310, + 590, + 429, + 601 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 590, + 429, + 601 + ], + "spans": [ + { + "bbox": [ + 310, + 590, + 429, + 601 + ], + "type": "text", + "content": "12: " + }, + { + "bbox": [ + 310, + 590, + 429, + 601 + ], + "type": "inline_equation", + "content": "\\bar{B}_n^{p,m} = \\mathbf{P}_n^{m|}B_n^{p,m}" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 310, + 602, + 472, + 613 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 602, + 472, + 613 + ], + "spans": [ + { + "bbox": [ + 310, + 602, + 472, + 613 + ], + "type": "text", + "content": "13: // To get bag-level representation" + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 310, + 613, + 484, + 632 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 613, + 484, + 632 + ], + "spans": [ + { + "bbox": [ + 310, + 613, + 484, + 632 + ], + "type": "text", + "content": "14: " + }, + { + "bbox": [ + 310, + 613, + 484, + 632 + ], + "type": "inline_equation", + "content": "H_{n}^{p,m} = \\mathcal{T}_{p}\\left(\\hat{B}_{n}^{p,m}\\right) / /" + }, + { + "bbox": [ + 310, + 613, + 484, + 632 + ], + "type": "text", + "content": " for histology" + } + ] + } + ], + "index": 25 + }, + { + "bbox": [ + 310, + 632, + 468, + 650 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 632, + 468, + 650 + ], + "spans": [ + { + "bbox": [ + 310, + 632, + 468, + 650 + ], + "type": "text", + "content": "15: " + }, + { + "bbox": [ + 310, + 632, + 468, + 650 + ], + "type": "inline_equation", + "content": "H_{n}^{g} = \\mathcal{T}_{g}\\left(\\hat{\\mathbf{B}}_{n}^{g}\\right) / /" + }, + { + "bbox": [ + 310, + 632, + 468, + 650 + ], + "type": "text", + "content": " for genomics" + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 310, + 651, + 489, + 662 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 651, + 489, + 662 + ], + "spans": [ + { + "bbox": [ + 310, + 651, + 489, + 662 + ], + "type": "text", + "content": "16: " + }, + { + "bbox": [ + 310, + 651, + 489, + 662 + ], + "type": "inline_equation", + "content": "H_{n}^{m} = H_{n}^{p,m} \\bowtie H_{n}^{g} // \\text{Concatenation}" + } + ] + } + ], + "index": 27 + }, + { + "bbox": [ + 310, + 662, + 522, + 673 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 662, + 522, + 673 + ], + "spans": [ + { + "bbox": [ + 310, + 662, + 522, + 673 + ], + "type": "text", + "content": "17: Calculate the overall loss function " + }, + { + "bbox": [ + 310, + 662, + 522, + 673 + ], + "type": "inline_equation", + "content": "\\mathcal{L}" + }, + { + "bbox": [ + 310, + 662, + 522, + 673 + ], + "type": "text", + "content": " of Eq. 6." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 310, + 674, + 545, + 697 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 674, + 545, + 697 + ], + "spans": [ + { + "bbox": [ + 310, + 674, + 545, + 697 + ], + "type": "text", + "content": "18: Update parameters of " + }, + { + "bbox": [ + 310, + 674, + 545, + 697 + ], + "type": "inline_equation", + "content": "f_{g}" + }, + { + "bbox": [ + 310, + 674, + 545, + 697 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 310, + 674, + 545, + 697 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{p}" + }, + { + "bbox": [ + 310, + 674, + 545, + 697 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 310, + 674, + 545, + 697 + ], + "type": "inline_equation", + "content": "\\mathcal{T}_{g}" + }, + { + "bbox": [ + 310, + 674, + 545, + 697 + ], + "type": "text", + "content": " and the last fully connected layers of " + }, + { + "bbox": [ + 310, + 674, + 545, + 697 + ], + "type": "inline_equation", + "content": "f_{p}" + }, + { + "bbox": [ + 310, + 674, + 545, + 697 + ], + "type": "text", + "content": " by Adam." + } + ] + } + ], + "index": 29 + }, + { + "bbox": [ + 310, + 698, + 356, + 707 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 310, + 698, + 356, + 707 + ], + "spans": [ + { + "bbox": [ + 310, + 698, + 356, + 707 + ], + "type": "text", + "content": "19: end for" + } + ] + } + ], + "index": 30 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "21244" + } + ] + } + ], + "index": 32 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 198, + 85 + ], + "type": "title", + 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Following the organization of genomic data in the previous work [5, 28] that categories them according to the biological functional impact, the expressive genomic bag can be organized as " + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_n^g = \\{\\mathbf{x}_{n,j}^g\\}_{j=1}^{M_g} \\in \\mathbb{R}^{M_g \\times d_j}" + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "text", + "content": " with " + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "inline_equation", + "content": "M_g" + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "text", + "content": " instances of unique functional categories. For " + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "inline_equation", + "content": "j" + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "text", + "content": "-th category, the corresponding genomic embedding consists of " + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "inline_equation", + "content": "d_j" + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "text", + "content": "-dimensional attributes encoded by a separated network " + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "inline_equation", + "content": "f_g^j(\\cdot)" + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "text", + "content": ". Similarly, a bag " + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^g \\in \\mathbb{R}^{M_g \\times d}" + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "text", + "content": " of genomic data with " + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "inline_equation", + "content": "M_g" + }, + { + "bbox": [ + 46, + 91, + 289, + 236 + ], + "type": "text", + "content": " instances can be constructed as follows:" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 73, + 243, + 287, + 262 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 73, + 243, + 287, + 262 + ], + "spans": [ + { + "bbox": [ + 73, + 243, + 287, + 262 + ], + "type": "interline_equation", + "content": "\\mathbf {B} _ {n} ^ {g} = \\{f _ {g} ^ {j} (\\mathbf {x} _ {n, j} ^ {g}): \\mathbf {x} _ {n, j} ^ {g} \\in \\mathbf {X} _ {n} ^ {g} \\} = \\{\\mathbf {b} _ {n, j} ^ {g} \\} _ {j = 1} ^ {M _ {g}}, \\quad (2)", + "image_path": "e09b53bb148dd5355305a549724c058d87b96310da6e1b38393055f2b1771d13.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 267, + 287, + 293 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 267, + 287, + 293 + ], + "spans": [ + { + "bbox": [ + 47, + 267, + 287, + 293 + ], + "type": "text", + "content": "which is aggregated to the bag-level embedding by a transformer encoder " + }, + { + "bbox": [ + 47, + 267, + 287, + 293 + ], + "type": "inline_equation", + "content": "H_{n}^{g} = \\mathcal{T}_{g}(\\mathbf{B}_{n}^{g})" + }, + { + "bbox": [ + 47, + 267, + 287, + 293 + ], + "type": "text", + "content": " as well." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 305, + 272, + 317 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 305, + 272, + 317 + ], + "spans": [ + { + "bbox": [ + 47, + 305, + 272, + 317 + ], + "type": "text", + "content": "3.1.3 Multimodal Survival Prediction Formulation" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "spans": [ + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": "Survival outcome prediction aims to predict the risk probability of an outcome event occurring before a specific time, in which the outcome event is not always observed, leading to a right-censored event. In this task, let " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "c \\in \\{0,1\\}" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": " be censor status indicating whether the outcome event is right-censored (" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "c = 1" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": ") or not (" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "c = 0" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": "), and " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "t \\in \\mathbb{R}^+" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": " refers to the overall survival time (in months). Given a training set of " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": " pathology-genomics pairs " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "\\mathcal{D} = \\{(\\mathbf{X}_n^p, \\mathbf{X}_n^g), c_n, t^n\\}_{n=1}^N" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": ", we can acquire the bag-level features " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "H_n^p" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": " of WSIs and " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "H_n^g" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": " of genomic data for " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "n" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": "-th patient data " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "\\mathbf{X}_n = ((\\mathbf{X}_n^p, \\mathbf{X}_n^g), c_n, t^n)" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": ", as described in Section 3.1.1 and 3.1.2. After integrating " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "H_n^p" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "H_n^g" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": " into the multimodal features " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "H_n" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": " by concatenation, we estimate the hazard function " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "h_n(t|H_n) = h_n(T = t | T \\geq t, H_n) \\in [0,1]" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": " which is viewed as the probability of death event occurring at around time point " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": ". Instead of predicting the overall survival time " + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "inline_equation", + "content": "t^n" + }, + { + "bbox": [ + 46, + 324, + 289, + 540 + ], + "type": "text", + "content": ", the survival prediction task is to estimate the ordinal risk of death via the cumulative survival function:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 98, + 546, + 287, + 578 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 98, + 546, + 287, + 578 + ], + "spans": [ + { + "bbox": [ + 98, + 546, + 287, + 578 + ], + "type": "interline_equation", + "content": "S _ {n} (t \\mid H _ {n}) = \\prod_ {z = 1} ^ {t} \\left(1 - h _ {n} (z \\mid H _ {n})\\right) \\tag {3}", + "image_path": "0651e76e171ab304675109aaaadcc7a27479fa6ca545df9236a0e02ebd3589bc.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 586, + 254, + 599 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 254, + 599 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 254, + 599 + ], + "type": "text", + "content": "3.2. Optimal Transport-based Co-Attention" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 604, + 289, + 717 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 604, + 289, + 717 + ], + "spans": [ + { + "bbox": [ + 46, + 604, + 289, + 717 + ], + "type": "text", + "content": "To identify TME-related instances of WSIs, we utilize the global potential structure consistency between TME interactions of pathology and genes co-expressions as the evidence of selecting instances, in which optimal transport is used to learn the optimal matching flow between a WSI feature bag " + }, + { + "bbox": [ + 46, + 604, + 289, + 717 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^p\\in \\mathbb{R}^{M_p\\times d}" + }, + { + "bbox": [ + 46, + 604, + 289, + 717 + ], + "type": "text", + "content": " and a genomic bag " + }, + { + "bbox": [ + 46, + 604, + 289, + 717 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^g\\in \\mathbb{R}^{M_g\\times d}" + }, + { + "bbox": [ + 46, + 604, + 289, + 717 + ], + "type": "text", + "content": ". Formally, an optimal transport from the WSI feature bag " + }, + { + "bbox": [ + 46, + 604, + 289, + 717 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^p = [\\mathbf{b}_{n,1}^p,\\mathbf{b}_{n,2}^p,\\dots ,\\mathbf{b}_{n,M_p}^p ]" + }, + { + "bbox": [ + 46, + 604, + 289, + 717 + ], + "type": "text", + "content": " to the genomic embedding " + }, + { + "bbox": [ + 46, + 604, + 289, + 717 + ], + "type": "inline_equation", + "content": "\\mathrm{bag}\\mathbf{B}_n^g = [\\mathbf{b}_{n,1}^g,\\mathbf{b}_{n,2}^g,\\dots ,\\mathbf{b}_{n,M_g}^g ]" + }, + { + "bbox": [ + 46, + 604, + 289, + 717 + ], + "type": "text", + "content": " can be defined by the" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 72, + 545, + 97 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 97 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 97 + ], + "type": "text", + "content": "discrete Kantorovich formulation [21] to search the overall optimal matching flow " + }, + { + "bbox": [ + 305, + 72, + 545, + 97 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_n" + }, + { + "bbox": [ + 305, + 72, + 545, + 97 + ], + "type": "text", + "content": " between " + }, + { + "bbox": [ + 305, + 72, + 545, + 97 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^p" + }, + { + "bbox": [ + 305, + 72, + 545, + 97 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 72, + 545, + 97 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^g" + }, + { + "bbox": [ + 305, + 72, + 545, + 97 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 337, + 105, + 545, + 126 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 337, + 105, + 545, + 126 + ], + "spans": [ + { + "bbox": [ + 337, + 105, + 545, + 126 + ], + "type": "interline_equation", + "content": "\\mathcal {W} \\left(\\mathbf {B} _ {n} ^ {p}, \\mathbf {B} _ {n} ^ {g}\\right) = \\min _ {\\mathbf {P} _ {n} \\in \\Pi \\left(\\mu_ {p}, \\mu_ {g}\\right)} < \\mathbf {P} _ {n}, \\mathbf {C} _ {n} > _ {F} \\tag {4}", + "image_path": "911c9630467dc32fb211d2e0c61b66d5cd0d26c7f98e23915bc8b68de545d5cf.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "spans": [ + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "inline_equation", + "content": "\\mathbf{C}_n\\geq 0\\in \\mathbb{R}^{M_p\\times M_g}" + }, + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "text", + "content": " is a cost matrix given by " + }, + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "inline_equation", + "content": "\\mathbf{C}_n^{u,v} = c(\\mathbf{b}_{n,u}^p,\\mathbf{b}_{n,v}^g)" + }, + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "text", + "content": " with a ground distance metric " + }, + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "inline_equation", + "content": "c(\\cdot)" + }, + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "text", + "content": " such as " + }, + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "inline_equation", + "content": "l_{2}" + }, + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "text", + "content": "-distance, that measures the distance of local pairwise instances " + }, + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "inline_equation", + "content": "\\mathbf{b}_{n,u}^p\\in \\mathbf{B}_n^p" + }, + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "text", + "content": " in the WSI bag and the genomic one of a unique functional category " + }, + { + "bbox": [ + 304, + 133, + 545, + 194 + ], + "type": "inline_equation", + "content": "\\mathbf{b}_{n,v}^g\\in \\mathbf{B}_n^g" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "spans": [ + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": "Here " + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "inline_equation", + "content": "\\Pi (\\mu_p,\\mu_g) = \\{\\mathbf{P}_n\\in \\mathbb{R}_+^{M_p\\times M_g}|\\mathbf{P}_n\\mathbf{1}_{M_g} = \\mu_p,\\mathbf{P}_n^\\top \\mathbf{1}_{M_p} = \\mu_g\\}" + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": " involves the marginal constraints of total mass equality between marginal distributions, " + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "inline_equation", + "content": "\\mu_{p}" + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "inline_equation", + "content": "\\mu_{g}" + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": ", for the WSI bag and the genomic bag, and " + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{1}_k" + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": " is a " + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "inline_equation", + "content": "k" + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": "-dimensional vector of ones. Specifically, " + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "inline_equation", + "content": "\\Pi (\\mu_p,\\mu_g)" + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": " refers to the set of joint probabilistic couplings between the two marginal empirical distributions of pathology data and genomic data. Intuitively, it describes how to distribute instances of a WSI bag " + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^p" + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": " to the genomic embedding of a genomic bag " + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^g" + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": " based on the cost matrix " + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "inline_equation", + "content": "\\mathbf{C}_n" + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": ", under the marginal constraints of total mass equality between distributions " + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "inline_equation", + "content": "\\mu_{p}" + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "inline_equation", + "content": "\\mu_{g}" + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": ". Note that " + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "inline_equation", + "content": "< \\cdot >_{F}" + }, + { + "bbox": [ + 304, + 194, + 545, + 424 + ], + "type": "text", + "content": " refers to the Frobenius dot product, and thus Eq. 4 encourages to achieve the overall minimum matching cost by finding optimal matching flow based on local pairwise similarity. In this way, the optimal transport of Eq. 4 is able to enforce a trade-off of instances within modality, which allows the model to capture the potential structure of visual interactions for histology and co-expressions for genomic data." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 425, + 545, + 484 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 425, + 545, + 484 + ], + "spans": [ + { + "bbox": [ + 304, + 425, + 545, + 484 + ], + "type": "text", + "content": "Once acquiring the optimal matching flow " + }, + { + "bbox": [ + 304, + 425, + 545, + 484 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_n^*" + }, + { + "bbox": [ + 304, + 425, + 545, + 484 + ], + "type": "text", + "content": ", informative instances of a WSI are identified by " + }, + { + "bbox": [ + 304, + 425, + 545, + 484 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{B}}_n^p = \\mathbf{P}_n^\\top \\mathbf{B}_n^p" + }, + { + "bbox": [ + 304, + 425, + 545, + 484 + ], + "type": "text", + "content": " to represent the WSI, which also aligns pathology distribution to genomics distribution under preserving the potential structure across modalities for alleviating heterogeneity." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 484, + 545, + 556 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 484, + 545, + 556 + ], + "spans": [ + { + "bbox": [ + 304, + 484, + 545, + 556 + ], + "type": "text", + "content": "As such, the proposed OT-based Co-Attention simultaneously addresses two issues: not only does it achieve the effective representation for gigapixel WSIs by identifying informative instances via OT matching, but marginal constraints of OT enable the selected instances to have global structure consistency with genomic data." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 563, + 476, + 576 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 563, + 476, + 576 + ], + "spans": [ + { + "bbox": [ + 306, + 563, + 476, + 576 + ], + "type": "text", + "content": "3.3. Optimization over Micro-Batch" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 580, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 580, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 580, + 545, + 713 + ], + "type": "text", + "content": "Due to the large size of the WSI bag, it is difficult to apply optimal transport for matching histology data and genomic data. Recent work [48] has validated that MIL on WSI can benefit from multiple subsets of a bag randomly sampled from the original WSI bag. It provides a way to train the model over Micro-Batch of a WSI, where micro-batch is defined as a subset sampled from a bag of WSI instances. Furthermore, inspired by a variant [13] of OT that offers a solution to approximate the original OT over mini-batches with a theoretical guarantee of convergence, we propose to use the variant UMBOT formulation [13] over micro-batch of WSI instead of the original OT over" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "21245" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 242, + 84 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 242, + 84 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 242, + 84 + ], + "type": "text", + "content": "all instances of a WSI. Then the Eq. 4 becomes:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 89, + 286, + 134 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 89, + 286, + 134 + ], + "spans": [ + { + "bbox": [ + 47, + 89, + 286, + 134 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {W} ^ {m} \\left(B _ {n} ^ {p, m}, \\mathbf {B} _ {n} ^ {g}\\right) = \\min _ {\\mathbf {P} _ {n} ^ {m} \\in \\Pi \\left(\\mu_ {p} ^ {m}, \\mu_ {g}\\right)} < \\mathbf {P} _ {n} ^ {m}, \\mathbf {C} _ {n} ^ {m} > _ {F} \\\\ + \\epsilon K L \\left(\\mathbf {P} _ {n} ^ {m} \\mid \\mu_ {p} ^ {m} \\otimes \\mu_ {g}\\right) + \\tau \\left(D _ {\\phi} \\left(\\mathbf {P} _ {n, p} ^ {m} \\mid \\mid \\mu_ {p} ^ {m}\\right) + D _ {\\phi} \\left(\\mathbf {P} _ {n, g} ^ {m} \\mid \\mid \\mu_ {g}\\right)\\right) \\tag {5} \\\\ \\end{array}", + "image_path": "ad7811e0e215c0183361d639d6484a14cce910ae68d4f7a070d5df84e55e3f4f.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "spans": [ + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "B_{n}^{p,m}" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": " is micro-batch of size " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": " sampled from " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^p" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": ". Similarly, " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "\\mathbf{C}_n^m \\in \\mathbb{R}^{m \\times M_g}" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": " is the cost matrix over micro-batch of WSI " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "B_{n}^{p,m}" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "\\mathbf{B}_n^g" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": ", and the optimal matching flow " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_n^m \\in \\mathbb{R}^{m \\times M_g}" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": " is optimized over micro-batch as well. Here " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_{n,p}^m" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_{n,g}^m" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": " represent the marginals of " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "\\mathbf{P}_n^m" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "D_{\\phi}" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": " is Csiszar divergences, " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "\\epsilon \\geq 0" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": " are the coefficients of marginal penalization and entropic regularization, respectively. " + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "inline_equation", + "content": "KL" + }, + { + "bbox": [ + 47, + 134, + 286, + 229 + ], + "type": "text", + "content": " refers to Kullback-Leibler divergence." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 229, + 286, + 301 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 229, + 286, + 301 + ], + "spans": [ + { + "bbox": [ + 47, + 229, + 286, + 301 + ], + "type": "text", + "content": "Computational complexity. With the benefit of UMBOT for approximating the original OT, the computational complexity of optimization is reduced from " + }, + { + "bbox": [ + 47, + 229, + 286, + 301 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(M^3\\log (M))" + }, + { + "bbox": [ + 47, + 229, + 286, + 301 + ], + "type": "text", + "content": " to " + }, + { + "bbox": [ + 47, + 229, + 286, + 301 + ], + "type": "inline_equation", + "content": "\\mathcal{O}(\\frac{M}{m}\\times m^2) = \\mathcal{O}(M\\times m)" + }, + { + "bbox": [ + 47, + 229, + 286, + 301 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 47, + 229, + 286, + 301 + ], + "type": "inline_equation", + "content": "M = \\max (M_p,M_g)" + }, + { + "bbox": [ + 47, + 229, + 286, + 301 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 229, + 286, + 301 + ], + "type": "inline_equation", + "content": "m\\ll M" + }, + { + "bbox": [ + 47, + 229, + 286, + 301 + ], + "type": "text", + "content": ". The whole optimization procedure of the proposed MOTCat is presented in Alg. 1" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 301, + 286, + 326 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 301, + 286, + 326 + ], + "spans": [ + { + "bbox": [ + 47, + 301, + 286, + 326 + ], + "type": "text", + "content": "Loss function. Following the previous work [5], the overall loss function is formulated by NLL-loss [46]:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 333, + 287, + 430 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 333, + 287, + 430 + ], + "spans": [ + { + "bbox": [ + 47, + 333, + 287, + 430 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {L} = - \\frac {m}{M _ {p}} \\sum_ {n = 1} ^ {N} \\sum_ {X _ {n} ^ {p, m} \\in \\mathbf {X} _ {n} ^ {p}} c _ {n} \\cdot \\log \\left(S _ {n} ^ {m} \\left(t _ {n} \\mid H _ {n} ^ {m}\\right)\\right) \\\\ - \\frac {m}{M _ {p}} \\sum_ {n = 1} ^ {N} \\sum_ {X _ {n} ^ {p, m} \\in \\mathbf {X} _ {n} ^ {p}} \\left\\{\\left(1 - c _ {n}\\right) \\cdot \\log \\left(S _ {n} ^ {m} \\left(t _ {n} - 1 \\mid H _ {n} ^ {m}\\right)\\right) \\right. \\\\ \\left. + \\left(1 - c _ {n}\\right) \\cdot \\log \\left(h _ {n} ^ {m} \\left(t _ {n} \\mid H _ {n} ^ {m}\\right)\\right) \\right\\} \\tag {6} \\\\ \\end{array}", + "image_path": "07263c4f3751a0ccd30943632b230bdb7f012d8e358e402446b428de69fa42c4.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "inline_equation", + "content": "H_{n}^{m}" + }, + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "text", + "content": " refers to the multimodal features over micro-batch formulated in line 16 of Alg. 1. " + }, + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "inline_equation", + "content": "h_{n}^{m}" + }, + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "inline_equation", + "content": "S_{n}^{m}" + }, + { + "bbox": [ + 47, + 430, + 287, + 479 + ], + "type": "text", + "content": " are the hazard function and cumulative survival function over micro-batch, respectively." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 488, + 123, + 502 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 488, + 123, + 502 + ], + "spans": [ + { + "bbox": [ + 47, + 488, + 123, + 502 + ], + "type": "text", + "content": "4. Experiment" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 509, + 287, + 652 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 509, + 287, + 652 + ], + "spans": [ + { + "bbox": [ + 46, + 509, + 287, + 652 + ], + "type": "text", + "content": "In this section, we first present datasets and settings following previous experimental protocols [5, 6] for fair comparisons. Next, we demonstrate the performance results of the proposed method compared with the state-of-the-art (SOTA) methods, including unimodal and multimodal approaches. After that, we investigate the effectiveness of each component in our method and the effect on the size of micro-batch strategy. Finally, from a statistical point of view, we present Kaplan-Meier survival curves and Logrank test to show the performance of survival analysis. Interpretable visualization for histology data and genomic data are presented in supplementary materials." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 659, + 169, + 672 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 659, + 169, + 672 + ], + "spans": [ + { + "bbox": [ + 47, + 659, + 169, + 672 + ], + "type": "text", + "content": "4.1. Datasets and Settings" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 677, + 287, + 713 + ], + "type": "text", + "content": "Datasets. To demonstrate the performance of the proposed method, we conducted various experiments over five public cancer datasets from The Cancer Genome Atlas (TCGA)" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 72, + 545, + 227 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 227 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 227 + ], + "type": "text", + "content": "that contains paired diagnostic WSIs and genomic data with ground-truth survival outcome: Bladder Urothelial Carcinoma (BLCA), Breast Invasive Carcinoma (BRCA), Uterine Corpus Endometrial Carcinoma (UCEC), Glioblastoma & Lower Grade Glioma (GBMLGG), and Lung Adenocarcinoma (LUAD). The number of cases for each cancer type is shown by " + }, + { + "bbox": [ + 304, + 72, + 545, + 227 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 304, + 72, + 545, + 227 + ], + "type": "text", + "content": " in Tab. 1. Note that cases of these cancer datasets used for all compared methods are not less than cases used in the proposed method. For genomic data, the number of unique functional categories " + }, + { + "bbox": [ + 304, + 72, + 545, + 227 + ], + "type": "inline_equation", + "content": "M_g" + }, + { + "bbox": [ + 304, + 72, + 545, + 227 + ], + "type": "text", + "content": " is set as 6 following [28, 5], including 1) Tumor Suppression, 2) Oncogenesis, 3) Protein Kinases, 4) Cellular Differentiation, 5) Transcription, and 6) Cytokines and Growth." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 228, + 545, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 228, + 545, + 300 + ], + "spans": [ + { + "bbox": [ + 304, + 228, + 545, + 300 + ], + "type": "text", + "content": "Evaluation. For each cancer dataset, we perform 5-fold cross-validation with a 4:1 ratio of training-validation sets and report the cross-validated concordance index (C-Index) and its standard deviation (std) to quantify the performance of correctly ranking the predicted patient risk scores with respect to overall survival." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 300, + 545, + 409 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 300, + 545, + 409 + ], + "spans": [ + { + "bbox": [ + 304, + 300, + 545, + 409 + ], + "type": "text", + "content": "Implementation. For each WSI, we first apply the OTSU's threshold method to segment tissue regions, and then non-overlapping " + }, + { + "bbox": [ + 304, + 300, + 545, + 409 + ], + "type": "inline_equation", + "content": "256 \\times 256" + }, + { + "bbox": [ + 304, + 300, + 545, + 409 + ], + "type": "text", + "content": " patches are extracted from the tissue region over " + }, + { + "bbox": [ + 304, + 300, + 545, + 409 + ], + "type": "inline_equation", + "content": "20 \\times" + }, + { + "bbox": [ + 304, + 300, + 545, + 409 + ], + "type": "text", + "content": " magnification. Then, we use ImageNet-pretrained [10] ResNet-50 [17] and a 256-d fully-connected layer as the feature encoder " + }, + { + "bbox": [ + 304, + 300, + 545, + 409 + ], + "type": "inline_equation", + "content": "f_{p}" + }, + { + "bbox": [ + 304, + 300, + 545, + 409 + ], + "type": "text", + "content": " to extract the 1024-d embedding for each patch, where parameters of ResNet-50 are frozen. For genomic data, we adopt SNN [22] as the feature encoder " + }, + { + "bbox": [ + 304, + 300, + 545, + 409 + ], + "type": "inline_equation", + "content": "f_{g}" + }, + { + "bbox": [ + 304, + 300, + 545, + 409 + ], + "type": "text", + "content": " following the setting of [5]." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "spans": [ + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "text", + "content": "During training, we follow the setting of [5] for a fair comparison. Specifically, we adopt Adam optimizer with the initial learning rate of " + }, + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "inline_equation", + "content": "2 \\times 10^{-4}" + }, + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "text", + "content": " and weight decay of " + }, + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "inline_equation", + "content": "1 \\times 10^{-5}" + }, + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "text", + "content": ". Due to the large size of WSIs, the batch size for WSIs is 1 with 32 gradient accumulation steps, and all experiments are trained for 20 epochs. The size of MicroBatch " + }, + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "inline_equation", + "content": "m" + }, + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "text", + "content": " is set as 256. Regarding the hyper-parameters of OT in Eq. 5, the coefficient of marginal penalization " + }, + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\tau" + }, + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "text", + "content": " is 0.5 for all cancer datasets, and the coefficient of entropic regularization " + }, + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 304, + 408, + 545, + 540 + ], + "type": "text", + "content": " is 0.05 for BLCA and LUAD, as well as 0.1 for BRCA, UCEC and GBMLGG." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 550, + 362, + 561 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 550, + 362, + 561 + ], + "spans": [ + { + "bbox": [ + 306, + 550, + 362, + 561 + ], + "type": "text", + "content": "4.2. Results" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 304, + 568, + 544, + 592 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 568, + 544, + 592 + ], + "spans": [ + { + "bbox": [ + 304, + 568, + 544, + 592 + ], + "type": "text", + "content": "We compare our method against the unimodal baselines and the multimodal SOTA methods as follows:" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 593, + 545, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 593, + 545, + 688 + ], + "spans": [ + { + "bbox": [ + 304, + 593, + 545, + 688 + ], + "type": "text", + "content": "Unimodal Baseline. For genomic data, we adopt SNN [22] that has been used previously for survival outcome prediction in the TCGA [4, 5], and SNNTrans [22, 36] which incorporates SNN as the feature extractor and TransMIL [36] as the global aggregation model for MIL. For histology, we compare the SOTA MIL methods AttnMIL [19], DeepAttnMISL [45], CLAM [32], TransMIL [36], and DTFDMIL [48]." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "content": "Multimodal SOTA. We compare four SOTA methods for multimodal survival outcome prediction including" + } + ] + } + ], + "index": 18 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "21246" + } + ] + } + ], + "index": 19 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 57, + 92, + 535, + 278 + ], + "blocks": [ + { + "bbox": [ + 47, + 69, + 545, + 91 + ], + "lines": [ + { + "bbox": [ + 47, + 69, + 545, + 91 + ], + "spans": [ + { + "bbox": [ + 47, + 69, + 545, + 91 + ], + "type": "text", + "content": "Table 1. C-Index (mean ± std) performance over five cancer datasets. Patho. and Geno. refer to pathology modality and genomic modality, respectively. The best results and the second-best results are highlighted in bold and in underline, respectively." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 57, + 92, + 535, + 278 + ], + "lines": [ + { + "bbox": [ + 57, + 92, + 535, + 278 + ], + "spans": [ + { + "bbox": [ + 57, + 92, + 535, + 278 + ], + "type": "table", + "html": "
ModelPatho.Geno.BLCA (N=373)BRCA (N=956)UCEC (N=480)GBMLGG (N=569)LUAD (N=453)
SNN* [22]✓0.618 ± 0.0220.624 ± 0.0600.679 ± 0.0400.834 ± 0.0120.611 ± 0.047
SNNTrans* [22, 36]✓0.659 ± 0.0320.647 ± 0.0630.656 ± 0.0380.839 ± 0.0140.638 ± 0.022
AttnMIL* [19]✓0.599 ± 0.0480.609 ± 0.0650.658 ± 0.0360.818 ± 0.0250.620 ± 0.061
DeepAttnMISL [45]✓0.504 ± 0.0420.524 ± 0.0430.597 ± 0.0590.734 ± 0.0290.548 ± 0.050
CLAM-SB* [32]✓0.559 ± 0.0340.573 ± 0.0440.644 ± 0.0610.779 ± 0.0310.594 ± 0.063
CLAM-MB* [32]✓0.565 ± 0.0270.578 ± 0.0320.609 ± 0.0820.776 ± 0.0340.582 ± 0.072
TransMIL* [36]✓0.575 ± 0.0340.666 ± 0.0290.655 ± 0.0460.798 ± 0.0430.642 ± 0.046
DTFD-MIL* [48]✓0.546 ± 0.0210.609 ± 0.0590.656 ± 0.0450.792 ± 0.0230.585 ± 0.066
Pathomic [4]✓✓0.586 ± 0.062--0.826 ± 0.0090.543 ± 0.065
PONET [34]✓✓0.643 ± 0.037---0.646 ± 0.047
Porpoise* [6]✓✓0.636 ± 0.0240.652 ± 0.0420.695 ± 0.0320.834 ± 0.0170.647 ± 0.031
MCAT* [5]✓✓0.672 ± 0.0320.659 ± 0.0310.649 ± 0.0430.835 ± 0.0240.659 ± 0.027
MOTCat (Ours)✓✓0.683 ± 0.0260.673 ± 0.0060.675 ± 0.0400.849 ± 0.0280.670 ± 0.038
", + "image_path": "61565ece6a852a6422ffcb54271161230511029b5d39f6a7d83b9fc356bed57b.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 297, + 284, + 310 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 297, + 284, + 310 + ], + "spans": [ + { + "bbox": [ + 47, + 297, + 284, + 310 + ], + "type": "text", + "content": "MCAT [5], Pathomic [4], Porpoise [6] and PONET [34]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 311, + 287, + 393 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 311, + 287, + 393 + ], + "spans": [ + { + "bbox": [ + 46, + 311, + 287, + 393 + ], + "type": "text", + "content": "Results are shown in Tab. 1, where the methods marked * are re-implemented and the best results are reported, and other results are obtained from their papers. Note that due to varying cancer datasets used in their works, not all results of the five datasets used in this work can be reported, and hence we use ' -' to indicate the results are not reported in their papers." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 395, + 287, + 538 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 395, + 287, + 538 + ], + "spans": [ + { + "bbox": [ + 46, + 395, + 287, + 538 + ], + "type": "text", + "content": "Unimodal vs. Multimodal. Compared with all unimodal approaches, the proposed method achieves the highest performance in 4 out of 5 cancer datasets, indicating the effective fusion of multimodal data in our method. Note that the overall performance of genomic data is better than that of histology, which validates the reasonability of using genomic data for guiding the selection of instances in WSIs. In particular, most multimodal methods are inferior to the unimodal model of genomics in UCEC dataset, suggesting the serious challenge in multimodal fusion. Nevertheless, the proposed method can achieve the comparative performance with genomic model on UCEC." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 540, + 287, + 660 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 540, + 287, + 660 + ], + "spans": [ + { + "bbox": [ + 46, + 540, + 287, + 660 + ], + "type": "text", + "content": "Multimodal SOTA v.s. MOTCat. In one-versus-all comparisons of multimodal models, the proposed method achieves superior performance on all benchmarks with " + }, + { + "bbox": [ + 46, + 540, + 287, + 660 + ], + "type": "inline_equation", + "content": "1.0\\% - 2.6\\%" + }, + { + "bbox": [ + 46, + 540, + 287, + 660 + ], + "type": "text", + "content": " performance gains except UCEC. In comparing the proposed method with the most similar work MCAT in multimodal fusion, our method gets better results on all datasets, indicating the effectiveness of learning the intramodal potential structure consistency from a global perspective between TME-related interactions of histology and genomic co-expression." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 670, + 141, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 670, + 141, + 683 + ], + "spans": [ + { + "bbox": [ + 47, + 670, + 141, + 683 + ], + "type": "text", + "content": "4.3. Ablation Study" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 47, + 689, + 287, + 715 + ], + "type": "text", + "content": "We first investigate the effectiveness of OT-based coattention component (denoted by OT) and the micro-batch" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 297, + 545, + 334 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 297, + 545, + 334 + ], + "spans": [ + { + "bbox": [ + 304, + 297, + 545, + 334 + ], + "type": "text", + "content": "strategy (denoted by MB). Furthermore, the effect on the size of micro-batch and the actual computational speed of our method are explored." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 335, + 545, + 432 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 335, + 545, + 432 + ], + "spans": [ + { + "bbox": [ + 304, + 335, + 545, + 432 + ], + "type": "text", + "content": "Component validation. As shown in Tab. 2, we observe that multimodal fusion can benefit from micro-batch strategy by comparing (a) and (b), and OT-based co-attention further improves the performance by approximating the original results with the averaged results over micro-batches via UMBOT. As a result, our method achieves the best overall performance. These improvements both demonstrate the effectiveness of each component for the proposed method." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 434, + 545, + 506 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 434, + 545, + 506 + ], + "spans": [ + { + "bbox": [ + 304, + 434, + 545, + 506 + ], + "type": "text", + "content": "Additionally, recent work [48] has claimed that MIL on WSIs can benefit from learning over sub-bags in a WSI, which is also validated by performance increases in variant (b). The reason why it can profit from micro-batch might be that it increases the number of bags, so that more features can be used for survival analysis." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 507, + 545, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 507, + 545, + 591 + ], + "spans": [ + { + "bbox": [ + 304, + 507, + 545, + 591 + ], + "type": "text", + "content": "Size of Micro-batch. To show the robustness of approximation to the size of Micro-batch strategy, we compare several variants of the proposed method over the varying sizes of micro-batch, as shown in the quantitative analysis of Fig. 3. The qualitative analysis of the effect on size of Micro-Batch can be found in the supplementary materials, which also achieves the consistent conclusion." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "content": "For the quantitative analysis in Fig. 3, two variants of the proposed method are compared: 1) UMBOT " + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "content": " EMD: To demonstrate the robustness of different OT variants, we replace UMBOT used in our method with the original OT (i.e. EMD) for comparison, which is equivalent to the Eq. (4) done over Micro-batch. 2) UMBOT " + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 304, + 594, + 545, + 714 + ], + "type": "text", + "content": " CoAttn: To compare the robustness of the proposed OT-based co-attention and the original co-attention, we replace UMBOT with the co-attention used in MCAT [5] and train the model over Micro-batch for comparison." + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "21247" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 91, + 545, + 152 + ], + "blocks": [ + { + "bbox": [ + 47, + 69, + 545, + 91 + ], + "lines": [ + { + "bbox": [ + 47, + 69, + 545, + 91 + ], + "spans": [ + { + "bbox": [ + 47, + 69, + 545, + 91 + ], + "type": "text", + "content": "Table 2. Ablation study assessing C-Index (mean ± std) performance of MOTCat over five datasets, in which version (c) in bold is the proposed method with full components, and (a) and (b) refer to its variants. The best results are marked in bold." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 47, + 91, + 545, + 152 + ], + "lines": [ + { + "bbox": [ + 47, + 91, + 545, + 152 + ], + "spans": [ + { + "bbox": [ + 47, + 91, + 545, + 152 + ], + "type": "table", + "html": "
VariantsOTMBBLCABRCAUCECGBMLGGLUAD
(a) MCAT0.672 ± 0.0320.659 ± 0.0310.649 ± 0.0430.835 ± 0.0240.659 ± 0.027
(b) MOTCat w/o OT✓0.663 ± 0.0250.666 ± 0.0170.663 ± 0.0310.845 ± 0.0230.673 ± 0.036
(c) MOTCat✓✓0.683 ± 0.0260.673 ± 0.0060.675 ± 0.0400.849 ± 0.0280.670 ± 0.038
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Boxplots of C-Index over various sizes of Micro-batch for our method and two variants on five cancer datasets, in which the green triangle means the averaged results of all sizes and the horizontal line in the box represents the median result." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + } + ], + "index": 5 + }, + { + "type": "image", + "bbox": [ + 383, + 168, + 543, + 269 + ], + "blocks": [ + { + "bbox": [ + 383, + 168, + 543, + 269 + ], + "lines": [ + { + "bbox": [ + 383, + 168, + 543, + 269 + ], + "spans": [ + { + "bbox": [ + 383, + 168, + 543, + 269 + ], + "type": "image", + "image_path": "043643c531f79873ed07a1347582545f133da90a28c51ebfe88f64d3ddfae42e.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 386, + 277, + 543, + 376 + ], + "blocks": [ + { + "bbox": [ + 386, + 277, + 543, + 376 + ], + "lines": [ + { + "bbox": [ + 386, + 277, + 543, + 376 + ], + "spans": [ + { + "bbox": [ + 386, + 277, + 543, + 376 + ], + "type": "image", + "image_path": "abdf0f9023965c62a40d85a337595bf84ac412b0e50ef9d596993185288765e9.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 426, + 289, + 558 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 426, + 289, + 558 + ], + "spans": [ + { + "bbox": [ + 46, + 426, + 289, + 558 + ], + "type": "text", + "content": "From the results of Fig. 3, we can see that 1) our method achieves the best averaged performance of various sizes compared with the two variants, especially on BRCA with the most samples of 956. 2) Further, on UCEC and LUAD datasets, the proposed method gets the most robust results. 3) Although the second variant UMBOT " + }, + { + "bbox": [ + 46, + 426, + 289, + 558 + ], + "type": "inline_equation", + "content": "\\rightarrow" + }, + { + "bbox": [ + 46, + 426, + 289, + 558 + ], + "type": "text", + "content": " CoAttn shows slightly better robustness on BLCA and BRCA, the performance of our method surpasses it by a large margin. In a nutshell, the proposed method achieves a better trade-off between performance and robustness, compared with different OT variants or the co-attention of MCAT." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": "Computational Speed. We measure the actual averaged computational speed for 10 WSIs (about 150k patches in total) on one GPU of NVIDIA GeForce RTX 3090. The proposed method is compared with a variant 'org-OT' that replaces UMBOT by the original OT. However, the original OT with the high complexity takes extreme long time for one WSI (about 20k patches), and thus we fail to measure the actual computational time for the original OT in a short time. Here we present the speed of our method, which suggests our method makes it practicable to apply OT to histology and genomics. Specifically, the training speed of the proposed method is " + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "inline_equation", + "content": "6540~\\mathrm{p / s}" + }, + { + "bbox": [ + 46, + 570, + 288, + 714 + ], + "type": "text", + "content": " (p/s refers to the number" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 426, + 546, + 450 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 426, + 546, + 450 + ], + "spans": [ + { + "bbox": [ + 304, + 426, + 546, + 450 + ], + "type": "text", + "content": "of processing patches per second) and the inference speed is " + }, + { + "bbox": [ + 304, + 426, + 546, + 450 + ], + "type": "inline_equation", + "content": "11885\\mathrm{p / s}" + }, + { + "bbox": [ + 304, + 426, + 546, + 450 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 305, + 459, + 419, + 472 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 459, + 419, + 472 + ], + "spans": [ + { + "bbox": [ + 305, + 459, + 419, + 472 + ], + "type": "text", + "content": "4.4. Statistical Analysis" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 478, + 547, + 646 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 478, + 547, + 646 + ], + "spans": [ + { + "bbox": [ + 304, + 478, + 547, + 646 + ], + "type": "text", + "content": "To show a statistical difference in patient stratification performance, we visualize the Kaplan-Meier survival curves for different methods, in which patients are separated into two groups of low-risk and high-risk based on predicted risk scores, and then the statistics on ground-truth survival time are presented for each group in Fig. 4. The Logrank test is conducted to measure the statistically significant difference in two groups of patients, where a lower P-value indicates better performance of patient stratification. From the results of Fig. 4, intuitively our method separates patients of low and high risk more clearly on all datasets. In the Logrank test, our method achieves a lower P-value on all datasets in comparison to MCAT, especially on BLCA, BRCA and UCEC with a large margin of magnitude." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 657, + 379, + 670 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 657, + 379, + 670 + ], + "spans": [ + { + "bbox": [ + 306, + 657, + 379, + 670 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 677, + 546, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 677, + 546, + 713 + ], + "spans": [ + { + "bbox": [ + 305, + 677, + 546, + 713 + ], + "type": "text", + "content": "In this paper, we present a novel Multimodal Optimal Transport-based Co-Attention Transformer with global structure consistency to tackle two important issues in mul" + } + ] + } + ], + "index": 15 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "21248" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 53, + 71, + 541, + 236 + ], + "blocks": [ + { + "bbox": [ + 53, + 71, + 541, + 236 + ], + "lines": [ + { + "bbox": [ + 53, + 71, + 541, + 236 + ], + "spans": [ + { + "bbox": [ + 53, + 71, + 541, + 236 + ], + "type": "image", + "image_path": "3a6391f8914dbb249aa49e79df36b9b76ef5350d26f6117130b79663c5464b7a.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 238, + 546, + 273 + ], + "lines": [ + { + "bbox": [ + 46, + 238, + 546, + 273 + ], + "spans": [ + { + "bbox": [ + 46, + 238, + 546, + 273 + ], + "type": "text", + "content": "Figure 4. Kaplan-Meier Analysis on five cancer datasets, where patient stratifications of low risk (green) and high risk (red) are presented. Shaded areas refer to the confidence intervals. P-value " + }, + { + "bbox": [ + 46, + 238, + 546, + 273 + ], + "type": "inline_equation", + "content": "< 0.05" + }, + { + "bbox": [ + 46, + 238, + 546, + 273 + ], + "type": "text", + "content": " means significant statistical difference in two groups, and lower P-value is better. (Zoom in for better viewing.)" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 291, + 289, + 471 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 291, + 289, + 471 + ], + "spans": [ + { + "bbox": [ + 46, + 291, + 289, + 471 + ], + "type": "text", + "content": "timodal learning of histology and genomics for survival prediction. First, we utilize a new OT-based Co-Attention to match pairwise instances between histology and genomics for selecting informative instances strongly related to tumor microenvironment, which provides a way to effectively represent gigapixel WSIs. Second, optimal transport offers a global awareness for modeling potential structure within modality, i.e. pathological interactions and genomic co-expression. Furthermore, to enable applying OT-based Co-Attention in practice, we propose a robust and efficient implementation over micro-batch of WSI bags, in which the approximation over micro-batch might provide a solution to update the parameters of extractor for patch images in an end-to-end way instead of extracting feature embeddings offline, which will be further explored in the future." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 483, + 145, + 497 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 483, + 145, + 497 + ], + "spans": [ + { + "bbox": [ + 47, + 483, + 145, + 497 + ], + "type": "text", + "content": "Acknowledgement" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 502, + 287, + 570 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 502, + 287, + 570 + ], + "spans": [ + { + "bbox": [ + 46, + 502, + 287, + 570 + ], + "type": "text", + "content": "This work was supported by National Natural Science Foundation of China (No. 62202403), Shenzhen Science and Technology Innovation Committee (Project No. SGDX20210823103201011) and Hong Kong Innovation and Technology Fund (No. PRP/034/22FX)." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 582, + 107, + 594 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 582, + 107, + 594 + ], + "spans": [ + { + "bbox": [ + 47, + 582, + 107, + 594 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 52, + 601, + 288, + 714 + ], + "type": "list", + "angle": 0, + "index": 8, + "blocks": [ + { + "bbox": [ + 52, + 601, + 287, + 668 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 601, + 287, + 668 + ], + "spans": [ + { + "bbox": [ + 52, + 601, + 287, + 668 + ], + "type": "text", + "content": "[1] Khalid AbdulJabbar, Shan E Ahmed Raza, Rachel Rosenthal, Mariam Jamal-Hanjani, Selvaraju Veeriah, Ayse Akarca, Tom Lund, David A Moore, Roberto Salgado, Maise Al Bakir, et al. 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Existing AVS methods focus on implicit feature fusion strategies, where models are trained to fit the discrete samples in the dataset. With a limited and less diverse dataset, the resulting performance is usually unsatisfactory. In contrast, we address this problem from an effective representation learning perspective, aiming to model the contribution of each modality explicitly. Specifically, we find that audio contains critical category information of the sound producers, and visual data provides candidate sound producer(s). Their shared information corresponds to the target sound producer(s) shown in the visual data. In this case, cross-modal shared representation learning is especially important for AVS. To achieve this, our ECMVAE factorizes the representations of each modality with a modality-shared representation and a modality-specific representation. An orthogonality constraint is applied between the shared and specific representations to maintain the exclusive attribute of the factorized latent code. Further, a mutual information maximization regularizer is introduced to achieve extensive exploration of each modality. Quantitative and qualitative evaluations on the AVSBench demonstrate the effectiveness of our approach, leading to a new state-of-the-art for AVS, with a 3.84 mIOU performance leap on the challenging MS3 subset for multiple sound source segmentation.", + "bbox": [ + 75, + 333, + 472, + 741 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 768, + 209, + 784 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Audio-visual data can work collaboratively towards a better perception of the scene. The audio-visual segmentation (AVS) [1] task aims to segment the objects from the video sequence that producing the sound in the audio. On", + "bbox": [ + 75, + 794, + 468, + 854 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "the one hand, the audio data provides category information for the localization of the object in the video. On the other hand, the visual data provides a sound producer pool with precise structure information of the foreground (sound producer(s)). Different from conventional multimodal settings, where each modality can be used individually for the target task, audio in AVS task serves as \"command\" to localize and segment the sound producer(s) from the visual data. In this case, the contribution of audio should be extensively explored for accurate foreground segmentation.", + "bbox": [ + 500, + 287, + 892, + 439 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The baseline model [1] focuses on implicit feature fusion via audio-visual cross attention. It purely relies on fitting the discrete samples in the dataset. Although reasonable performance is obtained, there are no constraints to guarantee the contribution of each modality, making it hard to decide if the audio data is effectively used, as the model can directly regress the final segmentation maps by only taking the video as input. Fortunately, we discover that each modality for AVS contains both shared and specific information. For example, the audio data includes both the information from the sound producers and the background noise, while the visual data shows the appearance of the entire scene, where the sound producers only take a small portion of it. In our specific task setting, we find modality factorization is suitable to model both the modality-shared representation, i.e. information of the sound producers, and the modality-specific representation toward a better understanding of the contribution of each modality.", + "bbox": [ + 496, + 441, + 892, + 714 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "The straightforward solution to learn the feature representation of the input data is through an auto-encoder (AE) framework. However, AE is mainly used for data compression, as the learned feature space is not continuous, which cannot provide a rich semantic correlation of the data. Differently, with latent space regularization, e.g. the latent space is assumed to be Gaussian in variational autoencoder (VAE) [2], VAE obtains semantic meaningful latent space, which is continuous, and it is also the basic requirement for reliable latent space factorization.", + "bbox": [ + 496, + 715, + 893, + 867 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "To learn the semantic correlated feature representation of the AVS data, we propose an Explicit Conditional Mul", + "bbox": [ + 498, + 869, + 893, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Corresponding author (daiyuchao@gmail.com).", + "bbox": [ + 99, + 862, + 401, + 875 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "This work was done when Yuxin Mao was an intern at Shanghai AI Laboratory.", + "bbox": [ + 76, + 875, + 468, + 900 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "954", + "bbox": [ + 485, + 944, + 511, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "timodal Variational Auto-Encoder (ECMVAE) for audiovisual segmentation to learn both the shared and the specific representation in the latent space of each modality. Our model is built upon a multimodal variational autoencoder [3, 4], with the Jensen-Shannon divergence to achieve a trade-off between sampling efficiency and sample quality. Based on the latent space factorization, we impose constraints for the shared and specific representations to explicitly maximize the contribution of each modality.", + "bbox": [ + 75, + 90, + 467, + 226 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Specifically, we first assume that one latent code of the factorized representation should contain independent information compared to others. Furthermore, for the fused representation, we further claim that it should be more informative for the target task compared with each modality. To achieve the former, we propose an information orthogonality constraint between the factorized representations of each modality to ensure that the modality-shared and modality-specific representations capture different aspects of the audio-visual input. For the latter, we fuse the factorized representations of each modality to construct a fused space. Then we introduce a mutual information maximization regularizer between the fused representations of each modality to extensively explore the contribution of each modality. Extensive experimental results demonstrate that our ECMVAE achieves state-of-the-art AVS performance. Our pipeline achieves a $3.84\\mathrm{mIOU}$ improvement for the challenging multiple sound source segmentation.", + "bbox": [ + 75, + 227, + 467, + 498 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "We summarize our main contributions as:", + "bbox": [ + 96, + 500, + 372, + 512 + ], + "page_idx": 1 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- An explicit semantic correlated feature representation learning framework for audio-visual segmentation is proposed with latent space factorization to capture both the modality-shared and specific representations.", + "- Based on the latent space factorization, we introduce a unimodal orthogonality constraint between the shared and specific representations and the cross-modal mutual-information maximization regularizer to extensively explore the contribution of each modality.", + "- State-of-the-art segmentation performance is achieved, showing both the effectiveness of each module and the contribution of each modality." + ], + "bbox": [ + 94, + 513, + 467, + 694 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 76, + 709, + 218, + 724 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Audio-Visual Segmentation. The Audio-Visual Segmentation (AVS) task is newly proposed, aiming to localize the sound producers with pixel-wise segmentation masks. Zhou et al. [1] propose an AVSBench dataset for audio-visual segmentation and provide a simple baseline based on temporal pixel-wise audio-visual interaction (TPAVI), which is a cross-modal attention [5] based fusion strategy. The other audio-visual collaboration tasks can be classified as audio-visual correspondence (AVC) [6, 7], event localization (AVEL) [8-13], event parsing (AVP) [14-16], etc. These methods require the fusion of audio and visual sig", + "bbox": [ + 75, + 734, + 467, + 900 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "nals. Such as audio-visual similarity modeling by computing the correlation matrix [6, 7], audio-visual cross attention [12, 13, 17], audio-guided Grad-CAM [18], or using a multimodal transformer for modeling the long-range dependencies between elements across modalities directly [19, 20]. However, the challenge and uniqueness of the AVS task are how to map the audio signals to fine-grained visual cues, i.e. per-pixel segmentation maps. This will rely on reliable modeling of visual and audio signals, as well as more effective fusion strategies.", + "bbox": [ + 496, + 90, + 890, + 242 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multimodal Variational Auto-encoders. The Multimodal Variational Auto-encoders (MVAEs) [3, 21–24] are a type of latent variable generative model to learn more generalizable representations from diverse modalities. To achieve this, the core of MVAE is the joint distribution estimation. The conventional unimodal VAEs [2, 25] are optimized by maximizing the evidence lower bound (ELBO), which includes a reconstruction term and the Kullback-Leibler (KL) divergence term to measure the divergence from the variational posterior to the prior distribution of the latent variable. In a multimodal setting, the KL divergence is defined between the joint posterior and joint prior across the modalities, which is often estimated by the product of experts (PoE) [26, 27] or the mixture of experts (MoE) [28]. Based on such a prerequisite, many works extend the basic MVAE definition, such as missing modality handling [24], latent space modeling [23, 28], effective divergence modeling [4], etc. However, previous MVAE based frameworks essentially focus on the multimodal image generation task. In this work, we bring the MVAE to the AVS task and propose the conditional version [25, 29] of MVAE with practical multimodal information constraints for segmentation.", + "bbox": [ + 496, + 246, + 890, + 579 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Mutual Information Estimation. Mutual Information (MI) captures the nonlinear statistical dependencies between variables, acting as a measure of actual dependence [30]. Specifically, for a pair of random variables $X$ and $Y$ , their MI $I(X;Y)$ is defined as the KL divergence of the joint distribution $p_{(X,Y)}$ from the product of the marginal distributions $p(X)$ and $p(Y)$ , which measures the shared information between $X$ and $Y$ . Although mutual information is simple in formation, as the log density ratio between the joint distribution $p_{(X,Y)}$ and product of marginals $p(X)\\otimes p(Y)$ is intractable, it is usually estimated [31-33] instead of computed directly, leading to both MI maximization with a lower bound [34, 35] and MI minimization with an upper bound [36]. The MI maximization is usually applied for effective self-supervised representation learning [37-41] for the unimodal data to guarantee reliable feature representation. For the multimodal tasks, when each modality of data contains partial information of the target, both MI maximization and minimization can be applied [42-50], where the former aims to explore the taskdriven feature across the modalities, and the latter is de", + "bbox": [ + 496, + 583, + 890, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "955", + "bbox": [ + 485, + 944, + 509, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "signed to explore the complementary information of different modalities. Extensive researches show that effective MI optimization can not only lead to informative representation learning [51-58] but also is beneficial for achieving adversarial robustness [59].", + "bbox": [ + 75, + 90, + 468, + 167 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Explicit Conditional Multimodal Learning", + "text_level": 1, + "bbox": [ + 76, + 181, + 457, + 200 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "We denote the input data of our used AVSbench dataset [1] is $X = \\{\\{x_{t}^{v}\\}_{t=1}^{T}, x^{a}\\}$ , i.e. the visual $\\{x_{t}^{v}\\}_{t=1}^{T}$ for $T$ non-overlapping yet continuous frames, audio $x^{a}$ of the current clip. $y = \\{y_{t}\\}_{t=1}^{T}$ is the output, i.e. the segmentation maps (we omit $t$ for clear presentation). The goal of audio-visual segmentation is to segment the objects from the video $\\{x_{t}^{v}\\}_{t=1}^{T}$ that produce the sound shown in the audio $x^{a}$ . We introduce an Explicit Conditional Multi-modal Variational Auto-Encoder (ECMVAE) using Jensen-Shannon divergence (Sec. 3.1) via latent space factorization (Sec. 3.2) to effectively model the shared representation between the two modalities (Sec. 3.3 and Sec. 3.4) for audio-visual segmentation. The overview of the proposed ECMVAE is shown in Fig. 1.", + "bbox": [ + 75, + 207, + 470, + 419 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Prerequisite", + "text_level": 1, + "bbox": [ + 76, + 429, + 207, + 445 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Conditional Variational Auto-encoder. We begin our prerequisite with the definition of the conditional variational auto-encoder (CVAE) [2, 25], which contains a generative process and an inference process. The generative process is to draw the latent variable $z$ from the prior distribution $p_{\\theta}(z|X)$ with a given $X$ , and generate the output via $p_{\\theta}(y|X,z)$ , where in our case $X$ and $y$ in the following derivations are $X = \\{\\{x_t^v\\}_{t=1}^T, x^a\\}$ and $y = \\{y_t\\}_{t=1}^T$ , respectively. The inference process of CVAE aims to infer the informative values of the latent variable $z$ given the observed data $X$ and $y$ by computing the posterior $p_{\\theta}(z|X,y)$ , which is intractable and usually approximated with the variational posterior $q_{\\phi}(z|X,y)$ . $\\theta$ and $\\phi$ are the parameters of the true posterior and the approximated variational posterior, respectively. CVAE is trained to find the optimal generation parameters $\\theta^*$ and inference parameters $\\phi^*$ following the maximum log-likelihood learning pipeline:", + "bbox": [ + 75, + 453, + 468, + 710 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{\\theta^ {*}, \\phi^ {*} \\right\\} = \\underset {\\theta , \\phi} {\\arg \\max } \\log p _ {\\theta} (y | X), \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 723, + 468, + 746 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where the log-likelihood term is achieved as:", + "bbox": [ + 76, + 758, + 374, + 773 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\log p _ {\\theta} (y | X) \\\\ = \\underbrace {\\mathbb {E} _ {q _ {\\phi} (z | X , y)} \\log p _ {\\theta} (y | X , z) - D _ {K L} (q _ {\\phi} (z | X , y) \\| p _ {\\theta} (z | X))} _ {\\text {E L B O} (X, y, \\theta , \\phi)} \\\\ + D _ {\\mathrm {K L}} \\left(q _ {\\phi} (z | X, y) \\| p _ {\\theta} (z | X, y)\\right). \\tag {2} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 81, + 787, + 470, + 875 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "By Jensen's inequality, the Kullback-Leibler (KL) divergence term $(D_{KL})$ in Eq. (2) is always greater or equal to zero, thus maximizing $\\log p_{\\theta}(y|X)$ can be achieved by maximizing the evidence lower bound $\\operatorname{ELBO}(X,y,\\theta,\\phi)$ :", + "bbox": [ + 498, + 90, + 890, + 151 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\left\\{\\theta^ {*}, \\phi^ {*} \\right\\} = \\arg \\max _ {\\theta , \\phi} \\log p _ {\\theta} (y | X) \\\\ = \\arg \\max _ {\\theta , \\phi} \\operatorname {E L B O} (X, y, \\theta , \\phi). \\tag {3} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 566, + 169, + 890, + 219 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "With the reparameterization trick [2], the KL term in $\\mathrm{ELBO}(X,y,\\theta ,\\phi)$ can be solved in closed-form if both the prior $p_{\\theta}(z|X)$ and posterior $q_{\\phi}(z|X,y)$ are Gaussian.", + "bbox": [ + 496, + 238, + 890, + 284 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Multimodal Conditional Variational Auto-encoder. For the unimodal setting, both $p_{\\theta}(z|X)$ and $q_{\\phi}(z|X,y)$ can be obtained via the reparameterization trick [2], leading to closed-form solution of the KL divergence as both $p_{\\theta}(z|X)$ and $q_{\\phi}(z|X,y)$ are Gaussian. For the multimodal AVS data, the joint posterior and joint prior need to be estimated before we perform the joint generation process. The conventional solution to model the joint distribution is through the product of experts (PoE) [26, 27] or the mixture of experts (MoE) [28]. For the former, the joint distribution is defined as the product of each individual expert, which is Gaussian when each expert is Gaussian, leading to closed form KL computation. However, for PoE, less accurate modeling of one expert will completely destroy the joint distribution modeling. Further, PoE shows limitations in modeling the unimodal contribution due to its multiplicative nature. The additive nature of the MoE makes it effective for the optimization of each individual expert. However, as no closed form exists for the KL term, importance sampling (IS) is usually needed, which is computationally less efficient.", + "bbox": [ + 496, + 286, + 892, + 588 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "JS Divergence Instead of KL Divergence. Although MoE is computationally less efficient compared with PoE, its individual modal contribution modeling is attractive. Based on MoE, the $D_{KL}$ term within $\\mathrm{ELBO}(X,y,\\theta ,\\phi)$ of Eq. (2) is the lower bound of the weighted sum of individual KLs:", + "bbox": [ + 496, + 590, + 890, + 666 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} D _ {K L} \\left(q _ {\\phi} (z | X, y) \\| p _ {\\theta} (z | X)\\right) \\\\ \\leq \\sum_ {k = 1} ^ {K} \\phi_ {k} D _ {K L} \\left(q _ {\\phi_ {k}} \\left(z \\mid x ^ {k}, y\\right) \\| p _ {\\theta} \\left(z \\mid x ^ {k}\\right)\\right). \\tag {4} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 563, + 684, + 890, + 744 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $K$ is the number of modalities, and $\\sum_{k}\\phi_{k} = 1$ . Although Eq. (4) is effective in providing lower bound with individual modal's distribution for ELBO in Eq. (2), no joint distribution is involved. Following [4], a dynamic prior $f_{K}$ is introduced, which is the mixture of the involved arguments (individual priors and posteriors), i.e. $f_{K}$ can be defined as the arithmetic means as in MoE.", + "bbox": [ + 496, + 761, + 890, + 866 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "With the non-negative nature of KL divergence and the definition of JS divergence, we obtain a new lower bound of", + "bbox": [ + 500, + 869, + 890, + 898 + ], + "page_idx": 2 + }, + { + "type": "page_footnote", + "text": "Please see the supplementary material for the complete derivation.", + "bbox": [ + 99, + 887, + 450, + 898 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "956", + "bbox": [ + 485, + 945, + 511, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/b288800dad90817567d768a8e323205ea75651fc5df89c1f0825f78a07879f3f.jpg", + "image_caption": [ + "Figure 1. Overview of the proposed ECMVAE for audio-visual segmentation. The feature extractors are used to extract backbone features for the two modalities. We also design three latent encoders $\\phi_{s^v},\\phi_{s^a},\\phi_c$ to achieve latent space factorization and obtain both task-driven shared representation $(c)$ and modality-related specific representation $(s^a,s^v)$ , achieving explicit multimodal representation learning. The decoder is introduced to obtain the final segmentation maps, indicating the sound producers of the audio-visual data." + ], + "image_footnote": [], + "bbox": [ + 102, + 88, + 872, + 294 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "ELBO in Eq. (2) as:", + "bbox": [ + 76, + 383, + 212, + 398 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\widehat {\\operatorname {E L B O}} (X, y, \\theta , \\phi) \\geq \\mathbb {E} _ {q _ {\\phi} (z | X, y)} \\log p _ {\\theta} (y | X, z) \\\\ - \\sum_ {k _ {1} = 1} ^ {K} \\pi_ {k _ {1}} D _ {K L} \\left(q _ {\\phi} (z | X, y) \\| f _ {K}\\right) - \\sum_ {k _ {2} = 1} ^ {K} \\pi_ {k _ {2}} D _ {K L} \\left(p _ {\\theta} (z | X) \\| f _ {K}\\right) \\\\ = \\underbrace {\\mathbb {E} _ {q _ {\\phi} (z | X , y)} \\log p _ {\\theta} (y | X , z) - \\operatorname {J S D} \\left(q _ {\\phi} (z | X , y) , p _ {\\theta} (z | X)\\right)} _ {\\widehat {\\text {E L B O}} (X, y, \\theta , \\phi)}, \\tag {5} \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 411, + 480, + 522 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $\\sum_{k=1}^{2K}\\pi_k = 1$ , and JSD represents JS divergence. Eq. (5) provides lower bound of ELBO in Eq. (2), namely $\\widehat{\\mathrm{ELBO}}(X,y,\\theta,\\phi)$ , which is proven more stable for training [4], and robust to noise.", + "bbox": [ + 75, + 523, + 468, + 585 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.2. Latent Space Factorization", + "text_level": 1, + "bbox": [ + 76, + 598, + 320, + 614 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Besides stable training and noise robustness, we are also interested in modeling both shared and specific information of the audio-visual input (see Fig. 1) to fully explore their contribution. For each pair of example $(x^{k},y)$ , where $x^{k}\\in \\{\\{x_{t}^{v}\\}_{t = 1}^{T},x^{a}\\}$ indexes the modalities with $K = 2$ in this paper, we factorize the latent space $z$ into a modality-shared latent code $c$ and modality-specific latent codes $s^a,s^v$ . Then $\\widehat{\\mathrm{ELBO}} (X,y,\\theta ,\\phi)$ is re-defined as:", + "bbox": [ + 75, + 622, + 468, + 746 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\widehat {\\mathrm {E L B O}} (X, y, \\theta , \\phi) \\\\ = \\sum_ {k = 1} ^ {K} \\mathbb {E} _ {q _ {\\phi_ {c}} (c | X, y)} \\left[ \\mathbb {E} _ {q _ {\\phi_ {s} k} (s ^ {k} | x ^ {k}, y)} \\left[ \\log p _ {\\theta} \\left(y \\mid x ^ {k}, s ^ {k}, c\\right) \\right] \\right] \\tag {6} \\\\ - \\beta \\sum_ {k = 1} ^ {K} D _ {K L} \\left(q _ {\\phi_ {s k}} \\left(s ^ {k} \\mid x ^ {k}, y\\right) \\mid p _ {\\theta} \\left(s ^ {k} \\mid x ^ {k}\\right)\\right) \\\\ - \\beta \\mathrm {J S D} \\left(q _ {\\phi_ {c}} (c | X, y), p _ {\\theta} (c | X)\\right), \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 91, + 758, + 468, + 875 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $q_{\\phi_c}(c|X,y)$ and $p_{\\theta}(c|X)$ are the posterior and prior distributions of the shared representation. $q_{\\phi_{s^k}}(s^k |x^k,y)$ and $p_{\\theta_{s^k}}(s^k |x^k)$ are the posterior and prior distribution of the modality-specific latent codes. $p_{\\theta}(y|x^{k},s^{k},c)$ is the prediction generation model. All these models can be parameterized by deep neural networks and optimized via stochastic gradient descent. The hyper-parameter $\\beta = 0.1$ is introduced to achieve stable learning [60].", + "bbox": [ + 496, + 383, + 890, + 508 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Efficient Sampling. The Eq. (6) shows that the generation process involves sampling from the joint shared posterior $q_{\\phi_c}(c|X,y)$ and posterior of modality-specific latent code $q_{\\phi_{s^k}}(s^k|x^k,y)$ of each modality, which is time-consuming. In practice, we first perform shared-specific representation fusion, and then we sample latent code from each fused space, achieving efficient sampling. Specifically, given the posterior of the latent codes $c \\sim q_{\\phi_c}(c|X,y) \\in \\mathbb{R}^{T \\times L}$ , $s^a \\sim q_{\\phi_{s^a}}(s^a|x^a,y) \\in \\mathbb{R}^{T \\times L}$ , $s^v \\sim q_{\\phi_{s^v}}(s^v|x^v,y) \\in \\mathbb{R}^{T \\times L}$ ( $L$ is the dimension of the latent space), we concatenate the shared representation with each specific representation to get the fused representation of each modality. Then we obtain $sc^a, sc^v$ , representing the fused feature of audio and visual data, respectively. To achieve the reconstruction of $p_\\theta(y|x^k,s^k,c)$ in Eq. (6), instead of performing sampling from each specific latent code and shared latent code, we sample from $sc^a, sc^v$ , and rewrite the reconstruction term, i.e. the first term in Eq. (6), as:", + "bbox": [ + 496, + 508, + 892, + 781 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {r e c}} = \\sum_ {s c \\in \\{s c ^ {a}, s c ^ {v} \\}} \\left[ \\mathbb {E} \\left[ \\log p _ {\\theta} (y | x, s c) \\right] \\right], \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 560, + 792, + 890, + 827 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $x$ corresponds to the modality of data, i.e. audio or visual, of the current fused latent code $sc$ .", + "bbox": [ + 496, + 839, + 890, + 868 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Hybrid Loss. As the VAE samples from the posterior for training and prior to testing. To achieve consistent training", + "bbox": [ + 496, + 869, + 890, + 900 + ], + "page_idx": 3 + }, + { + "type": "page_footnote", + "text": "Please refer to the supplementary material for detailed derivation.", + "bbox": [ + 99, + 887, + 444, + 898 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "957", + "bbox": [ + 485, + 944, + 509, + 955 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "and testing, we define a Gaussian stochastic neural network (GSNN) [25] based objective by sampling from the prior distribution as well to avoid the posterior/prior distribution gap, leading to the hybrid objective as:", + "bbox": [ + 75, + 90, + 468, + 151 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\widehat {\\operatorname {H E L B O}} (X, y, \\theta , \\phi) = \\alpha_ {1} \\widehat {\\operatorname {E L B O}} (X, y, \\theta , \\phi) + (1 - \\alpha_ {1}) \\mathcal {L} _ {\\mathrm {G S N N}}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 164, + 478, + 196 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\alpha_{1} = 0.5$ is used to balance the two objectives, $\\mathcal{L}_{\\mathrm{GSNN}}$ represents the reconstruction term of Eq. (6), which is achieved by sampling from the prior distribution.", + "bbox": [ + 75, + 196, + 468, + 242 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The latent space factorization is effective in generating modality-shared and specific representations. However, no constraints are applied to the representations, making it hard to decide the reliability of the latent codes. We tackle this issue by proposing a representation orthogonality constraint in Sec. 3.3 and a shared information completeness regularization in Sec. 3.4.", + "bbox": [ + 75, + 242, + 468, + 347 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.3. Representation Orthogonality Constraint", + "text_level": 1, + "bbox": [ + 76, + 358, + 429, + 375 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We introduce a representation orthogonality constraint to ensure that the modality-shared and modality-specific representations capture different information within each unimodal data. Specifically, given the latent codes $c, s^a, s^v$ , we introduce the difference loss [61] as:", + "bbox": [ + 75, + 382, + 468, + 455 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {d i f f}} = \\left\\| c ^ {T} s ^ {a} \\right\\| _ {F} ^ {2} + \\left\\| c ^ {T} s ^ {v} \\right\\| _ {F} ^ {2} + \\left\\| \\left(s ^ {a}\\right) ^ {T} s ^ {v} \\right\\| _ {F} ^ {2}, \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 122, + 468, + 468, + 487 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\| \\cdot \\| _F^2$ is the squared Frobenius norm. With the difference loss, we aim to obtain the exclusive feature in each factorized feature representation.", + "bbox": [ + 75, + 498, + 468, + 544 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Shared-Information Completeness", + "text_level": 1, + "bbox": [ + 76, + 555, + 375, + 571 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As discussed in Sec. 3.2, we fuse the shared representation with each modality-specific representation and obtain $sc^a$ , $sc^v$ , representing the task-related information from audio and visual, respectively. To explicitly model the effectiveness of the fused latent space, we treat them $(sc^a, sc^v)$ as two different views of the same target following representation learning [56, 57, 62], and introduce mutual information maximization as a regularizer to measure the shared information between $sc^a$ and $sc^v$ . Given two random variables $SC^a$ , $SC^v$ , the mutual information is defined as:", + "bbox": [ + 75, + 579, + 468, + 729 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nI \\left(S C ^ {a}; S C ^ {v}\\right) = \\mathbb {E} _ {p \\left(s c ^ {a}, s c ^ {v}\\right)} \\left[ \\log \\frac {p \\left(s c ^ {a} , s c ^ {v}\\right)}{p \\left(s c ^ {a}\\right) \\cdot p \\left(s c ^ {v}\\right)} \\right]. \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 86, + 739, + 468, + 773 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "According to Bayesian's law, we obtain the mutual information variational lower bound [35], namely $I_{\\mathrm{ba}}$ via:", + "bbox": [ + 76, + 785, + 468, + 816 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nI \\left(S C ^ {a}; S C ^ {v}\\right) \\geq \\mathbb {E} _ {p \\left(s c ^ {a}, s c ^ {v}\\right)} \\left[ \\log q _ {\\kappa} \\left(s c ^ {a} \\mid s c ^ {v}\\right) \\right] + H \\left(S C ^ {a}\\right) \\triangleq I _ {\\mathrm {b a}}, \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 76, + 825, + 468, + 854 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $q_{\\kappa}(sc^{a}|sc^{v})$ is the variational approximation of $p(sc^{a}|sc^{v})$ . Following [36], $q_{\\kappa}(sc^{a}|sc^{v})$ is formulated as a multivariate Gaussian distribution $q_{\\kappa}(sc^{a}|sc^{v}) =$", + "bbox": [ + 75, + 854, + 468, + 900 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "$\\mathcal{N}(sc^a |\\mu (sc^v),\\sigma^2 (sc^v)\\mathbf{I})$ to predict mean $\\mu (sc^v)$ and variance $\\sigma^2 (sc^v)$ , respectively, where each statistic is modeled with two fully connected layers with Tanh activation function in the middle, and $\\kappa$ represent parameters of the four fully connected layers. $H(SC^{a})$ is the differential entropy of $SC^a$ . As the audio encoder is fixed in this paper, we choose to simplify the entropy computation and treat $H(SC^{a})$ as a constant [63].", + "bbox": [ + 496, + 90, + 890, + 210 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Based on the variational lower bound $I_{\\mathrm{ba}}$ , we then define the shared-information completeness loss function as: $\\mathcal{L}_{\\mathrm{sic}} = -I_{\\mathrm{ba}}$ . Further, we introduce the hybrid loss function for the posterior and the prior distribution, leading to:", + "bbox": [ + 498, + 212, + 890, + 272 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\mathrm {s i c}} = - \\alpha_ {2} I _ {\\mathrm {b a}} ^ {\\mathrm {p o}} - (1 - \\alpha_ {2}) I _ {\\mathrm {b a}} ^ {\\mathrm {p r}}, \\tag {12}\n$$\n", + "text_format": "latex", + "bbox": [ + 593, + 281, + 890, + 299 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $I_{\\mathrm{ba}}^{\\mathrm{po}}(I_{\\mathrm{ba}}^{\\mathrm{pr}})$ is the lower bound of the mutual information for the posterior (prior) distribution, and $\\alpha_{2} = 0.5$ is introduced to balance the two objectives.", + "bbox": [ + 496, + 308, + 890, + 354 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.5. The Model", + "text_level": 1, + "bbox": [ + 500, + 363, + 619, + 378 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Four central modules or constraints are included in our framework (see Fig. 1), namely: 1) \"modal encoding\" to extract the feature of each modality; 2) \"latent space encoding\" for multimodal latent feature representation learning; 3) \"decoder\" for the segmentation maps prediction; 4) \"objective function\" for supervised learning and explicit multimodal representation constraints.", + "bbox": [ + 496, + 387, + 890, + 491 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Modal Encoding. We perform two branches with two encoders to encode the visual and audio data. For the visual branch, we use the ImageNet pre-trained backbone followed by a one-layer convolution as neck to produce the multi-scale visual features $\\{V_m\\}_{m=1}^4 \\in \\mathbb{R}^{T \\times h_m \\times w_m \\times C_m}$ , where $(h_m, w_m) = (H, W) / 2^{m+1}, C_m = 128$ . $H, W$ is the spatial resolution of the input video. We use PVTv2 [64] or ResNet50 [65] as our visual backbone, which keeps the same as AVSBench [1]. For the audio branch, we follow [1], and use a frozen VGGish [66] model pre-trained on AudioSet [67] to process the spectrogram of input audio to extract audio features $A \\in \\mathbb{R}^{T \\times d}$ , where $d = 128$ . And $T = 5$ denotes the length of the video. We also keep the temporal pixel-wise audio-visual interaction (TPAVI) [1] module in our framework, which is a cross-modal attention based fusion module that takes visual features as query and value, audio features as key to achieve multi-scale feature fusion in the feature space and obtain $\\{\\bar{V}_m\\}_{m=1}^4$ .", + "bbox": [ + 496, + 492, + 890, + 763 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Latent Space Encoding. The main idea of our proposed method is achieving modality encoding on a reliable latent space (Sec. 3.2), as shown in Fig. 1. We use $\\phi_{s^v},\\phi_{s^a},\\phi_c$ parameterized by three simple neural networks to get latent feature embedding $s^v,s^a,c\\in \\mathbb{R}^{T\\times L}$ as prior distributions $(L = 16)$ . For $\\phi_{s^v}$ , we use five convolutional layers followed by leakyReLU [68] with two fully connected layers to encode the input video sequence. While for $\\phi_{s^a}$ , we employ two fully connected layers to map the VGGish encoded", + "bbox": [ + 496, + 765, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "958", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "audio features into the latent space. Further, video sequence and audio features are fed into $\\phi_c$ jointly, thus we perform late fusion on the audio features and five convolutional layers followed by leakyReLU encoded visual features to obtain the joint distribution from the fused features. For the posterior network, we design three networks with the same structure and take the segmentation maps $y$ as input by concatenating the video sequence and segmentation maps. We omit drawing the posterior space in Fig. 1 for easy viewing. Decoder. We adopt the decoder of Panoptic-FPN [69] to decode the final segmentation maps for its flexibility and effectiveness, which is the same as AVSBench [1]. We expand $sc^a$ , $sc^v$ to feature map of the same spatial size as $\\bar{V}_4$ by adding two-dimensional gaussian noise with the tile operation, \"sampling\" is used to indicate this process in Fig.1. The decoder takes both the deterministic features $\\{\\bar{V}_m\\}_{m=1}^4$ produced by the TPAVI [1] module and the expanded latent codes $sc^a$ , $sc^v$ from the fused latent space as input to produce the final segmentation maps.", + "bbox": [ + 75, + 90, + 472, + 378 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Objective Function. As discussed above, our final objective function contains the optimization of the evidence lower bound and the practical constraints for latent space representation, and it can be defined as,", + "bbox": [ + 75, + 378, + 470, + 439 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\begin{array}{l} \\mathcal {L} = - \\widehat {\\mathrm {H E L B O}} (X, y, \\theta , \\phi) + \\lambda_ {1} \\mathcal {L} _ {\\text {d i f f}} \\tag {13} \\\\ + \\lambda_ {2} \\mathcal {L} _ {\\text {s i c}} + \\lambda_ {3} \\mathcal {L} _ {\\text {A V M}}, \\\\ \\end{array}\n$$\n", + "text_format": "latex", + "bbox": [ + 148, + 449, + 467, + 487 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\widehat{\\mathrm{HELBO}}(X, y, \\theta, \\phi)$ indicates the lower bound for our proposed ECMVAE optimization, which is defined in detail in Eq. (8) and Eq. (6). We use a weighted structure-aware function [70] to compute the hybrid reconstruction part in $\\widehat{\\mathrm{HELBO}}(X, y, \\theta, \\phi)$ . $\\mathcal{L}_{\\mathrm{diff}}$ and $\\mathcal{L}_{\\mathrm{sic}}$ are the orthogonality constraint and the shared-information completeness loss defined in Eq. (9) and Eq. (12). $\\mathcal{L}_{\\mathrm{AVM}}$ indicates the audio-visual mapping loss proposed by [1] as a regularization term to promote the similarity between the audio-visual features. Empirically, we set the hyper-parameters $\\{\\lambda_1, \\lambda_2, \\lambda_3\\}$ as $\\{0.001, 0.01, 0.5\\}$ for balanced training.", + "bbox": [ + 75, + 502, + 472, + 674 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4. Experimental Results", + "text_level": 1, + "bbox": [ + 76, + 686, + 282, + 702 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.1. Implementation Details", + "text_level": 1, + "bbox": [ + 76, + 710, + 294, + 727 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Datasets. We conduct experiments on the AVSBench [1] dataset, which contains 5,356 video sequences with corresponding audio data and binary per-pixel annotations. Each video in the dataset contains five frames, extracted separately from a five-second video, where the audio length is also five seconds. This dataset contains two settings, named S4 and MS3, for semi-supervised Single Sound Source Segmentation with only the first frame labeled, and fully supervised Multiple Sound Source Segmentation with all frames labeled. The evaluation is done for the entire five frames of the video under both S4 and MS3 settings on the test set.", + "bbox": [ + 75, + 734, + 472, + 902 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/bce0ce3d263e6dcabd51522404583c5e91063693c186458d3160660cfa820e66.jpg", + "table_caption": [ + "Table 1. Quantitative results on the AVSBench dataset [1] in terms of mIOU and F-score under S4 and MS3 settings. We both report the performance with R50 and PVT as a backbone for the results of AVSBench [1] and Ours." + ], + "table_footnote": [], + "table_body": "
MethodsS4MS3
mIoUF-scoremIoUF-score
VOS3DC [71]57.100.75936.920.503
SST [72]66.290.80142.570.572
SODiGAN [73]61.590.77842.890.544
LGVT [74]74.940.87340.710.593
AVSAVSBench (R50) [1]72.790.84847.880.578
AVSBench (PVT) [1]78.740.87954.000.645
Ours (R50)76.330.86548.690.607
Ours (PVT)81.740.90157.840.708
", + "bbox": [ + 501, + 148, + 885, + 320 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Training Details. We conduct experiments on Pytorch [75] with a single NVIDIA A100 GPU. The Adam [76] solver is used to optimize our network with a learning rate of $1 \\times 10^{-4}$ . The training batch size is set to 4. We train the network on the S4 subset for 15 epochs, and on the MS3 subset for 30 epochs. For the MS3 setting, we use all ground-truth of the five frames to build the posterior latent space of our model. While for S4, we repeat the ground-truth of the first frame five times to build the posterior latent space.", + "bbox": [ + 496, + 339, + 893, + 476 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.2. Comparison with Baseline Methods", + "text_level": 1, + "bbox": [ + 498, + 484, + 808, + 500 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Quantitative Comparison. Follow the comparison settings with AVSBench [1], we compare the performance of our ECMVAE with baseline AVS models and other related tasks, including video object segmentation (VOS) and salient object detection (SOD). The performance on Mean Intersection over Union (mIoU) and F-score is reported in Table 1. It can be observed that our method consistently achieves significantly superior segmentation performance than the state-of-the-art methods, especially with 3.00 and 3.84 higher mIoU than the previous AVS method [1], at the S4 and MS3 settings with PVTv2 (\"PVT\") backbone. There is also a consistent performance improvement with ResNet (\"R50\") backbone. The performance gain comes from our designed multimodal VAE with explicit constraints for representation learning. Our method also significantly outperforms the VOS and SOD methods, demonstrating the addition of audio information to the segmentation performance. Qualitative Comparison. We provide a qualitative comparison between our proposed method and [1] in Fig. 2. Our proposed ECMVAE provides a better audio temporal and spatial localization quality, leading to better segmentation performance, especially for the left samples, in localization of the piano keys, which is not salient but producing a sound in this scene. Our method also achieves better segmentation performance for background noise handling and richer foreground details in the right samples in Fig. 2.", + "bbox": [ + 496, + 508, + 890, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "959", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 5 + }, + { + "type": "image", + "img_path": "images/49a967a2442e76bb33d505ac530cc407fd96dfce94ef8516ba234d92e7af9330.jpg", + "image_caption": [ + "Figure 2. Qualitative comparison between our proposed ECMVAE and AVSBench [1]. Our method competently achieves high segmentation performance with better audio temporal and spatial localization quality and detail handling." + ], + "image_footnote": [], + "bbox": [ + 89, + 88, + 880, + 327 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.3. Ablation Studies", + "text_level": 1, + "bbox": [ + 76, + 386, + 240, + 400 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We conduct ablation studies of our proposed method. All variations are trained with the PVT backbone.", + "bbox": [ + 76, + 409, + 468, + 438 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/4310379cc345910ae0f353c22ea6ccb3d8d585704f009630fdb1008eb9656ca1.jpg", + "table_caption": [ + "Table 2. Ablation of the VAE based multimodal learning. We implement a \"CVAE\" without audio and \"CMVAE\" with audio-visual joint distribution estimation." + ], + "table_footnote": [], + "table_body": "
MethodsS4MS3
mIoUF-scoremIoUF-score
[1] w/o audio77.80-48.20-
CVAE78.120.87849.260.643
CMVAE80.050.88954.990.653
", + "bbox": [ + 112, + 494, + 426, + 585 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Multimodal VAE. We explore the effectiveness of the Multimodal VAE in Table 2. Firstly, we remove the audio part of the model and disable the TPAVI module to explore the importance of the audio information, leading to a simple unimodal CVAE [29] framework with only video input, which is denoted as \"CVAE\". For comparison, we implement a \"CMVAE\" using the audio signal but without the latent space factorization and our proposed constraints. The better performance of \"CMVAE\" compared with \"CVAE\" indicates the importance of audio for AVS, especially when multiple sound sources exist. We also brought the ablation result of the model without the audio input from [1] and compare it with \"CVAE\". The results show that in the absence of audio signals, the VAE structure can still improve segmentation performance, due to the ability of VAE to model the latent space of visual features.", + "bbox": [ + 75, + 598, + 468, + 838 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Latent Space Factorization. As described in Sec. 3.2, we factorize the latent space of multimodal VAE into modality-shared $(c)$ and modality-specific $(s^v$ and $s^a)$ representations. As reported in Table 3, removing the latent space", + "bbox": [ + 75, + 839, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/d4ba7ea2a4aef527419e7af58fa0f01433f31f66276feee0a4f882ddba1e9202.jpg", + "table_caption": [ + "Table 3. Ablation of the latent space factorization. \"Model\" indicates using VAE for latent factorization or using AE for feature factorization. \"Factor.\" denotes whether using factorization. \"dim.\" represents the size of the latent dimensions." + ], + "table_footnote": [], + "table_body": "
ModelFactor.dim.S4MS3
mIoUF-scoremIoUF-score
VAE-1680.050.88954.990.653
-4880.130.89055.090.657
✓1680.780.89356.380.676
AE--78.740.87954.000.645
✓-78.920.88154.820.651
", + "bbox": [ + 511, + 444, + 874, + 568 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "factorization leads to obvious performance degradation. We also train a non-factorized model with $2 \\times$ larger latent dimensions, which holds comparable latent space capacities with the factorized model. It can be seen that the performance gain from the larger latent space dimensions is not as obvious as the factorization strategy. Further, we compare feature factorization (\"AE\") on the feature space of [1] with our proposed latent space factorization (\"VAE\"). Table 3 shows that only performing factorization on a semantic meaningful and continuous latent space, i.e. via using VAE [2], can achieve larger performance improvements.", + "bbox": [ + 496, + 594, + 890, + 760 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "JS Divergence. We conduct experiments of PoE and MoE with KL divergence to show the trade-off of JS divergence between the computational efficiency of the inference process and the predictive quality of the generation process. The performance in Table 4 shows the effectiveness of JS divergence on both S4 and MS3 settings. Note that, \"PoE\", \"MoE\" and \"JS\" are based on our formulation of the task, which has not been explored in the AVS area.", + "bbox": [ + 496, + 762, + 890, + 882 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Orthogonality Constraint. As reported in Table 5, the or", + "bbox": [ + 500, + 885, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "960", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/f5a2dc69582dcdc3f04f63a395ba96e9c239ef1a036267b65f6ffdc357bcc028.jpg", + "image_caption": [ + "(a) Base Factorization" + ], + "image_footnote": [], + "bbox": [ + 122, + 88, + 302, + 190 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/a89d1d8f8cf1e0077e0c2adf494c536f0735ca0cb0801c5c78a984945c364a89.jpg", + "image_caption": [ + "(b) With $\\mathcal{L}_{\\mathrm{diff}}$" + ], + "image_footnote": [], + "bbox": [ + 303, + 89, + 483, + 190 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/01880b0c2b409f6f8e87696cff7d6daa28730d224bfe9f6a4d540dc1c39bb6ae.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 483, + 90, + 666, + 190 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/5b5fd72b0100ccc1a09ac35373c0b9526bc43c31b79b6b0acd3738bf1e4ae45e.jpg", + "image_caption": [ + "(d) With $\\mathcal{L}_{\\mathrm{diff}},\\mathcal{L}_{\\mathrm{sic}}$" + ], + "image_footnote": [], + "bbox": [ + 669, + 90, + 848, + 190 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2c81e795892e7fcc07efcd6e6c19ee93929c21b57715a5f43a7e276630b0c15b.jpg", + "image_caption": [ + "(c) With $\\mathcal{L}_{\\mathrm{sic}}$", + "Figure 3. Visualization of the modality-shared and modality-specific latent codes $(s^v, s^a, c)$ in the MS3 testing set using t-SNE [77] projections. Best viewed on screen." + ], + "image_footnote": [], + "bbox": [ + 359, + 205, + 622, + 218 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/085e159f3ba9dbc291425afe657693a87945e1edefb76c36b353a39d3c41dd3e.jpg", + "table_caption": [ + "Table 4. Ablation of the JS Divergence. We implement \"PoE\" and \"MoE\" with KL divergence, and a simple \"KL\" model." + ], + "table_footnote": [], + "table_body": "
MethodsS4MS3
mIoUF-scoremIoUF-score
KL80.780.89356.380.676
PoE81.380.89457.350.688
MoE81.490.89757.530.694
JS81.740.90157.840.708
", + "bbox": [ + 129, + 301, + 411, + 406 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/2fb211bed50769f18dd70ff4b08a0560e3d30b4d630bf9b484f46bc2349b6690.jpg", + "table_caption": [ + "Table 5. Ablation of the latent space constraints. $\\mathcal{L}_{\\mathrm{diff}}$ , $\\mathcal{L}_{\\mathrm{sic}}$ indicate our proposed loss functions for multimodal learning." + ], + "table_footnote": [], + "table_body": "
\\(\\mathcal{L}_{diff}\\)\\(\\mathcal{L}_{sic}\\)S4MS3
mIoUF-scoremIoUF-score
--81.090.89557.010.684
✓-81.510.89957.650.692
-✓81.470.89857.510.694
✓✓81.740.90157.840.708
", + "bbox": [ + 116, + 448, + 423, + 551 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "thogonality constraint provides $0.64\\mathrm{mIOU}$ gain under the MS3 setting, which facilitates the latent space factorization. We also perform t-SNE [77] projection to visualize the factorized latent code with and without such constraint. As compared between Fig. 3 (a) and (b), the three latent codes in the latent space are divided into different subspaces to ensure that each latent code encodes different information.", + "bbox": [ + 75, + 563, + 467, + 667 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Mutual Information Maximization. As compared in Table 5, the mutual information maximization by $\\mathcal{L}_{\\mathrm{sic}}$ also serves a crucial impact for the explicit constraint of the shared latent space and improves the mIOU from 57.51 to 57.84. Since the $\\mathcal{L}_{\\mathrm{sic}}$ maximizes the mutual information between $sc^v$ and $sc^a$ , which are fused from the factorization latent codes $s^v, s^a, c$ . This increases the amount of information contained in latent space and makes it more effective for facilitating factorization. Fig. 3 also confirms this view and demonstrates the effectiveness of $\\mathcal{L}_{\\mathrm{sic}}$ in achieving effective \"multi-view\" representation learning [56, 57, 62].", + "bbox": [ + 75, + 669, + 467, + 835 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.4. Analysis", + "text_level": 1, + "bbox": [ + 76, + 845, + 179, + 862 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Pre-training on the Single-source Subset. In AVS-Bench [1], they conducted experiments by initializing", + "bbox": [ + 75, + 869, + 467, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "model parameters by pre-training on S4 dataset. We also perform experiments with such setting (see Table 6). We can observe that both our method and AVSBench [1] can benefit from the model pre-trained on S4. The PVT-based model can gain $2.97\\%$ mIOU performance by such a strategy and reach $60.81\\%$ mIOU. The pre-training strategy can bring more significant improvements ( $8.87\\%$ mIOU) to ResNet50-based models and reach $57.56\\%$ mIOU, which is even higher than PVT-based models ( $57.34\\%$ ).", + "bbox": [ + 496, + 272, + 890, + 407 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/b9c4e632b9c1be13d33f8a8610ace9bc3262b546291d5ccaa347f7dfb18c0085.jpg", + "table_caption": [ + "Table 6. Performance comparison with different initialization strategies for MS3 dataset. As AVSBench [1] does not report its F-score in the paper, we only report its mIOU. The values in parentheses indicate the performance improvement based on S4 pre-training compared with training from scratch." + ], + "table_footnote": [], + "table_body": "
MethodsFrom scratchPre-trained on S4
mIoUF-scoremIoUF-score
AVSbench (R50) [1]47.88-54.33 (↑ 6.45)-
AVSbench (PVT) [1]54.00-57.34 (↑ 3.34)-
Ours (R50)48.690.60757.56 (↑ 8.87)0.674
Ours (PVT)57.840.70860.81 (↑ 2.97)0.729
", + "bbox": [ + 501, + 493, + 890, + 595 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/ec4908e717100251614810da22b759f14767217847e4a2c790227acb344376b0.jpg", + "table_caption": [ + "Table 7. Parameters and inference time." + ], + "table_footnote": [], + "table_body": "
MethodsR50PVT
Param. (M)Time (ms)Param. (M)Time (ms)
AVSBench [1]70.5028101.3253
Ours33.972391.1846
", + "bbox": [ + 500, + 633, + 890, + 710 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Parameters and Efficiency. In Table 7, we compare the parameters and inference time between ours and AVSBench. Note that although posterior nets and prior nets are used in our framework, as all the latent space encoders are quite lightweight (1M), thus our model capacity will not change significantly. Moreover, we replace the neck from ASPP [78] to one-layer convolution and reduce the number of neck channels from 256 to 128, which leads to smaller parameter numbers and faster inference speed.", + "bbox": [ + 496, + 719, + 890, + 854 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Limitations. Similar to the other VAE [2] based solutions, our model also suffers from the risk of posterior collapse, where the posterior of the latent variable is equal to", + "bbox": [ + 496, + 854, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "961", + "bbox": [ + 485, + 945, + 509, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "prior [79,80], making $y$ in our case not encoded in the latent variables. To avoid such phenomenon, contrastive learning [81, 82] can be studied to learn more compact features of each modality or score based diffusion models [83-86] can be investigated for more informative latent space.", + "bbox": [ + 75, + 90, + 472, + 167 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 76, + 179, + 196, + 194 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "We have worked on audio-visual segmentation (AVS), aiming to segment the sound producers of the scene. As audio data can be treated as \"command\", we argue extensive exploration of audio is critical for effective AVS. Inspired by this observation, we have introduced an Explicit Conditional Multimodal Variational Auto-Encoder (ECMVAE) for an audio-visual segmentation model with latent space factorization with explicit constraints to extensively explore the shared and specific representations of audio and visual data. Extensive experimental results verify the effectiveness of our proposed framework. Although we focused on AVS with two modalities, the proposed framework can be extended to more modalities and other audio-visual collaboration tasks [6, 13, 14].", + "bbox": [ + 75, + 203, + 472, + 415 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Acknowledgments", + "text_level": 1, + "bbox": [ + 76, + 426, + 256, + 445 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "This research was supported in part by the National Natural Science Foundation of China (62271410), and the Fundamental Research Funds for the Central Universities.", + "bbox": [ + 76, + 452, + 468, + 498 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 508, + 174, + 525 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Jinxing Zhou, Jianyuan Wang, Jiayi Zhang, Weixuan Sun, Jing Zhang, Stan Birchfield, Dan Guo, Lingpeng Kong, Meng Wang, and Yiran Zhong. Audio-visual segmentation. In European Conference on Computer Vision (ECCV), 2022. 1, 2, 3, 5, 6, 7, 8", + "[2] Diederik Kingma and Max Welling. Auto-encoding variational bayes. In International Conference on Learning Representations (ICLR), 2014. 1, 2, 3, 7, 8", + "[3] Mike Wu and Noah Goodman. 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Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.123, + 0.131, + 0.849, + 0.154 + ], + "angle": 0, + "content": "Multimodal Variational Auto-encoder based Audio-Visual Segmentation" + }, + { + "type": "text", + "bbox": [ + 0.175, + 0.18, + 0.796, + 0.2 + ], + "angle": 0, + "content": "Yuxin Mao\\(^{1}\\) Jing Zhang\\(^{2}\\) Mochu Xiang\\(^{1}\\) Yiran Zhong\\(^{3}\\) Yuchao Dai\\(^{1\\dagger}\\)" + }, + { + "type": "text", + "bbox": [ + 0.122, + 0.2, + 0.848, + 0.217 + ], + "angle": 0, + "content": "1Northwestern Polytechnical University & Shaanxi Key Laboratory of Information Acquisition and Processing" + }, + { + "type": "text", + "bbox": [ + 0.286, + 0.217, + 0.684, + 0.235 + ], + "angle": 0, + "content": "\\(^{2}\\)Australian National University \\(^{3}\\)Shanghai AI Laboratory" + }, + { + "type": "text", + "bbox": [ + 0.163, + 0.235, + 0.808, + 0.253 + ], + "angle": 0, + "content": "https://github.com/OpenNLPLab/MMVAE-AVS https://hpucvr.github.io/MMVAE-AVS" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.301, + 0.313, + 0.318 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.334, + 0.473, + 0.742 + ], + "angle": 0, + "content": "We propose an Explicit Conditional Multimodal Variational Auto-Encoder (ECMVAE) for audio-visual segmentation (AVS), aiming to segment sound sources in the video sequence. Existing AVS methods focus on implicit feature fusion strategies, where models are trained to fit the discrete samples in the dataset. With a limited and less diverse dataset, the resulting performance is usually unsatisfactory. In contrast, we address this problem from an effective representation learning perspective, aiming to model the contribution of each modality explicitly. Specifically, we find that audio contains critical category information of the sound producers, and visual data provides candidate sound producer(s). Their shared information corresponds to the target sound producer(s) shown in the visual data. In this case, cross-modal shared representation learning is especially important for AVS. To achieve this, our ECMVAE factorizes the representations of each modality with a modality-shared representation and a modality-specific representation. An orthogonality constraint is applied between the shared and specific representations to maintain the exclusive attribute of the factorized latent code. Further, a mutual information maximization regularizer is introduced to achieve extensive exploration of each modality. Quantitative and qualitative evaluations on the AVSBench demonstrate the effectiveness of our approach, leading to a new state-of-the-art for AVS, with a 3.84 mIOU performance leap on the challenging MS3 subset for multiple sound source segmentation." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.769, + 0.21, + 0.785 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.795, + 0.47, + 0.856 + ], + "angle": 0, + "content": "Audio-visual data can work collaboratively towards a better perception of the scene. The audio-visual segmentation (AVS) [1] task aims to segment the objects from the video sequence that producing the sound in the audio. On" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.288, + 0.893, + 0.44 + ], + "angle": 0, + "content": "the one hand, the audio data provides category information for the localization of the object in the video. On the other hand, the visual data provides a sound producer pool with precise structure information of the foreground (sound producer(s)). Different from conventional multimodal settings, where each modality can be used individually for the target task, audio in AVS task serves as \"command\" to localize and segment the sound producer(s) from the visual data. In this case, the contribution of audio should be extensively explored for accurate foreground segmentation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.442, + 0.893, + 0.715 + ], + "angle": 0, + "content": "The baseline model [1] focuses on implicit feature fusion via audio-visual cross attention. It purely relies on fitting the discrete samples in the dataset. Although reasonable performance is obtained, there are no constraints to guarantee the contribution of each modality, making it hard to decide if the audio data is effectively used, as the model can directly regress the final segmentation maps by only taking the video as input. Fortunately, we discover that each modality for AVS contains both shared and specific information. For example, the audio data includes both the information from the sound producers and the background noise, while the visual data shows the appearance of the entire scene, where the sound producers only take a small portion of it. In our specific task setting, we find modality factorization is suitable to model both the modality-shared representation, i.e. information of the sound producers, and the modality-specific representation toward a better understanding of the contribution of each modality." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.717, + 0.895, + 0.868 + ], + "angle": 0, + "content": "The straightforward solution to learn the feature representation of the input data is through an auto-encoder (AE) framework. However, AE is mainly used for data compression, as the learned feature space is not continuous, which cannot provide a rich semantic correlation of the data. Differently, with latent space regularization, e.g. the latent space is assumed to be Gaussian in variational autoencoder (VAE) [2], VAE obtains semantic meaningful latent space, which is continuous, and it is also the basic requirement for reliable latent space factorization." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.895, + 0.902 + ], + "angle": 0, + "content": "To learn the semantic correlated feature representation of the AVS data, we propose an Explicit Conditional Mul" + }, + { + "type": "page_footnote", + "bbox": [ + 0.1, + 0.863, + 0.403, + 0.876 + ], + "angle": 0, + "content": "† Corresponding author (daiyuchao@gmail.com)." + }, + { + "type": "page_footnote", + "bbox": [ + 0.078, + 0.876, + 0.47, + 0.901 + ], + "angle": 0, + "content": "This work was done when Yuxin Mao was an intern at Shanghai AI Laboratory." + }, + { + "type": "list", + "bbox": [ + 0.078, + 0.863, + 0.47, + 0.901 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.945, + 0.512, + 0.957 + ], + "angle": 0, + "content": "954" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.468, + 0.227 + ], + "angle": 0, + "content": "timodal Variational Auto-Encoder (ECMVAE) for audiovisual segmentation to learn both the shared and the specific representation in the latent space of each modality. Our model is built upon a multimodal variational autoencoder [3, 4], with the Jensen-Shannon divergence to achieve a trade-off between sampling efficiency and sample quality. Based on the latent space factorization, we impose constraints for the shared and specific representations to explicitly maximize the contribution of each modality." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.228, + 0.468, + 0.499 + ], + "angle": 0, + "content": "Specifically, we first assume that one latent code of the factorized representation should contain independent information compared to others. Furthermore, for the fused representation, we further claim that it should be more informative for the target task compared with each modality. To achieve the former, we propose an information orthogonality constraint between the factorized representations of each modality to ensure that the modality-shared and modality-specific representations capture different aspects of the audio-visual input. For the latter, we fuse the factorized representations of each modality to construct a fused space. Then we introduce a mutual information maximization regularizer between the fused representations of each modality to extensively explore the contribution of each modality. Extensive experimental results demonstrate that our ECMVAE achieves state-of-the-art AVS performance. Our pipeline achieves a \\(3.84\\mathrm{mIOU}\\) improvement for the challenging multiple sound source segmentation." + }, + { + "type": "text", + "bbox": [ + 0.097, + 0.5, + 0.374, + 0.513 + ], + "angle": 0, + "content": "We summarize our main contributions as:" + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.515, + 0.468, + 0.575 + ], + "angle": 0, + "content": "- An explicit semantic correlated feature representation learning framework for audio-visual segmentation is proposed with latent space factorization to capture both the modality-shared and specific representations." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.577, + 0.468, + 0.65 + ], + "angle": 0, + "content": "- Based on the latent space factorization, we introduce a unimodal orthogonality constraint between the shared and specific representations and the cross-modal mutual-information maximization regularizer to extensively explore the contribution of each modality." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.651, + 0.468, + 0.695 + ], + "angle": 0, + "content": "- State-of-the-art segmentation performance is achieved, showing both the effectiveness of each module and the contribution of each modality." + }, + { + "type": "list", + "bbox": [ + 0.096, + 0.515, + 0.468, + 0.695 + ], + "angle": 0, + "content": null + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.71, + 0.219, + 0.725 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.468, + 0.901 + ], + "angle": 0, + "content": "Audio-Visual Segmentation. The Audio-Visual Segmentation (AVS) task is newly proposed, aiming to localize the sound producers with pixel-wise segmentation masks. Zhou et al. [1] propose an AVSBench dataset for audio-visual segmentation and provide a simple baseline based on temporal pixel-wise audio-visual interaction (TPAVI), which is a cross-modal attention [5] based fusion strategy. The other audio-visual collaboration tasks can be classified as audio-visual correspondence (AVC) [6, 7], event localization (AVEL) [8-13], event parsing (AVP) [14-16], etc. These methods require the fusion of audio and visual sig" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.243 + ], + "angle": 0, + "content": "nals. Such as audio-visual similarity modeling by computing the correlation matrix [6, 7], audio-visual cross attention [12, 13, 17], audio-guided Grad-CAM [18], or using a multimodal transformer for modeling the long-range dependencies between elements across modalities directly [19, 20]. However, the challenge and uniqueness of the AVS task are how to map the audio signals to fine-grained visual cues, i.e. per-pixel segmentation maps. This will rely on reliable modeling of visual and audio signals, as well as more effective fusion strategies." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.247, + 0.892, + 0.58 + ], + "angle": 0, + "content": "Multimodal Variational Auto-encoders. The Multimodal Variational Auto-encoders (MVAEs) [3, 21–24] are a type of latent variable generative model to learn more generalizable representations from diverse modalities. To achieve this, the core of MVAE is the joint distribution estimation. The conventional unimodal VAEs [2, 25] are optimized by maximizing the evidence lower bound (ELBO), which includes a reconstruction term and the Kullback-Leibler (KL) divergence term to measure the divergence from the variational posterior to the prior distribution of the latent variable. In a multimodal setting, the KL divergence is defined between the joint posterior and joint prior across the modalities, which is often estimated by the product of experts (PoE) [26, 27] or the mixture of experts (MoE) [28]. Based on such a prerequisite, many works extend the basic MVAE definition, such as missing modality handling [24], latent space modeling [23, 28], effective divergence modeling [4], etc. However, previous MVAE based frameworks essentially focus on the multimodal image generation task. In this work, we bring the MVAE to the AVS task and propose the conditional version [25, 29] of MVAE with practical multimodal information constraints for segmentation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.584, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Mutual Information Estimation. Mutual Information (MI) captures the nonlinear statistical dependencies between variables, acting as a measure of actual dependence [30]. Specifically, for a pair of random variables \\( X \\) and \\( Y \\), their MI \\( I(X;Y) \\) is defined as the KL divergence of the joint distribution \\( p_{(X,Y)} \\) from the product of the marginal distributions \\( p(X) \\) and \\( p(Y) \\), which measures the shared information between \\( X \\) and \\( Y \\). Although mutual information is simple in formation, as the log density ratio between the joint distribution \\( p_{(X,Y)} \\) and product of marginals \\( p(X)\\otimes p(Y) \\) is intractable, it is usually estimated [31-33] instead of computed directly, leading to both MI maximization with a lower bound [34, 35] and MI minimization with an upper bound [36]. The MI maximization is usually applied for effective self-supervised representation learning [37-41] for the unimodal data to guarantee reliable feature representation. For the multimodal tasks, when each modality of data contains partial information of the target, both MI maximization and minimization can be applied [42-50], where the former aims to explore the taskdriven feature across the modalities, and the latter is de" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.945, + 0.511, + 0.957 + ], + "angle": 0, + "content": "955" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.168 + ], + "angle": 0, + "content": "signed to explore the complementary information of different modalities. Extensive researches show that effective MI optimization can not only lead to informative representation learning [51-58] but also is beneficial for achieving adversarial robustness [59]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.182, + 0.458, + 0.201 + ], + "angle": 0, + "content": "3. Explicit Conditional Multimodal Learning" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.208, + 0.471, + 0.42 + ], + "angle": 0, + "content": "We denote the input data of our used AVSbench dataset [1] is \\( X = \\{\\{x_{t}^{v}\\}_{t=1}^{T}, x^{a}\\} \\), i.e. the visual \\( \\{x_{t}^{v}\\}_{t=1}^{T} \\) for \\( T \\) non-overlapping yet continuous frames, audio \\( x^{a} \\) of the current clip. \\( y = \\{y_{t}\\}_{t=1}^{T} \\) is the output, i.e. the segmentation maps (we omit \\( t \\) for clear presentation). The goal of audio-visual segmentation is to segment the objects from the video \\( \\{x_{t}^{v}\\}_{t=1}^{T} \\) that produce the sound shown in the audio \\( x^{a} \\). We introduce an Explicit Conditional Multi-modal Variational Auto-Encoder (ECMVAE) using Jensen-Shannon divergence (Sec. 3.1) via latent space factorization (Sec. 3.2) to effectively model the shared representation between the two modalities (Sec. 3.3 and Sec. 3.4) for audio-visual segmentation. The overview of the proposed ECMVAE is shown in Fig. 1." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.43, + 0.208, + 0.446 + ], + "angle": 0, + "content": "3.1. Prerequisite" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.454, + 0.47, + 0.711 + ], + "angle": 0, + "content": "Conditional Variational Auto-encoder. We begin our prerequisite with the definition of the conditional variational auto-encoder (CVAE) [2, 25], which contains a generative process and an inference process. The generative process is to draw the latent variable \\( z \\) from the prior distribution \\( p_{\\theta}(z|X) \\) with a given \\( X \\), and generate the output via \\( p_{\\theta}(y|X,z) \\), where in our case \\( X \\) and \\( y \\) in the following derivations are \\( X = \\{\\{x_t^v\\}_{t=1}^T, x^a\\} \\) and \\( y = \\{y_t\\}_{t=1}^T \\), respectively. The inference process of CVAE aims to infer the informative values of the latent variable \\( z \\) given the observed data \\( X \\) and \\( y \\) by computing the posterior \\( p_{\\theta}(z|X,y) \\), which is intractable and usually approximated with the variational posterior \\( q_{\\phi}(z|X,y) \\). \\( \\theta \\) and \\( \\phi \\) are the parameters of the true posterior and the approximated variational posterior, respectively. CVAE is trained to find the optimal generation parameters \\( \\theta^* \\) and inference parameters \\( \\phi^* \\) following the maximum log-likelihood learning pipeline:" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.724, + 0.469, + 0.747 + ], + "angle": 0, + "content": "\\[\n\\left\\{\\theta^ {*}, \\phi^ {*} \\right\\} = \\underset {\\theta , \\phi} {\\arg \\max } \\log p _ {\\theta} (y | X), \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.759, + 0.375, + 0.774 + ], + "angle": 0, + "content": "where the log-likelihood term is achieved as:" + }, + { + "type": "equation", + "bbox": [ + 0.083, + 0.788, + 0.472, + 0.876 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\log p _ {\\theta} (y | X) \\\\ = \\underbrace {\\mathbb {E} _ {q _ {\\phi} (z | X , y)} \\log p _ {\\theta} (y | X , z) - D _ {K L} (q _ {\\phi} (z | X , y) \\| p _ {\\theta} (z | X))} _ {\\text {E L B O} (X, y, \\theta , \\phi)} \\\\ + D _ {\\mathrm {K L}} \\left(q _ {\\phi} (z | X, y) \\| p _ {\\theta} (z | X, y)\\right). \\tag {2} \\\\ \\end{array}\n\\]" + }, + { + "type": "page_footnote", + "bbox": [ + 0.1, + 0.888, + 0.451, + 0.9 + ], + "angle": 0, + "content": "Please see the supplementary material for the complete derivation." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.152 + ], + "angle": 0, + "content": "By Jensen's inequality, the Kullback-Leibler (KL) divergence term \\((D_{KL})\\) in Eq. (2) is always greater or equal to zero, thus maximizing \\(\\log p_{\\theta}(y|X)\\) can be achieved by maximizing the evidence lower bound \\(\\operatorname{ELBO}(X,y,\\theta,\\phi)\\):" + }, + { + "type": "equation", + "bbox": [ + 0.568, + 0.17, + 0.891, + 0.22 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\left\\{\\theta^ {*}, \\phi^ {*} \\right\\} = \\arg \\max _ {\\theta , \\phi} \\log p _ {\\theta} (y | X) \\\\ = \\arg \\max _ {\\theta , \\phi} \\operatorname {E L B O} (X, y, \\theta , \\phi). \\tag {3} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.239, + 0.892, + 0.285 + ], + "angle": 0, + "content": "With the reparameterization trick [2], the KL term in \\( \\mathrm{ELBO}(X,y,\\theta ,\\phi) \\) can be solved in closed-form if both the prior \\( p_{\\theta}(z|X) \\) and posterior \\( q_{\\phi}(z|X,y) \\) are Gaussian." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.287, + 0.893, + 0.589 + ], + "angle": 0, + "content": "Multimodal Conditional Variational Auto-encoder. For the unimodal setting, both \\( p_{\\theta}(z|X) \\) and \\( q_{\\phi}(z|X,y) \\) can be obtained via the reparameterization trick [2], leading to closed-form solution of the KL divergence as both \\( p_{\\theta}(z|X) \\) and \\( q_{\\phi}(z|X,y) \\) are Gaussian. For the multimodal AVS data, the joint posterior and joint prior need to be estimated before we perform the joint generation process. The conventional solution to model the joint distribution is through the product of experts (PoE) [26, 27] or the mixture of experts (MoE) [28]. For the former, the joint distribution is defined as the product of each individual expert, which is Gaussian when each expert is Gaussian, leading to closed form KL computation. However, for PoE, less accurate modeling of one expert will completely destroy the joint distribution modeling. Further, PoE shows limitations in modeling the unimodal contribution due to its multiplicative nature. The additive nature of the MoE makes it effective for the optimization of each individual expert. However, as no closed form exists for the KL term, importance sampling (IS) is usually needed, which is computationally less efficient." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.591, + 0.892, + 0.667 + ], + "angle": 0, + "content": "JS Divergence Instead of KL Divergence. Although MoE is computationally less efficient compared with PoE, its individual modal contribution modeling is attractive. Based on MoE, the \\(D_{KL}\\) term within \\(\\mathrm{ELBO}(X,y,\\theta ,\\phi)\\) of Eq. (2) is the lower bound of the weighted sum of individual KLs:" + }, + { + "type": "equation", + "bbox": [ + 0.564, + 0.685, + 0.891, + 0.745 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} D _ {K L} \\left(q _ {\\phi} (z | X, y) \\| p _ {\\theta} (z | X)\\right) \\\\ \\leq \\sum_ {k = 1} ^ {K} \\phi_ {k} D _ {K L} \\left(q _ {\\phi_ {k}} \\left(z \\mid x ^ {k}, y\\right) \\| p _ {\\theta} \\left(z \\mid x ^ {k}\\right)\\right). \\tag {4} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.762, + 0.892, + 0.867 + ], + "angle": 0, + "content": "where \\(K\\) is the number of modalities, and \\(\\sum_{k}\\phi_{k} = 1\\). Although Eq. (4) is effective in providing lower bound with individual modal's distribution for ELBO in Eq. (2), no joint distribution is involved. Following [4], a dynamic prior \\(f_{K}\\) is introduced, which is the mixture of the involved arguments (individual priors and posteriors), i.e. \\(f_{K}\\) can be defined as the arithmetic means as in MoE." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.871, + 0.892, + 0.9 + ], + "angle": 0, + "content": "With the non-negative nature of KL divergence and the definition of JS divergence, we obtain a new lower bound of" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.512, + 0.957 + ], + "angle": 0, + "content": "956" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.104, + 0.089, + 0.873, + 0.295 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.311, + 0.895, + 0.368 + ], + "angle": 0, + "content": "Figure 1. Overview of the proposed ECMVAE for audio-visual segmentation. The feature extractors are used to extract backbone features for the two modalities. We also design three latent encoders \\(\\phi_{s^v},\\phi_{s^a},\\phi_c\\) to achieve latent space factorization and obtain both task-driven shared representation \\((c)\\) and modality-related specific representation \\((s^a,s^v)\\), achieving explicit multimodal representation learning. The decoder is introduced to obtain the final segmentation maps, indicating the sound producers of the audio-visual data." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.384, + 0.214, + 0.4 + ], + "angle": 0, + "content": "ELBO in Eq. (2) as:" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.412, + 0.482, + 0.523 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\widehat {\\operatorname {E L B O}} (X, y, \\theta , \\phi) \\geq \\mathbb {E} _ {q _ {\\phi} (z | X, y)} \\log p _ {\\theta} (y | X, z) \\\\ - \\sum_ {k _ {1} = 1} ^ {K} \\pi_ {k _ {1}} D _ {K L} \\left(q _ {\\phi} (z | X, y) \\| f _ {K}\\right) - \\sum_ {k _ {2} = 1} ^ {K} \\pi_ {k _ {2}} D _ {K L} \\left(p _ {\\theta} (z | X) \\| f _ {K}\\right) \\\\ = \\underbrace {\\mathbb {E} _ {q _ {\\phi} (z | X , y)} \\log p _ {\\theta} (y | X , z) - \\operatorname {J S D} \\left(q _ {\\phi} (z | X , y) , p _ {\\theta} (z | X)\\right)} _ {\\widehat {\\text {E L B O}} (X, y, \\theta , \\phi)}, \\tag {5} \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.524, + 0.47, + 0.587 + ], + "angle": 0, + "content": "where \\(\\sum_{k=1}^{2K}\\pi_k = 1\\), and JSD represents JS divergence. Eq. (5) provides lower bound of ELBO in Eq. (2), namely \\(\\widehat{\\mathrm{ELBO}}(X,y,\\theta,\\phi)\\), which is proven more stable for training [4], and robust to noise." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.599, + 0.321, + 0.615 + ], + "angle": 0, + "content": "3.2. Latent Space Factorization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.623, + 0.47, + 0.747 + ], + "angle": 0, + "content": "Besides stable training and noise robustness, we are also interested in modeling both shared and specific information of the audio-visual input (see Fig. 1) to fully explore their contribution. For each pair of example \\((x^{k},y)\\), where \\(x^{k}\\in \\{\\{x_{t}^{v}\\}_{t = 1}^{T},x^{a}\\}\\) indexes the modalities with \\(K = 2\\) in this paper, we factorize the latent space \\(z\\) into a modality-shared latent code \\(c\\) and modality-specific latent codes \\(s^a,s^v\\). Then \\(\\widehat{\\mathrm{ELBO}} (X,y,\\theta ,\\phi)\\) is re-defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.093, + 0.759, + 0.469, + 0.875 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\widehat {\\mathrm {E L B O}} (X, y, \\theta , \\phi) \\\\ = \\sum_ {k = 1} ^ {K} \\mathbb {E} _ {q _ {\\phi_ {c}} (c | X, y)} \\left[ \\mathbb {E} _ {q _ {\\phi_ {s} k} (s ^ {k} | x ^ {k}, y)} \\left[ \\log p _ {\\theta} \\left(y \\mid x ^ {k}, s ^ {k}, c\\right) \\right] \\right] \\tag {6} \\\\ - \\beta \\sum_ {k = 1} ^ {K} D _ {K L} \\left(q _ {\\phi_ {s k}} \\left(s ^ {k} \\mid x ^ {k}, y\\right) \\mid p _ {\\theta} \\left(s ^ {k} \\mid x ^ {k}\\right)\\right) \\\\ - \\beta \\mathrm {J S D} \\left(q _ {\\phi_ {c}} (c | X, y), p _ {\\theta} (c | X)\\right), \\\\ \\end{array}\n\\]" + }, + { + "type": "page_footnote", + "bbox": [ + 0.1, + 0.888, + 0.446, + 0.9 + ], + "angle": 0, + "content": "Please refer to the supplementary material for detailed derivation." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.384, + 0.892, + 0.509 + ], + "angle": 0, + "content": "where \\( q_{\\phi_c}(c|X,y) \\) and \\( p_{\\theta}(c|X) \\) are the posterior and prior distributions of the shared representation. \\( q_{\\phi_{s^k}}(s^k |x^k,y) \\) and \\( p_{\\theta_{s^k}}(s^k |x^k) \\) are the posterior and prior distribution of the modality-specific latent codes. \\( p_{\\theta}(y|x^{k},s^{k},c) \\) is the prediction generation model. All these models can be parameterized by deep neural networks and optimized via stochastic gradient descent. The hyper-parameter \\( \\beta = 0.1 \\) is introduced to achieve stable learning [60]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.51, + 0.893, + 0.782 + ], + "angle": 0, + "content": "Efficient Sampling. The Eq. (6) shows that the generation process involves sampling from the joint shared posterior \\( q_{\\phi_c}(c|X,y) \\) and posterior of modality-specific latent code \\( q_{\\phi_{s^k}}(s^k|x^k,y) \\) of each modality, which is time-consuming. In practice, we first perform shared-specific representation fusion, and then we sample latent code from each fused space, achieving efficient sampling. Specifically, given the posterior of the latent codes \\( c \\sim q_{\\phi_c}(c|X,y) \\in \\mathbb{R}^{T \\times L} \\), \\( s^a \\sim q_{\\phi_{s^a}}(s^a|x^a,y) \\in \\mathbb{R}^{T \\times L} \\), \\( s^v \\sim q_{\\phi_{s^v}}(s^v|x^v,y) \\in \\mathbb{R}^{T \\times L} \\) (\\( L \\) is the dimension of the latent space), we concatenate the shared representation with each specific representation to get the fused representation of each modality. Then we obtain \\( sc^a, sc^v \\), representing the fused feature of audio and visual data, respectively. To achieve the reconstruction of \\( p_\\theta(y|x^k,s^k,c) \\) in Eq. (6), instead of performing sampling from each specific latent code and shared latent code, we sample from \\( sc^a, sc^v \\), and rewrite the reconstruction term, i.e. the first term in Eq. (6), as:" + }, + { + "type": "equation", + "bbox": [ + 0.562, + 0.794, + 0.892, + 0.828 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {r e c}} = \\sum_ {s c \\in \\{s c ^ {a}, s c ^ {v} \\}} \\left[ \\mathbb {E} \\left[ \\log p _ {\\theta} (y | x, s c) \\right] \\right], \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.84, + 0.892, + 0.869 + ], + "angle": 0, + "content": "where \\( x \\) corresponds to the modality of data, i.e. audio or visual, of the current fused latent code \\( sc \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.871, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Hybrid Loss. As the VAE samples from the posterior for training and prior to testing. To achieve consistent training" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.945, + 0.511, + 0.957 + ], + "angle": 0, + "content": "957" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.152 + ], + "angle": 0, + "content": "and testing, we define a Gaussian stochastic neural network (GSNN) [25] based objective by sampling from the prior distribution as well to avoid the posterior/prior distribution gap, leading to the hybrid objective as:" + }, + { + "type": "equation", + "bbox": [ + 0.077, + 0.165, + 0.479, + 0.197 + ], + "angle": 0, + "content": "\\[\n\\widehat {\\operatorname {H E L B O}} (X, y, \\theta , \\phi) = \\alpha_ {1} \\widehat {\\operatorname {E L B O}} (X, y, \\theta , \\phi) + (1 - \\alpha_ {1}) \\mathcal {L} _ {\\mathrm {G S N N}}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.198, + 0.469, + 0.243 + ], + "angle": 0, + "content": "where \\(\\alpha_{1} = 0.5\\) is used to balance the two objectives, \\(\\mathcal{L}_{\\mathrm{GSNN}}\\) represents the reconstruction term of Eq. (6), which is achieved by sampling from the prior distribution." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.243, + 0.469, + 0.348 + ], + "angle": 0, + "content": "The latent space factorization is effective in generating modality-shared and specific representations. However, no constraints are applied to the representations, making it hard to decide the reliability of the latent codes. We tackle this issue by proposing a representation orthogonality constraint in Sec. 3.3 and a shared information completeness regularization in Sec. 3.4." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.359, + 0.431, + 0.376 + ], + "angle": 0, + "content": "3.3. Representation Orthogonality Constraint" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.383, + 0.469, + 0.457 + ], + "angle": 0, + "content": "We introduce a representation orthogonality constraint to ensure that the modality-shared and modality-specific representations capture different information within each unimodal data. Specifically, given the latent codes \\( c, s^a, s^v \\), we introduce the difference loss [61] as:" + }, + { + "type": "equation", + "bbox": [ + 0.123, + 0.469, + 0.469, + 0.488 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {d i f f}} = \\left\\| c ^ {T} s ^ {a} \\right\\| _ {F} ^ {2} + \\left\\| c ^ {T} s ^ {v} \\right\\| _ {F} ^ {2} + \\left\\| \\left(s ^ {a}\\right) ^ {T} s ^ {v} \\right\\| _ {F} ^ {2}, \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.499, + 0.469, + 0.545 + ], + "angle": 0, + "content": "where \\(\\| \\cdot \\| _F^2\\) is the squared Frobenius norm. With the difference loss, we aim to obtain the exclusive feature in each factorized feature representation." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.556, + 0.377, + 0.572 + ], + "angle": 0, + "content": "3.4. Shared-Information Completeness" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.58, + 0.469, + 0.73 + ], + "angle": 0, + "content": "As discussed in Sec. 3.2, we fuse the shared representation with each modality-specific representation and obtain \\(sc^a\\), \\(sc^v\\), representing the task-related information from audio and visual, respectively. To explicitly model the effectiveness of the fused latent space, we treat them \\((sc^a, sc^v)\\) as two different views of the same target following representation learning [56, 57, 62], and introduce mutual information maximization as a regularizer to measure the shared information between \\(sc^a\\) and \\(sc^v\\). Given two random variables \\(SC^a\\), \\(SC^v\\), the mutual information is defined as:" + }, + { + "type": "equation", + "bbox": [ + 0.088, + 0.741, + 0.469, + 0.775 + ], + "angle": 0, + "content": "\\[\nI \\left(S C ^ {a}; S C ^ {v}\\right) = \\mathbb {E} _ {p \\left(s c ^ {a}, s c ^ {v}\\right)} \\left[ \\log \\frac {p \\left(s c ^ {a} , s c ^ {v}\\right)}{p \\left(s c ^ {a}\\right) \\cdot p \\left(s c ^ {v}\\right)} \\right]. \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.786, + 0.469, + 0.817 + ], + "angle": 0, + "content": "According to Bayesian's law, we obtain the mutual information variational lower bound [35], namely \\( I_{\\mathrm{ba}} \\) via:" + }, + { + "type": "equation", + "bbox": [ + 0.078, + 0.827, + 0.469, + 0.855 + ], + "angle": 0, + "content": "\\[\nI \\left(S C ^ {a}; S C ^ {v}\\right) \\geq \\mathbb {E} _ {p \\left(s c ^ {a}, s c ^ {v}\\right)} \\left[ \\log q _ {\\kappa} \\left(s c ^ {a} \\mid s c ^ {v}\\right) \\right] + H \\left(S C ^ {a}\\right) \\triangleq I _ {\\mathrm {b a}}, \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.469, + 0.901 + ], + "angle": 0, + "content": "where \\( q_{\\kappa}(sc^{a}|sc^{v}) \\) is the variational approximation of \\( p(sc^{a}|sc^{v}) \\). Following [36], \\( q_{\\kappa}(sc^{a}|sc^{v}) \\) is formulated as a multivariate Gaussian distribution \\( q_{\\kappa}(sc^{a}|sc^{v}) = \\)" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.091, + 0.892, + 0.212 + ], + "angle": 0, + "content": "\\(\\mathcal{N}(sc^a |\\mu (sc^v),\\sigma^2 (sc^v)\\mathbf{I})\\) to predict mean \\(\\mu (sc^v)\\) and variance \\(\\sigma^2 (sc^v)\\), respectively, where each statistic is modeled with two fully connected layers with Tanh activation function in the middle, and \\(\\kappa\\) represent parameters of the four fully connected layers. \\(H(SC^{a})\\) is the differential entropy of \\(SC^a\\). As the audio encoder is fixed in this paper, we choose to simplify the entropy computation and treat \\(H(SC^{a})\\) as a constant [63]." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.213, + 0.892, + 0.273 + ], + "angle": 0, + "content": "Based on the variational lower bound \\( I_{\\mathrm{ba}} \\), we then define the shared-information completeness loss function as: \\( \\mathcal{L}_{\\mathrm{sic}} = -I_{\\mathrm{ba}} \\). Further, we introduce the hybrid loss function for the posterior and the prior distribution, leading to:" + }, + { + "type": "equation", + "bbox": [ + 0.594, + 0.282, + 0.891, + 0.3 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\mathrm {s i c}} = - \\alpha_ {2} I _ {\\mathrm {b a}} ^ {\\mathrm {p o}} - (1 - \\alpha_ {2}) I _ {\\mathrm {b a}} ^ {\\mathrm {p r}}, \\tag {12}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.309, + 0.892, + 0.356 + ], + "angle": 0, + "content": "where \\( I_{\\mathrm{ba}}^{\\mathrm{po}}(I_{\\mathrm{ba}}^{\\mathrm{pr}}) \\) is the lower bound of the mutual information for the posterior (prior) distribution, and \\( \\alpha_{2} = 0.5 \\) is introduced to balance the two objectives." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.364, + 0.62, + 0.379 + ], + "angle": 0, + "content": "3.5. The Model" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.388, + 0.892, + 0.492 + ], + "angle": 0, + "content": "Four central modules or constraints are included in our framework (see Fig. 1), namely: 1) \"modal encoding\" to extract the feature of each modality; 2) \"latent space encoding\" for multimodal latent feature representation learning; 3) \"decoder\" for the segmentation maps prediction; 4) \"objective function\" for supervised learning and explicit multimodal representation constraints." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.493, + 0.892, + 0.765 + ], + "angle": 0, + "content": "Modal Encoding. We perform two branches with two encoders to encode the visual and audio data. For the visual branch, we use the ImageNet pre-trained backbone followed by a one-layer convolution as neck to produce the multi-scale visual features \\(\\{V_m\\}_{m=1}^4 \\in \\mathbb{R}^{T \\times h_m \\times w_m \\times C_m}\\), where \\((h_m, w_m) = (H, W) / 2^{m+1}, C_m = 128\\). \\(H, W\\) is the spatial resolution of the input video. We use PVTv2 [64] or ResNet50 [65] as our visual backbone, which keeps the same as AVSBench [1]. For the audio branch, we follow [1], and use a frozen VGGish [66] model pre-trained on AudioSet [67] to process the spectrogram of input audio to extract audio features \\(A \\in \\mathbb{R}^{T \\times d}\\), where \\(d = 128\\). And \\(T = 5\\) denotes the length of the video. We also keep the temporal pixel-wise audio-visual interaction (TPAVI) [1] module in our framework, which is a cross-modal attention based fusion module that takes visual features as query and value, audio features as key to achieve multi-scale feature fusion in the feature space and obtain \\(\\{\\bar{V}_m\\}_{m=1}^4\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.766, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Latent Space Encoding. The main idea of our proposed method is achieving modality encoding on a reliable latent space (Sec. 3.2), as shown in Fig. 1. We use \\(\\phi_{s^v},\\phi_{s^a},\\phi_c\\) parameterized by three simple neural networks to get latent feature embedding \\(s^v,s^a,c\\in \\mathbb{R}^{T\\times L}\\) as prior distributions \\((L = 16)\\). For \\(\\phi_{s^v}\\), we use five convolutional layers followed by leakyReLU [68] with two fully connected layers to encode the input video sequence. While for \\(\\phi_{s^a}\\), we employ two fully connected layers to map the VGGish encoded" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "958" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.091, + 0.473, + 0.379 + ], + "angle": 0, + "content": "audio features into the latent space. Further, video sequence and audio features are fed into \\(\\phi_c\\) jointly, thus we perform late fusion on the audio features and five convolutional layers followed by leakyReLU encoded visual features to obtain the joint distribution from the fused features. For the posterior network, we design three networks with the same structure and take the segmentation maps \\(y\\) as input by concatenating the video sequence and segmentation maps. We omit drawing the posterior space in Fig. 1 for easy viewing. Decoder. We adopt the decoder of Panoptic-FPN [69] to decode the final segmentation maps for its flexibility and effectiveness, which is the same as AVSBench [1]. We expand \\(sc^a\\), \\(sc^v\\) to feature map of the same spatial size as \\(\\bar{V}_4\\) by adding two-dimensional gaussian noise with the tile operation, \"sampling\" is used to indicate this process in Fig.1. The decoder takes both the deterministic features \\(\\{\\bar{V}_m\\}_{m=1}^4\\) produced by the TPAVI [1] module and the expanded latent codes \\(sc^a\\), \\(sc^v\\) from the fused latent space as input to produce the final segmentation maps." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.379, + 0.472, + 0.44 + ], + "angle": 0, + "content": "Objective Function. As discussed above, our final objective function contains the optimization of the evidence lower bound and the practical constraints for latent space representation, and it can be defined as," + }, + { + "type": "equation", + "bbox": [ + 0.15, + 0.45, + 0.468, + 0.488 + ], + "angle": 0, + "content": "\\[\n\\begin{array}{l} \\mathcal {L} = - \\widehat {\\mathrm {H E L B O}} (X, y, \\theta , \\phi) + \\lambda_ {1} \\mathcal {L} _ {\\text {d i f f}} \\tag {13} \\\\ + \\lambda_ {2} \\mathcal {L} _ {\\text {s i c}} + \\lambda_ {3} \\mathcal {L} _ {\\text {A V M}}, \\\\ \\end{array}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.503, + 0.473, + 0.675 + ], + "angle": 0, + "content": "where \\(\\widehat{\\mathrm{HELBO}}(X, y, \\theta, \\phi)\\) indicates the lower bound for our proposed ECMVAE optimization, which is defined in detail in Eq. (8) and Eq. (6). We use a weighted structure-aware function [70] to compute the hybrid reconstruction part in \\(\\widehat{\\mathrm{HELBO}}(X, y, \\theta, \\phi)\\). \\(\\mathcal{L}_{\\mathrm{diff}}\\) and \\(\\mathcal{L}_{\\mathrm{sic}}\\) are the orthogonality constraint and the shared-information completeness loss defined in Eq. (9) and Eq. (12). \\(\\mathcal{L}_{\\mathrm{AVM}}\\) indicates the audio-visual mapping loss proposed by [1] as a regularization term to promote the similarity between the audio-visual features. Empirically, we set the hyper-parameters \\(\\{\\lambda_1, \\lambda_2, \\lambda_3\\}\\) as \\(\\{0.001, 0.01, 0.5\\}\\) for balanced training." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.687, + 0.283, + 0.703 + ], + "angle": 0, + "content": "4. Experimental Results" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.712, + 0.295, + 0.728 + ], + "angle": 0, + "content": "4.1. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.473, + 0.903 + ], + "angle": 0, + "content": "Datasets. We conduct experiments on the AVSBench [1] dataset, which contains 5,356 video sequences with corresponding audio data and binary per-pixel annotations. Each video in the dataset contains five frames, extracted separately from a five-second video, where the audio length is also five seconds. This dataset contains two settings, named S4 and MS3, for semi-supervised Single Sound Source Segmentation with only the first frame labeled, and fully supervised Multiple Sound Source Segmentation with all frames labeled. The evaluation is done for the entire five frames of the video under both S4 and MS3 settings on the test set." + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.087, + 0.895, + 0.144 + ], + "angle": 0, + "content": "Table 1. Quantitative results on the AVSBench dataset [1] in terms of mIOU and F-score under S4 and MS3 settings. We both report the performance with R50 and PVT as a backbone for the results of AVSBench [1] and Ours." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.149, + 0.887, + 0.321 + ], + "angle": 0, + "content": "
MethodsS4MS3
mIoUF-scoremIoUF-score
VOS3DC [71]57.100.75936.920.503
SST [72]66.290.80142.570.572
SODiGAN [73]61.590.77842.890.544
LGVT [74]74.940.87340.710.593
AVSAVSBench (R50) [1]72.790.84847.880.578
AVSBench (PVT) [1]78.740.87954.000.645
Ours (R50)76.330.86548.690.607
Ours (PVT)81.740.90157.840.708
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.34, + 0.895, + 0.477 + ], + "angle": 0, + "content": "Training Details. We conduct experiments on Pytorch [75] with a single NVIDIA A100 GPU. The Adam [76] solver is used to optimize our network with a learning rate of \\( 1 \\times 10^{-4} \\). The training batch size is set to 4. We train the network on the S4 subset for 15 epochs, and on the MS3 subset for 30 epochs. For the MS3 setting, we use all ground-truth of the five frames to build the posterior latent space of our model. While for S4, we repeat the ground-truth of the first frame five times to build the posterior latent space." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.485, + 0.81, + 0.501 + ], + "angle": 0, + "content": "4.2. Comparison with Baseline Methods" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.509, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Quantitative Comparison. Follow the comparison settings with AVSBench [1], we compare the performance of our ECMVAE with baseline AVS models and other related tasks, including video object segmentation (VOS) and salient object detection (SOD). The performance on Mean Intersection over Union (mIoU) and F-score is reported in Table 1. It can be observed that our method consistently achieves significantly superior segmentation performance than the state-of-the-art methods, especially with 3.00 and 3.84 higher mIoU than the previous AVS method [1], at the S4 and MS3 settings with PVTv2 (\"PVT\") backbone. There is also a consistent performance improvement with ResNet (\"R50\") backbone. The performance gain comes from our designed multimodal VAE with explicit constraints for representation learning. Our method also significantly outperforms the VOS and SOD methods, demonstrating the addition of audio information to the segmentation performance. Qualitative Comparison. We provide a qualitative comparison between our proposed method and [1] in Fig. 2. Our proposed ECMVAE provides a better audio temporal and spatial localization quality, leading to better segmentation performance, especially for the left samples, in localization of the piano keys, which is not salient but producing a sound in this scene. Our method also achieves better segmentation performance for background noise handling and richer foreground details in the right samples in Fig. 2." + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "959" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.09, + 0.089, + 0.882, + 0.328 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.341, + 0.893, + 0.371 + ], + "angle": 0, + "content": "Figure 2. Qualitative comparison between our proposed ECMVAE and AVSBench [1]. Our method competently achieves high segmentation performance with better audio temporal and spatial localization quality and detail handling." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.387, + 0.241, + 0.401 + ], + "angle": 0, + "content": "4.3. Ablation Studies" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.41, + 0.469, + 0.439 + ], + "angle": 0, + "content": "We conduct ablation studies of our proposed method. All variations are trained with the PVT backbone." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.448, + 0.47, + 0.49 + ], + "angle": 0, + "content": "Table 2. Ablation of the VAE based multimodal learning. We implement a \"CVAE\" without audio and \"CMVAE\" with audio-visual joint distribution estimation." + }, + { + "type": "table", + "bbox": [ + 0.114, + 0.495, + 0.428, + 0.587 + ], + "angle": 0, + "content": "
MethodsS4MS3
mIoUF-scoremIoUF-score
[1] w/o audio77.80-48.20-
CVAE78.120.87849.260.643
CMVAE80.050.88954.990.653
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.599, + 0.469, + 0.839 + ], + "angle": 0, + "content": "Multimodal VAE. We explore the effectiveness of the Multimodal VAE in Table 2. Firstly, we remove the audio part of the model and disable the TPAVI module to explore the importance of the audio information, leading to a simple unimodal CVAE [29] framework with only video input, which is denoted as \"CVAE\". For comparison, we implement a \"CMVAE\" using the audio signal but without the latent space factorization and our proposed constraints. The better performance of \"CMVAE\" compared with \"CVAE\" indicates the importance of audio for AVS, especially when multiple sound sources exist. We also brought the ablation result of the model without the audio input from [1] and compare it with \"CVAE\". The results show that in the absence of audio signals, the VAE structure can still improve segmentation performance, due to the ability of VAE to model the latent space of visual features." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.469, + 0.901 + ], + "angle": 0, + "content": "Latent Space Factorization. As described in Sec. 3.2, we factorize the latent space of multimodal VAE into modality-shared \\((c)\\) and modality-specific \\((s^v\\) and \\(s^a)\\) representations. As reported in Table 3, removing the latent space" + }, + { + "type": "table_caption", + "bbox": [ + 0.499, + 0.383, + 0.892, + 0.439 + ], + "angle": 0, + "content": "Table 3. Ablation of the latent space factorization. \"Model\" indicates using VAE for latent factorization or using AE for feature factorization. \"Factor.\" denotes whether using factorization. \"dim.\" represents the size of the latent dimensions." + }, + { + "type": "table", + "bbox": [ + 0.512, + 0.445, + 0.875, + 0.569 + ], + "angle": 0, + "content": "
ModelFactor.dim.S4MS3
mIoUF-scoremIoUF-score
VAE-1680.050.88954.990.653
-4880.130.89055.090.657
✓1680.780.89356.380.676
AE--78.740.87954.000.645
✓-78.920.88154.820.651
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.595, + 0.892, + 0.761 + ], + "angle": 0, + "content": "factorization leads to obvious performance degradation. We also train a non-factorized model with \\(2 \\times\\) larger latent dimensions, which holds comparable latent space capacities with the factorized model. It can be seen that the performance gain from the larger latent space dimensions is not as obvious as the factorization strategy. Further, we compare feature factorization (\"AE\") on the feature space of [1] with our proposed latent space factorization (\"VAE\"). Table 3 shows that only performing factorization on a semantic meaningful and continuous latent space, i.e. via using VAE [2], can achieve larger performance improvements." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.763, + 0.892, + 0.883 + ], + "angle": 0, + "content": "JS Divergence. We conduct experiments of PoE and MoE with KL divergence to show the trade-off of JS divergence between the computational efficiency of the inference process and the predictive quality of the generation process. The performance in Table 4 shows the effectiveness of JS divergence on both S4 and MS3 settings. Note that, \"PoE\", \"MoE\" and \"JS\" are based on our formulation of the task, which has not been explored in the AVS area." + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.886, + 0.891, + 0.901 + ], + "angle": 0, + "content": "Orthogonality Constraint. As reported in Table 5, the or" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.511, + 0.957 + ], + "angle": 0, + "content": "960" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.123, + 0.089, + 0.303, + 0.191 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.159, + 0.193, + 0.27, + 0.203 + ], + "angle": 0, + "content": "(a) Base Factorization" + }, + { + "type": "image", + "bbox": [ + 0.305, + 0.09, + 0.484, + 0.191 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.361, + 0.193, + 0.434, + 0.205 + ], + "angle": 0, + "content": "(b) With \\(\\mathcal{L}_{\\mathrm{diff}}\\)" + }, + { + "type": "image", + "bbox": [ + 0.484, + 0.091, + 0.667, + 0.191 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.545, + 0.193, + 0.613, + 0.206 + ], + "angle": 0, + "content": "(c) With \\(\\mathcal{L}_{\\mathrm{sic}}\\)" + }, + { + "type": "image", + "bbox": [ + 0.671, + 0.091, + 0.849, + 0.191 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.712, + 0.193, + 0.815, + 0.206 + ], + "angle": 0, + "content": "(d) With \\(\\mathcal{L}_{\\mathrm{diff}},\\mathcal{L}_{\\mathrm{sic}}\\)" + }, + { + "type": "image", + "bbox": [ + 0.361, + 0.206, + 0.623, + 0.219 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.226, + 0.894, + 0.255 + ], + "angle": 0, + "content": "Figure 3. Visualization of the modality-shared and modality-specific latent codes \\((s^v, s^a, c)\\) in the MS3 testing set using t-SNE [77] projections. Best viewed on screen." + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.269, + 0.468, + 0.297 + ], + "angle": 0, + "content": "Table 4. Ablation of the JS Divergence. We implement \"PoE\" and \"MoE\" with KL divergence, and a simple \"KL\" model." + }, + { + "type": "table", + "bbox": [ + 0.13, + 0.303, + 0.412, + 0.407 + ], + "angle": 0, + "content": "
MethodsS4MS3
mIoUF-scoremIoUF-score
KL80.780.89356.380.676
PoE81.380.89457.350.688
MoE81.490.89757.530.694
JS81.740.90157.840.708
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.415, + 0.468, + 0.443 + ], + "angle": 0, + "content": "Table 5. Ablation of the latent space constraints. \\( \\mathcal{L}_{\\mathrm{diff}} \\), \\( \\mathcal{L}_{\\mathrm{sic}} \\) indicate our proposed loss functions for multimodal learning." + }, + { + "type": "table", + "bbox": [ + 0.117, + 0.449, + 0.424, + 0.552 + ], + "angle": 0, + "content": "
\\(\\mathcal{L}_{diff}\\)\\(\\mathcal{L}_{sic}\\)S4MS3
mIoUF-scoremIoUF-score
--81.090.89557.010.684
✓-81.510.89957.650.692
-✓81.470.89857.510.694
✓✓81.740.90157.840.708
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.564, + 0.468, + 0.669 + ], + "angle": 0, + "content": "thogonality constraint provides \\(0.64\\mathrm{mIOU}\\) gain under the MS3 setting, which facilitates the latent space factorization. We also perform t-SNE [77] projection to visualize the factorized latent code with and without such constraint. As compared between Fig. 3 (a) and (b), the three latent codes in the latent space are divided into different subspaces to ensure that each latent code encodes different information." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.67, + 0.468, + 0.837 + ], + "angle": 0, + "content": "Mutual Information Maximization. As compared in Table 5, the mutual information maximization by \\(\\mathcal{L}_{\\mathrm{sic}}\\) also serves a crucial impact for the explicit constraint of the shared latent space and improves the mIOU from 57.51 to 57.84. Since the \\(\\mathcal{L}_{\\mathrm{sic}}\\) maximizes the mutual information between \\(sc^v\\) and \\(sc^a\\), which are fused from the factorization latent codes \\(s^v, s^a, c\\). This increases the amount of information contained in latent space and makes it more effective for facilitating factorization. Fig. 3 also confirms this view and demonstrates the effectiveness of \\(\\mathcal{L}_{\\mathrm{sic}}\\) in achieving effective \"multi-view\" representation learning [56, 57, 62]." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.847, + 0.18, + 0.863 + ], + "angle": 0, + "content": "4.4. Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.871, + 0.468, + 0.902 + ], + "angle": 0, + "content": "Pre-training on the Single-source Subset. In AVS-Bench [1], they conducted experiments by initializing" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.273, + 0.892, + 0.409 + ], + "angle": 0, + "content": "model parameters by pre-training on S4 dataset. We also perform experiments with such setting (see Table 6). We can observe that both our method and AVSBench [1] can benefit from the model pre-trained on S4. The PVT-based model can gain \\(2.97\\%\\) mIOU performance by such a strategy and reach \\(60.81\\%\\) mIOU. The pre-training strategy can bring more significant improvements (\\(8.87\\%\\) mIOU) to ResNet50-based models and reach \\(57.56\\%\\) mIOU, which is even higher than PVT-based models (\\(57.34\\%\\))." + }, + { + "type": "table_caption", + "bbox": [ + 0.498, + 0.417, + 0.892, + 0.488 + ], + "angle": 0, + "content": "Table 6. Performance comparison with different initialization strategies for MS3 dataset. As AVSBench [1] does not report its F-score in the paper, we only report its mIOU. The values in parentheses indicate the performance improvement based on S4 pre-training compared with training from scratch." + }, + { + "type": "table", + "bbox": [ + 0.502, + 0.494, + 0.892, + 0.597 + ], + "angle": 0, + "content": "
MethodsFrom scratchPre-trained on S4
mIoUF-scoremIoUF-score
AVSbench (R50) [1]47.88-54.33 (↑ 6.45)-
AVSbench (PVT) [1]54.00-57.34 (↑ 3.34)-
Ours (R50)48.690.60757.56 (↑ 8.87)0.674
Ours (PVT)57.840.70860.81 (↑ 2.97)0.729
" + }, + { + "type": "table_caption", + "bbox": [ + 0.568, + 0.617, + 0.819, + 0.63 + ], + "angle": 0, + "content": "Table 7. Parameters and inference time." + }, + { + "type": "table", + "bbox": [ + 0.501, + 0.634, + 0.892, + 0.711 + ], + "angle": 0, + "content": "
MethodsR50PVT
Param. (M)Time (ms)Param. (M)Time (ms)
AVSBench [1]70.5028101.3253
Ours33.972391.1846
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.856 + ], + "angle": 0, + "content": "Parameters and Efficiency. In Table 7, we compare the parameters and inference time between ours and AVSBench. Note that although posterior nets and prior nets are used in our framework, as all the latent space encoders are quite lightweight (1M), thus our model capacity will not change significantly. Moreover, we replace the neck from ASPP [78] to one-layer convolution and reduce the number of neck channels from 256 to 128, which leads to smaller parameter numbers and faster inference speed." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Limitations. Similar to the other VAE [2] based solutions, our model also suffers from the risk of posterior collapse, where the posterior of the latent variable is equal to" + }, + { + "type": "page_number", + "bbox": [ + 0.486, + 0.946, + 0.51, + 0.957 + ], + "angle": 0, + "content": "961" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.168 + ], + "angle": 0, + "content": "prior [79,80], making \\( y \\) in our case not encoded in the latent variables. To avoid such phenomenon, contrastive learning [81, 82] can be studied to learn more compact features of each modality or score based diffusion models [83-86] can be investigated for more informative latent space." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.18, + 0.197, + 0.195 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.204, + 0.473, + 0.416 + ], + "angle": 0, + "content": "We have worked on audio-visual segmentation (AVS), aiming to segment the sound producers of the scene. As audio data can be treated as \"command\", we argue extensive exploration of audio is critical for effective AVS. Inspired by this observation, we have introduced an Explicit Conditional Multimodal Variational Auto-Encoder (ECMVAE) for an audio-visual segmentation model with latent space factorization with explicit constraints to extensively explore the shared and specific representations of audio and visual data. Extensive experimental results verify the effectiveness of our proposed framework. Although we focused on AVS with two modalities, the proposed framework can be extended to more modalities and other audio-visual collaboration tasks [6, 13, 14]." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.428, + 0.258, + 0.446 + ], + "angle": 0, + "content": "6. Acknowledgments" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.453, + 0.47, + 0.499 + ], + "angle": 0, + "content": "This research was supported in part by the National Natural Science Foundation of China (62271410), and the Fundamental Research Funds for the Central Universities." + }, + { + "type": "title", + "bbox": [ + 0.08, + 0.51, + 0.175, + 0.526 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.535, + 0.47, + 0.605 + ], + "angle": 0, + "content": "[1] Jinxing Zhou, Jianyuan Wang, Jiayi Zhang, Weixuan Sun, Jing Zhang, Stan Birchfield, Dan Guo, Lingpeng Kong, Meng Wang, and Yiran Zhong. Audio-visual segmentation. In European Conference on Computer Vision (ECCV), 2022. 1, 2, 3, 5, 6, 7, 8" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.608, + 0.472, + 0.65 + ], + "angle": 0, + "content": "[2] Diederik Kingma and Max Welling. Auto-encoding variational bayes. 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Existing AVS methods focus on implicit feature fusion strategies, where models are trained to fit the discrete samples in the dataset. With a limited and less diverse dataset, the resulting performance is usually unsatisfactory. In contrast, we address this problem from an effective representation learning perspective, aiming to model the contribution of each modality explicitly. Specifically, we find that audio contains critical category information of the sound producers, and visual data provides candidate sound producer(s). Their shared information corresponds to the target sound producer(s) shown in the visual data. In this case, cross-modal shared representation learning is especially important for AVS. To achieve this, our ECMVAE factorizes the representations of each modality with a modality-shared representation and a modality-specific representation. An orthogonality constraint is applied between the shared and specific representations to maintain the exclusive attribute of the factorized latent code. Further, a mutual information maximization regularizer is introduced to achieve extensive exploration of each modality. Quantitative and qualitative evaluations on the AVSBench demonstrate the effectiveness of our approach, leading to a new state-of-the-art for AVS, with a 3.84 mIOU performance leap on the challenging MS3 subset for multiple sound source segmentation. + +# 1. Introduction + +Audio-visual data can work collaboratively towards a better perception of the scene. The audio-visual segmentation (AVS) [1] task aims to segment the objects from the video sequence that producing the sound in the audio. On + +the one hand, the audio data provides category information for the localization of the object in the video. On the other hand, the visual data provides a sound producer pool with precise structure information of the foreground (sound producer(s)). Different from conventional multimodal settings, where each modality can be used individually for the target task, audio in AVS task serves as "command" to localize and segment the sound producer(s) from the visual data. In this case, the contribution of audio should be extensively explored for accurate foreground segmentation. + +The baseline model [1] focuses on implicit feature fusion via audio-visual cross attention. It purely relies on fitting the discrete samples in the dataset. Although reasonable performance is obtained, there are no constraints to guarantee the contribution of each modality, making it hard to decide if the audio data is effectively used, as the model can directly regress the final segmentation maps by only taking the video as input. Fortunately, we discover that each modality for AVS contains both shared and specific information. For example, the audio data includes both the information from the sound producers and the background noise, while the visual data shows the appearance of the entire scene, where the sound producers only take a small portion of it. In our specific task setting, we find modality factorization is suitable to model both the modality-shared representation, i.e. information of the sound producers, and the modality-specific representation toward a better understanding of the contribution of each modality. + +The straightforward solution to learn the feature representation of the input data is through an auto-encoder (AE) framework. However, AE is mainly used for data compression, as the learned feature space is not continuous, which cannot provide a rich semantic correlation of the data. Differently, with latent space regularization, e.g. the latent space is assumed to be Gaussian in variational autoencoder (VAE) [2], VAE obtains semantic meaningful latent space, which is continuous, and it is also the basic requirement for reliable latent space factorization. + +To learn the semantic correlated feature representation of the AVS data, we propose an Explicit Conditional Mul + +timodal Variational Auto-Encoder (ECMVAE) for audiovisual segmentation to learn both the shared and the specific representation in the latent space of each modality. Our model is built upon a multimodal variational autoencoder [3, 4], with the Jensen-Shannon divergence to achieve a trade-off between sampling efficiency and sample quality. Based on the latent space factorization, we impose constraints for the shared and specific representations to explicitly maximize the contribution of each modality. + +Specifically, we first assume that one latent code of the factorized representation should contain independent information compared to others. Furthermore, for the fused representation, we further claim that it should be more informative for the target task compared with each modality. To achieve the former, we propose an information orthogonality constraint between the factorized representations of each modality to ensure that the modality-shared and modality-specific representations capture different aspects of the audio-visual input. For the latter, we fuse the factorized representations of each modality to construct a fused space. Then we introduce a mutual information maximization regularizer between the fused representations of each modality to extensively explore the contribution of each modality. Extensive experimental results demonstrate that our ECMVAE achieves state-of-the-art AVS performance. Our pipeline achieves a $3.84\mathrm{mIOU}$ improvement for the challenging multiple sound source segmentation. + +We summarize our main contributions as: + +- An explicit semantic correlated feature representation learning framework for audio-visual segmentation is proposed with latent space factorization to capture both the modality-shared and specific representations. +- Based on the latent space factorization, we introduce a unimodal orthogonality constraint between the shared and specific representations and the cross-modal mutual-information maximization regularizer to extensively explore the contribution of each modality. +- State-of-the-art segmentation performance is achieved, showing both the effectiveness of each module and the contribution of each modality. + +# 2. Related Work + +Audio-Visual Segmentation. The Audio-Visual Segmentation (AVS) task is newly proposed, aiming to localize the sound producers with pixel-wise segmentation masks. Zhou et al. [1] propose an AVSBench dataset for audio-visual segmentation and provide a simple baseline based on temporal pixel-wise audio-visual interaction (TPAVI), which is a cross-modal attention [5] based fusion strategy. The other audio-visual collaboration tasks can be classified as audio-visual correspondence (AVC) [6, 7], event localization (AVEL) [8-13], event parsing (AVP) [14-16], etc. These methods require the fusion of audio and visual sig + +nals. Such as audio-visual similarity modeling by computing the correlation matrix [6, 7], audio-visual cross attention [12, 13, 17], audio-guided Grad-CAM [18], or using a multimodal transformer for modeling the long-range dependencies between elements across modalities directly [19, 20]. However, the challenge and uniqueness of the AVS task are how to map the audio signals to fine-grained visual cues, i.e. per-pixel segmentation maps. This will rely on reliable modeling of visual and audio signals, as well as more effective fusion strategies. + +Multimodal Variational Auto-encoders. The Multimodal Variational Auto-encoders (MVAEs) [3, 21–24] are a type of latent variable generative model to learn more generalizable representations from diverse modalities. To achieve this, the core of MVAE is the joint distribution estimation. The conventional unimodal VAEs [2, 25] are optimized by maximizing the evidence lower bound (ELBO), which includes a reconstruction term and the Kullback-Leibler (KL) divergence term to measure the divergence from the variational posterior to the prior distribution of the latent variable. In a multimodal setting, the KL divergence is defined between the joint posterior and joint prior across the modalities, which is often estimated by the product of experts (PoE) [26, 27] or the mixture of experts (MoE) [28]. Based on such a prerequisite, many works extend the basic MVAE definition, such as missing modality handling [24], latent space modeling [23, 28], effective divergence modeling [4], etc. However, previous MVAE based frameworks essentially focus on the multimodal image generation task. In this work, we bring the MVAE to the AVS task and propose the conditional version [25, 29] of MVAE with practical multimodal information constraints for segmentation. + +Mutual Information Estimation. Mutual Information (MI) captures the nonlinear statistical dependencies between variables, acting as a measure of actual dependence [30]. Specifically, for a pair of random variables $X$ and $Y$ , their MI $I(X;Y)$ is defined as the KL divergence of the joint distribution $p_{(X,Y)}$ from the product of the marginal distributions $p(X)$ and $p(Y)$ , which measures the shared information between $X$ and $Y$ . Although mutual information is simple in formation, as the log density ratio between the joint distribution $p_{(X,Y)}$ and product of marginals $p(X)\otimes p(Y)$ is intractable, it is usually estimated [31-33] instead of computed directly, leading to both MI maximization with a lower bound [34, 35] and MI minimization with an upper bound [36]. The MI maximization is usually applied for effective self-supervised representation learning [37-41] for the unimodal data to guarantee reliable feature representation. For the multimodal tasks, when each modality of data contains partial information of the target, both MI maximization and minimization can be applied [42-50], where the former aims to explore the taskdriven feature across the modalities, and the latter is de + +signed to explore the complementary information of different modalities. Extensive researches show that effective MI optimization can not only lead to informative representation learning [51-58] but also is beneficial for achieving adversarial robustness [59]. + +# 3. Explicit Conditional Multimodal Learning + +We denote the input data of our used AVSbench dataset [1] is $X = \{\{x_{t}^{v}\}_{t=1}^{T}, x^{a}\}$ , i.e. the visual $\{x_{t}^{v}\}_{t=1}^{T}$ for $T$ non-overlapping yet continuous frames, audio $x^{a}$ of the current clip. $y = \{y_{t}\}_{t=1}^{T}$ is the output, i.e. the segmentation maps (we omit $t$ for clear presentation). The goal of audio-visual segmentation is to segment the objects from the video $\{x_{t}^{v}\}_{t=1}^{T}$ that produce the sound shown in the audio $x^{a}$ . We introduce an Explicit Conditional Multi-modal Variational Auto-Encoder (ECMVAE) using Jensen-Shannon divergence (Sec. 3.1) via latent space factorization (Sec. 3.2) to effectively model the shared representation between the two modalities (Sec. 3.3 and Sec. 3.4) for audio-visual segmentation. The overview of the proposed ECMVAE is shown in Fig. 1. + +# 3.1. Prerequisite + +Conditional Variational Auto-encoder. We begin our prerequisite with the definition of the conditional variational auto-encoder (CVAE) [2, 25], which contains a generative process and an inference process. The generative process is to draw the latent variable $z$ from the prior distribution $p_{\theta}(z|X)$ with a given $X$ , and generate the output via $p_{\theta}(y|X,z)$ , where in our case $X$ and $y$ in the following derivations are $X = \{\{x_t^v\}_{t=1}^T, x^a\}$ and $y = \{y_t\}_{t=1}^T$ , respectively. The inference process of CVAE aims to infer the informative values of the latent variable $z$ given the observed data $X$ and $y$ by computing the posterior $p_{\theta}(z|X,y)$ , which is intractable and usually approximated with the variational posterior $q_{\phi}(z|X,y)$ . $\theta$ and $\phi$ are the parameters of the true posterior and the approximated variational posterior, respectively. CVAE is trained to find the optimal generation parameters $\theta^*$ and inference parameters $\phi^*$ following the maximum log-likelihood learning pipeline: + +$$ +\left\{\theta^ {*}, \phi^ {*} \right\} = \underset {\theta , \phi} {\arg \max } \log p _ {\theta} (y | X), \tag {1} +$$ + +where the log-likelihood term is achieved as: + +$$ +\begin{array}{l} \log p _ {\theta} (y | X) \\ = \underbrace {\mathbb {E} _ {q _ {\phi} (z | X , y)} \log p _ {\theta} (y | X , z) - D _ {K L} (q _ {\phi} (z | X , y) \| p _ {\theta} (z | X))} _ {\text {E L B O} (X, y, \theta , \phi)} \\ + D _ {\mathrm {K L}} \left(q _ {\phi} (z | X, y) \| p _ {\theta} (z | X, y)\right). \tag {2} \\ \end{array} +$$ + +By Jensen's inequality, the Kullback-Leibler (KL) divergence term $(D_{KL})$ in Eq. (2) is always greater or equal to zero, thus maximizing $\log p_{\theta}(y|X)$ can be achieved by maximizing the evidence lower bound $\operatorname{ELBO}(X,y,\theta,\phi)$ : + +$$ +\begin{array}{l} \left\{\theta^ {*}, \phi^ {*} \right\} = \arg \max _ {\theta , \phi} \log p _ {\theta} (y | X) \\ = \arg \max _ {\theta , \phi} \operatorname {E L B O} (X, y, \theta , \phi). \tag {3} \\ \end{array} +$$ + +With the reparameterization trick [2], the KL term in $\mathrm{ELBO}(X,y,\theta ,\phi)$ can be solved in closed-form if both the prior $p_{\theta}(z|X)$ and posterior $q_{\phi}(z|X,y)$ are Gaussian. + +Multimodal Conditional Variational Auto-encoder. For the unimodal setting, both $p_{\theta}(z|X)$ and $q_{\phi}(z|X,y)$ can be obtained via the reparameterization trick [2], leading to closed-form solution of the KL divergence as both $p_{\theta}(z|X)$ and $q_{\phi}(z|X,y)$ are Gaussian. For the multimodal AVS data, the joint posterior and joint prior need to be estimated before we perform the joint generation process. The conventional solution to model the joint distribution is through the product of experts (PoE) [26, 27] or the mixture of experts (MoE) [28]. For the former, the joint distribution is defined as the product of each individual expert, which is Gaussian when each expert is Gaussian, leading to closed form KL computation. However, for PoE, less accurate modeling of one expert will completely destroy the joint distribution modeling. Further, PoE shows limitations in modeling the unimodal contribution due to its multiplicative nature. The additive nature of the MoE makes it effective for the optimization of each individual expert. However, as no closed form exists for the KL term, importance sampling (IS) is usually needed, which is computationally less efficient. + +JS Divergence Instead of KL Divergence. Although MoE is computationally less efficient compared with PoE, its individual modal contribution modeling is attractive. Based on MoE, the $D_{KL}$ term within $\mathrm{ELBO}(X,y,\theta ,\phi)$ of Eq. (2) is the lower bound of the weighted sum of individual KLs: + +$$ +\begin{array}{l} D _ {K L} \left(q _ {\phi} (z | X, y) \| p _ {\theta} (z | X)\right) \\ \leq \sum_ {k = 1} ^ {K} \phi_ {k} D _ {K L} \left(q _ {\phi_ {k}} \left(z \mid x ^ {k}, y\right) \| p _ {\theta} \left(z \mid x ^ {k}\right)\right). \tag {4} \\ \end{array} +$$ + +where $K$ is the number of modalities, and $\sum_{k}\phi_{k} = 1$ . Although Eq. (4) is effective in providing lower bound with individual modal's distribution for ELBO in Eq. (2), no joint distribution is involved. Following [4], a dynamic prior $f_{K}$ is introduced, which is the mixture of the involved arguments (individual priors and posteriors), i.e. $f_{K}$ can be defined as the arithmetic means as in MoE. + +With the non-negative nature of KL divergence and the definition of JS divergence, we obtain a new lower bound of + +![](images/b288800dad90817567d768a8e323205ea75651fc5df89c1f0825f78a07879f3f.jpg) +Figure 1. Overview of the proposed ECMVAE for audio-visual segmentation. The feature extractors are used to extract backbone features for the two modalities. We also design three latent encoders $\phi_{s^v},\phi_{s^a},\phi_c$ to achieve latent space factorization and obtain both task-driven shared representation $(c)$ and modality-related specific representation $(s^a,s^v)$ , achieving explicit multimodal representation learning. The decoder is introduced to obtain the final segmentation maps, indicating the sound producers of the audio-visual data. + +ELBO in Eq. (2) as: + +$$ +\begin{array}{l} \widehat {\operatorname {E L B O}} (X, y, \theta , \phi) \geq \mathbb {E} _ {q _ {\phi} (z | X, y)} \log p _ {\theta} (y | X, z) \\ - \sum_ {k _ {1} = 1} ^ {K} \pi_ {k _ {1}} D _ {K L} \left(q _ {\phi} (z | X, y) \| f _ {K}\right) - \sum_ {k _ {2} = 1} ^ {K} \pi_ {k _ {2}} D _ {K L} \left(p _ {\theta} (z | X) \| f _ {K}\right) \\ = \underbrace {\mathbb {E} _ {q _ {\phi} (z | X , y)} \log p _ {\theta} (y | X , z) - \operatorname {J S D} \left(q _ {\phi} (z | X , y) , p _ {\theta} (z | X)\right)} _ {\widehat {\text {E L B O}} (X, y, \theta , \phi)}, \tag {5} \\ \end{array} +$$ + +where $\sum_{k=1}^{2K}\pi_k = 1$ , and JSD represents JS divergence. Eq. (5) provides lower bound of ELBO in Eq. (2), namely $\widehat{\mathrm{ELBO}}(X,y,\theta,\phi)$ , which is proven more stable for training [4], and robust to noise. + +# 3.2. Latent Space Factorization + +Besides stable training and noise robustness, we are also interested in modeling both shared and specific information of the audio-visual input (see Fig. 1) to fully explore their contribution. For each pair of example $(x^{k},y)$ , where $x^{k}\in \{\{x_{t}^{v}\}_{t = 1}^{T},x^{a}\}$ indexes the modalities with $K = 2$ in this paper, we factorize the latent space $z$ into a modality-shared latent code $c$ and modality-specific latent codes $s^a,s^v$ . Then $\widehat{\mathrm{ELBO}} (X,y,\theta ,\phi)$ is re-defined as: + +$$ +\begin{array}{l} \widehat {\mathrm {E L B O}} (X, y, \theta , \phi) \\ = \sum_ {k = 1} ^ {K} \mathbb {E} _ {q _ {\phi_ {c}} (c | X, y)} \left[ \mathbb {E} _ {q _ {\phi_ {s} k} (s ^ {k} | x ^ {k}, y)} \left[ \log p _ {\theta} \left(y \mid x ^ {k}, s ^ {k}, c\right) \right] \right] \tag {6} \\ - \beta \sum_ {k = 1} ^ {K} D _ {K L} \left(q _ {\phi_ {s k}} \left(s ^ {k} \mid x ^ {k}, y\right) \mid p _ {\theta} \left(s ^ {k} \mid x ^ {k}\right)\right) \\ - \beta \mathrm {J S D} \left(q _ {\phi_ {c}} (c | X, y), p _ {\theta} (c | X)\right), \\ \end{array} +$$ + +where $q_{\phi_c}(c|X,y)$ and $p_{\theta}(c|X)$ are the posterior and prior distributions of the shared representation. $q_{\phi_{s^k}}(s^k |x^k,y)$ and $p_{\theta_{s^k}}(s^k |x^k)$ are the posterior and prior distribution of the modality-specific latent codes. $p_{\theta}(y|x^{k},s^{k},c)$ is the prediction generation model. All these models can be parameterized by deep neural networks and optimized via stochastic gradient descent. The hyper-parameter $\beta = 0.1$ is introduced to achieve stable learning [60]. + +Efficient Sampling. The Eq. (6) shows that the generation process involves sampling from the joint shared posterior $q_{\phi_c}(c|X,y)$ and posterior of modality-specific latent code $q_{\phi_{s^k}}(s^k|x^k,y)$ of each modality, which is time-consuming. In practice, we first perform shared-specific representation fusion, and then we sample latent code from each fused space, achieving efficient sampling. Specifically, given the posterior of the latent codes $c \sim q_{\phi_c}(c|X,y) \in \mathbb{R}^{T \times L}$ , $s^a \sim q_{\phi_{s^a}}(s^a|x^a,y) \in \mathbb{R}^{T \times L}$ , $s^v \sim q_{\phi_{s^v}}(s^v|x^v,y) \in \mathbb{R}^{T \times L}$ ( $L$ is the dimension of the latent space), we concatenate the shared representation with each specific representation to get the fused representation of each modality. Then we obtain $sc^a, sc^v$ , representing the fused feature of audio and visual data, respectively. To achieve the reconstruction of $p_\theta(y|x^k,s^k,c)$ in Eq. (6), instead of performing sampling from each specific latent code and shared latent code, we sample from $sc^a, sc^v$ , and rewrite the reconstruction term, i.e. the first term in Eq. (6), as: + +$$ +\mathcal {L} _ {\text {r e c}} = \sum_ {s c \in \{s c ^ {a}, s c ^ {v} \}} \left[ \mathbb {E} \left[ \log p _ {\theta} (y | x, s c) \right] \right], \tag {7} +$$ + +where $x$ corresponds to the modality of data, i.e. audio or visual, of the current fused latent code $sc$ . + +Hybrid Loss. As the VAE samples from the posterior for training and prior to testing. To achieve consistent training + +and testing, we define a Gaussian stochastic neural network (GSNN) [25] based objective by sampling from the prior distribution as well to avoid the posterior/prior distribution gap, leading to the hybrid objective as: + +$$ +\widehat {\operatorname {H E L B O}} (X, y, \theta , \phi) = \alpha_ {1} \widehat {\operatorname {E L B O}} (X, y, \theta , \phi) + (1 - \alpha_ {1}) \mathcal {L} _ {\mathrm {G S N N}}, \tag {8} +$$ + +where $\alpha_{1} = 0.5$ is used to balance the two objectives, $\mathcal{L}_{\mathrm{GSNN}}$ represents the reconstruction term of Eq. (6), which is achieved by sampling from the prior distribution. + +The latent space factorization is effective in generating modality-shared and specific representations. However, no constraints are applied to the representations, making it hard to decide the reliability of the latent codes. We tackle this issue by proposing a representation orthogonality constraint in Sec. 3.3 and a shared information completeness regularization in Sec. 3.4. + +# 3.3. Representation Orthogonality Constraint + +We introduce a representation orthogonality constraint to ensure that the modality-shared and modality-specific representations capture different information within each unimodal data. Specifically, given the latent codes $c, s^a, s^v$ , we introduce the difference loss [61] as: + +$$ +\mathcal {L} _ {\text {d i f f}} = \left\| c ^ {T} s ^ {a} \right\| _ {F} ^ {2} + \left\| c ^ {T} s ^ {v} \right\| _ {F} ^ {2} + \left\| \left(s ^ {a}\right) ^ {T} s ^ {v} \right\| _ {F} ^ {2}, \tag {9} +$$ + +where $\| \cdot \| _F^2$ is the squared Frobenius norm. With the difference loss, we aim to obtain the exclusive feature in each factorized feature representation. + +# 3.4. Shared-Information Completeness + +As discussed in Sec. 3.2, we fuse the shared representation with each modality-specific representation and obtain $sc^a$ , $sc^v$ , representing the task-related information from audio and visual, respectively. To explicitly model the effectiveness of the fused latent space, we treat them $(sc^a, sc^v)$ as two different views of the same target following representation learning [56, 57, 62], and introduce mutual information maximization as a regularizer to measure the shared information between $sc^a$ and $sc^v$ . Given two random variables $SC^a$ , $SC^v$ , the mutual information is defined as: + +$$ +I \left(S C ^ {a}; S C ^ {v}\right) = \mathbb {E} _ {p \left(s c ^ {a}, s c ^ {v}\right)} \left[ \log \frac {p \left(s c ^ {a} , s c ^ {v}\right)}{p \left(s c ^ {a}\right) \cdot p \left(s c ^ {v}\right)} \right]. \tag {10} +$$ + +According to Bayesian's law, we obtain the mutual information variational lower bound [35], namely $I_{\mathrm{ba}}$ via: + +$$ +I \left(S C ^ {a}; S C ^ {v}\right) \geq \mathbb {E} _ {p \left(s c ^ {a}, s c ^ {v}\right)} \left[ \log q _ {\kappa} \left(s c ^ {a} \mid s c ^ {v}\right) \right] + H \left(S C ^ {a}\right) \triangleq I _ {\mathrm {b a}}, \tag {11} +$$ + +where $q_{\kappa}(sc^{a}|sc^{v})$ is the variational approximation of $p(sc^{a}|sc^{v})$ . Following [36], $q_{\kappa}(sc^{a}|sc^{v})$ is formulated as a multivariate Gaussian distribution $q_{\kappa}(sc^{a}|sc^{v}) =$ + +$\mathcal{N}(sc^a |\mu (sc^v),\sigma^2 (sc^v)\mathbf{I})$ to predict mean $\mu (sc^v)$ and variance $\sigma^2 (sc^v)$ , respectively, where each statistic is modeled with two fully connected layers with Tanh activation function in the middle, and $\kappa$ represent parameters of the four fully connected layers. $H(SC^{a})$ is the differential entropy of $SC^a$ . As the audio encoder is fixed in this paper, we choose to simplify the entropy computation and treat $H(SC^{a})$ as a constant [63]. + +Based on the variational lower bound $I_{\mathrm{ba}}$ , we then define the shared-information completeness loss function as: $\mathcal{L}_{\mathrm{sic}} = -I_{\mathrm{ba}}$ . Further, we introduce the hybrid loss function for the posterior and the prior distribution, leading to: + +$$ +\mathcal {L} _ {\mathrm {s i c}} = - \alpha_ {2} I _ {\mathrm {b a}} ^ {\mathrm {p o}} - (1 - \alpha_ {2}) I _ {\mathrm {b a}} ^ {\mathrm {p r}}, \tag {12} +$$ + +where $I_{\mathrm{ba}}^{\mathrm{po}}(I_{\mathrm{ba}}^{\mathrm{pr}})$ is the lower bound of the mutual information for the posterior (prior) distribution, and $\alpha_{2} = 0.5$ is introduced to balance the two objectives. + +# 3.5. The Model + +Four central modules or constraints are included in our framework (see Fig. 1), namely: 1) "modal encoding" to extract the feature of each modality; 2) "latent space encoding" for multimodal latent feature representation learning; 3) "decoder" for the segmentation maps prediction; 4) "objective function" for supervised learning and explicit multimodal representation constraints. + +Modal Encoding. We perform two branches with two encoders to encode the visual and audio data. For the visual branch, we use the ImageNet pre-trained backbone followed by a one-layer convolution as neck to produce the multi-scale visual features $\{V_m\}_{m=1}^4 \in \mathbb{R}^{T \times h_m \times w_m \times C_m}$ , where $(h_m, w_m) = (H, W) / 2^{m+1}, C_m = 128$ . $H, W$ is the spatial resolution of the input video. We use PVTv2 [64] or ResNet50 [65] as our visual backbone, which keeps the same as AVSBench [1]. For the audio branch, we follow [1], and use a frozen VGGish [66] model pre-trained on AudioSet [67] to process the spectrogram of input audio to extract audio features $A \in \mathbb{R}^{T \times d}$ , where $d = 128$ . And $T = 5$ denotes the length of the video. We also keep the temporal pixel-wise audio-visual interaction (TPAVI) [1] module in our framework, which is a cross-modal attention based fusion module that takes visual features as query and value, audio features as key to achieve multi-scale feature fusion in the feature space and obtain $\{\bar{V}_m\}_{m=1}^4$ . + +Latent Space Encoding. The main idea of our proposed method is achieving modality encoding on a reliable latent space (Sec. 3.2), as shown in Fig. 1. We use $\phi_{s^v},\phi_{s^a},\phi_c$ parameterized by three simple neural networks to get latent feature embedding $s^v,s^a,c\in \mathbb{R}^{T\times L}$ as prior distributions $(L = 16)$ . For $\phi_{s^v}$ , we use five convolutional layers followed by leakyReLU [68] with two fully connected layers to encode the input video sequence. While for $\phi_{s^a}$ , we employ two fully connected layers to map the VGGish encoded + +audio features into the latent space. Further, video sequence and audio features are fed into $\phi_c$ jointly, thus we perform late fusion on the audio features and five convolutional layers followed by leakyReLU encoded visual features to obtain the joint distribution from the fused features. For the posterior network, we design three networks with the same structure and take the segmentation maps $y$ as input by concatenating the video sequence and segmentation maps. We omit drawing the posterior space in Fig. 1 for easy viewing. Decoder. We adopt the decoder of Panoptic-FPN [69] to decode the final segmentation maps for its flexibility and effectiveness, which is the same as AVSBench [1]. We expand $sc^a$ , $sc^v$ to feature map of the same spatial size as $\bar{V}_4$ by adding two-dimensional gaussian noise with the tile operation, "sampling" is used to indicate this process in Fig.1. The decoder takes both the deterministic features $\{\bar{V}_m\}_{m=1}^4$ produced by the TPAVI [1] module and the expanded latent codes $sc^a$ , $sc^v$ from the fused latent space as input to produce the final segmentation maps. + +Objective Function. As discussed above, our final objective function contains the optimization of the evidence lower bound and the practical constraints for latent space representation, and it can be defined as, + +$$ +\begin{array}{l} \mathcal {L} = - \widehat {\mathrm {H E L B O}} (X, y, \theta , \phi) + \lambda_ {1} \mathcal {L} _ {\text {d i f f}} \tag {13} \\ + \lambda_ {2} \mathcal {L} _ {\text {s i c}} + \lambda_ {3} \mathcal {L} _ {\text {A V M}}, \\ \end{array} +$$ + +where $\widehat{\mathrm{HELBO}}(X, y, \theta, \phi)$ indicates the lower bound for our proposed ECMVAE optimization, which is defined in detail in Eq. (8) and Eq. (6). We use a weighted structure-aware function [70] to compute the hybrid reconstruction part in $\widehat{\mathrm{HELBO}}(X, y, \theta, \phi)$ . $\mathcal{L}_{\mathrm{diff}}$ and $\mathcal{L}_{\mathrm{sic}}$ are the orthogonality constraint and the shared-information completeness loss defined in Eq. (9) and Eq. (12). $\mathcal{L}_{\mathrm{AVM}}$ indicates the audio-visual mapping loss proposed by [1] as a regularization term to promote the similarity between the audio-visual features. Empirically, we set the hyper-parameters $\{\lambda_1, \lambda_2, \lambda_3\}$ as $\{0.001, 0.01, 0.5\}$ for balanced training. + +# 4. Experimental Results + +# 4.1. Implementation Details + +Datasets. We conduct experiments on the AVSBench [1] dataset, which contains 5,356 video sequences with corresponding audio data and binary per-pixel annotations. Each video in the dataset contains five frames, extracted separately from a five-second video, where the audio length is also five seconds. This dataset contains two settings, named S4 and MS3, for semi-supervised Single Sound Source Segmentation with only the first frame labeled, and fully supervised Multiple Sound Source Segmentation with all frames labeled. The evaluation is done for the entire five frames of the video under both S4 and MS3 settings on the test set. + +Table 1. Quantitative results on the AVSBench dataset [1] in terms of mIOU and F-score under S4 and MS3 settings. We both report the performance with R50 and PVT as a backbone for the results of AVSBench [1] and Ours. + +
MethodsS4MS3
mIoUF-scoremIoUF-score
VOS3DC [71]57.100.75936.920.503
SST [72]66.290.80142.570.572
SODiGAN [73]61.590.77842.890.544
LGVT [74]74.940.87340.710.593
AVSAVSBench (R50) [1]72.790.84847.880.578
AVSBench (PVT) [1]78.740.87954.000.645
Ours (R50)76.330.86548.690.607
Ours (PVT)81.740.90157.840.708
+ +Training Details. We conduct experiments on Pytorch [75] with a single NVIDIA A100 GPU. The Adam [76] solver is used to optimize our network with a learning rate of $1 \times 10^{-4}$ . The training batch size is set to 4. We train the network on the S4 subset for 15 epochs, and on the MS3 subset for 30 epochs. For the MS3 setting, we use all ground-truth of the five frames to build the posterior latent space of our model. While for S4, we repeat the ground-truth of the first frame five times to build the posterior latent space. + +# 4.2. Comparison with Baseline Methods + +Quantitative Comparison. Follow the comparison settings with AVSBench [1], we compare the performance of our ECMVAE with baseline AVS models and other related tasks, including video object segmentation (VOS) and salient object detection (SOD). The performance on Mean Intersection over Union (mIoU) and F-score is reported in Table 1. It can be observed that our method consistently achieves significantly superior segmentation performance than the state-of-the-art methods, especially with 3.00 and 3.84 higher mIoU than the previous AVS method [1], at the S4 and MS3 settings with PVTv2 ("PVT") backbone. There is also a consistent performance improvement with ResNet ("R50") backbone. The performance gain comes from our designed multimodal VAE with explicit constraints for representation learning. Our method also significantly outperforms the VOS and SOD methods, demonstrating the addition of audio information to the segmentation performance. Qualitative Comparison. We provide a qualitative comparison between our proposed method and [1] in Fig. 2. Our proposed ECMVAE provides a better audio temporal and spatial localization quality, leading to better segmentation performance, especially for the left samples, in localization of the piano keys, which is not salient but producing a sound in this scene. Our method also achieves better segmentation performance for background noise handling and richer foreground details in the right samples in Fig. 2. + +![](images/49a967a2442e76bb33d505ac530cc407fd96dfce94ef8516ba234d92e7af9330.jpg) +Figure 2. Qualitative comparison between our proposed ECMVAE and AVSBench [1]. Our method competently achieves high segmentation performance with better audio temporal and spatial localization quality and detail handling. + +# 4.3. Ablation Studies + +We conduct ablation studies of our proposed method. All variations are trained with the PVT backbone. + +Table 2. Ablation of the VAE based multimodal learning. We implement a "CVAE" without audio and "CMVAE" with audio-visual joint distribution estimation. + +
MethodsS4MS3
mIoUF-scoremIoUF-score
[1] w/o audio77.80-48.20-
CVAE78.120.87849.260.643
CMVAE80.050.88954.990.653
+ +Multimodal VAE. We explore the effectiveness of the Multimodal VAE in Table 2. Firstly, we remove the audio part of the model and disable the TPAVI module to explore the importance of the audio information, leading to a simple unimodal CVAE [29] framework with only video input, which is denoted as "CVAE". For comparison, we implement a "CMVAE" using the audio signal but without the latent space factorization and our proposed constraints. The better performance of "CMVAE" compared with "CVAE" indicates the importance of audio for AVS, especially when multiple sound sources exist. We also brought the ablation result of the model without the audio input from [1] and compare it with "CVAE". The results show that in the absence of audio signals, the VAE structure can still improve segmentation performance, due to the ability of VAE to model the latent space of visual features. + +Latent Space Factorization. As described in Sec. 3.2, we factorize the latent space of multimodal VAE into modality-shared $(c)$ and modality-specific $(s^v$ and $s^a)$ representations. As reported in Table 3, removing the latent space + +Table 3. Ablation of the latent space factorization. "Model" indicates using VAE for latent factorization or using AE for feature factorization. "Factor." denotes whether using factorization. "dim." represents the size of the latent dimensions. + +
ModelFactor.dim.S4MS3
mIoUF-scoremIoUF-score
VAE-1680.050.88954.990.653
-4880.130.89055.090.657
✓1680.780.89356.380.676
AE--78.740.87954.000.645
✓-78.920.88154.820.651
+ +factorization leads to obvious performance degradation. We also train a non-factorized model with $2 \times$ larger latent dimensions, which holds comparable latent space capacities with the factorized model. It can be seen that the performance gain from the larger latent space dimensions is not as obvious as the factorization strategy. Further, we compare feature factorization ("AE") on the feature space of [1] with our proposed latent space factorization ("VAE"). Table 3 shows that only performing factorization on a semantic meaningful and continuous latent space, i.e. via using VAE [2], can achieve larger performance improvements. + +JS Divergence. We conduct experiments of PoE and MoE with KL divergence to show the trade-off of JS divergence between the computational efficiency of the inference process and the predictive quality of the generation process. The performance in Table 4 shows the effectiveness of JS divergence on both S4 and MS3 settings. Note that, "PoE", "MoE" and "JS" are based on our formulation of the task, which has not been explored in the AVS area. + +Orthogonality Constraint. As reported in Table 5, the or + +![](images/f5a2dc69582dcdc3f04f63a395ba96e9c239ef1a036267b65f6ffdc357bcc028.jpg) +(a) Base Factorization + +![](images/a89d1d8f8cf1e0077e0c2adf494c536f0735ca0cb0801c5c78a984945c364a89.jpg) +(b) With $\mathcal{L}_{\mathrm{diff}}$ + +![](images/01880b0c2b409f6f8e87696cff7d6daa28730d224bfe9f6a4d540dc1c39bb6ae.jpg) + +![](images/5b5fd72b0100ccc1a09ac35373c0b9526bc43c31b79b6b0acd3738bf1e4ae45e.jpg) +(d) With $\mathcal{L}_{\mathrm{diff}},\mathcal{L}_{\mathrm{sic}}$ + +![](images/2c81e795892e7fcc07efcd6e6c19ee93929c21b57715a5f43a7e276630b0c15b.jpg) +(c) With $\mathcal{L}_{\mathrm{sic}}$ +Figure 3. Visualization of the modality-shared and modality-specific latent codes $(s^v, s^a, c)$ in the MS3 testing set using t-SNE [77] projections. Best viewed on screen. + +Table 4. Ablation of the JS Divergence. We implement "PoE" and "MoE" with KL divergence, and a simple "KL" model. + +
MethodsS4MS3
mIoUF-scoremIoUF-score
KL80.780.89356.380.676
PoE81.380.89457.350.688
MoE81.490.89757.530.694
JS81.740.90157.840.708
+ +Table 5. Ablation of the latent space constraints. $\mathcal{L}_{\mathrm{diff}}$ , $\mathcal{L}_{\mathrm{sic}}$ indicate our proposed loss functions for multimodal learning. + +
\(\mathcal{L}_{diff}\)\(\mathcal{L}_{sic}\)S4MS3
mIoUF-scoremIoUF-score
--81.090.89557.010.684
✓-81.510.89957.650.692
-✓81.470.89857.510.694
✓✓81.740.90157.840.708
+ +thogonality constraint provides $0.64\mathrm{mIOU}$ gain under the MS3 setting, which facilitates the latent space factorization. We also perform t-SNE [77] projection to visualize the factorized latent code with and without such constraint. As compared between Fig. 3 (a) and (b), the three latent codes in the latent space are divided into different subspaces to ensure that each latent code encodes different information. + +Mutual Information Maximization. As compared in Table 5, the mutual information maximization by $\mathcal{L}_{\mathrm{sic}}$ also serves a crucial impact for the explicit constraint of the shared latent space and improves the mIOU from 57.51 to 57.84. Since the $\mathcal{L}_{\mathrm{sic}}$ maximizes the mutual information between $sc^v$ and $sc^a$ , which are fused from the factorization latent codes $s^v, s^a, c$ . This increases the amount of information contained in latent space and makes it more effective for facilitating factorization. Fig. 3 also confirms this view and demonstrates the effectiveness of $\mathcal{L}_{\mathrm{sic}}$ in achieving effective "multi-view" representation learning [56, 57, 62]. + +# 4.4. Analysis + +Pre-training on the Single-source Subset. In AVS-Bench [1], they conducted experiments by initializing + +model parameters by pre-training on S4 dataset. We also perform experiments with such setting (see Table 6). We can observe that both our method and AVSBench [1] can benefit from the model pre-trained on S4. The PVT-based model can gain $2.97\%$ mIOU performance by such a strategy and reach $60.81\%$ mIOU. The pre-training strategy can bring more significant improvements ( $8.87\%$ mIOU) to ResNet50-based models and reach $57.56\%$ mIOU, which is even higher than PVT-based models ( $57.34\%$ ). + +Table 6. Performance comparison with different initialization strategies for MS3 dataset. As AVSBench [1] does not report its F-score in the paper, we only report its mIOU. The values in parentheses indicate the performance improvement based on S4 pre-training compared with training from scratch. + +
MethodsFrom scratchPre-trained on S4
mIoUF-scoremIoUF-score
AVSbench (R50) [1]47.88-54.33 (↑ 6.45)-
AVSbench (PVT) [1]54.00-57.34 (↑ 3.34)-
Ours (R50)48.690.60757.56 (↑ 8.87)0.674
Ours (PVT)57.840.70860.81 (↑ 2.97)0.729
+ +Table 7. Parameters and inference time. + +
MethodsR50PVT
Param. (M)Time (ms)Param. (M)Time (ms)
AVSBench [1]70.5028101.3253
Ours33.972391.1846
+ +Parameters and Efficiency. In Table 7, we compare the parameters and inference time between ours and AVSBench. Note that although posterior nets and prior nets are used in our framework, as all the latent space encoders are quite lightweight (1M), thus our model capacity will not change significantly. Moreover, we replace the neck from ASPP [78] to one-layer convolution and reduce the number of neck channels from 256 to 128, which leads to smaller parameter numbers and faster inference speed. + +Limitations. Similar to the other VAE [2] based solutions, our model also suffers from the risk of posterior collapse, where the posterior of the latent variable is equal to + +prior [79,80], making $y$ in our case not encoded in the latent variables. To avoid such phenomenon, contrastive learning [81, 82] can be studied to learn more compact features of each modality or score based diffusion models [83-86] can be investigated for more informative latent space. + +# 5. Conclusion + +We have worked on audio-visual segmentation (AVS), aiming to segment the sound producers of the scene. As audio data can be treated as "command", we argue extensive exploration of audio is critical for effective AVS. Inspired by this observation, we have introduced an Explicit Conditional Multimodal Variational Auto-Encoder (ECMVAE) for an audio-visual segmentation model with latent space factorization with explicit constraints to extensively explore the shared and specific representations of audio and visual data. Extensive experimental results verify the effectiveness of our proposed framework. Although we focused on AVS with two modalities, the proposed framework can be extended to more modalities and other audio-visual collaboration tasks [6, 13, 14]. + +# 6. Acknowledgments + +This research was supported in part by the National Natural Science Foundation of China (62271410), and the Fundamental Research Funds for the Central Universities. + +# References + +[1] Jinxing Zhou, Jianyuan Wang, Jiayi Zhang, Weixuan Sun, Jing Zhang, Stan Birchfield, Dan Guo, Lingpeng Kong, Meng Wang, and Yiran Zhong. Audio-visual segmentation. In European Conference on Computer Vision (ECCV), 2022. 1, 2, 3, 5, 6, 7, 8 +[2] Diederik Kingma and Max Welling. Auto-encoding variational bayes. In International Conference on Learning Representations (ICLR), 2014. 1, 2, 3, 7, 8 +[3] Mike Wu and Noah Goodman. Multimodal generative models for scalable weakly-supervised learning. In Advances in Neural Information Processing Systems (NeurIPS), 2018. 2 +[4] Thomas M. Sutter, Imant Daunhawer, and Julia E. Vogt. Multimodal generative learning utilizing jensen-shannon-divergence. 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Existing AVS methods focus on implicit feature fusion strategies, where models are trained to fit the discrete samples in the dataset. With a limited and less diverse dataset, the resulting performance is usually unsatisfactory. In contrast, we address this problem from an effective representation learning perspective, aiming to model the contribution of each modality explicitly. Specifically, we find that audio contains critical category information of the sound producers, and visual data provides candidate sound producer(s). Their shared information corresponds to the target sound producer(s) shown in the visual data. In this case, cross-modal shared representation learning is especially important for AVS. To achieve this, our ECMVAE factorizes the representations of each modality with a modality-shared representation and a modality-specific representation. An orthogonality constraint is applied between the shared and specific representations to maintain the exclusive attribute of the factorized latent code. Further, a mutual information maximization regularizer is introduced to achieve extensive exploration of each modality. Quantitative and qualitative evaluations on the AVSBench demonstrate the effectiveness of our approach, leading to a new state-of-the-art for AVS, with a 3.84 mIOU performance leap on the challenging MS3 subset for multiple sound source segmentation." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 609, + 128, + 621 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 609, + 128, + 621 + ], + "spans": [ + { + "bbox": [ + 47, + 609, + 128, + 621 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 629, + 287, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 629, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 46, + 629, + 287, + 677 + ], + "type": "text", + "content": "Audio-visual data can work collaboratively towards a better perception of the scene. The audio-visual segmentation (AVS) [1] task aims to segment the objects from the video sequence that producing the sound in the audio. On" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 306, + 228, + 546, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 228, + 546, + 348 + ], + "spans": [ + { + "bbox": [ + 306, + 228, + 546, + 348 + ], + "type": "text", + "content": "the one hand, the audio data provides category information for the localization of the object in the video. On the other hand, the visual data provides a sound producer pool with precise structure information of the foreground (sound producer(s)). Different from conventional multimodal settings, where each modality can be used individually for the target task, audio in AVS task serves as \"command\" to localize and segment the sound producer(s) from the visual data. In this case, the contribution of audio should be extensively explored for accurate foreground segmentation." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 350, + 546, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 350, + 546, + 566 + ], + "spans": [ + { + "bbox": [ + 304, + 350, + 546, + 566 + ], + "type": "text", + "content": "The baseline model [1] focuses on implicit feature fusion via audio-visual cross attention. It purely relies on fitting the discrete samples in the dataset. Although reasonable performance is obtained, there are no constraints to guarantee the contribution of each modality, making it hard to decide if the audio data is effectively used, as the model can directly regress the final segmentation maps by only taking the video as input. Fortunately, we discover that each modality for AVS contains both shared and specific information. For example, the audio data includes both the information from the sound producers and the background noise, while the visual data shows the appearance of the entire scene, where the sound producers only take a small portion of it. In our specific task setting, we find modality factorization is suitable to model both the modality-shared representation, i.e. information of the sound producers, and the modality-specific representation toward a better understanding of the contribution of each modality." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 567, + 547, + 687 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 567, + 547, + 687 + ], + "spans": [ + { + "bbox": [ + 304, + 567, + 547, + 687 + ], + "type": "text", + "content": "The straightforward solution to learn the feature representation of the input data is through an auto-encoder (AE) framework. However, AE is mainly used for data compression, as the learned feature space is not continuous, which cannot provide a rich semantic correlation of the data. Differently, with latent space regularization, e.g. the latent space is assumed to be Gaussian in variational autoencoder (VAE) [2], VAE obtains semantic meaningful latent space, which is continuous, and it is also the basic requirement for reliable latent space factorization." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 305, + 689, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 547, + 714 + ], + "type": "text", + "content": "To learn the semantic correlated feature representation of the AVS data, we propose an Explicit Conditional Mul" + } + ] + } + ], + "index": 14 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 61, + 683, + 246, + 693 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 683, + 246, + 693 + ], + "spans": [ + { + "bbox": [ + 61, + 683, + 246, + 693 + ], + "type": "text", + "content": "† Corresponding author (daiyuchao@gmail.com)." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 693, + 287, + 713 + ], + "type": "text", + "content": "This work was done when Yuxin Mao was an intern at Shanghai AI Laboratory." + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 297, + 748, + 313, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 748, + 313, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 748, + 313, + 757 + ], + "type": "text", + "content": "954" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 286, + 179 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 286, + 179 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 286, + 179 + ], + "type": "text", + "content": "timodal Variational Auto-Encoder (ECMVAE) for audiovisual segmentation to learn both the shared and the specific representation in the latent space of each modality. Our model is built upon a multimodal variational autoencoder [3, 4], with the Jensen-Shannon divergence to achieve a trade-off between sampling efficiency and sample quality. Based on the latent space factorization, we impose constraints for the shared and specific representations to explicitly maximize the contribution of each modality." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 180, + 286, + 395 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 180, + 286, + 395 + ], + "spans": [ + { + "bbox": [ + 46, + 180, + 286, + 395 + ], + "type": "text", + "content": "Specifically, we first assume that one latent code of the factorized representation should contain independent information compared to others. Furthermore, for the fused representation, we further claim that it should be more informative for the target task compared with each modality. To achieve the former, we propose an information orthogonality constraint between the factorized representations of each modality to ensure that the modality-shared and modality-specific representations capture different aspects of the audio-visual input. For the latter, we fuse the factorized representations of each modality to construct a fused space. Then we introduce a mutual information maximization regularizer between the fused representations of each modality to extensively explore the contribution of each modality. Extensive experimental results demonstrate that our ECMVAE achieves state-of-the-art AVS performance. Our pipeline achieves a " + }, + { + "bbox": [ + 46, + 180, + 286, + 395 + ], + "type": "inline_equation", + "content": "3.84\\mathrm{mIOU}" + }, + { + "bbox": [ + 46, + 180, + 286, + 395 + ], + "type": "text", + "content": " improvement for the challenging multiple sound source segmentation." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 59, + 396, + 228, + 406 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 59, + 396, + 228, + 406 + ], + "spans": [ + { + "bbox": [ + 59, + 396, + 228, + 406 + ], + "type": "text", + "content": "We summarize our main contributions as:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 407, + 286, + 550 + ], + "type": "list", + "angle": 0, + "index": 6, + "blocks": [ + { + "bbox": [ + 58, + 407, + 286, + 455 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 407, + 286, + 455 + ], + "spans": [ + { + "bbox": [ + 58, + 407, + 286, + 455 + ], + "type": "text", + "content": "- An explicit semantic correlated feature representation learning framework for audio-visual segmentation is proposed with latent space factorization to capture both the modality-shared and specific representations." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 58, + 456, + 286, + 514 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 456, + 286, + 514 + ], + "spans": [ + { + "bbox": [ + 58, + 456, + 286, + 514 + ], + "type": "text", + "content": "- Based on the latent space factorization, we introduce a unimodal orthogonality constraint between the shared and specific representations and the cross-modal mutual-information maximization regularizer to extensively explore the contribution of each modality." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 58, + 515, + 286, + 550 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 515, + 286, + 550 + ], + "spans": [ + { + "bbox": [ + 58, + 515, + 286, + 550 + ], + "type": "text", + "content": "- State-of-the-art segmentation performance is achieved, showing both the effectiveness of each module and the contribution of each modality." + } + ] + } + ], + "index": 5 + } + ], + "sub_type": "text" + }, + { + "bbox": [ + 47, + 562, + 134, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 562, + 134, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 562, + 134, + 574 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 286, + 713 + ], + "type": "text", + "content": "Audio-Visual Segmentation. The Audio-Visual Segmentation (AVS) task is newly proposed, aiming to localize the sound producers with pixel-wise segmentation masks. Zhou et al. [1] propose an AVSBench dataset for audio-visual segmentation and provide a simple baseline based on temporal pixel-wise audio-visual interaction (TPAVI), which is a cross-modal attention [5] based fusion strategy. The other audio-visual collaboration tasks can be classified as audio-visual correspondence (AVC) [6, 7], event localization (AVEL) [8-13], event parsing (AVP) [14-16], etc. These methods require the fusion of audio and visual sig" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 192 + ], + "type": "text", + "content": "nals. Such as audio-visual similarity modeling by computing the correlation matrix [6, 7], audio-visual cross attention [12, 13, 17], audio-guided Grad-CAM [18], or using a multimodal transformer for modeling the long-range dependencies between elements across modalities directly [19, 20]. However, the challenge and uniqueness of the AVS task are how to map the audio signals to fine-grained visual cues, i.e. per-pixel segmentation maps. This will rely on reliable modeling of visual and audio signals, as well as more effective fusion strategies." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 195, + 545, + 459 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 195, + 545, + 459 + ], + "spans": [ + { + "bbox": [ + 304, + 195, + 545, + 459 + ], + "type": "text", + "content": "Multimodal Variational Auto-encoders. The Multimodal Variational Auto-encoders (MVAEs) [3, 21–24] are a type of latent variable generative model to learn more generalizable representations from diverse modalities. To achieve this, the core of MVAE is the joint distribution estimation. The conventional unimodal VAEs [2, 25] are optimized by maximizing the evidence lower bound (ELBO), which includes a reconstruction term and the Kullback-Leibler (KL) divergence term to measure the divergence from the variational posterior to the prior distribution of the latent variable. In a multimodal setting, the KL divergence is defined between the joint posterior and joint prior across the modalities, which is often estimated by the product of experts (PoE) [26, 27] or the mixture of experts (MoE) [28]. Based on such a prerequisite, many works extend the basic MVAE definition, such as missing modality handling [24], latent space modeling [23, 28], effective divergence modeling [4], etc. However, previous MVAE based frameworks essentially focus on the multimodal image generation task. In this work, we bring the MVAE to the AVS task and propose the conditional version [25, 29] of MVAE with practical multimodal information constraints for segmentation." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "content": "Mutual Information Estimation. Mutual Information (MI) captures the nonlinear statistical dependencies between variables, acting as a measure of actual dependence [30]. Specifically, for a pair of random variables " + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "content": ", their MI " + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "inline_equation", + "content": "I(X;Y)" + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "content": " is defined as the KL divergence of the joint distribution " + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "inline_equation", + "content": "p_{(X,Y)}" + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "content": " from the product of the marginal distributions " + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "inline_equation", + "content": "p(X)" + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "inline_equation", + "content": "p(Y)" + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "content": ", which measures the shared information between " + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "inline_equation", + "content": "Y" + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "content": ". Although mutual information is simple in formation, as the log density ratio between the joint distribution " + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "inline_equation", + "content": "p_{(X,Y)}" + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "content": " and product of marginals " + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "inline_equation", + "content": "p(X)\\otimes p(Y)" + }, + { + "bbox": [ + 304, + 462, + 545, + 713 + ], + "type": "text", + "content": " is intractable, it is usually estimated [31-33] instead of computed directly, leading to both MI maximization with a lower bound [34, 35] and MI minimization with an upper bound [36]. The MI maximization is usually applied for effective self-supervised representation learning [37-41] for the unimodal data to guarantee reliable feature representation. For the multimodal tasks, when each modality of data contains partial information of the target, both MI maximization and minimization can be applied [42-50], where the former aims to explore the taskdriven feature across the modalities, and the latter is de" + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "text", + "content": "955" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": "signed to explore the complementary information of different modalities. Extensive researches show that effective MI optimization can not only lead to informative representation learning [51-58] but also is beneficial for achieving adversarial robustness [59]." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 144, + 280, + 159 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 144, + 280, + 159 + ], + "spans": [ + { + "bbox": [ + 47, + 144, + 280, + 159 + ], + "type": "text", + "content": "3. Explicit Conditional Multimodal Learning" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "spans": [ + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "text", + "content": "We denote the input data of our used AVSbench dataset [1] is " + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "inline_equation", + "content": "X = \\{\\{x_{t}^{v}\\}_{t=1}^{T}, x^{a}\\}" + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "text", + "content": ", i.e. the visual " + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "inline_equation", + "content": "\\{x_{t}^{v}\\}_{t=1}^{T}" + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "inline_equation", + "content": "T" + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "text", + "content": " non-overlapping yet continuous frames, audio " + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "inline_equation", + "content": "x^{a}" + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "text", + "content": " of the current clip. " + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "inline_equation", + "content": "y = \\{y_{t}\\}_{t=1}^{T}" + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "text", + "content": " is the output, i.e. the segmentation maps (we omit " + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "inline_equation", + "content": "t" + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "text", + "content": " for clear presentation). The goal of audio-visual segmentation is to segment the objects from the video " + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "inline_equation", + "content": "\\{x_{t}^{v}\\}_{t=1}^{T}" + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "text", + "content": " that produce the sound shown in the audio " + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "inline_equation", + "content": "x^{a}" + }, + { + "bbox": [ + 46, + 164, + 288, + 332 + ], + "type": "text", + "content": ". We introduce an Explicit Conditional Multi-modal Variational Auto-Encoder (ECMVAE) using Jensen-Shannon divergence (Sec. 3.1) via latent space factorization (Sec. 3.2) to effectively model the shared representation between the two modalities (Sec. 3.3 and Sec. 3.4) for audio-visual segmentation. The overview of the proposed ECMVAE is shown in Fig. 1." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 340, + 127, + 353 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 340, + 127, + 353 + ], + "spans": [ + { + "bbox": [ + 47, + 340, + 127, + 353 + ], + "type": "text", + "content": "3.1. Prerequisite" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "spans": [ + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": "Conditional Variational Auto-encoder. We begin our prerequisite with the definition of the conditional variational auto-encoder (CVAE) [2, 25], which contains a generative process and an inference process. The generative process is to draw the latent variable " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": " from the prior distribution " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "p_{\\theta}(z|X)" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": " with a given " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": ", and generate the output via " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "p_{\\theta}(y|X,z)" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": ", where in our case " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": " in the following derivations are " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "X = \\{\\{x_t^v\\}_{t=1}^T, x^a\\}" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "y = \\{y_t\\}_{t=1}^T" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": ", respectively. The inference process of CVAE aims to infer the informative values of the latent variable " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": " given the observed data " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": " by computing the posterior " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "p_{\\theta}(z|X,y)" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": ", which is intractable and usually approximated with the variational posterior " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "q_{\\phi}(z|X,y)" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "\\phi" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": " are the parameters of the true posterior and the approximated variational posterior, respectively. CVAE is trained to find the optimal generation parameters " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "\\theta^*" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": " and inference parameters " + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "inline_equation", + "content": "\\phi^*" + }, + { + "bbox": [ + 46, + 359, + 287, + 563 + ], + "type": "text", + "content": " following the maximum log-likelihood learning pipeline:" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 97, + 573, + 287, + 591 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 573, + 287, + 591 + ], + "spans": [ + { + "bbox": [ + 97, + 573, + 287, + 591 + ], + "type": "interline_equation", + "content": "\\left\\{\\theta^ {*}, \\phi^ {*} \\right\\} = \\underset {\\theta , \\phi} {\\arg \\max } \\log p _ {\\theta} (y | X), \\tag {1}", + "image_path": "97b119f4f2ad71cabdfa794ad0e37aaaf8d293d76c7453251c83960bb949d858.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 601, + 229, + 613 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 601, + 229, + 613 + ], + "spans": [ + { + "bbox": [ + 47, + 601, + 229, + 613 + ], + "type": "text", + "content": "where the log-likelihood term is achieved as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 50, + 624, + 288, + 693 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 50, + 624, + 288, + 693 + ], + "spans": [ + { + "bbox": [ + 50, + 624, + 288, + 693 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\log p _ {\\theta} (y | X) \\\\ = \\underbrace {\\mathbb {E} _ {q _ {\\phi} (z | X , y)} \\log p _ {\\theta} (y | X , z) - D _ {K L} (q _ {\\phi} (z | X , y) \\| p _ {\\theta} (z | X))} _ {\\text {E L B O} (X, y, \\theta , \\phi)} \\\\ + D _ {\\mathrm {K L}} \\left(q _ {\\phi} (z | X, y) \\| p _ {\\theta} (z | X, y)\\right). \\tag {2} \\\\ \\end{array}", + "image_path": "03816daff247c0460962dd294a2c5b05667c439b3b16209eed4328451f81b88e.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": "By Jensen's inequality, the Kullback-Leibler (KL) divergence term " + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "(D_{KL})" + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": " in Eq. (2) is always greater or equal to zero, thus maximizing " + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "\\log p_{\\theta}(y|X)" + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": " can be achieved by maximizing the evidence lower bound " + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "inline_equation", + "content": "\\operatorname{ELBO}(X,y,\\theta,\\phi)" + }, + { + "bbox": [ + 305, + 72, + 545, + 120 + ], + "type": "text", + "content": ":" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 347, + 134, + 545, + 174 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 347, + 134, + 545, + 174 + ], + "spans": [ + { + "bbox": [ + 347, + 134, + 545, + 174 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\left\\{\\theta^ {*}, \\phi^ {*} \\right\\} = \\arg \\max _ {\\theta , \\phi} \\log p _ {\\theta} (y | X) \\\\ = \\arg \\max _ {\\theta , \\phi} \\operatorname {E L B O} (X, y, \\theta , \\phi). \\tag {3} \\\\ \\end{array}", + "image_path": "b902b52c9fc304a20db8b0c9e52053120d526f5dbaa762c0bfb3765c628003d5.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 189, + 545, + 225 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 189, + 545, + 225 + ], + "spans": [ + { + "bbox": [ + 304, + 189, + 545, + 225 + ], + "type": "text", + "content": "With the reparameterization trick [2], the KL term in " + }, + { + "bbox": [ + 304, + 189, + 545, + 225 + ], + "type": "inline_equation", + "content": "\\mathrm{ELBO}(X,y,\\theta ,\\phi)" + }, + { + "bbox": [ + 304, + 189, + 545, + 225 + ], + "type": "text", + "content": " can be solved in closed-form if both the prior " + }, + { + "bbox": [ + 304, + 189, + 545, + 225 + ], + "type": "inline_equation", + "content": "p_{\\theta}(z|X)" + }, + { + "bbox": [ + 304, + 189, + 545, + 225 + ], + "type": "text", + "content": " and posterior " + }, + { + "bbox": [ + 304, + 189, + 545, + 225 + ], + "type": "inline_equation", + "content": "q_{\\phi}(z|X,y)" + }, + { + "bbox": [ + 304, + 189, + 545, + 225 + ], + "type": "text", + "content": " are Gaussian." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 227, + 546, + 466 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 227, + 546, + 466 + ], + "spans": [ + { + "bbox": [ + 304, + 227, + 546, + 466 + ], + "type": "text", + "content": "Multimodal Conditional Variational Auto-encoder. For the unimodal setting, both " + }, + { + "bbox": [ + 304, + 227, + 546, + 466 + ], + "type": "inline_equation", + "content": "p_{\\theta}(z|X)" + }, + { + "bbox": [ + 304, + 227, + 546, + 466 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 227, + 546, + 466 + ], + "type": "inline_equation", + "content": "q_{\\phi}(z|X,y)" + }, + { + "bbox": [ + 304, + 227, + 546, + 466 + ], + "type": "text", + "content": " can be obtained via the reparameterization trick [2], leading to closed-form solution of the KL divergence as both " + }, + { + "bbox": [ + 304, + 227, + 546, + 466 + ], + "type": "inline_equation", + "content": "p_{\\theta}(z|X)" + }, + { + "bbox": [ + 304, + 227, + 546, + 466 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 227, + 546, + 466 + ], + "type": "inline_equation", + "content": "q_{\\phi}(z|X,y)" + }, + { + "bbox": [ + 304, + 227, + 546, + 466 + ], + "type": "text", + "content": " are Gaussian. For the multimodal AVS data, the joint posterior and joint prior need to be estimated before we perform the joint generation process. The conventional solution to model the joint distribution is through the product of experts (PoE) [26, 27] or the mixture of experts (MoE) [28]. For the former, the joint distribution is defined as the product of each individual expert, which is Gaussian when each expert is Gaussian, leading to closed form KL computation. However, for PoE, less accurate modeling of one expert will completely destroy the joint distribution modeling. Further, PoE shows limitations in modeling the unimodal contribution due to its multiplicative nature. The additive nature of the MoE makes it effective for the optimization of each individual expert. However, as no closed form exists for the KL term, importance sampling (IS) is usually needed, which is computationally less efficient." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 468, + 545, + 528 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 468, + 545, + 528 + ], + "spans": [ + { + "bbox": [ + 304, + 468, + 545, + 528 + ], + "type": "text", + "content": "JS Divergence Instead of KL Divergence. Although MoE is computationally less efficient compared with PoE, its individual modal contribution modeling is attractive. Based on MoE, the " + }, + { + "bbox": [ + 304, + 468, + 545, + 528 + ], + "type": "inline_equation", + "content": "D_{KL}" + }, + { + "bbox": [ + 304, + 468, + 545, + 528 + ], + "type": "text", + "content": " term within " + }, + { + "bbox": [ + 304, + 468, + 545, + 528 + ], + "type": "inline_equation", + "content": "\\mathrm{ELBO}(X,y,\\theta ,\\phi)" + }, + { + "bbox": [ + 304, + 468, + 545, + 528 + ], + "type": "text", + "content": " of Eq. (2) is the lower bound of the weighted sum of individual KLs:" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 345, + 542, + 545, + 590 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 345, + 542, + 545, + 590 + ], + "spans": [ + { + "bbox": [ + 345, + 542, + 545, + 590 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} D _ {K L} \\left(q _ {\\phi} (z | X, y) \\| p _ {\\theta} (z | X)\\right) \\\\ \\leq \\sum_ {k = 1} ^ {K} \\phi_ {k} D _ {K L} \\left(q _ {\\phi_ {k}} \\left(z \\mid x ^ {k}, y\\right) \\| p _ {\\theta} \\left(z \\mid x ^ {k}\\right)\\right). \\tag {4} \\\\ \\end{array}", + "image_path": "3347464c0b37178a158cb6c1b187aada86a6333ab1cdb7b9d7e7c664550b1cd2.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 603, + 545, + 686 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 603, + 545, + 686 + ], + "spans": [ + { + "bbox": [ + 304, + 603, + 545, + 686 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 603, + 545, + 686 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 603, + 545, + 686 + ], + "type": "text", + "content": " is the number of modalities, and " + }, + { + "bbox": [ + 304, + 603, + 545, + 686 + ], + "type": "inline_equation", + "content": "\\sum_{k}\\phi_{k} = 1" + }, + { + "bbox": [ + 304, + 603, + 545, + 686 + ], + "type": "text", + "content": ". Although Eq. (4) is effective in providing lower bound with individual modal's distribution for ELBO in Eq. (2), no joint distribution is involved. Following [4], a dynamic prior " + }, + { + "bbox": [ + 304, + 603, + 545, + 686 + ], + "type": "inline_equation", + "content": "f_{K}" + }, + { + "bbox": [ + 304, + 603, + 545, + 686 + ], + "type": "text", + "content": " is introduced, which is the mixture of the involved arguments (individual priors and posteriors), i.e. " + }, + { + "bbox": [ + 304, + 603, + 545, + 686 + ], + "type": "inline_equation", + "content": "f_{K}" + }, + { + "bbox": [ + 304, + 603, + 545, + 686 + ], + "type": "text", + "content": " can be defined as the arithmetic means as in MoE." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 689, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 689, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 306, + 689, + 545, + 712 + ], + "type": "text", + "content": "With the non-negative nature of KL divergence and the definition of JS divergence, we obtain a new lower bound of" + } + ] + } + ], + "index": 16 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 61, + 703, + 276, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 703, + 276, + 712 + ], + "spans": [ + { + "bbox": [ + 61, + 703, + 276, + 712 + ], + "type": "text", + "content": "Please see the supplementary material for the complete derivation." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 313, + 757 + ], + "type": "text", + "content": "956" + } + ] + } + ], + "index": 17 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 63, + 70, + 534, + 233 + ], + "blocks": [ + { + "bbox": [ + 63, + 70, + 534, + 233 + ], + "lines": [ + { + "bbox": [ + 63, + 70, + 534, + 233 + ], + "spans": [ + { + "bbox": [ + 63, + 70, + 534, + 233 + ], + "type": "image", + "image_path": "b288800dad90817567d768a8e323205ea75651fc5df89c1f0825f78a07879f3f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 246, + 547, + 291 + ], + "lines": [ + { + "bbox": [ + 46, + 246, + 547, + 291 + ], + "spans": [ + { + "bbox": [ + 46, + 246, + 547, + 291 + ], + "type": "text", + "content": "Figure 1. Overview of the proposed ECMVAE for audio-visual segmentation. The feature extractors are used to extract backbone features for the two modalities. We also design three latent encoders " + }, + { + "bbox": [ + 46, + 246, + 547, + 291 + ], + "type": "inline_equation", + "content": "\\phi_{s^v},\\phi_{s^a},\\phi_c" + }, + { + "bbox": [ + 46, + 246, + 547, + 291 + ], + "type": "text", + "content": " to achieve latent space factorization and obtain both task-driven shared representation " + }, + { + "bbox": [ + 46, + 246, + 547, + 291 + ], + "type": "inline_equation", + "content": "(c)" + }, + { + "bbox": [ + 46, + 246, + 547, + 291 + ], + "type": "text", + "content": " and modality-related specific representation " + }, + { + "bbox": [ + 46, + 246, + 547, + 291 + ], + "type": "inline_equation", + "content": "(s^a,s^v)" + }, + { + "bbox": [ + 46, + 246, + 547, + 291 + ], + "type": "text", + "content": ", achieving explicit multimodal representation learning. The decoder is introduced to obtain the final segmentation maps, indicating the sound producers of the audio-visual data." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 304, + 130, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 304, + 130, + 316 + ], + "spans": [ + { + "bbox": [ + 47, + 304, + 130, + 316 + ], + "type": "text", + "content": "ELBO in Eq. (2) as:" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 326, + 294, + 414 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 326, + 294, + 414 + ], + "spans": [ + { + "bbox": [ + 47, + 326, + 294, + 414 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\widehat {\\operatorname {E L B O}} (X, y, \\theta , \\phi) \\geq \\mathbb {E} _ {q _ {\\phi} (z | X, y)} \\log p _ {\\theta} (y | X, z) \\\\ - \\sum_ {k _ {1} = 1} ^ {K} \\pi_ {k _ {1}} D _ {K L} \\left(q _ {\\phi} (z | X, y) \\| f _ {K}\\right) - \\sum_ {k _ {2} = 1} ^ {K} \\pi_ {k _ {2}} D _ {K L} \\left(p _ {\\theta} (z | X) \\| f _ {K}\\right) \\\\ = \\underbrace {\\mathbb {E} _ {q _ {\\phi} (z | X , y)} \\log p _ {\\theta} (y | X , z) - \\operatorname {J S D} \\left(q _ {\\phi} (z | X , y) , p _ {\\theta} (z | X)\\right)} _ {\\widehat {\\text {E L B O}} (X, y, \\theta , \\phi)}, \\tag {5} \\\\ \\end{array}", + "image_path": "5d24cc591b46454feb9b0394d75e34886fec8390a6ebba02754418c05988a064.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 415, + 287, + 464 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 415, + 287, + 464 + ], + "spans": [ + { + "bbox": [ + 46, + 415, + 287, + 464 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 415, + 287, + 464 + ], + "type": "inline_equation", + "content": "\\sum_{k=1}^{2K}\\pi_k = 1" + }, + { + "bbox": [ + 46, + 415, + 287, + 464 + ], + "type": "text", + "content": ", and JSD represents JS divergence. Eq. (5) provides lower bound of ELBO in Eq. (2), namely " + }, + { + "bbox": [ + 46, + 415, + 287, + 464 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathrm{ELBO}}(X,y,\\theta,\\phi)" + }, + { + "bbox": [ + 46, + 415, + 287, + 464 + ], + "type": "text", + "content": ", which is proven more stable for training [4], and robust to noise." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 474, + 196, + 487 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 474, + 196, + 487 + ], + "spans": [ + { + "bbox": [ + 47, + 474, + 196, + 487 + ], + "type": "text", + "content": "3.2. Latent Space Factorization" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "spans": [ + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "text", + "content": "Besides stable training and noise robustness, we are also interested in modeling both shared and specific information of the audio-visual input (see Fig. 1) to fully explore their contribution. For each pair of example " + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "inline_equation", + "content": "(x^{k},y)" + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "inline_equation", + "content": "x^{k}\\in \\{\\{x_{t}^{v}\\}_{t = 1}^{T},x^{a}\\}" + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "text", + "content": " indexes the modalities with " + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "inline_equation", + "content": "K = 2" + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "text", + "content": " in this paper, we factorize the latent space " + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "inline_equation", + "content": "z" + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "text", + "content": " into a modality-shared latent code " + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "inline_equation", + "content": "c" + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "text", + "content": " and modality-specific latent codes " + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "inline_equation", + "content": "s^a,s^v" + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "text", + "content": ". Then " + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathrm{ELBO}} (X,y,\\theta ,\\phi)" + }, + { + "bbox": [ + 46, + 493, + 287, + 591 + ], + "type": "text", + "content": " is re-defined as:" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 56, + 601, + 287, + 693 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 56, + 601, + 287, + 693 + ], + "spans": [ + { + "bbox": [ + 56, + 601, + 287, + 693 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\widehat {\\mathrm {E L B O}} (X, y, \\theta , \\phi) \\\\ = \\sum_ {k = 1} ^ {K} \\mathbb {E} _ {q _ {\\phi_ {c}} (c | X, y)} \\left[ \\mathbb {E} _ {q _ {\\phi_ {s} k} (s ^ {k} | x ^ {k}, y)} \\left[ \\log p _ {\\theta} \\left(y \\mid x ^ {k}, s ^ {k}, c\\right) \\right] \\right] \\tag {6} \\\\ - \\beta \\sum_ {k = 1} ^ {K} D _ {K L} \\left(q _ {\\phi_ {s k}} \\left(s ^ {k} \\mid x ^ {k}, y\\right) \\mid p _ {\\theta} \\left(s ^ {k} \\mid x ^ {k}\\right)\\right) \\\\ - \\beta \\mathrm {J S D} \\left(q _ {\\phi_ {c}} (c | X, y), p _ {\\theta} (c | X)\\right), \\\\ \\end{array}", + "image_path": "0949b368665aa23b3a2a8bfb64b6487da7196cf266df6171f7a74485b579a1d4.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "spans": [ + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "inline_equation", + "content": "q_{\\phi_c}(c|X,y)" + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "inline_equation", + "content": "p_{\\theta}(c|X)" + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "text", + "content": " are the posterior and prior distributions of the shared representation. " + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "inline_equation", + "content": "q_{\\phi_{s^k}}(s^k |x^k,y)" + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "inline_equation", + "content": "p_{\\theta_{s^k}}(s^k |x^k)" + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "text", + "content": " are the posterior and prior distribution of the modality-specific latent codes. " + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "inline_equation", + "content": "p_{\\theta}(y|x^{k},s^{k},c)" + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "text", + "content": " is the prediction generation model. All these models can be parameterized by deep neural networks and optimized via stochastic gradient descent. The hyper-parameter " + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "inline_equation", + "content": "\\beta = 0.1" + }, + { + "bbox": [ + 304, + 304, + 545, + 403 + ], + "type": "text", + "content": " is introduced to achieve stable learning [60]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "text", + "content": "Efficient Sampling. The Eq. (6) shows that the generation process involves sampling from the joint shared posterior " + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "inline_equation", + "content": "q_{\\phi_c}(c|X,y)" + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "text", + "content": " and posterior of modality-specific latent code " + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "inline_equation", + "content": "q_{\\phi_{s^k}}(s^k|x^k,y)" + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "text", + "content": " of each modality, which is time-consuming. In practice, we first perform shared-specific representation fusion, and then we sample latent code from each fused space, achieving efficient sampling. Specifically, given the posterior of the latent codes " + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "inline_equation", + "content": "c \\sim q_{\\phi_c}(c|X,y) \\in \\mathbb{R}^{T \\times L}" + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "inline_equation", + "content": "s^a \\sim q_{\\phi_{s^a}}(s^a|x^a,y) \\in \\mathbb{R}^{T \\times L}" + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "inline_equation", + "content": "s^v \\sim q_{\\phi_{s^v}}(s^v|x^v,y) \\in \\mathbb{R}^{T \\times L}" + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "text", + "content": " (" + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "text", + "content": " is the dimension of the latent space), we concatenate the shared representation with each specific representation to get the fused representation of each modality. Then we obtain " + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "inline_equation", + "content": "sc^a, sc^v" + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "text", + "content": ", representing the fused feature of audio and visual data, respectively. To achieve the reconstruction of " + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "inline_equation", + "content": "p_\\theta(y|x^k,s^k,c)" + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "text", + "content": " in Eq. (6), instead of performing sampling from each specific latent code and shared latent code, we sample from " + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "inline_equation", + "content": "sc^a, sc^v" + }, + { + "bbox": [ + 304, + 403, + 546, + 619 + ], + "type": "text", + "content": ", and rewrite the reconstruction term, i.e. the first term in Eq. (6), as:" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 343, + 628, + 545, + 655 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 343, + 628, + 545, + 655 + ], + "spans": [ + { + "bbox": [ + 343, + 628, + 545, + 655 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {r e c}} = \\sum_ {s c \\in \\{s c ^ {a}, s c ^ {v} \\}} \\left[ \\mathbb {E} \\left[ \\log p _ {\\theta} (y | x, s c) \\right] \\right], \\tag {7}", + "image_path": "e6b1688c4ebd7a39041f98394ee4e3696f98c4728b1b0659c05c35df28fe1ae9.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 665, + 545, + 688 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 665, + 545, + 688 + ], + "spans": [ + { + "bbox": [ + 304, + 665, + 545, + 688 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 665, + 545, + 688 + ], + "type": "inline_equation", + "content": "x" + }, + { + "bbox": [ + 304, + 665, + 545, + 688 + ], + "type": "text", + "content": " corresponds to the modality of data, i.e. audio or visual, of the current fused latent code " + }, + { + "bbox": [ + 304, + 665, + 545, + 688 + ], + "type": "inline_equation", + "content": "sc" + }, + { + "bbox": [ + 304, + 665, + 545, + 688 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 689, + 545, + 713 + ], + "type": "text", + "content": "Hybrid Loss. As the VAE samples from the posterior for training and prior to testing. To achieve consistent training" + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 61, + 703, + 272, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 61, + 703, + 272, + 712 + ], + "spans": [ + { + "bbox": [ + 61, + 703, + 272, + 712 + ], + "type": "text", + "content": "Please refer to the supplementary material for detailed derivation." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 748, + 312, + 757 + ], + "type": "text", + "content": "957" + } + ] + } + ], + "index": 14 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 120 + ], + "type": "text", + "content": "and testing, we define a Gaussian stochastic neural network (GSNN) [25] based objective by sampling from the prior distribution as well to avoid the posterior/prior distribution gap, leading to the hybrid objective as:" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 130, + 293, + 156 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 130, + 293, + 156 + ], + "spans": [ + { + "bbox": [ + 47, + 130, + 293, + 156 + ], + "type": "interline_equation", + "content": "\\widehat {\\operatorname {H E L B O}} (X, y, \\theta , \\phi) = \\alpha_ {1} \\widehat {\\operatorname {E L B O}} (X, y, \\theta , \\phi) + (1 - \\alpha_ {1}) \\mathcal {L} _ {\\mathrm {G S N N}}, \\tag {8}", + "image_path": "2bf5293ba61c1480f600f80d0f39f56da04aabac3b352357cb86281e7565a8fb.jpg" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 156, + 287, + 192 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 156, + 287, + 192 + ], + "spans": [ + { + "bbox": [ + 46, + 156, + 287, + 192 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 156, + 287, + 192 + ], + "type": "inline_equation", + "content": "\\alpha_{1} = 0.5" + }, + { + "bbox": [ + 46, + 156, + 287, + 192 + ], + "type": "text", + "content": " is used to balance the two objectives, " + }, + { + "bbox": [ + 46, + 156, + 287, + 192 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{GSNN}}" + }, + { + "bbox": [ + 46, + 156, + 287, + 192 + ], + "type": "text", + "content": " represents the reconstruction term of Eq. (6), which is achieved by sampling from the prior distribution." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 192, + 287, + 275 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 192, + 287, + 275 + ], + "spans": [ + { + "bbox": [ + 46, + 192, + 287, + 275 + ], + "type": "text", + "content": "The latent space factorization is effective in generating modality-shared and specific representations. However, no constraints are applied to the representations, making it hard to decide the reliability of the latent codes. We tackle this issue by proposing a representation orthogonality constraint in Sec. 3.3 and a shared information completeness regularization in Sec. 3.4." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 284, + 263, + 297 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 284, + 263, + 297 + ], + "spans": [ + { + "bbox": [ + 47, + 284, + 263, + 297 + ], + "type": "text", + "content": "3.3. Representation Orthogonality Constraint" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 303, + 287, + 361 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 303, + 287, + 361 + ], + "spans": [ + { + "bbox": [ + 46, + 303, + 287, + 361 + ], + "type": "text", + "content": "We introduce a representation orthogonality constraint to ensure that the modality-shared and modality-specific representations capture different information within each unimodal data. Specifically, given the latent codes " + }, + { + "bbox": [ + 46, + 303, + 287, + 361 + ], + "type": "inline_equation", + "content": "c, s^a, s^v" + }, + { + "bbox": [ + 46, + 303, + 287, + 361 + ], + "type": "text", + "content": ", we introduce the difference loss [61] as:" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 75, + 371, + 287, + 386 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 75, + 371, + 287, + 386 + ], + "spans": [ + { + "bbox": [ + 75, + 371, + 287, + 386 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {d i f f}} = \\left\\| c ^ {T} s ^ {a} \\right\\| _ {F} ^ {2} + \\left\\| c ^ {T} s ^ {v} \\right\\| _ {F} ^ {2} + \\left\\| \\left(s ^ {a}\\right) ^ {T} s ^ {v} \\right\\| _ {F} ^ {2}, \\tag {9}", + "image_path": "9af1a8711dab7c140e122ca28977788808c9ed8e8d8b42bc317f564c185d2434.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 395, + 287, + 431 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 395, + 287, + 431 + ], + "spans": [ + { + "bbox": [ + 46, + 395, + 287, + 431 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 395, + 287, + 431 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\| _F^2" + }, + { + "bbox": [ + 46, + 395, + 287, + 431 + ], + "type": "text", + "content": " is the squared Frobenius norm. With the difference loss, we aim to obtain the exclusive feature in each factorized feature representation." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 440, + 230, + 453 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 440, + 230, + 453 + ], + "spans": [ + { + "bbox": [ + 47, + 440, + 230, + 453 + ], + "type": "text", + "content": "3.4. Shared-Information Completeness" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "spans": [ + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "text", + "content": "As discussed in Sec. 3.2, we fuse the shared representation with each modality-specific representation and obtain " + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "inline_equation", + "content": "sc^a" + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "inline_equation", + "content": "sc^v" + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "text", + "content": ", representing the task-related information from audio and visual, respectively. To explicitly model the effectiveness of the fused latent space, we treat them " + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "inline_equation", + "content": "(sc^a, sc^v)" + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "text", + "content": " as two different views of the same target following representation learning [56, 57, 62], and introduce mutual information maximization as a regularizer to measure the shared information between " + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "inline_equation", + "content": "sc^a" + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "inline_equation", + "content": "sc^v" + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "text", + "content": ". Given two random variables " + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "inline_equation", + "content": "SC^a" + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "inline_equation", + "content": "SC^v" + }, + { + "bbox": [ + 46, + 459, + 287, + 578 + ], + "type": "text", + "content": ", the mutual information is defined as:" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 53, + 586, + 287, + 613 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 586, + 287, + 613 + ], + "spans": [ + { + "bbox": [ + 53, + 586, + 287, + 613 + ], + "type": "interline_equation", + "content": "I \\left(S C ^ {a}; S C ^ {v}\\right) = \\mathbb {E} _ {p \\left(s c ^ {a}, s c ^ {v}\\right)} \\left[ \\log \\frac {p \\left(s c ^ {a} , s c ^ {v}\\right)}{p \\left(s c ^ {a}\\right) \\cdot p \\left(s c ^ {v}\\right)} \\right]. \\tag {10}", + "image_path": "0010261c49eb4b2fc86b08bd08ab9417b08235301e28a983e30f429abdfedd24.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 622, + 287, + 647 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 622, + 287, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 622, + 287, + 647 + ], + "type": "text", + "content": "According to Bayesian's law, we obtain the mutual information variational lower bound [35], namely " + }, + { + "bbox": [ + 47, + 622, + 287, + 647 + ], + "type": "inline_equation", + "content": "I_{\\mathrm{ba}}" + }, + { + "bbox": [ + 47, + 622, + 287, + 647 + ], + "type": "text", + "content": " via:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 654, + 287, + 677 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 654, + 287, + 677 + ], + "spans": [ + { + "bbox": [ + 47, + 654, + 287, + 677 + ], + "type": "interline_equation", + "content": "I \\left(S C ^ {a}; S C ^ {v}\\right) \\geq \\mathbb {E} _ {p \\left(s c ^ {a}, s c ^ {v}\\right)} \\left[ \\log q _ {\\kappa} \\left(s c ^ {a} \\mid s c ^ {v}\\right) \\right] + H \\left(S C ^ {a}\\right) \\triangleq I _ {\\mathrm {b a}}, \\tag {11}", + "image_path": "f2388da2bed00de69ff412dac396342b3ada9d77652309170c6bc6709c14a97f.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "q_{\\kappa}(sc^{a}|sc^{v})" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": " is the variational approximation of " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "p(sc^{a}|sc^{v})" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": ". Following [36], " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "q_{\\kappa}(sc^{a}|sc^{v})" + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "text", + "content": " is formulated as a multivariate Gaussian distribution " + }, + { + "bbox": [ + 46, + 677, + 287, + 713 + ], + "type": "inline_equation", + "content": "q_{\\kappa}(sc^{a}|sc^{v}) =" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "inline_equation", + "content": "\\mathcal{N}(sc^a |\\mu (sc^v),\\sigma^2 (sc^v)\\mathbf{I})" + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": " to predict mean " + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "inline_equation", + "content": "\\mu (sc^v)" + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": " and variance " + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "inline_equation", + "content": "\\sigma^2 (sc^v)" + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": ", respectively, where each statistic is modeled with two fully connected layers with Tanh activation function in the middle, and " + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "inline_equation", + "content": "\\kappa" + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": " represent parameters of the four fully connected layers. " + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "inline_equation", + "content": "H(SC^{a})" + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": " is the differential entropy of " + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "inline_equation", + "content": "SC^a" + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": ". As the audio encoder is fixed in this paper, we choose to simplify the entropy computation and treat " + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "inline_equation", + "content": "H(SC^{a})" + }, + { + "bbox": [ + 304, + 72, + 545, + 167 + ], + "type": "text", + "content": " as a constant [63]." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 305, + 168, + 545, + 216 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 168, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 305, + 168, + 545, + 216 + ], + "type": "text", + "content": "Based on the variational lower bound " + }, + { + "bbox": [ + 305, + 168, + 545, + 216 + ], + "type": "inline_equation", + "content": "I_{\\mathrm{ba}}" + }, + { + "bbox": [ + 305, + 168, + 545, + 216 + ], + "type": "text", + "content": ", we then define the shared-information completeness loss function as: " + }, + { + "bbox": [ + 305, + 168, + 545, + 216 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{sic}} = -I_{\\mathrm{ba}}" + }, + { + "bbox": [ + 305, + 168, + 545, + 216 + ], + "type": "text", + "content": ". Further, we introduce the hybrid loss function for the posterior and the prior distribution, leading to:" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 363, + 223, + 545, + 237 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 363, + 223, + 545, + 237 + ], + "spans": [ + { + "bbox": [ + 363, + 223, + 545, + 237 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\mathrm {s i c}} = - \\alpha_ {2} I _ {\\mathrm {b a}} ^ {\\mathrm {p o}} - (1 - \\alpha_ {2}) I _ {\\mathrm {b a}} ^ {\\mathrm {p r}}, \\tag {12}", + "image_path": "383391b92f8d83c9b4dc6c1f3a970aea7f0e73772f2a0c37b1ecb9c127d337af.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 244, + 545, + 281 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 244, + 545, + 281 + ], + "spans": [ + { + "bbox": [ + 304, + 244, + 545, + 281 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 244, + 545, + 281 + ], + "type": "inline_equation", + "content": "I_{\\mathrm{ba}}^{\\mathrm{po}}(I_{\\mathrm{ba}}^{\\mathrm{pr}})" + }, + { + "bbox": [ + 304, + 244, + 545, + 281 + ], + "type": "text", + "content": " is the lower bound of the mutual information for the posterior (prior) distribution, and " + }, + { + "bbox": [ + 304, + 244, + 545, + 281 + ], + "type": "inline_equation", + "content": "\\alpha_{2} = 0.5" + }, + { + "bbox": [ + 304, + 244, + 545, + 281 + ], + "type": "text", + "content": " is introduced to balance the two objectives." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 288, + 379, + 300 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 288, + 379, + 300 + ], + "spans": [ + { + "bbox": [ + 306, + 288, + 379, + 300 + ], + "type": "text", + "content": "3.5. The Model" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 307, + 545, + 389 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 307, + 545, + 389 + ], + "spans": [ + { + "bbox": [ + 304, + 307, + 545, + 389 + ], + "type": "text", + "content": "Four central modules or constraints are included in our framework (see Fig. 1), namely: 1) \"modal encoding\" to extract the feature of each modality; 2) \"latent space encoding\" for multimodal latent feature representation learning; 3) \"decoder\" for the segmentation maps prediction; 4) \"objective function\" for supervised learning and explicit multimodal representation constraints." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "text", + "content": "Modal Encoding. We perform two branches with two encoders to encode the visual and audio data. For the visual branch, we use the ImageNet pre-trained backbone followed by a one-layer convolution as neck to produce the multi-scale visual features " + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "inline_equation", + "content": "\\{V_m\\}_{m=1}^4 \\in \\mathbb{R}^{T \\times h_m \\times w_m \\times C_m}" + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "inline_equation", + "content": "(h_m, w_m) = (H, W) / 2^{m+1}, C_m = 128" + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "inline_equation", + "content": "H, W" + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "text", + "content": " is the spatial resolution of the input video. We use PVTv2 [64] or ResNet50 [65] as our visual backbone, which keeps the same as AVSBench [1]. For the audio branch, we follow [1], and use a frozen VGGish [66] model pre-trained on AudioSet [67] to process the spectrogram of input audio to extract audio features " + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "inline_equation", + "content": "A \\in \\mathbb{R}^{T \\times d}" + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "inline_equation", + "content": "d = 128" + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "text", + "content": ". And " + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "inline_equation", + "content": "T = 5" + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "text", + "content": " denotes the length of the video. We also keep the temporal pixel-wise audio-visual interaction (TPAVI) [1] module in our framework, which is a cross-modal attention based fusion module that takes visual features as query and value, audio features as key to achieve multi-scale feature fusion in the feature space and obtain " + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "inline_equation", + "content": "\\{\\bar{V}_m\\}_{m=1}^4" + }, + { + "bbox": [ + 304, + 390, + 545, + 605 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "text", + "content": "Latent Space Encoding. The main idea of our proposed method is achieving modality encoding on a reliable latent space (Sec. 3.2), as shown in Fig. 1. We use " + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\phi_{s^v},\\phi_{s^a},\\phi_c" + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "text", + "content": " parameterized by three simple neural networks to get latent feature embedding " + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "inline_equation", + "content": "s^v,s^a,c\\in \\mathbb{R}^{T\\times L}" + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "text", + "content": " as prior distributions " + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "inline_equation", + "content": "(L = 16)" + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "text", + "content": ". For " + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\phi_{s^v}" + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "text", + "content": ", we use five convolutional layers followed by leakyReLU [68] with two fully connected layers to encode the input video sequence. While for " + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "inline_equation", + "content": "\\phi_{s^a}" + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "text", + "content": ", we employ two fully connected layers to map the VGGish encoded" + } + ] + } + ], + "index": 21 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "958" + } + ] + } + ], + "index": 22 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "text", + "content": "audio features into the latent space. Further, video sequence and audio features are fed into " + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "\\phi_c" + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "text", + "content": " jointly, thus we perform late fusion on the audio features and five convolutional layers followed by leakyReLU encoded visual features to obtain the joint distribution from the fused features. For the posterior network, we design three networks with the same structure and take the segmentation maps " + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "text", + "content": " as input by concatenating the video sequence and segmentation maps. We omit drawing the posterior space in Fig. 1 for easy viewing. Decoder. We adopt the decoder of Panoptic-FPN [69] to decode the final segmentation maps for its flexibility and effectiveness, which is the same as AVSBench [1]. We expand " + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "sc^a" + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "sc^v" + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "text", + "content": " to feature map of the same spatial size as " + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "\\bar{V}_4" + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "text", + "content": " by adding two-dimensional gaussian noise with the tile operation, \"sampling\" is used to indicate this process in Fig.1. The decoder takes both the deterministic features " + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "\\{\\bar{V}_m\\}_{m=1}^4" + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "text", + "content": " produced by the TPAVI [1] module and the expanded latent codes " + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "sc^a" + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "inline_equation", + "content": "sc^v" + }, + { + "bbox": [ + 46, + 72, + 289, + 300 + ], + "type": "text", + "content": " from the fused latent space as input to produce the final segmentation maps." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 300, + 288, + 348 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 300, + 288, + 348 + ], + "spans": [ + { + "bbox": [ + 46, + 300, + 288, + 348 + ], + "type": "text", + "content": "Objective Function. As discussed above, our final objective function contains the optimization of the evidence lower bound and the practical constraints for latent space representation, and it can be defined as," + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 91, + 356, + 286, + 386 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 91, + 356, + 286, + 386 + ], + "spans": [ + { + "bbox": [ + 91, + 356, + 286, + 386 + ], + "type": "interline_equation", + "content": "\\begin{array}{l} \\mathcal {L} = - \\widehat {\\mathrm {H E L B O}} (X, y, \\theta , \\phi) + \\lambda_ {1} \\mathcal {L} _ {\\text {d i f f}} \\tag {13} \\\\ + \\lambda_ {2} \\mathcal {L} _ {\\text {s i c}} + \\lambda_ {3} \\mathcal {L} _ {\\text {A V M}}, \\\\ \\end{array}", + "image_path": "ddfc50315cb644c02f72be41995ebeea16c5d28256ee493da6159e1150a92605.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "spans": [ + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathrm{HELBO}}(X, y, \\theta, \\phi)" + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "text", + "content": " indicates the lower bound for our proposed ECMVAE optimization, which is defined in detail in Eq. (8) and Eq. (6). We use a weighted structure-aware function [70] to compute the hybrid reconstruction part in " + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathrm{HELBO}}(X, y, \\theta, \\phi)" + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{diff}}" + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{sic}}" + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "text", + "content": " are the orthogonality constraint and the shared-information completeness loss defined in Eq. (9) and Eq. (12). " + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{AVM}}" + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "text", + "content": " indicates the audio-visual mapping loss proposed by [1] as a regularization term to promote the similarity between the audio-visual features. Empirically, we set the hyper-parameters " + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "inline_equation", + "content": "\\{\\lambda_1, \\lambda_2, \\lambda_3\\}" + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "text", + "content": " as " + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "inline_equation", + "content": "\\{0.001, 0.01, 0.5\\}" + }, + { + "bbox": [ + 46, + 398, + 289, + 534 + ], + "type": "text", + "content": " for balanced training." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 544, + 173, + 556 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 544, + 173, + 556 + ], + "spans": [ + { + "bbox": [ + 47, + 544, + 173, + 556 + ], + "type": "text", + "content": "4. Experimental Results" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 563, + 180, + 576 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 563, + 180, + 576 + ], + "spans": [ + { + "bbox": [ + 47, + 563, + 180, + 576 + ], + "type": "text", + "content": "4.1. Implementation Details" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 289, + 715 + ], + "type": "text", + "content": "Datasets. We conduct experiments on the AVSBench [1] dataset, which contains 5,356 video sequences with corresponding audio data and binary per-pixel annotations. Each video in the dataset contains five frames, extracted separately from a five-second video, where the audio length is also five seconds. This dataset contains two settings, named S4 and MS3, for semi-supervised Single Sound Source Segmentation with only the first frame labeled, and fully supervised Multiple Sound Source Segmentation with all frames labeled. The evaluation is done for the entire five frames of the video under both S4 and MS3 settings on the test set." + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 307, + 118, + 542, + 254 + ], + "blocks": [ + { + "bbox": [ + 304, + 68, + 547, + 114 + ], + "lines": [ + { + "bbox": [ + 304, + 68, + 547, + 114 + ], + "spans": [ + { + "bbox": [ + 304, + 68, + 547, + 114 + ], + "type": "text", + "content": "Table 1. Quantitative results on the AVSBench dataset [1] in terms of mIOU and F-score under S4 and MS3 settings. We both report the performance with R50 and PVT as a backbone for the results of AVSBench [1] and Ours." + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 118, + 542, + 254 + ], + "lines": [ + { + "bbox": [ + 307, + 118, + 542, + 254 + ], + "spans": [ + { + "bbox": [ + 307, + 118, + 542, + 254 + ], + "type": "table", + "html": "
MethodsS4MS3
mIoUF-scoremIoUF-score
VOS3DC [71]57.100.75936.920.503
SST [72]66.290.80142.570.572
SODiGAN [73]61.590.77842.890.544
LGVT [74]74.940.87340.710.593
AVSAVSBench (R50) [1]72.790.84847.880.578
AVSBench (PVT) [1]78.740.87954.000.645
Ours (R50)76.330.86548.690.607
Ours (PVT)81.740.90157.840.708
", + "image_path": "bce0ce3d263e6dcabd51522404583c5e91063693c186458d3160660cfa820e66.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_body" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 269, + 547, + 377 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 269, + 547, + 377 + ], + "spans": [ + { + "bbox": [ + 304, + 269, + 547, + 377 + ], + "type": "text", + "content": "Training Details. We conduct experiments on Pytorch [75] with a single NVIDIA A100 GPU. The Adam [76] solver is used to optimize our network with a learning rate of " + }, + { + "bbox": [ + 304, + 269, + 547, + 377 + ], + "type": "inline_equation", + "content": "1 \\times 10^{-4}" + }, + { + "bbox": [ + 304, + 269, + 547, + 377 + ], + "type": "text", + "content": ". The training batch size is set to 4. We train the network on the S4 subset for 15 epochs, and on the MS3 subset for 30 epochs. For the MS3 setting, we use all ground-truth of the five frames to build the posterior latent space of our model. While for S4, we repeat the ground-truth of the first frame five times to build the posterior latent space." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 384, + 495, + 396 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 384, + 495, + 396 + ], + "spans": [ + { + "bbox": [ + 305, + 384, + 495, + 396 + ], + "type": "text", + "content": "4.2. Comparison with Baseline Methods" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 403, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 403, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 403, + 545, + 715 + ], + "type": "text", + "content": "Quantitative Comparison. Follow the comparison settings with AVSBench [1], we compare the performance of our ECMVAE with baseline AVS models and other related tasks, including video object segmentation (VOS) and salient object detection (SOD). The performance on Mean Intersection over Union (mIoU) and F-score is reported in Table 1. It can be observed that our method consistently achieves significantly superior segmentation performance than the state-of-the-art methods, especially with 3.00 and 3.84 higher mIoU than the previous AVS method [1], at the S4 and MS3 settings with PVTv2 (\"PVT\") backbone. There is also a consistent performance improvement with ResNet (\"R50\") backbone. The performance gain comes from our designed multimodal VAE with explicit constraints for representation learning. Our method also significantly outperforms the VOS and SOD methods, demonstrating the addition of audio information to the segmentation performance. Qualitative Comparison. We provide a qualitative comparison between our proposed method and [1] in Fig. 2. Our proposed ECMVAE provides a better audio temporal and spatial localization quality, leading to better segmentation performance, especially for the left samples, in localization of the piano keys, which is not salient but producing a sound in this scene. Our method also achieves better segmentation performance for background noise handling and richer foreground details in the right samples in Fig. 2." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "959" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 55, + 70, + 539, + 259 + ], + "blocks": [ + { + "bbox": [ + 55, + 70, + 539, + 259 + ], + "lines": [ + { + "bbox": [ + 55, + 70, + 539, + 259 + ], + "spans": [ + { + "bbox": [ + 55, + 70, + 539, + 259 + ], + "type": "image", + "image_path": "49a967a2442e76bb33d505ac530cc407fd96dfce94ef8516ba234d92e7af9330.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 270, + 546, + 293 + ], + "lines": [ + { + "bbox": [ + 46, + 270, + 546, + 293 + ], + "spans": [ + { + "bbox": [ + 46, + 270, + 546, + 293 + ], + "type": "text", + "content": "Figure 2. Qualitative comparison between our proposed ECMVAE and AVSBench [1]. Our method competently achieves high segmentation performance with better audio temporal and spatial localization quality and detail handling." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 306, + 147, + 317 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 306, + 147, + 317 + ], + "spans": [ + { + "bbox": [ + 47, + 306, + 147, + 317 + ], + "type": "text", + "content": "4.3. Ablation Studies" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 324, + 287, + 347 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 324, + 287, + 347 + ], + "spans": [ + { + "bbox": [ + 47, + 324, + 287, + 347 + ], + "type": "text", + "content": "We conduct ablation studies of our proposed method. All variations are trained with the PVT backbone." + } + ] + } + ], + "index": 3 + }, + { + "type": "table", + "bbox": [ + 69, + 392, + 261, + 464 + ], + "blocks": [ + { + "bbox": [ + 46, + 354, + 287, + 388 + ], + "lines": [ + { + "bbox": [ + 46, + 354, + 287, + 388 + ], + "spans": [ + { + "bbox": [ + 46, + 354, + 287, + 388 + ], + "type": "text", + "content": "Table 2. Ablation of the VAE based multimodal learning. We implement a \"CVAE\" without audio and \"CMVAE\" with audio-visual joint distribution estimation." + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 69, + 392, + 261, + 464 + ], + "lines": [ + { + "bbox": [ + 69, + 392, + 261, + 464 + ], + "spans": [ + { + "bbox": [ + 69, + 392, + 261, + 464 + ], + "type": "table", + "html": "
MethodsS4MS3
mIoUF-scoremIoUF-score
[1] w/o audio77.80-48.20-
CVAE78.120.87849.260.643
CMVAE80.050.88954.990.653
", + "image_path": "4310379cc345910ae0f353c22ea6ccb3d8d585704f009630fdb1008eb9656ca1.jpg" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "table_body" + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 474, + 287, + 664 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 474, + 287, + 664 + ], + "spans": [ + { + "bbox": [ + 46, + 474, + 287, + 664 + ], + "type": "text", + "content": "Multimodal VAE. We explore the effectiveness of the Multimodal VAE in Table 2. Firstly, we remove the audio part of the model and disable the TPAVI module to explore the importance of the audio information, leading to a simple unimodal CVAE [29] framework with only video input, which is denoted as \"CVAE\". For comparison, we implement a \"CMVAE\" using the audio signal but without the latent space factorization and our proposed constraints. The better performance of \"CMVAE\" compared with \"CVAE\" indicates the importance of audio for AVS, especially when multiple sound sources exist. We also brought the ablation result of the model without the audio input from [1] and compare it with \"CVAE\". The results show that in the absence of audio signals, the VAE structure can still improve segmentation performance, due to the ability of VAE to model the latent space of visual features." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": "Latent Space Factorization. As described in Sec. 3.2, we factorize the latent space of multimodal VAE into modality-shared " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "(c)" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": " and modality-specific " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "(s^v" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "inline_equation", + "content": "s^a)" + }, + { + "bbox": [ + 46, + 665, + 287, + 713 + ], + "type": "text", + "content": " representations. As reported in Table 3, removing the latent space" + } + ] + } + ], + "index": 7 + }, + { + "type": "table", + "bbox": [ + 313, + 352, + 535, + 450 + ], + "blocks": [ + { + "bbox": [ + 305, + 303, + 545, + 347 + ], + "lines": [ + { + "bbox": [ + 305, + 303, + 545, + 347 + ], + "spans": [ + { + "bbox": [ + 305, + 303, + 545, + 347 + ], + "type": "text", + "content": "Table 3. Ablation of the latent space factorization. \"Model\" indicates using VAE for latent factorization or using AE for feature factorization. \"Factor.\" denotes whether using factorization. \"dim.\" represents the size of the latent dimensions." + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 313, + 352, + 535, + 450 + ], + "lines": [ + { + "bbox": [ + 313, + 352, + 535, + 450 + ], + "spans": [ + { + "bbox": [ + 313, + 352, + 535, + 450 + ], + "type": "table", + "html": "
ModelFactor.dim.S4MS3
mIoUF-scoremIoUF-score
VAE-1680.050.88954.990.653
-4880.130.89055.090.657
✓1680.780.89356.380.676
AE--78.740.87954.000.645
✓-78.920.88154.820.651
", + "image_path": "d4ba7ea2a4aef527419e7af58fa0f01433f31f66276feee0a4f882ddba1e9202.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "table_body" + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 471, + 545, + 602 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 471, + 545, + 602 + ], + "spans": [ + { + "bbox": [ + 304, + 471, + 545, + 602 + ], + "type": "text", + "content": "factorization leads to obvious performance degradation. We also train a non-factorized model with " + }, + { + "bbox": [ + 304, + 471, + 545, + 602 + ], + "type": "inline_equation", + "content": "2 \\times" + }, + { + "bbox": [ + 304, + 471, + 545, + 602 + ], + "type": "text", + "content": " larger latent dimensions, which holds comparable latent space capacities with the factorized model. It can be seen that the performance gain from the larger latent space dimensions is not as obvious as the factorization strategy. Further, we compare feature factorization (\"AE\") on the feature space of [1] with our proposed latent space factorization (\"VAE\"). Table 3 shows that only performing factorization on a semantic meaningful and continuous latent space, i.e. via using VAE [2], can achieve larger performance improvements." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 604, + 545, + 699 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 604, + 545, + 699 + ], + "spans": [ + { + "bbox": [ + 304, + 604, + 545, + 699 + ], + "type": "text", + "content": "JS Divergence. We conduct experiments of PoE and MoE with KL divergence to show the trade-off of JS divergence between the computational efficiency of the inference process and the predictive quality of the generation process. The performance in Table 4 shows the effectiveness of JS divergence on both S4 and MS3 settings. Note that, \"PoE\", \"MoE\" and \"JS\" are based on our formulation of the task, which has not been explored in the AVS area." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 306, + 701, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 701, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 306, + 701, + 545, + 713 + ], + "type": "text", + "content": "Orthogonality Constraint. As reported in Table 5, the or" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "960" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 75, + 70, + 185, + 151 + ], + "blocks": [ + { + "bbox": [ + 75, + 70, + 185, + 151 + ], + "lines": [ + { + "bbox": [ + 75, + 70, + 185, + 151 + ], + "spans": [ + { + "bbox": [ + 75, + 70, + 185, + 151 + ], + "type": "image", + "image_path": "f5a2dc69582dcdc3f04f63a395ba96e9c239ef1a036267b65f6ffdc357bcc028.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 97, + 152, + 165, + 160 + ], + "lines": [ + { + "bbox": [ + 97, + 152, + 165, + 160 + ], + "spans": [ + { + "bbox": [ + 97, + 152, + 165, + 160 + ], + "type": "text", + "content": "(a) Base Factorization" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 186, + 71, + 296, + 151 + ], + "blocks": [ + { + "bbox": [ + 186, + 71, + 296, + 151 + ], + "lines": [ + { + "bbox": [ + 186, + 71, + 296, + 151 + ], + "spans": [ + { + "bbox": [ + 186, + 71, + 296, + 151 + ], + "type": "image", + "image_path": "a89d1d8f8cf1e0077e0c2adf494c536f0735ca0cb0801c5c78a984945c364a89.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 220, + 152, + 265, + 162 + ], + "lines": [ + { + "bbox": [ + 220, + 152, + 265, + 162 + ], + "spans": [ + { + "bbox": [ + 220, + 152, + 265, + 162 + ], + "type": "text", + "content": "(b) With " + }, + { + "bbox": [ + 220, + 152, + 265, + 162 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{diff}}" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 296, + 72, + 408, + 151 + ], + "blocks": [ + { + "bbox": [ + 296, + 72, + 408, + 151 + ], + "lines": [ + { + "bbox": [ + 296, + 72, + 408, + 151 + ], + "spans": [ + { + "bbox": [ + 296, + 72, + 408, + 151 + ], + "type": "image", + "image_path": "01880b0c2b409f6f8e87696cff7d6daa28730d224bfe9f6a4d540dc1c39bb6ae.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + } + ], + "index": 4 + }, + { + "type": "image", + "bbox": [ + 410, + 72, + 519, + 151 + ], + "blocks": [ + { + "bbox": [ + 410, + 72, + 519, + 151 + ], + "lines": [ + { + "bbox": [ + 410, + 72, + 519, + 151 + ], + "spans": [ + { + "bbox": [ + 410, + 72, + 519, + 151 + ], + "type": "image", + "image_path": "5b5fd72b0100ccc1a09ac35373c0b9526bc43c31b79b6b0acd3738bf1e4ae45e.jpg" + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 435, + 152, + 498, + 163 + ], + "lines": [ + { + "bbox": [ + 435, + 152, + 498, + 163 + ], + "spans": [ + { + "bbox": [ + 435, + 152, + 498, + 163 + ], + "type": "text", + "content": "(d) With " + }, + { + "bbox": [ + 435, + 152, + 498, + 163 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{diff}},\\mathcal{L}_{\\mathrm{sic}}" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_caption" + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 220, + 163, + 381, + 173 + ], + "blocks": [ + { + "bbox": [ + 333, + 152, + 375, + 163 + ], + "lines": [ + { + "bbox": [ + 333, + 152, + 375, + 163 + ], + "spans": [ + { + "bbox": [ + 333, + 152, + 375, + 163 + ], + "type": "text", + "content": "(c) With " + }, + { + "bbox": [ + 333, + 152, + 375, + 163 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{sic}}" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 220, + 163, + 381, + 173 + ], + "lines": [ + { + "bbox": [ + 220, + 163, + 381, + 173 + ], + "spans": [ + { + "bbox": [ + 220, + 163, + 381, + 173 + ], + "type": "image", + "image_path": "2c81e795892e7fcc07efcd6e6c19ee93929c21b57715a5f43a7e276630b0c15b.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 178, + 547, + 201 + ], + "lines": [ + { + "bbox": [ + 46, + 178, + 547, + 201 + ], + "spans": [ + { + "bbox": [ + 46, + 178, + 547, + 201 + ], + "type": "text", + "content": "Figure 3. Visualization of the modality-shared and modality-specific latent codes " + }, + { + "bbox": [ + 46, + 178, + 547, + 201 + ], + "type": "inline_equation", + "content": "(s^v, s^a, c)" + }, + { + "bbox": [ + 46, + 178, + 547, + 201 + ], + "type": "text", + "content": " in the MS3 testing set using t-SNE [77] projections. Best viewed on screen." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "type": "table", + "bbox": [ + 79, + 239, + 252, + 322 + ], + "blocks": [ + { + "bbox": [ + 46, + 213, + 286, + 235 + ], + "lines": [ + { + "bbox": [ + 46, + 213, + 286, + 235 + ], + "spans": [ + { + "bbox": [ + 46, + 213, + 286, + 235 + ], + "type": "text", + "content": "Table 4. Ablation of the JS Divergence. We implement \"PoE\" and \"MoE\" with KL divergence, and a simple \"KL\" model." + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 79, + 239, + 252, + 322 + ], + "lines": [ + { + "bbox": [ + 79, + 239, + 252, + 322 + ], + "spans": [ + { + "bbox": [ + 79, + 239, + 252, + 322 + ], + "type": "table", + "html": "
MethodsS4MS3
mIoUF-scoremIoUF-score
KL80.780.89356.380.676
PoE81.380.89457.350.688
MoE81.490.89757.530.694
JS81.740.90157.840.708
", + "image_path": "085e159f3ba9dbc291425afe657693a87945e1edefb76c36b353a39d3c41dd3e.jpg" + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "table_body" + } + ], + "index": 11 + }, + { + "type": "table", + "bbox": [ + 71, + 355, + 259, + 437 + ], + "blocks": [ + { + "bbox": [ + 46, + 328, + 286, + 350 + ], + "lines": [ + { + "bbox": [ + 46, + 328, + 286, + 350 + ], + "spans": [ + { + "bbox": [ + 46, + 328, + 286, + 350 + ], + "type": "text", + "content": "Table 5. Ablation of the latent space constraints. " + }, + { + "bbox": [ + 46, + 328, + 286, + 350 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{diff}}" + }, + { + "bbox": [ + 46, + 328, + 286, + 350 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 46, + 328, + 286, + 350 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{sic}}" + }, + { + "bbox": [ + 46, + 328, + 286, + 350 + ], + "type": "text", + "content": " indicate our proposed loss functions for multimodal learning." + } + ] + } + ], + "index": 12, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 71, + 355, + 259, + 437 + ], + "lines": [ + { + "bbox": [ + 71, + 355, + 259, + 437 + ], + "spans": [ + { + "bbox": [ + 71, + 355, + 259, + 437 + ], + "type": "table", + "html": "
\\(\\mathcal{L}_{diff}\\)\\(\\mathcal{L}_{sic}\\)S4MS3
mIoUF-scoremIoUF-score
--81.090.89557.010.684
✓-81.510.89957.650.692
-✓81.470.89857.510.694
✓✓81.740.90157.840.708
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As compared between Fig. 3 (a) and (b), the three latent codes in the latent space are divided into different subspaces to ensure that each latent code encodes different information." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "spans": [ + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "text", + "content": "Mutual Information Maximization. As compared in Table 5, the mutual information maximization by " + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{sic}}" + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "text", + "content": " also serves a crucial impact for the explicit constraint of the shared latent space and improves the mIOU from 57.51 to 57.84. Since the " + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{sic}}" + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "text", + "content": " maximizes the mutual information between " + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "inline_equation", + "content": "sc^v" + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "inline_equation", + "content": "sc^a" + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "text", + "content": ", which are fused from the factorization latent codes " + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "inline_equation", + "content": "s^v, s^a, c" + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "text", + "content": ". This increases the amount of information contained in latent space and makes it more effective for facilitating factorization. Fig. 3 also confirms this view and demonstrates the effectiveness of " + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{\\mathrm{sic}}" + }, + { + "bbox": [ + 46, + 530, + 286, + 662 + ], + "type": "text", + "content": " in achieving effective \"multi-view\" representation learning [56, 57, 62]." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 47, + 670, + 110, + 683 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 670, + 110, + 683 + ], + "spans": [ + { + "bbox": [ + 47, + 670, + 110, + 683 + ], + "type": "text", + "content": "4.4. Analysis" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 46, + 689, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 689, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 689, + 286, + 714 + ], + "type": "text", + "content": "Pre-training on the Single-source Subset. In AVS-Bench [1], they conducted experiments by initializing" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "spans": [ + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "text", + "content": "model parameters by pre-training on S4 dataset. We also perform experiments with such setting (see Table 6). We can observe that both our method and AVSBench [1] can benefit from the model pre-trained on S4. The PVT-based model can gain " + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "inline_equation", + "content": "2.97\\%" + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "text", + "content": " mIOU performance by such a strategy and reach " + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "inline_equation", + "content": "60.81\\%" + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "text", + "content": " mIOU. The pre-training strategy can bring more significant improvements (" + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "inline_equation", + "content": "8.87\\%" + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "text", + "content": " mIOU) to ResNet50-based models and reach " + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "inline_equation", + "content": "57.56\\%" + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "text", + "content": " mIOU, which is even higher than PVT-based models (" + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "inline_equation", + "content": "57.34\\%" + }, + { + "bbox": [ + 304, + 216, + 545, + 323 + ], + "type": "text", + "content": ")." + } + ] + } + ], + "index": 18 + }, + { + "type": "table", + "bbox": [ + 307, + 391, + 545, + 472 + ], + "blocks": [ + { + "bbox": [ + 304, + 330, + 545, + 386 + ], + "lines": [ + { + "bbox": [ + 304, + 330, + 545, + 386 + ], + "spans": [ + { + "bbox": [ + 304, + 330, + 545, + 386 + ], + "type": "text", + "content": "Table 6. Performance comparison with different initialization strategies for MS3 dataset. As AVSBench [1] does not report its F-score in the paper, we only report its mIOU. The values in parentheses indicate the performance improvement based on S4 pre-training compared with training from scratch." + } + ] + } + ], + "index": 19, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 307, + 391, + 545, + 472 + ], + "lines": [ + { + "bbox": [ + 307, + 391, + 545, + 472 + ], + "spans": [ + { + "bbox": [ + 307, + 391, + 545, + 472 + ], + "type": "table", + "html": "
MethodsFrom scratchPre-trained on S4
mIoUF-scoremIoUF-score
AVSbench (R50) [1]47.88-54.33 (↑ 6.45)-
AVSbench (PVT) [1]54.00-57.34 (↑ 3.34)-
Ours (R50)48.690.60757.56 (↑ 8.87)0.674
Ours (PVT)57.840.70860.81 (↑ 2.97)0.729
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MethodsR50PVT
Param. (M)Time (ms)Param. (M)Time (ms)
AVSBench [1]70.5028101.3253
Ours33.972391.1846
", + "image_path": "ec4908e717100251614810da22b759f14767217847e4a2c790227acb344376b0.jpg" + } + ] + } + ], + "index": 22, + "angle": 0, + "type": "table_body" + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 570, + 545, + 677 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 677 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 677 + ], + "type": "text", + "content": "Parameters and Efficiency. In Table 7, we compare the parameters and inference time between ours and AVSBench. Note that although posterior nets and prior nets are used in our framework, as all the latent space encoders are quite lightweight (1M), thus our model capacity will not change significantly. Moreover, we replace the neck from ASPP [78] to one-layer convolution and reduce the number of neck channels from 256 to 128, which leads to smaller parameter numbers and faster inference speed." + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 713 + ], + "type": "text", + "content": "Limitations. Similar to the other VAE [2] based solutions, our model also suffers from the risk of posterior collapse, where the posterior of the latent variable is equal to" + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "spans": [ + { + "bbox": [ + 297, + 749, + 312, + 757 + ], + "type": "text", + "content": "961" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "content": "prior [79,80], making " + }, + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "inline_equation", + "content": "y" + }, + { + "bbox": [ + 46, + 72, + 289, + 133 + ], + "type": "text", + "content": " in our case not encoded in the latent variables. To avoid such phenomenon, contrastive learning [81, 82] can be studied to learn more compact features of each modality or score based diffusion models [83-86] can be investigated for more informative latent space." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 142, + 120, + 154 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 142, + 120, + 154 + ], + "spans": [ + { + "bbox": [ + 47, + 142, + 120, + 154 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 161, + 289, + 329 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 161, + 289, + 329 + ], + "spans": [ + { + "bbox": [ + 46, + 161, + 289, + 329 + ], + "type": "text", + "content": "We have worked on audio-visual segmentation (AVS), aiming to segment the sound producers of the scene. As audio data can be treated as \"command\", we argue extensive exploration of audio is critical for effective AVS. Inspired by this observation, we have introduced an Explicit Conditional Multimodal Variational Auto-Encoder (ECMVAE) for an audio-visual segmentation model with latent space factorization with explicit constraints to extensively explore the shared and specific representations of audio and visual data. Extensive experimental results verify the effectiveness of our proposed framework. Although we focused on AVS with two modalities, the proposed framework can be extended to more modalities and other audio-visual collaboration tasks [6, 13, 14]." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 338, + 157, + 353 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 338, + 157, + 353 + ], + "spans": [ + { + "bbox": [ + 47, + 338, + 157, + 353 + ], + "type": "text", + "content": "6. Acknowledgments" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 358, + 287, + 395 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 358, + 287, + 395 + ], + "spans": [ + { + "bbox": [ + 47, + 358, + 287, + 395 + ], + "type": "text", + "content": "This research was supported in part by the National Natural Science Foundation of China (62271410), and the Fundamental Research Funds for the Central Universities." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 48, + 403, + 107, + 416 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 403, + 107, + 416 + ], + "spans": [ + { + "bbox": [ + 48, + 403, + 107, + 416 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 53, + 423, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 423, + 287, + 479 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 423, + 287, + 479 + ], + "spans": [ + { + "bbox": [ + 53, + 423, + 287, + 479 + ], + "type": "text", + "content": "[1] Jinxing Zhou, Jianyuan Wang, Jiayi Zhang, Weixuan Sun, Jing Zhang, Stan Birchfield, Dan Guo, Lingpeng Kong, Meng Wang, and Yiran Zhong. 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Since the positive tissue is only a small fraction of the gigapixel WSI, existing MIL methods intuitively focus on identifying salient instances via attention mechanisms. However, this leads to a bias towards easy-to-classify instances while neglecting hard-to-classify instances. Some literature has revealed that hard examples are beneficial for modeling a discriminative boundary accurately. By applying such an idea at the instance level, we elaborate a novel MIL framework with masked hard instance mining (MHIM-MIL), which uses a Siamese structure (Teacher-Student) with a consistency constraint to explore the potential hard instances. With several instance masking strategies based on attention scores, MHIM-MIL employs a momentum teacher to implicitly mine hard instances for training the student model, which can be any attention-based MIL model. This counter-intuitive strategy essentially enables the student to learn a better discriminating boundary. Moreover, the student is used to update the teacher with an exponential moving average (EMA), which in turn identifies new hard instances for subsequent training iterations and stabilizes the optimization. Experimental results on the CAMELYON-16 and TCGA Lung Cancer datasets demonstrate that MHIM-MIL outperforms other latest methods in terms of performance and training cost. The code is available at: https://github.com/DearCaat/MHIM-MIL.", + "bbox": [ + 75, + 358, + 473, + 767 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 792, + 209, + 809 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Histopathological image analysis plays a crucial role in modern medicine, particularly in the treatment of cancer, where it serves as the gold standard for diagnosis [18, 20, 24,45]. Digitalizing pathological images into Whole Slide", + "bbox": [ + 76, + 818, + 468, + 878 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/06714f471733be7d568f02b60d494c91ea3d0609b44bbc3b07335560576141e5.jpg", + "image_caption": [ + "Figure 1: Left: Previous MIL models focus on the more salient instances. Right: MHIM-MIL mines an amount of hard-to-classify instances to learn a better boundary." + ], + "image_footnote": [], + "bbox": [ + 501, + 325, + 893, + 470 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Images (WSIs) through digital slide scanner has opened new avenues for computer-aided analysis [9, 26]. Due to the huge size of a WSI and the lack of pixel-level annotations, histopathological image analysis is commonly formulated as a multiple instance learning (MIL) task [10, 23, 31]. In MIL, each WSI (or slide) is a bag containing thousands of unlabeled instances (patches) cropped from the slide. With at least one instance being disease positive, the bag is deemed positive, otherwise negative.", + "bbox": [ + 496, + 551, + 893, + 688 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "However, the number of slides is limited and each slide contains a mass of instances with a low positive proportion. This imbalance would hinder the inference of bag labels [16, 43]. To alleviate this issue, several WSI classification methods [6, 16-18,26] employ an attention mechanism to aggregate salient instance features into a bag-level feature for WSI classification. Furthermore, some MIL frameworks [17,21,40,43] focus on the more salient instances in the bag and leverage them to facilitate WSI classification. For instance, existing frameworks [40, 43] propose to only select the instances that correspond to the top $K$ highest or lowest attention scores [17, 40] or patch probabilities [43] for yielding high-quality bag embedding for both training and testing.", + "bbox": [ + 496, + 689, + 895, + 900 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "*Corresponding Author.", + "bbox": [ + 94, + 887, + 225, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "4078", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "These salient instances are actually \"easy-to-classify\" instances, which are not optimal for training a discriminative WSI classification model. In conventional machine learning, such as Support Vector Machines (SVM) [13], samples near the category distribution boundary are more challenging to classify, but are more useful for depicting the classification boundary, as illustrated in Figure 1. Moreover, other deep learning works [25, 28, 33, 34] also reveal that mining hard samples for training can improve the generalization abilities of models. By applying such an idea at the instance level, we can better highlight the \"hard-to-classify\" instances that facilitate MIL model training, and benefit the final WSI classification. However, the lack of instance labels poses a challenge to the direct application of traditional hard sample mining strategies at the instance level.", + "bbox": [ + 76, + 90, + 472, + 316 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address this issue, we present a novel MIL framework based on masked hard instance mining strategies (MHIM) named MHIM-MIL. The main idea of MHIM is to mask out the instances with high attention scores to highlight the hard instances for model training. Based on this, we incorporate two other instance masking strategies to enhance training efficiency and mitigate the over-fitting risk. Another key design of MHIM-MIL is an instance attention generator based on a Siamese structure (Teacher-Student) [3, 8]. In MHIM-MIL, the MIL-based WSI classification model is the student network, which aggregates hard instances mined by a momentum teacher with different instance masking strategies. The momentum teacher is updated using an exponential moving average (EMA) of the student model. Moreover, the framework is optimized by inducing a consistency constraint that explores more supervised information beyond the limited slide label. Unlike the conventional MIL frameworks [40, 43], which adopt complex cascade gradient-updating structures, our method is more simple and does not require additional parameters. It not only improves efficiency but also provides improved performance stability. The contribution of this paper is summarized as follows,", + "bbox": [ + 76, + 318, + 472, + 664 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "- We propose a simple and efficient MIL framework with masked hard instance mining named MHIM-MIL. It implicitly mines hard instances with instance attention for training a more discriminative MIL model. Extensive experiments on two WSI datasets validate that MHIM boosts different MIL models and outperforms other latest methods in terms of performance and training cost.", + "bbox": [ + 94, + 676, + 468, + 797 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "- We propose several hybrid instance masking strategies for indirectly mining hard instances in MIL. These strategies not only address the reliance problem of conventional methods on instance-level supervision but also enhance the training efficiency of the model and mitigate the over-fitting risk.", + "bbox": [ + 94, + 809, + 468, + 901 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "- With the Siamese structure, we introduce a parameter-free momentum teacher to obtain instance attention scores more efficiently and stably. Moreover, we employ a consistency-based iterative optimization to improve the discriminability of both models progressively.", + "bbox": [ + 517, + 90, + 890, + 181 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 196, + 640, + 212 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Multiple Instance Learning in WSI Analysis", + "text_level": 1, + "bbox": [ + 500, + 222, + 874, + 239 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Multiple Instance Learning (MIL) [10] has been widely used in WSI analysis with its unique learning paradigm in recent years [17, 22, 26, 35, 40, 42]. MIL is a weakly supervised learning framework that utilizes coarse-grained bag labels for training instead of fine-grained instance annotations. Previous algorithms can be broadly categorized into two groups: instance-level [4, 12, 15, 40] and embedding-level [9, 27, 38, 39, 43]. The former obtain instance labels and aggregate them to obtain the bag label, whereas the latter aggregate all instance features into a high-level bag embedding for bag prediction. Most embedding-level methods share the basic idea of AB-MIL [16], which employs learnable weights to aggregate salient instance features into bag embedding. Furthermore, some MIL frameworks [17, 21, 40, 43] mine more salient instances making classification easier and facilitating classification. For example, Lu et al. selected the most salient instances based on their attention scores (e.g., maximum and minimum scores) to compute instance-level loss and improve performance [21]. Zhang et al. proposed a class activation map (CAM) based on the AB-MIL paradigm to better mine salient instances and used AB-MIL to aggregate them into bag embedding [43]. In addition, feature clustering methods [27, 37, 44] computed cluster centroids of all feature embeddings and used representative embeddings for the final prediction. However, all these methods focused excessively on salient instances in training, which are easy instances with high confidence scores and can be easily classified. As a result, they overlook the importance of hard instances for training. In this paper, we intend to mine hard instances for improving WSI classification performance.", + "bbox": [ + 496, + 244, + 893, + 715 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.2. Hard Sample Mining in Computer Vision", + "text_level": 1, + "bbox": [ + 500, + 724, + 854, + 742 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Hard sample mining is a popular technique to speed up convergence and enhance the discriminative power of the model in many deep learning areas, such as face recognition [25], object detection [29, 36], person re-identification [1, 28, 33, 34], and deep metric learning [30, 32]. The main idea behind this technique is to select the samples which are hard to classify correctly (i.e., hard negatives and hard positives) for alleviating the imbalance between positive and negative samples and facilitating model training. There are generally three groups of approaches", + "bbox": [ + 496, + 750, + 893, + 902 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "4079", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "for evaluating sample difficulty: loss-based [14], similarity-based [7], and learnable weight-based [41]. Typically, these strategies require complete sample supervision information. Drawing on the ideas of the above works, we propose a hard instance mining approach in MIL, mining hard examples at the instance level. In this, there are no complete instance labels, only the bag label is available. Similar to our approach, Li et al. utilized attention scores to identify salient instances from false negative bags to serve as hard negative instances and used them to compose the hard bags for improving classification performance [19]. A key difference is that we indirectly mine hard instances by masking out the most salient instances rather than directly locating hard negative instances.", + "bbox": [ + 75, + 90, + 472, + 303 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. Proposed Method", + "text_level": 1, + "bbox": [ + 76, + 316, + 250, + 333 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Background: MIL Formulation", + "text_level": 1, + "bbox": [ + 76, + 342, + 357, + 357 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In MIL, any input WSI $X$ is considered as a bag with multiple instances, which can be represented as $X = \\{x_{i}\\}_{i=1}^{N}$ . $x_{i}$ is a patch collected from the WSI and considered as the $i$ -th instance of $X$ . $N$ is the number of instances. For a classification task, there exists a known label $Y \\in C$ for the bag and an unknown label $y_{n} \\in C$ for each instance, where $C$ is the collection of category labels. The goal of a MIL model $\\mathcal{M}(\\cdot)$ is to predict the bag label with all instances $\\hat{Y} \\gets \\mathcal{M}(X)$ . The popular solution is to learn a bag representation $F$ from the extracted features of instances $Z = \\{z_{i}\\}_{i=1}^{N}$ in a bag, which is also referred as the instance aggregation step. And a classifier $\\mathcal{C}(\\cdot)$ , trained upon the $F$ , can be used to predict the bag label $\\hat{Y} \\gets \\mathcal{C}(F)$ . There are two ways to aggregate instances for achieving bag embedding. One is the attention-based aggregation [16] denoted as follows,", + "bbox": [ + 75, + 364, + 472, + 604 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nF = \\sum_ {i = 1} ^ {N} a _ {i} z _ {i} \\in \\mathbb {R} ^ {D}, \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 200, + 606, + 468, + 647 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $a_{i}$ is the learnable scalar weight for $z_{i}$ , and $D$ is the dimension of vector $F$ and $z_{i}$ . Many works [17, 21, 43] follow this formulation but differ in the ways they generate the attention score $a_{i}$ .", + "bbox": [ + 75, + 652, + 468, + 714 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Another is the multi-head self-attention (MSA) based aggregation [26]. In this fashion, a class token $z_0$ is embedded with the instance features to get the initial input sequence $Z^0 = [z_0, z_1, \\ldots, z_N] \\in \\mathbb{R}^{(N + 1) \\times D}$ for aggregating instance features. This can be formulated as,", + "bbox": [ + 75, + 713, + 468, + 789 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {h e a d} = A ^ {\\ell} \\left(Z ^ {\\ell - 1} W ^ {V}\\right) \\in \\mathbb {R} ^ {N \\times \\frac {D}{H}}, \\quad \\ell = 1 \\dots L \\tag {2}\n$$\n", + "text_format": "latex", + "bbox": [ + 84, + 799, + 467, + 825 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nZ ^ {\\ell} = \\operatorname {C o n c a t} \\left(\\operatorname {h e a d} _ {1}, \\dots , \\operatorname {h e a d} _ {H}\\right) W ^ {O}, \\quad \\ell = 1 \\dots L\n$$\n", + "text_format": "latex", + "bbox": [ + 88, + 823, + 439, + 839 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $W^{V}\\in \\mathbb{R}^{D\\times \\frac{D}{H}}$ and $W^{O}\\in \\mathbb{R}^{D\\times D}$ are the learnable projection matrices of MSA. $A^{\\ell}\\in \\mathbb{R}^{(N + 1)\\times (N + 1)}$ is the attention matrix of the $\\ell$ -th layer, $L$ is the number of MSA", + "bbox": [ + 75, + 853, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "block, and $H$ is the number of head in each MSA block. The bag embedding $F$ is the output class token at the final layer,", + "bbox": [ + 496, + 90, + 890, + 136 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\nF = Z _ {0} ^ {L}. \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 661, + 140, + 890, + 157 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "The self-attention-based bag embedding is essentially a special case of attention-based bag embedding in the multi-instance learning setting. Collectively, these approaches can be referred to as the general attention-based MIL method.", + "bbox": [ + 496, + 169, + 890, + 231 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. MHIM-MIL for WSI Classification", + "text_level": 1, + "bbox": [ + 498, + 244, + 807, + 260 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In general attention-based MIL frameworks, the attention scores of instances indicate the contributions of instances to the bag classification. The salient instances with high scores are useful for classifying WSI in the testing phase but are not conducive to training a MIL model with good generalization ability. Although hard samples have been proven to enhance the generalization ability of the model in many computer vision scenarios [11, 32-34], previous MIL works focus more on exploiting the salient instances and neglecting the utilization of hard instances in model optimization.", + "bbox": [ + 496, + 270, + 890, + 436 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "In this paper, we propose a simple and efficient MIL framework with Masked Hard Instance Mining (MHIM-MIL) to boost the WSI classification. As illustrated in Figure 2, the MHIM-MIL framework employs a Siamese structure during the training phase. The main component of our framework is a general attention-based MIL model (Student), denoted as $S(\\cdot)$ , for aggregating instance features. To increase the discriminatory difficulty of the student model and force it to focus on hard instances, we introduce a momentum teacher, denoted as $T(\\cdot)$ , to score the instances with attention weights and then employ some masked hard instance mining strategies to mask the salient instances while preserving the hard instances. After hard instance mining, all the mined features are forwarded into the student model for the inference of the bag label. The teacher shares the same network structure as the student model but does not need gradient-based updates. It is worth mentioning that, due to the varying number of instances within each bag, the non-batch gradient descent algorithm (i.e., SGD with batch size 1) is typically employed to optimize the MIL model. Therefore, compared to the traditional MIL frameworks with two-tier gradient updating models [40, 43], this Siamese structure makes training more stable and efficient with fewer parameters. The proposed framework can be defined as,", + "bbox": [ + 496, + 438, + 892, + 815 + ], + "page_idx": 2 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {Y} = \\mathcal {S} (\\hat {Z}) = \\mathcal {S} (M _ {\\mathcal {T}} (Z)), \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 596, + 818, + 890, + 844 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "where $M_{\\mathcal{T}}(\\cdot)$ denotes a masked hard instance mining strategy through the teacher model and $\\hat{Z}$ are the mined instances.", + "bbox": [ + 496, + 854, + 890, + 898 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "4080", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/5296ed3dbaf0ab29a083c63de78c5473ba2c1051791b50b2b10244c5c1d7150f.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 171, + 88, + 802, + 256 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/e4de11326178938e3deaff1123ab62f2b103d83883a15877a39d6db5479bb3c7.jpg", + "image_caption": [ + "Figure 2: Overview of proposed MHIM-MIL. A momentum teacher is used to compute attention scores for all instances. We mask instances based on attention with hard mining strategies and feed the remaining to the student model. The student is updated by a consistency loss term $\\mathcal{L}_{con}$ and a label error loss term $\\mathcal{L}_{cls}$ . The teacher parameters are updated with an Exponential Moving Average (EMA) of the student parameters without gradient updates. In the inference phase, we use the complete input instances and the student model only." + ], + "image_footnote": [], + "bbox": [ + 171, + 258, + 799, + 335 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Masked Hard Instance Mining Strategy", + "text_level": 1, + "bbox": [ + 76, + 438, + 419, + 455 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Conventional hard sample mining strategies are difficult to apply without instance-level supervision. We address this challenge by proposing masked hard instance mining strategies that use attention scores to implicitly mine hard instances by masking out easy instances with high attention scores. More specifically, given a complete sequence of instance features $Z = \\{z_{i}\\}_{i=1}^{N}$ as the input of the teacher model $\\mathcal{T}(\\cdot)$ , the teacher outputs the attention weight $a_{i}$ for each instance as follow,", + "bbox": [ + 75, + 462, + 472, + 598 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nA = \\left[ a _ {1}, \\dots , a _ {i}, \\dots , a _ {N} \\right] = \\mathcal {T} (Z). \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 608, + 468, + 626 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Then, we obtain the indices of the attention sequence in descending order by applying a sorting operation on $A$ ,", + "bbox": [ + 76, + 636, + 468, + 667 + ], + "page_idx": 3 + }, + { + "type": "equation", + "text": "\n$$\nI = \\left[ i _ {1}, i _ {2}, \\dots , i _ {N} \\right] = \\operatorname {S o r t} (A), \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 165, + 676, + 468, + 694 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "where $i_1$ is the index of the instance with the highest attention score while $i_N$ is the index of the one with the lowest score. With this index collection $I$ , we will present several masked hard instance mining strategies to select the hard instances. We define an $N$ -dimensional binary vector $M = [m_1, \\dots, m_i, \\dots, m_N]$ for encoding the mask flags of instances where $m_i \\in \\{0, 1\\}$ . If $m_i = 1$ , the $i$ -th instance is masked, otherwise, it is unmasked.", + "bbox": [ + 76, + 704, + 468, + 824 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "High Attention Masking: The simplest masked hard instance mining strategy is the High Attention Masking (HAM) strategy, which simply masks instances with the top $\\beta_{h}\\%$ highest attention scores. The instance mask flags under HAM are initialized as all zero vectors, $M_{h}(:) = 0$ .", + "bbox": [ + 76, + 824, + 470, + 901 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Then we collect the indices of the instances whose scores are ranked in the top $\\beta_h\\%$ , $I_h = [i_t]_{t=1}^{\\lceil \\beta_h\\% \\times N \\rceil}$ . Finally, we set the mask flags with these indices, $M_h(I_h) = 1$ . To ensure that positive instances are preserved within the un-masked sequences, we also utilized techniques such as mask ratio decay.", + "bbox": [ + 496, + 439, + 890, + 529 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Hybrid Masking: We combine HAM with several other instance masking strategies as hybrid masking strategies to achieve some specific properties in hard instance mining, as shown in Figure 3. We consider the obtained mask flags as a collection and employ the union operation for mask flag fusion. We design three hybrid masking strategies as follows:", + "bbox": [ + 496, + 529, + 892, + 633 + ], + "page_idx": 3 + }, + { + "type": "list", + "sub_type": "text", + "list_items": [ + "- L-HAM: We use the same pipeline as HAM to generate the mask flags $M_{l}$ for masking the instances with the top $\\beta_{l} \\%$ lowest attention scores in order to filter out the redundant uninformative instances and improve efficiency. To endow this property to HAM, we union the mask flags obtained by two strategies to get the new mask flags, $\\hat{M} = M_{h} \\cup M_{l}$ .", + "- R-HAM: Randomness is beneficial to reduce the risk of over-fitting. We generate a random mask flag vector $M_r$ with a given random ratio $\\beta_r\\%$ , and combine it with $M_h$ for introducing the randomness to the hard instance mining, $\\hat{M} = M_h \\cup M_r$ .", + "- LR-HAM: Combining the above strategies, we can obtain completely hybrid mask flags, $\\tilde{M} = M_h \\cup M_r \\cup M_l$ , which is expected to achieve both of the mentioned desirable properties." + ], + "bbox": [ + 517, + 642, + 893, + 901 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "4081", + "bbox": [ + 482, + 944, + 513, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/ff415e38d78b95bc030b6e341c833f222016d399ba0ede96bd2dc4eda02f1e2c.jpg", + "image_caption": [ + "Figure 3: Illustration of proposed hybrid masking strategy for hard instance mining." + ], + "image_footnote": [], + "bbox": [ + 78, + 87, + 225, + 204 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/f50a6e4d21146e114d8d41f25bb092acca5ba1ba527d45b2b5ceb2dc89b9a283.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 248, + 85, + 468, + 203 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Once the final mask flag $\\hat{M}$ is produced, the masked instance sequence will be obtained:", + "bbox": [ + 75, + 273, + 468, + 305 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\hat {Z} = M _ {\\mathcal {T}} (Z) = \\operatorname {M a s k} (Z, \\hat {M}) \\in \\mathbb {R} ^ {\\hat {N} \\times D}, \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 132, + 316, + 468, + 342 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the $\\hat{N}$ is the number of unmasked instances.", + "bbox": [ + 76, + 356, + 413, + 372 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "3.4. Consistency-based Iterative Optimization", + "text_level": 1, + "bbox": [ + 76, + 383, + 431, + 400 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Under the Siamese structure, while the teacher model guides the training of the student model, the new knowledge learned by the student model will also update the teacher model. This iterative optimization process progressively improves the mining ability of the teacher and the discriminability of the student. To further facilitate this optimization and explore additional supervised information provided by the momentum teacher, we propose a consistency loss that constrains the classification results of both models.", + "bbox": [ + 75, + 407, + 468, + 542 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Student Optimization: There are two losses in student optimization. One is the cross-entropy for measuring the bag label prediction loss,", + "bbox": [ + 75, + 545, + 468, + 589 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {c l s} = Y \\log \\hat {Y} + (1 - Y) \\log \\left(1 - \\hat {Y}\\right). \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 137, + 603, + 468, + 628 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Another is a consistency loss between the bag representation of student $F_{s}$ and momentum teacher $F_{t}$ ,", + "bbox": [ + 76, + 638, + 468, + 670 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\mathcal {L} _ {\\text {c o n}} = - \\operatorname {s o f t m a x} \\left(F _ {t} / \\tau\\right) \\log F _ {s} \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 161, + 684, + 468, + 700 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where the $\\tau > 0$ is a temperature parameter. Overall, the final optimization loss is as follows:", + "bbox": [ + 76, + 713, + 468, + 743 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{\\hat {\\theta_ {s}} \\right\\} \\leftarrow \\arg \\min _ {\\theta_ {s}} \\mathcal {L} = \\mathcal {L} _ {c l s} + \\alpha \\mathcal {L} _ {c o n} \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 151, + 756, + 468, + 780 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $\\theta_{s}$ is the parameters of $S(\\cdot)$ , and $\\alpha$ is scaling factor.", + "bbox": [ + 76, + 794, + 460, + 809 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Teacher Optimization: The parameters of momentum teacher $\\theta_{t}$ are updated by an exponential moving average (EMA) of the student parameters. The update rule is $\\theta_{t} \\gets \\lambda \\theta_{t} + (1 - \\lambda) \\theta_{s}$ , where $\\lambda$ is a hyperparameter. More importantly, the updated teacher is utilized in the next iteration of hard instance mining.", + "bbox": [ + 75, + 810, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4. Experiments and Results", + "text_level": 1, + "bbox": [ + 498, + 89, + 735, + 107 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.1. Datasets and Evaluation Metrics", + "text_level": 1, + "bbox": [ + 500, + 114, + 785, + 128 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "CAMELYON-16 [2] is a WSI dataset proposed for metastasis detection in breast cancer. The dataset contains a total of 400 WSIs, which are officially split into 270 for training and 130 for testing, and the testing sample ratio is $13/40 \\approx 1/3$ . Following [6, 21, 44], we adopt 3-times 3-fold cross-validation on this dataset to ensure that each slide is used in training and testing, which can alleviate the impact of data split and random seed on the model evaluation. Each fold has approximately 133 slides. We report the mean and standard deviation of performance metrics over 3 runs.", + "bbox": [ + 496, + 137, + 890, + 287 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "TCGA Lung Cancer includes two sub-type of cancers, Lung Adenocarcinoma (LUAD) and Lung Squamous Cell Carcinoma (LUSC). There are diagnostic slides, LUAD with 541 slides from 478 cases, and LUSC with 512 slides from 478 cases. We randomly split the dataset into training, validation, and testing sets with a ratio of 65:10:25 on the patient level. 4-fold cross-validation is adopted, and the mean and standard deviation of performance metrics of the 4 test folders are reported.", + "bbox": [ + 496, + 289, + 890, + 425 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We adopt the same data pre-processing as in the CLAM [21]. Following the previous work [21, 26] we leverage Accuracy, Area Under Curve (AUC), and F1-score to evaluate model performance. AUC is the primary performance metric in the binary classification task, and we only report AUC in ablation experiments. Please refer to the Supplementary Material for the details of these two datasets.", + "bbox": [ + 496, + 426, + 890, + 545 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.2. Implementation Details", + "text_level": 1, + "bbox": [ + 500, + 556, + 718, + 571 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The details on network architectures and training are described in Supplementary Material.", + "bbox": [ + 500, + 580, + 888, + 609 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Performance Comparison with Exiting Works", + "text_level": 1, + "bbox": [ + 500, + 619, + 887, + 636 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "We mainly compare with AB-MIL [16], DSMIL [17], CLAM-SB [21], CLAM-MB [21], TransMIL [26], and DTFD-MIL [43], all of which are attention-based MIL methods. In addition, we compared two traditional MIL pooling operations, Max-pooling and Mean-pooling. Due to the dataset differences, the results of all other methods are reproduced using the official code they provide under the same settings.", + "bbox": [ + 496, + 643, + 890, + 763 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "As shown in Table 1, max-pooling and mean-pooling perform poorly on two datasets compared to other methods. We attribute this to their insufficient modeling of key instance information. Simple pooling operations are prone to be misled by limited slides that contain numerous instances. This problem is especially severe on the CAMELYON-16 dataset, where the proportion of significant instances is extremely small. For example, max-pooling lags behind DTFD-MIL [43] by $13.87\\%$ on AUC. Attention-based", + "bbox": [ + 496, + 765, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "4082", + "bbox": [ + 480, + 944, + 514, + 955 + ], + "page_idx": 4 + }, + { + "type": "table", + "img_path": "images/cbf34a959051a7c4326b33f04da77ec9023cd7ae4d52272e024c53603e10cd8f.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
MethodCAMELYON-16TCGA Lung Cancer
AccuracyAUCF1-scoreAccuracyAUCF1-score
Max-pooling78.95±2.2881.28±3.7471.06±2.5981.49±1.2486.45±0.7180.56±1.09
Mean-pooling76.69±0.2080.07±0.7870.41±0.1684.14±2.9790.13±2.4083.39±3.14
AB-MIL [16]90.06±0.6094.00±0.8387.40±1.0588.03±2.1993.17±2.0587.41±2.42
DSMIL [17]90.17±1.0294.57±0.4087.65±1.1888.32±2.7093.71±1.8287.90±2.50
CLAM-SB [21]90.31±0.1294.65±0.3087.89±0.5987.74±2.2293.67±1.6487.36±2.24
CLAM-MB [21]90.14±0.8594.70±0.7688.10±0.6388.73±1.6293.69±0.5488.28±1.58
TransMIL [26]89.22±2.3293.51±2.1385.10±4.3387.08±1.9792.51±1.7686.40±2.08
DTFD-MIL [43]90.22±0.3695.15±0.1487.62±0.5988.23±2.1293.83±1.3987.71±2.04
MHIM-MIL (AB-MIL)91.81±0.8296.14±0.5289.94±0.7089.64±2.2594.97±1.7289.31±2.19
MHIM-MIL (TransMIL)91.98±0.8996.49±0.4890.13±1.0890.02±2.5994.87±2.1789.65±2.63
MHIM-MIL (DSMIL)92.48±0.3596.49±0.6590.75±0.7389.83±3.3795.53±1.7489.71±2.92
", + "bbox": [ + 129, + 88, + 841, + 290 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/33f1863c0a17285de6fae008db08290bba448e15c643424665147416c8c1057a.jpg", + "table_caption": [ + "Table 1: The performance of different MIL approaches on CAMELYON-16 (C16) and TCGA Lung Cancer (TCGA). The highest performance is in bold. The Accuracy and F1-score are determined by the optimal threshold." + ], + "table_footnote": [], + "table_body": "
ModelC16TCGAPara.TimeMem.
AB-MIL94.0093.17657K4.0s2.4G
CLAM-MB94.7093.69789K4.3s2.7G
DTFD-MIL95.1593.83987K5.2s2.1G
MHIM-MIL96.1494.97657K4.3s2.3G
TransMIL93.5192.512.67M13.1s10.6G
MHIM-MIL96.4994.872.67M10.1s5.5G
", + "bbox": [ + 84, + 348, + 460, + 468 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 2: Comparison of time and memory requirements of different MIL methods. We report the model size (Para.), the training time per epoch (Time), and the peak memory usage (Mem.) on the CAMELYON-16 dataset (C16).", + "bbox": [ + 75, + 479, + 470, + 541 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "methods achieve better performance on both datasets by focusing on salient instances. In particular, the representative MIL framework DTFD-MIL [43] benefits from the further exploration of significant instances and achieves the second-best performance on both datasets (95.15% AUC on CAMELYON-16 and 93.83% AUC on TCGA). However, it also suffers from overemphasizing salient instances during training, which limits its generalization. Our proposed MHIM-MIL achieves significant performance improvement on both datasets (+1.34% AUC on CAMELYON-16 and +1.70% AUC on TCGA) by mining hard instances during training, breaking the performance bottleneck. It is worth mentioning that we validate our framework on three representative MIL models, both of which can outperform the existing MIL methods.", + "bbox": [ + 75, + 559, + 468, + 785 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.4. Computational Cost Analysis", + "text_level": 1, + "bbox": [ + 76, + 800, + 339, + 816 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In this section, we report the training time and GPU memory requirements for running different MIL models on a 3090 GPU. The upper part of Table 2 compares some MIL frameworks that use AB-MIL [16] as a baseline. We observe that traditional MIL frameworks typically intro", + "bbox": [ + 75, + 824, + 468, + 902 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "duce additional parameters and reduce efficiency due to their complex structures. For example, the state-of-the-art framework DTFD-MIL [43] increases the parameter size by nearly twice (657K vs. 987K) and the training time by $30\\%$ . In contrast, MHIM-MIL achieves the most significant performance improvement with almost no extra computational cost due to the momentum teacher. Moreover, existing Transformer-based MIL methods are usually plagued by high computing costs due to their large number of parameters and self-attention operations. For instance, TransMIL [26], which first applies a pure Transformer MIL model to solve WSI classification problems, has $4 \\times$ more parameters than AB-MIL, $3 \\times$ longer training time, and almost $4.5 \\times$ higher memory consumption. Furthermore, the extremely long input sequences in WSI classification degrade the stability of such complex structures (2.13% AUC standard deviation on C16, which is the highest among all embedding-level MIL methods). With the masked hard instance mining strategy, the MHIM-MIL framework significantly reduces the computational cost (-24% training time and -48% memory usage) and enhances its stability (0.48% AUC standard deviation on C16). More details are provided in Supplementary Material.", + "bbox": [ + 496, + 351, + 893, + 699 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.5. Ablation Study", + "text_level": 1, + "bbox": [ + 500, + 713, + 653, + 729 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "4.5.1 Importance of the Different Components", + "text_level": 1, + "bbox": [ + 500, + 738, + 836, + 753 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Table 3 shows the effect of different modules in MHIMMIL on two datasets. The baseline methods are two representative attention-based MIL methods, namely AB-MIL [16] and TransMIL [26]. First, we introduce the naive masked hard instance mining strategy, which leverages the model itself to mine hard instances during training. This strategy improves AUC by $1.86\\%$ and $2.55\\%$ for the two MIL models on CAMELYON-16 respectively, indicating that concentrating on hard instances during training can as", + "bbox": [ + 496, + 763, + 890, + 902 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "4083", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/f7d74056fceb12fff7af876954cfc043f7f20382ebe877a6427ab911a4642caa.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
ModuleCAMELYON-16TCGA
AB.Trans.AB.Trans.
Baseline94.0093.5193.1792.51
+MHIM95.8696.0694.1493.75
+MHIM+Siam.95.8296.2494.5594.13
+MHIM+Siam.+Con.96.1496.4994.9794.87
", + "bbox": [ + 80, + 88, + 467, + 193 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/81cd2fdf2a8f6f3a4698966e61f2f7ef75e93bf1b83363a49f4be5c106f18b2b.jpg", + "table_caption": [ + "Table 3: The effect of different components in MHIM-MIL with two MIL models: AB-MIL (AB.) and TransMIL (Trans.). MHIM denotes the masked hard instance mining strategy. Siam. refers to the Siamese framework. Con. represents consistency loss." + ], + "table_footnote": [], + "table_body": "
StrategyCAMELYON-16TCGA
AB.Trans.AB.Trans.
Baseline94.0093.5193.1792.51
HAM95.6895.9093.8394.54
R-HAM96.1495.8894.7994.60
L-HAM95.8196.4994.3394.67
LR-HAM95.9296.3394.9794.87
", + "bbox": [ + 102, + 295, + 444, + 416 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "sist mainstream MIL models in building better classification boundaries. Further discussion on the masked hard instance mining strategy is presented in Section 4.5.2. Compared with the naive MHIM strategy, the third row of the table suggests that a Siamese structure [3,5,8] based on a momentum teacher is beneficial for more stable and effective mining of hard instances. We elaborate more on choosing the teacher model in Section 4.5.3. After adding consistency loss term to the objective function, our full MHIM-MIL framework achieves the best performance (96.49% AUC on CAMELYON-16 and 94 .97% AUC on TCGA). For subsequent ablation experiments, we include consistency loss by default to facilitate the optimization of our framework.", + "bbox": [ + 75, + 489, + 468, + 686 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5.2 Impact of the Different MHIM Strategies", + "text_level": 1, + "bbox": [ + 76, + 709, + 418, + 724 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "The masked hard instance mining strategy is the core design of our method. The main idea of this strategy is masking the most salient instances to indirectly mine hard instances to facilitate model training. Based on this idea, we devise three hybrid strategies (R-HAM, L-HAM, and LR-HAM) and present their impact in Table 4. The basic strategy, High Attention Masking (HAM), already boosts performance significantly, leading to AUC improvements of $1.68\\%$ and $2.39\\%$ for two MIL models on the CAMELYON-16 dataset, respectively. After introducing the other two strategies, different MIL models achieve performance improvements", + "bbox": [ + 75, + 734, + 468, + 902 + ], + "page_idx": 6 + }, + { + "type": "table", + "img_path": "images/30602555df4ad8f56e48b0bf933b4182fdfe0058bd778531305fc2fa39d2d5d8.jpg", + "table_caption": [ + "Table 4: Comparison between different masked hard instance mining strategies. The three hybrid strategies show varying performance across the benchmarks." + ], + "table_footnote": [], + "table_body": "
TeacherCAMELYON-16TCGA
AB.Trans.AB.Trans.
Baseline94.0093.5193.1792.51
Student copy95.8495.8693.6893.45
Init.95.8896.1294.6694.15
Momentum95.9696.1194.6594.45
Init.+Momentum96.1496.4994.9794.87
", + "bbox": [ + 521, + 88, + 874, + 207 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/eeb175c573c3a6fcfa3c2d6dcd4ccec2205eb6b58116e97c47412198800cb466.jpg", + "image_caption": [ + "Table 5: Comparison of different types of teachers. Momentum denotes the teacher is updated by EMA strategy. Init. indicates the initialization of the teacher with pretrained parameters. The bottom figure compares the stability of the momentum teacher and the non-batch gradient updated student during training." + ], + "image_footnote": [], + "bbox": [ + 560, + 210, + 828, + 316 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "on both datasets. Specifically, AB-MIL [16] shows more significant performance gains after introducing randomness (96.14% AUC on CAMELYON-16 with R-HAM) due to its better ability to filter out redundant information, while TransMIL [26] shows the reverse trend (96.49% AUC on CAMELYON-16 with L-HAM). Furthermore, the more complex three-hybrid strategy (LR-HAM) achieves the best performance on the TCGA dataset, which has a larger proportion of positive areas and more instances. Overall, our experiments validate the effectiveness of masked hard instance mining strategy, and the diversity of proposed strategies improves its applicability to different datasets and MIL models.", + "bbox": [ + 496, + 431, + 890, + 627 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "4.5.3 Impact of the Choice of Teacher Network", + "text_level": 1, + "bbox": [ + 498, + 648, + 841, + 665 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "In MHIM-MIL, we employ a Teacher model to mine hard instances and facilitate training of the Student model. In Table 5, we comprehensively investigate the effects of various choices of Teacher network. First, we utilize a single-model structure, which treats the Student model as the Teacher. The student conducts masked hard instance mining prior to training. Due to the non-batch gradient update, the unstable performance of the Student model makes the strategy susceptible to noise, so the performance is not optimal. Second, we adopt a momentum teacher, which shares the same network structure as the Student model and is updated with the EMA strategy. This updating strategy enhanced the stability of momentum teachers, as shown in the figure below, and enabled MHIM-MIL to achieve $0.97\\%$ and $1.00\\%$ performance improvement in TCGA under the two MIL mod", + "bbox": [ + 496, + 674, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "4084", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/166f3a78309f89aee0d474548cbf567a48aba0e95a9b883240057e3ccb1ab450.jpg", + "image_caption": [ + "Figure 4: Patch visualization produced by AB-MIL [16] (baseline) and MHIM-MIL. The blue lines outline the tumor regions. The brighter patch indicates higher attention scores. The cyan colors indicate high probabilities of being tumor for the corresponding locations. Ideally, the cyan patches should cover only the area within the blue lines. We show that focusing only on more salient regions reduces the generalization ability of the model and that hard instances can provide useful information for more accurate and comprehensive judgments." + ], + "image_footnote": [], + "bbox": [ + 80, + 87, + 478, + 412 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/770d6e0337e6ebf088ae33ebaff4dcfa814ed2d6725ac69e8f555b121771a843.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 493, + 88, + 888, + 412 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "els, respectively. With proper initialization, the momentum teacher achieves the best performance. However, a fixed initialization teacher fails to learn new knowledge, which emphasizes the significance of iterative optimization.", + "bbox": [ + 75, + 521, + 470, + 583 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "4.6. Visualization", + "text_level": 1, + "bbox": [ + 76, + 590, + 215, + 604 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To more intuitively understand the effect of the masked hard instance mining, we visualize the attention scores (bright patch) and tumor probabilities (cyan patch) of patches produced by AB-MIL and MHIM-MIL, as illustrated in Figure 4. Here, MHIM-MIL employs AB-MIL as its baseline model. We note that attention scores only indicate the regions of interest of models and are infeasible to reflect tumor probabilities [17, 43]. First, as shown in Figure 4, AB-MIL often assigns high tumor probabilities to patches in non-tumor areas. We attribute this phenomenon to the low generalization capability of conventional attention-based MIL models, which tend to focus only on salient regions during training. In contrast, MHIM-MIL trained with hard instances shows a much better generalization ability than the baseline model for noise robustness (rows 2 and 3 on the right) and for precise detection of challenging subtle tumor areas (row 3 on the left). More significantly, we find that focusing only on tumor areas leads to missing most of them, expanding the view to include some", + "bbox": [ + 75, + 613, + 472, + 902 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "\"irrelevant areas\" enables the model to make more complete judgments (rows 1 and 2 on the left). This phenomenon demonstrates how hard instances provide more useful information to help the model make more accurate and comprehensive judgments. We provide more details and an in-depth analysis of this patch visualization in Supplementary Material.", + "bbox": [ + 496, + 521, + 893, + 627 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 646, + 619, + 662 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This paper rethinks the impact of salient instances for MIL-based WSI classification algorithms. We demonstrate that attention-based MIL methods excessively prioritizing salient instances harm the generalization ability of the model. To address this issue, we have proposed several masked hard instance mining strategies that mask out salient patches and encourage the model to attend to informative regions for better discriminative learning. Through qualitative analysis, we have demonstrated that these strategies effectively alleviate the under-fitting problem of general AB-MIL to hard instances. We have also developed the MHIM-MIL framework that leverages momentum teacher and consistency loss to further enhance hard instance mining. Our experimental results demonstrate the superiority and generality of the MHIM-MIL framework over other lat", + "bbox": [ + 496, + 674, + 893, + 902 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "4085", + "bbox": [ + 482, + 944, + 514, + 955 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "est methods. In future work, we plan to devise a more precise localization scheme for hard instances that can facilitate model training and convergence.", + "bbox": [ + 76, + 90, + 468, + 137 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "6. Acknowledgement", + "text_level": 1, + "bbox": [ + 76, + 151, + 256, + 167 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "Reported research is partly supported by the National Natural Science Foundation of China under Grant 62176030, and the Natural Science Foundation of Chongqing under Grant cstc2021jcyj-msxmX0568.", + "bbox": [ + 76, + 176, + 468, + 238 + ], + "page_idx": 8 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 252, + 174, + 268 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Ejaz Ahmed, Michael Jones, and Tim K Marks. An improved deep learning architecture for person re-identification. 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Springer, 2022. 1" + ], + "bbox": [ + 501, + 92, + 890, + 893 + ], + "page_idx": 9 + }, + { + "type": "page_number", + "text": "4087", + "bbox": [ + 482, + 945, + 514, + 955 + ], + "page_idx": 9 + } +] \ No newline at end of file diff --git a/2023/Multiple Instance Learning Framework with Masked Hard Instance Mining for Whole Slide Image Classification/4186ce96-ecad-4ae2-bdd7-3d5e8448e342_model.json b/2023/Multiple Instance Learning Framework with Masked Hard Instance Mining for Whole Slide Image Classification/4186ce96-ecad-4ae2-bdd7-3d5e8448e342_model.json new file mode 100644 index 0000000000000000000000000000000000000000..b183fcf41070a6310898d3ac518cd7ffc42d6d7a --- /dev/null +++ b/2023/Multiple Instance Learning Framework with Masked Hard Instance Mining for Whole Slide Image Classification/4186ce96-ecad-4ae2-bdd7-3d5e8448e342_model.json @@ -0,0 +1,2024 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.085, + 0.13, + 0.888, + 0.177 + ], + "angle": 0, + "content": "Multiple Instance Learning Framework with Masked Hard Instance Mining for Whole Slide Image Classification" + }, + { + "type": "text", + "bbox": [ + 0.123, + 0.203, + 0.849, + 0.256 + ], + "angle": 0, + "content": "Wenhao Tang\\(^{1}\\) Sheng Huang\\(^{1*}\\) Xiaoxian Zhang\\(^{1}\\) Fengtao Zhou\\(^{2}\\) Yi Zhang\\(^{1}\\) Bo Liu\\(^{3}\\) \n\\(^{1}\\)Chongqing University \n\\(^{2}\\)The Hong Kong University of Science and Technology \n\\(^{3}\\)Walmart Global Tech" + }, + { + "type": "text", + "bbox": [ + 0.238, + 0.26, + 0.732, + 0.275 + ], + "angle": 0, + "content": "{whtang, huangsheng, zhangxiaoxian, zhangyii}@cqu.edu.cn" + }, + { + "type": "text", + "bbox": [ + 0.304, + 0.278, + 0.668, + 0.292 + ], + "angle": 0, + "content": "fzhouaf@connect.ust.hk, kfliubo@gmail.com" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.327, + 0.314, + 0.344 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.359, + 0.474, + 0.768 + ], + "angle": 0, + "content": "The whole slide image (WSI) classification is often formulated as a multiple instance learning (MIL) problem. Since the positive tissue is only a small fraction of the gigapixel WSI, existing MIL methods intuitively focus on identifying salient instances via attention mechanisms. However, this leads to a bias towards easy-to-classify instances while neglecting hard-to-classify instances. Some literature has revealed that hard examples are beneficial for modeling a discriminative boundary accurately. By applying such an idea at the instance level, we elaborate a novel MIL framework with masked hard instance mining (MHIM-MIL), which uses a Siamese structure (Teacher-Student) with a consistency constraint to explore the potential hard instances. With several instance masking strategies based on attention scores, MHIM-MIL employs a momentum teacher to implicitly mine hard instances for training the student model, which can be any attention-based MIL model. This counter-intuitive strategy essentially enables the student to learn a better discriminating boundary. Moreover, the student is used to update the teacher with an exponential moving average (EMA), which in turn identifies new hard instances for subsequent training iterations and stabilizes the optimization. Experimental results on the CAMELYON-16 and TCGA Lung Cancer datasets demonstrate that MHIM-MIL outperforms other latest methods in terms of performance and training cost. The code is available at: https://github.com/DearCaat/MHIM-MIL." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.794, + 0.21, + 0.81 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.819, + 0.47, + 0.88 + ], + "angle": 0, + "content": "Histopathological image analysis plays a crucial role in modern medicine, particularly in the treatment of cancer, where it serves as the gold standard for diagnosis [18, 20, 24,45]. Digitalizing pathological images into Whole Slide" + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.327, + 0.895, + 0.472 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.481, + 0.895, + 0.527 + ], + "angle": 0, + "content": "Figure 1: Left: Previous MIL models focus on the more salient instances. Right: MHIM-MIL mines an amount of hard-to-classify instances to learn a better boundary." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.895, + 0.689 + ], + "angle": 0, + "content": "Images (WSIs) through digital slide scanner has opened new avenues for computer-aided analysis [9, 26]. Due to the huge size of a WSI and the lack of pixel-level annotations, histopathological image analysis is commonly formulated as a multiple instance learning (MIL) task [10, 23, 31]. In MIL, each WSI (or slide) is a bag containing thousands of unlabeled instances (patches) cropped from the slide. With at least one instance being disease positive, the bag is deemed positive, otherwise negative." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.69, + 0.896, + 0.901 + ], + "angle": 0, + "content": "However, the number of slides is limited and each slide contains a mass of instances with a low positive proportion. This imbalance would hinder the inference of bag labels [16, 43]. To alleviate this issue, several WSI classification methods [6, 16-18,26] employ an attention mechanism to aggregate salient instance features into a bag-level feature for WSI classification. Furthermore, some MIL frameworks [17,21,40,43] focus on the more salient instances in the bag and leverage them to facilitate WSI classification. For instance, existing frameworks [40, 43] propose to only select the instances that correspond to the top \\(K\\) highest or lowest attention scores [17, 40] or patch probabilities [43] for yielding high-quality bag embedding for both training and testing." + }, + { + "type": "page_footnote", + "bbox": [ + 0.096, + 0.888, + 0.227, + 0.9 + ], + "angle": 0, + "content": "*Corresponding Author." + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4078" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.473, + 0.318 + ], + "angle": 0, + "content": "These salient instances are actually \"easy-to-classify\" instances, which are not optimal for training a discriminative WSI classification model. In conventional machine learning, such as Support Vector Machines (SVM) [13], samples near the category distribution boundary are more challenging to classify, but are more useful for depicting the classification boundary, as illustrated in Figure 1. Moreover, other deep learning works [25, 28, 33, 34] also reveal that mining hard samples for training can improve the generalization abilities of models. By applying such an idea at the instance level, we can better highlight the \"hard-to-classify\" instances that facilitate MIL model training, and benefit the final WSI classification. However, the lack of instance labels poses a challenge to the direct application of traditional hard sample mining strategies at the instance level." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.319, + 0.473, + 0.665 + ], + "angle": 0, + "content": "To address this issue, we present a novel MIL framework based on masked hard instance mining strategies (MHIM) named MHIM-MIL. The main idea of MHIM is to mask out the instances with high attention scores to highlight the hard instances for model training. Based on this, we incorporate two other instance masking strategies to enhance training efficiency and mitigate the over-fitting risk. Another key design of MHIM-MIL is an instance attention generator based on a Siamese structure (Teacher-Student) [3, 8]. In MHIM-MIL, the MIL-based WSI classification model is the student network, which aggregates hard instances mined by a momentum teacher with different instance masking strategies. The momentum teacher is updated using an exponential moving average (EMA) of the student model. Moreover, the framework is optimized by inducing a consistency constraint that explores more supervised information beyond the limited slide label. Unlike the conventional MIL frameworks [40, 43], which adopt complex cascade gradient-updating structures, our method is more simple and does not require additional parameters. It not only improves efficiency but also provides improved performance stability. The contribution of this paper is summarized as follows," + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.677, + 0.47, + 0.799 + ], + "angle": 0, + "content": "- We propose a simple and efficient MIL framework with masked hard instance mining named MHIM-MIL. It implicitly mines hard instances with instance attention for training a more discriminative MIL model. Extensive experiments on two WSI datasets validate that MHIM boosts different MIL models and outperforms other latest methods in terms of performance and training cost." + }, + { + "type": "text", + "bbox": [ + 0.096, + 0.81, + 0.47, + 0.902 + ], + "angle": 0, + "content": "- We propose several hybrid instance masking strategies for indirectly mining hard instances in MIL. These strategies not only address the reliance problem of conventional methods on instance-level supervision but also enhance the training efficiency of the model and mitigate the over-fitting risk." + }, + { + "type": "text", + "bbox": [ + 0.519, + 0.092, + 0.892, + 0.182 + ], + "angle": 0, + "content": "- With the Siamese structure, we introduce a parameter-free momentum teacher to obtain instance attention scores more efficiently and stably. Moreover, we employ a consistency-based iterative optimization to improve the discriminability of both models progressively." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.198, + 0.642, + 0.213 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.223, + 0.875, + 0.24 + ], + "angle": 0, + "content": "2.1. Multiple Instance Learning in WSI Analysis" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.246, + 0.895, + 0.717 + ], + "angle": 0, + "content": "Multiple Instance Learning (MIL) [10] has been widely used in WSI analysis with its unique learning paradigm in recent years [17, 22, 26, 35, 40, 42]. MIL is a weakly supervised learning framework that utilizes coarse-grained bag labels for training instead of fine-grained instance annotations. Previous algorithms can be broadly categorized into two groups: instance-level [4, 12, 15, 40] and embedding-level [9, 27, 38, 39, 43]. The former obtain instance labels and aggregate them to obtain the bag label, whereas the latter aggregate all instance features into a high-level bag embedding for bag prediction. Most embedding-level methods share the basic idea of AB-MIL [16], which employs learnable weights to aggregate salient instance features into bag embedding. Furthermore, some MIL frameworks [17, 21, 40, 43] mine more salient instances making classification easier and facilitating classification. For example, Lu et al. selected the most salient instances based on their attention scores (e.g., maximum and minimum scores) to compute instance-level loss and improve performance [21]. Zhang et al. proposed a class activation map (CAM) based on the AB-MIL paradigm to better mine salient instances and used AB-MIL to aggregate them into bag embedding [43]. In addition, feature clustering methods [27, 37, 44] computed cluster centroids of all feature embeddings and used representative embeddings for the final prediction. However, all these methods focused excessively on salient instances in training, which are easy instances with high confidence scores and can be easily classified. As a result, they overlook the importance of hard instances for training. In this paper, we intend to mine hard instances for improving WSI classification performance." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.726, + 0.855, + 0.743 + ], + "angle": 0, + "content": "2.2. Hard Sample Mining in Computer Vision" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.75, + 0.895, + 0.903 + ], + "angle": 0, + "content": "Hard sample mining is a popular technique to speed up convergence and enhance the discriminative power of the model in many deep learning areas, such as face recognition [25], object detection [29, 36], person re-identification [1, 28, 33, 34], and deep metric learning [30, 32]. The main idea behind this technique is to select the samples which are hard to classify correctly (i.e., hard negatives and hard positives) for alleviating the imbalance between positive and negative samples and facilitating model training. There are generally three groups of approaches" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4079" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.473, + 0.304 + ], + "angle": 0, + "content": "for evaluating sample difficulty: loss-based [14], similarity-based [7], and learnable weight-based [41]. Typically, these strategies require complete sample supervision information. Drawing on the ideas of the above works, we propose a hard instance mining approach in MIL, mining hard examples at the instance level. In this, there are no complete instance labels, only the bag label is available. Similar to our approach, Li et al. utilized attention scores to identify salient instances from false negative bags to serve as hard negative instances and used them to compose the hard bags for improving classification performance [19]. A key difference is that we indirectly mine hard instances by masking out the most salient instances rather than directly locating hard negative instances." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.318, + 0.251, + 0.334 + ], + "angle": 0, + "content": "3. Proposed Method" + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.343, + 0.358, + 0.358 + ], + "angle": 0, + "content": "3.1. Background: MIL Formulation" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.366, + 0.473, + 0.606 + ], + "angle": 0, + "content": "In MIL, any input WSI \\( X \\) is considered as a bag with multiple instances, which can be represented as \\( X = \\{x_{i}\\}_{i=1}^{N} \\). \\( x_{i} \\) is a patch collected from the WSI and considered as the \\( i \\)-th instance of \\( X \\). \\( N \\) is the number of instances. For a classification task, there exists a known label \\( Y \\in C \\) for the bag and an unknown label \\( y_{n} \\in C \\) for each instance, where \\( C \\) is the collection of category labels. The goal of a MIL model \\( \\mathcal{M}(\\cdot) \\) is to predict the bag label with all instances \\( \\hat{Y} \\gets \\mathcal{M}(X) \\). The popular solution is to learn a bag representation \\( F \\) from the extracted features of instances \\( Z = \\{z_{i}\\}_{i=1}^{N} \\) in a bag, which is also referred as the instance aggregation step. And a classifier \\( \\mathcal{C}(\\cdot) \\), trained upon the \\( F \\), can be used to predict the bag label \\( \\hat{Y} \\gets \\mathcal{C}(F) \\). There are two ways to aggregate instances for achieving bag embedding. One is the attention-based aggregation [16] denoted as follows," + }, + { + "type": "equation", + "bbox": [ + 0.202, + 0.607, + 0.47, + 0.648 + ], + "angle": 0, + "content": "\\[\nF = \\sum_ {i = 1} ^ {N} a _ {i} z _ {i} \\in \\mathbb {R} ^ {D}, \\tag {1}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.654, + 0.47, + 0.715 + ], + "angle": 0, + "content": "where \\( a_{i} \\) is the learnable scalar weight for \\( z_{i} \\), and \\( D \\) is the dimension of vector \\( F \\) and \\( z_{i} \\). Many works [17, 21, 43] follow this formulation but differ in the ways they generate the attention score \\( a_{i} \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.714, + 0.47, + 0.79 + ], + "angle": 0, + "content": "Another is the multi-head self-attention (MSA) based aggregation [26]. In this fashion, a class token \\( z_0 \\) is embedded with the instance features to get the initial input sequence \\( Z^0 = [z_0, z_1, \\ldots, z_N] \\in \\mathbb{R}^{(N + 1) \\times D} \\) for aggregating instance features. This can be formulated as," + }, + { + "type": "equation", + "bbox": [ + 0.086, + 0.8, + 0.468, + 0.827 + ], + "angle": 0, + "content": "\\[\n\\operatorname {h e a d} = A ^ {\\ell} \\left(Z ^ {\\ell - 1} W ^ {V}\\right) \\in \\mathbb {R} ^ {N \\times \\frac {D}{H}}, \\quad \\ell = 1 \\dots L \\tag {2}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.089, + 0.824, + 0.44, + 0.84 + ], + "angle": 0, + "content": "\\[\nZ ^ {\\ell} = \\operatorname {C o n c a t} \\left(\\operatorname {h e a d} _ {1}, \\dots , \\operatorname {h e a d} _ {H}\\right) W ^ {O}, \\quad \\ell = 1 \\dots L\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.854, + 0.47, + 0.901 + ], + "angle": 0, + "content": "where \\(W^{V}\\in \\mathbb{R}^{D\\times \\frac{D}{H}}\\) and \\(W^{O}\\in \\mathbb{R}^{D\\times D}\\) are the learnable projection matrices of MSA. \\(A^{\\ell}\\in \\mathbb{R}^{(N + 1)\\times (N + 1)}\\) is the attention matrix of the \\(\\ell\\)-th layer, \\(L\\) is the number of MSA" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.092, + 0.892, + 0.137 + ], + "angle": 0, + "content": "block, and \\( H \\) is the number of head in each MSA block. The bag embedding \\( F \\) is the output class token at the final layer," + }, + { + "type": "equation", + "bbox": [ + 0.663, + 0.141, + 0.892, + 0.159 + ], + "angle": 0, + "content": "\\[\nF = Z _ {0} ^ {L}. \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.17, + 0.892, + 0.232 + ], + "angle": 0, + "content": "The self-attention-based bag embedding is essentially a special case of attention-based bag embedding in the multi-instance learning setting. Collectively, these approaches can be referred to as the general attention-based MIL method." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.245, + 0.808, + 0.261 + ], + "angle": 0, + "content": "3.2. MHIM-MIL for WSI Classification" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.271, + 0.892, + 0.437 + ], + "angle": 0, + "content": "In general attention-based MIL frameworks, the attention scores of instances indicate the contributions of instances to the bag classification. The salient instances with high scores are useful for classifying WSI in the testing phase but are not conducive to training a MIL model with good generalization ability. Although hard samples have been proven to enhance the generalization ability of the model in many computer vision scenarios [11, 32-34], previous MIL works focus more on exploiting the salient instances and neglecting the utilization of hard instances in model optimization." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.439, + 0.893, + 0.816 + ], + "angle": 0, + "content": "In this paper, we propose a simple and efficient MIL framework with Masked Hard Instance Mining (MHIM-MIL) to boost the WSI classification. As illustrated in Figure 2, the MHIM-MIL framework employs a Siamese structure during the training phase. The main component of our framework is a general attention-based MIL model (Student), denoted as \\( S(\\cdot) \\), for aggregating instance features. To increase the discriminatory difficulty of the student model and force it to focus on hard instances, we introduce a momentum teacher, denoted as \\( T(\\cdot) \\), to score the instances with attention weights and then employ some masked hard instance mining strategies to mask the salient instances while preserving the hard instances. After hard instance mining, all the mined features are forwarded into the student model for the inference of the bag label. The teacher shares the same network structure as the student model but does not need gradient-based updates. It is worth mentioning that, due to the varying number of instances within each bag, the non-batch gradient descent algorithm (i.e., SGD with batch size 1) is typically employed to optimize the MIL model. Therefore, compared to the traditional MIL frameworks with two-tier gradient updating models [40, 43], this Siamese structure makes training more stable and efficient with fewer parameters. The proposed framework can be defined as," + }, + { + "type": "equation", + "bbox": [ + 0.598, + 0.819, + 0.892, + 0.845 + ], + "angle": 0, + "content": "\\[\n\\hat {Y} = \\mathcal {S} (\\hat {Z}) = \\mathcal {S} (M _ {\\mathcal {T}} (Z)), \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.856, + 0.892, + 0.9 + ], + "angle": 0, + "content": "where \\(M_{\\mathcal{T}}(\\cdot)\\) denotes a masked hard instance mining strategy through the teacher model and \\(\\hat{Z}\\) are the mined instances." + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4080" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.173, + 0.089, + 0.803, + 0.257 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.172, + 0.259, + 0.8, + 0.337 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.348, + 0.895, + 0.425 + ], + "angle": 0, + "content": "Figure 2: Overview of proposed MHIM-MIL. A momentum teacher is used to compute attention scores for all instances. We mask instances based on attention with hard mining strategies and feed the remaining to the student model. The student is updated by a consistency loss term \\(\\mathcal{L}_{con}\\) and a label error loss term \\(\\mathcal{L}_{cls}\\). The teacher parameters are updated with an Exponential Moving Average (EMA) of the student parameters without gradient updates. In the inference phase, we use the complete input instances and the student model only." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.439, + 0.42, + 0.456 + ], + "angle": 0, + "content": "3.3. Masked Hard Instance Mining Strategy" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.463, + 0.473, + 0.599 + ], + "angle": 0, + "content": "Conventional hard sample mining strategies are difficult to apply without instance-level supervision. We address this challenge by proposing masked hard instance mining strategies that use attention scores to implicitly mine hard instances by masking out easy instances with high attention scores. More specifically, given a complete sequence of instance features \\( Z = \\{z_{i}\\}_{i=1}^{N} \\) as the input of the teacher model \\( \\mathcal{T}(\\cdot) \\), the teacher outputs the attention weight \\( a_{i} \\) for each instance as follow," + }, + { + "type": "equation", + "bbox": [ + 0.153, + 0.609, + 0.47, + 0.627 + ], + "angle": 0, + "content": "\\[\nA = \\left[ a _ {1}, \\dots , a _ {i}, \\dots , a _ {N} \\right] = \\mathcal {T} (Z). \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.637, + 0.47, + 0.668 + ], + "angle": 0, + "content": "Then, we obtain the indices of the attention sequence in descending order by applying a sorting operation on \\(A\\)," + }, + { + "type": "equation", + "bbox": [ + 0.166, + 0.678, + 0.47, + 0.695 + ], + "angle": 0, + "content": "\\[\nI = \\left[ i _ {1}, i _ {2}, \\dots , i _ {N} \\right] = \\operatorname {S o r t} (A), \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.705, + 0.47, + 0.825 + ], + "angle": 0, + "content": "where \\( i_1 \\) is the index of the instance with the highest attention score while \\( i_N \\) is the index of the one with the lowest score. With this index collection \\( I \\), we will present several masked hard instance mining strategies to select the hard instances. We define an \\( N \\)-dimensional binary vector \\( M = [m_1, \\dots, m_i, \\dots, m_N] \\) for encoding the mask flags of instances where \\( m_i \\in \\{0, 1\\} \\). If \\( m_i = 1 \\), the \\( i \\)-th instance is masked, otherwise, it is unmasked." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.825, + 0.471, + 0.902 + ], + "angle": 0, + "content": "High Attention Masking: The simplest masked hard instance mining strategy is the High Attention Masking (HAM) strategy, which simply masks instances with the top \\(\\beta_{h}\\%\\) highest attention scores. The instance mask flags under HAM are initialized as all zero vectors, \\(M_{h}(:) = 0\\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.44, + 0.892, + 0.53 + ], + "angle": 0, + "content": "Then we collect the indices of the instances whose scores are ranked in the top \\(\\beta_h\\%\\), \\(I_h = [i_t]_{t=1}^{\\lceil \\beta_h\\% \\times N \\rceil}\\). Finally, we set the mask flags with these indices, \\(M_h(I_h) = 1\\). To ensure that positive instances are preserved within the un-masked sequences, we also utilized techniques such as mask ratio decay." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.53, + 0.893, + 0.635 + ], + "angle": 0, + "content": "Hybrid Masking: We combine HAM with several other instance masking strategies as hybrid masking strategies to achieve some specific properties in hard instance mining, as shown in Figure 3. We consider the obtained mask flags as a collection and employ the union operation for mask flag fusion. We design three hybrid masking strategies as follows:" + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.643, + 0.892, + 0.749 + ], + "angle": 0, + "content": "- L-HAM: We use the same pipeline as HAM to generate the mask flags \\( M_{l} \\) for masking the instances with the top \\( \\beta_{l} \\% \\) lowest attention scores in order to filter out the redundant uninformative instances and improve efficiency. To endow this property to HAM, we union the mask flags obtained by two strategies to get the new mask flags, \\( \\hat{M} = M_{h} \\cup M_{l} \\)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.757, + 0.894, + 0.833 + ], + "angle": 0, + "content": "- R-HAM: Randomness is beneficial to reduce the risk of over-fitting. We generate a random mask flag vector \\( M_r \\) with a given random ratio \\( \\beta_r\\% \\), and combine it with \\( M_h \\) for introducing the randomness to the hard instance mining, \\( \\hat{M} = M_h \\cup M_r \\)." + }, + { + "type": "text", + "bbox": [ + 0.518, + 0.84, + 0.894, + 0.902 + ], + "angle": 0, + "content": "- LR-HAM: Combining the above strategies, we can obtain completely hybrid mask flags, \\(\\tilde{M} = M_h \\cup M_r \\cup M_l\\), which is expected to achieve both of the mentioned desirable properties." + }, + { + "type": "list", + "bbox": [ + 0.518, + 0.643, + 0.894, + 0.902 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.514, + 0.957 + ], + "angle": 0, + "content": "4081" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.079, + 0.088, + 0.226, + 0.205 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.249, + 0.087, + 0.47, + 0.204 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.215, + 0.47, + 0.247 + ], + "angle": 0, + "content": "Figure 3: Illustration of proposed hybrid masking strategy for hard instance mining." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.274, + 0.47, + 0.306 + ], + "angle": 0, + "content": "Once the final mask flag \\(\\hat{M}\\) is produced, the masked instance sequence will be obtained:" + }, + { + "type": "equation", + "bbox": [ + 0.133, + 0.318, + 0.47, + 0.343 + ], + "angle": 0, + "content": "\\[\n\\hat {Z} = M _ {\\mathcal {T}} (Z) = \\operatorname {M a s k} (Z, \\hat {M}) \\in \\mathbb {R} ^ {\\hat {N} \\times D}, \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.357, + 0.414, + 0.373 + ], + "angle": 0, + "content": "where the \\(\\hat{N}\\) is the number of unmasked instances." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.384, + 0.433, + 0.401 + ], + "angle": 0, + "content": "3.4. Consistency-based Iterative Optimization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.409, + 0.47, + 0.544 + ], + "angle": 0, + "content": "Under the Siamese structure, while the teacher model guides the training of the student model, the new knowledge learned by the student model will also update the teacher model. This iterative optimization process progressively improves the mining ability of the teacher and the discriminability of the student. To further facilitate this optimization and explore additional supervised information provided by the momentum teacher, we propose a consistency loss that constrains the classification results of both models." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.546, + 0.47, + 0.59 + ], + "angle": 0, + "content": "Student Optimization: There are two losses in student optimization. One is the cross-entropy for measuring the bag label prediction loss," + }, + { + "type": "equation", + "bbox": [ + 0.138, + 0.604, + 0.47, + 0.629 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {c l s} = Y \\log \\hat {Y} + (1 - Y) \\log \\left(1 - \\hat {Y}\\right). \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.64, + 0.469, + 0.671 + ], + "angle": 0, + "content": "Another is a consistency loss between the bag representation of student \\( F_{s} \\) and momentum teacher \\( F_{t} \\)," + }, + { + "type": "equation", + "bbox": [ + 0.163, + 0.685, + 0.469, + 0.701 + ], + "angle": 0, + "content": "\\[\n\\mathcal {L} _ {\\text {c o n}} = - \\operatorname {s o f t m a x} \\left(F _ {t} / \\tau\\right) \\log F _ {s} \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.714, + 0.469, + 0.744 + ], + "angle": 0, + "content": "where the \\(\\tau > 0\\) is a temperature parameter. Overall, the final optimization loss is as follows:" + }, + { + "type": "equation", + "bbox": [ + 0.153, + 0.757, + 0.469, + 0.781 + ], + "angle": 0, + "content": "\\[\n\\left\\{\\hat {\\theta_ {s}} \\right\\} \\leftarrow \\arg \\min _ {\\theta_ {s}} \\mathcal {L} = \\mathcal {L} _ {c l s} + \\alpha \\mathcal {L} _ {c o n} \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.795, + 0.462, + 0.81 + ], + "angle": 0, + "content": "where \\(\\theta_{s}\\) is the parameters of \\(S(\\cdot)\\), and \\(\\alpha\\) is scaling factor." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.811, + 0.469, + 0.902 + ], + "angle": 0, + "content": "Teacher Optimization: The parameters of momentum teacher \\(\\theta_{t}\\) are updated by an exponential moving average (EMA) of the student parameters. The update rule is \\(\\theta_{t} \\gets \\lambda \\theta_{t} + (1 - \\lambda) \\theta_{s}\\), where \\(\\lambda\\) is a hyperparameter. More importantly, the updated teacher is utilized in the next iteration of hard instance mining." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.09, + 0.736, + 0.108 + ], + "angle": 0, + "content": "4. Experiments and Results" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.115, + 0.787, + 0.13 + ], + "angle": 0, + "content": "4.1. Datasets and Evaluation Metrics" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.138, + 0.892, + 0.289 + ], + "angle": 0, + "content": "CAMELYON-16 [2] is a WSI dataset proposed for metastasis detection in breast cancer. The dataset contains a total of 400 WSIs, which are officially split into 270 for training and 130 for testing, and the testing sample ratio is \\(13/40 \\approx 1/3\\). Following [6, 21, 44], we adopt 3-times 3-fold cross-validation on this dataset to ensure that each slide is used in training and testing, which can alleviate the impact of data split and random seed on the model evaluation. Each fold has approximately 133 slides. We report the mean and standard deviation of performance metrics over 3 runs." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.29, + 0.892, + 0.426 + ], + "angle": 0, + "content": "TCGA Lung Cancer includes two sub-type of cancers, Lung Adenocarcinoma (LUAD) and Lung Squamous Cell Carcinoma (LUSC). There are diagnostic slides, LUAD with 541 slides from 478 cases, and LUSC with 512 slides from 478 cases. We randomly split the dataset into training, validation, and testing sets with a ratio of 65:10:25 on the patient level. 4-fold cross-validation is adopted, and the mean and standard deviation of performance metrics of the 4 test folders are reported." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.427, + 0.892, + 0.546 + ], + "angle": 0, + "content": "We adopt the same data pre-processing as in the CLAM [21]. Following the previous work [21, 26] we leverage Accuracy, Area Under Curve (AUC), and F1-score to evaluate model performance. AUC is the primary performance metric in the binary classification task, and we only report AUC in ablation experiments. Please refer to the Supplementary Material for the details of these two datasets." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.557, + 0.719, + 0.573 + ], + "angle": 0, + "content": "4.2. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.581, + 0.89, + 0.611 + ], + "angle": 0, + "content": "The details on network architectures and training are described in Supplementary Material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.621, + 0.888, + 0.637 + ], + "angle": 0, + "content": "4.3. Performance Comparison with Exiting Works" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.892, + 0.765 + ], + "angle": 0, + "content": "We mainly compare with AB-MIL [16], DSMIL [17], CLAM-SB [21], CLAM-MB [21], TransMIL [26], and DTFD-MIL [43], all of which are attention-based MIL methods. In addition, we compared two traditional MIL pooling operations, Max-pooling and Mean-pooling. Due to the dataset differences, the results of all other methods are reproduced using the official code they provide under the same settings." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.766, + 0.892, + 0.901 + ], + "angle": 0, + "content": "As shown in Table 1, max-pooling and mean-pooling perform poorly on two datasets compared to other methods. We attribute this to their insufficient modeling of key instance information. Simple pooling operations are prone to be misled by limited slides that contain numerous instances. This problem is especially severe on the CAMELYON-16 dataset, where the proportion of significant instances is extremely small. For example, max-pooling lags behind DTFD-MIL [43] by \\(13.87\\%\\) on AUC. Attention-based" + }, + { + "type": "page_number", + "bbox": [ + 0.482, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4082" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.13, + 0.089, + 0.842, + 0.291 + ], + "angle": 0, + "content": "
MethodCAMELYON-16TCGA Lung Cancer
AccuracyAUCF1-scoreAccuracyAUCF1-score
Max-pooling78.95±2.2881.28±3.7471.06±2.5981.49±1.2486.45±0.7180.56±1.09
Mean-pooling76.69±0.2080.07±0.7870.41±0.1684.14±2.9790.13±2.4083.39±3.14
AB-MIL [16]90.06±0.6094.00±0.8387.40±1.0588.03±2.1993.17±2.0587.41±2.42
DSMIL [17]90.17±1.0294.57±0.4087.65±1.1888.32±2.7093.71±1.8287.90±2.50
CLAM-SB [21]90.31±0.1294.65±0.3087.89±0.5987.74±2.2293.67±1.6487.36±2.24
CLAM-MB [21]90.14±0.8594.70±0.7688.10±0.6388.73±1.6293.69±0.5488.28±1.58
TransMIL [26]89.22±2.3293.51±2.1385.10±4.3387.08±1.9792.51±1.7686.40±2.08
DTFD-MIL [43]90.22±0.3695.15±0.1487.62±0.5988.23±2.1293.83±1.3987.71±2.04
MHIM-MIL (AB-MIL)91.81±0.8296.14±0.5289.94±0.7089.64±2.2594.97±1.7289.31±2.19
MHIM-MIL (TransMIL)91.98±0.8996.49±0.4890.13±1.0890.02±2.5994.87±2.1789.65±2.63
MHIM-MIL (DSMIL)92.48±0.3596.49±0.6590.75±0.7389.83±3.3795.53±1.7489.71±2.92
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.302, + 0.893, + 0.334 + ], + "angle": 0, + "content": "Table 1: The performance of different MIL approaches on CAMELYON-16 (C16) and TCGA Lung Cancer (TCGA). The highest performance is in bold. The Accuracy and F1-score are determined by the optimal threshold." + }, + { + "type": "table", + "bbox": [ + 0.086, + 0.349, + 0.462, + 0.469 + ], + "angle": 0, + "content": "
ModelC16TCGAPara.TimeMem.
AB-MIL94.0093.17657K4.0s2.4G
CLAM-MB94.7093.69789K4.3s2.7G
DTFD-MIL95.1593.83987K5.2s2.1G
MHIM-MIL96.1494.97657K4.3s2.3G
TransMIL93.5192.512.67M13.1s10.6G
MHIM-MIL96.4994.872.67M10.1s5.5G
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.48, + 0.472, + 0.542 + ], + "angle": 0, + "content": "Table 2: Comparison of time and memory requirements of different MIL methods. We report the model size (Para.), the training time per epoch (Time), and the peak memory usage (Mem.) on the CAMELYON-16 dataset (C16)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.56, + 0.47, + 0.786 + ], + "angle": 0, + "content": "methods achieve better performance on both datasets by focusing on salient instances. In particular, the representative MIL framework DTFD-MIL [43] benefits from the further exploration of significant instances and achieves the second-best performance on both datasets (95.15% AUC on CAMELYON-16 and 93.83% AUC on TCGA). However, it also suffers from overemphasizing salient instances during training, which limits its generalization. Our proposed MHIM-MIL achieves significant performance improvement on both datasets (+1.34% AUC on CAMELYON-16 and +1.70% AUC on TCGA) by mining hard instances during training, breaking the performance bottleneck. It is worth mentioning that we validate our framework on three representative MIL models, both of which can outperform the existing MIL methods." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.801, + 0.34, + 0.817 + ], + "angle": 0, + "content": "4.4. Computational Cost Analysis" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.825, + 0.47, + 0.903 + ], + "angle": 0, + "content": "In this section, we report the training time and GPU memory requirements for running different MIL models on a 3090 GPU. The upper part of Table 2 compares some MIL frameworks that use AB-MIL [16] as a baseline. We observe that traditional MIL frameworks typically intro" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.352, + 0.895, + 0.7 + ], + "angle": 0, + "content": "duce additional parameters and reduce efficiency due to their complex structures. For example, the state-of-the-art framework DTFD-MIL [43] increases the parameter size by nearly twice (657K vs. 987K) and the training time by \\(30\\%\\). In contrast, MHIM-MIL achieves the most significant performance improvement with almost no extra computational cost due to the momentum teacher. Moreover, existing Transformer-based MIL methods are usually plagued by high computing costs due to their large number of parameters and self-attention operations. For instance, TransMIL [26], which first applies a pure Transformer MIL model to solve WSI classification problems, has \\(4 \\times\\) more parameters than AB-MIL, \\(3 \\times\\) longer training time, and almost \\(4.5 \\times\\) higher memory consumption. Furthermore, the extremely long input sequences in WSI classification degrade the stability of such complex structures (2.13% AUC standard deviation on C16, which is the highest among all embedding-level MIL methods). With the masked hard instance mining strategy, the MHIM-MIL framework significantly reduces the computational cost (-24% training time and -48% memory usage) and enhances its stability (0.48% AUC standard deviation on C16). More details are provided in Supplementary Material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.714, + 0.655, + 0.73 + ], + "angle": 0, + "content": "4.5. Ablation Study" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.739, + 0.838, + 0.755 + ], + "angle": 0, + "content": "4.5.1 Importance of the Different Components" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.903 + ], + "angle": 0, + "content": "Table 3 shows the effect of different modules in MHIMMIL on two datasets. The baseline methods are two representative attention-based MIL methods, namely AB-MIL [16] and TransMIL [26]. First, we introduce the naive masked hard instance mining strategy, which leverages the model itself to mine hard instances during training. This strategy improves AUC by \\(1.86\\%\\) and \\(2.55\\%\\) for the two MIL models on CAMELYON-16 respectively, indicating that concentrating on hard instances during training can as" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4083" + } + ], + [ + { + "type": "table", + "bbox": [ + 0.081, + 0.089, + 0.468, + 0.194 + ], + "angle": 0, + "content": "
ModuleCAMELYON-16TCGA
AB.Trans.AB.Trans.
Baseline94.0093.5193.1792.51
+MHIM95.8696.0694.1493.75
+MHIM+Siam.95.8296.2494.5594.13
+MHIM+Siam.+Con.96.1496.4994.9794.87
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.205, + 0.471, + 0.281 + ], + "angle": 0, + "content": "Table 3: The effect of different components in MHIM-MIL with two MIL models: AB-MIL (AB.) and TransMIL (Trans.). MHIM denotes the masked hard instance mining strategy. Siam. refers to the Siamese framework. Con. represents consistency loss." + }, + { + "type": "table", + "bbox": [ + 0.104, + 0.296, + 0.445, + 0.417 + ], + "angle": 0, + "content": "
StrategyCAMELYON-16TCGA
AB.Trans.AB.Trans.
Baseline94.0093.5193.1792.51
HAM95.6895.9093.8394.54
R-HAM96.1495.8894.7994.60
L-HAM95.8196.4994.3394.67
LR-HAM95.9296.3394.9794.87
" + }, + { + "type": "table_caption", + "bbox": [ + 0.076, + 0.427, + 0.47, + 0.473 + ], + "angle": 0, + "content": "Table 4: Comparison between different masked hard instance mining strategies. The three hybrid strategies show varying performance across the benchmarks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.49, + 0.47, + 0.687 + ], + "angle": 0, + "content": "sist mainstream MIL models in building better classification boundaries. Further discussion on the masked hard instance mining strategy is presented in Section 4.5.2. Compared with the naive MHIM strategy, the third row of the table suggests that a Siamese structure [3,5,8] based on a momentum teacher is beneficial for more stable and effective mining of hard instances. We elaborate more on choosing the teacher model in Section 4.5.3. After adding consistency loss term to the objective function, our full MHIM-MIL framework achieves the best performance (96.49% AUC on CAMELYON-16 and 94 .97% AUC on TCGA). For subsequent ablation experiments, we include consistency loss by default to facilitate the optimization of our framework." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.71, + 0.419, + 0.726 + ], + "angle": 0, + "content": "4.5.2 Impact of the Different MHIM Strategies" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.735, + 0.47, + 0.903 + ], + "angle": 0, + "content": "The masked hard instance mining strategy is the core design of our method. The main idea of this strategy is masking the most salient instances to indirectly mine hard instances to facilitate model training. Based on this idea, we devise three hybrid strategies (R-HAM, L-HAM, and LR-HAM) and present their impact in Table 4. The basic strategy, High Attention Masking (HAM), already boosts performance significantly, leading to AUC improvements of \\(1.68\\%\\) and \\(2.39\\%\\) for two MIL models on the CAMELYON-16 dataset, respectively. After introducing the other two strategies, different MIL models achieve performance improvements" + }, + { + "type": "table", + "bbox": [ + 0.522, + 0.089, + 0.875, + 0.208 + ], + "angle": 0, + "content": "
TeacherCAMELYON-16TCGA
AB.Trans.AB.Trans.
Baseline94.0093.5193.1792.51
Student copy95.8495.8693.6893.45
Init.95.8896.1294.6694.15
Momentum95.9696.1194.6594.45
Init.+Momentum96.1496.4994.9794.87
" + }, + { + "type": "image", + "bbox": [ + 0.561, + 0.211, + 0.829, + 0.317 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.498, + 0.315, + 0.892, + 0.406 + ], + "angle": 0, + "content": "Table 5: Comparison of different types of teachers. Momentum denotes the teacher is updated by EMA strategy. Init. indicates the initialization of the teacher with pretrained parameters. The bottom figure compares the stability of the momentum teacher and the non-batch gradient updated student during training." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.433, + 0.892, + 0.628 + ], + "angle": 0, + "content": "on both datasets. Specifically, AB-MIL [16] shows more significant performance gains after introducing randomness (96.14% AUC on CAMELYON-16 with R-HAM) due to its better ability to filter out redundant information, while TransMIL [26] shows the reverse trend (96.49% AUC on CAMELYON-16 with L-HAM). Furthermore, the more complex three-hybrid strategy (LR-HAM) achieves the best performance on the TCGA dataset, which has a larger proportion of positive areas and more instances. Overall, our experiments validate the effectiveness of masked hard instance mining strategy, and the diversity of proposed strategies improves its applicability to different datasets and MIL models." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.65, + 0.842, + 0.666 + ], + "angle": 0, + "content": "4.5.3 Impact of the Choice of Teacher Network" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.892, + 0.901 + ], + "angle": 0, + "content": "In MHIM-MIL, we employ a Teacher model to mine hard instances and facilitate training of the Student model. In Table 5, we comprehensively investigate the effects of various choices of Teacher network. First, we utilize a single-model structure, which treats the Student model as the Teacher. The student conducts masked hard instance mining prior to training. Due to the non-batch gradient update, the unstable performance of the Student model makes the strategy susceptible to noise, so the performance is not optimal. Second, we adopt a momentum teacher, which shares the same network structure as the Student model and is updated with the EMA strategy. This updating strategy enhanced the stability of momentum teachers, as shown in the figure below, and enabled MHIM-MIL to achieve \\(0.97\\%\\) and \\(1.00\\%\\) performance improvement in TCGA under the two MIL mod" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.956 + ], + "angle": 0, + "content": "4084" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.088, + 0.48, + 0.414 + ], + "angle": 0, + "content": null + }, + { + "type": "image", + "bbox": [ + 0.495, + 0.089, + 0.889, + 0.413 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.426, + 0.896, + 0.504 + ], + "angle": 0, + "content": "Figure 4: Patch visualization produced by AB-MIL [16] (baseline) and MHIM-MIL. The blue lines outline the tumor regions. The brighter patch indicates higher attention scores. The cyan colors indicate high probabilities of being tumor for the corresponding locations. Ideally, the cyan patches should cover only the area within the blue lines. We show that focusing only on more salient regions reduces the generalization ability of the model and that hard instances can provide useful information for more accurate and comprehensive judgments." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.522, + 0.471, + 0.584 + ], + "angle": 0, + "content": "els, respectively. With proper initialization, the momentum teacher achieves the best performance. However, a fixed initialization teacher fails to learn new knowledge, which emphasizes the significance of iterative optimization." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.591, + 0.216, + 0.606 + ], + "angle": 0, + "content": "4.6. Visualization" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.614, + 0.473, + 0.903 + ], + "angle": 0, + "content": "To more intuitively understand the effect of the masked hard instance mining, we visualize the attention scores (bright patch) and tumor probabilities (cyan patch) of patches produced by AB-MIL and MHIM-MIL, as illustrated in Figure 4. Here, MHIM-MIL employs AB-MIL as its baseline model. We note that attention scores only indicate the regions of interest of models and are infeasible to reflect tumor probabilities [17, 43]. First, as shown in Figure 4, AB-MIL often assigns high tumor probabilities to patches in non-tumor areas. We attribute this phenomenon to the low generalization capability of conventional attention-based MIL models, which tend to focus only on salient regions during training. In contrast, MHIM-MIL trained with hard instances shows a much better generalization ability than the baseline model for noise robustness (rows 2 and 3 on the right) and for precise detection of challenging subtle tumor areas (row 3 on the left). More significantly, we find that focusing only on tumor areas leads to missing most of them, expanding the view to include some" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.522, + 0.895, + 0.628 + ], + "angle": 0, + "content": "\"irrelevant areas\" enables the model to make more complete judgments (rows 1 and 2 on the left). This phenomenon demonstrates how hard instances provide more useful information to help the model make more accurate and comprehensive judgments. We provide more details and an in-depth analysis of this patch visualization in Supplementary Material." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.647, + 0.62, + 0.663 + ], + "angle": 0, + "content": "5. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.675, + 0.895, + 0.903 + ], + "angle": 0, + "content": "This paper rethinks the impact of salient instances for MIL-based WSI classification algorithms. We demonstrate that attention-based MIL methods excessively prioritizing salient instances harm the generalization ability of the model. To address this issue, we have proposed several masked hard instance mining strategies that mask out salient patches and encourage the model to attend to informative regions for better discriminative learning. Through qualitative analysis, we have demonstrated that these strategies effectively alleviate the under-fitting problem of general AB-MIL to hard instances. We have also developed the MHIM-MIL framework that leverages momentum teacher and consistency loss to further enhance hard instance mining. Our experimental results demonstrate the superiority and generality of the MHIM-MIL framework over other lat" + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.945, + 0.516, + 0.957 + ], + "angle": 0, + "content": "4085" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.077, + 0.092, + 0.47, + 0.138 + ], + "angle": 0, + "content": "est methods. In future work, we plan to devise a more precise localization scheme for hard instances that can facilitate model training and convergence." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.152, + 0.258, + 0.169 + ], + "angle": 0, + "content": "6. Acknowledgement" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.178, + 0.47, + 0.239 + ], + "angle": 0, + "content": "Reported research is partly supported by the National Natural Science Foundation of China under Grant 62176030, and the Natural Science Foundation of Chongqing under Grant cstc2021jcyj-msxmX0568." + }, + { + "type": "title", + "bbox": [ + 0.08, + 0.253, + 0.175, + 0.269 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.087, + 0.277, + 0.47, + 0.334 + ], + "angle": 0, + "content": "[1] Ejaz Ahmed, Michael Jones, and Tim K Marks. An improved deep learning architecture for person re-identification. 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Springer, 2022. 1" + }, + { + "type": "list", + "bbox": [ + 0.503, + 0.093, + 0.892, + 0.895 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.483, + 0.946, + 0.516, + 0.956 + ], + "angle": 0, + "content": "4087" + } + ] +] \ No newline at end of file diff --git a/2023/Multiple Instance Learning Framework with Masked Hard Instance Mining for Whole Slide Image Classification/4186ce96-ecad-4ae2-bdd7-3d5e8448e342_origin.pdf b/2023/Multiple Instance Learning Framework with Masked Hard Instance Mining for Whole Slide Image Classification/4186ce96-ecad-4ae2-bdd7-3d5e8448e342_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..47ce4c858c3ad339a11aa8ed97bbc23f028beb1d --- /dev/null +++ b/2023/Multiple Instance Learning Framework with Masked Hard Instance Mining for Whole Slide Image Classification/4186ce96-ecad-4ae2-bdd7-3d5e8448e342_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:7e1a099a86ae0083ecff5f903a748781cf12ed1f5fa3a30e5694031831e87639 +size 1483979 diff --git a/2023/Multiple Instance Learning Framework with Masked Hard Instance Mining for Whole Slide Image Classification/full.md b/2023/Multiple Instance Learning Framework with Masked Hard Instance Mining for Whole Slide Image Classification/full.md new file mode 100644 index 0000000000000000000000000000000000000000..81b83603a45a97754153ce75a4a59c68080d2df3 --- /dev/null +++ b/2023/Multiple Instance Learning Framework with Masked Hard Instance Mining for Whole Slide Image Classification/full.md @@ -0,0 +1,302 @@ +# Multiple Instance Learning Framework with Masked Hard Instance Mining for Whole Slide Image Classification + +Wenhao Tang $^{1}$ Sheng Huang $^{1*}$ Xiaoxian Zhang $^{1}$ Fengtao Zhou $^{2}$ Yi Zhang $^{1}$ Bo Liu $^{3}$ $^{1}$ Chongqing University + $^{2}$ The Hong Kong University of Science and Technology + $^{3}$ Walmart Global Tech + +{whtang, huangsheng, zhangxiaoxian, zhangyii}@cqu.edu.cn + +fzhouaf@connect.ust.hk, kfliubo@gmail.com + +# Abstract + +The whole slide image (WSI) classification is often formulated as a multiple instance learning (MIL) problem. Since the positive tissue is only a small fraction of the gigapixel WSI, existing MIL methods intuitively focus on identifying salient instances via attention mechanisms. However, this leads to a bias towards easy-to-classify instances while neglecting hard-to-classify instances. Some literature has revealed that hard examples are beneficial for modeling a discriminative boundary accurately. By applying such an idea at the instance level, we elaborate a novel MIL framework with masked hard instance mining (MHIM-MIL), which uses a Siamese structure (Teacher-Student) with a consistency constraint to explore the potential hard instances. With several instance masking strategies based on attention scores, MHIM-MIL employs a momentum teacher to implicitly mine hard instances for training the student model, which can be any attention-based MIL model. This counter-intuitive strategy essentially enables the student to learn a better discriminating boundary. Moreover, the student is used to update the teacher with an exponential moving average (EMA), which in turn identifies new hard instances for subsequent training iterations and stabilizes the optimization. Experimental results on the CAMELYON-16 and TCGA Lung Cancer datasets demonstrate that MHIM-MIL outperforms other latest methods in terms of performance and training cost. The code is available at: https://github.com/DearCaat/MHIM-MIL. + +# 1. Introduction + +Histopathological image analysis plays a crucial role in modern medicine, particularly in the treatment of cancer, where it serves as the gold standard for diagnosis [18, 20, 24,45]. Digitalizing pathological images into Whole Slide + +![](images/06714f471733be7d568f02b60d494c91ea3d0609b44bbc3b07335560576141e5.jpg) +Figure 1: Left: Previous MIL models focus on the more salient instances. Right: MHIM-MIL mines an amount of hard-to-classify instances to learn a better boundary. + +Images (WSIs) through digital slide scanner has opened new avenues for computer-aided analysis [9, 26]. Due to the huge size of a WSI and the lack of pixel-level annotations, histopathological image analysis is commonly formulated as a multiple instance learning (MIL) task [10, 23, 31]. In MIL, each WSI (or slide) is a bag containing thousands of unlabeled instances (patches) cropped from the slide. With at least one instance being disease positive, the bag is deemed positive, otherwise negative. + +However, the number of slides is limited and each slide contains a mass of instances with a low positive proportion. This imbalance would hinder the inference of bag labels [16, 43]. To alleviate this issue, several WSI classification methods [6, 16-18,26] employ an attention mechanism to aggregate salient instance features into a bag-level feature for WSI classification. Furthermore, some MIL frameworks [17,21,40,43] focus on the more salient instances in the bag and leverage them to facilitate WSI classification. For instance, existing frameworks [40, 43] propose to only select the instances that correspond to the top $K$ highest or lowest attention scores [17, 40] or patch probabilities [43] for yielding high-quality bag embedding for both training and testing. + +These salient instances are actually "easy-to-classify" instances, which are not optimal for training a discriminative WSI classification model. In conventional machine learning, such as Support Vector Machines (SVM) [13], samples near the category distribution boundary are more challenging to classify, but are more useful for depicting the classification boundary, as illustrated in Figure 1. Moreover, other deep learning works [25, 28, 33, 34] also reveal that mining hard samples for training can improve the generalization abilities of models. By applying such an idea at the instance level, we can better highlight the "hard-to-classify" instances that facilitate MIL model training, and benefit the final WSI classification. However, the lack of instance labels poses a challenge to the direct application of traditional hard sample mining strategies at the instance level. + +To address this issue, we present a novel MIL framework based on masked hard instance mining strategies (MHIM) named MHIM-MIL. The main idea of MHIM is to mask out the instances with high attention scores to highlight the hard instances for model training. Based on this, we incorporate two other instance masking strategies to enhance training efficiency and mitigate the over-fitting risk. Another key design of MHIM-MIL is an instance attention generator based on a Siamese structure (Teacher-Student) [3, 8]. In MHIM-MIL, the MIL-based WSI classification model is the student network, which aggregates hard instances mined by a momentum teacher with different instance masking strategies. The momentum teacher is updated using an exponential moving average (EMA) of the student model. Moreover, the framework is optimized by inducing a consistency constraint that explores more supervised information beyond the limited slide label. Unlike the conventional MIL frameworks [40, 43], which adopt complex cascade gradient-updating structures, our method is more simple and does not require additional parameters. It not only improves efficiency but also provides improved performance stability. The contribution of this paper is summarized as follows, + +- We propose a simple and efficient MIL framework with masked hard instance mining named MHIM-MIL. It implicitly mines hard instances with instance attention for training a more discriminative MIL model. Extensive experiments on two WSI datasets validate that MHIM boosts different MIL models and outperforms other latest methods in terms of performance and training cost. + +- We propose several hybrid instance masking strategies for indirectly mining hard instances in MIL. These strategies not only address the reliance problem of conventional methods on instance-level supervision but also enhance the training efficiency of the model and mitigate the over-fitting risk. + +- With the Siamese structure, we introduce a parameter-free momentum teacher to obtain instance attention scores more efficiently and stably. Moreover, we employ a consistency-based iterative optimization to improve the discriminability of both models progressively. + +# 2. Related Work + +# 2.1. Multiple Instance Learning in WSI Analysis + +Multiple Instance Learning (MIL) [10] has been widely used in WSI analysis with its unique learning paradigm in recent years [17, 22, 26, 35, 40, 42]. MIL is a weakly supervised learning framework that utilizes coarse-grained bag labels for training instead of fine-grained instance annotations. Previous algorithms can be broadly categorized into two groups: instance-level [4, 12, 15, 40] and embedding-level [9, 27, 38, 39, 43]. The former obtain instance labels and aggregate them to obtain the bag label, whereas the latter aggregate all instance features into a high-level bag embedding for bag prediction. Most embedding-level methods share the basic idea of AB-MIL [16], which employs learnable weights to aggregate salient instance features into bag embedding. Furthermore, some MIL frameworks [17, 21, 40, 43] mine more salient instances making classification easier and facilitating classification. For example, Lu et al. selected the most salient instances based on their attention scores (e.g., maximum and minimum scores) to compute instance-level loss and improve performance [21]. Zhang et al. proposed a class activation map (CAM) based on the AB-MIL paradigm to better mine salient instances and used AB-MIL to aggregate them into bag embedding [43]. In addition, feature clustering methods [27, 37, 44] computed cluster centroids of all feature embeddings and used representative embeddings for the final prediction. However, all these methods focused excessively on salient instances in training, which are easy instances with high confidence scores and can be easily classified. As a result, they overlook the importance of hard instances for training. In this paper, we intend to mine hard instances for improving WSI classification performance. + +# 2.2. Hard Sample Mining in Computer Vision + +Hard sample mining is a popular technique to speed up convergence and enhance the discriminative power of the model in many deep learning areas, such as face recognition [25], object detection [29, 36], person re-identification [1, 28, 33, 34], and deep metric learning [30, 32]. The main idea behind this technique is to select the samples which are hard to classify correctly (i.e., hard negatives and hard positives) for alleviating the imbalance between positive and negative samples and facilitating model training. There are generally three groups of approaches + +for evaluating sample difficulty: loss-based [14], similarity-based [7], and learnable weight-based [41]. Typically, these strategies require complete sample supervision information. Drawing on the ideas of the above works, we propose a hard instance mining approach in MIL, mining hard examples at the instance level. In this, there are no complete instance labels, only the bag label is available. Similar to our approach, Li et al. utilized attention scores to identify salient instances from false negative bags to serve as hard negative instances and used them to compose the hard bags for improving classification performance [19]. A key difference is that we indirectly mine hard instances by masking out the most salient instances rather than directly locating hard negative instances. + +# 3. Proposed Method + +# 3.1. Background: MIL Formulation + +In MIL, any input WSI $X$ is considered as a bag with multiple instances, which can be represented as $X = \{x_{i}\}_{i=1}^{N}$ . $x_{i}$ is a patch collected from the WSI and considered as the $i$ -th instance of $X$ . $N$ is the number of instances. For a classification task, there exists a known label $Y \in C$ for the bag and an unknown label $y_{n} \in C$ for each instance, where $C$ is the collection of category labels. The goal of a MIL model $\mathcal{M}(\cdot)$ is to predict the bag label with all instances $\hat{Y} \gets \mathcal{M}(X)$ . The popular solution is to learn a bag representation $F$ from the extracted features of instances $Z = \{z_{i}\}_{i=1}^{N}$ in a bag, which is also referred as the instance aggregation step. And a classifier $\mathcal{C}(\cdot)$ , trained upon the $F$ , can be used to predict the bag label $\hat{Y} \gets \mathcal{C}(F)$ . There are two ways to aggregate instances for achieving bag embedding. One is the attention-based aggregation [16] denoted as follows, + +$$ +F = \sum_ {i = 1} ^ {N} a _ {i} z _ {i} \in \mathbb {R} ^ {D}, \tag {1} +$$ + +where $a_{i}$ is the learnable scalar weight for $z_{i}$ , and $D$ is the dimension of vector $F$ and $z_{i}$ . Many works [17, 21, 43] follow this formulation but differ in the ways they generate the attention score $a_{i}$ . + +Another is the multi-head self-attention (MSA) based aggregation [26]. In this fashion, a class token $z_0$ is embedded with the instance features to get the initial input sequence $Z^0 = [z_0, z_1, \ldots, z_N] \in \mathbb{R}^{(N + 1) \times D}$ for aggregating instance features. This can be formulated as, + +$$ +\operatorname {h e a d} = A ^ {\ell} \left(Z ^ {\ell - 1} W ^ {V}\right) \in \mathbb {R} ^ {N \times \frac {D}{H}}, \quad \ell = 1 \dots L \tag {2} +$$ + +$$ +Z ^ {\ell} = \operatorname {C o n c a t} \left(\operatorname {h e a d} _ {1}, \dots , \operatorname {h e a d} _ {H}\right) W ^ {O}, \quad \ell = 1 \dots L +$$ + +where $W^{V}\in \mathbb{R}^{D\times \frac{D}{H}}$ and $W^{O}\in \mathbb{R}^{D\times D}$ are the learnable projection matrices of MSA. $A^{\ell}\in \mathbb{R}^{(N + 1)\times (N + 1)}$ is the attention matrix of the $\ell$ -th layer, $L$ is the number of MSA + +block, and $H$ is the number of head in each MSA block. The bag embedding $F$ is the output class token at the final layer, + +$$ +F = Z _ {0} ^ {L}. \tag {3} +$$ + +The self-attention-based bag embedding is essentially a special case of attention-based bag embedding in the multi-instance learning setting. Collectively, these approaches can be referred to as the general attention-based MIL method. + +# 3.2. MHIM-MIL for WSI Classification + +In general attention-based MIL frameworks, the attention scores of instances indicate the contributions of instances to the bag classification. The salient instances with high scores are useful for classifying WSI in the testing phase but are not conducive to training a MIL model with good generalization ability. Although hard samples have been proven to enhance the generalization ability of the model in many computer vision scenarios [11, 32-34], previous MIL works focus more on exploiting the salient instances and neglecting the utilization of hard instances in model optimization. + +In this paper, we propose a simple and efficient MIL framework with Masked Hard Instance Mining (MHIM-MIL) to boost the WSI classification. As illustrated in Figure 2, the MHIM-MIL framework employs a Siamese structure during the training phase. The main component of our framework is a general attention-based MIL model (Student), denoted as $S(\cdot)$ , for aggregating instance features. To increase the discriminatory difficulty of the student model and force it to focus on hard instances, we introduce a momentum teacher, denoted as $T(\cdot)$ , to score the instances with attention weights and then employ some masked hard instance mining strategies to mask the salient instances while preserving the hard instances. After hard instance mining, all the mined features are forwarded into the student model for the inference of the bag label. The teacher shares the same network structure as the student model but does not need gradient-based updates. It is worth mentioning that, due to the varying number of instances within each bag, the non-batch gradient descent algorithm (i.e., SGD with batch size 1) is typically employed to optimize the MIL model. Therefore, compared to the traditional MIL frameworks with two-tier gradient updating models [40, 43], this Siamese structure makes training more stable and efficient with fewer parameters. The proposed framework can be defined as, + +$$ +\hat {Y} = \mathcal {S} (\hat {Z}) = \mathcal {S} (M _ {\mathcal {T}} (Z)), \tag {4} +$$ + +where $M_{\mathcal{T}}(\cdot)$ denotes a masked hard instance mining strategy through the teacher model and $\hat{Z}$ are the mined instances. + +![](images/5296ed3dbaf0ab29a083c63de78c5473ba2c1051791b50b2b10244c5c1d7150f.jpg) + +![](images/e4de11326178938e3deaff1123ab62f2b103d83883a15877a39d6db5479bb3c7.jpg) +Figure 2: Overview of proposed MHIM-MIL. A momentum teacher is used to compute attention scores for all instances. We mask instances based on attention with hard mining strategies and feed the remaining to the student model. The student is updated by a consistency loss term $\mathcal{L}_{con}$ and a label error loss term $\mathcal{L}_{cls}$ . The teacher parameters are updated with an Exponential Moving Average (EMA) of the student parameters without gradient updates. In the inference phase, we use the complete input instances and the student model only. + +# 3.3. Masked Hard Instance Mining Strategy + +Conventional hard sample mining strategies are difficult to apply without instance-level supervision. We address this challenge by proposing masked hard instance mining strategies that use attention scores to implicitly mine hard instances by masking out easy instances with high attention scores. More specifically, given a complete sequence of instance features $Z = \{z_{i}\}_{i=1}^{N}$ as the input of the teacher model $\mathcal{T}(\cdot)$ , the teacher outputs the attention weight $a_{i}$ for each instance as follow, + +$$ +A = \left[ a _ {1}, \dots , a _ {i}, \dots , a _ {N} \right] = \mathcal {T} (Z). \tag {5} +$$ + +Then, we obtain the indices of the attention sequence in descending order by applying a sorting operation on $A$ , + +$$ +I = \left[ i _ {1}, i _ {2}, \dots , i _ {N} \right] = \operatorname {S o r t} (A), \tag {6} +$$ + +where $i_1$ is the index of the instance with the highest attention score while $i_N$ is the index of the one with the lowest score. With this index collection $I$ , we will present several masked hard instance mining strategies to select the hard instances. We define an $N$ -dimensional binary vector $M = [m_1, \dots, m_i, \dots, m_N]$ for encoding the mask flags of instances where $m_i \in \{0, 1\}$ . If $m_i = 1$ , the $i$ -th instance is masked, otherwise, it is unmasked. + +High Attention Masking: The simplest masked hard instance mining strategy is the High Attention Masking (HAM) strategy, which simply masks instances with the top $\beta_{h}\%$ highest attention scores. The instance mask flags under HAM are initialized as all zero vectors, $M_{h}(:) = 0$ . + +Then we collect the indices of the instances whose scores are ranked in the top $\beta_h\%$ , $I_h = [i_t]_{t=1}^{\lceil \beta_h\% \times N \rceil}$ . Finally, we set the mask flags with these indices, $M_h(I_h) = 1$ . To ensure that positive instances are preserved within the un-masked sequences, we also utilized techniques such as mask ratio decay. + +Hybrid Masking: We combine HAM with several other instance masking strategies as hybrid masking strategies to achieve some specific properties in hard instance mining, as shown in Figure 3. We consider the obtained mask flags as a collection and employ the union operation for mask flag fusion. We design three hybrid masking strategies as follows: + +- L-HAM: We use the same pipeline as HAM to generate the mask flags $M_{l}$ for masking the instances with the top $\beta_{l} \%$ lowest attention scores in order to filter out the redundant uninformative instances and improve efficiency. To endow this property to HAM, we union the mask flags obtained by two strategies to get the new mask flags, $\hat{M} = M_{h} \cup M_{l}$ . +- R-HAM: Randomness is beneficial to reduce the risk of over-fitting. We generate a random mask flag vector $M_r$ with a given random ratio $\beta_r\%$ , and combine it with $M_h$ for introducing the randomness to the hard instance mining, $\hat{M} = M_h \cup M_r$ . +- LR-HAM: Combining the above strategies, we can obtain completely hybrid mask flags, $\tilde{M} = M_h \cup M_r \cup M_l$ , which is expected to achieve both of the mentioned desirable properties. + +![](images/ff415e38d78b95bc030b6e341c833f222016d399ba0ede96bd2dc4eda02f1e2c.jpg) +Figure 3: Illustration of proposed hybrid masking strategy for hard instance mining. + +![](images/f50a6e4d21146e114d8d41f25bb092acca5ba1ba527d45b2b5ceb2dc89b9a283.jpg) + +Once the final mask flag $\hat{M}$ is produced, the masked instance sequence will be obtained: + +$$ +\hat {Z} = M _ {\mathcal {T}} (Z) = \operatorname {M a s k} (Z, \hat {M}) \in \mathbb {R} ^ {\hat {N} \times D}, \tag {7} +$$ + +where the $\hat{N}$ is the number of unmasked instances. + +# 3.4. Consistency-based Iterative Optimization + +Under the Siamese structure, while the teacher model guides the training of the student model, the new knowledge learned by the student model will also update the teacher model. This iterative optimization process progressively improves the mining ability of the teacher and the discriminability of the student. To further facilitate this optimization and explore additional supervised information provided by the momentum teacher, we propose a consistency loss that constrains the classification results of both models. + +Student Optimization: There are two losses in student optimization. One is the cross-entropy for measuring the bag label prediction loss, + +$$ +\mathcal {L} _ {c l s} = Y \log \hat {Y} + (1 - Y) \log \left(1 - \hat {Y}\right). \tag {8} +$$ + +Another is a consistency loss between the bag representation of student $F_{s}$ and momentum teacher $F_{t}$ , + +$$ +\mathcal {L} _ {\text {c o n}} = - \operatorname {s o f t m a x} \left(F _ {t} / \tau\right) \log F _ {s} \tag {9} +$$ + +where the $\tau > 0$ is a temperature parameter. Overall, the final optimization loss is as follows: + +$$ +\left\{\hat {\theta_ {s}} \right\} \leftarrow \arg \min _ {\theta_ {s}} \mathcal {L} = \mathcal {L} _ {c l s} + \alpha \mathcal {L} _ {c o n} \tag {10} +$$ + +where $\theta_{s}$ is the parameters of $S(\cdot)$ , and $\alpha$ is scaling factor. + +Teacher Optimization: The parameters of momentum teacher $\theta_{t}$ are updated by an exponential moving average (EMA) of the student parameters. The update rule is $\theta_{t} \gets \lambda \theta_{t} + (1 - \lambda) \theta_{s}$ , where $\lambda$ is a hyperparameter. More importantly, the updated teacher is utilized in the next iteration of hard instance mining. + +# 4. Experiments and Results + +# 4.1. Datasets and Evaluation Metrics + +CAMELYON-16 [2] is a WSI dataset proposed for metastasis detection in breast cancer. The dataset contains a total of 400 WSIs, which are officially split into 270 for training and 130 for testing, and the testing sample ratio is $13/40 \approx 1/3$ . Following [6, 21, 44], we adopt 3-times 3-fold cross-validation on this dataset to ensure that each slide is used in training and testing, which can alleviate the impact of data split and random seed on the model evaluation. Each fold has approximately 133 slides. We report the mean and standard deviation of performance metrics over 3 runs. + +TCGA Lung Cancer includes two sub-type of cancers, Lung Adenocarcinoma (LUAD) and Lung Squamous Cell Carcinoma (LUSC). There are diagnostic slides, LUAD with 541 slides from 478 cases, and LUSC with 512 slides from 478 cases. We randomly split the dataset into training, validation, and testing sets with a ratio of 65:10:25 on the patient level. 4-fold cross-validation is adopted, and the mean and standard deviation of performance metrics of the 4 test folders are reported. + +We adopt the same data pre-processing as in the CLAM [21]. Following the previous work [21, 26] we leverage Accuracy, Area Under Curve (AUC), and F1-score to evaluate model performance. AUC is the primary performance metric in the binary classification task, and we only report AUC in ablation experiments. Please refer to the Supplementary Material for the details of these two datasets. + +# 4.2. Implementation Details + +The details on network architectures and training are described in Supplementary Material. + +# 4.3. Performance Comparison with Exiting Works + +We mainly compare with AB-MIL [16], DSMIL [17], CLAM-SB [21], CLAM-MB [21], TransMIL [26], and DTFD-MIL [43], all of which are attention-based MIL methods. In addition, we compared two traditional MIL pooling operations, Max-pooling and Mean-pooling. Due to the dataset differences, the results of all other methods are reproduced using the official code they provide under the same settings. + +As shown in Table 1, max-pooling and mean-pooling perform poorly on two datasets compared to other methods. We attribute this to their insufficient modeling of key instance information. Simple pooling operations are prone to be misled by limited slides that contain numerous instances. This problem is especially severe on the CAMELYON-16 dataset, where the proportion of significant instances is extremely small. For example, max-pooling lags behind DTFD-MIL [43] by $13.87\%$ on AUC. Attention-based + +
MethodCAMELYON-16TCGA Lung Cancer
AccuracyAUCF1-scoreAccuracyAUCF1-score
Max-pooling78.95±2.2881.28±3.7471.06±2.5981.49±1.2486.45±0.7180.56±1.09
Mean-pooling76.69±0.2080.07±0.7870.41±0.1684.14±2.9790.13±2.4083.39±3.14
AB-MIL [16]90.06±0.6094.00±0.8387.40±1.0588.03±2.1993.17±2.0587.41±2.42
DSMIL [17]90.17±1.0294.57±0.4087.65±1.1888.32±2.7093.71±1.8287.90±2.50
CLAM-SB [21]90.31±0.1294.65±0.3087.89±0.5987.74±2.2293.67±1.6487.36±2.24
CLAM-MB [21]90.14±0.8594.70±0.7688.10±0.6388.73±1.6293.69±0.5488.28±1.58
TransMIL [26]89.22±2.3293.51±2.1385.10±4.3387.08±1.9792.51±1.7686.40±2.08
DTFD-MIL [43]90.22±0.3695.15±0.1487.62±0.5988.23±2.1293.83±1.3987.71±2.04
MHIM-MIL (AB-MIL)91.81±0.8296.14±0.5289.94±0.7089.64±2.2594.97±1.7289.31±2.19
MHIM-MIL (TransMIL)91.98±0.8996.49±0.4890.13±1.0890.02±2.5994.87±2.1789.65±2.63
MHIM-MIL (DSMIL)92.48±0.3596.49±0.6590.75±0.7389.83±3.3795.53±1.7489.71±2.92
+ +Table 1: The performance of different MIL approaches on CAMELYON-16 (C16) and TCGA Lung Cancer (TCGA). The highest performance is in bold. The Accuracy and F1-score are determined by the optimal threshold. + +
ModelC16TCGAPara.TimeMem.
AB-MIL94.0093.17657K4.0s2.4G
CLAM-MB94.7093.69789K4.3s2.7G
DTFD-MIL95.1593.83987K5.2s2.1G
MHIM-MIL96.1494.97657K4.3s2.3G
TransMIL93.5192.512.67M13.1s10.6G
MHIM-MIL96.4994.872.67M10.1s5.5G
+ +Table 2: Comparison of time and memory requirements of different MIL methods. We report the model size (Para.), the training time per epoch (Time), and the peak memory usage (Mem.) on the CAMELYON-16 dataset (C16). + +methods achieve better performance on both datasets by focusing on salient instances. In particular, the representative MIL framework DTFD-MIL [43] benefits from the further exploration of significant instances and achieves the second-best performance on both datasets (95.15% AUC on CAMELYON-16 and 93.83% AUC on TCGA). However, it also suffers from overemphasizing salient instances during training, which limits its generalization. Our proposed MHIM-MIL achieves significant performance improvement on both datasets (+1.34% AUC on CAMELYON-16 and +1.70% AUC on TCGA) by mining hard instances during training, breaking the performance bottleneck. It is worth mentioning that we validate our framework on three representative MIL models, both of which can outperform the existing MIL methods. + +# 4.4. Computational Cost Analysis + +In this section, we report the training time and GPU memory requirements for running different MIL models on a 3090 GPU. The upper part of Table 2 compares some MIL frameworks that use AB-MIL [16] as a baseline. We observe that traditional MIL frameworks typically intro + +duce additional parameters and reduce efficiency due to their complex structures. For example, the state-of-the-art framework DTFD-MIL [43] increases the parameter size by nearly twice (657K vs. 987K) and the training time by $30\%$ . In contrast, MHIM-MIL achieves the most significant performance improvement with almost no extra computational cost due to the momentum teacher. Moreover, existing Transformer-based MIL methods are usually plagued by high computing costs due to their large number of parameters and self-attention operations. For instance, TransMIL [26], which first applies a pure Transformer MIL model to solve WSI classification problems, has $4 \times$ more parameters than AB-MIL, $3 \times$ longer training time, and almost $4.5 \times$ higher memory consumption. Furthermore, the extremely long input sequences in WSI classification degrade the stability of such complex structures (2.13% AUC standard deviation on C16, which is the highest among all embedding-level MIL methods). With the masked hard instance mining strategy, the MHIM-MIL framework significantly reduces the computational cost (-24% training time and -48% memory usage) and enhances its stability (0.48% AUC standard deviation on C16). More details are provided in Supplementary Material. + +# 4.5. Ablation Study + +# 4.5.1 Importance of the Different Components + +Table 3 shows the effect of different modules in MHIMMIL on two datasets. The baseline methods are two representative attention-based MIL methods, namely AB-MIL [16] and TransMIL [26]. First, we introduce the naive masked hard instance mining strategy, which leverages the model itself to mine hard instances during training. This strategy improves AUC by $1.86\%$ and $2.55\%$ for the two MIL models on CAMELYON-16 respectively, indicating that concentrating on hard instances during training can as + +
ModuleCAMELYON-16TCGA
AB.Trans.AB.Trans.
Baseline94.0093.5193.1792.51
+MHIM95.8696.0694.1493.75
+MHIM+Siam.95.8296.2494.5594.13
+MHIM+Siam.+Con.96.1496.4994.9794.87
+ +Table 3: The effect of different components in MHIM-MIL with two MIL models: AB-MIL (AB.) and TransMIL (Trans.). MHIM denotes the masked hard instance mining strategy. Siam. refers to the Siamese framework. Con. represents consistency loss. + +
StrategyCAMELYON-16TCGA
AB.Trans.AB.Trans.
Baseline94.0093.5193.1792.51
HAM95.6895.9093.8394.54
R-HAM96.1495.8894.7994.60
L-HAM95.8196.4994.3394.67
LR-HAM95.9296.3394.9794.87
+ +sist mainstream MIL models in building better classification boundaries. Further discussion on the masked hard instance mining strategy is presented in Section 4.5.2. Compared with the naive MHIM strategy, the third row of the table suggests that a Siamese structure [3,5,8] based on a momentum teacher is beneficial for more stable and effective mining of hard instances. We elaborate more on choosing the teacher model in Section 4.5.3. After adding consistency loss term to the objective function, our full MHIM-MIL framework achieves the best performance (96.49% AUC on CAMELYON-16 and 94 .97% AUC on TCGA). For subsequent ablation experiments, we include consistency loss by default to facilitate the optimization of our framework. + +# 4.5.2 Impact of the Different MHIM Strategies + +The masked hard instance mining strategy is the core design of our method. The main idea of this strategy is masking the most salient instances to indirectly mine hard instances to facilitate model training. Based on this idea, we devise three hybrid strategies (R-HAM, L-HAM, and LR-HAM) and present their impact in Table 4. The basic strategy, High Attention Masking (HAM), already boosts performance significantly, leading to AUC improvements of $1.68\%$ and $2.39\%$ for two MIL models on the CAMELYON-16 dataset, respectively. After introducing the other two strategies, different MIL models achieve performance improvements + +Table 4: Comparison between different masked hard instance mining strategies. The three hybrid strategies show varying performance across the benchmarks. + +
TeacherCAMELYON-16TCGA
AB.Trans.AB.Trans.
Baseline94.0093.5193.1792.51
Student copy95.8495.8693.6893.45
Init.95.8896.1294.6694.15
Momentum95.9696.1194.6594.45
Init.+Momentum96.1496.4994.9794.87
+ +![](images/eeb175c573c3a6fcfa3c2d6dcd4ccec2205eb6b58116e97c47412198800cb466.jpg) +Table 5: Comparison of different types of teachers. Momentum denotes the teacher is updated by EMA strategy. Init. indicates the initialization of the teacher with pretrained parameters. The bottom figure compares the stability of the momentum teacher and the non-batch gradient updated student during training. + +on both datasets. Specifically, AB-MIL [16] shows more significant performance gains after introducing randomness (96.14% AUC on CAMELYON-16 with R-HAM) due to its better ability to filter out redundant information, while TransMIL [26] shows the reverse trend (96.49% AUC on CAMELYON-16 with L-HAM). Furthermore, the more complex three-hybrid strategy (LR-HAM) achieves the best performance on the TCGA dataset, which has a larger proportion of positive areas and more instances. Overall, our experiments validate the effectiveness of masked hard instance mining strategy, and the diversity of proposed strategies improves its applicability to different datasets and MIL models. + +# 4.5.3 Impact of the Choice of Teacher Network + +In MHIM-MIL, we employ a Teacher model to mine hard instances and facilitate training of the Student model. In Table 5, we comprehensively investigate the effects of various choices of Teacher network. First, we utilize a single-model structure, which treats the Student model as the Teacher. The student conducts masked hard instance mining prior to training. Due to the non-batch gradient update, the unstable performance of the Student model makes the strategy susceptible to noise, so the performance is not optimal. Second, we adopt a momentum teacher, which shares the same network structure as the Student model and is updated with the EMA strategy. This updating strategy enhanced the stability of momentum teachers, as shown in the figure below, and enabled MHIM-MIL to achieve $0.97\%$ and $1.00\%$ performance improvement in TCGA under the two MIL mod + +![](images/166f3a78309f89aee0d474548cbf567a48aba0e95a9b883240057e3ccb1ab450.jpg) +Figure 4: Patch visualization produced by AB-MIL [16] (baseline) and MHIM-MIL. The blue lines outline the tumor regions. The brighter patch indicates higher attention scores. The cyan colors indicate high probabilities of being tumor for the corresponding locations. Ideally, the cyan patches should cover only the area within the blue lines. We show that focusing only on more salient regions reduces the generalization ability of the model and that hard instances can provide useful information for more accurate and comprehensive judgments. + +![](images/770d6e0337e6ebf088ae33ebaff4dcfa814ed2d6725ac69e8f555b121771a843.jpg) + +els, respectively. With proper initialization, the momentum teacher achieves the best performance. However, a fixed initialization teacher fails to learn new knowledge, which emphasizes the significance of iterative optimization. + +# 4.6. Visualization + +To more intuitively understand the effect of the masked hard instance mining, we visualize the attention scores (bright patch) and tumor probabilities (cyan patch) of patches produced by AB-MIL and MHIM-MIL, as illustrated in Figure 4. Here, MHIM-MIL employs AB-MIL as its baseline model. We note that attention scores only indicate the regions of interest of models and are infeasible to reflect tumor probabilities [17, 43]. First, as shown in Figure 4, AB-MIL often assigns high tumor probabilities to patches in non-tumor areas. We attribute this phenomenon to the low generalization capability of conventional attention-based MIL models, which tend to focus only on salient regions during training. In contrast, MHIM-MIL trained with hard instances shows a much better generalization ability than the baseline model for noise robustness (rows 2 and 3 on the right) and for precise detection of challenging subtle tumor areas (row 3 on the left). More significantly, we find that focusing only on tumor areas leads to missing most of them, expanding the view to include some + +"irrelevant areas" enables the model to make more complete judgments (rows 1 and 2 on the left). This phenomenon demonstrates how hard instances provide more useful information to help the model make more accurate and comprehensive judgments. We provide more details and an in-depth analysis of this patch visualization in Supplementary Material. + +# 5. Conclusion + +This paper rethinks the impact of salient instances for MIL-based WSI classification algorithms. We demonstrate that attention-based MIL methods excessively prioritizing salient instances harm the generalization ability of the model. To address this issue, we have proposed several masked hard instance mining strategies that mask out salient patches and encourage the model to attend to informative regions for better discriminative learning. Through qualitative analysis, we have demonstrated that these strategies effectively alleviate the under-fitting problem of general AB-MIL to hard instances. We have also developed the MHIM-MIL framework that leverages momentum teacher and consistency loss to further enhance hard instance mining. Our experimental results demonstrate the superiority and generality of the MHIM-MIL framework over other lat + +est methods. In future work, we plan to devise a more precise localization scheme for hard instances that can facilitate model training and convergence. + +# 6. Acknowledgement + +Reported research is partly supported by the National Natural Science Foundation of China under Grant 62176030, and the Natural Science Foundation of Chongqing under Grant cstc2021jcyj-msxmX0568. + +# References + +[1] Ejaz Ahmed, Michael Jones, and Tim K Marks. An improved deep learning architecture for person re-identification. In Proceedings of the IEEE conference on computer vision and pattern recognition, pages 3908–3916, 2015. 2 +[2] Babak Ehteshami Bejnordi, Mitko Veta, Paul Johannes Van Diest, Bram Van Ginneken, Nico Karssemeijer, Geert Litjens, Jeroen AWM Van Der Laak, Meyke Hermsen, Quirine F Manson, Maschenka Balkenhol, et al. Diagnostic assessment of deep learning algorithms for detection of lymph node metastases in women with breast cancer. JAMA, 318(22):2199-2210, 2017. 5 +[3] Jane Bromley, Isabelle Guyon, Yann LeCun, Eduard Säckinger, and Roopak Shah. Signature verification using a" siamese" time delay neural network. 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Since the positive tissue is only a small fraction of the gigapixel WSI, existing MIL methods intuitively focus on identifying salient instances via attention mechanisms. However, this leads to a bias towards easy-to-classify instances while neglecting hard-to-classify instances. Some literature has revealed that hard examples are beneficial for modeling a discriminative boundary accurately. By applying such an idea at the instance level, we elaborate a novel MIL framework with masked hard instance mining (MHIM-MIL), which uses a Siamese structure (Teacher-Student) with a consistency constraint to explore the potential hard instances. With several instance masking strategies based on attention scores, MHIM-MIL employs a momentum teacher to implicitly mine hard instances for training the student model, which can be any attention-based MIL model. This counter-intuitive strategy essentially enables the student to learn a better discriminating boundary. Moreover, the student is used to update the teacher with an exponential moving average (EMA), which in turn identifies new hard instances for subsequent training iterations and stabilizes the optimization. Experimental results on the CAMELYON-16 and TCGA Lung Cancer datasets demonstrate that MHIM-MIL outperforms other latest methods in terms of performance and training cost. The code is available at: https://github.com/DearCaat/MHIM-MIL." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 628, + 128, + 641 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 628, + 128, + 641 + ], + "spans": [ + { + "bbox": [ + 47, + 628, + 128, + 641 + ], + "type": "text", + "content": "1. Introduction" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 648, + 287, + 696 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 648, + 287, + 696 + ], + "spans": [ + { + "bbox": [ + 47, + 648, + 287, + 696 + ], + "type": "text", + "content": "Histopathological image analysis plays a crucial role in modern medicine, particularly in the treatment of cancer, where it serves as the gold standard for diagnosis [18, 20, 24,45]. Digitalizing pathological images into Whole Slide" + } + ] + } + ], + "index": 9 + }, + { + "type": "image", + "bbox": [ + 307, + 258, + 547, + 373 + ], + "blocks": [ + { + "bbox": [ + 307, + 258, + 547, + 373 + ], + "lines": [ + { + "bbox": [ + 307, + 258, + 547, + 373 + ], + "spans": [ + { + "bbox": [ + 307, + 258, + 547, + 373 + ], + "type": "image", + "image_path": "06714f471733be7d568f02b60d494c91ea3d0609b44bbc3b07335560576141e5.jpg" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 380, + 547, + 417 + ], + "lines": [ + { + "bbox": [ + 305, + 380, + 547, + 417 + ], + "spans": [ + { + "bbox": [ + 305, + 380, + 547, + 417 + ], + "type": "text", + "content": "Figure 1: Left: Previous MIL models focus on the more salient instances. Right: MHIM-MIL mines an amount of hard-to-classify instances to learn a better boundary." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 437, + 547, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 547, + 545 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 547, + 545 + ], + "type": "text", + "content": "Images (WSIs) through digital slide scanner has opened new avenues for computer-aided analysis [9, 26]. Due to the huge size of a WSI and the lack of pixel-level annotations, histopathological image analysis is commonly formulated as a multiple instance learning (MIL) task [10, 23, 31]. In MIL, each WSI (or slide) is a bag containing thousands of unlabeled instances (patches) cropped from the slide. With at least one instance being disease positive, the bag is deemed positive, otherwise negative." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 546, + 548, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 546, + 548, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 546, + 548, + 713 + ], + "type": "text", + "content": "However, the number of slides is limited and each slide contains a mass of instances with a low positive proportion. This imbalance would hinder the inference of bag labels [16, 43]. To alleviate this issue, several WSI classification methods [6, 16-18,26] employ an attention mechanism to aggregate salient instance features into a bag-level feature for WSI classification. Furthermore, some MIL frameworks [17,21,40,43] focus on the more salient instances in the bag and leverage them to facilitate WSI classification. For instance, existing frameworks [40, 43] propose to only select the instances that correspond to the top " + }, + { + "bbox": [ + 304, + 546, + 548, + 713 + ], + "type": "inline_equation", + "content": "K" + }, + { + "bbox": [ + 304, + 546, + 548, + 713 + ], + "type": "text", + "content": " highest or lowest attention scores [17, 40] or patch probabilities [43] for yielding high-quality bag embedding for both training and testing." + } + ] + } + ], + "index": 13 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 703, + 138, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 703, + 138, + 712 + ], + "spans": [ + { + "bbox": [ + 58, + 703, + 138, + 712 + ], + "type": "text", + "content": "*Corresponding Author." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4078" + } + ] + } + ], + "index": 15 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 289, + 251 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 289, + 251 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 289, + 251 + ], + "type": "text", + "content": "These salient instances are actually \"easy-to-classify\" instances, which are not optimal for training a discriminative WSI classification model. In conventional machine learning, such as Support Vector Machines (SVM) [13], samples near the category distribution boundary are more challenging to classify, but are more useful for depicting the classification boundary, as illustrated in Figure 1. Moreover, other deep learning works [25, 28, 33, 34] also reveal that mining hard samples for training can improve the generalization abilities of models. By applying such an idea at the instance level, we can better highlight the \"hard-to-classify\" instances that facilitate MIL model training, and benefit the final WSI classification. However, the lack of instance labels poses a challenge to the direct application of traditional hard sample mining strategies at the instance level." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 252, + 289, + 526 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 252, + 289, + 526 + ], + "spans": [ + { + "bbox": [ + 47, + 252, + 289, + 526 + ], + "type": "text", + "content": "To address this issue, we present a novel MIL framework based on masked hard instance mining strategies (MHIM) named MHIM-MIL. The main idea of MHIM is to mask out the instances with high attention scores to highlight the hard instances for model training. Based on this, we incorporate two other instance masking strategies to enhance training efficiency and mitigate the over-fitting risk. Another key design of MHIM-MIL is an instance attention generator based on a Siamese structure (Teacher-Student) [3, 8]. In MHIM-MIL, the MIL-based WSI classification model is the student network, which aggregates hard instances mined by a momentum teacher with different instance masking strategies. The momentum teacher is updated using an exponential moving average (EMA) of the student model. Moreover, the framework is optimized by inducing a consistency constraint that explores more supervised information beyond the limited slide label. Unlike the conventional MIL frameworks [40, 43], which adopt complex cascade gradient-updating structures, our method is more simple and does not require additional parameters. It not only improves efficiency but also provides improved performance stability. The contribution of this paper is summarized as follows," + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 58, + 536, + 287, + 632 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 536, + 287, + 632 + ], + "spans": [ + { + "bbox": [ + 58, + 536, + 287, + 632 + ], + "type": "text", + "content": "- We propose a simple and efficient MIL framework with masked hard instance mining named MHIM-MIL. It implicitly mines hard instances with instance attention for training a more discriminative MIL model. Extensive experiments on two WSI datasets validate that MHIM boosts different MIL models and outperforms other latest methods in terms of performance and training cost." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 58, + 641, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 641, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 58, + 641, + 287, + 714 + ], + "type": "text", + "content": "- We propose several hybrid instance masking strategies for indirectly mining hard instances in MIL. These strategies not only address the reliance problem of conventional methods on instance-level supervision but also enhance the training efficiency of the model and mitigate the over-fitting risk." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 317, + 72, + 545, + 144 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 72, + 545, + 144 + ], + "spans": [ + { + "bbox": [ + 317, + 72, + 545, + 144 + ], + "type": "text", + "content": "- With the Siamese structure, we introduce a parameter-free momentum teacher to obtain instance attention scores more efficiently and stably. Moreover, we employ a consistency-based iterative optimization to improve the discriminability of both models progressively." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 306, + 156, + 392, + 168 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 156, + 392, + 168 + ], + "spans": [ + { + "bbox": [ + 306, + 156, + 392, + 168 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 306, + 176, + 535, + 190 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 176, + 535, + 190 + ], + "spans": [ + { + "bbox": [ + 306, + 176, + 535, + 190 + ], + "type": "text", + "content": "2.1. Multiple Instance Learning in WSI Analysis" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 194, + 547, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 194, + 547, + 567 + ], + "spans": [ + { + "bbox": [ + 304, + 194, + 547, + 567 + ], + "type": "text", + "content": "Multiple Instance Learning (MIL) [10] has been widely used in WSI analysis with its unique learning paradigm in recent years [17, 22, 26, 35, 40, 42]. MIL is a weakly supervised learning framework that utilizes coarse-grained bag labels for training instead of fine-grained instance annotations. Previous algorithms can be broadly categorized into two groups: instance-level [4, 12, 15, 40] and embedding-level [9, 27, 38, 39, 43]. The former obtain instance labels and aggregate them to obtain the bag label, whereas the latter aggregate all instance features into a high-level bag embedding for bag prediction. Most embedding-level methods share the basic idea of AB-MIL [16], which employs learnable weights to aggregate salient instance features into bag embedding. Furthermore, some MIL frameworks [17, 21, 40, 43] mine more salient instances making classification easier and facilitating classification. For example, Lu et al. selected the most salient instances based on their attention scores (e.g., maximum and minimum scores) to compute instance-level loss and improve performance [21]. Zhang et al. proposed a class activation map (CAM) based on the AB-MIL paradigm to better mine salient instances and used AB-MIL to aggregate them into bag embedding [43]. In addition, feature clustering methods [27, 37, 44] computed cluster centroids of all feature embeddings and used representative embeddings for the final prediction. However, all these methods focused excessively on salient instances in training, which are easy instances with high confidence scores and can be easily classified. As a result, they overlook the importance of hard instances for training. In this paper, we intend to mine hard instances for improving WSI classification performance." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 574, + 523, + 588 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 574, + 523, + 588 + ], + "spans": [ + { + "bbox": [ + 306, + 574, + 523, + 588 + ], + "type": "text", + "content": "2.2. Hard Sample Mining in Computer Vision" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 594, + 547, + 715 + ], + "type": "text", + "content": "Hard sample mining is a popular technique to speed up convergence and enhance the discriminative power of the model in many deep learning areas, such as face recognition [25], object detection [29, 36], person re-identification [1, 28, 33, 34], and deep metric learning [30, 32]. The main idea behind this technique is to select the samples which are hard to classify correctly (i.e., hard negatives and hard positives) for alleviating the imbalance between positive and negative samples and facilitating model training. There are generally three groups of approaches" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4079" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 289, + 240 + ], + "type": "text", + "content": "for evaluating sample difficulty: loss-based [14], similarity-based [7], and learnable weight-based [41]. Typically, these strategies require complete sample supervision information. Drawing on the ideas of the above works, we propose a hard instance mining approach in MIL, mining hard examples at the instance level. In this, there are no complete instance labels, only the bag label is available. Similar to our approach, Li et al. utilized attention scores to identify salient instances from false negative bags to serve as hard negative instances and used them to compose the hard bags for improving classification performance [19]. A key difference is that we indirectly mine hard instances by masking out the most salient instances rather than directly locating hard negative instances." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 251, + 153, + 264 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 251, + 153, + 264 + ], + "spans": [ + { + "bbox": [ + 47, + 251, + 153, + 264 + ], + "type": "text", + "content": "3. Proposed Method" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 271, + 219, + 283 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 271, + 219, + 283 + ], + "spans": [ + { + "bbox": [ + 47, + 271, + 219, + 283 + ], + "type": "text", + "content": "3.1. Background: MIL Formulation" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "spans": [ + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": "In MIL, any input WSI " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": " is considered as a bag with multiple instances, which can be represented as " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "X = \\{x_{i}\\}_{i=1}^{N}" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "x_{i}" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": " is a patch collected from the WSI and considered as the " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": "-th instance of " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "X" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": ". " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": " is the number of instances. For a classification task, there exists a known label " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "Y \\in C" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": " for the bag and an unknown label " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "y_{n} \\in C" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": " for each instance, where " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "C" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": " is the collection of category labels. The goal of a MIL model " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "\\mathcal{M}(\\cdot)" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": " is to predict the bag label with all instances " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "\\hat{Y} \\gets \\mathcal{M}(X)" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": ". The popular solution is to learn a bag representation " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": " from the extracted features of instances " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "Z = \\{z_{i}\\}_{i=1}^{N}" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": " in a bag, which is also referred as the instance aggregation step. And a classifier " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "\\mathcal{C}(\\cdot)" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": ", trained upon the " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": ", can be used to predict the bag label " + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "inline_equation", + "content": "\\hat{Y} \\gets \\mathcal{C}(F)" + }, + { + "bbox": [ + 46, + 289, + 289, + 479 + ], + "type": "text", + "content": ". There are two ways to aggregate instances for achieving bag embedding. One is the attention-based aggregation [16] denoted as follows," + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 123, + 480, + 287, + 513 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 123, + 480, + 287, + 513 + ], + "spans": [ + { + "bbox": [ + 123, + 480, + 287, + 513 + ], + "type": "interline_equation", + "content": "F = \\sum_ {i = 1} ^ {N} a _ {i} z _ {i} \\in \\mathbb {R} ^ {D}, \\tag {1}", + "image_path": "e65ed2beba3dbfb8105c4a1299c8972a46a91c59d145499e68f762c947cf9327.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "spans": [ + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "inline_equation", + "content": "a_{i}" + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "text", + "content": " is the learnable scalar weight for " + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "inline_equation", + "content": "z_{i}" + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "inline_equation", + "content": "D" + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "text", + "content": " is the dimension of vector " + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "inline_equation", + "content": "z_{i}" + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "text", + "content": ". Many works [17, 21, 43] follow this formulation but differ in the ways they generate the attention score " + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "inline_equation", + "content": "a_{i}" + }, + { + "bbox": [ + 46, + 517, + 287, + 566 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 565, + 287, + 625 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 565, + 287, + 625 + ], + "spans": [ + { + "bbox": [ + 46, + 565, + 287, + 625 + ], + "type": "text", + "content": "Another is the multi-head self-attention (MSA) based aggregation [26]. In this fashion, a class token " + }, + { + "bbox": [ + 46, + 565, + 287, + 625 + ], + "type": "inline_equation", + "content": "z_0" + }, + { + "bbox": [ + 46, + 565, + 287, + 625 + ], + "type": "text", + "content": " is embedded with the instance features to get the initial input sequence " + }, + { + "bbox": [ + 46, + 565, + 287, + 625 + ], + "type": "inline_equation", + "content": "Z^0 = [z_0, z_1, \\ldots, z_N] \\in \\mathbb{R}^{(N + 1) \\times D}" + }, + { + "bbox": [ + 46, + 565, + 287, + 625 + ], + "type": "text", + "content": " for aggregating instance features. This can be formulated as," + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 52, + 633, + 286, + 654 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 52, + 633, + 286, + 654 + ], + "spans": [ + { + "bbox": [ + 52, + 633, + 286, + 654 + ], + "type": "interline_equation", + "content": "\\operatorname {h e a d} = A ^ {\\ell} \\left(Z ^ {\\ell - 1} W ^ {V}\\right) \\in \\mathbb {R} ^ {N \\times \\frac {D}{H}}, \\quad \\ell = 1 \\dots L \\tag {2}", + "image_path": "4ce70b95384e4e2a5ec2d238c479080e725ab53c044f42259eafa01ef6bcb1fe.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 54, + 652, + 269, + 665 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 54, + 652, + 269, + 665 + ], + "spans": [ + { + "bbox": [ + 54, + 652, + 269, + 665 + ], + "type": "interline_equation", + "content": "Z ^ {\\ell} = \\operatorname {C o n c a t} \\left(\\operatorname {h e a d} _ {1}, \\dots , \\operatorname {h e a d} _ {H}\\right) W ^ {O}, \\quad \\ell = 1 \\dots L", + "image_path": "1ad2649bebdc90d65f9dd088dc1c03d476e6e0bfacfb7ec23af72bd9173639c0.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "type": "inline_equation", + "content": "W^{V}\\in \\mathbb{R}^{D\\times \\frac{D}{H}}" + }, + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "type": "inline_equation", + "content": "W^{O}\\in \\mathbb{R}^{D\\times D}" + }, + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "type": "text", + "content": " are the learnable projection matrices of MSA. " + }, + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "type": "inline_equation", + "content": "A^{\\ell}\\in \\mathbb{R}^{(N + 1)\\times (N + 1)}" + }, + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "type": "text", + "content": " is the attention matrix of the " + }, + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "type": "inline_equation", + "content": "\\ell" + }, + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "type": "text", + "content": "-th layer, " + }, + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 676, + 287, + 713 + ], + "type": "text", + "content": " is the number of MSA" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "spans": [ + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": "block, and " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "H" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": " is the number of head in each MSA block. The bag embedding " + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "inline_equation", + "content": "F" + }, + { + "bbox": [ + 304, + 72, + 545, + 108 + ], + "type": "text", + "content": " is the output class token at the final layer," + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 405, + 111, + 545, + 125 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 405, + 111, + 545, + 125 + ], + "spans": [ + { + "bbox": [ + 405, + 111, + 545, + 125 + ], + "type": "interline_equation", + "content": "F = Z _ {0} ^ {L}. \\tag {3}", + "image_path": "6a771ea1b77c36c2f56a1d71cc5e2f25de1fd3db0c6c4a211654b6e8ac973340.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 134, + 545, + 183 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 134, + 545, + 183 + ], + "spans": [ + { + "bbox": [ + 304, + 134, + 545, + 183 + ], + "type": "text", + "content": "The self-attention-based bag embedding is essentially a special case of attention-based bag embedding in the multi-instance learning setting. Collectively, these approaches can be referred to as the general attention-based MIL method." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 194, + 494, + 206 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 194, + 494, + 206 + ], + "spans": [ + { + "bbox": [ + 305, + 194, + 494, + 206 + ], + "type": "text", + "content": "3.2. MHIM-MIL for WSI Classification" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 304, + 214, + 545, + 346 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 214, + 545, + 346 + ], + "spans": [ + { + "bbox": [ + 304, + 214, + 545, + 346 + ], + "type": "text", + "content": "In general attention-based MIL frameworks, the attention scores of instances indicate the contributions of instances to the bag classification. The salient instances with high scores are useful for classifying WSI in the testing phase but are not conducive to training a MIL model with good generalization ability. Although hard samples have been proven to enhance the generalization ability of the model in many computer vision scenarios [11, 32-34], previous MIL works focus more on exploiting the salient instances and neglecting the utilization of hard instances in model optimization." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 347, + 546, + 646 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 347, + 546, + 646 + ], + "spans": [ + { + "bbox": [ + 304, + 347, + 546, + 646 + ], + "type": "text", + "content": "In this paper, we propose a simple and efficient MIL framework with Masked Hard Instance Mining (MHIM-MIL) to boost the WSI classification. As illustrated in Figure 2, the MHIM-MIL framework employs a Siamese structure during the training phase. The main component of our framework is a general attention-based MIL model (Student), denoted as " + }, + { + "bbox": [ + 304, + 347, + 546, + 646 + ], + "type": "inline_equation", + "content": "S(\\cdot)" + }, + { + "bbox": [ + 304, + 347, + 546, + 646 + ], + "type": "text", + "content": ", for aggregating instance features. To increase the discriminatory difficulty of the student model and force it to focus on hard instances, we introduce a momentum teacher, denoted as " + }, + { + "bbox": [ + 304, + 347, + 546, + 646 + ], + "type": "inline_equation", + "content": "T(\\cdot)" + }, + { + "bbox": [ + 304, + 347, + 546, + 646 + ], + "type": "text", + "content": ", to score the instances with attention weights and then employ some masked hard instance mining strategies to mask the salient instances while preserving the hard instances. After hard instance mining, all the mined features are forwarded into the student model for the inference of the bag label. The teacher shares the same network structure as the student model but does not need gradient-based updates. It is worth mentioning that, due to the varying number of instances within each bag, the non-batch gradient descent algorithm (i.e., SGD with batch size 1) is typically employed to optimize the MIL model. Therefore, compared to the traditional MIL frameworks with two-tier gradient updating models [40, 43], this Siamese structure makes training more stable and efficient with fewer parameters. The proposed framework can be defined as," + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 365, + 648, + 545, + 669 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 365, + 648, + 545, + 669 + ], + "spans": [ + { + "bbox": [ + 365, + 648, + 545, + 669 + ], + "type": "interline_equation", + "content": "\\hat {Y} = \\mathcal {S} (\\hat {Z}) = \\mathcal {S} (M _ {\\mathcal {T}} (Z)), \\tag {4}", + "image_path": "dc3fd69c1290c4cb914f798007e0aca2d0a769397965a3049f42983edbcd125a.jpg" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "spans": [ + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "type": "inline_equation", + "content": "M_{\\mathcal{T}}(\\cdot)" + }, + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "type": "text", + "content": " denotes a masked hard instance mining strategy through the teacher model and " + }, + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "type": "inline_equation", + "content": "\\hat{Z}" + }, + { + "bbox": [ + 304, + 677, + 545, + 712 + ], + "type": "text", + "content": " are the mined instances." + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "4080" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 105, + 70, + 491, + 203 + ], + "blocks": [ + { + "bbox": [ + 105, + 70, + 491, + 203 + ], + "lines": [ + { + "bbox": [ + 105, + 70, + 491, + 203 + ], + "spans": [ + { + "bbox": [ + 105, + 70, + 491, + 203 + ], + "type": "image", + "image_path": "5296ed3dbaf0ab29a083c63de78c5473ba2c1051791b50b2b10244c5c1d7150f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 105, + 205, + 489, + 266 + ], + "blocks": [ + { + "bbox": [ + 105, + 205, + 489, + 266 + ], + "lines": [ + { + "bbox": [ + 105, + 205, + 489, + 266 + ], + "spans": [ + { + "bbox": [ + 105, + 205, + 489, + 266 + ], + "type": "image", + "image_path": "e4de11326178938e3deaff1123ab62f2b103d83883a15877a39d6db5479bb3c7.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 275, + 547, + 336 + ], + "lines": [ + { + "bbox": [ + 46, + 275, + 547, + 336 + ], + "spans": [ + { + "bbox": [ + 46, + 275, + 547, + 336 + ], + "type": "text", + "content": "Figure 2: Overview of proposed MHIM-MIL. A momentum teacher is used to compute attention scores for all instances. We mask instances based on attention with hard mining strategies and feed the remaining to the student model. The student is updated by a consistency loss term " + }, + { + "bbox": [ + 46, + 275, + 547, + 336 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{con}" + }, + { + "bbox": [ + 46, + 275, + 547, + 336 + ], + "type": "text", + "content": " and a label error loss term " + }, + { + "bbox": [ + 46, + 275, + 547, + 336 + ], + "type": "inline_equation", + "content": "\\mathcal{L}_{cls}" + }, + { + "bbox": [ + 46, + 275, + 547, + 336 + ], + "type": "text", + "content": ". The teacher parameters are updated with an Exponential Moving Average (EMA) of the student parameters without gradient updates. In the inference phase, we use the complete input instances and the student model only." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 347, + 257, + 361 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 347, + 257, + 361 + ], + "spans": [ + { + "bbox": [ + 47, + 347, + 257, + 361 + ], + "type": "text", + "content": "3.3. Masked Hard Instance Mining Strategy" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 366, + 289, + 474 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 366, + 289, + 474 + ], + "spans": [ + { + "bbox": [ + 46, + 366, + 289, + 474 + ], + "type": "text", + "content": "Conventional hard sample mining strategies are difficult to apply without instance-level supervision. We address this challenge by proposing masked hard instance mining strategies that use attention scores to implicitly mine hard instances by masking out easy instances with high attention scores. More specifically, given a complete sequence of instance features " + }, + { + "bbox": [ + 46, + 366, + 289, + 474 + ], + "type": "inline_equation", + "content": "Z = \\{z_{i}\\}_{i=1}^{N}" + }, + { + "bbox": [ + 46, + 366, + 289, + 474 + ], + "type": "text", + "content": " as the input of the teacher model " + }, + { + "bbox": [ + 46, + 366, + 289, + 474 + ], + "type": "inline_equation", + "content": "\\mathcal{T}(\\cdot)" + }, + { + "bbox": [ + 46, + 366, + 289, + 474 + ], + "type": "text", + "content": ", the teacher outputs the attention weight " + }, + { + "bbox": [ + 46, + 366, + 289, + 474 + ], + "type": "inline_equation", + "content": "a_{i}" + }, + { + "bbox": [ + 46, + 366, + 289, + 474 + ], + "type": "text", + "content": " for each instance as follow," + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 93, + 482, + 287, + 496 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 482, + 287, + 496 + ], + "spans": [ + { + "bbox": [ + 93, + 482, + 287, + 496 + ], + "type": "interline_equation", + "content": "A = \\left[ a _ {1}, \\dots , a _ {i}, \\dots , a _ {N} \\right] = \\mathcal {T} (Z). \\tag {5}", + "image_path": "c2fbf4dde14368661473d5496300bf898ef577d6f27758f0893d1092b70f58b3.jpg" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 504, + 287, + 529 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 504, + 287, + 529 + ], + "spans": [ + { + "bbox": [ + 47, + 504, + 287, + 529 + ], + "type": "text", + "content": "Then, we obtain the indices of the attention sequence in descending order by applying a sorting operation on " + }, + { + "bbox": [ + 47, + 504, + 287, + 529 + ], + "type": "inline_equation", + "content": "A" + }, + { + "bbox": [ + 47, + 504, + 287, + 529 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 101, + 536, + 287, + 550 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 101, + 536, + 287, + 550 + ], + "spans": [ + { + "bbox": [ + 101, + 536, + 287, + 550 + ], + "type": "interline_equation", + "content": "I = \\left[ i _ {1}, i _ {2}, \\dots , i _ {N} \\right] = \\operatorname {S o r t} (A), \\tag {6}", + "image_path": "194663c246aba7fb46883fe2726ccefe929c7dfbff7896a9e3da49d272cea598.jpg" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "spans": [ + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "inline_equation", + "content": "i_1" + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "text", + "content": " is the index of the instance with the highest attention score while " + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "inline_equation", + "content": "i_N" + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "text", + "content": " is the index of the one with the lowest score. With this index collection " + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "inline_equation", + "content": "I" + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "text", + "content": ", we will present several masked hard instance mining strategies to select the hard instances. We define an " + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "inline_equation", + "content": "N" + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "text", + "content": "-dimensional binary vector " + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "inline_equation", + "content": "M = [m_1, \\dots, m_i, \\dots, m_N]" + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "text", + "content": " for encoding the mask flags of instances where " + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "inline_equation", + "content": "m_i \\in \\{0, 1\\}" + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "text", + "content": ". If " + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "inline_equation", + "content": "m_i = 1" + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "text", + "content": ", the " + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "inline_equation", + "content": "i" + }, + { + "bbox": [ + 47, + 558, + 287, + 653 + ], + "type": "text", + "content": "-th instance is masked, otherwise, it is unmasked." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 47, + 653, + 288, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 653, + 288, + 714 + ], + "spans": [ + { + "bbox": [ + 47, + 653, + 288, + 714 + ], + "type": "text", + "content": "High Attention Masking: The simplest masked hard instance mining strategy is the High Attention Masking (HAM) strategy, which simply masks instances with the top " + }, + { + "bbox": [ + 47, + 653, + 288, + 714 + ], + "type": "inline_equation", + "content": "\\beta_{h}\\%" + }, + { + "bbox": [ + 47, + 653, + 288, + 714 + ], + "type": "text", + "content": " highest attention scores. The instance mask flags under HAM are initialized as all zero vectors, " + }, + { + "bbox": [ + 47, + 653, + 288, + 714 + ], + "type": "inline_equation", + "content": "M_{h}(:) = 0" + }, + { + "bbox": [ + 47, + 653, + 288, + 714 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 348, + 545, + 419 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 348, + 545, + 419 + ], + "spans": [ + { + "bbox": [ + 304, + 348, + 545, + 419 + ], + "type": "text", + "content": "Then we collect the indices of the instances whose scores are ranked in the top " + }, + { + "bbox": [ + 304, + 348, + 545, + 419 + ], + "type": "inline_equation", + "content": "\\beta_h\\%" + }, + { + "bbox": [ + 304, + 348, + 545, + 419 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 304, + 348, + 545, + 419 + ], + "type": "inline_equation", + "content": "I_h = [i_t]_{t=1}^{\\lceil \\beta_h\\% \\times N \\rceil}" + }, + { + "bbox": [ + 304, + 348, + 545, + 419 + ], + "type": "text", + "content": ". Finally, we set the mask flags with these indices, " + }, + { + "bbox": [ + 304, + 348, + 545, + 419 + ], + "type": "inline_equation", + "content": "M_h(I_h) = 1" + }, + { + "bbox": [ + 304, + 348, + 545, + 419 + ], + "type": "text", + "content": ". To ensure that positive instances are preserved within the un-masked sequences, we also utilized techniques such as mask ratio decay." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 419, + 546, + 502 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 419, + 546, + 502 + ], + "spans": [ + { + "bbox": [ + 304, + 419, + 546, + 502 + ], + "type": "text", + "content": "Hybrid Masking: We combine HAM with several other instance masking strategies as hybrid masking strategies to achieve some specific properties in hard instance mining, as shown in Figure 3. We consider the obtained mask flags as a collection and employ the union operation for mask flag fusion. We design three hybrid masking strategies as follows:" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 317, + 509, + 547, + 714 + ], + "type": "list", + "angle": 0, + "index": 15, + "blocks": [ + { + "bbox": [ + 317, + 509, + 545, + 593 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 509, + 545, + 593 + ], + "spans": [ + { + "bbox": [ + 317, + 509, + 545, + 593 + ], + "type": "text", + "content": "- L-HAM: We use the same pipeline as HAM to generate the mask flags " + }, + { + "bbox": [ + 317, + 509, + 545, + 593 + ], + "type": "inline_equation", + "content": "M_{l}" + }, + { + "bbox": [ + 317, + 509, + 545, + 593 + ], + "type": "text", + "content": " for masking the instances with the top " + }, + { + "bbox": [ + 317, + 509, + 545, + 593 + ], + "type": "inline_equation", + "content": "\\beta_{l} \\%" + }, + { + "bbox": [ + 317, + 509, + 545, + 593 + ], + "type": "text", + "content": " lowest attention scores in order to filter out the redundant uninformative instances and improve efficiency. To endow this property to HAM, we union the mask flags obtained by two strategies to get the new mask flags, " + }, + { + "bbox": [ + 317, + 509, + 545, + 593 + ], + "type": "inline_equation", + "content": "\\hat{M} = M_{h} \\cup M_{l}" + }, + { + "bbox": [ + 317, + 509, + 545, + 593 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 317, + 599, + 547, + 659 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 599, + 547, + 659 + ], + "spans": [ + { + "bbox": [ + 317, + 599, + 547, + 659 + ], + "type": "text", + "content": "- R-HAM: Randomness is beneficial to reduce the risk of over-fitting. We generate a random mask flag vector " + }, + { + "bbox": [ + 317, + 599, + 547, + 659 + ], + "type": "inline_equation", + "content": "M_r" + }, + { + "bbox": [ + 317, + 599, + 547, + 659 + ], + "type": "text", + "content": " with a given random ratio " + }, + { + "bbox": [ + 317, + 599, + 547, + 659 + ], + "type": "inline_equation", + "content": "\\beta_r\\%" + }, + { + "bbox": [ + 317, + 599, + 547, + 659 + ], + "type": "text", + "content": ", and combine it with " + }, + { + "bbox": [ + 317, + 599, + 547, + 659 + ], + "type": "inline_equation", + "content": "M_h" + }, + { + "bbox": [ + 317, + 599, + 547, + 659 + ], + "type": "text", + "content": " for introducing the randomness to the hard instance mining, " + }, + { + "bbox": [ + 317, + 599, + 547, + 659 + ], + "type": "inline_equation", + "content": "\\hat{M} = M_h \\cup M_r" + }, + { + "bbox": [ + 317, + 599, + 547, + 659 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 317, + 665, + 547, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 665, + 547, + 714 + ], + "spans": [ + { + "bbox": [ + 317, + 665, + 547, + 714 + ], + "type": "text", + "content": "- LR-HAM: Combining the above strategies, we can obtain completely hybrid mask flags, " + }, + { + "bbox": [ + 317, + 665, + 547, + 714 + ], + "type": "inline_equation", + "content": "\\tilde{M} = M_h \\cup M_r \\cup M_l" + }, + { + "bbox": [ + 317, + 665, + 547, + 714 + ], + "type": "text", + "content": ", which is expected to achieve both of the mentioned desirable properties." + } + ] + } + ], + "index": 14 + } + ], + "sub_type": "text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 314, + 757 + ], + "type": "text", + "content": "4081" + } + ] + } + ], + "index": 16 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 69, + 138, + 162 + ], + "blocks": [ + { + "bbox": [ + 48, + 69, + 138, + 162 + ], + "lines": [ + { + "bbox": [ + 48, + 69, + 138, + 162 + ], + "spans": [ + { + "bbox": [ + 48, + 69, + 138, + 162 + ], + "type": "image", + "image_path": "ff415e38d78b95bc030b6e341c833f222016d399ba0ede96bd2dc4eda02f1e2c.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 170, + 287, + 195 + ], + "lines": [ + { + "bbox": [ + 46, + 170, + 287, + 195 + ], + "spans": [ + { + "bbox": [ + 46, + 170, + 287, + 195 + ], + "type": "text", + "content": "Figure 3: Illustration of proposed hybrid masking strategy for hard instance mining." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 152, + 68, + 287, + 161 + ], + "blocks": [ + { + "bbox": [ + 152, + 68, + 287, + 161 + ], + "lines": [ + { + "bbox": [ + 152, + 68, + 287, + 161 + ], + "spans": [ + { + "bbox": [ + 152, + 68, + 287, + 161 + ], + "type": "image", + "image_path": "f50a6e4d21146e114d8d41f25bb092acca5ba1ba527d45b2b5ceb2dc89b9a283.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 217, + 287, + 242 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 217, + 287, + 242 + ], + "spans": [ + { + "bbox": [ + 46, + 217, + 287, + 242 + ], + "type": "text", + "content": "Once the final mask flag " + }, + { + "bbox": [ + 46, + 217, + 287, + 242 + ], + "type": "inline_equation", + "content": "\\hat{M}" + }, + { + "bbox": [ + 46, + 217, + 287, + 242 + ], + "type": "text", + "content": " is produced, the masked instance sequence will be obtained:" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 81, + 251, + 287, + 271 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 81, + 251, + 287, + 271 + ], + "spans": [ + { + "bbox": [ + 81, + 251, + 287, + 271 + ], + "type": "interline_equation", + "content": "\\hat {Z} = M _ {\\mathcal {T}} (Z) = \\operatorname {M a s k} (Z, \\hat {M}) \\in \\mathbb {R} ^ {\\hat {N} \\times D}, \\tag {7}", + "image_path": "15421e5d5db657e36a699bbfaf16bb4651956bd6631860655b950b3ce5a33a1e.jpg" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 282, + 253, + 295 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 282, + 253, + 295 + ], + "spans": [ + { + "bbox": [ + 47, + 282, + 253, + 295 + ], + "type": "text", + "content": "where the " + }, + { + "bbox": [ + 47, + 282, + 253, + 295 + ], + "type": "inline_equation", + "content": "\\hat{N}" + }, + { + "bbox": [ + 47, + 282, + 253, + 295 + ], + "type": "text", + "content": " is the number of unmasked instances." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 304, + 264, + 317 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 304, + 264, + 317 + ], + "spans": [ + { + "bbox": [ + 47, + 304, + 264, + 317 + ], + "type": "text", + "content": "3.4. Consistency-based Iterative Optimization" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 323, + 287, + 430 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 323, + 287, + 430 + ], + "spans": [ + { + "bbox": [ + 46, + 323, + 287, + 430 + ], + "type": "text", + "content": "Under the Siamese structure, while the teacher model guides the training of the student model, the new knowledge learned by the student model will also update the teacher model. This iterative optimization process progressively improves the mining ability of the teacher and the discriminability of the student. To further facilitate this optimization and explore additional supervised information provided by the momentum teacher, we propose a consistency loss that constrains the classification results of both models." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 432, + 287, + 467 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 432, + 287, + 467 + ], + "spans": [ + { + "bbox": [ + 46, + 432, + 287, + 467 + ], + "type": "text", + "content": "Student Optimization: There are two losses in student optimization. One is the cross-entropy for measuring the bag label prediction loss," + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 84, + 478, + 287, + 498 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 84, + 478, + 287, + 498 + ], + "spans": [ + { + "bbox": [ + 84, + 478, + 287, + 498 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {c l s} = Y \\log \\hat {Y} + (1 - Y) \\log \\left(1 - \\hat {Y}\\right). \\tag {8}", + "image_path": "8d95ab5013c6765af21bd26e779ce3c77ee09ddad7a7ea03ed08ca29182a4341.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 506, + 287, + 531 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 506, + 287, + 531 + ], + "spans": [ + { + "bbox": [ + 47, + 506, + 287, + 531 + ], + "type": "text", + "content": "Another is a consistency loss between the bag representation of student " + }, + { + "bbox": [ + 47, + 506, + 287, + 531 + ], + "type": "inline_equation", + "content": "F_{s}" + }, + { + "bbox": [ + 47, + 506, + 287, + 531 + ], + "type": "text", + "content": " and momentum teacher " + }, + { + "bbox": [ + 47, + 506, + 287, + 531 + ], + "type": "inline_equation", + "content": "F_{t}" + }, + { + "bbox": [ + 47, + 506, + 287, + 531 + ], + "type": "text", + "content": "," + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 99, + 542, + 287, + 555 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 99, + 542, + 287, + 555 + ], + "spans": [ + { + "bbox": [ + 99, + 542, + 287, + 555 + ], + "type": "interline_equation", + "content": "\\mathcal {L} _ {\\text {c o n}} = - \\operatorname {s o f t m a x} \\left(F _ {t} / \\tau\\right) \\log F _ {s} \\tag {9}", + "image_path": "519bf373d998ebdcff5251b5a2c907dc08762de89fac7ce0bed060142e68acbd.jpg" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 47, + 565, + 287, + 589 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 565, + 287, + 589 + ], + "spans": [ + { + "bbox": [ + 47, + 565, + 287, + 589 + ], + "type": "text", + "content": "where the " + }, + { + "bbox": [ + 47, + 565, + 287, + 589 + ], + "type": "inline_equation", + "content": "\\tau > 0" + }, + { + "bbox": [ + 47, + 565, + 287, + 589 + ], + "type": "text", + "content": " is a temperature parameter. Overall, the final optimization loss is as follows:" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 93, + 599, + 287, + 618 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 93, + 599, + 287, + 618 + ], + "spans": [ + { + "bbox": [ + 93, + 599, + 287, + 618 + ], + "type": "interline_equation", + "content": "\\left\\{\\hat {\\theta_ {s}} \\right\\} \\leftarrow \\arg \\min _ {\\theta_ {s}} \\mathcal {L} = \\mathcal {L} _ {c l s} + \\alpha \\mathcal {L} _ {c o n} \\tag {10}", + "image_path": "c624c63cae36bc9a1e3d3a9a049d118431f232063aa47da24a3a594b76d6f3db.jpg" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 47, + 629, + 282, + 641 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 629, + 282, + 641 + ], + "spans": [ + { + "bbox": [ + 47, + 629, + 282, + 641 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 629, + 282, + 641 + ], + "type": "inline_equation", + "content": "\\theta_{s}" + }, + { + "bbox": [ + 47, + 629, + 282, + 641 + ], + "type": "text", + "content": " is the parameters of " + }, + { + "bbox": [ + 47, + 629, + 282, + 641 + ], + "type": "inline_equation", + "content": "S(\\cdot)" + }, + { + "bbox": [ + 47, + 629, + 282, + 641 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 47, + 629, + 282, + 641 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 47, + 629, + 282, + 641 + ], + "type": "text", + "content": " is scaling factor." + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "content": "Teacher Optimization: The parameters of momentum teacher " + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\theta_{t}" + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "content": " are updated by an exponential moving average (EMA) of the student parameters. The update rule is " + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\theta_{t} \\gets \\lambda \\theta_{t} + (1 - \\lambda) \\theta_{s}" + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "inline_equation", + "content": "\\lambda" + }, + { + "bbox": [ + 46, + 642, + 287, + 714 + ], + "type": "text", + "content": " is a hyperparameter. More importantly, the updated teacher is utilized in the next iteration of hard instance mining." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 71, + 450, + 85 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 71, + 450, + 85 + ], + "spans": [ + { + "bbox": [ + 305, + 71, + 450, + 85 + ], + "type": "text", + "content": "4. Experiments and Results" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 306, + 91, + 481, + 102 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 91, + 481, + 102 + ], + "spans": [ + { + "bbox": [ + 306, + 91, + 481, + 102 + ], + "type": "text", + "content": "4.1. Datasets and Evaluation Metrics" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 304, + 109, + 545, + 228 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 109, + 545, + 228 + ], + "spans": [ + { + "bbox": [ + 304, + 109, + 545, + 228 + ], + "type": "text", + "content": "CAMELYON-16 [2] is a WSI dataset proposed for metastasis detection in breast cancer. The dataset contains a total of 400 WSIs, which are officially split into 270 for training and 130 for testing, and the testing sample ratio is " + }, + { + "bbox": [ + 304, + 109, + 545, + 228 + ], + "type": "inline_equation", + "content": "13/40 \\approx 1/3" + }, + { + "bbox": [ + 304, + 109, + 545, + 228 + ], + "type": "text", + "content": ". Following [6, 21, 44], we adopt 3-times 3-fold cross-validation on this dataset to ensure that each slide is used in training and testing, which can alleviate the impact of data split and random seed on the model evaluation. Each fold has approximately 133 slides. We report the mean and standard deviation of performance metrics over 3 runs." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 229, + 545, + 337 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 229, + 545, + 337 + ], + "spans": [ + { + "bbox": [ + 304, + 229, + 545, + 337 + ], + "type": "text", + "content": "TCGA Lung Cancer includes two sub-type of cancers, Lung Adenocarcinoma (LUAD) and Lung Squamous Cell Carcinoma (LUSC). There are diagnostic slides, LUAD with 541 slides from 478 cases, and LUSC with 512 slides from 478 cases. We randomly split the dataset into training, validation, and testing sets with a ratio of 65:10:25 on the patient level. 4-fold cross-validation is adopted, and the mean and standard deviation of performance metrics of the 4 test folders are reported." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 338, + 545, + 432 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 338, + 545, + 432 + ], + "spans": [ + { + "bbox": [ + 304, + 338, + 545, + 432 + ], + "type": "text", + "content": "We adopt the same data pre-processing as in the CLAM [21]. Following the previous work [21, 26] we leverage Accuracy, Area Under Curve (AUC), and F1-score to evaluate model performance. AUC is the primary performance metric in the binary classification task, and we only report AUC in ablation experiments. Please refer to the Supplementary Material for the details of these two datasets." + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 441, + 440, + 453 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 441, + 440, + 453 + ], + "spans": [ + { + "bbox": [ + 306, + 441, + 440, + 453 + ], + "type": "text", + "content": "4.2. Implementation Details" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 306, + 460, + 544, + 483 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 460, + 544, + 483 + ], + "spans": [ + { + "bbox": [ + 306, + 460, + 544, + 483 + ], + "type": "text", + "content": "The details on network architectures and training are described in Supplementary Material." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 306, + 491, + 543, + 504 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 491, + 543, + 504 + ], + "spans": [ + { + "bbox": [ + 306, + 491, + 543, + 504 + ], + "type": "text", + "content": "4.3. Performance Comparison with Exiting Works" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 605 + ], + "type": "text", + "content": "We mainly compare with AB-MIL [16], DSMIL [17], CLAM-SB [21], CLAM-MB [21], TransMIL [26], and DTFD-MIL [43], all of which are attention-based MIL methods. In addition, we compared two traditional MIL pooling operations, Max-pooling and Mean-pooling. Due to the dataset differences, the results of all other methods are reproduced using the official code they provide under the same settings." + } + ] + } + ], + "index": 24 + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "text", + "content": "As shown in Table 1, max-pooling and mean-pooling perform poorly on two datasets compared to other methods. We attribute this to their insufficient modeling of key instance information. Simple pooling operations are prone to be misled by limited slides that contain numerous instances. This problem is especially severe on the CAMELYON-16 dataset, where the proportion of significant instances is extremely small. For example, max-pooling lags behind DTFD-MIL [43] by " + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "inline_equation", + "content": "13.87\\%" + }, + { + "bbox": [ + 304, + 606, + 545, + 713 + ], + "type": "text", + "content": " on AUC. Attention-based" + } + ] + } + ], + "index": 25 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 294, + 748, + 315, + 757 + ], + "type": "text", + "content": "4082" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 79, + 70, + 515, + 230 + ], + "blocks": [ + { + "bbox": [ + 79, + 70, + 515, + 230 + ], + "lines": [ + { + "bbox": [ + 79, + 70, + 515, + 230 + ], + "spans": [ + { + "bbox": [ + 79, + 70, + 515, + 230 + ], + "type": "table", + "html": "
MethodCAMELYON-16TCGA Lung Cancer
AccuracyAUCF1-scoreAccuracyAUCF1-score
Max-pooling78.95±2.2881.28±3.7471.06±2.5981.49±1.2486.45±0.7180.56±1.09
Mean-pooling76.69±0.2080.07±0.7870.41±0.1684.14±2.9790.13±2.4083.39±3.14
AB-MIL [16]90.06±0.6094.00±0.8387.40±1.0588.03±2.1993.17±2.0587.41±2.42
DSMIL [17]90.17±1.0294.57±0.4087.65±1.1888.32±2.7093.71±1.8287.90±2.50
CLAM-SB [21]90.31±0.1294.65±0.3087.89±0.5987.74±2.2293.67±1.6487.36±2.24
CLAM-MB [21]90.14±0.8594.70±0.7688.10±0.6388.73±1.6293.69±0.5488.28±1.58
TransMIL [26]89.22±2.3293.51±2.1385.10±4.3387.08±1.9792.51±1.7686.40±2.08
DTFD-MIL [43]90.22±0.3695.15±0.1487.62±0.5988.23±2.1293.83±1.3987.71±2.04
MHIM-MIL (AB-MIL)91.81±0.8296.14±0.5289.94±0.7089.64±2.2594.97±1.7289.31±2.19
MHIM-MIL (TransMIL)91.98±0.8996.49±0.4890.13±1.0890.02±2.5994.87±2.1789.65±2.63
MHIM-MIL (DSMIL)92.48±0.3596.49±0.6590.75±0.7389.83±3.3795.53±1.7489.71±2.92
", + "image_path": "cbf34a959051a7c4326b33f04da77ec9023cd7ae4d52272e024c53603e10cd8f.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 52, + 276, + 282, + 371 + ], + "blocks": [ + { + "bbox": [ + 46, + 239, + 546, + 264 + ], + "lines": [ + { + "bbox": [ + 46, + 239, + 546, + 264 + ], + "spans": [ + { + "bbox": [ + 46, + 239, + 546, + 264 + ], + "type": "text", + "content": "Table 1: The performance of different MIL approaches on CAMELYON-16 (C16) and TCGA Lung Cancer (TCGA). The highest performance is in bold. The Accuracy and F1-score are determined by the optimal threshold." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 52, + 276, + 282, + 371 + ], + "lines": [ + { + "bbox": [ + 52, + 276, + 282, + 371 + ], + "spans": [ + { + "bbox": [ + 52, + 276, + 282, + 371 + ], + "type": "table", + "html": "
ModelC16TCGAPara.TimeMem.
AB-MIL94.0093.17657K4.0s2.4G
CLAM-MB94.7093.69789K4.3s2.7G
DTFD-MIL95.1593.83987K5.2s2.1G
MHIM-MIL96.1494.97657K4.3s2.3G
TransMIL93.5192.512.67M13.1s10.6G
MHIM-MIL96.4994.872.67M10.1s5.5G
", + "image_path": "33f1863c0a17285de6fae008db08290bba448e15c643424665147416c8c1057a.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 380, + 288, + 429 + ], + "lines": [ + { + "bbox": [ + 46, + 380, + 288, + 429 + ], + "spans": [ + { + "bbox": [ + 46, + 380, + 288, + 429 + ], + "type": "text", + "content": "Table 2: Comparison of time and memory requirements of different MIL methods. We report the model size (Para.), the training time per epoch (Time), and the peak memory usage (Mem.) on the CAMELYON-16 dataset (C16)." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "text" + }, + { + "bbox": [ + 46, + 443, + 287, + 622 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 443, + 287, + 622 + ], + "spans": [ + { + "bbox": [ + 46, + 443, + 287, + 622 + ], + "type": "text", + "content": "methods achieve better performance on both datasets by focusing on salient instances. In particular, the representative MIL framework DTFD-MIL [43] benefits from the further exploration of significant instances and achieves the second-best performance on both datasets (95.15% AUC on CAMELYON-16 and 93.83% AUC on TCGA). However, it also suffers from overemphasizing salient instances during training, which limits its generalization. Our proposed MHIM-MIL achieves significant performance improvement on both datasets (+1.34% AUC on CAMELYON-16 and +1.70% AUC on TCGA) by mining hard instances during training, breaking the performance bottleneck. It is worth mentioning that we validate our framework on three representative MIL models, both of which can outperform the existing MIL methods." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 634, + 208, + 647 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 634, + 208, + 647 + ], + "spans": [ + { + "bbox": [ + 47, + 634, + 208, + 647 + ], + "type": "text", + "content": "4.4. Computational Cost Analysis" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 653, + 287, + 715 + ], + "type": "text", + "content": "In this section, we report the training time and GPU memory requirements for running different MIL models on a 3090 GPU. The upper part of Table 2 compares some MIL frameworks that use AB-MIL [16] as a baseline. We observe that traditional MIL frameworks typically intro" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 278, + 547, + 554 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 278, + 547, + 554 + ], + "spans": [ + { + "bbox": [ + 304, + 278, + 547, + 554 + ], + "type": "text", + "content": "duce additional parameters and reduce efficiency due to their complex structures. For example, the state-of-the-art framework DTFD-MIL [43] increases the parameter size by nearly twice (657K vs. 987K) and the training time by " + }, + { + "bbox": [ + 304, + 278, + 547, + 554 + ], + "type": "inline_equation", + "content": "30\\%" + }, + { + "bbox": [ + 304, + 278, + 547, + 554 + ], + "type": "text", + "content": ". In contrast, MHIM-MIL achieves the most significant performance improvement with almost no extra computational cost due to the momentum teacher. Moreover, existing Transformer-based MIL methods are usually plagued by high computing costs due to their large number of parameters and self-attention operations. For instance, TransMIL [26], which first applies a pure Transformer MIL model to solve WSI classification problems, has " + }, + { + "bbox": [ + 304, + 278, + 547, + 554 + ], + "type": "inline_equation", + "content": "4 \\times" + }, + { + "bbox": [ + 304, + 278, + 547, + 554 + ], + "type": "text", + "content": " more parameters than AB-MIL, " + }, + { + "bbox": [ + 304, + 278, + 547, + 554 + ], + "type": "inline_equation", + "content": "3 \\times" + }, + { + "bbox": [ + 304, + 278, + 547, + 554 + ], + "type": "text", + "content": " longer training time, and almost " + }, + { + "bbox": [ + 304, + 278, + 547, + 554 + ], + "type": "inline_equation", + "content": "4.5 \\times" + }, + { + "bbox": [ + 304, + 278, + 547, + 554 + ], + "type": "text", + "content": " higher memory consumption. Furthermore, the extremely long input sequences in WSI classification degrade the stability of such complex structures (2.13% AUC standard deviation on C16, which is the highest among all embedding-level MIL methods). With the masked hard instance mining strategy, the MHIM-MIL framework significantly reduces the computational cost (-24% training time and -48% memory usage) and enhances its stability (0.48% AUC standard deviation on C16). More details are provided in Supplementary Material." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 565, + 400, + 578 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 565, + 400, + 578 + ], + "spans": [ + { + "bbox": [ + 306, + 565, + 400, + 578 + ], + "type": "text", + "content": "4.5. Ablation Study" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 306, + 585, + 512, + 597 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 585, + 512, + 597 + ], + "spans": [ + { + "bbox": [ + 306, + 585, + 512, + 597 + ], + "type": "text", + "content": "4.5.1 Importance of the Different Components" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "content": "Table 3 shows the effect of different modules in MHIMMIL on two datasets. The baseline methods are two representative attention-based MIL methods, namely AB-MIL [16] and TransMIL [26]. First, we introduce the naive masked hard instance mining strategy, which leverages the model itself to mine hard instances during training. This strategy improves AUC by " + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "inline_equation", + "content": "1.86\\%" + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "inline_equation", + "content": "2.55\\%" + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "content": " for the two MIL models on CAMELYON-16 respectively, indicating that concentrating on hard instances during training can as" + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4083" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 70, + 286, + 153 + ], + "blocks": [ + { + "bbox": [ + 49, + 70, + 286, + 153 + ], + "lines": [ + { + "bbox": [ + 49, + 70, + 286, + 153 + ], + "spans": [ + { + "bbox": [ + 49, + 70, + 286, + 153 + ], + "type": "table", + "html": "
ModuleCAMELYON-16TCGA
AB.Trans.AB.Trans.
Baseline94.0093.5193.1792.51
+MHIM95.8696.0694.1493.75
+MHIM+Siam.95.8296.2494.5594.13
+MHIM+Siam.+Con.96.1496.4994.9794.87
", + "image_path": "f7d74056fceb12fff7af876954cfc043f7f20382ebe877a6427ab911a4642caa.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_body" + } + ], + "index": 0 + }, + { + "type": "table", + "bbox": [ + 63, + 234, + 272, + 330 + ], + "blocks": [ + { + "bbox": [ + 46, + 162, + 288, + 222 + ], + "lines": [ + { + "bbox": [ + 46, + 162, + 288, + 222 + ], + "spans": [ + { + "bbox": [ + 46, + 162, + 288, + 222 + ], + "type": "text", + "content": "Table 3: The effect of different components in MHIM-MIL with two MIL models: AB-MIL (AB.) and TransMIL (Trans.). MHIM denotes the masked hard instance mining strategy. Siam. refers to the Siamese framework. Con. represents consistency loss." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 63, + 234, + 272, + 330 + ], + "lines": [ + { + "bbox": [ + 63, + 234, + 272, + 330 + ], + "spans": [ + { + "bbox": [ + 63, + 234, + 272, + 330 + ], + "type": "table", + "html": "
StrategyCAMELYON-16TCGA
AB.Trans.AB.Trans.
Baseline94.0093.5193.1792.51
HAM95.6895.9093.8394.54
R-HAM96.1495.8894.7994.60
L-HAM95.8196.4994.3394.67
LR-HAM95.9296.3394.9794.87
", + "image_path": "81cd2fdf2a8f6f3a4698966e61f2f7ef75e93bf1b83363a49f4be5c106f18b2b.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "table_body" + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 388, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 388, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 388, + 287, + 544 + ], + "type": "text", + "content": "sist mainstream MIL models in building better classification boundaries. Further discussion on the masked hard instance mining strategy is presented in Section 4.5.2. Compared with the naive MHIM strategy, the third row of the table suggests that a Siamese structure [3,5,8] based on a momentum teacher is beneficial for more stable and effective mining of hard instances. We elaborate more on choosing the teacher model in Section 4.5.3. After adding consistency loss term to the objective function, our full MHIM-MIL framework achieves the best performance (96.49% AUC on CAMELYON-16 and 94 .97% AUC on TCGA). For subsequent ablation experiments, we include consistency loss by default to facilitate the optimization of our framework." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 562, + 256, + 574 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 562, + 256, + 574 + ], + "spans": [ + { + "bbox": [ + 47, + 562, + 256, + 574 + ], + "type": "text", + "content": "4.5.2 Impact of the Different MHIM Strategies" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 582, + 287, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 582, + 287, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 582, + 287, + 715 + ], + "type": "text", + "content": "The masked hard instance mining strategy is the core design of our method. The main idea of this strategy is masking the most salient instances to indirectly mine hard instances to facilitate model training. Based on this idea, we devise three hybrid strategies (R-HAM, L-HAM, and LR-HAM) and present their impact in Table 4. The basic strategy, High Attention Masking (HAM), already boosts performance significantly, leading to AUC improvements of " + }, + { + "bbox": [ + 46, + 582, + 287, + 715 + ], + "type": "inline_equation", + "content": "1.68\\%" + }, + { + "bbox": [ + 46, + 582, + 287, + 715 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 582, + 287, + 715 + ], + "type": "inline_equation", + "content": "2.39\\%" + }, + { + "bbox": [ + 46, + 582, + 287, + 715 + ], + "type": "text", + "content": " for two MIL models on the CAMELYON-16 dataset, respectively. After introducing the other two strategies, different MIL models achieve performance improvements" + } + ] + } + ], + "index": 6 + }, + { + "type": "table", + "bbox": [ + 319, + 70, + 535, + 164 + ], + "blocks": [ + { + "bbox": [ + 46, + 338, + 287, + 374 + ], + "lines": [ + { + "bbox": [ + 46, + 338, + 287, + 374 + ], + "spans": [ + { + "bbox": [ + 46, + 338, + 287, + 374 + ], + "type": "text", + "content": "Table 4: Comparison between different masked hard instance mining strategies. The three hybrid strategies show varying performance across the benchmarks." + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 319, + 70, + 535, + 164 + ], + "lines": [ + { + "bbox": [ + 319, + 70, + 535, + 164 + ], + "spans": [ + { + "bbox": [ + 319, + 70, + 535, + 164 + ], + "type": "table", + "html": "
TeacherCAMELYON-16TCGA
AB.Trans.AB.Trans.
Baseline94.0093.5193.1792.51
Student copy95.8495.8693.6893.45
Init.95.8896.1294.6694.15
Momentum95.9696.1194.6594.45
Init.+Momentum96.1496.4994.9794.87
", + "image_path": "30602555df4ad8f56e48b0bf933b4182fdfe0058bd778531305fc2fa39d2d5d8.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "table_body" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 343, + 167, + 507, + 251 + ], + "blocks": [ + { + "bbox": [ + 343, + 167, + 507, + 251 + ], + "lines": [ + { + "bbox": [ + 343, + 167, + 507, + 251 + ], + "spans": [ + { + "bbox": [ + 343, + 167, + 507, + 251 + ], + "type": "image", + "image_path": "eeb175c573c3a6fcfa3c2d6dcd4ccec2205eb6b58116e97c47412198800cb466.jpg" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 304, + 249, + 545, + 321 + ], + "lines": [ + { + "bbox": [ + 304, + 249, + 545, + 321 + ], + "spans": [ + { + "bbox": [ + 304, + 249, + 545, + 321 + ], + "type": "text", + "content": "Table 5: Comparison of different types of teachers. Momentum denotes the teacher is updated by EMA strategy. Init. indicates the initialization of the teacher with pretrained parameters. The bottom figure compares the stability of the momentum teacher and the non-batch gradient updated student during training." + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_caption" + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 342, + 545, + 497 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 342, + 545, + 497 + ], + "spans": [ + { + "bbox": [ + 304, + 342, + 545, + 497 + ], + "type": "text", + "content": "on both datasets. Specifically, AB-MIL [16] shows more significant performance gains after introducing randomness (96.14% AUC on CAMELYON-16 with R-HAM) due to its better ability to filter out redundant information, while TransMIL [26] shows the reverse trend (96.49% AUC on CAMELYON-16 with L-HAM). Furthermore, the more complex three-hybrid strategy (LR-HAM) achieves the best performance on the TCGA dataset, which has a larger proportion of positive areas and more instances. Overall, our experiments validate the effectiveness of masked hard instance mining strategy, and the diversity of proposed strategies improves its applicability to different datasets and MIL models." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 514, + 515, + 527 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 514, + 515, + 527 + ], + "spans": [ + { + "bbox": [ + 305, + 514, + 515, + 527 + ], + "type": "text", + "content": "4.5.3 Impact of the Choice of Teacher Network" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "content": "In MHIM-MIL, we employ a Teacher model to mine hard instances and facilitate training of the Student model. In Table 5, we comprehensively investigate the effects of various choices of Teacher network. First, we utilize a single-model structure, which treats the Student model as the Teacher. The student conducts masked hard instance mining prior to training. Due to the non-batch gradient update, the unstable performance of the Student model makes the strategy susceptible to noise, so the performance is not optimal. Second, we adopt a momentum teacher, which shares the same network structure as the Student model and is updated with the EMA strategy. This updating strategy enhanced the stability of momentum teachers, as shown in the figure below, and enabled MHIM-MIL to achieve " + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "inline_equation", + "content": "0.97\\%" + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "inline_equation", + "content": "1.00\\%" + }, + { + "bbox": [ + 304, + 534, + 545, + 713 + ], + "type": "text", + "content": " performance improvement in TCGA under the two MIL mod" + } + ] + } + ], + "index": 12 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4084" + } + ] + } + ], + "index": 13 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 69, + 293, + 327 + ], + "blocks": [ + { + "bbox": [ + 49, + 69, + 293, + 327 + ], + "lines": [ + { + "bbox": [ + 49, + 69, + 293, + 327 + ], + "spans": [ + { + "bbox": [ + 49, + 69, + 293, + 327 + ], + "type": "image", + "image_path": "166f3a78309f89aee0d474548cbf567a48aba0e95a9b883240057e3ccb1ab450.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 337, + 548, + 399 + ], + "lines": [ + { + "bbox": [ + 46, + 337, + 548, + 399 + ], + "spans": [ + { + "bbox": [ + 46, + 337, + 548, + 399 + ], + "type": "text", + "content": "Figure 4: Patch visualization produced by AB-MIL [16] (baseline) and MHIM-MIL. The blue lines outline the tumor regions. The brighter patch indicates higher attention scores. The cyan colors indicate high probabilities of being tumor for the corresponding locations. Ideally, the cyan patches should cover only the area within the blue lines. We show that focusing only on more salient regions reduces the generalization ability of the model and that hard instances can provide useful information for more accurate and comprehensive judgments." + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 302, + 70, + 544, + 327 + ], + "blocks": [ + { + "bbox": [ + 302, + 70, + 544, + 327 + ], + "lines": [ + { + "bbox": [ + 302, + 70, + 544, + 327 + ], + "spans": [ + { + "bbox": [ + 302, + 70, + 544, + 327 + ], + "type": "image", + "image_path": "770d6e0337e6ebf088ae33ebaff4dcfa814ed2d6725ac69e8f555b121771a843.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 413, + 288, + 462 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 413, + 288, + 462 + ], + "spans": [ + { + "bbox": [ + 46, + 413, + 288, + 462 + ], + "type": "text", + "content": "els, respectively. With proper initialization, the momentum teacher achieves the best performance. However, a fixed initialization teacher fails to learn new knowledge, which emphasizes the significance of iterative optimization." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 468, + 132, + 479 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 468, + 132, + 479 + ], + "spans": [ + { + "bbox": [ + 47, + 468, + 132, + 479 + ], + "type": "text", + "content": "4.6. Visualization" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 486, + 289, + 715 + ], + "type": "text", + "content": "To more intuitively understand the effect of the masked hard instance mining, we visualize the attention scores (bright patch) and tumor probabilities (cyan patch) of patches produced by AB-MIL and MHIM-MIL, as illustrated in Figure 4. Here, MHIM-MIL employs AB-MIL as its baseline model. We note that attention scores only indicate the regions of interest of models and are infeasible to reflect tumor probabilities [17, 43]. First, as shown in Figure 4, AB-MIL often assigns high tumor probabilities to patches in non-tumor areas. We attribute this phenomenon to the low generalization capability of conventional attention-based MIL models, which tend to focus only on salient regions during training. In contrast, MHIM-MIL trained with hard instances shows a much better generalization ability than the baseline model for noise robustness (rows 2 and 3 on the right) and for precise detection of challenging subtle tumor areas (row 3 on the left). More significantly, we find that focusing only on tumor areas leads to missing most of them, expanding the view to include some" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 413, + 547, + 497 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 413, + 547, + 497 + ], + "spans": [ + { + "bbox": [ + 304, + 413, + 547, + 497 + ], + "type": "text", + "content": "\"irrelevant areas\" enables the model to make more complete judgments (rows 1 and 2 on the left). This phenomenon demonstrates how hard instances provide more useful information to help the model make more accurate and comprehensive judgments. We provide more details and an in-depth analysis of this patch visualization in Supplementary Material." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 512, + 379, + 525 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 512, + 379, + 525 + ], + "spans": [ + { + "bbox": [ + 306, + 512, + 379, + 525 + ], + "type": "text", + "content": "5. Conclusion" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 534, + 547, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 534, + 547, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 534, + 547, + 715 + ], + "type": "text", + "content": "This paper rethinks the impact of salient instances for MIL-based WSI classification algorithms. We demonstrate that attention-based MIL methods excessively prioritizing salient instances harm the generalization ability of the model. To address this issue, we have proposed several masked hard instance mining strategies that mask out salient patches and encourage the model to attend to informative regions for better discriminative learning. Through qualitative analysis, we have demonstrated that these strategies effectively alleviate the under-fitting problem of general AB-MIL to hard instances. We have also developed the MHIM-MIL framework that leverages momentum teacher and consistency loss to further enhance hard instance mining. Our experimental results demonstrate the superiority and generality of the MHIM-MIL framework over other lat" + } + ] + } + ], + "index": 8 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 748, + 315, + 757 + ], + "type": "text", + "content": "4085" + } + ] + } + ], + "index": 9 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "spans": [ + { + "bbox": [ + 47, + 72, + 287, + 109 + ], + "type": "text", + "content": "est methods. In future work, we plan to devise a more precise localization scheme for hard instances that can facilitate model training and convergence." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 120, + 157, + 133 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 120, + 157, + 133 + ], + "spans": [ + { + "bbox": [ + 47, + 120, + 157, + 133 + ], + "type": "text", + "content": "6. Acknowledgement" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 140, + 287, + 189 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 140, + 287, + 189 + ], + "spans": [ + { + "bbox": [ + 47, + 140, + 287, + 189 + ], + "type": "text", + "content": "Reported research is partly supported by the National Natural Science Foundation of China under Grant 62176030, and the Natural Science Foundation of Chongqing under Grant cstc2021jcyj-msxmX0568." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 48, + 200, + 107, + 213 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 200, + 107, + 213 + ], + "spans": [ + { + "bbox": [ + 48, + 200, + 107, + 213 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 53, + 219, + 288, + 713 + ], + "type": "list", + "angle": 0, + "index": 13, + "blocks": [ + { + "bbox": [ + 53, + 219, + 287, + 264 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 53, + 219, + 287, + 264 + ], + "spans": [ + { + "bbox": [ + 53, + 219, + 287, + 264 + ], + "type": "text", + "content": "[1] Ejaz Ahmed, Michael Jones, and Tim K Marks. 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Springer, 2022. 1" + } + ] + } + ], + "index": 24 + } + ], + "sub_type": "ref_text" + } + ], + "discarded_blocks": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "spans": [ + { + "bbox": [ + 295, + 749, + 315, + 757 + ], + "type": "text", + "content": "4087" + } + ] + } + ], + "index": 26 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 9 + } + ], + "_backend": "vlm", + "_version_name": "2.6.4" +} \ No newline at end of file diff --git a/2023/Multiple Planar Object Tracking/16e4462f-086b-4e2c-b3e1-1c3bf9449c10_content_list.json b/2023/Multiple Planar Object Tracking/16e4462f-086b-4e2c-b3e1-1c3bf9449c10_content_list.json new file mode 100644 index 0000000000000000000000000000000000000000..5cb0486e07515ae9005f13740f44b5e8c4a88e14 --- /dev/null +++ b/2023/Multiple Planar Object Tracking/16e4462f-086b-4e2c-b3e1-1c3bf9449c10_content_list.json @@ -0,0 +1,1808 @@ +[ + { + "type": "text", + "text": "Multiple Planar Object Tracking", + "text_level": 1, + "bbox": [ + 316, + 130, + 653, + 152 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "https://zzcheng.top/MPOT", + "bbox": [ + 339, + 181, + 627, + 198 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Zhicheng Zhang", + "bbox": [ + 246, + 199, + 380, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Shengzhe Liu", + "bbox": [ + 444, + 199, + 557, + 215 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Jufeng Yang†", + "bbox": [ + 620, + 198, + 727, + 217 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "VCIP & TMCC & DISSec, College of Computer Science, Nankai University", + "bbox": [ + 181, + 217, + 787, + 234 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "gloryzzc6@sina.com, nkuliusz@163.com, yangjufeng@nankai.edu.cn", + "bbox": [ + 207, + 237, + 759, + 250 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Abstract", + "text_level": 1, + "bbox": [ + 233, + 286, + 313, + 301 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Tracking both location and pose of multiple planar objects (MPOT) is of great significance to numerous real-world applications. The greater degree-of-freedom of planar objects compared with common objects makes MPOT far more challenging than well-studied object tracking, especially when occlusion occurs. To address this challenging task, we are inspired by amodal perception that humans jointly track visible and invisible parts of the target, and propose a tracking framework that unifies appearance perception and occlusion reasoning. Specifically, we present a dual-branch network to track the visible part of planar objects, including vertexes and mask. Then, we develop an occlusion area localization strategy to infer the invisible part, i.e., the occluded region, followed by a two-stream attention network finally refining the prediction. To alleviate the lack of data in this field, we build the first large-scale benchmark dataset, namely MPOT-3K. It consists of 3,717 planar objects from 356 videos and contains 148,896 frames together with 687,417 annotations. The collected planar objects have 9 motion patterns and the videos are shot in 6 types of indoor and outdoor scenes. Extensive experiments demonstrate the superiority of our proposed method on the newly developed MPOT-3K as well as other two popular single planar object tracking datasets. The code and MPOT-3K dataset are released on https://zzcheng.top/MPOT.", + "bbox": [ + 73, + 318, + 473, + 698 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "1. Introduction", + "text_level": 1, + "bbox": [ + 76, + 727, + 209, + 742 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "Tracking multiple planar objects (MPOT) is a fundamental task in computer vision. It aims to explore the motion of planar objects, tracking both the location and pose of multiple targets simultaneously [40, 43, 56]. The planar object is defined as a plane belonging to a specific body [28] (e.g., box, building, or wall) in the form of four ordered vertexes [43, 70]. With the help of MPOT, we can track targets when multiple planar objects exist, e.g., different sur", + "bbox": [ + 75, + 753, + 468, + 875 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/937ced3cf9890481264f97a330ac56486cc9f006caeb167f6227e85b45eee099.jpg", + "image_caption": [ + "(a) Image of $i^{\\text{th}}$ frame" + ], + "image_footnote": [], + "bbox": [ + 503, + 285, + 756, + 397 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/6dbf3139bc53ec5ea02371cb4bd4c3cdda8d2e657920bf2102baf2f596be77e4.jpg", + "image_caption": [ + "POT VOS (DoF=8) (N/A)" + ], + "image_footnote": [], + "bbox": [ + 503, + 415, + 756, + 463 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/39f3c876b2c000cf2dff47ea00a2adb203aaa322e50ec0fa3a456176a6252bc7.jpg", + "image_caption": [ + "POT" + ], + "image_footnote": [], + "bbox": [ + 759, + 286, + 888, + 339 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/e781c25bb121d586812d666d028f0d5dd3e69488adc42c6dd2db2aadec017763.jpg", + "image_caption": [ + "VOS" + ], + "image_footnote": [], + "bbox": [ + 759, + 349, + 888, + 404 + ], + "page_idx": 0 + }, + { + "type": "image", + "img_path": "images/5af2e1c0ced27f87b7ad4bc621e418974039a43526de1ce5cda6b1e0d94b0824.jpg", + "image_caption": [ + "(b) Different tracking tasks", + "VOT/RVOT", + "(c) Tracking $\\mathbf{j}^{\\mathrm{th}}$ frame", + "Figure 1: Comparison with other vision tasks. Given an image (a), we present the ground truth for different tasks in (b). The corresponding Degree-of-Freedom (DoF) is reported at the bottom and the details are listed on the right side of each task. In (c), we show the tracking results for box-based tasks (e.g., VOT, RVOT), mask-based tasks (e.g., VOS), and POT, which can find the occluded regions (marked by the red line area) and provide pixel-to-pixel matching correspondence (colored points across frames)." + ], + "image_footnote": [], + "bbox": [ + 759, + 417, + 888, + 473 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "faces of an object [1] or planes from various objects [27]. It has attracted more and more attention attributed to various applications in augmented reality [57, 104], video editing [4, 20, 30], and robot navigation [92].", + "bbox": [ + 496, + 643, + 890, + 703 + ], + "page_idx": 0 + }, + { + "type": "text", + "text": "MPOT is closely related to well-known computer vision tasks in RGB tracking [32] (see Tab. 1). Both tasks involve tracking the target across subsequent frames of a video using the ground truth provided in the initial frame. However, it is more challenging in two aspects. 1) Tracking planar objects is of greater Degree-of-Freedom (DoF). As shown in Fig. 1(b), MPOT tracks both the pose and location of the target, which is described by an arbitrary quadrangle (i.e., four independent vertexes $(x_{1},y_{1},x_{2},y_{2},x_{3},y_{3},x_{4},y_{4})$ , whose DoF is 8 [44]). In contrast, it only needs to predict the position and size of an object $(x,y,w,h)$ in video object tracking (VOT), and Rotated VOT (RVOT) additionally requires the rotation angle. Even compared with video object", + "bbox": [ + 496, + 704, + 892, + 901 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "CVF", + "bbox": [ + 106, + 2, + 181, + 42 + ], + "page_idx": 0 + }, + { + "type": "header", + "text": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore.", + "bbox": [ + 238, + 0, + 807, + 46 + ], + "page_idx": 0 + }, + { + "type": "page_footnote", + "text": "† Corresponding author.", + "bbox": [ + 101, + 887, + 230, + 898 + ], + "page_idx": 0 + }, + { + "type": "page_number", + "text": "23460", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 0 + }, + { + "type": "table", + "img_path": "images/6df07e4fc3e37da7ff6ee7f1d7c5ef3e88a740ed266797426aa31da7119039c2.jpg", + "table_caption": [ + "Table 1: The comparison of MPOT with other video-related tasks. We compare MPOT with five RGB tracking tasks and four tasks with auxiliary modality information. The count of DoF comes from [44]." + ], + "table_footnote": [], + "table_body": "
ModalityTaskObjectScenario
Object categoryObject selectionMultiple objectsPixel correspondenceDoFOcclusion
RGBMOT [83]Limited, usually pedestrians or vehiclesDetectedYN4Y
MOTS [75]Limited, usually pedestrians or vehiclesDetectedYNN/AN
VOS [66]ArbitraryUser-specified in the first frameNNN/AN
VOT [21]ArbitraryUser-specified in the first frameNN4Y
RVOT [32]ArbitraryUser-specified in the first frameNN5Y
MPOTArbitraryUser-specified in the first frameYY8Y
RGB+DepthRGBDT [91]ArbitraryUser-specified in the first frameYN4Y
6DOP [50]Limited by training setDetectedYY6Y
6DPT [81]ArbitraryUser-specified in the first frameNY6Y
RGB+LIDAR3dOD [35]Limited by training setDetectedYN7Y
3dMOT [84]Limited, usually vehiclesDetectedYN7Y
", + "bbox": [ + 76, + 108, + 890, + 263 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "segmentation (VOS), an alternative that introduces masks at the pixel level, MPOT is a more challenging task. Because MPOT provides the matched correspondence for each pixel within the object region across frames [60] (e.g., colored points in Fig. 1(a)&(c)), which makes it possible for applications that require positional information like texture mapping [24]. Nevertheless, VOS that tracks the target area instead of per-pixel location can hardly achieve it. 2) Occlusion is another challenge that comes with MPOT. Not only the one in POT that manually occludes the camera, MPOT but introduces the occlusion raised by the layered position of multiple targets relative to the camera [77, 96] (see Fig. 1(c)). Besides, the occlusion is more complex than the ones in multiple object tracking (MOT). As discussed above, when occlusion occurs, MPOT estimates the pixel correspondence controlled by homography matrix $\\mathbf{H}$ [3], which tends to be sensitive and have a high condition number that can reach up to $5\\mathrm{e}^7$ [95]. This means that a tiny movement of the invisible part is extremely difficult to track.", + "bbox": [ + 75, + 277, + 472, + 580 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "To address the aforementioned limitations, our work draws the inspiration that humans consolidate the visible together with invisible parts of the target for tracking [96]. We propose a tracking framework comprised of procedures for appearance Perception and occlusion Reasoning, namely PRTrack. To track high DoF planar objects, we reformulate the problem of estimating homography matrix $\\mathbf{H}$ as predicting the mask and ordered vertexes for each planar object. With the high-dimensional mask, we can accurately locate the target area at the pixel level. Besides, the ordered vertexes provide per-pixel correspondence across frames for tracking the pose of planar objects. Therefore, in the stage of appearance perception, we propose a dual branch network to predict the ordered vertexes and masks of planar objects based on the historical visible information. For vertexes, we design an encoder with shifted sampling strategy based on the constraint that the vertexes always have a clockwise order. For mask, we aggregate the probability of multiple planar objects with a multi-layered layout, that is, a stack of occluders and occludees. Further, to solve the cases of complex occlusion, we develop an occlusion area", + "bbox": [ + 75, + 583, + 472, + 902 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "localization strategy to indicate the occluded part, by storing the movement of each planar object (i.e., historical H). To be specific, we factorize the sensitive homography matrix, which describes the relative movement of planar objects, into parameters of transition, rotation, and pose. Finally, with the prediction from the mentioned stages, we propose a two-stream self-attention network to jointly refine the predicted planar objects.", + "bbox": [ + 496, + 277, + 893, + 398 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Besides, since there is no available dataset in this field, we build a large-scale benchmark dataset, namely MPOT-3K. Specifically, we shoot 356 videos with 3,717 planar objects and 687,417 annotations. The videos are collected under 9 motion patterns, where the relative movement and occlusion are also included to simulate the real-world scene.", + "bbox": [ + 496, + 398, + 893, + 489 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "The contributions of this paper are two-fold: 1) We collect and annotate the first large-scale benchmark dataset for MPOT, where planar objects are diversely collected expelling bias. Our dataset will be released and boost research in this field. 2) We propose a tracking framework with unified motion and appearance models, which can accurately predict the pose and location of planar objects. Extensive experiments demonstrate the superiority of PRTrack against state-of-the-art approaches.", + "bbox": [ + 496, + 489, + 893, + 627 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2. Related Work", + "text_level": 1, + "bbox": [ + 500, + 640, + 640, + 656 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "2.1. Planar Object Tracking", + "text_level": 1, + "bbox": [ + 500, + 665, + 718, + 681 + ], + "page_idx": 1 + }, + { + "type": "text", + "text": "Benchmark Datasets. Current works focus on single planar object tracking and propose several POT datasets [19, 42, 43, 45, 70, 86]. Metaio [45] is the first dataset collected in the lab and the videos are collected by a monitored camera. Similarly, TMT [70] also shoots videos from the lab, where the annotations are automatically generated by aggregating the results of three planar object trackers. Due to the laboratory setting of the collection, videos in these datasets have similar backgrounds. Thus, POT210 [43] collects video data in the wild under seven motion patterns and encourages the diversity of the recorded videos with complex backgrounds. However, existing benchmarks are insufficient to mimic real-world settings where multiple targets exist. Therefore, our work extends the task into MPOT that", + "bbox": [ + 496, + 688, + 893, + 900 + ], + "page_idx": 1 + }, + { + "type": "page_number", + "text": "23461", + "bbox": [ + 478, + 944, + 517, + 957 + ], + "page_idx": 1 + }, + { + "type": "table", + "img_path": "images/4e648d69ebb31962933fe929808ded151752e776c9eb693cfdefcebb991b869c.jpg", + "table_caption": [ + "Table 2: Statistics of tracking datasets. \"I.\" and \"O.\" indicate indoor and outdoor, respectively. \"#\" denotes \"the number of\"." + ], + "table_footnote": [], + "table_body": "
BenchmarkUCSB [19]TMT [70]POIC [8]POT210 [43]POT280 [42]MOT16 [58]MPOT-3K
# Scenes112030401442
# Videos961002021028014356
# Targets96100202102801,2763,717
# Annotations7K-23K53K70K292K687K
Scene CategoryI.I.I.&O.I.&O.I.&O.O.I.&O.
Multiple ObjectsXXXXX✓✓
", + "bbox": [ + 80, + 116, + 467, + 205 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "simultaneously tracks multiple planar objects which can be applied in real-world applications like AR, robots, and art.", + "bbox": [ + 75, + 226, + 467, + 256 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Methods. POT trackers can be classified into region-based, keypoint-based, and hybrid methods. Region-based approaches [2, 3, 9, 17, 34, 68] focus on the whole planar region and estimate perspective transformation by closing up the template and the warped image. Keypoint-based methods [22, 61, 63, 79, 101] describe a planar object by the detected keypoints [54, 69] and associate objects across frames by computing the similarity between keypoints. As for hybrid methods, previous works [8, 9, 13, 94] exploit the robust feature descriptors for searching the optimal matching. A representative method [8] leverage gradient-based feature as criterion. As progress is made into the deep learning era [37, 82], CLKN [7] integrates deep features into the Lucas-Kanade algorithm for improving matching quality.", + "bbox": [ + 75, + 260, + 468, + 472 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "2.2. Visual Tracking", + "text_level": 1, + "bbox": [ + 76, + 492, + 235, + 508 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Single Object Tracking. It aims to locate and track a single target in a video [39, 48], which can be roughly grouped into box-based tracking [18, 55, 93] and mask-based tracking [41, 47, 60]. SiamFC [5] adopts the correlation layer to search the location which is described by the axis-aligned bounding box. Further, SiamMask [78] introduces rotation to describe the motion and predicts the object mask with the bounding box simultaneously. Meanwhile, mask-based tracking focuses on the accurate location of the targets. STM [62] addresses the problem of appearance change, leading to satisfactory results. Recently, PoST [60] explores the relationship between the mask and contour, building constraints for predicting the polygonal mask.", + "bbox": [ + 75, + 518, + 468, + 715 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Multiple Object Tracking. Existing works [14, 58] propose to track multiple objects of human interests simultaneously, with the assumption that all targets belong to a list of predefined classes [10, 11, 26, 36, 51, 90, 100, 102]. A large number of methods [49, 65, 80, 85, 99] are proposed to address the task. With the class assumption, they utilize object detectors to generate candidates in the manner of axis-aligned bounding boxes. Then the candidates are associated into trajectories. While both MPOT and MOT track multiple targets at the same time, the former faces more challenges since it handles arbitrary planar objects with greater DoF, as well as covers unrestricted classes [43].", + "bbox": [ + 75, + 719, + 468, + 900 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/4bfb2859ca249b52bf8987b5e034139656cf0d561cfdeae4dbaea60ff3875d2c.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 501, + 88, + 712, + 218 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/198514ab98c0952c1de7d52a76945f92f0eb79d1b479ca49cd1b22b12cd26979.jpg", + "image_caption": [ + "(a) Occurrence of occlusion in different scenes", + "(b) Statistics about occlusion", + "Figure 2: Statistics of occlusion in MPOT-3K. (a) shows the frequency of occlusion in six types of scenes, in which the number on the left indicates the number of planar objects being occluded and the one in shadow represents the corresponding proportion. (b) illustrates the number of occlusions per video as well as the temporal length per occlusion." + ], + "image_footnote": [], + "bbox": [ + 718, + 89, + 888, + 224 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3. The MPOT-3K Dataset", + "text_level": 1, + "bbox": [ + 500, + 335, + 718, + 352 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "MPOT is being less explored and limited by existing datasets designed to single planar object tracking. In this work, we construct the dataset MPOT-3K for introducing multiple targets. To the best of our knowledge, MPOT-3K is the first large-scale dataset for the challenging task of MPOT. This will help facilitate future research in computer vision (augmented reality, safety surveillance), robot (navigation, manipulation), and art (video editing).", + "bbox": [ + 496, + 362, + 890, + 484 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.1. Data Collecting", + "text_level": 1, + "bbox": [ + 500, + 494, + 656, + 510 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "Initially, we shoot 840 videos involving the motion of static and moving planar objects. For the static planar objects, we design six motion patterns (i.e., far-near movement, in-plane rotation, out-plane rotation, in-plane movement, motion blur, camera occlusion) by controlling the movements of camera as common practices [43,86]. For the moving planar objects, we consider the occlusions and relative movements among multiple planar objects and design two motion patterns (i.e., moving objects, moving occlusion). Besides, an unconstrained motion pattern is considered to further combine the above motion patterns. According to [87, 103], we record diverse videos from six types of indoor and outdoor scenes, including library, house, gallery, building, street, and village.", + "bbox": [ + 496, + 518, + 890, + 729 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "3.2. Data Annotation", + "text_level": 1, + "bbox": [ + 500, + 739, + 663, + 753 + ], + "page_idx": 2 + }, + { + "type": "text", + "text": "MPOT-3K is annotated by seven well-trained annotators. Following [43], we adopt a semi-automatic annotation scheme. First, the annotator labels one frame every five frames. Then, the annotated label is propagated to other unannotated frames by linear interpolation. Finally, the annotator corrects the propagated label. During annotation, we obey the following rules. First, we define what planar object is to be annotated according to [43, 70, 86]. The planar object should be easily presented by four ordered ver", + "bbox": [ + 496, + 763, + 890, + 900 + ], + "page_idx": 2 + }, + { + "type": "page_number", + "text": "23462", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 2 + }, + { + "type": "image", + "img_path": "images/3687c26235d3385e5011cbe5f17ec943b4d63971cce5048f703996ee24f45a40.jpg", + "image_caption": [ + "Figure 3: The pipeline of our method. Our tracking framework is divided into three stages. First, in appearance perception, we track the visible part of multiple planar objects via a dual-branch network, as coarse output. For the next stage of occlusion reasoning, the occlusion area is localized and then fed into a two-stream self-attention network for refining the predicted target. Finally, the memory pool module restores the high-confident tracked targets." + ], + "image_footnote": [], + "bbox": [ + 78, + 74, + 890, + 258 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "texas. To ensure that the criteria for selecting plane objects are consistent, we ask all the annotators to vote for filtering out inconsistent objects [52]. Second, we start annotating when the planar object is completely in view and end when the object has been fully occluded or out of view. Third, we annotate the spatial position of the planar object according to two principles: 1) We annotate the planar object which has four apparent lines, since the point is localized by inferring the intersection lines [67]. 2) We maintain the order of vertexes across video frames for pixel correspondence. Combining these principles, we can locate the planar object with four independent vertexes (i.e., a quadrangle).", + "bbox": [ + 75, + 328, + 472, + 511 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "3.3. Statistics", + "text_level": 1, + "bbox": [ + 76, + 525, + 184, + 540 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "After collecting and labeling, we yield a large-scale dataset MPOT-3K, where we obtain 356 videos with 3,717 planar objects from 42 scenes. The number of planar objects per video averages 10.44 and can reach 74 at most. MPOT-3K is divided into training, validation, and test sets in a proportion of 80:5:15. The split is performed at the scene level to ensure there's no overlap among splits. Hence the dataset avoids leakage since both the target and scene of the test set are expelled during training.", + "bbox": [ + 75, + 551, + 468, + 686 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "As shown in Tab. 2, we compare MPOT-3K with six datasets, which come from POT [8, 19, 42, 43, 70] and MOT [58] tasks. MPOT-3K contains over 9.8 times more annotations and 13.2 times more targets in all video frames than the largest POT dataset POT280. The number of targets is almost 3 times of the popular MOT16 dataset. Another strength of MPOT-3K lies in its diversity, which covers 9 motion patterns and 6 types of scenes. Besides, MPOT-3K introduces more complex occlusions. As shown in Fig. 2(a), we observe that occlusion occurs in all the scenes, where $39.9\\%$ of planar objects are occluded on average. Fig. 2(b) further illustrates that there are 3.6 occlusions happening in a video on average and each occlusion lasts 9.56 seconds.", + "bbox": [ + 75, + 688, + 470, + 900 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4. Methodology", + "text_level": 1, + "bbox": [ + 498, + 325, + 633, + 345 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "PRTrack consists of three main components (See Fig. 3): memory pool module, appearance perception network, and occlusion reasoning network. The memory pool module (Sec. 4.2) restores the previous predictions and expels the low-confident targets. Guided by previously tracked targets, the appearance perception network (Sec. 4.3) predicts mask together with the vertexes for each planar object. The occlusion reasoning network (Sec. 4.4) further takes all the tracked targets and corresponding occlusion area, which is indicated by the difference between motion-guided results among multiple targets and the predicted one.", + "bbox": [ + 496, + 352, + 890, + 518 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.1. Problem Reformulation", + "text_level": 1, + "bbox": [ + 498, + 527, + 718, + 542 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "Assume multiple planar objects exists in an RGB video where they are not from the training set, nor have detection results. Given the user-selected ones in the initial frame, the objective is to estimate their position change relative to the beginning, i.e., homography matrix, with which the pose change of targets can be obtained [56]. As shown in Fig. 4, we reformulate the tracking task as predicting the masks of the quadrangle $\\widehat{\\mathbf{M}} \\in \\mathbb{R}^{O \\times hw}$ and the heatmap of four ordered vertexes $\\widehat{\\mathbf{P}} \\in \\mathbb{R}^{O \\times 4hw}$ , where $O$ is the number of planar objects in the current frame. The layered masks represent the location of multiple planar objects [94] and the vertexes are used to track the pose of planar objects [56].", + "bbox": [ + 496, + 550, + 890, + 734 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "4.2. Memory Pool module", + "text_level": 1, + "bbox": [ + 498, + 741, + 702, + 758 + ], + "page_idx": 3 + }, + { + "type": "text", + "text": "From the viewpoint of human perception, one person tracks the targets by memorizing their historical appearance and trajectory [59]. Inspired by this, we leverage the images and predictions in previous T frames as guidance to track planar objects in the current one. For the previous frames, we record previously predicted heatmaps of ordered vertexes $\\mathbf{P_o}\\in \\mathbb{R}^{T\\times 4hw}$ , masks $\\mathbf{M_o}\\in \\mathbb{R}^{T\\times hw}$ , and the images $\\mathbf{I_o}\\in \\mathbb{R}^{T\\times 3hw}$ for the $o^{\\mathrm{th}}$ planar object. The memory pool $\\{(\\mathbf{P_o},\\mathbf{M_o},\\mathbf{I_o})\\}_{o = 1}^N$ stores the tracked N planar objects.", + "bbox": [ + 496, + 763, + 890, + 902 + ], + "page_idx": 3 + }, + { + "type": "page_number", + "text": "23463", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 3 + }, + { + "type": "image", + "img_path": "images/a430a51542a63ca7707737f6e3b84bc6565d99b7f32507ae5540da803d8ca02d.jpg", + "image_caption": [ + "(a) Image" + ], + "image_footnote": [], + "bbox": [ + 80, + 65, + 290, + 169 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/1c13be2fd6d8e8afd1f1869c6d096779fff5968f623aa5577d16dbd9cecbd06d.jpg", + "image_caption": [ + "(b) Mask of each target" + ], + "image_footnote": [], + "bbox": [ + 313, + 65, + 449, + 116 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/061ed77e8996d5eab9f35e545e7a305d28db8d42f1df0fa684903c44021ca542.jpg", + "image_caption": [ + "(c) Vertexes of each target", + "Figure 4: Illustration of the reformulated form of MPOT. We predict heatmaps of four ordered vertexes and the mask for each planar object. The stacked masks are built in a layered structure and are responsible for the occluders and occludees." + ], + "image_footnote": [], + "bbox": [ + 302, + 128, + 464, + 170 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "However, due to the challenge of accurately tracking multiple planar objects, the error accumulation [46] occurs because of memorizing incorrect predictions. To avoid this issue, we filter out the low-confident predictions. Given the current frame, PRTrack predicts the vertexes $\\widehat{P}^o \\in \\mathbb{R}^{4hw}$ and mask $\\widehat{M}^o \\in \\mathbb{R}^{hw}$ for the $o^{th}$ tracked planar object. We compute the confidence of the mask and vertexes as", + "bbox": [ + 75, + 253, + 467, + 359 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nM _ {c o n f} = \\min (\\left\\{\\max \\left(\\widehat {M ^ {o}}\\right) \\right\\} _ {o = 1} ^ {O}). \\tag {1}\n$$\n", + "text_format": "latex", + "bbox": [ + 158, + 361, + 467, + 388 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nP _ {c o n f} = \\min (\\{m a x (\\widehat {P} ^ {o}) \\} _ {o = 1} ^ {0})\n$$\n", + "text_format": "latex", + "bbox": [ + 166, + 386, + 375, + 402 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "The predictions with the confidences surpassing the threshold are restored in the memory pool module. The reuse gate is only applied during testing.", + "bbox": [ + 75, + 405, + 467, + 450 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.3. Appearance Perception", + "text_level": 1, + "bbox": [ + 76, + 460, + 290, + 474 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Our appearance perception network is built on top of the encoder-decoder architecture [62], with a backbone of ResNet50. For the current frame, we extract appearance feature $f_{cur} \\in \\mathbb{R}^{CHW}$ from an image, where $H, W, C$ denotes the width, height, and the number of channels of the feature. For previous frames, we extract features from vertexes, masks, and images, and sum the three features as $f_{pre} \\in \\mathbb{R}^{T \\times CHW}$ . The current image feature and previous target features are fed into the encoder network to yield appearance features $f_{T+1}^o \\in \\mathbb{R}^{CHW}$ for $o^{\\mathrm{th}}$ planar object. The plane structure branch and segmentation prior branch finally predict the coarse results of vertexes and masks.", + "bbox": [ + 75, + 482, + 468, + 662 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Vertex Encoder with Shifted Sampling Strategy. Considering the vertexes of the planar object provide the pixel correspondence across frames, each vertex is independent against others, thus they are organized in sequential order [47]. Therefore, we design an encoder with shifted sampling strategy to leverage the characteristic of vertexes (i.e., the clockwise order), as the feature extractor. As shown in Fig. 5, a random cyclic shift function $\\text{shift}(\\cdot, +r)$ is first applied to build the connection between the vertex heatmap $P_i \\in \\mathbb{R}^{HW}$ and its neighbors by shuffling position as", + "bbox": [ + 75, + 664, + 468, + 815 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\n\\operatorname {shift}(P, + r) = \\left[P_{(1 + r)\\% L},\\dots ,P_{(L + r)\\% L}\\right], \\tag{2}\n$$\n", + "text_format": "latex", + "bbox": [ + 124, + 819, + 467, + 835 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "where $L$ is the number of vertexes in the planar object and $r \\in \\{0,1,2,3\\}$ is a random number. % is the mod operation. Then, we apply $7 \\times 7$ convolutions [25] to extract the features of four ordered vertexes, separately. For modeling", + "bbox": [ + 75, + 839, + 468, + 901 + ], + "page_idx": 4 + }, + { + "type": "image", + "img_path": "images/bfd0fd72b9ef268ea18e65f6c379c04604a5ce237fb70b354cf6eef85d7a2678.jpg", + "image_caption": [ + "Figure 5: Illustration of our proposed vertex encoder. Given the vertex heatmaps, we random sample them by a cyclic shift operation, following a clockwise order and with an offset of $r$ . Note that PSB, as a counterpart, predicts the vertexes via a cyclic shift function with negative $r$ ." + ], + "image_footnote": [], + "bbox": [ + 501, + 63, + 893, + 167 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "the order between four vertices, we introduce the cosine positional embedding [74] and add it to the vertex representation. The positional embedding $\\pmb{f}_{emb} \\in \\mathbb{R}^{L \\times N}$ contains the N-d embeddings corresponding to the order information for the features of L vertices. The feature of ordered vertices is then extracted by a $7 \\times 7$ convolution to capture long-range spatial interaction between vertices.", + "bbox": [ + 496, + 252, + 890, + 356 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Plane Structure Branch (PSB). Given the shifted feature map of vertexes from the decoder, a $1 \\times 1$ convolution is attached with the sigmoid function to output the heatmap of the vertexes. The shifted vertex heatmaps are then aligned with the shifted input in Equ. 2 by using the reversed cyclic shift operation $\\text{shift}(\\cdot, -r)$ . Finally, we get the heatmaps of $o^{\\text{th}}$ planar object $P^{o} \\in \\mathbb{R}^{HW}$ by upsampling to the same resolution as the original image.", + "bbox": [ + 496, + 357, + 890, + 478 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Segmentation Prior Branch (SPB). The mask can accurately locate the planar object at the pixel level and capture the relative movement between objects such as occlusion [55,78]. Therefore, we utilize a $1 \\times 1$ convolution with the softmax function alongside the foreground/background dimension. Following [62], The probability of background $m_{bkg}$ and each foreground object $m_o$ are obtained by aggregating the output of model logits $\\in \\mathbb{R}^{O \\times HW}$ as", + "bbox": [ + 496, + 479, + 890, + 599 + ], + "page_idx": 4 + }, + { + "type": "equation", + "text": "\n$$\nm _ {o} = \\frac {\\exp \\left(\\operatorname {l o g i t s} _ {o}\\right)}{\\sum_ {i = 1} ^ {O} \\exp \\left(\\operatorname {l o g i t s} _ {i}\\right)}, \\quad m _ {b k g} = \\prod_ {i = 1} ^ {O} (1 - m _ {o}). \\tag {3}\n$$\n", + "text_format": "latex", + "bbox": [ + 509, + 599, + 890, + 638 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "Finally, the probability segmentation mask of $\\sigma^{\\mathrm{th}}$ planar object $M^{o} \\in \\mathbb{R}^{HW}$ are produced after softmax. The background probability map is attached in the last channel.", + "bbox": [ + 496, + 641, + 890, + 686 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "4.4. Occlusion Reasoning", + "text_level": 1, + "bbox": [ + 500, + 696, + 696, + 712 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "With the above coarse output perceiving from the visible part, we move to the next stage of reasoning the occluded part by the motion of planar objects (i.e., homography). In multiple object tracking, reasoning the occlusion by motion has been verified effective [97, 98], where a motion strategy is adopted to predict the future location of the target based on the historical trajectory. Inspired by this, we first develop a homography-guided strategy that locates the occlusion area and correct features from previous frames geometrically. We factorize the homography matrix into motion parameters that describe the common transformations, to estimate the sensitive homography matrix (as discussed", + "bbox": [ + 496, + 719, + 890, + 900 + ], + "page_idx": 4 + }, + { + "type": "page_number", + "text": "23464", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 4 + }, + { + "type": "text", + "text": "in Sec. 1). Then, for tracking both visible and invisible parts of planar objects, we design a two-stream self-attention network that takes both the appearance features of the current frame and the motion-guided features of the previous frame to refine the predicted planar object.", + "bbox": [ + 75, + 90, + 468, + 167 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Occlusion Area Localization Strategy. To avoid the sensitivity problem discussed in Sec. 1, we first introduce the geometric definition of homography matrix $\\mathbf{H} \\in \\mathbb{R}^{3 \\times 3}$ [23], and factorize it into similarity transformation $\\mathbf{H}^{\\mathrm{S}}$ and residual one $\\mathbf{H}^{\\Lambda}$ , with eight stable motion parameters of $h_p = (t_x, t_y, \\gamma, \\theta, k_1, k_2, v_1, v_2)$ as", + "bbox": [ + 76, + 167, + 467, + 253 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\mathbf {H} = \\mathbf {H} ^ {\\mathbf {S}} \\mathbf {H} ^ {\\boldsymbol {\\Lambda}} = \\left[ \\begin{array}{c c c} \\gamma \\cos \\theta & - \\gamma \\sin \\theta & t _ {x} \\\\ \\gamma \\sin \\theta & \\gamma \\cos \\theta & t _ {y} \\\\ 0 & 0 & 1 \\end{array} \\right] \\left[ \\begin{array}{c c c} k _ {1} & k _ {2} & 0 \\\\ 0 & \\frac {1}{k _ {1}} & 0 \\\\ v _ {1} & v _ {2} & 1 \\end{array} \\right], \\tag {4}\n$$\n", + "text_format": "latex", + "bbox": [ + 89, + 257, + 467, + 313 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $t_x, t_y$ are the transition offset, $\\gamma$ and $\\theta$ denote the change of scale and angle, and $k_1, k_2, v_1, v_2$ control the parameters of matrix $\\mathbf{H}^{\\Lambda}$ . Here, the motion parameters can be computed by solving a transcendental equation with eight variants. The location parameters can be written as $h_l = (x_1, y_1, x_2, y_2, x_3, y_3, x_4, y_4)$ .", + "bbox": [ + 75, + 314, + 467, + 405 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Specifically, the location parameters and homography are obtained from the coarse output of appearance perception, where we apply the Argmax function on heatmaps to get the coordinates of vertexes and compute the homography matrix between the coordinates from the current frame and the previous one. Then, the factorized homography $h_p$ and location parameters $h_l$ are fed into the Kalman Filter [29] and yield the corrected ones $\\widehat{h}_p, \\widehat{h}_l$ . Finally, homography matrix $\\hat{\\mathbf{H}}^{\\mathrm{o}}$ for the $o^{\\mathrm{th}}$ planar object in the current frame can be obtained.", + "bbox": [ + 75, + 407, + 467, + 561 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Given the predicted homography, the mask from previous frame $\\widehat{M}_p^o$ can be warped [3] by the perspective transformation $warp(\\widehat{M}_p^o,\\hat{\\mathbf{H}}^\\circ)$ . To locate occlusion area, the intuition is that the heatmap inferred by historical motion is robust to the occlusion on appearance. Meanwhile, the heatmap predicted based on appearance can accurately locate the planar objects in the current frame. As a result, we indicate the area of occlusion as", + "bbox": [ + 75, + 564, + 467, + 688 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\phi^ {o} = \\frac {1}{\\sum_ {i} \\delta_ {i}} \\sum_ {i} \\delta_ {i} \\cdot \\| w a r p \\left(\\widehat {M} _ {p} ^ {i}, \\hat {\\mathbf {H}} ^ {\\mathbf {i}}\\right) - M ^ {o} \\|, \\tag {5}\n$$\n", + "text_format": "latex", + "bbox": [ + 119, + 689, + 467, + 724 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\| \\cdot \\|$ is the distance function computed per pixel and $\\delta_{i}$ judges the mask confidence of $i^{\\mathrm{th}}$ planar object.", + "bbox": [ + 75, + 727, + 467, + 758 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Motion Reasoning Network. For reasoning the visible and invisible parts of planar objects, we leverage the occlusion indicator $\\phi^o$ as guidance, where the features $f_{T + 1}^{o}$ from the current frame are refined, together with the warped feature $warp(f_T^o,\\hat{\\mathbf{H}}^\\mathrm{o})$ from the previous frame. We denote these two features as $f_{a}$ and $f_{m}$ , respectively. The features are first flattened alongside spatial dimension $f_{a},f_{m}\\in \\mathbb{R}^{c_{d}\\times HW}$ . Then, we develop a multi-head self-attention (MHSA) mechanism [31] for extracting occlusion-aware features. For learning joint representation and encouraging", + "bbox": [ + 75, + 758, + 467, + 901 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "the interactions between appearance and motion, we feed both features into MHSA as", + "bbox": [ + 498, + 90, + 890, + 118 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\n\\left\\{ \\begin{array}{l} X = \\operatorname {C o n c a t} \\left(h _ {1}, \\dots , h _ {H}\\right) \\\\ h _ {i} = a _ {i} f \\mathbf {W} _ {\\mathbf {i}} ^ {\\mathbf {V}} \\\\ a _ {i} = \\operatorname {s o f t m a x} \\left(\\frac {\\left[ f \\mathbf {W} _ {\\mathbf {i}} ^ {\\mathbf {Q}} \\right] \\left[ f \\mathbf {W} _ {\\mathbf {i}} ^ {\\mathbf {K}} \\right] ^ {\\top}}{\\sqrt {d _ {k}}}\\right), \\\\ f = \\operatorname {C o n c a t} \\left(f _ {m}, f _ {a}\\right) \\end{array} \\right. \\tag {6}\n$$\n", + "text_format": "latex", + "bbox": [ + 573, + 119, + 890, + 190 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathbf{W}_{\\mathbf{i}}^{\\mathbf{Q}}, \\mathbf{W}_{\\mathbf{i}}^{\\mathbf{K}}$ , and $\\mathbf{W}_{\\mathbf{i}}^{\\mathbf{V}}$ are the matrixes. We then adopt MLP to extract representations for motion feature $X_{m}$ and appearance feature $X_{a}$ , respectively. For assembling, we integrate both features guided by indicator $\\phi^{o}$", + "bbox": [ + 498, + 194, + 890, + 255 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nF _ {o c c} = \\mathcal {F} _ {e n s} \\left(\\mathcal {F} _ {\\phi} \\left(X _ {a}\\right), X _ {m}\\right), \\tag {7}\n$$\n", + "text_format": "latex", + "bbox": [ + 598, + 256, + 890, + 272 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathcal{F}_{\\text{ens}}$ and $\\mathcal{F}_{\\phi}$ are $1 \\times 1$ convolution layer, $\\mathcal{F}_{\\phi}$ concatenates the occlusion indicator with input feature as guidance. Finally, given the mask and vertex heatmaps of the $o^{th}$ occluded planar object, we feed the features into the dual-branch network used in the stage of appearance perception again and obtain the refined vertexes $\\widehat{P}^o$ and mask $\\widehat{M}^o$ .", + "bbox": [ + 498, + 273, + 890, + 364 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5. Experiment", + "text_level": 1, + "bbox": [ + 500, + 378, + 622, + 396 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "5.1. Evaluation Metrics", + "text_level": 1, + "bbox": [ + 500, + 402, + 683, + 417 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "To evaluate methods on MPOT, following [15], we utilize the CLEAR metric [58] to complement the POT metrics. Note that existing POT metrics estimate the difference between ground truth and prediction in a pairwise manner (i.e., 1-box to 1-box). But it is not suitable for MPOT, since the number of predictions and ground truths are not always equal. Therefore, we match the set of ground truth $GT_{t}$ and prediction $P_{t}$ by bipartite matching [33]. Sequentially, we compute the difference of the matched pair by well-known POT distance Alignment Error [43,45,70] as", + "bbox": [ + 498, + 426, + 890, + 577 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nE _ {A L} (\\mathbf {p}, \\mathbf {g}) = \\sqrt {\\frac {\\sum_ {\\mathbf {j} = 1} ^ {4} \\left(\\mathbf {p} _ {\\mathbf {j}} - \\mathbf {g} _ {\\mathbf {j}}\\right) ^ {2}}{4}}, \\tag {8}\n$$\n", + "text_format": "latex", + "bbox": [ + 576, + 577, + 890, + 616 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $\\mathbf{p}$ and $\\mathbf{g}$ are the quadrangle of the prediction and ground truth. Then, the prediction and ground truth are split into tracked $T_{\\epsilon}^{t}$ , true positive $TP_{\\epsilon}^{t}$ , false negative $FN_{\\epsilon}^{t}$ , and false positive $FP_{\\epsilon}^{t}$ , according to distance $\\epsilon$ . We set $\\epsilon$ as 50 in our experiment due to the degree of challenge.", + "bbox": [ + 498, + 616, + 890, + 690 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "In POT, Precision $(Pr_{\\epsilon})$ is the commonly used metric based on the alignment error [43]. To complement the metrics, we report Recall $(Rc_{\\epsilon})$ to consider the cases of not being tracked. Furthermore, we propose Multiple Planar Object Tracking Distance $(D_{\\epsilon})$ as", + "bbox": [ + 498, + 691, + 890, + 766 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nD _ {\\epsilon} = \\frac {\\sum_ {t = 1} ^ {T} \\sum_ {t p \\in T P _ {\\epsilon} ^ {t} , q \\in T _ {\\epsilon} ^ {t}} E _ {A L} (t p , q)}{\\sum_ {t = 1} ^ {T} | T P _ {\\epsilon} ^ {t} |}. \\tag {9}\n$$\n", + "text_format": "latex", + "bbox": [ + 558, + 766, + 890, + 805 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "Naturally, we propose the Multiple Planar Object Tracking Accuracy $(Acc_{\\epsilon})$ based on $E_{AL}$ as.", + "bbox": [ + 500, + 804, + 888, + 833 + ], + "page_idx": 5 + }, + { + "type": "equation", + "text": "\n$$\nA c c _ {\\epsilon} = 1 - \\frac {\\sum_ {t = 1} ^ {T} \\left| F N _ {\\epsilon} ^ {t} \\right| + \\left| F P _ {\\epsilon} ^ {t} \\right| + \\left| I D S W _ {\\epsilon} ^ {t} \\right|}{3 \\cdot \\sum_ {t = 1} ^ {T} \\left| G T _ {t} \\right|}, \\tag {10}\n$$\n", + "text_format": "latex", + "bbox": [ + 517, + 833, + 890, + 869 + ], + "page_idx": 5 + }, + { + "type": "text", + "text": "where $IDSW_{\\epsilon}^{t}$ is the set of the identity switch [58] under the threshold $\\epsilon$ in $\\mathbf{t}^{th}$ frame, and $|\\cdot|$ indicates the mod oper-", + "bbox": [ + 498, + 869, + 890, + 901 + ], + "page_idx": 5 + }, + { + "type": "page_number", + "text": "23465", + "bbox": [ + 478, + 944, + 517, + 955 + ], + "page_idx": 5 + }, + { + "type": "table", + "img_path": "images/98bbb163c569c3f47ebff6bc0fbc7a304232b6d33a7b21c12bbb029e5f6b04f8.jpg", + "table_caption": [ + "Table 3: Comparison of two groups of methods on MPOT-3K. The results on five metrics including Success Rate, Multiple Planar Object Tracking Accuracy, Multiple Planar Object Tracking Distance, Precision, Recall, and Speed are reported. $\\uparrow (\\downarrow)$ denotes that the higher (lower) the score, the method performs better. Bold and underline indicate the highest and second-highest performance, respectively." + ], + "table_footnote": [], + "table_body": "
MethodsTraditionalDeepOurs
Motion PatternsMetricsCMT [61]NCC [71]CCRE [76]MI [17]GOP [8]Gracker [79]STM [62]PoST [60]LISRD [64]SMask [78]SRPN+ [38]SPoint [16]SOS [73]GIFT [53]HDN [95]
Overall\\( S_{0.8} \\uparrow \\)09.5000.1909.9926.7056.0367.9209.0733.5263.4364.0467.2371.8272.9175.8676.4082.51
\\( Acc_{\\epsilon} \\uparrow \\)64.2761.9534.3437.8262.2888.3852.0539.5572.3973.2975.3771.1770.0672.9979.5094.59
\\( Pr_{\\epsilon} \\uparrow \\)37.0503.6414.1223.5745.2585.6725.6425.0256.2358.3860.7054.5853.2356.4165.2192.85
\\( Rc_{\\epsilon} \\uparrow \\)10.2400.5519.0838.6062.7278.2523.0740.7480.4069.5574.4581.2585.3784.0282.5690.78
\\( D_{\\epsilon} \\downarrow \\)12.3042.1517.2708.6806.3705.2318.7922.7106.9317.0616.7707.6707.7607.8007.4405.07
Moving Occlusion\\( S_{0.8} \\uparrow \\)11.3400.0010.6926.4755.8563.6808.7818.1773.7963.2970.6270.9173.4272.9274.9680.29
\\( Acc_{\\epsilon} \\uparrow \\)67.2562.7856.2168.1081.4192.9355.4948.0491.7481.4683.2789.9292.2889.7488.7493.16
\\( Pr_{\\epsilon} \\uparrow \\)53.484.9233.5651.8270.0576.3029.6325.4586.3774.5775.9484.7384.3584.2182.0090.95
\\( Rc_{\\epsilon} \\uparrow \\)13.4700.6432.0161.5777.3081.9824.3728.9880.7067.6272.9785.3985.0385.5084.8688.27
\\( D_{\\epsilon} \\downarrow \\)06.3142.1421.2908.7904.1307.9216.5427.2606.4115.5714.2906.0606.1706.0506.2405.34
Moving Objects\\( S_{0.8} \\uparrow \\)09.3400.6911.2324.2952.2161.5808.0935.5267.7962.9565.4965.5070.3667.0270.0979.12
\\( Acc_{\\epsilon} \\uparrow \\)69.2263.8640.7847.4168.9692.5453.7741.9676.8880.3382.7278.4469.2978.5981.0594.29
\\( Pr_{\\epsilon} \\uparrow \\)60.2817.1019.2432.5752.5090.4828.3327.1360.8768.6272.0967.7552.4167.9767.1892.27
\\( Rc_{\\epsilon} \\uparrow \\)22.872.1924.2753.9572.5156.7725.2843.9687.7375.7579.2267.6686.0967.7984.4390.44
\\( D_{\\epsilon} \\downarrow \\)12.7143.2117.6606.8505.7104.1121.7719.9305.1514.9215.4804.2104.5304.1605.6305.46
Camera Occlusion\\( S_{0.8} \\uparrow \\)14.6100.0013.3141.7963.5966.4113.8040.2185.4662.4659.4088.8588.2889.4384.0192.46
\\( Acc_{\\epsilon} \\uparrow \\)63.5461.9334.2840.2861.7287.9851.7237.1574.0661.6668.7172.1871.9072.1084.5195.85
\\( Pr_{\\epsilon} \\uparrow \\)36.8900.3818.4227.8445.0488.2424.5925.3156.7644.8352.3154.6754.4254.6073.1695.84
\\( Rc_{\\epsilon} \\uparrow \\)13.1900.0628.3249.7467.3873.7521.7045.3784.3264.8670.7587.5787.1587.5084.5291.53
\\( D_{\\epsilon} \\downarrow \\)10.3129.3820.1007.7106.7304.6325.0520.0804.8214.4614.4504.8104.6204.7305.1804.59
Speed↑00.5801.9800.3101.2501.0003.1435.4411.9008.6331.5210.8709.3212.5126.6216.3712.64
", + "bbox": [ + 80, + 109, + 893, + 417 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "ation. To fairly compare along with the trajectory level, we adopt the success rate $(S_{\\alpha})$ with the distance threshold $\\alpha$ as", + "bbox": [ + 76, + 436, + 470, + 465 + ], + "page_idx": 6 + }, + { + "type": "equation", + "text": "\n$$\nS _ {\\alpha} = \\frac {| \\mathbb {C} |}{| \\mathbb {I} |}, \\mathbb {C} = \\left\\{i _ {n} \\in \\mathbb {I} \\right| \\frac {\\sum_ {t = 1} ^ {T} \\left| T _ {\\epsilon} ^ {t} \\right|}{\\sum_ {t = 1} ^ {T} \\left| G T _ {t} \\right|} > \\alpha \\}, \\tag {11}\n$$\n", + "text_format": "latex", + "bbox": [ + 112, + 477, + 468, + 516 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "where $\\mathbb{I}$ is the set of planar objects in the video.", + "bbox": [ + 76, + 520, + 390, + 535 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.2. Implementation Details", + "text_level": 1, + "bbox": [ + 76, + 545, + 294, + 560 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We compare our model with fifteen representative methods. These methods are implemented by official code or open-source libraries [6, 72]. We run evaluated single object trackers multiple times for different planar objects. And we equip them with the data association strategy based on [12], for integrating each single object tracker into tracking multiple targets online. Besides, we additionally give the reference frames of ground truth if the single object trackers fail to track. Different from other box-based trackers, mask-based trackers (e.g., STM) directly outputs the mask. Thus, we use a rotated box estimator [88] to transfer the mask. We implement PRTrack using two RTX3090 GPUs. In the training stage, we use data augmentations, including flip, pepper noise, rotation, contrast jittering, and perspective transformation. We adopt a data sampling strategy following [41]. We adopt Smooth L1 loss and Cross-Entropy loss for optimizing the predicted vertex heatmaps and masks. Similar to [62], we pretrain SPB on YouTubeVOS [89] and DAVIS [66] datasets. During inference, we use the ordered vertexes to build the planar objects and estimate the homography matrix. We set the threshold as 0.9 in the reuse gate by grid search and set $r$ in Equ. 2 as 0 during inference.", + "bbox": [ + 76, + 569, + 468, + 900 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "5.3. Results on MPOT-3K", + "text_level": 1, + "bbox": [ + 500, + 435, + 700, + 450 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "We compare our PRTrack with the other fifteen trackers on MPOT-3K, which contains six traditional POT trackers, four deep-based generic object trackers, and five deep-based planar object trackers. Tab. 3 reports the overall performance as well as the one in the challenging situations of moving occlusion, moving objects, and camera occlusion.", + "bbox": [ + 496, + 460, + 890, + 550 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Deep vs. Traditional Trackers. We can observe that the deep-based trackers have increased by $82.6\\%$ on average, on five metrics for overall performance. This is because deep-based trackers avoid taking some assumptions under the laboratory environment, such as the invariance to illumination and appearance change. Note that Gracker performs best in traditional trackers and achieves competitive performance with the deep-based tracker group. However, since MPOT-3K has many small planar objects, it can not extract sufficient information, thus resulting in suboptimal performance (i.e., $10.3\\%$ degradation in comparison with ours). In terms of deep-based trackers, STM predicts segmentation masks at the pixel level while ignoring the order of vertexes. Thus, it results in inferior performance, where only $9.0\\%$ of targets are correctly tracked.", + "bbox": [ + 496, + 551, + 890, + 777 + ], + "page_idx": 6 + }, + { + "type": "text", + "text": "Planar Object Trackers vs. Generic Object Trackers. Planar object trackers achieve higher performance (58.9% improvement) against generic object trackers, including SRPN+, SMask, STM, and PoST. A predominant reason is that the generic trackers are subject to the assumption of affine transformation, where only the coarse box estimation is required. Therefore, a powerful planar object tracker should be developed in this field.", + "bbox": [ + 496, + 779, + 890, + 900 + ], + "page_idx": 6 + }, + { + "type": "page_number", + "text": "23466", + "bbox": [ + 478, + 945, + 519, + 955 + ], + "page_idx": 6 + }, + { + "type": "image", + "img_path": "images/9f635b7d3f32b0622c8b4a686a297d059450fb855b97c6f5a5256412428d9ae6.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 78, + 56, + 271, + 183 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/5a567515146fced29c4d3cd7972f5a77d3892cde57c2ae027f18846aa3631cd2.jpg", + "image_caption": [], + "image_footnote": [], + "bbox": [ + 272, + 56, + 468, + 184 + ], + "page_idx": 7 + }, + { + "type": "image", + "img_path": "images/2826847f90906e62103655908e4f5cf24e3dca71bebb4f4b1a88913615ef853e.jpg", + "image_caption": [ + "(a) POT210", + "(b) POT280", + "(c) Challenging factors", + "Figure 6: Comparison on POT210 and POT280. The averaged Precision on two datasets with different thresholds are reported in (a) and (b), respectively. (c) further shows the performance under seven challenging factors. The data is extracted from [95]." + ], + "image_footnote": [], + "bbox": [ + 145, + 185, + 393, + 306 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "PRTrack vs. SOTA Trackers. PRTrack outperforms other methods with an average improvement of $6.4\\%$ . We also observe a large gain when there exists relative movement among multiple targets. To be specific, when facing challenging situations like moving objects, moving occlusion, and camera occlusion, PRTrack achieves a performance gain of $16.9\\%$ against other advanced algorithms.", + "bbox": [ + 75, + 393, + 468, + 500 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.4. Results on POT210 and POT280", + "text_level": 1, + "bbox": [ + 76, + 508, + 362, + 523 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "To verify the effectiveness of PRTrack on the traditional POT task, we conduct experiments on the POT210 and POT280 datasets, and compare PRTrack with eleven POT methods as shown in Fig. 6. Note that we do not fine-tune PRTrack on these two datasets, again verifying the generalization ability of PRTrack towards unseen scenes. Following [95], the averaged Precision is employed to evaluate all the methods. As the distance threshold $E_{AL}$ increases, the precision tends to be stable when $E_{AL} > 10$ . We notice that PRTrack achieves competitive performance in comparison with advanced algorithms. Besides, PRTrack shows its superiority when handling challenging cases such as occlusion and motion blur.", + "bbox": [ + 75, + 532, + 468, + 729 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "5.5. Ablation Study", + "text_level": 1, + "bbox": [ + 76, + 739, + 230, + 757 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We conduct ablation studies on MPOT-3K in Tab. 4 to explore the effectiveness of each component in PRTrack. Our baseline is the appearance perception module, without shifted encoder and auxiliary mask. For simplicity, we use \"i&j\" to denote the comparison between the $i^{\\text{th}}$ line and the $j^{\\text{th}}$ line in the rest of this subsection.", + "bbox": [ + 75, + 763, + 468, + 853 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "We first perform module-wise ablation studies in the highlighted lines, we observe that PRTrack obtains the largest performance gain of $11.6\\%$ (i.e., $3 \\& 9$ and $4 \\& 10$ )", + "bbox": [ + 75, + 854, + 468, + 901 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "Table 4: Ablation study of components and their variants of PRTrack on the validation split of MPOT-3K. The lines with background indicate the module-level ablation study. Here AP, OR, and RT are short of appearance perception, occlusion reasoning, and memory pool. SE and Fac denote the shifted encoder and factorized homography matrix. Msk represents the plane structure branch with mask information. Here, $*$ , $\\bullet$ , and $\\diamond$ are the fusion strategy (Fus), representing concatenation, attention-based, and indicator-based. Gat indicates the reuse gate.", + "bbox": [ + 498, + 58, + 890, + 176 + ], + "page_idx": 7 + }, + { + "type": "table", + "img_path": "images/336ceffd2d68e10f12d78a1006a85fc357582769ed336b5be31f14d1b1a96b09.jpg", + "table_caption": [], + "table_footnote": [], + "table_body": "
IdAPORRTMetrics
SEMskFacFusGat\\( S_{0.8} \\)↑\\( Acc_{\\epsilon} \\)↑\\( Pr \\)↑\\( Rc \\)↑\\( D_{\\epsilon} \\)↓
①✓45.2968.0146.7546.7119.56
②✓✓63.7686.8282.3676.9615.40
③✓✓75.8291.0886.2282.9612.57
④✓✓✓78.2091.4387.1986.4209.95
⑤✓✓✓✓*✓77.5391.4690.4186.2510.43
⑥✓✓✓✓•✓78.9991.4188.0785.8709.12
⑦✓✓✓◇✓79.2491.5088.1086.1308.95
⑧✓✓✓◇✓76.3890.5688.5882.3410.59
⑨✓✓✓✓◇80.4492.4889.6787.5407.38
⑩✓✓✓✓◇✓80.5892.7590.0088.0306.39
", + "bbox": [ + 503, + 178, + 888, + 321 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "with the occlusion reasoning module. Then we investigate the variants of each module. For appearance perception, we study how to leverage the order of vertexes. The boosting of $16.3\\%$ (i.e., $2 \\& 3$ and $8 \\& 10$ ) verifies that the proposed encoder avoids learning position bias, where the first vertex commonly comes from the top-left area. For occlusion reasoning, we find the solution to unify the appearance feature and motion feature. We first conduct experiments on alternative solutions of fusion (i.e., $5 \\& 6 \\& 10$ ), where our strategy achieves the best performance. Because the occlusion indicator provides the change of image against occlusion and joint embedding helps to introduce interaction between features. We also identify the effectiveness of homography factorization via the comparison of $7 \\& 10$ , with an average boosting of $7.2\\%$ . For memory pool, we investigate the accumulated error. With a gain of $4.4\\%$ (i.e., $3 \\& 4$ and $9 \\& 10$ ), we believe the proposed reuse gate can avoid the error derived from restoring the predictions.", + "bbox": [ + 496, + 340, + 890, + 613 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "6. Conclusion", + "text_level": 1, + "bbox": [ + 500, + 626, + 619, + 641 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "In this paper, we propose a novel method for tracking multiple planar objects simultaneously. We also build the first large-scale benchmark dataset MPOT-3K which contains sufficient data, is labeled by experienced annotators, and covers various scenes. Extensive experiments are conducted on both MPOT3K and the other two single planar object tracking datasets. The results demonstrate that PRTrack achieves SOTA performance on both tasks.", + "bbox": [ + 496, + 651, + 890, + 772 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "7. Acknowledgments", + "text_level": 1, + "bbox": [ + 500, + 784, + 679, + 801 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "This work was supported by the National Key Research and Development Program of China Grant (NO. 2018AAA0100400), Natural Science Foundation of Tianjin, China (NO.20JCJQJC00020), Fundamental Research Funds for the Central Universities, and Supercomputing Center of Nankai University (NKSC).", + "bbox": [ + 496, + 809, + 890, + 900 + ], + "page_idx": 7 + }, + { + "type": "page_number", + "text": "23467", + "bbox": [ + 478, + 944, + 519, + 957 + ], + "page_idx": 7 + }, + { + "type": "text", + "text": "References", + "text_level": 1, + "bbox": [ + 78, + 89, + 173, + 104 + ], + "page_idx": 8 + }, + { + "type": "list", + "sub_type": "ref_text", + "list_items": [ + "[1] Mark Ashdown, Matthew Flagg, Rahul Sukthankar, and James M Rehg. A flexible projector-camera system for multi-planar displays. In CVPR, 2004.", + "[2] Simon Baker and Iain Matthews. 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In ISMAR, 2010." + ], + "bbox": [ + 503, + 92, + 890, + 731 + ], + "page_idx": 10 + }, + { + "type": "page_number", + "text": "23470", + "bbox": [ + 478, + 944, + 519, + 955 + ], + "page_idx": 10 + } +] \ No newline at end of file diff --git a/2023/Multiple Planar Object Tracking/16e4462f-086b-4e2c-b3e1-1c3bf9449c10_model.json b/2023/Multiple Planar Object Tracking/16e4462f-086b-4e2c-b3e1-1c3bf9449c10_model.json new file mode 100644 index 0000000000000000000000000000000000000000..f4cca2f9a6d4d927d585afe9bc14ed3a2316a01f --- /dev/null +++ b/2023/Multiple Planar Object Tracking/16e4462f-086b-4e2c-b3e1-1c3bf9449c10_model.json @@ -0,0 +1,3005 @@ +[ + [ + { + "type": "header", + "bbox": [ + 0.107, + 0.003, + 0.182, + 0.043 + ], + "angle": 0, + "content": "CVF" + }, + { + "type": "header", + "bbox": [ + 0.239, + 0.001, + 0.808, + 0.047 + ], + "angle": 0, + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + }, + { + "type": "title", + "bbox": [ + 0.318, + 0.131, + 0.654, + 0.154 + ], + "angle": 0, + "content": "Multiple Planar Object Tracking" + }, + { + "type": "text", + "bbox": [ + 0.341, + 0.183, + 0.629, + 0.199 + ], + "angle": 0, + "content": "https://zzcheng.top/MPOT" + }, + { + "type": "text", + "bbox": [ + 0.247, + 0.2, + 0.381, + 0.217 + ], + "angle": 0, + "content": "Zhicheng Zhang" + }, + { + "type": "text", + "bbox": [ + 0.445, + 0.2, + 0.558, + 0.217 + ], + "angle": 0, + "content": "Shengzhe Liu" + }, + { + "type": "text", + "bbox": [ + 0.621, + 0.199, + 0.728, + 0.218 + ], + "angle": 0, + "content": "Jufeng Yang†" + }, + { + "type": "text", + "bbox": [ + 0.182, + 0.218, + 0.789, + 0.235 + ], + "angle": 0, + "content": "VCIP & TMCC & DISSec, College of Computer Science, Nankai University" + }, + { + "type": "text", + "bbox": [ + 0.209, + 0.238, + 0.76, + 0.251 + ], + "angle": 0, + "content": "gloryzzc6@sina.com, nkuliusz@163.com, yangjufeng@nankai.edu.cn" + }, + { + "type": "title", + "bbox": [ + 0.235, + 0.287, + 0.314, + 0.303 + ], + "angle": 0, + "content": "Abstract" + }, + { + "type": "text", + "bbox": [ + 0.075, + 0.319, + 0.474, + 0.699 + ], + "angle": 0, + "content": "Tracking both location and pose of multiple planar objects (MPOT) is of great significance to numerous real-world applications. The greater degree-of-freedom of planar objects compared with common objects makes MPOT far more challenging than well-studied object tracking, especially when occlusion occurs. To address this challenging task, we are inspired by amodal perception that humans jointly track visible and invisible parts of the target, and propose a tracking framework that unifies appearance perception and occlusion reasoning. Specifically, we present a dual-branch network to track the visible part of planar objects, including vertexes and mask. Then, we develop an occlusion area localization strategy to infer the invisible part, i.e., the occluded region, followed by a two-stream attention network finally refining the prediction. To alleviate the lack of data in this field, we build the first large-scale benchmark dataset, namely MPOT-3K. It consists of 3,717 planar objects from 356 videos and contains 148,896 frames together with 687,417 annotations. The collected planar objects have 9 motion patterns and the videos are shot in 6 types of indoor and outdoor scenes. Extensive experiments demonstrate the superiority of our proposed method on the newly developed MPOT-3K as well as other two popular single planar object tracking datasets. The code and MPOT-3K dataset are released on https://zzcheng.top/MPOT." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.728, + 0.21, + 0.743 + ], + "angle": 0, + "content": "1. Introduction" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.754, + 0.47, + 0.876 + ], + "angle": 0, + "content": "Tracking multiple planar objects (MPOT) is a fundamental task in computer vision. It aims to explore the motion of planar objects, tracking both the location and pose of multiple targets simultaneously [40, 43, 56]. The planar object is defined as a plane belonging to a specific body [28] (e.g., box, building, or wall) in the form of four ordered vertexes [43, 70]. With the help of MPOT, we can track targets when multiple planar objects exist, e.g., different sur" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.286, + 0.758, + 0.398 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.555, + 0.399, + 0.7, + 0.413 + ], + "angle": 0, + "content": "(a) Image of \\( i^{\\text{th}} \\) frame" + }, + { + "type": "image", + "bbox": [ + 0.504, + 0.416, + 0.758, + 0.464 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.506, + 0.466, + 0.607, + 0.486 + ], + "angle": 0, + "content": "POT VOS (DoF=8) (N/A)" + }, + { + "type": "image_caption", + "bbox": [ + 0.539, + 0.488, + 0.718, + 0.502 + ], + "angle": 0, + "content": "(b) Different tracking tasks" + }, + { + "type": "image", + "bbox": [ + 0.761, + 0.287, + 0.89, + 0.34 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.812, + 0.338, + 0.841, + 0.348 + ], + "angle": 0, + "content": "POT" + }, + { + "type": "image", + "bbox": [ + 0.761, + 0.35, + 0.889, + 0.405 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.811, + 0.406, + 0.842, + 0.416 + ], + "angle": 0, + "content": "VOS" + }, + { + "type": "image", + "bbox": [ + 0.761, + 0.418, + 0.889, + 0.474 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.791, + 0.474, + 0.863, + 0.485 + ], + "angle": 0, + "content": "VOT/RVOT" + }, + { + "type": "image_caption", + "bbox": [ + 0.746, + 0.486, + 0.892, + 0.502 + ], + "angle": 0, + "content": "(c) Tracking \\( \\mathbf{j}^{\\mathrm{th}} \\) frame" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.505, + 0.893, + 0.617 + ], + "angle": 0, + "content": "Figure 1: Comparison with other vision tasks. Given an image (a), we present the ground truth for different tasks in (b). The corresponding Degree-of-Freedom (DoF) is reported at the bottom and the details are listed on the right side of each task. In (c), we show the tracking results for box-based tasks (e.g., VOT, RVOT), mask-based tasks (e.g., VOS), and POT, which can find the occluded regions (marked by the red line area) and provide pixel-to-pixel matching correspondence (colored points across frames)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.644, + 0.892, + 0.704 + ], + "angle": 0, + "content": "faces of an object [1] or planes from various objects [27]. It has attracted more and more attention attributed to various applications in augmented reality [57, 104], video editing [4, 20, 30], and robot navigation [92]." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.705, + 0.893, + 0.902 + ], + "angle": 0, + "content": "MPOT is closely related to well-known computer vision tasks in RGB tracking [32] (see Tab. 1). Both tasks involve tracking the target across subsequent frames of a video using the ground truth provided in the initial frame. However, it is more challenging in two aspects. 1) Tracking planar objects is of greater Degree-of-Freedom (DoF). As shown in Fig. 1(b), MPOT tracks both the pose and location of the target, which is described by an arbitrary quadrangle (i.e., four independent vertexes \\((x_{1},y_{1},x_{2},y_{2},x_{3},y_{3},x_{4},y_{4})\\), whose DoF is 8 [44]). In contrast, it only needs to predict the position and size of an object \\((x,y,w,h)\\) in video object tracking (VOT), and Rotated VOT (RVOT) additionally requires the rotation angle. Even compared with video object" + }, + { + "type": "page_footnote", + "bbox": [ + 0.102, + 0.888, + 0.232, + 0.9 + ], + "angle": 0, + "content": "† Corresponding author." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "23460" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.08, + 0.894, + 0.108 + ], + "angle": 0, + "content": "Table 1: The comparison of MPOT with other video-related tasks. We compare MPOT with five RGB tracking tasks and four tasks with auxiliary modality information. The count of DoF comes from [44]." + }, + { + "type": "table", + "bbox": [ + 0.078, + 0.109, + 0.892, + 0.265 + ], + "angle": 0, + "content": "
ModalityTaskObjectScenario
Object categoryObject selectionMultiple objectsPixel correspondenceDoFOcclusion
RGBMOT [83]Limited, usually pedestrians or vehiclesDetectedYN4Y
MOTS [75]Limited, usually pedestrians or vehiclesDetectedYNN/AN
VOS [66]ArbitraryUser-specified in the first frameNNN/AN
VOT [21]ArbitraryUser-specified in the first frameNN4Y
RVOT [32]ArbitraryUser-specified in the first frameNN5Y
MPOTArbitraryUser-specified in the first frameYY8Y
RGB+DepthRGBDT [91]ArbitraryUser-specified in the first frameYN4Y
6DOP [50]Limited by training setDetectedYY6Y
6DPT [81]ArbitraryUser-specified in the first frameNY6Y
RGB+LIDAR3dOD [35]Limited by training setDetectedYN7Y
3dMOT [84]Limited, usually vehiclesDetectedYN7Y
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.279, + 0.473, + 0.581 + ], + "angle": 0, + "content": "segmentation (VOS), an alternative that introduces masks at the pixel level, MPOT is a more challenging task. Because MPOT provides the matched correspondence for each pixel within the object region across frames [60] (e.g., colored points in Fig. 1(a)&(c)), which makes it possible for applications that require positional information like texture mapping [24]. Nevertheless, VOS that tracks the target area instead of per-pixel location can hardly achieve it. 2) Occlusion is another challenge that comes with MPOT. Not only the one in POT that manually occludes the camera, MPOT but introduces the occlusion raised by the layered position of multiple targets relative to the camera [77, 96] (see Fig. 1(c)). Besides, the occlusion is more complex than the ones in multiple object tracking (MOT). As discussed above, when occlusion occurs, MPOT estimates the pixel correspondence controlled by homography matrix \\(\\mathbf{H}\\) [3], which tends to be sensitive and have a high condition number that can reach up to \\(5\\mathrm{e}^7\\) [95]. This means that a tiny movement of the invisible part is extremely difficult to track." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.584, + 0.473, + 0.903 + ], + "angle": 0, + "content": "To address the aforementioned limitations, our work draws the inspiration that humans consolidate the visible together with invisible parts of the target for tracking [96]. We propose a tracking framework comprised of procedures for appearance Perception and occlusion Reasoning, namely PRTrack. To track high DoF planar objects, we reformulate the problem of estimating homography matrix \\(\\mathbf{H}\\) as predicting the mask and ordered vertexes for each planar object. With the high-dimensional mask, we can accurately locate the target area at the pixel level. Besides, the ordered vertexes provide per-pixel correspondence across frames for tracking the pose of planar objects. Therefore, in the stage of appearance perception, we propose a dual branch network to predict the ordered vertexes and masks of planar objects based on the historical visible information. For vertexes, we design an encoder with shifted sampling strategy based on the constraint that the vertexes always have a clockwise order. For mask, we aggregate the probability of multiple planar objects with a multi-layered layout, that is, a stack of occluders and occludees. Further, to solve the cases of complex occlusion, we develop an occlusion area" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.279, + 0.895, + 0.4 + ], + "angle": 0, + "content": "localization strategy to indicate the occluded part, by storing the movement of each planar object (i.e., historical H). To be specific, we factorize the sensitive homography matrix, which describes the relative movement of planar objects, into parameters of transition, rotation, and pose. Finally, with the prediction from the mentioned stages, we propose a two-stream self-attention network to jointly refine the predicted planar objects." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.4, + 0.895, + 0.49 + ], + "angle": 0, + "content": "Besides, since there is no available dataset in this field, we build a large-scale benchmark dataset, namely MPOT-3K. Specifically, we shoot 356 videos with 3,717 planar objects and 687,417 annotations. The videos are collected under 9 motion patterns, where the relative movement and occlusion are also included to simulate the real-world scene." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.49, + 0.895, + 0.628 + ], + "angle": 0, + "content": "The contributions of this paper are two-fold: 1) We collect and annotate the first large-scale benchmark dataset for MPOT, where planar objects are diversely collected expelling bias. Our dataset will be released and boost research in this field. 2) We propose a tracking framework with unified motion and appearance models, which can accurately predict the pose and location of planar objects. Extensive experiments demonstrate the superiority of PRTrack against state-of-the-art approaches." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.641, + 0.642, + 0.657 + ], + "angle": 0, + "content": "2. Related Work" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.666, + 0.72, + 0.683 + ], + "angle": 0, + "content": "2.1. Planar Object Tracking" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.689, + 0.895, + 0.901 + ], + "angle": 0, + "content": "Benchmark Datasets. Current works focus on single planar object tracking and propose several POT datasets [19, 42, 43, 45, 70, 86]. Metaio [45] is the first dataset collected in the lab and the videos are collected by a monitored camera. Similarly, TMT [70] also shoots videos from the lab, where the annotations are automatically generated by aggregating the results of three planar object trackers. Due to the laboratory setting of the collection, videos in these datasets have similar backgrounds. Thus, POT210 [43] collects video data in the wild under seven motion patterns and encourages the diversity of the recorded videos with complex backgrounds. However, existing benchmarks are insufficient to mimic real-world settings where multiple targets exist. Therefore, our work extends the task into MPOT that" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.958 + ], + "angle": 0, + "content": "23461" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.078, + 0.09, + 0.47, + 0.117 + ], + "angle": 0, + "content": "Table 2: Statistics of tracking datasets. \"I.\" and \"O.\" indicate indoor and outdoor, respectively. \"#\" denotes \"the number of\"." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.117, + 0.468, + 0.207 + ], + "angle": 0, + "content": "
BenchmarkUCSB [19]TMT [70]POIC [8]POT210 [43]POT280 [42]MOT16 [58]MPOT-3K
# Scenes112030401442
# Videos961002021028014356
# Targets96100202102801,2763,717
# Annotations7K-23K53K70K292K687K
Scene CategoryI.I.I.&O.I.&O.I.&O.O.I.&O.
Multiple ObjectsXXXXX✓✓
" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.227, + 0.468, + 0.257 + ], + "angle": 0, + "content": "simultaneously tracks multiple planar objects which can be applied in real-world applications like AR, robots, and art." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.261, + 0.47, + 0.473 + ], + "angle": 0, + "content": "Methods. POT trackers can be classified into region-based, keypoint-based, and hybrid methods. Region-based approaches [2, 3, 9, 17, 34, 68] focus on the whole planar region and estimate perspective transformation by closing up the template and the warped image. Keypoint-based methods [22, 61, 63, 79, 101] describe a planar object by the detected keypoints [54, 69] and associate objects across frames by computing the similarity between keypoints. As for hybrid methods, previous works [8, 9, 13, 94] exploit the robust feature descriptors for searching the optimal matching. A representative method [8] leverage gradient-based feature as criterion. As progress is made into the deep learning era [37, 82], CLKN [7] integrates deep features into the Lucas-Kanade algorithm for improving matching quality." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.493, + 0.236, + 0.509 + ], + "angle": 0, + "content": "2.2. Visual Tracking" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.52, + 0.469, + 0.716 + ], + "angle": 0, + "content": "Single Object Tracking. It aims to locate and track a single target in a video [39, 48], which can be roughly grouped into box-based tracking [18, 55, 93] and mask-based tracking [41, 47, 60]. SiamFC [5] adopts the correlation layer to search the location which is described by the axis-aligned bounding box. Further, SiamMask [78] introduces rotation to describe the motion and predicts the object mask with the bounding box simultaneously. Meanwhile, mask-based tracking focuses on the accurate location of the targets. STM [62] addresses the problem of appearance change, leading to satisfactory results. Recently, PoST [60] explores the relationship between the mask and contour, building constraints for predicting the polygonal mask." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.72, + 0.47, + 0.901 + ], + "angle": 0, + "content": "Multiple Object Tracking. Existing works [14, 58] propose to track multiple objects of human interests simultaneously, with the assumption that all targets belong to a list of predefined classes [10, 11, 26, 36, 51, 90, 100, 102]. A large number of methods [49, 65, 80, 85, 99] are proposed to address the task. With the class assumption, they utilize object detectors to generate candidates in the manner of axis-aligned bounding boxes. Then the candidates are associated into trajectories. While both MPOT and MOT track multiple targets at the same time, the former faces more challenges since it handles arbitrary planar objects with greater DoF, as well as covers unrestricted classes [43]." + }, + { + "type": "image", + "bbox": [ + 0.503, + 0.089, + 0.714, + 0.219 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.502, + 0.225, + 0.726, + 0.235 + ], + "angle": 0, + "content": "(a) Occurrence of occlusion in different scenes" + }, + { + "type": "image", + "bbox": [ + 0.72, + 0.09, + 0.889, + 0.226 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.754, + 0.226, + 0.884, + 0.235 + ], + "angle": 0, + "content": "(b) Statistics about occlusion" + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.237, + 0.892, + 0.319 + ], + "angle": 0, + "content": "Figure 2: Statistics of occlusion in MPOT-3K. (a) shows the frequency of occlusion in six types of scenes, in which the number on the left indicates the number of planar objects being occluded and the one in shadow represents the corresponding proportion. (b) illustrates the number of occlusions per video as well as the temporal length per occlusion." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.337, + 0.719, + 0.353 + ], + "angle": 0, + "content": "3. The MPOT-3K Dataset" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.363, + 0.892, + 0.485 + ], + "angle": 0, + "content": "MPOT is being less explored and limited by existing datasets designed to single planar object tracking. In this work, we construct the dataset MPOT-3K for introducing multiple targets. To the best of our knowledge, MPOT-3K is the first large-scale dataset for the challenging task of MPOT. This will help facilitate future research in computer vision (augmented reality, safety surveillance), robot (navigation, manipulation), and art (video editing)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.495, + 0.657, + 0.511 + ], + "angle": 0, + "content": "3.1. Data Collecting" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.519, + 0.892, + 0.731 + ], + "angle": 0, + "content": "Initially, we shoot 840 videos involving the motion of static and moving planar objects. For the static planar objects, we design six motion patterns (i.e., far-near movement, in-plane rotation, out-plane rotation, in-plane movement, motion blur, camera occlusion) by controlling the movements of camera as common practices [43,86]. For the moving planar objects, we consider the occlusions and relative movements among multiple planar objects and design two motion patterns (i.e., moving objects, moving occlusion). Besides, an unconstrained motion pattern is considered to further combine the above motion patterns. According to [87, 103], we record diverse videos from six types of indoor and outdoor scenes, including library, house, gallery, building, street, and village." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.741, + 0.665, + 0.755 + ], + "angle": 0, + "content": "3.2. Data Annotation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.901 + ], + "angle": 0, + "content": "MPOT-3K is annotated by seven well-trained annotators. Following [43], we adopt a semi-automatic annotation scheme. First, the annotator labels one frame every five frames. Then, the annotated label is propagated to other unannotated frames by linear interpolation. Finally, the annotator corrects the propagated label. During annotation, we obey the following rules. First, we define what planar object is to be annotated according to [43, 70, 86]. The planar object should be easily presented by four ordered ver" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23462" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.075, + 0.892, + 0.259 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.261, + 0.894, + 0.317 + ], + "angle": 0, + "content": "Figure 3: The pipeline of our method. Our tracking framework is divided into three stages. First, in appearance perception, we track the visible part of multiple planar objects via a dual-branch network, as coarse output. For the next stage of occlusion reasoning, the occlusion area is localized and then fed into a two-stream self-attention network for refining the predicted target. Finally, the memory pool module restores the high-confident tracked targets." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.329, + 0.473, + 0.512 + ], + "angle": 0, + "content": "texas. To ensure that the criteria for selecting plane objects are consistent, we ask all the annotators to vote for filtering out inconsistent objects [52]. Second, we start annotating when the planar object is completely in view and end when the object has been fully occluded or out of view. Third, we annotate the spatial position of the planar object according to two principles: 1) We annotate the planar object which has four apparent lines, since the point is localized by inferring the intersection lines [67]. 2) We maintain the order of vertexes across video frames for pixel correspondence. Combining these principles, we can locate the planar object with four independent vertexes (i.e., a quadrangle)." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.526, + 0.185, + 0.541 + ], + "angle": 0, + "content": "3.3. Statistics" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.552, + 0.47, + 0.688 + ], + "angle": 0, + "content": "After collecting and labeling, we yield a large-scale dataset MPOT-3K, where we obtain 356 videos with 3,717 planar objects from 42 scenes. The number of planar objects per video averages 10.44 and can reach 74 at most. MPOT-3K is divided into training, validation, and test sets in a proportion of 80:5:15. The split is performed at the scene level to ensure there's no overlap among splits. Hence the dataset avoids leakage since both the target and scene of the test set are expelled during training." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.689, + 0.471, + 0.901 + ], + "angle": 0, + "content": "As shown in Tab. 2, we compare MPOT-3K with six datasets, which come from POT [8, 19, 42, 43, 70] and MOT [58] tasks. MPOT-3K contains over 9.8 times more annotations and 13.2 times more targets in all video frames than the largest POT dataset POT280. The number of targets is almost 3 times of the popular MOT16 dataset. Another strength of MPOT-3K lies in its diversity, which covers 9 motion patterns and 6 types of scenes. Besides, MPOT-3K introduces more complex occlusions. As shown in Fig. 2(a), we observe that occlusion occurs in all the scenes, where \\(39.9\\%\\) of planar objects are occluded on average. Fig. 2(b) further illustrates that there are 3.6 occlusions happening in a video on average and each occlusion lasts 9.56 seconds." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.327, + 0.635, + 0.346 + ], + "angle": 0, + "content": "4. Methodology" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.353, + 0.892, + 0.52 + ], + "angle": 0, + "content": "PRTrack consists of three main components (See Fig. 3): memory pool module, appearance perception network, and occlusion reasoning network. The memory pool module (Sec. 4.2) restores the previous predictions and expels the low-confident targets. Guided by previously tracked targets, the appearance perception network (Sec. 4.3) predicts mask together with the vertexes for each planar object. The occlusion reasoning network (Sec. 4.4) further takes all the tracked targets and corresponding occlusion area, which is indicated by the difference between motion-guided results among multiple targets and the predicted one." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.528, + 0.72, + 0.543 + ], + "angle": 0, + "content": "4.1. Problem Reformulation" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.551, + 0.892, + 0.735 + ], + "angle": 0, + "content": "Assume multiple planar objects exists in an RGB video where they are not from the training set, nor have detection results. Given the user-selected ones in the initial frame, the objective is to estimate their position change relative to the beginning, i.e., homography matrix, with which the pose change of targets can be obtained [56]. As shown in Fig. 4, we reformulate the tracking task as predicting the masks of the quadrangle \\(\\widehat{\\mathbf{M}} \\in \\mathbb{R}^{O \\times hw}\\) and the heatmap of four ordered vertexes \\(\\widehat{\\mathbf{P}} \\in \\mathbb{R}^{O \\times 4hw}\\), where \\(O\\) is the number of planar objects in the current frame. The layered masks represent the location of multiple planar objects [94] and the vertexes are used to track the pose of planar objects [56]." + }, + { + "type": "title", + "bbox": [ + 0.499, + 0.742, + 0.704, + 0.759 + ], + "angle": 0, + "content": "4.2. Memory Pool module" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.765, + 0.892, + 0.903 + ], + "angle": 0, + "content": "From the viewpoint of human perception, one person tracks the targets by memorizing their historical appearance and trajectory [59]. Inspired by this, we leverage the images and predictions in previous T frames as guidance to track planar objects in the current one. For the previous frames, we record previously predicted heatmaps of ordered vertexes \\(\\mathbf{P_o}\\in \\mathbb{R}^{T\\times 4hw}\\), masks \\(\\mathbf{M_o}\\in \\mathbb{R}^{T\\times hw}\\), and the images \\(\\mathbf{I_o}\\in \\mathbb{R}^{T\\times 3hw}\\) for the \\(o^{\\mathrm{th}}\\) planar object. The memory pool \\(\\{(\\mathbf{P_o},\\mathbf{M_o},\\mathbf{I_o})\\}_{o = 1}^N\\) stores the tracked N planar objects." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23463" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.081, + 0.066, + 0.291, + 0.17 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.154, + 0.171, + 0.209, + 0.183 + ], + "angle": 0, + "content": "(a) Image" + }, + { + "type": "image", + "bbox": [ + 0.315, + 0.066, + 0.45, + 0.117 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.31, + 0.117, + 0.445, + 0.128 + ], + "angle": 0, + "content": "(b) Mask of each target" + }, + { + "type": "image", + "bbox": [ + 0.303, + 0.129, + 0.465, + 0.171 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.303, + 0.171, + 0.453, + 0.183 + ], + "angle": 0, + "content": "(c) Vertexes of each target" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.183, + 0.468, + 0.237 + ], + "angle": 0, + "content": "Figure 4: Illustration of the reformulated form of MPOT. We predict heatmaps of four ordered vertexes and the mask for each planar object. The stacked masks are built in a layered structure and are responsible for the occluders and occludees." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.254, + 0.468, + 0.36 + ], + "angle": 0, + "content": "However, due to the challenge of accurately tracking multiple planar objects, the error accumulation [46] occurs because of memorizing incorrect predictions. To avoid this issue, we filter out the low-confident predictions. Given the current frame, PRTrack predicts the vertexes \\(\\widehat{P}^o \\in \\mathbb{R}^{4hw}\\) and mask \\(\\widehat{M}^o \\in \\mathbb{R}^{hw}\\) for the \\(o^{th}\\) tracked planar object. We compute the confidence of the mask and vertexes as" + }, + { + "type": "equation", + "bbox": [ + 0.16, + 0.362, + 0.468, + 0.39 + ], + "angle": 0, + "content": "\\[\nM _ {c o n f} = \\min (\\left\\{\\max \\left(\\widehat {M ^ {o}}\\right) \\right\\} _ {o = 1} ^ {O}). \\tag {1}\n\\]" + }, + { + "type": "equation", + "bbox": [ + 0.168, + 0.387, + 0.377, + 0.404 + ], + "angle": 0, + "content": "\\[\nP _ {c o n f} = \\min (\\{m a x (\\widehat {P} ^ {o}) \\} _ {o = 1} ^ {0})\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.406, + 0.468, + 0.451 + ], + "angle": 0, + "content": "The predictions with the confidences surpassing the threshold are restored in the memory pool module. The reuse gate is only applied during testing." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.461, + 0.292, + 0.476 + ], + "angle": 0, + "content": "4.3. Appearance Perception" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.483, + 0.469, + 0.664 + ], + "angle": 0, + "content": "Our appearance perception network is built on top of the encoder-decoder architecture [62], with a backbone of ResNet50. For the current frame, we extract appearance feature \\( f_{cur} \\in \\mathbb{R}^{CHW} \\) from an image, where \\( H, W, C \\) denotes the width, height, and the number of channels of the feature. For previous frames, we extract features from vertexes, masks, and images, and sum the three features as \\( f_{pre} \\in \\mathbb{R}^{T \\times CHW} \\). The current image feature and previous target features are fed into the encoder network to yield appearance features \\( f_{T+1}^o \\in \\mathbb{R}^{CHW} \\) for \\( o^{\\mathrm{th}} \\) planar object. The plane structure branch and segmentation prior branch finally predict the coarse results of vertexes and masks." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.665, + 0.469, + 0.816 + ], + "angle": 0, + "content": "Vertex Encoder with Shifted Sampling Strategy. Considering the vertexes of the planar object provide the pixel correspondence across frames, each vertex is independent against others, thus they are organized in sequential order [47]. Therefore, we design an encoder with shifted sampling strategy to leverage the characteristic of vertexes (i.e., the clockwise order), as the feature extractor. As shown in Fig. 5, a random cyclic shift function \\( \\text{shift}(\\cdot, +r) \\) is first applied to build the connection between the vertex heatmap \\( P_i \\in \\mathbb{R}^{HW} \\) and its neighbors by shuffling position as" + }, + { + "type": "equation", + "bbox": [ + 0.125, + 0.82, + 0.468, + 0.837 + ], + "angle": 0, + "content": "\\[\n\\operatorname {shift}(P, + r) = \\left[P_{(1 + r)\\% L},\\dots ,P_{(L + r)\\% L}\\right], \\tag{2}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.84, + 0.469, + 0.902 + ], + "angle": 0, + "content": "where \\( L \\) is the number of vertexes in the planar object and \\( r \\in \\{0,1,2,3\\} \\) is a random number. % is the mod operation. Then, we apply \\( 7 \\times 7 \\) convolutions [25] to extract the features of four ordered vertexes, separately. For modeling" + }, + { + "type": "image", + "bbox": [ + 0.502, + 0.064, + 0.894, + 0.168 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.499, + 0.169, + 0.892, + 0.237 + ], + "angle": 0, + "content": "Figure 5: Illustration of our proposed vertex encoder. Given the vertex heatmaps, we random sample them by a cyclic shift operation, following a clockwise order and with an offset of \\( r \\). Note that PSB, as a counterpart, predicts the vertexes via a cyclic shift function with negative \\( r \\)." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.253, + 0.892, + 0.357 + ], + "angle": 0, + "content": "the order between four vertices, we introduce the cosine positional embedding [74] and add it to the vertex representation. The positional embedding \\( \\pmb{f}_{emb} \\in \\mathbb{R}^{L \\times N} \\) contains the N-d embeddings corresponding to the order information for the features of L vertices. The feature of ordered vertices is then extracted by a \\( 7 \\times 7 \\) convolution to capture long-range spatial interaction between vertices." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.358, + 0.892, + 0.479 + ], + "angle": 0, + "content": "Plane Structure Branch (PSB). Given the shifted feature map of vertexes from the decoder, a \\(1 \\times 1\\) convolution is attached with the sigmoid function to output the heatmap of the vertexes. The shifted vertex heatmaps are then aligned with the shifted input in Equ. 2 by using the reversed cyclic shift operation \\(\\text{shift}(\\cdot, -r)\\). Finally, we get the heatmaps of \\(o^{\\text{th}}\\) planar object \\(P^{o} \\in \\mathbb{R}^{HW}\\) by upsampling to the same resolution as the original image." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.48, + 0.892, + 0.6 + ], + "angle": 0, + "content": "Segmentation Prior Branch (SPB). The mask can accurately locate the planar object at the pixel level and capture the relative movement between objects such as occlusion [55,78]. Therefore, we utilize a \\(1 \\times 1\\) convolution with the softmax function alongside the foreground/background dimension. Following [62], The probability of background \\(m_{bkg}\\) and each foreground object \\(m_o\\) are obtained by aggregating the output of model logits \\(\\in \\mathbb{R}^{O \\times HW}\\) as" + }, + { + "type": "equation", + "bbox": [ + 0.511, + 0.6, + 0.891, + 0.64 + ], + "angle": 0, + "content": "\\[\nm _ {o} = \\frac {\\exp \\left(\\operatorname {l o g i t s} _ {o}\\right)}{\\sum_ {i = 1} ^ {O} \\exp \\left(\\operatorname {l o g i t s} _ {i}\\right)}, \\quad m _ {b k g} = \\prod_ {i = 1} ^ {O} (1 - m _ {o}). \\tag {3}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.642, + 0.892, + 0.688 + ], + "angle": 0, + "content": "Finally, the probability segmentation mask of \\( \\sigma^{\\mathrm{th}} \\) planar object \\( M^{o} \\in \\mathbb{R}^{HW} \\) are produced after softmax. The background probability map is attached in the last channel." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.697, + 0.697, + 0.713 + ], + "angle": 0, + "content": "4.4. Occlusion Reasoning" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.72, + 0.892, + 0.901 + ], + "angle": 0, + "content": "With the above coarse output perceiving from the visible part, we move to the next stage of reasoning the occluded part by the motion of planar objects (i.e., homography). In multiple object tracking, reasoning the occlusion by motion has been verified effective [97, 98], where a motion strategy is adopted to predict the future location of the target based on the historical trajectory. Inspired by this, we first develop a homography-guided strategy that locates the occlusion area and correct features from previous frames geometrically. We factorize the homography matrix into motion parameters that describe the common transformations, to estimate the sensitive homography matrix (as discussed" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.519, + 0.957 + ], + "angle": 0, + "content": "23464" + } + ], + [ + { + "type": "text", + "bbox": [ + 0.076, + 0.092, + 0.47, + 0.168 + ], + "angle": 0, + "content": "in Sec. 1). Then, for tracking both visible and invisible parts of planar objects, we design a two-stream self-attention network that takes both the appearance features of the current frame and the motion-guided features of the previous frame to refine the predicted planar object." + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.169, + 0.468, + 0.254 + ], + "angle": 0, + "content": "Occlusion Area Localization Strategy. To avoid the sensitivity problem discussed in Sec. 1, we first introduce the geometric definition of homography matrix \\(\\mathbf{H} \\in \\mathbb{R}^{3 \\times 3}\\) [23], and factorize it into similarity transformation \\(\\mathbf{H}^{\\mathrm{S}}\\) and residual one \\(\\mathbf{H}^{\\Lambda}\\), with eight stable motion parameters of \\(h_p = (t_x, t_y, \\gamma, \\theta, k_1, k_2, v_1, v_2)\\) as" + }, + { + "type": "equation", + "bbox": [ + 0.09, + 0.258, + 0.468, + 0.314 + ], + "angle": 0, + "content": "\\[\n\\mathbf {H} = \\mathbf {H} ^ {\\mathbf {S}} \\mathbf {H} ^ {\\boldsymbol {\\Lambda}} = \\left[ \\begin{array}{c c c} \\gamma \\cos \\theta & - \\gamma \\sin \\theta & t _ {x} \\\\ \\gamma \\sin \\theta & \\gamma \\cos \\theta & t _ {y} \\\\ 0 & 0 & 1 \\end{array} \\right] \\left[ \\begin{array}{c c c} k _ {1} & k _ {2} & 0 \\\\ 0 & \\frac {1}{k _ {1}} & 0 \\\\ v _ {1} & v _ {2} & 1 \\end{array} \\right], \\tag {4}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.315, + 0.468, + 0.406 + ], + "angle": 0, + "content": "where \\( t_x, t_y \\) are the transition offset, \\( \\gamma \\) and \\( \\theta \\) denote the change of scale and angle, and \\( k_1, k_2, v_1, v_2 \\) control the parameters of matrix \\( \\mathbf{H}^{\\Lambda} \\). Here, the motion parameters can be computed by solving a transcendental equation with eight variants. The location parameters can be written as \\( h_l = (x_1, y_1, x_2, y_2, x_3, y_3, x_4, y_4) \\)." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.408, + 0.468, + 0.562 + ], + "angle": 0, + "content": "Specifically, the location parameters and homography are obtained from the coarse output of appearance perception, where we apply the Argmax function on heatmaps to get the coordinates of vertexes and compute the homography matrix between the coordinates from the current frame and the previous one. Then, the factorized homography \\( h_p \\) and location parameters \\( h_l \\) are fed into the Kalman Filter [29] and yield the corrected ones \\( \\widehat{h}_p, \\widehat{h}_l \\). Finally, homography matrix \\( \\hat{\\mathbf{H}}^{\\mathrm{o}} \\) for the \\( o^{\\mathrm{th}} \\) planar object in the current frame can be obtained." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.565, + 0.468, + 0.689 + ], + "angle": 0, + "content": "Given the predicted homography, the mask from previous frame \\(\\widehat{M}_p^o\\) can be warped [3] by the perspective transformation \\(warp(\\widehat{M}_p^o,\\hat{\\mathbf{H}}^\\circ)\\). To locate occlusion area, the intuition is that the heatmap inferred by historical motion is robust to the occlusion on appearance. Meanwhile, the heatmap predicted based on appearance can accurately locate the planar objects in the current frame. As a result, we indicate the area of occlusion as" + }, + { + "type": "equation", + "bbox": [ + 0.12, + 0.69, + 0.468, + 0.725 + ], + "angle": 0, + "content": "\\[\n\\phi^ {o} = \\frac {1}{\\sum_ {i} \\delta_ {i}} \\sum_ {i} \\delta_ {i} \\cdot \\| w a r p \\left(\\widehat {M} _ {p} ^ {i}, \\hat {\\mathbf {H}} ^ {\\mathbf {i}}\\right) - M ^ {o} \\|, \\tag {5}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.728, + 0.468, + 0.759 + ], + "angle": 0, + "content": "where \\( \\| \\cdot \\| \\) is the distance function computed per pixel and \\( \\delta_{i} \\) judges the mask confidence of \\( i^{\\mathrm{th}} \\) planar object." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.76, + 0.468, + 0.902 + ], + "angle": 0, + "content": "Motion Reasoning Network. For reasoning the visible and invisible parts of planar objects, we leverage the occlusion indicator \\(\\phi^o\\) as guidance, where the features \\(f_{T + 1}^{o}\\) from the current frame are refined, together with the warped feature \\(warp(f_T^o,\\hat{\\mathbf{H}}^\\mathrm{o})\\) from the previous frame. We denote these two features as \\(f_{a}\\) and \\(f_{m}\\), respectively. The features are first flattened alongside spatial dimension \\(f_{a},f_{m}\\in \\mathbb{R}^{c_{d}\\times HW}\\). Then, we develop a multi-head self-attention (MHSA) mechanism [31] for extracting occlusion-aware features. For learning joint representation and encouraging" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.092, + 0.892, + 0.119 + ], + "angle": 0, + "content": "the interactions between appearance and motion, we feed both features into MHSA as" + }, + { + "type": "equation", + "bbox": [ + 0.575, + 0.12, + 0.892, + 0.191 + ], + "angle": 0, + "content": "\\[\n\\left\\{ \\begin{array}{l} X = \\operatorname {C o n c a t} \\left(h _ {1}, \\dots , h _ {H}\\right) \\\\ h _ {i} = a _ {i} f \\mathbf {W} _ {\\mathbf {i}} ^ {\\mathbf {V}} \\\\ a _ {i} = \\operatorname {s o f t m a x} \\left(\\frac {\\left[ f \\mathbf {W} _ {\\mathbf {i}} ^ {\\mathbf {Q}} \\right] \\left[ f \\mathbf {W} _ {\\mathbf {i}} ^ {\\mathbf {K}} \\right] ^ {\\top}}{\\sqrt {d _ {k}}}\\right), \\\\ f = \\operatorname {C o n c a t} \\left(f _ {m}, f _ {a}\\right) \\end{array} \\right. \\tag {6}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.195, + 0.892, + 0.256 + ], + "angle": 0, + "content": "where \\(\\mathbf{W}_{\\mathbf{i}}^{\\mathbf{Q}}, \\mathbf{W}_{\\mathbf{i}}^{\\mathbf{K}}\\), and \\(\\mathbf{W}_{\\mathbf{i}}^{\\mathbf{V}}\\) are the matrixes. We then adopt MLP to extract representations for motion feature \\(X_{m}\\) and appearance feature \\(X_{a}\\), respectively. For assembling, we integrate both features guided by indicator \\(\\phi^{o}\\)" + }, + { + "type": "equation", + "bbox": [ + 0.599, + 0.257, + 0.892, + 0.273 + ], + "angle": 0, + "content": "\\[\nF _ {o c c} = \\mathcal {F} _ {e n s} \\left(\\mathcal {F} _ {\\phi} \\left(X _ {a}\\right), X _ {m}\\right), \\tag {7}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.274, + 0.892, + 0.366 + ], + "angle": 0, + "content": "where \\(\\mathcal{F}_{\\text{ens}}\\) and \\(\\mathcal{F}_{\\phi}\\) are \\(1 \\times 1\\) convolution layer, \\(\\mathcal{F}_{\\phi}\\) concatenates the occlusion indicator with input feature as guidance. Finally, given the mask and vertex heatmaps of the \\(o^{th}\\) occluded planar object, we feed the features into the dual-branch network used in the stage of appearance perception again and obtain the refined vertexes \\(\\widehat{P}^o\\) and mask \\(\\widehat{M}^o\\)." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.38, + 0.624, + 0.397 + ], + "angle": 0, + "content": "5. Experiment" + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.404, + 0.684, + 0.419 + ], + "angle": 0, + "content": "5.1. Evaluation Metrics" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.428, + 0.892, + 0.578 + ], + "angle": 0, + "content": "To evaluate methods on MPOT, following [15], we utilize the CLEAR metric [58] to complement the POT metrics. Note that existing POT metrics estimate the difference between ground truth and prediction in a pairwise manner (i.e., 1-box to 1-box). But it is not suitable for MPOT, since the number of predictions and ground truths are not always equal. Therefore, we match the set of ground truth \\(GT_{t}\\) and prediction \\(P_{t}\\) by bipartite matching [33]. Sequentially, we compute the difference of the matched pair by well-known POT distance Alignment Error [43,45,70] as" + }, + { + "type": "equation", + "bbox": [ + 0.577, + 0.578, + 0.891, + 0.617 + ], + "angle": 0, + "content": "\\[\nE _ {A L} (\\mathbf {p}, \\mathbf {g}) = \\sqrt {\\frac {\\sum_ {\\mathbf {j} = 1} ^ {4} \\left(\\mathbf {p} _ {\\mathbf {j}} - \\mathbf {g} _ {\\mathbf {j}}\\right) ^ {2}}{4}}, \\tag {8}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.617, + 0.892, + 0.691 + ], + "angle": 0, + "content": "where \\(\\mathbf{p}\\) and \\(\\mathbf{g}\\) are the quadrangle of the prediction and ground truth. Then, the prediction and ground truth are split into tracked \\(T_{\\epsilon}^{t}\\), true positive \\(TP_{\\epsilon}^{t}\\), false negative \\(FN_{\\epsilon}^{t}\\), and false positive \\(FP_{\\epsilon}^{t}\\), according to distance \\(\\epsilon\\). We set \\(\\epsilon\\) as 50 in our experiment due to the degree of challenge." + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.692, + 0.892, + 0.767 + ], + "angle": 0, + "content": "In POT, Precision \\((Pr_{\\epsilon})\\) is the commonly used metric based on the alignment error [43]. To complement the metrics, we report Recall \\((Rc_{\\epsilon})\\) to consider the cases of not being tracked. Furthermore, we propose Multiple Planar Object Tracking Distance \\((D_{\\epsilon})\\) as" + }, + { + "type": "equation", + "bbox": [ + 0.56, + 0.767, + 0.891, + 0.806 + ], + "angle": 0, + "content": "\\[\nD _ {\\epsilon} = \\frac {\\sum_ {t = 1} ^ {T} \\sum_ {t p \\in T P _ {\\epsilon} ^ {t} , q \\in T _ {\\epsilon} ^ {t}} E _ {A L} (t p , q)}{\\sum_ {t = 1} ^ {T} | T P _ {\\epsilon} ^ {t} |}. \\tag {9}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.5, + 0.805, + 0.89, + 0.834 + ], + "angle": 0, + "content": "Naturally, we propose the Multiple Planar Object Tracking Accuracy \\((Acc_{\\epsilon})\\) based on \\(E_{AL}\\) as." + }, + { + "type": "equation", + "bbox": [ + 0.518, + 0.834, + 0.891, + 0.871 + ], + "angle": 0, + "content": "\\[\nA c c _ {\\epsilon} = 1 - \\frac {\\sum_ {t = 1} ^ {T} \\left| F N _ {\\epsilon} ^ {t} \\right| + \\left| F P _ {\\epsilon} ^ {t} \\right| + \\left| I D S W _ {\\epsilon} ^ {t} \\right|}{3 \\cdot \\sum_ {t = 1} ^ {T} \\left| G T _ {t} \\right|}, \\tag {10}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.871, + 0.892, + 0.902 + ], + "angle": 0, + "content": "where \\( IDSW_{\\epsilon}^{t} \\) is the set of the identity switch [58] under the threshold \\( \\epsilon \\) in \\( \\mathbf{t}^{th} \\) frame, and \\( |\\cdot| \\) indicates the mod oper-" + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.518, + 0.957 + ], + "angle": 0, + "content": "23465" + } + ], + [ + { + "type": "table_caption", + "bbox": [ + 0.077, + 0.067, + 0.892, + 0.108 + ], + "angle": 0, + "content": "Table 3: Comparison of two groups of methods on MPOT-3K. The results on five metrics including Success Rate, Multiple Planar Object Tracking Accuracy, Multiple Planar Object Tracking Distance, Precision, Recall, and Speed are reported. \\(\\uparrow (\\downarrow)\\) denotes that the higher (lower) the score, the method performs better. Bold and underline indicate the highest and second-highest performance, respectively." + }, + { + "type": "table", + "bbox": [ + 0.081, + 0.11, + 0.894, + 0.419 + ], + "angle": 0, + "content": "
MethodsTraditionalDeepOurs
Motion PatternsMetricsCMT [61]NCC [71]CCRE [76]MI [17]GOP [8]Gracker [79]STM [62]PoST [60]LISRD [64]SMask [78]SRPN+ [38]SPoint [16]SOS [73]GIFT [53]HDN [95]
Overall\\( S_{0.8} \\uparrow \\)09.5000.1909.9926.7056.0367.9209.0733.5263.4364.0467.2371.8272.9175.8676.4082.51
\\( Acc_{\\epsilon} \\uparrow \\)64.2761.9534.3437.8262.2888.3852.0539.5572.3973.2975.3771.1770.0672.9979.5094.59
\\( Pr_{\\epsilon} \\uparrow \\)37.0503.6414.1223.5745.2585.6725.6425.0256.2358.3860.7054.5853.2356.4165.2192.85
\\( Rc_{\\epsilon} \\uparrow \\)10.2400.5519.0838.6062.7278.2523.0740.7480.4069.5574.4581.2585.3784.0282.5690.78
\\( D_{\\epsilon} \\downarrow \\)12.3042.1517.2708.6806.3705.2318.7922.7106.9317.0616.7707.6707.7607.8007.4405.07
Moving Occlusion\\( S_{0.8} \\uparrow \\)11.3400.0010.6926.4755.8563.6808.7818.1773.7963.2970.6270.9173.4272.9274.9680.29
\\( Acc_{\\epsilon} \\uparrow \\)67.2562.7856.2168.1081.4192.9355.4948.0491.7481.4683.2789.9292.2889.7488.7493.16
\\( Pr_{\\epsilon} \\uparrow \\)53.484.9233.5651.8270.0576.3029.6325.4586.3774.5775.9484.7384.3584.2182.0090.95
\\( Rc_{\\epsilon} \\uparrow \\)13.4700.6432.0161.5777.3081.9824.3728.9880.7067.6272.9785.3985.0385.5084.8688.27
\\( D_{\\epsilon} \\downarrow \\)06.3142.1421.2908.7904.1307.9216.5427.2606.4115.5714.2906.0606.1706.0506.2405.34
Moving Objects\\( S_{0.8} \\uparrow \\)09.3400.6911.2324.2952.2161.5808.0935.5267.7962.9565.4965.5070.3667.0270.0979.12
\\( Acc_{\\epsilon} \\uparrow \\)69.2263.8640.7847.4168.9692.5453.7741.9676.8880.3382.7278.4469.2978.5981.0594.29
\\( Pr_{\\epsilon} \\uparrow \\)60.2817.1019.2432.5752.5090.4828.3327.1360.8768.6272.0967.7552.4167.9767.1892.27
\\( Rc_{\\epsilon} \\uparrow \\)22.872.1924.2753.9572.5156.7725.2843.9687.7375.7579.2267.6686.0967.7984.4390.44
\\( D_{\\epsilon} \\downarrow \\)12.7143.2117.6606.8505.7104.1121.7719.9305.1514.9215.4804.2104.5304.1605.6305.46
Camera Occlusion\\( S_{0.8} \\uparrow \\)14.6100.0013.3141.7963.5966.4113.8040.2185.4662.4659.4088.8588.2889.4384.0192.46
\\( Acc_{\\epsilon} \\uparrow \\)63.5461.9334.2840.2861.7287.9851.7237.1574.0661.6668.7172.1871.9072.1084.5195.85
\\( Pr_{\\epsilon} \\uparrow \\)36.8900.3818.4227.8445.0488.2424.5925.3156.7644.8352.3154.6754.4254.6073.1695.84
\\( Rc_{\\epsilon} \\uparrow \\)13.1900.0628.3249.7467.3873.7521.7045.3784.3264.8670.7587.5787.1587.5084.5291.53
\\( D_{\\epsilon} \\downarrow \\)10.3129.3820.1007.7106.7304.6325.0520.0804.8214.4614.4504.8104.6204.7305.1804.59
Speed↑00.5801.9800.3101.2501.0003.1435.4411.9008.6331.5210.8709.3212.5126.6216.3712.64
" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.437, + 0.471, + 0.467 + ], + "angle": 0, + "content": "ation. To fairly compare along with the trajectory level, we adopt the success rate \\((S_{\\alpha})\\) with the distance threshold \\(\\alpha\\) as" + }, + { + "type": "equation", + "bbox": [ + 0.113, + 0.478, + 0.469, + 0.517 + ], + "angle": 0, + "content": "\\[\nS _ {\\alpha} = \\frac {| \\mathbb {C} |}{| \\mathbb {I} |}, \\mathbb {C} = \\left\\{i _ {n} \\in \\mathbb {I} \\right| \\frac {\\sum_ {t = 1} ^ {T} \\left| T _ {\\epsilon} ^ {t} \\right|}{\\sum_ {t = 1} ^ {T} \\left| G T _ {t} \\right|} > \\alpha \\}, \\tag {11}\n\\]" + }, + { + "type": "text", + "bbox": [ + 0.078, + 0.521, + 0.391, + 0.536 + ], + "angle": 0, + "content": "where \\(\\mathbb{I}\\) is the set of planar objects in the video." + }, + { + "type": "title", + "bbox": [ + 0.078, + 0.546, + 0.295, + 0.561 + ], + "angle": 0, + "content": "5.2. Implementation Details" + }, + { + "type": "text", + "bbox": [ + 0.077, + 0.57, + 0.47, + 0.901 + ], + "angle": 0, + "content": "We compare our model with fifteen representative methods. These methods are implemented by official code or open-source libraries [6, 72]. We run evaluated single object trackers multiple times for different planar objects. And we equip them with the data association strategy based on [12], for integrating each single object tracker into tracking multiple targets online. Besides, we additionally give the reference frames of ground truth if the single object trackers fail to track. Different from other box-based trackers, mask-based trackers (e.g., STM) directly outputs the mask. Thus, we use a rotated box estimator [88] to transfer the mask. We implement PRTrack using two RTX3090 GPUs. In the training stage, we use data augmentations, including flip, pepper noise, rotation, contrast jittering, and perspective transformation. We adopt a data sampling strategy following [41]. We adopt Smooth L1 loss and Cross-Entropy loss for optimizing the predicted vertex heatmaps and masks. Similar to [62], we pretrain SPB on YouTubeVOS [89] and DAVIS [66] datasets. During inference, we use the ordered vertexes to build the planar objects and estimate the homography matrix. We set the threshold as 0.9 in the reuse gate by grid search and set \\( r \\) in Equ. 2 as 0 during inference." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.436, + 0.702, + 0.451 + ], + "angle": 0, + "content": "5.3. Results on MPOT-3K" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.461, + 0.892, + 0.551 + ], + "angle": 0, + "content": "We compare our PRTrack with the other fifteen trackers on MPOT-3K, which contains six traditional POT trackers, four deep-based generic object trackers, and five deep-based planar object trackers. Tab. 3 reports the overall performance as well as the one in the challenging situations of moving occlusion, moving objects, and camera occlusion." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.553, + 0.892, + 0.779 + ], + "angle": 0, + "content": "Deep vs. Traditional Trackers. We can observe that the deep-based trackers have increased by \\(82.6\\%\\) on average, on five metrics for overall performance. This is because deep-based trackers avoid taking some assumptions under the laboratory environment, such as the invariance to illumination and appearance change. Note that Gracker performs best in traditional trackers and achieves competitive performance with the deep-based tracker group. However, since MPOT-3K has many small planar objects, it can not extract sufficient information, thus resulting in suboptimal performance (i.e., \\(10.3\\%\\) degradation in comparison with ours). In terms of deep-based trackers, STM predicts segmentation masks at the pixel level while ignoring the order of vertexes. Thus, it results in inferior performance, where only \\(9.0\\%\\) of targets are correctly tracked." + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.78, + 0.892, + 0.901 + ], + "angle": 0, + "content": "Planar Object Trackers vs. Generic Object Trackers. Planar object trackers achieve higher performance (58.9% improvement) against generic object trackers, including SRPN+, SMask, STM, and PoST. A predominant reason is that the generic trackers are subject to the assumption of affine transformation, where only the coarse box estimation is required. Therefore, a powerful planar object tracker should be developed in this field." + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.946, + 0.52, + 0.957 + ], + "angle": 0, + "content": "23466" + } + ], + [ + { + "type": "image", + "bbox": [ + 0.08, + 0.058, + 0.272, + 0.184 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.14, + 0.185, + 0.212, + 0.197 + ], + "angle": 0, + "content": "(a) POT210" + }, + { + "type": "image", + "bbox": [ + 0.274, + 0.058, + 0.47, + 0.185 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.335, + 0.185, + 0.409, + 0.197 + ], + "angle": 0, + "content": "(b) POT280" + }, + { + "type": "image", + "bbox": [ + 0.147, + 0.186, + 0.395, + 0.308 + ], + "angle": 0, + "content": null + }, + { + "type": "image_caption", + "bbox": [ + 0.221, + 0.31, + 0.36, + 0.323 + ], + "angle": 0, + "content": "(c) Challenging factors" + }, + { + "type": "image_caption", + "bbox": [ + 0.076, + 0.324, + 0.471, + 0.378 + ], + "angle": 0, + "content": "Figure 6: Comparison on POT210 and POT280. The averaged Precision on two datasets with different thresholds are reported in (a) and (b), respectively. (c) further shows the performance under seven challenging factors. The data is extracted from [95]." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.394, + 0.47, + 0.501 + ], + "angle": 0, + "content": "PRTrack vs. SOTA Trackers. PRTrack outperforms other methods with an average improvement of \\(6.4\\%\\). We also observe a large gain when there exists relative movement among multiple targets. To be specific, when facing challenging situations like moving objects, moving occlusion, and camera occlusion, PRTrack achieves a performance gain of \\(16.9\\%\\) against other advanced algorithms." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.51, + 0.364, + 0.525 + ], + "angle": 0, + "content": "5.4. Results on POT210 and POT280" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.534, + 0.47, + 0.73 + ], + "angle": 0, + "content": "To verify the effectiveness of PRTrack on the traditional POT task, we conduct experiments on the POT210 and POT280 datasets, and compare PRTrack with eleven POT methods as shown in Fig. 6. Note that we do not fine-tune PRTrack on these two datasets, again verifying the generalization ability of PRTrack towards unseen scenes. Following [95], the averaged Precision is employed to evaluate all the methods. As the distance threshold \\( E_{AL} \\) increases, the precision tends to be stable when \\( E_{AL} > 10 \\). We notice that PRTrack achieves competitive performance in comparison with advanced algorithms. Besides, PRTrack shows its superiority when handling challenging cases such as occlusion and motion blur." + }, + { + "type": "title", + "bbox": [ + 0.077, + 0.741, + 0.231, + 0.758 + ], + "angle": 0, + "content": "5.5. Ablation Study" + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.764, + 0.469, + 0.854 + ], + "angle": 0, + "content": "We conduct ablation studies on MPOT-3K in Tab. 4 to explore the effectiveness of each component in PRTrack. Our baseline is the appearance perception module, without shifted encoder and auxiliary mask. For simplicity, we use \"i&j\" to denote the comparison between the \\( i^{\\text{th}} \\) line and the \\( j^{\\text{th}} \\) line in the rest of this subsection." + }, + { + "type": "text", + "bbox": [ + 0.076, + 0.856, + 0.47, + 0.902 + ], + "angle": 0, + "content": "We first perform module-wise ablation studies in the highlighted lines, we observe that PRTrack obtains the largest performance gain of \\(11.6\\%\\) (i.e., \\(3 \\& 9\\) and \\(4 \\& 10\\))" + }, + { + "type": "text", + "bbox": [ + 0.499, + 0.059, + 0.892, + 0.178 + ], + "angle": 0, + "content": "Table 4: Ablation study of components and their variants of PRTrack on the validation split of MPOT-3K. The lines with background indicate the module-level ablation study. Here AP, OR, and RT are short of appearance perception, occlusion reasoning, and memory pool. SE and Fac denote the shifted encoder and factorized homography matrix. Msk represents the plane structure branch with mask information. Here, \\(*\\), \\(\\bullet\\), and \\(\\diamond\\) are the fusion strategy (Fus), representing concatenation, attention-based, and indicator-based. Gat indicates the reuse gate." + }, + { + "type": "table", + "bbox": [ + 0.504, + 0.179, + 0.89, + 0.322 + ], + "angle": 0, + "content": "
IdAPORRTMetrics
SEMskFacFusGat\\( S_{0.8} \\)↑\\( Acc_{\\epsilon} \\)↑\\( Pr \\)↑\\( Rc \\)↑\\( D_{\\epsilon} \\)↓
①✓45.2968.0146.7546.7119.56
②✓✓63.7686.8282.3676.9615.40
③✓✓75.8291.0886.2282.9612.57
④✓✓✓78.2091.4387.1986.4209.95
⑤✓✓✓✓*✓77.5391.4690.4186.2510.43
⑥✓✓✓✓•✓78.9991.4188.0785.8709.12
⑦✓✓✓◇✓79.2491.5088.1086.1308.95
⑧✓✓✓◇✓76.3890.5688.5882.3410.59
⑨✓✓✓✓◇80.4492.4889.6787.5407.38
⑩✓✓✓✓◇✓80.5892.7590.0088.0306.39
" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.342, + 0.892, + 0.614 + ], + "angle": 0, + "content": "with the occlusion reasoning module. Then we investigate the variants of each module. For appearance perception, we study how to leverage the order of vertexes. The boosting of \\(16.3\\%\\) (i.e., \\(2 \\& 3\\) and \\(8 \\& 10\\)) verifies that the proposed encoder avoids learning position bias, where the first vertex commonly comes from the top-left area. For occlusion reasoning, we find the solution to unify the appearance feature and motion feature. We first conduct experiments on alternative solutions of fusion (i.e., \\(5 \\& 6 \\& 10\\)), where our strategy achieves the best performance. Because the occlusion indicator provides the change of image against occlusion and joint embedding helps to introduce interaction between features. We also identify the effectiveness of homography factorization via the comparison of \\(7 \\& 10\\), with an average boosting of \\(7.2\\%\\). For memory pool, we investigate the accumulated error. With a gain of \\(4.4\\%\\) (i.e., \\(3 \\& 4\\) and \\(9 \\& 10\\)), we believe the proposed reuse gate can avoid the error derived from restoring the predictions." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.627, + 0.62, + 0.642 + ], + "angle": 0, + "content": "6. Conclusion" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.652, + 0.892, + 0.773 + ], + "angle": 0, + "content": "In this paper, we propose a novel method for tracking multiple planar objects simultaneously. We also build the first large-scale benchmark dataset MPOT-3K which contains sufficient data, is labeled by experienced annotators, and covers various scenes. Extensive experiments are conducted on both MPOT3K and the other two single planar object tracking datasets. The results demonstrate that PRTrack achieves SOTA performance on both tasks." + }, + { + "type": "title", + "bbox": [ + 0.5, + 0.785, + 0.68, + 0.803 + ], + "angle": 0, + "content": "7. Acknowledgments" + }, + { + "type": "text", + "bbox": [ + 0.498, + 0.81, + 0.892, + 0.901 + ], + "angle": 0, + "content": "This work was supported by the National Key Research and Development Program of China Grant (NO. 2018AAA0100400), Natural Science Foundation of Tianjin, China (NO.20JCJQJC00020), Fundamental Research Funds for the Central Universities, and Supercomputing Center of Nankai University (NKSC)." + }, + { + "type": "page_number", + "bbox": [ + 0.479, + 0.945, + 0.521, + 0.958 + ], + "angle": 0, + "content": "23467" + } + ], + [ + { + "type": "title", + "bbox": [ + 0.08, + 0.09, + 0.174, + 0.106 + ], + "angle": 0, + "content": "References" + }, + { + "type": "ref_text", + "bbox": [ + 0.096, + 0.117, + 0.468, + 0.158 + ], + "angle": 0, + "content": "[1] Mark Ashdown, Matthew Flagg, Rahul Sukthankar, and James M Rehg. A flexible projector-camera system for multi-planar displays. 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In ISMAR, 2010." + }, + { + "type": "list", + "bbox": [ + 0.504, + 0.093, + 0.892, + 0.732 + ], + "angle": 0, + "content": null + }, + { + "type": "page_number", + "bbox": [ + 0.48, + 0.945, + 0.52, + 0.957 + ], + "angle": 0, + "content": "23470" + } + ] +] \ No newline at end of file diff --git a/2023/Multiple Planar Object Tracking/16e4462f-086b-4e2c-b3e1-1c3bf9449c10_origin.pdf b/2023/Multiple Planar Object Tracking/16e4462f-086b-4e2c-b3e1-1c3bf9449c10_origin.pdf new file mode 100644 index 0000000000000000000000000000000000000000..f2e86837e5ecc7d2fc25e99006778fa49cc487e0 --- /dev/null +++ b/2023/Multiple Planar Object Tracking/16e4462f-086b-4e2c-b3e1-1c3bf9449c10_origin.pdf @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:b1c20f9794bcd53eef2b88872f2bbcd1dbde865f18ae4c7d0b98bc51e8af7e78 +size 2276296 diff --git a/2023/Multiple Planar Object Tracking/full.md b/2023/Multiple Planar Object Tracking/full.md new file mode 100644 index 0000000000000000000000000000000000000000..3f75bdddd4e90a0b3667f4c1a2c196a2a08daf50 --- /dev/null +++ b/2023/Multiple Planar Object Tracking/full.md @@ -0,0 +1,406 @@ +# Multiple Planar Object Tracking + +https://zzcheng.top/MPOT + +Zhicheng Zhang + +Shengzhe Liu + +Jufeng Yang† + +VCIP & TMCC & DISSec, College of Computer Science, Nankai University + +gloryzzc6@sina.com, nkuliusz@163.com, yangjufeng@nankai.edu.cn + +# Abstract + +Tracking both location and pose of multiple planar objects (MPOT) is of great significance to numerous real-world applications. The greater degree-of-freedom of planar objects compared with common objects makes MPOT far more challenging than well-studied object tracking, especially when occlusion occurs. To address this challenging task, we are inspired by amodal perception that humans jointly track visible and invisible parts of the target, and propose a tracking framework that unifies appearance perception and occlusion reasoning. Specifically, we present a dual-branch network to track the visible part of planar objects, including vertexes and mask. Then, we develop an occlusion area localization strategy to infer the invisible part, i.e., the occluded region, followed by a two-stream attention network finally refining the prediction. To alleviate the lack of data in this field, we build the first large-scale benchmark dataset, namely MPOT-3K. It consists of 3,717 planar objects from 356 videos and contains 148,896 frames together with 687,417 annotations. The collected planar objects have 9 motion patterns and the videos are shot in 6 types of indoor and outdoor scenes. Extensive experiments demonstrate the superiority of our proposed method on the newly developed MPOT-3K as well as other two popular single planar object tracking datasets. The code and MPOT-3K dataset are released on https://zzcheng.top/MPOT. + +# 1. Introduction + +Tracking multiple planar objects (MPOT) is a fundamental task in computer vision. It aims to explore the motion of planar objects, tracking both the location and pose of multiple targets simultaneously [40, 43, 56]. The planar object is defined as a plane belonging to a specific body [28] (e.g., box, building, or wall) in the form of four ordered vertexes [43, 70]. With the help of MPOT, we can track targets when multiple planar objects exist, e.g., different sur + +![](images/937ced3cf9890481264f97a330ac56486cc9f006caeb167f6227e85b45eee099.jpg) +(a) Image of $i^{\text{th}}$ frame + +![](images/6dbf3139bc53ec5ea02371cb4bd4c3cdda8d2e657920bf2102baf2f596be77e4.jpg) +POT VOS (DoF=8) (N/A) + +![](images/39f3c876b2c000cf2dff47ea00a2adb203aaa322e50ec0fa3a456176a6252bc7.jpg) +POT + +![](images/e781c25bb121d586812d666d028f0d5dd3e69488adc42c6dd2db2aadec017763.jpg) +VOS + +![](images/5af2e1c0ced27f87b7ad4bc621e418974039a43526de1ce5cda6b1e0d94b0824.jpg) +(b) Different tracking tasks +VOT/RVOT +(c) Tracking $\mathbf{j}^{\mathrm{th}}$ frame +Figure 1: Comparison with other vision tasks. Given an image (a), we present the ground truth for different tasks in (b). The corresponding Degree-of-Freedom (DoF) is reported at the bottom and the details are listed on the right side of each task. In (c), we show the tracking results for box-based tasks (e.g., VOT, RVOT), mask-based tasks (e.g., VOS), and POT, which can find the occluded regions (marked by the red line area) and provide pixel-to-pixel matching correspondence (colored points across frames). + +faces of an object [1] or planes from various objects [27]. It has attracted more and more attention attributed to various applications in augmented reality [57, 104], video editing [4, 20, 30], and robot navigation [92]. + +MPOT is closely related to well-known computer vision tasks in RGB tracking [32] (see Tab. 1). Both tasks involve tracking the target across subsequent frames of a video using the ground truth provided in the initial frame. However, it is more challenging in two aspects. 1) Tracking planar objects is of greater Degree-of-Freedom (DoF). As shown in Fig. 1(b), MPOT tracks both the pose and location of the target, which is described by an arbitrary quadrangle (i.e., four independent vertexes $(x_{1},y_{1},x_{2},y_{2},x_{3},y_{3},x_{4},y_{4})$ , whose DoF is 8 [44]). In contrast, it only needs to predict the position and size of an object $(x,y,w,h)$ in video object tracking (VOT), and Rotated VOT (RVOT) additionally requires the rotation angle. Even compared with video object + +Table 1: The comparison of MPOT with other video-related tasks. We compare MPOT with five RGB tracking tasks and four tasks with auxiliary modality information. The count of DoF comes from [44]. + +
ModalityTaskObjectScenario
Object categoryObject selectionMultiple objectsPixel correspondenceDoFOcclusion
RGBMOT [83]Limited, usually pedestrians or vehiclesDetectedYN4Y
MOTS [75]Limited, usually pedestrians or vehiclesDetectedYNN/AN
VOS [66]ArbitraryUser-specified in the first frameNNN/AN
VOT [21]ArbitraryUser-specified in the first frameNN4Y
RVOT [32]ArbitraryUser-specified in the first frameNN5Y
MPOTArbitraryUser-specified in the first frameYY8Y
RGB+DepthRGBDT [91]ArbitraryUser-specified in the first frameYN4Y
6DOP [50]Limited by training setDetectedYY6Y
6DPT [81]ArbitraryUser-specified in the first frameNY6Y
RGB+LIDAR3dOD [35]Limited by training setDetectedYN7Y
3dMOT [84]Limited, usually vehiclesDetectedYN7Y
+ +segmentation (VOS), an alternative that introduces masks at the pixel level, MPOT is a more challenging task. Because MPOT provides the matched correspondence for each pixel within the object region across frames [60] (e.g., colored points in Fig. 1(a)&(c)), which makes it possible for applications that require positional information like texture mapping [24]. Nevertheless, VOS that tracks the target area instead of per-pixel location can hardly achieve it. 2) Occlusion is another challenge that comes with MPOT. Not only the one in POT that manually occludes the camera, MPOT but introduces the occlusion raised by the layered position of multiple targets relative to the camera [77, 96] (see Fig. 1(c)). Besides, the occlusion is more complex than the ones in multiple object tracking (MOT). As discussed above, when occlusion occurs, MPOT estimates the pixel correspondence controlled by homography matrix $\mathbf{H}$ [3], which tends to be sensitive and have a high condition number that can reach up to $5\mathrm{e}^7$ [95]. This means that a tiny movement of the invisible part is extremely difficult to track. + +To address the aforementioned limitations, our work draws the inspiration that humans consolidate the visible together with invisible parts of the target for tracking [96]. We propose a tracking framework comprised of procedures for appearance Perception and occlusion Reasoning, namely PRTrack. To track high DoF planar objects, we reformulate the problem of estimating homography matrix $\mathbf{H}$ as predicting the mask and ordered vertexes for each planar object. With the high-dimensional mask, we can accurately locate the target area at the pixel level. Besides, the ordered vertexes provide per-pixel correspondence across frames for tracking the pose of planar objects. Therefore, in the stage of appearance perception, we propose a dual branch network to predict the ordered vertexes and masks of planar objects based on the historical visible information. For vertexes, we design an encoder with shifted sampling strategy based on the constraint that the vertexes always have a clockwise order. For mask, we aggregate the probability of multiple planar objects with a multi-layered layout, that is, a stack of occluders and occludees. Further, to solve the cases of complex occlusion, we develop an occlusion area + +localization strategy to indicate the occluded part, by storing the movement of each planar object (i.e., historical H). To be specific, we factorize the sensitive homography matrix, which describes the relative movement of planar objects, into parameters of transition, rotation, and pose. Finally, with the prediction from the mentioned stages, we propose a two-stream self-attention network to jointly refine the predicted planar objects. + +Besides, since there is no available dataset in this field, we build a large-scale benchmark dataset, namely MPOT-3K. Specifically, we shoot 356 videos with 3,717 planar objects and 687,417 annotations. The videos are collected under 9 motion patterns, where the relative movement and occlusion are also included to simulate the real-world scene. + +The contributions of this paper are two-fold: 1) We collect and annotate the first large-scale benchmark dataset for MPOT, where planar objects are diversely collected expelling bias. Our dataset will be released and boost research in this field. 2) We propose a tracking framework with unified motion and appearance models, which can accurately predict the pose and location of planar objects. Extensive experiments demonstrate the superiority of PRTrack against state-of-the-art approaches. + +# 2. Related Work + +# 2.1. Planar Object Tracking + +Benchmark Datasets. Current works focus on single planar object tracking and propose several POT datasets [19, 42, 43, 45, 70, 86]. Metaio [45] is the first dataset collected in the lab and the videos are collected by a monitored camera. Similarly, TMT [70] also shoots videos from the lab, where the annotations are automatically generated by aggregating the results of three planar object trackers. Due to the laboratory setting of the collection, videos in these datasets have similar backgrounds. Thus, POT210 [43] collects video data in the wild under seven motion patterns and encourages the diversity of the recorded videos with complex backgrounds. However, existing benchmarks are insufficient to mimic real-world settings where multiple targets exist. Therefore, our work extends the task into MPOT that + +Table 2: Statistics of tracking datasets. "I." and "O." indicate indoor and outdoor, respectively. "#" denotes "the number of". + +
BenchmarkUCSB [19]TMT [70]POIC [8]POT210 [43]POT280 [42]MOT16 [58]MPOT-3K
# Scenes112030401442
# Videos961002021028014356
# Targets96100202102801,2763,717
# Annotations7K-23K53K70K292K687K
Scene CategoryI.I.I.&O.I.&O.I.&O.O.I.&O.
Multiple ObjectsXXXXX✓✓
+ +simultaneously tracks multiple planar objects which can be applied in real-world applications like AR, robots, and art. + +Methods. POT trackers can be classified into region-based, keypoint-based, and hybrid methods. Region-based approaches [2, 3, 9, 17, 34, 68] focus on the whole planar region and estimate perspective transformation by closing up the template and the warped image. Keypoint-based methods [22, 61, 63, 79, 101] describe a planar object by the detected keypoints [54, 69] and associate objects across frames by computing the similarity between keypoints. As for hybrid methods, previous works [8, 9, 13, 94] exploit the robust feature descriptors for searching the optimal matching. A representative method [8] leverage gradient-based feature as criterion. As progress is made into the deep learning era [37, 82], CLKN [7] integrates deep features into the Lucas-Kanade algorithm for improving matching quality. + +# 2.2. Visual Tracking + +Single Object Tracking. It aims to locate and track a single target in a video [39, 48], which can be roughly grouped into box-based tracking [18, 55, 93] and mask-based tracking [41, 47, 60]. SiamFC [5] adopts the correlation layer to search the location which is described by the axis-aligned bounding box. Further, SiamMask [78] introduces rotation to describe the motion and predicts the object mask with the bounding box simultaneously. Meanwhile, mask-based tracking focuses on the accurate location of the targets. STM [62] addresses the problem of appearance change, leading to satisfactory results. Recently, PoST [60] explores the relationship between the mask and contour, building constraints for predicting the polygonal mask. + +Multiple Object Tracking. Existing works [14, 58] propose to track multiple objects of human interests simultaneously, with the assumption that all targets belong to a list of predefined classes [10, 11, 26, 36, 51, 90, 100, 102]. A large number of methods [49, 65, 80, 85, 99] are proposed to address the task. With the class assumption, they utilize object detectors to generate candidates in the manner of axis-aligned bounding boxes. Then the candidates are associated into trajectories. While both MPOT and MOT track multiple targets at the same time, the former faces more challenges since it handles arbitrary planar objects with greater DoF, as well as covers unrestricted classes [43]. + +![](images/4bfb2859ca249b52bf8987b5e034139656cf0d561cfdeae4dbaea60ff3875d2c.jpg) + +![](images/198514ab98c0952c1de7d52a76945f92f0eb79d1b479ca49cd1b22b12cd26979.jpg) +(a) Occurrence of occlusion in different scenes +(b) Statistics about occlusion +Figure 2: Statistics of occlusion in MPOT-3K. (a) shows the frequency of occlusion in six types of scenes, in which the number on the left indicates the number of planar objects being occluded and the one in shadow represents the corresponding proportion. (b) illustrates the number of occlusions per video as well as the temporal length per occlusion. + +# 3. The MPOT-3K Dataset + +MPOT is being less explored and limited by existing datasets designed to single planar object tracking. In this work, we construct the dataset MPOT-3K for introducing multiple targets. To the best of our knowledge, MPOT-3K is the first large-scale dataset for the challenging task of MPOT. This will help facilitate future research in computer vision (augmented reality, safety surveillance), robot (navigation, manipulation), and art (video editing). + +# 3.1. Data Collecting + +Initially, we shoot 840 videos involving the motion of static and moving planar objects. For the static planar objects, we design six motion patterns (i.e., far-near movement, in-plane rotation, out-plane rotation, in-plane movement, motion blur, camera occlusion) by controlling the movements of camera as common practices [43,86]. For the moving planar objects, we consider the occlusions and relative movements among multiple planar objects and design two motion patterns (i.e., moving objects, moving occlusion). Besides, an unconstrained motion pattern is considered to further combine the above motion patterns. According to [87, 103], we record diverse videos from six types of indoor and outdoor scenes, including library, house, gallery, building, street, and village. + +# 3.2. Data Annotation + +MPOT-3K is annotated by seven well-trained annotators. Following [43], we adopt a semi-automatic annotation scheme. First, the annotator labels one frame every five frames. Then, the annotated label is propagated to other unannotated frames by linear interpolation. Finally, the annotator corrects the propagated label. During annotation, we obey the following rules. First, we define what planar object is to be annotated according to [43, 70, 86]. The planar object should be easily presented by four ordered ver + +![](images/3687c26235d3385e5011cbe5f17ec943b4d63971cce5048f703996ee24f45a40.jpg) +Figure 3: The pipeline of our method. Our tracking framework is divided into three stages. First, in appearance perception, we track the visible part of multiple planar objects via a dual-branch network, as coarse output. For the next stage of occlusion reasoning, the occlusion area is localized and then fed into a two-stream self-attention network for refining the predicted target. Finally, the memory pool module restores the high-confident tracked targets. + +texas. To ensure that the criteria for selecting plane objects are consistent, we ask all the annotators to vote for filtering out inconsistent objects [52]. Second, we start annotating when the planar object is completely in view and end when the object has been fully occluded or out of view. Third, we annotate the spatial position of the planar object according to two principles: 1) We annotate the planar object which has four apparent lines, since the point is localized by inferring the intersection lines [67]. 2) We maintain the order of vertexes across video frames for pixel correspondence. Combining these principles, we can locate the planar object with four independent vertexes (i.e., a quadrangle). + +# 3.3. Statistics + +After collecting and labeling, we yield a large-scale dataset MPOT-3K, where we obtain 356 videos with 3,717 planar objects from 42 scenes. The number of planar objects per video averages 10.44 and can reach 74 at most. MPOT-3K is divided into training, validation, and test sets in a proportion of 80:5:15. The split is performed at the scene level to ensure there's no overlap among splits. Hence the dataset avoids leakage since both the target and scene of the test set are expelled during training. + +As shown in Tab. 2, we compare MPOT-3K with six datasets, which come from POT [8, 19, 42, 43, 70] and MOT [58] tasks. MPOT-3K contains over 9.8 times more annotations and 13.2 times more targets in all video frames than the largest POT dataset POT280. The number of targets is almost 3 times of the popular MOT16 dataset. Another strength of MPOT-3K lies in its diversity, which covers 9 motion patterns and 6 types of scenes. Besides, MPOT-3K introduces more complex occlusions. As shown in Fig. 2(a), we observe that occlusion occurs in all the scenes, where $39.9\%$ of planar objects are occluded on average. Fig. 2(b) further illustrates that there are 3.6 occlusions happening in a video on average and each occlusion lasts 9.56 seconds. + +# 4. Methodology + +PRTrack consists of three main components (See Fig. 3): memory pool module, appearance perception network, and occlusion reasoning network. The memory pool module (Sec. 4.2) restores the previous predictions and expels the low-confident targets. Guided by previously tracked targets, the appearance perception network (Sec. 4.3) predicts mask together with the vertexes for each planar object. The occlusion reasoning network (Sec. 4.4) further takes all the tracked targets and corresponding occlusion area, which is indicated by the difference between motion-guided results among multiple targets and the predicted one. + +# 4.1. Problem Reformulation + +Assume multiple planar objects exists in an RGB video where they are not from the training set, nor have detection results. Given the user-selected ones in the initial frame, the objective is to estimate their position change relative to the beginning, i.e., homography matrix, with which the pose change of targets can be obtained [56]. As shown in Fig. 4, we reformulate the tracking task as predicting the masks of the quadrangle $\widehat{\mathbf{M}} \in \mathbb{R}^{O \times hw}$ and the heatmap of four ordered vertexes $\widehat{\mathbf{P}} \in \mathbb{R}^{O \times 4hw}$ , where $O$ is the number of planar objects in the current frame. The layered masks represent the location of multiple planar objects [94] and the vertexes are used to track the pose of planar objects [56]. + +# 4.2. Memory Pool module + +From the viewpoint of human perception, one person tracks the targets by memorizing their historical appearance and trajectory [59]. Inspired by this, we leverage the images and predictions in previous T frames as guidance to track planar objects in the current one. For the previous frames, we record previously predicted heatmaps of ordered vertexes $\mathbf{P_o}\in \mathbb{R}^{T\times 4hw}$ , masks $\mathbf{M_o}\in \mathbb{R}^{T\times hw}$ , and the images $\mathbf{I_o}\in \mathbb{R}^{T\times 3hw}$ for the $o^{\mathrm{th}}$ planar object. The memory pool $\{(\mathbf{P_o},\mathbf{M_o},\mathbf{I_o})\}_{o = 1}^N$ stores the tracked N planar objects. + +![](images/a430a51542a63ca7707737f6e3b84bc6565d99b7f32507ae5540da803d8ca02d.jpg) +(a) Image + +![](images/1c13be2fd6d8e8afd1f1869c6d096779fff5968f623aa5577d16dbd9cecbd06d.jpg) +(b) Mask of each target + +![](images/061ed77e8996d5eab9f35e545e7a305d28db8d42f1df0fa684903c44021ca542.jpg) +(c) Vertexes of each target +Figure 4: Illustration of the reformulated form of MPOT. We predict heatmaps of four ordered vertexes and the mask for each planar object. The stacked masks are built in a layered structure and are responsible for the occluders and occludees. + +However, due to the challenge of accurately tracking multiple planar objects, the error accumulation [46] occurs because of memorizing incorrect predictions. To avoid this issue, we filter out the low-confident predictions. Given the current frame, PRTrack predicts the vertexes $\widehat{P}^o \in \mathbb{R}^{4hw}$ and mask $\widehat{M}^o \in \mathbb{R}^{hw}$ for the $o^{th}$ tracked planar object. We compute the confidence of the mask and vertexes as + +$$ +M _ {c o n f} = \min (\left\{\max \left(\widehat {M ^ {o}}\right) \right\} _ {o = 1} ^ {O}). \tag {1} +$$ + +$$ +P _ {c o n f} = \min (\{m a x (\widehat {P} ^ {o}) \} _ {o = 1} ^ {0}) +$$ + +The predictions with the confidences surpassing the threshold are restored in the memory pool module. The reuse gate is only applied during testing. + +# 4.3. Appearance Perception + +Our appearance perception network is built on top of the encoder-decoder architecture [62], with a backbone of ResNet50. For the current frame, we extract appearance feature $f_{cur} \in \mathbb{R}^{CHW}$ from an image, where $H, W, C$ denotes the width, height, and the number of channels of the feature. For previous frames, we extract features from vertexes, masks, and images, and sum the three features as $f_{pre} \in \mathbb{R}^{T \times CHW}$ . The current image feature and previous target features are fed into the encoder network to yield appearance features $f_{T+1}^o \in \mathbb{R}^{CHW}$ for $o^{\mathrm{th}}$ planar object. The plane structure branch and segmentation prior branch finally predict the coarse results of vertexes and masks. + +Vertex Encoder with Shifted Sampling Strategy. Considering the vertexes of the planar object provide the pixel correspondence across frames, each vertex is independent against others, thus they are organized in sequential order [47]. Therefore, we design an encoder with shifted sampling strategy to leverage the characteristic of vertexes (i.e., the clockwise order), as the feature extractor. As shown in Fig. 5, a random cyclic shift function $\text{shift}(\cdot, +r)$ is first applied to build the connection between the vertex heatmap $P_i \in \mathbb{R}^{HW}$ and its neighbors by shuffling position as + +$$ +\operatorname {shift}(P, + r) = \left[P_{(1 + r)\% L},\dots ,P_{(L + r)\% L}\right], \tag{2} +$$ + +where $L$ is the number of vertexes in the planar object and $r \in \{0,1,2,3\}$ is a random number. % is the mod operation. Then, we apply $7 \times 7$ convolutions [25] to extract the features of four ordered vertexes, separately. For modeling + +![](images/bfd0fd72b9ef268ea18e65f6c379c04604a5ce237fb70b354cf6eef85d7a2678.jpg) +Figure 5: Illustration of our proposed vertex encoder. Given the vertex heatmaps, we random sample them by a cyclic shift operation, following a clockwise order and with an offset of $r$ . Note that PSB, as a counterpart, predicts the vertexes via a cyclic shift function with negative $r$ . + +the order between four vertices, we introduce the cosine positional embedding [74] and add it to the vertex representation. The positional embedding $\pmb{f}_{emb} \in \mathbb{R}^{L \times N}$ contains the N-d embeddings corresponding to the order information for the features of L vertices. The feature of ordered vertices is then extracted by a $7 \times 7$ convolution to capture long-range spatial interaction between vertices. + +Plane Structure Branch (PSB). Given the shifted feature map of vertexes from the decoder, a $1 \times 1$ convolution is attached with the sigmoid function to output the heatmap of the vertexes. The shifted vertex heatmaps are then aligned with the shifted input in Equ. 2 by using the reversed cyclic shift operation $\text{shift}(\cdot, -r)$ . Finally, we get the heatmaps of $o^{\text{th}}$ planar object $P^{o} \in \mathbb{R}^{HW}$ by upsampling to the same resolution as the original image. + +Segmentation Prior Branch (SPB). The mask can accurately locate the planar object at the pixel level and capture the relative movement between objects such as occlusion [55,78]. Therefore, we utilize a $1 \times 1$ convolution with the softmax function alongside the foreground/background dimension. Following [62], The probability of background $m_{bkg}$ and each foreground object $m_o$ are obtained by aggregating the output of model logits $\in \mathbb{R}^{O \times HW}$ as + +$$ +m _ {o} = \frac {\exp \left(\operatorname {l o g i t s} _ {o}\right)}{\sum_ {i = 1} ^ {O} \exp \left(\operatorname {l o g i t s} _ {i}\right)}, \quad m _ {b k g} = \prod_ {i = 1} ^ {O} (1 - m _ {o}). \tag {3} +$$ + +Finally, the probability segmentation mask of $\sigma^{\mathrm{th}}$ planar object $M^{o} \in \mathbb{R}^{HW}$ are produced after softmax. The background probability map is attached in the last channel. + +# 4.4. Occlusion Reasoning + +With the above coarse output perceiving from the visible part, we move to the next stage of reasoning the occluded part by the motion of planar objects (i.e., homography). In multiple object tracking, reasoning the occlusion by motion has been verified effective [97, 98], where a motion strategy is adopted to predict the future location of the target based on the historical trajectory. Inspired by this, we first develop a homography-guided strategy that locates the occlusion area and correct features from previous frames geometrically. We factorize the homography matrix into motion parameters that describe the common transformations, to estimate the sensitive homography matrix (as discussed + +in Sec. 1). Then, for tracking both visible and invisible parts of planar objects, we design a two-stream self-attention network that takes both the appearance features of the current frame and the motion-guided features of the previous frame to refine the predicted planar object. + +Occlusion Area Localization Strategy. To avoid the sensitivity problem discussed in Sec. 1, we first introduce the geometric definition of homography matrix $\mathbf{H} \in \mathbb{R}^{3 \times 3}$ [23], and factorize it into similarity transformation $\mathbf{H}^{\mathrm{S}}$ and residual one $\mathbf{H}^{\Lambda}$ , with eight stable motion parameters of $h_p = (t_x, t_y, \gamma, \theta, k_1, k_2, v_1, v_2)$ as + +$$ +\mathbf {H} = \mathbf {H} ^ {\mathbf {S}} \mathbf {H} ^ {\boldsymbol {\Lambda}} = \left[ \begin{array}{c c c} \gamma \cos \theta & - \gamma \sin \theta & t _ {x} \\ \gamma \sin \theta & \gamma \cos \theta & t _ {y} \\ 0 & 0 & 1 \end{array} \right] \left[ \begin{array}{c c c} k _ {1} & k _ {2} & 0 \\ 0 & \frac {1}{k _ {1}} & 0 \\ v _ {1} & v _ {2} & 1 \end{array} \right], \tag {4} +$$ + +where $t_x, t_y$ are the transition offset, $\gamma$ and $\theta$ denote the change of scale and angle, and $k_1, k_2, v_1, v_2$ control the parameters of matrix $\mathbf{H}^{\Lambda}$ . Here, the motion parameters can be computed by solving a transcendental equation with eight variants. The location parameters can be written as $h_l = (x_1, y_1, x_2, y_2, x_3, y_3, x_4, y_4)$ . + +Specifically, the location parameters and homography are obtained from the coarse output of appearance perception, where we apply the Argmax function on heatmaps to get the coordinates of vertexes and compute the homography matrix between the coordinates from the current frame and the previous one. Then, the factorized homography $h_p$ and location parameters $h_l$ are fed into the Kalman Filter [29] and yield the corrected ones $\widehat{h}_p, \widehat{h}_l$ . Finally, homography matrix $\hat{\mathbf{H}}^{\mathrm{o}}$ for the $o^{\mathrm{th}}$ planar object in the current frame can be obtained. + +Given the predicted homography, the mask from previous frame $\widehat{M}_p^o$ can be warped [3] by the perspective transformation $warp(\widehat{M}_p^o,\hat{\mathbf{H}}^\circ)$ . To locate occlusion area, the intuition is that the heatmap inferred by historical motion is robust to the occlusion on appearance. Meanwhile, the heatmap predicted based on appearance can accurately locate the planar objects in the current frame. As a result, we indicate the area of occlusion as + +$$ +\phi^ {o} = \frac {1}{\sum_ {i} \delta_ {i}} \sum_ {i} \delta_ {i} \cdot \| w a r p \left(\widehat {M} _ {p} ^ {i}, \hat {\mathbf {H}} ^ {\mathbf {i}}\right) - M ^ {o} \|, \tag {5} +$$ + +where $\| \cdot \|$ is the distance function computed per pixel and $\delta_{i}$ judges the mask confidence of $i^{\mathrm{th}}$ planar object. + +Motion Reasoning Network. For reasoning the visible and invisible parts of planar objects, we leverage the occlusion indicator $\phi^o$ as guidance, where the features $f_{T + 1}^{o}$ from the current frame are refined, together with the warped feature $warp(f_T^o,\hat{\mathbf{H}}^\mathrm{o})$ from the previous frame. We denote these two features as $f_{a}$ and $f_{m}$ , respectively. The features are first flattened alongside spatial dimension $f_{a},f_{m}\in \mathbb{R}^{c_{d}\times HW}$ . Then, we develop a multi-head self-attention (MHSA) mechanism [31] for extracting occlusion-aware features. For learning joint representation and encouraging + +the interactions between appearance and motion, we feed both features into MHSA as + +$$ +\left\{ \begin{array}{l} X = \operatorname {C o n c a t} \left(h _ {1}, \dots , h _ {H}\right) \\ h _ {i} = a _ {i} f \mathbf {W} _ {\mathbf {i}} ^ {\mathbf {V}} \\ a _ {i} = \operatorname {s o f t m a x} \left(\frac {\left[ f \mathbf {W} _ {\mathbf {i}} ^ {\mathbf {Q}} \right] \left[ f \mathbf {W} _ {\mathbf {i}} ^ {\mathbf {K}} \right] ^ {\top}}{\sqrt {d _ {k}}}\right), \\ f = \operatorname {C o n c a t} \left(f _ {m}, f _ {a}\right) \end{array} \right. \tag {6} +$$ + +where $\mathbf{W}_{\mathbf{i}}^{\mathbf{Q}}, \mathbf{W}_{\mathbf{i}}^{\mathbf{K}}$ , and $\mathbf{W}_{\mathbf{i}}^{\mathbf{V}}$ are the matrixes. We then adopt MLP to extract representations for motion feature $X_{m}$ and appearance feature $X_{a}$ , respectively. For assembling, we integrate both features guided by indicator $\phi^{o}$ + +$$ +F _ {o c c} = \mathcal {F} _ {e n s} \left(\mathcal {F} _ {\phi} \left(X _ {a}\right), X _ {m}\right), \tag {7} +$$ + +where $\mathcal{F}_{\text{ens}}$ and $\mathcal{F}_{\phi}$ are $1 \times 1$ convolution layer, $\mathcal{F}_{\phi}$ concatenates the occlusion indicator with input feature as guidance. Finally, given the mask and vertex heatmaps of the $o^{th}$ occluded planar object, we feed the features into the dual-branch network used in the stage of appearance perception again and obtain the refined vertexes $\widehat{P}^o$ and mask $\widehat{M}^o$ . + +# 5. Experiment + +# 5.1. Evaluation Metrics + +To evaluate methods on MPOT, following [15], we utilize the CLEAR metric [58] to complement the POT metrics. Note that existing POT metrics estimate the difference between ground truth and prediction in a pairwise manner (i.e., 1-box to 1-box). But it is not suitable for MPOT, since the number of predictions and ground truths are not always equal. Therefore, we match the set of ground truth $GT_{t}$ and prediction $P_{t}$ by bipartite matching [33]. Sequentially, we compute the difference of the matched pair by well-known POT distance Alignment Error [43,45,70] as + +$$ +E _ {A L} (\mathbf {p}, \mathbf {g}) = \sqrt {\frac {\sum_ {\mathbf {j} = 1} ^ {4} \left(\mathbf {p} _ {\mathbf {j}} - \mathbf {g} _ {\mathbf {j}}\right) ^ {2}}{4}}, \tag {8} +$$ + +where $\mathbf{p}$ and $\mathbf{g}$ are the quadrangle of the prediction and ground truth. Then, the prediction and ground truth are split into tracked $T_{\epsilon}^{t}$ , true positive $TP_{\epsilon}^{t}$ , false negative $FN_{\epsilon}^{t}$ , and false positive $FP_{\epsilon}^{t}$ , according to distance $\epsilon$ . We set $\epsilon$ as 50 in our experiment due to the degree of challenge. + +In POT, Precision $(Pr_{\epsilon})$ is the commonly used metric based on the alignment error [43]. To complement the metrics, we report Recall $(Rc_{\epsilon})$ to consider the cases of not being tracked. Furthermore, we propose Multiple Planar Object Tracking Distance $(D_{\epsilon})$ as + +$$ +D _ {\epsilon} = \frac {\sum_ {t = 1} ^ {T} \sum_ {t p \in T P _ {\epsilon} ^ {t} , q \in T _ {\epsilon} ^ {t}} E _ {A L} (t p , q)}{\sum_ {t = 1} ^ {T} | T P _ {\epsilon} ^ {t} |}. \tag {9} +$$ + +Naturally, we propose the Multiple Planar Object Tracking Accuracy $(Acc_{\epsilon})$ based on $E_{AL}$ as. + +$$ +A c c _ {\epsilon} = 1 - \frac {\sum_ {t = 1} ^ {T} \left| F N _ {\epsilon} ^ {t} \right| + \left| F P _ {\epsilon} ^ {t} \right| + \left| I D S W _ {\epsilon} ^ {t} \right|}{3 \cdot \sum_ {t = 1} ^ {T} \left| G T _ {t} \right|}, \tag {10} +$$ + +where $IDSW_{\epsilon}^{t}$ is the set of the identity switch [58] under the threshold $\epsilon$ in $\mathbf{t}^{th}$ frame, and $|\cdot|$ indicates the mod oper- + +Table 3: Comparison of two groups of methods on MPOT-3K. The results on five metrics including Success Rate, Multiple Planar Object Tracking Accuracy, Multiple Planar Object Tracking Distance, Precision, Recall, and Speed are reported. $\uparrow (\downarrow)$ denotes that the higher (lower) the score, the method performs better. Bold and underline indicate the highest and second-highest performance, respectively. + +
MethodsTraditionalDeepOurs
Motion PatternsMetricsCMT [61]NCC [71]CCRE [76]MI [17]GOP [8]Gracker [79]STM [62]PoST [60]LISRD [64]SMask [78]SRPN+ [38]SPoint [16]SOS [73]GIFT [53]HDN [95]
Overall\( S_{0.8} \uparrow \)09.5000.1909.9926.7056.0367.9209.0733.5263.4364.0467.2371.8272.9175.8676.4082.51
\( Acc_{\epsilon} \uparrow \)64.2761.9534.3437.8262.2888.3852.0539.5572.3973.2975.3771.1770.0672.9979.5094.59
\( Pr_{\epsilon} \uparrow \)37.0503.6414.1223.5745.2585.6725.6425.0256.2358.3860.7054.5853.2356.4165.2192.85
\( Rc_{\epsilon} \uparrow \)10.2400.5519.0838.6062.7278.2523.0740.7480.4069.5574.4581.2585.3784.0282.5690.78
\( D_{\epsilon} \downarrow \)12.3042.1517.2708.6806.3705.2318.7922.7106.9317.0616.7707.6707.7607.8007.4405.07
Moving Occlusion\( S_{0.8} \uparrow \)11.3400.0010.6926.4755.8563.6808.7818.1773.7963.2970.6270.9173.4272.9274.9680.29
\( Acc_{\epsilon} \uparrow \)67.2562.7856.2168.1081.4192.9355.4948.0491.7481.4683.2789.9292.2889.7488.7493.16
\( Pr_{\epsilon} \uparrow \)53.484.9233.5651.8270.0576.3029.6325.4586.3774.5775.9484.7384.3584.2182.0090.95
\( Rc_{\epsilon} \uparrow \)13.4700.6432.0161.5777.3081.9824.3728.9880.7067.6272.9785.3985.0385.5084.8688.27
\( D_{\epsilon} \downarrow \)06.3142.1421.2908.7904.1307.9216.5427.2606.4115.5714.2906.0606.1706.0506.2405.34
Moving Objects\( S_{0.8} \uparrow \)09.3400.6911.2324.2952.2161.5808.0935.5267.7962.9565.4965.5070.3667.0270.0979.12
\( Acc_{\epsilon} \uparrow \)69.2263.8640.7847.4168.9692.5453.7741.9676.8880.3382.7278.4469.2978.5981.0594.29
\( Pr_{\epsilon} \uparrow \)60.2817.1019.2432.5752.5090.4828.3327.1360.8768.6272.0967.7552.4167.9767.1892.27
\( Rc_{\epsilon} \uparrow \)22.872.1924.2753.9572.5156.7725.2843.9687.7375.7579.2267.6686.0967.7984.4390.44
\( D_{\epsilon} \downarrow \)12.7143.2117.6606.8505.7104.1121.7719.9305.1514.9215.4804.2104.5304.1605.6305.46
Camera Occlusion\( S_{0.8} \uparrow \)14.6100.0013.3141.7963.5966.4113.8040.2185.4662.4659.4088.8588.2889.4384.0192.46
\( Acc_{\epsilon} \uparrow \)63.5461.9334.2840.2861.7287.9851.7237.1574.0661.6668.7172.1871.9072.1084.5195.85
\( Pr_{\epsilon} \uparrow \)36.8900.3818.4227.8445.0488.2424.5925.3156.7644.8352.3154.6754.4254.6073.1695.84
\( Rc_{\epsilon} \uparrow \)13.1900.0628.3249.7467.3873.7521.7045.3784.3264.8670.7587.5787.1587.5084.5291.53
\( D_{\epsilon} \downarrow \)10.3129.3820.1007.7106.7304.6325.0520.0804.8214.4614.4504.8104.6204.7305.1804.59
Speed↑00.5801.9800.3101.2501.0003.1435.4411.9008.6331.5210.8709.3212.5126.6216.3712.64
+ +ation. To fairly compare along with the trajectory level, we adopt the success rate $(S_{\alpha})$ with the distance threshold $\alpha$ as + +$$ +S _ {\alpha} = \frac {| \mathbb {C} |}{| \mathbb {I} |}, \mathbb {C} = \left\{i _ {n} \in \mathbb {I} \right| \frac {\sum_ {t = 1} ^ {T} \left| T _ {\epsilon} ^ {t} \right|}{\sum_ {t = 1} ^ {T} \left| G T _ {t} \right|} > \alpha \}, \tag {11} +$$ + +where $\mathbb{I}$ is the set of planar objects in the video. + +# 5.2. Implementation Details + +We compare our model with fifteen representative methods. These methods are implemented by official code or open-source libraries [6, 72]. We run evaluated single object trackers multiple times for different planar objects. And we equip them with the data association strategy based on [12], for integrating each single object tracker into tracking multiple targets online. Besides, we additionally give the reference frames of ground truth if the single object trackers fail to track. Different from other box-based trackers, mask-based trackers (e.g., STM) directly outputs the mask. Thus, we use a rotated box estimator [88] to transfer the mask. We implement PRTrack using two RTX3090 GPUs. In the training stage, we use data augmentations, including flip, pepper noise, rotation, contrast jittering, and perspective transformation. We adopt a data sampling strategy following [41]. We adopt Smooth L1 loss and Cross-Entropy loss for optimizing the predicted vertex heatmaps and masks. Similar to [62], we pretrain SPB on YouTubeVOS [89] and DAVIS [66] datasets. During inference, we use the ordered vertexes to build the planar objects and estimate the homography matrix. We set the threshold as 0.9 in the reuse gate by grid search and set $r$ in Equ. 2 as 0 during inference. + +# 5.3. Results on MPOT-3K + +We compare our PRTrack with the other fifteen trackers on MPOT-3K, which contains six traditional POT trackers, four deep-based generic object trackers, and five deep-based planar object trackers. Tab. 3 reports the overall performance as well as the one in the challenging situations of moving occlusion, moving objects, and camera occlusion. + +Deep vs. Traditional Trackers. We can observe that the deep-based trackers have increased by $82.6\%$ on average, on five metrics for overall performance. This is because deep-based trackers avoid taking some assumptions under the laboratory environment, such as the invariance to illumination and appearance change. Note that Gracker performs best in traditional trackers and achieves competitive performance with the deep-based tracker group. However, since MPOT-3K has many small planar objects, it can not extract sufficient information, thus resulting in suboptimal performance (i.e., $10.3\%$ degradation in comparison with ours). In terms of deep-based trackers, STM predicts segmentation masks at the pixel level while ignoring the order of vertexes. Thus, it results in inferior performance, where only $9.0\%$ of targets are correctly tracked. + +Planar Object Trackers vs. Generic Object Trackers. Planar object trackers achieve higher performance (58.9% improvement) against generic object trackers, including SRPN+, SMask, STM, and PoST. A predominant reason is that the generic trackers are subject to the assumption of affine transformation, where only the coarse box estimation is required. Therefore, a powerful planar object tracker should be developed in this field. + +![](images/9f635b7d3f32b0622c8b4a686a297d059450fb855b97c6f5a5256412428d9ae6.jpg) + +![](images/5a567515146fced29c4d3cd7972f5a77d3892cde57c2ae027f18846aa3631cd2.jpg) + +![](images/2826847f90906e62103655908e4f5cf24e3dca71bebb4f4b1a88913615ef853e.jpg) +(a) POT210 +(b) POT280 +(c) Challenging factors +Figure 6: Comparison on POT210 and POT280. The averaged Precision on two datasets with different thresholds are reported in (a) and (b), respectively. (c) further shows the performance under seven challenging factors. The data is extracted from [95]. + +PRTrack vs. SOTA Trackers. PRTrack outperforms other methods with an average improvement of $6.4\%$ . We also observe a large gain when there exists relative movement among multiple targets. To be specific, when facing challenging situations like moving objects, moving occlusion, and camera occlusion, PRTrack achieves a performance gain of $16.9\%$ against other advanced algorithms. + +# 5.4. Results on POT210 and POT280 + +To verify the effectiveness of PRTrack on the traditional POT task, we conduct experiments on the POT210 and POT280 datasets, and compare PRTrack with eleven POT methods as shown in Fig. 6. Note that we do not fine-tune PRTrack on these two datasets, again verifying the generalization ability of PRTrack towards unseen scenes. Following [95], the averaged Precision is employed to evaluate all the methods. As the distance threshold $E_{AL}$ increases, the precision tends to be stable when $E_{AL} > 10$ . We notice that PRTrack achieves competitive performance in comparison with advanced algorithms. Besides, PRTrack shows its superiority when handling challenging cases such as occlusion and motion blur. + +# 5.5. Ablation Study + +We conduct ablation studies on MPOT-3K in Tab. 4 to explore the effectiveness of each component in PRTrack. Our baseline is the appearance perception module, without shifted encoder and auxiliary mask. For simplicity, we use "i&j" to denote the comparison between the $i^{\text{th}}$ line and the $j^{\text{th}}$ line in the rest of this subsection. + +We first perform module-wise ablation studies in the highlighted lines, we observe that PRTrack obtains the largest performance gain of $11.6\%$ (i.e., $3 \& 9$ and $4 \& 10$ ) + +Table 4: Ablation study of components and their variants of PRTrack on the validation split of MPOT-3K. The lines with background indicate the module-level ablation study. Here AP, OR, and RT are short of appearance perception, occlusion reasoning, and memory pool. SE and Fac denote the shifted encoder and factorized homography matrix. Msk represents the plane structure branch with mask information. Here, $*$ , $\bullet$ , and $\diamond$ are the fusion strategy (Fus), representing concatenation, attention-based, and indicator-based. Gat indicates the reuse gate. + +
IdAPORRTMetrics
SEMskFacFusGat\( S_{0.8} \)↑\( Acc_{\epsilon} \)↑\( Pr \)↑\( Rc \)↑\( D_{\epsilon} \)↓
①✓45.2968.0146.7546.7119.56
②✓✓63.7686.8282.3676.9615.40
③✓✓75.8291.0886.2282.9612.57
④✓✓✓78.2091.4387.1986.4209.95
⑤✓✓✓✓*✓77.5391.4690.4186.2510.43
⑥✓✓✓✓•✓78.9991.4188.0785.8709.12
⑦✓✓✓◇✓79.2491.5088.1086.1308.95
⑧✓✓✓◇✓76.3890.5688.5882.3410.59
⑨✓✓✓✓◇80.4492.4889.6787.5407.38
⑩✓✓✓✓◇✓80.5892.7590.0088.0306.39
+ +with the occlusion reasoning module. Then we investigate the variants of each module. For appearance perception, we study how to leverage the order of vertexes. The boosting of $16.3\%$ (i.e., $2 \& 3$ and $8 \& 10$ ) verifies that the proposed encoder avoids learning position bias, where the first vertex commonly comes from the top-left area. For occlusion reasoning, we find the solution to unify the appearance feature and motion feature. We first conduct experiments on alternative solutions of fusion (i.e., $5 \& 6 \& 10$ ), where our strategy achieves the best performance. Because the occlusion indicator provides the change of image against occlusion and joint embedding helps to introduce interaction between features. We also identify the effectiveness of homography factorization via the comparison of $7 \& 10$ , with an average boosting of $7.2\%$ . For memory pool, we investigate the accumulated error. With a gain of $4.4\%$ (i.e., $3 \& 4$ and $9 \& 10$ ), we believe the proposed reuse gate can avoid the error derived from restoring the predictions. + +# 6. Conclusion + +In this paper, we propose a novel method for tracking multiple planar objects simultaneously. We also build the first large-scale benchmark dataset MPOT-3K which contains sufficient data, is labeled by experienced annotators, and covers various scenes. Extensive experiments are conducted on both MPOT3K and the other two single planar object tracking datasets. The results demonstrate that PRTrack achieves SOTA performance on both tasks. + +# 7. Acknowledgments + +This work was supported by the National Key Research and Development Program of China Grant (NO. 2018AAA0100400), Natural Science Foundation of Tianjin, China (NO.20JCJQJC00020), Fundamental Research Funds for the Central Universities, and Supercomputing Center of Nankai University (NKSC). + +# References + +[1] Mark Ashdown, Matthew Flagg, Rahul Sukthankar, and James M Rehg. A flexible projector-camera system for multi-planar displays. In CVPR, 2004. +[2] Simon Baker and Iain Matthews. Lucas-kanade 20 years on: A unifying framework. *IJCV*, 56(3):221–255, 2004. +[3] S. Benhimane and E. Malis. Real-time image-based tracking of planes using efficient second-order minimization. In IROS, 2004. +[4] Eric P. Bennett and Leonard McMillan. Proscenium: A framework for spatio-temporal video editing. In ACM MM, 2003. +[5] Luca Bertinetto, Jack Valmadre, Joao F Henriques, Andrea Vedaldi, and Philip HS Torr. Fully-convolutional siamese networks for object tracking. 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In ISMAR, 2010. \ No newline at end of file diff --git a/2023/Multiple Planar Object Tracking/images.zip b/2023/Multiple Planar Object Tracking/images.zip new file mode 100644 index 0000000000000000000000000000000000000000..699717d5797fa241544526e7b39395d5b0cab602 --- /dev/null +++ b/2023/Multiple Planar Object Tracking/images.zip @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:0a00d41d8577344ddb6f8c977a0d25647be58d256eb6160f42d2a1d0d11543f6 +size 717921 diff --git a/2023/Multiple Planar Object Tracking/layout.json b/2023/Multiple Planar Object Tracking/layout.json new file mode 100644 index 0000000000000000000000000000000000000000..1dc4bef172534c2b83a42fdaa8ee1f4ea23db831 --- /dev/null +++ b/2023/Multiple Planar Object Tracking/layout.json @@ -0,0 +1,11770 @@ +{ + "pdf_info": [ + { + "para_blocks": [ + { + "bbox": [ + 194, + 103, + 400, + 121 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 194, + 103, + 400, + 121 + ], + "spans": [ + { + "bbox": [ + 194, + 103, + 400, + 121 + ], + "type": "text", + "content": "Multiple Planar Object Tracking" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 208, + 144, + 384, + 157 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 208, + 144, + 384, + 157 + ], + "spans": [ + { + "bbox": [ + 208, + 144, + 384, + 157 + ], + "type": "text", + "content": "https://zzcheng.top/MPOT" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 151, + 158, + 233, + 171 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 151, + 158, + 233, + 171 + ], + "spans": [ + { + "bbox": [ + 151, + 158, + 233, + 171 + ], + "type": "text", + "content": "Zhicheng Zhang" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 272, + 158, + 341, + 171 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 272, + 158, + 341, + 171 + ], + "spans": [ + { + "bbox": [ + 272, + 158, + 341, + 171 + ], + "type": "text", + "content": "Shengzhe Liu" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 380, + 157, + 445, + 172 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 380, + 157, + 445, + 172 + ], + "spans": [ + { + "bbox": [ + 380, + 157, + 445, + 172 + ], + "type": "text", + "content": "Jufeng Yang†" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 111, + 172, + 482, + 186 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 111, + 172, + 482, + 186 + ], + "spans": [ + { + "bbox": [ + 111, + 172, + 482, + 186 + ], + "type": "text", + "content": "VCIP & TMCC & DISSec, College of Computer Science, Nankai University" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 127, + 188, + 465, + 198 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 127, + 188, + 465, + 198 + ], + "spans": [ + { + "bbox": [ + 127, + 188, + 465, + 198 + ], + "type": "text", + "content": "gloryzzc6@sina.com, nkuliusz@163.com, yangjufeng@nankai.edu.cn" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "spans": [ + { + "bbox": [ + 143, + 227, + 192, + 239 + ], + "type": "text", + "content": "Abstract" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 45, + 252, + 290, + 553 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 45, + 252, + 290, + 553 + ], + "spans": [ + { + "bbox": [ + 45, + 252, + 290, + 553 + ], + "type": "text", + "content": "Tracking both location and pose of multiple planar objects (MPOT) is of great significance to numerous real-world applications. The greater degree-of-freedom of planar objects compared with common objects makes MPOT far more challenging than well-studied object tracking, especially when occlusion occurs. To address this challenging task, we are inspired by amodal perception that humans jointly track visible and invisible parts of the target, and propose a tracking framework that unifies appearance perception and occlusion reasoning. Specifically, we present a dual-branch network to track the visible part of planar objects, including vertexes and mask. Then, we develop an occlusion area localization strategy to infer the invisible part, i.e., the occluded region, followed by a two-stream attention network finally refining the prediction. To alleviate the lack of data in this field, we build the first large-scale benchmark dataset, namely MPOT-3K. It consists of 3,717 planar objects from 356 videos and contains 148,896 frames together with 687,417 annotations. 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"bbox": [ + 305, + 399, + 546, + 488 + ], + "type": "text", + "content": "Figure 1: Comparison with other vision tasks. Given an image (a), we present the ground truth for different tasks in (b). The corresponding Degree-of-Freedom (DoF) is reported at the bottom and the details are listed on the right side of each task. In (c), we show the tracking results for box-based tasks (e.g., VOT, RVOT), mask-based tasks (e.g., VOS), and POT, which can find the occluded regions (marked by the red line area) and provide pixel-to-pixel matching correspondence (colored points across frames)." + } + ] + } + ], + "index": 25, + "angle": 0, + "type": "image_caption" + } + ], + "index": 22 + }, + { + "bbox": [ + 304, + 510, + 545, + 557 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 510, + 545, + 557 + ], + "spans": [ + { + "bbox": [ + 304, + 510, + 545, + 557 + ], + "type": "text", + "content": "faces of an object [1] or planes from various objects [27]. It has attracted more and more attention attributed to various applications in augmented reality [57, 104], video editing [4, 20, 30], and robot navigation [92]." + } + ] + } + ], + "index": 26 + }, + { + "bbox": [ + 304, + 558, + 546, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 558, + 546, + 714 + ], + "spans": [ + { + "bbox": [ + 304, + 558, + 546, + 714 + ], + "type": "text", + "content": "MPOT is closely related to well-known computer vision tasks in RGB tracking [32] (see Tab. 1). Both tasks involve tracking the target across subsequent frames of a video using the ground truth provided in the initial frame. However, it is more challenging in two aspects. 1) Tracking planar objects is of greater Degree-of-Freedom (DoF). As shown in Fig. 1(b), MPOT tracks both the pose and location of the target, which is described by an arbitrary quadrangle (i.e., four independent vertexes " + }, + { + "bbox": [ + 304, + 558, + 546, + 714 + ], + "type": "inline_equation", + "content": "(x_{1},y_{1},x_{2},y_{2},x_{3},y_{3},x_{4},y_{4})" + }, + { + "bbox": [ + 304, + 558, + 546, + 714 + ], + "type": "text", + "content": ", whose DoF is 8 [44]). In contrast, it only needs to predict the position and size of an object " + }, + { + "bbox": [ + 304, + 558, + 546, + 714 + ], + "type": "inline_equation", + "content": "(x,y,w,h)" + }, + { + "bbox": [ + 304, + 558, + 546, + 714 + ], + "type": "text", + "content": " in video object tracking (VOT), and Rotated VOT (RVOT) additionally requires the rotation angle. Even compared with video object" + } + ] + } + ], + "index": 27 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "spans": [ + { + "bbox": [ + 65, + 2, + 111, + 34 + ], + "type": "text", + "content": "CVF" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "header", + "angle": 0, + "lines": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "spans": [ + { + "bbox": [ + 146, + 0, + 494, + 37 + ], + "type": "text", + "content": "This ICCV paper is the Open Access version, provided by the Computer Vision Foundation. Except for this watermark, it is identical to the accepted version; the final published version of the proceedings is available on IEEE Xplore." + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 62, + 703, + 141, + 712 + ], + "type": "page_footnote", + "angle": 0, + "lines": [ + { + "bbox": [ + 62, + 703, + 141, + 712 + ], + "spans": [ + { + "bbox": [ + 62, + 703, + 141, + 712 + ], + "type": "text", + "content": "† Corresponding author." + } + ] + } + ], + "index": 28 + }, + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 757 + ], + "type": "text", + "content": "23460" + } + ] + } + ], + "index": 29 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 0 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 47, + 86, + 545, + 209 + ], + "blocks": [ + { + "bbox": [ + 47, + 63, + 547, + 85 + ], + "lines": [ + { + "bbox": [ + 47, + 63, + 547, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 63, + 547, + 85 + ], + "type": "text", + "content": "Table 1: The comparison of MPOT with other video-related tasks. We compare MPOT with five RGB tracking tasks and four tasks with auxiliary modality information. The count of DoF comes from [44]." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 47, + 86, + 545, + 209 + ], + "lines": [ + { + "bbox": [ + 47, + 86, + 545, + 209 + ], + "spans": [ + { + "bbox": [ + 47, + 86, + 545, + 209 + ], + "type": "table", + "html": "
ModalityTaskObjectScenario
Object categoryObject selectionMultiple objectsPixel correspondenceDoFOcclusion
RGBMOT [83]Limited, usually pedestrians or vehiclesDetectedYN4Y
MOTS [75]Limited, usually pedestrians or vehiclesDetectedYNN/AN
VOS [66]ArbitraryUser-specified in the first frameNNN/AN
VOT [21]ArbitraryUser-specified in the first frameNN4Y
RVOT [32]ArbitraryUser-specified in the first frameNN5Y
MPOTArbitraryUser-specified in the first frameYY8Y
RGB+DepthRGBDT [91]ArbitraryUser-specified in the first frameYN4Y
6DOP [50]Limited by training setDetectedYY6Y
6DPT [81]ArbitraryUser-specified in the first frameNY6Y
RGB+LIDAR3dOD [35]Limited by training setDetectedYN7Y
3dMOT [84]Limited, usually vehiclesDetectedYN7Y
", + "image_path": "6df07e4fc3e37da7ff6ee7f1d7c5ef3e88a740ed266797426aa31da7119039c2.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 220, + 289, + 460 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 220, + 289, + 460 + ], + "spans": [ + { + "bbox": [ + 46, + 220, + 289, + 460 + ], + "type": "text", + "content": "segmentation (VOS), an alternative that introduces masks at the pixel level, MPOT is a more challenging task. Because MPOT provides the matched correspondence for each pixel within the object region across frames [60] (e.g., colored points in Fig. 1(a)&(c)), which makes it possible for applications that require positional information like texture mapping [24]. Nevertheless, VOS that tracks the target area instead of per-pixel location can hardly achieve it. 2) Occlusion is another challenge that comes with MPOT. Not only the one in POT that manually occludes the camera, MPOT but introduces the occlusion raised by the layered position of multiple targets relative to the camera [77, 96] (see Fig. 1(c)). Besides, the occlusion is more complex than the ones in multiple object tracking (MOT). As discussed above, when occlusion occurs, MPOT estimates the pixel correspondence controlled by homography matrix " + }, + { + "bbox": [ + 46, + 220, + 289, + 460 + ], + "type": "inline_equation", + "content": "\\mathbf{H}" + }, + { + "bbox": [ + 46, + 220, + 289, + 460 + ], + "type": "text", + "content": " [3], which tends to be sensitive and have a high condition number that can reach up to " + }, + { + "bbox": [ + 46, + 220, + 289, + 460 + ], + "type": "inline_equation", + "content": "5\\mathrm{e}^7" + }, + { + "bbox": [ + 46, + 220, + 289, + 460 + ], + "type": "text", + "content": " [95]. This means that a tiny movement of the invisible part is extremely difficult to track." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "spans": [ + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "content": "To address the aforementioned limitations, our work draws the inspiration that humans consolidate the visible together with invisible parts of the target for tracking [96]. We propose a tracking framework comprised of procedures for appearance Perception and occlusion Reasoning, namely PRTrack. To track high DoF planar objects, we reformulate the problem of estimating homography matrix " + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{H}" + }, + { + "bbox": [ + 46, + 462, + 289, + 715 + ], + "type": "text", + "content": " as predicting the mask and ordered vertexes for each planar object. With the high-dimensional mask, we can accurately locate the target area at the pixel level. Besides, the ordered vertexes provide per-pixel correspondence across frames for tracking the pose of planar objects. Therefore, in the stage of appearance perception, we propose a dual branch network to predict the ordered vertexes and masks of planar objects based on the historical visible information. For vertexes, we design an encoder with shifted sampling strategy based on the constraint that the vertexes always have a clockwise order. For mask, we aggregate the probability of multiple planar objects with a multi-layered layout, that is, a stack of occluders and occludees. Further, to solve the cases of complex occlusion, we develop an occlusion area" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 304, + 220, + 547, + 316 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 220, + 547, + 316 + ], + "spans": [ + { + "bbox": [ + 304, + 220, + 547, + 316 + ], + "type": "text", + "content": "localization strategy to indicate the occluded part, by storing the movement of each planar object (i.e., historical H). To be specific, we factorize the sensitive homography matrix, which describes the relative movement of planar objects, into parameters of transition, rotation, and pose. Finally, with the prediction from the mentioned stages, we propose a two-stream self-attention network to jointly refine the predicted planar objects." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 304, + 316, + 547, + 388 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 316, + 547, + 388 + ], + "spans": [ + { + "bbox": [ + 304, + 316, + 547, + 388 + ], + "type": "text", + "content": "Besides, since there is no available dataset in this field, we build a large-scale benchmark dataset, namely MPOT-3K. Specifically, we shoot 356 videos with 3,717 planar objects and 687,417 annotations. The videos are collected under 9 motion patterns, where the relative movement and occlusion are also included to simulate the real-world scene." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 304, + 388, + 547, + 497 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 388, + 547, + 497 + ], + "spans": [ + { + "bbox": [ + 304, + 388, + 547, + 497 + ], + "type": "text", + "content": "The contributions of this paper are two-fold: 1) We collect and annotate the first large-scale benchmark dataset for MPOT, where planar objects are diversely collected expelling bias. Our dataset will be released and boost research in this field. 2) We propose a tracking framework with unified motion and appearance models, which can accurately predict the pose and location of planar objects. Extensive experiments demonstrate the superiority of PRTrack against state-of-the-art approaches." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 507, + 392, + 520 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 507, + 392, + 520 + ], + "spans": [ + { + "bbox": [ + 306, + 507, + 392, + 520 + ], + "type": "text", + "content": "2. Related Work" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 306, + 527, + 440, + 540 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 527, + 440, + 540 + ], + "spans": [ + { + "bbox": [ + 306, + 527, + 440, + 540 + ], + "type": "text", + "content": "2.1. Planar Object Tracking" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 545, + 547, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 545, + 547, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 545, + 547, + 713 + ], + "type": "text", + "content": "Benchmark Datasets. Current works focus on single planar object tracking and propose several POT datasets [19, 42, 43, 45, 70, 86]. Metaio [45] is the first dataset collected in the lab and the videos are collected by a monitored camera. Similarly, TMT [70] also shoots videos from the lab, where the annotations are automatically generated by aggregating the results of three planar object trackers. Due to the laboratory setting of the collection, videos in these datasets have similar backgrounds. Thus, POT210 [43] collects video data in the wild under seven motion patterns and encourages the diversity of the recorded videos with complex backgrounds. However, existing benchmarks are insufficient to mimic real-world settings where multiple targets exist. Therefore, our work extends the task into MPOT that" + } + ] + } + ], + "index": 9 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 758 + ], + "type": "text", + "content": "23461" + } + ] + } + ], + "index": 10 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 1 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 92, + 286, + 163 + ], + "blocks": [ + { + "bbox": [ + 47, + 71, + 287, + 92 + ], + "lines": [ + { + "bbox": [ + 47, + 71, + 287, + 92 + ], + "spans": [ + { + "bbox": [ + 47, + 71, + 287, + 92 + ], + "type": "text", + "content": "Table 2: Statistics of tracking datasets. \"I.\" and \"O.\" indicate indoor and outdoor, respectively. \"#\" denotes \"the number of\"." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 92, + 286, + 163 + ], + "lines": [ + { + "bbox": [ + 49, + 92, + 286, + 163 + ], + "spans": [ + { + "bbox": [ + 49, + 92, + 286, + 163 + ], + "type": "table", + "html": "
BenchmarkUCSB [19]TMT [70]POIC [8]POT210 [43]POT280 [42]MOT16 [58]MPOT-3K
# Scenes112030401442
# Videos961002021028014356
# Targets96100202102801,2763,717
# Annotations7K-23K53K70K292K687K
Scene CategoryI.I.I.&O.I.&O.I.&O.O.I.&O.
Multiple ObjectsXXXXX✓✓
", + "image_path": "4e648d69ebb31962933fe929808ded151752e776c9eb693cfdefcebb991b869c.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 46, + 179, + 286, + 203 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 179, + 286, + 203 + ], + "spans": [ + { + "bbox": [ + 46, + 179, + 286, + 203 + ], + "type": "text", + "content": "simultaneously tracks multiple planar objects which can be applied in real-world applications like AR, robots, and art." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 206, + 287, + 374 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 206, + 287, + 374 + ], + "spans": [ + { + "bbox": [ + 46, + 206, + 287, + 374 + ], + "type": "text", + "content": "Methods. POT trackers can be classified into region-based, keypoint-based, and hybrid methods. Region-based approaches [2, 3, 9, 17, 34, 68] focus on the whole planar region and estimate perspective transformation by closing up the template and the warped image. Keypoint-based methods [22, 61, 63, 79, 101] describe a planar object by the detected keypoints [54, 69] and associate objects across frames by computing the similarity between keypoints. As for hybrid methods, previous works [8, 9, 13, 94] exploit the robust feature descriptors for searching the optimal matching. A representative method [8] leverage gradient-based feature as criterion. As progress is made into the deep learning era [37, 82], CLKN [7] integrates deep features into the Lucas-Kanade algorithm for improving matching quality." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 390, + 144, + 403 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 390, + 144, + 403 + ], + "spans": [ + { + "bbox": [ + 47, + 390, + 144, + 403 + ], + "type": "text", + "content": "2.2. Visual Tracking" + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 411, + 287, + 567 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 411, + 287, + 567 + ], + "spans": [ + { + "bbox": [ + 46, + 411, + 287, + 567 + ], + "type": "text", + "content": "Single Object Tracking. It aims to locate and track a single target in a video [39, 48], which can be roughly grouped into box-based tracking [18, 55, 93] and mask-based tracking [41, 47, 60]. SiamFC [5] adopts the correlation layer to search the location which is described by the axis-aligned bounding box. Further, SiamMask [78] introduces rotation to describe the motion and predicts the object mask with the bounding box simultaneously. Meanwhile, mask-based tracking focuses on the accurate location of the targets. STM [62] addresses the problem of appearance change, leading to satisfactory results. Recently, PoST [60] explores the relationship between the mask and contour, building constraints for predicting the polygonal mask." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 570, + 287, + 713 + ], + "type": "text", + "content": "Multiple Object Tracking. Existing works [14, 58] propose to track multiple objects of human interests simultaneously, with the assumption that all targets belong to a list of predefined classes [10, 11, 26, 36, 51, 90, 100, 102]. A large number of methods [49, 65, 80, 85, 99] are proposed to address the task. With the class assumption, they utilize object detectors to generate candidates in the manner of axis-aligned bounding boxes. Then the candidates are associated into trajectories. While both MPOT and MOT track multiple targets at the same time, the former faces more challenges since it handles arbitrary planar objects with greater DoF, as well as covers unrestricted classes [43]." + } + ] + } + ], + "index": 6 + }, + { + "type": "image", + "bbox": [ + 307, + 70, + 436, + 173 + ], + "blocks": [ + { + "bbox": [ + 307, + 70, + 436, + 173 + ], + "lines": [ + { + "bbox": [ + 307, + 70, + 436, + 173 + ], + "spans": [ + { + "bbox": [ + 307, + 70, + 436, + 173 + ], + "type": "image", + "image_path": "4bfb2859ca249b52bf8987b5e034139656cf0d561cfdeae4dbaea60ff3875d2c.jpg" + } + ] + } + ], + "index": 7, + "angle": 0, + "type": "image_body" + } + ], + "index": 7 + }, + { + "type": "image", + "bbox": [ + 440, + 71, + 544, + 178 + ], + "blocks": [ + { + "bbox": [ + 307, + 178, + 444, + 186 + ], + "lines": [ + { + "bbox": [ + 307, + 178, + 444, + 186 + ], + "spans": [ + { + "bbox": [ + 307, + 178, + 444, + 186 + ], + "type": "text", + "content": "(a) Occurrence of occlusion in different scenes" + } + ] + } + ], + "index": 8, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 440, + 71, + 544, + 178 + ], + "lines": [ + { + "bbox": [ + 440, + 71, + 544, + 178 + ], + "spans": [ + { + "bbox": [ + 440, + 71, + 544, + 178 + ], + "type": "image", + "image_path": "198514ab98c0952c1de7d52a76945f92f0eb79d1b479ca49cd1b22b12cd26979.jpg" + } + ] + } + ], + "index": 9, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 461, + 178, + 541, + 186 + ], + "lines": [ + { + "bbox": [ + 461, + 178, + 541, + 186 + ], + "spans": [ + { + "bbox": [ + 461, + 178, + 541, + 186 + ], + "type": "text", + "content": "(b) Statistics about occlusion" + } + ] + } + ], + "index": 10, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 305, + 187, + 545, + 252 + ], + "lines": [ + { + "bbox": [ + 305, + 187, + 545, + 252 + ], + "spans": [ + { + "bbox": [ + 305, + 187, + 545, + 252 + ], + "type": "text", + "content": "Figure 2: Statistics of occlusion in MPOT-3K. (a) shows the frequency of occlusion in six types of scenes, in which the number on the left indicates the number of planar objects being occluded and the one in shadow represents the corresponding proportion. (b) illustrates the number of occlusions per video as well as the temporal length per occlusion." + } + ] + } + ], + "index": 11, + "angle": 0, + "type": "image_caption" + } + ], + "index": 9 + }, + { + "bbox": [ + 306, + 266, + 440, + 279 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 266, + 440, + 279 + ], + "spans": [ + { + "bbox": [ + 306, + 266, + 440, + 279 + ], + "type": "text", + "content": "3. The MPOT-3K Dataset" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 304, + 287, + 545, + 384 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 287, + 545, + 384 + ], + "spans": [ + { + "bbox": [ + 304, + 287, + 545, + 384 + ], + "type": "text", + "content": "MPOT is being less explored and limited by existing datasets designed to single planar object tracking. In this work, we construct the dataset MPOT-3K for introducing multiple targets. To the best of our knowledge, MPOT-3K is the first large-scale dataset for the challenging task of MPOT. This will help facilitate future research in computer vision (augmented reality, safety surveillance), robot (navigation, manipulation), and art (video editing)." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 392, + 402, + 404 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 392, + 402, + 404 + ], + "spans": [ + { + "bbox": [ + 306, + 392, + 402, + 404 + ], + "type": "text", + "content": "3.1. Data Collecting" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 411, + 545, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 411, + 545, + 578 + ], + "spans": [ + { + "bbox": [ + 304, + 411, + 545, + 578 + ], + "type": "text", + "content": "Initially, we shoot 840 videos involving the motion of static and moving planar objects. For the static planar objects, we design six motion patterns (i.e., far-near movement, in-plane rotation, out-plane rotation, in-plane movement, motion blur, camera occlusion) by controlling the movements of camera as common practices [43,86]. For the moving planar objects, we consider the occlusions and relative movements among multiple planar objects and design two motion patterns (i.e., moving objects, moving occlusion). Besides, an unconstrained motion pattern is considered to further combine the above motion patterns. According to [87, 103], we record diverse videos from six types of indoor and outdoor scenes, including library, house, gallery, building, street, and village." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 586, + 406, + 597 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 586, + 406, + 597 + ], + "spans": [ + { + "bbox": [ + 306, + 586, + 406, + 597 + ], + "type": "text", + "content": "3.2. Data Annotation" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 713 + ], + "type": "text", + "content": "MPOT-3K is annotated by seven well-trained annotators. Following [43], we adopt a semi-automatic annotation scheme. First, the annotator labels one frame every five frames. Then, the annotated label is propagated to other unannotated frames by linear interpolation. Finally, the annotator corrects the propagated label. During annotation, we obey the following rules. First, we define what planar object is to be annotated according to [43, 70, 86]. The planar object should be easily presented by four ordered ver" + } + ] + } + ], + "index": 17 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23462" + } + ] + } + ], + "index": 18 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 2 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 59, + 545, + 205 + ], + "blocks": [ + { + "bbox": [ + 48, + 59, + 545, + 205 + ], + "lines": [ + { + "bbox": [ + 48, + 59, + 545, + 205 + ], + "spans": [ + { + "bbox": [ + 48, + 59, + 545, + 205 + ], + "type": "image", + "image_path": "3687c26235d3385e5011cbe5f17ec943b4d63971cce5048f703996ee24f45a40.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 46, + 206, + 547, + 251 + ], + "lines": [ + { + "bbox": [ + 46, + 206, + 547, + 251 + ], + "spans": [ + { + "bbox": [ + 46, + 206, + 547, + 251 + ], + "type": "text", + "content": "Figure 3: The pipeline of our method. Our tracking framework is divided into three stages. First, in appearance perception, we track the visible part of multiple planar objects via a dual-branch network, as coarse output. For the next stage of occlusion reasoning, the occlusion area is localized and then fed into a two-stream self-attention network for refining the predicted target. Finally, the memory pool module restores the high-confident tracked targets." + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "bbox": [ + 46, + 260, + 289, + 405 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 260, + 289, + 405 + ], + "spans": [ + { + "bbox": [ + 46, + 260, + 289, + 405 + ], + "type": "text", + "content": "texas. To ensure that the criteria for selecting plane objects are consistent, we ask all the annotators to vote for filtering out inconsistent objects [52]. Second, we start annotating when the planar object is completely in view and end when the object has been fully occluded or out of view. Third, we annotate the spatial position of the planar object according to two principles: 1) We annotate the planar object which has four apparent lines, since the point is localized by inferring the intersection lines [67]. 2) We maintain the order of vertexes across video frames for pixel correspondence. Combining these principles, we can locate the planar object with four independent vertexes (i.e., a quadrangle)." + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 47, + 416, + 113, + 428 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 416, + 113, + 428 + ], + "spans": [ + { + "bbox": [ + 47, + 416, + 113, + 428 + ], + "type": "text", + "content": "3.3. Statistics" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 437, + 287, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 437, + 287, + 544 + ], + "spans": [ + { + "bbox": [ + 46, + 437, + 287, + 544 + ], + "type": "text", + "content": "After collecting and labeling, we yield a large-scale dataset MPOT-3K, where we obtain 356 videos with 3,717 planar objects from 42 scenes. The number of planar objects per video averages 10.44 and can reach 74 at most. MPOT-3K is divided into training, validation, and test sets in a proportion of 80:5:15. The split is performed at the scene level to ensure there's no overlap among splits. Hence the dataset avoids leakage since both the target and scene of the test set are expelled during training." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "spans": [ + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": "As shown in Tab. 2, we compare MPOT-3K with six datasets, which come from POT [8, 19, 42, 43, 70] and MOT [58] tasks. MPOT-3K contains over 9.8 times more annotations and 13.2 times more targets in all video frames than the largest POT dataset POT280. The number of targets is almost 3 times of the popular MOT16 dataset. Another strength of MPOT-3K lies in its diversity, which covers 9 motion patterns and 6 types of scenes. Besides, MPOT-3K introduces more complex occlusions. As shown in Fig. 2(a), we observe that occlusion occurs in all the scenes, where " + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "inline_equation", + "content": "39.9\\%" + }, + { + "bbox": [ + 46, + 545, + 288, + 713 + ], + "type": "text", + "content": " of planar objects are occluded on average. Fig. 2(b) further illustrates that there are 3.6 occlusions happening in a video on average and each occlusion lasts 9.56 seconds." + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 305, + 258, + 388, + 274 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 258, + 388, + 274 + ], + "spans": [ + { + "bbox": [ + 305, + 258, + 388, + 274 + ], + "type": "text", + "content": "4. Methodology" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 304, + 279, + 545, + 411 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 279, + 545, + 411 + ], + "spans": [ + { + "bbox": [ + 304, + 279, + 545, + 411 + ], + "type": "text", + "content": "PRTrack consists of three main components (See Fig. 3): memory pool module, appearance perception network, and occlusion reasoning network. The memory pool module (Sec. 4.2) restores the previous predictions and expels the low-confident targets. Guided by previously tracked targets, the appearance perception network (Sec. 4.3) predicts mask together with the vertexes for each planar object. The occlusion reasoning network (Sec. 4.4) further takes all the tracked targets and corresponding occlusion area, which is indicated by the difference between motion-guided results among multiple targets and the predicted one." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 305, + 418, + 440, + 430 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 418, + 440, + 430 + ], + "spans": [ + { + "bbox": [ + 305, + 418, + 440, + 430 + ], + "type": "text", + "content": "4.1. Problem Reformulation" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 436, + 545, + 582 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 436, + 545, + 582 + ], + "spans": [ + { + "bbox": [ + 304, + 436, + 545, + 582 + ], + "type": "text", + "content": "Assume multiple planar objects exists in an RGB video where they are not from the training set, nor have detection results. Given the user-selected ones in the initial frame, the objective is to estimate their position change relative to the beginning, i.e., homography matrix, with which the pose change of targets can be obtained [56]. As shown in Fig. 4, we reformulate the tracking task as predicting the masks of the quadrangle " + }, + { + "bbox": [ + 304, + 436, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathbf{M}} \\in \\mathbb{R}^{O \\times hw}" + }, + { + "bbox": [ + 304, + 436, + 545, + 582 + ], + "type": "text", + "content": " and the heatmap of four ordered vertexes " + }, + { + "bbox": [ + 304, + 436, + 545, + 582 + ], + "type": "inline_equation", + "content": "\\widehat{\\mathbf{P}} \\in \\mathbb{R}^{O \\times 4hw}" + }, + { + "bbox": [ + 304, + 436, + 545, + 582 + ], + "type": "text", + "content": ", where " + }, + { + "bbox": [ + 304, + 436, + 545, + 582 + ], + "type": "inline_equation", + "content": "O" + }, + { + "bbox": [ + 304, + 436, + 545, + 582 + ], + "type": "text", + "content": " is the number of planar objects in the current frame. The layered masks represent the location of multiple planar objects [94] and the vertexes are used to track the pose of planar objects [56]." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 305, + 587, + 430, + 601 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 587, + 430, + 601 + ], + "spans": [ + { + "bbox": [ + 305, + 587, + 430, + 601 + ], + "type": "text", + "content": "4.2. Memory Pool module" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "spans": [ + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "content": "From the viewpoint of human perception, one person tracks the targets by memorizing their historical appearance and trajectory [59]. Inspired by this, we leverage the images and predictions in previous T frames as guidance to track planar objects in the current one. For the previous frames, we record previously predicted heatmaps of ordered vertexes " + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{P_o}\\in \\mathbb{R}^{T\\times 4hw}" + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "content": ", masks " + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{M_o}\\in \\mathbb{R}^{T\\times hw}" + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "content": ", and the images " + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\mathbf{I_o}\\in \\mathbb{R}^{T\\times 3hw}" + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "content": " for the " + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "inline_equation", + "content": "o^{\\mathrm{th}}" + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "content": " planar object. The memory pool " + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "inline_equation", + "content": "\\{(\\mathbf{P_o},\\mathbf{M_o},\\mathbf{I_o})\\}_{o = 1}^N" + }, + { + "bbox": [ + 304, + 605, + 545, + 715 + ], + "type": "text", + "content": " stores the tracked N planar objects." + } + ] + } + ], + "index": 11 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23463" + } + ] + } + ], + "index": 12 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 3 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 49, + 52, + 178, + 134 + ], + "blocks": [ + { + "bbox": [ + 49, + 52, + 178, + 134 + ], + "lines": [ + { + "bbox": [ + 49, + 52, + 178, + 134 + ], + "spans": [ + { + "bbox": [ + 49, + 52, + 178, + 134 + ], + "type": "image", + "image_path": "a430a51542a63ca7707737f6e3b84bc6565d99b7f32507ae5540da803d8ca02d.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 94, + 135, + 127, + 144 + ], + "lines": [ + { + "bbox": [ + 94, + 135, + 127, + 144 + ], + "spans": [ + { + "bbox": [ + 94, + 135, + 127, + 144 + ], + "type": "text", + "content": "(a) Image" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 192, + 52, + 275, + 92 + ], + "blocks": [ + { + "bbox": [ + 192, + 52, + 275, + 92 + ], + "lines": [ + { + "bbox": [ + 192, + 52, + 275, + 92 + ], + "spans": [ + { + "bbox": [ + 192, + 52, + 275, + 92 + ], + "type": "image", + "image_path": "1c13be2fd6d8e8afd1f1869c6d096779fff5968f623aa5577d16dbd9cecbd06d.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 189, + 92, + 272, + 101 + ], + "lines": [ + { + "bbox": [ + 189, + 92, + 272, + 101 + ], + "spans": [ + { + "bbox": [ + 189, + 92, + 272, + 101 + ], + "type": "text", + "content": "(b) Mask of each target" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 185, + 102, + 284, + 135 + ], + "blocks": [ + { + "bbox": [ + 185, + 102, + 284, + 135 + ], + "lines": [ + { + "bbox": [ + 185, + 102, + 284, + 135 + ], + "spans": [ + { + "bbox": [ + 185, + 102, + 284, + 135 + ], + "type": "image", + "image_path": "061ed77e8996d5eab9f35e545e7a305d28db8d42f1df0fa684903c44021ca542.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 185, + 135, + 277, + 144 + ], + "lines": [ + { + "bbox": [ + 185, + 135, + 277, + 144 + ], + "spans": [ + { + "bbox": [ + 185, + 135, + 277, + 144 + ], + "type": "text", + "content": "(c) Vertexes of each target" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 144, + 286, + 187 + ], + "lines": [ + { + "bbox": [ + 46, + 144, + 286, + 187 + ], + "spans": [ + { + "bbox": [ + 46, + 144, + 286, + 187 + ], + "type": "text", + "content": "Figure 4: Illustration of the reformulated form of MPOT. We predict heatmaps of four ordered vertexes and the mask for each planar object. The stacked masks are built in a layered structure and are responsible for the occluders and occludees." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 201, + 286, + 285 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 201, + 286, + 285 + ], + "spans": [ + { + "bbox": [ + 46, + 201, + 286, + 285 + ], + "type": "text", + "content": "However, due to the challenge of accurately tracking multiple planar objects, the error accumulation [46] occurs because of memorizing incorrect predictions. To avoid this issue, we filter out the low-confident predictions. Given the current frame, PRTrack predicts the vertexes " + }, + { + "bbox": [ + 46, + 201, + 286, + 285 + ], + "type": "inline_equation", + "content": "\\widehat{P}^o \\in \\mathbb{R}^{4hw}" + }, + { + "bbox": [ + 46, + 201, + 286, + 285 + ], + "type": "text", + "content": " and mask " + }, + { + "bbox": [ + 46, + 201, + 286, + 285 + ], + "type": "inline_equation", + "content": "\\widehat{M}^o \\in \\mathbb{R}^{hw}" + }, + { + "bbox": [ + 46, + 201, + 286, + 285 + ], + "type": "text", + "content": " for the " + }, + { + "bbox": [ + 46, + 201, + 286, + 285 + ], + "type": "inline_equation", + "content": "o^{th}" + }, + { + "bbox": [ + 46, + 201, + 286, + 285 + ], + "type": "text", + "content": " tracked planar object. We compute the confidence of the mask and vertexes as" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 97, + 286, + 286, + 308 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 97, + 286, + 286, + 308 + ], + "spans": [ + { + "bbox": [ + 97, + 286, + 286, + 308 + ], + "type": "interline_equation", + "content": "M _ {c o n f} = \\min (\\left\\{\\max \\left(\\widehat {M ^ {o}}\\right) \\right\\} _ {o = 1} ^ {O}). \\tag {1}", + "image_path": "e3568990cfcc19e31eb2ae26964582a33a9138a0247fd6b4e50ceec64de741d0.jpg" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 102, + 306, + 230, + 319 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 102, + 306, + 230, + 319 + ], + "spans": [ + { + "bbox": [ + 102, + 306, + 230, + 319 + ], + "type": "interline_equation", + "content": "P _ {c o n f} = \\min (\\{m a x (\\widehat {P} ^ {o}) \\} _ {o = 1} ^ {0})", + "image_path": "8a79d36357dd62ef5ba211691366e84b728df7a2c1ce8be7bc82355777127dfd.jpg" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 46, + 321, + 286, + 357 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 321, + 286, + 357 + ], + "spans": [ + { + "bbox": [ + 46, + 321, + 286, + 357 + ], + "type": "text", + "content": "The predictions with the confidences surpassing the threshold are restored in the memory pool module. The reuse gate is only applied during testing." + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 47, + 365, + 178, + 376 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 365, + 178, + 376 + ], + "spans": [ + { + "bbox": [ + 47, + 365, + 178, + 376 + ], + "type": "text", + "content": "4.3. Appearance Perception" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "spans": [ + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "type": "text", + "content": "Our appearance perception network is built on top of the encoder-decoder architecture [62], with a backbone of ResNet50. For the current frame, we extract appearance feature " + }, + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "type": "inline_equation", + "content": "f_{cur} \\in \\mathbb{R}^{CHW}" + }, + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "type": "text", + "content": " from an image, where " + }, + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "type": "inline_equation", + "content": "H, W, C" + }, + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "type": "text", + "content": " denotes the width, height, and the number of channels of the feature. For previous frames, we extract features from vertexes, masks, and images, and sum the three features as " + }, + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "type": "inline_equation", + "content": "f_{pre} \\in \\mathbb{R}^{T \\times CHW}" + }, + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "type": "text", + "content": ". The current image feature and previous target features are fed into the encoder network to yield appearance features " + }, + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "type": "inline_equation", + "content": "f_{T+1}^o \\in \\mathbb{R}^{CHW}" + }, + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "type": "text", + "content": " for " + }, + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "type": "inline_equation", + "content": "o^{\\mathrm{th}}" + }, + { + "bbox": [ + 46, + 382, + 287, + 525 + ], + "type": "text", + "content": " planar object. The plane structure branch and segmentation prior branch finally predict the coarse results of vertexes and masks." + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 46, + 526, + 287, + 646 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 526, + 287, + 646 + ], + "spans": [ + { + "bbox": [ + 46, + 526, + 287, + 646 + ], + "type": "text", + "content": "Vertex Encoder with Shifted Sampling Strategy. Considering the vertexes of the planar object provide the pixel correspondence across frames, each vertex is independent against others, thus they are organized in sequential order [47]. Therefore, we design an encoder with shifted sampling strategy to leverage the characteristic of vertexes (i.e., the clockwise order), as the feature extractor. As shown in Fig. 5, a random cyclic shift function " + }, + { + "bbox": [ + 46, + 526, + 287, + 646 + ], + "type": "inline_equation", + "content": "\\text{shift}(\\cdot, +r)" + }, + { + "bbox": [ + 46, + 526, + 287, + 646 + ], + "type": "text", + "content": " is first applied to build the connection between the vertex heatmap " + }, + { + "bbox": [ + 46, + 526, + 287, + 646 + ], + "type": "inline_equation", + "content": "P_i \\in \\mathbb{R}^{HW}" + }, + { + "bbox": [ + 46, + 526, + 287, + 646 + ], + "type": "text", + "content": " and its neighbors by shuffling position as" + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 76, + 649, + 286, + 662 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 76, + 649, + 286, + 662 + ], + "spans": [ + { + "bbox": [ + 76, + 649, + 286, + 662 + ], + "type": "interline_equation", + "content": "\\operatorname {shift}(P, + r) = \\left[P_{(1 + r)\\% L},\\dots ,P_{(L + r)\\% L}\\right], \\tag{2}", + "image_path": "20a67b145ef66f2a0078082edbc209089cccc42153c249d2bd4b62012a37017b.jpg" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "L" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " is the number of vertexes in the planar object and " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "r \\in \\{0,1,2,3\\}" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " is a random number. % is the mod operation. Then, we apply " + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "inline_equation", + "content": "7 \\times 7" + }, + { + "bbox": [ + 46, + 665, + 287, + 714 + ], + "type": "text", + "content": " convolutions [25] to extract the features of four ordered vertexes, separately. For modeling" + } + ] + } + ], + "index": 15 + }, + { + "type": "image", + "bbox": [ + 307, + 50, + 547, + 133 + ], + "blocks": [ + { + "bbox": [ + 307, + 50, + 547, + 133 + ], + "lines": [ + { + "bbox": [ + 307, + 50, + 547, + 133 + ], + "spans": [ + { + "bbox": [ + 307, + 50, + 547, + 133 + ], + "type": "image", + "image_path": "bfd0fd72b9ef268ea18e65f6c379c04604a5ce237fb70b354cf6eef85d7a2678.jpg" + } + ] + } + ], + "index": 16, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 305, + 133, + 545, + 187 + ], + "lines": [ + { + "bbox": [ + 305, + 133, + 545, + 187 + ], + "spans": [ + { + "bbox": [ + 305, + 133, + 545, + 187 + ], + "type": "text", + "content": "Figure 5: Illustration of our proposed vertex encoder. Given the vertex heatmaps, we random sample them by a cyclic shift operation, following a clockwise order and with an offset of " + }, + { + "bbox": [ + 305, + 133, + 545, + 187 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 305, + 133, + 545, + 187 + ], + "type": "text", + "content": ". Note that PSB, as a counterpart, predicts the vertexes via a cyclic shift function with negative " + }, + { + "bbox": [ + 305, + 133, + 545, + 187 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 305, + 133, + 545, + 187 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 17, + "angle": 0, + "type": "image_caption" + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 200, + 545, + 282 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 200, + 545, + 282 + ], + "spans": [ + { + "bbox": [ + 304, + 200, + 545, + 282 + ], + "type": "text", + "content": "the order between four vertices, we introduce the cosine positional embedding [74] and add it to the vertex representation. The positional embedding " + }, + { + "bbox": [ + 304, + 200, + 545, + 282 + ], + "type": "inline_equation", + "content": "\\pmb{f}_{emb} \\in \\mathbb{R}^{L \\times N}" + }, + { + "bbox": [ + 304, + 200, + 545, + 282 + ], + "type": "text", + "content": " contains the N-d embeddings corresponding to the order information for the features of L vertices. The feature of ordered vertices is then extracted by a " + }, + { + "bbox": [ + 304, + 200, + 545, + 282 + ], + "type": "inline_equation", + "content": "7 \\times 7" + }, + { + "bbox": [ + 304, + 200, + 545, + 282 + ], + "type": "text", + "content": " convolution to capture long-range spatial interaction between vertices." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 283, + 545, + 379 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 283, + 545, + 379 + ], + "spans": [ + { + "bbox": [ + 304, + 283, + 545, + 379 + ], + "type": "text", + "content": "Plane Structure Branch (PSB). Given the shifted feature map of vertexes from the decoder, a " + }, + { + "bbox": [ + 304, + 283, + 545, + 379 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 304, + 283, + 545, + 379 + ], + "type": "text", + "content": " convolution is attached with the sigmoid function to output the heatmap of the vertexes. The shifted vertex heatmaps are then aligned with the shifted input in Equ. 2 by using the reversed cyclic shift operation " + }, + { + "bbox": [ + 304, + 283, + 545, + 379 + ], + "type": "inline_equation", + "content": "\\text{shift}(\\cdot, -r)" + }, + { + "bbox": [ + 304, + 283, + 545, + 379 + ], + "type": "text", + "content": ". Finally, we get the heatmaps of " + }, + { + "bbox": [ + 304, + 283, + 545, + 379 + ], + "type": "inline_equation", + "content": "o^{\\text{th}}" + }, + { + "bbox": [ + 304, + 283, + 545, + 379 + ], + "type": "text", + "content": " planar object " + }, + { + "bbox": [ + 304, + 283, + 545, + 379 + ], + "type": "inline_equation", + "content": "P^{o} \\in \\mathbb{R}^{HW}" + }, + { + "bbox": [ + 304, + 283, + 545, + 379 + ], + "type": "text", + "content": " by upsampling to the same resolution as the original image." + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 304, + 380, + 545, + 475 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 380, + 545, + 475 + ], + "spans": [ + { + "bbox": [ + 304, + 380, + 545, + 475 + ], + "type": "text", + "content": "Segmentation Prior Branch (SPB). The mask can accurately locate the planar object at the pixel level and capture the relative movement between objects such as occlusion [55,78]. Therefore, we utilize a " + }, + { + "bbox": [ + 304, + 380, + 545, + 475 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 304, + 380, + 545, + 475 + ], + "type": "text", + "content": " convolution with the softmax function alongside the foreground/background dimension. Following [62], The probability of background " + }, + { + "bbox": [ + 304, + 380, + 545, + 475 + ], + "type": "inline_equation", + "content": "m_{bkg}" + }, + { + "bbox": [ + 304, + 380, + 545, + 475 + ], + "type": "text", + "content": " and each foreground object " + }, + { + "bbox": [ + 304, + 380, + 545, + 475 + ], + "type": "inline_equation", + "content": "m_o" + }, + { + "bbox": [ + 304, + 380, + 545, + 475 + ], + "type": "text", + "content": " are obtained by aggregating the output of model logits " + }, + { + "bbox": [ + 304, + 380, + 545, + 475 + ], + "type": "inline_equation", + "content": "\\in \\mathbb{R}^{O \\times HW}" + }, + { + "bbox": [ + 304, + 380, + 545, + 475 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 312, + 475, + 545, + 506 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 312, + 475, + 545, + 506 + ], + "spans": [ + { + "bbox": [ + 312, + 475, + 545, + 506 + ], + "type": "interline_equation", + "content": "m _ {o} = \\frac {\\exp \\left(\\operatorname {l o g i t s} _ {o}\\right)}{\\sum_ {i = 1} ^ {O} \\exp \\left(\\operatorname {l o g i t s} _ {i}\\right)}, \\quad m _ {b k g} = \\prod_ {i = 1} ^ {O} (1 - m _ {o}). \\tag {3}", + "image_path": "4bd921a23b99986b838e60f73eb222560670ecd1e0e1fe1da7083f4e731f789f.jpg" + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 304, + 508, + 545, + 544 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 508, + 545, + 544 + ], + "spans": [ + { + "bbox": [ + 304, + 508, + 545, + 544 + ], + "type": "text", + "content": "Finally, the probability segmentation mask of " + }, + { + "bbox": [ + 304, + 508, + 545, + 544 + ], + "type": "inline_equation", + "content": "\\sigma^{\\mathrm{th}}" + }, + { + "bbox": [ + 304, + 508, + 545, + 544 + ], + "type": "text", + "content": " planar object " + }, + { + "bbox": [ + 304, + 508, + 545, + 544 + ], + "type": "inline_equation", + "content": "M^{o} \\in \\mathbb{R}^{HW}" + }, + { + "bbox": [ + 304, + 508, + 545, + 544 + ], + "type": "text", + "content": " are produced after softmax. The background probability map is attached in the last channel." + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 306, + 552, + 426, + 564 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 552, + 426, + 564 + ], + "spans": [ + { + "bbox": [ + 306, + 552, + 426, + 564 + ], + "type": "text", + "content": "4.4. Occlusion Reasoning" + } + ] + } + ], + "index": 23 + }, + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 570, + 545, + 713 + ], + "type": "text", + "content": "With the above coarse output perceiving from the visible part, we move to the next stage of reasoning the occluded part by the motion of planar objects (i.e., homography). In multiple object tracking, reasoning the occlusion by motion has been verified effective [97, 98], where a motion strategy is adopted to predict the future location of the target based on the historical trajectory. Inspired by this, we first develop a homography-guided strategy that locates the occlusion area and correct features from previous frames geometrically. We factorize the homography matrix into motion parameters that describe the common transformations, to estimate the sensitive homography matrix (as discussed" + } + ] + } + ], + "index": 24 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23464" + } + ] + } + ], + "index": 25 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 4 + }, + { + "para_blocks": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "spans": [ + { + "bbox": [ + 46, + 72, + 287, + 133 + ], + "type": "text", + "content": "in Sec. 1). Then, for tracking both visible and invisible parts of planar objects, we design a two-stream self-attention network that takes both the appearance features of the current frame and the motion-guided features of the previous frame to refine the predicted planar object." + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 47, + 133, + 286, + 201 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 133, + 286, + 201 + ], + "spans": [ + { + "bbox": [ + 47, + 133, + 286, + 201 + ], + "type": "text", + "content": "Occlusion Area Localization Strategy. To avoid the sensitivity problem discussed in Sec. 1, we first introduce the geometric definition of homography matrix " + }, + { + "bbox": [ + 47, + 133, + 286, + 201 + ], + "type": "inline_equation", + "content": "\\mathbf{H} \\in \\mathbb{R}^{3 \\times 3}" + }, + { + "bbox": [ + 47, + 133, + 286, + 201 + ], + "type": "text", + "content": " [23], and factorize it into similarity transformation " + }, + { + "bbox": [ + 47, + 133, + 286, + 201 + ], + "type": "inline_equation", + "content": "\\mathbf{H}^{\\mathrm{S}}" + }, + { + "bbox": [ + 47, + 133, + 286, + 201 + ], + "type": "text", + "content": " and residual one " + }, + { + "bbox": [ + 47, + 133, + 286, + 201 + ], + "type": "inline_equation", + "content": "\\mathbf{H}^{\\Lambda}" + }, + { + "bbox": [ + 47, + 133, + 286, + 201 + ], + "type": "text", + "content": ", with eight stable motion parameters of " + }, + { + "bbox": [ + 47, + 133, + 286, + 201 + ], + "type": "inline_equation", + "content": "h_p = (t_x, t_y, \\gamma, \\theta, k_1, k_2, v_1, v_2)" + }, + { + "bbox": [ + 47, + 133, + 286, + 201 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 1 + }, + { + "bbox": [ + 55, + 204, + 286, + 248 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 55, + 204, + 286, + 248 + ], + "spans": [ + { + "bbox": [ + 55, + 204, + 286, + 248 + ], + "type": "interline_equation", + "content": "\\mathbf {H} = \\mathbf {H} ^ {\\mathbf {S}} \\mathbf {H} ^ {\\boldsymbol {\\Lambda}} = \\left[ \\begin{array}{c c c} \\gamma \\cos \\theta & - \\gamma \\sin \\theta & t _ {x} \\\\ \\gamma \\sin \\theta & \\gamma \\cos \\theta & t _ {y} \\\\ 0 & 0 & 1 \\end{array} \\right] \\left[ \\begin{array}{c c c} k _ {1} & k _ {2} & 0 \\\\ 0 & \\frac {1}{k _ {1}} & 0 \\\\ v _ {1} & v _ {2} & 1 \\end{array} \\right], \\tag {4}", + "image_path": "a7d1d1b5d1777f294230f82cd7e2914fe6d3c657ffad431bc84d20d0960116cd.jpg" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "spans": [ + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "inline_equation", + "content": "t_x, t_y" + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "text", + "content": " are the transition offset, " + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "inline_equation", + "content": "\\gamma" + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "inline_equation", + "content": "\\theta" + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "text", + "content": " denote the change of scale and angle, and " + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "inline_equation", + "content": "k_1, k_2, v_1, v_2" + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "text", + "content": " control the parameters of matrix " + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "inline_equation", + "content": "\\mathbf{H}^{\\Lambda}" + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "text", + "content": ". Here, the motion parameters can be computed by solving a transcendental equation with eight variants. The location parameters can be written as " + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "inline_equation", + "content": "h_l = (x_1, y_1, x_2, y_2, x_3, y_3, x_4, y_4)" + }, + { + "bbox": [ + 46, + 249, + 286, + 321 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "spans": [ + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "type": "text", + "content": "Specifically, the location parameters and homography are obtained from the coarse output of appearance perception, where we apply the Argmax function on heatmaps to get the coordinates of vertexes and compute the homography matrix between the coordinates from the current frame and the previous one. Then, the factorized homography " + }, + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "type": "inline_equation", + "content": "h_p" + }, + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "type": "text", + "content": " and location parameters " + }, + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "type": "inline_equation", + "content": "h_l" + }, + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "type": "text", + "content": " are fed into the Kalman Filter [29] and yield the corrected ones " + }, + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "type": "inline_equation", + "content": "\\widehat{h}_p, \\widehat{h}_l" + }, + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "type": "text", + "content": ". Finally, homography matrix " + }, + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "type": "inline_equation", + "content": "\\hat{\\mathbf{H}}^{\\mathrm{o}}" + }, + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "type": "text", + "content": " for the " + }, + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "type": "inline_equation", + "content": "o^{\\mathrm{th}}" + }, + { + "bbox": [ + 46, + 323, + 286, + 445 + ], + "type": "text", + "content": " planar object in the current frame can be obtained." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 447, + 286, + 545 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 447, + 286, + 545 + ], + "spans": [ + { + "bbox": [ + 46, + 447, + 286, + 545 + ], + "type": "text", + "content": "Given the predicted homography, the mask from previous frame " + }, + { + "bbox": [ + 46, + 447, + 286, + 545 + ], + "type": "inline_equation", + "content": "\\widehat{M}_p^o" + }, + { + "bbox": [ + 46, + 447, + 286, + 545 + ], + "type": "text", + "content": " can be warped [3] by the perspective transformation " + }, + { + "bbox": [ + 46, + 447, + 286, + 545 + ], + "type": "inline_equation", + "content": "warp(\\widehat{M}_p^o,\\hat{\\mathbf{H}}^\\circ)" + }, + { + "bbox": [ + 46, + 447, + 286, + 545 + ], + "type": "text", + "content": ". To locate occlusion area, the intuition is that the heatmap inferred by historical motion is robust to the occlusion on appearance. Meanwhile, the heatmap predicted based on appearance can accurately locate the planar objects in the current frame. As a result, we indicate the area of occlusion as" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 73, + 546, + 286, + 574 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 73, + 546, + 286, + 574 + ], + "spans": [ + { + "bbox": [ + 73, + 546, + 286, + 574 + ], + "type": "interline_equation", + "content": "\\phi^ {o} = \\frac {1}{\\sum_ {i} \\delta_ {i}} \\sum_ {i} \\delta_ {i} \\cdot \\| w a r p \\left(\\widehat {M} _ {p} ^ {i}, \\hat {\\mathbf {H}} ^ {\\mathbf {i}}\\right) - M ^ {o} \\|, \\tag {5}", + "image_path": "c0188da03ebaa2fd5712fff0a289afe2e17fd5d63a3e7742c78a98f0ed25f35b.jpg" + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 46, + 576, + 286, + 601 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 576, + 286, + 601 + ], + "spans": [ + { + "bbox": [ + 46, + 576, + 286, + 601 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 46, + 576, + 286, + 601 + ], + "type": "inline_equation", + "content": "\\| \\cdot \\|" + }, + { + "bbox": [ + 46, + 576, + 286, + 601 + ], + "type": "text", + "content": " is the distance function computed per pixel and " + }, + { + "bbox": [ + 46, + 576, + 286, + 601 + ], + "type": "inline_equation", + "content": "\\delta_{i}" + }, + { + "bbox": [ + 46, + 576, + 286, + 601 + ], + "type": "text", + "content": " judges the mask confidence of " + }, + { + "bbox": [ + 46, + 576, + 286, + 601 + ], + "type": "inline_equation", + "content": "i^{\\mathrm{th}}" + }, + { + "bbox": [ + 46, + 576, + 286, + 601 + ], + "type": "text", + "content": " planar object." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "text", + "content": "Motion Reasoning Network. For reasoning the visible and invisible parts of planar objects, we leverage the occlusion indicator " + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "inline_equation", + "content": "\\phi^o" + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "text", + "content": " as guidance, where the features " + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "inline_equation", + "content": "f_{T + 1}^{o}" + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "text", + "content": " from the current frame are refined, together with the warped feature " + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "inline_equation", + "content": "warp(f_T^o,\\hat{\\mathbf{H}}^\\mathrm{o})" + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "text", + "content": " from the previous frame. We denote these two features as " + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "inline_equation", + "content": "f_{a}" + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "inline_equation", + "content": "f_{m}" + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "text", + "content": ", respectively. The features are first flattened alongside spatial dimension " + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "inline_equation", + "content": "f_{a},f_{m}\\in \\mathbb{R}^{c_{d}\\times HW}" + }, + { + "bbox": [ + 46, + 601, + 286, + 714 + ], + "type": "text", + "content": ". Then, we develop a multi-head self-attention (MHSA) mechanism [31] for extracting occlusion-aware features. For learning joint representation and encouraging" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 305, + 72, + 545, + 94 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 72, + 545, + 94 + ], + "spans": [ + { + "bbox": [ + 305, + 72, + 545, + 94 + ], + "type": "text", + "content": "the interactions between appearance and motion, we feed both features into MHSA as" + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 351, + 95, + 545, + 151 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 351, + 95, + 545, + 151 + ], + "spans": [ + { + "bbox": [ + 351, + 95, + 545, + 151 + ], + "type": "interline_equation", + "content": "\\left\\{ \\begin{array}{l} X = \\operatorname {C o n c a t} \\left(h _ {1}, \\dots , h _ {H}\\right) \\\\ h _ {i} = a _ {i} f \\mathbf {W} _ {\\mathbf {i}} ^ {\\mathbf {V}} \\\\ a _ {i} = \\operatorname {s o f t m a x} \\left(\\frac {\\left[ f \\mathbf {W} _ {\\mathbf {i}} ^ {\\mathbf {Q}} \\right] \\left[ f \\mathbf {W} _ {\\mathbf {i}} ^ {\\mathbf {K}} \\right] ^ {\\top}}{\\sqrt {d _ {k}}}\\right), \\\\ f = \\operatorname {C o n c a t} \\left(f _ {m}, f _ {a}\\right) \\end{array} \\right. \\tag {6}", + "image_path": "5254b38a619b589794a33ea0b06e9fa222eee6b8c0d9bb393f5855c4f7ec814c.jpg" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 305, + 154, + 545, + 202 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 154, + 545, + 202 + ], + "spans": [ + { + "bbox": [ + 305, + 154, + 545, + 202 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 154, + 545, + 202 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\mathbf{i}}^{\\mathbf{Q}}, \\mathbf{W}_{\\mathbf{i}}^{\\mathbf{K}}" + }, + { + "bbox": [ + 305, + 154, + 545, + 202 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 154, + 545, + 202 + ], + "type": "inline_equation", + "content": "\\mathbf{W}_{\\mathbf{i}}^{\\mathbf{V}}" + }, + { + "bbox": [ + 305, + 154, + 545, + 202 + ], + "type": "text", + "content": " are the matrixes. We then adopt MLP to extract representations for motion feature " + }, + { + "bbox": [ + 305, + 154, + 545, + 202 + ], + "type": "inline_equation", + "content": "X_{m}" + }, + { + "bbox": [ + 305, + 154, + 545, + 202 + ], + "type": "text", + "content": " and appearance feature " + }, + { + "bbox": [ + 305, + 154, + 545, + 202 + ], + "type": "inline_equation", + "content": "X_{a}" + }, + { + "bbox": [ + 305, + 154, + 545, + 202 + ], + "type": "text", + "content": ", respectively. For assembling, we integrate both features guided by indicator " + }, + { + "bbox": [ + 305, + 154, + 545, + 202 + ], + "type": "inline_equation", + "content": "\\phi^{o}" + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 366, + 203, + 545, + 216 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 366, + 203, + 545, + 216 + ], + "spans": [ + { + "bbox": [ + 366, + 203, + 545, + 216 + ], + "type": "interline_equation", + "content": "F _ {o c c} = \\mathcal {F} _ {e n s} \\left(\\mathcal {F} _ {\\phi} \\left(X _ {a}\\right), X _ {m}\\right), \\tag {7}", + "image_path": "6c985b98a99bbff2a05b60719580d921a6bdba1ce08f378cce8d5b062bf78c62.jpg" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "spans": [ + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\text{ens}}" + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\phi}" + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "text", + "content": " are " + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "inline_equation", + "content": "1 \\times 1" + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "text", + "content": " convolution layer, " + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "inline_equation", + "content": "\\mathcal{F}_{\\phi}" + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "text", + "content": " concatenates the occlusion indicator with input feature as guidance. Finally, given the mask and vertex heatmaps of the " + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "inline_equation", + "content": "o^{th}" + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "text", + "content": " occluded planar object, we feed the features into the dual-branch network used in the stage of appearance perception again and obtain the refined vertexes " + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "inline_equation", + "content": "\\widehat{P}^o" + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "text", + "content": " and mask " + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "inline_equation", + "content": "\\widehat{M}^o" + }, + { + "bbox": [ + 305, + 217, + 545, + 289 + ], + "type": "text", + "content": "." + } + ] + } + ], + "index": 13 + }, + { + "bbox": [ + 306, + 300, + 381, + 314 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 300, + 381, + 314 + ], + "spans": [ + { + "bbox": [ + 306, + 300, + 381, + 314 + ], + "type": "text", + "content": "5. Experiment" + } + ] + } + ], + "index": 14 + }, + { + "bbox": [ + 306, + 319, + 418, + 331 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 319, + 418, + 331 + ], + "spans": [ + { + "bbox": [ + 306, + 319, + 418, + 331 + ], + "type": "text", + "content": "5.1. Evaluation Metrics" + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 305, + 338, + 545, + 457 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 338, + 545, + 457 + ], + "spans": [ + { + "bbox": [ + 305, + 338, + 545, + 457 + ], + "type": "text", + "content": "To evaluate methods on MPOT, following [15], we utilize the CLEAR metric [58] to complement the POT metrics. Note that existing POT metrics estimate the difference between ground truth and prediction in a pairwise manner (i.e., 1-box to 1-box). But it is not suitable for MPOT, since the number of predictions and ground truths are not always equal. Therefore, we match the set of ground truth " + }, + { + "bbox": [ + 305, + 338, + 545, + 457 + ], + "type": "inline_equation", + "content": "GT_{t}" + }, + { + "bbox": [ + 305, + 338, + 545, + 457 + ], + "type": "text", + "content": " and prediction " + }, + { + "bbox": [ + 305, + 338, + 545, + 457 + ], + "type": "inline_equation", + "content": "P_{t}" + }, + { + "bbox": [ + 305, + 338, + 545, + 457 + ], + "type": "text", + "content": " by bipartite matching [33]. Sequentially, we compute the difference of the matched pair by well-known POT distance Alignment Error [43,45,70] as" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 353, + 457, + 545, + 488 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 353, + 457, + 545, + 488 + ], + "spans": [ + { + "bbox": [ + 353, + 457, + 545, + 488 + ], + "type": "interline_equation", + "content": "E _ {A L} (\\mathbf {p}, \\mathbf {g}) = \\sqrt {\\frac {\\sum_ {\\mathbf {j} = 1} ^ {4} \\left(\\mathbf {p} _ {\\mathbf {j}} - \\mathbf {g} _ {\\mathbf {j}}\\right) ^ {2}}{4}}, \\tag {8}", + "image_path": "fba0783cd727e5bb40a0748b930902b43ab0244c5436784c5fe6d217c3eabc6a.jpg" + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "spans": [ + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "inline_equation", + "content": "\\mathbf{p}" + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "inline_equation", + "content": "\\mathbf{g}" + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "text", + "content": " are the quadrangle of the prediction and ground truth. Then, the prediction and ground truth are split into tracked " + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "inline_equation", + "content": "T_{\\epsilon}^{t}" + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "text", + "content": ", true positive " + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "inline_equation", + "content": "TP_{\\epsilon}^{t}" + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "text", + "content": ", false negative " + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "inline_equation", + "content": "FN_{\\epsilon}^{t}" + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "text", + "content": ", and false positive " + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "inline_equation", + "content": "FP_{\\epsilon}^{t}" + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "text", + "content": ", according to distance " + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "text", + "content": ". We set " + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 305, + 488, + 545, + 547 + ], + "type": "text", + "content": " as 50 in our experiment due to the degree of challenge." + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 305, + 548, + 545, + 607 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 548, + 545, + 607 + ], + "spans": [ + { + "bbox": [ + 305, + 548, + 545, + 607 + ], + "type": "text", + "content": "In POT, Precision " + }, + { + "bbox": [ + 305, + 548, + 545, + 607 + ], + "type": "inline_equation", + "content": "(Pr_{\\epsilon})" + }, + { + "bbox": [ + 305, + 548, + 545, + 607 + ], + "type": "text", + "content": " is the commonly used metric based on the alignment error [43]. To complement the metrics, we report Recall " + }, + { + "bbox": [ + 305, + 548, + 545, + 607 + ], + "type": "inline_equation", + "content": "(Rc_{\\epsilon})" + }, + { + "bbox": [ + 305, + 548, + 545, + 607 + ], + "type": "text", + "content": " to consider the cases of not being tracked. Furthermore, we propose Multiple Planar Object Tracking Distance " + }, + { + "bbox": [ + 305, + 548, + 545, + 607 + ], + "type": "inline_equation", + "content": "(D_{\\epsilon})" + }, + { + "bbox": [ + 305, + 548, + 545, + 607 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 19 + }, + { + "bbox": [ + 342, + 607, + 545, + 638 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 342, + 607, + 545, + 638 + ], + "spans": [ + { + "bbox": [ + 342, + 607, + 545, + 638 + ], + "type": "interline_equation", + "content": "D _ {\\epsilon} = \\frac {\\sum_ {t = 1} ^ {T} \\sum_ {t p \\in T P _ {\\epsilon} ^ {t} , q \\in T _ {\\epsilon} ^ {t}} E _ {A L} (t p , q)}{\\sum_ {t = 1} ^ {T} | T P _ {\\epsilon} ^ {t} |}. \\tag {9}", + "image_path": "3bc2e6714422d186571e2e8b3d3d4c7e6055d47b6177af7e526b04c98394bec6.jpg" + } + ] + } + ], + "index": 20 + }, + { + "bbox": [ + 306, + 637, + 544, + 660 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 637, + 544, + 660 + ], + "spans": [ + { + "bbox": [ + 306, + 637, + 544, + 660 + ], + "type": "text", + "content": "Naturally, we propose the Multiple Planar Object Tracking Accuracy " + }, + { + "bbox": [ + 306, + 637, + 544, + 660 + ], + "type": "inline_equation", + "content": "(Acc_{\\epsilon})" + }, + { + "bbox": [ + 306, + 637, + 544, + 660 + ], + "type": "text", + "content": " based on " + }, + { + "bbox": [ + 306, + 637, + 544, + 660 + ], + "type": "inline_equation", + "content": "E_{AL}" + }, + { + "bbox": [ + 306, + 637, + 544, + 660 + ], + "type": "text", + "content": " as." + } + ] + } + ], + "index": 21 + }, + { + "bbox": [ + 317, + 660, + 545, + 689 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 317, + 660, + 545, + 689 + ], + "spans": [ + { + "bbox": [ + 317, + 660, + 545, + 689 + ], + "type": "interline_equation", + "content": "A c c _ {\\epsilon} = 1 - \\frac {\\sum_ {t = 1} ^ {T} \\left| F N _ {\\epsilon} ^ {t} \\right| + \\left| F P _ {\\epsilon} ^ {t} \\right| + \\left| I D S W _ {\\epsilon} ^ {t} \\right|}{3 \\cdot \\sum_ {t = 1} ^ {T} \\left| G T _ {t} \\right|}, \\tag {10}", + "image_path": "6f26fd895b7d7b4329ce9217b1dcc3474db9538b17c1b70a9982d15a13d1a9d1.jpg" + } + ] + } + ], + "index": 22 + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "spans": [ + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "inline_equation", + "content": "IDSW_{\\epsilon}^{t}" + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "content": " is the set of the identity switch [58] under the threshold " + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\epsilon" + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "content": " in " + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "inline_equation", + "content": "\\mathbf{t}^{th}" + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "content": " frame, and " + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "inline_equation", + "content": "|\\cdot|" + }, + { + "bbox": [ + 305, + 689, + 545, + 714 + ], + "type": "text", + "content": " indicates the mod oper-" + } + ] + } + ], + "index": 23 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 317, + 757 + ], + "type": "text", + "content": "23465" + } + ] + } + ], + "index": 24 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 5 + }, + { + "para_blocks": [ + { + "type": "table", + "bbox": [ + 49, + 87, + 547, + 331 + ], + "blocks": [ + { + "bbox": [ + 47, + 53, + 545, + 85 + ], + "lines": [ + { + "bbox": [ + 47, + 53, + 545, + 85 + ], + "spans": [ + { + "bbox": [ + 47, + 53, + 545, + 85 + ], + "type": "text", + "content": "Table 3: Comparison of two groups of methods on MPOT-3K. The results on five metrics including Success Rate, Multiple Planar Object Tracking Accuracy, Multiple Planar Object Tracking Distance, Precision, Recall, and Speed are reported. " + }, + { + "bbox": [ + 47, + 53, + 545, + 85 + ], + "type": "inline_equation", + "content": "\\uparrow (\\downarrow)" + }, + { + "bbox": [ + 47, + 53, + 545, + 85 + ], + "type": "text", + "content": " denotes that the higher (lower) the score, the method performs better. Bold and underline indicate the highest and second-highest performance, respectively." + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "table_caption" + }, + { + "bbox": [ + 49, + 87, + 547, + 331 + ], + "lines": [ + { + "bbox": [ + 49, + 87, + 547, + 331 + ], + "spans": [ + { + "bbox": [ + 49, + 87, + 547, + 331 + ], + "type": "table", + "html": "
MethodsTraditionalDeepOurs
Motion PatternsMetricsCMT [61]NCC [71]CCRE [76]MI [17]GOP [8]Gracker [79]STM [62]PoST [60]LISRD [64]SMask [78]SRPN+ [38]SPoint [16]SOS [73]GIFT [53]HDN [95]
Overall\\( S_{0.8} \\uparrow \\)09.5000.1909.9926.7056.0367.9209.0733.5263.4364.0467.2371.8272.9175.8676.4082.51
\\( Acc_{\\epsilon} \\uparrow \\)64.2761.9534.3437.8262.2888.3852.0539.5572.3973.2975.3771.1770.0672.9979.5094.59
\\( Pr_{\\epsilon} \\uparrow \\)37.0503.6414.1223.5745.2585.6725.6425.0256.2358.3860.7054.5853.2356.4165.2192.85
\\( Rc_{\\epsilon} \\uparrow \\)10.2400.5519.0838.6062.7278.2523.0740.7480.4069.5574.4581.2585.3784.0282.5690.78
\\( D_{\\epsilon} \\downarrow \\)12.3042.1517.2708.6806.3705.2318.7922.7106.9317.0616.7707.6707.7607.8007.4405.07
Moving Occlusion\\( S_{0.8} \\uparrow \\)11.3400.0010.6926.4755.8563.6808.7818.1773.7963.2970.6270.9173.4272.9274.9680.29
\\( Acc_{\\epsilon} \\uparrow \\)67.2562.7856.2168.1081.4192.9355.4948.0491.7481.4683.2789.9292.2889.7488.7493.16
\\( Pr_{\\epsilon} \\uparrow \\)53.484.9233.5651.8270.0576.3029.6325.4586.3774.5775.9484.7384.3584.2182.0090.95
\\( Rc_{\\epsilon} \\uparrow \\)13.4700.6432.0161.5777.3081.9824.3728.9880.7067.6272.9785.3985.0385.5084.8688.27
\\( D_{\\epsilon} \\downarrow \\)06.3142.1421.2908.7904.1307.9216.5427.2606.4115.5714.2906.0606.1706.0506.2405.34
Moving Objects\\( S_{0.8} \\uparrow \\)09.3400.6911.2324.2952.2161.5808.0935.5267.7962.9565.4965.5070.3667.0270.0979.12
\\( Acc_{\\epsilon} \\uparrow \\)69.2263.8640.7847.4168.9692.5453.7741.9676.8880.3382.7278.4469.2978.5981.0594.29
\\( Pr_{\\epsilon} \\uparrow \\)60.2817.1019.2432.5752.5090.4828.3327.1360.8768.6272.0967.7552.4167.9767.1892.27
\\( Rc_{\\epsilon} \\uparrow \\)22.872.1924.2753.9572.5156.7725.2843.9687.7375.7579.2267.6686.0967.7984.4390.44
\\( D_{\\epsilon} \\downarrow \\)12.7143.2117.6606.8505.7104.1121.7719.9305.1514.9215.4804.2104.5304.1605.6305.46
Camera Occlusion\\( S_{0.8} \\uparrow \\)14.6100.0013.3141.7963.5966.4113.8040.2185.4662.4659.4088.8588.2889.4384.0192.46
\\( Acc_{\\epsilon} \\uparrow \\)63.5461.9334.2840.2861.7287.9851.7237.1574.0661.6668.7172.1871.9072.1084.5195.85
\\( Pr_{\\epsilon} \\uparrow \\)36.8900.3818.4227.8445.0488.2424.5925.3156.7644.8352.3154.6754.4254.6073.1695.84
\\( Rc_{\\epsilon} \\uparrow \\)13.1900.0628.3249.7467.3873.7521.7045.3784.3264.8670.7587.5787.1587.5084.5291.53
\\( D_{\\epsilon} \\downarrow \\)10.3129.3820.1007.7106.7304.6325.0520.0804.8214.4614.4504.8104.6204.7305.1804.59
Speed↑00.5801.9800.3101.2501.0003.1435.4411.9008.6331.5210.8709.3212.5126.6216.3712.64
", + "image_path": "98bbb163c569c3f47ebff6bc0fbc7a304232b6d33a7b21c12bbb029e5f6b04f8.jpg" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "table_body" + } + ], + "index": 1 + }, + { + "bbox": [ + 47, + 346, + 288, + 369 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 346, + 288, + 369 + ], + "spans": [ + { + "bbox": [ + 47, + 346, + 288, + 369 + ], + "type": "text", + "content": "ation. To fairly compare along with the trajectory level, we adopt the success rate " + }, + { + "bbox": [ + 47, + 346, + 288, + 369 + ], + "type": "inline_equation", + "content": "(S_{\\alpha})" + }, + { + "bbox": [ + 47, + 346, + 288, + 369 + ], + "type": "text", + "content": " with the distance threshold " + }, + { + "bbox": [ + 47, + 346, + 288, + 369 + ], + "type": "inline_equation", + "content": "\\alpha" + }, + { + "bbox": [ + 47, + 346, + 288, + 369 + ], + "type": "text", + "content": " as" + } + ] + } + ], + "index": 2 + }, + { + "bbox": [ + 69, + 378, + 287, + 409 + ], + "type": "interline_equation", + "angle": 0, + "lines": [ + { + "bbox": [ + 69, + 378, + 287, + 409 + ], + "spans": [ + { + "bbox": [ + 69, + 378, + 287, + 409 + ], + "type": "interline_equation", + "content": "S _ {\\alpha} = \\frac {| \\mathbb {C} |}{| \\mathbb {I} |}, \\mathbb {C} = \\left\\{i _ {n} \\in \\mathbb {I} \\right| \\frac {\\sum_ {t = 1} ^ {T} \\left| T _ {\\epsilon} ^ {t} \\right|}{\\sum_ {t = 1} ^ {T} \\left| G T _ {t} \\right|} > \\alpha \\}, \\tag {11}", + "image_path": "71a8face67308df86933d5f91a088cb8c681c0b0c3ad37987896f78a995e8a79.jpg" + } + ] + } + ], + "index": 3 + }, + { + "bbox": [ + 47, + 412, + 239, + 424 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 412, + 239, + 424 + ], + "spans": [ + { + "bbox": [ + 47, + 412, + 239, + 424 + ], + "type": "text", + "content": "where " + }, + { + "bbox": [ + 47, + 412, + 239, + 424 + ], + "type": "inline_equation", + "content": "\\mathbb{I}" + }, + { + "bbox": [ + 47, + 412, + 239, + 424 + ], + "type": "text", + "content": " is the set of planar objects in the video." + } + ] + } + ], + "index": 4 + }, + { + "bbox": [ + 47, + 432, + 180, + 444 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 432, + 180, + 444 + ], + "spans": [ + { + "bbox": [ + 47, + 432, + 180, + 444 + ], + "type": "text", + "content": "5.2. Implementation Details" + } + ] + } + ], + "index": 5 + }, + { + "bbox": [ + 47, + 451, + 287, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 451, + 287, + 713 + ], + "spans": [ + { + "bbox": [ + 47, + 451, + 287, + 713 + ], + "type": "text", + "content": "We compare our model with fifteen representative methods. These methods are implemented by official code or open-source libraries [6, 72]. We run evaluated single object trackers multiple times for different planar objects. And we equip them with the data association strategy based on [12], for integrating each single object tracker into tracking multiple targets online. Besides, we additionally give the reference frames of ground truth if the single object trackers fail to track. Different from other box-based trackers, mask-based trackers (e.g., STM) directly outputs the mask. Thus, we use a rotated box estimator [88] to transfer the mask. We implement PRTrack using two RTX3090 GPUs. In the training stage, we use data augmentations, including flip, pepper noise, rotation, contrast jittering, and perspective transformation. We adopt a data sampling strategy following [41]. We adopt Smooth L1 loss and Cross-Entropy loss for optimizing the predicted vertex heatmaps and masks. Similar to [62], we pretrain SPB on YouTubeVOS [89] and DAVIS [66] datasets. During inference, we use the ordered vertexes to build the planar objects and estimate the homography matrix. We set the threshold as 0.9 in the reuse gate by grid search and set " + }, + { + "bbox": [ + 47, + 451, + 287, + 713 + ], + "type": "inline_equation", + "content": "r" + }, + { + "bbox": [ + 47, + 451, + 287, + 713 + ], + "type": "text", + "content": " in Equ. 2 as 0 during inference." + } + ] + } + ], + "index": 6 + }, + { + "bbox": [ + 306, + 345, + 429, + 357 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 345, + 429, + 357 + ], + "spans": [ + { + "bbox": [ + 306, + 345, + 429, + 357 + ], + "type": "text", + "content": "5.3. Results on MPOT-3K" + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 304, + 365, + 545, + 436 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 365, + 545, + 436 + ], + "spans": [ + { + "bbox": [ + 304, + 365, + 545, + 436 + ], + "type": "text", + "content": "We compare our PRTrack with the other fifteen trackers on MPOT-3K, which contains six traditional POT trackers, four deep-based generic object trackers, and five deep-based planar object trackers. Tab. 3 reports the overall performance as well as the one in the challenging situations of moving occlusion, moving objects, and camera occlusion." + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 304, + 437, + 545, + 616 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 437, + 545, + 616 + ], + "spans": [ + { + "bbox": [ + 304, + 437, + 545, + 616 + ], + "type": "text", + "content": "Deep vs. Traditional Trackers. We can observe that the deep-based trackers have increased by " + }, + { + "bbox": [ + 304, + 437, + 545, + 616 + ], + "type": "inline_equation", + "content": "82.6\\%" + }, + { + "bbox": [ + 304, + 437, + 545, + 616 + ], + "type": "text", + "content": " on average, on five metrics for overall performance. This is because deep-based trackers avoid taking some assumptions under the laboratory environment, such as the invariance to illumination and appearance change. Note that Gracker performs best in traditional trackers and achieves competitive performance with the deep-based tracker group. However, since MPOT-3K has many small planar objects, it can not extract sufficient information, thus resulting in suboptimal performance (i.e., " + }, + { + "bbox": [ + 304, + 437, + 545, + 616 + ], + "type": "inline_equation", + "content": "10.3\\%" + }, + { + "bbox": [ + 304, + 437, + 545, + 616 + ], + "type": "text", + "content": " degradation in comparison with ours). In terms of deep-based trackers, STM predicts segmentation masks at the pixel level while ignoring the order of vertexes. Thus, it results in inferior performance, where only " + }, + { + "bbox": [ + 304, + 437, + 545, + 616 + ], + "type": "inline_equation", + "content": "9.0\\%" + }, + { + "bbox": [ + 304, + 437, + 545, + 616 + ], + "type": "text", + "content": " of targets are correctly tracked." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 617, + 545, + 713 + ], + "type": "text", + "content": "Planar Object Trackers vs. Generic Object Trackers. Planar object trackers achieve higher performance (58.9% improvement) against generic object trackers, including SRPN+, SMask, STM, and PoST. A predominant reason is that the generic trackers are subject to the assumption of affine transformation, where only the coarse box estimation is required. Therefore, a powerful planar object tracker should be developed in this field." + } + ] + } + ], + "index": 10 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "spans": [ + { + "bbox": [ + 293, + 749, + 318, + 757 + ], + "type": "text", + "content": "23466" + } + ] + } + ], + "index": 11 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 6 + }, + { + "para_blocks": [ + { + "type": "image", + "bbox": [ + 48, + 45, + 166, + 145 + ], + "blocks": [ + { + "bbox": [ + 48, + 45, + 166, + 145 + ], + "lines": [ + { + "bbox": [ + 48, + 45, + 166, + 145 + ], + "spans": [ + { + "bbox": [ + 48, + 45, + 166, + 145 + ], + "type": "image", + "image_path": "9f635b7d3f32b0622c8b4a686a297d059450fb855b97c6f5a5256412428d9ae6.jpg" + } + ] + } + ], + "index": 0, + "angle": 0, + "type": "image_body" + } + ], + "index": 0 + }, + { + "type": "image", + "bbox": [ + 167, + 45, + 287, + 146 + ], + "blocks": [ + { + "bbox": [ + 167, + 45, + 287, + 146 + ], + "lines": [ + { + "bbox": [ + 167, + 45, + 287, + 146 + ], + "spans": [ + { + "bbox": [ + 167, + 45, + 287, + 146 + ], + "type": "image", + "image_path": "5a567515146fced29c4d3cd7972f5a77d3892cde57c2ae027f18846aa3631cd2.jpg" + } + ] + } + ], + "index": 2, + "angle": 0, + "type": "image_body" + } + ], + "index": 2 + }, + { + "type": "image", + "bbox": [ + 89, + 147, + 241, + 243 + ], + "blocks": [ + { + "bbox": [ + 85, + 146, + 129, + 156 + ], + "lines": [ + { + "bbox": [ + 85, + 146, + 129, + 156 + ], + "spans": [ + { + "bbox": [ + 85, + 146, + 129, + 156 + ], + "type": "text", + "content": "(a) POT210" + } + ] + } + ], + "index": 1, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 205, + 146, + 250, + 156 + ], + "lines": [ + { + "bbox": [ + 205, + 146, + 250, + 156 + ], + "spans": [ + { + "bbox": [ + 205, + 146, + 250, + 156 + ], + "type": "text", + "content": "(b) POT280" + } + ] + } + ], + "index": 3, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 89, + 147, + 241, + 243 + ], + "lines": [ + { + "bbox": [ + 89, + 147, + 241, + 243 + ], + "spans": [ + { + "bbox": [ + 89, + 147, + 241, + 243 + ], + "type": "image", + "image_path": "2826847f90906e62103655908e4f5cf24e3dca71bebb4f4b1a88913615ef853e.jpg" + } + ] + } + ], + "index": 4, + "angle": 0, + "type": "image_body" + }, + { + "bbox": [ + 135, + 245, + 220, + 255 + ], + "lines": [ + { + "bbox": [ + 135, + 245, + 220, + 255 + ], + "spans": [ + { + "bbox": [ + 135, + 245, + 220, + 255 + ], + "type": "text", + "content": "(c) Challenging factors" + } + ] + } + ], + "index": 5, + "angle": 0, + "type": "image_caption" + }, + { + "bbox": [ + 46, + 256, + 288, + 299 + ], + "lines": [ + { + "bbox": [ + 46, + 256, + 288, + 299 + ], + "spans": [ + { + "bbox": [ + 46, + 256, + 288, + 299 + ], + "type": "text", + "content": "Figure 6: Comparison on POT210 and POT280. The averaged Precision on two datasets with different thresholds are reported in (a) and (b), respectively. (c) further shows the performance under seven challenging factors. The data is extracted from [95]." + } + ] + } + ], + "index": 6, + "angle": 0, + "type": "image_caption" + } + ], + "index": 4 + }, + { + "bbox": [ + 46, + 312, + 287, + 396 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 312, + 287, + 396 + ], + "spans": [ + { + "bbox": [ + 46, + 312, + 287, + 396 + ], + "type": "text", + "content": "PRTrack vs. SOTA Trackers. PRTrack outperforms other methods with an average improvement of " + }, + { + "bbox": [ + 46, + 312, + 287, + 396 + ], + "type": "inline_equation", + "content": "6.4\\%" + }, + { + "bbox": [ + 46, + 312, + 287, + 396 + ], + "type": "text", + "content": ". We also observe a large gain when there exists relative movement among multiple targets. To be specific, when facing challenging situations like moving objects, moving occlusion, and camera occlusion, PRTrack achieves a performance gain of " + }, + { + "bbox": [ + 46, + 312, + 287, + 396 + ], + "type": "inline_equation", + "content": "16.9\\%" + }, + { + "bbox": [ + 46, + 312, + 287, + 396 + ], + "type": "text", + "content": " against other advanced algorithms." + } + ] + } + ], + "index": 7 + }, + { + "bbox": [ + 47, + 403, + 222, + 415 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 403, + 222, + 415 + ], + "spans": [ + { + "bbox": [ + 47, + 403, + 222, + 415 + ], + "type": "text", + "content": "5.4. Results on POT210 and POT280" + } + ] + } + ], + "index": 8 + }, + { + "bbox": [ + 46, + 422, + 287, + 578 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 422, + 287, + 578 + ], + "spans": [ + { + "bbox": [ + 46, + 422, + 287, + 578 + ], + "type": "text", + "content": "To verify the effectiveness of PRTrack on the traditional POT task, we conduct experiments on the POT210 and POT280 datasets, and compare PRTrack with eleven POT methods as shown in Fig. 6. Note that we do not fine-tune PRTrack on these two datasets, again verifying the generalization ability of PRTrack towards unseen scenes. Following [95], the averaged Precision is employed to evaluate all the methods. As the distance threshold " + }, + { + "bbox": [ + 46, + 422, + 287, + 578 + ], + "type": "inline_equation", + "content": "E_{AL}" + }, + { + "bbox": [ + 46, + 422, + 287, + 578 + ], + "type": "text", + "content": " increases, the precision tends to be stable when " + }, + { + "bbox": [ + 46, + 422, + 287, + 578 + ], + "type": "inline_equation", + "content": "E_{AL} > 10" + }, + { + "bbox": [ + 46, + 422, + 287, + 578 + ], + "type": "text", + "content": ". We notice that PRTrack achieves competitive performance in comparison with advanced algorithms. Besides, PRTrack shows its superiority when handling challenging cases such as occlusion and motion blur." + } + ] + } + ], + "index": 9 + }, + { + "bbox": [ + 47, + 586, + 141, + 600 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 47, + 586, + 141, + 600 + ], + "spans": [ + { + "bbox": [ + 47, + 586, + 141, + 600 + ], + "type": "text", + "content": "5.5. Ablation Study" + } + ] + } + ], + "index": 10 + }, + { + "bbox": [ + 46, + 605, + 287, + 676 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 605, + 287, + 676 + ], + "spans": [ + { + "bbox": [ + 46, + 605, + 287, + 676 + ], + "type": "text", + "content": "We conduct ablation studies on MPOT-3K in Tab. 4 to explore the effectiveness of each component in PRTrack. Our baseline is the appearance perception module, without shifted encoder and auxiliary mask. For simplicity, we use \"i&j\" to denote the comparison between the " + }, + { + "bbox": [ + 46, + 605, + 287, + 676 + ], + "type": "inline_equation", + "content": "i^{\\text{th}}" + }, + { + "bbox": [ + 46, + 605, + 287, + 676 + ], + "type": "text", + "content": " line and the " + }, + { + "bbox": [ + 46, + 605, + 287, + 676 + ], + "type": "inline_equation", + "content": "j^{\\text{th}}" + }, + { + "bbox": [ + 46, + 605, + 287, + 676 + ], + "type": "text", + "content": " line in the rest of this subsection." + } + ] + } + ], + "index": 11 + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "spans": [ + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": "We first perform module-wise ablation studies in the highlighted lines, we observe that PRTrack obtains the largest performance gain of " + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "11.6\\%" + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": " (i.e., " + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "3 \\& 9" + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "inline_equation", + "content": "4 \\& 10" + }, + { + "bbox": [ + 46, + 677, + 287, + 714 + ], + "type": "text", + "content": ")" + } + ] + } + ], + "index": 12 + }, + { + "bbox": [ + 305, + 46, + 545, + 140 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 305, + 46, + 545, + 140 + ], + "spans": [ + { + "bbox": [ + 305, + 46, + 545, + 140 + ], + "type": "text", + "content": "Table 4: Ablation study of components and their variants of PRTrack on the validation split of MPOT-3K. The lines with background indicate the module-level ablation study. Here AP, OR, and RT are short of appearance perception, occlusion reasoning, and memory pool. SE and Fac denote the shifted encoder and factorized homography matrix. Msk represents the plane structure branch with mask information. Here, " + }, + { + "bbox": [ + 305, + 46, + 545, + 140 + ], + "type": "inline_equation", + "content": "*" + }, + { + "bbox": [ + 305, + 46, + 545, + 140 + ], + "type": "text", + "content": ", " + }, + { + "bbox": [ + 305, + 46, + 545, + 140 + ], + "type": "inline_equation", + "content": "\\bullet" + }, + { + "bbox": [ + 305, + 46, + 545, + 140 + ], + "type": "text", + "content": ", and " + }, + { + "bbox": [ + 305, + 46, + 545, + 140 + ], + "type": "inline_equation", + "content": "\\diamond" + }, + { + "bbox": [ + 305, + 46, + 545, + 140 + ], + "type": "text", + "content": " are the fusion strategy (Fus), representing concatenation, attention-based, and indicator-based. Gat indicates the reuse gate." + } + ] + } + ], + "index": 13 + }, + { + "type": "table", + "bbox": [ + 308, + 141, + 544, + 255 + ], + "blocks": [ + { + "bbox": [ + 308, + 141, + 544, + 255 + ], + "lines": [ + { + "bbox": [ + 308, + 141, + 544, + 255 + ], + "spans": [ + { + "bbox": [ + 308, + 141, + 544, + 255 + ], + "type": "table", + "html": "
IdAPORRTMetrics
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⑤✓✓✓✓*✓77.5391.4690.4186.2510.43
⑥✓✓✓✓•✓78.9991.4188.0785.8709.12
⑦✓✓✓◇✓79.2491.5088.1086.1308.95
⑧✓✓✓◇✓76.3890.5688.5882.3410.59
⑨✓✓✓✓◇80.4492.4889.6787.5407.38
⑩✓✓✓✓◇✓80.5892.7590.0088.0306.39
", + "image_path": "336ceffd2d68e10f12d78a1006a85fc357582769ed336b5be31f14d1b1a96b09.jpg" + } + ] + } + ], + "index": 14, + "angle": 0, + "type": "table_body" + } + ], + "index": 14 + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "spans": [ + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "text", + "content": "with the occlusion reasoning module. Then we investigate the variants of each module. For appearance perception, we study how to leverage the order of vertexes. The boosting of " + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "inline_equation", + "content": "16.3\\%" + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "text", + "content": " (i.e., " + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "inline_equation", + "content": "2 \\& 3" + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "inline_equation", + "content": "8 \\& 10" + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "text", + "content": ") verifies that the proposed encoder avoids learning position bias, where the first vertex commonly comes from the top-left area. For occlusion reasoning, we find the solution to unify the appearance feature and motion feature. We first conduct experiments on alternative solutions of fusion (i.e., " + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "inline_equation", + "content": "5 \\& 6 \\& 10" + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "text", + "content": "), where our strategy achieves the best performance. Because the occlusion indicator provides the change of image against occlusion and joint embedding helps to introduce interaction between features. We also identify the effectiveness of homography factorization via the comparison of " + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "inline_equation", + "content": "7 \\& 10" + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "text", + "content": ", with an average boosting of " + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "inline_equation", + "content": "7.2\\%" + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "text", + "content": ". For memory pool, we investigate the accumulated error. With a gain of " + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "inline_equation", + "content": "4.4\\%" + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "text", + "content": " (i.e., " + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "inline_equation", + "content": "3 \\& 4" + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "text", + "content": " and " + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "inline_equation", + "content": "9 \\& 10" + }, + { + "bbox": [ + 304, + 270, + 545, + 486 + ], + "type": "text", + "content": "), we believe the proposed reuse gate can avoid the error derived from restoring the predictions." + } + ] + } + ], + "index": 15 + }, + { + "bbox": [ + 306, + 496, + 379, + 508 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 496, + 379, + 508 + ], + "spans": [ + { + "bbox": [ + 306, + 496, + 379, + 508 + ], + "type": "text", + "content": "6. Conclusion" + } + ] + } + ], + "index": 16 + }, + { + "bbox": [ + 304, + 516, + 545, + 612 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 516, + 545, + 612 + ], + "spans": [ + { + "bbox": [ + 304, + 516, + 545, + 612 + ], + "type": "text", + "content": "In this paper, we propose a novel method for tracking multiple planar objects simultaneously. We also build the first large-scale benchmark dataset MPOT-3K which contains sufficient data, is labeled by experienced annotators, and covers various scenes. Extensive experiments are conducted on both MPOT3K and the other two single planar object tracking datasets. The results demonstrate that PRTrack achieves SOTA performance on both tasks." + } + ] + } + ], + "index": 17 + }, + { + "bbox": [ + 306, + 621, + 416, + 635 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 306, + 621, + 416, + 635 + ], + "spans": [ + { + "bbox": [ + 306, + 621, + 416, + 635 + ], + "type": "text", + "content": "7. Acknowledgments" + } + ] + } + ], + "index": 18 + }, + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "angle": 0, + "lines": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "spans": [ + { + "bbox": [ + 304, + 641, + 545, + 713 + ], + "type": "text", + "content": "This work was supported by the National Key Research and Development Program of China Grant (NO. 2018AAA0100400), Natural Science Foundation of Tianjin, China (NO.20JCJQJC00020), Fundamental Research Funds for the Central Universities, and Supercomputing Center of Nankai University (NKSC)." + } + ] + } + ], + "index": 19 + } + ], + "discarded_blocks": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "page_number", + "angle": 0, + "lines": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "spans": [ + { + "bbox": [ + 293, + 748, + 318, + 758 + ], + "type": "text", + "content": "23467" + } + ] + } + ], + "index": 20 + } + ], + "page_size": [ + 612, + 792 + ], + "page_idx": 7 + }, + { + "para_blocks": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "title", + "angle": 0, + "lines": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "spans": [ + { + "bbox": [ + 48, + 71, + 106, + 83 + ], + "type": "text", + "content": "References" + } + ] + } + ], + "index": 0 + }, + { + "bbox": [ + 53, + 92, + 286, + 712 + ], + "type": "list", + "angle": 0, + "index": 18, + "blocks": [ + { + "bbox": [ + 58, + 92, + 286, + 125 + ], + "type": "ref_text", + "angle": 0, + "lines": [ + { + "bbox": [ + 58, + 92, + 286, + 125 + ], + "spans": [ + { + "bbox": [ + 58, + 92, + 286, + 125 + ], + "type": "text", + "content": "[1] Mark Ashdown, Matthew Flagg, Rahul Sukthankar, and James M Rehg. 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